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FrancophonIA
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Vikidia-EnFr

+Eyes are organs of the visual system. They provide animals with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and convert it into electro-chemical impulses in neurons. In higher organisms, the eye is a complex optical system which collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system.[1] Image-resolving eyes are present in molluscs, chordates and arthropods.[2]
+The most simple eyes, pit eyes, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light.[1] From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment and to the pretectal area to control the pupillary light reflex.
+Complex eyes can distinguish shapes and colours. The visual fields of many organisms, especially predators, involve large areas of binocular vision to improve depth perception. In other organisms, eyes are located so as to maximise the field of view, such as in rabbits and horses, which have monocular vision.
+The first proto-eyes evolved among animals 600 million years ago about the time of the Cambrian explosion.[3] The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in six of the ~35[a] main phyla.[1] In most vertebrates and some molluscs, the eye works by allowing light to enter and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for colour) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals for vision. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris; the relaxing or tightening of the muscles around the iris change the size of the pupil, thereby regulating the amount of light that enters the eye,[4] and reducing aberrations when there is enough light.[5] The eyes of most cephalopods, fish, amphibians and snakes have fixed lens shapes, and focusing vision is achieved by telescoping the lens—similar to how a camera focuses.[6]
+Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, may give either a single pixelated image or multiple images, per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors, which are arranged hexagonally, and which can give a full 360° field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image, creating vision. With each eye viewing a different thing, a fused image from all the eyes is produced in the brain, providing very different, high-resolution images.
+Possessing detailed hyperspectral colour vision, the Mantis shrimp has been reported to have the world's most complex colour vision system.[7] Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes. The number of lenses in such an eye varied; however, some trilobites had only one, and some had thousands of lenses in one eye.
+In contrast to compound eyes, simple eyes are those that have a single lens. For example, jumping spiders have a large pair of simple eyes with a narrow field of view, supported by an array of other, smaller eyes for peripheral vision. Some insect larvae, like caterpillars, have a different type of simple eye (stemmata) which usually provides only a rough image, but (as in sawfly larvae) can possess resolving powers of 4 degrees of arc, be polarization-sensitive and capable of increasing its absolute sensitivity at night by a factor of 1,000 or more.[8] Some of the simplest eyes, called ocelli, can be found in animals like some of the snails, which cannot actually "see" in the normal sense. They do have photosensitive cells, but no lens and no other means of projecting an image onto these cells. They can distinguish between light and dark, but no more. This enables snails to keep out of direct sunlight.
+In organisms dwelling near deep-sea vents, compound eyes have been secondarily simplified and adapted to spot the infra-red light produced by the hot vents—in this way the bearers can spot hot springs and avoid being boiled alive.[9]
+There are ten different eye layouts—indeed every technological method of capturing an optical image commonly used by human beings, with the exceptions of zoom and Fresnel lenses, occur in nature.[1] Eye types can be categorised into "simple eyes", with one concave photoreceptive surface, and "compound eyes", which comprise a number of individual lenses laid out on a convex surface.[1] Note that "simple" does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for almost any behaviour or environment. The only limitations specific to eye types are that of resolution—the physics of compound eyes prevents them from achieving a resolution better than 1°. Also, superposition eyes can achieve greater sensitivity than apposition eyes, so are better suited to dark-dwelling creatures.[1] Eyes also fall into two groups on the basis of their photoreceptor's cellular construction, with the photoreceptor cells either being cilliated (as in the vertebrates) or rhabdomeric. These two groups are not monophyletic; the cnidaria also possess cilliated cells,
+[10] and some gastropods,[11] as well as some annelids possess both.[12]
+Some organisms have photosensitive cells that do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms. These are not considered eyes because they lack enough structure to be considered an organ, and do not produce an image.[13]
+Simple eyes are rather ubiquitous, and lens-bearing eyes have evolved at least seven times in vertebrates, cephalopods, annelids, crustaceans and cubozoa.[14][failed verification]
+Pit eyes, also known as stemma, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light.[1] Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of "simple eyes". They are small, comprising up to about 100 cells covering about 100 µm.[1] The directionality can be improved by reducing the size of the aperture, by incorporating a reflective layer behind the receptor cells, or by filling the pit with a refractile material.[1]
+Pit vipers have developed pits that function as eyes by sensing thermal infra-red radiation, in addition to their optical wavelength eyes like those of other vertebrates (see infrared sensing in snakes). However, pit organs are fitted with receptors rather different to photoreceptors, namely a specific transient receptor potential channel (TRP channels) called TRPV1. The main difference is that photoreceptors are G-protein coupled receptors but TRP are ion channels.
+The resolution of pit eyes can be greatly improved by incorporating a material with a higher refractive index to form a lens, which may greatly reduce the blur radius encountered—hence increasing the resolution obtainable.[1] The most basic form, seen in some gastropods and annelids, consists of a lens of one refractive index. A far sharper image can be obtained using materials with a high refractive index, decreasing to the edges; this decreases the focal length and thus allows a sharp image to form on the retina.[1] This also allows a larger aperture for a given sharpness of image, allowing more light to enter the lens; and a flatter lens, reducing spherical aberration.[1] Such a non-homogeneous lens is necessary for the focal length to drop from about 4 times the lens radius, to 2.5 radii.[1]
+Heterogeneous eyes have evolved at least nine times: four or more times in gastropods, once in the copepods, once in the annelids, once in the cephalopods,[1] and once in the chitons, which have aragonite lenses.[15] No extant aquatic organisms possess homogeneous lenses; presumably the evolutionary pressure for a heterogeneous lens is great enough for this stage to be quickly "outgrown".[1]
+This eye creates an image that is sharp enough that motion of the eye can cause significant blurring. To minimise the effect of eye motion while the animal moves, most such eyes have stabilising eye muscles.[1]
+The ocelli of insects bear a simple lens, but their focal point always lies behind the retina; consequently, they can never form a sharp image. Ocelli (pit-type eyes of arthropods) blur the image across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the whole visual field; this fast response is further accelerated by the large nerve bundles which rush the information to the brain.[16] Focusing the image would also cause the sun's image to be focused on a few receptors, with the possibility of damage under the intense light; shielding the receptors would block out some light and thus reduce their sensitivity.[16]
+This fast response has led to suggestions that the ocelli of insects are used mainly in flight, because they can be used to detect sudden changes in which way is up (because light, especially UV light which is absorbed by vegetation, usually comes from above).[16]
+Some marine organisms bear more than one lens; for instance the copepod Pontella has three. The outer has a parabolic surface, countering the effects of spherical aberration while allowing a sharp image to be formed. Another copepod, Copilia, has two lenses in each eye, arranged like those in a telescope.[1] Such arrangements are rare and poorly understood, but represent an alternative construction.
+Multiple lenses are seen in some hunters such as eagles and jumping spiders, which have a refractive cornea: these have a negative lens, enlarging the observed image by up to 50% over the receptor cells, thus increasing their optical resolution.[1]
+In the eyes of most mammals, birds, reptiles, and most other terrestrial vertebrates (along with spiders and some insect larvae) the vitreous fluid has a higher refractive index than the air.[1] In general, the lens is not spherical. Spherical lenses produce spherical aberration. In refractive corneas, the lens tissue is corrected with inhomogeneous lens material (see Luneburg lens), or with an aspheric shape.[1] Flattening the lens has a disadvantage; the quality of vision is diminished away from the main line of focus. Thus, animals that have evolved with a wide field-of-view often have eyes that make use of an inhomogeneous lens.[1]
+As mentioned above, a refractive cornea is only useful out of water. In water, there is little difference in refractive index between the vitreous fluid and the surrounding water. Hence creatures that have returned to the water—penguins and seals, for example—lose their highly curved cornea and return to lens-based vision. An alternative solution, borne by some divers, is to have a very strongly focusing cornea.[1]
+An alternative to a lens is to line the inside of the eye with "mirrors", and reflect the image to focus at a central point.[1] The nature of these eyes means that if one were to peer into the pupil of an eye, one would see the same image that the organism would see, reflected back out.[1]
+Many small organisms such as rotifers, copepods and flatworms use such organs, but these are too small to produce usable images.[1] Some larger organisms, such as scallops, also use reflector eyes. The scallop Pecten has up to 100 millimetre-scale reflector eyes fringing the edge of its shell. It detects moving objects as they pass successive lenses.[1]
+There is at least one vertebrate, the spookfish, whose eyes include reflective optics for focusing of light. Each of the two eyes of a spookfish collects light from both above and below; the light coming from above is focused by a lens, while that coming from below, by a curved mirror composed of many layers of small reflective plates made of guanine crystals.[17]
+A compound eye may consist of thousands of individual photoreceptor units or ommatidia (ommatidium, singular). The image perceived is a combination of inputs from the numerous ommatidia (individual "eye units"), which are located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarisation of light.[18] Because the individual lenses are so small, the effects of diffraction impose a limit on the possible resolution that can be obtained (assuming that they do not function as phased arrays). This can only be countered by increasing lens size and number. To see with a resolution comparable to our simple eyes, humans would require very large compound eyes, around 11 metres (36 ft) in radius.[19]
+Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form a single erect image.[20] Compound eyes are common in arthropods, annelids and some bivalved molluscs.[21] Compound eyes in arthropods grow at their margins by the addition of new ommatidia.[22]
+Apposition eyes are the most common form of eyes and are presumably the ancestral form of compound eyes. They are found in all arthropod groups, although they may have evolved more than once within this phylum.[1] Some annelids and bivalves also have apposition eyes. They are also possessed by Limulus, the horseshoe crab, and there are suggestions that other chelicerates developed their simple eyes by reduction from a compound starting point.[1] (Some caterpillars appear to have evolved compound eyes from simple eyes in the opposite fashion.)
+Apposition eyes work by gathering a number of images, one from each eye, and combining them in the brain, with each eye typically contributing a single point of information. The typical apposition eye has a lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium.
+The second type is named the superposition eye. The superposition eye is divided into three types:
+The refracting superposition eye has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to the same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This type of compound eye, for which a minimal size exists below which effective superposition cannot occur,[23] is normally found in nocturnal insects, because it can create images up to 1000 times brighter than equivalent apposition eyes, though at the cost of reduced resolution.[24] In the parabolic superposition compound eye type, seen in arthropods such as mayflies, the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array. Long-bodied decapod crustaceans such as shrimp, prawns, crayfish and lobsters are alone in having reflecting superposition eyes, which also have a transparent gap but use corner mirrors instead of lenses.
+This eye type functions by refracting light, then using a parabolic mirror to focus the image; it combines features of superposition and apposition eyes.[9]
+Another kind of compound eye, found in males of Order Strepsiptera, employs a series of simple eyes—eyes having one opening that provides light for an entire image-forming retina. Several of these eyelets together form the strepsipteran compound eye, which is similar to the 'schizochroal' compound eyes of some trilobites.[25] Because each eyelet is a simple eye, it produces an inverted image; those images are combined in the brain to form one unified image. Because the aperture of an eyelet is larger than the facets of a compound eye, this arrangement allows vision under low light levels.[1]
+Good fliers such as flies or honey bees, or prey-catching insects such as praying mantis or dragonflies, have specialised zones of ommatidia organised into a fovea area which gives acute vision. In the acute zone, the eyes are flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. The black spot that can be seen on the compound eyes of such insects, which always seems to look directly at the observer, is called a pseudopupil. This occurs because the ommatidia which one observes "head-on" (along their optical axes) absorb the incident light, while those to one side reflect it.[26]
+There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there is the mysid shrimp, Dioptromysis paucispinosa. The shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there is a single large facet that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialised retina. The resulting eye is a mixture of a simple eye within a compound eye.
+Another version is a compound eye often referred to as "pseudofaceted", as seen in Scutigera.[27] This type of eye consists of a cluster of numerous ommatidia on each side of the head, organised in a way that resembles a true compound eye.
+The body of Ophiocoma wendtii, a type of brittle star, is covered with ommatidia, turning its whole skin into a compound eye. The same is true of many chitons. The tube feet of sea urchins contain photoreceptor proteins, which together act as a compound eye; they lack screening pigments, but can detect the directionality of light by the shadow cast by its opaque body.[28]
+The ciliary body is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. The inner layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina. The outer layer is highly pigmented, continuous with the retinal pigment epithelium, and constitutes the cells of the dilator muscle.
+The vitreous is the transparent, colourless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye.[29] It is produced by certain retinal cells. It is of rather similar composition to the cornea, but contains very few cells (mostly phagocytes which remove unwanted cellular debris in the visual field, as well as the hyalocytes of Balazs of the surface of the vitreous, which reprocess the hyaluronic acid), no blood vessels, and 98–99% of its volume is water (as opposed to 75% in the cornea) with salts, sugars, vitrosin (a type of collagen), a network of collagen type II fibres with the mucopolysaccharide hyaluronic acid, and also a wide array of proteins in micro amounts. Amazingly, with so little solid matter, it tautly holds the eye.
+Photoreception is phylogenetically very old, with various theories of phylogenesis.[30] The common origin (monophyly) of all animal eyes is now widely accepted as fact. This is based upon the shared genetic features of all eyes; that is, all modern eyes, varied as they are, have their origins in a proto-eye believed to have evolved some 540 million years ago,[31][32][33] and the PAX6 gene is considered a key factor in this. The majority of the advancements in early eyes are believed to have taken only a few million years to develop, since the first predator to gain true imaging would have touched off an "arms race"[34] among all species that did not flee the photopic environment. Prey animals and competing predators alike would be at a distinct disadvantage without such capabilities and would be less likely to survive and reproduce. Hence multiple eye types and subtypes developed in parallel (except those of groups, such as the vertebrates, that were only forced into the photopic environment at a late stage).
+Eyes in various animals show adaptation to their requirements. For example, the eye of a bird of prey has much greater visual acuity than a human eye, and in some cases can detect ultraviolet radiation. The different forms of eye in, for example, vertebrates and molluscs are examples of parallel evolution, despite their distant common ancestry. Phenotypic convergence of the geometry of cephalopod and most vertebrate eyes creates the impression that the vertebrate eye evolved from an imaging cephalopod eye, but this is not the case, as the reversed roles of their respective ciliary and rhabdomeric opsin classes[35] and different lens crystallins show.[36]
+The very earliest "eyes", called eye-spots, were simple patches of photoreceptor protein in unicellular animals. In multicellular beings, multicellular eyespots evolved, physically similar to the receptor patches for taste and smell. These eyespots could only sense ambient brightness: they could distinguish light and dark, but not the direction of the light source.[1]
+Through gradual change, the eye-spots of species living in well-lit environments depressed into a shallow "cup" shape. The ability to slightly discriminate directional brightness was achieved by using the angle at which the light hit certain cells to identify the source. The pit deepened over time, the opening diminished in size, and the number of photoreceptor cells increased, forming an effective pinhole camera that was capable of dimly distinguishing shapes.[37] However, the ancestors of modern hagfish, thought to be the protovertebrate,[35] were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. This would have led to a somewhat different evolutionary trajectory for the vertebrate eye than for other animal eyes.
+The thin overgrowth of transparent cells over the eye's aperture, originally formed to prevent damage to the eyespot, allowed the segregated contents of the eye chamber to specialise into a transparent humour that optimised colour filtering, blocked harmful radiation, improved the eye's refractive index, and allowed functionality outside of water. The transparent protective cells eventually split into two layers, with circulatory fluid in between that allowed wider viewing angles and greater imaging resolution, and the thickness of the transparent layer gradually increased, in most species with the transparent crystallin protein.[38]
+The gap between tissue layers naturally formed a biconvex shape, an optimally ideal structure for a normal refractive index. Independently, a transparent layer and a nontransparent layer split forward from the lens: the cornea and iris. Separation of the forward layer again formed a humour, the aqueous humour. This increased refractive power and again eased circulatory problems. Formation of a nontransparent ring allowed more blood vessels, more circulation, and larger eye sizes.[38]
+Eyes are generally adapted to the environment and life requirements of the organism which bears them. For instance, the distribution of photoreceptors tends to match the area in which the highest acuity is required, with horizon-scanning organisms, such as those that live on the African plains, having a horizontal line of high-density ganglia, while tree-dwelling creatures which require good all-round vision tend to have a symmetrical distribution of ganglia, with acuity decreasing outwards from the centre.
+Of course, for most eye types, it is impossible to diverge from a spherical form, so only the density of optical receptors can be altered. In organisms with compound eyes, it is the number of ommatidia rather than ganglia that reflects the region of highest data acquisition.[1]:23–24 Optical superposition eyes are constrained to a spherical shape, but other forms of compound eyes may deform to a shape where more ommatidia are aligned to, say, the horizon, without altering the size or density of individual ommatidia.[39] Eyes of horizon-scanning organisms have stalks so they can be easily aligned to the horizon when this is inclined, for example, if the animal is on a slope.[26]
+An extension of this concept is that the eyes of predators typically have a zone of very acute vision at their centre, to assist in the identification of prey.[39] In deep water organisms, it may not be the centre of the eye that is enlarged. The hyperiid amphipods are deep water animals that feed on organisms above them. Their eyes are almost divided into two, with the upper region thought to be involved in detecting the silhouettes of potential prey—or predators—against the faint light of the sky above. Accordingly, deeper water hyperiids, where the light against which the silhouettes must be compared is dimmer, have larger "upper-eyes", and may lose the lower portion of their eyes altogether.[39] In the giant Antarctic isopod Glyptonotus a small ventral compound eye is physically completely separated from the much larger dorsal compound eye.[40] Depth perception can be enhanced by having eyes which are enlarged in one direction; distorting the eye slightly allows the distance to the object to be estimated with a high degree of accuracy.[9]
+Acuity is higher among male organisms that mate in mid-air, as they need to be able to spot and assess potential mates against a very large backdrop.[39] On the other hand, the eyes of organisms which operate in low light levels, such as around dawn and dusk or in deep water, tend to be larger to increase the amount of light that can be captured.[39]
+It is not only the shape of the eye that may be affected by lifestyle. Eyes can be the most visible parts of organisms, and this can act as a pressure on organisms to have more transparent eyes at the cost of function.[39]
+Eyes may be mounted on stalks to provide better all-round vision, by lifting them above an organism's carapace; this also allows them to track predators or prey without moving the head.[9]
+Visual acuity, or resolving power, is "the ability to distinguish fine detail" and is the property of cone cells.[41] It is often measured in cycles per degree (CPD), which measures an angular resolution, or how much an eye can differentiate one object from another in terms of visual angles. Resolution in CPD can be measured by bar charts of different numbers of white/black stripe cycles. For example, if each pattern is 1.75 cm wide and is placed at 1 m distance from the eye, it will subtend an angle of 1 degree, so the number of white/black bar pairs on the pattern will be a measure of the cycles per degree of that pattern. The highest such number that the eye can resolve as stripes, or distinguish from a grey block, is then the measurement of visual acuity of the eye.
+For a human eye with excellent acuity, the maximum theoretical resolution is 50 CPD[42] (1.2 arcminute per line pair, or a 0.35 mm line pair, at 1 m). A rat can resolve only about 1 to 2 CPD.[43] A horse has higher acuity through most of the visual field of its eyes than a human has, but does not match the high acuity of the human eye's central fovea region.[44]
+Spherical aberration limits the resolution of a 7 mm pupil to about 3 arcminutes per line pair. At a pupil diameter of 3 mm, the spherical aberration is greatly reduced, resulting in an improved resolution of approximately 1.7 arcminutes per line pair.[45] A resolution of 2 arcminutes per line pair, equivalent to a 1 arcminute gap in an optotype, corresponds to 20/20 (normal vision) in humans.
+However, in the compound eye, the resolution is related to the size of individual ommatidia and the distance between neighbouring ommatidia. Physically these cannot be reduced in size to achieve the acuity seen with single lensed eyes as in mammals. Compound eyes have a much lower acuity than vertebrate eyes.[46]
+"Colour vision is the faculty of the organism to distinguish lights of different spectral qualities."[47] All organisms are restricted to a small range of electromagnetic spectrum; this varies from creature to creature, but is mainly between wavelengths of 400 and 700 nm.[48]
+This is a rather small section of the electromagnetic spectrum, probably reflecting the submarine evolution of the organ: water blocks out all but two small windows of the EM spectrum, and there has been no evolutionary pressure among land animals to broaden this range.[49]
+The most sensitive pigment, rhodopsin, has a peak response at 500 nm.[50] Small changes to the genes coding for this protein can tweak the peak response by a few nm;[2] pigments in the lens can also filter incoming light, changing the peak response.[2] Many organisms are unable to discriminate between colours, seeing instead in shades of grey; colour vision necessitates a range of pigment cells which are primarily sensitive to smaller ranges of the spectrum. In primates, geckos, and other organisms, these take the form of cone cells, from which the more sensitive rod cells evolved.[50] Even if organisms are physically capable of discriminating different colours, this does not necessarily mean that they can perceive the different colours; only with behavioural tests can this be deduced.[2]
+Most organisms with colour vision can detect ultraviolet light. This high energy light can be damaging to receptor cells. With a few exceptions (snakes, placental mammals), most organisms avoid these effects by having absorbent oil droplets around their cone cells. The alternative, developed by organisms that had lost these oil droplets in the course of evolution, is to make the lens impervious to UV light—this precludes the possibility of any UV light being detected, as it does not even reach the retina.[50]
+The retina contains two major types of light-sensitive photoreceptor cells used for vision: the rods and the cones.
+Rods cannot distinguish colours, but are responsible for low-light (scotopic) monochrome (black-and-white) vision; they work well in dim light as they contain a pigment, rhodopsin (visual purple), which is sensitive at low light intensity, but saturates at higher (photopic) intensities. Rods are distributed throughout the retina but there are none at the fovea and none at the blind spot. Rod density is greater in the peripheral retina than in the central retina.
+Cones are responsible for colour vision. They require brighter light to function than rods require. In humans, there are three types of cones, maximally sensitive to long-wavelength, medium-wavelength, and short-wavelength light (often referred to as red, green, and blue, respectively, though the sensitivity peaks are not actually at these colours). The colour seen is the combined effect of stimuli to, and responses from, these three types of cone cells. Cones are mostly concentrated in and near the fovea. Only a few are present at the sides of the retina. Objects are seen most sharply in focus when their images fall on the fovea, as when one looks at an object directly. Cone cells and rods are connected through intermediate cells in the retina to nerve fibres of the optic nerve. When rods and cones are stimulated by light, they connect through adjoining cells within the retina to send an electrical signal to the optic nerve fibres. The optic nerves send off impulses through these fibres to the brain.[50]
+The pigment molecules used in the eye are various, but can be used to define the evolutionary distance between different groups, and can also be an aid in determining which are closely related—although problems of convergence do exist.[50]
+Opsins are the pigments involved in photoreception. Other pigments, such as melanin, are used to shield the photoreceptor cells from light leaking in from the sides.
+The opsin protein group evolved long before the last common ancestor of animals, and has continued to diversify since.[2]
+There are two types of opsin involved in vision; c-opsins, which are associated with ciliary-type photoreceptor cells, and r-opsins, associated with rhabdomeric photoreceptor cells.[51] The eyes of vertebrates usually contain ciliary cells with c-opsins, and (bilaterian) invertebrates have rhabdomeric cells in the eye with r-opsins. However, some ganglion cells of vertebrates express r-opsins, suggesting that their ancestors used this pigment in vision, and that remnants survive in the eyes.[51] Likewise, c-opsins have been found to be expressed in the brain of some invertebrates. They may have been expressed in ciliary cells of larval eyes, which were subsequently resorbed into the brain on metamorphosis to the adult form.[51] C-opsins are also found in some derived bilaterian-invertebrate eyes, such as the pallial eyes of the bivalve molluscs; however, the lateral eyes (which were presumably the ancestral type for this group, if eyes evolved once there) always use r-opsins.[51]
+Cnidaria, which are an outgroup to the taxa mentioned above, express c-opsins—but r-opsins are yet to be found in this group.[51] Incidentally, the melanin produced in the cnidaria is produced in the same fashion as that in vertebrates, suggesting the common descent of this pigment.[51]
+The structures of the eye labelled
+Another view of the eye and the structures of the eye labelled

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+Asunción (UK: /əˌsʊnsiˈɒn/, US: /ɑːˌsuːnsiˈoʊn, ɑːsuːnˈsjoʊn/,[2][3][4] Spanish: [asunˈsjon]) is the capital and largest city of Paraguay.
+The city is located on the left bank of the Paraguay River, almost at the confluence of this river with the River Pilcomayo, on the South American continent. The Paraguay River and the Bay of Asunción in the northwest separate the city from the Occidental Region of Paraguay and Argentina in the south part of the city. The rest of the city is surrounded by the Central Department.
+The city is an autonomous capital district, not a part of any department. The metropolitan area, called Gran Asunción, includes the cities of San Lorenzo, Fernando de la Mora, Lambaré, Luque, Mariano Roque Alonso, Ñemby, San Antonio, Limpio, Capiatá and Villa Elisa, which are part of the Central Department. The Asunción metropolitan area has around two million inhabitants. The Municipality of Asunción is listed on the Asunción Stock Exchange, as BVPASA: MUA.
+Asunción is one of the oldest cities in South America and the longest continually inhabited area in the Río de la Plata Basin; for this reason it is known as "the Mother of Cities". From Asunción the colonial expeditions departed to found other cities, including the second foundation of Buenos Aires and other important cities such as Villarrica, Corrientes, Santa Fe and Santa Cruz de la Sierra.
+Asunción is considered a 'Gamma City' by the Globalization and World Cities Research Network.[5] It is the home of the national government, principal port, and the chief industrial and cultural center of the country. Near Asunción are the headquarters of the CONMEBOL, the continental governing body of association football in South America. Asunción is said to be one of the cheapest cities in the world for foreign visitors.[6]
+The Spanish conquistador Juan de Ayolas (died c. 1537) may have first visited the site of the future city on his way north, up the Paraguay River, looking for a passage to the mines of Alto Perú (present-day Bolivia). Later, Juan de Salazar y Espinosa and Gonzalo de Mendoza, a relative of Pedro de Mendoza, were sent in search of Ayolas, but failed to find him. On his way up and then down the river, de Salazar stopped briefly at a bay in the left bank to resupply his ships. He found the natives friendly, and decided to found a fort there in August 1537. He named it Nuestra Señora Santa María de la Asunción (Our Lady Saint Mary of the  Assumption – the Roman Catholic Church celebrates the Feast of the Assumption on August 15).[7]
+In 1542 natives destroyed Buenos Aires, and the Spaniards there fled to Asunción. Thus the city became the center of a large Spanish colonial province comprising part of Brazil, present-day Paraguay and northeastern Argentina: the Giant Province of the Indies. In 1603 Asunción was the seat of the First Synod of Asunción, which set guidelines for the evangelization of the natives in their lingua franca, Guaraní.
+In 1731 an uprising under José de Antequera y Castro was one of the first rebellions against Spanish colonial rule. The uprising failed, but it was the first sign of the independent spirit that was growing among the criollos, mestizos and natives of Paraguay. The event influenced the independence of Paraguay, which subsequently materialised in 1811. The secret meetings between the independence leaders to plan an ambush against the Spanish Governor in Paraguay (Bernardo de Velasco) took place at the home of Juana María de Lara, in downtown Asunción. On the night of May 14 and May 15, 1811, the rebels succeeded and forced governor Velasco to surrender. Today, Lara's former home, known as Casa de la Independencia (House of the Independence), operates as a museum and historical building.
+After Paraguay became independent, significant change occurred in Asunción. Under the rule of Gaspar Rodríguez de Francia (in office 1813–1840) roads were built throughout the city and the streets were named. However, during the presidency of Carlos Antonio López (President 1844–1862) Asunción (and Paraguay) saw further progress as the new president implemented new economic policies. More than 400 schools, metallurgic factories and the first railroad service in South America were built during the López presidency. After López died (1862), his son Francisco Solano López became the new president and led the country through the disastrous Paraguayan War that lasted for five years (1864-1870). On 1 January 1869, the capital city Asunción fell to Brazilian forces led by Gen. João de Souza da Fonseca Costa. After the end of the armed conflict, Brazilian troops occupied Asunción until 1876.
+Many historians[which?] have claimed that this war provoked a steady downfall of the city and country, since it massacred two thirds of the country's population. Progress slowed down greatly afterwards, and the economy stagnated.
+After the Paraguayan War, Asunción began a slow attempt at recovery. Towards the end of the 19th century and during the early years of the 20th century, a flow of immigrants from Europe and the Ottoman Empire came to the city. This led to a change in the appearance of the city as many new buildings were built and Asunción went through an era more prosperous than any since the war.
+Asunción's Downtown in 1872
+Asunción at night
+Harbour of Asuncion
+Asunción is located between the parallels 25° 15' and 25° 20' of south latitude and between the meridians 57° 40' and 57° 30' of west longitude. The city sits on the left bank of the Paraguay River, almost at the confluence of this river with the River Pilcomayo. The Paraguay River and the Bay of Asunción in the northwest separate the city from the Occidental Region of Paraguay and Argentina in the south part of the city. The rest of the city is surrounded by the Central Department.
+With its location along the Paraguay River, the city offers many landscapes; it spreads out over gentle hills in a pattern of rectangular blocks. Places such as Cerro Lambaré, a hill located in Lambaré, offer a spectacular show in the springtime because of the blossoming lapacho trees in the area. Parks such as Parque Independencia and Parque Carlos Antonio López offer large areas of typical Paraguayan vegetation and are frequented by tourists. There are several small hills and slightly elevated areas throughout the city, including Cabará, Clavel, Tarumá, Cachinga, and Tacumbú, among others.
+Asunción, seen from the International Space Station
+Mariscal Lopez Avenue, one of the largest in the city
+Democracy Square
+Asunción is organized geographically into districts and these in turn bring together the different neighborhoods.
+Asunción has a humid subtropical climate (Köppen: Cfa) that closely borders on a tropical savanna climate (Köppen Aw), characterized by hot, humid summers (average of 27.5 °C or 81.5 °F in January), and mild winters (average of 17.6 °C, 63.7 °F in July).[8]  Relative humidity is high throughout the year, so the heat index is higher than the true air temperature in the summer, and in the winter it can feel cooler.[citation needed] The average annual temperature is 23 °C (73 °F). The average annual precipitation is high, with 1,400 millimetres (55 in) distributed in over 80 days yearly. The highest recorded temperature was 42.0 °C (107.6 °F) on 2 January 1934, while the lowest recorded temperature was −1.2 °C (29.8 °F) on 27 June 2011.
+Snow is unknown in modern times, but it fell during the Little Ice Age, last time in June 1751. [9]
+Asunción generally has a very short dry season between May and September, but the coldest months are June, July and August. Slight frosts can occur on average one or two days a year. The wet season covers the remainder of the year.
+During the wet season, Asunción is generally hot and humid though towards the end of this season, it becomes noticeably cooler. In contrast, Asunción's dry season is pleasantly mild. Asuncion's annual precipitation values observe a summer maximum, due to severe subtropical summer thunderstorms which travel southward from northern Paraguay, originating in the Gran Chaco region of the northwestern part of the country. The wettest and driest months of the year are April and July, on average receiving respectively 166 mm (6.54 in) and 39 mm (1.54 in) of precipitation.
+The population is approximately 540,000 people in the city proper.[1]  Roughly 30% of Paraguay's 6 million people live within Greater Asunción. Sixty-five percent of the total population in the city are under the age of 30.[13]
+The population has increased greatly during the last few decades as a consequence of internal migration from other Departments of Paraguay, at first because of the economic boom in the 1970s, and later because of economic recession in the countryside. The adjacent cities in the Gran Asunción area, such as Luque, Lambaré, San Lorenzo, Fernando de la Mora and Mariano Roque Alonso, have absorbed most of this influx due to the low cost of the land and easy access to Asunción. The city has ranked as the least expensive city to live in for five years running by Mercer Human Resource Consulting.[14]
+Population by sex and age according to the 2002 census
+Approximately 90% of the population of Asunción professes Catholicism.[17]   The Catholic Archdiocese of Asunción covers an area of 2,582 square kilometres (997 square miles) including the city and surrounding area and has a total population of 1,780,000 of whom 1,612,000 are Catholic.[17] The Catholic Archbishop is Eustaquio Pastor Cuquejo Verga, C.SS.R.[17]  In Paraguay's capital there are also places of worship of other Christian denominations, the Church of Jesus Christ of Latter-day Saints, as well as of other religions including Islam, Buddhism and Judaism.[citation needed]
+Most people in Paraguay speak one of two languages as their principal language: Paraguayan Spanish (spoken by 56.9% of the population) and Guaraní (spoken by 90.1%). 27.4% of the population speaks the Jopará dialect, a mix of Guaraní with loanwords from Spanish (Creole). Other languages are represented by 4.5% of the population.[citation needed]
+The city has a large number of both public and private schools. The best-known public schools are the Colegio Nacional de la Capital (which is one of the oldest schools in the city, founded in 1877),  Colegio Técnico Nacional, Colegio Nacional Presidente Franco and Colegio Nacional Asunción Escalada. The best-known private schools are, American School of Asunción, Colegio San José, St. Annes School, Colegio del Sol, Colegio Santa Clara, Colegio Goethe and Colegio de la Asunción, Colegio Las Almenas, Colegio Campoalto, Colegio Dante Alighieri, Colegio San Francisco, Colegio San Ignacio de Loyola, Colegio Santa Teresa de Jesús, Colegio Inmaculado Corazón de María, Salesianito, Colegio Cristo Rey, Colegio Internacional.
+The main universities in the city are the Universidad Americana and the Universidad Nacional de Asunción (state-run). The Universidad Nacional de Asunción was founded in 1889 and has an enrollment of just over 40,000 students. The Universidad Católica Nuestra Señora de la Asunción was founded in 1960 and has a current enrollment of around 21,000 students. The Católica has a small campus in the downtown area next to the Cathedral and a larger campus in the Santa Ana neighborhood, outwards toward the adjoining city of Lambaré, while the Universidad Nacional has its main campus in the city of San Lorenzo, some 5 km (3 mi) eastward from Asunción. There are also a number of smaller privately run universities such as Uninorte, Universidad Católica Nuestra Señora de la Asunción and Universidad Autónoma de Asunción, among others.
+In terms of commerce, this sector has grown considerably in recent years stretching towards the suburbs where shopping malls and supermarkets have been built. Paraguay's only stock exchange, the BVPASA, is located here. The city itself is listed on it, as BVPASA: MUA.[citation needed]
+In Asuncion, the most important companies, businesses and investment groups are headquartered. The attractiveness of the city can be attributed to its easy going tax policies. Asunción has unrestrained taxes on the investments and movements of capital. In addition to this, the Asunción stock exchange traded up 485.7% in August 2012 relative to August 2011. There is also no income tax for investors in Bonds of Asunción Stock Exchange. Incentives like these attract significant foreign investment into the city. By many Latin American experts, Paraguay is tapped as one of the top three counties with the best investment climate in Latin America and the Caribbean as well it remains the most attractive nation of the hemisphere in doing business and is equipped with a series of legislations that protect strategic investments and guarantee a friendly environment for the development of large industrial plants and infrastructure projects. The city is the economic center of Paraguay, followed by Ciudad del Este and Encarnación.
+Because the Paraguay River runs right next to Asunción the city is served by a river terminal in the downtown area. This port is strategically located inside a bay and it is where most freight enters and leaves the country. There is a lesser terminal in the Sajonia neighbourhood, and a shuttle port in Ita Enramada, almost opposite the Argentine city of Clorinda, Formosa.
+Public transportation is used heavily and is served through buses that reach all the regions of the city and surrounding dormitory communities. The main long-distance bus terminal is on the Avenida República Argentina and its bus services connect all of the Departments of Paraguay, as well as international routes to nearby countries such as Argentina, Brazil, Bolivia and Uruguay.
+Silvio Pettirossi International Airport is Paraguay's main national and international gateway, located at Luque, suburb of the capital Asunción. It is named after Paraguayan aviator Silvio Petrossi and is formerly known as Presidente Stroessner International Airport. As Paraguay's busiest airport, it is the hub of TAM Paraguayan Airlines.
+The city is home to the Godoy Museum, the Museo Nacional de Bellas Artes (which contains paintings from the 19th century), the Church of La Encarnación, the Metropolitan Cathedral and the National Pantheon of the Heroes, a smaller version of Les Invalides in Paris, where many of the nation's heroes are entombed. Other landmarks include the Palacio de los López, the old Senate building (a modern building opened to house Congress in 2003) and the Casa de la Independencia (one of the few examples of colonial architecture remaining in the city).
+Calle Palma is the main street downtown where several historical buildings, plazas, shops, restaurants and cafés are located. The "Manzana de la Rivera", located in front of the Presidential Palace, is a series of old traditional homes that have been restored and serve as a museum showcasing the architectural evolution of the city. The old railway station maintains the old trains that now are used in tourist trips to the cities of Luque and Areguá.
+Asunción also has luxurious malls that contain shops selling well-known brands. The biggest shopping malls are Shopping del Sol; Mariscal López Shopping, Shopping Villa Morra in the central part of the city, Shopping Multiplaza on the outskirts of the city and the Mall Excelsior located downtown. Pinedo Shopping and San Lorenzo Shopping are the newest and also sizeable shopping malls located just 5.6 and 9.3 kilometres (3.5 and 5.8 mi) from Asunción's boundaries respectively, in the city of San Lorenzo, part of Greater Asunción. In 2016 a new shopping mall, La Galeria, was inaugurated. It is in between the blue towers, and is now the largest shopping mall in the country.
+Association football is the main sport in Paraguay, and Asunción is home to some of the most important and traditional teams in the country. These include Olimpia, Cerro Porteño, Club Libertad, Club Nacional, Club Guaraní and Club Sol de América, which have their own stadiums and sport facilities for affiliated members. The Defensores del Chaco stadium is the main football stadium of the country and is located in the neighbourhood of Sajonia, just a few blocks away from the centre of Asunción. Since it is a national stadium sometimes it is used for other activities such as rock concerts. Asunción is also the heart of Paraguayan rugby union.
+The nightlife revolves around two areas: one in the downtown part of the city and the other in the neighbourhoods of Manora and Las Carmelitas, a night full of nightclubs and bars.
+Asunción also hosts several symphony orchestras, and ballet, opera and theater companies. The most well known orchestras are the City of Asunción's Symphony Orchestra (OSCA), the National Symphony Orchestra and the Northern University Symphony Orchestra. Among professional ballet companies, most renowned are the Asunción Classic and Modern Municipal Ballet, the National Ballet and the Northern University Ballet. The main opera company is the Northern University Opera Company. A long-standing theater company is Arlequín Theater Foundation's. Traditional venues include the Municipal Theater, the Paraguayan-Japanese Center, the Central Bank's Great Lyric Theater, the Juan de Salazar Cultural Center, the Americas Theater, the Tom Jobim Theater, the Arlequín Theater and the Manzana de la Rivera. Asunción is also the center of Architecture in Paraguay.
+The choice of the seven treasures of cultural heritage material has been developed Asunción during the months of April and May 2009. Promoted by the  "Organización Capital Americana de la Cultura", with the collaboration of the Paraguayan authorities participating in the election was carried out with the intention to disclose the material cultural heritage of Assumption.[citation needed]
+A total of 45 candidates have chosen to become one of the treasures of cultural heritage material Assumption. The result of the vote, which involved 12,417 people, is as follows:
+The most read newspapers are: Diario La Nación, Diario Hoy, Diario ABC, Diario Última Hora, and Diario Crónica, although  the most successful are ABC and Última Hora.
+The most important tv channel are SNT and the other free to air channels Paravisión, Sur TV, Unicanal, Latele, C9N, RPC, Telefuturo and the public station of tv Paraguay TV.
+Asunción is twinned with:

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+Eyes are organs of the visual system. They provide animals with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and convert it into electro-chemical impulses in neurons. In higher organisms, the eye is a complex optical system which collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system.[1] Image-resolving eyes are present in molluscs, chordates and arthropods.[2]
+The most simple eyes, pit eyes, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light.[1] From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment and to the pretectal area to control the pupillary light reflex.
+Complex eyes can distinguish shapes and colours. The visual fields of many organisms, especially predators, involve large areas of binocular vision to improve depth perception. In other organisms, eyes are located so as to maximise the field of view, such as in rabbits and horses, which have monocular vision.
+The first proto-eyes evolved among animals 600 million years ago about the time of the Cambrian explosion.[3] The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in six of the ~35[a] main phyla.[1] In most vertebrates and some molluscs, the eye works by allowing light to enter and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for colour) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals for vision. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris; the relaxing or tightening of the muscles around the iris change the size of the pupil, thereby regulating the amount of light that enters the eye,[4] and reducing aberrations when there is enough light.[5] The eyes of most cephalopods, fish, amphibians and snakes have fixed lens shapes, and focusing vision is achieved by telescoping the lens—similar to how a camera focuses.[6]
+Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, may give either a single pixelated image or multiple images, per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors, which are arranged hexagonally, and which can give a full 360° field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image, creating vision. With each eye viewing a different thing, a fused image from all the eyes is produced in the brain, providing very different, high-resolution images.
+Possessing detailed hyperspectral colour vision, the Mantis shrimp has been reported to have the world's most complex colour vision system.[7] Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes. The number of lenses in such an eye varied; however, some trilobites had only one, and some had thousands of lenses in one eye.
+In contrast to compound eyes, simple eyes are those that have a single lens. For example, jumping spiders have a large pair of simple eyes with a narrow field of view, supported by an array of other, smaller eyes for peripheral vision. Some insect larvae, like caterpillars, have a different type of simple eye (stemmata) which usually provides only a rough image, but (as in sawfly larvae) can possess resolving powers of 4 degrees of arc, be polarization-sensitive and capable of increasing its absolute sensitivity at night by a factor of 1,000 or more.[8] Some of the simplest eyes, called ocelli, can be found in animals like some of the snails, which cannot actually "see" in the normal sense. They do have photosensitive cells, but no lens and no other means of projecting an image onto these cells. They can distinguish between light and dark, but no more. This enables snails to keep out of direct sunlight.
+In organisms dwelling near deep-sea vents, compound eyes have been secondarily simplified and adapted to spot the infra-red light produced by the hot vents—in this way the bearers can spot hot springs and avoid being boiled alive.[9]
+There are ten different eye layouts—indeed every technological method of capturing an optical image commonly used by human beings, with the exceptions of zoom and Fresnel lenses, occur in nature.[1] Eye types can be categorised into "simple eyes", with one concave photoreceptive surface, and "compound eyes", which comprise a number of individual lenses laid out on a convex surface.[1] Note that "simple" does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for almost any behaviour or environment. The only limitations specific to eye types are that of resolution—the physics of compound eyes prevents them from achieving a resolution better than 1°. Also, superposition eyes can achieve greater sensitivity than apposition eyes, so are better suited to dark-dwelling creatures.[1] Eyes also fall into two groups on the basis of their photoreceptor's cellular construction, with the photoreceptor cells either being cilliated (as in the vertebrates) or rhabdomeric. These two groups are not monophyletic; the cnidaria also possess cilliated cells,
+[10] and some gastropods,[11] as well as some annelids possess both.[12]
+Some organisms have photosensitive cells that do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms. These are not considered eyes because they lack enough structure to be considered an organ, and do not produce an image.[13]
+Simple eyes are rather ubiquitous, and lens-bearing eyes have evolved at least seven times in vertebrates, cephalopods, annelids, crustaceans and cubozoa.[14][failed verification]
+Pit eyes, also known as stemma, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light.[1] Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of "simple eyes". They are small, comprising up to about 100 cells covering about 100 µm.[1] The directionality can be improved by reducing the size of the aperture, by incorporating a reflective layer behind the receptor cells, or by filling the pit with a refractile material.[1]
+Pit vipers have developed pits that function as eyes by sensing thermal infra-red radiation, in addition to their optical wavelength eyes like those of other vertebrates (see infrared sensing in snakes). However, pit organs are fitted with receptors rather different to photoreceptors, namely a specific transient receptor potential channel (TRP channels) called TRPV1. The main difference is that photoreceptors are G-protein coupled receptors but TRP are ion channels.
+The resolution of pit eyes can be greatly improved by incorporating a material with a higher refractive index to form a lens, which may greatly reduce the blur radius encountered—hence increasing the resolution obtainable.[1] The most basic form, seen in some gastropods and annelids, consists of a lens of one refractive index. A far sharper image can be obtained using materials with a high refractive index, decreasing to the edges; this decreases the focal length and thus allows a sharp image to form on the retina.[1] This also allows a larger aperture for a given sharpness of image, allowing more light to enter the lens; and a flatter lens, reducing spherical aberration.[1] Such a non-homogeneous lens is necessary for the focal length to drop from about 4 times the lens radius, to 2.5 radii.[1]
+Heterogeneous eyes have evolved at least nine times: four or more times in gastropods, once in the copepods, once in the annelids, once in the cephalopods,[1] and once in the chitons, which have aragonite lenses.[15] No extant aquatic organisms possess homogeneous lenses; presumably the evolutionary pressure for a heterogeneous lens is great enough for this stage to be quickly "outgrown".[1]
+This eye creates an image that is sharp enough that motion of the eye can cause significant blurring. To minimise the effect of eye motion while the animal moves, most such eyes have stabilising eye muscles.[1]
+The ocelli of insects bear a simple lens, but their focal point always lies behind the retina; consequently, they can never form a sharp image. Ocelli (pit-type eyes of arthropods) blur the image across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the whole visual field; this fast response is further accelerated by the large nerve bundles which rush the information to the brain.[16] Focusing the image would also cause the sun's image to be focused on a few receptors, with the possibility of damage under the intense light; shielding the receptors would block out some light and thus reduce their sensitivity.[16]
+This fast response has led to suggestions that the ocelli of insects are used mainly in flight, because they can be used to detect sudden changes in which way is up (because light, especially UV light which is absorbed by vegetation, usually comes from above).[16]
+Some marine organisms bear more than one lens; for instance the copepod Pontella has three. The outer has a parabolic surface, countering the effects of spherical aberration while allowing a sharp image to be formed. Another copepod, Copilia, has two lenses in each eye, arranged like those in a telescope.[1] Such arrangements are rare and poorly understood, but represent an alternative construction.
+Multiple lenses are seen in some hunters such as eagles and jumping spiders, which have a refractive cornea: these have a negative lens, enlarging the observed image by up to 50% over the receptor cells, thus increasing their optical resolution.[1]
+In the eyes of most mammals, birds, reptiles, and most other terrestrial vertebrates (along with spiders and some insect larvae) the vitreous fluid has a higher refractive index than the air.[1] In general, the lens is not spherical. Spherical lenses produce spherical aberration. In refractive corneas, the lens tissue is corrected with inhomogeneous lens material (see Luneburg lens), or with an aspheric shape.[1] Flattening the lens has a disadvantage; the quality of vision is diminished away from the main line of focus. Thus, animals that have evolved with a wide field-of-view often have eyes that make use of an inhomogeneous lens.[1]
+As mentioned above, a refractive cornea is only useful out of water. In water, there is little difference in refractive index between the vitreous fluid and the surrounding water. Hence creatures that have returned to the water—penguins and seals, for example—lose their highly curved cornea and return to lens-based vision. An alternative solution, borne by some divers, is to have a very strongly focusing cornea.[1]
+An alternative to a lens is to line the inside of the eye with "mirrors", and reflect the image to focus at a central point.[1] The nature of these eyes means that if one were to peer into the pupil of an eye, one would see the same image that the organism would see, reflected back out.[1]
+Many small organisms such as rotifers, copepods and flatworms use such organs, but these are too small to produce usable images.[1] Some larger organisms, such as scallops, also use reflector eyes. The scallop Pecten has up to 100 millimetre-scale reflector eyes fringing the edge of its shell. It detects moving objects as they pass successive lenses.[1]
+There is at least one vertebrate, the spookfish, whose eyes include reflective optics for focusing of light. Each of the two eyes of a spookfish collects light from both above and below; the light coming from above is focused by a lens, while that coming from below, by a curved mirror composed of many layers of small reflective plates made of guanine crystals.[17]
+A compound eye may consist of thousands of individual photoreceptor units or ommatidia (ommatidium, singular). The image perceived is a combination of inputs from the numerous ommatidia (individual "eye units"), which are located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarisation of light.[18] Because the individual lenses are so small, the effects of diffraction impose a limit on the possible resolution that can be obtained (assuming that they do not function as phased arrays). This can only be countered by increasing lens size and number. To see with a resolution comparable to our simple eyes, humans would require very large compound eyes, around 11 metres (36 ft) in radius.[19]
+Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form a single erect image.[20] Compound eyes are common in arthropods, annelids and some bivalved molluscs.[21] Compound eyes in arthropods grow at their margins by the addition of new ommatidia.[22]
+Apposition eyes are the most common form of eyes and are presumably the ancestral form of compound eyes. They are found in all arthropod groups, although they may have evolved more than once within this phylum.[1] Some annelids and bivalves also have apposition eyes. They are also possessed by Limulus, the horseshoe crab, and there are suggestions that other chelicerates developed their simple eyes by reduction from a compound starting point.[1] (Some caterpillars appear to have evolved compound eyes from simple eyes in the opposite fashion.)
+Apposition eyes work by gathering a number of images, one from each eye, and combining them in the brain, with each eye typically contributing a single point of information. The typical apposition eye has a lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium.
+The second type is named the superposition eye. The superposition eye is divided into three types:
+The refracting superposition eye has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to the same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This type of compound eye, for which a minimal size exists below which effective superposition cannot occur,[23] is normally found in nocturnal insects, because it can create images up to 1000 times brighter than equivalent apposition eyes, though at the cost of reduced resolution.[24] In the parabolic superposition compound eye type, seen in arthropods such as mayflies, the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array. Long-bodied decapod crustaceans such as shrimp, prawns, crayfish and lobsters are alone in having reflecting superposition eyes, which also have a transparent gap but use corner mirrors instead of lenses.
+This eye type functions by refracting light, then using a parabolic mirror to focus the image; it combines features of superposition and apposition eyes.[9]
+Another kind of compound eye, found in males of Order Strepsiptera, employs a series of simple eyes—eyes having one opening that provides light for an entire image-forming retina. Several of these eyelets together form the strepsipteran compound eye, which is similar to the 'schizochroal' compound eyes of some trilobites.[25] Because each eyelet is a simple eye, it produces an inverted image; those images are combined in the brain to form one unified image. Because the aperture of an eyelet is larger than the facets of a compound eye, this arrangement allows vision under low light levels.[1]
+Good fliers such as flies or honey bees, or prey-catching insects such as praying mantis or dragonflies, have specialised zones of ommatidia organised into a fovea area which gives acute vision. In the acute zone, the eyes are flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. The black spot that can be seen on the compound eyes of such insects, which always seems to look directly at the observer, is called a pseudopupil. This occurs because the ommatidia which one observes "head-on" (along their optical axes) absorb the incident light, while those to one side reflect it.[26]
+There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there is the mysid shrimp, Dioptromysis paucispinosa. The shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there is a single large facet that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialised retina. The resulting eye is a mixture of a simple eye within a compound eye.
+Another version is a compound eye often referred to as "pseudofaceted", as seen in Scutigera.[27] This type of eye consists of a cluster of numerous ommatidia on each side of the head, organised in a way that resembles a true compound eye.
+The body of Ophiocoma wendtii, a type of brittle star, is covered with ommatidia, turning its whole skin into a compound eye. The same is true of many chitons. The tube feet of sea urchins contain photoreceptor proteins, which together act as a compound eye; they lack screening pigments, but can detect the directionality of light by the shadow cast by its opaque body.[28]
+The ciliary body is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. The inner layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina. The outer layer is highly pigmented, continuous with the retinal pigment epithelium, and constitutes the cells of the dilator muscle.
+The vitreous is the transparent, colourless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye.[29] It is produced by certain retinal cells. It is of rather similar composition to the cornea, but contains very few cells (mostly phagocytes which remove unwanted cellular debris in the visual field, as well as the hyalocytes of Balazs of the surface of the vitreous, which reprocess the hyaluronic acid), no blood vessels, and 98–99% of its volume is water (as opposed to 75% in the cornea) with salts, sugars, vitrosin (a type of collagen), a network of collagen type II fibres with the mucopolysaccharide hyaluronic acid, and also a wide array of proteins in micro amounts. Amazingly, with so little solid matter, it tautly holds the eye.
+Photoreception is phylogenetically very old, with various theories of phylogenesis.[30] The common origin (monophyly) of all animal eyes is now widely accepted as fact. This is based upon the shared genetic features of all eyes; that is, all modern eyes, varied as they are, have their origins in a proto-eye believed to have evolved some 540 million years ago,[31][32][33] and the PAX6 gene is considered a key factor in this. The majority of the advancements in early eyes are believed to have taken only a few million years to develop, since the first predator to gain true imaging would have touched off an "arms race"[34] among all species that did not flee the photopic environment. Prey animals and competing predators alike would be at a distinct disadvantage without such capabilities and would be less likely to survive and reproduce. Hence multiple eye types and subtypes developed in parallel (except those of groups, such as the vertebrates, that were only forced into the photopic environment at a late stage).
+Eyes in various animals show adaptation to their requirements. For example, the eye of a bird of prey has much greater visual acuity than a human eye, and in some cases can detect ultraviolet radiation. The different forms of eye in, for example, vertebrates and molluscs are examples of parallel evolution, despite their distant common ancestry. Phenotypic convergence of the geometry of cephalopod and most vertebrate eyes creates the impression that the vertebrate eye evolved from an imaging cephalopod eye, but this is not the case, as the reversed roles of their respective ciliary and rhabdomeric opsin classes[35] and different lens crystallins show.[36]
+The very earliest "eyes", called eye-spots, were simple patches of photoreceptor protein in unicellular animals. In multicellular beings, multicellular eyespots evolved, physically similar to the receptor patches for taste and smell. These eyespots could only sense ambient brightness: they could distinguish light and dark, but not the direction of the light source.[1]
+Through gradual change, the eye-spots of species living in well-lit environments depressed into a shallow "cup" shape. The ability to slightly discriminate directional brightness was achieved by using the angle at which the light hit certain cells to identify the source. The pit deepened over time, the opening diminished in size, and the number of photoreceptor cells increased, forming an effective pinhole camera that was capable of dimly distinguishing shapes.[37] However, the ancestors of modern hagfish, thought to be the protovertebrate,[35] were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. This would have led to a somewhat different evolutionary trajectory for the vertebrate eye than for other animal eyes.
+The thin overgrowth of transparent cells over the eye's aperture, originally formed to prevent damage to the eyespot, allowed the segregated contents of the eye chamber to specialise into a transparent humour that optimised colour filtering, blocked harmful radiation, improved the eye's refractive index, and allowed functionality outside of water. The transparent protective cells eventually split into two layers, with circulatory fluid in between that allowed wider viewing angles and greater imaging resolution, and the thickness of the transparent layer gradually increased, in most species with the transparent crystallin protein.[38]
+The gap between tissue layers naturally formed a biconvex shape, an optimally ideal structure for a normal refractive index. Independently, a transparent layer and a nontransparent layer split forward from the lens: the cornea and iris. Separation of the forward layer again formed a humour, the aqueous humour. This increased refractive power and again eased circulatory problems. Formation of a nontransparent ring allowed more blood vessels, more circulation, and larger eye sizes.[38]
+Eyes are generally adapted to the environment and life requirements of the organism which bears them. For instance, the distribution of photoreceptors tends to match the area in which the highest acuity is required, with horizon-scanning organisms, such as those that live on the African plains, having a horizontal line of high-density ganglia, while tree-dwelling creatures which require good all-round vision tend to have a symmetrical distribution of ganglia, with acuity decreasing outwards from the centre.
+Of course, for most eye types, it is impossible to diverge from a spherical form, so only the density of optical receptors can be altered. In organisms with compound eyes, it is the number of ommatidia rather than ganglia that reflects the region of highest data acquisition.[1]:23–24 Optical superposition eyes are constrained to a spherical shape, but other forms of compound eyes may deform to a shape where more ommatidia are aligned to, say, the horizon, without altering the size or density of individual ommatidia.[39] Eyes of horizon-scanning organisms have stalks so they can be easily aligned to the horizon when this is inclined, for example, if the animal is on a slope.[26]
+An extension of this concept is that the eyes of predators typically have a zone of very acute vision at their centre, to assist in the identification of prey.[39] In deep water organisms, it may not be the centre of the eye that is enlarged. The hyperiid amphipods are deep water animals that feed on organisms above them. Their eyes are almost divided into two, with the upper region thought to be involved in detecting the silhouettes of potential prey—or predators—against the faint light of the sky above. Accordingly, deeper water hyperiids, where the light against which the silhouettes must be compared is dimmer, have larger "upper-eyes", and may lose the lower portion of their eyes altogether.[39] In the giant Antarctic isopod Glyptonotus a small ventral compound eye is physically completely separated from the much larger dorsal compound eye.[40] Depth perception can be enhanced by having eyes which are enlarged in one direction; distorting the eye slightly allows the distance to the object to be estimated with a high degree of accuracy.[9]
+Acuity is higher among male organisms that mate in mid-air, as they need to be able to spot and assess potential mates against a very large backdrop.[39] On the other hand, the eyes of organisms which operate in low light levels, such as around dawn and dusk or in deep water, tend to be larger to increase the amount of light that can be captured.[39]
+It is not only the shape of the eye that may be affected by lifestyle. Eyes can be the most visible parts of organisms, and this can act as a pressure on organisms to have more transparent eyes at the cost of function.[39]
+Eyes may be mounted on stalks to provide better all-round vision, by lifting them above an organism's carapace; this also allows them to track predators or prey without moving the head.[9]
+Visual acuity, or resolving power, is "the ability to distinguish fine detail" and is the property of cone cells.[41] It is often measured in cycles per degree (CPD), which measures an angular resolution, or how much an eye can differentiate one object from another in terms of visual angles. Resolution in CPD can be measured by bar charts of different numbers of white/black stripe cycles. For example, if each pattern is 1.75 cm wide and is placed at 1 m distance from the eye, it will subtend an angle of 1 degree, so the number of white/black bar pairs on the pattern will be a measure of the cycles per degree of that pattern. The highest such number that the eye can resolve as stripes, or distinguish from a grey block, is then the measurement of visual acuity of the eye.
+For a human eye with excellent acuity, the maximum theoretical resolution is 50 CPD[42] (1.2 arcminute per line pair, or a 0.35 mm line pair, at 1 m). A rat can resolve only about 1 to 2 CPD.[43] A horse has higher acuity through most of the visual field of its eyes than a human has, but does not match the high acuity of the human eye's central fovea region.[44]
+Spherical aberration limits the resolution of a 7 mm pupil to about 3 arcminutes per line pair. At a pupil diameter of 3 mm, the spherical aberration is greatly reduced, resulting in an improved resolution of approximately 1.7 arcminutes per line pair.[45] A resolution of 2 arcminutes per line pair, equivalent to a 1 arcminute gap in an optotype, corresponds to 20/20 (normal vision) in humans.
+However, in the compound eye, the resolution is related to the size of individual ommatidia and the distance between neighbouring ommatidia. Physically these cannot be reduced in size to achieve the acuity seen with single lensed eyes as in mammals. Compound eyes have a much lower acuity than vertebrate eyes.[46]
+"Colour vision is the faculty of the organism to distinguish lights of different spectral qualities."[47] All organisms are restricted to a small range of electromagnetic spectrum; this varies from creature to creature, but is mainly between wavelengths of 400 and 700 nm.[48]
+This is a rather small section of the electromagnetic spectrum, probably reflecting the submarine evolution of the organ: water blocks out all but two small windows of the EM spectrum, and there has been no evolutionary pressure among land animals to broaden this range.[49]
+The most sensitive pigment, rhodopsin, has a peak response at 500 nm.[50] Small changes to the genes coding for this protein can tweak the peak response by a few nm;[2] pigments in the lens can also filter incoming light, changing the peak response.[2] Many organisms are unable to discriminate between colours, seeing instead in shades of grey; colour vision necessitates a range of pigment cells which are primarily sensitive to smaller ranges of the spectrum. In primates, geckos, and other organisms, these take the form of cone cells, from which the more sensitive rod cells evolved.[50] Even if organisms are physically capable of discriminating different colours, this does not necessarily mean that they can perceive the different colours; only with behavioural tests can this be deduced.[2]
+Most organisms with colour vision can detect ultraviolet light. This high energy light can be damaging to receptor cells. With a few exceptions (snakes, placental mammals), most organisms avoid these effects by having absorbent oil droplets around their cone cells. The alternative, developed by organisms that had lost these oil droplets in the course of evolution, is to make the lens impervious to UV light—this precludes the possibility of any UV light being detected, as it does not even reach the retina.[50]
+The retina contains two major types of light-sensitive photoreceptor cells used for vision: the rods and the cones.
+Rods cannot distinguish colours, but are responsible for low-light (scotopic) monochrome (black-and-white) vision; they work well in dim light as they contain a pigment, rhodopsin (visual purple), which is sensitive at low light intensity, but saturates at higher (photopic) intensities. Rods are distributed throughout the retina but there are none at the fovea and none at the blind spot. Rod density is greater in the peripheral retina than in the central retina.
+Cones are responsible for colour vision. They require brighter light to function than rods require. In humans, there are three types of cones, maximally sensitive to long-wavelength, medium-wavelength, and short-wavelength light (often referred to as red, green, and blue, respectively, though the sensitivity peaks are not actually at these colours). The colour seen is the combined effect of stimuli to, and responses from, these three types of cone cells. Cones are mostly concentrated in and near the fovea. Only a few are present at the sides of the retina. Objects are seen most sharply in focus when their images fall on the fovea, as when one looks at an object directly. Cone cells and rods are connected through intermediate cells in the retina to nerve fibres of the optic nerve. When rods and cones are stimulated by light, they connect through adjoining cells within the retina to send an electrical signal to the optic nerve fibres. The optic nerves send off impulses through these fibres to the brain.[50]
+The pigment molecules used in the eye are various, but can be used to define the evolutionary distance between different groups, and can also be an aid in determining which are closely related—although problems of convergence do exist.[50]
+Opsins are the pigments involved in photoreception. Other pigments, such as melanin, are used to shield the photoreceptor cells from light leaking in from the sides.
+The opsin protein group evolved long before the last common ancestor of animals, and has continued to diversify since.[2]
+There are two types of opsin involved in vision; c-opsins, which are associated with ciliary-type photoreceptor cells, and r-opsins, associated with rhabdomeric photoreceptor cells.[51] The eyes of vertebrates usually contain ciliary cells with c-opsins, and (bilaterian) invertebrates have rhabdomeric cells in the eye with r-opsins. However, some ganglion cells of vertebrates express r-opsins, suggesting that their ancestors used this pigment in vision, and that remnants survive in the eyes.[51] Likewise, c-opsins have been found to be expressed in the brain of some invertebrates. They may have been expressed in ciliary cells of larval eyes, which were subsequently resorbed into the brain on metamorphosis to the adult form.[51] C-opsins are also found in some derived bilaterian-invertebrate eyes, such as the pallial eyes of the bivalve molluscs; however, the lateral eyes (which were presumably the ancestral type for this group, if eyes evolved once there) always use r-opsins.[51]
+Cnidaria, which are an outgroup to the taxa mentioned above, express c-opsins—but r-opsins are yet to be found in this group.[51] Incidentally, the melanin produced in the cnidaria is produced in the same fashion as that in vertebrates, suggesting the common descent of this pigment.[51]
+The structures of the eye labelled
+Another view of the eye and the structures of the eye labelled

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+The esophagus, (American English) or oesophagus (British English; see spelling differences) (/ɪˈsɒfəɡəs/), informally known as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the stomach. The esophagus is a fibromuscular tube, about 25 cm (10 in) long in adults, which travels behind the trachea and heart, passes through the diaphragm and empties into the uppermost region of the stomach. During swallowing, the epiglottis tilts backwards to prevent food from going down the larynx and lungs. The word oesophagus is the Greek word οἰσοφάγος oisophagos, meaning "gullet".
+The wall of the esophagus from the lumen outwards consists of mucosa, submucosa (connective tissue), layers of muscle fibers between layers of fibrous tissue, and an outer layer of connective tissue. The mucosa is a stratified squamous epithelium of around three layers of squamous cells, which contrasts to the single layer of columnar cells of the stomach. The transition between these two types of epithelium is visible as a zig-zag line. Most of the muscle is smooth muscle although striated muscle predominates in its upper third. It has two muscular rings or sphincters in its wall, one at the top and one at the bottom. The lower sphincter helps to prevent reflux of acidic stomach content. The esophagus has a rich blood supply and venous drainage. Its smooth muscle is innervated by involuntary nerves (sympathetic nerves via the sympathetic trunk and parasympathetic nerves via the vagus nerve) and in addition voluntary nerves (lower motor neurons) which are carried in the vagus nerve to innervate its striated muscle.
+The esophagus may be affected by gastric reflux, cancer, prominent dilated blood vessels called varices that can bleed heavily, tears, constrictions, and disorders of motility. Diseases may cause difficulty swallowing (dysphagia), painful swallowing (odynophagia), chest pain, or cause no symptoms at all. Clinical investigations include X-rays when swallowing barium, endoscopy, and CT scans. Surgically,
+the esophagus is difficult to access.[1]
+The esophagus is one of the upper parts of the digestive system. There are taste buds on its upper part.[2] It begins at the back of the mouth, passing downwards through the rear part of the mediastinum, through the diaphragm, and into the stomach. In humans, the esophagus generally starts around the level of the sixth cervical vertebra behind the cricoid cartilage of the trachea, enters the diaphragm at about the level of the tenth thoracic vertebra, and ends at the cardia of the stomach, at the level of the eleventh thoracic vertebra.[3] The esophagus is usually about 25 cm (10 in) in length.[4]
+Many blood vessels serve the esophagus, with blood supply varying along its course. The upper parts of the esophagus and the upper esophageal sphincter receive blood from the inferior thyroid artery, the parts of the esophagus in the thorax from the bronchial arteries and branches directly from the thoracic aorta, and the lower parts of the esophagus and the lower esophageal sphincter receive blood from the left gastric artery and the left inferior phrenic artery.[5][6] The venous drainage also differs along the course of the esophagus. The upper and middle parts of the esophagus drain into the azygos and hemiazygos veins, and blood from the lower part drains into the left gastric vein. All these veins drain into the superior vena cava, with the exception of the left gastric vein, which is a branch of the portal vein.[5] Lymphatically, the upper third of the esophagus drains into the deep cervical lymph nodes, the middle into the superior and posterior mediastinal lymph nodes, and the lower esophagus into the gastric and celiac lymph nodes. This is similar to the lymphatic drainage of the abdominal structures that arise from the foregut, which all drain into the celiac nodes.[5]
+The upper esophagus lies at the back of the mediastinum behind the trachea, adjoining along the tracheoesophageal stripe, and in front of the erector spinae muscles and the vertebral column. The lower esophagus lies behind the heart and curves in front of the thoracic aorta. From the bifurcation of the trachea downwards, the esophagus passes behind the right pulmonary artery, left main bronchus, and left atrium. At this point it passes through the diaphragm.[3]
+The thoracic duct, which drains the majority of the body's lymph, passes behind the esophagus, curving from lying behind the esophagus on the right in the lower part of the esophagus, to lying behind the esophagus on the left in the upper esophagus. The esophagus also lies in front of parts of the hemiazygos veins and the intercostal veins on the right side. The vagus nerve divides and covers the esophagus in a plexus.[3]
+The esophagus has four points of constriction. When a corrosive substance, or a solid object is swallowed, it is most likely to lodge and damage one of these four points. These constrictions arise from particular structures that compress the esophagus. These constrictions are:[7]
+The esophagus is surrounded at the top and bottom by two muscular rings, known respectively as the upper esophageal sphincter and the lower esophageal sphincter.[3] These sphincters act to close the esophagus when food is not being swallowed. The upper esophageal sphincter is an anatomical sphincter, which is formed by lower portion of inferior pharyngeal constrictor, also known as cricopharyngeal sphincter due to its relation with cricoid cartilage of the larynx anteriorly. However, the lower esophageal sphincter is not an anatomical but rather a functional sphincter, meaning that it acts as a sphincter but does not have a distinct thickening like other sphincters.
+The upper esophageal sphincter surrounds the upper part of the esophagus. It consists of skeletal muscle but is not under voluntary control. Opening of the upper esophageal sphincter is triggered by the swallowing reflex. The primary muscle of the upper esophageal sphincter is the cricopharyngeal part of the inferior pharyngeal constrictor.[8]
+The lower esophageal sphincter, or gastroesophageal sphincter, surrounds the lower part of the esophagus at the junction between the esophagus and the stomach.[9] It is also called the cardiac sphincter or cardioesophageal sphincter, named from the adjacent part of the stomach, the cardia. Dysfunction of the gastroesophageal sphincter causes gastroesophageal reflux, which causes heartburn and if it happens often enough, can lead to gastroesophageal reflux disease, with damage of the esophageal mucosa.[10]
+The esophagus is innervated by the vagus nerve and the cervical and thoracic sympathetic trunk.[5] The vagus nerve has a parasympathetic function, supplying the muscles of the esophagus and stimulating glandular contraction. Two sets of nerve fibers travel in the vagus nerve to supply the muscles. The upper striated muscle, and upper esophageal sphincter, are supplied by neurons with bodies in the nucleus ambiguus, whereas fibers that supply the smooth muscle and lower esophageal sphincter have bodies situated in the dorsal motor nucleus.[5] The vagus nerve plays the primary role in initiating peristalsis.[11] The sympathetic trunk has a sympathetic function. It may enhance the function of the vagus nerve, increasing peristalsis and glandular activity, and causing sphincter contraction. In addition, sympathetic activation may relax the muscle wall and cause blood vessel constriction.[5] Sensation along the esophagus is supplied by both nerves, with gross sensation being passed in the vagus nerve and pain passed up the sympathetic trunk.[3]
+The gastro-esophageal junction (also known as the esophagogastric junction) is the junction between the esophagus and the stomach, at the lower end of the esophagus.[12] The pink color of the esophageal mucosa contrasts to the deeper red of the gastric mucosa,[5][13] and the mucosal transition can be seen as an irregular zig-zag line, which is often called the z-line.[14] Histological examination reveals abrupt transition between the stratified squamous epithelium of the esophagus and the simple columnar epithelium of the stomach.[15] Normally, the cardia of the stomach is immediately distal to the z-line[16] and the z-line coincides with the upper limit of the gastric folds of the cardia; however, when the anatomy of the mucosa is distorted in Barrets esophagus the true gastro-eshophageal junction can be identified by the upper limit of the gastric folds rather than the mucosal transition.[17] The functional location of the lower oesophageal sphincter is generally situated about 3 cm (1.2 in) below the z-line.[5]
+The human esophagus has a mucous membrane consisting of a tough stratified squamous epithelium without keratin, a smooth lamina propria, and a muscularis mucosae.[5] The epithelium of the esophagus has a relatively rapid turnover, and serves a protective function against the abrasive effects of food. In many animals the epithelium contains a layer of keratin, representing a coarser diet.[18] There are two types of glands, with mucus-secreting esophageal glands being found in the submucosa, and esophageal cardiac glands, similar to cardiac glands of the stomach, located in the lamina propria and most frequent in the terminal part of the organ.[18][19] The mucus from the glands gives a good protection to the lining.[20] The submucosa also contains the submucosal plexus, a network of nerve cells that is part of the enteric nervous system.[18]
+The muscular layer of the esophagus has two types of muscle. The upper third of the esophagus contains striated muscle, the lower third contains smooth muscle, and the middle third contains a mixture of both.[5] Muscle is arranged in two layers: one in which the muscle fibers run longitudinal to the esophagus, and the other in which the fibers encircle the esophagus. These are separated by the myenteric plexus, a tangled network of nerve fibers involved in the secretion of mucus and in peristalsis of the smooth muscle of the esophagus. The outermost layer of the esophagus is the adventitia in most of its length, with the abdominal part being covered in serosa. This makes it distinct from many other structures in the gastrointestinal tract that only have a serosa.[5]
+In early embryogenesis, the esophagus develops from the endodermal primitive gut tube. The ventral part of the embryo abuts the yolk sac. During the second week of embryological development, as the embryo grows, it begins to surround parts of the sac. The enveloped portions form the basis for the adult gastrointestinal tract.[21] The sac is surrounded by a network of vitelline arteries. Over time, these arteries consolidate into the three main arteries that supply the developing gastrointestinal tract: the celiac artery, superior mesenteric artery, and inferior mesenteric artery. The areas supplied by these arteries are used to define the midgut, hindgut and foregut.[21]
+The surrounded sac becomes the primitive gut. Sections of this gut begin to differentiate into the organs of the gastrointestinal tract, such as the esophagus, stomach, and intestines.[21] The esophagus develops as part of the foregut tube.[21] The innervation of the esophagus develops from the pharyngeal arches.[3]
+Food is ingested through the mouth and when swallowed passes first into the pharynx and then into the esophagus. The esophagus is thus one of the first components of the digestive system and the gastrointestinal tract. After food passes through the esophagus, it enters the stomach.[9] When food is being swallowed, the epiglottis moves backward to cover the larynx, preventing food from entering the trachea. At the same time, the upper esophageal sphincter relaxes, allowing a bolus of food to enter. Peristaltic contractions of the esophageal muscle push the food down the esophagus. These rhythmic contractions occur both as a reflex response to food that is in the mouth, and also as a response to the sensation of food within the esophagus itself. Along with peristalsis, the lower esophageal sphincter relaxes.[9]
+The stomach produces gastric acid, a strongly acidic mixture consisting of hydrochloric acid (HCl) and potassium and sodium salts to enable food digestion. Constriction of the upper and lower esophageal sphincters help to prevent reflux (backflow) of gastric contents and acid into the esophagus, protecting the esophageal mucosa. In addition, the acute angle of His and the lower crura of the diaphragm helps this sphincteric action.[9][22]
+About 20,000 protein-coding genes are expressed in human cells and nearly 70% of these genes are expressed in the normal esophagus.[23][24] Some 250 of these genes are more specifically expressed in the esophagus with less than 50 genes being highly specific. The corresponding esophagus-specific proteins are mainly involved in squamous differentiation such as keratins KRT13, KRT4 and KRT6C. Other specific proteins that help lubricate the inner surface of esophagus are mucins such as MUC21 and MUC22. Many genes with elevated expression are also shared with skin and other organs that are composed of squamous epithelia.[25]
+The main conditions affecting the esophagus are described here. For a more complete list, see esophageal disease.
+Inflammation of the esophagus is known as esophagitis. Reflux of gastric acids from the stomach, infection, substances ingested (for example, corrosives), some medications (such as bisphosphonates), and food allergies can all lead to esophagitis. Esophageal candidiasis is an infection of the yeast Candida albicans that may occur when a person is immunocompromised. As of 2014[update] the cause of some forms of esophagitis, such as eosinophilic esophagitis, is not known. Esophagitis can cause painful swallowing and is usually treated by managing the cause of the esophagitis - such as managing reflux or treating infection.[4]
+Prolonged esophagitis, particularly from gastric reflux, is one factor thought to play a role in the development of Barrett's esophagus. In this condition, there is metaplasia of the lining of the lower esophagus, which changes from stratified squamous epithelia to simple columnar epithelia. Barrett's esophagus is thought to be one of the main contributors to the development of esophageal cancer.[4]
+There are two main types of cancer of the esophagus. Squamous cell carcinoma is a carcinoma that can occur in the squamous cells lining the esophagus. This type is much more common in China and Iran. The other main type is an adenocarcinoma that occurs in the glands or columnar tissue of the esophagus. This is most common in developed countries in those with Barrett's esophagus, and occurs in the cuboidal cells.[4]
+In its early stages, esophageal cancer may not have any symptoms at all. When severe, esophageal cancer may eventually cause obstruction of the esophagus, making swallowing of any solid foods very difficult and causing weight loss. The progress of the cancer is staged using a system that measures how far into the esophageal wall the cancer has invaded, how many lymph nodes are affected, and whether there are any metastases in different parts of the body. Esophageal cancer is often managed with radiotherapy, chemotherapy, and may also be managed by partial surgical removal of the esophagus. Inserting a stent into the esophagus, or inserting a nasogastric tube, may also be used to ensure that a person is able to digest enough food and water. As of 2014[update], the prognosis for esophageal cancer is still poor, so palliative therapy may also be a focus of treatment.[4]
+Esophageal varices are swollen twisted branches of the azygous vein in the lower third of the esophagus. These blood vessels anastomose (join up) with those of the portal vein when portal hypertension develops.[26] These blood vessels are engorged more than normal, and in the worst cases may partially obstruct the esophagus. These blood vessels develop as part of a collateral circulation that occurs to drain blood from the abdomen as a result of portal hypertension, usually as a result of liver diseases such as cirrhosis.[4]:941–42 This collateral circulation occurs because the lower part of the esophagus drains into the left gastric vein, which is a branch of the portal vein. Because of the extensive venous plexus that exists between this vein and other veins, if portal hypertension occurs, the direction of blood drainage in this vein may reverse, with blood draining from the portal venous system, through the plexus. Veins in the plexus may engorge and lead to varices.[5][6]
+Esophageal varices often do not have symptoms until they rupture. A ruptured varix is considered a medical emergency, because varices can bleed a lot. A bleeding varix may cause a person to vomit blood, or suffer shock. To deal with a ruptured varix, a band may be placed around the bleeding blood vessel, or a small amount of a clotting agent may be injected near the bleed. A surgeon may also try to use a small inflatable balloon to apply pressure to stop the wound. IV fluids and blood products may be given in order to prevent hypovolemia from excess blood loss.[4]
+Several disorders affect the motility of food as it travels down the esophagus. This can cause difficult swallowing, called dysphagia, or painful swallowing, called odynophagia. Achalasia refers to a failure of the lower esophageal sphincter to relax properly, and generally develops later in life. This leads to progressive enlargement of the esophagus, and possibly eventual megaesophagus. A nutcracker esophagus refers to swallowing that can be extremely painful. Diffuse esophageal spasm is a spasm of the esophagus that can be one cause of chest pain. Such referred pain to the wall of the upper chest is quite common in esophageal conditions.[27] Sclerosis of the esophagus, such as with systemic sclerosis or in CREST syndrome may cause hardening of the walls of the esophagus and interfere with peristalsis.[4]
+Esophageal strictures are usually benign and typically develop after a person has had reflux for many years. Other strictures may include esophageal webs (which can also be congenital) and damage to the esophagus by radiotherapy, corrosive ingestion, or eosinophilic esophagitis. A Schatzki ring is fibrosis at the gastro-esophageal junction. Strictures may also develop in chronic anemia, and Plummer-Vinson syndrome.[4]
+Two of the most common congenital malformations affecting the esophagus are an esophageal atresia where the esophagus ends in a blind sac instead of connecting to the stomach; and an esophageal fistula – an abnormal connection between the esophagus and the trachea.[28] Both of these conditions usually occur together.[28] These are found in about 1 in 3500 births.[29] Half of these cases may be part of a syndrome where other abnormalities are also present, particularly of the heart or limbs. The other cases occur singly.[30]
+An X-ray of swallowed barium may be used to reveal the size and shape of the esophagus, and the presence of any masses. The esophagus may also be imaged using a flexible camera inserted into the esophagus, in a procedure called an endoscopy. If an endoscopy is used on the stomach, the camera will also have to pass through the esophagus. During an endoscopy, a biopsy may be taken. If cancer of the esophagus is being investigated, other methods, including a CT scan, may also be used.[4]
+The word esophagus (British English: oesophagus), comes from the Greek: οἰσοφάγος (oisophagos) meaning gullet. It derives from two roots (eosin) to carry and (phagos) to eat.[31] The use of the word oesophagus, has been documented in anatomical literature since at least the time of Hippocrates, who noted that "the oesophagus ... receives the greatest amount of what we consume." [32] Its existence in other animals and its relationship with the stomach was documented by the Roman naturalist Pliny the Elder (AD23–AD79),[33] and the peristaltic contractions of the esophagus have been documented since at least the time of Galen.[34]
+The first attempt at surgery on the esophagus focused in the neck, and was conducted in dogs by Theodore Billroth in 1871. In 1877 Czerny carried out surgery in people. By 1908, an operation had been performed by Voeckler to remove the esophagus, and in 1933 the first surgical removal of parts of the lower esophagus, (to control esophageal cancer), had been conducted.[35]
+The Nissen fundoplication, in which the stomach is wrapped around the lower esophageal sphincter to stimulate its function and control reflux, was first conducted by Rudolph Nissen in 1955.[35]
+In tetrapods, the pharynx is much shorter, and the esophagus correspondingly longer, than in fish. In the majority of vertebrates, the esophagus is simply a connecting tube, but in some birds, which regurgitate components to feed their young, it is extended towards the lower end to form a crop for storing food before it enters the true stomach.[36][37] In ruminants, animals with four stomachs, a groove called the sulcus reticuli is often found in the esophagus, allowing milk to drain directly into the hind stomach, the abomasum.[38] In the horse the esophagus is about 1.2 to 1.5 m (4 to 5 ft) in length, and carries food to the stomach. A muscular ring, called the cardiac sphincter, connects the stomach to the esophagus. This sphincter is very well developed in horses. This and the oblique angle at which the esophagus connects to the stomach explains why horses cannot vomit.[39] The esophagus is also the area of the digestive tract where horses may suffer from the condition known as choke.
+The esophagus of snakes is remarkable for the distension it undergoes when swallowing prey.[40]
+In most fish, the esophagus is extremely short, primarily due to the length of the pharynx (which is associated with the gills). However, some fish, including lampreys, chimaeras, and lungfish, have no true stomach, so that the esophagus effectively runs from the pharynx directly to the intestine, and is therefore somewhat longer.[36]
+In many vertebrates, the esophagus is lined by stratified squamous epithelium without glands. In fish, the esophagus is often lined with columnar epithelium,[37] and in amphibians, sharks and rays, the esophageal epithelium is ciliated, helping to wash food along, in addition to the action of muscular peristalsis.[36] In addition, in the bat Plecotus auritus, fish and some amphibians, glands secreting pepsinogen or hydrochloric acid have been found.[37]
+The muscle of the esophagus in many mammals is striated initially, but then becomes smooth muscle in the caudal third or so. In canines and ruminants, however, it is entirely striated to allow regurgitation to feed young (canines) or regurgitation to chew cud (ruminants). It is entirely smooth muscle in amphibians, reptiles and birds.[37]
+Contrary to popular belief,[41] an adult human body would not be able to pass through the esophagus of a whale, which generally measures less than 10 centimeters (4 in) in diameter, although in larger baleen whales it may be up to 25 centimeters (10 in) when fully distended.[42]
+A structure with the same name is often found in invertebrates, including molluscs and arthropods, connecting the oral cavity with the stomach.[43] In terms of the digestive system of snails and slugs, the mouth opens into an esophagus, which connects to the stomach. Because of torsion, which is the rotation of the main body of the animal during larval development, the esophagus usually passes around the stomach, and opens into its back, furthest from the mouth. In species that have undergone de-torsion, however, the esophagus may open into the anterior of the stomach, which is the reverse of the usual gastropod arrangement.[44] There is an extensive rostrum at the front of the esophagus in all carnivorous snails and slugs.[45] In the freshwater snail species Tarebia granifera, the brood pouch is above the esophagus.[46]
+In the cephalopods, the brain often surrounds the esophagus.[47]

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+The esophagus, (American English) or oesophagus (British English; see spelling differences) (/ɪˈsɒfəɡəs/), informally known as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the stomach. The esophagus is a fibromuscular tube, about 25 cm (10 in) long in adults, which travels behind the trachea and heart, passes through the diaphragm and empties into the uppermost region of the stomach. During swallowing, the epiglottis tilts backwards to prevent food from going down the larynx and lungs. The word oesophagus is the Greek word οἰσοφάγος oisophagos, meaning "gullet".
+The wall of the esophagus from the lumen outwards consists of mucosa, submucosa (connective tissue), layers of muscle fibers between layers of fibrous tissue, and an outer layer of connective tissue. The mucosa is a stratified squamous epithelium of around three layers of squamous cells, which contrasts to the single layer of columnar cells of the stomach. The transition between these two types of epithelium is visible as a zig-zag line. Most of the muscle is smooth muscle although striated muscle predominates in its upper third. It has two muscular rings or sphincters in its wall, one at the top and one at the bottom. The lower sphincter helps to prevent reflux of acidic stomach content. The esophagus has a rich blood supply and venous drainage. Its smooth muscle is innervated by involuntary nerves (sympathetic nerves via the sympathetic trunk and parasympathetic nerves via the vagus nerve) and in addition voluntary nerves (lower motor neurons) which are carried in the vagus nerve to innervate its striated muscle.
+The esophagus may be affected by gastric reflux, cancer, prominent dilated blood vessels called varices that can bleed heavily, tears, constrictions, and disorders of motility. Diseases may cause difficulty swallowing (dysphagia), painful swallowing (odynophagia), chest pain, or cause no symptoms at all. Clinical investigations include X-rays when swallowing barium, endoscopy, and CT scans. Surgically,
+the esophagus is difficult to access.[1]
+The esophagus is one of the upper parts of the digestive system. There are taste buds on its upper part.[2] It begins at the back of the mouth, passing downwards through the rear part of the mediastinum, through the diaphragm, and into the stomach. In humans, the esophagus generally starts around the level of the sixth cervical vertebra behind the cricoid cartilage of the trachea, enters the diaphragm at about the level of the tenth thoracic vertebra, and ends at the cardia of the stomach, at the level of the eleventh thoracic vertebra.[3] The esophagus is usually about 25 cm (10 in) in length.[4]
+Many blood vessels serve the esophagus, with blood supply varying along its course. The upper parts of the esophagus and the upper esophageal sphincter receive blood from the inferior thyroid artery, the parts of the esophagus in the thorax from the bronchial arteries and branches directly from the thoracic aorta, and the lower parts of the esophagus and the lower esophageal sphincter receive blood from the left gastric artery and the left inferior phrenic artery.[5][6] The venous drainage also differs along the course of the esophagus. The upper and middle parts of the esophagus drain into the azygos and hemiazygos veins, and blood from the lower part drains into the left gastric vein. All these veins drain into the superior vena cava, with the exception of the left gastric vein, which is a branch of the portal vein.[5] Lymphatically, the upper third of the esophagus drains into the deep cervical lymph nodes, the middle into the superior and posterior mediastinal lymph nodes, and the lower esophagus into the gastric and celiac lymph nodes. This is similar to the lymphatic drainage of the abdominal structures that arise from the foregut, which all drain into the celiac nodes.[5]
+The upper esophagus lies at the back of the mediastinum behind the trachea, adjoining along the tracheoesophageal stripe, and in front of the erector spinae muscles and the vertebral column. The lower esophagus lies behind the heart and curves in front of the thoracic aorta. From the bifurcation of the trachea downwards, the esophagus passes behind the right pulmonary artery, left main bronchus, and left atrium. At this point it passes through the diaphragm.[3]
+The thoracic duct, which drains the majority of the body's lymph, passes behind the esophagus, curving from lying behind the esophagus on the right in the lower part of the esophagus, to lying behind the esophagus on the left in the upper esophagus. The esophagus also lies in front of parts of the hemiazygos veins and the intercostal veins on the right side. The vagus nerve divides and covers the esophagus in a plexus.[3]
+The esophagus has four points of constriction. When a corrosive substance, or a solid object is swallowed, it is most likely to lodge and damage one of these four points. These constrictions arise from particular structures that compress the esophagus. These constrictions are:[7]
+The esophagus is surrounded at the top and bottom by two muscular rings, known respectively as the upper esophageal sphincter and the lower esophageal sphincter.[3] These sphincters act to close the esophagus when food is not being swallowed. The upper esophageal sphincter is an anatomical sphincter, which is formed by lower portion of inferior pharyngeal constrictor, also known as cricopharyngeal sphincter due to its relation with cricoid cartilage of the larynx anteriorly. However, the lower esophageal sphincter is not an anatomical but rather a functional sphincter, meaning that it acts as a sphincter but does not have a distinct thickening like other sphincters.
+The upper esophageal sphincter surrounds the upper part of the esophagus. It consists of skeletal muscle but is not under voluntary control. Opening of the upper esophageal sphincter is triggered by the swallowing reflex. The primary muscle of the upper esophageal sphincter is the cricopharyngeal part of the inferior pharyngeal constrictor.[8]
+The lower esophageal sphincter, or gastroesophageal sphincter, surrounds the lower part of the esophagus at the junction between the esophagus and the stomach.[9] It is also called the cardiac sphincter or cardioesophageal sphincter, named from the adjacent part of the stomach, the cardia. Dysfunction of the gastroesophageal sphincter causes gastroesophageal reflux, which causes heartburn and if it happens often enough, can lead to gastroesophageal reflux disease, with damage of the esophageal mucosa.[10]
+The esophagus is innervated by the vagus nerve and the cervical and thoracic sympathetic trunk.[5] The vagus nerve has a parasympathetic function, supplying the muscles of the esophagus and stimulating glandular contraction. Two sets of nerve fibers travel in the vagus nerve to supply the muscles. The upper striated muscle, and upper esophageal sphincter, are supplied by neurons with bodies in the nucleus ambiguus, whereas fibers that supply the smooth muscle and lower esophageal sphincter have bodies situated in the dorsal motor nucleus.[5] The vagus nerve plays the primary role in initiating peristalsis.[11] The sympathetic trunk has a sympathetic function. It may enhance the function of the vagus nerve, increasing peristalsis and glandular activity, and causing sphincter contraction. In addition, sympathetic activation may relax the muscle wall and cause blood vessel constriction.[5] Sensation along the esophagus is supplied by both nerves, with gross sensation being passed in the vagus nerve and pain passed up the sympathetic trunk.[3]
+The gastro-esophageal junction (also known as the esophagogastric junction) is the junction between the esophagus and the stomach, at the lower end of the esophagus.[12] The pink color of the esophageal mucosa contrasts to the deeper red of the gastric mucosa,[5][13] and the mucosal transition can be seen as an irregular zig-zag line, which is often called the z-line.[14] Histological examination reveals abrupt transition between the stratified squamous epithelium of the esophagus and the simple columnar epithelium of the stomach.[15] Normally, the cardia of the stomach is immediately distal to the z-line[16] and the z-line coincides with the upper limit of the gastric folds of the cardia; however, when the anatomy of the mucosa is distorted in Barrets esophagus the true gastro-eshophageal junction can be identified by the upper limit of the gastric folds rather than the mucosal transition.[17] The functional location of the lower oesophageal sphincter is generally situated about 3 cm (1.2 in) below the z-line.[5]
+The human esophagus has a mucous membrane consisting of a tough stratified squamous epithelium without keratin, a smooth lamina propria, and a muscularis mucosae.[5] The epithelium of the esophagus has a relatively rapid turnover, and serves a protective function against the abrasive effects of food. In many animals the epithelium contains a layer of keratin, representing a coarser diet.[18] There are two types of glands, with mucus-secreting esophageal glands being found in the submucosa, and esophageal cardiac glands, similar to cardiac glands of the stomach, located in the lamina propria and most frequent in the terminal part of the organ.[18][19] The mucus from the glands gives a good protection to the lining.[20] The submucosa also contains the submucosal plexus, a network of nerve cells that is part of the enteric nervous system.[18]
+The muscular layer of the esophagus has two types of muscle. The upper third of the esophagus contains striated muscle, the lower third contains smooth muscle, and the middle third contains a mixture of both.[5] Muscle is arranged in two layers: one in which the muscle fibers run longitudinal to the esophagus, and the other in which the fibers encircle the esophagus. These are separated by the myenteric plexus, a tangled network of nerve fibers involved in the secretion of mucus and in peristalsis of the smooth muscle of the esophagus. The outermost layer of the esophagus is the adventitia in most of its length, with the abdominal part being covered in serosa. This makes it distinct from many other structures in the gastrointestinal tract that only have a serosa.[5]
+In early embryogenesis, the esophagus develops from the endodermal primitive gut tube. The ventral part of the embryo abuts the yolk sac. During the second week of embryological development, as the embryo grows, it begins to surround parts of the sac. The enveloped portions form the basis for the adult gastrointestinal tract.[21] The sac is surrounded by a network of vitelline arteries. Over time, these arteries consolidate into the three main arteries that supply the developing gastrointestinal tract: the celiac artery, superior mesenteric artery, and inferior mesenteric artery. The areas supplied by these arteries are used to define the midgut, hindgut and foregut.[21]
+The surrounded sac becomes the primitive gut. Sections of this gut begin to differentiate into the organs of the gastrointestinal tract, such as the esophagus, stomach, and intestines.[21] The esophagus develops as part of the foregut tube.[21] The innervation of the esophagus develops from the pharyngeal arches.[3]
+Food is ingested through the mouth and when swallowed passes first into the pharynx and then into the esophagus. The esophagus is thus one of the first components of the digestive system and the gastrointestinal tract. After food passes through the esophagus, it enters the stomach.[9] When food is being swallowed, the epiglottis moves backward to cover the larynx, preventing food from entering the trachea. At the same time, the upper esophageal sphincter relaxes, allowing a bolus of food to enter. Peristaltic contractions of the esophageal muscle push the food down the esophagus. These rhythmic contractions occur both as a reflex response to food that is in the mouth, and also as a response to the sensation of food within the esophagus itself. Along with peristalsis, the lower esophageal sphincter relaxes.[9]
+The stomach produces gastric acid, a strongly acidic mixture consisting of hydrochloric acid (HCl) and potassium and sodium salts to enable food digestion. Constriction of the upper and lower esophageal sphincters help to prevent reflux (backflow) of gastric contents and acid into the esophagus, protecting the esophageal mucosa. In addition, the acute angle of His and the lower crura of the diaphragm helps this sphincteric action.[9][22]
+About 20,000 protein-coding genes are expressed in human cells and nearly 70% of these genes are expressed in the normal esophagus.[23][24] Some 250 of these genes are more specifically expressed in the esophagus with less than 50 genes being highly specific. The corresponding esophagus-specific proteins are mainly involved in squamous differentiation such as keratins KRT13, KRT4 and KRT6C. Other specific proteins that help lubricate the inner surface of esophagus are mucins such as MUC21 and MUC22. Many genes with elevated expression are also shared with skin and other organs that are composed of squamous epithelia.[25]
+The main conditions affecting the esophagus are described here. For a more complete list, see esophageal disease.
+Inflammation of the esophagus is known as esophagitis. Reflux of gastric acids from the stomach, infection, substances ingested (for example, corrosives), some medications (such as bisphosphonates), and food allergies can all lead to esophagitis. Esophageal candidiasis is an infection of the yeast Candida albicans that may occur when a person is immunocompromised. As of 2014[update] the cause of some forms of esophagitis, such as eosinophilic esophagitis, is not known. Esophagitis can cause painful swallowing and is usually treated by managing the cause of the esophagitis - such as managing reflux or treating infection.[4]
+Prolonged esophagitis, particularly from gastric reflux, is one factor thought to play a role in the development of Barrett's esophagus. In this condition, there is metaplasia of the lining of the lower esophagus, which changes from stratified squamous epithelia to simple columnar epithelia. Barrett's esophagus is thought to be one of the main contributors to the development of esophageal cancer.[4]
+There are two main types of cancer of the esophagus. Squamous cell carcinoma is a carcinoma that can occur in the squamous cells lining the esophagus. This type is much more common in China and Iran. The other main type is an adenocarcinoma that occurs in the glands or columnar tissue of the esophagus. This is most common in developed countries in those with Barrett's esophagus, and occurs in the cuboidal cells.[4]
+In its early stages, esophageal cancer may not have any symptoms at all. When severe, esophageal cancer may eventually cause obstruction of the esophagus, making swallowing of any solid foods very difficult and causing weight loss. The progress of the cancer is staged using a system that measures how far into the esophageal wall the cancer has invaded, how many lymph nodes are affected, and whether there are any metastases in different parts of the body. Esophageal cancer is often managed with radiotherapy, chemotherapy, and may also be managed by partial surgical removal of the esophagus. Inserting a stent into the esophagus, or inserting a nasogastric tube, may also be used to ensure that a person is able to digest enough food and water. As of 2014[update], the prognosis for esophageal cancer is still poor, so palliative therapy may also be a focus of treatment.[4]
+Esophageal varices are swollen twisted branches of the azygous vein in the lower third of the esophagus. These blood vessels anastomose (join up) with those of the portal vein when portal hypertension develops.[26] These blood vessels are engorged more than normal, and in the worst cases may partially obstruct the esophagus. These blood vessels develop as part of a collateral circulation that occurs to drain blood from the abdomen as a result of portal hypertension, usually as a result of liver diseases such as cirrhosis.[4]:941–42 This collateral circulation occurs because the lower part of the esophagus drains into the left gastric vein, which is a branch of the portal vein. Because of the extensive venous plexus that exists between this vein and other veins, if portal hypertension occurs, the direction of blood drainage in this vein may reverse, with blood draining from the portal venous system, through the plexus. Veins in the plexus may engorge and lead to varices.[5][6]
+Esophageal varices often do not have symptoms until they rupture. A ruptured varix is considered a medical emergency, because varices can bleed a lot. A bleeding varix may cause a person to vomit blood, or suffer shock. To deal with a ruptured varix, a band may be placed around the bleeding blood vessel, or a small amount of a clotting agent may be injected near the bleed. A surgeon may also try to use a small inflatable balloon to apply pressure to stop the wound. IV fluids and blood products may be given in order to prevent hypovolemia from excess blood loss.[4]
+Several disorders affect the motility of food as it travels down the esophagus. This can cause difficult swallowing, called dysphagia, or painful swallowing, called odynophagia. Achalasia refers to a failure of the lower esophageal sphincter to relax properly, and generally develops later in life. This leads to progressive enlargement of the esophagus, and possibly eventual megaesophagus. A nutcracker esophagus refers to swallowing that can be extremely painful. Diffuse esophageal spasm is a spasm of the esophagus that can be one cause of chest pain. Such referred pain to the wall of the upper chest is quite common in esophageal conditions.[27] Sclerosis of the esophagus, such as with systemic sclerosis or in CREST syndrome may cause hardening of the walls of the esophagus and interfere with peristalsis.[4]
+Esophageal strictures are usually benign and typically develop after a person has had reflux for many years. Other strictures may include esophageal webs (which can also be congenital) and damage to the esophagus by radiotherapy, corrosive ingestion, or eosinophilic esophagitis. A Schatzki ring is fibrosis at the gastro-esophageal junction. Strictures may also develop in chronic anemia, and Plummer-Vinson syndrome.[4]
+Two of the most common congenital malformations affecting the esophagus are an esophageal atresia where the esophagus ends in a blind sac instead of connecting to the stomach; and an esophageal fistula – an abnormal connection between the esophagus and the trachea.[28] Both of these conditions usually occur together.[28] These are found in about 1 in 3500 births.[29] Half of these cases may be part of a syndrome where other abnormalities are also present, particularly of the heart or limbs. The other cases occur singly.[30]
+An X-ray of swallowed barium may be used to reveal the size and shape of the esophagus, and the presence of any masses. The esophagus may also be imaged using a flexible camera inserted into the esophagus, in a procedure called an endoscopy. If an endoscopy is used on the stomach, the camera will also have to pass through the esophagus. During an endoscopy, a biopsy may be taken. If cancer of the esophagus is being investigated, other methods, including a CT scan, may also be used.[4]
+The word esophagus (British English: oesophagus), comes from the Greek: οἰσοφάγος (oisophagos) meaning gullet. It derives from two roots (eosin) to carry and (phagos) to eat.[31] The use of the word oesophagus, has been documented in anatomical literature since at least the time of Hippocrates, who noted that "the oesophagus ... receives the greatest amount of what we consume." [32] Its existence in other animals and its relationship with the stomach was documented by the Roman naturalist Pliny the Elder (AD23–AD79),[33] and the peristaltic contractions of the esophagus have been documented since at least the time of Galen.[34]
+The first attempt at surgery on the esophagus focused in the neck, and was conducted in dogs by Theodore Billroth in 1871. In 1877 Czerny carried out surgery in people. By 1908, an operation had been performed by Voeckler to remove the esophagus, and in 1933 the first surgical removal of parts of the lower esophagus, (to control esophageal cancer), had been conducted.[35]
+The Nissen fundoplication, in which the stomach is wrapped around the lower esophageal sphincter to stimulate its function and control reflux, was first conducted by Rudolph Nissen in 1955.[35]
+In tetrapods, the pharynx is much shorter, and the esophagus correspondingly longer, than in fish. In the majority of vertebrates, the esophagus is simply a connecting tube, but in some birds, which regurgitate components to feed their young, it is extended towards the lower end to form a crop for storing food before it enters the true stomach.[36][37] In ruminants, animals with four stomachs, a groove called the sulcus reticuli is often found in the esophagus, allowing milk to drain directly into the hind stomach, the abomasum.[38] In the horse the esophagus is about 1.2 to 1.5 m (4 to 5 ft) in length, and carries food to the stomach. A muscular ring, called the cardiac sphincter, connects the stomach to the esophagus. This sphincter is very well developed in horses. This and the oblique angle at which the esophagus connects to the stomach explains why horses cannot vomit.[39] The esophagus is also the area of the digestive tract where horses may suffer from the condition known as choke.
+The esophagus of snakes is remarkable for the distension it undergoes when swallowing prey.[40]
+In most fish, the esophagus is extremely short, primarily due to the length of the pharynx (which is associated with the gills). However, some fish, including lampreys, chimaeras, and lungfish, have no true stomach, so that the esophagus effectively runs from the pharynx directly to the intestine, and is therefore somewhat longer.[36]
+In many vertebrates, the esophagus is lined by stratified squamous epithelium without glands. In fish, the esophagus is often lined with columnar epithelium,[37] and in amphibians, sharks and rays, the esophageal epithelium is ciliated, helping to wash food along, in addition to the action of muscular peristalsis.[36] In addition, in the bat Plecotus auritus, fish and some amphibians, glands secreting pepsinogen or hydrochloric acid have been found.[37]
+The muscle of the esophagus in many mammals is striated initially, but then becomes smooth muscle in the caudal third or so. In canines and ruminants, however, it is entirely striated to allow regurgitation to feed young (canines) or regurgitation to chew cud (ruminants). It is entirely smooth muscle in amphibians, reptiles and birds.[37]
+Contrary to popular belief,[41] an adult human body would not be able to pass through the esophagus of a whale, which generally measures less than 10 centimeters (4 in) in diameter, although in larger baleen whales it may be up to 25 centimeters (10 in) when fully distended.[42]
+A structure with the same name is often found in invertebrates, including molluscs and arthropods, connecting the oral cavity with the stomach.[43] In terms of the digestive system of snails and slugs, the mouth opens into an esophagus, which connects to the stomach. Because of torsion, which is the rotation of the main body of the animal during larval development, the esophagus usually passes around the stomach, and opens into its back, furthest from the mouth. In species that have undergone de-torsion, however, the esophagus may open into the anterior of the stomach, which is the reverse of the usual gastropod arrangement.[44] There is an extensive rostrum at the front of the esophagus in all carnivorous snails and slugs.[45] In the freshwater snail species Tarebia granifera, the brood pouch is above the esophagus.[46]
+In the cephalopods, the brain often surrounds the esophagus.[47]

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+The egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own, at which point the animal hatches. An egg results from fertilization of an egg cell. Most arthropods, vertebrates (excluding live-bearing mammals), and mollusks lay eggs, although some, such as scorpions, do not.
+Reptile eggs, bird eggs, and monotreme eggs are laid out of water and are surrounded by a protective shell, either flexible or inflexible. Eggs laid on land or in nests are usually kept within a warm and favorable temperature range while the embryo grows. When the embryo is adequately developed it hatches, i.e., breaks out of the egg's shell. Some embryos have a temporary egg tooth they use to crack, pip, or break the eggshell or covering.
+The largest recorded egg is from a whale shark and was 30 cm × 14 cm × 9 cm (11.8 in × 5.5 in × 3.5 in) in size.[1] Whale shark eggs typically hatch within the mother. At 1.5 kg (3.3 lb) and up to 17.8 cm × 14 cm (7.0 in × 5.5 in), the ostrich egg is the largest egg of any living bird,[2] though the extinct elephant bird and some non-avian dinosaurs laid larger eggs. The bee hummingbird produces the smallest known bird egg, which weighs half of a gram (around 0.02 oz). Some eggs laid by reptiles and most fish, amphibians, insects, and other invertebrates can be even smaller.
+Reproductive structures similar to the egg in other kingdoms are termed "spores," or in spermatophytes "seeds," or in gametophytes "egg cells".
+Several major groups of animals typically have readily distinguishable eggs.
+The most common reproductive strategy for fish is known as oviparity, in which the female lays undeveloped eggs that are externally fertilized by a male. Typically large numbers of eggs are laid at one time (an adult female cod can produce 4–6 million eggs in one spawning) and the eggs are then left to develop without parental care. When the larvae hatch from the egg, they often carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a few days as they learn how to swim. Once the yolk is consumed, there is a critical point after which they must learn how to hunt and feed or they will die.
+A few fish, notably the rays and most sharks use ovoviviparity in which the eggs are fertilized and develop internally. However, the larvae still grow inside the egg consuming the egg's yolk and without any direct nourishment from the mother. The mother then gives birth to relatively mature young. In certain instances, the physically most developed offspring will devour its smaller siblings for further nutrition while still within the mother's body. This is known as intrauterine cannibalism.
+In certain scenarios, some fish such as the hammerhead shark and reef shark are viviparous, with the egg being fertilized and developed internally, but with the mother also providing direct nourishment.
+The eggs of fish and amphibians are jellylike. Cartilaginous fish (sharks, skates, rays, chimaeras) eggs are fertilized internally and exhibit a wide variety of both internal and external embryonic development. Most fish species spawn eggs that are fertilized externally, typically with the male inseminating the eggs after the female lays them. These eggs do not have a shell and would dry out in the air. Even air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, Chiromantis xerampelina.
+Bird eggs are laid by females and incubated for a time that varies according to the species; a single young hatches from each egg. Average clutch sizes range from one (as in condors) to about 17 (the grey partridge). Some birds lay eggs even when not fertilized (e.g. hens); it is not uncommon for pet owners to find their lone bird nesting on a clutch of unfertilized eggs, which are sometimes called wind-eggs.
+The default color of vertebrate eggs is the white of the calcium carbonate from which the shells are made, but some birds, mainly passerines, produce colored eggs. The pigment biliverdin and its zinc chelate give a green or blue ground color, and protoporphyrin produces reds and browns as a ground color or as spotting.
+Non-passerines typically have white eggs, except in some ground-nesting groups such as the Charadriiformes, sandgrouse and nightjars, where camouflage is necessary, and some parasitic cuckoos which have to match the passerine host's egg. Most passerines, in contrast, lay colored eggs, even if there is no need of cryptic colors.
+However some have suggested that the protoporphyrin markings on passerine eggs actually act to reduce brittleness by acting as a solid-state lubricant.[10] If there is insufficient calcium available in the local soil, the egg shell may be thin, especially in a circle around the broad end. Protoporphyrin speckling compensates for this, and increases inversely to the amount of calcium in the soil.[11]
+For the same reason, later eggs in a clutch are more spotted than early ones as the female's store of calcium is depleted.
+The color of individual eggs is also genetically influenced, and appears to be inherited through the mother only, suggesting that the gene responsible for pigmentation is on the sex-determining W chromosome (female birds are WZ, males ZZ).
+It used to be thought that color was applied to the shell immediately before laying, but subsequent research shows that coloration is an integral part of the development of the shell, with the same protein responsible for depositing calcium carbonate, or protoporphyrins when there is a lack of that mineral.
+In species such as the common guillemot, which nest in large groups, each female's eggs have very different markings, making it easier for females to identify their own eggs on the crowded cliff ledges on which they breed.
+Bird eggshells are diverse. For example:
+Tiny pores in bird eggshells allow the embryo to breathe. The domestic hen's egg has around 7000 pores.[12]
+Some bird eggshells have a coating of vaterite spherules, which is a rare polymorph of calcium carbonate. In Greater Ani Crotophaga major this vaterite coating is thought to act as a shock absorber, protecting the calcite shell from fracture during incubation, such as colliding with other eggs in the nest.[13]
+Most bird eggs have an oval shape, with one end rounded and the other more pointed. This shape results from the egg being forced through the oviduct. Muscles contract the oviduct behind the egg, pushing it forward. The egg's wall is still shapeable, and the pointed end develops at the back. Long, pointy eggs are an incidental consequence of having a streamlined body typical of birds with strong flying abilities; flight narrows the oviduct, which changes the type of egg a bird can lay.[14] Cliff-nesting birds often have highly conical eggs. They are less likely to roll off, tending instead to roll around in a tight circle; this trait is likely to have arisen due to evolution via natural selection. In contrast, many hole-nesting birds have nearly spherical eggs.[15]
+Many animals feed on eggs. For example, principal predators of the black oystercatcher's eggs include raccoons, skunks, mink, river and sea otters, gulls, crows and foxes. The stoat (Mustela erminea) and long-tailed weasel (M. frenata) steal ducks' eggs. Snakes of the genera Dasypeltis and Elachistodon specialize in eating eggs.
+Brood parasitism occurs in birds when one species lays its eggs in the nest of another. In some cases, the host's eggs are removed or eaten by the female, or expelled by her chick. Brood parasites include the cowbirds and many Old World cuckoos.
+An average whooping crane egg is 102 mm (4.0 in) long and weighs 208 g (7.3 oz)
+Eurasian oystercatcher eggs camouflaged in the nest
+Egg of a senegal parrot, a bird that nests in tree holes, on a 1 cm (0.39 in) grid
+Eggs of ostrich, emu, kiwi and chicken
+Finch egg next to American dime
+Eggs of duck, goose, guineafowl and chicken
+Eggs of ostrich, cassowary, chicken, flamingo, pigeon and blackbird
+Egg of an emu
+Egg from a chicken compared to a 1 euro coin, great tit egg and a corn grain
+Bird nest with brown marbling eggs of a robin
+Like amphibians, amniotes are air-breathing vertebrates, but they have complex eggs or embryos, including an amniotic membrane. Amniotes include reptiles (including dinosaurs and their descendants, birds) and mammals.
+Reptile eggs are often rubbery and are always initially white. They are able to survive in the air. Often the sex of the developing embryo is determined by the temperature of the surroundings, with cooler temperatures favouring males. Not all reptiles lay eggs; some are viviparous ("live birth").
+Dinosaurs laid eggs, some of which have been preserved as petrified fossils.
+Among mammals, early extinct species laid eggs, as do platypuses and echidnas (spiny anteaters). Platypuses and two genera of echidna are Australian monotremes. Marsupial and placental mammals do not lay eggs, but their unborn young do have the complex tissues that identify amniotes.
+The eggs of the egg-laying mammals (the platypus and the echidnas) are macrolecithal eggs very much like those of reptiles. The eggs of marsupials are likewise macrolecithal, but rather small, and develop inside the body of the female, but do not form a placenta. The young are born at a very early stage, and can be classified as a "larva" in the biological sense.[16]
+In placental mammals, the egg itself is void of yolk, but develops an umbilical cord from structures that in reptiles would form the yolk sac. Receiving nutrients from the mother, the fetus completes the development while inside the uterus.
+Eggs are common among invertebrates, including insects, spiders, mollusks, and crustaceans.
+All sexually reproducing life, including both plants and animals, produces gametes. The male gamete cell, sperm, is usually motile whereas the female gamete cell, the ovum, is generally larger and sessile. The male and female gametes combine to produce the zygote cell. In multicellular organisms the zygote subsequently divides in an organised manner into smaller more specialised cells, so that this new individual develops into an embryo. In most animals the embryo is the sessile initial stage of the individual life cycle, and is followed by the emergence (that is, the hatching) of a motile stage. The zygote or the ovum itself or the sessile organic vessel containing the developing embryo may be called the egg.
+A recent proposal suggests that the phylotypic animal body plans originated in cell aggregates before the existence of an egg stage of development. Eggs, in this view, were later evolutionary innovations, selected for their role in ensuring genetic uniformity among the cells of incipient multicellular organisms.[17]
+Scientists often classify animal reproduction according to the degree of development that occurs before the new individuals are expelled from the adult body, and by the yolk which the egg provides to nourish the embryo.
+Vertebrate eggs can be classified by the relative amount of yolk. Simple eggs with little yolk are called microlecithal, medium-sized eggs with some yolk are called mesolecithal, and large eggs with a large concentrated yolk are called macrolecithal.[7] This classification of eggs is based on the eggs of chordates, though the basic principle extends to the whole animal kingdom.
+Small eggs with little yolk are called microlecithal. The yolk is evenly distributed, so the cleavage of the egg cell cuts through and divides the egg into cells of fairly similar sizes. In sponges and cnidarians the dividing eggs develop directly into a simple larva, rather like a morula with cilia. In cnidarians, this stage is called the planula, and either develops directly into the adult animals or forms new adult individuals through a process of budding.[18]
+Microlecithal eggs require minimal yolk mass. Such eggs are found in flatworms, roundworms, annelids, bivalves, echinoderms, the lancelet and in most marine arthropods.[19] In anatomically simple animals, such as cnidarians and flatworms, the fetal development can be quite short, and even microlecithal eggs can undergo direct development. These small eggs can be produced in large numbers. In animals with high egg mortality, microlecithal eggs are the norm, as in bivalves and marine arthropods. However, the latter are more complex anatomically than e.g. flatworms, and the small microlecithal eggs do not allow full development. Instead, the eggs hatch into larvae, which may be markedly different from the adult animal.
+In placental mammals, where the embryo is nourished by the mother throughout the whole fetal period, the egg is reduced in size to essentially a naked egg cell.
+Mesolecithal eggs have comparatively more yolk than the microlecithal eggs. The yolk is concentrated in one part of the egg (the vegetal pole), with the cell nucleus and most of the cytoplasm in the other (the animal pole). The cell cleavage is uneven, and mainly concentrated in the cytoplasma-rich animal pole.[3]
+The larger yolk content of the mesolecithal eggs allows for a longer fetal development. Comparatively anatomically simple animals will be able to go through the full development and leave the egg in a form reminiscent of the adult animal. This is the situation found in hagfish and some snails.[4][19] Animals with smaller size eggs or more advanced anatomy will still have a distinct larval stage, though the larva will be basically similar to the adult animal, as in lampreys, coelacanth and the salamanders.[3]
+Eggs with a large yolk are called macrolecithal. The eggs are usually few in number, and the embryos have enough food to go through full fetal development in most groups.[7] Macrolecithal eggs are only found in selected representatives of two groups: Cephalopods and vertebrates.[7][20]
+Macrolecithal eggs go through a different type of development than other eggs. Due to the large size of the yolk, the cell division can not split up the yolk mass. The fetus instead develops as a plate-like structure on top of the yolk mass, and only envelopes it at a later stage.[7] A portion of the yolk mass is still present as an external or semi-external yolk sac at hatching in many groups. This form of fetal development is common in bony fish, even though their eggs can be quite small. Despite their macrolecithal structure, the small size of the eggs does not allow for direct development, and the eggs hatch to a larval stage ("fry"). In terrestrial animals with macrolecithal eggs, the large volume to surface ratio necessitates structures to aid in transport of oxygen and carbon dioxide, and for storage of waste products so that the embryo does not suffocate or get poisoned from its own waste while inside the egg, see amniote.[9]
+In addition to bony fish and cephalopods, macrolecithal eggs are found in cartilaginous fish, reptiles, birds and monotreme mammals.[3] The eggs of the coelacanths can reach a size of 9 cm (3.5 in) in diameter, and the young go through full development while in the uterus, living on the copious yolk.[21]
+Animals are commonly classified by their manner of reproduction, at the most general level distinguishing egg-laying (Latin. oviparous) from live-bearing (Latin. viviparous).
+These classifications are divided into more detail according to the development that occurs before the offspring are expelled from the adult's body. Traditionally:[22]
+The term hemotropic derives from the Latin for blood-feeding, contrasted with histotrophic for tissue-feeding.[27]
+Eggs laid by many different species, including birds, reptiles, amphibians, and fish, have probably been eaten by mankind for millennia. Popular choices for egg consumption are chicken, duck, roe, and caviar, but by a wide margin the egg most often humanly consumed is the chicken egg, typically unfertilized.
+According to the Kashrut, that is the set of Jewish dietary laws, kosher food may be consumed according to halakha (Jewish law). Kosher meat and milk (or derivatives) cannot be mixed (Deuteronomy 14:21) or stored together. Eggs are considered pareve (neither meat nor dairy) despite being an animal product and can be mixed with either milk or kosher meat. Mayonnaise, for instance, is usually marked "pareve" despite by definition containing egg.[28]
+Many vaccines for infectious diseases are produced in fertile chicken eggs. The basis of this technology was the discovery in 1931 by Alice Miles Woodruff and Ernest William Goodpasture at Vanderbilt University that the rickettsia and viruses that cause a variety of diseases will grow in chicken embryos. This enabled the development of vaccines against influenza, chicken pox, smallpox, yellow fever, typhus, Rocky mountain spotted fever and other diseases.
+The egg is a symbol of new life and rebirth in many cultures around the world. Christians view Easter eggs as symbolic of the resurrection of Jesus Christ.[29] A popular Easter tradition in some parts of the world is the decoration of hard-boiled eggs (usually by dyeing, but often by hand-painting or spray-painting). Adults often hide the eggs for children to find, an activity known as an Easter egg hunt. A similar tradition of egg painting exists in areas of the world influenced by the culture of Persia. Before the spring equinox in the Persian New Year tradition (called Norouz), each family member decorates a hard-boiled egg and sets them together in a bowl. The tradition of a dancing egg is held during the feast of Corpus Christi in Barcelona and other Catalan cities since the 16th century. It consists of an emptied egg, positioned over the water jet from a fountain, which starts turning without falling.[30]
+Although a food item, raw eggs are sometimes thrown at houses, cars, or people. This act, known commonly as "egging" in the various English-speaking countries, is a minor form of vandalism and, therefore, usually a criminal offense and is capable of damaging property (egg whites can degrade certain types of vehicle paint) as well as potentially causing serious eye injury. On Halloween, for example, trick or treaters have been known to throw eggs (and sometimes flour) at property or people from whom they received nothing.[citation needed] Eggs are also often thrown in protests, as they are inexpensive and nonlethal, yet very messy when broken.[31]
+Egg collecting was a popular hobby in some cultures, including among the first Australians. Traditionally, the embryo would be removed before a collector stored the egg shell.[32]
+Collecting eggs of wild birds is now banned by many jurisdictions, as the practice can threaten rare species. In the United Kingdom, the practice is prohibited by the Protection of Birds Act 1954 and Wildlife and Countryside Act 1981.[33] On the other hand, ongoing underground trading is becoming a serious issue.[34]
+Since the protection of wild bird eggs was regulated, early collections have come to the museums as curiosities. For example, the Australian Museum hosts a collection of about 20,000 registered clutches of eggs,[35] and the collection in Western Australia Museum has been archived in a gallery.[36] Scientists regard egg collections as a good natural-history data, as the details recorded in the collectors' notes have helped them to understand birds' nesting behaviors.[37]
+Insect eggs, in this case those of the Emperor gum moth, are often laid on the underside of leaves.
+Fish eggs, such as these herring eggs are often transparent and fertilized after laying.
+Skates and some sharks have a uniquely shaped egg case called a mermaid's purse.
+A Testudo hermanni emerging fully developed from a reptilian egg.
+A Schistosoma mekongi egg.
+Eggs of Huffmanela hamo, a nematode parasite in a fish
+Eggs of various parasites (mainly nematodes) from wild primates

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+The egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own, at which point the animal hatches. An egg results from fertilization of an egg cell. Most arthropods, vertebrates (excluding live-bearing mammals), and mollusks lay eggs, although some, such as scorpions, do not.
+Reptile eggs, bird eggs, and monotreme eggs are laid out of water and are surrounded by a protective shell, either flexible or inflexible. Eggs laid on land or in nests are usually kept within a warm and favorable temperature range while the embryo grows. When the embryo is adequately developed it hatches, i.e., breaks out of the egg's shell. Some embryos have a temporary egg tooth they use to crack, pip, or break the eggshell or covering.
+The largest recorded egg is from a whale shark and was 30 cm × 14 cm × 9 cm (11.8 in × 5.5 in × 3.5 in) in size.[1] Whale shark eggs typically hatch within the mother. At 1.5 kg (3.3 lb) and up to 17.8 cm × 14 cm (7.0 in × 5.5 in), the ostrich egg is the largest egg of any living bird,[2] though the extinct elephant bird and some non-avian dinosaurs laid larger eggs. The bee hummingbird produces the smallest known bird egg, which weighs half of a gram (around 0.02 oz). Some eggs laid by reptiles and most fish, amphibians, insects, and other invertebrates can be even smaller.
+Reproductive structures similar to the egg in other kingdoms are termed "spores," or in spermatophytes "seeds," or in gametophytes "egg cells".
+Several major groups of animals typically have readily distinguishable eggs.
+The most common reproductive strategy for fish is known as oviparity, in which the female lays undeveloped eggs that are externally fertilized by a male. Typically large numbers of eggs are laid at one time (an adult female cod can produce 4–6 million eggs in one spawning) and the eggs are then left to develop without parental care. When the larvae hatch from the egg, they often carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a few days as they learn how to swim. Once the yolk is consumed, there is a critical point after which they must learn how to hunt and feed or they will die.
+A few fish, notably the rays and most sharks use ovoviviparity in which the eggs are fertilized and develop internally. However, the larvae still grow inside the egg consuming the egg's yolk and without any direct nourishment from the mother. The mother then gives birth to relatively mature young. In certain instances, the physically most developed offspring will devour its smaller siblings for further nutrition while still within the mother's body. This is known as intrauterine cannibalism.
+In certain scenarios, some fish such as the hammerhead shark and reef shark are viviparous, with the egg being fertilized and developed internally, but with the mother also providing direct nourishment.
+The eggs of fish and amphibians are jellylike. Cartilaginous fish (sharks, skates, rays, chimaeras) eggs are fertilized internally and exhibit a wide variety of both internal and external embryonic development. Most fish species spawn eggs that are fertilized externally, typically with the male inseminating the eggs after the female lays them. These eggs do not have a shell and would dry out in the air. Even air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, Chiromantis xerampelina.
+Bird eggs are laid by females and incubated for a time that varies according to the species; a single young hatches from each egg. Average clutch sizes range from one (as in condors) to about 17 (the grey partridge). Some birds lay eggs even when not fertilized (e.g. hens); it is not uncommon for pet owners to find their lone bird nesting on a clutch of unfertilized eggs, which are sometimes called wind-eggs.
+The default color of vertebrate eggs is the white of the calcium carbonate from which the shells are made, but some birds, mainly passerines, produce colored eggs. The pigment biliverdin and its zinc chelate give a green or blue ground color, and protoporphyrin produces reds and browns as a ground color or as spotting.
+Non-passerines typically have white eggs, except in some ground-nesting groups such as the Charadriiformes, sandgrouse and nightjars, where camouflage is necessary, and some parasitic cuckoos which have to match the passerine host's egg. Most passerines, in contrast, lay colored eggs, even if there is no need of cryptic colors.
+However some have suggested that the protoporphyrin markings on passerine eggs actually act to reduce brittleness by acting as a solid-state lubricant.[10] If there is insufficient calcium available in the local soil, the egg shell may be thin, especially in a circle around the broad end. Protoporphyrin speckling compensates for this, and increases inversely to the amount of calcium in the soil.[11]
+For the same reason, later eggs in a clutch are more spotted than early ones as the female's store of calcium is depleted.
+The color of individual eggs is also genetically influenced, and appears to be inherited through the mother only, suggesting that the gene responsible for pigmentation is on the sex-determining W chromosome (female birds are WZ, males ZZ).
+It used to be thought that color was applied to the shell immediately before laying, but subsequent research shows that coloration is an integral part of the development of the shell, with the same protein responsible for depositing calcium carbonate, or protoporphyrins when there is a lack of that mineral.
+In species such as the common guillemot, which nest in large groups, each female's eggs have very different markings, making it easier for females to identify their own eggs on the crowded cliff ledges on which they breed.
+Bird eggshells are diverse. For example:
+Tiny pores in bird eggshells allow the embryo to breathe. The domestic hen's egg has around 7000 pores.[12]
+Some bird eggshells have a coating of vaterite spherules, which is a rare polymorph of calcium carbonate. In Greater Ani Crotophaga major this vaterite coating is thought to act as a shock absorber, protecting the calcite shell from fracture during incubation, such as colliding with other eggs in the nest.[13]
+Most bird eggs have an oval shape, with one end rounded and the other more pointed. This shape results from the egg being forced through the oviduct. Muscles contract the oviduct behind the egg, pushing it forward. The egg's wall is still shapeable, and the pointed end develops at the back. Long, pointy eggs are an incidental consequence of having a streamlined body typical of birds with strong flying abilities; flight narrows the oviduct, which changes the type of egg a bird can lay.[14] Cliff-nesting birds often have highly conical eggs. They are less likely to roll off, tending instead to roll around in a tight circle; this trait is likely to have arisen due to evolution via natural selection. In contrast, many hole-nesting birds have nearly spherical eggs.[15]
+Many animals feed on eggs. For example, principal predators of the black oystercatcher's eggs include raccoons, skunks, mink, river and sea otters, gulls, crows and foxes. The stoat (Mustela erminea) and long-tailed weasel (M. frenata) steal ducks' eggs. Snakes of the genera Dasypeltis and Elachistodon specialize in eating eggs.
+Brood parasitism occurs in birds when one species lays its eggs in the nest of another. In some cases, the host's eggs are removed or eaten by the female, or expelled by her chick. Brood parasites include the cowbirds and many Old World cuckoos.
+An average whooping crane egg is 102 mm (4.0 in) long and weighs 208 g (7.3 oz)
+Eurasian oystercatcher eggs camouflaged in the nest
+Egg of a senegal parrot, a bird that nests in tree holes, on a 1 cm (0.39 in) grid
+Eggs of ostrich, emu, kiwi and chicken
+Finch egg next to American dime
+Eggs of duck, goose, guineafowl and chicken
+Eggs of ostrich, cassowary, chicken, flamingo, pigeon and blackbird
+Egg of an emu
+Egg from a chicken compared to a 1 euro coin, great tit egg and a corn grain
+Bird nest with brown marbling eggs of a robin
+Like amphibians, amniotes are air-breathing vertebrates, but they have complex eggs or embryos, including an amniotic membrane. Amniotes include reptiles (including dinosaurs and their descendants, birds) and mammals.
+Reptile eggs are often rubbery and are always initially white. They are able to survive in the air. Often the sex of the developing embryo is determined by the temperature of the surroundings, with cooler temperatures favouring males. Not all reptiles lay eggs; some are viviparous ("live birth").
+Dinosaurs laid eggs, some of which have been preserved as petrified fossils.
+Among mammals, early extinct species laid eggs, as do platypuses and echidnas (spiny anteaters). Platypuses and two genera of echidna are Australian monotremes. Marsupial and placental mammals do not lay eggs, but their unborn young do have the complex tissues that identify amniotes.
+The eggs of the egg-laying mammals (the platypus and the echidnas) are macrolecithal eggs very much like those of reptiles. The eggs of marsupials are likewise macrolecithal, but rather small, and develop inside the body of the female, but do not form a placenta. The young are born at a very early stage, and can be classified as a "larva" in the biological sense.[16]
+In placental mammals, the egg itself is void of yolk, but develops an umbilical cord from structures that in reptiles would form the yolk sac. Receiving nutrients from the mother, the fetus completes the development while inside the uterus.
+Eggs are common among invertebrates, including insects, spiders, mollusks, and crustaceans.
+All sexually reproducing life, including both plants and animals, produces gametes. The male gamete cell, sperm, is usually motile whereas the female gamete cell, the ovum, is generally larger and sessile. The male and female gametes combine to produce the zygote cell. In multicellular organisms the zygote subsequently divides in an organised manner into smaller more specialised cells, so that this new individual develops into an embryo. In most animals the embryo is the sessile initial stage of the individual life cycle, and is followed by the emergence (that is, the hatching) of a motile stage. The zygote or the ovum itself or the sessile organic vessel containing the developing embryo may be called the egg.
+A recent proposal suggests that the phylotypic animal body plans originated in cell aggregates before the existence of an egg stage of development. Eggs, in this view, were later evolutionary innovations, selected for their role in ensuring genetic uniformity among the cells of incipient multicellular organisms.[17]
+Scientists often classify animal reproduction according to the degree of development that occurs before the new individuals are expelled from the adult body, and by the yolk which the egg provides to nourish the embryo.
+Vertebrate eggs can be classified by the relative amount of yolk. Simple eggs with little yolk are called microlecithal, medium-sized eggs with some yolk are called mesolecithal, and large eggs with a large concentrated yolk are called macrolecithal.[7] This classification of eggs is based on the eggs of chordates, though the basic principle extends to the whole animal kingdom.
+Small eggs with little yolk are called microlecithal. The yolk is evenly distributed, so the cleavage of the egg cell cuts through and divides the egg into cells of fairly similar sizes. In sponges and cnidarians the dividing eggs develop directly into a simple larva, rather like a morula with cilia. In cnidarians, this stage is called the planula, and either develops directly into the adult animals or forms new adult individuals through a process of budding.[18]
+Microlecithal eggs require minimal yolk mass. Such eggs are found in flatworms, roundworms, annelids, bivalves, echinoderms, the lancelet and in most marine arthropods.[19] In anatomically simple animals, such as cnidarians and flatworms, the fetal development can be quite short, and even microlecithal eggs can undergo direct development. These small eggs can be produced in large numbers. In animals with high egg mortality, microlecithal eggs are the norm, as in bivalves and marine arthropods. However, the latter are more complex anatomically than e.g. flatworms, and the small microlecithal eggs do not allow full development. Instead, the eggs hatch into larvae, which may be markedly different from the adult animal.
+In placental mammals, where the embryo is nourished by the mother throughout the whole fetal period, the egg is reduced in size to essentially a naked egg cell.
+Mesolecithal eggs have comparatively more yolk than the microlecithal eggs. The yolk is concentrated in one part of the egg (the vegetal pole), with the cell nucleus and most of the cytoplasm in the other (the animal pole). The cell cleavage is uneven, and mainly concentrated in the cytoplasma-rich animal pole.[3]
+The larger yolk content of the mesolecithal eggs allows for a longer fetal development. Comparatively anatomically simple animals will be able to go through the full development and leave the egg in a form reminiscent of the adult animal. This is the situation found in hagfish and some snails.[4][19] Animals with smaller size eggs or more advanced anatomy will still have a distinct larval stage, though the larva will be basically similar to the adult animal, as in lampreys, coelacanth and the salamanders.[3]
+Eggs with a large yolk are called macrolecithal. The eggs are usually few in number, and the embryos have enough food to go through full fetal development in most groups.[7] Macrolecithal eggs are only found in selected representatives of two groups: Cephalopods and vertebrates.[7][20]
+Macrolecithal eggs go through a different type of development than other eggs. Due to the large size of the yolk, the cell division can not split up the yolk mass. The fetus instead develops as a plate-like structure on top of the yolk mass, and only envelopes it at a later stage.[7] A portion of the yolk mass is still present as an external or semi-external yolk sac at hatching in many groups. This form of fetal development is common in bony fish, even though their eggs can be quite small. Despite their macrolecithal structure, the small size of the eggs does not allow for direct development, and the eggs hatch to a larval stage ("fry"). In terrestrial animals with macrolecithal eggs, the large volume to surface ratio necessitates structures to aid in transport of oxygen and carbon dioxide, and for storage of waste products so that the embryo does not suffocate or get poisoned from its own waste while inside the egg, see amniote.[9]
+In addition to bony fish and cephalopods, macrolecithal eggs are found in cartilaginous fish, reptiles, birds and monotreme mammals.[3] The eggs of the coelacanths can reach a size of 9 cm (3.5 in) in diameter, and the young go through full development while in the uterus, living on the copious yolk.[21]
+Animals are commonly classified by their manner of reproduction, at the most general level distinguishing egg-laying (Latin. oviparous) from live-bearing (Latin. viviparous).
+These classifications are divided into more detail according to the development that occurs before the offspring are expelled from the adult's body. Traditionally:[22]
+The term hemotropic derives from the Latin for blood-feeding, contrasted with histotrophic for tissue-feeding.[27]
+Eggs laid by many different species, including birds, reptiles, amphibians, and fish, have probably been eaten by mankind for millennia. Popular choices for egg consumption are chicken, duck, roe, and caviar, but by a wide margin the egg most often humanly consumed is the chicken egg, typically unfertilized.
+According to the Kashrut, that is the set of Jewish dietary laws, kosher food may be consumed according to halakha (Jewish law). Kosher meat and milk (or derivatives) cannot be mixed (Deuteronomy 14:21) or stored together. Eggs are considered pareve (neither meat nor dairy) despite being an animal product and can be mixed with either milk or kosher meat. Mayonnaise, for instance, is usually marked "pareve" despite by definition containing egg.[28]
+Many vaccines for infectious diseases are produced in fertile chicken eggs. The basis of this technology was the discovery in 1931 by Alice Miles Woodruff and Ernest William Goodpasture at Vanderbilt University that the rickettsia and viruses that cause a variety of diseases will grow in chicken embryos. This enabled the development of vaccines against influenza, chicken pox, smallpox, yellow fever, typhus, Rocky mountain spotted fever and other diseases.
+The egg is a symbol of new life and rebirth in many cultures around the world. Christians view Easter eggs as symbolic of the resurrection of Jesus Christ.[29] A popular Easter tradition in some parts of the world is the decoration of hard-boiled eggs (usually by dyeing, but often by hand-painting or spray-painting). Adults often hide the eggs for children to find, an activity known as an Easter egg hunt. A similar tradition of egg painting exists in areas of the world influenced by the culture of Persia. Before the spring equinox in the Persian New Year tradition (called Norouz), each family member decorates a hard-boiled egg and sets them together in a bowl. The tradition of a dancing egg is held during the feast of Corpus Christi in Barcelona and other Catalan cities since the 16th century. It consists of an emptied egg, positioned over the water jet from a fountain, which starts turning without falling.[30]
+Although a food item, raw eggs are sometimes thrown at houses, cars, or people. This act, known commonly as "egging" in the various English-speaking countries, is a minor form of vandalism and, therefore, usually a criminal offense and is capable of damaging property (egg whites can degrade certain types of vehicle paint) as well as potentially causing serious eye injury. On Halloween, for example, trick or treaters have been known to throw eggs (and sometimes flour) at property or people from whom they received nothing.[citation needed] Eggs are also often thrown in protests, as they are inexpensive and nonlethal, yet very messy when broken.[31]
+Egg collecting was a popular hobby in some cultures, including among the first Australians. Traditionally, the embryo would be removed before a collector stored the egg shell.[32]
+Collecting eggs of wild birds is now banned by many jurisdictions, as the practice can threaten rare species. In the United Kingdom, the practice is prohibited by the Protection of Birds Act 1954 and Wildlife and Countryside Act 1981.[33] On the other hand, ongoing underground trading is becoming a serious issue.[34]
+Since the protection of wild bird eggs was regulated, early collections have come to the museums as curiosities. For example, the Australian Museum hosts a collection of about 20,000 registered clutches of eggs,[35] and the collection in Western Australia Museum has been archived in a gallery.[36] Scientists regard egg collections as a good natural-history data, as the details recorded in the collectors' notes have helped them to understand birds' nesting behaviors.[37]
+Insect eggs, in this case those of the Emperor gum moth, are often laid on the underside of leaves.
+Fish eggs, such as these herring eggs are often transparent and fertilized after laying.
+Skates and some sharks have a uniquely shaped egg case called a mermaid's purse.
+A Testudo hermanni emerging fully developed from a reptilian egg.
+A Schistosoma mekongi egg.
+Eggs of Huffmanela hamo, a nematode parasite in a fish
+Eggs of various parasites (mainly nematodes) from wild primates

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+The egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own, at which point the animal hatches. An egg results from fertilization of an egg cell. Most arthropods, vertebrates (excluding live-bearing mammals), and mollusks lay eggs, although some, such as scorpions, do not.
+Reptile eggs, bird eggs, and monotreme eggs are laid out of water and are surrounded by a protective shell, either flexible or inflexible. Eggs laid on land or in nests are usually kept within a warm and favorable temperature range while the embryo grows. When the embryo is adequately developed it hatches, i.e., breaks out of the egg's shell. Some embryos have a temporary egg tooth they use to crack, pip, or break the eggshell or covering.
+The largest recorded egg is from a whale shark and was 30 cm × 14 cm × 9 cm (11.8 in × 5.5 in × 3.5 in) in size.[1] Whale shark eggs typically hatch within the mother. At 1.5 kg (3.3 lb) and up to 17.8 cm × 14 cm (7.0 in × 5.5 in), the ostrich egg is the largest egg of any living bird,[2] though the extinct elephant bird and some non-avian dinosaurs laid larger eggs. The bee hummingbird produces the smallest known bird egg, which weighs half of a gram (around 0.02 oz). Some eggs laid by reptiles and most fish, amphibians, insects, and other invertebrates can be even smaller.
+Reproductive structures similar to the egg in other kingdoms are termed "spores," or in spermatophytes "seeds," or in gametophytes "egg cells".
+Several major groups of animals typically have readily distinguishable eggs.
+The most common reproductive strategy for fish is known as oviparity, in which the female lays undeveloped eggs that are externally fertilized by a male. Typically large numbers of eggs are laid at one time (an adult female cod can produce 4–6 million eggs in one spawning) and the eggs are then left to develop without parental care. When the larvae hatch from the egg, they often carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a few days as they learn how to swim. Once the yolk is consumed, there is a critical point after which they must learn how to hunt and feed or they will die.
+A few fish, notably the rays and most sharks use ovoviviparity in which the eggs are fertilized and develop internally. However, the larvae still grow inside the egg consuming the egg's yolk and without any direct nourishment from the mother. The mother then gives birth to relatively mature young. In certain instances, the physically most developed offspring will devour its smaller siblings for further nutrition while still within the mother's body. This is known as intrauterine cannibalism.
+In certain scenarios, some fish such as the hammerhead shark and reef shark are viviparous, with the egg being fertilized and developed internally, but with the mother also providing direct nourishment.
+The eggs of fish and amphibians are jellylike. Cartilaginous fish (sharks, skates, rays, chimaeras) eggs are fertilized internally and exhibit a wide variety of both internal and external embryonic development. Most fish species spawn eggs that are fertilized externally, typically with the male inseminating the eggs after the female lays them. These eggs do not have a shell and would dry out in the air. Even air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, Chiromantis xerampelina.
+Bird eggs are laid by females and incubated for a time that varies according to the species; a single young hatches from each egg. Average clutch sizes range from one (as in condors) to about 17 (the grey partridge). Some birds lay eggs even when not fertilized (e.g. hens); it is not uncommon for pet owners to find their lone bird nesting on a clutch of unfertilized eggs, which are sometimes called wind-eggs.
+The default color of vertebrate eggs is the white of the calcium carbonate from which the shells are made, but some birds, mainly passerines, produce colored eggs. The pigment biliverdin and its zinc chelate give a green or blue ground color, and protoporphyrin produces reds and browns as a ground color or as spotting.
+Non-passerines typically have white eggs, except in some ground-nesting groups such as the Charadriiformes, sandgrouse and nightjars, where camouflage is necessary, and some parasitic cuckoos which have to match the passerine host's egg. Most passerines, in contrast, lay colored eggs, even if there is no need of cryptic colors.
+However some have suggested that the protoporphyrin markings on passerine eggs actually act to reduce brittleness by acting as a solid-state lubricant.[10] If there is insufficient calcium available in the local soil, the egg shell may be thin, especially in a circle around the broad end. Protoporphyrin speckling compensates for this, and increases inversely to the amount of calcium in the soil.[11]
+For the same reason, later eggs in a clutch are more spotted than early ones as the female's store of calcium is depleted.
+The color of individual eggs is also genetically influenced, and appears to be inherited through the mother only, suggesting that the gene responsible for pigmentation is on the sex-determining W chromosome (female birds are WZ, males ZZ).
+It used to be thought that color was applied to the shell immediately before laying, but subsequent research shows that coloration is an integral part of the development of the shell, with the same protein responsible for depositing calcium carbonate, or protoporphyrins when there is a lack of that mineral.
+In species such as the common guillemot, which nest in large groups, each female's eggs have very different markings, making it easier for females to identify their own eggs on the crowded cliff ledges on which they breed.
+Bird eggshells are diverse. For example:
+Tiny pores in bird eggshells allow the embryo to breathe. The domestic hen's egg has around 7000 pores.[12]
+Some bird eggshells have a coating of vaterite spherules, which is a rare polymorph of calcium carbonate. In Greater Ani Crotophaga major this vaterite coating is thought to act as a shock absorber, protecting the calcite shell from fracture during incubation, such as colliding with other eggs in the nest.[13]
+Most bird eggs have an oval shape, with one end rounded and the other more pointed. This shape results from the egg being forced through the oviduct. Muscles contract the oviduct behind the egg, pushing it forward. The egg's wall is still shapeable, and the pointed end develops at the back. Long, pointy eggs are an incidental consequence of having a streamlined body typical of birds with strong flying abilities; flight narrows the oviduct, which changes the type of egg a bird can lay.[14] Cliff-nesting birds often have highly conical eggs. They are less likely to roll off, tending instead to roll around in a tight circle; this trait is likely to have arisen due to evolution via natural selection. In contrast, many hole-nesting birds have nearly spherical eggs.[15]
+Many animals feed on eggs. For example, principal predators of the black oystercatcher's eggs include raccoons, skunks, mink, river and sea otters, gulls, crows and foxes. The stoat (Mustela erminea) and long-tailed weasel (M. frenata) steal ducks' eggs. Snakes of the genera Dasypeltis and Elachistodon specialize in eating eggs.
+Brood parasitism occurs in birds when one species lays its eggs in the nest of another. In some cases, the host's eggs are removed or eaten by the female, or expelled by her chick. Brood parasites include the cowbirds and many Old World cuckoos.
+An average whooping crane egg is 102 mm (4.0 in) long and weighs 208 g (7.3 oz)
+Eurasian oystercatcher eggs camouflaged in the nest
+Egg of a senegal parrot, a bird that nests in tree holes, on a 1 cm (0.39 in) grid
+Eggs of ostrich, emu, kiwi and chicken
+Finch egg next to American dime
+Eggs of duck, goose, guineafowl and chicken
+Eggs of ostrich, cassowary, chicken, flamingo, pigeon and blackbird
+Egg of an emu
+Egg from a chicken compared to a 1 euro coin, great tit egg and a corn grain
+Bird nest with brown marbling eggs of a robin
+Like amphibians, amniotes are air-breathing vertebrates, but they have complex eggs or embryos, including an amniotic membrane. Amniotes include reptiles (including dinosaurs and their descendants, birds) and mammals.
+Reptile eggs are often rubbery and are always initially white. They are able to survive in the air. Often the sex of the developing embryo is determined by the temperature of the surroundings, with cooler temperatures favouring males. Not all reptiles lay eggs; some are viviparous ("live birth").
+Dinosaurs laid eggs, some of which have been preserved as petrified fossils.
+Among mammals, early extinct species laid eggs, as do platypuses and echidnas (spiny anteaters). Platypuses and two genera of echidna are Australian monotremes. Marsupial and placental mammals do not lay eggs, but their unborn young do have the complex tissues that identify amniotes.
+The eggs of the egg-laying mammals (the platypus and the echidnas) are macrolecithal eggs very much like those of reptiles. The eggs of marsupials are likewise macrolecithal, but rather small, and develop inside the body of the female, but do not form a placenta. The young are born at a very early stage, and can be classified as a "larva" in the biological sense.[16]
+In placental mammals, the egg itself is void of yolk, but develops an umbilical cord from structures that in reptiles would form the yolk sac. Receiving nutrients from the mother, the fetus completes the development while inside the uterus.
+Eggs are common among invertebrates, including insects, spiders, mollusks, and crustaceans.
+All sexually reproducing life, including both plants and animals, produces gametes. The male gamete cell, sperm, is usually motile whereas the female gamete cell, the ovum, is generally larger and sessile. The male and female gametes combine to produce the zygote cell. In multicellular organisms the zygote subsequently divides in an organised manner into smaller more specialised cells, so that this new individual develops into an embryo. In most animals the embryo is the sessile initial stage of the individual life cycle, and is followed by the emergence (that is, the hatching) of a motile stage. The zygote or the ovum itself or the sessile organic vessel containing the developing embryo may be called the egg.
+A recent proposal suggests that the phylotypic animal body plans originated in cell aggregates before the existence of an egg stage of development. Eggs, in this view, were later evolutionary innovations, selected for their role in ensuring genetic uniformity among the cells of incipient multicellular organisms.[17]
+Scientists often classify animal reproduction according to the degree of development that occurs before the new individuals are expelled from the adult body, and by the yolk which the egg provides to nourish the embryo.
+Vertebrate eggs can be classified by the relative amount of yolk. Simple eggs with little yolk are called microlecithal, medium-sized eggs with some yolk are called mesolecithal, and large eggs with a large concentrated yolk are called macrolecithal.[7] This classification of eggs is based on the eggs of chordates, though the basic principle extends to the whole animal kingdom.
+Small eggs with little yolk are called microlecithal. The yolk is evenly distributed, so the cleavage of the egg cell cuts through and divides the egg into cells of fairly similar sizes. In sponges and cnidarians the dividing eggs develop directly into a simple larva, rather like a morula with cilia. In cnidarians, this stage is called the planula, and either develops directly into the adult animals or forms new adult individuals through a process of budding.[18]
+Microlecithal eggs require minimal yolk mass. Such eggs are found in flatworms, roundworms, annelids, bivalves, echinoderms, the lancelet and in most marine arthropods.[19] In anatomically simple animals, such as cnidarians and flatworms, the fetal development can be quite short, and even microlecithal eggs can undergo direct development. These small eggs can be produced in large numbers. In animals with high egg mortality, microlecithal eggs are the norm, as in bivalves and marine arthropods. However, the latter are more complex anatomically than e.g. flatworms, and the small microlecithal eggs do not allow full development. Instead, the eggs hatch into larvae, which may be markedly different from the adult animal.
+In placental mammals, where the embryo is nourished by the mother throughout the whole fetal period, the egg is reduced in size to essentially a naked egg cell.
+Mesolecithal eggs have comparatively more yolk than the microlecithal eggs. The yolk is concentrated in one part of the egg (the vegetal pole), with the cell nucleus and most of the cytoplasm in the other (the animal pole). The cell cleavage is uneven, and mainly concentrated in the cytoplasma-rich animal pole.[3]
+The larger yolk content of the mesolecithal eggs allows for a longer fetal development. Comparatively anatomically simple animals will be able to go through the full development and leave the egg in a form reminiscent of the adult animal. This is the situation found in hagfish and some snails.[4][19] Animals with smaller size eggs or more advanced anatomy will still have a distinct larval stage, though the larva will be basically similar to the adult animal, as in lampreys, coelacanth and the salamanders.[3]
+Eggs with a large yolk are called macrolecithal. The eggs are usually few in number, and the embryos have enough food to go through full fetal development in most groups.[7] Macrolecithal eggs are only found in selected representatives of two groups: Cephalopods and vertebrates.[7][20]
+Macrolecithal eggs go through a different type of development than other eggs. Due to the large size of the yolk, the cell division can not split up the yolk mass. The fetus instead develops as a plate-like structure on top of the yolk mass, and only envelopes it at a later stage.[7] A portion of the yolk mass is still present as an external or semi-external yolk sac at hatching in many groups. This form of fetal development is common in bony fish, even though their eggs can be quite small. Despite their macrolecithal structure, the small size of the eggs does not allow for direct development, and the eggs hatch to a larval stage ("fry"). In terrestrial animals with macrolecithal eggs, the large volume to surface ratio necessitates structures to aid in transport of oxygen and carbon dioxide, and for storage of waste products so that the embryo does not suffocate or get poisoned from its own waste while inside the egg, see amniote.[9]
+In addition to bony fish and cephalopods, macrolecithal eggs are found in cartilaginous fish, reptiles, birds and monotreme mammals.[3] The eggs of the coelacanths can reach a size of 9 cm (3.5 in) in diameter, and the young go through full development while in the uterus, living on the copious yolk.[21]
+Animals are commonly classified by their manner of reproduction, at the most general level distinguishing egg-laying (Latin. oviparous) from live-bearing (Latin. viviparous).
+These classifications are divided into more detail according to the development that occurs before the offspring are expelled from the adult's body. Traditionally:[22]
+The term hemotropic derives from the Latin for blood-feeding, contrasted with histotrophic for tissue-feeding.[27]
+Eggs laid by many different species, including birds, reptiles, amphibians, and fish, have probably been eaten by mankind for millennia. Popular choices for egg consumption are chicken, duck, roe, and caviar, but by a wide margin the egg most often humanly consumed is the chicken egg, typically unfertilized.
+According to the Kashrut, that is the set of Jewish dietary laws, kosher food may be consumed according to halakha (Jewish law). Kosher meat and milk (or derivatives) cannot be mixed (Deuteronomy 14:21) or stored together. Eggs are considered pareve (neither meat nor dairy) despite being an animal product and can be mixed with either milk or kosher meat. Mayonnaise, for instance, is usually marked "pareve" despite by definition containing egg.[28]
+Many vaccines for infectious diseases are produced in fertile chicken eggs. The basis of this technology was the discovery in 1931 by Alice Miles Woodruff and Ernest William Goodpasture at Vanderbilt University that the rickettsia and viruses that cause a variety of diseases will grow in chicken embryos. This enabled the development of vaccines against influenza, chicken pox, smallpox, yellow fever, typhus, Rocky mountain spotted fever and other diseases.
+The egg is a symbol of new life and rebirth in many cultures around the world. Christians view Easter eggs as symbolic of the resurrection of Jesus Christ.[29] A popular Easter tradition in some parts of the world is the decoration of hard-boiled eggs (usually by dyeing, but often by hand-painting or spray-painting). Adults often hide the eggs for children to find, an activity known as an Easter egg hunt. A similar tradition of egg painting exists in areas of the world influenced by the culture of Persia. Before the spring equinox in the Persian New Year tradition (called Norouz), each family member decorates a hard-boiled egg and sets them together in a bowl. The tradition of a dancing egg is held during the feast of Corpus Christi in Barcelona and other Catalan cities since the 16th century. It consists of an emptied egg, positioned over the water jet from a fountain, which starts turning without falling.[30]
+Although a food item, raw eggs are sometimes thrown at houses, cars, or people. This act, known commonly as "egging" in the various English-speaking countries, is a minor form of vandalism and, therefore, usually a criminal offense and is capable of damaging property (egg whites can degrade certain types of vehicle paint) as well as potentially causing serious eye injury. On Halloween, for example, trick or treaters have been known to throw eggs (and sometimes flour) at property or people from whom they received nothing.[citation needed] Eggs are also often thrown in protests, as they are inexpensive and nonlethal, yet very messy when broken.[31]
+Egg collecting was a popular hobby in some cultures, including among the first Australians. Traditionally, the embryo would be removed before a collector stored the egg shell.[32]
+Collecting eggs of wild birds is now banned by many jurisdictions, as the practice can threaten rare species. In the United Kingdom, the practice is prohibited by the Protection of Birds Act 1954 and Wildlife and Countryside Act 1981.[33] On the other hand, ongoing underground trading is becoming a serious issue.[34]
+Since the protection of wild bird eggs was regulated, early collections have come to the museums as curiosities. For example, the Australian Museum hosts a collection of about 20,000 registered clutches of eggs,[35] and the collection in Western Australia Museum has been archived in a gallery.[36] Scientists regard egg collections as a good natural-history data, as the details recorded in the collectors' notes have helped them to understand birds' nesting behaviors.[37]
+Insect eggs, in this case those of the Emperor gum moth, are often laid on the underside of leaves.
+Fish eggs, such as these herring eggs are often transparent and fertilized after laying.
+Skates and some sharks have a uniquely shaped egg case called a mermaid's purse.
+A Testudo hermanni emerging fully developed from a reptilian egg.
+A Schistosoma mekongi egg.
+Eggs of Huffmanela hamo, a nematode parasite in a fish
+Eggs of various parasites (mainly nematodes) from wild primates

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+Easter eggs, also called Paschal eggs,[1] are eggs that are sometimes decorated. They are usually used as gifts on the occasion of Easter. As such, Easter eggs are common during the season of Eastertide (Easter season). The oldest tradition is to use dyed and painted chicken eggs, but a modern custom is to substitute chocolate eggs wrapped in colored foil, hand-carved wooden eggs, or plastic eggs filled with confectionery such as chocolate. However, real eggs continue to be used in Central and Eastern European tradition.
+Although eggs, in general, were a traditional symbol of fertility and rebirth,[2] in Christianity, for the celebration of Eastertide, Easter eggs symbolize the empty tomb of Jesus, from which Jesus resurrected.[3][4][5] In addition, one ancient tradition was the staining of Easter eggs with the colour red "in memory of the blood of Christ, shed as at that time of his crucifixion."[3][6]
+This custom of the Easter egg, according to many sources, can be traced to early Christians of Mesopotamia, and from there it spread into Eastern Europe and Siberia through the Orthodox Churches, and later into Europe through the Catholic and Protestant Churches.[6][7][8][9] Other sources maintain  that the custom arose in western Europe during the Middle Ages as a result of the fact that Western Christians were prohibited from eating eggs during Lent, but were allowed to eat them when Easter arrived.[10][11]
+The practice of decorating eggshells is quite ancient,[12] with decorated, engraved ostrich eggs found in Africa which are 60,000 years old.[13] In the pre-dynastic period of Egypt and the early cultures of Mesopotamia and Crete, eggs were associated with death and rebirth, as well as with kingship, with decorated ostrich eggs, and representations of ostrich eggs in gold and silver, were commonly placed in graves of the ancient Sumerians and Egyptians as early as 5,000 years ago.[14] These cultural relationships may have influenced early Christian and Islamic cultures in those areas, as well as through mercantile, religious, and political links from those areas around the Mediterranean.[15]
+According to many sources, the Christian custom of Easter eggs, specifically, started among the early Christians of Mesopotamia, who stained eggs with red coloring "in memory of the blood of Christ, shed at His crucifixion".[7][16][6][8][9]  The Christian Church officially adopted the custom, regarding the eggs as a symbol of the resurrection of Jesus, with the Roman Ritual, the first edition of which was published in 1610 but which has texts of much older date, containing among the Easter Blessings of Food, one for eggs, along with those for lamb, bread, and new produce.[8][9]
+Lord, let the grace of your blessing + come upon these eggs, that they be healthful food for your faithful who eat them in thanksgiving for the resurrection of our Lord Jesus Christ, who lives and reigns with you forever and ever.[17]
+Sociology professor Kenneth Thompson discusses the spread of the Easter egg throughout Christendom, writing that "use of eggs at Easter seems to have come from Persia into the Greek Christian Churches of Mesopotamia, thence to Russia and Siberia through the medium of Orthodox Christianity. From the Greek Church the custom was adopted by either the Roman Catholics or the Protestants and then spread through Europe."[7] Both Thompson, as well as British orientalist Thomas Hyde state that in addition to dyeing the eggs red, the early Christians of Mesopotamia also stained Easter eggs green and yellow.[6][7]
+Peter Gainsford maintains that the association between eggs and Easter most likely arose in western Europe during the Middle Ages as a result of the fact that Catholic Christians were prohibited from eating eggs during Lent, but were allowed to eat them when Easter arrived.[10][11]
+Influential 19th century folklorist and philologist Jacob Grimm speculates, in the second volume of his Deutsche Mythologie, that the folk custom of Easter eggs among the continental Germanic peoples may have stemmed from springtime festivities of a Germanic goddess known in Old English as Ēostre (namesake of modern English Easter) and possibly known in Old High German as *Ostara (and thus namesake of Modern German Ostern 'Easter'). However, despite Grimm's speculation, there is no evidence to connect eggs with Ostara.[11] The use of eggs as favors or treats at Easter originated when they were prohibited during Lent.[10][11] A common practice in England in the medieval period was for children to go door-to-door begging for eggs on the Saturday before Lent began. People handed out eggs as special treats for children prior to their fast.[11]
+Although one of the Christian traditions are to use dyed or painted chicken eggs, a modern custom is to substitute chocolate eggs, or plastic eggs filled with candy such as jelly beans; as many people give up sweets as their Lenten sacrifice, individuals enjoy them at Easter after having abstained from them during the preceding forty days of Lent.[18] These eggs can be hidden for children to find on Easter morning, which may be left by the Easter Bunny. They may also be put in a basket filled with real or artificial straw to resemble a bird's nest.
+The Easter egg tradition may also have merged into the celebration of the end of the privations of Lent in the West.
+Historically, it was traditional to use up all of the household's eggs before Lent began.
+Eggs were originally forbidden during Lent as well as on other traditional fast days in Western Christianity (this tradition still continues among the Eastern Christian Churches). Likewise, in Eastern Christianity, meat, eggs, and dairy are all prohibited during the Lenten fast.
+This established the tradition of Pancake Day being celebrated on Shrove Tuesday. This day, the Tuesday before Ash Wednesday when Lent begins, is also known as Mardi Gras, a French phrase which translates as "Fat Tuesday" to mark the last consumption of eggs and dairy before Lent begins.
+In the Orthodox Church, Great Lent begins on Clean Monday, rather than Wednesday, so the household's dairy products would be used up in the preceding week, called Cheesefare Week.
+During Lent, since chickens would not stop producing eggs during this time, a larger than usual store might be available at the end of the fast. This surplus, if any, had to be eaten quickly to prevent spoiling. Then, with the coming of Easter, the eating of eggs resumes.  Some families cook a special meatloaf with eggs in it to be eaten with the Easter dinner.
+One would have been forced to hard boil the eggs that the chickens produced so as not to waste food, and for this reason the Spanish dish hornazo (traditionally eaten on and around Easter) contains hard-boiled eggs as a primary ingredient.
+In Hungary, eggs are used sliced in potato casseroles around the Easter period.
+Some Christians symbolically link the cracking open of Easter eggs with the empty tomb of Jesus.[19]
+In the Orthodox churches, Easter eggs are blessed by the priest at the end of the Paschal Vigil (which is equivalent to Holy Saturday), and distributed to the faithful. The egg is seen by followers of Christianity as a symbol of resurrection: while being dormant it contains a new life sealed within it.[3][4]
+Similarly, in the Roman Catholic Church in Poland, the so-called święconka, i.e. blessing of decorative baskets with a sampling of Easter eggs and other symbolic foods, is one of the most enduring and beloved Polish traditions on Holy Saturday.
+During Paschaltide, in some traditions the Pascal greeting with the Easter egg is even extended to the deceased. On either the second Monday or Tuesday of Pascha, after a memorial service people bring blessed eggs to the cemetery and bring the joyous paschal greeting, "Christ has risen", to their beloved departed (see Radonitza).
+In Greece, women traditionally dye the eggs with onion skins and vinegar on Thursday (also the day of Communion). These ceremonial eggs are known as kokkina avga. They also bake tsoureki for the Easter Sunday feast.[20] Red Easter eggs are sometimes served along the centerline of tsoureki (braided loaf of bread).[21][22]
+In Egypt, it is a tradition to decorate boiled eggs during Sham el-Nessim holiday, which falls every year after the Eastern Christian Easter.
+Coincidentally, every Passover, Jews place a hard-boiled egg on the Passover ceremonial plate, and the celebrants also eat hard-boiled eggs dipped in salt water as part of the ceremony.
+The dyeing of Easter eggs in different colours is commonplace, with colour being achieved through boiling the egg in natural substances (such as, onion peel (brown colour), oak or alder bark or walnut nutshell (black), beet juice (pink) etc.), or using artificial colourings.
+A greater variety of colour was often provided by tying on the onion skin with different coloured woollen yarn. In the North of England these are called pace-eggs or paste-eggs, from a dialectal form of Middle English pasche. They were usually eaten after an egg-jarping (egg tapping) competition.
+In the Orthodox and Eastern Catholic Churches, Easter eggs are dyed red to represent the blood of Christ, with further symbolism being found in the hard shell of the egg symbolizing the sealed Tomb of Christ — the cracking of which symbolized his resurrection from the dead. The tradition of red easter eggs was used by the Russian Orthodox Church.[23] The tradition to dying the easter eggs in an Onion tone exists in the cultures of Armenia, Georgia, Belarus, Russia, Czechia, Romania, and Israel.[24] The colour is made by boiling onion peel in water.[25][26]
+When boiling them with onion skins leaves can be attached prior to dying to create leaf patterns. The leaves are attached to the eggs before they are dyed with a transparent cloth to wrap the eggs with like inexpensive muslin or nylon stockings, leaving patterns once the leaves are removed after the dyeing process.[27][28] These eggs are part of Easter custom in many areas and often accompany other traditional Easter foods. Passover haminados are prepared with similar methods.
+Pysanky[29] are Ukrainian Easter eggs, decorated using a wax-resist (batik) method. The word comes from the verb pysaty, "to write", as the designs are not painted on, but written with beeswax.
+Decorating eggs for Easter using wax resistant batik is a popular method in some other eastern European countries.
+In some Mediterranean countries, especially in Lebanon, chicken eggs are boiled and decorated by dye and/or painting and used as decoration around the house. Then, on Easter Day, young kids would duel with them saying 'Christ is resurrected, Indeed, He is', breaking and eating them. This also happens in Georgia, Bulgaria, Cyprus, Greece, Macedonia, Romania, Russia, Serbia and Ukraine. In Easter Sunday friends and family hit each other's egg with their own. The one whose egg does not break is believed to be in for good luck in the future.
+In Germany, eggs decorate trees and bushes as Easter egg trees, and in several areas public wells as Osterbrunnen.
+There used to be a custom in Ukraine, during Easter celebrations to have krashanky on a table in a bowl with wheatgrass. The number of the krashanky equalled the number of departed family members.[30]
+Ukrainian Easter eggs
+Easter eggs from Sorbs
+Easter eggs from Lithuania
+Perforated egg from Germany, Sleeping Beauty
+Norwegian Easter eggs
+Easter eggs from Greece
+Perforated eggs
+Easter eggs from France
+American Easter egg from the White House Washington, D.C.
+Pace eggs boiled with onion skins and leaf patterns.
+Easter eggs decorated with straw
+Easter egg from Poland
+An egg hunt is a game in which decorated eggs, which may be hard-boiled chicken eggs, chocolate eggs, or artificial eggs containing candies, are hidden for children to find. The eggs often vary in size, and may be hidden both indoors and outdoors.[31] When the hunt is over, prizes may be given for the largest number of eggs collected, or for the largest or the smallest egg.[31]
+The central European Slavic nations (Czechs and Slovaks etc.) have a tradition of gathering eggs by gaining them from the females in return of whipping them with a pony-tail shaped whip made out of fresh willow branches and splashing them with water, by the Ruthenians called polivanja, which is supposed to give them health and beauty.
+Cascarones, a Latin American tradition now shared by many US States with high Hispanic demographics, are emptied and dried chicken eggs stuffed with confetti and sealed with a piece of tissue paper. The eggs are hidden in a similar tradition to the American Easter egg hunt and when found the children (and adults) break them over each other's heads.
+In order to enable children to take part in egg hunts despite visual impairment, eggs have been created that emit various clicks, beeps, noises, or music so that visually impaired children can easily hunt for Easter eggs.[32]
+Egg rolling is also a traditional Easter egg game played with eggs at Easter. In the United Kingdom, Germany, and other countries children traditionally rolled eggs down hillsides at Easter.[33] This tradition was taken to the New World by European settlers,[33][34] and continues to this day each Easter with an Easter egg roll on the White House lawn. Different nations have different versions of the game.
+In the North of England, during Eastertide, a traditional game is played where hard boiled pace eggs are distributed and each player hits the other player's egg with their own. This is known as "egg tapping", "egg dumping", or "egg jarping". The winner is the holder of the last intact egg. The annual egg jarping world championship is held every year over Easter in Peterlee, Durham.[35]
+It is also practiced in Italy (where it is called scuccetta), Bulgaria, Hungary, Croatia, Latvia, Lithuania, Lebanon, Macedonia, Romania, Serbia, Slovenia (where it is called turčanje or trkanje), Ukraine, Russia, and other countries. In parts of Austria, Bavaria and German-speaking Switzerland it is called Ostereiertitschen or Eierpecken. In parts of Europe it is also called epper, presumably from the German name Opfer, meaning "offering" and in Greece it is known as tsougrisma. In South Louisiana, this practice is called pocking eggs[36][37] and is slightly different. The Louisiana Creoles hold that the winner eats the eggs of the losers in each round.
+In the Greek Orthodox tradition, red eggs are also cracked together when people exchange Easter greetings.
+Egg dance is a traditional Easter game in which eggs are laid on the ground or floor and the goal is to dance among them without damaging any eggs[38] which originated in Germany. In the UK the dance is called the hop-egg.
+The Pace Egg plays are traditional village plays, with a rebirth theme. The drama takes the form of a combat between the hero and villain, in which the hero is killed and brought back to life. The plays take place in England during Easter.
+Chocolate eggs first appeared at the court of Louis XIV in Versailles and in 1725 the widow Giambone in Turin started producing chocolate eggs by filling empty chicken egg shells with molten chocolate. [39]In 1873 J.S. Fry & Sons of England introduced the first chocolate Easter egg in Britain. Manufacturing their first Easter egg in 1875, Cadbury created the modern chocolate Easter egg after developing a pure cocoa butter that could be moulded into smooth shapes.[40]
+In Western cultures, the giving of chocolate eggs is now commonplace, with 80 million Easter eggs sold in the UK alone. Formerly, the containers Easter eggs were sold in contained large amounts of plastic, although in the United Kingdom this has gradually been replaced with recyclable paper and cardboard.[41]
+Chocolate Easter egg
+Chocolate Easter egg bunny
+Easter egg with candy.
+Gladys as a Chocolate Easter Bunny with Easter eggs
+Kinder Surprise Egg, manufactured by Italian company Ferrero SpA
+In the Indian state of Goa, the Goan Catholic version of marzipan is used to make easter eggs. In the Philippines, mazapán de pili (Spanish for "pili marzipan") is made from pili nuts.
+Marzipan easter eggs
+The jewelled Easter eggs made by the Fabergé firm for the two last Russian Tsars are regarded as masterpieces of decorative arts. Most of these creations themselves contained hidden surprises such as clock-work birds, or miniature ships.
+In Bulgaria, Poland, Romania, Russia, Ukraine, and other Central European countries' folk traditions, and making artificial eggs out of porcelain for ladies is common.[42]:45
+Easter eggs are frequently depicted in sculpture, including a 8-metre (27 ft) sculpture of a pysanka standing in Vegreville, Alberta.
+Fabergé egg
+Giant easter egg, Bariloche, Argentina
+Giant pysanka from Vegreville, Alberta, Canada
+Giant easter egg or pisanica in Zagreb, Croatia
+Easter egg sculpture in Gogolin, Poland
+Giant easter egg in Suceava, Romania
+While the origin of Easter eggs can be explained in the symbolic terms described above, among followers of Eastern Christianity the legend says that Mary Magdalene was bringing cooked eggs to share with the other women at the tomb of Jesus, and the eggs in her basket miraculously turned bright red when she saw the risen Christ.[43]
+A different, but not necessarily conflicting legend concerns Mary Magdalene's efforts to spread the Gospel. According to this tradition, after the Ascension of Jesus, Mary went to the Emperor of Rome and greeted him with "Christ has risen," whereupon he pointed to an egg on his table and stated, "Christ has no more risen than that egg is red." After making this statement it is said the egg immediately turned blood red.[44]
+Red Easter eggs, known as kokkina avga (κόκκινα αυγά) in Greece and krashanki in Ukraine, are an Easter tradition and a distinct type of Easter egg prepared by various Orthodox Christian peoples.[45][46][47][48] The red eggs are part of Easter custom in many areas and often accompany other traditional Easter foods. Passover haminados are prepared with similar methods.
+Dark red eggs are a tradition in Greece and represent the blood of Christ shed on the cross.[49] The practice dates to the early Christian church in Mesopotamia.[8][9]
+In Greece, superstitions of the past included the custom of placing the first-dyed red egg at the home's iconostasis (place where icons are displayed) to ward off evil. The heads and backs of small lambs were also marked with the red dye to protect them.
+The egg is widely used as a symbol of the start of new life, just as new life emerges from an egg when the chick hatches out.[2]
+Painted eggs are used at the Iranian spring holidays, the Nowruz that marks the first day of spring or Equinox, and the beginning of the year in the Persian calendar. It is celebrated on the day of the astronomical Northward equinox, which usually occurs on March 21 or the previous/following day depending on where it is observed. The painted eggs symbolize fertility and are displayed on the Nowruz table, called Haft-Seen together with various other symbolic objects. There are sometimes one egg for each member of the family. The ancient Zoroastrians painted eggs for Nowruz, their New Year celebration, which falls on the Spring equinox. The tradition continues among Persians of Islamic, Zoroastrian, and other faiths today.[50] The Nowruz tradition has existed for at least 2,500 years. The sculptures on the walls of Persepolis show people carrying eggs for Nowruz to the king.[citation needed]
+The Neopagan holiday of Ostara occurs at roughly the same time as Easter. While it is often claimed that the use of painted eggs is an ancient, pre-Christian component of the celebration of Ostara, there are no historical accounts that ancient celebrations included this practice, apart from the Old High German lullaby which is believed by most to be a modern fabrication. Rather, the use of painted eggs has been adopted under the assumption that it might be a pre-Christian survival. In fact, modern scholarship has been unable to trace any association between eggs and a supposed goddess named Ostara before the 19th century, when early folklorists began to speculate about the possibility.[51]
+There are good grounds for the association between hares (later termed Easter bunnies) and bird eggs, through folklore confusion between hares' forms (where they raise their young) and plovers' nests.[52]
+In Judaism, a hard-boiled egg is an element of the Passover Seder, representing festival sacrifice. The children's game of hunting for the afikomen (a half-piece of matzo) has similarities to the Easter egg hunt tradition, by which the child who finds the hidden bread will be awarded a prize. In other homes, the children hide the afikoman and a parent must look for it; when the parents give up, the children demand a prize for revealing its location.
+Media related to Easter eggs at Wikimedia Commons

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+The egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own, at which point the animal hatches. An egg results from fertilization of an egg cell. Most arthropods, vertebrates (excluding live-bearing mammals), and mollusks lay eggs, although some, such as scorpions, do not.
+Reptile eggs, bird eggs, and monotreme eggs are laid out of water and are surrounded by a protective shell, either flexible or inflexible. Eggs laid on land or in nests are usually kept within a warm and favorable temperature range while the embryo grows. When the embryo is adequately developed it hatches, i.e., breaks out of the egg's shell. Some embryos have a temporary egg tooth they use to crack, pip, or break the eggshell or covering.
+The largest recorded egg is from a whale shark and was 30 cm × 14 cm × 9 cm (11.8 in × 5.5 in × 3.5 in) in size.[1] Whale shark eggs typically hatch within the mother. At 1.5 kg (3.3 lb) and up to 17.8 cm × 14 cm (7.0 in × 5.5 in), the ostrich egg is the largest egg of any living bird,[2] though the extinct elephant bird and some non-avian dinosaurs laid larger eggs. The bee hummingbird produces the smallest known bird egg, which weighs half of a gram (around 0.02 oz). Some eggs laid by reptiles and most fish, amphibians, insects, and other invertebrates can be even smaller.
+Reproductive structures similar to the egg in other kingdoms are termed "spores," or in spermatophytes "seeds," or in gametophytes "egg cells".
+Several major groups of animals typically have readily distinguishable eggs.
+The most common reproductive strategy for fish is known as oviparity, in which the female lays undeveloped eggs that are externally fertilized by a male. Typically large numbers of eggs are laid at one time (an adult female cod can produce 4–6 million eggs in one spawning) and the eggs are then left to develop without parental care. When the larvae hatch from the egg, they often carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a few days as they learn how to swim. Once the yolk is consumed, there is a critical point after which they must learn how to hunt and feed or they will die.
+A few fish, notably the rays and most sharks use ovoviviparity in which the eggs are fertilized and develop internally. However, the larvae still grow inside the egg consuming the egg's yolk and without any direct nourishment from the mother. The mother then gives birth to relatively mature young. In certain instances, the physically most developed offspring will devour its smaller siblings for further nutrition while still within the mother's body. This is known as intrauterine cannibalism.
+In certain scenarios, some fish such as the hammerhead shark and reef shark are viviparous, with the egg being fertilized and developed internally, but with the mother also providing direct nourishment.
+The eggs of fish and amphibians are jellylike. Cartilaginous fish (sharks, skates, rays, chimaeras) eggs are fertilized internally and exhibit a wide variety of both internal and external embryonic development. Most fish species spawn eggs that are fertilized externally, typically with the male inseminating the eggs after the female lays them. These eggs do not have a shell and would dry out in the air. Even air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, Chiromantis xerampelina.
+Bird eggs are laid by females and incubated for a time that varies according to the species; a single young hatches from each egg. Average clutch sizes range from one (as in condors) to about 17 (the grey partridge). Some birds lay eggs even when not fertilized (e.g. hens); it is not uncommon for pet owners to find their lone bird nesting on a clutch of unfertilized eggs, which are sometimes called wind-eggs.
+The default color of vertebrate eggs is the white of the calcium carbonate from which the shells are made, but some birds, mainly passerines, produce colored eggs. The pigment biliverdin and its zinc chelate give a green or blue ground color, and protoporphyrin produces reds and browns as a ground color or as spotting.
+Non-passerines typically have white eggs, except in some ground-nesting groups such as the Charadriiformes, sandgrouse and nightjars, where camouflage is necessary, and some parasitic cuckoos which have to match the passerine host's egg. Most passerines, in contrast, lay colored eggs, even if there is no need of cryptic colors.
+However some have suggested that the protoporphyrin markings on passerine eggs actually act to reduce brittleness by acting as a solid-state lubricant.[10] If there is insufficient calcium available in the local soil, the egg shell may be thin, especially in a circle around the broad end. Protoporphyrin speckling compensates for this, and increases inversely to the amount of calcium in the soil.[11]
+For the same reason, later eggs in a clutch are more spotted than early ones as the female's store of calcium is depleted.
+The color of individual eggs is also genetically influenced, and appears to be inherited through the mother only, suggesting that the gene responsible for pigmentation is on the sex-determining W chromosome (female birds are WZ, males ZZ).
+It used to be thought that color was applied to the shell immediately before laying, but subsequent research shows that coloration is an integral part of the development of the shell, with the same protein responsible for depositing calcium carbonate, or protoporphyrins when there is a lack of that mineral.
+In species such as the common guillemot, which nest in large groups, each female's eggs have very different markings, making it easier for females to identify their own eggs on the crowded cliff ledges on which they breed.
+Bird eggshells are diverse. For example:
+Tiny pores in bird eggshells allow the embryo to breathe. The domestic hen's egg has around 7000 pores.[12]
+Some bird eggshells have a coating of vaterite spherules, which is a rare polymorph of calcium carbonate. In Greater Ani Crotophaga major this vaterite coating is thought to act as a shock absorber, protecting the calcite shell from fracture during incubation, such as colliding with other eggs in the nest.[13]
+Most bird eggs have an oval shape, with one end rounded and the other more pointed. This shape results from the egg being forced through the oviduct. Muscles contract the oviduct behind the egg, pushing it forward. The egg's wall is still shapeable, and the pointed end develops at the back. Long, pointy eggs are an incidental consequence of having a streamlined body typical of birds with strong flying abilities; flight narrows the oviduct, which changes the type of egg a bird can lay.[14] Cliff-nesting birds often have highly conical eggs. They are less likely to roll off, tending instead to roll around in a tight circle; this trait is likely to have arisen due to evolution via natural selection. In contrast, many hole-nesting birds have nearly spherical eggs.[15]
+Many animals feed on eggs. For example, principal predators of the black oystercatcher's eggs include raccoons, skunks, mink, river and sea otters, gulls, crows and foxes. The stoat (Mustela erminea) and long-tailed weasel (M. frenata) steal ducks' eggs. Snakes of the genera Dasypeltis and Elachistodon specialize in eating eggs.
+Brood parasitism occurs in birds when one species lays its eggs in the nest of another. In some cases, the host's eggs are removed or eaten by the female, or expelled by her chick. Brood parasites include the cowbirds and many Old World cuckoos.
+An average whooping crane egg is 102 mm (4.0 in) long and weighs 208 g (7.3 oz)
+Eurasian oystercatcher eggs camouflaged in the nest
+Egg of a senegal parrot, a bird that nests in tree holes, on a 1 cm (0.39 in) grid
+Eggs of ostrich, emu, kiwi and chicken
+Finch egg next to American dime
+Eggs of duck, goose, guineafowl and chicken
+Eggs of ostrich, cassowary, chicken, flamingo, pigeon and blackbird
+Egg of an emu
+Egg from a chicken compared to a 1 euro coin, great tit egg and a corn grain
+Bird nest with brown marbling eggs of a robin
+Like amphibians, amniotes are air-breathing vertebrates, but they have complex eggs or embryos, including an amniotic membrane. Amniotes include reptiles (including dinosaurs and their descendants, birds) and mammals.
+Reptile eggs are often rubbery and are always initially white. They are able to survive in the air. Often the sex of the developing embryo is determined by the temperature of the surroundings, with cooler temperatures favouring males. Not all reptiles lay eggs; some are viviparous ("live birth").
+Dinosaurs laid eggs, some of which have been preserved as petrified fossils.
+Among mammals, early extinct species laid eggs, as do platypuses and echidnas (spiny anteaters). Platypuses and two genera of echidna are Australian monotremes. Marsupial and placental mammals do not lay eggs, but their unborn young do have the complex tissues that identify amniotes.
+The eggs of the egg-laying mammals (the platypus and the echidnas) are macrolecithal eggs very much like those of reptiles. The eggs of marsupials are likewise macrolecithal, but rather small, and develop inside the body of the female, but do not form a placenta. The young are born at a very early stage, and can be classified as a "larva" in the biological sense.[16]
+In placental mammals, the egg itself is void of yolk, but develops an umbilical cord from structures that in reptiles would form the yolk sac. Receiving nutrients from the mother, the fetus completes the development while inside the uterus.
+Eggs are common among invertebrates, including insects, spiders, mollusks, and crustaceans.
+All sexually reproducing life, including both plants and animals, produces gametes. The male gamete cell, sperm, is usually motile whereas the female gamete cell, the ovum, is generally larger and sessile. The male and female gametes combine to produce the zygote cell. In multicellular organisms the zygote subsequently divides in an organised manner into smaller more specialised cells, so that this new individual develops into an embryo. In most animals the embryo is the sessile initial stage of the individual life cycle, and is followed by the emergence (that is, the hatching) of a motile stage. The zygote or the ovum itself or the sessile organic vessel containing the developing embryo may be called the egg.
+A recent proposal suggests that the phylotypic animal body plans originated in cell aggregates before the existence of an egg stage of development. Eggs, in this view, were later evolutionary innovations, selected for their role in ensuring genetic uniformity among the cells of incipient multicellular organisms.[17]
+Scientists often classify animal reproduction according to the degree of development that occurs before the new individuals are expelled from the adult body, and by the yolk which the egg provides to nourish the embryo.
+Vertebrate eggs can be classified by the relative amount of yolk. Simple eggs with little yolk are called microlecithal, medium-sized eggs with some yolk are called mesolecithal, and large eggs with a large concentrated yolk are called macrolecithal.[7] This classification of eggs is based on the eggs of chordates, though the basic principle extends to the whole animal kingdom.
+Small eggs with little yolk are called microlecithal. The yolk is evenly distributed, so the cleavage of the egg cell cuts through and divides the egg into cells of fairly similar sizes. In sponges and cnidarians the dividing eggs develop directly into a simple larva, rather like a morula with cilia. In cnidarians, this stage is called the planula, and either develops directly into the adult animals or forms new adult individuals through a process of budding.[18]
+Microlecithal eggs require minimal yolk mass. Such eggs are found in flatworms, roundworms, annelids, bivalves, echinoderms, the lancelet and in most marine arthropods.[19] In anatomically simple animals, such as cnidarians and flatworms, the fetal development can be quite short, and even microlecithal eggs can undergo direct development. These small eggs can be produced in large numbers. In animals with high egg mortality, microlecithal eggs are the norm, as in bivalves and marine arthropods. However, the latter are more complex anatomically than e.g. flatworms, and the small microlecithal eggs do not allow full development. Instead, the eggs hatch into larvae, which may be markedly different from the adult animal.
+In placental mammals, where the embryo is nourished by the mother throughout the whole fetal period, the egg is reduced in size to essentially a naked egg cell.
+Mesolecithal eggs have comparatively more yolk than the microlecithal eggs. The yolk is concentrated in one part of the egg (the vegetal pole), with the cell nucleus and most of the cytoplasm in the other (the animal pole). The cell cleavage is uneven, and mainly concentrated in the cytoplasma-rich animal pole.[3]
+The larger yolk content of the mesolecithal eggs allows for a longer fetal development. Comparatively anatomically simple animals will be able to go through the full development and leave the egg in a form reminiscent of the adult animal. This is the situation found in hagfish and some snails.[4][19] Animals with smaller size eggs or more advanced anatomy will still have a distinct larval stage, though the larva will be basically similar to the adult animal, as in lampreys, coelacanth and the salamanders.[3]
+Eggs with a large yolk are called macrolecithal. The eggs are usually few in number, and the embryos have enough food to go through full fetal development in most groups.[7] Macrolecithal eggs are only found in selected representatives of two groups: Cephalopods and vertebrates.[7][20]
+Macrolecithal eggs go through a different type of development than other eggs. Due to the large size of the yolk, the cell division can not split up the yolk mass. The fetus instead develops as a plate-like structure on top of the yolk mass, and only envelopes it at a later stage.[7] A portion of the yolk mass is still present as an external or semi-external yolk sac at hatching in many groups. This form of fetal development is common in bony fish, even though their eggs can be quite small. Despite their macrolecithal structure, the small size of the eggs does not allow for direct development, and the eggs hatch to a larval stage ("fry"). In terrestrial animals with macrolecithal eggs, the large volume to surface ratio necessitates structures to aid in transport of oxygen and carbon dioxide, and for storage of waste products so that the embryo does not suffocate or get poisoned from its own waste while inside the egg, see amniote.[9]
+In addition to bony fish and cephalopods, macrolecithal eggs are found in cartilaginous fish, reptiles, birds and monotreme mammals.[3] The eggs of the coelacanths can reach a size of 9 cm (3.5 in) in diameter, and the young go through full development while in the uterus, living on the copious yolk.[21]
+Animals are commonly classified by their manner of reproduction, at the most general level distinguishing egg-laying (Latin. oviparous) from live-bearing (Latin. viviparous).
+These classifications are divided into more detail according to the development that occurs before the offspring are expelled from the adult's body. Traditionally:[22]
+The term hemotropic derives from the Latin for blood-feeding, contrasted with histotrophic for tissue-feeding.[27]
+Eggs laid by many different species, including birds, reptiles, amphibians, and fish, have probably been eaten by mankind for millennia. Popular choices for egg consumption are chicken, duck, roe, and caviar, but by a wide margin the egg most often humanly consumed is the chicken egg, typically unfertilized.
+According to the Kashrut, that is the set of Jewish dietary laws, kosher food may be consumed according to halakha (Jewish law). Kosher meat and milk (or derivatives) cannot be mixed (Deuteronomy 14:21) or stored together. Eggs are considered pareve (neither meat nor dairy) despite being an animal product and can be mixed with either milk or kosher meat. Mayonnaise, for instance, is usually marked "pareve" despite by definition containing egg.[28]
+Many vaccines for infectious diseases are produced in fertile chicken eggs. The basis of this technology was the discovery in 1931 by Alice Miles Woodruff and Ernest William Goodpasture at Vanderbilt University that the rickettsia and viruses that cause a variety of diseases will grow in chicken embryos. This enabled the development of vaccines against influenza, chicken pox, smallpox, yellow fever, typhus, Rocky mountain spotted fever and other diseases.
+The egg is a symbol of new life and rebirth in many cultures around the world. Christians view Easter eggs as symbolic of the resurrection of Jesus Christ.[29] A popular Easter tradition in some parts of the world is the decoration of hard-boiled eggs (usually by dyeing, but often by hand-painting or spray-painting). Adults often hide the eggs for children to find, an activity known as an Easter egg hunt. A similar tradition of egg painting exists in areas of the world influenced by the culture of Persia. Before the spring equinox in the Persian New Year tradition (called Norouz), each family member decorates a hard-boiled egg and sets them together in a bowl. The tradition of a dancing egg is held during the feast of Corpus Christi in Barcelona and other Catalan cities since the 16th century. It consists of an emptied egg, positioned over the water jet from a fountain, which starts turning without falling.[30]
+Although a food item, raw eggs are sometimes thrown at houses, cars, or people. This act, known commonly as "egging" in the various English-speaking countries, is a minor form of vandalism and, therefore, usually a criminal offense and is capable of damaging property (egg whites can degrade certain types of vehicle paint) as well as potentially causing serious eye injury. On Halloween, for example, trick or treaters have been known to throw eggs (and sometimes flour) at property or people from whom they received nothing.[citation needed] Eggs are also often thrown in protests, as they are inexpensive and nonlethal, yet very messy when broken.[31]
+Egg collecting was a popular hobby in some cultures, including among the first Australians. Traditionally, the embryo would be removed before a collector stored the egg shell.[32]
+Collecting eggs of wild birds is now banned by many jurisdictions, as the practice can threaten rare species. In the United Kingdom, the practice is prohibited by the Protection of Birds Act 1954 and Wildlife and Countryside Act 1981.[33] On the other hand, ongoing underground trading is becoming a serious issue.[34]
+Since the protection of wild bird eggs was regulated, early collections have come to the museums as curiosities. For example, the Australian Museum hosts a collection of about 20,000 registered clutches of eggs,[35] and the collection in Western Australia Museum has been archived in a gallery.[36] Scientists regard egg collections as a good natural-history data, as the details recorded in the collectors' notes have helped them to understand birds' nesting behaviors.[37]
+Insect eggs, in this case those of the Emperor gum moth, are often laid on the underside of leaves.
+Fish eggs, such as these herring eggs are often transparent and fertilized after laying.
+Skates and some sharks have a uniquely shaped egg case called a mermaid's purse.
+A Testudo hermanni emerging fully developed from a reptilian egg.
+A Schistosoma mekongi egg.
+Eggs of Huffmanela hamo, a nematode parasite in a fish
+Eggs of various parasites (mainly nematodes) from wild primates

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+The egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own, at which point the animal hatches. An egg results from fertilization of an egg cell. Most arthropods, vertebrates (excluding live-bearing mammals), and mollusks lay eggs, although some, such as scorpions, do not.
+Reptile eggs, bird eggs, and monotreme eggs are laid out of water and are surrounded by a protective shell, either flexible or inflexible. Eggs laid on land or in nests are usually kept within a warm and favorable temperature range while the embryo grows. When the embryo is adequately developed it hatches, i.e., breaks out of the egg's shell. Some embryos have a temporary egg tooth they use to crack, pip, or break the eggshell or covering.
+The largest recorded egg is from a whale shark and was 30 cm × 14 cm × 9 cm (11.8 in × 5.5 in × 3.5 in) in size.[1] Whale shark eggs typically hatch within the mother. At 1.5 kg (3.3 lb) and up to 17.8 cm × 14 cm (7.0 in × 5.5 in), the ostrich egg is the largest egg of any living bird,[2] though the extinct elephant bird and some non-avian dinosaurs laid larger eggs. The bee hummingbird produces the smallest known bird egg, which weighs half of a gram (around 0.02 oz). Some eggs laid by reptiles and most fish, amphibians, insects, and other invertebrates can be even smaller.
+Reproductive structures similar to the egg in other kingdoms are termed "spores," or in spermatophytes "seeds," or in gametophytes "egg cells".
+Several major groups of animals typically have readily distinguishable eggs.
+The most common reproductive strategy for fish is known as oviparity, in which the female lays undeveloped eggs that are externally fertilized by a male. Typically large numbers of eggs are laid at one time (an adult female cod can produce 4–6 million eggs in one spawning) and the eggs are then left to develop without parental care. When the larvae hatch from the egg, they often carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a few days as they learn how to swim. Once the yolk is consumed, there is a critical point after which they must learn how to hunt and feed or they will die.
+A few fish, notably the rays and most sharks use ovoviviparity in which the eggs are fertilized and develop internally. However, the larvae still grow inside the egg consuming the egg's yolk and without any direct nourishment from the mother. The mother then gives birth to relatively mature young. In certain instances, the physically most developed offspring will devour its smaller siblings for further nutrition while still within the mother's body. This is known as intrauterine cannibalism.
+In certain scenarios, some fish such as the hammerhead shark and reef shark are viviparous, with the egg being fertilized and developed internally, but with the mother also providing direct nourishment.
+The eggs of fish and amphibians are jellylike. Cartilaginous fish (sharks, skates, rays, chimaeras) eggs are fertilized internally and exhibit a wide variety of both internal and external embryonic development. Most fish species spawn eggs that are fertilized externally, typically with the male inseminating the eggs after the female lays them. These eggs do not have a shell and would dry out in the air. Even air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, Chiromantis xerampelina.
+Bird eggs are laid by females and incubated for a time that varies according to the species; a single young hatches from each egg. Average clutch sizes range from one (as in condors) to about 17 (the grey partridge). Some birds lay eggs even when not fertilized (e.g. hens); it is not uncommon for pet owners to find their lone bird nesting on a clutch of unfertilized eggs, which are sometimes called wind-eggs.
+The default color of vertebrate eggs is the white of the calcium carbonate from which the shells are made, but some birds, mainly passerines, produce colored eggs. The pigment biliverdin and its zinc chelate give a green or blue ground color, and protoporphyrin produces reds and browns as a ground color or as spotting.
+Non-passerines typically have white eggs, except in some ground-nesting groups such as the Charadriiformes, sandgrouse and nightjars, where camouflage is necessary, and some parasitic cuckoos which have to match the passerine host's egg. Most passerines, in contrast, lay colored eggs, even if there is no need of cryptic colors.
+However some have suggested that the protoporphyrin markings on passerine eggs actually act to reduce brittleness by acting as a solid-state lubricant.[10] If there is insufficient calcium available in the local soil, the egg shell may be thin, especially in a circle around the broad end. Protoporphyrin speckling compensates for this, and increases inversely to the amount of calcium in the soil.[11]
+For the same reason, later eggs in a clutch are more spotted than early ones as the female's store of calcium is depleted.
+The color of individual eggs is also genetically influenced, and appears to be inherited through the mother only, suggesting that the gene responsible for pigmentation is on the sex-determining W chromosome (female birds are WZ, males ZZ).
+It used to be thought that color was applied to the shell immediately before laying, but subsequent research shows that coloration is an integral part of the development of the shell, with the same protein responsible for depositing calcium carbonate, or protoporphyrins when there is a lack of that mineral.
+In species such as the common guillemot, which nest in large groups, each female's eggs have very different markings, making it easier for females to identify their own eggs on the crowded cliff ledges on which they breed.
+Bird eggshells are diverse. For example:
+Tiny pores in bird eggshells allow the embryo to breathe. The domestic hen's egg has around 7000 pores.[12]
+Some bird eggshells have a coating of vaterite spherules, which is a rare polymorph of calcium carbonate. In Greater Ani Crotophaga major this vaterite coating is thought to act as a shock absorber, protecting the calcite shell from fracture during incubation, such as colliding with other eggs in the nest.[13]
+Most bird eggs have an oval shape, with one end rounded and the other more pointed. This shape results from the egg being forced through the oviduct. Muscles contract the oviduct behind the egg, pushing it forward. The egg's wall is still shapeable, and the pointed end develops at the back. Long, pointy eggs are an incidental consequence of having a streamlined body typical of birds with strong flying abilities; flight narrows the oviduct, which changes the type of egg a bird can lay.[14] Cliff-nesting birds often have highly conical eggs. They are less likely to roll off, tending instead to roll around in a tight circle; this trait is likely to have arisen due to evolution via natural selection. In contrast, many hole-nesting birds have nearly spherical eggs.[15]
+Many animals feed on eggs. For example, principal predators of the black oystercatcher's eggs include raccoons, skunks, mink, river and sea otters, gulls, crows and foxes. The stoat (Mustela erminea) and long-tailed weasel (M. frenata) steal ducks' eggs. Snakes of the genera Dasypeltis and Elachistodon specialize in eating eggs.
+Brood parasitism occurs in birds when one species lays its eggs in the nest of another. In some cases, the host's eggs are removed or eaten by the female, or expelled by her chick. Brood parasites include the cowbirds and many Old World cuckoos.
+An average whooping crane egg is 102 mm (4.0 in) long and weighs 208 g (7.3 oz)
+Eurasian oystercatcher eggs camouflaged in the nest
+Egg of a senegal parrot, a bird that nests in tree holes, on a 1 cm (0.39 in) grid
+Eggs of ostrich, emu, kiwi and chicken
+Finch egg next to American dime
+Eggs of duck, goose, guineafowl and chicken
+Eggs of ostrich, cassowary, chicken, flamingo, pigeon and blackbird
+Egg of an emu
+Egg from a chicken compared to a 1 euro coin, great tit egg and a corn grain
+Bird nest with brown marbling eggs of a robin
+Like amphibians, amniotes are air-breathing vertebrates, but they have complex eggs or embryos, including an amniotic membrane. Amniotes include reptiles (including dinosaurs and their descendants, birds) and mammals.
+Reptile eggs are often rubbery and are always initially white. They are able to survive in the air. Often the sex of the developing embryo is determined by the temperature of the surroundings, with cooler temperatures favouring males. Not all reptiles lay eggs; some are viviparous ("live birth").
+Dinosaurs laid eggs, some of which have been preserved as petrified fossils.
+Among mammals, early extinct species laid eggs, as do platypuses and echidnas (spiny anteaters). Platypuses and two genera of echidna are Australian monotremes. Marsupial and placental mammals do not lay eggs, but their unborn young do have the complex tissues that identify amniotes.
+The eggs of the egg-laying mammals (the platypus and the echidnas) are macrolecithal eggs very much like those of reptiles. The eggs of marsupials are likewise macrolecithal, but rather small, and develop inside the body of the female, but do not form a placenta. The young are born at a very early stage, and can be classified as a "larva" in the biological sense.[16]
+In placental mammals, the egg itself is void of yolk, but develops an umbilical cord from structures that in reptiles would form the yolk sac. Receiving nutrients from the mother, the fetus completes the development while inside the uterus.
+Eggs are common among invertebrates, including insects, spiders, mollusks, and crustaceans.
+All sexually reproducing life, including both plants and animals, produces gametes. The male gamete cell, sperm, is usually motile whereas the female gamete cell, the ovum, is generally larger and sessile. The male and female gametes combine to produce the zygote cell. In multicellular organisms the zygote subsequently divides in an organised manner into smaller more specialised cells, so that this new individual develops into an embryo. In most animals the embryo is the sessile initial stage of the individual life cycle, and is followed by the emergence (that is, the hatching) of a motile stage. The zygote or the ovum itself or the sessile organic vessel containing the developing embryo may be called the egg.
+A recent proposal suggests that the phylotypic animal body plans originated in cell aggregates before the existence of an egg stage of development. Eggs, in this view, were later evolutionary innovations, selected for their role in ensuring genetic uniformity among the cells of incipient multicellular organisms.[17]
+Scientists often classify animal reproduction according to the degree of development that occurs before the new individuals are expelled from the adult body, and by the yolk which the egg provides to nourish the embryo.
+Vertebrate eggs can be classified by the relative amount of yolk. Simple eggs with little yolk are called microlecithal, medium-sized eggs with some yolk are called mesolecithal, and large eggs with a large concentrated yolk are called macrolecithal.[7] This classification of eggs is based on the eggs of chordates, though the basic principle extends to the whole animal kingdom.
+Small eggs with little yolk are called microlecithal. The yolk is evenly distributed, so the cleavage of the egg cell cuts through and divides the egg into cells of fairly similar sizes. In sponges and cnidarians the dividing eggs develop directly into a simple larva, rather like a morula with cilia. In cnidarians, this stage is called the planula, and either develops directly into the adult animals or forms new adult individuals through a process of budding.[18]
+Microlecithal eggs require minimal yolk mass. Such eggs are found in flatworms, roundworms, annelids, bivalves, echinoderms, the lancelet and in most marine arthropods.[19] In anatomically simple animals, such as cnidarians and flatworms, the fetal development can be quite short, and even microlecithal eggs can undergo direct development. These small eggs can be produced in large numbers. In animals with high egg mortality, microlecithal eggs are the norm, as in bivalves and marine arthropods. However, the latter are more complex anatomically than e.g. flatworms, and the small microlecithal eggs do not allow full development. Instead, the eggs hatch into larvae, which may be markedly different from the adult animal.
+In placental mammals, where the embryo is nourished by the mother throughout the whole fetal period, the egg is reduced in size to essentially a naked egg cell.
+Mesolecithal eggs have comparatively more yolk than the microlecithal eggs. The yolk is concentrated in one part of the egg (the vegetal pole), with the cell nucleus and most of the cytoplasm in the other (the animal pole). The cell cleavage is uneven, and mainly concentrated in the cytoplasma-rich animal pole.[3]
+The larger yolk content of the mesolecithal eggs allows for a longer fetal development. Comparatively anatomically simple animals will be able to go through the full development and leave the egg in a form reminiscent of the adult animal. This is the situation found in hagfish and some snails.[4][19] Animals with smaller size eggs or more advanced anatomy will still have a distinct larval stage, though the larva will be basically similar to the adult animal, as in lampreys, coelacanth and the salamanders.[3]
+Eggs with a large yolk are called macrolecithal. The eggs are usually few in number, and the embryos have enough food to go through full fetal development in most groups.[7] Macrolecithal eggs are only found in selected representatives of two groups: Cephalopods and vertebrates.[7][20]
+Macrolecithal eggs go through a different type of development than other eggs. Due to the large size of the yolk, the cell division can not split up the yolk mass. The fetus instead develops as a plate-like structure on top of the yolk mass, and only envelopes it at a later stage.[7] A portion of the yolk mass is still present as an external or semi-external yolk sac at hatching in many groups. This form of fetal development is common in bony fish, even though their eggs can be quite small. Despite their macrolecithal structure, the small size of the eggs does not allow for direct development, and the eggs hatch to a larval stage ("fry"). In terrestrial animals with macrolecithal eggs, the large volume to surface ratio necessitates structures to aid in transport of oxygen and carbon dioxide, and for storage of waste products so that the embryo does not suffocate or get poisoned from its own waste while inside the egg, see amniote.[9]
+In addition to bony fish and cephalopods, macrolecithal eggs are found in cartilaginous fish, reptiles, birds and monotreme mammals.[3] The eggs of the coelacanths can reach a size of 9 cm (3.5 in) in diameter, and the young go through full development while in the uterus, living on the copious yolk.[21]
+Animals are commonly classified by their manner of reproduction, at the most general level distinguishing egg-laying (Latin. oviparous) from live-bearing (Latin. viviparous).
+These classifications are divided into more detail according to the development that occurs before the offspring are expelled from the adult's body. Traditionally:[22]
+The term hemotropic derives from the Latin for blood-feeding, contrasted with histotrophic for tissue-feeding.[27]
+Eggs laid by many different species, including birds, reptiles, amphibians, and fish, have probably been eaten by mankind for millennia. Popular choices for egg consumption are chicken, duck, roe, and caviar, but by a wide margin the egg most often humanly consumed is the chicken egg, typically unfertilized.
+According to the Kashrut, that is the set of Jewish dietary laws, kosher food may be consumed according to halakha (Jewish law). Kosher meat and milk (or derivatives) cannot be mixed (Deuteronomy 14:21) or stored together. Eggs are considered pareve (neither meat nor dairy) despite being an animal product and can be mixed with either milk or kosher meat. Mayonnaise, for instance, is usually marked "pareve" despite by definition containing egg.[28]
+Many vaccines for infectious diseases are produced in fertile chicken eggs. The basis of this technology was the discovery in 1931 by Alice Miles Woodruff and Ernest William Goodpasture at Vanderbilt University that the rickettsia and viruses that cause a variety of diseases will grow in chicken embryos. This enabled the development of vaccines against influenza, chicken pox, smallpox, yellow fever, typhus, Rocky mountain spotted fever and other diseases.
+The egg is a symbol of new life and rebirth in many cultures around the world. Christians view Easter eggs as symbolic of the resurrection of Jesus Christ.[29] A popular Easter tradition in some parts of the world is the decoration of hard-boiled eggs (usually by dyeing, but often by hand-painting or spray-painting). Adults often hide the eggs for children to find, an activity known as an Easter egg hunt. A similar tradition of egg painting exists in areas of the world influenced by the culture of Persia. Before the spring equinox in the Persian New Year tradition (called Norouz), each family member decorates a hard-boiled egg and sets them together in a bowl. The tradition of a dancing egg is held during the feast of Corpus Christi in Barcelona and other Catalan cities since the 16th century. It consists of an emptied egg, positioned over the water jet from a fountain, which starts turning without falling.[30]
+Although a food item, raw eggs are sometimes thrown at houses, cars, or people. This act, known commonly as "egging" in the various English-speaking countries, is a minor form of vandalism and, therefore, usually a criminal offense and is capable of damaging property (egg whites can degrade certain types of vehicle paint) as well as potentially causing serious eye injury. On Halloween, for example, trick or treaters have been known to throw eggs (and sometimes flour) at property or people from whom they received nothing.[citation needed] Eggs are also often thrown in protests, as they are inexpensive and nonlethal, yet very messy when broken.[31]
+Egg collecting was a popular hobby in some cultures, including among the first Australians. Traditionally, the embryo would be removed before a collector stored the egg shell.[32]
+Collecting eggs of wild birds is now banned by many jurisdictions, as the practice can threaten rare species. In the United Kingdom, the practice is prohibited by the Protection of Birds Act 1954 and Wildlife and Countryside Act 1981.[33] On the other hand, ongoing underground trading is becoming a serious issue.[34]
+Since the protection of wild bird eggs was regulated, early collections have come to the museums as curiosities. For example, the Australian Museum hosts a collection of about 20,000 registered clutches of eggs,[35] and the collection in Western Australia Museum has been archived in a gallery.[36] Scientists regard egg collections as a good natural-history data, as the details recorded in the collectors' notes have helped them to understand birds' nesting behaviors.[37]
+Insect eggs, in this case those of the Emperor gum moth, are often laid on the underside of leaves.
+Fish eggs, such as these herring eggs are often transparent and fertilized after laying.
+Skates and some sharks have a uniquely shaped egg case called a mermaid's purse.
+A Testudo hermanni emerging fully developed from a reptilian egg.
+A Schistosoma mekongi egg.
+Eggs of Huffmanela hamo, a nematode parasite in a fish
+Eggs of various parasites (mainly nematodes) from wild primates

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+Easter eggs, also called Paschal eggs,[1] are eggs that are sometimes decorated. They are usually used as gifts on the occasion of Easter. As such, Easter eggs are common during the season of Eastertide (Easter season). The oldest tradition is to use dyed and painted chicken eggs, but a modern custom is to substitute chocolate eggs wrapped in colored foil, hand-carved wooden eggs, or plastic eggs filled with confectionery such as chocolate. However, real eggs continue to be used in Central and Eastern European tradition.
+Although eggs, in general, were a traditional symbol of fertility and rebirth,[2] in Christianity, for the celebration of Eastertide, Easter eggs symbolize the empty tomb of Jesus, from which Jesus resurrected.[3][4][5] In addition, one ancient tradition was the staining of Easter eggs with the colour red "in memory of the blood of Christ, shed as at that time of his crucifixion."[3][6]
+This custom of the Easter egg, according to many sources, can be traced to early Christians of Mesopotamia, and from there it spread into Eastern Europe and Siberia through the Orthodox Churches, and later into Europe through the Catholic and Protestant Churches.[6][7][8][9] Other sources maintain  that the custom arose in western Europe during the Middle Ages as a result of the fact that Western Christians were prohibited from eating eggs during Lent, but were allowed to eat them when Easter arrived.[10][11]
+The practice of decorating eggshells is quite ancient,[12] with decorated, engraved ostrich eggs found in Africa which are 60,000 years old.[13] In the pre-dynastic period of Egypt and the early cultures of Mesopotamia and Crete, eggs were associated with death and rebirth, as well as with kingship, with decorated ostrich eggs, and representations of ostrich eggs in gold and silver, were commonly placed in graves of the ancient Sumerians and Egyptians as early as 5,000 years ago.[14] These cultural relationships may have influenced early Christian and Islamic cultures in those areas, as well as through mercantile, religious, and political links from those areas around the Mediterranean.[15]
+According to many sources, the Christian custom of Easter eggs, specifically, started among the early Christians of Mesopotamia, who stained eggs with red coloring "in memory of the blood of Christ, shed at His crucifixion".[7][16][6][8][9]  The Christian Church officially adopted the custom, regarding the eggs as a symbol of the resurrection of Jesus, with the Roman Ritual, the first edition of which was published in 1610 but which has texts of much older date, containing among the Easter Blessings of Food, one for eggs, along with those for lamb, bread, and new produce.[8][9]
+Lord, let the grace of your blessing + come upon these eggs, that they be healthful food for your faithful who eat them in thanksgiving for the resurrection of our Lord Jesus Christ, who lives and reigns with you forever and ever.[17]
+Sociology professor Kenneth Thompson discusses the spread of the Easter egg throughout Christendom, writing that "use of eggs at Easter seems to have come from Persia into the Greek Christian Churches of Mesopotamia, thence to Russia and Siberia through the medium of Orthodox Christianity. From the Greek Church the custom was adopted by either the Roman Catholics or the Protestants and then spread through Europe."[7] Both Thompson, as well as British orientalist Thomas Hyde state that in addition to dyeing the eggs red, the early Christians of Mesopotamia also stained Easter eggs green and yellow.[6][7]
+Peter Gainsford maintains that the association between eggs and Easter most likely arose in western Europe during the Middle Ages as a result of the fact that Catholic Christians were prohibited from eating eggs during Lent, but were allowed to eat them when Easter arrived.[10][11]
+Influential 19th century folklorist and philologist Jacob Grimm speculates, in the second volume of his Deutsche Mythologie, that the folk custom of Easter eggs among the continental Germanic peoples may have stemmed from springtime festivities of a Germanic goddess known in Old English as Ēostre (namesake of modern English Easter) and possibly known in Old High German as *Ostara (and thus namesake of Modern German Ostern 'Easter'). However, despite Grimm's speculation, there is no evidence to connect eggs with Ostara.[11] The use of eggs as favors or treats at Easter originated when they were prohibited during Lent.[10][11] A common practice in England in the medieval period was for children to go door-to-door begging for eggs on the Saturday before Lent began. People handed out eggs as special treats for children prior to their fast.[11]
+Although one of the Christian traditions are to use dyed or painted chicken eggs, a modern custom is to substitute chocolate eggs, or plastic eggs filled with candy such as jelly beans; as many people give up sweets as their Lenten sacrifice, individuals enjoy them at Easter after having abstained from them during the preceding forty days of Lent.[18] These eggs can be hidden for children to find on Easter morning, which may be left by the Easter Bunny. They may also be put in a basket filled with real or artificial straw to resemble a bird's nest.
+The Easter egg tradition may also have merged into the celebration of the end of the privations of Lent in the West.
+Historically, it was traditional to use up all of the household's eggs before Lent began.
+Eggs were originally forbidden during Lent as well as on other traditional fast days in Western Christianity (this tradition still continues among the Eastern Christian Churches). Likewise, in Eastern Christianity, meat, eggs, and dairy are all prohibited during the Lenten fast.
+This established the tradition of Pancake Day being celebrated on Shrove Tuesday. This day, the Tuesday before Ash Wednesday when Lent begins, is also known as Mardi Gras, a French phrase which translates as "Fat Tuesday" to mark the last consumption of eggs and dairy before Lent begins.
+In the Orthodox Church, Great Lent begins on Clean Monday, rather than Wednesday, so the household's dairy products would be used up in the preceding week, called Cheesefare Week.
+During Lent, since chickens would not stop producing eggs during this time, a larger than usual store might be available at the end of the fast. This surplus, if any, had to be eaten quickly to prevent spoiling. Then, with the coming of Easter, the eating of eggs resumes.  Some families cook a special meatloaf with eggs in it to be eaten with the Easter dinner.
+One would have been forced to hard boil the eggs that the chickens produced so as not to waste food, and for this reason the Spanish dish hornazo (traditionally eaten on and around Easter) contains hard-boiled eggs as a primary ingredient.
+In Hungary, eggs are used sliced in potato casseroles around the Easter period.
+Some Christians symbolically link the cracking open of Easter eggs with the empty tomb of Jesus.[19]
+In the Orthodox churches, Easter eggs are blessed by the priest at the end of the Paschal Vigil (which is equivalent to Holy Saturday), and distributed to the faithful. The egg is seen by followers of Christianity as a symbol of resurrection: while being dormant it contains a new life sealed within it.[3][4]
+Similarly, in the Roman Catholic Church in Poland, the so-called święconka, i.e. blessing of decorative baskets with a sampling of Easter eggs and other symbolic foods, is one of the most enduring and beloved Polish traditions on Holy Saturday.
+During Paschaltide, in some traditions the Pascal greeting with the Easter egg is even extended to the deceased. On either the second Monday or Tuesday of Pascha, after a memorial service people bring blessed eggs to the cemetery and bring the joyous paschal greeting, "Christ has risen", to their beloved departed (see Radonitza).
+In Greece, women traditionally dye the eggs with onion skins and vinegar on Thursday (also the day of Communion). These ceremonial eggs are known as kokkina avga. They also bake tsoureki for the Easter Sunday feast.[20] Red Easter eggs are sometimes served along the centerline of tsoureki (braided loaf of bread).[21][22]
+In Egypt, it is a tradition to decorate boiled eggs during Sham el-Nessim holiday, which falls every year after the Eastern Christian Easter.
+Coincidentally, every Passover, Jews place a hard-boiled egg on the Passover ceremonial plate, and the celebrants also eat hard-boiled eggs dipped in salt water as part of the ceremony.
+The dyeing of Easter eggs in different colours is commonplace, with colour being achieved through boiling the egg in natural substances (such as, onion peel (brown colour), oak or alder bark or walnut nutshell (black), beet juice (pink) etc.), or using artificial colourings.
+A greater variety of colour was often provided by tying on the onion skin with different coloured woollen yarn. In the North of England these are called pace-eggs or paste-eggs, from a dialectal form of Middle English pasche. They were usually eaten after an egg-jarping (egg tapping) competition.
+In the Orthodox and Eastern Catholic Churches, Easter eggs are dyed red to represent the blood of Christ, with further symbolism being found in the hard shell of the egg symbolizing the sealed Tomb of Christ — the cracking of which symbolized his resurrection from the dead. The tradition of red easter eggs was used by the Russian Orthodox Church.[23] The tradition to dying the easter eggs in an Onion tone exists in the cultures of Armenia, Georgia, Belarus, Russia, Czechia, Romania, and Israel.[24] The colour is made by boiling onion peel in water.[25][26]
+When boiling them with onion skins leaves can be attached prior to dying to create leaf patterns. The leaves are attached to the eggs before they are dyed with a transparent cloth to wrap the eggs with like inexpensive muslin or nylon stockings, leaving patterns once the leaves are removed after the dyeing process.[27][28] These eggs are part of Easter custom in many areas and often accompany other traditional Easter foods. Passover haminados are prepared with similar methods.
+Pysanky[29] are Ukrainian Easter eggs, decorated using a wax-resist (batik) method. The word comes from the verb pysaty, "to write", as the designs are not painted on, but written with beeswax.
+Decorating eggs for Easter using wax resistant batik is a popular method in some other eastern European countries.
+In some Mediterranean countries, especially in Lebanon, chicken eggs are boiled and decorated by dye and/or painting and used as decoration around the house. Then, on Easter Day, young kids would duel with them saying 'Christ is resurrected, Indeed, He is', breaking and eating them. This also happens in Georgia, Bulgaria, Cyprus, Greece, Macedonia, Romania, Russia, Serbia and Ukraine. In Easter Sunday friends and family hit each other's egg with their own. The one whose egg does not break is believed to be in for good luck in the future.
+In Germany, eggs decorate trees and bushes as Easter egg trees, and in several areas public wells as Osterbrunnen.
+There used to be a custom in Ukraine, during Easter celebrations to have krashanky on a table in a bowl with wheatgrass. The number of the krashanky equalled the number of departed family members.[30]
+Ukrainian Easter eggs
+Easter eggs from Sorbs
+Easter eggs from Lithuania
+Perforated egg from Germany, Sleeping Beauty
+Norwegian Easter eggs
+Easter eggs from Greece
+Perforated eggs
+Easter eggs from France
+American Easter egg from the White House Washington, D.C.
+Pace eggs boiled with onion skins and leaf patterns.
+Easter eggs decorated with straw
+Easter egg from Poland
+An egg hunt is a game in which decorated eggs, which may be hard-boiled chicken eggs, chocolate eggs, or artificial eggs containing candies, are hidden for children to find. The eggs often vary in size, and may be hidden both indoors and outdoors.[31] When the hunt is over, prizes may be given for the largest number of eggs collected, or for the largest or the smallest egg.[31]
+The central European Slavic nations (Czechs and Slovaks etc.) have a tradition of gathering eggs by gaining them from the females in return of whipping them with a pony-tail shaped whip made out of fresh willow branches and splashing them with water, by the Ruthenians called polivanja, which is supposed to give them health and beauty.
+Cascarones, a Latin American tradition now shared by many US States with high Hispanic demographics, are emptied and dried chicken eggs stuffed with confetti and sealed with a piece of tissue paper. The eggs are hidden in a similar tradition to the American Easter egg hunt and when found the children (and adults) break them over each other's heads.
+In order to enable children to take part in egg hunts despite visual impairment, eggs have been created that emit various clicks, beeps, noises, or music so that visually impaired children can easily hunt for Easter eggs.[32]
+Egg rolling is also a traditional Easter egg game played with eggs at Easter. In the United Kingdom, Germany, and other countries children traditionally rolled eggs down hillsides at Easter.[33] This tradition was taken to the New World by European settlers,[33][34] and continues to this day each Easter with an Easter egg roll on the White House lawn. Different nations have different versions of the game.
+In the North of England, during Eastertide, a traditional game is played where hard boiled pace eggs are distributed and each player hits the other player's egg with their own. This is known as "egg tapping", "egg dumping", or "egg jarping". The winner is the holder of the last intact egg. The annual egg jarping world championship is held every year over Easter in Peterlee, Durham.[35]
+It is also practiced in Italy (where it is called scuccetta), Bulgaria, Hungary, Croatia, Latvia, Lithuania, Lebanon, Macedonia, Romania, Serbia, Slovenia (where it is called turčanje or trkanje), Ukraine, Russia, and other countries. In parts of Austria, Bavaria and German-speaking Switzerland it is called Ostereiertitschen or Eierpecken. In parts of Europe it is also called epper, presumably from the German name Opfer, meaning "offering" and in Greece it is known as tsougrisma. In South Louisiana, this practice is called pocking eggs[36][37] and is slightly different. The Louisiana Creoles hold that the winner eats the eggs of the losers in each round.
+In the Greek Orthodox tradition, red eggs are also cracked together when people exchange Easter greetings.
+Egg dance is a traditional Easter game in which eggs are laid on the ground or floor and the goal is to dance among them without damaging any eggs[38] which originated in Germany. In the UK the dance is called the hop-egg.
+The Pace Egg plays are traditional village plays, with a rebirth theme. The drama takes the form of a combat between the hero and villain, in which the hero is killed and brought back to life. The plays take place in England during Easter.
+Chocolate eggs first appeared at the court of Louis XIV in Versailles and in 1725 the widow Giambone in Turin started producing chocolate eggs by filling empty chicken egg shells with molten chocolate. [39]In 1873 J.S. Fry & Sons of England introduced the first chocolate Easter egg in Britain. Manufacturing their first Easter egg in 1875, Cadbury created the modern chocolate Easter egg after developing a pure cocoa butter that could be moulded into smooth shapes.[40]
+In Western cultures, the giving of chocolate eggs is now commonplace, with 80 million Easter eggs sold in the UK alone. Formerly, the containers Easter eggs were sold in contained large amounts of plastic, although in the United Kingdom this has gradually been replaced with recyclable paper and cardboard.[41]
+Chocolate Easter egg
+Chocolate Easter egg bunny
+Easter egg with candy.
+Gladys as a Chocolate Easter Bunny with Easter eggs
+Kinder Surprise Egg, manufactured by Italian company Ferrero SpA
+In the Indian state of Goa, the Goan Catholic version of marzipan is used to make easter eggs. In the Philippines, mazapán de pili (Spanish for "pili marzipan") is made from pili nuts.
+Marzipan easter eggs
+The jewelled Easter eggs made by the Fabergé firm for the two last Russian Tsars are regarded as masterpieces of decorative arts. Most of these creations themselves contained hidden surprises such as clock-work birds, or miniature ships.
+In Bulgaria, Poland, Romania, Russia, Ukraine, and other Central European countries' folk traditions, and making artificial eggs out of porcelain for ladies is common.[42]:45
+Easter eggs are frequently depicted in sculpture, including a 8-metre (27 ft) sculpture of a pysanka standing in Vegreville, Alberta.
+Fabergé egg
+Giant easter egg, Bariloche, Argentina
+Giant pysanka from Vegreville, Alberta, Canada
+Giant easter egg or pisanica in Zagreb, Croatia
+Easter egg sculpture in Gogolin, Poland
+Giant easter egg in Suceava, Romania
+While the origin of Easter eggs can be explained in the symbolic terms described above, among followers of Eastern Christianity the legend says that Mary Magdalene was bringing cooked eggs to share with the other women at the tomb of Jesus, and the eggs in her basket miraculously turned bright red when she saw the risen Christ.[43]
+A different, but not necessarily conflicting legend concerns Mary Magdalene's efforts to spread the Gospel. According to this tradition, after the Ascension of Jesus, Mary went to the Emperor of Rome and greeted him with "Christ has risen," whereupon he pointed to an egg on his table and stated, "Christ has no more risen than that egg is red." After making this statement it is said the egg immediately turned blood red.[44]
+Red Easter eggs, known as kokkina avga (κόκκινα αυγά) in Greece and krashanki in Ukraine, are an Easter tradition and a distinct type of Easter egg prepared by various Orthodox Christian peoples.[45][46][47][48] The red eggs are part of Easter custom in many areas and often accompany other traditional Easter foods. Passover haminados are prepared with similar methods.
+Dark red eggs are a tradition in Greece and represent the blood of Christ shed on the cross.[49] The practice dates to the early Christian church in Mesopotamia.[8][9]
+In Greece, superstitions of the past included the custom of placing the first-dyed red egg at the home's iconostasis (place where icons are displayed) to ward off evil. The heads and backs of small lambs were also marked with the red dye to protect them.
+The egg is widely used as a symbol of the start of new life, just as new life emerges from an egg when the chick hatches out.[2]
+Painted eggs are used at the Iranian spring holidays, the Nowruz that marks the first day of spring or Equinox, and the beginning of the year in the Persian calendar. It is celebrated on the day of the astronomical Northward equinox, which usually occurs on March 21 or the previous/following day depending on where it is observed. The painted eggs symbolize fertility and are displayed on the Nowruz table, called Haft-Seen together with various other symbolic objects. There are sometimes one egg for each member of the family. The ancient Zoroastrians painted eggs for Nowruz, their New Year celebration, which falls on the Spring equinox. The tradition continues among Persians of Islamic, Zoroastrian, and other faiths today.[50] The Nowruz tradition has existed for at least 2,500 years. The sculptures on the walls of Persepolis show people carrying eggs for Nowruz to the king.[citation needed]
+The Neopagan holiday of Ostara occurs at roughly the same time as Easter. While it is often claimed that the use of painted eggs is an ancient, pre-Christian component of the celebration of Ostara, there are no historical accounts that ancient celebrations included this practice, apart from the Old High German lullaby which is believed by most to be a modern fabrication. Rather, the use of painted eggs has been adopted under the assumption that it might be a pre-Christian survival. In fact, modern scholarship has been unable to trace any association between eggs and a supposed goddess named Ostara before the 19th century, when early folklorists began to speculate about the possibility.[51]
+There are good grounds for the association between hares (later termed Easter bunnies) and bird eggs, through folklore confusion between hares' forms (where they raise their young) and plovers' nests.[52]
+In Judaism, a hard-boiled egg is an element of the Passover Seder, representing festival sacrifice. The children's game of hunting for the afikomen (a half-piece of matzo) has similarities to the Easter egg hunt tradition, by which the child who finds the hidden bread will be awarded a prize. In other homes, the children hide the afikoman and a parent must look for it; when the parents give up, the children demand a prize for revealing its location.
+Media related to Easter eggs at Wikimedia Commons

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+Atheism is, in the broadest sense, an absence of belief in the existence of deities.[1][2][3][4] Less broadly, atheism is a rejection of the belief that any deities exist.[5][6] In an even narrower sense, atheism is specifically the position that there are no deities.[1][2][7][8] Atheism is contrasted with theism,[9][10] which, in its most general form, is the belief that at least one deity exists.[10][11][12]
+The etymological root for the word atheism originated before the 5th century BCE from the ancient Greek ἄθεος (atheos), meaning "without god(s)". In antiquity, it had multiple uses as a pejorative term applied to those thought to reject the gods worshiped by the larger society,[13] those who were forsaken by the gods, or those who had no commitment to belief in the gods.[14] The term denoted a social category created by orthodox religionists into which those who did not share their religious beliefs were placed.[14] The actual term atheism emerged first in the 16th century.[15] With the spread of freethought, skeptical inquiry, and subsequent increase in criticism of religion, application of the term narrowed in scope. The first individuals to identify themselves using the word atheist lived in the 18th century during the Age of Enlightenment.[16][15] The French Revolution, noted for its "unprecedented atheism," witnessed the first major political movement in history to advocate for the supremacy of human reason.[17]
+Arguments for atheism range from philosophical to social and historical approaches. Rationales for not believing in deities include arguments that there is a lack of empirical evidence,[18][19] the problem of evil, the argument from inconsistent revelations, the rejection of concepts that cannot be falsified, and the argument from nonbelief.[18][20] Nonbelievers contend that atheism is a more parsimonious position than theism and that everyone is born without beliefs in deities;[1] therefore, they argue that the burden of proof lies not on the atheist to disprove the existence of gods but on the theist to provide a rationale for theism.[21] Although some atheists have adopted secular philosophies (e.g. secular humanism),[22][23] there is no ideology or code of conduct to which all atheists adhere.[24]
+Since conceptions of atheism vary, accurate estimations of current numbers of atheists are difficult.[25] According to global Win-Gallup International studies, 13% of respondents were "convinced atheists" in 2012,[26] 11% were "convinced atheists" in 2015,[27] and in 2017, 9% were "convinced atheists".[28] However, other researchers have advised caution with WIN/Gallup figures since other surveys which have used the same wording for decades and have a bigger sample size have consistently reached lower figures.[29] An older survey by the British Broadcasting Corporation (BBC) in 2004 recorded atheists as comprising 8% of the world's population.[30] Other older estimates have indicated that atheists comprise 2% of the world's population, while the irreligious add a further 12%.[31] According to these polls, Europe and East Asia are the regions with the highest rates of atheism. In 2015, 61% of people in China reported that they were atheists.[32] The figures for a 2010 Eurobarometer survey in the European Union (EU) reported that 20% of the EU population claimed not to believe in "any sort of spirit, God or life force", with France (40%) and Sweden (34%) representing the highest values.[33]
+Writers disagree on how best to define and classify atheism,[34] contesting what supernatural entities are considered gods, whether it is a philosophic position in its own right or merely the absence of one, and whether it requires a conscious, explicit rejection. Atheism has been regarded as compatible with agnosticism,[35][36][37][38][39][40][41] but has also been contrasted with it.[42][43][44] A variety of categories have been used to distinguish the different forms of atheism.
+Some of the ambiguity and controversy involved in defining atheism arises from difficulty in reaching a consensus for the definitions of words like deity and god. The variety of wildly different conceptions of God and deities leads to differing ideas regarding atheism's applicability. The ancient Romans accused Christians of being atheists for not worshiping the pagan deities. Gradually, this view fell into disfavor as theism came to be understood as encompassing belief in any divinity.[45]
+With respect to the range of phenomena being rejected, atheism may counter anything from the existence of a deity, to the existence of any spiritual, supernatural, or transcendental concepts, such as those of Buddhism, Hinduism, Jainism, and Taoism.[46]
+Definitions of atheism also vary in the degree of consideration a person must put to the idea of gods to be considered an atheist. Atheism has sometimes been defined to include the simple absence of belief that any deities exist. This broad definition would include newborns and other people who have not been exposed to theistic ideas. As far back as 1772, Baron d'Holbach said that "All children are born Atheists; they have no idea of God."[47]
+Similarly, George H. Smith (1979) suggested that: "The man who is unacquainted with theism is an atheist because he does not believe in a god. This category would also include the child with the conceptual capacity to grasp the issues involved, but who is still unaware of those issues. The fact that this child does not believe in god qualifies him as an atheist."[48] Implicit atheism is "the absence of theistic belief without a conscious rejection of it" and explicit atheism is the conscious rejection of belief.
+For the purposes of his paper on "philosophical atheism", Ernest Nagel contested including the mere absence of theistic belief as a type of atheism.[49] Graham Oppy classifies as innocents those who never considered the question because they lack any understanding of what a god is. According to Oppy, these could be one-month-old babies, humans with severe traumatic brain injuries, or patients with advanced dementia.[50]
+Philosophers such as Antony Flew[51]
+and Michael Martin[45] have contrasted positive (strong/hard) atheism with negative (weak/soft) atheism. Positive atheism is the explicit affirmation that gods do not exist. Negative atheism includes all other forms of non-theism. According to this categorization, anyone who is not a theist is either a negative or a positive atheist.
+The terms weak and strong are relatively recent, while the terms negative and positive atheism are of older origin, having been used (in slightly different ways) in the philosophical literature[51] and in Catholic apologetics.[52]
+Under this demarcation of atheism, most agnostics qualify as negative atheists.
+While Martin, for example, asserts that agnosticism entails negative atheism,[38] many agnostics see their view as distinct from atheism,[53][54]
+which they may consider no more justified than theism or requiring an equal conviction.[53]
+The assertion of unattainability of knowledge for or against the existence of gods is sometimes seen as an indication that atheism requires a leap of faith.[55][56]
+Common atheist responses to this argument include that unproven religious propositions deserve as much disbelief as all other unproven propositions,[57]
+and that the unprovability of a god's existence does not imply equal probability of either possibility.[58]
+Australian philosopher J.J.C. Smart even argues that "sometimes a person who is really an atheist may describe herself, even passionately, as an agnostic because of unreasonable generalized philosophical skepticism which would preclude us from saying that we know anything whatever, except perhaps the truths of mathematics and formal logic."[59]
+Consequently, some atheist authors such as Richard Dawkins prefer distinguishing theist, agnostic and atheist positions along a spectrum of theistic probability—the likelihood that each assigns to the statement "God exists".[60]
+Before the 18th century, the existence of God was so accepted in the Western world that even the possibility of true atheism was questioned. This is called theistic innatism—the notion that all people believe in God from birth; within this view was the connotation that atheists are simply in denial.[61]
+There is also a position claiming that atheists are quick to believe in God in times of crisis, that atheists make deathbed conversions, or that "there are no atheists in foxholes".[62]
+There have, however, been examples to the contrary, among them examples of literal "atheists in foxholes".[63]
+Some atheists have challenged the need for the term "atheism". In his book Letter to a Christian Nation, Sam Harris wrote:
+In fact, "atheism" is a term that should not even exist. No one ever needs to identify himself as a "non-astrologer" or a "non-alchemist". We do not have words for people who doubt that Elvis is still alive or that aliens have traversed the galaxy only to molest ranchers and their cattle. Atheism is nothing more than the noises reasonable people make in the presence of unjustified religious beliefs.[64]
+Pragmatic atheism is the view one should reject a belief in a god or gods because it is unnecessary for a pragmatic life. This view is related to apatheism and practical atheism.[65]
+Atheists have also argued that people cannot know a God or prove the existence of a God. The latter is called agnosticism, which takes a variety of forms. In the philosophy of immanence, divinity is inseparable from the world itself, including a person's mind, and each person's consciousness is locked in the subject. According to this form of agnosticism, this limitation in perspective prevents any objective inference from belief in a god to assertions of its existence. The rationalistic agnosticism of Kant and the Enlightenment only accepts knowledge deduced with human rationality; this form of atheism holds that gods are not discernible as a matter of principle, and therefore cannot be known to exist. Skepticism, based on the ideas of Hume, asserts that certainty about anything is impossible, so one can never know for sure whether or not a god exists. Hume, however, held that such unobservable metaphysical concepts should be rejected as "sophistry and illusion".[67] The allocation of agnosticism to atheism is disputed; it can also be regarded as an independent, basic worldview.[68]
+Other arguments for atheism that can be classified as epistemological or ontological, including  ignosticism, assert the meaninglessness or unintelligibility of basic terms such as "God" and statements such as "God is all-powerful." Theological noncognitivism holds that the statement "God exists" does not express a proposition, but is nonsensical or cognitively meaningless. It has been argued both ways as to whether such individuals can be classified into some form of atheism or agnosticism. Philosophers A.J. Ayer and Theodore M. Drange reject both categories, stating that both camps accept "God exists" as a proposition; they instead place noncognitivism in its own category.[69][70]
+Philosopher, Zofia Zdybicka writes:
+"Metaphysical atheism ... includes all doctrines that hold to metaphysical monism (the homogeneity of reality). Metaphysical atheism may be either: a) absolute — an explicit denial of God's existence associated with materialistic monism (all materialistic trends, both in ancient and modern times); b) relative — the implicit denial of God in all philosophies that, while they accept the existence of an absolute, conceive of the absolute as not possessing any of the attributes proper to God: transcendence, a personal character or unity. Relative atheism is associated with idealistic monism (pantheism, panentheism, deism)."[71]
+Some atheists hold the view that the various conceptions of gods, such as the personal god of Christianity, are ascribed logically inconsistent qualities. Such atheists present deductive arguments against the existence of God, which assert the incompatibility between certain traits, such as perfection, creator-status, immutability, omniscience, omnipresence, omnipotence, omnibenevolence, transcendence, personhood (a personal being), non-physicality, justice, and mercy.[18]
+Theodicean atheists believe that the world as they experience it cannot be reconciled with the qualities commonly ascribed to God and gods by theologians. They argue that an omniscient, omnipotent, and omnibenevolent God is not compatible with a world where there is evil and suffering, and where divine love is hidden from many people.[20]
+A similar argument is attributed to Siddhartha Gautama, the founder of Buddhism.[73]
+Philosopher Ludwig Feuerbach[74]
+and psychoanalyst Sigmund Freud have argued that God and other religious beliefs are human inventions, created to fulfill various psychological and emotional wants or needs, or a projection mechanism from the 'Id' omnipotence; for Vladimir Lenin, in 'Materialism and Empirio-criticism', against the Russian Machism, the followers of Ernst Mach, Feuerbach was the final argument against belief in a god. This is also a view of many Buddhists.[75] Karl Marx and Friedrich Engels, influenced by the work of Feuerbach, argued that belief in God and religion are social functions, used by those in power to oppress the working class. According to Mikhail Bakunin, "the idea of God implies the abdication of human reason and justice; it is the most decisive negation of human liberty, and necessarily ends in the enslavement of mankind, in theory, and practice." He reversed Voltaire's aphorism that if God did not exist, it would be necessary to invent him, writing instead that "if God really existed, it would be necessary to abolish him."[76]
+Atheism is not mutually exclusive with respect to some religious and spiritual belief systems, including Hinduism, Jainism, Buddhism, Syntheism, Raëlism,[77] and Neopagan movements[78]
+such as Wicca.[79]
+Āstika schools in Hinduism hold atheism to be a valid path to moksha, but extremely difficult, for the atheist cannot expect any help from the divine on their journey.[80]
+Jainism believes the universe is eternal and has no need for a creator deity, however Tirthankaras are revered beings who can transcend space and time[81] and have more power than the god Indra.[82]
+Secular Buddhism does not advocate belief in gods. Early Buddhism was atheistic as Gautama Buddha's path involved no mention of gods. Later conceptions of Buddhism consider Buddha himself a god, suggest adherents can attain godhood, and revere Bodhisattvas[83]
+and Eternal Buddha.
+Apophatic theology is often assessed as being a version of atheism or agnosticism, since it cannot say truly that God exists.[84] "The comparison is crude, however, for conventional atheism treats the existence of God as a predicate that can be denied ("God is nonexistent"), whereas negative theology denies that God has predicates".[85] "God or the Divine is" without being able to attribute qualities about "what He is" would be the prerequisite of positive theology in negative theology that distinguishes theism from atheism. "Negative theology is a complement to, not the enemy of, positive theology".[86]
+Axiological, or constructive, atheism rejects the existence of gods in favor of a "higher absolute", such as humanity. This form of atheism favors humanity as the absolute source of ethics and values, and permits individuals to resolve moral problems without resorting to God. Marx and Freud used this argument to convey messages of liberation, full-development, and unfettered happiness.[68] One of the most common criticisms of atheism has been to the contrary: that denying the existence of a god either leads to moral relativism and leaves one with no moral or ethical foundation,[87] or renders life meaningless and miserable.[88] Blaise Pascal argued this view in his Pensées.[89]
+French philosopher Jean-Paul Sartre identified himself as a representative of an "atheist existentialism"[90]
+concerned less with denying the existence of God than with establishing that "man needs ... to find himself again and to understand that nothing can save him from himself, not even a valid proof of the existence of God."[91]
+Sartre said a corollary of his atheism was that "if God does not exist, there is at least one being in whom existence precedes essence, a being who exists before he can be defined by any concept, and ... this being is man."[90]
+The practical consequence of this atheism was described by Sartre as meaning that there are no a priori rules or absolute values that can be invoked to govern human conduct, and that humans are "condemned" to invent these for themselves, making "man" absolutely "responsible for everything he does".[92]
+Sociologist Phil Zuckerman analyzed previous social science research on secularity and non-belief, and concluded that societal well-being is positively correlated with irreligion. He found that there are much lower concentrations of atheism and secularity in poorer, less developed nations (particularly in Africa and South America) than in the richer industrialized democracies.[93][94]
+His findings relating specifically to atheism in the US were that compared to religious people in the US, "atheists and secular people" are less nationalistic, prejudiced, antisemitic, racist, dogmatic, ethnocentric, closed-minded, and authoritarian, and in US states with the highest percentages of atheists, the murder rate is lower than average. In the most religious states, the murder rate is higher than average.[95][96]
+People who self-identify as atheists are often assumed to be irreligious, but some sects within major religions reject the existence of a personal, creator deity.[98]
+In recent years, certain religious denominations have accumulated a number of openly atheistic followers, such as atheistic or humanistic Judaism[99][100]
+and Christian atheists.[101][102][103]
+The strictest sense of positive atheism does not entail any specific beliefs outside of disbelief in any deity; as such, atheists can hold any number of spiritual beliefs. For the same reason, atheists can hold a wide variety of ethical beliefs, ranging from the moral universalism of humanism, which holds that a moral code should be applied consistently to all humans, to moral nihilism, which holds that morality is meaningless.[104] Atheism is accepted as a valid philosophical position within some varieties of Hinduism, Jainism, and Buddhism.[105]
+Philosophers such as Slavoj Žižek,[106] Alain de Botton,[107] and Alexander Bard and Jan Söderqvist,[108] have all argued that atheists should reclaim religion as an act of defiance against theism, precisely not to leave religion as an unwarranted monopoly to theists.
+According to Plato's Euthyphro dilemma, the role of the gods in determining right from wrong is either unnecessary or arbitrary. The argument that morality must be derived from God, and cannot exist without a wise creator, has been a persistent feature of political if not so much philosophical debate.[109][110][111]
+Moral precepts such as "murder is wrong" are seen as divine laws, requiring a divine lawmaker and judge. However, many atheists argue that treating morality legalistically involves a false analogy, and that morality does not depend on a lawmaker in the same way that laws do.[112]
+Friedrich Nietzsche believed in a morality independent of theistic belief, and stated that morality based upon God "has truth only if God is truth—it stands or falls with faith in God.".[113][114][115] For Immanuel Kant the reason for adjusting to rules comes in its value as: 'Categorical Imperatives', that contain in itself the reason to be fulfilled.
+There exist normative ethical systems that do not require principles and rules to be given by a deity. Some include virtue ethics, social contract, Kantian ethics, utilitarianism, and Objectivism. Sam Harris has proposed that moral prescription (ethical rule making) is not just an issue to be explored by philosophy, but that we can meaningfully practice a science of morality. Any such scientific system must, nevertheless, respond to the criticism embodied in the naturalistic fallacy.[116]
+Philosophers Susan Neiman[117]
+and Julian Baggini[118]
+(among others) assert that behaving ethically only because of divine mandate is not true ethical behavior but merely blind obedience. Baggini argues that atheism is a superior basis for ethics, claiming that a moral basis external to religious imperatives is necessary to evaluate the morality of the imperatives themselves—to be able to discern, for example, that "thou shalt steal" is immoral even if one's religion instructs it—and that atheists, therefore, have the advantage of being more inclined to make such evaluations.[119]
+The contemporary British political philosopher Martin Cohen has offered the more historically telling example of Biblical injunctions in favor of torture and slavery as evidence of how religious injunctions follow political and social customs, rather than vice versa, but also noted that the same tendency seems to be true of supposedly dispassionate and objective philosophers.[120] Cohen extends this argument in more detail in Political Philosophy from Plato to Mao, where he argues that the Qur'an played a role in perpetuating social codes from the early 7th century despite changes in secular society.[121]
+Some prominent atheists—most recently Christopher Hitchens, Daniel Dennett, Sam Harris, and Richard Dawkins, and following such thinkers as Bertrand Russell, Robert G. Ingersoll, Voltaire, and novelist José Saramago—have criticized religions, citing harmful aspects of religious practices and doctrines.[122]
+The 19th-century German political theorist and sociologist Karl Marx called religion "the sigh of the oppressed creature, the heart of a heartless world, and the soul of soulless conditions. It is the opium of the people". He goes on to say, "The abolition of religion as the illusory happiness of the people is the demand for their real happiness. To call on them to give up their illusions about their condition is to call on them to give up a condition that requires illusions. The criticism of religion is, therefore, in embryo, the criticism of that vale of tears of which religion is the halo."[123] Lenin said that "every religious idea and every idea of God is unutterable vileness ... of the most dangerous kind, 'contagion' of the most abominable kind. Millions of sins, filthy deeds, acts of violence and physical contagions ... are far less dangerous than the subtle, spiritual idea of God decked out in the smartest ideological costumes ..."[124]
+Sam Harris criticizes Western religion's reliance on divine authority as lending itself to authoritarianism and dogmatism.[125]
+There is a correlation between religious fundamentalism and extrinsic religion (when religion is held because it serves ulterior interests)[126] and authoritarianism, dogmatism, and prejudice.[127]
+These arguments—combined with historical events that are argued to demonstrate the dangers of religion, such as the Crusades, inquisitions, witch trials, and terrorist attacks—have been used in response to claims of beneficial effects of belief in religion.[128]
+Believers counter-argue that some regimes that espouse atheism, such as the Soviet Union, have also been guilty of mass murder.[129][130] In response to those claims, atheists such as Sam Harris and Richard Dawkins have stated that Stalin's atrocities were influenced not by atheism but by dogmatic Marxism, and that while Stalin and Mao happened to be atheists, they did not do their deeds in the name of atheism.[131][132]
+In early ancient Greek, the adjective átheos (ἄθεος, from the privative ἀ- + θεός "god") meant "godless". It was first used as a term of censure roughly meaning "ungodly" or "impious". In the 5th century BCE, the word began to indicate more deliberate and active godlessness in the sense of "severing relations with the gods" or "denying the gods". The term ἀσεβής (asebēs) then came to be applied against those who impiously denied or disrespected the local gods, even if they believed in other gods. Modern translations of classical texts sometimes render átheos as "atheistic". As an abstract noun, there was also ἀθεότης (atheotēs), "atheism". Cicero transliterated the Greek word into the Latin átheos. The term found frequent use in the debate between early Christians and Hellenists, with each side attributing it, in the pejorative sense, to the other.[13]
+The term atheist (from Fr. athée), in the sense of "one who ... denies the existence of God or gods",[134]
+predates atheism in English, being first found as early as 1566,[135]
+and again in 1571.[136]
+Atheist as a label of practical godlessness was used at least as early as 1577.[137]
+The term atheism was derived from the French athéisme,[138] and appears in English about 1587.[139]
+An earlier work, from about 1534, used the term atheonism.[140][141]
+Related words emerged later: deist in 1621,[142]
+theist in 1662,[143]
+deism in 1675,[144]
+and theism in 1678.[145]
+At that time "deist" and "deism" already carried their modern meaning. The term theism came to be contrasted with deism.
+Karen Armstrong writes that "During the sixteenth and seventeenth centuries, the word 'atheist' was still reserved exclusively for polemic ... The term 'atheist' was an insult. Nobody would have dreamed of calling himself an atheist."[16]
+Atheism was first used to describe a self-avowed belief in late 18th-century Europe, specifically denoting disbelief in the monotheistic Abrahamic god.[146]
+In the 20th century, globalization contributed to the expansion of the term to refer to disbelief in all deities, though it remains common in Western society to describe atheism as simply "disbelief in God".[45]
+While the earliest-found usage of the term atheism is in 16th-century France,[138][139] ideas that would be recognized today as atheistic are documented from the Vedic period and the classical antiquity.
+Who really knows? Who will here proclaim it? Whence was it produced? Whence is this creation? The gods came afterwards, with the creation of this universe. Who then knows whence it has arisen?
+Atheistic schools are found in early Indian thought and have existed from the times of the historical Vedic religion.[150]
+Among the six orthodox schools of Hindu philosophy, Samkhya, the oldest philosophical school of thought, does not accept God, and the early Mimamsa also rejected the notion of God.[151]
+The thoroughly materialistic and anti-theistic philosophical Cārvāka (or Lokāyata) school that originated in India around the 6th century BCE is probably the most explicitly atheistic school of philosophy in India, similar to the Greek Cyrenaic school. This branch of Indian philosophy is classified as heterodox due to its rejection of the authority of Vedas and hence is not considered part of the six orthodox schools of Hinduism, but it is noteworthy as evidence of a materialistic movement within Hinduism.[152]
+Chatterjee and Datta explain that our understanding of Cārvāka philosophy is fragmentary, based largely on criticism of the ideas by other schools, and that it is not a living tradition:[153]
+Though materialism in some form or other has always been present in India, and occasional references are found in the Vedas, the Buddhistic literature, the Epics, as well as in the later philosophical works we do not find any systematic work on materialism, nor any organized school of followers as the other philosophical schools possess. But almost every work of the other schools states, for refutation, the materialistic views. Our knowledge of Indian materialism is chiefly based on these.
+Other Indian philosophies generally regarded as atheistic include Classical Samkhya and Purva Mimamsa. The rejection of a personal creator God is also seen in Jainism and Buddhism in India.[154]
+Western atheism has its roots in pre-Socratic Greek philosophy,[157][158] but atheism in the modern sense was extremely rare in ancient Greece.[159][160][158] Pre-Socratic Atomists such as Democritus attempted to explain the world in a purely materialistic way and interpreted religion as a human reaction to natural phenomena,[155] but did not explicitly deny the gods' existence.[155] Anaxagoras, whom Irenaeus calls "the atheist",[161] was accused of impiety and condemned for stating that "the sun is a type of incandescent stone", an affirmation with which he tried to deny the divinity of the celestial bodies.[162] In the late fifth century BCE, the Greek lyric poet Diagoras of Melos was sentenced to death in Athens under the charge of being a "godless person" (ἄθεος) after he made fun of the Eleusinian Mysteries,[159][160][155] but he fled the city to escape punishment.[159][160][155] Later writers have cited Diagoras as the "first atheist",[163][164] but he was probably not an atheist in the modern sense of the word.[160]
+A fragment from the lost satyr play Sisyphus, which has been attributed to both Critias and Euripides, claims that a clever man invented "the fear of the gods" in order to frighten people into behaving morally.[165][160][166][160][158] This statement, however, originally did not mean that the gods themselves were nonexistent, but rather that their powers were a hoax.[158] Atheistic statements have also been attributed to the philosopher Prodicus. Philodemus reports that Prodicus believed that "the gods of popular belief do not exist nor do they know, but primitive man, [out of admiration, deified] the fruits of the earth and virtually everything that contributed to his existence". Protagoras has sometimes been taken to be an atheist, but rather espoused agnostic views, commenting that "Concerning the gods I am unable to discover whether they exist or not, or what they are like in form; for there are many hindrances to knowledge, the obscurity of the subject and the brevity of human life."[167][159]
+The Athenian public associated Socrates (c. 470–399 BCE) with the trends in pre-Socratic philosophy towards naturalistic inquiry and the rejection of divine explanations for phenomena.[155][156] Aristophanes' comic play The Clouds (performed 423 BCE) portrays Socrates as teaching his students that the traditional Greek deities do not exist.[155][156] Socrates was later tried and executed under the charge of not believing in the gods of the state and instead worshipping foreign gods.[155][156] Socrates himself vehemently denied the charges of atheism at his trial[155][156][168] and all the surviving sources about him indicate that he was a very devout man, who prayed to the rising sun and believed that the oracle at Delphi spoke the word of Apollo.[155] Euhemerus (c. 300 BCE) published his view that the gods were only the deified rulers, conquerors and founders of the past, and that their cults and religions were in essence the continuation of vanished kingdoms and earlier political structures.[169] Although not strictly an atheist, Euhemerus was later criticized for having "spread atheism over the whole inhabited earth by obliterating the gods".[170]
+The most important Greek thinker in the development of atheism was Epicurus (c. 300 BCE).[158] Drawing on the ideas of Democritus and the Atomists, he espoused a materialistic philosophy according to which the universe was governed by the laws of chance without the need for divine intervention (see scientific determinism).[171] Although Epicurus still maintained that the gods existed,[172][158][171] he believed that they were uninterested in human affairs.[171] The aim of the Epicureans was to attain ataraxia ("peace of mind") and one important way of doing this was by exposing fear of divine wrath as irrational. The Epicureans also denied the existence of an afterlife and the need to fear divine punishment after death.[171]
+In the 3rd-century BCE, the Greek philosophers Theodorus Cyrenaicus[164][173] and Strato of Lampsacus[174] did not believe in the existence of gods.
+The Pyrrhonist philosopher Sextus Empiricus compiled a large number of ancient arguments against the existence of gods, recommending that one should suspend judgment regarding the matter.[175] His relatively large volume of surviving works had a lasting influence on later philosophers.[176]
+The meaning of "atheist" changed over the course of classical antiquity.[160] Early Christians were widely reviled as "atheists" because they did not believe in the existence of the Graeco-Roman deities.[177][160][178][179] During the Roman Empire, Christians were executed for their rejection of the Roman gods in general and the Imperial cult of ancient Rome in particular.[179][180] There was, however, a heavy struggle between Christians and pagans, in which each group accused the other of atheism, for not practicing the religion which they considered correct.[181] When Christianity became the state religion of Rome under Theodosius I in 381, heresy became a punishable offense.[180]
+During the Early Middle Ages, the Islamic world experienced a Golden Age. Along with advances in science and philosophy, Arab and Persian lands produced outspoken rationalists and atheists, including Muhammad al Warraq (fl. 9th century), Ibn al-Rawandi (827–911), Al-Razi (854–925), and Al-Maʿarri (973–1058). Al-Ma'arri wrote and taught that religion itself was a "fable invented by the ancients"[182] and that humans were "of two sorts: those with brains, but no religion, and those with religion, but no brains."[183]  Despite their being relatively prolific writers, little of their work survives, mainly being preserved through quotations and excerpts in later works by Muslim apologists attempting to refute them.[184] Other prominent Golden Age scholars have been associated with rationalist thought and atheism as well, although the current intellectual atmosphere in the Islamic world, and the scant evidence that survives from the era, make this point a contentious one today.
+In Europe, the espousal of atheistic views was rare during the Early Middle Ages and Middle Ages (see Medieval Inquisition); metaphysics and theology were the dominant interests pertaining to religion.[185] There were, however, movements within this period that furthered heterodox conceptions of the Christian god, including differing views of the nature, transcendence, and knowability of God. Individuals and groups such as Johannes Scotus Eriugena, David of Dinant, Amalric of Bena, and the Brethren of the Free Spirit maintained Christian viewpoints with pantheistic tendencies. Nicholas of Cusa held to a form of fideism he called docta ignorantia ("learned ignorance"), asserting that God is beyond human categorization, and thus our knowledge of him is limited to conjecture. William of Ockham inspired anti-metaphysical tendencies with his nominalistic limitation of human knowledge to singular objects, and asserted that the divine essence could not be intuitively or rationally apprehended by human intellect. Followers of Ockham, such as John of Mirecourt and Nicholas of Autrecourt furthered this view. The resulting division between faith and reason influenced later radical and reformist theologians such as John Wycliffe, Jan Hus, and Martin Luther.[185]
+The Renaissance did much to expand the scope of free thought and skeptical inquiry. Individuals such as Leonardo da Vinci sought experimentation as a means of explanation, and opposed arguments from religious authority. Other critics of religion and the Church during this time included Niccolò Machiavelli, Bonaventure des Périers, Michel de Montaigne, and François Rabelais.[176]
+Historian Geoffrey Blainey wrote that the Reformation had paved the way for atheists by attacking the authority of the Catholic Church, which in turn "quietly inspired other thinkers to attack the authority of the new Protestant churches".[186] Deism gained influence in France, Prussia, and England. The philosopher Baruch Spinoza was "probably the first well known 'semi-atheist' to announce himself in a Christian land in the modern era", according to Blainey. Spinoza believed that natural laws explained the workings of the universe. In 1661 he published his Short Treatise on God.[187]
+Criticism of Christianity became increasingly frequent in the 17th and 18th centuries, especially in France and England, where there appears to have been a religious malaise, according to contemporary sources. Some Protestant thinkers, such as Thomas Hobbes, espoused a materialist philosophy and skepticism toward supernatural occurrences, while Spinoza rejected divine providence in favor of a panentheistic naturalism. By the late 17th century, deism came to be openly espoused by intellectuals such as John Toland who coined the term "pantheist".[188]
+The first known explicit atheist was the German critic of religion Matthias Knutzen in his three writings of 1674.[189] He was followed by two other explicit atheist writers, the Polish ex-Jesuit philosopher Kazimierz Łyszczyński and in the 1720s by the French priest Jean Meslier.[190] In the course of the 18th century, other openly atheistic thinkers followed, such as Baron d'Holbach, Jacques-André Naigeon, and other French materialists.[191] John Locke in contrast, though an advocate of tolerance, urged authorities not to tolerate atheism, believing that the denial of God's existence would undermine the social order and lead to chaos.[192]
+The philosopher David Hume developed a skeptical epistemology grounded in empiricism, and Immanuel Kant's philosophy has strongly questioned the very possibility of a metaphysical knowledge. Both philosophers undermined the metaphysical basis of natural theology and criticized classical arguments for the existence of God.
+Blainey notes that, although Voltaire is widely considered to have strongly contributed to atheistic thinking during the Revolution, he also considered fear of God to have discouraged further disorder, having said "If God did not exist, it would be necessary to invent him."[193] In Reflections on the Revolution in France (1790), the philosopher Edmund Burke denounced atheism, writing of a "literary cabal" who had "some years ago formed something like a regular plan for the destruction of the Christian religion. This object they pursued with a degree of zeal which hitherto had been discovered only in the propagators of some system of piety ... These atheistical fathers have a bigotry of their own ...". But, Burke asserted, "man is by his constitution a religious animal" and "atheism is against, not only our reason, but our instincts; and ... it cannot prevail long".[194]
+Baron d'Holbach was a prominent figure in the French Enlightenment who is best known for his atheism and for his voluminous writings against religion, the most famous of them being The System of Nature (1770) but also Christianity Unveiled. One goal of the French Revolution was a restructuring and subordination of the clergy with respect to the state through the Civil Constitution of the Clergy. Attempts to enforce it led to anti-clerical violence and the expulsion of many clergy from France, lasting until the Thermidorian Reaction. The radical Jacobins seized power in 1793, ushering in the Reign of Terror. The Jacobins were deists and introduced the Cult of the Supreme Being as a new French state religion. Some atheists surrounding Jacques Hébert instead sought to establish a Cult of Reason, a form of atheistic pseudo-religion with a goddess personifying reason. The Napoleonic era further institutionalized the secularization of French society.
+In the latter half of the 19th century, atheism rose to prominence under the influence of rationalistic and freethinking philosophers. Many prominent German philosophers of this era denied the existence of deities and were critical of religion, including Ludwig Feuerbach, Arthur Schopenhauer, Max Stirner, Karl Marx, and Friedrich Nietzsche.[195]
+George Holyoake was the last person (1842) imprisoned in Great Britain due to atheist beliefs. Law notes that he may have also been the first imprisoned on such a charge. Stephen Law states that Holyoake "first coined the term 'secularism'".[196][197]
+Atheism, particularly in the form of practical atheism, advanced in many societies in the 20th century. Atheistic thought found recognition in a wide variety of other, broader philosophies, such as existentialism, objectivism, secular humanism, nihilism, anarchism, logical positivism, Marxism, feminism,[198] and the general scientific and rationalist movement.
+In addition, state atheism emerged in Eastern Europe and Asia during that period, particularly in the Soviet Union under Vladimir Lenin and Joseph Stalin, and in Communist China under Mao Zedong. Atheist and anti-religious policies in the Soviet Union included numerous legislative acts, the outlawing of religious instruction in the schools, and the emergence of the League of Militant Atheists.[199][200] After Mao, the Chinese Communist Party remains an atheist organization, and regulates, but does not forbid, the practice of religion in mainland China.[201][202][203]
+While Geoffrey Blainey has written that "the most ruthless leaders in the Second World War were atheists and secularists who were intensely hostile to both Judaism and Christianity",[204] Richard Madsen has pointed out that Hitler and Stalin each opened and closed churches as a matter of political expedience, and Stalin softened his opposition to Christianity in order to improve public acceptance of his regime during the war.[205] Blackford and Schüklenk have written that "the Soviet Union was undeniably an atheist state, and the same applies to Maoist China and Pol Pot's fanatical Khmer Rouge regime in Cambodia in the 1970s. That does not, however, show that the atrocities committed by these totalitarian dictatorships were the result of atheist beliefs, carried out in the name of atheism, or caused primarily by the atheistic aspects of the relevant forms of communism."[206]
+Logical positivism and scientism paved the way for neopositivism, analytical philosophy, structuralism, and naturalism. Neopositivism and analytical philosophy discarded classical rationalism and metaphysics in favor of strict empiricism and epistemological nominalism. Proponents such as Bertrand Russell emphatically rejected belief in God. In his early work, Ludwig Wittgenstein attempted to separate metaphysical and supernatural language from rational discourse. A.J. Ayer asserted the unverifiability and meaninglessness of religious statements, citing his adherence to the empirical sciences. Relatedly the applied structuralism of Lévi-Strauss sourced religious language to the human subconscious in denying its transcendental meaning. J.N. Findlay and J.J.C. Smart argued that the existence of God is not logically necessary. Naturalists and materialistic monists such as John Dewey considered the natural world to be the basis of everything, denying the existence of God or immortality.[59][207]
+Other leaders like Periyar E.V. Ramasamy, a prominent atheist leader of India, fought against Hinduism and Brahmins for discriminating and dividing people in the name of caste and religion.[208]
+This was highlighted in 1956 when he arranged for the erection of a statue depicting a Hindu god in a humble representation and made antitheistic statements.[209]
+Atheist Vashti McCollum was the plaintiff in a landmark 1948 Supreme Court case that struck down religious education in US public schools.[210] Madalyn Murray O'Hair was perhaps one of the most influential American atheists; she brought forth the 1963 Supreme Court case Murray v. Curlett which banned compulsory prayer in public schools.[211] In 1966, Time magazine asked "Is God Dead?"[212] in response to the Death of God theological movement, citing the estimation that nearly half of all people in the world lived under an anti-religious power, and millions more in Africa, Asia, and South America seemed to lack knowledge of the Christian view of theology.[213] The Freedom From Religion Foundation was co-founded by Anne Nicol Gaylor and her daughter, Annie Laurie Gaylor, in 1976 in the United States, and incorporated nationally in 1978. It promotes the separation of church and state.[214][215]
+Since the fall of the Berlin Wall, the number of actively anti-religious regimes has declined considerably. In 2006, Timothy Shah of the Pew Forum noted "a worldwide trend across all major religious groups, in which God-based and faith-based movements in general are experiencing increasing confidence and influence vis-à-vis secular movements and ideologies."[216]
+However, Gregory S. Paul and Phil Zuckerman consider this a myth and suggest that the actual situation is much more complex and nuanced.[217]
+A 2010 survey found that those identifying themselves as atheists or agnostics are on average more knowledgeable about religion than followers of major faiths. Nonbelievers scored better on questions about tenets central to Protestant and Catholic faiths. Only Mormon and Jewish faithful scored as well as atheists and agnostics.[218]
+In 2012, the first "Women in Secularism" conference was held in Arlington, Virginia.[219] Secular Woman was organized in 2012 as a national organization focused on nonreligious women.[220] The atheist feminist movement has also become increasingly focused on fighting sexism and sexual harassment within the atheist movement itself.[221]
+In August 2012, Jennifer McCreight (the organizer of Boobquake) founded a movement within atheism known as Atheism Plus, or A+, that "applies skepticism to everything, including social issues like sexism, racism, politics, poverty, and crime".[222][223][224]
+In 2013 the first atheist monument on American government property was unveiled at the Bradford County Courthouse in Florida: a 1,500-pound granite bench and plinth inscribed with quotes by Thomas Jefferson, Benjamin Franklin, and Madalyn Murray O'Hair.[225][226]
+"New Atheism" is the name that has been given to a movement among some early-21st-century atheist writers who have advocated the view that "religion should not simply be tolerated but should be countered, criticized, and exposed by rational argument wherever its influence arises."[227]
+The movement is commonly associated with Sam Harris, Daniel C. Dennett, Richard Dawkins, Victor J. Stenger, Christopher Hitchens, and to some extent Ayaan Hirsi Ali.[228][229] Several best-selling books by these authors, published between 2004 and 2007, form the basis for much of the discussion of "New" Atheism.[229] The new atheists and Dawkins in particular have been accused of committing the strawman fallacy[230] and of creating a new religion: Scientism.[231]
+In best selling books, the religiously motivated terrorist events of 9/11 and the partially successful attempts of the Discovery Institute to change the American science curriculum to include creationist ideas, together with support for those ideas from George W. Bush in 2005, have been cited by authors such as Harris, Dennett, Dawkins, Stenger, and Hitchens as evidence of a need to move toward a more secular society.[232]
+It is difficult to quantify the number of atheists in the world. Respondents to religious-belief polls may define "atheism" differently or draw different distinctions between atheism, non-religious beliefs, and non-theistic religious and spiritual beliefs.[234] A Hindu atheist would declare oneself as a Hindu, although also being an atheist at the same time.[235] A 2010 survey published in Encyclopædia Britannica found that the non-religious made up about 9.6% of the world's population, and atheists about 2.0%, with a very large majority based in Asia. This figure did not include those who follow atheistic religions, such as some Buddhists.[236] The average annual change for atheism from 2000 to 2010 was −0.17%.[236] Broad estimates of those who have an absence of belief in a god range from 500 million to 1.1 billion people worldwide.[237][238]
+According to global Win-Gallup International studies, 13% of respondents were "convinced atheists" in 2012,[239] 11% were "convinced atheists" in 2015,[27] and in 2017, 9% were "convinced atheists".[28] As of 2012[update], the top 10 surveyed countries with people who viewed themselves as "convinced atheists" were China (47%), Japan (31%), the Czech Republic (30%), France (29%), South Korea (15%), Germany (15%), Netherlands (14%), Austria (10%), Iceland (10%), Australia (10%), and the Republic of Ireland (10%).[240]
+According to the 2010 Eurobarometer Poll, the percentage of those polled who agreed with the statement "you don't believe there is any sort of spirit, God or life force" varied from a high percentage in France (40%), Czech Republic (37%), Sweden (34%), Netherlands (30%), and Estonia (29%); medium-high percentage in Germany (27%), Belgium (27%), UK (25%); to very low in Poland (5%), Greece (4%), Cyprus (3%), Malta (2%), and Romania (1%), with the European Union as a whole at 20%.[33] In a 2012 Eurobarometer poll on discrimination in the European Union, 16% of those polled considered themselves non believers/agnostics and 7% considered themselves atheists.[242]
+According to a Pew Research Center survey in 2012 religiously unaffiliated (including agnostics and atheists) make up about 18% of Europeans.[243] According to the same survey, the religiously unaffiliated are the majority of the population only in two European countries: Czech Republic (75%) and Estonia (60%).[243]
+There are another three countries, and one special administrative region of China or regions where the unaffiliated make up a majority of the population: North Korea (71%), Japan (57%), Hong Kong (56%), and China (52%).[243]
+According to the Australian Bureau of Statistics, 30% of Australians have "no religion", a category that includes atheists.[244]
+In a 2013 census, 42% of New Zealanders reported having no religion, up from 30% in 1991.[245] Men were more likely than women to report no religion.
+According to the World Values Survey, 4.4% of Americans self-identified as atheists in 2014.[246] However, the same survey showed that 11.1% of all respondents stated "no" when asked if they believed in God.[246] In 1984, these same figures were 1.1% and 2.2%, respectively. According to a 2014 report by the Pew Research Center, 3.1% of the US adult population identify as atheist, up from 1.6% in 2007; and within the religiously unaffiliated (or "no religion") demographic, atheists made up 13.6%.[247] According to the 2015 General Sociological Survey the number of atheists and agnostics in the US has remained relatively flat in the past 23 years since in 1991 only 2% identified as atheist and 4% identified as agnostic and in 2014 only 3% identified as atheists and 5% identified as agnostics.[248]
+According to the American Family Survey, 34% were found to be religiously unaffiliated in 2017 (23% 'nothing in particular', 6% agnostic, 5% atheist).[249][250] According to the Pew Research Center, in 2014, 22.8% of the American population does not identify with a religion, including atheists (3.1%) and agnostics (4%).[251] According to a PRRI survey, 24% of the population is unaffiliated. Atheists and agnostics combined make up about a quarter of this unaffiliated demographic.[252]
+In recent years, the profile of atheism has risen substantially in the Arab world.[253] In major cities across the region, such as Cairo, atheists have been organizing in cafés and social media, despite regular crackdowns from authoritarian governments.[253] A 2012 poll by Gallup International revealed that 5% of Saudis considered themselves to be "convinced atheists."[253] However, very few young people in the Arab world have atheists in their circle of friends or acquaintances. According to one study, less than 1% did in Morocco, Egypt, Saudi Arabia, or Jordan; only 3% to 7% in the United Arab Emirates, Bahrain, Kuwait, and Palestine.[254] When asked whether they have "seen or heard traces of atheism in [their] locality, community, and society" only about 3% to 8% responded yes in all the countries surveyed. The only exception was the UAE, with a percentage of 51%.[254]
+Various studies have reported positive correlations between levels of education, wealth and IQ with atheism.[255][256][257][95] In a 2008 study, researchers found intelligence to be negatively related to religious belief in Europe and the United States. In a sample of 137 countries, the correlation between national IQ and disbelief in God was found to be 0.60.[257] According to evolutionary psychologist Nigel Barber, atheism blossoms in places where most people feel economically secure, particularly in the social democracies of Europe, as there is less uncertainty about the future with extensive social safety nets and better health care resulting in a greater quality of life and higher life expectancy. By contrast, in underdeveloped countries, there are virtually no atheists.[258]
+The relationship between atheism and IQ, while statistically significant, is not a large one, and the reason for the relationship is not well understood.[255]  One hypothesis is that the negative relationship between IQ and religiosity is mediated by individual differences in noncomformity; in many countries, religious belief is a conformist choice, and there is evidence that more intelligent people are less likely to conform.[259] Another theory is that people of higher IQ are more likely to engage in analytical reasoning, and that disbelief in religion results from the application of higher level analytical reasoning to the assessment of religious claims.[255]
+Evolutionary psychologist Nigel Barber states that the reason atheists are more intelligent than religious people is better explained by social, environmental, and wealth factors which happen to correlate with loss of religious belief as well. He doubts that religion causes stupidity, noting that some highly intelligent people have also been religious, but he says it is plausible that higher intelligence correlates to rejection of improbable religious beliefs and that the situation between intelligence and rejection of religious beliefs is quite complex.[260] In a 2017 study, it was shown that compared to religious individuals, atheists have higher reasoning capacities and this difference seemed to be unrelated to sociodemographic factors such as age, education and country of origin.[261] In a 2015 study, researchers found that atheists score higher on cognitive reflection tests than theists, the authors wrote that "The fact that atheists score higher agrees with the literature showing that belief is an automatic manifestation of the mind and its default mode. Disbelieving seems to require deliberative cognitive ability."[262] A 2016 study, in which 4 new studies were reported and a meta-analysis of all previous research on the topic was performed, found that self-identified atheists scored 18.7% higher than theists on the cognitive reflection test and there is a negative correlation between religiosity and analytical thinking. The authors note that recently "it has been argued that analytic thinkers are not actually less religious; rather, the putative association may be a result of religiosity typically being measured after analytic thinking (an order effect)," however, they state "Our results indicate that the association between analytical thinking and religious disbelief is not caused by a simple order effect. There is good evidence that atheists and agnostics are more reflective than religious believers."[263]
+Statistically, atheists are held in poor regard across the globe. Non-atheists, and possibly even fellow atheists, seem to implicitly view atheists as prone to exhibit immoral behaviors ranging from mass murder to not paying at a restaurant.[264][265][266] In addition, according to a 2016 Pew Research Center publication, 15% of French people, 45% of Americans, and 99% of Indonesians explicitly believe that a person must believe in God to be moral. Pew furthermore noted that, in a U.S. poll, atheists and Muslims tied for the lowest rating among the major religious demographics on a "feeling thermometer".[267] Also, a study of religious college students found that they were more likely to perceive and interact with atheists negatively after considering their mortality, suggesting that these attitudes may be the result of death anxiety.[268]

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+A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name snail is also used for most of the members of the molluscan class Gastropoda that have a coiled shell that is large enough for the animal to retract completely into. When the word "snail" is used in this most general sense, it includes not just land snails but also numerous species of sea snails and freshwater snails. Gastropods that naturally lack a shell, or have only an internal shell, are mostly called slugs, and land snails that have only a very small shell (that they cannot retract into) are often called semi-slugs.
+Snails have considerable human relevance, including as food items, as pests, and as vectors of disease, and their shells are used as decorative objects and are incorporated into jewelry.[1] The snail has also had some cultural significance, tending to be associated with patience. The snail has also been used as a metaphor: someone who is not moving fast enough is "slow as a snail." The snail is the same or similar shape as the Cochlea.[2]
+Snails that respire using a lung belong to the group Pulmonata. As traditionally defined, the Pulmonata were found to be polyphyletic in a molecular study per Jörger et al., dating from 2010.[3] But snails with gills also form a polyphyletic group; in other words, snails with lungs and snails with gills form a number of taxonomic groups that are not necessarily more closely related to each other than they are related to some other groups.
+Both snails that have lungs and snails that have gills have diversified so widely over geological time that a few species with gills can be found on land and numerous species with lungs can be found in freshwater. Even a few marine species have lungs.
+Snails can be found in a very wide range of environments, including ditches, deserts, and the abyssal depths of the sea. Although land snails may be more familiar to laymen, marine snails constitute the majority of snail species, and have much greater diversity and a greater biomass. Numerous kinds of snail can also be found in fresh water.
+Most snails have thousands of microscopic tooth-like structures located on a banded ribbon-like tongue called a radula. The radula works like a file, ripping food into small pieces. Many snails are herbivorous, eating plants or rasping algae from surfaces with their radulae, though a few land species and many marine species are omnivores or predatory carnivores. Snails cannot absorb colored pigments when eating paper or cardboard so their feces are also colored.[4]
+Several species of the genus Achatina and related genera are known as giant African land snails; some grow to 15 in (38 cm) from snout to tail, and weigh 1 kg (2 lb).[5]  The largest living species of sea snail is Syrinx aruanus; its shell can measure up to 90 cm (35 in) in length, and the whole animal with the shell can weigh up to 18 kg (40 lb).  Recently, the smallest land snails, Angustopila dominikae,  have  been discovered in China, and measure 0.86mm long.[6]
+The snail Lymnaea makes decisions by using only two types of neurons: one deciding whether the snail is hungry, and the other deciding whether there is food in the vicinity.[1]
+The largest known land gastropod is the African giant snail Achatina achatina, the largest recorded specimen of which measured 39.3 centimetres (15.5 in) from snout to tail when fully extended, with a shell length of 27.3 cm (10.7 in) in December 1978. It weighed exactly 900 g (2 lb). Named Gee Geronimo, this snail was owned by Christopher Hudson (1955–79) of Hove, East Sussex, UK, and was collected in Sierra Leone in June 1976.[2]
+Gastropods that lack a conspicuous shell are commonly called slugs rather than snails.[3] Some species of slug have a maroon-brown shell, some have only an internal vestige that serves mainly as a calcium lactate repository, and others have some to no shell at all. Other than that there is little morphological difference between slugs and snails. There are however important differences in habitats and behavior.
+A shell-less animal is much more maneuverable and compressible, so even quite large land slugs can take advantage of habitats or retreats with very little space, retreats that would be inaccessible to a similar-sized snail. Slugs squeeze themselves into confined spaces such as under loose bark on trees or under stone slabs, logs or wooden boards lying on the ground. In such retreats they are in less danger from either predators or desiccation. Those are often suitable places for laying their eggs.
+Slugs as a group are far from monophyletic; scientifically speaking "slug" is a term of convenience with little taxonomic significance. The reduction or loss of the shell has evolved many times independently within several very different lineages of gastropods. The various taxa of land and sea gastropods with slug morphology occur within numerous higher taxonomic groups of shelled species; such independent slug taxa are not in general closely related to one another.
+Land snails are known as an agricultural and garden pest but some species are an edible delicacy and occasionally household pets.
+There are a variety of snail-control measures that gardeners and farmers use in an attempt to reduce damage to valuable plants. Traditional pesticides are still used, as are many less toxic control options such as concentrated garlic or wormwood solutions. Copper metal is also a snail repellent, and thus a copper band around the trunk of a tree will prevent snails from climbing up and reaching the foliage and fruit. A layer of a dry, finely ground, and scratchy substance such as diatomaceous earth can also deter snails.[4]
+The decollate snail (Rumina decollata) will capture and eat garden snails, and because of this it has sometimes been introduced as a biological pest control agent. However, this is not without problems, as the decollate snail is just as likely to attack and devour other gastropods that may represent a valuable part of the native fauna of the region.
+In French cuisine, edible snails are served for instance in Escargot à la Bourguignonne. The practice of rearing snails for food is known as heliciculture. For purposes of cultivation, the snails are kept in a dark place in a wired cage with dry straw or dry wood. Coppiced wine-grape vines are often used for this purpose. During the rainy period, the snails come out of hibernation and release most of their mucus onto the dry wood/straw. The snails are then prepared for cooking. Their texture when cooked is slightly chewy and tender.
+As well as being relished as gourmet food, several species of land snails provide an easily harvested source of protein to many people in poor communities around the world. Many land snails are valuable because they can feed on a wide range of agricultural wastes, such as shed leaves in banana plantations. In some countries, giant African land snails are produced commercially for food.
+Land snails, freshwater snails and sea snails are all eaten in many  countries. In certain parts of the world, snails are fried as for example, in Indonesia, they are fried as satay, a dish known as sate kakul. The eggs of certain snail species are eaten in a fashion similar to the way caviar is eaten.[citation needed]
+In Bulgaria, snails are traditionally cooked in an oven with rice or fried in a pan with vegetable oil and red paprika powder. Before they are used for those dishes, however, they are thoroughly boiled in hot water (for up to 90 minutes) and manually extracted from their shells. The two species most commonly used for food in the country are Helix lucorum and Helix pomatia.[citation needed]
+Snails and slug species that are not normally eaten in certain areas have occasionally been used as famine food in historical times. A history of Scotland written in the 1800s recounts a description of various snails and their use as food items in times of plague.[5]
+Skin creams derived from Cornu aspersum snails are sold for use on wrinkles, scars, dry skin, and acne. A research study suggested that secretions produced under stress by Cornu aspersa might facilitate regeneration of wounded tissue.[6]
+Because of its slowness, the snail has traditionally been seen as a symbol of laziness. In Christian culture, it has been used as a symbol of the deadly sin of sloth.[7][8] Psalms 58:8 uses snail slime as a metaphorical punishment. In Mayan mythology, the snail is associated with sexual desire, being personified by the god Uayeb.[9]
+Snails were widely noted and used in divination.[7] The Greek poet Hesiod wrote that snails signified the time to harvest by climbing the stalks, while the Aztec moon god Tecciztecatl bore a snail shell on his back. This symbolised rebirth; the snail's penchant for appearing and disappearing was analogised with the moon.[10]
+Professor Ronald Chase of McGill University in Montreal has suggested the ancient myth of Cupid's arrows might be based on early observations of the love dart behavior of the land snail species Cornu aspersum.[11]
+In contemporary speech, the expression "a snail's pace" is often used to describe a slow, inefficient process. The phrase "snail mail" is used to mean regular postal service delivery of paper messages as opposed to the delivery of email, which can be virtually instantaneous.
+Keong Emas (Javanese and Indonesian for Golden Snail) is a popular Javanese folklore about a princess magically transformed and contained in a golden snail shell. The folklore is a part of popular Javanese Panji cycle telling the stories about the prince Panji Asmoro Bangun (also known as Raden Inu Kertapati) and his consort, princess Dewi Sekartaji (also known as Dewi Chandra Kirana).
+Certain varieties of snails, notably the family Muricidae, produce a secretion that is a color-fast natural dye. The ancient Tyrian purple was made in this way as were other purple and blue dyes.[12][13][14] The extreme expense of extracting this secretion is sufficient quantities limited its use to the very wealthy. It is such dyes as these that led to certain shades of purple and blue being associated with royalty and wealth.[15]
+Throughout history, snails have been kept as pets. There are many famous snails such as Lefty (Born Jeremy) and within fiction, Gary and Brian the snail .[16]

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+The egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own, at which point the animal hatches. An egg results from fertilization of an egg cell. Most arthropods, vertebrates (excluding live-bearing mammals), and mollusks lay eggs, although some, such as scorpions, do not.
+Reptile eggs, bird eggs, and monotreme eggs are laid out of water and are surrounded by a protective shell, either flexible or inflexible. Eggs laid on land or in nests are usually kept within a warm and favorable temperature range while the embryo grows. When the embryo is adequately developed it hatches, i.e., breaks out of the egg's shell. Some embryos have a temporary egg tooth they use to crack, pip, or break the eggshell or covering.
+The largest recorded egg is from a whale shark and was 30 cm × 14 cm × 9 cm (11.8 in × 5.5 in × 3.5 in) in size.[1] Whale shark eggs typically hatch within the mother. At 1.5 kg (3.3 lb) and up to 17.8 cm × 14 cm (7.0 in × 5.5 in), the ostrich egg is the largest egg of any living bird,[2] though the extinct elephant bird and some non-avian dinosaurs laid larger eggs. The bee hummingbird produces the smallest known bird egg, which weighs half of a gram (around 0.02 oz). Some eggs laid by reptiles and most fish, amphibians, insects, and other invertebrates can be even smaller.
+Reproductive structures similar to the egg in other kingdoms are termed "spores," or in spermatophytes "seeds," or in gametophytes "egg cells".
+Several major groups of animals typically have readily distinguishable eggs.
+The most common reproductive strategy for fish is known as oviparity, in which the female lays undeveloped eggs that are externally fertilized by a male. Typically large numbers of eggs are laid at one time (an adult female cod can produce 4–6 million eggs in one spawning) and the eggs are then left to develop without parental care. When the larvae hatch from the egg, they often carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a few days as they learn how to swim. Once the yolk is consumed, there is a critical point after which they must learn how to hunt and feed or they will die.
+A few fish, notably the rays and most sharks use ovoviviparity in which the eggs are fertilized and develop internally. However, the larvae still grow inside the egg consuming the egg's yolk and without any direct nourishment from the mother. The mother then gives birth to relatively mature young. In certain instances, the physically most developed offspring will devour its smaller siblings for further nutrition while still within the mother's body. This is known as intrauterine cannibalism.
+In certain scenarios, some fish such as the hammerhead shark and reef shark are viviparous, with the egg being fertilized and developed internally, but with the mother also providing direct nourishment.
+The eggs of fish and amphibians are jellylike. Cartilaginous fish (sharks, skates, rays, chimaeras) eggs are fertilized internally and exhibit a wide variety of both internal and external embryonic development. Most fish species spawn eggs that are fertilized externally, typically with the male inseminating the eggs after the female lays them. These eggs do not have a shell and would dry out in the air. Even air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, Chiromantis xerampelina.
+Bird eggs are laid by females and incubated for a time that varies according to the species; a single young hatches from each egg. Average clutch sizes range from one (as in condors) to about 17 (the grey partridge). Some birds lay eggs even when not fertilized (e.g. hens); it is not uncommon for pet owners to find their lone bird nesting on a clutch of unfertilized eggs, which are sometimes called wind-eggs.
+The default color of vertebrate eggs is the white of the calcium carbonate from which the shells are made, but some birds, mainly passerines, produce colored eggs. The pigment biliverdin and its zinc chelate give a green or blue ground color, and protoporphyrin produces reds and browns as a ground color or as spotting.
+Non-passerines typically have white eggs, except in some ground-nesting groups such as the Charadriiformes, sandgrouse and nightjars, where camouflage is necessary, and some parasitic cuckoos which have to match the passerine host's egg. Most passerines, in contrast, lay colored eggs, even if there is no need of cryptic colors.
+However some have suggested that the protoporphyrin markings on passerine eggs actually act to reduce brittleness by acting as a solid-state lubricant.[10] If there is insufficient calcium available in the local soil, the egg shell may be thin, especially in a circle around the broad end. Protoporphyrin speckling compensates for this, and increases inversely to the amount of calcium in the soil.[11]
+For the same reason, later eggs in a clutch are more spotted than early ones as the female's store of calcium is depleted.
+The color of individual eggs is also genetically influenced, and appears to be inherited through the mother only, suggesting that the gene responsible for pigmentation is on the sex-determining W chromosome (female birds are WZ, males ZZ).
+It used to be thought that color was applied to the shell immediately before laying, but subsequent research shows that coloration is an integral part of the development of the shell, with the same protein responsible for depositing calcium carbonate, or protoporphyrins when there is a lack of that mineral.
+In species such as the common guillemot, which nest in large groups, each female's eggs have very different markings, making it easier for females to identify their own eggs on the crowded cliff ledges on which they breed.
+Bird eggshells are diverse. For example:
+Tiny pores in bird eggshells allow the embryo to breathe. The domestic hen's egg has around 7000 pores.[12]
+Some bird eggshells have a coating of vaterite spherules, which is a rare polymorph of calcium carbonate. In Greater Ani Crotophaga major this vaterite coating is thought to act as a shock absorber, protecting the calcite shell from fracture during incubation, such as colliding with other eggs in the nest.[13]
+Most bird eggs have an oval shape, with one end rounded and the other more pointed. This shape results from the egg being forced through the oviduct. Muscles contract the oviduct behind the egg, pushing it forward. The egg's wall is still shapeable, and the pointed end develops at the back. Long, pointy eggs are an incidental consequence of having a streamlined body typical of birds with strong flying abilities; flight narrows the oviduct, which changes the type of egg a bird can lay.[14] Cliff-nesting birds often have highly conical eggs. They are less likely to roll off, tending instead to roll around in a tight circle; this trait is likely to have arisen due to evolution via natural selection. In contrast, many hole-nesting birds have nearly spherical eggs.[15]
+Many animals feed on eggs. For example, principal predators of the black oystercatcher's eggs include raccoons, skunks, mink, river and sea otters, gulls, crows and foxes. The stoat (Mustela erminea) and long-tailed weasel (M. frenata) steal ducks' eggs. Snakes of the genera Dasypeltis and Elachistodon specialize in eating eggs.
+Brood parasitism occurs in birds when one species lays its eggs in the nest of another. In some cases, the host's eggs are removed or eaten by the female, or expelled by her chick. Brood parasites include the cowbirds and many Old World cuckoos.
+An average whooping crane egg is 102 mm (4.0 in) long and weighs 208 g (7.3 oz)
+Eurasian oystercatcher eggs camouflaged in the nest
+Egg of a senegal parrot, a bird that nests in tree holes, on a 1 cm (0.39 in) grid
+Eggs of ostrich, emu, kiwi and chicken
+Finch egg next to American dime
+Eggs of duck, goose, guineafowl and chicken
+Eggs of ostrich, cassowary, chicken, flamingo, pigeon and blackbird
+Egg of an emu
+Egg from a chicken compared to a 1 euro coin, great tit egg and a corn grain
+Bird nest with brown marbling eggs of a robin
+Like amphibians, amniotes are air-breathing vertebrates, but they have complex eggs or embryos, including an amniotic membrane. Amniotes include reptiles (including dinosaurs and their descendants, birds) and mammals.
+Reptile eggs are often rubbery and are always initially white. They are able to survive in the air. Often the sex of the developing embryo is determined by the temperature of the surroundings, with cooler temperatures favouring males. Not all reptiles lay eggs; some are viviparous ("live birth").
+Dinosaurs laid eggs, some of which have been preserved as petrified fossils.
+Among mammals, early extinct species laid eggs, as do platypuses and echidnas (spiny anteaters). Platypuses and two genera of echidna are Australian monotremes. Marsupial and placental mammals do not lay eggs, but their unborn young do have the complex tissues that identify amniotes.
+The eggs of the egg-laying mammals (the platypus and the echidnas) are macrolecithal eggs very much like those of reptiles. The eggs of marsupials are likewise macrolecithal, but rather small, and develop inside the body of the female, but do not form a placenta. The young are born at a very early stage, and can be classified as a "larva" in the biological sense.[16]
+In placental mammals, the egg itself is void of yolk, but develops an umbilical cord from structures that in reptiles would form the yolk sac. Receiving nutrients from the mother, the fetus completes the development while inside the uterus.
+Eggs are common among invertebrates, including insects, spiders, mollusks, and crustaceans.
+All sexually reproducing life, including both plants and animals, produces gametes. The male gamete cell, sperm, is usually motile whereas the female gamete cell, the ovum, is generally larger and sessile. The male and female gametes combine to produce the zygote cell. In multicellular organisms the zygote subsequently divides in an organised manner into smaller more specialised cells, so that this new individual develops into an embryo. In most animals the embryo is the sessile initial stage of the individual life cycle, and is followed by the emergence (that is, the hatching) of a motile stage. The zygote or the ovum itself or the sessile organic vessel containing the developing embryo may be called the egg.
+A recent proposal suggests that the phylotypic animal body plans originated in cell aggregates before the existence of an egg stage of development. Eggs, in this view, were later evolutionary innovations, selected for their role in ensuring genetic uniformity among the cells of incipient multicellular organisms.[17]
+Scientists often classify animal reproduction according to the degree of development that occurs before the new individuals are expelled from the adult body, and by the yolk which the egg provides to nourish the embryo.
+Vertebrate eggs can be classified by the relative amount of yolk. Simple eggs with little yolk are called microlecithal, medium-sized eggs with some yolk are called mesolecithal, and large eggs with a large concentrated yolk are called macrolecithal.[7] This classification of eggs is based on the eggs of chordates, though the basic principle extends to the whole animal kingdom.
+Small eggs with little yolk are called microlecithal. The yolk is evenly distributed, so the cleavage of the egg cell cuts through and divides the egg into cells of fairly similar sizes. In sponges and cnidarians the dividing eggs develop directly into a simple larva, rather like a morula with cilia. In cnidarians, this stage is called the planula, and either develops directly into the adult animals or forms new adult individuals through a process of budding.[18]
+Microlecithal eggs require minimal yolk mass. Such eggs are found in flatworms, roundworms, annelids, bivalves, echinoderms, the lancelet and in most marine arthropods.[19] In anatomically simple animals, such as cnidarians and flatworms, the fetal development can be quite short, and even microlecithal eggs can undergo direct development. These small eggs can be produced in large numbers. In animals with high egg mortality, microlecithal eggs are the norm, as in bivalves and marine arthropods. However, the latter are more complex anatomically than e.g. flatworms, and the small microlecithal eggs do not allow full development. Instead, the eggs hatch into larvae, which may be markedly different from the adult animal.
+In placental mammals, where the embryo is nourished by the mother throughout the whole fetal period, the egg is reduced in size to essentially a naked egg cell.
+Mesolecithal eggs have comparatively more yolk than the microlecithal eggs. The yolk is concentrated in one part of the egg (the vegetal pole), with the cell nucleus and most of the cytoplasm in the other (the animal pole). The cell cleavage is uneven, and mainly concentrated in the cytoplasma-rich animal pole.[3]
+The larger yolk content of the mesolecithal eggs allows for a longer fetal development. Comparatively anatomically simple animals will be able to go through the full development and leave the egg in a form reminiscent of the adult animal. This is the situation found in hagfish and some snails.[4][19] Animals with smaller size eggs or more advanced anatomy will still have a distinct larval stage, though the larva will be basically similar to the adult animal, as in lampreys, coelacanth and the salamanders.[3]
+Eggs with a large yolk are called macrolecithal. The eggs are usually few in number, and the embryos have enough food to go through full fetal development in most groups.[7] Macrolecithal eggs are only found in selected representatives of two groups: Cephalopods and vertebrates.[7][20]
+Macrolecithal eggs go through a different type of development than other eggs. Due to the large size of the yolk, the cell division can not split up the yolk mass. The fetus instead develops as a plate-like structure on top of the yolk mass, and only envelopes it at a later stage.[7] A portion of the yolk mass is still present as an external or semi-external yolk sac at hatching in many groups. This form of fetal development is common in bony fish, even though their eggs can be quite small. Despite their macrolecithal structure, the small size of the eggs does not allow for direct development, and the eggs hatch to a larval stage ("fry"). In terrestrial animals with macrolecithal eggs, the large volume to surface ratio necessitates structures to aid in transport of oxygen and carbon dioxide, and for storage of waste products so that the embryo does not suffocate or get poisoned from its own waste while inside the egg, see amniote.[9]
+In addition to bony fish and cephalopods, macrolecithal eggs are found in cartilaginous fish, reptiles, birds and monotreme mammals.[3] The eggs of the coelacanths can reach a size of 9 cm (3.5 in) in diameter, and the young go through full development while in the uterus, living on the copious yolk.[21]
+Animals are commonly classified by their manner of reproduction, at the most general level distinguishing egg-laying (Latin. oviparous) from live-bearing (Latin. viviparous).
+These classifications are divided into more detail according to the development that occurs before the offspring are expelled from the adult's body. Traditionally:[22]
+The term hemotropic derives from the Latin for blood-feeding, contrasted with histotrophic for tissue-feeding.[27]
+Eggs laid by many different species, including birds, reptiles, amphibians, and fish, have probably been eaten by mankind for millennia. Popular choices for egg consumption are chicken, duck, roe, and caviar, but by a wide margin the egg most often humanly consumed is the chicken egg, typically unfertilized.
+According to the Kashrut, that is the set of Jewish dietary laws, kosher food may be consumed according to halakha (Jewish law). Kosher meat and milk (or derivatives) cannot be mixed (Deuteronomy 14:21) or stored together. Eggs are considered pareve (neither meat nor dairy) despite being an animal product and can be mixed with either milk or kosher meat. Mayonnaise, for instance, is usually marked "pareve" despite by definition containing egg.[28]
+Many vaccines for infectious diseases are produced in fertile chicken eggs. The basis of this technology was the discovery in 1931 by Alice Miles Woodruff and Ernest William Goodpasture at Vanderbilt University that the rickettsia and viruses that cause a variety of diseases will grow in chicken embryos. This enabled the development of vaccines against influenza, chicken pox, smallpox, yellow fever, typhus, Rocky mountain spotted fever and other diseases.
+The egg is a symbol of new life and rebirth in many cultures around the world. Christians view Easter eggs as symbolic of the resurrection of Jesus Christ.[29] A popular Easter tradition in some parts of the world is the decoration of hard-boiled eggs (usually by dyeing, but often by hand-painting or spray-painting). Adults often hide the eggs for children to find, an activity known as an Easter egg hunt. A similar tradition of egg painting exists in areas of the world influenced by the culture of Persia. Before the spring equinox in the Persian New Year tradition (called Norouz), each family member decorates a hard-boiled egg and sets them together in a bowl. The tradition of a dancing egg is held during the feast of Corpus Christi in Barcelona and other Catalan cities since the 16th century. It consists of an emptied egg, positioned over the water jet from a fountain, which starts turning without falling.[30]
+Although a food item, raw eggs are sometimes thrown at houses, cars, or people. This act, known commonly as "egging" in the various English-speaking countries, is a minor form of vandalism and, therefore, usually a criminal offense and is capable of damaging property (egg whites can degrade certain types of vehicle paint) as well as potentially causing serious eye injury. On Halloween, for example, trick or treaters have been known to throw eggs (and sometimes flour) at property or people from whom they received nothing.[citation needed] Eggs are also often thrown in protests, as they are inexpensive and nonlethal, yet very messy when broken.[31]
+Egg collecting was a popular hobby in some cultures, including among the first Australians. Traditionally, the embryo would be removed before a collector stored the egg shell.[32]
+Collecting eggs of wild birds is now banned by many jurisdictions, as the practice can threaten rare species. In the United Kingdom, the practice is prohibited by the Protection of Birds Act 1954 and Wildlife and Countryside Act 1981.[33] On the other hand, ongoing underground trading is becoming a serious issue.[34]
+Since the protection of wild bird eggs was regulated, early collections have come to the museums as curiosities. For example, the Australian Museum hosts a collection of about 20,000 registered clutches of eggs,[35] and the collection in Western Australia Museum has been archived in a gallery.[36] Scientists regard egg collections as a good natural-history data, as the details recorded in the collectors' notes have helped them to understand birds' nesting behaviors.[37]
+Insect eggs, in this case those of the Emperor gum moth, are often laid on the underside of leaves.
+Fish eggs, such as these herring eggs are often transparent and fertilized after laying.
+Skates and some sharks have a uniquely shaped egg case called a mermaid's purse.
+A Testudo hermanni emerging fully developed from a reptilian egg.
+A Schistosoma mekongi egg.
+Eggs of Huffmanela hamo, a nematode parasite in a fish
+Eggs of various parasites (mainly nematodes) from wild primates

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+The onion (Allium cepa L., from Latin cepa "onion"), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus Allium. Its close relatives include the garlic, scallion, shallot, leek, chive,[2] and Chinese onion.[3]
+This genus also contains several other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion (Allium fistulosum), the tree onion (A. ×proliferum), and the Canada onion (Allium canadense). The name "wild onion" is applied to a number of Allium species, but A. cepa is exclusively known from cultivation. Its ancestral wild original form is not known, although escapes from cultivation have become established in some regions.[4] The onion is most frequently a biennial or a perennial plant, but is usually treated as an annual and harvested in its first growing season.
+The onion plant has a fan of hollow, bluish-green leaves and its bulb at the base of the plant begins to swell when a certain day-length is reached. The bulbs are composed of shortened, compressed, underground stems surrounded by fleshy modified scale (leaves) that envelop a central bud at the tip of the stem. In the autumn (or in spring, in the case of overwintering onions), the foliage dies down and the outer layers of the bulb become dry and brittle. The crop is harvested and dried and the onions are ready for use or storage. The crop is prone to attack by a number of pests and diseases, particularly the onion fly, the onion eelworm, and various fungi cause rotting. Some varieties of A. cepa, such as shallots and potato onions, produce multiple bulbs.
+Onions are cultivated and used around the world. As a food item, they are usually served cooked, as a vegetable or part of a prepared savoury dish, but can also be eaten raw or used to make pickles or chutneys. They are pungent when chopped and contain certain chemical substances which irritate the eyes.
+The onion plant (Allium cepa), also known as the bulb onion[5] or common onion,[6] is the most widely cultivated species of the genus Allium.[7][8]  It was first officially described by Carl Linnaeus in his 1753 work Species Plantarum.[9] A number of synonyms have appeared in its taxonomic history:
+A. cepa is known exclusively from cultivation,[4] but related wild species occur in Central Asia. The most closely related species include A. vavilovii (Popov & Vved.) and A. asarense (R.M. Fritsch & Matin) from Iran.[12] However, Zohary and Hopf state that "there are doubts whether the A. vavilovii collections tested represent genuine wild material or only feral derivatives of the crop."[13]
+The vast majority of cultivars of A. cepa belong to the "common onion group" (A. cepa var. cepa) and are usually referred to simply as "onions". The Aggregatum Group of cultivars (A. cepa var. aggregatum) includes both shallots and potato onions.[14]
+The genus Allium also contains a number of other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion (A. fistulosum), Egyptian onion (A. ×proliferum), and Canada onion (A. canadense).[6]
+Cepa is commonly accepted as Latin for "onion" and has an affinity with Ancient Greek: κάπια (kápia) and Albanian: qepë and is ancestral to Aromanian: tseapã, Catalan: ceba, Occitan: ceba, Spanish: cebolla, Italian: cipolla, and Romanian: ceapă. The English word chive is also derived from the Old French cive, which derived from cepa.
+The onion plant has been grown and selectively bred in cultivation for at least 7,000 years.  It is a biennial plant, but is usually grown as an annual. Modern varieties typically grow to a height of 15 to 45 cm (6 to 18 in). The leaves are yellowish- to bluish green and grow alternately in a flattened, fan-shaped swathe. They are fleshy, hollow, and cylindrical, with one flattened side. They are at their broadest about a quarter of the way up, beyond which they taper towards a blunt tip. The base of each leaf is a flattened, usually white sheath that grows out of the basal plate of a bulb. From the underside of the plate, a bundle of fibrous roots extends for a short way into the soil. As the onion matures, food reserves begin to accumulate in the leaf bases and the bulb of the onion swells.[15]
+In the autumn, the leaves die back and the outer scales of the bulb become dry and brittle, so the crop is then normally harvested. If left in the soil over winter, the growing point in the middle of the bulb begins to develop in the spring. New leaves appear and a long, stout, hollow stem expands, topped by a bract protecting a developing inflorescence. The inflorescence takes the form of a globular umbel of white flowers with parts in sixes. The seeds are glossy black and triangular in cross section.[15] The average pH of an onion is around 5.5.[16]
+Because the wild onion is extinct and ancient records of using onions span western and eastern Asia, the geographic origin of the onion is uncertain,[17][18] with likely domestication worldwide.[19] Onions have been variously described as having originated in Iran, the western Indian subcontinent and Central Asia.[17][20][21][22]
+Traces of onions recovered from Bronze Age settlements in China suggest that onions were used as far back as 5000 BCE, not only for their flavour, but the bulb's durability in storage and transport.[23][19][failed verification] Ancient Egyptians revered the onion bulb, viewing its spherical shape and concentric rings as symbols of eternal life.[19] Onions were used in Egyptian burials, as evidenced by onion traces found in the eye sockets of Ramesses IV.[24]
+Pliny the Elder of the first century CE wrote about the use of onions and cabbage in Pompeii. He documented Roman beliefs about the onion's ability to improve ocular ailments, aid in sleep, and heal everything from oral sores and toothaches to dog bites, lumbago, and even dysentery. Archaeologists unearthing Pompeii long after its 79 CE volcanic burial have found gardens resembling those in Pliny's detailed narratives.[19] According to texts collected in the fifth/sixth century CE under the authorial aegis of "Apicius" (said to have been a gourmet), onions were used in many Roman recipes.[19]
+In the Age of Discovery, onions were taken to North America by the first European settlers,[17] only to discover the plant readily available, and in wide use in Native American gastronomy.[17] According to diaries kept by certain of the first English colonists, the bulb onion was one of the first crops planted by the Pilgrim fathers.[19]
+Common onions are normally available in three colour varieties:
+While the large, mature onion bulb is most often eaten, onions can be eaten at immature stages. Young plants may be harvested before bulbing occurs and used whole as spring onions or scallions.  When an onion is harvested after bulbing has begun, but the onion is not yet mature, the plants are sometimes referred to as "summer" onions.[27]
+Additionally, onions may be bred and grown to mature at smaller sizes. Depending on the mature size and the purpose for which the onion is used, these may be referred to as pearl, boiler, or pickler onions, but differ from true pearl onions which are a different species.[27] Pearl and boiler onions may be cooked as a vegetable rather than as an ingredient and pickler onions are often preserved in vinegar as a long-lasting relish.[28]
+Onions are available in fresh, frozen, canned, caramelised, pickled, and chopped forms. The dehydrated product is available as kibbled, sliced, ring, minced, chopped, granulated, and powder forms.
+Onion powder is a seasoning widely used when the fresh ingredient is not available. It is made from finely ground, dehydrated onions, mainly the pungent varieties of bulb onions, and has a strong odour. Being dehydrated, it has a long shelf life and is available in several varieties: yellow, red, and white.[29]
+Onions are commonly chopped and used as an ingredient in various hearty warm dishes, and may also be used as a main ingredient in their own right, for example in French onion soup, creamed onions, and onion chutney. They are versatile and can be baked, boiled, braised, grilled, fried, roasted, sautéed, or eaten raw in salads.[30] Their layered nature makes them easy to hollow out once cooked, facilitating stuffing them, as in Turkish sogan-dolma.
+Onions pickled in vinegar are eaten as a snack around the world, and as a side serving in pubs and fish and chip shops throughout the United Kingdom and the Commonwealth. They are part of a traditional British pub's ploughman's lunch, usually served with crusty bread, English cheese, and ale.
+Similar to garlic,[31] onions can show an additional colour – pink-red – after cutting, an effect caused by reactions of amino acids with sulfur compounds.[32]
+Onions have particularly large cells that are readily observed under low magnification. Forming a single layer of cells, the bulb epidermis is easy to separate for educational, experimental, and breeding purposes.[33][34] Onions are therefore commonly used in science education to teach the use of a microscope for observing cell structure.[35]
+Onions are toxic to dogs, cats, guinea pigs, and many other animals.[36][37]
+Most onion cultivars are about 89% water, 9% carbohydrates (including 4% sugar and 2% dietary fibre), 1% protein, and negligible fat (table). Onions contain low amounts of essential nutrients and have an energy value of 166 kJ (40 Calories) in a 100 g (3.5 oz) amount. Onions contribute savoury flavour to dishes without contributing significant caloric content.[19]
+Considerable differences exist between onion varieties in phytochemical content, particularly for polyphenols, with shallots having the highest level, six times the amount found in Vidalia onions.[38] Yellow onions have the highest total flavonoid content, an amount 11 times higher than in white onions.[38] Red onions have considerable content of anthocyanin pigments, with at least 25 different compounds identified representing 10% of total flavonoid content.[38]
+Onion polyphenols are under basic research to determine their possible biological properties in humans.[38][39]
+Some people suffer from allergic reactions after handling onions.[40] Symptoms can include contact dermatitis, intense itching, rhinoconjunctivitis, blurred vision, bronchial asthma, sweating, and anaphylaxis. Allergic reactions may not occur when eating cooked onions, possibly due to the denaturing of the proteins from cooking.[41]
+Freshly cut onions often cause a stinging sensation in the eyes of people nearby, and often uncontrollable tears. This is caused by the release of a volatile liquid, syn-propanethial-S-oxide and its aerosol, which stimulates nerves in the eye.[7] This gas is produced by a chain of reactions which serve as a defence mechanism: chopping an onion causes damage to cells which releases enzymes called alliinases. These break down amino acid sulfoxides and generate sulfenic acids. A specific sulfenic acid, 1-propenesulfenic acid, is rapidly acted on by a second enzyme, the lacrimatory factor synthase, producing the syn-propanethial-S-oxide.[7] This gas diffuses through the air and soon reaches the eyes, where it activates sensory neurons. Lacrimal glands produce tears to dilute and flush out the irritant.[42]
+Eye irritation can be avoided by cutting onions under running water or submerged in a basin of water.[42] Leaving the root end intact also reduces irritation as the onion base has a higher concentration of sulphur compounds than the rest of the bulb.[43] Refrigerating the onions before use reduces the enzyme reaction rate and using a fan can blow the gas away from the eyes. The more often one chops onions, the less one experiences eye irritation.[44]
+The amount of sulfenic acids and lacrimal factor released and the irritation effect differs among Allium species. In 2008, the New Zealand Institute for Crop and Food Research created "no tears" onions by genetic modification to prevent the synthesis of lachrymatory factor synthase in onions.[45] One study suggests that consumers prefer the flavor of onions with lower LFS content.[46] However, since the LFS-silencing process involves reducing sulfur ingestion by the plant, it has also been suggested that LFS− onions are inferior in flavor.[47] A method for efficiently differentiating LFS− and LFS+ onions has been developed based on mass spectrometry, with potential application in high-volume production;[48] gas chromatography is also used to measure lachrymatory factor in onions.[49][50] In early 2018, Bayer released the first crop yield of commercially available LFS-silenced onions under the name "Sunions."[51] They were the product of 30 years of cross-breeding; genetic modification was not employed.[51][52]
+Guinea hen weed and honey garlic contain a similar lachrymatory factor.[53] Synthetic onion lachrymatory factor has been used in a study related to tear production,[54] and has been proposed as a nonlethal deterrent against thieves and intruders.[55][56]
+Onions are best cultivated in fertile soils that are well-drained. Sandy loams are good as they are low in sulphur, while clayey soils usually have a high sulphur content and produce pungent bulbs. Onions require a high level of nutrients in the soil. Phosphorus is often present in sufficient quantities, but may be applied before planting because of its low level of availability in cold soils. Nitrogen and potash can be applied at regular intervals during the growing season, the last application of nitrogen being at least four weeks before harvesting.[57] Bulbing onions are day-length sensitive; their bulbs begin growing only after the number of daylight hours has surpassed some minimal quantity. Most traditional European onions are referred to as "long-day" onions, producing bulbs only after 14 hours or more of daylight occurs. Southern European and North African varieties are often known as "intermediate-day" types, requiring only 12–13 hours of daylight to stimulate bulb formation. Finally, "short-day" onions, which have been developed in more recent times, are planted in mild-winter areas in the autumn and form bulbs in the early spring, and require only 11–12 hours of daylight to stimulate bulb formation.[58] Onions are a cool-weather crop and can be grown in USDA zones 3 to 9.[59] Hot temperatures or other stressful conditions cause them to "bolt", meaning that a flower stem begins to grow.[60]
+Onions may be grown from seeds or from partially grown bulbs called "sets". Because onion seeds are short-lived, fresh seeds germinate more effectively when sown in shallow drills, then thinning the plants in stages.[59][61] In suitable climates, certain cultivars can be sown in late summer and autumn to overwinter in the ground and produce early crops the following year.[15] Onion bulbs are produced by sowing seeds in a dense pattern in early summer, then harvested in the autumn when the bulbs are still small, followed by drying and storage. These bulbs planted the following spring grow into mature bulbs later in the growing season.[62] Certain cultivars used for growing and storing bulbs may not have such good storage characteristics as those grown directly from seed.[15]
+Routine care during the growing season involves keeping the rows free of competing weeds, especially when the plants are young. The plants are shallow-rooted and do not need much water when established. Bulbing usually takes place after 12 to 18 weeks. The bulbs can be gathered when needed to eat fresh, but if they will be stored, they are harvested after the leaves have died back naturally. In dry weather, they can be left on the surface of the soil for a few days for drying, then placed in nets, roped into strings, or laid in layers in shallow boxes. They are stored effectively in a well-ventilated, cool place.[15]
+Onions suffer from a number of plant disorders. The most serious for the home gardener are likely to be the onion fly, stem and bulb eelworm, white rot, and neck rot. Diseases affecting the foliage include rust and smut, downy mildew, and white tip disease. The bulbs may be affected by splitting, white rot, and neck rot. Shanking is a condition in which the central leaves turn yellow and the inner part of the bulb collapses into an unpleasant-smelling slime. Most of these disorders are best treated by removing and burning affected plants.[63] The larvae of the onion leaf miner or leek moth (Acrolepiopsis assectella) sometimes attack the foliage and may burrow down into the bulb.[64]
+The onion fly (Delia antiqua) lays eggs on the leaves and stems and on the ground close to onion, shallot, leek, and garlic plants. The fly is attracted to the crop by the smell of damaged tissue and is liable to occur after thinning. Plants grown from sets are less prone to attack. The larvae tunnel into the bulbs and the foliage wilts and turns yellow. The bulbs are disfigured and rot, especially in wet weather. Control measures may include crop rotation, the use of seed dressings, early sowing or planting, and the removal of infested plants.[65]
+The onion eelworm (Ditylenchus dipsaci), a tiny parasitic soil-living nematode, causes swollen, distorted foliage. Young plants are killed and older ones produce soft bulbs. No cure is known and affected plants should be uprooted and burned. The site should not be used for growing onions again for several years and should also be avoided for growing carrots, parsnips, and beans, which are also susceptible to the eelworm.[66]
+White rot of onions, leeks, and garlic is caused by the soil-borne fungus Sclerotium cepivorum. As the roots rot, the foliage turns yellow and wilts. The bases of the bulbs are attacked and become covered by a fluffy white mass of mycelia, which later produces small, globular black structures called sclerotia. These resting structures remain in the soil to reinfect a future crop. No cure for this fungal disease exists, so affected plants should be removed and destroyed and the ground used for unrelated crops in subsequent years.[67]
+Neck rot is a fungal disease affecting onions in storage. It is caused by Botrytis allii, which attacks the neck and upper parts of the bulb, causing a grey mould to develop. The symptoms often first occur where the bulb has been damaged and spread downwards in the affected scales. Large quantities of spores are produced and crust-like sclerotia may also develop. In time, a dry rot sets in and the bulb becomes a dry, mummified structure. This disease may be present throughout the growing period, but only manifests itself when the bulb is in storage. Antifungal seed dressings are available and the disease can be minimised by preventing physical damage to the bulbs at harvesting, careful drying and curing of the mature onions, and correct storage in a cool, dry place with plenty of circulating air.[68]
+In 2018, world production of onions and shallots (as green produce) was 5.5 million tonnes. led by China with 17% of the world total, and Mali, Niger, and Japan as secondary producers.[69]
+Cooking onions and sweet onions are better stored at room temperature, optimally in a single layer, in mesh bags in a dry, cool, dark, well-ventilated location. In this environment, cooking onions have a shelf life of three to four weeks and sweet onions one to two weeks. Cooking onions will absorb odours from apples and pears. Also, they draw moisture from vegetables with which they are stored which may cause them to decay.[59][70]
+Sweet onions have a greater water and sugar content than cooking onions. This makes them sweeter and milder tasting, but reduces their shelf life. Sweet onions can be stored refrigerated; they have a shelf life of around 1 month. Irrespective of type, any cut pieces of onion are best tightly wrapped, stored away from other produce, and used within two to three days.[43]
+Most of the diversity within A. cepa occurs within this group, the most economically important Allium crop. Plants within this group form large single bulbs, and are grown from seed or seed-grown sets. The majority of cultivated varieties grown for dry bulbs, salad onions, and pickling onions belong to this group.[14] The range of diversity found among these cultivars includes variation in photoperiod (length of day that triggers bulbing), storage life, flavour, and skin colour.[71] Common onions range from the pungent varieties used for dried soups and onion powder to the mild and hearty sweet onions, such as the Vidalia from Georgia, USA, or Walla Walla from Washington that can be sliced and eaten raw on a sandwich.
+This group contains shallots and potato onions, also referred to as multiplier onions. The bulbs are smaller than those of common onions, and a single plant forms an aggregate cluster of several bulbs from a master. They are propagated almost exclusively from daughter bulbs, although reproduction from seed is possible. Shallots are the most important subgroup within this group and comprise the only cultivars cultivated commercially. They form aggregate clusters of small, narrowly ovoid to pear-shaped bulbs. Potato onions differ from shallots in forming larger bulbs with fewer bulbs per cluster, and having a flattened (onion-like) shape. However, intermediate forms exist.[14]
+I'itoi onion is a prolific multiplier onion cultivated in the Baboquivari Peak Wilderness, Arizona area. This small-bulb type has a shallot-like flavour and is easy to grow and ideal for hot, dry climates. Bulbs are separated, and planted in the fall 1 in below the surface and 12 in apart. Bulbs will multiply into clumps and can be harvested throughout the cooler months. Tops die back in the heat of summer and may return with heavy rains; bulbs can remain in the ground or be harvested and stored in a cool dry place for planting in the fall. The plants rarely flower; propagation is by division.[72]
+A number of hybrids are cultivated that have A. cepa parentage, such as the diploid tree onion or Egyptian onion (A. ×proliferum), and the triploid onion (A. ×cornutum).
+The tree onion or Egyptian onion produces bulblets in the umbel instead of flowers, and is now known to be a hybrid of A. cepa and A. fistulosum. It has previously been treated as a variety of A. cepa, for example A. cepa var. proliferum, A. cepa var. bulbiferum, and A. cepa var. viviparum.[73][74] It has been grown for centuries in Japan and China for use as a salad onion.[75][6]
+The triploid onion is a hybrid species with three sets of chromosomes, two sets from A. cepa and the third set from an unknown parent.[74] Various clones of the triploid onion are grown locally in different regions, such as 'Ljutika' in Croatia, and 'Pran', 'Poonch', and 'Srinagar' in the India-Kashmir region. 'Pran' is grown extensively in the northern Indian provinces of Jammu and Kashmir. There are very small genetic differences between 'Pran' and the Croatian clone 'Ljutika', implying a monophyletic origin for this species.[76]
+Some authors have used the name A. cepa var. viviparum (Metzg.) Alef. for the triploid onion, but this name has also been applied to the Egyptian onion. The only name unambiguously connected with the triploid onion is A. ×cornutum.
+Spring onions or salad onions may be grown from the Welsh onion (A. fistulosum), as well as from A. cepa. Young plants of A. fistulosum and A. cepa look very similar, but may be distinguished by their leaves, which are circular in cross-section in A. fistulosum rather than flattened on one side.[77]

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+Ohio /oʊˈhaɪoʊ/ (listen) is a state in the East North Central region of the Midwestern United States. Of the fifty states, it is the 34th largest by area, the seventh most populous, and the tenth most densely populated. The state's capital and largest city is Columbus. Ohio is bordered by Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the west, and Michigan to the northwest.
+The state takes its name from the Ohio River, whose name in turn originated from the Seneca word  ohiːyo', meaning "good river", "great river" or "large creek".[15][16][17] Partitioned from the Northwest Territory, Ohio was the 17th state admitted to the Union on March 1, 1803, and the first under the Northwest Ordinance.[4][18] Ohio is historically known as the "Buckeye State" after its Ohio buckeye trees, and Ohioans are also known as "Buckeyes".[12]
+Ohio rose from the land west of Appalachia in colonial times through the Northwest Indian Wars as part of the Northwest Territory in the early frontier, to become the first non-colonial free state admitted to the union, to an industrial powerhouse in the 20th century before transitioning to a more information and service based economy in the 21st.
+The government of Ohio is composed of the executive branch, led by the governor; the legislative branch, which comprises the bicameral Ohio General Assembly; and the judicial branch, led by the state Supreme Court. Ohio occupies 16 seats in the United States House of Representatives.[19] Ohio is known for its status as both a swing state and a bellwether in national elections.[20] Seven presidents of the United States have come from Ohio.
+Ohio is an industrial state, ranking 8th out of 50 states in GDP (2015), is the third largest US state for manufacturing,[21] and is the second largest producer of automobiles behind Michigan.
+Ohio's geographic location has proven to be an asset for economic growth and expansion. Because Ohio links the Northeast to the Midwest, much cargo and business traffic passes through its borders along its well-developed highways. Ohio has the nation's 10th largest highway network and is within a one-day drive of 50% of North America's population and 70% of North America's manufacturing capacity.[22] To the north, Lake Erie gives Ohio 312 miles (502 km) of coastline,[23] which allows for numerous cargo ports. Ohio's southern border is defined by the Ohio River (with the border being at the 1792 low-water mark on the north side of the river),[24] and much of the northern border is defined by Lake Erie. Ohio's neighbors are Pennsylvania to the east, Michigan to the northwest, Lake Erie to the north, Indiana to the west, Kentucky on the south, and West Virginia on the southeast. Ohio's borders were defined by metes and bounds in the Enabling Act of 1802 as follows:
+Bounded on the east by the Pennsylvania line, on the south by the Ohio River, to the mouth of the Great Miami River, on the west by the line drawn due north from the mouth of the Great Miami aforesaid, and on the north by an east and west line drawn through the southerly extreme of Lake Michigan, running east after intersecting the due north line aforesaid, from the mouth of the Great Miami until it shall intersect Lake Erie or the territorial line, and thence with the same through Lake Erie to the Pennsylvania line aforesaid.
+Ohio is bounded by the Ohio River, but nearly all of the river itself belongs to Kentucky and West Virginia. In 1980, the U.S. Supreme Court held that, based on the wording of the cessation of territory by Virginia (which at the time included what is now Kentucky and West Virginia), the boundary between Ohio and Kentucky (and, by implication, West Virginia) is the northern low-water mark of the river as it existed in 1792.[24] Ohio has only that portion of the river between the river's 1792 low-water mark and the present high-water mark.
+The border with Michigan has also changed, as a result of the Toledo War, to angle slightly northeast to the north shore of the mouth of the Maumee River.
+Much of Ohio features glaciated till plains, with an exceptionally flat area in the northwest being known as the Great Black Swamp. This glaciated region in the northwest and central state is bordered to the east and southeast first by a belt known as the glaciated Allegheny Plateau, and then by another belt known as the unglaciated Allegheny Plateau. Most of Ohio is of low relief, but the unglaciated Allegheny Plateau features rugged hills and forests.
+The rugged southeastern quadrant of Ohio, stretching in an outward bow-like arc along the Ohio River from the West Virginia Panhandle to the outskirts of Cincinnati, forms a distinct socio-economic unit. Geologically similar to parts of West Virginia and southwestern Pennsylvania, this area's coal mining legacy, dependence on small pockets of old manufacturing establishments, and distinctive regional dialect set this section off from the rest of the state. In 1965 the United States Congress passed the Appalachian Regional Development Act, an attempt to "address the persistent poverty and growing economic despair of the Appalachian Region".[25] This act defines 29 Ohio counties as part of Appalachia.[26] While 1/3 of Ohio's land mass is part of the federally defined Appalachian region, only 12.8% of Ohioans live there (1.476 million people.)[27]
+Significant rivers within the state include the Cuyahoga River, Great Miami River, Maumee River, Muskingum River, and Scioto River. The rivers in the northern part of the state drain into the northern Atlantic Ocean via Lake Erie and the St. Lawrence River, and the rivers in the southern part of the state drain into the Gulf of Mexico via the Ohio River and then the Mississippi.
+The worst weather disaster in Ohio history occurred along the Great Miami River in 1913. Known as the Great Dayton Flood, the entire Miami River watershed flooded, including the downtown business district of Dayton. As a result, the Miami Conservancy District was created as the first major flood plain engineering project in Ohio and the United States.[28]
+Grand Lake St. Marys in the west-central part of the state was constructed as a supply of water for canals in the canal-building era of 1820–1850. For many years this body of water, over 20 square miles (52 km2), was the largest artificial lake in the world. Ohio's canal-building projects were not the economic fiasco that similar efforts were in other states. Some cities, such as Dayton, owe their industrial emergence to location on canals, and as late as 1910 interior canals carried much of the bulk freight of the state.
+The climate of Ohio is a humid continental climate (Köppen climate classification Dfa/Dfb) throughout most of the state, except in the extreme southern counties of Ohio's Bluegrass region section, which are located on the northern periphery of the humid subtropical climate (Cfa) and Upland South region of the United States. Summers are typically hot and humid throughout the state, while winters generally range from cool to cold. Precipitation in Ohio is moderate year-round. Severe weather is not uncommon in the state, although there are typically fewer tornado reports in Ohio than in states located in what is known as the Tornado Alley. Severe lake effect snowstorms are also not uncommon on the southeast shore of Lake Erie, which is located in an area designated as the Snowbelt.
+Although predominantly not in a subtropical climate, some warmer-climate flora and fauna do reach well into Ohio. For instance, some trees with more southern ranges, such as the blackjack oak, Quercus marilandica, are found at their northernmost in Ohio just north of the Ohio River. Also evidencing this climatic transition from a subtropical to continental climate, several plants such as the Southern magnolia (Magnolia grandiflora), Albizia julibrissin (mimosa), Crape Myrtle, and even the occasional needle palm are hardy landscape materials regularly used as street, yard, and garden plantings in the Bluegrass region of Ohio; but these same plants will simply not thrive in much of the rest of the state. This interesting change may be observed while traveling through Ohio on Interstate 75 from Cincinnati to Toledo; the observant traveler of this diverse state may even catch a glimpse of Cincinnati's common wall lizard, one of the few examples of permanent "subtropical" fauna in Ohio.
+Due to flooding resulting in severely damaged highways, Governor Mike DeWine declared a state of emergency in 37 Ohio counties in 2019.[29]
+The highest recorded temperature was 113 °F (45 °C), near Gallipolis on July 21, 1934.[31]
+The lowest recorded temperature was −39 °F (−39 °C), at Milligan on February 10, 1899,[32] during the Great Blizzard of 1899.[33]
+Although few have registered as noticeable to the average resident, more than 200 earthquakes with a magnitude of 2.0 or higher have occurred in Ohio since 1776.[34] The Western Ohio Seismic Zone and a portion of the Southern Great Lakes Seismic Zone are located in the state, and numerous faults lie under the surface.[34][35]
+The most substantial known earthquake in Ohio history was the Anna (Shelby County) earthquake,[36] which occurred on March 9, 1937. It was centered in western Ohio, and had a magnitude of 5.4, and was of intensity VIII.[37]
+Other significant earthquakes in Ohio include:[38] one of magnitude 4.8 near Lima on September 19, 1884;[39] one of magnitude 4.2 near Portsmouth on May 17, 1901;[40] and one of 5.0 in LeRoy Township in Lake County on January 31, 1986, which continued to trigger 13 aftershocks of magnitude 0.5 to 2.4 for two months.[41][42]
+Notable Ohio earthquakes in the 21st century include one occurring on December 31, 2011, approximately 4 kilometers (2.5 mi) northwest of Youngstown,[43] and one occurring on June 10, 2019, approximately 5 kilometers (3.1 mi) north-northwest of Eastlake under Lake Erie;[44] both registered a 4.0 magnitude.
+Columbus is both the capital of Ohio and its largest city, located near the geographic center of the state and well known for The Ohio State University. However, other Ohio cities function as economic and cultural centers of metropolitan areas. Akron, Canton, Cleveland, Mansfield, and Youngstown are in the Northeast, known for major industrial companies Goodyear Tire and Rubber and Timken, top ranked colleges Case Western Reserve University and Kent State University, the Cleveland Clinic, and cultural attractions including the Cleveland Museum of Art, Big Five group Cleveland Orchestra, Playhouse Square, the Pro Football Hall of Fame, and the Rock and Roll Hall of Fame. Lima and Toledo are the major cities in Northwest Ohio. Northwest Ohio is known for its glass making industry, and is home to Owens Corning and Owens-Illinois, two Fortune 500 corporations. Dayton and Springfield are located in the Miami Valley, which is home to the University of Dayton, the Dayton Ballet, and the extensive Wright-Patterson Air Force Base. Cincinnati anchors Southwest Ohio, home of Miami University and the University of Cincinnati, Cincinnati Union Terminal, Cincinnati Symphony Orchestra, and various Fortune 500 companies including Procter & Gamble, Kroger, Macy's, Inc., and Fifth Third Bank. Steubenville is the only metropolitan city in Appalachian Ohio, which is home to Hocking Hills State Park.
+The Cincinnati metropolitan area extends into Kentucky and Indiana, the Steubenville metropolitan area extends into West Virginia, the Toledo metropolitan area extends into Michigan, and the Youngstown metropolitan area extends into Pennsylvania.
+Ohio cities that function as centers of United States micropolitan areas include:
+Archeological evidence of spear points of both the Folsom and Clovis types indicate that the Ohio Valley was inhabited by nomadic people as early as 13,000 BC.[49] These early nomads disappeared from Ohio by 1,000 BC.[49] Between 1,000 and 800 BC, the sedentary Adena culture emerged. The Adena were able to establish "semi-permanent" villages because they domesticated plants, including, sunflowers, and "grew squash and possibly corn"; with hunting and gathering, this cultivation supported more settled, complex villages.[50] The most notable remnant of the Adena culture is the Great Serpent Mound, located in Adams County, Ohio.[50]
+Around 100 BC, the Adena evolved into the Hopewell people who were also mound builders. Their complex, large and technologically sophisticated earthworks can be found in modern-day Marietta, Newark, and Circleville.[51] They were also a prolific trading society, their trading network spanning a third of the continent.[52] The Hopewell disappeared from the Ohio Valley about 600 AD. The Mississippian Culture rose as the Hopewell Culture declined. Many Siouan-speaking peoples from the plains and east coast claim them as ancestors and say they lived throughout the Ohio region until approximately the 13th century.[53]
+There were three other cultures contemporaneous with the Mississippians: the Fort Ancient people, the Whittlesey Focus people[53] and the Monongahela Culture.[54] All three cultures disappeared in the 17th century. Their origins are unknown. The Shawnees may have absorbed the Fort Ancient people.[53] It is also possible that the Monongahela held no land in Ohio during the Colonial Era. The Mississippian Culture were close to and traded extensively with the Fort Ancient people.
+Indians in the Ohio Valley were greatly affected by the aggressive tactics of the Iroquois Confederation, based in central and western New York.[55] After the Beaver Wars in the mid-17th century, the Iroquois claimed much of the Ohio country as hunting and, more importantly, beaver-trapping ground. After the devastation of epidemics and war in the mid-17th century, which largely emptied the Ohio country of indigenous people[dubious  – discuss] by the mid-to-late 17th century, the land gradually became repopulated by the mostly Algonquian. Many of these Ohio-country nations were multi-ethnic (sometimes multi-linguistic) societies born out of the earlier devastation brought about by disease,[clarification needed] war, and subsequent social instability. They subsisted on agriculture (corn, sunflowers, beans, etc.) supplemented by seasonal hunts. By the 18th century, they were part of a larger global economy brought about by European entry into the fur trade.[56]
+The indigenous nations to inhabit Ohio in the historical period[vague] included the Iroquoian,[57] the Algonquian[58] & the Siouan.[59][60][61] Ohio country was also the site of Indian massacres, such as the Yellow Creek Massacre, Gnadenhutten and Pontiac's Rebellion school massacre.[62] Most Native Peoples who remained in Ohio were slowly bought out[where?] and convinced to leave[how?], or ordered to do so by law, in the early 19th century with the Indian Removal Act of 1830.
+During the 18th century, the French set up a system of trading posts to control the fur trade in the region. Beginning in 1754, France and Great Britain fought the French and Indian War. As a result of the Treaty of Paris, the French ceded control of Ohio and the remainder of the Old Northwest to Great Britain.
+Pontiac's Rebellion in the 1760s, however, posed a challenge to British military control.[63] This came to an end with the colonists' victory in the American Revolution. In the Treaty of Paris in 1783, Britain ceded all claims to Ohio country to the United States.
+The United States created the Northwest Territory under the Northwest Ordinance of 1787.[64] Slavery was not permitted in the new territory. Settlement began with the founding of Marietta by the Ohio Company of Associates, which had been formed by a group of American Revolutionary War veterans. Following the Ohio Company, the Miami Company (also referred to as the "Symmes Purchase") claimed the southwestern section, and the Connecticut Land Company surveyed and settled the Connecticut Western Reserve in present-day Northeast Ohio. Territorial surveyors from Fort Steuben began surveying an area of eastern Ohio called the Seven Ranges at about the same time.
+The old Northwest Territory originally included areas previously known as Ohio Country and Illinois Country. As Ohio prepared for statehood, the Indiana Territory was created, reducing the Northwest Territory to approximately the size of present-day Ohio plus the eastern half of the Lower Peninsula of Michigan and the eastern tip of the Upper Peninsula and a sliver of southeastern Indiana called "The Gore".
+Under the Northwest Ordinance, areas could be defined and admitted as states once their population reached 60,000. Although Ohio's population was only 45,000 in December 1801, Congress determined that it was growing rapidly and had already begun the path to statehood. In regards to the Leni Lenape natives, Congress decided that 10,000 acres on the Muskingum River in the present state of Ohio would "be set apart and the property thereof be vested in the Moravian Brethren ... or a society of the said Brethren for civilizing the Indians and promoting Christianity".[65]
+On February 19, 1803, U.S. president Thomas Jefferson signed an act of Congress that approved Ohio's boundaries and constitution.[66] However, Congress had never passed a resolution formally admitting Ohio as the 17th state. The current custom of Congress declaring an official date of statehood did not begin until 1812,[disputed  – discuss] with Louisiana's admission as the 18th state. Although no formal resolution of admission was required, when the oversight was discovered in 1953, as Ohio began preparations for celebrating its sesquicentennial, Ohio congressman George H. Bender introduced a bill in Congress to admit Ohio to the Union retroactive to March 1, 1803, the date on which the Ohio General Assembly first convened.[67] At a special session at the old state capital in Chillicothe, the Ohio state legislature approved a new petition for statehood which was delivered to Washington, D.C., on horseback. On August 7, 1953 (the year of Ohio's 150th anniversary), President Eisenhower signed a congressional joint resolution that officially declared March 1, 1803, the date of Ohio's admittance into the Union.[67][68][69]
+Ohio has had three capital cities: Chillicothe, Zanesville, and Columbus. Chillicothe was the capital from 1803 to 1810. The capital was then moved to Zanesville for two years, as part of a state legislative compromise to get a bill passed. The capital was then moved back to Chillicothe, which was the capital from 1812 to 1816. Finally, the capital was moved to Columbus, to have it near the geographic center of the state.
+Although many Native Americans had migrated west to evade American encroachment, others remained settled in the state, sometimes assimilating in part. In 1830 under President Andrew Jackson, the US government forced Indian Removal of most tribes to the Indian Territory west of the Mississippi River.
+In 1835, Ohio fought with Michigan in the Toledo War, a mostly bloodless boundary war over the Toledo Strip. Only one person was injured in the conflict. Congress intervened, making Michigan's admittance as a state conditional on ending the conflict. In exchange for giving up its claim to the Toledo Strip, Michigan was given the western two-thirds of the Upper Peninsula, in addition to the eastern third which was already considered part of the state.
+Ohio's central position and its population gave it an important place during the Civil War. The Ohio River was a vital artery for troop and supply movements, as were Ohio's railroads. The industry of Ohio made the state one of the most important states in the Union during the Civil war. Ohio contributed more soldiers per-capita than any other state in the Union. In 1862, the state's morale was badly shaken in the aftermath of the Battle of Shiloh, a costly victory in which Ohio forces suffered 2,000 casualties.[70] Later that year, when Confederate troops under the leadership of Stonewall Jackson threatened Washington, D.C., Ohio governor David Tod still could recruit 5,000 volunteers to provide three months of service.[71] From July 12 to July 23, 1863, Southern Ohio and Indiana were attacked in Morgan's Raid. While this raid was insignificant and small, it aroused fear among people in Ohio and Indiana.[72] Almost 35,000 Ohioans died in the conflict, and 30,000 were physically wounded.[73] By the end of the Civil War, the Union's top three generals–Ulysses S. Grant, William Tecumseh Sherman, and Philip Sheridan–were all from Ohio.[74][75]
+In 1912 a Constitutional Convention was held with Charles Burleigh Galbreath as secretary. The result reflected the concerns of the Progressive Era. It introduced the initiative and the referendum. Also, it allowed the General Assembly to put questions on the ballot for the people to ratify laws and constitutional amendments originating in the Legislature. Under the Jeffersonian principle that laws should be reviewed once a generation, the constitution provided for a recurring question to appear on Ohio's general election ballots every 20 years. The question asks whether a new convention is required. Although the question has appeared in 1932, 1952, 1972, and 1992, it has never been approved. Instead, constitutional amendments have been proposed by petition to the legislature hundreds of times and adopted in a majority of cases.
+From just over 45,000 residents in 1800, Ohio's population grew faster than 10% per decade (except for the 1940 census) until the 1970 census, which recorded just over 10.65 million Ohioans.[78] Growth then slowed for the next four decades.[79] The United States Census Bureau estimates that the population of Ohio was 11,689,100 on July 1, 2019, a 1.32% increase since the 2010 United States Census.[77] Ohio's population growth lags that of the entire United States, and Caucasians are found in a greater density than the United States average. As of 2000[update], Ohio's center of population is located in Morrow County,[80] in the county seat of Mount Gilead.[81] This is approximately 6,346 feet (1,934 m) south and west of Ohio's population center in 1990.[80]
+As of 2011, 27.6% of Ohio's children under the age of 1 belonged to minority groups.[82]
+6.2% of Ohio's population is under five years of age, 23.7 percent under 18 years of age, and 14.1 percent were 65 or older. Females made up approximately 51.2 percent of the population.
+Note: Births in table don't add up, because Hispanics are counted both by their ethnicity and by their race, giving a higher overall number.
+According to the 2010 United States Census, the racial composition of Ohio was the following:[89][90]
+In 2010, there were 469,700 foreign-born residents in Ohio, corresponding to 4.1% of the total population. Of these, 229,049 (2.0%) were naturalized US citizens and 240,699 (2.1%) were not.[13] The largest groups were:[94] Mexico (54,166), India (50,256), China (34,901), Germany (19,219), Philippines (16,410), United Kingdom (15,917), Canada (14,223), Russia (11,763), South Korea (11,307), and Ukraine (10,681). Though predominantly white, Ohio has large black populations in all major metropolitan areas throughout the state, Ohio has a significant Hispanic population made up of Mexicans in Toledo and Columbus, and Puerto Ricans in Cleveland and Columbus, and also has a significant and diverse Asian population in Columbus.
+The largest ancestry groups (which the Census defines as not including racial terms) in the state are:[13][95]
+Ancestries claimed by less than 1% of the population include Sub-Saharan African, Puerto Rican, Swiss, Swedish, Arab, Greek, Norwegian, Romanian, Austrian, Lithuanian, Finnish, West Indian, Portuguese and Slovene.
+About 6.7% of the population age 5 years and older reported speaking a language other than English, with 2.2% of the population speaking Spanish, 2.6% speaking other Indo-European languages, 1.1% speaking Asian and Austronesian languages, and 0.8% speaking other languages.[13] Numerically: 10,100,586 spoke English, 239,229 Spanish, 55,970 German, 38,990 Chinese, 33,125 Arabic, and 32,019 French. In addition 59,881 spoke a Slavic language and 42,673 spoke another West Germanic language according to the 2010 Census.[96] Ohio also had the nation's largest population of Slovene speakers, second largest of Slovak speakers, second largest of Pennsylvania Dutch (German) speakers, and the third largest of Serbian speakers.[97]
+According to a Pew Forum poll, as of 2008, 76% of Ohioans identified as Christian.[98] Specifically, 26% of Ohio's population identified as Evangelical Protestant, 22% as Mainline Protestant, and 21% as Catholic.[98] 17% of the population is unaffiliated with any religious body.[98] 1.3% (148,380) were Jewish.[99] There are also small minorities of Jehovah's Witnesses (1%), Muslims (1%), Hindus (<0.5%), Buddhists (<0.5%), Mormons (<0.5%), and other faiths (1-1.5%).[98]
+According to the Association of Religion Data Archives (ARDA), in 2010 the largest denominations by adherents were the Catholic Church with 1,992,567; the United Methodist Church with 496,232; the Evangelical Lutheran Church in America with 223,253, the Southern Baptist Convention with 171,000, the Christian Churches and Churches of Christ with 141,311, the United Church of Christ with 118,000, and the Presbyterian Church (USA) with 110,000.[100] With about 70,000 people in 2015 Ohio had the second largest Amish population of all states of the US.[101]
+According to the same data, a majority of Ohioans, 55%, feel religion is "very important", 30% that it is "somewhat important", and 15% that religion is "not too important/not important at all".[98] 36% of Ohioans indicate that they attend religious services at least once weekly, 35% occasionally, and 27% seldom or never.[98]
+According to the U.S. Census Bureau, the total number for employment in 2016 was 4,790,178. The total number of unique employer establishments was 252,201, while the total number of nonemployer establishments was 785,833.[103] In 2010, Ohio was ranked second in the country for best business climate by Site Selection magazine, based on a business-activity database.[104] The state has also won three consecutive Governor's Cup awards from the magazine, based on business growth and developments.[105] As of 2016[update], Ohio's gross domestic product (GDP) was $626 billion.[106] This ranks Ohio's economy as the seventh-largest of all fifty states and the District of Columbia.[107]
+The Small Business & Entrepreneurship Council ranked the state No. 10 for best business-friendly tax systems in their Business Tax Index 2009, including a top corporate tax and capital gains rate that were both ranked No. 6 at 1.9%.[108] Ohio was ranked No. 11 by the council for best friendly-policy states according to their Small Business Survival Index 2009.[109] The Directorship's Boardroom Guide ranked the state No. 13 overall for best business climate, including No. 7 for best litigation climate.[110] Forbes ranked the state No. 8 for best regulatory environment in 2009.[111] Ohio has five of the top 115 colleges in the nation, according to U.S. News and World Report's 2010 rankings,[112] and was ranked No. 8 by the same magazine in 2008 for best high schools.[113]
+Ohio's unemployment rate stands at 4.5% as of February 2018,[114] down from 10.7% in May 2010.[115][116] The state still lacks 45,000 jobs compared to the pre-recession numbers of 2007.[117] The labor force participation as of April 2015 is 63%, slightly above the national average.[117] Ohio's per capita income stands at $34,874.[107][118] As of 2016[update], Ohio's median household income is $52,334,[119] and 14.6% of the population is below the poverty line[120]
+The manufacturing and financial activities sectors each compose 18.3% of Ohio's GDP, making them Ohio's largest industries by percentage of GDP.[107] Ohio has the third largest manufacturing workforce behind California and Texas.[121][122] Ohio has the largest bioscience sector in the Midwest, and is a national leader in the "green" economy. Ohio is the largest producer in the country of plastics, rubber, fabricated metals, electrical equipment, and appliances.[123] 5,212,000 Ohioans are currently employed by wage or salary.[107]
+By employment, Ohio's largest sector is trade/transportation/utilities, which employs 1,010,000 Ohioans, or 19.4% of Ohio's workforce, while the health care and education sector employs 825,000 Ohioans (15.8%).[107] Government employs 787,000 Ohioans (15.1%), manufacturing employs 669,000 Ohioans (12.9%), and professional and technical services employs 638,000 Ohioans (12.2%).[107] Ohio's manufacturing sector is the third-largest of all fifty United States states in terms of gross domestic product.[107] Fifty-nine of the United States' top 1,000 publicly traded companies (by revenue in 2008) are headquartered in Ohio, including Procter & Gamble, Goodyear Tire & Rubber, AK Steel, Timken, Abercrombie & Fitch, and Wendy's.[124]
+Ohio is also one of 41 states with its own lottery,[125] the Ohio Lottery.[126] The Ohio Lottery has contributed over $15.5 billion to public education in its 34-year history.[127]
+Many major east–west transportation corridors go through Ohio. One of those pioneer routes, known in the early 20th century as "Main Market Route 3", was chosen in 1913 to become part of the historic Lincoln Highway which was the first road across America, connecting New York City to San Francisco. In Ohio, the Lincoln Highway linked many towns and cities together, including Canton, Mansfield, Wooster, Lima, and Van Wert. The arrival of the Lincoln Highway to Ohio was a major influence on the development of the state. Upon the advent of the federal numbered highway system in 1926, the Lincoln Highway through Ohio became U.S. Route 30.
+Ohio also is home to 228 miles (367 km) of the Historic National Road, now U.S. Route 40.
+Ohio has a highly developed network of roads and interstate highways. Major east-west through routes include the Ohio Turnpike (I-80/I-90) in the north, I-76 through Akron to Pennsylvania, I-70 through Columbus and Dayton, and the Appalachian Highway (State Route 32) running from West Virginia to Cincinnati. Major north–south routes include I-75 in the west through Toledo, Dayton, and Cincinnati, I-71 through the middle of the state from Cleveland through Columbus and Cincinnati into Kentucky, and I-77 in the eastern part of the state from Cleveland through Akron, Canton, New Philadelphia and Marietta south into West Virginia. Interstate 75 between Cincinnati and Dayton is one of the heaviest traveled sections of interstate in Ohio.
+Ohio also has a highly developed network of signed state bicycle routes. Many of them follow rail trails, with conversion ongoing. The Ohio to Erie Trail (route 1) connects Cincinnati, Columbus, and Cleveland. U.S. Bicycle Route 50 traverses Ohio from Steubenville to the Indiana state line outside Richmond.[128]
+Ohio has several long-distance hiking trails, the most prominent of which is the Buckeye Trail which extends 1,444 mi (2,324 km) in a loop around the state of Ohio. Part of it is on roads and part is on wooded trail. Additionally, the North Country Trail (the longest of the eleven National Scenic Trails authorized by Congress) and the American Discovery Trail (a system of recreational trails and roads that collectively form a coast-to-coast route across the mid-tier of the United States) pass through Ohio. Much of these two trails coincide with the Buckeye Trail.
+Ohio has five international airports, four commercial, and two military. The five international include Cleveland Hopkins International Airport, John Glenn Columbus International Airport, and Dayton International Airport, Ohio's third largest airport. Akron Fulton International Airport handles cargo and for private use. Rickenbacker International Airport is one of two military airfields which is also home to the 7th largest FedEx building in America.[citation needed] The other military airfield is Wright Patterson Air Force Base which is one of the largest Air Force bases in the United States. Other major airports are located in Toledo and Akron.
+Cincinnati/Northern Kentucky International Airport is in Hebron, Kentucky, and therefore is not listed above.
+The state government of Ohio consists of the executive, judicial, and legislative branches.[129][130][131]
+The executive branch is headed by the governor of Ohio.[129] The current governor is Mike DeWine since 2019, a member of the Republican Party.[132] A lieutenant governor succeeds the governor in the event of any removal from office, and performs any duties assigned by the governor.[133][134] The current lieutenant governor is Jon A. Husted. The other elected constitutional offices in the executive branch are the secretary of state (Frank LaRose), auditor (Keith Faber), treasurer (Robert Sprague), and attorney general (Dave Yost).[129]
+There are three levels of the Ohio state judiciary. The lowest level is the court of common pleas: each county maintains its own constitutionally mandated court of common pleas, which maintain jurisdiction over "all justiciable matters".[135] The intermediate-level court system is the district court system.[136] Twelve courts of appeals exist, each retaining jurisdiction over appeals from common pleas, municipal, and county courts in a set geographical area.[135] A case heard in this system is decided by a three-judge panel, and each judge is elected.[135]
+The highest-ranking court, the Ohio Supreme Court, is Ohio's "court of last resort".[137] A seven-justice panel composes the court, which, by its own discretion, hears appeals from the courts of appeals, and retains original jurisdiction over limited matters.[138]
+The Ohio General Assembly is a bicameral legislature consisting of the Senate and House of Representatives.[139] The Senate is composed of 33 districts, each of which is represented by one senator. Each senator represents approximately 330,000 constituents.[140] The House of Representatives is composed of 99 members.[141]
+Eight US presidents hailed from Ohio at the time of their elections, giving rise to its nickname "mother of presidents", a sobriquet it shares with Virginia. It is also termed "modern mother of presidents",[142] in contrast to Virginia's status as the origin of presidents earlier in American history. Seven presidents were born in Ohio, making it second to Virginia's eight. Virginia-born William Henry Harrison lived most of his life in Ohio and is also buried there. Harrison conducted his political career while living on the family compound, founded by his father-in-law, John Cleves Symmes, in North Bend, Ohio. The seven presidents born in Ohio were Ulysses S. Grant, Rutherford B. Hayes, James A. Garfield, Benjamin Harrison (grandson of William Henry Harrison), William McKinley, William Howard Taft and Warren G. Harding.[143] All seven were Republicans.
+Ohio is considered a swing state, being won by either the Democratic or Republican candidates reasonably each election. As a swing state, Ohio is usually targeted by both major-party campaigns, especially in competitive elections.[144] Pivotal in the election of 1888, Ohio has been a regular swing state since 1980.[145][146]
+Additionally, Ohio is considered a bellwether. Historian R. Douglas Hurt asserts that not since Virginia "had a state made such a mark on national political affairs".[147] The Economist notes that "This slice of the mid-west contains a bit of everything American—part north-eastern and part southern, part urban and part rural, part hardscrabble poverty and part booming
+suburb",[148] Since 1896, Ohio has had only two misses in the general election (Thomas E. Dewey in 1944 and Richard Nixon in 1960) and has the longest perfect streak of any state, voting for the winning presidential candidate in each election since 1964, and in 33 of the 37 held since the Civil War. No Republican has ever won the presidency without winning Ohio.
+As of 2019, there are more than 7.8 million registered Ohioan voters, with 1.3 million Democrats and 1.9 million Republicans. They are disproportionate in age, with a million more over 65 than there are 18- to 24-year-olds.[149] Since the 2010 midterm elections, Ohio's voter demographic has leaned towards the Republican Party.[150] The governor, Mike DeWine, is Republican, as well as all other non-judicial statewide elected officials, including Lieutenant Governor Jon A. Husted, Attorney General Dave Yost, State Auditor Keith Faber, Secretary of State Frank LaRose and State Treasurer Robert Sprague. In the Ohio State Senate the Republicans are the majority, 24–9, and in the Ohio House of Representatives the Republicans control the delegation 61–38.
+Losing two seats in the U.S. House of Representatives following the 2010 Census, Ohio has had 16 seats for the three presidential elections of the decade in 2012, 2016 and 2020.[151] As of the 2018 midterms, twelve federal representatives are Republicans while four are Democrats. Marcy Kaptur (D-09) is the most senior member of the Ohio delegation to the U.S. House of Representatives.[152] The senior U.S. senator, Sherrod Brown, is a Democrat, while the junior, Rob Portman, is a Republican.[153][154]
+Since 1994, the state has had a policy of purging infrequent voters from its rolls. In April 2016, a lawsuit was filed, challenging this policy on the grounds that it violated the National Voter Registration Act (NVRA) of 1993[155] and the Help America Vote Act of 2002.[156] In June, the federal district court ruled for the plaintiffs and entered a preliminary injunction applicable only to the November 2016 election. The preliminary injunction was upheld in September by the Court of Appeals for the Sixth Circuit. Had it not been upheld, thousands of voters would have been purged from the rolls just a few weeks before the election.[155]
+Still, it has been estimated that the state has removed up to two million voters since 2011.[157]
+Ohio's system of public education is outlined in Article VI of the state constitution, and in Title XXXIII of the Ohio Revised Code. Ohio University, the first university in the Northwest Territory, was also the first public institution in Ohio. Substantively, Ohio's system is similar to those found in other states. At the State level, the Ohio Department of Education, which is overseen by the Ohio State Board of Education, governs primary and secondary educational institutions. At the municipal level, there are approximately 700 school districts statewide. The Ohio Board of Regents coordinates and assists with Ohio's institutions of higher education which have recently been reorganized into the University System of Ohio under Governor Strickland. The system averages an annual enrollment of more than 400,000 students, making it one of the five largest state university systems in the U.S.
+Ohio schools consistently ranking in the top 50 nationally of the U.S. News & World Report of liberal arts colleges are Kenyon College, Oberlin College, and Denison University. Ranking in the top 100 nationally of the U.S. News & World Report of national research universities are Case Western Reserve University, Ohio State University and Miami University.[158]
+Ohio is home to some of the nation's highest-ranked public libraries.[159] The 2008 study by Thomas J. Hennen Jr. ranked Ohio as number one in a state-by-state comparison.[160] For 2008, 31 of Ohio's library systems were all ranked in the top ten for American cities of their population category.[159]
+The Ohio Public Library Information Network (OPLIN) is an organization that provides Ohio residents with internet access to their 251 public libraries. OPLIN also provides Ohioans with free home access to high-quality, subscription research databases.
+Ohio also offers the OhioLINK program, allowing Ohio's libraries (particularly those from colleges and universities) access to materials for the other libraries. The program is largely successful in allowing researchers for access to books and other media that might not be otherwise available.
+Ohio is home to nine professional sports teams in each of the five different major leagues in the United States. Current teams include the Cincinnati Reds and Cleveland Indians of Major League Baseball,[161][162] the Columbus Crew SC and FC Cincinnati of Major League Soccer,[163] the Cleveland Cavaliers of the National Basketball Association,[164] the Cincinnati Bengals and Cleveland Browns of the National Football League,[165] and the Columbus Blue Jackets of the National Hockey League.[166]
+Ohio has brought home seven World Series titles (Reds 1919, 1940, 1975, 1976, 1990; Indians 1920, 1948), one MLS Cup (Crew 2008), one NBA Championship (Cavaliers 2016), and nine NFL Championships (Pros 1920; Bulldogs 1922, 1923, 1924; Rams 1945; Browns 1950, 1954, 1955, 1964). Despite this success in the NFL in the first half of the 20th century, no Ohio team has won the Super Bowl since its inception in 1967 or made an appearance since 1989. No Ohio team has made an appearance in the Stanley Cup Finals.
+Ohio played a central role in the development of both Major League Baseball and the National Football League. Baseball's first fully professional team, the Cincinnati Red Stockings of 1869, were organized in Ohio.[167] An informal early-20th-century American football association, the Ohio League, was the direct predecessor of the NFL, although neither of Ohio's modern NFL franchises trace their roots to an Ohio League club. The Pro Football Hall of Fame is located in Canton.
+On a smaller scale, Ohio hosts minor league baseball, arena football, indoor football, mid-level hockey, and lower division soccer.
+Winter Guard International has hosted national championships in the UD Arena at the University of Dayton in Dayton, Ohio from 1983 - 1989, 1991 - 1996, 1998 - 2000, 2002 - 2003, and 2005 - 2020.
+The Mid-Ohio Sports Car Course has hosted several auto racing championships, including CART World Series, IndyCar Series, NASCAR Nationwide Series, Can-Am, Formula 5000, IMSA GT Championship, American Le Mans Series and Rolex Sports Car Series.
+The Grand Prix of Cleveland also hosted CART races from 1982 to 2007. The Eldora Speedway is a major dirt oval that hosts NASCAR Camping World Truck Series, World of Outlaws Sprint Cars and USAC Silver Crown Series races.
+Ohio hosts two PGA Tour events, the WGC-Bridgestone Invitational and Memorial Tournament.
+The Cincinnati Masters is an ATP World Tour Masters 1000 and WTA Premier 5 tennis tournament.
+Ohio has eight NCAA Division I Football Bowl Subdivision college football teams, divided among three different conferences. It has also experienced considerable success in the secondary and tertiary tiers of college football divisions.
+There is only one program in the Power Five conferences, the Ohio State Buckeyes, who play in the Big Ten Conference. The football team is fifth in all-time winning percentage, with a 922–326–53 overall record and a 24–26 bowl record as of 2019. The program has produced seven Heisman Trophy winners, forty conference titles, and eight undisputed national championships. The men's basketball program has appeared in the NCAA Division I Men's Basketball Tournament 27 times.
+In the Group of Five conferences, the Cincinnati Bearcats play as a member of the American Athletic Conference. Their men's basketball team has over 1,800 wins, 33 March Madness appearances, and is currently on a nine-year streak of appearances as of 2019. Six teams are represented in the Mid-American Conference: the Akron Zips, Bowling Green Falcons, Kent State Golden Flashes, Miami RedHawks, Ohio Bobcats and the Toledo Rockets. The MAC headquarters are in Cleveland. The Cincinnati–Miami rivalry game has been played in southwest Ohio every year since 1888, and is the oldest current non-conference NCAA football rivalry.
+Other Division I schools, either part of the NCAA Division I Football Championship Subdivision or not fielding in football include the Cleveland State Vikings, Xavier Musketeers, Wright State Raiders, and Youngstown State Penguins. Xavier's men's basketball has performed particularly well, with 27 March Madness appearances. Youngstown State's football has the third most NCAA Division I Football Championship wins, with 3.
+There are 12 NCAA Division II universities and 22 NCAA Division III universities in Ohio.
+Coordinates: 40°30′N 82°30′W / 40.5°N 82.5°W / 40.5; -82.5

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+The onion (Allium cepa L., from Latin cepa "onion"), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus Allium. Its close relatives include the garlic, scallion, shallot, leek, chive,[2] and Chinese onion.[3]
+This genus also contains several other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion (Allium fistulosum), the tree onion (A. ×proliferum), and the Canada onion (Allium canadense). The name "wild onion" is applied to a number of Allium species, but A. cepa is exclusively known from cultivation. Its ancestral wild original form is not known, although escapes from cultivation have become established in some regions.[4] The onion is most frequently a biennial or a perennial plant, but is usually treated as an annual and harvested in its first growing season.
+The onion plant has a fan of hollow, bluish-green leaves and its bulb at the base of the plant begins to swell when a certain day-length is reached. The bulbs are composed of shortened, compressed, underground stems surrounded by fleshy modified scale (leaves) that envelop a central bud at the tip of the stem. In the autumn (or in spring, in the case of overwintering onions), the foliage dies down and the outer layers of the bulb become dry and brittle. The crop is harvested and dried and the onions are ready for use or storage. The crop is prone to attack by a number of pests and diseases, particularly the onion fly, the onion eelworm, and various fungi cause rotting. Some varieties of A. cepa, such as shallots and potato onions, produce multiple bulbs.
+Onions are cultivated and used around the world. As a food item, they are usually served cooked, as a vegetable or part of a prepared savoury dish, but can also be eaten raw or used to make pickles or chutneys. They are pungent when chopped and contain certain chemical substances which irritate the eyes.
+The onion plant (Allium cepa), also known as the bulb onion[5] or common onion,[6] is the most widely cultivated species of the genus Allium.[7][8]  It was first officially described by Carl Linnaeus in his 1753 work Species Plantarum.[9] A number of synonyms have appeared in its taxonomic history:
+A. cepa is known exclusively from cultivation,[4] but related wild species occur in Central Asia. The most closely related species include A. vavilovii (Popov & Vved.) and A. asarense (R.M. Fritsch & Matin) from Iran.[12] However, Zohary and Hopf state that "there are doubts whether the A. vavilovii collections tested represent genuine wild material or only feral derivatives of the crop."[13]
+The vast majority of cultivars of A. cepa belong to the "common onion group" (A. cepa var. cepa) and are usually referred to simply as "onions". The Aggregatum Group of cultivars (A. cepa var. aggregatum) includes both shallots and potato onions.[14]
+The genus Allium also contains a number of other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion (A. fistulosum), Egyptian onion (A. ×proliferum), and Canada onion (A. canadense).[6]
+Cepa is commonly accepted as Latin for "onion" and has an affinity with Ancient Greek: κάπια (kápia) and Albanian: qepë and is ancestral to Aromanian: tseapã, Catalan: ceba, Occitan: ceba, Spanish: cebolla, Italian: cipolla, and Romanian: ceapă. The English word chive is also derived from the Old French cive, which derived from cepa.
+The onion plant has been grown and selectively bred in cultivation for at least 7,000 years.  It is a biennial plant, but is usually grown as an annual. Modern varieties typically grow to a height of 15 to 45 cm (6 to 18 in). The leaves are yellowish- to bluish green and grow alternately in a flattened, fan-shaped swathe. They are fleshy, hollow, and cylindrical, with one flattened side. They are at their broadest about a quarter of the way up, beyond which they taper towards a blunt tip. The base of each leaf is a flattened, usually white sheath that grows out of the basal plate of a bulb. From the underside of the plate, a bundle of fibrous roots extends for a short way into the soil. As the onion matures, food reserves begin to accumulate in the leaf bases and the bulb of the onion swells.[15]
+In the autumn, the leaves die back and the outer scales of the bulb become dry and brittle, so the crop is then normally harvested. If left in the soil over winter, the growing point in the middle of the bulb begins to develop in the spring. New leaves appear and a long, stout, hollow stem expands, topped by a bract protecting a developing inflorescence. The inflorescence takes the form of a globular umbel of white flowers with parts in sixes. The seeds are glossy black and triangular in cross section.[15] The average pH of an onion is around 5.5.[16]
+Because the wild onion is extinct and ancient records of using onions span western and eastern Asia, the geographic origin of the onion is uncertain,[17][18] with likely domestication worldwide.[19] Onions have been variously described as having originated in Iran, the western Indian subcontinent and Central Asia.[17][20][21][22]
+Traces of onions recovered from Bronze Age settlements in China suggest that onions were used as far back as 5000 BCE, not only for their flavour, but the bulb's durability in storage and transport.[23][19][failed verification] Ancient Egyptians revered the onion bulb, viewing its spherical shape and concentric rings as symbols of eternal life.[19] Onions were used in Egyptian burials, as evidenced by onion traces found in the eye sockets of Ramesses IV.[24]
+Pliny the Elder of the first century CE wrote about the use of onions and cabbage in Pompeii. He documented Roman beliefs about the onion's ability to improve ocular ailments, aid in sleep, and heal everything from oral sores and toothaches to dog bites, lumbago, and even dysentery. Archaeologists unearthing Pompeii long after its 79 CE volcanic burial have found gardens resembling those in Pliny's detailed narratives.[19] According to texts collected in the fifth/sixth century CE under the authorial aegis of "Apicius" (said to have been a gourmet), onions were used in many Roman recipes.[19]
+In the Age of Discovery, onions were taken to North America by the first European settlers,[17] only to discover the plant readily available, and in wide use in Native American gastronomy.[17] According to diaries kept by certain of the first English colonists, the bulb onion was one of the first crops planted by the Pilgrim fathers.[19]
+Common onions are normally available in three colour varieties:
+While the large, mature onion bulb is most often eaten, onions can be eaten at immature stages. Young plants may be harvested before bulbing occurs and used whole as spring onions or scallions.  When an onion is harvested after bulbing has begun, but the onion is not yet mature, the plants are sometimes referred to as "summer" onions.[27]
+Additionally, onions may be bred and grown to mature at smaller sizes. Depending on the mature size and the purpose for which the onion is used, these may be referred to as pearl, boiler, or pickler onions, but differ from true pearl onions which are a different species.[27] Pearl and boiler onions may be cooked as a vegetable rather than as an ingredient and pickler onions are often preserved in vinegar as a long-lasting relish.[28]
+Onions are available in fresh, frozen, canned, caramelised, pickled, and chopped forms. The dehydrated product is available as kibbled, sliced, ring, minced, chopped, granulated, and powder forms.
+Onion powder is a seasoning widely used when the fresh ingredient is not available. It is made from finely ground, dehydrated onions, mainly the pungent varieties of bulb onions, and has a strong odour. Being dehydrated, it has a long shelf life and is available in several varieties: yellow, red, and white.[29]
+Onions are commonly chopped and used as an ingredient in various hearty warm dishes, and may also be used as a main ingredient in their own right, for example in French onion soup, creamed onions, and onion chutney. They are versatile and can be baked, boiled, braised, grilled, fried, roasted, sautéed, or eaten raw in salads.[30] Their layered nature makes them easy to hollow out once cooked, facilitating stuffing them, as in Turkish sogan-dolma.
+Onions pickled in vinegar are eaten as a snack around the world, and as a side serving in pubs and fish and chip shops throughout the United Kingdom and the Commonwealth. They are part of a traditional British pub's ploughman's lunch, usually served with crusty bread, English cheese, and ale.
+Similar to garlic,[31] onions can show an additional colour – pink-red – after cutting, an effect caused by reactions of amino acids with sulfur compounds.[32]
+Onions have particularly large cells that are readily observed under low magnification. Forming a single layer of cells, the bulb epidermis is easy to separate for educational, experimental, and breeding purposes.[33][34] Onions are therefore commonly used in science education to teach the use of a microscope for observing cell structure.[35]
+Onions are toxic to dogs, cats, guinea pigs, and many other animals.[36][37]
+Most onion cultivars are about 89% water, 9% carbohydrates (including 4% sugar and 2% dietary fibre), 1% protein, and negligible fat (table). Onions contain low amounts of essential nutrients and have an energy value of 166 kJ (40 Calories) in a 100 g (3.5 oz) amount. Onions contribute savoury flavour to dishes without contributing significant caloric content.[19]
+Considerable differences exist between onion varieties in phytochemical content, particularly for polyphenols, with shallots having the highest level, six times the amount found in Vidalia onions.[38] Yellow onions have the highest total flavonoid content, an amount 11 times higher than in white onions.[38] Red onions have considerable content of anthocyanin pigments, with at least 25 different compounds identified representing 10% of total flavonoid content.[38]
+Onion polyphenols are under basic research to determine their possible biological properties in humans.[38][39]
+Some people suffer from allergic reactions after handling onions.[40] Symptoms can include contact dermatitis, intense itching, rhinoconjunctivitis, blurred vision, bronchial asthma, sweating, and anaphylaxis. Allergic reactions may not occur when eating cooked onions, possibly due to the denaturing of the proteins from cooking.[41]
+Freshly cut onions often cause a stinging sensation in the eyes of people nearby, and often uncontrollable tears. This is caused by the release of a volatile liquid, syn-propanethial-S-oxide and its aerosol, which stimulates nerves in the eye.[7] This gas is produced by a chain of reactions which serve as a defence mechanism: chopping an onion causes damage to cells which releases enzymes called alliinases. These break down amino acid sulfoxides and generate sulfenic acids. A specific sulfenic acid, 1-propenesulfenic acid, is rapidly acted on by a second enzyme, the lacrimatory factor synthase, producing the syn-propanethial-S-oxide.[7] This gas diffuses through the air and soon reaches the eyes, where it activates sensory neurons. Lacrimal glands produce tears to dilute and flush out the irritant.[42]
+Eye irritation can be avoided by cutting onions under running water or submerged in a basin of water.[42] Leaving the root end intact also reduces irritation as the onion base has a higher concentration of sulphur compounds than the rest of the bulb.[43] Refrigerating the onions before use reduces the enzyme reaction rate and using a fan can blow the gas away from the eyes. The more often one chops onions, the less one experiences eye irritation.[44]
+The amount of sulfenic acids and lacrimal factor released and the irritation effect differs among Allium species. In 2008, the New Zealand Institute for Crop and Food Research created "no tears" onions by genetic modification to prevent the synthesis of lachrymatory factor synthase in onions.[45] One study suggests that consumers prefer the flavor of onions with lower LFS content.[46] However, since the LFS-silencing process involves reducing sulfur ingestion by the plant, it has also been suggested that LFS− onions are inferior in flavor.[47] A method for efficiently differentiating LFS− and LFS+ onions has been developed based on mass spectrometry, with potential application in high-volume production;[48] gas chromatography is also used to measure lachrymatory factor in onions.[49][50] In early 2018, Bayer released the first crop yield of commercially available LFS-silenced onions under the name "Sunions."[51] They were the product of 30 years of cross-breeding; genetic modification was not employed.[51][52]
+Guinea hen weed and honey garlic contain a similar lachrymatory factor.[53] Synthetic onion lachrymatory factor has been used in a study related to tear production,[54] and has been proposed as a nonlethal deterrent against thieves and intruders.[55][56]
+Onions are best cultivated in fertile soils that are well-drained. Sandy loams are good as they are low in sulphur, while clayey soils usually have a high sulphur content and produce pungent bulbs. Onions require a high level of nutrients in the soil. Phosphorus is often present in sufficient quantities, but may be applied before planting because of its low level of availability in cold soils. Nitrogen and potash can be applied at regular intervals during the growing season, the last application of nitrogen being at least four weeks before harvesting.[57] Bulbing onions are day-length sensitive; their bulbs begin growing only after the number of daylight hours has surpassed some minimal quantity. Most traditional European onions are referred to as "long-day" onions, producing bulbs only after 14 hours or more of daylight occurs. Southern European and North African varieties are often known as "intermediate-day" types, requiring only 12–13 hours of daylight to stimulate bulb formation. Finally, "short-day" onions, which have been developed in more recent times, are planted in mild-winter areas in the autumn and form bulbs in the early spring, and require only 11–12 hours of daylight to stimulate bulb formation.[58] Onions are a cool-weather crop and can be grown in USDA zones 3 to 9.[59] Hot temperatures or other stressful conditions cause them to "bolt", meaning that a flower stem begins to grow.[60]
+Onions may be grown from seeds or from partially grown bulbs called "sets". Because onion seeds are short-lived, fresh seeds germinate more effectively when sown in shallow drills, then thinning the plants in stages.[59][61] In suitable climates, certain cultivars can be sown in late summer and autumn to overwinter in the ground and produce early crops the following year.[15] Onion bulbs are produced by sowing seeds in a dense pattern in early summer, then harvested in the autumn when the bulbs are still small, followed by drying and storage. These bulbs planted the following spring grow into mature bulbs later in the growing season.[62] Certain cultivars used for growing and storing bulbs may not have such good storage characteristics as those grown directly from seed.[15]
+Routine care during the growing season involves keeping the rows free of competing weeds, especially when the plants are young. The plants are shallow-rooted and do not need much water when established. Bulbing usually takes place after 12 to 18 weeks. The bulbs can be gathered when needed to eat fresh, but if they will be stored, they are harvested after the leaves have died back naturally. In dry weather, they can be left on the surface of the soil for a few days for drying, then placed in nets, roped into strings, or laid in layers in shallow boxes. They are stored effectively in a well-ventilated, cool place.[15]
+Onions suffer from a number of plant disorders. The most serious for the home gardener are likely to be the onion fly, stem and bulb eelworm, white rot, and neck rot. Diseases affecting the foliage include rust and smut, downy mildew, and white tip disease. The bulbs may be affected by splitting, white rot, and neck rot. Shanking is a condition in which the central leaves turn yellow and the inner part of the bulb collapses into an unpleasant-smelling slime. Most of these disorders are best treated by removing and burning affected plants.[63] The larvae of the onion leaf miner or leek moth (Acrolepiopsis assectella) sometimes attack the foliage and may burrow down into the bulb.[64]
+The onion fly (Delia antiqua) lays eggs on the leaves and stems and on the ground close to onion, shallot, leek, and garlic plants. The fly is attracted to the crop by the smell of damaged tissue and is liable to occur after thinning. Plants grown from sets are less prone to attack. The larvae tunnel into the bulbs and the foliage wilts and turns yellow. The bulbs are disfigured and rot, especially in wet weather. Control measures may include crop rotation, the use of seed dressings, early sowing or planting, and the removal of infested plants.[65]
+The onion eelworm (Ditylenchus dipsaci), a tiny parasitic soil-living nematode, causes swollen, distorted foliage. Young plants are killed and older ones produce soft bulbs. No cure is known and affected plants should be uprooted and burned. The site should not be used for growing onions again for several years and should also be avoided for growing carrots, parsnips, and beans, which are also susceptible to the eelworm.[66]
+White rot of onions, leeks, and garlic is caused by the soil-borne fungus Sclerotium cepivorum. As the roots rot, the foliage turns yellow and wilts. The bases of the bulbs are attacked and become covered by a fluffy white mass of mycelia, which later produces small, globular black structures called sclerotia. These resting structures remain in the soil to reinfect a future crop. No cure for this fungal disease exists, so affected plants should be removed and destroyed and the ground used for unrelated crops in subsequent years.[67]
+Neck rot is a fungal disease affecting onions in storage. It is caused by Botrytis allii, which attacks the neck and upper parts of the bulb, causing a grey mould to develop. The symptoms often first occur where the bulb has been damaged and spread downwards in the affected scales. Large quantities of spores are produced and crust-like sclerotia may also develop. In time, a dry rot sets in and the bulb becomes a dry, mummified structure. This disease may be present throughout the growing period, but only manifests itself when the bulb is in storage. Antifungal seed dressings are available and the disease can be minimised by preventing physical damage to the bulbs at harvesting, careful drying and curing of the mature onions, and correct storage in a cool, dry place with plenty of circulating air.[68]
+In 2018, world production of onions and shallots (as green produce) was 5.5 million tonnes. led by China with 17% of the world total, and Mali, Niger, and Japan as secondary producers.[69]
+Cooking onions and sweet onions are better stored at room temperature, optimally in a single layer, in mesh bags in a dry, cool, dark, well-ventilated location. In this environment, cooking onions have a shelf life of three to four weeks and sweet onions one to two weeks. Cooking onions will absorb odours from apples and pears. Also, they draw moisture from vegetables with which they are stored which may cause them to decay.[59][70]
+Sweet onions have a greater water and sugar content than cooking onions. This makes them sweeter and milder tasting, but reduces their shelf life. Sweet onions can be stored refrigerated; they have a shelf life of around 1 month. Irrespective of type, any cut pieces of onion are best tightly wrapped, stored away from other produce, and used within two to three days.[43]
+Most of the diversity within A. cepa occurs within this group, the most economically important Allium crop. Plants within this group form large single bulbs, and are grown from seed or seed-grown sets. The majority of cultivated varieties grown for dry bulbs, salad onions, and pickling onions belong to this group.[14] The range of diversity found among these cultivars includes variation in photoperiod (length of day that triggers bulbing), storage life, flavour, and skin colour.[71] Common onions range from the pungent varieties used for dried soups and onion powder to the mild and hearty sweet onions, such as the Vidalia from Georgia, USA, or Walla Walla from Washington that can be sliced and eaten raw on a sandwich.
+This group contains shallots and potato onions, also referred to as multiplier onions. The bulbs are smaller than those of common onions, and a single plant forms an aggregate cluster of several bulbs from a master. They are propagated almost exclusively from daughter bulbs, although reproduction from seed is possible. Shallots are the most important subgroup within this group and comprise the only cultivars cultivated commercially. They form aggregate clusters of small, narrowly ovoid to pear-shaped bulbs. Potato onions differ from shallots in forming larger bulbs with fewer bulbs per cluster, and having a flattened (onion-like) shape. However, intermediate forms exist.[14]
+I'itoi onion is a prolific multiplier onion cultivated in the Baboquivari Peak Wilderness, Arizona area. This small-bulb type has a shallot-like flavour and is easy to grow and ideal for hot, dry climates. Bulbs are separated, and planted in the fall 1 in below the surface and 12 in apart. Bulbs will multiply into clumps and can be harvested throughout the cooler months. Tops die back in the heat of summer and may return with heavy rains; bulbs can remain in the ground or be harvested and stored in a cool dry place for planting in the fall. The plants rarely flower; propagation is by division.[72]
+A number of hybrids are cultivated that have A. cepa parentage, such as the diploid tree onion or Egyptian onion (A. ×proliferum), and the triploid onion (A. ×cornutum).
+The tree onion or Egyptian onion produces bulblets in the umbel instead of flowers, and is now known to be a hybrid of A. cepa and A. fistulosum. It has previously been treated as a variety of A. cepa, for example A. cepa var. proliferum, A. cepa var. bulbiferum, and A. cepa var. viviparum.[73][74] It has been grown for centuries in Japan and China for use as a salad onion.[75][6]
+The triploid onion is a hybrid species with three sets of chromosomes, two sets from A. cepa and the third set from an unknown parent.[74] Various clones of the triploid onion are grown locally in different regions, such as 'Ljutika' in Croatia, and 'Pran', 'Poonch', and 'Srinagar' in the India-Kashmir region. 'Pran' is grown extensively in the northern Indian provinces of Jammu and Kashmir. There are very small genetic differences between 'Pran' and the Croatian clone 'Ljutika', implying a monophyletic origin for this species.[76]
+Some authors have used the name A. cepa var. viviparum (Metzg.) Alef. for the triploid onion, but this name has also been applied to the Egyptian onion. The only name unambiguously connected with the triploid onion is A. ×cornutum.
+Spring onions or salad onions may be grown from the Welsh onion (A. fistulosum), as well as from A. cepa. Young plants of A. fistulosum and A. cepa look very similar, but may be distinguished by their leaves, which are circular in cross-section in A. fistulosum rather than flattened on one side.[77]

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+Birds are a group of warm-blooded vertebrates constituting the class Aves, characterized by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5 cm (2 in) bee hummingbird to the 2.75 m (9 ft) ostrich. There are about ten thousand living species, more than half of which are passerine, or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in some birds, including ratites, penguins, and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming.
+Birds are a group of feathered theropod dinosaurs, and constitute the only living dinosaurs. Likewise, birds are considered reptiles in the modern cladistic sense of the term, and their closest living relatives are the crocodilians. Birds are descendants of the primitive avialans (whose members include Archaeopteryx) which first appeared about 160 million years ago (mya) in China. According to DNA evidence, modern birds (Neornithes) evolved in the Middle to Late Cretaceous, and diversified dramatically around the time of the Cretaceous–Paleogene extinction event 66 mya, which killed off the pterosaurs and all non-avian dinosaurs.
+Many social species pass on knowledge across generations, which is considered a form of culture. Birds are social, communicating with visual signals, calls, and songs, and participating in such behaviours as cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially (but not necessarily sexually) monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have breeding systems that are polygynous (one male with many females) or, rarely, polyandrous (one female with many males). Birds produce offspring by laying eggs which are fertilised through sexual reproduction. They are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching.
+Many species of birds are economically important as food for human consumption and raw material in manufacturing, with domesticated and undomesticated birds being important sources of eggs, meat, and feathers. Songbirds, parrots, and other species are popular as pets. Guano (bird excrement) is harvested for use as a fertiliser. Birds figure throughout human culture. About 120 to 130 species have become extinct due to human activity since the 17th century, and hundreds more before then. Human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry.
+The first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae.[3]
+Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use.[4] Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda.[5]
+Aves and a sister group, the order Crocodilia, contain the only living representatives of the reptile clade Archosauria. During the late 1990s, Aves was most commonly defined phylogenetically as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica.[6] However, an earlier definition proposed by Jacques Gauthier gained wide currency in the 21st century, and is used by many scientists including adherents of the Phylocode system. Gauthier defined Aves to include only the crown group of the set of modern birds. This was done by excluding most groups known only from fossils, and assigning them, instead, to the broader group Avialae,[7] in part to avoid the uncertainties about the placement of Archaeopteryx in relation to animals traditionally thought of as theropod dinosaurs.
+Gauthier and de Queiroz[8] identified four different definitions for the same biological name "Aves", which is a problem. The authors proposed to reserve the term Aves only for the crown group consisting of the last common ancestor of all living birds and all of its descendants, which corresponds to meaning number 4 below. He assigned other names to the other groups.
+Crocodiles
+Birds
+Turtles
+Lizards (including snakes)
+Under the fourth definition Archaeopteryx, traditionally considered one of the earliest members of Aves, is removed from this group, becoming a non-avian dinosaur instead. These proposals have been adopted by many researchers in the field of palaeontology and bird evolution, though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is often used synonymously with the vernacular term "bird" by these researchers.[9]
+†Coelurus
+†Ornitholestes
+†Ornithomimosauria
+†Alvarezsauridae
+†Oviraptorosauria
+Paraves
+Most researchers define Avialae as branch-based clade, though definitions vary. Many authors have used a definition similar to "all theropods closer to birds than to Deinonychus",[11][12] with Troodon being sometimes added as a second external specifier in case it is closer to birds than to Deinonychus.[13] Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on physical characteristics). Jacques Gauthier, who named Avialae in 1986, re-defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight, and the birds that descended from them.[8][14]
+Despite being currently one of the most widely used, the crown-group definition of Aves has been criticised by some researchers. Lee and Spencer (1997) argued that, contrary to what Gauthier defended, this definition would not increase the stability of the clade and the exact content of Aves will always be uncertain because any defined clade (either crown or not) will have few synapomorphies distinguishing it from its closest relatives. Their alternative definition is synonymous to Avifilopluma.[15]
+†Scansoriopterygidae
+†Eosinopteryx
+†Jinfengopteryx
+†Aurornis
+†Dromaeosauridae
+†Troodontidae
+Avialae
+Based on fossil and biological evidence, most scientists accept that birds are a specialised subgroup of theropod dinosaurs,[18] and more specifically, they are members of Maniraptora, a group of theropods which includes dromaeosaurids and oviraptorosaurs, among others.[19] As scientists have discovered more theropods closely related to birds, the previously clear distinction between non-birds and birds has become blurred. Recent discoveries in the Liaoning Province of northeast China, which demonstrate many small theropod feathered dinosaurs, contribute to this ambiguity.[20][21][22]
+The consensus view in contemporary palaeontology is that the flying theropods, or avialans, are the closest relatives of the deinonychosaurs, which include dromaeosaurids and troodontids.[23] Together, these form a group called Paraves. Some basal members of Deinonychosauria, such as Microraptor, have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal, have been able to glide, or both.[24][25] Unlike Archaeopteryx and the non-avialan feathered dinosaurs, who primarily ate meat, recent studies suggest that the first avialans were omnivores.[26]
+The Late Jurassic Archaeopteryx is well known as one of the first transitional fossils to be found, and it provided support for the theory of evolution in the late 19th century. Archaeopteryx was the first fossil to display both clearly traditional reptilian characteristics—teeth, clawed fingers, and a long, lizard-like tail—as well as wings with flight feathers similar to those of modern birds. It is not considered a direct ancestor of birds, though it is possibly closely related to the true ancestor.[27]
+Over 40% of key traits found in modern birds evolved during the 60 million year transition from the earliest bird-line archosaurs to the first maniraptoromorphs, i.e. the first dinosaurs closer to living birds than to Tyrannosaurus rex. The loss of osteoderms otherwise common in archosaurs and acquisition of primitive feathers might have occurred early during this phase.[10][29] After the appearance of Maniraptoromorpha, the next 40 million years marked a continuous reduction of body size and the accumulation of neotenic (juvenile-like) characteristics. Hypercarnivory became increasingly less common while braincases enlarged and forelimbs became longer.[10] The integument evolved into complex, pennaceous feathers.[29]
+The oldest known paravian (and probably the earliest avialan) fossils come from the Tiaojishan Formation of China, which has been dated to the late Jurassic period (Oxfordian stage), about 160 million years ago. The avialan species from this time period include Anchiornis huxleyi, Xiaotingia zhengi, and Aurornis xui.[9]
+The well-known probable early avialan, Archaeopteryx, dates from slightly later Jurassic rocks (about 155 million years old) from Germany. Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds, but were later lost during bird evolution. These features include enlarged claws on the second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial maneuvering.[30]
+Avialans diversified into a wide variety of forms during the Cretaceous Period. Many groups retained primitive characteristics, such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves).[31] Increasingly stiff tails (especially the outermost half) can be seen in the evolution of maniraptoromorphs, and this process culminated in the appearance of the pygostyle, an ossification of fused tail vertebrae.[10] In the late Cretaceous, about 100 million years ago, the ancestors of all modern birds evolved a more open pelvis, allowing them to lay larger eggs compared to body size.[32] Around 95 million years ago, they evolved a better sense of smell.[33]
+A third stage of bird evolution starting with Ornithothoraces (the "bird-chested" avialans) can be associated with the refining of aerodynamics and flight capabilities, and the loss or co-ossification of several skeletal features. Particularly significant are the development of an enlarged, keeled sternum and the alula, and the loss of grasping hands.
+[10]
+†Anchiornis
+†Archaeopteryx
+†Xiaotingia
+†Rahonavis
+†Jeholornis
+†Jixiangornis
+†Balaur
+†Zhongjianornis
+†Sapeornis
+†Confuciusornithiformes
+†Protopteryx
+†Pengornis
+Ornithothoraces
+†Enantiornithes
+†Archaeorhynchus
+†Patagopteryx
+†Vorona
+†Schizooura
+†Hongshanornithidae
+†Jianchangornis
+†Songlingornithidae
+†Gansus
+†Apsaravis
+†Hesperornithes
+†Ichthyornis
+†Vegavis
+Aves
+The first large, diverse lineage of short-tailed avialans to evolve were the Enantiornithes, or "opposite birds", so named because the construction of their shoulder bones was in reverse to that of modern birds. Enantiornithes occupied a wide array of ecological niches, from sand-probing shorebirds and fish-eaters to tree-dwelling forms and seed-eaters. While they were the dominant group of avialans during the Cretaceous period, enantiornithes became extinct along with many other dinosaur groups at the end of the Mesozoic era.[31]
+Many species of the second major avialan lineage to diversify, the Euornithes (meaning "true birds", because they include the ancestors of modern birds), were semi-aquatic and specialised in eating fish and other small aquatic organisms. Unlike the Enantiornithes, which dominated land-based and arboreal habitats, most early euornithes lacked perching adaptations and seem to have included shorebird-like species, waders, and swimming and diving species.
+The latter included the superficially gull-like Ichthyornis[35] and the Hesperornithiformes, which became so well adapted to hunting fish in marine environments that they lost the ability to fly and became primarily aquatic.[31] The early euornithes also saw the development of many traits associated with modern birds, like strongly keeled breastbones, toothless, beaked portions of their jaws (though most non-avian euornithes retained teeth in other parts of the jaws).[36] Euornithes also included the first avialans to develop true pygostyle and a fully mobile fan of tail feathers,[37] which may have replaced the "hind wing" as the primary mode of aerial maneuverability and braking in flight.[30]
+A study on mosaic evolution in the avian skull found that the last common ancestor of all Neornithes might have had a beak similar to that of the modern hook-billed vanga and a skull similar to that of the Eurasian golden oriole. As both species are small aerial and canopy foraging omnivores, a similar ecological niche was inferred for this hypothetical ancestor.[38]
+Struthioniformes
+Tinamiformes
+Other birds (Neoaves)
+Anseriformes
+Galliformes
+All modern birds lie within the crown group Aves (alternately Neornithes), which has two subdivisions: the Palaeognathae, which includes the flightless ratites (such as the ostriches) and the weak-flying tinamous, and the extremely diverse Neognathae, containing all other birds.[39] These two subdivisions are often given the rank of superorder,[40] although Livezey and Zusi assigned them "cohort" rank.[5] Depending on the taxonomic viewpoint, the number of known living bird species varies anywhere from 9,800[41] to 10,758.[42]
+The discovery of Vegavis, a late Cretaceous member of the Anatidae, proved that the diversification of modern birds started before the Cenozoic era.[43] The affinities of an earlier fossil, the possible galliform Austinornis lentus, dated to about 85 million years ago,[44] are still too controversial to provide a fossil evidence of modern bird diversification.
+Most studies agree on a Cretaceous age for the most recent common ancestor of modern birds but estimates range from the Middle Cretaceous[1] to the latest Late Cretaceous.[45] Similarly, there is no agreement on whether most of the early diversification of modern birds occurred before or after the Cretaceous–Palaeogene extinction event.[46] This disagreement is in part caused by a divergence in the evidence; most molecular dating studies suggests a Cretaceous evolutionary radiation, while fossil evidence points to a Cenozoic radiation (the so-called 'rocks' versus 'clocks' controversy). Previous attempts to reconcile molecular and fossil evidence have proved controversial,[46][47] but more recent estimates, using a more comprehensive sample of fossils and a new way of calibrating molecular clocks, showed that while modern birds originated early in the Late Cretaceous, a pulse of diversification in all major groups occurred around the Cretaceous–Palaeogene extinction event.[48]
+Cladogram of modern bird relationships based on Prum, R.O. et al. (2015)[45] with some clade names after Yuri, T. et al. (2013).[49]
+Struthioniformes[50] (ostriches)
+Rheiformes (rheas)
+Casuariiformes (cassowaries & emus)
+Apterygiformes (kiwi)
+†Aepyornithiformes (elephant birds)
+Tinamiformes (tinamous)
+†Dinornithiformes (moa)
+Galliformes (chickens and relatives)
+Anseriformes (ducks and relatives)
+Caprimulgiformes[50] (nightjars)
+Steatornithiformes (oilbird)
+Nyctibiiformes (potoos)
+Podargiformes (frogmouths)
+Apodiformes (swifts and hummingbirds)
+Musophagiformes (turacos)
+Otidiformes (bustards)
+Cuculiformes (cuckoos)
+Columbiformes (pigeons)
+Mesitornithiformes (mesites)
+Pterocliformes (sandgrouse)
+Gruiformes (rails and cranes)
+Phoenicopteriformes (flamingos)
+Podicipediformes (grebes)
+Charadriiformes (waders and relatives)
+Phaethontiformes (tropicbirds)
+Eurypygiformes (sunbittern and kagu)
+Gaviiformes[50] (loons)
+Procellariiformes (albatrosses and petrels)
+Sphenisciformes (penguins)
+Ciconiiformes (storks)
+Suliformes (boobies, cormorants, etc.)
+Pelecaniformes (pelicans, herons & ibises)
+Opisthocomiformes (hoatzin)
+Cathartiformes (New World vultures)
+Accipitriformes (hawks and relatives)
+Strigiformes (owls)
+Coliiformes (mouse birds)
+Leptosomiformes (cuckoo roller)
+Trogoniformes (trogons and quetzals)
+Bucerotiformes (hornbills and relatives)
+Coraciiformes (kingfishers and relatives)
+Piciformes (woodpeckers and relatives)
+Cariamiformes (seriemas)
+Falconiformes (falcons)
+Psittaciformes (parrots)
+Passeriformes (passerines)
+The classification of birds is a contentious issue. Sibley and Ahlquist's Phylogeny and Classification of Birds (1990) is a landmark work on the classification of birds,[51] although it is frequently debated and constantly revised. Most evidence seems to suggest the assignment of orders is accurate,[52] but scientists disagree about the relationships between the orders themselves; evidence from modern bird anatomy, fossils and DNA have all been brought to bear on the problem, but no strong consensus has emerged. More recently, new fossil and molecular evidence is providing an increasingly clear picture of the evolution of modern bird orders.[53][45]
+Birds live and breed in most terrestrial habitats and on all seven continents, reaching their southern extreme in the snow petrel's breeding colonies up to 440 kilometres (270 mi) inland in Antarctica.[55] The highest bird diversity occurs in tropical regions. It was earlier thought that this high diversity was the result of higher speciation rates in the tropics; however recent studies found higher speciation rates in the high latitudes that were offset by greater extinction rates than in the tropics.[56] Many species migrate annually over great distances and across oceans; several families of birds have adapted to life both on the world's oceans and in them, and some seabird species come ashore only to breed,[57] while some penguins have been recorded diving up to 300 metres (980 ft) deep.[58]
+Many bird species have established breeding populations in areas to which they have been introduced by humans. Some of these introductions have been deliberate; the ring-necked pheasant, for example, has been introduced around the world as a game bird.[59] Others have been accidental, such as the establishment of wild monk parakeets in several North American cities after their escape from captivity.[60] Some species, including cattle egret,[61] yellow-headed caracara[62] and galah,[63] have spread naturally far beyond their original ranges as agricultural practices created suitable new habitat.
+Compared with other vertebrates, birds have a body plan that shows many unusual adaptations, mostly to facilitate flight.
+The skeleton consists of very lightweight bones. They have large air-filled cavities (called pneumatic cavities) which connect with the respiratory system.[64] The skull bones in adults are fused and do not show cranial sutures.[65] The orbits are large and separated by a bony septum. The spine has cervical, thoracic, lumbar and caudal regions with the number of cervical (neck) vertebrae highly variable and especially flexible, but movement is reduced in the anterior thoracic vertebrae and absent in the later vertebrae.[66] The last few are fused with the pelvis to form the synsacrum.[65] The ribs are flattened and the sternum is keeled for the attachment of flight muscles except in the flightless bird orders. The forelimbs are modified into wings.[67] The wings are more or less developed depending on the species; the only known groups that lost their wings are the extinct moa and elephant birds.[68]
+Like the reptiles, birds are primarily uricotelic, that is, their kidneys extract nitrogenous waste from their bloodstream and excrete it as uric acid, instead of urea or ammonia, through the ureters into the intestine. Birds do not have a urinary bladder or external urethral opening and (with exception of the ostrich) uric acid is excreted along with faeces as a semisolid waste.[69][70][71] However, birds such as hummingbirds can be facultatively ammonotelic, excreting most of the nitrogenous wastes as ammonia.[72] They also excrete creatine, rather than creatinine like mammals.[65] This material, as well as the output of the intestines, emerges from the bird's cloaca.[73][74] The cloaca is a multi-purpose opening: waste is expelled through it, most birds mate by joining cloaca, and females lay eggs from it. In addition, many species of birds regurgitate pellets.[75]
+It is a common but not universal feature of altricial passerine nestlings (born helpless, under constant parental care) that instead of excreting directly into the nest, they produce a fecal sac. This is a mucus-covered pouch that allows parents to either dispose of the waste outside the nest or to recycle the waste through their own digestive system.[76]
+Males within Palaeognathae (with the exception of the kiwis), the Anseriformes (with the exception of screamers), and in rudimentary forms in Galliformes (but fully developed in Cracidae) possess a penis, which is never present in Neoaves.[77][78] The length is thought to be related to sperm competition.[79] When not copulating, it is hidden within the proctodeum compartment within the cloaca, just inside the vent. Female birds have sperm storage tubules[80] that allow sperm to remain viable long after copulation, a hundred days in some species.[81] Sperm from multiple males may compete through this mechanism. Most female birds have a single ovary and a single oviduct, both on the left side,[82] but there are exceptions: species in at least 16 different orders of birds have two ovaries. Even these species, however, tend to have a single oviduct.[82] It has been speculated that this might be an adaptation to flight, but males have two testes, and it is also observed that the gonads in both sexes decrease dramatically in size outside the breeding season.[83][84] Also terrestrial birds generally have a single ovary, as does the platypus, an egg-laying mammal. A more likely explanation is that the egg develops a shell while passing through the oviduct over a period of about a day, so that if two eggs were to develop at the same time, there would be a risk to survival.[82]
+Birds have two sexes: either female or male. The sex of birds is determined by the Z and W sex chromosomes, rather than by the X and Y chromosomes present in mammals. Male birds have two Z chromosomes (ZZ), and female birds have a W chromosome and a Z chromosome (WZ).[65]
+In nearly all species of birds, an individual's sex is determined at fertilisation. However, one recent study claimed to demonstrate temperature-dependent sex determination among the Australian brushturkey, for which higher temperatures during incubation resulted in a higher female-to-male sex ratio.[85] This, however, was later proven to not be the case. These birds do not exhibit temperature-dependent sex determination, but temperature-dependent sex mortality.[86]
+Birds have one of the most complex respiratory systems of all animal groups.[65] Upon inhalation, 75% of the fresh air bypasses the lungs and flows directly into a posterior air sac which extends from the lungs and connects with air spaces in the bones and fills them with air. The other 25% of the air goes directly into the lungs. When the bird exhales, the used air flows out of the lungs and the stored fresh air from the posterior air sac is simultaneously forced into the lungs. Thus, a bird's lungs receive a constant supply of fresh air during both inhalation and exhalation.[87] Sound production is achieved using the syrinx, a muscular chamber incorporating multiple tympanic membranes which diverges from the lower end of the trachea;[88] the trachea being elongated in some species, increasing the volume of vocalisations and the perception of the bird's size.[89]
+In birds, the main arteries taking blood away from the heart originate from the right aortic arch (or pharyngeal arch), unlike in the mammals where the left aortic arch forms this part of the aorta.[65] The postcava receives blood from the limbs via the renal portal system. Unlike in mammals, the circulating red blood cells in birds retain their nucleus.[90]
+The avian circulatory system is driven by a four-chambered, myogenic heart contained in a fibrous pericardial sac. This pericardial sac is filled with a serous fluid for lubrication.[91] The heart itself is divided into a right and left half, each with an atrium and ventricle. The atrium and ventricles of each side are separated by atrioventricular valves which prevent back flow from one chamber to the next during contraction. Being myogenic, the heart's pace is maintained by pacemaker cells found in the sinoatrial node, located on the right atrium.
+The sinoatrial node uses calcium to cause a depolarising signal transduction pathway from the atrium through right and left atrioventricular bundle which communicates contraction to the ventricles. The avian heart also consists of muscular arches that are made up of thick bundles of muscular layers. Much like a mammalian heart, the avian heart is composed of endocardial, myocardial and epicardial layers.[91] The atrium walls tend to be thinner than the ventricle walls, due to the intense ventricular contraction used to pump oxygenated blood throughout the body. Avian hearts are generally larger than mammalian hearts when compared to body mass. This adaptation allows more blood to be pumped to meet the high metabolic need associated with flight.[92]
+Birds have a very efficient system for diffusing oxygen into the blood; birds have a ten times greater surface area to gas exchange volume than mammals. As a result, birds have more blood in their capillaries per unit of volume of lung than a mammal.[92] The arteries are composed of thick elastic muscles to withstand the pressure of the ventricular contractions, and become more rigid as they move away from the heart. Blood moves through the arteries, which undergo vasoconstriction, and into arterioles which act as a transportation system to distribute primarily oxygen as well as nutrients to all tissues of the body.[93] As the arterioles move away from the heart and into individual organs and tissues they are further divided to increase surface area and slow blood flow. Blood travels through the arterioles and moves into the capillaries where gas exchange can occur.
+Capillaries are organized into capillary beds in tissues; it is here that blood exchanges oxygen for carbon dioxide waste. In the capillary beds, blood flow is slowed to allow maximum diffusion of oxygen into the tissues. Once the blood has become deoxygenated, it travels through venules then veins and back to the heart. Veins, unlike arteries, are thin and rigid as they do not need to withstand extreme pressure. As blood travels through the venules to the veins a funneling occurs called vasodilation bringing blood back to the heart.[93] Once the blood reaches the heart, it moves first into the right atrium, then the right ventricle to be pumped through the lungs for further gas exchange of carbon dioxide waste for oxygen. Oxygenated blood then flows from the lungs through the left atrium to the left ventricle where it is pumped out to the body.
+The nervous system is large relative to the bird's size.[65] The most developed part of the brain is the one that controls the flight-related functions, while the cerebellum coordinates movement and the cerebrum controls behaviour patterns, navigation, mating and nest building. Most birds have a poor sense of smell[94] with notable exceptions including kiwis,[95] New World vultures[96] and tubenoses.[97] The avian visual system is usually highly developed. Water birds have special flexible lenses, allowing accommodation for vision in air and water.[65] Some species also have dual fovea. Birds are tetrachromatic, possessing ultraviolet (UV) sensitive cone cells in the eye as well as green, red and blue ones.[98] They also have double cones, likely to mediate achromatic vision.[99]
+Many birds show plumage patterns in ultraviolet that are invisible to the human eye; some birds whose sexes appear similar to the naked eye are distinguished by the presence of ultraviolet reflective patches on their feathers. Male blue tits have an ultraviolet reflective crown patch which is displayed in courtship by posturing and raising of their nape feathers.[100] Ultraviolet light is also used in foraging—kestrels have been shown to search for prey by detecting the UV reflective urine trail marks left on the ground by rodents.[101] With the exception of pigeons and a few other species,[102] the eyelids of birds are not used in blinking. Instead the eye is lubricated by the nictitating membrane, a third eyelid that moves horizontally.[103] The nictitating membrane also covers the eye and acts as a contact lens in many aquatic birds.[65] The bird retina has a fan shaped blood supply system called the pecten.[65]
+Most birds cannot move their eyes, although there are exceptions, such as the great cormorant.[104] Birds with eyes on the sides of their heads have a wide visual field, while birds with eyes on the front of their heads, such as owls, have binocular vision and can estimate the depth of field.[105] The avian ear lacks external pinnae but is covered by feathers, although in some birds, such as the Asio, Bubo and Otus owls, these feathers form tufts which resemble ears. The inner ear has a cochlea, but it is not spiral as in mammals.[106]
+A few species are able to use chemical defences against predators; some Procellariiformes can eject an unpleasant stomach oil against an aggressor,[107] and some species of pitohuis from New Guinea have a powerful neurotoxin in their skin and feathers.[108]
+A lack of field observations limit our knowledge, but intraspecific conflicts are known to sometimes result in injury or death.[109] The screamers (Anhimidae), some jacanas (Jacana, Hydrophasianus), the spur-winged goose (Plectropterus), the torrent duck (Merganetta) and nine species of lapwing (Vanellus) use a sharp spur on the wing as a weapon. The steamer ducks (Tachyeres), geese and swans (Anserinae), the solitaire (Pezophaps), sheathbills (Chionis), some guans (Crax) and stone curlews (Burhinus) use a bony knob on the alular metacarpal to punch and hammer opponents.[109] The jacanas Actophilornis and Irediparra have an expanded, blade-like radius. The extinct Xenicibis was unique in having an elongate forelimb and massive hand which likely functioned in combat or defence as a jointed club or flail. Swans, for instance, may strike with the bony spurs and bite when defending eggs or young.[109]
+Feathers are a feature characteristic of birds (though also present in some dinosaurs not currently considered to be true birds). They facilitate flight, provide insulation that aids in thermoregulation, and are used in display, camouflage, and signalling.[65] There are several types of feathers, each serving its own set of purposes. Feathers are epidermal growths attached to the skin and arise only in specific tracts of skin called pterylae. The distribution pattern of these feather tracts (pterylosis) is used in taxonomy and systematics. The arrangement and appearance of feathers on the body, called plumage, may vary within species by age, social status,[110] and sex.[111]
+Plumage is regularly moulted; the standard plumage of a bird that has moulted after breeding is known as the "non-breeding" plumage, or—in the Humphrey–Parkes terminology—"basic" plumage; breeding plumages or variations of the basic plumage are known under the Humphrey–Parkes system as "alternate" plumages.[112] Moulting is annual in most species, although some may have two moults a year, and large birds of prey may moult only once every few years. Moulting patterns vary across species. In passerines, flight feathers are replaced one at a time with the innermost primary being the first. When the fifth of sixth primary is replaced, the outermost tertiaries begin to drop. After the innermost tertiaries are moulted, the secondaries starting from the innermost begin to drop and this proceeds to the outer feathers (centrifugal moult). The greater primary coverts are moulted in synchrony with the primary that they overlap.[113]
+A small number of species, such as ducks and geese, lose all of their flight feathers at once, temporarily becoming flightless.[114] As a general rule, the tail feathers are moulted and replaced starting with the innermost pair.[113] Centripetal moults of tail feathers are however seen in the Phasianidae.[115] The centrifugal moult is modified in the tail feathers of woodpeckers and treecreepers, in that it begins with the second innermost pair of feathers and finishes with the central pair of feathers so that the bird maintains a functional climbing tail.[113][116] The general pattern seen in passerines is that the primaries are replaced outward, secondaries inward, and the tail from centre outward.[117] Before nesting, the females of most bird species gain a bare brood patch by losing feathers close to the belly. The skin there is well supplied with blood vessels and helps the bird in incubation.[118]
+Feathers require maintenance and birds preen or groom them daily, spending an average of around 9% of their daily time on this.[119] The bill is used to brush away foreign particles and to apply waxy secretions from the uropygial gland; these secretions protect the feathers' flexibility and act as an antimicrobial agent, inhibiting the growth of feather-degrading bacteria.[120] This may be supplemented with the secretions of formic acid from ants, which birds receive through a behaviour known as anting, to remove feather parasites.[121]
+The scales of birds are composed of the same keratin as beaks, claws, and spurs. They are found mainly on the toes and metatarsus, but may be found further up on the ankle in some birds. Most bird scales do not overlap significantly, except in the cases of kingfishers and woodpeckers.
+The scales of birds are thought to be homologous to those of reptiles and mammals.[122]
+Most birds can fly, which distinguishes them from almost all other vertebrate classes. Flight is the primary means of locomotion for most bird species and is used for searching for food and for escaping from predators. Birds have various adaptations for flight, including a lightweight skeleton, two large flight muscles, the pectoralis (which accounts for 15% of the total mass of the bird) and the supracoracoideus, as well as a modified forelimb (wing) that serves as an aerofoil.[65]
+Wing shape and size generally determine a bird's flight style and performance; many birds combine powered, flapping flight with less energy-intensive soaring flight. About 60 extant bird species are flightless, as were many extinct birds.[123] Flightlessness often arises in birds on isolated islands, probably due to limited resources and the absence of land predators.[124] Although flightless, penguins use similar musculature and movements to "fly" through the water, as do some flight-capable birds such as auks, shearwaters and dippers.[125]
+Most birds are diurnal, but some birds, such as many species of owls and nightjars, are nocturnal or crepuscular (active during twilight hours), and many coastal waders feed when the tides are appropriate, by day or night.[126]
+Birds' diets are varied and often include nectar, fruit, plants, seeds, carrion, and various small animals, including other birds.[65] The digestive system of birds is unique, with a crop for storage and a gizzard that contains swallowed stones for grinding food to compensate for the lack of teeth.[127] Most birds are highly adapted for rapid digestion to aid with flight.[128] Some migratory birds have adapted to use protein stored in many parts of their bodies, including protein from the intestines, as additional energy during migration.[129]
+Birds that employ many strategies to obtain food or feed on a variety of food items are called generalists, while others that concentrate time and effort on specific food items or have a single strategy to obtain food are considered specialists.[65] Avian foraging strategies can vary widely by species. Many birds glean for insects, invertebrates, fruit, or seeds. Some hunt insects by suddenly attacking from a branch. Those species that seek pest insects are considered beneficial 'biological control agents' and their presence encouraged in biological pest control programmes.[130] Combined, insectivorous birds eat 400–500 million metric tons of arthropods annually.[131]
+Nectar feeders such as hummingbirds, sunbirds, lories, and lorikeets amongst others have specially adapted brushy tongues and in many cases bills designed to fit co-adapted flowers.[132] Kiwis and shorebirds with long bills probe for invertebrates; shorebirds' varied bill lengths and feeding methods result in the separation of ecological niches.[65][133] Loons, diving ducks, penguins and auks pursue their prey underwater, using their wings or feet for propulsion,[57] while aerial predators such as sulids, kingfishers and terns plunge dive after their prey. Flamingos, three species of prion, and some ducks are filter feeders.[134][135] Geese and dabbling ducks are primarily grazers.
+Some species, including frigatebirds, gulls,[136] and skuas,[137] engage in kleptoparasitism, stealing food items from other birds. Kleptoparasitism is thought to be a supplement to food obtained by hunting, rather than a significant part of any species' diet; a study of great frigatebirds stealing from masked boobies estimated that the frigatebirds stole at most 40% of their food and on average stole only 5%.[138] Other birds are scavengers; some of these, like vultures, are specialised carrion eaters, while others, like gulls, corvids, or other birds of prey, are opportunists.[139]
+Water is needed by many birds although their mode of excretion and lack of sweat glands reduces the physiological demands.[140] Some desert birds can obtain their water needs entirely from moisture in their food. They may also have other adaptations such as allowing their body temperature to rise, saving on moisture loss from evaporative cooling or panting.[141] Seabirds can drink seawater and have salt glands inside the head that eliminate excess salt out of the nostrils.[142]
+Most birds scoop water in their beaks and raise their head to let water run down the throat. Some species, especially of arid zones, belonging to the pigeon, finch, mousebird, button-quail and bustard families are capable of sucking up water without the need to tilt back their heads.[143] Some desert birds depend on water sources and sandgrouse are particularly well known for their daily congregations at waterholes. Nesting sandgrouse and many plovers carry water to their young by wetting their belly feathers.[144] Some birds carry water for chicks at the nest in their crop or regurgitate it along with food. The pigeon family, flamingos and penguins have adaptations to produce a nutritive fluid called crop milk that they provide to their chicks.[145]
+Feathers, being critical to the survival of a bird, require maintenance. Apart from physical wear and tear, feathers face the onslaught of fungi, ectoparasitic feather mites and bird lice.[146] The physical condition of feathers are maintained by preening often with the application of secretions from the preen gland. Birds also bathe in water or dust themselves. While some birds dip into shallow water, more aerial species may make aerial dips into water and arboreal species often make use of dew or rain that collect on leaves. Birds of arid regions make use of loose soil to dust-bathe. A behaviour termed as anting in which the bird encourages ants to run through their plumage is also thought to help them reduce the ectoparasite load in feathers. Many species will spread out their wings and expose them to direct sunlight and this too is thought to help in reducing fungal and ectoparasitic activity that may lead to feather damage.[147][148]
+Many bird species migrate to take advantage of global differences of seasonal temperatures, therefore optimising availability of food sources and breeding habitat. These migrations vary among the different groups. Many landbirds, shorebirds, and waterbirds undertake annual long-distance migrations, usually triggered by the length of daylight as well as weather conditions. These birds are characterised by a breeding season spent in the temperate or polar regions and a non-breeding season in the tropical regions or opposite hemisphere. Before migration, birds substantially increase body fats and reserves and reduce the size of some of their organs.[149][150]
+Migration is highly demanding energetically, particularly as birds need to cross deserts and oceans without refuelling. Landbirds have a flight range of around 2,500 km (1,600 mi) and shorebirds can fly up to 4,000 km (2,500 mi),[151] although the bar-tailed godwit is capable of non-stop flights of up to 10,200 km (6,300 mi).[152] Seabirds also undertake long migrations, the longest annual migration being those of sooty shearwaters, which nest in New Zealand and Chile and spend the northern summer feeding in the North Pacific off Japan, Alaska and California, an annual round trip of 64,000 km (39,800 mi).[153] Other seabirds disperse after breeding, travelling widely but having no set migration route. Albatrosses nesting in the Southern Ocean often undertake circumpolar trips between breeding seasons.[154]
+Some bird species undertake shorter migrations, travelling only as far as is required to avoid bad weather or obtain food. Irruptive species such as the boreal finches are one such group and can commonly be found at a location in one year and absent the next. This type of migration is normally associated with food availability.[155] Species may also travel shorter distances over part of their range, with individuals from higher latitudes travelling into the existing range of conspecifics; others undertake partial migrations, where only a fraction of the population, usually females and subdominant males, migrates.[156] Partial migration can form a large percentage of the migration behaviour of birds in some regions; in Australia, surveys found that 44% of non-passerine birds and 32% of passerines were partially migratory.[157]
+Altitudinal migration is a form of short-distance migration in which birds spend the breeding season at higher altitudes and move to lower ones during suboptimal conditions. It is most often triggered by temperature changes and usually occurs when the normal territories also become inhospitable due to lack of food.[158] Some species may also be nomadic, holding no fixed territory and moving according to weather and food availability. Parrots as a family are overwhelmingly neither migratory nor sedentary but considered to either be dispersive, irruptive, nomadic or undertake small and irregular migrations.[159]
+The ability of birds to return to precise locations across vast distances has been known for some time; in an experiment conducted in the 1950s, a Manx shearwater released in Boston in the United States returned to its colony in Skomer, in Wales within 13 days, a distance of 5,150 km (3,200 mi).[160] Birds navigate during migration using a variety of methods. For diurnal migrants, the sun is used to navigate by day, and a stellar compass is used at night. Birds that use the sun compensate for the changing position of the sun during the day by the use of an internal clock.[65] Orientation with the stellar compass depends on the position of the constellations surrounding Polaris.[161] These are backed up in some species by their ability to sense the Earth's geomagnetism through specialised photoreceptors.[162]
+Birds communicate using primarily visual and auditory signals. Signals can be interspecific (between species) and intraspecific (within species).
+Birds sometimes use plumage to assess and assert social dominance,[163] to display breeding condition in sexually selected species, or to make threatening displays, as in the sunbittern's mimicry of a large predator to ward off hawks and protect young chicks.[164] Variation in plumage also allows for the identification of birds, particularly between species.
+Visual communication among birds may also involve ritualised displays, which have developed from non-signalling actions such as preening, the adjustments of feather position, pecking, or other behaviour. These displays may signal aggression or submission or may contribute to the formation of pair-bonds.[65] The most elaborate displays occur during courtship, where "dances" are often formed from complex combinations of many possible component movements;[165] males' breeding success may depend on the quality of such displays.[166]
+Bird calls and songs, which are produced in the syrinx, are the major means by which birds communicate with sound. This communication can be very complex; some species can operate the two sides of the syrinx independently, allowing the simultaneous production of two different songs.[88]
+Calls are used for a variety of purposes, including mate attraction,[65] evaluation of potential mates,[167] bond formation, the claiming and maintenance of territories,[65] the identification of other individuals (such as when parents look for chicks in colonies or when mates reunite at the start of breeding season),[168] and the warning of other birds of potential predators, sometimes with specific information about the nature of the threat.[169] Some birds also use mechanical sounds for auditory communication. The Coenocorypha snipes of New Zealand drive air through their feathers,[170] woodpeckers drum for long-distance communication,[171] and palm cockatoos use tools to drum.[172]
+While some birds are essentially territorial or live in small family groups, other birds may form large flocks. The principal benefits of flocking are safety in numbers and increased foraging efficiency.[65] Defence against predators is particularly important in closed habitats like forests, where ambush predation is common and multiple eyes can provide a valuable early warning system. This has led to the development of many mixed-species feeding flocks, which are usually composed of small numbers of many species; these flocks provide safety in numbers but increase potential competition for resources.[174] Costs of flocking include bullying of socially subordinate birds by more dominant birds and the reduction of feeding efficiency in certain cases.[175]
+Birds sometimes also form associations with non-avian species. Plunge-diving seabirds associate with dolphins and tuna, which push shoaling fish towards the surface.[176] Hornbills have a mutualistic relationship with dwarf mongooses, in which they forage together and warn each other of nearby birds of prey and other predators.[177]
+The high metabolic rates of birds during the active part of the day is supplemented by rest at other times. Sleeping birds often use a type of sleep known as vigilant sleep, where periods of rest are interspersed with quick eye-opening "peeks", allowing them to be sensitive to disturbances and enable rapid escape from threats.[178] Swifts are believed to be able to sleep in flight and radar observations suggest that they orient themselves to face the wind in their roosting flight.[179] It has been suggested that there may be certain kinds of sleep which are possible even when in flight.[180]
+Some birds have also demonstrated the capacity to fall into slow-wave sleep one hemisphere of the brain at a time. The birds tend to exercise this ability depending upon its position relative to the outside of the flock. This may allow the eye opposite the sleeping hemisphere to remain vigilant for predators by viewing the outer margins of the flock. This adaptation is also known from marine mammals.[181] Communal roosting is common because it lowers the loss of body heat and decreases the risks associated with predators.[182] Roosting sites are often chosen with regard to thermoregulation and safety.[183]
+Many sleeping birds bend their heads over their backs and tuck their bills in their back feathers, although others place their beaks among their breast feathers. Many birds rest on one leg, while some may pull up their legs into their feathers, especially in cold weather. Perching birds have a tendon locking mechanism that helps them hold on to the perch when they are asleep. Many ground birds, such as quails and pheasants, roost in trees. A few parrots of the genus Loriculus roost hanging upside down.[184] Some hummingbirds go into a nightly state of torpor accompanied with a reduction of their metabolic rates.[185] This physiological adaptation shows in nearly a hundred other species, including owlet-nightjars, nightjars, and woodswallows. One species, the common poorwill, even enters a state of hibernation.[186] Birds do not have sweat glands, but they may cool themselves by moving to shade, standing in water, panting, increasing their surface area, fluttering their throat or by using special behaviours like urohidrosis to cool themselves.
+Ninety-five per cent of bird species are socially monogamous. These species pair for at least the length of the breeding season or—in some cases—for several years or until the death of one mate.[188] Monogamy allows for both paternal care and biparental care, which is especially important for species in which females require males' assistance for successful brood-rearing.[189] Among many socially monogamous species, extra-pair copulation (infidelity) is common.[190] Such behaviour typically occurs between dominant males and females paired with subordinate males, but may also be the result of forced copulation in ducks and other anatids.[191]
+For females, possible benefits of extra-pair copulation include getting better genes for her offspring and insuring against the possibility of infertility in her mate.[192] Males of species that engage in extra-pair copulations will closely guard their mates to ensure the parentage of the offspring that they raise.[193]
+Other mating systems, including polygyny, polyandry, polygamy, polygynandry, and promiscuity, also occur.[65] Polygamous breeding systems arise when females are able to raise broods without the help of males.[65] Some species may use more than one system depending on the circumstances.
+Breeding usually involves some form of courtship display, typically performed by the male.[194] Most displays are rather simple and involve some type of song. Some displays, however, are quite elaborate. Depending on the species, these may include wing or tail drumming, dancing, aerial flights, or communal lekking. Females are generally the ones that drive partner selection,[195] although in the polyandrous phalaropes, this is reversed: plainer males choose brightly coloured females.[196] Courtship feeding, billing and allopreening are commonly performed between partners, generally after the birds have paired and mated.[197]
+Homosexual behaviour has been observed in males or females in numerous species of birds, including copulation, pair-bonding, and joint parenting of chicks.[198] Over 130 avian species around the world engage in sexual interactions between the same sex or homosexual behaviors. "Same-sex courtship activities may involve elaborate displays, synchronized dances, gift-giving ceremonies, or behaviors at specific display areas including bowers, arenas, or leks."[199]
+Many birds actively defend a territory from others of the same species during the breeding season; maintenance of territories protects the food source for their chicks. Species that are unable to defend feeding territories, such as seabirds and swifts, often breed in colonies instead; this is thought to offer protection from predators. Colonial breeders defend small nesting sites, and competition between and within species for nesting sites can be intense.[200]
+All birds lay amniotic eggs with hard shells made mostly of calcium carbonate.[65] Hole and burrow nesting species tend to lay white or pale eggs, while open nesters lay camouflaged eggs. There are many exceptions to this pattern, however; the ground-nesting nightjars have pale eggs, and camouflage is instead provided by their plumage. Species that are victims of brood parasites have varying egg colours to improve the chances of spotting a parasite's egg, which forces female parasites to match their eggs to those of their hosts.[201]
+Bird eggs are usually laid in a nest. Most species create somewhat elaborate nests, which can be cups, domes, plates, beds scrapes, mounds, or burrows.[202] Some bird nests, however, are extremely primitive; albatross nests are no more than a scrape on the ground. Most birds build nests in sheltered, hidden areas to avoid predation, but large or colonial birds—which are more capable of defence—may build more open nests. During nest construction, some species seek out plant matter from plants with parasite-reducing toxins to improve chick survival,[203] and feathers are often used for nest insulation.[202] Some bird species have no nests; the cliff-nesting common guillemot lays its eggs on bare rock, and male emperor penguins keep eggs between their body and feet. The absence of nests is especially prevalent in ground-nesting species where the newly hatched young are precocial.
+Incubation, which optimises temperature for chick development, usually begins after the last egg has been laid.[65] In monogamous species incubation duties are often shared, whereas in polygamous species one parent is wholly responsible for incubation. Warmth from parents passes to the eggs through brood patches, areas of bare skin on the abdomen or breast of the incubating birds. Incubation can be an energetically demanding process; adult albatrosses, for instance, lose as much as 83 grams (2.9 oz) of body weight per day of incubation.[204] The warmth for the incubation of the eggs of megapodes comes from the sun, decaying vegetation or volcanic sources.[205] Incubation periods range from 10 days (in woodpeckers, cuckoos and passerine birds) to over 80 days (in albatrosses and kiwis).[65]
+The diversity of characteristics of birds is great, sometimes even in closely related species. Several avian characteristics are compared in the table below.[206][207]
+At the time of their hatching, chicks range in development from helpless to independent, depending on their species. Helpless chicks are termed altricial, and tend to be born small, blind, immobile and naked; chicks that are mobile and feathered upon hatching are termed precocial. Altricial chicks need help thermoregulating and must be brooded for longer than precocial chicks. The young of many bird species do not precisely fit into either the precocial or altricial category, having some aspects of each and thus fall somewhere on an "altricial-precocial spectrum".[208] Chicks at neither extreme but favoring one or the other may be termed semi-precocial[209] or semi-altricial.[210]
+The length and nature of parental care varies widely amongst different orders and species. At one extreme, parental care in megapodes ends at hatching; the newly hatched chick digs itself out of the nest mound without parental assistance and can fend for itself immediately.[211] At the other extreme, many seabirds have extended periods of parental care, the longest being that of the great frigatebird, whose chicks take up to six months to fledge and are fed by the parents for up to an additional 14 months.[212] The chick guard stage describes the period of breeding during which one of the adult birds is permanently present at the nest after chicks have hatched. The main purpose of the guard stage is to aid offspring to thermoregulate and protect them from predation.[213]
+In some species, both parents care for nestlings and fledglings; in others, such care is the responsibility of only one sex. In some species, other members of the same species—usually close relatives of the breeding pair, such as offspring from previous broods—will help with the raising of the young.[214] Such alloparenting is particularly common among the Corvida, which includes such birds as the true crows, Australian magpie and fairy-wrens,[215] but has been observed in species as different as the rifleman and red kite. Among most groups of animals, male parental care is rare. In birds, however, it is quite common—more so than in any other vertebrate class.[65] Although territory and nest site defence, incubation, and chick feeding are often shared tasks, there is sometimes a division of labour in which one mate undertakes all or most of a particular duty.[216]
+The point at which chicks fledge varies dramatically. The chicks of the Synthliboramphus murrelets, like the ancient murrelet, leave the nest the night after they hatch, following their parents out to sea, where they are raised away from terrestrial predators.[217] Some other species, such as ducks, move their chicks away from the nest at an early age. In most species, chicks leave the nest just before, or soon after, they are able to fly. The amount of parental care after fledging varies; albatross chicks leave the nest on their own and receive no further help, while other species continue some supplementary feeding after fledging.[218] Chicks may also follow their parents during their first migration.[219]
+Brood parasitism, in which an egg-layer leaves her eggs with another individual's brood, is more common among birds than any other type of organism.[220] After a parasitic bird lays her eggs in another bird's nest, they are often accepted and raised by the host at the expense of the host's own brood. Brood parasites may be either obligate brood parasites, which must lay their eggs in the nests of other species because they are incapable of raising their own young, or non-obligate brood parasites, which sometimes lay eggs in the nests of conspecifics to increase their reproductive output even though they could have raised their own young.[221] One hundred bird species, including honeyguides, icterids, and ducks, are obligate parasites, though the most famous are the cuckoos.[220] Some brood parasites are adapted to hatch before their host's young, which allows them to destroy the host's eggs by pushing them out of the nest or to kill the host's chicks; this ensures that all food brought to the nest will be fed to the parasitic chicks.[222]
+Birds have evolved a variety of mating behaviours, with the peacock tail being perhaps the most famous example of sexual selection and the Fisherian runaway. Commonly occurring sexual dimorphisms such as size and colour differences are energetically costly attributes that signal competitive breeding situations.[223] Many types of avian sexual selection have been identified; intersexual selection, also known as female choice; and intrasexual competition, where individuals of the more abundant sex compete with each other for the privilege to mate. Sexually selected traits often evolve to become more pronounced in competitive breeding situations until the trait begins to limit the individual's fitness. Conflicts between an individual fitness and signalling adaptations ensure that sexually selected ornaments such as plumage coloration and courtship behaviour are "honest" traits. Signals must be costly to ensure that only good-quality individuals can present these exaggerated sexual ornaments and behaviours.[224]
+Inbreeding causes early death (inbreeding depression) in the zebra finch Taeniopygia guttata.[225] Embryo survival (that is, hatching success of fertile eggs) was significantly lower for sib-sib mating pairs than for unrelated pairs.
+Darwin's finch Geospiza scandens experiences inbreeding depression (reduced survival of offspring) and the magnitude of this effect is influenced by environmental conditions such as low food availability.[226]
+Incestuous matings by the purple-crowned fairy wren Malurus coronatus result in severe fitness costs due to inbreeding depression (greater than 30% reduction in hatchability of eggs).[227] Females paired with related males may undertake extra pair matings (see Promiscuity#Other animals for 90% frequency in avian species) that can reduce the negative effects of inbreeding. However, there are ecological and demographic constraints on extra pair matings. Nevertheless, 43% of broods produced by incestuously paired females contained extra pair young.[227]
+Inbreeding depression occurs in the great tit (Parus major) when the offspring produced as a result of a mating between close relatives show reduced fitness. In natural populations of Parus major, inbreeding is avoided by dispersal of individuals from their birthplace, which reduces the chance of mating with a close relative.[228]
+Southern pied babblers Turdoides bicolor appear to avoid inbreeding in two ways. The first is through dispersal, and the second is by avoiding familiar group members as mates.[229] Although both males and females disperse locally, they move outside the range where genetically related individuals are likely to be encountered. Within their group, individuals only acquire breeding positions when the opposite-sex breeder is unrelated.
+Cooperative breeding in birds typically occurs when offspring, usually males, delay dispersal from their natal group in order to remain with the family to help rear younger kin.[230] Female offspring rarely stay at home, dispersing over distances that allow them to breed independently, or to join unrelated groups. In general, inbreeding is avoided because it leads to a reduction in progeny fitness (inbreeding depression) due largely to the homozygous expression of deleterious recessive alleles.[231] Cross-fertilisation between unrelated individuals ordinarily leads to the masking of deleterious recessive alleles in progeny.[232][233]
+Birds occupy a wide range of ecological positions.[173] While some birds are generalists, others are highly specialised in their habitat or food requirements. Even within a single habitat, such as a forest, the niches occupied by different species of birds vary, with some species feeding in the forest canopy, others beneath the canopy, and still others on the forest floor. Forest birds may be insectivores, frugivores, and nectarivores. Aquatic birds generally feed by fishing, plant eating, and piracy or kleptoparasitism. Birds of prey specialise in hunting mammals or other birds, while vultures are specialised scavengers. Avivores are animals that are specialised at preying on birds.
+Some nectar-feeding birds are important pollinators, and many frugivores play a key role in seed dispersal.[234] Plants and pollinating birds often coevolve,[235] and in some cases a flower's primary pollinator is the only species capable of reaching its nectar.[236]
+Birds are often important to island ecology. Birds have frequently reached islands that mammals have not; on those islands, birds may fulfil ecological roles typically played by larger animals. For example, in New Zealand nine species of moa were important browsers, as are the kererū and kokako today.[234] Today the plants of New Zealand retain the defensive adaptations evolved to protect them from the extinct moa.[237] Nesting seabirds may also affect the ecology of islands and surrounding seas, principally through the concentration of large quantities of guano, which may enrich the local soil[238] and the surrounding seas.[239]
+A wide variety of avian ecology field methods, including counts, nest monitoring, and capturing and marking, are used for researching avian ecology.
+Since birds are highly visible and common animals, humans have had a relationship with them since the dawn of man.[240] Sometimes, these relationships are mutualistic, like the cooperative honey-gathering among honeyguides and African peoples such as the Borana.[241] Other times, they may be commensal, as when species such as the house sparrow[242] have benefited from human activities. Several bird species have become commercially significant agricultural pests,[243] and some pose an aviation hazard.[244] Human activities can also be detrimental, and have threatened numerous bird species with extinction (hunting, avian lead poisoning, pesticides, roadkill, wind turbine kills[245] and predation by pet cats and dogs are common causes of death for birds).[246]
+Birds can act as vectors for spreading diseases such as psittacosis, salmonellosis, campylobacteriosis, mycobacteriosis (avian tuberculosis), avian influenza (bird flu), giardiasis, and cryptosporidiosis over long distances. Some of these are zoonotic diseases that can also be transmitted to humans.[247]
+Domesticated birds raised for meat and eggs, called poultry, are the largest source of animal protein eaten by humans; in 2003, 76 million tons of poultry and 61 million tons of eggs were produced worldwide.[248] Chickens account for much of human poultry consumption, though domesticated turkeys, ducks, and geese are also relatively common. Many species of birds are also hunted for meat. Bird hunting is primarily a recreational activity except in extremely undeveloped areas. The most important birds hunted in North and South America are waterfowl; other widely hunted birds include pheasants, wild turkeys, quail, doves, partridge, grouse, snipe, and woodcock.[249] Muttonbirding is also popular in Australia and New Zealand.[250] Although some hunting, such as that of muttonbirds, may be sustainable, hunting has led to the extinction or endangerment of dozens of species.[251]
+Other commercially valuable products from birds include feathers (especially the down of geese and ducks), which are used as insulation in clothing and bedding, and seabird faeces (guano), which is a valuable source of phosphorus and nitrogen. The War of the Pacific, sometimes called the Guano War, was fought in part over the control of guano deposits.[252]
+Birds have been domesticated by humans both as pets and for practical purposes. Colourful birds, such as parrots and mynas, are bred in captivity or kept as pets, a practice that has led to the illegal trafficking of some endangered species.[253] Falcons and cormorants have long been used for hunting and fishing, respectively. Messenger pigeons, used since at least 1 AD, remained important as recently as World War II. Today, such activities are more common either as hobbies, for entertainment and tourism,[254] or for sports such as pigeon racing.
+Amateur bird enthusiasts (called birdwatchers, twitchers or, more commonly, birders) number in the millions.[255] Many homeowners erect bird feeders near their homes to attract various species. Bird feeding has grown into a multimillion-dollar industry; for example, an estimated 75% of households in Britain provide food for birds at some point during the winter.[256]
+Birds play prominent and diverse roles in religion and mythology.
+In religion, birds may serve as either messengers or priests and leaders for a deity, such as in the Cult of Makemake, in which the Tangata manu of Easter Island served as chiefs[257] or as attendants, as in the case of Hugin and Munin, the two common ravens who whispered news into the ears of the Norse god Odin. In several civilisations of ancient Italy, particularly Etruscan and Roman religion, priests were involved in augury, or interpreting the words of birds while the "auspex" (from which the word "auspicious" is derived) watched their activities to foretell events.[258]
+They may also serve as religious symbols, as when Jonah (Hebrew: יוֹנָה‎, dove) embodied the fright, passivity, mourning, and beauty traditionally associated with doves.[259] Birds have themselves been deified, as in the case of the common peacock, which is perceived as Mother Earth by the Dravidians of India.[260] In the ancient world, doves were used as symbols of the Mesopotamian goddess Inanna (later known as Ishtar),[261][262] the Canaanite mother goddess Asherah,[261][262][263] and the Greek goddess Aphrodite.[264][265][261][262][266] In ancient Greece, Athena, the goddess of wisdom and patron deity of the city of Athens, had a little owl as her symbol.[267][268][269] In religious images preserved from the Inca and Tiwanaku empires, birds are depicted in the process of transgressing boundaries between earthly and underground spiritual realms.[270] Indigenous peoples of the central Andes maintain legends of birds passing to and from metaphysical worlds.[270]
+Birds have featured in culture and art since prehistoric times, when they were represented in early cave paintings.[271] Some birds have been perceived as monsters, including the mythological Roc and the Māori's legendary Pouākai, a giant bird capable of snatching humans.[272] Birds were later used as symbols of power, as in the magnificent Peacock Throne of the Mughal and Persian emperors.[273] With the advent of scientific interest in birds, many paintings of birds were commissioned for books.
+Among the most famous of these bird artists was John James Audubon, whose paintings of North American birds were a great commercial success in Europe and who later lent his name to the National Audubon Society.[274] Birds are also important figures in poetry; for example, Homer incorporated nightingales into his Odyssey, and Catullus used a sparrow as an erotic symbol in his Catullus 2.[275] The relationship between an albatross and a sailor is the central theme of Samuel Taylor Coleridge's The Rime of the Ancient Mariner, which led to the use of the term as a metaphor for a 'burden'.[276] Other English metaphors derive from birds; vulture funds and vulture investors, for instance, take their name from the scavenging vulture.[277]
+Perceptions of bird species vary across cultures. Owls are associated with bad luck, witchcraft, and death in parts of Africa,[278] but are regarded as wise across much of Europe.[279] Hoopoes were considered sacred in Ancient Egypt and symbols of virtue in Persia, but were thought of as thieves across much of Europe and harbingers of war in Scandinavia.[280] In heraldry, birds, especially eagles, often appear in coats of arms.[281]
+In music, birdsong has influenced composers and musicians in several ways: they can be inspired by birdsong; they can intentionally imitate bird song in a composition, as Vivaldi, Messiaen, and Beethoven did, along with many later composers; they can incorporate recordings of birds into their works, as Ottorino Respighi first did; or like Beatrice Harrison and David Rothenberg, they can duet with birds.[282][283][284][285]
+Although human activities have allowed the expansion of a few species, such as the barn swallow and European starling, they have caused population decreases or extinction in many other species. Over a hundred bird species have gone extinct in historical times,[286] although the most dramatic human-caused avian extinctions, eradicating an estimated 750–1800 species, occurred during the human colonisation of Melanesian, Polynesian, and Micronesian islands.[287] Many bird populations are declining worldwide, with 1,227 species listed as threatened by BirdLife International and the IUCN in 2009.[288][289]
+The most commonly cited human threat to birds is habitat loss.[290] Other threats include overhunting, accidental mortality due to collisions with buildings or vehicles, long-line fishing bycatch,[291] pollution (including oil spills and pesticide use),[292] competition and predation from nonnative invasive species,[293] and climate change.
+Governments and conservation groups work to protect birds, either by passing laws that preserve and restore bird habitat or by establishing captive populations for reintroductions. Such projects have produced some successes; one study estimated that conservation efforts saved 16 species of bird that would otherwise have gone extinct between 1994 and 2004, including the California condor and Norfolk parakeet.[294]

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+Birds are a group of warm-blooded vertebrates constituting the class Aves, characterized by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5 cm (2 in) bee hummingbird to the 2.75 m (9 ft) ostrich. There are about ten thousand living species, more than half of which are passerine, or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in some birds, including ratites, penguins, and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming.
+Birds are a group of feathered theropod dinosaurs, and constitute the only living dinosaurs. Likewise, birds are considered reptiles in the modern cladistic sense of the term, and their closest living relatives are the crocodilians. Birds are descendants of the primitive avialans (whose members include Archaeopteryx) which first appeared about 160 million years ago (mya) in China. According to DNA evidence, modern birds (Neornithes) evolved in the Middle to Late Cretaceous, and diversified dramatically around the time of the Cretaceous–Paleogene extinction event 66 mya, which killed off the pterosaurs and all non-avian dinosaurs.
+Many social species pass on knowledge across generations, which is considered a form of culture. Birds are social, communicating with visual signals, calls, and songs, and participating in such behaviours as cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially (but not necessarily sexually) monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have breeding systems that are polygynous (one male with many females) or, rarely, polyandrous (one female with many males). Birds produce offspring by laying eggs which are fertilised through sexual reproduction. They are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching.
+Many species of birds are economically important as food for human consumption and raw material in manufacturing, with domesticated and undomesticated birds being important sources of eggs, meat, and feathers. Songbirds, parrots, and other species are popular as pets. Guano (bird excrement) is harvested for use as a fertiliser. Birds figure throughout human culture. About 120 to 130 species have become extinct due to human activity since the 17th century, and hundreds more before then. Human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry.
+The first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae.[3]
+Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use.[4] Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda.[5]
+Aves and a sister group, the order Crocodilia, contain the only living representatives of the reptile clade Archosauria. During the late 1990s, Aves was most commonly defined phylogenetically as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica.[6] However, an earlier definition proposed by Jacques Gauthier gained wide currency in the 21st century, and is used by many scientists including adherents of the Phylocode system. Gauthier defined Aves to include only the crown group of the set of modern birds. This was done by excluding most groups known only from fossils, and assigning them, instead, to the broader group Avialae,[7] in part to avoid the uncertainties about the placement of Archaeopteryx in relation to animals traditionally thought of as theropod dinosaurs.
+Gauthier and de Queiroz[8] identified four different definitions for the same biological name "Aves", which is a problem. The authors proposed to reserve the term Aves only for the crown group consisting of the last common ancestor of all living birds and all of its descendants, which corresponds to meaning number 4 below. He assigned other names to the other groups.
+Crocodiles
+Birds
+Turtles
+Lizards (including snakes)
+Under the fourth definition Archaeopteryx, traditionally considered one of the earliest members of Aves, is removed from this group, becoming a non-avian dinosaur instead. These proposals have been adopted by many researchers in the field of palaeontology and bird evolution, though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is often used synonymously with the vernacular term "bird" by these researchers.[9]
+†Coelurus
+†Ornitholestes
+†Ornithomimosauria
+†Alvarezsauridae
+†Oviraptorosauria
+Paraves
+Most researchers define Avialae as branch-based clade, though definitions vary. Many authors have used a definition similar to "all theropods closer to birds than to Deinonychus",[11][12] with Troodon being sometimes added as a second external specifier in case it is closer to birds than to Deinonychus.[13] Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on physical characteristics). Jacques Gauthier, who named Avialae in 1986, re-defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight, and the birds that descended from them.[8][14]
+Despite being currently one of the most widely used, the crown-group definition of Aves has been criticised by some researchers. Lee and Spencer (1997) argued that, contrary to what Gauthier defended, this definition would not increase the stability of the clade and the exact content of Aves will always be uncertain because any defined clade (either crown or not) will have few synapomorphies distinguishing it from its closest relatives. Their alternative definition is synonymous to Avifilopluma.[15]
+†Scansoriopterygidae
+†Eosinopteryx
+†Jinfengopteryx
+†Aurornis
+†Dromaeosauridae
+†Troodontidae
+Avialae
+Based on fossil and biological evidence, most scientists accept that birds are a specialised subgroup of theropod dinosaurs,[18] and more specifically, they are members of Maniraptora, a group of theropods which includes dromaeosaurids and oviraptorosaurs, among others.[19] As scientists have discovered more theropods closely related to birds, the previously clear distinction between non-birds and birds has become blurred. Recent discoveries in the Liaoning Province of northeast China, which demonstrate many small theropod feathered dinosaurs, contribute to this ambiguity.[20][21][22]
+The consensus view in contemporary palaeontology is that the flying theropods, or avialans, are the closest relatives of the deinonychosaurs, which include dromaeosaurids and troodontids.[23] Together, these form a group called Paraves. Some basal members of Deinonychosauria, such as Microraptor, have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal, have been able to glide, or both.[24][25] Unlike Archaeopteryx and the non-avialan feathered dinosaurs, who primarily ate meat, recent studies suggest that the first avialans were omnivores.[26]
+The Late Jurassic Archaeopteryx is well known as one of the first transitional fossils to be found, and it provided support for the theory of evolution in the late 19th century. Archaeopteryx was the first fossil to display both clearly traditional reptilian characteristics—teeth, clawed fingers, and a long, lizard-like tail—as well as wings with flight feathers similar to those of modern birds. It is not considered a direct ancestor of birds, though it is possibly closely related to the true ancestor.[27]
+Over 40% of key traits found in modern birds evolved during the 60 million year transition from the earliest bird-line archosaurs to the first maniraptoromorphs, i.e. the first dinosaurs closer to living birds than to Tyrannosaurus rex. The loss of osteoderms otherwise common in archosaurs and acquisition of primitive feathers might have occurred early during this phase.[10][29] After the appearance of Maniraptoromorpha, the next 40 million years marked a continuous reduction of body size and the accumulation of neotenic (juvenile-like) characteristics. Hypercarnivory became increasingly less common while braincases enlarged and forelimbs became longer.[10] The integument evolved into complex, pennaceous feathers.[29]
+The oldest known paravian (and probably the earliest avialan) fossils come from the Tiaojishan Formation of China, which has been dated to the late Jurassic period (Oxfordian stage), about 160 million years ago. The avialan species from this time period include Anchiornis huxleyi, Xiaotingia zhengi, and Aurornis xui.[9]
+The well-known probable early avialan, Archaeopteryx, dates from slightly later Jurassic rocks (about 155 million years old) from Germany. Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds, but were later lost during bird evolution. These features include enlarged claws on the second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial maneuvering.[30]
+Avialans diversified into a wide variety of forms during the Cretaceous Period. Many groups retained primitive characteristics, such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves).[31] Increasingly stiff tails (especially the outermost half) can be seen in the evolution of maniraptoromorphs, and this process culminated in the appearance of the pygostyle, an ossification of fused tail vertebrae.[10] In the late Cretaceous, about 100 million years ago, the ancestors of all modern birds evolved a more open pelvis, allowing them to lay larger eggs compared to body size.[32] Around 95 million years ago, they evolved a better sense of smell.[33]
+A third stage of bird evolution starting with Ornithothoraces (the "bird-chested" avialans) can be associated with the refining of aerodynamics and flight capabilities, and the loss or co-ossification of several skeletal features. Particularly significant are the development of an enlarged, keeled sternum and the alula, and the loss of grasping hands.
+[10]
+†Anchiornis
+†Archaeopteryx
+†Xiaotingia
+†Rahonavis
+†Jeholornis
+†Jixiangornis
+†Balaur
+†Zhongjianornis
+†Sapeornis
+†Confuciusornithiformes
+†Protopteryx
+†Pengornis
+Ornithothoraces
+†Enantiornithes
+†Archaeorhynchus
+†Patagopteryx
+†Vorona
+†Schizooura
+†Hongshanornithidae
+†Jianchangornis
+†Songlingornithidae
+†Gansus
+†Apsaravis
+†Hesperornithes
+†Ichthyornis
+†Vegavis
+Aves
+The first large, diverse lineage of short-tailed avialans to evolve were the Enantiornithes, or "opposite birds", so named because the construction of their shoulder bones was in reverse to that of modern birds. Enantiornithes occupied a wide array of ecological niches, from sand-probing shorebirds and fish-eaters to tree-dwelling forms and seed-eaters. While they were the dominant group of avialans during the Cretaceous period, enantiornithes became extinct along with many other dinosaur groups at the end of the Mesozoic era.[31]
+Many species of the second major avialan lineage to diversify, the Euornithes (meaning "true birds", because they include the ancestors of modern birds), were semi-aquatic and specialised in eating fish and other small aquatic organisms. Unlike the Enantiornithes, which dominated land-based and arboreal habitats, most early euornithes lacked perching adaptations and seem to have included shorebird-like species, waders, and swimming and diving species.
+The latter included the superficially gull-like Ichthyornis[35] and the Hesperornithiformes, which became so well adapted to hunting fish in marine environments that they lost the ability to fly and became primarily aquatic.[31] The early euornithes also saw the development of many traits associated with modern birds, like strongly keeled breastbones, toothless, beaked portions of their jaws (though most non-avian euornithes retained teeth in other parts of the jaws).[36] Euornithes also included the first avialans to develop true pygostyle and a fully mobile fan of tail feathers,[37] which may have replaced the "hind wing" as the primary mode of aerial maneuverability and braking in flight.[30]
+A study on mosaic evolution in the avian skull found that the last common ancestor of all Neornithes might have had a beak similar to that of the modern hook-billed vanga and a skull similar to that of the Eurasian golden oriole. As both species are small aerial and canopy foraging omnivores, a similar ecological niche was inferred for this hypothetical ancestor.[38]
+Struthioniformes
+Tinamiformes
+Other birds (Neoaves)
+Anseriformes
+Galliformes
+All modern birds lie within the crown group Aves (alternately Neornithes), which has two subdivisions: the Palaeognathae, which includes the flightless ratites (such as the ostriches) and the weak-flying tinamous, and the extremely diverse Neognathae, containing all other birds.[39] These two subdivisions are often given the rank of superorder,[40] although Livezey and Zusi assigned them "cohort" rank.[5] Depending on the taxonomic viewpoint, the number of known living bird species varies anywhere from 9,800[41] to 10,758.[42]
+The discovery of Vegavis, a late Cretaceous member of the Anatidae, proved that the diversification of modern birds started before the Cenozoic era.[43] The affinities of an earlier fossil, the possible galliform Austinornis lentus, dated to about 85 million years ago,[44] are still too controversial to provide a fossil evidence of modern bird diversification.
+Most studies agree on a Cretaceous age for the most recent common ancestor of modern birds but estimates range from the Middle Cretaceous[1] to the latest Late Cretaceous.[45] Similarly, there is no agreement on whether most of the early diversification of modern birds occurred before or after the Cretaceous–Palaeogene extinction event.[46] This disagreement is in part caused by a divergence in the evidence; most molecular dating studies suggests a Cretaceous evolutionary radiation, while fossil evidence points to a Cenozoic radiation (the so-called 'rocks' versus 'clocks' controversy). Previous attempts to reconcile molecular and fossil evidence have proved controversial,[46][47] but more recent estimates, using a more comprehensive sample of fossils and a new way of calibrating molecular clocks, showed that while modern birds originated early in the Late Cretaceous, a pulse of diversification in all major groups occurred around the Cretaceous–Palaeogene extinction event.[48]
+Cladogram of modern bird relationships based on Prum, R.O. et al. (2015)[45] with some clade names after Yuri, T. et al. (2013).[49]
+Struthioniformes[50] (ostriches)
+Rheiformes (rheas)
+Casuariiformes (cassowaries & emus)
+Apterygiformes (kiwi)
+†Aepyornithiformes (elephant birds)
+Tinamiformes (tinamous)
+†Dinornithiformes (moa)
+Galliformes (chickens and relatives)
+Anseriformes (ducks and relatives)
+Caprimulgiformes[50] (nightjars)
+Steatornithiformes (oilbird)
+Nyctibiiformes (potoos)
+Podargiformes (frogmouths)
+Apodiformes (swifts and hummingbirds)
+Musophagiformes (turacos)
+Otidiformes (bustards)
+Cuculiformes (cuckoos)
+Columbiformes (pigeons)
+Mesitornithiformes (mesites)
+Pterocliformes (sandgrouse)
+Gruiformes (rails and cranes)
+Phoenicopteriformes (flamingos)
+Podicipediformes (grebes)
+Charadriiformes (waders and relatives)
+Phaethontiformes (tropicbirds)
+Eurypygiformes (sunbittern and kagu)
+Gaviiformes[50] (loons)
+Procellariiformes (albatrosses and petrels)
+Sphenisciformes (penguins)
+Ciconiiformes (storks)
+Suliformes (boobies, cormorants, etc.)
+Pelecaniformes (pelicans, herons & ibises)
+Opisthocomiformes (hoatzin)
+Cathartiformes (New World vultures)
+Accipitriformes (hawks and relatives)
+Strigiformes (owls)
+Coliiformes (mouse birds)
+Leptosomiformes (cuckoo roller)
+Trogoniformes (trogons and quetzals)
+Bucerotiformes (hornbills and relatives)
+Coraciiformes (kingfishers and relatives)
+Piciformes (woodpeckers and relatives)
+Cariamiformes (seriemas)
+Falconiformes (falcons)
+Psittaciformes (parrots)
+Passeriformes (passerines)
+The classification of birds is a contentious issue. Sibley and Ahlquist's Phylogeny and Classification of Birds (1990) is a landmark work on the classification of birds,[51] although it is frequently debated and constantly revised. Most evidence seems to suggest the assignment of orders is accurate,[52] but scientists disagree about the relationships between the orders themselves; evidence from modern bird anatomy, fossils and DNA have all been brought to bear on the problem, but no strong consensus has emerged. More recently, new fossil and molecular evidence is providing an increasingly clear picture of the evolution of modern bird orders.[53][45]
+Birds live and breed in most terrestrial habitats and on all seven continents, reaching their southern extreme in the snow petrel's breeding colonies up to 440 kilometres (270 mi) inland in Antarctica.[55] The highest bird diversity occurs in tropical regions. It was earlier thought that this high diversity was the result of higher speciation rates in the tropics; however recent studies found higher speciation rates in the high latitudes that were offset by greater extinction rates than in the tropics.[56] Many species migrate annually over great distances and across oceans; several families of birds have adapted to life both on the world's oceans and in them, and some seabird species come ashore only to breed,[57] while some penguins have been recorded diving up to 300 metres (980 ft) deep.[58]
+Many bird species have established breeding populations in areas to which they have been introduced by humans. Some of these introductions have been deliberate; the ring-necked pheasant, for example, has been introduced around the world as a game bird.[59] Others have been accidental, such as the establishment of wild monk parakeets in several North American cities after their escape from captivity.[60] Some species, including cattle egret,[61] yellow-headed caracara[62] and galah,[63] have spread naturally far beyond their original ranges as agricultural practices created suitable new habitat.
+Compared with other vertebrates, birds have a body plan that shows many unusual adaptations, mostly to facilitate flight.
+The skeleton consists of very lightweight bones. They have large air-filled cavities (called pneumatic cavities) which connect with the respiratory system.[64] The skull bones in adults are fused and do not show cranial sutures.[65] The orbits are large and separated by a bony septum. The spine has cervical, thoracic, lumbar and caudal regions with the number of cervical (neck) vertebrae highly variable and especially flexible, but movement is reduced in the anterior thoracic vertebrae and absent in the later vertebrae.[66] The last few are fused with the pelvis to form the synsacrum.[65] The ribs are flattened and the sternum is keeled for the attachment of flight muscles except in the flightless bird orders. The forelimbs are modified into wings.[67] The wings are more or less developed depending on the species; the only known groups that lost their wings are the extinct moa and elephant birds.[68]
+Like the reptiles, birds are primarily uricotelic, that is, their kidneys extract nitrogenous waste from their bloodstream and excrete it as uric acid, instead of urea or ammonia, through the ureters into the intestine. Birds do not have a urinary bladder or external urethral opening and (with exception of the ostrich) uric acid is excreted along with faeces as a semisolid waste.[69][70][71] However, birds such as hummingbirds can be facultatively ammonotelic, excreting most of the nitrogenous wastes as ammonia.[72] They also excrete creatine, rather than creatinine like mammals.[65] This material, as well as the output of the intestines, emerges from the bird's cloaca.[73][74] The cloaca is a multi-purpose opening: waste is expelled through it, most birds mate by joining cloaca, and females lay eggs from it. In addition, many species of birds regurgitate pellets.[75]
+It is a common but not universal feature of altricial passerine nestlings (born helpless, under constant parental care) that instead of excreting directly into the nest, they produce a fecal sac. This is a mucus-covered pouch that allows parents to either dispose of the waste outside the nest or to recycle the waste through their own digestive system.[76]
+Males within Palaeognathae (with the exception of the kiwis), the Anseriformes (with the exception of screamers), and in rudimentary forms in Galliformes (but fully developed in Cracidae) possess a penis, which is never present in Neoaves.[77][78] The length is thought to be related to sperm competition.[79] When not copulating, it is hidden within the proctodeum compartment within the cloaca, just inside the vent. Female birds have sperm storage tubules[80] that allow sperm to remain viable long after copulation, a hundred days in some species.[81] Sperm from multiple males may compete through this mechanism. Most female birds have a single ovary and a single oviduct, both on the left side,[82] but there are exceptions: species in at least 16 different orders of birds have two ovaries. Even these species, however, tend to have a single oviduct.[82] It has been speculated that this might be an adaptation to flight, but males have two testes, and it is also observed that the gonads in both sexes decrease dramatically in size outside the breeding season.[83][84] Also terrestrial birds generally have a single ovary, as does the platypus, an egg-laying mammal. A more likely explanation is that the egg develops a shell while passing through the oviduct over a period of about a day, so that if two eggs were to develop at the same time, there would be a risk to survival.[82]
+Birds have two sexes: either female or male. The sex of birds is determined by the Z and W sex chromosomes, rather than by the X and Y chromosomes present in mammals. Male birds have two Z chromosomes (ZZ), and female birds have a W chromosome and a Z chromosome (WZ).[65]
+In nearly all species of birds, an individual's sex is determined at fertilisation. However, one recent study claimed to demonstrate temperature-dependent sex determination among the Australian brushturkey, for which higher temperatures during incubation resulted in a higher female-to-male sex ratio.[85] This, however, was later proven to not be the case. These birds do not exhibit temperature-dependent sex determination, but temperature-dependent sex mortality.[86]
+Birds have one of the most complex respiratory systems of all animal groups.[65] Upon inhalation, 75% of the fresh air bypasses the lungs and flows directly into a posterior air sac which extends from the lungs and connects with air spaces in the bones and fills them with air. The other 25% of the air goes directly into the lungs. When the bird exhales, the used air flows out of the lungs and the stored fresh air from the posterior air sac is simultaneously forced into the lungs. Thus, a bird's lungs receive a constant supply of fresh air during both inhalation and exhalation.[87] Sound production is achieved using the syrinx, a muscular chamber incorporating multiple tympanic membranes which diverges from the lower end of the trachea;[88] the trachea being elongated in some species, increasing the volume of vocalisations and the perception of the bird's size.[89]
+In birds, the main arteries taking blood away from the heart originate from the right aortic arch (or pharyngeal arch), unlike in the mammals where the left aortic arch forms this part of the aorta.[65] The postcava receives blood from the limbs via the renal portal system. Unlike in mammals, the circulating red blood cells in birds retain their nucleus.[90]
+The avian circulatory system is driven by a four-chambered, myogenic heart contained in a fibrous pericardial sac. This pericardial sac is filled with a serous fluid for lubrication.[91] The heart itself is divided into a right and left half, each with an atrium and ventricle. The atrium and ventricles of each side are separated by atrioventricular valves which prevent back flow from one chamber to the next during contraction. Being myogenic, the heart's pace is maintained by pacemaker cells found in the sinoatrial node, located on the right atrium.
+The sinoatrial node uses calcium to cause a depolarising signal transduction pathway from the atrium through right and left atrioventricular bundle which communicates contraction to the ventricles. The avian heart also consists of muscular arches that are made up of thick bundles of muscular layers. Much like a mammalian heart, the avian heart is composed of endocardial, myocardial and epicardial layers.[91] The atrium walls tend to be thinner than the ventricle walls, due to the intense ventricular contraction used to pump oxygenated blood throughout the body. Avian hearts are generally larger than mammalian hearts when compared to body mass. This adaptation allows more blood to be pumped to meet the high metabolic need associated with flight.[92]
+Birds have a very efficient system for diffusing oxygen into the blood; birds have a ten times greater surface area to gas exchange volume than mammals. As a result, birds have more blood in their capillaries per unit of volume of lung than a mammal.[92] The arteries are composed of thick elastic muscles to withstand the pressure of the ventricular contractions, and become more rigid as they move away from the heart. Blood moves through the arteries, which undergo vasoconstriction, and into arterioles which act as a transportation system to distribute primarily oxygen as well as nutrients to all tissues of the body.[93] As the arterioles move away from the heart and into individual organs and tissues they are further divided to increase surface area and slow blood flow. Blood travels through the arterioles and moves into the capillaries where gas exchange can occur.
+Capillaries are organized into capillary beds in tissues; it is here that blood exchanges oxygen for carbon dioxide waste. In the capillary beds, blood flow is slowed to allow maximum diffusion of oxygen into the tissues. Once the blood has become deoxygenated, it travels through venules then veins and back to the heart. Veins, unlike arteries, are thin and rigid as they do not need to withstand extreme pressure. As blood travels through the venules to the veins a funneling occurs called vasodilation bringing blood back to the heart.[93] Once the blood reaches the heart, it moves first into the right atrium, then the right ventricle to be pumped through the lungs for further gas exchange of carbon dioxide waste for oxygen. Oxygenated blood then flows from the lungs through the left atrium to the left ventricle where it is pumped out to the body.
+The nervous system is large relative to the bird's size.[65] The most developed part of the brain is the one that controls the flight-related functions, while the cerebellum coordinates movement and the cerebrum controls behaviour patterns, navigation, mating and nest building. Most birds have a poor sense of smell[94] with notable exceptions including kiwis,[95] New World vultures[96] and tubenoses.[97] The avian visual system is usually highly developed. Water birds have special flexible lenses, allowing accommodation for vision in air and water.[65] Some species also have dual fovea. Birds are tetrachromatic, possessing ultraviolet (UV) sensitive cone cells in the eye as well as green, red and blue ones.[98] They also have double cones, likely to mediate achromatic vision.[99]
+Many birds show plumage patterns in ultraviolet that are invisible to the human eye; some birds whose sexes appear similar to the naked eye are distinguished by the presence of ultraviolet reflective patches on their feathers. Male blue tits have an ultraviolet reflective crown patch which is displayed in courtship by posturing and raising of their nape feathers.[100] Ultraviolet light is also used in foraging—kestrels have been shown to search for prey by detecting the UV reflective urine trail marks left on the ground by rodents.[101] With the exception of pigeons and a few other species,[102] the eyelids of birds are not used in blinking. Instead the eye is lubricated by the nictitating membrane, a third eyelid that moves horizontally.[103] The nictitating membrane also covers the eye and acts as a contact lens in many aquatic birds.[65] The bird retina has a fan shaped blood supply system called the pecten.[65]
+Most birds cannot move their eyes, although there are exceptions, such as the great cormorant.[104] Birds with eyes on the sides of their heads have a wide visual field, while birds with eyes on the front of their heads, such as owls, have binocular vision and can estimate the depth of field.[105] The avian ear lacks external pinnae but is covered by feathers, although in some birds, such as the Asio, Bubo and Otus owls, these feathers form tufts which resemble ears. The inner ear has a cochlea, but it is not spiral as in mammals.[106]
+A few species are able to use chemical defences against predators; some Procellariiformes can eject an unpleasant stomach oil against an aggressor,[107] and some species of pitohuis from New Guinea have a powerful neurotoxin in their skin and feathers.[108]
+A lack of field observations limit our knowledge, but intraspecific conflicts are known to sometimes result in injury or death.[109] The screamers (Anhimidae), some jacanas (Jacana, Hydrophasianus), the spur-winged goose (Plectropterus), the torrent duck (Merganetta) and nine species of lapwing (Vanellus) use a sharp spur on the wing as a weapon. The steamer ducks (Tachyeres), geese and swans (Anserinae), the solitaire (Pezophaps), sheathbills (Chionis), some guans (Crax) and stone curlews (Burhinus) use a bony knob on the alular metacarpal to punch and hammer opponents.[109] The jacanas Actophilornis and Irediparra have an expanded, blade-like radius. The extinct Xenicibis was unique in having an elongate forelimb and massive hand which likely functioned in combat or defence as a jointed club or flail. Swans, for instance, may strike with the bony spurs and bite when defending eggs or young.[109]
+Feathers are a feature characteristic of birds (though also present in some dinosaurs not currently considered to be true birds). They facilitate flight, provide insulation that aids in thermoregulation, and are used in display, camouflage, and signalling.[65] There are several types of feathers, each serving its own set of purposes. Feathers are epidermal growths attached to the skin and arise only in specific tracts of skin called pterylae. The distribution pattern of these feather tracts (pterylosis) is used in taxonomy and systematics. The arrangement and appearance of feathers on the body, called plumage, may vary within species by age, social status,[110] and sex.[111]
+Plumage is regularly moulted; the standard plumage of a bird that has moulted after breeding is known as the "non-breeding" plumage, or—in the Humphrey–Parkes terminology—"basic" plumage; breeding plumages or variations of the basic plumage are known under the Humphrey–Parkes system as "alternate" plumages.[112] Moulting is annual in most species, although some may have two moults a year, and large birds of prey may moult only once every few years. Moulting patterns vary across species. In passerines, flight feathers are replaced one at a time with the innermost primary being the first. When the fifth of sixth primary is replaced, the outermost tertiaries begin to drop. After the innermost tertiaries are moulted, the secondaries starting from the innermost begin to drop and this proceeds to the outer feathers (centrifugal moult). The greater primary coverts are moulted in synchrony with the primary that they overlap.[113]
+A small number of species, such as ducks and geese, lose all of their flight feathers at once, temporarily becoming flightless.[114] As a general rule, the tail feathers are moulted and replaced starting with the innermost pair.[113] Centripetal moults of tail feathers are however seen in the Phasianidae.[115] The centrifugal moult is modified in the tail feathers of woodpeckers and treecreepers, in that it begins with the second innermost pair of feathers and finishes with the central pair of feathers so that the bird maintains a functional climbing tail.[113][116] The general pattern seen in passerines is that the primaries are replaced outward, secondaries inward, and the tail from centre outward.[117] Before nesting, the females of most bird species gain a bare brood patch by losing feathers close to the belly. The skin there is well supplied with blood vessels and helps the bird in incubation.[118]
+Feathers require maintenance and birds preen or groom them daily, spending an average of around 9% of their daily time on this.[119] The bill is used to brush away foreign particles and to apply waxy secretions from the uropygial gland; these secretions protect the feathers' flexibility and act as an antimicrobial agent, inhibiting the growth of feather-degrading bacteria.[120] This may be supplemented with the secretions of formic acid from ants, which birds receive through a behaviour known as anting, to remove feather parasites.[121]
+The scales of birds are composed of the same keratin as beaks, claws, and spurs. They are found mainly on the toes and metatarsus, but may be found further up on the ankle in some birds. Most bird scales do not overlap significantly, except in the cases of kingfishers and woodpeckers.
+The scales of birds are thought to be homologous to those of reptiles and mammals.[122]
+Most birds can fly, which distinguishes them from almost all other vertebrate classes. Flight is the primary means of locomotion for most bird species and is used for searching for food and for escaping from predators. Birds have various adaptations for flight, including a lightweight skeleton, two large flight muscles, the pectoralis (which accounts for 15% of the total mass of the bird) and the supracoracoideus, as well as a modified forelimb (wing) that serves as an aerofoil.[65]
+Wing shape and size generally determine a bird's flight style and performance; many birds combine powered, flapping flight with less energy-intensive soaring flight. About 60 extant bird species are flightless, as were many extinct birds.[123] Flightlessness often arises in birds on isolated islands, probably due to limited resources and the absence of land predators.[124] Although flightless, penguins use similar musculature and movements to "fly" through the water, as do some flight-capable birds such as auks, shearwaters and dippers.[125]
+Most birds are diurnal, but some birds, such as many species of owls and nightjars, are nocturnal or crepuscular (active during twilight hours), and many coastal waders feed when the tides are appropriate, by day or night.[126]
+Birds' diets are varied and often include nectar, fruit, plants, seeds, carrion, and various small animals, including other birds.[65] The digestive system of birds is unique, with a crop for storage and a gizzard that contains swallowed stones for grinding food to compensate for the lack of teeth.[127] Most birds are highly adapted for rapid digestion to aid with flight.[128] Some migratory birds have adapted to use protein stored in many parts of their bodies, including protein from the intestines, as additional energy during migration.[129]
+Birds that employ many strategies to obtain food or feed on a variety of food items are called generalists, while others that concentrate time and effort on specific food items or have a single strategy to obtain food are considered specialists.[65] Avian foraging strategies can vary widely by species. Many birds glean for insects, invertebrates, fruit, or seeds. Some hunt insects by suddenly attacking from a branch. Those species that seek pest insects are considered beneficial 'biological control agents' and their presence encouraged in biological pest control programmes.[130] Combined, insectivorous birds eat 400–500 million metric tons of arthropods annually.[131]
+Nectar feeders such as hummingbirds, sunbirds, lories, and lorikeets amongst others have specially adapted brushy tongues and in many cases bills designed to fit co-adapted flowers.[132] Kiwis and shorebirds with long bills probe for invertebrates; shorebirds' varied bill lengths and feeding methods result in the separation of ecological niches.[65][133] Loons, diving ducks, penguins and auks pursue their prey underwater, using their wings or feet for propulsion,[57] while aerial predators such as sulids, kingfishers and terns plunge dive after their prey. Flamingos, three species of prion, and some ducks are filter feeders.[134][135] Geese and dabbling ducks are primarily grazers.
+Some species, including frigatebirds, gulls,[136] and skuas,[137] engage in kleptoparasitism, stealing food items from other birds. Kleptoparasitism is thought to be a supplement to food obtained by hunting, rather than a significant part of any species' diet; a study of great frigatebirds stealing from masked boobies estimated that the frigatebirds stole at most 40% of their food and on average stole only 5%.[138] Other birds are scavengers; some of these, like vultures, are specialised carrion eaters, while others, like gulls, corvids, or other birds of prey, are opportunists.[139]
+Water is needed by many birds although their mode of excretion and lack of sweat glands reduces the physiological demands.[140] Some desert birds can obtain their water needs entirely from moisture in their food. They may also have other adaptations such as allowing their body temperature to rise, saving on moisture loss from evaporative cooling or panting.[141] Seabirds can drink seawater and have salt glands inside the head that eliminate excess salt out of the nostrils.[142]
+Most birds scoop water in their beaks and raise their head to let water run down the throat. Some species, especially of arid zones, belonging to the pigeon, finch, mousebird, button-quail and bustard families are capable of sucking up water without the need to tilt back their heads.[143] Some desert birds depend on water sources and sandgrouse are particularly well known for their daily congregations at waterholes. Nesting sandgrouse and many plovers carry water to their young by wetting their belly feathers.[144] Some birds carry water for chicks at the nest in their crop or regurgitate it along with food. The pigeon family, flamingos and penguins have adaptations to produce a nutritive fluid called crop milk that they provide to their chicks.[145]
+Feathers, being critical to the survival of a bird, require maintenance. Apart from physical wear and tear, feathers face the onslaught of fungi, ectoparasitic feather mites and bird lice.[146] The physical condition of feathers are maintained by preening often with the application of secretions from the preen gland. Birds also bathe in water or dust themselves. While some birds dip into shallow water, more aerial species may make aerial dips into water and arboreal species often make use of dew or rain that collect on leaves. Birds of arid regions make use of loose soil to dust-bathe. A behaviour termed as anting in which the bird encourages ants to run through their plumage is also thought to help them reduce the ectoparasite load in feathers. Many species will spread out their wings and expose them to direct sunlight and this too is thought to help in reducing fungal and ectoparasitic activity that may lead to feather damage.[147][148]
+Many bird species migrate to take advantage of global differences of seasonal temperatures, therefore optimising availability of food sources and breeding habitat. These migrations vary among the different groups. Many landbirds, shorebirds, and waterbirds undertake annual long-distance migrations, usually triggered by the length of daylight as well as weather conditions. These birds are characterised by a breeding season spent in the temperate or polar regions and a non-breeding season in the tropical regions or opposite hemisphere. Before migration, birds substantially increase body fats and reserves and reduce the size of some of their organs.[149][150]
+Migration is highly demanding energetically, particularly as birds need to cross deserts and oceans without refuelling. Landbirds have a flight range of around 2,500 km (1,600 mi) and shorebirds can fly up to 4,000 km (2,500 mi),[151] although the bar-tailed godwit is capable of non-stop flights of up to 10,200 km (6,300 mi).[152] Seabirds also undertake long migrations, the longest annual migration being those of sooty shearwaters, which nest in New Zealand and Chile and spend the northern summer feeding in the North Pacific off Japan, Alaska and California, an annual round trip of 64,000 km (39,800 mi).[153] Other seabirds disperse after breeding, travelling widely but having no set migration route. Albatrosses nesting in the Southern Ocean often undertake circumpolar trips between breeding seasons.[154]
+Some bird species undertake shorter migrations, travelling only as far as is required to avoid bad weather or obtain food. Irruptive species such as the boreal finches are one such group and can commonly be found at a location in one year and absent the next. This type of migration is normally associated with food availability.[155] Species may also travel shorter distances over part of their range, with individuals from higher latitudes travelling into the existing range of conspecifics; others undertake partial migrations, where only a fraction of the population, usually females and subdominant males, migrates.[156] Partial migration can form a large percentage of the migration behaviour of birds in some regions; in Australia, surveys found that 44% of non-passerine birds and 32% of passerines were partially migratory.[157]
+Altitudinal migration is a form of short-distance migration in which birds spend the breeding season at higher altitudes and move to lower ones during suboptimal conditions. It is most often triggered by temperature changes and usually occurs when the normal territories also become inhospitable due to lack of food.[158] Some species may also be nomadic, holding no fixed territory and moving according to weather and food availability. Parrots as a family are overwhelmingly neither migratory nor sedentary but considered to either be dispersive, irruptive, nomadic or undertake small and irregular migrations.[159]
+The ability of birds to return to precise locations across vast distances has been known for some time; in an experiment conducted in the 1950s, a Manx shearwater released in Boston in the United States returned to its colony in Skomer, in Wales within 13 days, a distance of 5,150 km (3,200 mi).[160] Birds navigate during migration using a variety of methods. For diurnal migrants, the sun is used to navigate by day, and a stellar compass is used at night. Birds that use the sun compensate for the changing position of the sun during the day by the use of an internal clock.[65] Orientation with the stellar compass depends on the position of the constellations surrounding Polaris.[161] These are backed up in some species by their ability to sense the Earth's geomagnetism through specialised photoreceptors.[162]
+Birds communicate using primarily visual and auditory signals. Signals can be interspecific (between species) and intraspecific (within species).
+Birds sometimes use plumage to assess and assert social dominance,[163] to display breeding condition in sexually selected species, or to make threatening displays, as in the sunbittern's mimicry of a large predator to ward off hawks and protect young chicks.[164] Variation in plumage also allows for the identification of birds, particularly between species.
+Visual communication among birds may also involve ritualised displays, which have developed from non-signalling actions such as preening, the adjustments of feather position, pecking, or other behaviour. These displays may signal aggression or submission or may contribute to the formation of pair-bonds.[65] The most elaborate displays occur during courtship, where "dances" are often formed from complex combinations of many possible component movements;[165] males' breeding success may depend on the quality of such displays.[166]
+Bird calls and songs, which are produced in the syrinx, are the major means by which birds communicate with sound. This communication can be very complex; some species can operate the two sides of the syrinx independently, allowing the simultaneous production of two different songs.[88]
+Calls are used for a variety of purposes, including mate attraction,[65] evaluation of potential mates,[167] bond formation, the claiming and maintenance of territories,[65] the identification of other individuals (such as when parents look for chicks in colonies or when mates reunite at the start of breeding season),[168] and the warning of other birds of potential predators, sometimes with specific information about the nature of the threat.[169] Some birds also use mechanical sounds for auditory communication. The Coenocorypha snipes of New Zealand drive air through their feathers,[170] woodpeckers drum for long-distance communication,[171] and palm cockatoos use tools to drum.[172]
+While some birds are essentially territorial or live in small family groups, other birds may form large flocks. The principal benefits of flocking are safety in numbers and increased foraging efficiency.[65] Defence against predators is particularly important in closed habitats like forests, where ambush predation is common and multiple eyes can provide a valuable early warning system. This has led to the development of many mixed-species feeding flocks, which are usually composed of small numbers of many species; these flocks provide safety in numbers but increase potential competition for resources.[174] Costs of flocking include bullying of socially subordinate birds by more dominant birds and the reduction of feeding efficiency in certain cases.[175]
+Birds sometimes also form associations with non-avian species. Plunge-diving seabirds associate with dolphins and tuna, which push shoaling fish towards the surface.[176] Hornbills have a mutualistic relationship with dwarf mongooses, in which they forage together and warn each other of nearby birds of prey and other predators.[177]
+The high metabolic rates of birds during the active part of the day is supplemented by rest at other times. Sleeping birds often use a type of sleep known as vigilant sleep, where periods of rest are interspersed with quick eye-opening "peeks", allowing them to be sensitive to disturbances and enable rapid escape from threats.[178] Swifts are believed to be able to sleep in flight and radar observations suggest that they orient themselves to face the wind in their roosting flight.[179] It has been suggested that there may be certain kinds of sleep which are possible even when in flight.[180]
+Some birds have also demonstrated the capacity to fall into slow-wave sleep one hemisphere of the brain at a time. The birds tend to exercise this ability depending upon its position relative to the outside of the flock. This may allow the eye opposite the sleeping hemisphere to remain vigilant for predators by viewing the outer margins of the flock. This adaptation is also known from marine mammals.[181] Communal roosting is common because it lowers the loss of body heat and decreases the risks associated with predators.[182] Roosting sites are often chosen with regard to thermoregulation and safety.[183]
+Many sleeping birds bend their heads over their backs and tuck their bills in their back feathers, although others place their beaks among their breast feathers. Many birds rest on one leg, while some may pull up their legs into their feathers, especially in cold weather. Perching birds have a tendon locking mechanism that helps them hold on to the perch when they are asleep. Many ground birds, such as quails and pheasants, roost in trees. A few parrots of the genus Loriculus roost hanging upside down.[184] Some hummingbirds go into a nightly state of torpor accompanied with a reduction of their metabolic rates.[185] This physiological adaptation shows in nearly a hundred other species, including owlet-nightjars, nightjars, and woodswallows. One species, the common poorwill, even enters a state of hibernation.[186] Birds do not have sweat glands, but they may cool themselves by moving to shade, standing in water, panting, increasing their surface area, fluttering their throat or by using special behaviours like urohidrosis to cool themselves.
+Ninety-five per cent of bird species are socially monogamous. These species pair for at least the length of the breeding season or—in some cases—for several years or until the death of one mate.[188] Monogamy allows for both paternal care and biparental care, which is especially important for species in which females require males' assistance for successful brood-rearing.[189] Among many socially monogamous species, extra-pair copulation (infidelity) is common.[190] Such behaviour typically occurs between dominant males and females paired with subordinate males, but may also be the result of forced copulation in ducks and other anatids.[191]
+For females, possible benefits of extra-pair copulation include getting better genes for her offspring and insuring against the possibility of infertility in her mate.[192] Males of species that engage in extra-pair copulations will closely guard their mates to ensure the parentage of the offspring that they raise.[193]
+Other mating systems, including polygyny, polyandry, polygamy, polygynandry, and promiscuity, also occur.[65] Polygamous breeding systems arise when females are able to raise broods without the help of males.[65] Some species may use more than one system depending on the circumstances.
+Breeding usually involves some form of courtship display, typically performed by the male.[194] Most displays are rather simple and involve some type of song. Some displays, however, are quite elaborate. Depending on the species, these may include wing or tail drumming, dancing, aerial flights, or communal lekking. Females are generally the ones that drive partner selection,[195] although in the polyandrous phalaropes, this is reversed: plainer males choose brightly coloured females.[196] Courtship feeding, billing and allopreening are commonly performed between partners, generally after the birds have paired and mated.[197]
+Homosexual behaviour has been observed in males or females in numerous species of birds, including copulation, pair-bonding, and joint parenting of chicks.[198] Over 130 avian species around the world engage in sexual interactions between the same sex or homosexual behaviors. "Same-sex courtship activities may involve elaborate displays, synchronized dances, gift-giving ceremonies, or behaviors at specific display areas including bowers, arenas, or leks."[199]
+Many birds actively defend a territory from others of the same species during the breeding season; maintenance of territories protects the food source for their chicks. Species that are unable to defend feeding territories, such as seabirds and swifts, often breed in colonies instead; this is thought to offer protection from predators. Colonial breeders defend small nesting sites, and competition between and within species for nesting sites can be intense.[200]
+All birds lay amniotic eggs with hard shells made mostly of calcium carbonate.[65] Hole and burrow nesting species tend to lay white or pale eggs, while open nesters lay camouflaged eggs. There are many exceptions to this pattern, however; the ground-nesting nightjars have pale eggs, and camouflage is instead provided by their plumage. Species that are victims of brood parasites have varying egg colours to improve the chances of spotting a parasite's egg, which forces female parasites to match their eggs to those of their hosts.[201]
+Bird eggs are usually laid in a nest. Most species create somewhat elaborate nests, which can be cups, domes, plates, beds scrapes, mounds, or burrows.[202] Some bird nests, however, are extremely primitive; albatross nests are no more than a scrape on the ground. Most birds build nests in sheltered, hidden areas to avoid predation, but large or colonial birds—which are more capable of defence—may build more open nests. During nest construction, some species seek out plant matter from plants with parasite-reducing toxins to improve chick survival,[203] and feathers are often used for nest insulation.[202] Some bird species have no nests; the cliff-nesting common guillemot lays its eggs on bare rock, and male emperor penguins keep eggs between their body and feet. The absence of nests is especially prevalent in ground-nesting species where the newly hatched young are precocial.
+Incubation, which optimises temperature for chick development, usually begins after the last egg has been laid.[65] In monogamous species incubation duties are often shared, whereas in polygamous species one parent is wholly responsible for incubation. Warmth from parents passes to the eggs through brood patches, areas of bare skin on the abdomen or breast of the incubating birds. Incubation can be an energetically demanding process; adult albatrosses, for instance, lose as much as 83 grams (2.9 oz) of body weight per day of incubation.[204] The warmth for the incubation of the eggs of megapodes comes from the sun, decaying vegetation or volcanic sources.[205] Incubation periods range from 10 days (in woodpeckers, cuckoos and passerine birds) to over 80 days (in albatrosses and kiwis).[65]
+The diversity of characteristics of birds is great, sometimes even in closely related species. Several avian characteristics are compared in the table below.[206][207]
+At the time of their hatching, chicks range in development from helpless to independent, depending on their species. Helpless chicks are termed altricial, and tend to be born small, blind, immobile and naked; chicks that are mobile and feathered upon hatching are termed precocial. Altricial chicks need help thermoregulating and must be brooded for longer than precocial chicks. The young of many bird species do not precisely fit into either the precocial or altricial category, having some aspects of each and thus fall somewhere on an "altricial-precocial spectrum".[208] Chicks at neither extreme but favoring one or the other may be termed semi-precocial[209] or semi-altricial.[210]
+The length and nature of parental care varies widely amongst different orders and species. At one extreme, parental care in megapodes ends at hatching; the newly hatched chick digs itself out of the nest mound without parental assistance and can fend for itself immediately.[211] At the other extreme, many seabirds have extended periods of parental care, the longest being that of the great frigatebird, whose chicks take up to six months to fledge and are fed by the parents for up to an additional 14 months.[212] The chick guard stage describes the period of breeding during which one of the adult birds is permanently present at the nest after chicks have hatched. The main purpose of the guard stage is to aid offspring to thermoregulate and protect them from predation.[213]
+In some species, both parents care for nestlings and fledglings; in others, such care is the responsibility of only one sex. In some species, other members of the same species—usually close relatives of the breeding pair, such as offspring from previous broods—will help with the raising of the young.[214] Such alloparenting is particularly common among the Corvida, which includes such birds as the true crows, Australian magpie and fairy-wrens,[215] but has been observed in species as different as the rifleman and red kite. Among most groups of animals, male parental care is rare. In birds, however, it is quite common—more so than in any other vertebrate class.[65] Although territory and nest site defence, incubation, and chick feeding are often shared tasks, there is sometimes a division of labour in which one mate undertakes all or most of a particular duty.[216]
+The point at which chicks fledge varies dramatically. The chicks of the Synthliboramphus murrelets, like the ancient murrelet, leave the nest the night after they hatch, following their parents out to sea, where they are raised away from terrestrial predators.[217] Some other species, such as ducks, move their chicks away from the nest at an early age. In most species, chicks leave the nest just before, or soon after, they are able to fly. The amount of parental care after fledging varies; albatross chicks leave the nest on their own and receive no further help, while other species continue some supplementary feeding after fledging.[218] Chicks may also follow their parents during their first migration.[219]
+Brood parasitism, in which an egg-layer leaves her eggs with another individual's brood, is more common among birds than any other type of organism.[220] After a parasitic bird lays her eggs in another bird's nest, they are often accepted and raised by the host at the expense of the host's own brood. Brood parasites may be either obligate brood parasites, which must lay their eggs in the nests of other species because they are incapable of raising their own young, or non-obligate brood parasites, which sometimes lay eggs in the nests of conspecifics to increase their reproductive output even though they could have raised their own young.[221] One hundred bird species, including honeyguides, icterids, and ducks, are obligate parasites, though the most famous are the cuckoos.[220] Some brood parasites are adapted to hatch before their host's young, which allows them to destroy the host's eggs by pushing them out of the nest or to kill the host's chicks; this ensures that all food brought to the nest will be fed to the parasitic chicks.[222]
+Birds have evolved a variety of mating behaviours, with the peacock tail being perhaps the most famous example of sexual selection and the Fisherian runaway. Commonly occurring sexual dimorphisms such as size and colour differences are energetically costly attributes that signal competitive breeding situations.[223] Many types of avian sexual selection have been identified; intersexual selection, also known as female choice; and intrasexual competition, where individuals of the more abundant sex compete with each other for the privilege to mate. Sexually selected traits often evolve to become more pronounced in competitive breeding situations until the trait begins to limit the individual's fitness. Conflicts between an individual fitness and signalling adaptations ensure that sexually selected ornaments such as plumage coloration and courtship behaviour are "honest" traits. Signals must be costly to ensure that only good-quality individuals can present these exaggerated sexual ornaments and behaviours.[224]
+Inbreeding causes early death (inbreeding depression) in the zebra finch Taeniopygia guttata.[225] Embryo survival (that is, hatching success of fertile eggs) was significantly lower for sib-sib mating pairs than for unrelated pairs.
+Darwin's finch Geospiza scandens experiences inbreeding depression (reduced survival of offspring) and the magnitude of this effect is influenced by environmental conditions such as low food availability.[226]
+Incestuous matings by the purple-crowned fairy wren Malurus coronatus result in severe fitness costs due to inbreeding depression (greater than 30% reduction in hatchability of eggs).[227] Females paired with related males may undertake extra pair matings (see Promiscuity#Other animals for 90% frequency in avian species) that can reduce the negative effects of inbreeding. However, there are ecological and demographic constraints on extra pair matings. Nevertheless, 43% of broods produced by incestuously paired females contained extra pair young.[227]
+Inbreeding depression occurs in the great tit (Parus major) when the offspring produced as a result of a mating between close relatives show reduced fitness. In natural populations of Parus major, inbreeding is avoided by dispersal of individuals from their birthplace, which reduces the chance of mating with a close relative.[228]
+Southern pied babblers Turdoides bicolor appear to avoid inbreeding in two ways. The first is through dispersal, and the second is by avoiding familiar group members as mates.[229] Although both males and females disperse locally, they move outside the range where genetically related individuals are likely to be encountered. Within their group, individuals only acquire breeding positions when the opposite-sex breeder is unrelated.
+Cooperative breeding in birds typically occurs when offspring, usually males, delay dispersal from their natal group in order to remain with the family to help rear younger kin.[230] Female offspring rarely stay at home, dispersing over distances that allow them to breed independently, or to join unrelated groups. In general, inbreeding is avoided because it leads to a reduction in progeny fitness (inbreeding depression) due largely to the homozygous expression of deleterious recessive alleles.[231] Cross-fertilisation between unrelated individuals ordinarily leads to the masking of deleterious recessive alleles in progeny.[232][233]
+Birds occupy a wide range of ecological positions.[173] While some birds are generalists, others are highly specialised in their habitat or food requirements. Even within a single habitat, such as a forest, the niches occupied by different species of birds vary, with some species feeding in the forest canopy, others beneath the canopy, and still others on the forest floor. Forest birds may be insectivores, frugivores, and nectarivores. Aquatic birds generally feed by fishing, plant eating, and piracy or kleptoparasitism. Birds of prey specialise in hunting mammals or other birds, while vultures are specialised scavengers. Avivores are animals that are specialised at preying on birds.
+Some nectar-feeding birds are important pollinators, and many frugivores play a key role in seed dispersal.[234] Plants and pollinating birds often coevolve,[235] and in some cases a flower's primary pollinator is the only species capable of reaching its nectar.[236]
+Birds are often important to island ecology. Birds have frequently reached islands that mammals have not; on those islands, birds may fulfil ecological roles typically played by larger animals. For example, in New Zealand nine species of moa were important browsers, as are the kererū and kokako today.[234] Today the plants of New Zealand retain the defensive adaptations evolved to protect them from the extinct moa.[237] Nesting seabirds may also affect the ecology of islands and surrounding seas, principally through the concentration of large quantities of guano, which may enrich the local soil[238] and the surrounding seas.[239]
+A wide variety of avian ecology field methods, including counts, nest monitoring, and capturing and marking, are used for researching avian ecology.
+Since birds are highly visible and common animals, humans have had a relationship with them since the dawn of man.[240] Sometimes, these relationships are mutualistic, like the cooperative honey-gathering among honeyguides and African peoples such as the Borana.[241] Other times, they may be commensal, as when species such as the house sparrow[242] have benefited from human activities. Several bird species have become commercially significant agricultural pests,[243] and some pose an aviation hazard.[244] Human activities can also be detrimental, and have threatened numerous bird species with extinction (hunting, avian lead poisoning, pesticides, roadkill, wind turbine kills[245] and predation by pet cats and dogs are common causes of death for birds).[246]
+Birds can act as vectors for spreading diseases such as psittacosis, salmonellosis, campylobacteriosis, mycobacteriosis (avian tuberculosis), avian influenza (bird flu), giardiasis, and cryptosporidiosis over long distances. Some of these are zoonotic diseases that can also be transmitted to humans.[247]
+Domesticated birds raised for meat and eggs, called poultry, are the largest source of animal protein eaten by humans; in 2003, 76 million tons of poultry and 61 million tons of eggs were produced worldwide.[248] Chickens account for much of human poultry consumption, though domesticated turkeys, ducks, and geese are also relatively common. Many species of birds are also hunted for meat. Bird hunting is primarily a recreational activity except in extremely undeveloped areas. The most important birds hunted in North and South America are waterfowl; other widely hunted birds include pheasants, wild turkeys, quail, doves, partridge, grouse, snipe, and woodcock.[249] Muttonbirding is also popular in Australia and New Zealand.[250] Although some hunting, such as that of muttonbirds, may be sustainable, hunting has led to the extinction or endangerment of dozens of species.[251]
+Other commercially valuable products from birds include feathers (especially the down of geese and ducks), which are used as insulation in clothing and bedding, and seabird faeces (guano), which is a valuable source of phosphorus and nitrogen. The War of the Pacific, sometimes called the Guano War, was fought in part over the control of guano deposits.[252]
+Birds have been domesticated by humans both as pets and for practical purposes. Colourful birds, such as parrots and mynas, are bred in captivity or kept as pets, a practice that has led to the illegal trafficking of some endangered species.[253] Falcons and cormorants have long been used for hunting and fishing, respectively. Messenger pigeons, used since at least 1 AD, remained important as recently as World War II. Today, such activities are more common either as hobbies, for entertainment and tourism,[254] or for sports such as pigeon racing.
+Amateur bird enthusiasts (called birdwatchers, twitchers or, more commonly, birders) number in the millions.[255] Many homeowners erect bird feeders near their homes to attract various species. Bird feeding has grown into a multimillion-dollar industry; for example, an estimated 75% of households in Britain provide food for birds at some point during the winter.[256]
+Birds play prominent and diverse roles in religion and mythology.
+In religion, birds may serve as either messengers or priests and leaders for a deity, such as in the Cult of Makemake, in which the Tangata manu of Easter Island served as chiefs[257] or as attendants, as in the case of Hugin and Munin, the two common ravens who whispered news into the ears of the Norse god Odin. In several civilisations of ancient Italy, particularly Etruscan and Roman religion, priests were involved in augury, or interpreting the words of birds while the "auspex" (from which the word "auspicious" is derived) watched their activities to foretell events.[258]
+They may also serve as religious symbols, as when Jonah (Hebrew: יוֹנָה‎, dove) embodied the fright, passivity, mourning, and beauty traditionally associated with doves.[259] Birds have themselves been deified, as in the case of the common peacock, which is perceived as Mother Earth by the Dravidians of India.[260] In the ancient world, doves were used as symbols of the Mesopotamian goddess Inanna (later known as Ishtar),[261][262] the Canaanite mother goddess Asherah,[261][262][263] and the Greek goddess Aphrodite.[264][265][261][262][266] In ancient Greece, Athena, the goddess of wisdom and patron deity of the city of Athens, had a little owl as her symbol.[267][268][269] In religious images preserved from the Inca and Tiwanaku empires, birds are depicted in the process of transgressing boundaries between earthly and underground spiritual realms.[270] Indigenous peoples of the central Andes maintain legends of birds passing to and from metaphysical worlds.[270]
+Birds have featured in culture and art since prehistoric times, when they were represented in early cave paintings.[271] Some birds have been perceived as monsters, including the mythological Roc and the Māori's legendary Pouākai, a giant bird capable of snatching humans.[272] Birds were later used as symbols of power, as in the magnificent Peacock Throne of the Mughal and Persian emperors.[273] With the advent of scientific interest in birds, many paintings of birds were commissioned for books.
+Among the most famous of these bird artists was John James Audubon, whose paintings of North American birds were a great commercial success in Europe and who later lent his name to the National Audubon Society.[274] Birds are also important figures in poetry; for example, Homer incorporated nightingales into his Odyssey, and Catullus used a sparrow as an erotic symbol in his Catullus 2.[275] The relationship between an albatross and a sailor is the central theme of Samuel Taylor Coleridge's The Rime of the Ancient Mariner, which led to the use of the term as a metaphor for a 'burden'.[276] Other English metaphors derive from birds; vulture funds and vulture investors, for instance, take their name from the scavenging vulture.[277]
+Perceptions of bird species vary across cultures. Owls are associated with bad luck, witchcraft, and death in parts of Africa,[278] but are regarded as wise across much of Europe.[279] Hoopoes were considered sacred in Ancient Egypt and symbols of virtue in Persia, but were thought of as thieves across much of Europe and harbingers of war in Scandinavia.[280] In heraldry, birds, especially eagles, often appear in coats of arms.[281]
+In music, birdsong has influenced composers and musicians in several ways: they can be inspired by birdsong; they can intentionally imitate bird song in a composition, as Vivaldi, Messiaen, and Beethoven did, along with many later composers; they can incorporate recordings of birds into their works, as Ottorino Respighi first did; or like Beatrice Harrison and David Rothenberg, they can duet with birds.[282][283][284][285]
+Although human activities have allowed the expansion of a few species, such as the barn swallow and European starling, they have caused population decreases or extinction in many other species. Over a hundred bird species have gone extinct in historical times,[286] although the most dramatic human-caused avian extinctions, eradicating an estimated 750–1800 species, occurred during the human colonisation of Melanesian, Polynesian, and Micronesian islands.[287] Many bird populations are declining worldwide, with 1,227 species listed as threatened by BirdLife International and the IUCN in 2009.[288][289]
+The most commonly cited human threat to birds is habitat loss.[290] Other threats include overhunting, accidental mortality due to collisions with buildings or vehicles, long-line fishing bycatch,[291] pollution (including oil spills and pesticide use),[292] competition and predation from nonnative invasive species,[293] and climate change.
+Governments and conservation groups work to protect birds, either by passing laws that preserve and restore bird habitat or by establishing captive populations for reintroductions. Such projects have produced some successes; one study estimated that conservation efforts saved 16 species of bird that would otherwise have gone extinct between 1994 and 2004, including the California condor and Norfolk parakeet.[294]

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+Birds are a group of warm-blooded vertebrates constituting the class Aves, characterized by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5 cm (2 in) bee hummingbird to the 2.75 m (9 ft) ostrich. There are about ten thousand living species, more than half of which are passerine, or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in some birds, including ratites, penguins, and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming.
+Birds are a group of feathered theropod dinosaurs, and constitute the only living dinosaurs. Likewise, birds are considered reptiles in the modern cladistic sense of the term, and their closest living relatives are the crocodilians. Birds are descendants of the primitive avialans (whose members include Archaeopteryx) which first appeared about 160 million years ago (mya) in China. According to DNA evidence, modern birds (Neornithes) evolved in the Middle to Late Cretaceous, and diversified dramatically around the time of the Cretaceous–Paleogene extinction event 66 mya, which killed off the pterosaurs and all non-avian dinosaurs.
+Many social species pass on knowledge across generations, which is considered a form of culture. Birds are social, communicating with visual signals, calls, and songs, and participating in such behaviours as cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially (but not necessarily sexually) monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have breeding systems that are polygynous (one male with many females) or, rarely, polyandrous (one female with many males). Birds produce offspring by laying eggs which are fertilised through sexual reproduction. They are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching.
+Many species of birds are economically important as food for human consumption and raw material in manufacturing, with domesticated and undomesticated birds being important sources of eggs, meat, and feathers. Songbirds, parrots, and other species are popular as pets. Guano (bird excrement) is harvested for use as a fertiliser. Birds figure throughout human culture. About 120 to 130 species have become extinct due to human activity since the 17th century, and hundreds more before then. Human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry.
+The first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae.[3]
+Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use.[4] Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda.[5]
+Aves and a sister group, the order Crocodilia, contain the only living representatives of the reptile clade Archosauria. During the late 1990s, Aves was most commonly defined phylogenetically as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica.[6] However, an earlier definition proposed by Jacques Gauthier gained wide currency in the 21st century, and is used by many scientists including adherents of the Phylocode system. Gauthier defined Aves to include only the crown group of the set of modern birds. This was done by excluding most groups known only from fossils, and assigning them, instead, to the broader group Avialae,[7] in part to avoid the uncertainties about the placement of Archaeopteryx in relation to animals traditionally thought of as theropod dinosaurs.
+Gauthier and de Queiroz[8] identified four different definitions for the same biological name "Aves", which is a problem. The authors proposed to reserve the term Aves only for the crown group consisting of the last common ancestor of all living birds and all of its descendants, which corresponds to meaning number 4 below. He assigned other names to the other groups.
+Crocodiles
+Birds
+Turtles
+Lizards (including snakes)
+Under the fourth definition Archaeopteryx, traditionally considered one of the earliest members of Aves, is removed from this group, becoming a non-avian dinosaur instead. These proposals have been adopted by many researchers in the field of palaeontology and bird evolution, though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is often used synonymously with the vernacular term "bird" by these researchers.[9]
+†Coelurus
+†Ornitholestes
+†Ornithomimosauria
+†Alvarezsauridae
+†Oviraptorosauria
+Paraves
+Most researchers define Avialae as branch-based clade, though definitions vary. Many authors have used a definition similar to "all theropods closer to birds than to Deinonychus",[11][12] with Troodon being sometimes added as a second external specifier in case it is closer to birds than to Deinonychus.[13] Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on physical characteristics). Jacques Gauthier, who named Avialae in 1986, re-defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight, and the birds that descended from them.[8][14]
+Despite being currently one of the most widely used, the crown-group definition of Aves has been criticised by some researchers. Lee and Spencer (1997) argued that, contrary to what Gauthier defended, this definition would not increase the stability of the clade and the exact content of Aves will always be uncertain because any defined clade (either crown or not) will have few synapomorphies distinguishing it from its closest relatives. Their alternative definition is synonymous to Avifilopluma.[15]
+†Scansoriopterygidae
+†Eosinopteryx
+†Jinfengopteryx
+†Aurornis
+†Dromaeosauridae
+†Troodontidae
+Avialae
+Based on fossil and biological evidence, most scientists accept that birds are a specialised subgroup of theropod dinosaurs,[18] and more specifically, they are members of Maniraptora, a group of theropods which includes dromaeosaurids and oviraptorosaurs, among others.[19] As scientists have discovered more theropods closely related to birds, the previously clear distinction between non-birds and birds has become blurred. Recent discoveries in the Liaoning Province of northeast China, which demonstrate many small theropod feathered dinosaurs, contribute to this ambiguity.[20][21][22]
+The consensus view in contemporary palaeontology is that the flying theropods, or avialans, are the closest relatives of the deinonychosaurs, which include dromaeosaurids and troodontids.[23] Together, these form a group called Paraves. Some basal members of Deinonychosauria, such as Microraptor, have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal, have been able to glide, or both.[24][25] Unlike Archaeopteryx and the non-avialan feathered dinosaurs, who primarily ate meat, recent studies suggest that the first avialans were omnivores.[26]
+The Late Jurassic Archaeopteryx is well known as one of the first transitional fossils to be found, and it provided support for the theory of evolution in the late 19th century. Archaeopteryx was the first fossil to display both clearly traditional reptilian characteristics—teeth, clawed fingers, and a long, lizard-like tail—as well as wings with flight feathers similar to those of modern birds. It is not considered a direct ancestor of birds, though it is possibly closely related to the true ancestor.[27]
+Over 40% of key traits found in modern birds evolved during the 60 million year transition from the earliest bird-line archosaurs to the first maniraptoromorphs, i.e. the first dinosaurs closer to living birds than to Tyrannosaurus rex. The loss of osteoderms otherwise common in archosaurs and acquisition of primitive feathers might have occurred early during this phase.[10][29] After the appearance of Maniraptoromorpha, the next 40 million years marked a continuous reduction of body size and the accumulation of neotenic (juvenile-like) characteristics. Hypercarnivory became increasingly less common while braincases enlarged and forelimbs became longer.[10] The integument evolved into complex, pennaceous feathers.[29]
+The oldest known paravian (and probably the earliest avialan) fossils come from the Tiaojishan Formation of China, which has been dated to the late Jurassic period (Oxfordian stage), about 160 million years ago. The avialan species from this time period include Anchiornis huxleyi, Xiaotingia zhengi, and Aurornis xui.[9]
+The well-known probable early avialan, Archaeopteryx, dates from slightly later Jurassic rocks (about 155 million years old) from Germany. Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds, but were later lost during bird evolution. These features include enlarged claws on the second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial maneuvering.[30]
+Avialans diversified into a wide variety of forms during the Cretaceous Period. Many groups retained primitive characteristics, such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves).[31] Increasingly stiff tails (especially the outermost half) can be seen in the evolution of maniraptoromorphs, and this process culminated in the appearance of the pygostyle, an ossification of fused tail vertebrae.[10] In the late Cretaceous, about 100 million years ago, the ancestors of all modern birds evolved a more open pelvis, allowing them to lay larger eggs compared to body size.[32] Around 95 million years ago, they evolved a better sense of smell.[33]
+A third stage of bird evolution starting with Ornithothoraces (the "bird-chested" avialans) can be associated with the refining of aerodynamics and flight capabilities, and the loss or co-ossification of several skeletal features. Particularly significant are the development of an enlarged, keeled sternum and the alula, and the loss of grasping hands.
+[10]
+†Anchiornis
+†Archaeopteryx
+†Xiaotingia
+†Rahonavis
+†Jeholornis
+†Jixiangornis
+†Balaur
+†Zhongjianornis
+†Sapeornis
+†Confuciusornithiformes
+†Protopteryx
+†Pengornis
+Ornithothoraces
+†Enantiornithes
+†Archaeorhynchus
+†Patagopteryx
+†Vorona
+†Schizooura
+†Hongshanornithidae
+†Jianchangornis
+†Songlingornithidae
+†Gansus
+†Apsaravis
+†Hesperornithes
+†Ichthyornis
+†Vegavis
+Aves
+The first large, diverse lineage of short-tailed avialans to evolve were the Enantiornithes, or "opposite birds", so named because the construction of their shoulder bones was in reverse to that of modern birds. Enantiornithes occupied a wide array of ecological niches, from sand-probing shorebirds and fish-eaters to tree-dwelling forms and seed-eaters. While they were the dominant group of avialans during the Cretaceous period, enantiornithes became extinct along with many other dinosaur groups at the end of the Mesozoic era.[31]
+Many species of the second major avialan lineage to diversify, the Euornithes (meaning "true birds", because they include the ancestors of modern birds), were semi-aquatic and specialised in eating fish and other small aquatic organisms. Unlike the Enantiornithes, which dominated land-based and arboreal habitats, most early euornithes lacked perching adaptations and seem to have included shorebird-like species, waders, and swimming and diving species.
+The latter included the superficially gull-like Ichthyornis[35] and the Hesperornithiformes, which became so well adapted to hunting fish in marine environments that they lost the ability to fly and became primarily aquatic.[31] The early euornithes also saw the development of many traits associated with modern birds, like strongly keeled breastbones, toothless, beaked portions of their jaws (though most non-avian euornithes retained teeth in other parts of the jaws).[36] Euornithes also included the first avialans to develop true pygostyle and a fully mobile fan of tail feathers,[37] which may have replaced the "hind wing" as the primary mode of aerial maneuverability and braking in flight.[30]
+A study on mosaic evolution in the avian skull found that the last common ancestor of all Neornithes might have had a beak similar to that of the modern hook-billed vanga and a skull similar to that of the Eurasian golden oriole. As both species are small aerial and canopy foraging omnivores, a similar ecological niche was inferred for this hypothetical ancestor.[38]
+Struthioniformes
+Tinamiformes
+Other birds (Neoaves)
+Anseriformes
+Galliformes
+All modern birds lie within the crown group Aves (alternately Neornithes), which has two subdivisions: the Palaeognathae, which includes the flightless ratites (such as the ostriches) and the weak-flying tinamous, and the extremely diverse Neognathae, containing all other birds.[39] These two subdivisions are often given the rank of superorder,[40] although Livezey and Zusi assigned them "cohort" rank.[5] Depending on the taxonomic viewpoint, the number of known living bird species varies anywhere from 9,800[41] to 10,758.[42]
+The discovery of Vegavis, a late Cretaceous member of the Anatidae, proved that the diversification of modern birds started before the Cenozoic era.[43] The affinities of an earlier fossil, the possible galliform Austinornis lentus, dated to about 85 million years ago,[44] are still too controversial to provide a fossil evidence of modern bird diversification.
+Most studies agree on a Cretaceous age for the most recent common ancestor of modern birds but estimates range from the Middle Cretaceous[1] to the latest Late Cretaceous.[45] Similarly, there is no agreement on whether most of the early diversification of modern birds occurred before or after the Cretaceous–Palaeogene extinction event.[46] This disagreement is in part caused by a divergence in the evidence; most molecular dating studies suggests a Cretaceous evolutionary radiation, while fossil evidence points to a Cenozoic radiation (the so-called 'rocks' versus 'clocks' controversy). Previous attempts to reconcile molecular and fossil evidence have proved controversial,[46][47] but more recent estimates, using a more comprehensive sample of fossils and a new way of calibrating molecular clocks, showed that while modern birds originated early in the Late Cretaceous, a pulse of diversification in all major groups occurred around the Cretaceous–Palaeogene extinction event.[48]
+Cladogram of modern bird relationships based on Prum, R.O. et al. (2015)[45] with some clade names after Yuri, T. et al. (2013).[49]
+Struthioniformes[50] (ostriches)
+Rheiformes (rheas)
+Casuariiformes (cassowaries & emus)
+Apterygiformes (kiwi)
+†Aepyornithiformes (elephant birds)
+Tinamiformes (tinamous)
+†Dinornithiformes (moa)
+Galliformes (chickens and relatives)
+Anseriformes (ducks and relatives)
+Caprimulgiformes[50] (nightjars)
+Steatornithiformes (oilbird)
+Nyctibiiformes (potoos)
+Podargiformes (frogmouths)
+Apodiformes (swifts and hummingbirds)
+Musophagiformes (turacos)
+Otidiformes (bustards)
+Cuculiformes (cuckoos)
+Columbiformes (pigeons)
+Mesitornithiformes (mesites)
+Pterocliformes (sandgrouse)
+Gruiformes (rails and cranes)
+Phoenicopteriformes (flamingos)
+Podicipediformes (grebes)
+Charadriiformes (waders and relatives)
+Phaethontiformes (tropicbirds)
+Eurypygiformes (sunbittern and kagu)
+Gaviiformes[50] (loons)
+Procellariiformes (albatrosses and petrels)
+Sphenisciformes (penguins)
+Ciconiiformes (storks)
+Suliformes (boobies, cormorants, etc.)
+Pelecaniformes (pelicans, herons & ibises)
+Opisthocomiformes (hoatzin)
+Cathartiformes (New World vultures)
+Accipitriformes (hawks and relatives)
+Strigiformes (owls)
+Coliiformes (mouse birds)
+Leptosomiformes (cuckoo roller)
+Trogoniformes (trogons and quetzals)
+Bucerotiformes (hornbills and relatives)
+Coraciiformes (kingfishers and relatives)
+Piciformes (woodpeckers and relatives)
+Cariamiformes (seriemas)
+Falconiformes (falcons)
+Psittaciformes (parrots)
+Passeriformes (passerines)
+The classification of birds is a contentious issue. Sibley and Ahlquist's Phylogeny and Classification of Birds (1990) is a landmark work on the classification of birds,[51] although it is frequently debated and constantly revised. Most evidence seems to suggest the assignment of orders is accurate,[52] but scientists disagree about the relationships between the orders themselves; evidence from modern bird anatomy, fossils and DNA have all been brought to bear on the problem, but no strong consensus has emerged. More recently, new fossil and molecular evidence is providing an increasingly clear picture of the evolution of modern bird orders.[53][45]
+Birds live and breed in most terrestrial habitats and on all seven continents, reaching their southern extreme in the snow petrel's breeding colonies up to 440 kilometres (270 mi) inland in Antarctica.[55] The highest bird diversity occurs in tropical regions. It was earlier thought that this high diversity was the result of higher speciation rates in the tropics; however recent studies found higher speciation rates in the high latitudes that were offset by greater extinction rates than in the tropics.[56] Many species migrate annually over great distances and across oceans; several families of birds have adapted to life both on the world's oceans and in them, and some seabird species come ashore only to breed,[57] while some penguins have been recorded diving up to 300 metres (980 ft) deep.[58]
+Many bird species have established breeding populations in areas to which they have been introduced by humans. Some of these introductions have been deliberate; the ring-necked pheasant, for example, has been introduced around the world as a game bird.[59] Others have been accidental, such as the establishment of wild monk parakeets in several North American cities after their escape from captivity.[60] Some species, including cattle egret,[61] yellow-headed caracara[62] and galah,[63] have spread naturally far beyond their original ranges as agricultural practices created suitable new habitat.
+Compared with other vertebrates, birds have a body plan that shows many unusual adaptations, mostly to facilitate flight.
+The skeleton consists of very lightweight bones. They have large air-filled cavities (called pneumatic cavities) which connect with the respiratory system.[64] The skull bones in adults are fused and do not show cranial sutures.[65] The orbits are large and separated by a bony septum. The spine has cervical, thoracic, lumbar and caudal regions with the number of cervical (neck) vertebrae highly variable and especially flexible, but movement is reduced in the anterior thoracic vertebrae and absent in the later vertebrae.[66] The last few are fused with the pelvis to form the synsacrum.[65] The ribs are flattened and the sternum is keeled for the attachment of flight muscles except in the flightless bird orders. The forelimbs are modified into wings.[67] The wings are more or less developed depending on the species; the only known groups that lost their wings are the extinct moa and elephant birds.[68]
+Like the reptiles, birds are primarily uricotelic, that is, their kidneys extract nitrogenous waste from their bloodstream and excrete it as uric acid, instead of urea or ammonia, through the ureters into the intestine. Birds do not have a urinary bladder or external urethral opening and (with exception of the ostrich) uric acid is excreted along with faeces as a semisolid waste.[69][70][71] However, birds such as hummingbirds can be facultatively ammonotelic, excreting most of the nitrogenous wastes as ammonia.[72] They also excrete creatine, rather than creatinine like mammals.[65] This material, as well as the output of the intestines, emerges from the bird's cloaca.[73][74] The cloaca is a multi-purpose opening: waste is expelled through it, most birds mate by joining cloaca, and females lay eggs from it. In addition, many species of birds regurgitate pellets.[75]
+It is a common but not universal feature of altricial passerine nestlings (born helpless, under constant parental care) that instead of excreting directly into the nest, they produce a fecal sac. This is a mucus-covered pouch that allows parents to either dispose of the waste outside the nest or to recycle the waste through their own digestive system.[76]
+Males within Palaeognathae (with the exception of the kiwis), the Anseriformes (with the exception of screamers), and in rudimentary forms in Galliformes (but fully developed in Cracidae) possess a penis, which is never present in Neoaves.[77][78] The length is thought to be related to sperm competition.[79] When not copulating, it is hidden within the proctodeum compartment within the cloaca, just inside the vent. Female birds have sperm storage tubules[80] that allow sperm to remain viable long after copulation, a hundred days in some species.[81] Sperm from multiple males may compete through this mechanism. Most female birds have a single ovary and a single oviduct, both on the left side,[82] but there are exceptions: species in at least 16 different orders of birds have two ovaries. Even these species, however, tend to have a single oviduct.[82] It has been speculated that this might be an adaptation to flight, but males have two testes, and it is also observed that the gonads in both sexes decrease dramatically in size outside the breeding season.[83][84] Also terrestrial birds generally have a single ovary, as does the platypus, an egg-laying mammal. A more likely explanation is that the egg develops a shell while passing through the oviduct over a period of about a day, so that if two eggs were to develop at the same time, there would be a risk to survival.[82]
+Birds have two sexes: either female or male. The sex of birds is determined by the Z and W sex chromosomes, rather than by the X and Y chromosomes present in mammals. Male birds have two Z chromosomes (ZZ), and female birds have a W chromosome and a Z chromosome (WZ).[65]
+In nearly all species of birds, an individual's sex is determined at fertilisation. However, one recent study claimed to demonstrate temperature-dependent sex determination among the Australian brushturkey, for which higher temperatures during incubation resulted in a higher female-to-male sex ratio.[85] This, however, was later proven to not be the case. These birds do not exhibit temperature-dependent sex determination, but temperature-dependent sex mortality.[86]
+Birds have one of the most complex respiratory systems of all animal groups.[65] Upon inhalation, 75% of the fresh air bypasses the lungs and flows directly into a posterior air sac which extends from the lungs and connects with air spaces in the bones and fills them with air. The other 25% of the air goes directly into the lungs. When the bird exhales, the used air flows out of the lungs and the stored fresh air from the posterior air sac is simultaneously forced into the lungs. Thus, a bird's lungs receive a constant supply of fresh air during both inhalation and exhalation.[87] Sound production is achieved using the syrinx, a muscular chamber incorporating multiple tympanic membranes which diverges from the lower end of the trachea;[88] the trachea being elongated in some species, increasing the volume of vocalisations and the perception of the bird's size.[89]
+In birds, the main arteries taking blood away from the heart originate from the right aortic arch (or pharyngeal arch), unlike in the mammals where the left aortic arch forms this part of the aorta.[65] The postcava receives blood from the limbs via the renal portal system. Unlike in mammals, the circulating red blood cells in birds retain their nucleus.[90]
+The avian circulatory system is driven by a four-chambered, myogenic heart contained in a fibrous pericardial sac. This pericardial sac is filled with a serous fluid for lubrication.[91] The heart itself is divided into a right and left half, each with an atrium and ventricle. The atrium and ventricles of each side are separated by atrioventricular valves which prevent back flow from one chamber to the next during contraction. Being myogenic, the heart's pace is maintained by pacemaker cells found in the sinoatrial node, located on the right atrium.
+The sinoatrial node uses calcium to cause a depolarising signal transduction pathway from the atrium through right and left atrioventricular bundle which communicates contraction to the ventricles. The avian heart also consists of muscular arches that are made up of thick bundles of muscular layers. Much like a mammalian heart, the avian heart is composed of endocardial, myocardial and epicardial layers.[91] The atrium walls tend to be thinner than the ventricle walls, due to the intense ventricular contraction used to pump oxygenated blood throughout the body. Avian hearts are generally larger than mammalian hearts when compared to body mass. This adaptation allows more blood to be pumped to meet the high metabolic need associated with flight.[92]
+Birds have a very efficient system for diffusing oxygen into the blood; birds have a ten times greater surface area to gas exchange volume than mammals. As a result, birds have more blood in their capillaries per unit of volume of lung than a mammal.[92] The arteries are composed of thick elastic muscles to withstand the pressure of the ventricular contractions, and become more rigid as they move away from the heart. Blood moves through the arteries, which undergo vasoconstriction, and into arterioles which act as a transportation system to distribute primarily oxygen as well as nutrients to all tissues of the body.[93] As the arterioles move away from the heart and into individual organs and tissues they are further divided to increase surface area and slow blood flow. Blood travels through the arterioles and moves into the capillaries where gas exchange can occur.
+Capillaries are organized into capillary beds in tissues; it is here that blood exchanges oxygen for carbon dioxide waste. In the capillary beds, blood flow is slowed to allow maximum diffusion of oxygen into the tissues. Once the blood has become deoxygenated, it travels through venules then veins and back to the heart. Veins, unlike arteries, are thin and rigid as they do not need to withstand extreme pressure. As blood travels through the venules to the veins a funneling occurs called vasodilation bringing blood back to the heart.[93] Once the blood reaches the heart, it moves first into the right atrium, then the right ventricle to be pumped through the lungs for further gas exchange of carbon dioxide waste for oxygen. Oxygenated blood then flows from the lungs through the left atrium to the left ventricle where it is pumped out to the body.
+The nervous system is large relative to the bird's size.[65] The most developed part of the brain is the one that controls the flight-related functions, while the cerebellum coordinates movement and the cerebrum controls behaviour patterns, navigation, mating and nest building. Most birds have a poor sense of smell[94] with notable exceptions including kiwis,[95] New World vultures[96] and tubenoses.[97] The avian visual system is usually highly developed. Water birds have special flexible lenses, allowing accommodation for vision in air and water.[65] Some species also have dual fovea. Birds are tetrachromatic, possessing ultraviolet (UV) sensitive cone cells in the eye as well as green, red and blue ones.[98] They also have double cones, likely to mediate achromatic vision.[99]
+Many birds show plumage patterns in ultraviolet that are invisible to the human eye; some birds whose sexes appear similar to the naked eye are distinguished by the presence of ultraviolet reflective patches on their feathers. Male blue tits have an ultraviolet reflective crown patch which is displayed in courtship by posturing and raising of their nape feathers.[100] Ultraviolet light is also used in foraging—kestrels have been shown to search for prey by detecting the UV reflective urine trail marks left on the ground by rodents.[101] With the exception of pigeons and a few other species,[102] the eyelids of birds are not used in blinking. Instead the eye is lubricated by the nictitating membrane, a third eyelid that moves horizontally.[103] The nictitating membrane also covers the eye and acts as a contact lens in many aquatic birds.[65] The bird retina has a fan shaped blood supply system called the pecten.[65]
+Most birds cannot move their eyes, although there are exceptions, such as the great cormorant.[104] Birds with eyes on the sides of their heads have a wide visual field, while birds with eyes on the front of their heads, such as owls, have binocular vision and can estimate the depth of field.[105] The avian ear lacks external pinnae but is covered by feathers, although in some birds, such as the Asio, Bubo and Otus owls, these feathers form tufts which resemble ears. The inner ear has a cochlea, but it is not spiral as in mammals.[106]
+A few species are able to use chemical defences against predators; some Procellariiformes can eject an unpleasant stomach oil against an aggressor,[107] and some species of pitohuis from New Guinea have a powerful neurotoxin in their skin and feathers.[108]
+A lack of field observations limit our knowledge, but intraspecific conflicts are known to sometimes result in injury or death.[109] The screamers (Anhimidae), some jacanas (Jacana, Hydrophasianus), the spur-winged goose (Plectropterus), the torrent duck (Merganetta) and nine species of lapwing (Vanellus) use a sharp spur on the wing as a weapon. The steamer ducks (Tachyeres), geese and swans (Anserinae), the solitaire (Pezophaps), sheathbills (Chionis), some guans (Crax) and stone curlews (Burhinus) use a bony knob on the alular metacarpal to punch and hammer opponents.[109] The jacanas Actophilornis and Irediparra have an expanded, blade-like radius. The extinct Xenicibis was unique in having an elongate forelimb and massive hand which likely functioned in combat or defence as a jointed club or flail. Swans, for instance, may strike with the bony spurs and bite when defending eggs or young.[109]
+Feathers are a feature characteristic of birds (though also present in some dinosaurs not currently considered to be true birds). They facilitate flight, provide insulation that aids in thermoregulation, and are used in display, camouflage, and signalling.[65] There are several types of feathers, each serving its own set of purposes. Feathers are epidermal growths attached to the skin and arise only in specific tracts of skin called pterylae. The distribution pattern of these feather tracts (pterylosis) is used in taxonomy and systematics. The arrangement and appearance of feathers on the body, called plumage, may vary within species by age, social status,[110] and sex.[111]
+Plumage is regularly moulted; the standard plumage of a bird that has moulted after breeding is known as the "non-breeding" plumage, or—in the Humphrey–Parkes terminology—"basic" plumage; breeding plumages or variations of the basic plumage are known under the Humphrey–Parkes system as "alternate" plumages.[112] Moulting is annual in most species, although some may have two moults a year, and large birds of prey may moult only once every few years. Moulting patterns vary across species. In passerines, flight feathers are replaced one at a time with the innermost primary being the first. When the fifth of sixth primary is replaced, the outermost tertiaries begin to drop. After the innermost tertiaries are moulted, the secondaries starting from the innermost begin to drop and this proceeds to the outer feathers (centrifugal moult). The greater primary coverts are moulted in synchrony with the primary that they overlap.[113]
+A small number of species, such as ducks and geese, lose all of their flight feathers at once, temporarily becoming flightless.[114] As a general rule, the tail feathers are moulted and replaced starting with the innermost pair.[113] Centripetal moults of tail feathers are however seen in the Phasianidae.[115] The centrifugal moult is modified in the tail feathers of woodpeckers and treecreepers, in that it begins with the second innermost pair of feathers and finishes with the central pair of feathers so that the bird maintains a functional climbing tail.[113][116] The general pattern seen in passerines is that the primaries are replaced outward, secondaries inward, and the tail from centre outward.[117] Before nesting, the females of most bird species gain a bare brood patch by losing feathers close to the belly. The skin there is well supplied with blood vessels and helps the bird in incubation.[118]
+Feathers require maintenance and birds preen or groom them daily, spending an average of around 9% of their daily time on this.[119] The bill is used to brush away foreign particles and to apply waxy secretions from the uropygial gland; these secretions protect the feathers' flexibility and act as an antimicrobial agent, inhibiting the growth of feather-degrading bacteria.[120] This may be supplemented with the secretions of formic acid from ants, which birds receive through a behaviour known as anting, to remove feather parasites.[121]
+The scales of birds are composed of the same keratin as beaks, claws, and spurs. They are found mainly on the toes and metatarsus, but may be found further up on the ankle in some birds. Most bird scales do not overlap significantly, except in the cases of kingfishers and woodpeckers.
+The scales of birds are thought to be homologous to those of reptiles and mammals.[122]
+Most birds can fly, which distinguishes them from almost all other vertebrate classes. Flight is the primary means of locomotion for most bird species and is used for searching for food and for escaping from predators. Birds have various adaptations for flight, including a lightweight skeleton, two large flight muscles, the pectoralis (which accounts for 15% of the total mass of the bird) and the supracoracoideus, as well as a modified forelimb (wing) that serves as an aerofoil.[65]
+Wing shape and size generally determine a bird's flight style and performance; many birds combine powered, flapping flight with less energy-intensive soaring flight. About 60 extant bird species are flightless, as were many extinct birds.[123] Flightlessness often arises in birds on isolated islands, probably due to limited resources and the absence of land predators.[124] Although flightless, penguins use similar musculature and movements to "fly" through the water, as do some flight-capable birds such as auks, shearwaters and dippers.[125]
+Most birds are diurnal, but some birds, such as many species of owls and nightjars, are nocturnal or crepuscular (active during twilight hours), and many coastal waders feed when the tides are appropriate, by day or night.[126]
+Birds' diets are varied and often include nectar, fruit, plants, seeds, carrion, and various small animals, including other birds.[65] The digestive system of birds is unique, with a crop for storage and a gizzard that contains swallowed stones for grinding food to compensate for the lack of teeth.[127] Most birds are highly adapted for rapid digestion to aid with flight.[128] Some migratory birds have adapted to use protein stored in many parts of their bodies, including protein from the intestines, as additional energy during migration.[129]
+Birds that employ many strategies to obtain food or feed on a variety of food items are called generalists, while others that concentrate time and effort on specific food items or have a single strategy to obtain food are considered specialists.[65] Avian foraging strategies can vary widely by species. Many birds glean for insects, invertebrates, fruit, or seeds. Some hunt insects by suddenly attacking from a branch. Those species that seek pest insects are considered beneficial 'biological control agents' and their presence encouraged in biological pest control programmes.[130] Combined, insectivorous birds eat 400–500 million metric tons of arthropods annually.[131]
+Nectar feeders such as hummingbirds, sunbirds, lories, and lorikeets amongst others have specially adapted brushy tongues and in many cases bills designed to fit co-adapted flowers.[132] Kiwis and shorebirds with long bills probe for invertebrates; shorebirds' varied bill lengths and feeding methods result in the separation of ecological niches.[65][133] Loons, diving ducks, penguins and auks pursue their prey underwater, using their wings or feet for propulsion,[57] while aerial predators such as sulids, kingfishers and terns plunge dive after their prey. Flamingos, three species of prion, and some ducks are filter feeders.[134][135] Geese and dabbling ducks are primarily grazers.
+Some species, including frigatebirds, gulls,[136] and skuas,[137] engage in kleptoparasitism, stealing food items from other birds. Kleptoparasitism is thought to be a supplement to food obtained by hunting, rather than a significant part of any species' diet; a study of great frigatebirds stealing from masked boobies estimated that the frigatebirds stole at most 40% of their food and on average stole only 5%.[138] Other birds are scavengers; some of these, like vultures, are specialised carrion eaters, while others, like gulls, corvids, or other birds of prey, are opportunists.[139]
+Water is needed by many birds although their mode of excretion and lack of sweat glands reduces the physiological demands.[140] Some desert birds can obtain their water needs entirely from moisture in their food. They may also have other adaptations such as allowing their body temperature to rise, saving on moisture loss from evaporative cooling or panting.[141] Seabirds can drink seawater and have salt glands inside the head that eliminate excess salt out of the nostrils.[142]
+Most birds scoop water in their beaks and raise their head to let water run down the throat. Some species, especially of arid zones, belonging to the pigeon, finch, mousebird, button-quail and bustard families are capable of sucking up water without the need to tilt back their heads.[143] Some desert birds depend on water sources and sandgrouse are particularly well known for their daily congregations at waterholes. Nesting sandgrouse and many plovers carry water to their young by wetting their belly feathers.[144] Some birds carry water for chicks at the nest in their crop or regurgitate it along with food. The pigeon family, flamingos and penguins have adaptations to produce a nutritive fluid called crop milk that they provide to their chicks.[145]
+Feathers, being critical to the survival of a bird, require maintenance. Apart from physical wear and tear, feathers face the onslaught of fungi, ectoparasitic feather mites and bird lice.[146] The physical condition of feathers are maintained by preening often with the application of secretions from the preen gland. Birds also bathe in water or dust themselves. While some birds dip into shallow water, more aerial species may make aerial dips into water and arboreal species often make use of dew or rain that collect on leaves. Birds of arid regions make use of loose soil to dust-bathe. A behaviour termed as anting in which the bird encourages ants to run through their plumage is also thought to help them reduce the ectoparasite load in feathers. Many species will spread out their wings and expose them to direct sunlight and this too is thought to help in reducing fungal and ectoparasitic activity that may lead to feather damage.[147][148]
+Many bird species migrate to take advantage of global differences of seasonal temperatures, therefore optimising availability of food sources and breeding habitat. These migrations vary among the different groups. Many landbirds, shorebirds, and waterbirds undertake annual long-distance migrations, usually triggered by the length of daylight as well as weather conditions. These birds are characterised by a breeding season spent in the temperate or polar regions and a non-breeding season in the tropical regions or opposite hemisphere. Before migration, birds substantially increase body fats and reserves and reduce the size of some of their organs.[149][150]
+Migration is highly demanding energetically, particularly as birds need to cross deserts and oceans without refuelling. Landbirds have a flight range of around 2,500 km (1,600 mi) and shorebirds can fly up to 4,000 km (2,500 mi),[151] although the bar-tailed godwit is capable of non-stop flights of up to 10,200 km (6,300 mi).[152] Seabirds also undertake long migrations, the longest annual migration being those of sooty shearwaters, which nest in New Zealand and Chile and spend the northern summer feeding in the North Pacific off Japan, Alaska and California, an annual round trip of 64,000 km (39,800 mi).[153] Other seabirds disperse after breeding, travelling widely but having no set migration route. Albatrosses nesting in the Southern Ocean often undertake circumpolar trips between breeding seasons.[154]
+Some bird species undertake shorter migrations, travelling only as far as is required to avoid bad weather or obtain food. Irruptive species such as the boreal finches are one such group and can commonly be found at a location in one year and absent the next. This type of migration is normally associated with food availability.[155] Species may also travel shorter distances over part of their range, with individuals from higher latitudes travelling into the existing range of conspecifics; others undertake partial migrations, where only a fraction of the population, usually females and subdominant males, migrates.[156] Partial migration can form a large percentage of the migration behaviour of birds in some regions; in Australia, surveys found that 44% of non-passerine birds and 32% of passerines were partially migratory.[157]
+Altitudinal migration is a form of short-distance migration in which birds spend the breeding season at higher altitudes and move to lower ones during suboptimal conditions. It is most often triggered by temperature changes and usually occurs when the normal territories also become inhospitable due to lack of food.[158] Some species may also be nomadic, holding no fixed territory and moving according to weather and food availability. Parrots as a family are overwhelmingly neither migratory nor sedentary but considered to either be dispersive, irruptive, nomadic or undertake small and irregular migrations.[159]
+The ability of birds to return to precise locations across vast distances has been known for some time; in an experiment conducted in the 1950s, a Manx shearwater released in Boston in the United States returned to its colony in Skomer, in Wales within 13 days, a distance of 5,150 km (3,200 mi).[160] Birds navigate during migration using a variety of methods. For diurnal migrants, the sun is used to navigate by day, and a stellar compass is used at night. Birds that use the sun compensate for the changing position of the sun during the day by the use of an internal clock.[65] Orientation with the stellar compass depends on the position of the constellations surrounding Polaris.[161] These are backed up in some species by their ability to sense the Earth's geomagnetism through specialised photoreceptors.[162]
+Birds communicate using primarily visual and auditory signals. Signals can be interspecific (between species) and intraspecific (within species).
+Birds sometimes use plumage to assess and assert social dominance,[163] to display breeding condition in sexually selected species, or to make threatening displays, as in the sunbittern's mimicry of a large predator to ward off hawks and protect young chicks.[164] Variation in plumage also allows for the identification of birds, particularly between species.
+Visual communication among birds may also involve ritualised displays, which have developed from non-signalling actions such as preening, the adjustments of feather position, pecking, or other behaviour. These displays may signal aggression or submission or may contribute to the formation of pair-bonds.[65] The most elaborate displays occur during courtship, where "dances" are often formed from complex combinations of many possible component movements;[165] males' breeding success may depend on the quality of such displays.[166]
+Bird calls and songs, which are produced in the syrinx, are the major means by which birds communicate with sound. This communication can be very complex; some species can operate the two sides of the syrinx independently, allowing the simultaneous production of two different songs.[88]
+Calls are used for a variety of purposes, including mate attraction,[65] evaluation of potential mates,[167] bond formation, the claiming and maintenance of territories,[65] the identification of other individuals (such as when parents look for chicks in colonies or when mates reunite at the start of breeding season),[168] and the warning of other birds of potential predators, sometimes with specific information about the nature of the threat.[169] Some birds also use mechanical sounds for auditory communication. The Coenocorypha snipes of New Zealand drive air through their feathers,[170] woodpeckers drum for long-distance communication,[171] and palm cockatoos use tools to drum.[172]
+While some birds are essentially territorial or live in small family groups, other birds may form large flocks. The principal benefits of flocking are safety in numbers and increased foraging efficiency.[65] Defence against predators is particularly important in closed habitats like forests, where ambush predation is common and multiple eyes can provide a valuable early warning system. This has led to the development of many mixed-species feeding flocks, which are usually composed of small numbers of many species; these flocks provide safety in numbers but increase potential competition for resources.[174] Costs of flocking include bullying of socially subordinate birds by more dominant birds and the reduction of feeding efficiency in certain cases.[175]
+Birds sometimes also form associations with non-avian species. Plunge-diving seabirds associate with dolphins and tuna, which push shoaling fish towards the surface.[176] Hornbills have a mutualistic relationship with dwarf mongooses, in which they forage together and warn each other of nearby birds of prey and other predators.[177]
+The high metabolic rates of birds during the active part of the day is supplemented by rest at other times. Sleeping birds often use a type of sleep known as vigilant sleep, where periods of rest are interspersed with quick eye-opening "peeks", allowing them to be sensitive to disturbances and enable rapid escape from threats.[178] Swifts are believed to be able to sleep in flight and radar observations suggest that they orient themselves to face the wind in their roosting flight.[179] It has been suggested that there may be certain kinds of sleep which are possible even when in flight.[180]
+Some birds have also demonstrated the capacity to fall into slow-wave sleep one hemisphere of the brain at a time. The birds tend to exercise this ability depending upon its position relative to the outside of the flock. This may allow the eye opposite the sleeping hemisphere to remain vigilant for predators by viewing the outer margins of the flock. This adaptation is also known from marine mammals.[181] Communal roosting is common because it lowers the loss of body heat and decreases the risks associated with predators.[182] Roosting sites are often chosen with regard to thermoregulation and safety.[183]
+Many sleeping birds bend their heads over their backs and tuck their bills in their back feathers, although others place their beaks among their breast feathers. Many birds rest on one leg, while some may pull up their legs into their feathers, especially in cold weather. Perching birds have a tendon locking mechanism that helps them hold on to the perch when they are asleep. Many ground birds, such as quails and pheasants, roost in trees. A few parrots of the genus Loriculus roost hanging upside down.[184] Some hummingbirds go into a nightly state of torpor accompanied with a reduction of their metabolic rates.[185] This physiological adaptation shows in nearly a hundred other species, including owlet-nightjars, nightjars, and woodswallows. One species, the common poorwill, even enters a state of hibernation.[186] Birds do not have sweat glands, but they may cool themselves by moving to shade, standing in water, panting, increasing their surface area, fluttering their throat or by using special behaviours like urohidrosis to cool themselves.
+Ninety-five per cent of bird species are socially monogamous. These species pair for at least the length of the breeding season or—in some cases—for several years or until the death of one mate.[188] Monogamy allows for both paternal care and biparental care, which is especially important for species in which females require males' assistance for successful brood-rearing.[189] Among many socially monogamous species, extra-pair copulation (infidelity) is common.[190] Such behaviour typically occurs between dominant males and females paired with subordinate males, but may also be the result of forced copulation in ducks and other anatids.[191]
+For females, possible benefits of extra-pair copulation include getting better genes for her offspring and insuring against the possibility of infertility in her mate.[192] Males of species that engage in extra-pair copulations will closely guard their mates to ensure the parentage of the offspring that they raise.[193]
+Other mating systems, including polygyny, polyandry, polygamy, polygynandry, and promiscuity, also occur.[65] Polygamous breeding systems arise when females are able to raise broods without the help of males.[65] Some species may use more than one system depending on the circumstances.
+Breeding usually involves some form of courtship display, typically performed by the male.[194] Most displays are rather simple and involve some type of song. Some displays, however, are quite elaborate. Depending on the species, these may include wing or tail drumming, dancing, aerial flights, or communal lekking. Females are generally the ones that drive partner selection,[195] although in the polyandrous phalaropes, this is reversed: plainer males choose brightly coloured females.[196] Courtship feeding, billing and allopreening are commonly performed between partners, generally after the birds have paired and mated.[197]
+Homosexual behaviour has been observed in males or females in numerous species of birds, including copulation, pair-bonding, and joint parenting of chicks.[198] Over 130 avian species around the world engage in sexual interactions between the same sex or homosexual behaviors. "Same-sex courtship activities may involve elaborate displays, synchronized dances, gift-giving ceremonies, or behaviors at specific display areas including bowers, arenas, or leks."[199]
+Many birds actively defend a territory from others of the same species during the breeding season; maintenance of territories protects the food source for their chicks. Species that are unable to defend feeding territories, such as seabirds and swifts, often breed in colonies instead; this is thought to offer protection from predators. Colonial breeders defend small nesting sites, and competition between and within species for nesting sites can be intense.[200]
+All birds lay amniotic eggs with hard shells made mostly of calcium carbonate.[65] Hole and burrow nesting species tend to lay white or pale eggs, while open nesters lay camouflaged eggs. There are many exceptions to this pattern, however; the ground-nesting nightjars have pale eggs, and camouflage is instead provided by their plumage. Species that are victims of brood parasites have varying egg colours to improve the chances of spotting a parasite's egg, which forces female parasites to match their eggs to those of their hosts.[201]
+Bird eggs are usually laid in a nest. Most species create somewhat elaborate nests, which can be cups, domes, plates, beds scrapes, mounds, or burrows.[202] Some bird nests, however, are extremely primitive; albatross nests are no more than a scrape on the ground. Most birds build nests in sheltered, hidden areas to avoid predation, but large or colonial birds—which are more capable of defence—may build more open nests. During nest construction, some species seek out plant matter from plants with parasite-reducing toxins to improve chick survival,[203] and feathers are often used for nest insulation.[202] Some bird species have no nests; the cliff-nesting common guillemot lays its eggs on bare rock, and male emperor penguins keep eggs between their body and feet. The absence of nests is especially prevalent in ground-nesting species where the newly hatched young are precocial.
+Incubation, which optimises temperature for chick development, usually begins after the last egg has been laid.[65] In monogamous species incubation duties are often shared, whereas in polygamous species one parent is wholly responsible for incubation. Warmth from parents passes to the eggs through brood patches, areas of bare skin on the abdomen or breast of the incubating birds. Incubation can be an energetically demanding process; adult albatrosses, for instance, lose as much as 83 grams (2.9 oz) of body weight per day of incubation.[204] The warmth for the incubation of the eggs of megapodes comes from the sun, decaying vegetation or volcanic sources.[205] Incubation periods range from 10 days (in woodpeckers, cuckoos and passerine birds) to over 80 days (in albatrosses and kiwis).[65]
+The diversity of characteristics of birds is great, sometimes even in closely related species. Several avian characteristics are compared in the table below.[206][207]
+At the time of their hatching, chicks range in development from helpless to independent, depending on their species. Helpless chicks are termed altricial, and tend to be born small, blind, immobile and naked; chicks that are mobile and feathered upon hatching are termed precocial. Altricial chicks need help thermoregulating and must be brooded for longer than precocial chicks. The young of many bird species do not precisely fit into either the precocial or altricial category, having some aspects of each and thus fall somewhere on an "altricial-precocial spectrum".[208] Chicks at neither extreme but favoring one or the other may be termed semi-precocial[209] or semi-altricial.[210]
+The length and nature of parental care varies widely amongst different orders and species. At one extreme, parental care in megapodes ends at hatching; the newly hatched chick digs itself out of the nest mound without parental assistance and can fend for itself immediately.[211] At the other extreme, many seabirds have extended periods of parental care, the longest being that of the great frigatebird, whose chicks take up to six months to fledge and are fed by the parents for up to an additional 14 months.[212] The chick guard stage describes the period of breeding during which one of the adult birds is permanently present at the nest after chicks have hatched. The main purpose of the guard stage is to aid offspring to thermoregulate and protect them from predation.[213]
+In some species, both parents care for nestlings and fledglings; in others, such care is the responsibility of only one sex. In some species, other members of the same species—usually close relatives of the breeding pair, such as offspring from previous broods—will help with the raising of the young.[214] Such alloparenting is particularly common among the Corvida, which includes such birds as the true crows, Australian magpie and fairy-wrens,[215] but has been observed in species as different as the rifleman and red kite. Among most groups of animals, male parental care is rare. In birds, however, it is quite common—more so than in any other vertebrate class.[65] Although territory and nest site defence, incubation, and chick feeding are often shared tasks, there is sometimes a division of labour in which one mate undertakes all or most of a particular duty.[216]
+The point at which chicks fledge varies dramatically. The chicks of the Synthliboramphus murrelets, like the ancient murrelet, leave the nest the night after they hatch, following their parents out to sea, where they are raised away from terrestrial predators.[217] Some other species, such as ducks, move their chicks away from the nest at an early age. In most species, chicks leave the nest just before, or soon after, they are able to fly. The amount of parental care after fledging varies; albatross chicks leave the nest on their own and receive no further help, while other species continue some supplementary feeding after fledging.[218] Chicks may also follow their parents during their first migration.[219]
+Brood parasitism, in which an egg-layer leaves her eggs with another individual's brood, is more common among birds than any other type of organism.[220] After a parasitic bird lays her eggs in another bird's nest, they are often accepted and raised by the host at the expense of the host's own brood. Brood parasites may be either obligate brood parasites, which must lay their eggs in the nests of other species because they are incapable of raising their own young, or non-obligate brood parasites, which sometimes lay eggs in the nests of conspecifics to increase their reproductive output even though they could have raised their own young.[221] One hundred bird species, including honeyguides, icterids, and ducks, are obligate parasites, though the most famous are the cuckoos.[220] Some brood parasites are adapted to hatch before their host's young, which allows them to destroy the host's eggs by pushing them out of the nest or to kill the host's chicks; this ensures that all food brought to the nest will be fed to the parasitic chicks.[222]
+Birds have evolved a variety of mating behaviours, with the peacock tail being perhaps the most famous example of sexual selection and the Fisherian runaway. Commonly occurring sexual dimorphisms such as size and colour differences are energetically costly attributes that signal competitive breeding situations.[223] Many types of avian sexual selection have been identified; intersexual selection, also known as female choice; and intrasexual competition, where individuals of the more abundant sex compete with each other for the privilege to mate. Sexually selected traits often evolve to become more pronounced in competitive breeding situations until the trait begins to limit the individual's fitness. Conflicts between an individual fitness and signalling adaptations ensure that sexually selected ornaments such as plumage coloration and courtship behaviour are "honest" traits. Signals must be costly to ensure that only good-quality individuals can present these exaggerated sexual ornaments and behaviours.[224]
+Inbreeding causes early death (inbreeding depression) in the zebra finch Taeniopygia guttata.[225] Embryo survival (that is, hatching success of fertile eggs) was significantly lower for sib-sib mating pairs than for unrelated pairs.
+Darwin's finch Geospiza scandens experiences inbreeding depression (reduced survival of offspring) and the magnitude of this effect is influenced by environmental conditions such as low food availability.[226]
+Incestuous matings by the purple-crowned fairy wren Malurus coronatus result in severe fitness costs due to inbreeding depression (greater than 30% reduction in hatchability of eggs).[227] Females paired with related males may undertake extra pair matings (see Promiscuity#Other animals for 90% frequency in avian species) that can reduce the negative effects of inbreeding. However, there are ecological and demographic constraints on extra pair matings. Nevertheless, 43% of broods produced by incestuously paired females contained extra pair young.[227]
+Inbreeding depression occurs in the great tit (Parus major) when the offspring produced as a result of a mating between close relatives show reduced fitness. In natural populations of Parus major, inbreeding is avoided by dispersal of individuals from their birthplace, which reduces the chance of mating with a close relative.[228]
+Southern pied babblers Turdoides bicolor appear to avoid inbreeding in two ways. The first is through dispersal, and the second is by avoiding familiar group members as mates.[229] Although both males and females disperse locally, they move outside the range where genetically related individuals are likely to be encountered. Within their group, individuals only acquire breeding positions when the opposite-sex breeder is unrelated.
+Cooperative breeding in birds typically occurs when offspring, usually males, delay dispersal from their natal group in order to remain with the family to help rear younger kin.[230] Female offspring rarely stay at home, dispersing over distances that allow them to breed independently, or to join unrelated groups. In general, inbreeding is avoided because it leads to a reduction in progeny fitness (inbreeding depression) due largely to the homozygous expression of deleterious recessive alleles.[231] Cross-fertilisation between unrelated individuals ordinarily leads to the masking of deleterious recessive alleles in progeny.[232][233]
+Birds occupy a wide range of ecological positions.[173] While some birds are generalists, others are highly specialised in their habitat or food requirements. Even within a single habitat, such as a forest, the niches occupied by different species of birds vary, with some species feeding in the forest canopy, others beneath the canopy, and still others on the forest floor. Forest birds may be insectivores, frugivores, and nectarivores. Aquatic birds generally feed by fishing, plant eating, and piracy or kleptoparasitism. Birds of prey specialise in hunting mammals or other birds, while vultures are specialised scavengers. Avivores are animals that are specialised at preying on birds.
+Some nectar-feeding birds are important pollinators, and many frugivores play a key role in seed dispersal.[234] Plants and pollinating birds often coevolve,[235] and in some cases a flower's primary pollinator is the only species capable of reaching its nectar.[236]
+Birds are often important to island ecology. Birds have frequently reached islands that mammals have not; on those islands, birds may fulfil ecological roles typically played by larger animals. For example, in New Zealand nine species of moa were important browsers, as are the kererū and kokako today.[234] Today the plants of New Zealand retain the defensive adaptations evolved to protect them from the extinct moa.[237] Nesting seabirds may also affect the ecology of islands and surrounding seas, principally through the concentration of large quantities of guano, which may enrich the local soil[238] and the surrounding seas.[239]
+A wide variety of avian ecology field methods, including counts, nest monitoring, and capturing and marking, are used for researching avian ecology.
+Since birds are highly visible and common animals, humans have had a relationship with them since the dawn of man.[240] Sometimes, these relationships are mutualistic, like the cooperative honey-gathering among honeyguides and African peoples such as the Borana.[241] Other times, they may be commensal, as when species such as the house sparrow[242] have benefited from human activities. Several bird species have become commercially significant agricultural pests,[243] and some pose an aviation hazard.[244] Human activities can also be detrimental, and have threatened numerous bird species with extinction (hunting, avian lead poisoning, pesticides, roadkill, wind turbine kills[245] and predation by pet cats and dogs are common causes of death for birds).[246]
+Birds can act as vectors for spreading diseases such as psittacosis, salmonellosis, campylobacteriosis, mycobacteriosis (avian tuberculosis), avian influenza (bird flu), giardiasis, and cryptosporidiosis over long distances. Some of these are zoonotic diseases that can also be transmitted to humans.[247]
+Domesticated birds raised for meat and eggs, called poultry, are the largest source of animal protein eaten by humans; in 2003, 76 million tons of poultry and 61 million tons of eggs were produced worldwide.[248] Chickens account for much of human poultry consumption, though domesticated turkeys, ducks, and geese are also relatively common. Many species of birds are also hunted for meat. Bird hunting is primarily a recreational activity except in extremely undeveloped areas. The most important birds hunted in North and South America are waterfowl; other widely hunted birds include pheasants, wild turkeys, quail, doves, partridge, grouse, snipe, and woodcock.[249] Muttonbirding is also popular in Australia and New Zealand.[250] Although some hunting, such as that of muttonbirds, may be sustainable, hunting has led to the extinction or endangerment of dozens of species.[251]
+Other commercially valuable products from birds include feathers (especially the down of geese and ducks), which are used as insulation in clothing and bedding, and seabird faeces (guano), which is a valuable source of phosphorus and nitrogen. The War of the Pacific, sometimes called the Guano War, was fought in part over the control of guano deposits.[252]
+Birds have been domesticated by humans both as pets and for practical purposes. Colourful birds, such as parrots and mynas, are bred in captivity or kept as pets, a practice that has led to the illegal trafficking of some endangered species.[253] Falcons and cormorants have long been used for hunting and fishing, respectively. Messenger pigeons, used since at least 1 AD, remained important as recently as World War II. Today, such activities are more common either as hobbies, for entertainment and tourism,[254] or for sports such as pigeon racing.
+Amateur bird enthusiasts (called birdwatchers, twitchers or, more commonly, birders) number in the millions.[255] Many homeowners erect bird feeders near their homes to attract various species. Bird feeding has grown into a multimillion-dollar industry; for example, an estimated 75% of households in Britain provide food for birds at some point during the winter.[256]
+Birds play prominent and diverse roles in religion and mythology.
+In religion, birds may serve as either messengers or priests and leaders for a deity, such as in the Cult of Makemake, in which the Tangata manu of Easter Island served as chiefs[257] or as attendants, as in the case of Hugin and Munin, the two common ravens who whispered news into the ears of the Norse god Odin. In several civilisations of ancient Italy, particularly Etruscan and Roman religion, priests were involved in augury, or interpreting the words of birds while the "auspex" (from which the word "auspicious" is derived) watched their activities to foretell events.[258]
+They may also serve as religious symbols, as when Jonah (Hebrew: יוֹנָה‎, dove) embodied the fright, passivity, mourning, and beauty traditionally associated with doves.[259] Birds have themselves been deified, as in the case of the common peacock, which is perceived as Mother Earth by the Dravidians of India.[260] In the ancient world, doves were used as symbols of the Mesopotamian goddess Inanna (later known as Ishtar),[261][262] the Canaanite mother goddess Asherah,[261][262][263] and the Greek goddess Aphrodite.[264][265][261][262][266] In ancient Greece, Athena, the goddess of wisdom and patron deity of the city of Athens, had a little owl as her symbol.[267][268][269] In religious images preserved from the Inca and Tiwanaku empires, birds are depicted in the process of transgressing boundaries between earthly and underground spiritual realms.[270] Indigenous peoples of the central Andes maintain legends of birds passing to and from metaphysical worlds.[270]
+Birds have featured in culture and art since prehistoric times, when they were represented in early cave paintings.[271] Some birds have been perceived as monsters, including the mythological Roc and the Māori's legendary Pouākai, a giant bird capable of snatching humans.[272] Birds were later used as symbols of power, as in the magnificent Peacock Throne of the Mughal and Persian emperors.[273] With the advent of scientific interest in birds, many paintings of birds were commissioned for books.
+Among the most famous of these bird artists was John James Audubon, whose paintings of North American birds were a great commercial success in Europe and who later lent his name to the National Audubon Society.[274] Birds are also important figures in poetry; for example, Homer incorporated nightingales into his Odyssey, and Catullus used a sparrow as an erotic symbol in his Catullus 2.[275] The relationship between an albatross and a sailor is the central theme of Samuel Taylor Coleridge's The Rime of the Ancient Mariner, which led to the use of the term as a metaphor for a 'burden'.[276] Other English metaphors derive from birds; vulture funds and vulture investors, for instance, take their name from the scavenging vulture.[277]
+Perceptions of bird species vary across cultures. Owls are associated with bad luck, witchcraft, and death in parts of Africa,[278] but are regarded as wise across much of Europe.[279] Hoopoes were considered sacred in Ancient Egypt and symbols of virtue in Persia, but were thought of as thieves across much of Europe and harbingers of war in Scandinavia.[280] In heraldry, birds, especially eagles, often appear in coats of arms.[281]
+In music, birdsong has influenced composers and musicians in several ways: they can be inspired by birdsong; they can intentionally imitate bird song in a composition, as Vivaldi, Messiaen, and Beethoven did, along with many later composers; they can incorporate recordings of birds into their works, as Ottorino Respighi first did; or like Beatrice Harrison and David Rothenberg, they can duet with birds.[282][283][284][285]
+Although human activities have allowed the expansion of a few species, such as the barn swallow and European starling, they have caused population decreases or extinction in many other species. Over a hundred bird species have gone extinct in historical times,[286] although the most dramatic human-caused avian extinctions, eradicating an estimated 750–1800 species, occurred during the human colonisation of Melanesian, Polynesian, and Micronesian islands.[287] Many bird populations are declining worldwide, with 1,227 species listed as threatened by BirdLife International and the IUCN in 2009.[288][289]
+The most commonly cited human threat to birds is habitat loss.[290] Other threats include overhunting, accidental mortality due to collisions with buildings or vehicles, long-line fishing bycatch,[291] pollution (including oil spills and pesticide use),[292] competition and predation from nonnative invasive species,[293] and climate change.
+Governments and conservation groups work to protect birds, either by passing laws that preserve and restore bird habitat or by establishing captive populations for reintroductions. Such projects have produced some successes; one study estimated that conservation efforts saved 16 species of bird that would otherwise have gone extinct between 1994 and 2004, including the California condor and Norfolk parakeet.[294]

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+The okapi (/oʊˈkɑːpiː/; Okapia johnstoni), also known as the forest giraffe, Congolese giraffe, or zebra giraffe, is an artiodactyl mammal native to the northeast of the Democratic Republic of the Congo in Central Africa. Although the okapi has striped markings reminiscent of zebras, it is most closely related to the giraffe. The okapi and the giraffe are the only living members of the family Giraffidae.
+The okapi stands about 1.5 m (4.9 ft) tall at the shoulder and has a typical body length around 2.5 m (8.2 ft). Its weight ranges from 200 to 350 kg (440 to 770 lb). It has a long neck, and large, flexible ears. Its coat is a chocolate to reddish brown, much in contrast with the white horizontal stripes and rings on the legs, and white ankles.
+Male okapis have short, distinct horn-like protuberances on their heads called ossicones (which share similar features to the giraffe ossicones in terms of formation, structure and function)[2], less than 15 cm (5.9 in) in length. Females possess hair whorls, and ossicones are absent.
+Okapis are primarily diurnal, but may be active for a few hours in darkness. They are essentially solitary, coming together only to breed. Okapis are herbivores, feeding on tree leaves and buds, grasses, ferns, fruits, and fungi. Rut in males and estrus in females does not depend on the season. In captivity, estrous cycles recur every 15 days. The gestational period is around 440 to 450 days long, following which usually a single calf is born. The juveniles are kept in hiding, and nursing takes place infrequently. Juveniles start taking solid food from three months, and weaning takes place at six months.
+Okapis inhabit canopy forests at altitudes of 500–1,500 m (1,600–4,900 ft). They are endemic to the tropical forests of the Democratic Republic of the Congo, where they occur across the central, northern, and eastern regions. The International Union for the Conservation of Nature and Natural Resources  classifies the okapi as endangered. Major threats include habitat loss due to logging and human settlement. Extensive hunting for bushmeat and skin and illegal mining have also led to a decline in populations. The Okapi Conservation Project was established in 1987 to protect okapi populations.
+Although the okapi was unknown to the Western world until the 20th century, it may have been depicted since the early fifth century BCE on the façade of the Apadana at Persepolis, a gift from the Ethiopian procession to the Achaemenid kingdom.[3]
+For years, Europeans in Africa had heard of an animal that they came to call the African unicorn.[4][5] The animal was brought to prominent European attention by speculation on its existence found in press reports covering Henry Morton Stanley's journeys in 1887. In his travelogue of exploring the Congo, Stanley mentioned a kind of donkey that the natives called the atti, which scholars later identified as the okapi. Explorers may have seen the fleeting view of the striped backside as the animal fled through the bushes, leading to speculation that the okapi was some sort of rainforest zebra.[citation needed]
+When the British special commissioner in Uganda, Sir Harry Johnston, discovered some Pygmy inhabitants of the Congo being abducted by a showman for exhibition, he rescued them and promised to return them to their homes. The Pygmies fed Johnston's curiosity about the animal mentioned in Stanley's book. Johnston was puzzled by the okapi tracks the natives showed him; while he had expected to be on the trail of some sort of forest-dwelling horse, the tracks were of a cloven-hoofed beast.[6]
+Though Johnston did not see an okapi himself, he did manage to obtain pieces of striped skin and eventually a skull. From this skull, the okapi was correctly classified as a relative of the giraffe; in 1901, the species was formally recognized as Okapia johnstoni.[7]
+Okapia johnstoni was first described as Equus johnstoni by English zoologist Philip Lutley Sclater in 1901.[8] The generic name Okapia derives either from the Mbuba name okapi[9] or the related Lese Karo name o'api, while the specific name (johnstoni) is in recognition of Johnston, who first acquired an okapi specimen for science from the Ituri Forest.[7][10] Remains of a carcass were later sent to London by Johnston and became a media event in 1901.[11]
+In 1901, Sclater presented a painting of the okapi before the Zoological Society of London that depicted its physical features with some clarity. Much confusion arose regarding the taxonomical status of this newly discovered animal. Sir Harry Johnston himself called it a Helladotherium, or a relative of other extinct giraffids.[12] Based on the description of the okapi by Pygmies, who referred to it as a "horse", Sclater named the species Equus johnstoni.[13] Subsequently, zoologist Ray Lankester declared that the okapi represented an unknown genus of the Giraffidae, which he placed in its own genus, Okapia, and assigned the name Okapia johnstoni to the species.[14]
+In 1902, Swiss zoologist Charles Immanuel Forsyth Major suggested the inclusion of O. johnstoni in the extinct giraffid subfamily Palaeotraginae. However, the species was placed in its own subfamily Okapiinae, by Swedish palaeontologist Birger Bohlin in 1926,[15] mainly due to the lack of a cingulum, a major feature of the palaeotragids.[16] In 1986, Okapia was finally established as a sister genus of Giraffa on the basis of cladistic analysis. The two genera together with Palaeotragus constitute the tribe Giraffini.[17]
+The earliest members of the Giraffidae first appeared in the early Miocene in Africa, having diverged from the superficially deer-like climacoceratids. Giraffids spread into Europe and Asia by the middle Miocene in a first radiation. Another radiation began in the Pliocene, but was terminated by a decline in diversity in the Pleistocene.[18] Several important primitive giraffids existed more or less contemporaneously in the Miocene (23–10 million years ago), including Canthumeryx, Giraffokeryx, Palaeotragus, and Samotherium. According to palaeontologist and author Kathleen Hunt, Samotherium split into Okapia (18 million years ago) and Giraffa (12 million years ago).[19] However, J. D. Skinner argued that Canthumeryx gave rise to the okapi and giraffe through the latter three genera and that the okapi is the extant form of Palaeotragus.[20] The okapi is sometimes referred to as a living fossil, as it has existed as a species over a long geological time period, and morphologically resembles more primitive forms (e.g. Samotherium).[14][21]
+In 2016, a genetic study found that the common ancestor of giraffe and okapi lived about 11.5 million years ago.[22]
+The okapi is a medium-sized giraffid, standing 1.5 m (4 ft 11 in) tall at the shoulder. Its average body length is about 2.5 m (8 ft 2 in) and its weight ranges from 200 to 350 kg (440 to 770 lb).[23] It has a long neck, and large and flexible ears. The coat is a chocolate to reddish brown, much in contrast with the white horizontal stripes and rings on the legs and white ankles. The striking stripes make it resemble a zebra.[24] These features serve as an effective camouflage amidst dense vegetation. The face, throat, and chest are greyish white. Interdigital glands are present on all four feet, and are slightly larger on the front feet.[25] Male okapis have short, hair-covered horns called ossicones, less than 15 cm (5.9 in) in length. The okapi exhibits sexual dimorphism, with females 4.2 cm (1.7 in) taller on average, slightly redder, and lacking prominent ossicones, instead possessing hair whorls.[26][27]
+The okapi shows several adaptations to its tropical habitat. The large number of rod cells in the retina facilitate night vision, and an efficient olfactory system is present. The large auditory bullae allow a strong sense of hearing. The dental formula of the okapi is 0.0.3.33.1.3.3.[25] Teeth are low-crowned and finely cusped, and efficiently cut tender foliage. The large caecum and colon help in microbial digestion, and a quick rate of food passage allows for lower cell wall digestion than in other ruminants.[28]
+The okapi can be easily distinguished from its nearest extant relative, the giraffe. It is much smaller and shares more external similarities with the deer and bovids than with the giraffe. While both sexes possess horns in the giraffe, only males bear horns in the okapi. The okapi has large palatine sinuses, unique among the giraffids. Morphological similarities shared between the giraffe and the okapi include a similar gait – both use a pacing gait, stepping simultaneously with the front and the hind leg on the same side of the body, unlike other ungulates that walk by moving alternate legs on either side of the body[29] – and a long, black tongue (longer in the okapi) useful in plucking buds and leaves, as well as for grooming.[28]
+Okapis are primarily diurnal, but may be active for a few hours in darkness.[30] They are essentially solitary, coming together only to breed. They have overlapping home ranges and typically occur at densities around 0.6 animals per square kilometre.[24] Male home ranges average 13 km2 (5.0 sq mi), while female home ranges average 3–5 km2 (1.2–1.9 sq mi). Males migrate continuously, while females are sedentary.[31] Males often mark territories and bushes with their urine, while females use common defecation sites. Grooming is a common practice, focused at the earlobes and the neck. Okapis often rub their necks against trees, leaving a brown exudate.[25]
+The male is protective of his territory, but allows females to pass through the domain to forage. Males visit female home ranges at breeding time.[28] Although generally tranquil, the okapi can kick and butt with its head to show aggression. As the vocal cords are poorly developed, vocal communication is mainly restricted to three sounds — "chuff" (contact calls used by both sexes), "moan" (by females during courtship) and "bleat" (by infants under stress). Individuals may engage in Flehmen response, a visual expression in which the animal curls back its upper lips, displays the teeth, and inhales through the mouth for a few seconds. The leopard is the main natural predator of the okapi.[25]
+Okapis are herbivores, feeding on tree leaves and buds, grasses, ferns, fruits, and fungi. They are unique in the Ituri Forest as they are the only known mammal that feeds solely on understory vegetation, where they use their 18-inch tongues to selectively browse for suitable plants. The tongue is also used to groom their ears and eyes.[32] They prefer to feed in treefall gaps. The okapi has been known to feed on over 100 species of plants, some of which are known to be poisonous to humans and other animals. Fecal analysis shows that none of those 100 species dominates the diet of the okapi. Staple foods comprise shrubs and lianas. The main constituents of the diet are woody, dicotyledonous species; monocotyledonous plants are not eaten regularly. In the Ituri forest, the okapi feeds mainly upon the plant families Acanthaceae, Ebenaceae, Euphorbiaceae, Flacourtiaceae, Loganiaceae, Rubiaceae, and Violaceae.[25][31]
+Female okapis become sexually mature at about one-and-a-half years old, while males reach maturity after two years. Rut in males and estrous in females does not depend on the season. In captivity, estrous cycles recur every 15 days.[28][33] The male and the female begin courtship by circling, smelling, and licking each other. The male shows his interest by extending his neck, tossing his head, and protruding one leg forward. This is followed by mounting and copulation.[26]
+The gestational period is around 440 to 450 days long, following which usually a single calf is born, weighing 14–30 kg (31–66 lb). The udder of the pregnant female starts swelling 2 months before parturition, and vulval discharges may occur. Parturition takes 3–4 hours, and the female stands throughout this period, though she may rest during brief intervals. The mother consumes the afterbirth and extensively grooms the infant. Her milk is very rich in proteins and low in fat.[28]
+As in other ruminants, the infant can stand within 30 minutes of birth. Although generally similar to adults, newborn calves have false eyelashes, a long dorsal mane, and long white hairs in the stripes. These features gradually disappear and give way to the general appearance within a year. The juveniles are kept in hiding, and nursing takes place infrequently. Calves are known not to defecate for the first month or two of life, which is hypothesized to help avoid predator detection in their most vulnerable phase of life.[34] The growth rate of calves is appreciably high in the first few months of birth, after which it gradually declines. Juveniles start taking solid food from 3 months, and weaning takes place at 6 months. Horn development in males takes 1 year after birth. The okapi's typical lifespan is 20–30 years.[25]
+The okapi is endemic to the Democratic Republic of the Congo, where it occurs north and east of the Congo River. It ranges from the Maiko National Park northward to the Ituri rainforest, then through the river basins of the Rubi, Lake Tele, and Ebola to the west and the Ubangi River further north. Smaller populations exist west and south of the Congo River. It is also common in the Wamba and Epulu areas. It is extinct in Uganda.[1]
+The okapi inhabits canopy forests at altitudes of 500–1,500 m (1,600–4,900 ft). It occasionally uses seasonally inundated areas, but does not occur in gallery forests, swamp forests, and habitats disturbed by human settlements. In the wet season, it visits rocky inselbergs that offer forage uncommon elsewhere. Results of research conducted in the late 1980s in a mixed Cynometra forest indicated that the okapi population density averaged 0.53 animals per square kilometre.[31]
+In 2008, it was recorded in Virunga National Park.[35]
+The IUCN classifies the okapi as endangered.[36] It is fully protected under Congolese law. The Okapi Wildlife Reserve and Maiko National Park support significant populations of the okapi, though a steady decline in numbers has occurred due to several threats. Other areas of occurrence are the Rubi Tele Hunting Reserve and the Abumombanzi Reserve. Major threats include habitat loss due to logging and human settlement. Extensive hunting for bushmeat and skin and illegal mining have also led to population declines. A threat that has emerged quite recently is the presence of illegal armed groups around protected areas, inhibiting conservation and monitoring actions. A small population occurs north of the Virunga National Park, but is bereft of protection due to the presence of armed groups in the vicinity.[1] In June 2012, a gang of poachers attacked the headquarters of the Okapi Wildlife Reserve, killing six guards and other staff[37] as well as all 14 okapis at their breeding center.[38]
+The Okapi Conservation Project, established in 1987, works towards the conservation of the okapi, as well as the growth of the indigenous Mbuti people.[1] In November 2011, the White Oak Conservation center and Jacksonville Zoo and Gardens hosted an international meeting of the Okapi Species Survival Plan  and the Okapi European Endangered Species Programme  at Jacksonville, which was attended by representatives from zoos from the US, Europe, and Japan. The aim was to discuss the management of captive okapis and arrange support for okapi conservation. Many zoos in North America and Europe currently have okapis in captivity.[39]
+Around 100 okapis are in accredited Association of Zoos and Aquariums (AZA) zoos. The okapi population is managed in America by the AZA's Species Survival Plan, a breeding program that works to ensure genetic diversity in the captive population of endangered animals, while the EEP (European studbook) and ISB (Global studbook) are managed by Antwerp Zoo,[40] which was the first zoo to have an Okapi on display (in 1919), as well as one of the most successful in breeding them.[41]
+The Bronx Zoo was the first zoo in North America to exhibit okapi, in 1937.[42] They have had one of the most successful breeding programs, with 13 calves having been born since 1991.[43]
+The San Diego Zoo has exhibited okapis since 1956, and had their first birth of an okapi in 1962. Since then, over 60 births have occurred between the zoo and the San Diego Zoo Safari Park, with the most recent being Mosi, a male calf born in early August 2017 at the San Diego Zoo.[44]
+The Brookfield Zoo in Chicago has also greatly contributed to the captive population of okapis in accredited zoos. The zoo has had 28 okapi births since 1959.[45]
+Other North American Zoos that exhibit and breed okapis include the Denver Zoo and Cheyenne Mountain Zoo (Colorado); Houston Zoo, Dallas Zoo and San Antonio Zoo (Texas); Disney's Animal Kingdom, Miami Zoo and Tampa's Lowry Park Zoo (Florida); Los Angeles Zoo (California); Saint Louis Zoo (Missouri); Cincinnati Zoo and Columbus Zoo (Ohio); Memphis Zoo (Tennessee); Maryland Zoo (Maryland) and The Sedgwick County Zoo and Tanganyika Wildlife Park (Kansas); Roosevelt Park Zoo[46] (South Dakota), Omaha's Henry Doorly Zoo (Nebraska); Philadelphia Zoo (Philadelphia).[47]
+In Europe, zoos that exhibit and breed okapis include Madrid Zoo (Spain), Chester Zoo, London Zoo, Yorkshire Wildlife Park, Marwell Zoo, The Wild Place (United Kingdom); Dublin Zoo (Ireland); Berlin Zoo, Frankfurt Zoo, Wilhelma Zoo, Wuppertal Zoo, Cologne Zoo, Leipzig Zoo (Germany) and Antwerp Zoo (Belgium); Zoo Basel (Switzerland); Copenhagen Zoo (Denmark); Rotterdam Zoo, Safaripark Beekse Bergen (Netherlands) and Dvůr Králové Zoo (Czech Republic), Wrocław Zoo (Poland); Bioparc Zoo de Doué, ZooParc de Beauval (France); Lisbon Zoo (Portugal).[48][49]
+In Asia, only two zoos in Japan exhibit okapis; Ueno Zoo in Tokyo and Zoorasia in Yokohama.[50]

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+Oklahoma (/ˌoʊkləˈhoʊmə/ (listen))[25] is a state in the South Central region of the United States,[26] bordered by the state of Texas on the south and west, Kansas on the north, Missouri on the northeast, Arkansas on the east, New Mexico on the west, and Colorado on the northwest. It is the 20th-most extensive and the 28th-most populous of the 50 United States. Its residents are known as Oklahomans (or colloquially, "Okies"), and its capital and largest city is Oklahoma City.
+The state's name is derived from the Choctaw words okla and humma, meaning "red people".[27] It is also known informally by its nickname, "The Sooner State", in reference to the non-Native settlers who staked their claims on land before the official opening date of lands in the western Oklahoma Territory or before the Indian Appropriations Act of 1889, which increased European-American settlement in the eastern Indian Territory. Oklahoma Territory and Indian Territory were merged into the State of Oklahoma when it became the 46th state to enter the union on November 16, 1907.
+With ancient mountain ranges, prairie, mesas, and eastern forests, most of Oklahoma lies in the Great Plains, Cross Timbers, and the U.S. Interior Highlands, all regions prone to severe weather.[28] Oklahoma is on a confluence of three major American cultural regions and historically served as a route for cattle drives, a destination for Southern settlers, and a government-sanctioned territory for Native Americans. More than 25 Native American languages are spoken in Oklahoma.[29]
+A major producer of natural gas, oil, and agricultural products, Oklahoma relies on an economic base of aviation, energy, telecommunications, and biotechnology.[30] Oklahoma City and Tulsa serve as Oklahoma's primary economic anchors, with nearly two-thirds of Oklahomans living within their metropolitan statistical areas.[31]
+The name Oklahoma comes from the Choctaw phrase okla humma, literally meaning red people. Choctaw Nation Chief Allen Wright suggested the name in 1866 during treaty negotiations with the federal government on the use of Indian Territory, in which he envisioned an all-Indian state controlled by the United States Superintendent of Indian Affairs. Equivalent to the English word Indian, okla humma was a phrase in the Choctaw language that described Native American people as a whole. Oklahoma later became the de facto name for Oklahoma Territory, and it was officially approved in 1890, two years after the area was opened to white settlers.[27][32][33]
+In the Chickasaw language, the state is known as Oklahomma', in Arapaho as bo'oobe' (literally meaning red earth),[34] Pawnee: Uukuhuúwa,[35] and Cayuga: Gahnawiyoˀgeh.[36]
+Oklahoma is the 20th-largest state in the United States, covering an area of 69,899 square miles (181,040 km2), with 68,595 square miles (177,660 km2) of land and 1,304 square miles (3,380 km2) of water.[37] It lies partly in the Great Plains near the geographical center of the 48 contiguous states. It is bounded on the east by Arkansas and Missouri, on the north by Kansas, on the northwest by Colorado, on the far west by New Mexico, and on the south and near-west by Texas.
+Oklahoma is between the Great Plains and the Ozark Plateau in the Gulf of Mexico watershed,[38] generally sloping from the high plains of its western boundary to the low wetlands of its southeastern boundary.[39][40] Its highest and lowest points follow this trend, with its highest peak, Black Mesa, at 4,973 feet (1,516 m) above sea level, situated near its far northwest corner in the Oklahoma Panhandle. The state's lowest point is on the Little River near its far southeastern boundary near the town of Idabel, which dips to 289 feet (88 m) above sea level.[41]
+Among the most geographically diverse states, Oklahoma is one of four to harbor more than 10 distinct ecological regions, with 11 in its borders—more per square mile than in any other state.[28] Its western and eastern halves, however, are marked by extreme differences in geographical diversity: Eastern Oklahoma touches eight ecological regions and its western half contains three. Although having fewer ecological regions Western Oklahoma contains many rare, relic species.[28]
+Oklahoma has four primary mountain ranges: the Ouachita Mountains, the Arbuckle Mountains, the Wichita Mountains, and the Ozark Mountains.[39] Contained within the U.S. Interior Highlands region, the Ozark and Ouachita Mountains are the only major mountainous region between the Rocky Mountains and the Appalachians.[42] A portion of the Flint Hills stretches into north-central Oklahoma, and near the state's eastern border, The Oklahoma Tourism & Recreation Department regards Cavanal Hill as the world's tallest hill; at 1,999 feet (609 m), it fails their definition of a mountain by one foot.[43]
+The semi-arid high plains in the state's northwestern corner harbor few natural forests; the region has a rolling to flat landscape with intermittent canyons and mesa ranges like the Glass Mountains. Partial plains interrupted by small, sky island mountain ranges like the Antelope Hills and the Wichita Mountains dot southwestern Oklahoma; transitional prairie and oak savannas cover the central portion of the state. The Ozark and Ouachita Mountains rise from west to east over the state's eastern third, gradually increasing in elevation in an eastward direction.[40][44]
+More than 500 named creeks and rivers make up Oklahoma's waterways, and with 200 lakes created by dams, it holds the nation's highest number of artificial reservoirs.[43] Most of the state lies in two primary drainage basins belonging to the Red and Arkansas rivers, though the Lee and Little rivers also contain significant drainage basins.[44]
+Due to Oklahoma's location at the confluence of many geographic regions, the state's climatic regions have a high rate of biodiversity. Forests cover 24 percent of Oklahoma[43] and prairie grasslands composed of shortgrass, mixed-grass, and tallgrass prairie, harbor expansive ecosystems in the state's central and western portions, although cropland has largely replaced native grasses.[45] Where rainfall is sparse in the state's western regions, shortgrass prairie and shrublands are the most prominent ecosystems, though pinyon pines, red cedar (junipers), and ponderosa pines grow near rivers and creek beds in the panhandle's far western reaches.[45] Southwestern Oklahoma contains many rare, disjunct species including sugar maple, bigtooth maple, nolina and southern live oak.
+Marshlands, cypress forests and mixtures of shortleaf pine, loblolly pine, blue palmetto, and deciduous forests dominate the state's southeastern quarter, while mixtures of largely post oak, elm, red cedar (Juniperus virginiana) and pine forests cover northeastern Oklahoma.[44][45][46]
+The state holds populations of white-tailed deer, mule deer, antelope, coyotes, mountain lions, bobcats, elk, and birds such as quail, doves, cardinals, bald eagles, red-tailed hawks, and pheasants. In prairie ecosystems, American bison, greater prairie chickens, badgers, and armadillo are common, and some of the nation's largest prairie dog towns inhabit shortgrass prairie in the state's panhandle. The Cross Timbers, a region transitioning from prairie to woodlands in Central Oklahoma, harbors 351 vertebrate species. The Ouachita Mountains are home to black bear, red fox, gray fox, and river otter populations, which coexist with 328 vertebrate species in southeastern Oklahoma. Also, in southeastern Oklahoma lives the American alligator.[45]
+Oklahoma has fifty state parks,[47] six national parks or protected regions,[48] two national protected forests or grasslands,[49] and a network of wildlife preserves and conservation areas. Six percent of the state's 10 million acres (40,000 km2) of forest is public land,[46] including the western portions of the Ouachita National Forest, the largest and oldest national forest in the Southern United States.[50]
+With 39,000 acres (160 km2), the Tallgrass Prairie Preserve in north-central Oklahoma is the largest protected area of tallgrass prairie in the world and is part of an ecosystem that encompasses only ten percent of its former land area, once covering fourteen states.[51] In addition, the Black Kettle National Grassland covers 31,300 acres (127 km2) of prairie in southwestern Oklahoma.[52] The Wichita Mountains Wildlife Refuge is the oldest and largest of nine National Wildlife Refuges in the state[53] and was founded in 1901, encompassing 59,020 acres (238.8 km2).[54]
+Of Oklahoma's federally protected parks or recreational sites, the Chickasaw National Recreation Area is the largest, with 9,898.63 acres (40.0583 km2).[55] Other sites include the Santa Fe and Trail of Tears national historic trails, the Fort Smith and Washita Battlefield national historic sites, and the Oklahoma City National Memorial.[48]
+Oklahoma is in a humid subtropical region.[56] Oklahoma lies in a transition zone between semi-arid further to the west, humid continental to the north, and humid subtropical to the east and southeast. Most of the state lies in an area known as Tornado Alley characterized by frequent interaction between cold, dry air from Canada, warm to hot, dry air from Mexico and the Southwestern U.S., and warm, moist air from the Gulf of Mexico. The interactions between these three contrasting air currents produces severe weather (severe thunderstorms, damaging thunderstorm winds, large hail and tornadoes) with a frequency virtually unseen anywhere else on planet Earth.[41] An average 62 tornadoes strike the state per year—one of the highest rates in the world.[57]
+Because of Oklahoma's position between zones of differing prevailing temperature and winds, weather patterns within the state can vary widely over relatively short distances, and they can change drastically in a short time.[41] On November 11, 1911, the temperature at Oklahoma City reached 83 °F (28 °C) (the record high for that date), then a cold front of unprecedented intensity slammed across the state, causing the temperature to reach 17 °F (−8 °C) (the record low for that date) by midnight.[58] This type of phenomenon is also responsible for many of the tornadoes in the area, such as the 1912 Oklahoma tornado outbreak when a warm front traveled along a stalled cold front, resulting in an average of about one tornado per hour.[59]
+The humid subtropical climate (Koppen Cfa) of central, southern and eastern Oklahoma is influenced heavily by southerly winds bringing moisture from the Gulf of Mexico. Traveling westward, the climate transitions progressively toward a semi-arid zone (Koppen BSk) in the high plains of the Panhandle and other western areas from about Lawton westward, less frequently touched by southern moisture.[56] Precipitation and temperatures decline from east to west accordingly, with areas in the southeast averaging an annual temperature of 62 °F (17 °C) and an annual rainfall of generally over 40 in (1,020 mm) and up to 56 in (1,420 mm), while areas of the (higher-elevation) panhandle average 58 °F (14 °C), with an annual rainfall under 17 in (430 mm).[60]
+Over almost all of Oklahoma, winter is the driest season. Average monthly precipitation increases dramatically in the spring to a peak in May, the wettest month over most of the state, with its frequent and not uncommonly severe thunderstorm activity. Early June can still be wet, but most years see a marked decrease in rainfall during June and early July. Mid-summer (July and August) represents a secondary dry season over much of Oklahoma, with long stretches of hot weather with only sporadic thunderstorm activity not uncommon many years. Severe drought is common in the hottest summers, such as those of 1934, 1954, 1980 and 2011, all of which featured weeks on end of virtual rainlessness and highs well over 100 °F (38 °C). Average precipitation rises again from September to mid-October, representing a secondary wetter season, then declines from late October through December.[41]
+The entire state frequently experiences temperatures above 100 °F (38 °C) or below 0 °F (−18 °C),[56] though below-zero temperatures are rare in south-central and southeastern Oklahoma. Snowfall ranges from an average of less than 4 in (102 mm) in the south to just over 20 in (508 mm) on the border of Colorado in the panhandle.[41] The state is home to the Storm Prediction Center, the National Severe Storms Laboratory, and the Warning Decision Training Division, all part of the National Weather Service and in Norman.[61]
+Evidence suggests indigenous peoples traveled through Oklahoma as early as the last ice age.[64] Ancestors of the Wichita, Kichai, Teyas, Escanjaques, and Caddo lived in what is now Oklahoma. Southern Plains villagers lived in the central and west of the state, with a subgroup, the Panhandle culture people living in the panhandle region. Caddoan Mississippian culture peoples lived in the eastern part of the state. Spiro Mounds, in what is now Spiro, Oklahoma, was a major Mississippian mound complex that flourished between AD 850 and 1450.[65][66]
+The Spaniard Francisco Vázquez de Coronado traveled through the state in 1541,[67] but French explorers claimed the area in the 1700s.[68] In the 18th century, Kiowa, Apache, and Comanche entered the region from the west and Quapaw and Osage peoples moved into what is now eastern Oklahoma. French colonists claimed the region until 1803, when all the French territory west of the Mississippi River was acquired by the United States in the Louisiana Purchase.[67]
+The territory now known as Oklahoma was first a part of the Arkansas Territory from 1819 until 1828.
+During the 19th century, thousands of Native Americans were expelled from their ancestral homelands from across North America and transported to the area including and surrounding present-day Oklahoma. The Choctaw was the first of the Five Civilized Tribes to be removed from the Southeastern United States. The phrase "Trail of Tears" originated from a description of the removal of the Choctaw Nation in 1831, although the term is usually used for the Cherokee removal.[69]
+Seventeen thousand Cherokees and 2,000 of their black slaves were deported.[70] The area, already occupied by Osage and Quapaw tribes, was called for the Choctaw Nation until revised Native American and then later American policy redefined the boundaries to include other Native Americans. By 1890, more than 30 Native American nations and tribes had been concentrated on land within Indian Territory or "Indian Country".[71]
+All Five Civilized Tribes supported and signed treaties with the Confederate military during the American Civil War.[72] The Cherokee Nation had an internal civil war.[73] Slavery in Indian Territory was not abolished until 1866.[74]
+In the period between 1866 and 1899,[67] cattle ranches in Texas strove to meet the demands for food in eastern cities and railroads in Kansas promised to deliver in a timely manner. Cattle trails and cattle ranches developed as cowboys either drove their product north or settled illegally in Indian Territory.[67] In 1881, four of five major cattle trails on the western frontier traveled through Indian Territory.[75]
+Increased presence of white settlers in Indian Territory prompted the United States Government to establish the Dawes Act in 1887, which divided the lands of individual tribes into allotments for individual families, encouraging farming and private land ownership among Native Americans but expropriating land to the federal government. In the process, railroad companies took nearly half of Indian-held land within the territory for outside settlers and for purchase.[76]
+Major land runs, including the Land Run of 1889, were held for settlers where certain territories were opened to settlement starting at a precise time. Usually land was open to settlers on a first come first served basis.[77] Those who broke the rules by crossing the border into the territory before the official opening time were said to have been crossing the border sooner, leading to the term sooners, which eventually became the state's official nickname.[78]
+Deliberations to make the territory into a state began near the end of the 19th century, when the Curtis Act continued the allotment of Indian tribal land.
+Attempts to create an all-Indian state named Oklahoma and a later attempt to create an all-Indian state named Sequoyah failed but the Sequoyah Statehood Convention of 1905 eventually laid the groundwork for the Oklahoma Statehood Convention, which took place two years later.[79] On June 16, 1906, Congress enacted a statute authorizing the people of the Oklahoma and Indian Territories (as well what would become the states of Arizona and New Mexico) to form a constitution and state government in order to be admitted as a state.[80] On November 16, 1907, President Theodore Roosevelt issued Presidential Proclamation no. 780, establishing Oklahoma as the 46th state in the Union.[81]
+The new state became a focal point for the emerging oil industry, as discoveries of oil pools prompted towns to grow rapidly in population and wealth. Tulsa eventually became known as the "Oil Capital of the World" for most of the 20th century and oil investments fueled much of the state's early economy.[82] In 1927, Oklahoman businessman Cyrus Avery, known as the "Father of Route 66", began the campaign to create U.S. Route 66. Using a stretch of highway from Amarillo, Texas to Tulsa, Oklahoma to form the original portion of Highway 66, Avery spearheaded the creation of the U.S. Highway 66 Association to oversee the planning of Route 66, based in his hometown of Tulsa.[83]
+Oklahoma also has a rich African-American history. Many Black towns, founded by the Freedmen of the Five Tribes during Reconstruction, thrived in the early 20th century with the arrival of Black Exodusters who migrated from neighboring states, especially Kansas. The politician Edward P. McCabe encouraged Black settlers to come to what was then Indian Territory. McCabe discussed with President Theodore Roosevelt the possibility of making Oklahoma a majority-Black state.
+By the early 20th century, the Greenwood district of Tulsa was one of the most prosperous African-American communities in the United States.[84] Jim Crow laws had established racial segregation since before the start of the 20th century, but Tulsa's Black residents had created a thriving area.
+Social tensions were exacerbated by the revival of the Ku Klux Klan after 1915. The Tulsa race massacre broke out in 1921, with White mobs attacking Black people and carrying out a pogrom in Greenwood. In one of the costliest episodes of racist violence in American history, sixteen hours of rioting resulted in 35 city blocks destroyed, $1.8 million in property damage, and a death toll estimated to be as high as 300 people.[85] By the late 1920s, the Ku Klux Klan had declined to negligible influence within the state.[86]
+During the 1930s, parts of the state began suffering the consequences of poor farming practice. This period was known as the Dust Bowl, throughout which areas of Kansas, Texas, New Mexico and northwestern Oklahoma were hampered by long periods of little rainfall, strong winds, and abnormally high temperatures, sending thousands of farmers into poverty and forcing them to relocate to more fertile areas of the western United States.[87] Over a twenty-year period ending in 1950, the state saw its only historical decline in population, dropping 6.9 percent as impoverished families migrated out of the state after the Dust Bowl.
+Soil and water conservation projects markedly changed practices in the state and led to the construction of massive flood control systems and dams; they built hundreds of reservoirs and man-made lakes to supply water for domestic needs and agricultural irrigation. By the 1960s, Oklahoma had created more than 200 lakes, the most in the nation.[28][88]
+In 1995, Oklahoma City was the site of one of the most destructive act of domestic terrorism in American history. The Oklahoma City bombing of April 19, 1995, in which Timothy McVeigh detonated a large, crude explosive device outside the Alfred P. Murrah Federal Building, killed 168 people, including 19 children. For his crime, McVeigh was executed by the federal government on June 11, 2001. His accomplice, Terry Nichols, is serving life in prison without parole for helping plan the attack and prepare the explosive.[89]
+On May 31, 2016, several cities experienced record setting flooding.[90][91]
+On July 9, 2020, the Supreme Court of the United States determined in McGirt v. Oklahoma that the reservations of the Five Tribes, comprising much of Eastern Oklahoma, were never disestablished by Congress and thus are still "Indian Country" for the purposes of criminal law.[92]
+The United States Census Bureau estimates Oklahoma's population was 3,956,971 on July 1, 2019, a 5.48% increase since the 2010 United States Census.[94]
+At the 2010 Census, 68.7% of the population was non-Hispanic white, down from 88% in 1970,[95] 7.3% non-Hispanic black or African American, 8.2% non-Hispanic American Indian and Alaska Native, 1.7% non-Hispanic Asian, 0.1% non-Hispanic Native Hawaiian and Other Pacific Islander, 0.1% from some other race (non-Hispanic) and 5.1% of two or more races (non-Hispanic). 8.9% of Oklahoma's population was of Hispanic, Latino, or Spanish origin (they may be of any race).
+As of 2011[update], 47.3% of Oklahoma's population younger than age 1 were minorities, meaning they had at least one parent who was not non-Hispanic white.[98]
+As of 2005[update] Oklahoma's estimated ancestral makeup was 14.5% German, 13.1% American, 11.8% Irish, 9.6% English, 8.1% African American, and 11.4% Native American (including 7.9% Cherokee)[99] though the percentage of people claiming American Indian as their only race was 8.1%.[100] Most people from Oklahoma who self-identify as having American ancestry are of overwhelmingly English and Scots-Irish ancestry with significant amounts of Scottish and Welsh inflection as well.[101][102]
+The state had the second-highest number of Native Americans in 2002, estimated at 395,219, as well as the second-highest percentage among all states.[99]
+In 2011, U.S. Census Bureau American Community Survey data from 2005 to 2009 indicated about 5% of Oklahoma's residents were born outside the United States. This is lower than the national figure (about 12.5% of U.S. residents were foreign-born).[103]
+The center of population of Oklahoma is in Lincoln County near the town of Sparks.[104]
+The state's 2006 per capita personal income ranked 37th at $32,210, though it has the third-fastest-growing per capita income in the U.S.[105] Oklahoma ranks consistently among the lowest states in cost of living index.[106] The Oklahoma City suburb Nichols Hills is first on Oklahoma locations by per capita income at $73,661, though Tulsa County holds the highest average.[107][108] In 2011, 7.0% of Oklahomans were under the age of 5, 24.7% under 18, and 13.7% were 65 or older. Females made up 50.5% of the population.[109]
+The state is in the U.S. Census' Southern region. According to the 2010 United States Census, Oklahoma is the 28th-most populous state with 3,751,616 inhabitants but the 19th-largest by land area spanning 68,594.92 square miles (177,660.0 km2) of land.[110] Oklahoma is divided into 77 counties and contains 597 incorporated municipalities consisting of cities and towns.[111]
+In Oklahoma, cities are all those incorporated communities which are 1,000 or more in population and are incorporated as cities.[112] Towns are limited to town board type of municipal government. Cities may choose among aldermanic, mayoral, council-manager, and home-rule charter types of government.[113] Cities may also petition to incorporate as towns.[114]
+The English language has been official in the state of Oklahoma since 2010.[116] The variety of North American English spoken is called Oklahoma English, and this dialect is quite diverse with its uneven blending of features of North Midland, South Midland, and Southern dialects.[117] In 2000, 2,977,187 Oklahomans—92.6% of the resident population five years or older—spoke only English at home, a decrease from 95% in 1990.[117] 238,732 Oklahoma residents reported speaking a language other than English in the 2000 census, about 7.4% of the state's population.[117]
+The two most commonly spoken native North American languages are Cherokee and Choctaw with 10,000 Cherokee speakers living within the Cherokee Nation tribal jurisdiction area of eastern Oklahoma, and another 10,000 Choctaw speakers living in the Choctaw Nation directly south of the Cherokees.[118] Cherokee is an official language in the Cherokee Nation tribal jurisdiction area and in the United Keetoowah Band of Cherokee Indians.[4][5][6]
+In addition to Cherokee, more than 25 Native American languages are spoken in Oklahoma,[29] second only to California. However, only Cherokee, if any, exhibits some language vitality at present. The Ethnologue sees Cherokee as moribund because the only remaining active users of the language are members of the grandparent generation and older.
+Spanish is the second-most commonly spoken language in the state, with 141,060 speakers counted in 2000.[117] German has 13,444 speakers representing about 0.4% of the state's population,[117] and Vietnamese is spoken by 11,330 people,[117] or about 0.4% of the population,[117] many of whom live in the Asia District of Oklahoma City. Other languages include French with 8,258 speakers (0.3%), Chinese with 6,413 (0.2%), Korean with 3,948 (0.1%), Arabic with 3,265 (0.1%), other Asian languages with 3,134 (0.1%), Tagalog with 2,888 (0.1%), Japanese with 2,546 (0.1%), and African languages with 2,546 (0.1%).[117]
+Oklahoma is part of a geographical region characterized by conservative and Evangelical Christianity known as the "Bible Belt". Spanning the southern and eastern parts of the United States, the area is known for politically and socially conservative views, with the Republican Party having the greater number of voters registered between the two parties.[120] Tulsa, the state's second-largest city, home to Oral Roberts University, is sometimes called the "buckle of the Bible Belt".[121][122]
+According to the Pew Research Center, the majority of Oklahoma's religious adherents are Christian, accounting for about 80 percent of the population. The percentage of Catholics is half the national average, while the percentage of Evangelical Protestants is more than twice the national average (tied with Arkansas for the largest percentage of any state).[123]
+In 2010, the state's largest church memberships were in the Southern Baptist Convention (886,394 members), the United Methodist Church (282,347), the Roman Catholic Church (178,430), and the Assemblies of God (85,926) and The Church of Jesus Christ of Latter-day Saints[124] (47,349). Other religions represented in the state include Buddhism, Hinduism, and Islam.[125]
+In 2000, there were about 5,000 Jews and 6,000 Muslims, with ten congregations to each group.[126]
+Oklahoma religious makeup:[126][a]
+Oklahoma has been described as "the world's prison capital", with 1,079 of every 100,000 residents imprisoned in 2018, the highest incarceration rate of any state, and by comparison, higher than the incarceration rates of any country in the world.[127][128]
+Oklahoma is host to a diverse range of sectors including aviation, energy, transportation equipment, food processing, electronics, and telecommunications. Oklahoma is an important producer of natural gas, aircraft, and food.[30] The state ranks third in the nation for production of natural gas, is the 27th-most agriculturally productive state, and also ranks 5th in production of wheat.[129] Four Fortune 500 companies and six Fortune 1000 companies are headquartered in Oklahoma,[130] and it has been rated one of the most business-friendly states in the nation,[131] with the 7th-lowest tax burden in 2007.[132]
+In 2010, Oklahoma City-based Love's Travel Stops & Country Stores ranked 18th on the Forbes list of largest private companies, Tulsa-based QuikTrip ranked 37th, and Oklahoma City-based Hobby Lobby ranked 198th in 2010 report.[134] Oklahoma's gross domestic product grew from $131.9 billion in 2006 to $147.5 billion in 2010, a jump of 10.6 percent.[135] Oklahoma's gross domestic product per capita was $35,480 in 2010, which was ranked 40th among the states.[136]
+Though oil has historically dominated the state's economy, a collapse in the energy industry during the 1980s led to the loss of nearly 90,000 energy-related jobs between 1980 and 2000, severely damaging the local economy.[137] Oil accounted for 35 billion dollars in Oklahoma's economy in 2007,[138] and employment in the state's oil industry was outpaced by five other industries in 2007.[139] As of July 2017[update], the state's unemployment rate is 4.4%.[140]
+In mid-2011, Oklahoma had a civilian labor force of 1.7 million and non-farm employment fluctuated around 1.5 million.[139] The government sector provides the most jobs, with 339,300 in 2011, followed by the transportation and utilities sector, providing 279,500 jobs, and the sectors of education, business, and manufacturing, providing 207,800, 177,400, and 132,700 jobs, respectively.[139] Among the state's largest industries, the aerospace sector generates $11 billion annually.[131]
+Tulsa is home to the largest airline maintenance base in the world, which serves as the global maintenance and engineering headquarters for American Airlines.[141] In total, aerospace accounts for more than 10 percent of Oklahoma's industrial output, and it is one of the top 10 states in aerospace engine manufacturing.[30] Because of its position in the center of the United States, Oklahoma is also among the top states for logistic centers, and a major contributor to weather-related research.[131]
+The state is the top manufacturer of tires in North America and contains one of the fastest-growing biotechnology industries in the nation.[131] In 2005, international exports from Oklahoma's manufacturing industry totaled $4.3 billion, accounting for 3.6 percent of its economic impact.[142] Tire manufacturing, meat processing, oil and gas equipment manufacturing, and air conditioner manufacturing are the state's largest manufacturing industries.[143]
+Oklahoma is the nation's third-largest producer of natural gas, and its fifth-largest producer of crude oil. The state also has the second-greatest number of active drilling rigs,[138][144] and it is even ranked fifth in crude oil reserves.[145] While the state is ranked eighth for installed wind energy capacity in 2011,[146] it is at the bottom of states in usage of renewable energy, with 94% of its electricity being generated by non-renewable sources in 2009, including 25% from coal and 46% from natural gas.[147] Oklahoma has no nuclear power. Ranking 13th for total energy consumption per capita in 2009,[148] the state's energy costs were eighth-lowest in the nation.[149]
+As a whole, the oil energy industry contributes $35 billion to Oklahoma's gross domestic product (GDP), and employees of the state's oil-related companies earn an average of twice the state's typical yearly income.[138] In 2009, the state had 83,700 commercial oil wells churning 65.374 million barrels (10,393,600 m3) of crude oil.[150] Eight and a half percent of the nation's natural gas supply is held in Oklahoma, with 1.673 trillion cubic feet (47.4 km3) being produced in 2009.[150]
+The Oklahoma Stack Play is a geographic referenced area in the Anadarko Basin. The oil field "Sooner Trend", Anadarko basin and the counties of Kingfisher and Canadian make up the basis for the "Oklahoma STACK". Other Plays such as the Eagle Ford are geological rather than geographical.[151]
+According to Forbes magazine, Oklahoma City-based Devon Energy Corporation, Chesapeake Energy Corporation, and SandRidge Energy Corporation are the largest private oil-related companies in the nation,[152] and all Oklahoma's Fortune 500 companies are energy-related.[130] Tulsa's ONEOK and Williams Companies are the state's largest and second-largest companies respectively, also ranking as the nation's second- and third-largest companies in the field of energy, according to Fortune magazine.[153] The magazine also placed Devon Energy as the second-largest company in the mining and crude oil-producing industry in the nation, while Chesapeake Energy ranks seventh respectively in that sector and Oklahoma Gas & Electric ranks as the 25th-largest gas and electric utility company.[153]
+Oklahoma Gas & Electric, commonly referred to as OG&E (NYSE: OGE) operates four base electric power plants in Oklahoma. Two of them are coal-fired power plants: one in Muskogee, and the other in Red Rock. Two are gas-fired power plants: one in Harrah and the other in Konawa. OG&E was the first electric company in Oklahoma to generate electricity from wind farms in 2003.[154]
+The 27th-most agriculturally productive state, Oklahoma is fifth in cattle production and fifth in production of wheat.[129][157] Approximately 5.5 percent of American beef comes from Oklahoma, while the state produces 6.1 percent of American wheat, 4.2 percent of American pig products, and 2.2 percent of dairy products.[129]
+The state had 85,500 farms in 2012, collectively producing $4.3 billion in animal products and fewer than one billion dollars in crop output with more than $6.1 billion added to the state's gross domestic product.[129] Poultry and swine are its second- and third-largest agricultural industries.[157]
+With an educational system made up of public school districts and independent private institutions, Oklahoma had 638,817 students enrolled in 1,845 public primary, secondary, and vocational schools in 533 school districts as of 2008[update].[158] Oklahoma has the highest enrollment of Native American students in the nation with 126,078 students in the 2009–10 school year.[159] Oklahoma spent $7,755 for each student in 2008, and was 47th in the nation in expenditures per student,[158] though its growth of total education expenditures between 1992 and 2002 ranked 22nd.[160]
+The state is among the best in pre-kindergarten education, and the National Institute for Early Education Research rated it first in the United States with regard to standards, quality, and access to pre-kindergarten education in 2004, calling it a model for early childhood schooling.[161] High school dropout rate decreased from 3.1 to 2.5 percent between 2007 and 2008 with Oklahoma ranked among 18 other states with 3 percent or less dropout rate.[162] In 2004, the state ranked 36th in the nation for the relative number of adults with high school diplomas, though at 85.2 percent, it had the highest rate among Southern states.[163][164] According to a study conducted by the Pell Institute, Oklahoma ranks 48th in college-participation for low-income students.[165]
+The University of Oklahoma, Oklahoma State University, the University of Central Oklahoma, and Northeastern State University are the largest public institutions of higher education in Oklahoma, operating through one primary campus and satellite campuses throughout the state. The two state universities, along with Oklahoma City University and the University of Tulsa, rank among the country's best in undergraduate business programs.[166]
+Oklahoma City University School of Law, University of Oklahoma College of Law, and University of Tulsa College of Law are the state's only ABA-accredited institutions. Both University of Oklahoma and University of Tulsa are Tier 1 institutions, with the University of Oklahoma ranked 68th and the University of Tulsa ranked 86th in the nation.[167]
+Oklahoma holds eleven public regional universities,[168] including Northeastern State University, the second-oldest institution of higher education west of the Mississippi River,[169] also containing the only College of Optometry in Oklahoma[170] and the largest enrollment of Native American students in the nation by percentage and amount.[169][171] Langston University is Oklahoma's only historically black college. Six of the state's universities were placed in the Princeton Review's list of best 122 regional colleges in 2007,[172] and three made the list of top colleges for best value. The state has 55 post-secondary technical institutions operated by Oklahoma's CareerTech program for training in specific fields of industry or trade.[158]
+In the 2007–2008 school year, there were 181,973 undergraduate students, 20,014 graduate students, and 4,395 first-professional degree students enrolled in Oklahoma colleges. Of these students, 18,892 received a bachelor's degree, 5,386 received a master's degree, and 462 received a first professional degree. This means the state of Oklahoma produces an average of 38,278-degree-holders per completions component (i.e. July 1, 2007 – June 30, 2008). National average is 68,322 total degrees awarded per completions component.[173]
+Beginning on April 2, 2018, tens of thousands of K–12 public school teachers went on strike due to lack of funding. According to the National Education Association, teachers in Oklahoma had ranked 49th out of the 50 states in terms of teacher pay in 2016. The Oklahoma Legislature had passed a measure a week earlier to raise teacher salaries by $6,100, but it fell short of the $10,000 raise for teachers, $5,000 raise for other school employees, and $200 million increase in extra education funding many had sought.[174] A survey in 2019 found that the pay raise obtained by the strike lifted the State's teacher pay ranking to 34th in the nation.[175]
+The Cherokee Nation instigated a ten-year plan that involved growing new speakers of the Cherokee language from childhood as well as speaking it exclusively at home.[176] The plan was part of an ambitious goal that in fifty years would have at least 80% of their people fluent.[177] The Cherokee Preservation Foundation has invested $3 million into opening schools, training teachers, and developing curricula for language education, as well as initiating community gatherings where the language can be actively used.[177]
+A Cherokee language immersion school in Tahlequah, Oklahoma educates students from pre-school through eighth grade.[178]
+Oklahoma is placed in the South by the United States Census Bureau,[26] but other definitions place the state at least partly in the Southwest, Midwest,[179] Upland South,[180] and Great Plains.[181] Oklahomans have a high rate of English, Scotch-Irish, German, and Native American ancestry,[182] with 25 different native languages spoken.[29]
+Because many Native Americans were forced to move to Oklahoma when White settlement in North America increased, Oklahoma has much linguistic diversity. Mary Linn, an associate professor of anthropology at the University of Oklahoma and the associate curator of Native American languages at the Sam Noble Museum, notes Oklahoma also has high levels of language endangerment.[183]
+Sixty-seven Native American tribes are represented in Oklahoma,[67] including 39 federally recognized tribes, who are headquartered and have tribal jurisdictional areas in the state.[184] Western ranchers, Native American tribes, Southern settlers, and eastern oil barons have shaped the state's cultural predisposition, and its largest cities have been named among the most underrated cultural destinations in the United States.[185]
+Residents of Oklahoma are associated with traits of Southern hospitality—the 2006 Catalogue for Philanthropy (with data from 2004) ranks Oklahomans 7th in the nation for overall generosity.[186] The state has also been associated with a negative cultural stereotype first popularized by John Steinbeck's 1939 novel The Grapes of Wrath, which described the plight of uneducated, poverty-stricken Dust Bowl-era farmers deemed "Okies".[187][188] However, the term is often used in a positive manner by Oklahomans.[187]
+In the state's largest urban areas, pockets of jazz culture flourish,[190] and Native American, Mexican American, and Asian American communities produce music and art of their respective cultures.[191] The Oklahoma Mozart Festival in Bartlesville is one of the largest classical music festivals on the southern plains,[192] and Oklahoma City's Festival of the Arts has been named one of the top fine arts festivals in the nation.[190]
+The state has a rich history in ballet with five Native American ballerinas attaining worldwide fame. These were Yvonne Chouteau, sisters Marjorie and Maria Tallchief, Rosella Hightower and Moscelyne Larkin, known collectively as the Five Moons. The New York Times rates the Tulsa Ballet as one of the top ballet companies in the United States.[190] The Oklahoma City Ballet and University of Oklahoma's dance program were formed by ballerina Yvonne Chouteau and husband Miguel Terekhov. The University program was founded in 1962 and was the first fully accredited program of its kind in the United States.[193][194]
+In Sand Springs, an outdoor amphitheater called "Discoveryland!" is the official performance headquarters for the musical Oklahoma![195] Ridge Bond, native of McAlester, Oklahoma,[196] starred in the Broadway and International touring productions of Oklahoma!,[197][198][199][200] playing the role of "Curly McClain" in more than 2,600 performances.[197][201] In 1953 he was featured along with the Oklahoma! cast on a CBS Omnibus television broadcast.[201] Bond was instrumental in the Oklahoma! title song becoming the Oklahoma state song[196][202] and is also featured on the U.S. postage stamp commemorating the musical's 50th anniversary.[197][203] Historically, the state has produced musical styles such as The Tulsa Sound and western swing, which was popularized at Cain's Ballroom in Tulsa. The building, known as the "Carnegie Hall of Western Swing",[204] served as the performance headquarters of Bob Wills and the Texas Playboys during the 1930s.[205] Stillwater is known as the epicenter of Red Dirt music, the best-known proponent of which is the late Bob Childers.
+Prominent theatre companies in Oklahoma include, in the capital city, Oklahoma City Theatre Company, Carpenter Square Theatre, Oklahoma Shakespeare in the Park, and CityRep. CityRep is a professional company affording equity points to those performers and technical theatre professionals. In Tulsa, Oklahoma's oldest resident professional company is American Theatre Company, and Theatre Tulsa is the oldest community theatre company west of the Mississippi. Other companies in Tulsa include Heller Theatre and Tulsa Spotlight Theater. The cities of Norman, Lawton, and Stillwater, among others, also host well-reviewed community theatre companies.
+Oklahoma is in the nation's middle percentile in per capita spending on the arts, ranking 17th, and contains more than 300 museums.[190] The Philbrook Museum of Tulsa is considered one of the top 50 fine art museums in the United States,[189] and the Sam Noble Oklahoma Museum of Natural History in Norman, one of the largest university-based art and history museums in the country, documents the natural history of the region.[190] The collections of Thomas Gilcrease are housed in the Gilcrease Museum of Tulsa, which also holds the world's largest, most comprehensive collection of art and artifacts of the American West.[206]
+The Egyptian art collection at the Mabee-Gerrer Museum of Art in Shawnee is considered to be the finest Egyptian collection between Chicago and Los Angeles.[207] The Oklahoma City Museum of Art contains the most comprehensive collection of glass sculptures by artist Dale Chihuly in the world,[208] and Oklahoma City's National Cowboy & Western Heritage Museum documents the heritage of the American Western frontier.[190] With remnants of the Holocaust and artifacts relevant to Judaism, the Sherwin Miller Museum of Jewish Art of Tulsa preserves the largest collection of Jewish art in the Southwest United States.[209]
+Oklahoma's centennial celebration was named the top event in the United States for 2007 by the American Bus Association,[210] and consisted of multiple celebrations saving with the 100th anniversary of statehood on November 16, 2007. Annual ethnic festivals and events take place throughout the state such as Native American powwows and ceremonial events, and include festivals (as examples) in Scottish, Irish, German, Italian, Vietnamese, Chinese, Czech, Jewish, Arab, Mexican and African-American communities depicting cultural heritage or traditions.
+Oklahoma City is home to a few reoccurring events and festivals. During a ten-day run in Oklahoma City, the State Fair of Oklahoma attracts roughly one million people[211] along with the annual Festival of the Arts. Large national pow wows, various Latin and Asian heritage festivals, and cultural festivals such as the Juneteenth celebrations are held in Oklahoma City each year. The Oklahoma City Pride Parade has been held annually in late June since 1987 in the gay district of Oklahoma City on 39th and Penn.[212] The First Friday Art Walk in the Paseo Arts District is an art appreciation festival held the first Friday of every month.[213] Additionally, an annual art festival is held in the Paseo on Memorial Day Weekend.[214]
+The Tulsa State Fair attracts more than a million people each year during its ten-day run,[215] and the city's Mayfest festival entertained more than 375,000 in four days during 2007.[216] In 2006, Tulsa's Oktoberfest was named one of the top 10 in the world by USA Today and one of the top German food festivals in the nation by Bon Appétit magazine.[217]
+Norman plays host to the Norman Music Festival, a festival that highlights native Oklahoma bands and musicians. Norman is also host to the Medieval Fair of Norman, which has been held annually since 1976 and was Oklahoma's first medieval fair. The Fair was held first on the south oval of the University of Oklahoma campus and in the third year moved to the Duck Pond in Norman until the Fair became too big and moved to Reaves Park in 2003. The Medieval Fair of Norman is Oklahoma's "largest weekend event and the third-largest event in Oklahoma, and was selected by Events Media Network as one of the top 100 events in the nation".[218]
+Oklahoma has teams in basketball, football, arena football, baseball, soccer, hockey, and wrestling in Oklahoma City, Tulsa, Enid, Norman, and Lawton. The Oklahoma City Thunder of the National Basketball Association (NBA) is the state's only major league sports franchise. The state had a team in the Women's National Basketball Association, the Tulsa Shock, from 2010 through 2015, but the team relocated to Dallas–Fort Worth after that season[219] and became the Dallas Wings.[220]
+Oklahoma has teams in several minor leagues, including Minor League Baseball at the AAA and AA levels (Oklahoma City Dodgers and Tulsa Drillers, respectively), hockey's ECHL with the Tulsa Oilers, and a number of indoor football leagues. In the last-named sport, the state's most notable team was the Tulsa Talons, which played in the Arena Football League until 2012, when the team was moved to San Antonio. The Oklahoma Defenders replaced the Talons as Tulsa's only professional arena football team, playing the CPIFL. The Oklahoma City Blue, of the NBA G League, relocated to Oklahoma City from Tulsa in 2014, where they were formerly known as the Tulsa 66ers. Tulsa is the base for the Tulsa Revolution, which plays in the American Indoor Soccer League.[221] Enid and Lawton host professional basketball teams in the USBL and the CBA.
+The NBA's New Orleans Hornets became the first major league sports franchise based in Oklahoma when the team was forced to relocate to Oklahoma City's Ford Center, now known as Chesapeake Energy Arena, for two seasons following Hurricane Katrina in 2005.[222] In July 2008, the Seattle SuperSonics relocated to Oklahoma City and began to play at the Ford Center as the Oklahoma City Thunder for the 2008–09 season, becoming the state's first permanent major league franchise.[223]
+Collegiate athletics are a popular draw in the state. The state has four schools that compete at the highest level of college sports, NCAA Division I. The most prominent are the state's two members of the Big 12 Conference,[224] one of the so-called Power Five conferences of the top tier of college football, Division I FBS. The University of Oklahoma and Oklahoma State University average well over 50,000 fans attending their football games, and Oklahoma's football program ranked 12th in attendance among American colleges in 2010, with an average of 84,738 people attending its home games.[225] The two universities meet several times each year in rivalry matches known as the Bedlam Series, which are some of the greatest sporting draws to the state. Sports Illustrated magazine rates Oklahoma and Oklahoma State among the top colleges for athletics in the nation.[226][227]
+Two private institutions in Tulsa, the University of Tulsa and Oral Roberts University; are also Division I members. Tulsa competes in FBS football and other sports in the American Athletic Conference,[228] while Oral Roberts, which does not sponsor football,[229] is a member of the Summit League.[230] In addition, 12 of the state's smaller colleges and universities compete in NCAA Division II as members of three different conferences,[231][232][233] and eight other Oklahoma institutions participate in the NAIA, mostly within the Sooner Athletic Conference.[234]
+Regular LPGA tournaments are held at Cedar Ridge Country Club in Tulsa, and major championships for the PGA or LPGA have been played at Southern Hills Country Club in Tulsa, Oak Tree Country Club in Oklahoma City, and Cedar Ridge Country Club in Tulsa.[235] Rated one of the top golf courses in the nation, Southern Hills has hosted four PGA Championships, including one in 2007, and three U.S. Opens, the most recent in 2001.[236] Rodeos are popular throughout the state, and Guymon, in the state's panhandle, hosts one of the largest in the nation.[237]
+Oklahoma was the 21st-largest recipient of medical funding from the federal government in 2005, with health-related federal expenditures in the state totaling $75,801,364; immunizations, bioterrorism preparedness, and health education were the top three most funded medical items.[238] Instances of major diseases are near the national average in Oklahoma, and the state ranks at or slightly above the rest of the country in percentage of people with asthma, diabetes, cancer, and hypertension.[238]
+In 2000, Oklahoma ranked 45th in physicians per capita and slightly below the national average in nurses per capita, but was slightly above the national average in hospital beds per 100,000 people and above the national average in net growth of health services over a twelve-year period.[239] One of the worst states for percentage of insured people, nearly 25 percent of Oklahomans between the age of 18 and 64 did not have health insurance in 2005, the fifth-highest rate in the nation.[240]
+Oklahomans are in the upper half of Americans in terms of obesity prevalence, and the state is the 5th most obese in the nation, with 30.3 percent of its population at or near obesity.[241] Oklahoma ranked last among the 50 states in a 2007 study by the Commonwealth Fund on health care performance.[242]
+The OU Medical Center, Oklahoma's largest collection of hospitals, is the only hospital in the state designated a Level I trauma center by the American College of Surgeons. OU Medical Center is on the grounds of the Oklahoma Health Center in Oklahoma City, the state's largest concentration of medical research facilities.[243][244]
+The Cancer Treatment Centers of America at Southwestern Regional Medical Center in Tulsa is one of four such regional facilities nationwide, offering cancer treatment to the entire southwestern United States, and is one of the largest cancer treatment hospitals in the country.[245] The largest osteopathic teaching facility in the nation, Oklahoma State University Medical Center at Tulsa, also rates as one of the largest facilities in the field of neuroscience.[246][247]
+On June 26, 2018, Oklahoma made marijuana legal for medical purposes. This was a milestone for a state in the Bible Belt.
+Oklahoma City and Tulsa are the 45th- and 61st-largest media markets in the United States as ranked by Nielsen Media Research. The state's third-largest media market, Lawton-Wichita Falls, Texas, is ranked 149th nationally by the agency.[249] Broadcast television in Oklahoma began in 1949 when KFOR-TV (then WKY-TV) in Oklahoma City and KOTV-TV in Tulsa began broadcasting a few months apart.[250] Currently, all major American broadcast networks have affiliated television stations in the state.[251]
+The state has two primary newspapers. The Oklahoman, based in Oklahoma City, is the largest newspaper in the state and 54th-largest in the nation by circulation, with a weekday readership of 138,493 and a Sunday readership of 202,690. The Tulsa World, the second-most widely circulated newspaper in Oklahoma and 79th in the nation, holds a Sunday circulation of 132,969 and a weekday readership of 93,558.[248] Oklahoma's first newspaper was established in 1844, called the Cherokee Advocate, and was written in both Cherokee and English.[252] In 2006, there were more than 220 newspapers in the state, including 177 with weekly publications and 48 with daily publications.[252]
+The state's first radio station, WKY in Oklahoma City, signed on in 1920, followed by KRFU in Bristow, which later on moved to Tulsa and became KVOO in 1927.[253] In 2006, there were more than 500 radio stations in Oklahoma broadcasting with various local or nationally owned networks. Five universities in Oklahoma operate non-commercial, public radio stations/networks.[254]
+Oklahoma has a few ethnic-oriented TV stations broadcasting in Spanish and Asian languages, and there is some Native American programming. TBN, a Christian religious television network, has a studio in Tulsa, and built its first entirely TBN-owned affiliate in Oklahoma City in 1980.[255]
+Transportation in Oklahoma is generated by an anchor system of Interstate Highways, inter-city rail lines, airports, inland ports, and mass transit networks. Situated along an integral point in the United States Interstate network, Oklahoma contains three primary Interstate highways and four auxiliary Interstate Highways. In Oklahoma City, Interstate 35 intersects with Interstate 44 and Interstate 40, forming one of the most important intersections along the United States highway system.[256]
+More than 12,000 miles (19,000 km) of roads make up the state's major highway skeleton, including state-operated highways, ten turnpikes or major toll roads,[256] and the longest drivable stretch of Route 66 in the nation.[257] In 2008, Interstate 44 in Oklahoma City was Oklahoma's busiest highway, with a daily traffic volume of 123,300 cars.[258] In 2010, the state had the nation's third-highest number of bridges classified as structurally deficient, with nearly 5,212 bridges in disrepair, including 235 National Highway System Bridges.[259]
+Oklahoma's largest commercial airport is Will Rogers World Airport in Oklahoma City, averaging a yearly passenger count of more than 3.5 million (1.7 million boardings) in 2010.[260] Tulsa International Airport, the state's second-largest commercial airport, served more than 1.3 million boardings in 2010.[261] Between the two, six airlines operate in Oklahoma.[262][263] In terms of traffic, R. L. Jones Jr. (Riverside) Airport in Tulsa is the state's busiest airport, with 335,826 takeoffs and landings in 2008.[264] Oklahoma has more than 150 public-use airports.[265]
+Oklahoma is connected to the nation's rail network via Amtrak's Heartland Flyer, its only regional passenger rail line. It currently stretches from Oklahoma City to Fort Worth, Texas, though lawmakers began seeking funding in early 2007 to connect the Heartland Flyer to Tulsa.[266]
+Two inland ports on rivers serve Oklahoma: the Port of Muskogee and the Tulsa Port of Catoosa. The Tulsa Port of Catoosa is the one of the United State's most inland international ports, at head of navigation of the McClellan–Kerr Arkansas River Navigation System, which connects barge traffic from Tulsa and Muskogee to the Mississippi River.[267]  The port ships over two million tons of goods annually and is a designated foreign trade zone.
+Oklahoma is a constitutional republic with a government modeled after the Federal government of the United States, with executive, legislative, and judicial branches.[268] The state has 77 counties with jurisdiction over most local government functions within each respective domain,[40] five congressional districts, and a voting base with a plurality in the Republican Party.[269] State officials are elected by plurality voting in the state of Oklahoma.
+Oklahoma has capital punishment as a legal sentence, and the state has had (between 1976 through mid-2011) the highest per capita execution rate in the nation.[270]
+The Legislature of Oklahoma consists of the Senate and the House of Representatives. As the lawmaking branch of the state government, it is responsible for raising and distributing the money necessary to run the government. The Senate has 48 members serving four-year terms, while the House has 101 members with two-year terms. The state has a term limit for its legislature that restricts any one person to twelve cumulative years service between both legislative branches.[271][272]
+Oklahoma's judicial branch consists of the Oklahoma Supreme Court, the Oklahoma Court of Criminal Appeals, and 77 District Courts that each serve one county. The Oklahoma judiciary also contains two independent courts: a Court of Impeachment and the Oklahoma Court on the Judiciary. Oklahoma has two courts of last resort: the state Supreme Court hears civil cases, and the state Court of Criminal Appeals hears criminal cases (this split system exists only in Oklahoma and neighboring Texas). Judges of those two courts, as well as the Court of Civil Appeals are appointed by the Governor upon the recommendation of the state Judicial Nominating Commission, and are subject to a non-partisan retention vote on a six-year rotating schedule.[271]
+The executive branch consists of the Governor, their staff, and other elected officials. The principal head of government, the Governor is the chief executive of the Oklahoma executive branch, serving as the ex officio Commander-in-chief of the Oklahoma National Guard when not called into Federal use and reserving the power to veto bills passed through the Legislature. The responsibilities of the Executive branch include submitting the budget, ensuring state laws are enforced, and ensuring peace within the state is preserved.[273]
+The state is divided into 77 counties that govern locally, each headed by a three-member council of elected commissioners, a tax assessor, clerk, court clerk, treasurer, and sheriff.[274] While each municipality operates as a separate and independent local government with executive, legislative and judicial power, county governments maintain jurisdiction over both incorporated cities and non-incorporated areas within their boundaries, but have executive power but no legislative or judicial power. Both county and municipal governments collect taxes, employ a separate police force, hold elections, and operate emergency response services within their jurisdiction.[275][276] Other local government units include school districts, technology center districts, community college districts, rural fire departments, rural water districts, and other special use districts.
+Thirty-nine Native American tribal governments are based in Oklahoma, each holding limited powers within designated areas. While Indian reservations typical in most of the United States are not present in Oklahoma, tribal governments hold land granted during the Indian Territory era, but with limited jurisdiction and no control over state governing bodies such as municipalities and counties. Tribal governments are recognized by the United States as quasi-sovereign entities with executive, judicial, and legislative powers over tribal members and functions, but are subject to the authority of the United States Congress to revoke or withhold certain powers. The tribal governments are required to submit a constitution and any subsequent amendments to the United States Congress for approval.[277][278]
+Oklahoma has 11 substate districts including the two large Councils of Governments, INCOG in Tulsa (Indian Nations Council of Governments) and ACOG (Association of Central Oklahoma Governments).
+During the first half-century of statehood, it was considered a Democratic stronghold, being carried by the Republican Party in only two presidential elections (1920 and 1928). After the 1948 election, the state turned firmly Republican. Although registered Republicans were a minority in the state until 2015,[280] starting in 1952, Oklahoma has been carried by Republican presidential candidates in all but one election (1964).
+Generally, Republicans are strongest in the suburbs of Oklahoma City and Tulsa, as well as the Panhandle. Democrats are strongest in the eastern part of the state and Little Dixie, as well as the most heavily African American and inner parts of Oklahoma City and Tulsa. With a population of 8.6% Native American in the state, it is also worth noting most Native American precincts vote Democratic in margins exceeded only by African Americans.[281]
+Following the 2000 census, the Oklahoma delegation to the U.S. House of Representatives was reduced from six to five representatives, each serving one congressional district. In the current Congress, all but one of Oklahoma's entire delegation are Republicans.
+Oklahoma had 598 incorporated places in 2010, including four cities over 100,000 in population and 43 over 10,000.[282] Two of the fifty largest cities in the United States are in Oklahoma, Oklahoma City and Tulsa, and sixty-five percent of Oklahomans live within their metropolitan areas, or spheres of economic and social influence defined by the United States Census Bureau as a metropolitan statistical area. Oklahoma City, the state's capital and largest city, had the largest metropolitan area in the state in 2010, with 1,252,987 people, and the metropolitan area of Tulsa had 937,478 residents.[283] Between 2000 and 2010, the leading cities in population growth were Blanchard (172.4%), Elgin (78.2%), Jenks (77.0%), Piedmont (56.7%), Bixby (56.6%), and Owasso (56.3%).[282]
+In descending order of population, Oklahoma's largest cities in 2010 were: Oklahoma City (579,999, +14.6%), Tulsa (391,906, −0.3%), Norman (110,925, +15.9%), Broken Arrow (98,850, +32.0%), Lawton (96,867, +4.4%), Edmond (81,405, +19.2%), Moore (55,081, +33.9%), Midwest City (54,371, +0.5%), Enid (49,379, +5.0%), and Stillwater (45,688, +17.0%). Of the state's ten largest cities, three are outside the metropolitan areas of Oklahoma City and Tulsa, and only Lawton has a metropolitan statistical area of its own as designated by the United States Census Bureau, though the metropolitan statistical area of Fort Smith, Arkansas extends into the state.[107]
+Under Oklahoma law, municipalities are divided into two categories: cities, defined as having more than 1,000 residents, and towns, with under 1,000 residents. Both have legislative, judicial, and public power within their boundaries, but cities can choose between a mayor–council, council–manager, or strong mayor form of government, while towns operate through an elected officer system.[275]
+State law codifies Oklahoma's state emblems and honorary positions;[284] the Oklahoma Senate or House of Representatives may adopt resolutions designating others for special events and to benefit organizations. In 2012 the House passed HCR 1024, which would change the state motto from "Labor Omnia Vincit" to "Oklahoma—In God We Trust!" The author of the resolution stated a constituent researched the Oklahoma Constitution and found no "official" vote regarding "Labor Omnia Vincit", therefore opening the door for an entirely new motto.[285][286]
+Coordinates: 35°30′N 98°00′W / 35.5°N 98°W / 35.5; -98

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+Atheism is, in the broadest sense, an absence of belief in the existence of deities.[1][2][3][4] Less broadly, atheism is a rejection of the belief that any deities exist.[5][6] In an even narrower sense, atheism is specifically the position that there are no deities.[1][2][7][8] Atheism is contrasted with theism,[9][10] which, in its most general form, is the belief that at least one deity exists.[10][11][12]
+The etymological root for the word atheism originated before the 5th century BCE from the ancient Greek ἄθεος (atheos), meaning "without god(s)". In antiquity, it had multiple uses as a pejorative term applied to those thought to reject the gods worshiped by the larger society,[13] those who were forsaken by the gods, or those who had no commitment to belief in the gods.[14] The term denoted a social category created by orthodox religionists into which those who did not share their religious beliefs were placed.[14] The actual term atheism emerged first in the 16th century.[15] With the spread of freethought, skeptical inquiry, and subsequent increase in criticism of religion, application of the term narrowed in scope. The first individuals to identify themselves using the word atheist lived in the 18th century during the Age of Enlightenment.[16][15] The French Revolution, noted for its "unprecedented atheism," witnessed the first major political movement in history to advocate for the supremacy of human reason.[17]
+Arguments for atheism range from philosophical to social and historical approaches. Rationales for not believing in deities include arguments that there is a lack of empirical evidence,[18][19] the problem of evil, the argument from inconsistent revelations, the rejection of concepts that cannot be falsified, and the argument from nonbelief.[18][20] Nonbelievers contend that atheism is a more parsimonious position than theism and that everyone is born without beliefs in deities;[1] therefore, they argue that the burden of proof lies not on the atheist to disprove the existence of gods but on the theist to provide a rationale for theism.[21] Although some atheists have adopted secular philosophies (e.g. secular humanism),[22][23] there is no ideology or code of conduct to which all atheists adhere.[24]
+Since conceptions of atheism vary, accurate estimations of current numbers of atheists are difficult.[25] According to global Win-Gallup International studies, 13% of respondents were "convinced atheists" in 2012,[26] 11% were "convinced atheists" in 2015,[27] and in 2017, 9% were "convinced atheists".[28] However, other researchers have advised caution with WIN/Gallup figures since other surveys which have used the same wording for decades and have a bigger sample size have consistently reached lower figures.[29] An older survey by the British Broadcasting Corporation (BBC) in 2004 recorded atheists as comprising 8% of the world's population.[30] Other older estimates have indicated that atheists comprise 2% of the world's population, while the irreligious add a further 12%.[31] According to these polls, Europe and East Asia are the regions with the highest rates of atheism. In 2015, 61% of people in China reported that they were atheists.[32] The figures for a 2010 Eurobarometer survey in the European Union (EU) reported that 20% of the EU population claimed not to believe in "any sort of spirit, God or life force", with France (40%) and Sweden (34%) representing the highest values.[33]
+Writers disagree on how best to define and classify atheism,[34] contesting what supernatural entities are considered gods, whether it is a philosophic position in its own right or merely the absence of one, and whether it requires a conscious, explicit rejection. Atheism has been regarded as compatible with agnosticism,[35][36][37][38][39][40][41] but has also been contrasted with it.[42][43][44] A variety of categories have been used to distinguish the different forms of atheism.
+Some of the ambiguity and controversy involved in defining atheism arises from difficulty in reaching a consensus for the definitions of words like deity and god. The variety of wildly different conceptions of God and deities leads to differing ideas regarding atheism's applicability. The ancient Romans accused Christians of being atheists for not worshiping the pagan deities. Gradually, this view fell into disfavor as theism came to be understood as encompassing belief in any divinity.[45]
+With respect to the range of phenomena being rejected, atheism may counter anything from the existence of a deity, to the existence of any spiritual, supernatural, or transcendental concepts, such as those of Buddhism, Hinduism, Jainism, and Taoism.[46]
+Definitions of atheism also vary in the degree of consideration a person must put to the idea of gods to be considered an atheist. Atheism has sometimes been defined to include the simple absence of belief that any deities exist. This broad definition would include newborns and other people who have not been exposed to theistic ideas. As far back as 1772, Baron d'Holbach said that "All children are born Atheists; they have no idea of God."[47]
+Similarly, George H. Smith (1979) suggested that: "The man who is unacquainted with theism is an atheist because he does not believe in a god. This category would also include the child with the conceptual capacity to grasp the issues involved, but who is still unaware of those issues. The fact that this child does not believe in god qualifies him as an atheist."[48] Implicit atheism is "the absence of theistic belief without a conscious rejection of it" and explicit atheism is the conscious rejection of belief.
+For the purposes of his paper on "philosophical atheism", Ernest Nagel contested including the mere absence of theistic belief as a type of atheism.[49] Graham Oppy classifies as innocents those who never considered the question because they lack any understanding of what a god is. According to Oppy, these could be one-month-old babies, humans with severe traumatic brain injuries, or patients with advanced dementia.[50]
+Philosophers such as Antony Flew[51]
+and Michael Martin[45] have contrasted positive (strong/hard) atheism with negative (weak/soft) atheism. Positive atheism is the explicit affirmation that gods do not exist. Negative atheism includes all other forms of non-theism. According to this categorization, anyone who is not a theist is either a negative or a positive atheist.
+The terms weak and strong are relatively recent, while the terms negative and positive atheism are of older origin, having been used (in slightly different ways) in the philosophical literature[51] and in Catholic apologetics.[52]
+Under this demarcation of atheism, most agnostics qualify as negative atheists.
+While Martin, for example, asserts that agnosticism entails negative atheism,[38] many agnostics see their view as distinct from atheism,[53][54]
+which they may consider no more justified than theism or requiring an equal conviction.[53]
+The assertion of unattainability of knowledge for or against the existence of gods is sometimes seen as an indication that atheism requires a leap of faith.[55][56]
+Common atheist responses to this argument include that unproven religious propositions deserve as much disbelief as all other unproven propositions,[57]
+and that the unprovability of a god's existence does not imply equal probability of either possibility.[58]
+Australian philosopher J.J.C. Smart even argues that "sometimes a person who is really an atheist may describe herself, even passionately, as an agnostic because of unreasonable generalized philosophical skepticism which would preclude us from saying that we know anything whatever, except perhaps the truths of mathematics and formal logic."[59]
+Consequently, some atheist authors such as Richard Dawkins prefer distinguishing theist, agnostic and atheist positions along a spectrum of theistic probability—the likelihood that each assigns to the statement "God exists".[60]
+Before the 18th century, the existence of God was so accepted in the Western world that even the possibility of true atheism was questioned. This is called theistic innatism—the notion that all people believe in God from birth; within this view was the connotation that atheists are simply in denial.[61]
+There is also a position claiming that atheists are quick to believe in God in times of crisis, that atheists make deathbed conversions, or that "there are no atheists in foxholes".[62]
+There have, however, been examples to the contrary, among them examples of literal "atheists in foxholes".[63]
+Some atheists have challenged the need for the term "atheism". In his book Letter to a Christian Nation, Sam Harris wrote:
+In fact, "atheism" is a term that should not even exist. No one ever needs to identify himself as a "non-astrologer" or a "non-alchemist". We do not have words for people who doubt that Elvis is still alive or that aliens have traversed the galaxy only to molest ranchers and their cattle. Atheism is nothing more than the noises reasonable people make in the presence of unjustified religious beliefs.[64]
+Pragmatic atheism is the view one should reject a belief in a god or gods because it is unnecessary for a pragmatic life. This view is related to apatheism and practical atheism.[65]
+Atheists have also argued that people cannot know a God or prove the existence of a God. The latter is called agnosticism, which takes a variety of forms. In the philosophy of immanence, divinity is inseparable from the world itself, including a person's mind, and each person's consciousness is locked in the subject. According to this form of agnosticism, this limitation in perspective prevents any objective inference from belief in a god to assertions of its existence. The rationalistic agnosticism of Kant and the Enlightenment only accepts knowledge deduced with human rationality; this form of atheism holds that gods are not discernible as a matter of principle, and therefore cannot be known to exist. Skepticism, based on the ideas of Hume, asserts that certainty about anything is impossible, so one can never know for sure whether or not a god exists. Hume, however, held that such unobservable metaphysical concepts should be rejected as "sophistry and illusion".[67] The allocation of agnosticism to atheism is disputed; it can also be regarded as an independent, basic worldview.[68]
+Other arguments for atheism that can be classified as epistemological or ontological, including  ignosticism, assert the meaninglessness or unintelligibility of basic terms such as "God" and statements such as "God is all-powerful." Theological noncognitivism holds that the statement "God exists" does not express a proposition, but is nonsensical or cognitively meaningless. It has been argued both ways as to whether such individuals can be classified into some form of atheism or agnosticism. Philosophers A.J. Ayer and Theodore M. Drange reject both categories, stating that both camps accept "God exists" as a proposition; they instead place noncognitivism in its own category.[69][70]
+Philosopher, Zofia Zdybicka writes:
+"Metaphysical atheism ... includes all doctrines that hold to metaphysical monism (the homogeneity of reality). Metaphysical atheism may be either: a) absolute — an explicit denial of God's existence associated with materialistic monism (all materialistic trends, both in ancient and modern times); b) relative — the implicit denial of God in all philosophies that, while they accept the existence of an absolute, conceive of the absolute as not possessing any of the attributes proper to God: transcendence, a personal character or unity. Relative atheism is associated with idealistic monism (pantheism, panentheism, deism)."[71]
+Some atheists hold the view that the various conceptions of gods, such as the personal god of Christianity, are ascribed logically inconsistent qualities. Such atheists present deductive arguments against the existence of God, which assert the incompatibility between certain traits, such as perfection, creator-status, immutability, omniscience, omnipresence, omnipotence, omnibenevolence, transcendence, personhood (a personal being), non-physicality, justice, and mercy.[18]
+Theodicean atheists believe that the world as they experience it cannot be reconciled with the qualities commonly ascribed to God and gods by theologians. They argue that an omniscient, omnipotent, and omnibenevolent God is not compatible with a world where there is evil and suffering, and where divine love is hidden from many people.[20]
+A similar argument is attributed to Siddhartha Gautama, the founder of Buddhism.[73]
+Philosopher Ludwig Feuerbach[74]
+and psychoanalyst Sigmund Freud have argued that God and other religious beliefs are human inventions, created to fulfill various psychological and emotional wants or needs, or a projection mechanism from the 'Id' omnipotence; for Vladimir Lenin, in 'Materialism and Empirio-criticism', against the Russian Machism, the followers of Ernst Mach, Feuerbach was the final argument against belief in a god. This is also a view of many Buddhists.[75] Karl Marx and Friedrich Engels, influenced by the work of Feuerbach, argued that belief in God and religion are social functions, used by those in power to oppress the working class. According to Mikhail Bakunin, "the idea of God implies the abdication of human reason and justice; it is the most decisive negation of human liberty, and necessarily ends in the enslavement of mankind, in theory, and practice." He reversed Voltaire's aphorism that if God did not exist, it would be necessary to invent him, writing instead that "if God really existed, it would be necessary to abolish him."[76]
+Atheism is not mutually exclusive with respect to some religious and spiritual belief systems, including Hinduism, Jainism, Buddhism, Syntheism, Raëlism,[77] and Neopagan movements[78]
+such as Wicca.[79]
+Āstika schools in Hinduism hold atheism to be a valid path to moksha, but extremely difficult, for the atheist cannot expect any help from the divine on their journey.[80]
+Jainism believes the universe is eternal and has no need for a creator deity, however Tirthankaras are revered beings who can transcend space and time[81] and have more power than the god Indra.[82]
+Secular Buddhism does not advocate belief in gods. Early Buddhism was atheistic as Gautama Buddha's path involved no mention of gods. Later conceptions of Buddhism consider Buddha himself a god, suggest adherents can attain godhood, and revere Bodhisattvas[83]
+and Eternal Buddha.
+Apophatic theology is often assessed as being a version of atheism or agnosticism, since it cannot say truly that God exists.[84] "The comparison is crude, however, for conventional atheism treats the existence of God as a predicate that can be denied ("God is nonexistent"), whereas negative theology denies that God has predicates".[85] "God or the Divine is" without being able to attribute qualities about "what He is" would be the prerequisite of positive theology in negative theology that distinguishes theism from atheism. "Negative theology is a complement to, not the enemy of, positive theology".[86]
+Axiological, or constructive, atheism rejects the existence of gods in favor of a "higher absolute", such as humanity. This form of atheism favors humanity as the absolute source of ethics and values, and permits individuals to resolve moral problems without resorting to God. Marx and Freud used this argument to convey messages of liberation, full-development, and unfettered happiness.[68] One of the most common criticisms of atheism has been to the contrary: that denying the existence of a god either leads to moral relativism and leaves one with no moral or ethical foundation,[87] or renders life meaningless and miserable.[88] Blaise Pascal argued this view in his Pensées.[89]
+French philosopher Jean-Paul Sartre identified himself as a representative of an "atheist existentialism"[90]
+concerned less with denying the existence of God than with establishing that "man needs ... to find himself again and to understand that nothing can save him from himself, not even a valid proof of the existence of God."[91]
+Sartre said a corollary of his atheism was that "if God does not exist, there is at least one being in whom existence precedes essence, a being who exists before he can be defined by any concept, and ... this being is man."[90]
+The practical consequence of this atheism was described by Sartre as meaning that there are no a priori rules or absolute values that can be invoked to govern human conduct, and that humans are "condemned" to invent these for themselves, making "man" absolutely "responsible for everything he does".[92]
+Sociologist Phil Zuckerman analyzed previous social science research on secularity and non-belief, and concluded that societal well-being is positively correlated with irreligion. He found that there are much lower concentrations of atheism and secularity in poorer, less developed nations (particularly in Africa and South America) than in the richer industrialized democracies.[93][94]
+His findings relating specifically to atheism in the US were that compared to religious people in the US, "atheists and secular people" are less nationalistic, prejudiced, antisemitic, racist, dogmatic, ethnocentric, closed-minded, and authoritarian, and in US states with the highest percentages of atheists, the murder rate is lower than average. In the most religious states, the murder rate is higher than average.[95][96]
+People who self-identify as atheists are often assumed to be irreligious, but some sects within major religions reject the existence of a personal, creator deity.[98]
+In recent years, certain religious denominations have accumulated a number of openly atheistic followers, such as atheistic or humanistic Judaism[99][100]
+and Christian atheists.[101][102][103]
+The strictest sense of positive atheism does not entail any specific beliefs outside of disbelief in any deity; as such, atheists can hold any number of spiritual beliefs. For the same reason, atheists can hold a wide variety of ethical beliefs, ranging from the moral universalism of humanism, which holds that a moral code should be applied consistently to all humans, to moral nihilism, which holds that morality is meaningless.[104] Atheism is accepted as a valid philosophical position within some varieties of Hinduism, Jainism, and Buddhism.[105]
+Philosophers such as Slavoj Žižek,[106] Alain de Botton,[107] and Alexander Bard and Jan Söderqvist,[108] have all argued that atheists should reclaim religion as an act of defiance against theism, precisely not to leave religion as an unwarranted monopoly to theists.
+According to Plato's Euthyphro dilemma, the role of the gods in determining right from wrong is either unnecessary or arbitrary. The argument that morality must be derived from God, and cannot exist without a wise creator, has been a persistent feature of political if not so much philosophical debate.[109][110][111]
+Moral precepts such as "murder is wrong" are seen as divine laws, requiring a divine lawmaker and judge. However, many atheists argue that treating morality legalistically involves a false analogy, and that morality does not depend on a lawmaker in the same way that laws do.[112]
+Friedrich Nietzsche believed in a morality independent of theistic belief, and stated that morality based upon God "has truth only if God is truth—it stands or falls with faith in God.".[113][114][115] For Immanuel Kant the reason for adjusting to rules comes in its value as: 'Categorical Imperatives', that contain in itself the reason to be fulfilled.
+There exist normative ethical systems that do not require principles and rules to be given by a deity. Some include virtue ethics, social contract, Kantian ethics, utilitarianism, and Objectivism. Sam Harris has proposed that moral prescription (ethical rule making) is not just an issue to be explored by philosophy, but that we can meaningfully practice a science of morality. Any such scientific system must, nevertheless, respond to the criticism embodied in the naturalistic fallacy.[116]
+Philosophers Susan Neiman[117]
+and Julian Baggini[118]
+(among others) assert that behaving ethically only because of divine mandate is not true ethical behavior but merely blind obedience. Baggini argues that atheism is a superior basis for ethics, claiming that a moral basis external to religious imperatives is necessary to evaluate the morality of the imperatives themselves—to be able to discern, for example, that "thou shalt steal" is immoral even if one's religion instructs it—and that atheists, therefore, have the advantage of being more inclined to make such evaluations.[119]
+The contemporary British political philosopher Martin Cohen has offered the more historically telling example of Biblical injunctions in favor of torture and slavery as evidence of how religious injunctions follow political and social customs, rather than vice versa, but also noted that the same tendency seems to be true of supposedly dispassionate and objective philosophers.[120] Cohen extends this argument in more detail in Political Philosophy from Plato to Mao, where he argues that the Qur'an played a role in perpetuating social codes from the early 7th century despite changes in secular society.[121]
+Some prominent atheists—most recently Christopher Hitchens, Daniel Dennett, Sam Harris, and Richard Dawkins, and following such thinkers as Bertrand Russell, Robert G. Ingersoll, Voltaire, and novelist José Saramago—have criticized religions, citing harmful aspects of religious practices and doctrines.[122]
+The 19th-century German political theorist and sociologist Karl Marx called religion "the sigh of the oppressed creature, the heart of a heartless world, and the soul of soulless conditions. It is the opium of the people". He goes on to say, "The abolition of religion as the illusory happiness of the people is the demand for their real happiness. To call on them to give up their illusions about their condition is to call on them to give up a condition that requires illusions. The criticism of religion is, therefore, in embryo, the criticism of that vale of tears of which religion is the halo."[123] Lenin said that "every religious idea and every idea of God is unutterable vileness ... of the most dangerous kind, 'contagion' of the most abominable kind. Millions of sins, filthy deeds, acts of violence and physical contagions ... are far less dangerous than the subtle, spiritual idea of God decked out in the smartest ideological costumes ..."[124]
+Sam Harris criticizes Western religion's reliance on divine authority as lending itself to authoritarianism and dogmatism.[125]
+There is a correlation between religious fundamentalism and extrinsic religion (when religion is held because it serves ulterior interests)[126] and authoritarianism, dogmatism, and prejudice.[127]
+These arguments—combined with historical events that are argued to demonstrate the dangers of religion, such as the Crusades, inquisitions, witch trials, and terrorist attacks—have been used in response to claims of beneficial effects of belief in religion.[128]
+Believers counter-argue that some regimes that espouse atheism, such as the Soviet Union, have also been guilty of mass murder.[129][130] In response to those claims, atheists such as Sam Harris and Richard Dawkins have stated that Stalin's atrocities were influenced not by atheism but by dogmatic Marxism, and that while Stalin and Mao happened to be atheists, they did not do their deeds in the name of atheism.[131][132]
+In early ancient Greek, the adjective átheos (ἄθεος, from the privative ἀ- + θεός "god") meant "godless". It was first used as a term of censure roughly meaning "ungodly" or "impious". In the 5th century BCE, the word began to indicate more deliberate and active godlessness in the sense of "severing relations with the gods" or "denying the gods". The term ἀσεβής (asebēs) then came to be applied against those who impiously denied or disrespected the local gods, even if they believed in other gods. Modern translations of classical texts sometimes render átheos as "atheistic". As an abstract noun, there was also ἀθεότης (atheotēs), "atheism". Cicero transliterated the Greek word into the Latin átheos. The term found frequent use in the debate between early Christians and Hellenists, with each side attributing it, in the pejorative sense, to the other.[13]
+The term atheist (from Fr. athée), in the sense of "one who ... denies the existence of God or gods",[134]
+predates atheism in English, being first found as early as 1566,[135]
+and again in 1571.[136]
+Atheist as a label of practical godlessness was used at least as early as 1577.[137]
+The term atheism was derived from the French athéisme,[138] and appears in English about 1587.[139]
+An earlier work, from about 1534, used the term atheonism.[140][141]
+Related words emerged later: deist in 1621,[142]
+theist in 1662,[143]
+deism in 1675,[144]
+and theism in 1678.[145]
+At that time "deist" and "deism" already carried their modern meaning. The term theism came to be contrasted with deism.
+Karen Armstrong writes that "During the sixteenth and seventeenth centuries, the word 'atheist' was still reserved exclusively for polemic ... The term 'atheist' was an insult. Nobody would have dreamed of calling himself an atheist."[16]
+Atheism was first used to describe a self-avowed belief in late 18th-century Europe, specifically denoting disbelief in the monotheistic Abrahamic god.[146]
+In the 20th century, globalization contributed to the expansion of the term to refer to disbelief in all deities, though it remains common in Western society to describe atheism as simply "disbelief in God".[45]
+While the earliest-found usage of the term atheism is in 16th-century France,[138][139] ideas that would be recognized today as atheistic are documented from the Vedic period and the classical antiquity.
+Who really knows? Who will here proclaim it? Whence was it produced? Whence is this creation? The gods came afterwards, with the creation of this universe. Who then knows whence it has arisen?
+Atheistic schools are found in early Indian thought and have existed from the times of the historical Vedic religion.[150]
+Among the six orthodox schools of Hindu philosophy, Samkhya, the oldest philosophical school of thought, does not accept God, and the early Mimamsa also rejected the notion of God.[151]
+The thoroughly materialistic and anti-theistic philosophical Cārvāka (or Lokāyata) school that originated in India around the 6th century BCE is probably the most explicitly atheistic school of philosophy in India, similar to the Greek Cyrenaic school. This branch of Indian philosophy is classified as heterodox due to its rejection of the authority of Vedas and hence is not considered part of the six orthodox schools of Hinduism, but it is noteworthy as evidence of a materialistic movement within Hinduism.[152]
+Chatterjee and Datta explain that our understanding of Cārvāka philosophy is fragmentary, based largely on criticism of the ideas by other schools, and that it is not a living tradition:[153]
+Though materialism in some form or other has always been present in India, and occasional references are found in the Vedas, the Buddhistic literature, the Epics, as well as in the later philosophical works we do not find any systematic work on materialism, nor any organized school of followers as the other philosophical schools possess. But almost every work of the other schools states, for refutation, the materialistic views. Our knowledge of Indian materialism is chiefly based on these.
+Other Indian philosophies generally regarded as atheistic include Classical Samkhya and Purva Mimamsa. The rejection of a personal creator God is also seen in Jainism and Buddhism in India.[154]
+Western atheism has its roots in pre-Socratic Greek philosophy,[157][158] but atheism in the modern sense was extremely rare in ancient Greece.[159][160][158] Pre-Socratic Atomists such as Democritus attempted to explain the world in a purely materialistic way and interpreted religion as a human reaction to natural phenomena,[155] but did not explicitly deny the gods' existence.[155] Anaxagoras, whom Irenaeus calls "the atheist",[161] was accused of impiety and condemned for stating that "the sun is a type of incandescent stone", an affirmation with which he tried to deny the divinity of the celestial bodies.[162] In the late fifth century BCE, the Greek lyric poet Diagoras of Melos was sentenced to death in Athens under the charge of being a "godless person" (ἄθεος) after he made fun of the Eleusinian Mysteries,[159][160][155] but he fled the city to escape punishment.[159][160][155] Later writers have cited Diagoras as the "first atheist",[163][164] but he was probably not an atheist in the modern sense of the word.[160]
+A fragment from the lost satyr play Sisyphus, which has been attributed to both Critias and Euripides, claims that a clever man invented "the fear of the gods" in order to frighten people into behaving morally.[165][160][166][160][158] This statement, however, originally did not mean that the gods themselves were nonexistent, but rather that their powers were a hoax.[158] Atheistic statements have also been attributed to the philosopher Prodicus. Philodemus reports that Prodicus believed that "the gods of popular belief do not exist nor do they know, but primitive man, [out of admiration, deified] the fruits of the earth and virtually everything that contributed to his existence". Protagoras has sometimes been taken to be an atheist, but rather espoused agnostic views, commenting that "Concerning the gods I am unable to discover whether they exist or not, or what they are like in form; for there are many hindrances to knowledge, the obscurity of the subject and the brevity of human life."[167][159]
+The Athenian public associated Socrates (c. 470–399 BCE) with the trends in pre-Socratic philosophy towards naturalistic inquiry and the rejection of divine explanations for phenomena.[155][156] Aristophanes' comic play The Clouds (performed 423 BCE) portrays Socrates as teaching his students that the traditional Greek deities do not exist.[155][156] Socrates was later tried and executed under the charge of not believing in the gods of the state and instead worshipping foreign gods.[155][156] Socrates himself vehemently denied the charges of atheism at his trial[155][156][168] and all the surviving sources about him indicate that he was a very devout man, who prayed to the rising sun and believed that the oracle at Delphi spoke the word of Apollo.[155] Euhemerus (c. 300 BCE) published his view that the gods were only the deified rulers, conquerors and founders of the past, and that their cults and religions were in essence the continuation of vanished kingdoms and earlier political structures.[169] Although not strictly an atheist, Euhemerus was later criticized for having "spread atheism over the whole inhabited earth by obliterating the gods".[170]
+The most important Greek thinker in the development of atheism was Epicurus (c. 300 BCE).[158] Drawing on the ideas of Democritus and the Atomists, he espoused a materialistic philosophy according to which the universe was governed by the laws of chance without the need for divine intervention (see scientific determinism).[171] Although Epicurus still maintained that the gods existed,[172][158][171] he believed that they were uninterested in human affairs.[171] The aim of the Epicureans was to attain ataraxia ("peace of mind") and one important way of doing this was by exposing fear of divine wrath as irrational. The Epicureans also denied the existence of an afterlife and the need to fear divine punishment after death.[171]
+In the 3rd-century BCE, the Greek philosophers Theodorus Cyrenaicus[164][173] and Strato of Lampsacus[174] did not believe in the existence of gods.
+The Pyrrhonist philosopher Sextus Empiricus compiled a large number of ancient arguments against the existence of gods, recommending that one should suspend judgment regarding the matter.[175] His relatively large volume of surviving works had a lasting influence on later philosophers.[176]
+The meaning of "atheist" changed over the course of classical antiquity.[160] Early Christians were widely reviled as "atheists" because they did not believe in the existence of the Graeco-Roman deities.[177][160][178][179] During the Roman Empire, Christians were executed for their rejection of the Roman gods in general and the Imperial cult of ancient Rome in particular.[179][180] There was, however, a heavy struggle between Christians and pagans, in which each group accused the other of atheism, for not practicing the religion which they considered correct.[181] When Christianity became the state religion of Rome under Theodosius I in 381, heresy became a punishable offense.[180]
+During the Early Middle Ages, the Islamic world experienced a Golden Age. Along with advances in science and philosophy, Arab and Persian lands produced outspoken rationalists and atheists, including Muhammad al Warraq (fl. 9th century), Ibn al-Rawandi (827–911), Al-Razi (854–925), and Al-Maʿarri (973–1058). Al-Ma'arri wrote and taught that religion itself was a "fable invented by the ancients"[182] and that humans were "of two sorts: those with brains, but no religion, and those with religion, but no brains."[183]  Despite their being relatively prolific writers, little of their work survives, mainly being preserved through quotations and excerpts in later works by Muslim apologists attempting to refute them.[184] Other prominent Golden Age scholars have been associated with rationalist thought and atheism as well, although the current intellectual atmosphere in the Islamic world, and the scant evidence that survives from the era, make this point a contentious one today.
+In Europe, the espousal of atheistic views was rare during the Early Middle Ages and Middle Ages (see Medieval Inquisition); metaphysics and theology were the dominant interests pertaining to religion.[185] There were, however, movements within this period that furthered heterodox conceptions of the Christian god, including differing views of the nature, transcendence, and knowability of God. Individuals and groups such as Johannes Scotus Eriugena, David of Dinant, Amalric of Bena, and the Brethren of the Free Spirit maintained Christian viewpoints with pantheistic tendencies. Nicholas of Cusa held to a form of fideism he called docta ignorantia ("learned ignorance"), asserting that God is beyond human categorization, and thus our knowledge of him is limited to conjecture. William of Ockham inspired anti-metaphysical tendencies with his nominalistic limitation of human knowledge to singular objects, and asserted that the divine essence could not be intuitively or rationally apprehended by human intellect. Followers of Ockham, such as John of Mirecourt and Nicholas of Autrecourt furthered this view. The resulting division between faith and reason influenced later radical and reformist theologians such as John Wycliffe, Jan Hus, and Martin Luther.[185]
+The Renaissance did much to expand the scope of free thought and skeptical inquiry. Individuals such as Leonardo da Vinci sought experimentation as a means of explanation, and opposed arguments from religious authority. Other critics of religion and the Church during this time included Niccolò Machiavelli, Bonaventure des Périers, Michel de Montaigne, and François Rabelais.[176]
+Historian Geoffrey Blainey wrote that the Reformation had paved the way for atheists by attacking the authority of the Catholic Church, which in turn "quietly inspired other thinkers to attack the authority of the new Protestant churches".[186] Deism gained influence in France, Prussia, and England. The philosopher Baruch Spinoza was "probably the first well known 'semi-atheist' to announce himself in a Christian land in the modern era", according to Blainey. Spinoza believed that natural laws explained the workings of the universe. In 1661 he published his Short Treatise on God.[187]
+Criticism of Christianity became increasingly frequent in the 17th and 18th centuries, especially in France and England, where there appears to have been a religious malaise, according to contemporary sources. Some Protestant thinkers, such as Thomas Hobbes, espoused a materialist philosophy and skepticism toward supernatural occurrences, while Spinoza rejected divine providence in favor of a panentheistic naturalism. By the late 17th century, deism came to be openly espoused by intellectuals such as John Toland who coined the term "pantheist".[188]
+The first known explicit atheist was the German critic of religion Matthias Knutzen in his three writings of 1674.[189] He was followed by two other explicit atheist writers, the Polish ex-Jesuit philosopher Kazimierz Łyszczyński and in the 1720s by the French priest Jean Meslier.[190] In the course of the 18th century, other openly atheistic thinkers followed, such as Baron d'Holbach, Jacques-André Naigeon, and other French materialists.[191] John Locke in contrast, though an advocate of tolerance, urged authorities not to tolerate atheism, believing that the denial of God's existence would undermine the social order and lead to chaos.[192]
+The philosopher David Hume developed a skeptical epistemology grounded in empiricism, and Immanuel Kant's philosophy has strongly questioned the very possibility of a metaphysical knowledge. Both philosophers undermined the metaphysical basis of natural theology and criticized classical arguments for the existence of God.
+Blainey notes that, although Voltaire is widely considered to have strongly contributed to atheistic thinking during the Revolution, he also considered fear of God to have discouraged further disorder, having said "If God did not exist, it would be necessary to invent him."[193] In Reflections on the Revolution in France (1790), the philosopher Edmund Burke denounced atheism, writing of a "literary cabal" who had "some years ago formed something like a regular plan for the destruction of the Christian religion. This object they pursued with a degree of zeal which hitherto had been discovered only in the propagators of some system of piety ... These atheistical fathers have a bigotry of their own ...". But, Burke asserted, "man is by his constitution a religious animal" and "atheism is against, not only our reason, but our instincts; and ... it cannot prevail long".[194]
+Baron d'Holbach was a prominent figure in the French Enlightenment who is best known for his atheism and for his voluminous writings against religion, the most famous of them being The System of Nature (1770) but also Christianity Unveiled. One goal of the French Revolution was a restructuring and subordination of the clergy with respect to the state through the Civil Constitution of the Clergy. Attempts to enforce it led to anti-clerical violence and the expulsion of many clergy from France, lasting until the Thermidorian Reaction. The radical Jacobins seized power in 1793, ushering in the Reign of Terror. The Jacobins were deists and introduced the Cult of the Supreme Being as a new French state religion. Some atheists surrounding Jacques Hébert instead sought to establish a Cult of Reason, a form of atheistic pseudo-religion with a goddess personifying reason. The Napoleonic era further institutionalized the secularization of French society.
+In the latter half of the 19th century, atheism rose to prominence under the influence of rationalistic and freethinking philosophers. Many prominent German philosophers of this era denied the existence of deities and were critical of religion, including Ludwig Feuerbach, Arthur Schopenhauer, Max Stirner, Karl Marx, and Friedrich Nietzsche.[195]
+George Holyoake was the last person (1842) imprisoned in Great Britain due to atheist beliefs. Law notes that he may have also been the first imprisoned on such a charge. Stephen Law states that Holyoake "first coined the term 'secularism'".[196][197]
+Atheism, particularly in the form of practical atheism, advanced in many societies in the 20th century. Atheistic thought found recognition in a wide variety of other, broader philosophies, such as existentialism, objectivism, secular humanism, nihilism, anarchism, logical positivism, Marxism, feminism,[198] and the general scientific and rationalist movement.
+In addition, state atheism emerged in Eastern Europe and Asia during that period, particularly in the Soviet Union under Vladimir Lenin and Joseph Stalin, and in Communist China under Mao Zedong. Atheist and anti-religious policies in the Soviet Union included numerous legislative acts, the outlawing of religious instruction in the schools, and the emergence of the League of Militant Atheists.[199][200] After Mao, the Chinese Communist Party remains an atheist organization, and regulates, but does not forbid, the practice of religion in mainland China.[201][202][203]
+While Geoffrey Blainey has written that "the most ruthless leaders in the Second World War were atheists and secularists who were intensely hostile to both Judaism and Christianity",[204] Richard Madsen has pointed out that Hitler and Stalin each opened and closed churches as a matter of political expedience, and Stalin softened his opposition to Christianity in order to improve public acceptance of his regime during the war.[205] Blackford and Schüklenk have written that "the Soviet Union was undeniably an atheist state, and the same applies to Maoist China and Pol Pot's fanatical Khmer Rouge regime in Cambodia in the 1970s. That does not, however, show that the atrocities committed by these totalitarian dictatorships were the result of atheist beliefs, carried out in the name of atheism, or caused primarily by the atheistic aspects of the relevant forms of communism."[206]
+Logical positivism and scientism paved the way for neopositivism, analytical philosophy, structuralism, and naturalism. Neopositivism and analytical philosophy discarded classical rationalism and metaphysics in favor of strict empiricism and epistemological nominalism. Proponents such as Bertrand Russell emphatically rejected belief in God. In his early work, Ludwig Wittgenstein attempted to separate metaphysical and supernatural language from rational discourse. A.J. Ayer asserted the unverifiability and meaninglessness of religious statements, citing his adherence to the empirical sciences. Relatedly the applied structuralism of Lévi-Strauss sourced religious language to the human subconscious in denying its transcendental meaning. J.N. Findlay and J.J.C. Smart argued that the existence of God is not logically necessary. Naturalists and materialistic monists such as John Dewey considered the natural world to be the basis of everything, denying the existence of God or immortality.[59][207]
+Other leaders like Periyar E.V. Ramasamy, a prominent atheist leader of India, fought against Hinduism and Brahmins for discriminating and dividing people in the name of caste and religion.[208]
+This was highlighted in 1956 when he arranged for the erection of a statue depicting a Hindu god in a humble representation and made antitheistic statements.[209]
+Atheist Vashti McCollum was the plaintiff in a landmark 1948 Supreme Court case that struck down religious education in US public schools.[210] Madalyn Murray O'Hair was perhaps one of the most influential American atheists; she brought forth the 1963 Supreme Court case Murray v. Curlett which banned compulsory prayer in public schools.[211] In 1966, Time magazine asked "Is God Dead?"[212] in response to the Death of God theological movement, citing the estimation that nearly half of all people in the world lived under an anti-religious power, and millions more in Africa, Asia, and South America seemed to lack knowledge of the Christian view of theology.[213] The Freedom From Religion Foundation was co-founded by Anne Nicol Gaylor and her daughter, Annie Laurie Gaylor, in 1976 in the United States, and incorporated nationally in 1978. It promotes the separation of church and state.[214][215]
+Since the fall of the Berlin Wall, the number of actively anti-religious regimes has declined considerably. In 2006, Timothy Shah of the Pew Forum noted "a worldwide trend across all major religious groups, in which God-based and faith-based movements in general are experiencing increasing confidence and influence vis-à-vis secular movements and ideologies."[216]
+However, Gregory S. Paul and Phil Zuckerman consider this a myth and suggest that the actual situation is much more complex and nuanced.[217]
+A 2010 survey found that those identifying themselves as atheists or agnostics are on average more knowledgeable about religion than followers of major faiths. Nonbelievers scored better on questions about tenets central to Protestant and Catholic faiths. Only Mormon and Jewish faithful scored as well as atheists and agnostics.[218]
+In 2012, the first "Women in Secularism" conference was held in Arlington, Virginia.[219] Secular Woman was organized in 2012 as a national organization focused on nonreligious women.[220] The atheist feminist movement has also become increasingly focused on fighting sexism and sexual harassment within the atheist movement itself.[221]
+In August 2012, Jennifer McCreight (the organizer of Boobquake) founded a movement within atheism known as Atheism Plus, or A+, that "applies skepticism to everything, including social issues like sexism, racism, politics, poverty, and crime".[222][223][224]
+In 2013 the first atheist monument on American government property was unveiled at the Bradford County Courthouse in Florida: a 1,500-pound granite bench and plinth inscribed with quotes by Thomas Jefferson, Benjamin Franklin, and Madalyn Murray O'Hair.[225][226]
+"New Atheism" is the name that has been given to a movement among some early-21st-century atheist writers who have advocated the view that "religion should not simply be tolerated but should be countered, criticized, and exposed by rational argument wherever its influence arises."[227]
+The movement is commonly associated with Sam Harris, Daniel C. Dennett, Richard Dawkins, Victor J. Stenger, Christopher Hitchens, and to some extent Ayaan Hirsi Ali.[228][229] Several best-selling books by these authors, published between 2004 and 2007, form the basis for much of the discussion of "New" Atheism.[229] The new atheists and Dawkins in particular have been accused of committing the strawman fallacy[230] and of creating a new religion: Scientism.[231]
+In best selling books, the religiously motivated terrorist events of 9/11 and the partially successful attempts of the Discovery Institute to change the American science curriculum to include creationist ideas, together with support for those ideas from George W. Bush in 2005, have been cited by authors such as Harris, Dennett, Dawkins, Stenger, and Hitchens as evidence of a need to move toward a more secular society.[232]
+It is difficult to quantify the number of atheists in the world. Respondents to religious-belief polls may define "atheism" differently or draw different distinctions between atheism, non-religious beliefs, and non-theistic religious and spiritual beliefs.[234] A Hindu atheist would declare oneself as a Hindu, although also being an atheist at the same time.[235] A 2010 survey published in Encyclopædia Britannica found that the non-religious made up about 9.6% of the world's population, and atheists about 2.0%, with a very large majority based in Asia. This figure did not include those who follow atheistic religions, such as some Buddhists.[236] The average annual change for atheism from 2000 to 2010 was −0.17%.[236] Broad estimates of those who have an absence of belief in a god range from 500 million to 1.1 billion people worldwide.[237][238]
+According to global Win-Gallup International studies, 13% of respondents were "convinced atheists" in 2012,[239] 11% were "convinced atheists" in 2015,[27] and in 2017, 9% were "convinced atheists".[28] As of 2012[update], the top 10 surveyed countries with people who viewed themselves as "convinced atheists" were China (47%), Japan (31%), the Czech Republic (30%), France (29%), South Korea (15%), Germany (15%), Netherlands (14%), Austria (10%), Iceland (10%), Australia (10%), and the Republic of Ireland (10%).[240]
+According to the 2010 Eurobarometer Poll, the percentage of those polled who agreed with the statement "you don't believe there is any sort of spirit, God or life force" varied from a high percentage in France (40%), Czech Republic (37%), Sweden (34%), Netherlands (30%), and Estonia (29%); medium-high percentage in Germany (27%), Belgium (27%), UK (25%); to very low in Poland (5%), Greece (4%), Cyprus (3%), Malta (2%), and Romania (1%), with the European Union as a whole at 20%.[33] In a 2012 Eurobarometer poll on discrimination in the European Union, 16% of those polled considered themselves non believers/agnostics and 7% considered themselves atheists.[242]
+According to a Pew Research Center survey in 2012 religiously unaffiliated (including agnostics and atheists) make up about 18% of Europeans.[243] According to the same survey, the religiously unaffiliated are the majority of the population only in two European countries: Czech Republic (75%) and Estonia (60%).[243]
+There are another three countries, and one special administrative region of China or regions where the unaffiliated make up a majority of the population: North Korea (71%), Japan (57%), Hong Kong (56%), and China (52%).[243]
+According to the Australian Bureau of Statistics, 30% of Australians have "no religion", a category that includes atheists.[244]
+In a 2013 census, 42% of New Zealanders reported having no religion, up from 30% in 1991.[245] Men were more likely than women to report no religion.
+According to the World Values Survey, 4.4% of Americans self-identified as atheists in 2014.[246] However, the same survey showed that 11.1% of all respondents stated "no" when asked if they believed in God.[246] In 1984, these same figures were 1.1% and 2.2%, respectively. According to a 2014 report by the Pew Research Center, 3.1% of the US adult population identify as atheist, up from 1.6% in 2007; and within the religiously unaffiliated (or "no religion") demographic, atheists made up 13.6%.[247] According to the 2015 General Sociological Survey the number of atheists and agnostics in the US has remained relatively flat in the past 23 years since in 1991 only 2% identified as atheist and 4% identified as agnostic and in 2014 only 3% identified as atheists and 5% identified as agnostics.[248]
+According to the American Family Survey, 34% were found to be religiously unaffiliated in 2017 (23% 'nothing in particular', 6% agnostic, 5% atheist).[249][250] According to the Pew Research Center, in 2014, 22.8% of the American population does not identify with a religion, including atheists (3.1%) and agnostics (4%).[251] According to a PRRI survey, 24% of the population is unaffiliated. Atheists and agnostics combined make up about a quarter of this unaffiliated demographic.[252]
+In recent years, the profile of atheism has risen substantially in the Arab world.[253] In major cities across the region, such as Cairo, atheists have been organizing in cafés and social media, despite regular crackdowns from authoritarian governments.[253] A 2012 poll by Gallup International revealed that 5% of Saudis considered themselves to be "convinced atheists."[253] However, very few young people in the Arab world have atheists in their circle of friends or acquaintances. According to one study, less than 1% did in Morocco, Egypt, Saudi Arabia, or Jordan; only 3% to 7% in the United Arab Emirates, Bahrain, Kuwait, and Palestine.[254] When asked whether they have "seen or heard traces of atheism in [their] locality, community, and society" only about 3% to 8% responded yes in all the countries surveyed. The only exception was the UAE, with a percentage of 51%.[254]
+Various studies have reported positive correlations between levels of education, wealth and IQ with atheism.[255][256][257][95] In a 2008 study, researchers found intelligence to be negatively related to religious belief in Europe and the United States. In a sample of 137 countries, the correlation between national IQ and disbelief in God was found to be 0.60.[257] According to evolutionary psychologist Nigel Barber, atheism blossoms in places where most people feel economically secure, particularly in the social democracies of Europe, as there is less uncertainty about the future with extensive social safety nets and better health care resulting in a greater quality of life and higher life expectancy. By contrast, in underdeveloped countries, there are virtually no atheists.[258]
+The relationship between atheism and IQ, while statistically significant, is not a large one, and the reason for the relationship is not well understood.[255]  One hypothesis is that the negative relationship between IQ and religiosity is mediated by individual differences in noncomformity; in many countries, religious belief is a conformist choice, and there is evidence that more intelligent people are less likely to conform.[259] Another theory is that people of higher IQ are more likely to engage in analytical reasoning, and that disbelief in religion results from the application of higher level analytical reasoning to the assessment of religious claims.[255]
+Evolutionary psychologist Nigel Barber states that the reason atheists are more intelligent than religious people is better explained by social, environmental, and wealth factors which happen to correlate with loss of religious belief as well. He doubts that religion causes stupidity, noting that some highly intelligent people have also been religious, but he says it is plausible that higher intelligence correlates to rejection of improbable religious beliefs and that the situation between intelligence and rejection of religious beliefs is quite complex.[260] In a 2017 study, it was shown that compared to religious individuals, atheists have higher reasoning capacities and this difference seemed to be unrelated to sociodemographic factors such as age, education and country of origin.[261] In a 2015 study, researchers found that atheists score higher on cognitive reflection tests than theists, the authors wrote that "The fact that atheists score higher agrees with the literature showing that belief is an automatic manifestation of the mind and its default mode. Disbelieving seems to require deliberative cognitive ability."[262] A 2016 study, in which 4 new studies were reported and a meta-analysis of all previous research on the topic was performed, found that self-identified atheists scored 18.7% higher than theists on the cognitive reflection test and there is a negative correlation between religiosity and analytical thinking. The authors note that recently "it has been argued that analytic thinkers are not actually less religious; rather, the putative association may be a result of religiosity typically being measured after analytic thinking (an order effect)," however, they state "Our results indicate that the association between analytical thinking and religious disbelief is not caused by a simple order effect. There is good evidence that atheists and agnostics are more reflective than religious believers."[263]
+Statistically, atheists are held in poor regard across the globe. Non-atheists, and possibly even fellow atheists, seem to implicitly view atheists as prone to exhibit immoral behaviors ranging from mass murder to not paying at a restaurant.[264][265][266] In addition, according to a 2016 Pew Research Center publication, 15% of French people, 45% of Americans, and 99% of Indonesians explicitly believe that a person must believe in God to be moral. Pew furthermore noted that, in a U.S. poll, atheists and Muslims tied for the lowest rating among the major religious demographics on a "feeling thermometer".[267] Also, a study of religious college students found that they were more likely to perceive and interact with atheists negatively after considering their mortality, suggesting that these attitudes may be the result of death anxiety.[268]

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+Olfaction is a chemoreception that, through the sensory olfactory system, forms the perception of smell.[1] Olfaction has many purposes, such as the detection of hazards, pheromones, and food.
+Olfaction occurs when odorants bind to specific sites on olfactory receptors located in the nasal cavity.[2] Glomeruli aggregate signals from these receptors and transmit them to the olfactory bulb, where the sensory input will start to interact with parts of the brain responsible for smell identification, memory, and emotion.[3]
+Olfactory dysfunction arises as the result of many different peripheral and central disturbances, including upper respiratory infections, traumatic brain injury, and neurodegenerative disease.[4][5]
+Early scientific study of olfaction includes the extensive doctoral dissertation of Eleanor Gamble, published in 1898, which compared olfactory to other stimulus modalities, and implied that smell had a lower intensity discrimination.[6] As the Epicurean and atomistic Roman philosopher Lucretius (1st century BCE) speculated, different odors are attributed to different shapes and sizes of "atoms" (odor molecules in the modern understanding) that stimulate the olfactory organ [1]. A modern demonstration of that theory was the cloning of olfactory receptor proteins by Linda B. Buck and Richard Axel (who were awarded the Nobel Prize in 2004), and subsequent pairing of odor molecules to specific receptor proteins. Each odor receptor molecule recognizes only a particular molecular feature or class of odor molecules. Mammals have about a thousand genes that code for odor reception.[7] Of the genes that code for odor receptors, only a portion are functional. Humans have far fewer active odor receptor genes than other primates and other mammals.[8] In mammals, each olfactory receptor neuron expresses only one functional odor receptor.[9] Odor receptor nerve cells function like a key–lock system: if the airborne molecules of a certain chemical can fit into the lock, the nerve cell will respond. There are, at present, a number of competing theories regarding the mechanism of odor coding and perception. According to the shape theory, each receptor detects a feature of the odor molecule. The weak-shape theory, known as the odotope theory, suggests that different receptors detect only small pieces of molecules, and these minimal inputs are combined to form a larger olfactory perception (similar to the way visual perception is built up of smaller, information-poor sensations, combined and refined to create a detailed overall perception)[citation needed]. According to a new study, researchers have found that a functional relationship exists between molecular volume of odorants and the olfactory neural response.[10] An alternative theory, the vibration theory proposed by Luca Turin,[11][12] posits that odor receptors detect the frequencies of vibrations of odor molecules in the infrared range by quantum tunnelling. However, the behavioral predictions of this theory have been called into question.[13] There is no theory yet that explains olfactory perception completely.
+In vertebrates, smells are sensed by olfactory sensory neurons in the olfactory epithelium. The olfactory epithelium is made up of at least six morphologically and biochemically different cell types.[14] The proportion of olfactory epithelium compared to respiratory epithelium (not innervated, or supplied with nerves) gives an indication of the animal's olfactory sensitivity. Humans have about 10 cm2 (1.6 sq in) of olfactory epithelium, whereas some dogs have 170 cm2 (26 sq in). A dog's olfactory epithelium is also considerably more densely innervated, with a hundred times more receptors per square centimeter.[15] The sensory olfactory system integrates with other senses to form the perception of flavor.[16] Often, land organisms will have separate olfaction systems for smell and taste (orthonasal smell and retronasal smell), but water-dwelling organisms usually have only one system.[17]
+Molecules of odorants passing through the superior nasal concha of the nasal passages dissolve in the mucus that lines the superior portion of the cavity and are detected by olfactory receptors on the dendrites of the olfactory sensory neurons. This may occur by diffusion or by the binding of the odorant to odorant-binding proteins. The mucus overlying the epithelium contains mucopolysaccharides, salts, enzymes, and antibodies (these are highly important, as the olfactory neurons provide a direct passage for infection to pass to the brain). This mucus acts as a solvent for odor molecules, flows constantly, and is replaced approximately every ten minutes.
+In insects, smells are sensed by olfactory sensory neurons in the chemosensory sensilla, which are present in insect antenna, palps, and tarsa, but also on other parts of the insect body. Odorants penetrate into the cuticle pores of chemosensory sensilla and get in contact with insect odorant-binding proteins (OBPs) or Chemosensory proteins (CSPs), before activating the sensory neurons.
+The binding of the ligand (odor molecule or odorant) to the receptor leads to an action potential in the receptor neuron, via a second messenger pathway, depending on the organism. In mammals, the odorants stimulate adenylate cyclase to synthesize cAMP via a G protein called Golf. cAMP, which is the second messenger here, opens a cyclic nucleotide-gated ion channel (CNG), producing an influx of cations (largely Ca2+  with some Na+) into the cell, slightly depolarising it. The Ca2+ in turn opens a Ca2+-activated chloride channel, leading to efflux of Cl−, further depolarizing the cell and triggering an action potential. Ca2+ is then extruded through a sodium-calcium exchanger. A calcium-calmodulin complex also acts to inhibit the binding of cAMP to the cAMP-dependent channel, thus contributing to olfactory adaptation.
+The  main olfactory system of some mammals also contains small subpopulations of olfactory sensory neurons that detect and transduce odors somewhat differently. Olfactory sensory neurons that use trace amine-associated receptors (TAARs) to detect odors use the same second messenger signaling cascade as do the canonical olfactory sensory neurons.[18] Other subpopulations, such as those that express the receptor guanylyl cyclase GC-D (Gucy2d)[19] or the soluble guanylyl cyclase Gucy1b2,[20] use a cGMP cascade to transduce their odorant ligands.[21][22][23] These distinct subpopulations (olfactory subsystems) appear specialized for the detection of small groups of chemical stimuli.
+This mechanism of transduction is somewhat unusual, in that cAMP works by directly binding to the ion channel rather than through activation of protein kinase A. It is similar to the transduction mechanism for photoreceptors, in which the second messenger cGMP works by directly binding to ion channels, suggesting that maybe one of these receptors was evolutionarily adapted into the other. There are also considerable similarities in the immediate processing of stimuli by lateral inhibition.
+Averaged activity of the receptor neurons can be measured in several ways. In vertebrates, responses to an odor can be measured by an electro-olfactogram or through calcium imaging of receptor neuron terminals in the olfactory bulb. In insects, one can perform electroantennography or calcium imaging within the olfactory bulb.
+Olfactory sensory neurons project axons to the brain within the olfactory nerve, (cranial nerve I). These nerve fibers, lacking myelin sheaths, pass to the olfactory bulb of the brain through perforations in the cribriform plate, which in turn projects olfactory information to the olfactory cortex and other areas.[24] The axons from the olfactory receptors converge in the outer layer of the olfactory bulb within small (≈50 micrometers in diameter) structures called glomeruli. Mitral cells, located in the inner layer of the olfactory bulb, form synapses with the axons of the sensory neurons within glomeruli and send the information about the odor to other parts of the olfactory system, where multiple signals may be processed to form a synthesized olfactory perception. A large degree of convergence occurs, with 25,000 axons synapsing on 25 or so mitral cells, and with each of these mitral cells projecting to multiple glomeruli. Mitral cells also project to periglomerular cells and granular cells that inhibit the mitral cells surrounding it (lateral inhibition). Granular cells also mediate inhibition and excitation of mitral cells through pathways from centrifugal fibers and the anterior olfactory nuclei. Neuromodulators like acetylcholine, serotonin and norepinephrine all send axons to the olfactory bulb and have been implicated in gain modulation,[25] pattern separation,[26] and memory functions,[27] respectively.
+The mitral cells leave the olfactory bulb in the lateral olfactory tract, which synapses on five major regions of the cerebrum: the anterior olfactory nucleus, the olfactory tubercle, the amygdala, the piriform cortex, and the entorhinal cortex. The anterior olfactory nucleus projects, via the anterior commissure, to the contralateral olfactory bulb, inhibiting it. The piriform cortex has two major divisions with anatomically distinct organizations and functions. The anterior piriform cortex (APC) appears to be better at determining the chemical structure of the odorant molecules, and the posterior piriform cortex (PPC) has a strong role in categorizing odors and assessing similarities between odors (e.g. minty, woody, and citrus are odors that can, despite being highly variant chemicals, be distinguished via the PPC in a concentration-independent manner).[28] The piriform cortex projects to the medial dorsal nucleus of the thalamus, which then projects to the orbitofrontal cortex. The orbitofrontal cortex mediates conscious perception of the odor (citation needed). The three-layered piriform cortex projects to a number of thalamic and hypothalamic nuclei, the hippocampus and amygdala and the orbitofrontal cortex, but its function is largely unknown. The entorhinal cortex projects to the amygdala and is involved in emotional and autonomic responses to odor. It also projects to the hippocampus and is involved in motivation and memory. Odor information is stored in long-term memory and has strong connections to emotional memory. This is possibly due to the olfactory system's close anatomical ties to the limbic system and hippocampus, areas of the brain that have long been known to be involved in emotion and place memory, respectively.
+Since any one receptor is responsive to various odorants, and there is a great deal of convergence at the level of the olfactory bulb, it may seem strange that human beings are able to distinguish so many different odors. It seems that a highly complex form of processing must be occurring; however, as it can be shown that, while many neurons in the olfactory bulb (and even the pyriform cortex and amygdala) are responsive to many different odors, half the neurons in the orbitofrontal cortex are responsive to only one odor, and the rest to only a few. It has been shown through microelectrode studies that each individual odor gives a particular spatial map of excitation in the olfactory bulb. It is possible that the brain is able to distinguish specific odors through spatial encoding, but temporal coding must also be taken into account. Over time, the spatial maps change, even for one particular odor, and the brain must be able to process these details as well.
+Inputs from the two nostrils have separate inputs to the brain, with the result that, when each nostril takes up a different odorant, a person may experience perceptual rivalry in the olfactory sense akin to that of binocular rivalry.[29]
+In insects, smells are sensed by sensilla located on the antenna and maxillary palp and first processed by the antennal lobe (analogous to the olfactory bulb), and next by the mushroom bodies and lateral horn.
+Many animals, including most mammals and reptiles, but not humans[citation needed], have two distinct and segregated olfactory systems: a main olfactory system, which detects volatile stimuli, and an accessory olfactory system, which detects fluid-phase stimuli. Behavioral evidence suggests that these fluid-phase stimuli often function as pheromones, although pheromones can also be detected by the main olfactory system. In the accessory olfactory system, stimuli are detected by the vomeronasal organ, located in the vomer, between the nose and the mouth. Snakes use it to smell prey, sticking their tongue out and touching it to the organ. Some mammals make a facial expression called flehmen to direct stimuli to this organ.
+The sensory receptors of the accessory olfactory system are located in the vomeronasal organ. As in the main olfactory system, the axons of these sensory neurons project from the vomeronasal organ to the accessory olfactory bulb, which in the mouse is located on the dorsal-posterior portion of the main olfactory bulb. Unlike in the main olfactory system, the axons that leave the accessory olfactory bulb do not project to the brain's cortex but rather to targets in the amygdala and bed nucleus of the stria terminalis, and from there to the hypothalamus, where they may influence aggression and mating behavior.
+The MHC genes (known as HLA in humans) are a group of genes present in many animals and important for the immune system; in general, offspring from parents with differing MHC genes have a stronger immune system. Fish, mice, and female humans are able to smell some aspect of the MHC genes of potential sex partners and prefer partners with MHC genes different from their own.[30][31]
+Humans can detect blood relatives from olfaction.[32] Mothers can identify by body odor their biological children but not their stepchildren. Pre-adolescent children can olfactorily detect their full siblings but not half-siblings or step siblings, and this might explain incest avoidance and the Westermarck effect.[33] Functional imaging shows that this olfactory kinship detection process involves the frontal-temporal junction, the insula, and the dorsomedial prefrontal cortex, but not the primary or secondary olfactory cortices, or the related piriform cortex or orbitofrontal cortex.[34]
+The process by which olfactory information is coded in the brain to allow for proper perception is still being researched, and is not completely understood. When an odorant is detected by receptors, they in a sense break the odorant down, and then the brain puts the odorant back together for identification and perception.[35] The odorant binds to receptors that recognize only a specific functional group, or feature, of the odorant, which is why the chemical nature of the odorant is important.[36]
+After binding the odorant, the receptor is activated and will send a signal to the glomeruli.[36] Each glomerulus receives signals from multiple receptors that detect similar odorant features. Because several receptor types are activated due to the different chemical features of the odorant, several glomeruli are activated as well. All of the signals from the glomeruli are then sent to the brain, where the combination of glomeruli activation encodes the different chemical features of the odorant. The brain then essentially puts the pieces of the activation pattern back together in order to identify and perceive the odorant.[36] This distributed code allows the brain to detect specific odors in mixtures of many background odors.[37]
+It is a general idea that the layout of brain structures corresponds to physical features of stimuli (called topographic coding), and similar analogies have been made in olfaction with concepts such as a layout corresponding to chemical features (called chemotopy) or perceptual features.[38] While chemotopy remains a highly controversial concept,[39] evidence exists for perceptual information implemented in the spatial dimensions of olfactory networks.[38]
+Although conventional wisdom and lay literature, based on impressionistic findings in the 1920s, have long presented human olfaction as capable of distinguishing between roughly 10,000 unique odors, recent research has suggested that the average individual is capable of distinguishing over one trillion unique odors.[40] Researchers in the most recent study, which tested the psychophysical responses to combinations of over 128 unique odor molecules with combinations composed of up to 30 different component molecules, noted that this estimate is "conservative" and that some subjects of their research might be capable of deciphering between a thousand trillion odorants, adding that their worst performer could probably still distinguish between 80 million scents.[41] Authors of the study concluded, "This is far more than previous estimates of distinguishable olfactory stimuli. It demonstrates that the human olfactory system, with its hundreds of different olfactory receptors, far out performs the other senses in the number of physically different stimuli it can discriminate."[42] However, it was also noted by the authors that the ability to distinguish between smells is not analogous to being able to consistently identify them, and that subjects were not typically capable of identifying individual odor stimulants from within the odors the researchers had prepared from multiple odor molecules. In November 2014 the study was strongly criticized by Caltech scientist Markus Meister, who wrote that the study's "extravagant claims are based on errors of mathematical logic".[43][44] The logic of his paper has in turn been criticized by the authors of the original paper.[45]
+Different people smell different odors, and most of these differences are caused by genetic differences.[46] Although odorant receptor genes make up one of the largest gene families in the human genome, only a handful of genes have been linked conclusively to particular smells. For instance, the odorant receptor OR5A1 and its genetic variants (alleles) are responsible for our ability (or failure) to smell β-ionone, a key aroma in foods and beverages.[47] Similarly, the odorant receptor OR2J3 is associated with the ability to detect the "grassy" odor, cis-3-hexen-1-ol.[48] The preference (or dislike) of cilantro (coriander) has been linked to the olfactory receptor OR6A2.[49]
+Flavor perception is an aggregation of auditory, taste, haptic, and smell sensory information.[16] Retronasal smell plays the biggest role in the sensation of flavor. During the process of mastication, the tongue manipulates food to release odorants. These odorants enter the nasal cavity during exhalation.[50] The olfaction of food has the sensation of being in the mouth because of co-activation of the motor cortex and olfactory epithelium during mastication.[16]
+Olfaction, taste, and trigeminal receptors (also called chemesthesis) together contribute to flavor. The human tongue can distinguish only among five distinct qualities of taste, while the nose can distinguish among hundreds of substances, even in minute quantities. It is during exhalation that the olfaction contribution to flavor occurs, in contrast to that of proper smell, which occurs during the inhalation phase of breathing.[50] The olfactory system is the only human sense that bypasses the thalamus and connects directly to the forebrain.[51]
+Olfaction and sound information has been shown to converge in the olfactory tubercles of rodents.[52] This neural convergence is proposed to give rise to a perception termed smound.[53] Whereas a flavor results from interactions between smell and taste, a smound may result from interactions between smell and sound.
+The following are disorders associated with olfaction:
+Scientists have devised methods for quantifying the intensity of odors, in particular for the purpose of analyzing unpleasant or objectionable odors released by an industrial source into a community. Since the 1800s industrial countries have encountered incidents where proximity of an industrial source or landfill produced adverse reactions among nearby residents regarding airborne odor. The basic theory of odor analysis is to measure what extent of dilution with "pure" air is required before the sample in question is rendered indistinguishable from the "pure" or reference standard. Since each person perceives odor differently, an "odor panel" composed of several different people is assembled, each sniffing the same sample of diluted specimen air. A field olfactometer can be utilized to determine the magnitude of an odor.
+Many air management districts in the US have numerical standards of acceptability for the intensity of odor that is allowed to cross into a residential property. For example, the Bay Area Air Quality Management District has applied its standard in regulating numerous industries, landfills, and sewage treatment plants. Example applications this district has engaged are the San Mateo, California, wastewater treatment plant; the Shoreline Amphitheatre in Mountain View, California; and the IT Corporation waste ponds, Martinez, California.
+The tendrils of plants are especially sensitive to airborne volatile organic compounds. Parasites such as dodder make use of this in locating their preferred hosts and locking on to them.[55] The emission of volatile compounds is detected when foliage is browsed by animals. Threatened plants are then able to take defensive chemical measures, such as moving tannin compounds to their foliage. (See Plant perception).
+The importance and sensitivity of smell varies among different organisms; most mammals have a good sense of smell, whereas most birds do not, except the tubenoses (e.g., petrels and albatrosses), certain species of vultures, and the kiwis. Although, recent analysis of the chemical composition of volatile organic compounds (VOCs) from King Penguin feathers suggest that VOCs may provide olfactory cues, used by the penguins to locate their colony and recognise individuals.[56]  Among mammals, it is well developed in the carnivores and ungulates, which must always be aware of each other, and in those that smell for their food, such as moles. Having a strong sense of smell is referred to as macrosmatic.
+Figures suggesting greater or lesser sensitivity in various species reflect experimental findings from the reactions of animals exposed to aromas in known extreme dilutions. These are, therefore, based on perceptions by these animals, rather than mere nasal function. That is, the brain's smell-recognizing centers must react to the stimulus detected for the animal to be said to show a response to the smell in question. It is estimated that dogs, in general, have an olfactory sense approximately ten thousand to a hundred thousand times more acute than a human's.[57] This does not mean they are overwhelmed by smells our noses can detect; rather, it means they can discern a molecular presence when it is in much greater dilution in the carrier, air.
+Scenthounds as a group can smell one- to ten-million times more acutely than a human, and bloodhounds, which have the keenest sense of smell of any dogs,[citation needed] have noses ten- to one-hundred-million times more sensitive than a human's. They were bred for the specific purpose of tracking humans, and can detect a scent trail a few days old. The second-most-sensitive nose is possessed by the Basset Hound, which was bred to track and hunt rabbits and other small animals.
+Bears, such as the Silvertip Grizzly found in parts of North America, have a sense of smell seven times stronger than that of the bloodhound, essential for locating food underground. Using their elongated claws, bears dig deep trenches in search of burrowing animals and nests as well as roots, bulbs, and insects. Bears can detect the scent of food from up to eighteen miles away; because of their immense size, they often scavenge new kills, driving away the predators (including packs of wolves and human hunters) in the process.
+The sense of smell is less developed in the catarrhine primates, and nonexistent in cetaceans, which compensate with a well-developed sense of taste.[citation needed] In some strepsirrhines, such as the red-bellied lemur, scent glands occur atop the head. In many species, olfaction is highly tuned to pheromones; a male silkworm moth, for example, can sense a single molecule of bombykol.
+Fish, too, have a well-developed sense of smell, even though they inhabit an aquatic environment. Salmon utilize their sense of smell to identify and return to their home stream waters. Catfish use their sense of smell to identify other individual catfish and to maintain a social hierarchy. Many fishes use the sense of smell to identify mating partners or to alert to the presence of food.
+Since inbreeding is detrimental, it tends to be avoided. In the house mouse, the major urinary protein (MUP) gene cluster provides a highly polymorphic scent signal of genetic identity that appears to underlie kin recognition and inbreeding avoidance. Thus, there are fewer matings between mice sharing MUP haplotypes than would be expected if there were random mating.[58]

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+The olive, known by the botanical name Olea europaea, meaning "European olive", is a species of small tree in the family Oleaceae, found traditionally in the Mediterranean Basin. The species is cultivated in all the countries of the Mediterranean, as well as in South America, South Africa, Australia, New Zealand and the United States.[1][2] Olea europaea is the type species for the genus Olea.
+The olive's fruit, also called the olive, is of major agricultural importance in the Mediterranean region as the source of olive oil; it is one of the core ingredients in Mediterranean cuisine. The tree and its fruit give their name to the plant family, which also includes species such as lilacs, jasmine, Forsythia, and the true ash trees (Fraxinus).
+The word "olive" derives from Latin ŏlīva ("olive fruit", "olive tree"),[3] possibly through Etruscan 𐌄𐌋𐌄𐌉𐌅𐌀 (eleiva) from the archaic Proto-Greek form *ἐλαίϝα (*elaíwa) (Classic Greek ἐλαία elaía, "olive fruit", "olive tree").[4][5]
+The word "oil" originally meant "olive oil", from ŏlĕum,[6] ἔλαιον (élaion, "olive oil").[7][8] Also in multiple other languages the word for "oil" ultimately derives from the name of this tree and its fruit.
+The oldest attested forms of the Greek words are the Mycenaean 𐀁𐀨𐀷, e-ra-wa, and 𐀁𐀨𐀺, e-ra-wo or 𐀁𐁉𐀺, e-rai-wo, written in the Linear B syllabic script.[9][10]
+The olive tree, Olea europaea, is an evergreen tree or shrub native to Mediterranean Europe, Asia, and Africa. It is short and squat, and rarely exceeds 8–15 m (26–49 ft) in height.  'Pisciottana', a unique variety comprising 40,000 trees found only in the area around Pisciotta in the Campania region of southern Italy often exceeds this, with correspondingly large trunk diameters. The silvery green leaves are oblong, measuring 4–10 cm (1.6–3.9 in) long and 1–3 cm (0.39–1.18 in) wide. The trunk is typically gnarled and twisted.[11]
+The small, white, feathery flowers, with ten-cleft calyx and corolla, two stamens, and bifid stigma, are borne generally on the previous year's wood, in racemes springing from the axils of the leaves.
+The fruit is a small drupe 1–2.5 cm (0.39–0.98 in) long when ripe, thinner-fleshed and smaller in wild plants than in orchard cultivars. Olives are harvested in the green to purple stage.[12] Canned black olives have often been artificially blackened[13] (see below on processing) and may contain the chemical ferrous gluconate to improve the appearance.[14] Olea europaea contains a seed commonly referred to in American English as a pit, and in British English as a stone.[15]
+The six natural subspecies of Olea europaea are distributed over a wide range:[16][17]
+The subspecies O. e. maroccana and O. e. cerasiformis are respectively hexaploid and tetraploid.[18]
+Wild growing forms of the olive are sometimes treated as the species Olea oleaster.
+The trees referred to as white and black olives in Southeast Asia are not actually olives, but species of Canarium.[19]
+Hundreds of cultivars of the olive tree are known.[20][21] An olive's cultivar has a significant impact on its colour, size, shape, and growth characteristics, as well as the qualities of olive oil.[20] Olive cultivars may be used primarily for oil, eating, or both. Olives cultivated for consumption are generally referred to as table olives.[22]
+Since many olive cultivars are self-sterile or nearly so, they are generally planted in pairs with a single primary cultivar and a secondary cultivar selected for its ability to fertilize the primary one. In recent times, efforts have been directed at producing hybrid cultivars with qualities useful to farmers, such as resistance to disease, quick growth, and larger or more consistent crops.
+Fossil evidence indicates the olive tree had its origins some 20–40 million years ago in the Oligocene, in what is now corresponding to Italy and the eastern Mediterranean Basin.[23][24] The olive plant was first cultivated some 7,000 years ago in Mediterranean regions.[23][25]
+The edible olive seems to have coexisted with humans for about 5,000 to 6,000 years, going back to the early Bronze Age (3150 to 1200 BC). Its origin can be traced to the Levant based on written tablets, olive pits, and wood fragments found in ancient tombs.[26][27]
+The immediate ancestry of the cultivated olive is unknown. Fossil Olea pollen has been found in Macedonia and other places around the Mediterranean, indicating that this genus is an original element of the Mediterranean flora. Fossilized leaves of Olea were found in the palaeosols of the volcanic Greek island of Santorini (Thera) and were dated about 37,000 BP. Imprints of larvae of olive whitefly Aleurolobus (Aleurodes) olivinus were found on the leaves. The same insect is commonly found today on olive leaves, showing that the plant-animal co-evolutionary relations have not changed since that time.[28] Other leaves found on the same island are dated back to 60,000 BP, making them the oldest known olives from the Mediterranean.[29]
+As far back as 3000 BC, olives were grown commercially in Crete; they may have been the source of the wealth of the Minoan civilization.[30]
+Olives are not native to the Americas. Spanish colonists brought the olive to the New World, where its cultivation prospered in present-day Peru, Chile, and Argentina . The first seedlings from Spain were planted in Lima by Antonio de Rivera in 1560. Olive tree cultivation quickly spread along the valleys of South America's dry Pacific coast where the climate was similar to the Mediterranean.[31] Spanish missionaries established the tree in the 18th century in California. It was first cultivated at Mission San Diego de Alcalá in 1769 or later around 1795. Orchards were started at other missions, but in 1838, an inspection found only two olive orchards in California. Cultivation for oil gradually became a highly successful commercial venture from the 1860s onward.[32] In Japan, the first successful planting of olive trees happened in 1908 on Shodo Island, which became the cradle of olive cultivation.[33] An estimated 865 million olive trees are in the world today (as of 2005), and the vast majority of these are found in Mediterranean countries, with traditionally marginal areas accounting for no more than 25% of olive-planted area and 10% of oil production.[34]
+Olive oil has long been considered sacred and holy. The olive branch was often a symbol of abundance, glory, and peace. The leafy branches of the olive tree were ritually offered to deities and powerful figures as emblems of benediction and purification, and they were used to crown the victors of friendly games and bloody wars. Today, olive oil is still used in many religious ceremonies. Over the years, the olive has also been used to symbolize wisdom,  fertility, power, and purity.
+The olive was one of the main elements in ancient Israelite cuisine. Olive oil was used for not only food and cooking, but also lighting, sacrificial offerings, ointment, and anointment for priestly or royal office.[35]
+The olive tree is one of the first plants mentioned in the Hebrew Bible (the Christian Old Testament), and one of the most significant. An olive branch (or leaf, depending on translation) was brought back to Noah by a dove to demonstrate that the flood was over
+(Book of Genesis, 8:11). The olive is listed in Deuteronomy 8:8 as one of the seven species that are noteworthy products of the Land of Israel.[36]
+Olives are thought to have been domesticated in the third millennium BC at the latest, at which point they, along with grain and grapes, became part of Colin Renfrew’s triad of Greek staple crops that fueled the emergence of more complex societies.[37]. Olives, and especially (perfumed) olive oil, became a major export product during the Minoan and Mycenaean period. Dutch archaeologist Jorrit Kelder proposed that the Mycenaeans sent shipments of olive oil, probably alongside live olive branches, to the court of the Egyptian pharaoh Akhenaten as a diplomatic gift.[38]. In Egypt, these imported olive branches may have acquired ritual meaning, seeing that they are depicted as offerings on the wall of the Aten temple and were used in wreaths for the burial of Tutankhamen. It is likely that, as well as being used for culinary purposes, olive oil was also used to various other ends, including as a perfume.
+The ancient Greeks smeared olive oil on their bodies and hair as a matter of grooming and good health.
+Olive oil was used to anoint kings and athletes in ancient Greece. It was burnt in the sacred lamps of temples and was the "eternal flame" of the original Olympic games. Victors in these games were crowned with its leaves.
+In Homer's Odyssey, Odysseus crawls beneath two shoots of olive that grow from a single stock,[39] and in the Iliad, (XVII.53ff) there is a metaphoric description of a lone olive tree in the mountains, by a spring; the Greeks observed that the olive rarely thrives at a distance from the sea, which in Greece invariably means up mountain slopes. Greek myth attributed to the primordial culture-hero Aristaeus the understanding of olive husbandry, along with cheese-making and bee-keeping.[40] Olive was one of the woods used to fashion the most primitive Greek cult figures, called xoana, referring to their wooden material; they were reverently preserved for centuries.[41] It was purely a matter of local pride that the Athenians claimed that the olive grew first in Athens.[42] In an archaic Athenian foundation myth, Athena won the patronage of Attica from Poseidon with the gift of the olive. According to the fourth-century BC father of botany, Theophrastus, olive trees ordinarily attained an age around 200 years,[43] he mentions that the very olive tree of Athena still grew on the Acropolis; it was still to be seen there in the second century AD;[44] and when Pausanias was shown it, c. 170 AD, he reported "Legend also says that when the Persians fired Athens the olive was burnt down, but on the very day it was burnt it grew again to the height of two cubits."[45] Indeed, olive suckers sprout readily from the stump, and the great age of some existing olive trees shows that it was perfectly possible that the olive tree of the Acropolis dated to the Bronze Age. The olive was sacred to Athena and appeared on the Athenian coinage.
+Theophrastus, in On the Causes of Plants, does not give as systematic and detailed an account of olive husbandry as he does of the vine, but he makes clear (in 1.16.10) that the cultivated olive must be vegetatively propagated; indeed, the pits give rise to thorny, wild-type olives, spread far and wide by birds. Theophrastus reports how the bearing olive can be grafted on the wild olive, for which the Greeks had a separate name, kotinos.[46] In his Enquiry into Plants (2.1.2–4) he states that the olive can be propagated from a piece of the trunk, the root, a twig, or a stake.[47]
+According to Pliny the Elder, a vine, a fig tree, and an olive tree grew in the middle of the Roman Forum; the olive was planted to provide shade (the garden plot was recreated in the 20th century).[48] The Roman poet Horace mentions it in reference to his own diet, which he describes as very simple: "As for me, olives, endives, and smooth mallows provide sustenance."[49] Lord Monboddo comments on the olive in 1779 as one of the foods preferred by the ancients and as one of the most perfect foods.[50]
+Vitruvius describes of the use of charred olive wood in tying together walls and foundations in his De Architectura:
+The thickness of the wall should, in my opinion, be such that armed men meeting on top of it may pass one another without interference. In the thickness there should be set a very close succession of ties made of charred olive wood, binding the two faces of the wall together like pins, to give it lasting endurance. For that is a material which neither decay, nor the weather, nor time can harm, but even though buried in the earth or set in the water it keeps sound and useful forever. And so not only city walls but substructures in general and all walls that require a thickness like that of a city wall, will be long in falling to decay if tied in this manner.[51]
+The Mount of Olives east of Jerusalem is mentioned several times in the New Testament. The Allegory of the Olive Tree in St. Paul's Epistle to the Romans  refers to the scattering and gathering of Israel. It compares the Israelites to a tame olive tree and the Gentiles to a wild olive branch. The olive tree itself, as well as olive oil and olives, play an important role in the Bible.[52]
+The olive tree and olive oil are mentioned seven times in the Quran,[53] and the olive is praised as a precious fruit. Olive tree and olive-oil health benefits have been propounded in Prophetic medicine. Muhammad is reported to have said: "Take oil of olive and massage with it – it is a blessed tree" (Sunan al-Darimi, 69:103).
+Olives are substitutes for dates (if not available) during Ramadan fasting, and olive tree leaves are used as incense in some Muslim Mediterranean countries.[54]
+Olive trees in the groves around the Mediterranean Sea are centuries old, with some dated to 2000 years. An olive tree on the island of Brijuni (Brioni), Istria in Croatia, has a radiocarbon dating age of about 1,600 years. It still gives fruit (about 30 kg or 66 lb per year), which is made into olive oil.[55]
+An olive tree in west Athens, named "Plato's Olive Tree", is thought to be a remnant of the grove where Plato's Academy was situated, making it an estimated 2,400 years old.[56] The tree comprised a cavernous trunk from which a few branches were still sprouting in 1975, when a traffic accident caused a bus to uproot it.[56] Following that, the trunk was preserved and displayed in the nearby Agricultural University of Athens. In 2013, it was reported that the remaining part of the trunk was uprooted and stolen, allegedly to serve as firewood. A supposedly older tree, the "Peisistratos Tree", is located by the banks of the Cephisus River, in the municipality of Agioi Anargyroi, and is said to be a remnant of an olive grove that was planted by Athenian tyrant Peisistratos in the sixth century BC.[citation needed] Numerous ancient olive trees also exist near Pelion in Greece.[citation needed] The age of an olive tree in Crete, the Finix Olive, is claimed to be over 2,000 years old; this estimate is based on archaeological evidence around the tree.[57] The olive tree of Vouves, also in Crete, has an age estimated between 2000 and 4000 years.[58] An olive tree called Farga d'Arió in Ulldecona, Catalonia, Spain, has been estimated (with laser-perimetry methods) to date back to 314 AD, which would mean that it was planted when Constantine the Great was Roman emperor.[59]
+Some Italian olive trees are believed to date back to Ancient Rome (8th century BC to 5th century AD), although identifying progenitor trees in ancient sources is difficult. Several other trees of about 1,000 years old are within the same garden. The 15th-century trees of Olivo della Linza, at Alliste in the Province of Lecce in Apulia on the Italian mainland, were noted by Bishop Ludovico de Pennis during his pastoral visit to the Diocese of Nardò-Gallipoli in 1452.[60]
+The town of Bshaale, Lebanon claims to have the oldest olive trees in the world (4000 BC for the oldest), but no scientific study supports these claims. Other trees in the towns of Amioun appear to be at least 1,500 years old.[61][62]
+Throughout Israel and Palestine, dozens of ancient olive trees are found with estimated ages of 1,600–2,000 years; however, these estimates could not be supported by current scientific practices.[63] Ancient trees include two giant olive trees in Arraba and five trees in Deir Hanna, both in the Galilee region, which have been determined to be over 3,000 years old,[63] although no available data support the credibility of the study that produced these age estimates, and as such, the 3000 years age estimate can not be considered valid.  All seven trees continue to produce olives.
+Several trees in the Garden of Gethsemane (from the Hebrew words gat shemanim or olive press) in Jerusalem are claimed to date back to the time of Jesus.[64] A study conducted by the National Research Council of Italy in 2012 used carbon dating on older parts of the trunks of three trees from Gethsemane and came up with the dates of 1092, 1166, and 1198 AD, while DNA tests show that the trees were originally planted from the same parent plant.[65] According to molecular analysis, the tested trees showed the same allelic profile at all microsatellite loci analyzed which furthermore may indicate attempt to keep the lineage of an older species intact.[66] However, Bernabei writes, "All the tree trunks are hollow inside so that the central, older wood is missing . . . In the end, only three from a total of eight olive trees could be successfully dated.  The dated ancient olive trees do, however, not allow any hypothesis to be made with regard to the age of the remaining five giant olive trees."[67] Babcox concludes, "The roots of the eight oldest trees are possibly much older. Visiting guides to the garden often state that they are two thousand years old."[68]
+The 2,000-year-old[69] Bidni olive trees on the island of Malta, which have been confirmed through carbon dating,[70] have been protected since 1933,[71] and are also listed in UNESCO's Database of National Cultural Heritage Laws.[72] In 2011, after recognising their historical and landscape value, and in recognition of the fact that "only 20 trees remain from 40 at the beginning of the 20th century",[73] Maltese authorities declared the ancient Bidni olive grove at Bidnija, limits of Mosta, as a Tree Protected Area, in accordance with the provisions of the Trees and Woodlands Protection Regulations, 2011, as per Government Notice number 473/11.[74]
+Kaštela, Croatia
+Canneto Sabino, Italy
+Karystos, Euboia, Greece
+The olive tree, Olea europaea, has been cultivated for olive oil, fine wood, olive leaf, ornamental reasons, and the olive fruit. About 90% of all harvested olives are turned into oil, while about 10% are used as table olives.[20] The olive is one of the "trinity" or "triad" of basic ingredients in Mediterranean cuisine, the other two being wheat for bread, pasta, and couscous, and the grape for wine.[75][76]
+Table olives are classified by the IOC into three groups according to the degree of ripeness achieved before harvesting:[77]
+Raw or fresh olives are naturally very bitter; to make them palatable, olives must be cured and fermented, thereby removing oleuropein, a bitter phenolic compound that can reach levels of 14% of dry matter in young olives.[79] In addition to oleuropein, other phenolic compounds render freshly picked olives unpalatable and must also be removed or lowered in quantity through curing and fermentation. Generally speaking, phenolics reach their peak in young fruit and are converted as the fruit matures.[80] Once ripening occurs, the levels of phenolics sharply decline through their conversion to other organic products which render some cultivars edible immediately.[79] One example of an edible olive native to the island of Thasos is the throubes black olive, which when allowed to ripen in the sun, shrivel, and fall from the tree, is then edible.[81][82]
+The curing process may take from a few days, with lye, to a few months with brine or salt packing.[83] With the exception of California style and salt-cured olives, all methods of curing involve a major fermentation involving bacteria and yeast that is of equal importance to the final table olive product.[84] Traditional cures, using the natural microflora on the fruit to induce fermentation, lead to two important outcomes: the leaching out and breakdown of oleuropein and other unpalatable phenolic compounds, and the generation of favourable metabolites from bacteria and yeast, such as organic acids, probiotics, glycerol, and esters, which affect the sensory properties of the final table olives.[79] Mixed bacterial/yeast olive fermentations may have probiotic qualities.[85][86] Lactic acid is the most important metabolite, as it lowers the pH, acting as a natural preservative against the growth of unwanted pathogenic species. The result is table olives which can be stored without refrigeration. Fermentations dominated by lactic acid bacteria are, therefore, the most suitable method of curing olives. Yeast-dominated fermentations produce a different suite of metabolites which provide poorer preservation, so they are corrected with an acid such as citric acid in the final processing stage to provide microbial stability.[22]
+The many types of preparations for table olives depend on local tastes and traditions. The most important commercial examples are listed below.
+Lebanese or Phenician Type (olives with fermentation): Applied to green, semiripe, or ripe olives. Olives are soaked in salt water for 24-48 hours. Then, they are slightly crushed with a rock to fasten the fermentation process. The olives are stored for a period of up to a year in a container with salt water, fresh lemon juice, lemon peels, laurel and olive leaves, and rosemary. Some recipes may contain white vinegar or olive oil.
+Spanish or Sevillian type (olives with fermentation): Most commonly applied to green olive preparation, around 60% of all the world's table olives are produced with this method.[87] Olives are soaked in lye (dilute NaOH, 2–4%) for 8–10 hours to hydrolyse the oleuropein. They are usually considered "treated" when the lye has penetrated two-thirds of the way into the fruit. They are then washed once or several times in water to remove the caustic solution and transferred to fermenting vessels full of brine at typical concentrations of 8–12% NaCl.[88] The brine is changed on a regular basis to help remove the phenolic compounds. Fermentation is carried out by the natural microbiota present on the olives that survive the lye treatment process. Many organisms are involved, usually reflecting the local conditions or "Terroir" of the olives. During a typical fermentation gram-negative enterobacteria flourish in small numbers at first, but are rapidly outgrown by lactic acid bacteria species such as Leuconostoc mesenteroides, Lactobacillus plantarum, Lactobacillus brevis and Pediococcus damnosus. These bacteria produce lactic acid to help lower the pH of the brine and therefore stabilize the product against unwanted pathogenic species. A diversity of yeasts then accumulate in sufficient numbers to help complete the fermentation alongside the lactic acid bacteria. Yeasts commonly mentioned include the teleomorphs Pichia anomala, Pichia membranifaciens, Debaryomyces hansenii and Kluyveromyces marxianus.[22] Once fermented, the olives are placed in fresh brine and acid corrected, to be ready for market.
+Sicilian or Greek type (olives with fermentation): Applied to green, semiripe and ripe olives, they are almost identical to the Spanish type fermentation process, but the lye treatment process is skipped and the olives are placed directly in fermentation vessels full of brine (8–12% NaCl). The brine is changed on a regular basis to help remove the phenolic compounds. As the caustic treatment is avoided, lactic acid bacteria are only present in similar numbers to yeast and appear to be outdone by the abundant yeasts found on untreated olives. As very little acid is produced by the yeast fermentation, lactic, acetic, or citric acid is often added to the fermentation stage to stabilize the process.[84]
+Picholine or directly-brined type (olives with fermentation): Applied to green, semi-ripe, or ripe olives, they are soaked in lye typically for longer periods than Spanish style (e.g. 10–72 hours) until the solution has penetrated three-quarters of the way into the fruit. They are then washed and immediately brined and acid corrected with citric acid to achieve microbial stability. Fermentation still occurs carried out by acidogenic yeast and bacteria, but is more subdued than other methods. The brine is changed on a regular basis to help remove the phenolic compounds and a series of progressively stronger concentrations of salt are added until the product is fully stabilized and ready to be eaten.[22]
+Water-cured type (olives with fermentation): Applied to green, semi-ripe, or ripe olives, these are soaked in water or weak brine and this solution is changed on a daily basis for 10–14 days. The oleuropein is naturally dissolved and leached into the water and removed during a continual soak-wash cycle. Fermentation takes place during the water treatment stage and involves a mixed yeast/bacteria ecosystem. Sometimes, the olives are lightly cracked with a hammer or a stone to trigger fermentation and speed up the fermentation process. Once debittered, the olives are brined to concentrations of 8–12% NaCl and acid corrected, and are then ready to eat.[84]
+Salt-cured type (olives with minor fermentation): Applied only to ripe olives, they are usually produced in Morocco, Turkey, and other eastern Mediterranean countries. Once picked, the olives are vigorously washed and packed in alternating layers with salt. The high concentrations of salt draw the moisture out of olives, dehydrating and shriveling them until they look somewhat analogous to a raisin. Once packed in salt, fermentation is minimal and only initiated by the most halophilic yeast species such as Debaryomyces hansenii. Once cured, they are sold in their natural state without any additives.[22] So-called oil-cured olives are cured in salt, and then soaked in oil.[89]
+California or "artificial ripening" type (olives without fermentation): Applied to green and semi-ripe olives, they are placed in lye and soaked. Upon their removal, they are washed in water injected with compressed air. This process is repeated several times until both oxygen and lye have soaked through to the pit. The repeated, saturated exposure to air oxidises the skin and flesh of the fruit, turning it black in an artificial process that mimics natural ripening. Once fully oxidised or "blackened", they are brined and acid corrected and are then ready for eating.[77][78]
+Olive wood is very hard and is prized for its durability, colour, high combustion temperature, and interesting grain patterns.  Because of the commercial importance of the fruit, and the slow growth and relatively small size of the tree, olive wood and its products are relatively expensive.  Common uses of the wood include: kitchen utensils, carved wooden bowls, cutting boards, fine furniture, and decorative items.
+The yellow or light greenish-brown wood is often finely veined with a darker tint; being very hard and close-grained, it is valued by woodworkers.[90]
+In modern landscape design olive trees are frequently used as ornamental features for their distinctively gnarled trunks and "evergreen" silvery gray foliage.[91]
+The earliest evidence for the domestication of olives comes from the Chalcolithic period archaeological site of Teleilat el Ghassul in what is today modern Jordan. Farmers in ancient times believed that olive trees would not grow well if planted more than a certain distance from the sea; Theophrastus gives 300 stadia (55.6 km or 34.5 mi) as the limit. Modern experience does not always confirm this, and, though showing a preference for the coast, they have long been grown further inland in some areas with suitable climates, particularly in the southwestern Mediterranean (Iberia, northwest Africa) where winters are mild.
+Olives are cultivated in many regions of the world with Mediterranean climates, such as South Africa, Chile, Peru, Australia, Oregon, and California, and in areas with temperate climates such as New Zealand.[citation needed] They are also grown in the Córdoba Province, Argentina, which has a temperate climate with rainy summers and dry winters.[93]
+Olive trees show a marked preference for calcareous soils, flourishing best on limestone slopes and crags, and coastal climate conditions. They grow in any light soil, even on clay if well drained, but in rich soils, they are predisposed to disease and produce poorer oil than in poorer soil. (This was noted by Pliny the Elder.) Olives like hot weather and sunny positions without any shade, while temperatures below −10 °C (14 °F) may injure even a mature tree. They tolerate drought well, due to their sturdy and extensive root systems. Olive trees can live for several centuries and can remain productive for as long if they are pruned correctly and regularly.
+Only a handful of olive varieties can be used to cross-pollinate. 'Pendolino' olive trees are partially self-fertile, but pollenizers are needed for a large fruit crop. Other compatible olive tree pollinators include 'Leccino' and 'Maurino'. 'Pendolino' olive trees are used extensively as pollinizers in large olive tree groves.
+Olives are propagated by various methods. The preferred ways are cuttings and layers; the tree roots easily in favourable soil and throws up suckers from the stump when cut down. However, yields from trees grown from suckers or seeds are poor; they must be budded or grafted onto other specimens to do well.[95] Branches of various thickness cut into lengths around 1 m (3.3 ft) planted deeply in manured ground soon vegetate. Shorter pieces are sometimes laid horizontally in shallow trenches and, when covered with a few centimetres of soil, rapidly throw up sucker-like shoots. In Greece, grafting the cultivated tree on the wild tree is a common practice. In Italy, embryonic buds, which form small swellings on the stems, are carefully excised and planted under the soil surface, where they soon form a vigorous shoot.
+The olive is also sometimes grown from seed. To facilitate germination, the oily pericarp is first softened by slight rotting, or soaked in hot water or in an alkaline solution.
+In situations where extreme cold has damaged or killed the olive tree, the rootstock can survive and produce new shoots which in turn become new trees. In this way, olive trees can regenerate themselves. In Tuscany in 1985, a very severe frost destroyed many productive, and aged, olive trees and ruined many farmers' livelihoods. However, new shoots appeared in the spring and, once the dead wood was removed, became the basis for new fruit-producing trees. In this way, an olive tree can live for centuries or even millennia.
+Olives grow very slowly, and over many years, the trunk can attain a considerable diameter. A. P. de Candolle recorded one exceeding 10 m (33 ft) in girth. The trees rarely exceed 15 m (49 ft) in height, and are generally confined to much more limited dimensions by frequent pruning.
+Olea europaea is very hardy: drought-, disease- and fire-resistant, it can live to a great age. Its root system is robust and capable of regenerating the tree even if the above-ground structure is destroyed. The older the olive tree, the broader and more gnarled the trunk becomes. Many olive trees in the groves around the Mediterranean are said to be hundreds of years old, while an age of 2,000 years is claimed for a number of individual trees; in some cases, this has been scientifically verified.[96] See paragraph dealing with the topic.
+The crop from old trees is sometimes enormous, but they seldom bear well two years in succession, and in many cases, a large harvest occurs every sixth or seventh season.
+Where the olive is carefully cultivated, as in Languedoc and Provence, the trees are regularly pruned. The pruning preserves the flower-bearing shoots of the preceding year, while keeping the tree low enough to allow the easy gathering of the fruit.
+The spaces between the trees are regularly fertilized.
+Various pathologies can affect olives. The most serious pest is the olive fruit fly (Dacus oleae or Bactrocera oleae) which lays its eggs in the olive most commonly just before it becomes ripe in the autumn. The region surrounding the puncture rots, becomes brown, and takes a bitter taste, making the olive unfit for eating or for oil. For controlling the pest, the practice has been to spray with insecticides (organophosphates, e.g. dimethoate).  Classic organic methods have now been applied such as trapping, applying the bacterium Bacillus thuringiensis, and spraying with kaolin.  Such methods are obligatory for organic olives.
+A fungus, Cycloconium oleaginum, can infect the trees for several successive seasons, causing great damage to plantations. A species of bacterium, Pseudomonas savastanoi pv. oleae,[97] induces tumour growth in the shoots. Certain lepidopterous caterpillars feed on the leaves and flowers.
+Xylella fastidiosa bacteria, which can also infect citrus fruit and vines, has attacked olive trees in the Lecce province, Salento, Southern Italy causing the olive quick decline syndrome (OQDS).[98][99] The main vector is Philaenus spumarius (meadow spittlebug).[100]
+A pest which spreads through olive trees is the black scale bug, a small black scale insect that resembles a small black spot. They attach themselves firmly to olive trees and reduce the quality of the fruit; their main predators are wasps. The curculio beetle eats the edges of leaves, leaving sawtooth damage.[101]
+Rabbits eat the bark of olive trees and can do considerable damage, especially to young trees. If the bark is removed around the entire circumference of a tree, it is likely to die. Voles and mice also do damage by eating the roots of olives.
+At the northern edge of their cultivation zone, for instance in Southern France and north-central Italy, olive trees suffer occasionally from frost. Gales and long-continued rains during the gathering season also cause damage.
+Since its first domestication, O. europaea has been spreading back to the wild from planted groves. Its original wild populations in southern Europe have been largely swamped by feral plants.[102]
+In some other parts of the world where it has been introduced, most notably South Australia, the olive has become a major woody weed that displaces native vegetation. In South Australia, its seeds are spread by the introduced red fox and by many bird species, including the European starling and the native emu, into woodlands, where they germinate and eventually form a dense canopy that prevents regeneration of native trees.[103] As the climate of South Australia is very dry and bushfire prone, the oil-rich feral olive tree substantially increases the fire hazard of native sclerophyll woodlands.[104]
+Olives are harvested in the autumn and winter. More specifically in the Northern Hemisphere, green olives are picked from the end of September to about the middle of November. Blond olives are picked from the middle of October to the end of November, and black olives are collected from the middle of November to the end of January or early February. In southern Europe, harvesting is done for several weeks in winter, but the time varies in each country, and with the season and the cultivar.
+Most olives today are harvested by shaking the boughs or the whole tree. Using olives found lying on the ground can result in poor quality oil, due to damage. Another method involves standing on a ladder and "milking" the olives into a sack tied around the harvester's waist. This method produces high quality oil.[106]  A third method uses a device called an oli-net that wraps around the tree trunk and opens to form an umbrella-like catcher from which workers collect the fruit. Another method uses an electric tool, the oliviera, that has large tongs that spin around quickly, removing fruit from the tree. Olives harvested by this method are used for oil.
+Table olive varieties are more difficult to harvest, as workers must take care not to damage the fruit; baskets that hang around the worker's neck are used. In some places in Italy, Croatia, and Greece, olives are harvested by hand because the terrain is too mountainous for machines. As a result, the fruit is not bruised, which leads to a superior finished product. The method also involves sawing off branches, which is healthy for future production.[80]
+The amount of oil contained in the fruit differs greatly by cultivar; the pericarp is usually 60–70% oil. Typical yields are 1.5–2.2 kg (3.3–4.9 lb) of oil per tree per year.[57]
+Processing olives is done through curing and fermentation or drying in order for them to be edible. Lye and salt brine are used to cure olives from their bitter oleuropein compound. Olives are fermented by yeast and the brine allows bacteria to add flavor and act as a natural preservative by lowering the pH from other bacteria that would lead to spoilage.
+Olives are one of the most extensively cultivated fruit crops in the world.[107] In 2011, about 9.6 million hectares (24 million acres) were planted with olive trees, which is more than twice the amount of land devoted to apples, bananas, or mangoes. Only coconut trees and oil palms command more space.[108] Cultivation area tripled from 2.6 to 7.95 million hectares (6.4 to 19.6 million acres) between 1960 and 1998 and reached a peak of 10 million hectares (25 million acres) in 2008. The 10 largest producing countries, according to the Food and Agriculture Organization, are all located in the Mediterranean region and produce 95% of the world's olives.
+One hundred grams of cured green olives provide 146 calories, are a rich source of vitamin E (25% of the Daily Value, DV), and contain a large amount of sodium (104% DV); other nutrients are insignificant. Green olives are 75% water, 15% fat, 4% carbohydrates and 1% protein (table).
+The polyphenol composition of olive fruits varies during fruit ripening and during processing by fermentation when olives are immersed whole in brine or crushed to produce oil.[110] In raw fruit, total polyphenol contents, as measured by the Folin method, are 117 mg/100 g in black olives and 161 mg/100 g in green olives, compared to 55 and 21 mg/100 g for extra virgin and virgin olive oil, respectively.[110] Olive fruit contains several types of polyphenols, mainly tyrosols, phenolic acids, flavonols and flavones, and for black olives, anthocyanins. The main bitter flavor of olives before curing results from oleuropein and its aglycone which total in content, respectively, 72 and 82 mg/100 g in black olives, and 56 and 59 mg/100 g in green olives.[110]
+During the crushing, kneading and extraction of olive fruit to obtain olive oil, oleuropein, demethyloleuropein and ligstroside are hydrolyzed by endogenous beta-glucosidases to form aldehydic aglycones.
+Polyphenol content also varies with olive cultivar (Spanish Manzanillo highest) and the manner of presentation, with plain olives having higher contents than those that are pitted or stuffed.[111]
+Olive tree pollen is extremely allergenic, with an OPALS allergy scale rating of 10 out of 10.[112] Olea europaea is primarily wind-pollinated,[113] and their light, buoyant pollen is a strong trigger for asthma.[112] One popular variety, "Swan Hill", is widely sold as an "allergy-free" olive tree; however, this variety does bloom and produce allergenic pollen.[112]
+Olive tree trunk
+Olive flowers
+Olivo della Linza. 15th century
+A young olive plant, germinated from a seed
+Cailletier cultivar, with an olive harvest net on the ground, Contes, France
+Olive trees on Shōdo Island, Japan
+Olive grove near Alexandroupolis / Greece

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+The modern Olympic Games or Olympics (French: Jeux olympiques[1][2]) are leading international sporting events featuring summer and winter sports competitions in which thousands of athletes from around the world participate in a variety of competitions. The Olympic Games are considered the world's foremost sports competition with more than 200 nations participating.[3] The Olympic Games are normally held every four years, alternating between the Summer and Winter Games every two years in the four-year period.
+Their creation was inspired by the ancient Olympic Games (Ancient Greek: Ὀλυμπιακοί Ἀγῶνες), which were held in Olympia, Greece, from the 8th century BC to the 4th century AD. Baron Pierre de Coubertin founded the International Olympic Committee (IOC) in 1894, leading to the first modern Games in Athens in 1896. The IOC is the governing body of the Olympic Movement, with the Olympic Charter defining its structure and authority.
+The evolution of the Olympic Movement during the 20th and 21st centuries has resulted in several changes to the Olympic Games. Some of these adjustments include the creation of the Winter Olympic Games for snow and ice sports, the Paralympic Games for athletes with a disability, the Youth Olympic Games for athletes aged 14 to 18, the five Continental games (Pan American, African, Asian, European, and Pacific), and the World Games for sports that are not contested in the Olympic Games. The Deaflympics and Special Olympics are also endorsed by the IOC. The IOC has had to adapt to a variety of economic, political, and technological advancements. The abuse of amateur rules by the Eastern Bloc nations prompted the IOC to shift away from pure amateurism, as envisioned by Coubertin, to allowing participation of professional athletes. The growing importance of mass media created the issue of corporate sponsorship and commercialisation of the Games. World wars led to the cancellation of the 1916, 1940, and 1944 Games. Large-scale boycotts during the Cold War limited participation in the 1980 and 1984 Games,[4] and the 2020 Games were postponed to 2021 due to the COVID-19 pandemic.
+The Olympic Movement consists of international sports federations (IFs), National Olympic Committees (NOCs), and organising committees for each specific Olympic Games. As the decision-making body, the IOC is responsible for choosing the host city for each Games, and organises and funds the Games according to the Olympic Charter. The IOC also determines the Olympic programme, consisting of the sports to be contested at the Games. There are several Olympic rituals and symbols, such as the Olympic flag and torch, as well as the opening and closing ceremonies. Over 14,000 athletes competed at the 2016 Summer Olympics and 2018 Winter Olympics combined, in 35 different sports and over 400 events.[5][6] The first, second, and third-place finishers in each event receive Olympic medals: gold, silver, and bronze, respectively.
+The Games have grown so much that nearly every nation is now represented. This growth has created numerous challenges and controversies, including boycotts, doping, bribery, and a terrorist attack in 1972. Every two years the Olympics and its media exposure provide athletes with the chance to attain national and sometimes international fame. The Games also constitute an opportunity for the host city and country to showcase themselves to the world.
+The Ancient Olympic Games were religious and athletic festivals held every four years at the sanctuary of Zeus in Olympia, Greece. Competition was among representatives of several city-states and kingdoms of Ancient Greece. These Games featured mainly athletic but also combat sports such as wrestling and the pankration, horse and chariot racing events. It has been widely written that during the Games, all conflicts among the participating city-states were postponed until the Games were finished. This cessation of hostilities was known as the Olympic peace or truce.[7] This idea is a modern myth because the Greeks never suspended their wars. The truce did allow those religious pilgrims who were travelling to Olympia to pass through warring territories unmolested because they were protected by Zeus.[8] The origin of the Olympics is shrouded in mystery and legend;[9] one of the most popular myths identifies Heracles and his father Zeus as the progenitors of the Games.[10][11][12] According to legend, it was Heracles who first called the Games "Olympic" and established the custom of holding them every four years.[13] The myth continues that after Heracles completed his twelve labours, he built the Olympic Stadium as an honour to Zeus. Following its completion, he walked in a straight line for 200 steps and called this distance a "stadion" (Greek: στάδιον, Latin: stadium, "stage"), which later became a unit of distance. The most widely accepted inception date for the Ancient Olympics is 776 BC; this is based on inscriptions, found at Olympia, listing the winners of a footrace held every four years starting in 776 BC.[14] The Ancient Games featured running events, a pentathlon (consisting of a jumping event, discus and javelin throws, a foot race, and wrestling), boxing, wrestling, pankration, and equestrian events.[15][16] Tradition has it that Coroebus, a cook from the city of Elis, was the first Olympic champion.[17]
+The Olympics were of fundamental religious importance, featuring sporting events alongside ritual sacrifices honouring both Zeus (whose famous statue by Phidias stood in his temple at Olympia) and Pelops, divine hero and mythical king of Olympia. Pelops was famous for his chariot race with King Oenomaus of Pisatis.[18] The winners of the events were admired and immortalised in poems and statues.[19] The Games were held every four years, and this period, known as an Olympiad, was used by Greeks as one of their units of time measurement. The Games were part of a cycle known as the Panhellenic Games, which included the Pythian Games, the Nemean Games, and the Isthmian Games.[20]
+The Olympic Games reached their zenith in the 6th and 5th centuries BC, but then gradually declined in importance as the Romans gained power and influence in Greece. While there is no scholarly consensus as to when the Games officially ended, the most commonly held date is 393 AD, when the emperor Theodosius I decreed that all pagan cults and practices be eliminated.[21] Another date commonly cited is 426 AD, when his successor, Theodosius II, ordered the destruction of all Greek temples.[22]
+Various uses of the term "Olympic" to describe athletic events in the modern era have been documented since the 17th century. The first such event was the Cotswold Games or "Cotswold Olimpick Games", an annual meeting near Chipping Campden, England, involving various sports. It was first organised by the lawyer Robert Dover between 1612 and 1642, with several later celebrations leading up to the present day. The British Olympic Association, in its bid for the 2012 Olympic Games in London, mentioned these games as "the first stirrings of Britain's Olympic beginnings".[23]
+L'Olympiade de la République, a national Olympic festival held annually from 1796 to 1798 in Revolutionary France also attempted to emulate the ancient Olympic Games.[24] The competition included several disciplines from the ancient Greek Olympics. The 1796 Games also marked the introduction of the metric system into sport.[24]
+In 1834 and 1836, Olympic games were held in Ramlösa [sv] (Olympiska spelen i Ramlösa), and an additional in Stockholm, Sweden in 1843, all organised by Gustaf Johan Schartau and others. At most 25,000 spectators saw the games.[25]
+In 1850, an Olympian Class was started by William Penny Brookes at Much Wenlock, in Shropshire, England. In 1859, Brookes changed the name to the Wenlock Olympian Games. This annual sports festival continues to this day.[26] The Wenlock Olympian Society was founded by Brookes on 15 November 1860.[27]
+Between 1862 and 1867, Liverpool held an annual Grand Olympic Festival. Devised by John Hulley and Charles Melly, these games were the first to be wholly amateur in nature and international in outlook, although only 'gentlemen amateurs' could compete.[28][29] The programme of the first modern Olympiad in Athens in 1896 was almost identical to that of the Liverpool Olympics.[30] In 1865 Hulley, Brookes and E.G. Ravenstein founded the National Olympian Association in Liverpool, a forerunner of the British Olympic Association. Its articles of foundation provided the framework for the International Olympic Charter.[31] In 1866, a national Olympic Games in Great Britain was organised at London's Crystal Palace.[32]
+Greek interest in reviving the Olympic Games began with the Greek War of Independence from the Ottoman Empire in 1821. It was first proposed by poet and newspaper editor Panagiotis Soutsos in his poem "Dialogue of the Dead", published in 1833.[33] Evangelos Zappas, a wealthy Greek-Romanian philanthropist, first wrote to King Otto of Greece, in 1856, offering to fund a permanent revival of the Olympic Games.[34] Zappas sponsored the first Olympic Games in 1859, which was held in an Athens city square. Athletes participated from Greece and the Ottoman Empire. Zappas funded the restoration of the ancient Panathenaic Stadium so that it could host all future Olympic Games.[34]
+The stadium hosted Olympics in 1870 and 1875.[35] Thirty thousand spectators attended that Games in 1870, though no official attendance records are available for the 1875 Games.[36] In 1890, after attending the Olympian Games of the Wenlock Olympian Society, Baron Pierre de Coubertin was inspired to found the International Olympic Committee (IOC).[37] Coubertin built on the ideas and work of Brookes and Zappas with the aim of establishing internationally rotating Olympic Games that would occur every four years.[37] He presented these ideas during the first Olympic Congress of the newly created International Olympic Committee. This meeting was held from 16 to 23 June 1894, at the University of Paris. On the last day of the Congress, it was decided that the first Olympic Games to come under the auspices of the IOC would take place in Athens in 1896.[38] The IOC elected the Greek writer Demetrius Vikelas as its first president.[39]
+The first Games held under the auspices of the IOC was hosted in the Panathenaic Stadium in Athens in 1896. The Games brought together 14 nations and 241 athletes who competed in 43 events.[40] Zappas and his cousin Konstantinos Zappas had left the Greek government a trust to fund future Olympic Games. This trust was used to help finance the 1896 Games.[41][42][43] George Averoff contributed generously for the refurbishment of the stadium in preparation for the Games.[44] The Greek government also provided funding, which was expected to be recouped through the sale of tickets and from the sale of the first Olympic commemorative stamp set.[44]
+Greek officials and the public were enthusiastic about the experience of hosting an Olympic Games. This feeling was shared by many of the athletes, who even demanded that Athens be the permanent Olympic host city. The IOC intended for subsequent Games to be rotated to various host cities around the world. The second Olympics was held in Paris.[45]
+After the success of the 1896 Games, the Olympics entered a period of stagnation that threatened their survival. The Olympic Games held at the Paris Exposition in 1900 and the Louisiana Purchase Exposition at St. Louis in 1904 were side shows. This period was a low point for the Olympic Movement.[46] The Games rebounded when the 1906 Intercalated Games (so-called because they were the second Games held within the third Olympiad) were held in Athens. These Games were, but are not now, officially recognised by the IOC and no Intercalated Games have been held since. The Games attracted a broad international field of participants and generated great public interest. This marked the beginning of a rise in both the popularity and the size of the Olympics.[47]
+The Winter Olympics was created to feature snow and ice sports that were logistically impossible to hold during the Summer Games. Figure skating (in 1908 and 1920) and ice hockey (in 1920) were featured as Olympic events at the Summer Olympics. The IOC desired to expand this list of sports to encompass other winter activities. At the 1921 Olympic Congress in Lausanne, it was decided to hold a winter version of the Olympic Games. A winter sports week (it was actually 11 days) was held in 1924 in Chamonix, France, in connection with the Paris Games held three months later; this event became the first Winter Olympic Games.[48] Although it was intended that the same country host both the Winter and Summer Games in a given year, this idea was quickly abandoned. The IOC mandated that the Winter Games be celebrated every four years in the same year as their summer counterpart.[49] This tradition was upheld through the 1992 Games in Albertville, France; after that, beginning with the 1994 Games, the Winter Olympics were held every four years, two years after each Summer Olympics.[50]
+In 1948, Sir Ludwig Guttmann, determined to promote the rehabilitation of soldiers after World War II, organised a multi-sport event between several hospitals to coincide with the 1948 London Olympics. Guttmann's event, known then as the Stoke Mandeville Games, became an annual sports festival. Over the next twelve years, Guttmann and others continued their efforts to use sports as an avenue to healing. For the 1960 Olympic Games in Rome, Guttmann brought 400 athletes to compete in the "Parallel Olympics", which became known as the first Paralympics. Since then, the Paralympics have been held in every Olympic year. Since the 1988 Summer Olympics in Seoul, South Korea, the host city for the Olympics has also played host to the Paralympics.[51][D] In 2001 the International Olympic Committee (IOC) and the International Paralympic Committee (IPC) signed an agreement guaranteeing that host cities would be contracted to manage both the Olympic and Paralympic Games.[52][53] The agreement came into effect at the 2008 Summer Games in Beijing, and at the 2010 Winter Games in Vancouver.Two years before the 2012 Summer Games,the chairman of the LOCOG, Lord Coe, said about the Paralympics and Olympics in London that,
+We want to change public attitudes towards disability, celebrate the excellence of Paralympic sport and to enshrine from the very outset that the two Games are an integrated whole.[54]
+In 2010, the Olympic Games were complemented by the Youth Games, which give athletes between the ages of 14 and 18 the chance to compete. The Youth Olympic Games were conceived by IOC president Jacques Rogge in 2001 and approved during the 119th Congress of the IOC.[55][56] The first Summer Youth Games were held in Singapore from 14–26 August 2010, while the inaugural Winter Games were hosted in Innsbruck, Austria, two years later.[57] These Games will be shorter than the senior Games; the summer version will last twelve days, while the winter version will last nine days.[58] The IOC allows 3,500 athletes and 875 officials to participate at the Summer Youth Games, and 970 athletes and 580 officials at the Winter Youth Games.[59][60] The sports to be contested will coincide with those scheduled for the senior Games, however there will be variations on the sports including mixed NOC and mixed gender teams as well as a reduced number of disciplines and events.[61]
+From 241 participants representing 14 nations in 1896, the Games have grown to about 10,500 competitors from 204 nations at the 2012 Summer Olympics.[62] The scope and scale of the Winter Olympics is smaller. For example, Sochi hosted 2,873 athletes from 88 nations competing in 98 events during the 2014 Winter Olympics. During the Games most athletes and officials are housed in the Olympic Village. This village is intended to be a self-contained home for all the Olympic participants, and is furnished with cafeterias, health clinics, and locations for religious expression.[63]
+The IOC allowed the formation of National Olympic Committees representing nations that did not meet the strict requirements for political sovereignty that other international organisations demand. As a result, colonies and dependencies are permitted to compete at Olympic Games. Examples of this include territories such as Puerto Rico, Bermuda, and Hong Kong, all of which compete as separate nations despite being legally a part of another country.[64] The current version of the Charter allows for the establishment of new National Olympic Committees to represent nations which qualify as "an independent State recognised by the international community".[65] Therefore, it did not allow the formation of National Olympic Committees for Sint Maarten and Curaçao when they gained the same constitutional status as Aruba in 2010, although the IOC had recognised the Aruban Olympic Committee in 1986.[66][67] After 2012, Netherlands Antilles athletes can choose to represent either the Netherlands or Aruba.[68]
+The Oxford Olympics Study 2016 found that sports-related costs for the Summer Games since 1960 were on average US$5.2 billion and for the Winter Games $3.1 billion. This does not include wider infrastructure costs like roads, urban rail, and airports, which often cost as much or more than the sports-related costs. The most expensive Summer Games were Beijing 2008 at US$40–44[69] billion and the most expensive Winter Games were Sochi 2014 at US$51 billion.[70][71] As of 2016, costs per athlete were, on average, US$599,000 for the Summer Games and $1.3 million for the Winter Games. For London 2012, cost per athlete was $1.4 million; for Sochi 2014, $7.9 million.[71]
+Where ambitious construction for the 1976 games in Montreal and 1980 games in Moscow had saddled organisers with expenses greatly in excess of revenues, 1984 host Los Angeles strictly controlled expenses by using existing facilities that were paid for by corporate sponsors. The Olympic Committee led by Peter Ueberroth used some of the profits to endow the LA84 Foundation to promote youth sports in Southern California, educate coaches and maintain a sports library. The 1984 Summer Olympics are often considered the most financially successful modern Olympics and a model for future Games.[72]
+Budget overruns are common for the Games. Average overrun for Games since 1960 is 156% in real terms,[73] which means that actual costs turned out to be on average 2.56 times the budget that was estimated at the time of winning the bid to host the Games. Montreal 1976 had the highest cost overrun for Summer Games, and for any Games, at 720%; Lake Placid 1980 had the highest cost overrun for Winter Games, at 324%. London 2012 had a cost overrun of 76%, Sochi 2014 of 289%.[71]
+Many economists are sceptical about the economic benefits of hosting the Olympic Games, emphasising that such "mega-events" often have large costs while yielding relatively few tangible benefits in the long run.[74] Conversely hosting (or even bidding for) the Olympics appears to increase the host country's exports, as the host or candidate country sends a signal about trade openness when bidding to host the Games.[75] Moreover, research suggests that hosting the Summer Olympics has a strong positive effect on the philanthropic contributions of corporations headquartered in the host city, which seems to benefit the local nonprofit sector. This positive effect begins in the years leading up to the Games and might persist for several years afterwards, although not permanently. This finding suggests that hosting the Olympics might create opportunities for cities to influence local corporations in ways that benefit the local nonprofit sector and civil society.[76]
+The Games have also had significant negative effects on host communities; for example, the Centre on Housing Rights and Evictions reports that the Olympics displaced more than two million people over two decades, often disproportionately affecting disadvantaged groups.[77] The 2014 Winter Olympics in Sochi were the most expensive Olympic Games in history, costing in excess of US$50 billion. According to a report by the European Bank for Reconstruction and Development that was released at the time of the games, this cost will not boost Russia's national economy, but may attract business to Sochi and the southern Krasnodar region of Russia in the future as a result of improved services.[78] But by December 2014, The Guardian stated that Sochi "now feels like a ghost town", citing the spread-out nature of the stadiums and arenas, the still-unfinished construction, and the overall effects of Russia's political and economic turmoil.[79] Furthermore, at least four cities withdrew their bids for the 2022 Winter Olympics, citing the high costs or the lack of local support,[80] resulting in only a two-city race between Almaty, Kazakhstan and Beijing, China. Thus in July 2016, The Guardian stated that the biggest threat to the future of the Olympics is that very few cities want to host them.[81] Bidding for the 2024 Summer Olympics also became a two-city race between Paris and Los Angeles, so the IOC took the unusual step of simultaneously awarding both the 2024 Games to Paris and the 2028 Games to Los Angeles.[82] The 2028 Los Angeles bid was praised by the IOC for using a record-breaking number of existing and temporary facilities and relying on corporate money.[83]
+The Olympic Movement encompasses a large number of national and international sporting organisations and federations, recognised media partners, as well as athletes, officials, judges, and every other person and institution that agrees to abide by the rules of the Olympic Charter.[84] As the umbrella organisation of the Olympic Movement, the International Olympic Committee (IOC) is responsible for selecting the host city, overseeing the planning of the Olympic Games, updating and approving the sports program, and negotiating sponsorship and broadcasting rights.[85]
+The Olympic Movement is made of three major elements:
+French and English are the official languages of the Olympic Movement. The other language used at each Olympic Games is the language of the host country (or languages, if a country has more than one official language apart from French or English). Every proclamation (such as the announcement of each country during the parade of nations in the opening ceremony) is spoken in these three (or more) languages, or the main two depending on whether the host country is an English or French speaking country: French is always spoken first, followed by an English translation, and then the dominant language of the host nation (when this is not English or French).[89]
+The IOC has often been criticised for being an intractable organisation, with several members on the committee for life. The presidential terms of Avery Brundage and Juan Antonio Samaranch were especially controversial. Brundage fought strongly for amateurism and against the commercialization of the Olympic Games, even as these stands came to be seen as incongruous with the realities of modern sports. The advent of the state-sponsored athlete of the Eastern Bloc countries further eroded the ideology of the pure amateur, as it put self-financed amateurs of the Western countries at a disadvantage.[90] Brundage was accused of both racism, for resisting exclusion of apartheid South Africa, and antisemitism.[91] Under the Samaranch presidency, the office was accused of both nepotism and corruption.[92] Samaranch's ties with the Franco regime in Spain were also a source of criticism.[93]
+In 1998, it was reported that several IOC members had taken gifts from members of the Salt Lake City bid committee for the hosting of the 2002 Winter Olympics. Soon four independent investigations were underway: by the IOC, the United States Olympic Committee (USOC), the SLOC, and the United States Department of Justice. Although nothing strictly illegal had been done, it was felt that the acceptance of the gifts was morally dubious. As a result of the investigation, ten members of the IOC were expelled and another ten were sanctioned.[94] Stricter rules were adopted for future bids, and caps were put into place as to how much IOC members could accept from bid cities. Additionally, new term and age limits were put into place for IOC membership, and fifteen former Olympic athletes were added to the committee. Nevertheless, from sporting and business standpoints, the 2002 Olympics were one of the most successful Winter Olympiads in history; records were set in both the broadcasting and marketing programs. Over 2 billion viewers watched more than 13 billion viewer-hours.[95] The Games were also financially successful raising more money with fewer sponsors than any prior Olympic Games, which left SLOC with a surplus of $40 million. The surplus was used to create the Utah Athletic Foundation, which maintains and operates many of the remaining Olympic venues.[95]
+The 1999, it was reported that the Nagano Olympic bid committee had spent approximately $14 million to entertain the 62 IOC members and many of their companions. The precise figures are unknown since Nagano, after the IOC asked that the entertainment expenditures not be made public, destroyed the financial records.[96][97]
+A BBC documentary entitled Panorama: Buying the Games, aired in August 2004, investigated the taking of bribes in the bidding process for the 2012 Summer Olympics.[98] The documentary claimed it was possible to bribe IOC members into voting for a particular candidate city. After being narrowly defeated in their bid for the 2012 Summer Games,[99] Parisian mayor Bertrand Delanoë specifically accused the British prime minister Tony Blair and the London Bid Committee (headed by former Olympic champion Sebastian Coe) of breaking the bid rules. He cited French president Jacques Chirac as a witness; Chirac gave guarded interviews regarding his involvement.[100] The allegation was never fully explored. The Turin bid for the 2006 Winter Olympics was also shrouded in controversy. A prominent IOC member, Marc Hodler, strongly connected with the rival bid of Sion, Switzerland, alleged bribery of IOC officials by members of the Turin Organising Committee. These accusations led to a wide-ranging investigation. The allegations also served to sour many IOC members against Sion's bid and potentially helped Turin to capture the host city nomination.[101]
+In July 2012, the Anti-Defamation League called the continued refusal by the International Olympic Committee to hold a moment of silence at the opening ceremony for the eleven Israeli athletes killed by Palestinian terrorists at the 1972 Munich Olympics, "a continuing stubborn insensitivity and callousness to the memory of the murdered Israeli athletes."[102]
+The Olympics have been commercialised to various degrees since the initial 1896 Summer Olympics in Athens, when a number of companies paid for advertising,[103] including Kodak.[104][105] In 1908, Oxo, Odol mouthwash and Indian Foot Powder became official sponsors of the London Olympic Games.[106][107][108] Coca-Cola sponsored the 1928 Summer Olympics, and has subsequently remained a sponsor to the current time.[103] Before the IOC took control of sponsorship, national organising committees were responsible for negotiating their own contracts for sponsorship and the use of the Olympic symbols.[109]
+The IOC originally resisted funding by corporate sponsors. It was not until the retirement of IOC President Avery Brundage, in 1972, that the IOC began to explore the potential of the television medium and the lucrative advertising markets available to them.[109] Under the leadership of Juan Antonio Samaranch the Games began to shift toward international sponsors who sought to link their products to the Olympic brand.[110]
+During the first half of the 20th century, the IOC ran on a small budget.[110][111] As president of the IOC from 1952 to 1972, Avery Brundage rejected all attempts to link the Olympics with commercial interest.[109] Brundage believed the lobby of corporate interests would unduly impact the IOC's decision-making.[109] Brundage's resistance to this revenue stream meant the IOC left organising committees to negotiate their own sponsorship contracts and use the Olympic symbols.[109] When Brundage retired the IOC had US$2 million in assets; eight years later the IOC coffers had swelled to US$45 million.[109] This was primarily due to a shift in ideology toward expansion of the Games through corporate sponsorship and the sale of television rights.[109] When Juan Antonio Samaranch was elected IOC president in 1980 his desire was to make the IOC financially independent.[111]
+The 1984 Summer Olympics became a watershed moment in Olympic history. The Los Angeles-based organising committee, led by Peter Ueberroth, was able to generate a surplus of US$225 million, which was an unprecedented amount at that time.[112] The organising committee had been able to create such a surplus in part by selling exclusive sponsorship rights to select companies.[112] The IOC sought to gain control of these sponsorship rights. Samaranch helped to establish The Olympic Programme (TOP) in 1985, in order to create an Olympic brand.[110] Membership in TOP was, and is, very exclusive and expensive. Fees cost US$50 million for a four-year membership.[111] Members of TOP received exclusive global advertising rights for their product category, and use of the Olympic symbol, the interlocking rings, in their publications and advertisements.[113]
+The 1936 Summer Olympics in Berlin were the first Games to be broadcast on television, though only to local audiences.[114] The 1956 Winter Olympics were the first internationally televised Olympic Games,[115] and the following Winter Games had their broadcasting rights sold for the first time to specialised television broadcasting networks—CBS paid US$394,000 for the American rights.[116][110] In the following decades the Olympics became one of the ideological fronts of the Cold War, and the IOC wanted to take advantage of this heightened interest via the broadcast medium.[116] The sale of broadcast rights enabled the IOC to increase the exposure of the Olympic Games, thereby generating more interest, which in turn created more appeal to advertisers time on television. This cycle allowed the IOC to charge ever-increasing fees for those rights.[116] For example, CBS paid US$375 million for the American broadcast rights of the 1998 Nagano Games,[117] while NBC spent US$3.5 billion for the American rights of all the Olympic Games from 2000 to 2012.[110] In 2011, NBC agreed to a $4.38 billion contract with the International Olympic Committee to broadcast the Olympics through the 2020 games, the most expensive television rights deal in Olympic history.[118] NBC then agreed to a $7.75 billion contract extension on May 7, 2014, to air the Olympics through the 2032 games.[119] NBC also acquired the American television rights to the Youth Olympic Games, beginning in 2014,[120] and the Paralympic Games.[121] More than half of the Olympic Committee's global sponsors are American companies,[122] and NBC is one of the major sources of revenue for the IOC.[122]
+Viewership increased exponentially from the 1960s until the end of the century. This was due to the use of satellites to broadcast live television worldwide in 1964, and the introduction of colour television in 1968.[123] Global audience estimates for the 1968 Mexico City Games was 600 million, whereas at the Los Angeles Games of 1984, the audience numbers had increased to 900 million; that number swelled to 3.5 billion by the 1992 Summer Olympics in Barcelona.[124][125][126][127][128] With such high costs charged to broadcast the Games, the added pressure of the internet, and increased competition from cable, the television lobby demanded concessions from the IOC to boost ratings. The IOC responded by making a number of changes to the Olympic program. At the Summer Games, the gymnastics competition was expanded from seven to nine nights, and a Champions Gala was added to draw greater interest.[129] The IOC also expanded the swimming and diving programs, both popular sports with a broad base of television viewers.[129] Due to the substantial fees NBC has paid for rights to the Olympics, the IOC has allowed NBC to have influence on event scheduling to maximize U.S. television ratings when possible.[130][127][131][132]
+The sale of the Olympic brand has been controversial. The argument is that the Games have become indistinguishable from any other commercialised sporting spectacle.[113][133][133] Another criticism is that the Games are funded by host cities and national governments; the IOC incurs none of the cost, yet controls all the rights and profits from the Olympic symbols. The IOC also takes a percentage of all sponsorship and broadcast income.[113] Host cities continue to compete ardently for the right to host the Games, even though there is no certainty that they will earn back their investments.[134] Research has shown that trade is around 30 percent higher for countries that have hosted the Olympics.[135]
+The Olympic Movement uses symbols to represent the ideals embodied in the Olympic Charter. The Olympic symbol, better known as the Olympic rings, consists of five intertwined rings and represents the unity of the five inhabited continents (Africa, the Americas (when considered one continent), Asia, Europe, and Oceania). The coloured version of the rings—blue, yellow, black, green, and red—over a white field forms the Olympic flag. These colours were chosen because every nation had at least one of them on its national flag. The flag was adopted in 1914 but flown for the first time only at the 1920 Summer Olympics in Antwerp, Belgium. It has since been hoisted during each celebration of the Games.[136][137]
+The Olympic motto, Citius, Altius, Fortius, a Latin expression meaning "Faster, Higher, Stronger" was proposed by Pierre de Coubertin in 1894 and has been official since 1924. The motto was coined by Coubertin's friend, the Dominican priest Henri Didon OP, for a Paris youth gathering of 1891.[138]
+Coubertin's Olympic ideals are expressed in the Olympic creed:
+The most important thing in the Olympic Games is not to win but to take part, just as the most important thing in life is not the triumph but the struggle. The essential thing is not to have conquered but to have fought well.[136]
+Months before each Games, the Olympic Flame is lit at the Temple of Hera in Olympia in a ceremony that reflects ancient Greek rituals. A female performer, acting as a priestess joined by ten female performers as Vestal Virgins, ignites a torch by placing it inside a parabolic mirror which focuses the sun's rays; she then lights the torch of the first relay bearer, thus initiating the Olympic torch relay that will carry the flame to the host city's Olympic stadium, where it plays an important role in the opening ceremony.[139] Though the flame has been an Olympic symbol since 1928, the torch relay was only introduced at the 1936 Summer Games to promote the Third Reich.[136][140]
+The Olympic mascot, an animal or human figure representing the cultural heritage of the host country, was introduced in 1968. It has played an important part of the Games' identity promotion since the 1980 Summer Olympics, when the Soviet bear cub Misha reached international stardom. The mascot of the Summer Olympics in London was named Wenlock after the town of Much Wenlock in Shropshire. Much Wenlock still hosts the Wenlock Olympian Games, which were an inspiration to Pierre de Coubertin for the Olympic Games.[141]
+As mandated by the Olympic Charter, various elements frame the opening ceremony of the Olympic Games. This ceremony takes place before the events have occurred.[142][143] Most of these rituals were established at the 1920 Summer Olympics in Antwerp.[144] The ceremony typically starts with the entrance of the president of the host country followed by the hoisting of the host country's flag and a performance of its national anthem.[142][143] The host nation then presents artistic displays of music, singing, dance, and theatre representative of its culture.[144] The artistic presentations have grown in scale and complexity as successive hosts attempt to provide a ceremony that outlasts its predecessor's in terms of memorability. The opening ceremony of the Beijing Games reportedly cost $100 million, with much of the cost incurred in the artistic segment.[145]
+After the artistic portion of the ceremony, the athletes parade into the stadium grouped by nation. Greece is traditionally the first nation to enter in order to honour the origins of the Olympics. Nations then enter the stadium alphabetically according to the host country's chosen language, with the host country's athletes being the last to enter. During the 2004 Summer Olympics, which was hosted in Athens, Greece, the Greek flag entered the stadium first, while the Greek delegation entered last. Speeches are given, formally opening the Games. Finally, the Olympic torch is brought into the stadium and passed on until it reaches the final torch carrier, often a successful Olympic athlete from the host nation, who lights the Olympic flame in the stadium's cauldron.[142][143]
+The closing ceremony of the Olympic Games takes place after all sporting events have concluded. Flag-bearers from each participating country enter the stadium, followed by the athletes who enter together, without any national distinction.[146] Three national flags are hoisted while the corresponding national anthems are played: the flag of the current host country; the flag of Greece, to honour the birthplace of the Olympic Games; and the flag of the country hosting the next Summer or Winter Olympic Games.[146] The president of the organising committee and the IOC president make their closing speeches, the Games are officially closed, and the Olympic flame is extinguished.[147] In what is known as the Antwerp Ceremony, the mayor of the city that organised the Games transfers a special Olympic flag to the president of the IOC, who then passes it on to the mayor of the city hosting the next Olympic Games.[148] The next host nation then also briefly introduces itself with artistic displays of dance and theatre representative of its culture.[146]
+As is customary, the last medal presentation of the Games is held as part of the closing ceremony. Typically, the marathon medals are presented at the Summer Olympics,[146][149] while the cross-country skiing mass start medals are awarded at the Winter Olympics.[150]
+A medal ceremony is held after each Olympic event is concluded. The winner, second and third-place competitors or teams stand on top of a three-tiered rostrum to be awarded their respective medals.[151] After the medals are given out by an IOC member, the national flags of the three medallists are raised while the national anthem of the gold medallist's country plays.[152] Volunteering citizens of the host country also act as hosts during the medal ceremonies, as they aid the officials who present the medals and act as flag-bearers.[153] While in the Summer Olympics this ceremony is held on the ground where the event is played,[154] in the Winter Games it is usually held in a special "plaza".[155]
+The Olympic Games programme consists of 35 sports, 30 disciplines and 408 events. For example, wrestling is a Summer Olympic sport, comprising two disciplines: Greco-Roman and Freestyle. It is further broken down into fourteen events for men and four events for women, each representing a different weight class.[156] The Summer Olympics programme includes 26 sports, while the Winter Olympics programme features 15 sports.[157] Athletics, swimming, fencing, and artistic gymnastics are the only summer sports that have never been absent from the Olympic programme. Cross-country skiing, figure skating, ice hockey, Nordic combined, ski jumping, and speed skating have been featured at every Winter Olympics programme since its inception in 1924. Current Olympic sports, like badminton, basketball, and volleyball, first appeared on the programme as demonstration sports, and were later promoted to full Olympic sports. Some sports that were featured in earlier Games were later dropped from the programme.[158]
+Olympic sports are governed by international sports federations (IFs) recognised by the IOC as the global supervisors of those sports. There are 35 federations represented at the IOC.[159] There are sports recognised by the IOC that are not included on the Olympic program. These sports are not considered Olympic sports, but they can be promoted to this status during a programme revision that occurs in the first IOC session following a celebration of the Olympic Games.[160][161] During such revisions, sports can be excluded or included in the programme on the basis of a two-thirds majority vote of the members of the IOC.[162] There are recognised sports that have never been on an Olympic programme in any capacity, including chess and surfing.[163]
+In October and November 2004, the IOC established an Olympic Programme Commission, which was tasked with reviewing the sports on the Olympic programme and all non-Olympic recognised sports. The goal was to apply a systematic approach to establishing the Olympic programme for each celebration of the Games.[164] The commission formulated seven criteria to judge whether a sport should be included on the Olympic programme.[164] These criteria are history and tradition of the sport, universality, popularity of the sport, image, athletes' health, development of the International Federation that governs the sport, and costs of holding the sport.[164] From this study five recognised sports emerged as candidates for inclusion at the 2012 Summer Olympics: golf, karate, rugby sevens, roller sports and squash.[164] These sports were reviewed by the IOC Executive Board and then referred to the General Session in Singapore in July 2005. Of the five sports recommended for inclusion only two were selected as finalists: karate and squash.[164] Neither sport attained the required two-thirds vote and consequently they were not promoted to the Olympic programme.[164] In October 2009 the IOC voted to instate golf and rugby sevens as Olympic sports for the 2016 and 2020 Summer Olympic Games.[165]
+The 114th IOC Session, in 2002, limited the Summer Games programme to a maximum of 28 sports, 301 events, and 10,500 athletes.[164] Three years later, at the 117th IOC Session, the first major programme revision was performed, which resulted in the exclusion of baseball and softball from the official programme of the 2012 London Games. Since there was no agreement in the promotion of two other sports, the 2012 programme featured just 26 sports.[164] The 2016 and 2020 Games will return to the maximum of 28 sports given the addition of rugby and golf.[165]
+The ethos of the aristocracy as exemplified in the English public school greatly influenced Pierre de Coubertin.[166] The public schools subscribed to the belief that sport formed an important part of education, an attitude summed up in the saying mens sana in corpore sano, a sound mind in a sound body. In this ethos, a gentleman was one who became an all-rounder, not the best at one specific thing. There was also a prevailing concept of fairness, in which practising or training was considered tantamount to cheating.[166] Those who practised a sport professionally were considered to have an unfair advantage over those who practised it merely as a hobby.[166]
+The exclusion of professionals caused several controversies throughout the history of the modern Olympics. The 1912 Olympic pentathlon and decathlon champion Jim Thorpe was stripped of his medals when it was discovered that he had played semi-professional baseball before the Olympics. His medals were posthumously restored by the IOC in 1983 on compassionate grounds.[167] Swiss and Austrian skiers boycotted the 1936 Winter Olympics in support of their skiing teachers, who were not allowed to compete because they earned money with their sport and were thus considered professionals.[168]
+As class structure evolved through the 20th century, the definition of the amateur athlete as an aristocratic gentleman became outdated.[166] The advent of the state-sponsored "full-time amateur athlete" of the Eastern Bloc countries further eroded the ideology of the pure amateur, as it put the self-financed amateurs of the Western countries at a disadvantage.[169] Beginning in the 1970s, amateurism requirements were gradually phased out of the Olympic Charter. After the 1988 Games, the IOC decided to make all professional athletes eligible for the Olympics, subject to the approval of the IFs.[170]
+Near the end of the 1960s, the Canadian Amateur Hockey Association (CAHA) felt their amateur players could no longer be competitive against the Soviet team's full-time athletes and the other constantly improving European teams. They pushed for the ability to use players from professional leagues but met opposition from the IIHF and IOC. At the IIHF Congress in 1969, the IIHF decided to allow Canada to use nine non-NHL professional hockey players[171] at the 1970 World Championships in Montreal and Winnipeg, Manitoba, Canada.[172] The decision was reversed in January 1970 after Brundage said that ice hockey's status as an Olympic sport would be in jeopardy if the change was made.[171] In response, Canada withdrew from international ice hockey competition and officials stated that they would not return until "open competition" was instituted.[171][173] Günther Sabetzki became president of the IIHF in 1975 and helped to resolve the dispute with the CAHA. In 1976, the IIHF agreed to allow "open competition" between all players in the World Championships. However, NHL players were still not allowed to play in the Olympics until 1988, because of the IOC's amateur-only policy.[174]
+Greece, Australia, France, and United Kingdom are the only countries to be represented at every Olympic Games since their inception in 1896. While countries sometimes miss an Olympics due to a lack of qualified athletes, some choose to boycott a celebration of the Games for various reasons. The Olympic Council of Ireland boycotted the 1936 Berlin Games, because the IOC insisted its team needed to be restricted to the Irish Free State rather than representing the entire island of Ireland.[175]
+There were three boycotts of the 1956 Melbourne Olympics: the Netherlands, Spain, and Switzerland refused to attend because of the repression of the Hungarian uprising by the Soviet Union, but did send an equestrian delegation to Stockholm; Cambodia, Egypt, Iraq, and Lebanon boycotted the Games because of the Suez Crisis; and the People's Republic of China boycotted the Games due to the participation of the Republic of China, composed of athletes coming from Taiwan.[176]
+In 1972 and 1976 a large number of African countries threatened the IOC with a boycott to force them to ban South Africa and Rhodesia, because of their segregationist rule. New Zealand was also one of the African boycott targets, because its national rugby union team had toured apartheid-ruled South Africa. The IOC conceded in the first two cases, but refused to ban New Zealand on the grounds that rugby was not an Olympic sport.[177] Fulfilling their threat, twenty African countries were joined by Guyana and Iraq in a withdrawal from the Montreal Games, after a few of their athletes had already competed.[177][178]
+The Republic of China (Taiwan) was excluded from the 1976 Games by order of Pierre Elliott Trudeau, the prime minister of Canada. Trudeau's action was widely condemned as having brought shame on Canada for having succumbed to political pressure to keep the Chinese delegation from competing under its name.[179] The ROC refused a proposed compromise that would have still allowed them to use the ROC flag and anthem as long as the name was changed.[180] Athletes from Taiwan did not participate again until 1984, when they returned under the name of Chinese Taipei and with a special flag and anthem.[181]
+In 1980 and 1984, the Cold War opponents boycotted each other's Games. The United States and sixty-five other countries boycotted the Moscow Olympics in 1980 because of the Soviet invasion of Afghanistan. This boycott reduced the number of nations participating to 80, the lowest number since 1956.[182] The Soviet Union and 15 other nations countered by boycotting the Los Angeles Olympics of 1984. Although a boycott led by the Soviet Union depleted the field in certain sports, 140 National Olympic Committees took part, which was a record at the time.[4] The fact that Romania, a Warsaw Pact country, opted to compete despite Soviet demands led to a warm reception of the Romanian team by the United States. When the Romanian athletes entered during the opening ceremonies, they received a standing ovation from the spectators, which comprised mostly U.S. citizens. The boycotting nations of the Eastern Bloc staged their own alternate event, the Friendship Games, in July and August.[183][184]
+There had been growing calls for boycotts of Chinese goods and the 2008 Olympics in Beijing in protest of China's human rights record, and in response to Tibetan disturbances. Ultimately, no nation supported a boycott.[185][186] In August 2008, the government of Georgia called for a boycott of the 2014 Winter Olympics, set to be held in Sochi, Russia, in response to Russia's participation in the 2008 South Ossetia war.[187][188]
+The Olympic Games have been used as a platform to promote political ideologies almost from its inception. Nazi Germany wished to portray the National Socialist Party as benevolent and peace-loving when they hosted the 1936 Games, though they used the Games to display Aryan superiority.[189] Germany was the most successful nation at the Games, which did much to support their allegations of Aryan supremacy, but notable victories by African American Jesse Owens, who won four gold medals, and Hungarian Jew Ibolya Csák, blunted the message.[190] The Soviet Union did not participate until the 1952 Summer Olympics in Helsinki. Instead, starting in 1928, the Soviets organised an international sports event called Spartakiads. During the interwar period of the 1920s and 1930s, communist and socialist organisations in several countries, including the United States, attempted to counter what they called the "bourgeois" Olympics with the Workers Olympics.[191][192] It was not until the 1956 Summer Games that the Soviets emerged as a sporting superpower and, in doing so, took full advantage of the publicity that came with winning at the Olympics.[193] Soviet Union's success might be attributed to a heavy state's investment in sports to fulfill its political agenda on an international stage.[194][195][195]
+Individual athletes have also used the Olympic stage to promote their own political agenda. At the 1968 Summer Olympics in Mexico City, two American track and field athletes, Tommie Smith and John Carlos, who finished first and third in the 200 metres, performed the Black Power salute on the victory stand. The second-place finisher, Peter Norman of Australia, wore an Olympic Project for Human Rights badge in support of Smith and Carlos. In response to the protest, IOC president Avery Brundage ordered Smith and Carlos suspended from the US team and banned from the Olympic Village. When the US Olympic Committee refused, Brundage threatened to ban the entire US track team. This threat led to the expulsion of the two athletes from the Games.[196] In another notable incident in the gymnastics competition, while standing on the medal podium after the  balance beam event final, in which Natalia Kuchinskaya of the Soviet Union had controversially taken the gold, Czechoslovakian gymnast Věra Čáslavská quietly turned her head down and away during the playing of the Soviet national anthem. The action was Čáslavská's silent protest against the recent Soviet invasion of Czechoslovakia. Her protest was repeated when she accepted her medal for her floor exercise routine when the judges changed the preliminary scores of the Soviet Larisa Petrik to allow her to tie with Čáslavská for the gold. While Čáslavská's countrymen supported her actions and her outspoken opposition to Communism (she had publicly signed and supported Ludvik Vaculik's "Two Thousand Words" manifesto), the new regime responded by banning her from both sporting events and international travel for many years and made her an outcast from society until the fall of communism.
+Currently, the government of Iran has taken steps to avoid any competition between its athletes and those from Israel. An Iranian judoka, Arash Miresmaeili, did not compete in a match against an Israeli during the 2004 Summer Olympics. Although he was officially disqualified for being overweight, Miresmaeli was awarded US$125,000 in prize money by the Iranian government, an amount paid to all Iranian gold medal winners. He was officially cleared of intentionally avoiding the bout, but his receipt of the prize money raised suspicion.[197]
+In the early 20th century, many Olympic athletes began using drugs to improve their athletic abilities. For example, in 1904, Thomas Hicks, a gold medallist in the marathon, was given strychnine by his coach (at the time, taking different substances was allowed, as there was no data regarding the effect of these substances on a body of an athlete).[198] The only Olympic death linked to performance enhancing occurred at the 1960 Rome games. A Danish cyclist, Knud Enemark Jensen, fell from his bicycle and later died. A coroner's inquiry found that he was under the influence of amphetamines.[199] By the mid-1960s, sports federations started to ban the use of performance-enhancing drugs; in 1967 the IOC followed suit.[200]
+According to British journalist Andrew Jennings, a KGB colonel stated that the agency's officers had posed as anti-doping authorities from the International Olympic Committee to undermine doping tests and that Soviet athletes were "rescued with [these] tremendous efforts".[201] On the topic of the 1980 Summer Olympics, a 1989 Australian study said "There is hardly a medal winner at the Moscow Games, certainly not a gold medal winner, who is not on one sort of drug or another: usually several kinds. The Moscow Games might as well have been called the Chemists' Games."[201]
+Documents obtained in 2016 revealed the Soviet Union's plans for a statewide doping system in track and field in preparation for the 1984 Summer Olympics in Los Angeles. Dated prior to the country's decision to boycott the Games, the document detailed the existing steroids operations of the program, along with suggestions for further enhancements.[202] The communication, directed to the Soviet Union's head of track and field, was prepared by Dr. Sergei Portugalov of the Institute for Physical Culture. Portugalov was also one of the main figures involved in the implementation of the Russian doping program prior to the 2016 Summer Olympics.[202]
+The first Olympic athlete to test positive for the use of performance-enhancing drugs was Hans-Gunnar Liljenwall, a Swedish pentathlete at the 1968 Summer Olympics, who lost his bronze medal for alcohol use.[203] One of the  most publicised doping-related disqualifications occurred after the  1988 Summer Olympics where Canadian sprinter, Ben Johnson (who won the 100-metre dash) tested positive for stanozolol.[204]
+In 1999 the IOC formed the World Anti-Doping Agency (WADA) in an effort to systematise the research and detection of performance-enhancing drugs. There was a sharp increase in positive drug tests at the 2000 Summer Olympics and 2002 Winter Olympics due to improved testing conditions. Several medallists in weightlifting and cross-country skiing from post-Soviet states were disqualified because of doping offences. The IOC-established drug testing regimen (now known as the Olympic Standard) has set the worldwide benchmark that other sporting federations attempt to emulate.[205] During the Beijing games, 3,667 athletes were tested by the IOC under the auspices of the World Anti-Doping Agency. Both urine and blood tests were used to detect banned substances.[199][206] In London over 6,000 Olympic and Paralympic athletes were tested. Prior to the Games 107 athletes tested positive for banned substances and were not allowed to compete.[207][208][209]
+Doping in Russian sports has a systemic nature. Russia has had 44 Olympic medals stripped for doping violations – the most of any country, more than three times the number of the runner-up, and more than a quarter of the global total. From 2011 to 2015, more than a thousand Russian competitors in various sports, including summer, winter, and Paralympic sports, benefited from a cover-up.[210][211][212][213] Russia was partially banned from the 2016 Summer Olympics and was banned from the 2018 Winter Olympics (while being allowed to participate as the Olympic Athletes from Russia) due to the state-sponsored doping programme.[214][215]
+In December 2019, Russia got banned for four years from all major sporting events for systematic doping and lying to WADA.[216] The World Anti-Doping Agency (WADA) issued the ban on 9 December 2019, and the Russian anti-doping agency RUSADA has 21 days to make an appeal to the Court of Arbitration for Sport (CAS). The ban means Russian athletes will be allowed to compete under the Olympic flag. Russia is appealing the decision in CAS.[217]
+Women were first allowed to compete at the 1900 Summer Olympics in Paris, but at the 1992 Summer Olympics 35 countries were still only fielding all-male delegations.[218] This number dropped rapidly over the following years. In 2000, Bahrain sent two women competitors for the first time: Fatema Hameed Gerashi and Mariam Mohamed Hadi Al Hilli.[219] In 2004, Robina Muqimyar and Fariba Rezayee became the first women to compete for Afghanistan at the Olympics.[220] In 2008, the United Arab Emirates sent female athletes (Maitha Al Maktoum competed in taekwondo, and Latifa Al Maktoum in equestrian) to the Olympic Games for the first time. Both athletes were from Dubai's ruling family.[221]
+By 2010, only three countries had never sent female athletes to the Games: Brunei, Saudi Arabia, and Qatar. Brunei had taken part in only three celebrations of the Games, sending a single athlete on each occasion, but Saudi Arabia and Qatar had been competing regularly with all-male teams. In 2010, the International Olympic Committee announced it would "press" these countries to enable and facilitate the participation of women for the 2012 Summer Olympics. Anita DeFrantz, chair of the IOC's Women and Sports Commission, suggested that countries be barred if they prevented women from competing. Shortly thereafter, the Qatar Olympic Committee announced that it "hoped to send up to four female athletes in shooting and fencing" to the 2012 Summer Games in London.[222]
+In 2008, Ali Al-Ahmed, director of the Institute for Gulf Affairs, likewise called for Saudi Arabia to be barred from the Games, describing its ban on women athletes as a violation of the International Olympic Committee charter. He noted: "For the last 15 years, many international nongovernmental organisations worldwide have been trying to lobby the IOC for better enforcement of its own laws banning gender discrimination. ... While their efforts did result in increasing numbers of women Olympians, the IOC has been reluctant to take a strong position and threaten the discriminating countries with suspension or expulsion."[218] In July 2010, The Independent reported: "Pressure is growing on the International Olympic Committee to kick out Saudi Arabia, who are likely to be the only major nation not to include women in their Olympic team for 2012. ... Should Saudi Arabia ... send a male-only team to London, we understand they will face protests from equal rights and women's groups which threaten to disrupt the Games".[223]
+At the 2012 Olympic Games in London, United Kingdom, for the first time in Olympic history, every country competing included female athletes.[224] Saudi Arabia included two female athletes in its delegation; Qatar, four; and Brunei, one (Maziah Mahusin, in the 400m hurdles). Qatar made one of its first female Olympians, Bahiya al-Hamad (shooting), its flagbearer at the 2012 Games,[225] and runner Maryam Yusuf Jamal of Bahrain became the first Gulf female athlete to win a medal when she won a bronze for her showing in the 1500 m race.[226]
+The only sport on the Olympic programme that features men and women competing together is the equestrian disciplines. There is no "Women's Eventing", or 'Men's Dressage'. As of 2008, there were still more medal events for men than women. With the addition of women's boxing to the programme in the 2012 Summer Olympics, however, female athletes were able to compete in all the same sports as men.[227] In the winter Olympics, women are still unable to compete in the Nordic combined.[228] There are currently two Olympic events in which male athletes may not compete: synchronised swimming and rhythmic gymnastics.[229]
+Three Olympiads had to pass without a celebration of the Games because of war: the 1916 Games were cancelled because of World War I, and the summer and winter games of 1940 and 1944 were cancelled because of World War II. The Russo-Georgian War between Georgia and Russia erupted on the opening day of the 2008 Summer Olympics in Beijing. Both President Bush and Prime Minister Putin were attending the Olympics at that time and spoke together about the conflict at a luncheon hosted by Chinese president Hu Jintao.[230][231]
+Terrorism most directly affected the Olympic Games in 1972. When the Summer Games were held in Munich, Germany, eleven members of the Israeli Olympic team were taken hostage by the Palestinian terrorist group Black September in what is now known as the Munich massacre. The terrorists killed two of the athletes soon after they had taken them hostage and killed the other nine during a failed liberation attempt. A German police officer and five terrorists also perished.[232] Following the selection of Barcelona, Spain to host the 1992 Summer Olympics, the separatist ETA terrorist organisation launched attacks in the region, including the 1991 Vic bombing that killed ten people in a town that would also hold events.[233][234]
+Terrorism affected the last two Olympic Games held in the United States. During the Summer Olympics in 1996 in Atlanta, Georgia, a bomb was detonated at the Centennial Olympic Park, which killed two and injured 111 others. The bomb was set by Eric Rudolph, an American domestic terrorist, who is currently serving a life sentence for the bombing.[235] The 2002 Winter Olympics in Salt Lake City, Utah, took place just five months after the September 11 attacks, which meant a higher level of security than ever before provided for an Olympic Games. The opening ceremonies of the Games featured symbols of the day's events. They included the flag that flew at Ground Zero and honour guards of NYPD and FDNY members.[236]
+The Olympic Games have been criticized as upholding (and in some cases increasing) the colonial policies and practices of some host nations and cities either in the name of the Olympics by associated parties or directly by official Olympic bodies, such as the International Olympic Committee, host organising committees and official sponsors.
+Critics have argued that the Olympics have engaged in or caused: erroneous anthropological and colonial knowledge production; erasure; commodification[237] and appropriation of indigenous ceremonies and symbolism; theft and inappropriate display of indigenous objects; further encroachment on and support of the theft of indigenous lands; and neglect and/or intensification of poor social conditions for indigenous peoples. Such practices have been observed at: the 1904 Summer Olympics in St. Louis, MO; the 1976 Summer Olympics in Montreal, Quebec; the 1988 Winter Olympics in Calgary, Alberta; the 2008 Summer Olympics in Beijing, China; the 2010 Winter Olympics in Vancouver, BC; the 2012 Summer Olympics in London, England; the 2014 Winter Olympics in Sochi, Krasnodar Krai and the 2022 Winter Olympics in Beijing, China.
+The Olympic Charter requires that an athlete be a national of the country for which they compete. Dual nationals may compete for either country, as long as three years have passed since the competitor competed for the former country. However, if the NOCs and IF involved agree, then the IOC Executive Board may reduce or cancel this period.[238] This waiting period exists only for athletes who previously competed for one nation and want to compete for another. If an athlete gains a new or second nationality, then they do not need to wait any designated amount of time before participating for the new or second nation. The IOC is only concerned with issues of citizenship and nationality after individual nations have granted citizenship to athletes.[239]
+Athletes will sometimes become citizens of a different nation so they are able to compete in the Olympics. This is often because they are drawn to sponsorships or training facilities. It could also be because an athlete is unable to qualify from within their original country. In preparation for the 2014 Winter Games in Sochi Russian Olympic Committee naturalized a Korean-born short-track speed-skater Ahn Hyun-soo and an American-born snowboarder Vic Wild. They won a total of 5 golds and 1 bronze in Sochi.[240]
+One of the most famous cases of changing nationality for the Olympics was Zola Budd, a South African runner who emigrated to the United Kingdom because there was an apartheid-era ban on the Olympics in South Africa. Budd was eligible for British citizenship because her grandfather was born in Britain, but British citizens accused the government of expediting the citizenship process for her.[241]
+Other notable examples include Kenyan runner Bernard Lagat, who became a United States citizen in May 2004. The Kenyan constitution required that one renounce their Kenyan citizenship when they became a citizen of another nation. Lagat competed for Kenya in the 2004 Athens Olympics even though he had already become a United States citizen. According to Kenya, he was no longer a Kenyan citizen, jeopardising his silver medal. Lagat said he started the citizenship process in late 2003 and did not expect to become an American citizen until after the Athens games.[242]
+The athletes or teams who place first, second, or third in each event receive medals. The winners receive gold medals, which were solid gold until 1912, then made of gilded silver and now gold-plated silver. Every gold medal however must contain at least six grams of pure gold.[243] The runners-up receive silver medals and the third-place athletes are awarded bronze medals. In events contested by a single-elimination tournament (most notably boxing), third place might not be determined and both semifinal losers receive bronze medals. At the 1896 Olympics only the first two received a medal; silver for first and bronze for second. The current three-medal format was introduced at the 1904 Olympics.[244] From 1948 onward athletes placing fourth, fifth, and sixth have received certificates, which became officially known as Olympic diplomas; in 1984 Olympic diplomas for seventh- and eighth-place finishers were added. At the 2004 Summer Olympics in Athens, the gold, silver, and bronze medal winners were also given olive wreaths.[245] The IOC does not keep statistics of medals won on a national level (except for team sports), but NOCs and the media record medal statistics as a measure of success.[246]
+As of the 2016 Games in Rio de Janeiro, all of the current 206 NOCs and 19 obsolete NOCs have participated in at least one edition of the Summer Olympics. Competitors from Australia, France,[A] Great Britain,[B] Greece, and Switzerland[C] have competed in all twenty-eight Summer Olympic Games. Athletes competing under the Olympic flag, Mixed Teams and the Refugee Team have competed at six Games.
+A total of 119 NOCs (110 of the current 206 NOCs and nine obsolete NOCs) have participated in at least one Winter Games, and athletes from fourteen nations (Austria, Canada, Czech Republic, Finland, France, Great Britain, Hungary, Italy, Norway, Poland, Slovakia, Sweden, Switzerland, and the United States) have participated in all twenty-three Winter Games to date.
+The host city for an Olympic Games is usually chosen seven to eight years ahead of their celebration.[247] The process of selection is carried out in two phases that span a two-year period. The prospective host city applies to its country's National Olympic Committee; if more than one city from the same country submits a proposal to its NOC, the national committee typically holds an internal selection, since only one city per NOC can be presented to the International Olympic Committee for consideration. Once the deadline for submission of proposals by the NOCs is reached, the first phase (Application) begins with the applicant cities asked to complete a questionnaire regarding several key criteria related to the organisation of the Olympic Games.[248] In this form, the applicants must give assurances that they will comply with the Olympic Charter and with any other regulations established by the IOC Executive Committee.[247] The evaluation of the filled questionnaires by a specialised group provides the IOC with an overview of each applicant's project and their potential to host the Games. On the basis of this technical evaluation, the IOC Executive Board selects the applicants that will proceed to the candidature stage.[248]
+Once the candidate cities are selected, they must submit to the IOC a bigger and more detailed presentation of their project as part of a candidature file. Each city is thoroughly analysed by an evaluation commission. This commission will also visit the candidate cities, interviewing local officials and inspecting prospective venue sites, and submit a report on its findings one month prior to the IOC's final decision. During the interview process the candidate city must also guarantee that it will be able to fund the Games.[247] After the work of the evaluation commission, a list of candidates is presented to the General Session of the IOC, which must assemble in a country that does not have a candidate city in the running. The IOC members gathered in the Session have the final vote on the host city. Once elected, the host city bid committee (together with the NOC of the respective country) signs a Host City Contract with the IOC, officially becoming an Olympic host nation and host city.[247]
+By 2016, the Olympic Games will have been hosted by 44 cities in 23 countries. Since the 1988 Summer Olympics in Seoul, South Korea, the Olympics have been held in Asia or Oceania four times, a sharp increase compared to the previous 92 years of modern Olympic history. The 2016 Games in Rio de Janeiro were the first Olympics for a South American country. No bids from countries in Africa have succeeded.
+The United States hosted four Summer Games, more than any other nation. The British capital London holds the distinction of hosting three Olympic Games, all Summer, more than any other city. Paris, which previously hosted in 1900 and 1924, is due to host the Summer Games for a third time in 2024, and Los Angeles, which previously hosted in 1932 and 1984, is due to host the Summer Games for a third time in 2028. The other nations hosting the Summer Games at least twice are Germany, Australia, France and Greece. The other cities hosting the Summer Games at least twice are Los Angeles, Paris and Athens. With the 2020 Summer Olympic Games, Japan and Tokyo, respectively, will hold these statuses.
+The United States hosted four Winter Games, more than any other nation. The other nations hosting multiple Winter Games are France with three, while Switzerland, Austria, Norway, Japan, Canada and Italy have hosted twice. Among host cities, Lake Placid, Innsbruck and St. Moritz have played host to the Winter Olympic Games more than once, each holding that honour twice. The most recent Winter Games were held in Pyeongchang in 2018, South Korea's first Winter Olympics and second Olympics overall (including the 1988 Summer Olympics in Seoul).
+Beijing is due to host the 2022 Winter Olympics, which will make it the first city to host both the Summer and Winter Games.

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+Coordinates: 21°N 57°E / 21°N 57°E / 21; 57
+Oman (/oʊˈmɑːn/ (listen) oh-MAHN; Arabic: عمان‎ ʻumān [ʕʊˈmaːn]), officially the Sultanate of Oman (Arabic: سلْطنةُ عُمان‎ Salṭanat(u) ʻUmān), is a country on the southeastern coast of the Arabian Peninsula in Western Asia. Located in a strategically important position at the mouth of the Persian Gulf, the country shares land borders with the United Arab Emirates to the northwest, Saudi Arabia to the west, and Yemen to the southwest, and shares marine borders with Iran and Pakistan. The coast is formed by the Arabian Sea on the southeast and the Gulf of Oman on the northeast. The Madha and Musandam exclaves are surrounded by the UAE on their land borders, with the Strait of Hormuz (which it shares with Iran) and the Gulf of Oman forming Musandam's coastal boundaries.
+From the late 17th century, the Omani Sultanate was a powerful empire, vying with the Portuguese Empire and the British Empire for influence in the Persian Gulf and Indian Ocean. At its peak in the 19th century, Omani influence or control extended across the Strait of Hormuz to modern-day Iran and Pakistan, and as far south as Zanzibar.[8] When its power declined in the 20th century, the sultanate came under the influence of the United Kingdom. For over 300 years, the relations built between the two empires were based on mutual benefits. The UK recognized Oman's geographical importance as a trading hub that secured their trading lanes in the Persian Gulf and Indian Ocean and protected their empire in the Indian sub-continent. Historically, Muscat was the principal trading port of the Persian Gulf region. Muscat was also among the most important trading ports of the Indian Ocean.
+Sultan Qaboos bin Said al Said was the hereditary leader of the country, which is an absolute monarchy, from 1970 until his death on 10 January 2020.[9] His cousin, Haitham bin Tariq, was named as the country's new ruler following his death.[10]
+Oman is a member of the United Nations, the Arab League, the Gulf Cooperation Council, the Non-Aligned Movement and the Organisation of Islamic Cooperation. It has sizeable oil reserves, ranking 25th globally.[11][12] In 2010, the United Nations Development Programme ranked Oman as the most improved nation in the world in terms of development during the preceding 40 years.[13] A significant portion of its economy involves tourism and trading fish, dates and other agricultural produce. Oman is categorized as a high-income economy and ranks as the 69th most peaceful country in the world according to the Global Peace Index.[14]
+The origin of Oman's name is uncertain. It seems to be related to Pliny the Elder's Omana[15] and Ptolemy's Omanon (Ὄμανον ἐμπόριον),[16] both probably the ancient Sohar.[17] The city or region is typically etymologized in Arabic from aamen or amoun ("settled" people, as opposed to the Bedouin),[17] although a number of eponymous founders have been proposed (Oman bin Ibrahim al-Khalil, Oman bin Siba' bin Yaghthan bin Ibrahim, Oman bin Qahtan and the Biblical Lot) and others derive it from the name of a valley in Yemen at Ma'rib presumed to have been the origin of the city's founders, the Azd, a tribe migrating from Yemen.[18]
+At Aybut Al Auwal, in the Dhofar Governorate of Oman, a site was discovered in 2011 containing more than 100 surface scatters of stone tools, belonging to a regionally specific African lithic industry—the late Nubian Complex—known previously only from the northeast and Horn of Africa. Two optically stimulated luminescence age estimates place the Arabian Nubian Complex at 106,000 years old. This supports the proposition that early human populations moved from Africa into Arabia during the Late Pleistocene.[19]
+In recent years surveys have uncovered Palaeolithic and Neolithic sites on the eastern coast. Main Palaeolithic sites include Saiwan-Ghunaim in the Barr al-Hikman.[20] Archaeological remains are particularly numerous for the Bronze Age Umm an-Nar and Wadi Suq periods. Sites such as Bat show professional wheel-turned pottery, excellent hand-made stone vessels, a metals industry and monumental architecture
+.[21] The Early (1300‒300 BC) and Late Iron Ages (100 BC‒300 AD) show more differences than similarities to each other. Thereafter, until the coming of Ibadi Islam, little or nothing is known.
+During the 8th century BC, it is believed that the Yaarub, the descendant of Kahtan, ruled the entire region of Yemen, including Oman. Wathil bin Himyar bin Abd-Shams-Saba bin Jashjub bin Yaarub later ruled Oman.[22] It is thus believed that the Yaarubah were the first settlers in Oman from Yemen.[23]
+In the 1970s and 1980s scholars like John C. Wilkinson[24] believed by virtue of oral history that in the 6th century BC, the Achaemenids exerted control over the Omani peninsula, most likely ruling from a coastal centre such as Suhar.[25] Central Oman has its own indigenous Samad Late Iron Age cultural assemblage named eponymously from Samad al-Shan. In the northern part of the Oman Peninsula the Recent Pre-Islamic Period begins in the 3rd century BC and extends into the 3rd A.D. century. Whether or not Persians brought south-eastern Arabian under their control is a moot point, since the lack of Persian finds speak against this belief. M. Caussin de Percevel suggests that Shammir bin Wathil bin Himyar recognized the authority of Cyrus over Oman in 536 B.C.[22]
+Sumerian tablets referred to Oman as "Magan"[26][27] and in the Akkadian language "Makan",[28][29] a name which links Oman's ancient copper resources.[30] Mazoon, a Persian name used to refer to Oman's region, which was part of the Sasanian Empire.
+Over centuries tribes from western Arabia settled in Oman, making a living by fishing, farming, herding or stock breeding, and many present day Omani families trace their ancestral roots to other parts of Arabia. Arab migration to Oman started from northern-western and south-western Arabia and those who chose to settle had to compete with the indigenous population for the best arable land. When Arab tribes started to migrate to Oman, there were two distinct groups. One group, a segment of the Azd tribe migrated from the southwest of Arabia in A.D. 120[31]/200 following the collapse of Marib Dam, while the other group migrated a few centuries before the birth of Islam from central and northern Arabia, named Nizari (Nejdi). Other historians believe that the Yaarubah, like the Azd, from Qahtan but belong to an older branch, were the first settlers of Oman from Yemen, and then came the Azd.[23]
+The Azd settlers in Oman are descendants of Nasr bin Azd, a branch of Yaarub bin Qahtan, and were later known as "the Al-Azd of Oman".[31] Seventy years after the first Azd migration, another branch of Alazdi under Malik bin Fahm, the founder of Kingdom of Tanukhites on the west of Euphrates, is believed to have settled in Oman.[31] According to Al-Kalbi, Malik bin Fahm was the first settler of Alazd.[32] He is said to have first settled in Qalhat. By this account, Malik, with an armed force of more than 6000 men and horses, fought against the Marzban, who served an ambiguously named Persian king in the battle of Salut in Oman and eventually defeated the Persian forces.[23][33][34][35][36]  This account is, however, semi-legendary and seems to condense multiple centuries of migration and conflict into a story of two campaigns that exaggerate the success of the Arabs.  The account may also represent an amalgamation of various traditions from not only the Arab tribes but also the region's original inhabitants.  Furthermore, no date can be determined for the events of this story.[34][37][38]
+In the 7th century AD, Omanis came in contact with and accepted Islam.[39][40] The conversion of Omanis to Islam is ascribed to Amr ibn al-As, who was sent by the prophet Muhammad during the Expedition of Zaid ibn Haritha (Hisma). Amer was dispatched to meet with Jaifer and Abd, the sons of Julanda who ruled Oman. They appear to have readily embraced Islam.[41]
+Omani Azd used to travel to Basra for trade, which was a centre of Islam during the Umayyad empire. Omani Azd were granted a section of Basra, where they could settle and attend their needs. Many of the Omani Azd who settled in Basra became wealthy merchants and under their leader Muhallab bin Abi Sufrah started to expand their influence of power eastwards towards Khorasan. Ibadhi Islam originated in Basra by its founder Abdullah ibn Ibada around the year 650 CE, which the Omani Azd in Iraq followed. Later, Alhajjaj, the governor of Iraq, came into conflict with the Ibadhis, which forced them out to Oman. Among those who returned to Oman was the scholar Jaber bin Zaid. His return and the return of many other scholars greatly enhanced the Ibadhi movement in Oman.[42] Alhajjaj, also made an attempt to subjugate Oman, which was ruled by Suleiman and Said, the sons of Abbad bin Julanda. Alhajjaj dispatched Mujjaah bin Shiwah who was confronted by Said bin Abbad. The confrontation devastated Said's army. Thus, Said and his forces resorted to the Jebel Akhdar. Mujjaah and his forces went after Said and his forces and succeeded in besieging them from a position in "Wade Mastall". Mujjaah later moved towards the coast where he confronted Suleiman bin Abbad. The battle was won by Suleiman's forces. Alhajjaj, however, sent another force under Abdulrahman bin Suleiman and eventually won the war and took over the governance of Oman.[43][44][45]
+The first elective Imamate of Oman is believed to have been established shortly after the fall of the Umayyad Dynasty in 750/755 AD when Janah bin Abbada Alhinawi was elected.[42][46] Other scholars claim that Janah bin Abbada served as a Wali (governor) under Umayyad dynasty and later ratified the Imamate, while Julanda bin Masud was the first elected Imam of Oman in A.D. 751.[47][48] The first Imamate reached its peak power in the ninth A.D. century.[42] The Imamate established a maritime empire whose fleet controlled the Gulf during the time when trade with the Abbasid Dynasty, the East and Africa flourished.[49] The authority of the Imams started to decline due to power struggles, the constant interventions of Abbasid and the rise of the Seljuk Empire.[50][47]
+During the 11th and 12th centuries, Oman was controlled by the Seljuk Empire. They were expelled in 1154, when the Nabhani dynasty came to power.[50] The Nabhanis ruled as muluk, or kings, while the Imams were reduced to largely symbolic significance. The capital of the dynasty was Bahla.[51] The Banu Nabhan controlled the trade in frankincense on the overland route via Sohar to the Yabrin oasis, and then north to Bahrain, Baghdad and Damascus.[52] The mango-tree was introduced to Oman during the time of Nabhani dynasty, by ElFellah bin Muhsin.[23][53] The Nabhani dynasty started to deteriorate in 1507 when Portuguese colonisers captured the coastal city of Muscat, and gradually extended their control along the coast up to Sohar in the north and down to Sur in the southeast.[54] Other historians argue that the Nabhani dynasty ended earlier in A.D. 1435 when conflicts between the dynasty and Alhinawis arose, which led to the restoration of the elective Imamate.[23]
+A decade after Vasco da Gama's successful voyage around the Cape of Good Hope and to India in 1497–98, the Portuguese arrived in Oman and occupied Muscat for a 143-year period, from 1507 to 1650. In need of an outpost to protect their sea lanes, the Portuguese built up and fortified the city, where remnants of their colonial architectural style still exist. An Ottoman fleet captured Muscat in 1552, during the fight for control of the Persian Gulf and the Indian Ocean.[55]
+The Ottoman Turks temporarily captured Muscat from the Portuguese in 1581 and held it until 1588. During the 17th century, the Omanis were reunited by the Yaruba Imams. Nasir bin Murshid became the first Yaarubah Imam in 1624, when he was elected in Rustak. Nasir's energy and perseverance is believed to have earned him the election.[57] Imam Nasir succeeded in the 1650s to force the Portuguese colonisers out of Oman.[42] The Omanis over time established a maritime empire that later expelled the Portuguese from East Africa, which became an Omani colony. To capture Zanzibar Saif bin Sultan, the Imam of Oman, pressed down the Swahili Coast. A major obstacle to his progress was Fort Jesus, housing the garrison of a Portuguese settlement at Mombasa. After a two-year siege, the fort fell to Saif bin Sultan in 1698. Thereafter the Omanis easily ejected the Portuguese from other African coastal regions including Kilwa and Pemba. Saif bin Sultan occupied Bahrain in 1700. Qeshm was captured in 1720.[49][58] The rivalry within the house of Yaruba over power after the death of Imam Sultan in 1718 weakened the dynasty. With the power of the Yaruba Dynasty dwindling, Imam Saif bin Sultan II eventually asked for help against his rivals from Nader Shah of Persia. A Persian force arrived in March 1737 to aid Saif. From their base at Julfar, the Persian forces eventually rebelled against the Yaruba in 1743. The Persian empire then colonised Oman for a short period until 1747.[42][59]
+After the decolonization of Oman from the Persians, Ahmed bin Sa'id Albusaidi in 1749 became the elected Imam of Oman, with Rustaq serving as the capital. Since the Yaruba dynasty, the Omanis kept the elective system but, provided that the person is deemed qualified, gave preference to a member of the ruling family.[60] Following Imam Ahmed's death in 1783, his son, Said bin Ahmed became the elected Imam. His son, Seyyid Hamed bin Said, overthrew the representative of the Imam in Muscat and obtained the possession of Muscat fortress. Hamed ruled as "Seyyid". Afterwards, Seyyid Sultan bin Ahmed, the uncle of Seyyid Hamed, took over power. Seyyid Said bin Sultan succeeded Sultan bin Ahmed.[61][62] During the entire 19th century, in addition to Imam Said bin Ahmed who retained the title until he died in 1803, Azzan bin Qais was the only elected Imam of Oman. His rule started in 1868. However, the British refused to accept Imam Azzan as a ruler. The refusal played an instrumental role in deposing Imam Azzan in 1871 by a sultan who Britain deemed to be more acceptable.[63]
+Oman's Imam Sultan, defeated ruler of Muscat, was granted sovereignty over Gwadar, an area of modern-day Pakistan. This coastal city is located in the Makran region of what is now the far southwestern corner of Pakistan, near the present-day border of Iran, at the mouth of the Gulf of Oman.[note 1][64] After regaining control of Muscat, this sovereignty was continued via an appointed wali ("governor").s
+The British empire was keen to dominate southeast Arabia to stifle the growing power of other European states and to curb the Omani maritime power that grew during the 17th century.[65][49] The British empire over time, starting from the late 18th century, began to establish a series of treaties with the sultans with the objective of advancing British political and economic interest in Muscat, while granting the sultans military protection.[49][65] In 1798, the first treaty between the British East India Company and Albusaidi family was signed by Sultan bin Ahmed. The treaty was to block commercial competition of the French and the Dutch as well as obtain a concession to build a British factory at Bandar Abbas.[66][42][67] A second treaty was signed in 1800, which stipulated that a British representative shall reside at the port of Muscat and manage all external affairs with other states.[67] The British influence that grew during the nineteenth century over Muscat weakened the Omani Empire.[56]
+In 1854, a deed of cession of the Omani Kuria Muria islands to Britain was signed by the sultan of Muscat and the British government.[69] The British government achieved predominating control over Muscat, which, for the most part, impeded competition from other nations.[70] Between 1862 and 1892, the Political Residents, Lewis Pelly and Edward Ross, played an instrumental role in securing British supremacy over the Persian Gulf and Muscat by a system of indirect governance.[63] By the end of the 19th century, the British influence increased to the point that the sultans became heavily dependent on British loans and signed declarations to consult the British government on all important matters.[65][71][72][73] The Sultanate thus became a de facto British colony.[72][74]
+Zanzibar was a valuable property as the main slave market of the Swahili Coast, and became an increasingly important part of the Omani empire, a fact reflected by the decision of the 19th century sultan of Muscat, Sa'id ibn Sultan, to make it his main place of residence in 1837. Sa'id built impressive palaces and gardens in Zanzibar. Rivalry between his two sons was resolved, with the help of forceful British diplomacy, when one of them, Majid, succeeded to Zanzibar and to the many regions claimed by the family on the Swahili Coast. The other son, Thuwaini, inherited Muscat and Oman. Zanzibar influences in the Comoros archipelago in the Indian Ocean indirectly introduced Omani customs to the Comorian culture. These influences include clothing traditions and wedding ceremonies.[75] In 1856, under British direction, Zanzibar and Muscat became two different sultanates.[58]
+The Al Hajar Mountains, of which the Jebel Akhdar is a part, separate the country into two distinct regions: the interior, known as Oman, and the coastal area dominated by the capital, Muscat.[76] The British imperial development over Muscat and Oman during the 19th century led to the renewed revival of the Imamate cause in the interior of Oman, which has appeared in cycles for more than 1,200 years in Oman.[49] The British Political Agent, who resided in Muscat, owed the alienation of the interior of Oman to the vast influence of the British government over Muscat, which he described as being completely self-interested and without any regard to the social and political conditions of the locals.[77] In 1913, Imam Salim Alkharusi instigated an anti-Muscat rebellion that lasted until 1920 when the Imamate established peace with the Sultanate by signing the Treaty of Seeb.The treaty was brokered by Britain, which had no economic interest in the interior of Oman during that point of time. The treaty granted autonomous rule to the Imamate in the interior of Oman and recognized the sovereignty of the coast of Oman, the Sultanate of Muscat.[65][78][79][80] In 1920, Imam Salim Alkharusi died and Muhammad Alkhalili was elected.[42]
+On 10 January 1923, an agreement between the Sultanate and the British government was signed in which the Sultanate had to consult with the British political agent residing in Muscat and obtain the approval of the High Government of India to extract oil in the Sultanate.[81] On 31 July 1928, the Red Line Agreement was signed between Anglo-Persian Company (later renamed British Petroleum), Royal Dutch/Shell, Compagnie Française des Pétroles (later renamed Total), Near East Development Corporation (later renamed ExxonMobil) and Calouste Gulbenkian (an Armenian businessman) to collectively produce oil in the post-Ottoman Empire region, which included the Arabian peninsula, with each of the four major companies holding 23.75 percent of the shares while Calouste Gulbenkian held the remaining 5 percent shares. The agreement stipulated that none of the signatories was allowed to pursue the establishment of oil concessions within the agreed on area without including all other stakeholders. In 1929, the members of the agreement established Iraq Petroleum Company (IPC).[82] On 13 November 1931, Sultan Taimur bin Faisal abdicated.[83]
+Said bin Taimur became the sultan of Muscat officially on 10 February 1932. The rule of sultan Said bin Taimur, who was backed by the British government, was characterized as being feudal, reactionary and isolationist.[80][49][72][84] The British government maintained vast administrative control over the Sultanate as the defence secretary and chief of intelligence, chief adviser to the sultan and all ministers except for one were British.[72][85] In 1937, an agreement between the sultan and Iraq Petroleum Company (IPC), a consortium of oil companies that was  23.75% British owned, was signed to grant oil concessions to IPC. After failing to discover oil in the Sultanate, IPC was intensely interested in some promising geological formations near Fahud, an area located within the Imamate. IPC offered financial support to the sultan to raise an armed force against any potential resistance by the Imamate.[86][87]
+In 1955, the exclave coastal Makran strip acceded to Pakistan and was made a district of its Balochistan province, while Gwadar remained in Oman. On 8 September 1958, Pakistan purchased the Gwadar enclave from Oman for US$3 million.[note 2][88] Gwadar then became a tehsil in the Makran district.
+Sultan Said bin Taimur expressed his interest to the British government in occupying the Imamate right after the death of Imam Alkhalili and take advantage of potential instability that may occur within the Imamate when elections were due.[89] The British political agent in Muscat believed that the only method of gaining access to the oil reserves in the interior was by assisting the sultan in taking over the Imamate.[90] In 1946, the British government offered arms and ammunition, auxiliary supplies and officers to prepare the sultan to attack the interior of Oman.[91] In May 1954, Imam Alkhalili died and Ghalib Alhinai became the elected Imam of the Imamate of Oman.[92] Relations between the sultan of Muscat, Said bin Taimur, and Imam Ghalib Alhinai frayed over their dispute about oil concessions. Under the terms of the 1920 treaty of Seeb, the Sultan, backed by the British government, claimed all dealings with the oil company as his prerogative. The Imam, on the other hand, claimed that since the oil was in the Imamate territory, anything concerning it was an internal matter.[76]
+In December 1955, sultan Said bin Taimur sent troops of the Muscat and Oman Field Force to occupy the main centres in Oman, including Nizwa, the capital of the Imamate of Oman, and Ibri.[78][93] The Omanis in the interior led by Imam Ghalib Alhinai, Talib Alhinai, the brother of the Imam and the Wali (governor) of Rustaq, and Suleiman bin Hamyar, who was the Wali (governor) of Jebel Akhdar, defended the Imamate of Oman in the Jebel Akhdar War against British-backed attacks by the Sultanate. In July 1957, the Sultan's forces were withdrawing, but they were repeatedly ambushed, sustaining heavy casualties.[78] Sultan Said, however, with the intervention of British infantry (two companies of the Cameronians), armoured car detachments from the British Army and RAF aircraft, was able to suppress the rebellion.[94] The Imamate's forces retreated to the inaccessible Jebel Akhdar.[94][86]
+Colonel David Smiley, who had been seconded to organise the Sultan's Armed Forces, managed to isolate the mountain in autumn 1958 and found a route to the plateau from Wadi Bani Kharus.[95] On 4 August 1957, the British Foreign Secretary gave the approval to carry out air strikes without prior warning to the locals residing in the interior of Oman.[84] Between July and December 1958, the British RAF made 1,635 raids, dropping 1,094 tons and firing 900 rockets at the interior of Oman targeting insurgents, mountain top villages, water channels and crops.[72][84] On 27 January 1959, the Sultanate's forces occupied the mountain in a surprise operation.[95] Ghalib, Talib and Sulaiman managed to escape to Saudi Arabia, where the Imamate's cause was promoted until the 1970s.[95] The interior of Oman presented the case of Oman to the Arab League and the United Nations.[96][97] On 11 December 1963, the UN General Assembly decided to establish an Ad-Hoc Committee on Oman to study the 'Question of Oman' and report back to the General Assembly.[98] The UN General Assembly adopted the 'Question of Oman' resolution in 1965, 1966 and again in 1967 that called upon the British government to cease all repressive action against the locals, end British control over Oman and reaffirmed the inalienable right of the Omani people to self-determination and independence.[99][100][74][101][102][103]
+Oil reserves in Dhofar were discovered in 1964 and extraction began in 1967. In the Dhofar Rebellion, which began in 1965, pro-Soviet forces were pitted against government troops. As the rebellion threatened the Sultan's control of Dhofar, Sultan Said bin Taimur was deposed in a bloodless coup (1970) by his son Qaboos bin Said, who expanded the Sultan of Oman's Armed Forces, modernised the state's administration and introduced social reforms. The uprising was finally put down in 1975 with the help of forces from Iran, Jordan, Pakistan and the British Royal Air Force, army and Special Air Service.
+After deposing his father in 1970, Sultan Qaboos opened up the country, embarked on economic reforms, and followed a policy of modernisation marked by increased spending on health, education and welfare.[104] Slavery, once a cornerstone of the country's trade and development, was outlawed in 1970.[75]
+In 1981 Oman became a founding member of the six-nation Gulf Cooperation Council. Political reforms were eventually introduced. Historically, voters had been chosen from among tribal leaders, intellectuals and businessmen. In 1997 Sultan Qaboos decreed that women could vote for, and stand for election to, the Majlis al-Shura, the Consultative Assembly of Oman. Two women were duly elected to the body.
+In 2002, voting rights were extended to all citizens over the age of 21, and the first elections to the Consultative Assembly under the new rules were held in 2003. In 2004, the Sultan appointed Oman's first female minister with portfolio, Sheikha Aisha bint Khalfan bin Jameel al-Sayabiyah. She was appointed to the post of National Authority for Industrial Craftsmanship, an office that attempts to preserve and promote Oman's traditional crafts and stimulate industry.[105] Despite these changes, there was little change to the actual political makeup of the government. The Sultan continued to rule by decree. Nearly 100 suspected Islamists were arrested in 2005 and 31 people were convicted of trying to overthrow the government. They were ultimately pardoned in June of the same year.[11]
+Inspired by the Arab Spring uprisings taking place throughout the region, protests occurred in Oman during the early months of 2011. Although they did not call for the ousting of the regime, demonstrators demanded political reforms, improved living conditions and the creation of more jobs. They were dispersed by riot police in February 2011. Sultan Qaboos reacted by promising jobs and benefits. In October 2011, elections were held to the Consultative Assembly, to which Sultan Qaboos promised greater powers. The following year, the government began a crackdown on internet criticism. In September 2012, trials began of 'activists' accused of posting "abusive and provocative" criticism of the government online. Six were given jail terms of 12–18 months and fines of around $2,500 each.[106]
+Qaboos died on 10 January 2020, and the government declared three days of national mourning. He was buried the next day. [107]
+On 11 January 2020, Qaboos was succeeded by his first cousin Sultan Haitham bin Tariq Al Said.[108]
+Oman lies between latitudes 16° and 28° N, and longitudes 52° and 60° E. A vast gravel desert plain covers most of central Oman, with mountain ranges along the north (Al Hajar Mountains) and southeast coast (Qara or Dhofar Mountains),[109][110] where the country's main cities are located: the capital city Muscat, Sohar and Sur in the north, and Salalah in the south. Oman's climate is hot and dry in the interior and humid along the coast. During past epochs, Oman was covered by ocean, as evidenced by the large numbers of fossilized shells found in areas of the desert away from the modern coastline.
+The peninsula of Musandam (Musandem) exclave, which is strategically located on the Strait of Hormuz, is separated from the rest of Oman by the United Arab Emirates.[111] The series of small towns known collectively as Dibba are the gateway to the Musandam peninsula on land and the fishing villages of Musandam by sea, with boats available for hire at Khasab for trips into the Musandam peninsula by sea.
+Oman's other exclave, inside UAE territory, known as Madha, located halfway between the Musandam Peninsula and the main body of Oman,[111] is part of the Musandam governorate, covering approximately 75 km2 (29 sq mi). Madha's boundary was settled in 1969, with the north-east corner of Madha barely 10 m (32.8 ft) from the Fujairah road. Within the Madha exclave is a UAE enclave called Nahwa, belonging to the Emirate of Sharjah, situated about 8 km (5 mi) along a dirt track west of the town of New Madha, and consisting of about forty houses with a clinic and telephone exchange.[112]
+The central desert of Oman is an important source of meteorites for scientific analysis.[113]
+Like the rest of the Persian Gulf, Oman generally has one of the hottest climates in the world—with summer temperatures in Muscat and northern Oman averaging  30 to 40 °C (86.0 to 104.0 °F).[114] Oman receives little rainfall, with annual rainfall in Muscat averaging 100 mm (3.9 in), occurring mostly in January. In the south, the Dhofar Mountains area near Salalah has a tropical-like climate and receives seasonal rainfall from late June to late September as a result of monsoon winds from the Indian Ocean, leaving the summer air saturated with cool moisture and heavy fog.[115] Summer temperatures in Salalah range from 20 to 30 °C (68.0 to 86.0 °F)—relatively cool compared to northern Oman.[116]
+The mountain areas receive more rainfall, and annual rainfall on the higher parts of the Jabal Akhdar probably exceeds 400 mm (15.7 in).[117] Low temperatures in the mountainous areas leads to snow cover once every few years.[118] Some parts of the coast, particularly near the island of Masirah, sometimes receive no rain at all within the course of a year. The climate is generally very hot, with temperatures reaching around 54 °C (129.2 °F) (peak) in the hot season, from May to September.[119]
+On 26 June 2018 the city of Qurayyat set the record for highest minimum temperature in a 24-hour period, 42.6 °C (108.7 °F).[120]
+Desert shrub and desert grass, common to southern Arabia, are found in Oman, but vegetation is sparse in the interior plateau, which is largely gravel desert. The greater monsoon rainfall in Dhofar and the mountains makes the growth there more luxuriant during summer; coconut palms grow plentifully on the coastal plains of Dhofar and frankincense is produced in the hills, with abundant oleander and varieties of acacia. The Al Hajar Mountains are a distinct ecoregion, the highest points in eastern Arabia with wildlife including the Arabian tahr.
+Indigenous mammals include the leopard, hyena, fox, wolf, hare, oryx and ibex. Birds include the vulture, eagle, stork, bustard, Arabian partridge, bee eater, falcon and sunbird. In 2001, Oman had nine endangered species of mammals, five endangered types of birds,[citation needed] and nineteen threatened plant species. Decrees have been passed to protect endangered species, including the Arabian leopard, Arabian oryx, mountain gazelle, goitered gazelle, Arabian tahr, green sea turtle, hawksbill turtle and olive ridley turtle. However, the Arabian Oryx Sanctuary is the first site ever to be deleted from UNESCO's World Heritage List, following the government's 2007 decision to reduce the site's area by 90% in order to clear the way for oil prospectors.[121]
+In recent years, Oman has become one of the newer hot spots for whale watching, highlighting the critically endangered Arabian humpback whale, the most isolated and only non-migratory population in the world, sperm whales and pygmy blue whales.[122]
+Drought and limited rainfall contribute to shortages in the nation's water supply. Maintaining an adequate supply of water for agricultural and domestic use is one of Oman's most pressing environmental problems, with limited renewable water resources. 94% of available water is used in farming and 2% for industrial activity, with the majority sourced from fossil water in the desert areas and spring water in hills and mountains.
+In terms of climate action, major challenges remain to be solved, per the United Nations Sustainable Development 2019 index. The CO2 emissions from energy (tCO2/capita) and CO2 emissions embodied in fossil fuel exports (kg per capita) rates are very high, while imported CO2 emissions (tCO2/capita) and people affected by climate-related disasters (per 100,000 people) rates are low.[123]
+Drinking water is available throughout Oman, either piped or delivered. The soil in coastal plains, such as Salalah, have shown increased levels of salinity, due to over exploitation of ground water and encroachment by seawater on the water table. Pollution of beaches and other coastal areas by oil tanker traffic through the Strait of Hormuz and Gulf of Oman is also a persistent concern.[124]
+Local and national entities have noted unethical treatment of animals in Oman. In particular, stray dogs (and to a lesser extent, stray cats) are often the victims of torture, abuse or neglect.[125] The only approved method of decreasing the stray dog population is shooting by police officers. The Oman government has refused to implement a spay and neuter programme or create any animal shelters in the country. Cats, while seen as more acceptable than dogs, are viewed as pests and frequently die of starvation or illness.[126][127]
+In 2019, the World Health Organization (WHO) ranked Oman as the least polluted country in the Arab world, with a score of 37.7 in the pollution index. The country ranked 112th in Asia among the list of highest polluted countries.[128]
+Oman is a unitary state and an absolute monarchy,[129] in which all legislative, executive and judiciary power ultimately rests in the hands of the hereditary Sultan. Consequently, Freedom House has routinely rated the country "Not Free".[130]
+The sultan is the head of state and directly controls the foreign affairs and defence portfolios.[131] He has absolute power and issues laws by decree.[132][133]
+Oman is an absolute monarchy, with the Sultan's word having the force of law. The judiciary branch is subordinate to the Sultan. According to Oman's constitution, Sharia law is one of the sources of legislation. Sharia court departments within the civil court system are responsible for family-law matters, such as divorce and inheritance.
+Oman does not have a system of checks and balances, and thus no separation of powers.[9] All power is concentrated in the Sultan,[9] who is also chief of staff of the armed forces, Minister of Defence, Minister of Foreign Affairs and chairman of the Central Bank.[9] All legislation since 1970 has been promulgated through royal decrees, including the 1996 Basic Law.[9] The Sultan appoints judges, and can grant pardons and commute sentences.[9] The Sultan's authority is inviolable and the Sultan expects total subordination to his will.[9]
+The administration of justice is highly personalized, with limited due process protections, especially in political and security-related cases.[134] The Basic Statute of the State[135] is supposedly the cornerstone of the Omani legal system and it operates as a constitution for the country. The Basic Statute was issued in 1996 and thus far has only been amended once, in 2011,[136] in response to protests.
+Though Oman's legal code theoretically protects civil liberties and personal freedoms, both are regularly ignored by the regime.[9] Women and children face legal discrimination in many areas.[9] Women are excluded from certain state benefits, such as housing loans, and are refused equal rights under the personal status law.[9] Women also experience restrictions on their self-determination in respect to health and reproductive rights.[9]
+The Omani legislature is the bicameral Council of Oman, consisting of an upper chamber, the Council of State (Majlis ad-Dawlah) and a lower chamber, the Consultative Council (Majlis ash-Shoura).[137] Political parties are banned.[133] The upper chamber has 71 members, appointed by the Sultan from among prominent Omanis; it has only advisory powers.[138] The 84 members of the Consultative Council are elected by popular vote to serve four-year terms, but the Sultan makes the final selections and can negotiate the election results.[138] The members are appointed for three-year terms, which may be renewed once.[137] The last elections were held on 27 October 2019, and the next is due in October 2023. Oman's national anthem, As-Salam as-Sultani is dedicated to former Sultan Qaboos.
+Homosexual acts are illegal in Oman.[139] The practice of torture is widespread in Oman state penal institutions and has become the state's typical reaction to independent political expression.[140][141] Torture methods in use in Oman include mock execution, beating, hooding, solitary confinement, subjection to extremes of temperature and to constant noise, abuse and humiliation.[140] There have been numerous reports of torture and other inhumane forms of punishment perpetrated by Omani security forces on protesters and detainees.[142] Several prisoners detained in 2012 complained of sleep deprivation, extreme temperatures and solitary confinement.[143] Omani authorities kept Sultan al-Saadi, a social media activist, in solitary confinement, denied him access to his lawyer and family, forced him to wear a black bag over his head whenever he left his cell, including when using the toilet, and told him his family had "forsaken" him and asked for him to be imprisoned.[143]
+The Omani government decides who can or cannot be a journalist and this permission can be withdrawn at any time.[145] Censorship and self-censorship are a constant factor.[145] Omanis have limited access to political information through the media.[146] Access to news and information can be problematic: journalists have to be content with news compiled by the official news agency on some issues.[145] Through a decree by the Sultan, the government has now extended its control over the media to blogs and other websites.[145] Omanis cannot hold a public meeting without the government's approval.[145] Omanis who want to set up a non-governmental organisation of any kind need a licence.[145] To get a licence, they have to demonstrate that the organisation is "for legitimate objectives" and not "inimical to the social order".[145] The Omani government does not permit the formation of independent civil society associations.[142] Human Rights Watch issued on 2016, that an Omani court sentenced three journalists to prison and ordered the permanent closure of their newspaper, over an article that alleged corruption in the judiciary.[147]
+The law prohibits criticism of the Sultan and government in any form or medium.[145] Oman's police do not need search warrants to enter people's homes.[145] The law does not provide citizens with the right to change their government.[145] The Sultan retains ultimate authority on all foreign and domestic issues.[145] Government officials are not subject to financial disclosure laws.[145] Libel laws and concerns for national security have been used to suppress criticism of government figures and politically objectionable views.[145] Publication of books is limited and the government restricts their importation and distribution, as with other media products.[145]
+Merely mentioning the existence of such restrictions can land Omanis in trouble.[145] In 2009, a web publisher was fined and given a suspended jail sentence for revealing that a supposedly live TV programme was actually pre-recorded to eliminate any criticisms of the government.[145]
+Faced with so many restrictions, Omanis have resorted to unconventional methods for expressing their views.[145] Omanis sometimes use donkeys to express their views.[145] Writing about Gulf rulers in 2001, Dale Eickelman observed: "Only in Oman has the occasional donkey… been used as a mobile billboard to express anti-regime sentiments. There is no way in which police can maintain dignity in seizing and destroying a donkey on whose flank a political message has been inscribed."[145] Some people have been arrested for allegedly spreading fake news about the COVID-19 pandemic in Oman.[148]
+Omani citizens need government permission to marry foreigners.[143] The Ministry of Interior requires Omani citizens to obtain permission to marry foreigners (except nationals of GCC countries); permission is not automatically granted.[143] Citizen marriage to a foreigner abroad without ministry approval may result in denial of entry for the foreign spouse at the border and preclude children from claiming citizenship rights.[143] It also may result in a bar from government employment and a fine of 2,000 rials ($5,200).[143]
+In August 2014, The Omani writer and human rights defender Mohammed Alfazari, the founder and editor-in-chief of the e-magazine Mowatin "Citizen", disappeared after going to the police station in the Al-Qurum district of Muscat.[149] For several months the Omani government denied his detention and refused to disclose information about his whereabouts or condition.[149] On 17 July 2015, Alfazari left Oman seeking political asylum in UK after a travel ban was issued against him without providing any reasons and after his official documents including his national ID and passport were confiscated for more than 8 months.[150] There were more reports of politically motivated disappearances in the country.[143] In 2012, armed security forces arrested Sultan al-Saadi, a social media activist.[143] According to reports, authorities detained him at an unknown location for one month for comments he posted online critical of the government.[143] Authorities previously arrested al-Saadi in 2011 for participating in protests and again in 2012 for posting comments online deemed insulting to Sultan Qaboos.[143] In May 2012 security forces detained Ismael al-Meqbali, Habiba al-Hinai and Yaqoub al-Kharusi, human rights activists who were visiting striking oil workers.[143] Authorities released al-Hinai and al-Kharusi shortly after their detention but did not inform al-Meqbali's friends and family of his whereabouts for weeks.[143] Authorities pardoned al-Meqbali in March.[143] In December 2013, a Yemeni national disappeared in Oman after he was arrested at a checkpoint in Dhofar Governorate.[151] Omani authorities refuse to acknowledge his detention.[151] His whereabouts and condition remain unknown.[151]
+The National Human Rights Commission, established in 2008, is not independent from the regime.[9] It is chaired by the former deputy inspector general of Police and Customs and its members are appointed by royal decree.[9] In June 2012, one of its members requested that she be relieved of her duties because she disagreed with a statement made by the Commission justifying the arrest of intellectuals and bloggers and the restriction of freedom of expression in the name of respect for "the principles of religion and customs of the country".[9]
+Since the beginning of the "Omani Spring" in January 2011, a number of serious violations of civil rights have been reported, amounting to a critical deterioration of the human rights situation.[9] Prisons are inaccessible to independent monitors.[9] Members of the independent Omani Group of Human Rights have been harassed, arrested and sentenced to jail. There have been numerous testimonies of torture and other inhumane forms of punishment perpetrated by security forces on protesters and detainees.[9] The detainees were all peacefully exercising their right to freedom of expression and assembly.[9] Although authorities must obtain court orders to hold suspects in pre-trial detention, they do not regularly do this.[9] The penal code was amended in October 2011 to allow the arrest and detention of individuals without an arrest warrant from public prosecutors.[9]
+In January 2014, Omani intelligence agents arrested a Bahraini actor and handed him over to the Bahraini authorities on the same day of his arrest.[152] The actor has been subjected to a forced disappearance, his whereabouts and condition remain unknown.[152]
+The plight of domestic workers in Oman is a taboo subject.[153][154] In 2011, the Philippines government determined that out of all the countries in the Middle East, only Oman and Israel qualify as safe for Filipino migrants.[155] In 2012, it was reported that every 6 days, an Indian migrant in Oman commits suicide.[156][157] There has been a campaign urging authorities to check the migrant suicide rate.[158] In the 2014 Global Slavery Index, Oman is ranked No. 45 due to 26,000 people in slavery.[159][160] The descendants of servant tribes and slaves are victims of widespread discrimination.[142][161] Oman was one of the last countries to abolish slavery in 1970.[154]
+Since 1970, Oman has pursued a moderate foreign policy, and has expanded its diplomatic relations dramatically. Oman is among the very few Arab countries that have maintained friendly ties with Iran.[162][163] WikiLeaks disclosed US diplomatic cables which state that Oman helped free British sailors captured by Iran's navy in 2007.[164] The same cables also portray the Omani government as wishing to maintain cordial relations with Iran, and as having consistently resisted US diplomatic pressure to adopt a sterner stance.[165][166][167] Yusuf bin Alawi bin Abdullah is the Sultanate's Minister Responsible for Foreign Affairs.
+Oman allowed the British Royal Navy and Indian Navy access to the port facilities of Al Duqm Port & Drydock.[168]
+Oman's military and security expenditure as a percentage of GDP in 2015 was 16.5 percent, making it the world's highest rate in that year.[169] Oman's on-average military spending as a percentage of GDP between 2016 and 2018 was around 10 percent, while the world's average during the same period was 2.2 percent.[170]
+Oman's military manpower totalled 44,100 in 2006, including 25,000 men in the army, 4,200 sailors in the navy, and an air force with 4,100 personnel. The Royal Household maintained 5,000 Guards, 1,000 in Special Forces, 150 sailors in the Royal Yacht fleet, and 250 pilots and ground personnel in the Royal Flight squadrons. Oman also maintains a modestly sized paramilitary force of 4,400 men.[171]
+The Royal Army of Oman had 25,000 active personnel in 2006, plus a small contingent of Royal Household troops. Despite a comparative large military spending, it has been relatively slow to modernise its forces. Oman has a relatively limited number of tanks, including 6 M60A1, 73 M60A3 and 38 Challenger 2 main battle tanks, as well as 37 aging Scorpion light tanks.[171]
+The Royal Air Force of Oman has approximately 4,100 men, with only 36 combat aircraft and no armed helicopters. Combat aircraft include 20 aging Jaguars, 12 Hawk Mk 203s, 4 Hawk Mk 103s and 12 PC-9 turboprop trainers with a limited combat capability. It has one squadron of 12 F-16C/D aircraft. Oman also has 4 A202-18 Bravos and 8 MFI-17B Mushshaqs.[171]
+The Royal Navy of Oman had 4,200 men in 2000, and is headquartered at Seeb. It has bases at Ahwi, Ghanam Island, Mussandam and Salalah. In 2006, Oman had 10 surface combat vessels. These included two 1,450-ton Qahir class corvettes, and 8 ocean-going patrol boats. The Omani Navy had one 2,500-ton Nasr al Bahr class LSL (240 troops, 7 tanks) with a helicopter deck. Oman also had at least four landing craft.[171] Oman ordered three Khareef class corvettes from the VT Group for £400 million in 2007. They were built at Portsmouth.[172] In 2010 Oman spent US$4.074 billion on military expenditures, 8.5% of the gross domestic product.[173] The sultanate has a long history of association with the British military and defence industry.[174] According to SIPRI, Oman was the 23rd largest arms importer from 2012 to 2016.[175]
+The Sultanate is administratively divided into eleven governorates. Governorates are, in turn, divided into 60 wilayats.[176][177]
+Oman's Basic Statute of the State expresses in Article 11 that the "national economy is based on justice and the principles of a free economy."[178] By regional standards, Oman has a relatively diversified economy, but remains dependent on oil exports. In terms of monetary value, mineral fuels accounted for 82.2 percent of total product exports in 2018.[179] Tourism is the fastest-growing industry in Oman. Other sources of income, agriculture and industry, are small in comparison and account for less than 1% of the country's exports, but diversification is seen as a priority by the government. Agriculture, often subsistence in its character, produces dates, limes, grains and vegetables, but with less than 1% of the country under cultivation, Oman is likely to remain a net importer of food.
+Oman's socio-economic structure is described as being hyper-centralized rentier welfare state.[169] The largest 10 percent of corporations in Oman are the employers of almost 80 percent of Omani nationals in the private sector. Half of the private sector jobs are classified as elementary. One third of employed Omanis are in the private sector, while the remaining majority are in the public sector.[180] A hyper-centralized structure produces a monopoly-like economy, which hinders having a healthy competitive environment between businesses.[169]
+Since a slump in oil prices in 1998, Oman has made active plans to diversify its economy and is placing a greater emphasis on other areas of industry, namely tourism and infrastructure. Oman had a 2020 Vision to diversify the economy established in 1995, which targeted a decrease in oil's share to less than 10 percent of GDP by 2020, but it was rendered obsolete in 2011. Oman then established 2040 Vision.[169]
+A free-trade agreement with the United States took effect 1 January 2009, eliminated tariff barriers on all consumer and industrial products, and also provided strong protections for foreign businesses investing in Oman.[181] Tourism, another source of Oman's revenue, is on the rise.[182] A popular event is The Khareef Festival held in Salalah, Dhofar, which is 1,200 km from the capital city of Muscat, during the monsoon season (August) and is similar to Muscat Festival. During this latter event the mountains surrounding Salalah are popular with tourists as a result of the cool weather and lush greenery, rarely found anywhere else in Oman.[183]
+Oman's foreign workers send an estimated US$10 billion annually to their home states in Asia and Africa, more than half of them earning a monthly wage of less than US$400.[184] The largest foreign community is from the Indian states of Kerala, Tamil Nadu, Karnataka, Maharashtra, Gujarat and the Punjab,[185] representing more than half of entire workforce in Oman. Salaries for overseas workers are known to be less than for Omani nationals, though still from two to five times higher than for the equivalent job in India.[184]
+In terms of foreign direct investment (FDI), total investments in 2017 exceeded US$24billion. The highest share of FDI went to the oil and gas sector, which represented around US$13billion (54.2 percent), followed by financial intermediation, which represented US$3.66billion (15.3 percent). FDI is dominated by the United Kingdom with an estimated value of US$11.56billion (48 percent), followed by the UAE USD 2.6billion (10.8 percent), followed by Kuwait USD 1.1billion (4.6 percent).[186]
+Foreign Direct Investment (FDI) in Oman by country as of 2017.[186]
+Oman, in 2018 had a budget deficit of 32 percent of total revenue and a government debt to GDP of 47.5 percent.[187][188] Oman's military spending to GDP between 2016 and 2018 averaged 10 percent, while the world's average during the same period was 2.2 percent.[189] Oman's health spending to GDP between 2015 and 2016 averaged 4.3 percent, while the world's average during the same period was 10 percent.[190] Oman's research and development spending between 2016 and 2017 averaged 0.24 percent, which is significantly lower than the world's average (2.2 percent) during the same period.[191] Oman's government spending on education to GDP in 2016 was 6.11 percent, while the world's average was 4.8 percent (2015).[192]
+Oman's proved reserves of petroleum total about 5.5 billion barrels, 25th largest in the world.[162] Oil is extracted and processed by Petroleum Development Oman (PDO), with proven oil reserves holding approximately steady, although oil production has been declining.[197][198] The Ministry of Oil and Gas is responsible for all oil and gas infrastructure and projects in Oman.[199] Following the 1970s energy crisis, Oman doubled their oil output between 1979 and 1985.[200]
+In 2018, oil and gas represented 71 percent of the government's revenues.[187] In 2016, oil and gas share of the government's revenue represented 72 percent.[201] The government's reliance on oil and gas as a source of income dropped by 1 percent from 2016 to 2018. Oil and gas sector represented 30.1 percent of the nominal GDP in 2017.[202]
+Between 2000 and 2007, production fell by more than 26%, from 972,000 to 714,800 barrels per day.[203] Production has recovered to 816,000 barrels in 2009, and 930,000 barrels per day in 2012.[203] Oman's natural gas reserves are estimated at 849.5 billion cubic metres, ranking 28th in the world, and production in 2008 was about 24 billion cubic metres per year.[162]
+In September 2019, Oman was confirmed to become the first Middle Eastern country to host the International Gas Union Research Conference (IGRC 2020). This 16th iteration of the event will be held between 24 and 26 February 2020, in collaboration with Oman LNG, under the auspices of the Ministry of Oil and Gas.[204]
+Tourism in Oman has grown considerably recently, and it is expected to be one of the largest industries in the country.[205] The World Travel & Tourism Council stated that Oman is the fastest growing tourism destination in the Middle East.[206]
+Tourism contributed 2.8 percent to the Omani GDP in 2016. It grew from RO 505 million (US$1.3 billion) in 2009 to RO 719 million (US$1.8 billion) in 2017 (+42.3 percent growth). Citizens of the Gulf Cooperation Council (GCC), including Omanis who are residing outside of Oman, represent the highest ratio of all tourists visiting Oman, estimated to be 48 percent. The second highest number of visitors come from other Asian countries, who account for 17 percent of the total number of visitors.[207] A challenge to tourism development in Oman is the reliance on the government-owned firm, Omran, as a key actor to develop the tourism sector, which potentially creates a market barrier-to-entry of private-sector actors and a crowding out effect. Another key issue to the tourism sector is deepening the understanding of the ecosystem and biodiversity in Oman to guarantee their protection and preservation.[208]
+Oman has one of the most diverse environments in the Middle East with various tourist attractions and is particularly well known for adventure and cultural tourism.[182][209] Muscat, the capital of Oman, was named the second best city to visit in the world in 2012 by the travel guide publisher Lonely Planet.[210] Muscat also was chosen as the Capital of Arab Tourism of 2012.[211]
+In November 2019, Oman made the rule of visa on arrival an exception and introduced the concept of e-visa for tourists from all nationalities. Under the new laws, visitors were required to apply for the visa in advance by visiting Oman's online government portal.[212]
+In industry, innovation and infrastructure, Oman is still faced with "significant challenges", as per United Nations Sustainable Development Goals index, as of 2019. Oman has scored high on the rates of internet use, mobile broadband subscriptions, logistics performance and on the average of top 3 university rankings. Meanwhile, Oman scored low on the rate of scientific and technical publications and on research & development spending.[123] Oman's manufacturing value added to GDP rate in 2016 was 8.4 percent, which is lower than the average in the Arab world (9.8 percent) and world average (15.6 percent). In terms of research & development expenditures to GDP, Oman's share was on average 0.20 percent between 2011 and 2015, while the world's average during the same period was 2.11 percent.[213] The majority of firms in Oman operate in the oil and gas, construction and trade sectors.[208]
+Oman is refurbishing and expanding the ports infrastructure in Muscat, Duqm, Sohar and Salalah to expand tourism, local production and export shares. Oman is also expanding its downstream operations by constructing a refinery and petrochemical plant in Duqm with a 230,000 barrels per day capacity projected for completion by 2021.[186] The majority of industrial activity in Oman takes place in 8 industrial states and 4 free-zones. The industrial activity is mainly focused on mining-and-services, petrochemicals and construction materials.[208] The largest employers in the private-sector are the construction, wholesale-and-retail and manufacturing sectors, respectively. Construction accounts for nearly 48 percent of the total labour force, followed by wholesale-and-retail, which accounts for around 15 percent of total employment and manufacturing, which accounts for around 12 percent of employment in the private sector. The percentage of Omanis employed in the construction and manufacturing sectors is nevertheless low, as of 2011 statistics.[180]
+Oman, as per Global Innovation Index (2019) report, scores "below expectations" in innovation relative to countries classified under high income.[215] Oman in 2019 ranked 80 out of 129 countries in innovation index, which takes into consideration factors, such as, political environment, education, infrastructure and business sophistication.[216] Innovation, technology-based growth and economic diversification are hindered by an economic growth that relies on infrastructure expansion, which heavily depends on a high percentage of 'low-skilled' and 'low-wage' foreign labour. Another challenge to innovation is the dutch disease phenomenon, which creates an oil and gas investment lock-in, while relying heavily on imported products and services in other sectors. Such a locked-in system hinders local business growth and global competitiveness in other sectors, and thus impedes economic diversification.[208] The inefficiences and bottlenecks in business operations that are a result of heavy dependence on natural resources and 'addiction' to imports in Oman suggest a 'factor-driven economy'.[180] A third hindrance to innovation in Oman is an economic structure that is heavily dependent on few large firms, while granting few opportunities for SMEs to enter the market, which impedes healthy market-share competition between firms.[208] The ratio of patent applications per million people was 0.35 in 2016 and the MENA region average was 1.50, while the 'high-income' countries' average was approximately 48.0 during the same year.[217]
+Oman's fishing industry contributed 0.78 percent to the GDP in 2016. Fish exports between 2000 and 2016 grew from US$144 million to US$172 million (+19.4 percent). The main importer of Omani fish in 2016 was Vietnam, which imported almost US$80 million (46.5 percent) in value, and the second biggest importer was the United Arab Emirates, which imported around US$26 million (15 percent). The other main importers are Saudi Arabia, Brazil and China. Oman's consumption of fish is almost two times the world's average. The ratio of exported fish to total fish captured in tons fluctuated between 49 and 61 percent between 2006 and 2016. Omani strengths in the fishing industry comes from having a good market system, a long coastline (3,165 km) and wide water area. Oman, on the other hand, lacks sufficient infrastructure, research and development, quality and safety monitoring, together with a limited contribution by the fishing industry to GDP.[207]
+Dates represent 80 percent of all fruit crop production. Further, date farms employ 50 percent of the total agricultural area in the country. Oman's estimated production of dates in 2016 is 350,000 tons, making it the 9th largest producer of dates. The vast majority of date production (75 percent) comes from only 10 cultivars. Oman's total export of dates was US$12.6 million in 2016, almost equivalent to Oman's total imported value of dates, which was US$11.3 million in 2016. The main importer is India (around 60 percent of all imports). Oman's date exports remained steady between 2006 and 2016. Oman is considered to have good infrastructure for date production and support provision to cultivation and marketing, but lacks innovation in farming and cultivation, industrial coordination in the supply chain and encounter high losses of unused dates.[207]
+As of 2014[update], Oman's population is over 4 million, with 2.23 million Omani nationals and 1.76 million expatriates.[219] The total fertility rate in 2011 was estimated at 3.70.[220] Oman has a very young population, with 43 percent of its inhabitants under the age of 15. Nearly 50 percent of the population lives in Muscat and the Batinah coastal plain northwest of the capital. Omani people are predominantly of Arab, Baluchi and African origins.[162]
+Omani society is largely tribal[161][221][222] and encompasses three major identities:[161] that of the tribe, the Ibadi faith and maritime trade.[161] The first two identities are closely tied to tradition and are especially prevalent in the interior of the country, owing to lengthy periods of isolation.[161] The third identity pertains mostly to Muscat and the coastal areas of Oman, and is reflected by business, trade,[161] and the diverse origins of many Omanis, who trace their roots to Baloch, Al-Lawatia, Persia and historical Omani Zanzibar.[223] Consequently, the third identity is generally seen to be more open and tolerant towards others,[161] and is often in tension with the more traditional and insular identities of the interior.[161]
+Religion in Oman (2010)[224]
+Even though the Oman government does not keep statistics on religious affiliation, statistics from the US's Central Intelligence Agency state that adherents of Islam are in the majority at 85.9%, with Christians at 6.5%, Hindus at 5.5%, Buddhists at 0.8%, Jews less than 0.1%. Other religious affiliations have a proportion of 1% and the unaffiliated only 0.2%.
+Most Omanis are Muslims, most of whom follow the Ibadi[225] School of Islam, followed by the Twelver school of Shia Islam and Shafi`i school of Sunni Islam.
+Virtually all non-Muslims in Oman are foreign workers. Non-Muslim religious communities include various groups of Jains, Buddhists, Zoroastrians, Sikhs, Jews, Hindus and Christians. Christian communities are centred in the major urban areas of Muscat, Sohar and Salalah. These include Catholic, Eastern Orthodox and various Protestant congregations, organising along linguistic and ethnic lines. More than 50 different Christian groups, fellowships and assemblies are active in the Muscat metropolitan area, formed by migrant workers from Southeast Asia.
+There are also communities of ethnic Indian Hindus and Christians. Muscat has two Hindu temples. One of them is over a hundred years old. There is a significant Sikh community in Oman. Though there are no permanent gurdwaras, many smaller gurdwaras in makeshift camps exist and are recognised by the government. The Government of India had signed an accord in 2008 with the Omani government to build a permanent gurdwara but little progress has been made on the matter.[226]
+Arabic is the official language of Oman. It belongs to the Semitic branch of the Afroasiatic family.[178] Prior to Islam, Central Oman lay outside of the core area of spoken Arabic. Possibly Old South Arabian speakers dwelled from the Bāṭinah to Ẓafār.[227] Rare Musnad inscriptions have come to light in central Oman and in the Emirate of Sharjah, but the script says nothing about the language which it conveys.[228] A bilingual text from the 3rd century BCE is written in Aramaic and in musnad Hasiatic, which mentions a 'king of Oman' (mālk mn ʿmn).[229] Today the Mehri language is limited in its distribution to the area around Ṣalālah in Ẓafār and westward into the Yemen. But until the 18th or 19th century it was spoken further north, perhaps into Central Oman.[230] Baluchi (Southern Baluchi) is widely spoken in Oman.[231] Endangered indigenous languages in Oman include Kumzari, Bathari, Harsusi, Hobyot, Jibbali and Mehri.[232] Omani Sign Language is the language of the deaf community. Oman was also the first Arab country in the Persian Gulf to have German taught as a second language.[233] The Bedouin Arabs, who reached eastern and southeastern Arabia in migrational waves—the latest in the 18th century, brought their language and rule including the ruling families of Bahrain, Qatar and the United Arab Emirates.[234] At the most basic level, there are two kinds of dialects, those of settlers and those of Bedouin which share some features. Omani dialects preserve much vocabulary which has been lost in other Arabic dialects. C. Holes has argued convincingly that Omani Arabic has indigenous characteristics of its own which do not derive from Bedouin central Arabia. They are better preserved than in neighbouring countries.
+According to the CIA, besides Arabic, English, Baluchi (Southern Baluchi), Urdu and various Indian languages are the main languages spoken in Oman.[162] English is widely spoken in the business community and is taught at school from an early age. Almost all signs and writings appear in both Arabic and English at tourist sites.[182] Baluchi is the mother tongue of the Baloch people from Balochistan in western Pakistan, eastern Iran and southern Afghanistan. It is also used by some descendants of Sindhi sailors.[235] A significant number of residents also speak Urdu, due to the influx of Pakistani migrants during the late 1980s and 1990s. Additionally, Swahili is widely spoken in the country due to the historical relations between Oman and Zanzibar.[8]
+Outwardly, Oman shares many of the cultural characteristics of its Arab neighbours, particularly those in the Gulf Cooperation Council.[237] Despite these similarities, important factors make Oman unique in the Middle East.[237] These result as much from geography and history as from culture and economics.[237] The relatively recent and artificial nature of the state in Oman makes it difficult to describe a national culture;[237] however, sufficient cultural heterogeneity exists within its national boundaries to make Oman distinct from other Arab States of the Persian Gulf.[237] Oman's cultural diversity is greater than that of its Arab neighbours, given its historical expansion to the Swahili Coast and the Indian Ocean.[237]
+Oman has a long tradition of shipbuilding, as maritime travel played a major role in the Omanis' ability to stay in contact with the civilisations of the ancient world. Sur was one of the most famous shipbuilding cities of the Indian Ocean. The Al Ghanja ship takes one whole year to build. Other types of Omani ship include As Sunbouq and Al Badan.[238]
+In March 2016 archaeologists working off Al Hallaniyah Island identified a shipwreck believed to be that of the Esmeralda from Vasco da Gama's 1502–1503 fleet. The wreck was initially discovered in 1998. Later underwater excavations took place between 2013 and 2015 through a partnership between the Oman Ministry of Heritage and Culture and Blue Water Recoveries Ltd., a shipwreck recovery company. The vessel was identified through such artifacts as a "Portuguese coin minted for trade with India (one of only two coins of this type known to exist) and stone cannonballs engraved with what appear to be the initials of Vincente Sodré, da Gama's maternal uncle and the commander of the Esmeralda."[239]
+The male national dress in Oman consists of the dishdasha, a simple, ankle-length, collarless gown with long sleeves.[150] Most frequently white in colour, the dishdasha may also appear in a variety of other colours. Its main adornment, a tassel (furakha) sewn into the neckline, can be impregnated with perfume.[240] Underneath the dishdasha, men wear a plain, wide strip of cloth wrapped around the body from the waist down. The most noted regional differences in dishdasha designs are the style with which they are embroidered, which varies according to age group.[150] On formal occasions a black or beige cloak called a bisht may cover the dishdasha. The embroidery edging the cloak is often in silver or gold thread and it is intricate in detail.[240]
+Omani men wear two types of headdress:
+Some men carry the assa, a stick, which can have practical uses or is simply used as an accessory during formal events. Omani men, on the whole, wear sandals on their feet.[240]
+The khanjar (dagger) forms part of the national dress and men wear the khanjar on all formal public occasions and festivals.[150] It is traditionally worn at the waist. Sheaths may vary from simple covers to ornate silver or gold-decorated pieces.[240] It is a symbol of a man's origin, his manhood and courage. A depiction of a khanjar appears on the national flag.[150]
+Omani women wear eye-catching national costumes, with distinctive regional variations. All costumes incorporate vivid colours and vibrant embroidery and decorations. In the past, the choice of colours reflected a tribe's tradition. The Omani women's traditional costume comprises several garments: the kandoorah, which is a long tunic whose sleeves or radoon are adorned with hand-stitched embroidery of various designs. The dishdasha is worn over a pair of loose fitting trousers, tight at the ankles, known as a sirwal. Women also wear a head shawl most commonly referred to as the lihaf.[241]
+As of 2014[update] women reserve wearing their traditional dress for special occasions, and instead wear a loose black cloak called an abaya over their personal choice of clothing, whilst in some regions, particularly amongst the Bedouin, the burqa is still worn.[241] Women wear hijab, and though some women cover their faces and hands, most do not. The Sultan has forbidden the covering of faces in public office.[236]
+Music of Oman is extremely diverse due to Oman's imperial legacy. There are over 130 different forms of traditional Omani songs and dances. The Oman Centre for Traditional Music was established in 1984 to preserve them.[242] In 1985, Sultan Qaboos founded the Royal Oman Symphony Orchestra, an act attributed[by whom?] to his love for classical music. Instead of engaging foreign musicians, he decided to establish an orchestra made up of Omanis.[243] On 1 July 1987 at the Al Bustan Palace Hotel's Oman Auditorium the Royal Oman Symphony Orchestra gave its inaugural concert.[244]
+The cinema of Oman is very small, there being only one Omani film Al-Boom (2006) as of 2007[update]. Oman Arab Cinema Company LLC is the single largest motion picture exhibitor chain in Oman. It belongs to the Jawad Sultan Group of Companies, which has a history spanning more than 40 years in the Sultanate of Oman.[245] In popular music, a seven-minute music video about Oman went viral, achieving 500,000 views on YouTube within 10 days of being released on YouTube in November 2015. The a cappella production features three of the region's most popular talents: Kahliji musician Al Wasmi, Omani poet Mazin Al-Haddabi and actress Buthaina Al Raisi.[246]
+The government has continuously held a monopoly on television in Oman.  Oman TV is the only state-owned national television channel broadcaster in Oman. It began broadcasting for the first time from Muscat on 17 November 1974 and separately from Salalah on 25 November 1975. On 1 June 1979, the two stations at Muscat and Salalah linked by satellite to form a unified broadcasting service. Oman TV broadcasts four HD channels, including Oman TV General, Oman TV Sport, Oman TV Live and Oman TV Cultural.[247]
+Although private ownership of radio and television stations is permitted, Oman has only one privately owned television channel.[248] Majan TV is the first private TV channel in Oman. It began broadcasting on January 2009. However, Majan TV's official channel website was last updated in early 2010.[249] Moreover, the public has access to foreign broadcasts since the use of satellite receivers is allowed.[248][250]
+Oman Radio is the first and only state-owned radio channel.[248] It began broadcasting on the 30th, July 1970.[251] It operates both Arabic and English networks. Other private channels include Hala FM, Hi FM, Al-Wisal, Virgin Radio Oman FM and Merge. In early 2018, Muscat Media Group (MMG), trend-setting media group founded by late Essa bin Mohammed Al Zedjali, launched a new private radio stations in hopes of catering educative and entertaining programmes to the youth of the Sultanate.[252][253][254]
+Oman has nine main newspapers, five in Arabic and four in English.[255] Instead of relying on sales or state subsidies, private newspapers depend on advertising revenues to sustain themselves.[256]
+The media landscape in Oman has been continuously described as restrictive, censored, and subdued.[257] The Ministry of Information censors politically, culturally, or sexually offensive material in domestic or foreign media. The press freedom group Reporters Without Borders ranked the country 127th out of 180 countries on its 2018 World Press Freedom Index. In 2016, the government drew international criticism for suspending the newspaper Azamn and arresting three journalists after a report on corruption in the country's judiciary. Azamn was not allowed to reopen in 2017 although an appeal court ruled in late 2016 that the paper can resume operating.[256]
+Traditional art in Oman stems from its long heritage of material culture. Art movements in the 20th century reveal that the art scene in Oman began with early practices that included a range of tribal handicrafts and self-portraiture in painting since the 1960s.[258] However, since the inclusion of several Omani artists in international collections, art exhibitions, and events, such Alia Al Farsi, the first Omani artist to show at the last Venice Biennale and Radhika Khimji, the first Omani artist to exhibit at both the Marrakesh and Haiti Ghetto biennale, Oman's position as a newcomer to the contemporary art scene in recent years has been more important for Oman's international exposure.[259]
+Bait Muzna Gallery is the first art gallery in Oman. Established in 2000 by Sayyida Susan Al Said, Bait Muzna has served as a platform for emerging Omani artists to showcase their talent and place themselves on the wider art scene. In 2016, Bait Muzna opened a second space in Salalah to branch out and support art film and the digital art scene. The gallery has been primarily active as an art consultancy.[259][261]
+The Sultanate's flagship cultural institution, the National Museum of Oman, opened on 30 July 2016 with 14 permanent galleries. It showcases national heritage from the earliest human settlement in Oman two million years ago through to the present day. The museum takes a further step by presenting information on the material in Arabic Braille script for the visually impaired, the first museum to do this in the Gulf region.[259]
+The Omani Society for Fine Arts, established in 1993, offers educational programmes, workshops and artist grants for practitioners across varied disciplines. In 2016, the organisation opened its first exhibition on graphic design. It also hosted the "Paint for Peace" competition with 46 artists in honour of the country's 46th National Day, where Mazin al-Mamari won the top prize. The organisation has additional branches in Sohar, Buraimi and Salalah.[259]
+Bait Al- Zubair Museum is a private, family-funded museum that opened its doors to the public in 1998. In 1999, the museum received Sultan Qaboos’ Award for Architectural Excellence. Bait Al Zubair displays the family's collection of Omani artifacts that spans a number of centuries and reflect inherited skills that define Oman's society in the past and present. Located within Bait Al-Zubair, Gallery Sarah, which opened in October 2013, offers an array of paintings and photographs by established local and international artists. The gallery also occasionally holds lectures and workshops.[262]
+Omani cuisine is diverse and has been influenced by many cultures. Omanis usually eat their main daily meal at midday, while the evening meal is lighter. During Ramadan, dinner is served after the Taraweeh prayers, sometimes as late as 11 pm. However, these dinner timings differ according to each family; for instance, some families would choose to eat right after maghrib prayers and have dessert after taraweeh.
+Arsia, a festival meal served during celebrations, consists of mashed rice and meat (sometimes chicken). Another popular festival meal, shuwa, consists of meat cooked very slowly (sometimes for up to 2 days) in an underground clay oven. The meat becomes extremely tender and it is infused with spices and herbs before cooking to give it a very distinct taste. Fish is often used in main dishes too, and the kingfish is a popular ingredient. Mashuai is a meal consisting of a whole spit-roasted kingfish served with lemon rice.
+Rukhal bread is a thin, round bread originally baked over a fire made from palm leaves. It is eaten at any meal, typically served with Omani honey for breakfast or crumbled over curry for dinner. Chicken, fish, and lamb or mutton are regularly used in dishes. The Omani halwa is a very popular sweet, basically consisting of cooked raw sugar with nuts. There are many different flavors, the most popular ones being black halwa (original) and saffron halwa. Halwa is considered as a symbol of Omani hospitality, and is traditionally served with coffee. As is the case with most Arab states of the Persian Gulf, alcohol is only available over-the-counter to non-Muslims. Muslims can still purchase alcoholic drinks. Alcohol is served in many hotels and a few restaurants.
+In October 2004, the Omani government set up a Ministry of Sports Affairs to replace the General Organisation for Youth, Sports and Cultural Affairs. The 19th Arabian Gulf Cup took place in Muscat, from 4 to 17 January 2009 and was won by the Omani national football team. The 23rd Arabian Gulf Cup that took place in Kuwait, from 22 December 2017 until 5 January 2018 with Oman winning their second title, defeating the United Arab Emirates in the final on penalties following a goalless draw.
+Oman's traditional sports are dhow racing, horse racing, camel racing, bull fighting and falconry.[263] Association football, basketball, waterskiing and sandboarding are among the sports that have emerged quickly and gained popularity among the younger generation.[263]
+Ali Al-Habsi is an Omani professional association football player. As of 2020[update], he plays in the Football League Championship as a goalkeeper for West Brom.[264] The International Olympic Committee awarded[when?] the former GOYSCA its prestigious prize for Sporting excellence in recognition of its contributions to youth and sports and its efforts to promote the Olympic spirit and goals.
+The Oman Olympic Committee played a major part in organising the highly successful 2003 Olympic Days, which were of great benefit to the sports associations, clubs and young participants. The football association took part, along with the handball, basketball, rugby union, hockey, volleyball, athletics, swimming and tennis associations. In 2010 Muscat hosted the 2010 Asian Beach Games.
+Oman also hosts tennis tournaments in different age divisions each year. The Sultan Qaboos Sports Complex stadium contains a 50-meter swimming pool which is used for international tournaments from different schools in different countries. The Tour of Oman, a professional cycling 6-day stage race, takes place in February. Oman hosted the Asian 2011 FIFA Beach Soccer World Cup qualifiers, where 11 teams competed for three spots at the FIFA World Cup. Oman hosted the Men's and Women's 2012 Beach Handball World Championships at the Millennium Resort in Mussanah, from 8 to 13 July.[265] Oman has competed repeatedly for a position in the FIFA World Cup, but have yet qualified to compete in the tournament.
+Oman, along with Fujairah in the UAE, are the only regions in the Middle East that have a variant of bullfighting, known as 'bull-butting', organised within their territories.[266] Al-Batena area in Oman is specifically prominent for such events. It involves two bulls of the Brahman breed pitted against one another and as the name implies, they engage in a forceful barrage of headbutts. The first one to collapse or concede its ground is declared the loser. Most bull-butting matches are short affairs and last for less than 5 minutes.[266][267] The origins of bull-butting in Oman remain unknown, but many locals believe it was brought to Oman by the Moors of Spanish origin. Yet others say it has a direct connection with Portugal, which colonised the Omani coastline for nearly two centuries.[268]
+In Cricket, Oman qualified for the 2016 ICC World Twenty20 by securing sixth place in 2015 ICC World Twenty20 Qualifier. They have also been granted T20I status as they were among the top six teams in the qualifiers. On 30 October 2019, they qualified for 2020 T20 Cricket World Cup which will be hosted by Australia.
+Oman scored high as of 2019 on the percentage of students who complete lower secondary school and on the literacy rate between the age of 15 and 24, 99.7 percent and 98.7 percent, respectively. However, Oman's net primary school enrollment rate in 2019, which is 94.1 percent, is rated as "challenges remain" by the United Nations Sustainable Development Goals (UNSDG) standard. Oman's overall evaluation in quality of education, according to UNSDG, is 94.8 ("challenges remain") as of 2019.[123]
+Oman's higher education produces a surplus in humanities and liberal arts, while it produces an insufficient number in technical and scientific fields and required skill-sets to meet the market demand.[208] Further, sufficient human capital creates a business environment that can compete with, partner or attract foreign firms. Accreditation standards and mechanisms with a quality control that focuses on input assessments, rather than output, are areas of improvement in Oman, according to the United Nations Conference on Trade and Development 2014 report.[208] The transformation Index BTI 2018 report on Oman recommends that the education curriculum should focus more on the "promotion of personal initiative and critical perspective".[169]
+The adult literacy rate in 2010 was 86.9%.[270] Before 1970, only three formal schools existed in the entire country, with fewer than 1,000 students. Since Sultan Qaboos' ascension to power in 1970, the government has given high priority to education to develop a domestic work force, which the government considers a vital factor in the country's economic and social progress. Today, there are over 1,000 state schools and about 650,000 students.
+Oman's first university, Sultan Qaboos University, opened in 1986. The University of Nizwa is one of the fastest growing universities in Oman. Other post-secondary institutions in Oman include the Higher College of Technology and its six branches, six colleges of applied sciences (including a teachers' training college), a college of banking and financial studies, an institute of Sharia sciences, and several nursing institutes. Some 200 scholarships are awarded each year for study abroad.
+According to the Webometrics Ranking of World Universities, the top-ranking universities in the country are Sultan Qaboos University (1678th worldwide), the Dhofar University (6011th) and the University of Nizwa (6093rd).[271]
+Since 2003, Oman's undernourished share of the population has dropped from 11.7 percent to 5.4 percent in 2016, but the rate remains high (double) the level of high-income economies (2.7 percent) in 2016.[272] The UNSDG targets zero hunger by 2030.[273] Oman's coverage of essential health services in 2015 was 77 percent, which is relatively higher than the world's average of approximately 54 percent during the same year, but lower than high-income economies' level (83 percent) in 2015.[274]
+Since 1995, the percentage of Omani children who receive key vaccines has consistently been very high (above 99 percent). As for road incident death rates, Oman's rate has been decreasing since 1990, from 98.9 per 100,000 individuals to 47.1 per 100,000 in 2017, however, the rate remains significantly above average, which was 15.8 per 100,000 in 2017.[275] Oman's health spending to GDP between 2015 and 2016 averaged 4.3 percent, while the world's average during the same period averaged 10 percent.[190]
+As for mortality due to air pollution (household and ambient air pollution), Oman's rate was 53.9 per 100,000 population as of 2016.[276]
+Life expectancy at birth in Oman was estimated to be 76.1 years in 2010.[220] As of 2010[update], there were an estimated 2.1 physicians and 2.1 hospital beds per 1,000 people.[220] In 1993, 89% of the population had access to health care services. In 2000, 99% of the population had access to health care services.[citation needed] During the last three decades, the Oman health care system has demonstrated and reported great achievements in health care services and preventive and curative medicine. Oman has been making strides in health research too recently. Comprehensive research on the prevalence of skin diseases was performed in North batinah governorate.[277] In 2000, Oman's health system was ranked number 8 by the World Health Organization.[278]

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+A shadow is a dark (real image) area where light from a light source is blocked by an opaque object. It occupies all of the three-dimensional volume behind an object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or a reverse projection of the object blocking the light.
+A point source of light casts only a simple shadow, called an "umbra". For a non-point or "extended" source of light, the shadow is divided into the umbra, penumbra and antumbra. The wider the light source, the more blurred the shadow becomes.  If two penumbras overlap, the shadows appear to attract and merge.  This is known as the shadow blister effect.
+The outlines of the shadow zones can be found by tracing the rays of light emitted by the outermost regions of the extended light source. The umbra region does not receive any direct light from any part of the light source, and is the darkest. A viewer located in the umbra region cannot directly see any part of the light source.
+By contrast, the penumbra is illuminated by some parts of the light source, giving it an intermediate level of light intensity. A viewer located in the penumbra region will see the light source, but it is partially blocked by the object casting the shadow.
+If there is more than one light source, there will be several shadows, with the overlapping parts darker, and various combinations of brightnesses or even colors. The more diffuse the lighting is, the softer and more indistinct the shadow outlines become, until they disappear. The lighting of an overcast sky produces few visible shadows.
+The absence of diffusing atmospheric effects in the vacuum of outer space produces shadows that are stark and sharply delineated by high-contrast boundaries between light and dark.
+For a person or object touching the surface where the shadow is projected (e.g. a person standing on the ground, or a pole in the ground) the shadows converge at the point of contact.
+A shadow shows, apart from distortion, the same image as the silhouette when looking at the object from the sun-side, hence the mirror image of the silhouette seen from the other side.
+The names umbra, penumbra and antumbra are often used for the shadows cast by astronomical objects, though they are sometimes used to describe levels of darkness, such as in sunspots.  An astronomical object casts human-visible shadows when its apparent magnitude is equal or lower than -4.[2] The only astronomical objects able to project visible shadows onto Earth are the Sun, the Moon, and in the right conditions, Venus or Jupiter.[3] Night is caused by the hemisphere of a planet facing its orbital star blocking its sunlight.
+A shadow cast by the Earth onto the Moon is a lunar eclipse. Conversely, a shadow cast by the Moon onto the Earth is a solar eclipse.[4]
+The sun casts shadows which change dramatically through the day. The length of a shadow cast on the ground is proportional to the cotangent of the sun's elevation angle—its angle θ relative to the horizon. Near sunrise and sunset, when θ = 0° and cot(θ) = ∞, shadows can be extremely long. If the sun passes directly overhead (only possible in locations between the Tropics of Cancer and Capricorn), then θ = 90°, cot(θ) = 0, and shadows are cast directly underneath objects.
+Such variations have long aided travellers during their travels, especially in barren regions such as the Arabian Desert.[5]
+The farther the distance from the object blocking the light to the surface of projection, the larger the silhouette (they are considered proportional). Also, if the object is moving, the shadow cast by the object will project an image with dimensions (length) expanding proportionally faster than the object's own rate of movement. The increase of size and movement is also true if the distance between the object of interference and the light source are closer. This, however, does not mean the shadow may move faster than light, even when projected at vast distances, such as light years. The loss of light, which projects the shadow, will move towards the surface of projection at light speed.
+Although the edge of a shadow appears to "move" along a wall, in actuality the increase of a shadow's length is part of a new projection which propagates at the speed of light from the object of interference. Since there is no actual communication between points in a shadow (except for reflection or interference of light, at the speed of light), a shadow that projects over a surface of large distances (light years) cannot convey information between those distances with the shadow's edge.[6]
+Visual artists are usually very aware of colored light emitted or reflected from several sources, which can generate complex multicolored shadows. Chiaroscuro, sfumato, and silhouette are examples of artistic techniques which make deliberate use of shadow effects.
+During the daytime, a shadow cast by an opaque object illuminated by sunlight has a bluish tinge. This happens because of Rayleigh scattering, the same property that causes the sky to appear blue. The opaque object is able to block the light of the sun, but not the ambient light of the sky which is blue as the atmosphere molecules scatter blue light more effectively. As a result, the shadow appears bluish.[7]
+A shadow occupies a three-dimensional volume of space, but this is usually not visible until it projects onto a reflective surface. A light fog, mist, or dust cloud can reveal the 3D presence of volumetric patterns in light and shadow.
+Fog shadows may look odd to viewers who are not used to seeing shadows in three dimensions. A thin fog is just dense enough to be illuminated by the light that passes through the gaps in a structure or in a tree.  As a result, the path of an object's shadow through the fog becomes visible as a darkened volume. In a sense, these shadow lanes are the inverse of crepuscular rays caused by beams of light, but caused by the shadows of solid objects.
+Theatrical fog and strong beams of light are sometimes used by lighting designers and visual artists who seek to highlight three-dimensional aspects of their work.
+Oftentimes shadows of chain-linked fences and other such objects become inverted (light and dark areas are swapped) as they get farther from the object. A chain-link fence shadow will start with light diamonds and shadow outlines when it is touching the fence, but it will gradually blur. Eventually, if the fence is tall enough, the light pattern will go to shadow diamonds and light outlines.
+In photography, which is essentially recording patterns of light, shade, and color, "highlights" and "shadows" are the brightest and darkest parts, respectively, of a scene or image. Photographic exposure must be adjusted (unless special effects are wanted) to allow the film or sensor, which has limited dynamic range, to record detail in the highlights without them being washed out, and in the shadows without their becoming undifferentiated black areas.
+On satellite imagery and aerial photographs, taken vertically, tall buildings can be recognized as such by their long shadows (if the photographs are not taken in the tropics around noon), while these also show more of the shape of these buildings.
+Shadow as a term is often used for any occlusion or blockage, not just those with respect to light.  For example, a rain shadow is a dry area, which with respect to the prevailing wind direction, is beyond a mountain range; the elevated terrain impedes rainclouds from entering the dry zone. An acoustic shadow occurs when direct sound has been blocked or diverted around a given area.
+An unattended shade was thought by some cultures to be similar to that of a ghost. The name for the fear of shadows is "sciophobia" or "sciaphobia".
+Chhaya is the Hindu goddess of shadows.
+In heraldry, when a charge is supposedly shown "in shadow" (the appearance is of the charge merely being outlined in a neutral tint rather than being of one or more tinctures different from the field on which it is placed), it is technically described as "umbrated".  Supposedly, only a limited number of specific charges can be so depicted.[citation needed]
+Scientists from the National University of Singapore presented a shadow-effect energy generator (SEG), which consists of cells of gold deposited on a silicon wafer attached on a plastic film. The generator has a power density of 0.14 μW cm−2 under indoor conditions (0.001 sun).[8]
+Non-diffuse lighting in outer space causes deep shadows
+Reversed text in shadow
+Sutro Tower casts a 3D fog shadow
+This photo of jasmine flowers has only soft shadows cast by diffused light
+Clouds and shadows over the Mediterranean Sea
+Shadow cast by vapour trail of passing aircraft
+Tree shadow
+Shadow on the Castle
+Long shadow of a dead tree with its branches on dry fields, late afternoon
+When the sun is low, shadows become long, and details get the wrong proportions.

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+A shadow is a dark (real image) area where light from a light source is blocked by an opaque object. It occupies all of the three-dimensional volume behind an object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or a reverse projection of the object blocking the light.
+A point source of light casts only a simple shadow, called an "umbra". For a non-point or "extended" source of light, the shadow is divided into the umbra, penumbra and antumbra. The wider the light source, the more blurred the shadow becomes.  If two penumbras overlap, the shadows appear to attract and merge.  This is known as the shadow blister effect.
+The outlines of the shadow zones can be found by tracing the rays of light emitted by the outermost regions of the extended light source. The umbra region does not receive any direct light from any part of the light source, and is the darkest. A viewer located in the umbra region cannot directly see any part of the light source.
+By contrast, the penumbra is illuminated by some parts of the light source, giving it an intermediate level of light intensity. A viewer located in the penumbra region will see the light source, but it is partially blocked by the object casting the shadow.
+If there is more than one light source, there will be several shadows, with the overlapping parts darker, and various combinations of brightnesses or even colors. The more diffuse the lighting is, the softer and more indistinct the shadow outlines become, until they disappear. The lighting of an overcast sky produces few visible shadows.
+The absence of diffusing atmospheric effects in the vacuum of outer space produces shadows that are stark and sharply delineated by high-contrast boundaries between light and dark.
+For a person or object touching the surface where the shadow is projected (e.g. a person standing on the ground, or a pole in the ground) the shadows converge at the point of contact.
+A shadow shows, apart from distortion, the same image as the silhouette when looking at the object from the sun-side, hence the mirror image of the silhouette seen from the other side.
+The names umbra, penumbra and antumbra are often used for the shadows cast by astronomical objects, though they are sometimes used to describe levels of darkness, such as in sunspots.  An astronomical object casts human-visible shadows when its apparent magnitude is equal or lower than -4.[2] The only astronomical objects able to project visible shadows onto Earth are the Sun, the Moon, and in the right conditions, Venus or Jupiter.[3] Night is caused by the hemisphere of a planet facing its orbital star blocking its sunlight.
+A shadow cast by the Earth onto the Moon is a lunar eclipse. Conversely, a shadow cast by the Moon onto the Earth is a solar eclipse.[4]
+The sun casts shadows which change dramatically through the day. The length of a shadow cast on the ground is proportional to the cotangent of the sun's elevation angle—its angle θ relative to the horizon. Near sunrise and sunset, when θ = 0° and cot(θ) = ∞, shadows can be extremely long. If the sun passes directly overhead (only possible in locations between the Tropics of Cancer and Capricorn), then θ = 90°, cot(θ) = 0, and shadows are cast directly underneath objects.
+Such variations have long aided travellers during their travels, especially in barren regions such as the Arabian Desert.[5]
+The farther the distance from the object blocking the light to the surface of projection, the larger the silhouette (they are considered proportional). Also, if the object is moving, the shadow cast by the object will project an image with dimensions (length) expanding proportionally faster than the object's own rate of movement. The increase of size and movement is also true if the distance between the object of interference and the light source are closer. This, however, does not mean the shadow may move faster than light, even when projected at vast distances, such as light years. The loss of light, which projects the shadow, will move towards the surface of projection at light speed.
+Although the edge of a shadow appears to "move" along a wall, in actuality the increase of a shadow's length is part of a new projection which propagates at the speed of light from the object of interference. Since there is no actual communication between points in a shadow (except for reflection or interference of light, at the speed of light), a shadow that projects over a surface of large distances (light years) cannot convey information between those distances with the shadow's edge.[6]
+Visual artists are usually very aware of colored light emitted or reflected from several sources, which can generate complex multicolored shadows. Chiaroscuro, sfumato, and silhouette are examples of artistic techniques which make deliberate use of shadow effects.
+During the daytime, a shadow cast by an opaque object illuminated by sunlight has a bluish tinge. This happens because of Rayleigh scattering, the same property that causes the sky to appear blue. The opaque object is able to block the light of the sun, but not the ambient light of the sky which is blue as the atmosphere molecules scatter blue light more effectively. As a result, the shadow appears bluish.[7]
+A shadow occupies a three-dimensional volume of space, but this is usually not visible until it projects onto a reflective surface. A light fog, mist, or dust cloud can reveal the 3D presence of volumetric patterns in light and shadow.
+Fog shadows may look odd to viewers who are not used to seeing shadows in three dimensions. A thin fog is just dense enough to be illuminated by the light that passes through the gaps in a structure or in a tree.  As a result, the path of an object's shadow through the fog becomes visible as a darkened volume. In a sense, these shadow lanes are the inverse of crepuscular rays caused by beams of light, but caused by the shadows of solid objects.
+Theatrical fog and strong beams of light are sometimes used by lighting designers and visual artists who seek to highlight three-dimensional aspects of their work.
+Oftentimes shadows of chain-linked fences and other such objects become inverted (light and dark areas are swapped) as they get farther from the object. A chain-link fence shadow will start with light diamonds and shadow outlines when it is touching the fence, but it will gradually blur. Eventually, if the fence is tall enough, the light pattern will go to shadow diamonds and light outlines.
+In photography, which is essentially recording patterns of light, shade, and color, "highlights" and "shadows" are the brightest and darkest parts, respectively, of a scene or image. Photographic exposure must be adjusted (unless special effects are wanted) to allow the film or sensor, which has limited dynamic range, to record detail in the highlights without them being washed out, and in the shadows without their becoming undifferentiated black areas.
+On satellite imagery and aerial photographs, taken vertically, tall buildings can be recognized as such by their long shadows (if the photographs are not taken in the tropics around noon), while these also show more of the shape of these buildings.
+Shadow as a term is often used for any occlusion or blockage, not just those with respect to light.  For example, a rain shadow is a dry area, which with respect to the prevailing wind direction, is beyond a mountain range; the elevated terrain impedes rainclouds from entering the dry zone. An acoustic shadow occurs when direct sound has been blocked or diverted around a given area.
+An unattended shade was thought by some cultures to be similar to that of a ghost. The name for the fear of shadows is "sciophobia" or "sciaphobia".
+Chhaya is the Hindu goddess of shadows.
+In heraldry, when a charge is supposedly shown "in shadow" (the appearance is of the charge merely being outlined in a neutral tint rather than being of one or more tinctures different from the field on which it is placed), it is technically described as "umbrated".  Supposedly, only a limited number of specific charges can be so depicted.[citation needed]
+Scientists from the National University of Singapore presented a shadow-effect energy generator (SEG), which consists of cells of gold deposited on a silicon wafer attached on a plastic film. The generator has a power density of 0.14 μW cm−2 under indoor conditions (0.001 sun).[8]
+Non-diffuse lighting in outer space causes deep shadows
+Reversed text in shadow
+Sutro Tower casts a 3D fog shadow
+This photo of jasmine flowers has only soft shadows cast by diffused light
+Clouds and shadows over the Mediterranean Sea
+Shadow cast by vapour trail of passing aircraft
+Tree shadow
+Shadow on the Castle
+Long shadow of a dead tree with its branches on dry fields, late afternoon
+When the sun is low, shadows become long, and details get the wrong proportions.

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+An omnivore (/ˈɒmnɪvɔːr/) is an animal that has the ability to eat and survive on both plant and animal matter.[3] Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutrients and energy of the sources absorbed.[4] Often, they have the ability to incorporate food sources such as algae, fungi, and bacteria into their diet.[5][6][7]
+Omnivores come from diverse backgrounds that often independently evolved sophisticated consumption capabilities. For instance, dogs evolved from primarily carnivorous organisms (Carnivora) while pigs evolved from primarily herbivorous organisms (Artiodactyla).[8][9][10]  Despite this, physical characteristics such as tooth morphology may be reliable indicators of diet in mammals, with such  morphological adaptation having been observed in bears.[11][12]
+The variety of different animals that are classified as omnivores can be placed into further sub-categories depending on their feeding behaviors.  Frugivores include maned wolves and orangutans;[13][14] insectivores include swallows and pink fairy armadillos;[15][16] granivores include large ground finches and mice.
+All of these animals are omnivores, yet still fall into special niches in terms of feeding behavior and preferred foods. Being omnivores gives these animals more food security in stressful times or makes possible living in less consistent environments.[17]
+The word omnivore derives from the Latin omnis (all), and vora, from vorare, (to eat or devour), having been coined by the French and later adopted by the English in the 1800s.[18]  Traditionally the definition for omnivory was entirely behavioral by means of simply "including both animal and vegetable tissue in the diet.[19]"  In more recent times, with the advent of advanced technological capabilities in fields like gastroenterology, biologists have formulated a standardized variation of omnivore used for labeling a species' actual ability to obtain energy and nutrients from materials.[20][21]  This has subsequently conditioned two context specific definitions.
+The taxonomic utility of omnivore's traditional and behavioral definition is limited, since the diet, behavior, and phylogeny of one omnivorous species might be very different from that of another: for instance, an omnivorous pig digging for roots and scavenging for fruit and carrion is taxonomically and ecologically quite distinct from an omnivorous chameleon that eats leaves and insects. The term "omnivory" is also not always comprehensive because it does not deal with mineral foods such as salt licks and the consumption of plant and animal material for medical purposes which would not otherwise be consumed (i.e. zoopharmacognosy) within non-omnivores.
+Though Carnivora is a taxon for species classification, no such equivalent exists for omnivores, as omnivores are widespread across multiple taxonomic clades. The Carnivora order does not include all carnivorous species, and not all species within the Carnivora taxon are carnivorous. (The members of Carnivora are formally referred as carnivorans.)[27] It is common to find physiological carnivores consuming materials from plants or physiological herbivores  consuming material from animals, e.g. felines eating grass and deer eating birds.[28][29]  From a behavioral aspect, this would make them omnivores, but from the physiological standpoint, this may be due to zoopharmacognosy.  Physiologically, animals must be able to obtain both energy and nutrients from plant and animal materials to be considered omnivorous.  Thus, such animals are still able to be classified as carnivores and herbivores when they are just obtaining nutrients from materials originating from sources that do not seemingly complement their classification.  For instance, it is well documented that animals such as giraffes, camels, and cattle will gnaw on bones, preferably dry bones, for particular minerals and nutrients.[30] Felines, which are usually regarded as obligate carnivores, occasionally eat grass to regurgitate indigestibles (e.g. hair, bones), aid with hemoglobin production, and as a laxative.[31]
+Occasionally, it is found that animals historically classified as carnivorous may deliberately eat plant material.  For example, in 2013, it was considered that American alligators (Alligator mississippiensis) may be physiologically omnivorous once investigations had been conducted on why they occasionally eat fruits.  It was suggested that alligators probably ate fruits both accidentally but also deliberately.[32]
+"Life-history omnivores" is a specialized classification given to organisms that change their eating habits during their life cycle.[33]  Some species, such as grazing waterfowl like geese, are known to eat mainly animal tissue at one stage of their lives, but plant matter at another.[34] The same is true for many insects, such as beetles in the family Meloidae,[35] which begin by eating animal tissue as larvae, but change to eating plant matter after they mature. Likewise, many mosquito species in early life eat plants or assorted detritus, but as they mature, males continue to eat plant matter and nectar whereas the females (such as those of Anopheles, Aedes and Culex) also eat blood to reproduce effectively.[36]
+Although cases exist of herbivores eating meat and carnivores eating plant matter, the classification "omnivore" refers to the adaptation and main food source of the species in general, so these exceptions do not make either individual animals or the species as a whole omnivorous. For the concept of "omnivore" to be regarded as a scientific classification, some clear set of measurable and relevant criteria would need to be considered to differentiate between an "omnivore" and other categories, e.g. faunivore, folivore, and scavenger.[37] Some researchers argue that evolution of any species from herbivory to carnivory or carnivory to herbivory would be rare except via an intermediate stage of omnivory.[38]
+Various mammals are omnivorous in the wild, such as species of pigs,[39] badgers, bears, coatis, civets, hedgehogs, opossums, skunks, sloths, squirrels,[40] raccoons, chipmunks,[41] mice,[42] and rats.[43] The hominidae, including humans, chimpanzees, and orangutans, are also omnivores.[7][44][45]
+Most bear species are omnivores,[46] but individual diets can range from almost exclusively herbivorous (hypocarnivore) to almost exclusively carnivorous (hypercarnivore), depending on what food sources are available locally and seasonally. Polar bears are classified as carnivores, both taxonomically (they are in the order Carnivora), and behaviorally (they subsist on a largely carnivorous diet). Depending on the species of bear, there is generally a preference for one class of food, as plants and animals are digested differently. Wolf subspecies (including wolves, dogs, dingoes, and coyotes) eat some plant matter, but they have a general preference and are evolutionarily geared towards meat.[47] Also, the maned wolf is a canid whose diet is naturally 50% plant matter.
+While most mammals may display "omnivorous" behavior patterns depending on conditions of supply, culture, season and so on, they will generally prefer a particular class of food, to which their digestive processes are adapted. Like most arboreal species, most squirrels are primarily granivores, subsisting on nuts and seeds.[48] But like virtually all mammals, squirrels avidly consume some animal food when it becomes available. For example, the American eastern gray squirrel has been introduced by humans to parts of Britain, continental Europe and South Africa. Where it flourishes, its effect on populations of nesting birds is often serious, largely because of consumption of eggs and nestlings.[49][50]
+Various birds are omnivorous, with diets varying from berries and nectar to insects, worms, fish, and small rodents. Examples include cassowaries, chickens, crows[51] and related corvids, kea, rallidae, and rheas. In addition, some lizards, turtles, fish (such as piranhas and catfish), and invertebrates are also omnivorous.
+Quite often, mainly herbivorous creatures will eagerly eat small quantities of animal food when it becomes available. Although this is trivial most of the time, omnivorous or herbivorous birds, such as sparrows, often will feed their chicks insects while food is most needed for growth.[52] On close inspection it appears that nectar-feeding birds such as sunbirds rely on the ants and other insects that they find in flowers, not for a richer supply of protein, but for essential nutrients such as cobalt/vitamin b12 that are absent from nectar. Similarly, monkeys of many species eat maggoty fruit, sometimes in clear preference to sound fruit.[53] When to refer to such animals as omnivorous, or otherwise, is a question of context and emphasis, rather than of definition.

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+In physics, mathematics, and related fields, a wave is a disturbance (change from equilibrium) of one or more fields such that the field values oscillate repeatedly about a stable equilibrium (resting) value. If the relative amplitude of oscillation at different points in the field remains constant, the wave is said to be a standing wave. If the relative amplitude at different points in the field changes, the wave is said to be a traveling wave. Waves can only exist in fields when there is a force that tends to restore the field to equilibrium.
+The types of waves most commonly studied in physics are mechanical and electromagnetic. In a mechanical wave, stress and strain fields oscillate about a mechanical equilibrium.  A traveling mechanical wave is a local deformation (strain) in some physical medium that propagates from particle to particle by creating local stresses that cause strain in neighboring particles too.  For example, sound waves in air are variations of the local pressure that propagate by collisions between gas molecules.  Other examples of mechanical waves are seismic waves, gravity waves, vortices, and shock waves.  In an electromagnetic wave  the electric and magnetic fields oscillate. A traveling electromagnetic wave (light) consists of a combination of variable electric and magnetic fields, that propagates through space according to Maxwell's equations.  Electromagnetic waves can travel through transparent dielectric media or through a vacuum; examples include radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
+Other types of waves include gravitational waves, which are disturbances in a gravitational field that propagate according to general relativity; heat diffusion waves; plasma waves, that combine mechanical deformations and electromagnetic fields; reaction-diffusion waves, such as in the Belousov–Zhabotinsky reaction; and many more.
+Mechanical and electromagnetic waves transfer energy,[2], momentum, and information, but they do not transfer particles in the medium.  In mathematics and electronics waves are studied as signals.[3]  On the other hand, some waves do not appear to move at all, like standing waves (which are fundamental to music) and hydraulic jumps. Some, like the probability waves of quantum mechanics, may be completely static.
+A physical wave is almost always confined to some finite region of space, called its domain.  For example, the seismic waves generated by earthquakes are significant only in the interior and surface of the planet, so they can be ignored outside it.  However, waves with infinite domain, that extend over the whole space, are commonly studied in mathematics, and are very valuable tools for understanding physical waves in finite domains.
+A plane wave seems to travel in a definite direction, and has constant value over any plane perpendicular to that direction. Mathematically, the simplest waves are the sinusoidal ones in which each point in the field experiences simple harmonic motion. Complicated waves can often be described as the sum of many sinusoidal plane waves.  A plane wave can be a transverse, if its effect at each point is described by a vector that is perpendicular to the direction of propagation or energy transfer; or longitudinal, if the describing vectors are parallel to the direction of energy propagation. While mechanical waves can be both transverse and longitudinal, electromagnetic waves are transverse in free space.
+A wave can be described just like a field, namely as a function
+F
+(
+x
+,
+t
+)
+{\displaystyle F(x,t)}
+ where
+x
+{\displaystyle x}
+ is a position and
+t
+{\displaystyle t}
+ is a time.
+The value of
+x
+{\displaystyle x}
+ is a point of space, specifically in the region where the wave is defined.  In mathematical terms, it is usually a vector in the Cartesian three-dimensional space
+R
+3
+{\displaystyle \mathbb {R} ^{3}}
+.  However, in many cases one can ignore one dimension, and let
+x
+{\displaystyle x}
+ be a point of the Cartesian plane
+R
+2
+{\displaystyle \mathbb {R} ^{2}}
+.  This is the case, for example, when studying vibrations of a drum skin.  One may even restrict
+x
+{\displaystyle x}
+ to a point of the Cartesian line
+R
+{\displaystyle \mathbb {R} }
+ — that is, the set of real numbers. This is the case, for example, when studying vibrations in a violin string or recorder.   The time
+t
+{\displaystyle t}
+, on the other hand, is always assumed to be a scalar; that is, a real number.
+The value of
+F
+(
+x
+,
+t
+)
+{\displaystyle F(x,t)}
+ can be any physical quantity of interest assigned to the point
+x
+{\displaystyle x}
+ that may vary with time.  For example, if
+F
+{\displaystyle F}
+ represents the vibrations inside an elastic solid, the value of
+F
+(
+x
+,
+t
+)
+{\displaystyle F(x,t)}
+ is usually a vector that gives the current displacement from
+x
+{\displaystyle x}
+ of the material particles that would be at the point
+x
+{\displaystyle x}
+ in the absence of vibration.  For an electromagnetic wave, the value of
+F
+{\displaystyle F}
+ can be the electric field vector
+E
+{\displaystyle E}
+, or the magnetic field vector
+H
+{\displaystyle H}
+, or any related quantity, such as the Poynting vector
+E
+×
+H
+{\displaystyle E\times H}
+.  In fluid dynamics, the value of
+F
+(
+x
+,
+t
+)
+{\displaystyle F(x,t)}
+ could be the velocity vector of the fluid at the point
+x
+{\displaystyle x}
+, or any scalar property like pressure, temperature, or density. In a chemical reaction,
+F
+(
+x
+,
+t
+)
+{\displaystyle F(x,t)}
+ could be the concentration of some substance in the neighborhood of point
+x
+{\displaystyle x}
+ of the reaction medium.
+For any dimension
+d
+{\displaystyle d}
+ (1, 2, or 3), the wave's domain is then a subset
+D
+{\displaystyle D}
+ of
+R
+d
+{\displaystyle \mathbb {R} ^{d}}
+, such that the function value
+F
+(
+x
+,
+t
+)
+{\displaystyle F(x,t)}
+ is defined for any point
+x
+{\displaystyle x}
+ in
+D
+{\displaystyle D}
+. For example, when describing the motion of a drum skin, one can consider
+D
+{\displaystyle D}
+ to be a disk (circle) on the plane
+R
+2
+{\displaystyle \mathbb {R} ^{2}}
+ with center at the origin
+(
+0
+,
+0
+)
+{\displaystyle (0,0)}
+, and let
+F
+(
+x
+,
+t
+)
+{\displaystyle F(x,t)}
+ be the vertical displacement of the skin at the point
+x
+{\displaystyle x}
+ of
+D
+{\displaystyle D}
+ and at time
+t
+{\displaystyle t}
+.
+Sometimes one is interested in a single specific wave. More often, however, one needs to understand large set of possible waves; like all the ways that a drum skin can vibrate after being struck once with a drum stick, or all the possible radar echos one could get from an airplane that may be approaching an airport.
+In some of those situations, one may describe such a family of waves by a function
+F
+(
+A
+,
+B
+,
+…
+;
+x
+,
+t
+)
+{\displaystyle F(A,B,\ldots ;x,t)}
+ that depends on certain parameters
+A
+,
+B
+,
+…
+{\displaystyle A,B,\ldots }
+, besides
+x
+{\displaystyle x}
+ and
+t
+{\displaystyle t}
+.  Then one can obtain  different waves — that is, different functions of
+x
+{\displaystyle x}
+ and
+t
+{\displaystyle t}
+ — by choosing different values for those parameters.
+For example, the sound pressure inside a recorder that is playing a "pure" note is typically a standing wave, that can be written as
+The parameter
+A
+{\displaystyle A}
+ defines the amplitude of the wave (that is, the maximum sound pressure in the bore, which is related to the loudness of the note);
+c
+{\displaystyle c}
+ is the speed of sound;
+L
+{\displaystyle L}
+ is the length of the bore; and
+n
+{\displaystyle n}
+ is a positive integer (1,2,3,...) that specifies the number of nodes in the standing wave.  (The position
+x
+{\displaystyle x}
+ should be measured from the mouthpiece, and the time
+t
+{\displaystyle t}
+ from any moment at which the pressure at the mouthpiece is maximum. The quantity
+λ
+=
+4
+L
+/
+(
+2
+n
+−
+1
+)
+{\displaystyle \lambda =4L/(2n-1)}
+ is the wavelength of the emitted note, and
+f
+=
+c
+/
+λ
+{\displaystyle f=c/\lambda }
+ is its frequency.)  Many general properties of these waves can be inferred from this general equation, without choosing specific values for the parameters.
+As another example, it may be that the vibrations of a drum skin after a single strike depend only on the distance
+r
+{\displaystyle r}
+ from the center of the skin to the strike point, and on the strength
+s
+{\displaystyle s}
+ of the strike.  Then the vibration for all possible strikes can be described by a function
+F
+(
+r
+,
+s
+;
+x
+,
+t
+)
+{\displaystyle F(r,s;x,t)}
+.
+Sometimes the family of waves of interest has infinitely many parameters.  For example, one may want to describe what happens to the temperature in a metal bar when it is initially heated at various temperatures at different points along its length, and then allowed to cool by itself in vacuum.  In that case, instead of a scalar or vector, the parameter would have to be a function
+h
+{\displaystyle h}
+ such that
+h
+(
+x
+)
+{\displaystyle h(x)}
+ is the initial temperature at each point
+x
+{\displaystyle x}
+ of the bar.  Then the temperatures at later times can be expressed by a function
+F
+{\displaystyle F}
+ that depends on the function
+h
+{\displaystyle h}
+ (that is, a functional operator), so that the temperature at a later time is
+F
+(
+h
+;
+x
+,
+t
+)
+{\displaystyle F(h;x,t)}
+Another way to describe and study a family of waves is to give a mathematical equation that, instead of explicitly giving the value of
+F
+(
+x
+,
+t
+)
+{\displaystyle F(x,t)}
+, only constrains how those values can change with time.  Then the family of waves in question consists of all functions
+F
+{\displaystyle F}
+ that satisfy those constraints — that is, all solutions of the equation.
+This approach is extremely important in physics, because the constraints usually are a consequence of the physical processes that cause the wave to evolve.  For example, if
+F
+(
+x
+,
+t
+)
+{\displaystyle F(x,t)}
+ is the temperature inside a block of some homogeneous and isotropic solid material, its evolution is constrained by the partial differential equation
+where
+Q
+(
+p
+,
+f
+)
+{\displaystyle Q(p,f)}
+ is the heat that is being generated per unit of volume and time in the neighborhood of
+x
+{\displaystyle x}
+ at time
+t
+{\displaystyle t}
+ (for example, by chemical reactions happening there);
+x
+1
+,
+x
+2
+,
+x
+3
+{\displaystyle x_{1},x_{2},x_{3}}
+ are the Cartesian coordinates of the point
+x
+{\displaystyle x}
+;
+∂
+F
+/
+∂
+t
+{\displaystyle \partial F/\partial t}
+ is the (first) derivative of
+F
+{\displaystyle F}
+ with respect to
+t
+{\displaystyle t}
+; and
+∂
+2
+F
+/
+∂
+x
+i
+2
+{\displaystyle \partial ^{2}F/\partial x_{i}^{2}}
+ is the second derivative of
+F
+{\displaystyle F}
+ relative to
+x
+i
+{\displaystyle x_{i}}
+.  (The symbol "
+∂
+{\displaystyle \partial }
+" is meant to signify that, in the derivative with respect to some variable, all other variables must be considered fixed.)
+This equation can be derived from the laws of physics that govern the diffusion of heat in solid media.  For that reason, it is called the heat equation in mathematics, even though it applies to many other physical quantities besides temperatures.
+For another example, we can describe all possible sounds echoing within a container of gas by a function
+F
+(
+x
+,
+t
+)
+{\displaystyle F(x,t)}
+ that gives the pressure at a point
+x
+{\displaystyle x}
+ and time
+t
+{\displaystyle t}
+ within that container.  If the gas was initially at uniform temperature and composition, the evolution of
+F
+{\displaystyle F}
+ is constrained by the formula
+Here
+P
+(
+x
+,
+t
+)
+{\displaystyle P(x,t)}
+ is some extra compression force that is being applied to the gas near
+x
+{\displaystyle x}
+ by some external process, such as a loudspeaker or piston right next to
+p
+{\displaystyle p}
+.
+This same differential equation describes the behavior of mechanical vibrations and electromagnetic fields in a homogeneous isotropic non-conducting solid. Note that this equation differs from that of heat flow only in that the left-hand side is
+∂
+2
+F
+/
+∂
+t
+2
+{\displaystyle \partial ^{2}F/\partial t^{2}}
+, the second derivative of
+F
+{\displaystyle F}
+ with respect to time, rather than the first derivative
+∂
+F
+/
+∂
+t
+{\displaystyle \partial F/\partial t}
+.  Yet this small change makes a huge difference on the set of solutions
+F
+{\displaystyle F}
+.  This differential equation is called "the" wave equation in mathematics, even though it describes only one very special kind of waves.
+Consider a traveling transverse wave (which may be a pulse) on a string (the medium). Consider the string to have a single spatial dimension. Consider this wave as traveling
+This wave can then be described by the two-dimensional functions
+or, more generally, by d'Alembert's formula:[6]
+representing two component waveforms
+F
+{\displaystyle F}
+ and
+G
+{\displaystyle G}
+ traveling through the medium in opposite directions. A generalized representation of this wave can be obtained[7] as the partial differential equation
+General solutions are based upon Duhamel's principle.[8]
+The form or shape of F in d'Alembert's formula involves the argument x − vt. Constant values of this argument correspond to constant values of F, and these constant values occur if x increases at the same rate that vt increases.  That is, the wave shaped like the function F will move in the positive x-direction at velocity v (and G will propagate at the same speed in the negative x-direction).[9]
+In the case of a periodic function F with period λ, that is, F(x + λ − vt) = F(x  − vt), the periodicity of F in space means that a snapshot of the wave at a given time t finds the wave varying periodically in space with period λ (the wavelength of the wave). In a similar fashion, this periodicity of F implies a periodicity in time as well: F(x − v(t + T)) = F(x  − vt) provided vT = λ, so an observation of the wave at a fixed location x finds the wave undulating periodically in time with period T = λ/v.[10]
+The amplitude of a wave may be constant (in which case the wave is a c.w. or continuous wave), or may be modulated so as to vary with time and/or position. The outline of the variation in amplitude is called the envelope of the wave. Mathematically, the modulated wave can be written in the form:[11][12][13]
+where
+A
+(
+x
+,
+t
+)
+{\displaystyle A(x,\ t)}
+ is the amplitude envelope of the wave,
+k
+{\displaystyle k}
+ is the wavenumber and
+ϕ
+{\displaystyle \phi }
+ is the phase. If the group velocity
+v
+g
+{\displaystyle v_{g}}
+ (see below) is wavelength-independent, this equation can be simplified as:[14]
+showing that the envelope moves with the group velocity and retains its shape. Otherwise, in cases where the group velocity varies with wavelength, the pulse shape changes in a manner often described using an envelope equation.[14][15]
+There are two velocities that are associated with waves, the phase velocity and the group velocity.
+Phase velocity is the rate at which the phase of the wave propagates in space: any given phase of the wave (for example, the crest) will appear to travel at the phase velocity. The phase velocity is given in terms of the wavelength λ (lambda) and period T as
+Group velocity is a property of waves that have a defined envelope, measuring propagation through space (that is, phase velocity) of the overall shape of the waves' amplitudes – modulation or envelope of the wave.
+Mathematically, the most basic wave is the (spatially) one-dimensional sine wave (also called harmonic wave or sinusoid) with an amplitude
+u
+{\displaystyle u}
+ described by the equation:
+where
+The units of the amplitude depend on the type of wave. Transverse mechanical waves (for example, a wave on a string) have an amplitude expressed as a distance (for example, meters), longitudinal mechanical waves (for example, sound waves) use units of pressure (for example, pascals), and electromagnetic waves (a form of transverse vacuum wave) express the amplitude in terms of its electric field (for example, volts/meter).
+The wavelength
+λ
+{\displaystyle \lambda }
+ is the distance between two sequential crests or troughs (or other equivalent points), generally is measured in meters. A wavenumber
+k
+{\displaystyle k}
+, the spatial frequency of the wave in radians per unit distance (typically per meter), can be associated with the wavelength by the relation
+The period
+T
+{\displaystyle T}
+ is the time for one complete cycle of an oscillation of a wave. The frequency
+f
+{\displaystyle f}
+ is the number of periods per unit time (per second) and is typically measured in hertz denoted as Hz. These are related by:
+In other words, the frequency and period of a wave are reciprocals.
+The angular frequency
+ω
+{\displaystyle \omega }
+ represents the frequency in radians per second. It is related to the frequency or period by
+The wavelength
+λ
+{\displaystyle \lambda }
+ of a sinusoidal waveform traveling at constant speed
+v
+{\displaystyle v}
+ is given by:[16]
+where
+v
+{\displaystyle v}
+ is called the phase speed (magnitude of the phase velocity) of the wave and
+f
+{\displaystyle f}
+ is the wave's frequency.
+Wavelength can be a useful concept even if the wave is not periodic in space. For example, in an ocean wave approaching shore, the incoming wave undulates with a varying local wavelength that depends in part on the depth of the sea floor compared to the wave height. The analysis of the wave can be based upon comparison of the local wavelength with the local water depth.[17]
+Although arbitrary wave shapes will propagate unchanged in lossless linear time-invariant systems, in the presence of dispersion the sine wave is the unique shape that will propagate unchanged but for phase and amplitude, making it easy to analyze.[18]  Due to the Kramers–Kronig relations, a linear medium with dispersion also exhibits loss, so the sine wave propagating in a dispersive medium is attenuated in certain frequency ranges that depend upon the medium.[19]
+The sine function is periodic, so the sine wave or sinusoid has a wavelength in space and a period in time.[20][21]
+The sinusoid is defined for all times and distances, whereas in physical situations we usually deal with waves that exist for a limited span in space and duration in time. An arbitrary wave shape can be decomposed into an infinite set of sinusoidal waves by the use of Fourier analysis. As a result, the simple case of a single sinusoidal wave can be applied to more general cases.[22][23] In particular, many media are linear, or nearly so, so the calculation of arbitrary wave behavior can be found by adding up responses to individual sinusoidal waves using the superposition principle to find the solution for a general waveform.[24]  When a medium is nonlinear, then the response to complex waves cannot be determined from a sine-wave decomposition.
+A plane wave is a kind of wave whose value varies only in one spatial direction. That is, its value is constant on a plane that is perpendicular to that direction. Plane waves can be specified by a vector of unit length
+n
+^
+{\displaystyle {\hat {n}}}
+ indicating the direction that the wave varies in, and a wave profile describing how the wave varies as a function of the displacement along that direction (
+n
+^
+⋅
+x
+→
+{\displaystyle {\hat {n}}\cdot {\vec {x}}}
+) and time (
+t
+{\displaystyle t}
+). Since the wave profile only depends on the position
+x
+→
+{\displaystyle {\vec {x}}}
+ in the combination
+n
+^
+⋅
+x
+→
+{\displaystyle {\hat {n}}\cdot {\vec {x}}}
+, any displacement in directions perpendicular to
+n
+^
+{\displaystyle {\hat {n}}}
+ cannot affect the value of the field.
+Plane waves are often used to model electromagnetic waves far from a source. For electromagnetic plane waves, the electric and magnetic fields themselves are transverse to the direction of propagation, and also perpendicular to each other.
+A standing wave, also known as a stationary wave, is a wave that remains in a constant position. This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling in opposite directions.
+The sum of two counter-propagating waves (of equal amplitude and frequency) creates a standing wave.  Standing waves commonly arise when a boundary blocks further propagation of the wave, thus causing wave reflection, and therefore introducing a counter-propagating wave.  For example, when a violin string is displaced, transverse waves propagate out to where the string is held in place at the bridge and the nut, where the waves are reflected back.  At the bridge and nut, the two opposed waves are in antiphase and cancel each other, producing a node. Halfway between two nodes there is an antinode, where the two counter-propagating waves enhance each other maximally. There is no net propagation of energy over time.
+One-dimensional standing waves; the fundamental mode and the first 5 overtones.
+A two-dimensional standing wave on a disk; this is the fundamental mode.
+A standing wave on a disk with two nodal lines crossing at the center; this is an overtone.
+Waves exhibit common behaviors under a number of standard situations, for example:
+Waves normally move in a straight line (that is, rectilinearly) through a transmission medium. Such media can be classified into one or more of the following categories:
+Absorption of waves means, if a kind of wave strikes a matter, it will be absorbed by the matter.  When a wave with that same natural frequency impinges upon an atom, then the electrons of that atom will be set into vibrational motion. If a wave of a given frequency strikes a material with electrons having the same vibrational frequencies, then those electrons will absorb the energy of the wave and transform it into vibrational motion.
+When a wave strikes a reflective surface, it changes direction, such that the angle made by the incident wave and line normal to the surface equals the angle made by the reflected wave and the same normal line.
+Refraction is the phenomenon of a wave changing its speed. Mathematically, this means that the size of the phase velocity changes. Typically, refraction occurs when a wave passes from one medium into another. The amount by which a wave is refracted by a material is given by the refractive index of the material. The directions of incidence and refraction are related to the refractive indices of the two materials by Snell's law.
+A wave exhibits diffraction when it encounters an obstacle that bends the wave or when it spreads after emerging from an opening. Diffraction effects are more pronounced when the size of the obstacle or opening is comparable to the wavelength of the wave.
+Waves that encounter each other combine through superposition to create a new wave called an interference pattern. Important interference patterns occur for waves that are in phase.
+The phenomenon of polarization arises when wave motion can occur simultaneously in two orthogonal directions. Transverse waves can be polarized, for instance. When polarization is used as a descriptor without qualification, it usually refers to the special, simple case of linear polarization. A transverse wave is linearly polarized if it oscillates in only one direction or plane. In the case of linear polarization, it is often useful to add the relative orientation of that plane, perpendicular to the direction of travel, in which the oscillation occurs, such as "horizontal" for instance, if the plane of polarization is parallel to the ground. Electromagnetic waves propagating in free space, for instance, are transverse; they can be polarized by the use of a polarizing filter.
+Longitudinal waves, such as sound waves, do not exhibit polarization. For these waves there is only one direction of oscillation, that is, along the direction of travel.
+A wave undergoes dispersion when either the phase velocity or the group velocity depends on the wave frequency.
+Dispersion is most easily seen by letting white light pass through a prism, the result of which is to produce the spectrum of colours of the rainbow. Isaac Newton performed experiments with light and prisms, presenting his findings in the Opticks (1704) that white light consists of several colours and that these colours cannot be decomposed any further.[25]
+The speed of a transverse wave traveling along a vibrating string ( v ) is directly proportional to the square root of the tension of the string ( T ) over the linear mass density ( μ ):
+where the linear density μ is the mass per unit length of the string.
+Acoustic or sound waves travel at speed given by
+or the square root of the adiabatic bulk modulus divided by the ambient fluid density (see speed of sound).
+Seismic waves are waves of energy that travel through the Earth's layers, and are a result of earthquakes, volcanic eruptions, magma movement, large landslides and large man-made explosions that give out low-frequency acoustic energy.
+The Doppler effect (or the Doppler shift) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source.[26] It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.
+A shock wave is a type of propagating disturbance. When a wave moves faster than the local speed of sound in a fluid, it is a shock wave.  Like an ordinary wave, a shock wave carries energy and can propagate through a medium; however, it is characterized by an abrupt, nearly discontinuous change in pressure, temperature and density of the medium.[27]
+An electromagnetic wave consists of two waves that are oscillations of the electric and magnetic fields. An electromagnetic wave travels in a direction that is at right angles to the oscillation direction of both fields. In the 19th century, James Clerk Maxwell showed that, in vacuum, the electric and magnetic fields satisfy the wave equation both with speed equal to that of the speed of light. From this emerged the idea that light is an electromagnetic wave. Electromagnetic waves can have different frequencies (and thus wavelengths), giving rise to various types of radiation such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and Gamma rays.
+The Schrödinger equation describes the wave-like behavior of particles in quantum mechanics. Solutions of this equation are wave functions which can be used to describe the probability density of a particle.
+The Dirac equation is a relativistic wave equation detailing electromagnetic interactions. Dirac waves accounted for the fine details of the hydrogen spectrum in a completely rigorous way.  The wave equation also implied the existence of a new form of matter, antimatter, previously unsuspected and unobserved and which was experimentally confirmed.  In the context of quantum field theory, the Dirac equation is reinterpreted to describe quantum fields corresponding to spin-½ particles.
+Louis de Broglie postulated that all particles with momentum have a wavelength
+where h is Planck's constant, and p is the magnitude of the momentum of the particle. This hypothesis was at the basis of quantum mechanics. Nowadays, this wavelength is called the de Broglie wavelength. For example, the electrons in a CRT display have a de Broglie wavelength of about 10−13 m.
+A wave representing such a particle traveling in the k-direction is expressed by the wave function as follows:
+where the wavelength is determined by the wave vector k as:
+and the momentum by:
+However, a wave like this with definite wavelength is not localized in space, and so cannot represent a particle localized in space. To localize a particle, de Broglie proposed a superposition of different wavelengths ranging around a central value in a wave packet,[30] a waveform often used in quantum mechanics to describe the wave function of a particle. In a wave packet, the wavelength of the particle is not precise, and the local wavelength deviates on either side of the main wavelength value.
+In representing the wave function of a localized particle, the wave packet is often taken to have a Gaussian shape and is called a Gaussian wave packet.[31] Gaussian wave packets also are used to analyze water waves.[32]
+For example, a Gaussian wavefunction ψ might take the form:[33]
+at some initial time t = 0, where the central wavelength is related to the central wave vector k0 as λ0 = 2π / k0. It is well known from the theory of Fourier analysis,[34] or from the Heisenberg uncertainty principle (in the case of quantum mechanics) that a narrow range of wavelengths is necessary to produce a localized wave packet, and the more localized the envelope, the larger the spread in required wavelengths. The Fourier transform of a Gaussian is itself a Gaussian.[35] Given the Gaussian:
+the Fourier transform is:
+The Gaussian in space therefore is made up of waves:
+that is, a number of waves of wavelengths λ such that kλ = 2 π.
+The parameter σ decides the spatial spread of the Gaussian along the x-axis, while the Fourier transform shows a spread in wave vector k determined by 1/σ. That is, the smaller the extent in space, the larger the extent in k, and hence in λ = 2π/k.
+Gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. A ripple on a pond is one example.
+Gravitational waves also travel through space. The first observation of gravitational waves was announced on 11 February 2016.[36]
+Gravitational waves are disturbances in the curvature of spacetime, predicted by Einstein's theory of general relativity.

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+One Direction, often shortened to 1D, are an English-Irish pop boy band formed in London, England in 2010. The group is composed of Niall Horan, Liam Payne, Harry Styles and Louis Tomlinson; former member Zayn Malik departed from the group in 2015. The group signed with Simon Cowell's record label Syco Records after forming and finishing third in the seventh series of the British televised singing competition The X Factor in 2010. Propelled to global success by social media,[1][2][3] One Direction's five albums, Up All Night (2011), Take Me Home (2012), Midnight Memories (2013), Four (2014), and Made in the A.M. (2015), topped charts in most major markets, and generated hit singles including "What Makes You Beautiful", "Live While We're Young", "Best Song Ever", "Story of My Life" and "Drag Me Down".
+The group have won nearly 200 awards including seven Brit Awards, four MTV Video Music Awards, six Billboard Music Awards, seven American Music Awards (including Artist of the Year in 2014 and 2015), and 28 Teen Choice Awards. They have embarked on four world tours, two of which were all-stadium. In 2013, they earned an estimated $75 million, becoming the second highest earning celebrity under 30 according to Forbes.[4] The world’s best-selling artist of 2013, the International Federation of the Phonographic Industry (IFPI) named them the Global Recording Artist of the Year.[5] Forbes ranked them as the fourth highest-earning celebrities in the world in 2015,[6] and second in 2016.[7]
+After the release of Four, One Direction became the first band in the U.S. Billboard 200 history to have their first four albums debut at number one.[8] Their third album, Midnight Memories, was the best-selling album worldwide in 2013 with 4 million copies sold globally.[9] The band's Where We Are Tour, in support of Midnight Memories, was the highest-grossing concert tour in 2014, the highest-grossing tour by a vocal group in history, and the 15th highest-grossing concert tour of all time, grossing $290.2 million (unadjusted for inflation).[10] In 2014, Billboard named One Direction Artist of the Year.[11][12] The band went on hiatus in January 2016, allowing all members to pursue other projects.[13][14] As of 2020, the band have sold a total of 70 million records worldwide.[15]
+In 2010, Niall Horan, Zayn Malik, Liam Payne, Harry Styles, and Louis Tomlinson auditioned as solo candidates for the seventh series of the British televised singing competition The X Factor.[16] They all failed to progress in the "Boys" category at the bootcamp stage of the competition, but were instead put together to form a five-piece boy band,[17] thus qualifying for the "Groups" category. Nicole Scherzinger, a guest judge,[16][18][19] and Simon Cowell have both claimed to have come up with the idea of forming the band. In 2013, Cowell said that it "took him 10 minutes to put them together as a group".[20] Subsequently, the group got together for two weeks to get to know each other and to practice.[21][22] Styles came up with the name One Direction.[21] For their qualifying song at "judges' houses", and their first song as a group, One Direction sang an acoustic version of "Torn".[23] Cowell later commented that their performance convinced him that they "were confident, fun, like a gang of friends, and kind of fearless as well."[24] Within the first four weeks of the live shows, they were his final act in the competition. The group quickly gained popularity in the UK.[24]
+One Direction achieved third place in the competition and immediately after the final, their song "Forever Young", which would have been released if they had won The X Factor, was leaked onto the internet.[25] Shortly afterwards it was confirmed that One Direction had been signed by Cowell to a reported £2 million Syco Records record contract.[26] Recording for their debut album began in January 2011, as they flew to Los Angeles to work with RedOne, a record producer.[27] A book licensed by One Direction, One Direction: Forever Young (Our Official X Factor Story), was published by HarperCollins in February 2011,[28] subsequently topping The Sunday Times Best Seller list.[29] The same month, the boy band and other contestants from the series participated in the X Factor Live Tour. During the tour, the group performed for 500,000 people throughout the UK.[30] After the tour concluded in April 2011, the group continued working on their debut album.[27] Recording took place in Stockholm, London and Los Angeles, as One Direction worked with producers Carl Falk, Savan Kotecha, Steve Mac, and Rami Yacoub, among others.[31][32]
+Released in September 2011, One Direction's debut single, "What Makes You Beautiful", was a commercial and international success. It reached number one on the UK Singles Chart, after becoming the most pre-ordered Sony Music Entertainment single in history.[33][34] Subsequent singles, "Gotta Be You" and "One Thing", peaked in the UK Singles Chart top ten.[35][36] In November 2011, they signed a record deal with Columbia Records in North America.[37] Steve Barnett, the co-chairman of Columbia Records, said it was not a difficult decision to sign One Direction; "I just thought there was a void, and maybe they could seize and hold it."[38] That same month, they released Up All Night, their debut studio album, in the UK and Ireland. Critically commended for its appeal to the teenage audience,[39][40][41] it became the UK's fastest-selling debut album of 2011.[42] In December 2011, they embarked on their first headlining UK concert tour, the Up All Night Tour.[43]
+Upon One Direction's arrival in the US in February 2012, the group embarked on a radio promotion spree, as well as their first North American concert tour as an opening act for Big Time Rush, opening 16 shows after they had completed the first leg of the Up All Night Tour.[44][45] That month, they announced that an Oceania leg had been added to the tour.[46] They made their first US television appearance on The Today Show, at the Rockefeller Center; an estimated 15,000 fans descended on the plaza.[47] "What Makes You Beautiful" was officially released in the United States that same month,[48] where it debuted on the Billboard Hot 100 at number 28, becoming the highest debut for a British act since 1998.[49] On the US Billboard Hot 100, it reached as high as number four. As of June 2016, it has sold 4.8 million copies in the US[50] and over 7 million copes worldwide.[51] Up All Night was released internationally in March, and One Direction became the first UK group to have their debut album reach number one in the US,[52] and were inducted into the Guinness World Records as a result.[53] After the album's international release, it topped the charts in sixteen countries.[54] Up All Night also became the first album by a boy band to sell 500,000 digital copies in the US and, by August 2012, had sold over 3 million copies worldwide.[55][56] It was the third global best-selling album of the year, selling 4.5 million copies.[57] Following the success of the album, a North American leg of the tour was announced later that month.[58]
+The Up All Night Tour, comprising 62 shows, was met with positivity both critically and commercially, with critics praising their singing abilities and stage presence, and with tickets selling out in minutes.[59][60][61][62][63][64][65] A recording of a concert from the tour, Up All Night: The Live Tour, was released in May 2012.[66] In addition to the DVD topping the charts in twenty-five countries, its global sales had exceeded 1 million copies by August 2012.[56][67] One Direction's first book to be licensed in America, Dare to Dream: Life as One Direction, published in the US in May 2012, topped The New York Times Best Seller list.[68] In June 2012, Nick Gatfield, the chairman and chief executive officer of Sony Music Entertainment UK, stated how he expects One Direction to represent a $100 million business empire over 2013.[69] Gatfield stated, "What you might not know about One Direction is that they already represent a $50 million business and that's a figure we expect to double next year".[69] In August 2012, the group's record sales exceeded 8 million singles, 3 million albums, and 1 million DVDs, and they performed "What Makes You Beautiful" at the 2012 Summer Olympics closing ceremony in London, which represented the handover to Rio de Janeiro as the host of the 2016 Summer Olympics.[56][70] One Direction were the biggest winners of the 2012 MTV Video Music Awards winning their three nominations on 6 September 2012, including Best New Artist.[71]
+In April 2012, an American band that went by the same name filed a trademark infringement lawsuit.[72] According to the lawsuit, the US band had been using the name since 2009, recorded two albums and filed an application to register the trademark name in the US in February 2011.[72] The US band said they were entitled to three times the profits made by the UK band, as well as compensatory damages in excess of US$1 million.[72] The lawsuit claimed that Syco and Sony Music "chose to ignore the plaintiff's rights and wilfully infringed them" after they realised in early 2011 that the two bands shared the same name.[72] Syco Records subsequently counter-sued, suggesting the US group was trying to make money from One Direction's success and that the boy band was the first to use the name in US interstate commerce.[73] The BBC reported in September 2012 that the UK group won the legal dispute over the right to keep using their band name; the US band changed its name to Uncharted Shores.[73] The change of name was announced in a joint statement that also noted both groups were happy with the outcome.[73]
+In September 2012, "Live While We're Young", the lead single from the group's second album, was released, and was a global success. It reached the top ten in almost every country it charted in and recorded the highest one-week opening sales figure for a song by a non-US artist in the US.[74] A second single, "Little Things", resulted in the band's second number one single in the UK.[75] In November 2012, One Direction's second studio album, Take Me Home, was released.[76] It was an international hit, reaching number one in over 35 countries. Upon reaching number one on the Billboard 200, the group became the first boy band in US chart history to record two number-one albums in the same calendar year alongside becoming the first group since 2008 to record two number-one albums in the same year.[77] One Direction became the first group ever to have their first two albums reach atop the Billboard 200.[78] Take Me Home sold 540,000 copies in its first week in the US, debuted atop the Billboard 200, and topped the charts in more than thirty-four other countries.[79][80] Additionally, Up All Night and Take Me Home were the number three and number four best-selling albums of 2012 globally, each album selling over 4.4 million units worldwide.[81] The album and "Little Things" both debuted at number one in the UK simultaneously, making One Direction the youngest act in British chart history to achieve that.[82]
+Take Me Home was written in groups and has an average of just under five songwriters per track. Savan Kotecha, Rami Yacoub, and Carl Falk, who composed One Direction's hits "What Makes You Beautiful" and "One Thing", spent six months in Stockholm developing songs for the album, and were able to shape melodies around their tones.[83] One Direction began recording the album in May 2012, in Stockholm at Kinglet Studios.[84][85][86] The album cover artwork features the group surrounding a traditional British K2 red telephone box, a familiar sight on the streets of the UK.[87] Take Me Home garnered mixed reviews from music critics. There was praise for its quality of production, while it was criticised for its generic, rushed nature.[88][89][90][91][92][93]
+One Direction performed "Little Things" at the 2012 Royal Variety Performance in the presence of Queen Elizabeth II, and headlined a sold-out show at New York City's Madison Square Garden on 3 December 2012.[94][95] In February 2013, One Direction released a cover version of "One Way or Another" and "Teenage Kicks", "One Way or Another (Teenage Kicks)", as the 2013 Comic Relief single.[96] As part of their involvement with the UK charity, One Direction travelled to Ghana to volunteer at a children's hospital, visit a school and make donations.
+Following the release of Take Me Home, One Direction embarked on their second concert tour in February 2013, the Take Me Home Tour.[97] The concert tour consisted of 123 shows in Europe, North America, Asia, and Oceania. Ticket sales reached 300,000 within a day of release in the UK and Ireland, which included a six-date sell-out at the O2 Arena in London.[98] In the Australian and New Zealand markets, tickets grossed US$15.7 million, with all 190,000 tickets being sold for the eighteen shows to be held.[99] The tour received critical acclaim from music critics who praised the band's live vocals and their performance abilities and was a commercial success, selling 1,635,000 tickets from 134 shows.[100] In total, the tour grossed $114 million. The Official Charts Company revealed that One Direction had sold 2,425,000 records in the UK by February 2013.[101]
+"Best Song Ever", the lead single of the group's then-upcoming third studio album Midnight Memories, was released on 22 July 2013. The song[102][103] is their highest charting single in the US to date, reaching number two.[104] It broke the 24-Hour Vevo Record with 10.9 million views on YouTube (this was the second time the band held the record with "Live While We're Young" attaining 8.2 million views on 20 September 2012).[105][106] One Direction: This Is Us, a 3D documentary and concert film about the group directed by Morgan Spurlock and produced by Spurlock, Ben Winston, Adam Milano and Simon Cowell, was released by TriStar Pictures on 30 August 2013.[107] The film was a box office success, topping the UK and US box offices and grossing over $60 million worldwide, and became the fourth highest-grossing concert movie.[108]
+On 16 May 2013, the band announced their first all-stadium tour, the Where We Are Tour. Tickets for the tour sold out in minutes and more shows were added due to "overwhelming demand."[109] On 23 November 2013, in support of Midnight Memories, the band participated in "1D Day",[110][111] a day dedicated to One Direction fans. The day constituted of a landmark 7.5-hour socially interactive YouTube live-stream featuring live band performances, celebrity guests including, Simon Cowell, Cindy Crawford, Piers Morgan, and Jerry Springer. On 28 October 2013, the second single from Midnight Memories, "Story of My Life," was released, charting at number six in the US and at number two in the UK, while charting at number one in countries such as Mexico, Spain, Bulgaria, Denmark, and Ireland.[112][113]
+Midnight Memories was released globally on 25 November 2013. It debuted at number one in the UK and in the US, making them the first group to debut at number one on the Billboard 200 with its first three albums, and the second to reach the top after The Monkees in 1967.[114] The album was described by the band as edgier and as having a "slightly rockier tone" than their previous efforts.[115] Despite being released at the year's end, it was the best-selling album worldwide in 2013 with 4 million copies sold globally.[116] To promote the album, the band performed on both the American and British versions of The X Factor.[117]
+In December 2013, One Direction broke yet another UK sales record with the DVD and Blu-ray release of This Is Us. Nearly 270,000 copies of the film were sold in the UK within three days of its release, beating the record previously set by Michael Jackson's This Is It in 2010 by 10,000 copies.[118] The group was named among the Top Global artists of 2013 by the IFPI because of strong digital downloads, physical albums, on-demand streams, and music videos.[5]
+The band embarked on the Where We Are Tour on 25 April 2014, and it was concluded on 5 October 2014. Playing 69 shows with an average of 49,848 fans per show, the tour grossed over $290 million, becoming the highest-grossing concert tour in 2014, the 15th highest-grossing concert tour of all time, and the highest-grossing tour of all time by a vocal group.[119] The tour was attended by 3.4 million fans.[120] In August of that same year, the group released their third book, One Direction: Where We Are: Our Band, Our Story: 100% Official.
+On 21 July 2014, One Direction announced One Direction: Where We Are - The Concert Film, a film which documents the concerts of 28 and 29 June 2014 that took place in San Siro Stadium during their Where We Are Tour. After the announcement, the band announced the film would also have a limited 10–11 October 2014 international cinema release before its home media release in November 2014.[121] The group also released an autobiography book titled Who We Are on 25 September 2014.[122]
+On 8 September 2014, One Direction announced their fourth studio album to be titled Four, set to be released on 17 November 2014.[123][124][125] As part of the announcement, one of the songs from the album, "Fireproof" was released for free download for 24 hours on their official website.[123][124][125] "Steal My Girl", the album's lead single, was released on 29 September 2014,[126]
+receiving critical acclaim for its classic rock sound.[127] The second single from the album, "Night Changes", was released on 14 November, three days before the album's release. It also achieve platinum status, selling over one million units in the United States.[128] Four was released on 17 November 2014, topping the Billboard 200 and the UK Album Chart.[129][130] In total, in debuted at number one in 18 countries, selling 3.2 million copies.[131] It became the top charted album on iTunes in 67 countries.[132] One Direction became the only group in the 58-year history of the Billboard 200 albums chart to have their first four albums debut at number one.[133] In February 2015, the group embarked on their fourth world tour and second all-stadium tour, the On the Road Again Tour,[134] grossing $208 million, making it the second highest-grossing tour of 2015.[135]
+On 25 March 2015, the band released a statement announcing Malik's departure.[136][137][138] The group made their first official public appearance as a four-piece on The Late Late Show with James Corden on 14 May, where they confirmed that they would continue working without a new fifth member.[139] The On the Road Again tour concluded on 31 October 2015 after playing eighty shows in Australia, Asia, Africa, Europe, and North America. Grossing $208 million, over 2.3 million tickets were sold.[140]
+On 31 July 2015, the group released "Drag Me Down" without promotional material or announcement. Despite this, it still topped the charts in multiple countries, including France and Australia, making the song their first single to reach number one in those respective countries. It also reached number one in multiple other countries, including Ireland and the UK, while charting third in the United States. The single was the first single from their fifth studio album, Made in the A.M., and the first material released by the group after Malik's departure.[141] Following the release, it was revealed that the group would be going on hiatus in 2016.[142] On 22 September, the title for the fifth studio album, Made in the A.M., was officially announced along with promotional single "Infinity" being released.[143] The group began to reveal the track listing on their Snapchat stories to which it was later confirmed on iTunes.[144] In October, another single, "Perfect," was released. It reached the Billboard top ten, making it the group's second consecutive (after "Drag Me Down") and fifth overall top ten hit, breaking The Beatles' record for the most top ten Hot 100 debuts among bands.[145]
+Made in the A.M. was released on 13 November 2015,[146] topping the charts in the UK among other countries while reaching number two in the U.S. It was the sixth-best selling album of 2015. At the 2015 American Music Awards on 22 November, One Direction won the award for Artist of the Year for the second year in succession.[147] Louis Tomlinson later confirmed that the break would be around 18 months. On 13 December, One Direction performed on The X Factor final. Their last televised performance as a group, before their hiatus, was on Dick Clark's New Year's Rockin' Eve on 31 December 2015.[148]
+On 13 January 2016, Us Weekly published a report claiming that the group's hiatus would become a permanent split, with a "source" citing that each of the four remaining group members did not renew their contracts following the completion of the On The Road Again Tour in October 2015.[149] Representatives for the group denied said-report in a statement to Billboard, stating, "nothing has changed regarding hiatus plans for the group, and all will be revealed in due time from the band members' own mouths."[150][151] By May 2017, all members of the group had released solo singles.[152] Despite saying the hiatus would last 18 months, the band still are yet to confirm when they will reform.
+At the 2017 Brit Awards, One Direction won the Video of the Year award for their song "History". Payne accepted the award on the behalf of the band.[153] In February 2018, it was reported that the group has folded its touring company after having applied for removal within the Companies House registry in October 2017.[154][155]
+On 22 July 2020, One Direction posted on their Twitter, Instagram and YouTube accounts a picture with the words "10 Years of One Direction" written in it and the caption "Tomorrow! You and me got a whole lot of history #10YearsOf1D" in anticipation of their 10th anniversary the following day. The hashtag "10YearsofOneDiretion" started trending 1st on Twitter.[156][157][158]
+On 23 July 2020, One Direction announced a new website (10yearsof1d.com) for fans to relieve their favourite One Direction memories, but it soon crashed shortly after its announcement due to the high volume of fans entering at once.[159] Members Payne, Horan, Tomlinson and Styles also posted on their individual social media pages, thanking their fans and all five current/former members for the support given through the past 10 years.[160][161][162][163]
+At 16:00 (GMT+1) on 23 July 2020, One Direction premiered  a 4 minutes and 57 seconds video of memories of One Direction titled "10 Years of One Direction" in celebration of their anniversary.[164] The group then released a 10 Year Anniversary Schedule spanning from 23 July to 28 July 2020 where remastered 4K versions of their past music videos and a concert video is released daily.[165]
+One Direction's debut studio album, Up All Night (2011), is predominantly a pop music record, containing elements of teen pop, dance-pop, pop rock, with electropop and rock influences.[170][171][172][173] Digital Spy's Robert Copsey described the album as a "collection of PG pop rock with killer choruses",[174] while The New York Times considered it "full of easy rock-inflected pop, blithe and sometimes clever."[175] Jason Lipshutz of Billboard acknowledged that the album demonstrates an originality in sound that was "necessary for the revitalization of the boy band movement".[173] The songs "One Thing" and "What Makes You Beautiful" were particularly noted for the genres of power pop and pop rock, for their "powerhouse" guitar riffs and "forceful" choruses.[166][167][170][176]
+Their second studio album, Take Me Home (2012), is characterised by rock-inherited pop, prominent electric guitar riffs, bright synthesisers, a homogeneous sound and message, and the pitch-correcting software Auto-Tune.[91][92][93][177][178] Alexis Petridis of The Guardian interpreted its signature sound as a "peppy, synth-bolstered take on early-80s new-wave pop, heavy on clipped rhythms and chugging guitars," which, he said, is at least an improvement on the substitute contemporary R&B "that was once the grim lot of the boyband."[92] Jon Caramanica, writing in The New York Times, considered the album "far more mechanical" than their debut album, although noted that it is sonically and lyrically similar.[91] The album's lyricism speaks of falling in love, unrequited love, the insistence that flaws are what make a person unique, commitment, jealousy and longing for past significant others.[91][92][93][179]
+Erica Futterman for Rolling Stone favoured their live acoustic performances as both showing, "Horan's ability to play guitar, as well as One Direction's admirable live vocals. There was no need to worry about a backing track or a bum note, a pleasant realization at a pop show."[180] Herald Sun's Cameron Adams opined that One Direction have "strong pop voices".[181] Melody Lau of the National Post wrote, "It's easy to get lost in inherent appeal of their perfectly coiffed dos and almost-too-put-together preppy style but somewhere in the midst of all the love-struck squeals of teenage girls are guys who can actually sing and, to a certain extent, entertain."[182] Jane Stevenson of the portal site Canoe concurred: "What I didn't really prepare myself for was that they all can actually sing in concert."[183] Chris Richards, writing in The Washington Post, dissented from the approval: "As the five traded couplets, it was tough to imagine a future Justin Timberlake, Ricky Martin or Bobby Brown emerging from the pack. No one voice stood out."[184] Mike Wass of Idolator felt One Direction's "surprisingly accomplished effort" of Kings of Leon's "Use Somebody" proved that One Direction are "more than capable" of evolving their sound.[185]
+Their third album Midnight Memories (2013) is a pop rock record, a slight departure from the band's original teen pop sound. Liam Payne called Midnight Memories a "slightly rockier and edgier" album than their previous material. The album is heavily influenced by 80's rock[186] and folk music and briefly integrates elements of dubstep, notably in "Little White Lies". The album's lyrical themes primarily revolve around love, heartbreak and sexual intercourse. Many critics praised its lyrical depth and musical composition, as well as the group's level of involvement in the production process.[187]
+Their fourth album Four (2014) was released on 17 November 2014. Payne once again claimed that the album would be "edgier" and that the group had written most of the songs for it; Horan came up with the name of the album, commemorating the fact that it is One Direction's fourth record to date and that it has been four years since the band's formation. Signifying a further maturation of their pop sound, the album's first single, "Steal My Girl", was dubbed by Billboard as "no What Makes You Beautiful, but its Coldplay-like piano pop could be a good direction",[188] and that the band was "not entirely ready to let go of its bubble-gum days". Rolling Stone described the record as "saturated with retro vibes"; its songs "split the difference between big, splashy Eighties pop rock and more elegant Seventies flavours – a very pesky whipper-snapper move that's not so far from what Haim's hit "Days Are Gone" did last year."[189]
+In 2011, One Direction became the face of Pokemon Black and White, starring in a series of television adverts.[190] They were the first installments in the fifth generation of the Pokémon series of role-playing games.[191] They also launched Nokia C3 and Nokia C2-02 phones. To promote the launch Nokia made a series of photos of the band members using the phones to take photos of themselves.[192]
+In 2012, they teamed up with Colgate to launch their own One Direction Colgate MaxFresh Power Toothbrush, the One Direction Colgate Maxfresh Manual Toothbrush, and the One Direction Colgate MaxFresh Toothpaste.[193] The band was signed by Pepsi in a multimillion-dollar advertising deal in 2012.[194] Social media marketing included a tie up with Shazam, whereby consumers that used the digital music app in conjunction with the ad both on TV and online were be able to view exclusive content and link back to iTunes to buy One Direction's single, "Live While We're Young".[195] Mini figures based on members of the group were launched for the band's US fans after the agreement was signed by American firm Hasbro.[196][197] In October 2012, the band also signed up to endorse Filipino clothing brand, Penshoppe.[198]
+In 2013, One Direction announced pop-up shops around the world, including Brisbane, Toronto, Chicago, New York, Tokyo and Stockholm, selling exclusive merchandise.[199] Nabisco became the title sponsor of One Direction's North American tour.[200] The band became the new faces of Toyota VIOS, releasing behind-the-scenes look at their commercial for the vehicle.[201] One Direction's debut fragrance, Our Moment, launched at Harrods in London and on their website in 2013.[202] The full length advert for the fragrance was released on 24 August 2013, featuring the song "My Favourite Things".[203][204] The perfume was the best-selling famous fragrance of Christmas 2013.[205][206] In 2014, the band released their second scent That Moment.[207] The fragrance was released with a matching shower gel and body lotion.[208] They released a commercial for their third fragrance, "You & I", named after their 2014 song of the same name.[209]
+In 2015, One Direction appeared in an advert for the Toyota Vios. the commercial aired in Thailand.[210] Coca-Cola Mexico launched the session and full interview with One Direction, with a series of commercials in which Tomlinson, Payne, Styles and Horan showed us what it means to be a True Friend.[211] One Direction revealed their fourth fragrance ‘Between Us’ at The Sanderson in London, England on 24 June.[212] The band appeared in a Honda Civic ad which shows the quartet testing out the car's stereo, style and trunk space with a humorous tone and the tagline "It's all One Direction approved." The ad is set to the 1D single "Drag Me Down". The group's 2015 U.S. tour was also supported by Honda.[213]
+In 2011, the band performed on the BBC's Children in Need 2011 charity telethon. In 2012, they extended their involvement with Children in Need as they opened the telecast with a performance of their single "Live While We're Young". A prominent annual event in British television, the group said it was "incredible" to be involved in Children in Need as it was something that they had "always watched as children".[214]
+In February 2013, One Direction released "One Way or Another (Teenage Kicks)" (a medley of "One Way or Another" and "Teenage Kicks") as the 2013 single for the UK's other major charity telethon Comic Relief.[96] For ITV's Santa charity Christmas campaign, they filmed a set of pleas to their fans and the general public, asking them to donate £2.[215] The band have made numerous other appearances for charitable causes, including the 2011 Pride of Britain Awards where they presented 13-year-old quadruple amputee Danielle Bailey the Child of Courage award at her school assembly, and the 2014 Royal Variety Performance where they played in front of Prince William and Catherine at the London Palladium.[216][217]
+In September 2012, Niall Horan organised an event to raise money for Irish Autism Action and another charity, called Temporary Emergency Accommodation Mullingar, based in his hometown. Due to overwhelming demand to participate in the fundraising, the ticket website for the event broke down. Horan's brother Greg commented on the website crash, saying that "there were 500 tickets and they were all snapped up pretty quick".[218]
+In 2013, band members Liam Payne and Harry Styles partnered with Trekstock, a leading cancer charity to help raise money for cancer research.[219] As ambassadors of the charity, the duo collaborated to offer the chance for one fan and a friend to win an evening out with them in return for a donation to the charity as part of an exclusive "#HangwithLiam&Harry" global campaign. They had originally set a goal of raising $500,000 and ended up raising $784,984. Trekstock later added that this amount would allow them to "complete funding of their Hodgkin's lymphoma trial, in the hope of offering a much brighter future to thousands of children and young people affected by this form of disease." One Direction were named the most charitable in 2013 behind Taylor Swift by social change organisation DoSomething.org.[220] On 30 May 2013, the band announced a partnership with Office Depot on a limited-edition capsule collection of back to school supplies. They also confirmed that a portion of the proceeds from the alliance would go toward an anti-bullying educational program intended to promote kinder behaviour in schools.[221]
+In 2014, One Direction donated £600,000 for the Stand up to Cancer campaign by giving portions of their ticket sales revenues from their Where We Are Tour.[222] On 15 November 2014, One Direction joined the charity group Band Aid 30 along with other British and Irish pop acts, recording the latest version of the track "Do They Know It's Christmas?" at Sarm West Studios in Notting Hill, London, to raise money for the 2014 Ebola crisis in Western Africa.[223]
+In 2015, One Direction launched 'Action 1D' campaign to raise awareness of global issues. The initiative aims to end extreme poverty, tackle inequality and slow down climate change with the help of their millions of fans. It is part of the wider action/2015 campaign, a global citizen's movement that is all about the idea that 2015 can be the year when the world can set the agenda to end major global issues. One Direction will be asking their fans to describe the kind of world they want to live in by sharing powerful pieces of creative content, including videos and photos, using the hashtag #Action1D.[224] The quartet also starred in a campaign video, appealing to fans to join the movement.[225]
+Neil McCormick of The Daily Telegraph, in an article on One Direction's success in North America, notes that Americans had left a gap in the market and it took the prominence of Justin Bieber to demonstrate that there still was a market for "clean cut, wholesome, whiter-than-white, middle class parent friendly pop: cute boys advocating puppy love. And what could be better than one cute boy, if not five?"[226] One Direction have been described as sparking a resurgence in the interest in boy bands, and as forming part of a new "British Invasion" in the United States.[227][228][229][230][231] Bill Werde, a representative of Billboard magazine, commented, "There's a lot of possibility here, there's a lot of upside, that level of talent with those kinds of looks, it's really a perfect storm for a massive, massive successful phenomenon."[232] In NPR, Maria Sherman noticed that before One Direction's breakthrough, boy bands were "off the radar" since NSYNC went on an indefinite hiatus in 2002.[233]
+Sonny Takhar, the chief executive officer of Syco Records, attributes the breakthrough to the power of social media. "Sometimes you feel the song's the star, but it's not like that here – it's the act," he said. "It's a real moment. Social media has become the new radio, it's never broken an act globally like this before."[232] Will Bloomfield, the group's manager, added, "These guys live online, and so do their fans."[231] Their management employs a social media team and the members all tweet themselves, "which helps create the illusion that they couldn't be any closer to their fans," according to Caspar Llewellyn Smith, writing for The Guardian.[232] One Direction's Twitter account had amassed 10 million followers by February 2013, with the account gaining followers at an average of 21,000 per day.[234] In an approach pioneered by The Beatles, each member is known for his feature; Horan is "the cute one", Malik is "the quiet and mysterious one", Payne is "the sensible one", Styles is "the charming one" and Tomlinson is "the funny one".[235] Each member's individual identity is reinforced by their intentionally different personal styles. Caroline Watson, the band's original stylist, spoke about styling the band, "At the beginning I didn't want them all in black or all in leather—that whole stereotypical boy band thing." Instead, her original idea was for them to be the "male equivalent to the Spice Girls", with each member being a part of the group but still having his own individual style.[236]
+Horan commented on One Direction as a boy band, "People think that a boy band is air-grabs and [being] dressed in all one colour. We're boys in a band. We're trying to do something different from what people would think is the typical kind of boy band. We're trying to do different kinds of music and we're just trying to be ourselves, not squeaky clean."[237] Leah Collins, writing for the National Post, remarked they had succeeded on the latter front. "For the most part, that just means the group presents themselves as typical, goofy and uncensored teenage boys – posting jokey YouTube videos, for instance, or boozing at awards shows."[237] Writing for The Observer, Kitty Empire opined, "One Direction fulfill a great many boy band prerequisites (looks, soppy lyrics, tune-grasp, fame-lust) but their lack of routines points to the subtle digressions afoot here".[238]
+Headlining
+Opening act
+One Direction has received seven Brit Awards,[241] seven American Music Awards,[242] six Billboard Music Awards,[243] five Billboard Touring Awards, and four MTV Video Music Awards,[244] among other awards. One Direction holds the record as the most awarded act at the Teen Choice Awards with 28 wins from 31 nominations.[245]

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+Athena[b] or Athene,[c] often given the epithet Pallas,[d] is an ancient Greek goddess associated with wisdom, handicraft, and warfare[3] who was later syncretized with the Roman goddess Minerva.[4] Athena was regarded as the patron and protectress of various cities across Greece, particularly the city of Athens, from which she most likely received her name.[5] She's usually shown in art wearing a helmet and holding a spear. Her major symbols include owls, olive trees, snakes, and the Gorgoneion.
+From her origin as an Aegean palace goddess, Athena was closely associated with the city. She was known as Polias and Poliouchos (both derived from polis, meaning "city-state"), and her temples were usually located atop the fortified acropolis in the central part of the city. The Parthenon on the Athenian Acropolis is dedicated to her, along with numerous other temples and monuments. As the patron of craft and weaving, Athena was known as Ergane. She's also a warrior goddess, and was believed to lead soldiers into battle as Athena Promachos. Her main festival in Athens was the Panathenaia, which was celebrated during the month of Hekatombaion in midsummer and was the most important festival on the Athenian calendar.
+In Greek mythology, Athena was believed to have been born from the head of her father Zeus. In the founding myth of Athens, Athena bested Poseidon in a competition over patronage of the city by creating the first olive tree. She's known as Athena Parthenos "Athena the Virgin," but in one archaic Attic myth, the god Hephaestus tried and failed to rape her, resulting in Gaia giving birth to Erichthonius, an important Athenian founding hero. Athena was the patron goddess of heroic endeavor; she was believed to have aided the heroes Perseus, Heracles, Bellerophon, and Jason. Along with Aphrodite and Hera, Athena was one of the three goddesses whose feud resulted in the beginning of the Trojan War.
+She plays an active role in the Iliad, in which she assists the Achaeans and, in the Odyssey, she is the divine counselor to Odysseus. In the later writings of the Roman poet Ovid, Athena was said to have competed against the mortal Arachne in a weaving competition, afterwards transforming Arachne into the first spider; Ovid also describes how she transformed Medusa into a Gorgon after witnessing her being raped by Poseidon in her temple. Since the Renaissance, Athena has become an international symbol of wisdom, the arts, and classical learning. Western artists and allegorists have often used Athena as a symbol of freedom and democracy.
+Athena is associated with the city of Athens.[5][7] The name of the city in ancient Greek is Ἀθῆναι (Athȇnai), a plural toponym, designating the place where—according to myth—she presided over the Athenai, a sisterhood devoted to her worship.[6] In ancient times, scholars argued whether Athena was named after Athens or Athens after Athena.[5] Now scholars generally agree that the goddess takes her name from the city;[5][7] the ending -ene is common in names of locations, but rare for personal names.[5] Testimonies from different cities in ancient Greece attest that similar city goddesses were worshipped in other cities[6] and, like Athena, took their names from the cities where they were worshipped.[6] For example, in Mycenae there was a goddess called Mykene, whose sisterhood was known as Mykenai,[6] whereas at Thebes an analogous deity was called Thebe, and the city was known under the plural form Thebai (or Thebes, in English, where the 's' is the plural formation).[6] The name Athenai is likely of Pre-Greek origin because it contains the presumably Pre-Greek morpheme *-ān-.[8]
+In his dialogue Cratylus, the ancient Greek philosopher Plato (428–347 BC) gives some rather imaginative etymologies of Athena's name, based on the theories of the ancient Athenians and his own etymological speculations:
+That is a graver matter, and there, my friend, the modern interpreters of Homer may, I think, assist in explaining the view of the ancients. For most of these in their explanations of the poet, assert that he meant by Athena "mind" [νοῦς, noũs] and "intelligence" [διάνοια, diánoia], and the maker of names appears to have had a singular notion about her; and indeed calls her by a still higher title, "divine intelligence" [θεοῦ νόησις, theoũ nóēsis], as though he would say: This is she who has the mind of God [ἁ θεονόα, a theonóa). Perhaps, however, the name Theonoe may mean "she who knows divine things" [τὰ θεῖα νοοῦσα, ta theia noousa] better than others. Nor shall we be far wrong in supposing that the author of it wished to identify this Goddess with moral intelligence [εν έθει νόεσιν, en éthei nóesin], and therefore gave her the name Etheonoe; which, however, either he or his successors have altered into what they thought a nicer form, and called her Athena.
+Thus, Plato believed that Athena's name was derived from Greek Ἀθεονόα, Atheonóa—which the later Greeks rationalised as from the deity's (θεός, theós) mind (νοῦς, noũs). The second-century AD orator Aelius Aristides attempted to derive natural symbols from the etymological roots of Athena's names to be aether, air, earth, and moon.[9]
+Athena was originally the Aegean goddess of the palace, who presided over household crafts and protected the king.[11][12][13][14] A single Mycenaean Greek inscription 𐀀𐀲𐀙𐀡𐀴𐀛𐀊 a-ta-na po-ti-ni-ja /Athana potnia/ appears at Knossos in the Linear B tablets from the Late Minoan II-era "Room of the Chariot Tablets";[15][16][10] these comprise the earliest Linear B archive anywhere.[16] Although Athana potnia is often translated Mistress Athena,[17] it could also mean "the Potnia of Athana", or the Lady of Athens.[17][10] However, any connection to the city of Athens in the Knossos inscription is uncertain.[18] A sign series a-ta-no-dju-wa-ja appears in the still undeciphered corpus of Linear A tablets, written in the unclassified Minoan language.[19] This could be connected with the Linear B Mycenaean expressions a-ta-na po-ti-ni-ja and di-u-ja or di-wi-ja (Diwia, "of Zeus" or, possibly, related to a homonymous goddess),[16] resulting in a translation "Athena of Zeus" or "divine Athena". Similarly, in the Greek mythology and epic tradition, Athena figures as a daughter of Zeus (Διός θυγάτηρ; cfr. Dyeus).[20] However, the inscription quoted seems to be very similar to "a-ta-nū-tī wa-ya", quoted as SY Za 1 by Jan Best.[20] Best translates the initial a-ta-nū-tī, which is recurrent in line beginnings, as "I have given".[20]
+A Mycenean fresco depicts two women extending their hands towards a central figure, who is covered by an enormous figure-eight shield; this may depict the warrior-goddess with her palladion, or her palladion in an aniconic representation.[21][22] In the "Procession Fresco" at Knossos, which was reconstructed by the Mycenaeans,[23] two rows of figures carrying vessels seem to meet in front of a central figure,[23] which is probably the Minoan precursor to Athena.[23] The early twentieth-century scholar Martin Persson Nilsson argued that the Minoan snake goddess figurines are early representations of Athena.[11][12]
+Nilsson and others have claimed that, in early times, Athena was either an owl herself or a bird goddess in general.[24] In the third book of the Odyssey, she takes the form of a sea-eagle.[24] Proponents of this view argue that she dropped her prophylactic owl-mask before she lost her wings. "Athena, by the time she appears in art," Jane Ellen Harrison remarks, "has completely shed her animal form, has reduced the shapes she once wore of snake and bird to attributes, but occasionally in black-figure vase-paintings she still appears with wings."[25]
+It is generally agreed that the cult of Athena preserves some aspects of the Proto-Indo-European transfunctional goddess.[27][28] The cult of Athena may have also been influenced by those of Near Eastern warrior goddesses such as the East Semitic Ishtar and the Ugaritic Anat,[12][10] both of whom were often portrayed bearing arms.[12] Classical scholar Charles Penglase notes that Athena closely resembles Inanna in her role as a "terrifying warrior goddess"[29] and that both goddesses were closely linked with creation.[29] Athena's birth from the head of Zeus may be derived from the earlier Sumerian myth of Inanna's descent into and return from the Underworld.[30][31]
+Plato notes that the citizens of Sais in Egypt worshipped a goddess known as Neith,[e] whom he identifies with Athena.[32] Neith was the ancient Egyptian goddess of war and hunting, who was also associated with weaving; her worship began during the Egyptian Pre-Dynastic period. In Greek mythology, Athena was reported to have visited mythological sites in North Africa, including Libya's Triton River and the Phlegraean plain.[f] Based on these similarities, the Sinologist Martin Bernal created the "Black Athena" hypothesis, which claimed that Neith was brought to Greece from Egypt, along with "an enormous number of features of civilization and culture in the third and second millennia".[33][34] The "Black Athena" hypothesis stirred up widespread controversy near the end of the twentieth century,[35][36] but it has now been widely rejected by modern scholars.[37][38]
+In her aspect of Athena Polias, Athena was venerated as the goddess of the city and the protectress of the citadel.[12][39][40] In Athens, the Plynteria, or "Feast of the Bath", was observed every year at the end of the month of Thargelion.[41] The festival lasted for five days. During this period, the priestesses of Athena, or plyntrídes, performed a cleansing ritual within the Erechtheion, a sanctuary devoted to Athena and Poseidon.[42] Here Athena's statue was undressed, her clothes washed, and body purified.[42] Athena was worshipped at festivals such as Chalceia as Athena Ergane,[43][40] the patroness of various crafts, especially weaving.[43][40] She was also the patron of metalworkers and was believed to aid in the forging of armor and weapons.[43] During the late fifth century BC, the role of goddess of philosophy became a major aspect of Athena's cult.[44]
+As Athena Promachos, she was believed to lead soldiers into battle.[45][46] Athena represented the disciplined, strategic side of war, in contrast to her brother Ares, the patron of violence, bloodlust, and slaughter—"the raw force of war".[47][48] Athena was believed to only support those fighting for a just cause[47] and was thought to view war primarily as a means to resolve conflict.[47] The Greeks regarded Athena with much higher esteem than Ares.[47][48] Athena was especially worshipped in this role during the festivals of the Panathenaea and Pamboeotia,[49] both of which prominently featured displays of athletic and military prowess.[49] As the patroness of heroes and warriors, Athena was believed to favor those who used cunning and intelligence rather than brute strength.[50]
+In her aspect as a warrior maiden, Athena was known as Parthenos (Παρθένος "virgin"),[45][52][53] because, like her fellow goddesses Artemis and Hestia, she was believed to remain perpetually a virgin.[54][55][45][53][56] Athena's most famous temple, the Parthenon on the Athenian Acropolis, takes its name from this title.[56] According to Karl Kerényi, a scholar of Greek mythology, the name Parthenos is not merely an observation of Athena's virginity, but also a recognition of her role as enforcer of rules of sexual modesty and ritual mystery.[56] Even beyond recognition, the Athenians allotted the goddess value based on this pureness of virginity, which they upheld as a rudiment of female behavior.[56] Kerényi's study and theory of Athena explains her virginal epithet as a result of her relationship to her father Zeus and a vital, cohesive piece of her character throughout the ages.[56] This role is expressed in a number of stories about Athena. Marinus of Neapolis reports that when Christians removed the statue of the goddess from the Parthenon, a beautiful woman appeared in a dream to Proclus, a devotee of Athena, and announced that the "Athenian Lady" wished to dwell with him.[57]
+Athena was not only the patron goddess of Athens, but also other cities, including Argos, Sparta, Gortyn, Lindos, and Larisa.[46] The various cults of Athena were all branches of her panhellenic cult[46] and often proctored various initiation rites of Grecian youth, such as the passage into citizenship by young men or the passage of young women into marriage.[46] These cults were portals of a uniform socialization, even beyond mainland Greece.[46] Athena was frequently equated with Aphaea, a local goddess of the island of Aegina, originally from Crete and also associated with Artemis and the nymph Britomartis.[58] In Arcadia, she was assimilated with the ancient goddess Alea and worshiped as Athena Alea.[59] Sanctuaries dedicated to Athena Alea were located in the Laconian towns of Mantineia and Tegea. The temple of Athena Alea in Tegea was an important religious center of ancient Greece.[g] The geographer Pausanias was informed that the temenos had been founded by Aleus.[60]
+Athena had a major temple on the Spartan Acropolis,[61][40] where she was venerated as Poliouchos and Khalkíoikos ("of the Brazen House", often latinized as Chalcioecus).[61][40] This epithet may refer to the fact that cult statue held there may have been made of bronze,[61] that the walls of the temple itself may have been made of bronze,[61] or that Athena was the patron of metal-workers.[61] Bells made of terracotta and bronze were used in Sparta as part of Athena's cult.[61] An Ionic-style temple to Athena Polias was built at Priene in the fourth century BC.[62] It was designed by Pytheos of Priene,[63] the same architect who designed the Mausoleum at Halicarnassus.[63] The temple was dedicated by Alexander the Great[64] and an inscription from the temple declaring his dedication is now held in the British Museum.[62]
+Athena was known as Atrytone (Άτρυτώνη "the Unwearying"), Parthenos (Παρθένος "Virgin"), and Promachos (Πρόμαχος "she who fights in front"). The epithet Polias (Πολιάς "of the city"), refers to Athena's role as protectress of the city.[46] The epithet Ergane (Εργάνη "the Industrious") pointed her out as the patron of craftsmen and artisans.[46] Burkert notes that the Athenians sometimes simply called Athena "the Goddess", hē theós (ἡ θεός), certainly an ancient title.[5] After serving as the judge at the trial of Orestes in which he was acquitted of having murdered his mother Clytemnestra, Athena won the epithet Areia (Αρεία).[46]
+Athena was sometimes given the epithet Hippia (Ἵππια "of the horses", "equestrian"),[40][65] referring to her invention of the bit, bridle, chariot, and wagon.[40] The Greek geographer Pausanias mentions in his Guide to Greece that the temple of Athena Chalinitis ("the bridler")[65] in Corinth was located near the tomb of Medea's children.[65] Other epithets include Ageleia, Itonia and Aethyia, under which she was worshiped in Megara.[66][67] The word aíthyia (αἴθυια) signifies a "diver", also some diving bird species (possibly the shearwater) and figuratively, a "ship", so the name must reference Athena teaching the art of shipbuilding or navigation.[68] In a temple at Phrixa in Elis, reportedly built by Clymenus, she was known as Cydonia (Κυδωνία).[69]
+The Greek biographer Plutarch (AD 46–120) refers to an instance during the Parthenon's construction of her being called Athena Hygieia (Ὑγίεια, i. e. personified "Health") after inspiring a physician to a successful course of treatment.[70]
+In Homer's epic works, Athena's most common epithet is Glaukopis (γλαυκῶπις), which usually is translated as, "bright-eyed" or "with gleaming eyes".[71] The word is a combination of glaukós (γλαυκός, meaning "gleaming, silvery", and later, "bluish-green" or "gray")[72] and ṓps (ὤψ, "eye, face").[73] The word glaúx (γλαύξ,[74] "little owl")[75] is from the same root, presumably according to some, because of the bird's own distinctive eyes. Athena was clearly associated with the owl from very early on;[76] in archaic images, she is frequently depicted with an owl perched on her hand.[76] Through its association with Athena, the owl evolved into the national mascot of the Athenians and eventually became a symbol of wisdom.[4]
+In the Iliad (4.514), the Odyssey (3.378), the Homeric Hymns, and in Hesiod's Theogony, Athena is also given the curious epithet Tritogeneia (Τριτογένεια), whose significance remains unclear.[77] It could mean various things, including "Triton-born", perhaps indicating that the homonymous sea-deity was her parent according to some early myths.[77] One myth relates the foster father relationship of this Triton towards the half-orphan Athena, whom he raised alongside his own daughter Pallas.[78] Kerényi suggests that "Tritogeneia did not mean that she came into the world on any particular river or lake, but that she was born of the water itself; for the name Triton seems to be associated with water generally."[79][80] In Ovid's Metamorphoses, Athena is occasionally referred to as "Tritonia".
+Another possible meaning may be "triple-born" or "third-born", which may refer to a triad or to her status as the third daughter of Zeus or the fact she was born from Metis, Zeus, and herself; various legends list her as being the first child after Artemis and Apollo, though other legends identify her as Zeus' first child.[81] Several scholars have suggested a connection to the Rigvedic god Trita,[82] who was sometimes grouped in a body of three mythological poets.[82] Michael Janda has connected the myth of Trita to the scene in the Iliad in which the "three brothers" Zeus, Poseidon, and Hades divide the world between them, receiving the "broad sky", the sea, and the underworld respectively.[83][84] Janda further connects the myth of Athena being born of the head (i. e. the uppermost part) of Zeus, understanding Trito- (which perhaps originally meant "the third") as another word for "the sky".[83] In Janda's analysis of Indo-European mythology, this heavenly sphere is also associated with the mythological body of water surrounding the inhabited world (cfr. Triton's mother, Amphitrite).[83]
+Yet another possible meaning is mentioned in Diogenes Laertius' biography of Democritus, that Athena was called "Tritogeneia" because three things, on which all mortal life depends, come from her.[85]
+In the classical Olympian pantheon, Athena was regarded as the favorite daughter of Zeus, born fully armed from his forehead.[86][87][88][h] The story of her birth comes in several versions.[89][90][91] The earliest mention is in Book V of the Iliad, when Ares accuses Zeus of being biased in favor of Athena because "autos egeinao" (literally "you fathered her", but probably intended as "you gave birth to her").[92][93]
+In the version recounted by Hesiod in his Theogony, Zeus married the goddess Metis, who is described as the "wisest among gods and mortal men", and engaged in sexual intercourse with her.[94][95][93][96] After learning that Metis was pregnant, however, he became afraid that the unborn offspring would try to overthrow him, because Gaia and Ouranos had prophesied that Metis would bear children wiser than their father.[94][95][93][96] In order to prevent this, Zeus tricked Metis into letting him swallow her, but it was too late because Metis had already conceived.[94][97][93][96] A later account of the story from the Bibliotheca of Pseudo-Apollodorus, written in the second century AD, makes Metis Zeus's unwilling sexual partner, rather than his wife.[98][99] According to this version of the story, Metis transformed into many different shapes in effort to escape Zeus,[98][99] but Zeus successfully raped her and swallowed her.[98][99]
+After swallowing Metis, Zeus took six more wives in succession until he married his seventh and present wife, Hera.[96] Then Zeus experienced an enormous headache.[100][93][96] He was in such pain that he ordered someone (either Prometheus, Hephaestus, Hermes, Ares, or Palaemon, depending on the sources examined) to cleave his head open with the labrys, the double-headed Minoan axe.[101][93][102][99] Athena leaped from Zeus's head, fully grown and armed.[101][93][88][103] The "First Homeric Hymn to Athena" states in lines 9–16 that the gods were awestruck by Athena's appearance[104] and even Helios, the god of the sun, stopped his chariot in the sky.[104] Pindar, in his "Seventh Olympian Ode", states that she "cried aloud with a mighty shout" and that "the Sky and mother Earth shuddered before her."[105][104]
+Hesiod states that Hera was so annoyed at Zeus for having given birth to a child on his own that she conceived and bore Hephaestus by herself,[96] but in Imagines 2. 27 (trans. Fairbanks), the third-century AD Greek rhetorician Philostratus the Elder writes that Hera "rejoices" at Athena's birth "as though Athena were her daughter also." The second-century AD Christian apologist Justin Martyr takes issue with those pagans who erect at springs images of Kore, whom he interprets as Athena: "They said that Athena was the daughter of Zeus not from intercourse, but when the god had in mind the making of a world through a word (logos) his first thought was Athena."[106] According to a version of the story in a scholium on the Iliad (found nowhere else), when Zeus swallowed Metis, she was pregnant with Athena by the Cyclops Brontes.[107] The Etymologicum Magnum[108] instead deems Athena the daughter of the Daktyl Itonos.[109] Fragments attributed by the Christian Eusebius of Caesarea to the semi-legendary Phoenician historian Sanchuniathon, which Eusebius thought had been written before the Trojan war, make Athena instead the daughter of Cronus, a king of Byblos who visited "the inhabitable world" and bequeathed Attica to Athena.[110][111]
+Athena's epithet Pallas is derived either from πάλλω, meaning "to brandish [as a weapon]", or, more likely, from παλλακίς and related words, meaning "youth, young woman".[113] On this topic, Walter Burkert says "she is the Pallas of Athens, Pallas Athenaie, just as Hera of Argos is Here Argeie."[5] In later times, after the original meaning of the name had been forgotten, the Greeks invented myths to explain its origin, such as those reported by the Epicurean philosopher Philodemus and the Bibliotheca of Pseudo-Apollodorus, which claim that Pallas was originally a separate entity, whom Athena had slain in combat.[114]
+In one version of the myth, Pallas was the daughter of the sea-god Triton;[78] she and Athena were childhood friends, but Athena accidentally killed her during a friendly sparring match.[115] Distraught over what she had done, Athena took the name Pallas for herself as a sign of her grief.[115] In another version of the story, Pallas was a Gigante;[101] Athena slew him during the Gigantomachy and flayed off his skin to make her cloak, which she wore as a victory trophy.[101][12][116][117] In an alternative variation of the same myth, Pallas was instead Athena's father,[101][12] who attempted to assault his own daughter,[118] causing Athena to kill him and take his skin as a trophy.[119]
+The palladion was a statue of Athena that was said to have stood in her temple on the Trojan Acropolis.[120] Athena was said to have carved the statue herself in the likeness of her dead friend Pallas.[120] The statue had special talisman-like properties[120] and it was thought that, as long as it was in the city, Troy could never fall.[120] When the Greeks captured Troy, Cassandra, the daughter of Priam, clung to the palladion for protection,[120] but Ajax the Lesser violently tore her away from it and dragged her over to the other captives.[120] Athena was infuriated by this violation of her protection.[112] Although Agamemnon attempted to placate her anger with sacrifices, Athena sent a storm at Cape Kaphereos to destroy almost the entire Greek fleet and scatter all of the surviving ships across the Aegean.[121]
+In a founding myth reported by Pseudo-Apollodorus,[108] Athena competed with Poseidon for the patronage of Athens.[122] They agreed that each would give the Athenians one gift[122] and that Cecrops, the king of Athens, would determine which gift was better.[122] Poseidon struck the ground with his trident and a salt water spring sprang up;[122] this gave the Athenians access to trade and water.[123] Athens at its height was a significant sea power, defeating the Persian fleet at the Battle of Salamis[123]—but the water was salty and undrinkable.[123] In an alternative version of the myth from Vergil's Georgics,[108] Poseidon instead gave the Athenians the first horse.[122] Athena offered the first domesticated olive tree.[122][53] Cecrops accepted this gift[122] and declared Athena the patron goddess of Athens.[122] The olive tree brought wood, oil, and food,[123] and became a symbol of Athenian economic prosperity.[53][124] Robert Graves was of the opinion that "Poseidon's attempts to take possession of certain cities are political myths",[123] which reflect the conflict between matriarchal and patriarchal religions.[123]
+Pseudo-Apollodorus[108] records an archaic legend, which claims that Hephaestus once attempted to rape Athena, but she pushed him away, causing him to ejaculate on her thigh.[126][51][127] Athena wiped the semen off using a tuft of wool, which she tossed into the dust,[126][51][127] impregnating Gaia and causing her to give birth to Erichthonius.[126][51][127] Athena adopted Erichthonius as her son and raised him.[126][127] The Roman mythographer Hyginus[108] records a similar story in which Hephaestus demanded Zeus to let him marry Athena since he was the one who had smashed open Zeus's skull, allowing Athena to be born.[126] Zeus agreed to this and Hephaestus and Athena were married,[126] but, when Hephaestus was about to consummate the union, Athena vanished from the bridal bed, causing him to ejaculate on the floor, thus impregnating Gaia with Erichthonius.[126]
+The geographer Pausanias[108] records that Athena placed the infant Erichthonius into a small chest[128] (cista), which she entrusted to the care of the three daughters of Cecrops: Herse, Pandrosos, and Aglauros of Athens.[128] She warned the three sisters not to open the chest,[128] but did not explain to them why or what was in it.[128] Aglauros, and possibly one of the other sisters,[128] opened the chest.[128] Differing reports say that they either found that the child itself was a serpent, that it was guarded by a serpent, that it was guarded by two serpents, or that it had the legs of a serpent.[129] In Pausanias's story, the two sisters were driven mad by the sight of the chest's contents and hurled themselves off the Acropolis, dying instantly,[130] but an Attic vase painting shows them being chased by the serpent off the edge of the cliff instead.[130]
+Erichthonius was one of the most important founding heroes of Athens[51] and the legend of the daughters of Cecrops was a cult myth linked to the rituals of the Arrhephoria festival.[51][131] Pausanias records that, during the Arrhephoria, two young girls known as the Arrhephoroi, who lived near the temple of Athena Polias, would be given hidden objects by the priestess of Athena,[132] which they would carry on their heads down a natural underground passage.[132] They would leave the objects they had been given at the bottom of the passage and take another set of hidden objects,[132] which they would carry on their heads back up to the temple.[132] The ritual was performed in the dead of night[132] and no one, not even the priestess, knew what the objects were.[132] The serpent in the story may be the same one depicted coiled at Athena's feet in Pheidias's famous statue of the Athena Parthenos in the Parthenon.[125] Many of the surviving sculptures of Athena show this serpent.[125]
+Herodotus records that a serpent lived in a crevice on the north side of the summit of the Athenian Acropolis[125] and that the Athenians left a honey cake for it each month as an offering.[125] On the eve of the Second Persian invasion of Greece in 480 BC, the serpent did not eat the honey cake[125] and the Athenians interpreted it as a sign that Athena herself had abandoned them.[125] Another version of the myth of the Athenian maidens is told in Metamorphoses by the Roman poet Ovid (43 BC – 17 AD); in this late variant Hermes falls in love with Herse. Herse, Aglaulus, and Pandrosus go to the temple to offer sacrifices to Athena. Hermes demands help from Aglaulus to seduce Herse. Aglaulus demands money in exchange. Hermes gives her the money the sisters have already offered to Athena. As punishment for Aglaulus's greed, Athena asks the goddess Envy to make Aglaulus jealous of Herse. When Hermes arrives to seduce Herse, Aglaulus stands in his way instead of helping him as she had agreed. He turns her to stone.[133]
+According to Pseudo-Apollodorus's Bibliotheca, Athena advised Argos, the builder of the Argo, the ship on which the hero Jason and his band of Argonauts sailed, and aided in the ship's construction.[135][136] Pseudo-Apollodorus also records that Athena guided the hero Perseus in his quest to behead Medusa.[137][138][139] She and Hermes, the god of travelers, appeared to Perseus after he set off on his quest and gifted him with tools he would need to kill the Gorgon.[139][140] Athena gave Perseus a polished bronze shield to view Medusa's reflection rather than looking at her directly and thereby avoid being turned to stone.[139][141] Hermes gave him an adamantine scythe to cut off Medusa's head.[139][142] When Perseus swung his blade to behead Medusa, Athena guided it, allowing his scythe to cut it clean off.[139][141] According to Pindar's Thirteenth Olympian Ode, Athena helped the hero Bellerophon tame the winged horse Pegasus by giving him a bit.[143][144]
+In ancient Greek art, Athena is frequently shown aiding the hero Heracles.[145] She appears in four of the twelve metopes on the Temple of Zeus at Olympia depicting Heracles's Twelve Labors,[146][145] including the first, in which she passively watches him slay the Nemean lion,[145] and the tenth, in which she is shown actively helping him hold up the sky.[147] She is presented as his "stern ally",[148] but also the "gentle... acknowledger of his achievements."[148] Artistic depictions of Heracles's apotheosis show Athena driving him to Mount Olympus in her chariot and presenting him to Zeus for his deification.[147] In Aeschylus's tragedy Orestes, Athena intervenes to save Orestes from the wrath of the Erinyes and presides over his trial for the murder of his mother Clytemnestra.[149] When half the jury votes to acquit and the other half votes to convict, Athena casts the deciding vote to acquit Orestes[149] and declares that, from then on, whenever a jury is tied, the defendant shall always be acquitted.[150]
+In The Odyssey, Odysseus' cunning and shrewd nature quickly wins Athena's favour.[151][136] For the first part of the poem, however, she largely is confined to aiding him only from afar, mainly by implanting thoughts in his head during his journey home from Troy. Her guiding actions reinforce her role as the "protectress of heroes," or, as mythologian Walter Friedrich Otto dubbed her, the "goddess of nearness," due to her mentoring and motherly probing.[152][137][153] It is not until he washes up on the shore of the island of the Phaeacians, where Nausicaa is washing her clothes that Athena arrives personally to provide more tangible assistance.[154] She appears in Nausicaa's dreams to ensure that the princess rescues Odysseus and plays a role in his eventual escort to Ithaca.[155] Athena appears to Odysseus upon his arrival, disguised as a herdsman;[156][157][151] she initially lies and tells him that Penelope, his wife, has remarried and that he is believed to be dead,[156] but Odysseus lies back to her, employing skillful prevarications to protect himself.[158][157] Impressed by his resolve and shrewdness, she reveals herself and tells him what he needs to know in order to win back his kingdom.[159][157][151] She disguises him as an elderly beggar so that he will not be recognized by the suitors or Penelope,[160][157] and helps him to defeat the suitors.[160][161][157] Athena also appears to Odysseus's son Telemachus.[162] Her actions lead him to travel around to Odysseus's comrades and ask about his father.[163] He hears stories about some of Odysseus's journey.[163] Athena's push for Telemachos's journey helps him grow into the man role, that his father once held.[164] She also plays a role in ending the resultant feud against the suitors' relatives. She instructs Laertes to throw his spear and to kill Eupeithes, the father of Antinous.
+Athena and Heracles on an Attic red-figure kylix, 480–470 BC
+Athena, detail from a silver kantharos with Theseus in Crete (c. 440-435 BC), part of the Vassil Bojkov collection, Sofia, Bulgaria
+Silver coin showing Athena with Scylla decorated helmet and Heracles fighting the Nemean lion (Heraclea Lucania, 390-340 BC)
+Paestan red-figure bell-krater (c. 330 BC), showing Orestes at Delphi flanked by Athena and Pylades among the Erinyes and priestesses of Apollo, with the Pythia sitting behind them on her tripod
+The Gorgoneion appears to have originated as an apotropaic symbol intended to ward off evil.[165] In a late myth invented to explain the origins of the Gorgon,[166] Medusa is described as having been a young priestess who served in the temple of Athena in Athens.[167] Poseidon lusted after Medusa, and raped her in the temple of Athena,[167] refusing to allow her vow of chastity to stand in his way.[167] Upon discovering the desecration of her temple, Athena transformed Medusa into a hideous monster with serpents for hair whose gaze would turn any mortal to stone.[168]
+In his Twelfth Pythian Ode, Pindar recounts the story of how Athena invented the aulos, a kind of flute, in imitation of the lamentations of Medusa's sisters, the Gorgons, after she was beheaded by the hero Perseus.[169] According to Pindar, Athena gave the aulos to mortals as a gift.[169] Later, the comic playwright Melanippides of Melos (c. 480-430 BC) embellished the story in his comedy Marsyas,[169] claiming that Athena looked in the mirror while she was playing the aulos and saw how blowing into it puffed up her cheeks and made her look silly, so she threw the aulos away and cursed it so that whoever picked it up would meet an awful death.[169] The aulos was picked up by the satyr Marsyas, who was later killed by Apollo for his hubris.[169] Later, this version of the story became accepted as canonical[169] and the Athenian sculptor Myron created a group of bronze sculptures based on it, which was installed before the western front of the Parthenon in around 440 BC.[169]
+A myth told by the early third-century BC Hellenistic poet Callimachus in his Hymn 5 begins with Athena bathing in a spring on Mount Helicon at midday with one of her favorite companions, the nymph Chariclo.[127][170] Chariclo's son Tiresias happened to be hunting on the same mountain and came to the spring searching for water.[127][170] He inadvertently saw Athena naked, so she struck him blind to ensure he would never again see what man was not intended to see.[127][171][172] Chariclo intervened on her son's behalf and begged Athena to have mercy.[127][172][173] Athena replied that she could not restore Tiresias's eyesight,[127][172][173] so, instead, she gave him the ability to understand the language of the birds and thus foretell the future.[174][173][127]
+The fable of Arachne appears in Ovid's Metamorphoses (8 AD) (vi.5–54 and 129–145),[175][176][177] which is nearly the only extant source for the legend.[176][177] The story does not appear to have been well known prior to Ovid's rendition of it[176] and the only earlier reference to it is a brief allusion in Virgil's Georgics, (29 BC) (iv, 246) that does not mention Arachne by name.[177] According to Ovid, Arachne (whose name means spider in ancient Greek[178]) was the daughter of a famous dyer in Tyrian purple in Hypaipa of Lydia, and a weaving student of Athena.[179] She became so conceited of her skill as a weaver that she began claiming that her skill was greater than that of Athena herself.[179][180] Athena gave Arachne a chance to redeem herself by assuming the form of an old woman and warning Arachne not to offend the deities.[175][180] Arachne scoffed and wished for a weaving contest, so she could prove her skill.[181][180]
+Athena wove the scene of her victory over Poseidon in the contest for the patronage of Athens.[181][182][180] Athena's tapestry also depicted the 12 Olympian gods and defeat of mythological figures who challenged their authority.[183] Arachne's tapestry featured twenty-one episodes of the deities' infidelity,[181][182][180] including Zeus being unfaithful with Leda, with Europa, and with Danaë.[182] It represented the unjust and discrediting behavior of the gods towards mortals.[183] Athena admitted that Arachne's work was flawless,[181][180][182] but was outraged at Arachne's offensive choice of subject, which displayed the failings and transgressions of the deities.[181][180][182] Finally, losing her temper, Athena destroyed Arachne's tapestry and loom, striking it with her shuttle.[181][180][182] Athena then struck Arachne across the face with her staff four times.[181][180][182] Arachne hanged herself in despair,[181][180][182] but Athena took pity on her and brought her back from the dead in the form of a spider.[181][180][182]
+The myth of the Judgement of Paris is mentioned briefly in the Iliad,[184] but is described in depth in an epitome of the Cypria, a lost poem of the Epic Cycle,[185] which records that all the gods and goddesses as well as various mortals were invited to the marriage of Peleus and Thetis (the eventual parents of Achilles).[184] Only Eris, goddess of discord, was not invited.[185] She was annoyed at this, so she arrived with a golden apple inscribed with the word καλλίστῃ (kallistēi, "for the fairest"), which she threw among the goddesses.[186] Aphrodite, Hera, and Athena all claimed to be the fairest, and thus the rightful owner of the apple.[186][127]
+The goddesses chose to place the matter before Zeus, who, not wanting to favor one of the goddesses, put the choice into the hands of Paris, a Trojan prince.[186][127] After bathing in the spring of Mount Ida where Troy was situated, the goddesses appeared before Paris for his decision.[186] In the extant ancient depictions of the Judgement of Paris, Aphrodite is only occasionally represented nude, and Athena and Hera are always fully clothed.[187] Since the Renaissance, however, western paintings have typically portrayed all three goddesses as completely naked.[187]
+All three goddesses were ideally beautiful and Paris could not decide between them, so they resorted to bribes.[186] Hera tried to bribe Paris with power over all Asia and Europe,[186][127] and Athena offered fame and glory in battle,[186][127] but Aphrodite promised Paris that, if he were to choose her as the fairest, she would let him marry the most beautiful woman on earth.[188][127] This woman was Helen, who was already married to King Menelaus of Sparta.[188] Paris selected Aphrodite and awarded her the apple.[188][127] The other two goddesses were enraged and, as a direct result, sided with the Greeks in the Trojan War.[188][127]
+In Books V–VI of the Iliad, Athena aids the hero Diomedes, who, in the absence of Achilles, proves himself to be the most effective Greek warrior.[189][136] Several artistic representations from the early sixth century BC may show Athena and Diomedes,[189] including an early sixth-century BC shield band depicting Athena and an unidentified warrior riding on a chariot, a vase painting of a warrior with his charioteer facing Athena, and an inscribed clay plaque showing Diomedes and Athena riding in a chariot.[189] Numerous passages in the Iliad also mention Athena having previously served as the patron of Diomedes's father Tydeus.[190][191] When the Trojan women go to the temple of Athena on the Acropolis to plead her for protection from Diomedes, Athena ignores them.[112]
+In Book XXII of the Iliad, while Achilles is chasing Hector around the walls of Troy, Athena appears to Hector disguised as his brother Deiphobus[192] and persuades him to hold his ground so that they can fight Achilles together.[192] Then, Hector throws his spear at Achilles and misses, expecting Deiphobus to hand him another,[193] but Athena disappears instead, leaving Hector to face Achilles alone without his spear.[193] In Sophocles's tragedy Ajax, she punishes Odysseus's rival Ajax the Great, driving him insane and causing him to massacre the Achaeans' cattle, thinking that he is slaughtering the Achaeans themselves.[194] Even after Odysseus himself expresses pity for Ajax,[195] Athena declares, "To laugh at your enemies - what sweeter laughter can there be than that?" (lines 78–9).[195] Ajax later commits suicide as a result of his humiliation.[195]
+Athena appears frequently in classical Greek art, including on coins and in paintings on ceramics.[196][197] She is especially prominent in works produced in Athens.[196] In classical depictions, Athena is usually portrayed standing upright, wearing a full-length chiton.[198] She is most often represented dressed in armor like a male soldier[197][198][7] and wearing a Corinthian helmet raised high atop her forehead.[199][7][197] Her shield bears at its centre the aegis with the head of the gorgon (gorgoneion) in the center and snakes around the edge.[166] Sometimes she is shown wearing the aegis as a cloak.[197] As Athena Promachos, she is shown brandishing a spear.[196][7][197] Scenes in which Athena was represented include her birth from the head of Zeus, her battle with the Gigantes, the birth of Erichthonius, and the Judgement of Paris.[196]
+The Mourning Athena or Athena Meditating is a famous relief sculpture dating to around 470-460 BC[199][196] that has been interpreted to represent Athena Polias.[199] The most famous classical depiction of Athena was the Athena Parthenos, a now-lost 11.5 m (38 ft)[200] gold and ivory statue of her in the Parthenon created by the Athenian sculptor Phidias.[198][196] Copies reveal that this statue depicted Athena holding her shield in her left hand with Nike, the winged goddess of victory, standing in her right.[196] Athena Polias is also represented in a Neo-Attic relief now held in the Virginia Museum of Fine Arts,[199] which depicts her holding an owl in her hand[i] and wearing her characteristic Corinthian helmet while resting her shield against a nearby herma.[199] The Roman goddess Minerva adopted most of Athena's Greek iconographical associations,[201] but was also integrated into the Capitoline Triad.[201]
+Attic black-figure exaleiptron of the birth of Athena from the head of Zeus (c. 570–560 BC) by the C Painter[196]
+Attic red-figure kylix of Athena Promachos holding a spear and standing beside a Doric column (c. 500-490 BC)
+Restoration of the polychrome decoration of the Athena statue from the Aphaea temple at Aegina, c. 490 BC (from the exposition "Bunte Götter" by the Munich Glyptothek)
+The Mourning Athena relief (c. 470-460 BC)[199][196]
+Attic red-figure kylix showing Athena slaying the Gigante Enceladus (c. 550–500 BC)
+Relief of Athena and Nike slaying the Gigante Alkyoneus (?) from the Gigantomachy Frieze on the Pergamon Altar (early second century BC)
+Classical mosaic from a villa at Tusculum, 3rd century AD, now at Museo Pio-Clementino, Vatican
+Athena portrait by Eukleidas on a tetradrachm from Syracuse,Sicily c. 400 BC
+Mythological scene with Athena (left) and Herakles (right), on a stone palette of the Greco-Buddhist art of Gandhara, India
+Atena farnese, Roman copy of a Greek original from Phidias' circle, c. 430 AD, Museo Archeologico, Naples
+Early Christian writers, such as Clement of Alexandria and Firmicus, denigrated Athena as representative of all the things that were detestable about paganism;[203] they condemned her as "immodest and immoral".[204] During the Middle Ages, however, many attributes of Athena were given to the Virgin Mary,[204] who, in fourth century portrayals, was often depicted wearing the Gorgoneion.[204] Some even viewed the Virgin Mary as a warrior maiden, much like Athena Parthenos;[204] one anecdote tells that the Virgin Mary once appeared upon the walls of Constantinople when it was under siege by the Avars, clutching a spear and urging the people to fight.[205] During the Middle Ages, Athena became widely used as a Christian symbol and allegory, and she appeared on the family crests of certain noble houses.[206]
+During the Renaissance, Athena donned the mantle of patron of the arts and human endeavor;[207] allegorical paintings involving Athena were a favorite of the Italian Renaissance painters.[207] In Sandro Botticelli's painting Pallas and the Centaur, probably painted sometime in the 1480s, Athena is the personification of chastity, who is shown grasping the forelock of a centaur, who represents lust.[208][209] Andrea Mantegna's 1502 painting Minerva Expelling the Vices from the Garden of Virtue uses Athena as the personification of Graeco-Roman learning chasing the vices of medievalism from the garden of modern scholarship.[210][209][211] Athena is also used as the personification of wisdom in Bartholomeus Spranger's 1591 painting The Triumph of Wisdom or Minerva Victorious over Ignorance.[201]
+During the sixteenth and seventeenth centuries, Athena was used as a symbol for female rulers.[212] In his book A Revelation of the True Minerva (1582), Thomas Blennerhassett portrays Queen Elizabeth I of England as a "new Minerva" and "the greatest goddesse nowe on earth".[213] A series of paintings by Peter Paul Rubens depict Athena as Marie de' Medici's patron and mentor;[214] the final painting in the series goes even further and shows Marie de' Medici with Athena's iconography, as the mortal incarnation of the goddess herself.[214] The German sculptor Jean-Pierre-Antoine Tassaert later portrayed Catherine II of Russia as Athena in a marble bust in 1774.[201] During the French Revolution, statues of pagan gods were torn down all throughout France, but statues of Athena were not.[214] Instead, Athena was transformed into the personification of freedom and the republic[214] and a statue of the goddess stood in the center of the Place de la Revolution in Paris.[214] In the years following the Revolution, artistic representations of Athena proliferated.[215]
+A statue of Athena stands directly in front of the Austrian Parliament Building in Vienna,[216] and depictions of Athena have influenced other symbols of western freedom, including the Statue of Liberty and Britannia.[216] For over a century, a full-scale replica of the Parthenon has stood in Nashville, Tennessee.[217] In 1990, the curators added a gilded forty-two-foot (12.5 m) tall replica of Phidias's Athena Parthenos, built from concrete and fiberglass.[217] The state seal of California bears the image of Athena kneeling next to a brown grizzly bear.[218] Athena has occasionally appeared on modern coins, as she did on the ancient Athenian drachma. Her head appears on the $50 1915-S Panama-Pacific commemorative coin.[219]
+Pallas and the Centaur (c. 1482) by Sandro Botticelli
+Minerva Expelling the Vices from the Garden of Virtue (1502) by Andrea Mantegna[210][209][211]
+Athena Scorning the Advances of Hephaestus (c. 1555-1560) by Paris Bordone
+Minerva Victorious over Ignorance (c. 1591) by Bartholomeus Spranger
+Maria de Medici (1622) by Peter Paul Rubens, showing her as the incarnation of Athena[214]
+Minerva Protecting Peace from Mars (1629) by Peter Paul Rubens
+Pallas Athena (c. 1655) by Rembrandt
+Minerva Revealing Ithaca to Ulysses (fifteenth century) by Giuseppe Bottani
+Minerva and the Triumph of Jupiter (1706) by René-Antoine Houasse
+The Combat of Mars and Minerva (1771) by Joseph-Benoît Suvée
+Minerva Fighting Mars (1771) by Jacques-Louis David
+Minerva of Peace mosaic in the Library of Congress
+Athena on the Great Seal of California
+One of Sigmund Freud's most treasured possessions was a small, bronze sculpture of Athena, which sat on his desk.[220] Freud once described Athena as "a woman who is unapproachable and repels all sexual desires - since she displays the terrifying genitals of the Mother."[221] Feminist views on Athena are sharply divided;[221] some feminists regard her as a symbol of female empowerment,[221] while others regard her as "the ultimate patriarchal sell out... who uses her powers to promote and advance men rather than others of her sex."[221] In contemporary Wicca, Athena is venerated as an aspect of the Goddess[222] and some Wiccans believe that she may bestow the "Owl Gift" ("the ability to write and communicate clearly") upon her worshippers.[222] Due to her status as one of the twelve Olympians, Athena is a major deity in Hellenismos,[223] a Neopagan religion which seeks to authentically revive and recreate the religion of ancient Greece in the modern world.[224]
+Athena is a natural patron of universities: At Bryn Mawr College in Pennsylvania a statue of Athena (a replica of the original bronze one in the arts and archaeology library) resides in the Great Hall.[225] It is traditional at exam time for students to leave offerings to the goddess with a note asking for good luck,[225] or to repent for accidentally breaking any of the college's numerous other traditions.[225] Pallas Athena is the tutelary goddess of the international social fraternity Phi Delta Theta.[226] Her owl is also a symbol of the fraternity.[226]

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+Ungulates (pronounced /ˈʌŋɡjəleɪts/ UNG-gyə-layts) are members of a diverse clade of primarily large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses and tapirs, and even-toed ungulates such as cattle, pigs, giraffes, camels, deer, and hippopotamuses. Cetaceans are also even-toed ungulates although they do not have hooves. Most terrestrial ungulates use the tips of their toes, usually hoofed, to sustain their whole body weight while moving.
+The term means, roughly, "being hoofed" or "hoofed animal". As a descriptive term, "ungulate" normally excludes cetaceans (whales, dolphins, porpoises), as they do not possess most of the typical morphological characteristics of ungulates, but recent discoveries indicate that they were descended from early artiodactyls.[4] Ungulates are typically herbivorous and many employ specialized gut-bacteria to allow them to digest cellulose. Some modern species, such as pigs, are omnivorous. Some prehistoric species, such as mesonychians, were carnivorous.
+Ungulata is a clade (or in some taxonomies, a grand order) of mammals. The two orders of ungulates were the Perissodactyla (odd-toed ungulates) and Artiodactyla (even-toed ungulates). Hyracoidea (hyraxes), Sirenia (sea cows) (dugongs and manatees) and Proboscidea (elephants) were in the past included in a superorder called Paenungulata which was grouped with the ungulata. These three orders were now considered a clade and grouped in the Afrotheria clade while Ungulata is now grouped under the Laurasiatheria clade.
+In 2009 morphological[5][6][7][8] and molecular[9][10] work found that aardvarks, hyraxes, sea cows, and elephants were more closely related to each other and to sengis, tenrecs, and golden moles than to the perissodactyls and artiodactyls, and form the clade Afrotheria. Elephants, sea cows, and hyraxes were grouped together in the clade Paenungulata, while the aardvark has been considered as either a close relative to them or a close relative to sengis in the clade Afroinsectiphilia.[11] This is a striking example of convergent evolution.[12]
+There is now some dispute as to whether this smaller Ungulata is a cladistic (evolution-based) group, or merely a phenetic group (form taxon) or folk taxon (similar, but not necessarily related). Some studies have indeed found the mesaxonian ungulates and paraxonian ungulates to form a monophyletic lineage,[13][14][15] closely related to either the Ferae (the carnivorans and the pangolins)[16][17] in the clade Fereuungulata or to the bats.[18] Other studies found the two orders not that closely related, as some place the perissodactyls as close relatives to bats and Ferae in Pegasoferae[19] and others place the artiodactyls as close relatives to bats.[20]
+Below is a simplified taxonomy (assuming that ungulates do indeed form a natural grouping) with the extant families, in order of the relationships. Keep in mind that there were still some grey areas of conflict, such as the case with relationship of the pecoran families and the baleen whale families. See each family for the relationships of the species as well as the controversies in their respective article.
+Below is the general consensus of the phylogeny of the ungulate families.[22][23]
+Equidae
+Tapiridae
+Rhinocerotidae
+Camelidae
+Tayassuidae
+Suidae
+Hippopotamidae
+Balaenidae
+Cetotheriidae
+Eschrichtiidae
+Balaenopteridae
+Kogiidae
+Physeteridae
+Platanistidae
+Ziphiidae
+†Lipotidae
+Pontoporiidae
+Iniidae
+Delphinidae
+Monodontidae
+Phocoenidae
+Tragulidae
+Antilocapridae
+Giraffidae
+Cervidae
+Moschidae
+Bovidae
+Perissodactyla and Artiodactyla  include the majority of large land mammals. These two groups first appeared during the late Paleocene, rapidly spreading to a wide variety of species on numerous continents, and have developed in parallel since that time. Some scientists believed that modern ungulates were descended from an evolutionary grade of mammals known as the condylarths;[24] the earliest known member of the group was the tiny Protungulatum,[25] an ungulate that co-existed with the last of non-avian dinosaurs 66 million years ago; however, many authorities do not consider it a true placental, let alone an ungulate.[26] The enigmatic dinoceratans were among the first large herbivorous mammals, although their exact relationship with other mammals is still debated with one of the theories being that they might just be distant relatives to living ungulates; the most recent study recovers them as within the true ungulate assemblage, closest to Carodnia.[3]
+In Australia, the marsupial Chaeropus also developed hooves similar to those of artiodactyls,[27] an example of convergent evolution.
+Perissodactyls were said to have evolved from the Phenacodontidae, small, sheep-sized animals that were already showing signs of anatomical features that their descendants would inherit (the reduction of digit I and V for example).[29] By the start of the Eocene, 55 million years ago (Mya), they had diversified and spread out to occupy several continents. Horses and tapirs both evolved in North America;[30] rhinoceroses appear to have developed in Asia from tapir-like animals and then colonised the Americas during the middle Eocene (about 45 Mya). Of the approximately 15 families, only three survive (McKenna and Bell, 1997; Hooker, 2005). These families were very diverse in form and size; they included the enormous brontotheres and the bizarre chalicotheres. The largest perissodactyl, an Asian rhinoceros called Paraceratherium, reached 15 tonnes (17 tons), more than twice the weight of an elephant.[31]
+It has been found in a cladistic study that the anthracobunids and the desmostylians - two lineages that have been previously classified as Afrotherians (more specifically closer to elephants) - have been classified as a clade that is closely related to the perissodactyls.[1] The desmostylians were large amphibious quadrupeds with massive limbs and a short tail.[32] They grew to 1.8 metres (6 ft) in length and were thought to have weighed more than 200 kilograms (440 lb). Their fossils were known from the northern Pacific Rim,[33] from southern Japan through Russia, the Aleutian Islands and the Pacific coast of North America to the southern tip of Baja California. Their dental and skeletal form suggests desmostylians were aquatic herbivores dependent on littoral habitats. Their name refers to their highly distinctive molars, in which each cusp was modified into hollow columns, so that a typical molar would have resembled a cluster of pipes, or in the case of worn molars, volcanoes. They were the only marine mammals to have gone extinct.
+The South American meridiungulates contain the somewhat tapir-like pyrotheres and astrapotheres, the mesaxonic litopterns and the diverse notoungulates. As a whole, meridiungulates were said to have evolved from animals like Hyopsodus.[34] For a while their relationships with other ungulates were a mystery. Some paleontologists have even challenged the monophyly of Meridiungulata by suggesting that the pyrotheres may be more closely related to other mammals, such as Embrithopoda (an African order that were related to elephants) than to other South American ungulates.[35] A recent study based on bone collagen has found that at least litopterns and the notoungulates were closely related to the perissodactyls.[2]
+The oldest known fossils assigned to Equidae date from the early Eocene, 54 million years ago. They had been assigned to the genus Hyracotherium, but the type species of that genus is now considered not a member of this family, but the other species have been split off into different genera.  These early Equidae were fox-sized animals with three toes on the hind feet, and four on the front feet. They were herbivorous browsers on relatively soft plants, and already adapted for running. The complexity of their brains suggest that they already were alert and intelligent animals.[36] Later species reduced the number of toes, and developed teeth more suited for grinding up grasses and other tough plant food.
+Rhinocerotoids diverged from other perissodactyls by the early Eocene. Fossils of Hyrachyus eximus found in North America date to this period. This small hornless ancestor resembled a tapir or small horse more than a rhino. Three families, sometimes grouped together as the superfamily Rhinocerotoidea, evolved in the late Eocene: Hyracodontidae, Amynodontidae and Rhinocerotidae, thus creating an explosion of diversity unmatched for a while until environmental changes drastically eliminated several species.
+The first tapirids, such as Heptodon, appeared in the early Eocene.[37] They appeared very similar to modern forms, but were about half the size, and lacked the proboscis. The first true tapirs appeared in the Oligocene. By the Miocene, such genera as Miotapirus were almost indistinguishable from the extant species. Asian and American tapirs were believed to have diverged around 20 to 30 million years ago; and tapirs migrated from North America to South America around 3 million years ago, as part of the Great American Interchange.[38]
+Perissodactyls were the dominant group of large terrestrial browsers right through the Oligocene. However, the rise of grasses in the Miocene (about 20 Mya) saw a major change: the artiodactyl species with their more complex stomachs were better able to adapt to a coarse, low-nutrition diet, and soon rose to prominence. Nevertheless, many perissodactyl species survived and prospered until the late Pleistocene (about 10,000 years ago) when they faced the pressure of human hunting and habitat change.
+The artiodactyls were thought to have evolved from a small group of condylarths, Arctocyonidae, which were unspecialized, superficially raccoon-like to bear-like omnivores from the Early Paleocene
+(about 65 to 60 million years ago). They had relatively short limbs lacking specializations associated with their relatives (e.g. reduced side digits, fused bones, and hooves),[39] and long, heavy tails.  Their primitive anatomy makes it unlikely that they were able to run down prey, but with their powerful proportions, claws, and long canines, they may have been able to overpower smaller animals in surprise attacks.[40] Evidently these mammals soon evolved into two separate lineages: the mesonychians and the artiodactyls.
+Mesonychians were depicted as "wolves on hooves" and were the first major mammalian predators, appearing in the Paleocene.[41]  Early mesonychids had five digits on their feet, which probably rested flat on the ground during walking (plantigrade locomotion), but later mesonychids had four digits that ended in tiny hooves on all of their toes and were increasingly well adapted to running. Like running members of the even-toed ungulates, mesonychids (Pachyaena, for example) walked on their digits (digitigrade locomotion).[41] Mesonychians fared very poorly at the close of the Eocene epoch, with only one genus, Mongolestes,[42] surviving into the Early Oligocene epoch, as the climate changed and fierce competition arose from the better adapted creodonts.
+The first artiodactyls looked like today's chevrotains or pigs: small, short-legged creatures that ate leaves and the soft parts of plants. By the Late Eocene (46 million years ago), the three modern suborders had already developed: Suina (the pig group); Tylopoda (the camel group); and Ruminantia (the goat and cattle group). Nevertheless, artiodactyls were far from dominant at that time: the perissodactyls were much more successful and far more numerous. Artiodactyls survived in niche roles, usually occupying marginal habitats, and it is presumably at that time that they developed their complex digestive systems, which allowed them to survive on lower-grade food. While most artiodactyls were taking over the niches left behind by several extinct perissodactyls, one lineage of artiodactyls began to venture out into the seas.
+The traditional theory of cetacean evolution was that cetaceans were related to the mesonychids. These animals had unusual triangular teeth very similar to those of primitive cetaceans.  This is why scientists long believed that cetaceans evolved from a form of mesonychid. Today many scientists believe cetaceans evolved from the same stock that gave rise to hippopotamuses. This hypothesized ancestral group likely split into two branches around 54 million years ago.[4] One branch would evolve into cetaceans, possibly beginning about 52 million years ago with the proto-whale Pakicetus and other early cetacean ancestors collectively known as Archaeoceti, which eventually underwent aquatic adaptation into the completely aquatic cetaceans.[43] The other branch became the anthracotheres, a large family of four-legged beasts, the earliest of whom in the late Eocene would have resembled skinny hippopotamuses with comparatively small and narrow heads. All branches of the anthracotheres, except that which evolved into Hippopotamidae, became extinct during the Pliocene without leaving any descendants.[44] The family Raoellidae is said to be the closest artiodactyl family to the cetaceans.[45][46] Consequentially, new theories in cetacean evolution hypothesize that whales and their ancestors escaped predation, not competition, by slowly adapting to the ocean.[47][48][49]
+Ungulates were in high diversity in response to sexual selection and ecological events; the majority of ungulates lack a collar bone.[50] Terrestrial ungulates were for the most part herbivores, with some of them being grazers. However, there were exceptions to this as pigs, peccaries, hippos and duikers were known to have an omnivorous diet. Some cetaceans were the only modern ungulates that were carnivores; baleen whales consume significantly smaller animals in relation to their body size, such as small species of fish and krill; toothed whales, depending on the species, can consume a wide range of species: squid, fish, sharks, and other species of mammals such as seals and other whales. In terms of ecosystem ungulates have colonized all corners of the planet, from mountains to the ocean depths; grasslands to deserts and some have been domesticated by humans.
+Ungulates have developed specialized adaptations, especially in the areas of cranial appendages, dentition, and leg morphology including the modification of the astragalus (one of the ankle bones at the end of the lower leg) with a short, robust head.
+The hoof is the tip of a toe of an ungulate mammal, strengthened by a thick horny (keratin) covering. The hoof consists of a hard or rubbery sole, and a hard wall formed by a thick nail rolled around the tip of the toe. The weight of the animal is normally borne by both the sole and the edge of the hoof wall. Hooves grow continuously, and were constantly worn down by use. In most modern ungulates, the radius and ulna were fused along the length of the forelimb; early ungulates, such as the arctocyonids, did not share this unique skeletal structure.[51] The fusion of the radius and ulna prevents an ungulate from rotating its forelimb. Since this skeletal structure has no specific function in ungulates, it is considered a homologous characteristic that ungulates share with other mammals. This trait would have been passed down from a common ancestor. While the two orders of ungulates colloquial names were based on the number of toes of their members ("odd-toed" for the perissodactyls and "even-toed" for the terrestrial artiodactyls), it is not an accurate reason they were grouped. Tapirs have four toes in the front, yet they were members of the "odd-toed" order; peccaries and modern cetaceans were members of the "even-toed" order, yet peccaries have three toes in the front and whales were an extreme example as they have flippers instead of hooves. Scientists had classified them according to the distribution of their weight to their toes.
+Perissodactyls have a mesaxonic foot meaning that the weight is distributed on the third toe on all legs thanks to the plane symmetry of their feet. There has been reduction of toes from the common ancestor, with the classic example being horses with their single hooves. In consequence, there was an alternative name for the perissodactyls the nearly obsolete Mesaxonia. Perissodactyls were not the only lineage of mammals to have evolved this trait; the meridiungulates have evolved mesaxonic feet numerous times.
+Terrestrial artiodactyls have a paraxonic foot meaning that the weight is distributed on the third and the fourth toe on all legs. The majority of these mammals have cloven hooves, with two smaller ones known as the dewclaws that were located further up on the leg. The earliest cetaceans (the archaeocetes), also have this characteristic in the addition of also having both an astragalus and cuboid bone in the ankle, which were further diagnostic traits of artiodactyls.[52]
+In modern cetaceans, the front limbs have become pectoral fins and the hind parts were internal and reduced. Occasionally, the genes that code for longer extremities cause a modern cetacean to develop miniature legs (known as atavism). The main method of moving is an up-and-down motion with the tail fin, called the fluke, which is used for propulsion, while the pectoral fins together with the entire tail section provide directional control. All modern cetaceans still retain their digits despite the external appearance suggesting otherwise.
+Most ungulates have developed reduced canine teeth and specialized molars, including bunodont (low, rounded cusps) and hypsodont (high crowned) teeth. The development of hypsodonty has been of particular interest as this adaptation was strongly associated with the spread of grasslands during the Miocene about 25 million years. As forest biomes declined, grasslands spread, opening new niches for mammals. Many ungulates switched from browsing diets to grazing diets, and possibly driven by abrasive silica in grass, hypsodonty became common. However, recent evidence ties the evolution of hypsodonty to open, gritty habitats and not the grass itself. This is termed the Grit, not grass hypothesis.[53]
+Some ungulates completely lack upper incisors and instead have a dental pad to assist in browsing.[54][55] It can be found in camels, ruminants, and some toothed whales; modern baleen whales were remarkable in that they have baleen instead to filter out the krill from the water. On the other spectrum teeth have been evolved as weapons or sexual display seen in pigs and peccaries, some species of deer, musk deer, hippopotamuses, beaked whales and the Narwhal, with its long canine tooth.[56]
+Ungulates evolved a variety of cranial appendages that today can be found in cervoids (with the exception of musk deer). In oxen and antelope, the size and shape of the horns vary greatly, but the basic structure is always a pair of simple bony protrusions without branches, often having a spiral, twisted or fluted form, each covered in a permanent sheath of keratin. The unique horn structure is the only unambiguous morphological feature of bovids that distinguishes them from other pecorans.[57][58] Male horn development has been linked to sexual selection,[59][60] while the presence of horns in females is likely due to natural selection.[59][61] The horns of females were usually smaller than those of males, and were sometimes of a different shape. The horns of female bovids were thought to have evolved for defense against predators or to express territoriality, as nonterritorial females, which were able to use crypsis for predator defense, often do not have horns.[61]
+Rhinoceros horns, unlike those of other horned mammals, only consist of keratin. The horns rest on the nasal ridge of the animals skull.
+Antlers were unique to cervids and found mostly on males: only caribou and reindeer have antlers on the females, and these were normally smaller than those of the males. Nevertheless, fertile does from other species of deer have the capacity to produce antlers on occasion, usually due to increased testosterone levels.[62] Each antler grows from an attachment point on the skull called a pedicle. While an antler is growing, it is covered with highly vascular skin called velvet, which supplies oxygen and nutrients to the growing bone.[63]  Antlers were considered one of the most exaggerated cases of male secondary sexual traits in the animal kingdom,[64] and grow faster than any other mammal bone.[65]  Growth occurs at the tip, and is initially cartilage, which is mineralized to become bone. Once the antler has achieved its full size, the velvet is lost and the antler's bone dies. This dead bone structure is the mature antler.  In most cases, the bone at the base is destroyed by osteoclasts and the antlers fall off at some point.[63] As a result of their fast growth rate, antlers were considered a handicap since there is an incredible nutritional demand on deer to re-grow antlers annually, and thus can be honest signals of metabolic efficiency and food gathering capability.[66]
+Ossicones were horn-like (or antler-like) protuberances that can be found on the heads of giraffes and male okapis today. They were similar to the horns of antelopes and cattle, save that they were derived from ossified cartilage,[67] and that the ossicones remain covered in skin and fur, rather than horn.  Antlers (such as on deer) were derived from bone tissue: when mature, the skin and fur covering of the antlers, termed "velvet", is sloughed and scraped off to expose the bone of the antlers.
+Pronghorn were unique when compared to their relatives. Each "horn" of the pronghorn is composed of a slender, laterally flattened blade of bone that grows from the frontal bones of the skull, forming a permanent core. As in the Giraffidae, skin covers the bony cores, but in the pronghorn it develops into a keratinous sheath which is shed and regrown on an annual basis. Unlike the horns of the family Bovidae, the horn sheaths of the pronghorn were branched, each sheath possessing a forward-pointing tine (hence the name pronghorn). The horns of males were well developed.
+Many of the world's ungulate species exist only in relatively small populations in which some degree of inbreeding inevitably occurs.  A study of 16 species of captive ungulates revealed that juvenile survival of inbred young is generally lower than that of non-inbred young.[68]  (Also see Inbreeding depression).  These findings have implications for the genetic management of small ungulate populations.

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+A dream is a succession of images, ideas, emotions, and sensations that usually occur involuntarily in the mind during certain stages of sleep.[1] The content and purpose of dreams are not fully understood, although they have been a topic of scientific, philosophical and religious interest throughout recorded history. Dream interpretation is the attempt at drawing meaning from dreams and searching for an underlying message. The scientific study of dreams is called oneirology.[2]
+Dreams mainly occur in the rapid-eye movement (REM) stage of sleep—when brain activity is high and resembles that of being awake. REM sleep is revealed by continuous movements of the eyes during sleep. At times, dreams may occur during other stages of sleep. However, these dreams tend to be much less vivid or memorable.[3] The length of a dream can vary; they may last for a few seconds, or approximately 20–30 minutes.[3] People are more likely to remember the dream if they are awakened during the REM phase. The average person has three to five dreams per night, and some may have up to seven;[4] however, most dreams are immediately or quickly forgotten.[5] Dreams tend to last longer as the night progresses. During a full eight-hour night sleep, most dreams occur in the typical two hours of REM.[6] Dreams related to waking-life experiences are associated with REM theta activity, which suggests that emotional memory processing takes place in REM sleep.[7]
+Opinions about the meaning of dreams have varied and shifted through time and culture. Many endorse the Freudian theory of dreams – that dreams reveal insight into hidden desires and emotions.[qualify evidence] Other prominent theories include those suggesting that dreams assist in memory formation, problem solving, or simply are a product of random brain activation.[8]
+Sigmund Freud, who developed the psychological discipline of psychoanalysis, wrote extensively about dream theories and their interpretations in the early 1900s.[9] He explained dreams as manifestations of one's deepest desires and anxieties, often relating to repressed childhood memories or obsessions. Furthermore, he believed that virtually every dream topic, regardless of its content, represented the release of sexual tension.[10] In The Interpretation of Dreams (1899), Freud developed a psychological technique to interpret dreams and devised a series of guidelines to understand the symbols and motifs that appear in our dreams. In modern times, dreams have been seen as a connection to the unconscious mind. They range from normal and ordinary to overly surreal and bizarre. Dreams can have varying natures, such as being frightening, exciting, magical, melancholic, adventurous, or sexual. The events in dreams are generally outside the control of the dreamer, with the exception of lucid dreaming, where the dreamer is self-aware.[11] Dreams can at times make a creative thought occur to the person or give a sense of inspiration.[12]
+The Dreaming is a common term within the animist creation narrative of indigenous Australians for a personal, or group, creation and for what may be understood as the "timeless time" of formative creation and perpetual creating.[13]
+The ancient Sumerians in Mesopotamia have left evidence of dream interpretation dating back to at least 3100 BC.[14][15] Throughout Mesopotamian history, dreams were always held to be extremely important for divination[15][16] and Mesopotamian kings paid close attention to them.[15][14] Gudea, the king of the Sumerian city-state of Lagash (reigned c. 2144–2124 BC), rebuilt the temple of Ningirsu as the result of a dream in which he was told to do so.[15] The standard Akkadian Epic of Gilgamesh contains numerous accounts of the prophetic power of dreams.[15] First, Gilgamesh himself has two dreams foretelling the arrival of Enkidu.[15] Later, Enkidu dreams about the heroes' encounter with the giant Humbaba.[15] Dreams were also sometimes seen as a means of seeing into other worlds[15] and it was thought that the soul, or some part of it, moved out of the body of the sleeping person and actually visited the places and persons the dreamer saw in his or her sleep.[17] In Tablet VII of the epic, Enkidu recounts to Gilgamesh a dream in which he saw the gods Anu, Enlil, and Shamash condemn him to death.[15] He also has a dream in which he visits the Underworld.[15]
+The Assyrian king Ashurnasirpal II (reigned 883–859 BC) built a temple to Mamu, possibly the god of dreams, at Imgur-Enlil, near Kalhu.[15] The later Assyrian king Ashurbanipal (reigned 668–c. 627 BC) had a dream during a desperate military situation in which his divine patron, the goddess Ishtar, appeared to him and promised that she would lead him to victory.[15] The Babylonians and Assyrians divided dreams into "good," which were sent by the gods, and "bad," sent by demons.[16] A surviving collection of dream omens entitled Iškar Zaqīqu records various dream scenarios as well as prognostications of what will happen to the person who experiences each dream, apparently based on previous cases.[15][18] Some list different possible outcomes, based on occasions in which people experienced similar dreams with different results.[15] Dream scenarios mentioned include a variety of daily work events, journeys to different locations, family matters, sex acts, and encounters with human individuals, animals, and deities.[15]
+In ancient Egypt, as far back as 2000 BC, the Egyptians wrote down their dreams on papyrus. People with vivid and significant dreams were thought to be blessed and were considered special.[19] Ancient Egyptians believed that dreams were like oracles, bringing messages from the gods. They thought that the best way to receive divine revelation was through dreaming and thus they would induce (or "incubate") dreams. Egyptians would go to sanctuaries and sleep on special "dream beds" in hope of receiving advice, comfort, or healing from the gods.[20]
+In Chinese history, people wrote of two vital aspects of the soul of which one is freed from the body during slumber to journey in a dream realm, while the other remained in the body,[21] although this belief and dream interpretation had been questioned since early times, such as by the philosopher Wang Chong (27–97 AD).[21] The Indian text Upanishads, written between 900 and 500 BC, emphasizes two meanings of dreams. The first says that dreams are merely expressions of inner desires. The second is the belief of the soul leaving the body and being guided until awakened.
+The Greeks shared their beliefs with the Egyptians on how to interpret good and bad dreams, and the idea of incubating dreams. Morpheus, the Greek god of dreams, also sent warnings and prophecies to those who slept at shrines and temples. The earliest Greek beliefs about dreams were that their gods physically visited the dreamers, where they entered through a keyhole, exiting the same way after the divine message was given.
+Antiphon wrote the first known Greek book on dreams in the 5th century BC. In that century, other cultures influenced Greeks to develop the belief that souls left the sleeping body.[22] Hippocrates (469–399 BC) had a simple dream theory: during the day, the soul receives images; during the night, it produces images. Greek philosopher Aristotle (384–322 BC) believed dreams caused physiological activity. He thought dreams could analyze illness and predict diseases. Marcus Tullius Cicero, for his part, believed that all dreams are produced by thoughts and conversations a dreamer had during the preceding days.[23] Cicero's Somnium Scipionis described a lengthy dream vision, which in turn was commented on by Macrobius in his Commentarii in Somnium Scipionis.
+Herodotus in his The Histories, writes "The visions that occur to us in dreams are, more often than not, the things we have been concerned about during the day."[24]
+In Welsh history, The Dream of Rhonabwy (Welsh: Breuddwyd Rhonabwy) is a Middle Welsh prose tale. Set during the reign of Madog ap Maredudd, prince of Powys (died 1160), it is dated to the late 12th or 13th century. It survives in only one manuscript, the Red Book of Hergest, and has been associated with the Mabinogion since its publication by Lady Charlotte Guest in the 19th century. The bulk of the narrative describes a dream vision experienced by its central character, Rhonabwy, a retainer of Madog, in which he visits the time of King Arthur.[25]
+Also in Welsh history, the tale 'The Dream of Macsen Wledig' is a romanticised story about the Roman emperor Magnus Maximus, called Macsen Wledig in Welsh. Born in Hispania, he became a legionary commander in Britain, assembled a Celtic army and assumed the title of Emperor of the Western Roman Empire in 383. He was defeated in battle in 385 and beheaded at the direction of the Eastern Roman emperor.[26]
+In Judaism, dreams are considered part of the experience of the world that can be interpreted and from which lessons can be garnered. It is discussed in the Talmud, Tractate Berachot 55–60.
+The ancient Hebrews connected their dreams heavily with their religion, though the Hebrews were monotheistic and believed that dreams were the voice of one God alone. Hebrews also differentiated between good dreams (from God) and bad dreams (from evil spirits). The Hebrews, like many other ancient cultures, incubated dreams in order to receive a divine revelation. For example, the Hebrew prophet Samuel would "lie down and sleep in the temple at Shiloh before the Ark and receive the word of the Lord." Most of the dreams in the Bible are in the Book of Genesis.[27]
+Christians mostly shared the beliefs of the Hebrews and thought that dreams were of a supernatural character because the Old Testament includes frequent stories of dreams with divine inspiration. The most famous of these dream stories was Jacob's dream of a ladder that stretches from Earth to Heaven. Many Christians preach that God can speak to people through their dreams. The famous glossary, the Somniale Danielis, written in the name of Daniel, attempted to teach Christian populations to interpret their dreams.
+Iain R. Edgar has researched the role of dreams in Islam.[28] He has argued that dreams play an important role in the history of Islam and the lives of Muslims, since dream interpretation is the only way that Muslims can receive revelations from God since the death of the last prophet, Muhammad.[29]
+In the Mandukya Upanishad, part of the Veda scriptures of Indian Hinduism, a dream is one of three states that the soul experiences during its lifetime, the other two states being the waking state and the sleep state.[30]
+In Buddhism, ideas about dreams are similar to the classical and folk traditions in South Asia. The same dream is sometimes experienced by multiple people, as in the case of the Buddha-to-be, before he is leaving his home. It is described in the Mahāvastu that several of the Buddha's relatives had premonitory dreams preceding this. Some dreams are also seen to transcend time: the Buddha-to-be has certain dreams that are the same as those of previous Buddhas, the Lalitavistara states. In Buddhist literature, dreams often function as a "signpost" motif to mark certain stages in the life of the main character.[31]
+Buddhist views about dreams are expressed in the Pāli Commentaries and the Milinda Pañhā.[31]
+Some philosophers have concluded that what we think of as the "real world" could be or is an illusion (an idea known as the skeptical hypothesis about ontology).
+The first recorded mention of the idea was by Zhuangzi, and it is also discussed in Hinduism, which makes extensive use of the argument in its writings.[32] It was formally introduced to Western philosophy by Descartes in the 17th century in his Meditations on First Philosophy. Stimulus, usually an auditory one, becomes a part of a dream, eventually then awakening the dreamer.
+Some Indigenous American tribes and Mexican civilizations believe that dreams are a way of visiting and having contact with their ancestors.[33] Some Native American tribes used vision quests as a rite of passage, fasting and praying until an anticipated guiding dream was received, to be shared with the rest of the tribe upon their return.[34][35]
+The Middle Ages brought a harsh interpretation of dreams.[citation needed] They were seen as evil, and the images as temptations from the devil. Many believed that during sleep, the devil could fill the human mind with corrupting and harmful thoughts. Martin Luther, the Protestant Reformer, believed dreams were the work of the Devil. However, Catholics such as St. Augustine and St. Jerome claimed that the direction of their lives was heavily influenced by their dreams.[citation needed]
+The depiction of dreams in Renaissance and Baroque art is often related to Biblical narrative. Examples are Joachim's Dream (1304–1306) from the Scrovegni Chapel fresco cycle by Giotto, and Jacob's Dream (1639) by Jusepe de Ribera. Dreams and dark imaginings are the theme of several notable works of the Romantic era, such as Goya's etching The Sleep of Reason Produces Monsters (c. 1799) and Henry Fuseli's painting The Nightmare (1781). Salvador Dalí's Dream Caused by the Flight of a Bee around a Pomegranate a Second Before Awakening (1944) also investigates this theme through absurd juxtapositions of a nude lady, tigers leaping out of a pomegranate, and a spiderlike elephant walking in the background. Henri Rousseau's last painting was The Dream. Le Rêve ("The Dream") is a 1932 painting by Pablo Picasso.
+Dream frames were frequently used in medieval allegory to justify the narrative; The Book of the Duchess[36] and The Vision Concerning Piers Plowman[37] are two such dream visions. Even before them, in antiquity, the same device had been used by Cicero and Lucian of Samosata.
+They have also featured in fantasy and speculative fiction since the 19th century. One of the best-known dream worlds is Wonderland from Lewis Carroll's Alice's Adventures in Wonderland, as well as Looking-Glass Land from its sequel, Through the Looking-Glass. Unlike many dream worlds, Carroll's logic is like that of actual dreams, with transitions and flexible causality.
+Other fictional dream worlds include the Dreamlands of H.P. Lovecraft's Dream Cycle[38] and The Neverending Story's[39] world of Fantasia, which includes places like the Desert of Lost Dreams, the Sea of Possibilities and the Swamps of Sadness. Dreamworlds, shared hallucinations and other alternate realities feature in a number of works by Philip K. Dick, such as The Three Stigmata of Palmer Eldritch and Ubik. Similar themes were explored by Jorge Luis Borges, for instance in The Circular Ruins.
+Modern popular culture often conceives of dreams, like Freud, as expressions of the dreamer's deepest fears and desires.[40] The film version of The Wizard of Oz (1939) depicts a full-color dream that causes Dorothy to perceive her black-and-white reality and those with whom she shares it in a new way. In films such as Spellbound (1945), The Manchurian Candidate (1962), and Inception (2010), the protagonists must extract vital clues from surreal dreams.[41]
+Most dreams in popular culture are, however, not symbolic, but straightforward and realistic depictions of their dreamer's fears and desires.[41] Dream scenes may be indistinguishable from those set in the dreamer's real world, a narrative device that undermines the dreamer's and the audience's sense of security[41] and allows horror film protagonists, such as those of Carrie (1976), Friday the 13th (1980) or An American Werewolf in London (1981) to be suddenly attacked by dark forces while resting in seemingly safe places.[41]
+In speculative fiction, the line between dreams and reality may be blurred even more in the service of the story.[41] Dreams may be psychically invaded or manipulated (Dreamscape, 1984; the Nightmare on Elm Street films, 1984–2010; Inception, 2010) or even come literally true (as in The Lathe of Heaven, 1971). In Ursula K. Le Guin's book, The Lathe of Heaven (1971), the protagonist finds that his "effective" dreams can retroactively change reality. Peter Weir's 1977 Australian film The Last Wave makes a simple and straightforward postulate about the premonitory nature of dreams (from one of his Aboriginal characters) that "... dreams are the shadow of something real". In Kyell Gold's novel Green Fairy from the Dangerous Spirits series, the protagonist, Sol, experiences the memories of a dancer who died 100 years before through Absinthe induced dreams and after each dream something from it materializes into his reality. Such stories play to audiences' experiences with their own dreams, which feel as real to them.[41]
+Distinct types of dreams have been identified for REM and non-REM sleep stages. The vivid bizarre dreams that are commonly remembered upon waking up are primarily associated with REM sleep. Deep (stage 3 and 4) slow-wave sleep (NREM sleep) is commonly associated with more static, thoughtful dreams.[42] These dreams are primarily driven by the hippocampus in the process of long-term memory consolidation and predominantly include memories of events “as they happened” without the random novel combination of objects seen in REM sleep dreams. The rest of the article focuses on REM sleep dreaming, thereafter simply referred as dreaming.
+Since waking up usually happens during rapid eye movement sleep (REM), the vivid bizarre REM sleep dreams are the most common type of dreams that is remembered. (During REM sleep an electroencephalogram (EEG) shows brain activity that, among sleep states, is most like wakefulness.) During a typical lifespan, a person spends a total of about six years dreaming[43] (which is about two hours each night).[44] Most dreams only last 5 to 20 minutes.[43] It is unknown where in the brain dreams originate, if there is a single origin for dreams or if multiple portions of the brain are involved, or what the purpose of dreaming is for the body or mind.
+During REM sleep, the release of the neurotransmitters norepinephrine, serotonin and histamine is completely suppressed.[3][45][46]
+During most dreams, the person dreaming is not aware that they are dreaming, no matter how absurd or eccentric the dream is. The reason for this may be that the prefrontal cortex, the region of the brain responsible for logic and planning, exhibits decreased activity during dreams. This allows the dreamer to more actively interact with the dream without thinking about what might happen, since things that would normally stand out in reality blend in with the dream scenery.[47]
+When REM sleep episodes were timed for their duration and subjects were awakened to make reports before major editing or forgetting of their dreams could take place, subjects accurately reported the length of time they had been dreaming in an REM sleep state. Some researchers have speculated that "time dilation" effects only seem to be taking place upon reflection and do not truly occur within dreams.[48] This close correlation of REM sleep and dream experience was the basis of the first series of reports describing the nature of dreaming: that it is a regular nightly rather than occasional phenomenon, and is correlated with high-frequency activity within each sleep period occurring at predictable intervals of approximately every 60–90 minutes in all humans throughout the lifespan.
+REM sleep episodes and the dreams that accompany them lengthen progressively through the night, with the first episode being the shortest, of approximately 10–12 minutes duration, and the second and third episodes increasing to 15–20 minutes. Dreams at the end of the night may last as long as 15 minutes, although these may be experienced as several distinct episodes due to momentary arousals interrupting sleep as the night ends. Dream reports can be reported from normal subjects 50% of the time when they are awakened prior to the end of the first REM period. This rate of retrieval is increased to about 99% when awakenings are made from the last REM period of the night. The increase in the ability to recall dreams appears related to intensification across the night in the vividness of dream imagery, colors, and emotions.[49]
+One of the central questions of sleep research is what part of the brain is driving dreams' video-auditory experience. During waking, most of the mind's internal imagery is controlled from the front of the brain by the lateral prefrontal cortex (LPFC). Reasoning, planning, and strategizing are the results of the constructive imagination conducted by the LPFC, which acts like a puppeteer assembling objects stored in memory into novel combinations. During REM sleep, however the LPFC is inactive.[50][51] Furthermore, in people whose LPFC is damaged, dreams do not change at all, confirming that LPFC does not control dreaming.[52]
+During deep slow-wave sleep, imagery is primarily driven by the hippocampus in the process of long-term memory consolidation and predominantly includes memories of events “as they happened” without the random novel combination of objects seen in REM sleep dreams. During REM sleep, however, the communication between the neocortex and the hippocampus is disrupted by a high ACh level.[53]
+Without being driven by the LPFC (as in waking) and hippocampus (as in slow-wave sleep), it is unclear how exactly images appear in one's perception during REM sleep. A common explanation is that neuronal ensembles in the posterior cortical hot zone, primed by previous activity or current sensory or subcortical stimulation, activate spontaneously, triggered by the ponto-geniculo-occipital (PGO) waves that characterize REM sleep.[54] In the words of Hobson & McCarley, the neocortex is making “the best of a bad job in producing even partially coherent dream imagery from the relatively noisy signals sent up from the brain stem.”[55]
+It is also commonly accepted that the intensity of dreams during REM sleep can be dialed up or down by the dopaminergic cells of the ventral tegmental area. For example, drugs that block dopaminergic activity (e.g., haloperidol) inhibit unusually frequent and vivid dreaming, while the increase of dopamine (e.g., through l-dopa) stimulates excessive vivid dreaming and nightmares.[55]
+REM sleep and the ability to dream seem to be embedded in the biology of many animals in addition to humans. Scientific research suggests that all mammals experience REM.[58] The range of REM can be seen across species: dolphins experience minimal REM, while humans are in the middle of the scale and the armadillo and the opossum (a marsupial) are among the most prolific dreamers, judging from their REM patterns.[59]
+Studies have observed signs of dreaming in all mammals studied, including monkeys, dogs, cats, rats, elephants, and shrews. There have also been signs of dreaming in birds and reptiles.[60] Sleeping and dreaming are intertwined. Scientific research results regarding the function of dreaming in animals remain disputable; however, the function of sleeping in living organisms is increasingly clear. For example, sleep deprivation experiments conducted on rats and other animals have resulted in the deterioration of physiological functioning and actual tissue damage.[61]
+Some scientists argue that humans dream for the same reason other amniotes do. From a Darwinian perspective dreams would have to fulfill some kind of biological requirement, provide some benefit for natural selection to take place, or at least have no negative impact on fitness. In 2000 Antti Revonsuo, a professor at the University of Turku in Finland, claimed that centuries ago dreams would prepare humans for recognizing and avoiding danger by presenting a simulation of threatening events. The theory has therefore been called the threat-simulation theory.[62] According to Tsoukalas (2012) dreaming is related to the reactive patterns elicited by encounters with predators, a fact that is still evident in the control mechanisms of REM sleep (see below).[63][64]
+Many hypotheses have been proposed as to what function dreams perform, some of which have been contradicted by later empirical studies. It has also been proposed that dreams serve no particular purpose, and that they are simply a byproduct of biochemical processes that only occur in the brain during sleep.
+In the late 19th century, psychotherapist Sigmund Freud developed a theory (since discredited) that the content of dreams is driven by unconscious wish fulfillment. Freud called dreams the "royal road to the unconscious."[65] He theorized that the content of dreams reflects the dreamer's unconscious mind and specifically that dream content is shaped by unconscious wish fulfillment. He argued that important unconscious desires often relate to early childhood memories and experiences. Freud's theory describes dreams as having both manifest and latent content. Latent content relates to deep unconscious wishes or fantasies while manifest content is superficial and meaningless.[66] Manifest content often masks or obscures latent content.[67]
+In his early work, Freud argued that the vast majority of latent dream content is sexual in nature, but he later moved away from this categorical position. In Beyond the Pleasure Principle he considered how trauma or aggression could influence dream content. He also discussed supernatural origins in Dreams and Occultism, a lecture published in New Introductory Lectures on Psychoanalysis.[68]
+Late in life Freud acknowledged that "It is impossible to classify as wish fulfillments" the repetitive nightmares associated with posttraumatic stress disorder. Modern experimental studies weigh against many of Freud's theories regarding dreams. Freud's "dream-work" interpretation strategies have not been found to have empirical validity. His theory that dreams were the "guardians" of sleep, repressing and disguising bodily urges to ensure sleep continues, seems unlikely given studies of individuals who can sleep without dreaming. His assertions that repressed memory in infants re-surface decades later in adult dreams conflicts with modern research on memory. Freud's theory has difficulty explaining why young children have static and bland dreams, or why the emotions in most dreams are negative. On the plus side, modern researchers agree with Freud that dreams do have coherence, and that dream content connects to other psychological variables and often connect to recent waking thoughts (though not as often as Freud supposed).[69] Despite the lack of scientific evidence, dream interpretation services based on Freudian or other systems remain popular.[70]
+Carl Jung rejected many of Freud's theories. Jung expanded on Freud's idea that dream content relates to the dreamer's unconscious desires. He described dreams as messages to the dreamer and argued that dreamers should pay attention for their own good. He came to believe that dreams present the dreamer with revelations that can uncover and help to resolve emotional or religious problems and fears.[71]
+Jung wrote that recurring dreams show up repeatedly to demand attention, suggesting that the dreamer is neglecting an issue related to the dream. He called this "compensation." The dream balances the conscious belief and attitudes with an alternative. Jung did not believe that the conscious attitude was wrong and that the dream provided the true belief. He argued that good work with dreams takes both into account and comes up with a balanced viewpoint. He believed that many of the symbols or images from these dreams return with each dream. Jung believed that memories formed throughout the day also play a role in dreaming. These memories leave impressions for the unconscious to deal with when the ego is at rest. The unconscious mind re-enacts these glimpses of the past in the form of a dream. Jung called this a day residue.[72] Jung also argued that dreaming is not a purely individual concern, that all dreams are part of "one great web of psychological factors."
+Fritz Perls presented his theory of dreams as part of the holistic nature of Gestalt therapy. Dreams are seen as projections of parts of the self that have been ignored, rejected, or suppressed.[73] Jung argued that one could consider every person in the dream to represent an aspect of the dreamer, which he called the subjective approach to dreams. Perls expanded this point of view to say that even inanimate objects in the dream may represent aspects of the dreamer. The dreamer may, therefore, be asked to imagine being an object in the dream and to describe it, in order to bring into awareness the characteristics of the object that correspond with the dreamer's personality.
+In 1976 J. Allan Hobson and Robert McCarley proposed a new theory that changed dream research, challenging the previously held Freudian view of dreams as unconscious wishes to be interpreted. They assume that the same structures that induce REM sleep also generate sensory information. Hobson's 1976 research suggested that the signals interpreted as dreams originate in the brainstem during REM sleep. According to Hobson and other researchers, circuits in the brainstem are activated during REM sleep. Once these circuits are activated, areas of the limbic system involved in emotions, sensations, and memories, including the amygdala and hippocampus, become active. The brain synthesizes and interprets these activities; for example, changes in the physical environment such as temperature and humidity, or physical stimuli such as ejaculation, and attempts to create meaning from these signals, result in dreaming.
+However, research by Mark Solms suggests that dreams are generated in the forebrain, and that REM sleep and dreaming are not directly related.[74] While working in the neurosurgery department at hospitals in Johannesburg and London, Solms had access to patients with various brain injuries. He began to question patients about their dreams and confirmed that patients with damage to the parietal lobe stopped dreaming; this finding was in line with Hobson's 1977 theory. However, Solms did not encounter cases of loss of dreaming with patients having brainstem damage. This observation forced him to question Hobson's prevailing theory, which marked the brainstem as the source of the signals interpreted as dreams.
+Combining Hobson's activation synthesis hypothesis with Solms' findings, the continual-activation theory of dreaming presented by Jie Zhang proposes that dreaming is a result of brain activation and synthesis; at the same time, dreaming and REM sleep are controlled by different brain mechanisms. Zhang hypothesizes that the function of sleep is to process, encode, and transfer the data from the temporary memory store to the long-term memory store. During NREM sleep the conscious-related memory (declarative memory) is processed, and during REM sleep the unconscious-related memory (procedural memory) is processed.[75]
+Zhang assumes that during REM sleep the unconscious part of a brain is busy processing the procedural memory; meanwhile, the level of activation in the conscious part of the brain descends to a very low level as the inputs from the sensory systems are basically disconnected. This triggers the "continual-activation" mechanism to generate a data stream from the memory stores to flow through the conscious part of the brain. Zhang suggests that this pulsatile brain activation is the inducer of each dream. He proposes that, with the involvement of the brain associative thinking system, dreaming is, thereafter, self-maintained with the dreamer's own thinking until the next pulse of memory insertion. This explains why dreams have both characteristics of continuity (within a dream) and sudden changes (between two dreams).[75][76] A detailed explanation of how a dream is synthesized is given in a later paper.[77]
+According to Tsoukalas (2012) REM sleep is an evolutionary transformation of a well-known defensive mechanism, the tonic immobility reflex. This reflex, also known as animal hypnosis or death feigning, functions as the last line of defense against an attacking predator and consists of the total immobilization of the animal: the animal appears dead (cf. "playing possum"). Tsoukalas claims that the neurophysiology and phenomenology of this reaction shows striking similarities to REM sleep, a fact that suggests a deep evolutionary kinship. For example, both reactions exhibit brainstem control, paralysis, hippocampal theta and thermoregulatory changes. Tsoukalas claims that this theory integrates many earlier findings into a unified framework.[63][64]
+Eugen Tarnow suggests that dreams are ever-present excitations of long-term memory, even during waking life. The strangeness of dreams is due to the format of long-term memory, reminiscent of Penfield & Rasmussen's findings that electrical excitations of the cortex give rise to experiences similar to dreams. During waking life an executive function interprets long-term memory consistent with reality checking. Tarnow's theory is a reworking of Freud's theory of dreams in which Freud's unconscious is replaced with the long-term memory system and Freud's "Dream Work" describes the structure of long-term memory.[78]
+A 2001 study showed evidence that illogical locations, characters, and dream flow may help the brain strengthen the linking and consolidation of semantic memories.[79] These conditions may occur because, during REM sleep, the flow of information between the hippocampus and neocortex is reduced.[80]
+Increasing levels of the stress hormone cortisol late in sleep (often during REM sleep) causes this decreased communication. One stage of memory consolidation is the linking of distant but related memories. Payne and Nadal hypothesize these memories are then consolidated into a smooth narrative, similar to a process that happens when memories are created under stress.[81]
+Robert (1886),[82] a physician from Hamburg, was the first who suggested that dreams are a need and that they have the function to erase (a) sensory impressions that were not fully worked up, and (b) ideas that were not fully developed during the day. By the dream work, incomplete material is either removed (suppressed) or deepened and included into memory. Robert's ideas were cited repeatedly by Freud in his Die Traumdeutung. Hughlings Jackson (1911) viewed that sleep serves to sweep away unnecessary memories and connections from the day.
+This was revised in 1983 by Crick and Mitchison's "reverse learning" theory, which states that dreams are like the cleaning-up operations of computers when they are offline, removing (suppressing) parasitic nodes and other "junk" from the mind during sleep.[83][84] However, the opposite view that dreaming has an information handling, memory-consolidating function (Hennevin and Leconte, 1971) is also common.
+Coutts[85] describes[qualify evidence] dreams as playing a central role in a two-phase sleep process that improves the mind's ability to meet human needs during wakefulness. During the accommodation phase, mental schemas self-modify by incorporating dream themes. During the emotional selection phase, dreams test prior schema accommodations. Those that appear adaptive are retained, while those that appear maladaptive are culled. The cycle maps to the sleep cycle, repeating several times during a typical night's sleep. Alfred Adler suggested that dreams are often emotional preparations for solving problems, intoxicating an individual away from common sense toward private logic. The residual dream feelings may either reinforce or inhibit contemplated action.
+Numerous theories state that dreaming is a random by-product of REM sleep physiology and that it does not serve any natural purpose.[86] Flanagan claims that "dreams are evolutionary epiphenomena" and they have no adaptive function. "Dreaming came along as a free ride on a system designed to think and to sleep."[87]
+J.A. Hobson, for different reasons, also considers dreams epiphenomena. He believes that the substance of dreams have no significant influence on waking actions, and most people go about their daily lives perfectly well without remembering their dreams.[88] Hobson proposed the activation-synthesis theory, which states that "there is a randomness of dream imagery and the randomness synthesizes dream-generated images to fit the patterns of internally generated stimulations".[89] This theory is based on the physiology of REM sleep, and Hobson believes dreams are the outcome of the forebrain reacting to random activity beginning at the brainstem. The activation-synthesis theory hypothesizes that the peculiar nature of dreams is attributed to certain parts of the brain trying to piece together a story out of what is essentially bizarre information.[90] In 2005, Hobson published a book, Thirteen Dreams that Freud Never Had,[91] in which he analyzed his own dreams after having a stroke in 2001.
+Some evolutionary psychologists believe dreams serve some adaptive function for survival. Deirdre Barrett describes dreaming as simply "thinking in different biochemical state" and believes people continue to work on all the same problems—personal and objective—in that state.[92] Her research finds that anything—math, musical composition, business dilemmas—may get solved during dreaming.[93][94]
+Finnish psychologist Antti Revonsuo posits that dreams have evolved for "threat simulation" exclusively. According to the Threat Simulation Theory he proposes, during much of human evolution physical and interpersonal threats were serious, giving reproductive advantage to those who survived them. Therefore, dreaming evolved to replicate these threats and continually practice dealing with them. In support of this theory, Revonsuo shows that contemporary dreams comprise much more threatening events than people meet in daily non-dream life, and the dreamer usually engages appropriately with them.[95] It is suggested by this theory that dreams serve the purpose of allowing for the rehearsal of threatening scenarios in order to better prepare an individual for real-life threats.
+According to Tsoukalas (2012) the biology of dreaming is related to the reactive patterns elicited by predatorial encounters (especially the tonic immobility reflex), a fact that lends support to evolutionary theories claiming that dreams specialize in threat avoidance or emotional processing.[63]
+There are many other hypotheses about the function of dreams, including:[96]
+From the 1940s to 1985, Calvin S. Hall collected more than 50,000 dream reports at Western Reserve University. In 1966 Hall and Van De Castle published The Content Analysis of Dreams, in which they outlined a coding system to study 1,000 dream reports from college students.[102] Results indicated that participants from varying parts of the world demonstrated similarity in their dream content. Hall's complete dream reports were made publicly available in the mid-1990s by Hall's protégé William Domhoff.
+The visual nature of dreams is generally highly phantasmagoric; that is, different locations and objects continuously blend into each other. The visuals (including locations, characters/people, objects/artifacts) are generally reflective of a person's memories and experiences, but conversation can take on highly exaggerated and bizarre forms. Some dreams may even tell elaborate stories wherein the dreamer enters entirely new, complex worlds and awakes with ideas, thoughts and feelings never experienced prior to the dream.
+People who are blind from birth do not have visual dreams. Their dream contents are related to other senses like hearing, touch, smell and taste, whichever are present since birth.[103]
+In the Hall study, the most common emotion experienced in dreams was anxiety. Other emotions included abandonment, anger, fear, joy, and happiness. Negative emotions were much more common than positive ones.[102]
+The Hall data analysis shows that sexual dreams occur no more than 10% of the time and are more prevalent in young to mid-teens.[102] Another study showed that 8% of both men and women's dreams have sexual content.[104] In some cases, sexual dreams may result in orgasms or nocturnal emissions. These are colloquially known as wet dreams.[105]
+A small minority of people say that they dream only in black and white.[106][failed verification] A 2008 study by a researcher at the University of Dundee found that people who were only exposed to black-and-white television and film in childhood reported dreaming in black and white about 25% of the time.[107]
+There is evidence that certain medical conditions (normally only neurological conditions) can impact dreams. For instance, some people with synesthesia have never reported entirely black-and-white dreaming, and often have a difficult time imagining the idea of dreaming in only black and white.[108]
+Dream interpretation can be a result of subjective ideas and experiences. One study[8] found that most people believe that "their dreams reveal meaningful hidden truths". In one study[109] conducted in the United States, South Korea and India, they found that 74% of Indians, 65% of South Koreans and 56% of Americans believed their dream content provided them with meaningful insight into their unconscious beliefs and desires. This Freudian view of dreaming was believed by the largely non-scientific public significantly more than theories of dreaming that attribute dream content to memory consolidation, problem-solving, or random brain activity.
+In the paper, Morewedge and Norton (2009) also found that people attribute more importance to dream content than to similar thought content that occurs while they are awake. In one study, Americans were more likely to report that they would miss their flight if they dreamt of their plane crashing than if they thought of their plane crashing the night before flying (while awake), and that they would be as likely to miss their flight if they dreamt of their plane crashing the night before their flight as if there was an actual plane crash on the route they intended to take.[8] Not all dream content was considered equally important. Participants in their studies were more likely to perceive dreams to be meaningful when the content of dreams was in accordance with their beliefs and desires while awake. People were more likely to view a positive dream about a friend to be meaningful than a positive dream about someone they disliked, for example, and were more likely to view a negative dream about a person they disliked as meaningful than a negative dream about a person they liked.
+Therapy for recurring nightmares (often associated with posttraumatic stress disorder) can include imagining alternative scenarios that could begin at each step of the dream.[110]
+During the night, many external stimuli may bombard the senses, but the brain often interprets the stimulus and makes it a part of a dream to ensure continued sleep.[111] Dream incorporation is a phenomenon whereby an actual sensation, such as environmental sounds, is incorporated into dreams, such as hearing a phone ringing in a dream while it is ringing in reality or dreaming of urination while wetting the bed. The mind can, however, awaken an individual if they are in danger or if trained to respond to certain sounds, such as a baby crying.
+The term "dream incorporation" is also used in research examining the degree to which preceding daytime events become elements of dreams. Recent studies suggest that events in the day immediately preceding, and those about a week before, have the most influence.[112] Gary Alan Fine and Laura Fischer Leighton argue that “dreams are external to the individual mind” because “1) dreams are not willed by the individual self; 2) dreams reflect social reality; 3) dreams are public rhetoric; and 4) dreams are collectively interpretable.”[113]
+According to surveys, it is common for people to feel their dreams are predicting subsequent life events.[114] Psychologists have explained these experiences in terms of memory biases, namely a selective memory for accurate predictions and distorted memory so that dreams are retrospectively fitted onto life experiences.[114] The multi-faceted nature of dreams makes it easy to find connections between dream content and real events.[115] The term "veridical dream" has been used to indicate dreams that reveal or contain truths not yet known to the dreamer, whether future events or secrets.[116]
+In one experiment, subjects were asked to write down their dreams in a diary. This prevented the selective memory effect, and the dreams no longer seemed accurate about the future.[117] Another experiment gave subjects a fake diary of a student with apparently precognitive dreams. This diary described events from the person's life, as well as some predictive dreams and some non-predictive dreams. When subjects were asked to recall the dreams they had read, they remembered more of the successful predictions than unsuccessful ones.[118]
+Lucid dreaming is the conscious perception of one's state while dreaming. In this state the dreamer may often have some degree of control over their own actions within the dream or even the characters and the environment of the dream. Dream control has been reported to improve with practiced deliberate lucid dreaming, but the ability to control aspects of the dream is not necessary for a dream to qualify as "lucid" — a lucid dream is any dream during which the dreamer knows they are dreaming.[119] The occurrence of lucid dreaming has been scientifically verified.[120]
+Oneironaut is a term sometimes used for those who lucidly dream.
+In 1975, psychologist Keith Hearne successfully recorded a communication from a dreamer experiencing a lucid dream. On April 12, 1975, after agreeing to move his eyes left and right upon becoming lucid, the subject and Hearne's co-author on the resulting article, Alan Worsley, successfully carried out this task.[121]
+Years later, psychophysiologist Stephen LaBerge conducted similar work including:
+Communication between two dreamers has also been documented. The processes involved included EEG monitoring, ocular signaling, incorporation of reality in the form of red light stimuli and a coordinating website. The website tracked when both dreamers were dreaming and sent the stimulus to one of the dreamers where it was incorporated into the dream. This dreamer, upon becoming lucid, signaled with eye movements; this was detected by the website whereupon the stimulus was sent to the second dreamer, invoking incorporation into this dream.[123]
+Dreams of absent-minded transgression (DAMT) are dreams wherein the dreamer absentmindedly performs an action that he or she has been trying to stop (one classic example is of a quitting smoker having dreams of lighting a cigarette). Subjects who have had DAMT have reported waking with intense feelings of guilt. One study found a positive association between having these dreams and successfully stopping the behavior.[124]
+The recollection of dreams is extremely unreliable, though it is a skill that can be trained. Dreams can usually be recalled if a person is awakened while dreaming.[110] Women tend to have more frequent dream recall than men.[110] Dreams that are difficult to recall may be characterized by relatively little affect, and factors such as salience, arousal, and interference play a role in dream recall. Often, a dream may be recalled upon viewing or hearing a random trigger or stimulus. The salience hypothesis proposes that dream content that is salient, that is, novel, intense, or unusual, is more easily remembered. There is considerable evidence that vivid, intense, or unusual dream content is more frequently recalled.[125] A dream journal can be used to assist dream recall, for personal interest or psychotherapy purposes.
+For some people, sensations from the previous night's dreams are sometimes spontaneously experienced in falling asleep. However they are usually too slight and fleeting to allow dream recall. At least 95% of all dreams are not remembered. Certain brain chemicals necessary for converting short-term memories into long-term ones are suppressed during REM sleep. Unless a dream is particularly vivid and if one wakes during or immediately after it, the content of the dream is not remembered.[126] Recording or reconstructing dreams may one day assist with dream recall. Using technologies such as functional magnetic resonance imaging (fMRI) and electromyography (EMG), researchers have been able to record basic dream imagery,[127] dream speech activity[128] and dream motor behavior (such as walking and hand movements).[129][130]
+In line with the salience hypothesis, there is considerable evidence that people who have more vivid, intense or unusual dreams show better recall. There is evidence that continuity of consciousness is related to recall. Specifically, people who have vivid and unusual experiences during the day tend to have more memorable dream content and hence better dream recall. People who score high on measures of personality traits associated with creativity, imagination, and fantasy, such as openness to experience, daydreaming, fantasy proneness, absorption, and hypnotic susceptibility, tend to show more frequent dream recall.[125] There is also evidence for continuity between the bizarre aspects of dreaming and waking experience. That is, people who report more bizarre experiences during the day, such as people high in schizotypy (psychosis proneness) have more frequent dream recall and also report more frequent nightmares.[125]
+One theory of déjà vu attributes the feeling of having previously seen or experienced something to having dreamed about a similar situation or place, and forgetting about it until one seems to be mysteriously reminded of the situation or the place while awake.[131]
+A daydream is a visionary fantasy, especially one of happy, pleasant thoughts, hopes or ambitions, imagined as coming to pass, and experienced while awake.[132] There are many different types of daydreams, and there is no consistent definition amongst psychologists.[132] The general public also uses the term for a broad variety of experiences. Research by Harvard psychologist Deirdre Barrett has found that people who experience vivid dreamlike mental images reserve the word for these, whereas many other people refer to milder imagery, realistic future planning, review of past memories or just "spacing out"—i.e. one's mind going relatively blank—when they talk about "daydreaming."[133][134]'
+While daydreaming has long been derided as a lazy, non-productive pastime, it is now commonly acknowledged that daydreaming can be constructive in some contexts.[135] There are numerous examples of people in creative or artistic careers, such as composers, novelists and filmmakers, developing new ideas through daydreaming. Similarly, research scientists, mathematicians and physicists have developed new ideas by daydreaming about their subject areas.
+A hallucination, in the broadest sense of the word, is a perception in the absence of a stimulus. In a stricter sense, hallucinations are perceptions in a conscious and awake state, in the absence of external stimuli, and have qualities of real perception, in that they are vivid, substantial, and located in external objective space. The latter definition distinguishes hallucinations from the related phenomena of dreaming, which does not involve wakefulness.
+A nightmare is an unpleasant dream that can cause a strong negative emotional response from the mind, typically fear or horror, but also despair, anxiety and great sadness. The dream may contain situations of danger, discomfort, psychological or physical terror. Sufferers usually awaken in a state of distress and may be unable to return to sleep for a prolonged period of time.[136]
+A night terror, also known as a sleep terror or pavor nocturnus, is a parasomnia disorder that predominantly affects children, causing feelings of terror or dread. Night terrors should not be confused with nightmares, which are bad dreams that cause the feeling of horror or fear.

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+Ontario is one of the thirteen provinces and territories of Canada.[8][9] Located in Central Canada, it is Canada's most populous province, with 38.3 percent of the country's population, and is the second-largest province in total area.[10][11] Ontario is the fourth-largest jurisdiction in total area when the territories of the Northwest Territories and Nunavut are included.[2] It is home to the nation's capital city, Ottawa, and the nation's most populous city, Toronto,[12] which is also Ontario's provincial capital.
+Ontario is bordered by the province of Manitoba to the west, Hudson Bay and James Bay to the north, and Quebec to the east and northeast, and to the south by the U.S. states of (from west to east) Minnesota, Michigan, Ohio, Pennsylvania, and New York. Almost all of Ontario's 2,700 km (1,678 mi) border with the United States follows inland waterways: from the westerly Lake of the Woods, eastward along the major rivers and lakes of the Great Lakes/Saint Lawrence River drainage system. These include Rainy River, Pigeon River, Lake Superior, St. Marys River, Lake Huron, St. Clair River, Lake St. Clair, Detroit River, Lake Erie, Niagara River, Lake Ontario and the St. Lawrence River from Kingston, to the Quebec boundary just east of Cornwall. There is only about 1 km (0.6 mi) of land border, made up of portages including Height of Land Portage on the Minnesota border.[13]
+Ontario is sometimes conceptually divided into two regions, Northern Ontario and Southern Ontario. The great majority of Ontario's population and arable land is in the south. In contrast, the larger, northern part of Ontario is sparsely populated with cold winters and heavy forestation.[14]
+The province is named after Lake Ontario, a term thought to be derived from Ontarí:io, a Huron (Wyandot) word meaning "great lake",[15] or possibly skanadario, which means "beautiful water" in the Iroquoian languages.[16] Ontario has about 250,000 freshwater lakes.[17]
+The province consists of three main geographical regions:
+Despite the absence of any mountainous terrain in the province, there are large areas of uplands, particularly within the Canadian Shield which traverses the province from northwest to southeast and also above the Niagara Escarpment which crosses the south. The highest point is Ishpatina Ridge at 693 metres (2,274 ft) above sea level in Temagami, Northeastern Ontario. In the south, elevations of over 500 m (1,640 ft) are surpassed near Collingwood, above the Blue Mountains in the Dundalk Highlands and in hilltops near the Madawaska River in Renfrew County.
+The Carolinian forest zone covers most of the southwestern region of the province. The temperate and fertile Great Lakes-Saint Lawrence Valley in the south is part of the Eastern Great Lakes lowland forests ecoregion where the forest has now been largely replaced by agriculture, industrial and urban development. A well-known geographic feature is Niagara Falls, part of the Niagara Escarpment. The Saint Lawrence Seaway allows navigation to and from the Atlantic Ocean as far inland as Thunder Bay in Northwestern Ontario. Northern Ontario covers approximately 87% of the province's surface area; conversely Southern Ontario contains 94% of the population.
+Point Pelee is a peninsula of Lake Erie in southwestern Ontario (near Windsor and Detroit, Michigan) that is the southernmost extent of Canada's mainland. Pelee Island and Middle Island in Lake Erie extend slightly farther. All are south of 42°N – slightly farther south than the northern border of California.
+Ontario's climate varies by season and location.[18] Three air sources affect it: cold, dry, arctic air from the north (dominant factor during the winter months, and for a longer part of the year in far northern Ontario); Pacific polar air crossing in from the western Canadian Prairies/US Northern Plains; and warm, moist air from the Gulf of Mexico and the Atlantic Ocean.[19] The effects of these major air masses on temperature and precipitation depend mainly on latitude, proximity to major bodies of water and to a small extent, terrain relief.[19] In general, most of Ontario's climate is classified as humid continental.[19]
+Ontario has three main climatic regions:
+In the northeastern parts of Ontario, extending south as far as Kirkland Lake, the cold waters of Hudson Bay depress summer temperatures, making it cooler than other locations at similar latitudes. The same is true on the northern shore of Lake Superior, which cools hot humid air from the south, leading to cooler summer temperatures.[19] Along the eastern shores of Lake Superior and Lake Huron winter temperatures are slightly moderated but come with frequent heavy lake-effect snow squalls that increase seasonal snowfall totals to upwards of 3 m (10 ft) in some places. These regions have higher annual precipitation, in some places over 100 cm (39 in).
+Severe thunderstorms peak in summer. Windsor, in Southern (Southwestern) Ontario, has the most lightning strikes per year in Canada, averaging 33 days of thunderstorm activity per year.[22] In a typical year, Ontario averages 11 confirmed tornado touchdowns. However, over the last 4 years,[when?] it has had upwards of 20 tornado touchdowns per year, with the highest frequency in the Windsor-Essex – Chatham Kent area, though few are very destructive (the majority between F0 to F2 on the Fujita scale). Ontario had a record 29 tornadoes in both 2006 and 2009. Tropical depression remnants occasionally bring heavy rains and winds in the south, but are rarely deadly. A notable exception was Hurricane Hazel which struck Southern Ontario centred on Toronto, in October 1954.
+Prior to the arrival of the Europeans,[33] the region was inhabited by Algonquian (Ojibwe, Cree and Algonquin) in the northern/western portions, and Iroquois and Wyandot (Huron) people more in the south/east.[34] During the 17th century, the Algonquians and Hurons fought the Beaver Wars against the Iroquois.[35]
+The French explorer Étienne Brûlé explored part of the area in 1610–12.[36] The English explorer Henry Hudson sailed into Hudson Bay in 1611 and claimed the area for England.
+Samuel de Champlain reached Lake Huron in 1615, and French missionaries began to establish posts along the Great Lakes. French settlement was hampered by their hostilities with the Iroquois, who allied themselves with the British.[37] From 1634 to 1640, Hurons were devastated by European infectious diseases, such as measles and smallpox, to which they had no immunity.[38] By 1700, the Iroquois had seceded from Ontario and the Mississaugas of the Ojibwa had settled the north shore of Lake Ontario. The remaining Huron settled north of Quebec.
+The British established trading posts on Hudson Bay in the late 17th century and began a struggle for domination of Ontario with the French. After the French of New France were defeated during the Seven Years' War, the two powers awarded nearly all of France's North American possessions (New France) to Britain in the 1763 Treaty of Paris, including those lands of Ontario not already claimed by Britain. The British annexed the Ontario region to Quebec in 1774.[39]
+The first European settlements were in 1782–1784 when 5,000 American loyalists entered what is now Ontario following the American Revolution.[40] The Kingdom of Great Britain granted them 200 acres (81 ha) land and other items with which to rebuild their lives.[37] The British also set up reserves in Ontario for the Mohawks who had fought for the British and had lost their land in New York state. Other Iroquois, also displaced from New York were resettled in 1784 at the Six Nations reserve at the west end of Lake Ontario. The Mississaugas, displaced by European settlements, would later move to Six Nations also.
+The population of Canada west of the St. Lawrence-Ottawa River confluence substantially increased during this period, a fact recognized by the Constitutional Act of 1791, which split Quebec into the Canadas: Upper Canada southwest of the St. Lawrence-Ottawa River confluence, and Lower Canada east of it. John Graves Simcoe was appointed Upper Canada's first Lieutenant governor in 1793.[41]
+American troops in the War of 1812 invaded Upper Canada across the Niagara River and the Detroit River, but were defeated and pushed back by the British, Canadian fencibles and militias, and First Nations warriors. However, the Americans eventually gained control of Lake Erie and Lake Ontario. The 1813 Battle of York saw American troops defeat the garrison at the Upper Canada capital of York. The Americans looted the town and burned the Upper Canada Parliament Buildings during their brief occupation. The British would burn the American capital of Washington, D.C. in 1814.
+After the War of 1812, relative stability allowed for increasing numbers of immigrants to arrive from Europe rather than from the United States. As was the case in the previous decades, this immigration shift was encouraged by the colonial leaders. Despite affordable and often free land, many arriving newcomers, mostly from Britain and Ireland, found frontier life with the harsh climate difficult, and some of those with the means eventually returned home or went south. However, population growth far exceeded emigration in the following decades. It was a mostly agrarian-based society, but canal projects and a new network of plank roads spurred greater trade within the colony and with the United States, thereby improving previously damaged relations over time.
+Meanwhile, Ontario's numerous waterways aided travel and transportation into the interior and supplied water power for development. As the population increased, so did the industries and transportation networks, which in turn led to further development. By the end of the century, Ontario vied with Quebec as the nation's leader in terms of growth in population, industry, arts and communications.[42]
+Unrest in the colony began to chafe against the aristocratic Family Compact who governed while benefiting economically from the region's resources, and who did not allow elected bodies power. This resentment spurred republican ideals and sowed the seeds for early Canadian nationalism. Accordingly, rebellion in favour of responsible government rose in both regions; Louis-Joseph Papineau led the Lower Canada Rebellion and William Lyon Mackenzie, first Toronto mayor,[43] led the Upper Canada Rebellion. In Upper Canada, the rebellion was quickly a failure. William Lyon Mackenzie escaped to the United States, where he declared the Republic of Canada on Navy Island on the Niagara River.[44]
+Although both rebellions were put down in short order, the British government sent Lord Durham to investigate the causes. He recommended self-government be granted and Lower and Upper Canada be re-joined in an attempt to assimilate the French Canadians. Accordingly, the two colonies were merged into the Province of Canada by the Act of Union 1840, with the capital at Kingston, and Upper Canada becoming known as Canada West.[45] Parliamentary self-government was granted in 1848. There were heavy waves of immigration in the 1840s, and the population of Canada West more than doubled by 1851 over the previous decade. As a result, for the first time, the English-speaking population of Canada West surpassed the French-speaking population of Canada East, tilting the representative balance of power.
+An economic boom in the 1850s coincided with railway expansion across the province, further increasing the economic strength of Central Canada. With the repeal of the Corn Laws and a reciprocity agreement in place with the United States, various industries such as timber, mining, farming and alcohol distilling benefited tremendously.
+A political stalemate between the French- and English-speaking legislators, as well as fear of aggression from the United States during and immediately after the American Civil War, led the political elite to hold a series of conferences in the 1860s to effect a broader federal union of all British North American colonies. The British North America Act took effect on July 1, 1867, establishing the Dominion of Canada, initially with four provinces: Nova Scotia, New Brunswick, Quebec and Ontario. The Province of Canada was divided into Ontario and Quebec so that each linguistic group would have its own province. Both Quebec and Ontario were required by section 93 of the British North America Act to safeguard existing educational rights and privileges of Protestant and the Catholic minority. Thus, separate Catholic schools and school boards were permitted in Ontario. However, neither province had a constitutional requirement to protect its French- or English-speaking minority. Toronto was formally established as Ontario's provincial capital.
+Once constituted as a province, Ontario proceeded to assert its economic and legislative power. In 1872, the lawyer Oliver Mowat became Premier of Ontario and remained as premier until 1896. He fought for provincial rights, weakening the power of the federal government in provincial matters, usually through well-argued appeals to the Judicial Committee of the Privy Council. His battles with the federal government greatly decentralized Canada, giving the provinces far more power than John A. Macdonald had intended. He consolidated and expanded Ontario's educational and provincial institutions, created districts in Northern Ontario, and fought to ensure that those parts of Northwestern Ontario not historically part of Upper Canada (the vast areas north and west of the Lake Superior-Hudson Bay watershed, known as the District of Keewatin) would become part of Ontario, a victory embodied in the Canada (Ontario Boundary) Act, 1889. He also presided over the emergence of the province into the economic powerhouse of Canada. Mowat was the creator of what is often called Empire Ontario.
+Beginning with Sir John A. Macdonald's National Policy (1879) and the construction of the Canadian Pacific Railway (1875–1885) through Northern Ontario and the Canadian Prairies to British Columbia, Ontario manufacturing and industry flourished. However, population increase slowed after a large recession hit the province in 1893, thus slowing growth drastically but for only a few years. Many newly arrived immigrants and others moved west along the railway to the Prairie Provinces and British Columbia, sparsely settling Northern Ontario.
+Mineral exploitation accelerated in the late 19th century, leading to the rise of important mining centres in the northeast, such as Sudbury, Cobalt and Timmins. The province harnessed its water power to generate hydro-electric power and created the state-controlled Hydro-Electric Power Commission of Ontario, later Ontario Hydro. The availability of cheap electric power further facilitated the development of industry. The Ford Motor Company of Canada was established in 1904 and the McLaughlin Motor Car Company (later General Motors Canada) was founded in 1907. The motor vehicle industry became the most lucrative industry for the Ontario economy during the 20th century.
+In July 1912, the Conservative government of Sir James Whitney issued Regulation 17 which severely limited the availability of French-language schooling to the province's French-speaking minority. French Canadians reacted with outrage, journalist Henri Bourassa denouncing the "Prussians of Ontario". The regulation was eventually repealed in 1927.
+Influenced by events in the United States, the government of Sir William Hearst introduced prohibition of alcoholic drinks in 1916 with the passing of the Ontario Temperance Act. However, residents could distill and retain their own personal supply, and liquor producers could continue distillation and export for sale, allowing this already sizeable industry to strengthen further. Ontario became a hotbed for the illegal smuggling of liquor and the biggest supplier into the United States, which was under complete prohibition. Prohibition in Ontario came to an end in 1927 with the establishment of the Liquor Control Board of Ontario under the government of Howard Ferguson. The sale and consumption of liquor, wine, and beer are still controlled by some of the most extreme laws in North America to ensure strict community standards and revenue generation from the alcohol retail monopoly are upheld.
+The post-World War II period was one of exceptional prosperity and growth. Ontario has been the recipients of most immigration to Canada, largely immigrants from war-torn Europe in the 1950s and 1960s and following changes in federal immigration law, a massive influx of non-Europeans since the 1970s. From a largely ethnically British province, Ontario has rapidly become culturally very diverse.
+The nationalist movement in Quebec, particularly after the election of the Parti Québécois in 1976, contributed to driving many businesses and English-speaking people out of Quebec to Ontario, and as a result, Toronto surpassed Montreal as the largest city and economic centre of Canada.[46] Depressed economic conditions in the Maritime Provinces have also resulted in de-population of those provinces in the 20th century, with heavy migration into Ontario.[citation needed]
+Ontario's official language is English, although there exists a number of French-speaking communities across Ontario.[47] French-language services are made available for communities with a sizeable French-speaking population; a service that is ensured under the French Language Services Act of 1989.
+Until 1763, most of Ontario was considered part of New France by French claim. Rupert's Land, defined as the drainage basin of Hudson Bay, was claimed by Britain, and included much of today's Northern Ontario. The British defeated the armies of the French colony and its indigenous allies in the French and Indian War, part of the Seven Years' War global conflict. Concluding the war, the peace treaty between the European powers, known as the Treaty of Paris 1763, assigned almost all of France's possessions in North America to Britain, including parts that would later become Ontario not already part of Rupert's Land. Britain established the first Province of Quebec, encompassing contemporary Quebec and southern Ontario.
+After the American War of Independence, the first reserves for First Nations were established. These are situated at Six Nations (1784), Tyendinaga (1793) and Akwesasne (1795). Six Nations and Tyendinaga were established by the British for those indigenous groups who had fought on the side of the British, and were expelled from the new United States. Akwesasne was a pre-existing Mohawk community and its borders were formalized under the 1795 Jay Treaty.
+In 1788, while part of the Province of Quebec, southern Ontario was divided into four districts: Hesse, Lunenburg, Mecklenburg, and Nassau. In 1792, the four districts were renamed: Hesse became the Western District, Lunenburg became the Eastern District, Mecklenburg became the Midland District, and Nassau became the Home District. Counties were created within the districts.
+By 1798, there were eight districts: Eastern, Home, Johnstown, London, Midland, Newcastle, Niagara, and Western. By 1826, there were eleven districts: Bathurst, Eastern, Gore, Home, Johnstown, London, Midland, Newcastle, Niagara, Ottawa, and Western. By 1838, there were twenty districts: Bathurst, Brock, Colbourne, Dalhousie, Eastern, Gore, Home, Huron, Johnstown, London, Midland, Newcastle, Niagara, Ottawa, Prince Edward, Simcoe, Talbot, Victoria, Wellington, and Western.
+In 1849, the districts of southern Ontario were abolished by the Province of Canada, and county governments took over certain municipal responsibilities. The Province of Canada also began creating districts in sparsely populated Northern Ontario with the establishment of Algoma District and Nipissing District in 1858.
+The borders of Ontario, its new name in 1867, were provisionally expanded north and west. When the Province of Canada was formed, its borders were not entirely clear, and Ontario claimed eventually to reach all the way to the Rocky Mountains and Arctic Ocean. With Canada's acquisition of Rupert's Land, Ontario was interested in clearly defining its borders, especially since some of the new areas in which it was interested were rapidly growing. After the federal government asked Ontario to pay for construction in the new disputed area, the province asked for an elaboration on its limits, and its boundary was moved north to the 51st parallel north.[48]
+The northern and western boundaries of Ontario were in dispute after Canadian Confederation. Ontario's right to Northwestern Ontario was determined by the Judicial Committee of the Privy Council in 1884 and confirmed by the Canada (Ontario Boundary) Act, 1889 of the Parliament of the United Kingdom. By 1899, there were seven northern districts: Algoma, Manitoulin, Muskoka, Nipissing, Parry Sound, Rainy River, and Thunder Bay. Four more northern districts were created between 1907 and 1912: Cochrane, Kenora, Sudbury and Timiskaming.[49]
+In the 2016 census, Ontario had a population of 13,448,494 living in 5,169,174 of its 5,598,391 total dwellings, a 4.6 percent change from its 2011 population of 12,851,821. With a land area of 908,607.67 km2 (350,815.38 sq mi), it had a population density of 14.8/km2 (38.3/sq mi) in 2016.[50] The largest population centres in Ontario are Toronto, Ottawa, Hamilton, Kitchener, London and Oshawa which all have more than 300,000 inhabitants.
+The percentages given below add to more than 100 per cent because of dual responses (e.g., "French and Canadian" response generates an entry both in the category "French Canadian" and in the category "Canadian").
+The majority of Ontarians are of English or other European descent including large Scottish, Irish and Italian communities. Slightly less than 5 per cent of the population of Ontario is Franco-Ontarian, that is those whose native tongue is French, although those with French ancestry account for 11 per cent of the population. In relation to natural increase or inter-provincial migration, immigration is a huge population growth force in Ontario, as it has been over the last two centuries. More recent sources of immigrants with large or growing communities in Ontario include South Asians, Caribbeans, Latin Americans, Europeans, Asians, and Africans. Most populations have settled in the larger urban centres.
+In 2011, 25.9 per cent of the population consisted of visible minorities and 2.4 per cent of the population was Indigenous, mostly of First Nations and Métis descent. There was also a small number of Inuit people in the province. The number of Aboriginal people and visible minorities has been increasing at a faster rate than the general population of Ontario.[51]
+In 2011, the largest religious denominations in Ontario were the Roman Catholic Church (with 31.4% of the population), the United Church of Canada (7.5%), and the Anglican Church (6.1%). 23.1% of Ontarians had no religious affiliation, making it the second-largest religious grouping in the province after Roman Catholics.[52]
+The major religious groups in Ontario in 2011 were:
+In Ontario, Catholics are represented by the Assembly of Catholic Bishops of Ontario[53] and the Anglican Protestants by the Ecclesiastical Province of Ontario.[54] The Ecclesiastical Province covers most of the geographical province of Ontario[54]
+The principal language of Ontario is English, the province's de facto official language,[55] with approximately 97.2 per cent of Ontarians having proficiency in the language, although only 69.5 per cent of Ontarians reported English as their mother tongue in the 2016 Census.[56] English is one of two official languages of Canada, with the other being French. English and French are the official languages of the courts in Ontario. Approximately 4.6 per cent of the population were identified as francophones,[57][note 1] with 11.5 per cent of Ontarians having proficiency in French.[56] Approximately 11.2 per cent of the Ontarians reported being bilingual in both official languages of Canada.[56] Approximately 2.5 per cent of Ontarians have no proficiency in either English or French.[56]
+Franco-Ontarians are concentrated in the northeastern, eastern, and extreme Southern parts of the province, where under the French Language Services Act,[58] provincial government services are required to be available in French if at least 10 per cent of a designated area's population report French as their native language or if an urban centre has at least 5,000 francophones.
+Other languages spoken by residents include Arabic, Bengali, Cantonese, Dutch, Filipino, German, Greek, Gujarati, Hindi, Hebrew, Italian, Korean, Malayalam, Mandarin, Persian, Polish, Portuguese, Punjabi, Russian, Sinhalese, Somali, Spanish, Tamil, Tibetan, Ukrainian, Urdu, and Vietnamese.[59]
+Ontario is Canada's leading manufacturing province, accounting for 52% of the total national manufacturing shipments in 2004.[60] Ontario's largest trading partner is the American state of Michigan. As of April 2012[update], Moody's bond-rating agency rated Ontario debt at AA2/stable,[61] while S&P rated it AA-.[62] Dominion Bond Rating Service rated it AA(low) in January 2013.[63] Long known as a bastion of Canadian manufacturing and financial solvency, Ontario's public debt-to-GDP ratio is projected to be 38.4% in fiscal year 2023–2024.[64]
+Mining and the forest products industry, notably pulp and paper, are vital to the economy of Northern Ontario. As of 2011, roughly 200,000 ha are clearcut each year; herbicides for hardwood suppression are applied to a third of the total.[65] There has been controversy over the Ring of Fire mineral deposit, and whether the province can afford to spend CAD$2.25 billion on a road from the Trans-Canada Highway near Kenora to the deposit, currently valued at CAD$60 billion.[66]
+An abundance of natural resources, excellent transportation links to the North American heartland and the inland Great Lakes making ocean access possible via container ships, have all contributed to making manufacturing the principal industry of the province, found mainly in the Golden Horseshoe region, which is the largest industrialized area in Canada, the southern end of the region being part of the North American Rust Belt. Important products include motor vehicles, iron, steel, food, electrical appliances, machinery, chemicals, and paper.
+Hamilton is the largest steel manufacturing city in Canada followed closely by Sault Ste. Marie, and Sarnia is the centre for petrochemical production. Construction employed more than 6.5% of the province's work force in June 2011.[67] Ontario's steel industry was once centred in Hamilton. Hamilton harbour, which can be seen from the QEW Skyway bridge, is an industrial wasteland; U.S. Steel-owned Stelco announced in the autumn of 2013 that it would close in 2014, with the loss of 875 jobs. The move flummoxed a union representative, who seemed puzzled why a plant with capacity of 2 million tons per annum would be shut while Canada imported 8 million tons of steel the previous year.[68] Algoma Steel maintains a plant in Sault Ste Marie.
+Ontario surpassed Michigan in car production, assembling 2.696 million vehicles in 2004. Ontario has Chrysler plants in Windsor and Bramalea, two GM plants in Oshawa and one in Ingersoll, a Honda assembly plant in Alliston, Ford plants in Oakville and St. Thomas and Toyota assembly plants in Cambridge and Woodstock. However, as a result of steeply declining sales, in 2005, General Motors announced massive layoffs at production facilities across North America, including two large GM plants in Oshawa and a drive train facility in St. Catharines, that resulted in 8,000 job losses in Ontario alone. In 2006, Ford Motor Company announced between 25,000 and 30,000 layoffs phased until 2012; Ontario was spared the worst, but job losses were announced for the St Thomas facility and the Windsor Casting plant. However, these losses will be offset by Ford's recent announcement of a hybrid vehicle facility slated to begin production in 2007 at its Oakville plant and GM's re-introduction of the Camaro which will be produced in Oshawa. On December 4, 2008 Toyota announced the grand opening of the RAV4 plant in Woodstock,[69] and Honda also plans to add an engine plant at its facility in Alliston. Despite these new plants coming online, Ontario has not yet fully recovered following massive layoffs caused by the global recession; its unemployment rate was 7.3% in May 2013,[70] compared to 8.7 percent in January 2010[71] and approximately 6% in 2007. In September 2013, the Ontario government committed CAD$70.9 million to the Ford plant in Oakville, while the federal government committed CAD$71.1mn, to secure 2,800 jobs.[72] The province has lost 300,000 manufacturing jobs in the decade from 2003, and the Bank of Canada noted that "while the energy and mining industries have benefitted from these movements, the pressure on the manufacturing sector has intensified, since many firms in this sector were already dealing with growing competition from low-cost economies such as China."[73][74]
+Toronto, the capital of Ontario, is the centre of Canada's financial services and banking industry. Neighbouring cities are home to product distribution, IT centres, and manufacturing industries. Canada's Federal Government is the largest single employer in the National Capital Region, which centres on the border cities of Ontario's Ottawa and Quebec's Gatineau.[75][76]
+The information technology sector is important, particularly in the Silicon Valley North section of Ottawa, home to Canada's largest technology park.[77] IT is also important in the Waterloo Region, where the headquarters of BlackBerry is located.[78]
+Tourism contributes heavily to the economy of Central Ontario, peaking during the summer months owing to the abundance of fresh water recreation and wilderness found there in reasonable proximity to the major urban centres. At other times of the year, hunting, skiing and snowmobiling are popular. This region has some of the most vibrant fall colour displays anywhere on the continent, and tours directed at overseas visitors are organized to see them. Tourism also plays a key role in border cities with large casinos, among them Windsor, Cornwall, Sarnia and Niagara Falls, the latter of which attracts millions of US and other international visitors.[79]
+Once the dominant industry, agriculture occupies a small percentage of the population. However, much of the land in southern Ontario is given over to agriculture. As the following table shows, while the number of individual farms has steadily decreased and their overall size has shrunk at a lower rate, greater mechanization has supported increased supply to satisfy the ever-increasing demands of a growing population base; this has also meant a gradual increase in the total amount of land used for growing crops.
+Common types of farms reported in the 2001 census include those for cattle, small grains and dairy. The fruit- and wine industry is primarily on the Niagara Peninsula, Prince Edward County, and along the northern shore of Lake Erie, where tobacco farms are also situated. Market vegetables grow in the rich soils of the Holland Marsh near Newmarket. The area near Windsor is also very fertile. The Heinz plant in Leamington was taken over in these autumn of 2013 by Warren Buffett and a Brazilian partner, following which it put 740 people out of work.[81] Government subsidies followed shortly; Premier Kathleen Wynne offered CAD$200,000 to cushion the blow, and promised that another processed-food operator would soon be found.[82] On December 10, 2013, Kellogg's announced layoffs for more than 509 workers at a cereal manufacture plant in London.[83]
+The area defined as the Corn Belt covers much of the southwestern area of the province, extending as far north as close to Goderich, but corn and soy are grown throughout the southern portion of the province. Apple orchards are a common sight along the southern shore of Nottawasaga Bay (part of Georgian Bay) near Collingwood and along the northern shore of Lake Ontario near Cobourg. Tobacco production, centred in Norfolk County, has decreased, allowing an increase in alternative crops such as hazelnuts and ginseng. The Ontario origins of Massey Ferguson, once one of the largest farm-implement manufacturers in the world, indicate the importance agriculture once[citation needed] had to the Canadian economy.
+Southern Ontario's limited supply of agricultural land is going out of production at an increasing rate. Urban sprawl and farmland severances contribute to the loss of thousands of acres of productive agricultural land in Ontario each year. Over 2,000 farms and 150,000 acres (61,000 ha) of farmland in the GTA alone were lost to production in the two decades between 1976 and 1996. This loss represented approximately 18%". of Ontario's Class 1 farmland being converted to urban purposes. In addition, increasing rural severances provide ever-greater interference with agricultural production.[84] In an effort to protect the farmland and green spaces of the National Capital Region, and Greater Toronto Area, the Federal[85] and Provincial Governments introduced greenbelts around Ottawa[86] and the Golden Horseshoe, limiting urban development in these areas.[87]
+Ontario's rivers make it rich in hydroelectric energy.[88] In 2009, Ontario Power Generation generated 70 percent of the province's electricity, of which 51 percent is nuclear, 39% is hydroelectric and 10% is fossil-fuel derived.[89] By 2025, nuclear power is projected to supply 42%, while fossil-fuel-derived generation is projected to decrease slightly over the next 20 years.[90] Much of the newer power generation coming online in the last few years is natural gas or combined-cycle natural gas plants. OPG is not, however, responsible for the transmission of power, which is under the control of Hydro One.
+Despite its diverse range of power options, problems related to increasing consumption, lack of energy efficiency and aging nuclear reactors, Ontario has been forced in recent years to purchase power from its neighbours Quebec and Michigan to supplement its power needs during peak consumption periods. Ontario's basic domestic rate in 2010 was 11.17 cents per kWh; by contrast. Quebec's was 6.81.[91] In December 2013, the government projected a 42 percent hike by 2018, and 68 percent by 2033.[90] Industrial rates are projected to rise by 33% by 2018, and 55% in 2033.[90]
+The Green Energy and Green Economy Act, 2009 (GEA), takes a two-pronged approach to commercializing renewable energy; first, it aims to bring more renewable energy sources to the province; and secondly, it aims to adopt more energy-efficiency measures to help conserve energy. The bill envisaged appointing a Renewable Energy Facilitator to provide "one-window" assistance and support to project developers to facilitate project approvals.[92]
+The approvals process for transmission projects would also be streamlined and (for the first time in Ontario) the bill would enact standards for renewable energy projects. Homeowners would have access to incentives to develop small-scale renewables such as low- or no-interest loans to finance the capital cost of renewable energy generating facilities like solar panels.[92]
+Ontario is home to Niagara Falls, which supplies a large amount of electricity to the province. The Bruce Nuclear Generating Station, the largest operational nuclear power plant in the world, is also in Ontario and uses 8 CANDU reactors to generate electricity for the province.
+Ontario had the most wind energy capacity of the country with 4,900 MW of power (41% of Canada capacity).[93]
+The British North America Act 1867 section 69 stipulated "There shall be a Legislature for Ontario consisting of the Lieutenant Governor and of One House, styled the Legislative Assembly of Ontario." The assembly currently has 124 seats (increased from 107 as of the 42nd Ontario general election) representing ridings elected in a first-past-the-post system across the province.
+The legislative buildings at Queen's Park are the seat of government. Following the Westminster system, the leader of the party holding the most seats in the assembly is known as the "Premier and President of the Council" (Executive Council Act R.S.O. 1990). The Premier chooses the cabinet or Executive Council whose members are deemed ministers of the Crown.
+Although the Legislative Assembly Act (R.S.O. 1990) refers to "members of the assembly", the legislators are now commonly called MPPs (Members of the Provincial Parliament) in English and députés de l'Assemblée législative in French, but they have also been called MLAs (Members of the Legislative Assembly), and both are acceptable. The title of Prime Minister of Ontario, correct in French (le Premier ministre), is permissible in English but now generally avoided in favour of the title "Premier" to avoid confusion with the Prime Minister of Canada.
+Ontario has grown, from its roots in Upper Canada, into a modern jurisdiction. The old titles of the chief law officers, the Attorney-General and the Solicitor-General, remain in use. They both are responsible to the Legislature. The Attorney-General drafts the laws and is responsible for criminal prosecutions and the administration of justice, while the Solicitor-General is responsible for law enforcement and the police services of the province.
+The Municipal Act, 2001 (Ontario)[94] is the main statute governing the creation, administration and government of municipalities in the Canadian province of Ontario, other than the City of Toronto. After being passed in 2001, it came into force on January 1, 2003, replacing the previous Municipal Act.[95] Effective January 1, 2007, the Municipal Act, 2001 (the Act) was significantly amended by the Municipal Statute Law Amendment Act, 2006 (Bill 130).[96][97]
+Ontario has numerous political parties which run for election. The three main parties are the centre-right Progressive Conservative Party of Ontario, the social democratic Ontario New Democratic Party (NDP), the centre-left Ontario Liberal Party. The Progressive Conservatives, Liberals and New Democrats have each governed the province, while the Greens elected their first-ever member to the Legislative Assembly in 2018.
+The 2018 provincial election resulted in a Progressive Conservative majority under Doug Ford, who was sworn in to office on June 29.
+Statistics Canada's measure of a "metro area", the Census Metropolitan Area (CMA), roughly bundles together population figures from the core municipality with those from "commuter" municipalities.[98]
+*Parts of Quebec (including Gatineau) are included in the Ottawa CMA. The population of the Ottawa CMA, in both provinces, is shown.
+In Canada, education falls under provincial jurisdiction. Publicly funded elementary and secondary schools are administered by the Ontario Ministry of Education, while colleges and universities are administered by the Ontario Ministry of Training, Colleges and Universities. The Minister of Education is Stephen Lecce, and the Minister of Training, Colleges and Universities is Ross Romano.
+Higher education in Ontario includes postsecondary education and skills training regulated by the Ministry of Training, Colleges, and Universities and provided by universities, colleges of applied arts and technology, and private career colleges.[100] The minister is Merrilee Fullerton. The ministry administers laws covering 22 public universities,[101] 24 public colleges (21 Colleges of Applied Arts and Technology (CAATs) and three Institutes of Technology and Advanced Learning (ITALs)),[102] 17 privately funded religious universities,[103] and over 500 private career colleges.[104] The Canadian constitution provides each province with the responsibility for higher education and there is no corresponding national federal ministry of higher education.[105] Within Canadian federalism the division of responsibilities and taxing powers between the Ontario and Canadian governments creates the need for co-operation to fund and deliver higher education to students. Each higher education system aims to improve participation, access, and mobility for students. There are two central organizations that assist with the process of applying to Ontario universities and colleges: the Ontario Universities' Application Centre and Ontario College Application Service. While application services are centralized, admission and selection processes vary and are the purview of each institution. Admission to many Ontario postsecondary institutions can be highly competitive. Upon admission, students may get involved with regional student representation with the Canadian Federation of Students, the Canadian Alliance of Student Associations, the Ontario Undergraduate Student Alliance, or through the College Student Alliance in Ontario.
+In 2019, the government of Ontario passed legislation that established the Poet Laureate of Ontario.[106]
+In 1973, the first slogan to appear on licence plates in Ontario was "Keep It Beautiful". This was replaced by "Yours to Discover" in 1982,[107] apparently inspired by a tourism slogan, "Discover Ontario", dating back to 1927.[108] Plates with the French equivalent, Tant à découvrir, were made available to the public beginning in May 2008.[109] (From 1988 to 1990,[110] "Ontario Incredible"[111] gave "Yours to Discover" a brief respite.)
+In 2007, a new song replaced "A Place to Stand" after four decades. "There's No Place Like This" is featured in television advertising, performed by Ontario artists including Molly Johnson, Brian Byrne, Keshia Chanté,[112] as well as Tomi Swick and Arkells.
+The province has professional sports teams in baseball, basketball, Canadian football, ice hockey, lacrosse, rugby and soccer.
+Transportation routes in Ontario evolved from early waterway travel and First Nations paths followed by European explorers. Ontario has two major east–west routes, both starting from Montreal in the neighbouring province of Quebec. The northerly route, which was a major fur trade route, travels west from Montreal along the Ottawa River, then continues northwestward towards Manitoba. Major cities on or near the route include Ottawa, North Bay, Sudbury, Sault Ste. Marie, and Thunder Bay. The southerly route, which was driven by growth in settlements originated by the United Empire Loyalists and later other European immigrants, travels southwest from Montreal along the St. Lawrence River, Lake Ontario, and Lake Erie before entering the United States in Michigan. Major cities on or near the route include Kingston, Belleville, Peterborough, Oshawa, Toronto, Mississauga, Kitchener-Waterloo, Hamilton, London, Sarnia, and Windsor. This route was also heavily used by immigrants to the Midwestern US particularly in the late 19th century.
+Important airports in the province include Toronto Pearson International Airport, which is the busiest airport in Canada,[113] handling nearly 50 million passengers in 2018.[114] Ottawa Macdonald–Cartier International Airport is Ontario's second largest airport. Toronto/Pearson and Ottawa/Macdonald-Cartier form two of the three points in Canada's busiest set of air routes (the third point being Montréal–Pierre Elliott Trudeau International Airport). In addition to airports in Ottawa, and Toronto, the province also operates three other international airports, the John C. Munro Hamilton International Airport in Hamilton, the Thunder Bay International Airport in Thunder Bay and the London International Airport in London. John C. Munro Hamilton International Airport serves as cargo hub, reliever for Pearson, and a hub for ULCC Swoop.
+Most Ontario cities have regional airports, many of which have scheduled commuter flights from Air Canada Jazz or smaller airlines and charter companies – flights from the mid-size cities such as Thunder Bay, Sault Ste. Marie, Sudbury, North Bay, Timmins, Windsor, London, and Kingston feed directly into larger airports in Toronto and Ottawa. Bearskin Airlines also runs flights along the northerly east–west route, connecting Ottawa, North Bay, Sudbury, Sault Ste. Marie, Kitchener and Thunder Bay directly.
+Isolated towns and settlements in the northern areas of the province rely partly or entirely on air service for travel, goods, and even ambulance services (MEDIVAC), since much of the far northern area of the province cannot be reached by road or rail.
+Via Rail operates the inter-regional passenger train service on the Quebec City–Windsor Corridor, along with The Canadian, a transcontinental rail service from Southern Ontario to Vancouver, and the Sudbury–White River train. Additionally, Amtrak rail connects Ontario with key New York cities including Buffalo, Albany, and New York City. Ontario Northland provides rail service to destinations as far north as Moosonee near James Bay, connecting them with the south.
+Freight rail is dominated by the founding cross-country Canadian National Railway and CP Rail companies, which during the 1990s sold many short rail lines from their vast network to private companies operating mostly in the south.
+Regional commuter rail is limited to the provincially owned GO Transit, and serves a train-bus network spanning the Golden Horseshoe region, with Union Station in Toronto serving as the transport hub.
+There are several city rail-transit systems in the Province. The Toronto Transit Commission operates subways, as well as streetcars (being one of the busiest streetcar systems in North America). OC Transpo operates a  light rail metro system in Ottawa. In addition, Waterloo region operates a surface light rail system. Plans to build a light rail line is also underway in the Regional Municipality of Peel.
+400-series highways make up the primary vehicular network in the south of province, and they connect at a number of points to border crossings to the United States, and Quebec, the busiest being the Detroit–Windsor Tunnel and Ambassador Bridge and the Blue Water Bridge (via Highway 402). Some of the primary highways along the southern route are Highway 401, Highway 417, and Highway 400,[115][116] Highway 401 being the busiest highway in North America. Other provincial highways and regional roads inter-connect the remainder of the province.
+The Saint Lawrence Seaway, which extends across most of the southern portion of the province and connects to the Atlantic Ocean, is the primary water transportation route for cargo, particularly iron ore and grain. In the past, the Great Lakes and St. Lawrence River were also a major passenger transportation route, but over the past half century passenger travel has been reduced to ferry services and sightseeing cruises. Ontario's three largest ports are the Port of Hamilton, Port of Thunder Bay and the Port of Windsor. Ontario's only saltwater port is located in the town of Moosonee on James Bay.

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+The United Nations (UN) is an intergovernmental organization that aims to maintain international peace and security, develop friendly relations among nations, achieve international cooperation, and be a centre for harmonizing the actions of nations.[2] It is the largest, most familiar, most internationally represented and most powerful intergovernmental organization in the world. The UN is headquartered on international territory in New York City, with its other main offices in Geneva, Nairobi, Vienna and The Hague.
+The UN was established after World War II with the aim of preventing future wars, succeeding the ineffective League of Nations.[3] On 25 April 1945, 50 governments met in San Francisco for a conference and started drafting the UN Charter, which was adopted on 25 June 1945 and took effect on 24 October 1945, when the UN began operations. Pursuant to the Charter, the organization's objectives include maintaining international peace and security, protecting human rights, delivering humanitarian aid, promoting sustainable development, and upholding international law.[4] At its founding, the UN had 51 member states; this number grew to 193 in 2011,[5] representing almost all of the world's sovereign states.
+The organization's mission to preserve world peace was complicated in its early decades by the Cold War between the United States and Soviet Union and their respective allies. Its missions have consisted primarily of unarmed military observers and lightly armed troops with primarily monitoring, reporting and confidence-building roles.[6] UN membership grew significantly following widespread decolonization beginning in the 1960s. Since then, 80 former colonies have gained independence, including 11 trust territories that had been monitored by the Trusteeship Council.[7] By the 1970s, the UN's budget for economic and social development programmes far outstripped its spending on peacekeeping. After the end of the Cold War, the UN shifted and expanded its field operations, undertaking a wide variety of complex tasks.[8]
+The UN has six principal organs: the General Assembly; the Security Council; the Economic and Social Council (ECOSOC); the Trusteeship Council; the International Court of Justice; and the UN Secretariat. The UN System includes a multitude of specialized agencies, such as the World Bank Group, the World Health Organization, the World Food Programme, UNESCO, and UNICEF. Additionally, non-governmental organizations may be granted consultative status with ECOSOC and other agencies to participate in the UN's work. The UN's chief administrative officer is the Secretary-General, currently Portuguese politician and diplomat António Guterres, who began his five year-term on 1 January 2017. The organization is financed by assessed and voluntary contributions from its member states.
+The UN, its officers, and its agencies have won many Nobel Peace Prizes, though other evaluations of its effectiveness have been mixed. Some commentators believe the organization to be an important force for peace and human development, while others have called it ineffective, biased, or corrupt.
+In the century prior to the UN's creation, several international treaty organizations such as the International Committee of the Red Cross were formed to ensure protection and assistance for victims of armed conflict and strife.[9]
+In 1914, a political assassination in Sarajevo set off a chain of events that led to the outbreak of World War I. As more and more young men were sent down into the trenches, influential voices in the United States and Britain began calling for the establishment of a permanent international body to maintain peace in the postwar world. President Woodrow Wilson became a vocal advocate of this concept, and in 1918 he included a sketch of the international body in his 14-point proposal to end the war. In November 1918, the Central Powers agreed to an armistice to halt the killing in World War I. Two months later, the Allies met with Germany and Austria-Hungary at Versailles to hammer out formal peace terms. President Wilson wanted peace, but the United Kingdom and France disagreed, forcing harsh war reparations on their former enemies. The League of Nations was approved, and in the summer of 1919 Wilson presented the Treaty of Versailles and the Covenant of the League of Nations to the US Senate for ratification.  On 10 January 1920, the League of Nations formally came into being when the Covenant of the League of Nations, ratified by 42 nations in 1919, took effect.[10]
+However, at some point the League became ineffective when it failed to act against the Japanese invasion of Manchuria as in February 1933, 40 nations voted for Japan to withdraw from Manchuria but Japan voted against it and walked out of the League instead of withdrawing from Manchuria.[11] It also failed against the Second Italo-Ethiopian War despite trying to talk to Benito Mussolini as he used the time to send an army to Africa, so the League had a plan for Mussolini to just take a part of Ethiopia, but he ignored the League and invaded Ethiopia, the League tried putting sanctions on Italy, but Italy had already conquered Ethiopia and the League had failed.[12] After Italy conquered Ethiopia, Italy and other nations left the league. But all of them realized that it had failed and they began to re-arm as fast as possible.
+During 1938, Britain and France tried negotiating directly with Hitler but this failed in 1939 when Hitler invaded Czechoslovakia.
+When war broke out in 1939, the League closed down and its headquarters in Geneva remained empty throughout the war.[13]  Although the United States never joined the League, the country did support its economic and social missions through the work of private philanthropies and by sending representatives to committees.
+The earliest concrete plan for a new world organization began under the aegis of the U.S. State Department in 1939.[14] The text of the "Declaration by United Nations" was drafted at the White House on 29 December 1941, by President Franklin D. Roosevelt, Prime Minister Winston Churchill, and Roosevelt aide Harry Hopkins. It incorporated Soviet suggestions but left no role for France. "Four Policemen" was coined to refer to four major Allied countries, United States, United Kingdom, Soviet Union, and Republic of China, which emerged in the Declaration by United Nations.[15] Roosevelt first coined the term United Nations to describe the Allied countries.[a]  "On New Year's Day 1942, President Roosevelt, Prime Minister Churchill, Maxim Litvinov, of the USSR, and T. V. Soong, of China, signed a short document which later came to be known as the United Nations Declaration, and the next day the representatives of twenty-two other nations added their signatures."[16] The term United Nations was first officially used when 26 governments signed this Declaration. One major change from the Atlantic Charter was the addition of a provision for religious freedom, which Stalin approved after Roosevelt insisted.[17][18] By 1 March 1945, 21 additional states had signed.[19]
+A JOINT DECLARATION BY THE UNITED STATES OF AMERICA, THE UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND, THE UNION OF SOVIET SOCIALIST REPUBLICS, CHINA, AUSTRALIA, BELGIUM, CANADA, COSTA RICA, CUBA, CZECHOSLOVAKIA, DOMINICAN REPUBLIC, EL SALVADOR, GREECE, GUATEMALA, HAITI, HONDURAS, INDIA, LUXEMBOURG, NETHERLANDS, NEW ZEALAND, NICARAGUA, NORWAY, PANAMA, POLAND, SOUTH AFRICA, YUGOSLAVIA
+The Governments signatory hereto,
+Having subscribed to a common program of purposes and principles embodied in the Joint Declaration of the President of the United States of America and the Prime Minister of Great Britain dated August 14, 1941, known as the Atlantic Charter,
+Being convinced that complete victory over their enemies is essential to defend life, liberty, independence and religious freedom, and to preserve human rights and justice in their own lands as well as in other lands and that they are now engaged in a common struggle against savage and brutal forces seeking to subjugate the world,
+DECLARE:
+The foregoing declaration may be adhered to by other nations which are, or which may be, rendering material assistance and contributions in the struggle for victory over Hitlerism.
+During the war, "the United Nations" became the official term for the Allies. To join, countries had to sign the Declaration and declare war on the Axis.[20]
+The UN was formulated and negotiated among the delegations from the Allied Big Four (the United States, the United Kingdom, the Soviet Union and China) at the Dumbarton Oaks Conference from 21 September 1944 to 7 October 1944 and they agreed on the aims, structure and functioning of the UN.[21][22][23] After months of planning, the UN Conference on International Organization opened in San Francisco, 25 April 1945, attended by 50 governments and a number of non-governmental organizations involved in drafting the UN Charter.[24][25][26] "The heads of the delegations of the sponsoring countries took turns as chairman of the plenary meetings: Anthony Eden, of Britain, Edward Stettinius, of the United States, T. V. Soong, of China, and Vyacheslav Molotov, of the Soviet Union. At the later meetings, Lord Halifax deputized for Mister Eden, Wellington Koo for T. V. Soong, and Mister Gromyko for Mister Molotov."[27] The UN officially came into existence 24 October 1945, upon ratification of the Charter by the five permanent members of the Security Council—France, the Republic of China, the Soviet Union, the UK and the US—and by a majority of the other 46 signatories.[28]
+The first meetings of the General Assembly, with 51 nations represented,[b] and the Security Council took place in Methodist Central Hall, Westminster, London beginning on 10 January 1946.[28] Debates began at once covering topical issues including the presence of Russian troops in Iranian Azerbaijan, Great Britain's forces in Greece and within days the first veto was cast.[31]
+The General Assembly selected New York City as the site for the headquarters of the UN, construction began on 14 September 1948 and the facility was completed on 9 October 1952. Its site—like UN headquarters buildings in Geneva, Vienna, and Nairobi—is designated as international territory.[32] The Norwegian Foreign Minister, Trygve Lie, was elected as the first UN Secretary-General.[28]
+Though the UN's primary mandate was peacekeeping, the division between the US and USSR often paralysed the organization, generally allowing it to intervene only in conflicts distant from the Cold War.[33] Two notable exceptions were a Security Council resolution on 7 July 1950 authorizing a US-led coalition to repel the North Korean invasion of South Korea, passed in the absence of the USSR,[28][34] and the signing of the Korean Armistice Agreement on 27 July 1953.[35]
+On 29 November 1947, the General Assembly approved a resolution to partition Palestine, approving the creation of the state of Israel.[36] Two years later, Ralph Bunche, a UN official, negotiated an armistice to the resulting conflict.[37] On 7 November 1956, the first UN peacekeeping force was established to end the Suez Crisis;[38] however, the UN was unable to intervene against the USSR's simultaneous invasion of Hungary following that country's revolution.[39]
+On 14 July 1960, the UN established United Nations Operation in the Congo (UNOC), the largest military force of its early decades, to bring order to the breakaway State of Katanga, restoring it to the control of the Democratic Republic of the Congo by 11 May 1964.[40] While traveling to meet rebel leader Moise Tshombe during the conflict, Dag Hammarskjöld, often named as one of the UN's most effective Secretaries-General,[41] died in a plane crash; months later he was posthumously awarded the Nobel Peace Prize.[42] In 1964, Hammarskjöld's successor, U Thant, deployed the UN Peacekeeping Force in Cyprus, which would become one of the UN's longest-running peacekeeping missions.[43]
+With the spread of decolonization in the 1960s, the organization's membership saw an influx of newly independent nations. In 1960 alone, 17 new states joined the UN, 16 of them from Africa.[38] On 25 October 1971, with opposition from the United States, but with the support of many Third World nations, the mainland, communist People's Republic of China was given the Chinese seat on the Security Council in place of the Republic of China that occupied Taiwan; the vote was widely seen as a sign of waning US influence in the organization.[44] Third World nations organized into the Group of 77 coalition under the leadership of Algeria, which briefly became a dominant power at the UN.[45] On 10 November 1975, a bloc comprising the USSR and Third World nations passed a resolution, over the strenuous US and Israeli opposition, declaring Zionism to be racism; the resolution was repealed on 16 December 1991, shortly after the end of the Cold War.[46][47]
+With an increasing Third World presence and the failure of UN mediation in conflicts in the Middle East, Vietnam, and Kashmir, the UN increasingly shifted its attention to its ostensibly secondary goals of economic development and cultural exchange.[48] By the 1970s, the UN budget for social and economic development was far greater than its peacekeeping budget.
+After the Cold War, the UN saw a radical expansion in its peacekeeping duties, taking on more missions in ten years than it had in the previous four decades.[49] Between 1988 and 2000, the number of adopted Security Council resolutions more than doubled, and the peacekeeping budget increased more than tenfold.[50][51][52] The UN negotiated an end to the Salvadoran Civil War, launched a successful peacekeeping mission in Namibia, and oversaw democratic elections in post-apartheid South Africa and post-Khmer Rouge Cambodia.[53] In 1991, the UN authorized a US-led coalition that repulsed the Iraqi invasion of Kuwait.[54] Brian Urquhart, Under-Secretary-General from 1971 to 1985, later described the hopes raised by these successes as a "false renaissance" for the organization, given the more troubled missions that followed.[55]
+Though the UN Charter had been written primarily to prevent aggression by one nation against another, in the early 1990s the UN faced a number of simultaneous, serious crises within nations such as Somalia, Haiti, Mozambique, and the former Yugoslavia.[56] The UN mission in Somalia was widely viewed as a failure after the US withdrawal following casualties in the Battle of Mogadishu, and the UN mission to Bosnia faced "worldwide ridicule" for its indecisive and confused mission in the face of ethnic cleansing.[57] In 1994, the UN Assistance Mission for Rwanda failed to intervene in the Rwandan genocide amid indecision in the Security Council.[58]
+Beginning in the last decades of the Cold War, American and European critics of the UN condemned the organization for perceived mismanagement and corruption.[59] In 1984, US President Ronald Reagan, withdrew his nation's funding from United Nations Educational, Scientific and Cultural Organization (UNESCO) over allegations of mismanagement, followed by the UK and Singapore.[60][61] Boutros Boutros-Ghali, Secretary-General from 1992 to 1996, initiated a reform of the Secretariat, reducing the size of the organization somewhat.[62][63] His successor, Kofi Annan (1997–2006), initiated further management reforms in the face of threats from the US to withhold its UN dues.[63]
+From the late 1990s to the early 2000s, international interventions authorized by the UN took a wider variety of forms. The UN mission in the Sierra Leone Civil War of 1991–2002 was supplemented by British Royal Marines, and the invasion of Afghanistan in 2001 was overseen by NATO.[64] In 2003, the United States invaded Iraq despite failing to pass a UN Security Council resolution for authorization, prompting a new round of questioning of the organization's effectiveness.[65] Under the eighth Secretary-General, Ban Ki-moon, the UN intervened with peacekeepers in crises such as the War in Darfur in Sudan and the Kivu conflict in the Democratic Republic of Congo and sent observers and chemical weapons inspectors to the Syrian Civil War.[66] In 2013, an internal review of UN actions in the final battles of the Sri Lankan Civil War in 2009 concluded that the organization had suffered "systemic failure".[67] In 2010, the organization suffered the worst loss of life in its history, when 101 personnel died in the Haiti earthquake[68]
+The Millennium Summit was held in 2000 to discuss the UN's role in the 21st century.[69] The three day meeting was the largest gathering of world leaders in history, and culminated in the adoption by all member states of the Millennium Development Goals (MDGs), a commitment to achieve international development in areas such as poverty reduction, gender equality, and public health. Progress towards these goals, which were to be met by 2015, was ultimately uneven. The 2005 World Summit reaffirmed the UN's focus on promoting development, peacekeeping, human rights, and global security.[70] The Sustainable Development Goals were launched in 2015 to succeed the Millennium Development Goals.[71]
+In addition to addressing global challenges, the UN has sought to improve its accountability and democratic legitimacy by engaging more with civil society and fostering a global constituency.[72] In an effort to enhance transparency, in 2016 the organization held its first public debate between candidates for Secretary-General.[73] On 1 January 2017, Portuguese diplomat António Guterres, who previously served as UN High Commissioner for Refugees, became the ninth Secretary-General. Guterres has highlighted several key goals for his administration, including an emphasis on diplomacy for preventing conflicts, more effective peacekeeping efforts, and streamlining the organization to be more responsive and versatile to global needs.[74]
+The UN system is based on five principal organs: the General Assembly, the Security Council, the Economic and Social Council (ECOSOC), the International Court of Justice and the UN Secretariat.[75] A sixth principal organ, the Trusteeship Council, suspended operations on 1 November 1994, upon the independence of Palau, the last remaining UN trustee territory.[76]
+Four of the five principal organs are located at the main UN Headquarters in New York City.[77] The International Court of Justice is located in The Hague, while other major agencies are based in the UN offices at Geneva,[78] Vienna,[79] and Nairobi.[80] Other UN institutions are located throughout the world. The six official languages of the UN, used in intergovernmental meetings and documents, are Arabic, Chinese, English,  French, Russian, and Spanish.[81] On the basis of the Convention on the Privileges and Immunities of the United Nations, the UN and its agencies are immune from the laws of the countries where they operate, safeguarding the UN's impartiality with regard to the host and member countries.[82]
+Below the six organs sit, in the words of the author Linda Fasulo, "an amazing collection of entities and organizations, some of which are actually older than the UN itself and operate with almost complete independence from it".[83] These include specialized agencies, research, and training institutions, programs and funds, and other UN entities.[84]
+The UN obeys the Noblemaire principle, which is binding on any organization that belongs to the UN system. This principle calls for salaries that will draw and keep citizens of countries where salaries are highest, and also calls for equal pay for work of equal value independent of the employee's nationality.[85][86] In practice, the ICSC takes reference to the highest-paying national civil service.[87] Staff salaries are subject to an internal tax that is administered by the UN organizations.[85][88]
+The General Assembly is the main deliberative assembly of the UN. Composed of all UN member states, the assembly meets in regular yearly sessions, but emergency sessions can also be called.[90] The assembly is led by a president, elected from among the member states on a rotating regional basis, and 21 vice-presidents.[91] The first session convened 10 January 1946 in the Methodist Central Hall in London and included representatives of 51 nations.[28]
+When the General Assembly decides on important questions such as those on peace and security, admission of new members and budgetary matters, a two-thirds majority of those present and voting is required.[92][93] All other questions are decided by a majority vote. Each member country has one vote. Apart from the approval of budgetary matters, resolutions are not binding on the members. The Assembly may make recommendations on any matters within the scope of the UN, except matters of peace and security that are under consideration by the Security Council.[90]
+Draft resolutions can be forwarded to the General Assembly by its six main committees:[94]
+As well as by the following two committees:
+The Security Council is charged with maintaining peace and security among countries. While other organs of the UN can only make "recommendations" to member states, the Security Council has the power to make binding decisions that member states have agreed to carry out, under the terms of Charter Article 25.[95] The decisions of the council are known as United Nations Security Council resolutions.[96]
+The Security Council is made up of fifteen member states, consisting of five permanent members—China, France, Russia, the United Kingdom, and the United States—and ten non-permanent members elected for two-year terms by the General Assembly (with end of term date)—Belgium (term ends 2020), Dominican Republic (2020), Estonia (2021), Germany (2020), Indonesia (2020), Niger (2021), Saint Vincent and the Grenadines (2021), South Africa (2020), Tunisia (2021), and Vietnam (2021).[97] The five permanent members hold veto power over UN resolutions, allowing a permanent member to block adoption of a resolution, though not debate. The ten temporary seats are held for two-year terms, with five member states per year voted in by the General Assembly on a regional basis.[98] The presidency of the Security Council rotates alphabetically each month.[99]
+The UN Secretariat is headed by the secretary-general, assisted by the deputy secretary-general and a staff of international civil servants worldwide.[100] It provides studies, information, and facilities needed by UN bodies for their meetings. It also carries out tasks as directed by the Security Council, the General Assembly, the Economic and Social Council, and other UN bodies.[101]
+The secretary-general acts as the de facto spokesperson and leader of the UN. The position is defined in the UN Charter as the organization's "chief administrative officer".[102] Article 99 of the charter states that the secretary-general can bring to the Security Council's attention "any matter which in his opinion may threaten the maintenance of international peace and security", a phrase that Secretaries-General since Trygve Lie have interpreted as giving the position broad scope for action on the world stage.[103] The office has evolved into a dual role of an administrator of the UN organization and a diplomat and mediator addressing disputes between member states and finding consensus to global issues.[104]
+The secretary-general is appointed by the General Assembly, after being recommended by the Security Council, where the permanent members have veto power. There are no specific criteria for the post, but over the years it has become accepted that the post shall be held for one or two terms of five years.[105] The current Secretary-General is António Guterres, who replaced Ban Ki-moon in 2017.
+The International Court of Justice (ICJ), located in The Hague, in the Netherlands, is the primary judicial organ of the UN. Established in 1945 by the UN Charter, the Court began work in 1946 as the successor to the Permanent Court of International Justice. The ICJ is composed of 15 judges who serve 9-year terms and are appointed by the General Assembly; every sitting judge must be from a different nation.[107][108]
+It is based in the Peace Palace in The Hague, sharing the building with the Hague Academy of International Law, a private centre for the study of international law. The ICJ's primary purpose is to adjudicate disputes among states. The court has heard cases related to war crimes, illegal state interference, ethnic cleansing, and other issues.[109] The ICJ can also be called upon by other UN organs to provide advisory opinions.[107]
+It is the only organ that is not located in New York.
+The Economic and Social Council (ECOSOC) assists the General Assembly in promoting international economic and social co-operation and development. ECOSOC has 54 members, who are elected by the General Assembly for a three-year term. The president is elected for a one-year term and chosen amongst the small or middle powers represented on ECOSOC. The council has one annual meeting in July, held in either New York or Geneva. Viewed as separate from the specialized bodies it co-ordinates, ECOSOC's functions include information gathering, advising member nations, and making recommendations.[110][111] Owing to its broad mandate of co-ordinating many agencies, ECOSOC has at times been criticized as unfocused or irrelevant.[110][112]
+ECOSOC's subsidiary bodies include the United Nations Permanent Forum on Indigenous Issues, which advises UN agencies on issues relating to indigenous peoples; the United Nations Forum on Forests, which coordinates and promotes sustainable forest management; the United Nations Statistical Commission, which co-ordinates information-gathering efforts between agencies; and the Commission on Sustainable Development, which co-ordinates efforts between UN agencies and NGOs working towards sustainable development. ECOSOC may also grant consultative status to non-governmental organizations;[110] by 2004, more than 2,200 organizations had received this status.[113]
+The UN Charter stipulates that each primary organ of the United Nations can establish various specialized agencies to fulfil its duties.[114] Some best-known agencies are the International Atomic Energy Agency, the Food and Agriculture Organization, UNESCO (United Nations Educational, Scientific and Cultural Organization), the World Bank, and the World Health Organization (WHO). The UN performs most of its humanitarian work through these agencies. Examples include mass vaccination programmes (through WHO), the avoidance of famine and malnutrition (through the work of the WFP), and the protection of vulnerable and displaced people (for example, by UNHCR).[115]
+With the addition of South Sudan 14 July 2011,[5] there are 193 UN member states, including all undisputed independent states apart from Vatican City.[116][c]
+The UN Charter outlines the rules for membership:
+In addition, there are two non-member observer states of the United Nations General Assembly: the Holy See (which holds sovereignty over Vatican City) and the State of Palestine.[118] The Cook Islands and Niue, both states in free association with New Zealand, are full members of several UN specialized agencies and have had their "full treaty-making capacity" recognized by the Secretariat.[119]
+The Group of 77 (G77) at the UN is a loose coalition of developing nations, designed to promote its members' collective economic interests and create an enhanced joint negotiating capacity in the UN. Seventy-seven nations founded the organization, but by November 2013 the organization had since expanded to 133 member countries.[120] The group was founded 15 June 1964 by the "Joint Declaration of the Seventy-Seven Countries" issued at the United Nations Conference on Trade and Development (UNCTAD). The group held its first major meeting in Algiers in 1967, where it adopted the Charter of Algiers and established the basis for permanent institutional structures.[121]  With the adoption of the New International Economic Order by developing countries in the 1970s, the work of the G77 spread throughout the UN system.
+The UN, after approval by the Security Council, sends peacekeepers to regions where armed conflict has recently ceased or paused to enforce the terms of peace agreements and to discourage combatants from resuming hostilities. Since the UN does not maintain its own military, peacekeeping forces are voluntarily provided by member states. These soldiers are sometimes nicknamed "Blue Helmets" for their distinctive gear.[122][123] The peacekeeping force as a whole received the Nobel Peace Prize in 1988.[124]
+In September 2013, the UN had peacekeeping soldiers deployed on 15 missions. The largest was the United Nations Organization Stabilization Mission in the Democratic Republic of the Congo (MONUSCO), which included 20,688 uniformed personnel. The smallest, United Nations Military Observer Group in India and Pakistan (UNMOGIP), included 42 uniformed personnel responsible for monitoring the ceasefire in Jammu and Kashmir. UN peacekeepers with the United Nations Truce Supervision Organization (UNTSO) have been stationed in the Middle East since 1948, the longest-running active peacekeeping mission.[125]
+A study by the RAND Corporation in 2005 found the UN to be successful in two out of three peacekeeping efforts. It compared efforts at nation-building by the UN to those of the United States, and found that seven out of eight UN cases are at peace, as compared with four out of eight US cases at peace.[126] Also in 2005, the Human Security Report documented a decline in the number of wars, genocides, and human rights abuses since the end of the Cold War, and presented evidence, albeit circumstantial, that international activism—mostly spearheaded by the UN—has been the main cause of the decline in armed conflict in that period.[127] Situations in which the UN has not only acted to keep the peace but also intervened include the Korean War (1950–53) and the authorization of intervention in Iraq after the Gulf War (1990–91).[128]
+The UN has also drawn criticism for perceived failures. In many cases, member states have shown reluctance to achieve or enforce Security Council resolutions. Disagreements in the Security Council about military action and intervention are seen as having failed to prevent the Bangladesh genocide in 1971,[129] the Cambodian genocide in the 1970s,[130] and the Rwandan genocide in 1994.[131] Similarly, UN inaction is blamed for failing to either prevent the Srebrenica massacre in 1995 or complete the peacekeeping operations in 1992–93 during the Somali Civil War.[132] UN peacekeepers have also been accused of child rape, soliciting prostitutes, and sexual abuse during various peacekeeping missions in the Democratic Republic of the Congo,[133] Haiti,[134] Liberia,[135] Sudan and what is now South Sudan,[136] Burundi, and Ivory Coast.[137] Scientists cited UN peacekeepers from Nepal as the likely source of the 2010–13 Haiti cholera outbreak, which killed more than 8,000 Haitians following the 2010 Haiti earthquake.[138]
+In addition to peacekeeping, the UN is also active in encouraging disarmament. Regulation of armaments was included in the writing of the UN Charter in 1945 and was envisioned as a way of limiting the use of human and economic resources for their creation.[95] The advent of nuclear weapons came only weeks after the signing of the charter, resulting in the first resolution of the first General Assembly meeting calling for specific proposals for "the elimination from national armaments of atomic weapons and of all other major weapons adaptable to mass destruction".[139] The UN has been involved with arms-limitation treaties, such as the Outer Space Treaty (1967), the Treaty on the Non-Proliferation of Nuclear Weapons (1968), the Seabed Arms Control Treaty (1971), the Biological Weapons Convention (1972), the Chemical Weapons Convention (1992), and the Ottawa Treaty (1997), which prohibits landmines.[140] Three UN bodies oversee arms proliferation issues: the International Atomic Energy Agency, the Organisation for the Prohibition of Chemical Weapons, and the Comprehensive Nuclear-Test-Ban Treaty Organization Preparatory Commission.[141]
+One of the UN's primary purposes is "promoting and encouraging respect for human rights and for fundamental freedoms for all without distinction as to race, sex, language, or religion", and member states pledge to undertake "joint and separate action" to protect these rights.[114][142]
+In 1948, the General Assembly adopted a Universal Declaration of Human Rights, drafted by a committee headed by American diplomat and activist Eleanor Roosevelt, and including the French lawyer René Cassin. The document proclaims basic civil, political, and economic rights common to all human beings, though its effectiveness towards achieving these ends has been disputed since its drafting.[143] The Declaration serves as a "common standard of achievement for all peoples and all nations" rather than a legally binding document, but it has become the basis of two binding treaties, the 1966 International Covenant on Civil and Political Rights and International Covenant on Economic, Social and Cultural Rights.[144] In practice, the UN is unable to take significant action against human rights abuses without a Security Council resolution, though it does substantial work in investigating and reporting abuses.[145]
+In 1979, the General Assembly adopted the Convention on the Elimination of All Forms of Discrimination against Women, followed by the Convention on the Rights of the Child in 1989.[146] With the end of the Cold War, the push for human rights action took on new impetus.[147] The United Nations Commission on Human Rights was formed in 1993 to oversee human rights issues for the UN, following the recommendation of that year's World Conference on Human Rights. Jacques Fomerand, a scholar of the UN, describes this organization's mandate as "broad and vague", with only "meagre" resources to carry it out.[148] In 2006, it was replaced by a Human Rights Council consisting of 47 nations.[149] Also in 2006, the General Assembly passed a Declaration on the Rights of Indigenous Peoples,[150] and in 2011 it passed its first resolution recognizing the rights of LGBT people.[151]
+Other UN bodies responsible for women's rights issues include United Nations Commission on the Status of Women, a commission of ECOSOC founded in 1946; the United Nations Development Fund for Women, created in 1976; and the United Nations International Research and Training Institute for the Advancement of Women, founded in 1979.[152] The UN Permanent Forum on Indigenous Issues, one of three bodies with a mandate to oversee issues related to indigenous peoples, held its first session in 2002.[153]
+Millennium Development Goals[154]
+Another primary purpose of the UN is "to achieve international cooperation in solving international problems of an economic, social, cultural, or humanitarian character".[142] Numerous bodies have been created to work towards this goal, primarily under the authority of the General Assembly and ECOSOC.[155] In 2000, the 192 UN member states agreed to achieve eight Millennium Development Goals by 2015.[156] The Sustainable Development Goals were launched in 2015 to succeed the Millennium Development Goals.[71] The SDGs have an associated financing framework called the Addis Ababa Action Agenda.
+The UN Development Programme (UNDP), an organization for grant-based technical assistance founded in 1945, is one of the leading bodies in the field of international development. The organization also publishes the UN Human Development Index, a comparative measure ranking countries by poverty, literacy, education, life expectancy, and other factors.[157][158] The Food and Agriculture Organization (FAO), also founded in 1945, promotes agricultural development and food security.[159] UNICEF (the United Nations Children's Fund) was created in 1946 to aid European children after the Second World War and expanded its mission to provide aid around the world and to uphold the convention on the Rights of the Child.[160][161]
+The World Bank Group and International Monetary Fund (IMF) are independent, specialized agencies and observers within the UN framework, according to a 1947 agreement. They were initially formed separately from the UN through the Bretton Woods Agreement in 1944.[162] The World Bank provides loans for international development, while the IMF promotes international economic co-operation and gives emergency loans to indebted countries.[163]
+The World Health Organization (WHO), which focuses on international health issues and disease eradication, is another of the UN's largest agencies. In 1980, the agency announced that the eradication of smallpox had been completed. In subsequent decades, WHO largely eradicated polio, river blindness, and leprosy.[164] The Joint United Nations Programme on HIV/AIDS (UNAIDS), begun in 1996, co-ordinates the organization's response to the AIDS epidemic.[165] The UN Population Fund, which also dedicates part of its resources to combating HIV, is the world's largest source of funding for reproductive health and family planning services.[166]
+Along with the International Red Cross and Red Crescent Movement, the UN often takes a leading role in co-ordinating emergency relief.[167] The World Food Programme (WFP), created in 1961, provides food aid in response to famine, natural disasters, and armed conflict. The organization reports that it feeds an average of 90 million people in 80 nations each year.[167][168] The Office of the United Nations High Commissioner for Refugees (UNHCR), established in 1950, works to protect the rights of refugees, asylum seekers, and stateless people.[169] UNHCR and WFP programmes are funded by voluntary contributions from governments, corporations, and individuals, though the UNHCR's administrative costs are paid for by the UN's primary budget.[170]
+Since the UN's creation, over 80 colonies have attained independence. The General Assembly adopted the Declaration on the Granting of Independence to Colonial Countries and Peoples in 1960 with no votes against but abstentions from all major colonial powers. The UN works towards decolonization through groups including the UN Committee on Decolonization, created in 1962.[171] The committee lists seventeen remaining "Non-Self-Governing Territories", the largest and most populous of which is Western Sahara.[172]
+Beginning with the formation of the UN Environmental Programme (UNEP) in 1972, the UN has made environmental issues a prominent part of its agenda. A lack of success in the first two decades of UN work in this area led to the 1992 Earth Summit in Rio de Janeiro, Brazil, which sought to give new impetus to these efforts.[173] In 1988, the UNEP and the World Meteorological Organization (WMO), another UN organization, established the Intergovernmental Panel on Climate Change, which assesses and reports on research on global warming.[174] The UN-sponsored Kyoto Protocol, signed in 1997, set legally binding emissions reduction targets for ratifying states.[175]
+The UN also declares and co-ordinates international observances, periods of time to observe issues of international interest or concern. Examples include World Tuberculosis Day, Earth Day, and the International Year of Deserts and Desertification.[176]
+The UN is financed from assessed and voluntary contributions from member states. The General Assembly approves the regular budget and determines the assessment for each member. This is broadly based on the relative capacity of each country to pay, as measured by its gross national income (GNI), with adjustments for external debt and low per capita income.[178] The two-year budget for 2012–13 was $5.512 billion in total.[179]
+The Assembly has established the principle that the UN should not be unduly dependent on any one member to finance its operations. Thus, there is a "ceiling" rate, setting the maximum amount that any member can be assessed for the regular budget. In December 2000, the Assembly revised the scale of assessments in response to pressure from the United States. As part of that revision, the regular budget ceiling was reduced from 25% to 22%.[180] For the least developed countries (LDCs), a ceiling rate of 0.01% is applied.[178] In addition to the ceiling rates, the minimum amount assessed to any member nation (or "floor" rate) is set at 0.001% of the UN budget ($55,120 for the two year budget 2013–2014).[181]
+A large share of the UN's expenditure addresses its core mission of peace and security, and this budget is assessed separately from the main organizational budget.[182] The peacekeeping budget for the 2015–16 fiscal year was $8.27 billion, supporting 82,318 troops deployed in 15 missions around the world.[125] UN peace operations are funded by assessments, using a formula derived from the regular funding scale that includes a weighted surcharge for the five permanent Security Council members, who must approve all peacekeeping operations. This surcharge serves to offset discounted peacekeeping assessment rates for less developed countries.
+the largest contributors for the UN peacekeeping  financial operations for the period 2019–2021 are : the United States  27.89%  China 15.21%, Japan 8.56%, Germany 6.09% , the United Kingdom 5.78%, France 5.61%, Italy 3.30% and the Russian Federation 3.04%.[183]
+Special UN programmes not included in the regular budget, such as UNICEF and the World Food Programme, are financed by voluntary contributions from member governments, corporations, and private individuals.[184][185]
+A number of agencies and individuals associated with the UN have won the Nobel Peace Prize in recognition of their work. Two Secretaries-General, Dag Hammarskjöld, and Kofi Annan, were each awarded the prize (in 1961 and 2001, respectively), as were Ralph Bunche (1950), a UN negotiator, René Cassin (1968), a contributor to the Universal Declaration of Human Rights, and the US Secretary of State Cordell Hull (1945), the latter for his role in the organization's founding. Lester B. Pearson, the Canadian Secretary of State for External Affairs, was awarded the prize in 1957 for his role in organizing the UN's first peacekeeping force to resolve the Suez Crisis. UNICEF won the prize in 1965, the International Labour Organization in 1969, the UN Peace-Keeping Forces in 1988, the International Atomic Energy Agency (which reports to the UN) in 2005, and the UN-supported Organisation for the Prohibition of Chemical Weapons in 2013. The UN High Commissioner for Refugees was awarded in 1954 and 1981, becoming one of only two recipients to win the prize twice. The UN as a whole was awarded the prize in 2001, sharing it with Annan.[186] In 2007, IPCC received the prize "for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change."[187]
+Since its founding, there have been many calls for reform of the UN but little consensus on how to do so. Some want the UN to play a greater or more effective role in world affairs, while others want its role reduced to humanitarian work. There have also been numerous calls for the UN Security Council's membership to be increased, for different ways of electing the UN's Secretary-General, and for a UN Parliamentary Assembly. Jacques Fomerand states the most enduring divide in views of the UN is "the North–South split" between richer Northern nations and developing Southern nations. Southern nations tend to favour a more empowered UN with a stronger General Assembly, allowing them a greater voice in world affairs, while Northern nations prefer an economically laissez-faire UN that focuses on transnational threats such as terrorism.[188]
+After World War II, the French Committee of National Liberation was late to be recognized by the US as the government of France, and so the country was initially excluded from the conferences that created the new organization. The future French president Charles de Gaulle criticized the UN, famously calling it a machin ("contraption"), and was not convinced that a global security alliance would help maintain world peace, preferring direct defence treaties between countries.[189] Throughout the Cold War, both the US and USSR repeatedly accused the UN of favouring the other. In 1953, the USSR effectively forced the resignation of Trygve Lie, the Secretary-General, through its refusal to deal with him, while in the 1950s and 1960s, a popular US bumper sticker read, "You can't spell communism without U.N."[190] In a sometimes-misquoted statement, President George W. Bush stated in February 2003 (referring to UN uncertainty towards Iraqi provocations under the Saddam Hussein regime) that "free nations will not allow the UN to fade into history as an ineffective, irrelevant debating society."[191][192][193] In contrast, the French President, François Hollande, stated in 2012 that "France trusts the United Nations. She knows that no state, no matter how powerful, can solve urgent problems, fight for development and bring an end to all crises ... France wants the UN to be the centre of global governance."[194] Critics such as Dore Gold, an Israeli diplomat, Robert S. Wistrich, a British scholar, Alan Dershowitz, an American legal scholar, Mark Dreyfus, an Australian politician, and the Anti-Defamation League consider UN attention to Israel's treatment of Palestinians to be excessive.[195] In September 2015, Saudi Arabia's Faisal bin Hassan Trad has been elected Chair of the UN Human Rights Council panel that appoints independent experts,[196] a move criticized by human rights groups.[197][198]
+Since 1971, the Republic of China on Taiwan has been excluded from the UN and since then has always been rejected in new applications. Taiwanese citizens are also not allowed to enter the buildings of the United Nations with ROC passports. In this way, critics agree that the UN is failing its own development goals and guidelines. This criticism also brought pressure from the People's Republic of China, which regards the territories administered by the ROC as their own territory.[199][200]
+Critics have also accused the UN of bureaucratic inefficiency, waste, and corruption. In 1976, the General Assembly established the Joint Inspection Unit to seek out inefficiencies within the UN system. During the 1990s, the US withheld dues citing inefficiency and only started repayment on the condition that a major reforms initiative be introduced. In 1994, the Office of Internal Oversight Services (OIOS) was established by the General Assembly to serve as an efficiency watchdog.[201] In 1994, former Special Representative of the Secretary-General of the UN to Somalia Mohamed Sahnoun published "Somalia: The Missed Opportunities",[202] a book in which he analyses the reasons for the failure of the 1992 UN intervention in Somalia, showing that, between the start of the Somali civil war in 1988 and the fall of the Siad Barre regime in January 1991, the UN missed at least three opportunities to prevent major human tragedies; when the UN tried to provide humanitarian assistance, they were totally outperformed by NGOs, whose competence and dedication sharply contrasted with the UN's excessive caution and bureaucratic inefficiencies. If radical reform were not undertaken, warned Mohamed Sahnoun, then the UN would continue to respond to such crises with inept improvisation.[203] In 2004, the UN faced accusations that its recently ended Oil-for-Food Programme — in which Iraq had been allowed to trade oil for basic needs to relieve the pressure of sanctions — had suffered from widespread corruption, including billions of dollars of kickbacks. An independent inquiry created by the UN found that many of its officials had been involved, as well as raising "significant" questions about the role of Kojo Annan, the son of Kofi Annan.[204]
+In evaluating the UN as a whole, Jacques Fomerand writes that the "accomplishments of the United Nations in the last 60 years are impressive in their own terms. Progress in human development during the 20th century has been dramatic, and the UN and its agencies have certainly helped the world become a more hospitable and livable place for millions."[205] Evaluating the first 50 years of the UN's history, the author Stanley Meisler writes that "the United Nations never fulfilled the hopes of its founders, but it accomplished a great deal nevertheless", citing its role in decolonization and its many successful peacekeeping efforts.[206] The British historian Paul Kennedy states that while the organization has suffered some major setbacks, "when all its aspects are considered, the UN has brought great benefits to our generation and ... will bring benefits to our children's and grandchildren's generations as well."[207]
+Core features of the UN apparatus, such as the veto privileges of some nations in the Security Council, are often described as fundamentally undemocratic, contrary to the UN mission, and as a main cause of inaction on genocides and crimes against humanity.[208][209]
+The United Nations has inspired the extracurricular activity Model United Nations (MUN). MUN is a simulation of United Nations activity based on the UN agenda and following UN procedure. MUN is usually attended by high school and university students who organize conferences to simulate the various UN committees to discuss important issues of the day.[210] Today Model United Nations educates tens of thousands on United Nations activity around the world. Model United Nations has many famous and notable alumni, such as former Secretary-General of the United Nations Ban Ki-moon.[211]

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+The United Nations (UN) is an intergovernmental organization that aims to maintain international peace and security, develop friendly relations among nations, achieve international cooperation, and be a centre for harmonizing the actions of nations.[2] It is the largest, most familiar, most internationally represented and most powerful intergovernmental organization in the world. The UN is headquartered on international territory in New York City, with its other main offices in Geneva, Nairobi, Vienna and The Hague.
+The UN was established after World War II with the aim of preventing future wars, succeeding the ineffective League of Nations.[3] On 25 April 1945, 50 governments met in San Francisco for a conference and started drafting the UN Charter, which was adopted on 25 June 1945 and took effect on 24 October 1945, when the UN began operations. Pursuant to the Charter, the organization's objectives include maintaining international peace and security, protecting human rights, delivering humanitarian aid, promoting sustainable development, and upholding international law.[4] At its founding, the UN had 51 member states; this number grew to 193 in 2011,[5] representing almost all of the world's sovereign states.
+The organization's mission to preserve world peace was complicated in its early decades by the Cold War between the United States and Soviet Union and their respective allies. Its missions have consisted primarily of unarmed military observers and lightly armed troops with primarily monitoring, reporting and confidence-building roles.[6] UN membership grew significantly following widespread decolonization beginning in the 1960s. Since then, 80 former colonies have gained independence, including 11 trust territories that had been monitored by the Trusteeship Council.[7] By the 1970s, the UN's budget for economic and social development programmes far outstripped its spending on peacekeeping. After the end of the Cold War, the UN shifted and expanded its field operations, undertaking a wide variety of complex tasks.[8]
+The UN has six principal organs: the General Assembly; the Security Council; the Economic and Social Council (ECOSOC); the Trusteeship Council; the International Court of Justice; and the UN Secretariat. The UN System includes a multitude of specialized agencies, such as the World Bank Group, the World Health Organization, the World Food Programme, UNESCO, and UNICEF. Additionally, non-governmental organizations may be granted consultative status with ECOSOC and other agencies to participate in the UN's work. The UN's chief administrative officer is the Secretary-General, currently Portuguese politician and diplomat António Guterres, who began his five year-term on 1 January 2017. The organization is financed by assessed and voluntary contributions from its member states.
+The UN, its officers, and its agencies have won many Nobel Peace Prizes, though other evaluations of its effectiveness have been mixed. Some commentators believe the organization to be an important force for peace and human development, while others have called it ineffective, biased, or corrupt.
+In the century prior to the UN's creation, several international treaty organizations such as the International Committee of the Red Cross were formed to ensure protection and assistance for victims of armed conflict and strife.[9]
+In 1914, a political assassination in Sarajevo set off a chain of events that led to the outbreak of World War I. As more and more young men were sent down into the trenches, influential voices in the United States and Britain began calling for the establishment of a permanent international body to maintain peace in the postwar world. President Woodrow Wilson became a vocal advocate of this concept, and in 1918 he included a sketch of the international body in his 14-point proposal to end the war. In November 1918, the Central Powers agreed to an armistice to halt the killing in World War I. Two months later, the Allies met with Germany and Austria-Hungary at Versailles to hammer out formal peace terms. President Wilson wanted peace, but the United Kingdom and France disagreed, forcing harsh war reparations on their former enemies. The League of Nations was approved, and in the summer of 1919 Wilson presented the Treaty of Versailles and the Covenant of the League of Nations to the US Senate for ratification.  On 10 January 1920, the League of Nations formally came into being when the Covenant of the League of Nations, ratified by 42 nations in 1919, took effect.[10]
+However, at some point the League became ineffective when it failed to act against the Japanese invasion of Manchuria as in February 1933, 40 nations voted for Japan to withdraw from Manchuria but Japan voted against it and walked out of the League instead of withdrawing from Manchuria.[11] It also failed against the Second Italo-Ethiopian War despite trying to talk to Benito Mussolini as he used the time to send an army to Africa, so the League had a plan for Mussolini to just take a part of Ethiopia, but he ignored the League and invaded Ethiopia, the League tried putting sanctions on Italy, but Italy had already conquered Ethiopia and the League had failed.[12] After Italy conquered Ethiopia, Italy and other nations left the league. But all of them realized that it had failed and they began to re-arm as fast as possible.
+During 1938, Britain and France tried negotiating directly with Hitler but this failed in 1939 when Hitler invaded Czechoslovakia.
+When war broke out in 1939, the League closed down and its headquarters in Geneva remained empty throughout the war.[13]  Although the United States never joined the League, the country did support its economic and social missions through the work of private philanthropies and by sending representatives to committees.
+The earliest concrete plan for a new world organization began under the aegis of the U.S. State Department in 1939.[14] The text of the "Declaration by United Nations" was drafted at the White House on 29 December 1941, by President Franklin D. Roosevelt, Prime Minister Winston Churchill, and Roosevelt aide Harry Hopkins. It incorporated Soviet suggestions but left no role for France. "Four Policemen" was coined to refer to four major Allied countries, United States, United Kingdom, Soviet Union, and Republic of China, which emerged in the Declaration by United Nations.[15] Roosevelt first coined the term United Nations to describe the Allied countries.[a]  "On New Year's Day 1942, President Roosevelt, Prime Minister Churchill, Maxim Litvinov, of the USSR, and T. V. Soong, of China, signed a short document which later came to be known as the United Nations Declaration, and the next day the representatives of twenty-two other nations added their signatures."[16] The term United Nations was first officially used when 26 governments signed this Declaration. One major change from the Atlantic Charter was the addition of a provision for religious freedom, which Stalin approved after Roosevelt insisted.[17][18] By 1 March 1945, 21 additional states had signed.[19]
+A JOINT DECLARATION BY THE UNITED STATES OF AMERICA, THE UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND, THE UNION OF SOVIET SOCIALIST REPUBLICS, CHINA, AUSTRALIA, BELGIUM, CANADA, COSTA RICA, CUBA, CZECHOSLOVAKIA, DOMINICAN REPUBLIC, EL SALVADOR, GREECE, GUATEMALA, HAITI, HONDURAS, INDIA, LUXEMBOURG, NETHERLANDS, NEW ZEALAND, NICARAGUA, NORWAY, PANAMA, POLAND, SOUTH AFRICA, YUGOSLAVIA
+The Governments signatory hereto,
+Having subscribed to a common program of purposes and principles embodied in the Joint Declaration of the President of the United States of America and the Prime Minister of Great Britain dated August 14, 1941, known as the Atlantic Charter,
+Being convinced that complete victory over their enemies is essential to defend life, liberty, independence and religious freedom, and to preserve human rights and justice in their own lands as well as in other lands and that they are now engaged in a common struggle against savage and brutal forces seeking to subjugate the world,
+DECLARE:
+The foregoing declaration may be adhered to by other nations which are, or which may be, rendering material assistance and contributions in the struggle for victory over Hitlerism.
+During the war, "the United Nations" became the official term for the Allies. To join, countries had to sign the Declaration and declare war on the Axis.[20]
+The UN was formulated and negotiated among the delegations from the Allied Big Four (the United States, the United Kingdom, the Soviet Union and China) at the Dumbarton Oaks Conference from 21 September 1944 to 7 October 1944 and they agreed on the aims, structure and functioning of the UN.[21][22][23] After months of planning, the UN Conference on International Organization opened in San Francisco, 25 April 1945, attended by 50 governments and a number of non-governmental organizations involved in drafting the UN Charter.[24][25][26] "The heads of the delegations of the sponsoring countries took turns as chairman of the plenary meetings: Anthony Eden, of Britain, Edward Stettinius, of the United States, T. V. Soong, of China, and Vyacheslav Molotov, of the Soviet Union. At the later meetings, Lord Halifax deputized for Mister Eden, Wellington Koo for T. V. Soong, and Mister Gromyko for Mister Molotov."[27] The UN officially came into existence 24 October 1945, upon ratification of the Charter by the five permanent members of the Security Council—France, the Republic of China, the Soviet Union, the UK and the US—and by a majority of the other 46 signatories.[28]
+The first meetings of the General Assembly, with 51 nations represented,[b] and the Security Council took place in Methodist Central Hall, Westminster, London beginning on 10 January 1946.[28] Debates began at once covering topical issues including the presence of Russian troops in Iranian Azerbaijan, Great Britain's forces in Greece and within days the first veto was cast.[31]
+The General Assembly selected New York City as the site for the headquarters of the UN, construction began on 14 September 1948 and the facility was completed on 9 October 1952. Its site—like UN headquarters buildings in Geneva, Vienna, and Nairobi—is designated as international territory.[32] The Norwegian Foreign Minister, Trygve Lie, was elected as the first UN Secretary-General.[28]
+Though the UN's primary mandate was peacekeeping, the division between the US and USSR often paralysed the organization, generally allowing it to intervene only in conflicts distant from the Cold War.[33] Two notable exceptions were a Security Council resolution on 7 July 1950 authorizing a US-led coalition to repel the North Korean invasion of South Korea, passed in the absence of the USSR,[28][34] and the signing of the Korean Armistice Agreement on 27 July 1953.[35]
+On 29 November 1947, the General Assembly approved a resolution to partition Palestine, approving the creation of the state of Israel.[36] Two years later, Ralph Bunche, a UN official, negotiated an armistice to the resulting conflict.[37] On 7 November 1956, the first UN peacekeeping force was established to end the Suez Crisis;[38] however, the UN was unable to intervene against the USSR's simultaneous invasion of Hungary following that country's revolution.[39]
+On 14 July 1960, the UN established United Nations Operation in the Congo (UNOC), the largest military force of its early decades, to bring order to the breakaway State of Katanga, restoring it to the control of the Democratic Republic of the Congo by 11 May 1964.[40] While traveling to meet rebel leader Moise Tshombe during the conflict, Dag Hammarskjöld, often named as one of the UN's most effective Secretaries-General,[41] died in a plane crash; months later he was posthumously awarded the Nobel Peace Prize.[42] In 1964, Hammarskjöld's successor, U Thant, deployed the UN Peacekeeping Force in Cyprus, which would become one of the UN's longest-running peacekeeping missions.[43]
+With the spread of decolonization in the 1960s, the organization's membership saw an influx of newly independent nations. In 1960 alone, 17 new states joined the UN, 16 of them from Africa.[38] On 25 October 1971, with opposition from the United States, but with the support of many Third World nations, the mainland, communist People's Republic of China was given the Chinese seat on the Security Council in place of the Republic of China that occupied Taiwan; the vote was widely seen as a sign of waning US influence in the organization.[44] Third World nations organized into the Group of 77 coalition under the leadership of Algeria, which briefly became a dominant power at the UN.[45] On 10 November 1975, a bloc comprising the USSR and Third World nations passed a resolution, over the strenuous US and Israeli opposition, declaring Zionism to be racism; the resolution was repealed on 16 December 1991, shortly after the end of the Cold War.[46][47]
+With an increasing Third World presence and the failure of UN mediation in conflicts in the Middle East, Vietnam, and Kashmir, the UN increasingly shifted its attention to its ostensibly secondary goals of economic development and cultural exchange.[48] By the 1970s, the UN budget for social and economic development was far greater than its peacekeeping budget.
+After the Cold War, the UN saw a radical expansion in its peacekeeping duties, taking on more missions in ten years than it had in the previous four decades.[49] Between 1988 and 2000, the number of adopted Security Council resolutions more than doubled, and the peacekeeping budget increased more than tenfold.[50][51][52] The UN negotiated an end to the Salvadoran Civil War, launched a successful peacekeeping mission in Namibia, and oversaw democratic elections in post-apartheid South Africa and post-Khmer Rouge Cambodia.[53] In 1991, the UN authorized a US-led coalition that repulsed the Iraqi invasion of Kuwait.[54] Brian Urquhart, Under-Secretary-General from 1971 to 1985, later described the hopes raised by these successes as a "false renaissance" for the organization, given the more troubled missions that followed.[55]
+Though the UN Charter had been written primarily to prevent aggression by one nation against another, in the early 1990s the UN faced a number of simultaneous, serious crises within nations such as Somalia, Haiti, Mozambique, and the former Yugoslavia.[56] The UN mission in Somalia was widely viewed as a failure after the US withdrawal following casualties in the Battle of Mogadishu, and the UN mission to Bosnia faced "worldwide ridicule" for its indecisive and confused mission in the face of ethnic cleansing.[57] In 1994, the UN Assistance Mission for Rwanda failed to intervene in the Rwandan genocide amid indecision in the Security Council.[58]
+Beginning in the last decades of the Cold War, American and European critics of the UN condemned the organization for perceived mismanagement and corruption.[59] In 1984, US President Ronald Reagan, withdrew his nation's funding from United Nations Educational, Scientific and Cultural Organization (UNESCO) over allegations of mismanagement, followed by the UK and Singapore.[60][61] Boutros Boutros-Ghali, Secretary-General from 1992 to 1996, initiated a reform of the Secretariat, reducing the size of the organization somewhat.[62][63] His successor, Kofi Annan (1997–2006), initiated further management reforms in the face of threats from the US to withhold its UN dues.[63]
+From the late 1990s to the early 2000s, international interventions authorized by the UN took a wider variety of forms. The UN mission in the Sierra Leone Civil War of 1991–2002 was supplemented by British Royal Marines, and the invasion of Afghanistan in 2001 was overseen by NATO.[64] In 2003, the United States invaded Iraq despite failing to pass a UN Security Council resolution for authorization, prompting a new round of questioning of the organization's effectiveness.[65] Under the eighth Secretary-General, Ban Ki-moon, the UN intervened with peacekeepers in crises such as the War in Darfur in Sudan and the Kivu conflict in the Democratic Republic of Congo and sent observers and chemical weapons inspectors to the Syrian Civil War.[66] In 2013, an internal review of UN actions in the final battles of the Sri Lankan Civil War in 2009 concluded that the organization had suffered "systemic failure".[67] In 2010, the organization suffered the worst loss of life in its history, when 101 personnel died in the Haiti earthquake[68]
+The Millennium Summit was held in 2000 to discuss the UN's role in the 21st century.[69] The three day meeting was the largest gathering of world leaders in history, and culminated in the adoption by all member states of the Millennium Development Goals (MDGs), a commitment to achieve international development in areas such as poverty reduction, gender equality, and public health. Progress towards these goals, which were to be met by 2015, was ultimately uneven. The 2005 World Summit reaffirmed the UN's focus on promoting development, peacekeeping, human rights, and global security.[70] The Sustainable Development Goals were launched in 2015 to succeed the Millennium Development Goals.[71]
+In addition to addressing global challenges, the UN has sought to improve its accountability and democratic legitimacy by engaging more with civil society and fostering a global constituency.[72] In an effort to enhance transparency, in 2016 the organization held its first public debate between candidates for Secretary-General.[73] On 1 January 2017, Portuguese diplomat António Guterres, who previously served as UN High Commissioner for Refugees, became the ninth Secretary-General. Guterres has highlighted several key goals for his administration, including an emphasis on diplomacy for preventing conflicts, more effective peacekeeping efforts, and streamlining the organization to be more responsive and versatile to global needs.[74]
+The UN system is based on five principal organs: the General Assembly, the Security Council, the Economic and Social Council (ECOSOC), the International Court of Justice and the UN Secretariat.[75] A sixth principal organ, the Trusteeship Council, suspended operations on 1 November 1994, upon the independence of Palau, the last remaining UN trustee territory.[76]
+Four of the five principal organs are located at the main UN Headquarters in New York City.[77] The International Court of Justice is located in The Hague, while other major agencies are based in the UN offices at Geneva,[78] Vienna,[79] and Nairobi.[80] Other UN institutions are located throughout the world. The six official languages of the UN, used in intergovernmental meetings and documents, are Arabic, Chinese, English,  French, Russian, and Spanish.[81] On the basis of the Convention on the Privileges and Immunities of the United Nations, the UN and its agencies are immune from the laws of the countries where they operate, safeguarding the UN's impartiality with regard to the host and member countries.[82]
+Below the six organs sit, in the words of the author Linda Fasulo, "an amazing collection of entities and organizations, some of which are actually older than the UN itself and operate with almost complete independence from it".[83] These include specialized agencies, research, and training institutions, programs and funds, and other UN entities.[84]
+The UN obeys the Noblemaire principle, which is binding on any organization that belongs to the UN system. This principle calls for salaries that will draw and keep citizens of countries where salaries are highest, and also calls for equal pay for work of equal value independent of the employee's nationality.[85][86] In practice, the ICSC takes reference to the highest-paying national civil service.[87] Staff salaries are subject to an internal tax that is administered by the UN organizations.[85][88]
+The General Assembly is the main deliberative assembly of the UN. Composed of all UN member states, the assembly meets in regular yearly sessions, but emergency sessions can also be called.[90] The assembly is led by a president, elected from among the member states on a rotating regional basis, and 21 vice-presidents.[91] The first session convened 10 January 1946 in the Methodist Central Hall in London and included representatives of 51 nations.[28]
+When the General Assembly decides on important questions such as those on peace and security, admission of new members and budgetary matters, a two-thirds majority of those present and voting is required.[92][93] All other questions are decided by a majority vote. Each member country has one vote. Apart from the approval of budgetary matters, resolutions are not binding on the members. The Assembly may make recommendations on any matters within the scope of the UN, except matters of peace and security that are under consideration by the Security Council.[90]
+Draft resolutions can be forwarded to the General Assembly by its six main committees:[94]
+As well as by the following two committees:
+The Security Council is charged with maintaining peace and security among countries. While other organs of the UN can only make "recommendations" to member states, the Security Council has the power to make binding decisions that member states have agreed to carry out, under the terms of Charter Article 25.[95] The decisions of the council are known as United Nations Security Council resolutions.[96]
+The Security Council is made up of fifteen member states, consisting of five permanent members—China, France, Russia, the United Kingdom, and the United States—and ten non-permanent members elected for two-year terms by the General Assembly (with end of term date)—Belgium (term ends 2020), Dominican Republic (2020), Estonia (2021), Germany (2020), Indonesia (2020), Niger (2021), Saint Vincent and the Grenadines (2021), South Africa (2020), Tunisia (2021), and Vietnam (2021).[97] The five permanent members hold veto power over UN resolutions, allowing a permanent member to block adoption of a resolution, though not debate. The ten temporary seats are held for two-year terms, with five member states per year voted in by the General Assembly on a regional basis.[98] The presidency of the Security Council rotates alphabetically each month.[99]
+The UN Secretariat is headed by the secretary-general, assisted by the deputy secretary-general and a staff of international civil servants worldwide.[100] It provides studies, information, and facilities needed by UN bodies for their meetings. It also carries out tasks as directed by the Security Council, the General Assembly, the Economic and Social Council, and other UN bodies.[101]
+The secretary-general acts as the de facto spokesperson and leader of the UN. The position is defined in the UN Charter as the organization's "chief administrative officer".[102] Article 99 of the charter states that the secretary-general can bring to the Security Council's attention "any matter which in his opinion may threaten the maintenance of international peace and security", a phrase that Secretaries-General since Trygve Lie have interpreted as giving the position broad scope for action on the world stage.[103] The office has evolved into a dual role of an administrator of the UN organization and a diplomat and mediator addressing disputes between member states and finding consensus to global issues.[104]
+The secretary-general is appointed by the General Assembly, after being recommended by the Security Council, where the permanent members have veto power. There are no specific criteria for the post, but over the years it has become accepted that the post shall be held for one or two terms of five years.[105] The current Secretary-General is António Guterres, who replaced Ban Ki-moon in 2017.
+The International Court of Justice (ICJ), located in The Hague, in the Netherlands, is the primary judicial organ of the UN. Established in 1945 by the UN Charter, the Court began work in 1946 as the successor to the Permanent Court of International Justice. The ICJ is composed of 15 judges who serve 9-year terms and are appointed by the General Assembly; every sitting judge must be from a different nation.[107][108]
+It is based in the Peace Palace in The Hague, sharing the building with the Hague Academy of International Law, a private centre for the study of international law. The ICJ's primary purpose is to adjudicate disputes among states. The court has heard cases related to war crimes, illegal state interference, ethnic cleansing, and other issues.[109] The ICJ can also be called upon by other UN organs to provide advisory opinions.[107]
+It is the only organ that is not located in New York.
+The Economic and Social Council (ECOSOC) assists the General Assembly in promoting international economic and social co-operation and development. ECOSOC has 54 members, who are elected by the General Assembly for a three-year term. The president is elected for a one-year term and chosen amongst the small or middle powers represented on ECOSOC. The council has one annual meeting in July, held in either New York or Geneva. Viewed as separate from the specialized bodies it co-ordinates, ECOSOC's functions include information gathering, advising member nations, and making recommendations.[110][111] Owing to its broad mandate of co-ordinating many agencies, ECOSOC has at times been criticized as unfocused or irrelevant.[110][112]
+ECOSOC's subsidiary bodies include the United Nations Permanent Forum on Indigenous Issues, which advises UN agencies on issues relating to indigenous peoples; the United Nations Forum on Forests, which coordinates and promotes sustainable forest management; the United Nations Statistical Commission, which co-ordinates information-gathering efforts between agencies; and the Commission on Sustainable Development, which co-ordinates efforts between UN agencies and NGOs working towards sustainable development. ECOSOC may also grant consultative status to non-governmental organizations;[110] by 2004, more than 2,200 organizations had received this status.[113]
+The UN Charter stipulates that each primary organ of the United Nations can establish various specialized agencies to fulfil its duties.[114] Some best-known agencies are the International Atomic Energy Agency, the Food and Agriculture Organization, UNESCO (United Nations Educational, Scientific and Cultural Organization), the World Bank, and the World Health Organization (WHO). The UN performs most of its humanitarian work through these agencies. Examples include mass vaccination programmes (through WHO), the avoidance of famine and malnutrition (through the work of the WFP), and the protection of vulnerable and displaced people (for example, by UNHCR).[115]
+With the addition of South Sudan 14 July 2011,[5] there are 193 UN member states, including all undisputed independent states apart from Vatican City.[116][c]
+The UN Charter outlines the rules for membership:
+In addition, there are two non-member observer states of the United Nations General Assembly: the Holy See (which holds sovereignty over Vatican City) and the State of Palestine.[118] The Cook Islands and Niue, both states in free association with New Zealand, are full members of several UN specialized agencies and have had their "full treaty-making capacity" recognized by the Secretariat.[119]
+The Group of 77 (G77) at the UN is a loose coalition of developing nations, designed to promote its members' collective economic interests and create an enhanced joint negotiating capacity in the UN. Seventy-seven nations founded the organization, but by November 2013 the organization had since expanded to 133 member countries.[120] The group was founded 15 June 1964 by the "Joint Declaration of the Seventy-Seven Countries" issued at the United Nations Conference on Trade and Development (UNCTAD). The group held its first major meeting in Algiers in 1967, where it adopted the Charter of Algiers and established the basis for permanent institutional structures.[121]  With the adoption of the New International Economic Order by developing countries in the 1970s, the work of the G77 spread throughout the UN system.
+The UN, after approval by the Security Council, sends peacekeepers to regions where armed conflict has recently ceased or paused to enforce the terms of peace agreements and to discourage combatants from resuming hostilities. Since the UN does not maintain its own military, peacekeeping forces are voluntarily provided by member states. These soldiers are sometimes nicknamed "Blue Helmets" for their distinctive gear.[122][123] The peacekeeping force as a whole received the Nobel Peace Prize in 1988.[124]
+In September 2013, the UN had peacekeeping soldiers deployed on 15 missions. The largest was the United Nations Organization Stabilization Mission in the Democratic Republic of the Congo (MONUSCO), which included 20,688 uniformed personnel. The smallest, United Nations Military Observer Group in India and Pakistan (UNMOGIP), included 42 uniformed personnel responsible for monitoring the ceasefire in Jammu and Kashmir. UN peacekeepers with the United Nations Truce Supervision Organization (UNTSO) have been stationed in the Middle East since 1948, the longest-running active peacekeeping mission.[125]
+A study by the RAND Corporation in 2005 found the UN to be successful in two out of three peacekeeping efforts. It compared efforts at nation-building by the UN to those of the United States, and found that seven out of eight UN cases are at peace, as compared with four out of eight US cases at peace.[126] Also in 2005, the Human Security Report documented a decline in the number of wars, genocides, and human rights abuses since the end of the Cold War, and presented evidence, albeit circumstantial, that international activism—mostly spearheaded by the UN—has been the main cause of the decline in armed conflict in that period.[127] Situations in which the UN has not only acted to keep the peace but also intervened include the Korean War (1950–53) and the authorization of intervention in Iraq after the Gulf War (1990–91).[128]
+The UN has also drawn criticism for perceived failures. In many cases, member states have shown reluctance to achieve or enforce Security Council resolutions. Disagreements in the Security Council about military action and intervention are seen as having failed to prevent the Bangladesh genocide in 1971,[129] the Cambodian genocide in the 1970s,[130] and the Rwandan genocide in 1994.[131] Similarly, UN inaction is blamed for failing to either prevent the Srebrenica massacre in 1995 or complete the peacekeeping operations in 1992–93 during the Somali Civil War.[132] UN peacekeepers have also been accused of child rape, soliciting prostitutes, and sexual abuse during various peacekeeping missions in the Democratic Republic of the Congo,[133] Haiti,[134] Liberia,[135] Sudan and what is now South Sudan,[136] Burundi, and Ivory Coast.[137] Scientists cited UN peacekeepers from Nepal as the likely source of the 2010–13 Haiti cholera outbreak, which killed more than 8,000 Haitians following the 2010 Haiti earthquake.[138]
+In addition to peacekeeping, the UN is also active in encouraging disarmament. Regulation of armaments was included in the writing of the UN Charter in 1945 and was envisioned as a way of limiting the use of human and economic resources for their creation.[95] The advent of nuclear weapons came only weeks after the signing of the charter, resulting in the first resolution of the first General Assembly meeting calling for specific proposals for "the elimination from national armaments of atomic weapons and of all other major weapons adaptable to mass destruction".[139] The UN has been involved with arms-limitation treaties, such as the Outer Space Treaty (1967), the Treaty on the Non-Proliferation of Nuclear Weapons (1968), the Seabed Arms Control Treaty (1971), the Biological Weapons Convention (1972), the Chemical Weapons Convention (1992), and the Ottawa Treaty (1997), which prohibits landmines.[140] Three UN bodies oversee arms proliferation issues: the International Atomic Energy Agency, the Organisation for the Prohibition of Chemical Weapons, and the Comprehensive Nuclear-Test-Ban Treaty Organization Preparatory Commission.[141]
+One of the UN's primary purposes is "promoting and encouraging respect for human rights and for fundamental freedoms for all without distinction as to race, sex, language, or religion", and member states pledge to undertake "joint and separate action" to protect these rights.[114][142]
+In 1948, the General Assembly adopted a Universal Declaration of Human Rights, drafted by a committee headed by American diplomat and activist Eleanor Roosevelt, and including the French lawyer René Cassin. The document proclaims basic civil, political, and economic rights common to all human beings, though its effectiveness towards achieving these ends has been disputed since its drafting.[143] The Declaration serves as a "common standard of achievement for all peoples and all nations" rather than a legally binding document, but it has become the basis of two binding treaties, the 1966 International Covenant on Civil and Political Rights and International Covenant on Economic, Social and Cultural Rights.[144] In practice, the UN is unable to take significant action against human rights abuses without a Security Council resolution, though it does substantial work in investigating and reporting abuses.[145]
+In 1979, the General Assembly adopted the Convention on the Elimination of All Forms of Discrimination against Women, followed by the Convention on the Rights of the Child in 1989.[146] With the end of the Cold War, the push for human rights action took on new impetus.[147] The United Nations Commission on Human Rights was formed in 1993 to oversee human rights issues for the UN, following the recommendation of that year's World Conference on Human Rights. Jacques Fomerand, a scholar of the UN, describes this organization's mandate as "broad and vague", with only "meagre" resources to carry it out.[148] In 2006, it was replaced by a Human Rights Council consisting of 47 nations.[149] Also in 2006, the General Assembly passed a Declaration on the Rights of Indigenous Peoples,[150] and in 2011 it passed its first resolution recognizing the rights of LGBT people.[151]
+Other UN bodies responsible for women's rights issues include United Nations Commission on the Status of Women, a commission of ECOSOC founded in 1946; the United Nations Development Fund for Women, created in 1976; and the United Nations International Research and Training Institute for the Advancement of Women, founded in 1979.[152] The UN Permanent Forum on Indigenous Issues, one of three bodies with a mandate to oversee issues related to indigenous peoples, held its first session in 2002.[153]
+Millennium Development Goals[154]
+Another primary purpose of the UN is "to achieve international cooperation in solving international problems of an economic, social, cultural, or humanitarian character".[142] Numerous bodies have been created to work towards this goal, primarily under the authority of the General Assembly and ECOSOC.[155] In 2000, the 192 UN member states agreed to achieve eight Millennium Development Goals by 2015.[156] The Sustainable Development Goals were launched in 2015 to succeed the Millennium Development Goals.[71] The SDGs have an associated financing framework called the Addis Ababa Action Agenda.
+The UN Development Programme (UNDP), an organization for grant-based technical assistance founded in 1945, is one of the leading bodies in the field of international development. The organization also publishes the UN Human Development Index, a comparative measure ranking countries by poverty, literacy, education, life expectancy, and other factors.[157][158] The Food and Agriculture Organization (FAO), also founded in 1945, promotes agricultural development and food security.[159] UNICEF (the United Nations Children's Fund) was created in 1946 to aid European children after the Second World War and expanded its mission to provide aid around the world and to uphold the convention on the Rights of the Child.[160][161]
+The World Bank Group and International Monetary Fund (IMF) are independent, specialized agencies and observers within the UN framework, according to a 1947 agreement. They were initially formed separately from the UN through the Bretton Woods Agreement in 1944.[162] The World Bank provides loans for international development, while the IMF promotes international economic co-operation and gives emergency loans to indebted countries.[163]
+The World Health Organization (WHO), which focuses on international health issues and disease eradication, is another of the UN's largest agencies. In 1980, the agency announced that the eradication of smallpox had been completed. In subsequent decades, WHO largely eradicated polio, river blindness, and leprosy.[164] The Joint United Nations Programme on HIV/AIDS (UNAIDS), begun in 1996, co-ordinates the organization's response to the AIDS epidemic.[165] The UN Population Fund, which also dedicates part of its resources to combating HIV, is the world's largest source of funding for reproductive health and family planning services.[166]
+Along with the International Red Cross and Red Crescent Movement, the UN often takes a leading role in co-ordinating emergency relief.[167] The World Food Programme (WFP), created in 1961, provides food aid in response to famine, natural disasters, and armed conflict. The organization reports that it feeds an average of 90 million people in 80 nations each year.[167][168] The Office of the United Nations High Commissioner for Refugees (UNHCR), established in 1950, works to protect the rights of refugees, asylum seekers, and stateless people.[169] UNHCR and WFP programmes are funded by voluntary contributions from governments, corporations, and individuals, though the UNHCR's administrative costs are paid for by the UN's primary budget.[170]
+Since the UN's creation, over 80 colonies have attained independence. The General Assembly adopted the Declaration on the Granting of Independence to Colonial Countries and Peoples in 1960 with no votes against but abstentions from all major colonial powers. The UN works towards decolonization through groups including the UN Committee on Decolonization, created in 1962.[171] The committee lists seventeen remaining "Non-Self-Governing Territories", the largest and most populous of which is Western Sahara.[172]
+Beginning with the formation of the UN Environmental Programme (UNEP) in 1972, the UN has made environmental issues a prominent part of its agenda. A lack of success in the first two decades of UN work in this area led to the 1992 Earth Summit in Rio de Janeiro, Brazil, which sought to give new impetus to these efforts.[173] In 1988, the UNEP and the World Meteorological Organization (WMO), another UN organization, established the Intergovernmental Panel on Climate Change, which assesses and reports on research on global warming.[174] The UN-sponsored Kyoto Protocol, signed in 1997, set legally binding emissions reduction targets for ratifying states.[175]
+The UN also declares and co-ordinates international observances, periods of time to observe issues of international interest or concern. Examples include World Tuberculosis Day, Earth Day, and the International Year of Deserts and Desertification.[176]
+The UN is financed from assessed and voluntary contributions from member states. The General Assembly approves the regular budget and determines the assessment for each member. This is broadly based on the relative capacity of each country to pay, as measured by its gross national income (GNI), with adjustments for external debt and low per capita income.[178] The two-year budget for 2012–13 was $5.512 billion in total.[179]
+The Assembly has established the principle that the UN should not be unduly dependent on any one member to finance its operations. Thus, there is a "ceiling" rate, setting the maximum amount that any member can be assessed for the regular budget. In December 2000, the Assembly revised the scale of assessments in response to pressure from the United States. As part of that revision, the regular budget ceiling was reduced from 25% to 22%.[180] For the least developed countries (LDCs), a ceiling rate of 0.01% is applied.[178] In addition to the ceiling rates, the minimum amount assessed to any member nation (or "floor" rate) is set at 0.001% of the UN budget ($55,120 for the two year budget 2013–2014).[181]
+A large share of the UN's expenditure addresses its core mission of peace and security, and this budget is assessed separately from the main organizational budget.[182] The peacekeeping budget for the 2015–16 fiscal year was $8.27 billion, supporting 82,318 troops deployed in 15 missions around the world.[125] UN peace operations are funded by assessments, using a formula derived from the regular funding scale that includes a weighted surcharge for the five permanent Security Council members, who must approve all peacekeeping operations. This surcharge serves to offset discounted peacekeeping assessment rates for less developed countries.
+the largest contributors for the UN peacekeeping  financial operations for the period 2019–2021 are : the United States  27.89%  China 15.21%, Japan 8.56%, Germany 6.09% , the United Kingdom 5.78%, France 5.61%, Italy 3.30% and the Russian Federation 3.04%.[183]
+Special UN programmes not included in the regular budget, such as UNICEF and the World Food Programme, are financed by voluntary contributions from member governments, corporations, and private individuals.[184][185]
+A number of agencies and individuals associated with the UN have won the Nobel Peace Prize in recognition of their work. Two Secretaries-General, Dag Hammarskjöld, and Kofi Annan, were each awarded the prize (in 1961 and 2001, respectively), as were Ralph Bunche (1950), a UN negotiator, René Cassin (1968), a contributor to the Universal Declaration of Human Rights, and the US Secretary of State Cordell Hull (1945), the latter for his role in the organization's founding. Lester B. Pearson, the Canadian Secretary of State for External Affairs, was awarded the prize in 1957 for his role in organizing the UN's first peacekeeping force to resolve the Suez Crisis. UNICEF won the prize in 1965, the International Labour Organization in 1969, the UN Peace-Keeping Forces in 1988, the International Atomic Energy Agency (which reports to the UN) in 2005, and the UN-supported Organisation for the Prohibition of Chemical Weapons in 2013. The UN High Commissioner for Refugees was awarded in 1954 and 1981, becoming one of only two recipients to win the prize twice. The UN as a whole was awarded the prize in 2001, sharing it with Annan.[186] In 2007, IPCC received the prize "for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change."[187]
+Since its founding, there have been many calls for reform of the UN but little consensus on how to do so. Some want the UN to play a greater or more effective role in world affairs, while others want its role reduced to humanitarian work. There have also been numerous calls for the UN Security Council's membership to be increased, for different ways of electing the UN's Secretary-General, and for a UN Parliamentary Assembly. Jacques Fomerand states the most enduring divide in views of the UN is "the North–South split" between richer Northern nations and developing Southern nations. Southern nations tend to favour a more empowered UN with a stronger General Assembly, allowing them a greater voice in world affairs, while Northern nations prefer an economically laissez-faire UN that focuses on transnational threats such as terrorism.[188]
+After World War II, the French Committee of National Liberation was late to be recognized by the US as the government of France, and so the country was initially excluded from the conferences that created the new organization. The future French president Charles de Gaulle criticized the UN, famously calling it a machin ("contraption"), and was not convinced that a global security alliance would help maintain world peace, preferring direct defence treaties between countries.[189] Throughout the Cold War, both the US and USSR repeatedly accused the UN of favouring the other. In 1953, the USSR effectively forced the resignation of Trygve Lie, the Secretary-General, through its refusal to deal with him, while in the 1950s and 1960s, a popular US bumper sticker read, "You can't spell communism without U.N."[190] In a sometimes-misquoted statement, President George W. Bush stated in February 2003 (referring to UN uncertainty towards Iraqi provocations under the Saddam Hussein regime) that "free nations will not allow the UN to fade into history as an ineffective, irrelevant debating society."[191][192][193] In contrast, the French President, François Hollande, stated in 2012 that "France trusts the United Nations. She knows that no state, no matter how powerful, can solve urgent problems, fight for development and bring an end to all crises ... France wants the UN to be the centre of global governance."[194] Critics such as Dore Gold, an Israeli diplomat, Robert S. Wistrich, a British scholar, Alan Dershowitz, an American legal scholar, Mark Dreyfus, an Australian politician, and the Anti-Defamation League consider UN attention to Israel's treatment of Palestinians to be excessive.[195] In September 2015, Saudi Arabia's Faisal bin Hassan Trad has been elected Chair of the UN Human Rights Council panel that appoints independent experts,[196] a move criticized by human rights groups.[197][198]
+Since 1971, the Republic of China on Taiwan has been excluded from the UN and since then has always been rejected in new applications. Taiwanese citizens are also not allowed to enter the buildings of the United Nations with ROC passports. In this way, critics agree that the UN is failing its own development goals and guidelines. This criticism also brought pressure from the People's Republic of China, which regards the territories administered by the ROC as their own territory.[199][200]
+Critics have also accused the UN of bureaucratic inefficiency, waste, and corruption. In 1976, the General Assembly established the Joint Inspection Unit to seek out inefficiencies within the UN system. During the 1990s, the US withheld dues citing inefficiency and only started repayment on the condition that a major reforms initiative be introduced. In 1994, the Office of Internal Oversight Services (OIOS) was established by the General Assembly to serve as an efficiency watchdog.[201] In 1994, former Special Representative of the Secretary-General of the UN to Somalia Mohamed Sahnoun published "Somalia: The Missed Opportunities",[202] a book in which he analyses the reasons for the failure of the 1992 UN intervention in Somalia, showing that, between the start of the Somali civil war in 1988 and the fall of the Siad Barre regime in January 1991, the UN missed at least three opportunities to prevent major human tragedies; when the UN tried to provide humanitarian assistance, they were totally outperformed by NGOs, whose competence and dedication sharply contrasted with the UN's excessive caution and bureaucratic inefficiencies. If radical reform were not undertaken, warned Mohamed Sahnoun, then the UN would continue to respond to such crises with inept improvisation.[203] In 2004, the UN faced accusations that its recently ended Oil-for-Food Programme — in which Iraq had been allowed to trade oil for basic needs to relieve the pressure of sanctions — had suffered from widespread corruption, including billions of dollars of kickbacks. An independent inquiry created by the UN found that many of its officials had been involved, as well as raising "significant" questions about the role of Kojo Annan, the son of Kofi Annan.[204]
+In evaluating the UN as a whole, Jacques Fomerand writes that the "accomplishments of the United Nations in the last 60 years are impressive in their own terms. Progress in human development during the 20th century has been dramatic, and the UN and its agencies have certainly helped the world become a more hospitable and livable place for millions."[205] Evaluating the first 50 years of the UN's history, the author Stanley Meisler writes that "the United Nations never fulfilled the hopes of its founders, but it accomplished a great deal nevertheless", citing its role in decolonization and its many successful peacekeeping efforts.[206] The British historian Paul Kennedy states that while the organization has suffered some major setbacks, "when all its aspects are considered, the UN has brought great benefits to our generation and ... will bring benefits to our children's and grandchildren's generations as well."[207]
+Core features of the UN apparatus, such as the veto privileges of some nations in the Security Council, are often described as fundamentally undemocratic, contrary to the UN mission, and as a main cause of inaction on genocides and crimes against humanity.[208][209]
+The United Nations has inspired the extracurricular activity Model United Nations (MUN). MUN is a simulation of United Nations activity based on the UN agenda and following UN procedure. MUN is usually attended by high school and university students who organize conferences to simulate the various UN committees to discuss important issues of the day.[210] Today Model United Nations educates tens of thousands on United Nations activity around the world. Model United Nations has many famous and notable alumni, such as former Secretary-General of the United Nations Ban Ki-moon.[211]

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+OpenOffice.org (OOo), commonly known as OpenOffice, is a discontinued open-source office suite. It was an open-sourced version of the earlier StarOffice, which Sun Microsystems acquired in 1999 for internal use.
+OpenOffice included a word processor (Writer), a spreadsheet (Calc), a presentation application (Impress), a drawing application (Draw), a formula editor (Math), and a database management application (Base).[9] Its default file format was the OpenDocument Format (ODF), an ISO/IEC standard, which originated with OpenOffice.org. It could also read a wide variety of other file formats, with particular attention to those from Microsoft Office.
+Sun open-sourced the OpenOffice suite in July 2000 as a competitor to Microsoft Office,[10][11] releasing version 1.0 on 1 May 2002.[1]
+In 2011, Oracle Corporation, the then-owner of Sun, announced that it would no longer offer a commercial version of the suite[12] and donated the project to the Apache Foundation.[13][14]
+Apache renamed the software Apache OpenOffice.[15] Other active successor projects include LibreOffice (the most actively developed[16][17][18]) and NeoOffice (commercial, and available only for macOS).
+OpenOffice.org was primarily developed for Linux, Microsoft Windows and Solaris, and later for OS X, with ports to other operating systems. It was distributed under the GNU Lesser General Public License version 3 (LGPL); early versions were also available under the Sun Industry Standards Source License (SISSL).
+OpenOffice.org originated as StarOffice, a proprietary office suite developed by German company Star Division from 1985 on. In August 1999, Star Division was acquired by Sun Microsystems[19][20] for US$59.5 million,[21] as it was supposedly cheaper than licensing Microsoft Office for 42,000 staff.[22]
+On 19 July 2000 at OSCON, Sun Microsystems announced it would make the source code of StarOffice available for download with the intention of building an open-source development community around the software and of providing a free and open alternative to Microsoft Office.[10][11][23] The new project was known as OpenOffice.org,[24] and the code was released as open source on 13 October 2000.[25] The first public preview release was Milestone Build 638c, released in October 2001 (which quickly achieved 1 million downloads[19]); the final release of OpenOffice.org 1.0 was on 1 May 2002.[1]
+OpenOffice.org became the standard office suite on many Linux distros and spawned many derivative versions. It quickly became noteworthy competition to Microsoft Office,[26][27] achieving 14% penetration in the large enterprise market by 2004.[28]
+The OpenOffice.org XML file format – XML in a ZIP archive, easily machine-processable – was intended by Sun to become a standard interchange format for office documents,[29] to replace the different binary formats for each application that had been usual until then. Sun submitted the format to the Organization for the Advancement of Structured Information Standards (OASIS) in 2002 and it was adapted to form the OpenDocument standard in 2005,[30] which was ratified as ISO 26300 in 2006.[31] It was made OpenOffice.org's native format from version 2 on. Many governments and other organisations adopted OpenDocument, particularly given there was a free implementation of it readily available.
+Development of OpenOffice.org was sponsored primarily by Sun Microsystems, which used the code as the basis for subsequent versions of StarOffice. Developers who wished to contribute code were required to sign a Contributor Agreement[32][33] granting joint ownership of any contributions to Sun (and then Oracle), in support of the StarOffice business model.[34] This was controversial for many years.[23][35][36][37][38] An alternative Public Documentation Licence (PDL)[39] was also offered for documentation not intended for inclusion or integration into the project code base.[40]
+After acquiring Sun in January 2010, Oracle Corporation continued developing OpenOffice.org and StarOffice, which it renamed Oracle Open Office,[41] though with a reduction in assigned developers.[42] Oracle's lack of activity on or visible commitment to OpenOffice.org had also been noted by industry observers.[43] In September 2010, the majority[44][45] of outside OpenOffice.org developers left the project,[46][47] due to concerns over Sun and then Oracle's management of the project[48][49][50] and Oracle's handling of its open source portfolio in general,[51] to form The Document Foundation (TDF). TDF released the fork LibreOffice in January 2011,[52] which most Linux distributions soon moved to.[53][54][55][56] In April 2011, Oracle stopped development of OpenOffice.org[12] and fired the remaining Star Division development team.[34][57] Its reasons for doing so were not disclosed; some speculate that it was due to the loss of mindshare with much of the community moving to LibreOffice[58] while others suggest it was a commercial decision.[34]
+In June 2011, Oracle contributed the trademarks to the Apache Software Foundation.[59] It also contributed Oracle-owned code to Apache for relicensing under the Apache License,[60] at the suggestion of IBM (to whom Oracle had contractual obligations concerning the code),[23][61] as IBM did not want the code put under a copyleft license.[62] This code drop formed the basis for the Apache OpenOffice project.[63]
+During Sun's sponsorship, the OpenOffice.org project was governed by the Community Council, comprising OpenOffice.org community members. The Community Council suggested project goals and coordinated with producers of derivatives on long-term development planning issues.[64][65][66]
+Both Sun and Oracle are claimed to have made decisions without consulting the Council or in contravention to the council's recommendations,[67][68] leading to the majority of outside developers leaving for LibreOffice.[48] Oracle demanded in October 2010 that all Council members involved with the Document Foundation step down,[69] leaving the Community Council composed only of Oracle employees.[70]
+The project and software were informally referred to as OpenOffice since the Sun release, but since this term is a trademark held by Open Office Automatisering in Benelux since 1999,[71][72] OpenOffice.org was its formal name.[73]
+Due to a similar trademark issue (a Rio de Janeiro company that owned that trademark in Brazil), the Brazilian Portuguese version of the suite was distributed under the name BrOffice.org from 2004, with BrOffice.Org being the name of the associated local nonprofit from 2006.[74] (BrOffice.org moved to LibreOffice in December 2010.[75])
+OpenOffice.org 1.0 was launched under the following mission statement:[11]
+The mission of OpenOffice.org is to create, as a community, the leading international office suite that will run on all major platforms and provide access to all functionality and data through open-component based APIs and an XML-based file format.
+The suite contained no personal information manager, email client or calendar application analogous to Microsoft Outlook, despite one having been present in StarOffice 5.2. Such functionality was frequently requested.[78] The OpenOffice.org Groupware project, intended to replace Outlook and Microsoft Exchange Server, spun off in 2003 as OpenGroupware.org,[79] which is now SOGo. The project considered bundling Mozilla Thunderbird and Mozilla Lightning for OpenOffice.org 3.0.[78]
+The last version, 3.4 Beta 1, was available for IA-32 versions of Windows 2000 Service Pack 2 or later, Linux (IA-32 and x64), Solaris and OS X 10.4 or later, and the SPARC version of Solaris.[4][80]
+The latest versions of OpenOffice.org on other operating systems were:[81]
+OpenOffice.org included OpenSymbol, DejaVu,[84] the Liberation fonts (from 2.4) and the Gentium fonts (from 3.2).[85][86][87] Versions up to 2.3 included the Bitstream Vera fonts.[84][88] OpenOffice.org also used the default fonts of the running operating system.
+Fontwork is a feature that allows users to create stylized text with special effects differing from ordinary text with the added features of gradient colour fills, shaping, letter height, and character spacing. It is similar to WordArt used by Microsoft Word.  When OpenOffice.org saved documents in Microsoft Office file format, all Fontwork was converted into WordArt.[89][90]
+From version 2.0.4, OpenOffice.org supported third-party extensions.[91] As of April 2011, the OpenOffice Extension Repository listed more than 650 extensions.[92] Another list was maintained by the Free Software Foundation.[93][94]
+OpenOffice.org included OpenOffice Basic, a programming language similar to Microsoft Visual Basic for Applications (VBA). OpenOffice Basic was available in Writer, Calc and Base.[95] OpenOffice.org also had some Microsoft VBA macro support.
+OpenOffice.org could interact with databases (local or remote) using ODBC (Open Database Connectivity), JDBC (Java Database Connectivity) or SDBC (StarOffice Database Connectivity).[96]
+From Version 2.0 onward, OpenOffice.org used ISO/IEC 26300:2006[97] OpenDocument as its native format. Versions 2.0–2.3.0 default to the ODF 1.0 file format; versions 2.3.1–2.4.3 default to ODF 1.1; versions 3.0 onward default to ODF 1.2.
+OpenOffice.org 1 used OpenOffice.org XML as its native format. This was contributed to OASIS and OpenDocument was developed from it.[98]
+OpenOffice.org also claimed support for the following formats:[99][100]
+OpenOffice.org converted all external formats to and from an internal XML representation.
+The OpenOffice.org API was based on a component technology known as Universal Network Objects (UNO). It consisted of a wide range of interfaces defined in a CORBA-like interface description language.
+OpenOffice.org 1.0 was criticized for not having the look and feel of applications developed natively for the platforms on which it runs. Starting with version 2.0, OpenOffice.org used native widget toolkit, icons, and font-rendering libraries on GNOME, KDE and Windows.[104][105][106]
+The issue had been particularly pronounced on Mac OS X. Early versions of OpenOffice.org required the installation of X11.app or XDarwin (though the NeoOffice port supplied a native interface). Versions since 3.0 ran natively using Apple's Aqua GUI.[107]
+Although originally written in C++, OpenOffice.org became increasingly reliant on the Java Runtime Environment, even including a bundled JVM.[108] OpenOffice.org was criticized by the Free Software Foundation for its increasing dependency on Java, which was not free software.[109]
+The issue came to the fore in May 2005, when Richard Stallman appeared to call for a fork of the application in a posting on the Free Software Foundation website.[109] OpenOffice.org adopted a development guideline that future versions of OpenOffice.org would run on free implementations of Java and fixed the issues which previously prevented OpenOffice.org 2.0 from using free-software Java implementations.[110]
+On 13 November 2006, Sun committed to releasing Java under the GNU General Public License[111] and had released a free software Java, OpenJDK, by May 2007.
+In 2006, Lt. Col. Eric Filiol of the  Laboratoire de Virologie et de Cryptologie de l'ESAT demonstrated security weaknesses, in particular within macros.[112][113][114] In 2006, Kaspersky Lab demonstrated a proof of concept virus, "Stardust", for OpenOffice.org.[115] This showed OpenOffice.org viruses are possible, but there is no known virus "in the wild".
+As of October 2011, Secunia reported no known unpatched security flaws for the software.[116] A vulnerability in the inherited OpenOffice.org codebase was found and fixed in LibreOffice in October 2011[117] and Apache OpenOffice in May 2012.[118]
+The preview, Milestone 638c, was released October 2001.[19] OpenOffice.org 1.0 was released under both the LGPL and the SISSL[23] for Windows, Linux and Solaris[135] on 1 May 2002.[1][136] The version for Mac OS X (with X11 interface) was released on 23 June 2003.[137][138]
+OpenOffice.org 1.1 introduced One-click Export to PDF and Export presentations to Flash (.SWF). It also allowed third-party addons.[101]
+OpenOffice.org was used in 2005 by The Guardian to illustrate what it saw as the limitations of open-source software.[139]
+Work on version 2.0 began in early 2003 with the following goals (the "Q Product Concept"): better interoperability with Microsoft Office; improved speed and lower memory usage; greater scripting capabilities; better integration, particularly with GNOME; a more usable database; digital signatures; and improved usability.[140] It would also be the first version to default to OpenDocument. Sun released the first beta version on 4 March 2005.[141]
+On 2 September 2005, Sun announced that it was retiring SISSL to reduce license proliferation,[142] though some press analysts felt it was so that IBM could not reuse OpenOffice.org code without contributing back.[23] Versions after 2.0 beta 2 would use only the LGPL.[7]
+On 20 October 2005, OpenOffice.org 2.0 was released.[122] 2.0.1 was released eight weeks later, fixing minor bugs and introducing new features. As of the 2.0.3 release, OpenOffice.org changed its release cycle from 18 months to releasing updates every three months.[143]
+The OpenOffice.org 2 series attracted considerable press attention.[144][145][146][147][148][149][150][151] A PC Pro review awarded it 6 stars out of 6 and stated: "Our pick of the low-cost office suites has had a much-needed overhaul, and now battles Microsoft in terms of features, not just price."[152] Federal Computer Week listed OpenOffice.org as one of the "5 stars of open-source products",[153] noting in particular the importance of OpenDocument. ComputerWorld reported that for large government departments, migration to OpenOffice.org 2.0 cost one tenth of the price of upgrading to Microsoft Office 2007.[154]
+On 13 October 2008, version 3.0 was released, featuring the ability to import (though not export) Office Open XML documents, support for ODF 1.2, improved VBA macros, and a native interface port for OS X. It also introduced the new Start Center[130] and upgraded to LGPL version 3 as its license.[155]
+Version 3.2 included support for PostScript-based OpenType fonts. It warned users when ODF 1.2 Extended features had been used. An improvement to the document integrity check determined if an ODF document conformed to the ODF specification and offered a repair if necessary. Calc and Writer both reduced "cold start" time by 46% compared to version 3.0.[156] 3.2.1 was the first Oracle release.[134]
+Version 3.3, the last Oracle version, was released in January 2011.[157] New features include an updated print form, a FindBar and interface improvements for Impress.[158][159] The commercial version, Oracle Open Office 3.3 (StarOffice renamed), based on the beta, was released on 15 December 2010, as was the single release of Oracle Cloud Office (a proprietary product from an unrelated codebase).[41][160]
+A beta version of OpenOffice.org 3.4 was released on 12 April 2011, including new SVG import, improved ODF 1.2 support, and spreadsheet functionality.[4][2][161]
+Before the final version of OpenOffice.org 3.4 could be released, Oracle cancelled its sponsorship of development[12] and fired the remaining Star Division development team.[34][57]
+Problems arise in estimating the market share of OpenOffice.org because it could be freely distributed via download sites (including mirror sites), peer-to-peer networks, CDs, Linux distributions and so forth. The project tried to capture key adoption data in a market-share analysis,[162] listing known distribution totals, known deployments and conversions and analyst statements and surveys.
+According to Valve, as of July 2010, 14.63% of Steam users had OpenOffice.org installed on their machines.[163]
+A market-share analysis conducted by a web analytics service in 2010, based on over 200,000 Internet users, showed a wide range of adoption in different countries:[164] 0.2% in China, 9% in the US and the UK and over 20% in Poland, the Czech Republic, and Germany.
+Although Microsoft Office retained 95% of the general market — as measured by revenue — as of August 2007,[165] OpenOffice.org and StarOffice had secured 15–20% of the business market as of 2004[166][167] and a 2010 University of Colorado at Boulder study reported that OpenOffice.org had reached a point where it had an "irreversible" installed user base and that it would continue to grow.[168]
+The project claimed more than 98 million downloads as of September 2007[169] and 300 million total to the release of version 3.2 in February 2010.[170] The project claimed over one hundred million downloads for the OpenOffice.org 3 series within a year of release.[171]
+Large-scale users of OpenOffice.org included Singapore's Ministry of Defence,[172] and Banco do Brasil.[173] As of 2006[update] OpenOffice.org was the official office suite for the French Gendarmerie.[162]
+In India, several government organizations such as ESIC, IIT Bombay, National Bank for Agriculture and Rural Development, the Supreme Court of India, ICICI Bank,[174] and the Allahabad High Court,[175] which use Linux, completely relied on OpenOffice.org for their administration.
+In Japan, conversions from Microsoft Office to OpenOffice.org included many municipal offices: Sumoto, Hyōgo in 2004,[176] Ninomiya, Tochigi in 2006,[177][178] Aizuwakamatsu, Fukushima in 2008[179] (and to LibreOffice as of 2012[180]), Shikokuchūō, Ehime in 2009,[181] Minoh, Osaka in 2009[182] Toyokawa, Aichi,[183] Fukagawa, Hokkaido[184] and Katano, Osaka[185] in 2010 and Ryūgasaki, Ibaraki in 2011.[186] Corporate conversions included Assist in 2007[187] (and to LibreOffice on Ubuntu in 2011[188]), Sumitomo Electric Industries in 2008[189] (and to LibreOffice in 2012[190]), Toho Co., Ltd. in 2009[191][192] and Shinsei Financial Co., Ltd. in 2010.[193] Assist also provided support services for OpenOffice.org.[191][193]
+In July 2007, Everex, a division of First International Computer and the 9th-largest PC supplier in the U.S., began shipping systems preloaded with OpenOffice.org 2.2 into Wal-Mart, K-mart and Sam's Club outlets in North America.[194]
+A number of open source and proprietary products derive at least some code from OpenOffice.org, including AndrOpen Office,[195] Apache OpenOffice, ChinaOffice, Co-Create Office, EuroOffice 2005,[196] Go-oo, KaiOffice, IBM Lotus Symphony, IBM Workplace, Jambo OpenOffice (the first office suite in Swahili),[197][198][199] LibreOffice, MagyarOffice, MultiMedia Office, MYOffice 2007, NeoOffice, NextOffice, OfficeOne, OfficeTLE, OOo4Kids,[200] OpenOfficePL, OpenOffice.org Portable,[201] OpenOfficeT7, OpenOffice.ux.pl, OxOffice,[202] OxygenOffice Professional,[203][204] Pladao Office,[205] PlusOffice Mac,[206] RedOffice,[37][129][207] RomanianOffice, StarOffice/Oracle Open Office, SunShine Office, ThizOffice, UP Office, White Label Office,[208][209][210][211] WPS Office Storm (the 2004 edition of Kingsoft Office) and 602Office.[212]
+The OpenOffice.org website also listed a large variety of complementary products, including groupware systems.[213]
+Major derivatives include:
+In June 2011, Oracle contributed the OpenOffice.org code and trademarks to the Apache Software Foundation. The developer pool for the Apache project was proposed to be seeded by IBM employees, Linux distribution companies and public sector agencies.[214] IBM employees did the majority of the development,[215][216][217][218][219] including hiring ex-Star Division developers.[217] The Apache project removed or replaced as much code as possible from OpenOffice.org 3.4 beta 1, including fonts, under licenses unacceptable to Apache[220] and released 3.4.0 in May 2012.[118]
+The codebase for IBM's Lotus Symphony was donated to the Apache Software Foundation in 2012 and merged for Apache OpenOffice 4.0,[221] and Symphony was deprecated in favour of Apache OpenOffice.[218]
+While the project considers itself the unbroken continuation of OpenOffice.org,[222] others regard it as a fork,[23][215][216][223][224][225][226] or at the least a separate project.[227]
+In October 2014, Bruce Byfield, writing for Linux Magazine, said the project had "all but stalled [possibly] due to IBM's withdrawal from the project."[228] As of 2015[update], the project has no release manager,[229] and itself reports a lack of volunteer involvement and code contributions.[230] After ongoing problems with unfixed security vulnerabilities from 2015 onward,[231][232][233] in September 2016 the project started discussions on possibly retiring AOO.[234]
+Sun had stated in the original OpenOffice.org announcement in 2000 that the project would be run by a neutral foundation,[10] and put forward a more detailed proposal in 2001.[235] There were many calls to put this into effect over the ensuing years.[36][236][237][238] On 28 September 2010, in frustration at years of perceived neglect of the codebase and community by Sun and then Oracle,[68] members of the OpenOffice.org community announced a non-profit called The Document Foundation and a fork of OpenOffice.org named LibreOffice. Go-oo improvements were merged, and that project was retired in favour of LibreOffice.[239] The goal was to produce a vendor-independent office suite with ODF support and without any copyright assignment requirements.[240]
+Oracle was invited to become a member of the Document Foundation and was asked to donate the OpenOffice.org brand.[240][241] Oracle instead demanded that all members of the OpenOffice.org Community Council involved with the Document Foundation step down,[69] leaving the Council composed only of Oracle employees.[70]
+Most Linux distributions promptly replaced OpenOffice.org with LibreOffice;[53][54][55][56] Oracle Linux 6 also features LibreOffice rather than OpenOffice.org or Apache OpenOffice.[242][243][244] The project rapidly accumulated developers, development effort[245][246][247] and added features,[248] the majority of outside OpenOffice.org developers having moved to LibreOffice.[44][45][48] In March 2015, an LWN.net development comparison of LibreOffice with Apache OpenOffice concluded that "LibreOffice has won the battle for developer participation".[249]
+NeoOffice, an independent commercial port for Macintosh that tracked the main line of development, offered a native OS X Aqua user interface before OpenOffice.org did.[250] Later versions are derived from Go-oo, rather than directly from OpenOffice.org.[251] All versions from NeoOffice 3.1.1 to NeoOffice 2015 were based on OpenOffice.org 3.1.1, though latter versions included stability fixes from LibreOffice and Apache OpenOffice.[252] NeoOffice 2017 and later versions are fully based on LibreOffice.[253]
+The ooo-build patch set was started at Ximian in 2002, because Sun were slow to accept outside work on OpenOffice.org, even from corporate partners, and to make the build process easier on Linux. It tracked the main line of development and was not intended to constitute a fork.[254] Most Linux distributions used,[255] and worked together on,[256] ooo-build.
+Sun's contributions to OpenOffice.org had been declining for a number of years[236] and some developers were unwilling to assign copyright in their work to Sun,[38] particularly given the deal between Sun and IBM to license the code outside the LGPL.[34] On 2 October 2007, Novell announced that ooo-build would be available as a software package called Go-oo, not merely a patch set.[257] (The go-oo.org domain name had been in use by ooo-build as early as 2005.[258]) Sun reacted negatively, with Simon Phipps of Sun terming it "a hostile and competitive fork".[36] Many free software advocates worried that Go-oo was a Novell effort to incorporate Microsoft technologies, such as Office Open XML, that might be vulnerable to patent claims.[259] However, the office suite branded "OpenOffice.org" in most Linux distributions, having previously been ooo-build, soon in fact became Go-oo.[251][260][261]
+Go-oo also encouraged outside contributions, with rules similar to those later adopted for LibreOffice.[262] When LibreOffice forked, Go-oo was deprecated in favour of that project.
+OpenOffice Novell edition was a supported version of Go-oo.[263]
+The Workplace Managed Client in IBM Workplace 2.6 (23 January 2006[264]) incorporated code from OpenOffice.org 1.1.4,[23] the last version under the SISSL. This code was broken out into a separate application as Lotus Symphony (30 May 2008[265]), with a new interface based on Eclipse. Symphony 3.0 (21 October 2010[266]) was rebased on OpenOffice.org 3.0, with the code licensed privately from Sun. IBM's changes were donated to the Apache Software Foundation in 2012, Symphony was deprecated in favour of Apache OpenOffice[218] and its code was merged into Apache OpenOffice 4.0.[221]
+Sun used OpenOffice.org as a base for its commercial proprietary StarOffice application software, which was OpenOffice.org with some added proprietary components. Oracle bought Sun in January 2010 and quickly renamed StarOffice to Oracle Open Office.[267] Oracle discontinued development in April 2011.[12]

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+OpenOffice.org (OOo), commonly known as OpenOffice, is a discontinued open-source office suite. It was an open-sourced version of the earlier StarOffice, which Sun Microsystems acquired in 1999 for internal use.
+OpenOffice included a word processor (Writer), a spreadsheet (Calc), a presentation application (Impress), a drawing application (Draw), a formula editor (Math), and a database management application (Base).[9] Its default file format was the OpenDocument Format (ODF), an ISO/IEC standard, which originated with OpenOffice.org. It could also read a wide variety of other file formats, with particular attention to those from Microsoft Office.
+Sun open-sourced the OpenOffice suite in July 2000 as a competitor to Microsoft Office,[10][11] releasing version 1.0 on 1 May 2002.[1]
+In 2011, Oracle Corporation, the then-owner of Sun, announced that it would no longer offer a commercial version of the suite[12] and donated the project to the Apache Foundation.[13][14]
+Apache renamed the software Apache OpenOffice.[15] Other active successor projects include LibreOffice (the most actively developed[16][17][18]) and NeoOffice (commercial, and available only for macOS).
+OpenOffice.org was primarily developed for Linux, Microsoft Windows and Solaris, and later for OS X, with ports to other operating systems. It was distributed under the GNU Lesser General Public License version 3 (LGPL); early versions were also available under the Sun Industry Standards Source License (SISSL).
+OpenOffice.org originated as StarOffice, a proprietary office suite developed by German company Star Division from 1985 on. In August 1999, Star Division was acquired by Sun Microsystems[19][20] for US$59.5 million,[21] as it was supposedly cheaper than licensing Microsoft Office for 42,000 staff.[22]
+On 19 July 2000 at OSCON, Sun Microsystems announced it would make the source code of StarOffice available for download with the intention of building an open-source development community around the software and of providing a free and open alternative to Microsoft Office.[10][11][23] The new project was known as OpenOffice.org,[24] and the code was released as open source on 13 October 2000.[25] The first public preview release was Milestone Build 638c, released in October 2001 (which quickly achieved 1 million downloads[19]); the final release of OpenOffice.org 1.0 was on 1 May 2002.[1]
+OpenOffice.org became the standard office suite on many Linux distros and spawned many derivative versions. It quickly became noteworthy competition to Microsoft Office,[26][27] achieving 14% penetration in the large enterprise market by 2004.[28]
+The OpenOffice.org XML file format – XML in a ZIP archive, easily machine-processable – was intended by Sun to become a standard interchange format for office documents,[29] to replace the different binary formats for each application that had been usual until then. Sun submitted the format to the Organization for the Advancement of Structured Information Standards (OASIS) in 2002 and it was adapted to form the OpenDocument standard in 2005,[30] which was ratified as ISO 26300 in 2006.[31] It was made OpenOffice.org's native format from version 2 on. Many governments and other organisations adopted OpenDocument, particularly given there was a free implementation of it readily available.
+Development of OpenOffice.org was sponsored primarily by Sun Microsystems, which used the code as the basis for subsequent versions of StarOffice. Developers who wished to contribute code were required to sign a Contributor Agreement[32][33] granting joint ownership of any contributions to Sun (and then Oracle), in support of the StarOffice business model.[34] This was controversial for many years.[23][35][36][37][38] An alternative Public Documentation Licence (PDL)[39] was also offered for documentation not intended for inclusion or integration into the project code base.[40]
+After acquiring Sun in January 2010, Oracle Corporation continued developing OpenOffice.org and StarOffice, which it renamed Oracle Open Office,[41] though with a reduction in assigned developers.[42] Oracle's lack of activity on or visible commitment to OpenOffice.org had also been noted by industry observers.[43] In September 2010, the majority[44][45] of outside OpenOffice.org developers left the project,[46][47] due to concerns over Sun and then Oracle's management of the project[48][49][50] and Oracle's handling of its open source portfolio in general,[51] to form The Document Foundation (TDF). TDF released the fork LibreOffice in January 2011,[52] which most Linux distributions soon moved to.[53][54][55][56] In April 2011, Oracle stopped development of OpenOffice.org[12] and fired the remaining Star Division development team.[34][57] Its reasons for doing so were not disclosed; some speculate that it was due to the loss of mindshare with much of the community moving to LibreOffice[58] while others suggest it was a commercial decision.[34]
+In June 2011, Oracle contributed the trademarks to the Apache Software Foundation.[59] It also contributed Oracle-owned code to Apache for relicensing under the Apache License,[60] at the suggestion of IBM (to whom Oracle had contractual obligations concerning the code),[23][61] as IBM did not want the code put under a copyleft license.[62] This code drop formed the basis for the Apache OpenOffice project.[63]
+During Sun's sponsorship, the OpenOffice.org project was governed by the Community Council, comprising OpenOffice.org community members. The Community Council suggested project goals and coordinated with producers of derivatives on long-term development planning issues.[64][65][66]
+Both Sun and Oracle are claimed to have made decisions without consulting the Council or in contravention to the council's recommendations,[67][68] leading to the majority of outside developers leaving for LibreOffice.[48] Oracle demanded in October 2010 that all Council members involved with the Document Foundation step down,[69] leaving the Community Council composed only of Oracle employees.[70]
+The project and software were informally referred to as OpenOffice since the Sun release, but since this term is a trademark held by Open Office Automatisering in Benelux since 1999,[71][72] OpenOffice.org was its formal name.[73]
+Due to a similar trademark issue (a Rio de Janeiro company that owned that trademark in Brazil), the Brazilian Portuguese version of the suite was distributed under the name BrOffice.org from 2004, with BrOffice.Org being the name of the associated local nonprofit from 2006.[74] (BrOffice.org moved to LibreOffice in December 2010.[75])
+OpenOffice.org 1.0 was launched under the following mission statement:[11]
+The mission of OpenOffice.org is to create, as a community, the leading international office suite that will run on all major platforms and provide access to all functionality and data through open-component based APIs and an XML-based file format.
+The suite contained no personal information manager, email client or calendar application analogous to Microsoft Outlook, despite one having been present in StarOffice 5.2. Such functionality was frequently requested.[78] The OpenOffice.org Groupware project, intended to replace Outlook and Microsoft Exchange Server, spun off in 2003 as OpenGroupware.org,[79] which is now SOGo. The project considered bundling Mozilla Thunderbird and Mozilla Lightning for OpenOffice.org 3.0.[78]
+The last version, 3.4 Beta 1, was available for IA-32 versions of Windows 2000 Service Pack 2 or later, Linux (IA-32 and x64), Solaris and OS X 10.4 or later, and the SPARC version of Solaris.[4][80]
+The latest versions of OpenOffice.org on other operating systems were:[81]
+OpenOffice.org included OpenSymbol, DejaVu,[84] the Liberation fonts (from 2.4) and the Gentium fonts (from 3.2).[85][86][87] Versions up to 2.3 included the Bitstream Vera fonts.[84][88] OpenOffice.org also used the default fonts of the running operating system.
+Fontwork is a feature that allows users to create stylized text with special effects differing from ordinary text with the added features of gradient colour fills, shaping, letter height, and character spacing. It is similar to WordArt used by Microsoft Word.  When OpenOffice.org saved documents in Microsoft Office file format, all Fontwork was converted into WordArt.[89][90]
+From version 2.0.4, OpenOffice.org supported third-party extensions.[91] As of April 2011, the OpenOffice Extension Repository listed more than 650 extensions.[92] Another list was maintained by the Free Software Foundation.[93][94]
+OpenOffice.org included OpenOffice Basic, a programming language similar to Microsoft Visual Basic for Applications (VBA). OpenOffice Basic was available in Writer, Calc and Base.[95] OpenOffice.org also had some Microsoft VBA macro support.
+OpenOffice.org could interact with databases (local or remote) using ODBC (Open Database Connectivity), JDBC (Java Database Connectivity) or SDBC (StarOffice Database Connectivity).[96]
+From Version 2.0 onward, OpenOffice.org used ISO/IEC 26300:2006[97] OpenDocument as its native format. Versions 2.0–2.3.0 default to the ODF 1.0 file format; versions 2.3.1–2.4.3 default to ODF 1.1; versions 3.0 onward default to ODF 1.2.
+OpenOffice.org 1 used OpenOffice.org XML as its native format. This was contributed to OASIS and OpenDocument was developed from it.[98]
+OpenOffice.org also claimed support for the following formats:[99][100]
+OpenOffice.org converted all external formats to and from an internal XML representation.
+The OpenOffice.org API was based on a component technology known as Universal Network Objects (UNO). It consisted of a wide range of interfaces defined in a CORBA-like interface description language.
+OpenOffice.org 1.0 was criticized for not having the look and feel of applications developed natively for the platforms on which it runs. Starting with version 2.0, OpenOffice.org used native widget toolkit, icons, and font-rendering libraries on GNOME, KDE and Windows.[104][105][106]
+The issue had been particularly pronounced on Mac OS X. Early versions of OpenOffice.org required the installation of X11.app or XDarwin (though the NeoOffice port supplied a native interface). Versions since 3.0 ran natively using Apple's Aqua GUI.[107]
+Although originally written in C++, OpenOffice.org became increasingly reliant on the Java Runtime Environment, even including a bundled JVM.[108] OpenOffice.org was criticized by the Free Software Foundation for its increasing dependency on Java, which was not free software.[109]
+The issue came to the fore in May 2005, when Richard Stallman appeared to call for a fork of the application in a posting on the Free Software Foundation website.[109] OpenOffice.org adopted a development guideline that future versions of OpenOffice.org would run on free implementations of Java and fixed the issues which previously prevented OpenOffice.org 2.0 from using free-software Java implementations.[110]
+On 13 November 2006, Sun committed to releasing Java under the GNU General Public License[111] and had released a free software Java, OpenJDK, by May 2007.
+In 2006, Lt. Col. Eric Filiol of the  Laboratoire de Virologie et de Cryptologie de l'ESAT demonstrated security weaknesses, in particular within macros.[112][113][114] In 2006, Kaspersky Lab demonstrated a proof of concept virus, "Stardust", for OpenOffice.org.[115] This showed OpenOffice.org viruses are possible, but there is no known virus "in the wild".
+As of October 2011, Secunia reported no known unpatched security flaws for the software.[116] A vulnerability in the inherited OpenOffice.org codebase was found and fixed in LibreOffice in October 2011[117] and Apache OpenOffice in May 2012.[118]
+The preview, Milestone 638c, was released October 2001.[19] OpenOffice.org 1.0 was released under both the LGPL and the SISSL[23] for Windows, Linux and Solaris[135] on 1 May 2002.[1][136] The version for Mac OS X (with X11 interface) was released on 23 June 2003.[137][138]
+OpenOffice.org 1.1 introduced One-click Export to PDF and Export presentations to Flash (.SWF). It also allowed third-party addons.[101]
+OpenOffice.org was used in 2005 by The Guardian to illustrate what it saw as the limitations of open-source software.[139]
+Work on version 2.0 began in early 2003 with the following goals (the "Q Product Concept"): better interoperability with Microsoft Office; improved speed and lower memory usage; greater scripting capabilities; better integration, particularly with GNOME; a more usable database; digital signatures; and improved usability.[140] It would also be the first version to default to OpenDocument. Sun released the first beta version on 4 March 2005.[141]
+On 2 September 2005, Sun announced that it was retiring SISSL to reduce license proliferation,[142] though some press analysts felt it was so that IBM could not reuse OpenOffice.org code without contributing back.[23] Versions after 2.0 beta 2 would use only the LGPL.[7]
+On 20 October 2005, OpenOffice.org 2.0 was released.[122] 2.0.1 was released eight weeks later, fixing minor bugs and introducing new features. As of the 2.0.3 release, OpenOffice.org changed its release cycle from 18 months to releasing updates every three months.[143]
+The OpenOffice.org 2 series attracted considerable press attention.[144][145][146][147][148][149][150][151] A PC Pro review awarded it 6 stars out of 6 and stated: "Our pick of the low-cost office suites has had a much-needed overhaul, and now battles Microsoft in terms of features, not just price."[152] Federal Computer Week listed OpenOffice.org as one of the "5 stars of open-source products",[153] noting in particular the importance of OpenDocument. ComputerWorld reported that for large government departments, migration to OpenOffice.org 2.0 cost one tenth of the price of upgrading to Microsoft Office 2007.[154]
+On 13 October 2008, version 3.0 was released, featuring the ability to import (though not export) Office Open XML documents, support for ODF 1.2, improved VBA macros, and a native interface port for OS X. It also introduced the new Start Center[130] and upgraded to LGPL version 3 as its license.[155]
+Version 3.2 included support for PostScript-based OpenType fonts. It warned users when ODF 1.2 Extended features had been used. An improvement to the document integrity check determined if an ODF document conformed to the ODF specification and offered a repair if necessary. Calc and Writer both reduced "cold start" time by 46% compared to version 3.0.[156] 3.2.1 was the first Oracle release.[134]
+Version 3.3, the last Oracle version, was released in January 2011.[157] New features include an updated print form, a FindBar and interface improvements for Impress.[158][159] The commercial version, Oracle Open Office 3.3 (StarOffice renamed), based on the beta, was released on 15 December 2010, as was the single release of Oracle Cloud Office (a proprietary product from an unrelated codebase).[41][160]
+A beta version of OpenOffice.org 3.4 was released on 12 April 2011, including new SVG import, improved ODF 1.2 support, and spreadsheet functionality.[4][2][161]
+Before the final version of OpenOffice.org 3.4 could be released, Oracle cancelled its sponsorship of development[12] and fired the remaining Star Division development team.[34][57]
+Problems arise in estimating the market share of OpenOffice.org because it could be freely distributed via download sites (including mirror sites), peer-to-peer networks, CDs, Linux distributions and so forth. The project tried to capture key adoption data in a market-share analysis,[162] listing known distribution totals, known deployments and conversions and analyst statements and surveys.
+According to Valve, as of July 2010, 14.63% of Steam users had OpenOffice.org installed on their machines.[163]
+A market-share analysis conducted by a web analytics service in 2010, based on over 200,000 Internet users, showed a wide range of adoption in different countries:[164] 0.2% in China, 9% in the US and the UK and over 20% in Poland, the Czech Republic, and Germany.
+Although Microsoft Office retained 95% of the general market — as measured by revenue — as of August 2007,[165] OpenOffice.org and StarOffice had secured 15–20% of the business market as of 2004[166][167] and a 2010 University of Colorado at Boulder study reported that OpenOffice.org had reached a point where it had an "irreversible" installed user base and that it would continue to grow.[168]
+The project claimed more than 98 million downloads as of September 2007[169] and 300 million total to the release of version 3.2 in February 2010.[170] The project claimed over one hundred million downloads for the OpenOffice.org 3 series within a year of release.[171]
+Large-scale users of OpenOffice.org included Singapore's Ministry of Defence,[172] and Banco do Brasil.[173] As of 2006[update] OpenOffice.org was the official office suite for the French Gendarmerie.[162]
+In India, several government organizations such as ESIC, IIT Bombay, National Bank for Agriculture and Rural Development, the Supreme Court of India, ICICI Bank,[174] and the Allahabad High Court,[175] which use Linux, completely relied on OpenOffice.org for their administration.
+In Japan, conversions from Microsoft Office to OpenOffice.org included many municipal offices: Sumoto, Hyōgo in 2004,[176] Ninomiya, Tochigi in 2006,[177][178] Aizuwakamatsu, Fukushima in 2008[179] (and to LibreOffice as of 2012[180]), Shikokuchūō, Ehime in 2009,[181] Minoh, Osaka in 2009[182] Toyokawa, Aichi,[183] Fukagawa, Hokkaido[184] and Katano, Osaka[185] in 2010 and Ryūgasaki, Ibaraki in 2011.[186] Corporate conversions included Assist in 2007[187] (and to LibreOffice on Ubuntu in 2011[188]), Sumitomo Electric Industries in 2008[189] (and to LibreOffice in 2012[190]), Toho Co., Ltd. in 2009[191][192] and Shinsei Financial Co., Ltd. in 2010.[193] Assist also provided support services for OpenOffice.org.[191][193]
+In July 2007, Everex, a division of First International Computer and the 9th-largest PC supplier in the U.S., began shipping systems preloaded with OpenOffice.org 2.2 into Wal-Mart, K-mart and Sam's Club outlets in North America.[194]
+A number of open source and proprietary products derive at least some code from OpenOffice.org, including AndrOpen Office,[195] Apache OpenOffice, ChinaOffice, Co-Create Office, EuroOffice 2005,[196] Go-oo, KaiOffice, IBM Lotus Symphony, IBM Workplace, Jambo OpenOffice (the first office suite in Swahili),[197][198][199] LibreOffice, MagyarOffice, MultiMedia Office, MYOffice 2007, NeoOffice, NextOffice, OfficeOne, OfficeTLE, OOo4Kids,[200] OpenOfficePL, OpenOffice.org Portable,[201] OpenOfficeT7, OpenOffice.ux.pl, OxOffice,[202] OxygenOffice Professional,[203][204] Pladao Office,[205] PlusOffice Mac,[206] RedOffice,[37][129][207] RomanianOffice, StarOffice/Oracle Open Office, SunShine Office, ThizOffice, UP Office, White Label Office,[208][209][210][211] WPS Office Storm (the 2004 edition of Kingsoft Office) and 602Office.[212]
+The OpenOffice.org website also listed a large variety of complementary products, including groupware systems.[213]
+Major derivatives include:
+In June 2011, Oracle contributed the OpenOffice.org code and trademarks to the Apache Software Foundation. The developer pool for the Apache project was proposed to be seeded by IBM employees, Linux distribution companies and public sector agencies.[214] IBM employees did the majority of the development,[215][216][217][218][219] including hiring ex-Star Division developers.[217] The Apache project removed or replaced as much code as possible from OpenOffice.org 3.4 beta 1, including fonts, under licenses unacceptable to Apache[220] and released 3.4.0 in May 2012.[118]
+The codebase for IBM's Lotus Symphony was donated to the Apache Software Foundation in 2012 and merged for Apache OpenOffice 4.0,[221] and Symphony was deprecated in favour of Apache OpenOffice.[218]
+While the project considers itself the unbroken continuation of OpenOffice.org,[222] others regard it as a fork,[23][215][216][223][224][225][226] or at the least a separate project.[227]
+In October 2014, Bruce Byfield, writing for Linux Magazine, said the project had "all but stalled [possibly] due to IBM's withdrawal from the project."[228] As of 2015[update], the project has no release manager,[229] and itself reports a lack of volunteer involvement and code contributions.[230] After ongoing problems with unfixed security vulnerabilities from 2015 onward,[231][232][233] in September 2016 the project started discussions on possibly retiring AOO.[234]
+Sun had stated in the original OpenOffice.org announcement in 2000 that the project would be run by a neutral foundation,[10] and put forward a more detailed proposal in 2001.[235] There were many calls to put this into effect over the ensuing years.[36][236][237][238] On 28 September 2010, in frustration at years of perceived neglect of the codebase and community by Sun and then Oracle,[68] members of the OpenOffice.org community announced a non-profit called The Document Foundation and a fork of OpenOffice.org named LibreOffice. Go-oo improvements were merged, and that project was retired in favour of LibreOffice.[239] The goal was to produce a vendor-independent office suite with ODF support and without any copyright assignment requirements.[240]
+Oracle was invited to become a member of the Document Foundation and was asked to donate the OpenOffice.org brand.[240][241] Oracle instead demanded that all members of the OpenOffice.org Community Council involved with the Document Foundation step down,[69] leaving the Council composed only of Oracle employees.[70]
+Most Linux distributions promptly replaced OpenOffice.org with LibreOffice;[53][54][55][56] Oracle Linux 6 also features LibreOffice rather than OpenOffice.org or Apache OpenOffice.[242][243][244] The project rapidly accumulated developers, development effort[245][246][247] and added features,[248] the majority of outside OpenOffice.org developers having moved to LibreOffice.[44][45][48] In March 2015, an LWN.net development comparison of LibreOffice with Apache OpenOffice concluded that "LibreOffice has won the battle for developer participation".[249]
+NeoOffice, an independent commercial port for Macintosh that tracked the main line of development, offered a native OS X Aqua user interface before OpenOffice.org did.[250] Later versions are derived from Go-oo, rather than directly from OpenOffice.org.[251] All versions from NeoOffice 3.1.1 to NeoOffice 2015 were based on OpenOffice.org 3.1.1, though latter versions included stability fixes from LibreOffice and Apache OpenOffice.[252] NeoOffice 2017 and later versions are fully based on LibreOffice.[253]
+The ooo-build patch set was started at Ximian in 2002, because Sun were slow to accept outside work on OpenOffice.org, even from corporate partners, and to make the build process easier on Linux. It tracked the main line of development and was not intended to constitute a fork.[254] Most Linux distributions used,[255] and worked together on,[256] ooo-build.
+Sun's contributions to OpenOffice.org had been declining for a number of years[236] and some developers were unwilling to assign copyright in their work to Sun,[38] particularly given the deal between Sun and IBM to license the code outside the LGPL.[34] On 2 October 2007, Novell announced that ooo-build would be available as a software package called Go-oo, not merely a patch set.[257] (The go-oo.org domain name had been in use by ooo-build as early as 2005.[258]) Sun reacted negatively, with Simon Phipps of Sun terming it "a hostile and competitive fork".[36] Many free software advocates worried that Go-oo was a Novell effort to incorporate Microsoft technologies, such as Office Open XML, that might be vulnerable to patent claims.[259] However, the office suite branded "OpenOffice.org" in most Linux distributions, having previously been ooo-build, soon in fact became Go-oo.[251][260][261]
+Go-oo also encouraged outside contributions, with rules similar to those later adopted for LibreOffice.[262] When LibreOffice forked, Go-oo was deprecated in favour of that project.
+OpenOffice Novell edition was a supported version of Go-oo.[263]
+The Workplace Managed Client in IBM Workplace 2.6 (23 January 2006[264]) incorporated code from OpenOffice.org 1.1.4,[23] the last version under the SISSL. This code was broken out into a separate application as Lotus Symphony (30 May 2008[265]), with a new interface based on Eclipse. Symphony 3.0 (21 October 2010[266]) was rebased on OpenOffice.org 3.0, with the code licensed privately from Sun. IBM's changes were donated to the Apache Software Foundation in 2012, Symphony was deprecated in favour of Apache OpenOffice[218] and its code was merged into Apache OpenOffice 4.0.[221]
+Sun used OpenOffice.org as a base for its commercial proprietary StarOffice application software, which was OpenOffice.org with some added proprietary components. Oracle bought Sun in January 2010 and quickly renamed StarOffice to Oracle Open Office.[267] Oracle discontinued development in April 2011.[12]

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+OpenOffice.org (OOo), commonly known as OpenOffice, is a discontinued open-source office suite. It was an open-sourced version of the earlier StarOffice, which Sun Microsystems acquired in 1999 for internal use.
+OpenOffice included a word processor (Writer), a spreadsheet (Calc), a presentation application (Impress), a drawing application (Draw), a formula editor (Math), and a database management application (Base).[9] Its default file format was the OpenDocument Format (ODF), an ISO/IEC standard, which originated with OpenOffice.org. It could also read a wide variety of other file formats, with particular attention to those from Microsoft Office.
+Sun open-sourced the OpenOffice suite in July 2000 as a competitor to Microsoft Office,[10][11] releasing version 1.0 on 1 May 2002.[1]
+In 2011, Oracle Corporation, the then-owner of Sun, announced that it would no longer offer a commercial version of the suite[12] and donated the project to the Apache Foundation.[13][14]
+Apache renamed the software Apache OpenOffice.[15] Other active successor projects include LibreOffice (the most actively developed[16][17][18]) and NeoOffice (commercial, and available only for macOS).
+OpenOffice.org was primarily developed for Linux, Microsoft Windows and Solaris, and later for OS X, with ports to other operating systems. It was distributed under the GNU Lesser General Public License version 3 (LGPL); early versions were also available under the Sun Industry Standards Source License (SISSL).
+OpenOffice.org originated as StarOffice, a proprietary office suite developed by German company Star Division from 1985 on. In August 1999, Star Division was acquired by Sun Microsystems[19][20] for US$59.5 million,[21] as it was supposedly cheaper than licensing Microsoft Office for 42,000 staff.[22]
+On 19 July 2000 at OSCON, Sun Microsystems announced it would make the source code of StarOffice available for download with the intention of building an open-source development community around the software and of providing a free and open alternative to Microsoft Office.[10][11][23] The new project was known as OpenOffice.org,[24] and the code was released as open source on 13 October 2000.[25] The first public preview release was Milestone Build 638c, released in October 2001 (which quickly achieved 1 million downloads[19]); the final release of OpenOffice.org 1.0 was on 1 May 2002.[1]
+OpenOffice.org became the standard office suite on many Linux distros and spawned many derivative versions. It quickly became noteworthy competition to Microsoft Office,[26][27] achieving 14% penetration in the large enterprise market by 2004.[28]
+The OpenOffice.org XML file format – XML in a ZIP archive, easily machine-processable – was intended by Sun to become a standard interchange format for office documents,[29] to replace the different binary formats for each application that had been usual until then. Sun submitted the format to the Organization for the Advancement of Structured Information Standards (OASIS) in 2002 and it was adapted to form the OpenDocument standard in 2005,[30] which was ratified as ISO 26300 in 2006.[31] It was made OpenOffice.org's native format from version 2 on. Many governments and other organisations adopted OpenDocument, particularly given there was a free implementation of it readily available.
+Development of OpenOffice.org was sponsored primarily by Sun Microsystems, which used the code as the basis for subsequent versions of StarOffice. Developers who wished to contribute code were required to sign a Contributor Agreement[32][33] granting joint ownership of any contributions to Sun (and then Oracle), in support of the StarOffice business model.[34] This was controversial for many years.[23][35][36][37][38] An alternative Public Documentation Licence (PDL)[39] was also offered for documentation not intended for inclusion or integration into the project code base.[40]
+After acquiring Sun in January 2010, Oracle Corporation continued developing OpenOffice.org and StarOffice, which it renamed Oracle Open Office,[41] though with a reduction in assigned developers.[42] Oracle's lack of activity on or visible commitment to OpenOffice.org had also been noted by industry observers.[43] In September 2010, the majority[44][45] of outside OpenOffice.org developers left the project,[46][47] due to concerns over Sun and then Oracle's management of the project[48][49][50] and Oracle's handling of its open source portfolio in general,[51] to form The Document Foundation (TDF). TDF released the fork LibreOffice in January 2011,[52] which most Linux distributions soon moved to.[53][54][55][56] In April 2011, Oracle stopped development of OpenOffice.org[12] and fired the remaining Star Division development team.[34][57] Its reasons for doing so were not disclosed; some speculate that it was due to the loss of mindshare with much of the community moving to LibreOffice[58] while others suggest it was a commercial decision.[34]
+In June 2011, Oracle contributed the trademarks to the Apache Software Foundation.[59] It also contributed Oracle-owned code to Apache for relicensing under the Apache License,[60] at the suggestion of IBM (to whom Oracle had contractual obligations concerning the code),[23][61] as IBM did not want the code put under a copyleft license.[62] This code drop formed the basis for the Apache OpenOffice project.[63]
+During Sun's sponsorship, the OpenOffice.org project was governed by the Community Council, comprising OpenOffice.org community members. The Community Council suggested project goals and coordinated with producers of derivatives on long-term development planning issues.[64][65][66]
+Both Sun and Oracle are claimed to have made decisions without consulting the Council or in contravention to the council's recommendations,[67][68] leading to the majority of outside developers leaving for LibreOffice.[48] Oracle demanded in October 2010 that all Council members involved with the Document Foundation step down,[69] leaving the Community Council composed only of Oracle employees.[70]
+The project and software were informally referred to as OpenOffice since the Sun release, but since this term is a trademark held by Open Office Automatisering in Benelux since 1999,[71][72] OpenOffice.org was its formal name.[73]
+Due to a similar trademark issue (a Rio de Janeiro company that owned that trademark in Brazil), the Brazilian Portuguese version of the suite was distributed under the name BrOffice.org from 2004, with BrOffice.Org being the name of the associated local nonprofit from 2006.[74] (BrOffice.org moved to LibreOffice in December 2010.[75])
+OpenOffice.org 1.0 was launched under the following mission statement:[11]
+The mission of OpenOffice.org is to create, as a community, the leading international office suite that will run on all major platforms and provide access to all functionality and data through open-component based APIs and an XML-based file format.
+The suite contained no personal information manager, email client or calendar application analogous to Microsoft Outlook, despite one having been present in StarOffice 5.2. Such functionality was frequently requested.[78] The OpenOffice.org Groupware project, intended to replace Outlook and Microsoft Exchange Server, spun off in 2003 as OpenGroupware.org,[79] which is now SOGo. The project considered bundling Mozilla Thunderbird and Mozilla Lightning for OpenOffice.org 3.0.[78]
+The last version, 3.4 Beta 1, was available for IA-32 versions of Windows 2000 Service Pack 2 or later, Linux (IA-32 and x64), Solaris and OS X 10.4 or later, and the SPARC version of Solaris.[4][80]
+The latest versions of OpenOffice.org on other operating systems were:[81]
+OpenOffice.org included OpenSymbol, DejaVu,[84] the Liberation fonts (from 2.4) and the Gentium fonts (from 3.2).[85][86][87] Versions up to 2.3 included the Bitstream Vera fonts.[84][88] OpenOffice.org also used the default fonts of the running operating system.
+Fontwork is a feature that allows users to create stylized text with special effects differing from ordinary text with the added features of gradient colour fills, shaping, letter height, and character spacing. It is similar to WordArt used by Microsoft Word.  When OpenOffice.org saved documents in Microsoft Office file format, all Fontwork was converted into WordArt.[89][90]
+From version 2.0.4, OpenOffice.org supported third-party extensions.[91] As of April 2011, the OpenOffice Extension Repository listed more than 650 extensions.[92] Another list was maintained by the Free Software Foundation.[93][94]
+OpenOffice.org included OpenOffice Basic, a programming language similar to Microsoft Visual Basic for Applications (VBA). OpenOffice Basic was available in Writer, Calc and Base.[95] OpenOffice.org also had some Microsoft VBA macro support.
+OpenOffice.org could interact with databases (local or remote) using ODBC (Open Database Connectivity), JDBC (Java Database Connectivity) or SDBC (StarOffice Database Connectivity).[96]
+From Version 2.0 onward, OpenOffice.org used ISO/IEC 26300:2006[97] OpenDocument as its native format. Versions 2.0–2.3.0 default to the ODF 1.0 file format; versions 2.3.1–2.4.3 default to ODF 1.1; versions 3.0 onward default to ODF 1.2.
+OpenOffice.org 1 used OpenOffice.org XML as its native format. This was contributed to OASIS and OpenDocument was developed from it.[98]
+OpenOffice.org also claimed support for the following formats:[99][100]
+OpenOffice.org converted all external formats to and from an internal XML representation.
+The OpenOffice.org API was based on a component technology known as Universal Network Objects (UNO). It consisted of a wide range of interfaces defined in a CORBA-like interface description language.
+OpenOffice.org 1.0 was criticized for not having the look and feel of applications developed natively for the platforms on which it runs. Starting with version 2.0, OpenOffice.org used native widget toolkit, icons, and font-rendering libraries on GNOME, KDE and Windows.[104][105][106]
+The issue had been particularly pronounced on Mac OS X. Early versions of OpenOffice.org required the installation of X11.app or XDarwin (though the NeoOffice port supplied a native interface). Versions since 3.0 ran natively using Apple's Aqua GUI.[107]
+Although originally written in C++, OpenOffice.org became increasingly reliant on the Java Runtime Environment, even including a bundled JVM.[108] OpenOffice.org was criticized by the Free Software Foundation for its increasing dependency on Java, which was not free software.[109]
+The issue came to the fore in May 2005, when Richard Stallman appeared to call for a fork of the application in a posting on the Free Software Foundation website.[109] OpenOffice.org adopted a development guideline that future versions of OpenOffice.org would run on free implementations of Java and fixed the issues which previously prevented OpenOffice.org 2.0 from using free-software Java implementations.[110]
+On 13 November 2006, Sun committed to releasing Java under the GNU General Public License[111] and had released a free software Java, OpenJDK, by May 2007.
+In 2006, Lt. Col. Eric Filiol of the  Laboratoire de Virologie et de Cryptologie de l'ESAT demonstrated security weaknesses, in particular within macros.[112][113][114] In 2006, Kaspersky Lab demonstrated a proof of concept virus, "Stardust", for OpenOffice.org.[115] This showed OpenOffice.org viruses are possible, but there is no known virus "in the wild".
+As of October 2011, Secunia reported no known unpatched security flaws for the software.[116] A vulnerability in the inherited OpenOffice.org codebase was found and fixed in LibreOffice in October 2011[117] and Apache OpenOffice in May 2012.[118]
+The preview, Milestone 638c, was released October 2001.[19] OpenOffice.org 1.0 was released under both the LGPL and the SISSL[23] for Windows, Linux and Solaris[135] on 1 May 2002.[1][136] The version for Mac OS X (with X11 interface) was released on 23 June 2003.[137][138]
+OpenOffice.org 1.1 introduced One-click Export to PDF and Export presentations to Flash (.SWF). It also allowed third-party addons.[101]
+OpenOffice.org was used in 2005 by The Guardian to illustrate what it saw as the limitations of open-source software.[139]
+Work on version 2.0 began in early 2003 with the following goals (the "Q Product Concept"): better interoperability with Microsoft Office; improved speed and lower memory usage; greater scripting capabilities; better integration, particularly with GNOME; a more usable database; digital signatures; and improved usability.[140] It would also be the first version to default to OpenDocument. Sun released the first beta version on 4 March 2005.[141]
+On 2 September 2005, Sun announced that it was retiring SISSL to reduce license proliferation,[142] though some press analysts felt it was so that IBM could not reuse OpenOffice.org code without contributing back.[23] Versions after 2.0 beta 2 would use only the LGPL.[7]
+On 20 October 2005, OpenOffice.org 2.0 was released.[122] 2.0.1 was released eight weeks later, fixing minor bugs and introducing new features. As of the 2.0.3 release, OpenOffice.org changed its release cycle from 18 months to releasing updates every three months.[143]
+The OpenOffice.org 2 series attracted considerable press attention.[144][145][146][147][148][149][150][151] A PC Pro review awarded it 6 stars out of 6 and stated: "Our pick of the low-cost office suites has had a much-needed overhaul, and now battles Microsoft in terms of features, not just price."[152] Federal Computer Week listed OpenOffice.org as one of the "5 stars of open-source products",[153] noting in particular the importance of OpenDocument. ComputerWorld reported that for large government departments, migration to OpenOffice.org 2.0 cost one tenth of the price of upgrading to Microsoft Office 2007.[154]
+On 13 October 2008, version 3.0 was released, featuring the ability to import (though not export) Office Open XML documents, support for ODF 1.2, improved VBA macros, and a native interface port for OS X. It also introduced the new Start Center[130] and upgraded to LGPL version 3 as its license.[155]
+Version 3.2 included support for PostScript-based OpenType fonts. It warned users when ODF 1.2 Extended features had been used. An improvement to the document integrity check determined if an ODF document conformed to the ODF specification and offered a repair if necessary. Calc and Writer both reduced "cold start" time by 46% compared to version 3.0.[156] 3.2.1 was the first Oracle release.[134]
+Version 3.3, the last Oracle version, was released in January 2011.[157] New features include an updated print form, a FindBar and interface improvements for Impress.[158][159] The commercial version, Oracle Open Office 3.3 (StarOffice renamed), based on the beta, was released on 15 December 2010, as was the single release of Oracle Cloud Office (a proprietary product from an unrelated codebase).[41][160]
+A beta version of OpenOffice.org 3.4 was released on 12 April 2011, including new SVG import, improved ODF 1.2 support, and spreadsheet functionality.[4][2][161]
+Before the final version of OpenOffice.org 3.4 could be released, Oracle cancelled its sponsorship of development[12] and fired the remaining Star Division development team.[34][57]
+Problems arise in estimating the market share of OpenOffice.org because it could be freely distributed via download sites (including mirror sites), peer-to-peer networks, CDs, Linux distributions and so forth. The project tried to capture key adoption data in a market-share analysis,[162] listing known distribution totals, known deployments and conversions and analyst statements and surveys.
+According to Valve, as of July 2010, 14.63% of Steam users had OpenOffice.org installed on their machines.[163]
+A market-share analysis conducted by a web analytics service in 2010, based on over 200,000 Internet users, showed a wide range of adoption in different countries:[164] 0.2% in China, 9% in the US and the UK and over 20% in Poland, the Czech Republic, and Germany.
+Although Microsoft Office retained 95% of the general market — as measured by revenue — as of August 2007,[165] OpenOffice.org and StarOffice had secured 15–20% of the business market as of 2004[166][167] and a 2010 University of Colorado at Boulder study reported that OpenOffice.org had reached a point where it had an "irreversible" installed user base and that it would continue to grow.[168]
+The project claimed more than 98 million downloads as of September 2007[169] and 300 million total to the release of version 3.2 in February 2010.[170] The project claimed over one hundred million downloads for the OpenOffice.org 3 series within a year of release.[171]
+Large-scale users of OpenOffice.org included Singapore's Ministry of Defence,[172] and Banco do Brasil.[173] As of 2006[update] OpenOffice.org was the official office suite for the French Gendarmerie.[162]
+In India, several government organizations such as ESIC, IIT Bombay, National Bank for Agriculture and Rural Development, the Supreme Court of India, ICICI Bank,[174] and the Allahabad High Court,[175] which use Linux, completely relied on OpenOffice.org for their administration.
+In Japan, conversions from Microsoft Office to OpenOffice.org included many municipal offices: Sumoto, Hyōgo in 2004,[176] Ninomiya, Tochigi in 2006,[177][178] Aizuwakamatsu, Fukushima in 2008[179] (and to LibreOffice as of 2012[180]), Shikokuchūō, Ehime in 2009,[181] Minoh, Osaka in 2009[182] Toyokawa, Aichi,[183] Fukagawa, Hokkaido[184] and Katano, Osaka[185] in 2010 and Ryūgasaki, Ibaraki in 2011.[186] Corporate conversions included Assist in 2007[187] (and to LibreOffice on Ubuntu in 2011[188]), Sumitomo Electric Industries in 2008[189] (and to LibreOffice in 2012[190]), Toho Co., Ltd. in 2009[191][192] and Shinsei Financial Co., Ltd. in 2010.[193] Assist also provided support services for OpenOffice.org.[191][193]
+In July 2007, Everex, a division of First International Computer and the 9th-largest PC supplier in the U.S., began shipping systems preloaded with OpenOffice.org 2.2 into Wal-Mart, K-mart and Sam's Club outlets in North America.[194]
+A number of open source and proprietary products derive at least some code from OpenOffice.org, including AndrOpen Office,[195] Apache OpenOffice, ChinaOffice, Co-Create Office, EuroOffice 2005,[196] Go-oo, KaiOffice, IBM Lotus Symphony, IBM Workplace, Jambo OpenOffice (the first office suite in Swahili),[197][198][199] LibreOffice, MagyarOffice, MultiMedia Office, MYOffice 2007, NeoOffice, NextOffice, OfficeOne, OfficeTLE, OOo4Kids,[200] OpenOfficePL, OpenOffice.org Portable,[201] OpenOfficeT7, OpenOffice.ux.pl, OxOffice,[202] OxygenOffice Professional,[203][204] Pladao Office,[205] PlusOffice Mac,[206] RedOffice,[37][129][207] RomanianOffice, StarOffice/Oracle Open Office, SunShine Office, ThizOffice, UP Office, White Label Office,[208][209][210][211] WPS Office Storm (the 2004 edition of Kingsoft Office) and 602Office.[212]
+The OpenOffice.org website also listed a large variety of complementary products, including groupware systems.[213]
+Major derivatives include:
+In June 2011, Oracle contributed the OpenOffice.org code and trademarks to the Apache Software Foundation. The developer pool for the Apache project was proposed to be seeded by IBM employees, Linux distribution companies and public sector agencies.[214] IBM employees did the majority of the development,[215][216][217][218][219] including hiring ex-Star Division developers.[217] The Apache project removed or replaced as much code as possible from OpenOffice.org 3.4 beta 1, including fonts, under licenses unacceptable to Apache[220] and released 3.4.0 in May 2012.[118]
+The codebase for IBM's Lotus Symphony was donated to the Apache Software Foundation in 2012 and merged for Apache OpenOffice 4.0,[221] and Symphony was deprecated in favour of Apache OpenOffice.[218]
+While the project considers itself the unbroken continuation of OpenOffice.org,[222] others regard it as a fork,[23][215][216][223][224][225][226] or at the least a separate project.[227]
+In October 2014, Bruce Byfield, writing for Linux Magazine, said the project had "all but stalled [possibly] due to IBM's withdrawal from the project."[228] As of 2015[update], the project has no release manager,[229] and itself reports a lack of volunteer involvement and code contributions.[230] After ongoing problems with unfixed security vulnerabilities from 2015 onward,[231][232][233] in September 2016 the project started discussions on possibly retiring AOO.[234]
+Sun had stated in the original OpenOffice.org announcement in 2000 that the project would be run by a neutral foundation,[10] and put forward a more detailed proposal in 2001.[235] There were many calls to put this into effect over the ensuing years.[36][236][237][238] On 28 September 2010, in frustration at years of perceived neglect of the codebase and community by Sun and then Oracle,[68] members of the OpenOffice.org community announced a non-profit called The Document Foundation and a fork of OpenOffice.org named LibreOffice. Go-oo improvements were merged, and that project was retired in favour of LibreOffice.[239] The goal was to produce a vendor-independent office suite with ODF support and without any copyright assignment requirements.[240]
+Oracle was invited to become a member of the Document Foundation and was asked to donate the OpenOffice.org brand.[240][241] Oracle instead demanded that all members of the OpenOffice.org Community Council involved with the Document Foundation step down,[69] leaving the Council composed only of Oracle employees.[70]
+Most Linux distributions promptly replaced OpenOffice.org with LibreOffice;[53][54][55][56] Oracle Linux 6 also features LibreOffice rather than OpenOffice.org or Apache OpenOffice.[242][243][244] The project rapidly accumulated developers, development effort[245][246][247] and added features,[248] the majority of outside OpenOffice.org developers having moved to LibreOffice.[44][45][48] In March 2015, an LWN.net development comparison of LibreOffice with Apache OpenOffice concluded that "LibreOffice has won the battle for developer participation".[249]
+NeoOffice, an independent commercial port for Macintosh that tracked the main line of development, offered a native OS X Aqua user interface before OpenOffice.org did.[250] Later versions are derived from Go-oo, rather than directly from OpenOffice.org.[251] All versions from NeoOffice 3.1.1 to NeoOffice 2015 were based on OpenOffice.org 3.1.1, though latter versions included stability fixes from LibreOffice and Apache OpenOffice.[252] NeoOffice 2017 and later versions are fully based on LibreOffice.[253]
+The ooo-build patch set was started at Ximian in 2002, because Sun were slow to accept outside work on OpenOffice.org, even from corporate partners, and to make the build process easier on Linux. It tracked the main line of development and was not intended to constitute a fork.[254] Most Linux distributions used,[255] and worked together on,[256] ooo-build.
+Sun's contributions to OpenOffice.org had been declining for a number of years[236] and some developers were unwilling to assign copyright in their work to Sun,[38] particularly given the deal between Sun and IBM to license the code outside the LGPL.[34] On 2 October 2007, Novell announced that ooo-build would be available as a software package called Go-oo, not merely a patch set.[257] (The go-oo.org domain name had been in use by ooo-build as early as 2005.[258]) Sun reacted negatively, with Simon Phipps of Sun terming it "a hostile and competitive fork".[36] Many free software advocates worried that Go-oo was a Novell effort to incorporate Microsoft technologies, such as Office Open XML, that might be vulnerable to patent claims.[259] However, the office suite branded "OpenOffice.org" in most Linux distributions, having previously been ooo-build, soon in fact became Go-oo.[251][260][261]
+Go-oo also encouraged outside contributions, with rules similar to those later adopted for LibreOffice.[262] When LibreOffice forked, Go-oo was deprecated in favour of that project.
+OpenOffice Novell edition was a supported version of Go-oo.[263]
+The Workplace Managed Client in IBM Workplace 2.6 (23 January 2006[264]) incorporated code from OpenOffice.org 1.1.4,[23] the last version under the SISSL. This code was broken out into a separate application as Lotus Symphony (30 May 2008[265]), with a new interface based on Eclipse. Symphony 3.0 (21 October 2010[266]) was rebased on OpenOffice.org 3.0, with the code licensed privately from Sun. IBM's changes were donated to the Apache Software Foundation in 2012, Symphony was deprecated in favour of Apache OpenOffice[218] and its code was merged into Apache OpenOffice 4.0.[221]
+Sun used OpenOffice.org as a base for its commercial proprietary StarOffice application software, which was OpenOffice.org with some added proprietary components. Oracle bought Sun in January 2010 and quickly renamed StarOffice to Oracle Open Office.[267] Oracle discontinued development in April 2011.[12]

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+OpenOffice.org (OOo), commonly known as OpenOffice, is a discontinued open-source office suite. It was an open-sourced version of the earlier StarOffice, which Sun Microsystems acquired in 1999 for internal use.
+OpenOffice included a word processor (Writer), a spreadsheet (Calc), a presentation application (Impress), a drawing application (Draw), a formula editor (Math), and a database management application (Base).[9] Its default file format was the OpenDocument Format (ODF), an ISO/IEC standard, which originated with OpenOffice.org. It could also read a wide variety of other file formats, with particular attention to those from Microsoft Office.
+Sun open-sourced the OpenOffice suite in July 2000 as a competitor to Microsoft Office,[10][11] releasing version 1.0 on 1 May 2002.[1]
+In 2011, Oracle Corporation, the then-owner of Sun, announced that it would no longer offer a commercial version of the suite[12] and donated the project to the Apache Foundation.[13][14]
+Apache renamed the software Apache OpenOffice.[15] Other active successor projects include LibreOffice (the most actively developed[16][17][18]) and NeoOffice (commercial, and available only for macOS).
+OpenOffice.org was primarily developed for Linux, Microsoft Windows and Solaris, and later for OS X, with ports to other operating systems. It was distributed under the GNU Lesser General Public License version 3 (LGPL); early versions were also available under the Sun Industry Standards Source License (SISSL).
+OpenOffice.org originated as StarOffice, a proprietary office suite developed by German company Star Division from 1985 on. In August 1999, Star Division was acquired by Sun Microsystems[19][20] for US$59.5 million,[21] as it was supposedly cheaper than licensing Microsoft Office for 42,000 staff.[22]
+On 19 July 2000 at OSCON, Sun Microsystems announced it would make the source code of StarOffice available for download with the intention of building an open-source development community around the software and of providing a free and open alternative to Microsoft Office.[10][11][23] The new project was known as OpenOffice.org,[24] and the code was released as open source on 13 October 2000.[25] The first public preview release was Milestone Build 638c, released in October 2001 (which quickly achieved 1 million downloads[19]); the final release of OpenOffice.org 1.0 was on 1 May 2002.[1]
+OpenOffice.org became the standard office suite on many Linux distros and spawned many derivative versions. It quickly became noteworthy competition to Microsoft Office,[26][27] achieving 14% penetration in the large enterprise market by 2004.[28]
+The OpenOffice.org XML file format – XML in a ZIP archive, easily machine-processable – was intended by Sun to become a standard interchange format for office documents,[29] to replace the different binary formats for each application that had been usual until then. Sun submitted the format to the Organization for the Advancement of Structured Information Standards (OASIS) in 2002 and it was adapted to form the OpenDocument standard in 2005,[30] which was ratified as ISO 26300 in 2006.[31] It was made OpenOffice.org's native format from version 2 on. Many governments and other organisations adopted OpenDocument, particularly given there was a free implementation of it readily available.
+Development of OpenOffice.org was sponsored primarily by Sun Microsystems, which used the code as the basis for subsequent versions of StarOffice. Developers who wished to contribute code were required to sign a Contributor Agreement[32][33] granting joint ownership of any contributions to Sun (and then Oracle), in support of the StarOffice business model.[34] This was controversial for many years.[23][35][36][37][38] An alternative Public Documentation Licence (PDL)[39] was also offered for documentation not intended for inclusion or integration into the project code base.[40]
+After acquiring Sun in January 2010, Oracle Corporation continued developing OpenOffice.org and StarOffice, which it renamed Oracle Open Office,[41] though with a reduction in assigned developers.[42] Oracle's lack of activity on or visible commitment to OpenOffice.org had also been noted by industry observers.[43] In September 2010, the majority[44][45] of outside OpenOffice.org developers left the project,[46][47] due to concerns over Sun and then Oracle's management of the project[48][49][50] and Oracle's handling of its open source portfolio in general,[51] to form The Document Foundation (TDF). TDF released the fork LibreOffice in January 2011,[52] which most Linux distributions soon moved to.[53][54][55][56] In April 2011, Oracle stopped development of OpenOffice.org[12] and fired the remaining Star Division development team.[34][57] Its reasons for doing so were not disclosed; some speculate that it was due to the loss of mindshare with much of the community moving to LibreOffice[58] while others suggest it was a commercial decision.[34]
+In June 2011, Oracle contributed the trademarks to the Apache Software Foundation.[59] It also contributed Oracle-owned code to Apache for relicensing under the Apache License,[60] at the suggestion of IBM (to whom Oracle had contractual obligations concerning the code),[23][61] as IBM did not want the code put under a copyleft license.[62] This code drop formed the basis for the Apache OpenOffice project.[63]
+During Sun's sponsorship, the OpenOffice.org project was governed by the Community Council, comprising OpenOffice.org community members. The Community Council suggested project goals and coordinated with producers of derivatives on long-term development planning issues.[64][65][66]
+Both Sun and Oracle are claimed to have made decisions without consulting the Council or in contravention to the council's recommendations,[67][68] leading to the majority of outside developers leaving for LibreOffice.[48] Oracle demanded in October 2010 that all Council members involved with the Document Foundation step down,[69] leaving the Community Council composed only of Oracle employees.[70]
+The project and software were informally referred to as OpenOffice since the Sun release, but since this term is a trademark held by Open Office Automatisering in Benelux since 1999,[71][72] OpenOffice.org was its formal name.[73]
+Due to a similar trademark issue (a Rio de Janeiro company that owned that trademark in Brazil), the Brazilian Portuguese version of the suite was distributed under the name BrOffice.org from 2004, with BrOffice.Org being the name of the associated local nonprofit from 2006.[74] (BrOffice.org moved to LibreOffice in December 2010.[75])
+OpenOffice.org 1.0 was launched under the following mission statement:[11]
+The mission of OpenOffice.org is to create, as a community, the leading international office suite that will run on all major platforms and provide access to all functionality and data through open-component based APIs and an XML-based file format.
+The suite contained no personal information manager, email client or calendar application analogous to Microsoft Outlook, despite one having been present in StarOffice 5.2. Such functionality was frequently requested.[78] The OpenOffice.org Groupware project, intended to replace Outlook and Microsoft Exchange Server, spun off in 2003 as OpenGroupware.org,[79] which is now SOGo. The project considered bundling Mozilla Thunderbird and Mozilla Lightning for OpenOffice.org 3.0.[78]
+The last version, 3.4 Beta 1, was available for IA-32 versions of Windows 2000 Service Pack 2 or later, Linux (IA-32 and x64), Solaris and OS X 10.4 or later, and the SPARC version of Solaris.[4][80]
+The latest versions of OpenOffice.org on other operating systems were:[81]
+OpenOffice.org included OpenSymbol, DejaVu,[84] the Liberation fonts (from 2.4) and the Gentium fonts (from 3.2).[85][86][87] Versions up to 2.3 included the Bitstream Vera fonts.[84][88] OpenOffice.org also used the default fonts of the running operating system.
+Fontwork is a feature that allows users to create stylized text with special effects differing from ordinary text with the added features of gradient colour fills, shaping, letter height, and character spacing. It is similar to WordArt used by Microsoft Word.  When OpenOffice.org saved documents in Microsoft Office file format, all Fontwork was converted into WordArt.[89][90]
+From version 2.0.4, OpenOffice.org supported third-party extensions.[91] As of April 2011, the OpenOffice Extension Repository listed more than 650 extensions.[92] Another list was maintained by the Free Software Foundation.[93][94]
+OpenOffice.org included OpenOffice Basic, a programming language similar to Microsoft Visual Basic for Applications (VBA). OpenOffice Basic was available in Writer, Calc and Base.[95] OpenOffice.org also had some Microsoft VBA macro support.
+OpenOffice.org could interact with databases (local or remote) using ODBC (Open Database Connectivity), JDBC (Java Database Connectivity) or SDBC (StarOffice Database Connectivity).[96]
+From Version 2.0 onward, OpenOffice.org used ISO/IEC 26300:2006[97] OpenDocument as its native format. Versions 2.0–2.3.0 default to the ODF 1.0 file format; versions 2.3.1–2.4.3 default to ODF 1.1; versions 3.0 onward default to ODF 1.2.
+OpenOffice.org 1 used OpenOffice.org XML as its native format. This was contributed to OASIS and OpenDocument was developed from it.[98]
+OpenOffice.org also claimed support for the following formats:[99][100]
+OpenOffice.org converted all external formats to and from an internal XML representation.
+The OpenOffice.org API was based on a component technology known as Universal Network Objects (UNO). It consisted of a wide range of interfaces defined in a CORBA-like interface description language.
+OpenOffice.org 1.0 was criticized for not having the look and feel of applications developed natively for the platforms on which it runs. Starting with version 2.0, OpenOffice.org used native widget toolkit, icons, and font-rendering libraries on GNOME, KDE and Windows.[104][105][106]
+The issue had been particularly pronounced on Mac OS X. Early versions of OpenOffice.org required the installation of X11.app or XDarwin (though the NeoOffice port supplied a native interface). Versions since 3.0 ran natively using Apple's Aqua GUI.[107]
+Although originally written in C++, OpenOffice.org became increasingly reliant on the Java Runtime Environment, even including a bundled JVM.[108] OpenOffice.org was criticized by the Free Software Foundation for its increasing dependency on Java, which was not free software.[109]
+The issue came to the fore in May 2005, when Richard Stallman appeared to call for a fork of the application in a posting on the Free Software Foundation website.[109] OpenOffice.org adopted a development guideline that future versions of OpenOffice.org would run on free implementations of Java and fixed the issues which previously prevented OpenOffice.org 2.0 from using free-software Java implementations.[110]
+On 13 November 2006, Sun committed to releasing Java under the GNU General Public License[111] and had released a free software Java, OpenJDK, by May 2007.
+In 2006, Lt. Col. Eric Filiol of the  Laboratoire de Virologie et de Cryptologie de l'ESAT demonstrated security weaknesses, in particular within macros.[112][113][114] In 2006, Kaspersky Lab demonstrated a proof of concept virus, "Stardust", for OpenOffice.org.[115] This showed OpenOffice.org viruses are possible, but there is no known virus "in the wild".
+As of October 2011, Secunia reported no known unpatched security flaws for the software.[116] A vulnerability in the inherited OpenOffice.org codebase was found and fixed in LibreOffice in October 2011[117] and Apache OpenOffice in May 2012.[118]
+The preview, Milestone 638c, was released October 2001.[19] OpenOffice.org 1.0 was released under both the LGPL and the SISSL[23] for Windows, Linux and Solaris[135] on 1 May 2002.[1][136] The version for Mac OS X (with X11 interface) was released on 23 June 2003.[137][138]
+OpenOffice.org 1.1 introduced One-click Export to PDF and Export presentations to Flash (.SWF). It also allowed third-party addons.[101]
+OpenOffice.org was used in 2005 by The Guardian to illustrate what it saw as the limitations of open-source software.[139]
+Work on version 2.0 began in early 2003 with the following goals (the "Q Product Concept"): better interoperability with Microsoft Office; improved speed and lower memory usage; greater scripting capabilities; better integration, particularly with GNOME; a more usable database; digital signatures; and improved usability.[140] It would also be the first version to default to OpenDocument. Sun released the first beta version on 4 March 2005.[141]
+On 2 September 2005, Sun announced that it was retiring SISSL to reduce license proliferation,[142] though some press analysts felt it was so that IBM could not reuse OpenOffice.org code without contributing back.[23] Versions after 2.0 beta 2 would use only the LGPL.[7]
+On 20 October 2005, OpenOffice.org 2.0 was released.[122] 2.0.1 was released eight weeks later, fixing minor bugs and introducing new features. As of the 2.0.3 release, OpenOffice.org changed its release cycle from 18 months to releasing updates every three months.[143]
+The OpenOffice.org 2 series attracted considerable press attention.[144][145][146][147][148][149][150][151] A PC Pro review awarded it 6 stars out of 6 and stated: "Our pick of the low-cost office suites has had a much-needed overhaul, and now battles Microsoft in terms of features, not just price."[152] Federal Computer Week listed OpenOffice.org as one of the "5 stars of open-source products",[153] noting in particular the importance of OpenDocument. ComputerWorld reported that for large government departments, migration to OpenOffice.org 2.0 cost one tenth of the price of upgrading to Microsoft Office 2007.[154]
+On 13 October 2008, version 3.0 was released, featuring the ability to import (though not export) Office Open XML documents, support for ODF 1.2, improved VBA macros, and a native interface port for OS X. It also introduced the new Start Center[130] and upgraded to LGPL version 3 as its license.[155]
+Version 3.2 included support for PostScript-based OpenType fonts. It warned users when ODF 1.2 Extended features had been used. An improvement to the document integrity check determined if an ODF document conformed to the ODF specification and offered a repair if necessary. Calc and Writer both reduced "cold start" time by 46% compared to version 3.0.[156] 3.2.1 was the first Oracle release.[134]
+Version 3.3, the last Oracle version, was released in January 2011.[157] New features include an updated print form, a FindBar and interface improvements for Impress.[158][159] The commercial version, Oracle Open Office 3.3 (StarOffice renamed), based on the beta, was released on 15 December 2010, as was the single release of Oracle Cloud Office (a proprietary product from an unrelated codebase).[41][160]
+A beta version of OpenOffice.org 3.4 was released on 12 April 2011, including new SVG import, improved ODF 1.2 support, and spreadsheet functionality.[4][2][161]
+Before the final version of OpenOffice.org 3.4 could be released, Oracle cancelled its sponsorship of development[12] and fired the remaining Star Division development team.[34][57]
+Problems arise in estimating the market share of OpenOffice.org because it could be freely distributed via download sites (including mirror sites), peer-to-peer networks, CDs, Linux distributions and so forth. The project tried to capture key adoption data in a market-share analysis,[162] listing known distribution totals, known deployments and conversions and analyst statements and surveys.
+According to Valve, as of July 2010, 14.63% of Steam users had OpenOffice.org installed on their machines.[163]
+A market-share analysis conducted by a web analytics service in 2010, based on over 200,000 Internet users, showed a wide range of adoption in different countries:[164] 0.2% in China, 9% in the US and the UK and over 20% in Poland, the Czech Republic, and Germany.
+Although Microsoft Office retained 95% of the general market — as measured by revenue — as of August 2007,[165] OpenOffice.org and StarOffice had secured 15–20% of the business market as of 2004[166][167] and a 2010 University of Colorado at Boulder study reported that OpenOffice.org had reached a point where it had an "irreversible" installed user base and that it would continue to grow.[168]
+The project claimed more than 98 million downloads as of September 2007[169] and 300 million total to the release of version 3.2 in February 2010.[170] The project claimed over one hundred million downloads for the OpenOffice.org 3 series within a year of release.[171]
+Large-scale users of OpenOffice.org included Singapore's Ministry of Defence,[172] and Banco do Brasil.[173] As of 2006[update] OpenOffice.org was the official office suite for the French Gendarmerie.[162]
+In India, several government organizations such as ESIC, IIT Bombay, National Bank for Agriculture and Rural Development, the Supreme Court of India, ICICI Bank,[174] and the Allahabad High Court,[175] which use Linux, completely relied on OpenOffice.org for their administration.
+In Japan, conversions from Microsoft Office to OpenOffice.org included many municipal offices: Sumoto, Hyōgo in 2004,[176] Ninomiya, Tochigi in 2006,[177][178] Aizuwakamatsu, Fukushima in 2008[179] (and to LibreOffice as of 2012[180]), Shikokuchūō, Ehime in 2009,[181] Minoh, Osaka in 2009[182] Toyokawa, Aichi,[183] Fukagawa, Hokkaido[184] and Katano, Osaka[185] in 2010 and Ryūgasaki, Ibaraki in 2011.[186] Corporate conversions included Assist in 2007[187] (and to LibreOffice on Ubuntu in 2011[188]), Sumitomo Electric Industries in 2008[189] (and to LibreOffice in 2012[190]), Toho Co., Ltd. in 2009[191][192] and Shinsei Financial Co., Ltd. in 2010.[193] Assist also provided support services for OpenOffice.org.[191][193]
+In July 2007, Everex, a division of First International Computer and the 9th-largest PC supplier in the U.S., began shipping systems preloaded with OpenOffice.org 2.2 into Wal-Mart, K-mart and Sam's Club outlets in North America.[194]
+A number of open source and proprietary products derive at least some code from OpenOffice.org, including AndrOpen Office,[195] Apache OpenOffice, ChinaOffice, Co-Create Office, EuroOffice 2005,[196] Go-oo, KaiOffice, IBM Lotus Symphony, IBM Workplace, Jambo OpenOffice (the first office suite in Swahili),[197][198][199] LibreOffice, MagyarOffice, MultiMedia Office, MYOffice 2007, NeoOffice, NextOffice, OfficeOne, OfficeTLE, OOo4Kids,[200] OpenOfficePL, OpenOffice.org Portable,[201] OpenOfficeT7, OpenOffice.ux.pl, OxOffice,[202] OxygenOffice Professional,[203][204] Pladao Office,[205] PlusOffice Mac,[206] RedOffice,[37][129][207] RomanianOffice, StarOffice/Oracle Open Office, SunShine Office, ThizOffice, UP Office, White Label Office,[208][209][210][211] WPS Office Storm (the 2004 edition of Kingsoft Office) and 602Office.[212]
+The OpenOffice.org website also listed a large variety of complementary products, including groupware systems.[213]
+Major derivatives include:
+In June 2011, Oracle contributed the OpenOffice.org code and trademarks to the Apache Software Foundation. The developer pool for the Apache project was proposed to be seeded by IBM employees, Linux distribution companies and public sector agencies.[214] IBM employees did the majority of the development,[215][216][217][218][219] including hiring ex-Star Division developers.[217] The Apache project removed or replaced as much code as possible from OpenOffice.org 3.4 beta 1, including fonts, under licenses unacceptable to Apache[220] and released 3.4.0 in May 2012.[118]
+The codebase for IBM's Lotus Symphony was donated to the Apache Software Foundation in 2012 and merged for Apache OpenOffice 4.0,[221] and Symphony was deprecated in favour of Apache OpenOffice.[218]
+While the project considers itself the unbroken continuation of OpenOffice.org,[222] others regard it as a fork,[23][215][216][223][224][225][226] or at the least a separate project.[227]
+In October 2014, Bruce Byfield, writing for Linux Magazine, said the project had "all but stalled [possibly] due to IBM's withdrawal from the project."[228] As of 2015[update], the project has no release manager,[229] and itself reports a lack of volunteer involvement and code contributions.[230] After ongoing problems with unfixed security vulnerabilities from 2015 onward,[231][232][233] in September 2016 the project started discussions on possibly retiring AOO.[234]
+Sun had stated in the original OpenOffice.org announcement in 2000 that the project would be run by a neutral foundation,[10] and put forward a more detailed proposal in 2001.[235] There were many calls to put this into effect over the ensuing years.[36][236][237][238] On 28 September 2010, in frustration at years of perceived neglect of the codebase and community by Sun and then Oracle,[68] members of the OpenOffice.org community announced a non-profit called The Document Foundation and a fork of OpenOffice.org named LibreOffice. Go-oo improvements were merged, and that project was retired in favour of LibreOffice.[239] The goal was to produce a vendor-independent office suite with ODF support and without any copyright assignment requirements.[240]
+Oracle was invited to become a member of the Document Foundation and was asked to donate the OpenOffice.org brand.[240][241] Oracle instead demanded that all members of the OpenOffice.org Community Council involved with the Document Foundation step down,[69] leaving the Council composed only of Oracle employees.[70]
+Most Linux distributions promptly replaced OpenOffice.org with LibreOffice;[53][54][55][56] Oracle Linux 6 also features LibreOffice rather than OpenOffice.org or Apache OpenOffice.[242][243][244] The project rapidly accumulated developers, development effort[245][246][247] and added features,[248] the majority of outside OpenOffice.org developers having moved to LibreOffice.[44][45][48] In March 2015, an LWN.net development comparison of LibreOffice with Apache OpenOffice concluded that "LibreOffice has won the battle for developer participation".[249]
+NeoOffice, an independent commercial port for Macintosh that tracked the main line of development, offered a native OS X Aqua user interface before OpenOffice.org did.[250] Later versions are derived from Go-oo, rather than directly from OpenOffice.org.[251] All versions from NeoOffice 3.1.1 to NeoOffice 2015 were based on OpenOffice.org 3.1.1, though latter versions included stability fixes from LibreOffice and Apache OpenOffice.[252] NeoOffice 2017 and later versions are fully based on LibreOffice.[253]
+The ooo-build patch set was started at Ximian in 2002, because Sun were slow to accept outside work on OpenOffice.org, even from corporate partners, and to make the build process easier on Linux. It tracked the main line of development and was not intended to constitute a fork.[254] Most Linux distributions used,[255] and worked together on,[256] ooo-build.
+Sun's contributions to OpenOffice.org had been declining for a number of years[236] and some developers were unwilling to assign copyright in their work to Sun,[38] particularly given the deal between Sun and IBM to license the code outside the LGPL.[34] On 2 October 2007, Novell announced that ooo-build would be available as a software package called Go-oo, not merely a patch set.[257] (The go-oo.org domain name had been in use by ooo-build as early as 2005.[258]) Sun reacted negatively, with Simon Phipps of Sun terming it "a hostile and competitive fork".[36] Many free software advocates worried that Go-oo was a Novell effort to incorporate Microsoft technologies, such as Office Open XML, that might be vulnerable to patent claims.[259] However, the office suite branded "OpenOffice.org" in most Linux distributions, having previously been ooo-build, soon in fact became Go-oo.[251][260][261]
+Go-oo also encouraged outside contributions, with rules similar to those later adopted for LibreOffice.[262] When LibreOffice forked, Go-oo was deprecated in favour of that project.
+OpenOffice Novell edition was a supported version of Go-oo.[263]
+The Workplace Managed Client in IBM Workplace 2.6 (23 January 2006[264]) incorporated code from OpenOffice.org 1.1.4,[23] the last version under the SISSL. This code was broken out into a separate application as Lotus Symphony (30 May 2008[265]), with a new interface based on Eclipse. Symphony 3.0 (21 October 2010[266]) was rebased on OpenOffice.org 3.0, with the code licensed privately from Sun. IBM's changes were donated to the Apache Software Foundation in 2012, Symphony was deprecated in favour of Apache OpenOffice[218] and its code was merged into Apache OpenOffice 4.0.[221]
+Sun used OpenOffice.org as a base for its commercial proprietary StarOffice application software, which was OpenOffice.org with some added proprietary components. Oracle bought Sun in January 2010 and quickly renamed StarOffice to Oracle Open Office.[267] Oracle discontinued development in April 2011.[12]

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+OpenOffice.org (OOo), commonly known as OpenOffice, is a discontinued open-source office suite. It was an open-sourced version of the earlier StarOffice, which Sun Microsystems acquired in 1999 for internal use.
+OpenOffice included a word processor (Writer), a spreadsheet (Calc), a presentation application (Impress), a drawing application (Draw), a formula editor (Math), and a database management application (Base).[9] Its default file format was the OpenDocument Format (ODF), an ISO/IEC standard, which originated with OpenOffice.org. It could also read a wide variety of other file formats, with particular attention to those from Microsoft Office.
+Sun open-sourced the OpenOffice suite in July 2000 as a competitor to Microsoft Office,[10][11] releasing version 1.0 on 1 May 2002.[1]
+In 2011, Oracle Corporation, the then-owner of Sun, announced that it would no longer offer a commercial version of the suite[12] and donated the project to the Apache Foundation.[13][14]
+Apache renamed the software Apache OpenOffice.[15] Other active successor projects include LibreOffice (the most actively developed[16][17][18]) and NeoOffice (commercial, and available only for macOS).
+OpenOffice.org was primarily developed for Linux, Microsoft Windows and Solaris, and later for OS X, with ports to other operating systems. It was distributed under the GNU Lesser General Public License version 3 (LGPL); early versions were also available under the Sun Industry Standards Source License (SISSL).
+OpenOffice.org originated as StarOffice, a proprietary office suite developed by German company Star Division from 1985 on. In August 1999, Star Division was acquired by Sun Microsystems[19][20] for US$59.5 million,[21] as it was supposedly cheaper than licensing Microsoft Office for 42,000 staff.[22]
+On 19 July 2000 at OSCON, Sun Microsystems announced it would make the source code of StarOffice available for download with the intention of building an open-source development community around the software and of providing a free and open alternative to Microsoft Office.[10][11][23] The new project was known as OpenOffice.org,[24] and the code was released as open source on 13 October 2000.[25] The first public preview release was Milestone Build 638c, released in October 2001 (which quickly achieved 1 million downloads[19]); the final release of OpenOffice.org 1.0 was on 1 May 2002.[1]
+OpenOffice.org became the standard office suite on many Linux distros and spawned many derivative versions. It quickly became noteworthy competition to Microsoft Office,[26][27] achieving 14% penetration in the large enterprise market by 2004.[28]
+The OpenOffice.org XML file format – XML in a ZIP archive, easily machine-processable – was intended by Sun to become a standard interchange format for office documents,[29] to replace the different binary formats for each application that had been usual until then. Sun submitted the format to the Organization for the Advancement of Structured Information Standards (OASIS) in 2002 and it was adapted to form the OpenDocument standard in 2005,[30] which was ratified as ISO 26300 in 2006.[31] It was made OpenOffice.org's native format from version 2 on. Many governments and other organisations adopted OpenDocument, particularly given there was a free implementation of it readily available.
+Development of OpenOffice.org was sponsored primarily by Sun Microsystems, which used the code as the basis for subsequent versions of StarOffice. Developers who wished to contribute code were required to sign a Contributor Agreement[32][33] granting joint ownership of any contributions to Sun (and then Oracle), in support of the StarOffice business model.[34] This was controversial for many years.[23][35][36][37][38] An alternative Public Documentation Licence (PDL)[39] was also offered for documentation not intended for inclusion or integration into the project code base.[40]
+After acquiring Sun in January 2010, Oracle Corporation continued developing OpenOffice.org and StarOffice, which it renamed Oracle Open Office,[41] though with a reduction in assigned developers.[42] Oracle's lack of activity on or visible commitment to OpenOffice.org had also been noted by industry observers.[43] In September 2010, the majority[44][45] of outside OpenOffice.org developers left the project,[46][47] due to concerns over Sun and then Oracle's management of the project[48][49][50] and Oracle's handling of its open source portfolio in general,[51] to form The Document Foundation (TDF). TDF released the fork LibreOffice in January 2011,[52] which most Linux distributions soon moved to.[53][54][55][56] In April 2011, Oracle stopped development of OpenOffice.org[12] and fired the remaining Star Division development team.[34][57] Its reasons for doing so were not disclosed; some speculate that it was due to the loss of mindshare with much of the community moving to LibreOffice[58] while others suggest it was a commercial decision.[34]
+In June 2011, Oracle contributed the trademarks to the Apache Software Foundation.[59] It also contributed Oracle-owned code to Apache for relicensing under the Apache License,[60] at the suggestion of IBM (to whom Oracle had contractual obligations concerning the code),[23][61] as IBM did not want the code put under a copyleft license.[62] This code drop formed the basis for the Apache OpenOffice project.[63]
+During Sun's sponsorship, the OpenOffice.org project was governed by the Community Council, comprising OpenOffice.org community members. The Community Council suggested project goals and coordinated with producers of derivatives on long-term development planning issues.[64][65][66]
+Both Sun and Oracle are claimed to have made decisions without consulting the Council or in contravention to the council's recommendations,[67][68] leading to the majority of outside developers leaving for LibreOffice.[48] Oracle demanded in October 2010 that all Council members involved with the Document Foundation step down,[69] leaving the Community Council composed only of Oracle employees.[70]
+The project and software were informally referred to as OpenOffice since the Sun release, but since this term is a trademark held by Open Office Automatisering in Benelux since 1999,[71][72] OpenOffice.org was its formal name.[73]
+Due to a similar trademark issue (a Rio de Janeiro company that owned that trademark in Brazil), the Brazilian Portuguese version of the suite was distributed under the name BrOffice.org from 2004, with BrOffice.Org being the name of the associated local nonprofit from 2006.[74] (BrOffice.org moved to LibreOffice in December 2010.[75])
+OpenOffice.org 1.0 was launched under the following mission statement:[11]
+The mission of OpenOffice.org is to create, as a community, the leading international office suite that will run on all major platforms and provide access to all functionality and data through open-component based APIs and an XML-based file format.
+The suite contained no personal information manager, email client or calendar application analogous to Microsoft Outlook, despite one having been present in StarOffice 5.2. Such functionality was frequently requested.[78] The OpenOffice.org Groupware project, intended to replace Outlook and Microsoft Exchange Server, spun off in 2003 as OpenGroupware.org,[79] which is now SOGo. The project considered bundling Mozilla Thunderbird and Mozilla Lightning for OpenOffice.org 3.0.[78]
+The last version, 3.4 Beta 1, was available for IA-32 versions of Windows 2000 Service Pack 2 or later, Linux (IA-32 and x64), Solaris and OS X 10.4 or later, and the SPARC version of Solaris.[4][80]
+The latest versions of OpenOffice.org on other operating systems were:[81]
+OpenOffice.org included OpenSymbol, DejaVu,[84] the Liberation fonts (from 2.4) and the Gentium fonts (from 3.2).[85][86][87] Versions up to 2.3 included the Bitstream Vera fonts.[84][88] OpenOffice.org also used the default fonts of the running operating system.
+Fontwork is a feature that allows users to create stylized text with special effects differing from ordinary text with the added features of gradient colour fills, shaping, letter height, and character spacing. It is similar to WordArt used by Microsoft Word.  When OpenOffice.org saved documents in Microsoft Office file format, all Fontwork was converted into WordArt.[89][90]
+From version 2.0.4, OpenOffice.org supported third-party extensions.[91] As of April 2011, the OpenOffice Extension Repository listed more than 650 extensions.[92] Another list was maintained by the Free Software Foundation.[93][94]
+OpenOffice.org included OpenOffice Basic, a programming language similar to Microsoft Visual Basic for Applications (VBA). OpenOffice Basic was available in Writer, Calc and Base.[95] OpenOffice.org also had some Microsoft VBA macro support.
+OpenOffice.org could interact with databases (local or remote) using ODBC (Open Database Connectivity), JDBC (Java Database Connectivity) or SDBC (StarOffice Database Connectivity).[96]
+From Version 2.0 onward, OpenOffice.org used ISO/IEC 26300:2006[97] OpenDocument as its native format. Versions 2.0–2.3.0 default to the ODF 1.0 file format; versions 2.3.1–2.4.3 default to ODF 1.1; versions 3.0 onward default to ODF 1.2.
+OpenOffice.org 1 used OpenOffice.org XML as its native format. This was contributed to OASIS and OpenDocument was developed from it.[98]
+OpenOffice.org also claimed support for the following formats:[99][100]
+OpenOffice.org converted all external formats to and from an internal XML representation.
+The OpenOffice.org API was based on a component technology known as Universal Network Objects (UNO). It consisted of a wide range of interfaces defined in a CORBA-like interface description language.
+OpenOffice.org 1.0 was criticized for not having the look and feel of applications developed natively for the platforms on which it runs. Starting with version 2.0, OpenOffice.org used native widget toolkit, icons, and font-rendering libraries on GNOME, KDE and Windows.[104][105][106]
+The issue had been particularly pronounced on Mac OS X. Early versions of OpenOffice.org required the installation of X11.app or XDarwin (though the NeoOffice port supplied a native interface). Versions since 3.0 ran natively using Apple's Aqua GUI.[107]
+Although originally written in C++, OpenOffice.org became increasingly reliant on the Java Runtime Environment, even including a bundled JVM.[108] OpenOffice.org was criticized by the Free Software Foundation for its increasing dependency on Java, which was not free software.[109]
+The issue came to the fore in May 2005, when Richard Stallman appeared to call for a fork of the application in a posting on the Free Software Foundation website.[109] OpenOffice.org adopted a development guideline that future versions of OpenOffice.org would run on free implementations of Java and fixed the issues which previously prevented OpenOffice.org 2.0 from using free-software Java implementations.[110]
+On 13 November 2006, Sun committed to releasing Java under the GNU General Public License[111] and had released a free software Java, OpenJDK, by May 2007.
+In 2006, Lt. Col. Eric Filiol of the  Laboratoire de Virologie et de Cryptologie de l'ESAT demonstrated security weaknesses, in particular within macros.[112][113][114] In 2006, Kaspersky Lab demonstrated a proof of concept virus, "Stardust", for OpenOffice.org.[115] This showed OpenOffice.org viruses are possible, but there is no known virus "in the wild".
+As of October 2011, Secunia reported no known unpatched security flaws for the software.[116] A vulnerability in the inherited OpenOffice.org codebase was found and fixed in LibreOffice in October 2011[117] and Apache OpenOffice in May 2012.[118]
+The preview, Milestone 638c, was released October 2001.[19] OpenOffice.org 1.0 was released under both the LGPL and the SISSL[23] for Windows, Linux and Solaris[135] on 1 May 2002.[1][136] The version for Mac OS X (with X11 interface) was released on 23 June 2003.[137][138]
+OpenOffice.org 1.1 introduced One-click Export to PDF and Export presentations to Flash (.SWF). It also allowed third-party addons.[101]
+OpenOffice.org was used in 2005 by The Guardian to illustrate what it saw as the limitations of open-source software.[139]
+Work on version 2.0 began in early 2003 with the following goals (the "Q Product Concept"): better interoperability with Microsoft Office; improved speed and lower memory usage; greater scripting capabilities; better integration, particularly with GNOME; a more usable database; digital signatures; and improved usability.[140] It would also be the first version to default to OpenDocument. Sun released the first beta version on 4 March 2005.[141]
+On 2 September 2005, Sun announced that it was retiring SISSL to reduce license proliferation,[142] though some press analysts felt it was so that IBM could not reuse OpenOffice.org code without contributing back.[23] Versions after 2.0 beta 2 would use only the LGPL.[7]
+On 20 October 2005, OpenOffice.org 2.0 was released.[122] 2.0.1 was released eight weeks later, fixing minor bugs and introducing new features. As of the 2.0.3 release, OpenOffice.org changed its release cycle from 18 months to releasing updates every three months.[143]
+The OpenOffice.org 2 series attracted considerable press attention.[144][145][146][147][148][149][150][151] A PC Pro review awarded it 6 stars out of 6 and stated: "Our pick of the low-cost office suites has had a much-needed overhaul, and now battles Microsoft in terms of features, not just price."[152] Federal Computer Week listed OpenOffice.org as one of the "5 stars of open-source products",[153] noting in particular the importance of OpenDocument. ComputerWorld reported that for large government departments, migration to OpenOffice.org 2.0 cost one tenth of the price of upgrading to Microsoft Office 2007.[154]
+On 13 October 2008, version 3.0 was released, featuring the ability to import (though not export) Office Open XML documents, support for ODF 1.2, improved VBA macros, and a native interface port for OS X. It also introduced the new Start Center[130] and upgraded to LGPL version 3 as its license.[155]
+Version 3.2 included support for PostScript-based OpenType fonts. It warned users when ODF 1.2 Extended features had been used. An improvement to the document integrity check determined if an ODF document conformed to the ODF specification and offered a repair if necessary. Calc and Writer both reduced "cold start" time by 46% compared to version 3.0.[156] 3.2.1 was the first Oracle release.[134]
+Version 3.3, the last Oracle version, was released in January 2011.[157] New features include an updated print form, a FindBar and interface improvements for Impress.[158][159] The commercial version, Oracle Open Office 3.3 (StarOffice renamed), based on the beta, was released on 15 December 2010, as was the single release of Oracle Cloud Office (a proprietary product from an unrelated codebase).[41][160]
+A beta version of OpenOffice.org 3.4 was released on 12 April 2011, including new SVG import, improved ODF 1.2 support, and spreadsheet functionality.[4][2][161]
+Before the final version of OpenOffice.org 3.4 could be released, Oracle cancelled its sponsorship of development[12] and fired the remaining Star Division development team.[34][57]
+Problems arise in estimating the market share of OpenOffice.org because it could be freely distributed via download sites (including mirror sites), peer-to-peer networks, CDs, Linux distributions and so forth. The project tried to capture key adoption data in a market-share analysis,[162] listing known distribution totals, known deployments and conversions and analyst statements and surveys.
+According to Valve, as of July 2010, 14.63% of Steam users had OpenOffice.org installed on their machines.[163]
+A market-share analysis conducted by a web analytics service in 2010, based on over 200,000 Internet users, showed a wide range of adoption in different countries:[164] 0.2% in China, 9% in the US and the UK and over 20% in Poland, the Czech Republic, and Germany.
+Although Microsoft Office retained 95% of the general market — as measured by revenue — as of August 2007,[165] OpenOffice.org and StarOffice had secured 15–20% of the business market as of 2004[166][167] and a 2010 University of Colorado at Boulder study reported that OpenOffice.org had reached a point where it had an "irreversible" installed user base and that it would continue to grow.[168]
+The project claimed more than 98 million downloads as of September 2007[169] and 300 million total to the release of version 3.2 in February 2010.[170] The project claimed over one hundred million downloads for the OpenOffice.org 3 series within a year of release.[171]
+Large-scale users of OpenOffice.org included Singapore's Ministry of Defence,[172] and Banco do Brasil.[173] As of 2006[update] OpenOffice.org was the official office suite for the French Gendarmerie.[162]
+In India, several government organizations such as ESIC, IIT Bombay, National Bank for Agriculture and Rural Development, the Supreme Court of India, ICICI Bank,[174] and the Allahabad High Court,[175] which use Linux, completely relied on OpenOffice.org for their administration.
+In Japan, conversions from Microsoft Office to OpenOffice.org included many municipal offices: Sumoto, Hyōgo in 2004,[176] Ninomiya, Tochigi in 2006,[177][178] Aizuwakamatsu, Fukushima in 2008[179] (and to LibreOffice as of 2012[180]), Shikokuchūō, Ehime in 2009,[181] Minoh, Osaka in 2009[182] Toyokawa, Aichi,[183] Fukagawa, Hokkaido[184] and Katano, Osaka[185] in 2010 and Ryūgasaki, Ibaraki in 2011.[186] Corporate conversions included Assist in 2007[187] (and to LibreOffice on Ubuntu in 2011[188]), Sumitomo Electric Industries in 2008[189] (and to LibreOffice in 2012[190]), Toho Co., Ltd. in 2009[191][192] and Shinsei Financial Co., Ltd. in 2010.[193] Assist also provided support services for OpenOffice.org.[191][193]
+In July 2007, Everex, a division of First International Computer and the 9th-largest PC supplier in the U.S., began shipping systems preloaded with OpenOffice.org 2.2 into Wal-Mart, K-mart and Sam's Club outlets in North America.[194]
+A number of open source and proprietary products derive at least some code from OpenOffice.org, including AndrOpen Office,[195] Apache OpenOffice, ChinaOffice, Co-Create Office, EuroOffice 2005,[196] Go-oo, KaiOffice, IBM Lotus Symphony, IBM Workplace, Jambo OpenOffice (the first office suite in Swahili),[197][198][199] LibreOffice, MagyarOffice, MultiMedia Office, MYOffice 2007, NeoOffice, NextOffice, OfficeOne, OfficeTLE, OOo4Kids,[200] OpenOfficePL, OpenOffice.org Portable,[201] OpenOfficeT7, OpenOffice.ux.pl, OxOffice,[202] OxygenOffice Professional,[203][204] Pladao Office,[205] PlusOffice Mac,[206] RedOffice,[37][129][207] RomanianOffice, StarOffice/Oracle Open Office, SunShine Office, ThizOffice, UP Office, White Label Office,[208][209][210][211] WPS Office Storm (the 2004 edition of Kingsoft Office) and 602Office.[212]
+The OpenOffice.org website also listed a large variety of complementary products, including groupware systems.[213]
+Major derivatives include:
+In June 2011, Oracle contributed the OpenOffice.org code and trademarks to the Apache Software Foundation. The developer pool for the Apache project was proposed to be seeded by IBM employees, Linux distribution companies and public sector agencies.[214] IBM employees did the majority of the development,[215][216][217][218][219] including hiring ex-Star Division developers.[217] The Apache project removed or replaced as much code as possible from OpenOffice.org 3.4 beta 1, including fonts, under licenses unacceptable to Apache[220] and released 3.4.0 in May 2012.[118]
+The codebase for IBM's Lotus Symphony was donated to the Apache Software Foundation in 2012 and merged for Apache OpenOffice 4.0,[221] and Symphony was deprecated in favour of Apache OpenOffice.[218]
+While the project considers itself the unbroken continuation of OpenOffice.org,[222] others regard it as a fork,[23][215][216][223][224][225][226] or at the least a separate project.[227]
+In October 2014, Bruce Byfield, writing for Linux Magazine, said the project had "all but stalled [possibly] due to IBM's withdrawal from the project."[228] As of 2015[update], the project has no release manager,[229] and itself reports a lack of volunteer involvement and code contributions.[230] After ongoing problems with unfixed security vulnerabilities from 2015 onward,[231][232][233] in September 2016 the project started discussions on possibly retiring AOO.[234]
+Sun had stated in the original OpenOffice.org announcement in 2000 that the project would be run by a neutral foundation,[10] and put forward a more detailed proposal in 2001.[235] There were many calls to put this into effect over the ensuing years.[36][236][237][238] On 28 September 2010, in frustration at years of perceived neglect of the codebase and community by Sun and then Oracle,[68] members of the OpenOffice.org community announced a non-profit called The Document Foundation and a fork of OpenOffice.org named LibreOffice. Go-oo improvements were merged, and that project was retired in favour of LibreOffice.[239] The goal was to produce a vendor-independent office suite with ODF support and without any copyright assignment requirements.[240]
+Oracle was invited to become a member of the Document Foundation and was asked to donate the OpenOffice.org brand.[240][241] Oracle instead demanded that all members of the OpenOffice.org Community Council involved with the Document Foundation step down,[69] leaving the Council composed only of Oracle employees.[70]
+Most Linux distributions promptly replaced OpenOffice.org with LibreOffice;[53][54][55][56] Oracle Linux 6 also features LibreOffice rather than OpenOffice.org or Apache OpenOffice.[242][243][244] The project rapidly accumulated developers, development effort[245][246][247] and added features,[248] the majority of outside OpenOffice.org developers having moved to LibreOffice.[44][45][48] In March 2015, an LWN.net development comparison of LibreOffice with Apache OpenOffice concluded that "LibreOffice has won the battle for developer participation".[249]
+NeoOffice, an independent commercial port for Macintosh that tracked the main line of development, offered a native OS X Aqua user interface before OpenOffice.org did.[250] Later versions are derived from Go-oo, rather than directly from OpenOffice.org.[251] All versions from NeoOffice 3.1.1 to NeoOffice 2015 were based on OpenOffice.org 3.1.1, though latter versions included stability fixes from LibreOffice and Apache OpenOffice.[252] NeoOffice 2017 and later versions are fully based on LibreOffice.[253]
+The ooo-build patch set was started at Ximian in 2002, because Sun were slow to accept outside work on OpenOffice.org, even from corporate partners, and to make the build process easier on Linux. It tracked the main line of development and was not intended to constitute a fork.[254] Most Linux distributions used,[255] and worked together on,[256] ooo-build.
+Sun's contributions to OpenOffice.org had been declining for a number of years[236] and some developers were unwilling to assign copyright in their work to Sun,[38] particularly given the deal between Sun and IBM to license the code outside the LGPL.[34] On 2 October 2007, Novell announced that ooo-build would be available as a software package called Go-oo, not merely a patch set.[257] (The go-oo.org domain name had been in use by ooo-build as early as 2005.[258]) Sun reacted negatively, with Simon Phipps of Sun terming it "a hostile and competitive fork".[36] Many free software advocates worried that Go-oo was a Novell effort to incorporate Microsoft technologies, such as Office Open XML, that might be vulnerable to patent claims.[259] However, the office suite branded "OpenOffice.org" in most Linux distributions, having previously been ooo-build, soon in fact became Go-oo.[251][260][261]
+Go-oo also encouraged outside contributions, with rules similar to those later adopted for LibreOffice.[262] When LibreOffice forked, Go-oo was deprecated in favour of that project.
+OpenOffice Novell edition was a supported version of Go-oo.[263]
+The Workplace Managed Client in IBM Workplace 2.6 (23 January 2006[264]) incorporated code from OpenOffice.org 1.1.4,[23] the last version under the SISSL. This code was broken out into a separate application as Lotus Symphony (30 May 2008[265]), with a new interface based on Eclipse. Symphony 3.0 (21 October 2010[266]) was rebased on OpenOffice.org 3.0, with the code licensed privately from Sun. IBM's changes were donated to the Apache Software Foundation in 2012, Symphony was deprecated in favour of Apache OpenOffice[218] and its code was merged into Apache OpenOffice 4.0.[221]
+Sun used OpenOffice.org as a base for its commercial proprietary StarOffice application software, which was OpenOffice.org with some added proprietary components. Oracle bought Sun in January 2010 and quickly renamed StarOffice to Oracle Open Office.[267] Oracle discontinued development in April 2011.[12]

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+Athena[b] or Athene,[c] often given the epithet Pallas,[d] is an ancient Greek goddess associated with wisdom, handicraft, and warfare[3] who was later syncretized with the Roman goddess Minerva.[4] Athena was regarded as the patron and protectress of various cities across Greece, particularly the city of Athens, from which she most likely received her name.[5] She's usually shown in art wearing a helmet and holding a spear. Her major symbols include owls, olive trees, snakes, and the Gorgoneion.
+From her origin as an Aegean palace goddess, Athena was closely associated with the city. She was known as Polias and Poliouchos (both derived from polis, meaning "city-state"), and her temples were usually located atop the fortified acropolis in the central part of the city. The Parthenon on the Athenian Acropolis is dedicated to her, along with numerous other temples and monuments. As the patron of craft and weaving, Athena was known as Ergane. She's also a warrior goddess, and was believed to lead soldiers into battle as Athena Promachos. Her main festival in Athens was the Panathenaia, which was celebrated during the month of Hekatombaion in midsummer and was the most important festival on the Athenian calendar.
+In Greek mythology, Athena was believed to have been born from the head of her father Zeus. In the founding myth of Athens, Athena bested Poseidon in a competition over patronage of the city by creating the first olive tree. She's known as Athena Parthenos "Athena the Virgin," but in one archaic Attic myth, the god Hephaestus tried and failed to rape her, resulting in Gaia giving birth to Erichthonius, an important Athenian founding hero. Athena was the patron goddess of heroic endeavor; she was believed to have aided the heroes Perseus, Heracles, Bellerophon, and Jason. Along with Aphrodite and Hera, Athena was one of the three goddesses whose feud resulted in the beginning of the Trojan War.
+She plays an active role in the Iliad, in which she assists the Achaeans and, in the Odyssey, she is the divine counselor to Odysseus. In the later writings of the Roman poet Ovid, Athena was said to have competed against the mortal Arachne in a weaving competition, afterwards transforming Arachne into the first spider; Ovid also describes how she transformed Medusa into a Gorgon after witnessing her being raped by Poseidon in her temple. Since the Renaissance, Athena has become an international symbol of wisdom, the arts, and classical learning. Western artists and allegorists have often used Athena as a symbol of freedom and democracy.
+Athena is associated with the city of Athens.[5][7] The name of the city in ancient Greek is Ἀθῆναι (Athȇnai), a plural toponym, designating the place where—according to myth—she presided over the Athenai, a sisterhood devoted to her worship.[6] In ancient times, scholars argued whether Athena was named after Athens or Athens after Athena.[5] Now scholars generally agree that the goddess takes her name from the city;[5][7] the ending -ene is common in names of locations, but rare for personal names.[5] Testimonies from different cities in ancient Greece attest that similar city goddesses were worshipped in other cities[6] and, like Athena, took their names from the cities where they were worshipped.[6] For example, in Mycenae there was a goddess called Mykene, whose sisterhood was known as Mykenai,[6] whereas at Thebes an analogous deity was called Thebe, and the city was known under the plural form Thebai (or Thebes, in English, where the 's' is the plural formation).[6] The name Athenai is likely of Pre-Greek origin because it contains the presumably Pre-Greek morpheme *-ān-.[8]
+In his dialogue Cratylus, the ancient Greek philosopher Plato (428–347 BC) gives some rather imaginative etymologies of Athena's name, based on the theories of the ancient Athenians and his own etymological speculations:
+That is a graver matter, and there, my friend, the modern interpreters of Homer may, I think, assist in explaining the view of the ancients. For most of these in their explanations of the poet, assert that he meant by Athena "mind" [νοῦς, noũs] and "intelligence" [διάνοια, diánoia], and the maker of names appears to have had a singular notion about her; and indeed calls her by a still higher title, "divine intelligence" [θεοῦ νόησις, theoũ nóēsis], as though he would say: This is she who has the mind of God [ἁ θεονόα, a theonóa). Perhaps, however, the name Theonoe may mean "she who knows divine things" [τὰ θεῖα νοοῦσα, ta theia noousa] better than others. Nor shall we be far wrong in supposing that the author of it wished to identify this Goddess with moral intelligence [εν έθει νόεσιν, en éthei nóesin], and therefore gave her the name Etheonoe; which, however, either he or his successors have altered into what they thought a nicer form, and called her Athena.
+Thus, Plato believed that Athena's name was derived from Greek Ἀθεονόα, Atheonóa—which the later Greeks rationalised as from the deity's (θεός, theós) mind (νοῦς, noũs). The second-century AD orator Aelius Aristides attempted to derive natural symbols from the etymological roots of Athena's names to be aether, air, earth, and moon.[9]
+Athena was originally the Aegean goddess of the palace, who presided over household crafts and protected the king.[11][12][13][14] A single Mycenaean Greek inscription 𐀀𐀲𐀙𐀡𐀴𐀛𐀊 a-ta-na po-ti-ni-ja /Athana potnia/ appears at Knossos in the Linear B tablets from the Late Minoan II-era "Room of the Chariot Tablets";[15][16][10] these comprise the earliest Linear B archive anywhere.[16] Although Athana potnia is often translated Mistress Athena,[17] it could also mean "the Potnia of Athana", or the Lady of Athens.[17][10] However, any connection to the city of Athens in the Knossos inscription is uncertain.[18] A sign series a-ta-no-dju-wa-ja appears in the still undeciphered corpus of Linear A tablets, written in the unclassified Minoan language.[19] This could be connected with the Linear B Mycenaean expressions a-ta-na po-ti-ni-ja and di-u-ja or di-wi-ja (Diwia, "of Zeus" or, possibly, related to a homonymous goddess),[16] resulting in a translation "Athena of Zeus" or "divine Athena". Similarly, in the Greek mythology and epic tradition, Athena figures as a daughter of Zeus (Διός θυγάτηρ; cfr. Dyeus).[20] However, the inscription quoted seems to be very similar to "a-ta-nū-tī wa-ya", quoted as SY Za 1 by Jan Best.[20] Best translates the initial a-ta-nū-tī, which is recurrent in line beginnings, as "I have given".[20]
+A Mycenean fresco depicts two women extending their hands towards a central figure, who is covered by an enormous figure-eight shield; this may depict the warrior-goddess with her palladion, or her palladion in an aniconic representation.[21][22] In the "Procession Fresco" at Knossos, which was reconstructed by the Mycenaeans,[23] two rows of figures carrying vessels seem to meet in front of a central figure,[23] which is probably the Minoan precursor to Athena.[23] The early twentieth-century scholar Martin Persson Nilsson argued that the Minoan snake goddess figurines are early representations of Athena.[11][12]
+Nilsson and others have claimed that, in early times, Athena was either an owl herself or a bird goddess in general.[24] In the third book of the Odyssey, she takes the form of a sea-eagle.[24] Proponents of this view argue that she dropped her prophylactic owl-mask before she lost her wings. "Athena, by the time she appears in art," Jane Ellen Harrison remarks, "has completely shed her animal form, has reduced the shapes she once wore of snake and bird to attributes, but occasionally in black-figure vase-paintings she still appears with wings."[25]
+It is generally agreed that the cult of Athena preserves some aspects of the Proto-Indo-European transfunctional goddess.[27][28] The cult of Athena may have also been influenced by those of Near Eastern warrior goddesses such as the East Semitic Ishtar and the Ugaritic Anat,[12][10] both of whom were often portrayed bearing arms.[12] Classical scholar Charles Penglase notes that Athena closely resembles Inanna in her role as a "terrifying warrior goddess"[29] and that both goddesses were closely linked with creation.[29] Athena's birth from the head of Zeus may be derived from the earlier Sumerian myth of Inanna's descent into and return from the Underworld.[30][31]
+Plato notes that the citizens of Sais in Egypt worshipped a goddess known as Neith,[e] whom he identifies with Athena.[32] Neith was the ancient Egyptian goddess of war and hunting, who was also associated with weaving; her worship began during the Egyptian Pre-Dynastic period. In Greek mythology, Athena was reported to have visited mythological sites in North Africa, including Libya's Triton River and the Phlegraean plain.[f] Based on these similarities, the Sinologist Martin Bernal created the "Black Athena" hypothesis, which claimed that Neith was brought to Greece from Egypt, along with "an enormous number of features of civilization and culture in the third and second millennia".[33][34] The "Black Athena" hypothesis stirred up widespread controversy near the end of the twentieth century,[35][36] but it has now been widely rejected by modern scholars.[37][38]
+In her aspect of Athena Polias, Athena was venerated as the goddess of the city and the protectress of the citadel.[12][39][40] In Athens, the Plynteria, or "Feast of the Bath", was observed every year at the end of the month of Thargelion.[41] The festival lasted for five days. During this period, the priestesses of Athena, or plyntrídes, performed a cleansing ritual within the Erechtheion, a sanctuary devoted to Athena and Poseidon.[42] Here Athena's statue was undressed, her clothes washed, and body purified.[42] Athena was worshipped at festivals such as Chalceia as Athena Ergane,[43][40] the patroness of various crafts, especially weaving.[43][40] She was also the patron of metalworkers and was believed to aid in the forging of armor and weapons.[43] During the late fifth century BC, the role of goddess of philosophy became a major aspect of Athena's cult.[44]
+As Athena Promachos, she was believed to lead soldiers into battle.[45][46] Athena represented the disciplined, strategic side of war, in contrast to her brother Ares, the patron of violence, bloodlust, and slaughter—"the raw force of war".[47][48] Athena was believed to only support those fighting for a just cause[47] and was thought to view war primarily as a means to resolve conflict.[47] The Greeks regarded Athena with much higher esteem than Ares.[47][48] Athena was especially worshipped in this role during the festivals of the Panathenaea and Pamboeotia,[49] both of which prominently featured displays of athletic and military prowess.[49] As the patroness of heroes and warriors, Athena was believed to favor those who used cunning and intelligence rather than brute strength.[50]
+In her aspect as a warrior maiden, Athena was known as Parthenos (Παρθένος "virgin"),[45][52][53] because, like her fellow goddesses Artemis and Hestia, she was believed to remain perpetually a virgin.[54][55][45][53][56] Athena's most famous temple, the Parthenon on the Athenian Acropolis, takes its name from this title.[56] According to Karl Kerényi, a scholar of Greek mythology, the name Parthenos is not merely an observation of Athena's virginity, but also a recognition of her role as enforcer of rules of sexual modesty and ritual mystery.[56] Even beyond recognition, the Athenians allotted the goddess value based on this pureness of virginity, which they upheld as a rudiment of female behavior.[56] Kerényi's study and theory of Athena explains her virginal epithet as a result of her relationship to her father Zeus and a vital, cohesive piece of her character throughout the ages.[56] This role is expressed in a number of stories about Athena. Marinus of Neapolis reports that when Christians removed the statue of the goddess from the Parthenon, a beautiful woman appeared in a dream to Proclus, a devotee of Athena, and announced that the "Athenian Lady" wished to dwell with him.[57]
+Athena was not only the patron goddess of Athens, but also other cities, including Argos, Sparta, Gortyn, Lindos, and Larisa.[46] The various cults of Athena were all branches of her panhellenic cult[46] and often proctored various initiation rites of Grecian youth, such as the passage into citizenship by young men or the passage of young women into marriage.[46] These cults were portals of a uniform socialization, even beyond mainland Greece.[46] Athena was frequently equated with Aphaea, a local goddess of the island of Aegina, originally from Crete and also associated with Artemis and the nymph Britomartis.[58] In Arcadia, she was assimilated with the ancient goddess Alea and worshiped as Athena Alea.[59] Sanctuaries dedicated to Athena Alea were located in the Laconian towns of Mantineia and Tegea. The temple of Athena Alea in Tegea was an important religious center of ancient Greece.[g] The geographer Pausanias was informed that the temenos had been founded by Aleus.[60]
+Athena had a major temple on the Spartan Acropolis,[61][40] where she was venerated as Poliouchos and Khalkíoikos ("of the Brazen House", often latinized as Chalcioecus).[61][40] This epithet may refer to the fact that cult statue held there may have been made of bronze,[61] that the walls of the temple itself may have been made of bronze,[61] or that Athena was the patron of metal-workers.[61] Bells made of terracotta and bronze were used in Sparta as part of Athena's cult.[61] An Ionic-style temple to Athena Polias was built at Priene in the fourth century BC.[62] It was designed by Pytheos of Priene,[63] the same architect who designed the Mausoleum at Halicarnassus.[63] The temple was dedicated by Alexander the Great[64] and an inscription from the temple declaring his dedication is now held in the British Museum.[62]
+Athena was known as Atrytone (Άτρυτώνη "the Unwearying"), Parthenos (Παρθένος "Virgin"), and Promachos (Πρόμαχος "she who fights in front"). The epithet Polias (Πολιάς "of the city"), refers to Athena's role as protectress of the city.[46] The epithet Ergane (Εργάνη "the Industrious") pointed her out as the patron of craftsmen and artisans.[46] Burkert notes that the Athenians sometimes simply called Athena "the Goddess", hē theós (ἡ θεός), certainly an ancient title.[5] After serving as the judge at the trial of Orestes in which he was acquitted of having murdered his mother Clytemnestra, Athena won the epithet Areia (Αρεία).[46]
+Athena was sometimes given the epithet Hippia (Ἵππια "of the horses", "equestrian"),[40][65] referring to her invention of the bit, bridle, chariot, and wagon.[40] The Greek geographer Pausanias mentions in his Guide to Greece that the temple of Athena Chalinitis ("the bridler")[65] in Corinth was located near the tomb of Medea's children.[65] Other epithets include Ageleia, Itonia and Aethyia, under which she was worshiped in Megara.[66][67] The word aíthyia (αἴθυια) signifies a "diver", also some diving bird species (possibly the shearwater) and figuratively, a "ship", so the name must reference Athena teaching the art of shipbuilding or navigation.[68] In a temple at Phrixa in Elis, reportedly built by Clymenus, she was known as Cydonia (Κυδωνία).[69]
+The Greek biographer Plutarch (AD 46–120) refers to an instance during the Parthenon's construction of her being called Athena Hygieia (Ὑγίεια, i. e. personified "Health") after inspiring a physician to a successful course of treatment.[70]
+In Homer's epic works, Athena's most common epithet is Glaukopis (γλαυκῶπις), which usually is translated as, "bright-eyed" or "with gleaming eyes".[71] The word is a combination of glaukós (γλαυκός, meaning "gleaming, silvery", and later, "bluish-green" or "gray")[72] and ṓps (ὤψ, "eye, face").[73] The word glaúx (γλαύξ,[74] "little owl")[75] is from the same root, presumably according to some, because of the bird's own distinctive eyes. Athena was clearly associated with the owl from very early on;[76] in archaic images, she is frequently depicted with an owl perched on her hand.[76] Through its association with Athena, the owl evolved into the national mascot of the Athenians and eventually became a symbol of wisdom.[4]
+In the Iliad (4.514), the Odyssey (3.378), the Homeric Hymns, and in Hesiod's Theogony, Athena is also given the curious epithet Tritogeneia (Τριτογένεια), whose significance remains unclear.[77] It could mean various things, including "Triton-born", perhaps indicating that the homonymous sea-deity was her parent according to some early myths.[77] One myth relates the foster father relationship of this Triton towards the half-orphan Athena, whom he raised alongside his own daughter Pallas.[78] Kerényi suggests that "Tritogeneia did not mean that she came into the world on any particular river or lake, but that she was born of the water itself; for the name Triton seems to be associated with water generally."[79][80] In Ovid's Metamorphoses, Athena is occasionally referred to as "Tritonia".
+Another possible meaning may be "triple-born" or "third-born", which may refer to a triad or to her status as the third daughter of Zeus or the fact she was born from Metis, Zeus, and herself; various legends list her as being the first child after Artemis and Apollo, though other legends identify her as Zeus' first child.[81] Several scholars have suggested a connection to the Rigvedic god Trita,[82] who was sometimes grouped in a body of three mythological poets.[82] Michael Janda has connected the myth of Trita to the scene in the Iliad in which the "three brothers" Zeus, Poseidon, and Hades divide the world between them, receiving the "broad sky", the sea, and the underworld respectively.[83][84] Janda further connects the myth of Athena being born of the head (i. e. the uppermost part) of Zeus, understanding Trito- (which perhaps originally meant "the third") as another word for "the sky".[83] In Janda's analysis of Indo-European mythology, this heavenly sphere is also associated with the mythological body of water surrounding the inhabited world (cfr. Triton's mother, Amphitrite).[83]
+Yet another possible meaning is mentioned in Diogenes Laertius' biography of Democritus, that Athena was called "Tritogeneia" because three things, on which all mortal life depends, come from her.[85]
+In the classical Olympian pantheon, Athena was regarded as the favorite daughter of Zeus, born fully armed from his forehead.[86][87][88][h] The story of her birth comes in several versions.[89][90][91] The earliest mention is in Book V of the Iliad, when Ares accuses Zeus of being biased in favor of Athena because "autos egeinao" (literally "you fathered her", but probably intended as "you gave birth to her").[92][93]
+In the version recounted by Hesiod in his Theogony, Zeus married the goddess Metis, who is described as the "wisest among gods and mortal men", and engaged in sexual intercourse with her.[94][95][93][96] After learning that Metis was pregnant, however, he became afraid that the unborn offspring would try to overthrow him, because Gaia and Ouranos had prophesied that Metis would bear children wiser than their father.[94][95][93][96] In order to prevent this, Zeus tricked Metis into letting him swallow her, but it was too late because Metis had already conceived.[94][97][93][96] A later account of the story from the Bibliotheca of Pseudo-Apollodorus, written in the second century AD, makes Metis Zeus's unwilling sexual partner, rather than his wife.[98][99] According to this version of the story, Metis transformed into many different shapes in effort to escape Zeus,[98][99] but Zeus successfully raped her and swallowed her.[98][99]
+After swallowing Metis, Zeus took six more wives in succession until he married his seventh and present wife, Hera.[96] Then Zeus experienced an enormous headache.[100][93][96] He was in such pain that he ordered someone (either Prometheus, Hephaestus, Hermes, Ares, or Palaemon, depending on the sources examined) to cleave his head open with the labrys, the double-headed Minoan axe.[101][93][102][99] Athena leaped from Zeus's head, fully grown and armed.[101][93][88][103] The "First Homeric Hymn to Athena" states in lines 9–16 that the gods were awestruck by Athena's appearance[104] and even Helios, the god of the sun, stopped his chariot in the sky.[104] Pindar, in his "Seventh Olympian Ode", states that she "cried aloud with a mighty shout" and that "the Sky and mother Earth shuddered before her."[105][104]
+Hesiod states that Hera was so annoyed at Zeus for having given birth to a child on his own that she conceived and bore Hephaestus by herself,[96] but in Imagines 2. 27 (trans. Fairbanks), the third-century AD Greek rhetorician Philostratus the Elder writes that Hera "rejoices" at Athena's birth "as though Athena were her daughter also." The second-century AD Christian apologist Justin Martyr takes issue with those pagans who erect at springs images of Kore, whom he interprets as Athena: "They said that Athena was the daughter of Zeus not from intercourse, but when the god had in mind the making of a world through a word (logos) his first thought was Athena."[106] According to a version of the story in a scholium on the Iliad (found nowhere else), when Zeus swallowed Metis, she was pregnant with Athena by the Cyclops Brontes.[107] The Etymologicum Magnum[108] instead deems Athena the daughter of the Daktyl Itonos.[109] Fragments attributed by the Christian Eusebius of Caesarea to the semi-legendary Phoenician historian Sanchuniathon, which Eusebius thought had been written before the Trojan war, make Athena instead the daughter of Cronus, a king of Byblos who visited "the inhabitable world" and bequeathed Attica to Athena.[110][111]
+Athena's epithet Pallas is derived either from πάλλω, meaning "to brandish [as a weapon]", or, more likely, from παλλακίς and related words, meaning "youth, young woman".[113] On this topic, Walter Burkert says "she is the Pallas of Athens, Pallas Athenaie, just as Hera of Argos is Here Argeie."[5] In later times, after the original meaning of the name had been forgotten, the Greeks invented myths to explain its origin, such as those reported by the Epicurean philosopher Philodemus and the Bibliotheca of Pseudo-Apollodorus, which claim that Pallas was originally a separate entity, whom Athena had slain in combat.[114]
+In one version of the myth, Pallas was the daughter of the sea-god Triton;[78] she and Athena were childhood friends, but Athena accidentally killed her during a friendly sparring match.[115] Distraught over what she had done, Athena took the name Pallas for herself as a sign of her grief.[115] In another version of the story, Pallas was a Gigante;[101] Athena slew him during the Gigantomachy and flayed off his skin to make her cloak, which she wore as a victory trophy.[101][12][116][117] In an alternative variation of the same myth, Pallas was instead Athena's father,[101][12] who attempted to assault his own daughter,[118] causing Athena to kill him and take his skin as a trophy.[119]
+The palladion was a statue of Athena that was said to have stood in her temple on the Trojan Acropolis.[120] Athena was said to have carved the statue herself in the likeness of her dead friend Pallas.[120] The statue had special talisman-like properties[120] and it was thought that, as long as it was in the city, Troy could never fall.[120] When the Greeks captured Troy, Cassandra, the daughter of Priam, clung to the palladion for protection,[120] but Ajax the Lesser violently tore her away from it and dragged her over to the other captives.[120] Athena was infuriated by this violation of her protection.[112] Although Agamemnon attempted to placate her anger with sacrifices, Athena sent a storm at Cape Kaphereos to destroy almost the entire Greek fleet and scatter all of the surviving ships across the Aegean.[121]
+In a founding myth reported by Pseudo-Apollodorus,[108] Athena competed with Poseidon for the patronage of Athens.[122] They agreed that each would give the Athenians one gift[122] and that Cecrops, the king of Athens, would determine which gift was better.[122] Poseidon struck the ground with his trident and a salt water spring sprang up;[122] this gave the Athenians access to trade and water.[123] Athens at its height was a significant sea power, defeating the Persian fleet at the Battle of Salamis[123]—but the water was salty and undrinkable.[123] In an alternative version of the myth from Vergil's Georgics,[108] Poseidon instead gave the Athenians the first horse.[122] Athena offered the first domesticated olive tree.[122][53] Cecrops accepted this gift[122] and declared Athena the patron goddess of Athens.[122] The olive tree brought wood, oil, and food,[123] and became a symbol of Athenian economic prosperity.[53][124] Robert Graves was of the opinion that "Poseidon's attempts to take possession of certain cities are political myths",[123] which reflect the conflict between matriarchal and patriarchal religions.[123]
+Pseudo-Apollodorus[108] records an archaic legend, which claims that Hephaestus once attempted to rape Athena, but she pushed him away, causing him to ejaculate on her thigh.[126][51][127] Athena wiped the semen off using a tuft of wool, which she tossed into the dust,[126][51][127] impregnating Gaia and causing her to give birth to Erichthonius.[126][51][127] Athena adopted Erichthonius as her son and raised him.[126][127] The Roman mythographer Hyginus[108] records a similar story in which Hephaestus demanded Zeus to let him marry Athena since he was the one who had smashed open Zeus's skull, allowing Athena to be born.[126] Zeus agreed to this and Hephaestus and Athena were married,[126] but, when Hephaestus was about to consummate the union, Athena vanished from the bridal bed, causing him to ejaculate on the floor, thus impregnating Gaia with Erichthonius.[126]
+The geographer Pausanias[108] records that Athena placed the infant Erichthonius into a small chest[128] (cista), which she entrusted to the care of the three daughters of Cecrops: Herse, Pandrosos, and Aglauros of Athens.[128] She warned the three sisters not to open the chest,[128] but did not explain to them why or what was in it.[128] Aglauros, and possibly one of the other sisters,[128] opened the chest.[128] Differing reports say that they either found that the child itself was a serpent, that it was guarded by a serpent, that it was guarded by two serpents, or that it had the legs of a serpent.[129] In Pausanias's story, the two sisters were driven mad by the sight of the chest's contents and hurled themselves off the Acropolis, dying instantly,[130] but an Attic vase painting shows them being chased by the serpent off the edge of the cliff instead.[130]
+Erichthonius was one of the most important founding heroes of Athens[51] and the legend of the daughters of Cecrops was a cult myth linked to the rituals of the Arrhephoria festival.[51][131] Pausanias records that, during the Arrhephoria, two young girls known as the Arrhephoroi, who lived near the temple of Athena Polias, would be given hidden objects by the priestess of Athena,[132] which they would carry on their heads down a natural underground passage.[132] They would leave the objects they had been given at the bottom of the passage and take another set of hidden objects,[132] which they would carry on their heads back up to the temple.[132] The ritual was performed in the dead of night[132] and no one, not even the priestess, knew what the objects were.[132] The serpent in the story may be the same one depicted coiled at Athena's feet in Pheidias's famous statue of the Athena Parthenos in the Parthenon.[125] Many of the surviving sculptures of Athena show this serpent.[125]
+Herodotus records that a serpent lived in a crevice on the north side of the summit of the Athenian Acropolis[125] and that the Athenians left a honey cake for it each month as an offering.[125] On the eve of the Second Persian invasion of Greece in 480 BC, the serpent did not eat the honey cake[125] and the Athenians interpreted it as a sign that Athena herself had abandoned them.[125] Another version of the myth of the Athenian maidens is told in Metamorphoses by the Roman poet Ovid (43 BC – 17 AD); in this late variant Hermes falls in love with Herse. Herse, Aglaulus, and Pandrosus go to the temple to offer sacrifices to Athena. Hermes demands help from Aglaulus to seduce Herse. Aglaulus demands money in exchange. Hermes gives her the money the sisters have already offered to Athena. As punishment for Aglaulus's greed, Athena asks the goddess Envy to make Aglaulus jealous of Herse. When Hermes arrives to seduce Herse, Aglaulus stands in his way instead of helping him as she had agreed. He turns her to stone.[133]
+According to Pseudo-Apollodorus's Bibliotheca, Athena advised Argos, the builder of the Argo, the ship on which the hero Jason and his band of Argonauts sailed, and aided in the ship's construction.[135][136] Pseudo-Apollodorus also records that Athena guided the hero Perseus in his quest to behead Medusa.[137][138][139] She and Hermes, the god of travelers, appeared to Perseus after he set off on his quest and gifted him with tools he would need to kill the Gorgon.[139][140] Athena gave Perseus a polished bronze shield to view Medusa's reflection rather than looking at her directly and thereby avoid being turned to stone.[139][141] Hermes gave him an adamantine scythe to cut off Medusa's head.[139][142] When Perseus swung his blade to behead Medusa, Athena guided it, allowing his scythe to cut it clean off.[139][141] According to Pindar's Thirteenth Olympian Ode, Athena helped the hero Bellerophon tame the winged horse Pegasus by giving him a bit.[143][144]
+In ancient Greek art, Athena is frequently shown aiding the hero Heracles.[145] She appears in four of the twelve metopes on the Temple of Zeus at Olympia depicting Heracles's Twelve Labors,[146][145] including the first, in which she passively watches him slay the Nemean lion,[145] and the tenth, in which she is shown actively helping him hold up the sky.[147] She is presented as his "stern ally",[148] but also the "gentle... acknowledger of his achievements."[148] Artistic depictions of Heracles's apotheosis show Athena driving him to Mount Olympus in her chariot and presenting him to Zeus for his deification.[147] In Aeschylus's tragedy Orestes, Athena intervenes to save Orestes from the wrath of the Erinyes and presides over his trial for the murder of his mother Clytemnestra.[149] When half the jury votes to acquit and the other half votes to convict, Athena casts the deciding vote to acquit Orestes[149] and declares that, from then on, whenever a jury is tied, the defendant shall always be acquitted.[150]
+In The Odyssey, Odysseus' cunning and shrewd nature quickly wins Athena's favour.[151][136] For the first part of the poem, however, she largely is confined to aiding him only from afar, mainly by implanting thoughts in his head during his journey home from Troy. Her guiding actions reinforce her role as the "protectress of heroes," or, as mythologian Walter Friedrich Otto dubbed her, the "goddess of nearness," due to her mentoring and motherly probing.[152][137][153] It is not until he washes up on the shore of the island of the Phaeacians, where Nausicaa is washing her clothes that Athena arrives personally to provide more tangible assistance.[154] She appears in Nausicaa's dreams to ensure that the princess rescues Odysseus and plays a role in his eventual escort to Ithaca.[155] Athena appears to Odysseus upon his arrival, disguised as a herdsman;[156][157][151] she initially lies and tells him that Penelope, his wife, has remarried and that he is believed to be dead,[156] but Odysseus lies back to her, employing skillful prevarications to protect himself.[158][157] Impressed by his resolve and shrewdness, she reveals herself and tells him what he needs to know in order to win back his kingdom.[159][157][151] She disguises him as an elderly beggar so that he will not be recognized by the suitors or Penelope,[160][157] and helps him to defeat the suitors.[160][161][157] Athena also appears to Odysseus's son Telemachus.[162] Her actions lead him to travel around to Odysseus's comrades and ask about his father.[163] He hears stories about some of Odysseus's journey.[163] Athena's push for Telemachos's journey helps him grow into the man role, that his father once held.[164] She also plays a role in ending the resultant feud against the suitors' relatives. She instructs Laertes to throw his spear and to kill Eupeithes, the father of Antinous.
+Athena and Heracles on an Attic red-figure kylix, 480–470 BC
+Athena, detail from a silver kantharos with Theseus in Crete (c. 440-435 BC), part of the Vassil Bojkov collection, Sofia, Bulgaria
+Silver coin showing Athena with Scylla decorated helmet and Heracles fighting the Nemean lion (Heraclea Lucania, 390-340 BC)
+Paestan red-figure bell-krater (c. 330 BC), showing Orestes at Delphi flanked by Athena and Pylades among the Erinyes and priestesses of Apollo, with the Pythia sitting behind them on her tripod
+The Gorgoneion appears to have originated as an apotropaic symbol intended to ward off evil.[165] In a late myth invented to explain the origins of the Gorgon,[166] Medusa is described as having been a young priestess who served in the temple of Athena in Athens.[167] Poseidon lusted after Medusa, and raped her in the temple of Athena,[167] refusing to allow her vow of chastity to stand in his way.[167] Upon discovering the desecration of her temple, Athena transformed Medusa into a hideous monster with serpents for hair whose gaze would turn any mortal to stone.[168]
+In his Twelfth Pythian Ode, Pindar recounts the story of how Athena invented the aulos, a kind of flute, in imitation of the lamentations of Medusa's sisters, the Gorgons, after she was beheaded by the hero Perseus.[169] According to Pindar, Athena gave the aulos to mortals as a gift.[169] Later, the comic playwright Melanippides of Melos (c. 480-430 BC) embellished the story in his comedy Marsyas,[169] claiming that Athena looked in the mirror while she was playing the aulos and saw how blowing into it puffed up her cheeks and made her look silly, so she threw the aulos away and cursed it so that whoever picked it up would meet an awful death.[169] The aulos was picked up by the satyr Marsyas, who was later killed by Apollo for his hubris.[169] Later, this version of the story became accepted as canonical[169] and the Athenian sculptor Myron created a group of bronze sculptures based on it, which was installed before the western front of the Parthenon in around 440 BC.[169]
+A myth told by the early third-century BC Hellenistic poet Callimachus in his Hymn 5 begins with Athena bathing in a spring on Mount Helicon at midday with one of her favorite companions, the nymph Chariclo.[127][170] Chariclo's son Tiresias happened to be hunting on the same mountain and came to the spring searching for water.[127][170] He inadvertently saw Athena naked, so she struck him blind to ensure he would never again see what man was not intended to see.[127][171][172] Chariclo intervened on her son's behalf and begged Athena to have mercy.[127][172][173] Athena replied that she could not restore Tiresias's eyesight,[127][172][173] so, instead, she gave him the ability to understand the language of the birds and thus foretell the future.[174][173][127]
+The fable of Arachne appears in Ovid's Metamorphoses (8 AD) (vi.5–54 and 129–145),[175][176][177] which is nearly the only extant source for the legend.[176][177] The story does not appear to have been well known prior to Ovid's rendition of it[176] and the only earlier reference to it is a brief allusion in Virgil's Georgics, (29 BC) (iv, 246) that does not mention Arachne by name.[177] According to Ovid, Arachne (whose name means spider in ancient Greek[178]) was the daughter of a famous dyer in Tyrian purple in Hypaipa of Lydia, and a weaving student of Athena.[179] She became so conceited of her skill as a weaver that she began claiming that her skill was greater than that of Athena herself.[179][180] Athena gave Arachne a chance to redeem herself by assuming the form of an old woman and warning Arachne not to offend the deities.[175][180] Arachne scoffed and wished for a weaving contest, so she could prove her skill.[181][180]
+Athena wove the scene of her victory over Poseidon in the contest for the patronage of Athens.[181][182][180] Athena's tapestry also depicted the 12 Olympian gods and defeat of mythological figures who challenged their authority.[183] Arachne's tapestry featured twenty-one episodes of the deities' infidelity,[181][182][180] including Zeus being unfaithful with Leda, with Europa, and with Danaë.[182] It represented the unjust and discrediting behavior of the gods towards mortals.[183] Athena admitted that Arachne's work was flawless,[181][180][182] but was outraged at Arachne's offensive choice of subject, which displayed the failings and transgressions of the deities.[181][180][182] Finally, losing her temper, Athena destroyed Arachne's tapestry and loom, striking it with her shuttle.[181][180][182] Athena then struck Arachne across the face with her staff four times.[181][180][182] Arachne hanged herself in despair,[181][180][182] but Athena took pity on her and brought her back from the dead in the form of a spider.[181][180][182]
+The myth of the Judgement of Paris is mentioned briefly in the Iliad,[184] but is described in depth in an epitome of the Cypria, a lost poem of the Epic Cycle,[185] which records that all the gods and goddesses as well as various mortals were invited to the marriage of Peleus and Thetis (the eventual parents of Achilles).[184] Only Eris, goddess of discord, was not invited.[185] She was annoyed at this, so she arrived with a golden apple inscribed with the word καλλίστῃ (kallistēi, "for the fairest"), which she threw among the goddesses.[186] Aphrodite, Hera, and Athena all claimed to be the fairest, and thus the rightful owner of the apple.[186][127]
+The goddesses chose to place the matter before Zeus, who, not wanting to favor one of the goddesses, put the choice into the hands of Paris, a Trojan prince.[186][127] After bathing in the spring of Mount Ida where Troy was situated, the goddesses appeared before Paris for his decision.[186] In the extant ancient depictions of the Judgement of Paris, Aphrodite is only occasionally represented nude, and Athena and Hera are always fully clothed.[187] Since the Renaissance, however, western paintings have typically portrayed all three goddesses as completely naked.[187]
+All three goddesses were ideally beautiful and Paris could not decide between them, so they resorted to bribes.[186] Hera tried to bribe Paris with power over all Asia and Europe,[186][127] and Athena offered fame and glory in battle,[186][127] but Aphrodite promised Paris that, if he were to choose her as the fairest, she would let him marry the most beautiful woman on earth.[188][127] This woman was Helen, who was already married to King Menelaus of Sparta.[188] Paris selected Aphrodite and awarded her the apple.[188][127] The other two goddesses were enraged and, as a direct result, sided with the Greeks in the Trojan War.[188][127]
+In Books V–VI of the Iliad, Athena aids the hero Diomedes, who, in the absence of Achilles, proves himself to be the most effective Greek warrior.[189][136] Several artistic representations from the early sixth century BC may show Athena and Diomedes,[189] including an early sixth-century BC shield band depicting Athena and an unidentified warrior riding on a chariot, a vase painting of a warrior with his charioteer facing Athena, and an inscribed clay plaque showing Diomedes and Athena riding in a chariot.[189] Numerous passages in the Iliad also mention Athena having previously served as the patron of Diomedes's father Tydeus.[190][191] When the Trojan women go to the temple of Athena on the Acropolis to plead her for protection from Diomedes, Athena ignores them.[112]
+In Book XXII of the Iliad, while Achilles is chasing Hector around the walls of Troy, Athena appears to Hector disguised as his brother Deiphobus[192] and persuades him to hold his ground so that they can fight Achilles together.[192] Then, Hector throws his spear at Achilles and misses, expecting Deiphobus to hand him another,[193] but Athena disappears instead, leaving Hector to face Achilles alone without his spear.[193] In Sophocles's tragedy Ajax, she punishes Odysseus's rival Ajax the Great, driving him insane and causing him to massacre the Achaeans' cattle, thinking that he is slaughtering the Achaeans themselves.[194] Even after Odysseus himself expresses pity for Ajax,[195] Athena declares, "To laugh at your enemies - what sweeter laughter can there be than that?" (lines 78–9).[195] Ajax later commits suicide as a result of his humiliation.[195]
+Athena appears frequently in classical Greek art, including on coins and in paintings on ceramics.[196][197] She is especially prominent in works produced in Athens.[196] In classical depictions, Athena is usually portrayed standing upright, wearing a full-length chiton.[198] She is most often represented dressed in armor like a male soldier[197][198][7] and wearing a Corinthian helmet raised high atop her forehead.[199][7][197] Her shield bears at its centre the aegis with the head of the gorgon (gorgoneion) in the center and snakes around the edge.[166] Sometimes she is shown wearing the aegis as a cloak.[197] As Athena Promachos, she is shown brandishing a spear.[196][7][197] Scenes in which Athena was represented include her birth from the head of Zeus, her battle with the Gigantes, the birth of Erichthonius, and the Judgement of Paris.[196]
+The Mourning Athena or Athena Meditating is a famous relief sculpture dating to around 470-460 BC[199][196] that has been interpreted to represent Athena Polias.[199] The most famous classical depiction of Athena was the Athena Parthenos, a now-lost 11.5 m (38 ft)[200] gold and ivory statue of her in the Parthenon created by the Athenian sculptor Phidias.[198][196] Copies reveal that this statue depicted Athena holding her shield in her left hand with Nike, the winged goddess of victory, standing in her right.[196] Athena Polias is also represented in a Neo-Attic relief now held in the Virginia Museum of Fine Arts,[199] which depicts her holding an owl in her hand[i] and wearing her characteristic Corinthian helmet while resting her shield against a nearby herma.[199] The Roman goddess Minerva adopted most of Athena's Greek iconographical associations,[201] but was also integrated into the Capitoline Triad.[201]
+Attic black-figure exaleiptron of the birth of Athena from the head of Zeus (c. 570–560 BC) by the C Painter[196]
+Attic red-figure kylix of Athena Promachos holding a spear and standing beside a Doric column (c. 500-490 BC)
+Restoration of the polychrome decoration of the Athena statue from the Aphaea temple at Aegina, c. 490 BC (from the exposition "Bunte Götter" by the Munich Glyptothek)
+The Mourning Athena relief (c. 470-460 BC)[199][196]
+Attic red-figure kylix showing Athena slaying the Gigante Enceladus (c. 550–500 BC)
+Relief of Athena and Nike slaying the Gigante Alkyoneus (?) from the Gigantomachy Frieze on the Pergamon Altar (early second century BC)
+Classical mosaic from a villa at Tusculum, 3rd century AD, now at Museo Pio-Clementino, Vatican
+Athena portrait by Eukleidas on a tetradrachm from Syracuse,Sicily c. 400 BC
+Mythological scene with Athena (left) and Herakles (right), on a stone palette of the Greco-Buddhist art of Gandhara, India
+Atena farnese, Roman copy of a Greek original from Phidias' circle, c. 430 AD, Museo Archeologico, Naples
+Early Christian writers, such as Clement of Alexandria and Firmicus, denigrated Athena as representative of all the things that were detestable about paganism;[203] they condemned her as "immodest and immoral".[204] During the Middle Ages, however, many attributes of Athena were given to the Virgin Mary,[204] who, in fourth century portrayals, was often depicted wearing the Gorgoneion.[204] Some even viewed the Virgin Mary as a warrior maiden, much like Athena Parthenos;[204] one anecdote tells that the Virgin Mary once appeared upon the walls of Constantinople when it was under siege by the Avars, clutching a spear and urging the people to fight.[205] During the Middle Ages, Athena became widely used as a Christian symbol and allegory, and she appeared on the family crests of certain noble houses.[206]
+During the Renaissance, Athena donned the mantle of patron of the arts and human endeavor;[207] allegorical paintings involving Athena were a favorite of the Italian Renaissance painters.[207] In Sandro Botticelli's painting Pallas and the Centaur, probably painted sometime in the 1480s, Athena is the personification of chastity, who is shown grasping the forelock of a centaur, who represents lust.[208][209] Andrea Mantegna's 1502 painting Minerva Expelling the Vices from the Garden of Virtue uses Athena as the personification of Graeco-Roman learning chasing the vices of medievalism from the garden of modern scholarship.[210][209][211] Athena is also used as the personification of wisdom in Bartholomeus Spranger's 1591 painting The Triumph of Wisdom or Minerva Victorious over Ignorance.[201]
+During the sixteenth and seventeenth centuries, Athena was used as a symbol for female rulers.[212] In his book A Revelation of the True Minerva (1582), Thomas Blennerhassett portrays Queen Elizabeth I of England as a "new Minerva" and "the greatest goddesse nowe on earth".[213] A series of paintings by Peter Paul Rubens depict Athena as Marie de' Medici's patron and mentor;[214] the final painting in the series goes even further and shows Marie de' Medici with Athena's iconography, as the mortal incarnation of the goddess herself.[214] The German sculptor Jean-Pierre-Antoine Tassaert later portrayed Catherine II of Russia as Athena in a marble bust in 1774.[201] During the French Revolution, statues of pagan gods were torn down all throughout France, but statues of Athena were not.[214] Instead, Athena was transformed into the personification of freedom and the republic[214] and a statue of the goddess stood in the center of the Place de la Revolution in Paris.[214] In the years following the Revolution, artistic representations of Athena proliferated.[215]
+A statue of Athena stands directly in front of the Austrian Parliament Building in Vienna,[216] and depictions of Athena have influenced other symbols of western freedom, including the Statue of Liberty and Britannia.[216] For over a century, a full-scale replica of the Parthenon has stood in Nashville, Tennessee.[217] In 1990, the curators added a gilded forty-two-foot (12.5 m) tall replica of Phidias's Athena Parthenos, built from concrete and fiberglass.[217] The state seal of California bears the image of Athena kneeling next to a brown grizzly bear.[218] Athena has occasionally appeared on modern coins, as she did on the ancient Athenian drachma. Her head appears on the $50 1915-S Panama-Pacific commemorative coin.[219]
+Pallas and the Centaur (c. 1482) by Sandro Botticelli
+Minerva Expelling the Vices from the Garden of Virtue (1502) by Andrea Mantegna[210][209][211]
+Athena Scorning the Advances of Hephaestus (c. 1555-1560) by Paris Bordone
+Minerva Victorious over Ignorance (c. 1591) by Bartholomeus Spranger
+Maria de Medici (1622) by Peter Paul Rubens, showing her as the incarnation of Athena[214]
+Minerva Protecting Peace from Mars (1629) by Peter Paul Rubens
+Pallas Athena (c. 1655) by Rembrandt
+Minerva Revealing Ithaca to Ulysses (fifteenth century) by Giuseppe Bottani
+Minerva and the Triumph of Jupiter (1706) by René-Antoine Houasse
+The Combat of Mars and Minerva (1771) by Joseph-Benoît Suvée
+Minerva Fighting Mars (1771) by Jacques-Louis David
+Minerva of Peace mosaic in the Library of Congress
+Athena on the Great Seal of California
+One of Sigmund Freud's most treasured possessions was a small, bronze sculpture of Athena, which sat on his desk.[220] Freud once described Athena as "a woman who is unapproachable and repels all sexual desires - since she displays the terrifying genitals of the Mother."[221] Feminist views on Athena are sharply divided;[221] some feminists regard her as a symbol of female empowerment,[221] while others regard her as "the ultimate patriarchal sell out... who uses her powers to promote and advance men rather than others of her sex."[221] In contemporary Wicca, Athena is venerated as an aspect of the Goddess[222] and some Wiccans believe that she may bestow the "Owl Gift" ("the ability to write and communicate clearly") upon her worshippers.[222] Due to her status as one of the twelve Olympians, Athena is a major deity in Hellenismos,[223] a Neopagan religion which seeks to authentically revive and recreate the religion of ancient Greece in the modern world.[224]
+Athena is a natural patron of universities: At Bryn Mawr College in Pennsylvania a statue of Athena (a replica of the original bronze one in the arts and archaeology library) resides in the Great Hall.[225] It is traditional at exam time for students to leave offerings to the goddess with a note asking for good luck,[225] or to repent for accidentally breaking any of the college's numerous other traditions.[225] Pallas Athena is the tutelary goddess of the international social fraternity Phi Delta Theta.[226] Her owl is also a symbol of the fraternity.[226]

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+Opera is a freeware web browser for Microsoft Windows, Android, iOS, macOS, and Linux operating systems[7][8] developed by Opera Software.[9][10][11] Opera is a Chromium-based browser using the Blink layout engine. It differentiates itself because of a distinct user interface and other features.
+Opera was conceived at Telenor as a research project in 1994 and was bought by Opera Software in 1995. It was a commercial software for the first ten years and had its own proprietary Presto layout engine. The Presto versions of Opera received many awards, but Presto development ended after a milestone transition to Chromium in 2013.
+There are also three mobile versions called Opera Mobile, Opera Touch,[12] and Opera Mini. A gaming browser called Opera GX was launched on 11 June 2019.[13]
+Opera began in 1994 as a research project at Telenor, the largest Norwegian telecommunications company.
+In 1995, it branched out into a separate company named Opera Software.[14]
+Opera was first publicly released in 1996 with version 2.10,[15] which only ran on Microsoft Windows 95 at that time.[16]
+In an attempt to capitalize on the emerging market for Internet-connected handheld devices, a project to port Opera to mobile device platforms was started in 1998.[16]
+Opera 4.0, released in 2000,[15] included a new cross-platform core that facilitated the creation of editions of Opera for multiple operating systems and platforms.[17]
+Up to this point, Opera was trialware and had to be purchased after the trial period ended. Version 5.0 (released in 2000) saw the end of this requirement. Instead, Opera became ad-sponsored, displaying advertisements to users who had not paid for it.[18] Later versions of Opera gave the user the choice of seeing banner ads or targeted text advertisements from Google.
+With version 8.5 (released in 2005) the advertisements were completely removed and the primary financial support for the browser came through revenue from Google (which is by contract Opera's default search engine).[19]
+Among the new features introduced in version 9.1 (released in 2006) was fraud protection using technology from GeoTrust, a digital certificate provider, and PhishTank, an organization that tracks known phishing web sites.[20] This feature was further improved and expanded in version 9.5, when GeoTrust was replaced with Netcraft, and malware protection from Haute Secure was added.[21]
+In 2006, Opera Software ASA was released as well as Internet Channel and Nintendo DS Browser for Nintendo's DS and Wii gaming systems.[22][23][24][25]
+A new JavaScript engine called Carakan, after the Javanese alphabet, was introduced with version 10.50.[26] According to Opera Software, Carakan made Opera 10.50 more than seven times faster in SunSpider than Opera 10.10.[27][28][29]
+On the 16th of December 2010, Opera 11 was released, featuring extensions,[30] tab stacking (where dragging one tab over another allows creating a group of tabs), visual mouse gestures and changes to the address bar.[31]
+Opera 12 was released on 14 June 2012.[32]
+On 12 February 2013, Opera Software announced that it would drop its own Presto layout engine in favour of WebKit as implemented by Google's Chrome browser, using code from the Chromium project. Opera Software planned as well to contribute code to WebKit.[33] On 3 April 2013, Google announced that it would fork components from WebKit to form a new layout engine known as Blink; the same day, Opera Software confirmed that it would follow Google in implementing the Blink layout engine.[34]
+On 28 May 2013, a beta release of Opera 15 was made available,[35] the first version is based on the Chromium project.[36][37] Many distinctive Opera features of the previous versions were dropped, and Opera Mail was separated into a standalone application derived from Opera 12.[38]
+In November 2016, the original Norwegian owner of Opera sold his stake in the business to a Chinese consortium under the name Golden Brick Capital Private Equity Fund I Limited Partnership for $600 million.[39][40][41] An earlier deal was not approved by regulators.[42]
+In January 2017, the source code of Opera 12.15 (one of the last few versions that was still based on the Presto layout engine) was leaked.[43]
+To demonstrate how radically different a browser could look, Opera Neon, dubbed a "concept browser", was released in January 2017. PC World compared it to demo models that automakers and hardware vendors release to show their visions of the future. Instead of a Speed Dial (also explained in the following chapter "Features"), it displays the frequently accessed websites in resemblance to a desktop with computer icons scattered all over it in an artistic formation.[44][45]
+Opera has originated features later adopted by other web browsers, including: Speed Dial, pop-up blocking, re-opening recently closed pages, private browsing, and tabbed browsing.[46][47] Opera includes a bookmarks bar and a download manager. Opera also has "Speed Dial", which allows the user to add an unlimited number of pages shown in thumbnail form in a page displayed when a new tab is opened. Speed Dial allows the user to more easily navigate to the selected web pages.[46][47][48]
+It is possible to control some aspects of the browser using the keyboard shortcuts.[49] Page zooming allows text, images and other content such as Adobe Flash Player, Java platform and Scalable Vector Graphics to be increased or decreased in size to help those with impaired vision.[50]
+Opera Software claims that when the Opera Turbo mode is enabled, the compression servers compress requested web pages (except HTTPS pages) by up to 50%, depending upon the content, before sending them to the users.[51] This process reduces the amount of data transferred and is particularly useful for crowded or slow network connections, making web pages load faster or when there are costs dependent on the total amount of data usage.[51] This technique is also used in Opera Mini for mobile devices[52] and smartwatches.[53]
+One security feature is the option to delete private data, such as HTTP cookies, browsing history, items in cache and passwords with the click of a button.[54] This lets users erase personal data after browsing from a shared computer.
+When visiting a site, Opera displays a security badge in the address bar which shows details about the website, including security certificates.[55] Opera's fraud and malware protection warns the user about suspicious web pages and is enabled by default. It checks the requested page against several databases of known phishing and malware websites, called blacklists.[55]
+In January 2007, Asa Dotzler of the competing Mozilla Corporation accused Opera Software of downplaying information about security vulnerabilities in Opera, (which were fixed in December 2006). Dotzler claimed that users were not clearly informed of security vulnerabilities that were present in the previous version of Opera and thus they would not realize that they needed to upgrade to the latest version or else risk being exploited by hackers.[56] Opera Software responded to these accusations on the next day.[57]
+In 2016, a free virtual private network (VPN) service was implemented in the browser.[58] Opera said that this would allow encrypted access to websites otherwise blocked, and provide security on public WiFi networks.[59] Either VPN or Turbo can be enabled, but not both.[60] It was later determined that the browser "VPN" operated the same as a proxy rather than other VPN services.[61]
+In July 2018, Opera was listed on the NASDAQ stock exchange [62] in New York City at an initial offering of $12 per share.
+In 2018, a built-in cryptocurrency wallet to the Opera Web Browser was released.[63] Announcing that they would be the first browser with a built-in Crypto Wallet.[64] On 13 December 2018 they released a video showing many decentralized applications like Cryptokitties running on the Android version of the Opera Web Browser.[65]
+In March 2020,  Opera updated its Android browser to access .crypto domains, making it the first browser to be able to support a domain name system (DNS) which is not part of the traditional DNS directly without the need of a plugin or add-on.[66] This was through a collaboration with a San Francisco based startup, Unstoppable Domains.[67][68]
+Opera was one of the first browsers to support Cascading Style Sheets (CSS).[69]
+Opera Software uses a release cycle consisting of three "streams" (which correspond to phases of development) that can be downloaded and installed independently of each other: "developer", "beta" and "stable". New features are first introduced in the developer build, then, depending on user feedback, may progress to the beta version and eventually be released.[70]
+The developer stream allows early testing of new features, mainly targeting developers, extension creators, and early adopters. Opera developer is not intended for everyday browsing as it is unstable and is prone to failure or crashing, but it enables advanced users to try out new features that are still under development, without affecting their normal installation of the browser. New versions of the browser are released frequently, generally a few times a week.[71]
+The beta stream, formerly known as "Opera Next", is a feature complete package, allowing stability and quality to mature before the final release. A new version is released every couple of weeks.[72]
+Both streams can be installed alongside the official release without interference. Each has a different icon to help the user distinguish between the variants.
+In 2005, Adobe Systems opted to integrate Opera's rendering engine, Presto, into its Adobe Creative Suite applications. Opera technology was employed in Adobe GoLive, Adobe Photoshop, Adobe Dreamweaver, and other components of the Adobe Creative Suite.[74][75] Opera's layout engine is also found in Virtual Mechanics SiteSpinner Pro.[76] The Internet Channel is a version of the Opera 9 web browser for use on the Nintendo Wii created by Opera Software and Nintendo.[77] Opera Software is also implemented in the Nintendo DS Browser for Nintendo's handheld systems.
+Versions with the Presto layout engine have been positively reviewed,[78][79][80] although they have been criticized for website compatibility issues.[81][82] Because of this issue, Opera 8.01 and higher had included workarounds to help certain popular but problematic web sites display properly.[83][84]
+Versions with the Blink layout engine have been criticized by some users for missing features such as UI customization, and for abandoning Opera Software's own Presto layout engine.[85][86][87][88] Despite that, versions with the Blink layout engine have been praised for being fast and stable, for handling the latest web standards and for having a better website compatibility and a modern-style user interface.[89][90][91]
+Over the years, Opera for personal computers has received several awards. These awards include:[92]
+Related web browsers:
+Web browsers:
+Essential features:

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+Opera  is a form of theatre in which music has a leading role and the parts are taken by singers, but is distinct from musical theatre.[1] Such a "work" (the literal translation of the Italian word "opera") is typically a collaboration between a composer and a librettist[2] and incorporates a number of the performing arts, such as acting, scenery, costume, and sometimes dance or ballet. The performance is typically given in an opera house, accompanied by an orchestra or smaller musical ensemble, which since the early 19th century has been led by a conductor.
+Opera is a key part of the Western classical music tradition.[3] Originally understood as an entirely sung piece, in contrast to a play with songs, opera has come to include numerous genres, including some that include spoken dialogue such as musical theatre, Singspiel and Opéra comique. In traditional number opera, singers employ two styles of singing: recitative, a speech-inflected style,[4] and self-contained arias. The 19th century saw the rise of the continuous music drama.
+Opera originated in Italy at the end of the 16th century (with Jacopo Peri's mostly lost Dafne, produced in Florence in 1598) especially from works by Claudio Monteverdi, notably L'Orfeo, and soon spread through the rest of Europe: Heinrich Schütz in Germany, Jean-Baptiste Lully in France, and Henry Purcell in England all helped to establish their national traditions in the 17th century. In the 18th century, Italian opera continued to dominate most of Europe (except France), attracting foreign composers such as George Frideric Handel. Opera seria was the most prestigious form of Italian opera, until Christoph Willibald Gluck reacted against its artificiality with his "reform" operas in the 1760s. The most renowned figure of late 18th-century opera is Wolfgang Amadeus Mozart, who began with opera seria but is most famous for his Italian comic operas, especially The Marriage of Figaro (Le nozze di Figaro), Don Giovanni, and Così fan tutte, as well as Die Entführung aus dem Serail (The Abduction from the Seraglio), and The Magic Flute (Die Zauberflöte), landmarks in the German tradition.
+The first third of the 19th century saw the high point of the bel canto style, with Gioachino Rossini, Gaetano Donizetti and Vincenzo Bellini all creating works that are still performed. It also saw the advent of Grand Opera typified by the works of Auber and Meyerbeer. The mid-to-late 19th century was a golden age of opera, led and dominated by Giuseppe Verdi in Italy and Richard Wagner in Germany. The popularity of opera continued through the verismo era in Italy and contemporary French opera through to Giacomo Puccini and Richard Strauss in the early 20th century. During the 19th century, parallel operatic traditions emerged in central and eastern Europe, particularly in Russia and Bohemia. The 20th century saw many experiments with modern styles, such as atonality and serialism (Arnold Schoenberg and Alban Berg), Neoclassicism (Igor Stravinsky), and Minimalism (Philip Glass and John Adams). With the rise of recording technology, singers such as Enrico Caruso and Maria Callas became known to much wider audiences that went beyond the circle of opera fans. Since the invention of radio and television, operas were also performed on (and written for) these media. Beginning in 2006, a number of major opera houses began to present live high-definition video transmissions of their performances in cinemas all over the world. Since 2009, complete performances can be downloaded and are live streamed.
+The words of an opera are known as the libretto (literally "small book"). Some composers, notably Wagner, have written their own libretti; others have worked in close collaboration with their librettists, e.g. Mozart with Lorenzo Da Ponte. Traditional opera, often referred to as "number opera", consists of two modes of singing: recitative, the plot-driving passages sung in a style designed to imitate and emphasize the inflections of speech,[4] and aria (an "air" or formal song) in which the characters express their emotions in a more structured melodic style. Vocal duets, trios and other ensembles often occur, and choruses are used to comment on the action. In some forms of opera, such as singspiel, opéra comique, operetta, and semi-opera, the recitative is mostly replaced by spoken dialogue. Melodic or semi-melodic passages occurring in the midst of, or instead of, recitative, are also referred to as arioso. The terminology of the various kinds of operatic voices is described in detail below.[5] During both the Baroque and Classical periods, recitative could appear in two basic forms, each of which was accompanied by a different instrumental ensemble: secco (dry) recitative, sung with a free rhythm dictated by the accent of the words, accompanied only by basso continuo, which was usually a harpsichord and a cello; or accompagnato (also known as strumentato) in which the orchestra provided accompaniment. Over the 18th century, arias were increasingly accompanied by the orchestra. By the 19th century, accompagnato had gained the upper hand, the orchestra played a much bigger role, and Wagner revolutionized opera by abolishing almost all distinction between aria and recitative in his quest for what Wagner termed "endless melody". Subsequent composers have tended to follow Wagner's example, though some, such as Stravinsky in his The Rake's Progress have bucked the trend. The changing role of the orchestra in opera is described in more detail below.
+The Italian word opera means "work", both in the sense of the labour done and the result produced. The Italian word derives from the Latin opera, a singular noun meaning "work" and also the plural of the noun opus. According to the Oxford English Dictionary, the Italian word was first used in the sense "composition in which poetry, dance, and music are combined" in 1639; the first recorded English usage in this sense dates to 1648.[6]
+Dafne by Jacopo Peri was the earliest composition considered opera, as understood today. It was written around 1597, largely under the inspiration of an elite circle of literate Florentine humanists who gathered as the "Camerata de' Bardi". Significantly, Dafne was an attempt to revive the classical Greek drama, part of the wider revival of antiquity characteristic of the Renaissance. The members of the Camerata considered that the "chorus" parts of Greek dramas were originally sung, and possibly even the entire text of all roles; opera was thus conceived as a way of "restoring" this situation. Dafne, however, is lost. A later work by Peri, Euridice, dating from 1600, is the first opera score to have survived to the present day. The honour of being the first opera still to be regularly performed, however, goes to Claudio Monteverdi's L'Orfeo, composed for the court of Mantua in 1607.[7] The Mantua court of the Gonzagas, employers of Monteverdi, played a significant role in the origin of opera employing not only court singers of the concerto delle donne (till 1598), but also one of the first actual "opera singers", Madama Europa.[8]
+Opera did not remain confined to court audiences for long. In 1637, the idea of a "season" (often during the carnival) of publicly attended operas supported by ticket sales emerged in Venice. Monteverdi had moved to the city from Mantua and composed his last operas, Il ritorno d'Ulisse in patria and L'incoronazione di Poppea, for the Venetian theatre in the 1640s. His most important follower Francesco Cavalli helped spread opera throughout Italy. In these early Baroque operas, broad comedy was blended with tragic elements in a mix that jarred some educated sensibilities, sparking the first of opera's many reform movements, sponsored by the Arcadian Academy, which came to be associated with the poet Metastasio, whose libretti helped crystallize the genre of opera seria, which became the leading form of Italian opera until the end of the 18th century. Once the Metastasian ideal had been firmly established, comedy in Baroque-era opera was reserved for what came to be called opera buffa.
+Before such elements were forced out of opera seria, many libretti had featured a separately unfolding comic plot as sort of an "opera-within-an-opera". One reason for this was an attempt to attract members of the growing merchant class, newly wealthy, but still not as cultured as the nobility, to the public opera houses. These separate plots were almost immediately resurrected in a separately developing tradition that partly derived from the commedia dell'arte, a long-flourishing improvisatory stage tradition of Italy. Just as intermedi had once been performed in between the acts of stage plays, operas in the new comic genre of "intermezzi", which developed largely in Naples in the 1710s and '20s, were initially staged during the intermissions of opera seria. They became so popular, however, that they were soon being offered as separate productions.
+Opera seria was elevated in tone and highly stylised in form, usually consisting of secco recitative interspersed with long da capo arias. These afforded great opportunity for virtuosic singing and during the golden age of opera seria the singer really became the star. The role of the hero was usually written for the high-pitched male castrato voice, which was produced by castration of the singer before puberty, which prevented a boy's larynx from being transformed at puberty. Castrati such as Farinelli and Senesino, as well as female sopranos such as Faustina Bordoni, became in great demand throughout Europe as opera seria ruled the stage in every country except France.  Farinelli was one of the most famous singers of the 18th century. Italian opera set the Baroque standard. Italian libretti were the norm, even when a German composer like Handel found himself composing the likes of Rinaldo and Giulio Cesare for London audiences. Italian libretti remained dominant in the classical period as well, for example in the operas of Mozart, who wrote in Vienna near the century's close. Leading Italian-born composers of opera seria include Alessandro Scarlatti, Vivaldi and Porpora.[9]
+Opera seria had its weaknesses and critics. The taste for embellishment on behalf of the superbly trained singers, and the use of spectacle as a replacement for dramatic purity and unity drew attacks. Francesco Algarotti's Essay on the Opera (1755) proved to be an inspiration for Christoph Willibald Gluck's reforms. He advocated that opera seria had to return to basics and that all the various elements—music (both instrumental and vocal), ballet, and staging—must be subservient to the overriding drama. In 1765 Melchior Grimm published "Poème lyrique", an influential article for the Encyclopédie on lyric and opera librettos.[10][11][12][13][14] Several composers of the period, including Niccolò Jommelli and Tommaso Traetta, attempted to put these ideals into practice. The first to succeed however, was Gluck. Gluck strove to achieve a "beautiful simplicity". This is evident in his first reform opera, Orfeo ed Euridice, where his non-virtuosic vocal melodies are supported by simple harmonies and a richer orchestra presence throughout.
+Gluck's reforms have had resonance throughout operatic history. Weber, Mozart, and Wagner, in particular, were influenced by his ideals. Mozart, in many ways Gluck's successor, combined a superb sense of drama, harmony, melody, and counterpoint to write a series of comic operas with libretti by Lorenzo Da Ponte, notably Le nozze di Figaro, Don Giovanni, and Così fan tutte, which remain among the most-loved, popular and well-known operas today. But Mozart's contribution to opera seria was more mixed; by his time it was dying away, and in spite of such fine works as Idomeneo and La clemenza di Tito, he would not succeed in bringing the art form back to life again.[15]
+The bel canto opera movement flourished in the early 19th century and is exemplified by the operas of Rossini, Bellini, Donizetti, Pacini, Mercadante and many others. Literally "beautiful singing", bel canto opera derives from the Italian stylistic singing school of the same name. Bel canto lines are typically florid and intricate, requiring supreme agility and pitch control. Examples of famous operas in the bel canto style include Rossini's Il barbiere di Siviglia and La Cenerentola, as well as Bellini's Norma, La sonnambula and I puritani and Donizetti's Lucia di Lammermoor, L'elisir d'amore and Don Pasquale.
+Following the bel canto era, a more direct, forceful style was rapidly popularized by Giuseppe Verdi, beginning with his biblical opera Nabucco. This opera, and the ones that would follow in Verdi's career, revolutionized Italian opera, changing it from merely a display of vocal fireworks, with Rossini's and Donizetti's works, to dramatic story-telling. Verdi's operas resonated with the growing spirit of Italian nationalism in the post-Napoleonic era, and he quickly became an icon of the patriotic movement for a unified Italy. In the early 1850s, Verdi produced his three most popular operas: Rigoletto, Il trovatore and La traviata. The first of these, Rigoletto, proved the most daring and revolutionary. In it, Verdi blurs the distinction between the aria and recitative as it never before was, leading the opera to be "an unending string of duets". La traviata was also novel. It tells the story of courtesan, and is often cited as one of the first "realistic" operas,[citation needed] because rather than featuring great kings and figures from literature, it focuses on the tragedies of ordinary life and society. After these, he continued to develop his style, composing perhaps the greatest French Grand Opera, Don Carlos, and ending his career with two Shakespeare-inspired works, Otello and Falstaff, which reveal how far Italian opera had grown in sophistication since the early 19th century. These final two works showed Verdi at his most masterfully orchestrated, and are both incredibly influential, and modern. In Falstaff, Verdi sets the preeminent standard for the form and style that would dominate opera throughout the twentieth century. Rather than long, suspended melodies, Falstaff contains many little motifs and mottos, that, rather than being expanded upon, are introduced and subsequently dropped, only to be brought up again later. These motifs never are expanded upon, and just as the audience expects a character to launch into a long melody, a new character speaks, introducing a new phrase. This fashion of opera directed opera from Verdi, onward, exercising tremendous influence on his successors Giacomo Puccini, Richard Strauss, and Benjamin Britten.[16]
+After Verdi, the sentimental "realistic" melodrama of verismo appeared in Italy. This was a style introduced by Pietro Mascagni's Cavalleria rusticana and Ruggero Leoncavallo's Pagliacci that came to dominate the world's opera stages with such popular works as Giacomo Puccini's La bohème, Tosca, and Madama Butterfly. Later Italian composers, such as Berio and Nono, have experimented with modernism.[17]
+The first German opera was Dafne, composed by Heinrich Schütz in 1627, but the music score has not survived. Italian opera held a great sway over German-speaking countries until the late 18th century. Nevertheless, native forms would develop in spite of this influence. In 1644, Sigmund Staden produced the first Singspiel, Seelewig, a popular form of German-language opera in which singing alternates with spoken dialogue. In the late 17th century and early 18th century, the Theater am Gänsemarkt in Hamburg presented German operas by Keiser, Telemann and Handel. Yet most of the major German composers of the time, including Handel himself, as well as Graun, Hasse and later Gluck, chose to write most of their operas in foreign languages, especially Italian. In contrast to Italian opera, which was generally composed for the aristocratic class, German opera was generally composed for the masses and tended to feature simple folk-like melodies, and it was not until the arrival of Mozart that German opera was able to match its Italian counterpart in musical sophistication.[18] The theatre company of Abel Seyler pioneered serious German-language opera in the 1770s, marking a break with the previous simpler musical entertainment.[19][20]
+Mozart's Singspiele, Die Entführung aus dem Serail (1782) and Die Zauberflöte (1791) were an important breakthrough in achieving international recognition for German opera. The tradition was developed in the 19th century by Beethoven with his Fidelio (1805), inspired by the climate of the French Revolution. Carl Maria von Weber established German Romantic opera in opposition to the dominance of Italian bel canto. His Der Freischütz (1821) shows his genius for creating a supernatural atmosphere. Other opera composers of the time include Marschner, Schubert and Lortzing, but the most significant figure was undoubtedly Wagner.
+Wagner was one of the most revolutionary and controversial composers in musical history. Starting under the influence of Weber and Meyerbeer, he gradually evolved a new concept of opera as a Gesamtkunstwerk (a "complete work of art"), a fusion of music, poetry and painting. He greatly increased the role and power of the orchestra, creating scores with a complex web of leitmotifs, recurring themes often associated with the characters and concepts of the drama, of which prototypes can be heard in his earlier operas such as Der fliegende Holländer, Tannhäuser and Lohengrin; and he was prepared to violate accepted musical conventions, such as tonality, in his quest for greater expressivity. In his mature music dramas, Tristan und Isolde, Die Meistersinger von Nürnberg, Der Ring des Nibelungen and Parsifal, he abolished the distinction between aria and recitative in favour of a seamless flow of "endless melody". Wagner also brought a new philosophical dimension to opera in his works, which were usually based on stories from Germanic or Arthurian legend. Finally, Wagner built his own opera house at Bayreuth with part of the patronage from Ludwig II of Bavaria, exclusively dedicated to performing his own works in the style he wanted.
+Opera would never be the same after Wagner and for many composers his legacy proved a heavy burden. On the other hand, Richard Strauss accepted Wagnerian ideas but took them in wholly new directions, along with incorporating the new form introduced by Verdi. He first won fame with the scandalous Salome and the dark tragedy Elektra, in which tonality was pushed to the limits. Then Strauss changed tack in his greatest success, Der Rosenkavalier, where Mozart and Viennese waltzes became as important an influence as Wagner. Strauss continued to produce a highly varied body of operatic works, often with libretti by the poet Hugo von Hofmannsthal. Other composers who made individual contributions to German opera in the early 20th century include Alexander von Zemlinsky, Erich Korngold, Franz Schreker, Paul Hindemith, Kurt Weill and the Italian-born Ferruccio Busoni. The operatic innovations of Arnold Schoenberg and his successors are discussed in the section on modernism.[21]
+During the late 19th century, the Austrian composer Johann Strauss II, an admirer of the French-language operettas composed by Jacques Offenbach, composed several German-language operettas, the most famous of which was Die Fledermaus, which is still regularly performed today.[22] Nevertheless, rather than copying the style of Offenbach, the operettas of Strauss II had distinctly Viennese flavor to them, which have cemented the Strauss II's place as one of the most renowned operetta composers of all time.
+In rivalry with imported Italian opera productions, a separate French tradition was founded by the Italian Jean-Baptiste Lully at the court of King Louis XIV. Despite his foreign origin, Lully established an Academy of Music and monopolised French opera from 1672. Starting with Cadmus et Hermione, Lully and his librettist Quinault created tragédie en musique, a form in which dance music and choral writing were particularly prominent. Lully's operas also show a concern for expressive recitative which matched the contours of the French language. In the 18th century, Lully's most important successor was Jean-Philippe Rameau, who composed five tragédies en musique as well as numerous works in other genres such as opéra-ballet, all notable for their rich orchestration and harmonic daring. Despite the popularity of Italian opera seria throughout much of Europe during the Baroque period, Italian opera never gained much of a foothold in France, where its own national operatic tradition was more popular instead.[23] After Rameau's death, the German Gluck was persuaded to produce six operas for the Parisian stage in the 1770s. They show the influence of Rameau, but simplified and with greater focus on the drama. At the same time, by the middle of the 18th century another genre was gaining popularity in France: opéra comique. This was the equivalent of the German singspiel, where arias alternated with spoken dialogue. Notable examples in this style were produced by Monsigny, Philidor and, above all, Grétry. During the Revolutionary period, composers such as Étienne Méhul and Luigi Cherubini, who were followers of Gluck, brought a new seriousness to the genre, which had never been wholly "comic" in any case. Another phenomenon of this period was the 'propaganda opera' celebrating revolutionary successes, e.g. Gossec's Le triomphe de la République (1793).
+By the 1820s, Gluckian influence in France had given way to a taste for Italian bel canto, especially after the arrival of Rossini in Paris. Rossini's Guillaume Tell helped found the new genre of Grand Opera, a form whose most famous exponent was another foreigner, Giacomo Meyerbeer. Meyerbeer's works, such as Les Huguenots, emphasised virtuoso singing and extraordinary stage effects. Lighter opéra comique also enjoyed tremendous success in the hands of Boïeldieu, Auber, Hérold and Adam. In this climate, the operas of the French-born composer Hector Berlioz struggled to gain a hearing. Berlioz's epic masterpiece Les Troyens, the culmination of the Gluckian tradition, was not given a full performance for almost a hundred years.
+In the second half of the 19th century, Jacques Offenbach created operetta with witty and cynical works such as Orphée aux enfers, as well as the opera Les Contes d'Hoffmann; Charles Gounod scored a massive success with Faust; and Georges Bizet composed Carmen, which, once audiences learned to accept its blend of Romanticism and realism, became the most popular of all opéra comiques. Jules Massenet, Camille Saint-Saëns and Léo Delibes all composed works which are still part of the standard repertory, examples being Massenet's Manon, Saint-Saëns' Samson et Dalila and Delibes' Lakmé.  Their operas formed another genre, the Opera Lyrique, combined opera comique and grand opera. It is less grandiose than grand opera, but without the spoken dialogue of opera comique.  At the same time, the influence of Richard Wagner was felt as a challenge to the French tradition. Many French critics angrily rejected Wagner's music dramas while many French composers closely imitated them with variable success. Perhaps the most interesting response came from Claude Debussy. As in Wagner's works, the orchestra plays a leading role in Debussy's unique opera Pelléas et Mélisande (1902) and there are no real arias, only recitative. But the drama is understated, enigmatic and completely un-Wagnerian.
+Other notable 20th-century names include Ravel, Dukas, Roussel and Milhaud. Francis Poulenc is one of the very few post-war composers of any nationality whose operas (which include Dialogues des Carmélites) have gained a foothold in the international repertory. Olivier Messiaen's lengthy sacred drama Saint François d'Assise (1983) has also attracted widespread attention.[24]
+In England, opera's antecedent was the 17th-century jig. This was an afterpiece that came at the end of a play. It was frequently libellous and scandalous and consisted in the main of dialogue set to music arranged from popular tunes. In this respect, jigs anticipate the ballad operas of the 18th century. At the same time, the French masque was gaining a firm hold at the English Court, with even more lavish splendour and highly realistic scenery than had been seen before. Inigo Jones became the quintessential designer of these productions, and this style was to dominate the English stage for three centuries. These masques contained songs and dances. In Ben Jonson's Lovers Made Men (1617), "the whole masque was sung after the Italian manner, stilo recitativo".[25] The approach of the English Commonwealth closed theatres and halted any developments that may have led to the establishment of English opera. However, in 1656, the dramatist Sir William Davenant produced The Siege of Rhodes. Since his theatre was not licensed to produce drama, he asked several of the leading composers (Lawes, Cooke, Locke, Coleman and Hudson) to set sections of it to music. This success was followed by The Cruelty of the Spaniards in Peru (1658) and The History of Sir Francis Drake (1659). These pieces were encouraged by Oliver Cromwell because they were critical of Spain. With the English Restoration, foreign (especially French) musicians were welcomed back. In 1673, Thomas Shadwell's Psyche, patterned on the 1671 'comédie-ballet' of the same name produced by Molière and Jean-Baptiste Lully. William Davenant produced The Tempest in the same year, which was the first musical adaption of a Shakespeare play (composed by Locke and Johnson).[25] About 1683, John Blow composed Venus and Adonis, often thought of as the first true English-language opera.
+Blow's immediate successor was the better known Henry Purcell. Despite the success of his masterwork Dido and Aeneas (1689), in which the action is furthered by the use of Italian-style recitative, much of Purcell's best work was not involved in the composing of typical opera, but instead, he usually worked within the constraints of the semi-opera format, where isolated scenes and masques are contained within the structure of a spoken play, such as Shakespeare in Purcell's The Fairy-Queen (1692) and Beaumont and Fletcher in The Prophetess (1690) and Bonduca (1696). The main characters of the play tend not to be involved in the musical scenes, which means that Purcell was rarely able to develop his characters through song. Despite these hindrances, his aim (and that of his collaborator John Dryden) was to establish serious opera in England, but these hopes ended with Purcell's early death at the age of 36.
+Following Purcell, the popularity of opera in England dwindled for several decades. A revived interest in opera occurred in the 1730s which is largely attributed to Thomas Arne, both for his own compositions and for alerting Handel to the commercial possibilities of large-scale works in English. Arne was the first English composer to experiment with Italian-style all-sung comic opera, with his greatest success being Thomas and Sally in 1760. His opera Artaxerxes (1762) was the first attempt to set a full-blown opera seria in English and was a huge success, holding the stage until the 1830s. Although Arne imitated many elements of Italian opera, he was perhaps the only English composer at that time who was able to move beyond the Italian influences and create his own unique and distinctly English voice. His modernized ballad opera, Love in a Village (1762), began a vogue for pastiche opera that lasted well into the 19th century. Charles Burney wrote that Arne introduced "a light, airy, original, and pleasing melody, wholly different from that of Purcell or Handel, whom all English composers had either pillaged or imitated".
+Besides Arne, the other dominating force in English opera at this time was George Frideric Handel, whose opera serias filled the London operatic stages for decades and influenced most home-grown composers, like John Frederick Lampe, who wrote using Italian models. This situation continued throughout the 18th and 19th centuries, including in the work of Michael William Balfe, and the operas of the great Italian composers, as well as those of Mozart, Beethoven, and Meyerbeer, continued to dominate the musical stage in England.
+The only exceptions were ballad operas, such as John Gay's The Beggar's Opera (1728), musical burlesques, European operettas, and late Victorian era light operas, notably the Savoy Operas of W. S. Gilbert and Arthur Sullivan, all of which types of musical entertainments frequently spoofed operatic conventions. Sullivan wrote only one grand opera, Ivanhoe (following the efforts of a number of young English composers beginning about 1876),[25] but he claimed that even his light operas constituted part of a school of "English" opera, intended to supplant the French operettas (usually performed in bad translations) that had dominated the London stage from the mid-19th century into the 1870s. London's Daily Telegraph agreed, describing The Yeomen of the Guard as "a genuine English opera, forerunner of many others, let us hope, and possibly significant of an advance towards a national lyric stage".[26] Sullivan produced a few light operas in the 1890s that were of a more serious nature than those in the G&S series, including Haddon Hall and The Beauty Stone, but Ivanhoe (which ran for 155 consecutive performances, using alternating casts—a record until Broadway's La bohème) survives as his only Grand Opera.
+In the 20th century, English opera began to assert more independence, with works of Ralph Vaughan Williams and in particular Benjamin Britten, who in a series of works that remain in standard repertory today, revealed an excellent flair for the dramatic and superb musicality. More recently Sir Harrison Birtwistle has emerged as one of Britain's most significant contemporary composers from his first opera Punch and Judy to his most recent critical success in The Minotaur. In the first decade of the 21st century, the librettist of an early Birtwistle opera, Michael Nyman, has been focusing on composing operas, including Facing Goya, Man and Boy: Dada, and Love Counts. Today composers such as Thomas Adès continue to export English opera abroad.[27]
+Also in the 20th century, American composers like George Gershwin (Porgy and Bess), Scott Joplin (Treemonisha), Leonard Bernstein (Candide), Gian Carlo Menotti, Douglas Moore, and Carlisle Floyd began to contribute English-language operas infused with touches of popular musical styles. They were followed by composers such as Philip Glass (Einstein on the Beach), Mark Adamo, John Corigliano (The Ghosts of Versailles), Robert Moran, John Adams (Nixon in China), André Previn and Jake Heggie. Many contemporary 21st century opera composers have emerged such as Missy Mazzoli, Kevin Puts, Tom Cipullo, Huang Ruo, David T. Little, Terence Blanchard, Jennifer Higdon, Tobias Picker, Michael Ching, and Ricky Ian Gordon.
+Opera was brought to Russia in the 1730s by the Italian operatic troupes and soon it became an important part of entertainment for the Russian Imperial Court and aristocracy. Many foreign composers such as Baldassare Galuppi, Giovanni Paisiello, Giuseppe Sarti, and Domenico Cimarosa (as well as various others) were invited to Russia to compose new operas, mostly in the Italian language. Simultaneously some domestic musicians like Maksym Berezovsky and Dmitry Bortniansky were sent abroad to learn to write operas. The first opera written in Russian was Tsefal i Prokris by the Italian composer Francesco Araja (1755). The development of Russian-language opera was supported by the Russian composers Vasily Pashkevich, Yevstigney Fomin and Alexey Verstovsky.
+However, the real birth of Russian opera came with Mikhail Glinka and his two great operas A Life for the Tsar (1836) and Ruslan and Lyudmila (1842). After him, during the 19th century in Russia, there were written such operatic masterpieces as Rusalka and The Stone Guest by Alexander Dargomyzhsky, Boris Godunov and Khovanshchina by Modest Mussorgsky, Prince Igor by Alexander Borodin, Eugene Onegin and The Queen of Spades by Pyotr Tchaikovsky, and The Snow Maiden and Sadko by Nikolai Rimsky-Korsakov. These developments mirrored the growth of Russian nationalism across the artistic spectrum, as part of the more general Slavophilism movement.
+In the 20th century, the traditions of Russian opera were developed by many composers including Sergei Rachmaninoff in his works The Miserly Knight and Francesca da Rimini, Igor Stravinsky in Le Rossignol, Mavra, Oedipus rex, and The Rake's Progress, Sergei Prokofiev in The Gambler, The Love for Three Oranges, The Fiery Angel, Betrothal in a Monastery, and War and Peace; as well as Dmitri Shostakovich in The Nose and Lady Macbeth of the Mtsensk District, Edison Denisov in L'écume des jours, and Alfred Schnittke in Life with an Idiot and Historia von D. Johann Fausten.[28]
+Spain also produced its own distinctive form of opera, known as zarzuela, which had two separate flowerings: one from the mid-17th century through the mid-18th century, and another beginning around 1850. During the late 18th century up until the mid-19th century, Italian opera was immensely popular in Spain, supplanting the native form.
+Czech composers also developed a thriving national opera movement of their own in the 19th century, starting with Bedřich Smetana, who wrote eight operas including the internationally popular The Bartered Bride. Antonín Dvořák, most famous for Rusalka, wrote 13 operas; and Leoš Janáček gained international recognition in the 20th century for his innovative works including Jenůfa, The Cunning Little Vixen, and Káťa Kabanová.
+In Russian Eastern Europe, several national operas began to emerge. Ukrainian opera was developed by Semen Hulak-Artemovsky (1813–1873) whose most famous work Zaporozhets za Dunayem (A Cossack Beyond the Danube) is regularly performed around the world. Other Ukrainian opera composers include Mykola Lysenko (Taras Bulba and Natalka Poltavka), Heorhiy Maiboroda, and Yuliy Meitus. At the turn of the century, a distinct national opera movement also began to emerge in Georgia under the leadership Zacharia Paliashvili, who fused local folk songs and stories with 19th-century Romantic classical themes.
+The key figure of Hungarian national opera in the 19th century was Ferenc Erkel, whose works mostly dealt with historical themes. Among his most often performed operas are Hunyadi László and Bánk bán. The most famous modern Hungarian opera is Béla Bartók's Duke Bluebeard's Castle.
+Stanisław Moniuszko's opera Straszny Dwór (in English The Haunted Manor) (1861–64) represents a nineteenth-century peak of Polish national opera.[29] In the 20th century, other operas created by Polish composers included King Roger by Karol Szymanowski and Ubu Rex by Krzysztof Penderecki.
+The first known opera from Turkey (the Ottoman Empire) was Arshak II, which was an Armenian opera composed by an ethnic Armenian composer Tigran Chukhajian in 1868 and partially performed in 1873. It was fully staged in 1945 in Armenia.
+The first years of the Soviet Union saw the emergence of new national operas, such as the Koroğlu (1937) by the Azerbaijani composer Uzeyir Hajibeyov. The first Kyrgyz opera, Ai-Churek, premiered in Moscow at the Bolshoi Theatre on 26 May 1939, during Kyrgyz Art Decade. It was composed by Vladimir Vlasov, Abdylas Maldybaev and Vladimir Fere. The libretto was written by Joomart Bokonbaev, Jusup Turusbekov, and Kybanychbek Malikov. The opera is based on the Kyrgyz heroic epic Manas.[30][31]
+In Iran, opera gained more attention after the introduction of Western classical music in the late 19th century. However, it took until mid 20th century for Iranian composers to start experiencing with the field, especially as the construction of the Roudaki Hall in 1967, made possible staging of a large variety of works for stage. Perhaps, the most famous Iranian opera is Rostam and Sohrab by Loris Tjeknavorian premiered not until the early 2000s.
+Chinese contemporary classical opera, a Chinese language form of Western style opera that is distinct from traditional Chinese opera, has had operas dating back to The White Haired Girl in 1945.[32][33][34]
+In Latin America, opera started as a result of European colonisation. The first opera ever written in the Americas was La púrpura de la rosa, by Tomás de Torrejón y Velasco, although Partenope, by the Mexican Manuel de Zumaya, was the first opera written from a composer born in Latin America (music now lost). The first Brazilian opera for a libretto in Portuguese was A Noite de São João, by Elias Álvares Lobo. However, Antonio Carlos Gomes is generally regarded as the most outstanding Brazilian composer, having a relative success in Italy with its Brazilian-themed operas with Italian librettos, such as Il Guarany. Opera in Argentina developed in the 20th century after the inauguration of Teatro Colón in Buenos Aires—with the opera Aurora, by Ettore Panizza, being heavily influenced by the Italian tradition, due to immigration. Other important composers from Argentina include Felipe Boero and Alberto Ginastera.
+Perhaps the most obvious stylistic manifestation of modernism in opera is the development of atonality. The move away from traditional tonality in opera had begun with Richard Wagner, and in particular the Tristan chord. Composers such as Richard Strauss, Claude Debussy, Giacomo Puccini[citation needed], Paul Hindemith, Benjamin Britten and Hans Pfitzner pushed Wagnerian harmony further with a more extreme use of chromaticism and greater use of dissonance. Another aspect of modernist opera is the shift away from long, suspended melodies, to short quick mottos, as first illustrated by Giuseppe Verdi in his Falstaff. Composers such as Strauss, Britten, Shostakovich and Stravinsky adopted and expanded upon this style.
+Operatic modernism truly began in the operas of two Viennese composers, Arnold Schoenberg and his student Alban Berg, both composers and advocates of atonality and its later development (as worked out by Schoenberg), dodecaphony. Schoenberg's early musico-dramatic works, Erwartung (1909, premiered in 1924) and Die glückliche Hand display heavy use of chromatic harmony and dissonance in general. Schoenberg also occasionally used Sprechstimme.
+The two operas of Schoenberg's pupil Alban Berg, Wozzeck (1925) and Lulu (incomplete at his death in 1935) share many of the same characteristics as described above, though Berg combined his highly personal interpretation of Schoenberg's twelve-tone technique with melodic passages of a more traditionally tonal nature (quite Mahlerian in character) which perhaps partially explains why his operas have remained in standard repertory, despite their controversial music and plots. Schoenberg's theories have influenced (either directly or indirectly) significant numbers of opera composers ever since, even if they themselves did not compose using his techniques.
+Composers thus influenced include the Englishman Benjamin Britten, the German Hans Werner Henze, and the Russian Dmitri Shostakovich. (Philip Glass also makes use of atonality, though his style is generally described as minimalist, usually thought of as another 20th-century development.)[35]
+However, operatic modernism's use of atonality also sparked a backlash in the form of neoclassicism. An early leader of this movement was Ferruccio Busoni, who in 1913 wrote the libretto for his neoclassical number opera Arlecchino (first performed in 1917).[36] Also among the vanguard was the Russian Igor Stravinsky. After composing music for the Diaghilev-produced ballets Petrushka (1911) and The Rite of Spring (1913), Stravinsky turned to neoclassicism, a development culminating in his opera-oratorio Oedipus Rex (1927).  Stravinsky had already turned away from the modernist trends of his early ballets to produce small-scale works that do not fully qualify as opera, yet certainly contain many operatic elements, including Renard (1916: "a burlesque in song and dance") and The Soldier's Tale (1918: "to be read, played, and danced"; in both cases the descriptions and instructions are those of the composer). In the latter, the actors declaim portions of speech to a specified rhythm over instrumental accompaniment, peculiarly similar to the older German genre of Melodrama.  Well after his Rimsky-Korsakov-inspired works The Nightingale (1914), and Mavra (1922), Stravinsky continued to ignore serialist technique and eventually wrote a full-fledged 18th-century-style diatonic number opera The Rake's Progress (1951). His resistance to serialism (an attitude he reversed following Schoenberg's death) proved to be an inspiration for many[who?] other composers.[37]
+A common trend throughout the 20th century, in both opera and general orchestral repertoire, is the use of smaller orchestras as a cost-cutting measure; the grand Romantic-era orchestras with huge string sections, multiple harps, extra horns, and exotic percussion instruments were no longer feasible. As government and private patronage of the arts decreased throughout the 20th century, new works were often commissioned and performed with smaller budgets, very often resulting in chamber-sized works, and short, one-act operas. Many of Benjamin Britten's operas are scored for as few as 13 instrumentalists; Mark Adamo's two-act realization of Little Women is scored for 18 instrumentalists.
+Another feature of late 20th-century opera is the emergence of contemporary historical operas, in contrast to the tradition of basing operas on more distant history, the re-telling of contemporary fictional stories or plays, or on myth or legend. The Death of Klinghoffer, Nixon in China, and Doctor Atomic by John Adams, Dead Man Walking by Jake Heggie, and Anna Nicole by Mark-Anthony Turnage exemplify the dramatisation onstage of events in recent living memory, where characters portrayed in the opera were alive at the time of the premiere performance.
+The Metropolitan Opera in the US reports that the average age of its audience is now 60.[38] Many opera companies have experienced a similar trend, and opera company websites are replete with attempts to attract a younger audience. This trend is part of the larger trend of greying audiences for classical music since the last decades of the 20th century.[39] In an effort to attract younger audiences, the Metropolitan Opera offers a student discount on ticket purchases.[40]
+Smaller companies in the US have a more fragile existence, and they usually depend on a "patchwork quilt" of support from state and local governments, local businesses, and fundraisers. Nevertheless, some smaller companies have found ways of drawing new audiences. Opera Carolina offer discounts and happy hour events to the 21- to 40-year-old demographic.[41] In addition to radio and television broadcasts of opera performances, which have had some success in gaining new audiences, broadcasts of live performances in HD to movie theatres have shown the potential to reach new audiences. Since 2006, the Met has broadcast live performances to several hundred movie screens all over the world.[42]
+By the late 1930s, some musicals began to be written with a more operatic structure. These works include complex polyphonic ensembles and reflect musical developments of their times. Porgy and Bess (1935), influenced by jazz styles, and Candide (1956), with its sweeping, lyrical passages and farcical parodies of opera, both opened on Broadway but became accepted as part of the opera repertory. Popular musicals such as Show Boat, West Side Story, Brigadoon, Sweeney Todd, Passion, Evita, The Light in the Piazza, The Phantom of the Opera and others tell dramatic stories through complex music and in the 2010s they are sometimes seen in opera houses.[43] The Most Happy Fella (1952) is quasi-operatic and has been revived by the New York City Opera. Other rock influenced musicals, such as Tommy (1969) and Jesus Christ Superstar (1971), Les Misérables (1980), Rent (1996), Spring Awakening (2006), and Natasha, Pierre & The Great Comet of 1812 (2012) employ various operatic conventions, such as through composition, recitative instead of dialogue, and leitmotifs.
+A subtle type of sound electronic reinforcement called acoustic enhancement is used in some modern concert halls and theatres where operas are performed. Although none of the major opera houses "...use traditional, Broadway-style sound reinforcement, in which most if not all singers are equipped with radio microphones mixed to a series of unsightly loudspeakers scattered throughout the theatre", many use a sound reinforcement system for acoustic enhancement and for subtle boosting of offstage voices, child singers, onstage dialogue, and sound effects (e.g., church bells in Tosca or thunder effects in Wagnerian operas).[44]
+Operatic vocal technique evolved, in a time before electronic amplification, to allow singers to produce enough volume to be heard over an orchestra, without the instrumentalists having to substantially compromise their volume.
+Singers and the roles they play are classified by voice type, based on the tessitura, agility, power and timbre of their voices. Male singers can be classified by vocal range as bass, bass-baritone, baritone, tenor and countertenor, and female singers as contralto, mezzo-soprano and soprano. (Men sometimes sing in the "female" vocal ranges, in which case they are termed sopranist or countertenor. The countertenor is commonly encountered in opera, sometimes singing parts written for castrati—men neutered at a young age specifically to give them a higher singing range.) Singers are then further classified by size—for instance, a soprano can be described as a lyric soprano, coloratura, soubrette, spinto, or dramatic soprano. These terms, although not fully describing a singing voice, associate the singer's voice with the roles most suitable to the singer's vocal characteristics.
+Yet another sub-classification can be made according to acting skills or requirements, for example the basso buffo who often must be a specialist in patter as well as a comic actor. This is carried out in detail in the Fach system of German speaking countries, where historically opera and spoken drama were often put on by the same repertory company.
+A particular singer's voice may change drastically over his or her lifetime, rarely reaching vocal maturity until the third decade, and sometimes not until middle age. Two French voice types, premiere dugazon and deuxieme dugazon, were named after successive stages in the career of Louise-Rosalie Lefebvre (Mme. Dugazon). Other terms originating in the star casting system of the Parisian theatres are baryton-martin and soprano falcon.
+The soprano voice has typically been used as the voice of choice for the female protagonist of the opera since the latter half of the 18th century. Earlier, it was common for that part to be sung by any female voice, or even a castrato. The current emphasis on a wide vocal range was primarily an invention of the Classical period. Before that, the vocal virtuosity, not range, was the priority, with soprano parts rarely extending above a high A (Handel, for example, only wrote one role extending to a high C), though the castrato Farinelli was alleged to possess a top D (his lower range was also extraordinary, extending to tenor C). The mezzo-soprano, a term of comparatively recent origin, also has a large repertoire, ranging from the female lead in Purcell's Dido and Aeneas to such heavyweight roles as Brangäne in Wagner's Tristan und Isolde (these are both roles sometimes sung by sopranos; there is quite a lot of movement between these two voice-types). For the true contralto, the range of parts is more limited, which has given rise to the insider joke that contraltos only sing "witches, bitches, and britches" roles. In recent years many of the "trouser roles" from the Baroque era, originally written for women, and those originally sung by castrati, have been reassigned to countertenors.
+The tenor voice, from the Classical era onwards, has traditionally been assigned the role of male protagonist. Many of the most challenging tenor roles in the repertory were written during the bel canto era, such as Donizetti's sequence of 9 Cs above middle C during La fille du régiment. With Wagner came an emphasis on vocal heft for his protagonist roles, with this vocal category described as Heldentenor; this heroic voice had its more Italianate counterpart in such roles as Calaf in Puccini's Turandot. Basses have a long history in opera, having been used in opera seria in supporting roles, and sometimes for comic relief (as well as providing a contrast to the preponderance of high voices in this genre). The bass repertoire is wide and varied, stretching from the comedy of Leporello in Don Giovanni to the nobility of Wotan in Wagner's Ring Cycle, to the conflicted King Phillip of Verdi's Don Carlos. In between the bass and the tenor is the baritone, which also varies in weight from say, Guglielmo in Mozart's Così fan tutte to Posa in Verdi's Don Carlos; the actual designation "baritone" was not standard until the mid-19th century.
+Early performances of opera were too infrequent for singers to make a living exclusively from the style, but with the birth of commercial opera in the mid-17th century, professional performers began to emerge. The role of the male hero was usually entrusted to a castrato, and by the 18th century, when Italian opera was performed throughout Europe, leading castrati who possessed extraordinary vocal virtuosity, such as Senesino and Farinelli, became international stars. The career of the first major female star (or prima donna), Anna Renzi, dates to the mid-17th century. In the 18th century, a number of Italian sopranos gained international renown and often engaged in fierce rivalry, as was the case with Faustina Bordoni and Francesca Cuzzoni, who started a fist fight with one another during a performance of a Handel opera. The French disliked castrati, preferring their male heroes to be sung by an haute-contre (a high tenor), of which Joseph Legros (1739–1793) was a leading example.[45]
+Though opera patronage has decreased in the last century in favor of other arts and media (such as musicals, cinema, radio, television and recordings), mass media and the advent of recording have supported the popularity of many famous singers including Maria Callas, Enrico Caruso, Amelita Galli-Curci, Kirsten Flagstad, Juan Arvizu,[46][47] Nestor Mesta Chayres,[48][49][50]
+Mario Del Monaco, Renata Tebaldi, Risë Stevens, Alfredo Kraus, Franco Corelli, Montserrat Caballé, Joan Sutherland, Birgit Nilsson, Nellie Melba, Rosa Ponselle, Beniamino Gigli, Jussi Björling, Feodor Chaliapin, Cecilia Bartoli, Renée Fleming, Marilyn Horne, Bryn Terfel and "The Three Tenors" (Luciano Pavarotti, Plácido Domingo, and José Carreras).
+Before the 1700s, Italian operas used a small string orchestra, but it rarely played to accompany the singers. Opera solos during this period were accompanied by the basso continuo group, which consisted of the harpsichord, "plucked instruments" such as lute and a bass instrument.[51] The string orchestra typically only played when the singer was not singing, such as during a singer's "...entrances and exits, between vocal numbers, [or] for [accompanying] dancing". Another role for the orchestra during this period was playing an orchestral ritornello to mark the end of a singer's solo.[51] During the early 1700s, some composers began to use the string orchestra to mark certain aria or recitatives "...as special"; by 1720, most arias were accompanied by orchestra. Opera composers such as Domenico Sarro, Leonardo Vinci, Giambattista Pergolesi, Leonardo Leo, and Johann Adolf Hasse added new instruments to the opera orchestra and gave the instruments new roles. They added wind instruments to the strings and used orchestral instruments to play instrumental solos, as a way to mark certain arias as special.[51]
+The orchestra has also provided an instrumental overture before the singers come onstage since the 1600s. Peri's Euridice opens with a brief instrumental ritornello, and Monteverdi's L'Orfeo (1607) opens with a toccata, in this case a fanfare for muted trumpets. The French overture as found in Jean-Baptiste Lully's operas[52] consist of a slow introduction in a marked "dotted rhythm", followed by a lively movement in fugato style. The overture was frequently followed by a series of dance tunes before the curtain rose. This overture style was also used in English opera, most notably in Henry Purcell's Dido and Aeneas. Handel also uses the French overture form in some of his Italian operas such as Giulio Cesare.[53]
+In Italy, a distinct form called "overture" arose in the 1680s, and became established particularly through the operas of Alessandro Scarlatti, and spread throughout Europe, supplanting the French form as the standard operatic overture by the mid-18th century.[54] It uses three generally homophonic movements: fast–slow–fast. The opening movement was normally in duple metre and in a major key; the slow movement in earlier examples was short, and could be in a contrasting key; the concluding movement was dance-like, most often with rhythms of the gigue or minuet, and returned to the key of the opening section. As the form evolved, the first movement may incorporate fanfare-like elements and took on the pattern of so-called "sonatina form" (sonata form without a development section), and the slow section became more extended and lyrical.[54]
+In Italian opera after about 1800, the "overture" became known as the sinfonia.[55] Fisher also notes the term Sinfonia avanti l'opera (literally, the "symphony before the opera") was "an early term for a sinfonia used to begin an opera, that is, as an overture as opposed to one serving to begin a later section of the work".[55] In 19th-century opera, in some operas, the overture, Vorspiel, Einleitung, Introduction, or whatever else it may be called, was the portion of the music which takes place before the curtain rises; a specific, rigid form was no longer required for the overture.
+The role of the orchestra in accompanying the singers changed over the 19th century, as the Classical style transitioned to the Romantic era. In general, orchestras got bigger, new instruments were added, such as additional percussion instruments (e.g., bass drum, cymbals, snare drum, etc.). The orchestration of orchestra parts also developed over the 19th century. In Wagnerian operas, the forefronting of the orchestra went beyond the overture. In Wagnerian operas such as Tristan, the orchestra often played the recurrent musical themes or leitmotifs, a role which gave a prominence to the orchestra which "...elevated its status to that of a prima donna".[56] Wagner's operas were scored with unprecedented scope and complexity, adding more brass instruments and huge ensemble sizes: indeed, his score to Das Rheingold calls for six harps.
+As the role of the orchestra and other instrumental ensembles changed over the history of opera, so did the role of leading the musicians. In the Baroque era, the musicians were usually directed by the harpsichord player, although the French composer Lully is known to have conducted with a long staff. In the 1800s, during the Classical period, the first violinist, also known as the concertmaster, would lead the orchestra while sitting. Over time, some directors began to stand up and use hand and arm gestures to lead the performers. Eventually this role of music director became termed the conductor, and a podium was used to make it easier for all the musicians to see him or her. By the time Wagnerian operas were introduced, the complexity of the works and the huge orchestras used to play them gave the conductor an increasingly important role. Modern opera conductors have a challenging role: they have to direct both the orchestra in the orchestra pit and the singers up on stage.
+Since the days of Handel and Mozart, many composers have favored Italian as the language for the libretto of their operas. From the Bel Canto era to Verdi, composers would sometimes supervise versions of their operas in both Italian and French. Because of this, operas such as Lucia di Lammermoor or Don Carlos are today deemed canonical in both their French and Italian versions.[57]
+Till the mid 1950s, it was acceptable to produce operas in translations even if these had not been authorized by the composer or the original librettists. For example, opera houses in Italy routinely staged Wagner in Italian.[58] After WWII, opera scholarship improved, artists refocused on the original versions, and translations fell out of favor. Knowledge of European languages, especially Italian, French, and German, is today an important part of the training for professional singers."The biggest chunk of operatic training is in linguistics and musicianship," explains mezzo-soprano Dolora Zajick. "[I have to understand] not only what I'm singing, but what everyone else is singing. I sing Italian, Czech, Russian, French, German, English."[59]
+In the 1980s, supertitles (sometimes called surtitles) began to appear. Although supertitles were first almost universally condemned as a distraction,[60] today many opera houses provide either supertitles, generally projected above the theatre's proscenium arch, or individual seat screens where spectators can choose from more than one language. TV broadcasts typically include subtitles even if intended for an audience who knows well the language (for example, a RAI broadcast of an Italian opera). These subtitles target not only the hard of hearing but the audience generally, since a sung discourse is much harder to understand than a spoken one—even in the ears of native speakers. Subtitles in one or more languages have become standard in opera broadcasts, simulcasts, and DVD editions.
+Today, operas are only rarely performed in translation. Exceptions include the English National Opera, the Opera Theatre of Saint Louis, Opera Theater of Pittsburgh, and Opera South East,[61] which favor English translations.[62] Another exception are opera productions intended for a young audience, such as Humperdinck's Hansel and Gretel[63] and some productions of Mozart's The Magic Flute.[64]
+Outside the US, and especially in Europe, most opera houses receive public subsidies from taxpayers.[65] In Milan, Italy, 60% of La Scala's annual budget of €115 million is from ticket sales and private donations, with the remaining 40% coming from public funds.[66] In 2005, La Scala received 25% of Italy's total state subsidy of €464 million for the performing arts.[67] In the UK, Arts Council England provides funds to Opera North, the Royal Opera House, Welsh National Opera, and English National Opera. Between 2012 and 2015, these four opera companies along with the English National Ballet, Birmingham Royal Ballet and Northern Ballet accounted for 22% of the funds in the Arts Council's national portfolio. During that period, the Council undertook an analysis of its funding for large-scale opera and ballet companies, setting recommendations and targets for the companies to meet prior to the 2015–2018 funding decisions.[68] In February 2015, concerns over English National Opera's business plan led to the Arts Council placing it "under special funding arrangements" in what The Independent termed "the unprecedented step" of threatening to withdraw public funding if the Council's concerns were not met by 2017.[69] European public funding to opera has led to a disparity between the number of year-round opera houses in Europe and the United States. For example, "Germany has about 80-year-round opera houses [as of 2004], while the U.S., with more than three times the population, does not have any. Even the Met only has a seven-month season."[70]
+A milestone for opera broadcasting in the U.S. was achieved on 24 December 1951, with the live broadcast of Amahl and the Night Visitors, an opera in one act by Gian Carlo Menotti. It was the first opera specifically composed for television in America.[71] Another milestone occurred in Italy in 1992 when Tosca was broadcast live from its original Roman settings and times of the day:  The first act came from the 16th-century Church of Sant'Andrea della Valle at noon on Saturday; the 16th-century Palazzo Farnese was the setting for the second at 8:15 P.M.; and on Sunday at 6 A.M., the third act was broadcast from Castel Sant'Angelo. The production was transmitted via satellite to 105 countries.[72]
+Major opera companies have begun presenting their performances in local cinemas throughout the United States and many other countries. The Metropolitan Opera began a series of live high-definition video transmissions to cinemas around the world in 2006.[73] In 2007, Met performances were shown in over 424 theaters in 350 U.S. cities. La bohème went out to 671 screens worldwide. San Francisco Opera began prerecorded video transmissions in March 2008. As of June 2008, approximately 125 theaters in 117 U.S. cities carry the showings. The HD video opera transmissions are presented via the same HD digital cinema projectors used for major Hollywood films.[74] European opera houses and festivals including the Royal Opera in London, La Scala in Milan, the Salzburg Festival, La Fenice in Venice, and the Maggio Musicale in Florence have also transmitted their productions to theaters in cities around the world since 2006, including 90 cities in the U.S.[75][76]
+The emergence of the Internet has also affected the way in which audiences consume opera. In 2009 the British Glyndebourne Festival Opera offered for the first time an online digital video download of its complete 2007 production of Tristan und Isolde. In 2013 season the festival streamed all six of its productions online.[77][78] In July 2012 the first online community opera was premiered at the Savonlinna Opera Festival. Titled Free Will, it was created by members of the Internet group Opera By You. Its 400 members from 43 countries wrote the libretto, composed the music, and designed the sets and costumes using the Wreckamovie web platform. Savonlinna Opera Festival provided professional soloists, an 80-member choir, a symphony orchestra, and the stage machinery. It was performed live at the festival and streamed live on the internet.[79]

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+Opera  is a form of theatre in which music has a leading role and the parts are taken by singers, but is distinct from musical theatre.[1] Such a "work" (the literal translation of the Italian word "opera") is typically a collaboration between a composer and a librettist[2] and incorporates a number of the performing arts, such as acting, scenery, costume, and sometimes dance or ballet. The performance is typically given in an opera house, accompanied by an orchestra or smaller musical ensemble, which since the early 19th century has been led by a conductor.
+Opera is a key part of the Western classical music tradition.[3] Originally understood as an entirely sung piece, in contrast to a play with songs, opera has come to include numerous genres, including some that include spoken dialogue such as musical theatre, Singspiel and Opéra comique. In traditional number opera, singers employ two styles of singing: recitative, a speech-inflected style,[4] and self-contained arias. The 19th century saw the rise of the continuous music drama.
+Opera originated in Italy at the end of the 16th century (with Jacopo Peri's mostly lost Dafne, produced in Florence in 1598) especially from works by Claudio Monteverdi, notably L'Orfeo, and soon spread through the rest of Europe: Heinrich Schütz in Germany, Jean-Baptiste Lully in France, and Henry Purcell in England all helped to establish their national traditions in the 17th century. In the 18th century, Italian opera continued to dominate most of Europe (except France), attracting foreign composers such as George Frideric Handel. Opera seria was the most prestigious form of Italian opera, until Christoph Willibald Gluck reacted against its artificiality with his "reform" operas in the 1760s. The most renowned figure of late 18th-century opera is Wolfgang Amadeus Mozart, who began with opera seria but is most famous for his Italian comic operas, especially The Marriage of Figaro (Le nozze di Figaro), Don Giovanni, and Così fan tutte, as well as Die Entführung aus dem Serail (The Abduction from the Seraglio), and The Magic Flute (Die Zauberflöte), landmarks in the German tradition.
+The first third of the 19th century saw the high point of the bel canto style, with Gioachino Rossini, Gaetano Donizetti and Vincenzo Bellini all creating works that are still performed. It also saw the advent of Grand Opera typified by the works of Auber and Meyerbeer. The mid-to-late 19th century was a golden age of opera, led and dominated by Giuseppe Verdi in Italy and Richard Wagner in Germany. The popularity of opera continued through the verismo era in Italy and contemporary French opera through to Giacomo Puccini and Richard Strauss in the early 20th century. During the 19th century, parallel operatic traditions emerged in central and eastern Europe, particularly in Russia and Bohemia. The 20th century saw many experiments with modern styles, such as atonality and serialism (Arnold Schoenberg and Alban Berg), Neoclassicism (Igor Stravinsky), and Minimalism (Philip Glass and John Adams). With the rise of recording technology, singers such as Enrico Caruso and Maria Callas became known to much wider audiences that went beyond the circle of opera fans. Since the invention of radio and television, operas were also performed on (and written for) these media. Beginning in 2006, a number of major opera houses began to present live high-definition video transmissions of their performances in cinemas all over the world. Since 2009, complete performances can be downloaded and are live streamed.
+The words of an opera are known as the libretto (literally "small book"). Some composers, notably Wagner, have written their own libretti; others have worked in close collaboration with their librettists, e.g. Mozart with Lorenzo Da Ponte. Traditional opera, often referred to as "number opera", consists of two modes of singing: recitative, the plot-driving passages sung in a style designed to imitate and emphasize the inflections of speech,[4] and aria (an "air" or formal song) in which the characters express their emotions in a more structured melodic style. Vocal duets, trios and other ensembles often occur, and choruses are used to comment on the action. In some forms of opera, such as singspiel, opéra comique, operetta, and semi-opera, the recitative is mostly replaced by spoken dialogue. Melodic or semi-melodic passages occurring in the midst of, or instead of, recitative, are also referred to as arioso. The terminology of the various kinds of operatic voices is described in detail below.[5] During both the Baroque and Classical periods, recitative could appear in two basic forms, each of which was accompanied by a different instrumental ensemble: secco (dry) recitative, sung with a free rhythm dictated by the accent of the words, accompanied only by basso continuo, which was usually a harpsichord and a cello; or accompagnato (also known as strumentato) in which the orchestra provided accompaniment. Over the 18th century, arias were increasingly accompanied by the orchestra. By the 19th century, accompagnato had gained the upper hand, the orchestra played a much bigger role, and Wagner revolutionized opera by abolishing almost all distinction between aria and recitative in his quest for what Wagner termed "endless melody". Subsequent composers have tended to follow Wagner's example, though some, such as Stravinsky in his The Rake's Progress have bucked the trend. The changing role of the orchestra in opera is described in more detail below.
+The Italian word opera means "work", both in the sense of the labour done and the result produced. The Italian word derives from the Latin opera, a singular noun meaning "work" and also the plural of the noun opus. According to the Oxford English Dictionary, the Italian word was first used in the sense "composition in which poetry, dance, and music are combined" in 1639; the first recorded English usage in this sense dates to 1648.[6]
+Dafne by Jacopo Peri was the earliest composition considered opera, as understood today. It was written around 1597, largely under the inspiration of an elite circle of literate Florentine humanists who gathered as the "Camerata de' Bardi". Significantly, Dafne was an attempt to revive the classical Greek drama, part of the wider revival of antiquity characteristic of the Renaissance. The members of the Camerata considered that the "chorus" parts of Greek dramas were originally sung, and possibly even the entire text of all roles; opera was thus conceived as a way of "restoring" this situation. Dafne, however, is lost. A later work by Peri, Euridice, dating from 1600, is the first opera score to have survived to the present day. The honour of being the first opera still to be regularly performed, however, goes to Claudio Monteverdi's L'Orfeo, composed for the court of Mantua in 1607.[7] The Mantua court of the Gonzagas, employers of Monteverdi, played a significant role in the origin of opera employing not only court singers of the concerto delle donne (till 1598), but also one of the first actual "opera singers", Madama Europa.[8]
+Opera did not remain confined to court audiences for long. In 1637, the idea of a "season" (often during the carnival) of publicly attended operas supported by ticket sales emerged in Venice. Monteverdi had moved to the city from Mantua and composed his last operas, Il ritorno d'Ulisse in patria and L'incoronazione di Poppea, for the Venetian theatre in the 1640s. His most important follower Francesco Cavalli helped spread opera throughout Italy. In these early Baroque operas, broad comedy was blended with tragic elements in a mix that jarred some educated sensibilities, sparking the first of opera's many reform movements, sponsored by the Arcadian Academy, which came to be associated with the poet Metastasio, whose libretti helped crystallize the genre of opera seria, which became the leading form of Italian opera until the end of the 18th century. Once the Metastasian ideal had been firmly established, comedy in Baroque-era opera was reserved for what came to be called opera buffa.
+Before such elements were forced out of opera seria, many libretti had featured a separately unfolding comic plot as sort of an "opera-within-an-opera". One reason for this was an attempt to attract members of the growing merchant class, newly wealthy, but still not as cultured as the nobility, to the public opera houses. These separate plots were almost immediately resurrected in a separately developing tradition that partly derived from the commedia dell'arte, a long-flourishing improvisatory stage tradition of Italy. Just as intermedi had once been performed in between the acts of stage plays, operas in the new comic genre of "intermezzi", which developed largely in Naples in the 1710s and '20s, were initially staged during the intermissions of opera seria. They became so popular, however, that they were soon being offered as separate productions.
+Opera seria was elevated in tone and highly stylised in form, usually consisting of secco recitative interspersed with long da capo arias. These afforded great opportunity for virtuosic singing and during the golden age of opera seria the singer really became the star. The role of the hero was usually written for the high-pitched male castrato voice, which was produced by castration of the singer before puberty, which prevented a boy's larynx from being transformed at puberty. Castrati such as Farinelli and Senesino, as well as female sopranos such as Faustina Bordoni, became in great demand throughout Europe as opera seria ruled the stage in every country except France.  Farinelli was one of the most famous singers of the 18th century. Italian opera set the Baroque standard. Italian libretti were the norm, even when a German composer like Handel found himself composing the likes of Rinaldo and Giulio Cesare for London audiences. Italian libretti remained dominant in the classical period as well, for example in the operas of Mozart, who wrote in Vienna near the century's close. Leading Italian-born composers of opera seria include Alessandro Scarlatti, Vivaldi and Porpora.[9]
+Opera seria had its weaknesses and critics. The taste for embellishment on behalf of the superbly trained singers, and the use of spectacle as a replacement for dramatic purity and unity drew attacks. Francesco Algarotti's Essay on the Opera (1755) proved to be an inspiration for Christoph Willibald Gluck's reforms. He advocated that opera seria had to return to basics and that all the various elements—music (both instrumental and vocal), ballet, and staging—must be subservient to the overriding drama. In 1765 Melchior Grimm published "Poème lyrique", an influential article for the Encyclopédie on lyric and opera librettos.[10][11][12][13][14] Several composers of the period, including Niccolò Jommelli and Tommaso Traetta, attempted to put these ideals into practice. The first to succeed however, was Gluck. Gluck strove to achieve a "beautiful simplicity". This is evident in his first reform opera, Orfeo ed Euridice, where his non-virtuosic vocal melodies are supported by simple harmonies and a richer orchestra presence throughout.
+Gluck's reforms have had resonance throughout operatic history. Weber, Mozart, and Wagner, in particular, were influenced by his ideals. Mozart, in many ways Gluck's successor, combined a superb sense of drama, harmony, melody, and counterpoint to write a series of comic operas with libretti by Lorenzo Da Ponte, notably Le nozze di Figaro, Don Giovanni, and Così fan tutte, which remain among the most-loved, popular and well-known operas today. But Mozart's contribution to opera seria was more mixed; by his time it was dying away, and in spite of such fine works as Idomeneo and La clemenza di Tito, he would not succeed in bringing the art form back to life again.[15]
+The bel canto opera movement flourished in the early 19th century and is exemplified by the operas of Rossini, Bellini, Donizetti, Pacini, Mercadante and many others. Literally "beautiful singing", bel canto opera derives from the Italian stylistic singing school of the same name. Bel canto lines are typically florid and intricate, requiring supreme agility and pitch control. Examples of famous operas in the bel canto style include Rossini's Il barbiere di Siviglia and La Cenerentola, as well as Bellini's Norma, La sonnambula and I puritani and Donizetti's Lucia di Lammermoor, L'elisir d'amore and Don Pasquale.
+Following the bel canto era, a more direct, forceful style was rapidly popularized by Giuseppe Verdi, beginning with his biblical opera Nabucco. This opera, and the ones that would follow in Verdi's career, revolutionized Italian opera, changing it from merely a display of vocal fireworks, with Rossini's and Donizetti's works, to dramatic story-telling. Verdi's operas resonated with the growing spirit of Italian nationalism in the post-Napoleonic era, and he quickly became an icon of the patriotic movement for a unified Italy. In the early 1850s, Verdi produced his three most popular operas: Rigoletto, Il trovatore and La traviata. The first of these, Rigoletto, proved the most daring and revolutionary. In it, Verdi blurs the distinction between the aria and recitative as it never before was, leading the opera to be "an unending string of duets". La traviata was also novel. It tells the story of courtesan, and is often cited as one of the first "realistic" operas,[citation needed] because rather than featuring great kings and figures from literature, it focuses on the tragedies of ordinary life and society. After these, he continued to develop his style, composing perhaps the greatest French Grand Opera, Don Carlos, and ending his career with two Shakespeare-inspired works, Otello and Falstaff, which reveal how far Italian opera had grown in sophistication since the early 19th century. These final two works showed Verdi at his most masterfully orchestrated, and are both incredibly influential, and modern. In Falstaff, Verdi sets the preeminent standard for the form and style that would dominate opera throughout the twentieth century. Rather than long, suspended melodies, Falstaff contains many little motifs and mottos, that, rather than being expanded upon, are introduced and subsequently dropped, only to be brought up again later. These motifs never are expanded upon, and just as the audience expects a character to launch into a long melody, a new character speaks, introducing a new phrase. This fashion of opera directed opera from Verdi, onward, exercising tremendous influence on his successors Giacomo Puccini, Richard Strauss, and Benjamin Britten.[16]
+After Verdi, the sentimental "realistic" melodrama of verismo appeared in Italy. This was a style introduced by Pietro Mascagni's Cavalleria rusticana and Ruggero Leoncavallo's Pagliacci that came to dominate the world's opera stages with such popular works as Giacomo Puccini's La bohème, Tosca, and Madama Butterfly. Later Italian composers, such as Berio and Nono, have experimented with modernism.[17]
+The first German opera was Dafne, composed by Heinrich Schütz in 1627, but the music score has not survived. Italian opera held a great sway over German-speaking countries until the late 18th century. Nevertheless, native forms would develop in spite of this influence. In 1644, Sigmund Staden produced the first Singspiel, Seelewig, a popular form of German-language opera in which singing alternates with spoken dialogue. In the late 17th century and early 18th century, the Theater am Gänsemarkt in Hamburg presented German operas by Keiser, Telemann and Handel. Yet most of the major German composers of the time, including Handel himself, as well as Graun, Hasse and later Gluck, chose to write most of their operas in foreign languages, especially Italian. In contrast to Italian opera, which was generally composed for the aristocratic class, German opera was generally composed for the masses and tended to feature simple folk-like melodies, and it was not until the arrival of Mozart that German opera was able to match its Italian counterpart in musical sophistication.[18] The theatre company of Abel Seyler pioneered serious German-language opera in the 1770s, marking a break with the previous simpler musical entertainment.[19][20]
+Mozart's Singspiele, Die Entführung aus dem Serail (1782) and Die Zauberflöte (1791) were an important breakthrough in achieving international recognition for German opera. The tradition was developed in the 19th century by Beethoven with his Fidelio (1805), inspired by the climate of the French Revolution. Carl Maria von Weber established German Romantic opera in opposition to the dominance of Italian bel canto. His Der Freischütz (1821) shows his genius for creating a supernatural atmosphere. Other opera composers of the time include Marschner, Schubert and Lortzing, but the most significant figure was undoubtedly Wagner.
+Wagner was one of the most revolutionary and controversial composers in musical history. Starting under the influence of Weber and Meyerbeer, he gradually evolved a new concept of opera as a Gesamtkunstwerk (a "complete work of art"), a fusion of music, poetry and painting. He greatly increased the role and power of the orchestra, creating scores with a complex web of leitmotifs, recurring themes often associated with the characters and concepts of the drama, of which prototypes can be heard in his earlier operas such as Der fliegende Holländer, Tannhäuser and Lohengrin; and he was prepared to violate accepted musical conventions, such as tonality, in his quest for greater expressivity. In his mature music dramas, Tristan und Isolde, Die Meistersinger von Nürnberg, Der Ring des Nibelungen and Parsifal, he abolished the distinction between aria and recitative in favour of a seamless flow of "endless melody". Wagner also brought a new philosophical dimension to opera in his works, which were usually based on stories from Germanic or Arthurian legend. Finally, Wagner built his own opera house at Bayreuth with part of the patronage from Ludwig II of Bavaria, exclusively dedicated to performing his own works in the style he wanted.
+Opera would never be the same after Wagner and for many composers his legacy proved a heavy burden. On the other hand, Richard Strauss accepted Wagnerian ideas but took them in wholly new directions, along with incorporating the new form introduced by Verdi. He first won fame with the scandalous Salome and the dark tragedy Elektra, in which tonality was pushed to the limits. Then Strauss changed tack in his greatest success, Der Rosenkavalier, where Mozart and Viennese waltzes became as important an influence as Wagner. Strauss continued to produce a highly varied body of operatic works, often with libretti by the poet Hugo von Hofmannsthal. Other composers who made individual contributions to German opera in the early 20th century include Alexander von Zemlinsky, Erich Korngold, Franz Schreker, Paul Hindemith, Kurt Weill and the Italian-born Ferruccio Busoni. The operatic innovations of Arnold Schoenberg and his successors are discussed in the section on modernism.[21]
+During the late 19th century, the Austrian composer Johann Strauss II, an admirer of the French-language operettas composed by Jacques Offenbach, composed several German-language operettas, the most famous of which was Die Fledermaus, which is still regularly performed today.[22] Nevertheless, rather than copying the style of Offenbach, the operettas of Strauss II had distinctly Viennese flavor to them, which have cemented the Strauss II's place as one of the most renowned operetta composers of all time.
+In rivalry with imported Italian opera productions, a separate French tradition was founded by the Italian Jean-Baptiste Lully at the court of King Louis XIV. Despite his foreign origin, Lully established an Academy of Music and monopolised French opera from 1672. Starting with Cadmus et Hermione, Lully and his librettist Quinault created tragédie en musique, a form in which dance music and choral writing were particularly prominent. Lully's operas also show a concern for expressive recitative which matched the contours of the French language. In the 18th century, Lully's most important successor was Jean-Philippe Rameau, who composed five tragédies en musique as well as numerous works in other genres such as opéra-ballet, all notable for their rich orchestration and harmonic daring. Despite the popularity of Italian opera seria throughout much of Europe during the Baroque period, Italian opera never gained much of a foothold in France, where its own national operatic tradition was more popular instead.[23] After Rameau's death, the German Gluck was persuaded to produce six operas for the Parisian stage in the 1770s. They show the influence of Rameau, but simplified and with greater focus on the drama. At the same time, by the middle of the 18th century another genre was gaining popularity in France: opéra comique. This was the equivalent of the German singspiel, where arias alternated with spoken dialogue. Notable examples in this style were produced by Monsigny, Philidor and, above all, Grétry. During the Revolutionary period, composers such as Étienne Méhul and Luigi Cherubini, who were followers of Gluck, brought a new seriousness to the genre, which had never been wholly "comic" in any case. Another phenomenon of this period was the 'propaganda opera' celebrating revolutionary successes, e.g. Gossec's Le triomphe de la République (1793).
+By the 1820s, Gluckian influence in France had given way to a taste for Italian bel canto, especially after the arrival of Rossini in Paris. Rossini's Guillaume Tell helped found the new genre of Grand Opera, a form whose most famous exponent was another foreigner, Giacomo Meyerbeer. Meyerbeer's works, such as Les Huguenots, emphasised virtuoso singing and extraordinary stage effects. Lighter opéra comique also enjoyed tremendous success in the hands of Boïeldieu, Auber, Hérold and Adam. In this climate, the operas of the French-born composer Hector Berlioz struggled to gain a hearing. Berlioz's epic masterpiece Les Troyens, the culmination of the Gluckian tradition, was not given a full performance for almost a hundred years.
+In the second half of the 19th century, Jacques Offenbach created operetta with witty and cynical works such as Orphée aux enfers, as well as the opera Les Contes d'Hoffmann; Charles Gounod scored a massive success with Faust; and Georges Bizet composed Carmen, which, once audiences learned to accept its blend of Romanticism and realism, became the most popular of all opéra comiques. Jules Massenet, Camille Saint-Saëns and Léo Delibes all composed works which are still part of the standard repertory, examples being Massenet's Manon, Saint-Saëns' Samson et Dalila and Delibes' Lakmé.  Their operas formed another genre, the Opera Lyrique, combined opera comique and grand opera. It is less grandiose than grand opera, but without the spoken dialogue of opera comique.  At the same time, the influence of Richard Wagner was felt as a challenge to the French tradition. Many French critics angrily rejected Wagner's music dramas while many French composers closely imitated them with variable success. Perhaps the most interesting response came from Claude Debussy. As in Wagner's works, the orchestra plays a leading role in Debussy's unique opera Pelléas et Mélisande (1902) and there are no real arias, only recitative. But the drama is understated, enigmatic and completely un-Wagnerian.
+Other notable 20th-century names include Ravel, Dukas, Roussel and Milhaud. Francis Poulenc is one of the very few post-war composers of any nationality whose operas (which include Dialogues des Carmélites) have gained a foothold in the international repertory. Olivier Messiaen's lengthy sacred drama Saint François d'Assise (1983) has also attracted widespread attention.[24]
+In England, opera's antecedent was the 17th-century jig. This was an afterpiece that came at the end of a play. It was frequently libellous and scandalous and consisted in the main of dialogue set to music arranged from popular tunes. In this respect, jigs anticipate the ballad operas of the 18th century. At the same time, the French masque was gaining a firm hold at the English Court, with even more lavish splendour and highly realistic scenery than had been seen before. Inigo Jones became the quintessential designer of these productions, and this style was to dominate the English stage for three centuries. These masques contained songs and dances. In Ben Jonson's Lovers Made Men (1617), "the whole masque was sung after the Italian manner, stilo recitativo".[25] The approach of the English Commonwealth closed theatres and halted any developments that may have led to the establishment of English opera. However, in 1656, the dramatist Sir William Davenant produced The Siege of Rhodes. Since his theatre was not licensed to produce drama, he asked several of the leading composers (Lawes, Cooke, Locke, Coleman and Hudson) to set sections of it to music. This success was followed by The Cruelty of the Spaniards in Peru (1658) and The History of Sir Francis Drake (1659). These pieces were encouraged by Oliver Cromwell because they were critical of Spain. With the English Restoration, foreign (especially French) musicians were welcomed back. In 1673, Thomas Shadwell's Psyche, patterned on the 1671 'comédie-ballet' of the same name produced by Molière and Jean-Baptiste Lully. William Davenant produced The Tempest in the same year, which was the first musical adaption of a Shakespeare play (composed by Locke and Johnson).[25] About 1683, John Blow composed Venus and Adonis, often thought of as the first true English-language opera.
+Blow's immediate successor was the better known Henry Purcell. Despite the success of his masterwork Dido and Aeneas (1689), in which the action is furthered by the use of Italian-style recitative, much of Purcell's best work was not involved in the composing of typical opera, but instead, he usually worked within the constraints of the semi-opera format, where isolated scenes and masques are contained within the structure of a spoken play, such as Shakespeare in Purcell's The Fairy-Queen (1692) and Beaumont and Fletcher in The Prophetess (1690) and Bonduca (1696). The main characters of the play tend not to be involved in the musical scenes, which means that Purcell was rarely able to develop his characters through song. Despite these hindrances, his aim (and that of his collaborator John Dryden) was to establish serious opera in England, but these hopes ended with Purcell's early death at the age of 36.
+Following Purcell, the popularity of opera in England dwindled for several decades. A revived interest in opera occurred in the 1730s which is largely attributed to Thomas Arne, both for his own compositions and for alerting Handel to the commercial possibilities of large-scale works in English. Arne was the first English composer to experiment with Italian-style all-sung comic opera, with his greatest success being Thomas and Sally in 1760. His opera Artaxerxes (1762) was the first attempt to set a full-blown opera seria in English and was a huge success, holding the stage until the 1830s. Although Arne imitated many elements of Italian opera, he was perhaps the only English composer at that time who was able to move beyond the Italian influences and create his own unique and distinctly English voice. His modernized ballad opera, Love in a Village (1762), began a vogue for pastiche opera that lasted well into the 19th century. Charles Burney wrote that Arne introduced "a light, airy, original, and pleasing melody, wholly different from that of Purcell or Handel, whom all English composers had either pillaged or imitated".
+Besides Arne, the other dominating force in English opera at this time was George Frideric Handel, whose opera serias filled the London operatic stages for decades and influenced most home-grown composers, like John Frederick Lampe, who wrote using Italian models. This situation continued throughout the 18th and 19th centuries, including in the work of Michael William Balfe, and the operas of the great Italian composers, as well as those of Mozart, Beethoven, and Meyerbeer, continued to dominate the musical stage in England.
+The only exceptions were ballad operas, such as John Gay's The Beggar's Opera (1728), musical burlesques, European operettas, and late Victorian era light operas, notably the Savoy Operas of W. S. Gilbert and Arthur Sullivan, all of which types of musical entertainments frequently spoofed operatic conventions. Sullivan wrote only one grand opera, Ivanhoe (following the efforts of a number of young English composers beginning about 1876),[25] but he claimed that even his light operas constituted part of a school of "English" opera, intended to supplant the French operettas (usually performed in bad translations) that had dominated the London stage from the mid-19th century into the 1870s. London's Daily Telegraph agreed, describing The Yeomen of the Guard as "a genuine English opera, forerunner of many others, let us hope, and possibly significant of an advance towards a national lyric stage".[26] Sullivan produced a few light operas in the 1890s that were of a more serious nature than those in the G&S series, including Haddon Hall and The Beauty Stone, but Ivanhoe (which ran for 155 consecutive performances, using alternating casts—a record until Broadway's La bohème) survives as his only Grand Opera.
+In the 20th century, English opera began to assert more independence, with works of Ralph Vaughan Williams and in particular Benjamin Britten, who in a series of works that remain in standard repertory today, revealed an excellent flair for the dramatic and superb musicality. More recently Sir Harrison Birtwistle has emerged as one of Britain's most significant contemporary composers from his first opera Punch and Judy to his most recent critical success in The Minotaur. In the first decade of the 21st century, the librettist of an early Birtwistle opera, Michael Nyman, has been focusing on composing operas, including Facing Goya, Man and Boy: Dada, and Love Counts. Today composers such as Thomas Adès continue to export English opera abroad.[27]
+Also in the 20th century, American composers like George Gershwin (Porgy and Bess), Scott Joplin (Treemonisha), Leonard Bernstein (Candide), Gian Carlo Menotti, Douglas Moore, and Carlisle Floyd began to contribute English-language operas infused with touches of popular musical styles. They were followed by composers such as Philip Glass (Einstein on the Beach), Mark Adamo, John Corigliano (The Ghosts of Versailles), Robert Moran, John Adams (Nixon in China), André Previn and Jake Heggie. Many contemporary 21st century opera composers have emerged such as Missy Mazzoli, Kevin Puts, Tom Cipullo, Huang Ruo, David T. Little, Terence Blanchard, Jennifer Higdon, Tobias Picker, Michael Ching, and Ricky Ian Gordon.
+Opera was brought to Russia in the 1730s by the Italian operatic troupes and soon it became an important part of entertainment for the Russian Imperial Court and aristocracy. Many foreign composers such as Baldassare Galuppi, Giovanni Paisiello, Giuseppe Sarti, and Domenico Cimarosa (as well as various others) were invited to Russia to compose new operas, mostly in the Italian language. Simultaneously some domestic musicians like Maksym Berezovsky and Dmitry Bortniansky were sent abroad to learn to write operas. The first opera written in Russian was Tsefal i Prokris by the Italian composer Francesco Araja (1755). The development of Russian-language opera was supported by the Russian composers Vasily Pashkevich, Yevstigney Fomin and Alexey Verstovsky.
+However, the real birth of Russian opera came with Mikhail Glinka and his two great operas A Life for the Tsar (1836) and Ruslan and Lyudmila (1842). After him, during the 19th century in Russia, there were written such operatic masterpieces as Rusalka and The Stone Guest by Alexander Dargomyzhsky, Boris Godunov and Khovanshchina by Modest Mussorgsky, Prince Igor by Alexander Borodin, Eugene Onegin and The Queen of Spades by Pyotr Tchaikovsky, and The Snow Maiden and Sadko by Nikolai Rimsky-Korsakov. These developments mirrored the growth of Russian nationalism across the artistic spectrum, as part of the more general Slavophilism movement.
+In the 20th century, the traditions of Russian opera were developed by many composers including Sergei Rachmaninoff in his works The Miserly Knight and Francesca da Rimini, Igor Stravinsky in Le Rossignol, Mavra, Oedipus rex, and The Rake's Progress, Sergei Prokofiev in The Gambler, The Love for Three Oranges, The Fiery Angel, Betrothal in a Monastery, and War and Peace; as well as Dmitri Shostakovich in The Nose and Lady Macbeth of the Mtsensk District, Edison Denisov in L'écume des jours, and Alfred Schnittke in Life with an Idiot and Historia von D. Johann Fausten.[28]
+Spain also produced its own distinctive form of opera, known as zarzuela, which had two separate flowerings: one from the mid-17th century through the mid-18th century, and another beginning around 1850. During the late 18th century up until the mid-19th century, Italian opera was immensely popular in Spain, supplanting the native form.
+Czech composers also developed a thriving national opera movement of their own in the 19th century, starting with Bedřich Smetana, who wrote eight operas including the internationally popular The Bartered Bride. Antonín Dvořák, most famous for Rusalka, wrote 13 operas; and Leoš Janáček gained international recognition in the 20th century for his innovative works including Jenůfa, The Cunning Little Vixen, and Káťa Kabanová.
+In Russian Eastern Europe, several national operas began to emerge. Ukrainian opera was developed by Semen Hulak-Artemovsky (1813–1873) whose most famous work Zaporozhets za Dunayem (A Cossack Beyond the Danube) is regularly performed around the world. Other Ukrainian opera composers include Mykola Lysenko (Taras Bulba and Natalka Poltavka), Heorhiy Maiboroda, and Yuliy Meitus. At the turn of the century, a distinct national opera movement also began to emerge in Georgia under the leadership Zacharia Paliashvili, who fused local folk songs and stories with 19th-century Romantic classical themes.
+The key figure of Hungarian national opera in the 19th century was Ferenc Erkel, whose works mostly dealt with historical themes. Among his most often performed operas are Hunyadi László and Bánk bán. The most famous modern Hungarian opera is Béla Bartók's Duke Bluebeard's Castle.
+Stanisław Moniuszko's opera Straszny Dwór (in English The Haunted Manor) (1861–64) represents a nineteenth-century peak of Polish national opera.[29] In the 20th century, other operas created by Polish composers included King Roger by Karol Szymanowski and Ubu Rex by Krzysztof Penderecki.
+The first known opera from Turkey (the Ottoman Empire) was Arshak II, which was an Armenian opera composed by an ethnic Armenian composer Tigran Chukhajian in 1868 and partially performed in 1873. It was fully staged in 1945 in Armenia.
+The first years of the Soviet Union saw the emergence of new national operas, such as the Koroğlu (1937) by the Azerbaijani composer Uzeyir Hajibeyov. The first Kyrgyz opera, Ai-Churek, premiered in Moscow at the Bolshoi Theatre on 26 May 1939, during Kyrgyz Art Decade. It was composed by Vladimir Vlasov, Abdylas Maldybaev and Vladimir Fere. The libretto was written by Joomart Bokonbaev, Jusup Turusbekov, and Kybanychbek Malikov. The opera is based on the Kyrgyz heroic epic Manas.[30][31]
+In Iran, opera gained more attention after the introduction of Western classical music in the late 19th century. However, it took until mid 20th century for Iranian composers to start experiencing with the field, especially as the construction of the Roudaki Hall in 1967, made possible staging of a large variety of works for stage. Perhaps, the most famous Iranian opera is Rostam and Sohrab by Loris Tjeknavorian premiered not until the early 2000s.
+Chinese contemporary classical opera, a Chinese language form of Western style opera that is distinct from traditional Chinese opera, has had operas dating back to The White Haired Girl in 1945.[32][33][34]
+In Latin America, opera started as a result of European colonisation. The first opera ever written in the Americas was La púrpura de la rosa, by Tomás de Torrejón y Velasco, although Partenope, by the Mexican Manuel de Zumaya, was the first opera written from a composer born in Latin America (music now lost). The first Brazilian opera for a libretto in Portuguese was A Noite de São João, by Elias Álvares Lobo. However, Antonio Carlos Gomes is generally regarded as the most outstanding Brazilian composer, having a relative success in Italy with its Brazilian-themed operas with Italian librettos, such as Il Guarany. Opera in Argentina developed in the 20th century after the inauguration of Teatro Colón in Buenos Aires—with the opera Aurora, by Ettore Panizza, being heavily influenced by the Italian tradition, due to immigration. Other important composers from Argentina include Felipe Boero and Alberto Ginastera.
+Perhaps the most obvious stylistic manifestation of modernism in opera is the development of atonality. The move away from traditional tonality in opera had begun with Richard Wagner, and in particular the Tristan chord. Composers such as Richard Strauss, Claude Debussy, Giacomo Puccini[citation needed], Paul Hindemith, Benjamin Britten and Hans Pfitzner pushed Wagnerian harmony further with a more extreme use of chromaticism and greater use of dissonance. Another aspect of modernist opera is the shift away from long, suspended melodies, to short quick mottos, as first illustrated by Giuseppe Verdi in his Falstaff. Composers such as Strauss, Britten, Shostakovich and Stravinsky adopted and expanded upon this style.
+Operatic modernism truly began in the operas of two Viennese composers, Arnold Schoenberg and his student Alban Berg, both composers and advocates of atonality and its later development (as worked out by Schoenberg), dodecaphony. Schoenberg's early musico-dramatic works, Erwartung (1909, premiered in 1924) and Die glückliche Hand display heavy use of chromatic harmony and dissonance in general. Schoenberg also occasionally used Sprechstimme.
+The two operas of Schoenberg's pupil Alban Berg, Wozzeck (1925) and Lulu (incomplete at his death in 1935) share many of the same characteristics as described above, though Berg combined his highly personal interpretation of Schoenberg's twelve-tone technique with melodic passages of a more traditionally tonal nature (quite Mahlerian in character) which perhaps partially explains why his operas have remained in standard repertory, despite their controversial music and plots. Schoenberg's theories have influenced (either directly or indirectly) significant numbers of opera composers ever since, even if they themselves did not compose using his techniques.
+Composers thus influenced include the Englishman Benjamin Britten, the German Hans Werner Henze, and the Russian Dmitri Shostakovich. (Philip Glass also makes use of atonality, though his style is generally described as minimalist, usually thought of as another 20th-century development.)[35]
+However, operatic modernism's use of atonality also sparked a backlash in the form of neoclassicism. An early leader of this movement was Ferruccio Busoni, who in 1913 wrote the libretto for his neoclassical number opera Arlecchino (first performed in 1917).[36] Also among the vanguard was the Russian Igor Stravinsky. After composing music for the Diaghilev-produced ballets Petrushka (1911) and The Rite of Spring (1913), Stravinsky turned to neoclassicism, a development culminating in his opera-oratorio Oedipus Rex (1927).  Stravinsky had already turned away from the modernist trends of his early ballets to produce small-scale works that do not fully qualify as opera, yet certainly contain many operatic elements, including Renard (1916: "a burlesque in song and dance") and The Soldier's Tale (1918: "to be read, played, and danced"; in both cases the descriptions and instructions are those of the composer). In the latter, the actors declaim portions of speech to a specified rhythm over instrumental accompaniment, peculiarly similar to the older German genre of Melodrama.  Well after his Rimsky-Korsakov-inspired works The Nightingale (1914), and Mavra (1922), Stravinsky continued to ignore serialist technique and eventually wrote a full-fledged 18th-century-style diatonic number opera The Rake's Progress (1951). His resistance to serialism (an attitude he reversed following Schoenberg's death) proved to be an inspiration for many[who?] other composers.[37]
+A common trend throughout the 20th century, in both opera and general orchestral repertoire, is the use of smaller orchestras as a cost-cutting measure; the grand Romantic-era orchestras with huge string sections, multiple harps, extra horns, and exotic percussion instruments were no longer feasible. As government and private patronage of the arts decreased throughout the 20th century, new works were often commissioned and performed with smaller budgets, very often resulting in chamber-sized works, and short, one-act operas. Many of Benjamin Britten's operas are scored for as few as 13 instrumentalists; Mark Adamo's two-act realization of Little Women is scored for 18 instrumentalists.
+Another feature of late 20th-century opera is the emergence of contemporary historical operas, in contrast to the tradition of basing operas on more distant history, the re-telling of contemporary fictional stories or plays, or on myth or legend. The Death of Klinghoffer, Nixon in China, and Doctor Atomic by John Adams, Dead Man Walking by Jake Heggie, and Anna Nicole by Mark-Anthony Turnage exemplify the dramatisation onstage of events in recent living memory, where characters portrayed in the opera were alive at the time of the premiere performance.
+The Metropolitan Opera in the US reports that the average age of its audience is now 60.[38] Many opera companies have experienced a similar trend, and opera company websites are replete with attempts to attract a younger audience. This trend is part of the larger trend of greying audiences for classical music since the last decades of the 20th century.[39] In an effort to attract younger audiences, the Metropolitan Opera offers a student discount on ticket purchases.[40]
+Smaller companies in the US have a more fragile existence, and they usually depend on a "patchwork quilt" of support from state and local governments, local businesses, and fundraisers. Nevertheless, some smaller companies have found ways of drawing new audiences. Opera Carolina offer discounts and happy hour events to the 21- to 40-year-old demographic.[41] In addition to radio and television broadcasts of opera performances, which have had some success in gaining new audiences, broadcasts of live performances in HD to movie theatres have shown the potential to reach new audiences. Since 2006, the Met has broadcast live performances to several hundred movie screens all over the world.[42]
+By the late 1930s, some musicals began to be written with a more operatic structure. These works include complex polyphonic ensembles and reflect musical developments of their times. Porgy and Bess (1935), influenced by jazz styles, and Candide (1956), with its sweeping, lyrical passages and farcical parodies of opera, both opened on Broadway but became accepted as part of the opera repertory. Popular musicals such as Show Boat, West Side Story, Brigadoon, Sweeney Todd, Passion, Evita, The Light in the Piazza, The Phantom of the Opera and others tell dramatic stories through complex music and in the 2010s they are sometimes seen in opera houses.[43] The Most Happy Fella (1952) is quasi-operatic and has been revived by the New York City Opera. Other rock influenced musicals, such as Tommy (1969) and Jesus Christ Superstar (1971), Les Misérables (1980), Rent (1996), Spring Awakening (2006), and Natasha, Pierre & The Great Comet of 1812 (2012) employ various operatic conventions, such as through composition, recitative instead of dialogue, and leitmotifs.
+A subtle type of sound electronic reinforcement called acoustic enhancement is used in some modern concert halls and theatres where operas are performed. Although none of the major opera houses "...use traditional, Broadway-style sound reinforcement, in which most if not all singers are equipped with radio microphones mixed to a series of unsightly loudspeakers scattered throughout the theatre", many use a sound reinforcement system for acoustic enhancement and for subtle boosting of offstage voices, child singers, onstage dialogue, and sound effects (e.g., church bells in Tosca or thunder effects in Wagnerian operas).[44]
+Operatic vocal technique evolved, in a time before electronic amplification, to allow singers to produce enough volume to be heard over an orchestra, without the instrumentalists having to substantially compromise their volume.
+Singers and the roles they play are classified by voice type, based on the tessitura, agility, power and timbre of their voices. Male singers can be classified by vocal range as bass, bass-baritone, baritone, tenor and countertenor, and female singers as contralto, mezzo-soprano and soprano. (Men sometimes sing in the "female" vocal ranges, in which case they are termed sopranist or countertenor. The countertenor is commonly encountered in opera, sometimes singing parts written for castrati—men neutered at a young age specifically to give them a higher singing range.) Singers are then further classified by size—for instance, a soprano can be described as a lyric soprano, coloratura, soubrette, spinto, or dramatic soprano. These terms, although not fully describing a singing voice, associate the singer's voice with the roles most suitable to the singer's vocal characteristics.
+Yet another sub-classification can be made according to acting skills or requirements, for example the basso buffo who often must be a specialist in patter as well as a comic actor. This is carried out in detail in the Fach system of German speaking countries, where historically opera and spoken drama were often put on by the same repertory company.
+A particular singer's voice may change drastically over his or her lifetime, rarely reaching vocal maturity until the third decade, and sometimes not until middle age. Two French voice types, premiere dugazon and deuxieme dugazon, were named after successive stages in the career of Louise-Rosalie Lefebvre (Mme. Dugazon). Other terms originating in the star casting system of the Parisian theatres are baryton-martin and soprano falcon.
+The soprano voice has typically been used as the voice of choice for the female protagonist of the opera since the latter half of the 18th century. Earlier, it was common for that part to be sung by any female voice, or even a castrato. The current emphasis on a wide vocal range was primarily an invention of the Classical period. Before that, the vocal virtuosity, not range, was the priority, with soprano parts rarely extending above a high A (Handel, for example, only wrote one role extending to a high C), though the castrato Farinelli was alleged to possess a top D (his lower range was also extraordinary, extending to tenor C). The mezzo-soprano, a term of comparatively recent origin, also has a large repertoire, ranging from the female lead in Purcell's Dido and Aeneas to such heavyweight roles as Brangäne in Wagner's Tristan und Isolde (these are both roles sometimes sung by sopranos; there is quite a lot of movement between these two voice-types). For the true contralto, the range of parts is more limited, which has given rise to the insider joke that contraltos only sing "witches, bitches, and britches" roles. In recent years many of the "trouser roles" from the Baroque era, originally written for women, and those originally sung by castrati, have been reassigned to countertenors.
+The tenor voice, from the Classical era onwards, has traditionally been assigned the role of male protagonist. Many of the most challenging tenor roles in the repertory were written during the bel canto era, such as Donizetti's sequence of 9 Cs above middle C during La fille du régiment. With Wagner came an emphasis on vocal heft for his protagonist roles, with this vocal category described as Heldentenor; this heroic voice had its more Italianate counterpart in such roles as Calaf in Puccini's Turandot. Basses have a long history in opera, having been used in opera seria in supporting roles, and sometimes for comic relief (as well as providing a contrast to the preponderance of high voices in this genre). The bass repertoire is wide and varied, stretching from the comedy of Leporello in Don Giovanni to the nobility of Wotan in Wagner's Ring Cycle, to the conflicted King Phillip of Verdi's Don Carlos. In between the bass and the tenor is the baritone, which also varies in weight from say, Guglielmo in Mozart's Così fan tutte to Posa in Verdi's Don Carlos; the actual designation "baritone" was not standard until the mid-19th century.
+Early performances of opera were too infrequent for singers to make a living exclusively from the style, but with the birth of commercial opera in the mid-17th century, professional performers began to emerge. The role of the male hero was usually entrusted to a castrato, and by the 18th century, when Italian opera was performed throughout Europe, leading castrati who possessed extraordinary vocal virtuosity, such as Senesino and Farinelli, became international stars. The career of the first major female star (or prima donna), Anna Renzi, dates to the mid-17th century. In the 18th century, a number of Italian sopranos gained international renown and often engaged in fierce rivalry, as was the case with Faustina Bordoni and Francesca Cuzzoni, who started a fist fight with one another during a performance of a Handel opera. The French disliked castrati, preferring their male heroes to be sung by an haute-contre (a high tenor), of which Joseph Legros (1739–1793) was a leading example.[45]
+Though opera patronage has decreased in the last century in favor of other arts and media (such as musicals, cinema, radio, television and recordings), mass media and the advent of recording have supported the popularity of many famous singers including Maria Callas, Enrico Caruso, Amelita Galli-Curci, Kirsten Flagstad, Juan Arvizu,[46][47] Nestor Mesta Chayres,[48][49][50]
+Mario Del Monaco, Renata Tebaldi, Risë Stevens, Alfredo Kraus, Franco Corelli, Montserrat Caballé, Joan Sutherland, Birgit Nilsson, Nellie Melba, Rosa Ponselle, Beniamino Gigli, Jussi Björling, Feodor Chaliapin, Cecilia Bartoli, Renée Fleming, Marilyn Horne, Bryn Terfel and "The Three Tenors" (Luciano Pavarotti, Plácido Domingo, and José Carreras).
+Before the 1700s, Italian operas used a small string orchestra, but it rarely played to accompany the singers. Opera solos during this period were accompanied by the basso continuo group, which consisted of the harpsichord, "plucked instruments" such as lute and a bass instrument.[51] The string orchestra typically only played when the singer was not singing, such as during a singer's "...entrances and exits, between vocal numbers, [or] for [accompanying] dancing". Another role for the orchestra during this period was playing an orchestral ritornello to mark the end of a singer's solo.[51] During the early 1700s, some composers began to use the string orchestra to mark certain aria or recitatives "...as special"; by 1720, most arias were accompanied by orchestra. Opera composers such as Domenico Sarro, Leonardo Vinci, Giambattista Pergolesi, Leonardo Leo, and Johann Adolf Hasse added new instruments to the opera orchestra and gave the instruments new roles. They added wind instruments to the strings and used orchestral instruments to play instrumental solos, as a way to mark certain arias as special.[51]
+The orchestra has also provided an instrumental overture before the singers come onstage since the 1600s. Peri's Euridice opens with a brief instrumental ritornello, and Monteverdi's L'Orfeo (1607) opens with a toccata, in this case a fanfare for muted trumpets. The French overture as found in Jean-Baptiste Lully's operas[52] consist of a slow introduction in a marked "dotted rhythm", followed by a lively movement in fugato style. The overture was frequently followed by a series of dance tunes before the curtain rose. This overture style was also used in English opera, most notably in Henry Purcell's Dido and Aeneas. Handel also uses the French overture form in some of his Italian operas such as Giulio Cesare.[53]
+In Italy, a distinct form called "overture" arose in the 1680s, and became established particularly through the operas of Alessandro Scarlatti, and spread throughout Europe, supplanting the French form as the standard operatic overture by the mid-18th century.[54] It uses three generally homophonic movements: fast–slow–fast. The opening movement was normally in duple metre and in a major key; the slow movement in earlier examples was short, and could be in a contrasting key; the concluding movement was dance-like, most often with rhythms of the gigue or minuet, and returned to the key of the opening section. As the form evolved, the first movement may incorporate fanfare-like elements and took on the pattern of so-called "sonatina form" (sonata form without a development section), and the slow section became more extended and lyrical.[54]
+In Italian opera after about 1800, the "overture" became known as the sinfonia.[55] Fisher also notes the term Sinfonia avanti l'opera (literally, the "symphony before the opera") was "an early term for a sinfonia used to begin an opera, that is, as an overture as opposed to one serving to begin a later section of the work".[55] In 19th-century opera, in some operas, the overture, Vorspiel, Einleitung, Introduction, or whatever else it may be called, was the portion of the music which takes place before the curtain rises; a specific, rigid form was no longer required for the overture.
+The role of the orchestra in accompanying the singers changed over the 19th century, as the Classical style transitioned to the Romantic era. In general, orchestras got bigger, new instruments were added, such as additional percussion instruments (e.g., bass drum, cymbals, snare drum, etc.). The orchestration of orchestra parts also developed over the 19th century. In Wagnerian operas, the forefronting of the orchestra went beyond the overture. In Wagnerian operas such as Tristan, the orchestra often played the recurrent musical themes or leitmotifs, a role which gave a prominence to the orchestra which "...elevated its status to that of a prima donna".[56] Wagner's operas were scored with unprecedented scope and complexity, adding more brass instruments and huge ensemble sizes: indeed, his score to Das Rheingold calls for six harps.
+As the role of the orchestra and other instrumental ensembles changed over the history of opera, so did the role of leading the musicians. In the Baroque era, the musicians were usually directed by the harpsichord player, although the French composer Lully is known to have conducted with a long staff. In the 1800s, during the Classical period, the first violinist, also known as the concertmaster, would lead the orchestra while sitting. Over time, some directors began to stand up and use hand and arm gestures to lead the performers. Eventually this role of music director became termed the conductor, and a podium was used to make it easier for all the musicians to see him or her. By the time Wagnerian operas were introduced, the complexity of the works and the huge orchestras used to play them gave the conductor an increasingly important role. Modern opera conductors have a challenging role: they have to direct both the orchestra in the orchestra pit and the singers up on stage.
+Since the days of Handel and Mozart, many composers have favored Italian as the language for the libretto of their operas. From the Bel Canto era to Verdi, composers would sometimes supervise versions of their operas in both Italian and French. Because of this, operas such as Lucia di Lammermoor or Don Carlos are today deemed canonical in both their French and Italian versions.[57]
+Till the mid 1950s, it was acceptable to produce operas in translations even if these had not been authorized by the composer or the original librettists. For example, opera houses in Italy routinely staged Wagner in Italian.[58] After WWII, opera scholarship improved, artists refocused on the original versions, and translations fell out of favor. Knowledge of European languages, especially Italian, French, and German, is today an important part of the training for professional singers."The biggest chunk of operatic training is in linguistics and musicianship," explains mezzo-soprano Dolora Zajick. "[I have to understand] not only what I'm singing, but what everyone else is singing. I sing Italian, Czech, Russian, French, German, English."[59]
+In the 1980s, supertitles (sometimes called surtitles) began to appear. Although supertitles were first almost universally condemned as a distraction,[60] today many opera houses provide either supertitles, generally projected above the theatre's proscenium arch, or individual seat screens where spectators can choose from more than one language. TV broadcasts typically include subtitles even if intended for an audience who knows well the language (for example, a RAI broadcast of an Italian opera). These subtitles target not only the hard of hearing but the audience generally, since a sung discourse is much harder to understand than a spoken one—even in the ears of native speakers. Subtitles in one or more languages have become standard in opera broadcasts, simulcasts, and DVD editions.
+Today, operas are only rarely performed in translation. Exceptions include the English National Opera, the Opera Theatre of Saint Louis, Opera Theater of Pittsburgh, and Opera South East,[61] which favor English translations.[62] Another exception are opera productions intended for a young audience, such as Humperdinck's Hansel and Gretel[63] and some productions of Mozart's The Magic Flute.[64]
+Outside the US, and especially in Europe, most opera houses receive public subsidies from taxpayers.[65] In Milan, Italy, 60% of La Scala's annual budget of €115 million is from ticket sales and private donations, with the remaining 40% coming from public funds.[66] In 2005, La Scala received 25% of Italy's total state subsidy of €464 million for the performing arts.[67] In the UK, Arts Council England provides funds to Opera North, the Royal Opera House, Welsh National Opera, and English National Opera. Between 2012 and 2015, these four opera companies along with the English National Ballet, Birmingham Royal Ballet and Northern Ballet accounted for 22% of the funds in the Arts Council's national portfolio. During that period, the Council undertook an analysis of its funding for large-scale opera and ballet companies, setting recommendations and targets for the companies to meet prior to the 2015–2018 funding decisions.[68] In February 2015, concerns over English National Opera's business plan led to the Arts Council placing it "under special funding arrangements" in what The Independent termed "the unprecedented step" of threatening to withdraw public funding if the Council's concerns were not met by 2017.[69] European public funding to opera has led to a disparity between the number of year-round opera houses in Europe and the United States. For example, "Germany has about 80-year-round opera houses [as of 2004], while the U.S., with more than three times the population, does not have any. Even the Met only has a seven-month season."[70]
+A milestone for opera broadcasting in the U.S. was achieved on 24 December 1951, with the live broadcast of Amahl and the Night Visitors, an opera in one act by Gian Carlo Menotti. It was the first opera specifically composed for television in America.[71] Another milestone occurred in Italy in 1992 when Tosca was broadcast live from its original Roman settings and times of the day:  The first act came from the 16th-century Church of Sant'Andrea della Valle at noon on Saturday; the 16th-century Palazzo Farnese was the setting for the second at 8:15 P.M.; and on Sunday at 6 A.M., the third act was broadcast from Castel Sant'Angelo. The production was transmitted via satellite to 105 countries.[72]
+Major opera companies have begun presenting their performances in local cinemas throughout the United States and many other countries. The Metropolitan Opera began a series of live high-definition video transmissions to cinemas around the world in 2006.[73] In 2007, Met performances were shown in over 424 theaters in 350 U.S. cities. La bohème went out to 671 screens worldwide. San Francisco Opera began prerecorded video transmissions in March 2008. As of June 2008, approximately 125 theaters in 117 U.S. cities carry the showings. The HD video opera transmissions are presented via the same HD digital cinema projectors used for major Hollywood films.[74] European opera houses and festivals including the Royal Opera in London, La Scala in Milan, the Salzburg Festival, La Fenice in Venice, and the Maggio Musicale in Florence have also transmitted their productions to theaters in cities around the world since 2006, including 90 cities in the U.S.[75][76]
+The emergence of the Internet has also affected the way in which audiences consume opera. In 2009 the British Glyndebourne Festival Opera offered for the first time an online digital video download of its complete 2007 production of Tristan und Isolde. In 2013 season the festival streamed all six of its productions online.[77][78] In July 2012 the first online community opera was premiered at the Savonlinna Opera Festival. Titled Free Will, it was created by members of the Internet group Opera By You. Its 400 members from 43 countries wrote the libretto, composed the music, and designed the sets and costumes using the Wreckamovie web platform. Savonlinna Opera Festival provided professional soloists, an 80-member choir, a symphony orchestra, and the stage machinery. It was performed live at the festival and streamed live on the internet.[79]

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+Opera is a freeware web browser for Microsoft Windows, Android, iOS, macOS, and Linux operating systems[7][8] developed by Opera Software.[9][10][11] Opera is a Chromium-based browser using the Blink layout engine. It differentiates itself because of a distinct user interface and other features.
+Opera was conceived at Telenor as a research project in 1994 and was bought by Opera Software in 1995. It was a commercial software for the first ten years and had its own proprietary Presto layout engine. The Presto versions of Opera received many awards, but Presto development ended after a milestone transition to Chromium in 2013.
+There are also three mobile versions called Opera Mobile, Opera Touch,[12] and Opera Mini. A gaming browser called Opera GX was launched on 11 June 2019.[13]
+Opera began in 1994 as a research project at Telenor, the largest Norwegian telecommunications company.
+In 1995, it branched out into a separate company named Opera Software.[14]
+Opera was first publicly released in 1996 with version 2.10,[15] which only ran on Microsoft Windows 95 at that time.[16]
+In an attempt to capitalize on the emerging market for Internet-connected handheld devices, a project to port Opera to mobile device platforms was started in 1998.[16]
+Opera 4.0, released in 2000,[15] included a new cross-platform core that facilitated the creation of editions of Opera for multiple operating systems and platforms.[17]
+Up to this point, Opera was trialware and had to be purchased after the trial period ended. Version 5.0 (released in 2000) saw the end of this requirement. Instead, Opera became ad-sponsored, displaying advertisements to users who had not paid for it.[18] Later versions of Opera gave the user the choice of seeing banner ads or targeted text advertisements from Google.
+With version 8.5 (released in 2005) the advertisements were completely removed and the primary financial support for the browser came through revenue from Google (which is by contract Opera's default search engine).[19]
+Among the new features introduced in version 9.1 (released in 2006) was fraud protection using technology from GeoTrust, a digital certificate provider, and PhishTank, an organization that tracks known phishing web sites.[20] This feature was further improved and expanded in version 9.5, when GeoTrust was replaced with Netcraft, and malware protection from Haute Secure was added.[21]
+In 2006, Opera Software ASA was released as well as Internet Channel and Nintendo DS Browser for Nintendo's DS and Wii gaming systems.[22][23][24][25]
+A new JavaScript engine called Carakan, after the Javanese alphabet, was introduced with version 10.50.[26] According to Opera Software, Carakan made Opera 10.50 more than seven times faster in SunSpider than Opera 10.10.[27][28][29]
+On the 16th of December 2010, Opera 11 was released, featuring extensions,[30] tab stacking (where dragging one tab over another allows creating a group of tabs), visual mouse gestures and changes to the address bar.[31]
+Opera 12 was released on 14 June 2012.[32]
+On 12 February 2013, Opera Software announced that it would drop its own Presto layout engine in favour of WebKit as implemented by Google's Chrome browser, using code from the Chromium project. Opera Software planned as well to contribute code to WebKit.[33] On 3 April 2013, Google announced that it would fork components from WebKit to form a new layout engine known as Blink; the same day, Opera Software confirmed that it would follow Google in implementing the Blink layout engine.[34]
+On 28 May 2013, a beta release of Opera 15 was made available,[35] the first version is based on the Chromium project.[36][37] Many distinctive Opera features of the previous versions were dropped, and Opera Mail was separated into a standalone application derived from Opera 12.[38]
+In November 2016, the original Norwegian owner of Opera sold his stake in the business to a Chinese consortium under the name Golden Brick Capital Private Equity Fund I Limited Partnership for $600 million.[39][40][41] An earlier deal was not approved by regulators.[42]
+In January 2017, the source code of Opera 12.15 (one of the last few versions that was still based on the Presto layout engine) was leaked.[43]
+To demonstrate how radically different a browser could look, Opera Neon, dubbed a "concept browser", was released in January 2017. PC World compared it to demo models that automakers and hardware vendors release to show their visions of the future. Instead of a Speed Dial (also explained in the following chapter "Features"), it displays the frequently accessed websites in resemblance to a desktop with computer icons scattered all over it in an artistic formation.[44][45]
+Opera has originated features later adopted by other web browsers, including: Speed Dial, pop-up blocking, re-opening recently closed pages, private browsing, and tabbed browsing.[46][47] Opera includes a bookmarks bar and a download manager. Opera also has "Speed Dial", which allows the user to add an unlimited number of pages shown in thumbnail form in a page displayed when a new tab is opened. Speed Dial allows the user to more easily navigate to the selected web pages.[46][47][48]
+It is possible to control some aspects of the browser using the keyboard shortcuts.[49] Page zooming allows text, images and other content such as Adobe Flash Player, Java platform and Scalable Vector Graphics to be increased or decreased in size to help those with impaired vision.[50]
+Opera Software claims that when the Opera Turbo mode is enabled, the compression servers compress requested web pages (except HTTPS pages) by up to 50%, depending upon the content, before sending them to the users.[51] This process reduces the amount of data transferred and is particularly useful for crowded or slow network connections, making web pages load faster or when there are costs dependent on the total amount of data usage.[51] This technique is also used in Opera Mini for mobile devices[52] and smartwatches.[53]
+One security feature is the option to delete private data, such as HTTP cookies, browsing history, items in cache and passwords with the click of a button.[54] This lets users erase personal data after browsing from a shared computer.
+When visiting a site, Opera displays a security badge in the address bar which shows details about the website, including security certificates.[55] Opera's fraud and malware protection warns the user about suspicious web pages and is enabled by default. It checks the requested page against several databases of known phishing and malware websites, called blacklists.[55]
+In January 2007, Asa Dotzler of the competing Mozilla Corporation accused Opera Software of downplaying information about security vulnerabilities in Opera, (which were fixed in December 2006). Dotzler claimed that users were not clearly informed of security vulnerabilities that were present in the previous version of Opera and thus they would not realize that they needed to upgrade to the latest version or else risk being exploited by hackers.[56] Opera Software responded to these accusations on the next day.[57]
+In 2016, a free virtual private network (VPN) service was implemented in the browser.[58] Opera said that this would allow encrypted access to websites otherwise blocked, and provide security on public WiFi networks.[59] Either VPN or Turbo can be enabled, but not both.[60] It was later determined that the browser "VPN" operated the same as a proxy rather than other VPN services.[61]
+In July 2018, Opera was listed on the NASDAQ stock exchange [62] in New York City at an initial offering of $12 per share.
+In 2018, a built-in cryptocurrency wallet to the Opera Web Browser was released.[63] Announcing that they would be the first browser with a built-in Crypto Wallet.[64] On 13 December 2018 they released a video showing many decentralized applications like Cryptokitties running on the Android version of the Opera Web Browser.[65]
+In March 2020,  Opera updated its Android browser to access .crypto domains, making it the first browser to be able to support a domain name system (DNS) which is not part of the traditional DNS directly without the need of a plugin or add-on.[66] This was through a collaboration with a San Francisco based startup, Unstoppable Domains.[67][68]
+Opera was one of the first browsers to support Cascading Style Sheets (CSS).[69]
+Opera Software uses a release cycle consisting of three "streams" (which correspond to phases of development) that can be downloaded and installed independently of each other: "developer", "beta" and "stable". New features are first introduced in the developer build, then, depending on user feedback, may progress to the beta version and eventually be released.[70]
+The developer stream allows early testing of new features, mainly targeting developers, extension creators, and early adopters. Opera developer is not intended for everyday browsing as it is unstable and is prone to failure or crashing, but it enables advanced users to try out new features that are still under development, without affecting their normal installation of the browser. New versions of the browser are released frequently, generally a few times a week.[71]
+The beta stream, formerly known as "Opera Next", is a feature complete package, allowing stability and quality to mature before the final release. A new version is released every couple of weeks.[72]
+Both streams can be installed alongside the official release without interference. Each has a different icon to help the user distinguish between the variants.
+In 2005, Adobe Systems opted to integrate Opera's rendering engine, Presto, into its Adobe Creative Suite applications. Opera technology was employed in Adobe GoLive, Adobe Photoshop, Adobe Dreamweaver, and other components of the Adobe Creative Suite.[74][75] Opera's layout engine is also found in Virtual Mechanics SiteSpinner Pro.[76] The Internet Channel is a version of the Opera 9 web browser for use on the Nintendo Wii created by Opera Software and Nintendo.[77] Opera Software is also implemented in the Nintendo DS Browser for Nintendo's handheld systems.
+Versions with the Presto layout engine have been positively reviewed,[78][79][80] although they have been criticized for website compatibility issues.[81][82] Because of this issue, Opera 8.01 and higher had included workarounds to help certain popular but problematic web sites display properly.[83][84]
+Versions with the Blink layout engine have been criticized by some users for missing features such as UI customization, and for abandoning Opera Software's own Presto layout engine.[85][86][87][88] Despite that, versions with the Blink layout engine have been praised for being fast and stable, for handling the latest web standards and for having a better website compatibility and a modern-style user interface.[89][90][91]
+Over the years, Opera for personal computers has received several awards. These awards include:[92]
+Related web browsers:
+Web browsers:
+Essential features: