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+A centaur (/ˈsɛntɔːr/; Greek: κένταυρος, kéntauros, Latin: centaurus), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse.[2][3] Centaurs are thought of in many Greek myths as being as wild as untamed horses, and were said to have inhabited the region of Magnesia and Mount Pelion in Thessaly, the Foloi oak forest in Elis, and the Malean peninsula in southern Laconia. Centaurs are subsequently featured in Roman mythology, and were familiar figures in the medieval bestiary. They remain a staple of modern fantastic literature.
+
+The centaurs were usually said to have been born of Ixion and Nephele.[4] As the story goes, Nephele was a cloud made into the likeness of Hera in a plot to trick Ixion into revealing his lust for Hera to Zeus. Ixion seduced Nephele and from that relationship centaurs were created.[5] Another version, however, makes them children of Centaurus, a man who mated with the Magnesian mares. Centaurus was either himself the son of Ixion and Nephele (inserting an additional generation) or of Apollo and the nymph Stilbe. In the latter version of the story, Centaurus's twin brother was Lapithes, ancestor of the Lapiths.
+
+Another tribe of centaurs was said to have lived on Cyprus.  According to Nonnus, they were fathered by Zeus, who, in frustration after Aphrodite had eluded him, spilled his seed on the ground of that land. Unlike those of mainland Greece, the Cyprian centaurs were horned.[6][7]
+
+There were also the Lamian Pheres, twelve rustic daimones (spirits) of the Lamos river. They were set by Zeus to guard the infant Dionysos, protecting him from the machinations of Hera, but the enraged goddess transformed them into ox-horned Centaurs. The Lamian Pheres later accompanied Dionysos in his campaign against the Indians.[8]
+
+The centaur's half-human, half-horse composition has led many writers to treat them as liminal beings, caught between the two natures they embody in contrasting myths; they are both the embodiment of untamed nature, as in their battle with the Lapiths (their kin), and conversely, teachers like Chiron.[citation needed]
+
+The Centaurs are best known for their fight with the Lapiths who, according to one origin myth, would have been cousins to the centaurs. The battle, called the Centauromachy, was caused by the centaurs' attempt to carry off Hippodamia and the rest of the Lapith women on the day of Hippodamia's marriage to Pirithous, who was the king of the Lapithae and a son of Ixion. Theseus, a hero and founder of cities, who happened to be present, threw the balance in favour of the Lapiths by assisting Pirithous in the battle. The Centaurs were driven off or destroyed.[9][10][11] Another Lapith hero, Caeneus, who was invulnerable to weapons, was beaten into the earth by Centaurs wielding rocks and the branches of trees. In her article "The Centaur: Its History and Meaning in Human Culture," Elizabeth Lawrence claims that the contests between the centaurs and the Lapiths typify the struggle between civilization and barbarism.[12]
+
+The Centauromachy is most famously portrayed in the Parthenon metopes by Phidias and in a Renaissance-era sculpture by Michelangelo.
+
+The Greek word kentauros is generally regarded as being of obscure origin.[13] The etymology from ken + tauros, "piercing bull," was a euhemerist suggestion in Palaephatus' rationalizing text on Greek mythology, On Incredible Tales (Περὶ ἀπίστων), which included mounted archers from a village called Nephele eliminating a herd of bulls that were the scourge of Ixion's kingdom.[14] Another possible related etymology can be "bull-slayer".[15]
+
+The most common theory holds that the idea of centaurs came from the first reaction of a non-riding culture, as in the Minoan Aegean world, to nomads who were mounted on horses. The theory suggests that such riders would appear as half-man, half-animal. Bernal Díaz del Castillo reported that the Aztecs also had this misapprehension about Spanish cavalrymen.[16] The Lapith tribe of Thessaly, who were the kinsmen of the Centaurs in myth, were described as the inventors of horse-riding by Greek writers. The Thessalian tribes also claimed their horse breeds were descended from the centaurs.
+
+Robert Graves (relying on the work of Georges Dumézil,[17] who argued for tracing the centaurs back to the Indian Gandharva), speculated that the centaurs were a dimly remembered, pre-Hellenic fraternal earth cult who had the horse as a totem.[18] A similar theory was incorporated into Mary Renault's The Bull from the Sea.
+
+Though female centaurs, called centaurides or centauresses, are not mentioned in early Greek literature and art, they do appear occasionally in later antiquity. A Macedonian mosaic of the 4th century BC is one of the earliest examples of the centauress in art.[19] Ovid also mentions a centauress named Hylonome[i] who committed suicide when her husband Cyllarus was killed in the war with the Lapiths.[20]
+
+The Kalibangan cylinder seal, dated to be around 2600-1900 BC,[21] found at the site of Indus-Valley civilization shows a battle between men in the presence of centaur-like creatures.[22][21] Other sources claim the creatures represented are actually half human and half tigers, later evolving into the Hindu Goddess of War.[23][24] These seals are also evidence of Indus-Mesopotamia relations in the 3rd millennium BC.
+
+In a popular legend associated with Pazhaya Sreekanteswaram Temple in Thiruvananthapuram, the curse of a saintly Brahmin transformed a handsome Yadava prince into a creature having a horse's body and the prince's head, arms, and torso in place of the head and neck of the horse.
+
+Kinnaras, another half-man, half-horse mythical creature from Indian mythology, appeared in various ancient texts, arts, and sculptures from all around India. It is shown as a horse with the torso of a man where the horse's head would be, and is similar to a Greek centaur.[25][26]
+
+A centaur-like half-human, half-equine creature called Polkan appeared in Russian folk art and lubok prints of the 17th–19th centuries. Polkan is originally based on Pulicane, a half-dog from Andrea da Barberino's poem I Reali di Francia, which was once popular in the Slavonic world in prosaic translations.
+
+The extensive Mycenaean pottery found at Ugarit included two fragmentary Mycenaean terracotta figures which have been tentatively identified as centaurs. This finding suggests a Bronze Age origin for these creatures of myth.[27] A painted terracotta centaur was found in the "Hero's tomb" at Lefkandi, and by the Geometric period, centaurs figure among the first representational figures painted on Greek pottery. An often-published Geometric period bronze of a warrior face-to-face with a centaur is at the Metropolitan Museum of Art.[28]
+
+In Greek art of the Archaic period, centaurs are depicted in three different forms.  Some centaurs are depicted with a human torso attached to the body of a horse at the withers, where the horse's neck would be; this form, designated "Class A" by Professor Paul Baur, later became standard.  "Class B" centaurs are depicted with a human body and legs joined at the waist to the hindquarters of a horse; in some cases centaurs of both Class A and Class B appear together.  A third type, designated "Class C", depicts centaurs with human forelegs terminating in hooves. Baur describes this as an apparent development of Aeolic art, which never became particularly widespread.[29]  At a later period, paintings on some amphorae depict winged centaurs.[30]
+
+Centaurs were also frequently depicted in Roman art. One example is the pair of centaurs drawing the chariot of Constantine the Great and his family in the Great Cameo of Constantine (circa AD 314–16), which embodies wholly pagan imagery, and contrasts sharply with the popular image of Constantine as the patron of early Christianity.[31][32]
+
+Centaurs preserved a Dionysian connection in the 12th-century Romanesque carved capitals of Mozac Abbey in the Auvergne. Other similar capitals depict harvesters, boys riding goats (a further Dionysiac theme), and griffins guarding the chalice that held the wine. Centaurs are also shown on a number of Pictish carved stones from north-east Scotland erected in the 8th–9th centuries AD (e.g., at Meigle, Perthshire). Though outside the limits of the Roman Empire, these depictions appear to be derived from Classical prototypes.
+
+The John C. Hodges library at The University of Tennessee hosts a permanent exhibit of a "Centaur from Volos" in its library. The exhibit, made by sculptor Bill Willers by combining a study human skeleton with the skeleton of a Shetland pony, is entitled "Do you believe in Centaurs?". According to the exhibitors, it was meant to mislead students in order to make them more critically aware.[33]
+
+Another exhibit by Willers is now on long-term display at the International Wildlife Museum in Tucson, Arizona.  The full-mount skeleton of a Centaur, built by Skulls Unlimited International, Inc., is on display along with several other fabled creatures, including the Cyclopes, Unicorn, and Griffin.
+
+Centaurs are common in European heraldry, although more frequent in continental than in British arms. A centaur holding a bow is referred to as a sagittarius.[34]
+
+Jerome's version of the Life of St Anthony the Great, written by Athanasius of Alexandria about the hermit monk of Egypt, was widely disseminated in the Middle Ages; it relates Anthony's encounter with a centaur who challenged the saint, but was forced to admit that the old gods had been overthrown. The episode was often depicted in The Meeting of St Anthony Abbot and St Paul the Hermit by the painter Stefano di Giovanni, who was known as "Sassetta".[35] Of the two episodic depictions of the hermit Anthony's travel to greet the hermit Paul, one is his encounter with the demonic figure of a centaur along the pathway in a wood.
+
+Lucretius, in his first-century BC philosophical poem On the Nature of Things, denied the existence of centaurs based on their differing rate of growth. He states that at the age of three years, horses are in the prime of their life while humans at the same age are still little more than babies, making hybrid animals impossible.[36]
+
+C.S. Lewis' The Chronicles of Narnia series depicts centaurs as the wisest and noblest of creatures. Narnian Centaurs are gifted at stargazing, prophecy, healing, and warfare; a fierce and valiant race always faithful to the High King Aslan the Lion.
+
+In J.K. Rowling's Harry Potter series, centaurs live in the Forbidden Forest close to Hogwarts, preferring to avoid contact with humans. They live in societies called herds and are skilled at archery, healing, and astrology, but like in the original myths, they are known to have some wild and barbarous tendencies.
+
+With the exception of Chiron, the centaurs in Rick Riordan's Percy Jackson & the Olympians are seen as wild party-goers who use a lot of American slang. Chiron retains his mythological role as a trainer of heroes and is skilled in archery. In Riordan's subsequent series, Heroes of Olympus, another group of centaurs are depicted with more animalistic features (such as horns) and appear as villains, serving the Gigantes.
+
+Philip Jose Farmer's World of Tiers series (1965) includes centaurs, called Half-Horses or Hoi Kentauroi. His creations address several of the metabolic problems of such creatures—how could the human mouth and nose intake sufficient air to sustain both itself and the horse body and, similarly, how could the human ingest sufficient food to sustain both parts.
+
+Brandon Mull's Fablehaven series features centaurs that live in an area called Grunhold. The centaurs are portrayed as a proud, elitist group of beings that consider themselves superior to all other creatures. The fourth book also has a variation on the species called an Alcetaur, which is part man, part moose.
+
+The myth of the centaur appears in John Updike's novel The Centaur. The author depicts a rural Pennsylvanian town as seen through the optics of the myth of the centaur. An unknown and marginalized local school teacher, just like the mythological Chiron did for Prometheus, gave up his life for the future of his son who had chosen to be an independent artist in New York.
+
+Diosphos Painter, white-ground lekythos (500 BC)
+
+Botticelli, Pallas and Centaur (1482–83)
+
+Antonio Canova, Theseus Defeats the Centaur (1805-1819)
+
+Prince Bova fights Polkan, Russian lubok (1860)
+
+A bronze statue of a centaur, after the Furietti Centaurs
+
+Other hybrid creatures appear in Greek mythology, always with some liminal connection that links Hellenic culture with archaic or non-Hellenic cultures:
+
+Also,
+
+Additionally, Bucentaur, the name of several historically important Venetian vessels, was linked to a posited ox-centaur or βουκένταυρος (boukentauros) by fanciful and likely spurious folk-etymology.

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+A Christmas tree is a decorated tree, usually an evergreen conifer, such as a spruce, pine or fir, or an artificial tree of similar appearance, associated with the celebration of Christmas, originating in Northern Europe.[1] The custom was developed in medieval Livonia (present-day Estonia and Latvia), and in early modern Germany where Protestant Germans brought decorated trees into their homes.[2][3] It acquired popularity beyond the Lutheran areas of Germany[2][4] and the Baltic countries during the second half of the 19th century, at first among the upper classes.[5] The Catholic Church had long resisted this Protestant custom and the Christmas Tree stood for the first time in Vatican in 1982.
+
+The tree was traditionally decorated with "roses made of colored paper, apples, wafers, tinsel, [and] sweetmeats". In the 18th century, it began to be illuminated by candles, which were ultimately replaced by Christmas lights after the advent of electrification. Today, there is a wide variety of traditional and modern ornaments, such as garlands, baubles, tinsel, and candy canes. An angel or star might be placed at the top of the tree to represent the Angel Gabriel or the Star of Bethlehem, respectively, from the Nativity.[6][7] Edible items such as gingerbread, chocolate and other sweets are also popular and are tied to or hung from the tree's branches with ribbons.
+
+In the Western Christian tradition, Christmas trees are variously erected on days such as the first day of Advent or even as late as Christmas Eve depending on the country;[8] customs of the same faith hold that the two traditional days when Christmas decorations, such as the Christmas tree, are removed are Twelfth Night and, if they are not taken down on that day, Candlemas, the latter of which ends the Christmas-Epiphany season in some denominations.[8][9]
+
+The Christmas tree is sometimes compared with the "Yule-tree", especially in discussions of its folkloric origins.[10][11][12]
+
+Modern Christmas trees originated during the Renaissance in early modern Germany. Its 16th-century origins are sometimes associated with Protestant Christian reformer Martin Luther, who is said to have first added lighted candles to an evergreen tree.[13][14][15]
+
+The earliest known firmly dated representation of a Christmas tree is on the keystone sculpture of a private home in Turckheim, Alsace (then part of Germany, today France), with the date 1576.[16]
+
+Modern Christmas trees have been related to the "tree of paradise" of medieval mystery plays that were given on 24 December, the commemoration and name day of Adam and Eve in various countries. In such plays, a tree decorated with apples (to represent the forbidden fruit) and wafers (to represent the Eucharist and redemption) was used as a setting for the play. Like the Christmas crib, the Paradise tree was later placed in homes. The apples were replaced by round objects such as shiny red balls.[11][12][17][18][19][20]
+
+At the end of the Middle Ages, an early predecessor appears referred in the Regiment of the Order of Cister in the 15th century, in Alcobaça, Portugal. The Regiment of the local high-Sacristans of the Cistercian Order refers to what may be considered the oldest references to the Christmas tree: "Note on how to put the Christmas branch, scilicet: On the Christmas eve, you will look for a large Branch of green laurel, and you shall reap many red oranges, and place them on the branches that come of the laurel, specifically as you have seen, and in every orange you shall put a candle, and hang the Branch by a rope in the pole, which shall be by the candle of the altar-mor."[21]
+
+The relevance of ancient pre-Christian customs to the 16th-century German initiation of the Christmas tree custom is disputed.[by whom?] Resistance to the custom was often because of its supposed Lutheran origins.[22]
+
+Other sources have offered a connection between the symbolism of the first documented Christmas trees in Alsace around 1600 and the trees of pre-Christian traditions. For example, according to the Encyclopædia Britannica, "The use of evergreen trees, wreaths, and garlands to symbolize eternal life was a custom of the ancient Egyptians, Chinese, and Hebrews. Tree worship was common among the pagan Europeans and survived their conversion to Christianity in the Scandinavian customs of decorating the house and barn with evergreens at the New Year to scare away the devil and of setting up a tree for the birds during Christmas time."[23]
+
+During the Roman mid-winter festival of Saturnalia, houses were decorated with wreaths of evergreen plants, along with other antecedent customs now associated with Christmas.[24]
+
+The Vikings and Saxons worshiped trees.[24] The story of Saint Boniface cutting down Donar's Oak illustrates the pagan practices in 8th century among the Germans. A later folk version of the story adds the detail that an evergreen tree grew in place of the felled oak, telling them about how its triangular shape reminds humanity of the Trinity and how it points to heaven.[25][26]
+
+Georgians have their own traditional Christmas tree called Chichilaki, made from dried up hazelnut or walnut branches that are shaped to form a small coniferous tree.[27] These pale-colored ornaments differ in height from 20 cm (7.9 in) to 3 meters (9.8 feet). Chichilakis are most common in the Guria and Samegrelo regions of Georgia near the Black Sea, but they can also be found in some stores around the capital of Tbilisi.[citation needed]
+Georgians believe that Chichilaki resembles the famous beard of St. Basil the Great, because Eastern Orthodox Church commemorates St. Basil on 1 January.
+
+In Poland, there is a folk tradition dating back to an old pre-Christian pagan custom of suspending a branch of fir, spruce or pine from the ceiling, called podłaźniczka, during the time of the Koliada winter festival.[28] The branches were decorated with apples, nuts, acorns and stars made of straw. In more recent times, the decorations also included colored paper cutouts (wycinanki), wafers, cookies and Christmas baubles. According to old pagan beliefs, the branch's powers were linked to good harvest and prosperity.[29]
+
+The custom lasted among some of the rural peasants until the early 20th century, particularly in the regions of Lesser Poland and Upper Silesia.[30] Most often the branches were hung above the wigilia dinner table on Christmas Eve from the rafters. Beginning in the mid-19th century, the tradition over time was almost completely replaced by the German practice of decorating a Christmas tree.[31] The custom was partly revived in the 1970s and continues in some homes.[32]
+
+Customs of erecting decorated trees in wintertime can be traced to Christmas celebrations in Renaissance-era guilds in Northern Germany and Livonia. The first evidence of decorated trees associated with Christmas Day are trees in guildhalls decorated with sweets to be enjoyed by the apprentices and children. In Livonia (present-day Estonia and Latvia), in 1441, 1442, 1510 and 1514, the Brotherhood of Blackheads erected a tree for the holidays in their guild houses in Reval (now Tallinn) and Riga. On the last night of the celebrations leading up to the holidays, the tree was taken to the Town Hall Square, where the members of the brotherhood danced around it.[33]
+
+A Bremen guild chronicle of 1570 reports that a small tree decorated with "apples, nuts, dates, pretzels and paper flowers" was erected in the guild-house for the benefit of the guild members' children, who collected the dainties on Christmas Day.[34] In 1584, the pastor and chronicler Balthasar Russow in his Chronica der Provinz Lyfflandt (1584) wrote of an established tradition of setting up a decorated spruce at the market square, where the young men "went with a flock of maidens and women, first sang and danced there and then set the tree aflame".
+
+After the Protestant Reformation, such trees are seen in the houses of upper-class Protestant families as a counterpart to the Catholic Christmas cribs. This transition from the guild hall to the bourgeois family homes in the Protestant parts of Germany ultimately gives rise to the modern tradition as it developed in the 18th and 19th centuries.
+
+By the early 18th century, the custom had become common in towns of the upper Rhineland, but it had not yet spread to rural areas. Wax candles, expensive items at the time, are found in attestations from the late 18th century.
+
+Along the lower Rhine, an area of Roman Catholic majority, the Christmas tree was largely regarded as a Protestant custom. As a result, it remained confined to the upper Rhineland for a relatively long period of time. The custom did eventually gain wider acceptance beginning around 1815 by way of Prussian officials who emigrated there following the Congress of Vienna.
+
+In the 19th century, the Christmas tree was taken to be an expression of German culture and of Gemütlichkeit, especially among emigrants overseas.[35]
+
+A decisive factor in winning general popularity was the German army's decision to place Christmas trees in its barracks and military hospitals during the Franco-Prussian War. Only at the start of the 20th century did Christmas trees appear inside churches, this time in a new brightly lit form.[36]
+
+In the early 19th century, the custom became popular among the nobility and spread to royal courts as far as Russia. Princess Henrietta of Nassau-Weilburg introduced the Christmas tree to Vienna in 1816, and the custom spread across Austria in the following years. In France, the first Christmas tree was introduced in 1840 by the duchesse d'Orléans. In Denmark a Danish newspaper claims that the first attested Christmas tree was lit in 1808 by countess Wilhemine of Holsteinborg. It was the aging countess who told the story of the first Danish Christmas tree to the Danish writer Hans Christian Andersen in 1865. He had published a fairy tale called The Fir-Tree in 1844, recounting the fate of a fir tree being used as a Christmas tree.[37]
+
+Although the tradition of decorating churches and homes with evergreens at Christmas was long established,[39] the custom of decorating an entire small tree was unknown in Britain until some two centuries ago. At the time of the personal union with Hanover, George III's German-born wife, Charlotte of Mecklenburg-Strelitz, introduced a Christmas tree at a party she gave for children in 1800.[40] The custom did not at first spread much beyond the royal family.[41] Queen Victoria as a child was familiar with it and a tree was placed in her room every Christmas. In her journal for Christmas Eve 1832, the delighted 13-year-old princess wrote:[42]
+
+After dinner ... we then went into the drawing room near the dining room ... There were two large round tables on which were placed two trees hung with lights and sugar ornaments. All the presents being placed round the trees ...
+
+After Victoria's marriage to her German cousin Prince Albert, by 1841 the custom became even more widespread[43] as wealthier middle-class families followed the fashion. In 1842 a newspaper advert for Christmas trees makes clear their smart cachet, German origins and association with children and gift-giving.[44] An illustrated book, The Christmas Tree, describing their use and origins in detail, was on sale in December 1844.[45] On 2 January 1846 Elizabeth Fielding (née Fox Strangways) wrote from Laycock Abbey to William Henry Fox-Talbot: "Constance is extremely busy preparing the Bohemian Xmas Tree. It is made from Caroline's[46] description of those she saw in Germany".[47] In 1847 Prince Albert wrote: "I must now seek in the children an echo of what Ernest [his brother] and I were in the old time, of what we felt and thought; and their delight in the Christmas trees is not less than ours used to be".[48] A boost to the trend was given in 1848[49] when The Illustrated London News,[50] in a report picked up by other papers,[51] described the trees in Windsor Castle in detail and showed the main tree, surrounded by the royal family, on its cover. In fewer than ten years their use in better-off homes was widespread. By 1856 a northern provincial newspaper contained an advert alluding casually to them,[52] as well as reporting the accidental death of a woman whose dress caught fire as she lit the tapers on a Christmas tree.[53] They had not yet spread down the social scale though, as a report from Berlin in 1858 contrasts the situation there where "Every family has its own" with that of Britain, where Christmas trees were still the preserve of the wealthy or the "romantic".[54]
+
+Their use at public entertainments, charity bazaars and in hospitals made them increasingly familiar however, and in 1906 a charity was set up specifically to ensure even poor children in London slums "who had never seen a Christmas tree" would enjoy one that year.[55] Anti-German sentiment after World War I briefly reduced their popularity[56] but the effect was short-lived,[57] and by the mid-1920s the use of Christmas trees had spread to all classes.[58] In 1933 a restriction on the importation of foreign trees led to the "rapid growth of a new industry" as the growing of Christmas trees within Britain became commercially viable due to the size of demand.[59] By 2013 the number of trees grown in Britain for the Christmas market was approximately eight million[60] and their display in homes, shops and public spaces a normal part of the Christmas season.
+
+The tradition was introduced to North America in the winter of 1781 by Hessian soldiers stationed in the Province of Québec (1763–1791) to garrison the colony against American attack. General Friedrich Adolf Riedesel and his wife, the Baroness von Riedesel, held a Christmas party for the officers at Sorel, Quebec, delighting their guests with a fir tree decorated with candles and fruits.[61]
+
+The Christmas tree became very common in the United States in the early nineteenth century. The first image of a Christmas tree was published in 1836 as the frontispiece to The Stranger's Gift by Hermann Bokum. The first mention of the Christmas tree in American literature was in a story in the 1836 edition of The Token and Atlantic Souvenir, titled "New Year's Day", by Catherine Maria Sedgwick, where she tells the story of a German maid decorating her mistress's tree. Also, a woodcut of the British Royal family with their Christmas tree at Windsor Castle, initially published in The Illustrated London News December 1848, was copied in the United States at Christmas 1850, in Godey's Lady's Book. Godey's copied it exactly, except for the removal of the Queen's tiara and Prince Albert's moustache, to remake the engraving into an American scene.[62] The republished Godey's image became the first widely circulated picture of a decorated evergreen Christmas tree in America. Art historian Karal Ann Marling called Prince Albert and Queen Victoria, shorn of their royal trappings, "the first influential American Christmas tree".[63] Folk-culture historian Alfred Lewis Shoemaker states, "In all of America there was no more important medium in spreading the Christmas tree in the decade 1850–60 than Godey's Lady's Book". The image was reprinted in 1860, and by the 1870s, putting up a Christmas tree had become even more common in America.[62]
+
+Several cities in the United States with German connections lay claim to that country's first Christmas tree: Windsor Locks, Connecticut, claims that a Hessian soldier put up a Christmas tree in 1777 while imprisoned at the Noden-Reed House,[64] while the "First Christmas Tree in America" is also claimed by Easton, Pennsylvania, where German settlers purportedly erected a Christmas tree in 1816. In his diary, Matthew Zahm of Lancaster, Pennsylvania, recorded the use of a Christmas tree in 1821, leading Lancaster to also lay claim to the first Christmas tree in America.[65] Other accounts credit Charles Follen, a German immigrant to Boston, for being the first to introduce to America the custom of decorating a Christmas tree.[66] August Imgard, a German immigrant living in Wooster, Ohio, is said to be the first to popularize the practice of decorating a tree with candy canes.[citation needed] In 1847, Imgard cut a blue spruce tree from a woods outside town, had the Wooster village tinsmith construct a star, and placed the tree in his house, decorating it with paper ornaments, gilded nuts and Kuchen.[67] German immigrant Charles Minnigerode accepted a position as a professor of humanities at the College of William & Mary in Williamsburg, Virginia, in 1842, where he taught Latin and Greek. Entering into the social life of the Virginia Tidewater, Minnigerode introduced the German custom of decorating an evergreen tree at Christmas at the home of law professor St. George Tucker, thereby becoming another of many influences that prompted Americans to adopt the practice at about that time.[68] An 1853 article on Christmas customs in Pennsylvania defines them as mostly "German in origin", including the Christmas tree, which is "planted in a flower pot filled with earth, and its branches are covered with presents, chiefly of confectionary, for the younger members of the family." The article distinguishes between customs in different states however, claiming that in New England generally "Christmas is not much celebrated", whereas in Pennsylvania and New York it is.[69]
+
+When Edward H. Johnson was vice president of the Edison Electric Light Company, a predecessor of Con Edison, he created the first known electrically illuminated Christmas tree at his home in New York City in 1882. Johnson became the "Father of Electric Christmas Tree Lights".[70]
+
+The lyrics sung in the United States to the German tune O Tannenbaum begin "O Christmas tree ...", giving rise to the mistaken idea that the German word Tannenbaum (fir tree) means "Christmas tree", the German word for which is instead Weihnachtsbaum.
+
+The Christmas tree by Winslow Homer, 1858
+
+Christmas in the Netherlands, c. 1899
+
+Illustration for Harper's Bazaar, published 1 January 1870
+
+Christmas tree depicted as Christmas card by Prang & Co. (Boston) 1880
+
+Vera Komissarzhevskaya as Nora in Ibsen's A Doll's House (c. 1904). Photo by Elena Mrozovskaya.
+
+An Italian-American family on Christmas, 1924
+
+In Russia, the Christmas tree was banned after the October Revolution[71] but then reinstated as a New-year spruce (Новогодняя ёлка, Novogodnyaya yolka) in 1935. It became a fully secular icon of the New Year holiday, for example, the crowning star was regarded not as a symbol of Bethlehem Star, but as the Red star. Decorations, such as figurines of airplanes, bicycles, space rockets, cosmonauts, and characters of Russian fairy tales, were produced. This tradition persists after the fall of the USSR, with the New Year holiday outweighing the Christmas (7 January) for a wide majority of Russian people.[72]
+
+The TV special A Charlie Brown Christmas (1965) was influential on the pop culture surrounding the Christmas tree. Aluminum Christmas trees were popular during the early 1960s in the US. They were satirized in the Charlie Brown show and came to be seen as symbolizing the commercialization of Christmas. The term Charlie Brown Christmas tree, describing any poor-looking or malformed little tree, also derives from the 1965 TV special, based on the appearance of Charlie Brown's Christmas tree.[73]
+
+Christmas tree with presents
+
+Christmas Tree in the cozy room at the Wisconsin Governor's mansion.
+
+Christmas tea with Christmas Tree at an espresso shop in Eugene, Oregon
+
+A Soviet-era (1960s) New Year tree decoration depicting a cosmonaut
+
+Christmas Trees in church
+
+An aluminum Christmas tree
+
+Since the early 20th century, it has become common in many cities, towns, and department stores to put up public Christmas trees outdoors, such as the Macy's Great Tree in Atlanta (since 1948), the Rockefeller Center Christmas Tree in New York City, and the large Christmas tree at Victoria Square in Adelaide.
+
+The use of fire retardant allows many indoor public areas to place real trees and be compliant with code. Licensed applicants of fire retardant solution spray the tree, tag the tree, and provide a certificate for inspection. Real trees are popular with high end visual merchandising displays around the world. Leading global retailers such as Apple often place real trees in their window displays. In 2009, Apple placed two Fraser fir trees in every one of its retail establishments.[citation needed]
+
+The United States' National Christmas Tree has been lit each year since 1923 on the South Lawn of the White House, becoming part of what evolved into a major holiday event at the White House. President Jimmy Carter lit only the crowning star atop the tree in 1979 in honor of the Americans being held hostage in Iran.[74] The same was true in 1980, except the tree was fully lit for 417 seconds, one second for each day the hostages had been in captivity.[74]
+
+During most of the 1970s and 1980s, the largest decorated Christmas tree in the world was put up every year on the property of the National Enquirer in Lantana, Florida. This tradition grew into one of the most spectacular and celebrated events in the history of southern Florida, but was discontinued on the death of the paper's founder in the late 1980s.[75]
+
+In some cities, a charity event called the Festival of Trees is organized, in which multiple trees are decorated and displayed.
+
+The giving of Christmas trees has also often been associated with the end of hostilities. After the signing of the Armistice in 1918 the city of Manchester sent a tree, and £500 to buy chocolate and cakes, for the children of the much-bombarded town of Lille in northern France.[76] In some cases the trees represent special commemorative gifts, such as in Trafalgar Square in London, where the City of Oslo, Norway presents a tree to the people of London as a token of appreciation for the British support of Norwegian resistance during the Second World War; in Boston, where the tree is a gift from the province of Nova Scotia, in thanks for rapid deployment of supplies and rescuers to the 1917 ammunition ship explosion that leveled the city of Halifax; and in Newcastle upon Tyne, where the main civic Christmas tree is an annual gift from the city of Bergen, in thanks for the part played by soldiers from Newcastle in liberating Bergen from Nazi occupation.[77] Norway also annually gifts a Christmas tree to Washington, D.C. as a symbol of friendship between Norway and the US and as an expression of gratitude from Norway for the help received from the US during World War II.[78]
+
+Christmas tree in Milan, Italy, 2008
+
+Christmas tree in Vatican City, 2007
+
+Christmas tree in Salerno old town, Italy, 2008.
+
+Trafalgar Square Christmas tree
+
+Christmas tree on Minin and Pozharsky Square, 2018. Nizhny Novgorod, Russia
+
+Rockefeller Center Christmas Tree
+
+Christmas tree on the Römerberg in Frankfurt (2008)
+
+in Lisbon (2005), at 75 metres (246 feet) the tallest Christmas tree in Europe.
+
+Boston's Christmas Tree.
+
+An Árbol navideño luminoso in Madrid (2011)
+
+Christmas tree in Warsaw
+
+Christmas tree in South Coast Plaza, California
+
+Christmas tree in Stockholm at the NK department store
+
+Christmas trees in Ocean Terminal, Harbour City, Hong Kong
+
+Christmas tree in Lugano (2018)
+
+Christmas tree in Vilnius old town, Lithuania, 2017.
+
+A "Chrismon tree" is a Christmas tree decorated with explicitly Christian symbols in white and gold.[79][80]
+First introduced by North American Lutherans in 1957,[81] the practice has rapidly spread to other Christian denominations,[82] including Anglicans,[83]
+Catholics,[84] Methodists,[85] and the Reformed.[86]
+
+"Chrismon" (plural "Chrismons") was adopted for the type of Christmas decoration and explained as a portmanteau of "Christ-monogram" (a Christogram).[87][88]
+
+Both setting up and taking down a Christmas tree are associated with specific dates. Traditionally, Christmas trees were not brought in and decorated until Christmas Eve (24 December)[citation needed] or, in the traditions celebrating Christmas Eve rather than the first day of Christmas, 23 December, and then removed the day after Twelfth Night (5 January); to have a tree up before or after these dates was even considered bad luck,[citation needed] and that to avoid bad luck from affecting the house's residents, the tree must be left up until after the following Twelfth Night passes.
+
+In many areas, it has become customary to set up one's Christmas tree at the beginning of the Advent season.[89] Americans will put up a Christmas tree after Thanksgiving (the fourth Thursday of November),[90] and Christmas decorations can show up even earlier in retail stores, often the day after Halloween (31 October). In Canada many stores wait until after Remembrance Day, as to show respect to fallen soldiers.[91] Some households do not put up the tree until the second week of December, and leave it up until 6 January (Epiphany). In Germany, traditionally the tree is put up on 24 December and taken down on 7 January, though many start one or two weeks earlier, and in Roman Catholic homes the tree may be kept until 2 February (Candlemas).[why?][citation needed]
+
+In Italy, Ireland and Argentina, along with many countries in Latin America, the Christmas tree is put up on 8 December (Immaculate Conception day) and left up until 6 January. In Australia, the Christmas tree is usually put up on 1 December, which occurs about two weeks before the school summer holidays (except for South Australia, where most people put up their tree in November following the completion of the Adelaide Christmas Pageant, a time frame that has started to filter into other states as the official time Christmas decorations and in store Santa Claus start to appear) and is left up until it is taken down.[citation needed] Some traditions suggest that Christmas trees may be kept up until no later than 2 February, the feast of the Presentation of Jesus at the Temple (Candlemas), when the Christmas season effectively closes.[92] Superstitions say that it is a bad sign if Christmas greenery is not removed by Candlemas Eve.[93]
+
+Christmas ornaments are decorations (usually made of glass, metal, wood, or ceramics) that are used to decorate a Christmas tree. The first decorated trees were adorned with apples, white candy canes and pastries in the shapes of stars, hearts and flowers. Glass baubles were first made in Lauscha, Germany, and also garlands of glass beads and tin figures that could be hung on trees. The popularity of these decorations grew into the production of glass figures made by highly skilled artisans with clay molds.
+
+Tinsel and several types of garland or ribbon are commonly used to decorate a Christmas tree. Silvered saran-based tinsel was introduced later. Delicate mold-blown and painted colored glass Christmas ornaments were a specialty of the glass factories in the Thuringian Forest, especially in Lauscha in the late 19th century, and have since become a large industry, complete with famous-name designers. Baubles are another common decoration, consisting of small hollow glass or plastic spheres coated with a thin metallic layer to make them reflective, with a further coating of a thin pigmented polymer in order to provide coloration.
+Lighting with electric lights (Christmas lights or, in the United Kingdom, fairy lights) is commonly done. A tree-topper, sometimes an angel but more frequently a star, completes the decoration.
+
+In the late 1800s, home-made white Christmas trees were made by wrapping strips of cotton batting around leafless branches creating the appearance of a snow-laden tree.
+In the 1940s and 1950s, popularized by Hollywood films in the late 1930s, flocking was very popular on the West Coast of the United States. There were home flocking kits that could be used with vacuum cleaners. In the 1980s some trees were sprayed with fluffy white flocking to simulate snow.
+
+A transparent Christmas bauble
+
+A golden bauble decorating a Christmas tree
+
+Christmas baubles
+
+A snowman-shaped decoration painted as a baseball
+
+A toy bear Christmas decoration.
+
+Fabergé egg as a Christmas decoration.
+
+Christmas decorations
+
+Red ornamented Christmas bauble
+
+Christmas baubles
+
+Each year, 33 to 36 million Christmas trees are produced in America, and 50 to 60 million are produced in Europe. In 1998, there were about 15,000 growers in America (a third of them "choose and cut" farms). In that same year, it was estimated that Americans spent $1.5 billion on Christmas trees.[94] By 2016 that had climbed to $2.04 billion for natural trees and a further $1.86 billion for artificial trees. In Europe, 75 million trees worth €2.4 billion ($3.2 billion) are harvested annually.[95]
+
+The average cost of a live cut tree in the United States was $64 in 2015 and this rose to $73 in 2017. The price is expected to hold steady for the next year.[96]
+
+The most commonly used species are fir (Abies), which have the benefit of not shedding their needles when they dry out, as well as retaining good foliage color and scent; but species in other genera are also used.
+
+In northern Europe most commonly used are:
+
+In North America, Central America, South America and Australia most commonly used are:
+
+Several other species are used to a lesser extent. Less-traditional conifers are sometimes used, such as giant sequoia, Leyland cypress, Monterey cypress and eastern juniper. Various types of spruce tree are also used for Christmas trees (including the blue spruce and, less commonly, the white spruce); but spruces begin to lose their needles rapidly upon being cut, and spruce needles are often sharp, making decorating uncomfortable. Virginia pine is still available on some tree farms in the southeastern United States; however, its winter color is faded. The long-needled eastern white pine is also used there, though it is an unpopular Christmas tree in most parts of the country, owing also to its faded winter coloration and limp branches, making decorating difficult with all but the lightest ornaments. Norfolk Island pine is sometimes used, particularly in Oceania, and in Australia, some species of the genera Casuarina and Allocasuarina are also occasionally used as Christmas trees. But, by far, the most common tree is the Pinus radiata Monterey pine. Adenanthos sericeus or Albany woolly bush is commonly sold in southern Australia as a potted living Christmas tree. Hemlock species are generally considered unsuitable as Christmas trees due to their poor needle retention and inability to support the weight of lights and ornaments.
+
+Some trees, frequently referred to as "living Christmas trees", are sold live with roots and soil, often from a plant nursery, to be stored at nurseries in planters or planted later outdoors and enjoyed (and often decorated) for years or decades. Others are produced in a container and sometimes as topiary for a porch or patio. However, when done improperly, the combination of root loss caused by digging, and the indoor environment of high temperature and low humidity is very detrimental to the tree's health; additionally, the warmth of an indoor climate will bring the tree out of its natural winter dormancy, leaving it little protection when put back outside into a cold outdoor climate. Often Christmas trees are a large attraction for living animals, including mice and spiders. Thus, the survival rate of these trees is low.[97] However, when done properly, replanting provides higher survival rates.[98]
+
+European tradition prefers the open aspect of naturally grown, unsheared trees, while in North America (outside western areas where trees are often wild-harvested on public lands)[99] there is a preference for close-sheared trees with denser foliage, but less space to hang decorations.
+
+In the past, Christmas trees were often harvested from wild forests, but now almost all are commercially grown on tree farms. Almost all Christmas trees in the United States are grown on Christmas tree farms where they are cut after about ten years of growth and new trees planted. According to the United States Department of Agriculture's agriculture census for 2007, 21,537 farms were producing conifers for the cut Christmas tree market in America, 5,717.09 square kilometres (1,412,724 acres) were planted in Christmas trees.[100]
+
+The life cycle of a Christmas tree from the seed to a 2-metre (7 ft) tree takes, depending on species and treatment in cultivation, between eight and twelve years. First, the seed is extracted from cones harvested from older trees. These seeds are then usually grown in nurseries and then sold to Christmas tree farms at an age of three to four years. The remaining development of the tree greatly depends on the climate, soil quality, as well as the cultivation and how the trees are tended by the Christmas tree farmer.[101]
+
+The first artificial Christmas trees were developed in Germany during the 19th century,[102][103][self-published source?] though earlier examples exist.[104] These "trees" were made using goose feathers that were dyed green,[102] as one response by Germans to continued deforestation.[103] Feather Christmas trees ranged widely in size, from a small 2-inch (51 mm) tree to a large 98-inch (2,500 mm) tree sold in department stores during the 1920s.[105] Often, the tree branches were tipped with artificial red berries which acted as candle holders.[106]
+
+Over the years, other styles of artificial Christmas trees have evolved and become popular. In 1930, the U.S.-based Addis Brush Company created the first artificial Christmas tree made from brush bristles.[107] Another type of artificial tree is the aluminum Christmas tree,[103] first manufactured in Chicago in 1958,[108] and later in Manitowoc, Wisconsin, where the majority of the trees were produced.[109] Most modern artificial Christmas trees are made from plastic recycled from used packaging materials, such as polyvinyl chloride (PVC).[103] Approximately 10% of artificial Christmas trees are using virgin suspension PVC resin; despite being plastic most artificial trees are not recyclable or biodegradable.[110]
+
+Other trends have developed in the early 2000s as well. Optical fiber Christmas trees come in two major varieties; one resembles a traditional Christmas tree.[111] One Dallas-based company offers "holographic mylar" trees in many hues.[104] Tree-shaped objects made from such materials as cardboard,[112] glass,[113] ceramic or other materials can be found in use as tabletop decorations. Upside-down artificial Christmas trees became popular for a short time and were originally introduced as a marketing gimmick; they allowed consumers to get closer to ornaments for sale in retail stores and opened up floor space for more products.[114]
+Artificial trees became increasingly popular during the late 20th century.[103] Users of artificial Christmas trees assert that they are more convenient, and, because they are reusable, much cheaper than their natural alternative.[103] They are also considered much safer[115] as natural trees can be a significant fire hazard. Between 2001 and 2007 artificial Christmas tree sales in the U.S. jumped from 7.3 million to 17.4 million.[116] Currently it is estimated that around 58% of Christmas trees used in the United States are artificial while numbers in the United Kingdom are indicated to be around 66%.[117]
+
+A tree with fibre optic lights
+
+White Christmas tree
+
+Spanish artificial Christmas tree
+
+A chrismon tree (St. Alban's Anglican Cathedral, Oviedo, Florida)
+
+An artificial Aluminum Christmas tree
+
+Artificial tree
+
+The debate about the environmental impact of artificial trees is ongoing. Generally, natural tree growers contend that artificial trees are more environmentally harmful than their natural counterparts.[116] However, trade groups such as the American Christmas Tree Association, continue to refute that artificial trees are more harmful to the environment, and maintain that the PVC used in Christmas trees has excellent recyclable properties.[118]
+
+Live trees are typically grown as a crop and replanted in rotation after cutting, often providing suitable habitat for wildlife.[citation needed] Alternately, live trees can be donated to livestock farmers who find that such trees uncontaminated by chemical additives are excellent fodder.[119] In some cases management of Christmas tree crops can result in poor habitat since it sometimes involves heavy input of pesticides.[120]
+Concerns have been raised[by whom?] about people cutting down old and rare conifers, such as the Keteleeria evelyniana and Abies fraseri, for Christmas trees.[citation needed]
+
+Real or cut trees are used only for a short time, but can be recycled and used as mulch, wildlife habitat, or used to prevent erosion.[121][122][123] Real trees are carbon-neutral, they emit no more carbon dioxide by being cut down and disposed of than they absorb while growing.[124] However, emissions can occur from farming activities and transportation. An independent life-cycle assessment study, conducted by a firm of experts in sustainable development, states that a natural tree will generate 3.1 kg (6.8 lb) of greenhouse gases every year (based on purchasing 5 km (3.1 miles) from home) whereas the artificial tree will produce 48.3 kg (106 lb) over its lifetime.[125] Some people use living Christmas or potted trees for several seasons, providing a longer life cycle for each tree. Living Christmas trees can be purchased or rented from local market growers. Rentals are picked up after the holidays, while purchased trees can be planted by the owner after use or donated to local tree adoption or urban reforestation services.[126] Smaller and younger trees may be replanted after each season, with the following year running up to the next Christmas allowing the tree to carry out further growth.
+
+Most artificial trees are made of recycled PVC rigid sheets using tin stabilizer in the recent years. In the past, lead was often used as a stabilizer in PVC, but is now banned by Chinese laws.[citation needed]
+The use of lead stabilizer in Chinese imported trees has been an issue of concern among politicians and scientists over recent years. A 2004 study found that while in general artificial trees pose little health risk from lead contamination, there do exist "worst-case scenarios" where major health risks to young children exist.[127] A 2008 United States Environmental Protection Agency report found that as the PVC in artificial Christmas trees aged it began to degrade.[128] The report determined that of the fifty million artificial trees in the United States approximately twenty million were nine or more years old, the point where dangerous lead contamination levels are reached.[128] A professional study on the life-cycle assessment of both real and artificial Christmas trees revealed that one must use an artificial Christmas tree at least twenty years to leave an environmental footprint as small as the natural Christmas tree.[125]
+
+The earliest legend of the origin of the Christmas tree dates back to 723, involving Saint Boniface[129] as he was evangelizing Germany. According to a story not mentioned in his biographies (vitae), he stumbled upon a pagan gathering where a group of people dancing under a decorated oak tree were about to sacrifice a baby in the name of Thor. Boniface took an axe and called on the name of Jesus. In one swipe, he managed to take down the entire tree, to the crowd's astonishment. Behind the fallen tree was a baby fir. Boniface said, "let this tree be the symbol of the true God, its leaves are ever green and will not die." The tree's needles pointed to heaven. Tradition holds that trees were used in formerly pagan homes from that moment forth, but decorated in the name of Jesus.[130]
+
+The Christmas tree was first recorded to be used by German Lutherans in the 16th century, with records indicating that a Christmas tree was placed in the Cathedral of Strasbourg in 1539, under the leadership of the Protestant Reformer, Martin Bucer.[131][132] In the United States, these "German Lutherans brought the decorated Christmas tree with them; the Moravians put lighted candles on those trees."[133][134] When decorating the Christmas tree, many individuals place a star at the top of the tree symbolizing the Star of Bethlehem, a fact recorded by The School Journal in 1897.[6][135] Professor David Albert Jones of the University of Oxford writes that in the 19th century, it became popular for people to also use an angel to top the Christmas tree in order to symbolize the angels mentioned in the accounts of the Nativity of Jesus.[7]
+
+Under the Marxist-Leninist doctrine of state atheism in the Soviet Union, after its foundation in 1917, Christmas celebrations—along with other religious holidays—were prohibited as a result of the Soviet anti-religious campaign.[136][137][138] The League of Militant Atheists encouraged school pupils to campaign against Christmas traditions, among them being the Christmas tree, as well as other Christian holidays, including Easter; the League established an anti-religious holiday to be the 31st of each month as a replacement.[139] With the Christmas tree being prohibited in accordance with Soviet anti-religious legislation, people supplanted the former Christmas custom with New Year's trees.[138][140] In 1935 the tree was brought back as New Year tree and became a secular, not a religious holiday.
+
+Pope John Paul II introduced the Christmas tree custom to the Vatican in 1982. Although at first disapproved of by some as out of place at the centre of the Roman Catholic Church, the Vatican Christmas Tree has become an integral part of the Vatican Christmas celebrations,[141] and in 2005 Pope Benedict XVI spoke of it as part of the normal Christmas decorations in Catholic homes.[142] In 2004, Pope John Paul called the Christmas tree a symbol of Christ. This very ancient custom, he said, exalts the value of life, as in winter what is evergreen becomes a sign of undying life, and it reminds Christians of the "tree of life" of Genesis 2:9, an image of Christ, the supreme gift of God to humanity.[143] In the previous year he said: "Beside the crib, the Christmas tree, with its twinkling lights, reminds us that with the birth of Jesus the tree of life has blossomed anew in the desert of humanity. The crib and the tree: precious symbols, which hand down in time the true meaning of Christmas."[144] The Catholic Church's official Book of Blessings has a service for the blessing of the Christmas tree in a home.[145] The Episcopal Church in The Anglican Family Prayer Book, which has the imprimatur of The Rt. Rev. Catherine S. Roskam of the Anglican Communion, has long had a ritual titled Blessing of a Christmas Tree, as well as Blessing of a Crèche, for use in the church and the home.[146]
+
+Chrismon trees are a variety developed in 1957 by a Lutheran laywoman in Virginia, as a specifically religious version appropriate for a church's Christmas celebrations, although most Christian churches continue to display the traditional Christmas tree in their sanctuaries during Christmastide.[147]
+
+In 2005, the city of Boston renamed the spruce tree used to decorate the Boston Common a "Holiday Tree" rather than a "Christmas Tree".[148] The name change was reversed after the city was threatened with several lawsuits.[149]

en/3340.html.txt

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+
+
+A mushroom or toadstool is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground, on soil, or on its food source.
+
+The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus; hence the word "mushroom" is most often applied to those fungi (Basidiomycota, Agaricomycetes) that have a stem (stipe), a cap (pileus), and gills (lamellae, sing. lamella) on the underside of the cap. "Mushroom" also describes a variety of other gilled fungi, with or without stems, therefore the term is used to describe the fleshy fruiting bodies of some Ascomycota. These gills produce microscopic spores that help the fungus spread across the ground or its occupant surface.
+
+Forms deviating from the standard morphology usually have more specific names, such as "bolete", "puffball", "stinkhorn", and "morel", and gilled mushrooms themselves are often called "agarics" in reference to their similarity to Agaricus or their order Agaricales. By extension, the term "mushroom" can also refer to either the entire fungus when in culture, the thallus (called a mycelium) of species forming the fruiting bodies called mushrooms, or the species itself.
+
+The terms "mushroom" and "toadstool" go back centuries and were never precisely defined, nor was there consensus on application. During the 15th and 16th centuries, the terms mushrom, mushrum, muscheron, mousheroms, mussheron, or musserouns were used.[2]
+
+The term "mushroom" and its variations may have been derived from the French word mousseron in reference to moss (mousse). Delineation between edible and poisonous fungi is not clear-cut, so a "mushroom" may be edible, poisonous, or unpalatable.
+
+Cultural or social phobias of mushrooms and fungi may be related. The term "fungophobia" was coined by William Delisle Hay of England, who noted a national superstition or fear of "toadstools".[3][4][5]
+
+The word "toadstool" has apparent analogies in Dutch padde(n)stoel (toad-stool/chair, mushroom) and German Krötenschwamm (toad-fungus, alt. word for panther cap). In German folklore and old fairy tales, toads are often depicted sitting on toadstool mushrooms and catching, with their tongues, the flies that are said to be drawn to the Fliegenpilz, a German name for the toadstool, meaning "flies' mushroom". This is how the mushroom got another of its names, Krötenstuhl (a less-used German name for the mushroom), literally translating to "toad-stool".
+
+Identifying mushrooms requires a basic understanding of their macroscopic structure. Most are Basidiomycetes and gilled. Their spores, called basidiospores, are produced on the gills and fall in a fine rain of powder from under the caps as a result. At the microscopic level, the basidiospores are shot off basidia and then fall between the gills in the dead air space. As a result, for most mushrooms, if the cap is cut off and placed gill-side-down overnight, a powdery impression reflecting the shape of the gills (or pores, or spines, etc.) is formed (when the fruit body is sporulating). The color of the powdery print, called a spore print, is used to help classify mushrooms and can help to identify them. Spore print colors include white (most common), brown, black, purple-brown, pink, yellow, and creamy, but almost never blue, green, or red.[6]
+
+While modern identification of mushrooms is quickly becoming molecular, the standard methods for identification are still used by most and have developed into a fine art harking back to medieval times and the Victorian era, combined with microscopic examination. The presence of juices upon breaking, bruising reactions, odors, tastes, shades of color, habitat, habit, and season are all considered by both amateur and professional mycologists. Tasting and smelling mushrooms carries its own hazards because of poisons and allergens. Chemical tests are also used for some genera.[7]
+
+In general, identification to genus can often be accomplished in the field using a local mushroom guide. Identification to species, however, requires more effort; one must remember that a mushroom develops from a button stage into a mature structure, and only the latter can provide certain characteristics needed for the identification of the species. However, over-mature specimens lose features and cease producing spores. Many novices have mistaken humid water marks on paper for white spore prints, or discolored paper from oozing liquids on lamella edges for colored spored prints.
+
+Typical mushrooms are the fruit bodies of members of the order Agaricales, whose type genus is Agaricus and type species is the field mushroom, Agaricus campestris. However, in modern molecularly defined classifications, not all members of the order Agaricales produce mushroom fruit bodies, and many other gilled fungi, collectively called mushrooms, occur in other orders of the class Agaricomycetes. For example, chanterelles are in the Cantharellales, false chanterelles such as Gomphus are in the Gomphales, milk-cap mushrooms (Lactarius, Lactifluus) and russulas (Russula), as well as Lentinellus, are in the Russulales, while the tough, leathery genera Lentinus and Panus are among the Polyporales, but Neolentinus is in the Gloeophyllales, and the little pin-mushroom genus, Rickenella, along with similar genera, are in the Hymenochaetales.
+
+Within the main body of mushrooms, in the Agaricales, are common fungi like the common fairy-ring mushroom, shiitake, enoki, oyster mushrooms, fly agarics and other Amanitas, magic mushrooms like species of Psilocybe, paddy straw mushrooms, shaggy manes, etc.
+
+An atypical mushroom is the lobster mushroom, which is a deformed, cooked-lobster-colored parasitized fruitbody of a Russula or Lactarius, colored and deformed by the mycoparasitic Ascomycete Hypomyces lactifluorum.[8]
+
+Other mushrooms are not gilled, so the term "mushroom" is loosely used, and giving a full account of their classifications is difficult. Some have pores underneath (and are usually called boletes), others have spines, such as the hedgehog mushroom and other tooth fungi, and so on. "Mushroom" has been used for polypores, puffballs, jelly fungi, coral fungi, bracket fungi, stinkhorns, and cup fungi. Thus, the term is more one of common application to macroscopic fungal fruiting bodies than one having precise taxonomic meaning. Approximately 14,000 species of mushrooms are described.[9]
+
+A mushroom develops from a nodule, or pinhead, less than two millimeters in diameter, called a primordium, which is typically found on or near the surface of the substrate. It is formed within the mycelium, the mass of threadlike hyphae that make up the fungus. The primordium enlarges into a roundish structure of interwoven hyphae roughly resembling an egg, called a "button". The button has a cottony roll of mycelium, the universal veil, that surrounds the developing fruit body. As the egg expands, the universal veil ruptures and may remain as a cup, or volva, at the base of the stalk, or as warts or volval patches on the cap. Many mushrooms lack a universal veil, therefore they do not have either a volva or volval patches. Often, a second layer of tissue, the partial veil, covers the bladelike gills that bear spores. As the cap expands, the veil breaks, and remnants of the partial veil may remain as a ring, or annulus, around the middle of the stalk or as fragments hanging from the margin of the cap. The ring may be skirt-like as in some species of Amanita, collar-like as in many species of Lepiota, or merely the faint remnants of a cortina (a partial veil composed of filaments resembling a spiderweb), which is typical of the genus Cortinarius. Mushrooms lacking partial veils do not form an annulus.[10]
+
+The stalk (also called the stipe, or stem) may be central and support the cap in the middle, or it may be off-center and/or lateral, as in species of Pleurotus and Panus. In other mushrooms, a stalk may be absent, as in the polypores that form shelf-like brackets. Puffballs lack a stalk, but may have a supporting base. Other mushrooms, such as truffles, jellies, earthstars, and bird's nests, usually do not have stalks, and a specialized mycological vocabulary exists to describe their parts.
+
+The way the gills attach to the top of the stalk is an important feature of mushroom morphology. Mushrooms in the genera Agaricus, Amanita, Lepiota and Pluteus, among others, have free gills that do not extend to the top of the stalk. Others have decurrent gills that extend down the stalk, as in the genera Omphalotus and Pleurotus. There are a great number of variations between the extremes of free and decurrent, collectively called attached gills. Finer distinctions are often made to distinguish the types of attached gills: adnate gills, which adjoin squarely to the stalk; notched gills, which are notched where they join the top of the stalk; adnexed gills, which curve upward to meet the stalk, and so on. These distinctions between attached gills are sometimes difficult to interpret, since gill attachment may change as the mushroom matures, or with different environmental conditions.[11]
+
+A hymenium is a layer of microscopic spore-bearing cells that covers the surface of gills. In the nongilled mushrooms, the hymenium lines the inner surfaces of the tubes of boletes and polypores, or covers the teeth of spine fungi and the branches of corals. In the Ascomycota, spores develop within microscopic elongated, sac-like cells called asci, which typically contain eight spores in each ascus. The Discomycetes, which contain the cup, sponge, brain, and some club-like fungi, develop an exposed layer of asci, as on the inner surfaces of cup fungi or within the pits of morels. The Pyrenomycetes, tiny dark-colored fungi that live on a wide range of substrates including soil, dung, leaf litter, and decaying wood, as well as other fungi, produce minute, flask-shaped structures called perithecia, within which the asci develop.[12]
+
+In the Basidiomycetes, usually four spores develop on the tips of thin projections called sterigmata, which extend from club-shaped cells called a basidia. The fertile portion of the Gasteromycetes, called a gleba, may become powdery as in the puffballs or slimy as in the stinkhorns. Interspersed among the asci are threadlike sterile cells called paraphyses. Similar structures called cystidia often occur within the hymenium of the Basidiomycota. Many types of cystidia exist, and assessing their presence, shape, and size is often used to verify the identification of a mushroom.[12]
+
+The most important microscopic feature for identification of mushrooms is the spores. Their color, shape, size, attachment, ornamentation, and reaction to chemical tests often can be the crux of an identification. A spore often has a protrusion at one end, called an apiculus, which is the point of attachment to the basidium, termed the apical germ pore, from which the hypha emerges when the spore germinates.[12]
+
+Many species of mushrooms seemingly appear overnight, growing or expanding rapidly. This phenomenon is the source of several common expressions in the English language including "to mushroom" or "mushrooming" (expanding rapidly in size or scope) and "to pop up like a mushroom" (to appear unexpectedly and quickly).  In reality, all species of mushrooms take several days to form primordial mushroom fruit bodies, though they do expand rapidly by the absorption of fluids.[citation needed]
+
+The cultivated mushroom, as well as the common field mushroom, initially form a minute fruiting body, referred to as the pin stage because of their small size. Slightly expanded, they are called buttons, once again because of the relative size and shape. Once such stages are formed, the mushroom can rapidly pull in water from its mycelium and expand, mainly by inflating preformed cells that took several days to form in the primordia.[citation needed]
+
+Similarly, there are other mushrooms, like Parasola plicatilis (formerly Coprinus plicatlis), that grow rapidly overnight and may disappear by late afternoon on a hot day after rainfall.[13] The primordia form at ground level in lawns in humid spaces under the thatch and after heavy rainfall or in dewy conditions balloon to full size in a few hours, release spores, and then collapse. They "mushroom" to full size.[citation needed]
+
+Not all mushrooms expand overnight; some grow very slowly and add tissue to their fruiting bodies by growing from the edges of the colony or by inserting hyphae. For example, Pleurotus nebrodensis grows slowly, and because of this combined with human collection, it is now critically endangered.[14]
+
+Though mushroom fruiting bodies are short-lived, the underlying mycelium can itself be long-lived and massive. A colony of Armillaria solidipes (formerly known as Armillaria ostoyae) in Malheur National Forest in the United States is estimated to be 2,400 years old, possibly older, and spans an estimated 2,200 acres (8.9 km2).[15] Most of the fungus is underground and in decaying wood or dying tree roots in the form of white mycelia combined with black shoelace-like rhizomorphs that bridge colonized separated woody substrates.[16]
+
+Raw brown mushrooms are 92% water, 4% carbohydrates, 2% protein and less than 1% fat. In a 100 gram (3.5 ounce) amount, raw mushrooms provide 22 calories and are a rich source (20% or more of the Daily Value, DV) of B vitamins, such as riboflavin, niacin and pantothenic acid, selenium (37% DV) and copper (25% DV), and a moderate source (10-19% DV) of phosphorus, zinc and potassium (table). They have minimal or no vitamin C and sodium content.
+
+The vitamin D content of a mushroom depends on postharvest handling, in particular the unintended exposure to sunlight. The US Department of Agriculture provided evidence that UV-exposed mushrooms contain substantial amounts of vitamin D.[17] When exposed to ultraviolet (UV) light, even after harvesting,[18] ergosterol in mushrooms is converted to vitamin D2,[19] a process now used intentionally to supply fresh vitamin D mushrooms for the functional food grocery market.[20] In a comprehensive safety assessment of producing vitamin D in fresh mushrooms, researchers showed that artificial UV light technologies were equally effective for vitamin D production as in mushrooms exposed to natural sunlight, and that UV light has a long record of safe use for production of vitamin D in food.[20]
+
+Mushrooms are used extensively in cooking, in many cuisines (notably Chinese, Korean, European, and Japanese).
+
+Most mushrooms sold in supermarkets have been commercially grown on mushroom farms. The most popular of these, Agaricus bisporus, is considered safe for most people to eat because it is grown in controlled, sterilized environments. Several varieties of A. bisporus are grown commercially, including whites, crimini, and portobello. Other cultivated species available at many grocers include Hericium erinaceus, shiitake, maitake (hen-of-the-woods), Pleurotus, and enoki. In recent years, increasing affluence in developing countries has led to a considerable growth in interest in mushroom cultivation, which is now seen as a potentially important economic activity for small farmers.[21]
+
+China is a major edible mushroom producer.[22] The country produces about half of all cultivated mushrooms, and around 2.7 kilograms (6.0 lb) of mushrooms are consumed per person per year by 1.4 billion people.[23] In 2014, Poland was the world's largest mushroom exporter, reporting an estimated 194,000 tonnes (191,000 long tons; 214,000 short tons) annually.[24]
+
+Separating edible from poisonous species requires meticulous attention to detail; there is no single trait by which all toxic mushrooms can be identified, nor one by which all edible mushrooms can be identified. People who collect mushrooms for consumption are known as mycophagists,[25] and the act of collecting them for such is known as mushroom hunting, or simply "mushrooming". Even edible mushrooms may produce allergic reactions in susceptible individuals, from a mild asthmatic response to severe anaphylactic shock.[26][27] Even the cultivated A. bisporus contains small amounts of hydrazines, the most abundant of which is agaritine (a mycotoxin and carcinogen).[28] However, the hydrazines are destroyed by moderate heat when cooking.[29]
+
+A number of species of mushrooms are poisonous; although some resemble certain edible species, consuming them could be fatal. Eating mushrooms gathered in the wild is risky and should only be undertaken by individuals knowledgeable in mushroom identification. Common best practice is for wild mushroom pickers to focus on collecting a small number of visually distinctive, edible mushroom species that cannot be easily confused with poisonous varieties.
+
+Many mushroom species produce secondary metabolites that can be toxic, mind-altering, antibiotic, antiviral, or bioluminescent.  Although there are only a small number of deadly species, several others can cause particularly severe and unpleasant symptoms.  Toxicity likely plays a role in protecting the function of the basidiocarp: the mycelium has expended considerable energy and protoplasmic material to develop a structure to efficiently distribute its spores. One defense against consumption and premature destruction is the evolution of chemicals that render the mushroom inedible, either causing the consumer to vomit the meal (see emetics), or to learn to avoid consumption altogether. In addition, due to the propensity of mushrooms to absorb heavy metals, including those that are radioactive, European mushrooms may, as late as 2008, include toxicity from the 1986 Chernobyl disaster and continue to be studied.[30][31]
+
+Mushrooms with psychoactive properties have long played a role in various native medicine traditions in cultures all around the world. They have been used as sacrament in rituals aimed at mental and physical healing, and to facilitate visionary states. One such ritual is the velada ceremony. A practitioner of traditional mushroom use is the shaman or curandera (priest-healer).[32]
+
+Psilocybin mushrooms possess psychedelic properties. Commonly known as "magic mushrooms" or "'shrooms", they are openly available in smart shops in many parts of the world, or on the black market in those countries that have outlawed their sale. Psilocybin mushrooms have been reported as facilitating profound and life-changing insights often described as mystical experiences. Recent scientific work has supported these claims, as well as the long-lasting effects of such induced spiritual experiences.[33]
+
+Psilocybin, a naturally occurring chemical in certain psychedelic mushrooms such as Psilocybe cubensis, is being studied for its ability to help people suffering from psychological disorders, such as obsessive–compulsive disorder. Minute amounts have been reported to stop cluster and migraine headaches.[35] A double-blind study, done by the Johns Hopkins Hospital, showed psychedelic mushrooms could provide people an experience with substantial personal meaning and spiritual significance.  In the study, one third of the subjects reported ingestion of psychedelic mushrooms was the single most spiritually significant event of their lives. Over two-thirds reported it among their five most meaningful and spiritually significant events.  On the other hand, one-third of the subjects reported extreme anxiety. However, the anxiety went away after a short period of time.[36] Psilocybin mushrooms have also shown to be successful in treating addiction, specifically with alcohol and cigarettes.[37]
+
+A few species in the genus Amanita, most recognizably A. muscaria, but also A. pantherina, among others, contain the psychoactive compound muscimol.  The muscimol-containing chemotaxonomic group of Amanitas contains no amatoxins or phallotoxins, and as such are not hepatoxic, though if not properly cured will be non-lethally neurotoxic due to the presence of ibotenic acid. The Amanita intoxication is similar to Z-drugs in that it includes CNS depressant and sedative-hypnotic effects, but also dissociation and delirium in high doses.
+
+Some mushrooms are used or studied as possible treatments for diseases, particularly their extracts, including polysaccharides, glycoproteins and proteoglycans.[38] In some countries, extracts of polysaccharide-K, schizophyllan, polysaccharide peptide, or lentinan are government-registered adjuvant cancer therapies,[39][40] even though clinical evidence of efficacy in humans has not been confirmed.[41]
+
+Historically in traditional Chinese medicine, mushrooms are believed to have medicinal value,[42] although there is no evidence for such uses.
+
+Mushrooms can be used for dyeing wool and other natural fibers. The chromophores of mushroom dyes are organic compounds and produce strong and vivid colors, and all colors of the spectrum can be achieved with mushroom dyes. Before the invention of synthetic dyes, mushrooms were the source of many textile dyes.[43]
+
+Some fungi, types of polypores loosely called mushrooms, have been used as fire starters (known as tinder fungi).
+
+Mushrooms and other fungi play a role in the development of new biological remediation techniques (e.g., using mycorrhizae to spur plant growth) and filtration technologies (e.g. using fungi to lower bacterial levels in contaminated water).[44]

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+The cat (Felis catus) is a domestic species of small carnivorous mammal.[1][2] It is the only domesticated species in the family Felidae and is often referred to as the domestic cat to distinguish it from the wild members of the family.[4] A cat can either be a house cat, a farm cat or a feral cat; the latter ranges freely and avoids human contact.[5] Domestic cats are valued by humans for companionship and their ability to hunt rodents. About 60 cat breeds are recognized by various cat registries.[6]
+
+The cat is similar in anatomy to the other felid species: it has a strong flexible body, quick reflexes, sharp teeth and retractable claws adapted to killing small prey. Its night vision and sense of smell are well developed. Cat communication includes vocalizations like meowing, purring, trilling, hissing, growling and grunting as well as cat-specific body language. It is a solitary hunter but a social species. It can hear sounds too faint or too high in frequency for human ears, such as those made by mice and other small mammals. It is a predator that is most active at dawn and dusk.[7] It secretes and perceives pheromones.[8]
+
+Female domestic cats can have kittens from spring to late autumn, with litter sizes often ranging from two to five kittens.[9] Domestic cats are bred and shown at events as registered pedigreed cats, a hobby known as cat fancy. Failure to control breeding of pet cats by spaying and neutering, as well as abandonment of pets, resulted in large numbers of feral cats worldwide, contributing to the extinction of entire bird, mammal, and reptile species, and evoking population control.[10]
+
+Cats were first domesticated in the Near East around 7500 BC.[11] It was long thought that cat domestication was initiated in Ancient Egypt, as since around 3100 BC veneration was given to cats in ancient Egypt.[12][13]
+
+As of 2017[update], the domestic cat was the second-most popular pet in the United States by number of pets owned, after freshwater fish,[14] with 95 million cats owned.[15][16] In the United Kingdom, around 7.3 million cats lived in more than 4.8 million households as of 2019[update].[17]
+
+The origin of the English word 'cat', Old English catt, is thought to be the Late Latin word cattus, which was first used at the beginning of the 6th century.[18] It was suggested that the word 'cattus' is derived from an Egyptian precursor of Coptic ϣⲁⲩ šau, "tomcat", or its feminine form suffixed with -t.[19]
+The Late Latin word is also thought to be derived from Afro-Asiatic languages.[20] The Nubian word kaddîska "wildcat" and Nobiin kadīs are possible sources or cognates.[21] The Nubian word may be a loan from Arabic قَطّ‎ qaṭṭ ~ قِطّ qiṭṭ. It is "equally likely that the forms might derive from an ancient Germanic word, imported into Latin and thence to Greek and to Syriac and Arabic".[22] The word may be derived from Germanic and Northern European languages, and ultimately be borrowed from Uralic, cf. Northern Sami gáđfi, "female stoat", and Hungarian hölgy, "stoat"; from Proto-Uralic *käďwä, "female (of a furred animal)".[23]
+
+The English puss, extended as pussy and pussycat, is attested from the 16th century and may have been introduced from Dutch poes or from Low German puuskatte, related to Swedish kattepus, or Norwegian pus, pusekatt. Similar forms exist in Lithuanian puižė and Irish puisín or puiscín. The etymology of this word is unknown, but it may have simply arisen from a sound used to attract a cat.[24][25]
+
+A male cat is called a tom or tomcat[26] (or a gib,[27] if neutered) An unspayed female is called a queen,[28] especially in a cat-breeding context. A juvenile cat is referred to as a kitten. In Early Modern English, the word kitten was interchangeable with the now-obsolete word catling.[29] A group of cats can be referred to as a clowder or a glaring.[30]
+
+The scientific name Felis catus was proposed by Carl Linnaeus in 1758 for a domestic cat.[1][2]
+Felis catus domesticus was proposed by Johann Christian Polycarp Erxleben in 1777.[3]
+Felis daemon proposed by Konstantin Alekseevich Satunin in 1904 was a black cat from the Transcaucasus, later identified as a domestic cat.[31][32]
+
+In 2003, the International Commission on Zoological Nomenclature ruled that the domestic cat is a distinct species, namely Felis catus.[33][34]
+In 2007, it was considered a subspecies of the European wildcat, F. silvestris catus, following results of phylogenetic research.[35][36]  In 2017, the IUCN Cat Classification Taskforce followed the recommendation of the ICZN in regarding the domestic cat as a distinct species, Felis catus.[37]
+
+The domestic cat is a member of the Felidae, a family that had a common ancestor about 10–15 million years ago.[38]
+The genus Felis diverged from the Felidae around 6–7 million years ago.[39]
+Results of phylogenetic research confirm that the wild Felis species evolved through sympatric or parapatric speciation, whereas the domestic cat evolved through artificial selection.[40] The domesticated cat and its closest wild ancestor are both diploid organisms that possess 38 chromosomes[41] and roughly 20,000 genes.[42]
+The leopard cat (Prionailurus bengalensis) was tamed independently in China around 5500 BCE. This line of partially domesticated cats leaves no trace in the domestic cat populations of today.[43]
+
+The earliest known indication for the taming of an African wildcat (F. lybica) was excavated close by a human Neolithic  grave in Shillourokambos, southern Cyprus, dating to about 9,200 to 9,500 years before present. Since there is no evidence of native mammalian fauna on Cyprus, the inhabitants of this Neolithic village most likely brought the cat and other wild mammals to the island from the Middle Eastern mainland.[44] Scientists therefore assume that African wildcats were attracted to early human settlements in the Fertile Crescent by rodents, in particular the house mouse (Mus musculus), and were tamed by Neolithic farmers. This commensal relationship between early farmers and tamed cats lasted thousands of years. As agricultural practices spread, so did tame and domesticated cats.[11][6] Wildcats of Egypt contributed to the maternal gene pool of the domestic cat at a later time.[45]
+The earliest known evidence for the occurrence of the domestic cat in Greece dates to around 1200 BCE. Greek, Phoenician, Carthaginian and Etruscan traders introduced domestic cats to southern Europe.[46]
+During the Roman Empire they were introduced to Corsica and Sardinia before the beginning of the 1st millennium.[47]
+By the 5th century BCE, they were familiar animals around settlements in Magna Graecia and Etruria.[48]
+By the end of the Roman Empire in the 5th century, the Egyptian domestic cat lineage had arrived in a Baltic Sea port in northern Germany.[45]
+
+During domestication, cats have undergone only minor changes in anatomy and behavior, and they are still capable of surviving in the wild. Several natural behaviors and characteristics of wildcats may have pre-adapted them for domestication as pets. These traits include their small size, social nature, obvious body language, love of play and relatively high intelligence. Captive Leopardus cats may also display affectionate behavior toward humans, but were not domesticated.[49] House cats often mate with feral cats,[50] producing hybrids such as the Kellas cat in Scotland.[51] Hybridisation between domestic and other Felinae species is also possible.[52]
+
+Development of cat breeds started in the mid 19th century.[53]
+An analysis of the domestic cat genome revealed that the ancestral wildcat genome was significantly altered in the process of domestication, as specific mutations were selected to develop cat breeds.[54] Most breeds are founded on random-bred domestic cats. Genetic diversity of these breeds varies between regions, and is lowest in purebred populations, which show more than 20 deleterious genetic disorders.[55]
+
+The domestic cat has a smaller skull and shorter bones than the European wildcat.[56]
+It averages about 46 cm (18 in) in head-to-body length and 23–25 cm (9–10 in) in height, with about 30 cm (12 in) long tails. Males are larger than females.[57]
+Adult domestic cats typically weigh between 4 and 5 kg (9 and 11 lb).[40]
+
+Cats have seven cervical vertebrae (as do most mammals); 13 thoracic vertebrae (humans have 12); seven lumbar vertebrae (humans have five); three sacral vertebrae (as do most mammals, but humans have five); and a variable number of caudal vertebrae in the tail (humans have only vestigial caudal vertebrae, fused into an internal coccyx).[58]:11 The extra lumbar and thoracic vertebrae account for the cat's spinal mobility and flexibility. Attached to the spine are 13 ribs, the shoulder, and the pelvis.[58]:16 Unlike human arms, cat forelimbs are attached to the shoulder by free-floating clavicle bones which allow them to pass their body through any space into which they can fit their head.[59]
+
+The cat skull is unusual among mammals in having very large eye sockets and a powerful specialized jaw.[60]:35 Within the jaw, cats have teeth adapted for killing prey and tearing meat. When it overpowers its prey, a cat delivers a lethal neck bite with its two long canine teeth, inserting them between two of the prey's vertebrae and severing its spinal cord, causing irreversible paralysis and death.[61] Compared to other felines, domestic cats have narrowly spaced canine teeth relative to the size of their jaw, which is an adaptation to their preferred prey of small rodents, which have small vertebrae.[61] The premolar and first molar together compose the carnassial pair on each side of the mouth, which efficiently shears meat into small pieces, like a pair of scissors. These are vital in feeding, since cats' small molars cannot chew food effectively, and cats are largely incapable of mastication.[60]:37 Although cats tend to have better teeth than most humans, with decay generally less likely because of a thicker protective layer of enamel, a less damaging saliva, less retention of food particles between teeth, and a diet mostly devoid of sugar, they are nonetheless subject to occasional tooth loss and infection.[62]
+
+The cat is digitigrade. It walks on the toes, with the bones of the feet making up the lower part of the visible leg.[63] Unlike most mammals, it uses a "pacing" gait and moves both legs on one side of the body before the legs on the other side. It registers directly by placing each hind paw close to the track of the corresponding fore paw, minimizing noise and visible tracks. This also provides sure footing for hind paws when navigating rough terrain. As it speeds up walking to trotting, its gait changes to a "diagonal" gait: The diagonally opposite hind and fore legs move simultaneously.[64]
+
+Cats have protractable and retractable claws.[65] In their normal, relaxed position, the claws are sheathed with the skin and fur around the paw's toe pads. This keeps the claws sharp by preventing wear from contact with the ground and allows the silent stalking of prey. The claws on the fore feet are typically sharper than those on the hind feet.[66] Cats can voluntarily extend their claws on one or more paws. They may extend their claws in hunting or self-defense, climbing, kneading, or for extra traction on soft surfaces. Cats shed the outside layer of their claw sheaths when scratching rough surfaces.[67]
+
+Most cats have five claws on their front paws, and four on their rear paws. The dewclaw is proximal to the other claws. More proximally is a protrusion which appears to be a sixth "finger". This special feature of the front paws, on the inside of the wrists has no function in normal walking, but is thought to be an antiskidding device used while jumping. Some cat breeds are prone to having extra digits (“polydactyly”).[68] Polydactylous cats occur along North America's northeast coast and in Great Britain.[69]
+
+Cats have excellent night vision and can see at only one-sixth the light level required for human vision.[60]:43 This is partly the result of cat eyes having a tapetum lucidum, which reflects any light that passes through the retina back into the eye, thereby increasing the eye's sensitivity to dim light.[70] Large pupils are an adaptation to dim light. The domestic cat has slit pupils, which allow it to focus bright light without chromatic aberration.[71] At low light, a cat's pupils expand to cover most of the exposed surface of its eyes.[72] However, the domestic cat has rather poor color vision and only two types of cone cells, optimized for sensitivity to blue and yellowish green; its ability to distinguish between red and green is limited.[73] A response to middle wavelengths from a system other than the rod cells might be due to a third type of cone. However, this appears to be an adaptation to low light levels rather than representing true trichromatic vision.[74]
+
+The domestic cat's hearing is most acute in the range of 500 Hz to 32 kHz.[75] It can detect an extremely broad range of frequencies ranging from 55 Hz to 79,000 Hz. It can hear a range of 10.5 octaves, while humans and dogs can hear ranges of about 9 octaves.[76][77]
+Its hearing sensitivity is enhanced by its large movable outer ears, the pinnae, which amplify sounds and help detect the location of a noise. It can detect ultrasound, which enables it to detect ultrasonic calls made by rodent prey.[78][79]
+
+Cats have an acute sense of smell, due in part to their well-developed olfactory bulb and a large surface of olfactory mucosa, about 5.8 square centimetres (29⁄32 square inch) in area, which is about twice that of humans.[80] Cats and many other animals have a Jacobson's organ in their mouths that is used in the behavioral process of flehmening. It allows them to sense certain aromas in a way that humans cannot. Cats are sensitive to pheromones such as 3-mercapto-3-methylbutan-1-ol,[81] which they use to communicate through urine spraying and marking with scent glands.[82] Many cats also respond strongly to plants that contain nepetalactone, especially catnip, as they can detect that substance at less than one part per billion.[83] About 70–80% of cats are affected by nepetalactone.[84] This response is also produced by other plants, such as silver vine (Actinidia polygama) and the herb valerian; it may be caused by the smell of these plants mimicking a pheromone and stimulating cats' social or sexual behaviors.[85]
+
+Cats have relatively few taste buds compared to humans (470 or so versus more than 9,000 on the human tongue).[86] Domestic and wild cats share a taste receptor gene mutation that keeps their sweet taste buds from binding to sugary molecules, leaving them with no ability to taste sweetness.[87] Their taste buds instead respond to acids, amino acids like protein, and bitter tastes.[88] Cats also have a distinct temperature preference for their food, preferring food with a temperature around 38 °C (100 °F) which is similar to that of a fresh kill and routinely rejecting food presented cold or refrigerated (which would signal to the cat that the "prey" item is long dead and therefore possibly toxic or decomposing).[86]
+
+To aid with navigation and sensation, cats have dozens of movable whiskers (vibrissae) over their body, especially their faces. These provide information on the width of gaps and on the location of objects in the dark, both by touching objects directly and by sensing air currents; they also trigger protective blink reflexes to protect the eyes from damage.[60]:47
+
+Most breeds of cat have a noted fondness for sitting in high places, or perching. A higher place may serve as a concealed site from which to hunt; domestic cats strike prey by pouncing from a perch such as a tree branch. Another possible explanation is that height gives the cat a better observation point, allowing it to survey its territory. A cat falling from heights of up to 3 meters can right itself and land on its paws.[89]
+During a fall from a high place, a cat reflexively twists its body and rights itself to land on its feet using its acute sense of balance and flexibility. This reflex is known as the cat righting reflex.[90]
+An individual cat always rights itself in the same way during a fall, provided it has sufficient time to do so. The height required for this to occur is around 90 cm (2 ft 11 in).[91]
+Several explanations have been proposed for this phenomenon since the late 19th century:
+
+Outdoor cats are active both day and night, although they tend to be slightly more active at night.[95] Domestic cats spend the majority of their time in the vicinity of their homes, but can range many hundreds of meters from this central point. They establish territories that vary considerably in size, in one study ranging from 7 to 28 hectares (17–69 acres).[96] The timing of cats' activity is quite flexible and varied, which means house cats may be more active in the morning and evening, as a response to greater human activity at these times.[97]
+
+Cats conserve energy by sleeping more than most animals, especially as they grow older. The daily duration of sleep varies, usually between 12 and 16 hours, with 13 and 14 being the average. Some cats can sleep as much as 20 hours. The term "cat nap" for a short rest refers to the cat's tendency to fall asleep (lightly) for a brief period. While asleep, cats experience short periods of rapid eye movement sleep often accompanied by muscle twitches, which suggests they are dreaming.[98]
+
+The social behavior of the domestic cat ranges from widely dispersed individuals to feral cat colonies that gather around a food source, based on groups of co-operating females.[99][100] Within such groups, one cat is usually dominant over the others.[101] Each cat in a colony holds a distinct territory, with sexually active males having the largest territories, which are about 10 times larger than those of female cats and may overlap with several females' territories. These territories are marked by urine spraying, by rubbing objects at head height with secretions from facial glands, and by defecation.[82] Between these territories are neutral areas where cats watch and greet one another without territorial conflicts. Outside these neutral areas, territory holders usually chase away stranger cats, at first by staring, hissing, and growling and, if that does not work, by short but noisy and violent attacks. Despite some cats cohabiting in colonies, they do not have a social survival strategy, or a pack mentality and always hunt alone.[102]
+
+However, some pet cats are poorly socialized. In particular, older cats show aggressiveness towards newly arrived kittens, which include biting and scratching; this type of behavior is known as feline asocial aggression.[103]
+
+Life in proximity to humans and other domestic animals has led to a symbiotic social adaptation in cats, and cats may express great affection toward humans or other animals. Ethologically, the human keeper of a cat functions as a sort of surrogate for the cat's mother.[104] Adult cats live their lives in a kind of extended kittenhood, a form of behavioral neoteny. Their high-pitched sounds may mimic the cries of a hungry human infant, making them particularly difficult for humans to ignore.[105]
+
+Domestic cats' scent rubbing behavior towards humans or other cats is thought to be a feline means for social bonding.[106]
+
+Domestic cats use many vocalizations for communication, including purring, trilling, hissing, growling/snarling, grunting, and several different forms of meowing.[7] Their body language, including position of ears and tail, relaxation of the whole body, and kneading of the paws, are all indicators of mood. The tail and ears are particularly important social signal mechanisms in cats. A raised tail indicates a friendly greeting, and flattened ears indicates hostility. Tail-raising also indicates the cat's position in the group's social hierarchy, with dominant individuals raising their tails less often than subordinate ones.[107] Feral cats are generally silent.[108]:208 Nose-to-nose touching is also a common greeting and may be followed by social grooming, which is solicited by one of the cats raising and tilting its head.[100]
+
+Purring may have developed as an evolutionary advantage as a signalling mechanism of reassurance between mother cats and nursing kittens. Post-nursing cats often purr as a sign of contentment: when being petted, becoming relaxed,[109][110] or eating. The mechanism by which cats purr is elusive. The cat has no unique anatomical feature that is clearly responsible for the sound.[111]
+
+Cats are known for spending considerable amounts of time licking their coats to keep them clean.[112] The cat's tongue has backwards-facing spines about 500 μm long, which are called papillae. These contain keratin which makes them rigid[113] so the papillae act like a hairbrush. Some cats, particularly longhaired cats, occasionally regurgitate hairballs of fur that have collected in their stomachs from grooming. These clumps of fur are usually sausage-shaped and about 2–3 cm (3⁄4–1 1⁄4 in) long. Hairballs can be prevented with remedies that ease elimination of the hair through the gut, as well as regular grooming of the coat with a comb or stiff brush.[112]
+
+Among domestic cats, males are more likely to fight than females.[114] Among feral cats, the most common reason for cat fighting is competition between two males to mate with a female. In such cases, most fights are won by the heavier male.[115] Another common reason for fighting in domestic cats is the difficulty of establishing territories within a small home.[114] Female cats also fight over territory or to defend their kittens. Neutering will decrease or eliminate this behavior in many cases, suggesting that the behavior is linked to sex hormones.[116]
+
+When cats become aggressive, they try to make themselves appear larger and more threatening by raising their fur, arching their backs, turning sideways and hissing or spitting.[117] Often, the ears are pointed down and back to avoid damage to the inner ear and potentially listen for any changes behind them while focused forward. They may also vocalize loudly and bare their teeth in an effort to further intimidate their opponent. Fights usually consist of grappling and delivering powerful slaps to the face and body with the forepaws as well as bites. Cats also throw themselves to the ground in a defensive posture to rake their opponent's belly with their powerful hind legs.[118]
+
+Serious damage is rare, as the fights are usually short in duration, with the loser running away with little more than a few scratches to the face and ears. However, fights for mating rights are typically more severe and injuries may include deep puncture wounds and lacerations. Normally, serious injuries from fighting are limited to infections of scratches and bites, though these can occasionally kill cats if untreated. In addition, bites are probably the main route of transmission of feline immunodeficiency virus.[119] Sexually active males are usually involved in many fights during their lives, and often have decidedly battered faces with obvious scars and cuts to their ears and nose.[120]
+
+The shape and structure of cats' cheeks is insufficient to suck. They lap with the tongue to draw liquid upwards into their mouths. Lapping at a rate of four times a second, the cat touches the smooth tip of its tongue to the surface of the water, and quickly retracts it like a corkscrew, drawing water upwards.[121][122]
+
+Feral cats and free-fed house cats consume several small meals in a day. The frequency and size of meals varies between individuals. They select food based on its temperature, smell and texture; they dislike chilled foods and respond most strongly to moist foods rich in amino acids, which are similar to meat. Cats reject novel flavors (a response termed neophobia) and learn quickly to avoid foods that have tasted unpleasant in the past.[102][123] They also avoid sweet food and milk. Most adult cats are lactose intolerant; the sugar in milk is not easily digested and may cause soft stools or diarrhea.[124] Some also develop odd eating habits and like to eat or chew on things like wool, plastic, cables, paper, string, aluminum foil, or even coal. This condition, pica, can threaten their health, depending on the amount and toxicity of the items eaten.[125]
+
+Cats hunt small prey, primarily birds and rodents,[126] and are often used as a form of pest control.[127][128] Cats use two hunting strategies, either stalking prey actively, or waiting in ambush until an animal comes close enough to be captured.[129] The strategy used depends on the prey species in the area, with cats waiting in ambush outside burrows, but tending to actively stalk birds.[130]:153 Domestic cats are a major predator of wildlife in the United States, killing an estimated 1.4 to 3.7 billion birds and 6.9 to 20.7 billion mammals annually.[131]
+Certain species appear more susceptible than others; for example, 30% of house sparrow mortality is linked to the domestic cat.[132] In the recovery of ringed robins (Erithacus rubecula) and dunnocks (Prunella modularis), 31% of deaths were a result of cat predation.[133] In parts of North America, the presence of larger carnivores such as coyotes which prey on cats and other small predators reduces the effect of predation by cats and other small predators such as opossums and raccoons on bird numbers and variety.[134]
+
+Perhaps the best-known element of cats' hunting behavior, which is commonly misunderstood and often appalls cat owners because it looks like torture, is that cats often appear to "play" with prey by releasing it after capture. This cat and mouse behavior is due to an instinctive imperative to ensure that the prey is weak enough to be killed without endangering the cat.[135]
+Another poorly understood element of cat hunting behavior is the presentation of prey to human guardians. One explanation is that cats adopt humans into their social group and share excess kill with others in the group according to the dominance hierarchy, in which humans are reacted to as if they are at, or near, the top.[136] Another explanation is that they attempt to teach their guardians to hunt or to help their human as if feeding "an elderly cat, or an inept kitten".[137] This hypothesis is inconsistent with the fact that male cats also bring home prey, despite males having negligible involvement in raising kittens.[130]:153
+
+On islands, birds can contribute as much as 60% of a cat's diet.[138] In nearly all cases, however, the cat cannot be identified as the sole cause for reducing the numbers of island birds, and in some instances, eradication of cats has caused a "mesopredator release" effect;[139] where the suppression of top carnivores creates an abundance of smaller predators that cause a severe decline in their shared prey. Domestic cats are, however, known to be a contributing factor to the decline of many species, a factor that has ultimately led, in some cases, to extinction. The South Island piopio, Chatham rail,[133] and the New Zealand merganser[140] are a few from a long list, with the most extreme case being the flightless Lyall's wren, which was driven to extinction only a few years after its discovery.[141][142]
+One feral cat in New Zealand killed 102 New Zealand lesser short-tailed bats in seven days.[143] In the US, feral and free-ranging domestic cats kill an estimated 6.3 – 22.3 billion mammals annually.[131]
+
+In Australia, the impact of cats on mammal populations is even greater than the impact of habitat loss.[144] More than one million reptiles are killed by feral cats each day, representing 258 species.[145] Cats have contributed to the extinction of the Navassa curly-tailed lizard and Chioninia coctei.[146]
+
+Domestic cats, especially young kittens, are known for their love of play. This behavior mimics hunting and is important in helping kittens learn to stalk, capture, and kill prey.[147] Cats also engage in play fighting, with each other and with humans. This behavior may be a way for cats to practice the skills needed for real combat, and might also reduce any fear they associate with launching attacks on other animals.[148]
+
+Cats also tend to play with toys more when they are hungry.[149] Owing to the close similarity between play and hunting, cats prefer to play with objects that resemble prey, such as small furry toys that move rapidly, but rapidly lose interest. They become habituated to a toy they have played with before.[150] String is often used as a toy, but if it is eaten, it can become caught at the base of the cat's tongue and then move into the intestines, a medical emergency which can cause serious illness, even death.[151] Owing to the risks posed by cats eating string, it is sometimes replaced with a laser pointer's dot, which cats may chase.[152]
+
+Female cats called queens are polyestrous with several estrus cycles during a year, lasting usually 21 days. They are usually ready to mate between early February and August.[153]
+
+Several males, called tomcats, are attracted to a female in heat. They fight over her, and the victor wins the right to mate. At first, the female rejects the male, but eventually, the female allows the male to mate. The female utters a loud yowl as the male pulls out of her because a male cat's penis has a band of about 120–150 backward-pointing penile spines, which are about 1 mm (1⁄32 in) long; upon withdrawal of the penis, the spines rake the walls of the female's vagina, which acts to induce ovulation. This act also occurs to clear the vagina of other sperm in the context of a second (or more) mating, thus giving the later males a larger chance of conception.[154]
+
+After mating, the female cleans her vulva thoroughly. If a male attempts to mate with her at this point, the female attacks him. After about 20 to 30 minutes, once the female is finished grooming, the cycle will repeat.[155]
+Because ovulation is not always triggered by a single mating, females may not be impregnated by the first male with which they mate.[156] Furthermore, cats are superfecund; that is, a female may mate with more than one male when she is in heat, with the result that different kittens in a litter may have different fathers.[155]
+
+The morula forms 124 hours after conception. At 148 hours, early blastocysts form. At 10–12 days, implantation occurs.[157]
+The gestation of queens lasts between 64 and 67 days, with an average of 65 days.[153][158]
+Data on the reproductive capacity of more than 2,300 free-ranging queens were collected during a study between May 1998 and October 2000. They had one to six kittens per litter, with an average of three kittens. They produced a mean of 1.4 litters per year, but a maximum of three litters in a year. Of 169 kittens, 127 died before they were six months old due to a trauma caused in most cases by dog attacks and road accidents.[9]
+The first litter is usually smaller than subsequent litters. Kittens are weaned between six and seven weeks of age. Queens normally reach sexual maturity at 5–10 months, and males at 5–7 months. This varies depending on breed.[155] Kittens reach puberty at the age of 9–10 months.[153]
+
+Cats are ready to go to new homes at about 12 weeks of age, when they are ready to leave their mother.[159] They can be surgically sterilized (spayed or castrated) as early as seven weeks to limit unwanted reproduction.[160] This surgery also prevents undesirable sex-related behavior, such as aggression, territory marking (spraying urine) in males and yowling (calling) in females. Traditionally, this surgery was performed at around six to nine months of age, but it is increasingly being performed before puberty, at about three to six months.[161] In the United States, about 80% of household cats are neutered.[162]
+
+The average lifespan of pet cats has risen in recent decades. In the early 1980s, it was about seven years,[163]:33[164] rising to 9.4 years in 1995[163]:33 and 15.1 years in 2018.[165] Some cats have been reported as surviving into their 30s,[166] with the oldest known cat, Creme Puff, dying at a verified age of 38.[167]
+
+Spaying or neutering increases life expectancy: one study found neutered male cats live twice as long as intact males, while spayed female cats live 62% longer than intact females.[163]:35 Having a cat neutered confers health benefits, because castrated males cannot develop testicular cancer, spayed females cannot develop uterine or ovarian cancer, and both have a reduced risk of mammary cancer.[168]
+
+Despite widespread concern about the welfare of free-roaming cats, the lifespans of neutered feral cats in managed colonies compare favorably with those of pet cats.[169]:45[170]:1358[171][172][173][174]
+
+About two hundred fifty heritable genetic disorders have been identified in cats, many similar to human inborn errors of metabolism.[175] The high level of similarity among the metabolism of mammals allows many of these feline diseases to be diagnosed using genetic tests that were originally developed for use in humans, as well as the use of cats as animal models in the study of the human diseases.[176][177]
+Diseases affecting domestic cats include acute infections, parasitic infestations, injuries, and chronic diseases such as kidney disease, thyroid disease, and arthritis. Vaccinations are available for many infectious diseases, as are treatments to eliminate parasites such as worms and fleas.[178]
+
+The domestic cat is a cosmopolitan species and occurs across much of the world.[55] It is adaptable and now present on all continents except Antarctica, and on 118 of the 131 main groups of islands—even on isolated islands such as the Kerguelen Islands.[179][180]
+Due to its ability to thrive in almost any terrestrial habitat, it is among the world's most invasive species.[181]
+As it is little altered from the wildcat, it can readily interbreed with the wildcat. This hybridization poses a danger to the genetic distinctiveness of some wildcat populations, particularly in Scotland and Hungary and possibly also the Iberian Peninsula.[52] It lives on small islands with no human inhabitants.[182]
+Feral cats can live in forests, grasslands, tundra, coastal areas, agricultural land, scrublands, urban areas, and wetlands.[183]
+
+Feral cats are domestic cats that were born in or have reverted to a wild state. They are unfamiliar with and wary of humans and roam freely in urban and rural areas.[10] The numbers of feral cats is not known, but estimates of the United States feral population range from twenty-five to sixty million.[10] Feral cats may live alone, but most are found in large colonies, which occupy a specific territory and are usually associated with a source of food.[184] Famous feral cat colonies are found in Rome around the Colosseum and Forum Romanum, with cats at some of these sites being fed and given medical attention by volunteers.[185]
+
+Public attitudes towards feral cats vary widely, ranging from seeing them as free-ranging pets, to regarding them as vermin.[186] One common approach to reducing the feral cat population is termed "trap-neuter-return", where the cats are trapped, neutered, immunized against diseases such as rabies and the feline panleukopenia and leukemia viruses, and then released.[187] Before releasing them back into their feral colonies, the attending veterinarian often nips the tip off one ear to mark it as neutered and inoculated, since these cats may be trapped again. Volunteers continue to feed and give care to these cats throughout their lives. Given this support, their lifespans are increased, and behavior and nuisance problems caused by competition for food are reduced.[184]
+
+Some feral cats can be successfully socialised and 're-tamed' for adoption; young cats, especially kittens[188] and cats that have had prior experience and contact with humans are the most receptive to these efforts.
+
+Cats are common pets throughout the world, and their worldwide population exceeds 500 million as of 2007.[189] Cats have been used for millennia to control rodents, notably around grain stores and aboard ships, and both uses extend to the present day.[190][191]
+
+As well as being kept as pets, cats are also used in the international fur[192] and leather industries for making coats, hats, blankets, and stuffed toys;[193] and shoes, gloves, and musical instruments respectively[194] (about 24 cats are needed to make a cat-fur coat).[195] This use has been outlawed in the United States, Australia, and the European Union in 2007.[196] Cat pelts have been used for superstitious purposes as part of the practise of witchcraft,[197] and are still made into blankets in Switzerland as folk remedies believed to help rheumatism.[198] In the Western intellectual tradition, the idea of cats as everyday objects have served to illustrate problems of quantum mechanics in the Schrödinger's cat thought experiment.
+
+A few attempts to build a cat census have been made over the years, both through associations or national and international organizations (such as the Canadian Federation of Humane Societies's one[199]) and over the Internet,[200][201] but such a task does not seem simple to achieve. General estimates for the global population of domestic cats range widely from anywhere between 200 million to 600 million.[202][203][204][205][206]
+Walter Chandoha made his career photographing cats after his 1949 images of Loco, an especially charming stray taken in, were published around the world. He is reported to have photographed 90,000 cats during his career and maintained an archive of 225,000 images that he drew from for publications during his lifetime.[207]
+
+A cat show is a judged event in which the owners of cats compete to win titles in various cat-registering organizations by entering their cats to be judged after a breed standard.[208][209] Both pedigreed and non-purebred companion ("moggy") cats are admissible, although the rules differ from organization to organization.  Competing cats are compared to the applicable breed standard,[210] and assessed for temperament and apparent health; the owners of those judged to be most ideal awarded a prize. Moggies are judged based on their temperament and healthy appearance. Some events also include activity judging, such as trained navigation of obstacle course.  Often, at the end of the year, all of the points accrued at various shows are added up and more national and regional titles are awarded to champion cats.
+
+Cats can be infected or infested with viruses, bacteria, fungus, protozoans, arthropods or worms that can transmit diseases to humans.[211] In some cases, the cat exhibits no symptoms of the disease,[212] However, the same disease can then become evident in a human.  The likelihood that a person will become diseased depends on the age and immune status of the person. Humans who have cats living in their home or in close association are more likely to become infected, however, those who do not keep cats as pets might also acquire infections from cat feces and parasites exiting the cat's body.[211][213] Some of the infections of most concern include salmonella, cat-scratch disease and toxoplasmosis.[212]
+
+In ancient Egypt, cats were worshipped, and the goddess Bastet often depicted in cat form, sometimes taking on the war-like aspect of a lioness. The Greek historian Herodotus reported that killing a cat was forbidden, and when a household cat died, the entire family mourned and shaved their eyebrows. Families took their dead cats to the sacred city of Bubastis, where they were embalmed and buried in sacred repositories. Herodotus expressed astonishment at the domestic cats in Egypt, because he had only ever seen wildcats.[214]
+Ancient Greeks and Romans kept weasels as pets, which were seen as the ideal rodent-killers. The earliest unmistakable evidence of the Greeks having domestic cats comes from two coins from Magna Graecia dating to the mid-fifth century BC showing Iokastos and Phalanthos, the legendary founders of Rhegion and Taras respectively, playing with their pet cats. The usual ancient Greek word for 'cat' was ailouros, meaning 'thing with the waving tail'. Cats are rarely mentioned in ancient Greek literature. Aristotle remarked in his History of Animals that "female cats are naturally lecherous." The Greeks later syncretized their own goddess Artemis with the Egyptian goddess Bastet, adopting Bastet's associations with cats and ascribing them to Artemis. In Ovid's Metamorphoses, when the deities flee to Egypt and take animal forms, the goddess Diana turns into a cat.[215][216] Cats eventually displaced ferrets as the pest control of choice because they were more pleasant to have around the house and were more enthusiastic hunters of mice. During the Middle Ages, many of Artemis's associations with cats were grafted onto the Virgin Mary. Cats are often shown in icons of Annunciation and of the Holy Family and, according to Italian folklore, on the same night that Mary gave birth to Jesus, a cat in Bethlehem gave birth to a kitten.[217] Domestic cats were spread throughout much of the rest of the world during the Age of Discovery, as ships' cats were carried on sailing ships to control shipboard rodents and as good-luck charms.[46]
+
+Several ancient religions believed cats are exalted souls, companions or guides for humans, that are all-knowing but mute so they cannot influence decisions made by humans. In Japan, the maneki neko cat is a symbol of good fortune.[218] In Norse mythology, Freyja, the goddess of love, beauty, and fertility, is depicted as riding a chariot drawn by cats.[219] In Jewish legend, the first cat was living in the house of the first man Adam as a pet that got rid of mice. The cat was once partnering with the first dog before the latter broke an oath they had made which resulted in enmity between the descendants of these two animals. It is also written that neither cats nor foxes are represented in the water, while every other animal has an incarnation species in the water.[220] Although no species are sacred in Islam, cats are revered by Muslims. Some Western writers have stated Muhammad had a favorite cat, Muezza.[221] He is reported to have loved cats so much, "he would do without his cloak rather than disturb one that was sleeping on it".[222] The story has no origin in early Muslim writers, and seems to confuse a story of a later Sufi saint, Ahmed ar-Rifa'i, centuries after Muhammad.[223] One of the companions of Muhammad was known as Abu Hurayrah ("father of the kitten"), in reference to his documented affection to cats.[224]
+
+Many cultures have negative superstitions about cats. An example would be the belief that a black cat "crossing one's path" leads to bad luck, or that cats are witches' familiars used to augment a witch's powers and skills. The killing of cats in Medieval Ypres, Belgium, is commemorated in the innocuous present-day Kattenstoet (cat parade).[225] In medieval France, cats would be burnt alive as a form of entertainment. According to Norman Davies, the assembled people "shrieked with laughter as the animals, howling with pain, were singed, roasted, and finally carbonized".[226]
+
+"It was the custom to burn a basket, barrel, or sack full of live cats, which was hung from a tall mast in the midst of the bonfire; sometimes a fox was burned. The people collected the embers and ashes of the fire and took them home, believing that they brought good luck. The French kings often witnessed these spectacles and even lit the bonfire with their own hands. In 1648 Louis XIV, crowned with a wreath of roses and carrying a bunch of roses in his hand, kindled the fire, danced at it and partook of the banquet afterwards in the town hall. But this was the last occasion when a monarch presided at the midsummer bonfire in Paris. At Metz midsummer fires were lighted with great pomp on the esplanade, and a dozen cats, enclosed in wicker cages, were burned alive in them, to the amusement of the people. Similarly at Gap, in the department of the Hautes-Alpes, cats used to be roasted over the midsummer bonfire."[227]
+
+According to a myth in many cultures, cats have multiple lives. In many countries, they are believed to have nine lives, but in Italy, Germany, Greece, Brazil and some Spanish-speaking regions, they are said to have seven lives,[228][229] while in Turkish and Arabic traditions, the number of lives is six.[230] The myth is attributed to the natural suppleness and swiftness cats exhibit to escape life-threatening situations. Also lending credence to this myth is the fact that falling cats often land on their feet, using an instinctive righting reflex to twist their bodies around. Nonetheless, cats can still be injured or killed by a high fall.[231]

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+German (Deutsch, pronounced [dɔʏtʃ] (listen)) is a West Germanic language that is mainly spoken in Central Europe. It is the most widely spoken and official or co-official language in Germany, Austria, Switzerland, South Tyrol in Italy, the German-speaking Community of Belgium, and Liechtenstein. It is one of the three official languages of Luxembourg and a co-official language in the Opole Voivodeship in Poland. The German language is most similar to other languages within the West Germanic language branch, including Afrikaans, Dutch, English, the Frisian languages, Low German/Low Saxon, Luxembourgish, and Yiddish. It also contains close similarities in vocabulary to Danish, Norwegian and Swedish, although they belong to the North Germanic group. German is the second most widely spoken Germanic language, after English.
+
+One of the major languages of the world, German is a native language to almost 100 million people worldwide and the most widely spoken native language in the European Union.[6] German is the third most commonly spoken foreign language in the EU after English and French, making it the second biggest language in the EU in terms of overall speakers. German is also the second most widely taught foreign language in the EU after English at primary school level (but third after English and French at lower secondary level), the fourth most widely taught non-English language in the US (after Spanish, French and American Sign Language), the second most commonly used scientific language and the third most widely used language on websites after English and Russian. The German-speaking countries are ranked fifth in terms of annual publication of new books, with one tenth of all books (including e-books) in the world being published in German. In the United Kingdom, German and French are the most sought-after foreign languages for businesses (with 49% and 50% of businesses identifying these two languages as the most useful, respectively).[7]
+
+German is an inflected language with four cases for nouns, pronouns and adjectives (nominative, accusative, genitive, dative), three genders (masculine, feminine, neuter), two numbers (singular, plural), and strong and weak verbs. It derives the majority of its vocabulary from the ancient Germanic branch of the Indo-European language family. Some of its vocabulary is derived from Latin and Greek, and fewer are borrowed from French and Modern English. German is a pluricentric language, with its standardized variants being (German, Austrian, and Swiss Standard German). It is also notable for its broad spectrum of dialects, with many unique varieties existing in Europe and other parts of the world. Italy recognizes all the German-speaking minorities in its territory as national historic minorities and protects the varieties of German spoken in several regions of Northern Italy besides South Tyrol.[8][9] Due to the limited intelligibility between certain varieties and Standard German, as well as the lack of an undisputed, scientific difference between a "dialect" and a "language", some German varieties or dialect groups (e.g. Low German or Plautdietsch[3]) can be described as either "languages" or "dialects".
+
+Modern Standard German is a West Germanic language in the Germanic branch of the Indo-European languages. The Germanic languages are traditionally subdivided into three branches: North Germanic, East Germanic, and West Germanic. The first of these branches survives in modern Danish, Swedish, Norwegian, Faroese, and Icelandic, all of which are descended from Old Norse. The East Germanic languages are now extinct, and Gothic is the only language in this branch which survives in written texts. The West Germanic languages, however, have undergone extensive dialectal subdivision and are now represented in modern languages such as English, German, Dutch, Yiddish, Afrikaans, and others.[10]
+
+Within the West Germanic language dialect continuum, the Benrath and Uerdingen lines (running through Düsseldorf-Benrath and Krefeld-Uerdingen, respectively) serve to distinguish the Germanic dialects that were affected by the High German consonant shift (south of Benrath) from those that were not (north of Uerdingen). The various regional dialects spoken south of these lines are grouped as High German dialects (nos. 29–34 on the map), while those spoken to the north comprise the Low German/Low Saxon (nos. 19–24) and Low Franconian (no. 25) dialects. As members of the West Germanic language family, High German, Low German, and Low Franconian can be further distinguished historically as Irminonic, Ingvaeonic, and Istvaeonic, respectively. This classification indicates their historical descent from dialects spoken by the Irminones (also known as the Elbe group), Ingvaeones (or North Sea Germanic group), and Istvaeones (or Weser-Rhine group).[10]
+
+Standard German is based on a combination of Thuringian-Upper Saxon and Upper Franconian and Bavarian dialects, which are Central German and Upper German dialects, belonging to the Irminonic High German dialect group (nos. 29–34). German is therefore closely related to the other languages based on High German dialects, such as Luxembourgish (based on Central Franconian dialects – no. 29), and Yiddish. Also closely related to Standard German are the Upper German dialects spoken in the southern German-speaking countries, such as Swiss German (Alemannic dialects – no. 34), and the various Germanic dialects spoken in the French region of Grand Est, such as Alsatian (mainly Alemannic, but also Central- and Upper Franconian (no. 32) dialects) and Lorraine Franconian (Central Franconian – no. 29).
+
+After these High German dialects, standard German is less closely related to languages based on Low Franconian dialects (e.g. Dutch and Afrikaans) or Low German/Low Saxon dialects (spoken in northern Germany and southern Denmark), neither of which underwent the High German consonant shift. As has been noted, the former of these dialect types is Istvaeonic and the latter Ingvaeonic, whereas the High German dialects are all Irminonic: the differences between these languages and standard German are therefore considerable. Also related to German are the Frisian languages—North Frisian (spoken in Nordfriesland – no. 28), Saterland Frisian (spoken in Saterland – no. 27), and West Frisian (spoken in Friesland – no. 26)—as well as the Anglic languages of English and Scots. These Anglo-Frisian dialects are all members of the Ingvaeonic family of West Germanic languages, which did not take part in the High German consonant shift.
+
+The history of the German language begins with the High German consonant shift during the migration period, which separated Old High German (OHG) dialects from Old Saxon. This sound shift involved a drastic change in the pronunciation of both voiced and voiceless stop consonants (b, d, g, and p, t, k, respectively). The primary effects of the shift were the following:
+
+While there is written evidence of the Old High German language in several Elder Futhark inscriptions from as early as the 6th century AD (such as the Pforzen buckle), the Old High German period is generally seen as beginning with the Abrogans (written c.765–775), a Latin-German glossary supplying over 3,000 OHG words with their Latin equivalents. After the Abrogans, the first coherent works written in OHG appear in the 9th century, chief among them being the Muspilli, the Merseburg Charms, and the Hildebrandslied, as well as a number of other religious texts (the Georgslied, the Ludwigslied, the Evangelienbuch, and translated hymns and prayers).[11][12] The Muspilli is a Christian poem written in a Bavarian dialect offering an account of the soul after the Last Judgment, and the Merseburg Charms are transcriptions of spells and charms from the pagan Germanic tradition. Of particular interest to scholars, however, has been the Hildebrandslied, a secular epic poem telling the tale of an estranged father and son unknowingly meeting each other in battle. Linguistically this text is highly interesting due to the mixed use of Old Saxon and Old High German dialects in its composition. The written works of this period stem mainly from the Alamanni, Bavarian, and Thuringian groups, all belonging to the Elbe Germanic group (Irminones), which had settled in what is now southern-central Germany and Austria between the 2nd and 6th centuries during the great migration.[11]
+
+In general, the surviving texts of OHG show a wide range of dialectal diversity with very little written uniformity. The early written tradition of OHG survived mostly through monasteries and scriptoria as local translations of Latin originals; as a result, the surviving texts are written in highly disparate regional dialects and exhibit significant Latin influence, particularly in vocabulary.[11] At this point monasteries, where most written works were produced, were dominated by Latin, and German saw only occasional use in official and ecclesiastical writing.
+
+The German language through the OHG period was still predominantly a spoken language, with a wide range of dialects and a much more extensive oral tradition than a written one. Having just emerged from the High German consonant shift, OHG was also a relatively new and volatile language still undergoing a number of phonetic, phonological, morphological, and syntactic changes. The scarcity of written work, instability of the language, and widespread illiteracy of the time explain the lack of standardization up to the end of the OHG period in 1050.
+
+While there is no complete agreement over the dates of the Middle High German (MHG) period, it is generally seen as lasting from 1050 to 1350.[13][14] This was a period of significant expansion of the geographical territory occupied by Germanic tribes, and consequently of the number of German speakers. Whereas during the Old High German period the Germanic tribes extended only as far east as the Elbe and Saale rivers, the MHG period saw a number of these tribes expanding beyond this eastern boundary into Slavic territory (known as the Ostsiedlung). With the increasing wealth and geographic spread of the Germanic groups came greater use of German in the courts of nobles as the standard language of official proceedings and literature.[14][15] A clear example of this is the mittelhochdeutsche Dichtersprache employed in the Hohenstaufen court in Swabia as a standardized supra-dialectal written language. While these efforts were still regionally bound, German began to be used in place of Latin for certain official purposes, leading to a greater need for regularity in written conventions.
+
+While the major changes of the MHG period were socio-cultural, German was still undergoing significant linguistic changes in syntax, phonetics, and morphology as well (e.g. diphthongization of certain vowel sounds: hus (OHG "house")→haus (MHG), and weakening of unstressed short vowels to schwa [ə]: taga (OHG "days")→tage (MHG)).[16]
+
+A great wealth of texts survives from the MHG period. Significantly, these texts include a number of impressive secular works, such as the Nibelungenlied, an epic poem telling the story of the dragon-slayer Siegfried (c. 13th century), and the Iwein, an Arthurian verse poem by Hartmann von Aue (c. 1203), as well as several lyric poems and courtly romances such as Parzival and Tristan. Also noteworthy is the Sachsenspiegel, the first book of laws written in Middle Low German (c. 1220). The abundance and especially the secular character of the literature of the MHG period demonstrate the beginnings of a standardized written form of German, as well as the desire of poets and authors to be understood by individuals on supra-dialectal terms.
+
+The Middle High German period is generally seen as ending when the 1346-53 Black Death decimated Europe's population.[13]
+
+Modern German begins with the Early New High German (ENHG) period, which the influential German philologist Wilhelm Scherer dates 1350–1650, terminating with the end of the Thirty Years' War.[13] This period saw the further displacement of Latin by German as the primary language of courtly proceedings and, increasingly, of literature in the German states. While these states were still under the control of the Holy Roman Empire and far from any form of unification, the desire for a cohesive written language that would be understandable across the many German-speaking principalities and kingdoms was stronger than ever. As a spoken language German remained highly fractured throughout this period, with a vast number of often mutually incomprehensible regional dialects being spoken throughout the German states; the invention of the printing press c. 1440 and the publication of Luther's vernacular translation of the Bible in 1534, however, had an immense effect on standardizing German as a supra-dialectal written language.
+
+The ENHG period saw the rise of several important cross-regional forms of chancery German, one being gemeine tiutsch, used in the court of the Holy Roman Emperor Maximilian I, and the other being Meißner Deutsch, used in the Electorate of Saxony in the Duchy of Saxe-Wittenberg.[17] Alongside these courtly written standards, the invention of the printing press led to the development of a number of printers' languages (Druckersprachen) aimed at making printed material readable and understandable across as many diverse dialects of German as possible.[18] The greater ease of production and increased availability of written texts brought about increased standardization in the written form of German.
+
+One of the central events in the development of ENHG was the publication of Luther's translation of the Bible into German (the New Testament was published in 1522; the Old Testament was published in parts and completed in 1534). Luther based his translation primarily on the Meißner Deutsch of Saxony, spending much time among the population of Saxony researching the dialect so as to make the work as natural and accessible to German speakers as possible. Copies of Luther's Bible featured a long list of glosses for each region, translating words which were unknown in the region into the regional dialect. Luther said the following concerning his translation method:
+
+One who would talk German does not ask the Latin how he shall do it; he must ask the mother in the home, the children on the streets, the common man in the market-place and note carefully how they talk, then translate accordingly. They will then understand what is said to them because it is German. When Christ says 'ex abundantia cordis os loquitur,' I would translate, if I followed the papists, aus dem Überflusz des Herzens redet der Mund. But tell me is this talking German? What German understands such stuff? No, the mother in the home and the plain man would say, Wesz das Herz voll ist, des gehet der Mund über.[19]
+
+With Luther's rendering of the Bible in the vernacular, German asserted itself against the dominance of Latin as a legitimate language for courtly, literary, and now ecclesiastical subject-matter. Furthermore, his Bible was ubiquitous in the German states: nearly every household possessed a copy.[20] Nevertheless, even with the influence of Luther's Bible as an unofficial written standard, a widely accepted standard for written German did not appear until the middle of the 18th century.[21]
+
+German was the language of commerce and government in the Habsburg Empire, which encompassed a large area of Central and Eastern Europe. Until the mid-19th century, it was essentially the language of townspeople throughout most of the Empire. Its use indicated that the speaker was a merchant or someone from an urban area, regardless of nationality.
+
+Some cities, such as Prague (German: Prag) and Budapest (Buda, German: Ofen), were gradually Germanized in the years after their incorporation into the Habsburg domain. Others, such as Pozsony (German: Pressburg, now Bratislava), were originally settled during the Habsburg period and were primarily German at that time. Prague, Budapest and Bratislava, as well as cities like Zagreb (German: Agram) and Ljubljana (German: Laibach), contained significant German minorities.
+
+In the eastern provinces of Banat, Bukovina, and Transylvania (German: Banat, Buchenland, Siebenbürgen), German was the predominant language not only in the larger towns – such as Temeschburg (Timișoara), Hermannstadt (Sibiu) and Kronstadt (Brașov) – but also in many smaller localities in the surrounding areas.[22]
+
+The most comprehensive guide to the vocabulary of the German language is found within the Deutsches Wörterbuch. This dictionary was created by the Brothers Grimm and is composed of 16 parts which were issued between 1852 and 1860.[23] In 1872, grammatical and orthographic rules first appeared in the Duden Handbook.[24]
+
+In 1901, the 2nd Orthographical Conference ended with a complete standardization of the German language in its written form and the Duden Handbook was declared its standard definition.[25] The Deutsche Bühnensprache (literally, German stage language) had established conventions for German pronunciation in theatres (Bühnendeutsch[26]) three years earlier; however, this was an artificial standard that did not correspond to any traditional spoken dialect. Rather, it was based on the pronunciation of Standard German in Northern Germany, although it was subsequently regarded often as a general prescriptive norm, despite differing pronunciation traditions especially in the Upper-German-speaking regions that still characterize the dialect of the area today – especially the pronunciation of the ending -ig as [ɪk] instead of [ɪç]. In Northern Germany, Standard German was a foreign language to most inhabitants, whose native dialects were subsets of Low German. It was usually encountered only in writing or formal speech; in fact, most of Standard German was a written language, not identical to any spoken dialect, throughout the German-speaking area until well into the 19th century.
+
+Official revisions of some of the rules from 1901 were not issued until the controversial German orthography reform of 1996 was made the official standard by governments of all German-speaking countries.[27] Media and written works are now almost all produced in Standard German (often called Hochdeutsch, "High German") which is understood in all areas where German is spoken.
+
+Approximate distribution of native German speakers (assuming a rounded total of 95 million) worldwide
+
+Due to the German diaspora as well as German being the second most widely spoken language in Europe and the third most widely taught foreign language in the US[28] and the EU (in upper secondary education)[29] amongst others, the geographical distribution of German speakers (or "Germanophones") spans all inhabited continents. As for the number of speakers of any language worldwide, an assessment is always compromised by the lack of sufficient, reliable data. For an exact, global number of native German speakers, this is further complicated by the existence of several varieties whose status as separate "languages" or "dialects" is disputed for political and/or linguistic reasons, including quantitatively strong varieties like certain forms of Alemannic (e.g., Alsatian) and Low German/Plautdietsch.[3] Depending on the inclusion or exclusion of certain varieties, it is estimated that approximately 90–95 million people speak German as a first language,[30][31] 10–25 million as a second language,[30] and 75–100 million as a foreign language.[1] This would imply the existence of approximately 175–220 million German speakers worldwide.[32] It is estimated that including every person studying German, regardless of their actual proficiency, would amount to about 280 million people worldwide with at least some knowledge of German.
+
+In Europe, German is the second most widely spoken mother tongue (after Russian) and the second biggest language in terms of overall speakers (after English). The area in central Europe where the majority of the population speaks German as a first language and has German as a (co-)official language is called the "German Sprachraum". It comprises an estimated 88 million native speakers and 10 million who speak German as a second language (e.g. immigrants).[30] Excluding regional minority languages, German is the only official language of the following countries:
+
+German is a co-official language of the following countries:
+
+Although expulsions and (forced) assimilation after the two World Wars greatly diminished them, minority communities of mostly bilingual German native speakers exist in areas both adjacent to and detached from the Sprachraum.
+
+Within Europe and Asia, German is a recognized minority language in the following countries:
+
+In France, the High German varieties of Alsatian and Moselle Franconian are identified as "regional languages", but the European Charter for Regional and Minority Languages of 1998 has not yet been ratified by the government.[39] In the Netherlands, the Limburgish, Frisian, and Low German languages are protected regional languages according to the European Charter for Regional and Minority Languages;[33] however, they are widely considered separate languages and neither German nor Dutch dialects.
+
+Namibia was a colony of the German Empire from 1884 to 1919. Mostly descending from German settlers who immigrated during this time, 25–30,000 people still speak German as a native tongue today.[40] The period of German colonialism in Namibia also led to the evolution of a Standard German-based pidgin language called "Namibian Black German", which became a second language for parts of the indigenous population. Although it is nearly extinct today, some older Namibians still have some knowledge of it.[41]
+
+German, along with English and Afrikaans, was a co-official language of Namibia from 1984 until its independence from South Africa in 1990. At this point, the Namibian government perceived Afrikaans and German as symbols of apartheid and colonialism, and decided English would be the sole official language, stating that it was a "neutral" language as there were virtually no English native speakers in Namibia at that time.[40] German, Afrikaans and several indigenous languages became "national languages" by law, identifying them as elements of the cultural heritage of the nation and ensuring that the state acknowledged and supported their presence in the country. Today, German is used in a wide variety of spheres, especially business and tourism, as well as the churches (most notably the German-speaking Evangelical Lutheran Church in Namibia (GELK)), schools (e.g. the Deutsche Höhere Privatschule Windhoek), literature (German-Namibian authors include Giselher W. Hoffmann), radio (the Namibian Broadcasting Corporation produces radio programs in German), and music (e.g. artist EES). The Allgemeine Zeitung is one of the three biggest newspapers in Namibia and the only German-language daily in Africa.[40]
+
+Mostly originating from different waves of immigration during the 19th and 20th centuries, an estimated 12,000 people speak German or a German variety as a first language in South Africa.[42] One of the largest communities consists of the speakers of "Nataler Deutsch",[43] a variety of Low German concentrated in and around Wartburg. The small town of Kroondal in the North-West Province also has a mostly German-speaking population. The South African constitution identifies German as a "commonly used" language and the Pan South African Language Board is obligated to promote and ensure respect for it.[44] The community is strong enough that several German International schools are supported, such as the Deutsche Schule Pretoria.
+
+In the United States, the states of North Dakota and South Dakota are the only states where German is the most common language spoken at home after English.[45] German geographical names can be found throughout the Midwest region of the country, such as New Ulm and many other towns in Minnesota; Bismarck (North Dakota's state capital), Munich, Karlsruhe, and Strasburg (named after a town near Odessa in Ukraine)[46] in North Dakota; New Braunfels, Fredericksburg, Weimar, and Muenster in Texas; Corn (formerly Korn), Kiefer and Berlin in Oklahoma; and Kiel, Berlin, and Germantown in Wisconsin.
+
+In Brazil, the largest concentrations of German speakers are in the states of Rio Grande do Sul (where Riograndenser Hunsrückisch developed), Santa Catarina, Paraná, São Paulo and Espírito Santo.[47]
+
+There are important concentrations of German-speaking descendants in Argentina, Chile, Paraguay, Venezuela, Peru, and Bolivia.[42]
+
+The impact of nineteenth century German immigration to southern Chile was such that Valdivia was for a while a Spanish-German bilingual city with "German signboards and placards alongside the Spanish".[54] The prestige[note 4] the German language caused it to acquire qualities of a superstratum in southern Chile.[56] The word for blackberry, a ubiquitous plant in southern Chile, is murra, instead of the ordinary Spanish words mora and zarzamora, from Valdivia to the Chiloé Archipelago and in some towns in the Aysén Region.[56] The use of rr is an adaptation of guttural sounds found in German but difficult to pronounce in Spanish.[56] Similarly the name for marbles, a traditional children's game, is different in Southern Chile compared to areas further north. From Valdivia to the Aysén Region this game is called bochas, in contrast to the word bolitas used further north.[56] The word bocha is likely a derivative of the German Bocciaspiel.[56]
+
+In Australia, the state of South Australia experienced a pronounced wave of immigration in the 1840s from Prussia (particularly the Silesia region). With the prolonged isolation from other German speakers and contact with Australian English, a unique dialect known as Barossa German developed, spoken predominantly in the Barossa Valley near Adelaide. Usage of German sharply declined with the advent of World War I, due to the prevailing anti-German sentiment in the population and related government action. It continued to be used as a first language into the 20th century, but its use is now limited to a few older speakers.[57]
+
+German migration to New Zealand in the 19th century was less pronounced than migration from Britain, Ireland, and perhaps even Scandinavia. Despite this there were significant pockets of German-speaking communities which lasted until the first decades of the 20th century. German speakers settled principally in Puhoi, Nelson, and Gore. At the last census (2013), 36,642 people in New Zealand spoke German, making it the third most spoken European language after English and French and overall the ninth most spoken language.[58]
+
+There is also an important German creole being studied and recovered, named Unserdeutsch, spoken in the former German colony of German New Guinea, across Micronesia and in northern Australia (i.e. coastal parts of Queensland and Western Australia) by a few elderly people. The risk of its extinction is serious and efforts to revive interest in the language are being implemented by scholars.[59]
+
+Like French and Spanish, German has become a standard second foreign language in the western world.[1][60] German ranks second (after English) among the best known foreign languages in the EU (on a par with French)[1] as well as in Russia.[61] In terms of student numbers across all levels of education, German ranks third in the EU (after English and French)[29] as well as in the United States (after Spanish and French).[28][62] In 2015, approximately 15.4 million people were in the process of learning German across all levels of education worldwide.[60] As this number remained relatively stable since 2005 (± 1 million), roughly 75–100 million people able to communicate in German as a foreign language can be inferred, assuming an average course duration of three years and other estimated parameters. According to a 2012 survey, 47 million people within the EU (i.e., up to two-thirds of the 75–100 million worldwide) claimed to have sufficient German skills to have a conversation. Within the EU, not counting countries where it is an official language, German as a foreign language is most popular in Eastern and northern Europe, namely the Czech Republic, Croatia, Denmark, the Netherlands, Slovakia, Hungary, Slovenia, Sweden and Poland.[1][63] German was once, and to some extent still is, a lingua franca in those parts of Europe.[64]
+
+The basis of Standard German is the Luther Bible, which was translated by Martin Luther and which had originated from the Saxon court language (it being a convenient norm).[65] However, there are places where the traditional regional dialects have been replaced by new vernaculars based on standard German; that is the case in large stretches of Northern Germany but also in major cities in other parts of the country. It is important to note, however, that the colloquial standard German differs greatly from the formal written language, especially in grammar and syntax, in which it has been influenced by dialectal speech.
+
+Standard German differs regionally among German-speaking countries in vocabulary and some instances of pronunciation and even grammar and orthography. This variation must not be confused with the variation of local dialects. Even though the regional varieties of standard German are only somewhat influenced by the local dialects, they are very distinct. German is thus considered a pluricentric language.
+
+In most regions, the speakers use a continuum from more dialectal varieties to more standard varieties depending on the circumstances.
+
+In German linguistics, German dialects are distinguished from varieties of standard German.
+The varieties of standard German refer to the different local varieties of the pluricentric standard German. They differ only slightly in lexicon and phonology. In certain regions, they have replaced the traditional German dialects, especially in Northern Germany.
+
+In the German-speaking parts of Switzerland, mixtures of dialect and standard are very seldom used, and the use of Standard German is largely restricted to the written language. About 11% of the Swiss residents speak High German (Standard German) at home, but this is mainly due to German immigrants.[67] This situation has been called a medial diglossia. Swiss Standard German is used in the Swiss education system, while Austrian Standard German is officially used in the Austrian education system.
+
+A mixture of dialect and standard does not normally occur in Northern Germany either. The traditional varieties there are Low German, whereas Standard German is a High German "variety". Because their linguistic distance is greater, they do not mesh with Standard German the way that High German dialects (such as Bavarian, Swabian, and Hessian) can.
+
+The German dialects are the traditional local varieties of the language; many of them are not mutually intelligibile with standard German, and they have great differences in lexicon, phonology, and syntax. If a narrow definition of language based on mutual intelligibility is used, many German dialects are considered to be separate languages (for instance in the Ethnologue). However, such a point of view is unusual in German linguistics.
+
+The German dialect continuum is traditionally divided most broadly into High German and Low German, also called Low Saxon. However, historically, High German dialects and Low Saxon/Low German dialects do not belong to the same language. Nevertheless, in today's Germany, Low Saxon/Low German is often perceived as a dialectal variation of Standard German on a functional level even by many native speakers. The same phenomenon is found in the eastern Netherlands, as the traditional dialects are not always identified with their Low Saxon/Low German origins, but with Dutch.[68][better source needed]
+
+The variation among the German dialects is considerable, with often only neighbouring dialects being mutually intelligible. Some dialects are not intelligible to people who know only Standard German. However, all German dialects belong to the dialect continuum of High German and Low Saxon.
+
+Middle Low German was the lingua franca of the Hanseatic League. It was the predominant language in Northern Germany until the 16th century. In 1534, the Luther Bible was published. The translation is considered to be an important step towards the evolution of the Early New High German. It aimed to be understandable to a broad audience and was based mainly on Central and Upper German varieties. The Early New High German language gained more prestige than Low German and became the language of science and literature. Around the same time, the Hanseatic League, based around northern ports, lost its importance as new trade routes to Asia and the Americas were established, and the most powerful German states of that period were located in Middle and Southern Germany.
+
+The 18th and 19th centuries were marked by mass education in Standard German in schools. Gradually, Low German came to be politically viewed as a mere dialect spoken by the uneducated. Today, Low Saxon can be divided in two groups: Low Saxon varieties with a reasonable level of Standard German influence and varieties of Standard German with a Low Saxon influence known as Missingsch. Sometimes, Low Saxon and Low Franconian varieties are grouped together because both are unaffected by the High German consonant shift. However, the proportion of the population who can understand and speak it has decreased continuously since World War II. The largest cities in the Low German area are Hamburg and Dortmund.
+
+The Low Franconian dialects are the dialects that are more closely related to Dutch than to Low German. Most of the Low Franconian dialects are spoken in the Netherlands and Belgium, where they are considered as dialects of Dutch, which is itself a Low Franconian language. In Germany, Low Franconian dialects are spoken in the northwest of North Rhine-Westphalia, along the Lower Rhine. The Low Franconian dialects spoken in Germany are referred to as Meuse-Rhenish or Low Rhenish. In the north of the German Low Franconian language area, North Low Franconian dialects (also referred to as Cleverlands or as dialects of South Guelderish) are spoken. These dialects are more closely related to Dutch (also North Low Franconian) than the South Low Franconian dialects (also referred to as East Limburgish and, east of the Rhine, Bergish), which are spoken in the south of the German Low Franconian language area. The South Low Franconian dialects are more closely related to Limburgish than to Dutch, and are transitional dialects between Low Franconian and Ripuarian (Central Franconian). The East Bergish dialects are the easternmost Low Franconian dialects, and are transitional dialects between North- and South Low Franconian, and Westphalian (Low German), with most of their features being North Low Franconian. The largest cities in the German Low Franconian area are Düsseldorf and Duisburg.
+
+The High German dialects consist of the Central German, High Franconian, and Upper German dialects. The High Franconian dialects are transitional dialects between Central and Upper German. The High German varieties spoken by the Ashkenazi Jews have several unique features and are considered as a separate language, Yiddish, written with the Hebrew alphabet.
+
+The Central German dialects are spoken in Central Germany, from Aachen in the west to Görlitz in the east. They consist of Franconian dialects in the west (West Central German) and non-Franconian dialects in the east (East Central German). Modern Standard German is mostly based on Central German dialects.
+
+The Franconian, West Central German dialects are the Central Franconian dialects (Ripuarian and Moselle Franconian) and the Rhine Franconian dialects (Hessian and Palatine). These dialects are considered as
+
+Luxembourgish as well as the Transylvanian Saxon dialect spoken in Transylvania are based on Moselle Franconian dialects. The largest cities in the Franconian Central German area are Cologne and Frankfurt.
+
+Further east, the non-Franconian, East Central German dialects are spoken (Thuringian, Upper Saxon, Ore Mountainian, and Lusatian-New Markish, and earlier, in the then German-speaking parts of Silesia also Silesian, and in then German southern East Prussia also High Prussian). The largest cities in the East Central German area are Berlin and Leipzig.
+
+The High Franconian dialects are transitional dialects between Central and Upper German. They consist of the East and South Franconian dialects.
+
+The East Franconian dialect branch is one of the most spoken dialect branches in Germany. These dialects are spoken in the region of Franconia and in the central parts of Saxon Vogtland. Franconia consists of the Bavarian districts of Upper, Middle, and Lower Franconia, the region of South Thuringia (Thuringia), and the eastern parts of the region of Heilbronn-Franken (Tauber Franconia and Hohenlohe) in Baden-Württemberg. The largest cities in the East Franconian area are Nuremberg and Würzburg.
+
+South Franconian is mainly spoken in northern Baden-Württemberg in Germany, but also in the northeasternmost part of the region of Alsace in France. While these dialects are considered as dialects of German in Baden-Württemberg, they are considered as dialects of Alsatian in Alsace (most Alsatian dialects are Low Alemannic, however). The largest cities in the South Franconian area are Karlsruhe and Heilbronn.
+
+The Upper German dialects are the Alemannic dialects in the west and the Bavarian dialects in the east.
+
+Alemannic dialects are spoken in Switzerland (High Alemannic in the densely populated Swiss Plateau, in the south also Highest Alemannic, and Low Alemannic in Basel), Baden-Württemberg (Swabian and Low Alemannic, in the southwest also High Alemannic), Bavarian Swabia (Swabian, in the southwesternmost part also Low Alemannic), Vorarlberg (Low, High, and Highest Alemannic), Alsace (Low Alemannic, in the southernmost part also High Alemannic), Liechtenstein (High and Highest Alemannic), and in the Tyrolean district of Reutte (Swabian). The Alemannic dialects are considered as Alsatian in Alsace. The largest cities in the Alemannic area are Stuttgart and Zürich.
+
+Bavarian dialects are spoken in Austria (Vienna, Lower and Upper Austria, Styria, Carinthia, Salzburg, Burgenland, and in most parts of Tyrol), Bavaria (Upper and Lower Bavaria as well as Upper Palatinate), South Tyrol, southwesternmost Saxony (Southern Vogtlandian), and in the Swiss village of Samnaun. The largest cities in the Bavarian area are Vienna and Munich.
+
+German is a fusional language with a moderate degree of inflection, with three grammatical genders; as such, there can be a large number of words derived from the same root.
+
+German nouns inflect by case, gender, and number:
+
+This degree of inflection is considerably less than in Old High German and other old Indo-European languages such as Latin, Ancient Greek, and Sanskrit, and it is also somewhat less than, for instance, Old English, modern Icelandic, or Russian. The three genders have collapsed in the plural. With four cases and three genders plus plural, there are 16 permutations of case and gender/number of the article (not the nouns), but there are only six forms of the definite article, which together cover all 16 permutations. In nouns, inflection for case is required in the singular for strong masculine and neuter nouns only in the genitive and in the dative (only in fixed or archaic expressions), and even this is losing ground to substitutes in informal speech.[69] The singular dative noun ending is considered archaic or at least old-fashioned in almost all contexts and is almost always dropped in writing, except in poetry, songs, proverbs, and other petrified forms. Weak masculine nouns share a common case ending for genitive, dative, and accusative in the singular. Feminine nouns are not declined in the singular. The plural has an inflection for the dative. In total, seven inflectional endings (not counting plural markers) exist in German: -s, -es, -n, -ns, -en, -ens, -e.
+
+In German orthography, nouns and most words with the syntactical function of nouns are capitalised to make it easier for readers to determine the function of a word within a sentence (Am Freitag ging ich einkaufen. – "On Friday I went shopping."; Eines Tages kreuzte er endlich auf. – "One day he finally showed up.") This convention is almost unique to German today (shared perhaps only by the closely related Luxembourgish language and several insular dialects of the North Frisian language), but it was historically common in other languages such as Danish (which abolished the capitalization of nouns in 1948) and English.
+
+Like the other Germanic languages, German forms noun compounds in which the first noun modifies the category given by the second: Hundehütte ("dog hut"; specifically: "dog kennel"). Unlike English, whose newer compounds or combinations of longer nouns are often written "open" with separating spaces, German (like some other Germanic languages) nearly always uses the "closed" form without spaces, for example: Baumhaus ("tree house"). Like English, German allows arbitrarily long compounds in theory (see also English compounds). The longest German word verified to be actually in (albeit very limited) use is Rindfleischetikettierungsüberwachungsaufgabenübertragungsgesetz, which, literally translated, is "beef labelling supervision duties assignment law" [from Rind (cattle), Fleisch (meat), Etikettierung(s) (labelling), Überwachung(s) (supervision), Aufgaben (duties), Übertragung(s) (assignment), Gesetz (law)]. However, examples like this are perceived by native speakers as excessively bureaucratic, stylistically awkward, or even satirical.
+
+The inflection of standard German verbs includes:
+
+The meaning of basic verbs can be expanded and sometimes radically changed through the use of a number of prefixes. Some prefixes have a specific meaning; the prefix zer- refers to destruction, as in zerreißen (to tear apart), zerbrechen (to break apart), zerschneiden (to cut apart). Other prefixes have only the vaguest meaning in themselves; ver- is found in a number of verbs with a large variety of meanings, as in versuchen (to try) from suchen (to seek), vernehmen (to interrogate) from nehmen (to take), verteilen (to distribute) from teilen (to share), verstehen (to understand) from stehen (to stand).
+
+Other examples include the following:
+haften (to stick), verhaften (to detain); kaufen (to buy), verkaufen (to sell); hören (to hear), aufhören (to cease); fahren (to drive), erfahren (to experience).
+
+Many German verbs have a separable prefix, often with an adverbial function. In finite verb forms, it is split off and moved to the end of the clause and is hence considered by some to be a "resultative particle". For example, mitgehen, meaning "to go along", would be split, giving Gehen Sie mit? (Literal: "Go you with?"; Idiomatic: "Are you going along?").
+
+Indeed, several parenthetical clauses may occur between the prefix of a finite verb and its complement (ankommen = to arrive, er kam an = he arrived, er ist angekommen = he has arrived):
+
+A selectively literal translation of this example to illustrate the point might look like this:
+
+German word order is generally with the V2 word order restriction and also with the SOV word order restriction for main clauses. For polar questions, exclamations, and wishes, the finite verb always has the first position. In subordinate clauses, the verb occurs at the very end.
+
+German requires a verbal element (main verb or auxiliary verb) to appear second in the sentence. The verb is preceded by the topic of the sentence. The element in focus appears at the end of the sentence. For a sentence without an auxiliary, these are several possibilities:
+
+The position of a noun in a German sentence has no bearing on its being a subject, an object or another argument. In a declarative sentence in English, if the subject does not occur before the predicate, the sentence could well be misunderstood.
+
+However, German's flexible word order allows one to emphasise specific words:
+
+Normal word order:
+
+Object in front:
+
+Adverb of time in front:
+
+Both time expressions in front:
+
+Another possibility:
+
+Swapped adverbs:
+
+Swapped object:
+
+The flexible word order also allows one to use language "tools" (such as poetic meter and figures of speech) more freely.
+
+When an auxiliary verb is present, it appears in second position, and the main verb appears at the end. This occurs notably in the creation of the perfect tense. Many word orders are still possible:
+
+The main verb may appear in first position to put stress on the action itself. The auxiliary verb is still in second position.
+
+Sentences using modal verbs place the infinitive at the end. For example, the English sentence "Should he go home?" would be rearranged in German to say "Should he (to) home go?" (Soll er nach Hause gehen?). Thus, in sentences with several subordinate or relative clauses, the infinitives are clustered at the end. Compare the similar clustering of prepositions in the following (highly contrived) English sentence: "What did you bring that book that I do not like to be read to out of up for?"
+
+German subordinate clauses have all verbs clustered at the end. Given that auxiliaries encode future, passive, modality, and the perfect, very long chains of verbs at the end of the sentence can occur. In these constructions, the past participle formed with ge- is often replaced by the infinitive.
+
+The order at the end of such strings is subject to variation, but the second one in the last example is unusual.
+
+Most German vocabulary is derived from the Germanic branch of the Indo-European language family.[70] However, there is a significant amount of loanwords from other languages, in particular Latin, Greek, Italian, French, and most recently English.[71] In the early 19th century, Joachim Heinrich Campe estimated that one fifth of the total German vocabulary was of French or Latin origin.[72]
+
+Latin words were already imported into the predecessor of the German language during the Roman Empire and underwent all the characteristic phonetic changes in German. Their origin is thus no longer recognizable for most speakers (e.g. Pforte, Tafel, Mauer, Käse, Köln from Latin porta, tabula, murus, caseus, Colonia). Borrowing from Latin continued after the fall of the Roman Empire during Christianization, mediated by the church and monasteries. Another important influx of Latin words can be observed during Renaissance humanism. In a scholarly context, the borrowings from Latin have continued until today, in the last few decades often indirectly through borrowings from English. During the 15th to 17th centuries, the influence of Italian was great, leading to many Italian loanwords in the fields of architecture, finance, and music. The influence of the French language in the 17th to 19th centuries resulted in an even greater import of French words. The English influence was already present in the 19th century, but it did not become dominant until the second half of the 20th century.
+
+Thus, Notker Labeo was able to translate Aristotelian treatises into pure (Old High) German in the decades after the year 1000.[73] The tradition of loan translation was revitalized in the 18th century with linguists like Joachim Heinrich Campe, who introduced close to 300 words that are still used in modern German. Even today, there are movements that try to promote the Ersatz (substitution) of foreign words that are deemed unnecessary with German alternatives.[74] It is claimed that this would also help in spreading modern or scientific notions among the less educated and as well democratise public life.
+
+As in English, there are many pairs of synonyms due to the enrichment of the Germanic vocabulary with loanwords from Latin and Latinized Greek. These words often have different connotations from their Germanic counterparts and are usually perceived as more scholarly.
+
+The size of the vocabulary of German is difficult to estimate. The Deutsches Wörterbuch (German Dictionary) initiated by Jacob and Wilhelm Grimm already contained over 330,000 headwords in its first edition. The modern German scientific vocabulary is estimated at nine million words and word groups (based on the analysis of 35 million sentences of a corpus in Leipzig, which as of July 2003 included 500 million words in total).[75]
+
+The Duden is the de facto official dictionary of the German language, first published by Konrad Duden in 1880. The Duden is updated regularly, with new editions appearing every four or five years. As of August 2017[update], it was in its 27th edition and in 12 volumes, each covering different aspects such as loanwords, etymology, pronunciation, synonyms, and so forth.The first of these volumes, Die deutsche Rechtschreibung (German Orthography), has long been the prescriptive source for the spelling of German. The Duden has become the bible of the German language, being the definitive set of rules regarding grammar, spelling and usage of German.[76]
+
+The Österreichisches Wörterbuch ("Austrian Dictionary"), abbreviated ÖWB, is the official dictionary of the German language in the Republic of Austria. It is edited by a group of linguists under the authority of the Austrian Federal Ministry of Education, Arts and Culture (German: Bundesministerium für Unterricht, Kunst und Kultur). It is the Austrian counterpart to the German Duden and contains a number of terms unique to Austrian German or more frequently used or differently pronounced there.[77] A considerable amount of this "Austrian" vocabulary is also common in Southern Germany, especially Bavaria, and some of it is used in Switzerland as well. Since the 39th edition in 2001 the orthography of the ÖWB has been adjusted to the German spelling reform of 1996. The dictionary is also officially used in the Italian province of South Tyrol.
+
+This is a selection of cognates in both English and German. Instead of the usual infinitive ending -en, German verbs are indicated by a hyphen after their stems. Words that are written with capital letters in German are nouns.
+
+German is written in the Latin alphabet. In addition to the 26 standard letters, German has three vowels with an umlaut mark, namely ä, ö and ü, as well as the eszett or scharfes s (sharp s): ß. In Switzerland and Liechtenstein, ss is used instead of ß. Since ß can never occur at the beginning of a word, it has no traditional uppercase form.
+
+Written texts in German are easily recognisable as such by distinguishing features such as umlauts and certain orthographical features – German is the only major language that capitalizes all nouns, a relic of a widespread practice in Northern Europe in the early modern era (including English for a while, in the 1700s) – and the frequent occurrence of long compounds. Because legibility and convenience set certain boundaries, compounds consisting of more than three or four nouns are almost exclusively found in humorous contexts. (In contrast, although English can also string nouns together, it usually separates the nouns with spaces. For example, "toilet bowl cleaner".)
+
+Before the German orthography reform of 1996, ß replaced ss after long vowels and diphthongs and before consonants, word-, or partial-word endings. In reformed spelling, ß replaces ss only after long vowels and diphthongs.
+
+Since there is no traditional capital form of ß, it was replaced by SS when capitalization was required. For example, Maßband (tape measure) became MASSBAND in capitals. An exception was the use of ß in legal documents and forms when capitalizing names. To avoid confusion with similar names, lower case ß was maintained (thus "KREßLEIN" instead of "KRESSLEIN"). Capital ß (ẞ) was ultimately adopted into German orthography in 2017, ending a long orthographic debate (thus "KREẞLEIN and KRESSLEIN").[78]
+
+Umlaut vowels (ä, ö, ü) are commonly transcribed with ae, oe, and ue if the umlauts are not available on the keyboard or other medium used. In the same manner ß can be transcribed as ss. Some operating systems use key sequences to extend the set of possible characters to include, amongst other things, umlauts; in Microsoft Windows this is done using Alt codes. German readers understand these transcriptions (although they appear unusual), but they are avoided if the regular umlauts are available, because they are a makeshift and not proper spelling. (In Westphalia and Schleswig-Holstein, city and family names exist where the extra e has a vowel lengthening effect, e.g. Raesfeld [ˈraːsfɛlt], Coesfeld [ˈkoːsfɛlt] and Itzehoe [ɪtsəˈhoː], but this use of the letter e after a/o/u does not occur in the present-day spelling of words other than proper nouns.)
+
+There is no general agreement on where letters with umlauts occur in the sorting sequence. Telephone directories treat them by replacing them with the base vowel followed by an e. Some dictionaries sort each umlauted vowel as a separate letter after the base vowel, but more commonly words with umlauts are ordered immediately after the same word without umlauts. As an example in a telephone book Ärzte occurs after Adressenverlage but before Anlagenbauer (because Ä is replaced by Ae). In a dictionary Ärzte comes after Arzt, but in some dictionaries Ärzte and all other words starting with Ä may occur after all words starting with A. In some older dictionaries or indexes, initial Sch and St are treated as separate letters and are listed as separate entries after S, but they are usually treated as S+C+H and S+T.
+
+Written German also typically uses an alternative opening inverted comma (quotation mark) as in "Guten Morgen!".
+
+Until the early 20th century, German was mostly printed in blackletter typefaces (mostly in Fraktur, but also in Schwabacher) and written in corresponding handwriting (for example Kurrent and Sütterlin). These variants of the Latin alphabet are very different from the serif or sans-serif Antiqua typefaces used today, and the handwritten forms in particular are difficult for the untrained to read. The printed forms, however, were claimed by some to be more readable when used for Germanic languages.[79] (Often, foreign names in a text were printed in an Antiqua typeface even though the rest of the text was in Fraktur.) The Nazis initially promoted Fraktur and Schwabacher because they were considered Aryan, but they abolished them in 1941, claiming that these letters were Jewish.[80] It is also believed that the Nazi régime had banned this script as they realized that Fraktur would inhibit communication in the territories occupied during World War II.[81]
+
+The Fraktur script however remains present in everyday life in pub signs, beer brands and other forms of advertisement, where it is used to convey a certain rusticality and antiquity.
+
+A proper use of the long s (langes s), ſ, is essential for writing German text in Fraktur typefaces. Many Antiqua typefaces also include the long s. A specific set of rules applies for the use of long s in German text, but nowadays it is rarely used in Antiqua typesetting. Any lower case "s" at the beginning of a syllable would be a long s, as opposed to a terminal s or short s (the more common variation of the letter s), which marks the end of a syllable; for example, in differentiating between the words Wachſtube (guard-house) and Wachstube (tube of polish/wax). One can easily decide which "s" to use by appropriate hyphenation, (Wach-ſtube vs. Wachs-tube). The long s only appears in lower case.
+
+The orthography reform of 1996 led to public controversy and considerable dispute. The states (Bundesländer) of North Rhine-Westphalia and Bavaria refused to accept it. At one point, the dispute reached the highest court, which quickly dismissed it, claiming that the states had to decide for themselves and that only in schools could the reform be made the official rule – everybody else could continue writing as they had learned it. After 10 years, without any intervention by the federal parliament, a major revision was installed in 2006, just in time for the coming school year. In 2007, some traditional spellings were finally invalidated; however, in 2008, many of the old comma rules were again put in force.
+
+The most noticeable change was probably in the use of the letter ß, called scharfes s (Sharp S) or ess-zett (pronounced ess-tsett). Traditionally, this letter was used in three situations:
+
+Examples are Füße, paßt, and daß. Currently, only the first rule is in effect, making the correct spellings Füße, passt, and dass. The word Fuß 'foot' has the letter ß because it contains a long vowel, even though that letter occurs at the end of a syllable. The logic of this change is that an 'ß' is a single letter whereas 'ss' are two letters, so the same distinction applies as (for example) between the words den and denn.
+
+In German, vowels (excluding diphthongs; see below) are either short or long, as follows:
+
+Short /ɛ/ is realized as [ɛ] in stressed syllables (including secondary stress), but as [ə] in unstressed syllables. Note that stressed short /ɛ/ can be spelled either with e or with ä (for instance, hätte 'would have' and Kette 'chain' rhyme). In general, the short vowels are open and the long vowels are close. The one exception is the open /ɛː/ sound of long Ä; in some varieties of standard German, /ɛː/ and /eː/ have merged into [eː], removing this anomaly. In that case, pairs like Bären/Beeren 'bears/berries' or Ähre/Ehre 'spike (of wheat)/honour' become homophonous (see: Captain Bluebear).
+
+In many varieties of standard German, an unstressed /ɛr/ is not pronounced [ər] but vocalised to [ɐ].
+
+Whether any particular vowel letter represents the long or short phoneme is not completely predictable, although the following regularities exist:
+
+Both of these rules have exceptions (e.g. hat [hat] "has" is short despite the first rule; Mond [moːnt] "moon" is long despite the second rule). For an i that is neither in the combination ie (making it long) nor followed by a double consonant or cluster (making it short), there is no general rule. In some cases, there are regional differences. In central Germany (Hesse), the o in the proper name "Hoffmann" is pronounced long, whereas most other Germans would pronounce it short. The same applies to the e in the geographical name "Mecklenburg" for people in that region. The word Städte "cities" is pronounced with a short vowel [ˈʃtɛtə] by some (Jan Hofer, ARD Television) and with a long vowel [ˈʃtɛːtə] by others (Marietta Slomka, ZDF Television). Finally, a vowel followed by ch can be short (Fach [fax] "compartment", Küche [ˈkʏçə] "kitchen") or long (Suche [ˈzuːxə] "search", Bücher [ˈbyːçɐ] "books") almost at random. Thus, Lache is homographous between [laːxə] Lache "puddle" and [laxə] Lache "manner of laughing" (colloquial) or lache! "laugh!" (imperative).
+
+German vowels can form the following digraphs (in writing) and diphthongs (in pronunciation); note that the pronunciation of some of them (ei, äu, eu) is very different from what one would expect when considering the component letters:
+
+Additionally, the digraph ie generally represents the phoneme /iː/, which is not a diphthong. In many varieties, an /r/ at the end of a syllable is vocalised. However, a sequence of a vowel followed by such a vocalised /r/ is not a phonemic diphthong: Bär [bɛːɐ̯] "bear", er [eːɐ̯] "he", wir [viːɐ̯] "we", Tor [toːɐ̯] "gate", kurz [kʊɐ̯ts] "short", Wörter [vœɐ̯tɐ] "words".
+
+In most varieties of standard German, syllables that begin with a vowel are preceded by a glottal stop [ʔ].
+
+With approximately 26 phonemes, the German consonant system exhibits an average number of consonants in comparison with other languages. One of the more noteworthy ones is the unusual affricate /p͡f/. The consonant inventory of the standard language is shown below.
+
+German does not have any dental fricatives (as English th). The th sound, which the English language still has, disappeared on the continent in German with the consonant shifts between the 8th and 10th centuries.[83] It is sometimes possible to find parallels between English and German by replacing the English th with d in German: "Thank" → in German Dank, "this" and "that" → dies and das, "thou" (old 2nd person singular pronoun) → du, "think" → denken, "thirsty" → durstig and many other examples.
+
+Likewise, the gh in Germanic English words, pronounced in several different ways in modern English (as an f or not at all), can often be linked to German ch: "to laugh" → lachen, "through" → durch, "high" → hoch, "naught" → nichts, "light" → leicht or Licht, "sight" → Sicht, "daughter" → Tochter, "neighbour" → Nachbar.
+
+The German language is used in German literature and can be traced back to the Middle Ages, with the most notable authors of the period being Walther von der Vogelweide and Wolfram von Eschenbach.
+The Nibelungenlied, whose author remains unknown, is also an important work of the epoch. The fairy tales collected and published by Jacob and Wilhelm Grimm in the 19th century became famous throughout the world.
+
+Reformer and theologian Martin Luther, who was the first to translate the Bible into German, is widely credited for having set the basis for the modern "High German" language. Among the best-known poets and authors in German are Lessing, Goethe, Schiller, Kleist, Hoffmann, Brecht, Heine, and Kafka. Fourteen German-speaking people have won the Nobel Prize in literature: Theodor Mommsen, Rudolf Christoph Eucken, Paul von Heyse, Gerhart Hauptmann, Carl Spitteler, Thomas Mann, Nelly Sachs, Hermann Hesse, Heinrich Böll, Elias Canetti, Günter Grass, Elfriede Jelinek, Herta Müller and Peter Handke, making it the second most awarded linguistic region (together with French) after English.
+
+English has taken many loanwords from German, often without any change of spelling (aside from frequently eliminating umlauts and not capitalizing nouns):
+
+Several organisations promote the use and learning of the German language:
+
+The government-backed Goethe-Institut[85] (named after Johann Wolfgang von Goethe) aims to enhance the knowledge of German culture and language within Europe and the rest of the world. This is done by holding exhibitions and conferences with German-related themes, and providing training and guidance in the learning and use of the German language. For example, the Goethe-Institut teaches the Goethe-Zertifikat German language qualification.
+
+The Dortmund-based Verein Deutsche Sprache (VDS), founded in 1997, supports the German language and is the largest language association of citizens in the world. The VDS has more than thirty-five thousand members in over seventy countries. Its founder, statistics professor Dr. Walter Krämer, has remained chairperson of the association from its formation.[86]
+
+The German state broadcaster Deutsche Welle provides radio and television broadcasts in German and 30 other languages across the globe.[87] Its German language services are spoken slowly and thus tailored for learners. Deutsche Welle also provides an e-learning website for teaching German.

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+
+Niagara Falls /naɪˈæɡrə, naɪˈæɡərə/ is a group of three waterfalls at the southern end of Niagara Gorge, spanning the border between the province of Ontario in Canada and the state of New York in the United States. The largest of the three is Horseshoe Falls, also known as Canadian Falls, which straddles the international border of the two countries.[1] The smaller American Falls and Bridal Veil Falls lie within the United States. Bridal Veil Falls are separated from Horseshoe Falls by Goat Island and from American Falls by Luna Island, with both islands situated in New York.
+
+Located on the Niagara River, which drains Lake Erie into Lake Ontario, the combined falls have the highest flow rate of any waterfall in North America that has a vertical drop of more than 50 metres (160 ft). During peak daytime tourist hours, more than 168,000 m3  (six million cubic feet) of water goes over the crest of the falls every minute.[2] Horseshoe Falls is the most powerful waterfall in North America, as measured by flow rate.[3]
+
+The falls are 27 kilometres (17 mi) north-northwest of Buffalo, New York, and 121 kilometres (75 mi) south-southeast of Toronto, between the twin cities of Niagara Falls, Ontario, and Niagara Falls, New York. Niagara Falls was formed when glaciers receded at the end of the Wisconsin glaciation (the last ice age), and water from the newly formed Great Lakes carved a path through the Niagara Escarpment en route to the Atlantic Ocean.
+
+Niagara Falls is famed both for its beauty and as a valuable source of hydroelectric power. Balancing recreational, commercial, and industrial uses has been a challenge for the stewards of the falls since the 19th century.
+
+The Horseshoe Falls drop about 57 metres (187 ft),[4] while the height of the American Falls varies between 21 and 30 metres (69 and 98 ft) because of the presence of giant boulders at its base. The larger Horseshoe Falls are about 790 metres (2,590 ft) wide, while the American Falls are 320 metres (1,050 ft) wide. The distance between the American extremity of the Niagara Falls and the Canadian extremity is 3,409 feet (1,039 m).
+
+The peak flow over Horseshoe Falls was recorded at 6,400 cubic metres (230,000 cu ft) per second.[5] The average annual flow rate is 2,400 cubic metres (85,000 cu ft) per second.[6] Since the flow is a direct function of the Lake Erie water elevation, it typically peaks in late spring or early summer. During the summer months, at least 2,800 cubic metres (99,000 cu ft) per second of water traverses the falls, some 90% of which goes over the Horseshoe Falls, while the balance is diverted to hydroelectric facilities. This is accomplished by employing a weir – the International Control Dam – with movable gates upstream from the Horseshoe Falls.
+
+The falls' flow is further halved at night, and, during the low tourist season in the winter, remains a minimum of 1,400 cubic metres (49,000 cu ft) per second. Water diversion is regulated by the 1950 Niagara Treaty and is administered by the International Niagara Board of Control (IJC).[7] The verdant green color of the water flowing over the Niagara Falls is a byproduct of the estimated 60 tonnes/minute of dissolved salts and "rock flour" (very finely ground rock) generated by the erosive force of the Niagara River itself.[8]
+
+The features that became Niagara Falls were created by the Wisconsin glaciation about 10,000 years ago.[9] The retreat of the ice sheet left behind a large amount of meltwater (see Lake Algonquin, Lake Chicago, Glacial Lake Iroquois, and Champlain Sea) that filled up the basins that the glaciers had carved, thus creating the Great Lakes as we know them today.[10][11] Scientists argue there is an old valley, St David's Buried Gorge, buried by glacial drift, at the approximate location of the present Welland Canal.
+
+When the ice melted, the upper Great Lakes emptied into the Niagara River, which followed the rearranged topography across the Niagara Escarpment. In time, the river cut a gorge through the north-facing cliff, or cuesta.[12] Because of the interactions of three major rock formations, the rocky bed did not erode evenly. The top rock formation was composed of erosion-resistant limestone and dolomite of the Lockport Formation. That hard layer of stone eroded more slowly than the underlying materials. The aerial photo on the right clearly shows the hard caprock, the Lockport Formation (Middle Silurian), which underlies the rapids above the falls, and approximately the upper third of the high gorge wall.[12] Immediately below the hard-rock formation, comprising about two-thirds of the cliff, lay the weaker, softer, sloping Rochester Formation (Lower Silurian). This formation was composed mainly of shale, though it has some thin limestone layers. It also contains ancient fossils. In time, the river eroded the soft layer that supported the hard layers, undercutting the hard caprock, which gave way in great chunks. This process repeated countless times, eventually carving out the falls.
+
+Submerged in the river in the lower valley, hidden from view, is the Queenston Formation (Upper Ordovician), which is composed of shales and fine sandstones. All three formations were laid down in an ancient sea, their differences of character deriving from changing conditions within that sea.
+
+About 10,900 years ago, the Niagara Falls was between present-day Queenston, Ontario, and Lewiston, New York, but erosion of their crest has caused the waterfalls to retreat approximately 6.8 miles (10.9 km) southward.[13] The Horseshoe Falls, which are about 2,600 feet (790 m) wide, have also changed their shape through the process of erosion; evolving from a small arch to a horseshoe bend, to the present day gigantic V.[14] Just upstream from the falls' current location, Goat Island splits the course of the Niagara River, resulting in the separation of the mostly Canadian Horseshoe Falls to the west from the American and Bridal Veil Falls to the east. Engineering has slowed erosion and recession.[15]
+
+The current rate of erosion is approximately 30 centimeters (1 ft) per year, down from a historical average of 0.91 m (3 ft) per year. According to the timeline of the far future, in roughly 50,000 years Niagara Falls will have eroded the remaining 32 kilometres (20 mi) to Lake Erie and cease to exist.[8]
+
+In the 1870s, sightseers had limited access to Niagara Falls and often had to pay for a glimpse, and industrialization threatened to carve up Goat Island to further expand commercial development.[16] Other industrial encroachments and lack of public access led to a conservation movement in the U.S. known as Free Niagara, led by such notables as Hudson River School artist Frederic Edwin Church, landscape designer Frederick Law Olmsted, and architect Henry Hobson Richardson. Church approached Lord Dufferin, governor-general of Canada, with a proposal for international discussions on the establishment of a public park.[17]
+
+Goat Island was one of the inspirations for the American side of the effort. William Dorsheimer, moved by the scene from the island, brought Olmsted to Buffalo in 1868 to design a city park system and helped promote Olmsted's career. In 1879, the New York state legislature commissioned Olmsted and James T. Gardner to survey the falls and to create the single most important document in the Niagara preservation movement, a Special Report on the preservation of Niagara Falls.[18] The report advocated for State purchase, restoration and preservation through public ownership of the scenic lands surrounding Niagara Falls. Restoring the former beauty of the falls was described in the report as a "sacred obligation to mankind."[19] In 1883, New York Governor Grover Cleveland drafted legislation authorizing acquisition of lands for a state reservation at Niagara, and the Niagara Falls Association, a private citizens group founded in 1882, mounted a great letter-writing campaign and petition drive in support of the park. Professor Charles Eliot Norton and Olmsted were among the leaders of the public campaign, while New York Governor Alonzo Cornell opposed.[20]
+
+Preservationists' efforts were rewarded on April 30, 1885, when Governor David B. Hill signed legislation creating the Niagara Reservation, New York's first state park. New York State began to purchase land from developers, under the charter of the Niagara Reservation State Park. In the same year, the province of Ontario established the Queen Victoria Niagara Falls Park for the same purpose. On the Canadian side, the Niagara Parks Commission governs land usage along the entire course of the Niagara River, from Lake Erie to Lake Ontario.[21]
+
+In 1887, Olmsted and Calvert Vaux issued a supplemental report detailing plans to restore the falls. Their intent was "to restore and conserve the natural surroundings of the Falls of Niagara, rather than to attempt to add anything thereto," and the report anticipated fundamental questions. How would preservationists provide access without destroying the beauty of the falls? How would they restore natural landscapes damaged by man? They planned a park with scenic roadways, paths and a few shelters designed to protect the landscape while allowing large numbers of visitors to enjoy the falls.[22] Commemorative statues, shops, restaurants, and a 1959 glass and metal observation tower were added later. Preservationists continue to strive to strike a balance between Olmsted's idyllic vision and the realities of administering a popular scenic attraction.[23]
+
+Preservation efforts continued well into the 20th century. J. Horace McFarland, the Sierra Club, and the Appalachian Mountain Club persuaded the United States Congress in 1906 to enact legislation to preserve the falls by regulating the waters of the Niagara River.[24] The act sought, in cooperation with the Canadian government, to restrict diversion of water, and a treaty resulted in 1909 that limited the total amount of water diverted from the falls by both nations to approximately 56,000 cubic feet (1,600 m3) per second. That limitation remained in effect until 1950.[25]
+
+Erosion control efforts have always been of extreme importance. Underwater weirs redirect the most damaging currents, and the top of the falls has also been strengthened. In June 1969, the Niagara River was completely diverted from the American Falls for several months through construction of a temporary rock and earth dam.[26] During this time, two bodies were removed from under the falls, including a man who had been seen jumping over the falls, and the body of a woman, which was discovered once the falls dried.[27][28]
+
+While the Horseshoe Falls absorbed the extra flow, the U.S. Army Corps of Engineers studied the riverbed and mechanically bolted and strengthened any faults they found; faults that would, if left untreated, have hastened the retreat of the American Falls. A plan to remove the huge mound of talus deposited in 1954 was abandoned owing to cost,[29] and in November 1969, the temporary dam was dynamited, restoring flow to the American Falls.[30] Even after these undertakings, Luna Island, the small piece of land between the main waterfall and the Bridal Veil, remained off limits to the public for years owing to fears that it was unstable and could collapse into the gorge.
+
+Commercial interests have continued to encroach on the land surrounding the state park, including the construction of several tall buildings (most of them hotels) on the Canadian side. The result is a significant alteration and urbanisation of the landscape. One study indicated it has caused the airflow near the falls to change direction. Students at the University of Guelph demonstrated, using scale models, that as air passes over the top of the new hotels it causes a breeze to roll down the south sides of the buildings and spill into the gorge below the falls, where it feeds into a whirlpool of moisture and air. The inference was that a documented rise in the number of "mist days" was a result of these breezes, where mist days refers to the mist plume of the falls reaching landside.[31] In 1996 there were 29 mist days recorded, but by 2003 that number had risen to 68.[32] Another study has discounted this opinion and linked mist production to the difference in air and water temperature at the falls. However, this study does not offer opinion as to why mist days have been increasing, just that the hotel breezes are an unlikely cause.[33]
+
+In 2013, New York State began an effort to renovate The Sisters Islands located on Goat Island. New York State used funds from the re-licensing of the New York Power Authority hydroelectric plant downriver in Lewiston, New York, to rebuild walking paths on the Three Sisters Islands and to plant native vegetation on the islands. The state also renovated the area around Prospect Point at the brink of the American Falls in the state park.
+
+Theories differ as to the origin of the name of the falls. According to Iroquoian scholar Bruce Trigger, Niagara is derived from the name given to a branch of the local native Neutral Confederacy, who are described as being called the Niagagarega people on several late-17th-century French maps of the area.[35] According to George R. Stewart, it comes from the name of an Iroquois town called Onguiaahra, meaning "point of land cut in two".[36]
+
+Henry Schoolcraft reported:
+
+Niagara Falls. This name is Mohawk. It means, according to Mrs. Kerr, the neck; the term being first applied to the portage or neck of land, between lakes Erie and Ontario. By referring to Mr. Elliott's vocabulary, (chapter xi) it will be seen that the human neck, that is, according to the concrete vocabulary, his neck, is onyara. Red Jacket pronounced the word Niagara to me, in the spring of 1820, as if written O-ne-au-ga-rah.[37]
+
+Many figures have been suggested as first circulating a European eyewitness description of Niagara Falls. The Frenchman Samuel de Champlain visited the area as early as 1604 during his exploration of Canada, and members of his party reported to him the spectacular waterfalls, which he described in his journals. The Finnish-Swedish naturalist Pehr Kalm explored the area in the early 18th century and is credited with the first scientific description of the falls. The consensus honoree for the first description is the Belgian missionary Louis Hennepin, who observed and described the falls in 1677, earlier than Kalm, after traveling with the explorer René-Robert Cavelier, Sieur de La Salle, thus bringing the falls to the attention of Europeans. Further complicating matters, there is credible evidence the French Jesuit missionary Paul Ragueneau visited the falls some 35 years before Hennepin's visit while working among the Huron First Nation in Canada. Jean de Brébeuf also may have visited the falls, while spending time with the Neutral Nation.[38]
+
+In 1762, Captain Thomas Davies, a British Army officer and artist, surveyed the area and painted the watercolor, An East View of the Great Cataract of Niagara, the first eyewitness painting of the falls.[39][40]
+
+During the 19th century, tourism became popular, and by mid-century, it was the area's main industry. Theodosia Burr Alston (daughter of Vice President Aaron Burr) and her husband Joseph Alston were the first recorded couple to honeymoon there in 1801.[41] Napoleon Bonaparte's brother Jérôme visited with his bride in the early 19th century.[42]
+
+In 1825, British explorer John Franklin visited the falls while passing through New York en route to Cumberland House as part of his second Arctic expedition, calling them "so justly celebrated as the first in the world for grandeur".[43]
+
+In March 1848, an ice blockage caused the falls to stop; no water (or at best a trickle) fell for as much as 40 hours. Waterwheels stopped, and mills and factories shut down for having no power.[44]
+
+Later that year, demand for passage over the Niagara River led to the building of a footbridge and then Charles Ellet's Niagara Suspension Bridge. This was supplanted by German-born John Augustus Roebling's Niagara Falls Suspension Bridge in 1855. After the American Civil War, the New York Central Railroad publicized Niagara Falls as a focus of pleasure and honeymoon visits. With increased railroad traffic, in 1886, Leffert Buck replaced Roebling's wood and stone bridge with the predominantly steel bridge that still carries trains over the Niagara River today. The first steel archway bridge near the falls was completed in 1897. Known today as the Whirlpool Rapids Bridge, it carries passenger vehicles and trains between Canada (through Canadian Customs Border Control) and the U.S.A. just downstream of the falls.
+
+In about 1840, the English industrial chemist Hugh Lee Pattinson traveled to Canada, stopping at the Niagara Falls long enough to make the earliest known photograph of the falls, a daguerreotype in the collection of Newcastle University. It was once believed that the small figure standing silhouetted with a top hat was added by an engraver working from imagination as well as the daguerreotype as his source, but the figure is clearly present in the photograph.[45] Because of the very long exposure required, of ten minutes or more, the figure is assumed by Canada's Niagara Parks agency to be Pattinson himself.[45] The image is left-right inverted and taken from the Canadian side.[46] Pattinson made other photographs of the Horseshoe Falls as well as of Rome and Paris. These were then transferred to engravings to illustrate Noël Marie Paymal Lerebours' Excursions Daguerriennes (Paris, 1841–1864).[47]
+
+On 6 August 1918, an iron scow became stuck on the rocks above the falls.[48] The two men on the scow were rescued but the vessel remained trapped on rocks in the river, and is still visible there in a deteriorate state, although its position shifted by 50 meters during a storm on 31 October 2019.[49] Daredevil William "Red" Hill Sr. was particularly praised for his role in the rescue.[50]
+
+After the First World War, tourism boomed again, as automobiles made getting to the falls much easier. The story of Niagara Falls in the 20th century is largely that of efforts to harness the energy of the falls for hydroelectric power, and to control the development on both sides that threaten the area's natural beauty. In 1941, the Niagara Falls Bridge Commission completed the third current crossing in the immediate area of Niagara Falls with the Rainbow Bridge, carrying both pedestrian and vehicular traffic between the two countries and Canadian and U.S. customs for each country.
+
+Before the late 20th century, the northeastern end of the Horseshoe Falls was in the United States, flowing around the Terrapin Rocks, which were once connected to Goat Island by a series of bridges. In 1955, the area between the rocks and Goat Island was filled in, creating Terrapin Point.[51] In the early 1980s, the U.S. Army Corps of Engineers filled in more land and built diversion dams and retaining walls to force the water away from Terrapin Point. Altogether, 400 ft (120 m) of the Horseshoe Falls were eliminated, including 100 ft (30 m) on the Canadian side. According to author Ginger Strand, the Horseshoe Falls is now entirely in Canada.[52] Other sources say "most of" Horseshoe Falls is in Canada.[53]
+
+The only recorded freeze-up of the river and falls was due to an ice jam on March 29, 1848. In 1912, the American Falls was completely frozen but the other two kept flowing. Although the falls commonly ice up most winters, the river and the falls do not freeze completely. The years 1885, 1902, 1906, 1911, 1932, 1936, 2014, 2017 and 2019 are noted for partial freezing of the falls.[54][55][56]
+
+A so-called ice bridge was also common in certain years at the base of the falls and was used by people who wanted to cross the river before bridges had been built. During some winters, the ice sheet was as thick as 40 feet (12m) to 100 feet (30m) but that thickness has not occurred since 1954. The ice bridge of 1841 was said to be at least 100 feet thick.   
+[57] On 12 February 1912, the ice bridge which had formed on 15 January began breaking up while people were still on it. Many escaped but three died during the event, later named the Ice Bridge Disaster or Tragedy.[58]
+
+A number of bridges have spanned the Niagara River in the general vicinity of the falls. The first, not far from the Whirlpool, was a suspension bridge above the gorge. It opened for use by the public in July 1848 and remained in use until 1855. A second bridge in the Upper Falls area was commissioned, with two levels or decks, one for use by the Great Western Railway. This Niagara Falls Suspension Bridge opened in 1855. In 1882, the Grand Trunk Railway took over control of the second deck after it absorbed the Great Western company. Significant structural improvements were made in the late 1870s and then in 1886; this bridge remained in use until 1897.[59]
+
+Due to the volume of traffic, the decision was made to construct a new arch bridge nearby: under and around the existing bridge. After it opened in September 1897, a decision was made to remove and scrap the Railway Suspension Bridge. This new bridge was initially known as the Niagara Railway Arch, or Lower Steel Arch Bridge; it had two decks, the lower one used for carriages and the upper for trains. In 1937, it was renamed the Whirlpool Rapids Bridge and remains in use today. All of the structures built up to that time were referred to as Lower Niagara bridges and were some distance from the falls.[59]
+
+The first bridge in the so-called Upper Niagara area (closer to the falls) was a two level suspension structure that opened in January 1869; it was destroyed during a severe storm in January 1889. The replacement was built quickly and opened in May of the same year. In order to handle heavy traffic a second bridge was commissioned, slightly closer to the American Falls. This one was fully made of steel and opened to traffic in June 1897; it was known as the Upper Steel Arch Bridge, but was often called the Honeymoon Bridge. The single level included a track for trolleys and space for carriages and pedestrians. The design led to the bridge being very close to the surface of the river and in January, 1938, an ice jam twisted the steel frame of the bridge which later collapsed, on January 27, 1938.[60]
+
+Another Lower Niagara bridge had been commissioned in 1883 by Cornelius Vanderbilt for use by railways at a location roughly approximately 200 feet south of the Railway Suspension Bridge. This one was of an entirely different design; it was a Cantilever bridge to provide greater strength. The Niagara Cantilever Bridge had two cantilevers which were joined by steel sections; it opened officially in December 1883 and improvements were made over the years for a stronger structure. As rail traffic was increasing, the Michigan Central Railroad company decided to build a new bridge in 1923, to be located between the Lower Steel Arch Bridge and the Cantilever Bridge. The Michigan Central Railway Bridge opened in February 1925 and remained in use until the early 21st century. The Cantilever Bridge was removed and scrapped after the new rail bridge opened.[59] Nonetheless, it was inducted into the North America Railway Hall of Fame in 2006.[61][59]
+
+There was a lengthy dispute as to which agency should build the replacement for the Niagara Railway Arch, or Lower Steel Arch Bridge in the Upper Niagara area. When that was resolved, construction of a steel bridge commenced in February 1940. Named the Rainbow Bridge, and featuring two lanes for traffic separated by a barrier, this one opened in November 1941. It remains in use today.[60]
+
+The enormous energy of Niagara Falls has long been recognized as a potential source of power. The first known effort to harness the waters was in 1759, when Daniel Joncaire built a small canal above the falls to power his sawmill.[62] Augustus and Peter Porter purchased this area and all of American Falls in 1805 from the New York state government, and enlarged the original canal to provide hydraulic power for their gristmill and tannery. In 1853, the Niagara Falls Hydraulic Power and Mining Company was chartered, which eventually constructed the canals that would be used to generate electricity.[63] In 1881, under the leadership of Jacob F. Schoellkopf, the Niagara River's first hydroelectric generating station was built. The water fell 86 feet (26 m) and generated direct current electricity, which ran the machinery of local mills and lit up some of the village streets.
+
+The Niagara Falls Power Company, a descendant of Schoellkopf's firm, formed the Cataract Company headed by Edward Dean Adams,[64] with the intent of expanding Niagara Falls' power capacity. In 1890, a five-member International Niagara Commission headed by Sir William Thomson among other distinguished scientists deliberated on the expansion of Niagara hydroelectric capacity based on seventeen proposals, but could not select any as the best combined project for hydraulic development and distribution. In 1893, Westinghouse Electric (which had built the smaller-scale Ames Hydroelectric Generating Plant near Ophir, Colorado, two years earlier) was hired to design a system to generate alternating current on Niagara Falls, and three years after that this large-scale AC power system was created (activated on August 26, 1895).[65] The Adams Power Plant Transformer House remains as a landmark of the original system.
+
+By 1896, financing from moguls including J.P. Morgan, John Jacob Astor IV, and the Vanderbilts had fueled the construction of giant underground conduits leading to turbines generating upwards of 100,000 horsepower (75 MW), sent as far as Buffalo, 20 miles (32 km) away. Some of the original designs for the power transmission plants were created by the Swiss firm Faesch & Piccard, which also constructed the original 5,000 hp waterwheels.
+
+Private companies on the Canadian side also began to harness the energy of the falls. The Government of Ontario eventually brought power transmission operations under public control in 1906, distributing Niagara's energy to various parts of the Canadian province.
+
+Other hydropower plants were also being built along the Niagara River. But in 1956, disaster struck when the region's largest hydropower station was partially destroyed in a landslide. This drastically reduced power production and put tens of thousands of manufacturing jobs at stake. In 1957, Congress passed the Niagara Redevelopment Act,[66] which granted the New York Power Authority the right to fully develop the United States' share of the Niagara River's hydroelectric potential.[67]
+
+In 1961, when the Niagara Falls hydroelectric project went online, it was the largest hydropower facility in the Western world. Today, Niagara is still the largest electricity producer in New York state, with a generating capacity of 2.4 GW. Up to 1,420 cubic metres (380,000 US gal) of water a second is diverted from the Niagara River through conduits under the city of Niagara Falls to the Lewiston and Robert Moses power plants. Currently between 50% and 75% of the Niagara River's flow is diverted via four huge tunnels that arise far upstream from the waterfalls. The water then passes through hydroelectric turbines that supply power to nearby areas of Canada and the United States before returning to the river well past the falls.[68] This water spins turbines that power generators, converting mechanical energy into electrical energy. When electrical demand is low, the Lewiston units can operate as pumps to transport water from the lower bay back up to the plant's reservoir, allowing this water to be used again during the daytime when electricity use peaks. During peak electrical demand, the same Lewiston pumps are reversed and actually become generators, similar to those at the Moses plant.[67]
+
+To preserve Niagara Falls' natural beauty, a 1950 treaty signed by the U.S. and Canada limited water usage by the power plants. The treaty allows higher summertime diversion at night when tourists are fewer and during the winter months when there are even fewer tourists.[69] This treaty, designed to ensure an "unbroken curtain of water" flowing over the falls, states that during daylight time during the tourist season (April 1 to October 31) there must be 100,000 cubic feet per second (2,800 m3/s) of water flowing over the falls, and during the night and off-tourist season there must be 50,000 cubic feet per second (1,400 m3/s) of water flowing over the falls. This treaty is monitored by the International Niagara Board of Control, using a NOAA gauging station above the falls. During winter, the Power Authority of New York works with Ontario Power Generation to prevent ice on the Niagara River from interfering with power production or causing flooding of shoreline property. One of their joint efforts is an 8,800-foot-long (2,700 m) ice boom, which prevents the buildup of ice, yet allows water to continue flowing downstream.[67] In addition to minimum water volume, the crest of the Horseshoe falls was reduced to maintain an uninterrupted "curtain of water."[70]
+
+The most powerful hydroelectric stations on the Niagara River are the Sir Adam Beck 1 and 2 on the Canadian side and the Robert Moses Niagara Power Plant and the Lewiston Pump Generating Plant on the American side. Together, Niagara's generating stations can produce about 4.4 gigawatts of power.
+
+In August 2005 Ontario Power Generation, which is responsible for the Sir Adam Beck stations, started a major civil engineering project, called the Niagara Tunnel Project, to increase power production by building a new 12.7-metre (42 ft) diameter, 10.2-kilometre-long (6.3 mi) water diversion tunnel. It was officially placed into service in March 2013, helping to increase the generating complex's nameplate capacity by 150 megawatts. It did so by tapping water from farther up the Niagara River than was possible with the preexisting arrangement. The tunnel provided new hydroelectricity for approximately 160,000 homes.[71][72]
+
+Ships can bypass Niagara Falls by means of the Welland Canal, which was improved and incorporated into the Saint Lawrence Seaway in the mid-1950s. While the seaway diverted water traffic from nearby Buffalo and led to the demise of its steel and grain mills, other industries in the Niagara River valley flourished with the help of the electric power produced by the river. However, since the 1970s the region has declined economically.
+
+The cities of Niagara Falls, Ontario, Canada, and Niagara Falls, New York, United States, are connected by two international bridges. The Rainbow Bridge, just downriver from the falls, affords the closest view of the falls and is open to non-commercial vehicle traffic and pedestrians. The Whirlpool Rapids Bridge lies one mile (1.6 km) north of the Rainbow Bridge and is the oldest bridge over the Niagara River. Nearby Niagara Falls International Airport and Buffalo Niagara International Airport were named after the waterfall, as were Niagara University, countless local businesses, and even an asteroid.[73]
+
+
+
+In October 1829, Sam Patch, who called himself "the Yankee Leapster", jumped from a high tower into the gorge below the falls and survived; this began a long tradition of daredevils trying to go over the falls.
+
+Englishman Captain Matthew Webb, the first man to swim the English Channel, drowned in 1883 trying to swim the rapids downriver from the falls.[74]
+
+On October 24, 1901, 63-year-old Michigan school teacher Annie Edson Taylor became the first person to go over the falls in a barrel as a publicity stunt; she survived, bleeding, but otherwise unharmed. Soon after exiting the barrel, she said, "No one ought ever do that again."[75] Before Taylor's attempt, on October 19 her domestic cat named Iagara was sent over the Horseshoe Falls in her barrel to test its strength. Contrary to rumours at the time, the cat survived the plunge unharmed and later posed with Taylor in photographs.[76] Since Taylor's historic ride, over a dozen people have intentionally gone over the falls in or on a device, despite her advice. Some have survived unharmed, but others have drowned or been severely injured. Survivors face charges and stiff fines, as it is now illegal, on both sides of the border, to attempt to go over the falls.
+
+Bobby Leach went over the Horseshoe Falls in a crude steel barrel in 1911, and needed rescuing by William "Red" Hill Sr..[77] Hill would again come to the rescue of Leach following his failed attempt to swim the Niagara Gorge in 1920.
+
+In 1918, there was a near disaster when a barge working upriver, known locally as the Niagara Scow, broke its tow line and almost plunged over the falls. The two workers on board saved themselves by grounding the vessel on rocks just short of the falls, where it has remained ever since. "Red" Hill was credited with the rescue of the two boatmen.[78] In October 2019, as a result of inclement weather, the Niagara Scow finally moved from its original resting place, moving closer to the brink of Horseshoe Falls.[79]
+
+In 1928, "Smiling Jean" Lussier tried an entirely different concept, going over the falls in a large rubber ball; he was successful and survived the ordeal.[80]
+
+Charles Stephens, a 58-year-old barber from Bristol, England, went over the falls in a wooden barrel in July 1920 and was the first person to die in an endeavor of this type.[81]
+
+In the "Miracle at Niagara", Roger Woodward, a seven-year-old American boy, was swept over the Horseshoe Falls after their boat lost power on July 9, 1960; two tourists pulled his 17-year-old sister Deanne from the river only 20 feet (6.1 m) from the lip of the Horseshoe Falls at Goat Island.[82] Minutes later, Woodward was plucked from the roiling plunge pool beneath the Horseshoe Falls after grabbing a life ring thrown to him by the crew of the Maid of the Mist boat.[83][84] The third person who had been in the boat, James Hunicutt, did not survive the mishap.[85]
+
+On July 2, 1984, Canadian Karel Soucek from Hamilton, Ontario, plunged over the Horseshoe Falls in a barrel with only minor injuries. Soucek was fined $500 for performing the stunt without a license. In 1985, he was fatally injured while attempting to re-create the Niagara drop at the Houston Astrodome. His aim was to climb into a barrel hoisted to the rafters of the Astrodome and to drop 180 feet (55 m) into a water tank on the floor. After his barrel released prematurely, it hit the side of the tank and he died the next day from his injuries.[86][87]
+
+In August 1985, Steve Trotter, an aspiring stuntman from Rhode Island, became the youngest person ever (age 22) and the first American in 25 years to go over the falls in a barrel. Ten years later, Trotter went over the falls again, becoming the second person to go over the falls twice and survive. It was also the second-ever "duo"; Lori Martin joined Trotter for the barrel ride over the falls. They survived the fall but their barrel became stuck at the bottom of the falls, requiring a rescue.[88]
+
+On September 28, 1989, Niagara natives Peter DeBernardi (age 42) and Jeffery James Petkovich (age 25) became the first "team" to make it over the falls in a two-person barrel. The stunt was conceived by DeBenardi, who wanted to discourage youth from following in his path of addictive drug use. The pair emerged shortly after going over with minor injuries and were charged with performing an illegal stunt under the Niagara Parks Act.[89]
+
+On June 5, 1990, Jesse Sharp, a whitewater canoeist from Tennessee paddled over the falls in a closed deck canoe. He neglected to wear a helmet to make his face more visible for photographs of the event. He also did not wear a life vest because he believed it would hinder his escape from the hydraulics at the base of the falls. His boat flushed out of the falls, but his body was never found.[90]
+
+On September 27, 1993, John "David" Munday, of Caistor Centre, Ontario, completed his second journey over the falls.[91]
+
+On October 1, 1995, Robert Douglas "Firecracker" Overacker went over the falls on a Jet Ski to raise awareness for the homeless. His rocket-propelled parachute failed to open and he plunged to his death. Overacker's body was recovered before he was pronounced dead at Niagara General Hospital.[92]
+
+Kirk Jones of Canton, Michigan, became the first known person to survive a plunge over the Horseshoe Falls without a flotation device on October 20, 2003. According to some reports, Jones had attempted to commit suicide,[93] he survived the 16-story fall with only battered ribs, scrapes, and bruises.[94][95] Jones tried going over the falls again in 2017, this time, using a large inflatable ball, but died in the process.[96][97] Later reports revealed that Jones had arranged for a friend to shoot video clips of his stunt.
+[98]
+
+On March 11, 2009, a man survived an unprotected trip over the Horseshoe Falls, and when rescued from the river, was reported to be suffering from severe hypothermia and a large wound to his head. His identity was never released. Eyewitnesses reported seeing the man intentionally enter the water.[99][100]
+
+On May 21, 2012, an unidentified man in his early 40s became the fourth person to survive an unprotected trip over the Horseshoe Falls. Eyewitness reports show he "deliberately jumped" into the Niagara River after climbing over a railing.[101][102]
+
+On July 8, 2019, at roughly 4 am, officers responded to a report of a person in crisis at the brink of the Canadian side of the falls. Once officers got to the scene, the man climbed the retaining wall, jumped into the river and went over the Horseshoe Falls. Authorities subsequently began to search the lower Niagara River basin, where the man was found sitting on the rocks at the water's edge.[103]
+
+Other daredevils have made crossing the gorge their goal, starting with the successful passage by Jean François "Blondin" Gravelet, who crossed Niagara Gorge in 1859.[105] Between 1859 and 1896 a wire-walking craze emerged, resulting in frequent feats over the river below the falls. One inexperienced walker slid down his safety rope. Only one man fell to his death, at night and under mysterious circumstances, at the anchoring place for his wire.[106]
+
+Maria Spelterini, a 23-year-old Italian was the first and only woman to cross the Niagara River gorge; she did so on a tightrope, on 8 July 1876. She repeated the stunt several times during the same month. During one crossing she was blindfolded and during another, her ankles and wrists were handcuffed.[107]
+
+The tightrope walkers drew huge crowds to witness their exploits. Their wires ran across the gorge, near the current Rainbow Bridge, not over the waterfall itself. Blondin made his first gorge crossing on a tightrope on 30 June 1859 and did so again eight times that year. His most difficult crossing occurred on August 14, when he carried his manager, Harry Colcord, on his back.[108]   His final crossing, on 8 September 1860, was witnessed by the Prince of Wales.[106]
+
+Among the many competitors was Ontario's William Hunt, who billed himself as "The Great Farini"; his first crossing was in 1860. Farini competed with Blondin in performing outrageous stunts over the gorge.[109] On 8 August  1864 however, an attempt failed and he needed to be rescued.[110]
+
+On 15 June 2012, high wire artist Nik Wallenda became the first person to walk across the falls area in 116 years, after receiving special permission from both governments.[111] The full length of his tightrope was 1,800 feet (550 m).[112] Wallenda crossed near the brink of the Horseshoe Falls, unlike walkers who had crossed farther downstream. According to Wallenda, it was the longest unsupported tightrope walk in history.[113] He carried his passport on the trip and was required to present it upon arrival on the Canadian side of the falls.[114]
+
+Peak visitor traffic occurs in the summertime, when Niagara Falls are both a daytime and evening attraction. From the Canadian side, floodlights illuminate both sides of the falls for several hours after dark (until midnight). The number of visitors in 2007 was expected to total 20 million, and by 2009 the annual rate was expected to top 28 million tourists.[115]
+
+The oldest and best known tourist attraction at Niagara Falls is the Maid of the Mist boat cruise, named for an ancient Ongiara Indian mythical character, which has carried passengers into the rapids immediately below the falls since 1846. Cruise boats operate from boat docks on both sides of the falls, with the Maid of the Mist operating from the American side and Hornblower Cruises (originally Maid of the Mist until 2014[116]) from the Canadian side.[117][118]
+
+From the U.S. side, the American Falls can be viewed from walkways along Prospect Point Park, which also features the Prospect Point Observation Tower and a boat dock for the Maid of the Mist. Goat Island offers more views of the falls and is accessible by foot and automobile traffic by bridge above the American Falls. From Goat Island, the Cave of the Winds is accessible by elevator and leads hikers to a point beneath Bridal Veil Falls. Also on Goat Island are the Three Sisters Islands, the Power Portal where a statue of Nikola Tesla (the inventor whose patents for the AC induction motor and other devices for AC power transmission helped make the harnessing of the falls possible) can be seen, and a walking path that enables views of the rapids, the Niagara River, the gorge, and all of the falls. Most of these attractions lie within the Niagara Falls State Park.[119]
+
+The Niagara Scenic Trolley offers guided trips along the American Falls and around Goat Island. Panoramic and aerial views of the falls can also be viewed by helicopter. The Niagara Gorge Discovery Center showcases the natural and local history of Niagara Falls and the Niagara Gorge. A casino and luxury hotel was opened in Niagara Falls, New York, by the Seneca Indian tribe. The Seneca Niagara Casino & Hotel occupies the former Niagara Falls Convention Center. The new hotel is the first addition to the city's skyline since completion of the United Office Building in the 1920s.[119][120]
+
+On the Canadian side, Queen Victoria Park features manicured gardens, platforms offering views of both the American and Horseshoe Falls, and underground walkways leading into observation rooms that yield the illusion of being within the falling waters. Along the Niagara River, the Niagara River Recreational Trail runs 35 miles (56 km) from Fort Erie to Fort George, and includes many historical sites from the War of 1812.[121]
+
+The observation deck of the nearby Skylon Tower offers the highest view of the falls, and in the opposite direction gives views as far as Toronto. Along with the Tower Hotel (built as the Seagrams Tower, later renamed the Heritage Tower, the Royal Inn Tower, the Royal Center Tower, the Panasonic Tower, the Minolta Tower, and most recently the Konica Minolta Tower[122] before receiving its current name in 2010), it is one of two towers in Canada with a view of the falls.[123]
+
+The Whirlpool Aero Car, built in 1916 from a design by Spanish engineer Leonardo Torres y Quevedo, is a cable car that takes passengers over the Niagara Whirlpool on the Canadian side. The Journey Behind the Falls consists of an observation platform and series of tunnels near the bottom of the Horseshoe Falls on the Canadian side.[124]
+
+There are two casinos on the Canadian side of Niagara Falls, the Niagara Fallsview Casino Resort and Casino Niagara.[125]
+
+Already a huge tourist attraction and favorite spot for honeymooners, Niagara Falls visits rose sharply in 1953 after the release of Niagara, a movie starring Marilyn Monroe and Joseph Cotten.[126]
+
+The 1956 animated short Niagara Fools featured Woody Woodpecker attempting to go over the falls in a barrel.[127] The falls was a featured location in the major motion picture Superman II in 1980,[128] and was itself the subject of a popular IMAX movie, Niagara: Miracles, Myths and Magic.[129] Illusionist David Copperfield performed a trick in which he appeared to travel over the Horseshoe Falls in 1990.[130]
+
+The falls, or more particularly, the tourist-supported complex near the falls, was the setting of the short-lived Canadian-shot US television show Wonderfalls in early 2004. Location footage of the falls was shot in October 2006 to portray "World's End" of the movie Pirates of the Caribbean: At World's End.[131] Professional kayaker Rafa Ortiz's preparation to paddle over the falls in a kayak is documented in the 2015 film Chasing Niagara.[132]
+
+Composer Ferde Grofé was commissioned by the Niagara Falls Power Generation project in 1960 to compose the Niagara Falls Suite in honor of the completion of the first stage of hydroelectric work at the falls.[133] In 1997, composer Michael Daugherty composed Niagara Falls, a piece for concert band inspired by the falls.[134]
+
+The Niagara Falls area features as the base camp for a German aerial invasion of the United States in the H. G. Wells novel The War in the Air.[135]
+
+Many poets have been inspired to write about the falls. Among them was the Cuban poet José Maria Heredia, who wrote the poem "Niagara". There are commemorative plaques on both sides of the falls recognising the poem.[136]
+
+In the original 1920s and 1930s Buck Rogers stories and newspaper cartoons, Buck Rogers, in his adventures in the 25th century that take place on Earth.[137]
+
+Part of Mark Twain's 1893 short story, "Extract from Adam's Diary" is set at Niagara Falls.[138]
+
+The Bulgarian writer Aleko Konstantinov portrays the impressiveness of the Niagara Falls in his book, To Chicago and Back.
+
+In 2014, the writer Alessandro Baricco published the book Smith & Wesson recounting the story of Rachel Green going over the falls.
+
+The Niagara Falls were such an attraction to landscape artists that, writes John Howat, they were "the most popular, the most often treated, and the tritest single item of subject matter to appear in eighteenth- and nineteenth-century European and American landscape painting".[139]
+
+A General View of the Falls of Niagara by Alvan Fisher, 1820
+
+Distant View of Niagara Falls by Thomas Cole, 1830
+
+Niagara Fälle. Les chûtes du Niagara. Niagara Falls by Karl Bodmer, circa 1832
+
+Voute sous la Chute du Niagara – Niagara Falls, circa 1841
+
+Niagara by Frederic Edwin Church, 1857
+
+Underneath Niagara Falls by Ferdinand Richardt, 1862
+
+Niagara by Louis Rémy Mignot, circa 1866
+
+Falls of Niagara from Below by Albert Bierstadt, 1869
+
+Niagara Falls by William Morris Hunt, 1878
+
+Niagara Falls, circa 1880

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+The Twelve Labours of Heracles or Hercules (Greek: οἱ Ἡρακλέους ἆθλοι, hoi Hērakléous âthloi)[1][2] are a series of episodes concerning a penance carried out by Heracles, the greatest of the Greek heroes, whose name was later romanised as Hercules. They were accomplished at the service of King Eurystheus. The episodes were later connected by a continuous narrative. The establishment of a fixed cycle of twelve labours was attributed by the Greeks to an epic poem, now lost, written by Peisander, dated about 600 BC.[3] After Heracles killed his wife and children, he went to the oracle at Delphi. He prayed to the god Apollo for guidance. Heracles was told to serve the king of Mycenae, Eurystheus, for ten years. During this time, he is sent to perform a series of difficult feats, called labours.[4]
+
+Driven mad by Hera  (queen of the gods), Heracles slew his sons by his wife Megara.[5] After recovering his sanity, Heracles deeply regretted his actions; he was purified by King Thespius, then traveled to Delphi to inquire how he could atone for his actions. Pythia, the Oracle of Delphi, advised him to go to Tiryns and serve his cousin, King Eurystheus, for ten years, performing whatever labours Eurystheus might set him; in return, he would be rewarded with immortality. Heracles despaired at this, loathing to serve a man whom he knew to be far inferior to himself, yet fearing to oppose his father Zeus. Eventually, he placed himself at Eurystheus's disposal.
+
+Eurystheus originally ordered Heracles to perform ten labours. Heracles accomplished these tasks, but Eurystheus refused to recognize two: the slaying of the Lernaean Hydra, as Heracles' nephew and charioteer Iolaus had helped him; and the cleansing of the Augeas, because Heracles accepted payment for the labour. Eurystheus set two more tasks (fetching the Golden Apples of Hesperides and capturing Cerberus), which Heracles also performed, bringing the total number of tasks to twelve.
+
+As they survive, the labours of Heracles are not recounted in any single place, but must be reassembled from many sources. Ruck and Staples[6] assert that there is no one way to interpret the labours, but that six were located in the Peloponnese, culminating with the rededication of Olympia. Six others took the hero farther afield, to places that were, per Ruck, "all previously strongholds of Hera or the 'Goddess' and were Entrances to the Netherworld".[6] In each case, the pattern was the same: Heracles was sent to kill or subdue, or to fetch back for Eurystheus (as Hera's representative) a magical animal or plant.
+
+A famous depiction of the labours in Greek sculpture is found on the metopes of the Temple of Zeus at Olympia, which date to the 450s BC.[citation needed]
+
+In his labours, Heracles was sometimes accompanied by a male companion (an eromenos), according to Licymnius[citation needed] and others, such as Iolaus, his nephew. Although he was supposed to perform only ten labours, this assistance led to two labours being disqualified: Eurystheus refused to recognize slaying the Hydra, because Iolaus helped him, and the cleansing of the Augean stables, because Heracles was paid for his services and/or because the rivers did the work. Several of the labours involved the offspring (by various accounts) of Typhon and his mate Echidna, all overcome by Heracles.
+
+A traditional order of the labours found in the Bibliotheca[7] by Pseudo-Apollodorus is:
+
+Heracles wandered the area until he came to the town of Cleonae. There he met a boy who said that if Heracles slew the Nemean lion and returned alive within 30 days, the town would sacrifice a lion to Zeus, but if he did not return within 30 days or if he died, the boy would sacrifice himself to Zeus. Another version claims that he met Molorchos, a shepherd who had lost his son to the lion, saying that if he came back within 30 days, a ram would be sacrificed to Zeus. If he did not return within 30 days, it would be sacrificed to the dead Heracles as a mourning offering.
+
+While searching for the lion, Heracles fletched some arrows to use against it, not knowing that its golden fur was impenetrable. When he found and shot the lion, firing at it with his bow, he discovered the fur's protective property as the arrow bounced harmlessly off the creature's thigh. After some time, Heracles made the lion return to his cave. The cave had two entrances, one of which Heracles blocked; he then entered the other. In those dark and close quarters, Heracles stunned the beast with his club and, using his immense strength, strangled it to death. During the fight the lion bit off one of his fingers.[8] Others say that he shot arrows at it, eventually shooting it in the unarmored mouth. After slaying the lion, he tried to skin it with a knife from his belt, but failed. He then tried sharpening the knife with a stone and even tried with the stone itself. Finally, Athena, noticing the hero's plight, told Heracles to use one of the lion's own claws to skin the pelt. Others say that Heracles' armor was, in fact, the hide of the Lion of Cithaeron.
+
+When he returned on the 30th day carrying the carcass of the lion on his shoulders, King Eurystheus was amazed and terrified. Eurystheus forbade him ever again to enter the city; from then on he was to display the fruits of his labours outside the city gates. Eurystheus would then tell Heracles his tasks through a herald, not personally. Eurystheus even had a large bronze jar made for him in which to hide from Heracles if need be. Eurystheus then warned him that the tasks would become increasingly difficult.
+
+Heracles' second labour was to slay the Lernaean Hydra, which Hera had raised just to slay Heracles. Upon reaching the swamp near Lake Lerna, where the Hydra dwelt, Heracles used a cloth to cover his mouth and nose to protect himself from the poisonous fumes. He fired flaming arrows into the Hydra's lair, the spring of Amymone, a deep cave that it only came out of to terrorize neighboring villages.[9] He then confronted the Hydra, wielding a harvesting sickle (according to some early vase-paintings), a sword or his famed club. Ruck and Staples (1994: 170) have pointed out that the chthonic creature's reaction was botanical: upon cutting off each of its heads he found that two grew back, an expression of the hopelessness of such a struggle for any but the hero. Additionally, one of the Hydra's heads - the middle one - was immortal.
+
+The details of the struggle are explicit in the Bibliotheca (2.5.2): realizing that he could not defeat the Hydra in this way, Heracles called on his nephew Iolaus for help. His nephew then came upon the idea (possibly inspired by Athena) of using a firebrand to scorch the neck stumps after each decapitation. Heracles cut off each head and Iolaus cauterized the open stumps. Seeing that Heracles was winning the struggle, Hera sent a giant crab to distract him. He crushed it under his mighty foot. He cut off the Hydra's one immortal head with a golden sword given to him by Athena. Heracles placed it under a great rock on the sacred way between Lerna and Elaius (Kerenyi 1959:144), and dipped his arrows in the Hydra's poisonous blood, and so his second task was complete. The alternative version of this myth is that after cutting off one head, he then dipped his sword in it and used its venom to burn each head so it could not grow back. Hera, upset that Heracles had slain the beast she raised to kill him, placed it in the dark blue vault of the sky as the constellation Hydra. She then turned the crab into the constellation Cancer.
+
+Later, Heracles used an arrow dipped in the Hydra's poisonous blood to kill the centaur Nessus; and Nessus's tainted blood was applied to the Tunic of Nessus, by which the centaur had his posthumous revenge. Both Strabo and Pausanias report that the stench of the river Anigrus in Elis, making all the fish of the river inedible, was reputed to be due to the Hydra's venom, washed from the arrows Heracles used on the centaur.[10]
+
+Eurystheus and Hera were greatly angered that Heracles had survived the Nemean Lion and the Lernaean Hydra. For the third labour, they found a task which they thought would spell doom for the hero. It was not slaying a beast or monster, as it had already been established that Heracles could overcome even the most fearsome opponents. Instead, Eurystheus ordered him to capture the Ceryneian Hind, which was so fast that it could outrun an arrow.
+
+After beginning the search, Heracles awoke from sleeping and saw the hind by the glint on its antlers. Heracles then chased the hind on foot for a full year through Greece, Thrace, Istria, and the land of the Hyperboreans. In some versions, he captured the hind while it slept, rendering it lame with a trap net. In other versions, he encountered Artemis in her temple; she told him to leave the hind and tell Eurystheus all that had happened, and his third labour would be considered to be completed. Yet another version claims that Heracles trapped the Hind with an arrow between its forelegs.
+
+Eurystheus had given Heracles this task hoping to incite Artemis' anger at Heracles for his desecration of her sacred animal. As he was returning with the hind, Heracles encountered Artemis and her brother Apollo. He begged the goddess for forgiveness, explaining that he had to catch it as part of his penance, but he promised to return it. Artemis forgave him, foiling Eurystheus' plan to have her punish him.
+
+Upon bringing the hind to Eurystheus, he was told that it was to become part of the King's menagerie. Heracles knew that he had to return the hind as he had promised, so he agreed to hand it over on the condition that Eurystheus himself come out and take it from him. The King came out, but the moment that Heracles let the hind go, it sprinted back to its mistress and Heracles left, saying that Eurystheus had not been quick enough.
+
+Eurystheus was disappointed that Heracles had overcome yet another creature and was humiliated by the hind's escape, so he assigned Heracles another dangerous task. By some accounts, the fourth labour was to bring the fearsome Erymanthian Boar back to Eurystheus alive (there is no single definitive telling of the labours). On the way to Mount Erymanthos where the boar lived, Heracles visited Pholus ("caveman"), a kind and hospitable centaur and old friend. Heracles ate with Pholus in his cavern (though the centaur devoured his meat raw) and asked for wine. Pholus had only one jar of wine, a gift from Dionysus to all the centaurs on Mount Erymanthos. Heracles convinced him to open it, and the smell attracted the other centaurs. They did not understand that wine needs to be tempered with water, became drunk, and attacked Heracles. Heracles shot at them with his poisonous arrows, killing many, and the centaurs retreated all the way to Chiron's cave.
+
+Pholus was curious why the arrows caused so much death. He picked one up but dropped it, and the arrow stabbed his hoof, poisoning him. One version states that a stray arrow hit Chiron as well. He was immortal, but he still felt the pain. Chiron's pain was so great that he volunteered to give up his immortality and take the place of Prometheus, who had been chained to the top of a mountain to have his liver eaten daily by an eagle. Prometheus' torturer, the eagle, continued its torture on Chiron, so Heracles shot it dead with an arrow. It is generally accepted that the tale was meant to show Heracles as being the recipient of Chiron's surrendered immortality. However, this tale contradicts the fact that Chiron later taught Achilles. The tale of the centaurs sometimes appears in other parts of the twelve labours, as does the freeing of Prometheus.
+
+Heracles had visited Chiron to gain advice on how to catch the boar, and Chiron had told him to drive it into thick snow, which sets this labour in mid-winter. Heracles caught the boar, bound it, and carried it back to Eurystheus, who was frightened of it and ducked down in his half-buried storage pithos, begging Heracles to get rid of the beast.
+
+The fifth labour was to clean the stables of King Augeas. This assignment was intended to be both humiliating (rather than impressive, as the previous labours had been) and impossible, since the livestock were divinely healthy (and immortal) and therefore produced an enormous quantity of dung. The Augean Stables (/ɔːˈdʒiːən/) had not been cleaned in over 30 years, and over 1,000 cattle lived there. However, Heracles succeeded by re-routing the rivers Alpheus and Peneus to wash out the filth.
+
+Before starting on the task, Heracles had asked Augeas for one-tenth of the cattle if he finished the task in one day, and Augeas agreed. But afterwards Augeas refused to honour the agreement on the grounds that Heracles had been ordered to carry out the task by Eurystheus anyway. Heracles claimed his reward in court, and was supported by Augeas' son Phyleus. Augeas banished them both before the court had ruled. Heracles returned, slew Augeas, and gave his kingdom to Phyleus. Heracles then founded the Olympic Games.
+The success of this labour was ultimately discounted as the rushing waters had done the work of cleaning the stables and because Heracles was paid for doing the labour. 
+Eurystheus said that Heracles still had seven labours to perform.[11]
+
+The sixth labour was to defeat the Stymphalian birds, man-eating birds with beaks made of bronze and sharp metallic feathers they could launch at their victims. They were sacred to Ares, the god of war. Furthermore, their dung was highly toxic. They had migrated to Lake Stymphalia in Arcadia, where they bred quickly and took over the countryside, destroying local crops, fruit trees, and townspeople. Heracles could not go too far into the swamp, for it would not support his weight. Athena, noticing the hero's plight, gave Heracles a rattle which Hephaestus had made especially for the occasion. Heracles shook the rattle and frightened the birds into the air. Heracles then shot many of them with his arrows. The rest flew far away, never to return. The Argonauts would later encounter them.
+
+The seventh labour was to capture the Cretan Bull, father of the Minotaur. Heracles sailed to Crete, where King Minos gave Heracles permission to take the bull away and even offered him assistance (which Heracles declined, plausibly because he did not want the labour to be discounted as before).[12] The bull had been wreaking havoc on Crete by uprooting crops and leveling orchard walls. Heracles sneaked up behind the bull and then used his hands to throttle it (stopping before it was killed), and then shipped it back to Tiryns. Eurystheus, who hid in his pithos at first sight of the creature, wanted to sacrifice the bull to Hera, who hated Heracles. She refused the sacrifice because it reflected glory on Heracles. The bull was released and wandered into Marathon, becoming known as the Marathonian Bull.[12] Theseus would later sacrifice the bull to Athena and/or Apollo.
+
+As the eighth of his Twelve Labours, also categorised as the second of the Non-Peloponneisan labours,[13] Heracles was sent by King Eurystheus to steal the Mares from Diomedes. The mares’ madness was attributed to their unnatural diet which consisted of the flesh[14] of unsuspecting guests or strangers to the island.[15] Some versions of the myth say that the mares also expelled fire when they breathed.[16] The Mares, which were the terror of Thrace, were kept tethered by iron chains to a bronze manger in the now vanished city of Tirida[17] and were named Podargos (the swift), Lampon (the shining), Xanthos (the yellow) and Deinos (or Deinus, the terrible).[18] Although very similar, there are slight variances in the exact details regarding the mares’ capture.
+
+In one version, Heracles brought a number of volunteers to help him capture the giant horses.[17] After overpowering Diomedes’ men, Heracles broke the chains that tethered the horses and drove the mares down to sea. Unaware that the mares were man-eating and uncontrollable, Heracles left them in the charge of his favored companion, Abderus, while he left to fight Diomedes. Upon his return, Heracles found that the boy was eaten. As revenge, Heracles fed Diomedes to his own horses and then founded Abdera next to the boy's tomb.[15]
+
+In another version, Heracles, who was visiting the island, stayed awake so that he didn't have his throat cut by Diomedes in the night, and cut the chains binding the horses once everyone was asleep. Having scared the horses onto the high ground of a knoll, Heracles quickly dug a trench through the peninsula, filling it with water and thus flooding the low-lying plain. When Diomedes and his men turned to flee, Heracles killed them with an axe (or a club[17]), and fed Diomedes’ body to the horses to calm them.
+
+In yet another version, Heracles first captured Diomedes and fed him to the mares before releasing them. Only after realizing that their King was dead did his men, the Bistonians,[15][17] attack Heracles. Upon seeing the mares charging at them, led in a chariot by Abderus, the Bistonians turned and fled.
+
+All versions have eating human flesh make the horses calmer, giving Heracles the opportunity to bind their mouths shut, and easily take them back to King Eurystheus, who dedicated the horses to Hera.[19] In some versions, they were allowed to roam freely around Argos, having become permanently calm, but in others, Eurystheus ordered the horses taken to Olympus to be sacrificed to Zeus, but Zeus refused them, and sent wolves, lions, and bears to kill them.[20] Roger Lancelyn Green states in his Tales of the Greek Heroes that the mares’ descendants were used in the Trojan War, and survived even to the time of Alexander the Great.[17][21] After the incident, Eurystheus sent Heracles to bring back Hippolyta's Girdle.
+
+Eurystheus' daughter Admete wanted the Belt of Hippolyta, queen of the Amazons, a gift from her father Ares. To please his daughter, Eurystheus ordered Heracles to retrieve the belt as his ninth labour.
+
+Taking a band of friends with him, Heracles set sail, stopping at the island of Paros, which was inhabited by some sons of Minos. The sons killed two of Heracles' companions, an act which set Heracles on a rampage. He killed two of the sons of Minos and threatened the other inhabitants until he was offered two men to replace his fallen companions. Heracles agreed and took two of Minos' grandsons, Alcaeus and Sthenelus. They continued their voyage and landed at the court of Lycus, whom Heracles defended in a battle against King Mygdon of Bebryces. After killing King Mygdon, Heracles gave much of the land to his friend Lycus. Lycus called the land Heraclea. The crew then set off for Themiscyra, where Hippolyta lived.
+
+All would have gone well for Heracles had it not been for Hera. Hippolyta, impressed with Heracles and his exploits, agreed to give him the belt and would have done so had Hera not disguised herself and walked among the Amazons sowing seeds of distrust. She claimed the strangers were plotting to carry off the queen of the Amazons. Alarmed, the women set off on horseback to confront Heracles. When Heracles saw them, he thought Hippolyta had been plotting such treachery all along and had never meant to hand over the belt, so he killed her, took the belt and returned to Eurystheus.
+
+The tenth labour was to obtain the Cattle of the three-bodied giant Geryon. In the fullest account in the Bibliotheca of Pseudo-Apollodorus,[22] Heracles had to go to the island of Erytheia in the far west (sometimes identified with the Hesperides, or with the island which forms the city of Cádiz) to get the cattle. On the way there, he crossed the Libyan desert[23] and became so frustrated at the heat that he shot an arrow at the Sun. The sun-god Helios "in admiration of his courage" gave Heracles the golden cup Helios used to sail across the sea from west to east each night. Heracles rode the cup to Erytheia; Heracles in the cup was a favorite motif on black-figure pottery.[citation needed] Such a magical conveyance undercuts any literal geography for Erytheia, the "red island" of the sunset.
+
+When Heracles landed at Erytheia, he was confronted by the two-headed dog Orthrus. With one blow from his olive-wood club, Heracles killed Orthrus. Eurytion the herdsman came to assist Orthrus, but Heracles dealt with him the same way.
+
+On hearing the commotion, Geryon sprang into action, carrying three shields and three spears, and wearing three helmets. He attacked Heracles at the River Anthemus, but was slain by one of Heracles' poisoned arrows. Heracles shot so forcefully that the arrow pierced Geryon's forehead, "and Geryon bent his neck over to one side, like a poppy that spoils its delicate shapes, shedding its petals all at once."[24]
+
+Heracles then had to herd the cattle back to Eurystheus. In Roman versions of the narrative, Heracles drove the cattle over the Aventine Hill on the future site of Rome. The giant Cacus, who lived there, stole some of the cattle as Heracles slept, making the cattle walk backwards so that they left no trail, a repetition of the trick of the young Hermes. According to some versions, Heracles drove his remaining cattle past the cave, where Cacus had hidden the stolen animals, and they began calling out to each other. In other versions, Cacus' sister Caca told Heracles where he was. Heracles then killed Cacus, and set up an altar on the spot, later the site of Rome's Forum Boarium (the cattle market).
+
+To annoy Heracles, Hera sent a gadfly to bite the cattle, irritate them, and scatter them. Within a year, Heracles retrieved them. Hera then sent a flood which raised the level of a river so much that Heracles could not cross with the cattle. He piled stones into the river to make the water shallower. When he finally reached the court of Eurystheus, the cattle were sacrificed to Hera.
+
+After Heracles completed the first ten labours, Eurystheus gave him two more, claiming that slaying the Hydra did not count (because Iolaus helped Heracles), neither did cleaning the Augean Stables (either because he was paid for the job or because the rivers did the work).
+
+The first additional labour was to steal three of the golden apples from the garden of the Hesperides. Heracles first caught the Old Man of the Sea, the shapeshifting sea god,[25] to learn where the Garden of the Hesperides was located.[26]
+
+In some variations, Heracles, either at the start or at the end of this task, meets Antaeus, who was invincible as long as he touched his mother, Gaia, the Earth. Heracles killed Antaeus by holding him aloft and crushing him in a bear hug.[27]
+
+Herodotus claims that Heracles stopped in Egypt, where King Busiris decided to make him the yearly sacrifice, but Heracles burst out of his chains.
+
+Heracles finally made his way to the garden of the Hesperides, where he encountered Atlas holding up the heavens on his shoulders. Heracles persuaded Atlas to get the three golden Apples for him by offering to hold up the heavens in his place for a little while. Atlas could get the apples because, in this version, he was the father or otherwise related to the Hesperides. This would have made the labour – like the Hydra and the Augean stables – void because Heracles had received help. When Atlas returned, he decided that he did not want to take the heavens back, and instead offered to deliver the apples himself, but Heracles tricked him by agreeing to remain in place of Atlas on the condition that Atlas relieve him temporarily while Heracles adjusted his cloak. Atlas agreed, but Heracles reneged and walked away with the apples. According to an alternative version, Heracles slew Ladon, the dragon who guarded the apples instead. Eurystheus was furious that Heracles had accomplished something that Eurystheus thought could not possibly be done.
+
+The twelfth and final labour was the capture of Cerberus, the three-headed, dragon-tailed dog that was the guardian of the gates of the Underworld. To prepare for his descent into the Underworld, Heracles went to Eleusis (or Athens) to be initiated in the Eleusinian Mysteries. He entered the Underworld, and Hermes and Athena were his guides.
+
+While in the Underworld, Heracles met Theseus and Pirithous. The two companions had been imprisoned by Hades for attempting to kidnap Persephone. One tradition tells of snakes coiling around their legs, then turning into stone; another that Hades feigned hospitality and prepared a feast inviting them to sit. They unknowingly sat in chairs of forgetfulness and were permanently ensnared. When Heracles had pulled Theseus first from his chair, some of his thigh stuck to it (this explains the supposedly lean thighs of Athenians), but the Earth shook at the attempt to liberate Pirithous, whose desire to have the goddess for himself was so insulting he was doomed to stay behind.
+
+Heracles found Hades and asked permission to bring Cerberus to the surface, which Hades agreed to if Heracles could subdue the beast without using weapons. Heracles overpowered Cerberus with his bare hands and slung the beast over his back. He carried Cerberus out of the Underworld through a cavern entrance in the Peloponnese and brought it to Eurystheus, who again fled into his pithos.  Eurystheus begged Heracles to return Cerberus to the Underworld, offering in return to release him from any further labours when Cerberus disappeared back to his master.
+
+After completing the Twelve Labours, one tradition says Heracles joined Jason and the Argonauts in their quest for the Golden Fleece. However, Herodorus (c. 400 BC) disputed this and denied Heracles ever sailed with the Argonauts. A separate tradition (e.g. Argonautica) has Heracles accompany the Argonauts, but he did not travel with them as far as Colchis.
+
+Some ancient Greeks found allegorical meanings of a moral, psychological or philosophical nature in the Labours of Heracles.  This trend became more prominent in the Renaissance.[28]  For example, Heraclitus the Grammarian wrote in his Homeric Problems:
+
+I turn to Heracles. We must not suppose he attained such power in those days as a result of his physical strength. Rather, he was a man of intellect, an initiate in heavenly wisdom, who, as it were, shed light on philosophy, which had been hidden in deep darkness. The most authoritative of the Stoics agree with this account.... The (Erymanthian) boar which he overcame is the common incontinence of men; the (Nemean) lion is the indiscriminate rush towards improper goals; in the same way, by fettering irrational passions he gave rise to the belief that he had fettered the violent (Cretan) bull. He banished cowardice also from the world, in the shape of the hind of Ceryneia. There was another "labor" too, not properly so called, in which he cleared out the mass of dung (from the Augean stables) — in other words, the foulness that disfigures humanity. The (Stymphalian) birds he scattered are the windy hopes that feed our lives; the many-headed hydra that he burned, as it were, with the fires of exhortation, is pleasure, which begins to grow again as soon as it is cut out.

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+The Twelve Labours of Heracles or Hercules (Greek: οἱ Ἡρακλέους ἆθλοι, hoi Hērakléous âthloi)[1][2] are a series of episodes concerning a penance carried out by Heracles, the greatest of the Greek heroes, whose name was later romanised as Hercules. They were accomplished at the service of King Eurystheus. The episodes were later connected by a continuous narrative. The establishment of a fixed cycle of twelve labours was attributed by the Greeks to an epic poem, now lost, written by Peisander, dated about 600 BC.[3] After Heracles killed his wife and children, he went to the oracle at Delphi. He prayed to the god Apollo for guidance. Heracles was told to serve the king of Mycenae, Eurystheus, for ten years. During this time, he is sent to perform a series of difficult feats, called labours.[4]
+
+Driven mad by Hera  (queen of the gods), Heracles slew his sons by his wife Megara.[5] After recovering his sanity, Heracles deeply regretted his actions; he was purified by King Thespius, then traveled to Delphi to inquire how he could atone for his actions. Pythia, the Oracle of Delphi, advised him to go to Tiryns and serve his cousin, King Eurystheus, for ten years, performing whatever labours Eurystheus might set him; in return, he would be rewarded with immortality. Heracles despaired at this, loathing to serve a man whom he knew to be far inferior to himself, yet fearing to oppose his father Zeus. Eventually, he placed himself at Eurystheus's disposal.
+
+Eurystheus originally ordered Heracles to perform ten labours. Heracles accomplished these tasks, but Eurystheus refused to recognize two: the slaying of the Lernaean Hydra, as Heracles' nephew and charioteer Iolaus had helped him; and the cleansing of the Augeas, because Heracles accepted payment for the labour. Eurystheus set two more tasks (fetching the Golden Apples of Hesperides and capturing Cerberus), which Heracles also performed, bringing the total number of tasks to twelve.
+
+As they survive, the labours of Heracles are not recounted in any single place, but must be reassembled from many sources. Ruck and Staples[6] assert that there is no one way to interpret the labours, but that six were located in the Peloponnese, culminating with the rededication of Olympia. Six others took the hero farther afield, to places that were, per Ruck, "all previously strongholds of Hera or the 'Goddess' and were Entrances to the Netherworld".[6] In each case, the pattern was the same: Heracles was sent to kill or subdue, or to fetch back for Eurystheus (as Hera's representative) a magical animal or plant.
+
+A famous depiction of the labours in Greek sculpture is found on the metopes of the Temple of Zeus at Olympia, which date to the 450s BC.[citation needed]
+
+In his labours, Heracles was sometimes accompanied by a male companion (an eromenos), according to Licymnius[citation needed] and others, such as Iolaus, his nephew. Although he was supposed to perform only ten labours, this assistance led to two labours being disqualified: Eurystheus refused to recognize slaying the Hydra, because Iolaus helped him, and the cleansing of the Augean stables, because Heracles was paid for his services and/or because the rivers did the work. Several of the labours involved the offspring (by various accounts) of Typhon and his mate Echidna, all overcome by Heracles.
+
+A traditional order of the labours found in the Bibliotheca[7] by Pseudo-Apollodorus is:
+
+Heracles wandered the area until he came to the town of Cleonae. There he met a boy who said that if Heracles slew the Nemean lion and returned alive within 30 days, the town would sacrifice a lion to Zeus, but if he did not return within 30 days or if he died, the boy would sacrifice himself to Zeus. Another version claims that he met Molorchos, a shepherd who had lost his son to the lion, saying that if he came back within 30 days, a ram would be sacrificed to Zeus. If he did not return within 30 days, it would be sacrificed to the dead Heracles as a mourning offering.
+
+While searching for the lion, Heracles fletched some arrows to use against it, not knowing that its golden fur was impenetrable. When he found and shot the lion, firing at it with his bow, he discovered the fur's protective property as the arrow bounced harmlessly off the creature's thigh. After some time, Heracles made the lion return to his cave. The cave had two entrances, one of which Heracles blocked; he then entered the other. In those dark and close quarters, Heracles stunned the beast with his club and, using his immense strength, strangled it to death. During the fight the lion bit off one of his fingers.[8] Others say that he shot arrows at it, eventually shooting it in the unarmored mouth. After slaying the lion, he tried to skin it with a knife from his belt, but failed. He then tried sharpening the knife with a stone and even tried with the stone itself. Finally, Athena, noticing the hero's plight, told Heracles to use one of the lion's own claws to skin the pelt. Others say that Heracles' armor was, in fact, the hide of the Lion of Cithaeron.
+
+When he returned on the 30th day carrying the carcass of the lion on his shoulders, King Eurystheus was amazed and terrified. Eurystheus forbade him ever again to enter the city; from then on he was to display the fruits of his labours outside the city gates. Eurystheus would then tell Heracles his tasks through a herald, not personally. Eurystheus even had a large bronze jar made for him in which to hide from Heracles if need be. Eurystheus then warned him that the tasks would become increasingly difficult.
+
+Heracles' second labour was to slay the Lernaean Hydra, which Hera had raised just to slay Heracles. Upon reaching the swamp near Lake Lerna, where the Hydra dwelt, Heracles used a cloth to cover his mouth and nose to protect himself from the poisonous fumes. He fired flaming arrows into the Hydra's lair, the spring of Amymone, a deep cave that it only came out of to terrorize neighboring villages.[9] He then confronted the Hydra, wielding a harvesting sickle (according to some early vase-paintings), a sword or his famed club. Ruck and Staples (1994: 170) have pointed out that the chthonic creature's reaction was botanical: upon cutting off each of its heads he found that two grew back, an expression of the hopelessness of such a struggle for any but the hero. Additionally, one of the Hydra's heads - the middle one - was immortal.
+
+The details of the struggle are explicit in the Bibliotheca (2.5.2): realizing that he could not defeat the Hydra in this way, Heracles called on his nephew Iolaus for help. His nephew then came upon the idea (possibly inspired by Athena) of using a firebrand to scorch the neck stumps after each decapitation. Heracles cut off each head and Iolaus cauterized the open stumps. Seeing that Heracles was winning the struggle, Hera sent a giant crab to distract him. He crushed it under his mighty foot. He cut off the Hydra's one immortal head with a golden sword given to him by Athena. Heracles placed it under a great rock on the sacred way between Lerna and Elaius (Kerenyi 1959:144), and dipped his arrows in the Hydra's poisonous blood, and so his second task was complete. The alternative version of this myth is that after cutting off one head, he then dipped his sword in it and used its venom to burn each head so it could not grow back. Hera, upset that Heracles had slain the beast she raised to kill him, placed it in the dark blue vault of the sky as the constellation Hydra. She then turned the crab into the constellation Cancer.
+
+Later, Heracles used an arrow dipped in the Hydra's poisonous blood to kill the centaur Nessus; and Nessus's tainted blood was applied to the Tunic of Nessus, by which the centaur had his posthumous revenge. Both Strabo and Pausanias report that the stench of the river Anigrus in Elis, making all the fish of the river inedible, was reputed to be due to the Hydra's venom, washed from the arrows Heracles used on the centaur.[10]
+
+Eurystheus and Hera were greatly angered that Heracles had survived the Nemean Lion and the Lernaean Hydra. For the third labour, they found a task which they thought would spell doom for the hero. It was not slaying a beast or monster, as it had already been established that Heracles could overcome even the most fearsome opponents. Instead, Eurystheus ordered him to capture the Ceryneian Hind, which was so fast that it could outrun an arrow.
+
+After beginning the search, Heracles awoke from sleeping and saw the hind by the glint on its antlers. Heracles then chased the hind on foot for a full year through Greece, Thrace, Istria, and the land of the Hyperboreans. In some versions, he captured the hind while it slept, rendering it lame with a trap net. In other versions, he encountered Artemis in her temple; she told him to leave the hind and tell Eurystheus all that had happened, and his third labour would be considered to be completed. Yet another version claims that Heracles trapped the Hind with an arrow between its forelegs.
+
+Eurystheus had given Heracles this task hoping to incite Artemis' anger at Heracles for his desecration of her sacred animal. As he was returning with the hind, Heracles encountered Artemis and her brother Apollo. He begged the goddess for forgiveness, explaining that he had to catch it as part of his penance, but he promised to return it. Artemis forgave him, foiling Eurystheus' plan to have her punish him.
+
+Upon bringing the hind to Eurystheus, he was told that it was to become part of the King's menagerie. Heracles knew that he had to return the hind as he had promised, so he agreed to hand it over on the condition that Eurystheus himself come out and take it from him. The King came out, but the moment that Heracles let the hind go, it sprinted back to its mistress and Heracles left, saying that Eurystheus had not been quick enough.
+
+Eurystheus was disappointed that Heracles had overcome yet another creature and was humiliated by the hind's escape, so he assigned Heracles another dangerous task. By some accounts, the fourth labour was to bring the fearsome Erymanthian Boar back to Eurystheus alive (there is no single definitive telling of the labours). On the way to Mount Erymanthos where the boar lived, Heracles visited Pholus ("caveman"), a kind and hospitable centaur and old friend. Heracles ate with Pholus in his cavern (though the centaur devoured his meat raw) and asked for wine. Pholus had only one jar of wine, a gift from Dionysus to all the centaurs on Mount Erymanthos. Heracles convinced him to open it, and the smell attracted the other centaurs. They did not understand that wine needs to be tempered with water, became drunk, and attacked Heracles. Heracles shot at them with his poisonous arrows, killing many, and the centaurs retreated all the way to Chiron's cave.
+
+Pholus was curious why the arrows caused so much death. He picked one up but dropped it, and the arrow stabbed his hoof, poisoning him. One version states that a stray arrow hit Chiron as well. He was immortal, but he still felt the pain. Chiron's pain was so great that he volunteered to give up his immortality and take the place of Prometheus, who had been chained to the top of a mountain to have his liver eaten daily by an eagle. Prometheus' torturer, the eagle, continued its torture on Chiron, so Heracles shot it dead with an arrow. It is generally accepted that the tale was meant to show Heracles as being the recipient of Chiron's surrendered immortality. However, this tale contradicts the fact that Chiron later taught Achilles. The tale of the centaurs sometimes appears in other parts of the twelve labours, as does the freeing of Prometheus.
+
+Heracles had visited Chiron to gain advice on how to catch the boar, and Chiron had told him to drive it into thick snow, which sets this labour in mid-winter. Heracles caught the boar, bound it, and carried it back to Eurystheus, who was frightened of it and ducked down in his half-buried storage pithos, begging Heracles to get rid of the beast.
+
+The fifth labour was to clean the stables of King Augeas. This assignment was intended to be both humiliating (rather than impressive, as the previous labours had been) and impossible, since the livestock were divinely healthy (and immortal) and therefore produced an enormous quantity of dung. The Augean Stables (/ɔːˈdʒiːən/) had not been cleaned in over 30 years, and over 1,000 cattle lived there. However, Heracles succeeded by re-routing the rivers Alpheus and Peneus to wash out the filth.
+
+Before starting on the task, Heracles had asked Augeas for one-tenth of the cattle if he finished the task in one day, and Augeas agreed. But afterwards Augeas refused to honour the agreement on the grounds that Heracles had been ordered to carry out the task by Eurystheus anyway. Heracles claimed his reward in court, and was supported by Augeas' son Phyleus. Augeas banished them both before the court had ruled. Heracles returned, slew Augeas, and gave his kingdom to Phyleus. Heracles then founded the Olympic Games.
+The success of this labour was ultimately discounted as the rushing waters had done the work of cleaning the stables and because Heracles was paid for doing the labour. 
+Eurystheus said that Heracles still had seven labours to perform.[11]
+
+The sixth labour was to defeat the Stymphalian birds, man-eating birds with beaks made of bronze and sharp metallic feathers they could launch at their victims. They were sacred to Ares, the god of war. Furthermore, their dung was highly toxic. They had migrated to Lake Stymphalia in Arcadia, where they bred quickly and took over the countryside, destroying local crops, fruit trees, and townspeople. Heracles could not go too far into the swamp, for it would not support his weight. Athena, noticing the hero's plight, gave Heracles a rattle which Hephaestus had made especially for the occasion. Heracles shook the rattle and frightened the birds into the air. Heracles then shot many of them with his arrows. The rest flew far away, never to return. The Argonauts would later encounter them.
+
+The seventh labour was to capture the Cretan Bull, father of the Minotaur. Heracles sailed to Crete, where King Minos gave Heracles permission to take the bull away and even offered him assistance (which Heracles declined, plausibly because he did not want the labour to be discounted as before).[12] The bull had been wreaking havoc on Crete by uprooting crops and leveling orchard walls. Heracles sneaked up behind the bull and then used his hands to throttle it (stopping before it was killed), and then shipped it back to Tiryns. Eurystheus, who hid in his pithos at first sight of the creature, wanted to sacrifice the bull to Hera, who hated Heracles. She refused the sacrifice because it reflected glory on Heracles. The bull was released and wandered into Marathon, becoming known as the Marathonian Bull.[12] Theseus would later sacrifice the bull to Athena and/or Apollo.
+
+As the eighth of his Twelve Labours, also categorised as the second of the Non-Peloponneisan labours,[13] Heracles was sent by King Eurystheus to steal the Mares from Diomedes. The mares’ madness was attributed to their unnatural diet which consisted of the flesh[14] of unsuspecting guests or strangers to the island.[15] Some versions of the myth say that the mares also expelled fire when they breathed.[16] The Mares, which were the terror of Thrace, were kept tethered by iron chains to a bronze manger in the now vanished city of Tirida[17] and were named Podargos (the swift), Lampon (the shining), Xanthos (the yellow) and Deinos (or Deinus, the terrible).[18] Although very similar, there are slight variances in the exact details regarding the mares’ capture.
+
+In one version, Heracles brought a number of volunteers to help him capture the giant horses.[17] After overpowering Diomedes’ men, Heracles broke the chains that tethered the horses and drove the mares down to sea. Unaware that the mares were man-eating and uncontrollable, Heracles left them in the charge of his favored companion, Abderus, while he left to fight Diomedes. Upon his return, Heracles found that the boy was eaten. As revenge, Heracles fed Diomedes to his own horses and then founded Abdera next to the boy's tomb.[15]
+
+In another version, Heracles, who was visiting the island, stayed awake so that he didn't have his throat cut by Diomedes in the night, and cut the chains binding the horses once everyone was asleep. Having scared the horses onto the high ground of a knoll, Heracles quickly dug a trench through the peninsula, filling it with water and thus flooding the low-lying plain. When Diomedes and his men turned to flee, Heracles killed them with an axe (or a club[17]), and fed Diomedes’ body to the horses to calm them.
+
+In yet another version, Heracles first captured Diomedes and fed him to the mares before releasing them. Only after realizing that their King was dead did his men, the Bistonians,[15][17] attack Heracles. Upon seeing the mares charging at them, led in a chariot by Abderus, the Bistonians turned and fled.
+
+All versions have eating human flesh make the horses calmer, giving Heracles the opportunity to bind their mouths shut, and easily take them back to King Eurystheus, who dedicated the horses to Hera.[19] In some versions, they were allowed to roam freely around Argos, having become permanently calm, but in others, Eurystheus ordered the horses taken to Olympus to be sacrificed to Zeus, but Zeus refused them, and sent wolves, lions, and bears to kill them.[20] Roger Lancelyn Green states in his Tales of the Greek Heroes that the mares’ descendants were used in the Trojan War, and survived even to the time of Alexander the Great.[17][21] After the incident, Eurystheus sent Heracles to bring back Hippolyta's Girdle.
+
+Eurystheus' daughter Admete wanted the Belt of Hippolyta, queen of the Amazons, a gift from her father Ares. To please his daughter, Eurystheus ordered Heracles to retrieve the belt as his ninth labour.
+
+Taking a band of friends with him, Heracles set sail, stopping at the island of Paros, which was inhabited by some sons of Minos. The sons killed two of Heracles' companions, an act which set Heracles on a rampage. He killed two of the sons of Minos and threatened the other inhabitants until he was offered two men to replace his fallen companions. Heracles agreed and took two of Minos' grandsons, Alcaeus and Sthenelus. They continued their voyage and landed at the court of Lycus, whom Heracles defended in a battle against King Mygdon of Bebryces. After killing King Mygdon, Heracles gave much of the land to his friend Lycus. Lycus called the land Heraclea. The crew then set off for Themiscyra, where Hippolyta lived.
+
+All would have gone well for Heracles had it not been for Hera. Hippolyta, impressed with Heracles and his exploits, agreed to give him the belt and would have done so had Hera not disguised herself and walked among the Amazons sowing seeds of distrust. She claimed the strangers were plotting to carry off the queen of the Amazons. Alarmed, the women set off on horseback to confront Heracles. When Heracles saw them, he thought Hippolyta had been plotting such treachery all along and had never meant to hand over the belt, so he killed her, took the belt and returned to Eurystheus.
+
+The tenth labour was to obtain the Cattle of the three-bodied giant Geryon. In the fullest account in the Bibliotheca of Pseudo-Apollodorus,[22] Heracles had to go to the island of Erytheia in the far west (sometimes identified with the Hesperides, or with the island which forms the city of Cádiz) to get the cattle. On the way there, he crossed the Libyan desert[23] and became so frustrated at the heat that he shot an arrow at the Sun. The sun-god Helios "in admiration of his courage" gave Heracles the golden cup Helios used to sail across the sea from west to east each night. Heracles rode the cup to Erytheia; Heracles in the cup was a favorite motif on black-figure pottery.[citation needed] Such a magical conveyance undercuts any literal geography for Erytheia, the "red island" of the sunset.
+
+When Heracles landed at Erytheia, he was confronted by the two-headed dog Orthrus. With one blow from his olive-wood club, Heracles killed Orthrus. Eurytion the herdsman came to assist Orthrus, but Heracles dealt with him the same way.
+
+On hearing the commotion, Geryon sprang into action, carrying three shields and three spears, and wearing three helmets. He attacked Heracles at the River Anthemus, but was slain by one of Heracles' poisoned arrows. Heracles shot so forcefully that the arrow pierced Geryon's forehead, "and Geryon bent his neck over to one side, like a poppy that spoils its delicate shapes, shedding its petals all at once."[24]
+
+Heracles then had to herd the cattle back to Eurystheus. In Roman versions of the narrative, Heracles drove the cattle over the Aventine Hill on the future site of Rome. The giant Cacus, who lived there, stole some of the cattle as Heracles slept, making the cattle walk backwards so that they left no trail, a repetition of the trick of the young Hermes. According to some versions, Heracles drove his remaining cattle past the cave, where Cacus had hidden the stolen animals, and they began calling out to each other. In other versions, Cacus' sister Caca told Heracles where he was. Heracles then killed Cacus, and set up an altar on the spot, later the site of Rome's Forum Boarium (the cattle market).
+
+To annoy Heracles, Hera sent a gadfly to bite the cattle, irritate them, and scatter them. Within a year, Heracles retrieved them. Hera then sent a flood which raised the level of a river so much that Heracles could not cross with the cattle. He piled stones into the river to make the water shallower. When he finally reached the court of Eurystheus, the cattle were sacrificed to Hera.
+
+After Heracles completed the first ten labours, Eurystheus gave him two more, claiming that slaying the Hydra did not count (because Iolaus helped Heracles), neither did cleaning the Augean Stables (either because he was paid for the job or because the rivers did the work).
+
+The first additional labour was to steal three of the golden apples from the garden of the Hesperides. Heracles first caught the Old Man of the Sea, the shapeshifting sea god,[25] to learn where the Garden of the Hesperides was located.[26]
+
+In some variations, Heracles, either at the start or at the end of this task, meets Antaeus, who was invincible as long as he touched his mother, Gaia, the Earth. Heracles killed Antaeus by holding him aloft and crushing him in a bear hug.[27]
+
+Herodotus claims that Heracles stopped in Egypt, where King Busiris decided to make him the yearly sacrifice, but Heracles burst out of his chains.
+
+Heracles finally made his way to the garden of the Hesperides, where he encountered Atlas holding up the heavens on his shoulders. Heracles persuaded Atlas to get the three golden Apples for him by offering to hold up the heavens in his place for a little while. Atlas could get the apples because, in this version, he was the father or otherwise related to the Hesperides. This would have made the labour – like the Hydra and the Augean stables – void because Heracles had received help. When Atlas returned, he decided that he did not want to take the heavens back, and instead offered to deliver the apples himself, but Heracles tricked him by agreeing to remain in place of Atlas on the condition that Atlas relieve him temporarily while Heracles adjusted his cloak. Atlas agreed, but Heracles reneged and walked away with the apples. According to an alternative version, Heracles slew Ladon, the dragon who guarded the apples instead. Eurystheus was furious that Heracles had accomplished something that Eurystheus thought could not possibly be done.
+
+The twelfth and final labour was the capture of Cerberus, the three-headed, dragon-tailed dog that was the guardian of the gates of the Underworld. To prepare for his descent into the Underworld, Heracles went to Eleusis (or Athens) to be initiated in the Eleusinian Mysteries. He entered the Underworld, and Hermes and Athena were his guides.
+
+While in the Underworld, Heracles met Theseus and Pirithous. The two companions had been imprisoned by Hades for attempting to kidnap Persephone. One tradition tells of snakes coiling around their legs, then turning into stone; another that Hades feigned hospitality and prepared a feast inviting them to sit. They unknowingly sat in chairs of forgetfulness and were permanently ensnared. When Heracles had pulled Theseus first from his chair, some of his thigh stuck to it (this explains the supposedly lean thighs of Athenians), but the Earth shook at the attempt to liberate Pirithous, whose desire to have the goddess for himself was so insulting he was doomed to stay behind.
+
+Heracles found Hades and asked permission to bring Cerberus to the surface, which Hades agreed to if Heracles could subdue the beast without using weapons. Heracles overpowered Cerberus with his bare hands and slung the beast over his back. He carried Cerberus out of the Underworld through a cavern entrance in the Peloponnese and brought it to Eurystheus, who again fled into his pithos.  Eurystheus begged Heracles to return Cerberus to the Underworld, offering in return to release him from any further labours when Cerberus disappeared back to his master.
+
+After completing the Twelve Labours, one tradition says Heracles joined Jason and the Argonauts in their quest for the Golden Fleece. However, Herodorus (c. 400 BC) disputed this and denied Heracles ever sailed with the Argonauts. A separate tradition (e.g. Argonautica) has Heracles accompany the Argonauts, but he did not travel with them as far as Colchis.
+
+Some ancient Greeks found allegorical meanings of a moral, psychological or philosophical nature in the Labours of Heracles.  This trend became more prominent in the Renaissance.[28]  For example, Heraclitus the Grammarian wrote in his Homeric Problems:
+
+I turn to Heracles. We must not suppose he attained such power in those days as a result of his physical strength. Rather, he was a man of intellect, an initiate in heavenly wisdom, who, as it were, shed light on philosophy, which had been hidden in deep darkness. The most authoritative of the Stoics agree with this account.... The (Erymanthian) boar which he overcame is the common incontinence of men; the (Nemean) lion is the indiscriminate rush towards improper goals; in the same way, by fettering irrational passions he gave rise to the belief that he had fettered the violent (Cretan) bull. He banished cowardice also from the world, in the shape of the hind of Ceryneia. There was another "labor" too, not properly so called, in which he cleared out the mass of dung (from the Augean stables) — in other words, the foulness that disfigures humanity. The (Stymphalian) birds he scattered are the windy hopes that feed our lives; the many-headed hydra that he burned, as it were, with the fires of exhortation, is pleasure, which begins to grow again as soon as it is cut out.

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+The Lord of the Rings is an epic[1] high-fantasy novel written by English author and scholar J. R. R. Tolkien. The story began as a sequel to Tolkien's 1937 fantasy novel The Hobbit but eventually developed into a much larger work. Written in stages between 1937 and 1949, The Lord of the Rings is one of the best-selling novels ever written, with over 150 million copies sold.[2]
+
+The title of the novel refers to the story's main antagonist, the Dark Lord Sauron,[a] who had in an earlier age created the One Ring to rule the other Rings of Power as the ultimate weapon in his campaign to conquer and rule all of Middle-earth. From quiet beginnings in the Shire, a hobbit land not unlike the English countryside, the story ranges across Middle-earth, following the course of the War of the Ring through the eyes of its characters, most notably the hobbits Frodo, Sam, Merry and Pippin.
+
+Although generally known to readers as a trilogy, the work was initially intended by Tolkien to be one volume of a two-volume set, the other to be The Silmarillion, but this idea was dismissed by his publisher.[4][5] For economic reasons, The Lord of the Rings was published in three volumes over the course of a year from 29 July 1954 to 20 October 1955.[4][6] The three volumes were titled The Fellowship of the Ring, The Two Towers and The Return of the King. Structurally, the novel is divided internally into six books, two per volume, with several appendices of background material included at the end. Some editions combine the entire work into a single volume, per the author's original intent. The Lord of the Rings has since been reprinted numerous times and translated into 38 languages.
+
+Tolkien's work has been the subject of extensive analysis of its themes and origins. Although a major work in itself, the story was only the last movement of a larger epic Tolkien had worked on since 1917,[7] in a process he described as mythopoeia.[b] Influences on this earlier work, and on the story of The Lord of the Rings, include philology, mythology, religion, the architecture of Oxford, England, and the author's distaste for the effects of industrialization, as well as earlier fantasy works and Tolkien's experiences in World War I.[9] The Lord of the Rings in its turn is considered to have had a great effect on modern fantasy; the impact of Tolkien's works is such that the use of the words "Tolkienian" and "Tolkienesque" has been recorded in the Oxford English Dictionary.[10]
+
+The enduring popularity of The Lord of the Rings has led to numerous references in popular culture, the founding of many societies by fans of Tolkien's works,[11] and the publication of many books about Tolkien and his works. The Lord of the Rings has inspired, and continues to inspire, artwork, music, films and television, video games, board games, and subsequent literature. Award-winning adaptations of The Lord of the Rings have been made for radio, theatre, and film.[12] In 2003, it was named Britain's best novel of all time in the BBC's The Big Read. In 2015, the BBC ranked The Lord of the Rings 26th on its list of the 100 greatest British novels.[13]
+
+The narrative follows on from The Hobbit, in which the hobbit Bilbo Baggins finds the Ring, which had been in the possession of the creature Gollum. The story begins in the Shire, where Frodo Baggins inherits the Ring from Bilbo, his cousin[c] and guardian. Neither hobbit is aware of the Ring's nature, but Gandalf the Grey, a wizard and an old friend of Bilbo, suspects it to be the Ring lost by Sauron, the Dark Lord, long ago. Seventeen years later, after Gandalf confirms this is true, he tells Frodo the history of the Ring and counsels him to take it away from the Shire. Frodo sets out, accompanied by his gardener, servant and friend, Samwise "Sam" Gamgee, and two cousins, Meriadoc "Merry" Brandybuck and Peregrin "Pippin" Took. They are nearly caught by the Nazgûl, but shake off their pursuers by cutting through the Old Forest. There they are aided by Tom Bombadil, a strange and merry fellow who lives with his wife Goldberry in the forest.
+
+The hobbits reach the town of Bree, where they encounter a Ranger named Strider, whom Gandalf had mentioned in a letter. Strider persuades the hobbits to take him on as their guide and protector. Together, they leave Bree after another close escape from the Nazgûl. On the hill of Weathertop, they are again attacked by the Nazgûl, who wound Frodo with a cursed blade. Strider fights them off and leads the hobbits towards the Elven refuge of Rivendell. Frodo falls deathly ill from the wound. The Nazgûl nearly capture him at the Ford of Bruinen, but flood waters summoned by Elrond, master of Rivendell, rise up and overwhelm them.
+
+Frodo recovers in Rivendell under Elrond's care. The Council of Elrond discusses the history of Sauron and the Ring. Strider is revealed to be Aragorn, Isildur's heir. Gandalf reports that the chief wizard Saruman has betrayed them and is now working to become a power in his own right. The Council decides that the Ring must be destroyed, but that can only be done by sending it to the fire of Mount Doom in Mordor, where it was forged. Frodo takes this task upon himself. Elrond, with the advice of Gandalf, chooses companions for him. The Company of the Ring, also called the Fellowship of the Ring, are nine in number: Frodo, Sam, Merry, Pippin, Aragorn, Gandalf, Gimli the Dwarf, Legolas the Elf, and the Man Boromir, son of Denethor, the Ruling Steward of the land of Gondor.
+
+After a failed attempt to cross the Misty Mountains over the Redhorn Pass, the Company take the perilous path through the Mines of Moria. They learn of the fate of Balin and his colony of Dwarves. After surviving an attack, they are pursued by Orcs and by a Balrog, an ancient fire demon. Gandalf faces the Balrog, and both of them fall into the abyss. The others escape and find refuge in the Elven forest of Lothlórien, where they are counselled by its rulers, Galadriel and Celeborn.
+
+With boats and gifts from Galadriel, the Company travel down the River Anduin to the hill of Amon Hen. There, Boromir tries to take the Ring from Frodo, but Frodo puts it on and disappears. Frodo chooses to go alone to Mordor, but Sam guesses what he intends and goes with him.
+
+Uruk-hai sent by Saruman and other Orcs sent by Sauron kill Boromir and capture Merry and Pippin. Aragorn, Gimli and Legolas debate which pair of hobbits to follow. They decide to pursue the Orcs taking Merry and Pippin to Saruman. In the kingdom of Rohan, the Orcs are slain by a company of Rohirrim. Merry and Pippin escape into Fangorn Forest, where they are befriended by Treebeard, the oldest of the tree-like Ents. Aragorn, Gimli and Legolas track the hobbits to Fangorn. There they unexpectedly meet Gandalf.
+
+Gandalf explains that he slew the Balrog. Darkness took him, but he was sent back to Middle-earth to complete his mission. He is clothed in white and is now Gandalf the White, for he has taken Saruman's place as the chief of the wizards. Gandalf assures his friends that Merry and Pippin are safe. Together they ride to Edoras, capital of Rohan. Gandalf frees Théoden, King of Rohan, from the influence of Saruman's spy Gríma Wormtongue. Théoden musters his fighting strength and rides with his men to the ancient fortress of Helm's Deep, while Gandalf departs to seek help from Treebeard.
+
+Meanwhile, the Ents, roused by Merry and Pippin from their peaceful ways, attack Isengard, Saruman's stronghold, and trap the wizard in the tower of Orthanc. Gandalf convinces Treebeard to send an army of Huorns to Théoden's aid. Gandalf brings an army of Rohirrim to Helm's Deep, and they defeat the Orcs, who flee into the forest of Huorns, never to be seen again. Gandalf offers Saruman a chance to turn away from evil. When Saruman refuses to listen, Gandalf strips him of his rank and most of his powers.
+
+After Saruman crawls back to his prison, Wormtongue drops a sphere to try to kill Gandalf. Pippin picks it up. It is revealed to be a palantír, a seeing-stone that Saruman used to speak with Sauron and through which Saruman was ensnared. Pippin is seen by Sauron. Gandalf rides for Minas Tirith, chief city of Gondor, taking Pippin with him.
+
+Frodo and Sam capture Gollum, who has followed them from Moria. They force him to guide them to Mordor. They find that the Black Gate of Mordor is too well guarded, so instead they travel to a secret way Gollum knows. On the way, they encounter Faramir, who, unlike his brother Boromir, resists the temptation to seize the Ring. Gollum – who is torn between his loyalty to Frodo and his desire for the Ring – betrays Frodo by leading him to the great spider Shelob in the tunnels of Cirith Ungol. Frodo falls to Shelob's sting. But with the help of Galadriel's gifts, Sam fights off the spider. Believing Frodo to be dead, Sam takes the Ring to continue the quest alone. Orcs find Frodo; Sam overhears them and learns that Frodo is still alive.
+
+Sauron sends a great army against Gondor. Gandalf arrives at Minas Tirith to warn Denethor of the attack, while Théoden musters the Rohirrim to ride to Gondor's aid. Minas Tirith is besieged. Denethor is deceived by Sauron and falls into despair. He burns himself alive on a pyre, nearly taking his son Faramir with him. Aragorn, accompanied by Legolas, Gimli and the Rangers of the North, takes the Paths of the Dead to recruit the Dead Men of Dunharrow, who are bound by a curse which denies them rest until they fulfil their ancient forsworn oath to fight for the King of Gondor.
+
+Following Aragorn, the Army of the Dead strikes terror into the Corsairs of Umbar invading southern Gondor. Aragorn defeats the Corsairs and uses their ships to transport the men of southern Gondor up the Anduin, reaching Minas Tirith just in time to turn the tide of battle. Théoden's niece Éowyn, who joined the army in disguise, slays the Lord of the Nazgûl with help from Merry. Together, Gondor and Rohan defeat Sauron's army in the Battle of the Pelennor Fields, though at great cost. Théoden is killed, and Éowyn and Merry are wounded.
+
+Meanwhile, Sam rescues Frodo from the tower of Cirith Ungol. They set out across Mordor. Aragorn leads an army of men from Gondor and Rohan to march on the Black Gate to distract Sauron from his true danger. His army is vastly outnumbered by the great might of Sauron. Frodo and Sam reach the edge of the Cracks of Doom, but Frodo cannot resist the Ring any longer. He claims it for himself and puts it on his finger.
+
+Gollum suddenly reappears. He struggles with Frodo and bites off Frodo's finger with the Ring still on it. Celebrating wildly, Gollum loses his footing and falls into the Fire, taking the Ring with him. When the Ring is destroyed, Sauron loses his power forever. All he created collapses, the Nazgûl perish, and his armies are thrown into such disarray that Aragorn's forces emerge victorious.
+
+Aragorn is crowned King of Arnor and Gondor, and weds Arwen, daughter of Elrond. The four hobbits make their way back to the Shire, only to find that it has been taken over by men directed by one "Sharkey" (whom they later discover to be Saruman). The hobbits raise a rebellion and liberate the Shire, though 19 hobbits are killed and 30 wounded. Frodo stops the hobbits from killing the wizard after Saruman attempts to stab Frodo, but Gríma turns on Saruman and kills him in front of Bag End, Frodo's home. He is slain in turn by hobbit archers, and the War of the Ring comes to its true end on Frodo's very doorstep.
+
+Merry and Pippin are celebrated as heroes. Sam marries Rosie Cotton and uses his gifts from Galadriel to help heal the Shire. But Frodo is still wounded in body and spirit, having borne the Ring for so long. A few years later, in the company of Bilbo and Gandalf, Frodo sails from the Grey Havens west over the Sea to the Undying Lands to find peace.
+
+In the appendices, Sam gives his daughter Elanor the Red Book of Westmarch, which contains the story of Bilbo's adventures and the War of the Ring as witnessed by the hobbits. Sam is then said to have crossed west over the Sea himself, the last of the Ring-bearers.
+
+Tolkien presents The Lord of the Rings within a fictional frame-story where he is not the original author, but merely the translator of part of an ancient document, the Red Book of Westmarch. Various details of the frame-story appear in the Prologue, its 'Note on Shire Records', and in the Appendices, notably Appendix F. In this frame-story, the Red Book is also the source of Tolkien's other works relating to Middle-earth: The Hobbit, The Silmarillion, and The Adventures of Tom Bombadil.[14]
+
+The Lord of the Rings started as a sequel to J. R. R. Tolkien's work The Hobbit, published in 1937.[15] The popularity of The Hobbit had led George Allen & Unwin, the publishers, to request a sequel. Tolkien warned them that he wrote quite slowly, and responded with several stories he had already developed. Having rejected his contemporary drafts for The Silmarillion, putting on hold Roverandom, and accepting Farmer Giles of Ham, Allen & Unwin thought more stories about hobbits would be popular.[16] So at the age of 45, Tolkien began writing the story that would become The Lord of the Rings. The story would not be finished until 12 years later, in 1949, and would not be fully published until 1955, when Tolkien was 63 years old.
+
+Persuaded by his publishers, he started "a new Hobbit" in December 1937.[15] After several false starts, the story of the One Ring emerged. The idea for the first chapter ("A Long-Expected Party") arrived fully formed, although the reasons behind Bilbo's disappearance, the significance of the Ring, and the title The Lord of the Rings did not arrive until the spring of 1938.[15] Originally, he planned to write a story in which Bilbo had used up all his treasure and was looking for another adventure to gain more; however, he remembered the Ring and its powers and thought that would be a better focus for the new work.[15] As the story progressed, he also brought in elements from The Silmarillion mythology.[17]
+
+Writing was slow, because Tolkien had a full-time academic position teaching linguistics (with a focus on languages with linguistic elements he incorporated into his books, such as Old English).[18] "I have spent nearly all the vacation-times of seventeen years examining [...] Writing stories in prose or verse has been stolen, often guiltily, from time already mortgaged..."[19] Tolkien abandoned The Lord of the Rings during most of 1943 and only restarted it in April 1944,[15] as a serial for his son Christopher Tolkien, who was sent chapters as they were written while he was serving in South Africa with the Royal Air Force. Tolkien made another major effort in 1946, and showed the manuscript to his publishers in 1947.[15] The story was effectively finished the next year, but Tolkien did not complete the revision of earlier parts of the work until 1949.[15] The original manuscripts, which total 9,250 pages, now reside in the J. R. R. Tolkien Collection at Marquette University.[20]
+
+Unusually for 20th century novels, the prose narrative is supplemented throughout by over 60 pieces of poetry. These include verse and songs of many genres: for wandering, marching to war, drinking, and having a bath; narrating ancient myths, riddles, prophecies, and magical incantations; of praise and lament (elegy). Some, such as riddles, charms, elegies, and narrating heroic actions are found in Old English poetry.[21] Scholars have stated that the poetry is essential for the fiction to work aesthetically and thematically; it adds information not given in the prose; and it brings out characters and their backgrounds.[22][23] The poetry has been judged to be of high technical skill, which Tolkien carried across into his prose, for instance writing much of Tom Bombadil's speech in metre.[24]
+
+The influence of the Welsh language, which Tolkien had learned, is summarized in his essay English and Welsh: "If I may once more refer to my work. The Lord of the Rings, in evidence: the names of persons and places in this story were mainly composed on patterns deliberately modelled on those of Welsh (closely similar but not identical). This element in the tale has given perhaps more pleasure to more readers than anything else in it."[25]
+
+The Lord of the Rings developed as a personal exploration by Tolkien of his interests in philology, religion (particularly Catholicism[26]), fairy tales, Norse and general Germanic mythology,[27][28] and also Celtic,[29][better source needed] Slavic,[30][31][32] Persian,[33] Greek,[34] and Finnish mythology.[35] Tolkien acknowledged, and external critics have verified, the influences of George MacDonald and William Morris[36] and the Anglo-Saxon poem Beowulf.[37] The question of a direct influence of Wagner's The Nibelung's Ring on Tolkien's work is debated by critics.
+
+Tolkien included neither any explicit religion nor cult in his work. Rather the themes, moral philosophy, and cosmology of The Lord of the Rings reflect his Catholic worldview. In one of his letters Tolkien states, "The Lord of the Rings is of course a fundamentally religious and Catholic work; unconsciously so at first, but consciously in the revision. That is why I have not put in, or have cut out, practically all references to anything like 'religion', to cults or practices, in the imaginary world. For the religious element is absorbed into the story and the symbolism."[26]
+
+Some locations and characters were inspired by Tolkien's childhood in Birmingham, where he first lived near Sarehole Mill, and later near Edgbaston Reservoir.[39] There are also hints of the Black Country, which is within easy reach of northwest Edgbaston. This shows in such names as "Underhill", and the description of Saruman's industrialization of Isengard and The Shire. It has been suggested that the Shire and its surroundings were based on the countryside around Stonyhurst College in Lancashire where Tolkien frequently stayed during the 1940s, but this claim is disputed by reputable Tolkien scholars.[40][41] The work was influenced by the effects of his military service during World War I, to the point that one critic diagnosed Frodo as suffering from posttraumatic stress disorder, which was called "shell-shock" at the Battle of the Somme, in which Tolkien served.[42]
+
+A dispute with his publisher, George Allen & Unwin, led to the book being offered to Collins in 1950. Tolkien intended The Silmarillion (itself largely unrevised at this point) to be published along with The Lord of the Rings, but A&U were unwilling to do this. After Milton Waldman, his contact at Collins, expressed the belief that The Lord of the Rings itself "urgently wanted cutting", Tolkien eventually demanded that they publish the book in 1952.[43] Collins did not; and so Tolkien wrote to Allen and Unwin, saying, "I would gladly consider the publication of any part of the stuff", fearing his work would never see the light of day.[15]
+
+For publication, the book was divided into three volumes to minimize any potential financial loss due to the high cost of type-setting and modest anticipated sales: The Fellowship of the Ring (Books I and II), The Two Towers (Books III and IV), and The Return of the King (Books V and VI plus six appendices).[44] Delays in producing appendices, maps and especially an index led to the volumes being published later than originally hoped – on 29 July 1954, on 11 November 1954 and on 20 October 1955 respectively in the United Kingdom. In the United States, Houghton Mifflin published The Fellowship of the Ring on 21 October 1954, The Two Towers on 21 April 1955, and The Return of the King on 5 January 1956.[45]
+
+The Return of the King was especially delayed due to Tolkien revising the ending and preparing appendices (some of which had to be left out because of space constraints). Tolkien did not like the title The Return of the King, believing it gave away too much of the storyline, but deferred to his publisher's preference.[46] Tolkien wrote that the title The Two Towers "can be left ambiguous,"[47] but also considered naming the two as Orthanc and Barad-dûr, Minas Tirith and Barad-dûr, or Orthanc and the Tower of Cirith Ungol.[47][48] However, a month later he wrote a note published at the end of The Fellowship of the Ring and later drew a cover illustration, both of which identified the pair as Minas Morgul and Orthanc.[49][50]
+
+Tolkien was initially opposed to titles being given to each two-book volume, preferring instead the use of book titles: e.g. The Lord of the Rings: Vol. 1, The Ring Sets Out and The Ring Goes South; Vol. 2, The Treason of Isengard and The Ring Goes East; Vol. 3, The War of the Ring and The End of the Third Age. However these individual book titles were later scrapped, and after pressure from his publishers, Tolkien initially suggested the titles: Vol. 1, The Shadow Grows; Vol. 2, The Ring in the Shadow; Vol. 3, The War of the Ring or The Return of the King.[51][52]
+
+Because the three-volume binding was so widely distributed, the work is often referred to as the Lord of the Rings "trilogy". In a letter to the poet W. H. Auden (who famously reviewed the final volume in 1956[53]), Tolkien himself made use of the term "trilogy" for the work[54] though he did at other times consider this incorrect, as it was written and conceived as a single book.[55] It is also often called a novel; however, Tolkien also objected to this term as he viewed it as a heroic romance.[56]
+
+The books were published under a profit-sharing arrangement, whereby Tolkien would not receive an advance or royalties until the books had broken even, after which he would take a large share of the profits.[57] It has ultimately become one of the best-selling novels ever written, with 50 million copies sold by 2003[58] and over 150 million copies sold by 2007.[2]
+
+The book was published in the UK by Allen & Unwin until 1990 when the publisher and its assets were acquired by HarperCollins.[59][60]
+
+In the early 1960s Donald A. Wollheim, science fiction editor of the paperback publisher Ace Books, claimed that The Lord of the Rings was not protected in the United States under American copyright law because Houghton Mifflin, the US hardcover publisher, had neglected to copyright the work in the United States.[61][62] Then, in 1965, Ace Books proceeded to publish an edition, unauthorized by Tolkien and without paying royalties to him. Tolkien took issue with this and quickly notified his fans of this objection.[63] Grass-roots pressure from these fans became so great that Ace Books withdrew their edition and made a nominal payment to Tolkien.[64][65]
+
+Authorized editions followed from Ballantine Books and Houghton Mifflin to tremendous commercial success. Tolkien undertook various textual revisions to produce a version of the book that would be published with his consent and establish an unquestioned US copyright. This text became the Second Edition of The Lord of the Rings, published in 1965.[64] The first Ballantine paperback edition was printed in October that year, and sold a quarter of a million copies within ten months. On 4 September 1966, the novel debuted on New York Times' Paperback Bestsellers list as number three, and was number one by 4 December, a position it held for eight weeks.[66] Houghton Mifflin editions after 1994 consolidate variant revisions by Tolkien, and corrections supervised by Christopher Tolkien, which resulted, after some initial glitches, in a computer-based unified text.[67]
+
+In 2004, for the 50th Anniversary Edition, Wayne G. Hammond and Christina Scull, under supervision from Christopher Tolkien, studied and revised the text to eliminate as many errors and inconsistencies as possible, some of which had been introduced by well-meaning compositors of the first printing in 1954, and never been corrected.[68] The 2005 edition of the book contained further corrections noticed by the editors and submitted by readers. Further corrections were added to the 60th Anniversary Edition in 2014.[69]
+
+Several editions, notably the 50th Anniversary Edition, combine all three books into one volume, with the result that pagination varies widely over the various editions.
+
+From 1988 to 1992 Christopher Tolkien published the surviving drafts of The Lord of The Rings, chronicling and illuminating with commentary the stages of the text's development, in volumes 6–9 of his History of Middle-earth series. The four volumes carry the titles The Return of the Shadow, The Treason of Isengard, The War of the Ring, and Sauron Defeated.
+
+The novel has been translated, with varying degrees of success, into at least 56 languages.[70] Tolkien, an expert in philology, examined many of these translations, and made comments on each that reflect both the translation process and his work. As he was unhappy with some choices made by early translators, such as the Swedish translation by Åke Ohlmarks,[71] Tolkien wrote a "Guide to the Names in The Lord of the Rings" (1967). Because The Lord of the Rings purports to be a translation of the fictitious Red Book of Westmarch, with the English language representing the Westron of the "original", Tolkien suggested that translators attempt to capture the interplay between English and the invented nomenclature of the English work, and gave several examples along with general guidance.
+
+While early reviews for The Lord of the Rings were mixed, reviews in various media have been, on the whole, highly positive and acknowledge Tolkien's literary achievement as a significant one. The initial review in the Sunday Telegraph described it as "among the greatest works of imaginative fiction of the twentieth century".[72] The Sunday Times echoed this sentiment, stating that "the English-speaking world is divided into those who have read The Lord of the Rings and The Hobbit and those who are going to read them."[72] The New York Herald Tribune also seemed to have an idea of how popular the books would become, writing in its review that they were "destined to outlast our time".[73] W. H. Auden, an admirer of Tolkien's writings, regarded The Lord of the Rings as a "masterpiece", further stating that in some cases it outdid the achievement of John Milton's Paradise Lost.[74] Kenneth F Slater [75] wrote in Nebula Science Fiction, April 1955, "... if you don’t read it, you have missed one of the finest books of its type ever to appear" [76]
+
+New York Times reviewer Judith Shulevitz criticized the "pedantry" of Tolkien's literary style, saying that he "formulated a high-minded belief in the importance of his mission as a literary preservationist, which turns out to be death to literature itself".[77] Critic Richard Jenkyns, writing in The New Republic, criticized the work for a lack of psychological depth. Both the characters and the work itself are, according to Jenkyns, "anemic, and lacking in fibre".[78] Even within Tolkien's literary group, The Inklings, reviews were mixed. Hugo Dyson complained loudly at its readings.[79][80] However, another Inkling, C. S. Lewis, had very different feelings, writing, "here are beauties which pierce like swords or burn like cold iron. Here is a book which will break your heart." Despite these reviews and its lack of paperback printing until the 1960s, The Lord of the Rings initially sold well in hardback.[7]
+
+In 1957, The Lord of the Rings was awarded the International Fantasy Award. Despite its numerous detractors, the publication of the Ace Books and Ballantine paperbacks helped The Lord of the Rings become immensely popular in the United States in the 1960s. The book has remained so ever since, ranking as one of the most popular works of fiction of the twentieth century, judged by both sales and reader surveys.[81] In the 2003 "Big Read" survey conducted in Britain by the BBC, The Lord of the Rings was found to be the "Nation's best-loved book". In similar 2004 polls both Germany[82] and Australia[83] also found The Lord of the Rings to be their favourite book. In a 1999 poll of Amazon.com customers, The Lord of the Rings was judged to be their favourite "book of the millennium".[84]
+
+C. S. Lewis observed that the writing is rich in that some of the 'good' characters have darker sides, and likewise some of the villains have "good impulses".[85]
+
+Although The Lord of the Rings was published in the 1950s, Tolkien insisted that the One Ring was not an allegory for the atomic bomb,[86] nor were his works a strict allegory of any kind, but were open to interpretation as the reader saw fit.[87][88]
+
+A few critics have found what they consider racial elements in the story, which are generally based upon their views of how Tolkien's imagery depicts good and evil, characters' race (e.g. Elf, Dwarf, Hobbit, Southron, Númenórean, Orc), and how the characters' race is seen as determining their behaviour.[89][90][91] On the contrary, counter-arguments note that race-focused critiques often omit relevant textual evidence,[92][93][94] cite imagery from adaptations rather than the work itself,[95] ignore the absence of evidence of racist attitudes or events in the author's personal life,[92][95][96] and claim that the perception of racism is itself a marginal view.[96]
+
+The opinions that pit races against each other most likely reflect Tolkien's criticism of war rather than a racist perspective. In The Two Towers, the character Samwise sees a fallen foe, a man of colour, and considers the humanity of this fallen Southron.[97] Director Peter Jackson, in the director's commentary of this scene, argues that Tolkien isn't projecting negativity towards the individual soldier because of his race, but against the evil authority that is driving them.[98] These sentiments, Jackson argues, arose from Tolkien's experience in the Great War and found their way into his writings to show the evils of war itself, not of other races.
+
+Critics have also seen social class rather than race as being the determining factor in the portrayal of good and evil.[92] Commentators such as science fiction author David Brin have interpreted the work to hold unquestioning devotion to a traditional elitist social structure.[99] In his essay "Epic Pooh", science fiction and fantasy author Michael Moorcock critiques the world-view displayed by the book as deeply conservative, in both the "paternalism" of the narrative voice and the power-structures in the narrative.[100] Tom Shippey cites the origin of this portrayal of evil as a reflection of the prejudices of European middle-classes during the inter-war years towards the industrial working class.[101]
+
+Other observers have described Christian themes in the work, specifically Roman Catholicism.[102]
+
+The book has been read as fitting the model of Joseph Campbell's "monomyth".[103]
+
+The Lord of the Rings has been adapted for film, radio and stage.
+
+The book has been adapted for radio four times. In 1955 and 1956, the BBC broadcast The Lord of the Rings, a 13-part radio adaptation of the story. In the 1960s radio station WBAI produced a short radio adaptation. A 1979 dramatization of The Lord of the Rings was broadcast in the United States and subsequently issued on tape and CD. In 1981, the BBC broadcast The Lord of the Rings, a new dramatization in 26 half-hour instalments. This dramatization of The Lord of the Rings has subsequently been made available on both tape and CD both by the BBC and other publishers. For this purpose it is generally edited into 13 one-hour episodes.
+
+Filmmakers who attempted to adapt Tolkien's works include William Snyder, Peter Shaffer, John Boorman, Ralph Bakshi, Peter Jackson and Guillermo del Toro. Other filmmakers and producers who were interested in an adaptation included Walt Disney, Al Brodax, Forrest J Ackerman, Samuel Gelfman, Denis O'Dell and Heinz Edelmann.
+
+Following J. R. R. Tolkien's sale of the film rights for The Lord of the Rings to United Artists in 1969, rock band The Beatles considered a corresponding film project. David Lean was approached to direct, and while intrigued, was busy with Ryan's Daughter. The next choice, Stanley Kubrick, had to first familiarize himself with the books, only to then say they were unfilmable due to their immensity.[104][105] Michaelangelo Antonioni was contacted, and Heinz Edelmann even offered doing it in animation, but the project fell apart.[106] British director John Boorman also tried to make an adaptation of The Lord of the Rings for United Artists in 1970. After the script was written, which included many changes to the story and the characters, the production company scrapped the project, thinking it too expensive and too risky.[107]
+
+Two film adaptations of the book have been made. The first was J. R. R. Tolkien's The Lord of the Rings (1978), by animator Ralph Bakshi, the first part of what was originally intended to be a two-part adaptation of the story; it covers The Fellowship of the Ring and part of The Two Towers. A three-issue comic book version of the movie was also published in Europe (but not printed in English), with illustrations by Luis Bermejo.
+
+The second and more commercially successful adaptation was Peter Jackson's live action The Lord of the Rings film trilogy, produced by New Line Cinema and released in three instalments as The Lord of the Rings: The Fellowship of the Ring (2001), The Lord of the Rings: The Two Towers (2002), and The Lord of the Rings: The Return of the King (2003). All three parts won multiple Academy Awards, including consecutive Best Picture nominations. The final instalment of this trilogy was the second film to break the one-billion-dollar barrier and won a total of 11 Oscars (something only two other films in history, Ben-Hur and Titanic, have accomplished), including Best Picture, Best Director and Best Adapted Screenplay. Jackson later reprised his role as director, writer and producer to make a prequel trilogy based on The Hobbit.
+
+The Hunt for Gollum, a fan film based on elements of the appendices to The Lord of the Rings, was released on the internet in May 2009 and has been covered in major media.[108] Born of Hope, written by Paula DiSante, directed by Kate Madison, and released in December 2009, is a fan film based upon the appendices of The Lord of the Rings.[109]
+
+Rankin and Bass used a loophole in the publication of The Hobbit and The Lord of the Rings (which made them public domain in the US) to make animated TV specials based on The Hobbit, released in 1977, and a sequel based on the closing chapters of The Return of the King, which came out in 1980.
+
+In 2017, Amazon acquired the global television rights to The Lord of the Rings for a multi-season television series of new stories set before The Hobbit and The Lord of the Rings,[110]  based on J.R.R. Tolkien's writings about events of the Second Age of Middle-earth.[111] Amazon said the deal included potential for spin-off series as well.[112][113] It was later revealed that the show will apparently be set in the early second age, during the time of the Forging of the Rings,[114] and will allegedly be a prequel to the live-action films.[115]
+
+It was projected in 2018 to be the most expensive TV show ever produced.[116] Much of it will be produced in New Zealand.[117][118][119][120] The cast includes Robert Aramayo, Owain Arthur, Nazanin Boniadi, Tom Budge, Morfydd Clark (as Galadriel),[121] Ismael Cruz Córdova, Ema Horvath, Markella Kavenagh, Joseph Mawle, Tyroe Muhafidin, Sophia Nomvete, Megan Richards, Dylan Smith, Charlie Vickers, Daniel Weyman,[122] and Maxim Baldry.[123]
+
+In 1990, Recorded Books published an audio version of The Lord of the Rings,[124] with British actor Rob Inglis – who had previously starred in his own one-man stage productions of The Hobbit and The Lord of the Rings – reading. A large-scale musical theatre adaptation, The Lord of the Rings was first staged in Toronto, Ontario, Canada in 2006 and opened in London in June 2007.
+
+The enormous popularity of Tolkien's work expanded the demand for fantasy fiction. Largely thanks to The Lord of the Rings, the genre flowered throughout the 1960s, and enjoys popularity to the present day. The opus has spawned many imitators, such as The Sword of Shannara, which Lin Carter called "the single most cold-blooded, complete rip-off of another book that I have ever read".[125]
+Dungeons & Dragons, which popularized the role-playing game (RPG) genre in the 1970s, features many races found in The Lord of the Rings, most notably halflings (another term for hobbits), elves, dwarves, half-elves, orcs, and dragons. However, Gary Gygax, lead designer of the game, maintained that he was influenced very little by The Lord of the Rings, stating that he included these elements as a marketing move to draw on the popularity the work enjoyed at the time he was developing the game.[126]
+
+Because D&D has gone on to influence many popular role-playing video games, the influence of The Lord of the Rings extends to many of them as well, with titles such as Dragon Quest,[127][128] the Ultima series, EverQuest, the Warcraft series, and the Elder Scrolls series of games[129] as well as video games set in Middle-earth itself.
+
+Research also suggests that some consumers of fantasy games derive their motivation from trying to create an epic fantasy narrative which is influenced by The Lord of the Rings.[130]
+
+In 1965, songwriter Donald Swann, who was best known for his collaboration with Michael Flanders as Flanders & Swann, set six poems from The Lord of the Rings and one from The Adventures of Tom Bombadil ("Errantry") to music. When Swann met with Tolkien to play the songs for his approval, Tolkien suggested for "Namárië" (Galadriel's lament) a setting reminiscent of plain chant, which Swann accepted.[131] The songs were published in 1967 as The Road Goes Ever On: A Song Cycle,[132] and a recording of the songs performed by singer William Elvin with Swann on piano was issued that same year by Caedmon Records as Poems and Songs of Middle Earth.[133]
+
+Rock bands of the 1970s were musically and lyrically inspired by the fantasy embracing counter-culture of the time; British 70s rock band Led Zeppelin recorded several songs that contain explicit references to The Lord of the Rings, such as mentioning Gollum in "Ramble On", the Misty Mountains in "Misty Mountain Hop", and Ringwraiths in "The Battle of Evermore". In 1970, the Swedish musician Bo Hansson released an instrumental concept album based on the book titled Sagan om ringen (translated as "The Saga of the Ring", which was the title of the Swedish translation of The Lord of the Rings at the time).[134] The album was subsequently released internationally as Music Inspired by Lord of the Rings in 1972.[134]
+
+The songs "Rivendell" and "The Necromancer" by the progressive rock band Rush were inspired by Tolkien. Styx also paid homage to Tolkien on their album Pieces of Eight with the song "Lords of the Ring", while Black Sabbath's song, "The Wizard", which appeared on their debut album, was influenced by Tolkien's hero, Gandalf. Progressive rock group Camel paid homage to the text in their lengthy composition "Nimrodel/The Procession/The White Rider", and progressive rock band Barclay James Harvest was inspired by the character Galadriel to write a song by that name, and used "Bombadil", the name of another character, as a pseudonym under which their 1972 single "Breathless"/"When the City Sleeps" was released; there are other references scattered through the BJH oeuvre.
+
+Later, from the 1980s to the present day, many heavy metal acts have been influenced by Tolkien. Blind Guardian has written many songs relating to Middle-earth, including the full concept album Nightfall in Middle Earth. Almost the entire discography of Battlelore are Tolkien-themed. Summoning's music is based upon Tolkien and holds the distinction of the being the only artist to have crafted a song entirely in the Black Speech of Mordor. Gorgoroth, Cirith Ungol and Amon Amarth take their names from an area of Mordor, and Burzum take their name from the Black Speech of Mordor. The Finnish metal band Nightwish and the Norwegian metal band Tristania have also incorporated many Tolkien references into their music. American heavy metal band Megadeth released two songs titled "This Day We Fight!" and "How the Story Ends", which were both inspired by The Lord of the Rings.[135] German folk metal band Eichenschild is named for Thorin Oakenshield, a character in The Hobbit, and naturally has a number of Tolkien-themed songs. They are not to be confused with the '70s folk rock band Thorin Eichenschild.
+
+In 1988, Dutch composer and trombonist Johan de Meij completed his Symphony No. 1 "The Lord of the Rings", which encompassed 5 movements, titled "Gandalf", "Lothlórien", "Gollum", "Journey in the Dark", and "Hobbits". In 1989 the symphony was awarded the Sudler Composition Award, awarded biennially for best wind band composition. The Danish Tolkien Ensemble have released a number of albums that feature the complete poems and songs of The Lord of the Rings set to music, with some featuring recitation by Christopher Lee. In 2018, de Meij completed his Symphony No. 5 "Return to Middle Earth" in 2018, which has 6 movements titled "Mîri na Fëanor (Fëanor’s Jewels)", "Tinúviel (Nightingale)", "Ancalagon i-môr (Ancalagon, The Black)", "Arwen Undómiel (Evenstar)", "Dagor Delothrin (The War of Wrath)", and "Thuringwethil (Woman of Secret Shadow)".
+
+Enya wrote an instrumental piece called "Lothlórien" in 1991, and composed two songs for the film The Lord of the Rings: The Fellowship of the Ring—"May It Be" (sung in English and Quenya) and "Aníron" (sung in Sindarin).
+
+The 2020 modern classical album "Music for Piano and Strings" by pianist and composer Holger Skepeneit contains two Lord of the Rings-inspired pieces, "Laced with Ithildin" and "Nimrodel's Voice".
+
+The Lord of the Rings has had a profound and wide-ranging impact on popular culture, beginning with its publication in the 1950s, but especially throughout the 1960s and 1970s, during which time young people embraced it as a countercultural saga.[136] "Frodo Lives!" and "Gandalf for President" were two phrases popular amongst United States Tolkien fans during this time.[137]
+
+Parodies like the Harvard Lampoon's Bored of the Rings, the VeggieTales episode "Lord of the Beans", the South Park episode "The Return of the Fellowship of the Ring to the Two Towers", the Futurama film Bender's Game, The Adventures of Jimmy Neutron: Boy Genius episode "Lights! Camera! Danger!", The Big Bang Theory episode "The Precious Fragmentation", and the American Dad! episode "The Return of the Bling" are testimony to the work's continual presence in popular culture.
+
+In 1969, Tolkien sold the merchandising rights to The Lord of The Rings (and The Hobbit) to United Artists under an agreement stipulating a lump sum payment of £10,000[138] plus a 7.5% royalty after costs,[139] payable to Allen & Unwin and the author.[140] In 1976, three years after the author's death, United Artists sold the rights to Saul Zaentz Company, who now trade as Tolkien Enterprises. Since then all "authorized" merchandise has been signed-off by Tolkien Enterprises, although the intellectual property rights of the specific likenesses of characters and other imagery from various adaptations is generally held by the adaptors.[141]
+
+Outside any commercial exploitation from adaptations, from the late 1960s onwards there has been an increasing variety of original licensed merchandise, from posters and calendars created by illustrators such as Barbara Remington[142], Pauline Baynes and the Brothers Hildebrandt, to figurines and miniatures to computer, video, tabletop and role-playing games. Recent examples include the Spiel des Jahres award-winning (for "best use of literature in a game") board game The Lord of the Rings by Reiner Knizia and the Golden Joystick award-winning massively multiplayer online role-playing game, The Lord of the Rings Online: Shadows of Angmar by Turbine, Inc..
+
+The Lord of the Rings has been mentioned in numerous songs including "The Ballad of Bilbo Baggins" by Leonard Nimoy, Led Zeppelin's "Misty Mountain Hop", "Over the Hills and Far Away", "Ramble On", and "The Battle of Evermore", Genesis' song "Stagnation" (from Trespass, 1970) was about Gollum, Rush included the song "Rivendell" on their second studio album Fly by Night, and Argent included the song "Lothlorien" on the 1971 album Ring of Hands.
+
+Steve Peregrin Took (born Stephen Ross Porter) of British rock band T. Rex took his name from the hobbit Peregrin Took (better known as Pippin). Took later recorded under the pseudonym 'Shagrat the Vagrant', before forming a band called Shagrat in 1970.
+
+On 5 November 2019, the BBC News listed The Lord of the Rings on its list of the 100 most influential novels.[143]

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+The Lord of the Rings is an epic[1] high-fantasy novel written by English author and scholar J. R. R. Tolkien. The story began as a sequel to Tolkien's 1937 fantasy novel The Hobbit but eventually developed into a much larger work. Written in stages between 1937 and 1949, The Lord of the Rings is one of the best-selling novels ever written, with over 150 million copies sold.[2]
+
+The title of the novel refers to the story's main antagonist, the Dark Lord Sauron,[a] who had in an earlier age created the One Ring to rule the other Rings of Power as the ultimate weapon in his campaign to conquer and rule all of Middle-earth. From quiet beginnings in the Shire, a hobbit land not unlike the English countryside, the story ranges across Middle-earth, following the course of the War of the Ring through the eyes of its characters, most notably the hobbits Frodo, Sam, Merry and Pippin.
+
+Although generally known to readers as a trilogy, the work was initially intended by Tolkien to be one volume of a two-volume set, the other to be The Silmarillion, but this idea was dismissed by his publisher.[4][5] For economic reasons, The Lord of the Rings was published in three volumes over the course of a year from 29 July 1954 to 20 October 1955.[4][6] The three volumes were titled The Fellowship of the Ring, The Two Towers and The Return of the King. Structurally, the novel is divided internally into six books, two per volume, with several appendices of background material included at the end. Some editions combine the entire work into a single volume, per the author's original intent. The Lord of the Rings has since been reprinted numerous times and translated into 38 languages.
+
+Tolkien's work has been the subject of extensive analysis of its themes and origins. Although a major work in itself, the story was only the last movement of a larger epic Tolkien had worked on since 1917,[7] in a process he described as mythopoeia.[b] Influences on this earlier work, and on the story of The Lord of the Rings, include philology, mythology, religion, the architecture of Oxford, England, and the author's distaste for the effects of industrialization, as well as earlier fantasy works and Tolkien's experiences in World War I.[9] The Lord of the Rings in its turn is considered to have had a great effect on modern fantasy; the impact of Tolkien's works is such that the use of the words "Tolkienian" and "Tolkienesque" has been recorded in the Oxford English Dictionary.[10]
+
+The enduring popularity of The Lord of the Rings has led to numerous references in popular culture, the founding of many societies by fans of Tolkien's works,[11] and the publication of many books about Tolkien and his works. The Lord of the Rings has inspired, and continues to inspire, artwork, music, films and television, video games, board games, and subsequent literature. Award-winning adaptations of The Lord of the Rings have been made for radio, theatre, and film.[12] In 2003, it was named Britain's best novel of all time in the BBC's The Big Read. In 2015, the BBC ranked The Lord of the Rings 26th on its list of the 100 greatest British novels.[13]
+
+The narrative follows on from The Hobbit, in which the hobbit Bilbo Baggins finds the Ring, which had been in the possession of the creature Gollum. The story begins in the Shire, where Frodo Baggins inherits the Ring from Bilbo, his cousin[c] and guardian. Neither hobbit is aware of the Ring's nature, but Gandalf the Grey, a wizard and an old friend of Bilbo, suspects it to be the Ring lost by Sauron, the Dark Lord, long ago. Seventeen years later, after Gandalf confirms this is true, he tells Frodo the history of the Ring and counsels him to take it away from the Shire. Frodo sets out, accompanied by his gardener, servant and friend, Samwise "Sam" Gamgee, and two cousins, Meriadoc "Merry" Brandybuck and Peregrin "Pippin" Took. They are nearly caught by the Nazgûl, but shake off their pursuers by cutting through the Old Forest. There they are aided by Tom Bombadil, a strange and merry fellow who lives with his wife Goldberry in the forest.
+
+The hobbits reach the town of Bree, where they encounter a Ranger named Strider, whom Gandalf had mentioned in a letter. Strider persuades the hobbits to take him on as their guide and protector. Together, they leave Bree after another close escape from the Nazgûl. On the hill of Weathertop, they are again attacked by the Nazgûl, who wound Frodo with a cursed blade. Strider fights them off and leads the hobbits towards the Elven refuge of Rivendell. Frodo falls deathly ill from the wound. The Nazgûl nearly capture him at the Ford of Bruinen, but flood waters summoned by Elrond, master of Rivendell, rise up and overwhelm them.
+
+Frodo recovers in Rivendell under Elrond's care. The Council of Elrond discusses the history of Sauron and the Ring. Strider is revealed to be Aragorn, Isildur's heir. Gandalf reports that the chief wizard Saruman has betrayed them and is now working to become a power in his own right. The Council decides that the Ring must be destroyed, but that can only be done by sending it to the fire of Mount Doom in Mordor, where it was forged. Frodo takes this task upon himself. Elrond, with the advice of Gandalf, chooses companions for him. The Company of the Ring, also called the Fellowship of the Ring, are nine in number: Frodo, Sam, Merry, Pippin, Aragorn, Gandalf, Gimli the Dwarf, Legolas the Elf, and the Man Boromir, son of Denethor, the Ruling Steward of the land of Gondor.
+
+After a failed attempt to cross the Misty Mountains over the Redhorn Pass, the Company take the perilous path through the Mines of Moria. They learn of the fate of Balin and his colony of Dwarves. After surviving an attack, they are pursued by Orcs and by a Balrog, an ancient fire demon. Gandalf faces the Balrog, and both of them fall into the abyss. The others escape and find refuge in the Elven forest of Lothlórien, where they are counselled by its rulers, Galadriel and Celeborn.
+
+With boats and gifts from Galadriel, the Company travel down the River Anduin to the hill of Amon Hen. There, Boromir tries to take the Ring from Frodo, but Frodo puts it on and disappears. Frodo chooses to go alone to Mordor, but Sam guesses what he intends and goes with him.
+
+Uruk-hai sent by Saruman and other Orcs sent by Sauron kill Boromir and capture Merry and Pippin. Aragorn, Gimli and Legolas debate which pair of hobbits to follow. They decide to pursue the Orcs taking Merry and Pippin to Saruman. In the kingdom of Rohan, the Orcs are slain by a company of Rohirrim. Merry and Pippin escape into Fangorn Forest, where they are befriended by Treebeard, the oldest of the tree-like Ents. Aragorn, Gimli and Legolas track the hobbits to Fangorn. There they unexpectedly meet Gandalf.
+
+Gandalf explains that he slew the Balrog. Darkness took him, but he was sent back to Middle-earth to complete his mission. He is clothed in white and is now Gandalf the White, for he has taken Saruman's place as the chief of the wizards. Gandalf assures his friends that Merry and Pippin are safe. Together they ride to Edoras, capital of Rohan. Gandalf frees Théoden, King of Rohan, from the influence of Saruman's spy Gríma Wormtongue. Théoden musters his fighting strength and rides with his men to the ancient fortress of Helm's Deep, while Gandalf departs to seek help from Treebeard.
+
+Meanwhile, the Ents, roused by Merry and Pippin from their peaceful ways, attack Isengard, Saruman's stronghold, and trap the wizard in the tower of Orthanc. Gandalf convinces Treebeard to send an army of Huorns to Théoden's aid. Gandalf brings an army of Rohirrim to Helm's Deep, and they defeat the Orcs, who flee into the forest of Huorns, never to be seen again. Gandalf offers Saruman a chance to turn away from evil. When Saruman refuses to listen, Gandalf strips him of his rank and most of his powers.
+
+After Saruman crawls back to his prison, Wormtongue drops a sphere to try to kill Gandalf. Pippin picks it up. It is revealed to be a palantír, a seeing-stone that Saruman used to speak with Sauron and through which Saruman was ensnared. Pippin is seen by Sauron. Gandalf rides for Minas Tirith, chief city of Gondor, taking Pippin with him.
+
+Frodo and Sam capture Gollum, who has followed them from Moria. They force him to guide them to Mordor. They find that the Black Gate of Mordor is too well guarded, so instead they travel to a secret way Gollum knows. On the way, they encounter Faramir, who, unlike his brother Boromir, resists the temptation to seize the Ring. Gollum – who is torn between his loyalty to Frodo and his desire for the Ring – betrays Frodo by leading him to the great spider Shelob in the tunnels of Cirith Ungol. Frodo falls to Shelob's sting. But with the help of Galadriel's gifts, Sam fights off the spider. Believing Frodo to be dead, Sam takes the Ring to continue the quest alone. Orcs find Frodo; Sam overhears them and learns that Frodo is still alive.
+
+Sauron sends a great army against Gondor. Gandalf arrives at Minas Tirith to warn Denethor of the attack, while Théoden musters the Rohirrim to ride to Gondor's aid. Minas Tirith is besieged. Denethor is deceived by Sauron and falls into despair. He burns himself alive on a pyre, nearly taking his son Faramir with him. Aragorn, accompanied by Legolas, Gimli and the Rangers of the North, takes the Paths of the Dead to recruit the Dead Men of Dunharrow, who are bound by a curse which denies them rest until they fulfil their ancient forsworn oath to fight for the King of Gondor.
+
+Following Aragorn, the Army of the Dead strikes terror into the Corsairs of Umbar invading southern Gondor. Aragorn defeats the Corsairs and uses their ships to transport the men of southern Gondor up the Anduin, reaching Minas Tirith just in time to turn the tide of battle. Théoden's niece Éowyn, who joined the army in disguise, slays the Lord of the Nazgûl with help from Merry. Together, Gondor and Rohan defeat Sauron's army in the Battle of the Pelennor Fields, though at great cost. Théoden is killed, and Éowyn and Merry are wounded.
+
+Meanwhile, Sam rescues Frodo from the tower of Cirith Ungol. They set out across Mordor. Aragorn leads an army of men from Gondor and Rohan to march on the Black Gate to distract Sauron from his true danger. His army is vastly outnumbered by the great might of Sauron. Frodo and Sam reach the edge of the Cracks of Doom, but Frodo cannot resist the Ring any longer. He claims it for himself and puts it on his finger.
+
+Gollum suddenly reappears. He struggles with Frodo and bites off Frodo's finger with the Ring still on it. Celebrating wildly, Gollum loses his footing and falls into the Fire, taking the Ring with him. When the Ring is destroyed, Sauron loses his power forever. All he created collapses, the Nazgûl perish, and his armies are thrown into such disarray that Aragorn's forces emerge victorious.
+
+Aragorn is crowned King of Arnor and Gondor, and weds Arwen, daughter of Elrond. The four hobbits make their way back to the Shire, only to find that it has been taken over by men directed by one "Sharkey" (whom they later discover to be Saruman). The hobbits raise a rebellion and liberate the Shire, though 19 hobbits are killed and 30 wounded. Frodo stops the hobbits from killing the wizard after Saruman attempts to stab Frodo, but Gríma turns on Saruman and kills him in front of Bag End, Frodo's home. He is slain in turn by hobbit archers, and the War of the Ring comes to its true end on Frodo's very doorstep.
+
+Merry and Pippin are celebrated as heroes. Sam marries Rosie Cotton and uses his gifts from Galadriel to help heal the Shire. But Frodo is still wounded in body and spirit, having borne the Ring for so long. A few years later, in the company of Bilbo and Gandalf, Frodo sails from the Grey Havens west over the Sea to the Undying Lands to find peace.
+
+In the appendices, Sam gives his daughter Elanor the Red Book of Westmarch, which contains the story of Bilbo's adventures and the War of the Ring as witnessed by the hobbits. Sam is then said to have crossed west over the Sea himself, the last of the Ring-bearers.
+
+Tolkien presents The Lord of the Rings within a fictional frame-story where he is not the original author, but merely the translator of part of an ancient document, the Red Book of Westmarch. Various details of the frame-story appear in the Prologue, its 'Note on Shire Records', and in the Appendices, notably Appendix F. In this frame-story, the Red Book is also the source of Tolkien's other works relating to Middle-earth: The Hobbit, The Silmarillion, and The Adventures of Tom Bombadil.[14]
+
+The Lord of the Rings started as a sequel to J. R. R. Tolkien's work The Hobbit, published in 1937.[15] The popularity of The Hobbit had led George Allen & Unwin, the publishers, to request a sequel. Tolkien warned them that he wrote quite slowly, and responded with several stories he had already developed. Having rejected his contemporary drafts for The Silmarillion, putting on hold Roverandom, and accepting Farmer Giles of Ham, Allen & Unwin thought more stories about hobbits would be popular.[16] So at the age of 45, Tolkien began writing the story that would become The Lord of the Rings. The story would not be finished until 12 years later, in 1949, and would not be fully published until 1955, when Tolkien was 63 years old.
+
+Persuaded by his publishers, he started "a new Hobbit" in December 1937.[15] After several false starts, the story of the One Ring emerged. The idea for the first chapter ("A Long-Expected Party") arrived fully formed, although the reasons behind Bilbo's disappearance, the significance of the Ring, and the title The Lord of the Rings did not arrive until the spring of 1938.[15] Originally, he planned to write a story in which Bilbo had used up all his treasure and was looking for another adventure to gain more; however, he remembered the Ring and its powers and thought that would be a better focus for the new work.[15] As the story progressed, he also brought in elements from The Silmarillion mythology.[17]
+
+Writing was slow, because Tolkien had a full-time academic position teaching linguistics (with a focus on languages with linguistic elements he incorporated into his books, such as Old English).[18] "I have spent nearly all the vacation-times of seventeen years examining [...] Writing stories in prose or verse has been stolen, often guiltily, from time already mortgaged..."[19] Tolkien abandoned The Lord of the Rings during most of 1943 and only restarted it in April 1944,[15] as a serial for his son Christopher Tolkien, who was sent chapters as they were written while he was serving in South Africa with the Royal Air Force. Tolkien made another major effort in 1946, and showed the manuscript to his publishers in 1947.[15] The story was effectively finished the next year, but Tolkien did not complete the revision of earlier parts of the work until 1949.[15] The original manuscripts, which total 9,250 pages, now reside in the J. R. R. Tolkien Collection at Marquette University.[20]
+
+Unusually for 20th century novels, the prose narrative is supplemented throughout by over 60 pieces of poetry. These include verse and songs of many genres: for wandering, marching to war, drinking, and having a bath; narrating ancient myths, riddles, prophecies, and magical incantations; of praise and lament (elegy). Some, such as riddles, charms, elegies, and narrating heroic actions are found in Old English poetry.[21] Scholars have stated that the poetry is essential for the fiction to work aesthetically and thematically; it adds information not given in the prose; and it brings out characters and their backgrounds.[22][23] The poetry has been judged to be of high technical skill, which Tolkien carried across into his prose, for instance writing much of Tom Bombadil's speech in metre.[24]
+
+The influence of the Welsh language, which Tolkien had learned, is summarized in his essay English and Welsh: "If I may once more refer to my work. The Lord of the Rings, in evidence: the names of persons and places in this story were mainly composed on patterns deliberately modelled on those of Welsh (closely similar but not identical). This element in the tale has given perhaps more pleasure to more readers than anything else in it."[25]
+
+The Lord of the Rings developed as a personal exploration by Tolkien of his interests in philology, religion (particularly Catholicism[26]), fairy tales, Norse and general Germanic mythology,[27][28] and also Celtic,[29][better source needed] Slavic,[30][31][32] Persian,[33] Greek,[34] and Finnish mythology.[35] Tolkien acknowledged, and external critics have verified, the influences of George MacDonald and William Morris[36] and the Anglo-Saxon poem Beowulf.[37] The question of a direct influence of Wagner's The Nibelung's Ring on Tolkien's work is debated by critics.
+
+Tolkien included neither any explicit religion nor cult in his work. Rather the themes, moral philosophy, and cosmology of The Lord of the Rings reflect his Catholic worldview. In one of his letters Tolkien states, "The Lord of the Rings is of course a fundamentally religious and Catholic work; unconsciously so at first, but consciously in the revision. That is why I have not put in, or have cut out, practically all references to anything like 'religion', to cults or practices, in the imaginary world. For the religious element is absorbed into the story and the symbolism."[26]
+
+Some locations and characters were inspired by Tolkien's childhood in Birmingham, where he first lived near Sarehole Mill, and later near Edgbaston Reservoir.[39] There are also hints of the Black Country, which is within easy reach of northwest Edgbaston. This shows in such names as "Underhill", and the description of Saruman's industrialization of Isengard and The Shire. It has been suggested that the Shire and its surroundings were based on the countryside around Stonyhurst College in Lancashire where Tolkien frequently stayed during the 1940s, but this claim is disputed by reputable Tolkien scholars.[40][41] The work was influenced by the effects of his military service during World War I, to the point that one critic diagnosed Frodo as suffering from posttraumatic stress disorder, which was called "shell-shock" at the Battle of the Somme, in which Tolkien served.[42]
+
+A dispute with his publisher, George Allen & Unwin, led to the book being offered to Collins in 1950. Tolkien intended The Silmarillion (itself largely unrevised at this point) to be published along with The Lord of the Rings, but A&U were unwilling to do this. After Milton Waldman, his contact at Collins, expressed the belief that The Lord of the Rings itself "urgently wanted cutting", Tolkien eventually demanded that they publish the book in 1952.[43] Collins did not; and so Tolkien wrote to Allen and Unwin, saying, "I would gladly consider the publication of any part of the stuff", fearing his work would never see the light of day.[15]
+
+For publication, the book was divided into three volumes to minimize any potential financial loss due to the high cost of type-setting and modest anticipated sales: The Fellowship of the Ring (Books I and II), The Two Towers (Books III and IV), and The Return of the King (Books V and VI plus six appendices).[44] Delays in producing appendices, maps and especially an index led to the volumes being published later than originally hoped – on 29 July 1954, on 11 November 1954 and on 20 October 1955 respectively in the United Kingdom. In the United States, Houghton Mifflin published The Fellowship of the Ring on 21 October 1954, The Two Towers on 21 April 1955, and The Return of the King on 5 January 1956.[45]
+
+The Return of the King was especially delayed due to Tolkien revising the ending and preparing appendices (some of which had to be left out because of space constraints). Tolkien did not like the title The Return of the King, believing it gave away too much of the storyline, but deferred to his publisher's preference.[46] Tolkien wrote that the title The Two Towers "can be left ambiguous,"[47] but also considered naming the two as Orthanc and Barad-dûr, Minas Tirith and Barad-dûr, or Orthanc and the Tower of Cirith Ungol.[47][48] However, a month later he wrote a note published at the end of The Fellowship of the Ring and later drew a cover illustration, both of which identified the pair as Minas Morgul and Orthanc.[49][50]
+
+Tolkien was initially opposed to titles being given to each two-book volume, preferring instead the use of book titles: e.g. The Lord of the Rings: Vol. 1, The Ring Sets Out and The Ring Goes South; Vol. 2, The Treason of Isengard and The Ring Goes East; Vol. 3, The War of the Ring and The End of the Third Age. However these individual book titles were later scrapped, and after pressure from his publishers, Tolkien initially suggested the titles: Vol. 1, The Shadow Grows; Vol. 2, The Ring in the Shadow; Vol. 3, The War of the Ring or The Return of the King.[51][52]
+
+Because the three-volume binding was so widely distributed, the work is often referred to as the Lord of the Rings "trilogy". In a letter to the poet W. H. Auden (who famously reviewed the final volume in 1956[53]), Tolkien himself made use of the term "trilogy" for the work[54] though he did at other times consider this incorrect, as it was written and conceived as a single book.[55] It is also often called a novel; however, Tolkien also objected to this term as he viewed it as a heroic romance.[56]
+
+The books were published under a profit-sharing arrangement, whereby Tolkien would not receive an advance or royalties until the books had broken even, after which he would take a large share of the profits.[57] It has ultimately become one of the best-selling novels ever written, with 50 million copies sold by 2003[58] and over 150 million copies sold by 2007.[2]
+
+The book was published in the UK by Allen & Unwin until 1990 when the publisher and its assets were acquired by HarperCollins.[59][60]
+
+In the early 1960s Donald A. Wollheim, science fiction editor of the paperback publisher Ace Books, claimed that The Lord of the Rings was not protected in the United States under American copyright law because Houghton Mifflin, the US hardcover publisher, had neglected to copyright the work in the United States.[61][62] Then, in 1965, Ace Books proceeded to publish an edition, unauthorized by Tolkien and without paying royalties to him. Tolkien took issue with this and quickly notified his fans of this objection.[63] Grass-roots pressure from these fans became so great that Ace Books withdrew their edition and made a nominal payment to Tolkien.[64][65]
+
+Authorized editions followed from Ballantine Books and Houghton Mifflin to tremendous commercial success. Tolkien undertook various textual revisions to produce a version of the book that would be published with his consent and establish an unquestioned US copyright. This text became the Second Edition of The Lord of the Rings, published in 1965.[64] The first Ballantine paperback edition was printed in October that year, and sold a quarter of a million copies within ten months. On 4 September 1966, the novel debuted on New York Times' Paperback Bestsellers list as number three, and was number one by 4 December, a position it held for eight weeks.[66] Houghton Mifflin editions after 1994 consolidate variant revisions by Tolkien, and corrections supervised by Christopher Tolkien, which resulted, after some initial glitches, in a computer-based unified text.[67]
+
+In 2004, for the 50th Anniversary Edition, Wayne G. Hammond and Christina Scull, under supervision from Christopher Tolkien, studied and revised the text to eliminate as many errors and inconsistencies as possible, some of which had been introduced by well-meaning compositors of the first printing in 1954, and never been corrected.[68] The 2005 edition of the book contained further corrections noticed by the editors and submitted by readers. Further corrections were added to the 60th Anniversary Edition in 2014.[69]
+
+Several editions, notably the 50th Anniversary Edition, combine all three books into one volume, with the result that pagination varies widely over the various editions.
+
+From 1988 to 1992 Christopher Tolkien published the surviving drafts of The Lord of The Rings, chronicling and illuminating with commentary the stages of the text's development, in volumes 6–9 of his History of Middle-earth series. The four volumes carry the titles The Return of the Shadow, The Treason of Isengard, The War of the Ring, and Sauron Defeated.
+
+The novel has been translated, with varying degrees of success, into at least 56 languages.[70] Tolkien, an expert in philology, examined many of these translations, and made comments on each that reflect both the translation process and his work. As he was unhappy with some choices made by early translators, such as the Swedish translation by Åke Ohlmarks,[71] Tolkien wrote a "Guide to the Names in The Lord of the Rings" (1967). Because The Lord of the Rings purports to be a translation of the fictitious Red Book of Westmarch, with the English language representing the Westron of the "original", Tolkien suggested that translators attempt to capture the interplay between English and the invented nomenclature of the English work, and gave several examples along with general guidance.
+
+While early reviews for The Lord of the Rings were mixed, reviews in various media have been, on the whole, highly positive and acknowledge Tolkien's literary achievement as a significant one. The initial review in the Sunday Telegraph described it as "among the greatest works of imaginative fiction of the twentieth century".[72] The Sunday Times echoed this sentiment, stating that "the English-speaking world is divided into those who have read The Lord of the Rings and The Hobbit and those who are going to read them."[72] The New York Herald Tribune also seemed to have an idea of how popular the books would become, writing in its review that they were "destined to outlast our time".[73] W. H. Auden, an admirer of Tolkien's writings, regarded The Lord of the Rings as a "masterpiece", further stating that in some cases it outdid the achievement of John Milton's Paradise Lost.[74] Kenneth F Slater [75] wrote in Nebula Science Fiction, April 1955, "... if you don’t read it, you have missed one of the finest books of its type ever to appear" [76]
+
+New York Times reviewer Judith Shulevitz criticized the "pedantry" of Tolkien's literary style, saying that he "formulated a high-minded belief in the importance of his mission as a literary preservationist, which turns out to be death to literature itself".[77] Critic Richard Jenkyns, writing in The New Republic, criticized the work for a lack of psychological depth. Both the characters and the work itself are, according to Jenkyns, "anemic, and lacking in fibre".[78] Even within Tolkien's literary group, The Inklings, reviews were mixed. Hugo Dyson complained loudly at its readings.[79][80] However, another Inkling, C. S. Lewis, had very different feelings, writing, "here are beauties which pierce like swords or burn like cold iron. Here is a book which will break your heart." Despite these reviews and its lack of paperback printing until the 1960s, The Lord of the Rings initially sold well in hardback.[7]
+
+In 1957, The Lord of the Rings was awarded the International Fantasy Award. Despite its numerous detractors, the publication of the Ace Books and Ballantine paperbacks helped The Lord of the Rings become immensely popular in the United States in the 1960s. The book has remained so ever since, ranking as one of the most popular works of fiction of the twentieth century, judged by both sales and reader surveys.[81] In the 2003 "Big Read" survey conducted in Britain by the BBC, The Lord of the Rings was found to be the "Nation's best-loved book". In similar 2004 polls both Germany[82] and Australia[83] also found The Lord of the Rings to be their favourite book. In a 1999 poll of Amazon.com customers, The Lord of the Rings was judged to be their favourite "book of the millennium".[84]
+
+C. S. Lewis observed that the writing is rich in that some of the 'good' characters have darker sides, and likewise some of the villains have "good impulses".[85]
+
+Although The Lord of the Rings was published in the 1950s, Tolkien insisted that the One Ring was not an allegory for the atomic bomb,[86] nor were his works a strict allegory of any kind, but were open to interpretation as the reader saw fit.[87][88]
+
+A few critics have found what they consider racial elements in the story, which are generally based upon their views of how Tolkien's imagery depicts good and evil, characters' race (e.g. Elf, Dwarf, Hobbit, Southron, Númenórean, Orc), and how the characters' race is seen as determining their behaviour.[89][90][91] On the contrary, counter-arguments note that race-focused critiques often omit relevant textual evidence,[92][93][94] cite imagery from adaptations rather than the work itself,[95] ignore the absence of evidence of racist attitudes or events in the author's personal life,[92][95][96] and claim that the perception of racism is itself a marginal view.[96]
+
+The opinions that pit races against each other most likely reflect Tolkien's criticism of war rather than a racist perspective. In The Two Towers, the character Samwise sees a fallen foe, a man of colour, and considers the humanity of this fallen Southron.[97] Director Peter Jackson, in the director's commentary of this scene, argues that Tolkien isn't projecting negativity towards the individual soldier because of his race, but against the evil authority that is driving them.[98] These sentiments, Jackson argues, arose from Tolkien's experience in the Great War and found their way into his writings to show the evils of war itself, not of other races.
+
+Critics have also seen social class rather than race as being the determining factor in the portrayal of good and evil.[92] Commentators such as science fiction author David Brin have interpreted the work to hold unquestioning devotion to a traditional elitist social structure.[99] In his essay "Epic Pooh", science fiction and fantasy author Michael Moorcock critiques the world-view displayed by the book as deeply conservative, in both the "paternalism" of the narrative voice and the power-structures in the narrative.[100] Tom Shippey cites the origin of this portrayal of evil as a reflection of the prejudices of European middle-classes during the inter-war years towards the industrial working class.[101]
+
+Other observers have described Christian themes in the work, specifically Roman Catholicism.[102]
+
+The book has been read as fitting the model of Joseph Campbell's "monomyth".[103]
+
+The Lord of the Rings has been adapted for film, radio and stage.
+
+The book has been adapted for radio four times. In 1955 and 1956, the BBC broadcast The Lord of the Rings, a 13-part radio adaptation of the story. In the 1960s radio station WBAI produced a short radio adaptation. A 1979 dramatization of The Lord of the Rings was broadcast in the United States and subsequently issued on tape and CD. In 1981, the BBC broadcast The Lord of the Rings, a new dramatization in 26 half-hour instalments. This dramatization of The Lord of the Rings has subsequently been made available on both tape and CD both by the BBC and other publishers. For this purpose it is generally edited into 13 one-hour episodes.
+
+Filmmakers who attempted to adapt Tolkien's works include William Snyder, Peter Shaffer, John Boorman, Ralph Bakshi, Peter Jackson and Guillermo del Toro. Other filmmakers and producers who were interested in an adaptation included Walt Disney, Al Brodax, Forrest J Ackerman, Samuel Gelfman, Denis O'Dell and Heinz Edelmann.
+
+Following J. R. R. Tolkien's sale of the film rights for The Lord of the Rings to United Artists in 1969, rock band The Beatles considered a corresponding film project. David Lean was approached to direct, and while intrigued, was busy with Ryan's Daughter. The next choice, Stanley Kubrick, had to first familiarize himself with the books, only to then say they were unfilmable due to their immensity.[104][105] Michaelangelo Antonioni was contacted, and Heinz Edelmann even offered doing it in animation, but the project fell apart.[106] British director John Boorman also tried to make an adaptation of The Lord of the Rings for United Artists in 1970. After the script was written, which included many changes to the story and the characters, the production company scrapped the project, thinking it too expensive and too risky.[107]
+
+Two film adaptations of the book have been made. The first was J. R. R. Tolkien's The Lord of the Rings (1978), by animator Ralph Bakshi, the first part of what was originally intended to be a two-part adaptation of the story; it covers The Fellowship of the Ring and part of The Two Towers. A three-issue comic book version of the movie was also published in Europe (but not printed in English), with illustrations by Luis Bermejo.
+
+The second and more commercially successful adaptation was Peter Jackson's live action The Lord of the Rings film trilogy, produced by New Line Cinema and released in three instalments as The Lord of the Rings: The Fellowship of the Ring (2001), The Lord of the Rings: The Two Towers (2002), and The Lord of the Rings: The Return of the King (2003). All three parts won multiple Academy Awards, including consecutive Best Picture nominations. The final instalment of this trilogy was the second film to break the one-billion-dollar barrier and won a total of 11 Oscars (something only two other films in history, Ben-Hur and Titanic, have accomplished), including Best Picture, Best Director and Best Adapted Screenplay. Jackson later reprised his role as director, writer and producer to make a prequel trilogy based on The Hobbit.
+
+The Hunt for Gollum, a fan film based on elements of the appendices to The Lord of the Rings, was released on the internet in May 2009 and has been covered in major media.[108] Born of Hope, written by Paula DiSante, directed by Kate Madison, and released in December 2009, is a fan film based upon the appendices of The Lord of the Rings.[109]
+
+Rankin and Bass used a loophole in the publication of The Hobbit and The Lord of the Rings (which made them public domain in the US) to make animated TV specials based on The Hobbit, released in 1977, and a sequel based on the closing chapters of The Return of the King, which came out in 1980.
+
+In 2017, Amazon acquired the global television rights to The Lord of the Rings for a multi-season television series of new stories set before The Hobbit and The Lord of the Rings,[110]  based on J.R.R. Tolkien's writings about events of the Second Age of Middle-earth.[111] Amazon said the deal included potential for spin-off series as well.[112][113] It was later revealed that the show will apparently be set in the early second age, during the time of the Forging of the Rings,[114] and will allegedly be a prequel to the live-action films.[115]
+
+It was projected in 2018 to be the most expensive TV show ever produced.[116] Much of it will be produced in New Zealand.[117][118][119][120] The cast includes Robert Aramayo, Owain Arthur, Nazanin Boniadi, Tom Budge, Morfydd Clark (as Galadriel),[121] Ismael Cruz Córdova, Ema Horvath, Markella Kavenagh, Joseph Mawle, Tyroe Muhafidin, Sophia Nomvete, Megan Richards, Dylan Smith, Charlie Vickers, Daniel Weyman,[122] and Maxim Baldry.[123]
+
+In 1990, Recorded Books published an audio version of The Lord of the Rings,[124] with British actor Rob Inglis – who had previously starred in his own one-man stage productions of The Hobbit and The Lord of the Rings – reading. A large-scale musical theatre adaptation, The Lord of the Rings was first staged in Toronto, Ontario, Canada in 2006 and opened in London in June 2007.
+
+The enormous popularity of Tolkien's work expanded the demand for fantasy fiction. Largely thanks to The Lord of the Rings, the genre flowered throughout the 1960s, and enjoys popularity to the present day. The opus has spawned many imitators, such as The Sword of Shannara, which Lin Carter called "the single most cold-blooded, complete rip-off of another book that I have ever read".[125]
+Dungeons & Dragons, which popularized the role-playing game (RPG) genre in the 1970s, features many races found in The Lord of the Rings, most notably halflings (another term for hobbits), elves, dwarves, half-elves, orcs, and dragons. However, Gary Gygax, lead designer of the game, maintained that he was influenced very little by The Lord of the Rings, stating that he included these elements as a marketing move to draw on the popularity the work enjoyed at the time he was developing the game.[126]
+
+Because D&D has gone on to influence many popular role-playing video games, the influence of The Lord of the Rings extends to many of them as well, with titles such as Dragon Quest,[127][128] the Ultima series, EverQuest, the Warcraft series, and the Elder Scrolls series of games[129] as well as video games set in Middle-earth itself.
+
+Research also suggests that some consumers of fantasy games derive their motivation from trying to create an epic fantasy narrative which is influenced by The Lord of the Rings.[130]
+
+In 1965, songwriter Donald Swann, who was best known for his collaboration with Michael Flanders as Flanders & Swann, set six poems from The Lord of the Rings and one from The Adventures of Tom Bombadil ("Errantry") to music. When Swann met with Tolkien to play the songs for his approval, Tolkien suggested for "Namárië" (Galadriel's lament) a setting reminiscent of plain chant, which Swann accepted.[131] The songs were published in 1967 as The Road Goes Ever On: A Song Cycle,[132] and a recording of the songs performed by singer William Elvin with Swann on piano was issued that same year by Caedmon Records as Poems and Songs of Middle Earth.[133]
+
+Rock bands of the 1970s were musically and lyrically inspired by the fantasy embracing counter-culture of the time; British 70s rock band Led Zeppelin recorded several songs that contain explicit references to The Lord of the Rings, such as mentioning Gollum in "Ramble On", the Misty Mountains in "Misty Mountain Hop", and Ringwraiths in "The Battle of Evermore". In 1970, the Swedish musician Bo Hansson released an instrumental concept album based on the book titled Sagan om ringen (translated as "The Saga of the Ring", which was the title of the Swedish translation of The Lord of the Rings at the time).[134] The album was subsequently released internationally as Music Inspired by Lord of the Rings in 1972.[134]
+
+The songs "Rivendell" and "The Necromancer" by the progressive rock band Rush were inspired by Tolkien. Styx also paid homage to Tolkien on their album Pieces of Eight with the song "Lords of the Ring", while Black Sabbath's song, "The Wizard", which appeared on their debut album, was influenced by Tolkien's hero, Gandalf. Progressive rock group Camel paid homage to the text in their lengthy composition "Nimrodel/The Procession/The White Rider", and progressive rock band Barclay James Harvest was inspired by the character Galadriel to write a song by that name, and used "Bombadil", the name of another character, as a pseudonym under which their 1972 single "Breathless"/"When the City Sleeps" was released; there are other references scattered through the BJH oeuvre.
+
+Later, from the 1980s to the present day, many heavy metal acts have been influenced by Tolkien. Blind Guardian has written many songs relating to Middle-earth, including the full concept album Nightfall in Middle Earth. Almost the entire discography of Battlelore are Tolkien-themed. Summoning's music is based upon Tolkien and holds the distinction of the being the only artist to have crafted a song entirely in the Black Speech of Mordor. Gorgoroth, Cirith Ungol and Amon Amarth take their names from an area of Mordor, and Burzum take their name from the Black Speech of Mordor. The Finnish metal band Nightwish and the Norwegian metal band Tristania have also incorporated many Tolkien references into their music. American heavy metal band Megadeth released two songs titled "This Day We Fight!" and "How the Story Ends", which were both inspired by The Lord of the Rings.[135] German folk metal band Eichenschild is named for Thorin Oakenshield, a character in The Hobbit, and naturally has a number of Tolkien-themed songs. They are not to be confused with the '70s folk rock band Thorin Eichenschild.
+
+In 1988, Dutch composer and trombonist Johan de Meij completed his Symphony No. 1 "The Lord of the Rings", which encompassed 5 movements, titled "Gandalf", "Lothlórien", "Gollum", "Journey in the Dark", and "Hobbits". In 1989 the symphony was awarded the Sudler Composition Award, awarded biennially for best wind band composition. The Danish Tolkien Ensemble have released a number of albums that feature the complete poems and songs of The Lord of the Rings set to music, with some featuring recitation by Christopher Lee. In 2018, de Meij completed his Symphony No. 5 "Return to Middle Earth" in 2018, which has 6 movements titled "Mîri na Fëanor (Fëanor’s Jewels)", "Tinúviel (Nightingale)", "Ancalagon i-môr (Ancalagon, The Black)", "Arwen Undómiel (Evenstar)", "Dagor Delothrin (The War of Wrath)", and "Thuringwethil (Woman of Secret Shadow)".
+
+Enya wrote an instrumental piece called "Lothlórien" in 1991, and composed two songs for the film The Lord of the Rings: The Fellowship of the Ring—"May It Be" (sung in English and Quenya) and "Aníron" (sung in Sindarin).
+
+The 2020 modern classical album "Music for Piano and Strings" by pianist and composer Holger Skepeneit contains two Lord of the Rings-inspired pieces, "Laced with Ithildin" and "Nimrodel's Voice".
+
+The Lord of the Rings has had a profound and wide-ranging impact on popular culture, beginning with its publication in the 1950s, but especially throughout the 1960s and 1970s, during which time young people embraced it as a countercultural saga.[136] "Frodo Lives!" and "Gandalf for President" were two phrases popular amongst United States Tolkien fans during this time.[137]
+
+Parodies like the Harvard Lampoon's Bored of the Rings, the VeggieTales episode "Lord of the Beans", the South Park episode "The Return of the Fellowship of the Ring to the Two Towers", the Futurama film Bender's Game, The Adventures of Jimmy Neutron: Boy Genius episode "Lights! Camera! Danger!", The Big Bang Theory episode "The Precious Fragmentation", and the American Dad! episode "The Return of the Bling" are testimony to the work's continual presence in popular culture.
+
+In 1969, Tolkien sold the merchandising rights to The Lord of The Rings (and The Hobbit) to United Artists under an agreement stipulating a lump sum payment of £10,000[138] plus a 7.5% royalty after costs,[139] payable to Allen & Unwin and the author.[140] In 1976, three years after the author's death, United Artists sold the rights to Saul Zaentz Company, who now trade as Tolkien Enterprises. Since then all "authorized" merchandise has been signed-off by Tolkien Enterprises, although the intellectual property rights of the specific likenesses of characters and other imagery from various adaptations is generally held by the adaptors.[141]
+
+Outside any commercial exploitation from adaptations, from the late 1960s onwards there has been an increasing variety of original licensed merchandise, from posters and calendars created by illustrators such as Barbara Remington[142], Pauline Baynes and the Brothers Hildebrandt, to figurines and miniatures to computer, video, tabletop and role-playing games. Recent examples include the Spiel des Jahres award-winning (for "best use of literature in a game") board game The Lord of the Rings by Reiner Knizia and the Golden Joystick award-winning massively multiplayer online role-playing game, The Lord of the Rings Online: Shadows of Angmar by Turbine, Inc..
+
+The Lord of the Rings has been mentioned in numerous songs including "The Ballad of Bilbo Baggins" by Leonard Nimoy, Led Zeppelin's "Misty Mountain Hop", "Over the Hills and Far Away", "Ramble On", and "The Battle of Evermore", Genesis' song "Stagnation" (from Trespass, 1970) was about Gollum, Rush included the song "Rivendell" on their second studio album Fly by Night, and Argent included the song "Lothlorien" on the 1971 album Ring of Hands.
+
+Steve Peregrin Took (born Stephen Ross Porter) of British rock band T. Rex took his name from the hobbit Peregrin Took (better known as Pippin). Took later recorded under the pseudonym 'Shagrat the Vagrant', before forming a band called Shagrat in 1970.
+
+On 5 November 2019, the BBC News listed The Lord of the Rings on its list of the 100 most influential novels.[143]

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+
+In botany, a tree is a perennial plant with an elongated stem, or trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are usable as lumber or plants above a specified height. In wider definitions, the taller palms, tree ferns, bananas, and bamboos are also trees. Trees are not a taxonomic group but include a variety of plant species that have independently evolved a trunk and branches as a way to tower above other plants to compete for sunlight. Trees tend to be long-lived, some reaching several thousand years old.  Trees have been in existence for 370 million years. It is estimated that there are some three trillion mature trees in the world.[1]
+
+A tree typically has many secondary branches supported clear of the ground by the trunk. This trunk typically contains woody tissue for strength, and vascular tissue to carry materials from one part of the tree to another. For most trees it is surrounded by a layer of bark which serves as a protective barrier. Below the ground, the roots branch and spread out widely; they serve to anchor the tree and extract moisture and nutrients from the soil. Above ground, the branches divide into smaller branches and shoots. The shoots typically bear leaves, which capture light energy and convert it into sugars by photosynthesis, providing the food for the tree's growth and development.
+
+Trees usually reproduce using seeds. Flowers and fruit may be present, but some trees, such as conifers, instead have pollen cones and seed cones. Palms, bananas, and bamboos also produce seeds, but tree ferns produce spores instead.
+
+Trees play a significant role in reducing erosion and moderating the climate. They remove carbon dioxide from the atmosphere and store large quantities of carbon in their tissues. Trees and forests provide a habitat for many species of animals and plants. Tropical rainforests are among the most biodiverse habitats in the world. Trees provide shade and shelter, timber for construction, fuel for cooking and heating, and fruit for food as well as having many other uses. In parts of the world, forests are shrinking as trees are cleared to increase the amount of land available for agriculture. Because of their longevity and usefulness, trees have always been revered, with sacred groves in various cultures, and they play a role in many of the world's mythologies.
+
+Although "tree" is a term of common parlance, there is no universally recognised precise definition of what a tree is, either botanically or in common language.[2] In its broadest sense, a tree is any plant with the general form of an elongated stem, or trunk, which supports the photosynthetic leaves or branches at some distance above the ground.[3] Trees are also typically defined by height,[4] with smaller plants from 0.5 to 10 m (1.6 to 32.8 ft) being called shrubs,[5] so the minimum height of a tree is only loosely defined.[4] Large herbaceous plants such as papaya and bananas are trees in this broad sense.[2][6]
+
+A commonly applied narrower definition is that a tree has a woody trunk formed by secondary growth, meaning that the trunk thickens each year by growing outwards, in addition to the primary upwards growth from the growing tip.[4][7] Under such a definition, herbaceous plants such as palms, bananas and papayas are not considered trees regardless of their height, growth form or stem girth. Certain monocots may be considered trees under a slightly looser definition;[8] while the Joshua tree, bamboos and palms do not have secondary growth and never produce true wood with growth rings,[9][10] they may produce "pseudo-wood" by lignifying cells formed by primary growth.[11] Tree species in the genus Dracaena, despite also being monocots, do have secondary growth caused by meristem in their trunk, but it is different from the thickening meristem found in dicotyledonous trees.[12]
+
+Aside from structural definitions, trees are commonly defined by use; for instance, as those plants which yield lumber.[13]
+
+The tree growth habit is an evolutionary adaptation found in different groups of plants: by growing taller, trees are able to compete better for sunlight.[14] Trees tend to be tall and long-lived,[15] some reaching several thousand years old.[16] Several trees are among the oldest organisms now living.[17] Trees have modified structures such as thicker stems composed of specialised cells that add structural strength and durability, allowing them to grow taller than many other plants and to spread out their foliage. They differ from shrubs, which have a similar growth form, by usually growing larger and having a single main stem;[5] but there is no consistent distinction between a tree and a shrub,[18] made more confusing by the fact that trees may be reduced in size under harsher environmental conditions such as on mountains and subarctic areas. The tree form has evolved separately in unrelated classes of plants in response to similar environmental challenges, making it a classic example of parallel evolution. With an estimated 60,000-100,000 species, the number of trees worldwide might total twenty-five per cent of all living plant species.[19][20] The greatest number of these grow in tropical regions and many of these areas have not yet been fully surveyed by botanists, making tree diversity and ranges poorly known.[21]
+
+The majority of tree species are angiosperms. There are about 1000 species of gymnosperm trees,[22] including conifers, cycads, ginkgophytes and gnetales; they produce seeds which are not enclosed in fruits, but in open structures such as pine cones, and many have tough waxy leaves, such as pine needles.[23] Most angiosperm trees are eudicots, the "true dicotyledons", so named because the seeds contain two cotyledons or seed leaves. There are also some trees among the old lineages of flowering plants called  basal angiosperms or paleodicots; these include Amborella, Magnolia, nutmeg and avocado,[24] while trees such as bamboo, palms and bananas are monocots.
+
+Wood gives structural strength to the trunk of most types of tree; this supports the plant as it grows larger. The vascular system of trees allows water, nutrients and other chemicals to be distributed around the plant, and without it trees would not be able to grow as large as they do. Trees, as relatively tall plants, need to draw water up the stem through the xylem from the roots by the suction produced as water evaporates from the leaves. If insufficient water is available the leaves will die.[25] The three main parts of trees include the root, stem, and leaves; they are integral parts of the vascular system which interconnects all the living cells. In trees and other plants that develop wood, the vascular cambium allows the expansion of vascular tissue that produces woody growth. Because this growth ruptures the epidermis of the stem, woody plants also have a cork cambium that develops among the phloem. The cork cambium gives rise to thickened cork cells to protect the surface of the plant and reduce water loss. Both the production of wood and the production of cork are forms of secondary growth.[26]
+
+Trees are either evergreen, having foliage that persists and remains green throughout the year,[27] or deciduous, shedding their leaves at the end of the growing season and then having a dormant period without foliage.[28] Most conifers are evergreens, but larches (Larix and Pseudolarix) are deciduous, dropping their needles each autumn, and some species of cypress (Glyptostrobus, Metasequoia and Taxodium) shed small leafy shoots annually in a process known as cladoptosis.[5] The crown is the spreading top of a tree including the branches and leaves,[29] while the uppermost layer in a forest, formed by the crowns of the trees, is known as the canopy.[30] A sapling is a young tree.[31]
+
+Many tall palms are herbaceous[32] monocots; these do not undergo secondary growth and never produce wood.[9][10] In many tall palms, the terminal bud on the main stem is the only one to develop, so they have unbranched trunks with large spirally arranged leaves. Some of the tree ferns, order Cyatheales, have tall straight trunks, growing up to 20 metres (66 ft), but these are composed not of wood but of rhizomes which grow vertically and are covered by numerous adventitious roots.[33]
+
+The number of trees in the world, according to a 2015 estimate, is 3.04 trillion, of which 1.39 trillion (46%) are in the tropics or sub-tropics, 0.61 trillion (20%) in the temperate zones, and 0.74 trillion (24%) in the coniferous boreal forests. The estimate is about eight times higher than previous estimates, and is based on tree densities measured on over 400,000 plots. It remains subject to a wide margin of error, not least because the samples are mainly from Europe and North America. The estimate suggests that about 15 billion trees are cut down annually and about 5 billion are planted. In the 12,000 years since the start of human agriculture, the number of trees worldwide has decreased by 46%.[1][34][35][36]
+
+In suitable environments, such as the Daintree Rainforest in Queensland, or the mixed podocarp and broadleaf forest of Ulva Island, New Zealand, forest is the more-or-less stable climatic climax community at the end of a plant succession, where open areas such as grassland are colonised by taller plants, which in turn give way to trees that eventually form a forest canopy.[37][38]
+
+In cool temperate regions, conifers often predominate; a widely distributed climax community in the far north of the northern hemisphere is moist taiga or northern coniferous forest (also called boreal forest).[39][40] Taiga is the world's largest land biome, forming 29% of the world's forest cover.[41] The long cold winter of the far north is unsuitable for plant growth and trees must grow rapidly in the short summer season when the temperature rises and the days are long. Light is very limited under their dense cover and there may be little plant life on the forest floor, although fungi may abound.[42] Similar woodland is found on mountains where the altitude causes the average temperature to be lower thus reducing the length of the growing season.[43]
+
+Where rainfall is relatively evenly spread across the seasons in temperate regions, temperate broadleaf and mixed forest typified by species like oak, beech, birch and maple is found.[44] Temperate forest is also found in the southern hemisphere, as for example in the Eastern Australia temperate forest, characterised by Eucalyptus forest and open acacia woodland.[45]
+
+In tropical regions with a monsoon or monsoon-like climate, where a drier part of the year alternates with a wet period as in the Amazon rainforest, different species of broad-leaved trees dominate the forest, some of them being deciduous.[46] In tropical regions with a drier savanna climate and insufficient rainfall to support dense forests, the canopy is not closed, and plenty of sunshine reaches the ground which is covered with grass and scrub. Acacia and baobab are well adapted to living in such areas.[47]
+
+The roots of a tree serve to anchor it to the ground and gather water and nutrients to transfer to all parts of the tree. They are also used for reproduction, defence, survival, energy storage and many other purposes. The radicle or embryonic root is the first part of a seedling to emerge from the seed during the process of germination. This develops into a taproot which goes straight downwards. Within a few weeks lateral roots branch out of the side of this and grow horizontally through the upper layers of the soil. In most trees, the taproot eventually withers away and the wide-spreading laterals remain. Near the tip of the finer roots are single cell root hairs. These are in immediate contact with the soil particles and can absorb water and nutrients such as potassium in solution. The roots require oxygen to respire and only a few species such as mangroves and the pond cypress (Taxodium ascendens) can live in permanently waterlogged soil.[48]
+
+In the soil, the roots encounter the hyphae of fungi. Many of these are known as mycorrhiza and form a mutualistic relationship with the tree roots. Some are specific to a single tree species, which will not flourish in the absence of its mycorrhizal associate. Others are generalists and associate with many species. The tree acquires minerals such as phosphorus from the fungus, while the fungus obtains the carbohydrate products of photosynthesis from the tree.[49] The hyphae of the fungus can link different trees and a network is formed, transferring nutrients and signals from one place to another.[50] The fungus promotes growth of the roots and helps protect the trees against predators and pathogens. It can also limit damage done to a tree by pollution as the fungus accumulate heavy metals within its tissues.[51] Fossil evidence shows that roots have been associated with mycorrhizal fungi since the early Paleozoic, four hundred million years ago, when the first vascular plants colonised dry land.[52]
+
+Some trees such as the alders (Alnus species) have a symbiotic relationship with Frankia species, a filamentous bacterium that can fix nitrogen from the air, converting it into ammonia. They have actinorhizal root nodules on their roots in which the bacteria live. This process enables the tree to live in low nitrogen habitats where they would otherwise be unable to thrive.[53] The plant hormones called cytokinins initiate root nodule formation, in a process closely related to mycorrhizal association.[54]
+
+It has been demonstrated that some trees are interconnected through their root system, forming a colony. The interconnections are made by the inosculation process, a kind of natural grafting or welding of vegetal tissues. The tests to demonstrate this networking are performed by injecting chemicals, sometimes radioactive, into a tree, and then checking for its presence in neighbouring trees.[55]
+
+The roots are, generally, an underground part of the tree, but some tree species have evolved roots that are aerial. The common purposes for aerial roots may be of two kinds, to contribute to the mechanical stability of the tree, and to obtain oxygen from air. An instance of mechanical stability enhancement is the red mangrove that develops prop roots that loop out of the trunk and branches and descend vertically into the mud.[56] A similar structure is developed by the Indian banyan.[57] Many large trees have buttress roots which flare out from the lower part of the trunk. These brace the tree rather like angle brackets and provide stability, reducing sway in high winds. They are particularly prevalent in tropical rainforests where the soil is poor and the roots are close to the surface.[58]
+
+Some tree species have developed root extensions that pop out of soil, in order to get oxygen, when it is not available in the soil because of excess water. These root extensions are called pneumatophores, and are present, among others, in black mangrove and pond cypress.[56]
+
+The main purpose of the trunk is to raise the leaves above the ground, enabling the tree to overtop other plants and outcompete them for light.[59] It also transports water and nutrients from the roots to the aerial parts of the tree, and distributes the food produced by the leaves to all other parts, including the roots.[60]
+
+In the case of angiosperms and gymnosperms, the outermost layer of the trunk is the bark, mostly composed of dead cells of phellem (cork).[61] It provides a thick, waterproof covering to the living inner tissue. It protects the trunk against the elements, disease, animal attack and fire. It is perforated by a large number of fine breathing pores called lenticels, through which oxygen diffuses. Bark is continually replaced by a living layer of cells called the cork cambium or phellogen.[61] The London plane (Platanus × acerifolia) periodically sheds its bark in large flakes. Similarly, the bark of the silver birch (Betula pendula) peels off in strips. As the tree's girth expands, newer layers of bark are larger in circumference, and the older layers develop fissures in many species. In some trees such as the pine (Pinus species) the bark exudes sticky resin which deters attackers whereas in rubber trees (Hevea brasiliensis) it is a milky latex that oozes out. The quinine bark tree (Cinchona officinalis) contains bitter substances to make the bark unpalatable.[60] Large tree-like plants with lignified trunks in the Pteridophyta, Arecales, Cycadophyta and Poales such as the tree ferns, palms, cycads and bamboos have different structures and outer coverings.[62]
+
+Although the bark functions as a protective barrier, it is itself attacked by boring insects such as beetles. These lay their eggs in crevices and the larvae chew their way through the cellulose tissues leaving a gallery of tunnels. This may allow fungal spores to gain admittance and attack the tree. Dutch elm disease is caused by a fungus (Ophiostoma species) carried from one elm tree to another by various beetles. The tree reacts to the growth of the fungus by blocking off the xylem tissue carrying sap upwards and the branch above, and eventually the whole tree, is deprived of nourishment and dies. In Britain in the 1990s, 25 million elm trees were killed by this disease.[63]
+
+The innermost layer of bark is known as the phloem and this is involved in the transport of the sap containing the sugars made by photosynthesis to other parts of the tree. It is a soft spongy layer of living cells, some of which are arranged end to end to form tubes. These are supported by parenchyma cells which provide padding and include fibres for strengthening the tissue.[64] Inside the phloem is a layer of undifferentiated cells one cell thick called the vascular cambium layer. The cells are continually dividing, creating phloem cells on the outside and wood cells known as xylem on the inside.[65]
+
+The newly created xylem is the sapwood. It is composed of water-conducting cells and associated cells which are often living, and is usually pale in colour. It transports water and minerals from the roots to the upper parts of the tree. The oldest, inner part of the sapwood is progressively converted into heartwood as new sapwood is formed at the cambium. The conductive cells of the heartwood are blocked in some species. Heartwood is usually darker in colour than the sapwood. It is the dense central core of the trunk giving it rigidity. Three quarters of the dry mass of the xylem is cellulose, a polysaccharide, and most of the remainder is lignin, a complex polymer. A transverse section through a tree trunk or a horizontal core will show concentric circles or lighter or darker wood – tree rings.[66] These rings are the annual growth rings[67][68] There may also be rays running at right angles to growth rings. These are vascular rays which are thin sheets of living tissue permeating the wood.[66] Many older trees may become hollow but may still stand upright for many years.[69]
+
+Trees do not usually grow continuously throughout the year but mostly have spurts of active expansion followed by periods of rest. This pattern of growth is related to climatic conditions; growth normally ceases when conditions are either too cold or too dry. In readiness for the inactive period, trees form buds to protect the meristem, the zone of active growth. Before the period of dormancy, the last few leaves produced at the tip of a twig form scales. These are thick, small and closely wrapped and enclose the growing point in a waterproof sheath. Inside this bud there is a rudimentary stalk and neatly folded miniature leaves, ready to expand when the next growing season arrives. Buds also form in the axils of the leaves ready to produce new side shoots. A few trees, such as the eucalyptus, have "naked buds" with no protective scales and some conifers, such as the Lawson's cypress, have no buds but instead have little pockets of meristem concealed among the scale-like leaves.[70]
+
+When growing conditions improve, such as the arrival of warmer weather and the longer days associated with spring in temperate regions, growth starts again. The expanding shoot pushes its way out, shedding the scales in the process. These leave behind scars on the surface of the twig. The whole year's growth may take place in just a few weeks. The new stem is unlignified at first and may be green and downy. The Arecaceae (palms) have their leaves spirally arranged on an unbranched trunk.[70] In some tree species in temperate climates, a second spurt of growth, a Lammas growth may occur which is believed to be a strategy to compensate for loss of early foliage to insect predators.[71]
+
+Primary growth is the elongation of the stems and roots. Secondary growth consists of a progressive thickening and strengthening of the tissues as the outer layer of the epidermis is converted into bark and the cambium layer creates new phloem and xylem cells. The bark is inelastic.[72] Eventually the growth of a tree slows down and stops and it gets no taller. If damage occurs the tree may in time become hollow.[73]
+
+Leaves are structures specialised for photosynthesis and are arranged on the tree in such a way as to maximise their exposure to light without shading each other.[74] They are an important investment by the tree and may be thorny or contain phytoliths, lignins, tannins or poisons to discourage herbivory. Trees have evolved leaves in a wide range of shapes and sizes, in response to environmental pressures including climate and predation. They can be broad or needle-like, simple or compound, lobed or entire, smooth or hairy, delicate or tough, deciduous or evergreen. The needles of coniferous trees are compact but are structurally similar to those of broad-leaved trees. They are adapted for life in environments where resources are low or water is scarce. Frozen ground may limit water availability and conifers are often found in colder places at higher altitudes and higher latitudes than broad leaved trees. In conifers such as fir trees, the branches hang down at an angle to the trunk, enabling them to shed snow. In contrast, broad leaved trees in temperate regions deal with winter weather by shedding their leaves. When the days get shorter and the temperature begins to decrease, the leaves no longer make new chlorophyll and the red and yellow pigments already present in the blades become apparent.[74] Synthesis in the leaf of a plant hormone called auxin also ceases. This causes the cells at the junction of the petiole and the twig to weaken until the joint breaks and the leaf floats to the ground. In tropical and subtropical regions, many trees keep their leaves all year round. Individual leaves may fall intermittently and be replaced by new growth but most leaves remain intact for some time. Other tropical species and those in arid regions may shed all their leaves annually, such as at the start of the dry season.[75] Many deciduous trees flower before the new leaves emerge.[76] A few trees do not have true leaves but instead have structures with similar external appearance such as Phylloclades – modified stem structures[77] – as seen in the genus Phyllocladus.[78]
+
+Trees can be pollinated either by wind or by animals, mostly insects. Many angiosperm trees are insect pollinated. Wind pollination may take advantage of increased wind speeds high above the ground.[79] Trees use a variety of methods of seed dispersal. Some rely on wind, with winged or plumed seeds. Others rely on animals, for example with edible fruits. Others again eject their seeds (ballistic dispersal), or use gravity so that seeds fall and sometimes roll.[80]
+
+Seeds are the primary way that trees reproduce and their seeds vary greatly in size and shape. Some of the largest seeds come from trees, but the largest tree, Sequoiadendron giganteum, produces one of the smallest tree seeds.[81] The great diversity in tree fruits and seeds reflects the many different ways that tree species have evolved to disperse their offspring.
+
+For a tree seedling to grow into an adult tree it needs light. If seeds only fell straight to the ground, competition among the concentrated saplings and the shade of the parent would likely prevent it from flourishing. Many seeds such as birch are small and have papery wings to aid dispersal by the wind. Ash trees and maples have larger seeds with blade shaped wings which spiral down to the ground when released. The kapok tree has cottony threads to catch the breeze.[82]
+
+The seeds of conifers, the largest group of gymnosperms, are enclosed in a cone and most species have seeds that are light and papery that can be blown considerable distances once free from the cone.[83] Sometimes the seed remains in the cone for years waiting for a trigger event to liberate it. Fire stimulates release and germination of seeds of the jack pine, and also enriches the forest floor with wood ash and removes competing vegetation.[84] Similarly, a number of angiosperms including Acacia cyclops and Acacia mangium have seeds that germinate better after exposure to high temperatures.[85]
+
+The flame tree Delonix regia does not rely on fire but shoots its seeds through the air when the two sides of its long pods crack apart explosively on drying.[82] The miniature cone-like catkins of alder trees produce seeds that contain small droplets of oil that help disperse the seeds on the surface of water. Mangroves often grow in water and some species have propagules, which are buoyant fruits with seeds that start germinating before becoming detached from the parent tree.[86][87] These float on the water and may become lodged on emerging mudbanks and successfully take root.[82]
+
+Other seeds, such as apple pips and plum stones, have fleshy receptacles and smaller fruits like hawthorns have seeds enclosed in edible tissue; animals including mammals and birds eat the fruits and either discard the seeds, or swallow them so they pass through the gut to be deposited in the animal's droppings well away from the parent tree. The germination of some seeds is improved when they are processed in this way.[88] Nuts may be gathered by animals such as squirrels that cache any not immediately consumed.[89] Many of these caches are never revisited, the nut-casing softens with rain and frost, and the seed germinates in the spring.[90] Pine cones may similarly be hoarded by red squirrels, and grizzly bears may help to disperse the seed by raiding squirrel caches.[91]
+
+The single extant species of Ginkgophyta (Ginkgo biloba) has fleshy seeds produced at the ends of short branches on female trees,[92] and Gnetum, a tropical and subtropical group of gymnosperms produce seeds at the tip of a shoot axis.[93]
+
+The earliest trees were tree ferns, horsetails and lycophytes, which grew in forests in the Carboniferous period. The first tree may have been Wattieza, fossils of which have been found in New York State in 2007 dating back to the Middle Devonian (about 385 million years ago). Prior to this discovery, Archaeopteris was the earliest known tree.[94] Both of these reproduced by spores rather than seeds and are considered to be links between ferns and the gymnosperms which evolved in the Triassic period. The gymnosperms include conifers, cycads, gnetales and ginkgos and these may have appeared as a result of a whole genome duplication event which took place about 319 million years ago.[95] Ginkgophyta was once a widespread diverse group[96] of which the only survivor is the maidenhair tree Ginkgo biloba. This is considered to be a living fossil because it is virtually unchanged from the fossilised specimens found in Triassic deposits.[97]
+
+During the Mesozoic (245 to 66 million years ago) the conifers flourished and became adapted to live in all the major terrestrial habitats. Subsequently, the tree forms of flowering plants evolved during the Cretaceous period. These began to displace the conifers during the Tertiary era (66 to 2 million years ago) when forests covered the globe.[98] When the climate cooled 1.5 million years ago and the first of four ice ages occurred, the forests retreated as the ice advanced. In the interglacials, trees recolonised the land that had been covered by ice, only to be driven back again in the next ice age.[98]
+
+Trees are an important part of the terrestrial ecosystem,[99] providing essential habitats including many kinds of forest for communities of organisms. Epiphytic plants such as ferns, some mosses, liverworts, orchids and some species of parasitic plants (e.g., mistletoe) hang from branches;[100] these along with arboreal lichens, algae, and fungi provide micro-habitats for themselves and for other organisms, including animals. Leaves, flowers and fruits are seasonally available. On the ground underneath trees there is shade, and often there is undergrowth, leaf litter, and decaying wood that provide other habitat.[101][102] Trees stabilise the soil, prevent rapid run-off of rain water, help prevent desertification, have a role in climate control and help in the maintenance of biodiversity and ecosystem balance.[103]
+
+Many species of tree support their own specialised invertebrates. In their natural habitats, 284 different species of insect have been found on the English oak (Quercus robur)[104] and 306 species of invertebrate on the Tasmanian oak (Eucalyptus obliqua).[105] Non-native tree species provide a less biodiverse community, for example in the United Kingdom the sycamore (Acer pseudoplatanus), which originates from southern Europe, has few associated invertebrate species, though its bark supports a wide range of lichens, bryophytes and other epiphytes.[106]
+
+In ecosystems such as mangrove swamps, trees play a role in developing the habitat, since the roots of the mangrove trees reduce the speed of flow of tidal currents and trap water-borne sediment, reducing the water depth and creating suitable conditions for further mangrove colonisation. Thus mangrove swamps tend to extend seawards in suitable locations.[107] Mangrove swamps also provide an effective buffer against the more damaging effects of cyclones and tsunamis.[108]
+
+Silviculture is the practice of controlling the establishment, growth, composition, health, and quality of forests, which are areas that have a high density of trees. Cultivated trees are planted and tended by humans, usually because they provide food (fruits or nuts), ornamental beauty, or some type of wood product that benefits people. An area of land planted with fruit or nut trees is an orchard.[109] A small wooded area, usually with no undergrowth, is called a grove[110] and a small wood or thicket of trees and bushes is called a coppice or copse.[111] A large area of land covered with trees and undergrowth is called woodland or forest.[112] An area of woodland composed primarily of trees established by planting or artificial seeding is known as a plantation.[113]
+
+Trees are the source of many of the world's best known fleshy fruits. Apples, pears, plums, cherries and citrus are all grown commercially in temperate climates and a wide range of edible fruits are found in the tropics. Other commercially important fruit include dates, figs and olives. Palm oil is obtained from the fruits of the oil palm (Elaeis guineensis). The fruits of the cocoa tree (Theobroma cacao) are used to make cocoa and chocolate and the berries of coffee trees, Coffea arabica and Coffea canephora, are processed to extract the coffee beans. In many rural areas of the world, fruit is gathered from forest trees for consumption.[114] Many trees bear edible nuts which can loosely be described as being large, oily kernels found inside a hard shell. These include coconuts (Cocos nucifera), Brazil nuts (Bertholletia excelsa), pecans (Carya illinoinensis), hazel nuts (Corylus), almonds (Prunus dulcis), walnuts (Juglans regia), pistachios (Pistacia vera) and many others. They are high in nutritive value and contain high-quality protein, vitamins and minerals as well as dietary fibre.[115] A variety of nut oils are extracted by pressing for culinary use; some such as walnut, pistachio and hazelnut oils are prized for their distinctive flavours, but they tend to spoil quickly.[116]
+
+In temperate climates there is a sudden movement of sap at the end of the winter as trees prepare to burst into growth. In North America, the sap of the sugar maple (Acer saccharum) is most often used in the production of a sweet liquid, maple syrup. About 90% of the sap is water, the remaining 10% being a mixture of various sugars and certain minerals. The sap is harvested by drilling holes in the trunks of the trees and collecting the liquid that flows out of the inserted spigots. It is piped to a sugarhouse where it is heated to concentrate it and improve its flavour. Similarly in northern Europe the spring rise in the sap of the silver birch (Betula pendula) is tapped and collected, either to be drunk fresh or fermented into an alcoholic drink. In Alaska, the sap of the sweet birch (Betula lenta) is made into a syrup with a sugar content of 67%. Sweet birch sap is more dilute than maple sap; a hundred litres are required to make one litre of birch syrup.[117]
+
+Various parts of trees are used as spices. These include cinnamon, made from the bark of the cinnamon tree (Cinnamomum zeylanicum) and allspice, the dried small fruits of the pimento tree (Pimenta dioica). Nutmeg is a seed found in the fleshy fruit of the nutmeg tree (Myristica fragrans) and cloves are the unopened flower buds of the clove tree (Syzygium aromaticum).[118]
+
+Many trees have flowers rich in nectar which are attractive to bees. The production of forest honey is an important industry in rural areas of the developing world where it is undertaken by small-scale beekeepers using traditional methods.[119] The flowers of the elder (Sambucus) are used to make elderflower cordial and petals of the plum (Prunus spp.) can be candied.[120] Sassafras oil is a flavouring obtained from distilling bark from the roots of the sassafras tree (Sassafras albidum).
+
+The leaves of trees are widely gathered as fodder for livestock and some can be eaten by humans but they tend to be high in tannins which makes them bitter. Leaves of the curry tree (Murraya koenigii) are eaten, those of kaffir lime (Citrus × hystrix) (in Thai food)[121] and Ailanthus (in Korean dishes such as bugak) and those of the European bay tree (Laurus nobilis) and the California bay tree (Umbellularia californica) are used for flavouring food.[118] Camellia sinensis, the source of tea, is a small tree but seldom reaches its full height, being heavily pruned to make picking the leaves easier.[122]
+
+Wood smoke can be used to preserve food. In the hot smoking process the food is exposed to smoke and heat in a controlled environment. The food is ready to eat when the process is complete, having been tenderised and flavoured by the smoke it has absorbed. In the cold process, the temperature is not allowed to rise above 100 °F (38 °C). The flavour of the food is enhanced but raw food requires further cooking. If it is to be preserved, meat should be cured before cold smoking.[123]
+
+Wood has traditionally been used for fuel, especially in rural areas. In less developed nations it may be the only fuel available and collecting firewood is often a time consuming task as it becomes necessary to travel further and further afield in the search for fuel.[124] It is often burned inefficiently on an open fire. In more developed countries other fuels are available and burning wood is a choice rather than a necessity. Modern wood-burning stoves are very fuel efficient and new products such as wood pellets are available to burn.[125]
+
+Charcoal can be made by slow pyrolysis of wood by heating it in the absence of air in a kiln. The carefully stacked branches, often oak, are burned with a very limited amount of air. The process of converting them into charcoal takes about fifteen hours. Charcoal is used as a fuel in barbecues and by blacksmiths and has many industrial and other uses.[126]
+
+Timber, "trees that are grown in order to produce wood"[127] is cut into lumber (sawn wood) for use in construction. Wood has been an important, easily available material for construction since humans started building shelters. Engineered wood products are available which bind the particles, fibres or veneers of wood together with adhesives to form composite materials. Plastics have taken over from wood for some traditional uses.[128]
+
+Wood is used in the construction of buildings, bridges, trackways, piles, poles for power lines, masts for boats, pit props, railway sleepers, fencing, hurdles, shuttering for concrete, pipes, scaffolding and pallets. In housebuilding it is used in joinery, for making joists, roof trusses, roofing shingles, thatching, staircases, doors, window frames, floor boards, parquet flooring, panelling and cladding.[129]
+
+Wood is used to construct carts, farm implements, boats, dugout canoes and in shipbuilding. It is used for making furniture, tool handles, boxes, ladders, musical instruments, bows, weapons, matches, clothes pegs, brooms, shoes, baskets, turnery, carving, toys, pencils, rollers, cogs, wooden screws, barrels, coffins, skittles, veneers, artificial limbs, oars, skis, wooden spoons, sports equipment and wooden balls.[129]
+
+Wood is pulped for paper and used in the manufacture of cardboard and made into engineered wood products for use in construction such as fibreboard, hardboard, chipboard and plywood.[129] The wood of conifers is known as softwood while that of broad-leaved trees is hardwood.[130]
+
+Besides inspiring artists down the centuries, trees have been used to create art. Living trees have been used in bonsai and in tree shaping, and both living and dead specimens have been sculpted into sometimes fantastic shapes.[131]
+
+Bonsai (盆栽, lit. The art of growing a miniature tree or trees in a low-sided pot or tray) is the practice of hòn non bộ originated in China and spread to Japan more than a thousand years ago, there are similar practices in other cultures like the living miniature landscapes of Vietnam hòn non bộ. The word bonsai is often used in English as an umbrella term for all miniature trees in containers or pots.[132]
+
+The purposes of bonsai are primarily contemplation (for the viewer) and the pleasant exercise of effort and ingenuity (for the grower).[133] Bonsai practice focuses on long-term cultivation and shaping of one or more small trees growing in a container, beginning with a cutting, seedling, or small tree of a species suitable for bonsai development. Bonsai can be created from nearly any perennial woody-stemmed tree or shrub species[134] that produces true branches and can be cultivated to remain small through pot confinement with crown and root pruning. Some species are popular as bonsai material because they have characteristics, such as small leaves or needles, that make them appropriate for the compact visual scope of bonsai and a miniature deciduous forest can even be created using such species as Japanese maple, Japanese zelkova or hornbeam.[135]
+
+Tree shaping is the practice of changing living trees and other woody plants into man made shapes for art and useful structures. There are a few different methods[136] of shaping a tree. There is a gradual method and there is an instant method. The gradual method slowly guides the growing tip along predetermined pathways over time whereas the instant method bends and weaves saplings 2 to 3 m (6.6 to 9.8 ft) long into a shape that becomes more rigid as they thicken up.[137] Most artists use grafting of living trunks, branches, and roots, for art or functional structures and there are plans to grow "living houses" with the branches of trees knitting together to give a solid, weatherproof exterior combined with an interior application of straw and clay to provide a stucco-like inner surface.[137]
+
+Tree shaping has been practised for at least several hundred years, the oldest known examples being the living root bridges built and maintained by the Khasi people of Meghalaya, India using the roots of the rubber tree (Ficus elastica).[138][139]
+
+Cork is produced from the thick bark of the cork oak (Quercus suber). It is harvested from the living trees about once every ten years in an environmentally sustainable industry.[140] More than half the world's cork comes from Portugal and is largely used to make stoppers for wine bottles.[141] Other uses include floor tiles, bulletin boards, balls, footwear, cigarette tips, packaging, insulation and joints in woodwind instruments.[141]
+
+The bark of other varieties of oak has traditionally been used in Europe for the tanning of hides though bark from other species of tree has been used elsewhere. The active ingredient, tannin, is extracted and after various preliminary treatments, the skins are immersed in a series of vats containing solutions in increasing concentrations. The tannin causes the hide to become supple, less affected by water and more resistant to bacterial attack.[142]
+
+At least 120 drugs come from plant sources, many of them from the bark of trees.[143] Quinine originates from the cinchona tree (Cinchona) and was for a long time the remedy of choice for the treatment of malaria.[144] Aspirin was synthesised to replace the sodium salicylate derived from the bark of willow trees (Salix) which had unpleasant side effects.[145] The anti-cancer drug Paclitaxel is derived from taxol, a substance found in the bark of the Pacific yew (Taxus brevifolia).[146] Other tree based drugs come from the paw-paw (Carica papaya), the cassia (Cassia spp.), the cocoa tree (Theobroma cacao), the tree of life (Camptotheca acuminata) and the downy birch (Betula pubescens).[143]
+
+The papery bark of the white birch tree (Betula papyrifera) was used extensively by Native Americans. Wigwams were covered by it and canoes were constructed from it. Other uses included food containers, hunting and fishing equipment, musical instruments, toys and sledges.[147] Nowadays, bark chips, a by-product of the timber industry, are used as a mulch and as a growing medium for epiphytic plants that need a soil-free compost.[148]
+
+Trees create a visual impact in the same way as do other landscape features and give a sense of maturity and permanence to park and garden. They are grown for the beauty of their forms, their foliage, flowers, fruit and bark and their siting is of major importance in creating a landscape. They can be grouped informally, often surrounded by plantings of bulbs, laid out in stately avenues or used as specimen trees. As living things, their appearance changes with the season and from year to year.[149]
+
+Trees are often planted in town environments where they are known as street trees or amenity trees. They can provide shade and cooling through evapotranspiration, absorb greenhouse gases and pollutants, intercept rainfall, and reduce the risk of flooding. Scientific studies show that street trees help cities be more sustainable, and improve the physical and mental wellbeing of the citizens. [150] It has been shown that they are beneficial to humans in creating a sense of well-being and reducing stress. Many towns have initiated tree-planting programmes.[151] In London for example, there is an initiative to plant 20,000 new street trees and to have an increase in tree cover of 5% by 2025, equivalent to one tree for every resident.[152]
+
+Latex is a sticky defensive secretion that protects plants against herbivores. Many trees produce it when injured but the main source of the latex used to make natural rubber is the Pará rubber tree (Hevea brasiliensis). Originally used to create bouncy balls and for the waterproofing of cloth, natural rubber is now mainly used in tyres for which synthetic materials have proved less durable.[153] The latex exuded by the balatá tree (Manilkara bidentata) is used to make golf balls and is similar to gutta-percha, made from the latex of the "getah perca" tree Palaquium. This is also used as an insulator, particularly of undersea cables, and in dentistry, walking sticks and gun butts. It has now largely been replaced by synthetic materials.[154]
+
+Resin is another plant exudate that may have a defensive purpose. It is a viscous liquid composed mainly of volatile terpenes and is produced mostly by coniferous trees. It is used in varnishes, for making small castings and in ten-pin bowling balls. When heated, the terpenes are driven off and the remaining product is called "rosin" and is used by stringed instrumentalists on their bows. Some resins contain essential oils and are used in incense and aromatherapy. Fossilised resin is known as amber and was mostly formed in the Cretaceous (145 to 66 million years ago) or more recently. The resin that oozed out of trees sometimes trapped insects or spiders and these are still visible in the interior of the amber.[155]
+
+The camphor tree (Cinnamomum camphora) produces an essential oil[118] and the eucalyptus tree (Eucalyptus globulus) is the main source of eucalyptus oil which is used in medicine, as a fragrance and in industry.[156]
+
+Dead trees pose a safety risk, especially during high winds and severe storms, and removing dead trees involves a financial burden, whereas the presence of healthy trees can clean the air, increase property values, and reduce the temperature of the built environment and thereby reduce building cooling costs. During times of drought, trees can fall into water stress, which may cause a tree to become more susceptible to disease and insect problems, and ultimately may lead to a tree's death. Irrigating trees during dry periods can reduce the risk of water stress and death.[157]
+
+Trees have been venerated since time immemorial. To the ancient Celts, certain trees, especially the oak, ash and thorn, held special significance[158] as providing fuel, building materials, ornamental objects and weaponry. Other cultures have similarly revered trees, often linking the lives and fortunes of individuals to them or using them as oracles. In Greek mythology, dryads were believed to be shy nymphs who inhabited trees.
+
+The Oubangui people of west Africa plant a tree when a child is born. As the tree flourishes, so does the child but if the tree fails to thrive, the health of the child is considered at risk. When it flowers it is time for marriage. Gifts are left at the tree periodically and when the individual dies, their spirit is believed to live on in the tree.[159]
+
+Trees have their roots in the ground and their trunk and branches extended towards the sky. This concept is found in many of the world's religions as a tree which links the underworld and the earth and holds up the heavens. In Norse mythology, Yggdrasil is a central cosmic tree whose roots and branches extend to various worlds. Various creatures live on it.[160] In India, Kalpavriksha is a wish-fulfilling tree, one of the nine jewels that emerged from the primitive ocean. Icons are placed beneath it to be worshipped, tree nymphs inhabit the branches and it grants favours to the devout who tie threads round the trunk.[161] Democracy started in North America when the Great Peacemaker formed the Iroquois Confederacy, inspiring the warriors of the original five American nations to bury their weapons under the Tree of Peace, an eastern white pine (Pinus strobus).[162] In the creation story in the Bible, the tree of life and the knowledge of good and evil was planted by God in the Garden of Eden.[163]
+
+Sacred groves exist in China, India, Africa and elsewhere. They are places where the deities live and where all the living things are either sacred or are companions of the gods. Folklore lays down the supernatural penalties that will result if desecration takes place for example by the felling of trees. Because of their protected status, sacred groves may be the only relicts of ancient forest and have a biodiversity much greater than the surrounding area.[164]
+Some Ancient Indian tree deities, such as Puliyidaivalaiyamman, the Tamil deity of the  tamarind tree, or Kadambariyamman, associated with the kadamba tree were seen as manifestations of a goddess who offers her blessings by giving fruits in abundance.[165]
+
+Trees have a theoretical maximum height of 130 m (430 ft),[166] but the tallest known specimen on earth is believed to be a coast redwood (Sequoia sempervirens) at Redwood National Park, California. It has been named Hyperion and is 115.85 m (380.1 ft) tall.[167] In 2006, it was reported to be 379.1 ft (115.5 m) tall.[168] The tallest known broad-leaved tree is a mountain ash (Eucalyptus regnans) growing in Tasmania with a height of 99.8 m (327 ft).[169]
+
+The largest tree by volume is believed to be a giant sequoia (Sequoiadendron giganteum) known as the General Sherman Tree in the Sequoia National Park in Tulare County, California. Only the trunk is used in the calculation and the volume is estimated to be 1,487 m3 (52,500 cu ft).[170]
+
+The oldest living tree with a verified age is also in California. It is a Great Basin bristlecone pine (Pinus longaeva) growing in the White Mountains. It has been dated by drilling a core sample and counting the annual rings. It is estimated to currently be 5,069 years old.[a][171]
+
+A little farther south, at Santa Maria del Tule, Oaxaca, Mexico, is the tree with the broadest trunk. It is a Montezuma cypress (Taxodium mucronatum) known as Árbol del Tule and its diameter at breast height is 11.62 m (38.1 ft) giving it a girth of 36.2 m (119 ft). The tree's trunk is far from round and the exact dimensions may be misleading as the circumference includes much empty space between the large buttress roots.[172]
+
+Wohlleben, Peter; Flannery, Tim F.; Simard, S.; Billinghurst, Jane (2016). The Hidden Life of Trees: What They Feel, How They Communicate: Discoveries from a Secret World. ISBN 978-1-77164-248-4. OCLC 933722592.

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+
+Snakes are elongated, legless, carnivorous reptiles of the suborder Serpentes.[2] Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads with their highly mobile jaws. To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side, and most have only one functional lung. Some species retain a pelvic girdle with a pair of vestigial claws on either side of the cloaca. Lizards have evolved elongate bodies without limbs or with greatly reduced limbs about twenty-five times independently via convergent evolution, leading to many lineages of legless lizards.[3]  Legless lizards resemble snakes, but several common groups of legless lizards have eyelids and external ears, which snakes lack, although this rule is not universal (see Amphisbaenia, Dibamidae, and Pygopodidae).
+
+Living snakes are found on every continent except Antarctica, and on most smaller land masses; exceptions include some large islands, such as Ireland, Iceland, Greenland, the Hawaiian archipelago, and the islands of New Zealand, and many small islands of the Atlantic and central Pacific oceans.[4] Additionally, sea snakes are widespread throughout the Indian and Pacific Oceans. More than 20 families are currently recognized, comprising about 520 genera and about 3,600 species.[5][6] They range in size from the tiny, 10.4 cm (4.1 in)-long Barbados thread snake[7] to the reticulated python of 6.95 meters (22.8 ft) in length.[8] The fossil species Titanoboa cerrejonensis was 12.8 meters (42 ft) long.[9] Snakes are thought to have evolved from either burrowing or aquatic lizards, perhaps during the Jurassic period, with the earliest known fossils dating to between 143 and 167 Ma ago.[10] The diversity of modern snakes appeared during the Paleocene epoch (c 66 to 56 Ma ago, after the Cretaceous–Paleogene extinction event). The oldest preserved descriptions of snakes can be found in the Brooklyn Papyrus.
+
+Most species are nonvenomous and those that have venom use it primarily to kill and subdue prey rather than for self-defense. Some possess venom potent enough to cause painful injury or death to humans. Nonvenomous snakes either swallow prey alive or kill by constriction.
+
+The English word snake comes from Old English snaca, itself from Proto-Germanic *snak-an- (cf. Germanic Schnake "ring snake", Swedish snok "grass snake"), from Proto-Indo-European root *(s)nēg-o- "to crawl", "to creep", which also gave sneak as well as Sanskrit nāgá "snake".[11] The word ousted adder, as adder went on to narrow in meaning, though in Old English næddre was the general word for snake.[12] The other term, serpent, is from French, ultimately from Indo-European *serp- (to creep),[13] which also gave Ancient Greek hérpō (ἕρπω) "I crawl".
+
+Leptotyphlopidae
+
+Anomalepididae
+
+Typhlopidae
+
+Anilius
+
+Tropidophiidae
+
+Uropeltidae
+
+Anomochilus
+
+Cylindrophis
+
+Pythonidae
+
+Xenopeltis
+
+Loxocemus
+
+Acrochordidae
+
+Xenodermidae
+
+Pareidae
+
+Viperidae
+
+Homalopsidae
+
+Lamprophiidae
+
+Elapidae
+
+Colubridae
+
+Boidae
+
+Erycinae
+
+Calabaria
+
+Ungaliophiinae
+
+Sanzinia
+
+Candoia
+
+The fossil record of snakes is relatively poor because snake skeletons are typically small and fragile making fossilization uncommon. Fossils readily identifiable as snakes (though often retaining hind limbs) first appear in the fossil record during the Cretaceous period.[15] The earliest known true snake fossils (members of the crown group Serpentes) come from the marine simoliophiids, the oldest of which is the Late Cretaceous (Cenomanian age) Haasiophis terrasanctus,[1] dated to between 112 and 94 million years old.[16]
+
+Based on comparative anatomy, there is consensus that snakes descended from lizards.[17]:11[18] Pythons and boas—primitive groups among modern snakes—have vestigial hind limbs: tiny, clawed digits known as anal spurs, which are used to grasp during mating.[17]:11[19] The families Leptotyphlopidae and Typhlopidae also possess remnants of the pelvic girdle, appearing as horny projections when visible.
+
+Front limbs are nonexistent in all known snakes. This is caused by the evolution of their Hox genes, controlling limb morphogenesis. The axial skeleton of the snakes’ common ancestor, like most other tetrapods, had regional specializations consisting of cervical (neck), thoracic (chest), lumbar (lower back), sacral (pelvic), and caudal (tail) vertebrae. Early in snake evolution, the Hox gene expression in the axial skeleton responsible for the development of the thorax became dominant. As a result, the vertebrae anterior to the hindlimb buds (when present) all have the same thoracic-like identity (except from the atlas, axis, and 1–3 neck vertebrae). In other words, most of a snake's skeleton is an extremely extended thorax. Ribs are found exclusively on the thoracic vertebrae. Neck, lumbar and pelvic vertebrae are very reduced in number (only 2–10 lumbar and pelvic vertebrae are present), while only a short tail remains of the caudal vertebrae. However, the tail is still long enough to be of important use in many species, and is modified in some aquatic and tree-dwelling species.
+
+Many modern snake groups originated during the Paleocene, alongside the adaptive radiation of mammals following the extinction of (non-avian) dinosaurs. The expansion of grasslands in North America also led to an explosive radiation among snakes.[20]  Previously, snakes were a minor component of the North American fauna, but during the Miocene, the number of species and their prevalence increased dramatically with the first appearances of vipers and elapids in North America and the significant diversification of Colubridae (including the origin of many modern genera such as Nerodia, Lampropeltis, Pituophis, and Pantherophis).[20]
+
+There is fossil evidence to suggest that snakes may have evolved from burrowing lizards, such as the varanids (or a similar group) during the Cretaceous Period.[21] An early fossil snake relative, Najash rionegrina, was a two-legged burrowing animal with a sacrum, and was fully terrestrial.[22] One extant analog of these putative ancestors is the earless monitor Lanthanotus of Borneo (though it also is semiaquatic).[23] Subterranean species evolved bodies streamlined for burrowing, and eventually lost their limbs.[23] According to this hypothesis, features such as the transparent, fused eyelids (brille) and loss of external ears evolved to cope with fossorial difficulties, such as scratched corneas and dirt in the ears.[21][23] Some primitive snakes are known to have possessed hindlimbs, but their pelvic bones lacked a direct connection to the vertebrae. These include fossil species like Haasiophis, Pachyrhachis and Eupodophis, which are slightly older than Najash.[19]
+
+This hypothesis was strengthened in 2015 by the discovery of a 113m year-old fossil of a four-legged snake in Brazil that has been named Tetrapodophis amplectus. It has many snake-like features, is adapted for burrowing and its stomach indicates that it was preying on other animals.[24] It is currently uncertain if Tetrapodophis is a snake or another species, in the squamate order, as a snake-like body has independently evolved at least 26 times. Tetrapodophis does not have distinctive snake features in its spine and skull.[25][26]
+
+An alternative hypothesis, based on morphology, suggests the ancestors of snakes were related to mosasaurs—extinct aquatic reptiles from the Cretaceous—which in turn are thought to have derived from varanid lizards.[18] According to this hypothesis, the fused, transparent eyelids of snakes are thought to have evolved to combat marine conditions (corneal water loss through osmosis), and the external ears were lost through disuse in an aquatic environment. This ultimately led to an animal similar to today's sea snakes. In the Late Cretaceous, snakes recolonized land, and continued to diversify into today's snakes. Fossilized snake remains are known from early Late Cretaceous marine sediments, which is consistent with this hypothesis; particularly so, as they are older than the terrestrial Najash rionegrina. Similar skull structure, reduced or absent limbs, and other anatomical features found in both mosasaurs and snakes lead to a positive cladistical correlation, although some of these features are shared with varanids.[citation needed]
+
+Tetrapodophis
+
+Pachyrhachis
+
+Eupodophis descouensi
+
+Eupodophis descouensi hind leg
+
+Genetic studies in recent years have indicated snakes are not as closely related to monitor lizards as was once believed—and therefore not to mosasaurs, the proposed ancestor in the aquatic scenario of their evolution. However, more evidence links mosasaurs to snakes than to varanids. Fragmented remains found from the Jurassic and Early Cretaceous indicate deeper fossil records for these groups, which may potentially refute either hypothesis.[27][28]
+
+In 2016 two studies reported that limb loss in snakes is associated with DNA mutations in the Zone of Polarizing Activity Regulatory Sequence (ZRS), a regulatory region of the sonic hedgehog gene which is critically required for limb development. More advanced snakes have no remnants of limbs, but basal snakes such as pythons and boas do have traces of highly reduced, vestigial hind limbs. Python embryos even have fully developed hind limb buds, but their later development is stopped by the DNA mutations in the ZRS.[29][30][31][32]
+
+There are over 2,900 species of snakes ranging as far northward as the Arctic Circle in Scandinavia and southward through Australia.[18] Snakes can be found on every continent except Antarctica, in the sea, and as high as 16,000 feet (4,900 m) in the Himalayan Mountains of Asia.[18][33]:143 There are numerous islands from which snakes are absent, such as Ireland, Iceland, and New Zealand[4][33] (although New Zealand's waters are infrequently visited by the yellow-bellied sea snake and the banded sea krait).[34]
+
+All modern snakes are grouped within the suborder Serpentes in Linnean taxonomy, part of the order Squamata, though their precise placement within squamates remains controversial.[5]
+
+The two infraorders of Serpentes are: Alethinophidia and Scolecophidia.[5] This separation is based on morphological characteristics and mitochondrial DNA sequence similarity. Alethinophidia is sometimes split into Henophidia and Caenophidia, with the latter consisting of "colubroid" snakes (colubrids, vipers, elapids, hydrophiids, and atractaspids) and acrochordids, while the other alethinophidian families comprise Henophidia.[35] While not extant today, the Madtsoiidae, a family of giant, primitive, python-like snakes, was around until 50,000 years ago in Australia, represented by genera such as Wonambi.
+
+There are numerous debates in the systematics within the group. For instance, many sources classify Boidae and Pythonidae as one family, while some keep the Elapidae and Hydrophiidae (sea snakes) separate for practical reasons despite their extremely close relation.
+
+Recent molecular studies support the monophyly of the clades of modern snakes, scolecophidians, typhlopids + anomalepidids, alethinophidians, core alethinophidians, uropeltids (Cylindrophis, Anomochilus, uropeltines), macrostomatans, booids, boids, pythonids and caenophidians.[14]
+
+
+
+While snakes are limbless reptiles, which evolved from (and are grouped with) lizards, there are many other species of lizards which have lost their limbs independently and superficially look similar to snakes. These include the slowworm and glass snake.
+
+Other serpentine tetrapods unrelated to snakes include caecilians (amphibians), amphisbaenians (near-lizard squamates), and the extinct aistopods (amphibians).
+
+The now extinct Titanoboa cerrejonensis snakes were 12.8 m (42 ft) in length.[9] By comparison, the largest extant snakes are the reticulated python, which measures about 6.95 m (22.8 ft) long,[8] and the green anaconda, which measures about 5.21 m (17.1 ft) long and is considered the heaviest snake on Earth at 97.5 kg (215 lb).[39]
+
+At the other end of the scale, the smallest extant snake is Leptotyphlops carlae, with a length of about 10.4 cm (4.1 in).[7] Most snakes are fairly small animals, approximately 1 m (3.3 ft) in length.[40]
+
+Pit vipers, pythons, and some boas have infrared-sensitive receptors in deep grooves on the snout, which allow them to "see" the radiated heat of warm-blooded prey. In pit vipers, the grooves are located between the nostril and the eye in a large "pit" on each side of the head. Other infrared-sensitive snakes have multiple, smaller labial pits lining the upper lip, just below the nostrils.[41]
+
+Snakes use smell to track their prey. They smell by using their forked tongues to collect airborne particles, then passing them to the vomeronasal organ or Jacobson's organ in the mouth for examination.[41] The fork in the tongue gives snakes a sort of directional sense of smell and taste simultaneously.[41] They keep their tongues constantly in motion, sampling particles from the air, ground, and water, analyzing the chemicals found, and determining the presence of prey or predators in the local environment. In water-dwelling snakes, such as the anaconda, the tongue functions efficiently underwater.[41]
+
+The underside is very sensitive to vibration. This allows snakes to be able to sense approaching animals by detecting faint vibrations in the ground.[41]
+
+Snake vision varies greatly, from only being able to distinguish light from dark to keen eyesight, but the main trend is that their vision is adequate although not sharp, and allows them to track movements.[42] Generally, vision is best in arboreal snakes and weakest in burrowing snakes. Some snakes, such as the Asian vine snake (genus Ahaetulla), have binocular vision, with both eyes capable of focusing on the same point. Most snakes focus by moving the lens back and forth in relation to the retina, while in the other amniote groups, the lens is stretched. Many nocturnal snakes have slit pupils while diurnal snakes have round pupils. Most species possess three visual pigments and are probably able to see two primary colors in daylight. It's concluded that the last common ancestors of all snakes had UV-sensitive vision, but that most snakes that depends on their eyesight to hunt in daylight have evolved lenses that act as sunglasses which filters out UV-light, and probably also sharpens their vision by improving the contrasts.[43]
+
+The skin of a snake is covered in scales. Contrary to the popular notion of snakes being slimy because of possible confusion of snakes with worms, snakeskin has a smooth, dry texture. Most snakes use specialized belly scales to travel, gripping surfaces. The body scales may be smooth, keeled, or granular. The eyelids of a snake are transparent "spectacle" scales, which remain permanently closed, also known as brille.
+
+The shedding of scales is called ecdysis (or in normal usage, molting or sloughing). In the case of snakes, the complete outer layer of skin is shed in one layer.[44] Snake scales are not discrete, but extensions of the epidermis—hence they are not shed separately but as a complete outer layer during each molt, akin to a sock being turned inside out.[45]
+
+Snakes have a wide diversity of skin coloration patterns. These patterns are often related to behavior, such as a tendency to have to flee from predators. Snakes that are plain or have longitudinal stripes often have to escape from predators, with the pattern (or lack thereof) not providing reference points to predators, thus allowing the snake to escape without being notice. Plain snakes usually adopt active hunting strategies, as their pattern allows them to send little information to prey about motion. Blotched snakes, on the other hand, usually use ambush-based strategies, likely because it helps them blend into an environment with irregularly shaped objects, like sticks or rocks. Spotted patterning can similarly help snakes to blend into their environment.[46]
+
+The shape and number of scales on the head, back, and belly are often characteristic and used for taxonomic purposes. Scales are named mainly according to their positions on the body. In "advanced" (Caenophidian) snakes, the broad belly scales and rows of dorsal scales correspond to the vertebrae, allowing scientists to count the vertebrae without dissection.
+
+Molting, or ecdysis, serves a number of functions. Firstly, the old and worn skin is replaced; secondly, it helps get rid of parasites such as mites and ticks. Renewal of the skin by molting is supposed to allow growth in some animals such as insects; however, this has been disputed in the case of snakes.[45][47]
+
+Molting occurs periodically throughout the snake's life. Before a molt, the snake stops eating and often hides or moves to a safe place. Just before shedding, the skin becomes dull and dry looking and the eyes become cloudy or blue-colored. The inner surface of the old skin liquefies. This causes the old skin to separate from the new skin beneath it. After a few days, the eyes clear and the snake "crawls" out of its old skin. The old skin breaks near the mouth and the snake wriggles out, aided by rubbing against rough surfaces. In many cases, the cast skin peels backward over the body from head to tail in one piece, like pulling a sock off inside-out. A new, larger, brighter layer of skin has formed underneath.[45][48]
+
+An older snake may shed its skin only once or twice a year. But a younger snake, still growing, may shed up to four times a year.[48] The discarded skin gives a perfect imprint of the scale pattern, and it is usually possible to identify the snake if the discarded skin is reasonably intact.[45] This periodic renewal has led to the snake being a symbol of healing and medicine, as pictured in the Rod of Asclepius.[49]
+
+Scale counts can sometimes be used to tell the sex of a snake when the species is not distinctly sexually dimorphic. A probe is inserted into the cloaca until it can go no further. The probe is marked at the point where it stops, removed, and compared to the subcaudal depth by laying it alongside the scales.[50] The scalation count determines whether the snake is a male or female as hemipenes of a male will probe to a different depth (usually longer) than the cloaca of a female.[50][clarification needed]
+
+The skeleton of most snakes consists solely of the skull, hyoid, vertebral column, and ribs, though henophidian snakes retain vestiges of the pelvis and rear limbs.
+
+The skull of the snake consists of a solid and complete neurocranium, to which many of the other bones are only loosely attached, particularly the highly mobile jaw bones, which facilitate manipulation and ingestion of large prey items. The left and right sides of the lower jaw are joined only by a flexible ligament at the anterior tips, allowing them to separate widely, while the posterior end of the lower jaw bones articulate with a quadrate bone, allowing further mobility. The bones of the mandible and quadrate bones can also pick up ground borne vibrations.[51]  Because the sides of the jaw can move independently of one another, snakes resting their jaws on a surface have sensitive stereo hearing which can detect the position of prey. The jaw-quadrate-stapes pathway is capable of detecting vibrations on the angstrom scale, despite the absence of an outer ear and the ossicle mechanism of impedance matching used in other vertebrates to receive vibrations from the air.[52][53]
+
+The hyoid is a small bone located posterior and ventral to the skull, in the 'neck' region, which serves as an attachment for muscles of the snake's tongue, as it does in all other tetrapods.
+
+The vertebral column consists of anywhere between 200 and 400 (or more) vertebrae. Tail vertebrae are comparatively few in number (often less than 20% of the total) and lack ribs, while body vertebrae each have two ribs articulating with them. The vertebrae have projections that allow for strong muscle attachment enabling locomotion without limbs.
+
+Autotomy of the tail, a feature found in some lizards is absent in most snakes.[54] Caudal autotomy in snakes is rare and is intervertebral, unlike that in lizards, which is intravertebral—that is, the break happens along a predefined fracture plane present on a vertebra.[55][56]
+
+In some snakes, most notably boas and pythons, there are vestiges of the hindlimbs in the form of a pair of pelvic spurs. These small, claw-like protrusions on each side of the cloaca are the external portion of the vestigial hindlimb skeleton, which includes the remains of an ilium and femur.
+
+Snakes are polyphyodonts with teeth that are continuously replaced.[57]
+
+Snake's and other reptiles have a three-chambered heart that controls the circulatory system via the left and right atrium, and one ventricle.[58] Internally, the ventricle is divided into three interconnected cavities which include the cavum arteriosum, the cavum pulmonale, and the cavum venosum.[59] The cavum venosum receives deoxygenated blood from the right atrium while the cavum arteriosum receives oxygenated blood directly from the left atrium. Located beneath the cavum venosum is the cavum pulmonale, which pumps blood to the pulmonary trunk.[60]
+
+The snake's heart is encased in a sac, called the pericardium, located at the bifurcation of the bronchi. The heart is able to move around, however, owing to the lack of a diaphragm. This adjustment protects the heart from potential damage when large ingested prey is passed through the esophagus. The spleen is attached to the gall bladder and pancreas and filters the blood. The thymus is located in fatty tissue above the heart and is responsible for the generation of immune cells in the blood. The cardiovascular system of snakes is also unique for the presence of a renal portal system in which the blood from the snake's tail passes through the kidneys before returning to the heart.[61]
+
+The vestigial left lung is often small or sometimes even absent, as snakes' tubular bodies require all of their organs to be long and thin.[61] In the majority of species, only one lung is functional. This lung contains a vascularized anterior portion and a posterior portion that does not function in gas exchange.[61] This 'saccular lung' is used for hydrostatic purposes to adjust buoyancy in some aquatic snakes and its function remains unknown in terrestrial species.[61] Many organs that are paired, such as kidneys or reproductive organs, are staggered within the body, with one located ahead of the other.[61]
+
+Snakes have no lymph nodes.[61]
+
+Cobras, vipers, and closely related species use venom to immobilize, injure or kill their prey. The venom is modified saliva, delivered through fangs.[17]:243 The fangs of 'advanced' venomous snakes like viperids and elapids are hollow to inject venom more effectively, while the fangs of rear-fanged snakes such as the boomslang merely have a groove on the posterior edge to channel venom into the wound. Snake venoms are often prey specific—their role in self-defense is secondary.[17]:243
+
+Venom, like all salivary secretions, is a predigestant that initiates the breakdown of food into soluble compounds, facilitating proper digestion. Even nonvenomous snake bites (like any animal bite) will cause tissue damage.[17]:209
+
+Certain birds, mammals, and other snakes (such as kingsnakes) that prey on venomous snakes have developed resistance and even immunity to certain venoms.[17]:243 Venomous snakes include three families of snakes, and do not constitute a formal classification group used in taxonomy.
+
+The colloquial term "poisonous snake" is generally an incorrect label for snakes. A poison is inhaled or ingested, whereas venom produced by snakes is injected into its victim via fangs.[62] There are, however, two exceptions: Rhabdophis sequesters toxins from the toads it eats, then secretes them from nuchal glands to ward off predators, and a small unusual population of garter snakes in the U.S. state of Oregon retains enough toxins in their livers from the newts they eat to be effectively poisonous to small local predators (such as crows and foxes).[63]
+
+Snake venoms are complex mixtures of proteins, and are stored in venom glands at the back of the head.[63] In all venomous snakes, these glands open through ducts into grooved or hollow teeth in the upper jaw.[17]:243[62] These proteins can potentially be a mix of neurotoxins (which attack the nervous system), hemotoxins (which attack the circulatory system), cytotoxins, bungarotoxins and many other toxins that affect the body in different ways.[62] Almost all snake venom contains hyaluronidase, an enzyme that ensures rapid diffusion of the venom.[17]:243
+
+Venomous snakes that use hemotoxins usually have fangs in the front of their mouths, making it easier for them to inject the venom into their victims.[62] Some snakes that use neurotoxins (such as the mangrove snake) have fangs in the back of their mouths, with the fangs curled backwards.[64] This makes it difficult both for the snake to use its venom and for scientists to milk them.[62] Elapids, however, such as cobras and kraits are proteroglyphous—they possess hollow fangs that cannot be erected toward the front of their mouths, and cannot "stab" like a viper. They must actually bite the victim.[17]:242
+
+It has recently been suggested that all snakes may be venomous to a certain degree, with harmless snakes having weak venom and no fangs.[65] Most snakes currently labelled "nonvenomous" would still be considered harmless according to this theory, as they either lack a venom delivery method or are incapable of delivering enough to endanger a human. This theory postulates that snakes may have evolved from a common lizard ancestor that was venomous—and that venomous lizards like the gila monster, beaded lizard, monitor lizards, and the now-extinct mosasaurs may also have derived from it. They share this venom clade with various other saurian species.
+
+Venomous snakes are classified in two taxonomic families:
+
+There is a third family containing the opistoglyphous (rear-fanged) snakes (as well as the majority of other snake species):
+
+Although a wide range of reproductive modes are used by snakes, all snakes employ internal fertilization. This is accomplished by means of paired, forked hemipenes, which are stored, inverted, in the male's tail.[66] The hemipenes are often grooved, hooked, or spined in order to grip the walls of the female's cloaca.[67][66]
+
+Most species of snakes lay eggs which they abandon shortly after laying. However, a few species (such as the king cobra) actually construct nests and stay in the vicinity of the hatchlings after incubation.[66] Most pythons coil around their egg-clutches and remain with them until they hatch.[68] A female python will not leave the eggs, except to occasionally bask in the sun or drink water. She will even "shiver" to generate heat to incubate the eggs.[68]
+
+Some species of snake are ovoviviparous and retain the eggs within their bodies until they are almost ready to hatch.[69][70] Recently, it has been confirmed that several species of snake are fully viviparous, such as the boa constrictor and green anaconda, nourishing their young through a placenta as well as a yolk sac, which is highly unusual among reptiles, or anything else outside of requiem sharks or placental mammals.[69][70] Retention of eggs and live birth are most often associated with colder environments.[66][70]
+
+Sexual selection in snakes is demonstrated by the 3,000 species that each use different tactics in acquiring mates.[71] Ritual combat between males for the females they want to mate with includes topping, a behavior exhibited by most viperids in which one male will twist around the vertically elevated fore body of its opponent and forcing it downward. It is common for neck biting to occur while the snakes are entwined.[72]
+
+Parthenogenesis is a natural form of reproduction in which growth and development of embryos occur without fertilization. Agkistrodon contortrix (copperhead) and Agkistrodon piscivorus (cotton mouth) can reproduce by facultative parthenogenesis. That is, they are capable of switching from a sexual mode of reproduction to an asexual mode.[73] The type of parthenogenesis that likely occurs is automixis with terminal fusion, a process in which two terminal products from the same meiosis fuse to form a diploid zygote. This process leads to genome wide homozygosity, expression of deleterious recessive alleles and often to developmental abnormalities. Both captive-born and wild-born A. contortrix and A. piscivorus appear to be capable of this form of parthenogenesis.[73]
+
+Reproduction in squamate reptiles is almost exclusively sexual. Males ordinarily have a ZZ pair of sex determining chromosomes, and females a ZW pair. However, the Colombian Rainbow boa (Epicrates maurus) can also reproduce by facultative parthenogenesis resulting in production of WW female progeny.[74] The WW females are likely produced by terminal automixis.
+
+In regions where winters are colder than snakes can tolerate while remaining active, local species will brumate. Unlike hibernation, in which mammals are actually asleep, brumating reptiles are awake but inactive. Individual snakes may brumate in burrows, under rock piles, or inside fallen trees, or snakes may aggregate in large numbers at hibernacula.
+
+All snakes are strictly carnivorous, eating small animals including lizards, frogs, other snakes, small mammals, birds, eggs, fish, snails, worms or insects.[17][3][18][75] Because snakes cannot bite or tear their food to pieces, they must swallow prey whole. The body size of a snake has a major influence on its eating habits. Smaller snakes eat smaller prey. Juvenile pythons might start out feeding on lizards or mice and graduate to small deer or antelope as an adult, for example.
+
+The snake's jaw is a complex structure. Contrary to the popular belief that snakes can dislocate their jaws, snakes have a very flexible lower jaw, the two halves of which are not rigidly attached, and numerous other joints in their skull (see snake skull), allowing them to open their mouths wide enough to swallow their prey whole, even if it is larger in diameter than the snake itself.[75] For example, the African egg-eating snake has flexible jaws adapted for eating eggs much larger than the diameter of its head.[17]:81 This snake has no teeth, but does have bony protrusions on the inside edge of its spine, which it uses to break shells when it eats eggs.[17]:81
+
+While the majority of snakes eat a variety of prey animals, there is some specialization by some species. King cobras and the Australian bandy-bandy consume other snakes. Snakes of the family Pareidae have more teeth on the right side of their mouths than on the left, as the shells of their prey usually spiral clockwise.[17]:184[76][77]
+
+Some snakes have a venomous bite, which they use to kill their prey before eating it.[75][78] Other snakes kill their prey by constriction.[75] Still others swallow their prey whole and alive.[17]:81[75]
+
+After eating, snakes become dormant while the process of digestion takes place.[50] Digestion is an intense activity, especially after consumption of large prey. In species that feed only sporadically, the entire intestine enters a reduced state between meals to conserve energy. The digestive system is then 'up-regulated' to full capacity within 48 hours of prey consumption. Being ectothermic ("cold-blooded"), the surrounding temperature plays a large role in snake digestion. The ideal temperature for snakes to digest is 30 °C (86 °F). So much metabolic energy is involved in a snake's digestion that in the South American rattlesnake (Crotalus durissus), surface body temperature increases by as much as 1.2 °C (2.2 °F) during the digestive process.[79] Because of this, a snake disturbed after having eaten recently will often regurgitate its prey to be able to escape the perceived threat. When undisturbed, the digestive process is highly efficient, with the snake's digestive enzymes dissolving and absorbing everything but the prey's hair (or feathers) and claws, which are excreted along with waste.
+
+The lack of limbs does not impede the movement of snakes. They have developed several different modes of locomotion to deal with particular environments. Unlike the gaits of limbed animals, which form a continuum, each mode of snake locomotion is discrete and distinct from the others; transitions between modes are abrupt.[80][81]
+
+Lateral undulation is the sole mode of aquatic locomotion, and the most common mode of terrestrial locomotion.[81] In this mode, the body of the snake alternately flexes to the left and right, resulting in a series of rearward-moving "waves".[80] While this movement appears rapid, snakes have rarely been documented moving faster than two body-lengths per second, often much less.[82] This mode of movement has the same net cost of transport (calories burned per meter moved) as running in lizards of the same mass.[83]
+
+Terrestrial lateral undulation is the most common mode of terrestrial locomotion for most snake species.[80] In this mode, the posteriorly moving waves push against contact points in the environment, such as rocks, twigs, irregularities in the soil, etc.[80] Each of these environmental objects, in turn, generates a reaction force directed forward and towards the midline of the snake, resulting in forward thrust while the lateral components cancel out.[84] The speed of this movement depends upon the density of push-points in the environment, with a medium density of about 8[clarification needed] along the snake's length being ideal.[82] The wave speed is precisely the same as the snake speed, and as a result, every point on the snake's body follows the path of the point ahead of it, allowing snakes to move through very dense vegetation and small openings.[84]
+
+When swimming, the waves become larger as they move down the snake's body, and the wave travels backwards faster than the snake moves forwards.[85] Thrust is generated by pushing their body against the water, resulting in the observed slip. In spite of overall similarities, studies show that the pattern of muscle activation is different in aquatic versus terrestrial lateral undulation, which justifies calling them separate modes.[86] All snakes can laterally undulate forward (with backward-moving waves), but only sea snakes have been observed reversing the motion (moving backwards with forward-moving waves).[80]
+
+Most often employed by colubroid snakes (colubrids, elapids, and vipers) when the snake must move in an environment that lacks irregularities to push against (rendering lateral undulation impossible), such as a slick mud flat, or a sand dune, sidewinding is a modified form of lateral undulation in which all of the body segments oriented in one direction remain in contact with the ground, while the other segments are lifted up, resulting in a peculiar "rolling" motion.[87][88] This mode of locomotion overcomes the slippery nature of sand or mud by pushing off with only static portions on the body, thereby minimizing slipping.[87] The static nature of the contact points can be shown from the tracks of a sidewinding snake, which show each belly scale imprint, without any smearing. This mode of locomotion has very low caloric cost, less than ⅓ of the cost for a lizard to move the same distance.[83] Contrary to popular belief, there is no evidence that sidewinding is associated with the sand being hot.[87]
+
+When push-points are absent, but there is not enough space to use sidewinding because of lateral constraints, such as in tunnels, snakes rely on concertina locomotion.[80][88] In this mode, the snake braces the posterior portion of its body against the tunnel wall while the front of the snake extends and straightens.[87] The front portion then flexes and forms an anchor point, and the posterior is straightened and pulled forwards. This mode of locomotion is slow and very demanding, up to seven times the cost of laterally undulating over the same distance.[83] This high cost is due to the repeated stops and starts of portions of the body as well as the necessity of using active muscular effort to brace against the tunnel walls.
+
+The movement of snakes in arboreal habitats has only recently been studied.[89] While on tree branches, snakes use several modes of locomotion depending on species and bark texture.[89] In general, snakes will use a modified form of concertina locomotion on smooth branches, but will laterally undulate if contact points are available.[89] Snakes move faster on small branches and when contact points are present, in contrast to limbed animals, which do better on large branches with little 'clutter'.[89]
+
+Gliding snakes (Chrysopelea) of Southeast Asia launch themselves from branch tips, spreading their ribs and laterally undulating as they glide between trees.[87][90][91] These snakes can perform a controlled glide for hundreds of feet depending upon launch altitude and can even turn in midair.[87][90]
+
+The slowest mode of snake locomotion is rectilinear locomotion, which is also the only one where the snake does not need to bend its body laterally, though it may do so when turning.[92] In this mode, the belly scales are lifted and pulled forward before being placed down and the body pulled over them. Waves of movement and stasis pass posteriorly, resulting in a series of ripples in the skin.[92] The ribs of the snake do not move in this mode of locomotion and this method is most often used by large pythons, boas, and vipers when stalking prey across open ground as the snake's movements are subtle and harder to detect by their prey in this manner.[87]
+
+Snakes do not ordinarily prey on humans. Unless startled or injured, most snakes prefer to avoid contact and will not attack humans. With the exception of large constrictors, nonvenomous snakes are not a threat to humans. The bite of a nonvenomous snake is usually harmless; their teeth are not adapted for tearing or inflicting a deep puncture wound, but rather grabbing and holding. Although the possibility of infection and tissue damage is present in the bite of a nonvenomous snake, venomous snakes present far greater hazard to humans.[17]:209 The World Health Organisation (WHO) lists snakebite under the "other neglected conditions" category.[95]
+
+Documented deaths resulting from snake bites are uncommon. Nonfatal bites from venomous snakes may result in the need for amputation of a limb or part thereof. Of the roughly 725 species of venomous snakes worldwide, only 250 are able to kill a human with one bite. Australia averages only one fatal snake bite per year. In India, 250,000 snakebites are recorded in a single year, with as many as 50,000 recorded initial deaths.[96] The WHO estimates that on the order of 100 000 people die each year as a result of snake bites, and around three times as many amputations and other permanent disabilities are caused by snakebites annually.[97]
+
+The treatment for a snakebite is as variable as the bite itself. The most common and effective method is through antivenom (or antivenin), a serum made from the venom of the snake. Some antivenom is species-specific (monovalent) while some is made for use with multiple species in mind (polyvalent). In the United States for example, all species of venomous snakes are pit vipers, with the exception of the coral snake. To produce antivenom, a mixture of the venoms of the different species of rattlesnakes, copperheads, and cottonmouths is injected into the body of a horse in ever-increasing dosages until the horse is immunized. Blood is then extracted from the immunized horse. The serum is separated and further purified and freeze-dried. It is reconstituted with sterile water and becomes antivenom. For this reason, people who are allergic to horses are more likely to suffer an allergic reaction to antivenom.[98] Antivenom for the more dangerous species (such as mambas, taipans, and cobras) is made in a similar manner in India, South Africa, and Australia, although these antivenoms are species-specific.
+
+In some parts of the world, especially in India, snake charming is a roadside show performed by a charmer. In such a show, the snake charmer carries a basket that contains a snake that he seemingly charms by playing tunes from his flutelike musical instrument, to which the snake responds.[99] Snakes lack external ears, though they do have internal ears, and respond to the movement of the flute, not the actual noise.[99]
+
+The Wildlife Protection Act of 1972 in India technically proscribes snake charming on grounds of reducing animal cruelty. Other snake charmers also have a snake and mongoose show, where both the animals have a mock fight; however, this is not very common, as the snakes, as well as the mongooses, may be seriously injured or killed. Snake charming as a profession is dying out in India because of competition from modern forms of entertainment and environment laws proscribing the practice. Many Indians have never seen snake charming and it is becoming a folktale of the past.[99][100][101][102]
+
+The Irulas tribe of Andhra Pradesh and Tamil Nadu in India have been hunter-gatherers in the hot, dry plains forests, and have practiced the art of snake catching for generations. They have a vast knowledge of snakes in the field. They generally catch the snakes with the help of a simple stick. Earlier, the Irulas caught thousands of snakes for the snake-skin industry. After the complete ban of the snake-skin industry in India and protection of all snakes under the Indian Wildlife (Protection) Act 1972, they formed the Irula Snake Catcher's Cooperative and switched to catching snakes for removal of venom, releasing them in the wild after four extractions. The venom so collected is used for producing life-saving antivenom, biomedical research and for other medicinal products.[103] The Irulas are also known to eat some of the snakes they catch and are very useful in rat extermination in the villages.
+
+Despite the existence of snake charmers, there have also been professional snake catchers or wranglers. Modern-day snake trapping involves a herpetologist using a long stick with a V- shaped end. Some television show hosts, like Bill Haast, Austin Stevens, Steve Irwin, and Jeff Corwin, prefer to catch them using bare hands.
+
+While not commonly thought of as food in most cultures, in others the consumption of snakes is acceptable, or even considered a delicacy. Snake soup of Cantonese cuisine is consumed by locals in autumn, to warm up their body. Western cultures document the consumption of snakes under extreme circumstances of hunger.[104] Cooked rattlesnake meat is an exception, which is commonly consumed in Texas[105] and parts of the Midwestern United States. In Asian countries such as China, Taiwan, Thailand, Indonesia, Vietnam and Cambodia, drinking the blood of snakes—particularly the cobra—is believed to increase sexual virility.[106] The blood is drained while the cobra is still alive when possible, and is usually mixed with some form of liquor to improve the taste.[106]
+
+In some Asian countries, the use of snakes in alcohol is also accepted. In such cases, the body of a snake or several snakes is left to steep in a jar or container of liquor. It is claimed that this makes the liquor stronger (as well as more expensive). One example of this is the Habu snake sometimes placed in the Okinawan liquor Habushu (ブ酒,) also known as "Habu Sake".[107]
+
+Snake wine (蛇酒) is an alcoholic beverage produced by infusing whole snakes in rice wine or grain alcohol. The drink was first recorded to have been consumed in China during the Western Zhou dynasty and considered an important curative and believed to reinvigorate a person according to traditional Chinese medicine.[108]
+
+In the Western world, some snakes (especially docile species such as the ball python and corn snake) are kept as pets. To meet this demand a captive breeding industry has developed. Snakes bred in captivity tend to make better pets and are considered preferable to wild caught specimens.[109] Snakes can be very low maintenance pets, especially compared to more traditional species. They require minimal space, as most common species do not exceed 5 feet (1.5 m) in length. Pet snakes can be fed relatively infrequently, usually once every 5 to 14 days. Certain snakes have a lifespan of more than 40 years if given proper care.
+
+In ancient Mesopotamia, Nirah, the messenger god of Ištaran, was represented as a serpent on kudurrus, or boundary stones.[110] Representations of two intertwined serpents are common in Sumerian art and Neo-Sumerian artwork[110] and still appear sporadically on cylinder seals and amulets until as late as the thirteenth century BC.[110] The horned viper (Cerastes cerastes) appears in Kassite and Neo-Assyrian kudurrus[110] and is invoked in Assyrian texts as a magical protective entity.[110] A dragon-like creature with horns, the body and neck of a snake, the forelegs of a lion, and the hind-legs of a bird appears in Mesopotamian art from the Akkadian Period until the Hellenistic Period (323 BC–31 BC).[110] This creature, known in Akkadian as the mušḫuššu, meaning "furious serpent", was used as a symbol for particular deities and also as a general protective emblem.[110] It seems to have originally been the attendant of the Underworld god Ninazu,[110] but later became the attendant to the Hurrian storm-god Tishpak, as well as, later, Ninazu's son Ningishzida, the Babylonian national god Marduk, the scribal god Nabu, and the Assyrian national god Ashur.[110]
+
+In Egyptian history, the snake occupies a primary role with the Nile cobra adorning the crown of the pharaoh in ancient times. It was worshipped as one of the gods and was also used for sinister purposes: murder of an adversary and ritual suicide (Cleopatra).[citation needed] The ouroboros was a well-known ancient Egyptian symbol of a serpent swallowing its own tail.[111] The precursor to the ouroboros was the "Many-Faced",[111] a serpent with five heads, who, according to the Amduat, the oldest surviving Book of the Afterlife, was said to coil around the corpse of the sun god Ra protectively.[111] The earliest surviving depiction of a "true" ouroboros comes from the gilded shrines in the tomb of Tutankhamun.[111] In the early centuries AD, the ouroboros was adopted as a symbol by Gnostic Christians[111] and chapter 136 of the Pistis Sophia, an early Gnostic text, describes "a great dragon whose tail is in its mouth".[111] In medieval alchemy, the ouroboros became a typical western dragon with wings, legs, and a tail.[111]
+
+In the Bible, King Nahash of Ammon, whose name means "Snake", is depicted very negatively, as a particularly cruel and despicable enemy of the ancient Hebrews.
+
+The ancient Greeks used the Gorgoneion, a depiction of a hideous face with serpents for hair, as an apotropaic symbol to ward off evil.[112] In a Greek myth described by Pseudo-Apollodorus in his Bibliotheca, Medusa was a Gorgon with serpents for hair whose gaze turned all those who looked at her to stone and was slain by the hero Perseus.[113][114][115] In the Roman poet Ovid's Metamorphoses, Medusa is said to have once been a beautiful priestess of Athena, whom Athena turned into a serpent-haired monster after she was raped by the god Poseidon in Athena's temple.[116] In another myth referenced by the Boeotian poet Hesiod and described in detail by Pseudo-Apollodorus, the hero Heracles is said to have slain the Lernaean Hydra,[117][118] a multiple-headed serpent which dwelt in the swamps of Lerna.[117][118]
+
+The legendary account of the foundation of Thebes mentioned a monster snake guarding the spring from which the new settlement was to draw its water. In fighting and killing the snake, the companions of the founder Cadmus all perished – leading to the term "Cadmean victory" (i.e. a victory involving one's own ruin).[citation needed]
+
+Three medical symbols involving snakes that are still used today are Bowl of Hygieia, symbolizing pharmacy, and the Caduceus and Rod of Asclepius, which are symbols denoting medicine in general.[49]
+
+One of the etymologies proposed for the common female first name Linda is that it might derive from Old German Lindi or Linda, meaning a serpent.
+
+India is often called the land of snakes and is steeped in tradition regarding snakes.[119] Snakes are worshipped as gods even today with many women pouring milk on snake pits (despite snakes' aversion for milk).[119] The cobra is seen on the neck of Shiva and Vishnu is depicted often as sleeping on a seven-headed snake or within the coils of a serpent.[120] There are also several temples in India solely for cobras sometimes called Nagraj (King of Snakes) and it is believed that snakes are symbols of fertility. There is a Hindu festival called Nag Panchami each year on which day snakes are venerated and prayed to. See also Nāga.[citation needed]
+
+In India there is another mythology about snakes. Commonly known in Hindi as "Ichchhadhari" snakes. Such snakes can take the form of any living creature, but prefer human form. These mythical snakes possess a valuable gem called "Mani", which is more brilliant than diamond. There are many stories in India about greedy people trying to possess this gem and ending up getting killed.[citation needed]
+
+The snake is one of the 12 celestial animals of Chinese zodiac, in the Chinese calendar.[121]
+
+Many ancient Peruvian cultures worshipped nature.[122] They emphasized animals and often depicted snakes in their art.[123]
+
+Snakes are a part of Hindu worship. A festival, Nag Panchami, in which participants worship either images of or live Nāgas (cobras) is celebrated every year. Most images of Lord Shiva depict snake around his neck. Puranas have various stories associated with snakes. In the Puranas, Shesha is said to hold all the planets of the Universe on his hoods and to constantly sing the glories of Vishnu from all his mouths. He is sometimes referred to as "Ananta-Shesha", which means "Endless Shesha". Other notable snakes in Hinduism are Ananta, Vasuki, Taxak, Karkotaka and Pingala. The term Nāga is used to refer to entities that take the form of large snakes in Hinduism and Buddhism.
+
+Snakes have also been widely revered, such as in ancient Greece, where the serpent was seen as a healer. Asclepius carried a serpent wound around his wand, a symbol seen today on many ambulances.
+
+In religious terms, the snake and jaguar are arguably the most important animals in ancient Mesoamerica. "In states of ecstasy, lords dance a serpent dance; great descending snakes adorn and support buildings from Chichen Itza to Tenochtitlan, and the Nahuatl word coatl meaning serpent or twin, forms part of primary deities such as Mixcoatl, Quetzalcoatl, and Coatlicue."[124] In both Maya and Aztec calendars, the fifth day of the week was known as Snake Day.
+
+In Judaism, the snake of brass is also a symbol of healing, of one's life being saved from imminent death.[125]
+
+In some parts of Christianity, Christ's redemptive work is compared to saving one's life through beholding the Nehushtan (serpent of brass).[126] Snake handlers use snakes as an integral part of church worship in order to exhibit their faith in divine protection. However, more commonly in Christianity, the serpent has been seen as a representative of evil and sly plotting, which can be seen in the description in Genesis chapter 3 of a snake in the Garden of Eden tempting Eve.[127] Saint Patrick is reputed to have expelled all snakes from Ireland while converting the country to Christianity in the 5th century, thus explaining the absence of snakes there.
+
+In Christianity and Judaism, the snake makes its infamous appearance in the first book of the Bible when a serpent appears before the first couple Adam and Eve and tempts them with the forbidden fruit from the Tree of Knowledge.[127] The snake returns in Exodus when Moses, as a sign of God's power, turns his staff into a snake and when Moses made the Nehushtan, a bronze snake on a pole that when looked at cured the people of bites from the snakes that plagued them in the desert. The serpent makes its final appearance symbolizing Satan in the Book of Revelation: "And he laid hold on the dragon the old serpent, which is the devil and Satan, and bound him for a thousand years."[128]
+
+In Neo-Paganism and Wicca, the snake is seen as a symbol of wisdom and knowledge.
+
+Several compounds from snake venoms are being researched as potential treatments or preventatives for pain, cancers, arthritis, stroke, heart disease, hemophilia, and hypertension, and to control bleeding (e.g. during surgery).[130][131][132]
+
+Caldwell MW, Nydam RL, Palci A, Apesteguía S (January 2015). "The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution". Nature Communications. 6 (5996): 5996. Bibcode:2015NatCo...6.5996C. doi:10.1038/ncomms6996. PMID 25625704.

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+
+
+Coordinates: 40°N 100°W / 40°N 100°W / 40; -100
+
+The United States of America (USA), commonly known as the United States (U.S. or US) or America, is a country mostly located in central North America, between Canada and Mexico. It consists of 50 states, a federal district, five major self-governing territories, and various possessions.[i] At 3.8 million square miles (9.8 million km2), it is the world's third- or fourth-largest country by total area.[e] With a 2019 estimated population of over 328 million,[7] the U.S. is the third most populous country in the world. The Americans are a racially and ethnically diverse population that has been shaped through centuries of immigration. The capital is Washington, D.C., and the most populous city is New York City.
+
+Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago,[19] and European colonization began in the 16th century. The United States emerged from the thirteen British colonies established along the East Coast. Numerous disputes between Great Britain and the colonies led to the American Revolutionary War lasting between 1775 and 1783, leading to independence.[20] Beginning in the late 18th century, the United States vigorously expanded across North America, gradually acquiring new territories,[21] killing and displacing Native Americans, and admitting new states. By 1848, the United States spanned the continent.[21]
+Slavery was legal in much of the United States until the second half of the 19th century, when the American Civil War led to its abolition.[22][23]
+
+The Spanish–American War and World War I entrenched the U.S. as a world power, a status confirmed by the outcome of World War II. It was the first country to develop nuclear weapons and is the only country to have used them in warfare. During the Cold War, the United States and the Soviet Union competed in the Space Race, culminating with the 1969 Apollo 11 mission, the spaceflight that first landed humans on the Moon. The end of the Cold War and collapse of the Soviet Union in 1991 left the United States as the world's sole superpower.[24]
+
+The United States is a federal republic and a representative democracy. It is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States (OAS), NATO, and other international organizations. It is a permanent member of the United Nations Security Council.
+
+A highly developed country, the United States is the world's largest economy and accounts for approximately a quarter of global gross domestic product (GDP).[25] The United States is the world's largest importer and the second-largest exporter of goods, by value.[26][27] Although its population is only 4.3% of the world total,[28] it holds 29.4% of the total wealth in the world, the largest share held by any country.[29] Despite income and wealth disparities, the United States continues to rank high in measures of socioeconomic performance, including average wage, median income, median wealth, human development, per capita GDP, and worker productivity.[30][31] It is the foremost military power in the world, making up more than a third of global military spending,[32] and is a leading political, cultural, and scientific force internationally.[33]
+
+The first known use of the name "America" dates back to 1507, when it appeared on a world map created by the German cartographer Martin Waldseemüller. On this map, the name applied to South America in honor of the Italian explorer Amerigo Vespucci.[34] After returning from his expeditions, Vespucci first postulated that the West Indies did not represent Asia's eastern limit, as initially thought by Christopher Columbus, but instead were part of an entirely separate landmass thus far unknown to the Europeans.[35] In 1538, the Flemish cartographer Gerardus Mercator used the name "America" on his own world map, applying it to the entire Western Hemisphere.[36]
+
+The first documentary evidence of the phrase "United States of America" dates from a January 2, 1776 letter written by Stephen Moylan, Esq., to Lt. Col. Joseph Reed, George Washington's aide-de-camp and Muster-Master General of the Continental Army. Moylan expressed his wish to go "with full and ample powers from the United States of America to Spain" to seek assistance in the revolutionary war effort.[37][38][39] The first known publication of the phrase "United States of America" was in an anonymous essay in The Virginia Gazette newspaper in Williamsburg, Virginia, on April 6, 1776.[40]
+
+The second draft of the Articles of Confederation, prepared by John Dickinson and completed no later than June 17, 1776, declared "The name of this Confederation shall be the 'United States of America'".[41] The final version of the Articles sent to the states for ratification in late 1777 contains the sentence "The Stile of this Confederacy shall be 'The United States of America'".[42] In June 1776, Thomas Jefferson wrote the phrase "UNITED STATES OF AMERICA" in all capitalized letters in the headline of his "original Rough draught" of the Declaration of Independence.[41] This draft of the document did not surface until June 21, 1776, and it is unclear whether it was written before or after Dickinson used the term in his June 17 draft of the Articles of Confederation.[41]
+
+The short form "United States" is also standard. Other common forms are the "U.S.," the "USA," and "America." Colloquial names are the "U.S. of A." and, internationally, the "States." "Columbia," a name popular in poetry and songs of the late 18th century, derives its origin from Christopher Columbus; it appears in the name "District of Columbia." Many landmarks and institutions in the Western Hemisphere bear his name, including the country of Colombia.[43]
+
+The phrase "United States" was originally plural, a description of a collection of independent states—e.g., "the United States are"—including in the Thirteenth Amendment to the United States Constitution, ratified in 1865.[44] The singular form—e.g., "the United States is"—became popular after the end of the Civil War. The singular form is now standard; the plural form is retained in the idiom "these United States." The difference is more significant than usage; it is a difference between a collection of states and a unit.[45]
+
+A citizen of the United States is an "American." "United States," "American" and "U.S." refer to the country adjectivally ("American values," "U.S. forces"). In English, the word "American" rarely refers to topics or subjects not directly connected with the United States.[46]
+
+It has been generally accepted that the first inhabitants of North America migrated from Siberia by way of the Bering land bridge and arrived at least 12,000 years ago; however, increasing evidence suggests an even earlier arrival.[19][47][48] After crossing the land bridge, the Paleo-Indians moved southward along the Pacific coast[49] and through an interior ice-free corridor.[50] The Clovis culture, which appeared around 11,000 BC, was initially believed to represent the first wave of human settlement of the Americas.[51][52] It is likely these represent the first of three major waves of migration into North America.[53]
+
+Over time, indigenous cultures in North America grew increasingly complex, and some, such as the pre-Columbian Mississippian culture in the southeast, developed advanced agriculture, grand architecture, and state-level societies.[54] The Mississippian culture flourished in the south from 800 to 1600 AD, extending from the Mexican border down through Florida.[55] Its city state Cahokia is the largest, most complex pre-Columbian archaeological site in the modern-day United States.[56] In the Four Corners region, Ancestral Puebloan culture developed from centuries of agricultural experimentation.[57]
+
+Three UNESCO World Heritage Sites in the United States are credited to the Pueblos: Mesa Verde National Park, Chaco Culture National Historical Park, and Taos Pueblo.[58][59] The earthworks constructed by Native Americans of the Poverty Point culture have also been designated a UNESCO World Heritage site. In the southern Great Lakes region, the Iroquois Confederacy was established at some point between the twelfth and fifteenth centuries.[60] Most prominent along the Atlantic coast were the Algonquian tribes, who practiced hunting and trapping, along with limited cultivation.
+
+With the progress of European colonization in the territories of the contemporary United States, the Native Americans were often conquered and displaced.[61] The native population of America declined after European arrival for various reasons,[62][63] primarily diseases such as smallpox and measles.[64][65]
+
+Estimating the native population of North America at the time of European contact is difficult.[66][67] Douglas H. Ubelaker of the Smithsonian Institution estimated that there was a population of 92,916 in the south Atlantic states and a population of 473,616 in the Gulf states,[68] but most academics regard this figure as too low.[66] Anthropologist Henry F. Dobyns believed the populations were much higher, suggesting 1,100,000 along the shores of the gulf of Mexico, 2,211,000 people living between Florida and Massachusetts, 5,250,000 in the Mississippi Valley and tributaries and 697,000 people in the Florida peninsula.[66][67]
+
+In the early days of colonization, many European settlers were subject to food shortages, disease, and attacks from Native Americans. Native Americans were also often at war with neighboring tribes and allied with Europeans in their colonial wars. In many cases, however, natives and settlers came to depend on each other. Settlers traded for food and animal pelts; natives for guns, ammunition and other European goods.[69] Natives taught many settlers to cultivate corn, beans, and squash. European missionaries and others felt it was important to "civilize" the Native Americans and urged them to adopt European agricultural techniques and lifestyles.[70][71]
+
+With the advancement of European colonization in North America, the Native Americans were often conquered and displaced.[72] The first Europeans to arrive in the contiguous United States were Spanish conquistadors such as Juan Ponce de León, who made his first visit to Florida in 1513. Even earlier, Christopher Columbus landed in Puerto Rico on his 1493 voyage. The Spanish set up the first settlements in Florida and New Mexico such as Saint Augustine[73] and Santa Fe. The French established their own as well along the Mississippi River. Successful English settlement on the eastern coast of North America began with the Virginia Colony in 1607 at Jamestown and with the Pilgrims' Plymouth Colony in 1620. Many settlers were dissenting Christian groups who came seeking religious freedom. The continent's first elected legislative assembly, Virginia's House of Burgesses, was created in 1619. The Mayflower Compact, signed by the Pilgrims before disembarking, and the Fundamental Orders of Connecticut, established precedents for the pattern of representative self-government and constitutionalism that would develop throughout the American colonies.[74][75]
+
+Most settlers in every colony were small farmers, though other industries were formed. Cash crops included tobacco, rice, and wheat. Extraction industries grew up in furs, fishing and lumber. Manufacturers produced rum and ships, and by the late colonial period, Americans were producing one-seventh of the world's iron supply.[76] Cities eventually dotted the coast to support local economies and serve as trade hubs. English colonists were supplemented by waves of Scotch-Irish immigrants and other groups. As coastal land grew more expensive, freed indentured servants claimed lands further west.[77]
+
+A large-scale slave trade with English privateers began.[78] Because of less disease and better food and treatment, the life expectancy of slaves was much higher in North America than further south, leading to a rapid increase in the numbers of slaves.[79][80] Colonial society was largely divided over the religious and moral implications of slavery, and colonies passed acts for and against the practice.[81][82] But by the turn of the 18th century, African slaves were replacing indentured servants for cash crop labor, especially in the South.[83]
+
+With the establishment of the Province of Georgia in 1732, the 13 colonies that would become the United States of America were administered by the British as overseas dependencies.[84] All nonetheless had local governments with elections open to most free men.[85] With extremely high birth rates, low death rates, and steady settlement, the colonial population grew rapidly. Relatively small Native American populations were eclipsed.[86] The Christian revivalist movement of the 1730s and 1740s known as the Great Awakening fueled interest both in religion and in religious liberty.[87]
+
+During the Seven Years' War (known in the United States as the French and Indian War), British forces seized Canada from the French, but the francophone population remained politically isolated from the southern colonies. Excluding the Native Americans, who were being conquered and displaced, the 13 British colonies had a population of over 2.1 million in 1770, about a third that of Britain. Despite continuing, new arrivals, the rate of natural increase was such that by the 1770s only a small minority of Americans had been born overseas.[88] The colonies' distance from Britain had allowed the development of self-government, but their unprecedented success motivated monarchs to periodically seek to reassert royal authority.[89]
+
+In 1774, the Spanish Navy ship Santiago, under Juan Pérez, entered and anchored in an inlet of Nootka Sound, Vancouver Island, in present-day British Columbia. Although the Spanish did not land, natives paddled to the ship to trade furs for abalone shells from California.[90] At the time, the Spanish were able to monopolize the trade between Asia and North America, granting limited licenses to the Portuguese. When the Russians began establishing a growing fur trading system in Alaska, the Spanish began to challenge the Russians, with Pérez's voyage being the first of many to the Pacific Northwest.[91][j]
+
+During his third and final voyage, Captain James Cook became the first European to begin formal contact with Hawaii.[93] Captain Cook's last voyage included sailing along the coast of North America and Alaska searching for a Northwest Passage for approximately nine months.[94]
+
+The American Revolutionary War was the first successful colonial war of independence against a European power. Americans had developed an ideology of "republicanism" asserting that government rested on the will of the people as expressed in their local legislatures. They demanded their rights as Englishmen and "no taxation without representation". The British insisted on administering the empire through Parliament, and the conflict escalated into war.[95]
+
+The Second Continental Congress unanimously adopted the Declaration of Independence, which asserted that Great Britain was not protecting Americans' unalienable rights. July 4 is celebrated annually as Independence Day.[96] In 1777, the Articles of Confederation established a decentralized government that operated until 1789.[96]
+
+Following the decisive Franco-American victory at Yorktown in 1781,[97] Britain signed the peace treaty of 1783, and American sovereignty was internationally recognized and the country was granted all lands east of the Mississippi River. Nationalists led the Philadelphia Convention of 1787 in writing the United States Constitution, ratified in state conventions in 1788. The federal government was reorganized into three branches, on the principle of creating salutary checks and balances, in 1789. George Washington, who had led the Continental Army to victory, was the first president elected under the new constitution. The Bill of Rights, forbidding federal restriction of personal freedoms and guaranteeing a range of legal protections, was adopted in 1791.[98]
+
+Although the federal government criminalized the international slave trade in 1808, after 1820, cultivation of the highly profitable cotton crop exploded in the Deep South, and along with it, the slave population.[99][100][101] The Second Great Awakening, especially 1800–1840, converted millions to evangelical Protestantism. In the North, it energized multiple social reform movements, including abolitionism;[102] in the South, Methodists and Baptists proselytized among slave populations.[103]
+
+Americans' eagerness to expand westward prompted a long series of American Indian Wars.[104] The Louisiana Purchase of French-claimed territory in 1803 almost doubled the nation's area.[105] The War of 1812, declared against Britain over various grievances and fought to a draw, strengthened U.S. nationalism.[106] A series of military incursions into Florida led Spain to cede it and other Gulf Coast territory in 1819.[107] The expansion was aided by steam power, when steamboats began traveling along America's large water systems, many of which were connected by new canals, such as the Erie and the I&M; then, even faster railroads began their stretch across the nation's land.[108]
+
+From 1820 to 1850, Jacksonian democracy began a set of reforms which included wider white male suffrage; it led to the rise of the Second Party System of Democrats and Whigs as the dominant parties from 1828 to 1854. The Trail of Tears in the 1830s exemplified the Indian removal policy that forcibly resettled Indians into the west on Indian reservations. The U.S. annexed the Republic of Texas in 1845 during a period of expansionist Manifest destiny.[109] The 1846 Oregon Treaty with Britain led to U.S. control of the present-day American Northwest.[110] Victory in the Mexican–American War resulted in the 1848 Mexican Cession of California and much of the present-day American Southwest.[111]
+The California Gold Rush of 1848–49 spurred migration to the Pacific coast, which led to the California Genocide[112][113][114][115] and the creation of additional western states.[116] After the Civil War, new transcontinental railways made relocation easier for settlers, expanded internal trade and increased conflicts with Native Americans.[117] In 1869, a new Peace Policy nominally promised to protect Native Americans from abuses, avoid further war, and secure their eventual U.S. citizenship. Nonetheless, large-scale conflicts continued throughout the West into the 1900s.
+
+Irreconcilable sectional conflict regarding the slavery of Africans and African Americans ultimately led to the American Civil War.[118] Initially, states entering the Union had alternated between slave and free states, keeping a sectional balance in the Senate, while free states outstripped slave states in population and in the House of Representatives. But with additional western territory and more free-soil states, tensions between slave and free states mounted with arguments over federalism and disposition of the territories, as well as whether to expand or restrict slavery.[119]
+
+With the 1860 election of Republican Abraham Lincoln, conventions in thirteen slave states ultimately declared secession and formed the Confederate States of America (the "South" or the "Confederacy"), while the federal government (the "Union") maintained that secession was illegal.[119] In order to bring about this secession, military action was initiated by the secessionists, and the Union responded in kind. The ensuing war would become the deadliest military conflict in American history, resulting in the deaths of approximately 618,000 soldiers as well as many civilians.[120] The Union initially simply fought to keep the country united. Nevertheless, as casualties mounted after 1863 and Lincoln delivered his Emancipation Proclamation, the main purpose of the war from the Union's viewpoint became the abolition of slavery. Indeed, when the Union ultimately won the war in April 1865, each of the states in the defeated South was required to ratify the Thirteenth Amendment, which prohibited slavery.
+
+The government enacted three constitutional amendments in the years after the war: the aforementioned Thirteenth as well as the Fourteenth Amendment providing citizenship to the nearly four million African Americans who had been slaves,[121] and the Fifteenth Amendment ensuring in theory that African Americans had the right to vote. The war and its resolution led to a substantial increase in federal power[122] aimed at reintegrating and rebuilding the South while guaranteeing the rights of the newly freed slaves.
+
+Reconstruction began in earnest following the war. While President Lincoln attempted to foster friendship and forgiveness between the Union and the former Confederacy, his assassination on April 14, 1865, drove a wedge between North and South again. Republicans in the federal government made it their goal to oversee the rebuilding of the South and to ensure the rights of African Americans. They persisted until the Compromise of 1877 when the Republicans agreed to cease protecting the rights of African Americans in the South in order for Democrats to concede the presidential election of 1876.
+
+Southern white Democrats, calling themselves "Redeemers," took control of the South after the end of Reconstruction. From 1890 to 1910 the Redeemers established so-called Jim Crow laws, disenfranchising most blacks and some poor whites throughout the region. Blacks faced racial segregation, especially in the South.[123] They also occasionally experienced vigilante violence, including lynching.[124]
+
+In the North, urbanization and an unprecedented influx of immigrants from Southern and Eastern Europe supplied a surplus of labor for the country's industrialization and transformed its culture.[126] National infrastructure including telegraph and transcontinental railroads spurred economic growth and greater settlement and development of the American Old West. The later invention of electric light and the telephone would also affect communication and urban life.[127]
+
+The United States fought Indian Wars west of the Mississippi River from 1810 to at least 1890.[128] Most of these conflicts ended with the cession of Native American territory and their confinement to Indian reservations. This further expanded acreage under mechanical cultivation, increasing surpluses for international markets.[129] Mainland expansion also included the purchase of Alaska from Russia in 1867.[130] In 1893, pro-American elements in Hawaii overthrew the monarchy and formed the Republic of Hawaii, which the U.S. annexed in 1898. Puerto Rico, Guam, and the Philippines were ceded by Spain in the same year, following the Spanish–American War.[131] American Samoa was acquired by the United States in 1900 after the end of the Second Samoan Civil War.[132] The U.S. Virgin Islands were purchased from Denmark in 1917.[133]
+
+Rapid economic development during the late 19th and early 20th centuries fostered the rise of many prominent industrialists. Tycoons like Cornelius Vanderbilt, John D. Rockefeller, and Andrew Carnegie led the nation's progress in railroad, petroleum, and steel industries. Banking became a major part of the economy, with J. P. Morgan playing a notable role. The American economy boomed, becoming the world's largest, and the United States achieved great power status.[134] These dramatic changes were accompanied by social unrest and the rise of populist, socialist, and anarchist movements.[135] This period eventually ended with the advent of the Progressive Era, which saw significant reforms including women's suffrage, alcohol prohibition, regulation of consumer goods, greater antitrust measures to ensure competition and attention to worker conditions.[136][137][138]
+
+The United States remained neutral from the outbreak of World War I in 1914 until 1917, when it joined the war as an "associated power," alongside the formal Allies of World War I, helping to turn the tide against the Central Powers. In 1919, President Woodrow Wilson took a leading diplomatic role at the Paris Peace Conference and advocated strongly for the U.S. to join the League of Nations. However, the Senate refused to approve this and did not ratify the Treaty of Versailles that established the League of Nations.[139]
+
+In 1920, the women's rights movement won passage of a constitutional amendment granting women's suffrage.[140] The 1920s and 1930s saw the rise of radio for mass communication and the invention of early television.[141] The prosperity of the Roaring Twenties ended with the Wall Street Crash of 1929 and the onset of the Great Depression. After his election as president in 1932, Franklin D. Roosevelt responded with the New Deal.[142] The Great Migration of millions of African Americans out of the American South began before World War I and extended through the 1960s;[143] whereas the Dust Bowl of the mid-1930s impoverished many farming communities and spurred a new wave of western migration.[144]
+
+At first effectively neutral during World War II, the United States began supplying materiel to the Allies in March 1941 through the Lend-Lease program. On December 7, 1941, the Empire of Japan launched a surprise attack on Pearl Harbor, prompting the United States to join the Allies against the Axis powers.[145] Although Japan attacked the United States first, the U.S. nonetheless pursued a "Europe first" defense policy.[146] The United States thus left its vast Asian colony, the Philippines, isolated and fighting a losing struggle against Japanese invasion and occupation, as military resources were devoted to the European theater. During the war, the United States was referred to as one of the "Four Policemen"[147] of Allies power who met to plan the postwar world, along with Britain, the Soviet Union and China.[148][149] Although the nation lost around 400,000 military personnel,[150] it emerged relatively undamaged from the war with even greater economic and military influence.[151]
+
+The United States played a leading role in the Bretton Woods and Yalta conferences with the United Kingdom, the Soviet Union, and other Allies, which signed agreements on new international financial institutions and Europe's postwar reorganization. As an Allied victory was won in Europe, a 1945 international conference held in San Francisco produced the United Nations Charter, which became active after the war.[152] The United States and Japan then fought each other in the largest naval battle in history, the Battle of Leyte Gulf.[153][154] The United States eventually developed the first nuclear weapons and used them on Japan in the cities of Hiroshima and Nagasaki; the Japanese surrendered on September 2, ending World War II.[155][156]
+
+After World War II, the United States and the Soviet Union competed for power, influence, and prestige during what became known as the Cold War, driven by an ideological divide between capitalism and communism.[157] They dominated the military affairs of Europe, with the U.S. and its NATO allies on one side and the USSR and its Warsaw Pact allies on the other. The U.S. developed a policy of containment towards the expansion of communist influence. While the U.S. and Soviet Union engaged in proxy wars and developed powerful nuclear arsenals, the two countries avoided direct military conflict.[citation needed]
+
+The United States often opposed Third World movements that it viewed as Soviet-sponsored, and occasionally pursued direct action for regime change against left-wing governments, even supporting right-wing authoritarian governments at times.[158] American troops fought communist Chinese and North Korean forces in the Korean War of 1950–53.[159] The Soviet Union's 1957 launch of the first artificial satellite and its 1961 launch of the first manned spaceflight initiated a "Space Race" in which the United States became the first nation to land a man on the moon in 1969.[159] A proxy war in Southeast Asia eventually evolved into full American participation, as the Vietnam War.[citation needed]
+
+At home, the U.S. experienced sustained economic expansion and a rapid growth of its population and middle class. Construction of an Interstate Highway System transformed the nation's infrastructure over the following decades. Millions moved from farms and inner cities to large suburban housing developments.[160][161] In 1959 Hawaii became the 50th and last U.S. state added to the country.[162] The growing Civil Rights Movement used nonviolence to confront segregation and discrimination, with Martin Luther King Jr. becoming a prominent leader and figurehead. A combination of court decisions and legislation, culminating in the Civil Rights Act of 1968, sought to end racial discrimination.[163][164][165] Meanwhile, a counterculture movement grew which was fueled by opposition to the Vietnam war, black nationalism, and the sexual revolution.
+
+The launch of a "War on Poverty" expanded entitlements and welfare spending, including the creation of Medicare and Medicaid, two programs that provide health coverage to the elderly and poor, respectively, and the means-tested Food Stamp Program and Aid to Families with Dependent Children.[166]
+
+The 1970s and early 1980s saw the onset of stagflation. After his election in 1980, President Ronald Reagan responded to economic stagnation with free-market oriented reforms. Following the collapse of détente, he abandoned "containment" and initiated the more aggressive "rollback" strategy towards the USSR.[167][168][169][170][171] After a surge in female labor participation over the previous decade, by 1985 the majority of women aged 16 and over were employed.[172]
+
+The late 1980s brought a "thaw" in relations with the USSR, and its collapse in 1991 finally ended the Cold War.[173][174][175][176] This brought about unipolarity[177] with the U.S. unchallenged as the world's dominant superpower. The concept of Pax Americana, which had appeared in the post-World War II period, gained wide popularity as a term for the post-Cold War new world order.[citation needed]
+
+After the Cold War, the conflict in the Middle East triggered a crisis in 1990, when Iraq under Saddam Hussein invaded and attempted to annex Kuwait, an ally of the United States. Fearing the instability would spread to other regions, President George H. W. Bush launched Operation Desert Shield, a defensive force buildup in Saudi Arabia, and Operation Desert Storm, in a staging titled the Gulf War; waged by coalition forces from 34 nations, led by the United States against Iraq ending in the expulsion of Iraqi forces from Kuwait and restoration of the monarchy.[178]
+
+Originating within U.S. military defense networks, the Internet spread to international academic platforms and then to the public in the 1990s, greatly affecting the global economy, society, and culture.[179] Due to the dot-com boom, stable monetary policy, and reduced social welfare spending, the 1990s saw the longest economic expansion in modern U.S. history.[180] Beginning in 1994, the U.S. entered into the North American Free Trade Agreement (NAFTA), prompting trade among the U.S., Canada, and Mexico to soar.[181]
+
+On September 11, 2001, Al-Qaeda terrorists struck the World Trade Center in New York City and the Pentagon near Washington, D.C., killing nearly 3,000 people.[182] In response, the United States launched the War on Terror, which included a war in Afghanistan and the 2003–11 Iraq War.[183][184]
+
+Government policy designed to promote affordable housing,[185] widespread failures in corporate and regulatory governance,[186] and historically low interest rates set by the Federal Reserve[187] led to the mid-2000s housing bubble, which culminated with the 2008 financial crisis, the nation's largest economic contraction since the Great Depression.[188] Barack Obama, the first African-American[189] and multiracial[190] president, was elected in 2008 amid the crisis,[191] and subsequently passed stimulus measures and the Dodd–Frank Act in an attempt to mitigate its negative effects and ensure there would not be a repeat of the crisis. In 2010, the Obama administration passed the Affordable Care Act, which made the most sweeping reforms to the nation's healthcare system in nearly five decades, including mandates, subsidies and insurance exchanges.[citation needed]
+
+American forces in Iraq were withdrawn in large numbers in 2009 and 2010, and the war in the region was declared formally over in December 2011.[192] But months earlier, Operation Neptune Spear led to the death of the leader of Al-Qaeda in Pakistan.[193] In the presidential election of 2016, Republican Donald Trump was elected as the 45th president of the United States. On January 20, 2020, the first case of COVID-19 in the United States was confirmed.[194] As of July 2020, the United States has over 4 million COVID-19 cases and over 145,000 deaths.[195] The United States is, by far, the country with the most cases of COVID-19 since April 11, 2020.[196]
+
+The 48 contiguous states and the District of Columbia occupy a combined area of 3,119,884.69 square miles (8,080,464.3 km2). Of this area, 2,959,064.44 square miles (7,663,941.7 km2) is contiguous land, composing 83.65% of total U.S. land area.[197][198] Hawaii, occupying an archipelago in the central Pacific, southwest of North America, is 10,931 square miles (28,311 km2) in area. The populated territories of Puerto Rico, American Samoa, Guam, Northern Mariana Islands, and U.S. Virgin Islands together cover 9,185 square miles (23,789 km2).[199] Measured by only land area, the United States is third in size behind Russia and China, just ahead of Canada.[200]
+
+The United States is the world's third- or fourth-largest nation by total area (land and water), ranking behind Russia and Canada and nearly equal to China. The ranking varies depending on how two territories disputed by China and India are counted, and how the total size of the United States is measured.[e][201][202]
+
+The coastal plain of the Atlantic seaboard gives way further inland to deciduous forests and the rolling hills of the Piedmont.[203] The Appalachian Mountains divide the eastern seaboard from the Great Lakes and the grasslands of the Midwest.[204] The Mississippi–Missouri River, the world's fourth longest river system, runs mainly north–south through the heart of the country. The flat, fertile prairie of the Great Plains stretches to the west, interrupted by a highland region in the southeast.[204]
+
+The Rocky Mountains, west of the Great Plains, extend north to south across the country, peaking around 14,000 feet (4,300 m) in Colorado.[205] Farther west are the rocky Great Basin and deserts such as the Chihuahua and Mojave.[206] The Sierra Nevada and Cascade mountain ranges run close to the Pacific coast, both ranges reaching altitudes higher than 14,000 feet (4,300 m). The lowest and highest points in the contiguous United States are in the state of California,[207] and only about 84 miles (135 km) apart.[208] At an elevation of 20,310 feet (6,190.5 m), Alaska's Denali is the highest peak in the country and in North America.[209] Active volcanoes are common throughout Alaska's Alexander and Aleutian Islands, and Hawaii consists of volcanic islands. The supervolcano underlying Yellowstone National Park in the Rockies is the continent's largest volcanic feature.[210]
+
+The United States, with its large size and geographic variety, includes most climate types. To the east of the 100th meridian, the climate ranges from humid continental in the north to humid subtropical in the south.[211] The Great Plains west of the 100th meridian are semi-arid. Much of the Western mountains have an alpine climate. The climate is arid in the Great Basin, desert in the Southwest, Mediterranean in coastal California, and oceanic in coastal Oregon and Washington and southern Alaska. Most of Alaska is subarctic or polar. Hawaii and the southern tip of Florida are tropical, as well as its territories in the Caribbean and the Pacific.[212] States bordering the Gulf of Mexico are prone to hurricanes, and most of the world's tornadoes occur in the country, mainly in Tornado Alley areas in the Midwest and South.[213] Overall, the United States has the world's most violent weather, receiving more high-impact extreme weather incidents than any other country in the world.[214]
+
+The U.S. ecology is megadiverse: about 17,000 species of vascular plants occur in the contiguous United States and Alaska, and more than 1,800 species of flowering plants are found in Hawaii, few of which occur on the mainland.[216] The United States is home to 428 mammal species, 784 bird species, 311 reptile species, and 295 amphibian species,[217] as well as about 91,000 insect species.[218]
+
+There are 62 national parks and hundreds of other federally managed parks, forests, and wilderness areas.[219] Altogether, the government owns about 28% of the country's land area,[220] mostly in the western states.[221] Most of this land is protected, though some is leased for oil and gas drilling, mining, logging, or cattle ranching, and about .86% is used for military purposes.[222][223]
+
+Environmental issues include debates on oil and nuclear energy, dealing with air and water pollution, the economic costs of protecting wildlife, logging and deforestation,[224][225] and international responses to global warming.[226][227] The most prominent environmental agency is the Environmental Protection Agency (EPA), created by presidential order in 1970.[228] The idea of wilderness has shaped the management of public lands since 1964, with the Wilderness Act.[229] The Endangered Species Act of 1973 is intended to protect threatened and endangered species and their habitats, which are monitored by the United States Fish and Wildlife Service.[230]
+
+The U.S. Census Bureau officially estimated the country's population to be 328,239,523 as of July 1, 2019.[231] In addition, the Census Bureau provides a continuously updated U.S. Population Clock that approximates the latest population of the 50 states and District of Columbia based on the Bureau's most recent demographic trends.[234] According to the clock, on May 23, 2020, the U.S. population exceeded 329 million residents, with a net gain of one person every 19 seconds, or about 4,547 people per day. The United States is the third most populous nation in the world, after China and India. In 2018 the median age of the United States population was 38.1 years.[235]
+
+In 2018, there were almost 90 million immigrants and U.S.-born children of immigrants (second-generation Americans) in the United States, accounting for 28% of the overall U.S. population.[236] The United States has a very diverse population; 37 ancestry groups have more than one million members.[237] German Americans are the largest ethnic group (more than 50 million)—followed by Irish Americans (circa 37 million), Mexican Americans (circa 31 million) and English Americans (circa 28 million).[238][239]
+
+White Americans (mostly European ancestry) are the largest racial group at 73.1% of the population; African Americans are the nation's largest racial minority and third-largest ancestry group.[237] Asian Americans are the country's second-largest racial minority; the three largest Asian American ethnic groups are Chinese Americans, Filipino Americans, and Indian Americans.[237] The largest American community with European ancestry is German Americans, which consists of more than 14% of the total population.[240] In 2010, the U.S. population included an estimated 5.2 million people with some American Indian or Alaska Native ancestry (2.9 million exclusively of such ancestry) and 1.2 million with some native Hawaiian or Pacific island ancestry (0.5 million exclusively).[241] The census counted more than 19 million people of "Some Other Race" who were "unable to identify with any" of its five official race categories in 2010, more than 18.5 million (97%) of whom are of Hispanic ethnicity.[241]
+
+In 2017, out of the U.S. foreign-born population, some 45% (20.7 million) were naturalized citizens, 27% (12.3 million) were lawful permanent residents (including many eligible to become citizens), 6% (2.2 million) were temporary lawful residents, and 23% (10.5 million) were unauthorized immigrants.[242] Among current living immigrants to the U.S., the top five countries of birth are Mexico, China, India, the Philippines and El Salvador. Until 2017 and 2018, the United States led the world in refugee resettlement for decades, admitted more refugees than the rest of the world combined.[243] From fiscal year 1980 until 2017, 55% of refugees came from Asia, 27% from Europe, 13% from Africa, and 4% from Latin America.[243]
+
+A 2017 United Nations report projected that the U.S. would be one of nine countries in which world population growth through 2050 would be concentrated.[244] A 2020 U.S. Census Bureau report projected the population of the country could be anywhere between 320 million and 447 million by 2060, depending on the rate of in-migration; in all projected scenarios, a lower fertility rate and increases in life expectancy would result in an aging population.[245] The United States has an annual birth rate of 13 per 1,000, which is five births per 1,000 below the world average.[246] Its population growth rate is positive at 0.7%, higher than that of many developed nations.[247]
+
+About 82% of Americans live in urban areas (including suburbs);[202] about half of those reside in cities with populations over 50,000.[248] In 2008, 273 incorporated municipalities had populations over 100,000, nine cities had more than one million residents, and four cities had over two million (namely New York, Los Angeles, Chicago, and Houston).[249] Estimates for the year 2018 show that 53 metropolitan areas have populations greater than one million. Many metros in the South, Southwest and West grew significantly between 2010 and 2018. The Dallas and Houston metros increased by more than a million people, while the Washington, D.C., Miami, Atlanta, and Phoenix metros all grew by more than 500,000 people.
+
+English (specifically, American English) is the de facto national language of the United States. Although there is no official language at the federal level, some laws—such as U.S. naturalization requirements—standardize English. In 2010, about 230 million, or 80% of the population aged five years and older, spoke only English at home. 12% of the population speaks Spanish at home, making it the second most common language. Spanish is also the most widely taught second language.[250][251]
+
+Both Hawaiian and English are official languages in Hawaii.[252] In addition to English, Alaska recognizes twenty official Native languages,[253][k] and South Dakota recognizes Sioux.[254] While neither has an official language, New Mexico has laws providing for the use of both English and Spanish, as Louisiana does for English and French.[255] Other states, such as California, mandate the publication of Spanish versions of certain government documents including court forms.[256]
+
+Several insular territories grant official recognition to their native languages, along with English: Samoan[257] is officially recognized by American Samoa and Chamorro[258] is an official language of Guam. Both Carolinian and Chamorro have official recognition in the Northern Mariana Islands.[259]
+Spanish is an official language of Puerto Rico and is more widely spoken than English there.[260]
+
+The most widely taught foreign languages in the United States, in terms of enrollment numbers from kindergarten through university undergraduate education, are Spanish (around 7.2 million students), French (1.5 million), and German (500,000). Other commonly taught languages include Latin, Japanese, ASL, Italian, and Chinese.[261][262] 18% of all Americans claim to speak both English and another language.[263]
+
+Religion in the United States (2017)[266]
+
+The First Amendment of the U.S. Constitution guarantees the free exercise of religion and forbids Congress from passing laws respecting its establishment.
+
+In a 2013 survey, 56% of Americans said religion played a "very important role in their lives," a far higher figure than that of any other Western nation.[267] In a 2009 Gallup poll, 42% of Americans said they attended church weekly or almost weekly; the figures ranged from a low of 23% in Vermont to a high of 63% in Mississippi.[268]
+
+In a 2014 survey, 70.6% of adults in the United States identified themselves as Christians;[269] Protestants accounted for 46.5%, while Roman Catholics, at 20.8%, formed the largest single Christian group.[270] In 2014, 5.9% of the U.S. adult population claimed a non-Christian religion.[271] These include Judaism (1.9%), Islam (0.9%), Hinduism (0.7%), and Buddhism (0.7%).[271] The survey also reported that 22.8% of Americans described themselves as agnostic, atheist or simply having no religion—up from 8.2% in 1990.[270][272][273] There are also Unitarian Universalist, Scientologist, Baha'i, Sikh, Jain, Shinto, Zoroastrian, Confucian, Satanist, Taoist, Druid, Native American, Afro-American, traditional African, Wiccan, Gnostic, humanist and deist communities.[274][275]
+
+Protestantism is the largest Christian religious grouping in the United States, accounting for almost half of all Americans. Baptists collectively form the largest branch of Protestantism at 15.4%,[276] and the Southern Baptist Convention is the largest individual Protestant denomination at 5.3% of the U.S. population.[276] Apart from Baptists, other Protestant categories include nondenominational Protestants, Methodists, Pentecostals, unspecified Protestants, Lutherans, Presbyterians, Congregationalists, other Reformed, Episcopalians/Anglicans, Quakers, Adventists, Holiness, Christian fundamentalists, Anabaptists, Pietists, and multiple others.[276]
+
+As with other Western countries, the U.S. is becoming less religious. Irreligion is growing rapidly among Americans under 30.[277] Polls show that overall American confidence in organized religion has been declining since the mid to late 1980s,[278] and that younger Americans, in particular, are becoming increasingly irreligious.[271][279] In a 2012 study, the Protestant share of the U.S. population had dropped to 48%, thus ending its status as religious category of the majority for the first time.[280][281] Americans with no religion have 1.7 children compared to 2.2 among Christians. The unaffiliated are less likely to marry with 37% marrying compared to 52% of Christians.[282]
+
+The Bible Belt is an informal term for a region in the Southern United States in which socially conservative evangelical Protestantism is a significant part of the culture and Christian church attendance across the denominations is generally higher than the nation's average. By contrast, religion plays the least important role in New England and in the Western United States.[268]
+
+As of 2018[update], 52% of Americans age 15 and over were married, 6% were widowed, 10% were divorced, and 32% had never been married.[283] Women now work mostly outside the home and receive the majority of bachelor's degrees.[284]
+
+The U.S. teenage pregnancy rate is 26.5 per 1,000 women. The rate has declined by 57% since 1991.[285] Abortion is legal throughout the country. Abortion rates, currently 241 per 1,000 live births and 15 per 1,000 women aged 15–44, are falling but remain higher than most Western nations.[286] In 2013, the average age at first birth was 26 and 41% of births were to unmarried women.[287]
+
+The total fertility rate in 2016 was 1820.5 births per 1000 women.[288] Adoption in the United States is common and relatively easy from a legal point of view (compared to other Western countries).[289] As of 2001[update], with more than 127,000 adoptions, the U.S. accounted for nearly half of the total number of adoptions worldwide.[needs update][290] Same-sex marriage is legal nationwide, and it is legal for same-sex couples to adopt. Polygamy is illegal throughout the U.S.[291]
+
+In 2019, the U.S. had the world's highest rate of children living in single-parent households.[292]
+
+The United States had a life expectancy of 78.6 years at birth in 2017, which was the third year of declines in life expectancy following decades of continuous increase. The recent decline, primarily among the age group 25 to 64, is largely due to sharp increases in the drug overdose and suicide rates; the country has one of the highest suicide rates among wealthy countries.[293][294] Life expectancy was highest among Asians and Hispanics and lowest among blacks.[295][296] According to CDC and Census Bureau data, deaths from suicide, alcohol and drug overdoses hit record highs in 2017.[297]
+
+Increasing obesity in the United States and health improvements elsewhere contributed to lowering the country's rank in life expectancy from 11th in the world in 1987, to 42nd in 2007, and as of 2017 the country had the lowest life expectancy among Japan, Canada, Australia, the UK, and seven countries of western Europe.[298][299] Obesity rates have more than doubled in the last 30 years and are the highest in the industrialized world.[300][301] Approximately one-third of the adult population is obese and an additional third is overweight.[302] Obesity-related type 2 diabetes is considered epidemic by health care professionals.[303]
+
+In 2010, coronary artery disease, lung cancer, stroke, chronic obstructive pulmonary diseases, and traffic accidents caused the most years of life lost in the U.S. Low back pain, depression, musculoskeletal disorders, neck pain, and anxiety caused the most years lost to disability. The most harmful risk factors were poor diet, tobacco smoking, obesity, high blood pressure, high blood sugar, physical inactivity, and alcohol use. Alzheimer's disease, drug abuse, kidney disease, cancer, and falls caused the most additional years of life lost over their age-adjusted 1990 per-capita rates.[304] U.S. teenage pregnancy and abortion rates are substantially higher than in other Western nations, especially among blacks and Hispanics.[305]
+
+Health-care coverage in the United States is a combination of public and private efforts and is not universal. In 2017, 12.2% of the population did not carry health insurance.[306] The subject of uninsured and underinsured Americans is a major political issue.[307][308] Federal legislation, passed in early 2010, roughly halved the uninsured share of the population, though the bill and its ultimate effect are issues of controversy.[309][310] The U.S. health-care system far outspends any other nation, measured both in per capita spending and as percentage of GDP.[311] At the same time, the U.S. is a global leader in medical innovation.[312]
+
+American public education is operated by state and local governments, regulated by the United States Department of Education through restrictions on federal grants. In most states, children are required to attend school from the age of six or seven (generally, kindergarten or first grade) until they turn 18 (generally bringing them through twelfth grade, the end of high school); some states allow students to leave school at 16 or 17.[313]
+
+About 12% of children are enrolled in parochial or nonsectarian private schools. Just over 2% of children are homeschooled.[314] The U.S. spends more on education per student than any nation in the world, spending more than $11,000 per elementary student in 2010 and more than $12,000 per high school student.[315][needs update] Some 80% of U.S. college students attend public universities.[316]
+
+Of Americans 25 and older, 84.6% graduated from high school, 52.6% attended some college, 27.2% earned a bachelor's degree, and 9.6% earned graduate degrees.[317] The basic literacy rate is approximately 99%.[202][318] The United Nations assigns the United States an Education Index of 0.97, tying it for 12th in the world.[319]
+
+The United States has many private and public institutions of higher education. The majority of the world's top universities, as listed by various ranking organizations, are in the U.S.[320][321][322] There are also local community colleges with generally more open admission policies, shorter academic programs, and lower tuition.
+
+In 2018, U21, a network of research-intensive universities, ranked the United States first in the world for breadth and quality of higher education, and 15th when GDP was a factor.[323] As for public expenditures on higher education, the U.S. trails some other OECD nations but spends more per student than the OECD average, and more than all nations in combined public and private spending.[315][324] As of 2018[update], student loan debt exceeded 1.5 trillion dollars.[325][326]
+
+The United States is a federal republic of 50 states, a federal district, five territories and several uninhabited island possessions.[327][328][329] It is the world's oldest surviving federation. It is a federal republic and a representative democracy, "in which majority rule is tempered by minority rights protected by law."[330] For 2018, the U.S. ranked 25th on the Democracy Index.[331] On Transparency International's 2019 Corruption Perceptions Index its public sector position deteriorated from a score of 76 in 2015 to 69 in 2019.[332]
+
+In the American federalist system, citizens are usually subject to three levels of government: federal, state, and local. The local government's duties are commonly split between county and municipal governments. In almost all cases, executive and legislative officials are elected by a plurality vote of citizens by district.
+
+The government is regulated by a system of checks and balances defined by the U.S. Constitution, which serves as the country's supreme legal document.[333] The original text of the Constitution establishes the structure and responsibilities of the federal government and its relationship with the individual states. Article One protects the right to the "great writ" of habeas corpus. The Constitution has been amended 27 times;[334] the first ten amendments, which make up the Bill of Rights, and the Fourteenth Amendment form the central basis of Americans' individual rights. All laws and governmental procedures are subject to judicial review and any law ruled by the courts to be in violation of the Constitution is voided. The principle of judicial review, not explicitly mentioned in the Constitution, was established by the Supreme Court in Marbury v. Madison (1803)[335] in a decision handed down by Chief Justice John Marshall.[336]
+
+The federal government comprises three branches:
+
+The House of Representatives has 435 voting members, each representing a congressional district for a two-year term. House seats are apportioned among the states by population. Each state then draws single-member districts to conform with the census apportionment. The District of Columbia and the five major U.S. territories each have one member of Congress—these members are not allowed to vote.[341]
+
+The Senate has 100 members with each state having two senators, elected at-large to six-year terms; one-third of Senate seats are up for election every two years. The District of Columbia and the five major U.S. territories do not have senators.[341] The president serves a four-year term and may be elected to the office no more than twice. The president is not elected by direct vote, but by an indirect electoral college system in which the determining votes are apportioned to the states and the District of Columbia.[342] The Supreme Court, led by the chief justice of the United States, has nine members, who serve for life.[343]
+
+The state governments are structured in a roughly similar fashion, though Nebraska has a unicameral legislature.[344] The governor (chief executive) of each state is directly elected. Some state judges and cabinet officers are appointed by the governors of the respective states, while others are elected by popular vote.
+
+The 50 states are the principal administrative divisions in the country. These are subdivided into counties or county equivalents and further divided into municipalities. The District of Columbia is a federal district that contains the capital of the United States, Washington, D.C.[345] The states and the District of Columbia choose the president of the United States. Each state has presidential electors equal to the number of their representatives and senators in Congress; the District of Columbia has three (because of the 23rd Amendment).[346] Territories of the United States such as Puerto Rico do not have presidential electors, and so people in those territories cannot vote for the president.[341]
+
+The United States also observes tribal sovereignty of the American Indian nations to a limited degree, as it does with the states' sovereignty. American Indians are U.S. citizens and tribal lands are subject to the jurisdiction of the U.S. Congress and the federal courts. Like the states they have a great deal of autonomy, but also like the states, tribes are not allowed to make war, engage in their own foreign relations, or print and issue currency.[347]
+
+Citizenship is granted at birth in all states, the District of Columbia, and all major U.S. territories except American Samoa.[348][349][m]
+
+The United States has operated under a two-party system for most of its history.[352] For elective offices at most levels, state-administered primary elections choose the major party nominees for subsequent general elections. Since the general election of 1856, the major parties have been the Democratic Party, founded in 1824, and the Republican Party, founded in 1854. Since the Civil War, only one third-party presidential candidate—former president Theodore Roosevelt, running as a Progressive in 1912—has won as much as 20% of the popular vote. The president and vice president are elected by the Electoral College.[353]
+
+In American political culture, the center-right Republican Party is considered "conservative" and the center-left Democratic Party is considered "liberal."[354][355] The states of the Northeast and West Coast and some of the Great Lakes states, known as "blue states," are relatively liberal. The "red states" of the South and parts of the Great Plains and Rocky Mountains are relatively conservative.
+
+Republican Donald Trump, the winner of the 2016 presidential election, is serving as the 45th president of the United States.[356] Leadership in the Senate includes Republican vice president Mike Pence, Republican president pro tempore Chuck Grassley, Majority Leader Mitch McConnell, and Minority Leader Chuck Schumer.[357] Leadership in the House includes Speaker of the House Nancy Pelosi, Majority Leader Steny Hoyer, and Minority Leader Kevin McCarthy.[358]
+
+In the 116th United States Congress, the House of Representatives is controlled by the Democratic Party and the Senate is controlled by the Republican Party, giving the U.S. a split Congress. The Senate consists of 53 Republicans and 45 Democrats with two Independents who caucus with the Democrats; the House consists of 233 Democrats, 196 Republicans, and 1 Libertarian.[359] Of state governors, there are 26 Republicans and 24 Democrats. Among the D.C. mayor and the five territorial governors, there are two Republicans, one Democrat, one New Progressive, and two Independents.[360]
+
+The United States has an established structure of foreign relations. It is a permanent member of the United Nations Security Council. New York City is home to the United Nations Headquarters. Almost all countries have embassies in Washington, D.C., and many have consulates around the country. Likewise, nearly all nations host American diplomatic missions. However, Iran, North Korea, Bhutan, and the Republic of China (Taiwan) do not have formal diplomatic relations with the United States (although the U.S. still maintains unofficial relations with Bhutan and Taiwan).[361] It is a member of the G7,[362] G20, and OECD.
+
+The United States has a "Special Relationship" with the United Kingdom[363] and strong ties with India, Canada,[364] Australia,[365] New Zealand,[366] the Philippines,[367] Japan,[368] South Korea,[369] Israel,[370] and several European Union countries, including France, Italy, Germany, Spain and Poland.[371] It works closely with fellow NATO members on military and security issues and with its neighbors through the Organization of American States and free trade agreements such as the trilateral North American Free Trade Agreement with Canada and Mexico. Colombia is traditionally considered by the United States as its most loyal ally in South America.[372][373]
+
+The U.S. exercises full international defense authority and responsibility for Micronesia, the Marshall Islands and Palau through the Compact of Free Association.[374]
+
+Taxation in the United States is levied at the federal, state, and local government levels. This includes taxes on income, payroll, property, sales, imports, estates, and gifts, as well as various fees. Taxation in the United States is based on citizenship, not residency.[375] Both non-resident citizens and Green Card holders living abroad are taxed on their income irrespective of where they live or where their income is earned. The United States is one of the only countries in the world to do so.[376]
+
+In 2010 taxes collected by federal, state and municipal governments amounted to 24.8% of GDP.[377] Based on CBO estimates,[378] under 2013 tax law the top 1% will be paying the highest average tax rates since 1979, while other income groups will remain at historic lows.[379] For 2018, the effective tax rate for the wealthiest 400 households was 23%, compared to 24.2% for the bottom half of U.S. households.[380]
+
+
+
+During fiscal year 2012, the federal government spent $3.54 trillion on a budget or cash basis, down $60 billion or 1.7% vs. fiscal year 2011 spending of $3.60 trillion. Major categories of fiscal year 2012 spending included: Medicare & Medicaid (23%), Social Security (22%), Defense Department (19%), non-defense discretionary (17%), other mandatory (13%) and interest (6%).[382]
+
+The total national debt of the United States in the United States was $18.527 trillion (106% of the GDP) in 2014.[383][n] The United States has the largest external debt in the world[387] and the 34th largest government debt as a % of GDP in the world.[388]
+
+The president is the commander-in-chief of the country's armed forces and appoints its leaders, the Secretary of Defense and the Joint Chiefs of Staff. The United States Department of Defense administers the armed forces, including the Army, Marine Corps, Navy, Air Force, and Space Force. The Coast Guard is run by the Department of Homeland Security in peacetime and by the Department of the Navy during times of war. In 2008, the armed forces had 1.4 million personnel on active duty. The Reserves and National Guard brought the total number of troops to 2.3 million. The Department of Defense also employed about 700,000 civilians, not including contractors.[389]
+
+Military service is voluntary, though conscription may occur in wartime through the Selective Service System.[390] American forces can be rapidly deployed by the Air Force's large fleet of transport aircraft, the Navy's 11 active aircraft carriers, and Marine expeditionary units at sea with the Navy's Atlantic and Pacific fleets. The military operates 865 bases and facilities abroad,[391] and maintains deployments greater than 100 active duty personnel in 25 foreign countries.[392]
+
+The military budget of the United States in 2011 was more than $700 billion, 41% of global military spending. At 4.7% of GDP, the rate was the second-highest among the top 15 military spenders, after Saudi Arabia.[393]  Defense spending plays a major role in science and technology investment, with roughly half of U.S. federal research and development funded by the Department of Defense.[394] Defense's share of the overall U.S. economy has generally declined in recent decades, from Cold War peaks of 14.2% of GDP in 1953 and 69.5% of federal outlays in 1954 to 4.7% of GDP and 18.8% of federal outlays in 2011.[395]
+
+The country is one of the five recognized nuclear weapons states and possesses the second largest stockpile of nuclear weapons in the world.[396] More than 90% of the world's 14,000 nuclear weapons are owned by Russia and the United States.[397]
+
+Law enforcement in the United States is primarily the responsibility of local police departments and sheriff's offices, with state police providing broader services. Federal agencies such as the Federal Bureau of Investigation (FBI) and the U.S. Marshals Service have specialized duties, including protecting civil rights, national security and enforcing U.S. federal courts' rulings and federal laws.[398] State courts conduct most criminal trials while federal courts handle certain designated crimes as well as certain appeals from the state criminal courts.
+
+A cross-sectional analysis of the World Health Organization Mortality Database from 2010 showed that United States "homicide rates were 7.0 times higher than in other high-income countries, driven by a gun homicide rate that was 25.2 times higher."[399] In 2016, the US murder rate was 5.4 per 100,000.[400] Gun ownership rights, guaranteed by the Second Amendment, continue to be the subject of contention.
+
+The United States has the highest documented incarceration rate and largest prison population in the world.[401] As of 2020, the Prison Policy Initiative reported that there were some 2.3 million people incarcerated.[402]  The imprisonment rate for all prisoners sentenced to more than a year in state or federal facilities is 478 per 100,000 in 2013.[403] According to the Federal Bureau of Prisons, the majority of inmates held in federal prisons are convicted of drug offenses.[404] About 9% of prisoners are held in privatized prisons.[402] The practice of privately operated prisons began in the 1980s and has been a subject of contention.[405]
+
+Capital punishment is sanctioned in the United States for certain federal and military crimes, and at the state level in 30 states.[406][407] No executions took place from 1967 to 1977, owing in part to a U.S. Supreme Court ruling striking down arbitrary imposition of the death penalty. Since the decision there have been more than 1,300 executions, a majority of these taking place in three states: Texas, Virginia, and Oklahoma.[408] Meanwhile, several states have either abolished or struck down death penalty laws. In 2019, the country had the sixth-highest number of executions in the world, following China, Iran, Saudi Arabia, Iraq, and Egypt.[409]
+
+According to the International Monetary Fund, the U.S. GDP of $16.8 trillion constitutes 24% of the gross world product at market exchange rates and over 19% of the gross world product at purchasing power parity (PPP).[417] The United States is the largest importer of goods and second-largest exporter, though exports per capita are relatively low. In 2010, the total U.S. trade deficit was $635 billion.[418] Canada, China, Mexico, Japan, and Germany are its top trading partners.[419]
+
+From 1983 to 2008, U.S. real compounded annual GDP growth was 3.3%, compared to a 2.3% weighted average for the rest of the G7.[420] The country ranks ninth in the world in nominal GDP per capita[421] and sixth in GDP per capita at PPP.[417] The U.S. dollar is the world's primary reserve currency.[422]
+
+In 2009, the private sector was estimated to constitute 86.4% of the economy.[425] While its economy has reached a postindustrial level of development, the United States remains an industrial power.[426] Consumer spending comprised 68% of the U.S. economy in 2015.[427] In August 2010, the American labor force consisted of 154.1 million people (50%). With 21.2 million people, government is the leading field of employment. The largest private employment sector is health care and social assistance, with 16.4 million people. It has a smaller welfare state and redistributes less income through government action than most European nations.[428]
+
+The United States is the only advanced economy that does not guarantee its workers paid vacation[429] and is one of a few countries in the world without paid family leave as a legal right.[430] While federal law does not require sick leave, it is a common benefit for government workers and full-time employees at corporations.[431] 74% of full-time American workers get paid sick leave, according to the Bureau of Labor Statistics, although only 24% of part-time workers get the same benefits.[431] In 2009, the United States had the third-highest workforce productivity per person in the world, behind Luxembourg and Norway. It was fourth in productivity per hour, behind those two countries and the Netherlands.[432]
+
+
+
+The United States has been a leader in technological innovation since the late 19th century and scientific research since the mid-20th century. Methods for producing interchangeable parts were developed by the U.S. War Department by the Federal Armories during the first half of the 19th century. This technology, along with the establishment of a machine tool industry, enabled the U.S. to have large-scale manufacturing of sewing machines, bicycles, and other items in the late 19th century and became known as the American system of manufacturing. Factory electrification in the early 20th century and introduction of the assembly line and other labor-saving techniques created the system of mass production.[433] In the 21st century, approximately two-thirds of research and development funding comes from the private sector.[434] The United States leads the world in scientific research papers and impact factor.[435][436]
+
+In 1876, Alexander Graham Bell was awarded the first U.S. patent for the telephone. Thomas Edison's research laboratory, one of the first of its kind, developed the phonograph, the first long-lasting light bulb, and the first viable movie camera.[437] The latter led to emergence of the worldwide entertainment industry. In the early 20th century, the automobile companies of Ransom E. Olds and Henry Ford popularized the assembly line. The Wright brothers, in 1903, made the first sustained and controlled heavier-than-air powered flight.[438]
+
+The rise of fascism and Nazism in the 1920s and 30s led many European scientists, including Albert Einstein, Enrico Fermi, and John von Neumann, to immigrate to the United States.[439] During World War II, the Manhattan Project developed nuclear weapons, ushering in the Atomic Age, while the Space Race produced rapid advances in rocketry, materials science, and aeronautics.[440][441]
+
+The invention of the transistor in the 1950s, a key active component in practically all modern electronics, led to many technological developments and a significant expansion of the U.S. technology industry.[442] This, in turn, led to the establishment of many new technology companies and regions around the country such as Silicon Valley in California. Advancements by American microprocessor companies such as Advanced Micro Devices (AMD), and Intel along with both computer software and hardware companies that include Adobe Systems, Apple Inc., IBM, Microsoft, and Sun Microsystems created and popularized the personal computer. The ARPANET was developed in the 1960s to meet Defense Department requirements, and became the first of a series of networks which evolved into the Internet.[443]
+
+Accounting for 4.24% of the global population, Americans collectively possess 29.4% of the world's total wealth, and Americans make up roughly half of the world's population of millionaires.[444] The Global Food Security Index ranked the U.S. number one for food affordability and overall food security in March 2013.[445] Americans on average have more than twice as much living space per dwelling and per person as European Union residents, and more than every EU nation.[446] For 2017 the United Nations Development Programme ranked the United States 13th among 189 countries in its Human Development Index and 25th among 151 countries in its inequality-adjusted HDI (IHDI).[447]
+
+Wealth, like income and taxes, is highly concentrated; the richest 10% of the adult population possess 72% of the country's household wealth, while the bottom half claim only 2%.[448] According to a September 2017 report by the Federal Reserve, the top 1% controlled 38.6% of the country's wealth in 2016.[449] According to a 2018 study by the OECD, the United States has a larger percentage of low-income workers than almost any other developed nation. This is largely because at-risk workers get almost no government support and are further set back by a very weak collective bargaining system.[450] The top one percent of income-earners accounted for 52 percent of the income gains from 2009 to 2015, where income is defined as market income excluding government transfers.[451] In 2018, U.S. income inequality reached the highest level ever recorded by the Census Bureau.[452]
+
+After years of stagnation, median household income reached a record high in 2016 following two consecutive years of record growth. Income inequality remains at record highs however, with the top fifth of earners taking home more than half of all overall income.[454] The rise in the share of total annual income received by the top one percent, which has more than doubled from nine percent in 1976 to 20 percent in 2011, has significantly affected income inequality,[455] leaving the United States with one of the widest income distributions among OECD nations.[456]  The extent and relevance of income inequality is a matter of debate.[457][458][459]
+
+Between June 2007 and November 2008, the global recession led to falling asset prices around the world. Assets owned by Americans lost about a quarter of their value.[460] Since peaking in the second quarter of 2007, household wealth was down $14 trillion, but has since increased $14 trillion over 2006 levels.[461] At the end of 2014, household debt amounted to $11.8 trillion,[462] down from $13.8 trillion at the end of 2008.[463]
+
+There were about 578,424 sheltered and unsheltered homeless persons in the US in January 2014, with almost two-thirds staying in an emergency shelter or transitional housing program.[464] In 2011, 16.7 million children lived in food-insecure households, about 35% more than 2007 levels, though only 1.1% of U.S. children, or 845,000, saw reduced food intake or disrupted eating patterns at some point during the year, and most cases were not chronic.[465] As of June 2018[update], 40 million people, roughly 12.7% of the U.S. population, were living in poverty, with 18.5 million of those living in deep poverty (a family income below one-half of the poverty threshold) and over five million live "in 'Third World' conditions." In 2016, 13.3 million children were living in poverty, which made up 32.6% of the impoverished population.[466] In 2017, the U.S. state or territory with the lowest poverty rate was New Hampshire (7.6%), and the one with the highest was American Samoa (65%).[467][468][469]
+
+Personal transportation is dominated by automobiles, which operate on a network of 4 million miles (6.4 million kilometers) of public roads.[471] The United States has the world's second-largest automobile market,[472] and has the highest rate of per-capita vehicle ownership in the world, with 765 vehicles per 1,000 Americans (1996).[473][needs update] In 2017, there were 255,009,283 non-two wheel motor vehicles, or about 910 vehicles per 1,000 people.[474]
+
+The civil airline industry is entirely privately owned and has been largely deregulated since 1978, while most major airports are publicly owned.[475] The three largest airlines in the world by passengers carried are US-based; American Airlines is number one after its 2013 acquisition by US Airways.[476] Of the world's 50 busiest passenger airports, 16 are in the United States, including the busiest, Hartsfield–Jackson Atlanta International Airport.[477]
+
+The United States energy market is about 29,000 terawatt hours per year.[478] In 2005, 40% of this energy came from petroleum, 23% from coal, and 22% from natural gas. The remainder was supplied by nuclear and renewable energy sources.[479]
+
+Since 2007, the total greenhouse gas emissions by the United States are the second highest by country, exceeded only by China.[480] The United States has historically been the world's largest producer of greenhouse gases, and greenhouse gas emissions per capita remain high.[481]
+
+The United States is home to many cultures and a wide variety of ethnic groups, traditions, and values.[483][484] Aside from the Native American, Native Hawaiian, and Native Alaskan populations, nearly all Americans or their ancestors settled or immigrated within the past five centuries.[485] Mainstream American culture is a Western culture largely derived from the traditions of European immigrants with influences from many other sources, such as traditions brought by slaves from Africa.[483][486] More recent immigration from Asia and especially Latin America has added to a cultural mix that has been described as both a homogenizing melting pot, and a heterogeneous salad bowl in which immigrants and their descendants retain distinctive cultural characteristics.[483]
+
+Americans have traditionally been characterized by a strong work ethic, competitiveness, and individualism,[487] as well as a unifying belief in an "American creed" emphasizing liberty, equality, private property, democracy, rule of law, and a preference for limited government.[488] Americans are extremely charitable by global standards. According to a 2006 British study, Americans gave 1.67% of GDP to charity, more than any other nation studied.[489][490][491]
+
+The American Dream, or the perception that Americans enjoy high social mobility, plays a key role in attracting immigrants.[492] Whether this perception is accurate has been a topic of debate.[493][494][495][496][420][497] While mainstream culture holds that the United States is a classless society,[498] scholars identify significant differences between the country's social classes, affecting socialization, language, and values.[499] While Americans tend  to greatly value socioeconomic achievement, being ordinary or average is also generally seen as a positive attribute.[500]
+
+In the 18th and early 19th centuries, American art and literature took most of its cues from Europe. Writers such as Washington Irving, Nathaniel Hawthorne, Edgar Allan Poe, and Henry David Thoreau established a distinctive American literary voice by the middle of the 19th century. Mark Twain and poet Walt Whitman were major figures in the century's second half; Emily Dickinson, virtually unknown during her lifetime, is now recognized as an essential American poet.[501] A work seen as capturing fundamental aspects of the national experience and character—such as Herman Melville's Moby-Dick (1851), Twain's The Adventures of Huckleberry Finn (1885), F. Scott Fitzgerald's The Great Gatsby (1925) and Harper Lee's To Kill a Mockingbird (1960)—may be dubbed the "Great American Novel."[502]
+
+Twelve U.S. citizens have won the Nobel Prize in Literature, most recently Bob Dylan in 2016. William Faulkner, Ernest Hemingway and John Steinbeck are often named among the most influential writers of the 20th century.[503] Popular literary genres such as the Western and hardboiled crime fiction developed in the United States. The Beat Generation writers opened up new literary approaches, as have postmodernist authors such as John Barth, Thomas Pynchon, and Don DeLillo.[504]
+
+The transcendentalists, led by Thoreau and Ralph Waldo Emerson, established the first major American philosophical movement. After the Civil War, Charles Sanders Peirce and then William James and John Dewey were leaders in the development of pragmatism. In the 20th century, the work of W. V. O. Quine and Richard Rorty, and later Noam Chomsky, brought analytic philosophy to the fore of American philosophical academia. John Rawls and Robert Nozick also led a revival of political philosophy.
+
+In the visual arts, the Hudson River School was a mid-19th-century movement in the tradition of European naturalism. The 1913 Armory Show in New York City, an exhibition of European modernist art, shocked the public and transformed the U.S. art scene.[505] Georgia O'Keeffe, Marsden Hartley, and others experimented with new, individualistic styles. Major artistic movements such as the abstract expressionism of Jackson Pollock and Willem de Kooning and the pop art of Andy Warhol and Roy Lichtenstein developed largely in the United States. The tide of modernism and then postmodernism has brought fame to American architects such as Frank Lloyd Wright, Philip Johnson, and Frank Gehry.[506] Americans have long been important in the modern artistic medium of photography, with major photographers including Alfred Stieglitz, Edward Steichen, Edward Weston, and Ansel Adams.[507]
+
+Mainstream American cuisine is similar to that in other Western countries. Wheat is the primary cereal grain with about three-quarters of grain products made of wheat flour[508] and many dishes use indigenous ingredients, such as turkey, venison, potatoes, sweet potatoes, corn, squash, and maple syrup which were consumed by Native Americans and early European settlers.[509] These homegrown foods are part of a shared national menu on one of America's most popular holidays, Thanksgiving, when some Americans make traditional foods to celebrate the occasion.[510]
+
+The American fast food industry, the world's largest,[511] pioneered the drive-through format in the 1940s.[512] Characteristic dishes such as apple pie, fried chicken, pizza, hamburgers, and hot dogs derive from the recipes of various immigrants. French fries, Mexican dishes such as burritos and tacos, and pasta dishes freely adapted from Italian sources are widely consumed.[513] Americans drink three times as much coffee as tea.[514] Marketing by U.S. industries is largely responsible for making orange juice and milk ubiquitous breakfast beverages.[515][516]
+
+Although little known at the time, Charles Ives's work of the 1910s established him as the first major U.S. composer in the classical tradition, while experimentalists such as Henry Cowell and John Cage created a distinctive American approach to classical composition. Aaron Copland and George Gershwin developed a new synthesis of popular and classical music.
+
+The rhythmic and lyrical styles of African-American music have deeply influenced American music at large, distinguishing it from European and African traditions. Elements from folk idioms such as the blues and what is now known as old-time music were adopted and transformed into popular genres with global audiences. Jazz was developed by innovators such as Louis Armstrong and Duke Ellington early in the 20th century. Country music developed in the 1920s, and rhythm and blues in the 1940s.[517]
+
+Elvis Presley and Chuck Berry were among the mid-1950s pioneers of rock and roll. Rock bands such as Metallica, the Eagles, and Aerosmith are among the highest grossing in worldwide sales.[518][519][520] In the 1960s, Bob Dylan emerged from the folk revival to become one of America's most celebrated songwriters and James Brown led the development of funk.
+
+More recent American creations include hip hop and house music. American pop stars such as Elvis Presley, Michael Jackson, and Madonna have become global celebrities,[517] as have contemporary musical artists such as Taylor Swift, Britney Spears, Katy Perry, Beyoncé, Jay-Z, Eminem, Kanye West, and Ariana Grande.[521]
+
+Hollywood, a northern district of Los Angeles, California, is one of the leaders in motion picture production.[522] The world's first commercial motion picture exhibition was given in New York City in 1894, using Thomas Edison's Kinetoscope.[523] Since the early 20th century, the U.S. film industry has largely been based in and around Hollywood, although in the 21st century an increasing number of films are not made there, and film companies have been subject to the forces of globalization.[524]
+
+Director D. W. Griffith, the top American filmmaker during the silent film period, was central to the development of film grammar, and producer/entrepreneur Walt Disney was a leader in both animated film and movie merchandising.[525] Directors such as John Ford redefined the image of the American Old West, and, like others such as John Huston, broadened the possibilities of cinema with location shooting. The industry enjoyed its golden years, in what is commonly referred to as the "Golden Age of Hollywood," from the early sound period until the early 1960s,[526] with screen actors such as John Wayne and Marilyn Monroe becoming iconic figures.[527][528] In the 1970s, "New Hollywood" or the "Hollywood Renaissance"[529] was defined by grittier films influenced by French and Italian realist pictures of the post-war period.[530] In more recent times, directors such as Steven Spielberg, George Lucas and James Cameron have gained renown for their blockbuster films, often characterized by high production costs and earnings.
+
+Notable films topping the American Film Institute's AFI 100 list include Orson Welles's Citizen Kane (1941), which is frequently cited as the greatest film of all time,[531][532] Casablanca (1942), The Godfather (1972), Gone with the Wind (1939), Lawrence of Arabia (1962), The Wizard of Oz (1939), The Graduate (1967), On the Waterfront (1954), Schindler's List (1993), Singin' in the Rain (1952), It's a Wonderful Life (1946) and Sunset Boulevard (1950).[533] The Academy Awards, popularly known as the Oscars, have been held annually by the Academy of Motion Picture Arts and Sciences since 1929,[534] and the Golden Globe Awards have been held annually since January 1944.[535]
+
+American football is by several measures the most popular spectator sport;[537] the National Football League (NFL) has the highest average attendance of any sports league in the world, and the Super Bowl is watched by tens of millions globally. Baseball has been regarded as the U.S. national sport since the late 19th century, with Major League Baseball (MLB) being the top league. Basketball and ice hockey are the country's next two leading professional team sports, with the top leagues being the National Basketball Association (NBA) and the National Hockey League (NHL). College football and basketball attract large audiences.[538] In soccer, the country hosted the 1994 FIFA World Cup, the men's national soccer team qualified for ten World Cups and the women's team has won the FIFA Women's World Cup four times; Major League Soccer is the sport's highest league in the United States (featuring 23 American and three Canadian teams). The market for professional sports in the United States is roughly $69 billion, roughly 50% larger than that of all of Europe, the Middle East, and Africa combined.[539]
+
+Eight Olympic Games have taken place in the United States. The 1904 Summer Olympics in St. Louis, Missouri were the first ever Olympic Games held outside of Europe.[540] As of 2017[update], the United States has won 2,522 medals at the Summer Olympic Games, more than any other country, and 305 in the Winter Olympic Games, the second most behind Norway.[541]
+While most major U.S. sports such as baseball and American football have evolved out of European practices, basketball, volleyball, skateboarding, and snowboarding are American inventions, some of which have become popular worldwide. Lacrosse and surfing arose from Native American and Native Hawaiian activities that predate Western contact.[542] The most watched individual sports are golf and auto racing, particularly NASCAR.[543][544]
+
+The four major broadcasters in the U.S. are the National Broadcasting Company (NBC), Columbia Broadcasting System (CBS), American Broadcasting Company (ABC), and Fox Broadcasting Company (FOX). The four major broadcast television networks are all commercial entities. Cable television offers hundreds of channels catering to a variety of niches.[545] Americans listen to radio programming, also largely commercial, on average just over two-and-a-half hours a day.[546]
+
+In 1998, the number of U.S. commercial radio stations had grown to 4,793 AM stations and 5,662 FM stations. In addition, there are 1,460 public radio stations. Most of these stations are run by universities and public authorities for educational purposes and are financed by public or private funds, subscriptions, and corporate underwriting. Much public-radio broadcasting is supplied by NPR. NPR was incorporated in February 1970 under the Public Broadcasting Act of 1967; its television counterpart, PBS, was created by the same legislation. As of September 30, 2014[update], there are 15,433 licensed full-power radio stations in the U.S. according to the U.S. Federal Communications Commission (FCC).[547]
+
+Well-known newspapers include The Wall Street Journal, The New York Times, and USA Today.[548] Although the cost of publishing has increased over the years, the price of newspapers has generally remained low, forcing newspapers to rely more on advertising revenue and on articles provided by a major wire service, such as the Associated Press or Reuters, for their national and world coverage. With very few exceptions, all the newspapers in the U.S. are privately owned, either by large chains such as Gannett or McClatchy, which own dozens or even hundreds of newspapers; by small chains that own a handful of papers; or in a situation that is increasingly rare, by individuals or families. Major cities often have "alternative weeklies" to complement the mainstream daily papers, such as New York City's The Village Voice or Los Angeles' LA Weekly. Major cities may also support a local business journal, trade papers relating to local industries, and papers for local ethnic and social groups. Aside from web portals and search engines, the most popular websites are Facebook, YouTube, Wikipedia, Yahoo!, eBay, Amazon, and Twitter.[549]
+
+More than 800 publications are produced in Spanish, the second most commonly used language in the United States behind English.[550][551]
+
+Internet sources
+

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+Jean-Baptiste Poquelin (baptised 15 January 1622; died 17 February 1673), known by his stage name Molière (UK: /ˈmɒliɛər, ˈmoʊl-/, US: /moʊlˈjɛər, ˌmoʊliˈɛər/,[1][2][3] French: [mɔljɛʁ]), was a French playwright, actor and poet, widely regarded as one of the greatest writers in the French language and universal literature. His extant works include comedies, farces, tragicomedies, comédie-ballets and more. His plays have been translated into every major living language and are performed at the Comédie-Française more often than those of any other playwright today.[4] His influence is such that the French language itself is often referred to as the "language of Molière".[5][6]
+
+Born into a prosperous family and having studied at the Collège de Clermont (now Lycée Louis-le-Grand), Molière was well suited to begin a life in the theatre. Thirteen years as an itinerant actor helped him polish his comic abilities while he began writing, combining Commedia dell'arte elements with the more refined French comedy.[7]
+
+Through the patronage of aristocrats including Philippe I, Duke of Orléans—the brother of Louis XIV—Molière procured a command performance before the King at the Louvre. Performing a classic play by Pierre Corneille and a farce of his own, The Doctor in Love, Molière was granted the use of salle du Petit-Bourbon near the Louvre, a spacious room appointed for theatrical performances. Later, he was granted the use of the theatre in the Palais-Royal. In both locations Molière found success among Parisians with plays such as The Affected Ladies, The School for Husbands and The School for Wives. This royal favour brought a royal pension to his troupe and the title Troupe du Roi ("The King's Troupe"). Molière continued as the official author of court entertainments.[8]
+
+Despite the adulation of the court and Parisians, Molière's satires attracted criticism from churchmen. For Tartuffe's impiety, the Catholic Church denounced this study of religious hypocrisy followed by the Parliament's ban, while Don Juan was withdrawn and never restaged by Molière.[9]  His hard work in so many theatrical capacities took its toll on his health and, by 1667, he was forced to take a break from the stage. In 1673, during a production of his final play, The Imaginary Invalid, Molière, who suffered from pulmonary tuberculosis, was seized by a coughing fit and a haemorrhage while playing the hypochondriac Argan. He finished the performance but collapsed again and died a few hours later.[8]
+
+Molière was born in Paris shortly before his christening as Jean Poquelin on 15 January 1622. Known as Jean-Baptiste, he was the first son of Jean Poquelin and Marie Cressé, who had married on 27 April 1621.[10] His mother was the daughter of a prosperous bourgeois family.[11] Upon seeing him for the first time, a maid exclaimed, "Le nez!", a reference to the infant's large nose.  Molière was called "Le Nez" by his family from that time.[12] He lost his mother when he was eleven, and he does not seem to have been particularly close to his father. After his mother's death, he lived with his father above the Pavillon des Singes on the rue Saint-Honoré, an affluent area of Paris. It is likely that his education commenced with studies at a Parisian elementary school,[13] followed by his enrolment in the prestigious Jesuit Collège de Clermont, where he completed his studies in a strict academic environment and got a first taste of life on the stage.[14]
+
+In 1631, his father Jean Poquelin purchased from the court of Louis XIII the posts of "valet de chambre ordinaire et tapissier du Roi" ("valet of the King's chamber and keeper of carpets and upholstery"). His son assumed the same posts in 1641.[15] The title required only three months' work and an initial cost of 1,200 livres; the title paid 300 livres a year and provided a number of lucrative contracts. Molière also studied as a provincial lawyer some time around 1642, probably in Orléans, but it is not documented that he ever qualified. So far he had followed his father's plans, which had served him well; he had mingled with nobility at the Collège de Clermont and seemed destined for a career in office.
+
+In June 1643, when Molière was 21, he decided to abandon his social class and pursue a career on the stage. Taking leave of his father, he joined the actress Madeleine Béjart, with whom he had crossed paths before, and founded the Illustre Théâtre with 630 livres. They were later joined by Madeleine's brother and sister.
+
+The new theatre troupe went bankrupt in 1645. Molière had become head of the troupe, due in part, perhaps, to his acting prowess and his legal training. However, the troupe had acquired large debts, mostly for the rent of the theatre (a court for jeu de paume), for which they owed 2000 livres. Historians differ as to whether his father or the lover of a member of his troupe paid his debts; either way, after a 24-hour stint in prison he returned to the acting circuit. It was at this time that he began to use the pseudonym Molière, possibly inspired by a small village of the same name in the Midi near Le Vigan. It was also likely that he changed his name to spare his father the shame of having an actor in the family (actors, although no longer vilified by the state under Louis XIV, were still not allowed to be buried in sacred ground).
+
+After his imprisonment, he and Madeleine began a theatrical circuit of the provinces with a new theatre troupe; this life was to last about twelve years, during which he initially played in the company of Charles Dufresne, and subsequently created a company of his own, which had sufficient success and obtained the patronage of Philippe I, Duke of Orléans. Few plays survive from this period. The most noteworthy are L'Étourdi ou les Contretemps (The Bungler) and Le Docteur Amoureux (The Doctor in Love); with these two plays, Molière moved away from the heavy influence of the Italian improvisational Commedia dell'arte, and displayed his talent for mockery. In the course of his travels he met Armand, Prince of Conti, the governor of Languedoc, who became his patron, and named his company after him. This friendship later ended when Armand, having contracted syphilis from a courtesan, turned towards religion and joined Molière's enemies in the Parti des Dévots and the Compagnie de Saint Sacrement.
+
+In Lyon, Mademoiselle Du Parc, known as Marquise, joined the company. Marquise was courted, in vain, by Pierre Corneille and later became the lover of Jean Racine. Racine offered Molière his tragedy Théagène et Chariclée (one of the first works he wrote after he had abandoned his theology studies), but Molière would not perform it, though he encouraged Racine to pursue his artistic career. It is said that soon thereafter Molière became angry with Racine when he was told that he had secretly presented his tragedy to the company of the Hôtel de Bourgogne as well.
+
+Molière was forced to reach Paris in stages, staying outside for a few weeks in order to promote himself with society gentlemen and allow his reputation to feed in to Paris. Molière reached Paris in 1658 and performed in front of the King at the Louvre (then for rent as a theatre) in Corneille's tragedy Nicomède and in the farce Le Docteur Amoureux with some success. He was awarded the title of Troupe de Monsieur (Monsieur being the honorific for the king's brother Philippe I, Duke of Orléans). With the help of Monsieur, his company was allowed to share the theatre in the large hall of the Petit-Bourbon with the famous Italian Commedia dell'arte company of Tiberio Fiorillo, famous for his character of Scaramouche. (The two companies performed in the theatre on different nights.) The premiere of Molière's Les Précieuses Ridicules (The Affected Young Ladies) took place at the Petit-Bourbon on 18 November 1659.
+
+Les Précieuses Ridicules was the first of Molière's many attempts to satirize certain societal mannerisms and affectations then common in France. It is widely accepted that the plot was based on Samuel Chappuzeau's Le Cercle des Femmes of 1656. He primarily mocks the Académie Française, a group created by Richelieu under a royal patent to establish the rules of the fledgling French theatre. The Académie preached unity of time, action, and styles of verse. Molière is often associated with the claim that comedy castigat ridendo mores or "criticises customs through humour" (a phrase in fact coined by his contemporary Jean de Santeuil and sometimes mistaken for a classical Latin proverb).[16]
+
+Despite his own preference for tragedy, which he had tried to further with the Illustre Théâtre, Molière became famous for his farces, which were generally in one act and performed after the tragedy. Some of these farces were only partly written, and were played in the style of Commedia dell'arte with improvisation over a canovaccio (a vague plot outline). He began to write full, five-act comedies in verse (L'Étourdi (Lyon, 1654) and Le dépit amoureux (Béziers, 1656)), which although immersed in the gags of contemporary Italian troupes, were successful as part of Madeleine Béjart and Molière's plans to win aristocratic patronage and, ultimately, move the troupe to a position in a Paris theater-venue.[17] Later Molière concentrated on writing musical comedies, in which the drama is interrupted by songs and/or dances, but for years the fundamentals of numerous comedy-traditions would remain strong, especially Italian (e.g. the semi-improvisatory style that in the 1750s writers started calling commedia dell'arte), Spanish, and French plays, all also drawing on classical models (e.g. Plautus and Terence), especially the trope of the clever slave/servant.[18]
+
+Les précieuses ridicules won Molière the attention and the criticism of many, but it was not a popular success. He then asked Fiorillo to teach him the techniques of Commedia dell'arte. His 1660 play Sganarelle, ou Le Cocu imaginaire (The Imaginary Cuckold) seems to be a tribute both to Commedia dell'arte and to his teacher. Its theme of marital relationships dramatizes Molière's pessimistic views on the falsity inherent in human relationships. This view is also evident in his later works and was a source of inspiration for many later authors, including (in a different field and with different effect) Luigi Pirandello. It describes a kind of round dance where two couples believe that each of their partners has been betrayed by the other's and is the first in Molière's "Jealousy series", which includes Dom Garcie de Navarre, L'École des maris and L'École des femmes.
+
+In 1660 the Petit-Bourbon was demolished to make way for the eastern expansion of the Louvre, but Molière's company was allowed to move into the abandoned theatre in the east wing of the Palais-Royal. After a period of refurbishment they opened there on 20 January 1661. In order to please his patron, Monsieur, who was so enthralled with entertainment and art that he was soon excluded from state affairs, Molière wrote and played Dom Garcie de Navarre ou Le Prince jaloux (The Jealous Prince, 4 February 1661), a heroic comedy derived from a work of Cicognini's. Two other comedies of the same year were the successful L'École des maris (The School for Husbands) and Les Fâcheux, subtitled Comédie faite pour les divertissements du Roi (a comedy for the King's amusements) because it was performed during a series of parties that Nicolas Fouquet gave in honor of the sovereign. These entertainments led Jean-Baptiste Colbert to demand the arrest of Fouquet for wasting public money, and he was condemned to life imprisonment.[19]
+
+On 20 February 1662 Molière married Armande Béjart, whom he believed to be the sister of Madeleine. (She may instead have been her illegitimate daughter with the Duke of Modena.) The same year he premiered L'École des femmes (The School for Wives), subsequently regarded as a masterpiece. It poked fun at the limited education that was given to daughters of rich families and reflected Molière's own marriage. Both this work and his marriage attracted much criticism. The play sparked the protest called the "Quarrel of L'École des femmes". On the artistic side he responded with two lesser-known works: La Critique de "L'École des femmes", in which he imagined the spectators of his previous work attending it. The piece mocks the people who had criticised L'École des femmes by showing them at dinner after watching the play; it addresses all the criticism raised about the piece by presenting the critics' arguments and then dismissing them. This was the so-called Guerre comique (War of Comedy), in which the opposite side was taken by writers like Donneau de Visé, Edmé Boursault, and Montfleury.
+
+But more serious opposition was brewing, focusing on Molière's politics and his personal life. A so-called parti des Dévots arose in French high society, who protested against Molière's excessive "realism" and irreverence, which were causing some embarrassment. These people accused Molière of having married his daughter. The Prince of Conti, once Molière's friend, joined them. Molière had other enemies, too, among them the Jansenists and some traditional authors. However, the king expressed support for the author, granting him a pension and agreeing to be the godfather of Molière's first son. Boileau also supported him through statements that he included in his Art poétique.
+
+Molière's friendship with Jean-Baptiste Lully influenced him towards writing his Le Mariage forcé and La Princesse d'Élide (subtitled as Comédie galante mêlée de musique et d'entrées de ballet), written for royal "divertissements" at the Palace of Versailles.
+
+Tartuffe, ou L'Imposteur was also performed at Versailles, in 1664, and created the greatest scandal of Molière's artistic career. Its depiction of the hypocrisy of the dominant classes was taken as an outrage and violently contested. It also aroused the wrath of the Jansenists and the play was banned.
+
+Molière was always careful not to attack the institution of monarchy. He earned a position as one of the king's favourites and enjoyed his protection from the attacks of the court. The king allegedly suggested that Molière suspend performances of Tartuffe, and the author rapidly wrote Dom Juan ou le Festin de Pierre to replace it. It was a strange work, derived from a work by Tirso de Molina and rendered in a prose that still seems modern today. It describes the story of an atheist who becomes a religious hypocrite and for this is punished by God. This work too was quickly suspended. The king, demonstrating his protection once again, became the new official sponsor of Molière's troupe.
+
+With music by Lully, Molière presented L'Amour médecin (Love Doctor or Medical Love). Subtitles on this occasion reported that the work was given "par ordre du Roi" (by order of the king) and this work was received much more warmly than its predecessors.
+
+In 1666, Le Misanthrope was produced. It is now widely regarded as Molière's most refined masterpiece, the one with the highest moral content, but it was little appreciated at its time. It caused the "conversion" of Donneau de Visé, who became fond of his theatre. But it was a commercial flop, forcing Molière to immediately write Le médecin malgré lui (The Doctor Despite Himself), a satire against the official sciences. This was a success despite a moral treatise by the Prince of Conti, criticizing the theatre in general and Molière in particular. In several of his plays, Molière depicted the physicians of his day as pompous individuals who speak (poor) Latin to impress others with false erudition, and know only clysters and bleedings as (ineffective) remedies.
+
+After the Mélicerte and the Pastorale comique, he tried again to perform a revised Tartuffe in 1667, this time with the name of Panulphe or L'Imposteur. As soon as the King left Paris for a tour, Lamoignon and the archbishop banned the play. The King finally imposed respect for Tartuffe a few years later, after he had gained more power over the clergy.
+
+Molière, now ill, wrote less. Le Sicilien ou L'Amour peintre was written for festivities at the castle of Saint-Germain-en-Laye, and was followed in 1668 by Amphitryon, inspired both by Plautus' work of the same name and Jean Rotrou's successful reconfiguration of the drama. With some conjecture, Molière's play can be seen to allude to the love affairs of Louis XIV, then king of France. George Dandin, ou Le mari confondu (The Confounded Husband) was little appreciated, but success returned with L'Avare (The Miser), now very well known.
+
+With Lully he again used music for Monsieur de Pourceaugnac, for Les Amants magnifiques, and finally for Le Bourgeois gentilhomme (The Middle Class Gentleman), another of his masterpieces. It is claimed to be particularly directed against Colbert, the minister who had condemned his old patron Fouquet. The collaboration with Lully ended with a tragédie et ballet, Psyché, written in collaboration with Pierre Corneille and Philippe Quinault.
+
+In 1672, Madeleine Béjart died, and Molière suffered from this loss and from the worsening of his own illness. Nevertheless, he wrote a successful Les Fourberies de Scapin ("Scapin's Deceits"), a farce and a comedy in five acts. His following play, La Comtesse d'Escarbagnas, is considered one of his lesser works.
+
+Les Femmes savantes (The Learned Ladies) of 1672 is considered another of Molière's masterpieces. It was born from the termination of the legal use of music in theatre, since Lully had patented the opera in France (and taken most of the best available singers for his own performances), so Molière had to go back to his traditional genre. It was a great success, and it led to his last work (see below), which is still held in high esteem.
+
+In his 14 years in Paris, Molière singlehandedly wrote 31 of the 85 plays performed on his stage.
+
+In 1661, Molière introduced the comédies-ballets in conjunction with Les Fâcheux.  These ballets were a transitional form of dance performance between the court ballets of Louis XIV and the art of professional theatre which was developing in the advent of the use of the proscenium stage.[20]   The comédies-ballets developed accidentally when Molière was enlisted to mount both a play and a ballet in the honor of Louis XIV and found that he did not have a big enough cast to meet these demands.  Molière therefore decided to combine the ballet and the play so that his goal could be met while the performers catch their breath and change costume.[20] The risky move paid off and Molière was asked to produce twelve more comédies-ballets before his death.[20] During the comédies-ballets, Molière collaborated with Pierre Beauchamp.[20] Beauchamp codified the five balletic positions of the feet and arms and was partly responsible for the creation of the Beauchamp-Feuillet dance notation.[21] Molière also collaborated with Jean-Baptiste Lully.[20] Lully was a dancer, choreographer, and composer, whose dominant reign at the Paris Opéra lasted fifteen years.  Under his command, ballet and opera rightly became professional arts unto themselves.[22] The comédies-ballets closely integrated dance with music and the action of the play and the style of continuity distinctly separated these performances from the court ballets of the time;[23] additionally, the comédies-ballets demanded that both the dancers and the actors play an important role in advancing the story. Similar to the court ballets, both professionally trained dancers and courtiers socialized together at the comédies-ballets - Louis XIV even played the part of an Egyptian in Molière's Le Mariage forcé (1664) and also appeared as Neptune and Apollo in his retirement performance of Les Amants magnifiques (1670).[23]
+
+Molière suffered from pulmonary tuberculosis, possibly contracted when he was imprisoned for debt as a young man. One of the most famous moments in Molière's life was his last, which became legend: he collapsed on stage in a fit of coughing and haemorrhaging while performing in the last play he had written, which had lavish ballets performed to the music of Marc-Antoine Charpentier and which ironically was entitled Le Malade imaginaire (The Imaginary Invalid). Molière insisted on completing his performance. Afterwards he collapsed again with another, larger haemorrhage before being taken home, where he died a few hours later, without receiving the last rites because two priests refused to visit him while a third arrived too late. The superstition that green brings bad luck to actors is said to originate from the colour of the clothing he was wearing at the time of his death.
+
+Under French law at the time, actors were not allowed to be buried in the sacred ground of a cemetery. However, Molière's widow, Armande, asked the King if her spouse could be granted a normal funeral at night. The King agreed and Molière's body was buried in the part of the cemetery reserved for unbaptised infants.
+
+In 1792 his remains were brought to the museum of French monuments and in 1817 transferred to Père Lachaise Cemetery in Paris, close to those of La Fontaine.
+
+Though conventional thinkers, religious leaders and medical professionals in Molière's time criticised his work, their ideas did not really diminish his widespread success with the public. Other playwrights and companies began to emulate his dramatic style in England and in France. Molière's works continued to garner positive feedback in 18th-century England, but they were not so warmly welcomed in France at this time. However, during the French Restoration of the 19th century, Molière's comedies became popular with both the French public and the critics. Romanticists admired his plays for the unconventional individualism they portrayed. 20th-century scholars have carried on this interest in Molière and his plays and have continued to study a wide array of issues relating to this playwright. Many critics now are shifting their attention from the philosophical, religious and moral implications in his comedies to the more objective study of his comic technique.[24]
+
+Molière's works were translated into English prose by John Ozell in 1714,[25] but the first complete version in English, by Baker and Miller in 1739, remained "influential" and was long reprinted.[26] The first to offer full translations of Molière's verse plays such as Tartuffe into English verse was Curtis Hidden Page, who produced blank verse versions of three of the plays in his 1908 translation.[27] Since then, notable translations have been made by Richard Wilbur, Donald M. Frame, and many others.
+
+In his memoir A Terrible Liar, actor Hume Cronyn writes that, in 1962, celebrated actor Laurence Olivier criticized Molière. According to Cronyn, he mentioned to Olivier that he (Cronyn) was about to play the title role in The Miser, and that Olivier then responded, "Molière? Funny as a baby's open grave." Cronyn comments on the incident: "You may imagine how that made me feel. Fortunately, he was dead wrong."[28]
+
+Author Martha Bellinger points out that:
+
+[Molière] has been accused of not having a consistent, organic style, of using faulty grammar, of mixing his metaphors, and of using unnecessary words for the purpose of filling out his lines. All these things are occasionally true, but they are trifles in comparison to the wealth of character he portrayed, to his brilliancy of wit, and to the resourcefulness of his technique. He was wary of sensibility or pathos; but in place of pathos he had "melancholy — a puissant and searching melancholy, which strangely sustains his inexhaustible mirth and his triumphant gaiety".[29]
+
+Molière is considered the creator of modern French comedy. Many words or phrases used in Molière's plays are still used in current French:
+
+French and 
+Francophone literature
+
+French literature 
+By category 
+French language
+
+Medieval
+16th century • 17th century
+18th century • 19th century
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+
+Francophone literature
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+
+Chronological list
+
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+Short story writers
+
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+
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+
+Literary theory •
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+
+Molière • Racine •
+Balzac
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+Zola •
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+
+France • Literature
+
+Molière plays a small part in Alexandre Dumas's novel The Vicomte of Bragelonne, in which he is seen taking inspiration from the muskeeter Porthos for his central character in Le Bourgeois Gentilhomme.
+
+Russian writer Mikhail Bulgakov wrote a semi-fictitious biography-tribute to Molière, titled Life of Mr. de Molière. Written 1932–1933, first published 1962.
+
+The French 1978 film simply titled Molière directed by Ariane Mnouchkine and starring Philippe Caubère presents his complete biography. It was in competition for the Palme d'Or at Cannes in 1978.
+
+He is portrayed among other writers in The Blasphemers' Banquet (1989).
+
+The 2000 film Le Roi Danse (The King Dances), in which Molière is played by Tchéky Karyo, shows his collaborations with Jean-Baptiste Lully, as well as his illness and on-stage death.
+
+The 2007 French film Molière was more loosely based on the life of Molière, starring Romain Duris, Fabrice Luchini and Ludivine Sagnier.
+
+David Hirson's play La Bête, itself in the style of Molière, includes the character Elomire as an anagrammatic parody of him.

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+A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. There are no official definitions for the generic term river as applied to  geographic features,[1] although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and northeast England, and "beck" in northern England. Sometimes a river is defined as being larger than a creek,[2] but not always: the language is vague.[1]
+
+Rivers are part of the hydrological cycle. Water generally collects in a river from precipitation through a drainage basin from surface runoff and other sources such as groundwater recharge, springs, and the release of stored water in natural ice and snowpacks (e.g., from glaciers).
+
+Rivers and streams are often considered major features within a landscape, however, they actually only cover around 0.1% of the land on Earth. They are made more obvious and significant to humans by the fact that many human cities and civilizations are built around the freshwater supplied by rivers and streams.[3] Most of the major cities of the world are situated on the banks of rivers, as they are, or were, used as a source of water, for obtaining food, for transport, as borders, as a defensive measure, as a source of hydropower to drive machinery, for bathing, and as a means of disposing of waste.
+
+Potamology is the scientific study of rivers, while limnology is the study of inland waters in general.
+
+A river begins at a source (or more often several sources), follows a path called a course, and ends at a mouth or mouths. The water in a river is usually confined to a channel, made up of a stream bed between banks. In larger rivers there is often also a wider floodplain shaped by flood-waters over-topping the channel. Floodplains may be very wide in relation to the size of the river channel. This distinction between river channel and floodplain can be blurred, especially in urban areas where the floodplain of a river channel can become greatly developed by housing and industry.
+
+Rivers can flow down mountains, through valleys (depressions) or along plains, and can create canyons or gorges.
+
+The term upriver (or upstream) refers to the direction towards the source of the river, i.e. against the direction of flow. Likewise, the term downriver (or downstream) describes the direction towards the mouth of the river, in which the current flows.
+
+The term left bank refers to the left bank in the direction of flow, right bank to the right.
+
+The river channel typically contains a single stream of water, but some rivers flow as several interconnecting streams of water, producing a braided river.[4] Extensive braided rivers are now found in only a few regions worldwide,[citation needed] such as the South Island of New Zealand. They also occur on peneplains and some of the larger river deltas. Anastamosing rivers are similar to braided rivers and are quite rare. They have multiple sinuous channels carrying large volumes of sediment. There are rare cases of river bifurcation in which a river divides and the resultant flows ending in different seas. An example is the bifurcation of Nerodime River in Kosovo.
+
+A river flowing in its channel is a source of energy which acts on the river channel to change its shape and form. In 1757, the German hydrologist Albert Brahms empirically observed that the submerged weight of objects that may be carried away by a river is proportional to the sixth power of the river flow speed.[5] This formulation is also sometimes called Airy's law.[6] Thus, if the speed of flow is doubled, the flow would dislodge objects with 64 times as much submerged weight. In mountainous torrential zones this can be seen as erosion channels through hard rocks and the creation of sands and gravels from the destruction of larger rocks. A river valley that was created from a U-shaped glaciated valley, can often easily be identified by the V-shaped channel that it has carved. In the middle reaches where a river flows over flatter land, meanders may form through erosion of the river banks and deposition on the inside of bends. Sometimes the river will cut off a loop, shortening the channel and forming an oxbow lake or billabong. Rivers that carry large amounts of sediment may develop conspicuous deltas at their mouths. Rivers whose mouths are in saline tidal waters may form estuaries.
+
+Throughout the course of the river, the total volume of water transported downstream will often be a combination of the free water flow together with a substantial volume flowing through sub-surface rocks and gravels that underlie the river and its floodplain (called the hyporheic zone). For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow.
+
+Most but not all rivers flow on the surface. Subterranean rivers flow underground in caves or caverns. Such rivers are frequently found in regions with limestone geologic formations. Subglacial streams are the braided rivers that flow at the beds of glaciers and ice sheets, permitting meltwater to be discharged at the front of the glacier. Because of the gradient in pressure due to the overlying weight of the glacier, such streams can even flow uphill.
+
+An intermittent river (or ephemeral river) only flows occasionally and can be dry for several years at a time. These rivers are found in regions with limited or highly variable rainfall, or can occur because of geologic conditions such as a highly permeable river bed. Some ephemeral rivers flow during the summer months but not in the winter. Such rivers are typically fed from chalk aquifers which recharge from winter rainfall. In England these rivers are called bournes and give their name to places such as Bournemouth and Eastbourne. Even in humid regions, the location where flow begins in the smallest tributary streams generally moves upstream in response to precipitation and downstream in its absence or when active summer vegetation diverts water for evapotranspiration. Normally-dry rivers in arid zones are often identified as arroyos or other regional names.
+
+The meltwater from large hailstorms can create a slurry of water, hail and sand or soil, forming temporary rivers.[7]
+
+Rivers have been classified by many criteria including their topography, their biotic status, and their relevance to white water rafting or canoeing activities.
+
+Rivers can generally be classified as either alluvial, bedrock, or some mix of the two. Alluvial rivers have channels and floodplains that are self-formed in unconsolidated or weakly consolidated sediments. They erode their banks and deposit material on bars and their floodplains. Bedrock rivers form when the river downcuts through the modern sediments and into the underlying bedrock. This occurs in regions that have experienced some kind of uplift (thereby steepening river gradients) or in which a particular hard lithology causes a river to have a steepened reach that has not been covered in modern alluvium. Bedrock rivers very often contain alluvium on their beds; this material is important in eroding and sculpting the channel. Rivers that go through patches of bedrock and patches of deep alluvial cover are classified as mixed bedrock-alluvial.
+
+Alluvial rivers can be further classified by their channel pattern as meandering, braided, wandering, anastomose, or straight. The morphology of an alluvial river reach is controlled by a combination of sediment supply, substrate composition, discharge, vegetation, and bed aggradation.
+
+At the start of the 20th century William Morris Davis devised the "cycle of erosion" method of classifying rivers based on their "age". Although Davis's system is still found in many books today, after the 1950s and 1960s it became increasingly criticized and rejected by geomorphologists. His scheme did not produce testable hypotheses and was therefore deemed non-scientific.[8] Examples of Davis's river "ages" include:
+
+The ways in which a river's characteristics vary between its upper and lower course are summarized by the Bradshaw model. Power-law relationships between channel slope, depth, and width are given as a function of discharge by "river regime".
+
+There are several systems of classification based on biotic conditions typically assigning classes from the most oligotrophic or unpolluted through to the most eutrophic or polluted.[9] Other systems are based on a whole eco-system approach such as developed by the New Zealand Ministry for the Environment.[10]
+In Europe, the requirements of the Water Framework Directive has led to the development of a wide range of classification methods including classifications based on fishery status[11]
+A system of river zonation used in francophone communities[12][13]  divides rivers into three primary zones:
+
+The  International Scale of River Difficulty is used to rate the challenges of navigation—particularly those with rapids. Class I is the easiest and Class VI is the hardest.
+
+The Strahler Stream Order ranks rivers based on the connectivity and hierarchy of contributing tributaries. Headwaters are first order while the Amazon River is twelfth order. Approximately 80% of the rivers and streams in the world are of the first and second order.
+
+In certain languages, distinctions are made among rivers based on their stream order. In French, for example, rivers that run to the sea are called fleuve, while other rivers are called rivière. For example, in Canada, the Churchill River in Manitoba is called la rivière Churchill as it runs to Hudson Bay, but the Churchill River in Labrador is called le fleuve Churchill as it runs to the Atlantic Ocean. As most rivers in France are known by their names only without the word rivière or fleuve (e.g. la Seine, not le fleuve Seine, even though the Seine is classed as a fleuve), one of the most prominent rivers in the Francophonie commonly known as fleuve is le fleuve Saint-Laurent (the Saint Lawrence River).
+
+Since many fleuves are large and prominent, receiving many tributaries, the word is sometimes used to refer to certain large rivers that flow into other fleuves; however, even small streams that run to the sea are called fleuve (e.g. fleuve côtier, "coastal fleuve").
+
+Rivers have been a source of food since pre-history.[14] They are often a rich source of fish and other edible aquatic life, and are a major source of fresh water, which can be used for drinking and irrigation. Rivers help to determine the urban form of cities and neighbourhoods and their corridors often present opportunities for urban renewal through the development of foreshoreways such as river walks. Rivers also provide an easy means of disposing of waste water and, in much of the less developed world, other wastes.
+
+Rivers have been used for navigation for thousands of years. The earliest evidence of navigation is found in the Indus Valley Civilization, which existed in northwestern India around 3300 BC.[15] Riverine navigation provides a cheap means of transport, and is still used extensively on most major rivers of the world like the Amazon, the Ganges, the Nile, the Mississippi, and the Indus. Since river boats are often not regulated, they contribute a large amount to global greenhouse gas emissions, and to local cancer due to inhaling of particulates emitted by the transports.[16][17]
+
+Rivers have been important in determining political boundaries and defending countries. For example, the Danube was a long-standing border of the Roman Empire, and today it forms most of the border between Bulgaria and Romania. The Mississippi in North America and the Rhine in Europe are major east-west boundaries in those continents. The Orange and Limpopo Rivers in southern Africa form the boundaries between provinces and countries along their routes.
+
+In some heavily forested regions such as Scandinavia and Canada, lumberjacks use the river to float felled trees downstream to lumber camps for further processing, saving much effort and cost by transporting the huge heavy logs by natural means.
+
+Fast flowing rivers and waterfalls are widely used as sources of energy, via watermills and hydroelectric plants. Evidence of watermills shows them in use for many hundreds of years, for instance in Orkney at Dounby Click Mill. Prior to the invention of steam power, watermills for grinding cereals and for processing wool and other textiles were common across Europe. In the 1890s the first machines to generate power from river water were established at places such as Cragside in Northumberland and in recent decades there has been a significant increase in the development of large scale power generation from water, especially in wet mountainous regions such as Norway.
+
+The coarse sediments, gravel, and sand, generated and moved by rivers are extensively used in construction. In parts of the world this can generate extensive new lake habitats as gravel pits re-fill with water. In other circumstances it can destabilise the river bed and the course of the river and cause severe damage to spawning fish populations which rely on stable gravel formations for egg laying. In upland rivers, rapids with whitewater or even waterfalls occur. Rapids are often used for recreation, such as whitewater kayaking.[18]
+
+The organisms in the riparian zone respond to changes in river channel location and patterns of flow. The ecosystem of rivers is generally described by the river continuum concept, which has some additions and refinements to allow for dams and waterfalls and temporary extensive flooding. The concept describes the river as a system in which the physical parameters, the availability of food particles and the composition of the ecosystem are continuously changing along its length. The food (energy) that remains from the upstream part is used downstream.
+
+The general pattern is that the first order streams contain particulate matter (decaying leaves from the surrounding forests) which is processed there by shredders like Plecoptera larvae. The products of these shredders are used by collectors, such as Hydropsychidae, and further downstream algae that create the primary production become the main food source of the organisms. All changes are gradual and the distribution of each species can be described as a normal curve, with the highest density where the conditions are optimal. In rivers succession is virtually absent and the composition of the ecosystem stays fixed in time.
+
+The chemistry of rivers is complex and depends on inputs from the atmosphere, the geology through which it travels and the inputs from man's activities. The chemical composition of the water has a large impact on the ecology of that water for both plants and animals and it also affects the uses that may be made of the river water. Understanding and characterising river water chemistry requires a well designed and managed sampling and analysis.
+
+Some rivers generate brackish water by having their river mouth in the ocean.
+
+Flooding is a natural part of a river's cycle. The majority of the erosion of river channels and the erosion and deposition on the associated floodplains occur during the flood stage. In many developed areas, human activity has changed the form of river channels, altering magnitudes and frequencies of flooding. Some examples of this are the building of levees, the straightening of channels, and the draining of natural wetlands. In many cases human activities in rivers and floodplains have dramatically increased the risk of flooding. Straightening rivers allows water to flow more rapidly downstream, increasing the risk of flooding places further downstream. Building on flood plains removes flood storage, which again exacerbates downstream flooding. The building of levees only protects the area behind the levees and not those further downstream. Levees and flood-banks can also increase flooding upstream because of the back-water pressure as the river flow is impeded by the narrow channel banks. Detention basins finally also reduce the risk of flooding significantly by being able to take up some of the flood water.
+
+Studying the flows of rivers is one aspect of hydrology.[19]
+
+Rivers flow downhill with their power derived from gravity. The direction can involve all directions of the compass and can be a complex meandering path.[20][21][22]
+
+Rivers flowing downhill, from river source to river mouth, do not necessarily take the shortest path. For alluvial streams, straight and braided rivers have very low sinuosity and flow directly down hill, while meandering rivers flow from side to side across a valley. Bedrock rivers typically flow in either a fractal pattern, or a pattern that is determined by weaknesses in the bedrock, such as faults, fractures, or more erodible layers.
+
+Volumetric flow rate, also known as discharge, volume flow rate, and rate of water flow, is the volume of water which passes through a given cross-section of the river channel per unit time. It is typically measured in cubic metres per second (cumec) or cubic feet per second (cfs), where 1 m3/s = 35.51 ft3/s; it is sometimes also measured in litres or gallons per second.
+
+Volumetric flow rate can be thought of as the mean velocity of the flow through a given cross-section, times that cross-sectional area. Mean velocity can be approximated through the use of the Law of the Wall. In general, velocity increases with the depth (or hydraulic radius) and slope of the river channel, while the cross-sectional area scales with the depth and the width: the double-counting of depth shows the importance of this variable in determining the discharge through the channel.
+
+In its youthful stage the river causes  erosion in the water-course, deepening the valley. Hydraulic action loosens and dislodges the rock which further erodes the banks and the river bed. Over time, this deepens the river bed and creates steeper sides which are then weathered.
+
+The steepened nature of the banks causes the sides of the valley to move downslope causing the valley to become V-shaped.
+
+Waterfalls also form in the youthful river valley where a band of hard rock overlays a layer of soft rock. Differential erosion occurs as the river  erodes the soft rock more readily than the hard rock, this leaves the hard rock more elevated and stands out from the river below. A plunge pool forms at the bottom and deepens as a result of hydraulic action and abrasion.[23]
+
+Sediment yield is the total quantity of particulate matter (suspended or bedload) reaching the outlet of a drainage basin over a fixed time frame. Yield is usually expressed as kilograms per square kilometre per year. Sediment delivery processes are affected by a myriad of factors such as drainage area size, basin slope, climate, sediment type (lithology), vegetation cover, and human land use / management practices. The theoretical concept of the 'sediment delivery ratio' (ratio between yield and total amount of sediment eroded) captures the fact that not all of the sediment is eroded within a  certain catchment that reaches out to the outlet (due to, for example, deposition on floodplains). Such storage opportunities are typically increased in catchments of larger size, thus leading to a lower yield and sediment delivery ratio.
+
+Rivers are often managed or controlled to make them more useful or less disruptive to human activity.
+
+River management is a continuous activity as rivers tend to 'undo' the modifications made by people. Dredged channels silt up, sluice mechanisms deteriorate with age, levees and dams may suffer seepage or catastrophic failure. The benefits sought through managing rivers may often be offset by the social and economic costs of mitigating the bad effects of such management. As an example, in parts of the developed world, rivers have been confined within channels to free up flat flood-plain land for development. Floods can inundate such development at high financial cost and often with loss of life.
+
+Rivers are increasingly managed for habitat conservation, as they are critical for many aquatic and riparian plants, resident and migratory fishes, waterfowl, birds of prey, migrating birds, and many mammals.

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+The Punic Wars were a series of three wars fought between Rome and Carthage from 264 BC to 146 BC. The main cause of the Punic Wars was the conflicts of interest between the existing Carthaginian Empire and the expanding Roman Republic. The Romans were initially interested in expansion via Sicily (which at that time was a cultural melting pot), part of which lay under Carthaginian control. At the start of the First Punic War (264–241 BC), Carthage was the dominant power of the Western Mediterranean, with an extensive maritime empire. Rome was a rapidly ascending power in Italy, but it lacked the naval power of Carthage. The Second Punic War (218–201 BC) witnessed Hannibal's crossing of the Alps in 218 BC, followed by a prolonged but ultimately failed campaign of Carthage's Hannibal in mainland Italy. By the end of the Third Punic War (149–146 BC), after more than a hundred years and the loss of many hundreds of thousands of soldiers from both sides, Rome had conquered Carthage's empire, completely destroyed the city, and became the most powerful state of the Western Mediterranean.
+
+With the end of the Macedonian Wars – which ran concurrently with the Punic Wars – and the defeat of the Seleucid King Antiochus III the Great in the Roman–Seleucid War (Treaty of Apamea, 188 BC) in the eastern sea, Rome emerged as the dominant Mediterranean power and one of the most powerful cities in classical antiquity. The Roman victories over Carthage in these wars gave Rome a preeminent status it would retain until the 5th century AD.
+
+The main source for almost every aspect of the Punic Wars[note 1] is the historian Polybius (c. 200 – c. 118 BC), a Greek sent to Rome in 167 BC as a hostage.[2] His works include a now-lost manual on military tactics,[3] but he is now known for The Histories, written sometime after 146 BC.[4][5] Polybius's work is considered broadly objective and largely neutral as between Carthaginian and Roman points of view.[6][7] Polybius was an analytical historian and wherever possible personally interviewed participants, from both sides, in the events he wrote about.[8][9][10] He accompanied the Roman general Scipio Aemilianus during his campaign in North Africa which resulted in a Roman victory in the Third Punic War.[11]
+
+The accuracy of Polybius's account has been much debated over the past 150 years, but the modern consensus is to accept it largely at face value, and the details of the war in modern sources are largely based on interpretations of Polybius's account.[2][12][13] The modern historian Andrew Curry sees Polybius as being "fairly reliable";[14] while Craige Champion describes him as "a remarkably well-informed, industrious, and insightful historian".[15]
+
+Other, later, ancient histories of the war exist, although often in fragmentary or summary form.[16] Modern historians usually take into account the writings of various Roman annalists, some contemporary; the Sicilian Greek Diodorus Siculus; the later Roman historians Livy (who relied heavily on Polybius[17]), Plutarch, Appian (whose account of the Third Punic War is especially valuable[18]) and Dio Cassius.[19] The classicist Adrian Goldsworthy states "Polybius' account is usually to be preferred when it differs with any of our other accounts".[note 2][9] Other sources include inscriptions, archaeological evidence and empirical evidence from reconstructions such as the trireme Olympias.[20]
+
+The Roman Republic had been aggressively expanding in the southern Italian mainland for a century before the First Punic War.[21] It had conquered peninsular Italy south of the River Arno by 272 BC, when the Greek cities of southern Italy (Magna Graecia) submitted at the conclusion of the Pyrrhic War.[22] During this period Carthage, with its capital in what is now Tunisia, had come to dominate southern Spain, much of the coastal regions of North Africa, the Balearic Islands, Corsica, Sardinia, and the western half of Sicily in a military and commercial empire.[23]
+
+Beginning in 480 BC, Carthage had fought a series of inconclusive wars against the Greek city states of Sicily, led by Syracuse.[24] By 264 BC Carthage and Rome were the preeminent powers in the western Mediterranean.[25] The two states had several times asserted their mutual friendship via formal alliances: in 509 BC, 348 BC and around 279 BC. Relationships were good, with strong commercial links. During the Pyrrhic War of 280–275 BC, against a king of Epirus who alternately fought Rome in Italy and Carthage on Sicily, Carthage provided materiel to the Romans and on at least one occasion used its navy to ferry a Roman force.[26][27]
+
+The two states had several times asserted their mutual friendship via formal alliances: in 509 BC, 348 BC and around 279 BC. Relationships were good, with strong commercial links. During the Pyrrhic War of 280–275 BC, against a king of Epirus who alternately fought Rome in Italy and Carthage on Sicily, Carthage provided materiel to the Romans and on at least one occasion used its navy to ferry a Roman force.[26][27] Rome's expansion into southern Italy probably made it inevitable that it would eventually clash with Carthage over Sicily on some pretext. The immediate cause of the war was the issue of control of the Sicilian town of Messana (modern Messina).[28] In 264 BC Carthage and Rome went to war, starting the First Punic War.[29]
+
+Most male Roman citizens were eligible for military service and would serve as infantry, a better-off minority providing a cavalry component. Traditionally, when at war the Romans would raise two legions, each of 4,200 infantry[note 3] and 300 cavalry. A few infantry served as javelin-armed skirmishers. The balance were equipped as heavy infantry, with body armour, a large shield and short thrusting swords. They were divided into three ranks, of which the front rank also carried two javelins, while the second and third ranks had a thrusting spear instead. Both legionary sub-units and individual legionaries fought in relatively open order. It was the long-standing Roman procedure to elect two men each year, known as consuls, to each lead an army. An army was usually formed by combining a Roman legion with a similarly sized and equipped legion provided by their Latin allies.[32][33]
+
+Carthaginian citizens only served in their army if there was a direct threat to the city. When they did they fought as well-armoured heavy infantry armed with long thrusting spears, although they were notoriously ill-trained and ill-disciplined. In most circumstances Carthage recruited foreigners to make up its army. Many would be from North Africa, a majority during the First Punic War, which provided several types of fighters including: close-order infantry equipped with large shields, helmets, short swords and long thrusting spears; javelin-armed light infantry skirmishers; close-order shock cavalry carrying spears; and light cavalry skirmishers who threw javelins from a distance and avoided close combat.[34][35][36] Both Spain and Gaul provided large numbers of experienced infantry, especially during the Second Punic War; they were mostly unarmoured troops who would charge ferociously, but had a reputation for breaking off if a combat was protracted.[37][38][39] The close order Libyan infantry and the citizen-militia would fight in a tightly packed formation known as a phalanx.[35] On occasion some of the infantry would wear captured Roman armour, especially among Hannibal's troops.[40] Slingers were frequently recruited from the Balearic Islands.[41][42] The Carthaginians also employed war elephants; North Africa had indigenous African forest elephants at the time.[note 4][38][44]
+
+Garrison duty and land blockades were the most common operations for both armies.[45][46] When armies were campaigning, surprise attacks, ambushes and strategems were common.[35][47] More formal battles were usually preceded by the two armies camping a mile or two apart (2–3 km) for days or weeks; sometimes forming up in battle order each day. If neither commander could see an advantage, both sides might march off without engaging.[48] Forming up in battle order was a complicated and premeditated affair, which took several hours. Infantry were usually positioned in the centre of the battle line, with light infantry skirmishers to their front and cavalry on each flank.[49] Many battles were decided when one side's infantry force was attacked in the flank or rear and they were partially or wholly enveloped.[35]
+
+Quinqueremes, meaning "five-oarsmen",[50] provided the workhorses of the Roman and Carthaginian fleets throughout the Punic Wars.[51] So ubiquitous was the type that Polybius uses it as a shorthand for "warship" in general.[52] A quinquereme carried a crew of 300: 280 oarsmen and 20 deck crew and officers.[53] It would also normally carry a complement of 40 marines,[54] if battle was thought to be imminent this would be increased to as many as 120.[55][56] In 260 BC Romans set out to construct a fleet and used a shipwrecked Carthaginian quinquereme as a blueprint for their own.[57]
+
+As novice shipwrights, the Romans built copies that were heavier than the Carthaginian vessels, and so slower and less manoeuvrable.[58] Getting the oarsmen to row as a unit, let alone to execute more complex battle manoeuvres, required long and arduous training.[59] At least half of the oarsmen would need to have had some experience if the ship was to be handled effectively.[60] As a result, the Romans were initially at a disadvantage against the more experienced Carthaginians. To counter this, the Romans introduced the corvus, a bridge 1.2 metres (4 feet) wide and 11 metres (36 feet) long, with a heavy spike on the underside, which was designed to pierce and anchor into an enemy ship's deck.[55] This allowed Roman legionaries acting as marines to board enemy ships and capture them, rather than employing the previously traditional tactic of ramming.[61]
+
+All warships were equipped with rams, a triple set of 60-centimetre-wide  (2 ft) bronze blades weighing up to 270 kilograms (600 lb) positioned at the waterline. In the century prior to the Punic Wars, boarding had become increasingly common and ramming had declined, as the larger and heavier vessels adopted in this period lacked the speed and manoeuvrability necessary to ram, while their sturdier construction reduced the ram's effect even in case of a successful attack. The Roman adaptation of the corvus was a continuation of this trend and compensated for their initial disadvantage in ship-manoeuvring skills. The added weight in the prow compromised both the ship's manoeuvrability and its seaworthiness, and in rough sea conditions the corvus became useless; part way through the First Punic War the Romans ceased using it.[61][62][63]
+
+The war began with the Romans gaining a foothold on Sicily at Messana (modern Messina).[64] The Romans then pressed Syracuse, the only significant independent power on the island, into allying with them[65] and laid siege to Carthage's main base at Akragas.[66] A large Carthaginian army attempted to lift the siege in 262 BC, but was heavily defeated at the Battle of Akragas. That night the Carthaginian garrison escaped and the Romans seized the city and its inhabitants, selling 25,000 of them into slavery.[67] The Romans then built a navy to challenge Carthage's,[68] and using the corvus inflicted several defeats.[69][70][71] A Carthaginian base on Corsica was seized, but an attack on Sardinia was repulsed; the base on Corsica was then lost.[72]
+
+Taking advantage of their naval victories the Romans launched an invasion of North Africa,[73] which the Carthaginians intercepted. At the Battle of Cape Ecnomus the Carthaginians were again beaten;[74] this was possibly the largest naval battle in history by the number of combatants involved.[75][76][77] The invasion initially went well and in 255 BC the Carthaginians sued for peace; the proposed terms were so harsh they fought on,[78] defeating the invaders.[79] The Romans sent a fleet to evacuate their survivors and the Carthaginians opposed it at the Battle of Cape Hermaeum off Africa; the Carthaginians were heavily defeated.[80] The Roman fleet, in turn, was devastated by a storm while returning to Italy, losing most of its ships and over 100,000 men.[80][81][82]
+
+The war continued, with neither side able to gain a decisive advantage.[83] The Carthaginians attacked and recaptured Akragas in 255 BC, but not believing they could hold the city, they razed and abandoned it.[84][85] The Romans rapidly rebuilt their fleet, adding 220 new ships, and captured Panormus (modern Palermo) in 254 BC.[86] The next year they lost another 150 ships to a storm.[87] In 251 BC the Carthaginians attempted to recapture Panormus, but were defeated in a battle outside the walls.[88][89] Slowly the Romans had occupied most of Sicily; in 249 BC they besieged the last two Carthaginian strongholds – in the extreme west.[90] They also launched a surprise attack on the Carthaginian fleet, but were defeated at the Battle of Drepana.[91] The Carthaginians followed up their victory and most of the remaining Roman warships were lost at the Battle of Phintias.[92] After several years of stalemate,[93] the Romans rebuilt their fleet again in 243 BC[94] and effectively blockaded the Carthaginian garrisons[95]. Carthage assembled a fleet which attempted to relieve them, but it was destroyed at the Battle of the Aegates Islands in 241 BC,[96][97] forcing the cut-off Carthaginian troops on Sicily to negotiate for peace.[98][95]
+
+A treaty was agreed. By its terms Carthage paid 3,200 talents of silver[note 5][note 6] in reparations and Sicily was annexed as a Roman province.[96] Henceforth Rome considered itself the leading military power in the western Mediterranean, and increasingly the Mediterranean region as a whole. The immense effort of repeatedly building large fleets of galleys during the war laid the foundation for Rome's maritime dominance for 600 years.[100]
+
+The Mercenary War began in 241 BC as a dispute over the payment of wages owed to 20,000 foreign soldiers who had fought for Carthage on Sicily during the First Punic War. When a compromise seemed to have been reached the army erupted into full-scale mutiny under the leadership of Spendius and Matho. 70,000 Africans from Carthage's oppressed dependant territories flocked to join them, bringing supplies and finance. War-weary Carthage fared poorly in the initial engagements, especially under the generalship of Hanno. Hamilcar Barca, a veteran of the campaigns in Sicily (and father of Hannibal Barca), was given joint command of the army in 240 BC; and supreme command in 239 BC. He campaigned successfully, initially demonstrating leniency in an attempt to woo the rebels over. To prevent this, in 240 BC Spendius tortured 700 Carthaginian prisoners to death, and henceforth the war was pursued with great brutality.
+
+By early 237 BC, after numerous setbacks, the rebels were defeated and their cities brought back under Carthaginian rule. An expedition was prepared to reoccupy Sardinia, where mutinous soldiers had slaughtered all Carthaginians. The Roman Senate stated they considered the preparation of this force an act of war, and demanded Carthage cede Sardinia and Corsica, and pay an additional 1,200-talent indemnity.[101][102][note 7] Weakened by 30 years of war, Carthage agreed rather than again enter into conflict with Rome.[103] Polybius considered this "contrary to all justice"[101] and modern historians have variously described the Romans' behaviour as "unprovoked aggression and treaty-breaking",[101] "shamelessly opportunistic"[104] and an "unscrupulous act".[105] These events fuelled resentment in Carthage, which was not reconciled to Rome's perception of its situation. This breach of the recently signed treaty has been considered to be the single greatest cause of war with Carthage breaking out again in 218 BC in the Second Punic War.[106][107][108]
+
+With the suppression of the rebellion, Hamilcar Barca understood that Carthage needed to strengthen its economic and military base if it were to again confront Rome.[110] After the First Punic War, Carthaginian possessions in Iberia (modern Spain and Portugal) were limited to a handful of prosperous coastal cities.[111] Hamilcar took the army which he had led to victory in the Mercenary War and led it to Iberia in 237 BC. He carved out a quasi-monarchial, autonomous state in south-east Iberia.[112] This gave Carthage the silver mines, agricultural wealth, manpower, military facilities such as shipyards and territorial depth to stand up to future Roman demands with confidence.[113][114] Hamilcar ruled as a viceroy and was succeeded by his son-in-law, Hasdrubal, in the early 220s BC and then his son, Hannibal, in 221 BC.[115] In 226 BC the Ebro Treaty was agreed, specifying the Ebro River as the northern boundary of the Carthaginian sphere of influence.[116] A little later Rome made a separate treaty with the city of Saguntum, well south of the Ebro.[117]
+
+In 219 BC a Carthaginian army under Hannibal besieged, captured and sacked Saguntum.[106][118] In spring 218 BC Rome declared war on Carthage.[119] There were three main military theatres in the war: Italy, where Hannibal defeated the Roman legions repeatedly, with occasional subsidiary campaigns in Sicily and Greece; Iberia, where Hasdrubal, a younger brother of Hannibal, defended the Carthaginian colonial cities with mixed success until moving into Italy; and Africa, where the war was decided.
+
+In 218 BC there was some naval skirmishing in the waters around Sicily. The Romans beat off a Carthaginian attack[120][121] and captured the island of Malta.[122] In Cisalpine Gaul (modern northern Italy), the major Gallic tribes attacked the Roman colonies, causing the Romans to flee to Mutina (modern Modena), which the they besieged. A Roman relief army raised the siege, but was then ambushed and besieged itself.[123] An army had been raised to campaign in Iberia under the brothers Gnaeus and Publius Scipio and the Roman Senate detached one Roman and one allied legion from it tosend to the region. The Scipios had to raise fresh troops to replace these and thus could not set out for Iberia until September.[124]
+
+Meanwhile, Hannibal assembled a Carthaginian army in New Carthage (modern Cartagena) and led it northwards along the coast in May or June. It entered Gaul and took an inland route, to avoid the Roman allies along the coast.[125] At the Battle of Rhone Crossing, Hannibal defeated a force of local Allobroges that sought to bar his way.[126] A Roman fleet carrying the Scipio brothers' army landed at Rome's ally Massalia (modern Marseille) at the mouth of the Rhone.[127] Hannibal evaded the Romans and Gnaeus Scipio continued to Iberia with the Roman army;[128][129] Publius returned to Rome.[129] The Carthaginians reached the foot of the Alps by late autumn[125] and crossed them, surmounting the difficulties of climate, terrain[125]> and the guerrilla tactics of the native tribes. The exact route is disputed. Hannibal arrived with 20,000 infantry, 6,000 cavalry, and an unknown number of elephants[65] in what is now Piedmont, northern Italy. The Romans were still in their winter quarters. His surprise entry into the Italian peninsula led to the termination of Rome's planned campaign for the year, an invasion of Africa.[130]
+
+Hannibal's first action was to take the chief city of the hostile Taurini (in the area of modern-day Turin). His army then routed the cavalry and light infantry of the Romans under Publius Scipio at the Battle of Ticinus.[131] As a result, most of the Gallic tribes declared for the Carthaginian cause, and Hannibal's army grew to over 40,000 men.[132] A large Roman army under the command of Sempronius Longus was lured into combat by Hannibal at the Battle of the Trebia, encircled and destroyed.[133] Only 10,000 Romans out of 42,000 were able to cut their way to safety. Gauls now joined Hannibal's army in large numbers, bringing it up to 60,000 men.[132] The Romans stationed an army at Arretium and one on the Adriatic coast to block Hannibal's advance into central Italy.[134]
+
+In early spring 217 BC, the Carthaginians crossed the Apennines unopposed, taking a difficult but unguarded route.[135] Hannibal attempted without success to draw the main Roman army under Gaius Flaminius into a pitched battle by devastating the area they had been sent to protect.[136] Hannibal then cut off the Roman army from Rome, which provoked Flaminius into a hasty pursuit without proper reconnaissance.[137] Then, in a defile on the shore of Lake Trasimenus, Hannibal set an ambush[137] and in the Battle of Lake Trasimene completely defeated the Roman army and killed Flaminius.[137] 15,000 Romans were killed and 15,000 taken prisoner. 4,000 Roman cavalry from their other army were also engaged and wiped out.[138] The prisoners were sold as slaves if they were Romans, but released if they were from one of Rome's Latin allies.[139] Hannibal hoped that some of these allies could be persuaded to defect, and marched south in the hope of winning over allies among the ethnic Greek and Italic city states.[134]
+
+The Romans, panicked by these heavy defeats, appointed Quintus Fabius Maximus as dictator.[139] Fabius invented the Fabian strategy of avoiding open battle with his opponent, but constantly skirmishing with small detachments of the enemy. This was not popular among the soldiers, the Roman public nor the Roman elite, since he avoided battle while Italy was being devastated by the enemy.[134] Hannibal marched through the richest and most fertile provinces of Italy, hoping that the devastation would draw Fabius into battle, but Fabius refused.[140]
+
+At the elections of 216 BC the more aggressive minded Gaius Terentius Varro and Lucius Aemilius Paullus were elected as consuls.[141] The Roman Senate authorized the raising of double-sized armies, a force of 86,000 men, the largest in Roman history up to that point.[141] Paullus and Varro marched southward to confront Hannibal, who accepted battle on the open plain near Cannae. In the Battle of Cannae The Roman legions forced their way through Hannibal's deliberately weak centre, but the Libyans on the wings swung around their advance, menacing their flanks.[142] Hasdrubal led Carthaginian cavalry on the left wing and routed the Roman cavalry opposite, then swept around the rear of the Romans to attack the cavalry on the other wing. He then charged into the legions' from behind.[142] As a result, the Roman infantry was surrounded with no means of escape.[142] At least 67,500 Romans were killed or captured.[142].
+
+Gnaeus Scipio continued on from Massala in the summer of 218 BC to Iberia (modern Spain and Portugal), where he won support among the local tribes.[128] The Carthaginian commander in the area refused to wait for reinforcements and attacked Scipio at the Battle of Cissa in late 218 BC and was defeated.[128][143] In 217 BC, the Carthaginians moved to engage the combined Roman and Massalian fleet at the Battle of Ebro River. The 40 Carthaginian and Iberian vessels were beaten by 55 Roman and Massalian ships in the second naval engagement of the war, with 29 Carthaginian ships lost. Carthaginian forces retreated, but the Romans remained confined to the area between the Ebro and Pyrenees.[143]
+
+The Roman army in Spain was preventing the Carthaginians from sending reinforcements from Iberia to Hannibal or to the insurgent Gauls in northern Italy.[143] Hasdrubal marched into Roman territory in 215 BC, besieged a pro-Roman town and offered battle at Dertosa. After a hard-fought battle, he was defeated although both sides suffered heavy losses.[144] Hasdrubal was now unable to reinforce Hannibal in Italy.[144][128]
+
+The Carthaginians suffered a wave of defections of local Celtiberian tribes to Rome.[128] The Scipio brothers captured Saguntum in 212 BC.[144] In 211, they hired 20,000 Celtiberian mercenaries to reinforce their army.[144] Observing that the three Carthaginian armies were deployed apart from each other, the Scipios split their forces.[144] Publius moved to attack Mago Barca near Castulo, while Gnaeus marched on Hasdrubal.[144] This stratagy resulted in the Battle of Castulo and the Battle of Ilorca, usually combined as the Battle of the Upper Baetis.[128][144] Both battles ended in complete defeat for the Romans, with both of the Scipio brothers being killed, as Hasdrubal had bribed the Romans' mercenaries to desert.[128][144] The Romans retreated to their coastal stronghold north of the Ebro, from which the Carthaginians failed to expel them.[144][128] Claudius Nero brought over reinforcements in 210 and stabilized the situation.[144]
+
+In 210 BC, Scipio Africanus arrived in Spain with further reinforcements.[145] In a carefully planned assault in 209 BC, he captured the lightly-defended centre of Carthaginian power in Spain, Cartago Nova.[146][145] Scipio had the population slaughtered and a vast booty of gold, silver and siege artillery was taken.[147][145] He liberated the Iberian hostages kept by the Carthaginians to ensure the loyalty of the Iberian tribes,[147][145] although many of them were subsequently to fight against the Romans.[145]
+
+In 206 BC, at the Battle of Ilipa, Scipio with 48,000 men, half Italians and half Iberians, defeated a Carthaginian army of 54,500 men and 32 elephants under the command of Mago Barca, Hasdrubal Gisco and Masinissa This sealed the fate of the Carthaginian presence in Iberia.[148][145] It was followed by the Roman capture of Gades after the city rebelled against Carthaginian rule.[149]
+
+Later that year a dangerous mutiny broke out among Roman troops at their camp at Sucro. It initially attracted support from Iberian leaders, disappointed that Roman forces had remained in the peninsula after the expulsion of the Carthaginians. It was effectively put down by Scipio Africanus. In 205 BC a last attempt was made by Mago to recapture New Carthage when the Roman occupiers were shaken by another mutiny and an Iberian uprising, but he was repulsed. Mago left Spain for Italy with his remaining forces.[147] In 203 BC Carthage succeeded in recruiting at least 4,000 mercenaries from Iberia, despite Rome's nominal control.[150]
+
+In 213 BC Syphax, a powerful Numidian king in North Africa,[144] declared for Rome. Rome sent advisers to train his soldiers[144] and he waged war against the Carthaginian ally Gala.[144] In 206 BC the Carthaginians ended this drain on their resources by dividing several Numidian kingdoms with him. One of those disinherited was the Numidian prince Masinissa, who was thus driven into the arms of Rome.[151]
+
+In 205 BC Scipio Africanus was given command of the legions in Sicily and allowed to enroll volunteers for his plan to end the war by an invasion of Africa.[152] After landing in Africa in 204 BC, he was joined by Masinissa and a force of Numidian cavalry.[153] Scipio then besieged and failed to take the city of Utica.[154] When a Carthaginian and Numidian relief army under Hasdrubal Barca and Syphax moved to confront him, he mounted a surprise attack and destroyed it.[155] In 203 BC Scipio confronted a second Carthaginian army and destroyed at the Battle of the Great Plains. King Syphax was pursued and taken prisoner at the Battle of Cirta and Masinissa seized a large part of his kingdom with Roman help.[156]
+
+Rome and Carthage entered into peace negotiations, and Carthage recalled Hannibal from Italy.[157] Largely due to mutual mistrust the negotiations came to nothing.[158] Hannibal was placed in command of another army, based his veterans from Italy and newly raised troops from Africa, but with few cavalry.[159] The decisive Battle of Zama followed in October 202 BC.[160] Unlike most battles of the Second Punic War, the Romans had superiority in cavalry and the Carthaginians in infantry.[159] Hannibal attempted to use 80 elephants to break into the Roman infantry formation, but the Romans countered them effectively and they routed back through the Carthaginian ranks.[161] The Roman and Allied Numidian cavalry drove the Carthaginian cavalry from the field. The two sides' infantry fought inconclusively until the Roman cavalry returned and attacked his rear. The Carthaginian formation collapsed; Hannibal was one of the few to escape the field.[160]
+
+The peace treaty imposed on the Carthaginians stripped them of all of their overseas territories, and some of their African ones. An indemnity of 10,000 silver talents[note 8] was to be paid over 50 years. Hostages were taken. Carthage was forbidden to possess war elephants and its fleet was restricted to 10 warships. It was prohibited from waging war outside Africa, and in Africa only with Rome's express permission. Many senior Carthaginians wanted to reject it, but Hannibal spoke strongly in its favour and it was accepted in spring 201 BC.[162] Henceforth it was clear that Carthage was politically subordinate to Rome.[163]
+
+At the end of the war, Masinissa emerged as by far the most powerful ruler among the Numidians.[164] Over the following 48 years he repeatedly took advantage of Carthage's inability to protect its possessions. Whenever Carthage petioned Rome for redress, or permission to take military action, Rome backed its ally, Masinissa, and refused.[165] Masinissa's seizures of and raids into Carthaginian territory became increasingly flagrant. In 151 BC Carthage raised a large army, the treaty notwithstanding, and counter attacked the Numidians. The campaign ended in disaster and the army surrendered.[166] Carthage had paid off its indemnity and was prospering economically, but was no military threat to Rome.[167][168] Elements in the Roman Senate had long wished to destroy Carthage, and with the breach of the treaty as a casus belli, war was declared in 149 BC.[166]
+
+In 149 BC a Roman army of approximately 50,000 men, jointly commanded by both consuls, landed near Utica, 35 kilometres (22 mi) north of Carthage.[169] Rome demanded that if war were to be avoided, the Carthaginians must hand over all of their armaments. Vast amounts of materiel delivered, including 200,000 sets of armour, 2,000 catapults and a large number of warships.[170] This done, the Romans demanded that the Carthaginians burn their city and relocate at least 10 miles (16 km) from the sea; the Carthaginians broke off negotiations and set to recreating their armoury.[171]
+
+As well as manning the walls of Carthage, the Carthaginians formed a field army under Hasdrubal, which was based 25 kilometres (16 mi) to the south.[173][174] The Roman army moved to lay siege to Carthage, but its walls were so strong and its citizen-militia so determined that it was unable to make any impact, while the Carthaginians struck back effectively. Their army effectively raided the Roman lines of communication,[174] and in 148 BC Carthaginian fire ships destroyed many Roman vessels. The main Roman camp was in a swamp, which caused an outbreak of disease during the summer.[175] The Romans moved their camp, and their ships, further away; so that they were more blockading than closely besieging the city.[176] The war dragged on into 147 BC.[174]
+
+In early 147 BC Scipio Aemilianus, an adopted grandson of Scipio Africanus who had distinguished himself during the previous two years' fighting, was elected consul and took control of the war.[166][177] The Carthaginians continued to resist vigorously: they constructed warships and during the summer twice gave battle to the Roman fleet, losing both times.[177] The Romans launched an assault on the walls; after confused fighting they broke into the city, but lost in the dark, withdrew. Hasdrubal and his army withdrew into the city to reinforce the garrison.[178] Roman prisoners were taken and Hasdrubal had them tortured to death on the walls, in view of the Roman army. He was reinforcing the will to resist in the Carthaginian citizens; from this point there could be no possibility of negotiations. Some members of the city council denounced his actions and Hasdrubal had them too put to death and took over control of the city.[177][179] With no Carthaginian army in the field those cities which had remained loyal went over to the Romans or were captured.[180]
+
+resulted in a three-year siege before he breached the walls, sacked the city, and systematically burned Carthage to the ground in 146 BC. When the war ended, the surviving 50,000 Carthaginians, a small part of the pre-war population, were sold into slavery.[181] Carthage was systematically burned for 17 days; the city's walls and buildings were utterly destroyed.[182] The notion that Roman forces then sowed the city with salt to ensure that nothing would grow there again is a 20th-century invention.[183]
+
+The remaining Carthaginian territories were annexed by Rome and reconstituted to become the Roman province of Africa. Numerous significant Punic cities, such as those in Mauretania, were taken over and rebuilt by the Romans.[184] Utica, the Punic city which changed loyalties at the beginning of the siege, became the capital of the Roman province of Africa.[185] A century later, the site of Carthage was rebuilt as a Roman city by Julius Caesar, and would become one of the main cities of Roman Africa by the time of the Empire.
+
+Rome still exists as the capital of Italy; the ruins of Carthage lie 16 kilometres (10 mi) east of modern Tunis on the North African coast.[186]
+

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+See text.
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+Insects or Insecta (from Latin insectum) are hexapod invertebrates and the largest group within the arthropod phylum. Definitions and circumscriptions vary; usually, insects comprise a class within the Arthropoda. As used here, the term Insecta is synonymous with Ectognatha. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed legs, compound eyes and one pair of antennae. Insects are the most diverse group of animals; they include more than a million described species and represent more than half of all known living organisms.[2][3] The total number of extant species is estimated at between six and ten million;[2][4][5] potentially over 90% of the animal life forms on Earth are insects.[5][6] Insects may be found in nearly all environments, although only a small number of species reside in the oceans, which are dominated by another arthropod group, crustaceans.
+
+Nearly all insects hatch from eggs. Insect growth is constrained by the inelastic exoskeleton and development involves a series of molts. The immature stages often differ from the adults in structure, habit and habitat, and can include a passive pupal stage in those groups that undergo  four-stage metamorphosis. Insects that undergo three-stage metamorphosis lack a pupal stage and adults develop through a series of nymphal stages.[7] The higher level relationship of the insects is unclear. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 55 to 70 cm (22 to 28 in). The most diverse insect groups appear to have coevolved with flowering plants.
+
+Adult insects typically move about by walking, flying, or sometimes swimming. As it allows for rapid yet stable movement, many insects adopt a tripedal gait in which they walk with their legs touching the ground in alternating triangles, composed of the front and rear on one side with the middle on the other side. Insects are the only invertebrates to have evolved flight, and all flying insects derive from one common ancestor. Many insects spend at least part of their lives under water, with larval adaptations that include gills, and some adult insects are aquatic and have adaptations for swimming. Some species, such as water striders, are capable of walking on the surface of water. Insects are mostly solitary, but some, such as certain bees, ants and termites, are social and live in large, well-organized colonies. Some insects, such as earwigs, show maternal care, guarding their eggs and young. Insects can communicate with each other in a variety of ways. Male moths can sense the pheromones of female moths over great distances. Other species communicate with sounds: crickets stridulate, or rub their wings together, to attract a mate and repel other males. Lampyrid beetles  communicate with light.
+
+Humans regard certain insects as pests, and attempt to control them using insecticides, and a host of other techniques. Some insects damage crops by feeding on sap, leaves, fruits, or wood. Some species are parasitic, and may vector diseases. Some insects perform complex ecological roles; blow-flies, for example, help consume carrion but also spread diseases. Insect pollinators are essential to the life cycle of many flowering plant species on which most organisms, including humans, are at least partly dependent; without them, the terrestrial portion of the biosphere would be devastated.[8] Many insects are considered ecologically beneficial as predators and a few provide direct economic benefit. Silkworms produce silk and honey bees produce honey and both have been domesticated by humans. Insects are consumed as food in 80% of the world's nations, by people in roughly 3000 ethnic groups.[9][10] Human activities also have effects on insect biodiversity.
+
+The word "insect" comes from the Latin word insectum, meaning "with a notched or divided body", or literally "cut into", from the neuter singular perfect passive participle of insectare, "to cut into, to cut up", from in- "into" and secare "to cut";[11] because insects appear "cut into" three sections. A calque of Greek ἔντομον [éntomon], "cut into sections", Pliny the Elder introduced the Latin designation as a loan-translation of the Greek word ἔντομος (éntomos) or "insect" (as in entomology), which was Aristotle's term for this class of life, also in reference to their "notched" bodies. "Insect" first appears documented in English in 1601 in Holland's translation of Pliny. Translations of Aristotle's term also form the usual word for "insect" in Welsh (trychfil, from trychu "to cut" and  mil, "animal"), Serbo-Croatian (zareznik, from rezati, "to cut"), Russian (насекомое nasekomoje, from seč'/-sekat', "to cut"), etc.[11][12]
+
+The precise definition of the taxon Insecta and the equivalent English name "insect" varies; three alternative definitions are shown in the table.
+
+In the broadest circumscription, Insecta sensu lato consists of all hexapods.[13][14] Traditionally, insects defined in this way were divided into "Apterygota" (the first five groups in the table)—the wingless insects—and Pterygota—the winged and secondarily wingless insects.[15] However, modern phylogenetic studies have shown that "Apterygota" is not monophyletic,[16] and so does not form a good taxon. A narrower circumscription restricts insects to those hexapods with external mouthparts, and comprises only the last three groups in the table. In this sense, Insecta sensu stricto is equivalent to Ectognatha.[13][16] In the narrowest circumscription, insects are restricted to hexapods that are either winged or descended from winged ancestors. Insecta sensu strictissimo is then equivalent to Pterygota.[17] For the purposes of this article, the middle definition is used; insects consist of two wingless taxa, Archaeognatha (jumping bristletails) and Zygentoma (silverfish), plus the winged or secondarily wingless Pterygota.
+
+Hexapoda (Insecta, Collembola, Diplura, Protura)
+
+Crustacea (crabs, shrimp, isopods, etc.)
+
+Pauropoda
+
+Diplopoda (millipedes)
+
+Chilopoda (centipedes)
+
+Symphyla
+
+Arachnida (spiders, scorpions, mites, ticks, etc.)
+
+Eurypterida (sea scorpions: extinct)
+
+Xiphosura (horseshoe crabs)
+
+Pycnogonida (sea spiders)
+
+†Trilobites (extinct)
+
+A phylogenetic tree of the arthropods and related groups[18]
+
+The evolutionary relationship of insects to other animal groups remains unclear.
+
+Although traditionally grouped with millipedes and centipedes—possibly on the basis of convergent adaptations to terrestrialisation[19]—evidence has emerged favoring closer evolutionary ties with crustaceans. In the Pancrustacea theory, insects, together with Entognatha, Remipedia, and Cephalocarida, make up a natural clade labeled Miracrustacea.[20]
+
+Insects form a single clade, closely related to crustaceans and myriapods.[21]
+
+Other terrestrial arthropods, such as centipedes, millipedes, scorpions, spiders, woodlice, mites, and ticks are sometimes confused with insects since their body plans can appear similar, sharing (as do all arthropods) a jointed exoskeleton. However, upon closer examination, their features differ significantly; most noticeably, they do not have the six-legged characteristic of adult insects.[22]
+
+The higher-level phylogeny of the arthropods continues to be a matter of debate and research. In 2008, researchers at Tufts University uncovered what they believe is the world's oldest known full-body impression of a primitive flying insect, a 300-million-year-old specimen from the Carboniferous period.[23] The oldest definitive insect fossil is the Devonian Rhyniognatha hirsti, from the 396-million-year-old Rhynie chert. It may have superficially resembled a modern-day silverfish insect. This species already possessed dicondylic mandibles (two articulations in the mandible), a feature associated with winged insects, suggesting that wings may already have evolved at this time. Thus, the first insects probably appeared earlier, in the Silurian period.[1][24]
+
+Four super radiations of insects have occurred: beetles (from about 300 million years ago), flies (from about 250 million years ago), moths and wasps (both from about 150 million years ago).[25] These four groups account for the majority of described species. The flies and moths along with the fleas evolved from the Mecoptera.
+
+The origins of insect flight remain obscure, since the earliest winged insects currently known appear to have been capable fliers. Some extinct insects had an additional pair of winglets attaching to the first segment of the thorax, for a total of three pairs. As of 2009, no evidence suggests the insects were a particularly successful group of animals before they evolved to have wings.[26]
+
+Late Carboniferous and Early Permian insect orders include both extant groups, their stem groups,[27] and a number of Paleozoic groups, now extinct. During this era, some giant dragonfly-like forms reached wingspans of 55 to 70 cm (22 to 28 in), making them far larger than any living insect. This gigantism may have been due to higher atmospheric oxygen levels that allowed increased respiratory efficiency relative to today. The lack of flying vertebrates could have been another factor. Most extinct orders of insects developed during the Permian period that began around 270 million years ago. Many of the early groups became extinct during the Permian-Triassic extinction event, the largest mass extinction in the history of the Earth, around 252 million years ago.[28]
+
+The remarkably successful Hymenoptera appeared as long as 146 million years ago in the Cretaceous period, but achieved their wide diversity more recently in the Cenozoic era, which began 66 million years ago. A number of highly successful insect groups evolved in conjunction with flowering plants, a powerful illustration of coevolution.[29]
+
+Many modern insect genera developed during the Cenozoic. Insects from this period on are often found preserved in amber, often in perfect condition. The body plan, or morphology, of such specimens is thus easily compared with modern species. The study of fossilized insects is called paleoentomology.
+
+Archaeognatha (Hump-backed/jumping bristletails)
+
+Zygentoma (silverfish, firebrats, fishmoths)
+
+†Carbotriplurida
+
+†Bojophlebiidae
+
+Odonatoptera (Dragonflies)
+
+Panephemeroptera (Mayflies)
+
+Zoraptera (Angel insects)
+
+Dermaptera (earwigs)
+
+Plecoptera (stoneflies)
+
+Orthoptera (grasshoppers, crickets, katydids)
+
+Mantodea (praying mantises)
+
+Blattodea (cockroaches & termites)
+
+Grylloblattodea (ice-crawlers)
+
+Mantophasmatodea (gladiators)
+
+Phasmatodea (Stick insects)
+
+Embioptera (Web spinners)
+
+Psocodea (Book lice, barkice & sucking lice)
+
+Hemiptera (true bugs)
+
+Thysanoptera (Thrips)
+
+Hymenoptera (sawflies, wasps, bees, ants)
+
+Strepsiptera
+
+Coleoptera (Beetles)
+
+Rhaphidioptera
+
+Neuroptera (Lacewings)
+
+Megaloptera
+
+Lepidoptera (Butterflies & moths)
+
+Trichoptera (Caddisflies)
+
+Diptera (True flies)
+
+Nannomecoptera
+
+Mecoptera (scorpionflies)
+
+Neomecoptera (winter scorpionflies)
+
+Siphonaptera (Fleas)
+
+A cladogram based on the works of Sroka, Staniczek & Bechly 2014,[30] Prokop et al. 2017[31] & Wipfler et al. 2019.[32]
+
+Cladogram of living insect groups,[33] with numbers of species in each group.[5] The Apterygota, Palaeoptera, and Exopterygota are possibly paraphyletic groups.
+
+Traditional morphology-based or appearance-based systematics have usually given the Hexapoda the rank of superclass,[34]:180 and identified four groups within it: insects (Ectognatha), springtails (Collembola), Protura, and Diplura, the latter three being grouped together as the Entognatha on the basis of internalized mouth parts. Supraordinal relationships have undergone numerous changes with the advent of methods based on evolutionary history and genetic data. A recent theory is that the Hexapoda are polyphyletic (where the last common ancestor was not a member of the group), with the entognath classes having separate evolutionary histories from the Insecta.[35] Many of the traditional appearance-based taxa have been shown to be paraphyletic, so rather than using ranks like subclass, superorder, and infraorder, it has proved better to use monophyletic groupings (in which the last common ancestor is a member of the group). The following represents the best-supported monophyletic groupings for the Insecta.
+
+Insects can be divided into two groups historically treated as subclasses: wingless insects, known as Apterygota, and winged insects, known as Pterygota. The Apterygota consist of the primitively wingless order of the silverfish (Zygentoma). Archaeognatha make up the Monocondylia based on the shape of their mandibles, while Zygentoma and Pterygota are grouped together as Dicondylia. The Zygentoma themselves possibly are not monophyletic, with the family Lepidotrichidae being a sister group to the Dicondylia (Pterygota and the remaining Zygentoma).[36][37]
+
+Paleoptera and Neoptera are the winged orders of insects differentiated by the presence of hardened body parts called sclerites, and in the Neoptera, muscles that allow their wings to fold flatly over the abdomen. Neoptera can further be divided into incomplete metamorphosis-based (Polyneoptera and Paraneoptera) and complete metamorphosis-based groups. It has proved difficult to clarify the relationships between the orders in Polyneoptera because of constant new findings calling for revision of the taxa. For example, the Paraneoptera have turned out to be more closely related to the Endopterygota than to the rest of the Exopterygota. The recent molecular finding that the traditional louse orders Mallophaga and Anoplura are derived from within Psocoptera has led to the new taxon Psocodea.[38] Phasmatodea and Embiidina have been suggested to form the Eukinolabia.[39] Mantodea, Blattodea, and Isoptera are thought to form a monophyletic group termed Dictyoptera.[40]
+
+The Exopterygota likely are paraphyletic in regard to the Endopterygota. Matters that have incurred controversy include Strepsiptera and Diptera grouped together as Halteria based on a reduction of one of the wing pairs—a position not well-supported in the entomological community.[41] The Neuropterida are often lumped or split on the whims of the taxonomist. Fleas are now thought to be closely related to boreid mecopterans.[42] Many questions remain in the basal relationships among endopterygote orders, particularly the Hymenoptera.
+
+The study of the classification or taxonomy of any insect is called systematic entomology. If one works with a more specific order or even a family, the term may also be made specific to that order or family, for example systematic dipterology.
+
+Insects are prey for a variety of organisms, including terrestrial vertebrates. The earliest vertebrates on land existed 400 million years ago and were large amphibious piscivores. Through gradual evolutionary change, insectivory was the next diet type to evolve.[43]
+
+Insects were among the earliest terrestrial herbivores and acted as major selection agents on plants.[29] Plants evolved chemical defenses against this herbivory and the insects, in turn, evolved mechanisms to deal with plant toxins. Many insects make use of these toxins to protect themselves from their predators. Such insects often advertise their toxicity using warning colors.[44] This successful evolutionary pattern has also been used by mimics. Over time, this has led to complex groups of coevolved species. Conversely, some interactions between plants and insects, like pollination, are beneficial to both organisms. Coevolution has led to the development of very specific mutualisms in such systems.
+
+Estimates on the total number of insect species, or those within specific orders, often vary considerably. Globally, averages of these estimates suggest there are around 1.5 million beetle species and 5.5 million insect species, with about 1 million insect species currently found and described.[45]
+
+Between 950,000–1,000,000 of all described species are insects, so over 50% of all described eukaryotes (1.8 million) are insects (see illustration). With only 950,000 known non-insects, if the actual number of insects is 5.5 million, they may represent over 80% of the total.  As only about 20,000 new species of all organisms are described each year, most insect species may remain undescribed, unless the rate of species descriptions greatly increases. Of the 24 orders of insects, four dominate in terms of numbers of described species; at least 670,000 identified species belong to Coleoptera, Diptera, Hymenoptera or Lepidoptera.
+
+As of 2017, at least 66 insect species extinctions had been recorded in the previous 500 years, which generally occurred on oceanic islands.[47] Declines in insect abundance have been attributed to artificial lighting,[48] land use changes such as urbanization or agricultural use,[49][50] pesticide use,[51] and invasive species.[52] Studies summarized in a 2019 review suggested a large proportion of insect species are threatened with extinction in the 21st century.[53] Though ecologist Manu Sanders notes the 2019 review was biased by mostly excluding data showing increases or stability in insect population, with the studies limited to specific geographic areas and specific groups of species.[54] A larger meta-study published in 2020, analyzing data from 166 long-term surveys, suggested that populations of terrestrial insects are decreasing by about 9% per decade.[55][56] Claims of pending mass insect extinctions or "insect apocalypse" based on a subset of these studies have been popularized in news reports, but often extrapolate beyond the study data or hyperbolize study findings.[57] Other areas have shown increases in some insect species, although trends in most regions are currently unknown. It is difficult to assess long-term trends in insect abundance or diversity because historical measurements are generally not known for many species. Robust data to assess at-risk areas or species is especially lacking for arctic and tropical regions and a majority of the southern hemisphere.[57]
+
+Insects have segmented bodies supported by exoskeletons, the hard outer covering made mostly of chitin. The segments of the body are organized into three distinctive but interconnected units, or tagmata: a head, a thorax and an abdomen.[58] The head supports a pair of sensory antennae, a pair of compound eyes, zero to three simple eyes (or ocelli) and three sets of variously modified appendages that form the mouthparts. The thorax is made up of three segments: the prothorax, mesothorax and the metathorax. Each thoracic segment supports one pair of legs. The meso- and metathoracic segments may each have a pair of wings, depending on the insect. The abdomen consists of eleven segments, though in a few species of insects, these segments may be fused together or reduced in size. The abdomen also contains most of the digestive, respiratory, excretory and reproductive internal structures.[34]:22–48 Considerable variation and many adaptations in the body parts of insects occur, especially wings, legs, antenna and mouthparts.
+
+The head is enclosed in a hard, heavily sclerotized, unsegmented, exoskeletal head capsule, or epicranium, which contains most of the sensing organs, including the antennae, ocellus or eyes, and the mouthparts. Of all the insect orders, Orthoptera displays the most features found in other insects, including the sutures and sclerites.[59] Here, the vertex, or the apex (dorsal region), is situated between the compound eyes for insects with a hypognathous and opisthognathous head. In prognathous insects, the vertex is not found between the compound eyes, but rather, where the ocelli are normally. This is because the primary axis of the head is rotated 90° to become parallel to the primary axis of the body. In some species, this region is modified and assumes a different name.[59]:13
+
+The thorax is a tagma composed of three sections, the prothorax, mesothorax and the metathorax. The anterior segment, closest to the head, is the prothorax, with the major features being the first pair of legs and the pronotum. The middle segment is the mesothorax, with the major features being the second pair of legs and the anterior wings. The third and most posterior segment, abutting the abdomen, is the metathorax, which features the third pair of legs and the posterior wings. Each segment is dilineated by an intersegmental suture. Each segment has four basic regions. The dorsal surface is called the tergum (or notum) to distinguish it from the abdominal terga.[34] The two lateral regions are called the pleura (singular: pleuron) and the ventral aspect is called the sternum. In turn, the notum of the prothorax is called the pronotum, the notum for the mesothorax is called the mesonotum and the notum for the metathorax is called the metanotum. Continuing with this logic, the mesopleura and metapleura, as well as the mesosternum and metasternum, are used.[59]
+
+The abdomen is the largest tagma of the insect, which typically consists of 11–12 segments and is less strongly sclerotized than the head or thorax. Each segment of the abdomen is represented by a sclerotized tergum and sternum. Terga are separated from each other and from the adjacent sterna or pleura by membranes. Spiracles are located in the pleural area. Variation of this ground plan includes the fusion of terga or terga and sterna to form continuous dorsal or ventral shields or a conical tube. Some insects bear a sclerite in the pleural area called a laterotergite. Ventral sclerites are sometimes called laterosternites. During the embryonic stage of many insects and the postembryonic stage of primitive insects, 11 abdominal segments are present. In modern insects there is a tendency toward reduction in the number of the abdominal segments, but the primitive number of 11 is maintained during embryogenesis. Variation in abdominal segment number is considerable. If the Apterygota are considered to be indicative of the ground plan for pterygotes, confusion reigns: adult Protura have 12 segments, Collembola have 6. The orthopteran family Acrididae has 11 segments, and a fossil specimen of Zoraptera has a 10-segmented abdomen.[59]
+
+The insect outer skeleton, the cuticle, is made up of two layers: the epicuticle, which is a thin and waxy water resistant outer layer and contains no chitin, and a lower layer called the procuticle. The procuticle is chitinous and much thicker than the epicuticle and has two layers: an outer layer known as the exocuticle and an inner layer known as the endocuticle. The tough and flexible endocuticle is built from numerous layers of fibrous chitin and proteins, criss-crossing each other in a sandwich pattern, while the exocuticle is rigid and hardened.[34]:22–24 The exocuticle is greatly reduced in many insects during their larval stages, e.g., caterpillars. It is also reduced in soft-bodied adult insects.
+
+Insects are the only invertebrates to have developed active flight capability, and this has played an important role in their success.[34]:186 Their flight muscles are able to contract multiple times for each single nerve impulse, allowing the wings to beat faster than would ordinarily be possible.
+
+Having their muscles attached to their exoskeletons is efficient and allows more muscle connections.
+
+The nervous system of an insect can be divided into a brain and a ventral nerve cord. The head capsule is made up of six fused segments, each with either a pair of ganglia, or a cluster of nerve cells outside of the brain. The first three pairs of ganglia are fused into the brain, while the three following pairs are fused into a structure of three pairs of ganglia under the insect's esophagus, called the subesophageal ganglion.[34]:57
+
+The thoracic segments have one ganglion on each side, which are connected into a pair, one pair per segment. This arrangement is also seen in the abdomen but only in the first eight segments. Many species of insects have reduced numbers of ganglia due to fusion or reduction.[60] Some cockroaches have just six ganglia in the abdomen, whereas the wasp Vespa crabro has only two in the thorax and three in the abdomen. Some insects, like the house fly Musca domestica, have all the body ganglia fused into a single large thoracic ganglion.
+
+At least a few insects have nociceptors, cells that detect and transmit signals responsible for the sensation of pain.[61][failed verification] This was discovered in 2003 by studying the variation in reactions of larvae of the common fruitfly Drosophila to the touch of a heated probe and an unheated one. The larvae reacted to the touch of the heated probe with a stereotypical rolling behavior that was not exhibited when the larvae were touched by the unheated probe.[62] Although nociception has been demonstrated in insects, there is no consensus that insects feel pain consciously[63]
+
+Insects are capable of learning.[64]
+
+An insect uses its digestive system to extract nutrients and other substances from the food it consumes.[65] Most of this food is ingested in the form of macromolecules and other complex substances like proteins, polysaccharides, fats and nucleic acids. These macromolecules must be broken down by catabolic reactions into smaller molecules like amino acids and simple sugars before being used by cells of the body for energy, growth, or reproduction. This break-down process is known as digestion.
+
+There is extensive variation among different orders, life stages, and even castes in the digestive system of insects.[66] This is the result of extreme adaptations to various lifestyles. The present description focus on a generalized composition of the digestive system of an adult orthopteroid insect, which is considered basal to interpreting particularities of other groups.
+
+The main structure of an insect's digestive system is a long enclosed tube called the alimentary canal, which runs lengthwise through the body. The alimentary canal directs food unidirectionally from the mouth to the anus. It has three sections, each of which performs a different process of digestion. In addition to the alimentary canal, insects also have paired salivary glands and salivary reservoirs. These structures usually reside in the thorax, adjacent to the foregut.[34]:70–77 The salivary glands (element 30 in numbered diagram) in an insect's mouth produce saliva. The salivary ducts lead from the glands to the reservoirs and then forward through the head to an opening called the salivarium, located behind the hypopharynx. By moving its mouthparts (element 32 in numbered diagram) the insect can mix its food with saliva. The mixture of saliva and food then travels through the salivary tubes into the mouth, where it begins to break down.[67][68] Some insects, like flies, have extra-oral digestion. Insects using extra-oral digestion expel digestive enzymes onto their food to break it down. This strategy allows insects to extract a significant proportion of the available nutrients from the food source.[69]:31 The gut is where almost all of insects' digestion takes place. It can be divided into the foregut, midgut and hindgut.
+
+The first section of the alimentary canal is the foregut (element 27 in numbered diagram), or stomodaeum. The foregut is lined with a cuticular lining made of chitin and proteins as protection from tough food. The foregut includes the buccal cavity (mouth), pharynx, esophagus and crop and proventriculus (any part may be highly modified), which both store food and signify when to continue passing onward to the midgut.[34]:70
+
+Digestion starts in buccal cavity (mouth) as partially chewed food is broken down by saliva from the salivary glands. As the salivary glands produce fluid and carbohydrate-digesting enzymes (mostly amylases), strong muscles in the pharynx pump fluid into the buccal cavity, lubricating the food like the salivarium does, and helping blood feeders, and xylem and phloem feeders.
+
+From there, the pharynx passes food to the esophagus, which could be just a simple tube passing it on to the crop and proventriculus, and then onward to the midgut, as in most insects. Alternately, the foregut may expand into a very enlarged crop and proventriculus, or the crop could just be a diverticulum, or fluid-filled structure, as in some Diptera species.[69]:30–31
+
+Once food leaves the crop, it passes to the midgut (element 13 in numbered diagram), also known as the mesenteron, where the majority of digestion takes place. Microscopic projections from the midgut wall, called microvilli, increase the surface area of the wall and allow more nutrients to be absorbed; they tend to be close to the origin of the midgut. In some insects, the role of the microvilli and where they are located may vary. For example, specialized microvilli producing digestive enzymes may more likely be near the end of the midgut, and absorption near the origin or beginning of the midgut.[69]:32
+
+In the hindgut (element 16 in numbered diagram), or proctodaeum, undigested food particles are joined by uric acid to form fecal pellets. The rectum absorbs 90% of the water in these fecal pellets, and the dry pellet is then eliminated through the anus (element 17), completing the process of digestion. Envaginations at the anterior end of the hindgut form the Malpighian tubules, which form the main excretory system of insects.
+
+Insects may have one to hundreds of Malpighian tubules (element 20). These tubules remove nitrogenous wastes from the hemolymph of the insect and regulate osmotic balance. Wastes and solutes are emptied directly into the alimentary canal, at the junction between the midgut and hindgut.[34]:71–72, 78–80
+
+The reproductive system of female insects consist of a pair of ovaries, accessory glands, one or more spermathecae, and ducts connecting these parts. The ovaries are made up of a number of egg tubes, called ovarioles, which vary in size and number by species. The number of eggs that the insect is able to make vary by the number of ovarioles with the rate that eggs can develop being also influenced by ovariole design. Female insects are able make eggs, receive and store sperm, manipulate sperm from different males, and lay eggs. Accessory glands or glandular parts of the oviducts produce a variety of substances for sperm maintenance, transport and fertilization, as well as for protection of eggs. They can produce glue and protective substances for coating eggs or tough coverings for a batch of eggs called oothecae. Spermathecae are tubes or sacs in which sperm can be stored between the time of mating and the time an egg is fertilized.[59]:880
+
+For males, the reproductive system is the testis, suspended in the body cavity by tracheae and the fat body. Most male insects have a pair of testes, inside of which are sperm tubes or follicles that are enclosed within a membranous sac. The follicles connect to the vas deferens by the vas efferens, and the two tubular vasa deferentia connect to a median ejaculatory duct that leads to the outside. A portion of the vas deferens is often enlarged to form the seminal vesicle, which stores the sperm before they are discharged into the female. The seminal vesicles have glandular linings that secrete nutrients for nourishment and maintenance of the sperm. The ejaculatory duct is derived from an invagination of the epidermal cells during development and, as a result, has a cuticular lining. The terminal portion of the ejaculatory duct may be sclerotized to form the intromittent organ, the aedeagus. The remainder of the male reproductive system is derived from embryonic mesoderm, except for the germ cells, or spermatogonia, which descend from the primordial pole cells very early during embryogenesis.[59]:885
+
+Insect respiration is accomplished without lungs. Instead, the insect respiratory system uses a system of internal tubes and sacs through which gases either diffuse or are actively pumped, delivering oxygen directly to tissues that need it via their trachea (element 8 in numbered diagram). In most insects, air is taken in through openings on the sides of the abdomen and thorax called spiracles.
+
+The respiratory system is an important factor that limits the size of insects. As insects get larger, this type of oxygen transport is less efficient and thus the heaviest insect currently weighs less than 100 g. However, with increased atmospheric oxygen levels, as were present in the late Paleozoic, larger insects were possible, such as dragonflies with wingspans of more than two feet.[70]
+
+There are many different patterns of gas exchange demonstrated by different groups of insects. Gas exchange patterns in insects can range from continuous and diffusive ventilation, to discontinuous gas exchange.[34]:65–68 During continuous gas exchange, oxygen is taken in and carbon dioxide is released in a continuous cycle. In discontinuous gas exchange, however, the insect takes in oxygen while it is active and small amounts of carbon dioxide are released when the insect is at rest.[71] Diffusive ventilation is simply a form of continuous gas exchange that occurs by diffusion rather than physically taking in the oxygen. Some species of insect that are submerged also have adaptations to aid in respiration. As larvae, many insects have gills that can extract oxygen dissolved in water, while others need to rise to the water surface to replenish air supplies, which may be held or trapped in special structures.[72][73]
+
+Because oxygen is delivered directly to tissues via tracheoles, the circulatory system is not used to carry oxygen, and is therefore greatly reduced. The insect circulatory system is open; it has no veins or arteries, and instead consists of little more than a single, perforated dorsal tube that pulses peristaltically. This dorsal blood vessel (element 14) is divided into two sections: the heart and aorta. The dorsal blood vessel circulates the hemolymph, arthropods' fluid analog of blood, from the rear of the body cavity forward.[34]:61–65[74] Hemolymph is composed of plasma in which hemocytes are suspended. Nutrients, hormones, wastes, and other substances are transported throughout the insect body in the hemolymph. Hemocytes include many types of cells that are important for immune responses, wound healing, and other functions. Hemolymph pressure may be increased by muscle contractions or by swallowing air into the digestive system to aid in moulting.[75] Hemolymph is also a major part of the open circulatory system of other arthropods, such as spiders and crustaceans.[76][77]
+
+The majority of insects hatch from eggs. The fertilization and development takes place inside the egg, enclosed by a shell (chorion) that consists of maternal tissue. In contrast to eggs of other arthropods, most insect eggs are drought resistant. This is because inside the chorion two additional membranes develop from embryonic tissue, the amnion and the serosa. This serosa secretes a cuticle rich in chitin that protects the embryo against desiccation. In Schizophora however the serosa does not develop, but these flies lay their eggs in damp places, such as rotting matter.[78] Some species of insects, like the cockroach Blaptica dubia, as well as juvenile aphids and tsetse flies, are ovoviviparous. The eggs of ovoviviparous animals develop entirely inside the female, and then hatch immediately upon being laid.[7] Some other species, such as those in the genus of cockroaches known as Diploptera, are viviparous, and thus gestate inside the mother and are born alive.[34]:129, 131, 134–135 Some insects, like parasitic wasps, show polyembryony, where a single fertilized egg divides into many and in some cases thousands of separate embryos.[34]:136–137 Insects may be univoltine, bivoltine or multivoltine, i.e. they may have one, two or many broods (generations) in a year.[79]
+
+Other developmental and reproductive variations include haplodiploidy, polymorphism, paedomorphosis or peramorphosis, sexual dimorphism, parthenogenesis and more rarely hermaphroditism.[34]:143 In haplodiploidy, which is a type of sex-determination system, the offspring's sex is determined by the number of sets of chromosomes an individual receives. This system is typical in bees and wasps.[80] Polymorphism is where a species may have different morphs or forms, as in the oblong winged katydid, which has four different varieties: green, pink and yellow or tan. Some insects may retain phenotypes that are normally only seen in juveniles; this is called paedomorphosis. In peramorphosis, an opposite sort of phenomenon, insects take on previously unseen traits after they have matured into adults. Many insects display sexual dimorphism, in which males and females have notably different appearances, such as the moth Orgyia recens as an exemplar of sexual dimorphism in insects.
+
+Some insects use parthenogenesis, a process in which the female can reproduce and give birth without having the eggs fertilized by a male. Many aphids undergo a form of parthenogenesis, called cyclical parthenogenesis, in which they alternate between one or many generations of asexual and sexual reproduction.[81][82] In summer, aphids are generally female and parthenogenetic; in the autumn, males may be produced for sexual reproduction. Other insects produced by parthenogenesis are bees, wasps and ants, in which they spawn males. However, overall, most individuals are female, which are produced by fertilization. The males are haploid and the females are diploid.[7] More rarely, some insects display hermaphroditism, in which a given individual has both male and female reproductive organs.
+
+Insect life-histories show adaptations to withstand cold and dry conditions. Some temperate region insects are capable of activity during winter, while some others migrate to a warmer climate or go into a state of torpor.[83] Still other insects have evolved mechanisms of diapause that allow eggs or pupae to survive these conditions.[84]
+
+Metamorphosis in insects is the biological process of development all insects must undergo. There are two forms of metamorphosis: incomplete metamorphosis and complete metamorphosis.
+
+Hemimetabolous insects, those with incomplete metamorphosis, change gradually by undergoing a series of molts. An insect molts when it outgrows its exoskeleton, which does not stretch and would otherwise restrict the insect's growth. The molting process begins as the insect's epidermis secretes a new epicuticle inside the old one. After this new epicuticle is secreted, the epidermis releases a mixture of enzymes that digests the endocuticle and thus detaches the old cuticle. When this stage is complete, the insect makes its body swell by taking in a large quantity of water or air, which makes the old cuticle split along predefined weaknesses where the old exocuticle was thinnest.[34]:142[85]
+
+Immature insects that go through incomplete metamorphosis are called nymphs or in the case of dragonflies and damselflies, also naiads. Nymphs are similar in form to the adult except for the presence of wings, which are not developed until adulthood. With each molt, nymphs grow larger and become more similar in appearance to adult insects.
+
+Holometabolism, or complete metamorphosis, is where the insect changes in four stages, an egg or embryo, a larva, a pupa and the adult or imago. In these species, an egg hatches to produce a larva, which is generally worm-like in form. This worm-like form can be one of several varieties: eruciform (caterpillar-like), scarabaeiform (grub-like), campodeiform (elongated, flattened and active), elateriform (wireworm-like) or vermiform (maggot-like). The larva grows and eventually becomes a pupa, a stage marked by reduced movement and often sealed within a cocoon. There are three types of pupae: obtect, exarate or coarctate. Obtect pupae are compact, with the legs and other appendages enclosed. Exarate pupae have their legs and other appendages free and extended. Coarctate pupae develop inside the larval skin.[34]:151 Insects undergo considerable change in form during the pupal stage, and emerge as adults. Butterflies are a well-known example of insects that undergo complete metamorphosis, although most insects use this life cycle. Some insects have evolved this system to hypermetamorphosis.
+
+Complete metamorphosis is a trait of the most diverse insect group, the Endopterygota.[34]:143 Endopterygota includes 11 Orders, the largest being Diptera (flies), Lepidoptera (butterflies and moths), and Hymenoptera (bees, wasps, and ants), and Coleoptera (beetles). This form of development is exclusive to insects and not seen in any other arthropods.
+
+Many insects possess very sensitive and specialized organs of perception. Some insects such as bees can perceive ultraviolet wavelengths, or detect polarized light, while the antennae of male moths can detect the pheromones of female moths over distances of many kilometers.[86] The yellow paper wasp (Polistes versicolor) is known for its wagging movements as a form of communication within the colony; it can waggle with a frequency of 10.6±2.1 Hz (n=190). These wagging movements can signal the arrival of new material into the nest and aggression between workers can be used to stimulate others to increase foraging expeditions.[87] There is a pronounced tendency for there to be a trade-off between visual acuity and chemical or tactile acuity, such that most insects with well-developed eyes have reduced or simple antennae, and vice versa. There are a variety of different mechanisms by which insects perceive sound; while the patterns are not universal, insects can generally hear sound if they can produce it. Different insect species can have varying hearing, though most insects can hear only a narrow range of frequencies related to the frequency of the sounds they can produce. Mosquitoes have been found to hear up to 2 kHz, and some grasshoppers can hear up to 50 kHz.[88] Certain predatory and parasitic insects can detect the characteristic sounds made by their prey or hosts, respectively. For instance, some nocturnal moths can perceive the ultrasonic emissions of bats, which helps them avoid predation.[34]:87–94 Insects that feed on blood have special sensory structures that can detect infrared emissions, and use them to home in on their hosts.
+
+Some insects display a rudimentary sense of numbers,[89] such as the solitary wasps that prey upon a single species. The mother wasp lays her eggs in individual cells and provides each egg with a number of live caterpillars on which the young feed when hatched. Some species of wasp always provide five, others twelve, and others as high as twenty-four caterpillars per cell. The number of caterpillars is different among species, but always the same for each sex of larva. The male solitary wasp in the genus Eumenes is smaller than the female, so the mother of one species supplies him with only five caterpillars; the larger female receives ten caterpillars in her cell.
+
+A few insects, such as members of the families Poduridae and Onychiuridae (Collembola), Mycetophilidae (Diptera) and the beetle families Lampyridae, Phengodidae, Elateridae and Staphylinidae are bioluminescent. The most familiar group are the fireflies, beetles of the family Lampyridae. Some species are able to control this light generation to produce flashes. The function varies with some species using them to attract mates, while others use them to lure prey. Cave dwelling larvae of Arachnocampa (Mycetophilidae, fungus gnats) glow to lure small flying insects into sticky strands of silk.[90]
+Some fireflies of the genus Photuris mimic the flashing of female Photinus species to attract males of that species, which are then captured and devoured.[91] The colors of emitted light vary from dull blue (Orfelia fultoni, Mycetophilidae) to the familiar greens and the rare reds (Phrixothrix tiemanni, Phengodidae).[92]
+
+Most insects, except some species of cave crickets, are able to perceive light and dark. Many species have acute vision capable of detecting minute movements. The eyes may include simple eyes or ocelli as well as compound eyes of varying sizes. Many species are able to detect light in the infrared, ultraviolet and the visible light wavelengths. Color vision has been demonstrated in many species and phylogenetic analysis suggests that UV-green-blue trichromacy existed from at least the Devonian period between 416 and 359 million years ago.[93]
+
+Insects were the earliest organisms to produce and sense sounds. Insects make sounds mostly by mechanical action of appendages. In grasshoppers and crickets, this is achieved by stridulation. Cicadas make the loudest sounds among the insects by producing and amplifying sounds with special modifications to their body to form tymbals and associated musculature. The African cicada Brevisana brevis has been measured at 106.7 decibels at a distance of 50 cm (20 in).[94] Some insects, such as the Helicoverpa zea moths, hawk moths and Hedylid butterflies, can hear ultrasound and take evasive action when they sense that they have been detected by bats.[95][96] Some moths produce ultrasonic clicks that were once thought to have a role in jamming bat echolocation. The ultrasonic clicks were subsequently found to be produced mostly by unpalatable moths to warn bats, just as warning colorations are used against predators that hunt by sight.[97] Some otherwise palatable moths have evolved to mimic these calls.[98] More recently, the claim that some moths can jam bat sonar has been revisited. Ultrasonic recording and high-speed infrared videography of bat-moth interactions suggest the palatable tiger moth really does defend against attacking big brown bats using ultrasonic clicks that jam bat sonar.[99]
+
+Very low sounds are also produced in various species of Coleoptera, Hymenoptera, Lepidoptera, Mantodea and Neuroptera. These low sounds are simply the sounds made by the insect's movement. Through microscopic stridulatory structures located on the insect's muscles and joints, the normal sounds of the insect moving are amplified and can be used to warn or communicate with other insects. Most sound-making insects also have tympanal organs that can perceive airborne sounds. Some species in Hemiptera, such as the corixids (water boatmen), are known to communicate via underwater sounds.[100] Most insects are also able to sense vibrations transmitted through surfaces.
+
+Communication using surface-borne vibrational signals is more widespread among insects because of size constraints in producing air-borne sounds.[101] Insects cannot effectively produce low-frequency sounds, and high-frequency sounds tend to disperse more in a dense environment (such as foliage), so insects living in such environments communicate primarily using substrate-borne vibrations.[102] The mechanisms of production of vibrational signals are just as diverse as those for producing sound in insects.
+
+Some species use vibrations for communicating within members of the same species, such as to attract mates as in the songs of the shield bug Nezara viridula.[103] Vibrations can also be used to communicate between entirely different species; lycaenid (gossamer-winged butterfly) caterpillars, which are myrmecophilous (living in a mutualistic association with ants) communicate with ants in this way.[104] The Madagascar hissing cockroach has the ability to press air through its spiracles to make a hissing noise as a sign of aggression;[105] the death's-head hawkmoth makes a squeaking noise by forcing air out of their pharynx when agitated, which may also reduce aggressive worker honey bee behavior when the two are in close proximity.[106]
+
+Chemical communications in animals rely on a variety of aspects including taste and smell. Chemoreception is the physiological response of a sense organ (i.e. taste or smell) to a chemical stimulus where the chemicals act as signals to regulate the state or activity of a cell. A semiochemical is a message-carrying chemical that is meant to attract, repel, and convey information. Types of semiochemicals include pheromones and kairomones. One example is the butterfly Phengaris arion which uses chemical signals as a form of mimicry to aid in predation.[107]
+
+In addition to the use of sound for communication, a wide range of insects have evolved chemical means for communication. These chemicals, termed semiochemicals, are often derived from plant metabolites include those meant to attract, repel and provide other kinds of information. Pheromones, a type of semiochemical, are used for attracting mates of the opposite sex, for aggregating conspecific individuals of both sexes, for deterring other individuals from approaching, to mark a trail, and to trigger aggression in nearby individuals. Allomones benefit their producer by the effect they have upon the receiver. Kairomones benefit their receiver instead of their producer. Synomones benefit the producer and the receiver. While some chemicals are targeted at individuals of the same species, others are used for communication across species. The use of scents is especially well known to have developed in social insects.[34]:96–105
+
+Social insects, such as termites, ants and many bees and wasps, are the most familiar species of eusocial animals.[108] They live together in large well-organized colonies that may be so tightly integrated and genetically similar that the colonies of some species are sometimes considered superorganisms. It is sometimes argued that the various species of honey bee are the only invertebrates (and indeed one of the few non-human groups) to have evolved a system of abstract symbolic communication where a behavior is used to represent and convey specific information about something in the environment. In this communication system, called dance language, the angle at which a bee dances represents a direction relative to the sun, and the length of the dance represents the distance to be flown.[34]:309–311 Though perhaps not as advanced as honey bees, bumblebees also potentially have some social communication behaviors. Bombus terrestris, for example, exhibit a faster learning curve for visiting unfamiliar, yet rewarding flowers, when they can see a conspecific foraging on the same species.[109]
+
+Only insects that live in nests or colonies demonstrate any true capacity for fine-scale spatial orientation or homing. This can allow an insect to return unerringly to a single hole a few millimeters in diameter among thousands of apparently identical holes clustered together, after a trip of up to several kilometers' distance. In a phenomenon known as philopatry, insects that hibernate have shown the ability to recall a specific location up to a year after last viewing the area of interest.[110] A few insects seasonally migrate large distances between different geographic regions (e.g., the overwintering areas of the monarch butterfly).[34]:14
+
+The eusocial insects build nests, guard eggs, and provide food for offspring full-time (see Eusociality).
+Most insects, however, lead short lives as adults, and rarely interact with one another except to mate or compete for mates. A small number exhibit some form of parental care, where they will at least guard their eggs, and sometimes continue guarding their offspring until adulthood, and possibly even feeding them. Another simple form of parental care is to construct a nest (a burrow or an actual construction, either of which may be simple or complex), store provisions in it, and lay an egg upon those provisions. The adult does not contact the growing offspring, but it nonetheless does provide food. This sort of care is typical for most species of bees and various types of wasps.[111]
+
+Insects are the only group of invertebrates to have developed flight. The evolution of insect wings has been a subject of debate. Some entomologists suggest that the wings are from paranotal lobes, or extensions from the insect's exoskeleton called the nota, called the paranotal theory. Other theories are based on a pleural origin. These theories include suggestions that wings originated from modified gills, spiracular flaps or as from an appendage of the epicoxa. The epicoxal theory suggests the insect wings are modified epicoxal exites, a modified appendage at the base of the legs or coxa.[112] In the Carboniferous age, some of the Meganeura dragonflies had as much as a 50 cm (20 in) wide wingspan. The appearance of gigantic insects has been found to be consistent with high atmospheric oxygen. The respiratory system of insects constrains their size, however the high oxygen in the atmosphere allowed larger sizes.[113] The largest flying insects today are much smaller, with the largest wingspan belonging to the white witch moth (Thysania agrippina), at approximately 28 cm (11 in).[114]
+
+Insect flight has been a topic of great interest in aerodynamics due partly to the inability of steady-state theories to explain the lift generated by the tiny wings of insects. But insect wings are in motion, with flapping and vibrations, resulting in churning and eddies, and the misconception that physics says "bumblebees can't fly" persisted throughout most of the twentieth century.
+
+Unlike birds, many small insects are swept along by the prevailing winds[115] although many of the larger insects are known to make migrations. Aphids are known to be transported long distances by low-level jet streams.[116] As such, fine line patterns associated with converging winds within weather radar imagery, like the WSR-88D radar network, often represent large groups of insects.[117]
+
+Many adult insects use six legs for walking and have adopted a tripedal gait. The tripedal gait allows for rapid walking while always having a stable stance and has been studied extensively in cockroaches and ants. The legs are used in alternate triangles touching the ground. For the first step, the middle right leg and the front and rear left legs are in contact with the ground and move the insect forward, while the front and rear right leg and the middle left leg are lifted and moved forward to a new position. When they touch the ground to form a new stable triangle the other legs can be lifted and brought forward in turn and so on.[118] The purest form of the tripedal gait is seen in insects moving at high speeds. However, this type of locomotion is not rigid and insects can adapt a variety of gaits. For example, when moving slowly, turning, avoiding obstacles, climbing or slippery surfaces, four (tetrapod) or more feet (wave-gait[119]) may be touching the ground. Insects can also adapt their gait to cope with the loss of one or more limbs.
+
+Cockroaches are among the fastest insect runners and, at full speed, adopt a bipedal run to reach a high velocity in proportion to their body size. As cockroaches move very quickly, they need to be video recorded at several hundred frames per second to reveal their gait. More sedate locomotion is seen in the stick insects or walking sticks (Phasmatodea). A few insects have evolved to walk on the surface of the water, especially members of the Gerridae family, commonly known as water striders. A few species of ocean-skaters in the genus Halobates even live on the surface of open oceans, a habitat that has few insect species.[120]
+
+Insect walking is of particular interest as an alternative form of locomotion in robots. The study of insects and bipeds has a significant impact on possible robotic methods of transport. This may allow new robots to be designed that can traverse terrain that robots with wheels may be unable to handle.[118]
+
+A large number of insects live either part or the whole of their lives underwater. In many of the more primitive orders of insect, the immature stages are spent in an aquatic environment. Some groups of insects, like certain water beetles, have aquatic adults as well.[72]
+
+Many of these species have adaptations to help in under-water locomotion. Water beetles and water bugs have legs adapted into paddle-like structures. Dragonfly naiads use jet propulsion, forcibly expelling water out of their rectal chamber.[121] Some species like the water striders are capable of walking on the surface of water. They can do this because their claws are not at the tips of the legs as in most insects, but recessed in a special groove further up the leg; this prevents the claws from piercing the water's surface film.[72] Other insects such as the Rove beetle Stenus are known to emit pygidial gland secretions that reduce surface tension making it possible for them to move on the surface of water by Marangoni propulsion (also known by the German term Entspannungsschwimmen).[122][123]
+
+Insect ecology is the scientific study of how insects, individually or as a community, interact with the surrounding environment or ecosystem.[124]:3 Insects play one of the most important roles in their ecosystems, which includes many roles, such as soil turning and aeration, dung burial, pest control, pollination and wildlife nutrition. An example is the beetles, which are scavengers that feed on dead animals and fallen trees and thereby recycle biological materials into forms found useful by other organisms.[125] These insects, and others, are responsible for much of the process by which topsoil is created.[34]:3, 218–228
+
+Insects are mostly soft bodied, fragile and almost defenseless compared to other, larger lifeforms. The immature stages are small, move slowly or are immobile, and so all stages are exposed to predation and parasitism. Insects then have a variety of defense strategies to avoid being attacked by predators or parasitoids. These include camouflage, mimicry, toxicity and active defense.[127]
+
+Camouflage is an important defense strategy, which involves the use of coloration or shape to blend into the surrounding environment.[128] This sort of protective coloration is common and widespread among beetle families, especially those that feed on wood or vegetation, such as many of the leaf beetles (family Chrysomelidae) or weevils. In some of these species, sculpturing or various colored scales or hairs cause the beetle to resemble bird dung or other inedible objects. Many of those that live in sandy environments blend in with the coloration of the substrate.[127] Most phasmids are known for effectively replicating the forms of sticks and leaves, and the bodies of some species (such as O. macklotti and Palophus centaurus) are covered in mossy or lichenous outgrowths that supplement their disguise. Very rarely, a species may have the ability to change color as their surroundings shift (Bostra scabrinota). In a further behavioral adaptation to supplement crypsis, a number of species have been noted to perform a rocking motion where the body is swayed from side to side that is thought to reflect the movement of leaves or twigs swaying in the breeze. Another method by which stick insects avoid predation and resemble twigs is by feigning death (catalepsy), where the insect enters a motionless state that can be maintained for a long period. The nocturnal feeding habits of adults also aids Phasmatodea in remaining concealed from predators.[129]
+
+Another defense that often uses color or shape to deceive potential enemies is mimicry. A number of longhorn beetles (family Cerambycidae) bear a striking resemblance to wasps, which helps them avoid predation even though the beetles are in fact harmless.[127] Batesian and Müllerian mimicry complexes are commonly found in Lepidoptera. Genetic polymorphism and natural selection give rise to otherwise edible species (the mimic) gaining a survival advantage by resembling inedible species (the model). Such a mimicry complex is referred to as Batesian. One of the most famous examples, where the viceroy butterfly was long believed to be a Batesian mimic of the inedible monarch, was later disproven, as the viceroy is more toxic than the monarch, and this resemblance is now considered to be a case of Müllerian mimicry.[126] In Müllerian mimicry, inedible species, usually within a taxonomic order, find it advantageous to resemble each other so as to reduce the sampling rate by predators who need to learn about the insects' inedibility. Taxa from the toxic genus Heliconius form one of the most well known Müllerian complexes.[130]
+
+Chemical defense is another important defense found among species of Coleoptera and Lepidoptera, usually being advertised by bright colors, such as the monarch butterfly. They obtain their toxicity by sequestering the chemicals from the plants they eat into their own tissues. Some Lepidoptera manufacture their own toxins. Predators that eat poisonous butterflies and moths may become sick and vomit violently, learning not to eat those types of species; this is actually the basis of Müllerian mimicry. A predator who has previously eaten a poisonous lepidopteran may avoid other species with similar markings in the future, thus saving many other species as well.[131] Some ground beetles of the family Carabidae can spray chemicals from their abdomen with great accuracy, to repel predators.[127]
+
+Pollination is the process by which pollen is transferred in the reproduction of plants, thereby enabling fertilisation and sexual reproduction. Most flowering plants require an animal to do the transportation. While other animals are included as pollinators, the majority of pollination is done by insects.[132] Because insects usually receive benefit for the pollination in the form of energy rich nectar it is a grand example of mutualism. The various flower traits (and combinations thereof) that differentially attract one type of pollinator or another are known as pollination syndromes. These arose through complex plant-animal adaptations. Pollinators find flowers through bright colorations, including ultraviolet, and attractant pheromones. The study of pollination by insects is known as anthecology.
+
+Many insects are parasites of other insects such as the parasitoid wasps. These insects are known as entomophagous parasites. They can be beneficial due to their devastation of pests that can destroy crops and other resources. Many insects have a parasitic relationship with humans such as the mosquito. These insects are known to spread diseases such as malaria and yellow fever and because of such, mosquitoes indirectly cause more deaths of humans than any other animal.
+
+Many insects are considered pests by humans. Insects commonly regarded as pests include those that are parasitic (e.g. lice, bed bugs), transmit diseases (mosquitoes, flies), damage structures (termites), or destroy agricultural goods (locusts, weevils). Many entomologists are involved in various forms of pest control, as in research for companies to produce insecticides, but increasingly rely on methods of biological pest control, or biocontrol. Biocontrol uses one organism to reduce the population density of another organism—the pest—and is considered a key element of integrated pest management.[133][134]
+
+Despite the large amount of effort focused at controlling insects, human attempts to kill pests with insecticides can backfire. If used carelessly, the poison can kill all kinds of organisms in the area, including insects' natural predators, such as birds, mice and other insectivores. The effects of DDT's use exemplifies how some insecticides can threaten wildlife beyond intended populations of pest insects.[135][136]
+
+Although pest insects attract the most attention, many insects are beneficial to the environment and to humans. Some insects, like wasps, bees, butterflies and ants, pollinate flowering plants. Pollination is a mutualistic relationship between plants and insects. As insects gather nectar from different plants of the same species, they also spread pollen from plants on which they have previously fed. This greatly increases plants' ability to cross-pollinate, which maintains and possibly even improves their evolutionary fitness. This ultimately affects humans since ensuring healthy crops is critical to agriculture. As well as pollination ants help with seed distribution of plants. This helps to spread the plants, which increases plant diversity. This leads to an overall better environment.[137] A serious environmental problem is the decline of populations of pollinator insects, and a number of species of insects are now cultured primarily for pollination management in order to have sufficient pollinators in the field, orchard or greenhouse at bloom time.[138]:240–243 Another solution, as shown in Delaware, has been to raise native plants to help support native pollinators like L. vierecki.[139] Insects also produce useful substances such as honey, wax, lacquer and silk. Honey bees have been cultured by humans for thousands of years for honey, although contracting for crop pollination is becoming more significant for beekeepers. The silkworm has greatly affected human history, as silk-driven trade established relationships between China and the rest of the world.
+
+Insectivorous insects, or insects that feed on other insects, are beneficial to humans if they eat insects that could cause damage to agriculture and human structures. For example, aphids feed on crops and cause problems for farmers, but ladybugs feed on aphids, and can be used as a means to significantly reduce pest aphid populations. While birds are perhaps more visible predators of insects, insects themselves account for the vast majority of insect consumption. Ants also help control animal populations by consuming small vertebrates.[140] Without predators to keep them in check, insects can undergo almost unstoppable population explosions.[34]:328–348[34]:400[141][142]
+
+Insects are also used in medicine, for example fly larvae (maggots) were formerly used to treat wounds to prevent or stop gangrene, as they would only consume dead flesh. This treatment is finding modern usage in some hospitals. Recently insects have also gained attention as potential sources of drugs and other medicinal substances.[143] Adult insects, such as crickets and insect larvae of various kinds, are also commonly used as fishing bait.[144]
+
+Insects play important roles in biological research. For example, because of its small size, short generation time and high fecundity, the common fruit fly Drosophila melanogaster is a model organism for studies in the genetics of higher eukaryotes. D. melanogaster has been an essential part of studies into principles like genetic linkage, interactions between genes, chromosomal genetics, development, behavior and evolution. Because genetic systems are well conserved among eukaryotes, understanding basic cellular processes like DNA replication or transcription in fruit flies can help to understand those processes in other eukaryotes, including humans.[145] The genome of D. melanogaster was sequenced in 2000, reflecting the organism's important role in biological research. It was found that 70% of the fly genome is similar to the human genome, supporting the evolution theory.[146]
+
+In some cultures, insects, especially deep-fried cicadas, are considered to be delicacies, whereas in other places they form part of the normal diet. Insects have a high protein content for their mass, and some authors suggest their potential as a major source of protein in human nutrition.[34]:10–13 In most first-world countries, however, entomophagy (the eating of insects), is taboo.[147]
+Since it is impossible to entirely eliminate pest insects from the human food chain, insects are inadvertently present in many foods, especially grains. Food safety laws in many countries do not prohibit insect parts in food, but rather limit their quantity. According to cultural materialist anthropologist Marvin Harris, the eating of insects is taboo in cultures that have other protein sources such as fish or livestock.
+
+Due to the abundance of insects and a worldwide concern of food shortages, the Food and Agriculture Organization of the United Nations considers that the world may have to, in the future, regard the prospects of eating insects as a food staple. Insects are noted for their nutrients, having a high content of protein, minerals and fats and are eaten by one-third of the global population.[148]
+
+Several insect species such as the black soldier fly or the housefly in their maggot forms, as well as beetle larvae such as mealworms can be processed and used as feed for farmed animals such as chicken, fish and pigs.[149]
+
+Insect larvae (i.e. black soldier fly larvae) can provide protein, grease, and chitin. The grease is usable in the pharmaceutical industry (cosmetics,[150] surfactants for shower gel) -hereby replacing other vegetable oils as palm oil.[151]
+
+Also, insect cooking oil, insect butter and fatty alcohols can be made from such insects as the superworm (Zophobas morio).[152][153]
+
+Many species of insects are sold and kept as pets.
+
+Scarab beetles held religious and cultural symbolism in Old Egypt, Greece and some shamanistic Old World cultures. The ancient Chinese regarded cicadas as symbols of rebirth or immortality. In Mesopotamian literature, the epic poem of Gilgamesh has allusions to Odonata that signify the impossibility of immortality. Among the Aborigines of Australia of the Arrernte language groups, honey ants and witchety grubs served as personal clan totems. In the case of the 'San' bush-men of the Kalahari, it is the praying mantis that holds much cultural significance including creation and zen-like patience in waiting.[34]:9

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+
+The Solar System[b] is the gravitationally bound system of the Sun and the objects that orbit it, either directly or indirectly.[c] Of the objects that orbit the Sun directly, the largest are the eight planets,[d] with the remainder being smaller objects, the dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly—the moons—two are larger than the smallest planet, Mercury.[e]
+
+The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system's mass is in the Sun, with the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest planets, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.
+
+The Solar System also contains smaller objects.[f] The asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, and beyond them a newly discovered population of sednoids. Within these populations, some objects are large enough to have rounded under their own gravity, though there is considerable debate as to how many there will prove to be.[9][10] Such objects are categorized as dwarf planets. The only certain dwarf planet is Pluto, with another trans-Neptunian object, Eris, expected to be, and the asteroid Ceres at least close to being a dwarf planet.[f] In addition to these two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds, freely travel between regions. Six of the planets, the six largest possible dwarf planets, and many of the smaller bodies are orbited by natural satellites, usually termed "moons" after the Moon. Each of the outer planets is encircled by planetary rings of dust and other small objects.
+
+The solar wind, a stream of charged particles flowing outwards from the Sun, creates a bubble-like region in the interstellar medium known as the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium; it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The Solar System is located in the Orion Arm, 26,000 light-years from the center of the Milky Way galaxy.
+
+For most of history, humanity did not recognize or understand the concept of the Solar System. Most people up to the Late Middle Ages–Renaissance believed Earth to be stationary at the centre of the universe and categorically different from the divine or ethereal objects that moved through the sky. Although the Greek philosopher Aristarchus of Samos had speculated on a heliocentric reordering of the cosmos, Nicolaus Copernicus was the first to develop a mathematically predictive heliocentric system.[11][12]
+
+In the 17th century, Galileo discovered that the Sun was marked with sunspots, and that Jupiter had four satellites in orbit around it.[13] Christiaan Huygens followed on from Galileo's discoveries by discovering Saturn's moon Titan and the shape of the rings of Saturn.[14] Edmond Halley realised in 1705 that repeated sightings of a comet were recording the same object, returning regularly once every 75–76 years. This was the first evidence that anything other than the planets orbited the Sun.[15] Around this time (1704), the term "Solar System" first appeared in English.[16] In 1838, Friedrich Bessel successfully measured a stellar parallax, an apparent shift in the position of a star created by Earth's motion around the Sun, providing the first direct, experimental proof of heliocentrism.[17] Improvements in observational astronomy and the use of unmanned spacecraft have since enabled the detailed investigation of other bodies orbiting the Sun.
+
+The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99.86% of the system's known mass and dominates it gravitationally.[18] The Sun's four largest orbiting bodies, the giant planets, account for 99% of the remaining mass, with Jupiter and Saturn together comprising more than 90%. The remaining objects of the Solar System (including the four terrestrial planets, the dwarf planets, moons, asteroids, and comets) together comprise less than 0.002% of the Solar System's total mass.[g]
+
+Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic, whereas comets and Kuiper belt objects are frequently at significantly greater angles to it.[22][23] As a result of the formation of the Solar System planets, and most other objects, orbit the Sun in the same direction that the Sun is rotating (counter-clockwise, as viewed from above Earth's north pole).[24] There are exceptions, such as Halley's Comet. Most of the larger moons orbit their planets in this prograde direction (with Triton being the largest retrograde exception) and most larger objects rotate themselves in the same direction (with Venus being a notable retrograde exception).
+
+The overall structure of the charted regions of the Solar System consists of the Sun, four relatively small inner planets surrounded by a belt of mostly rocky asteroids, and four giant planets surrounded by the Kuiper belt of mostly icy objects. Astronomers sometimes informally divide this structure into separate regions. The inner Solar System includes the four terrestrial planets and the asteroid belt. The outer Solar System is beyond the asteroids, including the four giant planets.[25] Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct region consisting of the objects beyond Neptune.[26]
+
+Most of the planets in the Solar System have secondary systems of their own, being orbited by planetary objects called natural satellites, or moons (two of which, Titan and Ganymede, are larger than the planet Mercury), and, in the case of the four giant planets, by planetary rings, thin bands of tiny particles that orbit them in unison. Most of the largest natural satellites are in synchronous rotation, with one face permanently turned toward their parent.
+
+Kepler's laws of planetary motion describe the orbits of objects about the Sun. Following Kepler's laws, each object travels along an ellipse with the Sun at one focus. Objects closer to the Sun (with smaller semi-major axes) travel more quickly because they are more affected by the Sun's gravity. On an elliptical orbit, a body's distance from the Sun varies over the course of its year. A body's closest approach to the Sun is called its perihelion, whereas its most distant point from the Sun is called its aphelion. The orbits of the planets are nearly circular, but many comets, asteroids, and Kuiper belt objects follow highly elliptical orbits. The positions of the bodies in the Solar System can be predicted using numerical models.
+
+Although the Sun dominates the system by mass, it accounts for only about 2% of the angular momentum.[27][28] The planets, dominated by Jupiter, account for most of the rest of the angular momentum due to the combination of their mass, orbit, and distance from the Sun, with a possibly significant contribution from comets.[27]
+
+The Sun, which comprises nearly all the matter in the Solar System, is composed of roughly 98% hydrogen and helium.[29] Jupiter and Saturn, which comprise nearly all the remaining matter, are also primarily composed of hydrogen and helium.[30][31] A composition gradient exists in the Solar System, created by heat and light pressure from the Sun; those objects closer to the Sun, which are more affected by heat and light pressure, are composed of elements with high melting points. Objects farther from the Sun are composed largely of materials with lower melting points.[32] The boundary in the Solar System beyond which those volatile substances could condense is known as the frost line, and it lies at roughly 5 AU from the Sun.[4]
+
+The objects of the inner Solar System are composed mostly of rock,[33] the collective name for compounds with high melting points, such as silicates, iron or nickel, that remained solid under almost all conditions in the protoplanetary nebula.[34] Jupiter and Saturn are composed mainly of gases, the astronomical term for materials with extremely low melting points and high vapour pressure, such as hydrogen, helium, and neon, which were always in the gaseous phase in the nebula.[34] Ices, like water, methane, ammonia, hydrogen sulfide, and carbon dioxide,[33] have melting points up to a few hundred kelvins.[34] They can be found as ices, liquids, or gases in various places in the Solar System, whereas in the nebula they were either in the solid or gaseous phase.[34] Icy substances comprise the majority of the satellites of the giant planets, as well as most of Uranus and Neptune (the so-called "ice giants") and the numerous small objects that lie beyond Neptune's orbit.[33][35] Together, gases and ices are referred to as volatiles.[36]
+
+The distance from Earth to the Sun is 1 astronomical unit [AU] (150,000,000 km; 93,000,000 mi). For comparison, the radius of the Sun is 0.0047 AU (700,000 km). Thus, the Sun occupies 0.00001% (10−5 %) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly one millionth (10−6) that of the Sun. Jupiter, the largest planet, is 5.2 astronomical units (780,000,000 km) from the Sun and has a radius of 71,000 km (0.00047 AU), whereas the most distant planet, Neptune, is 30 AU (4.5×109 km) from the Sun.
+
+With a few exceptions, the farther a planet or belt is from the Sun, the larger the distance between its orbit and the orbit of the next nearer object to the Sun. For example, Venus is approximately 0.33 AU farther out from the Sun than Mercury, whereas Saturn is 4.3 AU out from Jupiter, and Neptune lies 10.5 AU out from Uranus. Attempts have been made to determine a relationship between these orbital distances (for example, the Titius–Bode law),[37] but no such theory has been accepted. The images at the beginning of this section show the orbits of the various constituents of the Solar System on different scales.
+
+Some Solar System models attempt to convey the relative scales involved in the Solar System on human terms. Some are small in scale (and may be mechanical—called orreries)—whereas others extend across cities or regional areas.[38] The largest such scale model, the Sweden Solar System, uses the 110-metre (361 ft) Ericsson Globe in Stockholm as its substitute Sun, and, following the scale, Jupiter is a 7.5-metre (25-foot) sphere at Stockholm Arlanda Airport, 40 km (25 mi) away, whereas the farthest current object, Sedna, is a 10 cm (4 in) sphere in Luleå, 912 km (567 mi) away.[39][40]
+
+If the Sun–Neptune distance is scaled to 100 metres, then the Sun would be about 3 cm in diameter (roughly two-thirds the diameter of a golf ball), the giant planets would be all smaller than about 3 mm, and Earth's diameter along with that of the other terrestrial planets would be smaller than a flea (0.3 mm) at this scale.[41]
+
+Distances of selected bodies of the Solar System from the Sun. The left and right edges of each bar correspond to the perihelion and aphelion of the body, respectively, hence long bars denote high orbital eccentricity. The radius of the Sun is 0.7 million km, and the radius of Jupiter (the largest planet) is 0.07 million km, both too small to resolve on this image.
+
+The Solar System formed 4.568 billion years ago from the gravitational collapse of a region within a large molecular cloud.[h] This initial cloud was likely several light-years across and probably birthed several stars.[43] As is typical of molecular clouds, this one consisted mostly of hydrogen, with some helium, and small amounts of heavier elements fused by previous generations of stars. As the region that would become the Solar System, known as the pre-solar nebula,[44] collapsed, conservation of angular momentum caused it to rotate faster. The centre, where most of the mass collected, became increasingly hotter than the surrounding disc.[43] As the contracting nebula rotated faster, it began to flatten into a protoplanetary disc with a diameter of roughly 200 AU[43] and a hot, dense protostar at the centre.[45][46] The planets formed by accretion from this disc,[47] in which dust and gas gravitationally attracted each other, coalescing to form ever larger bodies. Hundreds of protoplanets may have existed in the early Solar System, but they either merged or were destroyed, leaving the planets, dwarf planets, and leftover minor bodies.
+
+Due to their higher boiling points, only metals and silicates could exist in solid form in the warm inner Solar System close to the Sun, and these would eventually form the rocky planets of Mercury, Venus, Earth, and Mars. Because metallic elements only comprised a very small fraction of the solar nebula, the terrestrial planets could not grow very large. The giant planets (Jupiter, Saturn, Uranus, and Neptune) formed further out, beyond the frost line, the point between the orbits of Mars and Jupiter where material is cool enough for volatile icy compounds to remain solid. The ices that formed these planets were more plentiful than the metals and silicates that formed the terrestrial inner planets, allowing them to grow massive enough to capture large atmospheres of hydrogen and helium, the lightest and most abundant elements. Leftover debris that never became planets congregated in regions such as the asteroid belt, Kuiper belt, and Oort cloud. The Nice model is an explanation for the creation of these regions and how the outer planets could have formed in different positions and migrated to their current orbits through various gravitational interactions.
+
+Within 50 million years, the pressure and density of hydrogen in the centre of the protostar became great enough for it to begin thermonuclear fusion.[49] The temperature, reaction rate, pressure, and density increased until hydrostatic equilibrium was achieved: the thermal pressure equalled the force of gravity. At this point, the Sun became a main-sequence star.[50] The main-sequence phase, from beginning to end, will last about 10 billion years for the Sun compared to around two billion years for all other phases of the Sun's pre-remnant life combined.[51] Solar wind from the Sun created the heliosphere and swept away the remaining gas and dust from the protoplanetary disc into interstellar space, ending the planetary formation process. The Sun is growing brighter; early in its main-sequence life its brightness was 70% that of what it is today.[52]
+
+The Solar System will remain roughly as we know it today until the hydrogen in the core of the Sun has been entirely converted to helium, which will occur roughly 5 billion years from now. This will mark the end of the Sun's main-sequence life. At this time, the core of the Sun will contract with hydrogen fusion occurring along a shell surrounding the inert helium, and the energy output will be much greater than at present. The outer layers of the Sun will expand to roughly 260 times its current diameter, and the Sun will become a red giant. Because of its vastly increased surface area, the surface of the Sun will be considerably cooler (2,600 K at its coolest) than it is on the main sequence.[51] The expanding Sun is expected to vaporize Mercury and render Earth uninhabitable. Eventually, the core will be hot enough for helium fusion; the Sun will burn helium for a fraction of the time it burned hydrogen in the core. The Sun is not massive enough to commence the fusion of heavier elements, and nuclear reactions in the core will dwindle. Its outer layers will move away into space, leaving a white dwarf, an extraordinarily dense object, half the original mass of the Sun but only the size of Earth.[53] The ejected outer layers will form what is known as a planetary nebula, returning some of the material that formed the Sun—but now enriched with heavier elements like carbon—to the interstellar medium.
+
+The Sun is the Solar System's star and by far its most massive component. Its large mass (332,900 Earth masses),[54] which comprises 99.86% of all the mass in the Solar System,[55] produces temperatures and densities in its core high enough to sustain nuclear fusion of hydrogen into helium, making it a main-sequence star.[56] This releases an enormous amount of energy, mostly radiated into space as electromagnetic radiation peaking in visible light.[57]
+
+The Sun is a G2-type main-sequence star. Hotter main-sequence stars are more luminous. The Sun's temperature is intermediate between that of the hottest stars and that of the coolest stars. Stars brighter and hotter than the Sun are rare, whereas substantially dimmer and cooler stars, known as red dwarfs, make up 85% of the stars in the Milky Way.[58][59]
+
+The Sun is a population I star; it has a higher abundance of elements heavier than hydrogen and helium ("metals" in astronomical parlance) than the older population II stars.[60] Elements heavier than hydrogen and helium were formed in the cores of ancient and exploding stars, so the first generation of stars had to die before the Universe could be enriched with these atoms. The oldest stars contain few metals, whereas stars born later have more. This high metallicity is thought to have been crucial to the Sun's development of a planetary system because the planets form from the accretion of "metals".[61]
+
+The vast majority of the Solar System consists of a near-vacuum known as the interplanetary medium. Along with light, the Sun radiates a continuous stream of charged particles (a plasma) known as the solar wind. This stream of particles spreads outwards at roughly 1.5 million kilometres per hour,[62] creating a tenuous atmosphere that permeates the interplanetary medium out to at least 100 AU (see § Heliosphere).[63] Activity on the Sun's surface, such as solar flares and coronal mass ejections, disturbs the heliosphere, creating space weather and causing geomagnetic storms.[64] The largest structure within the heliosphere is the heliospheric current sheet, a spiral form created by the actions of the Sun's rotating magnetic field on the interplanetary medium.[65][66]
+
+Earth's magnetic field stops its atmosphere from being stripped away by the solar wind.[67] Venus and Mars do not have magnetic fields, and as a result the solar wind is causing their atmospheres to gradually bleed away into space.[68] Coronal mass ejections and similar events blow a magnetic field and huge quantities of material from the surface of the Sun. The interaction of this magnetic field and material with Earth's magnetic field funnels charged particles into Earth's upper atmosphere, where its interactions create aurorae seen near the magnetic poles.
+
+The heliosphere and planetary magnetic fields (for those planets that have them) partially shield the Solar System from high-energy interstellar particles called cosmic rays. The density of cosmic rays in the interstellar medium and the strength of the Sun's magnetic field change on very long timescales, so the level of cosmic-ray penetration in the Solar System varies, though by how much is unknown.[69]
+
+The interplanetary medium is home to at least two disc-like regions of cosmic dust. The first, the zodiacal dust cloud, lies in the inner Solar System and causes the zodiacal light. It was likely formed by collisions within the asteroid belt brought on by gravitational interactions with the planets.[70] The second dust cloud extends from about 10 AU to about 40 AU, and was probably created by similar collisions within the Kuiper belt.[71][72]
+
+The inner Solar System is the region comprising the terrestrial planets and the asteroid belt.[73] Composed mainly of silicates and metals, the objects of the inner Solar System are relatively close to the Sun; the radius of this entire region is less than the distance between the orbits of Jupiter and Saturn. This region is also within the frost line, which is a little less than 5 AU (about 700 million km) from the Sun.[74]
+
+The four terrestrial or inner planets have dense, rocky compositions, few or no moons, and no ring systems. They are composed largely of refractory minerals, such as the silicates—which form their crusts and mantles—and metals, such as iron and nickel, which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather; all have impact craters and tectonic surface features, such as rift valleys and volcanoes. The term inner planet should not be confused with inferior planet, which designates those planets that are closer to the Sun than Earth is (i.e. Mercury and Venus).
+
+Mercury (0.4 AU from the Sun) is the closest planet to the Sun and on average, all seven other planets.[75][76] The smallest planet in the Solar System (0.055 M⊕), Mercury has no natural satellites. Besides impact craters, its only known geological features are lobed ridges or rupes that were probably produced by a period of contraction early in its history.[77] Mercury's very tenuous atmosphere consists of atoms blasted off its surface by the solar wind.[78] Its relatively large iron core and thin mantle have not yet been adequately explained. Hypotheses include that its outer layers were stripped off by a giant impact, or that it was prevented from fully accreting by the young Sun's energy.[79][80]
+
+Venus (0.7 AU from the Sun) is close in size to Earth (0.815 M⊕) and, like Earth, has a thick silicate mantle around an iron core, a substantial atmosphere, and evidence of internal geological activity. It is much drier than Earth, and its atmosphere is ninety times as dense. Venus has no natural satellites. It is the hottest planet, with surface temperatures over 400 °C (752 °F), most likely due to the amount of greenhouse gases in the atmosphere.[81] No definitive evidence of current geological activity has been detected on Venus, but it has no magnetic field that would prevent depletion of its substantial atmosphere, which suggests that its atmosphere is being replenished by volcanic eruptions.[82]
+
+Earth (1 AU from the Sun) is the largest and densest of the inner planets, the only one known to have current geological activity, and the only place where life is known to exist.[83] Its liquid hydrosphere is unique among the terrestrial planets, and it is the only planet where plate tectonics has been observed. Earth's atmosphere is radically different from those of the other planets, having been altered by the presence of life to contain 21% free oxygen.[84] It has one natural satellite, the Moon, the only large satellite of a terrestrial planet in the Solar System.
+
+Mars (1.5 AU from the Sun) is smaller than Earth and Venus (0.107 M⊕). It has an atmosphere of mostly carbon dioxide with a surface pressure of 6.1 millibars (roughly 0.6% of that of Earth).[85] Its surface, peppered with vast volcanoes, such as Olympus Mons, and rift valleys, such as Valles Marineris, shows geological activity that may have persisted until as recently as 2 million years ago.[86] Its red colour comes from iron oxide (rust) in its soil.[87] Mars has two tiny natural satellites (Deimos and Phobos) thought to be either captured asteroids,[88] or ejected debris from a massive impact early in Mars's history.[89]
+
+Asteroids except for the largest, Ceres, are classified as small Solar System bodies[f] and are composed mainly of refractory rocky and metallic minerals, with some ice.[90][91] They range from a few metres to hundreds of kilometres in size. Asteroids smaller than one meter are usually called meteoroids and micrometeoroids (grain-sized), depending on different, somewhat arbitrary definitions.
+
+The asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3 AU from the Sun. It is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter.[92] The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter.[93] Despite this, the total mass of the asteroid belt is unlikely to be more than a thousandth of that of Earth.[21] The asteroid belt is very sparsely populated; spacecraft routinely pass through without incident.
+
+Ceres (2.77 AU) is the largest asteroid, a protoplanet, and a dwarf planet.[f] It has a diameter of slightly under 1000 km, and a mass large enough for its own gravity to pull it into a spherical shape. Ceres was considered a planet when it was discovered in 1801, and was reclassified to asteroid in the 1850s as further observations revealed additional asteroids.[94] It was classified as a dwarf planet in 2006 when the definition of a planet was created.
+
+Asteroids in the asteroid belt are divided into asteroid groups and families based on their orbital characteristics. Asteroid moons are asteroids that orbit larger asteroids. They are not as clearly distinguished as planetary moons, sometimes being almost as large as their partners. The asteroid belt also contains main-belt comets, which may have been the source of Earth's water.[95]
+
+Jupiter trojans are located in either of Jupiter's L4 or L5 points (gravitationally stable regions leading and trailing a planet in its orbit); the term trojan is also used for small bodies in any other planetary or satellite Lagrange point. Hilda asteroids are in a 2:3 resonance with Jupiter; that is, they go around the Sun three times for every two Jupiter orbits.[96]
+
+The inner Solar System also contains near-Earth asteroids, many of which cross the orbits of the inner planets.[97] Some of them are potentially hazardous objects.
+
+The outer region of the Solar System is home to the giant planets and their large moons. The centaurs and many short-period comets also orbit in this region. Due to their greater distance from the Sun, the solid objects in the outer Solar System contain a higher proportion of volatiles, such as water, ammonia, and methane than those of the inner Solar System because the lower temperatures allow these compounds to remain solid.
+
+The four outer planets, or giant planets (sometimes called Jovian planets), collectively make up 99% of the mass known to orbit the Sun.[g] Jupiter and Saturn are together more than 400 times the mass of Earth and consist overwhelmingly of hydrogen and helium. Uranus and Neptune are far less massive—less than 20 Earth masses (M⊕) each—and are composed primarily of ices. For these reasons, some astronomers suggest they belong in their own category, ice giants.[98] All four giant planets have rings, although only Saturn's ring system is easily observed from Earth. The term superior planet designates planets outside Earth's orbit and thus includes both the outer planets and Mars.
+
+Jupiter (5.2 AU), at 318 M⊕, is 2.5 times the mass of all the other planets put together. It is composed largely of hydrogen and helium. Jupiter's strong internal heat creates semi-permanent features in its atmosphere, such as cloud bands and the Great Red Spot. Jupiter has 79 known satellites. The four largest, Ganymede, Callisto, Io, and Europa, show similarities to the terrestrial planets, such as volcanism and internal heating.[99] Ganymede, the largest satellite in the Solar System, is larger than Mercury.
+
+Saturn (9.5 AU), distinguished by its extensive ring system, has several similarities to Jupiter, such as its atmospheric composition and magnetosphere. Although Saturn has 60% of Jupiter's volume, it is less than a third as massive, at 95 M⊕. Saturn is the only planet of the Solar System that is less dense than water.[100] The rings of Saturn are made up of small ice and rock particles. Saturn has 82 confirmed satellites composed largely of ice. Two of these, Titan and Enceladus, show signs of geological activity.[101] Titan, the second-largest moon in the Solar System, is larger than Mercury and the only satellite in the Solar System with a substantial atmosphere.
+
+Uranus (19.2 AU), at 14 M⊕, is the lightest of the outer planets. Uniquely among the planets, it orbits the Sun on its side; its axial tilt is over ninety degrees to the ecliptic. It has a much colder core than the other giant planets and radiates very little heat into space.[102] Uranus has 27 known satellites, the largest ones being Titania, Oberon, Umbriel, Ariel, and Miranda.
+
+Neptune (30.1 AU), though slightly smaller than Uranus, is more massive (17 M⊕) and hence more dense. It radiates more internal heat, but not as much as Jupiter or Saturn.[103] Neptune has 14 known satellites. The largest, Triton, is geologically active, with geysers of liquid nitrogen.[104] Triton is the only large satellite with a retrograde orbit. Neptune is accompanied in its orbit by several minor planets, termed Neptune trojans, that are in 1:1 resonance with it.
+
+The centaurs are icy comet-like bodies whose orbits have semi-major axes greater than Jupiter's (5.5 AU) and less than Neptune's (30 AU). The largest known centaur, 10199 Chariklo, has a diameter of about 250 km.[105] The first centaur discovered, 2060 Chiron, has also been classified as comet (95P) because it develops a coma just as comets do when they approach the Sun.[106]
+
+Comets are small Solar System bodies,[f] typically only a few kilometres across, composed largely of volatile ices. They have highly eccentric orbits, generally a perihelion within the orbits of the inner planets and an aphelion far beyond Pluto. When a comet enters the inner Solar System, its proximity to the Sun causes its icy surface to sublimate and ionise, creating a coma: a long tail of gas and dust often visible to the naked eye.
+
+Short-period comets have orbits lasting less than two hundred years. Long-period comets have orbits lasting thousands of years. Short-period comets are thought to originate in the Kuiper belt, whereas long-period comets, such as Hale–Bopp, are thought to originate in the Oort cloud. Many comet groups, such as the Kreutz Sungrazers, formed from the breakup of a single parent.[107] Some comets with hyperbolic orbits may originate outside the Solar System, but determining their precise orbits is difficult.[108] Old comets that have had most of their volatiles driven out by solar warming are often categorised as asteroids.[109]
+
+Beyond the orbit of Neptune lies the area of the "trans-Neptunian region", with the doughnut-shaped Kuiper belt, home of Pluto and several other dwarf planets, and an overlapping disc of scattered objects, which is tilted toward the plane of the Solar System and reaches much further out than the Kuiper belt. The entire region is still largely unexplored. It appears to consist overwhelmingly of many thousands of small worlds—the largest having a diameter only a fifth that of Earth and a mass far smaller than that of the Moon—composed mainly of rock and ice. This region is sometimes described as the "third zone of the Solar System", enclosing the inner and the outer Solar System.[110]
+
+The Kuiper belt is a great ring of debris similar to the asteroid belt, but consisting mainly of objects composed primarily of ice.[111] It extends between 30 and 50 AU from the Sun. Though it is estimated to contain anything from dozens to thousands of dwarf planets, it is composed mainly of small Solar System bodies. Many of the larger Kuiper belt objects, such as Quaoar, Varuna, and Orcus, may prove to be dwarf planets with further data. There are estimated to be over 100,000 Kuiper belt objects with a diameter greater than 50 km, but the total mass of the Kuiper belt is thought to be only a tenth or even a hundredth the mass of Earth.[20] Many Kuiper belt objects have multiple satellites,[112] and most have orbits that take them outside the plane of the ecliptic.[113]
+
+The Kuiper belt can be roughly divided into the "classical" belt and the resonances.[111] Resonances are orbits linked to that of Neptune (e.g. twice for every three Neptune orbits, or once for every two). The first resonance begins within the orbit of Neptune itself. The classical belt consists of objects having no resonance with Neptune, and extends from roughly 39.4 AU to 47.7 AU.[114] Members of the classical Kuiper belt are classified as cubewanos, after the first of their kind to be discovered, 15760 Albion (which previously had the provisional designation 1992 QB1), and are still in near primordial, low-eccentricity orbits.[115]
+
+The dwarf planet Pluto (39 AU average) is the largest known object in the Kuiper belt. When discovered in 1930, it was considered to be the ninth planet; this changed in 2006 with the adoption of a formal definition of planet. Pluto has a relatively eccentric orbit inclined 17 degrees to the ecliptic plane and ranging from 29.7 AU from the Sun at perihelion (within the orbit of Neptune) to 49.5 AU at aphelion. Pluto has a 3:2 resonance with Neptune, meaning that Pluto orbits twice round the Sun for every three Neptunian orbits. Kuiper belt objects whose orbits share this resonance are called plutinos.[116]
+
+Charon, the largest of Pluto's moons, is sometimes described as part of a binary system with Pluto, as the two bodies orbit a barycentre of gravity above their surfaces (i.e. they appear to "orbit each other"). Beyond Charon, four much smaller moons, Styx, Nix, Kerberos, and Hydra, orbit within the system.
+
+Makemake (45.79 AU average), although smaller than Pluto, is the largest known object in the classical Kuiper belt (that is, a Kuiper belt object not in a confirmed resonance with Neptune). Makemake is the brightest object in the Kuiper belt after Pluto. It was assigned a naming committee under the expectation that it would prove to be a dwarf planet in 2008.[6] Its orbit is far more inclined than Pluto's, at 29°.[117]
+
+Haumea (43.13 AU average) is in an orbit similar to Makemake, except that it is in a temporary 7:12 orbital resonance with Neptune.[118]
+It was named under the same expectation that it would prove to be a dwarf planet, though subsequent observations have indicated that it may not be a dwarf planet after all.[119]
+
+The scattered disc, which overlaps the Kuiper belt but extends out to about 200 AU, is thought to be the source of short-period comets. Scattered-disc objects are thought to have been ejected into erratic orbits by the gravitational influence of Neptune's early outward migration. Most scattered disc objects (SDOs) have perihelia within the Kuiper belt but aphelia far beyond it (some more than 150 AU from the Sun). SDOs' orbits are also highly inclined to the ecliptic plane and are often almost perpendicular to it. Some astronomers consider the scattered disc to be merely another region of the Kuiper belt and describe scattered disc objects as "scattered Kuiper belt objects".[120] Some astronomers also classify centaurs as inward-scattered Kuiper belt objects along with the outward-scattered residents of the scattered disc.[121]
+
+Eris (68 AU average) is the largest known scattered disc object, and caused a debate about what constitutes a planet, because it is 25% more massive than Pluto[122] and about the same diameter. It is the most massive of the known dwarf planets. It has one known moon, Dysnomia. Like Pluto, its orbit is highly eccentric, with a perihelion of 38.2 AU (roughly Pluto's distance from the Sun) and an aphelion of 97.6 AU, and steeply inclined to the ecliptic plane.
+
+The point at which the Solar System ends and interstellar space begins is not precisely defined because its outer boundaries are shaped by two separate forces: the solar wind and the Sun's gravity. The limit of the solar wind's influence is roughly four times Pluto's distance from the Sun; this heliopause, the outer boundary of the heliosphere, is considered the beginning of the interstellar medium.[63] The Sun's Hill sphere, the effective range of its gravitational dominance, is thought to extend up to a thousand times farther and encompasses the theorized Oort cloud.[123]
+
+The heliosphere is a stellar-wind bubble, a region of space dominated by the Sun, which radiates at roughly 400 km/s its solar wind, a stream of charged particles, until it collides with the wind of the interstellar medium.
+
+The collision occurs at the termination shock, which is roughly 80–100 AU from the Sun upwind of the interstellar medium and roughly 200 AU from the Sun downwind.[124] Here the wind slows dramatically, condenses and becomes more turbulent,[124] forming a great oval structure known as the heliosheath. This structure is thought to look and behave very much like a comet's tail, extending outward for a further 40 AU on the upwind side but tailing many times that distance downwind; evidence from Cassini and Interstellar Boundary Explorer spacecraft has suggested that it is forced into a bubble shape by the constraining action of the interstellar magnetic field.[125]
+
+The outer boundary of the heliosphere, the heliopause, is the point at which the solar wind finally terminates and is the beginning of interstellar space.[63] Voyager 1 and Voyager 2 are reported to have passed the termination shock and entered the heliosheath, at 94 and 84 AU from the Sun, respectively.[126][127] Voyager 1 is reported to have crossed the heliopause in August 2012.[128]
+
+The shape and form of the outer edge of the heliosphere is likely affected by the fluid dynamics of interactions with the interstellar medium as well as solar magnetic fields prevailing to the south, e.g. it is bluntly shaped with the northern hemisphere extending 9 AU farther than the southern hemisphere.[124] Beyond the heliopause, at around 230 AU, lies the bow shock, a plasma "wake" left by the Sun as it travels through the Milky Way.[129]
+
+Due to a lack of data, conditions in local interstellar space are not known for certain. It is expected that NASA's Voyager spacecraft, as they pass the heliopause, will transmit valuable data on radiation levels and solar wind to Earth.[130] How well the heliosphere shields the Solar System from cosmic rays is poorly understood. A NASA-funded team has developed a concept of a "Vision Mission" dedicated to sending a probe to the heliosphere.[131][132]
+
+90377 Sedna (520 AU average) is a large, reddish object with a gigantic, highly elliptical orbit that takes it from about 76 AU at perihelion to 940 AU at aphelion and takes 11,400 years to complete. Mike Brown, who discovered the object in 2003, asserts that it cannot be part of the scattered disc or the Kuiper belt because its perihelion is too distant to have been affected by Neptune's migration. He and other astronomers consider it to be the first in an entirely new population, sometimes termed "distant detached objects" (DDOs), which also may include the object 2000 CR105, which has a perihelion of 45 AU, an aphelion of 415 AU, and an orbital period of 3,420 years.[133] Brown terms this population the "inner Oort cloud" because it may have formed through a similar process, although it is far closer to the Sun.[134] Sedna is very likely a dwarf planet, though its shape has yet to be determined. The second unequivocally detached object, with a perihelion farther than Sedna's at roughly 81 AU, is 2012 VP113, discovered in 2012. Its aphelion is only half that of Sedna's, at 400–500 AU.[135][136]
+
+The Oort cloud is a hypothetical spherical cloud of up to a trillion icy objects that is thought to be the source for all long-period comets and to surround the Solar System at roughly 50,000 AU (around 1 light-year (ly)), and possibly to as far as 100,000 AU (1.87 ly). It is thought to be composed of comets that were ejected from the inner Solar System by gravitational interactions with the outer planets. Oort cloud objects move very slowly, and can be perturbed by infrequent events, such as collisions, the gravitational effects of a passing star, or the galactic tide, the tidal force exerted by the Milky Way.[137][138]
+
+Much of the Solar System is still unknown. The Sun's gravitational field is estimated to dominate the gravitational forces of surrounding stars out to about two light years (125,000 AU). Lower estimates for the radius of the Oort cloud, by contrast, do not place it farther than 50,000 AU.[139] Despite discoveries such as Sedna, the region between the Kuiper belt and the Oort cloud, an area tens of thousands of AU in radius, is still virtually unmapped. There are also ongoing studies of the region between Mercury and the Sun.[140] Objects may yet be discovered in the Solar System's uncharted regions.
+
+Currently, the furthest known objects, such as Comet West, have aphelia around 70,000 AU from the Sun, but as the Oort cloud becomes better known, this may change.
+
+The Solar System is located in the Milky Way, a barred spiral galaxy with a diameter of about 100,000 light-years containing more than 100 billion stars.[141] The Sun resides in one of the Milky Way's outer spiral arms, known as the Orion–Cygnus Arm or Local Spur.[142] The Sun lies between 25,000 and 28,000 light-years from the Galactic Centre,[143] and its speed within the Milky Way is about 220 km/s, so that it completes one revolution every 225–250 million years. This revolution is known as the Solar System's galactic year.[144] The solar apex, the direction of the Sun's path through interstellar space, is near the constellation Hercules in the direction of the current location of the bright star Vega.[145] The plane of the ecliptic lies at an angle of about 60° to the galactic plane.[i]
+
+The Solar System's location in the Milky Way is a factor in the evolutionary history of life on Earth. Its orbit is close to circular, and orbits near the Sun are at roughly the same speed as that of the spiral arms.[147][148] Therefore, the Sun passes through arms only rarely. Because spiral arms are home to a far larger concentration of supernovae, gravitational instabilities, and radiation that could disrupt the Solar System, this has given Earth long periods of stability for life to evolve.[147] The Solar System also lies well outside the star-crowded environs of the galactic centre. Near the centre, gravitational tugs from nearby stars could perturb bodies in the Oort cloud and send many comets into the inner Solar System, producing collisions with potentially catastrophic implications for life on Earth. The intense radiation of the galactic centre could also interfere with the development of complex life.[147] Even at the Solar System's current location, some scientists have speculated that recent supernovae may have adversely affected life in the last 35,000 years, by flinging pieces of expelled stellar core towards the Sun, as radioactive dust grains and larger, comet-like bodies.[149]
+
+The Solar System is in the Local Interstellar Cloud or Local Fluff. It is thought to be near the neighbouring G-Cloud but it is not known if the Solar System is embedded in the Local Interstellar Cloud, or if it is in the region where the Local Interstellar Cloud and G-Cloud are interacting.[150][151] The Local Interstellar Cloud is an area of denser cloud in an otherwise sparse region known as the Local Bubble, an hourglass-shaped cavity in the interstellar medium roughly 300 light-years (ly) across. The bubble is suffused with high-temperature plasma, that suggests it is the product of several recent supernovae.[152]
+
+There are relatively few stars within ten light-years of the Sun. The closest is the triple star system Alpha Centauri, which is about 4.4 light-years away. Alpha Centauri A and B are a closely tied pair of Sun-like stars, whereas the small red dwarf, Proxima Centauri, orbits the pair at a distance of 0.2 light-year. In 2016, a potentially habitable exoplanet was confirmed to be orbiting Proxima Centauri, called Proxima Centauri b, the closest confirmed exoplanet to the Sun.[153] The stars next closest to the Sun are the red dwarfs Barnard's Star (at 5.9 ly), Wolf 359 (7.8 ly), and Lalande 21185 (8.3 ly).
+
+The largest nearby star is Sirius, a bright main-sequence star roughly 8.6 light-years away and roughly twice the Sun's mass and that is orbited by a white dwarf, Sirius B. The nearest brown dwarfs are the binary Luhman 16 system at 6.6 light-years. Other systems within ten light-years are the binary red-dwarf system Luyten 726-8 (8.7 ly) and the solitary red dwarf Ross 154 (9.7 ly).[154] The closest solitary Sun-like star to the Solar System is Tau Ceti at 11.9 light-years. It has roughly 80% of the Sun's mass but only 60% of its luminosity.[155] The closest known free-floating planetary-mass object to the Sun is WISE 0855−0714,[156] an object with a mass less than 10 Jupiter masses roughly 7 light-years away.
+
+Compared to many other planetary systems, the Solar System stands out in lacking planets interior to the orbit of Mercury.[157][158] The known Solar System also lacks super-Earths (Planet Nine could be a super-Earth beyond the known Solar System).[157] Uncommonly, it has only small rocky planets and large gas giants; elsewhere planets of intermediate size are typical—both rocky and gas—so there is no "gap" as seen between the size of Earth and of Neptune (with a radius 3.8 times as large). Also, these super-Earths have closer orbits than Mercury.[157] This led to the hypothesis that all planetary systems start with many close-in planets, and that typically a sequence of their collisions causes consolidation of mass into few larger planets, but in case of the Solar System the collisions caused their destruction and ejection.[159][160]
+
+The orbits of Solar System planets are nearly circular. Compared to other systems, they have smaller orbital eccentricity.[157] Although there are attempts to explain it partly with a bias in the radial-velocity detection method and partly with long interactions of a quite high number of planets, the exact causes remain undetermined.[157][161]
+
+This section is a sampling of Solar System bodies, selected for size and quality of imagery, and sorted by volume. Some omitted objects are larger than the ones included here, notably Eris, because these have not been imaged in high quality.
+
+Venus, Earth (Pale Blue Dot), Jupiter, Saturn, Uranus, Neptune (13 September 1996).
+
+Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Observable universe → UniverseEach arrow (→) may be read as "within" or "part of".
+

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+
+A game is a structured form of play, usually undertaken for entertainment or fun, and sometimes used as an educational tool.[1] Games are distinct from work, which is usually carried out for remuneration, and from art, which is more often an expression of aesthetic or ideological elements. However, the distinction is not clear-cut, and many games are also considered to be work (such as professional players of spectator sports or games) or art (such as jigsaw puzzles or games involving an artistic layout such as Mahjong, solitaire, or some video games).
+
+Games are sometimes played purely for enjoyment, sometimes for achievement or reward as well. They can be played alone, in teams, or online; by amateurs or by professionals. The players may have an audience of non-players, such as when people are entertained by watching a chess championship. On the other hand, players in a game may constitute their own audience as they take their turn to play. Often, part of the entertainment for children playing a game is deciding who is part of their audience and who is a player.
+
+Key components of games are goals, rules, challenge, and interaction. Games generally involve mental or physical stimulation, and often both. Many games help develop practical skills, serve as a form of exercise, or otherwise perform an educational, simulational, or psychological role.
+
+Attested as early as 2600 BC,[2][3] games are a universal part of human experience and present in all cultures. The Royal Game of Ur, Senet, and Mancala are some of the oldest known games.[4]
+
+Ludwig Wittgenstein was probably the first academic philosopher to address the definition of the word game. In his Philosophical Investigations,[5] Wittgenstein argued that the elements of games, such as play, rules, and competition, all fail to adequately define what games are. From this, Wittgenstein concluded that people apply the term game to a range of disparate human activities that bear to one another only what one might call family resemblances. As the following game definitions show, this conclusion was not a final one and today many philosophers, like Thomas Hurka, think that Wittgenstein was wrong and that Bernard Suits' definition is a good answer to the problem.[6]
+
+French sociologist Roger Caillois, in his book Les jeux et les hommes (Games and Men),[7] defined a game as an activity that must have the following characteristics:
+
+Game designer Chris Crawford defined the term in the context of computers.[8] using a series of dichotomies:
+
+Crawford's definition may thus be rendered as[original research?]: an interactive, goal-oriented activity made for money, with active agents to play against, in which players (including active agents) can interfere with each other.
+
+Other definitions, however, as well as history, show that entertainment and games are not necessarily undertaken for monetary gain.
+
+Games can be characterized by "what the player does".[8] This is often referred to as gameplay. Major key elements identified in this context are tools and rules that define the overall context of game.
+
+Games are often classified by the components required to play them (e.g. miniatures, a ball, cards, a board and pieces, or a computer). In places where the use of leather is well-established, the ball has been a popular game piece throughout recorded history, resulting in a worldwide popularity of ball games such as rugby, basketball, soccer (football), cricket, tennis, and volleyball. Other tools are more idiosyncratic to a certain region. Many countries in Europe, for instance, have unique standard decks of playing cards. Other games such as chess may be traced primarily through the development and evolution of its game pieces.
+
+Many game tools are tokens, meant to represent other things. A token may be a pawn on a board, play money, or an intangible item such as a point scored.
+
+Games such as hide-and-seek or tag do not use any obvious tool; rather, their interactivity is defined by the environment. Games with the same or similar rules may have different gameplay if the environment is altered. For example, hide-and-seek in a school building differs from the same game in a park; an auto race can be radically different depending on the track or street course, even with the same cars.
+
+Whereas games are often characterized by their tools, they are often defined by their rules. While rules are subject to variations and changes, enough change in the rules usually results in a "new" game. For instance, baseball can be played with "real" baseballs or with wiffleballs. However, if the players decide to play with only three bases, they are arguably playing a different game. There are exceptions to this in that some games deliberately involve the changing of their own rules, but even then there are often immutable meta-rules.
+
+Rules generally determine the time-keeping system, the rights and responsibilities of the players, and each player's goals. Player rights may include when they may spend resources or move tokens.
+
+The rules of a game are to be distinguished from its aims.[16][17] For most competitive games, the ultimate ‘aim’ is winning: in this sense, checkmate is the aim of chess.[18] Common win conditions are being first to amass a certain quota of points or tokens (as in Settlers of Catan), having the greatest number of tokens at the end of the game (as in Monopoly), or some relationship of one's game tokens to those of one's opponent (as in chess's checkmate). However, when we talk about the aims of a game, we also refer to intermediate aims: the things that you have to do in order to win the game. For instance, an intermediate aim in football is to score goals, because scoring goals will increase your likelihood to win the game (but isn't alone sufficient to win the game).
+
+Aims are not just a 'special' kind of rules: the difference between the rules of a game and the aims of a game is a fundamental one. This can be seen by considering some examples. The aim of chess is to checkmate, but although it is expected that players will try to checkmate each other, it is not a rule of chess that a player must checkmate the other player whenever he can (as a matter of fact, unskilled players often fail to take the opportunity to do so). Similarly, it is not a rule of football that a player must score a goal if he shoots a penalty (it is only expected, and not required, that he will try). On a general level, the distinction between the rules and the aims of a game can be characterised as follows: an aim identifies a sufficient condition for successful action, whereas the rule identifies a necessary condition for permissible action.[17] While meeting the aims often requires a certain degree of skill and (in some cases) luck, following the rules of a game merely requires knowledge of the rules and some careful attempt to follow them; it rarely (if ever) requires luck or demanding skills.
+
+A game's tools and rules will result in its requiring skill, strategy, luck, or a combination thereof, and are classified accordingly.
+
+Games of skill include games of physical skill, such as wrestling, tug of war, hopscotch, target shooting, and stake, and games of mental skill such as checkers and chess. Games of strategy include checkers, chess, Go, arimaa, and tic-tac-toe, and often require special equipment to play them. Games of chance include gambling games (blackjack, Mahjong, roulette, etc.), as well as snakes and ladders and rock, paper, scissors; most require equipment such as cards or dice. However, most games contain two or all three of these elements. For example, American football and baseball involve both physical skill and strategy while tiddlywinks, poker, and Monopoly combine strategy and chance. Many card and board games combine all three; most trick-taking games involve mental skill, strategy, and an element of chance, as do many strategic board games such as Risk, Settlers of Catan, and Carcassonne.
+
+Most games require multiple players. However, single-player games are unique in respect to the type of challenges a player faces. Unlike a game with multiple players competing with or against each other to reach the game's goal, a one-player game is a battle solely against an element of the environment (an artificial opponent), against one's own skills, against time, or against chance. Playing with a yo-yo or playing tennis against a wall is not generally recognized as playing a game due to the lack of any formidable opposition. Many games described as "single-player" may be termed actually puzzles or recreations.
+
+A multiplayer game is a game of several players who may be independent opponents or teams. Games with many independent players are difficult to analyze formally using game theory as the players may form and switch coalitions.[19] The term "game" in this context may mean either a true game played for entertainment, or a competitive activity describable in principle by mathematical game theory.
+
+John Nash proved that games with several players have a stable solution provided that coalitions between players are disallowed. Nash won the Nobel prize for economics for this important result which extended von Neumann's theory of zero-sum games. Nash's stable solution is known as the Nash equilibrium.[20]
+
+If cooperation between players is allowed, then the game becomes more complex; many concepts have been developed to analyze such games. While these have had some partial success in the fields of economics, politics and conflict, no good general theory has yet been developed.[20]
+
+In quantum game theory, it has been found that the introduction of quantum information into multiplayer games allows a new type of equilibrium strategy not found in traditional games. The entanglement of players's choices can have the effect of a contract by preventing players from profiting from what is known as betrayal.[21]
+
+Games can take a variety of forms, from competitive sports to board games and video games.
+
+Many sports require special equipment and dedicated playing fields, leading to the involvement of a community much larger than the group of players. A city or town may set aside such resources for the organization of sports leagues.
+
+Popular sports may have spectators who are entertained just by watching games. A community will often align itself with a local sports team that supposedly represents it (even if the team or most of its players only recently moved in); they often align themselves against their opponents or have traditional rivalries. The concept of fandom began with sports fans.
+
+Certain competitive sports, such as racing and gymnastics, are not games by definitions such as Crawford's (see above) – despite the inclusion of many in the Olympic Games – because competitors do not interact with their opponents; they simply challenge each other in indirect ways.
+
+Lawn games are outdoor games that can be played on a lawn; an area of mowed grass (or alternately, on graded soil) generally smaller than a sports field (pitch). Variations of many games that are traditionally played on a sports field are marketed as "lawn games" for home use in a front or back yard. Common lawn games include horseshoes, sholf, croquet, bocce, lawn bowls, and stake.
+
+A tabletop game is a game where the elements of play are confined to a small area and require little physical exertion, usually simply placing, picking up and moving game pieces. Most of these games are played at a table around which the players are seated and on which the game's elements are located. However, many games falling into this category, particularly party games, are more free-form in their play and can involve physical activity such as mime. Still, these games do not require a large area in which to play them, large amounts of strength or stamina, or specialized equipment other than what comes in a box.
+
+This class of games includes any game in which the skill element involved relates to manual dexterity or hand-eye coordination, but excludes the class of video games (see below). Games such as jacks, paper football, and Jenga require only very portable or improvised equipment and can be played on any flat level surface, while other examples, such as pinball, billiards, air hockey, foosball, and table hockey require specialized tables or other self-contained modules on which the game is played. The advent of home video game systems largely replaced some of these, such as table hockey, however air hockey, billiards, pinball and foosball remain popular fixtures in private and public game rooms. These games and others, as they require reflexes and coordination, are generally performed more poorly by intoxicated persons but are unlikely to result in injury because of this; as such the games are popular as drinking games. In addition, dedicated drinking games such as quarters and beer pong also involve physical coordination and are popular for similar reasons.
+
+Board games use as a central tool a board on which the players' status, resources, and progress are tracked using physical tokens. Many also involve dice or cards. Most games that simulate war are board games (though a large number of video games have been created to simulate strategic combat), and the board may be a map on which the players' tokens move. Virtually all board games involve "turn-based" play; one player contemplates and then makes a move, then the next player does the same, and a player can only act on their turn. This is opposed to "real-time" play as is found in some card games, most sports and most video games.
+
+Some games, such as chess and Go, are entirely deterministic, relying only on the strategy element for their interest. Such games are usually described as having "perfect information"; the only unknown is the exact thought processes of one's opponent, not the outcome of any unknown event inherent in the game (such as a card draw or die roll). Children's games, on the other hand, tend to be very luck-based, with games such as Candy Land and Chutes and Ladders having virtually no decisions to be made. By some definitions, such as that by Greg Costikyan, they are not games since there are no decisions to make which affect the outcome.[22] Many other games involving a high degree of luck do not allow direct attacks between opponents; the random event simply determines a gain or loss in the standing of the current player within the game, which is independent of any other player; the "game" then is actually a "race" by definitions such as Crawford's.
+
+Most other board games combine strategy and luck factors; the game of backgammon requires players to decide the best strategic move based on the roll of two dice. Trivia games have a great deal of randomness based on the questions a person gets. German-style board games are notable for often having rather less of a luck factor than many board games.
+
+Board game groups include race games, roll-and-move games, abstract strategy games, word games, and wargames, as well as trivia and other elements. Some board games fall into multiple groups or incorporate elements of other genres: Cranium is one popular example, where players must succeed in each of four skills: artistry, live performance, trivia, and language.
+
+Card games use a deck of cards as their central tool. These cards may be a standard Anglo-American (52-card) deck of playing cards (such as for bridge, poker, Rummy, etc.), a regional deck using 32, 36 or 40 cards and different suit signs (such as for the popular German game skat), a tarot deck of 78 cards (used in Europe to play a variety of trick-taking games collectively known as Tarot, Tarock or Tarocchi games), or a deck specific to the individual game (such as Set or 1000 Blank White Cards). Uno and Rook are examples of games that were originally played with a standard deck and have since been commercialized with customized decks. Some collectible card games such as Magic: The Gathering are played with a small selection of cards that have been collected or purchased individually from large available sets.
+
+Some board games include a deck of cards as a gameplay element, normally for randomization or to keep track of game progress. Conversely, some card games such as Cribbage use a board with movers, normally to keep score. The differentiation between the two genres in such cases depends on which element of the game is foremost in its play; a board game using cards for random actions can usually use some other method of randomization, while Cribbage can just as easily be scored on paper. These elements as used are simply the traditional and easiest methods to achieve their purpose.
+
+Dice games use a number of dice as their central element. Board games often use dice for a randomization element, and thus each roll of the dice has a profound impact on the outcome of the game, however dice games are differentiated in that the dice do not determine the success or failure of some other element of the game; they instead are the central indicator of the person's standing in the game. Popular dice games include Yahtzee, Farkle, Bunco, Liar's dice/Perudo, and Poker dice. As dice are, by their very nature, designed to produce apparently random numbers, these games usually involve a high degree of luck, which can be directed to some extent by the player through more strategic elements of play and through tenets of probability theory. Such games are thus popular as gambling games; the game of Craps is perhaps the most famous example, though Liar's dice and Poker dice were originally conceived of as gambling games.
+
+Domino games are similar in many respects to card games, but the generic device is instead a set of tiles called dominoes, which traditionally each have two ends, each with a given number of dots, or "pips", and each combination of two possible end values as it appears on a tile is unique in the set. The games played with dominoes largely center around playing a domino from the player's "hand" onto the matching end of another domino, and the overall object could be to always be able to make a play, to make all open endpoints sum to a given number or multiple, or simply to play all dominoes from one's hand onto the board. Sets vary in the number of possible dots on one end, and thus of the number of combinations and pieces; the most common set historically is double-six, though in more recent times "extended" sets such as double-nine have been introduced to increase the number of dominoes available, which allows larger hands and more players in a game. Muggins, Mexican Train, and Chicken Foot are very popular domino games. Texas 42 is a domino game more similar in its play to a "trick-taking" card game.
+
+Variations of traditional dominoes abound: Triominoes are similar in theory but are triangular and thus have three values per tile. Similarly, a game known as Quad-Ominos uses four-sided tiles.
+
+Some other games use tiles in place of cards; Rummikub is a variant of the Rummy card game family that uses tiles numbered in ascending rank among four colors, very similar in makeup to a 2-deck "pack" of Anglo-American playing cards. Mahjong is another game very similar to Rummy that uses a set of tiles with card-like values and art.
+
+Lastly, some games use graphical tiles to form a board layout, on which other elements of the game are played. Settlers of Catan and Carcassonne are examples. In each, the "board" is made up of a series of tiles; in Settlers of Catan the starting layout is random but static, while in Carcassonne the game is played by "building" the board tile-by-tile. Hive, an abstract strategy game using tiles as moving pieces, has mechanical and strategic elements similar to chess, although it has no board; the pieces themselves both form the layout and can move within it.
+
+Pencil and paper games require little or no specialized equipment other than writing materials, though some such games have been commercialized as board games (Scrabble, for instance, is based on the idea of a crossword puzzle, and tic-tac-toe sets with a boxed grid and pieces are available commercially). These games vary widely, from games centering on a design being drawn such as Pictionary and "connect-the-dots" games like sprouts, to letter and word games such as Boggle and Scattergories, to solitaire and logic puzzle games such as Sudoku and crossword puzzles.
+
+A guessing game has as its core a piece of information that one player knows, and the object is to coerce others into guessing that piece of information without actually divulging it in text or spoken word. Charades is probably the most well-known game of this type, and has spawned numerous commercial variants that involve differing rules on the type of communication to be given, such as Catch Phrase, Taboo, Pictionary, and similar. The genre also includes many game shows such as Win, Lose or Draw, Password and $25,000 Pyramid.
+
+Video games are computer- or microprocessor-controlled games. Computers can create virtual spaces for a wide variety of game types. Some video games simulate conventional game objects like cards or dice, while others can simulate environs either grounded in reality or fantastical in design, each with its own set of rules or goals.
+
+A computer or video game uses one or more input devices, typically a button/joystick combination (on arcade games); a keyboard, mouse or trackball (computer games); or a controller or a motion sensitive tool (console games). More esoteric devices such as paddle controllers have also been used for input.
+
+There are many genres of video game; the first commercial video game, Pong, was a simple simulation of table tennis. As processing power increased, new genres such as adventure and action games were developed that involved a player guiding a character from a third person perspective through a series of obstacles. This "real-time" element cannot be easily reproduced by a board game, which is generally limited to "turn-based" strategy; this advantage allows video games to simulate situations such as combat more realistically. Additionally, the playing of a video game does not require the same physical skill, strength or danger as a real-world representation of the game, and can provide either very realistic, exaggerated or impossible physics, allowing for elements of a fantastical nature, games involving physical violence, or simulations of sports. Lastly, a computer can, with varying degrees of success, simulate one or more human opponents in traditional table games such as chess, leading to simulations of such games that can be played by a single player.
+
+In more open-ended computer simulations, also known as sandbox-style games, the game provides a virtual environment in which the player may be free to do whatever they like within the confines of this universe. Sometimes, there is a lack of goals or opposition, which has stirred some debate on whether these should be considered "games" or "toys". (Crawford specifically mentions Will Wright's SimCity as an example of a toy.)[8]
+
+Online games have been part of culture from the very earliest days of networked and time-shared computers. Early commercial systems such as Plato were at least as widely famous for their games as for their strictly educational value. In 1958, Tennis for Two dominated Visitor's Day and drew attention to the oscilloscope at the Brookhaven National Laboratory; during the 1980s, Xerox PARC was known mainly for Maze War, which was offered as a hands-on demo to visitors.
+
+Modern online games are played using an Internet connection; some have dedicated client programs, while others require only a web browser. Some simpler browser games appeal to more casual gaming demographic groups (notably older audiences) that otherwise play very few video games.[23]
+
+Role-playing games, often abbreviated as RPGs, are a type of game in which the participants (usually) assume the roles of characters acting in a fictional setting. The original role playing games – or at least those explicitly marketed as such – are played with a handful of participants, usually face-to-face, and keep track of the developing fiction with pen and paper. Together, the players may collaborate on a story involving those characters; create, develop, and "explore" the setting; or vicariously experience an adventure outside the bounds of everyday life. Pen-and-paper role-playing games include, for example, Dungeons & Dragons and GURPS.
+
+The term role-playing game has also been appropriated by the video game industry to describe a genre of video games. These may be single-player games where one player experiences a programmed environment and story, or they may allow players to interact through the internet. The experience is usually quite different from traditional role-playing games. Single-player games include Final Fantasy, Fable, The Elder Scrolls, and Mass Effect. Online multi-player games, often referred to as Massively Multiplayer Online role playing games, or MMORPGs, include RuneScape, EverQuest 2, Guild Wars, MapleStory, Anarchy Online, and Dofus. As of 2009[update], the most successful MMORPG has been World of Warcraft, which controls the vast majority of the market.[24]
+
+Business games can take a variety of forms, from interactive board games to interactive games involving different props (balls, ropes, hoops, etc.) and different kinds of activities. The purpose of these games is to link to some aspect of organizational performance and to generate discussions about business improvement. Many business games focus on organizational behaviors. Some of these are computer simulations while others are simple designs for play and debriefing. Team building is a common focus of such activities.
+
+The term "game" can include simulation[25][26] or re-enactment of various activities or use in "real life" for various purposes: e.g., training, analysis, prediction. Well-known examples are war games and role-playing. The root of this meaning may originate in the human prehistory of games deduced by anthropology from observing primitive cultures, in which children's games mimic the activities of adults to a significant degree: hunting, warring, nursing, etc. These kinds of games are preserved in modern times.[original research?]

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+In botany, a tree is a perennial plant with an elongated stem, or trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are usable as lumber or plants above a specified height. In wider definitions, the taller palms, tree ferns, bananas, and bamboos are also trees. Trees are not a taxonomic group but include a variety of plant species that have independently evolved a trunk and branches as a way to tower above other plants to compete for sunlight. Trees tend to be long-lived, some reaching several thousand years old.  Trees have been in existence for 370 million years. It is estimated that there are some three trillion mature trees in the world.[1]
+
+A tree typically has many secondary branches supported clear of the ground by the trunk. This trunk typically contains woody tissue for strength, and vascular tissue to carry materials from one part of the tree to another. For most trees it is surrounded by a layer of bark which serves as a protective barrier. Below the ground, the roots branch and spread out widely; they serve to anchor the tree and extract moisture and nutrients from the soil. Above ground, the branches divide into smaller branches and shoots. The shoots typically bear leaves, which capture light energy and convert it into sugars by photosynthesis, providing the food for the tree's growth and development.
+
+Trees usually reproduce using seeds. Flowers and fruit may be present, but some trees, such as conifers, instead have pollen cones and seed cones. Palms, bananas, and bamboos also produce seeds, but tree ferns produce spores instead.
+
+Trees play a significant role in reducing erosion and moderating the climate. They remove carbon dioxide from the atmosphere and store large quantities of carbon in their tissues. Trees and forests provide a habitat for many species of animals and plants. Tropical rainforests are among the most biodiverse habitats in the world. Trees provide shade and shelter, timber for construction, fuel for cooking and heating, and fruit for food as well as having many other uses. In parts of the world, forests are shrinking as trees are cleared to increase the amount of land available for agriculture. Because of their longevity and usefulness, trees have always been revered, with sacred groves in various cultures, and they play a role in many of the world's mythologies.
+
+Although "tree" is a term of common parlance, there is no universally recognised precise definition of what a tree is, either botanically or in common language.[2] In its broadest sense, a tree is any plant with the general form of an elongated stem, or trunk, which supports the photosynthetic leaves or branches at some distance above the ground.[3] Trees are also typically defined by height,[4] with smaller plants from 0.5 to 10 m (1.6 to 32.8 ft) being called shrubs,[5] so the minimum height of a tree is only loosely defined.[4] Large herbaceous plants such as papaya and bananas are trees in this broad sense.[2][6]
+
+A commonly applied narrower definition is that a tree has a woody trunk formed by secondary growth, meaning that the trunk thickens each year by growing outwards, in addition to the primary upwards growth from the growing tip.[4][7] Under such a definition, herbaceous plants such as palms, bananas and papayas are not considered trees regardless of their height, growth form or stem girth. Certain monocots may be considered trees under a slightly looser definition;[8] while the Joshua tree, bamboos and palms do not have secondary growth and never produce true wood with growth rings,[9][10] they may produce "pseudo-wood" by lignifying cells formed by primary growth.[11] Tree species in the genus Dracaena, despite also being monocots, do have secondary growth caused by meristem in their trunk, but it is different from the thickening meristem found in dicotyledonous trees.[12]
+
+Aside from structural definitions, trees are commonly defined by use; for instance, as those plants which yield lumber.[13]
+
+The tree growth habit is an evolutionary adaptation found in different groups of plants: by growing taller, trees are able to compete better for sunlight.[14] Trees tend to be tall and long-lived,[15] some reaching several thousand years old.[16] Several trees are among the oldest organisms now living.[17] Trees have modified structures such as thicker stems composed of specialised cells that add structural strength and durability, allowing them to grow taller than many other plants and to spread out their foliage. They differ from shrubs, which have a similar growth form, by usually growing larger and having a single main stem;[5] but there is no consistent distinction between a tree and a shrub,[18] made more confusing by the fact that trees may be reduced in size under harsher environmental conditions such as on mountains and subarctic areas. The tree form has evolved separately in unrelated classes of plants in response to similar environmental challenges, making it a classic example of parallel evolution. With an estimated 60,000-100,000 species, the number of trees worldwide might total twenty-five per cent of all living plant species.[19][20] The greatest number of these grow in tropical regions and many of these areas have not yet been fully surveyed by botanists, making tree diversity and ranges poorly known.[21]
+
+The majority of tree species are angiosperms. There are about 1000 species of gymnosperm trees,[22] including conifers, cycads, ginkgophytes and gnetales; they produce seeds which are not enclosed in fruits, but in open structures such as pine cones, and many have tough waxy leaves, such as pine needles.[23] Most angiosperm trees are eudicots, the "true dicotyledons", so named because the seeds contain two cotyledons or seed leaves. There are also some trees among the old lineages of flowering plants called  basal angiosperms or paleodicots; these include Amborella, Magnolia, nutmeg and avocado,[24] while trees such as bamboo, palms and bananas are monocots.
+
+Wood gives structural strength to the trunk of most types of tree; this supports the plant as it grows larger. The vascular system of trees allows water, nutrients and other chemicals to be distributed around the plant, and without it trees would not be able to grow as large as they do. Trees, as relatively tall plants, need to draw water up the stem through the xylem from the roots by the suction produced as water evaporates from the leaves. If insufficient water is available the leaves will die.[25] The three main parts of trees include the root, stem, and leaves; they are integral parts of the vascular system which interconnects all the living cells. In trees and other plants that develop wood, the vascular cambium allows the expansion of vascular tissue that produces woody growth. Because this growth ruptures the epidermis of the stem, woody plants also have a cork cambium that develops among the phloem. The cork cambium gives rise to thickened cork cells to protect the surface of the plant and reduce water loss. Both the production of wood and the production of cork are forms of secondary growth.[26]
+
+Trees are either evergreen, having foliage that persists and remains green throughout the year,[27] or deciduous, shedding their leaves at the end of the growing season and then having a dormant period without foliage.[28] Most conifers are evergreens, but larches (Larix and Pseudolarix) are deciduous, dropping their needles each autumn, and some species of cypress (Glyptostrobus, Metasequoia and Taxodium) shed small leafy shoots annually in a process known as cladoptosis.[5] The crown is the spreading top of a tree including the branches and leaves,[29] while the uppermost layer in a forest, formed by the crowns of the trees, is known as the canopy.[30] A sapling is a young tree.[31]
+
+Many tall palms are herbaceous[32] monocots; these do not undergo secondary growth and never produce wood.[9][10] In many tall palms, the terminal bud on the main stem is the only one to develop, so they have unbranched trunks with large spirally arranged leaves. Some of the tree ferns, order Cyatheales, have tall straight trunks, growing up to 20 metres (66 ft), but these are composed not of wood but of rhizomes which grow vertically and are covered by numerous adventitious roots.[33]
+
+The number of trees in the world, according to a 2015 estimate, is 3.04 trillion, of which 1.39 trillion (46%) are in the tropics or sub-tropics, 0.61 trillion (20%) in the temperate zones, and 0.74 trillion (24%) in the coniferous boreal forests. The estimate is about eight times higher than previous estimates, and is based on tree densities measured on over 400,000 plots. It remains subject to a wide margin of error, not least because the samples are mainly from Europe and North America. The estimate suggests that about 15 billion trees are cut down annually and about 5 billion are planted. In the 12,000 years since the start of human agriculture, the number of trees worldwide has decreased by 46%.[1][34][35][36]
+
+In suitable environments, such as the Daintree Rainforest in Queensland, or the mixed podocarp and broadleaf forest of Ulva Island, New Zealand, forest is the more-or-less stable climatic climax community at the end of a plant succession, where open areas such as grassland are colonised by taller plants, which in turn give way to trees that eventually form a forest canopy.[37][38]
+
+In cool temperate regions, conifers often predominate; a widely distributed climax community in the far north of the northern hemisphere is moist taiga or northern coniferous forest (also called boreal forest).[39][40] Taiga is the world's largest land biome, forming 29% of the world's forest cover.[41] The long cold winter of the far north is unsuitable for plant growth and trees must grow rapidly in the short summer season when the temperature rises and the days are long. Light is very limited under their dense cover and there may be little plant life on the forest floor, although fungi may abound.[42] Similar woodland is found on mountains where the altitude causes the average temperature to be lower thus reducing the length of the growing season.[43]
+
+Where rainfall is relatively evenly spread across the seasons in temperate regions, temperate broadleaf and mixed forest typified by species like oak, beech, birch and maple is found.[44] Temperate forest is also found in the southern hemisphere, as for example in the Eastern Australia temperate forest, characterised by Eucalyptus forest and open acacia woodland.[45]
+
+In tropical regions with a monsoon or monsoon-like climate, where a drier part of the year alternates with a wet period as in the Amazon rainforest, different species of broad-leaved trees dominate the forest, some of them being deciduous.[46] In tropical regions with a drier savanna climate and insufficient rainfall to support dense forests, the canopy is not closed, and plenty of sunshine reaches the ground which is covered with grass and scrub. Acacia and baobab are well adapted to living in such areas.[47]
+
+The roots of a tree serve to anchor it to the ground and gather water and nutrients to transfer to all parts of the tree. They are also used for reproduction, defence, survival, energy storage and many other purposes. The radicle or embryonic root is the first part of a seedling to emerge from the seed during the process of germination. This develops into a taproot which goes straight downwards. Within a few weeks lateral roots branch out of the side of this and grow horizontally through the upper layers of the soil. In most trees, the taproot eventually withers away and the wide-spreading laterals remain. Near the tip of the finer roots are single cell root hairs. These are in immediate contact with the soil particles and can absorb water and nutrients such as potassium in solution. The roots require oxygen to respire and only a few species such as mangroves and the pond cypress (Taxodium ascendens) can live in permanently waterlogged soil.[48]
+
+In the soil, the roots encounter the hyphae of fungi. Many of these are known as mycorrhiza and form a mutualistic relationship with the tree roots. Some are specific to a single tree species, which will not flourish in the absence of its mycorrhizal associate. Others are generalists and associate with many species. The tree acquires minerals such as phosphorus from the fungus, while the fungus obtains the carbohydrate products of photosynthesis from the tree.[49] The hyphae of the fungus can link different trees and a network is formed, transferring nutrients and signals from one place to another.[50] The fungus promotes growth of the roots and helps protect the trees against predators and pathogens. It can also limit damage done to a tree by pollution as the fungus accumulate heavy metals within its tissues.[51] Fossil evidence shows that roots have been associated with mycorrhizal fungi since the early Paleozoic, four hundred million years ago, when the first vascular plants colonised dry land.[52]
+
+Some trees such as the alders (Alnus species) have a symbiotic relationship with Frankia species, a filamentous bacterium that can fix nitrogen from the air, converting it into ammonia. They have actinorhizal root nodules on their roots in which the bacteria live. This process enables the tree to live in low nitrogen habitats where they would otherwise be unable to thrive.[53] The plant hormones called cytokinins initiate root nodule formation, in a process closely related to mycorrhizal association.[54]
+
+It has been demonstrated that some trees are interconnected through their root system, forming a colony. The interconnections are made by the inosculation process, a kind of natural grafting or welding of vegetal tissues. The tests to demonstrate this networking are performed by injecting chemicals, sometimes radioactive, into a tree, and then checking for its presence in neighbouring trees.[55]
+
+The roots are, generally, an underground part of the tree, but some tree species have evolved roots that are aerial. The common purposes for aerial roots may be of two kinds, to contribute to the mechanical stability of the tree, and to obtain oxygen from air. An instance of mechanical stability enhancement is the red mangrove that develops prop roots that loop out of the trunk and branches and descend vertically into the mud.[56] A similar structure is developed by the Indian banyan.[57] Many large trees have buttress roots which flare out from the lower part of the trunk. These brace the tree rather like angle brackets and provide stability, reducing sway in high winds. They are particularly prevalent in tropical rainforests where the soil is poor and the roots are close to the surface.[58]
+
+Some tree species have developed root extensions that pop out of soil, in order to get oxygen, when it is not available in the soil because of excess water. These root extensions are called pneumatophores, and are present, among others, in black mangrove and pond cypress.[56]
+
+The main purpose of the trunk is to raise the leaves above the ground, enabling the tree to overtop other plants and outcompete them for light.[59] It also transports water and nutrients from the roots to the aerial parts of the tree, and distributes the food produced by the leaves to all other parts, including the roots.[60]
+
+In the case of angiosperms and gymnosperms, the outermost layer of the trunk is the bark, mostly composed of dead cells of phellem (cork).[61] It provides a thick, waterproof covering to the living inner tissue. It protects the trunk against the elements, disease, animal attack and fire. It is perforated by a large number of fine breathing pores called lenticels, through which oxygen diffuses. Bark is continually replaced by a living layer of cells called the cork cambium or phellogen.[61] The London plane (Platanus × acerifolia) periodically sheds its bark in large flakes. Similarly, the bark of the silver birch (Betula pendula) peels off in strips. As the tree's girth expands, newer layers of bark are larger in circumference, and the older layers develop fissures in many species. In some trees such as the pine (Pinus species) the bark exudes sticky resin which deters attackers whereas in rubber trees (Hevea brasiliensis) it is a milky latex that oozes out. The quinine bark tree (Cinchona officinalis) contains bitter substances to make the bark unpalatable.[60] Large tree-like plants with lignified trunks in the Pteridophyta, Arecales, Cycadophyta and Poales such as the tree ferns, palms, cycads and bamboos have different structures and outer coverings.[62]
+
+Although the bark functions as a protective barrier, it is itself attacked by boring insects such as beetles. These lay their eggs in crevices and the larvae chew their way through the cellulose tissues leaving a gallery of tunnels. This may allow fungal spores to gain admittance and attack the tree. Dutch elm disease is caused by a fungus (Ophiostoma species) carried from one elm tree to another by various beetles. The tree reacts to the growth of the fungus by blocking off the xylem tissue carrying sap upwards and the branch above, and eventually the whole tree, is deprived of nourishment and dies. In Britain in the 1990s, 25 million elm trees were killed by this disease.[63]
+
+The innermost layer of bark is known as the phloem and this is involved in the transport of the sap containing the sugars made by photosynthesis to other parts of the tree. It is a soft spongy layer of living cells, some of which are arranged end to end to form tubes. These are supported by parenchyma cells which provide padding and include fibres for strengthening the tissue.[64] Inside the phloem is a layer of undifferentiated cells one cell thick called the vascular cambium layer. The cells are continually dividing, creating phloem cells on the outside and wood cells known as xylem on the inside.[65]
+
+The newly created xylem is the sapwood. It is composed of water-conducting cells and associated cells which are often living, and is usually pale in colour. It transports water and minerals from the roots to the upper parts of the tree. The oldest, inner part of the sapwood is progressively converted into heartwood as new sapwood is formed at the cambium. The conductive cells of the heartwood are blocked in some species. Heartwood is usually darker in colour than the sapwood. It is the dense central core of the trunk giving it rigidity. Three quarters of the dry mass of the xylem is cellulose, a polysaccharide, and most of the remainder is lignin, a complex polymer. A transverse section through a tree trunk or a horizontal core will show concentric circles or lighter or darker wood – tree rings.[66] These rings are the annual growth rings[67][68] There may also be rays running at right angles to growth rings. These are vascular rays which are thin sheets of living tissue permeating the wood.[66] Many older trees may become hollow but may still stand upright for many years.[69]
+
+Trees do not usually grow continuously throughout the year but mostly have spurts of active expansion followed by periods of rest. This pattern of growth is related to climatic conditions; growth normally ceases when conditions are either too cold or too dry. In readiness for the inactive period, trees form buds to protect the meristem, the zone of active growth. Before the period of dormancy, the last few leaves produced at the tip of a twig form scales. These are thick, small and closely wrapped and enclose the growing point in a waterproof sheath. Inside this bud there is a rudimentary stalk and neatly folded miniature leaves, ready to expand when the next growing season arrives. Buds also form in the axils of the leaves ready to produce new side shoots. A few trees, such as the eucalyptus, have "naked buds" with no protective scales and some conifers, such as the Lawson's cypress, have no buds but instead have little pockets of meristem concealed among the scale-like leaves.[70]
+
+When growing conditions improve, such as the arrival of warmer weather and the longer days associated with spring in temperate regions, growth starts again. The expanding shoot pushes its way out, shedding the scales in the process. These leave behind scars on the surface of the twig. The whole year's growth may take place in just a few weeks. The new stem is unlignified at first and may be green and downy. The Arecaceae (palms) have their leaves spirally arranged on an unbranched trunk.[70] In some tree species in temperate climates, a second spurt of growth, a Lammas growth may occur which is believed to be a strategy to compensate for loss of early foliage to insect predators.[71]
+
+Primary growth is the elongation of the stems and roots. Secondary growth consists of a progressive thickening and strengthening of the tissues as the outer layer of the epidermis is converted into bark and the cambium layer creates new phloem and xylem cells. The bark is inelastic.[72] Eventually the growth of a tree slows down and stops and it gets no taller. If damage occurs the tree may in time become hollow.[73]
+
+Leaves are structures specialised for photosynthesis and are arranged on the tree in such a way as to maximise their exposure to light without shading each other.[74] They are an important investment by the tree and may be thorny or contain phytoliths, lignins, tannins or poisons to discourage herbivory. Trees have evolved leaves in a wide range of shapes and sizes, in response to environmental pressures including climate and predation. They can be broad or needle-like, simple or compound, lobed or entire, smooth or hairy, delicate or tough, deciduous or evergreen. The needles of coniferous trees are compact but are structurally similar to those of broad-leaved trees. They are adapted for life in environments where resources are low or water is scarce. Frozen ground may limit water availability and conifers are often found in colder places at higher altitudes and higher latitudes than broad leaved trees. In conifers such as fir trees, the branches hang down at an angle to the trunk, enabling them to shed snow. In contrast, broad leaved trees in temperate regions deal with winter weather by shedding their leaves. When the days get shorter and the temperature begins to decrease, the leaves no longer make new chlorophyll and the red and yellow pigments already present in the blades become apparent.[74] Synthesis in the leaf of a plant hormone called auxin also ceases. This causes the cells at the junction of the petiole and the twig to weaken until the joint breaks and the leaf floats to the ground. In tropical and subtropical regions, many trees keep their leaves all year round. Individual leaves may fall intermittently and be replaced by new growth but most leaves remain intact for some time. Other tropical species and those in arid regions may shed all their leaves annually, such as at the start of the dry season.[75] Many deciduous trees flower before the new leaves emerge.[76] A few trees do not have true leaves but instead have structures with similar external appearance such as Phylloclades – modified stem structures[77] – as seen in the genus Phyllocladus.[78]
+
+Trees can be pollinated either by wind or by animals, mostly insects. Many angiosperm trees are insect pollinated. Wind pollination may take advantage of increased wind speeds high above the ground.[79] Trees use a variety of methods of seed dispersal. Some rely on wind, with winged or plumed seeds. Others rely on animals, for example with edible fruits. Others again eject their seeds (ballistic dispersal), or use gravity so that seeds fall and sometimes roll.[80]
+
+Seeds are the primary way that trees reproduce and their seeds vary greatly in size and shape. Some of the largest seeds come from trees, but the largest tree, Sequoiadendron giganteum, produces one of the smallest tree seeds.[81] The great diversity in tree fruits and seeds reflects the many different ways that tree species have evolved to disperse their offspring.
+
+For a tree seedling to grow into an adult tree it needs light. If seeds only fell straight to the ground, competition among the concentrated saplings and the shade of the parent would likely prevent it from flourishing. Many seeds such as birch are small and have papery wings to aid dispersal by the wind. Ash trees and maples have larger seeds with blade shaped wings which spiral down to the ground when released. The kapok tree has cottony threads to catch the breeze.[82]
+
+The seeds of conifers, the largest group of gymnosperms, are enclosed in a cone and most species have seeds that are light and papery that can be blown considerable distances once free from the cone.[83] Sometimes the seed remains in the cone for years waiting for a trigger event to liberate it. Fire stimulates release and germination of seeds of the jack pine, and also enriches the forest floor with wood ash and removes competing vegetation.[84] Similarly, a number of angiosperms including Acacia cyclops and Acacia mangium have seeds that germinate better after exposure to high temperatures.[85]
+
+The flame tree Delonix regia does not rely on fire but shoots its seeds through the air when the two sides of its long pods crack apart explosively on drying.[82] The miniature cone-like catkins of alder trees produce seeds that contain small droplets of oil that help disperse the seeds on the surface of water. Mangroves often grow in water and some species have propagules, which are buoyant fruits with seeds that start germinating before becoming detached from the parent tree.[86][87] These float on the water and may become lodged on emerging mudbanks and successfully take root.[82]
+
+Other seeds, such as apple pips and plum stones, have fleshy receptacles and smaller fruits like hawthorns have seeds enclosed in edible tissue; animals including mammals and birds eat the fruits and either discard the seeds, or swallow them so they pass through the gut to be deposited in the animal's droppings well away from the parent tree. The germination of some seeds is improved when they are processed in this way.[88] Nuts may be gathered by animals such as squirrels that cache any not immediately consumed.[89] Many of these caches are never revisited, the nut-casing softens with rain and frost, and the seed germinates in the spring.[90] Pine cones may similarly be hoarded by red squirrels, and grizzly bears may help to disperse the seed by raiding squirrel caches.[91]
+
+The single extant species of Ginkgophyta (Ginkgo biloba) has fleshy seeds produced at the ends of short branches on female trees,[92] and Gnetum, a tropical and subtropical group of gymnosperms produce seeds at the tip of a shoot axis.[93]
+
+The earliest trees were tree ferns, horsetails and lycophytes, which grew in forests in the Carboniferous period. The first tree may have been Wattieza, fossils of which have been found in New York State in 2007 dating back to the Middle Devonian (about 385 million years ago). Prior to this discovery, Archaeopteris was the earliest known tree.[94] Both of these reproduced by spores rather than seeds and are considered to be links between ferns and the gymnosperms which evolved in the Triassic period. The gymnosperms include conifers, cycads, gnetales and ginkgos and these may have appeared as a result of a whole genome duplication event which took place about 319 million years ago.[95] Ginkgophyta was once a widespread diverse group[96] of which the only survivor is the maidenhair tree Ginkgo biloba. This is considered to be a living fossil because it is virtually unchanged from the fossilised specimens found in Triassic deposits.[97]
+
+During the Mesozoic (245 to 66 million years ago) the conifers flourished and became adapted to live in all the major terrestrial habitats. Subsequently, the tree forms of flowering plants evolved during the Cretaceous period. These began to displace the conifers during the Tertiary era (66 to 2 million years ago) when forests covered the globe.[98] When the climate cooled 1.5 million years ago and the first of four ice ages occurred, the forests retreated as the ice advanced. In the interglacials, trees recolonised the land that had been covered by ice, only to be driven back again in the next ice age.[98]
+
+Trees are an important part of the terrestrial ecosystem,[99] providing essential habitats including many kinds of forest for communities of organisms. Epiphytic plants such as ferns, some mosses, liverworts, orchids and some species of parasitic plants (e.g., mistletoe) hang from branches;[100] these along with arboreal lichens, algae, and fungi provide micro-habitats for themselves and for other organisms, including animals. Leaves, flowers and fruits are seasonally available. On the ground underneath trees there is shade, and often there is undergrowth, leaf litter, and decaying wood that provide other habitat.[101][102] Trees stabilise the soil, prevent rapid run-off of rain water, help prevent desertification, have a role in climate control and help in the maintenance of biodiversity and ecosystem balance.[103]
+
+Many species of tree support their own specialised invertebrates. In their natural habitats, 284 different species of insect have been found on the English oak (Quercus robur)[104] and 306 species of invertebrate on the Tasmanian oak (Eucalyptus obliqua).[105] Non-native tree species provide a less biodiverse community, for example in the United Kingdom the sycamore (Acer pseudoplatanus), which originates from southern Europe, has few associated invertebrate species, though its bark supports a wide range of lichens, bryophytes and other epiphytes.[106]
+
+In ecosystems such as mangrove swamps, trees play a role in developing the habitat, since the roots of the mangrove trees reduce the speed of flow of tidal currents and trap water-borne sediment, reducing the water depth and creating suitable conditions for further mangrove colonisation. Thus mangrove swamps tend to extend seawards in suitable locations.[107] Mangrove swamps also provide an effective buffer against the more damaging effects of cyclones and tsunamis.[108]
+
+Silviculture is the practice of controlling the establishment, growth, composition, health, and quality of forests, which are areas that have a high density of trees. Cultivated trees are planted and tended by humans, usually because they provide food (fruits or nuts), ornamental beauty, or some type of wood product that benefits people. An area of land planted with fruit or nut trees is an orchard.[109] A small wooded area, usually with no undergrowth, is called a grove[110] and a small wood or thicket of trees and bushes is called a coppice or copse.[111] A large area of land covered with trees and undergrowth is called woodland or forest.[112] An area of woodland composed primarily of trees established by planting or artificial seeding is known as a plantation.[113]
+
+Trees are the source of many of the world's best known fleshy fruits. Apples, pears, plums, cherries and citrus are all grown commercially in temperate climates and a wide range of edible fruits are found in the tropics. Other commercially important fruit include dates, figs and olives. Palm oil is obtained from the fruits of the oil palm (Elaeis guineensis). The fruits of the cocoa tree (Theobroma cacao) are used to make cocoa and chocolate and the berries of coffee trees, Coffea arabica and Coffea canephora, are processed to extract the coffee beans. In many rural areas of the world, fruit is gathered from forest trees for consumption.[114] Many trees bear edible nuts which can loosely be described as being large, oily kernels found inside a hard shell. These include coconuts (Cocos nucifera), Brazil nuts (Bertholletia excelsa), pecans (Carya illinoinensis), hazel nuts (Corylus), almonds (Prunus dulcis), walnuts (Juglans regia), pistachios (Pistacia vera) and many others. They are high in nutritive value and contain high-quality protein, vitamins and minerals as well as dietary fibre.[115] A variety of nut oils are extracted by pressing for culinary use; some such as walnut, pistachio and hazelnut oils are prized for their distinctive flavours, but they tend to spoil quickly.[116]
+
+In temperate climates there is a sudden movement of sap at the end of the winter as trees prepare to burst into growth. In North America, the sap of the sugar maple (Acer saccharum) is most often used in the production of a sweet liquid, maple syrup. About 90% of the sap is water, the remaining 10% being a mixture of various sugars and certain minerals. The sap is harvested by drilling holes in the trunks of the trees and collecting the liquid that flows out of the inserted spigots. It is piped to a sugarhouse where it is heated to concentrate it and improve its flavour. Similarly in northern Europe the spring rise in the sap of the silver birch (Betula pendula) is tapped and collected, either to be drunk fresh or fermented into an alcoholic drink. In Alaska, the sap of the sweet birch (Betula lenta) is made into a syrup with a sugar content of 67%. Sweet birch sap is more dilute than maple sap; a hundred litres are required to make one litre of birch syrup.[117]
+
+Various parts of trees are used as spices. These include cinnamon, made from the bark of the cinnamon tree (Cinnamomum zeylanicum) and allspice, the dried small fruits of the pimento tree (Pimenta dioica). Nutmeg is a seed found in the fleshy fruit of the nutmeg tree (Myristica fragrans) and cloves are the unopened flower buds of the clove tree (Syzygium aromaticum).[118]
+
+Many trees have flowers rich in nectar which are attractive to bees. The production of forest honey is an important industry in rural areas of the developing world where it is undertaken by small-scale beekeepers using traditional methods.[119] The flowers of the elder (Sambucus) are used to make elderflower cordial and petals of the plum (Prunus spp.) can be candied.[120] Sassafras oil is a flavouring obtained from distilling bark from the roots of the sassafras tree (Sassafras albidum).
+
+The leaves of trees are widely gathered as fodder for livestock and some can be eaten by humans but they tend to be high in tannins which makes them bitter. Leaves of the curry tree (Murraya koenigii) are eaten, those of kaffir lime (Citrus × hystrix) (in Thai food)[121] and Ailanthus (in Korean dishes such as bugak) and those of the European bay tree (Laurus nobilis) and the California bay tree (Umbellularia californica) are used for flavouring food.[118] Camellia sinensis, the source of tea, is a small tree but seldom reaches its full height, being heavily pruned to make picking the leaves easier.[122]
+
+Wood smoke can be used to preserve food. In the hot smoking process the food is exposed to smoke and heat in a controlled environment. The food is ready to eat when the process is complete, having been tenderised and flavoured by the smoke it has absorbed. In the cold process, the temperature is not allowed to rise above 100 °F (38 °C). The flavour of the food is enhanced but raw food requires further cooking. If it is to be preserved, meat should be cured before cold smoking.[123]
+
+Wood has traditionally been used for fuel, especially in rural areas. In less developed nations it may be the only fuel available and collecting firewood is often a time consuming task as it becomes necessary to travel further and further afield in the search for fuel.[124] It is often burned inefficiently on an open fire. In more developed countries other fuels are available and burning wood is a choice rather than a necessity. Modern wood-burning stoves are very fuel efficient and new products such as wood pellets are available to burn.[125]
+
+Charcoal can be made by slow pyrolysis of wood by heating it in the absence of air in a kiln. The carefully stacked branches, often oak, are burned with a very limited amount of air. The process of converting them into charcoal takes about fifteen hours. Charcoal is used as a fuel in barbecues and by blacksmiths and has many industrial and other uses.[126]
+
+Timber, "trees that are grown in order to produce wood"[127] is cut into lumber (sawn wood) for use in construction. Wood has been an important, easily available material for construction since humans started building shelters. Engineered wood products are available which bind the particles, fibres or veneers of wood together with adhesives to form composite materials. Plastics have taken over from wood for some traditional uses.[128]
+
+Wood is used in the construction of buildings, bridges, trackways, piles, poles for power lines, masts for boats, pit props, railway sleepers, fencing, hurdles, shuttering for concrete, pipes, scaffolding and pallets. In housebuilding it is used in joinery, for making joists, roof trusses, roofing shingles, thatching, staircases, doors, window frames, floor boards, parquet flooring, panelling and cladding.[129]
+
+Wood is used to construct carts, farm implements, boats, dugout canoes and in shipbuilding. It is used for making furniture, tool handles, boxes, ladders, musical instruments, bows, weapons, matches, clothes pegs, brooms, shoes, baskets, turnery, carving, toys, pencils, rollers, cogs, wooden screws, barrels, coffins, skittles, veneers, artificial limbs, oars, skis, wooden spoons, sports equipment and wooden balls.[129]
+
+Wood is pulped for paper and used in the manufacture of cardboard and made into engineered wood products for use in construction such as fibreboard, hardboard, chipboard and plywood.[129] The wood of conifers is known as softwood while that of broad-leaved trees is hardwood.[130]
+
+Besides inspiring artists down the centuries, trees have been used to create art. Living trees have been used in bonsai and in tree shaping, and both living and dead specimens have been sculpted into sometimes fantastic shapes.[131]
+
+Bonsai (盆栽, lit. The art of growing a miniature tree or trees in a low-sided pot or tray) is the practice of hòn non bộ originated in China and spread to Japan more than a thousand years ago, there are similar practices in other cultures like the living miniature landscapes of Vietnam hòn non bộ. The word bonsai is often used in English as an umbrella term for all miniature trees in containers or pots.[132]
+
+The purposes of bonsai are primarily contemplation (for the viewer) and the pleasant exercise of effort and ingenuity (for the grower).[133] Bonsai practice focuses on long-term cultivation and shaping of one or more small trees growing in a container, beginning with a cutting, seedling, or small tree of a species suitable for bonsai development. Bonsai can be created from nearly any perennial woody-stemmed tree or shrub species[134] that produces true branches and can be cultivated to remain small through pot confinement with crown and root pruning. Some species are popular as bonsai material because they have characteristics, such as small leaves or needles, that make them appropriate for the compact visual scope of bonsai and a miniature deciduous forest can even be created using such species as Japanese maple, Japanese zelkova or hornbeam.[135]
+
+Tree shaping is the practice of changing living trees and other woody plants into man made shapes for art and useful structures. There are a few different methods[136] of shaping a tree. There is a gradual method and there is an instant method. The gradual method slowly guides the growing tip along predetermined pathways over time whereas the instant method bends and weaves saplings 2 to 3 m (6.6 to 9.8 ft) long into a shape that becomes more rigid as they thicken up.[137] Most artists use grafting of living trunks, branches, and roots, for art or functional structures and there are plans to grow "living houses" with the branches of trees knitting together to give a solid, weatherproof exterior combined with an interior application of straw and clay to provide a stucco-like inner surface.[137]
+
+Tree shaping has been practised for at least several hundred years, the oldest known examples being the living root bridges built and maintained by the Khasi people of Meghalaya, India using the roots of the rubber tree (Ficus elastica).[138][139]
+
+Cork is produced from the thick bark of the cork oak (Quercus suber). It is harvested from the living trees about once every ten years in an environmentally sustainable industry.[140] More than half the world's cork comes from Portugal and is largely used to make stoppers for wine bottles.[141] Other uses include floor tiles, bulletin boards, balls, footwear, cigarette tips, packaging, insulation and joints in woodwind instruments.[141]
+
+The bark of other varieties of oak has traditionally been used in Europe for the tanning of hides though bark from other species of tree has been used elsewhere. The active ingredient, tannin, is extracted and after various preliminary treatments, the skins are immersed in a series of vats containing solutions in increasing concentrations. The tannin causes the hide to become supple, less affected by water and more resistant to bacterial attack.[142]
+
+At least 120 drugs come from plant sources, many of them from the bark of trees.[143] Quinine originates from the cinchona tree (Cinchona) and was for a long time the remedy of choice for the treatment of malaria.[144] Aspirin was synthesised to replace the sodium salicylate derived from the bark of willow trees (Salix) which had unpleasant side effects.[145] The anti-cancer drug Paclitaxel is derived from taxol, a substance found in the bark of the Pacific yew (Taxus brevifolia).[146] Other tree based drugs come from the paw-paw (Carica papaya), the cassia (Cassia spp.), the cocoa tree (Theobroma cacao), the tree of life (Camptotheca acuminata) and the downy birch (Betula pubescens).[143]
+
+The papery bark of the white birch tree (Betula papyrifera) was used extensively by Native Americans. Wigwams were covered by it and canoes were constructed from it. Other uses included food containers, hunting and fishing equipment, musical instruments, toys and sledges.[147] Nowadays, bark chips, a by-product of the timber industry, are used as a mulch and as a growing medium for epiphytic plants that need a soil-free compost.[148]
+
+Trees create a visual impact in the same way as do other landscape features and give a sense of maturity and permanence to park and garden. They are grown for the beauty of their forms, their foliage, flowers, fruit and bark and their siting is of major importance in creating a landscape. They can be grouped informally, often surrounded by plantings of bulbs, laid out in stately avenues or used as specimen trees. As living things, their appearance changes with the season and from year to year.[149]
+
+Trees are often planted in town environments where they are known as street trees or amenity trees. They can provide shade and cooling through evapotranspiration, absorb greenhouse gases and pollutants, intercept rainfall, and reduce the risk of flooding. Scientific studies show that street trees help cities be more sustainable, and improve the physical and mental wellbeing of the citizens. [150] It has been shown that they are beneficial to humans in creating a sense of well-being and reducing stress. Many towns have initiated tree-planting programmes.[151] In London for example, there is an initiative to plant 20,000 new street trees and to have an increase in tree cover of 5% by 2025, equivalent to one tree for every resident.[152]
+
+Latex is a sticky defensive secretion that protects plants against herbivores. Many trees produce it when injured but the main source of the latex used to make natural rubber is the Pará rubber tree (Hevea brasiliensis). Originally used to create bouncy balls and for the waterproofing of cloth, natural rubber is now mainly used in tyres for which synthetic materials have proved less durable.[153] The latex exuded by the balatá tree (Manilkara bidentata) is used to make golf balls and is similar to gutta-percha, made from the latex of the "getah perca" tree Palaquium. This is also used as an insulator, particularly of undersea cables, and in dentistry, walking sticks and gun butts. It has now largely been replaced by synthetic materials.[154]
+
+Resin is another plant exudate that may have a defensive purpose. It is a viscous liquid composed mainly of volatile terpenes and is produced mostly by coniferous trees. It is used in varnishes, for making small castings and in ten-pin bowling balls. When heated, the terpenes are driven off and the remaining product is called "rosin" and is used by stringed instrumentalists on their bows. Some resins contain essential oils and are used in incense and aromatherapy. Fossilised resin is known as amber and was mostly formed in the Cretaceous (145 to 66 million years ago) or more recently. The resin that oozed out of trees sometimes trapped insects or spiders and these are still visible in the interior of the amber.[155]
+
+The camphor tree (Cinnamomum camphora) produces an essential oil[118] and the eucalyptus tree (Eucalyptus globulus) is the main source of eucalyptus oil which is used in medicine, as a fragrance and in industry.[156]
+
+Dead trees pose a safety risk, especially during high winds and severe storms, and removing dead trees involves a financial burden, whereas the presence of healthy trees can clean the air, increase property values, and reduce the temperature of the built environment and thereby reduce building cooling costs. During times of drought, trees can fall into water stress, which may cause a tree to become more susceptible to disease and insect problems, and ultimately may lead to a tree's death. Irrigating trees during dry periods can reduce the risk of water stress and death.[157]
+
+Trees have been venerated since time immemorial. To the ancient Celts, certain trees, especially the oak, ash and thorn, held special significance[158] as providing fuel, building materials, ornamental objects and weaponry. Other cultures have similarly revered trees, often linking the lives and fortunes of individuals to them or using them as oracles. In Greek mythology, dryads were believed to be shy nymphs who inhabited trees.
+
+The Oubangui people of west Africa plant a tree when a child is born. As the tree flourishes, so does the child but if the tree fails to thrive, the health of the child is considered at risk. When it flowers it is time for marriage. Gifts are left at the tree periodically and when the individual dies, their spirit is believed to live on in the tree.[159]
+
+Trees have their roots in the ground and their trunk and branches extended towards the sky. This concept is found in many of the world's religions as a tree which links the underworld and the earth and holds up the heavens. In Norse mythology, Yggdrasil is a central cosmic tree whose roots and branches extend to various worlds. Various creatures live on it.[160] In India, Kalpavriksha is a wish-fulfilling tree, one of the nine jewels that emerged from the primitive ocean. Icons are placed beneath it to be worshipped, tree nymphs inhabit the branches and it grants favours to the devout who tie threads round the trunk.[161] Democracy started in North America when the Great Peacemaker formed the Iroquois Confederacy, inspiring the warriors of the original five American nations to bury their weapons under the Tree of Peace, an eastern white pine (Pinus strobus).[162] In the creation story in the Bible, the tree of life and the knowledge of good and evil was planted by God in the Garden of Eden.[163]
+
+Sacred groves exist in China, India, Africa and elsewhere. They are places where the deities live and where all the living things are either sacred or are companions of the gods. Folklore lays down the supernatural penalties that will result if desecration takes place for example by the felling of trees. Because of their protected status, sacred groves may be the only relicts of ancient forest and have a biodiversity much greater than the surrounding area.[164]
+Some Ancient Indian tree deities, such as Puliyidaivalaiyamman, the Tamil deity of the  tamarind tree, or Kadambariyamman, associated with the kadamba tree were seen as manifestations of a goddess who offers her blessings by giving fruits in abundance.[165]
+
+Trees have a theoretical maximum height of 130 m (430 ft),[166] but the tallest known specimen on earth is believed to be a coast redwood (Sequoia sempervirens) at Redwood National Park, California. It has been named Hyperion and is 115.85 m (380.1 ft) tall.[167] In 2006, it was reported to be 379.1 ft (115.5 m) tall.[168] The tallest known broad-leaved tree is a mountain ash (Eucalyptus regnans) growing in Tasmania with a height of 99.8 m (327 ft).[169]
+
+The largest tree by volume is believed to be a giant sequoia (Sequoiadendron giganteum) known as the General Sherman Tree in the Sequoia National Park in Tulare County, California. Only the trunk is used in the calculation and the volume is estimated to be 1,487 m3 (52,500 cu ft).[170]
+
+The oldest living tree with a verified age is also in California. It is a Great Basin bristlecone pine (Pinus longaeva) growing in the White Mountains. It has been dated by drilling a core sample and counting the annual rings. It is estimated to currently be 5,069 years old.[a][171]
+
+A little farther south, at Santa Maria del Tule, Oaxaca, Mexico, is the tree with the broadest trunk. It is a Montezuma cypress (Taxodium mucronatum) known as Árbol del Tule and its diameter at breast height is 11.62 m (38.1 ft) giving it a girth of 36.2 m (119 ft). The tree's trunk is far from round and the exact dimensions may be misleading as the circumference includes much empty space between the large buttress roots.[172]
+
+Wohlleben, Peter; Flannery, Tim F.; Simard, S.; Billinghurst, Jane (2016). The Hidden Life of Trees: What They Feel, How They Communicate: Discoveries from a Secret World. ISBN 978-1-77164-248-4. OCLC 933722592.

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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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+The lion (Panthera leo) is a species in the family Felidae and a member of the genus Panthera. It is most recognisable for its muscular, deep-chested body, short, rounded head, round ears, and a hairy tuft at the end of its tail. It is sexually dimorphic; adult male lions have a prominent mane. With a typical head-to-body length of 184–208 cm (72–82 in) they are larger than females at 160–184 cm (63–72 in). It is a social species, forming groups called prides. A lion pride consists of a few adult males, related females and cubs. Groups of female lions usually hunt together, preying mostly on large ungulates. The lion is an apex and keystone predator, although some lions scavenge when opportunities occur, and have been known to hunt humans, although the species typically does not.
+
+Typically, the lion inhabits grasslands and savannas, but is absent in dense forests. It is usually more diurnal than other big cats, but when persecuted it adapts to being active at night and at twilight. In the Pleistocene, the lion ranged throughout Eurasia, Africa and North America, but today it has been reduced to fragmented populations in sub-Saharan Africa and one critically endangered population in western India. It has been listed as Vulnerable on the IUCN Red List since 1996 because populations in African countries have declined by about 43% since the early 1990s. Lion populations are untenable outside designated protected areas. Although the cause of the decline is not fully understood, habitat loss and conflicts with humans are the greatest causes for concern.
+
+One of the most widely recognised animal symbols in human culture, the lion has been extensively depicted in sculptures and paintings, on national flags, and in contemporary films and literature. Lions have been kept in menageries since the time of the Roman Empire and have been a key species sought for exhibition in zoological gardens across the world since the late 18th century. Cultural depictions of lions were prominent in the Upper Paleolithic period; carvings and paintings from the Lascaux and Chauvet Caves in France have been dated to 17,000 years ago, and depictions have occurred in virtually all ancient and medieval cultures that coincided with the lion's former and current ranges.
+
+The word 'lion' is derived from Latin: leo[4] and Ancient Greek: λέων (leon).[5] The word lavi (Hebrew: לָבִיא‎) may also be related.[6] The generic name Panthera is traceable to the classical Latin word 'panthēra' and the ancient Greek word πάνθηρ 'panther'.[7] Panthera is phonetically similar to the Sanskrit word पाण्डर pând-ara meaning 'pale yellow, whitish, white'.[8]
+
+Felis leo was the scientific name used by Carl Linnaeus in 1758, who described the lion in his work Systema Naturae.[3] The genus name Panthera was coined by German naturalist Lorenz Oken in 1816.[13] Between the mid-18th and mid-20th centuries, 26 lion specimens were described and proposed as subspecies, of which 11 were recognised as valid in 2005.[1] They were distinguished mostly by the size and colour of their manes and of their skins.[14]
+
+In the 19th and 20th centuries, several lion type specimens were described and proposed as subspecies, with about a dozen recognised as valid taxa until 2017.[1]
+Between 2008 and 2016, IUCN Red List assessors used only two subspecific names: P. l. leo for African lion populations and P. l. persica for the Asiatic lion population.[2][15][16] In 2017, the Cat Classification Task Force of the Cat Specialist Group revised lion taxonomy, and recognises two subspecies based on results of several phylogeographic studies on lion evolution, namely:[17]
+
+Lion samples from some parts of the Ethiopian Highlands cluster genetically with those from Cameroon and Chad, while lions from other areas of Ethiopia cluster with samples from East Africa. Researchers therefore assume Ethiopia is a contact zone between the two subspecies.[20]
+Genome-wide data of a wild-born historical lion sample from Sudan showed that it clustered with P. l. leo in mtDNA-based phylogenies, but with a high affinity to P. l. melanochaita. This result suggested that the taxonomic position of lions in Central Africa may require revision.[21]
+
+Other lion subspecies or sister species to the modern lion existed in prehistoric times:[22]
+
+Phylogenetic analyses of nuclear and mitochondrial DNA from all Felidae species indicate that their evolutionary radiation began in Asia in the Miocene around 14.45 to 8.38 million years ago to 16.76 to 6.46 million years ago. The Panthera lineage is estimated to have genetically diverged from the common ancestor of the Felidae around 9.32 to 4.47 million years ago to 11.75 to 0.97 million years ago.[9][35][36]
+The geographic origin of the Panthera is most likely northern Central Asia.[37]
+Results of analyses differ in the phylogenetic relationship of the lion; it was thought to form a sister group with the jaguar (P. onca) that diverged 3.46 to 1.22 million years ago,[9] but also with the leopard (P. pardus) that diverged 3.1 to 1.95 million years ago[11][12] to 4.32 to 0.02 million years ago. Hybridisation between lion and snow leopard (P. uncia) ancestors possibly continued until about 2.1 million years ago.[36]
+The lion-leopard clade was distributed in the Asian and African Palearctic since at least the early Pliocene.[37] The earliest fossils recognisable as lions were found at Olduvai Gorge in Tanzania and are estimated to be up to 2 million years old.[35]
+
+Estimates for the divergence time of the modern and cave lion lineages range from 529,000 to 392,000 years ago based on mutation rate per generation time of the modern lion. There is no evidence for gene flow between the two lineages, indicating that they did not share the same geographic area.[21] The Eurasian and American cave lions became extinct at the end of the last glacial period without mitochondrial descendants on other continents.[29][38][39] The modern lion was probably widely distributed in Africa during the Middle Pleistocene and started to diverge in sub-Saharan Africa during the Late Pleistocene. Lion populations in East and Southern Africa became separated from populations in West and North Africa when the equatorial rainforest expanded 183,500 to 81,800 years ago.[40]
+They shared a common ancestor probably between 98,000 and 52,000 years ago.[21]
+Due to the expansion of the Sahara between 83,100 and 26,600 years ago, lion populations in West and North Africa became separated. As the rainforest decreased and thus gave rise to more open habitats, lions moved from West to Central Africa. Lions from North Africa dispersed to southern Europe and Asia between 38,800 and 8,300 ago.[40]
+
+Extinction of lions in southern Europe, North Africa and the Middle East interrupted gene flow between lion populations in Asia and Africa. Genetic evidence revealed numerous mutations in lion samples from East and Southern Africa, which indicates that this group has a longer evolutionary history than genetically less diverse lion samples from Asia and West and Central Africa.[41]
+A whole genome-wide sequence of lion samples showed that samples from West Africa shared alleles with samples from Southern Africa, and samples from Central Africa shared alleles with samples from Asia. This phenomenon indicates that Central Africa was a melting pot of lion populations after they had become isolated, possibly migrating through corridors in the Nile Basin during the early Holocene.[21]
+
+In zoos, lions have been bred with tigers to create hybrids for the curiosity of visitors or for scientific purpose.[42][43] The liger is bigger than a lion and a tiger, whereas most tigons are relatively small compared to their parents because of reciprocal gene effects.[44][45] The leopon is a hybrid between a lion and leopard.[46]
+
+The lion is a muscular, deep-chested cat with a short, rounded head, a reduced neck and round ears. Its fur varies in colour from light buff to silvery grey, yellowish red and dark brown. The colours of the underparts are generally lighter. A new-born lion has dark spots, which fade as the cub reaches adulthood, although faint spots often may still be seen on the legs and underparts. The lion is the only member of the cat family that displays obvious sexual dimorphism. Males have broader heads and a prominent mane that grows downwards and backwards covering most of the head, neck, shoulders, and chest. The mane is typically brownish and tinged with yellow, rust and black hairs.[47][48]
+
+The tail of all lions ends in a dark, hairy tuft that in some lions conceals an approximately 5 mm (0.20 in)-long, hard "spine" or "spur" that is formed from the final, fused sections of tail bone. The functions of the spur are unknown. The tuft is absent at birth and develops at around ​5 1⁄2 months of age. It is readily identifiable by the age of seven months.[49]
+
+Of the living felid species, the lion is rivaled only by the tiger in length, weight and height at the shoulder.[50] Its skull is very similar to that of the tiger, although the frontal region is usually more depressed and flattened, and has a slightly shorter postorbital region and broader nasal openings than those of the tiger. Due to the amount of skull variation in the two species, usually only the structure of the lower jaw can be used as a reliable indicator of species.[51][52]
+
+The size and weight of adult lions varies across global range and habitats.[53][54][55][56] Accounts of a few individuals that were larger than average exist from Africa and India.[47][57][58][59]
+
+The male lion's mane is the most recognisable feature of the species.[14] It may have evolved around 320,000–190,000 years ago.[61] It starts growing when lions are about a year old. Mane colour varies and darkens with age; research shows its colour and size are influenced by environmental factors such as average ambient temperature. Mane length apparently signals fighting success in male–male relationships; darker-maned individuals may have longer reproductive lives and higher offspring survival, although they suffer in the hottest months of the year. The presence, absence, colour and size of the mane are associated with genetic precondition, sexual maturity, climate and testosterone production; the rule of thumb is that a darker, fuller mane indicates a healthier animal. In Serengeti National Park, female lions favour males with dense, dark manes as mates.[62][63] The main purpose of the mane is thought be the protection of the neck and throat in territorial fights with rivals.[64] Cool ambient temperature in European and North American zoos may result in a heavier mane.[65] Asiatic lions usually have sparser manes than average African lions.[66]
+
+Almost all male lions in Pendjari National Park are either maneless or have very short manes.[67] Maneless lions have also been reported in Senegal, in Sudan's Dinder National Park and in Tsavo East National Park, Kenya.[68] The original male white lion from Timbavati in South Africa was also maneless. The hormone testosterone has been linked to mane growth; castrated lions often have little to no mane because the removal of the gonads inhibits testosterone production.[69] Increased testosterone may be the cause of maned lionesses reported in northern Botswana.[70]
+
+The white lion is a rare morph with a genetic condition called leucism which is caused by a double recessive allele. It is not albino; it has normal pigmentation in the eyes and skin. White lions have occasionally been encountered in and around Kruger National Park and the adjacent Timbavati Private Game Reserve in eastern South Africa. They were removed from the wild in the 1970s, thus decreasing the white lion gene pool. Nevertheless, 17 births have been recorded in five prides between 2007 and 2015.[71] White lions are selected for breeding in captivity.[72] They have reportedly been bred in camps in South Africa for use as trophies to be killed during canned hunts.[73]
+
+African lions live in scattered populations across Sub-Saharan Africa. The lion prefers grassy plains and savannahs, scrub bordering rivers and open woodlands with bushes. It is absent from rainforest and rarely enters closed forest. On Mount Elgon, the lion has been recorded up to an elevation of 3,600 m (11,800 ft) and close to the snow line on Mount Kenya.[47] Lions occur in savannah grasslands with scattered acacia trees, which serve as shade.[74] The Asiatic lion now survives only in and around Gir National Park in Gujarat, western India. Its habitat is a mixture of dry savannah forest and very dry, deciduous scrub forest.[15]
+
+In Africa, the range of the lion originally spanned most of the central rainforest zone and the Sahara desert.[75] In the 1960s, it became extinct in North Africa, except in the southern part of Sudan.[76][77][78]
+
+In southern Europe and Asia, the lion once ranged in regions where climatic conditions supported an abundance of prey.[79] In Greece, it was common as reported by Herodotus in 480 BC; it was considered rare by 300 BC and extirpated by AD 100.[47] It was present in the Caucasus until the 10th century.[52] It lived in Palestine until the Middle Ages, and in Southwest Asia until the late 19th century. By the late 19th century, it had been extirpated in most of Turkey.[80] The last live lion in Iran was sighted in 1942 about 65 km (40 mi) northwest of Dezful,[81] although the corpse of a lioness was found on the banks of the Karun river in Khūzestān Province in 1944.[82] It once ranged from Sind and Punjab in Pakistan to Bengal and the Narmada River in central India.[83]
+
+Lions spend much of their time resting; they are inactive for about 20 hours per day.[84] Although lions can be active at any time, their activity generally peaks after dusk with a period of socialising, grooming and defecating. Intermittent bursts of activity continue until dawn, when hunting most often takes place. They spend an average of two hours a day walking and 50 minutes eating.[85]
+
+The lion is the most social of all wild felid species, living in groups of related individuals with their offspring. Such a group is called a "pride". Groups of male lions are called "coalitions".[86] Females form the stable social unit in a pride and do not tolerate outside females.[87] Membership changes only with the births and deaths of lionesses,[88] although some females leave and become nomadic.[89] The average pride consists of around 15 lions, including several adult females and up to four males and their cubs of both sexes. Large prides, consisting of up to 30 individuals, have been observed.[90] The sole exception to this pattern is the Tsavo lion pride that always has just one adult male.[91] Male cubs are excluded from their maternal pride when they reach maturity at around two or three years of age.[89]
+
+Some lions are "nomads" that range widely and move around sporadically, either in pairs or alone.[86] Pairs are more frequent among related males who have been excluded from their birth pride. A lion may switch lifestyles; nomads can become residents and vice versa.[92] Interactions between prides and nomads tend to be hostile, although pride females in estrus allow nomadic males to approach them.[93] Males spend years in a nomadic phase before gaining residence in a pride.[94] A study undertaken in the Serengeti National Park revealed that nomadic coalitions gain residency at between 3.5 and 7.3 years of age.[95] In Kruger National Park, dispersing male lions move more than 25 km (16 mi) away from their natal pride in search of their own territory. Females lions stay closer to their natal pride. Therefore, female lions in an area are more closely related to each other than male lions in the same area.[96]
+
+The area occupied by a pride is called a "pride area" whereas that occupied by a nomad is a "range".[86] Males associated with a pride tend to stay on the fringes, patrolling their territory. The reasons for the development of sociality in lionesses—the most pronounced in any cat species—are the subject of much debate. Increased hunting success appears to be an obvious reason, but this is uncertain upon examination; coordinated hunting allows for more successful predation but also ensures non-hunting members reduce per capita calorific intake. Some females, however, take a role raising cubs that may be left alone for extended periods. Members of the pride tend to regularly play the same role in hunts and hone their skills. The health of the hunters is the primary need for the survival of the pride; hunters are the first to consume the prey at the site it is taken. Other benefits include possible kin selection; sharing food within the family; protecting the young, maintaining territory and individual insurance against injury and hunger.[57]
+
+Both males and females defend the pride against intruders, but the male lion is better-suited for this purpose due to its stockier, more powerful build. Some individuals consistently lead the defence against intruders, while others lag behind.[97] Lions tend to assume specific roles in the pride; slower-moving individuals may provide other valuable services to the group.[98] Alternatively, there may be rewards associated with being a leader that fends off intruders; the rank of lionesses in the pride is reflected in these responses.[99] The male or males associated with the pride must defend their relationship with the pride from outside males who may attempt to usurp them.
+
+Asiatic lion prides differ in group composition. Male Asiatic lions are solitary or associate with up to three males, forming a loose pride while females associate with up to 12 other females, forming a stronger pride together with their cubs. Female and male lions associate only when mating.[100] Coalitions of males hold territory for a longer time than single lions. Males in coalitions of three or four individuals exhibit a pronounced hierarchy, in which one male dominates the others and mates more frequently.[101]
+
+The lion is a generalist hypercarnivore[102] and is considered to be both an apex and keystone predator due to its wide prey spectrum.[103] Its prey consists mainly of mammals—particularly ungulates—weighing 190–550 kg (420–1,210 lb) with a preference for blue wildebeest, plains zebra, African buffalo, gemsbok and giraffe. Lions also hunt common warthog depending on availability, although the species is below the preferred weight range.[104] In India, sambar deer and chital are the most commonly recorded wild prey,[48][104][105] while domestic livestock may contribute significantly to their diet.[105] They usually avoid fully grown adult elephants, rhinoceroses and hippopotamus, as well as small prey like dik-dik, hyrax, hare and monkey.[104][106] Unusual prey items include porcupines and small reptiles. Lions kill other predators such as leopard, cheetah and spotted hyena but seldom consume them.[107]
+
+Young lions first display stalking behaviour at around three months of age, although they do not participate in hunting until they are almost a year old and begin to hunt effectively when nearing the age of two.[108] Single lions are capable of bringing down zebra and wildebeest, while larger prey like buffalo and giraffe are riskier.[92] 
+In Chobe National Park, large prides have been observed hunting African bush elephants up to around 15 years old.[109][110] In typical hunts, each lioness has a favoured position in the group, either stalking prey on the "wing", then attacking, or moving a smaller distance in the centre of the group and capturing prey fleeing from other lionesses. Males attached to prides do not usually participate in group hunting.[111] Some evidence suggests, however, that males are just as successful as females; they are typically solo hunters who ambush prey in small bushland.[112]
+
+Lions are not particularly known for their stamina; for instance, a lioness' heart comprises only 0.57% of her body weight and a male's is about 0.45% of his body weight, whereas a hyena's heart comprises almost 1% of its body weight.[113] Thus, lions run quickly only in short bursts[114] and need to be close to their prey before starting the attack. They take advantage of factors that reduce visibility; many kills take place near some form of cover or at night.[115] The lion's attack is short and powerful; they attempt to catch prey with a fast rush and final leap. They usually pull it down by the rump and kill by a strangling bite to the throat. They also kill prey by enclosing its mouth and nostrils in their jaws.[116]
+
+Lions typically consume prey at the location of the hunt but sometimes drag large prey into cover.[117] They tend to squabble over kills, particularly the males. Cubs suffer most when food is scarce but otherwise all pride members eat their fill, including old and crippled lions, which can live on leftovers.[92] Large kills are shared more widely among pride members.[118] An adult lioness requires an average of about 5 kg (11 lb) of meat per day while males require about 7 kg (15 lb).[119] Lions gorge themselves and eat up to 30 kg (66 lb) in one session;[82] if it is unable to consume all of the kill, it rests for a few hours before continuing to eat. On hot days, the pride retreats to shade with one or two males standing guard.[117] Lions defend their kills from scavengers such as vultures and hyenas.[92]
+
+Lions scavenge on carrion when the opportunity arises; they scavenge animals dead from natural causes such as disease or those that were killed by other predators. Scavenging lions keep a constant lookout for circling vultures, which indicate the death or distress of an animal.[120] Most carrion on which both hyenas and lions feed upon are killed by hyenas rather than lions.[56] Carrion is thought to provide a large part of lion diet.[121]
+
+Lions and spotted hyenas occupy a similar ecological niche and where they coexist they compete for prey and carrion; a review of data across several studies indicates a dietary overlap of 58.6%.[122] Lions typically ignore spotted hyenas unless the lions are on a kill or are being harassed by the hyenas, while the latter tend to visibly react to the presence of lions, with or without the presence of food. Lions seize the kills of spotted hyenas; in the Ngorongoro crater it is common for lions to subsist largely on kills stolen from hyenas, causing the hyenas to increase their kill rate.[123] In Botswana's Chobe National Park, the situation is reversed; hyenas frequently challenge lions and steal their kills, obtaining food from 63% of all lion kills.[124] When confronted on a kill by lions, spotted hyenas may either leave or wait patiently at a distance of 30–100 m (100–330 ft) until the lions have finished.[125] Hyenas are bold enough to feed alongside lions and to force the lions off a kill. The two species attack one another even when there is no food involved for no apparent reason.[126][127] Lion predation can account for up to 71% of hyena deaths in Etosha National Park. Spotted hyenas have adapted by frequently mobbing lions that enter their territories.[128] When the lion population in Kenya's Masai Mara National Reserve declined, the spotted hyena population increased rapidly.[129] Experiments on captive spotted hyenas show that specimens without prior experience with lions act indifferently to the sight of them, but will react fearfully to lion scent.[123]
+
+Lions tend to dominate cheetahs and leopards, steal their kills and kill their cubs and even adults when given the chance.[130] Cheetahs in particular often lose their kills to lions or other predators.[131] A study in the Serengeti ecosystem revealed that lions killed at least 17 of 125 cheetah cubs born between 1987 and 1990.[132] Cheetahs avoid their competitors by using different temporal and habitat niches.[133] Leopards are able to take refuge in trees; lionesses, however, occasionally attempt to retrieve leopard kills from trees.[134] Lions similarly dominate African wild dogs, taking their kills and preying on young and rarely adult dogs. Population densities of wild dogs are low in areas where lions are more abundant.[135] However, there are a few reported cases of old and wounded lions falling prey to wild dogs.[136][137] Lions also charge at Nile crocodiles; depending on the size of the crocodile and the lion, either can lose kills or carrion to the other. Lions have been observed killing crocodiles that ventured onto land.[138] Lions also enter waterways, evidenced by the occasional lion claw found in crocodile stomachs.[139]
+
+Most lionesses reproduce by the time they are four years of age.[140] Lions do not mate at a specific time of year and the females are polyestrous.[141] Like those of other cats, the male lion's penis has spines that point backward. During withdrawal of the penis, the spines rake the walls of the female's vagina, which may cause ovulation.[142][143] A lioness may mate with more than one male when she is in heat.[144] Generation length of the lion is about seven years.[145] The average gestation period is around 110 days;[141] the female gives birth to a litter of between one and four cubs in a secluded den, which may be a thicket, a reed-bed, a cave, or some other sheltered area, usually away from the pride. She will often hunt alone while the cubs are still helpless, staying relatively close to the den.[146] Lion cubs are born blind; their eyes open around seven days after birth. They weigh 1.2–2.1 kg (2.6–4.6 lb) at birth and are almost helpless, beginning to crawl a day or two after birth and walking around three weeks of age.[147] To avoid a buildup of scent attracting the attention of predators, the lioness moves her cubs to a new den site several times a month, carrying them one-by-one by the nape of the neck.[146]
+
+Usually, the mother does not integrate herself and her cubs back into the pride until the cubs are six to eight weeks old.[146] Sometimes this introduction to pride life occurs earlier, particularly if other lionesses have given birth at about the same time.[92][148] When first introduced to the rest of the pride, lion cubs lack confidence when confronted with adults other than their mother. They soon begin to immerse themselves in the pride life, however, playing among themselves or attempting to initiate play with the adults.[148] Lionesses with cubs of their own are more likely to be tolerant of another lioness's cubs than lionesses without cubs. Male tolerance of the cubs varies—sometimes a male will patiently let the cubs play with his tail or his mane, while another may snarl and bat the cubs away.[149]
+
+Pride lionesses often synchronise their reproductive cycles and communal rearing and suckling of the young, which suckle indiscriminately from any or all of the nursing females in the pride. The synchronisation of births is advantageous because the cubs grow to being roughly the same size and have an equal chance of survival, and sucklings are not dominated by older cubs.[92][148] Weaning occurs after six or seven months. Male lions reach maturity at about three years of age and at four to five years are capable of challenging and displacing adult males associated with another pride. They begin to age and weaken at between 10 and 15 years of age at the latest.[150]
+
+When one or more new males oust the previous males associated with a pride, the victors often kill any existing young cubs, perhaps because females do not become fertile and receptive until their cubs mature or die. Females often fiercely defend their cubs from a usurping male but are rarely successful unless a group of three or four mothers within a pride join forces against the male.[151] Cubs also die from starvation and abandonment, and predation by leopards, hyenas and wild dogs.[137][92] Up to 80% of lion cubs will die before the age of two.[152] Both male and female lions may be ousted from prides to become nomads, although most females usually remain with their birth pride. When a pride becomes too large, however, the youngest generation of female cubs may be forced to leave to find their own territory. When a new male lion takes over a pride, adolescents both male and female may be evicted.[153] Lions of both sexes may be involved in group homosexual and courtship activities; males will also head-rub and roll around with each other before simulating sex together.[154][155]
+
+Although adult lions have no natural predators, evidence suggests most die violently from attacks by humans or other lions.[156] Lions often inflict serious injuries on members of other prides they encounter in territorial disputes or members of the home pride when fighting at a kill.[157] Crippled lions and cubs may fall victim to hyenas and leopards or be trampled by buffalo or elephants. Careless lions may be maimed when hunting prey.[158]
+
+Ticks commonly infest the ears, neck and groin regions of lions.[159][160] Adult forms of several species of the tapeworm genus Taenia have been isolated from lion intestines, having been ingested as larvae in antelope meat.[161] Lions in the Ngorongoro Crater were afflicted by an outbreak of stable fly (Stomoxys calcitrans) in 1962; this resulted in lions becoming emaciated and covered in bloody, bare patches. Lions sought unsuccessfully to evade the biting flies by climbing trees or crawling into hyena burrows; many died or migrated and the local population dropped from 70 to 15 individuals.[162] A more recent outbreak in 2001 killed six lions.[163]
+
+Captive lions have been infected with canine distemper virus (CDV) since at least the mid 1970s.[164] CDV is spread by domestic dogs and other carnivores; a 1994 outbreak in Serengeti National Park resulted in many lions developing neurological symptoms such as seizures. During the outbreak, several lions died from pneumonia and encephalitis.[165] Feline immunodeficiency virus and lentivirus also affect captive lions.[166][167]
+
+When resting, lion socialisation occurs through a number of behaviours; the animal's expressive movements are highly developed. The most common peaceful, tactile gestures are head rubbing and social licking,[168] which have been compared with the role of allogrooming among primates.[169] Head rubbing—nuzzling the forehead, face and neck against another lion—appears to be a form of greeting[170] and is seen often after an animal has been apart from others or after a fight or confrontation. Males tend to rub other males, while cubs and females rub females.[171] Social licking often occurs in tandem with head rubbing; it is generally mutual and the recipient appears to express pleasure. The head and neck are the most common parts of the body licked; this behaviour may have arisen out of utility because lions cannot lick these areas themselves.[172]
+
+Lions have an array of facial expressions and body postures that serve as visual gestures.[173] A common facial expression is the "grimace face" or flehmen response, which a lion makes when sniffing chemical signals and involves an open mouth with bared teeth, raised muzzle, wrinkled nose closed eyes and relaxed ears.[174] Lions also use chemical and visual marking; males will spray and scrape plots of ground and objects within the territory.[173]
+
+The lion's repertoire of vocalisations is large; variations in intensity and pitch appear to be central to communication. Most lion vocalisations are variations of growling, snarling, meowing and roaring. Other sounds produced include purring, puffing, bleating and humming. Roaring is used to advertise its presence. Lions most often roar at night, a sound that can be heard from a distance of 8 kilometres (5.0 mi).[175] They tend to roar in a very characteristic manner starting with a few deep, long roars that subside into a series of shorter ones.[176][177]
+
+The lion is listed as Vulnerable on the IUCN Red List.[2]
+
+Several large and well-managed protected areas in Africa host large lion populations. Where an infrastructure for wildlife tourism has been developed, cash revenue for park management and local communities is a strong incentive for lion conservation.[2] Most lions now live in East and Southern Africa; their numbers are rapidly decreasing, and fell by an estimated 30–50% in the late half of the 20th century. Primary causes of the decline include disease and human interference.[2] In 1975, it was estimated that since the 1950s, lion numbers had decreased by half to 200,000 or fewer.[178] Estimates of the African lion population range between 16,500 and 47,000 living in the wild in 2002–2004.[179][76]
+
+In the Republic of the Congo, Odzala-Kokoua National Park was considered a lion stronghold in the 1990s. By 2014, no lions were recorded in the protected area so the population is considered locally extinct.[180] The West African lion population is isolated from the one in Central Africa, with little or no exchange of breeding individuals. In 2015, it was estimated that this population consists of about 400 animals, including fewer than 250 mature individuals. They persist in three protected areas in the region, mostly in one population in the W A P protected area complex, shared by Benin, Burkina Faso and Niger. This population is listed as Critically Endangered.[16] Field surveys in the WAP ecosystem revealed that lion occupancy is lowest in the W National Park, and higher in areas with permanent staff and thus better protection.[181]
+
+A population occurs in Cameroon's Waza National Park, where between approximately 14 and 21 animals persisted as of 2009.[182] In addition, 50 to 150 lions are estimated to be present in Burkina Faso's Arly-Singou ecosystem.[183] In 2015, an adult male lion and a female lion were sighted in Ghana's Mole National Park. These were the first sightings of lions in the country in 39 years.[184] In the same year, a population of up to 200 lions that was previously thought to have been extirpated was filmed in the Alatash National Park, Ethiopia, close to the Sudanese border.[185][186]
+
+In 2005, Lion Conservation Strategies were developed for West and Central Africa, and or East and Southern Africa. The strategies seek to maintain suitable habitat, ensure a sufficient wild prey base for lions, reduce factors that lead to further fragmentation of populations, and make lion–human coexistence sustainable.[187][188]
+Lion depredation on livestock is significantly reduced in areas where herders keep livestock in improved enclosures. Such measures contribute to mitigating human–lion conflict.[189]
+
+The last refuge of the Asiatic lion population is the 1,412 km2 (545 sq mi) Gir National Park and surrounding areas in the region of Saurashtra or Kathiawar Peninsula in Gujarat State, India. The population has risen from approximately 180 lions in 1974 to about 400 in 2010.[190] It is geographically isolated, which can lead to inbreeding and reduced genetic diversity. Since 2008, the Asiatic lion has been listed as Endangered on the IUCN Red List.[15] By 2015, the population had grown to 523 individuals inhabiting an area of 7,000 km2 (2,700 sq mi) in Saurashtra.[191][192][193] The Asiatic Lion Census conducted in 2017 recorded about 650 individuals.[194]
+
+The presence of numerous human habitations close to the National Park results in conflict between lions, local people and their livestock.[195][191] Some consider the presence of lions a benefit, as they keep populations of crop damaging herbivores in check.[196] The establishment of a second, independent Asiatic lion population in Kuno Wildlife Sanctuary, located in Madhya Pradesh was planned but in 2017, the Asiatic Lion Reintroduction Project seemed unlikely to be implemented.[197][198]
+
+Lions imported to Europe before the middle of the 19th century were possibly foremost Barbary lions from North Africa, or Cape lions from Southern Africa.[199]
+Another 11 animals thought to be Barbary lions kept in Addis Ababa Zoo are descendants of animals owned by Emperor Haile Selassie. WildLink International in collaboration with Oxford University launched an ambitious International Barbary Lion Project with the aim of identifying and breeding Barbary lions in captivity for eventual reintroduction into a national park in the Atlas Mountains of Morocco.[200] However, a genetic analysis showed that the captive lions at Addis Ababa Zoo were not Barbary lions, but rather closely related to wild lions in Chad and Cameroon.[201]
+
+In 1982, the Association of Zoos and Aquariums started a Species Survival Plan for the Asiatic lion to increase its chances of survival. In 1987, it was found that most lions in North American zoos were hybrids between African and Asiatic lions.[202]
+Breeding programs need to note origins of the participating animals to avoid cross-breeding different subspecies and thus reducing their conservation value.[203]
+Captive breeding of lions was halted to eliminate individuals of unknown origin and pedigree. Wild-born lions were imported to American zoos from Africa between 1989 and 1995. Breeding was continued in 1998 in the frame of an African lion Species Survival Plan.[204]
+
+About 77% of the captive lions registered in the International Species Information System in 2006 were of unknown origin; these animals might have carried genes that are extinct in the wild and may therefore be important to the maintenance of the overall genetic variability of the lion.[65]
+
+Lions are part of a group of exotic animals that have been central to zoo exhibits since the late 18th century. Although many modern zoos are more selective about their exhibits,[205] there are more than 1,000 African and 100 Asiatic lions in zoos and wildlife parks around the world. They are considered an ambassador species and are kept for tourism, education and conservation purposes.[206] Lions can live over twenty years in captivity; a lion in Honolulu Zoo died at the age of 22 in August 2007. His two sisters, born in 1986, were still alive in August 2007.[207]
+
+The first European "zoos" spread among noble and royal families in the 13th century, and until the 17th century were called seraglios; at that time they came to be called menageries, an extension of the cabinet of curiosities. They spread from France and Italy during the Renaissance to the rest of Europe.[208] In England, although the seraglio tradition was less developed, lions were kept at the Tower of London in a seraglio established by King John in the 13th century;[209][210] this was probably stocked with animals from an earlier menagerie started in 1125 by Henry I at his hunting lodge in Woodstock, Oxfordshire, where according to William of Malmesbury lions had been stocked.[211]
+
+Lions were kept in cramped and squalid conditions at London Zoo until a larger lion house with roomier cages was built in the 1870s.[212] Further changes took place in the early 20th century when Carl Hagenbeck designed enclosures with concrete "rocks", more open space and a moat instead of bars, more closely resembling a natural habitat. Hagenbeck designed lion enclosures for both Melbourne Zoo and Sydney's Taronga Zoo; although his designs were popular, the use of bars and caged enclosures prevailed in many zoos until the 1960s.[213] In the late 20th century, larger, more natural enclosures and the use of wire mesh or laminated glass instead of lowered dens allowed visitors to come closer than ever to the animals; some attractions such as the Cat Forest/Lion Overlook of Oklahoma City Zoological Park placed the den on ground level, higher than visitors.[214]
+
+Lion taming has been part of both established circuses and individual acts such as Siegfried & Roy. The practice began in the early 19th century by Frenchman Henri Martin and American Isaac Van Amburgh, who both toured widely and whose techniques were copied by a number of followers.[215] Van Amburgh performed before Queen Victoria in 1838 when he toured Great Britain. Martin composed a pantomime titled Les Lions de Mysore ("the lions of Mysore"), an idea Amburgh quickly borrowed. These acts eclipsed equestrianism acts as the central display of circus shows and entered public consciousness in the early 20th century with cinema. In demonstrating the superiority of human over animal, lion taming served a purpose similar to animal fights of previous centuries.[215] The ultimate proof of a tamer's dominance and control over a lion is demonstrated by the placing of the tamer's head in the lion's mouth. The now-iconic lion tamer's chair was possibly first used by American Clyde Beatty (1903–1965).[216]
+
+Lion hunting has occurred since ancient times and was often a royal pastime; intended to demonstrate the power of the king over nature. The earliest surviving record of lion hunting is an ancient Egyptian inscription dated circa 1380 BC that mentions Pharaoh Amenhotep III killing 102 lions "with his own arrows" during the first ten years of his rule. The Assyrians would release captive lions in a reserved space for the king to hunt; this event would be watched by spectators as the king and his men, on horseback or chariots, killed the lions with arrows and spears. Lions were also hunted during the Mughal Empire, where Emperor Jahangir is said to have excelled at it.[217] In Ancient Rome, lions were kept by emperors for hunts as well as gladiator fights and executions.[218]
+
+The Maasai people have traditionally viewed the killing of lions as a rite of passage. Historically, lions were hunted by individuals, however, due to reduced lion populations, elders discourage solo lion hunts.[219] During the European colonisation of Africa in the 19th century, the hunting of lions was encouraged because they were considered as vermin and lion hides fetched £1 each.[220] The widely reproduced imagery of the heroic hunter chasing lions would dominate a large part of the century.[221] Trophy hunting of lions in recent years has been met with controversy; notably with the killing of Cecil the lion in mid-2015.[222]
+
+Lions do not usually hunt humans but some (usually males) seem to seek them out. One well-publicised case is the Tsavo maneaters; in 1898, 28 officially recorded railway workers building the Kenya-Uganda Railway were taken by lions over nine months during the construction of a bridge in Kenya.[223] The hunter who killed the lions wrote a book detailing the animals' predatory behaviour; they were larger than normal and lacked manes, and one seemed to suffer from tooth decay. The infirmity theory, including tooth decay, is not favoured by all researchers; an analysis of teeth and jaws of man-eating lions in museum collections suggests that while tooth decay may explain some incidents, prey depletion in human-dominated areas is a more likely cause of lion predation on humans.[224] Sick or injured animals may be more prone to man-eating but the behaviour is not unusual, nor necessarily aberrant.[225]
+
+Lions' proclivity for man-eating has been systematically examined. American and Tanzanian scientists report that man-eating behaviour in rural areas of Tanzania increased greatly from 1990 to 2005. At least 563 villagers were attacked and many eaten over this period. The incidents occurred near Selous National Park in Rufiji District and in Lindi Province near the Mozambican border. While the expansion of villages into bush country is one concern, the authors argue conservation policy must mitigate the danger because in this case, conservation contributes directly to human deaths. Cases in Lindi in which lions seize humans from the centres of substantial villages have been documented.[226] Another study of 1,000 people attacked by lions in southern Tanzania between 1988 and 2009 found that the weeks following the full moon, when there was less moonlight, were a strong indicator of increased night-time attacks on people.[227]
+
+According to Robert R. Frump, Mozambican refugees regularly crossing Kruger National Park, South Africa, at night are attacked and eaten by lions; park officials have said man-eating is a problem there. Frump said thousands may have been killed in the decades after apartheid sealed the park and forced refugees to cross the park at night. For nearly a century before the border was sealed, Mozambicans had regularly crossed the park in daytime with little harm.[228]
+
+The lion is one of the most widely recognised animal symbols in human culture. It has been extensively depicted in sculptures and paintings, on national flags, and in contemporary films and literature.[47] It appeared as a symbol for strength and nobility in cultures across Europe, Asia and Africa, despite incidents of attacks on people. The lion has been depicted as "king of the jungle" and "king of beasts", and thus became a popular symbol for royalty and stateliness.[230] The lion is also used as a symbol of sporting teams.[231][232][233]
+
+Depictions of lions are known from the Upper Paleolithic period. Carvings and paintings of lions discovered in the Lascaux and Chauvet Caves in France have been dated to 15,000 to 17,000 years old.[234][229] A lioness-headed ivory carving found in Vogelherd cave in the Swabian Alb, southwest Germany, is dubbed Löwenmensch (lion-human) in German. The sculpture has been dated to least 32,000 years old—and as early as 40,000 years ago[235]—and originated from the Aurignacian culture.[29]
+
+In sub-Saharan Africa, the lion has been a common character in stories, proverbs and dances, but rarely featured in visual arts.[236] In some cultures, the lion symbolises power and royalty.[237] In Swahili language, the lion is known as simba which also means "aggressive", "king" and "strong".[55] Some rulers had the word "lion" in their nickname. Sundiata Keita of the Mali Empire was called "Lion of Mali".[238] The founder of the Waalo kingdom is said to have been raised by lions and returned to his people part-lion to unite them using the knowledge he learned from the lions.[237]
+
+In parts of West Africa, lions symbolised the top class of their social hierarchies.[237] In more heavily forested areas where lions were rare, the leopard represented the top of the hierarchy.[236] In parts of West and East Africa, the lion is associated with healing and is regarded as the link between seers and the supernatural. In other East African traditions, the lion is the symbol of laziness.[237] In much of African folklore, the lion is portrayed as having low intelligence and is easily tricked by other animals.[238]
+
+The ancient Egyptians portrayed several of their war deities as lionesses, which they revered as fierce hunters. Egyptian deities associated with lions include Sekhmet, Bast, Mafdet, Menhit, Pakhet and Tefnut.[230] These deities were often connected with the sun god Ra and his fierce heat, and their dangerous power was invoked to guard people or sacred places. The sphinx, a figure with a lion's body and the head of a human or other creature, represented a pharaoh or deity who had taken on this protective role.[239]
+
+The lion was a prominent symbol in ancient Mesopotamia from Sumer up to Assyrian and Babylonian times, where it was strongly associated with kingship.[240] Lions were among the major symbols of the goddess Inanna/Ishtar.[241][242] The Lion of Babylon was the foremost symbol of the Babylonian Empire.[243] The Lion Hunt of Ashurbanipal is a famous sequence of Assyrian palace reliefs from c. 640 BC, now in the British Museum.[244] The Lion of Judah is the biblical emblem of the tribe of Judah and the later Kingdom of Judah.[245] Lions are frequently mentioned in the Bible; notably in the Book of Daniel in which the eponymous hero refuses to worship King Darius and is forced to sleep in the lions' den where he is miraculously unharmed (Dan 6). In the Book of Judges, Samson kills a lion as he travels to visit a Philistine woman.(Judg 14).[246]
+
+Indo-Persian chroniclers regarded the lion as keeper of order in the realm of animals. The Sanskrit word mrigendra signifies a lion as king of animals in general or deer in particular.[247]
+Narasimha, the man-lion, is one of ten avatars of the Hindu god Vishnu.[248] Singh is an ancient Indian vedic name meaning "lion", dating back over 2,000 years. It was originally used only by Rajputs, a Hindu Kshatriya or military caste but is used by millions of Hindu Rajputs and more than twenty million Sikhs today.[249] The Lion Capital of Ashoka, erected by Emperor Ashoka in the 3rd century CE, depicts four lions standing back to back. It was made the National Emblem of India in 1950.[250] The lion is also symbolic for the Sinhalese people;[251] the term derived from the Indo-Aryan Sinhala, meaning the "lion people" or "people with lion blood", while a sword-wielding lion is the central figure on the national flag of Sri Lanka.[252]
+
+The lion is a common motif in Chinese art; it was first used in art during the late Spring and Autumn period (fifth or sixth century BC) and became more popular during the Han Dynasty (206 BC – AD 220) when imperial guardian lions started to be placed in front of imperial palaces for protection. Because lions have never been native to China, early depictions were somewhat unrealistic; after the introduction of Buddhist art to China in the Tang Dynasty after the sixth century AD, lions were usually depicted wingless with shorter, thicker bodies and curly manes.[253] The lion dance is a traditional dance in Chinese culture in which performers in lion costumes mimic a lion's movements, often with musical accompaniment from cymbals, drums and gongs. They are performed at Chinese New Year, the August Moon Festival and other celebratory occasions for good luck.[254]
+
+Lion-headed figures and amulets were excavated in tombs in the Greek islands of Crete, Euboea, Rhodes, Paros and Chios. They are associated with the Egyptian deity Sekhmet and date to the early Iron Age between the 9th and 6th centuries BC.[255] The lion is featured in several of Aesop's fables, notably The Lion and the Mouse.[256] The Nemean lion was symbolic in ancient Greece and Rome, represented as the constellation and zodiac sign Leo, and described in mythology, where it was killed and worn by the hero Heracles,[257] symbolising victory over death.[258] Lancelot and Gawain were also heroes slaying lions in the Middle Ages. In some medieval stories, lions were portrayed as allies and companions.[259] "Lion" was the nickname of several medieval warrior-rulers with a reputation for bravery, such as Richard the Lionheart.[230]
+
+Lions continue to appear in modern literature as characters including the messianic Aslan in the 1950 novel The Lion, the Witch and the Wardrobe and The Chronicles of Narnia series by C. S. Lewis,[260] and the comedic Cowardly Lion in L. Frank Baum's 1900 The Wonderful Wizard of Oz.[261] Lion symbolism was used from the advent of cinema; one of the most iconic and widely recognised lions is Leo, which has been the mascot for Metro-Goldwyn-Mayer studios since the 1920s.[262] The 1966 film Born Free features Elsa the lioness and is based on the 1960 non-fiction book with the same title.[263] The lion's role as king of the beasts has been used in the 1994 Disney animated feature film The Lion King.[264]
+
+Lions are frequently depicted on coats of arms, either as a device on shields or as supporters, but the lioness is used much less frequently.[265] The heraldic lion is particularly common in British arms. It is traditionally depicted in a great variety of attitudes, although within French heraldry only lions rampant are considered to be lions; feline figures in any other position are instead referred to as leopards.[266]

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+
+The sea, the world ocean, or simply the ocean is the connected body of salty water that covers over 70% of Earth's surface (361,132,000 square kilometres (139,434,000 sq mi), with a total volume of roughly 1,332,000,000 cubic kilometres (320,000,000 cu mi)).[1] It moderates Earth's climate and has important roles in the water cycle, carbon cycle, and nitrogen cycle. It has been travelled and explored since ancient times, while the scientific study of the sea—oceanography—dates broadly from the voyages of Captain James Cook to explore the Pacific Ocean between 1768 and 1779. The word sea is also used to denote smaller, partly landlocked sections of the ocean and certain large, entirely landlocked, saltwater lakes, such as the Caspian Sea and the Dead Sea.
+
+The most abundant solid dissolved in seawater is sodium chloride. The water also contains salts of magnesium, calcium, and potassium, amongst many other elements, some in minute concentrations. Salinity varies widely, being lower near the surface and the mouths of large rivers and higher in the depths of the ocean; however, the relative proportions of dissolved salts varies little across the oceans. Winds blowing over the surface of the sea produce waves, which break when they enter shallow water. Winds also create surface currents through friction, setting up slow but stable circulations of water throughout the oceans. The directions of the circulation are governed by factors including the shapes of the continents and Earth's rotation (the Coriolis effect). Deep-sea currents, known as the global conveyor belt, carry cold water from near the poles to every ocean. Tides, the generally twice-daily rise and fall of sea levels, are caused by Earth's rotation and the gravitational effects of the orbiting Moon and, to a lesser extent, of the Sun. Tides may have a very high range in bays or estuaries. Submarine earthquakes arising from tectonic plate movements under the oceans can lead to destructive tsunamis, as can volcanoes, huge landslides or the impact of large meteorites.
+
+A wide variety of organisms, including bacteria, protists, algae, plants, fungi, and animals, live in the sea, which offers a wide range of marine habitats and ecosystems, ranging vertically from the sunlit surface and shoreline to the great depths and pressures of the cold, dark abyssal zone, and in latitude from the cold waters under polar ice caps to the colourful diversity of coral reefs in tropical regions. Many of the major groups of organisms evolved in the sea and life may have started there.
+
+The sea provides substantial supplies of food for humans, mainly fish, but also shellfish, mammals and seaweed, whether caught by fishermen or farmed underwater. Other human uses of the sea include trade, travel, mineral extraction, power generation, warfare, and leisure activities such as swimming, sailing, and scuba diving. Many of these activities create marine pollution. The sea is important in human culture, with major appearances in literature at least since Homer's Odyssey, in marine art, in cinema, in theatre and in classical music. Symbolically, the sea appears as monsters such as Scylla in mythology and represents the unconscious mind in dream interpretation.
+
+The sea is the interconnected system of all the Earth's oceanic waters, including the Atlantic, Pacific, Indian, Southern and Arctic Oceans.[2] However, the word "sea" can also be used for many specific, much smaller bodies of seawater, such as the North Sea or the Red Sea. There is no sharp distinction between seas and oceans, though generally seas are smaller, and are often partly (as marginal seas) or wholly (as inland seas) bordered by land.[3] However, the Sargasso Sea has no coastline and lies within a circular current, the North Atlantic Gyre.[4](p90) Seas are generally larger than lakes and contain salt water, but the Sea of Galilee is a freshwater lake.[5][a] The United Nations Convention on the Law of the Sea states that all of the ocean is "sea".[9][10][b]
+
+Earth is the only known planet with seas of liquid water on its surface,[4](p22) although Mars possesses ice caps and similar planets in other solar systems may have oceans.[12] Earth's 1,335,000,000 cubic kilometers (320,000,000 cu mi) of sea contain about 97.2 percent of its known water[13][c] and cover more than 70 percent of its surface.[4](p7) Another 2.15% of Earth's water is frozen, found in the sea ice covering the Arctic Ocean, the ice cap covering Antarctica and its adjacent seas, and various glaciers and surface deposits around the world. The remainder (about 0.65% of the whole) form underground reservoirs or various stages of the water cycle, containing the freshwater encountered and used by most terrestrial life: vapor in the air, the clouds it slowly forms, the rain falling from them, and the lakes and rivers spontaneously formed as its waters flow again and again to the sea.[13]
+
+The scientific study of water and Earth's water cycle is hydrology; hydrodynamics studies the physics of water in motion. The more recent study of the sea in particular is oceanography. This began as the study of the shape of the ocean's currents[18] but has since expanded into a large and multidisciplinary field:[19] it examines the properties of seawater; studies waves, tides, and currents; charts coastlines and maps the seabeds; and studies marine life.[20] The subfield dealing with the sea's motion, its forces, and the forces acting upon it is known as physical oceanography.[21] Marine biology (biological oceanography) studies the plants, animals, and other organisms inhabiting marine ecosystems. Both are informed by chemical oceanography, which studies the behavior of elements and molecules within the oceans: particularly, at the moment, the ocean's role in the carbon cycle and carbon dioxide's role in the increasing acidification of seawater. Marine and maritime geography charts the shape and shaping of the sea, while marine geology (geological oceanography) has provided evidence of continental drift and the composition and structure of the Earth, clarified the process of sedimentation, and assisted the study of volcanism and earthquakes.[19]
+
+The water in the sea was thought to come from the Earth's volcanoes, starting 4 billion years ago, released by degassing from molten rock.[4](pp24–25) More recent work suggests much of the Earth's water may come from comets.[22] A characteristic of seawater is that it is salty. Salinity is usually measured in parts per thousand (‰ or per mil), and the open ocean has about 35 grams (1.2 oz) solids per litre, a salinity of 35 ‰. The Mediterranean Sea is slightly higher at 38 ‰,[23] while the salinity of the northern Red Sea can reach 41‰.[24] In contrast, some landlocked hypersaline lakes have a much higher salinity, for example the Dead Sea has 300 grams (11 oz) dissolved solids per litre (300 ‰).
+
+While the constituents of table salt sodium and chloride make up about 85 percent of the solids in solution, there are also other metal ions such as magnesium and calcium, and negative ions including sulphate, carbonate, and bromide. Despite variations in the levels of salinity in different seas, the relative composition of the dissolved salts is stable throughout the world's oceans.[25][26] Seawater is too saline for humans to drink safely, as the kidneys cannot excrete urine as salty as seawater.[27]
+
+Although the amount of salt in the ocean remains relatively constant within the scale of millions of years, various factors affect the salinity of a body of water.[28] Evaporation and by-product of ice formation (known as "brine rejection") increase salinity, whereas precipitation, sea ice melt, and runoff from land reduce it.[28] The Baltic Sea, for example, has many rivers flowing into it, and thus the sea could be considered as brackish.[29] Meanwhile, the Red Sea is very salty due to its high evaporation rate.[30]
+
+Sea temperature depends on the amount of solar radiation falling on its surface. In the tropics, with the sun nearly overhead, the temperature of the surface layers can rise to over 30 °C (86 °F) while near the poles the temperature in equilibrium with the sea ice is about −2 °C (28 °F). There is a continuous circulation of water in the oceans. Warm surface currents cool as they move away from the tropics, and the water becomes denser and sinks. The cold water moves back towards the equator as a deep sea current, driven by changes in the temperature and density of the water, before eventually welling up again towards the surface. Deep seawater has a temperature between −2 °C (28 °F) and 5 °C (41 °F) in all parts of the globe.[31]
+
+Seawater with a typical salinity of 35‰ has a freezing point of about −1.8 °C (28.8 °F).[32] When its temperature becomes low enough, ice crystals form on the surface. These break into small pieces and coalesce into flat discs that form a thick suspension known as frazil. In calm conditions this freezes into a thin flat sheet known as nilas, which thickens as new ice forms on its underside. In more turbulent seas, frazil crystals join together into flat discs known as pancakes. These slide under each other and coalesce to form floes. In the process of freezing, salt water and air are trapped between the ice crystals. Nilas may have a salinity of 12–15 ‰, but by the time the sea ice is one year old, this falls to 4–6 ‰.[33]
+
+The amount of oxygen found in seawater depends primarily on the plants growing in it. These are mainly algae, including phytoplankton, with some vascular plants such as seagrasses. In daylight the photosynthetic activity of these plants produces oxygen, which dissolves in the seawater and is used by marine animals. At night, photosynthesis stops, and the amount of dissolved oxygen declines. In the deep sea, where insufficient light penetrates for plants to grow, there is very little dissolved oxygen. In its absence, organic material is broken down by anaerobic bacteria producing hydrogen sulphide.[34] Global warming is likely to reduce levels of oxygen in surface waters, since the solubility of oxygen in water falls at higher temperatures.[35]
+The amount of light that penetrates the sea depends on the angle of the sun, the weather conditions and the turbidity of the water. Much light gets reflected at the surface, and red light gets absorbed in the top few metres. Yellow and green light reach greater depths, and blue and violet light may penetrate as deep as 1,000 metres (3,300 ft). There is insufficient light for photosynthesis and plant growth beyond a depth of about 200 metres (660 ft).[36]
+
+Wind blowing over the surface of a body of water forms waves that are perpendicular to the direction of the wind. The friction between air and water caused by a gentle breeze on a pond causes ripples to form. A strong blow over the ocean causes larger waves as the moving air pushes against the raised ridges of water. The waves reach their maximum height when the rate at which they are travelling nearly matches the speed of the wind. In open water, when the wind blows continuously as happens in the Southern Hemisphere in the Roaring Forties, long, organised masses of water called swell roll across the ocean.[4](pp83–84)[37][38][d] If the wind dies down, the wave formation is reduced, but already-formed waves continue to travel in their original direction until they meet land. The size of the waves depends on the fetch, the distance that the wind has blown over the water and the strength and duration of that wind. When waves meet others coming from different directions, interference between the two can produce broken, irregular seas.[37] Constructive interference can cause individual (unexpected) rogue waves much higher than normal.[39] Most waves are less than 3 m (10 ft) high[39] and it is not unusual for strong storms to double or triple that height;[40] offshore construction such as wind farms and oil platforms use metocean statistics from measurements in computing the wave forces (due to for instance the hundred-year wave) they are designed against.[41] Rogue waves, however, have been documented at heights above 25 meters (82 ft).[42][43]
+
+The top of a wave is known as the crest, the lowest point between waves is the trough and the distance between the crests is the wavelength. The wave is pushed across the surface of the sea by the wind, but this represents a transfer of energy and not a horizontal movement of water. As waves approach land and move into shallow water, they change their behavior. If approaching at an angle, waves may bend (refraction) or wrap rocks and headlands (diffraction). When the wave reaches a point where its deepest oscillations of the water contact the seabed, they begin to slow down. This pulls the crests closer together and increases the waves' height, which is called wave shoaling. When the ratio of the wave's height to the water depth increases above a certain limit, it "breaks", toppling over in a mass of foaming water.[39] This rushes in a sheet up the beach before retreating into the sea under the influence of gravity.[37]
+
+A tsunami is an unusual form of wave caused by an infrequent powerful event such as an underwater earthquake or landslide, a meteorite impact, a volcanic eruption or a collapse of land into the sea. These events can temporarily lift or lower the surface of the sea in the affected area, usually by a few feet. The potential energy of the displaced seawater is turned into kinetic energy, creating a shallow wave, a tsunami, radiating outwards at a velocity proportional to the square root of the depth of the water and which therefore travels much faster in the open ocean than on a continental shelf.[44] In the deep open sea, tsunamis have wavelengths of around 80 to 300 miles (130 to 480 km), travel at speeds of over 600 miles per hour (970 km/hr)[45] and usually have a height of less than three feet, so they often pass unnoticed at this stage.[46] In contrast, ocean surface waves caused by winds have wavelengths of a few hundred feet, travel at up to 65 miles per hour (105 km/h) and are up to 45 feet (14 metres) high.[46]
+
+A trigger event on the continental shelf may cause a local tsunami on the land side and a distant tsunami that travels out across the ocean. The energy of the wave is dissipated only gradually, but is spread out over the wave front, so as the wave radiates away from the source, the front gets longer and the average energy reduces, so distant shores will, on average, be hit by weaker waves. However, as the speed of the wave is controlled by the water depth, it does not travel at the same speed in all directions, and this affects the direction of the wave front – an effect known as refraction – which can focus the strength of the advancing tsunami on some areas and weaken it in others according to undersea topography.[47][48]
+
+As a tsunami moves into shallower water its speed decreases, its wavelength shortens and its amplitude increases enormously,[46] behaving in the same way as a wind-generated wave in shallow water, but on a vastly greater scale. Either the trough or the crest of a tsunami can arrive at the coast first.[44] In the former case, the sea draws back and leaves subtidal areas close to the shore exposed which provides a useful warning for people on land.[49] When the crest arrives, it does not usually break but rushes inland, flooding all in its path. Much of the destruction may be caused by the flood water draining back into the sea after the tsunami has struck, dragging debris and people with it. Often several tsunami are caused by a single geological event and arrive at intervals of between eight minutes and two hours. The first wave to arrive on shore may not be the biggest or most destructive.[44] Occasionally, a tsunami may transform into a bore, typically in a shallow bay or an estuary.[45]
+
+Wind blowing over the surface of the sea causes friction at the interface between air and sea. Not only does this cause waves to form but it also makes the surface seawater move in the same direction as the wind. Although winds are variable, in any one place they predominantly blow from a single direction and thus a surface current can be formed. Westerly winds are most frequent in the mid-latitudes while easterlies dominate the tropics.[50] When water moves in this way, other water flows in to fill the gap and a circular movement of surface currents known as a gyre is formed. There are five main gyres in the world's oceans: two in the Pacific, two in the Atlantic and one in the Indian Ocean. Other smaller gyres are found in lesser seas and a single gyre flows around Antarctica. These gyres have followed the same routes for millennia, guided by the topography of the land, the wind direction and the Coriolis effect. The surface currents flow in a clockwise direction in the Northern Hemisphere and anticlockwise in the Southern Hemisphere. The water moving away from the equator is warm, and that flowing in the reverse direction has lost most of its heat. These currents tend to moderate the Earth's climate, cooling the equatorial region and warming regions at higher latitudes.[51] Global climate and weather forecasts are powerfully affected by the world ocean, so global climate modelling makes use of ocean circulation models as well as models of other major components such as the atmosphere, land surfaces, aerosols and sea ice.[52] Ocean models make use of a branch of physics, geophysical fluid dynamics, that describes the large-scale flow of fluids such as seawater.[53]
+
+Surface currents only affect the top few hundred metres (yards) of the sea, but there are also large-scale flows in the ocean depths caused by the movement of deep water masses. A main deep ocean current flows through all the world's oceans and is known as the thermohaline circulation or global conveyor belt. This movement is slow and is driven by differences in density of the water caused by variations in salinity and temperature.[54] At high latitudes the water is chilled by the low atmospheric temperature and becomes saltier as sea ice crystallizes out. Both these factors make it denser, and the water sinks. From the deep sea near Greenland, such water flows southwards between the continental landmasses on either side of the Atlantic. When it reaches the Antarctic, it is joined by further masses of cold, sinking water and flows eastwards. It then splits into two streams that move northwards into the Indian and Pacific Oceans. Here it is gradually warmed, becomes less dense, rises towards the surface and loops back on itself. It takes a thousand years for this circulation pattern to be completed.[51]
+
+Besides gyres, there are temporary surface currents that occur under specific conditions. When waves meet a shore at an angle, a longshore current is created as water is pushed along parallel to the coastline. The water swirls up onto the beach at right angles to the approaching waves but drains away straight down the slope under the effect of gravity. The larger the breaking waves, the longer the beach and the more oblique the wave approach, the stronger is the longshore current.[55] These currents can shift great volumes of sand or pebbles, create spits and make beaches disappear and water channels silt up.[51] A rip current can occur when water piles up near the shore from advancing waves and is funnelled out to sea through a channel in the seabed. It may occur at a gap in a sandbar or near a man-made structure such as a groyne. These strong currents can have a velocity of 3 ft (0.9 m) per second, can form at different places at different stages of the tide and can carry away unwary bathers.[56] Temporary upwelling currents occur when the wind pushes water away from the land and deeper water rises to replace it. This cold water is often rich in nutrients and creates blooms of phytoplankton and a great increase in the productivity of the sea.[51]
+
+Tides are the regular rise and fall in water level experienced by seas and oceans in response to the gravitational influences of the Moon and the Sun, and the effects of the Earth's rotation. During each tidal cycle, at any given place the water rises to a maximum height known as "high tide" before ebbing away again to the minimum "low tide" level. As the water recedes, it uncovers more and more of the foreshore, also known as the intertidal zone. The difference in height between the high tide and low tide is known as the tidal range or tidal amplitude.[57][58]
+
+Most places experience two high tides each day, occurring at intervals of about 12 hours and 25 minutes. This is half the 24 hours and 50 minute period that it takes for the Earth to make a complete revolution and return the Moon to its previous position relative to an observer. The Moon's mass is some 27 million times smaller than the Sun, but it is 400 times closer to the Earth.[59] Tidal force or tide-raising force decreases rapidly with distance, so the moon has more than twice as great an effect on tides as the Sun.[59] A bulge is formed in the ocean at the place where the Earth is closest to the Moon, because it is also where the effect of the Moon's gravity is stronger. On the opposite side of the Earth, the lunar force is at its weakest and this causes another bulge to form. As the Moon rotates around the Earth, so do these ocean bulges move around the Earth. The gravitational attraction of the Sun is also working on the seas, but its effect on tides is less powerful than that of the Moon, and when the Sun, Moon and Earth are all aligned (full moon and new moon), the combined effect results in the high "spring tides". In contrast, when the Sun is at 90° from the Moon as viewed from Earth, the combined gravitational effect on tides is less causing the lower "neap tides".[57]
+
+Tidal flows of seawater are resisted by the water's inertia and can be affected by land masses. In places like the Gulf of Mexico where land constrains the movement of the bulges, only one set of tides may occur each day. Inshore from an island there may be a complex daily cycle with four high tides. The island straits at Chalkis on Euboea experience strong currents which abruptly switch direction, generally four times per day but up to 12 times per day when the moon and the sun are 90 degrees apart.[60] Where there is a funnel-shaped bay or estuary, the tidal range can be magnified. The Bay of Fundy is the classic example of this and can experience spring tides of 15 m (49 ft). Although tides are regular and predictable, the height of high tides can be lowered by offshore winds and raised by onshore winds. The high pressure at the centre of an anticyclones pushes down on the water and is associated with abnormally low tides while low-pressure areas may cause extremely high tides.[57] A storm surge can occur when high winds pile water up against the coast in a shallow area and this, coupled with a low pressure system, can raise the surface of the sea at high tide dramatically. In 1900, Galveston, Texas experienced a 15 ft (5 m) surge during a hurricane that overwhelmed the city, killing over 3,500 people and destroying 3,636 homes.[61]
+
+The Earth is composed of a magnetic central core, a mostly liquid mantle and a hard rigid outer shell (or lithosphere), which is composed of the Earth's rocky crust and the deeper mostly solid outer layer of the mantle. On land the crust is known as the continental crust while under the sea it is known as the oceanic crust. The latter is composed of relatively dense basalt and is some five to ten kilometres (three to six miles) thick. The relatively thin lithosphere floats on the weaker and hotter mantle below and is fractured into a number of tectonic plates.[62] In mid-ocean, magma is constantly being thrust through the seabed between adjoining plates to form mid-oceanic ridges and here convection currents within the mantle tend to drive the two plates apart. Parallel to these ridges and nearer the coasts, one oceanic plate may slide beneath another oceanic plate in a process known as subduction. Deep trenches are formed here and the process is accompanied by friction as the plates grind together. The movement proceeds in jerks which cause earthquakes, heat is produced and magma is forced up creating underwater mountains, some of which may form chains of volcanic islands near to deep trenches. Near some of the boundaries between the land and sea, the slightly denser oceanic plates slide beneath the continental plates and more subduction trenches are formed. As they grate together, the continental plates are deformed and buckle causing mountain building and seismic activity.[63][64]
+
+The Earth's deepest trench is the Mariana Trench which extends for about 2,500 kilometres (1,600 mi) across the seabed. It is near the Mariana Islands, a volcanic archipelago in the West Pacific, and though it averages just 68 kilometres (42 mi) wide, its deepest point is 10.994 kilometres (nearly 7 miles) below the surface of the sea.[65] An even longer trench runs alongside the coast of Peru and Chile, reaching a depth of 8,065 metres (26,460 ft) and extending for approximately 5,900 kilometres (3,700 mi). It occurs where the oceanic Nazca Plate slides under the continental South American Plate and is associated with the upthrust and volcanic activity of the Andes.[66]
+
+The zone where land meets sea is known as the coast and the part between the lowest spring tides and the upper limit reached by splashing waves is the shore. A beach is the accumulation of sand or shingle on the shore.[67] A headland is a point of land jutting out into the sea and a larger promontory is known as a cape. The indentation of a coastline, especially between two headlands, is a bay, a small bay with a narrow inlet is a cove and a large bay may be referred to as a gulf.[68] Coastlines are influenced by a number of factors including the strength of the waves arriving on the shore, the gradient of the land margin, the composition and hardness of the coastal rock, the inclination of the off-shore slope and the changes of the level of the land due to local uplift or submergence. Normally, waves roll towards the shore at the rate of six to eight per minute and these are known as constructive waves as they tend to move material up the beach and have little erosive effect. Storm waves arrive on shore in rapid succession and are known as destructive waves as the swash moves beach material seawards. Under their influence, the sand and shingle on the beach is ground together and abraded. Around high tide, the power of a storm wave impacting on the foot of a cliff has a shattering effect as air in cracks and crevices is compressed and then expands rapidly with release of pressure. At the same time, sand and pebbles have an erosive effect as they are thrown against the rocks. This tends to undercut the cliff, and normal weathering processes such as the action of frost follows, causing further destruction. Gradually, a wave-cut platform develops at the foot of the cliff and this has a protective effect, reducing further wave-erosion.[67]
+
+Material worn from the margins of the land eventually ends up in the sea. Here it is subject to attrition as currents flowing parallel to the coast scour out channels and transport sand and pebbles away from their place of origin. Sediment carried to the sea by rivers settles on the seabed causing deltas to form in estuaries. All these materials move back and forth under the influence of waves, tides and currents.[67] Dredging removes material and deepens channels but may have unexpected effects elsewhere on the coastline. Governments make efforts to prevent flooding of the land by the building of breakwaters, seawalls, dykes and levees and other sea defences. For instance, the Thames Barrier is designed to protect London from a storm surge,[69] while the failure of the dykes and levees around New Orleans during Hurricane Katrina created a humanitarian crisis in the United States. Land reclamation in Hong Kong also permitted the construction of Hong Kong International Airport through the leveling and expansion of two smaller islands.[70]
+
+Over most of geologic time, the sea level has been higher than it is today.[4](p74) The main factor affecting sea level over time is the result of changes in the oceanic crust, with a downward trend expected to continue in the very long term.[71] At the last glacial maximum, some 20,000 years ago, the sea level was 120 metres (390 ft) below its present-day level. For at least the last 100 years, sea level has been rising at an average rate of about 1.8 millimetres (0.071 in) per year.[72] Most of this rise can be attributed to an increase in the temperature of the sea and the resulting slight thermal expansion of the upper 500 metres (1,600 ft) of water. Additional contributions, as much as one quarter of the total, come from water sources on land, such as melting snow and glaciers and extraction of groundwater for irrigation and other agricultural and human needs.[73] The rising trend from global warming is expected to continue until at least the end of the 21st century.[74]
+
+The sea plays a part in the water or hydrological cycle, in which water evaporates from the ocean, travels through the atmosphere as vapour, condenses, falls as rain or snow, thereby sustaining life on land, and largely returns to the sea.[75] Even in the Atacama Desert, where little rain ever falls, dense clouds of fog known as the camanchaca blow in from the sea and support plant life.[76]
+
+In central Asia and other large land masses, there are endorheic basins which have no outlet to the sea, separated from the ocean by mountains or other natural geologic features that prevent the water draining away. The Caspian Sea is the largest one of these. Its main inflow is from the River Volga, there is no outflow and the evaporation of water makes it saline as dissolved minerals accumulate. The Aral Sea in Kazakhstan and Uzbekistan, and Pyramid Lake in the western United States are further examples of large, inland saline water-bodies without drainage. Some endorheic lakes are less salty, but all are sensitive to variations in the quality of the inflowing water.[77]
+
+Oceans contain the greatest quantity of actively cycled carbon in the world and are second only to the lithosphere in the amount of carbon they store.[78] The oceans' surface layer holds large amounts of dissolved organic carbon that is exchanged rapidly with the atmosphere. The deep layer's concentration of dissolved inorganic carbon is about 15 percent higher than that of the surface layer[79] and it remains there for much longer periods of time.[80] Thermohaline circulation exchanges carbon between these two layers.[78]
+
+Carbon enters the ocean as atmospheric carbon dioxide dissolves in the surface layers and is converted into carbonic acid, carbonate, and bicarbonate:[81]
+
+It can also enter through rivers as dissolved organic carbon and is converted by photosynthetic organisms into organic carbon. This can either be exchanged throughout the food chain or precipitated into the deeper, more carbon rich layers as dead soft tissue or in shells and bones as calcium carbonate. It circulates in this layer for long periods of time before either being deposited as sediment or being returned to surface waters through thermohaline circulation.[80]
+
+Seawater is slightly alkaline and had an average pH of about 8.2 over the past 300 million years.[82] More recently, anthropogenic activities have steadily increased the carbon dioxide content of the atmosphere; about 30–40% of the added CO2 is absorbed by the oceans, forming carbonic acid and lowering the pH (now below 8.1[82]) through a process called ocean acidification.[83][84][85] The pH is expected to reach 7.7 (representing a 3-fold increase in hydrogen ion concentration) by the year 2100, which is a significant change in a century.[86][e]
+
+One important element for the formation of skeletal material in marine animals is calcium, but calcium carbonate becomes more soluble with pressure, so carbonate shells and skeletons dissolve below its compensation depth.[88] Calcium carbonate also becomes more soluble at lower pH, so ocean acidification is likely to have profound effects on marine organisms with calcareous shells, such as oysters, clams, sea urchins, and corals,[89] because their ability to form shells will be reduced,[90] and the carbonate compensation depth will rise closer to the sea surface. Affected planktonic organisms will include the snail-like molluscs known as pteropods, and single-celled algae called coccolithophorids and foraminifera. All of these are important parts of the food chain and a diminution in their numbers will have significant consequences. In tropical regions, corals are likely to be severely affected as it becomes more difficult to build their calcium carbonate skeletons,[91] in turn adversely impacting other reef dwellers.[86]
+
+The current rate of ocean chemistry change appears to be without precedent in Earth's geological history, making it unclear how well marine ecosystems will be able to adapt to the shifting conditions of the near future.[92] Of particular concern is the manner in which the combination of acidification with the expected additional stressors of higher temperatures and lower oxygen levels will impact the seas.[93]
+
+The oceans are home to a diverse collection of life forms that use it as a habitat. Since sunlight illuminates only the upper layers, the major part of the ocean exists in permanent darkness. As the different depth and temperature zones each provide habitat for a unique set of species, the marine environment as a whole encompasses an immense diversity of life.[94] Marine habitats range from surface water to the deepest oceanic trenches, including coral reefs, kelp forests, seagrass meadows, tidepools, muddy, sandy and rocky seabeds, and the open pelagic zone. The organisms living in the sea range from whales 30 metres (100 ft) long to microscopic phytoplankton and zooplankton, fungi, and bacteria. Marine life plays an important part in the carbon cycle as photosynthetic organisms convert dissolved carbon dioxide into organic carbon and it is economically important to humans for providing fish for use as food.[95][96](pp204–229)
+
+Life may have originated in the sea and all the major groups of animals are represented there. Scientists differ as to precisely where in the sea life arose: the Miller-Urey experiments suggested a dilute chemical "soup" in open water, but more recent suggestions include volcanic hot springs, fine-grained clay sediments, or deep-sea "black smoker" vents, all of which would have provided protection from damaging ultraviolet radiation which was not blocked by the early Earth's atmosphere.[4](pp138–140)
+
+Marine habitats can be divided horizontally into coastal and open ocean habitats. Coastal habitats extend from the shoreline to the edge of the continental shelf. Most marine life is found in coastal habitats, even though the shelf area occupies only 7 percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of the continental shelf. Alternatively, marine habitats can be divided vertically into pelagic (open water), demersal (just above the seabed) and benthic (sea bottom) habitats. A third division is by latitude: from polar seas with ice shelves, sea ice and icebergs, to temperate and tropical waters.[4](pp150–151)
+
+Coral reefs, the so-called "rainforests of the sea", occupy less than 0.1 percent of the world's ocean surface, yet their ecosystems include 25 percent of all marine species.[97] The best-known are tropical coral reefs such as Australia's Great Barrier Reef, but cold water reefs harbour a wide array of species including corals (only six of which contribute to reef formation).[4](pp204–207)[98]
+
+Marine primary producers — plants and microscopic organisms in the plankton — are widespread and very essential for the ecosystem. It has been estimated that half of the world's oxygen is produced by phytoplankton.[99][100] About 45 percent of the sea's primary production of living material is contributed by diatoms.[101] Much larger algae, commonly known as seaweeds, are important locally; Sargassum forms floating drifts, while kelp form seabed forests.[96](pp246–255) Flowering plants in the form of seagrasses grow in "meadows" in sandy shallows,[102] mangroves line the coast in tropical and subtropical regions[103] and salt-tolerant plants thrive in regularly inundated salt marshes.[104] All of these habitats are able to sequester large quantities of carbon and support a biodiverse range of larger and smaller animal life.[105]
+
+Light is only able to penetrate the top 200 metres (660 ft) so this is the only part of the sea where plants can grow.[36] The surface layers are often deficient in biologically active nitrogen compounds. The marine nitrogen cycle consists of complex microbial transformations which include the fixation of nitrogen, its assimilation, nitrification, anammox and denitrification.[106] Some of these processes take place in deep water so that where there is an upwelling of cold waters, and also near estuaries where land-sourced nutrients are present, plant growth is higher. This means that the most productive areas, rich in plankton and therefore also in fish, are mainly coastal.[4](pp160–163)
+
+There is a broader spectrum of higher animal taxa in the sea than on land, many marine species have yet to be discovered and the number known to science is expanding annually.[107] Some vertebrates such as seabirds, seals and sea turtles return to the land to breed but fish, cetaceans and sea snakes have a completely aquatic lifestyle and many invertebrate phyla are entirely marine. In fact, the oceans teem with life and provide many varying microhabitats.[107] One of these is the surface film which, even though tossed about by the movement of waves, provides a rich environment and is home to bacteria, fungi, microalgae, protozoa, fish eggs and various larvae.[108]
+
+The pelagic zone contains macro- and microfauna and myriad zooplankton which drift with the currents. Most of the smallest organisms are the larvae of fish and marine invertebrates which liberate eggs in vast numbers because the chance of any one embryo surviving to maturity is so minute.[109] The zooplankton feed on phytoplankton and on each other and form a basic part of the complex food chain that extends through variously sized fish and other nektonic organisms to large squid, sharks, porpoises, dolphins and whales.[110] Some marine creatures make large migrations, either to other regions of the ocean on a seasonal basis or vertical migrations daily, often ascending to feed at night and descending to safety by day.[111] Ships can introduce or spread invasive species through the discharge of ballast water or the transport of organisms that have accumulated as part of the fouling community on the hulls of vessels.[112]
+
+The demersal zone supports many animals that feed on benthic organisms or seek protection from predators and the seabed provides a range of habitats on or under the surface of the substrate which are used by creatures adapted to these conditions. The tidal zone with its periodic exposure to the dehydrating air is home to barnacles, molluscs and crustaceans. The neritic zone has many organisms that need light to flourish. Here, among algal encrusted rocks live sponges, echinoderms, polychaete worms, sea anemones and other invertebrates. Corals often contain photosynthetic symbionts and live in shallow waters where light penetrates. The extensive calcareous skeletons they extrude build up into coral reefs which are an important feature of the seabed. These provide a biodiverse habitat for reef dwelling organisms. There is less sea life on the floor of deeper seas but marine life also flourishes around seamounts that rise from the depths, where fish and other animals congregate to spawn and feed. Close to the seabed live demersal fish that feed largely on pelagic organisms or benthic invertebrates.[113] Exploration of the deep sea by submersibles revealed a new world of creatures living on the seabed that scientists had not previously known to exist. Some like the detrivores rely on organic material falling to the ocean floor. Others cluster round deep sea hydrothermal vents where mineral-rich flows of water emerge from the seabed, supporting communities whose primary producers are sulphide-oxidising chemoautotrophic bacteria, and whose consumers include specialised bivalves, sea anemones, barnacles, crabs, worms and fish, often found nowhere else.[4](p212) A dead whale sinking to the bottom of the ocean provides food for an assembly of organisms which similarly rely largely on the actions of sulphur-reducing bacteria. Such places support unique biomes where many new microbes and other lifeforms have been discovered.[114]
+
+Humans have travelled the seas since they first built sea-going craft. Mesopotamians were using bitumen to caulk their reed boats and, a little later, masted sails.[115] By c. 3000 BC, Austronesians on Taiwan had begun spreading into maritime Southeast Asia.[116] Subsequently, the Austronesian "Lapita" peoples displayed great feats of navigation, reaching out from the Bismarck Archipelago to as far away as Fiji, Tonga, and Samoa.[117] Their descendants continued to travel thousands of miles between tiny islands on outrigger canoes,[118] and in the process they found many new islands, including Hawaii, Easter Island (Rapa Nui), and New Zealand.[119]
+
+The Ancient Egyptians and Phoenicians explored the Mediterranean and Red Sea with the Egyptian Hannu reaching the Arabian Peninsula and the African Coast around 2750 BC.[120] In the 1st millennium BC, Phoenicians and Greeks established colonies throughout the Mediterranean and the Black Sea.[121] Around 500 BC, the Carthaginian navigator Hanno left a detailed periplus of an Atlantic journey that reached at least Senegal and possibly Mount Cameroon.[122][123] In the early Mediaeval period, the Vikings crossed the North Atlantic and even reached the northeastern fringes of North America.[124] Novgorodians had also been sailing the White Sea since the 13th century or before.[125] Meanwhile, the seas along the eastern and southern Asian coast were used by Arab and Chinese traders.[126] The Chinese Ming Dynasty had a fleet of 317 ships with 37,000 men under Zheng He in the early fifteenth century, sailing the Indian and Pacific Oceans.[4](pp12–13) In the late fifteenth century, Western European mariners started making longer voyages of exploration in search of trade. Bartolomeu Dias rounded the Cape of Good Hope in 1487 and Vasco da Gama reached India via the Cape in 1498. Christopher Columbus sailed from Cadiz in 1492, attempting to reach the eastern lands of India and Japan by the novel means of travelling westwards. He made landfall instead on an island in the Caribbean Sea and a few years later, the Venetian navigator John Cabot reached Newfoundland. The Italian Amerigo Vespucci, after whom America was named, explored the South American coastline in voyages made between 1497 and 1502, discovering the mouth of the Amazon River.[4](pp12–13) In 1519 the Portuguese navigator Ferdinand Magellan led the Spanish Magellan-Elcano expedition which would be the first to sail around the world.[4](pp12–13)
+
+As for the history of navigational instrument, a compass was first used by the ancient Greeks and Chinese to show where north lies and the direction in which the ship is heading. The latitude (an angle which ranges from 0° at the equator to 90° at the poles) was determined by measuring the angle between the Sun, Moon or a specific star and the horizon by the use of an astrolabe, Jacob's staff or sextant. The longitude (a line on the globe joining the two poles) could only be calculated with an accurate chronometer to show the exact time difference between the ship and a fixed point such as the Greenwich Meridian. In 1759, John Harrison, a clockmaker, designed such an instrument and James Cook used it in his voyages of exploration.[127] Nowadays, the Global Positioning System (GPS) using over thirty satellites enables accurate navigation worldwide.[127]
+
+With regards to maps that are vital for navigation, in the second century, Ptolemy mapped the whole known world from the "Fortunatae Insulae", Cape Verde or Canary Islands, eastward to the Gulf of Thailand. This map was used in 1492 when Christopher Columbus set out on his voyages of discovery.[128] Subsequently, Gerardus Mercator made a practical map of the world in 1538, his map projection conveniently making rhumb lines straight.[4](pp12–13) By the eighteenth century better maps had been made and part of the objective of James Cook on his voyages was to further map the ocean. Scientific study has continued with the depth recordings of the Tuscarora, the oceanic research of the Challenger voyages (1872–1876), the work of the Scandinavian seamen Roald Amundsen and Fridtjof Nansen, the Michael Sars expedition in 1910, the German Meteor expedition of 1925, the Antarctic survey work of Discovery II in 1932, and others since.[19] Furthermore, in 1921, the International Hydrographic Organization was set up, and it constitutes the authority on hydrographic surveying and nautical charting.[129]
+
+Scientific oceanography began with the voyages of Captain James Cook from 1768 to 1779, describing the Pacific with unprecedented precision from 71 degrees South to 71 degrees North.[4](p14) John Harrison's chronometers supported Cook's accurate navigation and charting on two of these voyages, permanently improving the standard attainable for subsequent work.[4](p14) Other expeditions followed in the nineteenth century, from Russia, France, the Netherlands and the United States as well as Britain.[4](p15) On HMS Beagle, which provided Charles Darwin with ideas and materials for his 1859 book On the Origin of Species, the ship's captain, Robert FitzRoy, charted the seas and coasts and published his four-volume report of the ship's three voyages in 1839.[4](p15) Edward Forbes's 1854 book, Distribution of Marine Life argued that no life could exist below around 600 metres (2000 feet). This was proven wrong by the British biologists W. B. Carpenter and C. Wyville Thomson, who in 1868 discovered life in deep water by dredging.[4](p15) Wyville Thompson became chief scientist on the Challenger expedition of 1872–1876, which effectively created the science of oceanography.[4](p15)
+
+On her 68,890-nautical-mile (127,580 km) journey round the globe, HMS Challenger discovered about 4,700 new marine species, and made 492 deep sea soundings, 133 bottom dredges, 151 open water trawls and 263 serial water temperature observations.[130] In the southern Atlantic in 1898/1899, Carl Chun on the Valdivia brought many new life forms to the surface from depths of over 4,000 metres (13,000 ft). The first observations of deep-sea animals in their natural environment were made in 1930 by William Beebe and Otis Barton who descended to 434 metres (1,424 ft) in the spherical steel Bathysphere.[131] This was lowered by cable but by 1960 a self-powered submersible, Trieste developed by Jacques Piccard, took Piccard and Don Walsh to the deepest part of the Earth's oceans, the Mariana Trench in the Pacific, reaching a record depth of about 10,915 metres (35,810 ft),[132] a feat not repeated until 2012 when James Cameron piloted the Deepsea Challenger to similar depths.[133] An atmospheric diving suit can be worn for deep sea operations, with a new world record being set in 2006 when a US Navy diver descended to 2,000 feet (610 m) in one of these articulated, pressurized suits.[134]
+
+At great depths, no light penetrates through the water layers from above and the pressure is extreme. For deep sea exploration it is necessary to use specialist vehicles, either remotely operated underwater vehicles with lights and cameras or manned submersibles. The battery-operated Mir submersibles have a three-man crew and can descend to 20,000 feet (6,000 m). They have viewing ports, 5,000-watt lights, video equipment and manipulator arms for collecting samples, placing probes or pushing the vehicle across the sea bed when the thrusters would stir up excessive sediment.[135]
+
+Bathymetry is the mapping and study of the topography of the ocean floor. Methods used for measuring the depth of the sea include single or multibeam echosounders, laser airborne depth sounders and the calculation of depths from satellite remote sensing data. This information is used for determining the routes of undersea cables and pipelines, for choosing suitable locations for siting oil rigs and offshore wind turbines and for identifying possible new fisheries.[136]
+
+Ongoing oceanographic research includes marine lifeforms, conservation, the marine environment, the chemistry of the ocean, the studying and modelling of climate dynamics, the air-sea boundary, weather patterns, ocean resources, renewable energy, waves and currents, and the design and development of new tools and technologies for investigating the deep.[137] Whereas in the 1960s and 1970s research could focus on taxonomy and basic biology, in the 2010s attention has shifted to larger topics such as climate change.[138] Researchers make use of satellite-based remote sensing for surface waters, with research ships, moored observatories and autonomous underwater vehicles to study and monitor all parts of the sea.[139]
+
+"Freedom of the seas" is a principle in international law dating from the seventeenth century. It stresses freedom to navigate the oceans and disapproves of war fought in international waters.[140] Today, this concept is enshrined in the United Nations Convention on the Law of the Sea (UNCLOS), the third version of which came into force in 1994. Article 87(1) states: "The high seas are open to all states, whether coastal or land-locked." Article 87(1) (a) to (f) gives a non-exhaustive list of freedoms including navigation, overflight, the laying of submarine cables, building artificial islands, fishing and scientific research.[140] The safety of shipping is regulated by the International Maritime Organization. Its objectives include developing and maintaining a regulatory framework for shipping, maritime safety, environmental concerns, legal matters, technical co-operation and maritime security.[141]
+
+UNCLOS defines various areas of water. "Internal waters" are on the landward side of a baseline and foreign vessels have no right of passage in these. "Territorial waters" extend to 12 nautical miles (22 kilometres; 14 miles) from the coastline and in these waters, the coastal state is free to set laws, regulate use and exploit any resource. A "contiguous zone" extending a further 12 nautical miles allows for hot pursuit of vessels suspected of infringing laws in four specific areas: customs, taxation, immigration and pollution. An "exclusive economic zone" extends for 200 nautical miles (370 kilometres; 230 miles) from the baseline. Within this area, the coastal nation has sole exploitation rights over all natural resources. The "continental shelf" is the natural prolongation of the land territory to the continental margin's outer edge, or 200 nautical miles from the coastal state's baseline, whichever is greater. Here the coastal nation has the exclusive right to harvest minerals and also living resources "attached" to the seabed.[140]
+
+Control of the sea is important to the security of a maritime nation, and the naval blockade of a port can be used to cut off food and supplies in time of war. Battles have been fought on the sea for more than 3,000 years. In about 1210 B.C., Suppiluliuma II, the king of the Hittites, defeated and burned a fleet from Alashiya (modern Cyprus).[142] In the decisive 480 B.C. Battle of Salamis, the Greek general Themistocles trapped the far larger fleet of the Persian king Xerxes in a narrow channel and attacked vigorously, destroying 200 Persian ships for the loss of 40 Greek vessels.[143] At the end of the Age of Sail, the English navy, led by Horatio Nelson, broke the power of the combined French and Spanish fleets at the 1805 Battle of Trafalgar.[144]
+
+With steam and the industrial production of steel plate came greatly increased firepower in the shape of the dreadnought battleships armed with long-range guns. In 1905, the Japanese fleet decisively defeated the Russian fleet, which had travelled over 18,000 nautical miles (33,000 km), at the Battle of Tsushima.[145] Dreadnoughts fought inconclusively in the First World War at the 1916 Battle of Jutland between the Royal Navy's Grand Fleet and the Imperial German Navy's High Seas Fleet.[146] In the Second World War, the British victory at the 1940 Battle of Taranto showed that naval air power was sufficient to overcome the largest warships,[147] foreshadowing the decisive sea-battles of the Pacific War including the Battles of the Coral Sea, Midway, the Philippine Sea, and the climactic Battle of Leyte Gulf, in all of which the dominant ships were aircraft carriers.[148][149]
+
+Submarines became important in naval warfare in World War I, when German submarines, known as U-boats, sank nearly 5,000 Allied merchant ships,[150] including however the RMS Lusitania, so helping to bring the United States into the war.[151] In World War II, almost 3,000 Allied ships were sunk by U-boats attempting to block the flow of supplies to Britain,[152] but the Allies broke the blockade in the Battle of the Atlantic, which lasted the whole length of the war, sinking 783 U-boats.[153] Since 1960, several nations have maintained fleets of nuclear-powered ballistic missile submarines, vessels equipped to launch ballistic missiles with nuclear warheads from under the sea. Some of these are kept permanently on patrol.[154][155]
+
+Sailing ships or packets carried mail overseas, one of the earliest being the Dutch service to Batavia in the 1670s.[156] These added passenger accommodation, but in cramped conditions. Later, scheduled services were offered but the time journeys took depended much on the weather. When steamships replaced sailing vessels, ocean-going liners took over the task of carrying people. By the beginning of the twentieth century, crossing the Atlantic took about five days and shipping companies competed to own the largest and fastest vessels. The Blue Riband was an unofficial accolade given to the fastest liner crossing the Atlantic in regular service. The Mauretania held the title with 26.06 knots (48.26 km/h) for twenty years from 1909.[157] The Hales Trophy, another award for the fastest commercial crossing of the Atlantic, was won by the United States in 1952 for a crossing that took three days, ten hours and forty minutes.[158]
+
+The great liners were comfortable but expensive in fuel and staff. The age of the trans-Atlantic liners waned as cheap intercontinental flights became available. In 1958, a regular scheduled air service between New York and Paris taking seven hours doomed the Atlantic ferry service to oblivion. One by one the vessels were laid up, some were scrapped, others became cruise ships for the leisure industry and still others floating hotels.[159]
+
+Maritime trade has existed for millennia. The Ptolemaic dynasty had developed trade with India using the Red Sea ports and in the first millennium BC the Arabs, Phoenicians, Israelites and Indians traded in luxury goods such as spices, gold, and precious stones.[160] The Phoenicians were noted sea traders and under the Greeks and Romans, commerce continued to thrive. With the collapse of the Roman Empire, European trade dwindled but it continued to flourish among the kingdoms of Africa, the Middle East, India, China and southeastern Asia.[161] From the 16th to the 19th centuries, about 13 million people were shipped across the Atlantic to be sold as slaves in the Americas.[162]
+
+Nowadays, large quantities of goods are transported by sea, especially across the Atlantic and around the Pacific Rim. A major trade route passes through the Pillars of Hercules, across the Mediterranean and the Suez Canal to the Indian Ocean and through the Straits of Malacca; much trade also passes through the English Channel.[163] Shipping lanes are the routes on the open sea used by cargo vessels, traditionally making use of trade winds and currents. Over 60 percent of the world's container traffic is conveyed on the top twenty trade routes.[164] Increased melting of Arctic ice since 2007 enables ships to travel the Northwest Passage for some weeks in summertime, avoiding the longer routes via the Suez Canal or the Panama Canal.[165]
+Shipping is supplemented by air freight, a more expensive process mostly used for particularly valuable or perishable cargoes. Seaborne trade carries more than US$4 trillion worth of goods each year.[166]
+
+There are two main kinds of freight, bulk cargo and break bulk or general cargo, most of which is now transported in containers. Commodities in the form of liquids, powder or particles are carried loose in the holds of bulk carriers and include oil, grain, coal, ore, scrap metal, sand and gravel. Break bulk cargo is usually manufactured goods and is transported in packages, often stacked on pallets. Before the arrival of containerization in the 1950s, these goods were loaded, transported and unloaded piecemeal.[167] The use of containers has greatly increased the efficiency and decreased the cost of moving them[168] with most freight now traveling in standard sized, lockable containers loaded on purpose-built container ships at dedicated terminals.[169][169] Freight forwarding firms book cargo, arrange pickup and delivery, and manage documentation.[170]
+
+Fish and other fishery products are among the most widely consumed sources of protein and other essential nutrients.[171] In 2009, 16.6% of the world's intake of animal protein and 6.5% of all protein consumed came from fish.[171] In order to fulfill this need, coastal countries have exploited marine resources in their exclusive economic zone, although fishing vessels are increasingly venturing further afield to exploit stocks in international waters.[172] In 2011, the total world production of fish, including aquaculture, was estimated to be 154 million tonnes, of which most was for human consumption.[171] The harvesting of wild fish accounted for 90.4 million tonnes, while annually increasing aquaculture contributes the rest.[171] The north west Pacific is by far the most productive area with 20.9 million tonnes (27 percent of the global marine catch) in 2010.[171] In addition, the number of fishing vessels in 2010 reached 4.36 million, whereas the number of people employed in the primary sector of fish production in the same year amounted to 54.8 million.[171]
+
+Modern fishing vessels include fishing trawlers with a small crew, stern trawlers, purse seiners, long-line factory vessels and large factory ships which are designed to stay at sea for weeks, processing and freezing great quantities of fish. The equipment used to capture the fish may be purse seines, other seines, trawls, dredges, gillnets and long-lines and the fish species most frequently targeted are herring, cod, anchovy, tuna, flounder, mullet, squid and salmon. Overexploitation itself has become a serious concern; it does not only cause the depletion of fish stocks, but also substantially reduce the size of predatory fish populations.[173] It has been estimated that "industrialized fisheries typically reduced community biomass by 80% within 15 years of exploitation."[173] In order to avoid overexploitation, many countries have introduced quotas in their own waters.[174] However, recovery efforts often entail substantial costs to local economies or food provision. Nonetheless, research published in Nature in April 2018 found that the aggressive effort of the Indonesian Minister of Maritime Affairs and Fisheries of Indonesia Susi Pudjiastuti to curtail illegal fishing has "reduced total fishing effort by at least 25%, (...) [potentially] generate a 14% increase in catch and a 12% increase in profit."[175] Therefore, the paper concluded that "many nations can recover their fisheries while avoiding these short-term costs by sharply addressing illegal, unreported and unregulated (IUU) fishing."[175]
+
+Artisan fishing methods include rod and line, harpoons, skin diving, traps, throw nets and drag nets. Traditional fishing boats are powered by paddle, wind or outboard motors and operate in near-shore waters. The Food and Agriculture Organization is encouraging the development of local fisheries to provide food security to coastal communities and help alleviate poverty.[176]
+
+As well as the wild stock, about 79 million tonnes (78M long tons; 87M short tons) of food and non-food products were produced by aquaculture in 2010, an all-time high. About six hundred species of plants and animals were cultured, some for use in seeding wild populations. The animals raised included finfish, aquatic reptiles, crustaceans, molluscs, sea cucumbers, sea urchins, sea squirts and jellyfish.[171] Integrated mariculture has the advantage that there is a readily available supply of planktonic food in the ocean, and waste is removed naturally.[177] Various methods are employed. Mesh enclosures for finfish can be suspended in the open seas, cages can be used in more sheltered waters or ponds can be refreshed with water at each high tide. Shrimps can be reared in shallow ponds connected to the open sea.[178] Ropes can be hung in water to grow algae, oysters and mussels. Oysters can be reared on trays or in mesh tubes. Sea cucumbers can be ranched on the seabed.[179] Captive breeding programmes have raised lobster larvae for release of juveniles into the wild resulting in an increased lobster harvest in Maine.[180] At least 145 species of seaweed – red, green, and brown algae – are eaten worldwide, and some have long been farmed in Japan and other Asian countries; there is great potential for additional algaculture.[181] Few maritime flowering plants are widely used for food but one example is marsh samphire which is eaten both raw and cooked.[182] A major difficulty for aquaculture is the tendency towards monoculture and the associated risk of widespread disease. In the 1990s, disease wiped out China's farmed Farrer's scallop and white shrimp and required their replacement by other species.[183] Aquaculture is also associated with environmental risks; for instance, shrimp farming has caused the destruction of important mangrove forests throughout southeast Asia.[184]
+
+Use of the sea for leisure developed in the nineteenth century, and became a significant industry in the twentieth century.[185] Maritime leisure activities are varied, and include self-organized trips cruising, yachting, powerboat racing[186] and fishing;[187] commercially organized voyages on cruise ships;[188] and trips on smaller vessels for ecotourism such as whale watching and coastal birdwatching.[189]
+
+Humans enjoy venturing into the sea; children paddle and splash in the shallows and many people take pleasure in bathing and relaxing on the beach. This was not always the case, with sea bathing becoming the vogue in Europe in the 18th century after Dr. William Buchan advocated the practice for health reasons.[190] Surfing is a sport in which a wave is ridden by a surfer, with or without a surfboard. Other marine water sports include kite surfing, where a power kite propels a manned board across the water,[191] windsurfing, where the power is provided by a fixed, manoeuvrable sail[192] and water skiing, where a powerboat is used to pull a skier.[193]
+
+Beneath the surface, freediving is necessarily restricted to shallow descents. Pearl divers have traditionally greased their skins, put cotton in their ears and clips on their noses and dived to 40 feet (12 m) with baskets to collect oysters.[194] Human eyes are not adapted for use underwater but vision can be improved by wearing a diving mask. Other useful equipment includes fins and snorkels, and scuba equipment allows underwater breathing and hence a longer time can be spent beneath the surface.[195] The depths that can be reached by divers and the length of time they can stay underwater is limited by the increase of pressure they experience as they descend and the need to prevent decompression sickness as they return to the surface. Recreational divers are advised to restrict themselves to depths of 100 feet (30 m) beyond which the danger of nitrogen narcosis increases. Deeper dives can be made with specialised equipment and training.[195]
+
+The sea offers a very large supply of energy carried by ocean waves, tides, salinity differences, and ocean temperature differences which can be harnessed to generate electricity.[196] Forms of 'green' marine energy include tidal power, marine current power, osmotic power, ocean thermal energy and wave power.[196][197]
+
+Tidal power uses generators to produce electricity from tidal flows, sometimes by using a dam to store and then release seawater. The Rance barrage, 1 kilometre (0.62 mi) long, near St Malo in Brittany opened in 1967; it generates about 0.5 GW, but it has been followed by few similar schemes.[4](pp111–112)
+
+The large and highly variable energy of waves gives them enormous destructive capability, making affordable and reliable wave machines problematic to develop. A small 2 MW commercial wave power plant, "Osprey", was built in Northern Scotland in 1995 about 300 metres (1000 ft) offshore. It was soon damaged by waves, then destroyed by a storm.[4](p112) Marine current power could provide populated areas close to the sea with a significant part of their energy needs.[198] In principle, it could be harnessed by open-flow turbines; sea bed systems are available, but limited to a depth of about 40 metres (130 ft).[199]
+
+Offshore wind power is captured by wind turbines placed out at sea; it has the advantage that wind speeds are higher than on land, though wind farms are more costly to construct offshore.[200] The first offshore wind farm was installed in Denmark in 1991,[201] and the installed capacity of European offshore wind farms reached 3 GW in 2010.[202]
+
+Electricity power stations are often located on the coast or beside an estuary so that the sea can be used as a heat sink. A colder heat sink enables more efficient power generation, which is important for expensive nuclear power plants in particular.[203]
+
+The seabed contains enormous reserves of minerals which can be exploited by dredging. This has advantages over land-based mining in that equipment can be built at specialised shipyards and infrastructure costs are lower. Disadvantages include problems caused by waves and tides, the tendency for excavations to silt up and the washing away of spoil heaps. There is a risk of coastal erosion and environmental damage.[204]
+
+Seafloor massive sulphide deposits are potential sources of silver, gold, copper, lead and zinc and trace metals since their discovery in the 1960s. They form when geothermally heated water is emitted from deep sea hydrothermal vents known as "black smokers". The ores are of high quality but prohibitively costly to extract.[205] Small scale mining of the deep sea floor is being developed off the coast of Papua New Guinea using robotic techniques, but the obstacles are formidable.[206]
+
+There are large deposits of petroleum, as oil and natural gas, in rocks beneath the seabed. Offshore platforms and drilling rigs extract the oil or gas and store it for transport to land. Offshore oil and gas production can be difficult due to the remote, harsh environment.[207] Drilling for oil in the sea has environmental impacts. Animals may be disorientated by seismic waves used to locate deposits, and there is debate as to whether this causes the beaching of whales.[208] Toxic substances such as mercury, lead and arsenic may be released. The infrastructure may cause damage, and oil may be spilt.[209]
+
+Large quantities of methane clathrate exist on the seabed and in ocean sediment at a temperature of around 2 °C (36 °F) and these are of interest as a potential energy source. Some estimates put the amount available at between one and 5 million cubic kilometres (0.24 to 1.2 million cubic miles).[210] Also on the seabed are manganese nodules formed of layers of iron, manganese and other hydroxides around a core. In the Pacific these may cover up to 30 percent of the deep ocean floor. The minerals precipitate from seawater and grow very slowly. Their commercial extraction for nickel was investigated in the 1970s but abandoned in favour of more convenient sources.[211] In suitable locations, diamonds are gathered from the seafloor using suction hoses to bring gravel ashore. In deeper waters, mobile seafloor crawlers are used and the deposits are pumped to a vessel above. In Namibia, more diamonds are now collected from marine sources than by conventional methods on land.[212]
+
+The sea holds enormous quantities of valuable dissolved minerals.[213] The most important, Salt for table and industrial use has been harvested by solar evaporation from shallow ponds since prehistoric times. Bromine, accumulated after being leached from the land, is economically recovered from the Dead Sea, where it occurs at 55,000 parts per million (ppm).[214]
+
+Desalination is the technique of removing salts from seawater to leave fresh water suitable for drinking or irrigation. The two main processing methods, vacuum distillation and reverse osmosis, use large quantities of energy. Desalination is normally only undertaken where fresh water from other sources is in short supply or energy is plentiful, as in the excess heat generated by power stations. The brine produced as a by-product contains some toxic materials and is returned to the sea.[215]
+
+Many substances enter the sea as a result of human activities. Combustion products are transported in the air and deposited into the sea by precipitation. Industrial outflows and sewage contribute heavy metals, pesticides, PCBs, disinfectants, household cleaning products and other synthetic chemicals. These become concentrated in the surface film and in marine sediment, especially estuarine mud. The result of all this contamination is largely unknown because of the large number of substances involved and the lack of information on their biological effects.[216] The heavy metals of greatest concern are copper, lead, mercury, cadmium and zinc which may be bio-accumulated by marine organisms and are passed up the food chain.[217]
+
+Much floating plastic rubbish does not biodegrade, instead disintegrating over time and eventually breaking down to the molecular level. Rigid plastics may float for years.[218] In the centre of the Pacific gyre there is a permanent floating accumulation of mostly plastic waste[219] and there is a similar garbage patch in the Atlantic.[220] Foraging sea birds such as the albatross and petrel may mistake debris for food, and accumulate indigestible plastic in their digestive systems. Turtles and whales have been found with plastic bags and fishing line in their stomachs. Microplastics may sink, threatening filter feeders on the seabed.[221]
+
+Most oil pollution in the sea comes from cities and industry.[222] Oil is dangerous for marine animals. It can clog the feathers of sea birds, reducing their insulating effect and the birds' buoyancy, and be ingested when they preen themselves in an attempt to remove the contaminant. Marine mammals are less seriously affected but may be chilled through the removal of their insulation, blinded, dehydrated or poisoned. Benthic invertebrates are swamped when the oil sinks, fish are poisoned and the food chain is disrupted. In the short term, oil spills result in wildlife populations being decreased and unbalanced, leisure activities being affected and the livelihoods of people dependant on the sea being devastated.[223] The marine environment has self-cleansing properties and naturally occurring bacteria will act over time to remove oil from the sea. In the Gulf of Mexico, where oil-eating bacteria are already present, they take only a few days to consume spilt oil.[224]
+
+Run-off of fertilisers from agricultural land is a major source of pollution in some areas and the discharge of raw sewage has a similar effect. The extra nutrients provided by these sources can cause excessive plant growth. Nitrogen is often the limiting factor in marine systems, and with added nitrogen, algal blooms and red tides can lower the oxygen level of the water and kill marine animals. Such events have created dead zones in the Baltic Sea and the Gulf of Mexico.[222] Some algal blooms are caused by cyanobacteria that make shellfish that filter feed on them toxic, harming animals like sea otters.[225] Nuclear facilities too can pollute. The Irish Sea was contaminated by radioactive caesium-137 from the former Sellafield nuclear fuel processing plant[226] and nuclear accidents may also cause radioactive material to seep into the sea, as did the disaster at the Fukushima Daiichi Nuclear Power Plant in 2011.[227]
+
+The dumping of waste (including oil, noxious liquids, sewage and garbage) at sea is governed by international law. The London Convention (1972) is a United Nations agreement to control ocean dumping which had been ratified by 89 countries by 8 June 2012.[228] MARPOL 73/78 is a convention to minimize pollution of the seas by ships. By May 2013, 152 maritime nations had ratified MARPOL.[229]
+
+Several nomadic indigenous groups in Maritime Southeast Asia live in boats and derive nearly all they need from the sea. The Moken people live on the coasts of Thailand and Burma and islands in the Andaman Sea.[230] The Bajau people are originally from the Sulu Archipelago, Mindanao and northern Borneo.[231] Some Sea Gypsies are accomplished free-divers, able to descend to depths of 30 metres (98 ft), though many are adopting a more settled, land-based way of life.[232][233]
+
+The indigenous peoples of the Arctic such as the Chukchi, Inuit, Inuvialuit and Yup'iit hunt marine mammals including seals and whales,[234] and the Torres Strait Islanders of Australia include ownership of the Great Barrier Reef among their possessions. They live a traditional life on the islands involving hunting, fishing, gardening and trading with neighbouring peoples in Papua and mainland Aboriginal Australians.[235]
+
+The sea appears in human culture in contradictory ways, as both powerful but serene and as beautiful but dangerous.[4](p10) It has its place in literature, art, poetry, film, theatre, classical music, mythology and dream interpretation.[236] The Ancients personified it, believing it to be under the control of a being who needed to be appeased, and symbolically, it has been perceived as a hostile environment populated by fantastic creatures; the Leviathan of the Bible,[237] Scylla in Greek mythology,[238] Isonade in Japanese mythology,[239] and the kraken of late Norse mythology.[240]
+
+The sea and ships have been depicted in art ranging from simple drawings on the walls of huts in Lamu[236] to seascapes by Joseph Turner. In Dutch Golden Age painting, artists such as Jan Porcellis, Hendrick Dubbels, Willem van de Velde the Elder and his son, and Ludolf Bakhuizen celebrated the sea and the Dutch navy at the peak of its military prowess.[241][242] The Japanese artist Katsushika Hokusai created colour prints of the moods of the sea, including The Great Wave off Kanagawa.[4](p8)
+
+Music too has been inspired by the ocean, sometimes by composers who lived or worked near the shore and saw its many different aspects. Sea shanties, songs that were chanted by mariners to help them perform arduous tasks, have been woven into compositions and impressions in music have been created of calm waters, crashing waves and storms at sea.[243] Classical sea-related music includes Richard Wagner's The Flying Dutchman,[244] Claude Debussy's La mer (1903–05),[245] Charles Villiers Stanford's Songs of the Sea (1904) and Songs of the Fleet (1910), Edward Elgar's Sea Pictures (1899) and Ralph Vaughan Williams' A Sea Symphony (1903–1909).[246]
+
+As a symbol, the sea has for centuries played a role in literature, poetry and dreams. Sometimes it is there just as a gentle background but often it introduces such themes as storm, shipwreck, battle, hardship, disaster, the dashing of hopes and death.[247] In his epic poem the Odyssey, written in the 8th century BC,[248] Homer describes the ten-year voyage of the Greek hero Odysseus who struggles to return home across the sea's many hazards after the war described in the Iliad.[249] The sea is a recurring theme in the Haiku poems of the Japanese Edo period poet Matsuo Bashō (松尾 芭蕉) (1644–1694).[250] In modern literature, sea-inspired novels have been written by Joseph Conrad — drawn from his experience at sea,[251] Herman Wouk,[252] and Herman Melville.[253] In the works of psychiatrist Carl Jung, the sea symbolizes the personal and the collective unconscious in dream interpretation, the depths of the sea symbolizing the depths of the unconscious mind.[254]
+

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+
+
+Muscle is a soft tissue found in most animals. Muscle cells contain protein filaments of actin and myosin  that slide past one another, producing a contraction that changes both the length and the shape of the cell. Muscles function to produce force and motion. They are primarily responsible for maintaining and changing posture, locomotion, as well as movement of internal organs, such as the contraction of the heart and the movement of food through the digestive system via peristalsis.
+
+Muscle tissues are derived from the mesodermal layer of embryonic germ cells in a process known as myogenesis.  There are three types of muscle, skeletal or striated, cardiac, and smooth. Muscle action can be classified as being either voluntary or involuntary. Cardiac and smooth muscles contract without conscious thought and are termed involuntary, whereas the skeletal muscles contract upon command.[1] Skeletal muscles in turn can be divided into fast and slow twitch fibers.
+
+Muscles are predominantly powered by the oxidation of fats and carbohydrates, but anaerobic chemical reactions are also used, particularly by fast twitch fibers. These chemical reactions produce adenosine triphosphate (ATP) molecules that are used to power the movement of the myosin heads.[2]
+
+The term muscle is derived from the Latin musculus meaning "little mouse" perhaps because of the shape of certain muscles or because contracting muscles look like mice moving under the skin.[3][4]
+
+The anatomy of muscles includes gross anatomy, which comprises all the muscles of an organism, and microanatomy, which comprises the structures of a single muscle.
+
+Muscle tissue is a soft tissue, and is one of the four fundamental types of tissue present in animals. There are three types of muscle tissue recognized in vertebrates:
+
+Cardiac and skeletal muscles are "striated" in that they contain sarcomeres that are packed into highly regular arrangements of bundles; the myofibrils of smooth muscle cells are not arranged in sarcomeres and so are not striated. While the sarcomeres in skeletal muscles are arranged in regular, parallel bundles, cardiac muscle sarcomeres connect at branching, irregular angles (called intercalated discs). Striated muscle contracts and relaxes in short, intense bursts, whereas smooth muscle sustains longer or even near-permanent contractions.
+
+The muscle fibers embedded in skeletal muscle are relatively classified into a spectrum of types given their morphological and physiological properties. Given a certain assortment of these properties, muscle fibers are categorized as slow-twitch (low force, slowly fatiguing fibers), fast twitch (high force, rapidly fatiguing fibers), or somewhere in between those two types (i.e. intermediate fibers). Some of the defining morphological and physiological properties used for the categorization of muscle fibers include: the number of mitochondria contained in the fiber, the amount of glycolytic, lipolytic, and other cellular respiration enzymes, M and Z band characteristics, energy source (i.e. glycogen or fat), histology color, and contraction speed and duration. Note that there is no standard procedure for classifying muscle fiber types. The properties chosen for classification depends on the particular muscle. For example, the properties used for distinguishing fast, intermediate, and slow muscle fibers can be different for invertebrate flight and jump muscle. [6] To further complicate this classification scheme, the mitochondria content and other morphological properties within a muscle fiber can change with exercise and age. [7]
+
+The density of mammalian skeletal muscle tissue is about 1.06 kg/liter.[10] This can be contrasted with the density of adipose tissue (fat), which is 0.9196 kg/liter.[11] This makes muscle tissue approximately 15% denser than fat tissue.
+
+Skeletal muscles are sheathed by a tough layer of connective tissue called the epimysium. The epimysium anchors muscle tissue to tendons at each end, where the epimysium becomes thicker and collagenous. It also protects muscles from friction against other muscles and bones. Within the epimysium are multiple bundles called fascicles, each of which contains 10 to 100 or more muscle fibers collectively sheathed by a perimysium. Besides surrounding each fascicle, the perimysium is a pathway for nerves and the flow of blood within the muscle. The threadlike muscle fibers are the individual muscle cells (myocytes), and each cell is encased within its own endomysium of collagen fibers. Thus, the overall muscle consists of fibers (cells) that are bundled into fascicles, which are themselves grouped together to form muscles.  At each level of bundling, a collagenous membrane surrounds the bundle, and these membranes support muscle function both by resisting passive stretching of the tissue and by distributing forces applied to the muscle.[12] Scattered throughout the muscles are muscle spindles that provide sensory feedback information to the central nervous system. (This grouping structure is analogous to the  organization of nerves which uses epineurium, perineurium, and endoneurium).
+
+This same bundles-within-bundles structure is replicated within the muscle cells. Within the cells of the muscle are myofibrils, which themselves are bundles of protein filaments.  The term "myofibril" should not be confused with "myofiber", which is a simply another name for a muscle cell. Myofibrils are complex strands of several kinds of protein filaments organized together into repeating units called sarcomeres. The striated appearance of both skeletal and cardiac muscle results from the regular pattern of sarcomeres within their cells. Although both of these types of muscle contain sarcomeres, the fibers in cardiac muscle are typically branched to form a network. Cardiac muscle fibers are interconnected by intercalated discs,[13] giving that tissue the appearance of a syncytium.
+
+The filaments in a sarcomere are composed of actin and myosin.
+
+The gross anatomy of a muscle is the most important indicator of its role in the body.  There is an important distinction seen between pennate muscles and other muscles. In most muscles, all the fibers are oriented in the same direction, running in a line from the origin to the insertion. However, In pennate muscles, the individual fibers are oriented at an angle relative to the line of action, attaching to the origin and insertion tendons at each end. Because the contracting fibers are pulling at an angle to the overall action of the muscle, the change in length is smaller, but this same orientation allows for more fibers (thus more force) in a muscle of a given size. Pennate muscles are usually found where their length change is less important than maximum force, such as the rectus femoris.
+
+Skeletal muscle is arranged in discrete muscles, an example of which is the biceps brachii (biceps). The tough, fibrous epimysium of skeletal muscle is both connected to and continuous with the tendons.  In turn, the tendons connect to the periosteum layer surrounding the bones, permitting the transfer of force from the muscles to the skeleton.  Together, these fibrous layers, along with tendons and ligaments, constitute the deep fascia of the body.
+
+The muscular system consists of all the muscles present in a single body.  There are approximately 650 skeletal muscles in the human body,[14] but an exact number is difficult to define. The difficulty lies partly in the fact that different sources group the muscles differently and partly in that some muscles, such as palmaris longus, are not always present.
+
+A muscular slip is a narrow length of muscle that acts to augment a larger muscle or muscles.
+
+The muscular system is one component of the musculoskeletal system, which includes not only the muscles but also the bones, joints, tendons, and other structures that permit movement.
+
+All muscles are derived from paraxial mesoderm. The paraxial mesoderm is divided along the embryo's length into somites, corresponding to the segmentation of the body (most obviously seen in the vertebral column.[15] Each somite has 3 divisions, sclerotome (which forms vertebrae), dermatome (which forms skin), and myotome (which forms muscle). The myotome is divided into two sections, the epimere and hypomere, which form epaxial and hypaxial muscles, respectively. The only epaxial muscles in humans are the erector spinae and small intervertebral muscles, and are innervated by the dorsal rami of the spinal nerves. All other muscles, including those of the limbs are hypaxial, and inervated by the ventral rami of the spinal nerves.[15]
+
+During development, myoblasts (muscle progenitor cells) either remain in the somite to form muscles associated with the vertebral column or migrate out into the body to form all other muscles. Myoblast migration is preceded by the formation of connective tissue frameworks, usually formed from the somatic lateral plate mesoderm. Myoblasts follow chemical signals to the appropriate locations, where they fuse into elongate skeletal muscle cells.[15]
+
+The three types of muscle (skeletal, cardiac and smooth) have significant differences. However, all three use the movement of actin against myosin to create contraction. In skeletal muscle, contraction is stimulated by electrical impulses transmitted by the nerves, the  motoneurons (motor nerves) in particular. Cardiac and smooth muscle contractions are stimulated by internal pacemaker cells which regularly contract, and propagate contractions to other muscle cells they are in contact with. All skeletal muscle and many smooth muscle contractions are facilitated by the neurotransmitter acetylcholine.
+
+The action a muscle generates is determined by the origin and insertion locations. The cross-sectional area of a muscle (rather than volume or length) determines the amount of force it can generate by defining the number of "sarcomeres" which can operate in parallel. Each skeletal muscle contains long units called myofibrils, and each myofibril is a chain of sarcomeres. Since contraction occurs at the same time for all connected sarcomeres in a muscles cell, these chains of sarcomeres shorten together, thus shortening the muscle fiber, resulting in overall length change.[16] The amount of force applied to the external environment is determined by lever mechanics, specifically the ratio of in-lever to out-lever. For example, moving the insertion point of the biceps more distally on the radius (farther from the joint of rotation) would increase the force generated during flexion (and, as a result, the maximum weight lifted in this movement), but decrease the maximum speed of flexion. Moving the insertion point proximally (closer to the joint of rotation) would result in decreased force but increased velocity. This can be most easily seen by comparing the limb of a mole to a horse—in the former, the insertion point is positioned to maximize force (for digging), while in the latter, the insertion point is positioned to maximize speed (for running).
+
+The efferent leg of the peripheral nervous system is responsible for conveying commands to the muscles and glands, and is ultimately responsible for voluntary movement.  Nerves move muscles in response to voluntary and autonomic (involuntary) signals from the brain. Deep muscles, superficial muscles, muscles of the face and internal muscles all correspond with dedicated regions in the primary motor cortex of the brain, directly anterior to the central sulcus that divides the frontal and parietal lobes.
+
+In addition, muscles react to reflexive nerve stimuli that do not always send signals all the way to the brain. In this case, the signal from the afferent fiber does not reach the brain, but produces the reflexive movement by direct connections with the efferent nerves in the spine. However, the majority of muscle activity is volitional, and the result of complex interactions between various areas of the brain.
+
+Nerves that control skeletal muscles in mammals correspond with neuron groups along the primary motor cortex of the brain's cerebral cortex. Commands are routed through the basal ganglia and are modified by input from the cerebellum before being relayed through the pyramidal tract to the spinal cord and from there to the motor end plate at the muscles. Along the way, feedback, such as that of the extrapyramidal system contribute signals to influence muscle tone and response.
+
+Deeper muscles such as those involved in posture often are controlled from nuclei in the brain stem and basal ganglia.
+
+In skeletal muscles, muscle spindles convey information about the degree of muscle length and stretch to the central nervous system to assist in maintaining posture and joint position. The sense of where our bodies are in space is called proprioception, the perception of body awareness, the "unconscious" awareness of where the various regions of the body are located at any one time. Several areas in the brain coordinate movement and position with the feedback information gained from proprioception. The cerebellum and red nucleus in particular continuously sample position against movement and make minor corrections to assure smooth motion.[citation needed]
+
+Muscular activity accounts for much of the body's energy consumption. All muscle cells produce adenosine triphosphate (ATP) molecules which are used to power the movement of the myosin heads. Muscles have a short-term store of energy in the form of creatine phosphate which is generated from ATP and can regenerate ATP when needed with creatine kinase. Muscles also keep a storage form of glucose in the form of glycogen. Glycogen can be rapidly converted to glucose when energy is required for sustained, powerful contractions. Within the voluntary skeletal muscles, the glucose molecule can be metabolized anaerobically in a process called glycolysis which produces two ATP and two lactic acid molecules in the process (note that in aerobic conditions, lactate is not formed; instead pyruvate is formed and transmitted through the citric acid cycle). Muscle cells also contain globules of fat, which are used for energy during aerobic exercise. The aerobic energy systems take longer to produce the ATP and reach peak efficiency, and requires many more biochemical steps, but produces significantly more ATP than anaerobic glycolysis. Cardiac muscle on the other hand, can readily consume any of the three macronutrients (protein, glucose and fat) aerobically without a 'warm up' period and always extracts the maximum ATP yield from any molecule involved. The heart, liver and red blood cells will also consume lactic acid produced and excreted by skeletal muscles during exercise.
+
+At rest, skeletal muscle consumes 54.4 kJ/kg (13.0 kcal/kg) per day. This is larger than adipose tissue (fat) at 18.8 kJ/kg (4.5 kcal/kg), and bone at 9.6 kJ/kg (2.3 kcal/kg).[17]
+
+The efficiency of human muscle has been measured (in the context of rowing and cycling) at 18% to 26%. The efficiency is defined as the ratio of mechanical work output to the total metabolic cost, as can be calculated from oxygen consumption. This low efficiency is the result of about 40% efficiency of generating ATP from food energy, losses in converting energy from ATP into mechanical work inside the muscle, and mechanical losses inside the body. The latter two losses are dependent on the type of exercise and the type of muscle fibers being used (fast-twitch or slow-twitch). For an overall efficiency of 20 percent, one watt of mechanical power is equivalent to 4.3 kcal per hour. For example, one manufacturer of rowing equipment calibrates its rowing ergometer to count burned calories as equal to four times the actual mechanical work, plus 300 kcal per hour,[18] this amounts to about 20 percent efficiency at 250 watts of mechanical output.  The mechanical energy output of a cyclic contraction can depend upon many factors, including activation timing, muscle strain trajectory, and rates of force rise & decay.  These can be synthesized experimentally using work loop analysis.
+
+Muscle is a result of three factors that overlap: physiological strength (muscle size, cross sectional area, available crossbridging, responses to training), neurological strength (how strong or weak is the signal that tells the muscle to contract), and mechanical strength (muscle's force angle on the lever, moment arm length, joint capabilities).[citation needed]
+
+Vertebrate muscle typically produces approximately 25–33 N (5.6–7.4 lbf) of force per square centimeter of muscle cross-sectional area when isometric and at optimal length.[19]  Some invertebrate muscles, such as in crab claws, have much longer sarcomeres than vertebrates, resulting in many more sites for actin and myosin to bind and thus much greater force per square centimeter at the cost of much slower speed.  The force generated by a contraction can be measured non-invasively using either mechanomyography or phonomyography, be measured in vivo using tendon strain (if a prominent tendon is present), or be measured directly using more invasive methods.
+
+The strength of any given muscle, in terms of force exerted on the skeleton, depends upon length, shortening speed, cross sectional area, pennation, sarcomere length, myosin isoforms, and neural activation of motor units.  Significant reductions in muscle strength can indicate underlying pathology, with the chart at right used as a guide.
+
+Since three factors affect muscular strength simultaneously and muscles never work individually, it is misleading to compare strength in individual muscles, and state that one is the "strongest". But below are several muscles whose strength is noteworthy for different reasons.
+
+Exercise is often recommended as a means of improving motor skills, fitness, muscle and bone strength, and joint function. Exercise has several effects upon muscles, connective tissue, bone, and the nerves that stimulate the muscles.  One such effect is muscle hypertrophy, an increase in size of muscle due to an increase in the number of muscle fibers or cross-sectional area of myofibrils.[21] The degree of hypertrophy and other exercise induced changes in muscle depends on the intensity and duration of exercise.
+
+Generally, there are two types of exercise regimes, aerobic and anaerobic. Aerobic exercise (e.g. marathons) involves low intensity, but long duration activities during which, the muscles used are below their maximal contraction strength. Aerobic activities rely on the aerobic respiration (i.e. citric acid cycle and electron transport chain) for metabolic energy by consuming fat, protein carbohydrates, and oxygen. Muscles involved in aerobic exercises contain a higher percentage of Type I (or slow-twitch) muscle fibers, which primarily contain mitochondrial and oxidation enzymes associated with aerobic respiration. [22][23]   On the contrary, anaerobic exercise is associated with short duration, but high intensity exercise (e.g. sprinting and  weight lifting). The anaerobic activities predominately use Type II, fast-twitch, muscle fibers.[24] Type II muscle fibers rely on glucogenesis for energy during anaerobic exercise.[25] During anaerobic exercise, type II fibers consume little oxygen, protein and fat, produces large amounts of lactic acid and are fatigable. Many exercises are partially aerobic and anaerobic; for example, soccer and rock climbing.
+
+The presence of lactic acid has an inhibitory effect on ATP generation within the muscle. It can even stop ATP production if the intracellular concentration becomes too high. However, endurance training mitigates the buildup of lactic acid through increased capillarization and myoglobin.[26] This increases the ability to remove waste products, like lactic acid, out of the muscles in order to not impair muscle function. Once moved out of muscles, lactic acid can be used by other muscles or body tissues as a source of energy, or transported to the liver where it is converted back to pyruvate. In addition to increasing the level of lactic acid, strenuous exercise results in the loss of potassium ions in muscle. This may facilitate the recovery of muscle function by protecting against fatigue .[27]
+
+Delayed onset muscle soreness is pain or discomfort that may be felt one to three days after exercising and generally subsides two to three days after which. Once thought to be caused by lactic acid build-up, a more recent theory is that it is caused by tiny tears in the muscle fibers caused by eccentric contraction, or unaccustomed training levels. Since lactic acid disperses fairly rapidly, it could not explain pain experienced days after exercise.[28]
+
+Independent of strength and performance measures, muscles can be induced to grow larger by a number of factors, including hormone signaling, developmental factors, strength training, and disease.  Contrary to popular belief, the number of muscle fibres cannot be increased through exercise.  Instead, muscles grow larger through a combination of muscle cell growth as new protein filaments are added along with additional mass provided by undifferentiated satellite cells alongside the existing muscle cells.[14]
+
+Biological factors such as age and hormone levels can affect muscle hypertrophy. During puberty in males, hypertrophy occurs at an accelerated rate as the levels of growth-stimulating hormones produced by the body increase. Natural hypertrophy normally stops at full growth in the late teens. As testosterone is one of the body's major growth hormones, on average, men find hypertrophy much easier to achieve than women. Taking additional testosterone or other anabolic steroids will increase muscular hypertrophy.
+
+Muscular, spinal and neural factors all affect muscle building.  Sometimes a person may notice an increase in strength in a given muscle even though only its opposite has been subject to exercise, such as when a bodybuilder finds her left biceps stronger after completing a regimen focusing only on the right biceps.  This phenomenon is called cross education.[citation needed]
+
+During ordinary living activities, between 1 and 2 percent of muscle is broken down and rebuilt daily. Inactivity and starvation in mammals lead to atrophy of skeletal muscle, a decrease in muscle mass that may be accompanied by a smaller number and size of the muscle cells as well as lower protein content.[29] Muscle atrophy may also result from the natural aging process or from disease.
+
+In humans, prolonged periods of immobilization, as in the cases of bed rest or astronauts flying in space, are known to result in muscle weakening and atrophy. Atrophy is of particular interest to the manned spaceflight community, because the weightlessness experienced in spaceflight results is a loss of as much as 30% of mass in some muscles.[30][31]  Such consequences are also noted in small hibernating mammals like the golden-mantled ground squirrels and brown bats.[32]
+
+During aging, there is a gradual decrease in the ability to maintain skeletal muscle function and mass, known as sarcopenia. The exact cause of sarcopenia is unknown, but it may be due to a combination of the gradual failure in the "satellite cells" that help to regenerate skeletal muscle fibers, and a decrease in sensitivity to or the availability of critical secreted growth factors that are necessary to maintain muscle mass and satellite cell survival. Sarcopenia is a normal aspect of aging, and is not actually a disease state yet can be linked to many injuries in the elderly population as well as decreasing quality of life.[33]
+
+There are also many diseases and conditions that cause muscle atrophy. Examples include cancer and AIDS, which induce a body wasting syndrome called cachexia. Other syndromes or conditions that can induce skeletal muscle atrophy are congestive heart disease and some diseases of the liver.
+
+Neuromuscular diseases are those that affect the muscles and/or their nervous control. In general, problems with nervous control can cause spasticity or paralysis, depending on the location and nature of the problem. A large proportion of neurological disorders, ranging from cerebrovascular accident (stroke) and Parkinson's disease to Creutzfeldt–Jakob disease, can lead to problems with movement or motor coordination.
+
+Symptoms of muscle diseases may include weakness, spasticity, myoclonus and myalgia. Diagnostic procedures that may reveal muscular disorders include testing creatine kinase levels in the blood and electromyography (measuring electrical activity in muscles). In some cases, muscle biopsy may be done to identify a myopathy, as well as genetic testing to identify DNA abnormalities associated with specific myopathies and dystrophies.
+
+A non-invasive elastography technique that measures muscle noise is undergoing experimentation to provide a way of monitoring neuromuscular disease. The sound produced by a muscle comes from the shortening of actomyosin filaments along the axis of the muscle. During contraction, the muscle shortens along its longitudinal axis and expands across the transverse axis, producing vibrations at the surface.[34]
+
+The evolutionary origin of muscle cells in metazoans is a highly debated topic. In one line of thought scientists have believed that muscle cells evolved once and thus all animals with muscles cells have a single common ancestor. In the other line of thought, scientists believe muscles cells evolved more than once and any morphological or structural similarities are due to convergent evolution and genes that predate the evolution of muscle and even the mesoderm—the germ layer from which many scientists believe true muscle cells derive.
+
+Schmid and Seipel argue that the origin of muscle cells is a monophyletic trait that occurred concurrently with the development of the digestive and nervous systems of all animals and that this origin can be traced to a single metazoan ancestor in which muscle cells are present. They argue that molecular and morphological similarities between the muscles cells in cnidaria and ctenophora are similar enough to those of bilaterians that there would be one ancestor in metazoans from which muscle cells derive. In this case, Schmid and Seipel argue that the last common ancestor of bilateria, ctenophora, and cnidaria was a triploblast or an organism with three germ layers and that diploblasty, meaning an organism with two germ layers, evolved secondarily due to their observation of the lack of mesoderm or muscle found in most cnidarians and ctenophores. By comparing the morphology of cnidarians and ctenophores to bilaterians, Schmid and Seipel were able to conclude that there were myoblast-like structures in the tentacles and gut of some species of cnidarians and in the tentacles of ctenophores. Since this is a structure unique to muscle cells, these scientists determined based on the data collected by their peers that this is a marker for striated muscles similar to that observed in bilaterians. The authors also remark that the muscle cells found in cnidarians and ctenophores are often contests due to the origin of these muscle cells being the ectoderm rather than the mesoderm or mesendoderm. The origin of true muscles cells is argued by others to be the endoderm portion of the mesoderm and the endoderm. However, Schmid and Seipel counter this skepticism about whether or not the muscle cells found in ctenophores and cnidarians are true muscle cells by considering that cnidarians develop through a medusa stage and polyp stage. They observe that in the hydrozoan medusa stage there is a layer of cells that separate from the distal side of the ectoderm to form the striated muscle cells in a way that seems similar to that of the mesoderm and call this third separated layer of cells the ectocodon. They also argue that not all muscle cells are derived from the mesendoderm in bilaterians with key examples being that in both the eye muscles of vertebrates and the muscles of spiralians these cells derive from the ectodermal mesoderm rather than the endodermal mesoderm. Furthermore, Schmid and Seipel argue that since myogenesis does occur in cnidarians with the help of molecular regulatory elements found in the specification of muscles cells in bilaterians that there is evidence for a single origin for striated muscle.[35]
+
+In contrast to this argument for a single origin of muscle cells, Steinmetz et al. argue that molecular markers such as the myosin II protein used to determine this single origin of striated muscle actually predate the formation of muscle cells. This author uses an example of the contractile elements present in the porifera or sponges that do truly lack this striated muscle containing this protein. Furthermore, Steinmetz et al. present evidence for a polyphyletic origin of striated muscle cell development through their analysis of morphological and molecular markers that are present in bilaterians and absent in cnidarians, ctenophores, and bilaterians. Steimetz et al. showed that the traditional morphological and regulatory markers such as actin, the ability to couple myosin side chains phosphorylation to higher concentrations of the positive concentrations of calcium, and other MyHC elements are present in all metazoans not just the organisms that have been shown to have muscle cells. Thus, the usage of any of these structural or regulatory elements in determining whether or not the muscle cells of the cnidarians and ctenophores are similar enough to the muscle cells of the bilaterians to confirm a single lineage is questionable according to Steinmetz et al. Furthermore, Steinmetz et al. explain that the orthologues of the MyHc genes that have been used to hypothesize the origin of striated muscle occurred through a gene duplication event that predates the first true muscle cells (meaning striated muscle), and they show that the MyHc genes are present in the sponges that have contractile elements but no true muscle cells. Furthermore, Steinmetz et all showed that the localization of this duplicated set of genes that serve both the function of facilitating the formation of striated muscle genes and cell regulation and movement genes were already separated into striated myhc and non-muscle myhc. This separation of the duplicated set of genes is shown through the localization of the striated myhc to the contractile vacuole in sponges while the non-muscle myhc was more diffusely expressed during developmental cell shape and change. Steinmetz et al. found a similar pattern of localization in cnidarians with except with the cnidarian N. vectensis having this striated muscle marker present in the smooth muscle of the digestive track. Thus, Steinmetz et al. argue that the pleisiomorphic trait of the separated orthologues of myhc cannot be used to determine the monophylogeny of muscle, and additionally argue that the presence of a striated muscle marker in the smooth muscle of this cnidarian shows a fundamentally different mechanism of muscle cell development and structure in cnidarians.[36]
+
+Steinmetz et al. continue to argue for multiple origins of striated muscle in the metazoans by explaining that a key set of genes used to form the troponin complex for muscle regulation and formation in bilaterians is missing from the cnidarians and ctenophores, and of 47 structural and regulatory proteins observed, Steinmetz et al. were not able to find even on unique striated muscle cell protein that was expressed in both cnidarians and bilaterians. Furthermore, the Z-disc seemed to have evolved differently even within bilaterians and there is a great deal diversity of proteins developed even between this clade, showing a large degree of radiation for muscle cells. Through this divergence of the Z-disc, Steimetz et al. argue that there are only four common protein components that were present in all bilaterians muscle ancestors and that of these for necessary Z-disc components only an actin protein that they have already argued is an uninformative marker through its pleisiomorphic state is present in cnidarians. Through further molecular marker testing, Steinmetz et al. observe that non-bilaterians lack many regulatory and structural components necessary for bilaterians muscle formation and do not find any unique set of proteins to both bilaterians and cnidarians and ctenophores that are not present in earlier, more primitive animals such as the sponges and amoebozoans. Through this analysis the authors conclude that due to the lack of elements that bilaterians muscles are dependent on for structure and usage, nonbilaterian muscles must be of a different origin with a different set regulatory and structural proteins.[36]
+
+In another take on the argument, Andrikou and Arnone use the newly available data on gene regulatory networks to look at how the hierarchy of genes and morphogens and other mechanism of tissue specification diverge and are similar among early deuterostomes and protostomes. By understanding not only what genes are present in all bilaterians but also the time and place of deployment of these genes, Andrikou and Arnone discuss a deeper understanding of the evolution of myogenesis.[37]
+
+In their paper Andrikou and Arnone argue that to truly understand the evolution of muscle cells the function of transcriptional regulators must be understood in the context of other external and internal interactions. Through their analysis, Andrikou and Arnone found that there were conserved orthologues of the gene regulatory network in both invertebrate bilaterians and in cnidarians. They argue that having this common, general regulatory circuit allowed for a high degree of divergence from a single well functioning network. Andrikou and Arnone found that the orthologues of genes found in vertebrates had been changed through different types of structural mutations in the invertebrate deuterostomes and protostomes, and they argue that these structural changes in the genes allowed for a large divergence of muscle function and muscle formation in these species. Andrikou and Arnone were able to recognize not only any difference due to mutation in the genes found in vertebrates and invertebrates but also the integration of species specific genes that could also cause divergence from the original gene regulatory network function. Thus, although a common muscle patterning system has been determined, they argue that this could be due to a more ancestral gene regulatory network being coopted several times across lineages with additional genes and mutations causing very divergent development of muscles. Thus it seems that myogenic patterning framework may be an ancestral trait. However, Andrikou and Arnone explain that the basic muscle patterning structure must also be considered in combination with the cis regulatory elements present at different times during development. In contrast with the high level of gene family apparatuses structure, Andrikou and Arnone found that the cis regulatory elements were not well conserved both in time and place in the network which could show a large degree of divergence in the formation of muscle cells. Through this analysis, it seems that the myogenic GRN is an ancestral GRN with actual changes in myogenic function and structure possibly being linked to later coopts of genes at different times and places.[37]
+
+Evolutionarily, specialized forms of skeletal and cardiac muscles predated the divergence of the vertebrate/arthropod evolutionary line.[38] This indicates that these types of muscle developed in a common ancestor sometime before 700 million years ago (mya). Vertebrate smooth muscle was found to have evolved independently from the skeletal and cardiac muscle types.
+

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+In ancient Greek religion and mythology, the Muses (Ancient Greek: Μοῦσαι, Moũsai, Modern Greek: Μούσες) are the inspirational goddesses of literature, science, and the arts. They were considered the source of the knowledge embodied in the poetry, lyric songs, and myths that were related orally for centuries in ancient Greek culture.
+
+The word "muse" can refer in general to anyone or anything which inspires an artist, musician, or writer.[1]
+
+The word "Muses" (Ancient Greek: Μοῦσαι, Moũsai) perhaps came from the o-grade of the Proto-Indo-European root *men- (the basic meaning of which is "put in mind" in verb formations with transitive function and "have in mind" in those with intransitive function),[2] or from root *men- ("to tower, mountain") since all the most important cult-centres of the Muses were on mountains or hills.[3] R. S. P. Beekes rejects the latter etymology and suggests that a Pre-Greek origin is also possible.[4]
+
+The earliest known records of the Nine Muses are from Boeotia, the homeland of Hesiod. Some ancient authorities thought that the Nine Muses were of Thracian origin.[5] There, a tradition persisted that the Muses had once been three in number.[6]
+
+In the first century BC, Diodorus Siculus cited Homer and Hesiod to the contrary, observing:
+
+Writers similarly disagree also concerning the number of the Muses; for some say that there are three, and others that there are nine, but the number nine has prevailed since it rests upon the authority of the most distinguished men, such as Homer and Hesiod and others like them.[7]
+
+Diodorus states (Book I.18) that Osiris first recruited the nine Muses, along with the satyrs, while passing through Aethiopia, before embarking on a tour of all Asia and Europe, teaching the arts of cultivation wherever he went.
+
+According to Hesiod's account (c. 600 BC), generally followed by the writers of antiquity, the Nine Muses were the nine daughters of Zeus and Mnemosyne (i.e., "Memory" personified), figuring as personifications of knowledge and the arts, especially poetry, literature, dance and music.
+
+The Roman scholar Varro (116–27 BC) relates that there are only three Muses: one born from the movement of water, another who makes sound by striking the air, and a third who is embodied only in the human voice. They were called Melete or "Practice", Mneme or "Memory" and Aoide or "Song". Three ancient Muses were also reported in Plutarch's (46–120 AD) Quaestiones Convivales[8] (9.I4.2–4).[9]
+
+However, the classical understanding of the Muses tripled their triad and established a set of nine goddesses, who embody the arts and inspire creation with their graces through remembered and improvised song and mime, writing, traditional music, and dance. It was not until Hellenistic times that the following systematic set of functions was assigned to them, and even then there was some variation in both their names and their attributes: Calliope (epic poetry), Clio (history), Euterpe (flutes and lyric poetry), Thalia (comedy and pastoral poetry), Melpomene (tragedy), Terpsichore (dance), Erato (love poetry), Polyhymnia (sacred poetry), and Urania (astronomy).
+
+According to Pausanias in the later second century AD,[10] there were originally three Muses, worshipped on Mount Helicon in Boeotia: Aoide ("song" or "tune"), Melete ("practice" or "occasion"), and Mneme ("memory").[11] Together, these three form the complete picture of the preconditions of poetic art in cult practice.
+
+In Delphi three Muses were worshiped as well, but with other names: Nete, Mese, and Hypate, which are assigned as the names of the three chords of the ancient musical instrument, the lyre.[12]
+
+Alternatively, later they were called Cephisso, Apollonis, and Borysthenis, names which characterize them as daughters of Apollo.[13]
+
+In a later tradition, a set of four Muses were recognized: Thelxinoë, Aoide, Archē, and Melete, said to be daughters of Zeus and Plusia or of Ouranos.[14]
+
+One of the people frequently associated with the Muses was Pierus. By some he was called the father (by a Pimpleian nymph, called Antiope by Cicero) of a total of seven Muses, called Neilṓ (Νειλώ), Tritṓnē (Τριτώνη), Asōpṓ (Ἀσωπώ), Heptápora (Ἑπτάπορα), Achelōís, Tipoplṓ (Τιποπλώ), and Rhodía (Ῥοδία).[15][16]
+
+According to Hesiod's Theogony (seventh century BC), they were daughters of Zeus, king of the gods, and Mnemosyne, Titan goddess of memory. Hesiod in Theogony narrates that the Muses brought to people forgetfulness, that is, the forgetfulness of pain and the cessation of obligations.[17]
+
+For Alcman and Mimnermus, they were even more primordial, springing from the early deities Ouranos and Gaia. Gaia is Mother Earth, an early mother goddess who was worshipped at Delphi from prehistoric times, long before the site was rededicated to Apollo, possibly indicating a transfer to association with him after that time.
+
+Sometimes the Muses are referred to as water nymphs, associated with the springs of Helicon and with Pieris. It was said that the winged horse Pegasus touched his hooves to the ground on Helicon, causing four sacred springs to burst forth, from which the Muses, also known as pegasides, were born.[18][19] Athena later tamed the horse and presented him to the Muses (compare the Roman inspiring nymphs of springs, the Camenae, the Völva of Norse Mythology and also the apsaras in the mythology of classical India).
+
+Classical writers set Apollo as their leader, Apollon Mousagetēs ("Apollo Muse-leader").[20] In one myth, the Muses judged a contest between Apollo and Marsyas. They also gathered the pieces of the dead body of Orpheus, son of Calliope, and buried them in Leivithra. In a later myth, Thamyris challenged them to a singing contest. They won and punished Thamyris by blinding him and robbing him of his singing ability.
+
+According to a myth from Ovid's Metamorphoses—alluding to the connection of Pieria with the Muses—Pierus, king of Macedon, had nine daughters he named after the nine Muses, believing that their skills were a great match to the Muses. He thus challenged the Muses to a match, resulting in his daughters, the Pierides, being turned into chattering jays (with κίσσα often erroneously translated as magpies) for their presumption.[21]
+
+Pausanias records a tradition of two generations of Muses; the first are the daughters of Ouranos and Gaia, the second of Zeus and Mnemosyne. Another, rarer genealogy is that they are daughters of Harmonia (the daughter of Aphrodite and Ares), which contradicts the myth in which they were dancing at the wedding of Harmonia and Cadmus.
+
+Calliope had Ialemus and  Orpheus with Apollo. But according to a variation, the father of Orpheus was actually Oeagrus, but Apollo adopted the boy and taught him the skill of lyre. Calliope trained him in singing.
+
+Linus was said[by whom?] to have been the son of Apollo and one of the Muses, either Calliope or Terpsichore or Urania. Rhesus was the son of Strymon and Calliope or Euterpe.
+
+The sirens were the children of Achelous and Melpomene or Terpsichore. Kleopheme was the daughter of Erato and Malos. Hyacinthus was the son Clio, according to an unpopular account.
+
+Hymenaeus was assigned as Apollo's son by one of the muses, either Calliope, or Clio, or Terpsichore, or Urania. Corybantes were the children of Thalia and Apollo.
+
+The Muses had several temples and shrines in ancient Greece, their two main cult centres being Mount Helikon in Boiotia and Pieria in Makedonia. 
+Strabo wrote:
+
+The cult of the Muses was also commonly connected to that of Apollo.
+
+Some Greek writers give the names of the nine Muses as Kallichore, Helike, Eunike, Thelxinoë, Terpsichore, Euterpe, Eukelade, Dia, and Enope.[23]
+
+In Renaissance and Neoclassical art, the dissemination of emblem books such as Cesare Ripa's Iconologia (1593 and many further editions) helped standardize the depiction of the Muses in sculpture and painting, so they could be distinguished by certain props. These props, or emblems, became readily identifiable by the viewer, enabling one immediately to recognize the Muse and the art with which she had become associated. Here again, Calliope (epic poetry) carries a writing tablet; Clio (history) carries a scroll and books; Euterpe (song and elegiac poetry) carries a flute, the aulos; Erato (lyric poetry) is often seen with a lyre and a crown of roses; Melpomene (tragedy) is often seen with a tragic mask; Polyhymnia (sacred poetry) is often seen with a pensive expression; Terpsichore (choral dance and song) is often seen dancing and carrying a lyre; Thalia (comedy) is often seen with a comic mask; and Urania (astronomy) carries a pair of compasses and the celestial globe.
+
+The Greek word mousa is a common noun as well as a type of goddess: it literally means "art" or "poetry". According to Pindar, to "carry a mousa" is "to excel in the arts". The word derives from the Indo-European root men-, which is also the source of Greek Mnemosyne and mania, English "mind", "mental" and "monitor", Sanskrit mantra and Avestan Mazda.[24]
+
+The Muses, therefore, were both the embodiments and sponsors of performed metrical speech: mousike (whence the English term "music") was just "one of the arts of the Muses". Others included Science, Geography, Mathematics, Philosophy, and especially Art, Drama, and inspiration. In the archaic period, before the widespread availability of books (scrolls), this included nearly all of learning. The first Greek book on astronomy, by Thales, took the form of dactylic hexameters, as did many works of pre-Socratic philosophy. Both Plato and the Pythagoreans explicitly included philosophy as a sub-species of mousike.[25] The Histories of Herodotus, whose primary medium of delivery was public recitation, were divided by Alexandrian editors into nine books, named after the nine Muses.
+
+For poet and "law-giver" Solon,[26] the Muses were "the key to the good life"; since they brought both prosperity and friendship. Solon sought to perpetuate his political reforms by establishing recitations of his poetry—complete with invocations to his practical-minded Muses—by Athenian boys at festivals each year. He believed that the Muses would help inspire people to do their best.
+
+Ancient authors and their imitators invoke Muses when writing poetry, hymns or epic history. The invocation occurs near the beginning of their work. It asks for help or inspiration from the Muses, or simply invites the Muse to sing directly through the author.
+
+Originally, the invocation of the Muse was an indication that the speaker was working inside the poetic tradition, according to the established formulas. For example:
+
+Sing to me of the man, Muse, the man of twists and turns
+
+driven time and again off course, once he had plundered
+the hallowed heights of Troy.
+
+O Muse! the causes and the crimes relate;
+
+What goddess was provok'd, and whence her hate;
+For what offense the Queen of Heav'n began
+To persecute so brave, so just a man; [...]
+
+Besides Homer and Virgil, other famous works that included an invocation of the Muse are the first of the carmina by Catullus, Ovid's Metamorphoses and Amores, Dante's Inferno (Canto II), Chaucer's Troilus and Criseyde (Book II), Shakespeare's Henry V (Act 1, Prologue), his 38th sonnet, and Milton's Paradise Lost (openings of Books 1 and 7).
+
+When Pythagoras arrived at Croton, his first advice to the Crotoniates was to build a shrine to the Muses at the center of the city, to promote civic harmony and learning. Local cults of the Muses often became associated with springs or with fountains. The Muses themselves were sometimes called Aganippids because of their association with a fountain called Aganippe. Other fountains, Hippocrene and Pirene, were also important locations associated with the Muses. Some sources occasionally referred to the Muses as "Corycides" (or "Corycian nymphs") after a cave on Mount Parnassos, called the Corycian Cave. Pausanias referred to the Muses by the surnames "Ardalides" or "Ardaliotides", because of a sanctuary to them at Troezen said to have been built by the mythical Ardalus.
+
+The Muses were venerated especially in Boeotia, in the Valley of the Muses near Helicon, and in Delphi and the Parnassus, where Apollo became known as Mousagetes ("Muse-leader") after the sites were rededicated to his cult.
+
+Often Muse-worship was associated with the hero-cults of poets: the tombs of Archilochus on Thasos and of Hesiod and Thamyris in Boeotia all played host to festivals in which poetic recitations accompanied sacrifices to the Muses. The Library of Alexandria and its circle of scholars formed around a mousaion (i.e., "museum" or shrine of the Muses) close to the tomb of Alexander the Great. Many Enlightenment figures sought to re-establish a "Cult of the Muses" in the 18th century. A famous Masonic lodge in pre-Revolutionary Paris was called Les Neuf Soeurs ("The Nine Sisters", that is, the Nine Muses); Voltaire, Benjamin Franklin, Danton, and other influential Enlightenment figures attended it. As a side-effect of this movement the word "museum" (originally, "cult place of the Muses") came to refer to a place for the public display of knowledge.
+
+The Muses are explicitly used in modern English to refer to an artistic inspiration, as when one cites one's own artistic muse, and also implicit in words and phrases such as "amuse", "museum" (Latinised from mouseion—a place where the Muses were worshipped), "music", and "musing upon".[27] In current literature, the influential role that the Muse plays has been extended to the political sphere.[28]
+
+In New Orleans, Louisiana, there are streets named for all nine Muses. It is commonly held that the local pronunciation of the names has been colorfully anglicized in an unusual manner by the "Yat" dialect. The pronunciations are actually in line with the French, Spanish and Creole roots of the city.[29]
+
+Terpsichore
+
+Erato
+
+Clio
+
+Thalia
+
+Polyhymnia
+
+Calliope
+
+Apollo and the Muses
+
+Euterpe
+
+Parnassus
+
+Urania and Melpomene

en/3365.html.txt

@@ -0,0 +1,433 @@
+
+
+
+
+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 Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma,[18][19] with internal convective motion that generates a magnetic field via a dynamo process.[20] It is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometers (864,000 miles), or 109 times that of Earth, and its mass is about 330,000 times that of Earth. It accounts for about 99.86% of the total mass of the Solar System.[21]
+Roughly three quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.[22]
+
+The Sun is a G-type main-sequence star (G2V) based on its spectral class. As such, it is informally and not completely accurately referred to as a yellow dwarf (its light is closer to white than yellow). It formed approximately 4.6 billion[a][14][23] years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core. It is thought that almost all stars form by this process.
+
+The Sun currently fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result. This energy, which can take between 10,000 and 170,000 years to escape from its core, is the source of the Sun's light and heat. When hydrogen fusion in its core has diminished to the point at which the Sun is no longer in hydrostatic equilibrium, its core will undergo a marked increase in density and temperature while its outer layers expand, eventually transforming the Sun into a red giant. It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury and Venus, and render Earth uninhabitable – but not for about five billion years. After this, it will shed its outer layers and become a dense type of cooling star known as a white dwarf, and no longer produce energy by fusion, but still glow and give off heat from its previous fusion.
+
+The enormous effect of the Sun on Earth has been recognized since prehistoric times, and the Sun has been regarded by some cultures as a deity. The synodic rotation of Earth and its orbit around the Sun are the basis of solar calendars, one of which is the predominant calendar in use today.
+
+The English word sun developed from Old English sunne. Cognates appear in other Germanic languages, including West Frisian sinne, Dutch zon, Low German Sünn, Standard German Sonne, Bavarian Sunna, Old Norse sunna and Gothic sunnō. All these words stem from Proto-Germanic *sunnōn.[24][25] This is ultimately related to the word for "sun" in other branches of the Indo-European language family, though in most cases a nominative stem with an l is found, rather than the genitive stem in n, as for example in Latin sōl, Greek ἥλιος hēlios, Welsh haul and Russian солнце solntse (pronounced sontse), as well as (with *l > r) Sanskrit स्वर svár and Persian خور‎ xvar. Indeed, the l-stem survived in Proto-Germanic as well, as *sōwelan, which gave rise to Gothic sauil (alongside sunnō) and Old Norse prosaic sól (alongside poetic sunna), and through it the words for "sun" in the modern Scandinavian languages: Swedish and Danish solen, Icelandic sólin, etc.[25]
+
+In English, the Greek and Latin words occur in poetry as personifications of the Sun, Helios /ˈhiːliəs/ and Sol /ˈsɒl/,[2][1] while in science fiction "Sol" may be used as a name for the Sun to distinguish it from others. The term "sol" with a lower-case 's' is used by planetary astronomers for the duration of a solar day on another planet such as Mars.[26]
+
+The principal adjectives for the Sun in English are sunny for sunlight and, in technical contexts, solar /ˈsoʊlər/,[3] from Latin sol[27] – the latter found in terms such as solar day, solar eclipse and Solar System (occasionally Sol system).
+From the Greek helios comes the rare adjective heliac /ˈhiːliæk/.[28]
+
+The English weekday name Sunday stems from Old English Sunnandæg "sun's day", a Germanic interpretation of the Latin phrase diēs sōlis, itself a translation of the Greek ἡμέρα ἡλίου hēmera hēliou "day of the sun".[29]
+
+The Sun is a G-type main-sequence star that comprises about 99.86% of the mass of the Solar System. The Sun has an absolute magnitude of +4.83, estimated to be brighter than about 85% of the stars in the Milky Way, most of which are red dwarfs.[30][31] The Sun is a Population I, or heavy-element-rich,[b] star.[32] The formation of the Sun may have been triggered by shockwaves from one or more nearby supernovae.[33] This is suggested by a high abundance of heavy elements in the Solar System, such as gold and uranium, relative to the abundances of these elements in so-called Population II, heavy-element-poor, stars. The heavy elements could most plausibly have been produced by endothermic nuclear reactions during a supernova, or by transmutation through neutron absorption within a massive second-generation star.[32]
+
+The Sun is by far the brightest object in the Earth's sky, with an apparent magnitude of −26.74.[34][35] This is about 13 billion times brighter than the next brightest star, Sirius, which has an apparent magnitude of −1.46. One astronomical unit (about 150,000,000 km; 93,000,000 mi) is defined as the mean distance of the Sun's center to Earth's center, though the distance varies as Earth moves from perihelion in January to aphelion in July.[36] At this average distance, light travels from the Sun's horizon to Earth's horizon in about 8 minutes and 19 seconds, while light from the closest points of the Sun and Earth takes about two seconds less. The energy of this sunlight supports almost all life[c] on Earth by photosynthesis,[37] and drives Earth's climate and weather.
+
+The Sun does not have a definite boundary, but its density decreases exponentially with increasing height above the photosphere.[38] For the purpose of measurement, the Sun's radius is considered to be the distance from its center to the edge of the photosphere, the apparent visible surface of the Sun.[39] By this measure, the Sun is a near-perfect sphere with an oblateness estimated at about 9 millionths,[40] which means that its polar diameter differs from its equatorial diameter by only 10 kilometres (6.2 mi).[41] The tidal effect of the planets is weak and does not significantly affect the shape of the Sun.[42] The Sun rotates faster at its equator than at its poles. This differential rotation is caused by convective motion due to heat transport and the Coriolis force due to the Sun's rotation. In a frame of reference defined by the stars, the rotational period is approximately 25.6 days at the equator and 33.5 days at the poles. Viewed from Earth as it orbits the Sun, the apparent rotational period of the Sun at its equator is about 28 days.[43] Viewed from a vantage point above its north pole, the Sun rotates counterclockwise around its axis of spin.[d][44]
+
+The solar constant is the amount of power that the Sun deposits per unit area that is directly exposed to sunlight. The solar constant is equal to approximately 1,368 W/m2 (watts per square meter) at a distance of one astronomical unit (AU) from the Sun (that is, on or near Earth).[45] Sunlight on the surface of Earth is attenuated by Earth's atmosphere, so that less power arrives at the surface (closer to 1,000 W/m2) in clear conditions when the Sun is near the zenith.[46] Sunlight at the top of Earth's atmosphere is composed (by total energy) of about 50% infrared light, 40% visible light, and 10% ultraviolet light.[47] The atmosphere in particular filters out over 70% of solar ultraviolet, especially at the shorter wavelengths.[48] Solar ultraviolet radiation ionizes Earth's dayside upper atmosphere, creating the electrically conducting ionosphere.[49]
+
+The Sun's color is white, with a CIE color-space index near (0.3, 0.3), when viewed from space or when the Sun is high in the sky. When measuring all the photons emitted, the Sun is emitting more photons in the green portion of the spectrum than any other.[50][51] When the Sun is low in the sky, atmospheric scattering renders the Sun yellow, red, orange, or magenta. Despite its typical whiteness, most people mentally picture the Sun as yellow; the reasons for this are the subject of debate.[52]
+The Sun is a G2V star, with G2 indicating its surface temperature of approximately 5,778 K (5,505 °C, 9,941 °F), and V that it, like most stars, is a main-sequence star.[53][54] The average luminance of the Sun is about 1.88 giga candela per square metre, but as viewed through Earth's atmosphere, this is lowered to about 1.44 Gcd/m2.[e] However, the luminance is not constant across the disk of the Sun (limb darkening).
+
+The Sun is composed primarily of the chemical elements hydrogen and helium. At this time in the Sun's life, they account for 74.9% and 23.8% of the mass of the Sun in the photosphere, respectively.[55] All heavier elements, called metals in astronomy, account for less than 2% of the mass, with oxygen (roughly 1% of the Sun's mass), carbon (0.3%), neon (0.2%), and iron (0.2%) being the most abundant.[56]
+
+The Sun's original chemical composition was inherited from the interstellar medium out of which it formed. Originally it would have contained about 71.1% hydrogen, 27.4% helium, and 1.5% heavier elements.[55] The hydrogen and most of the helium in the Sun would have been produced by Big Bang nucleosynthesis in the first 20 minutes of the universe, and the heavier elements were produced by previous generations of stars before the Sun was formed, and spread into the interstellar medium during the final stages of stellar life and by events such as supernovae.[57]
+
+Since the Sun formed, the main fusion process has involved fusing hydrogen into helium. Over the past 4.6 billion years, the amount of helium and its location within the Sun has gradually changed. Within the core, the proportion of helium has increased from about 24% to about 60% due to fusion, and some of the helium and heavy elements have settled from the photosphere towards the center of the Sun because of gravity. The proportions of metals (heavier elements) is unchanged. Heat is transferred outward from the Sun's core by radiation rather than by convection (see Radiative zone below), so the fusion products are not lifted outward by heat; they remain in the core[58] and gradually an inner core of helium has begun to form that cannot be fused because presently the Sun's core is not hot or dense enough to fuse helium. In the current photosphere the helium fraction is reduced, and the metallicity is only 84% of what it was in the protostellar phase (before nuclear fusion in the core started). In the future, helium will continue to accumulate in the core, and in about 5 billion years this gradual build-up will eventually cause the Sun to exit the main sequence and become a red giant.[59]
+
+The chemical composition of the photosphere is normally considered representative of the composition of the primordial Solar System.[60] The solar heavy-element abundances described above are typically measured both using spectroscopy of the Sun's photosphere and by measuring abundances in meteorites that have never been heated to melting temperatures. These meteorites are thought to retain the composition of the protostellar Sun and are thus not affected by settling of heavy elements. The two methods generally agree well.[22]
+
+In the 1970s, much research focused on the abundances of iron-group elements in the Sun.[61][62] Although significant research was done, until 1978 it was difficult to determine the abundances of some iron-group elements (e.g. cobalt and manganese) via spectrography because of their hyperfine structures.[61]
+
+The first largely complete set of oscillator strengths of singly ionized iron-group elements were made available in the 1960s,[63] and these were subsequently improved.[64] In 1978, the abundances of singly ionized elements of the iron group were derived.[61]
+
+Various authors have considered the existence of a gradient in the isotopic compositions of solar and planetary noble gases,[65] e.g. correlations between isotopic compositions of neon and xenon in the Sun and on the planets.[66]
+
+Prior to 1983, it was thought that the whole Sun has the same composition as the solar atmosphere.[67] In 1983, it was claimed that it was fractionation in the Sun itself that caused the isotopic-composition relationship between the planetary and solar-wind-implanted noble gases.[67]
+
+The structure of the Sun contains the following layers:
+
+The core of the Sun extends from the center to about 20–25% of the solar radius.[68] It has a density of up to 150 g/cm3[69][70] (about 150 times the density of water) and a temperature of close to 15.7 million kelvin (K).[70] By contrast, the Sun's surface temperature is approximately 5800 K. Recent analysis of SOHO mission data favors a faster rotation rate in the core than in the radiative zone above.[68] Through most of the Sun's life, energy has been produced by nuclear fusion in the core region through a series of nuclear reactions called the p–p (proton–proton) chain; this process converts hydrogen into helium.[71] Only 0.8% of the energy generated in the Sun comes from another sequence of fusion reactions called the CNO cycle, though this proportion is expected to increase as the Sun becomes older.[72]
+
+The core is the only region in the Sun that produces an appreciable amount of thermal energy through fusion; 99% of the power is generated within 24% of the Sun's radius, and by 30% of the radius, fusion has stopped nearly entirely. The remainder of the Sun is heated by this energy as it is transferred outwards through many successive layers, finally to the solar photosphere where it escapes into space through radiation (photons) or advection (massive particles).[53][73]
+
+The proton–proton chain occurs around 9.2×1037 times each second in the core, converting about 3.7×1038 protons into alpha particles (helium nuclei) every second (out of a total of ~8.9×1056 free protons in the Sun), or about 6.2×1011 kg/s.[53] Fusing four free protons (hydrogen nuclei) into a single alpha particle (helium nucleus) releases around 0.7% of the fused mass as energy,[74] so the Sun releases energy at the mass–energy conversion rate of 4.26 million metric tons per second (which requires 600 metric megatons of hydrogen [75]), for 384.6 yottawatts (3.846×1026 W),[5] or 9.192×1010 megatons of TNT per second. The large power output of the Sun is mainly due to the huge size and density of its core (compared to Earth and objects on Earth), with only a fairly small amount of power being generated per cubic metre. Theoretical models of the Sun's interior indicate a maximum power density, or energy production, of approximately 276.5 watts per cubic metre at the center of the core,[76] which is about the same rate of power production as takes place in reptile metabolism or a compost pile.[77][f]
+
+The fusion rate in the core is in a self-correcting equilibrium: a slightly higher rate of fusion would cause the core to heat up more and expand slightly against the weight of the outer layers, reducing the density and hence the fusion rate and correcting the perturbation; and a slightly lower rate would cause the core to cool and shrink slightly, increasing the density and increasing the fusion rate and again reverting it to its present rate.[78][79]
+
+From the core out to about 0.7 solar radii, thermal radiation is the primary means of energy transfer.[80] The temperature drops from approximately 7 million to 2 million kelvins with increasing distance from the core.[70] This temperature gradient is less than the value of the adiabatic lapse rate and hence cannot drive convection, which explains why the transfer of energy through this zone is by radiation instead of thermal convection.[70] Ions of hydrogen and helium emit photons, which travel only a brief distance before being reabsorbed by other ions.[80] The density drops a hundredfold (from 20 g/cm3 to 0.2 g/cm3) from 0.25 solar radii to the 0.7 radii, the top of the radiative zone.[80]
+
+The radiative zone and the convective zone are separated by a transition layer, the tachocline. This is a region where the sharp regime change between the uniform rotation of the radiative zone and the differential rotation of the convection zone results in a large shear between the two—a condition where successive horizontal layers slide past one another.[81] Presently, it is hypothesized (see Solar dynamo) that a magnetic dynamo within this layer generates the Sun's magnetic field.[70]
+
+The Sun's convection zone extends from 0.7 solar radii (500,000 km) to near the surface. In this layer, the solar plasma is not dense enough or hot enough to transfer the heat energy of the interior outward via radiation. Instead, the density of the plasma is low enough to allow convective currents to develop and move the Sun's energy outward towards its surface. Material heated at the tachocline picks up heat and expands, thereby reducing its density and allowing it to rise. As a result, an orderly motion of the mass develops into thermal cells that carry the majority of the heat outward to the Sun's photosphere above. Once the material diffusively and radiatively cools just beneath the photospheric surface, its density increases, and it sinks to the base of the convection zone, where it again picks up heat from the top of the radiative zone and the convective cycle continues. At the photosphere, the temperature has dropped to 5,700 K and the density to only 0.2 g/m3 (about 1/6,000 the density of air at sea level).[70]
+
+The thermal columns of the convection zone form an imprint on the surface of the Sun giving it a granular appearance called the solar granulation at the smallest scale and supergranulation at larger scales. Turbulent convection in this outer part of the solar interior sustains "small-scale" dynamo action over the near-surface volume of the Sun.[70] The Sun's thermal columns are Bénard cells and take the shape of hexagonal prisms.[82]
+
+The visible surface of the Sun, the photosphere, is the layer below which the Sun becomes opaque to visible light.[83] Photons produced in this layer escape the Sun through the transparent solar atmosphere above it and become solar radiation, sunlight. The change in opacity is due to the decreasing amount of H− ions, which absorb visible light easily.[83] Conversely, the visible light we see is produced as electrons react with hydrogen atoms to produce H− ions.[84][85]
+The photosphere is tens to hundreds of kilometers thick, and is slightly less opaque than air on Earth. Because the upper part of the photosphere is cooler than the lower part, an image of the Sun appears brighter in the center than on the edge or limb of the solar disk, in a phenomenon known as limb darkening.[83] The spectrum of sunlight has approximately the spectrum of a black-body radiating at 5777 K, interspersed with atomic absorption lines from the tenuous layers above the photosphere. The photosphere has a particle density of ~1023 m−3 (about 0.37% of the particle number per volume of Earth's atmosphere at sea level). The photosphere is not fully ionized—the extent of ionization is about 3%, leaving almost all of the hydrogen in atomic form.[86]
+
+During early studies of the optical spectrum of the photosphere, some absorption lines were found that did not correspond to any chemical elements then known on Earth. In 1868, Norman Lockyer hypothesized that these absorption lines were caused by a new element that he dubbed helium, after the Greek Sun god Helios. Twenty-five years later, helium was isolated on Earth.[87]
+
+During a total solar eclipse, when the disk of the Sun is covered by that of the Moon, parts of the Sun's surrounding atmosphere can be seen. It is composed of four distinct parts: the chromosphere, the transition region, the corona and the heliosphere.
+
+The coolest layer of the Sun is a temperature minimum region extending to about 500 km above the photosphere, and has a temperature of about 4,100 K.[83] This part of the Sun is cool enough to allow the existence of simple molecules such as carbon monoxide and water, which can be detected via their absorption spectra.[88]
+
+The chromosphere, transition region, and corona are much hotter than the surface of the Sun.[83] The reason is not well understood, but evidence suggests that Alfvén waves may have enough energy to heat the corona.[89]
+
+Above the temperature minimum layer is a layer about 2,000 km thick, dominated by a spectrum of emission and absorption lines.[83] It is called the chromosphere from the Greek root chroma, meaning color, because the chromosphere is visible as a colored flash at the beginning and end of total solar eclipses.[80] The temperature of the chromosphere increases gradually with altitude, ranging up to around 20,000 K near the top.[83] In the upper part of the chromosphere helium becomes partially ionized.[90]
+
+Above the chromosphere, in a thin (about 200 km) transition region, the temperature rises rapidly from around 20000 K in the upper chromosphere to coronal temperatures closer to 1000000 K.[91] The temperature increase is facilitated by the full ionization of helium in the transition region, which significantly reduces radiative cooling of the plasma.[90] The transition region does not occur at a well-defined altitude. Rather, it forms a kind of nimbus around chromospheric features such as spicules and filaments, and is in constant, chaotic motion.[80] The transition region is not easily visible from Earth's surface, but is readily observable from space by instruments sensitive to the extreme ultraviolet portion of the spectrum.[92]
+
+The corona is the next layer of the Sun. The low corona, near the surface of the Sun, has a particle density around 1015 m−3 to 1016 m−3.[90][g] The average temperature of the corona and solar wind is about 1,000,000–2,000,000 K; however, in the hottest regions it is 8,000,000–20,000,000 K.[91] Although no complete theory yet exists to account for the temperature of the corona, at least some of its heat is known to be from magnetic reconnection.[91][93]
+The corona is the extended atmosphere of the Sun, which has a volume much larger than the volume enclosed by the Sun's photosphere. A flow of plasma outward from the Sun into interplanetary space is the solar wind.[93]
+
+The heliosphere, the tenuous outermost atmosphere of the Sun, is filled with the solar wind plasma. This outermost layer of the Sun is defined to begin at the distance where the flow of the solar wind becomes superalfvénic—that is, where the flow becomes faster than the speed of Alfvén waves,[94] at approximately 20 solar radii (0.1 AU).
+Turbulence and dynamic forces in the heliosphere cannot affect the shape of the solar corona within, because the information can only travel at the speed of Alfvén waves. The solar wind travels outward continuously through the heliosphere,[95][96] forming the solar magnetic field into a spiral shape,[93] until it impacts the heliopause more than 50 AU from the Sun. In December 2004, the Voyager 1 probe passed through a shock front that is thought to be part of the heliopause.[97] In late 2012 Voyager 1 recorded a marked increase in cosmic ray collisions and a sharp drop in lower energy particles from the solar wind, which suggested that the probe had passed through the heliopause and entered the interstellar medium.[98]
+
+High-energy gamma ray photons initially released with fusion reactions in the core are almost immediately absorbed by the solar plasma of the radiative zone, usually after traveling only a few millimeters. Re-emission happens in a random direction and usually at a slightly lower energy. With this sequence of emissions and absorptions, it takes a long time for radiation to reach the Sun's surface. Estimates of the photon travel time range between 10,000 and 170,000 years.[99] In contrast, it takes only 2.3 seconds for the neutrinos, which account for about 2% of the total energy production of the Sun, to reach the surface. Because energy transport in the Sun is a process that involves photons in thermodynamic equilibrium with matter, the time scale of energy transport in the Sun is longer, on the order of 30,000,000 years. This is the time it would take the Sun to return to a stable state, if the rate of energy generation in its core were suddenly changed.[100]
+
+Neutrinos are also released by the fusion reactions in the core, but, unlike photons, they rarely interact with matter, so almost all are able to escape the Sun immediately. For many years measurements of the number of neutrinos produced in the Sun were lower than theories predicted by a factor of 3. This discrepancy was resolved in 2001 through the discovery of the effects of neutrino oscillation: the Sun emits the number of neutrinos predicted by the theory, but neutrino detectors were missing ​2⁄3 of them because the neutrinos had changed flavor by the time they were detected.[101]
+
+The Sun has a magnetic field that varies across the surface of the Sun. Its polar field is 1–2 gauss (0.0001–0.0002 T), whereas the field is typically 3,000 gauss (0.3 T) in features on the Sun called sunspots and 10–100 gauss (0.001–0.01 T) in solar prominences.[5]
+
+The magnetic field also varies in time and location. The quasi-periodic 11-year solar cycle is the most prominent variation in which the number and size of sunspots waxes and wanes.[20][103][104]
+
+Sunspots are visible as dark patches on the Sun's photosphere, and correspond to concentrations of magnetic field where the convective transport of heat is inhibited from the solar interior to the surface. As a result, sunspots are slightly cooler than the surrounding photosphere, so they appear dark. At a typical solar minimum, few sunspots are visible, and occasionally none can be seen at all. Those that do appear are at high solar latitudes. As the solar cycle progresses towards its maximum, sunspots tend to form closer to the solar equator, a phenomenon known as Spörer's law. The largest sunspots can be tens of thousands of kilometers across.[105]
+
+An 11-year sunspot cycle is half of a 22-year Babcock–Leighton dynamo cycle, which corresponds to an oscillatory exchange of energy between toroidal and poloidal solar magnetic fields. At solar-cycle maximum, the external poloidal dipolar magnetic field is near its dynamo-cycle minimum strength, but an internal toroidal quadrupolar field, generated through differential rotation within the tachocline, is near its maximum strength. At this point in the dynamo cycle, buoyant upwelling within the convective zone forces emergence of toroidal magnetic field through the photosphere, giving rise to pairs of sunspots, roughly aligned east–west and having footprints with opposite magnetic polarities. The magnetic polarity of sunspot pairs alternates every solar cycle, a phenomenon known as the Hale cycle.[106][107]
+
+During the solar cycle's declining phase, energy shifts from the internal toroidal magnetic field to the external poloidal field, and sunspots diminish in number and size. At solar-cycle minimum, the toroidal field is, correspondingly, at minimum strength, sunspots are relatively rare, and the poloidal field is at its maximum strength. With the rise of the next 11-year sunspot cycle, differential rotation shifts magnetic energy back from the poloidal to the toroidal field, but with a polarity that is opposite to the previous cycle. The process carries on continuously, and in an idealized, simplified scenario, each 11-year sunspot cycle corresponds to a change, then, in the overall polarity of the Sun's large-scale magnetic field.[108][109]
+
+The solar magnetic field extends well beyond the Sun itself. The electrically conducting solar wind plasma carries the Sun's magnetic field into space, forming what is called the interplanetary magnetic field.[93] In an approximation known as ideal magnetohydrodynamics, plasma particles only move along the magnetic field lines. As a result, the outward-flowing solar wind stretches the interplanetary magnetic field outward, forcing it into a roughly radial structure. For a simple dipolar solar magnetic field, with opposite hemispherical polarities on either side of the solar magnetic equator, a thin current sheet is formed in the solar wind.[93] At great distances, the rotation of the Sun twists the dipolar magnetic field and corresponding current sheet into an Archimedean spiral structure called the Parker spiral.[93] The interplanetary magnetic field is much stronger than the dipole component of the solar magnetic field. The Sun's dipole magnetic field of 50–400 μT (at the photosphere) reduces with the inverse-cube of the distance to about 0.1 nT at the distance of Earth. However, according to spacecraft observations the interplanetary field at Earth's location is around 5 nT, about a hundred times greater.[110] The difference is due to magnetic fields generated by electrical currents in the plasma surrounding the Sun.
+
+The Sun's magnetic field leads to many effects that are collectively called solar activity. Solar flares and coronal-mass ejections tend to occur at sunspot groups. Slowly changing high-speed streams of solar wind are emitted from coronal holes at the photospheric surface. Both coronal-mass ejections and high-speed streams of solar wind carry plasma and interplanetary magnetic field outward into the Solar System.[111] The effects of solar activity on Earth include auroras at moderate to high latitudes and the disruption of radio communications and electric power. Solar activity is thought to have played a large role in the formation and evolution of the Solar System.
+
+With solar-cycle modulation of sunspot number comes a corresponding modulation of space weather conditions, including those surrounding Earth where technological systems can be affected.
+
+In December 2019, a new type of solar magnetic explosion was observed, known as forced magnetic reconnection. Previously, in a process called spontaneous magnetic reconnection, it was observed that the solar magnetic field lines diverge explosively and then converge again instantaneously. Forced Magnetic Reconnection was similar, but it was triggered by an explosion in the corona.[112]
+
+Long-term secular change in sunspot number is thought, by some scientists, to be correlated with long-term change in solar irradiance,[113] which, in turn, might influence Earth's long-term climate.[114]
+For example, in the 17th century, the solar cycle appeared to have stopped entirely for several decades; few sunspots were observed during a period known as the Maunder minimum. This coincided in time with the era of the Little Ice Age, when Europe experienced unusually cold temperatures.[115] Earlier extended minima have been discovered through analysis of tree rings and appear to have coincided with lower-than-average global temperatures.[116]
+
+A recent theory claims that there are magnetic instabilities in the core of the Sun that cause fluctuations with periods of either 41,000 or 100,000 years. These could provide a better explanation of the ice ages than the Milankovitch cycles.[117][118]
+
+The Sun today is roughly halfway through the most stable part of its life. It has not changed dramatically for over four billion[a] years, and will remain fairly stable for more than five billion more. However, after hydrogen fusion in its core has stopped, the Sun will undergo dramatic changes, both internally and externally.
+
+The Sun formed about 4.6 billion years ago from the collapse of part of a giant molecular cloud that consisted mostly of hydrogen and helium and that probably gave birth to many other stars.[119] This age is estimated using computer models of stellar evolution and through nucleocosmochronology.[14] The result is consistent with the radiometric date of the oldest Solar System material, at 4.567 billion years ago.[120][121] Studies of ancient meteorites reveal traces of stable daughter nuclei of short-lived isotopes, such as iron-60, that form only in exploding, short-lived stars. This indicates that one or more supernovae must have occurred near the location where the Sun formed. A shock wave from a nearby supernova would have triggered the formation of the Sun by compressing the matter within the molecular cloud and causing certain regions to collapse under their own gravity.[122] As one fragment of the cloud collapsed it also began to rotate due to conservation of angular momentum and heat up with the increasing pressure. Much of the mass became concentrated in the center, whereas the rest flattened out into a disk that would become the planets and other Solar System bodies. Gravity and pressure within the core of the cloud generated a lot of heat as it accreted more matter from the surrounding disk, eventually triggering nuclear fusion.
+
+HD 162826 and HD 186302 are hypothesized stellar siblings of the Sun, having formed in the same molecular cloud.
+
+The Sun is about halfway through its main-sequence stage, during which nuclear fusion reactions in its core fuse hydrogen into helium. Each second, more than four million tonnes of matter are converted into energy within the Sun's core, producing neutrinos and solar radiation. At this rate, the Sun has so far converted around 100 times the mass of Earth into energy, about 0.03% of the total mass of the Sun. The Sun will spend a total of approximately 10 billion years as a main-sequence star.[124] The Sun is gradually becoming hotter during its time on the main sequence, because the helium atoms in the core occupy less volume than the hydrogen atoms that were fused. The core is therefore shrinking, allowing the outer layers of the Sun to move closer to the center and experience a stronger gravitational force, according to the inverse-square law. This stronger force increases the pressure on the core, which is resisted by a gradual increase in the rate at which fusion occurs. This process speeds up as the core gradually becomes denser. It is estimated that the Sun has become 30% brighter in the last 4.5 billion years.[125] At present, it is increasing in brightness by about 1% every 100 million years.[126]
+
+The Sun does not have enough mass to explode as a supernova. Instead it will exit the main sequence in approximately 5 billion years and start to turn into a red giant.[127][128] As a red giant, the Sun will grow so large that it will engulf Mercury, Venus, and probably Earth.[128][129]
+
+Even before it becomes a red giant, the luminosity of the Sun will have nearly doubled, and Earth will receive as much sunlight as Venus receives today. Once the core hydrogen is exhausted in 5.4 billion years, the Sun will expand into a subgiant phase and slowly double in size over about half a billion years. It will then expand more rapidly over about half a billion years until it is over two hundred times larger than today and a couple of thousand times more luminous. This then starts the red-giant-branch phase where the Sun will spend around a billion years and lose around a third of its mass.[128]
+
+After the red-giant branch the Sun has approximately 120 million years of active life left, but much happens. First, the core, full of degenerate helium ignites violently in the helium flash, where it is estimated that 6% of the core, itself 40% of the Sun's mass, will be converted into carbon within a matter of minutes through the triple-alpha process.[130] The Sun then shrinks to around 10 times its current size and 50 times the luminosity, with a temperature a little lower than today. It will then have reached the red clump or horizontal branch, but a star of the Sun's mass does not evolve blueward along the horizontal branch. Instead, it just becomes moderately larger and more luminous over about 100 million years as it continues to react helium in the core.[128]
+
+When the helium is exhausted, the Sun will repeat the expansion it followed when the hydrogen in the core was exhausted, except that this time it all happens faster, and the Sun becomes larger and more luminous. This is the asymptotic-giant-branch phase, and the Sun is alternately reacting hydrogen in a shell or helium in a deeper shell. After about 20 million years on the early asymptotic giant branch, the Sun becomes increasingly unstable, with rapid mass loss and thermal pulses that increase the size and luminosity for a few hundred years every 100,000 years or so. The thermal pulses become larger each time, with the later pulses pushing the luminosity to as much as 5,000 times the current level and the radius to over 1 AU.[131] According to a 2008 model, Earth's orbit is shrinking due to tidal forces (and, eventually, drag from the lower chromosphere), so that it will be engulfed by the Sun near the tip of the red giant branch phase, 3.8 and 1 million years after Mercury and Venus have respectively had the same fate. Models vary depending on the rate and timing of mass loss. Models that have higher mass loss on the red-giant branch produce smaller, less luminous stars at the tip of the asymptotic giant branch, perhaps only 2,000 times the luminosity and less than 200 times the radius.[128] For the Sun, four thermal pulses are predicted before it completely loses its outer envelope and starts to make a planetary nebula. By the end of that phase—lasting approximately 500,000 years—the Sun will only have about half of its current mass.
+
+The post-asymptotic-giant-branch evolution is even faster. The luminosity stays approximately constant as the temperature increases, with the ejected half of the Sun's mass becoming ionized into a planetary nebula as the exposed core reaches 30,000 K. The final naked core, a white dwarf, will have a temperature of over 100,000 K, and contain an estimated 54.05% of the Sun's present day mass.[128] The planetary nebula will disperse in about 10,000 years, but the white dwarf will survive for trillions of years before fading to a hypothetical black dwarf.[132][133]
+
+The Sun lies close to the inner rim of the Milky Way's Orion Arm, in the Local Interstellar Cloud or the Gould Belt, at a distance of 7.5–8.5 kiloparsecs (24–28 kly) from the Galactic Center.[134][135]
+[136][137][138][139]
+The Sun is contained within the Local Bubble, a space of rarefied hot gas, possibly produced by the supernova remnant Geminga,[140] or multiple supernovae in subgroup B1 of the Pleiades moving group.[141] The distance between the local arm and the next arm out, the Perseus Arm, is about 6,500 light-years.[142] The Sun, and thus the Solar System, is found in what scientists call the galactic habitable zone.
+The Apex of the Sun's Way, or the solar apex, is the direction that the Sun travels relative to other nearby stars. This motion is towards a point in the constellation Hercules, near the star Vega.
+
+Within 32.6 ly of the Sun there are 315 known stars in 227 systems, as of 2000, including 163 single stars. It is estimated that a further 130 systems within this range have not yet been identified. Out to 81.5 ly, there may be up to 7,500 stars, of which around 2,600 are known. The number of substellar objects in that volume are expected to be comparable to the number of stars.[143] Of the 50 nearest stellar systems within 17 light-years from Earth (the closest being the red dwarf Proxima Centauri at approximately 4.2 light-years), the Sun ranks fourth in mass.[144]
+
+The Sun orbits the center of the Milky Way, and it is presently moving in the direction of the constellation of Cygnus. A simple model of the motion of a star in the galaxy gives the galactic coordinates X, Y, and Z as:
+
+where U, V, and W are the respective velocities with respect to the local standard of rest, A and B are the Oort constants, 
+
+
+
+
+Ω
+
+0
+
+
+=
+A
+−
+B
+
+
+{\displaystyle \Omega _{0}=A-B}
+
+ is the angular velocity of galactic rotation for the local standard of rest, 
+
+
+
+κ
+=
+
+
+−
+4
+
+Ω
+
+0
+
+
+B
+
+
+
+
+{\displaystyle \kappa ={\sqrt {-4\Omega _{0}B}}}
+
+ is the "epicyclic frequency", and ν is the vertical oscillation frequency.[145] For the sun, the present values of U, V, and W are estimated as 
+
+
+
+(
+U
+(
+0
+)
+,
+V
+(
+0
+)
+,
+W
+(
+0
+)
+)
+=
+(
+10.00
+,
+5.25
+,
+7.17
+)
+
+
+{\displaystyle (U(0),V(0),W(0))=(10.00,5.25,7.17)}
+
+ km/s, and estimates for the other constants are A = 15.5 km/s/kpc, B = −12.2 km/s/kpc, κ = 37 km/s/kpc, and ν=74 km/s/kpc. We take X(0) and Y(0) to be zero and Z(0) is estimated to be 17 parsecs.[146] This model implies that the Sun circulates around a point that is itself going around the galaxy. The period of the Sun's circulation around the point is 
+
+
+
+2
+π
+
+/
+
+κ
+
+
+{\displaystyle 2\pi /\kappa }
+
+. which, using the equivalence that a parsec equals 1 km/s times 0.978 million years, comes to 166 million years, shorter than the time it takes for the point to go around the galaxy. In the (X, Y) coordinates, the Sun describes an ellipse around the point, whose length in the Y direction is
+
+and whose width in the X direction is
+
+The ratio of length to width of this ellipse, the same for all stars in our neighborhood, is 
+
+
+
+2
+Ω
+
+/
+
+κ
+≈
+1.50.
+
+
+{\displaystyle 2\Omega /\kappa \approx 1.50.}
+
+
+The moving point is presently at
+
+The oscillation in the Z direction takes the Sun
+
+above the galactic plane and the same distance below it, with a period of 
+
+
+
+2
+π
+
+/
+
+ν
+
+
+{\displaystyle 2\pi /\nu }
+
+ or 83 million years, approximately 2.7 times per orbit.[147] Although 
+
+
+
+2
+π
+
+/
+
+
+Ω
+
+0
+
+
+
+
+{\displaystyle 2\pi /\Omega _{0}}
+
+ is 222 million years, the value of 
+
+
+
+Ω
+
+
+{\displaystyle \Omega }
+
+ at the point around which the Sun circulates is
+
+(see Oort constants), corresponding to 235 million years, and this is the time that the point takes to go once around the galaxy. Other stars with the same value of 
+
+
+
+X
++
+V
+
+/
+
+(
+2
+B
+)
+
+
+{\displaystyle X+V/(2B)}
+
+ have to take the same amount of time to go around the galaxy as the sun and thus remain in the same general vicinity as the Sun.
+
+The Sun's orbit around the Milky Way is perturbed due to the non-uniform mass distribution in Milky Way, such as that in and between the galactic spiral arms. It has been argued that the Sun's passage through the higher density spiral arms often coincides with mass extinctions on Earth, perhaps due to increased impact events.[148] It takes the Solar System about 225–250 million years to complete one orbit through the Milky Way (a galactic year),[149] so it is thought to have completed 20–25 orbits during the lifetime of the Sun. The orbital speed of the Solar System about the center of the Milky Way is approximately 251 km/s (156 mi/s).[150] At this speed, it takes around 1,190 years for the Solar System to travel a distance of 1 light-year, or 7 days to travel 1 AU.[151]
+
+The Milky Way is moving with respect to the cosmic microwave background radiation (CMB) in the direction of the constellation Hydra with a speed of 550 km/s, and the Sun's resultant velocity with respect to the CMB is about 370 km/s in the direction of Crater or Leo.[152]
+
+The Sun is moved by the gravitational pull of the planets. One can think of the barycentre of the Solar System as being stationary (or as moving in a steady motion around the galaxy). The centre of the sun is always within 2.2 solar radii of the barycentre. This motion of the Sun is mainly due to Jupiter, Saturn, Uranus, and Neptune. For some periods of several decades, the motion is rather regular, forming a trefoil pattern, whereas between these periods it appears more chaotic.[153] After 179 years (nine times the synodic period of Jupiter and Saturn) the pattern more or less repeats, but rotated by about 24°.[154] The orbits of the inner planets, including of the Earth, are similarly displaced by the same graviational forces, so the movement of the Sun has little effect on the relative positions of the Earth and the Sun or on solar irradiance on the Earth as a function of time.[155]
+
+The temperature of the photosphere is approximately 6,000 K, whereas the temperature of the corona reaches 1000000–2000000 K.[91] The high temperature of the corona shows that it is heated by something other than direct heat conduction from the photosphere.[93]
+
+It is thought that the energy necessary to heat the corona is provided by turbulent motion in the convection zone below the photosphere, and two main mechanisms have been proposed to explain coronal heating.[91] The first is wave heating, in which sound, gravitational or magnetohydrodynamic waves are produced by turbulence in the convection zone.[91] These waves travel upward and dissipate in the corona, depositing their energy in the ambient matter in the form of heat.[156] The other is magnetic heating, in which magnetic energy is continuously built up by photospheric motion and released through magnetic reconnection in the form of large solar flares and myriad similar but smaller events—nanoflares.[157]
+
+Currently, it is unclear whether waves are an efficient heating mechanism. All waves except Alfvén waves have been found to dissipate or refract before reaching the corona.[158] In addition, Alfvén waves do not easily dissipate in the corona. Current research focus has therefore shifted towards flare heating mechanisms.[91]
+
+Theoretical models of the Sun's development suggest that 3.8 to 2.5 billion years ago, during the Archean eon, the Sun was only about 75% as bright as it is today. Such a weak star would not have been able to sustain liquid water on Earth's surface, and thus life should not have been able to develop. However, the geological record demonstrates that Earth has remained at a fairly constant temperature throughout its history, and that the young Earth was somewhat warmer than it is today. One theory among scientists is that the atmosphere of the young Earth contained much larger quantities of greenhouse gases (such as carbon dioxide, methane) than are present today, which trapped enough heat to compensate for the smaller amount of solar energy reaching it.[159]
+
+However, examination of Archaean sediments appears inconsistent with the hypothesis of high greenhouse concentrations. Instead, the moderate temperature range may be explained by a lower surface albedo brought about by less continental area and the "lack of biologically induced cloud condensation nuclei". This would have led to increased absorption of solar energy, thereby compensating for the lower solar output.[160]
+
+The enormous effect of the Sun on Earth has been recognized since prehistoric times, and the Sun has been regarded by some cultures as a solar deity.
+
+The Sun has been an object of veneration in many cultures throughout human history. Humanity's most fundamental understanding of the Sun is as the luminous disk in the sky, whose presence above the horizon creates day and whose absence causes night. In many prehistoric and ancient cultures, the Sun was thought to be a solar deity or other supernatural entity. Worship of the Sun was central to civilizations such as the ancient Egyptians, the Inca of South America and the Aztecs of what is now Mexico. In religions such as Hinduism, the Sun is still considered a god. Many ancient monuments were constructed with solar phenomena in mind; for example, stone megaliths accurately mark the summer or winter solstice (some of the most prominent megaliths are located in Nabta Playa, Egypt; Mnajdra, Malta and at Stonehenge, England); Newgrange, a prehistoric human-built mount in Ireland, was designed to detect the winter solstice; the pyramid of El Castillo at Chichén Itzá in Mexico is designed to cast shadows in the shape of serpents climbing the pyramid at the vernal and autumnal equinoxes.
+
+The Egyptians portrayed the god Ra as being carried across the sky in a solar barque, accompanied by lesser gods, and to the Greeks, he was Helios, carried by a chariot drawn by fiery horses. From the reign of Elagabalus in the late Roman Empire the Sun's birthday was a holiday celebrated as Sol Invictus (literally "Unconquered Sun") soon after the winter solstice, which may have been an antecedent to Christmas. Regarding the fixed stars, the Sun appears from Earth to revolve once a year along the ecliptic through the zodiac, and so Greek astronomers categorized it as one of the seven planets (Greek planetes, "wanderer"); the naming of the days of the weeks after the seven planets dates to the Roman era.[161][162][163]
+
+In the early first millennium BC, Babylonian astronomers observed that the Sun's motion along the ecliptic is not uniform, though they did not know why; it is today known that this is due to the movement of Earth in an elliptic orbit around the Sun, with Earth moving faster when it is nearer to the Sun at perihelion and moving slower when it is farther away at aphelion.[164]
+
+One of the first people to offer a scientific or philosophical explanation for the Sun was the Greek philosopher Anaxagoras. He reasoned that it was not the chariot of Helios, but instead a giant flaming ball of metal even larger than the land of the Peloponnesus and that the Moon reflected the light of the Sun.[165] For teaching this heresy, he was imprisoned by the authorities and sentenced to death, though he was later released through the intervention of Pericles. Eratosthenes estimated the distance between Earth and the Sun in the 3rd century BC as "of stadia myriads 400 and 80000", the translation of which is ambiguous, implying either 4,080,000 stadia (755,000 km) or 804,000,000 stadia (148 to 153 million kilometers or 0.99 to 1.02 AU); the latter value is correct to within a few percent. In the 1st century AD, Ptolemy estimated the distance as 1,210 times the radius of Earth, approximately 7.71 million kilometers (0.0515 AU).[166]
+
+The theory that the Sun is the center around which the planets orbit was first proposed by the ancient Greek Aristarchus of Samos in the 3rd century BC, and later adopted by Seleucus of Seleucia (see Heliocentrism). This view was developed in a more detailed mathematical model of a heliocentric system in the 16th century by Nicolaus Copernicus.
+
+Observations of sunspots were recorded during the Han Dynasty (206 BC–AD 220) by Chinese astronomers, who maintained records of these observations for centuries. Averroes also provided a description of sunspots in the 12th century.[167] The invention of the telescope in the early 17th century permitted detailed observations of sunspots by Thomas Harriot, Galileo Galilei and other astronomers. Galileo posited that sunspots were on the surface of the Sun rather than small objects passing between Earth and the Sun.[168]
+
+Arabic astronomical contributions include Al-Battani's discovery that the direction of the Sun's apogee (the place in the Sun's orbit against the fixed stars where it seems to be moving slowest) is changing.[169] (In modern heliocentric terms, this is caused by a gradual motion of the aphelion of the Earth's orbit). Ibn Yunus observed more than 10,000 entries for the Sun's position for many years using a large astrolabe.[170]
+
+From an observation of a transit of Venus in 1032, the Persian astronomer and polymath Ibn Sina concluded that Venus is closer to Earth than the Sun.[171] In 1672 Giovanni Cassini and Jean Richer determined the distance to Mars and were thereby able to calculate the distance to the Sun.
+
+In 1666, Isaac Newton observed the Sun's light using a prism, and showed that it is made up of light of many colors.[172] In 1800, William Herschel discovered infrared radiation beyond the red part of the solar spectrum.[173] The 19th century saw advancement in spectroscopic studies of the Sun; Joseph von Fraunhofer recorded more than 600 absorption lines in the spectrum, the strongest of which are still often referred to as Fraunhofer lines. In the early years of the modern scientific era, the source of the Sun's energy was a significant puzzle. Lord Kelvin suggested that the Sun is a gradually cooling liquid body that is radiating an internal store of heat.[174] Kelvin and Hermann von Helmholtz then proposed a gravitational contraction mechanism to explain the energy output, but the resulting age estimate was only 20 million years, well short of the time span of at least 300 million years suggested by some geological discoveries of that time.[174][175] In 1890 Joseph Lockyer, who discovered helium in the solar spectrum, proposed a meteoritic hypothesis for the formation and evolution of the Sun.[176]
+
+Not until 1904 was a documented solution offered. Ernest Rutherford suggested that the Sun's output could be maintained by an internal source of heat, and suggested radioactive decay as the source.[177] However, it would be Albert Einstein who would provide the essential clue to the source of the Sun's energy output with his mass–energy equivalence relation E = mc2.[178] In 1920, Sir Arthur Eddington proposed that the pressures and temperatures at the core of the Sun could produce a nuclear fusion reaction that merged hydrogen (protons) into helium nuclei, resulting in a production of energy from the net change in mass.[179] The preponderance of hydrogen in the Sun was confirmed in 1925 by Cecilia Payne using the ionization theory developed by Meghnad Saha. The theoretical concept of fusion was developed in the 1930s by the astrophysicists Subrahmanyan Chandrasekhar and Hans Bethe. Hans Bethe calculated the details of the two main energy-producing nuclear reactions that power the Sun.[180][181] In 1957, Margaret Burbidge, Geoffrey Burbidge, William Fowler and Fred Hoyle showed that most of the elements in the universe have been synthesized by nuclear reactions inside stars, some like the Sun.[182]
+
+The first satellites designed for long term observation of the Sun from interplanetary space were NASA's Pioneers 6, 7, 8 and 9, which were launched between 1959 and 1968. These probes orbited the Sun at a distance similar to that of Earth, and made the first detailed measurements of the solar wind and the solar magnetic field. Pioneer 9 operated for a particularly long time, transmitting data until May 1983.[184][185]
+
+In the 1970s, two Helios spacecraft and the Skylab Apollo Telescope Mount provided scientists with significant new data on solar wind and the solar corona. The Helios 1 and 2 probes were U.S.–German collaborations that studied the solar wind from an orbit carrying the spacecraft inside Mercury's orbit at perihelion.[186] The Skylab space station, launched by NASA in 1973, included a solar observatory module called the Apollo Telescope Mount that was operated by astronauts resident on the station.[92] Skylab made the first time-resolved observations of the solar transition region and of ultraviolet emissions from the solar corona.[92] Discoveries included the first observations of coronal mass ejections, then called "coronal transients", and of coronal holes, now known to be intimately associated with the solar wind.[186]
+
+In 1980, the Solar Maximum Mission was launched by NASA. This spacecraft was designed to observe gamma rays, X-rays and UV radiation from solar flares during a time of high solar activity and solar luminosity. Just a few months after launch, however, an electronics failure caused the probe to go into standby mode, and it spent the next three years in this inactive state. In 1984 Space Shuttle Challenger mission STS-41C retrieved the satellite and repaired its electronics before re-releasing it into orbit. The Solar Maximum Mission subsequently acquired thousands of images of the solar corona before re-entering Earth's atmosphere in June 1989.[187]
+
+Launched in 1991, Japan's Yohkoh (Sunbeam) satellite observed solar flares at X-ray wavelengths. Mission data allowed scientists to identify several different types of flares, and demonstrated that the corona away from regions of peak activity was much more dynamic and active than had previously been supposed. Yohkoh observed an entire solar cycle but went into standby mode when an annular eclipse in 2001 caused it to lose its lock on the Sun. It was destroyed by atmospheric re-entry in 2005.[188]
+
+One of the most important solar missions to date has been the Solar and Heliospheric Observatory, jointly built by the European Space Agency and NASA and launched on 2 December 1995.[92] Originally intended to serve a two-year mission, a mission extension through 2012 was approved in October 2009.[189] It has proven so useful that a follow-on mission, the Solar Dynamics Observatory (SDO), was launched in February 2010.[190] Situated at the Lagrangian point between Earth and the Sun (at which the gravitational pull from both is equal), SOHO has provided a constant view of the Sun at many wavelengths since its launch.[92] Besides its direct solar observation, SOHO has enabled the discovery of a large number of comets, mostly tiny sungrazing comets that incinerate as they pass the Sun.[191]
+
+All these satellites have observed the Sun from the plane of the ecliptic, and so have only observed its equatorial regions in detail. The Ulysses probe was launched in 1990 to study the Sun's polar regions. It first traveled to Jupiter, to "slingshot" into an orbit that would take it far above the plane of the ecliptic. Once Ulysses was in its scheduled orbit, it began observing the solar wind and magnetic field strength at high solar latitudes, finding that the solar wind from high latitudes was moving at about 750 km/s, which was slower than expected, and that there were large magnetic waves emerging from high latitudes that scattered galactic cosmic rays.[192]
+
+Elemental abundances in the photosphere are well known from spectroscopic studies, but the composition of the interior of the Sun is more poorly understood. A solar wind sample return mission, Genesis, was designed to allow astronomers to directly measure the composition of solar material.[193]
+
+The Solar Terrestrial Relations Observatory (STEREO) mission was launched in October 2006. Two identical spacecraft were launched into orbits that cause them to (respectively) pull further ahead of and fall gradually behind Earth. This enables stereoscopic imaging of the Sun and solar phenomena, such as coronal mass ejections.[194][195]
+
+The Parker Solar Probe was launched in 2018 aboard a Delta IV Heavy rocket and will reach a perigee of 0.046 AU in 2025, making it the closest-orbiting manmade satellite as the first spacecraft to fly low into the solar corona.[196]
+
+The Indian Space Research Organisation has scheduled the launch of a 100 kg satellite named Aditya for mid 2020. Its main instrument will be a coronagraph for studying the dynamics of the solar corona.[197]
+
+The brightness of the Sun can cause pain from looking at it with the naked eye; however, doing so for brief periods is not hazardous for normal non-dilated eyes.[198][199] Looking directly at the Sun causes phosphene visual artifacts and temporary partial blindness. It also delivers about 4 milliwatts of sunlight to the retina, slightly heating it and potentially causing damage in eyes that cannot respond properly to the brightness.[200][201] UV exposure gradually yellows the lens of the eye over a period of years, and is thought to contribute to the formation of cataracts, but this depends on general exposure to solar UV, and not whether one looks directly at the Sun.[202] Long-duration viewing of the direct Sun with the naked eye can begin to cause UV-induced, sunburn-like lesions on the retina after about 100 seconds, particularly under conditions where the UV light from the Sun is intense and well focused;[203][204] conditions are worsened by young eyes or new lens implants (which admit more UV than aging natural eyes), Sun angles near the zenith, and observing locations at high altitude.
+
+Viewing the Sun through light-concentrating optics such as binoculars may result in permanent damage to the retina without an appropriate filter that blocks UV and substantially dims the sunlight. When using an attenuating filter to view the Sun, the viewer is cautioned to use a filter specifically designed for that use. Some improvised filters that pass UV or IR rays, can actually harm the eye at high brightness levels.[205]
+Herschel wedges, also called Solar Diagonals, are effective and inexpensive for small telescopes. The sunlight that is destined for the eyepiece is reflected from an unsilvered surface of a piece of glass. Only a very small fraction of the incident light is reflected. The rest passes through the glass and leaves the instrument. If the glass breaks because of the heat, no light at all is reflected, making the device fail-safe. Simple filters made of darkened glass allow the full intensity of sunlight to pass through if they break, endangering the observer's eyesight. Unfiltered binoculars can deliver hundreds of times as much energy as using the naked eye, possibly causing immediate damage. It is claimed that even brief glances at the midday Sun through an unfiltered telescope can cause permanent damage.[206]
+
+Partial solar eclipses are hazardous to view because the eye's pupil is not adapted to the unusually high visual contrast: the pupil dilates according to the total amount of light in the field of view, not by the brightest object in the field. During partial eclipses most sunlight is blocked by the Moon passing in front of the Sun, but the uncovered parts of the photosphere have the same surface brightness as during a normal day. In the overall gloom, the pupil expands from ~2 mm to ~6 mm, and each retinal cell exposed to the solar image receives up to ten times more light than it would looking at the non-eclipsed Sun. This can damage or kill those cells, resulting in small permanent blind spots for the viewer.[207] The hazard is insidious for inexperienced observers and for children, because there is no perception of pain: it is not immediately obvious that one's vision is being destroyed.
+
+During sunrise and sunset, sunlight is attenuated because of Rayleigh scattering and Mie scattering from a particularly long passage through Earth's atmosphere,[208] and the Sun is sometimes faint enough to be viewed comfortably with the naked eye or safely with optics (provided there is no risk of bright sunlight suddenly appearing through a break between clouds). Hazy conditions, atmospheric dust, and high humidity contribute to this atmospheric attenuation.[209]
+
+An optical phenomenon, known as a green flash, can sometimes be seen shortly after sunset or before sunrise. The flash is caused by light from the Sun just below the horizon being bent (usually through a temperature inversion) towards the observer. Light of shorter wavelengths (violet, blue, green) is bent more than that of longer wavelengths (yellow, orange, red) but the violet and blue light is scattered more, leaving light that is perceived as green.[210]
+
+Ultraviolet light from the Sun has antiseptic properties and can be used to sanitize tools and water. It also causes sunburn, and has other biological effects such as the production of vitamin D and sun tanning. It is also the main cause of skin cancer. Ultraviolet light is strongly attenuated by Earth's ozone layer, so that the amount of UV varies greatly with latitude and has been partially responsible for many biological adaptations, including variations in human skin color in different regions of the Earth.[211]
+
+The Sun has eight known planets. This includes four terrestrial planets (Mercury, Venus, Earth, and Mars), two gas giants (Jupiter and Saturn), and two ice giants (Uranus and Neptune). The Solar System also has at least five dwarf planets, an asteroid belt, numerous comets, and a large number of icy bodies which lie beyond the orbit of Neptune.
+
+Solar deities play a major role in many world religions and mythologies.[212] The ancient Sumerians believed that the sun was Utu,[213][214] the god of justice and twin brother of Inanna, the Queen of Heaven,[213] who was identified as the planet Venus.[214] Later, Utu was identified with the East Semitic god Shamash.[213][214] Utu was regarded as a helper-deity, who aided those in distress,[213] and, in iconography, he is usually portrayed with a long beard and clutching a saw,[213] which represented his role as the dispenser of justice.[213]
+
+From at least the Fourth Dynasty of Ancient Egypt, the Sun was worshipped as the god Ra, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the New Empire period, the Sun became identified with the dung beetle, whose spherical ball of dung was identified with the Sun. In the form of the sun disc Aten, the Sun had a brief resurgence during the Amarna Period when it again became the preeminent, if not only, divinity for the Pharaoh Akhenaton.[215][216]
+
+In Proto-Indo-European religion, the Sun was personified as the goddess *Seh2ul.[217][218] Derivatives of this goddess in Indo-European languages include the Old Norse Sól, Sanskrit Surya, Gaulish Sulis, Lithuanian Saulė, and Slavic Solntse.[218] In ancient Greek religion, the sun deity was the male god Helios,[219] but traces of an earlier female solar deity are preserved in Helen of Troy.[219] In later times, Helios was syncretized with Apollo.[220]
+
+In the Bible, Malachi 4:2 mentions the "Sun of Righteousness" (sometimes translated as the "Sun of Justice"),[221] which some Christians have interpreted as a reference to the Messiah (Christ).[222] In ancient Roman culture, Sunday was the day of the sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background. The symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions. In paganism, the Sun was a source of life, giving warmth and illumination to mankind. It was the center of a popular cult among Romans, who would stand at dawn to catch the first rays of sunshine as they prayed. The celebration of the winter solstice (which influenced Christmas) was part of the Roman cult of the unconquered Sun (Sol Invictus). Christian churches were built with an orientation so that the congregation faced toward the sunrise in the East.[223]
+
+Tonatiuh, the Aztec god of the sun, was usually depicted holding arrows and a shield[224] and was closely associated with the practice of human sacrifice.[224] The sun goddess Amaterasu is the most important deity in the Shinto religion,[225][226] and she is believed to be the direct ancestor of all Japanese emperors.[225]
+
+Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Observable universe → UniverseEach arrow (→) may be read as "within" or "part of".

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+A bone is a rigid organ that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and enable mobility. Bones come in a variety of shapes and sizes and have a complex internal and external structure. They are lightweight yet strong and hard, and serve multiple functions.
+
+Bone tissue (osseous tissue) is a hard tissue, a type of dense connective tissue.  It has a honeycomb-like matrix internally, which helps to give the bone rigidity.  Bone tissue is made up of different types of bone cells. Osteoblasts and osteocytes are involved in the formation and mineralization of bone; osteoclasts are involved in the resorption of bone tissue. Modified (flattened) osteoblasts become the lining cells that form a protective layer on the bone surface. The mineralised matrix of bone tissue has an organic component of mainly collagen called ossein and an inorganic component of bone mineral made up of various salts. Bone tissue is a mineralized tissue of two types, cortical bone and cancellous bone. Other types of tissue found in bones include bone marrow, endosteum, periosteum, nerves, blood vessels and cartilage.
+
+In the human body at birth, there are approximately 270 bones present; many of these fuse together during development, leaving a total of 206 separate bones in the adult, not counting numerous small sesamoid bones.[1][2] The largest bone in the body is the femur or thigh-bone, and the smallest is the stapes in the middle ear.
+
+The Greek word for bone is ὀστέον ("osteon"), hence the many terms that use it as a prefix—such as osteopathy.
+
+Bone is not uniformly solid, but consists of a flexible matrix (about 30%) and bound minerals (about 70%) which are intricately woven and endlessly remodeled by a group of specialized bone cells. Their unique composition and design allows bones to be relatively hard and strong, while remaining lightweight.
+
+Bone matrix is 90 to 95% composed of elastic collagen fibers, also known as ossein,[3] and the remainder is ground substance.[4] The elasticity of collagen improves fracture resistance.[5] The matrix is hardened by the binding of inorganic mineral salt, calcium phosphate, in a chemical arrangement known as calcium hydroxylapatite. It is the bone mineralization that give bones rigidity.
+
+Bone is actively constructed and remodeled throughout life by special bone cells known as osteoblasts and osteoclasts. Within any single bone, the tissue is woven into two main patterns, known as cortical and cancellous bone, and each with different appearance and characteristics.
+
+The hard outer layer of bones is composed of cortical bone, which is also called compact bone as it is much denser than cancellous bone. It forms the hard exterior (cortex) of bones. The cortical bone gives bone its smooth, white, and solid appearance, and accounts for 80% of the total bone mass of an adult human skeleton.[6] It facilitates bone's main functions - to support the whole body, to protect organs, to provide levers for movement, and to store and release chemical elements, mainly calcium. It consists of multiple microscopic columns, each called an osteon or Haversian system. Each column is multiple layers of osteoblasts and osteocytes around a central canal called the haversian canal. Volkmann's canals at right angles connect the osteons together. The columns are metabolically active, and as bone is reabsorbed and created the nature and location of the cells within the osteon will change. Cortical bone is covered by a periosteum on its outer surface, and an endosteum on its inner surface. The endosteum is the boundary between the cortical bone and the cancellous bone.[7] The primary anatomical and functional unit of cortical bone is the osteon.
+
+Cancellous bone, also called trabecular or spongy bone,[7] is the internal tissue of the skeletal bone and is an open cell porous network. Cancellous bone has a higher surface-area-to-volume ratio than cortical bone and it is less dense. This makes it weaker and more flexible. The greater surface area also makes it suitable for metabolic activities such as the exchange of calcium ions. Cancellous bone is typically found at the ends of long bones, near joints and in the interior of vertebrae. Cancellous bone is highly vascular and often contains red bone marrow where hematopoiesis, the production of blood cells, occurs. The primary anatomical and functional unit of cancellous bone is the trabecula. The trabeculae are aligned towards the mechanical load distribution that a bone experiences within long bones such as the femur.  As far as short bones are concerned, trabecular alignment has been studied in the vertebral pedicle.[8] Thin formations of osteoblasts covered in endosteum create an irregular network of spaces,[9] known as trabeculae. Within these spaces are bone marrow and hematopoietic stem cells that give rise to platelets, red blood cells and white blood cells.[9] Trabecular marrow is composed of a network of rod- and plate-like elements that make the overall organ lighter and allow room for blood vessels and marrow. Trabecular bone accounts for the remaining 20% of total bone mass but has nearly ten times the surface area of compact bone.[10]
+
+The words cancellous and trabecular refer to the tiny lattice-shaped units (trabeculae) that form the tissue. It was first illustrated accurately in the engravings of Crisóstomo Martinez.[11]
+
+Bone marrow, also known as myeloid tissue in red bone marrow, can be found in almost any bone that holds cancellous tissue.  In newborns, all such bones are filled exclusively with red marrow or hematopoietic marrow, but as the child ages the hematopoietic fraction decreases in quantity and the fatty/ yellow fraction called marrow adipose tissue (MAT) increases in quantity.  In adults, red marrow is mostly found in the bone marrow of the femur, the ribs, the vertebrae and pelvic bones.[12]
+
+Bone is a metabolically active tissue composed of several types of cells. These cells include osteoblasts, which are involved in the creation and mineralization of bone tissue, osteocytes, and osteoclasts, which are involved in the reabsorption of bone tissue. Osteoblasts and osteocytes are derived from osteoprogenitor cells, but osteoclasts are derived from the same cells that differentiate to form macrophages and monocytes.[13] Within the marrow of the bone there are also hematopoietic stem cells. These cells give rise to other cells, including white blood cells, red blood cells, and platelets.[14]
+
+Osteoblasts are mononucleate bone-forming cells. They are located on the surface of osteon seams and make a protein mixture known as osteoid, which mineralizes to become bone.[15] The osteoid seam is a narrow region of newly formed organic matrix, not yet mineralized, located on the surface of a bone. Osteoid is primarily composed of Type I collagen. Osteoblasts also manufacture hormones, such as prostaglandins, to act on the bone itself. The osteoblast creates and repairs new bone by actually building around itself. First, the osteoblast puts up collagen fibers. These collagen fibers are used as a framework for the osteoblasts' work. The osteoblast then deposits calcium phosphate which is hardened by hydroxide and bicarbonate ions. The brand new bone created by the osteoblast is called osteoid.[16] Once the osteoblast is finished working it is actually trapped inside the bone once it hardens. When the osteoblast becomes trapped, it becomes known as an osteocyte.[17] Other osteoblasts remain on the top of the new bone and are used to protect the underlying bone, these become known as lining cells.
+
+Osteocytes are mostly inactive osteoblasts.[13] Osteocytes originate from osteoblasts that have migrated into and become trapped and surrounded by bone matrix that they themselves produced.[7] The spaces they occupy are known as lacunae. Osteocytes have many processes that reach out to meet osteoblasts and other osteocytes probably for the purposes of communication.[18] Osteocytes remain in contact with other cells in the bone through gap junctions—coupled cell processes—which pass through small channels in the bone matrix called the canaliculi.
+
+Osteoclasts are very large multinucleate cells that are responsible for the breakdown of bones by the process of bone resorption. New bone is then formed by the osteoblasts. Bone is constantly remodelled by the resorption of osteoclasts and created by osteoblasts.[13] Osteoclasts are large cells with multiple nuclei located on bone surfaces in what are called Howship's lacunae (or resorption pits). These lacunae are the result of surrounding bone tissue that has been reabsorbed.[19] Because the osteoclasts are derived from a monocyte stem-cell lineage, they are equipped with phagocytic-like mechanisms similar to circulating macrophages.[13] Osteoclasts mature and/or migrate to discrete bone surfaces. Upon arrival, active enzymes, such as tartrate resistant acid phosphatase, are secreted against the mineral substrate.[citation needed] The reabsorption of bone by osteoclasts also plays a role in calcium homeostasis.[19]
+
+Bones consist of living cells embedded in a mineralized organic matrix. This matrix consists of organic components, mainly type I collagen – "organic" referring to materials produced as a result of the human body – and inorganic components, primarily hydroxyapatite and other salts of calcium and phosphate. Above 30% of the acellular part of bone consists of the organic components, and 70% of salts.[20] The collagen fibers give bone its tensile strength, and the interspersed crystals of hydroxyapatite give bone its compressive strength. These effects are synergistic.[20]
+
+The inorganic composition of bone (bone mineral) is primarily formed from salts of calcium and phosphate, the major salt being hydroxyapatite (Ca10(PO4)6(OH)2).[20] The exact composition of the matrix may be subject to change over time due to nutrition and biomineralization, with the ratio of calcium to phosphate varying between 1.3 and 2.0 (per weight), and trace minerals such as magnesium, sodium, potassium and carbonate also being found.[20]
+
+Type I collagen composes 90–95% of the organic matrix, with remainder of the matrix being a homogenous liquid called ground substance consisting of proteoglycans such as hyaluronic acid and chondroitin sulfate,[20] as well as non-collagenous proteins such as osteocalcin, osteopontin or bone sialoprotein. Collagen consists of strands of repeating units, which give bone tensile strength, and are arranged in an overlapping fashion that prevents shear stress. The function of ground substance is not fully known.[20] Two types of bone can be identified microscopically according to the arrangement of collagen: woven and lamellar.
+
+Woven bone is produced when osteoblasts produce osteoid rapidly, which occurs initially in all fetal bones, but is later replaced by more resilient lamellar bone. In adults woven bone is created after fractures or in Paget's disease. Woven bone is weaker, with a smaller number of randomly oriented collagen fibers, but forms quickly; it is for this appearance of the fibrous matrix that the bone is termed woven. It is soon replaced by lamellar bone, which is highly organized in concentric sheets with a much lower proportion of osteocytes to surrounding tissue. Lamellar bone, which makes its first appearance in humans in the fetus during the third trimester,[22] is stronger and filled with many collagen fibers parallel to other fibers in the same layer (these parallel columns are called osteons).  In cross-section, the fibers run in opposite directions in alternating layers, much like in plywood, assisting in the bone's ability to resist torsion forces. After a fracture, woven bone forms initially and is gradually replaced by lamellar bone during a process known as "bony substitution." Compared to woven bone, lamellar bone formation takes place more slowly. The orderly deposition of collagen fibers restricts the formation of osteoid to about 1 to 2 µm per day. Lamellar bone also requires a relatively flat surface to lay the collagen fibers in parallel or concentric layers.[23]
+
+The extracellular matrix of bone is laid down by osteoblasts, which secrete both collagen and ground substance. These synthesise collagen within the cell, and then secrete collagen fibrils. The collagen fibers rapidly polymerise to form collagen strands. At this stage they are not yet mineralised, and are called "osteoid". Around the strands calcium and phosphate precipitate on the surface of these strands, within days to weeks becoming crystals of hydroxyapatite.[20]
+
+In order to mineralise the bone, the osteoblasts secrete vesicles containing alkaline phosphatase. This cleaves the phosphate groups and acts as the foci for calcium and phosphate deposition. The vesicles then rupture and act as a centre for crystals to grow on. More particularly, bone mineral is formed from globular and plate structures.[24][25]
+
+There are five types of bones in the human body: long, short, flat, irregular, and sesamoid.[26]
+
+In the study of anatomy, anatomists use a number of anatomical terms to describe the appearance, shape and function of bones. Other anatomical terms are also used to describe the location of bones. Like other anatomical terms, many of these derive from Latin and Greek. Some anatomists still use Latin to refer to bones. The term "osseous", and the prefix "osteo-", referring to things related to bone, are still used commonly today.
+
+Some examples of terms used to describe bones include the term "foramen" to describe a hole through which something passes, and a "canal" or "meatus" to describe a tunnel-like structure. A protrusion from a bone can be called a number of terms, including a "condyle", "crest", "spine", "eminence", "tubercle" or "tuberosity", depending on the protrusion's shape and location. In general, long bones are said to have a "head", "neck", and "body".
+
+When two bones join together, they are said to "articulate". If the two bones have a fibrous connection and are relatively immobile, then the joint is called a "suture".
+
+The formation of bone is called ossification. During the fetal stage of development this occurs by two processes: intramembranous ossification and endochondral ossification.[31] Intramembranous ossification involves the formation of bone from connective tissue whereas endochondral ossification involves the formation of bone from cartilage.
+
+Intramembranous ossification mainly occurs during formation of the flat bones of the skull but also the mandible, maxilla, and clavicles; the bone is formed from connective tissue such as mesenchyme tissue rather than from cartilage. The process includes: the development of the ossification center, calcification, trabeculae formation and the development of the periosteum.[32]
+
+Endochondral ossification occurs in long bones and most other bones in the body; it involves the development of bone from cartilage. This process includes the development of a cartilage model, its growth and development, development of the primary and secondary ossification centers, and the formation of articular cartilage and the epiphyseal plates.[33]
+
+Endochondral ossification begins with points in the cartilage called "primary ossification centers." They mostly appear during fetal development, though a few short bones begin their primary ossification after birth. They are responsible for the formation of the diaphyses of long bones, short bones and certain parts of irregular bones. Secondary ossification occurs after birth, and forms the epiphyses of long bones and the extremities of irregular and flat bones. The diaphysis and both epiphyses of a long bone are separated by a growing zone of cartilage (the epiphyseal plate). At skeletal maturity (18 to 25 years of age), all of the cartilage is replaced by bone, fusing the diaphysis and both epiphyses together (epiphyseal closure).[34] In the upper limbs, only the diaphyses of the long bones and scapula are ossified. The epiphyses, carpal bones, coracoid process, medial border of the scapula, and acromion are still cartilaginous.[35]
+
+The following steps are followed in the conversion of cartilage to bone:
+
+Bones have a variety of functions:
+
+Bones serve a variety of mechanical functions. Together the bones in the body form the skeleton. They provide a frame to keep the body supported, and an attachment point for skeletal muscles, tendons, ligaments and joints, which function together to generate and transfer forces so that individual body parts or the whole body can be manipulated in three-dimensional space (the interaction between bone and muscle is studied in biomechanics).
+
+Bones protect internal organs, such as the skull protecting the brain or the ribs protecting the heart and lungs. Because of the way that bone is formed, bone has a high compressive strength of about 170 MPa (1800 kgf/cm²),[5] poor tensile strength of 104–121 MPa, and a very low shear stress strength (51.6 MPa).[37][38] This means that bone resists pushing (compressional) stress well, resist pulling (tensional) stress less well, but only poorly resists shear stress (such as due to torsional loads). While bone is essentially brittle, bone does have a significant degree of elasticity, contributed chiefly by collagen.
+
+Mechanically, bones also have a special role in hearing. The ossicles are three small bones in the middle ear which are involved in sound transduction.
+
+The cancellous part of bones contain bone marrow. Bone marrow produces blood cells in a process called hematopoiesis.[39] Blood cells that are created in bone marrow include red blood cells, platelets and white blood cells.[40] Progenitor cells such as the hematopoietic stem cell divide in a process called mitosis to produce precursor cells. These include precursors which eventually give rise to white blood cells, and erythroblasts which give rise to red blood cells.[41] Unlike red and white blood cells, created by mitosis, platelets are shed from very large cells called megakaryocytes.[42] This process of progressive differentiation occurs within the bone marrow. After the cells are matured, they enter the circulation.[43] Every day, over 2.5 billion red blood cells and platelets, and 50–100 billion granulocytes are produced in this way.[14]
+
+As well as creating cells, bone marrow is also one of the major sites where defective or aged red blood cells are destroyed.[14]
+
+°Determined by the species, age, and the type of bone, bone cells make up to 15 percent of the bone. Growth factor storage – mineralized bone matrix stores important growth factors such as insulin-like growth factors, transforming growth factor, bone morphogenetic proteins and others.[46]
+
+Bone is constantly being created and replaced in a process known as remodeling. This ongoing turnover of bone is a process of resorption followed by replacement of bone with little change in shape. This is accomplished through osteoblasts and osteoclasts. Cells are stimulated by a variety of signals, and together referred to as a remodeling unit. Approximately 10% of the skeletal mass of an adult is remodelled each year.[52] The purpose of remodeling is to regulate calcium homeostasis, repair microdamaged bones from everyday stress, and to shape the skeleton during growth.[citation needed] Repeated stress, such as weight-bearing exercise or bone healing, results in the bone thickening at the points of maximum stress (Wolff's law). It has been hypothesized that this is a result of bone's piezoelectric properties, which cause bone to generate small electrical potentials under stress.[53]
+
+The action of osteoblasts and osteoclasts are controlled by a number of chemical enzymes that either promote or inhibit the activity of the bone remodeling cells, controlling the rate at which bone is made, destroyed, or changed in shape. The cells also use paracrine signalling to control the activity of each other.[citation needed] For example, the rate at which osteoclasts resorb bone is inhibited by calcitonin and osteoprotegerin.  Calcitonin is produced by parafollicular cells in the thyroid gland, and can bind to receptors on osteoclasts to directly inhibit osteoclast activity. Osteoprotegerin is secreted by osteoblasts and is able to bind RANK-L, inhibiting osteoclast stimulation.[54]
+
+Osteoblasts can also be stimulated to increase bone mass through increased secretion of osteoid and by inhibiting the ability of osteoclasts to break down osseous tissue.[citation needed] Increased secretion of osteoid is stimulated by the secretion of growth hormone by the pituitary, thyroid hormone and the sex hormones (estrogens and androgens). These hormones also promote increased secretion of osteoprotegerin.[54] Osteoblasts can also be induced to secrete a number of cytokines that promote reabsorption of bone by stimulating osteoclast activity and differentiation from progenitor cells. Vitamin D, parathyroid hormone and stimulation from osteocytes induce osteoblasts to increase secretion of RANK-ligand and interleukin 6, which cytokines then stimulate increased reabsorption of bone by osteoclasts. These same compounds also increase secretion of macrophage colony-stimulating factor by osteoblasts, which promotes the differentiation of progenitor cells into osteoclasts, and decrease secretion of osteoprotegerin.[citation needed]
+
+Bone volume is determined by the rates of bone formation and bone resorption. Recent research has suggested that certain growth factors may work to locally alter bone formation by increasing osteoblast activity. Numerous bone-derived growth factors have been isolated and classified via bone cultures. These factors include insulin-like growth factors I and II, transforming growth factor-beta, fibroblast growth factor, platelet-derived growth factor, and bone morphogenetic proteins.[55] Evidence suggests that bone cells produce growth factors for extracellular storage in the bone matrix. The release of these growth factors from the bone matrix could cause the proliferation of osteoblast precursors. Essentially, bone growth factors may act as potential determinants of local bone formation.[55] Research has suggested that cancellous bone volume in postmenopausal osteoporosis may be determined by the relationship between the total bone forming surface and the percent of surface resorption.[56]
+
+A number of diseases can affect bone, including arthritis, fractures, infections, osteoporosis and tumours. Conditions relating to bone can be managed by a variety of doctors, including rheumatologists for joints, and orthopedic surgeons, who may conduct surgery to fix broken bones. Other doctors, such as rehabilitation specialists may be involved in recovery, radiologists in interpreting the findings on imaging, and pathologists in investigating the cause of the disease, and family doctors may play a role in preventing complications of bone disease such as osteoporosis.
+
+When a doctor sees a patient, a history and exam will be taken. Bones are then often imaged, called radiography. This might include ultrasound X-ray, CT scan, MRI scan and other imaging such as a Bone scan, which may be used to investigate cancer.[57] Other tests such as a blood test for autoimmune markers may be taken, or a synovial fluid aspirate may be taken.[57]
+
+In normal bone, fractures occur when there is significant force applied, or repetitive trauma over a long time. Fractures can also occur when a bone is weakened, such as with osteoporosis, or when there is a structural problem, such as when the bone remodels excessively (such as Paget's disease) or is the site of the growth of cancer.[58] Common fractures include wrist fractures and hip fractures, associated with osteoporosis, vertebral fractures associated with high-energy trauma and cancer, and fractures of long-bones. Not all fractures are painful.[58] When serious, depending on the fractures type and location, complications may include flail chest, compartment syndromes or fat embolism.
+Compound fractures involve the bone's penetration through the skin. Some complex fractures can be treated by the use of bone grafting procedures that replace missing bone portions.
+
+Fractures and their underlying causes can be investigated by X-rays, CT scans and MRIs.[58] Fractures are described by their location and shape, and several classification systems exist, depending on the location of the fracture. A common long bone fracture in children is a Salter–Harris fracture.[59] When fractures are managed, pain relief is often given, and the fractured area is often immobilised. This is to promote bone healing. In addition, surgical measures such as internal fixation may be used. Because of the immobilisation, people with fractures are often advised to undergo rehabilitation.[58]
+
+There are several types of tumour that can affect bone; examples of benign bone tumours include osteoma, osteoid osteoma, osteochondroma, osteoblastoma, enchondroma, giant cell tumour of bone, and aneurysmal bone cyst.[60]
+
+Cancer can arise in bone tissue, and bones are also a common site for other cancers to spread (metastasise) to.[61] Cancers that arise in bone are called "primary" cancers, although such cancers are rare.[61] Metastases within bone are "secondary" cancers, with the most common being breast cancer, lung cancer, prostate cancer, thyroid cancer, and kidney cancer.[61] Secondary cancers that affect bone can either destroy bone (called a "lytic" cancer) or create bone (a "sclerotic" cancer). Cancers of the bone marrow inside the bone can also affect bone tissue, examples including leukemia and multiple myeloma. Bone may also be affected by cancers in other parts of the body. Cancers in other parts of the body may release parathyroid hormone or parathyroid hormone-related peptide. This increases bone reabsorption, and can lead to bone fractures.
+
+Bone tissue that is destroyed or altered as a result of cancers is distorted, weakened, and more prone to fracture. This may lead to compression of the spinal cord, destruction of the marrow resulting in bruising, bleeding and immunosuppression, and is one cause of bone pain. If the cancer is metastatic, then there might be other symptoms depending on the site of the original cancer. Some bone cancers can also be felt.
+
+Cancers of the bone are managed according to their type, their stage, prognosis, and what symptoms they cause. Many primary cancers of bone are treated with radiotherapy. Cancers of bone marrow may be treated with chemotherapy, and other forms of targeted therapy such as immunotherapy may be used.[62] Palliative care, which focuses on maximising a person's quality of life, may play a role in management, particularly if the likelihood of survival within five years is poor.
+
+Osteoporosis is a disease of bone where there is reduced bone mineral density, increasing the likelihood of fractures.[63]  Osteoporosis is defined in women by the World Health Organization as a bone mineral density of 2.5 standard deviations below peak bone mass, relative to the age and sex-matched average. This density is measured using dual energy X-ray absorptiometry (DEXA), with the term "established osteoporosis" including the presence of a fragility fracture.[64] Osteoporosis is most common in women after menopause, when it is called "postmenopausal osteoporosis", but may develop in men and premenopausal women in the presence of particular hormonal disorders and other chronic diseases or as a result of smoking and medications, specifically glucocorticoids.[63] Osteoporosis usually has no symptoms until a fracture occurs.[63] For this reason, DEXA scans are often done in people with one or more risk factors, who have developed osteoporosis and are at risk of fracture.[63]
+
+Osteoporosis treatment includes advice to stop smoking, decrease alcohol consumption, exercise regularly, and have a healthy diet. Calcium and trace mineral supplements may also be advised, as may Vitamin D. When medication is used, it may include bisphosphonates, Strontium ranelate, and hormone replacement therapy.[65]
+
+Osteopathic medicine is a school of medical thought originally developed based on the idea of the link between the musculoskeletal system and overall health, but now very similar to mainstream medicine. As of 2012[update], over 77,000 physicians in the United States are trained in osteopathic medical schools.[66]
+
+The study of bones and teeth is referred to as osteology. It is frequently used in anthropology, archeology and forensic science for a variety of tasks. This can include determining the nutritional, health, age or injury status of the individual the bones were taken from. Preparing fleshed bones for these types of studies can involve the process of maceration.
+
+Typically anthropologists and archeologists study bone tools made by Homo sapiens and Homo neanderthalensis.  Bones can serve a number of uses such as projectile points or artistic pigments, and can also be made from external bones such as antlers.
+
+Bird skeletons are very lightweight. Their bones are smaller and thinner, to aid flight. Among mammals, bats come closest to birds in terms of bone density, suggesting that small dense bones are a flight adaptation. Many bird bones have little marrow due to their being hollow.[67]
+
+A bird's beak is primarily made of bone as projections of the mandibles which are covered in keratin.
+
+A deer's antlers are composed of bone which is an unusual example of bone being outside the skin of the animal once the velvet is shed.[68]
+
+The extinct predatory fish Dunkleosteus had sharp edges of hard exposed bone along its jaws.[69][70]
+
+Many animals possess an exoskeleton that is not made of bone. These include insects and crustaceans.
+
+The proportion of cortical bone that is 80% in the human skeleton may be much lower in other animals, especially in marine mammals and marine turtles, or in various Mesozoic marine reptiles, such as ichthyosaurs,[71] among others.[72]
+
+Many animals, particularly herbivores, practice osteophagy – the eating of bones. This is presumably carried out in order to replenish lacking phosphate.
+
+Many bone diseases that affect humans also affect other vertebrates – an example of one disorder is skeletal fluorosis.
+
+Bones from slaughtered animals have a number of uses. In prehistoric times, they have been used for making bone tools.[73] They have further been used in bone carving, already important in prehistoric art, and also in modern time as crafting materials for buttons, beads, handles, bobbins, calculation aids, head nuts, dice, poker chips, pick-up sticks, ornaments, etc. A special genre is scrimshaw.[citation needed]
+
+Bone glue can be made by prolonged boiling of ground or cracked bones, followed by filtering and evaporation to thicken the resulting fluid. Historically once important, bone glue and other animal glues today have only a few specialized uses, such as in antiques restoration. Essentially the same process, with further refinement, thickening and drying, is used to make gelatin.
+
+Broth is made by simmering several ingredients for a long time, traditionally including bones.
+
+Bone char, a porous, black, granular material primarily used for filtration and also as a black pigment, is produced by charring mammal bones.
+
+Oracle bone script was a writing system used in Ancient China based on inscriptions in bones. Its name originates from oracle bones, which were mainly ox clavicle. The Ancient Chinese (mainly in the Shang Dynasty), would write their questions on the Oracle Bone, and burn the bone, and where the bone cracked would be the answer for the questions.
+
+To point the bone at someone is considered bad luck in some cultures, such as Australian aborigines, such as by the Kurdaitcha.
+
+The wishbones of fowl have been used for divination, and are still customarily used in a tradition to determine which one of two people pulling on either prong of the bone may make a wish.
+
+Various cultures throughout history have adopted the custom of shaping an infant's head by the practice of artificial cranial deformation.  A widely practised
+custom in China was that of foot binding to limit the normal growth of the foot.
+
+Cells in bone marrow
+
+Scanning electron microscope of bone at 100x magnification
+
+Structure detail of an animal bone

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+an enclaved country within the border of South Africa.
+
+Coordinates: 29°36′S 28°18′E / 29.6°S 28.3°E / -29.6; 28.3
+
+– in Africa (light blue & dark grey)– in the African Union (light blue)
+
+Lesotho (/ləˈsuːtuː/ (listen),[6] Sotho pronunciation: [lɪˈsʊːtʰʊ]), officially the Kingdom of Lesotho (Sotho: 'Muso oa Lesotho), is an enclaved country within the border of South Africa. Along with the Vatican City and San Marino, it is one of only three independent states completely surrounded by the territory of another country, and the only one outside the Italian peninsula that is not a microstate. Lesotho is just over 30,000 km2 (11,583 sq mi) and has a population of around 2 million. Its capital and largest city is Maseru. The official language is Sesotho.
+
+Lesotho was previously the British Crown Colony of Basutoland, but it declared independence from the United Kingdom on 4 October 1966. It is now a fully sovereign state and is a member of the United Nations, the Commonwealth of Nations, the African Union, and the Southern African Development Community (SADC). The name Lesotho roughly translates to "the land of the people who speak Sesotho".[7][8]
+
+The original inhabitants of the area now known as Lesotho were the San people. Examples of their rock art can be found in the mountains throughout the area.[9]
+
+Modern Lesotho, then called Basutoland, emerged as a single polity under King Moshoeshoe I in 1822. Moshoeshoe, a son of Mokhachane, a minor chief of the Bakoteli lineage, formed his own clan and became a chief around 1804. Between 1821 and 1823, he and his followers settled at the Butha-Buthe Mountain, joining with former adversaries in resistance against the Lifaqane associated with the reign of Shaka Zulu from 1818 to 1828.
+
+Further evolution of the state emerged from conflicts between British Empire and Dutch colonists leaving the Cape Colony following its seizure from the French-allied Dutch by the British in 1795, and also from the Orange River Sovereignty and subsequent Orange Free State. Missionaries Thomas Arbousset, Eugène Casalis and Constant Gosselin from the Paris Evangelical Missionary Society, invited by Moshoeshoe I, were placed at Morija, developing Sesotho orthography and printed works in the Sesotho language between 1837 and 1855. Casalis, acting as translator and providing advice on foreign affairs, helped set up diplomatic channels and acquire guns for use against the encroaching Europeans and the Griqua people.
+
+Trekboers from the Cape Colony arrived on the western borders of Basutoland and claimed rights to its land, the first of which being Jan de Winnaar, who settled in the Matlakeng area in May–June 1838. Incoming Boers attempted to colonise the land between the two rivers and even north of the Caledon, claiming that it had been abandoned by the Sotho people. Moshoeshoe subsequently signed a treaty with the British Governor of the Cape Colony, Sir George Thomas Napier, that annexed the Orange River Sovereignty where many Boers had settled. These outraged Boers were suppressed in a brief skirmish in 1848. In 1851, a British force was defeated by the Basotho army at Kolonyama, provoking an embarrassing war for the British. After repelling another British attack in 1852, Moshoeshoe sent an appeal to the British commander that settled the dispute diplomatically, and then defeated the Batlokoa in 1853.
+In 1854, the British pulled out of the region, and in 1858, Moshoeshoe fought a series of wars with the Boers in what is known as the Free State–Basotho War. As a result, Moshoeshoe lost a great portion of the western lowlands. The last war with the Boers ended in 1867 when Moshoeshoe appealed to Queen Victoria, who agreed to make Basutoland a British protectorate in 1868.
+
+In 1869, the British signed a treaty at Aliwal North with the Boers that defined the boundaries of Basutoland. This treaty effectively reduced Moshoeshoe's kingdom to half its previous size by ceding away its western territories.
+
+Following the cession in 1869, the British transferred functions from Moshoeshoe's capital in Thaba Bosiu to a police camp on the northwest border, Maseru, until eventually the administration of Basutoland was transferred to the Cape Colony in 1871. Moshoeshoe died on 11 March 1870, marking the end of the traditional era and the beginning of the colonial era of Basutoland. He was buried at Thaba Bosiu.
+
+In the early years of British rule between 1871 and 1884, Basutoland was treated similarly to other territories that had been forcibly annexed, much to the humiliation of the Basotho, leading to the Basuto Gun War in 1880-1881.[10][11]
+
+In 1884, Basutoland was restored as a protectorate with Maseru as its capital, but remained under direct rule by a governor, though effective internal power was wielded by traditional tribal chiefs.
+
+Basutoland gained its independence from Britain and became the Kingdom of Lesotho in 1966.[12]
+
+In January 1970, the ruling Basotho National Party (BNP) lost the first post-independence general elections, with 23 seats to the Basotho Congress Party's (BCP) 36. Prime Minister Leabua Jonathan refused to cede power to the BCP, instead declaring himself Tona Kholo (Sesotho: 'prime minister'), and imprisoning the BCP leadership.
+
+BCP began a rebellion and then received training in Libya for its Lesotho Liberation Army (LLA) under the pretense of being Azanian People's Liberation Army (APLA) soldiers of the Pan Africanist Congress (PAC). Deprived of arms and supplies by the Sibeko faction of the PAC in 1978, the 178-strong LLA was rescued from their Tanzanian base by the financial assistance of a Maoist PAC officer, but they launched the guerrilla war with only a handful of old weapons. The main force was defeated in northern Lesotho, and later guerrillas launched sporadic but usually ineffectual attacks. The campaign was severely compromised when BCP's leader, Ntsu Mokhehle, went to Pretoria. In the early 1980s, several Basotho who sympathised with the exiled BCP were threatened with death and attacked by the government of Leabua Jonathan. On 4 September 1981, the family of Benjamin Masilo was attacked. In the attack his 3-year-old grandson died. Exactly four days later, Edgar Mahlomola Motuba, the editor of the popular newspaper Leselinyana la Lesotho, was abducted from his home together with two friends and murdered.
+
+The BNP ruled from 1966 until January 1970. What later ensued was a de facto government led by Dr. Leabua Jonathan until 1986 when a military coup forced it out of office. The Transitional Military Council that came to power granted executive powers to King Moshoeshoe II, who was until then a ceremonial monarch. But in 1987 the King was forced into exile after coming up with a six-page memorandum on how he wanted the Lesotho's constitution to be, which would have given him more executive powers than the military government had originally agreed to. His son was installed as King Letsie III in his place.
+
+The chairman of the military junta, Major General Justin Metsing Lekhanya, was ousted in 1991 and replaced by Major General Elias Phisoana Ramaema, who handed over power to a democratically elected government of the BCP in 1993. Moshoeshoe II returned from exile in 1992 as an ordinary citizen. After the return to democratic government, King Letsie III tried unsuccessfully to persuade the BCP government to reinstate his father (Moshoeshoe II) as head of state.
+
+In August 1994, Letsie III staged a military-backed coup that deposed the BCP government, after the BCP government refused to reinstate his father, Moshoeshoe II, according to Lesotho's constitution. The new government did not receive full international recognition. Member states of the Southern African Development Community (SADC) engaged in negotiations to reinstate the BCP government. One of the conditions Letsie III put forward for this was that his father should be re-installed as head of state. After protracted negotiations, the BCP government was reinstated and Letsie III abdicated in favour of his father in 1995, but he ascended the throne again when Moshoeshoe II died at the age of fifty-seven in a supposed road accident, when his car plunged off a mountain road during the early hours of 15 January 1996. According to a government statement, Moshoeshoe had set out at 1 am to visit his cattle at Matsieng and was returning to Maseru through the Maluti Mountains when his car left the road.[13]
+
+In 1997, the ruling BCP split over leadership disputes. Prime Minister Ntsu Mokhehle formed a new party, the Lesotho Congress for Democracy (LCD), and was followed by a majority of members of parliament, which enabled him to form a new government. Pakalitha Mosisili succeeded Mokhehle as party leader and the LCD won the general elections in 1998. Although the elections were pronounced free and fair by local and international observers and a subsequent special commission appointed by SADC, the opposition political parties rejected the results.
+
+Opposition protests in the country intensified, culminating in a peaceful demonstration outside the royal palace in August 1998. Exact details of what followed are greatly disputed, both in Lesotho and South Africa. While the Botswana Defence Force troops were welcomed, tensions with South African National Defence Force troops were high, resulting in fighting. Incidences of sporadic rioting intensified when South African troops hoisted a South African flag over the Royal Palace. By the time the SADC forces withdrew in May 1999, much of the capital of Maseru lay in ruins, and the southern provincial capital towns of Mafeteng and Mohale's Hoek had lost over a third of their commercial real estate. A significant number of South Africans and Basotho also died in the fighting.
+
+An Interim Political Authority (IPA), charged with reviewing the electoral structure in the country, was created in December 1998. The IPA devised a proportional electoral system to ensure that the opposition would be represented in the National Assembly. The new system retained the existing 80 elected Assembly seats, but added 40 seats to be filled on a proportional basis. Elections were held under this new system in May 2002, and the LCD won again, gaining 54 percent of the vote. But for the first time, opposition political parties won significant numbers of seats, and despite some irregularities and threats of violence from Major General Lekhanya, Lesotho experienced its first peaceful election. Nine opposition parties now hold all 40 of the proportional seats, with the BNP having the largest share (21). The LCD has 79 of the 80 constituency-based seats. Although its elected members participate in the National Assembly, the BNP has launched several legal challenges to the elections, including a recount; none has been successful.
+
+On 30 August 2014, an alleged abortive military "coup" took place, forcing then Prime Minister Thomas Thabane to flee to South Africa for three days.[14][15]
+On May 19 2020, Thomas Thabane formally stepped down as prime minister of Lesotho following months of pressure after he was named as a suspect in the murder of his ex-wife.[16]
+
+The Lesotho Government is a parliamentary or constitutional monarchy. The Prime Minister, Moeketsi Majoro, is the head of government and has executive authority. The King of Lesotho, Letsie III, serves a largely ceremonial function; he no longer possesses any executive authority and is prohibited from actively participating in political initiatives.
+
+The All Basotho Convention (ABC) leads a coalition government in the National Assembly, the lower house of parliament.
+
+The upper house of parliament, called the Senate, is composed of 22 principal chiefs whose membership is hereditary, and 11 appointees of the king, acting on the advice of the prime minister.
+
+The constitution provides for an independent judicial system, made up of the High Court, the Court of Appeal, Magistrate's Courts, and traditional courts that exist predominantly in rural areas. All but one of the Justices on the Court of Appeal are South African jurists. There is no trial by jury; rather, judges make rulings alone or, in the case of criminal trials, with two other judges as observers.
+
+The constitution also protects basic civil liberties, including freedom of speech, freedom of association, freedom of the press, freedom of peaceful assembly and freedom of religion. Lesotho was ranked 12th out of 48 sub-Saharan African countries in the 2008 Ibrahim Index of African Governance.[17]
+
+As of 2010[update] the People's Charter Movement called for the practical annexation of the country by South Africa due to the HIV epidemic. Nearly a quarter of the population tests positive for HIV.[18] The country has also faced high unemployment, economic collapse, a weak currency and poor travel documents restricting movement. An African Union report called for economic integration of Lesotho with South Africa but stopped short of suggesting annexation. In May 2010 the Charter Movement delivered a petition to the South African High Commission requesting integration. South Africa's home affairs spokesman Ronnie Mamoepa rejected the idea that Lesotho should be treated as a special case. "It is a sovereign country like South Africa. We sent envoys to our neighbours – Botswana, Zimbabwe, Swaziland and Lesotho – before we enforced the passport rule. When you travel from Britain to South Africa, don't you expect to use a passport?"[19]
+
+Lesotho's geographic location makes it extremely vulnerable to political and economic developments in South Africa. It is a member of many regional economic organisations, including the Southern African Development Community (SADC),[20] and the Southern African Customs Union (SACU).[21] It is also active in the United Nations (UN), the African Union (AU), the Non-Aligned Movement, the Commonwealth, and many other international organisations.[22]
+
+Prince Seeiso Simoné Seeiso is the present High Commissioner of the Kingdom of Lesotho to the Court of St. James's. The UN is represented by a resident mission as well, including UNDP, UNICEF, WHO, FAO, WFP, UNFPA and UNAIDS.
+
+Lesotho also has maintained ties with the United Kingdom (Wales in particular), Germany, the United States and other Western states. Although in 1990 it broke relations with the People's Republic of China (PRC) and re-established relations with the Republic of China (Taiwan), it later restored ties with the PRC.
+
+Lesotho also recognises the State of Palestine.[23] From 2014 up until 2018 Lesotho also recognized the Republic of Kosovo.[24]
+
+In the past, it was a strong public opponent of apartheid in South Africa and granted a number of South African refugees political asylum during the apartheid era.[23]
+
+In 2019, Lesotho signed the UN treaty on the Prohibition of Nuclear Weapons.[25]
+
+Lesotho does not have a single code containing its laws; it draws them from a variety of sources including: Constitution, Legislation, Common Law, Judicial precedent, Customary Law, and Authoritative texts.[26]
+
+The Constitution of Lesotho came into force after the publication of the Commencement Order. Constitutionally, legislation refers to laws that have been passed by both houses of parliament and have been assented to by the king (section 78(1)). Subordinate legislation refers to laws passed by other bodies to which parliament has by virtue of section 70(2) of the Constitution validly delegated such legislative powers. These include government publications, ministerial orders, ministerial regulations and municipal by-laws.
+
+Although Lesotho shares with South Africa, Botswana, Swaziland, Namibia and Zimbabwe a mixed general legal system which resulted from the interaction between the Roman-Dutch Civilian law and the English Common Law, its general law operates independently. Lesotho also applies the common law, which refers to unwritten law or law from non-statutory sources, but excludes customary law. Decisions from South African courts are only persuasive, and courts refer to them in formulating their decisions. Decisions from similar jurisdictions can also be cited for their persuasive value. Magistrates' courts decisions do not become precedent since these are lower courts. They are, however, bound by decisions of the High Court and the Court of Appeal. The most powerful court in the Lesotho justice system is the Court of Appeal, which is the final appellate forum on all matters. It has a supervisory and review jurisdiction over all the courts of Lesotho.
+
+Lesotho has a dual legal system consisting of customary and general laws operating side by side. Customary law is made up of the customs of the Basotho, written and codified in the Laws of Lerotholi. The general law on the other hand consists of Roman Dutch Law imported from the Cape and the Lesotho statutes. The codification of customary law came about after a council was appointed in 1903 to advise the British Resident Commissioner on which laws would be best for governing the Basotho. Until this time, the Basotho customs and laws were passed down from generation to generation through oral tradition. The council was given the task of codifying them, and they came up with the Laws of Lerotholi which are applied by customary courts today (local courts). Written works of eminent authors have persuasive value in the courts of Lesotho. These include writings of the old authorities as well as contemporary writers from similar jurisdictions.
+
+For administrative purposes, Lesotho is divided into ten districts, each headed by a district administrator. Each district has a capital known as a camptown.
+
+The districts are subdivided into 80 constituencies, which consist of 129 local community councils.
+
+Lesotho covers 30,355 km2 (11,720 sq mi). It is the only independent state in the world that lies entirely above 1,000 metres (3,281 ft) in elevation. Its lowest point of 1,400 metres (4,593 ft) is thus the highest lowest point of any country in the world. Over 80 percent of the country lies above 1,800 metres (5,906 ft). Lesotho is also the southernmost landlocked country in the world and is entirely surrounded by South Africa. It lies between latitudes 28° and 31°S, and longitudes 27° and 30°E. About 12% of Lesotho is arable land, however, this land is vulnerable to soil erosion, and it is estimated that 40 million tons of soil are lost each year due to erosion.[27]
+
+Because of its elevation, Lesotho remains cooler throughout the year than other regions at the same latitude. Most of the rain falls as summer thunderstorms. Maseru and surrounding lowlands often reach 30 °C (86 °F) in summer. Winters can be cold with the lowlands getting down to −7 °C (19 °F) and the highlands to −18 °C (0 °F) at times. Snow is common in the highlands between May and September; the higher peaks can experience snowfalls year-round. Rainfall in Lesotho is highly variable regarding both when and where precipitation occurs. Despite Lesotho's small size, annual precipitation can vary from 500mm annual in one area to 1200mm in another because of elevation.[27] The summer season that stretches from October to April sees the most rainfall, and from December to February, the majority of the country receives over 100mm of rain a month.[27] The least monthly rainfall in Lesotho occurs in June when most regions receive less than 15mm a month.[27]
+
+Periodic droughts have a serious effect on Lesotho's majority rural population as many people living outside of urban areas rely on subsistence farming or small scale agriculture as their primary source of income.[28] Droughts in Lesotho are exacerbated by poor agricultural practices as well as high rates of HIV/AIDS.[29] The World Fact Book lists periodic droughts under the 'Natural Hazard' section of Lesotho's section of the publication.[30]
+
+In 2007, Lesotho experienced its worst drought in 30 years and was advised by the United Nations to declare a state of emergency to get aid from international organizations.[28] Erratic weather and the corresponding decline of the humanitarian situation still present Lesotho with problems currently. The Famine Early Warning System Network most recently reported that the rainy season of 2018/2019 not only started a month later than normal but also has recorded below-average amounts of rain.[31] Also, data from the Climate Hazards Group InfraRed Precipitation Station (CHIRP) shows rainfall in Lesotho between October 2018 and February 2019 ranged from 55% to 80% below normal rates.[31]
+
+In March 2019, the Lesotho Vulnerability Assessment and Analysis Committee conducted a report that initially predicted that 487,857 people in the country need humanitarian assistance because of the effects of drought.[31]
+
+There are a variety of different ways drought in Lesotho has led to the need for humanitarian assistance. Poor hygiene practices that result from a lack of clean water can cause cases of typhoid and diarrhea. Lack of available water also indirectly leads to an increased risk for women and girls who collect water for household consumption as they must spend more time and travel long distances while running the risk of physically or sexually assaulted.[31] Drought in Lesotho also leads to both migration to more urban areas and immigration to South Africa for new opportunities and to escape food insecurity.[29] The report also found that between July 2019 and June 2020 640,000 people in Lesotho are expected to be affected by food insecurity as a result of unproductive harvests as well as the corresponding rise in food prices because of the drought.[31]
+
+There are known to be 339 bird species in Lesotho, including 10 globally threatened species and 2 introduced species, 17 reptile species, including geckos, snakes and lizards, and 60 mammal species endemic to Lesotho, including the endangered white-tailed rat.
+
+Lesotho's flora is Alpine, due to the high and mountainous terrain. The Katse Botanical Gardens houses a collection of medicinal plants and has a large seed bank of plants from the Malibamat'so River area.[32][33]
+
+Lesotho is geographically surrounded by South Africa and economically integrated with it. The economy of Lesotho is based on agriculture, livestock, manufacturing and mining, and depends heavily on inflows of workers' remittances and receipts from the Southern African Customs Union (SACU).[34][35] The majority of households subsist on farming. The formal sector employment consists mainly of female workers in the apparel sector, male migrant labour, primarily miners in South Africa for three to nine months, and employment by the Government of Lesotho (GOL). The western lowlands form the main agricultural zone. Almost 50 percent of the population earn income through informal crop cultivation or animal husbandry with nearly two-thirds of the country's income coming from the agricultural sector. The percentage of the population living below USD Purchasing Power Parity (PPP) US$1.25/day fell from 48 percent to 44 percent between 1995 and 2003.[34] The country is among the "Low Human Development" countries (rank 160 of 187 on the Human Development Index as classified by the UNDP, with 52 years of life expectancy at birth.[36][37] Adult literacy is as high as 82 percent. Among the children below the age of five years, 20 percent are under weight.[38]
+
+Lesotho has taken advantage of the African Growth and Opportunity Act (AGOA) to become the largest exporter of garments to the US from sub-Saharan Africa.[39] US brands and retailers sourcing from Lesotho include: Foot Locker, Gap, Gloria Vanderbilt, JCPenney, Levi Strauss, Saks, Sears, Timberland and Wal-Mart.[40] In mid-2004 its employment reached over 50,000, mainly female workers, marking the first time that manufacturing sector workers outnumbered government employees. In 2008 it exported goods worth 487 million dollars mainly to the US. Since 2004, employment in the sector has dwindled to about 45,000 in mid-2011 due to international competition in the garment sector. It was the largest formal sector employer in Lesotho in 2011.[41] In 2007, the average earnings of an employee in the textile sector were US$103 per month, and the official minimum wage for a general textile worker was US$93 per month. The average gross national income per capita in 2008 was US$83 per month.[41] The sector initiated a major program to fight HIV/AIDS called Apparel Lesotho Alliance to Fight AIDS (ALAFA). It is an industry-wide program providing disease prevention and treatment for workers.[42]
+
+Water and diamonds are Lesotho's significant natural resources.[34] Water is used through the 21-year, multibillion-dollar Lesotho Highlands Water Project (LHWP), under the authority of the Lesotho Highlands Development Authority. The project commenced in 1986.[43] The LHWP is designed to capture, store, and transfer water from the Orange River system to South Africa's Free State and greater Johannesburg area, which features a large concentration of South African industry, population, and agriculture. Completion of the first phase of the project has made Lesotho almost completely self-sufficient in the production of electricity and generated approximately US$70 million in 2010 from the sale of electricity and water to South Africa.[44] The World Bank, African Development Bank, European Investment Bank, and many other bilateral donors financed the project.
+
+Diamonds are produced at the Letšeng, Mothae, Liqhobong, and Kao mines, which combined are estimated to produce 240,000 carats of diamonds in 2014, worth US$300 million. The Letšeng mine is estimated to produce diamonds with an average value of US$2172/carat, making it the world's richest mine on an average price per carat basis.[45] The sector suffered a setback in 2008 as the result of the world recession, but rebounded in 2010 and 2011. Export of diamonds reached US$230 million in 2010–2011.[46] In 1957, a South African adventurer, colonel Jack Scott, accompanied by a young man named Keith Whitelock, set out prospecting for diamonds. They found their diamond mine at 3,100 m elevation, on top of the Maluti Mountains in northeastern Lesotho, some 70 km from Mokhotlong at Letšeng. In 1967, a 601-carat (120.2 g) diamond (Lesotho Brown) was discovered in the mountains by a Mosotho woman. In August 2006, a 603-carat (120.6 g) white diamond, the Lesotho Promise, was discovered at the Letšeng-la-Terae mine. Another 478-carat (95.6 g) diamond was discovered at the same location in 2008.[47]
+
+Lesotho has progressed in moving from a predominantly subsistence-oriented economy to a lower middle income economy exporting natural resources and manufacturing goods. The exporting sectors have brought higher and more secure incomes to a significant portion of the population.[34]
+
+However, the global economic crisis hit the Lesotho economy hard. Lesotho suffered a loss of textile exports and jobs in this sector due largely to the economic slowdown in the United States, one of their major export destinations. Reduced diamond mining and exports, including a drop in the price of diamonds as well as a drop in SACU revenues due to the economic slowdown in the South African economy also contributed to the crisis. Finally reduction in worker remittances due to weakening of the South African economy and contraction of the mining sector and related job losses in South Africa contributed to in 2009, Lesotho's GDP growth slowing to 0.9 percent.[34]
+
+The official currency is the loti (plural: maloti), but can be used interchangeably with the South African rand. Lesotho, Eswatini, Namibia, and South Africa also form a common currency and exchange control area known as the Common Monetary Area (CMA). The loti is at par with the rand. One hundred lisente (singular: sente) equal one loti.
+
+Lesotho is a member of the Southern African Customs Union (SACU), in which tariffs have been eliminated on the trade of goods between other member countries Botswana, Namibia, South Africa, and Eswatini. Lesotho has received economic aid from a variety of sources, including the United States, the World Bank, Republic of Ireland, the United Kingdom, the European Union, and Germany.
+
+Lesotho has a population of approximately 2,108,328[1][2]. The population distribution of Lesotho is 25 percent urban and 75 percent rural. However, it is estimated that the annual increase in urban population is 3.5 percent.[48] Population density is lower in the highlands than in the western lowlands. Although the majority of the population—60.2 percent—is between 15 and 64 years of age, Lesotho has a substantial youth population numbering around 34.8 percent.[48]
+
+Lesotho's ethno-linguistic structure consists almost entirely of the Basotho, a Bantu-speaking people: an estimated 99.7 percent of the people identify as Basotho. In this regard, Lesotho is part of a handful of sub-Saharan African countries that are nation states with a single dominant cultural ethnic group and language; majority of sub-Saharan African nations' borders were drawn by colonial powers and do not correspond to ethnic boundaries or pre-colonial polities.[49] Basotho subgroups include the Bafokeng (totems: phoka (dew), 'mutla (hare)), Batloung (totem: tlou (elephant)), Baphuthi (totem: phuthi), Bakuena (totem: kuena (crocodile)), Bataung (totem: tau (lion)), Batšoeneng (totem: tšoene), and Matebele.
+
+The main language, Sesotho, is also the first official and administrative language, and it is what Basotho speak on an ordinary basis.
+
+The population of Lesotho is estimated to be more than 95 percent Christian.[50] Protestants account for 50 percent of the population, (Evangelicals 17.5 percent, Anglicans 7.5 percent, Pentecostals 21.9 percent and other Christians an additional 8.5 percent).[51] Catholics represent nearly 40 percent of the population, served by the province of the Metropolitan Archbishop of Maseru and his three suffragans (the bishops of Leribe, Mohale's Hoek and Qacha's Nek), who also form the national episcopal conference. Non-Christian religions represent only 1.5% of the population, and those of no religion 3.5%.[51]
+
+According to recent estimates, 85 percent of women and 68 percent of men over the age of 15 are literate.[52] As such, Lesotho holds one of the highest literacy rates in Africa,[48] in part because Lesotho invests over 12 percent of its GDP in education.[53] Unlike in most other countries, in Lesotho female literacy (84.93 percent) exceeds male literacy (67.75 percent) by 17.18 percentage points. According to a study by the Southern and Eastern Africa Consortium for Monitoring Educational Quality in 2000, 37 percent of grade six pupils in Lesotho (average age 14 years) are at or above reading level four, "Reading for Meaning."[54] A pupil at this level of literacy can read ahead or backwards through various parts of text to link and interpret information. Although education is not compulsory, the Government of Lesotho is incrementally implementing a program for free primary education.[55]
+
+Despite their literacy, Lesotho's residents struggle for access to vital services, such as healthcare, travel and educational resources, as, according to the International Telecommunication Union, only 3.4 percent of the population use the Internet. A service from Econet Telecom Lesotho expanded the country's access to email through entry-level, low-end mobile phones and, consequently, improved access to educational information. The African Library Project works to establish school and village libraries in partnership with US Peace Corps Lesotho[56] and the Butha Buthe District of Education.
+
+Life expectancy at birth in Lesotho in 2016 was 51 years for men and 55 for women. Infant mortality is about 8.3%. In 2019 life expectancy was estimated at 52 years for men and women.[37]
+
+As of 2018, Lesotho's adult HIV/AIDS prevalence rate of 23.6% was the second highest in the world, after eSwatini.[57]
+
+The country has the highest incidence of tuberculosis in the world.[58]
+
+The internal and external security of Lesotho is the responsibility of the Defence Commission, which is established and defined by article 145 of the Lesotho national Constitution. The Prime Minister is the Chairman ex officio, and there are six other Defence Commission members, namely the Commander and Deputy Commander of the Lesotho Defence Force, the Commissioner and Assistant Commissioner of the Lesotho Mounted Police Service, and the Director and Deputy Director of the Lesotho National Security Service. The Defence Commission has power to strategically direct the defence force, the police, and the prison service, but not the security service, which is answerable only to the Government. The Defence Commission has power to appoint or remove the senior staff of the defence force, police, and prison service, but not the security service, whose Director and Deputy Director are personal appointments of the Prime Minister.[59]
+
+The Lesotho Defence Force (LDF) is established under article 146 of the national Constitution, and charged with the maintenance of internal security and the defence of Lesotho. Its chief officer is designated Commander by the Constitution,[60] and usually holds the rank of lieutenant-general. The LDF has a total strength of just over 3,000. The largest component is infantry, but they are supported by small artillery, logistics, and air force units, and a single armoured reconnaissance company. Since 2000, Lesotho Defence Forces have been trained by a small contingent of Indian Army Training Team, led by a Brigadier.[citation needed]
+
+The Lesotho Mounted Police Service (LMPS) is established under article 147 of the national Constitution, and charged with the maintenance of law and order. Its chief officer is designated Commissioner by the Constitution. The LMPS provides uniformed policing, criminal detection, and traffic policing. There are specialist units dealing with high-tech crime, immigration, wildlife, and terrorism. The current force has existed, despite changes of name, continuously since 1872.
+
+The Lesotho National Security Service (LNSS) is established under article 148 of the national Constitution, and charged with the protection of national security. Its chief officer is designated Director by the Constitution. The LNSS is an intelligence service, reporting directly to the Government. The power to appoint or dismiss a Director is vested directly in the Prime Minister.
+
+Traditional musical instruments include the lekolulo, a kind of flute used by herding boys, the setolo-tolo, played by men using their mouth, and the woman's stringed thomo.
+
+The national anthem of Lesotho is "Lesotho Fatše La Bo-ntata Rona", which literally translates into "Lesotho, Land of Our Fore-Fathers".
+
+The traditional style of housing in Lesotho is called a mokhoro. Many older houses, especially in smaller towns and villages, are of this type, with walls usually constructed from large stones cemented together. Baked mud bricks and especially concrete blocks are also used nowadays, with thatched roofs still common, although often replaced by corrugated roofing sheets.
+
+Traditional attire revolves around the Basotho blanket, a thick covering made primarily of wool. The blankets are ubiquitous throughout the country during all seasons, and worn differently by men and women.
+
+The Morija Arts & Cultural Festival is a prominent Sesotho arts and music festival. It is held annually in the historical town of Morija, where the first missionaries arrived in 1833.
+
+The cuisine of Lesotho includes African traditions and British influences.[61]
+The national dish of Lesotho is Motoho, a fermented sorghum porridge eaten throughout the country.
+
+Because Lesotho has limited food resources, a majority of families in the country raise their own food and livestock to support themselves and their families.
+
+Some staple foods include papa, a cornmeal porridge covered with a sauce consisting of various vegetables. Tea and locally brewed beer are popular choices for beverages.[62]
+
+2018 film Black Panther director Ryan Coogler stated that his depiction of Wakanda was inspired by Lesotho.[63][64] Basotho blankets also became more known as a result of the film.[65]
+
+Significant levels of child labour exist in Lesotho, and the country is in the process of formulating an Action Program on the Elimination of Child Labor (APEC). According to the UN, Lesotho has the highest rape rate of any country (91.6 per 100,000 people rate for reported rape in 2008).[66]
+
+Treatment of people with disabilities is another major issue facing the country. According to the Lesotho Census of 2006, around four percent of the population is thought to have some sort of disability. However, there are concerns regarding the reliability of the methodologies used and the real figure is thought to be closer to the global estimate of 15 percent. According to a survey conducted by the Lesotho National Federation of Organisations of the Disabled in conjunction with SINTEF,[67] people with disability in Lesotho face significant social and cultural barriers which prevent them from accessing education, healthcare, and employment on an equal basis with others.
+
+On 2 December 2008 Lesotho became the 42nd country in the world to sign the UN Convention on the Rights of Persons with Disabilities. However, to date the treaty has yet to be domesticated. Despite lobbying efforts from disabled persons organisations, there have been no moves to develop disability specific legislation to protect the rights of people with disabilities. Although the National Disability and Rehabilitation Policy was developed in 2011, thus far there has been no budget allocated for its implementation.
+
+Sexual violence in Lesotho is a serious problem. International data from UNODC found the incidence of rapes recorded in 2008 by the police to be the highest in Lesotho.[68]
+
+One study in Lesotho found that 61 percent of women reported having experienced sexual violence at some point in their lives, of which 22 percent reported being physically forced to have sexual intercourse.[69] In the 2009 DHS survey 15.7 percent of men said that a husband is justified in hitting or beating his wife if she refuses to have sex with him, while 16 percent said a husband is justified to use force to have sex.[70] In another study, researchers have concluded that "Given the high prevalence of HIV in Lesotho, programs should address women's right to control their sexuality."[71]
+
+The Married Persons Equality Act 2006 gives equal rights to wives in regard to their husbands, abolishing the husband's marital power.[72]
+
+The World Economic Forum's 2020 Gender Gap Report ranks Lesotho 88th in the world for gender parity, while neighboring South Africa ranks 17th.[73]
+
+Click on a coloured area to see an article about English in that country or region

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+A shrub or bush is a small- to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrub can be deciduous or evergreen .
+They are distinguished from trees by their multiple stems and shorter height, less than 6 m-10 m (20 ft–33 ft) tall.[1][2] Small shrubs, less than 2 m (6.6 ft) tall are sometimes termed subshrubs.[3]
+
+Shrubs are perennial woody plants, and therefore have persistent woody stems above ground (compare with herbaceous plants).[2] Usually shrubs are distinguished from trees by their height and multiple stems. Some shrubs are deciduous (e.g. hawthorn) and others evergreen (e.g. holly).[2] Ancient Greek philosopher Theophrastus divided the plant world into trees, shrubs and herbs.[4]
+
+Some definitions state that a shrub is less than 6 m and tree is over 6 m. Others use 10 m as the cut off point.[2] Many species of tree may not reach this mature height because of less than ideal growing conditions, and resemble a shrub sized plant. However such species have the potential to grow taller under the ideal growing conditions for that plant.
+
+Small, low shrubs, generally less than 2 m (6.6 ft) tall, such as lavender, periwinkle and most small garden varieties of rose, are often termed subshrubs.[3]
+
+Most definitions characterize shrubs as possessing multiple stems with no main trunk.[2]  This is because the stems have branched below ground level. There are exceptions to this, with some shrubs having main trunks, but these tend to be very short and divide into multiple stems close to ground level. Many trees can grow in multiple stemmed forms also, such as oak or ash.[2][clarification needed]
+
+An area of cultivated shrubs in a park or a garden is known as a shrubbery.[5] When clipped as topiary, suitable species or varieties of shrubs develop dense foliage and many small leafy branches growing close together.[6] Many shrubs respond well to renewal pruning, in which hard cutting back to a "stool" results in long new stems known as "canes".[clarification needed] Other shrubs respond better to selective pruning to reveal their structure and character.
+
+Shrubs in common garden practice are generally considered broad-leaved plants, though some smaller conifers such as mountain pine and common juniper are also shrubby in structure. Species that grow into a shrubby habit may be either deciduous or evergreen.[7]
+
+In botany and ecology, a shrub is more specifically used to describe the particular physical structural or plant life-form of woody plants which are less than 8 metres (26 ft) high and usually have many stems arising at or near the base.[clarification needed] For example, a descriptive system widely adopted in Australia is based on structural characteristics based on life-form, plus the height and amount of foliage cover of the tallest layer or dominant species.[8]
+
+For shrubs 2–8 metres (6.6–26.2 ft) high the following structural forms are categorized:
+
+For shrubs less than 2 metres (6.6 ft) high the following structural forms are categorized:
+
+Those marked with * can also develop into tree form.

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+
+
+
+
+The European Union (EU) is a political and economic union of 27 member states that are located primarily in Europe.[11] Its members have a combined area of 4,233,255.3 km2 (1,634,469.0 sq mi) and an estimated total population of about 447 million. The EU has developed an internal single market through a standardised system of laws that apply in all member states in those matters, and only those matters, where members have agreed to act as one. EU policies aim to ensure the free movement of people, goods, services and capital within the internal market;[12] enact legislation in justice and home affairs; and maintain common policies on trade,[13] agriculture,[14] fisheries and regional development.[15] Passport controls have been abolished for travel within the Schengen Area.[16] A monetary union was established in 1999, coming into full force in 2002, and is composed of 19 EU member states which use the euro currency. The EU has often been described as a sui generis political entity (without precedent or comparison).[17][18]
+
+The EU and European citizenship were established when the Maastricht Treaty came into force in 1993.[19] The EU traces its origins to the European Coal and Steel Community (ECSC) and the European Economic Community (EEC), established, respectively, by the 1951 Treaty of Paris and 1957 Treaty of Rome. The original members of what came to be known as the European Communities were the Inner Six: Belgium, France, Italy, Luxembourg, the Netherlands, and West Germany. The Communities and their successors have grown in size by the accession of new member states and in power by the addition of policy areas to their remit. The latest major amendment to the constitutional basis of the EU, the Treaty of Lisbon, came into force in 2009.
+
+On 31 January 2020, the United Kingdom became the first member state to leave the EU.[20] Following a 2016 referendum, the UK signified its intention to leave and negotiated a withdrawal agreement. The UK is in a transitional phase until at least 31 December 2020, during which it remains subject to EU law and part of the EU single market and customs union. Before this, three territories of member states had left the EU or its forerunners, these being French Algeria (in 1962, upon independence), Greenland (in 1985, following a referendum) and Saint Barthélemy (in 2012).
+
+Containing in 2020 some 5.8% of the world population,[d] the EU (excluding the United Kingdom) had generated a nominal gross domestic product (GDP) of around US$15.5 trillion in 2019,[8] constituting approximately 18% of global nominal GDP.[22] Additionally, all EU countries have a very high Human Development Index according to the United Nations Development Programme. In 2012, the EU was awarded the Nobel Peace Prize.[23] Through the Common Foreign and Security Policy, the union has developed a role in external relations and defence. It maintains permanent diplomatic missions throughout the world and represents itself at the United Nations, the World Trade Organization, the G7 and the G20. Due to its global influence, the European Union has been described as an emerging superpower.[24]
+
+The following timeline outlines the legal inception of the European Union (EU), from the post-war period until the union's founding and consolidation³ in 1993 and 2009, respectively. This integration ― also referred to as the European project or the construction of Europe (French: la construction européenne) ― involved treaty-based European cooperation in various policy areas, including the European Communities that were founded in the 1950s in the spirit of the Schuman Declaration.
+
+
+
+During the centuries following the fall of Rome in 476, several European states viewed themselves as translatio imperii ("transfer of rule") of the defunct Roman Empire: the Frankish Empire (481–843) and the Holy Roman Empire (962–1806) were thereby attempts to resurrect Rome in the West.[e] This political philosophy of a supra-national rule over the continent, similar to the example of the ancient Roman Empire, resulted in the early Middle Ages in the concept of a renovatio imperii ("restoration of the empire"),[26] either in the forms of the Reichsidee ("imperial idea") or the religiously inspired Imperium Christianum ("christian empire").[27][28] Medieval Christendom[29][30] and the political power of the Papacy[31][32] are often cited as conducive to European integration and unity.
+
+In the oriental parts of the continent, the Russian Tsardom, and ultimately the Empire (1547–1917), declared Moscow to be Third Rome and inheritor of the Eastern tradition after the fall of Constantinople in 1453.[33] The gap between Greek East and Latin West had already been widened by the political scission of the Roman Empire in the 4th century and the Great Schism of 1054, and would be eventually widened again by the Iron Curtain (1945–1991).[34]
+
+Pan-European political thought truly emerged during the 19th century, inspired by the liberal ideas of the French and American Revolutions after the demise of Napoléon's Empire (1804–1815). In the decades following the outcomes of the Congress of Vienna, ideals of European unity flourished across the continent, especially in the writings of Wojciech Jastrzębowski,[35] Giuseppe Mazzini,[36] or Theodore de Korwin Szymanowski.[37] The term United States of Europe (French: États-Unis d'Europe) was used at that time by Victor Hugo during a speech at the International Peace Congress held in Paris in 1849:[38]
+
+A day will come when all nations on our continent will form a European brotherhood ... A day will come when we shall see ... the United States of America and the United States of Europe face to face, reaching out for each other across the seas.
+
+During the interwar period, the consciousness that national markets in Europe were interdependent though confrontational, along with the observation of a larger and growing US market on the other side of the ocean, nourished the urge for the economic integration of the continent.[39] In 1920, advocating the creation of a European economic union, British economist John Maynard Keynes wrote that "a Free Trade Union should be established ... to impose no protectionist tariffs whatever against the produce of other members of the Union."[40] During the same decade, Richard von Coudenhove-Kalergi, one of the first to imagine of a modern political union of Europe, founded the Pan-Europa Movement.[41] His ideas influenced his contemporaries, among which then Prime Minister of France Aristide Briand. In 1929, the latter gave a speech in favour of a European Union before the assembly of the League of Nations, precursor of the United Nations.[42] In a radio address in March 1943, with war still raging, Britain's leader Sir Winston Churchill spoke warmly of "restoring the true greatness of Europe" once victory had been achieved, and mused on the post-war creation of a "Council of Europe" which would bring the European nations together to build peace.[43][44]
+
+After World War II, European integration was seen as an antidote to the extreme nationalism which had devastated parts of the continent.[45] In a speech delivered on 19 September 1946 at the University of Zürich, Switzerland, Winston Churchill went further and advocated the emergence of a United States of Europe.[46] The 1948 Hague Congress was a pivotal moment in European federal history, as it led to the creation of the European Movement International and of the College of Europe, where Europe's future leaders would live and study together.[47]
+
+It also led directly to the founding of the Council of Europe in 1949, the first great effort to bring the nations of Europe together, initially ten of them. The Council focused primarily on values—human rights and democracy—rather than on economic or trade issues, and was always envisaged as a forum where sovereign governments could choose to work together, with no supra-national authority. It raised great hopes of further European integration, and there were fevered debates in the two years that followed as to how this could be achieved.
+
+But in 1952, disappointed at what they saw as the lack of progress within the Council of Europe, six nations decided to go further and created the European Coal and Steel Community, which was declared to be "a first step in the federation of Europe".[48] This community helped to economically integrate and coordinate the large number of Marshall Plan funds from the United States.[49] European leaders Alcide De Gasperi from Italy, Jean Monnet and Robert Schuman from France, and Paul-Henri Spaak from Belgium understood that coal and steel were the two industries essential for waging war, and believed that by tying their national industries together, future war between their nations became much less likely.[50] These men and others are officially credited as the founding fathers of the European Union.
+
+In 1957, Belgium, France, Italy, Luxembourg, the Netherlands, and West Germany signed the Treaty of Rome, which created the European Economic Community (EEC) and established a customs union. They also signed another pact creating the European Atomic Energy Community (Euratom) for co-operation in developing nuclear energy. Both treaties came into force in 1958.[50]
+
+The EEC and Euratom were created separately from the ECSC and they shared the same courts and the Common Assembly. The EEC was headed by Walter Hallstein (Hallstein Commission) and Euratom was headed by Louis Armand (Armand Commission) and then Étienne Hirsch. Euratom was to integrate sectors in nuclear energy while the EEC would develop a customs union among members.[51][52]
+
+During the 1960s, tensions began to show, with France seeking to limit supranational power. Nevertheless, in 1965 an agreement was reached and on 1 July 1967 the Merger Treaty created a single set of institutions for the three communities, which were collectively referred to as the European Communities.[53][54] Jean Rey presided over the first merged Commission (Rey Commission).[55]
+
+In 1973, the Communities were enlarged to include Denmark (including Greenland, which later left the Communities in 1985, following a dispute over fishing rights), Ireland, and the United Kingdom.[56] Norway had negotiated to join at the same time, but Norwegian voters rejected membership in a referendum. In 1979, the first direct elections to the European Parliament were held.[57]
+
+Greece joined in 1981, Portugal and Spain following in 1986.[58] In 1985, the Schengen Agreement paved the way for the creation of open borders without passport controls between most member states and some non-member states.[59] In 1986, the European flag began to be used by the EEC[60] and the Single European Act was signed.
+
+In 1990, after the fall of the Eastern Bloc, the former East Germany became part of the Communities as part of a reunified Germany.[61]
+
+The European Union was formally established when the Maastricht Treaty—whose main architects were Helmut Kohl and François Mitterrand—came into force on 1 November 1993.[19][62] The treaty also gave the name European Community to the EEC, even if it was referred as such before the treaty. With further enlargement planned to include the former communist states of Central and Eastern Europe, as well as Cyprus and Malta, the Copenhagen criteria for candidate members to join the EU were agreed upon in June 1993. The expansion of the EU introduced a new level of complexity and discord.[63] In 1995, Austria, Finland, and Sweden joined the EU.
+
+In 2002, euro banknotes and coins replaced national currencies in 12 of the member states. Since then, the eurozone has increased to encompass 19 countries. The euro currency became the second largest reserve currency in the world. In 2004, the EU saw its biggest enlargement to date when Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia, and Slovenia joined the Union.[64]
+
+In 2007, Bulgaria and Romania became EU members. The same year, Slovenia adopted the euro,[64] followed in 2008 by Cyprus and Malta, by Slovakia in 2009, by Estonia in 2011, by Latvia in 2014, and by Lithuania in 2015.
+
+On 1 December 2009, the Lisbon Treaty entered into force and reformed many aspects of the EU. In particular, it changed the legal structure of the European Union, merging the EU three pillars system into a single legal entity provisioned with a legal personality, created a permanent President of the European Council, the first of which was Herman Van Rompuy, and strengthened the position of the High Representative of the Union for Foreign Affairs and Security Policy.[65][66]
+
+In 2012, the EU received the Nobel Peace Prize for having "contributed to the advancement of peace and reconciliation, democracy, and human rights in Europe."[67][68] In 2013, Croatia became the 28th EU member.[69]
+
+From the beginning of the 2010s, the cohesion of the European Union has been tested by several issues, including a debt crisis in some of the Eurozone countries, increasing migration from Africa and Asia, and the United Kingdom's withdrawal from the EU.[70] A referendum in the UK on its membership of the European Union was held in 2016, with 51.9% of participants voting to leave.[71] The UK formally notified the European Council of its decision to leave on 29 March 2017, initiating the formal withdrawal procedure for leaving the EU; following extensions to the process, the UK left the European Union on 31 January 2020, though most areas of EU law will continue to apply to the UK for a transition period lasting until the end of 2020 at the earliest.[72]
+
+As of 1 February 2020[update], the population of the European Union was about 447 million people (5.8% of the world population).[73][74] In 2015, 5.1 million children were born in the EU-28 corresponding to a birth rate of 10 per 1,000, which is 8 births below the world average.[75] For comparison, the EU-28 birth rate had stood at 10.6 in 2000, 12.8 in 1985 and 16.3 in 1970.[76] Its population growth rate was positive at an estimated 0.23% in 2016.[77]
+
+In 2010, 47.3 million people who lived in the EU were born outside their resident country. This corresponds to 9.4% of the total EU population. Of these, 31.4 million (6.3%) were born outside the EU and 16.0 million (3.2%) were born in another EU member state. The largest absolute numbers of people born outside the EU were in Germany (6.4 million), France (5.1 million), the United Kingdom (4.7 million), Spain (4.1 million), Italy (3.2 million), and the Netherlands (1.4 million).[78] In 2017, approximately 825,000 people acquired citizenship of a member state of the European Union. The largest groups were nationals of Morocco, Albania, India, Turkey and Pakistan.[79] 2.4 million immigrants from non-EU countries entered the EU in 2017.[80][81]
+
+The EU contains about 40 urban areas with populations of over one million. The largest metropolitan area in the EU is Paris.[82] These are followed by Madrid, Barcelona, Berlin, Rhine-Ruhr, Rome, and Milan, all with a metropolitan population of over 4 million.[83]
+
+The EU also has numerous polycentric urbanised regions like Rhine-Ruhr (Cologne, Dortmund, Düsseldorf et al.), Randstad (Amsterdam, Rotterdam, The Hague, Utrecht et al.), Frankfurt Rhine-Main (Frankfurt), the Flemish Diamond (Antwerp, Brussels, Leuven, Ghent et al.) and Upper Silesian area (Katowice, Ostrava et al.).[82]
+
+
+
+The European Union has 24 official languages: Bulgarian, Croatian, Czech, Danish, Dutch, English, Estonian, Finnish, French, German, Greek, Hungarian, Italian, Irish, Latvian, Lithuanian, Maltese, Polish, Portuguese, Romanian, Slovak, Slovene, Spanish, and Swedish. Important documents, such as legislation, are translated into every official language and the European Parliament provides translation for documents and plenary sessions.[89][90][91]
+
+Due to the high number of official languages, most of the institutions use only a handful of working languages.[92] The European Commission conducts its internal business in three procedural languages: English, French, and German. Similarly, the Court of Justice of the European Union uses French as the working language,[93] while the European Central Bank conducts its business primarily in English.[94][95]
+
+Even though language policy is the responsibility of member states, EU institutions promote multilingualism among its citizens.[h][96] English is the most widely spoken language in the EU, being understood by 51% of the EU population when counting both native and non-native speakers.[97] German is the most widely spoken mother tongue (18% of the EU population), and the second most widely understood foreign language, followed by French (13% of the EU population). In addition, both are official languages of several EU member states. More than half (56%) of EU citizens are able to engage in a conversation in a language other than their mother tongue.[98]
+
+A total of twenty official languages of the EU belong to the Indo-European language family, represented by the Balto-Slavic,[i] the Italic,[j] the Germanic,[k] the Hellenic,[l] and the Celtic[m] branches. Only four languages, namely Hungarian, Finnish, Estonian (all three Uralic), and Maltese (Semitic), are not Indo-European languages.[99] The three official alphabets of the European Union (Cyrillic, Latin, and modern Greek) all derive from the Archaic Greek scripts.[3][100]
+
+Luxembourgish (in Luxembourg) and Turkish (in Cyprus) are the only two national languages that are not official languages of the EU. On 26 February 2016 it was made public that Cyprus has asked to make Turkish an official EU language, in a “gesture” that could help solve the division of the country.[101] Already in 2004, it was planned that Turkish would become an official language when Cyprus reunites.[102]
+
+Besides the 24 official languages, there are about 150 regional and minority languages, spoken by up to 50 million people.[99] Catalan, Galician and Basque are not recognised official languages of the European Union but have semi-official status in one member state (Spain): therefore, official translations of the treaties are made into them and citizens have the right to correspond with the institutions in these languages.[103][104] The European Charter for Regional or Minority Languages ratified by most EU states provides general guidelines that states can follow to protect their linguistic heritage. The European Day of Languages is held annually on 26 September and is aimed at encouraging language learning across Europe.[105]
+
+The EU has no formal connection to any religion. The Article 17 of the Treaty on the Functioning of the European Union[106] recognises the "status under national law of churches and religious associations" as well as that of "philosophical and non-confessional organisations".[107]
+
+The preamble to the Treaty on European Union mentions the "cultural, religious and humanist inheritance of Europe".[107] Discussion over the draft texts of the European Constitution and later the Treaty of Lisbon included proposals to mention Christianity or a god, or both, in the preamble of the text, but the idea faced opposition and was dropped.[108]
+
+Christians in the European Union are divided among members of Catholicism (both Roman and Eastern Rite), numerous Protestant denominations (Anglicans, Lutherans, and Reformed forming the bulk of this category), and the Eastern Orthodox Church. In 2009, the EU had an estimated Muslim population of 13 million,[109] and an estimated Jewish population of over a million.[110] The other world religions of Buddhism, Hinduism, and Sikhism are also represented in the EU population.
+
+According to new polls about religiosity in the European Union in 2015 by Eurobarometer, Christianity is the largest religion in the European Union, accounting for 71.6% of the EU population. Catholics are the largest Christian group, accounting for 45.3% of the EU population, while Protestants make up 11.1%, Eastern Orthodox make up 9.6%, and other Christians make up 5.6%.[4]
+
+Eurostat's Eurobarometer opinion polls showed in 2005 that 52% of EU citizens believed in a god, 27% in "some sort of spirit or life force", and 18% had no form of belief.[111] Many countries have experienced falling church attendance and membership in recent years.[112] The countries where the fewest people reported a religious belief were Estonia (16%) and the Czech Republic (19%).[111] The most religious countries were Malta (95%, predominantly Catholic) as well as Cyprus and Romania (both predominantly Orthodox) each with about 90% of citizens professing a belief in their respective god. Across the EU, belief was higher among women, older people, those with religious upbringing, those who left school at 15 or 16, and those "positioning themselves on the right of the political scale".[111]
+
+Through successive enlargements, the European Union has grown from the six founding states (Belgium, France, West Germany, Italy, Luxembourg, and the Netherlands) to the current 27. Countries accede to the union by becoming party to the founding treaties, thereby subjecting themselves to the privileges and obligations of EU membership. This entails a partial delegation of sovereignty to the institutions in return for representation within those institutions, a practice often referred to as "pooling of sovereignty".[113][114]
+
+To become a member, a country must meet the Copenhagen criteria, defined at the 1993 meeting of the European Council in Copenhagen. These require a stable democracy that respects human rights and the rule of law; a functioning market economy; and the acceptance of the obligations of membership, including EU law. Evaluation of a country's fulfilment of the criteria is the responsibility of the European Council.[115] Article 50 of the Lisbon Treaty provides the basis for a member to leave the Union. Two territories have left the Union: Greenland (an autonomous province of Denmark) withdrew in 1985;[116] the United Kingdom formally invoked Article 50 of the Consolidated Treaty on European Union in 2017, and became the only sovereign state to leave when it withdrew from the EU in 2020.
+
+There are six countries that are recognised as candidates for membership: Albania, Iceland, North Macedonia,[n] Montenegro, Serbia, and Turkey,[117] though Iceland suspended negotiations in 2013.[118] Bosnia and Herzegovina and Kosovo are officially recognised as potential candidates,[117] with Bosnia and Herzegovina having submitted a membership application.
+
+The four countries forming the European Free Trade Association (EFTA) are not EU members, but have partly committed to the EU's economy and regulations: Iceland, Liechtenstein and Norway, which are a part of the single market through the European Economic Area, and Switzerland, which has similar ties through bilateral treaties.[119][120] The relationships of the European microstates, Andorra, Monaco, San Marino, and Vatican City include the use of the euro and other areas of co-operation.[121] The following 27 sovereign states (of which the map only shows territories situated in and around Europe) constitute the European Union:[122]
+
+The EU's member states cover an area of 4,233,262 square kilometres (1,634,472 sq mi).[p] The EU's highest peak is Mont Blanc in the Graian Alps, 4,810.45 metres (15,782 ft) above sea level.[123] The lowest points in the EU are Lammefjorden, Denmark and Zuidplaspolder, Netherlands, at 7 m (23 ft) below sea level.[124]
+The landscape, climate, and economy of the EU are influenced by its coastline, which is 65,993 kilometres (41,006 mi) long.
+
+65,993 km (41,006 mi) coastline dominates the European climate (Natural Park of Penyal d'Ifac, Spain)
+
+Mont Blanc in the Alps is the highest peak in the EU
+
+The Danube (pictured in Budapest), is the longest river in the European Union
+
+Repovesi National Park in Finland, where there are some 187,888 lakes larger than 500 square metres (5,382 sq ft)
+
+Including the overseas territories of France which are located outside the continent of Europe, but which are members of the union, the EU experiences most types of climate from Arctic (north-east Europe) to tropical (French Guiana), rendering meteorological averages for the EU as a whole meaningless. The majority of the population lives in areas with a temperate maritime climate (North-Western Europe and Central Europe), a Mediterranean climate (Southern Europe), or a warm summer continental or hemiboreal climate (Northern Balkans and Central Europe).[125]
+
+The EU's population is highly urbanised, with some 75% of inhabitants living in urban areas as of 2006. Cities are largely spread out across the EU with a large grouping in and around the Benelux.[126]
+
+The EU operates through a hybrid system of supranational and intergovernmental decision-making,[127][128] and according to the principles of conferral (which says that it should act only within the limits of the competences conferred on it by the treaties) and of subsidiarity (which says that it should act only where an objective cannot be sufficiently achieved by the member states acting alone). Laws made by the EU institutions are passed in a variety of forms.[129] Generally speaking, they can be classified into two groups: those which come into force without the necessity for national implementation measures (regulations) and those which specifically require national implementation measures (directives).[130]
+
+Constitutionally, the EU bears some resemblance to both a confederation and a federation,[131][132] but has not formally defined itself as either. (It does not have a formal constitution: its status is defined by the Treaty of European Union and the Treaty on the Functioning of the European Union). It is more integrated than a traditional confederation of states because the general level of government widely employs qualified majority voting in some decision-making among the member states, rather than relying exclusively on unanimity.[133][134] It is less integrated than a federal state because it is not a state in its own right: sovereignty continues to flow 'from the bottom up', from the several peoples of the separate member states, rather than from a single undifferentiated whole. This is reflected in the fact that the member states remain the 'masters of the Treaties', retaining control over the allocation of competences to the Union through constitutional change (thus retaining so-called Kompetenz-kompetenz); in that they retain control of the use of armed force; they retain control of taxation; and in that they retain a right of unilateral withdrawal from the Union under Article 50 of the Treaty on European Union. In addition, the principle of subsidiarity requires that only those matters that need to be determined collectively are so determined.
+
+The European Union has seven principal decision-making bodies, its institutions: the European Parliament, the European Council, the Council of the European Union, the European Commission, the Court of Justice of the European Union, the European Central Bank and the European Court of Auditors. Competence in scrutinising and amending legislation is shared between the Council of the European Union and the European Parliament, while executive tasks are performed by the European Commission and in a limited capacity by the European Council (not to be confused with the aforementioned Council of the European Union). The monetary policy of the eurozone is determined by the European Central Bank. The interpretation and the application of EU law and the treaties are ensured by the Court of Justice of the European Union. The EU budget is scrutinised by the European Court of Auditors. There are also a number of ancillary bodies which advise the EU or operate in a specific area.
+
+EU policy is in general promulgated by EU directives, which are then implemented in the domestic legislation of its member states, and EU regulations, which are immediately enforceable in all member states. Lobbying at EU level by special interest groups is regulated to try to balance the aspirations of private initiatives with public interest decision-making process[135]
+
+The European Parliament is one of three legislative institutions of the EU, which together with the Council of the European Union is tasked with amending and approving the Commission's proposals.
+The 705 Members of the European Parliament (MEPs) are directly elected by EU citizens every five years on the basis of proportional representation. MEPs are elected on a national basis and they sit according to political groups rather than their nationality. Each country has a set number of seats and is divided into sub-national constituencies where this does not affect the proportional nature of the voting system.[136]
+
+In the ordinary legislative procedure, the European Commission proposes legislation, which requires the joint approval of the European Parliament and the Council of the European Union to pass. This process applies to nearly all areas, including the EU budget. The Parliament is the final body to approve or reject the proposed membership of the Commission, and can attempt motions of censure on the Commission by appeal to the Court of Justice. The President of the European Parliament (currently David Sassoli) carries out the role of speaker in Parliament and represents it externally. The President and Vice-Presidents are elected by MEPs every two and a half years.[137]
+
+The European Council gives political direction to the EU. It convenes at least four times a year and comprises the President of the European Council (currently Charles Michel), the President of the European Commission and one representative per member state (either its head of state or head of government). The High Representative of the Union for Foreign Affairs and Security Policy (currently Josep Borrell) also takes part in its meetings. It has been described by some as the Union's "supreme political authority".[138] It is actively involved in the negotiation of treaty changes and defines the EU's policy agenda and strategies.
+
+The European Council uses its leadership role to sort out disputes between member states and the institutions, and to resolve political crises and disagreements over controversial issues and policies. It acts externally as a "collective head of state" and ratifies important documents (for example, international agreements and treaties).[139]
+
+Tasks for the President of the European Council are ensuring the external representation of the EU,[140] driving consensus and resolving divergences among member states, both during meetings of the European Council and over the periods between them.
+
+The European Council should not be mistaken for the Council of Europe, an international organisation independent of the EU based in Strasbourg.
+
+The European Commission acts both as the EU's executive arm, responsible for the day-to-day running of the EU, and also the legislative initiator, with the sole power to propose laws for debate.[141][142][143] The Commission is 'guardian of the Treaties' and is responsible for their efficient operation and policing.[144] It operates de facto as a cabinet government,[citation needed] with 27 Commissioners for different areas of policy, one from each member state, though Commissioners are bound to represent the interests of the EU as a whole rather than their home state.
+
+One of the 27 is the President of the European Commission (Jean-Claude Juncker for 2014–2019), appointed by the European Council, subject to the Parliament's approval. After the President, the most prominent Commissioner is the High Representative of the Union for Foreign Affairs and Security Policy, who is ex-officio a Vice-President of the Commission and is also chosen by the European Council.[145] The other 26 Commissioners are subsequently appointed by the Council of the European Union in agreement with the nominated President. The 27 Commissioners as a single body are subject to approval (or otherwise) by vote of the European Parliament.
+
+The Council of the European Union (also called the "Council"[146] and the "Council of Ministers", its former title)[147] forms one half of the EU's legislature. It consists of a government minister from each member state and meets in different compositions depending on the policy area being addressed. Notwithstanding its different configurations, it is considered to be one single body.[148] In addition to its legislative functions, the Council also exercises executive functions in relations to the Common Foreign and Security Policy.
+
+In some policies, there are several member states that ally with strategic partners within the Union. Examples of such alliances include the Visegrad Group, Benelux, the Baltic Assembly, the New Hanseatic League, and the Craiova Group.
+
+The EU had an agreed budget of €120.7 billion for the year 2007 and €864.3 billion for the period 2007–2013,[150] representing 1.10% and 1.05% of the EU-27's GNI forecast for the respective periods. In 1960, the budget of the then European Economic Community was 0.03% of GDP.[151]
+
+In the 2010 budget of €141.5 billion, the largest single expenditure item is "cohesion & competitiveness" with around 45% of the total budget.[152] Next comes "agriculture" with approximately 31% of the total.[152] "Rural development, environment and fisheries" takes up around 11%.[152] "Administration" accounts for around 6%.[152] The "EU as a global partner" and "citizenship, freedom, security and justice" bring up the rear with approximately 6% and 1% respectively.[152]
+
+The Court of Auditors is legally obliged to provide the Parliament and the Council (specifically, the Economic and Financial Affairs Council) with "a statement of assurance as to the reliability of the accounts and the legality and regularity of the underlying transactions".[153] The Court also gives opinions and proposals on financial legislation and anti-fraud actions.[154] The Parliament uses this to decide whether to approve the Commission's handling of the budget.
+
+The European Court of Auditors has signed off the European Union accounts every year since 2007 and, while making it clear that the European Commission has more work to do, has highlighted that most of the errors take place at national level.[155][156] In their report on 2009 the auditors found that five areas of Union expenditure, agriculture and the cohesion fund, were materially affected by error.[157] The European Commission estimated in 2009 that the financial effect of irregularities was €1,863 million.[158]
+
+EU member states retain all powers not explicitly handed to the European Union. In some areas the EU enjoys exclusive competence. These are areas in which member states have renounced any capacity to enact legislation. In other areas the EU and its member states share the competence to legislate. While both can legislate, member states can only legislate to the extent to which the EU has not. In other policy areas the EU can only co-ordinate, support and supplement member state action but cannot enact legislation with the aim of harmonising national laws.[159]
+
+That a particular policy area falls into a certain category of competence is not necessarily indicative of what legislative procedure is used for enacting legislation within that policy area. Different legislative procedures are used within the same category of competence, and even with the same policy area.
+
+The distribution of competences in various policy areas between Member States and the Union is divided in the following three categories:
+
+The EU is based on a series of treaties. These first established the European Community and the EU, and then made amendments to those founding treaties.[161] These are power-giving treaties which set broad policy goals and establish institutions with the necessary legal powers to implement those goals. These legal powers include the ability to enact legislation[q] which can directly affect all member states and their inhabitants.[r] The EU has legal personality, with the right to sign agreements and international treaties.[162]
+
+Under the principle of supremacy, national courts are required to enforce the treaties that their member states have ratified, and thus the laws enacted under them, even if doing so requires them to ignore conflicting national law, and (within limits) even constitutional provisions.[s]
+
+The direct effect and supremacy doctrines were not explicitly set out in the European Treaties but were developed by the Court of Justice itself over the 1960s, apparently under the influence of its then most influential judge, Frenchman Robert Lecourt[163]
+
+The judicial branch of the EU—formally called the Court of Justice of the European Union—consists of two courts: the Court of Justice and the General Court.[164]
+The Court of Justice primarily deals with cases taken by member states, the institutions, and cases referred to it by the courts of member states.[165] Because of the doctrines of direct effect and supremacy, many judgments of the Court of Justice are automatically applicable within the internal legal orders of the member states.
+
+The General Court mainly deals with cases taken by individuals and companies directly before the EU's courts,[166] and the European Union Civil Service Tribunal adjudicates in disputes between the European Union and its civil service.[167] Decisions from the General Court can be appealed to the Court of Justice but only on a point of law.[168]
+
+The treaties declare that the EU itself is "founded on the values of respect for human dignity, freedom, democracy, equality, the rule of law and respect for human rights, including the rights of persons belonging to minorities ... in a society in which pluralism, non-discrimination, tolerance, justice, solidarity and equality between women and men prevail."[169]
+
+In 2009, the Lisbon Treaty gave legal effect to the Charter of Fundamental Rights of the European Union. The charter is a codified catalogue of fundamental rights against which the EU's legal acts can be judged. It consolidates many rights which were previously recognised by the Court of Justice and derived from the "constitutional traditions common to the member states."[170] The Court of Justice has long recognised fundamental rights and has, on occasion, invalidated EU legislation based on its failure to adhere to those fundamental rights.[171]
+
+Signing the European Convention on Human Rights (ECHR) is a condition for EU membership.[t] Previously, the EU itself could not accede to the Convention as it is neither a state[u] nor had the competence to accede.[v] The Lisbon Treaty and Protocol 14 to the ECHR have changed this: the former binds the EU to accede to the Convention while the latter formally permits it.
+
+The EU is independent from the Council of Europe, although they share purpose and ideas,  especially on the rule of law, human rights and democracy. Furthermore, the European Convention on Human Rights and European Social Charter, as well as the source of law for the Charter of Fundamental Rights are created by the Council of Europe. The EU has also promoted human rights issues in the wider world. The EU opposes the death penalty and has proposed its worldwide abolition. Abolition of the death penalty is a condition for EU membership.[172]
+
+The main legal acts of the EU come in three forms: regulations, directives, and decisions. Regulations become law in all member states the moment they come into force, without the requirement for any implementing measures,[w] and automatically override conflicting domestic provisions.[q] Directives require member states to achieve a certain result while leaving them discretion as to how to achieve the result. The details of how they are to be implemented are left to member states.[x] When the time limit for implementing directives passes, they may, under certain conditions, have direct effect in national law against member states.
+
+Decisions offer an alternative to the two above modes of legislation. They are legal acts which only apply to specified individuals, companies or a particular member state. They are most often used in competition law, or on rulings on State Aid, but are also frequently used for procedural or administrative matters within the institutions. Regulations, directives, and decisions are of equal legal value and apply without any formal hierarchy.[173]
+
+The European Ombudsman was established by the Maastricht Treaty. The ombudsman is elected by the European Parliament for the length of the Parliament's term, and the position is renewable.[174] Any EU citizen or entity may appeal to the ombudsman to investigate an EU institution on the grounds of maladministration (administrative irregularities, unfairness, discrimination, abuse of power, failure to reply, refusal of information or unnecessary delay).[175] Emily O'Reilly is the current ombudsman since 2013.[176]
+
+The borders inside the Schengen Area between Germany and Austria
+
+Europol Headquarters in The Hague, Netherlands
+
+Eurojust Headquarters in The Hague, Netherlands
+
+Seat of Frontex in Warsaw, Poland
+
+Since the creation of the EU in 1993, it has developed its competencies in the area of justice and home affairs; initially at an intergovernmental level and later by supranationalism. Accordingly, the Union has legislated in areas such as extradition,[177] family law,[178] asylum law,[179] and criminal justice.[180] Prohibitions against sexual and nationality discrimination have a long standing in the treaties.[y] In more recent years, these have been supplemented by powers to legislate against discrimination based on race, religion, disability, age, and sexual orientation.[z] By virtue of these powers, the EU has enacted legislation on sexual discrimination in the work-place, age discrimination, and racial discrimination.[aa]
+
+The Union has also established agencies to co-ordinate police, prosecutorial and immigrations controls across the member states: Europol for co-operation of police forces,[181] Eurojust for co-operation between prosecutors,[182] and Frontex for co-operation between border control authorities.[183] The EU also operates the Schengen Information System[16] which provides a common database for police and immigration authorities. This co-operation had to particularly be developed with the advent of open borders through the Schengen Agreement and the associated cross border crime.
+
+Foreign policy co-operation between member states dates from the establishment of the Community in 1957, when member states negotiated as a bloc in international trade negotiations under the EU's common commercial policy.[184] Steps for a more wide-ranging co-ordination in foreign relations began in 1970 with the establishment of European Political Cooperation which created an informal consultation process between member states with the aim of forming common foreign policies. In 1987 the European Political Cooperation was introduced on a formal basis by the Single European Act. EPC was renamed as the Common Foreign and Security Policy (CFSP) by the Maastricht Treaty.[185]
+
+The aims of the CFSP are to promote both the EU's own interests and those of the international community as a whole, including the furtherance of international co-operation, respect for human rights, democracy, and the rule of law.[186] The CFSP requires unanimity among the member states on the appropriate policy to follow on any particular issue. The unanimity and difficult issues treated under the CFSP sometimes lead to disagreements, such as those which occurred over the war in Iraq.[187]
+
+The coordinator and representative of the CFSP within the EU is the High Representative of the Union for Foreign Affairs and Security Policy who speaks on behalf of the EU in foreign policy and defence matters, and has the task of articulating the positions expressed by the member states on these fields of policy into a common alignment. The High Representative heads up the European External Action Service (EEAS), a unique EU department[188] that has been officially implemented and operational since 1 December 2010 on the occasion of the first anniversary of the entry into force of the Treaty of Lisbon.[189] The EEAS will serve as a foreign ministry and diplomatic corps for the European Union.[190]
+
+Besides the emerging international policy of the European Union, the international influence of the EU is also felt through enlargement. The perceived benefits of becoming a member of the EU act as an incentive for both political and economic reform in states wishing to fulfil the EU's accession criteria, and are considered an important factor contributing to the reform of European formerly Communist countries.[191]:762 This influence on the internal affairs of other countries is generally referred to as "soft power", as opposed to military "hard power".[192]
+
+The predecessors of the European Union were not devised as a military alliance because NATO was largely seen as appropriate and sufficient for defence purposes.[193] 21 EU members are members of NATO[194] while the remaining member states follow policies of neutrality.[195] The Western European Union, a military alliance with a mutual defence clause, was disbanded in 2010 as its role had been transferred to the EU.[196]
+
+France is the only member officially recognised as a nuclear weapon state holding a permanent seat on the United Nations Security Council. Most EU member states opposed the Nuclear Weapon Ban Treaty.[197]
+
+Following the Kosovo War in 1999, the European Council agreed that "the Union must have the capacity for autonomous action, backed by credible military forces, the means to decide to use them, and the readiness to do so, in order to respond to international crises without prejudice to actions by NATO". To that end, a number of efforts were made to increase the EU's military capability, notably the Helsinki Headline Goal process. After much discussion, the most concrete result was the EU Battlegroups initiative, each of which is planned to be able to deploy quickly about 1500 personnel.[198]
+
+EU forces have been deployed on peacekeeping missions from middle and northern Africa to the western Balkans and western Asia.[199] EU military operations are supported by a number of bodies, including the European Defence Agency, European Union Satellite Centre and the European Union Military Staff.[200] Frontex is an agency of the EU established to manage the cooperation between national border guards securing its external borders. It aims to detect and stop illegal immigration, human trafficking and terrorist infiltration. In 2015 the European Commission presented its proposal for a new European Border and Coast Guard Agency having a stronger role and mandate along with national authorities for border management. In an EU consisting of 27 members, substantial security and defence co-operation is increasingly relying on collaboration among all member states.[201]
+
+The European Commission's Humanitarian Aid and Civil Protection department, or "ECHO", provides humanitarian aid from the EU to developing countries. In 2012, its budget amounted to €874 million, 51% of the budget went to Africa and 20% to Asia, Latin America, the Caribbean and Pacific, and 20% to the Middle East and Mediterranean.[202]
+
+Humanitarian aid is financed directly by the budget (70%) as part of the financial instruments for external action and also by the European Development Fund (30%).[203] The EU's external action financing is divided into 'geographic' instruments and 'thematic' instruments.[203] The 'geographic' instruments provide aid through the Development Cooperation Instrument (DCI, €16.9 billion, 2007–2013), which must spend 95% of its budget on official development assistance (ODA), and from the European Neighbourhood and Partnership Instrument (ENPI), which contains some relevant programmes.[203] The European Development Fund (EDF, €22.7 billion for the period 2008–2013 and €30.5 billion for the period 2014–2020) is made up of voluntary contributions by member states, but there is pressure to merge the EDF into the budget-financed instruments to encourage increased contributions to match the 0.7% target and allow the European Parliament greater oversight.[203][204]
+
+In 2016, the average among EU countries was 0.4% and five had met or exceeded the 0.7% target: Denmark, Germany, Luxembourg, Sweden and the United Kingdom.[205] If considered collectively, EU member states are the largest contributor of foreign aid in the world.[206][207]
+
+The EU uses foreign relations instruments like the European Neighbourhood Policy which seeks to tie those countries to the east and south of the European territory of the EU to the Union. These countries, primarily developing countries, include some who seek to one day become either a member state of the European Union, or more closely integrated with the European Union. The EU offers financial assistance to countries within the European Neighbourhood, so long as they meet the strict conditions of government reform, economic reform and other issues surrounding positive transformation. This process is normally underpinned by an Action Plan, as agreed by both Brussels and the target country.
+
+International recognition of sustainable development as a key element is growing steadily. Its role was recognized in three major UN summits on sustainable development: the 1992 UN Conference on Environment and Development (UNCED) in Rio de Janeiro, Brazil; the 2002 World Summit on Sustainable Development (WSSD) in Johannesburg, South Africa; and the 2012 UN Conference on Sustainable Development (UNCSD) in Rio de Janeiro. Other key global agreements are the Paris Agreement and the 2030 Agenda for Sustainable Development (United Nations, 2015). The SDGs recognize that all countries must stimulate action in the following key areas - people, planet, prosperity, peace and partnership - in order to tackle the global challenges that are crucial for the survival of humanity.
+
+EU development action is based on the European Consensus on Development, which was endorsed on 20 December 2005 by EU Member States, the Council, the European Parliament and the Commission.[208] It is applied from the principles of Capability approach and Rights-based approach to development.
+
+Partnership and cooperation agreements are bilateral agreements with non-member nations.[209]
+
+The European Union is the largest exporter in the world[213] and as of 2008 the largest importer of goods and services.[214][215] Internal trade between the member states is aided by the removal of barriers to trade such as tariffs and border controls. In the eurozone, trade is helped by not having any currency differences to deal with amongst most members.[216]
+
+The European Union Association Agreement does something similar for a much larger range of countries, partly as a so-called soft approach ('a carrot instead of a stick') to influence the politics in those countries.
+The European Union represents all its members at the World Trade Organization (WTO), and acts on behalf of member states in any disputes. When the EU negotiates trade related agreement outside the WTO framework, the subsequent agreement must be approved by each individual EU member state government.[216]
+
+The European Union has concluded free trade agreements (FTAs)[217] and other agreements with a trade component with many countries worldwide and is negotiating with many others.[218]
+
+As a political entity the European Union is represented in the World Trade Organization (WTO). EU member states own the estimated second largest after the United States (US$105 trillion) net wealth in the world, equal to around 20% (~€60 trillion) of the US$360 trillion (~€300 trillion)[219] global wealth.[220]
+
+19 member states have joined a monetary union known as the eurozone, which uses the euro as a single currency. The currency union represents 342 million EU citizens.[221] The euro is the second largest reserve currency as well as the second most traded currency in the world after the United States dollar.[222][223][224]
+
+Of the top 500 largest corporations in the world measured by revenue in 2010, 161 had their headquarters in the EU.[225] In 2016, unemployment in the EU stood at 8.9%[226] while inflation was at 2.2%, and the current account balance at −0.9% of GDP. The average annual net earnings in the European Union was around €24,000 (US$30,000)[227] in 2015.
+
+There is a significant variation in Nominal GDP per capita within individual EU states. The difference between the richest and poorest regions (281 NUTS-2 regions of the Nomenclature of Territorial Units for Statistics) ranged, in 2017, from 31% (Severozapaden, Bulgaria) of the EU28 average (€30,000) to 253% (Luxembourg), or from €4,600 to €92,600.[228]
+
+Two of the original core objectives of the European Economic Community were the development of a common market, subsequently becoming a single market, and a customs union between its member states. The single market involves the free circulation of goods, capital, people, and services within the EU,[221] and the customs union involves the application of a common external tariff on all goods entering the market. Once goods have been admitted into the market they cannot be subjected to customs duties, discriminatory taxes or import quotas, as they travel internally. The non-EU member states of Iceland, Norway, Liechtenstein and Switzerland participate in the single market but not in the customs union.[119] Half the trade in the EU is covered by legislation harmonised by the EU.[229]
+
+Free movement of capital is intended to permit movement of investments such as property purchases and buying of shares between countries.[230] Until the drive towards economic and monetary union the development of the capital provisions had been slow. Post-Maastricht there has been a rapidly developing corpus of ECJ judgements regarding this initially neglected freedom. The free movement of capital is unique insofar as it is granted equally to non-member states.
+
+The free movement of persons means that EU citizens can move freely between member states to live, work, study or retire in another country. This required the lowering of administrative formalities and recognition of professional qualifications of other states.[231]
+
+The free movement of services and of establishment allows self-employed persons to move between member states to provide services on a temporary or permanent basis. While services account for 60–70% of GDP, legislation in the area is not as developed as in other areas. This lacuna has been addressed by the recently passed Directive on services in the internal market which aims to liberalise the cross border provision of services.[232] According to the Treaty the provision of services is a residual freedom that only applies if no other freedom is being exercised.
+
+The creation of a European single currency became an official objective of the European Economic Community in 1969. In 1992, having negotiated the structure and procedures of a currency union, the member states signed the Maastricht Treaty and were legally bound to fulfil the agreed-on rules including the convergence criteria if they wanted to join the monetary union. The states wanting to participate had first to join the European Exchange Rate Mechanism.
+
+In 1999 the currency union started, first as an accounting currency with eleven member states joining. In 2002, the currency was fully put into place, when euro notes and coins were issued and national currencies began to phase out in the eurozone, which by then consisted of 12 member states. The eurozone (constituted by the EU member states which have adopted the euro) has since grown to 19 countries.[233][ab]
+
+The euro, and the monetary policies of those who have adopted it in agreement with the EU, are under the control of the European Central Bank (ECB).[234] The ECB is the central bank for the eurozone, and thus controls monetary policy in that area with an agenda to maintain price stability. It is at the centre of the European System of Central Banks, which comprehends all EU national central banks and is controlled by its General Council, consisting of the President of the ECB, who is appointed by the European Council, the Vice-President of the ECB, and the governors of the national central banks of all 27 EU member states.[235]
+
+The European System of Financial Supervision is an institutional architecture of the EU's framework of financial supervision composed by three authorities: the European Banking Authority, the European Insurance and Occupational Pensions Authority and the European Securities and Markets Authority. To complement this framework, there is also a European Systemic Risk Board under the responsibility of the ECB. The aim of this financial control system is to ensure the economic stability of the EU.[236]
+
+To prevent the joining states from getting into financial trouble or crisis after entering the monetary union, they were obliged in the Maastricht treaty to fulfil important financial obligations and procedures, especially to show budgetary discipline and a high degree of sustainable economic convergence, as well as to avoid excessive government deficits and limit the government debt to a sustainable level.
+
+The European Commission working sectors are: Aeronautics, automotive, biotechnology, chemicals, construction, cosmetics, defense, electronics, firearms, food and drink, gambling, healthcare, maritime, mechanics, medical, postal, raw materials, space, textile, tourism, toys and Social economy (Societas cooperativa Europaea).
+
+In 2006, the EU-27 had a gross inland energy consumption of 1,825 million tonnes of oil equivalent (toe).[237] Around 46% of the energy consumed was produced within the member states while 54% was imported.[237] In these statistics, nuclear energy is treated as primary energy produced in the EU, regardless of the source of the uranium, of which less than 3% is produced in the EU.[238]
+
+The EU has had legislative power in the area of energy policy for most of its existence; this has its roots in the original European Coal and Steel Community. The introduction of a mandatory and comprehensive European energy policy was approved at the meeting of the European Council in October 2005, and the first draft policy was published in January 2007.[239]
+
+The EU has five key points in its energy policy: increase competition in the internal market, encourage investment and boost interconnections between electricity grids; diversify energy resources with better systems to respond to a crisis; establish a new treaty framework for energy co-operation with Russia while improving relations with energy-rich states in Central Asia[240] and North Africa; use existing energy supplies more efficiently while increasing renewable energy commercialisation; and finally increase funding for new energy technologies.[239]
+
+In 2007, EU countries as a whole imported 82% of their oil, 57% of their natural gas[241] and 97.48% of their uranium[238] demands. There is a strong dependence on Russian energy that the EU has been attempting to reduce.[242]
+
+The EU is working to improve cross-border infrastructure within the EU, for example through the Trans-European Networks (TEN). Projects under TEN include the Channel Tunnel, LGV Est, the Fréjus Rail Tunnel, the Öresund Bridge, the Brenner Base Tunnel and the Strait of Messina Bridge. In 2010 the estimated network covers: 75,200 kilometres (46,700 mi) of roads; 78,000 kilometres (48,000 mi) of railways; 330 airports; 270 maritime harbours; and 210 internal harbours.[243][244]
+
+Rail transport in Europe is being synchronised with the European Rail Traffic Management System (ERTMS), an initiative to greatly enhance safety, increase efficiency of trains and enhance cross-border interoperability of rail transport in Europe by replacing signalling equipment with digitised mostly wireless versions and by creating a single Europe-wide standard for train control and command systems.
+
+The developing European transport policies will increase the pressure on the environment in many regions by the increased transport network. In the pre-2004 EU members, the major problem in transport deals with congestion and pollution. After the recent enlargement, the new states that joined since 2004 added the problem of solving accessibility to the transport agenda.[245] The Polish road network was upgraded such as the A4 autostrada.[246]
+
+The Galileo positioning system is another EU infrastructure project. Galileo is a proposed Satellite navigation system, to be built by the EU and launched by the European Space Agency (ESA). The Galileo project was launched partly to reduce the EU's dependency on the US-operated Global Positioning System, but also to give more complete global coverage and allow for greater accuracy, given the aged nature of the GPS system.[247]
+
+The Common Agricultural Policy (CAP) is one of the long lasting policies of the European Community.[248] The policy has the objectives of increasing agricultural production, providing certainty in food supplies, ensuring a high quality of life for farmers, stabilising markets, and ensuring reasonable prices for consumers.[ad] It was, until recently, operated by a system of subsidies and market intervention. Until the 1990s, the policy accounted for over 60% of the then European Community's annual budget, and as of 2013[update] accounts for around 34%.[249]
+
+The policy's price controls and market interventions led to considerable overproduction. These were intervention stores of products bought up by the Community to maintain minimum price levels. To dispose of surplus stores, they were often sold on the world market at prices considerably below Community guaranteed prices, or farmers were offered subsidies (amounting to the difference between the Community and world prices) to export their products outside the Community. This system has been criticised for under-cutting farmers outside Europe, especially those in the developing world.[250] Supporters of CAP argue that the economic support which it gives to farmers provides them with a reasonable standard of living.[250]
+
+Since the beginning of the 1990s, the CAP has been subject to a series of reforms. Initially, these reforms included the introduction of set-aside in 1988, where a proportion of farm land was deliberately withdrawn from production, milk quotas and, more recently, the 'de-coupling' (or disassociation) of the money farmers receive from the EU and the amount they produce (by the Fischler reforms in 2004). Agriculture expenditure will move away from subsidy payments linked to specific produce, toward direct payments based on farm size. This is intended to allow the market to dictate production levels.[248] One of these reforms entailed the modification of the EU's sugar regime, which previously divided the sugar market between member states and certain African-Caribbean nations with a privileged relationship with the EU.[251]
+
+The EU operates a competition policy intended to ensure undistorted competition within the single market.[ae]
+
+The Competition Commissioner, currently Margrethe Vestager, is one of the most powerful positions in the Commission, notable for the ability to affect the commercial interests of trans-national corporations.[citation needed] For example, in 2001 the Commission for the first time prevented a merger between two companies based in the United States (GE and Honeywell) which had already been approved by their national authority.[252] Another high-profile case against Microsoft, resulted in the Commission fining Microsoft over €777 million following nine years of legal action.[253]
+
+The EU seasonally adjusted unemployment rate was 6.7% in September 2018.[254] The euro area unemployment rate was 8.1%.[254] Among the member states, the lowest unemployment rates were recorded in the Czech Republic (2.3%), Germany and Poland (both 3.4%), and the highest in Spain (14.9%) and Greece (19.0 in July 2018).[254]
+
+The EU has long sought to mitigate the effects of free markets by protecting workers rights and preventing social and environmental dumping. To this end it has adopted laws establishing minimum employment and environmental standards. These included the Working Time Directive and the Environmental Impact Assessment Directive. The EU has also sought to coordinate the social security and health systems of member states to facilitate individuals exercising free movement rights and to ensure they maintain their ability to access social security and health services in other member states.
+
+The European Social Charter is the main body that recognizes the social rights of European citizens.
+
+A European unemployment insurance has been proposed among others by the commissioner of Jobs Nicolas Schmit.[255]
+
+Since 2019 there is a European Commissioner for Equality; a European Institute for Gender Equality has existed since 2007.
+
+Housing, youth, childhood, Functional diversity or elderly care are supportive competencies of the European Union and can be financed by the European Social Fund.
+
+Structural Funds and Cohesion Funds are supporting the development of underdeveloped regions of the EU. Such regions are primarily located in the states of central and southern Europe.[256][257] Several funds provide emergency aid, support for candidate members to transform their country to conform to the EU's standard (Phare, ISPA, and SAPARD), and support to the Commonwealth of Independent States (TACIS). TACIS has now become part of the worldwide EuropeAid programme.
+
+Demographic transition to a society of aging population, low fertility-rates and depopulation of non-metropolitan regions is tackled within this policies.
+
+In 1957, when the EEC was founded, it had no environmental policy.[258] Over the past 50 years, an increasingly dense network of legislation has been created, extending to all areas of environmental protection, including air pollution, water quality, waste management, nature conservation, and the control of chemicals, industrial hazards, and biotechnology.[259] According to the Institute for European Environmental Policy, environmental law comprises over 500 Directives, Regulations and Decisions, making environmental policy a core area of European politics.[260]
+
+European policy-makers originally increased the EU's capacity to act on environmental issues by defining it as a trade problem.[261]
+Trade barriers and competitive distortions in the Common Market could emerge due to the different environmental standards in each member state.[262] In subsequent years, the environment became a formal policy area, with its own policy actors, principles and procedures. The legal basis for EU environmental policy was established with the introduction of the Single European Act in 1987.[260]
+
+Initially, EU environmental policy focused on Europe. More recently, the EU has demonstrated leadership in global environmental governance, e.g. the role of the EU in securing the ratification and coming into force of the Kyoto Protocol despite opposition from the United States. This international dimension is reflected in the EU's Sixth Environmental Action Programme,[263] which recognises that its objectives can only be achieved if key international agreements are actively supported and properly implemented both at EU level and worldwide. The Lisbon Treaty further strengthened the leadership ambitions.[264] EU law has played a significant role in improving habitat and species protection in Europe, as well as contributing to improvements in air and water quality and waste management.[260]
+
+Mitigating climate change is one of the top priorities of EU environmental policy. In 2007, member states agreed that, in the future, 20% of the energy used across the EU must be renewable, and carbon dioxide emissions have to be lower in 2020 by at least 20% compared to 1990 levels.[265] The EU has adopted an emissions trading system to incorporate carbon emissions into the economy.[266] The European Green Capital is an annual award given to cities that focuses on the environment, energy efficiency, and quality of life in urban areas to create smart city.
+
+In the Elections to the European Parliament in 2019, the green parties increased their power, possibly because of the rise of post materialist values.[267]
+
+Proposals to reach a zero carbon economy in the European Union by 2050 were suggested in 2018 - 2019. Almost all member states supported that goal at an EU summit in June 2019. The Czech Republic, Estonia, Hungary, and Poland disagreed.[268]
+
+Basic education is an area where the EU's role is limited to supporting national governments. In higher education, the policy was developed in the 1980s in programmes supporting exchanges and mobility. The most visible of these has been the Erasmus Programme, a university exchange programme which began in 1987. In its first 20 years, it supported international exchange opportunities for well over 1.5 million university and college students and became a symbol of European student life.[269]
+
+There are similar programmes for school pupils and teachers, for trainees in vocational education and training, and for adult learners in the Lifelong Learning Programme 2007–2013. These programmes are designed to encourage a wider knowledge of other countries and to spread good practices in the education and training fields across the EU.[270][271] Through its support of the Bologna Process, the EU is supporting comparable standards and compatible degrees across Europe.
+
+Scientific development is facilitated through the EU's Framework Programmes, the first of which started in 1984. The aims of EU policy in this area are to co-ordinate and stimulate research. The independent European Research Council allocates EU funds to European or national research projects.[272] EU research and technological framework programmes deal in a number of areas, for example energy where the aim is to develop a diverse mix of renewable energy to help the environment and to reduce dependence on imported fuels.[273]
+
+The EU has no major competences in the field of health care and Article 35 of the Charter of Fundamental Rights of the European Union affirms that "A high level of human health protection shall be ensured in the definition and implementation of all Union policies and activities". The European Commission's Directorate-General for Health and Consumers seeks to align national laws on the protection of people's health, on the consumers' rights, on the safety of food and other products.[274][275][276]
+
+All EU and many other European countries offer their citizens a free European Health Insurance Card which, on a reciprocal basis, provides insurance for emergency medical treatment insurance when visiting other participating European countries.[277] A directive on cross-border healthcare aims at promoting co-operation on health care between member states and facilitating access to safe and high-quality cross-border healthcare for European patients.[278][279][280]
+
+The EU has some of the highest levels of life expectancy in the world, with Spain, Italy, Sweden, France, Malta, Ireland, Netherlands, Luxembourg, and Greece all among the world's top 20 countries with the highest life expectancy.[281] In general, life expectancy is lower in Eastern Europe than in Western Europe.[282] In 2018, the EU region with the highest life expectancy was Madrid, Spain at 85.2 years, followed by the Spanish regions of La Rioja and Castilla y León both at 84.3 years, Trentino in Italy at 84.3 years and Île-de-France in France at 84.2 years. The overall life expectancy in the EU in 2018 was 81.0 years, higher than the World average of 72.6 years.[283]
+
+Cultural co-operation between member states has been an interest of the EU since its inclusion as a community competency in the Maastricht Treaty.[284] Actions taken in the cultural area by the EU include the Culture 2000 seven-year programme,[284] the European Cultural Month event,[285] and orchestras such as the European Union Youth Orchestra.[286] The European Capital of Culture programme selects one or more cities in every year to assist the cultural development of that city.[287]
+
+Association football is by far the most popular sport in the European Union by the number of registered players. The other sports with the most participants in clubs are tennis, basketball, swimming, athletics, golf, gymnastics, equestrian sports, handball, volleyball and sailing.[288]
+
+Sport is mainly the responsibility of the member states or other international organisations, rather than of the EU. There are some EU policies that have affected sport, such as the free movement of workers, which was at the core of the Bosman ruling that prohibited national football leagues from imposing quotas on foreign players with European citizenship.[289]
+
+The Treaty of Lisbon requires any application of economic rules to take into account the specific nature of sport and its structures based on voluntary activity.[290] This followed lobbying by governing organisations such as the International Olympic Committee and FIFA, due to objections over the application of free market principles to sport, which led to an increasing gap between rich and poor clubs.[291] The EU does fund a programme for Israeli, Jordanian, Irish, and British football coaches, as part of the Football 4 Peace project.[292]
+
+The flag used is the Flag of Europe, which consists of a circle of 12 golden stars on a blue background. Originally designed in 1955 for the Council of Europe, the flag was adopted by the European Communities, the predecessors of the present Union, in 1986. The Council of Europe gave the flag a symbolic description in the following terms,[293] though the official symbolic description adopted by the EU omits the reference to the "Western world":[294]
+
+Against the blue sky of the Western world, the stars symbolise the peoples of Europe in a form of a circle, the sign of union. The number of stars is invariably twelve, the figure twelve being the symbol of perfection and entirety.
+
+United in Diversity was adopted as the motto of the Union in the year 2000, having been selected from proposals submitted by school pupils.[295] Since 1985, the flag day of the Union has been Europe Day, on 9 May (the date of the 1950 Schuman declaration). The anthem of the Union is an instrumental version of the prelude to the Ode to Joy, the 4th movement of Ludwig van Beethoven's ninth symphony. The anthem was adopted by European Community leaders in 1985 and has since been played on official occasions.[296]
+Besides naming the continent, the Greek mythological figure of Europa has frequently been employed as a personification of Europe. Known from the myth in which Zeus seduces her in the guise of a white bull, Europa has also been referred to in relation to the present Union. Statues of Europa and the bull decorate several of the Union's institutions and a portrait of her is seen on the 2013 series of Euro banknotes. The bull is, for its part, depicted on all residence permit cards.[297]
+
+Charles the Great, also known as Charlemagne (Latin: Carolus Magnus) and later recognised as Pater Europae ("Father of Europe"),[298][299][300] has a symbolic relevance to Europe. The Commission has named one of its central buildings in Brussels after Charlemagne and the city of Aachen has since 1949 awarded the Charlemagne Prize to champions of European unification.[301] Since 2008, the organisers of this prize, in conjunction with the European Parliament, have awarded the Charlemagne Youth Prize in recognition of similar efforts by young people.[302]
+
+Media freedom is a fundamental right that applies to all member states of the European Union and its citizens, as defined in the EU Charter of Fundamental Rights as well as the European Convention on Human Rights.[303]:1 Within the EU enlargement process, guaranteeing media freedom is named a "key indicator of a country's readiness to become part of the EU".[304]
+
+The majority of media in the European Union are national-oriented. Some EU-wide media focusing on European affairs have emerged since the early 1990s, such as Euronews, EUobserver, EURACTIV or Politico Europe.[305][306] ARTE is a public Franco-German TV network that promotes programming in the areas of culture and the arts. 80% of its programming are provided in equal proportion by the two member companies, while the remainder is being provided by the European Economic Interest Grouping ARTE GEIE and the channel's European partners.[307]
+
+The MEDIA Programme of the European Union has supported the European popular film and audiovisual industries since 1991. It provides support for the development, promotion and distribution of European works within Europe and beyond.[308]
+
+The European Union has had a significant positive economic impact on most member states.[309] According to a 2019 study of the member states who joined from 1973 to 2004, "without European integration, per capita incomes would have been, on average, approximately 10% lower in the first ten years after joining the EU."[309] Greece was the exception reported by the study, which analysed up to 2008, "to avoid confounding effects from the global financial crisis".[309]
+
+The European Union has contributed to peace in Europe, in particular by pacifying border disputes.[310][311]
+
+The European Union has contributed to the spread of democracy, in particular by encouraging democratic reforms in aspiring Eastern European member states after the collapse of the USSR.[312][313] Thomas Risse wrote in 2009, "there is a consensus in the literature on Eastern Europe that the EU membership perspective had a huge anchoring effects for the new democracies."[313] However, R. Daniel Keleman argues that over time, the EU has proved beneficial to leaders who are overseeing democratic backsliding, as the EU is reluctant to intervene in domestic politics, gives the authoritarians funds which they can use to strengthen their regimes, and because freedom of movement within the EU allows dissenting citizens to leave their backsliding countries.[314]
+
+Official:
+
+Overviews and data:
+
+News and interviews:
+
+Educational resources:

en/3373.html.txt

@@ -0,0 +1,132 @@
+
+
+Nordic territories that are not part of Scandinavia:
+
+Scandinavia[b] (/ˌskændɪˈneɪviə/ SKAN-dih-NAY-vee-ə) is a subregion in Northern Europe, with strong historical, cultural, and linguistic ties. The term Scandinavia in local usage covers the three kingdoms of Denmark, Norway, and Sweden. The majority national languages of these three belong to the Scandinavian dialect continuum, and are mutually intelligible North Germanic languages.[4]
+
+In English usage, Scandinavia also sometimes refers more narrowly to the Scandinavian Peninsula, or more broadly so as to include the Åland Islands, the Faroe Islands, Finland and Iceland.[3][a]
+
+The broader definition is similar to what are locally called the Nordic countries, which also include the remote Norwegian islands of Svalbard and Jan Mayen and Greenland, a constituent country within the Kingdom of Denmark.[5]
+
+The geography of Scandinavia is extremely varied. Notable are the Norwegian fjords, the Scandinavian Mountains, the flat, low areas in Denmark and the archipelagos of Sweden and Norway. Sweden has many lakes and moraines, legacies of the ice age, which ended about ten millennia ago.
+
+The southern and by far most populous regions of Scandinavia have a temperate climate. Scandinavia extends north of the Arctic Circle, but has relatively mild weather for its latitude due to the Gulf Stream. Many of the Scandinavian mountains have an alpine tundra climate.
+
+The climate varies from north to south and from west to east: a marine west coast climate (Cfb) typical of western Europe dominates in Denmark, southernmost part of Sweden and along the west coast of Norway reaching north to 65°N, with orographic lift giving more mm/year precipitation (<5000 mm) in some areas in western Norway. The central part – from Oslo to Stockholm – has a humid continental climate (Dfb), which gradually gives way to subarctic climate (Dfc) further north and cool marine west coast climate (Cfc) along the northwestern coast.[6] A small area along the northern coast east of the North Cape has tundra climate (Et) as a result of a lack of summer warmth. The Scandinavian Mountains block the mild and moist air coming from the southwest, thus northern Sweden and the Finnmarksvidda plateau in Norway receive little precipitation and have cold winters. Large areas in the Scandinavian mountains have alpine tundra climate.
+
+The warmest temperature ever recorded in Scandinavia is 38.0 °C in Målilla (Sweden).[7] The coldest temperature ever recorded is −52.6 °C in Vuoggatjålme, Arjeplog (Sweden).[8]  The coldest month was February 1985 in Vittangi (Sweden) with a mean of −27.2 °C.[8]
+
+Southwesterly winds further warmed by foehn wind can give warm temperatures in narrow Norwegian fjords in winter. Tafjord has recorded 17.9 °C in January and Sunndal 18.9 °C in February.
+
+The words Scandinavia and Scania (Skåne, the southernmost province of Sweden) are both thought to go back to the Proto-Germanic compound *Skaðin-awjō (the ð represented in Latin by t or d), which appears later in Old English as Scedenig and in Old Norse as Skáney.[9] The earliest identified source for the name Scandinavia is Pliny the Elder's Natural History, dated to the first century AD.
+
+Various references to the region can also be found in Pytheas, Pomponius Mela, Tacitus, Ptolemy, Procopius and Jordanes, usually in the form of Scandza. It is believed that the name used by Pliny may be of West Germanic origin, originally denoting Scania.[10] According to some scholars, the Germanic stem can be reconstructed as *skaðan- and meaning "danger" or "damage".[11] The second segment of the name has been reconstructed as *awjō, meaning "land on the water" or "island". The name Scandinavia would then mean "dangerous island", which is considered to refer to the treacherous sandbanks surrounding Scania.[11] Skanör in Scania, with its long Falsterbo reef, has the same stem (skan) combined with -ör, which means "sandbanks".
+
+Alternatively, Sca(n)dinavia and Skáney, along with the Old Norse goddess name Skaði, may be related to Proto-Germanic *skaðwa- (meaning "shadow"). John McKinnell comments that this etymology suggests that the goddess Skaði may have once been a personification of the geographical region of Scandinavia or associated with the underworld.[12]
+
+Another possibility is that all or part of the segments of the name came from the pre-Germanic Mesolithic people inhabiting the region.[13] In modernity, Scandinavia is a peninsula, but between approximately 10,300 and 9,500 years ago the southern part of Scandinavia was an island separated from the northern peninsula, with water exiting the Baltic Sea through the area where Stockholm is now located.[14] Correspondingly, some Basque scholars have presented the idea that the segment sk that appears in *Skaðinawjō is connected to the name for the Euzko peoples, akin to Basques, that populated Paleolithic Europe. According to one scholar, Scandinavian people share particular genetic markers with the Basque people.[13][unreliable source?]
+
+The Latin names in Pliny's text gave rise to different forms in medieval Germanic texts. In Jordanes' history of the Goths (AD 551), the form Scandza is the name used for their original home, separated by sea from the land of Europe (chapter 1, 4).[15] Where Jordanes meant to locate this quasi-legendary island is still a hotly debated issue, both in scholarly discussions and in the nationalistic discourse of various European countries.[16][17] The form Scadinavia as the original home of the Langobards appears in Paulus Diaconus' Historia Langobardorum,[18] but in other versions of Historia Langobardorum appear the forms Scadan, Scandanan, Scadanan and Scatenauge.[19] Frankish sources used Sconaowe and Aethelweard, an Anglo-Saxon historian, used Scani.[20][21] In Beowulf, the forms Scedenige and Scedeland are used while the Alfredian translation of Orosius and Wulfstan's travel accounts used the Old English Sconeg.[21]
+
+The earliest Sami yoik texts written down refer to the world as Skadesi-suolo (north Sami) and Skađsuâl (east Sami), meaning "Skaði's island". Svennung considers the Sami name to have been introduced as a loan word from the North Germanic languages;[22] "Skaði" is the giant stepmother of Freyr and Freyja in Norse mythology. It has been suggested that Skaði to some extent is modeled on a Sami woman. The name for Skade's father Thjazi is known in Sami as Čáhci, "the waterman"; and her son with Odin, Saeming, can be interpreted as a descendant of Saam the Sami population.[23][24] Older joik texts give evidence of the old Sami belief about living on an island and state that the wolf is known as suolu gievra, meaning "the strong one on the island". The Sami place name Sulliidčielbma means "the island's threshold" and Suoločielgi means "the island's back".
+
+In recent substrate studies, Sami linguists have examined the initial cluster sk- in words used in Sami and concluded that sk- is a phonotactic structure of alien origin.[25]
+
+Although the term Scandinavia used by Pliny the Elder probably originated in the ancient Germanic languages, the modern form Scandinavia does not descend directly from the ancient Germanic term. Rather the word was brought into use in Europe by scholars borrowing the term from ancient sources like Pliny, and was used vaguely for Scania and the southern region of the peninsula.[26]
+
+The term was popularised by the linguistic and cultural Scandinavist movement, which asserted the common heritage and cultural unity of the Scandinavian countries and rose to prominence in the 1830s.[26] The popular usage of the term in Sweden, Denmark and Norway as a unifying concept became established in the nineteenth century through poems such as Hans Christian Andersen's "I am a Scandinavian" of 1839. After a visit to Sweden, Andersen became a supporter of early political Scandinavism. In a letter describing the poem to a friend, he wrote: "All at once I understood how related the Swedes, the Danes and the Norwegians are, and with this feeling I wrote the poem immediately after my return: 'We are one people, we are called Scandinavians!'".
+
+The influence of Scandinavism as a Scandinavist political movement peaked in the middle of the nineteenth century, between the First Schleswig War (1848–1850) and the Second Schleswig War (1864).
+
+The Swedish king also proposed a unification of Denmark, Norway and Sweden into a single united kingdom. The background for the proposal was the tumultuous events during the Napoleonic Wars in the beginning of the century. This war resulted in Finland (formerly the eastern third of Sweden) becoming the Russian Grand Duchy of Finland in 1809 and Norway (de jure in union with Denmark since 1387, although de facto treated as a province) becoming independent in 1814, but thereafter swiftly forced to accept a personal union with Sweden. The dependent territories Iceland, the Faroe Islands and Greenland, historically part of Norway, remained with Denmark in accordance with the Treaty of Kiel. Sweden and Norway were thus united under the Swedish monarch, but Finland's inclusion in the Russian Empire excluded any possibility for a political union between Finland and any of the other Nordic countries.
+
+The end of the Scandinavian political movement came when Denmark was denied the military support promised from Sweden and Norway to annex the (Danish) Duchy of Schleswig, which together with the (German) Duchy of Holstein had been in personal union with Denmark. The Second war of Schleswig followed in 1864, a brief but disastrous war between Denmark and Prussia (supported by Austria). Schleswig-Holstein was conquered by Prussia and after Prussia's success in the Franco-Prussian War a Prussian-led German Empire was created and a new power-balance of the Baltic sea countries was established. The Scandinavian Monetary Union, established in 1873, lasted until World War I.
+
+The term Scandinavia (sometimes specified in English as Continental Scandinavia or mainland Scandinavia) is commonly used strictly for Denmark, Norway and Sweden as a subset of the Nordic countries (known in Norwegian, Danish, and Swedish as Norden; Finnish: Pohjoismaat, Icelandic: Norðurlöndin, Faroese: Norðurlond).[27]
+
+However, in English usage, the term Scandinavia is sometimes used as a synonym or near-synonym for Nordic countries.[5][28][29][30][31][32][33][34][35][36]
+
+Debate about which meaning is more appropriate is complicated by the fact that usage in English is different from usage in the Scandinavian languages themselves (which use Scandinavia in the narrow meaning), and by the fact that the question of whether a country belongs to Scandinavia is politicised: people from the Nordic world beyond Norway, Denmark and Sweden may be offended at being either included in or excluded from the category of "Scandinavia".[37]
+
+Nordic countries is used unambiguously for Denmark, Norway, Sweden, Finland and Iceland, including their associated territories (Svalbard,[citation needed] Greenland, the Faroe Islands and the Åland Islands).[5]
+
+In addition to the mainland Scandinavian countries of:
+
+The Nordic countries also consist of:
+
+The clearest example of the use of the term Scandinavia as a political and societal construct is the unique position of Finland, based largely on the fact that most of modern-day Finland was part of Sweden for more than six centuries (see: Finland under Swedish rule), thus to much of the world associating Finland with all of Scandinavia. But the creation of a Finnish identity is unique in the region in that it was formed in relation to two different imperial models, the Swedish[38] and the Russian.[39][40][41]
+
+There is also the geological term Fennoscandia (sometimes Fennoscandinavia),  which in technical use refers to the Fennoscandian Shield (or Baltic Shield), that is the Scandinavian peninsula (Norway and Sweden), Finland and Karelia (excluding Denmark and other parts of the wider Nordic world). The terms Fennoscandia and Fennoscandinavia are sometimes used in a broader, political sense to refer to Norway, Sweden, Denmark, and Finland.[42]
+
+Whereas both narrow and broad conceptions of Scandinavian countries are straightforwardly defined, there is much ambiguity and political contestation as to which people are Scandinavian people (or Scandinavians). English dictionaries usually define the noun Scandinavian as meaning any inhabitant of Scandinavia (which might be narrowly conceived or broadly conceived).[43][44][45] However, the noun Scandinavian is frequently used as a synonym for speakers of Scandinavian languages (languages descended from Old Norse).  This usage can exclude the indigenous Sámi people of Scandinavia, as well as other non-Scandinavian-speaking inhabitants of the region.[46]
+
+Thus, based on intersecting cultural and geographic definitions, Scandinavians always include Scandinavian-speaking Swedes, Norwegians, and Danes (and, earlier, ancient speakers of the North Germanic languages).
+
+In usages based on cultural/linguistic definitions (native speakers of North Germanic languages), Scandinavians also include Faroe Islanders, Icelanders, the Swedish-speaking population of Finland, the Swedish-speaking population of Estonia, and the Scandinavian diaspora.
+
+In usages based on geographical definitions (inhabitants of Continental Scandinavia), Scandinavians include Sami people and, depending on how broad an understanding of Scandinavia is being used, Finns and Inuit.[32]
+
+Two language groups have coexisted on the Scandinavian peninsula since prehistory—the North Germanic languages (Scandinavian languages) and the Sami languages.[47]
+
+The majority of the population of Scandinavia (including Iceland and the Faroe Islands) today derive their language from several North Germanic tribes who once inhabited the southern part of Scandinavia and spoke a Germanic language that evolved into Old Norse and from Old Norse into Danish, Swedish, Norwegian, Faroese, and Icelandic. The Danish, Norwegian and Swedish languages form a dialect continuum and are known as the Scandinavian languages—all of which are considered mutually intelligible with one another. Faroese and Icelandic, sometimes referred to as insular Scandinavian languages, are intelligible in continental Scandinavian languages only to a limited extent.
+
+A small minority of Scandinavians are Sami people, concentrated in the extreme north of Scandinavia.
+
+Finland (sometimes included in Scandinavia in English usage) is mainly populated by speakers of Finnish, with a minority of approximately 5%[48] of Swedish speakers. However, Finnish is also spoken as a recognized minority language in Sweden, including in distinctive varieties sometimes known as Meänkieli. Finnish is distantly related to the Sami languages, but these are entirely different in origin to the Scandinavian languages.
+
+German (in Denmark), Yiddish and Romani are recognized minority languages in parts of Scandinavia. More recent migrations has added even more languages. Apart from Sami and the languages of minority groups speaking a variant of the majority language of a neighboring state, the following minority languages in Scandinavia are protected under the European Charter for Regional or Minority Languages: Yiddish, Romani Chib/Romanes and Romani.
+
+The North Germanic languages of Scandinavia are traditionally divided into an East Scandinavian branch (Danish and Swedish) and a West Scandinavian branch (Norwegian, Icelandic and Faroese),[49][50] but because of changes appearing in the languages since 1600 the East Scandinavian and West Scandinavian branches are now usually reconfigured into Insular Scandinavian (ö-nordisk/øy-nordisk) featuring Icelandic and Faroese[51] and Continental Scandinavian (Skandinavisk), comprising Danish, Norwegian and Swedish.[52]
+
+The modern division is based on the degree of mutual comprehensibility between the languages in the two branches.[53] The populations of the Scandinavian countries, with common Scandinavian roots in language, can—at least with some training—understand each other's standard languages as they appear in print and are heard on radio and television.
+
+The reason Danish, Swedish and the two official written versions of Norwegian (Nynorsk and Bokmål) are traditionally viewed as different languages, rather than dialects of one common language, is that each is a well-established standard language in its respective country.
+
+Danish, Swedish and Norwegian have since medieval times been influenced to varying degrees by Middle Low German and standard German. That influence came from not just proximity but also that Denmark and later Denmark-Norway ruling over the German speaking region of Holstein, and in Sweden with its close trade with the Hanseatic League.
+
+Norwegians are accustomed to variation and may perceive Danish and Swedish only as slightly more distant dialects. This is because they have two official written standards, in addition to the habit of strongly holding on to local dialects. The people of Stockholm, Sweden and Copenhagen, Denmark have the greatest difficulty in understanding other Scandinavian languages.[54] In the Faroe Islands and Iceland, learning Danish is mandatory. This causes Faroese people as well as Icelandic people to become bilingual in two very distinct North Germanic languages, making it relatively easy for them to understand the other two Mainland Scandinavian languages.[55][56]
+
+Although Iceland was under the political control of Denmark until a much later date (1918), very little influence and borrowing from Danish has occurred in the Icelandic language.[57] Icelandic remained the preferred language among the ruling classes in Iceland. Danish was not used for official communications, most of the royal officials were of Icelandic descent and the language of the church and law courts remained Icelandic.[58]
+
+The Scandinavian languages are (as a language family) unrelated to Finnish, Estonian and Sami languages, which as Uralic languages are distantly related to Hungarian. Owing to the close proximity, there is still a great deal of borrowing from the Swedish and Norwegian languages in the Finnish and Sami languages.[59] The long history of linguistic influence of Swedish on Finnish is also due to the fact that Finnish, the language of the majority in Finland, was treated as a minority language while Finland was part of Sweden. Finnish-speakers had to learn Swedish in order to advance to higher positions.[60] Swedish spoken in today's Finland includes a lot of words that are borrowed from Finnish, whereas the written language remains closer to that of Sweden.
+
+Finland is officially bilingual, with Finnish and Swedish having mostly the same status at national level. Finland's majority population are Finns, whose mother tongue is either Finnish (approximately 95%), Swedish or both. The Swedish-speakers live mainly on the coastline starting from approximately the city of Porvoo (in the Gulf of Finland) up to the city of Kokkola (in the Bay of Bothnia). The Åland Islands, an autonomous province of Finland situated in the Baltic Sea between Finland and Sweden, are entirely Swedish-speaking. Children are taught the other official language at school: for Swedish-speakers this is Finnish (usually from the 3rd grade), while for Finnish-speakers it is Swedish (usually from the 3rd, 5th or 7th grade).[citation needed]
+
+Finnish speakers constitute a language minority in Sweden and Norway. Meänkieli and Kven are Finnish dialects spoken in Swedish Lapland and Norwegian Lapland.
+
+The Sami languages are indigenous minority languages in Scandinavia.[61] They belong to their own branch of the Uralic language family and are unrelated to the North Germanic languages other than by limited grammatical (particularly lexical) characteristics resulting from prolonged contact.[59] Sami is divided into several languages or dialects.[62] Consonant gradation is a feature in both Finnish and northern Sami dialects, but it is not present in south Sami, which is considered to have a different language history. According to the Sami Information Centre of the Sami Parliament in Sweden, southern Sami may have originated in an earlier migration from the south into the Scandinavian peninsula.[59]
+
+A key ancient description of Scandinavia was provided by Pliny the Elder, though his mentions of Scatinavia and surrounding areas are not always easy to decipher. Writing in the capacity of a Roman admiral, he introduces the northern region by declaring to his Roman readers that there are 23 islands "Romanis armis cognitae" ("known to Roman arms") in this area. According to Pliny, the "clarissima" ("most famous") of the region's islands is Scatinavia, of unknown size. There live the Hilleviones. The belief that Scandinavia was an island became widespread among classical authors during the first century and dominated descriptions of Scandinavia in classical texts during the centuries that followed.
+
+Pliny begins his description of the route to Scatinavia by referring to the mountain of Saevo ("mons Saevo ibi"), the Codanus Bay ("Codanus sinus") and the Cimbrian promontory.[63] The geographical features have been identified in various ways. By some scholars, Saevo is thought to be the mountainous Norwegian coast at the entrance to Skagerrak and the Cimbrian peninsula is thought to be Skagen, the north tip of Jutland, Denmark. As described, Saevo and Scatinavia can also be the same place.
+
+Pliny mentions Scandinavia one more time: in Book VIII he says that the animal called achlis (given in the accusative, achlin, which is not Latin) was born on the island of Scandinavia.[64] The animal grazes, has a big upper lip and some mythical attributes.
+
+The name Scandia, later used as a synonym for Scandinavia, also appears in Pliny's Naturalis Historia (Natural History), but is used for a group of Northern European islands which he locates north of Britannia. Scandia thus does not appear to be denoting the island Scadinavia in Pliny's text. The idea that Scadinavia may have been one of the Scandiae islands was instead introduced by Ptolemy (c. 90 – c. 168 AD), a mathematician, geographer and astrologer of Roman Egypt. He used the name Skandia for the biggest, most easterly of the three Scandiai islands, which according to him were all located east of Jutland.[11]
+
+Neither Pliny's nor Ptolemy's lists of Scandinavian tribes include the Suiones mentioned by Tacitus. Some early Swedish scholars of the Swedish Hyperborean school[65] and of the ninettenth-century romantic nationalism period proceeded to synthesize the different versions by inserting references to the Suiones, arguing that they must have been referred to in the original texts and obscured over time by spelling mistakes or various alterations.[66][67]
+
+During a period of Christianization and state formation in the 10th–13th centuries, numerous Germanic petty kingdoms and chiefdoms were unified into three kingdoms:
+
+The three Scandinavian kingdoms joined in 1387 in the Kalmar Union under Queen Margaret I of Denmark. Sweden left the union in 1523 under King Gustav Vasa. In the aftermath of Sweden's secession from the Kalmar Union, civil war broke out in Denmark and Norway—the Protestant Reformation followed. When things had settled, the Norwegian Privy Council was abolished—it assembled for the last time in 1537. A personal union, entered into by the kingdoms of Denmark and Norway in 1536, lasted until 1814. Three sovereign successor states have subsequently emerged from this unequal union: Denmark, Norway and Iceland.
+
+The borders between the three countries got the shape they have had since in the middle of the seventeenth century: In the 1645 Treaty of Brömsebro, Denmark–Norway ceded the Norwegian provinces of Jämtland, Härjedalen and Idre and Särna, as well as the Baltic Sea islands of Gotland and Ösel (in Estonia) to Sweden. The Treaty of Roskilde, signed in 1658, forced Denmark–Norway to cede the Danish provinces Scania, Blekinge, Halland, Bornholm and the Norwegian provinces of Båhuslen and Trøndelag to Sweden. The 1660 Treaty of Copenhagen forced Sweden to return Bornholm and Trøndelag to Denmark–Norway, and to give up its recent claims to the island Funen.[69]
+
+In the east, Finland, was a fully incorporated part of Sweden since medieval times until the Napoleonic wars, when it was ceded to Russia. Despite many wars over the years since the formation of the three kingdoms, Scandinavia has been politically and culturally close.
+
+Denmark–Norway as a historiographical name refers to the former political union consisting of the kingdoms of Denmark and Norway, including the Norwegian dependencies of Iceland, Greenland and the Faroe Islands. The corresponding adjective and demonym is Dano-Norwegian. During Danish rule, Norway kept its separate laws, coinage and army as well as some institutions such as a royal chancellor. Norway's old royal line had died out with the death of Olav IV[70] in 1387, but Norway's remaining a hereditary kingdom became an important factor for the Oldenburg dynasty of Denmark–Norway in its struggles to win elections as kings of Denmark.
+
+The Treaty of Kiel (14 January 1814) formally dissolved the Dano-Norwegian union and ceded the territory of Norway proper to the King of Sweden, but Denmark retained Norway's overseas possessions. However, widespread Norwegian resistance to the prospect of a union with Sweden induced the governor of Norway, crown prince Christian Frederick (later Christian VIII of Denmark), to call a constituent assembly at Eidsvoll in April 1814. The assembly drew up a liberal constitution and elected Christian Frederick to the throne of Norway. Following a Swedish invasion during the summer, the peace conditions of the Convention of Moss (14 August 1814) specified that king Christian Frederik had to resign, but Norway would keep its independence and its constitution within a personal union with Sweden. Christian Frederik formally abdicated on 10 August 1814 and returned to Denmark. The Norwegian parliament Storting elected king Charles XIII of Sweden as king of Norway on 4 November.
+
+The Storting dissolved the union between Sweden and Norway in 1905, after which the Norwegians elected Prince Charles of Denmark as king of Norway: he reigned as Haakon VII.
+
+The economies of the countries of Scandinavia are amongst the strongest in Europe.[71] There is a generous welfare system in Sweden, Denmark, Norway and Finland.[72]
+
+Various promotional agencies of the Nordic countries in the United States (such as The American-Scandinavian Foundation, established in 1910 by the Danish American industrialist Niels Poulsen) serve to promote market and tourism interests in the region. Today, the five Nordic heads of state act as the organization's patrons and according to the official statement by the organization its mission is "to promote the Nordic region as a whole while increasing the visibility of Denmark, Finland, Iceland, Norway and Sweden in New York City and the United States".[73] The official tourist boards of Scandinavia sometimes cooperate under one umbrella, such as the Scandinavian Tourist Board.[74] The cooperation was introduced for the Asian market in 1986, when the Swedish national tourist board joined the Danish national tourist board to coordinate intergovernmental promotion of the two countries. Norway's government entered one year later. All five Nordic governments participate in the joint promotional efforts in the United States through the Scandinavian Tourist Board of North America.[75]
+
+
+
+
+
+
+

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+A lighthouse is a tower, building, or another type of structure designed to emit light from a system of lamps and lenses and to serve as a navigational aid for maritime pilots at sea or on inland waterways.
+
+Lighthouses mark dangerous coastlines, hazardous shoals, reefs, rocks, and safe entries to harbors; they also assist in aerial navigation.  Once widely used, the number of operational lighthouses has declined due to the expense of maintenance and has become uneconomical since the advent of cheaper and often much more effective electronic navigational systems.
+
+Before the development of clearly defined ports, mariners were guided by fires built on hilltops. Since elevating the fire would improve the visibility, placing the fire on a platform became a practice that led to the development of the lighthouse.[1] In antiquity, the lighthouse functioned more as an entrance marker to ports than as a warning signal for reefs and promontories, unlike many modern lighthouses. The most famous lighthouse structure from antiquity was the Pharos of Alexandria, Egypt, which collapsed following a series of earthquakes between 956 and 1323.
+
+The intact Tower of Hercules at A Coruña, Spain gives insight into ancient lighthouse construction; other evidence about lighthouses exists in depictions on coins and mosaics, of which many represent the lighthouse at Ostia. Coins from Alexandria, Ostia, and Laodicea in Syria also exist.
+
+The modern era of lighthouses began at the turn of the 18th century, as lighthouse construction boomed in lockstep with burgeoning levels of transatlantic commerce. Advances in structural engineering and new and efficient lighting equipment allowed for the creation of larger and more powerful lighthouses, including ones exposed to the sea. The function of lighthouses shifted toward the provision of a visible warning against shipping hazards, such as rocks or reefs.
+
+The Eddystone Rocks were a major shipwreck hazard for mariners sailing through the English Channel.[2] The first lighthouse built there was an octagonal wooden structure, anchored by 12 iron stanchions secured in the rock, and was built by Henry Winstanley from 1696 to 1698. His lighthouse was the first tower in the world to have been fully exposed to the open sea.[3]
+
+The civil engineer, John Smeaton, rebuilt the lighthouse from 1756–59;[4] his tower marked a major step forward in the design of lighthouses and remained in use until 1877. He modeled the shape of his lighthouse on that of an oak tree, using granite blocks. He rediscovered and used "hydraulic lime", a form of concrete that will set under water used by the Romans, and developed a technique of securing the granite blocks together using dovetail joints and marble dowels.[5] The dovetailing feature served to improve the structural stability, although Smeaton also had to taper the thickness of the tower towards the top, for which he curved the tower inwards on a gentle gradient. This profile had the added advantage of allowing some of the energy of the waves to dissipate on impact with the walls. His lighthouse was the prototype for the modern lighthouse and influenced all subsequent engineers.[6]
+
+One such influence was Robert Stevenson, himself a seminal figure in the development of lighthouse design and construction.[7] His greatest achievement was the construction of the Bell Rock Lighthouse in 1810, one of the most impressive feats of engineering of the age. This structure was based upon Smeaton's design, but with several improved features, such as the incorporation of rotating lights, alternating between red and white.[8] Stevenson worked for the Northern Lighthouse Board for nearly fifty years[7] during which time he designed and oversaw the construction and later improvement of numerous lighthouses. He innovated in the choice of light sources, mountings, reflector design, the use of Fresnel lenses, and in rotation and shuttering systems providing lighthouses with individual signatures allowing them to be identified by seafarers. He also invented the movable jib and the balance-crane as a necessary part for lighthouse construction.
+
+Alexander Mitchell designed the first screw-pile lighthouse – his lighthouse was built on piles that were screwed into the sandy or muddy seabed. Construction of his design began in 1838 at the mouth of the Thames and was known as the Maplin Sands lighthouse, and first lit in 1841.[9] Although its construction began later, the Wyre Light in Fleetwood, Lancashire, was the first to be lit (in 1840).[9]
+
+The Vittoria Light in Trieste it is one of the tallest lighthouses in the world.[10]
+
+The source of illumination had generally been wood pyres or burning coal. The Argand lamp, invented in 1782 by the Swiss scientist, Aimé Argand, revolutionized lighthouse illumination with its steady smokeless flame. Early models used ground glass which was sometimes tinted around the wick. Later models used a mantle of thorium dioxide suspended over the flame, creating a bright, steady light.[11] The Argand lamp used whale oil, colza, olive oil[12] or other vegetable oil as fuel which was supplied by a gravity feed from a reservoir mounted above the burner. The lamp was first produced by Matthew Boulton, in partnership with Argand, in 1784 and became the standard for lighthouses for over a century.
+
+South Foreland Lighthouse was the first tower to successfully use an electric light in 1875. The lighthouse's carbon arc lamps were powered by a steam-driven magneto.[13] John Richardson Wigham was the first to develop a system for gas illumination of lighthouses. His improved gas 'crocus' burner at the Baily Lighthouse near Dublin was 13 times more powerful than the most brilliant light then known.[14]
+
+The vaporized oil burner was invented in 1901 by Arthur Kitson, and improved by David Hood at Trinity House. The fuel was vaporized at high pressure and burned to heat the mantle, giving an output of over six times the luminosity of traditional oil lights. The use of gas as illuminant became widely available with the invention of the Dalén light by Swedish engineer, Gustaf Dalén. He used Agamassan (Aga), a substrate, to absorb the gas allowing safe storage and hence commercial exploitation. Dalén also invented the 'sun valve', which automatically regulated the light and turned it off during the daytime. The technology was the predominant form of light source in lighthouses from the 1900s through the 1960s, when electric lighting had become dominant.[15]
+
+With the development of the steady illumination of the Argand lamp, the application of optical lenses to increase and focus the light intensity became a practical possibility. William Hutchinson developed the first practical optical system in 1763, known as a catoptric system. This rudimentary system effectively collimated the emitted light into a concentrated beam, thereby greatly increasing the light's visibility.[16] The ability to focus the light led to the first revolving lighthouse beams, where the light would appear to the mariners as a series of intermittent flashes. It also became possible to transmit complex signals using the light flashes.
+
+French physicist and engineer Augustin-Jean Fresnel developed the multi-part Fresnel lens for use in lighthouses. His design allowed for the construction of lenses of large aperture and short focal length, without the mass and volume of material that would be required by a lens of conventional design. A Fresnel lens can be made much thinner than a comparable conventional lens, in some cases taking the form of a flat sheet. A Fresnel lens can also capture more oblique light from a light source, thus allowing the light from a lighthouse equipped with one to be visible over greater distances.
+
+The first Fresnel lens was used in 1823 in the Cordouan lighthouse at the mouth of the Gironde estuary; its light could be seen from more than 20 miles (32 km) out.[17] Fresnel's invention increased the luminosity of the lighthouse lamp by a factor of four and his system is still in common use.
+
+The advent of electrification, and automatic lamp changers began to make lighthouse keepers obsolete. For many years, lighthouses still had keepers, partly because lighthouse keepers could serve as a rescue service if necessary. Improvements in maritime navigation and safety such as the Global Positioning System (GPS) have led to the phasing out of non-automated lighthouses across the world.[18] In Canada, this trend has been stopped and there are still 50 staffed light stations, with 27 on the west coast alone.[19]
+
+Remaining modern lighthouses are usually illuminated by a single stationary flashing light powered by solar-charged batteries mounted on a steel skeleton tower.[20] Where the power requirement is too great for solar power, cycle charging by diesel generator is used: to save fuel and to increase periods between maintenance the light is battery powered, with the generator only coming into use when the battery has to be charged.[21]
+
+John Smeaton is noteworthy for having designed the third and most famous Eddystone Lighthouse, but some builders are well known for their work in building multiple lighthouses. The Stevenson family (Robert, Alan, David, Thomas, David Alan, and Charles) made lighthouse building a three-generation profession in Scotland. Irishman Alexander Mitchell invented and built a number of screwpile lighthouses despite his blindness. Englishman James Douglass was knighted for his work on lighthouses.
+
+United States Army Corps of Engineers Lieutenant George Meade built numerous lighthouses along the Atlantic and Gulf coasts before gaining wider fame as the winning general at the Battle of Gettysburg.  Colonel Orlando M. Poe, engineer to General William Tecumseh Sherman in the Siege of Atlanta, designed and built some of the most exotic lighthouses in the most difficult locations on the U.S. Great Lakes.[22]
+
+French merchant navy officer Marius Michel Pasha built almost a hundred lighthouses along the coasts of the Ottoman Empire in a period of twenty years after the Crimean War (1853–1856).[23]
+
+In a lighthouse, the source of light is called the "lamp" (whether electric or fuelled by oil) and the concentration of the light is by the "lens" or "optic". Originally lit by open fires and later candles, the Argand hollow wick lamp and parabolic reflector were introduced in the late 18th century.
+
+Whale oil was also used with wicks as the source of light. Kerosene became popular in the 1870s and electricity and carbide (acetylene gas) began replacing kerosene around the turn of the 20th century.[20] Carbide was promoted by the Dalén light which automatically lit the lamp at nightfall and extinguished it at dawn.
+
+During the Cold-War, many remote Soviet lighthouses were powered by radioisotope thermoelectric generators (RTGs). These had the advantage of providing power day or night and did not need refuelling or maintenance. However, after the breakdown of the Soviet Union, there are no official records of the locations or condition of all of these lighthouses.[24] As time passes, their condition is degrading; many have fallen victim to vandalism and scrap metal thieves, who may not be aware of the dangerous radioactive contents.[25]
+
+Before modern strobe lights, lenses were used to concentrate the light from a continuous source.  Vertical light rays of the lamp are redirected into a horizontal plane, and horizontally the light is focused into one or a few directions at a time, with the light beam swept around. As a result, in addition to seeing the side of the light beam, the light is directly visible from greater distances, and with an identifying light characteristic.
+
+This concentration of light is accomplished with a rotating lens assembly. In early lighthouses, the light source was a kerosene lamp or, earlier, an animal or vegetable oil Argand lamp, and the lenses rotated by a weight driven clockwork assembly wound by lighthouse keepers, sometimes as often as every two hours. The lens assembly sometimes floated in liquid mercury to reduce friction.  In more modern lighthouses, electric lights and motor drives were used, generally powered by diesel electric generators. These also supplied electricity for the lighthouse keepers.[20]
+
+Efficiently concentrating the light from a large omnidirectional light source requires a very large diameter lens. This would require a very thick and heavy lens if a conventional lens were used.  The Fresnel lens (pronounced /freɪˈnɛl/) focused 85% of a lamp's light versus the 20% focused with the parabolic reflectors of the time. Its design enabled construction of lenses of large size and short focal length without the weight and volume of material in conventional lens designs.[26]
+
+Fresnel lighthouse lenses are ranked by order, a measure of refracting power, with a first order lens being the largest, most powerful and expensive; and a sixth order lens being the smallest.  The order is based on the focal length of the lens. A first order lens has the longest focal length, with the sixth being the shortest. Coastal lighthouses generally use first, second, or third order lenses, while harbor lights and beacons use fourth, fifth, or sixth order lenses.[27]
+
+Some lighthouses, such as those at Cape Race, Newfoundland, and Makapuu Point, Hawaii, used a more powerful hyperradiant Fresnel lens manufactured by the firm of Chance Brothers.
+
+In recent times, many Fresnel lenses have been replaced by rotating aerobeacons which require less maintenance.  In modern automated lighthouses, this system of rotating lenses is often replaced by a high intensity light that emits brief omnidirectional flashes (concentrating the light in time rather than direction). These lights are similar to obstruction lights used to warn aircraft of tall structures. Recent innovations are "Vega Lights", and initial experiments with light-emitting diode (LED) panels.[20]
+
+Experimental installations of laser lights, either at high power to provide a "line of light" in the sky or, utilising low power, aimed towards mariners have identified problems of increased complexity in installation and maintenance, and high power requirements.[28]
+
+In any of these designs an observer, rather than seeing a continuous weak light, sees a brighter light during short time intervals. These instants of bright light are arranged to create a light characteristic or pattern specific to a lighthouse.[29] For example, the Scheveningen Lighthouse flashes are alternately 2.5 and 7.5 seconds. Some lights have sectors of a particular color (usually formed by colored panes in the lantern) to distinguish safe water areas from dangerous shoals. Modern lighthouses often have unique reflectors or Racon transponders so the radar signature of the light is also unique.
+
+While lighthouse buildings differ depending on the location and purpose, they tend to have common components.
+
+A light station comprises the lighthouse tower and all outbuildings, such as the keeper's living quarters, fuel house, boathouse, and fog-signaling building. The Lighthouse itself consists of a tower structure supporting the lantern room where the light operates.
+
+The lantern room is the glassed-in housing at the top of a lighthouse tower containing the lamp and lens. Its glass storm panes are supported by metal Astragal bars running vertically or diagonally. At the top of the lantern room is a stormproof ventilator designed to remove the smoke of the lamps and the heat that builds in the glass enclosure. A lightning rod and grounding system connected to the metal cupola roof provides a safe conduit for any lightning strikes.
+
+Immediately beneath the lantern room is usually a Watch Room or Service Room where fuel and other supplies were kept and where the keeper prepared the lanterns for the night and often stood watch. The clockworks (for rotating the lenses) were also located there. On a lighthouse tower, an open platform called the gallery is often located outside the watch room (called the Main Gallery) or Lantern Room (Lantern Gallery). This was mainly used for cleaning the outside of the windows of the Lantern Room.[30]
+
+Lighthouses near to each other that are similar in shape are often painted in a unique pattern so they can easily be recognized during daylight, a marking known as a daymark. The black and white barber pole spiral pattern of Cape Hatteras Lighthouse is one example. Race Rocks Light in western Canada is painted in horizontal black and white bands to stand out against the horizon.
+
+For effectiveness, the lamp must be high enough to be seen before the danger is reached by a mariner. The minimum height is calculated by trigonometric formula 
+
+
+
+d
+=
+1.17
+
+
+H
+
+
+
+
+{\displaystyle d=1.17{\sqrt {H}}}
+
+ where H is the height above water in feet, and d is the distance to the horizon in nautical miles.[31]
+
+Where dangerous shoals are located far off a flat sandy beach, the prototypical tall masonry coastal lighthouse is constructed to assist the navigator making a landfall after an ocean crossing.  Often these are cylindrical to reduce the effect of wind on a tall structure, such as Cape May Light. Smaller versions of this design are often used as harbor lights to mark the entrance into a harbor, such as New London Harbor Light.
+
+Where a tall cliff exists, a smaller structure may be placed on top such as at Horton Point Light. Sometimes, such a location can be too high, for example along the west coast of the United States, where frequent low clouds can obscure the light. In these cases, lighthouses are placed below clifftop to ensure that they can still be seen at the surface during periods of fog or low clouds, as at Point Reyes Lighthouse. Another victim of fog was the Old Point Loma lighthouse, which was replaced in 1891 with a lower lighthouse, New Point Loma lighthouse.
+
+As technology advanced, prefabricated skeletal iron or steel structures tended to be used for lighthouses constructed in the 20th century. These often have a narrow cylindrical core surrounded by an open lattice work bracing, such as Finns Point Range Light.
+
+Sometimes a lighthouse needs to be constructed in the water itself.  Wave-washed lighthouses are masonry structures constructed to withstand water impact, such as Eddystone Lighthouse in Britain and the St. George Reef Light of California.  In shallower bays, Screw-pile lighthouse ironwork structures are screwed into the seabed and a low wooden structure is placed above the open framework, such as Thomas Point Shoal Lighthouse. As screw piles can be disrupted by ice, steel caisson lighthouses such as Orient Point Light are used in cold climates.  Orient Long Beach Bar Light (Bug Light) is a blend of a screw pile light that was converted to a caisson light because of the threat of ice damage.[32]
+
+In waters too deep for a conventional structure, a lightship might be used instead of a lighthouse, such as the former lightship Columbia.  Most of these have now been replaced by fixed light platforms (such as Ambrose Light) similar to those used for offshore oil exploration.[33]
+
+Aligning two fixed points on land provides a navigator with a line of position called a range in North America and a transit in Britain. Ranges can be used to precisely align a vessel within a narrow channel such as a river. With landmarks of a range illuminated with a set of fixed lighthouses, nighttime navigation is possible.
+
+Such paired lighthouses are called range lights in North America and leading lights in the United Kingdom. The closer light is referred to as the beacon or front range; the further light is called the rear range. The rear range light is almost always taller than the front.
+
+When a vessel is on the correct course, the two lights align vertically, but when the observer is out of position, the difference in alignment indicates the direction of travel to correct the course.
+
+There are two types of lighthouses: ones that are located on land, and ones that are offshore. A land lighthouse is simply a lighthouse constructed to aid navigation over land, rather than water. Historically, they were constructed in areas of flatland where the featureless landscape and prevailing weather conditions (e.g. winter fog) might cause travelers to become easily disorientated and lost. In such a landscape a high tower with a bright lantern could be visible for many miles.
+
+One example of such a structure is Dunston Pillar, an 18th-century tower built to help travelers crossing the heathland of mid-Lincolnshire and to lessen the danger to them from highwaymen. Due to general improvements in transport and navigation throughout the 19th century, land lighthouses became almost totally obsolete as aids to travelers in remote places.
+
+Offshore Lighthouses are lighthouses that are not close to land.[34] There can be a number of reasons for these lighthouses to be built.  There can be a shoal, reef or submerged island several miles from land.
+
+The current Cordouan Lighthouse was completed in 1611 7 kilometres (4.3 mi) from the shore on a small islet, but was built on a previous lighthouse that can be traced back to 880 and is the oldest surviving lighthouse in France. It is connected to the mainland by a causeway. The oldest surviving oceanic offshore lighthouse is Bell Rock Lighthouse in the North Sea, off the coast of Scotland.[35]
+
+In the United States, lighthouses are maintained by the United States Coast Guard (USCG).[36]
+Those in England and Wales are looked after by Trinity House; in Scotland, by the Northern Lighthouse Board; and in Ireland by the Commissioners of Irish Lights. In Canada, they are managed by the Canadian Coast Guard. In Australia, lighthouses are conducted by the Australian Maritime Safety Authority.
+
+The Soviet Union built a number of automated lighthouses powered by radioisotope thermoelectric generators in remote locations. They operated for long periods without external support with great reliability.[37] However numerous installations deteriorated, were stolen, or vandalized. Some cannot be found due to poor record keeping.[38]
+
+In India (Bharat), Lighthouses are maintained by Directorate General of Lighthouses and Lightships which comes under the Ministry of Shipping.[39]
+
+As lighthouses became less essential to navigation, many of their historic structures faced demolition or neglect. In the United States, the National Historic Lighthouse Preservation Act of 2000 provides for the transfer of lighthouse structures to local governments and private non-profit groups, while the USCG continues to maintain the lamps and lenses. In Canada, the Nova Scotia Lighthouse Preservation Society won heritage status for Sambro Island Lighthouse, and sponsored the Heritage Lighthouse Protection Act to change Canadian federal laws to protect lighthouses.[40]
+
+Many groups formed to restore and save lighthouses around the world. They include the World Lighthouse Society and the United States Lighthouse Society.[41] A further international group is the Amateur Radio Lighthouse Society, which sends amateur radio operators to publicize the preservation of remote lighthouses throughout the world.[42]
+
+Lighthouses were once regarded as an archetypal public good, because ships could benefit from the light without being forced to pay.

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+A planet, in astronomy, is one of a class of celestial bodies that orbit stars. (A dwarf planet is a similar, but officially mutually exclusive, class of body.)
+
+Planet or Planets may also refer to:

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+A planet, in astronomy, is one of a class of celestial bodies that orbit stars. (A dwarf planet is a similar, but officially mutually exclusive, class of body.)
+
+Planet or Planets may also refer to:

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+A planet, in astronomy, is one of a class of celestial bodies that orbit stars. (A dwarf planet is a similar, but officially mutually exclusive, class of body.)
+
+Planet or Planets may also refer to:

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+
+
+
+
+Plants are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, plants were treated as one of two kingdoms including all living things that were not animals, and all algae and fungi were treated as plants. However, all current definitions of Plantae exclude the fungi and some algae, as well as the prokaryotes (the archaea and bacteria). By one definition, plants form the clade Viridiplantae (Latin name for "green plants"), a group that includes the flowering plants, conifers and other gymnosperms, ferns and their allies, hornworts, liverworts, mosses and the green algae, but excludes the red and brown algae.
+
+Green plants obtain most of their energy from sunlight via photosynthesis by primary chloroplasts that are derived from endosymbiosis with cyanobacteria. Their chloroplasts contain chlorophylls a and b, which gives them their green color. Some plants are parasitic or mycotrophic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize. Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is also common.
+
+There are about 320,000 species of plants, of which the great majority, some 260–290 thousand, produce seeds.[5] Green plants provide a substantial proportion of the world's molecular oxygen,[6] and are the basis of most of Earth's ecosystems. Plants that produce grain, fruit and vegetables also form basic human foods and have been domesticated for millennia. Plants have many cultural and other uses, as ornaments, building materials, writing material and, in great variety, they have been the source of medicines and psychoactive drugs. The scientific study of plants is known as botany, a branch of biology.
+
+All living things were traditionally placed into one of two groups, plants and animals. This classification may date from Aristotle (384 BC – 322 BC), who made the distinction between plants, which generally do not move, and animals, which often are mobile to catch their food. Much later, when Linnaeus (1707–1778) created the basis of the modern system of scientific classification, these two groups became the kingdoms Vegetabilia (later Metaphyta or Plantae) and Animalia (also called Metazoa). Since then, it has become clear that the plant kingdom as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these organisms are still often considered plants, particularly in popular contexts.[citation needed]
+
+The term "plant" generally implies the possession of the following traits: multicellularity, possession of cell walls containing cellulose, and the ability to carry out photosynthesis with primary chloroplasts.[7][8]
+
+When the name Plantae or plant is applied to a specific group of organisms or taxon, it usually refers to one of four concepts. From least to most inclusive, these four groupings are:
+
+Another way of looking at the relationships between the different groups that have been called "plants" is through a cladogram, which shows their evolutionary relationships. These are not yet completely settled, but one accepted relationship between the three groups described above is shown below[clarification needed].[16][17][18][19][20][21][22] Those which have been called "plants" are in bold (some minor groups have been omitted).
+
+Rhodophyta (red algae)
+
+Rhodelphidia (predatorial)
+
+Picozoa
+
+Glaucophyta (glaucophyte algae)
+
+Mesostigmatophyceae
+
+Chlorokybophyceae
+
+Spirotaenia
+
+Chlorophyta
+
+Charales (stoneworts)
+
+land plants or embryophytes
+
+Cryptista
+
+The way in which the groups of green algae are combined and named varies considerably between authors.
+
+Algae comprise several different groups of organisms which produce food by photosynthesis and thus have traditionally been included in the plant kingdom. The seaweeds range from large multicellular algae to single-celled organisms and are classified into three groups, the green algae, red algae and brown algae. There is good evidence that the brown algae evolved independently from the others, from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria, and they are no longer classified as plants as defined here.[23][24]
+
+The Viridiplantae, the green plants – green algae and land plants – form a clade, a group consisting of all the descendants of a common ancestor. With a few exceptions, the green plants have the following features in common; primary chloroplasts derived from cyanobacteria containing chlorophylls a and b, cell walls containing cellulose, and food stores in the form of starch contained within the plastids. They undergo closed mitosis without centrioles, and typically have mitochondria with flat cristae. The chloroplasts of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic cyanobacteria.
+
+Two additional groups, the Rhodophyta (red algae) and Glaucophyta (glaucophyte algae), also have primary chloroplasts that appear to be derived directly from endosymbiotic cyanobacteria, although they differ from Viridiplantae in the pigments which are used in photosynthesis and so are different in colour. These groups also differ from green plants in that the storage polysaccharide is floridean starch and is stored in the cytoplasm rather than in the plastids. They appear to have had a common origin with Viridiplantae and the three groups form the clade Archaeplastida, whose name implies that their chloroplasts were derived from a single ancient endosymbiotic event. This is the broadest modern definition of the term 'plant'.
+
+In contrast, most other algae (e.g. brown algae/diatoms, haptophytes, dinoflagellates, and euglenids) not only have different pigments but also have chloroplasts with three or four surrounding membranes. They are not close relatives of the Archaeplastida, presumably having acquired chloroplasts separately from ingested or symbiotic green and red algae. They are thus not included in even the broadest modern definition of the plant kingdom, although they were in the past.
+
+The green plants or Viridiplantae were traditionally divided into the green algae (including the stoneworts) and the land plants. However, it is now known that the land plants evolved from within a group of green algae, so that the green algae by themselves are a paraphyletic group, i.e. a group that excludes some of the descendants of a common ancestor. Paraphyletic groups are generally avoided in modern classifications, so that in recent treatments the Viridiplantae have been divided into two clades, the Chlorophyta and the Streptophyta (including the land plants and Charophyta).[25][26]
+
+The Chlorophyta (a name that has also been used for all green algae) are the sister group to the Charophytes, from which the land plants evolved. There are about 4,300 species,[27] mainly unicellular or multicellular marine organisms such as the sea lettuce, Ulva.
+
+The other group within the Viridiplantae are the mainly freshwater or terrestrial Streptophyta, which consists of the land plants together with the Charophyta, itself consisting of several groups of green algae such as the desmids and stoneworts. Streptophyte algae are either unicellular or form multicellular filaments, branched or unbranched.[26] The genus Spirogyra is a filamentous streptophyte alga familiar to many, as it is often used in teaching and is one of the organisms responsible for the algal "scum" on ponds. The freshwater stoneworts strongly resemble land plants and are believed to be their closest relatives.[citation needed] Growing immersed in fresh water, they consist of a central stalk with whorls of branchlets.
+
+Linnaeus' original classification placed the fungi within the Plantae, since they were unquestionably neither animals or minerals and these were the only other alternatives. With 19th century developments in microbiology, Ernst Haeckel introduced the new kingdom Protista in addition to Plantae and Animalia, but whether fungi were best placed in the Plantae or should be reclassified as protists remained controversial.  In 1969, Robert Whittaker proposed the creation of the kingdom Fungi. Molecular evidence has since shown that the most recent common ancestor (concestor), of the Fungi was probably more similar to that of the Animalia than to that of Plantae or any other kingdom.[28]
+
+Whittaker's original reclassification was based on the fundamental difference in nutrition between the Fungi and the Plantae. Unlike plants, which generally gain carbon through photosynthesis, and so are called autotrophs, fungi do not possess chloroplasts and generally obtain carbon by breaking down and absorbing surrounding materials, and so are called heterotrophic saprotrophs. In addition, the substructure of multicellular fungi is different from that of plants, taking the form of many chitinous microscopic strands called hyphae, which may be further subdivided into cells or may form a syncytium containing many eukaryotic nuclei. Fruiting bodies, of which mushrooms are the most familiar example, are the reproductive structures of fungi, and are unlike any structures produced by plants.[citation needed]
+
+The table below shows some species count estimates of different green plant (Viridiplantae) divisions. It suggests there are about 300,000 species of living Viridiplantae, of which 85–90% are flowering plants. (Note: as these are from different sources and different dates, they are not necessarily comparable, and like all species counts, are subject to a degree of uncertainty in some cases.)
+
+(6,600–10,300)
+
+(18,100–20,200)
+
+(12,200)
+
+(259,511)
+
+The naming of plants is governed by the International Code of Nomenclature for algae, fungi, and plants and International Code of Nomenclature for Cultivated Plants (see cultivated plant taxonomy).
+
+The evolution of plants has resulted in increasing levels of complexity, from the earliest algal mats, through bryophytes, lycopods, ferns to the complex gymnosperms and angiosperms of today. Plants in all of these groups continue to thrive, especially in the environments in which they evolved.
+
+An algal scum formed on the land 1,200 million years ago, but it was not until the Ordovician Period, around 450 million years ago, that land plants appeared.[39] However, new evidence from the study of carbon isotope ratios in Precambrian rocks has suggested that complex photosynthetic plants developed on the earth over 1000 m.y.a.[40] For more than a century it has been assumed that the ancestors of land plants evolved in aquatic environments and then adapted to a life on land, an idea usually credited to botanist Frederick Orpen Bower in his 1908 book The Origin of a Land Flora. A recent alternative view, supported by genetic evidence, is that they evolved from terrestrial single-celled algae,[41] and that even the common ancestor of red and green algae, and the unicellular freshwater algae glaucophytes, originated in a terrestrial environment in freshwater biofilms or microbial mats.[42] Primitive land plants began to diversify in the late Silurian Period, around 420 million years ago, and the results of their diversification are displayed in remarkable detail in an early Devonian fossil assemblage from the Rhynie chert. This chert preserved early plants in cellular detail, petrified in volcanic springs. By the middle of the Devonian Period most of the features recognised in plants today are present, including roots, leaves and secondary wood, and by late Devonian times seeds had evolved.[43] Late Devonian plants had thereby reached a degree of sophistication that allowed them to form forests of tall trees. Evolutionary innovation continued in the Carboniferous and later geological periods and is ongoing today. Most plant groups were relatively unscathed by the Permo-Triassic extinction event, although the structures of communities changed. This may have set the scene for the evolution of flowering plants in the Triassic (~200 million years ago), which exploded in the Cretaceous and Tertiary. The latest major group of plants to evolve were the grasses, which became important in the mid Tertiary, from around 40 million years ago. The grasses, as well as many other groups, evolved new mechanisms of metabolism to survive the low CO2 and warm, dry conditions of the tropics over the last 10 million years.
+
+A 1997 proposed phylogenetic tree of Plantae, after Kenrick and Crane,[44] is as follows, with modification to the Pteridophyta from Smith et al.[45] The Prasinophyceae are a paraphyletic assemblage of early diverging green algal lineages, but are treated as a group outside the Chlorophyta:[46] later authors have not followed this suggestion.
+
+Prasinophyceae (micromonads)
+
+Spermatophytes (seed plants)
+
+Progymnospermophyta †
+
+Pteridopsida (true ferns)
+
+Marattiopsida
+
+Equisetopsida (horsetails)
+
+Psilotopsida (whisk ferns & adders'-tongues)
+
+Cladoxylopsida †
+
+Lycopodiophyta
+
+Zosterophyllophyta †
+
+Rhyniophyta †
+
+Aglaophyton †
+
+Horneophytopsida †
+
+Bryophyta (mosses)
+
+Anthocerotophyta (hornworts)
+
+Marchantiophyta (liverworts)
+
+Charophyta
+
+Trebouxiophyceae (Pleurastrophyceae)
+
+Chlorophyceae
+
+Ulvophyceae
+
+A newer proposed classification follows Leliaert et al. 2011[47] and modified with Silar 2016[20][21][48][49] for the green algae clades and Novíkov & Barabaš-Krasni 2015[50] for the land plants clade. Notice that the Prasinophyceae are here placed inside the Chlorophyta.
+
+Mesostigmatophyceae
+
+Chlorokybophyceae
+
+Spirotaenia
+
+Chlorophyta inc. Prasinophyceae
+
+Streptofilum
+
+Klebsormidiophyta
+
+Charophyta Rabenhorst 1863 emend. Lewis & McCourt 2004 (Stoneworts)
+
+Coleochaetophyta
+
+Zygnematophyta
+
+Marchantiophyta (Liverworts)
+
+Bryophyta (True mosses)
+
+Anthocerotophyta (Non-flowering hornworts)
+
+†Horneophyta
+
+†Aglaophyta
+
+Tracheophyta (Vascular Plants)
+
+Later, a phylogeny based on genomes and transcriptomes from 1,153 plant species was proposed.[51] The placing of algal groups is supported by phylogenies based on genomes from the Mesostigmatophyceae and Chlorokybophyceae that have since been sequenced.[52][53] The classification of Bryophyta is supported both by Puttick et al. 2018,[54] and by phylogenies involving the hornwort genomes that have also since been sequenced.[55][56]
+
+Rhodophyta
+
+Glaucophyta
+
+Chlorophyta
+
+Prasinococcales
+
+
+
+Mesostigmatophyceae
+
+Chlorokybophyceae
+
+Spirotaenia
+
+Klebsormidiales
+
+Chara
+
+Coleochaetales
+
+Zygnematophyceae
+
+Hornworts
+
+Liverworts
+
+Mosses
+
+Lycophytes
+
+Ferns
+
+Gymnosperms
+
+Angiosperms
+
+The plants that are likely most familiar to us are the multicellular land plants, called embryophytes. Embryophytes include the vascular plants, such as ferns, conifers and flowering plants. They also include the bryophytes, of which mosses and liverworts are the most common.
+
+All of these plants have eukaryotic cells with cell walls composed of cellulose, and most obtain their energy through photosynthesis, using light, water and carbon dioxide to synthesize food. About three hundred plant species do not photosynthesize but are parasites on other species of photosynthetic plants. Embryophytes are distinguished from green algae, which represent a mode of photosynthetic life similar to the kind modern plants are believed to have evolved from, by having specialized reproductive organs protected by non-reproductive tissues.
+
+Bryophytes first appeared during the early Paleozoic. They mainly live in habitats where moisture is available for significant periods, although some species, such as Targionia, are desiccation-tolerant. Most species of bryophytes remain small throughout their life-cycle. This involves an alternation between two generations: a haploid stage, called the gametophyte, and a diploid stage, called the sporophyte. In bryophytes, the sporophyte is always unbranched and remains nutritionally dependent on its parent gametophyte. The embryophytes have the ability to secrete a cuticle on their outer surface, a waxy layer that confers resistant to desiccation. In the mosses and hornworts a cuticle is usually only produced on the sporophyte. Stomata are absent from liverworts, but occur on the sporangia of mosses and hornworts, allowing gas exchange.
+
+Vascular plants first appeared during the Silurian period, and by the Devonian had diversified and spread into many different terrestrial environments. They developed a number of adaptations that allowed them to spread into increasingly more arid places, notably the vascular tissues xylem and phloem, that transport water and food throughout the organism. Root systems capable of obtaining soil water and nutrients also evolved during the Devonian. In modern vascular plants, the sporophyte is typically large, branched, nutritionally independent and long-lived, but there is increasing evidence that Paleozoic gametophytes were just as complex as the sporophytes. The gametophytes of all vascular plant groups evolved to become reduced in size and prominence in the life cycle.
+
+In seed plants, the microgametophyte is reduced from a multicellular free-living organism to a few cells in a pollen grain and the miniaturised megagametophyte remains inside the megasporangium, attached to and dependent on the parent plant. A megasporangium enclosed in a protective layer called an integument is known as an ovule. After fertilisation by means of sperm produced by pollen grains, an embryo sporophyte develops inside the ovule. The integument becomes a seed coat, and the ovule develops into a seed. Seed plants can survive and reproduce in extremely arid conditions, because they are not dependent on free water for the movement of sperm, or the development of free living gametophytes.
+
+The first seed plants, pteridosperms (seed ferns), now extinct, appeared in the Devonian and diversified through the Carboniferous. They were the ancestors of modern gymnosperms, of which four surviving groups are widespread today, particularly the conifers, which are dominant trees in several biomes. The name gymnosperm comes from the Greek composite word γυμνόσπερμος (γυμνός gymnos, "naked" and σπέρμα sperma, "seed"), as the ovules and subsequent seeds are not enclosed in a protective structure (carpels or fruit), but are borne naked, typically on cone scales.
+
+Plant fossils include roots, wood, leaves, seeds, fruit, pollen, spores, phytoliths, and amber (the fossilized resin produced by some plants). Fossil land plants are recorded in terrestrial, lacustrine, fluvial and nearshore marine sediments. Pollen, spores and algae (dinoflagellates and acritarchs) are used for dating sedimentary rock sequences. The remains of fossil plants are not as common as fossil animals, although plant fossils are locally abundant in many regions worldwide.
+
+The earliest fossils clearly assignable to Kingdom Plantae are fossil green algae from the Cambrian. These fossils resemble calcified multicellular members of the Dasycladales. Earlier Precambrian fossils are known that resemble single-cell green algae, but definitive identity with that group of algae is uncertain.
+
+The earliest fossils attributed to green algae date from the Precambrian (ca. 1200 mya).[57][58] The resistant outer walls of prasinophyte cysts (known as phycomata) are well preserved in fossil deposits of the Paleozoic (ca. 250–540 mya). A filamentous fossil (Proterocladus) from middle Neoproterozoic deposits (ca. 750 mya) has been attributed to the Cladophorales, while the oldest reliable records of the Bryopsidales, Dasycladales) and stoneworts are from the Paleozoic.[46][59]
+
+The oldest known fossils of embryophytes date from the Ordovician, though such fossils are fragmentary. By the Silurian, fossils of whole plants are preserved, including the simple vascular plant Cooksonia in mid-Silurian and the much larger and more complex lycophyte Baragwanathia longifolia in late Silurian. From the early Devonian Rhynie chert, detailed fossils of lycophytes and rhyniophytes have been found that show details of the individual cells within the plant organs and the symbiotic association of these plants with fungi of the order Glomales. The Devonian period also saw the evolution of leaves and roots, and the first modern tree, Archaeopteris. This tree with fern-like foliage and a trunk with conifer-like wood was heterosporous producing spores of two different sizes, an early step in the evolution of seeds.[60]
+
+The Coal measures are a major source of Paleozoic plant fossils, with many groups of plants in existence at this time. The spoil heaps of coal mines are the best places to collect; coal itself is the remains of fossilised plants, though structural detail of the plant fossils is rarely visible in coal. In the Fossil Grove at Victoria Park in Glasgow, Scotland, the stumps of Lepidodendron trees are found in their original growth positions.
+
+The fossilized remains of conifer and angiosperm roots, stems and branches may be locally abundant in lake and inshore sedimentary rocks from the Mesozoic and Cenozoic eras. Sequoia and its allies, magnolia, oak, and palms are often found.
+
+Petrified wood is common in some parts of the world, and is most frequently found in arid or desert areas where it is more readily exposed by erosion. Petrified wood is often heavily silicified (the organic material replaced by silicon dioxide), and the impregnated tissue is often preserved in fine detail. Such specimens may be cut and polished using lapidary equipment. Fossil forests of petrified wood have been found in all continents.
+
+Fossils of seed ferns such as Glossopteris are widely distributed throughout several continents of the Southern Hemisphere, a fact that gave support to Alfred Wegener's early ideas regarding Continental drift theory.
+
+Most of the solid material in a plant is taken from the atmosphere. Through the process of photosynthesis, most plants use the energy in sunlight to convert carbon dioxide from the atmosphere, plus water, into simple sugars. These sugars are then used as building blocks and form the main structural component of the plant. Chlorophyll, a green-colored, magnesium-containing pigment is essential to this process; it is generally present in plant leaves, and often in other plant parts as well. Parasitic plants, on the other hand, use the resources of their host to provide the materials needed for metabolism and growth.
+
+Plants usually rely on soil primarily for support and water (in quantitative terms), but they also obtain compounds of nitrogen, phosphorus, potassium, magnesium and other elemental nutrients from the soil. Epiphytic and lithophytic plants depend on air and nearby debris for nutrients, and carnivorous plants supplement their nutrient requirements, particularly for nitrogen and phosphorus, with insect prey that they capture. For the majority of plants to grow successfully they also require oxygen in the atmosphere and around their roots (soil gas) for respiration. Plants use oxygen and glucose (which may be produced from stored starch) to provide energy.[61] Some plants grow as submerged aquatics, using oxygen dissolved in the surrounding water, and a few specialized vascular plants, such as mangroves and reed (Phragmites australis),[62] can grow with their roots in anoxic conditions.
+
+The genome of a plant controls its growth. For example, selected varieties or genotypes of wheat grow rapidly, maturing within 110 days, whereas others, in the same environmental conditions, grow more slowly and mature within 155 days.[63]
+
+Growth is also determined by environmental factors, such as temperature, available water, available light, carbon dioxide and available nutrients in the soil. Any change in the availability of these external conditions will be reflected in the plant's growth and the timing of its development.[citation needed]
+
+Biotic factors also affect plant growth. Plants can be so crowded that no single individual produces normal growth, causing etiolation and chlorosis. Optimal plant growth can be hampered by grazing animals, suboptimal soil composition, lack of mycorrhizal fungi, and attacks by insects or plant diseases, including those caused by bacteria, fungi, viruses, and nematodes.[63]
+
+Simple plants like algae may have short life spans as individuals, but their populations are commonly seasonal. Annual plants grow and reproduce within one growing season, biennial plants grow for two growing seasons and usually reproduce in second year, and perennial plants live for many growing seasons and once mature will often reproduce annually. These designations often depend on climate and other environmental factors. Plants that are annual in alpine or temperate regions can be biennial or perennial in warmer climates. Among the vascular plants, perennials include both evergreens that keep their leaves the entire year, and deciduous plants that lose their leaves for some part of it. In temperate and boreal climates, they generally lose their leaves during the winter; many tropical plants lose their leaves during the dry season.[citation needed]
+
+The growth rate of plants is extremely variable. Some mosses grow less than 0.001 millimeters per hour (mm/h), while most trees grow 0.025–0.250 mm/h. Some climbing species, such as kudzu, which do not need to produce thick supportive tissue, may grow up to 12.5 mm/h.[citation needed]
+
+Plants protect themselves from frost and dehydration stress with antifreeze proteins, heat-shock proteins and sugars (sucrose is common). LEA (Late Embryogenesis Abundant) protein expression is induced by stresses and protects other proteins from aggregation as a result of desiccation and freezing.[64]
+
+When water freezes in plants, the consequences for the plant depend very much on whether the freezing occurs within cells (intracellularly) or outside cells in intercellular spaces.[65] Intracellular freezing, which usually kills the cell[66] regardless of the hardiness of the plant and its tissues, seldom occurs in nature because rates of cooling are rarely high enough to support it. Rates of cooling of several degrees Celsius per minute are typically needed to cause intracellular formation of ice.[67] At rates of cooling of a few degrees Celsius per hour, segregation of ice occurs in intercellular spaces.[68] This may or may not be lethal, depending on the hardiness of the tissue. At freezing temperatures, water in the intercellular spaces of plant tissue freezes first, though the water may remain unfrozen until temperatures drop below −7 °C (19 °F).[65] After the initial formation of intercellular ice, the cells shrink as water is lost to the segregated ice, and the cells undergo freeze-drying. This dehydration is now considered the fundamental cause of freezing injury.
+
+Plants are continuously exposed to a range of biotic and abiotic stresses.  These stresses often cause DNA damage directly, or indirectly via the generation of reactive oxygen species.[69] Plants are capable of a DNA damage response that is a critical mechanism for maintaining genome stability.[70] The DNA damage response is particularly important during seed germination, since seed quality tends to deteriorate with age in association with DNA damage accumulation.[71] During germination repair processes are activated to deal with this accumulated DNA damage.[72] In particular, single- and double-strand breaks in DNA can be repaired.[73] The DNA checkpoint kinase ATM has a key role in integrating progression through germination with repair responses to the DNA damages accumulated by the aged seed.[74]
+
+Plant cells are typically distinguished by their large water-filled central vacuole, chloroplasts, and rigid cell walls that are made up of cellulose, hemicellulose, and pectin. Cell division is also characterized by the development of a phragmoplast for the construction of a cell plate in the late stages of cytokinesis. Just as in animals, plant cells differentiate and develop into multiple cell types. Totipotent meristematic cells can differentiate into vascular, storage, protective (e.g. epidermal layer), or reproductive tissues, with more primitive plants lacking some tissue types.[75]
+
+Plants are photosynthetic, which means that they manufacture their own food molecules using energy obtained from light. The primary mechanism plants have for capturing light energy is the pigment chlorophyll. All green plants contain two forms of chlorophyll, chlorophyll a and chlorophyll b. The latter of these pigments is not found in red or brown algae.
+The simple equation of photosynthesis is as follows:
+
+By means of cells that behave like nerves, plants receive and distribute within their systems information about incident light intensity and quality. Incident light that stimulates a chemical reaction in one leaf, will cause a chain reaction of signals to the entire plant via a type of cell termed a bundle sheath cell. Researchers, from the Warsaw University of Life Sciences in Poland, found that plants have a specific memory for varying light conditions, which prepares their immune systems against seasonal pathogens.[76] Plants use pattern-recognition receptors to recognize conserved microbial signatures. This recognition triggers an immune response. The first plant receptors of conserved microbial signatures were identified in rice (XA21, 1995)[77] and in Arabidopsis thaliana (FLS2, 2000).[78] Plants also carry immune receptors that recognize highly variable pathogen effectors. These include the NBS-LRR class of proteins.
+
+Vascular plants differ from other plants in that nutrients are transported between their different parts through specialized structures, called xylem and phloem. They also have roots for taking up water and minerals. The xylem moves water and minerals from the root to the rest of the plant, and the phloem provides the roots with sugars and other nutrient produced by the leaves.[75]
+
+Plants have some of the largest genomes among all organisms.[79] The largest plant genome (in terms of gene number) is that of wheat (Triticum asestivum), predicted to encode ≈94,000 genes[80] and thus almost 5 times as many as the human genome. The first plant genome sequenced was that of Arabidopsis thaliana which encodes about 25,500 genes.[81] In terms of sheer DNA sequence, the smallest published genome is that of the carnivorous bladderwort (Utricularia gibba) at 82 Mb (although it still encodes 28,500 genes)[82] while the largest, from the Norway Spruce (Picea abies), extends over 19,600 Mb (encoding about 28,300 genes).[83]
+
+The photosynthesis conducted by land plants and algae is the ultimate source of energy and organic material in nearly all ecosystems. Photosynthesis, at first by cyanobacteria and later by photosynthetic eukaryotes, radically changed the composition of the early Earth's anoxic atmosphere, which as a result is now 21% oxygen. Animals and most other organisms are aerobic, relying on oxygen; those that do not are confined to relatively rare anaerobic environments. Plants are the primary producers in most terrestrial ecosystems and form the basis of the food web in those ecosystems. Many animals rely on plants for shelter as well as oxygen and food.[citation needed]
+
+Land plants are key components of the water cycle and several other biogeochemical cycles. Some plants have coevolved with nitrogen fixing bacteria, making plants an important part of the nitrogen cycle. Plant roots play an essential role in soil development and the prevention of soil erosion.[citation needed]
+
+Plants are distributed almost worldwide. While they inhabit a multitude of biomes and ecoregions, few can be found beyond the tundras at the northernmost regions of continental shelves. At the southern extremes, plants of the Antarctic flora have adapted tenaciously to the prevailing conditions.[citation needed]
+
+Plants are often the dominant physical and structural component of habitats where they occur. Many of the Earth's biomes are named for the type of vegetation because plants are the dominant organisms in those biomes, such as grasslands, taiga and tropical rainforest.[citation needed]
+
+Numerous animals have coevolved with plants. Many animals pollinate flowers in exchange for food in the form of pollen or nectar. Many animals disperse seeds, often by eating fruit and passing the seeds in their feces. Myrmecophytes are plants that have coevolved with ants. The plant provides a home, and sometimes food, for the ants. In exchange, the ants defend the plant from herbivores and sometimes competing plants. Ant wastes provide organic fertilizer.
+
+The majority of plant species have various kinds of fungi associated with their root systems in a kind of mutualistic symbiosis known as mycorrhiza. The fungi help the plants gain water and mineral nutrients from the soil, while the plant gives the fungi carbohydrates manufactured in photosynthesis. Some plants serve as homes for endophytic fungi that protect the plant from herbivores by producing toxins. The fungal endophyte, Neotyphodium coenophialum, in tall fescue (Festuca arundinacea) does tremendous economic damage to the cattle industry in the U.S.
+
+Various forms of parasitism are also fairly common among plants, from the semi-parasitic mistletoe that merely takes some nutrients from its host, but still has photosynthetic leaves, to the fully parasitic broomrape and toothwort that acquire all their nutrients through connections to the roots of other plants, and so have no chlorophyll. Some plants, known as myco-heterotrophs, parasitize mycorrhizal fungi, and hence act as epiparasites on other plants.
+
+Many plants are epiphytes, meaning they grow on other plants, usually trees, without parasitizing them. Epiphytes may indirectly harm their host plant by intercepting mineral nutrients and light that the host would otherwise receive. The weight of large numbers of epiphytes may break tree limbs. Hemiepiphytes like the strangler fig begin as epiphytes but eventually set their own roots and overpower and kill their host. Many orchids, bromeliads, ferns and mosses often grow as epiphytes. Bromeliad epiphytes accumulate water in leaf axils to form phytotelmata that may contain complex aquatic food webs.[84]
+
+Approximately 630 plants are carnivorous, such as the Venus Flytrap (Dionaea muscipula) and sundew (Drosera species). They trap small animals and digest them to obtain mineral nutrients, especially nitrogen and phosphorus.[85]
+
+The study of plant uses by people is called economic botany or ethnobotany.[86] Human cultivation of plants is part of agriculture, which is the basis of human civilization.[87] Plant agriculture is subdivided into agronomy, horticulture and forestry.[88]
+
+Humans depend on plants for food, either directly or as feed for domestic animals. Agriculture deals with the production of food crops, and has played a key role in the history of world civilizations. Agriculture includes agronomy for arable crops, horticulture for vegetables and fruit, and forestry for timber.[89] About 7,000 species of plant have been used for food, though most of today's food is derived from only 30 species. The major staples include cereals such as rice and wheat, starchy roots and tubers such as cassava and potato, and legumes such as peas and beans. Vegetable oils such as olive oil provide lipids, while fruit and vegetables contribute vitamins and minerals to the diet.[90]
+
+Medicinal plants are a primary source of organic compounds, both for their medicinal and physiological effects, and for the industrial synthesis of a vast array of organic chemicals.[91] Many hundreds of medicines are derived from plants, both traditional medicines used in herbalism[92][93] and chemical substances purified from plants or first identified in them, sometimes by ethnobotanical search, and then synthesised for use in modern medicine. Modern medicines derived from plants include aspirin, taxol, morphine, quinine, reserpine, colchicine, digitalis and vincristine. Plants used in herbalism include ginkgo, echinacea, feverfew, and Saint John's wort. The pharmacopoeia of Dioscorides, De Materia Medica, describing some 600 medicinal plants, was written between 50 and 70 AD and remained in use in Europe and the Middle East until around 1600 AD; it was the precursor of all modern pharmacopoeias.[94][95][96]
+
+Plants grown as industrial crops are the source of a wide range of products used in manufacturing, sometimes so intensively as to risk harm to the environment.[97] Nonfood products include essential oils, natural dyes, pigments, waxes, resins, tannins, alkaloids, amber and cork. Products derived from plants include soaps, shampoos, perfumes, cosmetics, paint, varnish, turpentine, rubber, latex, lubricants, linoleum, plastics, inks, and gums. Renewable fuels from plants include firewood, peat and other biofuels.[98][99] The fossil fuels coal, petroleum and natural gas are derived from the remains of aquatic organisms including phytoplankton in geological time.[100]
+
+Structural resources and fibres from plants are used to construct dwellings and to manufacture clothing. Wood is used not only for buildings, boats, and furniture, but also for smaller items such as musical instruments and sports equipment. Wood is pulped to make paper and cardboard.[101] Cloth is often made from cotton, flax, ramie or synthetic fibres such as rayon and acetate derived from plant cellulose. Thread used to sew cloth likewise comes in large part from cotton.[102]
+
+Thousands of plant species are cultivated for aesthetic purposes as well as to provide shade, modify temperatures, reduce wind, abate noise, provide privacy, and prevent soil erosion. Plants are the basis of a multibillion-dollar per year tourism industry, which includes travel to historic gardens, national parks, rainforests, forests with colorful autumn leaves, and festivals such as Japan's[103] and America's cherry blossom festivals.[104]
+
+While some gardens are planted with food crops, many are planted for aesthetic, ornamental, or conservation purposes. Arboretums and botanical gardens are public collections of living plants. In private outdoor gardens, lawn grasses, shade trees, ornamental trees, shrubs, vines, herbaceous perennials and bedding plants are used. Gardens may cultivate the plants in a naturalistic state, or may sculpture their growth, as with topiary or espalier. Gardening is the most popular leisure activity in the U.S., and working with plants or horticulture therapy is beneficial for rehabilitating people with disabilities.[citation needed]
+
+Plants may also be grown or kept indoors as houseplants, or in specialized buildings such as greenhouses that are designed for the care and cultivation of living plants. Venus Flytrap, sensitive plant and resurrection plant are examples of plants sold as novelties. There are also art forms specializing in the arrangement of cut or living plant, such as bonsai, ikebana, and the arrangement of cut or dried flowers. Ornamental plants have sometimes changed the course of history, as in tulipomania.[105]
+
+Architectural designs resembling plants appear in the capitals of Ancient Egyptian columns, which were carved to resemble either the Egyptian white lotus or the papyrus.[106] Images of plants are often used in painting and photography, as well as on textiles, money, stamps, flags and coats of arms.[citation needed]
+
+Basic biological research has often been done with plants. In genetics, the breeding of pea plants allowed Gregor Mendel to derive the basic laws governing inheritance,[107] and examination of chromosomes in maize allowed Barbara McClintock to demonstrate their connection to inherited traits.[108] The plant Arabidopsis thaliana is used in laboratories as a model organism to understand how genes control the growth and development of plant structures.[109] NASA predicts that space stations or space colonies will one day rely on plants for life support.[110]
+
+Ancient trees are revered and many are famous. Tree rings themselves are an important method of dating in archeology, and serve as a record of past climates.[citation needed]
+
+Plants figure prominently in mythology, religion and literature. They are used as national and state emblems, including state trees and state flowers. Plants are often used as memorials, gifts and to mark special occasions such as births, deaths, weddings and holidays. The arrangement of flowers may be used to send hidden messages.[citation needed]
+
+Weeds are unwanted plants growing in managed environments such as farms, urban areas, gardens, lawns, and parks. People have spread plants beyond their native ranges and some of these introduced plants become invasive, damaging existing ecosystems by displacing native species, and sometimes becoming serious weeds of cultivation.[citation needed]
+
+Plants may cause harm to animals, including people. Plants that produce windblown pollen invoke allergic reactions in people who suffer from hay fever. A wide variety of plants are poisonous. Toxalbumins are plant poisons fatal to most mammals and act as a serious deterrent to consumption. Several plants cause skin irritations when touched, such as poison ivy. Certain plants contain psychotropic chemicals, which are extracted and ingested or smoked, including nicotine from tobacco, cannabinoids from Cannabis sativa, cocaine from Erythroxylon coca and opium from opium poppy. Smoking causes damage to health or even death, while some drugs may also be harmful or fatal to people.[111][112] Both illegal and legal drugs derived from plants may have negative effects on the economy, affecting worker productivity and law enforcement costs.[113][114]

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@@ -0,0 +1,180 @@
+
+
+The lungs are the primary organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their function in the respiratory system is to extract oxygen from the atmosphere and transfer it into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange. Respiration is driven by different muscular systems in different species. Mammals, reptiles and birds use their different muscles to support and foster breathing. In early tetrapods, air was driven into the lungs by the pharyngeal muscles via buccal pumping, a mechanism still seen in amphibians. In humans, the main muscle of respiration that drives breathing is the diaphragm. The lungs also provide airflow that makes vocal sounds including human speech possible.
+
+Humans have two lungs, a right lung, and a left lung.  They are situated within the thoracic cavity of the chest. The right lung is bigger than the left, which shares space in the chest with the heart. The lungs together weigh approximately 1.3 kilograms (2.9 lb), and the right is heavier. The lungs are part of the lower respiratory tract that begins at the trachea and branches into the bronchi and bronchioles, and which receive air breathed in via the conducting zone. The conducting zone ends at the terminal bronchioles. These divide into the respiratory bronchioles of the respiratory zone which divide into alveolar ducts that give rise to the alveolar sacs that contain the alveoli, where gas exchange takes place. Alveoli are also sparsely present on the walls of the respiratory bronchioles and alveolar ducts. Together, the lungs contain approximately 2,400 kilometres (1,500 mi) of airways and 300 to 500 million alveoli. Each lung is enclosed within a pleural sac that contains pleural fluid, which allows the inner and outer walls to slide over each other whilst breathing takes place, without much friction. This sac also divides each lung into sections called lobes. The right lung has three lobes and the left has two. The lobes are further divided into  bronchopulmonary segments and  pulmonary lobules. The lungs have a unique blood supply, receiving deoxygenated blood from the heart in the pulmonary circulation for the purposes of receiving oxygen and releasing carbon dioxide, and a separate supply of oxygenated blood to the tissue of the lungs, in the bronchial circulation.
+
+The tissue of the lungs can be affected by a number of respiratory diseases, including pneumonia and lung cancer. Chronic obstructive pulmonary disease includes chronic bronchitis and emphysema, and can be related to smoking or exposure to harmful substances.  A number of occupational lung diseases can be caused by substances such as coal dust, asbestos fibres, and crystalline silica dust. Diseases such as bronchitis can also affect the respiratory tract. Medical terms related to the lung often begin with pulmo-, from the Latin pulmonarius (of the lungs) as in pulmonology, or with pneumo- (from Greek πνεύμων "lung") as in pneumonia.
+
+In embryonic development, the lungs begin to develop as an outpouching of the foregut, a tube which goes on to form the upper part of the digestive system. When the lungs are formed the fetus is held in the fluid-filled amniotic sac and so they do not function to breathe. Blood is also diverted from the lungs through the ductus arteriosus. At birth however, air begins to pass through the lungs, and the diversionary duct closes, so that the lungs can begin to respire. The lungs only fully develop in early childhood.
+
+The lungs are located in the chest on either side of the heart in the rib cage. They are conical in shape with a narrow rounded apex at the top, and a broad concave base that rests on the convex surface of the diaphragm.[1] The apex of the lung extends into the root of the neck, reaching shortly above the level of the sternal end of the first rib. The lungs stretch from close to the backbone in the rib cage to the front of the chest and downwards from the lower part of the trachea to the diaphragm.[1] The left lung shares space with the heart, and has an indentation in its border called the cardiac notch of the left lung to accommodate this.[2][3] The front and outer sides of the lungs face the ribs, which make light indentations on their surfaces. The medial surfaces of the lungs face towards the centre of the chest, and lie against the heart, great vessels, and the carina where the trachea divides into the two main bronchi.[3]  The cardiac impression is an indentation formed on the surfaces of the lungs where they rest against the heart.
+
+Both lungs have a central recession called the  hilum at the root of the lung, where the blood vessels and airways pass into the lungs.[1] There are also bronchopulmonary lymph nodes on the hilum.[3]
+
+The lungs are surrounded by the pulmonary pleurae. The pleurae are two serous membranes; the outer parietal pleura lines the inner wall of the rib cage and the inner visceral pleura directly lines the surface of the lungs. Between the pleurae is a potential space called the pleural cavity containing a thin layer of lubricating pleural fluid.
+
+Lower
+
+Lingula
+
+Each lung is divided into lobes by the infoldings of the pleura as fissures.  The fissures are double folds of pleura that section the lungs and help in their expansion.[5]
+
+The main or primary bronchi enter the lungs at the hilum and initially branch into secondary bronchi also known as lobar bronchi that supply air to each lobe of the lung. The lobar bronchi branch into tertiary bronchi also known as segmental bronchi and these supply air to the further divisions of the lobes known as bronchopulmonary segments. Each bronchopulmonary segment has its own (segmental) bronchus and arterial supply.[6] Segments for the left and right lung are shown in the table.[4] The segmental anatomy is useful clinically for localising disease processes in the lungs.[4] A segment is a discrete unit that can be surgically removed without seriously affecting surrounding tissue.[7]
+
+The right lung has both more lobes and segments than the left. It is divided into three lobes, an upper, middle, and a lower lobe by two fissures, one oblique and one horizontal.[8] The upper, horizontal fissure, separates the upper from the middle lobe. It begins in the lower oblique fissure near the posterior border of the lung, and, running horizontally forward, cuts the anterior border on a level with the sternal end of the fourth costal cartilage; on the mediastinal surface it may be traced back to the hilum.[1]
+
+The lower, oblique fissure, separates the lower from the middle and upper lobes and is closely aligned with the oblique fissure in the left lung.[1][5]
+
+The mediastinal surface of the right lung is indented by a number of nearby structures. The heart sits in an impression called the cardiac impression. Above the hilum of the lung is an arched groove for the azygos vein, and above this is a wide groove for the superior vena cava and right brachiocephalic vein; behind this, and close to the top of the lung is a groove for the brachiocephalic artery. There is a groove for the esophagus behind the hilum and the pulmonary ligament, and near the lower part of the esophageal groove is a deeper groove for the inferior vena cava before it enters the heart.[3]
+
+The weight of the right lung varies between individuals, with a standard reference range in men of 155–720 g (0.342–1.587 lb)[9] and in women of 100–590 g (0.22–1.30 lb).[10]
+
+The left lung is divided into two lobes, an upper and a lower lobe, by the oblique fissure, which extends from the costal to the mediastinal surface of the lung both above and below the hilum.[1] The left lung, unlike the right, does not have a middle lobe, though it does have a homologous feature, a projection of the upper lobe termed the lingula.  Its name means "little tongue". The lingula on the left lung serves as an anatomic parallel to the middle lobe on the right lung, with both areas being predisposed to similar infections and anatomic complications.[11][12] There are two bronchopulmonary segments of the lingula: superior and inferior.[1]
+
+The mediastinal surface of the left lung has a large cardiac impression where the heart sits. This is deeper and larger than that on the right lung, at which level the heart projects to the left.[3]
+
+On the same surface, immediately above the hilum, is a well-marked curved groove for  the aortic arch, and a groove below it for the descending aorta. The left subclavian artery, a branch off the aortic arch, sits in a groove from the arch to near the apex of the lung. A shallower groove in front of the artery and near the edge of the lung, lodges the left brachiocephalic vein. The esophagus may sit in a wider shallow impression at the base of the lung.[3]
+
+The weight of the left lung, by standard reference range, in men is 110–675 g (0.243–1.488 lb)[9] in women 105–515 g (0.231–1.135 lb).[10]
+
+The lungs are part of the lower respiratory tract, and accommodate the bronchial airways when they branch from the trachea. The bronchial airways terminate in alveoli, the lung parenchyma (the tissue in between), and veins, arteries, nerves, and lymphatic vessels.[3][13] The trachea and bronchi have plexuses of lymph capillaries in their mucosa and submucosa. The smaller bronchi have a single layer of lymph capillaries, and they are absent in the alveoli.[14] Each lung is surrounded by a serous membrane of visceral pleura, which has an underlying layer of loose connective tissue attached to the substance of the lung.[15]
+
+The connective tissue of the lungs is made up of elastic and collagen fibres that are interspersed between the capillaries and the alveolar walls. Elastin is the key protein of the extracellular matrix and is the main component of the elastic fibres.[16] Elastin gives the necessary elasticity and resilience required for the persistent stretching involved in breathing, known as lung compliance. It is also responsible for the elastic recoil needed. Elastin is more concentrated in areas of high stress such as the openings of the alveoli, and alveolar junctions.[16] The connective tissue links all the alveoli to form the lung parenchyma which has a sponge-like appearance. The alveoli have interconnecting air passages in their walls known as the pores of Kohn.[17]
+
+All of the lower respiratory tract including the trachea, bronchi, and bronchioles is lined with respiratory epithelium. This is a ciliated epithelium interspersed with goblet cells which produce mucin the main component of mucus, ciliated cells, basal cells, and in the terminal bronchioles–club cells with actions similar to basal cells, and macrophages. The epithelial cells, and the submucosal glands throughout the respiratory tract secrete airway surface liquid (ASL), the composition of which is tightly regulated and determines how well mucociliary clearance works.[18]
+
+Pulmonary neuroendocrine cells are found throughout the respiratory epithelium including the alveolar epithelium,[19] though they only account for around 0.5 per cent of the total epithelial population.[20] PNECs are innervated airway epithelial cells that are particularly focused at airway junction points.[20] These cells can produce serotonin, dopamine, and norepinephrine, as well as polypeptide products. Cytoplasmic processes from the pulmonary neuroendocrine cells extend into the airway lumen where they may sense the composition of inspired gas.[21]
+
+In the bronchi there are incomplete tracheal rings of cartilage and smaller plates of cartilage that keep them open.[22]:472 Bronchioles are too narrow to support cartilage and their walls are of smooth muscle, and this is largely absent in the narrower respiratory bronchioles which are mainly just of epithelium.[22]:472 The absence of cartilage in the terminal bronchioles gives them an alternative name of membranous bronchioles.[23]
+
+The conducting zone of the respiratory tract ends at the terminal bronchioles when they branch into the respiratory bronchioles. This marks the beginning of an acinus which includes the respiratory bronchioles, the alveolar ducts, alveolar sacs, and alveoli.[24] This is also called the terminal respiratory unit.[25] An acinus measures up to 10 mm in diameter.[24] A primary pulmonary lobule is that part of the acinus that includes the alveolar ducts, sacs, and alveoli but does not include the respiratory bronchioles.[26] The unit described as the secondary pulmonary lobule is the lobule most referred to as the pulmonary lobule or respiratory lobule.[22]:489[27] This lobule is a discrete unit that is the smallest component of the lung that can be seen without aid. The secondary pulmonary lobule is likely to be made up of between 30 and 50 primary lobules.[26] The lobule is supplied by a terminal bronchiole that branches into respiratory bronchioles. The respiratory bronchioles supply the alveoli in each acinus and is accompanied by a pulmonary artery branch. Each lobule is enclosed by an interlobular septa. Each acinus is incompletely separated by an interlobular septa.[24]
+
+The respiratory bronchiole gives rise to the alveolar ducts that lead to the alveolar sacs, which contain two or more alveoli.[17] The walls of the alveoli are extremely thin allowing a fast rate of diffusion.  The alveoli have interconnecting small air passages in their walls known as the pores of Kohn.[17]
+
+Alveoli consist of two types of alveolar cell and an alveolar macrophage. The two types of cell are known as type I and type II cells[28] (also known as pneumocytes).[3] Types I and II make up the walls and alveolar septa. Type I cells provide 95% of the surface area of each alveoli and are flat ("squamous"), and Type II cells generally cluster in the corners of the alveoli and have a cuboidal shape.[29] Despite this, cells occur in a roughly equal ratio of 1:1 or 6:4.[28][29]
+
+Type I are squamous epithelial cells that make up the alveolar wall structure. They have extremely thin walls that enable an easy gas exchange.[28] These type I cells also make up the alveolar septa which separate each alveolus. The septa consist of an epithelial lining and associated basement membranes.[29] Type I cells are not able to divide, and consequently rely on differentiation from Type II cells.[29]
+
+Type II are larger and they line the alveoli and produce and secrete epithelial lining fluid, and lung surfactant.[30][28] Type II cells are able to divide and differentiate to Type I cells.[29]
+
+The alveolar macrophages have an important immunological role. They remove substances which deposit in the alveoli including loose red blood cells that have been forced out from blood vessels.[29]
+
+There is a large presence of microorganisms in the lungs known as the lung microbiome or microbiota. The lung microbiome interacts with the airway epithelial cells. The microbiome is complex in healthy people, and altered in diseases such as asthma and COPD. The lung microbiome is dynamic and significant changes can take place in COPD following infection with rhinovirus. The interaction between the microbiome and the epithelial cells is of probable importance in the maintenance of stable homeostasis.[31] Fungal genera that are commonly found in the lung microbiota, known as the lung mycobiome include Candida, Malassezia, Saccharomyces, and Aspergillus.[32][33]
+
+The lower respiratory tract is part of the respiratory system, and consists of the trachea and the structures below this including the lungs.[28] The trachea receives air from the pharynx and travels down to a place where it splits (the carina) into a right and left bronchus. These supply air to the right and left lungs, splitting progressively into the secondary and tertiary bronchi for the lobes of the lungs, and into smaller and smaller bronchioles until they become the respiratory bronchioles. These in turn supply air through alveolar ducts into the alveoli, where the exchange of gases take place.[28] Oxygen breathed in, diffuses through the walls of the alveoli into the enveloping capillaries and into the circulation,[17] and carbon dioxide diffuses from the blood into the lungs to be breathed out.
+
+Estimates of the total surface area of lungs vary from 50 to 75 square metres (540 to 810 sq ft);[28][29] although this is often quoted in textbooks and the media being "the size of a tennis court",[29][34][35] it is actually less than half the size of a singles court.[36]
+
+The bronchi in the conducting zone are reinforced with hyaline cartilage in order to hold open the airways. The bronchioles have no cartilage and are surrounded instead by smooth muscle.[29]  Air is warmed to 37 °C (99 °F), humidified and cleansed by the conducting zone. Particles from the air being removed by the cilia on the respiratory epithelium lining the passageways,[37] in a process called mucociliary clearance.
+
+Pulmonary stretch receptors in the smooth muscle of the airways initiate a reflex known as the Hering–Breuer reflex that prevents the lungs from over-inflation, during forceful inspiration.
+
+The lungs have a dual blood supply provided by a bronchial and a pulmonary circulation.[38] The bronchial circulation supplies oxygenated blood to the airways of the lungs, through the bronchial arteries that leave the aorta.  There are usually three arteries, two to the left lung and one to the right, and they branch alongside the bronchi and bronchioles.[28] The pulmonary circulation carries deoxygenated blood from the heart to the lungs and returns the oxygenated blood to the heart to supply the rest of the body.[28]
+
+The blood volume of the lungs is about 450 millilitres on average, about 9% of the total blood volume of the entire circulatory system. This quantity can easily fluctuate from between one-half and twice the normal volume.  Also, in the event of blood loss through hemorrhage, blood from the lungs can partially compensate by automatically transferring to the systemic circulation.[39]
+
+The lungs are supplied by nerves of the autonomic nervous system. Input from the parasympathetic nervous system occurs via the vagus nerve.[38] When stimulated by acetylcholine, this causes constriction of the smooth muscle lining the bronchus and bronchioles, and increases the secretions from glands.[40][page needed] The lungs also have a sympathetic tone from norepinephrine acting on the beta 2 adrenoceptors in the respiratory tract, which causes bronchodilation.[41]
+
+The action of breathing takes place because of nerve signals sent by the respiratory center in the brainstem, along the phrenic nerve from the cervical plexus to the diaphragm.[42]
+
+The lobes of the lung are subject to anatomical variations.[43] A horizontal interlobar fissure was found to be incomplete in 25% of right lungs, or even absent in 11% of all cases. An accessory fissure was also found in 14% and 22% of left and right lungs, respectively.[44] An oblique fissure was found to be incomplete in 21% to 47% of left lungs.[45] In some cases a fissure is absent, or extra, resulting in a right lung with only two lobes, or a left lung with three lobes.[43]
+
+A variation in the airway branching structure has been found specifically in the central airway
+branching. This variation is associated with the development of COPD in adulthood.[46]
+
+The development of the human lungs arise from the laryngotracheal groove and develop to maturity over several weeks in the foetus and for several years following birth.[47]
+
+The larynx, trachea, bronchi and lungs that make up the respiratory tract, begin to form during the fourth week of embryogenesis[48] from the lung bud which appears ventrally to the caudal portion of the foregut.[49]
+
+The respiratory tract has a branching structure, and is also known as the respiratory tree.[50] In the embryo this structure is developed in the process of branching morphogenesis, and is generated by the repeated splitting of the tip of the branch. In the development of the lungs (as in some other organs) the epithelium forms branching tubes.The lung has a left-right symmetry and each bud known as a bronchial bud grows out as a tubular epithelium that becomes a bronchus. Each bronchus branches into bronchioles.[51] The branching is a result of the tip of each tube bifurcating.[50] The branching process forms the bronchi, bronchioles, and ultimately the alveoli.[50] The four genes mostly associated with branching morphogenesis in the lung are the intercellular signalling protein – sonic hedgehog (SHH), fibroblast growth factors FGF10 and FGFR2b, and bone morphogenetic protein BMP4. FGF10 is seen to have the most prominent role. FGF10 is a paracrine signalling molecule needed for epithelial branching, and SHH inhibits FGF10.[50][51] The development of the alveoli is influenced by a different mechanism whereby continued bifurcation is stopped and the distal tips become dilated to form the alveoli.
+
+At the end of the fourth week the lung bud divides into two, the right and left primary bronchial buds on each side of the trachea.[52][53] During the fifth week the right bud branches into three secondary bronchial buds and the left branches into two secondary bronchial buds. These give rise to the lobes of the lungs, three on the right and two on the left. Over the following week, the secondary buds branch into tertiary buds, about ten on each side.[53] From the sixth week to the sixteenth week, the major elements of the lungs appear except the alveoli.[54] From week 16 to week 26, the bronchi enlarge and lung tissue becomes highly vascularised. Bronchioles and alveolar ducts also develop. By week 26 the terminal bronchioles have formed which branch into two respiratory bronchioles.[55] During the period covering the 26th week until birth the important blood–air barrier is established. Specialised type I alveolar cells where gas exchange will take place, together with the type II alveolar cells that secrete pulmonary surfactant, appear. The surfactant reduces the surface tension at the air-alveolar surface which allows expansion of the alveolar sacs. The alveolar sacs contain the primitive alveoli that form at the end of the alveolar ducts,[56]
+and their appearance around the seventh month marks the point at which limited respiration would be possible, and the premature baby could survive.[47]
+
+The developing lung is particularly vulnerable to changes in the levels of vitamin A. Vitamin A deficiency has been linked to changes in the epithelial lining of the lung and in the lung parenchyma. This can disrupt the normal physiology of the lung and predispose to respiratory diseases. Severe nutritional deficiency in vitamin A results in a reduction in the formation of the alveolar walls (septa) and to notable changes in the respiratory epithelium; alterations are noted in the extracellular matrix and in the protein content of the basement membrane. The extracellular matrix maintains lung elasticity; the basement membrane is associated with alveolar epithelium and is important in the blood-air barrier. The deficiency is associated with functional defects and disease states. Vitamin A is crucial in the development of the alveoli which continues for several years after birth.[57]
+
+At birth, the baby's lungs are filled with fluid secreted by the lungs and are not inflated. After birth the infant's central nervous system reacts to the sudden change in temperature and environment. This triggers the first breath, within about 10 seconds after delivery.[58] Before birth, the lungs are filled with fetal lung fluid.[59]      After the first breath, the fluid is quickly absorbed into the body or exhaled. The resistance in the lung's blood vessels decreases giving an increased surface area for gas exchange, and the lungs begin to breathe spontaneously. This accompanies other changes which result in an increased amount of blood entering the lung tissues.[58]
+
+At birth the lungs are very undeveloped with only around one sixth of the alveoli of the adult lung present.[47] The alveoli continue to form into early adulthood, and their ability to form when necessary is seen in the regeneration of the lung.[60][61] Alveolar septa have a double capillary network instead of the single network of the developed lung. Only after the maturation of the capillary network can the lung enter a normal phase of growth. Following the early growth in numbers of alveoli there is another stage of the alveoli being enlarged.[62]
+
+The major function of the lungs is gas exchange between the lungs and the blood.[63] The alveolar and pulmonary capillary gases equilibrate across the thin blood–air barrier.[30][64][65] This thin membrane (about 0.5 –2 μm thick) is folded into about 300 million alveoli, providing an extremely large surface area (estimates varying between 70 and 145 m2) for gas exchange to occur.[64][66]
+
+The lungs are not capable of expanding to breathe on their own, and will only do so when there is an increase in the volume of the thoracic cavity.[67] This is achieved by the muscles of respiration, through the contraction of the diaphragm, and the intercostal muscles which pull the rib cage upwards as shown in the diagram.[68] During breathing out the muscles relax, returning the lungs to their resting position.[69] At this point the lungs contain the functional residual capacity (FRC) of air, which, in the adult human, has a volume of about 2.5–3.0 litres.[69]
+
+During heavy breathing as in exertion, a large number of accessory muscles in the neck and abdomen are recruited, that during exhalation pull the ribcage down, decreasing the volume of the thoracic cavity.[69] The FRC is now decreased, but since the lungs cannot be emptied completely there is still about a litre of residual air left.[69] Lung function testing is carried out to evaluate lung volumes and capacities.
+
+The lungs possess several characteristics which protect against infection. The respiratory tract is lined by respiratory epithelium or respiratory mucosa, with hair-like projections called cilia that beat rhythmically and carry mucus. This mucociliary clearance is an important defence system against air-borne infection.[30] The dust particles and bacteria in the inhaled air are caught in the mucosal surface of the airways, and are moved up towards the pharynx by the rhythmic upward beating action of the cilia.[29][70]:661–730 The lining of the lung also secretes immunoglobulin A which protects against respiratory infections;[70] goblet cells secrete mucus[29] which also contains several antimicrobial compounds such as defensins, antiproteases, and antioxidants.[70] A rare type of specialised cell called a pulmonary ionocyte that is suggested may regulate mucus viscosity has been described.[71][72][73] In addition, the lining of the lung also contains macrophages, immune cells which engulf and destroy debris and microbes that enter the lung in a process known as phagocytosis; and dendritic cells which present antigens to activate components of the adaptive immune system such as T-cells and B-cells.[70]
+
+The size of the respiratory tract and the flow of air also protect the lungs from larger particles. Smaller particles deposit in the mouth and behind the mouth in the oropharynx, and larger particles are trapped in nasal hair after inhalation.[70]
+
+In addition to their function in respiration, the lungs have a number of other functions. They are involved in maintaining homeostasis, helping in the regulation of blood pressure as part of the renin–angiotensin system. The inner lining of the blood vessels secretes angiotensin-converting enzyme (ACE) an enzyme that catalyses the conversion of angiotensin I to angiotensin II.[74] The lungs are involved in the blood's acid-base homeostasis by expelling carbon dioxide when breathing.[67][75]
+
+The lungs also serve a protective role. Several blood-borne substances, such as a few types of prostaglandins, leukotrienes, serotonin and bradykinin, are excreted through the lungs.[74] Drugs and other substances can be absorbed, modified or excreted in the lungs.[67][76] The lungs filter out small blood clots from veins and prevent them from entering arteries and causing strokes.[75]
+
+The lungs also play a pivotal role in speech by providing air and airflow for the creation of vocal sounds,[67][77] and other paralanguage communications such as sighs and gasps.
+
+New research suggests a role of the lungs in the production of blood platelets.[78]
+
+About 20,000 protein coding genes are expressed in human cells and almost 75% of these genes are expressed in the normal lung.[79][80] A little less than 200 of these genes are more specifically expressed in the lung with less than 20 genes being highly lung specific. The highest expression of lung specific proteins are different surfactant proteins,[30] such as SFTPA1, SFTPB and SFTPC, and napsin, expressed in type II pneumocytes. Other proteins with elevated expression in the lung are the dynein protein DNAH5 in ciliated cells, and the secreted SCGB1A1 protein in mucus-secreting  goblet cells of the airway mucosa.[81]
+
+Lungs can be affected by a variety of diseases. Pulmonology is the medical speciality that deals with diseases involving the respiratory tract,[82] and cardiothoracic surgery is the surgical field that deals with surgery of the lungs.[83]
+
+Inflammatory conditions of the lung tissue are pneumonia, of the respiratory tract are bronchitis and bronchiolitis, and of the pleurae surrounding the lungs pleurisy. Inflammation is usually caused by infections due to bacteria or viruses. When the lung tissue is inflamed due to other causes it is called pneumonitis. One major cause of bacterial pneumonia is tuberculosis.[70] Chronic infections often occur in those with immunodeficiency and can include a fungal infection by Aspergillus fumigatus that can lead to an aspergilloma forming in the lung.[70][84]
+
+A pulmonary embolism is a blood clot that becomes lodged in the pulmonary arteries. The majority of emboli arise because of deep vein thrombosis in the legs. Pulmonary emboli may be investigated using a ventilation/perfusion scan, a CT scan of the arteries of the lung, or blood tests such as the D-dimer.[70] Pulmonary hypertension describes an increased pressure at the beginning of the pulmonary artery that has a large number of differing causes.[70] Other rarer conditions may also affect the blood supply of the lung, such as granulomatosis with polyangiitis, which causes inflammation of the small blood vessels of the lungs and kidneys.[70]
+
+A lung contusion is a bruise caused by chest trauma. It results in hemorrhage of the alveoli causing a build-up of fluid which can impair breathing, and this can be either mild or severe.
+The function of the lungs can also be affected by compression from fluid in the pleural cavity pleural effusion, or other substances such as air (pneumothorax), blood (hemothorax), or rarer causes. These may be investigated using a chest X-ray or CT scan, and may require the insertion of a surgical drain until the underlying cause is identified and treated.[70]
+
+Asthma, chronic bronchitis, bronchiectasis and chronic obstructive pulmonary disease (COPD) are all obstructive lung diseases characterised by airway obstruction. This limits the amount of air that is able to enter alveoli because of constriction of the bronchial tree, due to inflammation. Obstructive lung diseases are often identified because of symptoms and diagnosed with pulmonary function tests such as spirometry. Many obstructive lung diseases are managed by avoiding triggers (such as dust mites or smoking), with symptom control such as bronchodilators, and with suppression of inflammation (such as through corticosteroids) in severe cases. A common cause of chronic bronchitis, and emphysema, is smoking; and common causes of bronchiectasis include severe infections and cystic fibrosis. The definitive cause of asthma is not yet known.[70]
+
+The breakdown of alveolar tissue, often as a result of tobacco-smoking leads to emphysema, which can become severe enough to develop into COPD. Elastase breaks down the elastin in the lung's connective tissue that can also result in emphysema. Elastase is inhibited by the acute-phase protein, alpha-1 antitrypsin, and when there is a deficiency in this, emphysema can develop. With persistent stress from smoking, the airway basal cells become disarranged and lose their regenerative ability needed to repair the epithelial barrier. The disorganised basal cells are seen to be responsible for the major airway changes that are characteristic of COPD, and with continued stress can undergo a malignant transformation. Studies have shown that the initial development of emphysema is centred on the early changes in the airway epithelium of the small airways.[85] Basal cells become further deranged in a smoker's transition to clinically defined COPD.[85]
+
+Some types of chronic lung diseases are classified as restrictive lung disease, because of a restriction in the amount of lung tissue involved in respiration. These include pulmonary fibrosis which can occur when the lung is inflamed for a long period of time. Fibrosis in the lung replaces functioning lung tissue with fibrous connective tissue. This can be due to a large variety of occupational lung diseases such as Coalworker's pneumoconiosis, autoimmune diseases or more rarely to a reaction to medication.[70] Severe respiratory disorders, where spontaneous breathing is not enough to maintain life, may need the use of mechanical ventilation to ensure an adequate supply of air.
+
+Lung cancer can either arise directly from lung tissue or as a result of metastasis from another part of the body. There are two main types of primary tumour described as either small-cell or non-small-cell lung carcinomas. The major risk factor for cancer is smoking. Once a cancer is identified it is staged using scans such as a CT scan and a sample of tissue (a biopsy) is taken. Cancers may be treated by surgically removing the tumour, radiotherapy, chemotherapy or combinations thereof, or with the aim of symptom control.[70] Lung cancer screening is being recommended in the United States for high-risk populations.[86]
+
+Congenital disorders include cystic fibrosis, pulmonary hypoplasia (an incomplete development of the lungs)[87]congenital diaphragmatic hernia, and infant respiratory distress syndrome caused by a deficiency in lung surfactant. An azygos lobe is a congenital anatomical variation which though usually without effect can cause problems in thoracoscopic procedures.[88]
+
+A pneumothorax (collapsed lung) is an abnormal collection of air in the pleural space that causes an uncoupling of the lung from the chest wall.[89] The lung cannot expand against the air pressure inside the pleural space. An easy to understand example is a traumatic pneumothorax, where air enters the pleural space from outside the body, as occurs with puncture to the chest wall. Similarly, scuba divers ascending while holding their breath with their lungs fully inflated can cause air sacs (alveoli) to burst and leak high pressure air into the pleural space.
+
+As part of a physical examination in response to respiratory symptoms of shortness of breath, and cough, a lung examination may be carried out. This exam includes palpation and auscultation.[90] The areas of the lungs that can be listened to using a stethoscope are called the lung fields, and these are the posterior, lateral, and anterior lung fields. The posterior fields can be listened to from the back and include: the lower lobes (taking up three quarters of the posterior fields); the anterior fields taking up the other quarter; and the lateral fields under the axillae, the left axilla for the lingual, the right axilla for the middle right lobe. The anterior fields can also be auscultated from the front.[91] Abnormal breathing sounds heard during a lung exam can indicate the presence of a lung condition; wheezing for example is commonly associated with asthma and COPD.
+
+Lung function testing is carried out by evaluating a person's capacity to inhale and exhale in different circumstances.[92] The volume of air inhaled and exhaled by a person at rest is the tidal volume (normally 500-750mL); the inspiratory reserve volume and expiratory reserve volume are the additional amounts a person is able to forcibly inhale and exhale respectively. The summed total of forced inspiration and expiration is a person's vital capacity. Not all air is expelled from the lungs even after a forced breath out; the remainder of the air is called the residual volume. Together these terms are referred to as lung volumes.[92]
+
+Pulmonary plethysmographs are used to measure functional residual capacity.[93] Functional residual capacity cannot be measured by tests that rely on breathing out, as a person is only able to breathe a maximum of 80% of their total functional capacity.[94] The total lung capacity depends on the person's age, height, weight, and sex, and normally ranges between 4 and 6 litres.[92] Females tend to have a 20–25% lower capacity than males. Tall people tend to have a larger total lung capacity than shorter people. Smokers have a lower capacity than nonsmokers. Thinner persons tend to have a larger capacity. Lung capacity can be increased by physical training as much as 40% but the effect may be modified by exposure to air pollution.[94][95]
+
+Other lung function tests include spirometry, measuring the amount (volume) and flow of air that can be inhaled and exhaled. The maximum volume of breath that can be exhaled is called the vital capacity. In particular, how much a person is able to exhale in one second (called forced expiratory volume (FEV1)) as a proportion of how much they are able to exhale in total (FEV). This ratio, the FEV1/FEV ratio, is important to distinguish whether a lung disease is restrictive or obstructive.[70][92] Another test is that of the lung's  diffusing capacity – this is a measure of the transfer of gas from air to the blood in the lung capillaries.
+
+The lungs of birds are relatively small, but are connected to 8 or 9 air sacs that extend through much of the body, and are in turn connected to air spaces within the bones. On inhalation, air travels through the trachea of a bird into the air sacs. Air then travels continuously from the air sacs at the back, through the lungs, which are relatively fixed in size, to the air sacs at the front. From here, the air is exhaled. These fixed size lungs are called "circulatory lungs", as distinct from the "bellows-type lungs" found in most other animals.[96][98]
+
+The lungs of birds contain millions of tiny parallel passages called parabronchi. Small sacs called atria radiate from the walls of the tiny passages; these, like the alveoli in other lungs, are the site of gas exchange by simple diffusion.[98] The blood flow around the parabronchi and their atria forms a cross-current process of gas exchange (see diagram on the right).[96][97]
+
+The air sacs, which hold air, do not contribute much to gas exchange, despite being thin-walled, as they are poorly vascularised. The air sacs expand and contract due to changes in the volume in the thorax and abdomen. This volume change is caused by the movement of the sternum and ribs and this movement is often synchronised with movement of the flight muscles.[99]
+
+Parabronchi in which the air flow is unidirectional are called paleopulmonic parabronchi and are found in all birds. Some birds, however, have, in addition, a lung structure where the air flow in the parabronchi is bidirectional. These are termed neopulmonic parabronchi.[98]
+
+The lungs of most reptiles have a single bronchus running down the centre, from which numerous branches reach out to individual pockets throughout the lungs. These pockets are similar to alveoli in mammals, but much larger and fewer in number. These give the lung a sponge-like texture. In tuataras, snakes, and some lizards, the lungs are simpler in structure, similar to that of typical amphibians.[99]
+
+Snakes and limbless lizards typically possess only the right lung as a major respiratory organ; the left lung is greatly reduced, or even absent. Amphisbaenians, however, have the opposite arrangement, with a major left lung, and a reduced or absent right lung.[99]
+
+Both crocodilians and monitor lizards have developed lungs similar to those of birds, providing a unidirectional airflow and even possessing air sacs.[100] The now extinct pterosaurs have seemingly even further refined this type of lung, extending the airsacs into the wing membranes and, in the case of lonchodectids, tupuxuara, and azhdarchoids, the hindlimbs.[101]
+
+Reptilian lungs typically receive air via expansion and contraction of the ribs driven by axial muscles and buccal pumping. Crocodilians also rely on the hepatic piston method, in which the liver is pulled back by a muscle anchored to the pubic bone (part of the pelvis) called the diaphragmaticus,[102] which in turn creates negative pressure in the crocodile's thoracic cavity, allowing air to be moved into the lungs by Boyle's law. Turtles, which are unable to move their ribs, instead use their forelimbs and pectoral girdle to force air in and out of the lungs.[99]
+
+The lungs of most frogs and other amphibians are simple and balloon-like, with gas exchange limited to the outer surface of the lung. This is not very efficient, but amphibians have low metabolic demands and can also quickly dispose of carbon dioxide by diffusion across their skin in water, and supplement their oxygen supply by the same method. Amphibians employ a positive pressure system to get air to their lungs, forcing air down into the lungs by buccal pumping. This is distinct from most higher vertebrates, who use a breathing system driven by negative pressure where the lungs are inflated by expanding the rib cage.[103] In buccal pumping, the floor of the mouth is lowered, filling the mouth cavity with air. The throat muscles then presses the throat against the underside of the skull, forcing the air into the lungs.[104]
+
+Due to the possibility of respiration across the skin combined with small size, all known lungless tetrapods are amphibians. The majority of salamander species are lungless salamanders, which respirate through their skin and tissues lining their mouth. This necessarily restricts their size: all are small and rather thread-like in appearance, maximising skin surface relative to body volume.[105] Other known lungless tetrapods are the Bornean flat-headed frog[106] and Atretochoana eiselti, a caecilian.[107]
+
+The lungs of amphibians typically have a few narrow internal walls (septa) of soft tissue around the outer walls, increasing the respiratory surface area and giving the lung a honey-comb appearance. In some salamanders even these are lacking, and the lung has a smooth wall. In caecilians, as in snakes, only the right lung attains any size or development.[99]
+
+The lungs of lungfish are similar to those of amphibians, with few, if any, internal septa. In the Australian lungfish, there is only a single lung, albeit divided into two lobes. Other lungfish and Polypterus, however, have two lungs, which are located in the upper part of the body, with the connecting duct curving around and above the esophagus. The blood supply also twists around the esophagus, suggesting that the lungs originally evolved in the ventral part of the body, as in other vertebrates.[99]
+
+Some invertebrates have lung-like structures that serve a similar respiratory purpose as, but are not evolutionarily related to, vertebrate lungs. Some arachnids, such as spiders and scorpions, have structures called book lungs used for atmospheric gas exchange. Some species of spider have four pairs of book lungs but most have two pairs.[108] Scorpions have spiracles on their body for the entrance of air to the book lungs.[109]
+
+The coconut crab is terrestrial and uses structures called branchiostegal lungs to breathe air.[110] They cannot swim and would drown in water, yet they possess a rudimentary set of gills. They can breathe on land and hold their breath underwater.[111] The branchiostegal lungs are seen as a developmental adaptive stage from water-living to enable land-living, or from fish to amphibian.[112]
+
+Pulmonates are mostly land snails and slugs that have developed a simple lung from the mantle cavity. An externally located opening called the pneumostome allows air to be taken into the mantle cavity lung.[113][114]
+
+The lungs of today's terrestrial vertebrates and the gas bladders of today's fish are believed to have evolved from simple sacs, as outpocketings of the esophagus, that allowed early fish to gulp air under oxygen-poor conditions.[115] These outpocketings first arose in the  bony fish. In most of the ray-finned fish the sacs evolved into closed off gas bladders, while a number of carp, trout, herring, catfish, and eels have retained the physostome condition with the sack being open to the esophagus. In more basal bony fish, such as the gar, bichir, bowfin and the lobe-finned fish, the bladders have evolved to primarily function as lungs.[115] The lobe-finned fish gave rise to the land-based tetrapods. Thus, the lungs of vertebrates are homologous to the gas bladders of fish (but not to their gills).[116]

en/338.html.txt

@@ -0,0 +1,377 @@
+
+
+A circle is a shape consisting of all points in a plane that are a given distance from a given point, the centre; equivalently it is the curve traced out by a point that moves in a plane so that its distance from a given point is constant. The distance between any point of the circle and the centre is called the radius. This article is about circles in Euclidean geometry, and, in particular, the Euclidean plane, except where otherwise noted.
+
+Specifically, a circle is a simple closed curve that divides the plane into two regions: an interior and an exterior. In everyday use, the term "circle" may be used interchangeably to refer to either the boundary of the figure, or to the whole figure including its interior; in strict technical usage, the circle is only the boundary and the whole figure is called a disc.
+
+A circle may also be defined as a special kind of ellipse in which the two foci are coincident and the eccentricity is 0, or the two-dimensional shape enclosing the most area per unit perimeter squared, using calculus of variations.
+
+A circle is a plane figure bounded by one curved line, and such that all straight lines drawn from a certain point within it to the bounding line, are equal. The bounding line is called its circumference and the point, its centre.
+
+In the field of topology, a circle isn't limited to the geometric concept, but to all of its homeomorphisms. Two topological circles are equivalent if one can be transformed into the other via a deformation of R3 upon itself (known as an ambient isotopy).[2]
+
+All of the specified regions may be considered as open, that is, not containing their boundaries, or as closed, including their respective boundaries.
+
+The word circle derives from the Greek κίρκος/κύκλος (kirkos/kuklos), itself a metathesis of the Homeric Greek κρίκος (krikos), meaning "hoop" or "ring".[3] The origins of the words circus and circuit are closely related.
+
+The circle has been known since before the beginning of recorded history. Natural circles would have been observed, such as the Moon, Sun, and a short plant stalk blowing in the wind on sand, which forms a circle shape in the sand. The circle is the basis for the wheel, which, with related inventions such as gears, makes much of modern machinery possible. In mathematics, the study of the circle has helped inspire the development of geometry, astronomy and calculus.
+
+Early science, particularly geometry and astrology and astronomy, was connected to the divine for most medieval scholars, and many believed that there was something intrinsically "divine" or "perfect" that could be found in circles.[4][5]
+
+Some highlights in the history of the circle are:
+
+The ratio of a circle's circumference to its diameter is π (pi), an irrational constant approximately equal to 3.141592654. Thus the circumference C is related to the radius r and diameter d by:
+
+As proved by Archimedes, in his Measurement of a Circle, the area enclosed by a circle is equal to that of a triangle whose base has the length of the circle's circumference and whose height equals the circle's radius,[8] which comes to π multiplied by the radius squared:
+
+Equivalently, denoting diameter by d,
+
+that is, approximately 79% of the circumscribing square (whose side is of length d).
+
+The circle is the plane curve enclosing the maximum area for a given arc length. This relates the circle to a problem in the calculus of variations, namely the isoperimetric inequality.
+
+Equation of a circle
+In an x–y Cartesian coordinate system, the circle with centre coordinates (a, b) and radius r is the set of all points (x, y) such that
+
+This equation, known as the Equation of the Circle, follows from the Pythagorean theorem applied to any point on the circle: as shown in the adjacent diagram, the radius is the hypotenuse of a right-angled triangle whose other sides are of length |x − a| and |y − b|. If the circle is centred at the origin (0, 0), then the equation simplifies to
+
+Parametric form 
+The equation can be written in parametric form using the trigonometric functions sine and cosine as
+
+where t is a parametric variable in the range 0 to 2π, interpreted geometrically as the angle that the ray from (a, b) to (x, y) makes with the positive x-axis.
+
+An alternative parametrisation of the circle is:
+
+In this parameterisation, the ratio of t to r can be interpreted geometrically as the stereographic projection of the line passing through the centre parallel to the x-axis (see Tangent half-angle substitution). However, this parameterisation works only if t is made to range not only through all reals but also to a point at infinity; otherwise, the leftmost point of the circle would be omitted.
+
+3-point-form 
+The equation of the circle determined by three points 
+
+
+
+(
+
+x
+
+1
+
+
+,
+
+y
+
+1
+
+
+)
+,
+(
+
+x
+
+2
+
+
+,
+
+y
+
+2
+
+
+)
+,
+(
+
+x
+
+3
+
+
+,
+
+y
+
+3
+
+
+)
+
+
+{\displaystyle (x_{1},y_{1}),(x_{2},y_{2}),(x_{3},y_{3})}
+
+ not on a line is obtained by a conversion of the 3-point-form of a circle's equation
+
+Homogeneous form
+In homogeneous coordinates, each conic section with the equation of a circle has the form
+
+It can be proven that a conic section is a circle exactly when it contains (when extended to the complex projective plane) the points I(1: i: 0) and J(1: −i: 0). These points are called the circular points at infinity.
+
+In polar coordinates, the equation of a circle is:
+
+where a is the radius of the circle, 
+
+
+
+(
+r
+,
+θ
+)
+
+
+{\displaystyle (r,\theta )}
+
+ is the polar coordinate of a generic point on the circle, and 
+
+
+
+(
+
+r
+
+0
+
+
+,
+ϕ
+)
+
+
+{\displaystyle (r_{0},\phi )}
+
+ is the polar coordinate of the centre of the circle (i.e., r0 is the distance from the origin to the centre of the circle, and φ is the anticlockwise angle from the positive x-axis to the line connecting the origin to the centre of the circle). For a circle centred on the origin, i.e. r0 = 0, this reduces to simply r = a. When r0 = a, or when the origin lies on the circle, the equation becomes
+
+In the general case, the equation can be solved for r, giving
+
+Note that without the ± sign, the equation would in some cases describe only half a circle.
+
+In the complex plane, a circle with a centre at c and radius r has the equation:
+
+In parametric form, this can be written:
+
+The slightly generalised equation
+
+for real p, q and complex g is sometimes called a generalised circle. This becomes the above equation for a circle with 
+
+
+
+p
+=
+1
+,
+ 
+g
+=
+−
+
+
+c
+¯
+
+
+,
+ 
+q
+=
+
+r
+
+2
+
+
+−
+
+|
+
+c
+
+
+|
+
+
+2
+
+
+
+
+{\displaystyle p=1,\ g=-{\overline {c}},\ q=r^{2}-|c|^{2}}
+
+, since 
+
+
+
+
+|
+
+z
+−
+c
+
+
+|
+
+
+2
+
+
+=
+z
+
+
+z
+¯
+
+
+−
+
+
+c
+¯
+
+
+z
+−
+c
+
+
+z
+¯
+
+
++
+c
+
+
+c
+¯
+
+
+
+
+{\displaystyle |z-c|^{2}=z{\overline {z}}-{\overline {c}}z-c{\overline {z}}+c{\overline {c}}}
+
+. Not all generalised circles are actually circles: a generalised circle is either a (true) circle or a line.
+
+The tangent line through a point P on the circle is perpendicular to the diameter passing through P. If P = (x1, y1) and the circle has centre (a, b) and radius r, then the tangent line is perpendicular to the line from (a, b) to (x1, y1), so it has the form (x1 − a)x + (y1 – b)y = c. Evaluating at (x1, y1) determines the value of c and the result is that the equation of the tangent is
+
+or
+
+If y1 ≠ b then the slope of this line is
+
+This can also be found using implicit differentiation.
+
+When the centre of the circle is at the origin then the equation of the tangent line becomes
+
+and its slope is
+
+An inscribed angle (examples are the blue and green angles in the figure) is exactly half the corresponding central angle (red). Hence, all inscribed angles that subtend the same arc (pink) are equal. Angles inscribed on the arc (brown) are supplementary. In particular, every inscribed angle that subtends a diameter is a right angle (since the central angle is 180 degrees).
+
+Another proof of this result, which relies only on two chord properties given above, is as follows. Given a chord of length y and with sagitta of length x, since the sagitta intersects the midpoint of the chord, we know it is part of a diameter of the circle. Since the diameter is twice the radius, the "missing" part of the diameter is (2r − x) in length. Using the fact that one part of one chord times the other part is equal to the same product taken along a chord intersecting the first chord, we find that (2r − x)x = (y / 2)2. Solving for r, we find the required result.
+
+There are many compass-and-straightedge constructions resulting in circles.
+
+The simplest and most basic is the construction given the centre of the circle and a point on the circle. Place the fixed leg of the compass on the centre point, the movable leg on the point on the circle and rotate the compass.
+
+Apollonius of Perga showed that a circle may also be defined as the set of points in a plane having a constant ratio (other than 1) of distances to two fixed foci, A and B.[12][13] (The set of points where the distances are equal is the perpendicular bisector of segment AB, a line.) That circle is sometimes said to be drawn about two points.
+
+The proof is in two parts. First, one must prove that, given two foci A and B and a ratio of distances, any point P satisfying the ratio of distances must fall on a particular circle. Let C be another point, also satisfying the ratio and lying on segment AB. By the angle bisector theorem the line segment PC will bisect the interior angle APB, since the segments are similar:
+
+Analogously, a line segment PD through some point D on AB extended bisects the corresponding exterior angle BPQ where Q is on AP extended. Since the interior and exterior angles sum to 180 degrees, the angle CPD is exactly 90 degrees, i.e., a right angle. The set of points P such that angle CPD is a right angle forms a circle, of which CD is a diameter.
+
+Second, see[14]:p.15 for a proof that every point on the indicated circle satisfies the given ratio.
+
+A closely related property of circles involves the geometry of the cross-ratio of points in the complex plane. If A, B, and C are as above, then the circle of Apollonius for these three points is the collection of points P for which the absolute value of the cross-ratio is equal to one:
+
+Stated another way, P is a point on the circle of Apollonius if and only if the cross-ratio [A,B;C,P] is on the unit circle in the complex plane.
+
+If C is the midpoint of the segment AB, then the collection of points P satisfying the Apollonius condition
+
+is not a circle, but rather a line.
+
+Thus, if A, B, and C are given distinct points in the plane, then the locus of points P satisfying the above equation is called a "generalised circle." It may either be a true circle or a line. In this sense a line is a generalised circle of infinite radius.
+
+In every triangle a unique circle, called the incircle, can be inscribed such that it is tangent to each of the three sides of the triangle.[15]
+
+About every triangle a unique circle, called the circumcircle, can be circumscribed such that it goes through each of the triangle's three vertices.[16]
+
+A tangential polygon, such as a tangential quadrilateral, is any convex polygon within which a circle can be inscribed that is tangent to each side of the polygon.[17] Every regular polygon and every triangle is a tangential polygon.
+
+A cyclic polygon is any convex polygon about which a circle can be circumscribed, passing through each vertex. A well-studied example is the cyclic quadrilateral. Every regular polygon and every triangle is a cyclic polygon. A polygon that is both cyclic and tangential is called a bicentric polygon.
+
+A hypocycloid is a curve that is inscribed in a given circle by tracing a fixed point on a smaller circle that rolls within and tangent to the given circle.
+
+The circle can be viewed as a limiting case of each of various other figures:
+
+Defining a circle as the set of points with a fixed distance from a point, different shapes can be considered circles under different definitions of distance. In p-norm, distance is determined by
+
+In Euclidean geometry, p = 2, giving the familiar
+
+In taxicab geometry, p = 1. Taxicab circles are squares with sides oriented at a 45° angle to the coordinate axes. While each side would have length 
+
+
+
+
+
+2
+
+
+r
+
+
+{\displaystyle {\sqrt {2}}r}
+
+ using a Euclidean metric, where r is the circle's radius, its length in taxicab geometry is 2r. Thus, a circle's circumference is 8r. Thus, the value of a geometric analog to 
+
+
+
+π
+
+
+{\displaystyle \pi }
+
+ is 4 in this geometry. The formula for the unit circle in taxicab geometry is 
+
+
+
+
+|
+
+x
+
+|
+
++
+
+|
+
+y
+
+|
+
+=
+1
+
+
+{\displaystyle |x|+|y|=1}
+
+ in Cartesian coordinates and
+
+in polar coordinates.
+
+A circle of radius 1 (using this distance) is the von Neumann neighborhood of its center.
+
+A circle of radius r for the Chebyshev distance (L∞ metric) on a plane is also a square with side length 2r parallel to the coordinate axes, so planar Chebyshev distance can be viewed as equivalent by rotation and scaling to planar taxicab distance. However, this equivalence between L1 and L∞ metrics does not generalize to higher dimensions.
+
+Squaring the circle is the problem, proposed by ancient geometers, of constructing a square with the same area as a given circle by using only a finite number of steps with compass and straightedge.
+
+In 1882, the task was proven to be impossible, as a consequence of the Lindemann–Weierstrass theorem, which proves that pi (π) is a transcendental number, rather than an algebraic irrational number; that is, it is not the root of any polynomial with rational coefficients.
+
+From the time of the earliest known civilisations – such as the Assyrians and ancient Egyptians, those in the Indus Valley and along the Yellow River in China, and the Western civilisations of ancient Greece and Rome during classical Antiquity – the circle has been used directly or indirectly in visual art to convey the artist’s message and to express certain ideas.
+However, differences in worldview (beliefs and culture) had a great impact on artists’ perceptions. While some emphasised the circle’s perimeter to demonstrate their democratic manifestation, others focused on its centre to symbolise the concept of cosmic unity. In mystical doctrines, the circle mainly symbolises the infinite and cyclical nature of existence, but in religious traditions it represents heavenly bodies and divine spirits.
+The circle signifies many sacred and spiritual concepts, including unity, infinity, wholeness, the universe, divinity, balance, stability and perfection, among others. Such concepts have been conveyed in cultures worldwide through the use of symbols, for example, a compass, a halo, the vesica piscis and its derivatives (fish, eye, aureole, mandorla, etc.), the ouroboros, the Dharma wheel, a rainbow, mandalas, rose windows and so forth. [18]
+
+
+
+
+

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+
+
+The skeleton  is the body part that provides support, shape and protection to the soft tissues and delicate organs of animals. There are several different skeletal types: the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside the body, the hydroskeleton, a flexible skeleton supported by fluid pressure, and the cytoskeleton present in the cytoplasm of all cells, including bacteria, and archaea. The term comes from Greek  σκελετός (skeletós), meaning 'dried up'.[1]
+
+There are two major types of skeletons: solid and fluid. Solid skeletons can be internal, called an endoskeleton, or external, called an exoskeleton, and may be further classified as pliant (elastic/movable) or rigid (hard/non-movable).[2] Fluid skeletons are always internal.
+
+Exoskeletons are external, and are found in many invertebrates; they enclose and protect the soft tissues and organs of the body. Some kinds of exoskeletons undergo periodic moulting or ecdysis as the animal grows, as is the case in many arthropods including insects and crustaceans.
+
+The exoskeleton of insects is not only a form of protection, but also serves as a surface for muscle attachment, as a watertight protection against drying, and as a sense organ to interact with the environment. The shell of mollusks also performs all of the same functions, except that in most cases it does not contain sense organs.
+
+An external skeleton can be quite heavy in relation to the overall mass of an animal, so on land, organisms that have an exoskeleton are mostly relatively small. Somewhat larger aquatic animals can support an exoskeleton because weight is less of a consideration underwater. The southern giant clam, a species of extremely large saltwater clam in the Pacific Ocean, has a shell that is massive in both size and weight. Syrinx aruanus is a species of sea snail with a very large shell.
+
+The endoskeleton is the internal support structure of an animal, composed of mineralized tissue and is typical of vertebrates. Endoskeletons vary in complexity from functioning purely for support (as in the case of sponges), to serving as an attachment site for muscles and a mechanism for transmitting muscular forces. A true endoskeleton is derived from mesodermal tissue. Such a skeleton is present in echinoderms and chordates.
+
+Pliant skeletons are capable of movement; thus, when stress is applied to the skeletal structure, it deforms and then reverts to its original shape. This skeletal structure is used in some invertebrates, for instance in the hinge of bivalve shells or the mesoglea of cnidarians such as jellyfish. Pliant skeletons are beneficial because only muscle contractions are needed to bend the skeleton; upon muscle relaxation, the skeleton will return to its original shape. Cartilage is one material that a pliant skeleton may be composed of, but most pliant skeletons are formed from a mixture of proteins, polysaccharides, and water.[2] For additional structure or protection, pliant skeletons may be supported by rigid skeletons. Organisms that have pliant skeletons typically live in water, which supports body structure in the absence of a rigid skeleton.[3]
+
+Rigid skeletons are not capable of movement when stressed, creating a strong support system most common in terrestrial animals. Such a skeleton type used by animals that live in water are more for protection (such as barnacle and snail shells) or for fast-moving animals that require additional support of musculature needed for swimming through water. Rigid skeletons are formed from materials including chitin (in arthropods), calcium compounds such as calcium carbonate (in stony corals and mollusks) and silicate (for diatoms and radiolarians).
+
+The cytoskeleton (gr. kytos = cell) is used to stabilize and preserve the form of the cells. It is a dynamic structure that maintains cell shape, protects the cell, enables cellular motion (using structures such as flagella, cilia and lamellipodia), and plays important roles in both intracellular transport (the movement of vesicles and organelles, for example) and cellular division.
+
+A hydrostatic skeleton is a semi-rigid, soft tissue structure filled with liquid under pressure, surrounded by muscles. Longitudinal and circular muscles around their body sectors allow movement by alternate lengthening and contractions along their lengths. A common example of this is the earthworm.
+
+The endoskeletons of echinoderms and some other soft-bodied invertebrates such as jellyfish and earthworms are also termed hydrostatic; a body cavity the coelom is filled with coelomic fluid and the pressure from this fluid acts together with the surrounding muscles to change the organism's shape and produce movement.
+
+The skeleton of sponges consists of microscopic calcareous or silicious spicules. The demosponges include 90% of all species of sponges. Their "skeletons" are made of spicules consisting of fibers of the protein spongin, the mineral silica, or both. Where spicules of silica are present, they have a different shape from those in the otherwise similar glass sponges.[4]
+
+The skeleton of the echinoderms, which include, among other things, the starfish, is composed of calcite and a small amount of magnesium oxide. It lies below the epidermis in the mesoderm and is within cell clusters of frame-forming cells. This structure formed is porous and therefore firm and at the same time light. It coalesces into small calcareous ossicles (bony plates), which can grow in all directions and thus can replace the loss of a body part. Connected by joints, the individual skeletal parts can be moved by the muscles.
+
+In most vertebrates, the main skeletal component is referred to as bone. These bones compose a unique skeletal system for each type of animal. Another important component is cartilage which in mammals is found mainly in the joint areas. In other animals, such as the cartilaginous fishes, which include the sharks, the skeleton is composed entirely of cartilage. The segmental pattern of the skeleton is present in all vertebrates (mammals, birds, fish, reptiles and amphibians) with basic units being repeated. This segmental pattern is particularly evident in the vertebral column and the ribcage.
+
+Bones in addition to supporting the body also serve, at the cellular level, as calcium and phosphate storage.
+
+The skeleton, which forms the support structure inside the fish is either made of cartilage as in the (Chondrichthyes), or bones as in the (Osteichthyes). The main skeletal element is the vertebral column, composed of articulating vertebrae which are lightweight yet strong. The ribs attach to the spine and there are no limbs or limb girdles. They are supported only by the muscles. The main external features of the fish, the fins, are composed of either bony or soft spines called rays, which with the exception of the caudal fin (tail fin), have no direct connection with the spine. They are supported by the muscles which compose the main part of the trunk.
+
+The bird skeleton is highly adapted for flight. It is extremely lightweight, yet still strong enough to withstand the stresses of taking off, flying, and landing. One key adaptation is the fusing of bones into single ossifications, such as the pygostyle. Because of this, birds usually have a smaller number of bones than other terrestrial vertebrates. Birds also lack teeth or even a true jaw, instead having evolved a beak, which is far more lightweight. The beaks of many baby birds have a projection called an egg tooth, which facilitates their exit from the amniotic egg.
+
+To facilitate the movement of marine mammals in water, the hind legs were either lost altogether, as in the whales and manatees, or united in a single tail fin as in the pinnipeds (seals). In the whale, the cervical vertebrae are typically fused, an adaptation trading flexibility for stability during swimming.[5][6]
+
+The skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs, heart and spinal cord. Although the teeth do not consist of tissue commonly found in bones, the teeth are usually considered as members of the skeletal system.[7]
+The biggest bone in the body is the femur in the upper leg, and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises around 14% of the total body weight,[8] and half of this weight is water.
+
+Fused bones include those of the pelvis and the cranium. Not all bones are interconnected directly: There are three bones in each middle ear called the ossicles that articulate only with each other. The hyoid bone, which is located in the neck and serves as the point of attachment for the tongue, does not articulate with any other bones in the body, being supported by muscles and ligaments.
+
+There are 206 bones in the adult human skeleton, although this number depends on whether the pelvic bones (the hip bones on each side) are counted as one or three bones on each side (ilium, ischium, and pubis), whether the coccyx or tail bone is counted as one or four separate bones, and does not count the variable wormian bones between skull sutures. Similarly, the sacrum is usually counted as a single bone, rather than five fused vertebrae. There is also a variable number of small sesamoid bones, commonly found in tendons. The patella or kneecap on each side is an example of a larger sesamoid bone. The patellae are counted in the total, as they are constant. The number of bones varies between individuals and with age – newborn babies have over 270 bones[9][10][11] some of which fuse together. These bones are organized into a longitudinal axis, the axial skeleton, to which the appendicular skeleton is attached.[12]
+
+The human skeleton takes 20 years before it is fully developed, and the bones contain marrow, which produces blood cells.
+
+There exist several general differences between the male and female skeletons. The male skeleton, for example, is generally larger and heavier than the female skeleton. In the female skeleton, the bones of the skull are generally less angular. The female skeleton also has wider and shorter breastbone and slimmer wrists. There exist significant differences between the male and female pelvis which are related to the female's pregnancy and childbirth capabilities. The female pelvis is wider and shallower than the male pelvis. Female pelvises also have an enlarged pelvic outlet and a wider and more circular pelvic inlet. The angle between the pubic bones is known to be sharper in males, which results in a more circular, narrower, and near heart-shaped pelvis.[13][14]
+
+Bones are rigid organs that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue. Bones have a variety of shapes with a complex internal and external structure they are also lightweight, yet strong and hard. One of the types of tissue that makes up bone tissue is mineralized tissue and this
+gives it rigidity and a honeycomb-like three-dimensional internal structure. Other types of tissue found in bones include marrow, endosteum and periosteum, nerves, blood vessels and cartilage.
+
+During embryonic development the precursor to bone development is cartilage that mostly becomes replaced by bone, after flesh such as muscle has formed around it. Cartilage is a stiff and inflexible connective tissue found in many areas including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs. It is not as hard and rigid as bone but is stiffer and less flexible than muscle.
+
+Cartilage is composed of specialized cells called chondrocytes that produce a large amount of extracellular matrix composed of Type II collagen (except fibrocartilage which also contains type I collagen) fibers, abundant ground substance rich in proteoglycans, and elastin fibers. Cartilage is classified in three types, elastic cartilage, hyaline cartilage and fibrocartilage, which differ in the relative amounts of these three main components.
+
+Unlike other connective tissues, cartilage does not contain blood vessels. The chondrocytes are supplied by diffusion, helped by the pumping action generated by compression of the articular cartilage or flexion of the elastic cartilage. Thus, compared to other connective tissues, cartilage grows and repairs more slowly.
+
+In Western culture, the human skeleton is oftentimes seen as a fearful symbol of death and the paranormal.  It is a popular motif in the holiday Halloween, as well as Day of the Dead.
+
+Skeletons can also be found in movies. Skeletons in movies can be often depicted coming to life, commonly in horror movies. Skeletons can also be depicted in movies wearing chainmail, helmets, and shields. Commonly holding an axe or sword. In these types of movies they are commonly getting attacked, "killed", or fighting with character(s). Skeletons can also be found in a more "welcoming" and "friendly" way in movies. Such as, playing as a decoration, a Halloween costume/face paint, ETC. Another way skeletons can be shown in movies is debatably more common than the other depictions is a sign of severe burning from things such as chemicals, fire, and acid. This can also be a case of deterioration over time.[15]
+
+Media related to Skeletons at Wikimedia Commons

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+
+
+The kidneys are two bean-shaped organs found in vertebrates.[1] They are located on the left and right in the retroperitoneal space, and in adult humans are about 12 centimetres (4 1⁄2 inches) in length.[2][3][1] They receive blood from the paired renal arteries; blood exits into the paired renal veins. Each kidney is attached to a ureter, a tube that carries excreted urine to the bladder.
+
+The nephron is the structural and functional unit of the kidney. Each human adult kidney contains around 1 million nephrons, while a mouse kidney contains only about 12,500 nephrons. The kidney participates in the control of the volume of various body fluids, fluid osmolality, acid-base balance, various electrolyte concentrations, and removal of toxins. Filtration occurs in the glomerulus: one-fifth of the blood volume that enters the kidneys is filtered. Examples of substances reabsorbed are solute-free water, sodium, bicarbonate, glucose, and amino acids.  Examples of substances secreted are hydrogen, ammonium, potassium and uric acid. The kidneys also carry out functions independent of the nephron. For example, they convert a precursor of vitamin D to its active form, calcitriol; and synthesize the hormones erythropoietin and renin.
+
+Renal physiology is the study of kidney function. Nephrology is the medical specialty which addresses diseases of kidney function:  these include chronic kidney disease, nephritic and nephrotic syndromes, acute kidney injury, and pyelonephritis. Urology addresses diseases of kidney (and urinary tract) anatomy: these include cancer, renal cysts, kidney stones and ureteral stones, and urinary tract obstruction.[4]
+
+Procedures used in the management of kidney disease include chemical and microscopic examination of the urine (urinalysis), measurement of kidney function by calculating the estimated glomerular filtration rate (eGFR) using the serum creatinine; and kidney biopsy and CT scan to evaluate for abnormal anatomy. Dialysis and kidney transplantation are used to treat kidney failure; one (or both sequentially) of these are almost always used when renal function drops below 15%. Nephrectomy is frequently used to cure renal cell carcinoma.
+
+In humans, the kidneys are located high in the abdominal cavity, one on each side of the spine, and lie in a retroperitoneal position at a slightly oblique angle.[5] The asymmetry within the abdominal cavity, caused by the position of the liver, typically results in the right kidney being slightly lower and smaller than the left, and being placed slightly more to the middle than the left kidney.[6][7][8] The left kidney is approximately at the vertebral level T12 to L3,[9] and the right is slightly lower. The right kidney sits just below the diaphragm and posterior to the liver. The left kidney sits below the diaphragm and posterior to the spleen. On top of each kidney is an adrenal gland. The upper parts of the kidneys are partially protected by the 11th and 12th ribs. Each kidney, with its adrenal gland is surrounded by two layers of fat: the perirenal fat present between renal fascia and renal capsule and pararenal fat superior to the renal fascia.
+
+The kidney is a bean-shaped structure with a convex and a concave border. A recessed area on the concave border is the renal hilum, where the renal artery enters the kidney and the renal vein and ureter leave. The kidney is surrounded by tough fibrous tissue, the renal capsule, which is itself surrounded by perirenal fat, renal fascia, and pararenal fat. The anterior (front) surface of these tissues is the peritoneum, while the posterior (rear) surface is the transversalis fascia.
+
+The superior pole of the right kidney is adjacent to the liver. For the left kidney, it is next to the spleen. Both, therefore, move down upon inhalation.
+
+A Danish study measured the median renal length to be 11.2 cm (4 7⁄16 in) on the left side and 10.9 cm (4 5⁄16 in) on the right side in adults. Median renal volumes were 146 cm3 (8 15⁄16 cu in) on the left and 134 cm3 (8 3⁄16 cu in) on the right.[12]
+
+The functional substance, or parenchyma, of the kidney is divided into two major structures: the outer renal cortex and the inner renal medulla. Grossly, these structures take the shape of eight to 18 cone-shaped renal lobes, each containing renal cortex surrounding a portion of medulla called a renal pyramid.[13] Between the renal pyramids are projections of cortex called renal columns. Nephrons, the urine-producing functional structures of the kidney, span the cortex and medulla. The initial filtering portion of a nephron is the renal corpuscle, which is located in the cortex. This is followed by a renal tubule that passes from the cortex deep into the medullary pyramids. Part of the renal cortex, a medullary ray is a collection of renal tubules that drain into a single collecting duct.
+
+The tip, or papilla, of each pyramid empties urine into a minor calyx; minor calyces empty into major calyces, and major calyces empty into the renal pelvis. This becomes the ureter. At the hilum, the ureter and renal vein exit the kidney and the renal artery enters. Hilar fat and lymphatic tissue with lymph nodes surround these structures. The hilar fat is contiguous with a fat-filled cavity called the renal sinus. The renal sinus collectively contains the renal pelvis and calyces and separates these structures from the renal medullary tissue.[14]
+
+The kidneys possess no overtly moving structures.
+
+A CT scan of the abdomen showing the position of the kidneys. The left cross-section in the upper abdomen shows the liver on the left side of scan (right side of body). Center: cross-section showing the kidneys below the liver and spleen. Right: further cross-section through the left kidney.
+
+Image showing the structures that the kidney lies near.
+
+Cross-section through a cadaveric specimen showing the position of the kidneys.
+
+The kidneys receive blood from the renal arteries, left and right, which branch directly from the abdominal aorta. Despite their relatively small size, the kidneys receive approximately 20% of the cardiac output.[13] Each renal artery branches into segmental arteries, dividing further into interlobar arteries, which penetrate the renal capsule and extend through the renal columns between the renal pyramids. The interlobar arteries then supply blood to the arcuate arteries that run through the boundary of the cortex and the medulla. Each arcuate artery supplies several interlobular arteries that feed into the afferent arterioles that supply the glomeruli.
+
+Blood drains from the kidneys, ultimately into the inferior vena cava. After filtration occurs, the blood moves through a small network of small veins (venules) that converge into interlobular veins. As with the arteriole distribution, the veins follow the same pattern: the interlobular provide blood to the arcuate veins then back to the interlobar veins, which come to form the renal veins which exiting the kidney .
+
+The kidney and nervous system communicate via the renal plexus, whose fibers course along the renal arteries to reach each kidney.[15] Input from the sympathetic nervous system triggers vasoconstriction in the kidney, thereby reducing renal blood flow.[15] The kidney also receives input from the parasympathetic nervous system, by way of the renal branches of the vagus nerve; the function of this is yet unclear.[15][16] Sensory input from the kidney travels to the T10-11 levels of the spinal cord and is sensed in the corresponding dermatome.[15] Thus, pain in the flank region may be referred from corresponding kidney.[15]
+
+Renal histology is the study of the microscopic structure of the kidney. Distinct cell types include:
+
+About 20,000 protein coding genes are expressed in human cells and almost 70% of these genes are expressed in normal, adult kidneys.[17][18] Just over 300 genes are more specifically expressed in the kidney, with only some 50 genes being highly specific for the kidney. Many of the corresponding kidney specific proteins are expressed in the cell membrane and function as transporter proteins. The highest expressed kidney specific protein is uromodulin, the most abundant protein in urine with functions that prevent calcification and growth of bacteria. Specific proteins are expressed in the different compartments of the kidney with podocin and nephrin expressed in glomeruli,  Solute carrier family protein SLC22A8 expressed in proximal tubules, calbindin expressed in distal tubules and aquaporin 2 expressed in the collecting duct cells.[19]
+
+The mammalian kidney develops from intermediate mesoderm. Kidney development, also called nephrogenesis, proceeds through a series of three successive developmental phases: the pronephros, mesonephros, and metanephros. The metanephros are primordia of the permanent kidney.[20]
+
+The kidneys excrete a variety of waste products produced by metabolism into the urine. The microscopic structural and functional unit of the kidney is the nephron. It processes the blood supplied to it via filtration, reabsorption, secretion and excretion; the consequence of those processes is the production of urine. These include the nitrogenous wastes urea, from protein catabolism, and uric acid, from nucleic acid metabolism.  The ability of mammals and some birds to concentrate wastes into a volume of urine much smaller than the volume of blood from which the wastes were extracted is dependent on an elaborate countercurrent multiplication mechanism. This requires several independent nephron characteristics to operate: a tight hairpin configuration of the tubules, water and ion permeability in the descending limb of the loop, water impermeability in the ascending loop, and active ion transport out of most of the ascending limb. In addition, passive countercurrent exchange by the vessels carrying the blood supply to the nephron is essential for enabling this function.
+
+The kidney participates in whole-body homeostasis, regulating acid-base balance, electrolyte concentrations, extracellular fluid volume, and blood pressure. The kidney accomplishes these homeostatic functions both independently and in concert with other organs, particularly those of the endocrine system. Various endocrine hormones coordinate these endocrine functions; these include renin, angiotensin II, aldosterone, antidiuretic hormone, and atrial natriuretic peptide, among others.
+
+Filtration, which takes place at the renal corpuscle, is the process by which cells and large proteins are retained while materials of smaller molecular weights are[21] filtered from the blood to make an ultrafiltrate that eventually becomes urine. The kidney generates 180 liters of filtrate a day. The process is also known as hydrostatic filtration due to the hydrostatic pressure exerted on the capillary walls.
+
+Reabsorption is the transport of molecules from this ultrafiltrate and into the peritubular capillary. It is accomplished via selective receptors on the luminal cell membrane. Water is 55% reabsorbed in the proximal tubule. Glucose at normal plasma levels is completely reabsorbed in the proximal tubule. The mechanism for this is the Na+/glucose cotransporter. A plasma level of 350 mg/dL will fully saturate the transporters and glucose will be lost in the urine. A plasma glucose level of approximately 160 is sufficient to allow glucosuria, which is an important clinical clue to diabetes mellitus.
+
+Amino acids are reabsorbed by sodium dependent transporters in the proximal tubule. Hartnup disease is a deficiency of the tryptophan amino acid transporter, which results in pellagra.[22]
+
+Secretion is the reverse of reabsorption: molecules are transported from the peritubular capillary through the interstitial fluid, then through the renal tubular cell and into the ultrafiltrate.
+
+The last step in the processing of the ultrafiltrate is excretion: the ultrafiltrate passes out of the nephron and travels through a tube called the collecting duct, which is part of the collecting duct system, and then to the ureters where it is renamed  urine. In addition to transporting the ultrafiltrate, the collecting duct also takes part in reabsorption.
+
+The kidneys secrete a variety of hormones, including erythropoietin, calcitriol, and renin. Erythropoietin is released in response to hypoxia (low levels of oxygen at tissue level) in the renal circulation. It stimulates erythropoiesis (production of red blood cells) in the bone marrow. Calcitriol, the activated form of vitamin D, promotes intestinal absorption of calcium and the renal reabsorption of phosphate.  Renin is an enzyme which regulates angiotensin and aldosterone levels.
+
+Although the kidney cannot directly sense blood, long-term regulation of blood pressure predominantly depends upon the kidney. This primarily occurs through maintenance of the extracellular fluid compartment, the size of which depends on the plasma sodium concentration. Renin is the first in a series of important chemical messengers that make up the renin–angiotensin system. Changes in renin ultimately alter the output of this system, principally the hormones angiotensin II and aldosterone. Each hormone acts via multiple mechanisms, but both increase the kidney's absorption of sodium chloride, thereby expanding the extracellular fluid compartment and raising blood pressure. When renin levels are elevated, the concentrations of angiotensin II and aldosterone increase, leading to increased sodium chloride reabsorption, expansion of the extracellular fluid compartment, and an increase in blood pressure. Conversely, when renin levels are low, angiotensin II and aldosterone levels decrease, contracting the extracellular fluid compartment, and decreasing blood pressure.
+
+Two organ systems, the kidneys and lungs, maintain acid-base homeostasis, which is the maintenance of pH around a relatively stable value. The lungs contribute to acid-base homeostasis by regulating carbon dioxide (CO2) concentration.  The kidneys have two very important roles in maintaining the acid-base balance: to reabsorb and regenerate bicarbonate from urine, and to excrete hydrogen ions and fixed acids (anions of acids) into urine.
+
+The kidneys help maintain the water and salt level of the body. Any significant rise in plasma osmolality is detected by the hypothalamus, which communicates directly with the posterior pituitary gland. An increase in osmolality causes the gland to secrete antidiuretic hormone (ADH), resulting in water reabsorption by the kidney and an increase in urine concentration. The two factors work together to return the plasma osmolality to its normal levels.
+
+Various calculations and methods are used to try to measure kidney function. Renal clearance is the volume of plasma from which the substance is completely cleared from the blood per unit time. The filtration fraction is the amount of plasma that is actually filtered through the kidney. This can be defined using the equation. The kidney is a very complex organ and mathematical modelling has been used to better understand kidney function at several scales, including fluid uptake and secretion.[23][24]
+
+Nephrology is the subspeciality under Internal Medicine that deals with kidney function and disease states related to renal malfunction and their management including dialysis and kidney transplantation. Urology is the specialty under Surgery that deals with kidney structure abnormalities such as kidney cancer and cysts and problems with urinary tract. Nephrologists are internists, and urologists are surgeons, whereas both are often called "kidney doctors". There are overlapping areas that both nephrologists and urologists can provide care such as kidney stones and kidney related infections.
+
+There are many causes of kidney disease. Some causes are acquired over the course of life, such as diabetic nephropathy whereas others are congenital, such as polycystic kidney disease.
+
+Medical terms related to the kidneys commonly use terms such as renal and the prefix nephro-. The adjective renal, meaning related to the kidney, is from the Latin rēnēs, meaning kidneys; the prefix nephro- is from the Ancient Greek word for kidney, nephros (νεφρός).[25] For example, surgical removal of the kidney is a nephrectomy, while a reduction in kidney function is called renal dysfunction.
+
+Generally, humans can live normally with just one kidney, as one has more functioning renal tissue than is needed to survive. Only when the amount of functioning kidney tissue is greatly diminished does one develop chronic kidney disease. Renal replacement therapy, in the form of dialysis or kidney transplantation, is indicated when the glomerular filtration rate has fallen very low or if the renal dysfunction leads to severe symptoms.
+
+Dialysis is a treatment that substitutes for the function of normal kidneys. Dialysis may be instituted when approximately 85%-90% of kidney function is lost, as indicated by a glomerular filtration rate (GFR) of less than 15. Dialysis removes metabolic waste products as well as excess water and sodium (thereby contributing to regulating blood pressure); and maintains many chemical levels within the body. Life expectancy is 5–10 years for those on dialysis; some live up to 30 years. Dialysis can occur via the blood (through a catheter or arteriovenous fistula), or through the peritoneum (peritoneal dialysis) Dialysis is typically administered three times a week for several hours at free-standing dialysis centers, allowing recipients to lead an otherwise essentially normal life.[26]
+
+Many renal diseases are diagnosed on the basis of a detailed medical history, and physical examination.[citation needed] The medical history takes into account present and past symptoms, especially those of kidney disease; recent infections; exposure to substances toxic to the kidney; and family history of kidney disease.
+
+Kidney function is tested for using blood tests and urine tests. A usual blood test is for urea and electrolytes, known as a U and E. Creatinine is also tested for. Urine tests such as urinalysis can evaluate for pH, protein, glucose, and the presence of blood. Microscopic analysis can also identify the presence of urinary casts and crystals.[30] The glomerular filtration rate (GFR) can be calculated.[30]
+
+Renal ultrasonography is essential in the diagnosis and management of kidney-related diseases.[31] Other modalities, such as CT and MRI, should always be considered as supplementary imaging modalities in the assessment of renal disease.[31]
+
+The role of the renal biopsy is to diagnose renal disease in which the etiology is not clear based upon noninvasive means (clinical history, past medical history, medication history, physical exam, laboratory studies, imaging studies). In general, a renal pathologist will perform a detailed morphological evaluation and integrate the morphologic findings with the clinical history and laboratory data, ultimately arriving at a pathological diagnosis. A renal pathologist is a physician who has undergone general training in anatomic pathology and additional specially training in the interpretation of renal biopsy specimens.
+
+Ideally, multiple core sections are obtained and evaluated for adequacy (presence of glomeruli) intraoperatively. A pathologist/pathology assistant divides the specimen(s) for submission for light microscopy, immunofluorescence microscopy and electron microscopy.
+
+The pathologist will examine the specimen using light microscopy with multiple staining techniques (hematoxylin and eosin/H&E, PAS, trichrome, silver stain) on multiple level sections. Multiple immunofluorescence stains are performed to evaluate for antibody, protein and complement deposition. Finally, ultra-structural examination is performed with electron microscopy and may reveal the presence of electron-dense deposits or other characteristic abnormalities that may suggest an etiology for the patient's renal disease.
+
+In the majority of vertebrates, the mesonephros persists into the adult, albeit usually fused with the more advanced metanephros; only in amniotes is the mesonephros restricted to the embryo. The kidneys of fish and amphibians are typically narrow, elongated organs, occupying a significant portion of the trunk. The collecting ducts from each cluster of nephrons usually drain into an archinephric duct, which is homologous with the vas deferens of amniotes. However, the situation is not always so simple; in cartilaginous fish and some amphibians, there is also a shorter duct, similar to the amniote ureter, which drains the posterior (metanephric) parts of the kidney, and joins with the archinephric duct at the bladder or cloaca. Indeed, in many cartilaginous fish, the anterior portion of the kidney may degenerate or cease to function altogether in the adult.[32]
+
+In the most primitive vertebrates, the hagfish and lampreys, the kidney is unusually simple: it consists of a row of nephrons, each emptying directly into the archinephric duct. Invertebrates may possess excretory organs that are sometimes referred to as "kidneys", but, even in Amphioxus, these are never homologous with the kidneys of vertebrates, and are more accurately referred to by other names, such as nephridia.[32] In amphibians, kidneys and the urinary bladder harbour specialized parasites, monogeneans of the family Polystomatidae.[33]
+
+The kidneys of reptiles consist of a number of lobules arranged in a broadly linear pattern. Each lobule contains a single branch of the ureter in its centre, into which the collecting ducts empty. Reptiles have relatively few nephrons compared with other amniotes of a similar size, possibly because of their lower metabolic rate.[32]
+
+Birds have relatively large, elongated kidneys, each of which is divided into three or more distinct lobes. The lobes consists of several small, irregularly arranged, lobules, each centred on a branch of the ureter. Birds have small glomeruli, but about twice as many nephrons as similarly sized mammals.[32]
+
+The human kidney is fairly typical of that of mammals. Distinctive features of the mammalian kidney, in comparison with that of other vertebrates, include the presence of the renal pelvis and renal pyramids and a clearly distinguishable cortex and medulla. The latter feature is due to the presence of elongated loops of Henle; these are much shorter in birds, and not truly present in other vertebrates (although the nephron often has a short intermediate segment between the convoluted tubules). It is only in mammals that the kidney takes on its classical "kidney" shape, although there are some exceptions, such as the multilobed reniculate kidneys of pinnipeds and cetaceans.[32]
+
+Kidneys of various animals show evidence of evolutionary adaptation and have long been studied in ecophysiology and comparative physiology. Kidney morphology, often indexed as the relative medullary thickness, is associated with habitat aridity among species of mammals[34] and diet (e.g., carnivores have only long loops of Henle).[24]
+
+In ancient Egypt, the kidneys, like the heart, were left inside the mummified bodies, unlike other organs which were removed. Comparing this to the biblical statements, and to drawings of human body with the heart and two kidneys portraying a set of scales for weighing justice, it seems that the Egyptian beliefs had also connected the kidneys with judgement and perhaps with moral decisions.[35]
+
+According to studies in modern and ancient Hebrew, various body organs in humans and animals served also an emotional or logical role, today mostly attributed to the brain and the endocrine system. The kidney is mentioned in several biblical verses in conjunction with the heart, much as the bowels were understood to be the "seat" of emotion – grief, joy and pain.[36] Similarly, the Talmud (Berakhoth 61.a) states that one of the two kidneys counsels what is good, and the other evil.
+
+In the sacrifices offered at the biblical Tabernacle and later on at the temple in Jerusalem, the priests were instructed[37] to remove the kidneys and the adrenal gland covering the kidneys of the sheep, goat and cattle offerings, and to burn them on the altar, as the holy part of the "offering for God" never to be eaten.[38]
+
+In ancient India, according to the Ayurvedic medical systems, the kidneys were considered the beginning of the excursion channels system, the 'head' of the Mutra Srotas, receiving from all other systems, and therefore important in determining a person's health balance and temperament by the balance and mixture of the three 'Dosha's – the three health elements: Vatha (or Vata) – air, Pitta – bile, and Kapha – mucus. The temperament and health of a person can then be seen in the resulting color of the urine.[39]
+
+Modern Ayurveda practitioners, a practice which is characterized as pseudoscience,[40] have attempted to revive these methods in medical procedures as part of Ayurveda Urine therapy.[41] These procedures have been called "nonsensical" by skeptics.[42]
+
+The Latin term renes is related to the English word "reins", a synonym for the kidneys in Shakespearean English (e.g. Merry Wives of Windsor 3.5), which was also the time when the King James Version of the Bible was translated. Kidneys were once popularly regarded as the seat of the conscience and reflection,[43][44] and a number of verses in the Bible (e.g. Ps. 7:9, Rev. 2:23) state that God searches out and inspects the kidneys, or "reins", of humans, together with the heart.
+
+The kidneys, like other offal, can be cooked and eaten.
+
+Kidneys are usually grilled or sautéed, but in more complex dishes they are stewed with a sauce that will improve their flavor. In many preparations, kidneys are combined with pieces of meat or liver, as in mixed grill. Dishes include the British steak and kidney pie, the Swedish hökarpanna (pork and kidney stew), the French rognons de veau sauce moutarde (veal kidneys in mustard sauce) and the Spanish riñones al Jerez (kidneys stewed in sherry sauce) .[45]
+
+Kidney stones have been identified and recorded about as long as written historical records exist.[46] The urinary tract including the ureters, as well as their function to drain urine from the kidneys, has been described by Galen in the second century AD.[47]
+
+The first to examine the ureter through an internal approach, called ureteroscopy, rather than surgery was Hampton Young in 1929.[46] This was improved on by VF Marshall who is the first published use of a flexible endoscope based on fiber optics, which occurred in 1964.[46] The insertion of a drainage tube into the renal pelvis, bypassing the uterers and urinary tract, called nephrostomy], was first described in 1941. Such an approach differed greatly from the open surgical approaches within the urinary system employed during the preceeding two millenia.[46]
+
+Right Kidney
+
+Kidney
+
+Right Kidney
+
+Right kidney
+
+Left kidney
+
+Kidneys
+
+Left kidney

en/3382.html.txt

@@ -0,0 +1,233 @@
+
+
+See text for extinct groups.
+
+Reptiles are tetrapod animals in the class Reptilia, comprising today's turtles, crocodilians, snakes, amphisbaenians, lizards, tuatara, and their extinct relatives. The study of these traditional reptile orders, historically combined with that of modern amphibians, is called herpetology.
+
+Because some reptiles are more closely related to birds than they are to other reptiles (e.g., crocodiles are more closely related to birds than they are to lizards), the traditional groups of "reptiles" listed above do not together constitute a monophyletic grouping or clade (consisting of all descendants of a common ancestor). For this reason, many modern scientists prefer to consider the birds part of Reptilia as well, thereby making Reptilia a monophyletic class, including all living diapsids.[1][2][3][4] The term reptiles is sometimes used as shorthand for 'non-avian Reptilia'.[5][6]
+
+The earliest known proto-reptiles originated around 312 million years ago during the Carboniferous period, having evolved from advanced reptiliomorph tetrapods that became increasingly adapted to life on dry land. Some early examples include the lizard-like Hylonomus and Casineria. In addition to the living reptiles, there are many diverse groups that are now extinct, in some cases due to mass extinction events. In particular, the Cretaceous–Paleogene extinction event wiped out the pterosaurs, plesiosaurs, ornithischians, and sauropods, alongside many species of theropods, crocodyliforms, and squamates (e.g., mosasaurs).
+
+Modern non-avian reptiles inhabit all the continents except Antarctica, although some birds are found on the periphery of Antarctica. Several living subgroups are recognized: Testudines (turtles and tortoises), 350 species;[7] Rhynchocephalia (tuatara from New Zealand), 1 species;[7][8] Squamata (lizards, snakes, and worm lizards), over 10,200 species;[7] and Crocodilia (crocodiles, gharials, caimans, and alligators), 24 species.[7]
+
+Reptiles are tetrapod vertebrates, creatures that either have four limbs or, like snakes, are descended from four-limbed ancestors. Unlike amphibians, reptiles do not have an aquatic larval stage. Most reptiles are oviparous, although several species of squamates are viviparous, as were some extinct aquatic clades[9] – the fetus develops within the mother, contained in a placenta rather than an eggshell. As amniotes, reptile eggs are surrounded by membranes for protection and transport, which adapt them to reproduction on dry land. Many of the viviparous species feed their fetuses through various forms of placenta analogous to those of mammals, with some providing initial care for their hatchlings. Extant reptiles range in size from a tiny gecko, Sphaerodactylus ariasae, which can grow up to 17 mm (0.7 in) to the saltwater crocodile, Crocodylus porosus, which can reach 6 m (19.7 ft) in length and weigh over 1,000 kg (2,200 lb).
+
+In the 13th century the category of reptile was recognized in Europe as consisting of a miscellany of egg-laying creatures, including "snakes, various fantastic monsters, lizards, assorted amphibians, and worms", as recorded by Vincent of Beauvais in his Mirror of Nature.[10]
+In the 18th century, the reptiles were, from the outset of classification, grouped with the amphibians. Linnaeus, working from species-poor Sweden, where the common adder and grass snake are often found hunting in water, included all reptiles and amphibians in class "III – Amphibia" in his Systema Naturæ.[11]
+The terms reptile and amphibian were largely interchangeable, reptile (from Latin repere, 'to creep') being preferred by the French.[12] Josephus Nicolaus Laurenti was the first to formally use the term Reptilia for an expanded selection of reptiles and amphibians basically similar to that of Linnaeus.[13] Today, the two groups are still commonly treated under the single heading herpetology.
+
+It was not until the beginning of the 19th century that it became clear that reptiles and amphibians are, in fact, quite different animals, and Pierre André Latreille erected the class Batracia (1825) for the latter, dividing the tetrapods into the four familiar classes of reptiles, amphibians, birds, and mammals.[14] The British anatomist Thomas Henry Huxley made Latreille's definition popular and, together with Richard Owen, expanded Reptilia to include the various fossil "antediluvian monsters", including dinosaurs and the mammal-like (synapsid) Dicynodon he helped describe. This was not the only possible classification scheme: In the Hunterian lectures delivered at the Royal College of Surgeons in 1863, Huxley grouped the vertebrates into mammals, sauroids, and ichthyoids (the latter containing the fishes and amphibians). He subsequently proposed the names of Sauropsida and Ichthyopsida for the latter two groups.[15] In 1866, Haeckel demonstrated that vertebrates could be divided based on their reproductive strategies, and that reptiles, birds, and mammals were united by the amniotic egg.
+
+The terms Sauropsida ('lizard faces') and Theropsida ('beast faces') were used again in 1916 by E.S. Goodrich to distinguish between lizards, birds, and their relatives on the one hand (Sauropsida) and mammals and their extinct relatives (Theropsida) on the other. Goodrich supported this division by the nature of the hearts and blood vessels in each group, and other features, such as the structure of the forebrain. According to Goodrich, both lineages evolved from an earlier stem group, Protosauria ("first lizards") in which he included some animals today considered reptile-like amphibians, as well as early reptiles.[16]
+
+In 1956, D.M.S. Watson observed that the first two groups diverged very early in reptilian history, so he divided Goodrich's Protosauria between them. He also reinterpreted Sauropsida and Theropsida to exclude birds and mammals, respectively. Thus his Sauropsida included Procolophonia, Eosuchia, Millerosauria, Chelonia (turtles), Squamata (lizards and snakes), Rhynchocephalia, Crocodilia, "thecodonts" (paraphyletic basal Archosauria), non-avian dinosaurs, pterosaurs, ichthyosaurs, and sauropterygians.[17]
+
+In the late 19th century, a number of definitions of Reptilia were offered. The traits listed by Lydekker in 1896, for example, include a single occipital condyle, a jaw joint formed by the quadrate and articular bones, and certain characteristics of the vertebrae.[18] The animals singled out by these formulations, the amniotes other than the mammals and the birds, are still those considered reptiles today.[19]
+
+The synapsid/sauropsid division supplemented another approach, one that split the reptiles into four subclasses based on the number and position of temporal fenestrae, openings in the sides of the skull behind the eyes. This classification was initiated by Henry Fairfield Osborn and elaborated and made popular by Romer's classic Vertebrate Paleontology.[20][21] Those four subclasses were:
+
+The composition of Euryapsida was uncertain. Ichthyosaurs were, at times, considered to have arisen independently of the other euryapsids, and given the older name Parapsida. Parapsida was later discarded as a group for the most part (ichthyosaurs being classified as incertae sedis or with Euryapsida). However, four (or three if Euryapsida is merged into Diapsida) subclasses remained more or less universal for non-specialist work throughout the 20th century. It has largely been abandoned by recent researchers: in particular, the anapsid condition has been found to occur so variably among unrelated groups that it is not now considered a useful distinction.[22]
+
+By the early 21st century, vertebrate paleontologists were beginning to adopt phylogenetic taxonomy, in which all groups are defined in such a way as to be monophyletic; that is, groups include all descendants of a particular ancestor. The reptiles as historically defined are paraphyletic, since they exclude both birds and mammals. These respectively evolved from dinosaurs and from early therapsids, which were both traditionally called reptiles.[23] Birds are more closely related to crocodilians than the latter are to the rest of extant reptiles. Colin Tudge wrote:
+
+Mammals are a clade, and therefore the cladists are happy to acknowledge the traditional taxon Mammalia; and birds, too, are a clade, universally ascribed to the formal taxon Aves. Mammalia and Aves are, in fact, subclades within the grand clade of the Amniota. But the traditional class Reptilia is not a clade. It is just a section of the clade Amniota: the section that is left after the Mammalia and Aves have been hived off. It cannot be defined by synapomorphies, as is the proper way. Instead, it is defined by a combination of the features it has and the features it lacks: reptiles are the amniotes that lack fur or feathers. At best, the cladists suggest, we could say that the traditional Reptilia are 'non-avian, non-mammalian amniotes'.[19]
+
+Despite the early proposals for replacing the paraphyletic Reptilia with a monophyletic Sauropsida, which includes birds, that term was never adopted widely or, when it was, was not applied consistently.[1] When Sauropsida was used, it often had the same content or even the same definition as Reptilia. In 1988, Jacques Gauthier proposed a cladistic definition of Reptilia as a monophyletic node-based crown group containing turtles, lizards and snakes, crocodilians, and birds, their common ancestor and all its descendants. While Gauthier's definition was close to the modern consensus, nonetheless, it became considered inadequate because the actual relationship of turtles to other reptiles was not yet well understood at this time.[1] Major revisions since have included the reassignment of synapsids as non-reptiles, and classification of turtles as diapsids.[1]
+
+A variety of other definitions were proposed by other scientists in the years following Gauthier's paper. The first such new definition, which attempted to adhere to the standards of the PhyloCode, was published by Modesto and Anderson in 2004. Modesto and Anderson reviewed the many previous definitions and proposed a modified definition, which they intended to retain most traditional content of the group while keeping it stable and monophyletic. They defined Reptilia as all amniotes closer to Lacerta agilis and Crocodylus niloticus than to Homo sapiens. This stem-based definition is equivalent to the more common definition of Sauropsida, which Modesto and Anderson synonymized with Reptilia, since the latter is better known and more frequently used. Unlike most previous definitions of Reptilia, however, Modesto and Anderson's definition includes birds,[1] as they are within the clade that includes both lizards and crocodiles.[1]
+
+Classification to order level of the reptiles, after Benton, 2014.[24][25]
+
+The cladogram presented here illustrates the "family tree" of reptiles, and follows a simplified version of the relationships found by M.S. Lee, in 2013.[26] All genetic studies have supported the hypothesis that turtles are diapsids; some have placed turtles within archosauriformes,[26][27][28][29][30][31] though a few have recovered turtles as lepidosauriformes instead.[32] The cladogram below used a combination of genetic (molecular) and fossil (morphological) data to obtain its results.[26]
+
+Synapsida (mammals and their extinct relatives)
+
+†Millerettidae
+
+†Eunotosaurus
+
+†Lanthanosuchidae
+
+†Procolophonoidea
+
+†Pareiasauromorpha
+
+†Captorhinidae
+
+†Paleothyris
+
+†Araeoscelidia
+
+†Claudiosaurus
+
+†Younginiformes
+
+†Kuehneosauridae
+
+Rhynchocephalia (tuatara and their extinct relatives)
+
+Squamata (lizards and snakes)
+
+†Choristodera
+
+†Prolacertiformes
+
+†Trilophosaurus
+
+†Rhynchosauria
+
+Archosauriformes (crocodiles, birds, dinosaurs and extinct relatives)
+
+†Eosauropterygia
+
+†Placodontia
+
+†Sinosaurosphargis
+
+†Odontochelys
+
+†Proganochelys
+
+Testudines (turtles)
+
+The placement of turtles has historically been highly variable. Classically, turtles were considered to be related to the primitive anapsid reptiles.[33] Molecular work has usually placed turtles within the diapsids. As of 2013, three turtle genomes have been sequenced.[34] The results place turtles as a sister clade to the archosaurs, the group that includes crocodiles, dinosaurs, and birds.[35] However, in their comparative analysis of the timing of organogenesis, Werneburg and Sánchez-Villagra (2009) found support for the hypothesis that turtles belong to a separate clade within Sauropsida, outside the saurian clade altogether.[36]
+
+The origin of the reptiles lies about 310–320 million years ago, in the steaming swamps of the late Carboniferous period, when the first reptiles evolved from advanced reptiliomorphs.[3]
+
+The oldest known animal that may have been an amniote is Casineria (though it may have been a temnospondyl).[37][38][39] A series of footprints from the fossil strata of Nova Scotia dated to 315 Ma show typical reptilian toes and imprints of scales.[40] These tracks are attributed to Hylonomus, the oldest unquestionable reptile known.[41]
+It was a small, lizard-like animal, about 20 to 30 centimetres (7.9 to 11.8 in) long, with numerous sharp teeth indicating an insectivorous diet.[42] Other examples include Westlothiana (for the moment considered a reptiliomorph rather than a true amniote)[43] and Paleothyris, both of similar build and presumably similar habit.
+
+The earliest amniotes, including stem-reptiles (those amniotes closer to modern reptiles than to mammals), were largely overshadowed by larger stem-tetrapods, such as Cochleosaurus, and remained a small, inconspicuous part of the fauna until the Carboniferous Rainforest Collapse.[44] This sudden collapse affected several large groups. Primitive tetrapods were particularly devastated, while stem-reptiles fared better, being ecologically adapted to the drier conditions that followed. Primitive tetrapods, like modern amphibians, need to return to water to lay eggs; in contrast, amniotes, like modern reptiles – whose eggs possess a shell that allows them to be laid on land – were better adapted to the new conditions. Amniotes acquired new niches at a faster rate than before the collapse and at a much faster rate than primitive tetrapods. They acquired new feeding strategies including herbivory and carnivory, previously only having been insectivores and piscivores.[44] From this point forward, reptiles dominated communities and had a greater diversity than primitive tetrapods, setting the stage for the Mesozoic (known as the Age of Reptiles).[45] One of the best known early stem-reptiles is Mesosaurus, a genus from the Early Permian that had returned to water, feeding on fish.
+
+It was traditionally assumed that the first reptiles retained an anapsid skull inherited from their ancestors.[46] This type of skull has a skull roof with only holes for the nostrils, eyes and a pineal eye.[33] The discoveries of synapsid-like openings (see below) in the skull roof of the skulls of several members of Parareptilia (the clade containing most of the amniotes traditionally referred to as "anapsids"), including lanthanosuchoids, millerettids, bolosaurids, some nycteroleterids, some procolophonoids and at least some mesosaurs[47][48][49] made it more ambiguous and it's currently uncertain whether the ancestral amniote had an anapsid-like or synapsid-like skull.[49] These animals are traditionally referred to as "anapsids", and form a paraphyletic basic stock from which other groups evolved.[1] Very shortly after the first amniotes appeared, a lineage called Synapsida split off; this group was characterized by a temporal opening in the skull behind each eye to give room for the jaw muscle to move. These are the "mammal-like amniotes", or stem-mammals, that later gave rise to the true mammals.[50] Soon after, another group evolved a similar trait, this time with a double opening behind each eye, earning them the name Diapsida ("two arches").[46] The function of the holes in these groups was to lighten the skull and give room for the jaw muscles to move, allowing for a more powerful bite.[33]
+
+Turtles have been traditionally believed to be surviving parareptiles, on the basis of their anapsid skull structure, which was assumed to be primitive trait.[51] The rationale for this classification has been disputed, with some arguing that turtles are diapsids that evolved anapsid skulls in order to improve their armor.[3] Later morphological phylogenetic studies with this in mind placed turtles firmly within Diapsida.[52] All molecular studies have strongly upheld the placement of turtles within diapsids, most commonly as a sister group to extant archosaurs.[28][29][30][31]
+
+With the close of the Carboniferous, the amniotes became the dominant tetrapod fauna. While primitive, terrestrial reptiliomorphs still existed, the synapsid amniotes evolved the first truly terrestrial megafauna (giant animals) in the form of pelycosaurs, such as Edaphosaurus and the carnivorous Dimetrodon. In the mid-Permian period, the climate became drier, resulting in a change of fauna: The pelycosaurs were replaced by the therapsids.[53]
+
+The parareptiles, whose massive skull roofs had no postorbital holes, continued and flourished throughout the Permian. The pareiasaurian parareptiles reached giant proportions in the late Permian, eventually disappearing at the close of the period (the turtles being possible survivors).[53]
+
+Early in the period, the modern reptiles, or crown-group reptiles, evolved and split into two main lineages: the Archosauromorpha (forebears of turtles, crocodiles, and dinosaurs) and the Lepidosauromorpha (predecessors of modern lizards and tuataras). Both groups remained lizard-like and relatively small and inconspicuous during the Permian.
+
+The close of the Permian saw the greatest mass extinction known (see the Permian–Triassic extinction event), an event prolonged by the combination of two or more distinct extinction pulses.[54] Most of the earlier parareptile and synapsid megafauna disappeared, being replaced by the true reptiles, particularly archosauromorphs. These were characterized by elongated hind legs and an erect pose, the early forms looking somewhat like long-legged crocodiles. The archosaurs became the dominant group during the Triassic period, though it took 30 million years before their diversity was as great as the animals that lived in the Permian.[54] Archosaurs developed into the well-known dinosaurs and pterosaurs, as well as the ancestors of crocodiles. Since reptiles, first rauisuchians and then dinosaurs, dominated the Mesozoic era, the interval is popularly known as the "Age of Reptiles". The dinosaurs also developed smaller forms, including the feather-bearing smaller theropods. In the Cretaceous period, these gave rise to the first true birds.[55]
+
+The sister group to Archosauromorpha is Lepidosauromorpha, containing lizards and tuataras, as well as their fossil relatives. Lepidosauromorpha contained at least one major group of the Mesozoic sea reptiles: the mosasaurs, which lived during the Cretaceous period. The phylogenetic placement of other main groups of fossil sea reptiles – the ichthyopterygians (including ichthyosaurs) and the sauropterygians, which evolved in the early Triassic – is more controversial. Different authors linked these groups either to lepidosauromorphs[56] or to archosauromorphs,[57][58][59] and ichthyopterygians were also argued to be diapsids that did not belong to the least inclusive clade containing lepidosauromorphs and archosauromorphs.[60]
+
+The close of the Cretaceous period saw the demise of the Mesozoic era reptilian megafauna (see the Cretaceous–Paleogene extinction event). Of the large marine reptiles, only sea turtles were left; and of the non-marine large reptiles, only the semi-aquatic crocodiles and broadly similar choristoderes survived the extinction, with the latter becoming extinct in the Miocene.[62] Of the great host of dinosaurs dominating the Mesozoic, only the small beaked birds survived. This dramatic extinction pattern at the end of the Mesozoic led into the Cenozoic. Mammals and birds filled the empty niches left behind by the reptilian megafauna and, while reptile diversification slowed, bird and mammal diversification took an exponential turn.[45] However, reptiles were still important components of the megafauna, particularly in the form of large and giant tortoises.[63][64]
+
+After the extinction of most archosaur and marine reptile lines by the end of the Cretaceous, reptile diversification continued throughout the Cenozoic. Squamates took a massive hit during the KT-event, only recovering ten million years after it,[65] but they underwent a great radiation event once they recovered, and today squamates make up the majority of living reptiles (> 95%).[66][67] Approximately 10,000 extant species of traditional reptiles are known, with birds adding about 10,000 more, almost twice the number of mammals, represented by about 5,700 living species (excluding domesticated species).[68]
+
+All squamates and turtles have a three-chambered heart consisting of two atria, one variably partitioned ventricle, and two aortas that lead to the systemic circulation. The degree of mixing of oxygenated and deoxygenated blood in the three-chambered heart varies depending on the species and physiological state. Under different conditions, deoxygenated blood can be shunted back to the body or oxygenated blood can be shunted back to the lungs. This variation in blood flow has been hypothesized to allow more effective thermoregulation and longer diving times for aquatic species, but has not been shown to be a fitness advantage.[69]
+
+For example, Iguana hearts, like the majority of the squamates hearts, are composed of three chambers with two aorta and one ventricle, cardiac involuntary muscles.[70] The main structures of the heart are the sinus venosus, the pacemaker, the left atrium, the right atruim, the atrioventricular valve, the cavum venosum, cavum arteriosum, the cavum pulmonale, the muscular ridge, the ventricular ridge, pulmonary veins, and paired aortic arches.[71]
+
+Some squamate species (e.g., pythons and monitor lizards) have three-chambered hearts that become functionally four-chambered hearts during contraction. This is made possible by a muscular ridge that subdivides the ventricle during ventricular diastole and completely divides it during ventricular systole. Because of this ridge, some of these squamates are capable of producing ventricular pressure differentials that are equivalent to those seen in mammalian and avian hearts.[72]
+
+Crocodilians have an anatomically four-chambered heart, similar to birds, but also have two systemic aortas and are therefore capable of bypassing their pulmonary circulation.[73]
+
+Modern non-avian reptiles exhibit some form of cold-bloodedness (i.e. some mix of poikilothermy, ectothermy, and bradymetabolism) so that they have limited physiological means of keeping the body temperature constant and often rely on external sources of heat. Due to a less stable core temperature than birds and mammals, reptilian biochemistry requires enzymes capable of maintaining efficiency over a greater range of temperatures than in the case for warm-blooded animals. The optimum body temperature range varies with species, but is typically below that of warm-blooded animals; for many lizards, it falls in the 24°–35 °C (75°–95 °F) range,[74] while extreme heat-adapted species, like the American desert iguana Dipsosaurus dorsalis, can have optimal physiological temperatures in the mammalian range, between 35° and 40 °C (95° and 104 °F).[75] While the optimum temperature is often encountered when the animal is active, the low basal metabolism makes body temperature drop rapidly when the animal is inactive.
+
+As in all animals, reptilian muscle action produces heat. In large reptiles, like leatherback turtles, the low surface-to-volume ratio allows this metabolically produced heat to keep the animals warmer than their environment even though they do not have a warm-blooded metabolism.[76] This form of homeothermy is called gigantothermy; it has been suggested as having been common in large dinosaurs and other extinct large-bodied reptiles.[77][78]
+
+The benefit of a low resting metabolism is that it requires far less fuel to sustain bodily functions. By using temperature variations in their surroundings, or by remaining cold when they do not need to move, reptiles can save considerable amounts of energy compared to endothermic animals of the same size.[79] A crocodile needs from a tenth to a fifth of the food necessary for a lion of the same weight and can live half a year without eating.[80] Lower food requirements and adaptive metabolisms allow reptiles to dominate the animal life in regions where net calorie availability is too low to sustain large-bodied mammals and birds.
+
+It is generally assumed that reptiles are unable to produce the sustained high energy output necessary for long distance chases or flying.[81] Higher energetic capacity might have been responsible for the evolution of warm-bloodedness in birds and mammals.[82] However, investigation of correlations between active capacity and thermophysiology show a weak relationship.[83] Most extant reptiles are carnivores with a sit-and-wait feeding strategy; whether reptiles are cold blooded due to their ecology  is not clear. Energetic studies on some reptiles have shown active capacities equal to or greater than similar sized warm-blooded animals.[84]
+
+All reptiles breathe using lungs. Aquatic turtles have developed more permeable skin, and some species have modified their cloaca to increase the area for gas exchange.[85] Even with these adaptations, breathing is never fully accomplished without lungs. Lung ventilation is accomplished differently in each main reptile group. In squamates, the lungs are ventilated almost exclusively by the axial musculature. This is also the same musculature that is used during locomotion. Because of this constraint, most squamates are forced to hold their breath during intense runs. Some, however, have found a way around it. Varanids, and a few other lizard species, employ buccal pumping as a complement to their normal "axial breathing". This allows the animals to completely fill their lungs during intense locomotion, and thus remain aerobically active for a long time. Tegu lizards are known to possess a proto-diaphragm, which separates the pulmonary cavity from the visceral cavity. While not actually capable of movement, it does allow for greater lung inflation, by taking the weight of the viscera off the lungs.[86]
+
+Crocodilians actually have a muscular diaphragm that is analogous to the mammalian diaphragm. The difference is that the muscles for the crocodilian diaphragm pull the pubis (part of the pelvis, which is movable in crocodilians) back, which brings the liver down, thus freeing space for the lungs to expand. This type of diaphragmatic setup has been referred to as the "hepatic piston". The airways form a number of double tubular chambers within each lung. On inhalation and exhalation air moves through the airways in the same direction, thus creating a unidirectional airflow through the lungs. A similar system is found in birds,[87] monitor lizards[88] and iguanas.[89]
+
+Most reptiles lack a secondary palate, meaning that they must hold their breath while swallowing. Crocodilians have evolved a bony secondary palate that allows them to continue breathing while remaining submerged (and protect their brains against damage by struggling prey). Skinks (family Scincidae) also have evolved a bony secondary palate, to varying degrees. Snakes took a different approach and extended their trachea instead. Their tracheal extension sticks out like a fleshy straw, and allows these animals to swallow large prey without suffering from asphyxiation.[90]
+
+How turtles and tortoises breathe has been the subject of much study. To date, only a few species have been studied thoroughly enough to get an idea of how those turtles breathe. The varied results indicate that turtles and tortoises have found a variety of solutions to this problem.
+
+The difficulty is that most turtle shells are rigid and do not allow for the type of expansion and contraction that other amniotes use to ventilate their lungs. Some turtles, such as the Indian flapshell (Lissemys punctata), have a sheet of muscle that envelops the lungs. When it contracts, the turtle can exhale. When at rest, the turtle can retract the limbs into the body cavity and force air out of the lungs. When the turtle protracts its limbs, the pressure inside the lungs is reduced, and the turtle can suck air in. Turtle lungs are attached to the inside of the top of the shell (carapace), with the bottom of the lungs attached (via connective tissue) to the rest of the viscera. By using a series of special muscles (roughly equivalent to a diaphragm), turtles are capable of pushing their viscera up and down, resulting in effective respiration, since many of these muscles have attachment points in conjunction with their forelimbs (indeed, many of the muscles expand into the limb pockets during contraction).[91]
+
+Breathing during locomotion has been studied in three species, and they show different patterns. Adult female green sea turtles do not breathe as they crutch along their nesting beaches. They hold their breath during terrestrial locomotion and breathe in bouts as they rest. North American box turtles breathe continuously during locomotion, and the ventilation cycle is not coordinated with the limb movements.[92] This is because they use their abdominal muscles to breathe during locomotion. The last species to have been studied is the red-eared slider, which also breathes during locomotion, but takes smaller breaths during locomotion than during small pauses between locomotor bouts, indicating that there may be mechanical interference between the limb movements and the breathing apparatus. Box turtles have also been observed to breathe while completely sealed up inside their shells.[92]
+
+Reptilian skin is covered in a horny epidermis, making it watertight and enabling reptiles to live on dry land, in contrast to amphibians. Compared to mammalian skin, that of reptiles is rather thin and lacks the thick dermal layer that produces leather in mammals.[93]
+Exposed parts of reptiles are protected by scales or scutes, sometimes with a bony base (osteoderms), forming armor. In lepidosaurians, such as lizards and snakes, the whole skin is covered in overlapping epidermal scales. Such scales were once thought to be typical of the class Reptilia as a whole, but are now known to occur only in lepidosaurians.[citation needed] The scales found in turtles and crocodiles are of dermal, rather than epidermal, origin and are properly termed scutes.[citation needed] In turtles, the body is hidden inside a hard shell composed of fused scutes.
+
+Lacking a thick dermis, reptilian leather is not as strong as mammalian leather. It is used in leather-wares for decorative purposes for shoes, belts and handbags, particularly crocodile skin.
+
+Reptiles shed their skin through a process called ecdysis which occurs continuously throughout their lifetime. In particular, younger reptiles tend to shed once every 5–6 weeks while adults shed 3–4 times a year.[94] Younger reptiles shed more because of their rapid growth rate. Once full size, the frequency of shedding drastically decreases. The process of ecdysis involves forming a new layer of skin under the old one. Proteolytic enzymes and lymphatic fluid is secreted between the old and new layers of skin. Consequently, this lifts the old skin from the new one allowing shedding to occur.[95] Snakes will shed from the head to the tail while lizards shed in a "patchy pattern".[95] Dysecdysis, a common skin disease in snakes and lizards, will occur when ecdysis, or shedding, fails.[96] There are numerous reasons why shedding fails and can be related to inadequate humidity and temperature, nutritional deficiencies, dehydration and traumatic injuries.[95] Nutritional deficiencies decrease proteolytic enzymes while dehydration reduces lymphatic fluids to separate the skin layers. Traumatic injuries on the other hand, form scars that will not allow new scales to form and disrupt the process of ecdysis.[96]
+
+Excretion is performed mainly by two small kidneys. In diapsids, uric acid is the main nitrogenous waste product; turtles, like mammals, excrete mainly urea. Unlike the kidneys of mammals and birds, reptile kidneys are unable to produce liquid urine more concentrated than their body fluid. This is because they lack a specialized structure called a loop of Henle, which is present in the nephrons of birds and mammals. Because of this, many reptiles use the colon to aid in the reabsorption of water. Some are also able to take up water stored in the bladder. Excess salts are also excreted by nasal and lingual salt glands in some reptiles.[97]
+
+In all reptiles the urinogenital ducts and the anus both empty into an organ called a cloaca. In some reptiles, a midventral wall in the cloaca may open into a urinary bladder, but not all. It is present in all turtles and tortoises as well as most lizards, but is lacking in the monitor lizard, the legless lizards. It is absent in the snakes, alligators, and crocodiles.[98]
+
+Many turtles, tortoises, and lizards have proportionally very large bladders. Charles Darwin noted that the Galapagos tortoise had a bladder which could store up to 20% of its body weight.[99] Such adaptations are the result of environments such as remote islands and deserts where water is very scarce.[100]:143 Other desert-dwelling reptiles have large bladders that can store a long-term reservoir of water for up to several months and aid in osmoregulation.[101]
+
+Turtles have two or more accessory urinary bladders, located lateral to the neck of the urinary bladder and dorsal to the pubis, occupying a significant portion of their body cavity.[102] Their bladder is also usually bilobed with a left and right section. The right section is located under the liver, which prevents large stones from remaining in that side while the left section is more likely to have calculi.[103]
+
+Most reptiles are insectivorous or carnivorous and have simple and comparatively short digestive tracts due to meat being fairly simple to break down and digest. Digestion is slower than in mammals, reflecting their lower resting metabolism and their inability to divide and masticate their food.[104] Their poikilotherm metabolism has very low energy requirements, allowing large reptiles like crocodiles and large constrictors to live from a single large meal for months, digesting it slowly.[80]
+
+While modern reptiles are predominantly carnivorous, during the early history of reptiles several groups produced some herbivorous megafauna: in the Paleozoic, the pareiasaurs; and in the Mesozoic several lines of dinosaurs.[45] Today, turtles are the only predominantly herbivorous reptile group, but several lines of agamas and iguanas have evolved to live wholly or partly on plants.[105]
+
+Herbivorous reptiles face the same problems of mastication as herbivorous mammals but, lacking the complex teeth of mammals, many species swallow rocks and pebbles (so called gastroliths) to aid in digestion: The rocks are washed around in the stomach, helping to grind up plant matter.[105] Fossil gastroliths have been found associated with both ornithopods and sauropods, though whether they actually functioned as a gastric mill in the latter is disputed.[106][107] Salt water crocodiles also use gastroliths as ballast, stabilizing them in the water or helping them to dive.[108] A dual function as both stabilizing ballast and digestion aid has been suggested for gastroliths found in plesiosaurs.[109]
+
+The reptilian nervous system contains the same basic part of the amphibian brain, but the reptile cerebrum and cerebellum are slightly larger. Most typical sense organs are well developed with certain exceptions, most notably the snake's lack of external ears (middle and inner ears are present). There are twelve pairs of cranial nerves.[110] Due to their short cochlea, reptiles use electrical tuning to expand their range of audible frequencies.
+
+Reptiles are generally considered less intelligent than mammals and birds.[33] The size of their brain relative to their body is much less than that of mammals, the encephalization quotient being about one tenth of that of mammals,[111] though larger reptiles can show more complex brain development. Larger lizards, like the monitors, are known to exhibit complex behavior, including cooperation[112] and cognitive abilities allowing them to optimize their foraging and territoriality over time.[113] Crocodiles have relatively larger brains and show a fairly complex social structure. The Komodo dragon is even known to engage in play,[114] as are turtles, which are also considered to be social creatures,[115] and sometimes switch between monogamy and promiscuity in their sexual behavior.[citation needed] One study found that wood turtles were better than white rats at learning to navigate mazes.[116] Another study found that giant tortoises are capable of learning through operant conditioning, visual discrimination and retained learned behaviors with long-term memory.[117] Sea turtles have been regarded as having simple brains, but their flippers are used for a variety of foraging tasks (holding, bracing, corralling) in common with marine mammals.[118]
+
+Most reptiles are diurnal animals. The vision is typically adapted to daylight conditions, with color vision and more advanced visual depth perception than in amphibians and most mammals.
+
+Reptiles usually have excellent vision, allowing them to detect shapes and motions at long distances. They often have only a few Rod cells and have poor vision in low-light conditions. At the same time they have cells called “double cones” which give them sharp color vision and enable them to see ultraviolet wavelengths.[119] In some species, such as blind snakes, vision is reduced.
+
+Many lepidosaurs have a photosensory organ on the top of their heads called the parietal eye, which are also called third eye, pineal eye or pineal gland. This “eye” does not work the same way as a normal eye does as it has only a rudimentary retina and lens and thus, cannot form images. It is however sensitive to changes in light and dark and can detect movement.[119]
+
+Some snakes have extra sets of visual organs (in the loosest sense of the word) in the form of pits sensitive to infrared radiation (heat). Such heat-sensitive pits are particularly well developed in the pit vipers, but are also found in boas and pythons. These pits allow the snakes to sense the body heat of birds and mammals, enabling pit vipers to hunt rodents in the dark.[120]
+
+Most reptiles including birds possess a nictitating membrane, a translucent third eyelid which is drawn over the eye from the inner corner. Notably, it protects a crocodilian's eyeball surface while allowing a degree of vision underwater.[121] However, many squamates, geckos and snakes in particular, lack eyelids, which are replaced by a transparent scale. This is called the brille, spectacle, or eyecap. The brille is usually not visible, except for when the snake molts, and it protects the eyes from dust and dirt.[122]
+
+Reptiles generally reproduce sexually, though some are capable of asexual reproduction. All reproductive activity occurs through the cloaca, the single exit/entrance at the base of the tail where waste is also eliminated. Most reptiles have copulatory organs, which are usually retracted or inverted and stored inside the body. In turtles and crocodilians, the male has a single median penis, while squamates, including snakes and lizards, possess a pair of hemipenes, only one of which is typically used in each session. Tuatara, however, lack copulatory organs, and so the male and female simply press their cloacas together as the male discharges sperm.[123]
+
+Most reptiles lay amniotic eggs covered with leathery or calcareous shells. An amnion, chorion, and allantois are present during embryonic life. The eggshell (1) protects the crocodile embryo (11) and keeps it from drying out, but it is flexible to allow gas exchange. The chorion (6) aids in gas exchange between the inside and outside of the egg. It allows carbon dioxide to exit the egg and oxygen gas to enter the egg. The albumin (9) further protects the embryo and serves as a reservoir for water and protein. The allantois (8) is a sac that collects the metabolic waste produced by the embryo. The amniotic sac (10) contains amniotic fluid (12) which protects and cushions the embryo. The amnion (5) aids in osmoregulation and serves as a saltwater reservoir. The yolk sac (2) surrounding the yolk (3) contains protein and fat rich nutrients that are absorbed by the embryo via vessels (4) that allow the embryo to grow and metabolize. The air space (7) provides the embryo with oxygen while it is hatching. This ensures that the embryo will not suffocate while it is hatching. There are no larval stages of development. Viviparity and ovoviviparity have evolved in many extinct clades of reptiles and in squamates. In the latter group, many species, including all boas and most vipers, utilize this mode of reproduction. The degree of viviparity varies; some species simply retain the eggs until just before hatching, others provide maternal nourishment to supplement the yolk, and yet others lack any yolk and provide all nutrients via a structure similar to the mammalian placenta. The earliest documented case of viviparity in reptiles is the Early Permian mesosaurs,[124] although some individuals or taxa in that clade may also have been oviparous because a putative isolated egg has also been found. Several groups of Mesozoic marine reptiles also exhibited viviparity, such as mosasaurs, ichthyosaurs, and Sauropterygia, a group that include pachypleurosaurs and Plesiosauria.[9]
+
+Asexual reproduction has been identified in squamates in six families of lizards and one snake. In some species of squamates, a population of females is able to produce a unisexual diploid clone of the mother. This form of asexual reproduction, called parthenogenesis, occurs in several species of gecko, and is particularly widespread in the teiids (especially Aspidocelis) and lacertids (Lacerta). In captivity, Komodo dragons (Varanidae) have reproduced by parthenogenesis.
+
+Parthenogenetic species are suspected to occur among chameleons, agamids, xantusiids, and typhlopids.
+
+Some reptiles exhibit temperature-dependent sex determination (TDSD), in which the incubation temperature determines whether a particular egg hatches as male or female. TDSD is most common in turtles and crocodiles, but also occurs in lizards and tuatara.[125] To date, there has been no confirmation of whether TDSD occurs in snakes.[126]
+
+Many small reptiles, such as snakes and lizards that live on the ground or in the water, are vulnerable to being preyed on by all kinds of carnivorous animals. Thus avoidance is the most common form of defense in reptiles.[127] At the first sign of danger, most snakes and lizards crawl away into the undergrowth, and turtles and crocodiles will plunge into water and sink out of sight.
+
+Reptiles tend to avoid confrontation through camouflage. Two major groups of reptile predators are birds and other reptiles, both of which have well developed color vision. Thus the skins of many reptiles have cryptic coloration of plain or mottled gray, green, and brown to allow them to blend into the background of their natural environment.[128] Aided by the reptiles' capacity for remaining motionless for long periods, the camouflage of many snakes is so effective that people or domestic animals are most typically bitten because they accidentally step on them.[129]
+
+When camouflage fails to protect them, blue-tongued skinks will try to ward off attackers by displaying their blue tongues, and the frill-necked lizard will display its brightly colored frill. These same displays are used in territorial disputes and during courtship.[130] If danger arises so suddenly that flight is useless, crocodiles, turtles, some lizards, and some snakes hiss loudly when confronted by an enemy. Rattlesnakes rapidly vibrate the tip of the tail, which is composed of a series of nested, hollow beads to ward of approaching danger.
+
+In contrast to the normal drab coloration of most reptiles, the lizards of the genus Heloderma (the Gila monster and the beaded lizard) and many of the coral snakes have high-contrast warning coloration, warning potential predators they are venomous.[131] A number of non-venomous North American snake species have colorful markings similar to those of the coral snake, an oft cited example of Batesian mimicry.[132][133]
+
+Camouflage does not always fool a predator. When caught out, snake species adopt different defensive tactics and use a complicated set of behaviors when attacked. Some first elevate their head and spread out the skin of their neck in an effort to look large and threatening. Failure of this strategy may lead to other measures practiced particularly by cobras, vipers, and closely related species, which use venom to attack. The venom is modified saliva, delivered through fangs from a venom gland.[134][135] Some non-venomous snakes, such as American hognose snakes or European grass snake, play dead when in danger; some, including the grass snake, exude a foul-smelling liquid to deter attackers.[136][137]
+
+When a crocodilian is concerned about its safety, it will gape to expose the teeth and yellow tongue. If this doesn't work, the crocodilian gets a little more agitated and typically begins to make hissing sounds. After this, the crocodilian will start to change its posture dramatically to make itself look more intimidating. The body is inflated to increase apparent size. If absolutely necessary it may decide to attack an enemy.
+
+Some species try to bite immediately. Some will use their heads as sledgehammers and literally smash an opponent, some will rush or swim toward the threat from a distance, even chasing the opponent onto land or galloping after it.[138] The main weapon in all crocodiles is the bite, which can generate very high bite force. Many species also possess canine-like teeth. These are used primarily for seizing prey, but are also used in fighting and display.[139]
+
+Geckos, skinks, and other lizards that are captured by the tail will shed part of the tail structure through a process called autotomy and thus be able to flee. The detached tail will continue to wiggle, creating a deceptive sense of continued struggle and distracting the predator's attention from the fleeing prey animal. The detached tails of leopard geckos can wiggle for up to 20 minutes.[140] In many species the tails are of a separate and dramatically more intense color than the rest of the body so as to encourage potential predators to strike for the tail first. In the shingleback skink and some species of geckos, the tail is short and broad and resembles the head, so that the predators may attack it rather than the more vulnerable front part.[141]
+
+Reptiles that are capable of shedding their tails can partially regenerate them over a period of weeks. The new section will however contain cartilage rather than bone, and will never grow to the same length as the original tail. It is often also distinctly discolored compared to the rest of the body and may lack some of the external sculpting features seen in the original tail.[142]
+
+Dinosaurs have been widely depicted in culture since the English palaeontologist Richard Owen coined the name dinosaur in 1842. As soon as 1854, the Crystal Palace Dinosaurs were on display to the public in south London.[143][144] One dinosaur appeared in literature even earlier, as Charles Dickens placed a Megalosaurus in the first chapter of his novel Bleak House in 1852.[145] The dinosaurs featured in books, films, television programs, artwork, and other media have been used for both education and entertainment. The depictions range from the realistic, as in the television documentaries of the 1990s and first decade of the 21st century, or the fantastic, as in the monster movies of the 1950s and 1960s.[144][146][147]
+
+The snake or serpent has played a powerful symbolic role in different cultures. In Egyptian history, the Nile cobra adorned the crown of the pharaoh. It was worshipped as one of the gods and was also used for sinister purposes: murder of an adversary and ritual suicide (Cleopatra). In Greek mythology snakes are associated with deadly antagonists, as a chthonic symbol, roughly translated as earthbound. The nine-headed Lernaean Hydra that Hercules defeated and the three Gorgon sisters are children of Gaia, the earth. Medusa was one of the three Gorgon sisters who Perseus defeated. Medusa is described as a hideous mortal, with snakes instead of hair and the power to turn men to stone with her gaze. After killing her, Perseus gave her head to Athena who fixed it to her shield called the Aegis. The Titans are depicted in art with their legs replaced by bodies of snakes for the same reason: They are children of Gaia, so they are bound to the earth.[148] In Hinduism, snakes are worshipped as gods, with many women pouring milk on snake pits. The cobra is seen on the neck of Shiva, while Vishnu is depicted often as sleeping on a seven-headed snake or within the coils of a serpent. There are temples in India solely for cobras sometimes called Nagraj (King of Snakes), and it is believed that snakes are symbols of fertility. In the annual Hindu festival of Nag Panchami, snakes are venerated and prayed to.[149] In religious terms, the snake and jaguar are arguably the most important animals in ancient Mesoamerica. "In states of ecstasy, lords dance a serpent dance; great descending snakes adorn and support buildings from Chichen Itza to Tenochtitlan, and the Nahuatl word coatl meaning serpent or twin, forms part of primary deities such as Mixcoatl, Quetzalcoatl, and Coatlicue."[150] In Christianity and Judaism, a serpent appears in Genesis to tempt Adam and Eve with the forbidden fruit from the Tree of Knowledge of Good and Evil.[151]
+
+The turtle has a prominent position as a symbol of steadfastness and tranquility in religion, mythology, and folklore from around the world.[152] A tortoise's longevity is suggested by its long lifespan and its shell, which was thought to protect it from any foe.[153] In the cosmological myths of several cultures a World Turtle carries the world upon its back or supports the heavens.[154]
+
+Deaths from snakebites are uncommon in many parts of the world, but are still counted in tens of thousands per year in India.[155] Snakebite can be treated with antivenom made from the venom of the snake. To produce antivenom, a mixture of the venoms of different species of snake is injected into the body of a horse in ever-increasing dosages until the horse is immunized. Blood is then extracted; the serum is separated, purified and freeze-dried.[156] The cytotoxic effect of snake venom is being researched as a potential treatment for cancers.[157]
+
+Lizards such as the Gila monster produce toxins with medical applications. Gila toxin reduces plasma glucose; the substance is now synthesised for use in the anti-diabetes drug exenatide (Byetta).[158] Another toxin from Gila monster saliva has been studied for use as an anti-Alzheimer's drug.[159]
+
+Geckos have also been used as medicine, especially in China.[160] Turtles have been used in Chinese traditional medicine for thousands of years, with every part of the turtle believed to have medical benefits. There is a lack of scientific evidence that would correlate claimed medical benefits to turtle consumption. Growing demand for turtle meat has placed pressure on vulnerable wild populations of turtles.[161]
+
+Crocodiles are protected in many parts of the world, and are farmed commercially. Their hides are tanned and used to make leather goods such as shoes and handbags; crocodile meat is also considered a delicacy.[162] The most commonly farmed species are the saltwater and Nile crocodiles. Farming has resulted in an increase in the saltwater crocodile population in Australia, as eggs are usually harvested from the wild, so landowners have an incentive to conserve their habitat. Crocodile leather is made into wallets, briefcases, purses, handbags, belts, hats, and shoes. Crocodile oil has been used for various purposes.[163]
+
+Snakes are also farmed, primarily in East and Southeast Asia, and their production has become more intensive in the last decade. Snake farming has been troubling for conservation in the past as it can lead to overexploitation of wild snakes and their natural prey to supply the farms. However,  farming snakes can limit the hunting of wild snakes, while reducing the slaughter of higher-order vertebrates like cows. The energy efficiency of snakes is higher than expected for carnivores, due to their ectothermy and low metabolism. Waste protein from the poultry and pig industries is used as feed in snake farms.[164] Snake farms produce meat, snake skin, and antivenom.
+
+Turtle farming is another known but controversial practice. Turtles have been farmed for a variety of reasons, ranging from food to traditional medicine, the pet trade, and scientific conservation. Demand for turtle meat and medicinal products is one of the main threats to turtle conservation in Asia. Though commercial breeding would seem to insulate wild populations, it can stoke the demand for them and increase wild captures.[165][161] Even the potentially appealing concept of raising turtles at a farm to release into the wild is questioned by some veterinarians who have had some experience with farm operations. They caution that this may introduce into the wild populations infectious diseases that occur on the farm, but have not (yet) been occurring in the wild.[166][167]
+
+In the Western world, some snakes (especially docile species such as the ball python and corn snake) are kept as pets.[168] Numerous species of lizard are kept as pets, including bearded dragons,[169] iguanas, anoles,[170] and geckos (such as the popular leopard gecko).[169]
+
+Turtles and tortoises are an increasingly popular pet, but keeping them can be challenging due to particular requirements, such as temperature control and a varied diet, as well as the long lifespans of turtles, who can potentially outlive their owners. Good hygiene and significant maintenance is necessary when keeping reptiles, due to the risks of Salmonella and other pathogens.[171]
+
+A herpetarium is a zoological exhibition space for reptiles or amphibians.

en/3383.html.txt

@@ -0,0 +1,219 @@
+
+
+Carcharhiniformes
+Heterodontiformes
+Hexanchiformes
+Lamniformes
+Orectolobiformes
+Pristiophoriformes
+Squaliformes
+Squatiniformes
+† Cladoselachiformes
+† Hybodontiformes
+† Symmoriida
+† Xenacanthida (Xenacantiformes)
+† Elegestolepis
+
+Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii) and are the sister group to the rays. However, the term "shark" has also been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus, as well as other Chondrichthyes such as the holocephalid eugenedontidans.
+
+Under this broader definition, the earliest known sharks date back to more than 420 million years ago.[2] Acanthodians are often referred to as "spiny sharks"; though they are not part of Chondrichthyes proper, they are a paraphyletic assemblage leading to cartilaginous fish as a whole.  Since then, sharks have diversified into over 500 species. They range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species of only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (40 ft) in length.[3] Sharks are found in all seas and are common to depths of 2,000 metres (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark, which can be found in both seawater and freshwater.[4] Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have numerous sets of replaceable teeth.[5]
+
+Well-known species such as the tiger shark, blue shark, great white shark, mako shark, thresher shark, and hammerhead shark are apex predators—organisms at the top of their underwater food chain. Many shark populations are threatened by human activities.
+
+Until the 16th century,[6] sharks were known to mariners as "sea dogs".[7] This is still evidential in several species termed "dogfish," or the porbeagle.
+
+The etymology of the word "shark" is uncertain, the most likely etymology states that the original sense of the word was that of "predator, one who preys on others" from the Dutch schurk, meaning "villain, scoundrel" (cf. card shark, loan shark, etc.), which was later applied to the fish due to its predatory behaviour.[8]
+
+A now disproven theory is that it derives from the Yucatec Maya word xok (pronounced 'shok'), meaning "fish".[9] 
+Evidence for this etymology came from the Oxford English Dictionary, which notes shark first came into use after Sir John Hawkins' sailors exhibited one in London in 1569 and posted "sharke" to refer to the large sharks of the Caribbean Sea. However, the Middle English Dictionary records an isolated occurrence of the word shark (referring to a sea fish) in a letter written by Thomas Beckington in 1442, which rules out a New World etymology.[10]
+
+Evidence for the existence of sharks dates from the Ordovician period, 450–420 million years ago, before land vertebrates existed and before a variety of plants had colonized the continents.[2] Only scales have been recovered from the first sharks and not all paleontologists agree that these are from true sharks, suspecting that these scales are actually those of thelodont agnathans.[11] The oldest generally accepted shark scales are from about 420 million years ago, in the Silurian period.[11] The first sharks looked very different from modern sharks.[12] At this time the most common shark tooth is the cladodont, a style of thin tooth with three tines like a trident, apparently to help catch fish. The majority of modern sharks can be traced back to around 100 million years ago.[13] Most fossils are of teeth, often in large numbers. Partial skeletons and even complete fossilized remains have been discovered. Estimates suggest that sharks grow tens of thousands of teeth over a lifetime, which explains the abundant fossils. The teeth consist of easily fossilized calcium phosphate, an apatite. When a shark dies, the decomposing skeleton breaks up, scattering the apatite prisms. Preservation requires rapid burial in bottom sediments.
+
+Among the most ancient and primitive sharks is Cladoselache, from about 370 million years ago,[12] which has been found within Paleozoic strata in Ohio, Kentucky, and Tennessee. At that point in Earth's history these rocks made up the soft bottom sediments of a large, shallow ocean, which stretched across much of North America. Cladoselache was only about 1 metre (3.3 ft) long with stiff triangular fins and slender jaws.[12] Its teeth had several pointed cusps, which wore down from use. From the small number of teeth found together, it is most likely that Cladoselache did not replace its teeth as regularly as modern sharks. Its caudal fins had a similar shape to the great white sharks and the pelagic shortfin and longfin makos. The presence of whole fish arranged tail-first in their stomachs suggest that they were fast swimmers with great agility.
+
+Most fossil sharks from about 300 to 150 million years ago can be assigned to one of two groups. The Xenacanthida was almost exclusive to freshwater environments.[14][15] By the time this group became extinct about 220 million years ago, they had spread worldwide. The other group, the hybodonts, appeared about 320 million years ago and lived mostly in the oceans, but also in freshwater.[citation needed] The results of a 2014 study of the gill structure of an unusually well preserved 325-million-year-old fossil suggested that sharks are not "living fossils", but rather have evolved more extensively than previously thought over the hundreds of millions of years they have been around.[16]
+
+Modern sharks began to appear about 100 million years ago.[13] Fossil mackerel shark teeth date to the Early Cretaceous. One of the most recently evolved families is the hammerhead shark (family Sphyrnidae), which emerged in the Eocene.[17] The oldest white shark teeth date from 60 to 66 million years ago, around the time of the extinction of the dinosaurs. In early white shark evolution there are at least two lineages: one lineage is of white sharks with coarsely serrated teeth and it probably gave rise to the modern great white shark, and another lineage is of white sharks with finely serrated teeth. These sharks attained gigantic proportions and include the extinct megatoothed shark, C. megalodon. Like most extinct sharks, C. megalodon is also primarily known from its fossil teeth and vertebrae. This giant shark reached a total length (TL) of more than 16 metres (52 ft).[18][19] C. megalodon may have approached a maxima of 20.3 metres (67 ft) in total length and 103 metric tons (114 short tons) in mass.[20] Paleontological evidence suggests that this shark was an active predator of large cetaceans.[20]
+
+Sharks belong to the superorder Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes. The Elasmobranchii also include rays and skates; the Chondrichthyes also include Chimaeras. It was thought that the sharks form a polyphyletic group: some sharks are more closely related to rays than they are to some other sharks,[21] but current molecular studies support monophyly of both groups of sharks and batoids.[22][23]
+
+The superorder Selachimorpha is divided into Galea (or Galeomorphii), and Squalea (or Squalomorphii). The Galeans are the Heterodontiformes, Orectolobiformes, Lamniformes, and Carcharhiniformes. Lamnoids and Carcharhinoids are usually placed in one clade, but recent studies show the Lamnoids and Orectoloboids are a clade. Some scientists now think that Heterodontoids may be Squalean. The Squaleans are divided into Hexanchiformes and Squalomorpha. The former includes cow shark and frilled shark, though some authors propose both families to be moved to separate orders. The Squalomorpha contains the Squaliformes and the Hypnosqualea. The Hypnosqualea may be invalid. It includes the Squatiniformes, and the Pristorajea, which may also be invalid, but includes the Pristiophoriformes and the Batoidea.[21][24]
+
+There are more than 470 species of sharks split across twelve orders, including four orders of sharks that have gone extinct:[24]
+
+Shark teeth are embedded in the gums rather than directly affixed to the jaw, and are constantly replaced throughout life. Multiple rows of replacement teeth grow in a groove on the inside of the jaw and steadily move forward in comparison to a conveyor belt; some sharks lose 30,000 or more teeth in their lifetime. The rate of tooth replacement varies from once every 8 to 10 days to several months. In most species, teeth are replaced one at a time as opposed to the simultaneous replacement of an entire row, which is observed in the cookiecutter shark.[25]
+
+Tooth shape depends on the shark's diet: those that feed on mollusks and crustaceans have dense and flattened teeth used for crushing, those that feed on fish have needle-like teeth for gripping, and those that feed on larger prey such as mammals have pointed lower teeth for gripping and triangular upper teeth with serrated edges for cutting. The teeth of plankton-feeders such as the basking shark are small and non-functional.[26]
+
+Shark skeletons are very different from those of bony fish and terrestrial vertebrates. Sharks and other cartilaginous fish (skates and rays) have skeletons made of cartilage and connective tissue. Cartilage is flexible and durable, yet is about half the normal density of bone. This reduces the skeleton's weight, saving energy.[27] Because sharks do not have rib cages, they can easily be crushed under their own weight on land.[28]
+
+The jaws of sharks, like those of rays and skates, are not attached to the cranium. The jaw's surface (in comparison to the shark's vertebrae and gill arches) needs extra support due to its heavy exposure to physical stress and its need for strength. It has a layer of tiny hexagonal plates called "tesserae", which are crystal blocks of calcium salts arranged as a mosaic.[29] This gives these areas much of the same strength found in the bony tissue found in other animals.
+
+Generally sharks have only one layer of tesserae, but the jaws of large specimens, such as the bull shark, tiger shark, and the great white shark, have two to three layers or more, depending on body size. The jaws of a large great white shark may have up to five layers.[27] In the rostrum (snout), the cartilage can be spongy and flexible to absorb the power of impacts.
+
+Fin skeletons are elongated and supported with soft and unsegmented rays named ceratotrichia, filaments of elastic protein resembling the horny keratin in hair and feathers.[30] Most sharks have eight fins. Sharks can only drift away from objects directly in front of them because their fins do not allow them to move in the tail-first direction.[28]
+
+Unlike bony fish, sharks have a complex dermal corset made of flexible collagenous fibers and arranged as a helical network surrounding their body. This works as an outer skeleton, providing attachment for their swimming muscles and thus saving energy.[31] Their dermal teeth give them hydrodynamic advantages as they reduce turbulence when swimming.[32]
+
+Tails provide thrust, making speed and acceleration dependent on tail shape. Caudal fin shapes vary considerably between shark species, due to their evolution in separate environments. Sharks possess a heterocercal caudal fin in which the dorsal portion is usually noticeably larger than the ventral portion. This is because the shark's vertebral column extends into that dorsal portion, providing a greater surface area for muscle attachment. This allows more efficient locomotion among these negatively buoyant cartilaginous fish. By contrast, most bony fish possess a homocercal caudal fin.[33]
+
+Tiger sharks have a large upper lobe, which allows for slow cruising and sudden bursts of speed. The tiger shark must be able to twist and turn in the water easily when hunting to support its varied diet, whereas the porbeagle shark, which hunts schooling fish such as mackerel and herring, has a large lower lobe to help it keep pace with its fast-swimming prey.[34] Other tail adaptations help sharks catch prey more directly, such as the thresher shark's usage of its powerful, elongated upper lobe to stun fish and squid.
+
+Unlike bony fish, sharks do not have gas-filled swim bladders for buoyancy. Instead, sharks rely on a large liver filled with oil that contains squalene, and their cartilage, which is about half the normal density of bone.[31] Their liver constitutes up to 30% of their total body mass.[35] The liver's effectiveness is limited, so sharks employ dynamic lift to maintain depth while swimming. Sand tiger sharks store air in their stomachs, using it as a form of swim bladder.  Bottom-dwelling sharks, like the nurse shark, have negative buoyancy, allowing them to rest on the ocean floor.
+
+Some sharks, if inverted or stroked on the nose, enter a natural state of tonic immobility. Researchers use this condition to handle sharks safely.[36]
+
+Like other fish, sharks extract oxygen from seawater as it passes over their gills. Unlike other fish, shark gill slits are not covered, but lie in a row behind the head. A modified slit called a spiracle lies just behind the eye, which assists the shark with taking in water during respiration and plays a major role in bottom–dwelling sharks. Spiracles are reduced or missing in active pelagic sharks.[26] While the shark is moving, water passes through the mouth and over the gills in a process known as "ram ventilation". While at rest, most sharks pump water over their gills to ensure a constant supply of oxygenated water. A small number of species have lost the ability to pump water through their gills and must swim without rest. These species are obligate ram ventilators and would presumably asphyxiate if unable to move. Obligate ram ventilation is also true of some pelagic bony fish species.[37][38]
+
+The respiration and circulation process begins when deoxygenated blood travels to the shark's two-chambered heart. Here the shark pumps blood to its gills via the ventral aorta artery where it branches into afferent brachial arteries. Reoxygenation takes place in the gills and the reoxygenated blood flows into the efferent brachial arteries, which come together to form the dorsal aorta. The blood flows from the dorsal aorta throughout the body. The deoxygenated blood from the body then flows through the posterior cardinal veins and enters the posterior cardinal sinuses. From there blood enters the heart ventricle and the cycle repeats.[39]
+
+Most sharks are "cold-blooded" or, more precisely, poikilothermic, meaning that their internal body temperature matches that of their ambient environment. Members of the family Lamnidae (such as the shortfin mako shark and the great white shark) are homeothermic and maintain a higher body temperature than the surrounding water. In these sharks, a strip of aerobic red muscle located near the center of the body generates the heat, which the body retains via a countercurrent exchange mechanism by a system of blood vessels called the rete mirabile ("miraculous net"). The common thresher and bigeye thresher sharks have a similar mechanism for maintaining an elevated body temperature.[40]
+
+In contrast to bony fish, with the exception of the coelacanth,[41] the blood and other tissue of sharks and Chondrichthyes is generally isotonic to their marine environments because of the high concentration of urea (up to 2.5%[42]) and trimethylamine N-oxide (TMAO), allowing them to be in osmotic balance with the seawater. This adaptation prevents most sharks from surviving in freshwater, and they are therefore confined to marine environments. A few exceptions exist, such as the bull shark, which has developed a way to change its kidney function to excrete large amounts of urea.[35] When a shark dies, the urea is broken down to ammonia by bacteria, causing the dead body to gradually smell strongly of ammonia.[43][44]
+
+Research in 1930 by Homer W. Smith showed that sharks' urine doesn't contain sufficient sodium to avoid hypernatremia, and it was postulated that there must be an additional mechanism for salt secretion. In 1960 it was discovered at the Mount Desert Island Biological Laboratory in Salsbury Cove, Maine that sharks have a type of salt gland located at the end of the intestine, known as the "rectal gland", whose function is the secretion of chlorides.[45]
+
+Digestion can take a long time. The food moves from the mouth to a J-shaped stomach, where it is stored and initial digestion occurs.[46] Unwanted items may never get past the stomach, and instead the shark either vomits or turns its stomachs inside out and ejects unwanted items from its mouth.[47]
+
+One of the biggest differences between the digestive systems of sharks and mammals is that sharks have much shorter intestines. This short length is achieved by the spiral valve with multiple turns within a single short section instead of a long tube-like intestine. The valve provides a long surface area, requiring food to circulate inside the short gut until fully digested, when remaining waste products pass into the cloaca.[46]
+
+Biofluorescence is a characteristic of a few shark species, such as the swell shark and the chain catshark, the mechanism of which is unique among marine animals and depends upon a small molecule metabolite.[48]
+
+Sharks have keen olfactory senses, located in the short duct (which is not fused, unlike bony fish) between the anterior and posterior nasal openings, with some species able to detect as little as one part per million of blood in seawater.[49]
+
+Sharks have the ability to determine the direction of a given scent based on the timing of scent detection in each nostril.[50] This is similar to the method mammals use to determine direction of sound.
+
+They are more attracted to the chemicals found in the intestines of many species, and as a result often linger near or in sewage outfalls. Some species, such as nurse sharks, have external barbels that greatly increase their ability to sense prey.
+
+Shark eyes are similar to the eyes of other vertebrates, including similar lenses, corneas and retinas, though their eyesight is well adapted to the marine environment with the help of a tissue called tapetum lucidum. This tissue is behind the retina and reflects light back to it, thereby increasing visibility in the dark waters. The effectiveness of the tissue varies, with some sharks having stronger nocturnal adaptations. Many sharks can contract and dilate their pupils, like humans, something no teleost fish can do. Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some species have nictitating membranes. This membrane covers the eyes while hunting and when the shark is being attacked. However, some species, including the great white shark (Carcharodon carcharias), do not have this membrane, but instead roll their eyes backwards to protect them when striking prey. The importance of sight in shark hunting behavior is debated. Some believe that electro- and chemoreception are more significant, while others point to the nictating membrane as evidence that sight is important. Presumably, the shark would not protect its eyes were they unimportant. The use of sight probably varies with species and water conditions. The shark's field of vision can swap between monocular and stereoscopic at any time.[51] A micro-spectrophotometry study of 17 species of shark found 10 had only rod photoreceptors and no cone cells in their retinas giving them good night vision while making them colorblind. The remaining seven species had in addition to rods a single type of cone photoreceptor sensitive to green and, seeing only in shades of grey and green, are believed to be effectively colorblind. The study indicates that an object's contrast against the background, rather than colour, may be more important for object detection.[52]
+[53][54]
+
+Although it is hard to test the hearing of sharks, they may have a sharp sense of hearing and can possibly hear prey from many miles away.[55] A small opening on each side of their heads (not the spiracle) leads directly into the inner ear through a thin channel. The lateral line shows a similar arrangement, and is open to the environment via a series of openings called lateral line pores. This is a reminder of the common origin of these two vibration- and sound-detecting organs that are grouped together as the acoustico-lateralis system. In bony fish and tetrapods the external opening into the inner ear has been lost.
+
+The ampullae of Lorenzini are the electroreceptor organs. They number in the hundreds to thousands. Sharks use the ampullae of Lorenzini to detect the electromagnetic fields that all living things produce.[56] This helps sharks (particularly the hammerhead shark) find prey. The shark has the greatest electrical sensitivity of any animal. Sharks find prey hidden in sand by detecting the electric fields they produce. Ocean currents moving in the magnetic field of the Earth also generate electric fields that sharks can use for orientation and possibly navigation.[57]
+
+This system is found in most fish, including sharks. It is a tactile sensory system which allows the organism to detect water speed and pressure changes near by.[58] The main component of the system is the neuromast, a cell similar to hair cells present in the vertebrate ear that interact with the surrounding aquatic environment. This helps sharks distinguish between the currents around them, obstacles off on their periphery, and struggling prey out of visual view. The shark can sense frequencies in the range of 25 to 50 Hz.[59]
+
+Shark lifespans vary by species. Most live 20 to 30 years. The spiny dogfish has one of the longest lifespans at more than 100 years.[60] Whale sharks (Rhincodon typus) may also live over 100 years.[61] Earlier estimates suggested the Greenland shark (Somniosus microcephalus) could reach about 200 years, but a recent study found that a 5.02-metre-long (16.5 ft) specimen was 392 ± 120 years old (i.e., at least 272 years old), making it the longest-lived vertebrate known.[62][63]
+
+Unlike most bony fish, sharks are K-selected reproducers, meaning that they produce a small number of well-developed young as opposed to a large number of poorly developed young. Fecundity in sharks ranges from 2 to over 100 young per reproductive cycle.[64] Sharks mature slowly relative to many other fish. For example, lemon sharks reach sexual maturity at around age 13–15.[65]
+
+Sharks practice internal fertilization.[66] The posterior part of a male shark's pelvic fins are modified into a pair of intromittent organs called claspers, analogous to a mammalian penis, of which one is used to deliver sperm into the female.[67]
+
+Mating has rarely been observed in sharks.[68] The smaller catsharks often mate with the male curling around the female. In less flexible species the two sharks swim parallel to each other while the male inserts a clasper into the female's oviduct. Females in many of the larger species have bite marks that appear to be a result of a male grasping them to maintain position during mating. The bite marks may also come from courtship behavior: the male may bite the female to show his interest. In some species, females have evolved thicker skin to withstand these bites.[67]
+
+There have been a number of documented cases in which a female shark who has not been in contact with a male has conceived a pup on her own through parthenogenesis.[69][70] The details of this process are not well understood, but genetic fingerprinting showed that the pups had no paternal genetic contribution, ruling out sperm storage. The extent of this behavior in the wild is unknown. Mammals are now the only major vertebrate group in which asexual reproduction has not been observed.
+
+Scientists say that asexual reproduction in the wild is rare, and probably a last-ditch effort to reproduce when a mate is not present. Asexual reproduction diminishes genetic diversity, which helps build defenses against threats to the species. Species that rely solely on it risk extinction. Asexual reproduction may have contributed to the blue shark's decline off the Irish coast.[71]
+
+Sharks display three ways to bear their young, varying by species, oviparity, viviparity and ovoviviparity.[72][73]
+
+Most sharks are ovoviviparous, meaning that the eggs hatch in the oviduct within the mother's body and that the egg's yolk and fluids secreted by glands in the walls of the oviduct nourishes the embryos. The young continue to be nourished by the remnants of the yolk and the oviduct's fluids. As in viviparity, the young are born alive and fully functional. Lamniforme sharks practice oophagy, where the first embryos to hatch eat the remaining eggs.  Taking this a step further,  sand tiger shark pups cannibalistically consume neighboring embryos.  The survival strategy for ovoviviparous species is to brood the young to a comparatively large size before birth. The whale shark is now classified as ovoviviparous rather than oviparous, because extrauterine eggs are now thought to have been aborted. Most ovoviviparous sharks give birth in sheltered areas, including bays, river mouths and shallow reefs. They choose such areas for protection from predators (mainly other sharks) and the abundance of food. Dogfish have the longest known gestation period of any shark, at 18 to 24 months. Basking sharks and frilled sharks appear to have even longer gestation periods, but accurate data are lacking.[72]
+
+Some species are oviparous, laying their fertilized eggs in the water. In most oviparous shark species, an egg case with the consistency of leather protects the developing embryo(s). These cases may be corkscrewed into crevices for protection. The egg case is commonly called a mermaid's purse. Oviparous sharks include the horn shark, catshark, Port Jackson shark, and swellshark.[72][74]
+
+Viviparity is the gestation of young without the use of a traditional egg, and results in live birth.[75] Viviparity in sharks can be placental or aplacental.[75] Young are born fully formed and self-sufficient.[75] Hammerheads, the requiem sharks (such as the bull and blue sharks), and smoothhounds are viviparous.[64][72]
+
+The classic view describes a solitary hunter, ranging the oceans in search of food. However, this applies to only a few species. Most live far more social, sedentary, benthic lives, and appear likely to have their own distinct personalities.[76] Even solitary sharks meet for breeding or at rich hunting grounds, which may lead them to cover thousands of miles in a year.[77] Shark migration patterns may be even more complex than in birds, with many sharks covering entire ocean basins.
+
+Sharks can be highly social, remaining in large schools. Sometimes more than 100 scalloped hammerheads congregate around seamounts and islands, e.g., in the Gulf of California.[35] Cross-species social hierarchies exist. For example, oceanic whitetip sharks dominate silky sharks of comparable size during feeding.[64]
+
+When approached too closely some sharks perform a threat display. This usually consists of exaggerated swimming movements, and can vary in intensity according to the threat level.[78]
+
+In general, sharks swim ("cruise") at an average speed of 8 kilometres per hour (5.0 mph), but when feeding or attacking, the average shark can reach speeds upwards of 19 kilometres per hour (12 mph). The shortfin mako shark, the fastest shark and one of the fastest fish, can burst at speeds up to 50 kilometres per hour (31 mph).[79] The great white shark is also capable of speed bursts. These exceptions may be due to the warm-blooded, or homeothermic, nature of these sharks' physiology. Sharks can travel 70 to 80 km in a day.[80]
+
+Sharks possess brain-to-body mass ratios that are similar to mammals and birds,[81] and have exhibited apparent curiosity and behavior resembling play in the wild.[82][83]
+
+There is evidence that juvenile lemon sharks can use observational learning in their investigation of novel objects in their environment.[84]
+
+All sharks need to keep water flowing over their gills in order for them to breathe; however, not all species need to be moving to do this. Those that are able to breathe while not swimming do so by using their spiracles to force water over their gills, thereby allowing them to extract oxygen from the water. It has been recorded that their eyes remain open while in this state and actively follow the movements of divers swimming around them[85] and as such they are not truly asleep.
+
+Species that do need to swim continuously to breathe go through a process known as sleep swimming, in which the shark is essentially unconscious. It is known from experiments conducted on the spiny dogfish that its spinal cord, rather than its brain, coordinates swimming, so spiny dogfish can continue to swim while sleeping, and this also may be the case in larger shark species.[85] In 2016 a great white shark was captured on video for the first time in a state researchers believed was sleep swimming.[86]
+
+Most sharks are carnivorous.[87] Basking sharks, whale sharks, and megamouth sharks have independently evolved different strategies for filter feeding plankton: basking sharks practice ram feeding, whale sharks use suction to take in plankton and small fishes, and megamouth sharks make suction feeding more efficient by using the luminescent tissue inside of their mouths to attract prey in the deep ocean. This type of feeding requires gill rakers—long, slender filaments that form a very efficient sieve—analogous to the baleen plates of the great whales. The shark traps the plankton in these filaments and swallows from time to time in huge mouthfuls. Teeth in these species are comparatively small because they are not needed for feeding.[87]
+
+Other highly specialized feeders include cookiecutter sharks, which feed on flesh sliced out of other larger fish and marine mammals. Cookiecutter teeth are enormous compared to the animal's size. The lower teeth are particularly sharp. Although they have never been observed feeding, they are believed to latch onto their prey and use their thick lips to make a seal, twisting their bodies to rip off flesh.[35]
+
+Some seabed–dwelling species are highly effective ambush predators. Angel sharks and wobbegongs use camouflage to lie in wait and suck prey into their mouths.[88] Many benthic sharks feed solely on crustaceans which they crush with their flat molariform teeth.
+
+Other sharks feed on squid or fish, which they swallow whole. The viper dogfish has teeth it can point outwards to strike and capture prey that it then swallows intact. The great white and other large predators either swallow small prey whole or take huge bites out of large animals. Thresher sharks use their long tails to stun shoaling fishes, and sawsharks either stir prey from the seabed or slash at swimming prey with their tooth-studded rostra.
+
+Many sharks, including the whitetip reef shark are cooperative feeders and hunt in packs to herd and capture elusive prey. These social sharks are often migratory, traveling huge distances around ocean basins in large schools. These migrations may be partly necessary to find new food sources.[89]
+
+Sharks are found in all seas. They generally do not live in fresh water, with a few exceptions such as the bull shark and the river shark which can swim both in seawater and freshwater.[90] Sharks are common down to depths of 2,000 metres (7,000 ft), and some live even deeper, but they are almost entirely absent below 3,000 metres (10,000 ft). The deepest confirmed report of a shark is a Portuguese dogfish at 3,700 metres (12,100 ft).[91]
+
+In 2006 the International Shark Attack File (ISAF) undertook an investigation into 96 alleged shark attacks, confirming 62 of them as unprovoked attacks and 16 as provoked attacks. The average number of fatalities worldwide per year between 2001 and 2006 from unprovoked shark attacks is 4.3.[92]
+
+Contrary to popular belief, only a few sharks are dangerous to humans. Out of more than 470 species, only four have been involved in a significant number of fatal, unprovoked attacks on humans: the great white, oceanic whitetip, tiger, and bull sharks.[93][94] These sharks are large, powerful predators, and may sometimes attack and kill people. Despite being responsible for attacks on humans they have all been filmed without using a protective cage.[95]
+
+The perception of sharks as dangerous animals has been popularized by publicity given to a few isolated unprovoked attacks, such as the Jersey Shore shark attacks of 1916, and through popular fictional works about shark attacks, such as the Jaws film series. Jaws author Peter Benchley, as well as Jaws director Steven Spielberg, later attempted to dispel the image of sharks as man-eating monsters.[96]
+
+To help avoid an unprovoked attack, humans should not wear jewelry or metal that is shiny and refrain from splashing around too much.[97]
+
+In general, sharks show little pattern of attacking humans specifically. Research indicates that when humans do become the object of a shark attack, it is possible that the shark has mistaken the human for species that are its normal prey, such as seals.[98][99]
+
+Until recently, only a few benthic species of shark, such as hornsharks, leopard sharks and catsharks, had survived in aquarium conditions for a year or more. This gave rise to the belief that sharks, as well as being difficult to capture and transport, were difficult to care for. More knowledge has led to more species (including the large pelagic sharks) living far longer in captivity, along with safer transportation techniques that have enabled long distance transportation.[100] The great white shark had never been successfully held in captivity for long periods of time until September 2004, when the Monterey Bay Aquarium successfully kept a young female for 198 days before releasing her.
+
+Most species are not suitable for home aquaria, and not every species sold by pet stores are appropriate. Some species can flourish in home saltwater aquaria.[101] Uninformed or unscrupulous dealers sometimes sell juvenile sharks like the nurse shark, which upon reaching adulthood is far too large for typical home aquaria.[101] Public aquaria generally do not accept donated specimens that have outgrown their housing. Some owners have been tempted to release them.[101] Species appropriate to home aquaria represent considerable spatial and financial investments as they generally approach adult lengths of 3 feet (90 cm) and can live up to 25 years.[101]
+
+Sharks figure prominently in Hawaiian mythology. Stories tell of men with shark jaws on their back who could change between shark and human form. A common theme was that a shark-man would warn beach-goers of sharks in the waters. The beach-goers would laugh and ignore the warnings and get eaten by the shark-man who warned them. Hawaiian mythology also includes many shark gods. Among a fishing people, the most popular of all aumakua, or deified ancestor guardians, are shark aumakua. Kamaku describes in detail how to offer a corpse to become a shark. The body transforms gradually until the kahuna can point the awe-struck family to the markings on the shark's body that correspond to the clothing in which the beloved's body had been wrapped. Such a shark aumakua becomes the family pet, receiving food, and driving fish into the family net and warding off danger. Like all aumakua it had evil uses such as helping kill enemies. The ruling chiefs typically forbade such sorcery. Many Native Hawaiian families claim such an aumakua, who is known by name to the whole community.[102]
+
+Kamohoali'i is the best known and revered of the shark gods, he was the older and favored brother of Pele,[103] and helped and journeyed with her to Hawaii. He was able to assume all human and fish forms. A summit cliff on the crater of Kilauea is one of his most sacred spots. At one point he had a heiau (temple or shrine) dedicated to him on every piece of land that jutted into the ocean on the island of Molokai. Kamohoali'i was an ancestral god, not a human who became a shark and banned the eating of humans after eating one herself.[104][105] In Fijian mythology, Dakuwaqa was a shark god who was the eater of lost souls.
+
+On the island of Tutuila in American Samoa (a U.S. territory), there is a location called Turtle and Shark (Laumei ma Malie) which is important in Samoan culture — the location is the site of a legend called O Le Tala I Le Laumei Ma Le Malie, in which two humans are said to have transformed into a turtle and a shark.[106][107][108] According to the U.S. National Park Service, "Villagers from nearby Vaitogi continue to reenact an important aspect of the legend at Turtle and Shark by performing a ritual song intended to summon the legendary animals to the ocean surface, and visitors are frequently amazed to see one or both of these creatures emerge from the sea in apparent response to this call."[106]
+
+In contrast to the complex portrayals by Hawaiians and other Pacific Islanders, the European and Western view of sharks has historically been mostly of fear and malevolence.[109] Sharks are used in popular culture commonly as eating machines, notably in the Jaws novel and the film of the same name, along with its sequels.[110] Sharks are threats in other films such as Deep Blue Sea, The Reef, and others, although they are sometimes used for comedic effect such as in Finding Nemo and the Austin Powers series. 
+Sharks tend to be seen quite often in cartoons whenever a scene involves the ocean. Such examples include the Tom and Jerry cartoons, Jabberjaw, and other shows produced by Hanna-Barbera. They also are used commonly as a clichéd means of killing off a character that is held up by a rope or some similar object as the sharks swim right below them, or the character may be standing on a plank above shark infested waters.[citation needed]
+
+A popular myth is that sharks are immune to disease and cancer, but this is not scientifically supported. Sharks have been known to get cancer.[111][112] Both diseases and parasites affect sharks. The evidence that sharks are at least resistant to cancer and disease is mostly anecdotal and there have been few, if any, scientific or statistical studies that show sharks to have heightened immunity to disease.[113]
+Other apparently false claims are that fins prevent cancer[114] and treat osteoarthritis.[115] No scientific proof supports these claims; at least one study has shown shark cartilage of no value in cancer treatment.[116]
+
+It is estimated that 100 million sharks are killed by people every year, due to commercial and recreational fishing.[117][118]
+
+Shark finning yields are estimated at 1.44 million metric tons for 2000, and 1.41 million tons for 2010. Based on an analysis of average shark weights, this translates into a total annual mortality estimate of about 100 million sharks in 2000, and about 97 million sharks in 2010, with a total range of possible values between 63 and 273 million sharks per year.[119][120] Sharks are a common seafood in many places, including Japan and Australia. In the Australian state of Victoria, shark is the most commonly used fish in fish and chips,[citation needed] in which fillets are battered and deep-fried or crumbed and grilled. In fish and chip shops, shark is called flake. In India, small sharks or baby sharks (called sora in Tamil language, Telugu language) are sold in local markets. Since the flesh is not developed, cooking the flesh breaks it into powder, which is then fried in oil and spices (called sora puttu/sora poratu). The soft bones can be easily chewed. They are considered a delicacy in coastal Tamil Nadu. Icelanders ferment Greenland sharks to produce a delicacy called hákarl.[121] During a four-year period from 1996 to 2000, an estimated 26 to 73 million sharks were killed and traded annually in commercial markets.[122]
+
+Sharks are often killed for shark fin soup. Fishermen capture live sharks, fin them, and dump the finless animal back into the water. Shark finning involves removing the fin with a hot metal blade.[118] The resulting immobile shark soon dies from suffocation or predators.[123] Shark fin has become a major trade within black markets all over the world. Fins sell for about $300/lb in 2009.[124] Poachers illegally fin millions each year. Few governments enforce laws that protect them.[120] In 2010 Hawaii became the first U.S. state to prohibit the possession, sale, trade or distribution of shark fins.[125] From 1996 to 2000, an estimated 38 million sharks had been killed per year for harvesting shark fins.[122] It is estimated by TRAFFIC that over 14,000 tonnes of shark fins were exported into Singapore between 2005–2007 and 2012–2014.[126]
+
+Shark fin soup is a status symbol in Asian countries and is erroneously considered healthy and full of nutrients. Scientific research has revealed, however, that high concentrations of BMAA are present in shark fins.[127] Because BMAA is a neurotoxin, consumption of shark fin soup and cartilage pills, therefore, may pose a health risk.[128] BMAA is under study for its pathological role in neurodegegerative diseases such as, ALS, Alzheimer's disease, and Parkinson's disease.
+
+Sharks are also killed for meat. European diners consume dogfishes, smoothhounds, catsharks, makos, porbeagle and also skates and rays.[129] However, the U.S. FDA lists sharks as one of four fish (with swordfish, king mackerel, and tilefish) whose high mercury content is hazardous to children and pregnant women.
+
+Sharks generally reach sexual maturity only after many years and produce few offspring in comparison to other harvested fish. Harvesting sharks before they reproduce severely impacts future populations. Capture induced premature birth and abortion (collectively called capture-induced parturition) occurs frequently in sharks/rays when fished.[66] Capture-induced parturition is rarely considered in fisheries management despite being shown to occur in at least 12% of live bearing sharks and rays (88 species to date).[66]
+
+The majority of shark fisheries have little monitoring or management. The rise in demand for shark products increases pressure on fisheries.[36] Major declines in shark stocks have been recorded—some species have been depleted by over 90% over the past 20–30 years with population declines of 70% not unusual.[130] A study by the International Union for Conservation of Nature suggests that one quarter of all known species of sharks and rays are threatened by extinction and 25 species were classified as critically endangered.[131][132]
+
+In 2014, a shark cull in Western Australia killed dozens of sharks (mostly tiger sharks) using drum lines,[133] until it was cancelled after public protests and a decision by the Western Australia EPA; from 2014 to 2017, there was an "imminent threat" policy in Western Australia in which sharks that "threatened" humans in the ocean were shot and killed.[134] This "imminent threat" policy was criticized by senator Rachel Siewart for killing endangered sharks.[135] The "imminent threat" policy was cancelled in March 2017.[136] In August 2018, the Western Australia government announced a plan to re-introduce drum lines (though, this time the drum lines are "SMART" drum lines).[137]
+
+From 1962 to the present,[138] the government of Queensland has targeted and killed sharks in large numbers by using drum lines, under a "shark control" program—this program has also inadvertently killed large numbers of other animals such as dolphins; it has also killed endangered hammerhead sharks.[139][140][141][142] Queensland's drum line program has been called "outdated, cruel and ineffective".[142] From 2001 to 2018, a total of 10,480 sharks were killed on lethal drum lines in Queensland, including in the Great Barrier Reef.[143] From 1962 to 2018, roughly 50,000 sharks were killed by Queensland authorities.[144]
+
+The government of New South Wales has a program that deliberately kills sharks using nets.[141][145] The current net program in New South Wales has been described as being "extremely destructive" to marine life, including sharks.[146] Between 1950 and 2008, 352 tiger sharks and 577 great white sharks were killed in the nets in New South Wales — also during this period, a total of 15,135 marine animals were killed in the nets, including dolphins, whales, turtles, dugongs, and critically endangered grey nurse sharks.[147] There has been a very large decrease in the number of sharks in eastern Australia, and the shark-killing programs in Queensland and New South Wales are partly responsible for this decrease.[144]
+
+Kwazulu-Natal, an area of South Africa, has a shark-killing program using nets and drum lines—these nets and drum lines have killed turtles and dolphins, and have been criticized for killing wildlife.[148] During a 30-year period, more than 33,000 sharks have been killed in KwaZulu-Natal's shark-killing program — during the same 30-year period, 2,211 turtles, 8,448 rays, and 2,310 dolphins were killed in KwaZulu-Natal.[148] Authorities on the French island of Réunion kill about 100 sharks per year.[149]
+
+Killing sharks negatively affects the marine ecosystem.[150][151] Jessica Morris of Humane Society International calls shark culling a "knee-jerk reaction" and says, "sharks are top order predators that play an important role in the functioning of marine ecosystems. We need them for healthy oceans."[152]
+
+George H. Burgess, the former[153] director of the International Shark Attack File, "describes [shark] culling as a form of revenge, satisfying a public demand for blood and little else";[154] he also said shark culling is a "retro-type move reminiscent of what people would have done in the 1940s and 50s, back when we didn't have an ecological conscience and before we knew the consequences of our actions."[154] Jane Williamson, an associate professor in marine ecology at Macquarie University, says "There is no scientific support for the concept that culling sharks in a particular area will lead to a decrease in shark attacks and increase ocean safety."[155]
+
+Other threats include habitat alteration, damage and loss from coastal development, pollution and the impact of fisheries on the seabed and prey species.[156] The 2007 documentary Sharkwater exposed how sharks are being hunted to extinction.[157]
+
+In 1991, South Africa was the first country in the world to declare Great White sharks a legally protected species[158] (however, the KwaZulu-Natal Sharks Board is allowed to kill great white sharks in its "shark control" program in eastern South Africa).[148]
+
+Intending to ban the practice of shark finning while at sea, the United States Congress passed the Shark Finning Prohibition Act in 2000.[159]  Two years later the Act saw its first legal challenge in United States v. Approximately 64,695 Pounds of Shark Fins.  In 2008 a Federal Appeals Court ruled that a loophole in the law allowed non-fishing vessels to purchase shark fins from fishing vessels while on the high seas.[160]  Seeking to close the loophole, the Shark Conservation Act was passed by Congress in December 2010, and it was signed into law in January 2011.[161][162]
+
+In 2003, the European Union introduced a general shark finning ban for all vessels of all nationalities in Union waters and for all vessels flying a flag of one of its member states.[163] This prohibition was amended in June 2013 to close remaining loopholes.[164]
+
+In 2009, the International Union for Conservation of Nature's IUCN Red List of Endangered Species named 64 species, one-third of all oceanic shark species, as being at risk of extinction due to fishing and shark finning.[165][166]
+
+In 2010, the Convention on International Trade in Endangered Species (CITES) rejected proposals from the United States and Palau that would have required countries to strictly regulate trade in several species of scalloped hammerhead, oceanic whitetip and spiny dogfish sharks. The majority, but not the required two-thirds of voting delegates, approved the proposal. China, by far the world's largest shark market, and Japan, which battles all attempts to extend the convention to marine species, led the opposition.[167][168] In March 2013, three endangered commercially valuable sharks, the hammerheads, the oceanic whitetip and porbeagle were added to Appendix 2 of CITES, bringing shark fishing and commerce of these species under licensing and regulation.[169]
+
+In 2010, Greenpeace International added the school shark, shortfin mako shark, mackerel shark, tiger shark and spiny dogfish to its seafood red list, a list of common supermarket fish that are often sourced from unsustainable fisheries.[170] Advocacy group Shark Trust campaigns to limit shark fishing. Advocacy group Seafood Watch directs American consumers to not eat sharks.[171]
+
+Under the auspices of the Convention on the Conservation of Migratory Species of Wild Animals (CMS), also known as the Bonn Convention, the Memorandum of Understanding on the Conservation of Migratory Sharks was concluded and came into effect in March 2010. It was the first global instrument concluded under CMS and aims at facilitating international coordination for the protection, conservation and management of migratory sharks, through multilateral, intergovernmental discussion and scientific research.
+
+In July 2013, New York state, a major market and entry point for shark fins, banned the shark fin trade joining
+seven other states of the United States and the three Pacific U.S territories in providing legal protection to sharks.[172]
+
+In the United States, and as of January 16, 2019, 12 states including (Massachusetts, Maryland, Delaware, California, Illinois, Hawaii, Oregon, Nevada, Rhode Island, Washington, New York and Texas) along with 3 U.S. territories (American Samoa, Guam and the Northern Mariana Islands) have passed laws against the sale or possession of shark fins.[173][174]
+
+Several regions now have shark sanctuaries or have banned shark fishing — these regions include American Samoa, the Bahamas, the Cook Islands, French Polynesia, Guam, the Maldives, the Marshall Islands, Micronesia, the Northern Mariana Islands, and Palau.[175][176]
+