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Amy Hawkins and Jeffrey Wasserstrom of The Atlantic stated in 2019 that the book is widely available in Mainland China for several reasons: censors believe the general public is unlikely to read a highbrow book , because the elites who do read books feel connected to the ruling party anyway, and because the Communist Party sees being too aggressive in blocking cultural products as a liability. The authors stated "It was—and remains—as easy to buy 1984 and Animal Farm in Shenzhen or Shanghai as it is in London or Los Angeles." An enhanced version of the book, launched in India in 2017, was widely praised for capturing the author's intent, by republishing the proposed preface of the First Edition and the preface he wrote for the Ukrainian edition. Analysis Animalism The pigs Snowball, Napoleon, and Squealer adapt Old Major's ideas into "a complete system of thought", which they formally name Animalism, an allegoric reference to Communism, not to be confused with the philosophy Animalism. Soon after, Napoleon and Squealer partake in activities associated with the humans (drinking alcohol, sleeping in beds, trading), which were explicitly prohibited by the Seven Commandments. Squealer is employed to alter the Seven Commandments to account for this humanisation, an allusion to the Soviet government's revising of history in order to exercise control of the people's beliefs about themselves and their society. The original commandments are: Whatever goes upon two legs is an enemy. Whatever goes upon four legs, or has wings, is a friend. No animal shall wear clothes. No animal shall sleep in a bed. No animal shall drink alcohol. No animal shall kill any other animal. All animals are equal. These commandments are also distilled into the maxim "Four legs good, two legs bad!" which is primarily used by the sheep on the farm, often to disrupt discussions and disagreements between animals on the nature of Animalism. Later, Napoleon and his pigs secretly revise some commandments to clear themselves of accusations of law-breaking. The changed commandments are as follows, with the changes bolded: Eventually, these are replaced with the maxims, "All animals are equal, but some animals are more equal than others", and "Four legs good, two legs better" as the pigs become more human. This is an ironic twist to the original purpose of the Seven Commandments, which were supposed to keep order within Animal Farm by uniting the animals together against the humans and preventing animals from following the humans' evil habits. Through the revision of the commandments, Orwell demonstrates how simply political dogma can be turned into malleable propaganda. Significance and allegory Orwell biographer Jeffrey Meyers has written, "virtually every detail has political significance in this allegory." Orwell himself wrote in 1946, "Of course I intended it primarily as a satire on the Russian revolution ... [and] that kind of revolution (violent conspiratorial revolution, led by unconsciously power-hungry people) can only lead to a change of masters [-] revolutions only effect a radical improvement when the masses are alert."

Amy Hawkins and Jeffrey Wasserstrom of The Atlantic stated in 2019 that the book is widely available in Mainland China for several reasons: censors believe the general public is unlikely to read a highbrow book , because the elites who do read books feel connected to the ruling party anyway, and because the Communist Party sees being too aggressive in blocking cultural products as a liability. The authors stated "It was—and remains—as easy to buy 1984 and Animal Farm in Shenzhen or Shanghai as it is in London or Los Angeles." An enhanced version of the book, launched in India in 2017, was widely praised for capturing the author's intent, by republishing the proposed preface of the First Edition and the preface he wrote for the Ukrainian edition. Analysis Animalism The pigs Snowball, Napoleon, and Squealer adapt Old Major's ideas into "a complete system of thought", which they formally name Animalism, an allegoric reference to Communism, not to be confused with the philosophy Animalism. Soon after, Napoleon and Squealer partake in activities associated with the humans (drinking alcohol, sleeping in beds, trading), which were explicitly prohibited by the Seven Commandments. Squealer is employed to alter the Seven Commandments to account for this humanisation, an allusion to the Soviet government's revising of history in order to exercise control of the people's beliefs about themselves and their society. The original commandments are: Whatever goes upon two legs is an enemy. Whatever goes upon four legs, or has wings, is a friend. No animal shall wear clothes. No animal shall sleep in a bed. No animal shall drink alcohol. No animal shall kill any other animal. All animals are equal. These commandments are also distilled into the maxim "Four legs good, two legs bad!" which is primarily used by the sheep on the farm, often to disrupt discussions and disagreements between animals on the nature of Animalism. Later, Napoleon and his pigs secretly revise some commandments to clear themselves of accusations of law-breaking. The changed commandments are as follows, with the changes bolded: Eventually, these are replaced with the maxims, "All animals are equal, but some animals are more equal than others", and "Four legs good, two legs better" as the pigs become more human. This is an ironic twist to the original purpose of the Seven Commandments, which were supposed to keep order within Animal Farm by uniting the animals together against the humans and preventing animals from following the humans' evil habits. Through the revision of the commandments, Orwell demonstrates how simply political dogma can be turned into malleable propaganda. Significance and allegory Orwell biographer Jeffrey Meyers has written, "virtually every detail has political significance in this allegory." Orwell himself wrote in 1946, "Of course I intended it primarily as a satire on the Russian revolution ... [and] that kind of revolution (violent conspiratorial revolution, led by unconsciously power-hungry people) can only lead to a change of masters [-] revolutions only effect a radical improvement when the masses are alert."

In a preface for a 1947 Ukrainian edition, he stated, "for the past ten years I have been convinced that the destruction of the Soviet myth was essential if we wanted a revival of the socialist movement. On my return from Spain [in 1937] I thought of exposing the Soviet myth in a story that could be easily understood by almost anyone and which could be easily translated into other languages." The revolt of the animals against Farmer Jones is Orwell's analogy with the October 1917 Bolshevik Revolution. The Battle of the Cowshed has been said to represent the allied invasion of Soviet Russia in 1918, and the defeat of the White Russians in the Russian Civil War. The pigs' rise to preeminence mirrors the rise of a Stalinist bureaucracy in the USSR, just as Napoleon's emergence as the farm's sole leader reflects Stalin's emergence. The pigs' appropriation of milk and apples for their own use, "the turning point of the story" as Orwell termed it in a letter to Dwight Macdonald, stands as an analogy for the crushing of the left-wing 1921 Kronstadt revolt against the Bolsheviks, and the difficult efforts of the animals to build the windmill suggest the various Five Year Plans. The puppies controlled by Napoleon parallel the nurture of the secret police in the Stalinist structure, and the pigs' treatment of the other animals on the farm recalls the internal terror faced by the populace in the 1930s. In chapter seven, when the animals confess their non-existent crimes and are killed, Orwell directly alludes to the purges, confessions and show trials of the late 1930s. These contributed to Orwell's conviction that the Bolshevik revolution had been corrupted and the Soviet system become rotten. Peter Edgerly Firchow and Peter Davison contend that the Battle of the Windmill, specifically referencing the Battle of Stalingrad and the Battle of Moscow, represents World War II. During the battle, Orwell first wrote, "All the animals, including Napoleon" took cover. Orwell had the publisher alter this to "All the animals except Napoleon" in recognition of Stalin's decision to remain in Moscow during the German advance. Orwell requested the change after he met Józef Czapski in Paris in March 1945. Czapski, a survivor of the Katyn Massacre and an opponent of the Soviet regime, told Orwell, as Orwell wrote to Arthur Koestler, that it had been "the character [and] greatness of Stalin" that saved Russia from the German invasion.

In a preface for a 1947 Ukrainian edition, he stated, "for the past ten years I have been convinced that the destruction of the Soviet myth was essential if we wanted a revival of the socialist movement. On my return from Spain [in 1937] I thought of exposing the Soviet myth in a story that could be easily understood by almost anyone and which could be easily translated into other languages." The revolt of the animals against Farmer Jones is Orwell's analogy with the October 1917 Bolshevik Revolution. The Battle of the Cowshed has been said to represent the allied invasion of Soviet Russia in 1918, and the defeat of the White Russians in the Russian Civil War. The pigs' rise to preeminence mirrors the rise of a Stalinist bureaucracy in the USSR, just as Napoleon's emergence as the farm's sole leader reflects Stalin's emergence. The pigs' appropriation of milk and apples for their own use, "the turning point of the story" as Orwell termed it in a letter to Dwight Macdonald, stands as an analogy for the crushing of the left-wing 1921 Kronstadt revolt against the Bolsheviks, and the difficult efforts of the animals to build the windmill suggest the various Five Year Plans. The puppies controlled by Napoleon parallel the nurture of the secret police in the Stalinist structure, and the pigs' treatment of the other animals on the farm recalls the internal terror faced by the populace in the 1930s. In chapter seven, when the animals confess their non-existent crimes and are killed, Orwell directly alludes to the purges, confessions and show trials of the late 1930s. These contributed to Orwell's conviction that the Bolshevik revolution had been corrupted and the Soviet system become rotten. Peter Edgerly Firchow and Peter Davison contend that the Battle of the Windmill, specifically referencing the Battle of Stalingrad and the Battle of Moscow, represents World War II. During the battle, Orwell first wrote, "All the animals, including Napoleon" took cover. Orwell had the publisher alter this to "All the animals except Napoleon" in recognition of Stalin's decision to remain in Moscow during the German advance. Orwell requested the change after he met Józef Czapski in Paris in March 1945. Czapski, a survivor of the Katyn Massacre and an opponent of the Soviet regime, told Orwell, as Orwell wrote to Arthur Koestler, that it had been "the character [and] greatness of Stalin" that saved Russia from the German invasion.

In a preface for a 1947 Ukrainian edition, he stated, "for the past ten years I have been convinced that the destruction of the Soviet myth was essential if we wanted a revival of the socialist movement. On my return from Spain [in 1937] I thought of exposing the Soviet myth in a story that could be easily understood by almost anyone and which could be easily translated into other languages." The revolt of the animals against Farmer Jones is Orwell's analogy with the October 1917 Bolshevik Revolution. The Battle of the Cowshed has been said to represent the allied invasion of Soviet Russia in 1918, and the defeat of the White Russians in the Russian Civil War. The pigs' rise to preeminence mirrors the rise of a Stalinist bureaucracy in the USSR, just as Napoleon's emergence as the farm's sole leader reflects Stalin's emergence. The pigs' appropriation of milk and apples for their own use, "the turning point of the story" as Orwell termed it in a letter to Dwight Macdonald, stands as an analogy for the crushing of the left-wing 1921 Kronstadt revolt against the Bolsheviks, and the difficult efforts of the animals to build the windmill suggest the various Five Year Plans. The puppies controlled by Napoleon parallel the nurture of the secret police in the Stalinist structure, and the pigs' treatment of the other animals on the farm recalls the internal terror faced by the populace in the 1930s. In chapter seven, when the animals confess their non-existent crimes and are killed, Orwell directly alludes to the purges, confessions and show trials of the late 1930s. These contributed to Orwell's conviction that the Bolshevik revolution had been corrupted and the Soviet system become rotten. Peter Edgerly Firchow and Peter Davison contend that the Battle of the Windmill, specifically referencing the Battle of Stalingrad and the Battle of Moscow, represents World War II. During the battle, Orwell first wrote, "All the animals, including Napoleon" took cover. Orwell had the publisher alter this to "All the animals except Napoleon" in recognition of Stalin's decision to remain in Moscow during the German advance. Orwell requested the change after he met Józef Czapski in Paris in March 1945. Czapski, a survivor of the Katyn Massacre and an opponent of the Soviet regime, told Orwell, as Orwell wrote to Arthur Koestler, that it had been "the character [and] greatness of Stalin" that saved Russia from the German invasion.

Other connections that writers have suggested illustrate Orwell's telescoping of Russian history from 1917 to 1943 include the wave of rebelliousness that ran through the countryside after the Rebellion, which stands for the abortive revolutions in Hungary and in Germany (Ch IV); the conflict between Napoleon and Snowball (Ch V), parallelling "the two rival and quasi-Messianic beliefs that seemed pitted against one another: Trotskyism, with its faith in the revolutionary vocation of the proletariat of the West; and Stalinism with its glorification of Russia's socialist destiny"; Napoleon's dealings with Whymper and the Willingdon markets (Ch VI), paralleling the Treaty of Rapallo; and Frederick's forged bank notes, parallelling the Hitler-Stalin pact of August 1939, after which Frederick attacks Animal Farm without warning and destroys the windmill. The book's close, with the pigs and men in a kind of rapprochement, reflected Orwell's view of the 1943 Tehran Conference that seemed to display the establishment of "the best possible relations between the USSR and the West" – but in reality were destined, as Orwell presciently predicted, to continue to unravel. The disagreement between the allies and the start of the Cold War is suggested when Napoleon and Pilkington, both suspicious, each "played an ace of spades simultaneously". Similarly, the music in the novel, starting with "Beasts of England" and the later anthems, parallels "The Internationale" and its adoption and repudiation by the Soviet authorities as the anthem of the USSR in the 1920s and 1930s. Adaptations Stage productions In 2021, the National Youth Theatre toured a stage version of Animal Farm. A solo version, adapted and performed by Guy Masterson, premièred at the Traverse Theatre Edinburgh in January 1995 and has toured worldwide since. A theatrical version, with music by Richard Peaslee and lyrics by Adrian Mitchell, was staged at the National Theatre London on 25 April 1984, directed by Peter Hall. It toured nine cities in 1985. A new adaptation written and directed by Robert Icke, designed by Bunny Christie with puppetry designed and directed by Toby Olié opened at the Birmingham Repertory Theatre in January 2022 before touring the UK. Films Animal Farm has been adapted to film twice. Both differ from the novel and have been accused of taking significant liberties, including sanitising some aspects. Animal Farm (1954) is an animated film, in which Napoleon is eventually overthrown in a second revolution. In 1974, E. Howard Hunt revealed that he had been sent by the CIA's Psychological Warfare department to obtain the film rights from Orwell's widow, and the resulting 1954 animation was funded by the agency. Animal Farm (1999) is a live-action TV version that shows Napoleon's regime collapsing in on itself, with the farm having new human owners, reflecting the collapse of Soviet communism. Andy Serkis is directing a film adaptation for Netflix, with Matt Reeves producing. Serkis began work on the film after finishing directing duties for Venom: Let There Be Carnage. Radio dramatisations A BBC radio version, produced by Rayner Heppenstall, was broadcast in January 1947.

Other connections that writers have suggested illustrate Orwell's telescoping of Russian history from 1917 to 1943 include the wave of rebelliousness that ran through the countryside after the Rebellion, which stands for the abortive revolutions in Hungary and in Germany (Ch IV); the conflict between Napoleon and Snowball (Ch V), parallelling "the two rival and quasi-Messianic beliefs that seemed pitted against one another: Trotskyism, with its faith in the revolutionary vocation of the proletariat of the West; and Stalinism with its glorification of Russia's socialist destiny"; Napoleon's dealings with Whymper and the Willingdon markets (Ch VI), paralleling the Treaty of Rapallo; and Frederick's forged bank notes, parallelling the Hitler-Stalin pact of August 1939, after which Frederick attacks Animal Farm without warning and destroys the windmill. The book's close, with the pigs and men in a kind of rapprochement, reflected Orwell's view of the 1943 Tehran Conference that seemed to display the establishment of "the best possible relations between the USSR and the West" – but in reality were destined, as Orwell presciently predicted, to continue to unravel. The disagreement between the allies and the start of the Cold War is suggested when Napoleon and Pilkington, both suspicious, each "played an ace of spades simultaneously". Similarly, the music in the novel, starting with "Beasts of England" and the later anthems, parallels "The Internationale" and its adoption and repudiation by the Soviet authorities as the anthem of the USSR in the 1920s and 1930s. Adaptations Stage productions In 2021, the National Youth Theatre toured a stage version of Animal Farm. A solo version, adapted and performed by Guy Masterson, premièred at the Traverse Theatre Edinburgh in January 1995 and has toured worldwide since. A theatrical version, with music by Richard Peaslee and lyrics by Adrian Mitchell, was staged at the National Theatre London on 25 April 1984, directed by Peter Hall. It toured nine cities in 1985. A new adaptation written and directed by Robert Icke, designed by Bunny Christie with puppetry designed and directed by Toby Olié opened at the Birmingham Repertory Theatre in January 2022 before touring the UK. Films Animal Farm has been adapted to film twice. Both differ from the novel and have been accused of taking significant liberties, including sanitising some aspects. Animal Farm (1954) is an animated film, in which Napoleon is eventually overthrown in a second revolution. In 1974, E. Howard Hunt revealed that he had been sent by the CIA's Psychological Warfare department to obtain the film rights from Orwell's widow, and the resulting 1954 animation was funded by the agency. Animal Farm (1999) is a live-action TV version that shows Napoleon's regime collapsing in on itself, with the farm having new human owners, reflecting the collapse of Soviet communism. Andy Serkis is directing a film adaptation for Netflix, with Matt Reeves producing. Serkis began work on the film after finishing directing duties for Venom: Let There Be Carnage. Radio dramatisations A BBC radio version, produced by Rayner Heppenstall, was broadcast in January 1947.

Other connections that writers have suggested illustrate Orwell's telescoping of Russian history from 1917 to 1943 include the wave of rebelliousness that ran through the countryside after the Rebellion, which stands for the abortive revolutions in Hungary and in Germany (Ch IV); the conflict between Napoleon and Snowball (Ch V), parallelling "the two rival and quasi-Messianic beliefs that seemed pitted against one another: Trotskyism, with its faith in the revolutionary vocation of the proletariat of the West; and Stalinism with its glorification of Russia's socialist destiny"; Napoleon's dealings with Whymper and the Willingdon markets (Ch VI), paralleling the Treaty of Rapallo; and Frederick's forged bank notes, parallelling the Hitler-Stalin pact of August 1939, after which Frederick attacks Animal Farm without warning and destroys the windmill. The book's close, with the pigs and men in a kind of rapprochement, reflected Orwell's view of the 1943 Tehran Conference that seemed to display the establishment of "the best possible relations between the USSR and the West" – but in reality were destined, as Orwell presciently predicted, to continue to unravel. The disagreement between the allies and the start of the Cold War is suggested when Napoleon and Pilkington, both suspicious, each "played an ace of spades simultaneously". Similarly, the music in the novel, starting with "Beasts of England" and the later anthems, parallels "The Internationale" and its adoption and repudiation by the Soviet authorities as the anthem of the USSR in the 1920s and 1930s. Adaptations Stage productions In 2021, the National Youth Theatre toured a stage version of Animal Farm. A solo version, adapted and performed by Guy Masterson, premièred at the Traverse Theatre Edinburgh in January 1995 and has toured worldwide since. A theatrical version, with music by Richard Peaslee and lyrics by Adrian Mitchell, was staged at the National Theatre London on 25 April 1984, directed by Peter Hall. It toured nine cities in 1985. A new adaptation written and directed by Robert Icke, designed by Bunny Christie with puppetry designed and directed by Toby Olié opened at the Birmingham Repertory Theatre in January 2022 before touring the UK. Films Animal Farm has been adapted to film twice. Both differ from the novel and have been accused of taking significant liberties, including sanitising some aspects. Animal Farm (1954) is an animated film, in which Napoleon is eventually overthrown in a second revolution. In 1974, E. Howard Hunt revealed that he had been sent by the CIA's Psychological Warfare department to obtain the film rights from Orwell's widow, and the resulting 1954 animation was funded by the agency. Animal Farm (1999) is a live-action TV version that shows Napoleon's regime collapsing in on itself, with the farm having new human owners, reflecting the collapse of Soviet communism. Andy Serkis is directing a film adaptation for Netflix, with Matt Reeves producing. Serkis began work on the film after finishing directing duties for Venom: Let There Be Carnage. Radio dramatisations A BBC radio version, produced by Rayner Heppenstall, was broadcast in January 1947.

Orwell listened to the production at his home in Canonbury Square, London, with Hugh Gordon Porteous, amongst others. Orwell later wrote to Heppenstall that Porteous, "who had not read the book, grasped what was happening after a few minutes." A further radio production, again using Orwell's own dramatisation of the book, was broadcast in January 2013 on BBC Radio 4. Tamsin Greig narrated, and the cast included Nicky Henson as Napoleon, Toby Jones as the propagandist Squealer, and Ralph Ineson as Boxer. Comic strip In 1950, Norman Pett and his writing partner Don Freeman were secretly hired by the Information Research Department (IRD), a secret wing of the British Foreign Office, to adapt Animal Farm into a comic strip. This comic was not published in the U.K. but ran in Brazilian and Burmese newspapers. See also Information Research Department Authoritarian personality History of Soviet Russia and the Soviet Union (1917–1927) History of the Soviet Union (1927–1953) Ideocracy New class Anthems in Animal Farm Animals, an album based on Animal Farm Books Gulliver's Travels was a favourite book of Orwell's. Swift reverses the role of horses and human beings in the fourth book. Orwell brought to Animal Farm "a dose of Swiftian misanthropy, looking ahead to a time 'when the human race had finally been overthrown.'" Bunt (Revolt), published in 1924, is a book by Polish Nobel laureate Władysław Reymont with a theme similar to Animal Farms. White Acre vs. Black Acre, published in 1856 and written by William M. Burwell, is a satirical novel that features allegories for slavery in the United States similar to Animal Farms portrayal of Soviet history. George Orwell's own Nineteen Eighty-Four, a classic dystopian novel about totalitarianism. References Explanatory notes Citations General sources Further reading O'Neill, Terry, Readings on Animal Farm (1998), Greenhaven Press. . External links Animal Farm Book Notes from Literapedia Excerpts from Orwell's letters to his agent concerning Animal Farm Literary Journal review Orwell's original preface to the book Animal Farm Revisited by John Molyneux, International Socialism, 44 (1989) Animal Farm at the British Library Animal Farm (1954) 1945 British novels Allegory British novellas British novels adapted into films British novels adapted into plays British novels adapted into television shows British political novels British satirical novels Cats in literature Cattle in literature Censored books Dogs in literature Dystopian novels English novels Hugo Award for Best Novella winning works Novels about animals Novels about propaganda Novels about revolutionaries Novels about totalitarianism Novels adapted into comics Novels adapted into radio programs Novels by George Orwell Pigs in literature Political literature Roman à clef novels Satirical novels Secker & Warburg books

Orwell listened to the production at his home in Canonbury Square, London, with Hugh Gordon Porteous, amongst others. Orwell later wrote to Heppenstall that Porteous, "who had not read the book, grasped what was happening after a few minutes." A further radio production, again using Orwell's own dramatisation of the book, was broadcast in January 2013 on BBC Radio 4. Tamsin Greig narrated, and the cast included Nicky Henson as Napoleon, Toby Jones as the propagandist Squealer, and Ralph Ineson as Boxer. Comic strip In 1950, Norman Pett and his writing partner Don Freeman were secretly hired by the Information Research Department (IRD), a secret wing of the British Foreign Office, to adapt Animal Farm into a comic strip. This comic was not published in the U.K. but ran in Brazilian and Burmese newspapers. See also Information Research Department Authoritarian personality History of Soviet Russia and the Soviet Union (1917–1927) History of the Soviet Union (1927–1953) Ideocracy New class Anthems in Animal Farm Animals, an album based on Animal Farm Books Gulliver's Travels was a favourite book of Orwell's. Swift reverses the role of horses and human beings in the fourth book. Orwell brought to Animal Farm "a dose of Swiftian misanthropy, looking ahead to a time 'when the human race had finally been overthrown.'" Bunt (Revolt), published in 1924, is a book by Polish Nobel laureate Władysław Reymont with a theme similar to Animal Farms. White Acre vs. Black Acre, published in 1856 and written by William M. Burwell, is a satirical novel that features allegories for slavery in the United States similar to Animal Farms portrayal of Soviet history. George Orwell's own Nineteen Eighty-Four, a classic dystopian novel about totalitarianism. References Explanatory notes Citations General sources Further reading O'Neill, Terry, Readings on Animal Farm (1998), Greenhaven Press. . External links Animal Farm Book Notes from Literapedia Excerpts from Orwell's letters to his agent concerning Animal Farm Literary Journal review Orwell's original preface to the book Animal Farm Revisited by John Molyneux, International Socialism, 44 (1989) Animal Farm at the British Library Animal Farm (1954) 1945 British novels Allegory British novellas British novels adapted into films British novels adapted into plays British novels adapted into television shows British political novels British satirical novels Cats in literature Cattle in literature Censored books Dogs in literature Dystopian novels English novels Hugo Award for Best Novella winning works Novels about animals Novels about propaganda Novels about revolutionaries Novels about totalitarianism Novels adapted into comics Novels adapted into radio programs Novels by George Orwell Pigs in literature Political literature Roman à clef novels Satirical novels Secker & Warburg books

Orwell listened to the production at his home in Canonbury Square, London, with Hugh Gordon Porteous, amongst others. Orwell later wrote to Heppenstall that Porteous, "who had not read the book, grasped what was happening after a few minutes." A further radio production, again using Orwell's own dramatisation of the book, was broadcast in January 2013 on BBC Radio 4. Tamsin Greig narrated, and the cast included Nicky Henson as Napoleon, Toby Jones as the propagandist Squealer, and Ralph Ineson as Boxer. Comic strip In 1950, Norman Pett and his writing partner Don Freeman were secretly hired by the Information Research Department (IRD), a secret wing of the British Foreign Office, to adapt Animal Farm into a comic strip. This comic was not published in the U.K. but ran in Brazilian and Burmese newspapers. See also Information Research Department Authoritarian personality History of Soviet Russia and the Soviet Union (1917–1927) History of the Soviet Union (1927–1953) Ideocracy New class Anthems in Animal Farm Animals, an album based on Animal Farm Books Gulliver's Travels was a favourite book of Orwell's. Swift reverses the role of horses and human beings in the fourth book. Orwell brought to Animal Farm "a dose of Swiftian misanthropy, looking ahead to a time 'when the human race had finally been overthrown.'" Bunt (Revolt), published in 1924, is a book by Polish Nobel laureate Władysław Reymont with a theme similar to Animal Farms. White Acre vs. Black Acre, published in 1856 and written by William M. Burwell, is a satirical novel that features allegories for slavery in the United States similar to Animal Farms portrayal of Soviet history. George Orwell's own Nineteen Eighty-Four, a classic dystopian novel about totalitarianism. References Explanatory notes Citations General sources Further reading O'Neill, Terry, Readings on Animal Farm (1998), Greenhaven Press. . External links Animal Farm Book Notes from Literapedia Excerpts from Orwell's letters to his agent concerning Animal Farm Literary Journal review Orwell's original preface to the book Animal Farm Revisited by John Molyneux, International Socialism, 44 (1989) Animal Farm at the British Library Animal Farm (1954) 1945 British novels Allegory British novellas British novels adapted into films British novels adapted into plays British novels adapted into television shows British political novels British satirical novels Cats in literature Cattle in literature Censored books Dogs in literature Dystopian novels English novels Hugo Award for Best Novella winning works Novels about animals Novels about propaganda Novels about revolutionaries Novels about totalitarianism Novels adapted into comics Novels adapted into radio programs Novels by George Orwell Pigs in literature Political literature Roman à clef novels Satirical novels Secker & Warburg books

Amphibian Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Thus amphibians typically start out as larvae living in water, but some species have developed behavioural adaptations to bypass this. The young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a secondary respiratory surface and some small terrestrial salamanders and frogs lack lungs and rely entirely on their skin. They are superficially similar to lizards but, along with mammals and birds, reptiles are amniotes and do not require water bodies in which to breed. With their complex reproductive needs and permeable skins, amphibians are often ecological indicators; in recent decades there has been a dramatic decline in amphibian populations for many species around the globe. The earliest amphibians ("crown") evolved in the Carboniferous period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. They diversified and became dominant during the Carboniferous and Permian periods, but were later displaced by reptiles and other vertebrates. Over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia. The three modern orders of amphibians are Anura (the frogs), Urodela (the salamanders), and Apoda (the caecilians). The number of known amphibian species is approximately 8,000, of which nearly 90% are frogs. The smallest amphibian (and vertebrate) in the world is a frog from New Guinea (Paedophryne amauensis) with a length of just . The largest living amphibian is the South China giant salamander (Andrias sligoi), but this is dwarfed by the extinct Prionosuchus from the middle Permian of Brazil. The study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology. Classification The word amphibian is derived from the Ancient Greek term (), which means 'both kinds of life', meaning 'of both kinds' and meaning 'life'. The term was initially used as a general adjective for animals that could live on land or in water, including seals and otters. Traditionally, the class Amphibia includes all tetrapod vertebrates that are not amniotes. Amphibia in its widest sense () was divided into three subclasses, two of which are extinct: Subclass Lepospondyli† (small Paleozoic group, which are more closely related to amniotes than Lissamphibia) Subclass Temnospondyli† (diverse Paleozoic and early Mesozoic grade) Subclass Lissamphibia (all modern amphibians, including frogs, toads, salamanders, newts and caecilians) Salientia (frogs, toads and relatives): Jurassic to present—7,360 current species in 53 families Caudata (salamanders, newts and relatives): Jurassic to present—764 current species in 9 families Gymnophiona (caecilians and relatives): Jurassic to present—215 current species in 10 families Allocaudata† (Albanerpetontidae) Middle Jurassic - Early Pleistocene The actual number of species in each group depends on the taxonomic classification followed.

Amphibian Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Thus amphibians typically start out as larvae living in water, but some species have developed behavioural adaptations to bypass this. The young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a secondary respiratory surface and some small terrestrial salamanders and frogs lack lungs and rely entirely on their skin. They are superficially similar to lizards but, along with mammals and birds, reptiles are amniotes and do not require water bodies in which to breed. With their complex reproductive needs and permeable skins, amphibians are often ecological indicators; in recent decades there has been a dramatic decline in amphibian populations for many species around the globe. The earliest amphibians ("crown") evolved in the Carboniferous period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. They diversified and became dominant during the Carboniferous and Permian periods, but were later displaced by reptiles and other vertebrates. Over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia. The three modern orders of amphibians are Anura (the frogs), Urodela (the salamanders), and Apoda (the caecilians). The number of known amphibian species is approximately 8,000, of which nearly 90% are frogs. The smallest amphibian (and vertebrate) in the world is a frog from New Guinea (Paedophryne amauensis) with a length of just . The largest living amphibian is the South China giant salamander (Andrias sligoi), but this is dwarfed by the extinct Prionosuchus from the middle Permian of Brazil. The study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology. Classification The word amphibian is derived from the Ancient Greek term (), which means 'both kinds of life', meaning 'of both kinds' and meaning 'life'. The term was initially used as a general adjective for animals that could live on land or in water, including seals and otters. Traditionally, the class Amphibia includes all tetrapod vertebrates that are not amniotes. Amphibia in its widest sense () was divided into three subclasses, two of which are extinct: Subclass Lepospondyli† (small Paleozoic group, which are more closely related to amniotes than Lissamphibia) Subclass Temnospondyli† (diverse Paleozoic and early Mesozoic grade) Subclass Lissamphibia (all modern amphibians, including frogs, toads, salamanders, newts and caecilians) Salientia (frogs, toads and relatives): Jurassic to present—7,360 current species in 53 families Caudata (salamanders, newts and relatives): Jurassic to present—764 current species in 9 families Gymnophiona (caecilians and relatives): Jurassic to present—215 current species in 10 families Allocaudata† (Albanerpetontidae) Middle Jurassic - Early Pleistocene The actual number of species in each group depends on the taxonomic classification followed.

The two most common systems are the classification adopted by the website AmphibiaWeb, University of California, Berkeley and the classification by herpetologist Darrel Frost and the American Museum of Natural History, available as the online reference database "Amphibian Species of the World". The numbers of species cited above follows Frost and the total number of known amphibian species as of March 31, 2019 is exactly 8,000, of which nearly 90% are frogs. With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a polyparaphyletic group without unique defining features apart from shared primitive characteristics. Classification varies according to the preferred phylogeny of the author and whether they use a stem-based or a node-based classification. Traditionally, amphibians as a class are defined as all tetrapods with a larval stage, while the group that includes the common ancestors of all living amphibians (frogs, salamanders and caecilians) and all their descendants is called Lissamphibia. The phylogeny of Paleozoic amphibians is uncertain, and Lissamphibia may possibly fall within extinct groups, like the Temnospondyli (traditionally placed in the subclass Labyrinthodontia) or the Lepospondyli, and in some analyses even in the amniotes. This means that advocates of phylogenetic nomenclature have removed a large number of basal Devonian and Carboniferous amphibian-type tetrapod groups that were formerly placed in Amphibia in Linnaean taxonomy, and included them elsewhere under cladistic taxonomy. If the common ancestor of amphibians and amniotes is included in Amphibia, it becomes a paraphyletic group. All modern amphibians are included in the subclass Lissamphibia, which is usually considered a clade, a group of species that have evolved from a common ancestor. The three modern orders are Anura (the frogs), Caudata (or Urodela, the salamanders), and Gymnophiona (or Apoda, the caecilians). It has been suggested that salamanders arose separately from a Temnospondyl-like ancestor, and even that caecilians are the sister group of the advanced reptiliomorph amphibians, and thus of amniotes. Although the fossils of several older proto-frogs with primitive characteristics are known, the oldest "true frog" is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona. It is anatomically very similar to modern frogs. The oldest known caecilian is another Early Jurassic species, Eocaecilia micropodia, also from Arizona. The earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China. Authorities disagree as to whether Salientia is a superorder that includes the order Anura, or whether Anura is a sub-order of the order Salientia. The Lissamphibia are traditionally divided into three orders, but an extinct salamander-like family, the Albanerpetontidae, is now considered part of Lissamphibia alongside the superorder Salientia. Furthermore, Salientia includes all three recent orders plus the Triassic proto-frog, Triadobatrachus. Evolutionary history The first major groups of amphibians ("stem") developed in the Devonian period, around 370 million years ago, from lobe-finned fish which were similar to the modern coelacanth and lungfish. These ancient lobe-finned fish had evolved multi-jointed leg-like fins with digits that enabled them to crawl along the sea bottom.

The two most common systems are the classification adopted by the website AmphibiaWeb, University of California, Berkeley and the classification by herpetologist Darrel Frost and the American Museum of Natural History, available as the online reference database "Amphibian Species of the World". The numbers of species cited above follows Frost and the total number of known amphibian species as of March 31, 2019 is exactly 8,000, of which nearly 90% are frogs. With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a polyparaphyletic group without unique defining features apart from shared primitive characteristics. Classification varies according to the preferred phylogeny of the author and whether they use a stem-based or a node-based classification. Traditionally, amphibians as a class are defined as all tetrapods with a larval stage, while the group that includes the common ancestors of all living amphibians (frogs, salamanders and caecilians) and all their descendants is called Lissamphibia. The phylogeny of Paleozoic amphibians is uncertain, and Lissamphibia may possibly fall within extinct groups, like the Temnospondyli (traditionally placed in the subclass Labyrinthodontia) or the Lepospondyli, and in some analyses even in the amniotes. This means that advocates of phylogenetic nomenclature have removed a large number of basal Devonian and Carboniferous amphibian-type tetrapod groups that were formerly placed in Amphibia in Linnaean taxonomy, and included them elsewhere under cladistic taxonomy. If the common ancestor of amphibians and amniotes is included in Amphibia, it becomes a paraphyletic group. All modern amphibians are included in the subclass Lissamphibia, which is usually considered a clade, a group of species that have evolved from a common ancestor. The three modern orders are Anura (the frogs), Caudata (or Urodela, the salamanders), and Gymnophiona (or Apoda, the caecilians). It has been suggested that salamanders arose separately from a Temnospondyl-like ancestor, and even that caecilians are the sister group of the advanced reptiliomorph amphibians, and thus of amniotes. Although the fossils of several older proto-frogs with primitive characteristics are known, the oldest "true frog" is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona. It is anatomically very similar to modern frogs. The oldest known caecilian is another Early Jurassic species, Eocaecilia micropodia, also from Arizona. The earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China. Authorities disagree as to whether Salientia is a superorder that includes the order Anura, or whether Anura is a sub-order of the order Salientia. The Lissamphibia are traditionally divided into three orders, but an extinct salamander-like family, the Albanerpetontidae, is now considered part of Lissamphibia alongside the superorder Salientia. Furthermore, Salientia includes all three recent orders plus the Triassic proto-frog, Triadobatrachus. Evolutionary history The first major groups of amphibians ("stem") developed in the Devonian period, around 370 million years ago, from lobe-finned fish which were similar to the modern coelacanth and lungfish. These ancient lobe-finned fish had evolved multi-jointed leg-like fins with digits that enabled them to crawl along the sea bottom.

The two most common systems are the classification adopted by the website AmphibiaWeb, University of California, Berkeley and the classification by herpetologist Darrel Frost and the American Museum of Natural History, available as the online reference database "Amphibian Species of the World". The numbers of species cited above follows Frost and the total number of known amphibian species as of March 31, 2019 is exactly 8,000, of which nearly 90% are frogs. With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a polyparaphyletic group without unique defining features apart from shared primitive characteristics. Classification varies according to the preferred phylogeny of the author and whether they use a stem-based or a node-based classification. Traditionally, amphibians as a class are defined as all tetrapods with a larval stage, while the group that includes the common ancestors of all living amphibians (frogs, salamanders and caecilians) and all their descendants is called Lissamphibia. The phylogeny of Paleozoic amphibians is uncertain, and Lissamphibia may possibly fall within extinct groups, like the Temnospondyli (traditionally placed in the subclass Labyrinthodontia) or the Lepospondyli, and in some analyses even in the amniotes. This means that advocates of phylogenetic nomenclature have removed a large number of basal Devonian and Carboniferous amphibian-type tetrapod groups that were formerly placed in Amphibia in Linnaean taxonomy, and included them elsewhere under cladistic taxonomy. If the common ancestor of amphibians and amniotes is included in Amphibia, it becomes a paraphyletic group. All modern amphibians are included in the subclass Lissamphibia, which is usually considered a clade, a group of species that have evolved from a common ancestor. The three modern orders are Anura (the frogs), Caudata (or Urodela, the salamanders), and Gymnophiona (or Apoda, the caecilians). It has been suggested that salamanders arose separately from a Temnospondyl-like ancestor, and even that caecilians are the sister group of the advanced reptiliomorph amphibians, and thus of amniotes. Although the fossils of several older proto-frogs with primitive characteristics are known, the oldest "true frog" is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona. It is anatomically very similar to modern frogs. The oldest known caecilian is another Early Jurassic species, Eocaecilia micropodia, also from Arizona. The earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China. Authorities disagree as to whether Salientia is a superorder that includes the order Anura, or whether Anura is a sub-order of the order Salientia. The Lissamphibia are traditionally divided into three orders, but an extinct salamander-like family, the Albanerpetontidae, is now considered part of Lissamphibia alongside the superorder Salientia. Furthermore, Salientia includes all three recent orders plus the Triassic proto-frog, Triadobatrachus. Evolutionary history The first major groups of amphibians ("stem") developed in the Devonian period, around 370 million years ago, from lobe-finned fish which were similar to the modern coelacanth and lungfish. These ancient lobe-finned fish had evolved multi-jointed leg-like fins with digits that enabled them to crawl along the sea bottom.

Some fish had developed primitive lungs that help them breathe air when the stagnant pools of the Devonian swamps were low in oxygen. They could also use their strong fins to hoist themselves out of the water and onto dry land if circumstances so required. Eventually, their bony fins would evolve into limbs and they would become the ancestors to all tetrapods, including modern amphibians, reptiles, birds, and mammals. Despite being able to crawl on land, many of these prehistoric tetrapodomorph fish still spent most of their time in the water. They had started to develop lungs, but still breathed predominantly with gills. Many examples of species showing transitional features have been discovered. Ichthyostega was one of the first primitive amphibians, with nostrils and more efficient lungs. It had four sturdy limbs, a neck, a tail with fins and a skull very similar to that of the lobe-finned fish, Eusthenopteron. Amphibians evolved adaptations that allowed them to stay out of the water for longer periods. Their lungs improved and their skeletons became heavier and stronger, better able to support the weight of their bodies on land. They developed "hands" and "feet" with five or more digits; the skin became more capable of retaining body fluids and resisting desiccation. The fish's hyomandibula bone in the hyoid region behind the gills diminished in size and became the stapes of the amphibian ear, an adaptation necessary for hearing on dry land. An affinity between the amphibians and the teleost fish is the multi-folded structure of the teeth and the paired supra-occipital bones at the back of the head, neither of these features being found elsewhere in the animal kingdom. At the end of the Devonian period (360 million years ago), the seas, rivers and lakes were teeming with life while the land was the realm of early plants and devoid of vertebrates, though some, such as Ichthyostega, may have sometimes hauled themselves out of the water. It is thought they may have propelled themselves with their forelimbs, dragging their hindquarters in a similar manner to that used by the elephant seal. In the early Carboniferous (360 to 345 million years ago), the climate became wet and warm. Extensive swamps developed with mosses, ferns, horsetails and calamites. Air-breathing arthropods evolved and invaded the land where they provided food for the carnivorous amphibians that began to adapt to the terrestrial environment. There were no other tetrapods on the land and the amphibians were at the top of the food chain, occupying the ecological position currently held by the crocodile. Though equipped with limbs and the ability to breathe air, most still had a long tapering body and strong tail. They were the top land predators, sometimes reaching several metres in length, preying on the large insects of the period and the many types of fish in the water.

Some fish had developed primitive lungs that help them breathe air when the stagnant pools of the Devonian swamps were low in oxygen. They could also use their strong fins to hoist themselves out of the water and onto dry land if circumstances so required. Eventually, their bony fins would evolve into limbs and they would become the ancestors to all tetrapods, including modern amphibians, reptiles, birds, and mammals. Despite being able to crawl on land, many of these prehistoric tetrapodomorph fish still spent most of their time in the water. They had started to develop lungs, but still breathed predominantly with gills. Many examples of species showing transitional features have been discovered. Ichthyostega was one of the first primitive amphibians, with nostrils and more efficient lungs. It had four sturdy limbs, a neck, a tail with fins and a skull very similar to that of the lobe-finned fish, Eusthenopteron. Amphibians evolved adaptations that allowed them to stay out of the water for longer periods. Their lungs improved and their skeletons became heavier and stronger, better able to support the weight of their bodies on land. They developed "hands" and "feet" with five or more digits; the skin became more capable of retaining body fluids and resisting desiccation. The fish's hyomandibula bone in the hyoid region behind the gills diminished in size and became the stapes of the amphibian ear, an adaptation necessary for hearing on dry land. An affinity between the amphibians and the teleost fish is the multi-folded structure of the teeth and the paired supra-occipital bones at the back of the head, neither of these features being found elsewhere in the animal kingdom. At the end of the Devonian period (360 million years ago), the seas, rivers and lakes were teeming with life while the land was the realm of early plants and devoid of vertebrates, though some, such as Ichthyostega, may have sometimes hauled themselves out of the water. It is thought they may have propelled themselves with their forelimbs, dragging their hindquarters in a similar manner to that used by the elephant seal. In the early Carboniferous (360 to 345 million years ago), the climate became wet and warm. Extensive swamps developed with mosses, ferns, horsetails and calamites. Air-breathing arthropods evolved and invaded the land where they provided food for the carnivorous amphibians that began to adapt to the terrestrial environment. There were no other tetrapods on the land and the amphibians were at the top of the food chain, occupying the ecological position currently held by the crocodile. Though equipped with limbs and the ability to breathe air, most still had a long tapering body and strong tail. They were the top land predators, sometimes reaching several metres in length, preying on the large insects of the period and the many types of fish in the water.

Some fish had developed primitive lungs that help them breathe air when the stagnant pools of the Devonian swamps were low in oxygen. They could also use their strong fins to hoist themselves out of the water and onto dry land if circumstances so required. Eventually, their bony fins would evolve into limbs and they would become the ancestors to all tetrapods, including modern amphibians, reptiles, birds, and mammals. Despite being able to crawl on land, many of these prehistoric tetrapodomorph fish still spent most of their time in the water. They had started to develop lungs, but still breathed predominantly with gills. Many examples of species showing transitional features have been discovered. Ichthyostega was one of the first primitive amphibians, with nostrils and more efficient lungs. It had four sturdy limbs, a neck, a tail with fins and a skull very similar to that of the lobe-finned fish, Eusthenopteron. Amphibians evolved adaptations that allowed them to stay out of the water for longer periods. Their lungs improved and their skeletons became heavier and stronger, better able to support the weight of their bodies on land. They developed "hands" and "feet" with five or more digits; the skin became more capable of retaining body fluids and resisting desiccation. The fish's hyomandibula bone in the hyoid region behind the gills diminished in size and became the stapes of the amphibian ear, an adaptation necessary for hearing on dry land. An affinity between the amphibians and the teleost fish is the multi-folded structure of the teeth and the paired supra-occipital bones at the back of the head, neither of these features being found elsewhere in the animal kingdom. At the end of the Devonian period (360 million years ago), the seas, rivers and lakes were teeming with life while the land was the realm of early plants and devoid of vertebrates, though some, such as Ichthyostega, may have sometimes hauled themselves out of the water. It is thought they may have propelled themselves with their forelimbs, dragging their hindquarters in a similar manner to that used by the elephant seal. In the early Carboniferous (360 to 345 million years ago), the climate became wet and warm. Extensive swamps developed with mosses, ferns, horsetails and calamites. Air-breathing arthropods evolved and invaded the land where they provided food for the carnivorous amphibians that began to adapt to the terrestrial environment. There were no other tetrapods on the land and the amphibians were at the top of the food chain, occupying the ecological position currently held by the crocodile. Though equipped with limbs and the ability to breathe air, most still had a long tapering body and strong tail. They were the top land predators, sometimes reaching several metres in length, preying on the large insects of the period and the many types of fish in the water.

They still needed to return to water to lay their shell-less eggs, and even most modern amphibians have a fully aquatic larval stage with gills like their fish ancestors. It was the development of the amniotic egg, which prevents the developing embryo from drying out, that enabled the reptiles to reproduce on land and which led to their dominance in the period that followed. After the Carboniferous rainforest collapse amphibian dominance gave way to reptiles, and amphibians were further devastated by the Permian–Triassic extinction event. During the Triassic Period (250 to 200 million years ago), the reptiles continued to out-compete the amphibians, leading to a reduction in both the amphibians' size and their importance in the biosphere. According to the fossil record, Lissamphibia, which includes all modern amphibians and is the only surviving lineage, may have branched off from the extinct groups Temnospondyli and Lepospondyli at some period between the Late Carboniferous and the Early Triassic. The relative scarcity of fossil evidence precludes precise dating, but the most recent molecular study, based on multilocus sequence typing, suggests a Late Carboniferous/Early Permian origin for extant amphibians. The origins and evolutionary relationships between the three main groups of amphibians is a matter of debate. A 2005 molecular phylogeny, based on rDNA analysis, suggests that salamanders and caecilians are more closely related to each other than they are to frogs. It also appears that the divergence of the three groups took place in the Paleozoic or early Mesozoic (around 250 million years ago), before the breakup of the supercontinent Pangaea and soon after their divergence from the lobe-finned fish. The briefness of this period, and the swiftness with which radiation took place, would help account for the relative scarcity of primitive amphibian fossils. There are large gaps in the fossil record, but the discovery of a Gerobatrachus hottoni from the Early Permian in Texas in 2008 provided a missing link with many of the characteristics of modern frogs. Molecular analysis suggests that the frog–salamander divergence took place considerably earlier than the palaeontological evidence indicates. Newer research indicates that the common ancestor of all Lissamphibians lived about 315 million years ago, and that stereospondyls are the closest relatives to the caecilians. As they evolved from lunged fish, amphibians had to make certain adaptations for living on land, including the need to develop new means of locomotion. In the water, the sideways thrusts of their tails had propelled them forward, but on land, quite different mechanisms were required. Their vertebral columns, limbs, limb girdles and musculature needed to be strong enough to raise them off the ground for locomotion and feeding. Terrestrial adults discarded their lateral line systems and adapted their sensory systems to receive stimuli via the medium of the air. They needed to develop new methods to regulate their body heat to cope with fluctuations in ambient temperature. They developed behaviours suitable for reproduction in a terrestrial environment.

They still needed to return to water to lay their shell-less eggs, and even most modern amphibians have a fully aquatic larval stage with gills like their fish ancestors. It was the development of the amniotic egg, which prevents the developing embryo from drying out, that enabled the reptiles to reproduce on land and which led to their dominance in the period that followed. After the Carboniferous rainforest collapse amphibian dominance gave way to reptiles, and amphibians were further devastated by the Permian–Triassic extinction event. During the Triassic Period (250 to 200 million years ago), the reptiles continued to out-compete the amphibians, leading to a reduction in both the amphibians' size and their importance in the biosphere. According to the fossil record, Lissamphibia, which includes all modern amphibians and is the only surviving lineage, may have branched off from the extinct groups Temnospondyli and Lepospondyli at some period between the Late Carboniferous and the Early Triassic. The relative scarcity of fossil evidence precludes precise dating, but the most recent molecular study, based on multilocus sequence typing, suggests a Late Carboniferous/Early Permian origin for extant amphibians. The origins and evolutionary relationships between the three main groups of amphibians is a matter of debate. A 2005 molecular phylogeny, based on rDNA analysis, suggests that salamanders and caecilians are more closely related to each other than they are to frogs. It also appears that the divergence of the three groups took place in the Paleozoic or early Mesozoic (around 250 million years ago), before the breakup of the supercontinent Pangaea and soon after their divergence from the lobe-finned fish. The briefness of this period, and the swiftness with which radiation took place, would help account for the relative scarcity of primitive amphibian fossils. There are large gaps in the fossil record, but the discovery of a Gerobatrachus hottoni from the Early Permian in Texas in 2008 provided a missing link with many of the characteristics of modern frogs. Molecular analysis suggests that the frog–salamander divergence took place considerably earlier than the palaeontological evidence indicates. Newer research indicates that the common ancestor of all Lissamphibians lived about 315 million years ago, and that stereospondyls are the closest relatives to the caecilians. As they evolved from lunged fish, amphibians had to make certain adaptations for living on land, including the need to develop new means of locomotion. In the water, the sideways thrusts of their tails had propelled them forward, but on land, quite different mechanisms were required. Their vertebral columns, limbs, limb girdles and musculature needed to be strong enough to raise them off the ground for locomotion and feeding. Terrestrial adults discarded their lateral line systems and adapted their sensory systems to receive stimuli via the medium of the air. They needed to develop new methods to regulate their body heat to cope with fluctuations in ambient temperature. They developed behaviours suitable for reproduction in a terrestrial environment.

They still needed to return to water to lay their shell-less eggs, and even most modern amphibians have a fully aquatic larval stage with gills like their fish ancestors. It was the development of the amniotic egg, which prevents the developing embryo from drying out, that enabled the reptiles to reproduce on land and which led to their dominance in the period that followed. After the Carboniferous rainforest collapse amphibian dominance gave way to reptiles, and amphibians were further devastated by the Permian–Triassic extinction event. During the Triassic Period (250 to 200 million years ago), the reptiles continued to out-compete the amphibians, leading to a reduction in both the amphibians' size and their importance in the biosphere. According to the fossil record, Lissamphibia, which includes all modern amphibians and is the only surviving lineage, may have branched off from the extinct groups Temnospondyli and Lepospondyli at some period between the Late Carboniferous and the Early Triassic. The relative scarcity of fossil evidence precludes precise dating, but the most recent molecular study, based on multilocus sequence typing, suggests a Late Carboniferous/Early Permian origin for extant amphibians. The origins and evolutionary relationships between the three main groups of amphibians is a matter of debate. A 2005 molecular phylogeny, based on rDNA analysis, suggests that salamanders and caecilians are more closely related to each other than they are to frogs. It also appears that the divergence of the three groups took place in the Paleozoic or early Mesozoic (around 250 million years ago), before the breakup of the supercontinent Pangaea and soon after their divergence from the lobe-finned fish. The briefness of this period, and the swiftness with which radiation took place, would help account for the relative scarcity of primitive amphibian fossils. There are large gaps in the fossil record, but the discovery of a Gerobatrachus hottoni from the Early Permian in Texas in 2008 provided a missing link with many of the characteristics of modern frogs. Molecular analysis suggests that the frog–salamander divergence took place considerably earlier than the palaeontological evidence indicates. Newer research indicates that the common ancestor of all Lissamphibians lived about 315 million years ago, and that stereospondyls are the closest relatives to the caecilians. As they evolved from lunged fish, amphibians had to make certain adaptations for living on land, including the need to develop new means of locomotion. In the water, the sideways thrusts of their tails had propelled them forward, but on land, quite different mechanisms were required. Their vertebral columns, limbs, limb girdles and musculature needed to be strong enough to raise them off the ground for locomotion and feeding. Terrestrial adults discarded their lateral line systems and adapted their sensory systems to receive stimuli via the medium of the air. They needed to develop new methods to regulate their body heat to cope with fluctuations in ambient temperature. They developed behaviours suitable for reproduction in a terrestrial environment.

Their skins were exposed to harmful ultraviolet rays that had previously been absorbed by the water. The skin changed to become more protective and prevent excessive water loss. Characteristics The superclass Tetrapoda is divided into four classes of vertebrate animals with four limbs. Reptiles, birds and mammals are amniotes, the eggs of which are either laid or carried by the female and are surrounded by several membranes, some of which are impervious. Lacking these membranes, amphibians require water bodies for reproduction, although some species have developed various strategies for protecting or bypassing the vulnerable aquatic larval stage. They are not found in the sea with the exception of one or two frogs that live in brackish water in mangrove swamps; the Anderson's salamander meanwhile occurs in brackish or salt water lakes. On land, amphibians are restricted to moist habitats because of the need to keep their skin damp. Modern amphibians have a simplified anatomy compared to their ancestors due to paedomorphosis, caused by two evolutionary trends: miniaturization and an unusually large genome, which result in a slower growth and development rate compared to other vertebrates. Another reason for their size is associated with their rapid metamorphosis, which seems to have evolved only in the ancestors of lissamphibia; in all other known lines the development was much more gradual. Because a remodeling of the feeding apparatus means they don't eat during the metamorphosis, the metamorphosis has to go faster the smaller the individual is, so it happens at an early stage when the larvae are still small. (The largest species of salamanders don't go through a metamorphosis.) Amphibians that lay eggs on land often go through the whole metamorphosis inside the egg. An anamniotic terrestrial egg is less than 1 cm in diameter due to diffusion problems, a size which puts a limit on the amount of posthatching growth. The smallest amphibian (and vertebrate) in the world is a microhylid frog from New Guinea (Paedophryne amauensis) first discovered in 2012. It has an average length of and is part of a genus that contains four of the world's ten smallest frog species. The largest living amphibian is the Chinese giant salamander (Andrias davidianus) but this is a great deal smaller than the largest amphibian that ever existed—the extinct Prionosuchus, a crocodile-like temnospondyl dating to 270 million years ago from the middle Permian of Brazil. The largest frog is the African Goliath frog (Conraua goliath), which can reach and weigh . Amphibians are ectothermic (cold-blooded) vertebrates that do not maintain their body temperature through internal physiological processes. Their metabolic rate is low and as a result, their food and energy requirements are limited. In the adult state, they have tear ducts and movable eyelids, and most species have ears that can detect airborne or ground vibrations. They have muscular tongues, which in many species can be protruded. Modern amphibians have fully ossified vertebrae with articular processes. Their ribs are usually short and may be fused to the vertebrae.

Their skins were exposed to harmful ultraviolet rays that had previously been absorbed by the water. The skin changed to become more protective and prevent excessive water loss. Characteristics The superclass Tetrapoda is divided into four classes of vertebrate animals with four limbs. Reptiles, birds and mammals are amniotes, the eggs of which are either laid or carried by the female and are surrounded by several membranes, some of which are impervious. Lacking these membranes, amphibians require water bodies for reproduction, although some species have developed various strategies for protecting or bypassing the vulnerable aquatic larval stage. They are not found in the sea with the exception of one or two frogs that live in brackish water in mangrove swamps; the Anderson's salamander meanwhile occurs in brackish or salt water lakes. On land, amphibians are restricted to moist habitats because of the need to keep their skin damp. Modern amphibians have a simplified anatomy compared to their ancestors due to paedomorphosis, caused by two evolutionary trends: miniaturization and an unusually large genome, which result in a slower growth and development rate compared to other vertebrates. Another reason for their size is associated with their rapid metamorphosis, which seems to have evolved only in the ancestors of lissamphibia; in all other known lines the development was much more gradual. Because a remodeling of the feeding apparatus means they don't eat during the metamorphosis, the metamorphosis has to go faster the smaller the individual is, so it happens at an early stage when the larvae are still small. (The largest species of salamanders don't go through a metamorphosis.) Amphibians that lay eggs on land often go through the whole metamorphosis inside the egg. An anamniotic terrestrial egg is less than 1 cm in diameter due to diffusion problems, a size which puts a limit on the amount of posthatching growth. The smallest amphibian (and vertebrate) in the world is a microhylid frog from New Guinea (Paedophryne amauensis) first discovered in 2012. It has an average length of and is part of a genus that contains four of the world's ten smallest frog species. The largest living amphibian is the Chinese giant salamander (Andrias davidianus) but this is a great deal smaller than the largest amphibian that ever existed—the extinct Prionosuchus, a crocodile-like temnospondyl dating to 270 million years ago from the middle Permian of Brazil. The largest frog is the African Goliath frog (Conraua goliath), which can reach and weigh . Amphibians are ectothermic (cold-blooded) vertebrates that do not maintain their body temperature through internal physiological processes. Their metabolic rate is low and as a result, their food and energy requirements are limited. In the adult state, they have tear ducts and movable eyelids, and most species have ears that can detect airborne or ground vibrations. They have muscular tongues, which in many species can be protruded. Modern amphibians have fully ossified vertebrae with articular processes. Their ribs are usually short and may be fused to the vertebrae.

Their skins were exposed to harmful ultraviolet rays that had previously been absorbed by the water. The skin changed to become more protective and prevent excessive water loss. Characteristics The superclass Tetrapoda is divided into four classes of vertebrate animals with four limbs. Reptiles, birds and mammals are amniotes, the eggs of which are either laid or carried by the female and are surrounded by several membranes, some of which are impervious. Lacking these membranes, amphibians require water bodies for reproduction, although some species have developed various strategies for protecting or bypassing the vulnerable aquatic larval stage. They are not found in the sea with the exception of one or two frogs that live in brackish water in mangrove swamps; the Anderson's salamander meanwhile occurs in brackish or salt water lakes. On land, amphibians are restricted to moist habitats because of the need to keep their skin damp. Modern amphibians have a simplified anatomy compared to their ancestors due to paedomorphosis, caused by two evolutionary trends: miniaturization and an unusually large genome, which result in a slower growth and development rate compared to other vertebrates. Another reason for their size is associated with their rapid metamorphosis, which seems to have evolved only in the ancestors of lissamphibia; in all other known lines the development was much more gradual. Because a remodeling of the feeding apparatus means they don't eat during the metamorphosis, the metamorphosis has to go faster the smaller the individual is, so it happens at an early stage when the larvae are still small. (The largest species of salamanders don't go through a metamorphosis.) Amphibians that lay eggs on land often go through the whole metamorphosis inside the egg. An anamniotic terrestrial egg is less than 1 cm in diameter due to diffusion problems, a size which puts a limit on the amount of posthatching growth. The smallest amphibian (and vertebrate) in the world is a microhylid frog from New Guinea (Paedophryne amauensis) first discovered in 2012. It has an average length of and is part of a genus that contains four of the world's ten smallest frog species. The largest living amphibian is the Chinese giant salamander (Andrias davidianus) but this is a great deal smaller than the largest amphibian that ever existed—the extinct Prionosuchus, a crocodile-like temnospondyl dating to 270 million years ago from the middle Permian of Brazil. The largest frog is the African Goliath frog (Conraua goliath), which can reach and weigh . Amphibians are ectothermic (cold-blooded) vertebrates that do not maintain their body temperature through internal physiological processes. Their metabolic rate is low and as a result, their food and energy requirements are limited. In the adult state, they have tear ducts and movable eyelids, and most species have ears that can detect airborne or ground vibrations. They have muscular tongues, which in many species can be protruded. Modern amphibians have fully ossified vertebrae with articular processes. Their ribs are usually short and may be fused to the vertebrae.

Their skulls are mostly broad and short, and are often incompletely ossified. Their skin contains little keratin and lacks scales, apart from a few fish-like scales in certain caecilians. The skin contains many mucous glands and in some species, poison glands (a type of granular gland). The hearts of amphibians have three chambers, two atria and one ventricle. They have a urinary bladder and nitrogenous waste products are excreted primarily as urea. Most amphibians lay their eggs in water and have aquatic larvae that undergo metamorphosis to become terrestrial adults. Amphibians breathe by means of a pump action in which air is first drawn into the buccopharyngeal region through the nostrils. These are then closed and the air is forced into the lungs by contraction of the throat. They supplement this with gas exchange through the skin. Anura The order Anura (from the Ancient Greek a(n)- meaning "without" and oura meaning "tail") comprises the frogs and toads. They usually have long hind limbs that fold underneath them, shorter forelimbs, webbed toes with no claws, no tails, large eyes and glandular moist skin. Members of this order with smooth skins are commonly referred to as frogs, while those with warty skins are known as toads. The difference is not a formal one taxonomically and there are numerous exceptions to this rule. Members of the family Bufonidae are known as the "true toads". Frogs range in size from the Goliath frog (Conraua goliath) of West Africa to the Paedophryne amauensis, first described in Papua New Guinea in 2012, which is also the smallest known vertebrate. Although most species are associated with water and damp habitats, some are specialised to live in trees or in deserts. They are found worldwide except for polar areas. Anura is divided into three suborders that are broadly accepted by the scientific community, but the relationships between some families remain unclear. Future molecular studies should provide further insights into their evolutionary relationships. The suborder Archaeobatrachia contains four families of primitive frogs. These are Ascaphidae, Bombinatoridae, Discoglossidae and Leiopelmatidae which have few derived features and are probably paraphyletic with regard to other frog lineages. The six families in the more evolutionarily advanced suborder Mesobatrachia are the fossorial Megophryidae, Pelobatidae, Pelodytidae, Scaphiopodidae and Rhinophrynidae and the obligatorily aquatic Pipidae. These have certain characteristics that are intermediate between the two other suborders. Neobatrachia is by far the largest suborder and includes the remaining families of modern frogs, including most common species. Ninety-six percent of the over 5,000 extant species of frog are neobatrachians. Caudata The order Caudata (from the Latin cauda meaning "tail") consists of the salamanders—elongated, low-slung animals that mostly resemble lizards in form. This is a symplesiomorphic trait and they are no more closely related to lizards than they are to mammals. Salamanders lack claws, have scale-free skins, either smooth or covered with tubercles, and tails that are usually flattened from side to side and often finned.

Their skulls are mostly broad and short, and are often incompletely ossified. Their skin contains little keratin and lacks scales, apart from a few fish-like scales in certain caecilians. The skin contains many mucous glands and in some species, poison glands (a type of granular gland). The hearts of amphibians have three chambers, two atria and one ventricle. They have a urinary bladder and nitrogenous waste products are excreted primarily as urea. Most amphibians lay their eggs in water and have aquatic larvae that undergo metamorphosis to become terrestrial adults. Amphibians breathe by means of a pump action in which air is first drawn into the buccopharyngeal region through the nostrils. These are then closed and the air is forced into the lungs by contraction of the throat. They supplement this with gas exchange through the skin. Anura The order Anura (from the Ancient Greek a(n)- meaning "without" and oura meaning "tail") comprises the frogs and toads. They usually have long hind limbs that fold underneath them, shorter forelimbs, webbed toes with no claws, no tails, large eyes and glandular moist skin. Members of this order with smooth skins are commonly referred to as frogs, while those with warty skins are known as toads. The difference is not a formal one taxonomically and there are numerous exceptions to this rule. Members of the family Bufonidae are known as the "true toads". Frogs range in size from the Goliath frog (Conraua goliath) of West Africa to the Paedophryne amauensis, first described in Papua New Guinea in 2012, which is also the smallest known vertebrate. Although most species are associated with water and damp habitats, some are specialised to live in trees or in deserts. They are found worldwide except for polar areas. Anura is divided into three suborders that are broadly accepted by the scientific community, but the relationships between some families remain unclear. Future molecular studies should provide further insights into their evolutionary relationships. The suborder Archaeobatrachia contains four families of primitive frogs. These are Ascaphidae, Bombinatoridae, Discoglossidae and Leiopelmatidae which have few derived features and are probably paraphyletic with regard to other frog lineages. The six families in the more evolutionarily advanced suborder Mesobatrachia are the fossorial Megophryidae, Pelobatidae, Pelodytidae, Scaphiopodidae and Rhinophrynidae and the obligatorily aquatic Pipidae. These have certain characteristics that are intermediate between the two other suborders. Neobatrachia is by far the largest suborder and includes the remaining families of modern frogs, including most common species. Ninety-six percent of the over 5,000 extant species of frog are neobatrachians. Caudata The order Caudata (from the Latin cauda meaning "tail") consists of the salamanders—elongated, low-slung animals that mostly resemble lizards in form. This is a symplesiomorphic trait and they are no more closely related to lizards than they are to mammals. Salamanders lack claws, have scale-free skins, either smooth or covered with tubercles, and tails that are usually flattened from side to side and often finned.

Their skulls are mostly broad and short, and are often incompletely ossified. Their skin contains little keratin and lacks scales, apart from a few fish-like scales in certain caecilians. The skin contains many mucous glands and in some species, poison glands (a type of granular gland). The hearts of amphibians have three chambers, two atria and one ventricle. They have a urinary bladder and nitrogenous waste products are excreted primarily as urea. Most amphibians lay their eggs in water and have aquatic larvae that undergo metamorphosis to become terrestrial adults. Amphibians breathe by means of a pump action in which air is first drawn into the buccopharyngeal region through the nostrils. These are then closed and the air is forced into the lungs by contraction of the throat. They supplement this with gas exchange through the skin. Anura The order Anura (from the Ancient Greek a(n)- meaning "without" and oura meaning "tail") comprises the frogs and toads. They usually have long hind limbs that fold underneath them, shorter forelimbs, webbed toes with no claws, no tails, large eyes and glandular moist skin. Members of this order with smooth skins are commonly referred to as frogs, while those with warty skins are known as toads. The difference is not a formal one taxonomically and there are numerous exceptions to this rule. Members of the family Bufonidae are known as the "true toads". Frogs range in size from the Goliath frog (Conraua goliath) of West Africa to the Paedophryne amauensis, first described in Papua New Guinea in 2012, which is also the smallest known vertebrate. Although most species are associated with water and damp habitats, some are specialised to live in trees or in deserts. They are found worldwide except for polar areas. Anura is divided into three suborders that are broadly accepted by the scientific community, but the relationships between some families remain unclear. Future molecular studies should provide further insights into their evolutionary relationships. The suborder Archaeobatrachia contains four families of primitive frogs. These are Ascaphidae, Bombinatoridae, Discoglossidae and Leiopelmatidae which have few derived features and are probably paraphyletic with regard to other frog lineages. The six families in the more evolutionarily advanced suborder Mesobatrachia are the fossorial Megophryidae, Pelobatidae, Pelodytidae, Scaphiopodidae and Rhinophrynidae and the obligatorily aquatic Pipidae. These have certain characteristics that are intermediate between the two other suborders. Neobatrachia is by far the largest suborder and includes the remaining families of modern frogs, including most common species. Ninety-six percent of the over 5,000 extant species of frog are neobatrachians. Caudata The order Caudata (from the Latin cauda meaning "tail") consists of the salamanders—elongated, low-slung animals that mostly resemble lizards in form. This is a symplesiomorphic trait and they are no more closely related to lizards than they are to mammals. Salamanders lack claws, have scale-free skins, either smooth or covered with tubercles, and tails that are usually flattened from side to side and often finned.

They range in size from the Chinese giant salamander (Andrias davidianus), which has been reported to grow to a length of , to the diminutive Thorius pennatulus from Mexico which seldom exceeds in length. Salamanders have a mostly Laurasian distribution, being present in much of the Holarctic region of the northern hemisphere. The family Plethodontidae is also found in Central America and South America north of the Amazon basin; South America was apparently invaded from Central America by about the start of the Miocene, 23 million years ago. Urodela is a name sometimes used for all the extant species of salamanders. Members of several salamander families have become paedomorphic and either fail to complete their metamorphosis or retain some larval characteristics as adults. Most salamanders are under long. They may be terrestrial or aquatic and many spend part of the year in each habitat. When on land, they mostly spend the day hidden under stones or logs or in dense vegetation, emerging in the evening and night to forage for worms, insects and other invertebrates. The suborder Cryptobranchoidea contains the primitive salamanders. A number of fossil cryptobranchids have been found, but there are only three living species, the Chinese giant salamander (Andrias davidianus), the Japanese giant salamander (Andrias japonicus) and the hellbender (Cryptobranchus alleganiensis) from North America. These large amphibians retain several larval characteristics in their adult state; gills slits are present and the eyes are unlidded. A unique feature is their ability to feed by suction, depressing either the left side of their lower jaw or the right. The males excavate nests, persuade females to lay their egg strings inside them, and guard them. As well as breathing with lungs, they respire through the many folds in their thin skin, which has capillaries close to the surface. The suborder Salamandroidea contains the advanced salamanders. They differ from the cryptobranchids by having fused prearticular bones in the lower jaw, and by using internal fertilisation. In salamandrids, the male deposits a bundle of sperm, the spermatophore, and the female picks it up and inserts it into her cloaca where the sperm is stored until the eggs are laid. The largest family in this group is Plethodontidae, the lungless salamanders, which includes 60% of all salamander species. The family Salamandridae includes the true salamanders and the name "newt" is given to members of its subfamily Pleurodelinae. The third suborder, Sirenoidea, contains the four species of sirens, which are in a single family, Sirenidae. Members of this order are eel-like aquatic salamanders with much reduced forelimbs and no hind limbs. Some of their features are primitive while others are derived. Fertilisation is likely to be external as sirenids lack the cloacal glands used by male salamandrids to produce spermatophores and the females lack spermathecae for sperm storage. Despite this, the eggs are laid singly, a behaviour not conducive for external fertilisation. Gymnophiona The order Gymnophiona (from the Greek gymnos meaning "naked" and ophis meaning "serpent") or Apoda comprises the caecilians.

They range in size from the Chinese giant salamander (Andrias davidianus), which has been reported to grow to a length of , to the diminutive Thorius pennatulus from Mexico which seldom exceeds in length. Salamanders have a mostly Laurasian distribution, being present in much of the Holarctic region of the northern hemisphere. The family Plethodontidae is also found in Central America and South America north of the Amazon basin; South America was apparently invaded from Central America by about the start of the Miocene, 23 million years ago. Urodela is a name sometimes used for all the extant species of salamanders. Members of several salamander families have become paedomorphic and either fail to complete their metamorphosis or retain some larval characteristics as adults. Most salamanders are under long. They may be terrestrial or aquatic and many spend part of the year in each habitat. When on land, they mostly spend the day hidden under stones or logs or in dense vegetation, emerging in the evening and night to forage for worms, insects and other invertebrates. The suborder Cryptobranchoidea contains the primitive salamanders. A number of fossil cryptobranchids have been found, but there are only three living species, the Chinese giant salamander (Andrias davidianus), the Japanese giant salamander (Andrias japonicus) and the hellbender (Cryptobranchus alleganiensis) from North America. These large amphibians retain several larval characteristics in their adult state; gills slits are present and the eyes are unlidded. A unique feature is their ability to feed by suction, depressing either the left side of their lower jaw or the right. The males excavate nests, persuade females to lay their egg strings inside them, and guard them. As well as breathing with lungs, they respire through the many folds in their thin skin, which has capillaries close to the surface. The suborder Salamandroidea contains the advanced salamanders. They differ from the cryptobranchids by having fused prearticular bones in the lower jaw, and by using internal fertilisation. In salamandrids, the male deposits a bundle of sperm, the spermatophore, and the female picks it up and inserts it into her cloaca where the sperm is stored until the eggs are laid. The largest family in this group is Plethodontidae, the lungless salamanders, which includes 60% of all salamander species. The family Salamandridae includes the true salamanders and the name "newt" is given to members of its subfamily Pleurodelinae. The third suborder, Sirenoidea, contains the four species of sirens, which are in a single family, Sirenidae. Members of this order are eel-like aquatic salamanders with much reduced forelimbs and no hind limbs. Some of their features are primitive while others are derived. Fertilisation is likely to be external as sirenids lack the cloacal glands used by male salamandrids to produce spermatophores and the females lack spermathecae for sperm storage. Despite this, the eggs are laid singly, a behaviour not conducive for external fertilisation. Gymnophiona The order Gymnophiona (from the Greek gymnos meaning "naked" and ophis meaning "serpent") or Apoda comprises the caecilians.

They range in size from the Chinese giant salamander (Andrias davidianus), which has been reported to grow to a length of , to the diminutive Thorius pennatulus from Mexico which seldom exceeds in length. Salamanders have a mostly Laurasian distribution, being present in much of the Holarctic region of the northern hemisphere. The family Plethodontidae is also found in Central America and South America north of the Amazon basin; South America was apparently invaded from Central America by about the start of the Miocene, 23 million years ago. Urodela is a name sometimes used for all the extant species of salamanders. Members of several salamander families have become paedomorphic and either fail to complete their metamorphosis or retain some larval characteristics as adults. Most salamanders are under long. They may be terrestrial or aquatic and many spend part of the year in each habitat. When on land, they mostly spend the day hidden under stones or logs or in dense vegetation, emerging in the evening and night to forage for worms, insects and other invertebrates. The suborder Cryptobranchoidea contains the primitive salamanders. A number of fossil cryptobranchids have been found, but there are only three living species, the Chinese giant salamander (Andrias davidianus), the Japanese giant salamander (Andrias japonicus) and the hellbender (Cryptobranchus alleganiensis) from North America. These large amphibians retain several larval characteristics in their adult state; gills slits are present and the eyes are unlidded. A unique feature is their ability to feed by suction, depressing either the left side of their lower jaw or the right. The males excavate nests, persuade females to lay their egg strings inside them, and guard them. As well as breathing with lungs, they respire through the many folds in their thin skin, which has capillaries close to the surface. The suborder Salamandroidea contains the advanced salamanders. They differ from the cryptobranchids by having fused prearticular bones in the lower jaw, and by using internal fertilisation. In salamandrids, the male deposits a bundle of sperm, the spermatophore, and the female picks it up and inserts it into her cloaca where the sperm is stored until the eggs are laid. The largest family in this group is Plethodontidae, the lungless salamanders, which includes 60% of all salamander species. The family Salamandridae includes the true salamanders and the name "newt" is given to members of its subfamily Pleurodelinae. The third suborder, Sirenoidea, contains the four species of sirens, which are in a single family, Sirenidae. Members of this order are eel-like aquatic salamanders with much reduced forelimbs and no hind limbs. Some of their features are primitive while others are derived. Fertilisation is likely to be external as sirenids lack the cloacal glands used by male salamandrids to produce spermatophores and the females lack spermathecae for sperm storage. Despite this, the eggs are laid singly, a behaviour not conducive for external fertilisation. Gymnophiona The order Gymnophiona (from the Greek gymnos meaning "naked" and ophis meaning "serpent") or Apoda comprises the caecilians.

These are long, cylindrical, limbless animals with a snake- or worm-like form. The adults vary in length from 8 to 75 centimetres (3 to 30 inches) with the exception of Thomson's caecilian (Caecilia thompsoni), which can reach . A caecilian's skin has a large number of transverse folds and in some species contains tiny embedded dermal scales. It has rudimentary eyes covered in skin, which are probably limited to discerning differences in light intensity. It also has a pair of short tentacles near the eye that can be extended and which have tactile and olfactory functions. Most caecilians live underground in burrows in damp soil, in rotten wood and under plant debris, but some are aquatic. Most species lay their eggs underground and when the larvae hatch, they make their way to adjacent bodies of water. Others brood their eggs and the larvae undergo metamorphosis before the eggs hatch. A few species give birth to live young, nourishing them with glandular secretions while they are in the oviduct. Caecilians have a mostly Gondwanan distribution, being found in tropical regions of Africa, Asia and Central and South America. Anatomy and physiology Skin The integumentary structure contains some typical characteristics common to terrestrial vertebrates, such as the presence of highly cornified outer layers, renewed periodically through a moulting process controlled by the pituitary and thyroid glands. Local thickenings (often called warts) are common, such as those found on toads. The outside of the skin is shed periodically mostly in one piece, in contrast to mammals and birds where it is shed in flakes. Amphibians often eat the sloughed skin. Caecilians are unique among amphibians in having mineralized dermal scales embedded in the dermis between the furrows in the skin. The similarity of these to the scales of bony fish is largely superficial. Lizards and some frogs have somewhat similar osteoderms forming bony deposits in the dermis, but this is an example of convergent evolution with similar structures having arisen independently in diverse vertebrate lineages. Amphibian skin is permeable to water. Gas exchange can take place through the skin (cutaneous respiration) and this allows adult amphibians to respire without rising to the surface of water and to hibernate at the bottom of ponds. To compensate for their thin and delicate skin, amphibians have evolved mucous glands, principally on their heads, backs and tails. The secretions produced by these help keep the skin moist. In addition, most species of amphibian have granular glands that secrete distasteful or poisonous substances. Some amphibian toxins can be lethal to humans while others have little effect. The main poison-producing glands, the parotoids, produce the neurotoxin bufotoxin and are located behind the ears of toads, along the backs of frogs, behind the eyes of salamanders and on the upper surface of caecilians. The skin colour of amphibians is produced by three layers of pigment cells called chromatophores.

These are long, cylindrical, limbless animals with a snake- or worm-like form. The adults vary in length from 8 to 75 centimetres (3 to 30 inches) with the exception of Thomson's caecilian (Caecilia thompsoni), which can reach . A caecilian's skin has a large number of transverse folds and in some species contains tiny embedded dermal scales. It has rudimentary eyes covered in skin, which are probably limited to discerning differences in light intensity. It also has a pair of short tentacles near the eye that can be extended and which have tactile and olfactory functions. Most caecilians live underground in burrows in damp soil, in rotten wood and under plant debris, but some are aquatic. Most species lay their eggs underground and when the larvae hatch, they make their way to adjacent bodies of water. Others brood their eggs and the larvae undergo metamorphosis before the eggs hatch. A few species give birth to live young, nourishing them with glandular secretions while they are in the oviduct. Caecilians have a mostly Gondwanan distribution, being found in tropical regions of Africa, Asia and Central and South America. Anatomy and physiology Skin The integumentary structure contains some typical characteristics common to terrestrial vertebrates, such as the presence of highly cornified outer layers, renewed periodically through a moulting process controlled by the pituitary and thyroid glands. Local thickenings (often called warts) are common, such as those found on toads. The outside of the skin is shed periodically mostly in one piece, in contrast to mammals and birds where it is shed in flakes. Amphibians often eat the sloughed skin. Caecilians are unique among amphibians in having mineralized dermal scales embedded in the dermis between the furrows in the skin. The similarity of these to the scales of bony fish is largely superficial. Lizards and some frogs have somewhat similar osteoderms forming bony deposits in the dermis, but this is an example of convergent evolution with similar structures having arisen independently in diverse vertebrate lineages. Amphibian skin is permeable to water. Gas exchange can take place through the skin (cutaneous respiration) and this allows adult amphibians to respire without rising to the surface of water and to hibernate at the bottom of ponds. To compensate for their thin and delicate skin, amphibians have evolved mucous glands, principally on their heads, backs and tails. The secretions produced by these help keep the skin moist. In addition, most species of amphibian have granular glands that secrete distasteful or poisonous substances. Some amphibian toxins can be lethal to humans while others have little effect. The main poison-producing glands, the parotoids, produce the neurotoxin bufotoxin and are located behind the ears of toads, along the backs of frogs, behind the eyes of salamanders and on the upper surface of caecilians. The skin colour of amphibians is produced by three layers of pigment cells called chromatophores.

These are long, cylindrical, limbless animals with a snake- or worm-like form. The adults vary in length from 8 to 75 centimetres (3 to 30 inches) with the exception of Thomson's caecilian (Caecilia thompsoni), which can reach . A caecilian's skin has a large number of transverse folds and in some species contains tiny embedded dermal scales. It has rudimentary eyes covered in skin, which are probably limited to discerning differences in light intensity. It also has a pair of short tentacles near the eye that can be extended and which have tactile and olfactory functions. Most caecilians live underground in burrows in damp soil, in rotten wood and under plant debris, but some are aquatic. Most species lay their eggs underground and when the larvae hatch, they make their way to adjacent bodies of water. Others brood their eggs and the larvae undergo metamorphosis before the eggs hatch. A few species give birth to live young, nourishing them with glandular secretions while they are in the oviduct. Caecilians have a mostly Gondwanan distribution, being found in tropical regions of Africa, Asia and Central and South America. Anatomy and physiology Skin The integumentary structure contains some typical characteristics common to terrestrial vertebrates, such as the presence of highly cornified outer layers, renewed periodically through a moulting process controlled by the pituitary and thyroid glands. Local thickenings (often called warts) are common, such as those found on toads. The outside of the skin is shed periodically mostly in one piece, in contrast to mammals and birds where it is shed in flakes. Amphibians often eat the sloughed skin. Caecilians are unique among amphibians in having mineralized dermal scales embedded in the dermis between the furrows in the skin. The similarity of these to the scales of bony fish is largely superficial. Lizards and some frogs have somewhat similar osteoderms forming bony deposits in the dermis, but this is an example of convergent evolution with similar structures having arisen independently in diverse vertebrate lineages. Amphibian skin is permeable to water. Gas exchange can take place through the skin (cutaneous respiration) and this allows adult amphibians to respire without rising to the surface of water and to hibernate at the bottom of ponds. To compensate for their thin and delicate skin, amphibians have evolved mucous glands, principally on their heads, backs and tails. The secretions produced by these help keep the skin moist. In addition, most species of amphibian have granular glands that secrete distasteful or poisonous substances. Some amphibian toxins can be lethal to humans while others have little effect. The main poison-producing glands, the parotoids, produce the neurotoxin bufotoxin and are located behind the ears of toads, along the backs of frogs, behind the eyes of salamanders and on the upper surface of caecilians. The skin colour of amphibians is produced by three layers of pigment cells called chromatophores.

These three cell layers consist of the melanophores (occupying the deepest layer), the guanophores (forming an intermediate layer and containing many granules, producing a blue-green colour) and the lipophores (yellow, the most superficial layer). The colour change displayed by many species is initiated by hormones secreted by the pituitary gland. Unlike bony fish, there is no direct control of the pigment cells by the nervous system, and this results in the colour change taking place more slowly than happens in fish. A vividly coloured skin usually indicates that the species is toxic and is a warning sign to predators. Skeletal system and locomotion Amphibians have a skeletal system that is structurally homologous to other tetrapods, though with a number of variations. They all have four limbs except for the legless caecilians and a few species of salamander with reduced or no limbs. The bones are hollow and lightweight. The musculoskeletal system is strong to enable it to support the head and body. The bones are fully ossified and the vertebrae interlock with each other by means of overlapping processes. The pectoral girdle is supported by muscle, and the well-developed pelvic girdle is attached to the backbone by a pair of sacral ribs. The ilium slopes forward and the body is held closer to the ground than is the case in mammals. In most amphibians, there are four digits on the fore foot and five on the hind foot, but no claws on either. Some salamanders have fewer digits and the amphiumas are eel-like in appearance with tiny, stubby legs. The sirens are aquatic salamanders with stumpy forelimbs and no hind limbs. The caecilians are limbless. They burrow in the manner of earthworms with zones of muscle contractions moving along the body. On the surface of the ground or in water they move by undulating their body from side to side. In frogs, the hind legs are larger than the fore legs, especially so in those species that principally move by jumping or swimming. In the walkers and runners the hind limbs are not so large, and the burrowers mostly have short limbs and broad bodies. The feet have adaptations for the way of life, with webbing between the toes for swimming, broad adhesive toe pads for climbing, and keratinised tubercles on the hind feet for digging (frogs usually dig backwards into the soil). In most salamanders, the limbs are short and more or less the same length and project at right angles from the body. Locomotion on land is by walking and the tail often swings from side to side or is used as a prop, particularly when climbing. In their normal gait, only one leg is advanced at a time in the manner adopted by their ancestors, the lobe-finned fish. Some salamanders in the genus Aneides and certain plethodontids climb trees and have long limbs, large toepads and prehensile tails.

These three cell layers consist of the melanophores (occupying the deepest layer), the guanophores (forming an intermediate layer and containing many granules, producing a blue-green colour) and the lipophores (yellow, the most superficial layer). The colour change displayed by many species is initiated by hormones secreted by the pituitary gland. Unlike bony fish, there is no direct control of the pigment cells by the nervous system, and this results in the colour change taking place more slowly than happens in fish. A vividly coloured skin usually indicates that the species is toxic and is a warning sign to predators. Skeletal system and locomotion Amphibians have a skeletal system that is structurally homologous to other tetrapods, though with a number of variations. They all have four limbs except for the legless caecilians and a few species of salamander with reduced or no limbs. The bones are hollow and lightweight. The musculoskeletal system is strong to enable it to support the head and body. The bones are fully ossified and the vertebrae interlock with each other by means of overlapping processes. The pectoral girdle is supported by muscle, and the well-developed pelvic girdle is attached to the backbone by a pair of sacral ribs. The ilium slopes forward and the body is held closer to the ground than is the case in mammals. In most amphibians, there are four digits on the fore foot and five on the hind foot, but no claws on either. Some salamanders have fewer digits and the amphiumas are eel-like in appearance with tiny, stubby legs. The sirens are aquatic salamanders with stumpy forelimbs and no hind limbs. The caecilians are limbless. They burrow in the manner of earthworms with zones of muscle contractions moving along the body. On the surface of the ground or in water they move by undulating their body from side to side. In frogs, the hind legs are larger than the fore legs, especially so in those species that principally move by jumping or swimming. In the walkers and runners the hind limbs are not so large, and the burrowers mostly have short limbs and broad bodies. The feet have adaptations for the way of life, with webbing between the toes for swimming, broad adhesive toe pads for climbing, and keratinised tubercles on the hind feet for digging (frogs usually dig backwards into the soil). In most salamanders, the limbs are short and more or less the same length and project at right angles from the body. Locomotion on land is by walking and the tail often swings from side to side or is used as a prop, particularly when climbing. In their normal gait, only one leg is advanced at a time in the manner adopted by their ancestors, the lobe-finned fish. Some salamanders in the genus Aneides and certain plethodontids climb trees and have long limbs, large toepads and prehensile tails.

These three cell layers consist of the melanophores (occupying the deepest layer), the guanophores (forming an intermediate layer and containing many granules, producing a blue-green colour) and the lipophores (yellow, the most superficial layer). The colour change displayed by many species is initiated by hormones secreted by the pituitary gland. Unlike bony fish, there is no direct control of the pigment cells by the nervous system, and this results in the colour change taking place more slowly than happens in fish. A vividly coloured skin usually indicates that the species is toxic and is a warning sign to predators. Skeletal system and locomotion Amphibians have a skeletal system that is structurally homologous to other tetrapods, though with a number of variations. They all have four limbs except for the legless caecilians and a few species of salamander with reduced or no limbs. The bones are hollow and lightweight. The musculoskeletal system is strong to enable it to support the head and body. The bones are fully ossified and the vertebrae interlock with each other by means of overlapping processes. The pectoral girdle is supported by muscle, and the well-developed pelvic girdle is attached to the backbone by a pair of sacral ribs. The ilium slopes forward and the body is held closer to the ground than is the case in mammals. In most amphibians, there are four digits on the fore foot and five on the hind foot, but no claws on either. Some salamanders have fewer digits and the amphiumas are eel-like in appearance with tiny, stubby legs. The sirens are aquatic salamanders with stumpy forelimbs and no hind limbs. The caecilians are limbless. They burrow in the manner of earthworms with zones of muscle contractions moving along the body. On the surface of the ground or in water they move by undulating their body from side to side. In frogs, the hind legs are larger than the fore legs, especially so in those species that principally move by jumping or swimming. In the walkers and runners the hind limbs are not so large, and the burrowers mostly have short limbs and broad bodies. The feet have adaptations for the way of life, with webbing between the toes for swimming, broad adhesive toe pads for climbing, and keratinised tubercles on the hind feet for digging (frogs usually dig backwards into the soil). In most salamanders, the limbs are short and more or less the same length and project at right angles from the body. Locomotion on land is by walking and the tail often swings from side to side or is used as a prop, particularly when climbing. In their normal gait, only one leg is advanced at a time in the manner adopted by their ancestors, the lobe-finned fish. Some salamanders in the genus Aneides and certain plethodontids climb trees and have long limbs, large toepads and prehensile tails.

In aquatic salamanders and in frog tadpoles, the tail has dorsal and ventral fins and is moved from side to side as a means of propulsion. Adult frogs do not have tails and caecilians have only very short ones. Salamanders use their tails in defence and some are prepared to jettison them to save their lives in a process known as autotomy. Certain species in the Plethodontidae have a weak zone at the base of the tail and use this strategy readily. The tail often continues to twitch after separation which may distract the attacker and allow the salamander to escape. Both tails and limbs can be regenerated. Adult frogs are unable to regrow limbs but tadpoles can do so. Circulatory system Amphibians have a juvenile stage and an adult stage, and the circulatory systems of the two are distinct. In the juvenile (or tadpole) stage, the circulation is similar to that of a fish; the two-chambered heart pumps the blood through the gills where it is oxygenated, and is spread around the body and back to the heart in a single loop. In the adult stage, amphibians (especially frogs) lose their gills and develop lungs. They have a heart that consists of a single ventricle and two atria. When the ventricle starts contracting, deoxygenated blood is pumped through the pulmonary artery to the lungs. Continued contraction then pumps oxygenated blood around the rest of the body. Mixing of the two bloodstreams is minimized by the anatomy of the chambers. Nervous and sensory systems The nervous system is basically the same as in other vertebrates, with a central brain, a spinal cord, and nerves throughout the body. The amphibian brain is less well developed than that of reptiles, birds and mammals but is similar in morphology and function to that of a fish. It is believed amphibians are capable of perceiving pain. The brain consists of equal parts, cerebrum, midbrain and cerebellum. Various parts of the cerebrum process sensory input, such as smell in the olfactory lobe and sight in the optic lobe, and it is additionally the centre of behaviour and learning. The cerebellum is the center of muscular coordination and the medulla oblongata controls some organ functions including heartbeat and respiration. The brain sends signals through the spinal cord and nerves to regulate activity in the rest of the body. The pineal body, known to regulate sleep patterns in humans, is thought to produce the hormones involved in hibernation and aestivation in amphibians. Tadpoles retain the lateral line system of their ancestral fishes, but this is lost in terrestrial adult amphibians. Some caecilians possess electroreceptors that allow them to locate objects around them when submerged in water. The ears are well developed in frogs. There is no external ear, but the large circular eardrum lies on the surface of the head just behind the eye. This vibrates and sound is transmitted through a single bone, the stapes, to the inner ear.

In aquatic salamanders and in frog tadpoles, the tail has dorsal and ventral fins and is moved from side to side as a means of propulsion. Adult frogs do not have tails and caecilians have only very short ones. Salamanders use their tails in defence and some are prepared to jettison them to save their lives in a process known as autotomy. Certain species in the Plethodontidae have a weak zone at the base of the tail and use this strategy readily. The tail often continues to twitch after separation which may distract the attacker and allow the salamander to escape. Both tails and limbs can be regenerated. Adult frogs are unable to regrow limbs but tadpoles can do so. Circulatory system Amphibians have a juvenile stage and an adult stage, and the circulatory systems of the two are distinct. In the juvenile (or tadpole) stage, the circulation is similar to that of a fish; the two-chambered heart pumps the blood through the gills where it is oxygenated, and is spread around the body and back to the heart in a single loop. In the adult stage, amphibians (especially frogs) lose their gills and develop lungs. They have a heart that consists of a single ventricle and two atria. When the ventricle starts contracting, deoxygenated blood is pumped through the pulmonary artery to the lungs. Continued contraction then pumps oxygenated blood around the rest of the body. Mixing of the two bloodstreams is minimized by the anatomy of the chambers. Nervous and sensory systems The nervous system is basically the same as in other vertebrates, with a central brain, a spinal cord, and nerves throughout the body. The amphibian brain is less well developed than that of reptiles, birds and mammals but is similar in morphology and function to that of a fish. It is believed amphibians are capable of perceiving pain. The brain consists of equal parts, cerebrum, midbrain and cerebellum. Various parts of the cerebrum process sensory input, such as smell in the olfactory lobe and sight in the optic lobe, and it is additionally the centre of behaviour and learning. The cerebellum is the center of muscular coordination and the medulla oblongata controls some organ functions including heartbeat and respiration. The brain sends signals through the spinal cord and nerves to regulate activity in the rest of the body. The pineal body, known to regulate sleep patterns in humans, is thought to produce the hormones involved in hibernation and aestivation in amphibians. Tadpoles retain the lateral line system of their ancestral fishes, but this is lost in terrestrial adult amphibians. Some caecilians possess electroreceptors that allow them to locate objects around them when submerged in water. The ears are well developed in frogs. There is no external ear, but the large circular eardrum lies on the surface of the head just behind the eye. This vibrates and sound is transmitted through a single bone, the stapes, to the inner ear.

In aquatic salamanders and in frog tadpoles, the tail has dorsal and ventral fins and is moved from side to side as a means of propulsion. Adult frogs do not have tails and caecilians have only very short ones. Salamanders use their tails in defence and some are prepared to jettison them to save their lives in a process known as autotomy. Certain species in the Plethodontidae have a weak zone at the base of the tail and use this strategy readily. The tail often continues to twitch after separation which may distract the attacker and allow the salamander to escape. Both tails and limbs can be regenerated. Adult frogs are unable to regrow limbs but tadpoles can do so. Circulatory system Amphibians have a juvenile stage and an adult stage, and the circulatory systems of the two are distinct. In the juvenile (or tadpole) stage, the circulation is similar to that of a fish; the two-chambered heart pumps the blood through the gills where it is oxygenated, and is spread around the body and back to the heart in a single loop. In the adult stage, amphibians (especially frogs) lose their gills and develop lungs. They have a heart that consists of a single ventricle and two atria. When the ventricle starts contracting, deoxygenated blood is pumped through the pulmonary artery to the lungs. Continued contraction then pumps oxygenated blood around the rest of the body. Mixing of the two bloodstreams is minimized by the anatomy of the chambers. Nervous and sensory systems The nervous system is basically the same as in other vertebrates, with a central brain, a spinal cord, and nerves throughout the body. The amphibian brain is less well developed than that of reptiles, birds and mammals but is similar in morphology and function to that of a fish. It is believed amphibians are capable of perceiving pain. The brain consists of equal parts, cerebrum, midbrain and cerebellum. Various parts of the cerebrum process sensory input, such as smell in the olfactory lobe and sight in the optic lobe, and it is additionally the centre of behaviour and learning. The cerebellum is the center of muscular coordination and the medulla oblongata controls some organ functions including heartbeat and respiration. The brain sends signals through the spinal cord and nerves to regulate activity in the rest of the body. The pineal body, known to regulate sleep patterns in humans, is thought to produce the hormones involved in hibernation and aestivation in amphibians. Tadpoles retain the lateral line system of their ancestral fishes, but this is lost in terrestrial adult amphibians. Some caecilians possess electroreceptors that allow them to locate objects around them when submerged in water. The ears are well developed in frogs. There is no external ear, but the large circular eardrum lies on the surface of the head just behind the eye. This vibrates and sound is transmitted through a single bone, the stapes, to the inner ear.

Only high-frequency sounds like mating calls are heard in this way, but low-frequency noises can be detected through another mechanism. There is a patch of specialized haircells, called papilla amphibiorum, in the inner ear capable of detecting deeper sounds. Another feature, unique to frogs and salamanders, is the columella-operculum complex adjoining the auditory capsule which is involved in the transmission of both airborne and seismic signals. The ears of salamanders and caecilians are less highly developed than those of frogs as they do not normally communicate with each other through the medium of sound. The eyes of tadpoles lack lids, but at metamorphosis, the cornea becomes more dome-shaped, the lens becomes flatter, and eyelids and associated glands and ducts develop. The adult eyes are an improvement on invertebrate eyes and were a first step in the development of more advanced vertebrate eyes. They allow colour vision and depth of focus. In the retinas are green rods, which are receptive to a wide range of wavelengths. Digestive and excretory systems Many amphibians catch their prey by flicking out an elongated tongue with a sticky tip and drawing it back into the mouth before seizing the item with their jaws. Some use inertial feeding to help them swallow the prey, repeatedly thrusting their head forward sharply causing the food to move backwards in their mouth by inertia. Most amphibians swallow their prey whole without much chewing so they possess voluminous stomachs. The short oesophagus is lined with cilia that help to move the food to the stomach and mucus produced by glands in the mouth and pharynx eases its passage. The enzyme chitinase produced in the stomach helps digest the chitinous cuticle of arthropod prey. Amphibians possess a pancreas, liver and gall bladder. The liver is usually large with two lobes. Its size is determined by its function as a glycogen and fat storage unit, and may change with the seasons as these reserves are built or used up. Adipose tissue is another important means of storing energy and this occurs in the abdomen (in internal structures called fat bodies), under the skin and, in some salamanders, in the tail. There are two kidneys located dorsally, near the roof of the body cavity. Their job is to filter the blood of metabolic waste and transport the urine via ureters to the urinary bladder where it is stored before being passed out periodically through the cloacal vent. Larvae and most aquatic adult amphibians excrete the nitrogen as ammonia in large quantities of dilute urine, while terrestrial species, with a greater need to conserve water, excrete the less toxic product urea. Some tree frogs with limited access to water excrete most of their metabolic waste as uric acid. Respiratory system The lungs in amphibians are primitive compared to those of amniotes, possessing few internal septa and large alveoli, and consequently having a comparatively slow diffusion rate for oxygen entering the blood. Ventilation is accomplished by buccal pumping.

Only high-frequency sounds like mating calls are heard in this way, but low-frequency noises can be detected through another mechanism. There is a patch of specialized haircells, called papilla amphibiorum, in the inner ear capable of detecting deeper sounds. Another feature, unique to frogs and salamanders, is the columella-operculum complex adjoining the auditory capsule which is involved in the transmission of both airborne and seismic signals. The ears of salamanders and caecilians are less highly developed than those of frogs as they do not normally communicate with each other through the medium of sound. The eyes of tadpoles lack lids, but at metamorphosis, the cornea becomes more dome-shaped, the lens becomes flatter, and eyelids and associated glands and ducts develop. The adult eyes are an improvement on invertebrate eyes and were a first step in the development of more advanced vertebrate eyes. They allow colour vision and depth of focus. In the retinas are green rods, which are receptive to a wide range of wavelengths. Digestive and excretory systems Many amphibians catch their prey by flicking out an elongated tongue with a sticky tip and drawing it back into the mouth before seizing the item with their jaws. Some use inertial feeding to help them swallow the prey, repeatedly thrusting their head forward sharply causing the food to move backwards in their mouth by inertia. Most amphibians swallow their prey whole without much chewing so they possess voluminous stomachs. The short oesophagus is lined with cilia that help to move the food to the stomach and mucus produced by glands in the mouth and pharynx eases its passage. The enzyme chitinase produced in the stomach helps digest the chitinous cuticle of arthropod prey. Amphibians possess a pancreas, liver and gall bladder. The liver is usually large with two lobes. Its size is determined by its function as a glycogen and fat storage unit, and may change with the seasons as these reserves are built or used up. Adipose tissue is another important means of storing energy and this occurs in the abdomen (in internal structures called fat bodies), under the skin and, in some salamanders, in the tail. There are two kidneys located dorsally, near the roof of the body cavity. Their job is to filter the blood of metabolic waste and transport the urine via ureters to the urinary bladder where it is stored before being passed out periodically through the cloacal vent. Larvae and most aquatic adult amphibians excrete the nitrogen as ammonia in large quantities of dilute urine, while terrestrial species, with a greater need to conserve water, excrete the less toxic product urea. Some tree frogs with limited access to water excrete most of their metabolic waste as uric acid. Respiratory system The lungs in amphibians are primitive compared to those of amniotes, possessing few internal septa and large alveoli, and consequently having a comparatively slow diffusion rate for oxygen entering the blood. Ventilation is accomplished by buccal pumping.

Only high-frequency sounds like mating calls are heard in this way, but low-frequency noises can be detected through another mechanism. There is a patch of specialized haircells, called papilla amphibiorum, in the inner ear capable of detecting deeper sounds. Another feature, unique to frogs and salamanders, is the columella-operculum complex adjoining the auditory capsule which is involved in the transmission of both airborne and seismic signals. The ears of salamanders and caecilians are less highly developed than those of frogs as they do not normally communicate with each other through the medium of sound. The eyes of tadpoles lack lids, but at metamorphosis, the cornea becomes more dome-shaped, the lens becomes flatter, and eyelids and associated glands and ducts develop. The adult eyes are an improvement on invertebrate eyes and were a first step in the development of more advanced vertebrate eyes. They allow colour vision and depth of focus. In the retinas are green rods, which are receptive to a wide range of wavelengths. Digestive and excretory systems Many amphibians catch their prey by flicking out an elongated tongue with a sticky tip and drawing it back into the mouth before seizing the item with their jaws. Some use inertial feeding to help them swallow the prey, repeatedly thrusting their head forward sharply causing the food to move backwards in their mouth by inertia. Most amphibians swallow their prey whole without much chewing so they possess voluminous stomachs. The short oesophagus is lined with cilia that help to move the food to the stomach and mucus produced by glands in the mouth and pharynx eases its passage. The enzyme chitinase produced in the stomach helps digest the chitinous cuticle of arthropod prey. Amphibians possess a pancreas, liver and gall bladder. The liver is usually large with two lobes. Its size is determined by its function as a glycogen and fat storage unit, and may change with the seasons as these reserves are built or used up. Adipose tissue is another important means of storing energy and this occurs in the abdomen (in internal structures called fat bodies), under the skin and, in some salamanders, in the tail. There are two kidneys located dorsally, near the roof of the body cavity. Their job is to filter the blood of metabolic waste and transport the urine via ureters to the urinary bladder where it is stored before being passed out periodically through the cloacal vent. Larvae and most aquatic adult amphibians excrete the nitrogen as ammonia in large quantities of dilute urine, while terrestrial species, with a greater need to conserve water, excrete the less toxic product urea. Some tree frogs with limited access to water excrete most of their metabolic waste as uric acid. Respiratory system The lungs in amphibians are primitive compared to those of amniotes, possessing few internal septa and large alveoli, and consequently having a comparatively slow diffusion rate for oxygen entering the blood. Ventilation is accomplished by buccal pumping.

Most amphibians, however, are able to exchange gases with the water or air via their skin. To enable sufficient cutaneous respiration, the surface of their highly vascularised skin must remain moist to allow the oxygen to diffuse at a sufficiently high rate. Because oxygen concentration in the water increases at both low temperatures and high flow rates, aquatic amphibians in these situations can rely primarily on cutaneous respiration, as in the Titicaca water frog and the hellbender salamander. In air, where oxygen is more concentrated, some small species can rely solely on cutaneous gas exchange, most famously the plethodontid salamanders, which have neither lungs nor gills. Many aquatic salamanders and all tadpoles have gills in their larval stage, with some (such as the axolotl) retaining gills as aquatic adults. Reproduction For the purpose of reproduction most amphibians require fresh water although some lay their eggs on land and have developed various means of keeping them moist. A few (e.g. Fejervarya raja) can inhabit brackish water, but there are no true marine amphibians. There are reports, however, of particular amphibian populations unexpectedly invading marine waters. Such was the case with the Black Sea invasion of the natural hybrid Pelophylax esculentus reported in 2010. Several hundred frog species in adaptive radiations (e.g., Eleutherodactylus, the Pacific Platymantis, the Australo-Papuan microhylids, and many other tropical frogs), however, do not need any water for breeding in the wild. They reproduce via direct development, an ecological and evolutionary adaptation that has allowed them to be completely independent from free-standing water. Almost all of these frogs live in wet tropical rainforests and their eggs hatch directly into miniature versions of the adult, passing through the tadpole stage within the egg. Reproductive success of many amphibians is dependent not only on the quantity of rainfall, but the seasonal timing. In the tropics, many amphibians breed continuously or at any time of year. In temperate regions, breeding is mostly seasonal, usually in the spring, and is triggered by increasing day length, rising temperatures or rainfall. Experiments have shown the importance of temperature, but the trigger event, especially in arid regions, is often a storm. In anurans, males usually arrive at the breeding sites before females and the vocal chorus they produce may stimulate ovulation in females and the endocrine activity of males that are not yet reproductively active. In caecilians, fertilisation is internal, the male extruding an intromittent organ, the , and inserting it into the female cloaca. The paired Müllerian glands inside the male cloaca secrete a fluid which resembles that produced by mammalian prostate glands and which may transport and nourish the sperm. Fertilisation probably takes place in the oviduct. The majority of salamanders also engage in internal fertilisation. In most of these, the male deposits a spermatophore, a small packet of sperm on top of a gelatinous cone, on the substrate either on land or in the water.

Most amphibians, however, are able to exchange gases with the water or air via their skin. To enable sufficient cutaneous respiration, the surface of their highly vascularised skin must remain moist to allow the oxygen to diffuse at a sufficiently high rate. Because oxygen concentration in the water increases at both low temperatures and high flow rates, aquatic amphibians in these situations can rely primarily on cutaneous respiration, as in the Titicaca water frog and the hellbender salamander. In air, where oxygen is more concentrated, some small species can rely solely on cutaneous gas exchange, most famously the plethodontid salamanders, which have neither lungs nor gills. Many aquatic salamanders and all tadpoles have gills in their larval stage, with some (such as the axolotl) retaining gills as aquatic adults. Reproduction For the purpose of reproduction most amphibians require fresh water although some lay their eggs on land and have developed various means of keeping them moist. A few (e.g. Fejervarya raja) can inhabit brackish water, but there are no true marine amphibians. There are reports, however, of particular amphibian populations unexpectedly invading marine waters. Such was the case with the Black Sea invasion of the natural hybrid Pelophylax esculentus reported in 2010. Several hundred frog species in adaptive radiations (e.g., Eleutherodactylus, the Pacific Platymantis, the Australo-Papuan microhylids, and many other tropical frogs), however, do not need any water for breeding in the wild. They reproduce via direct development, an ecological and evolutionary adaptation that has allowed them to be completely independent from free-standing water. Almost all of these frogs live in wet tropical rainforests and their eggs hatch directly into miniature versions of the adult, passing through the tadpole stage within the egg. Reproductive success of many amphibians is dependent not only on the quantity of rainfall, but the seasonal timing. In the tropics, many amphibians breed continuously or at any time of year. In temperate regions, breeding is mostly seasonal, usually in the spring, and is triggered by increasing day length, rising temperatures or rainfall. Experiments have shown the importance of temperature, but the trigger event, especially in arid regions, is often a storm. In anurans, males usually arrive at the breeding sites before females and the vocal chorus they produce may stimulate ovulation in females and the endocrine activity of males that are not yet reproductively active. In caecilians, fertilisation is internal, the male extruding an intromittent organ, the , and inserting it into the female cloaca. The paired Müllerian glands inside the male cloaca secrete a fluid which resembles that produced by mammalian prostate glands and which may transport and nourish the sperm. Fertilisation probably takes place in the oviduct. The majority of salamanders also engage in internal fertilisation. In most of these, the male deposits a spermatophore, a small packet of sperm on top of a gelatinous cone, on the substrate either on land or in the water.

Most amphibians, however, are able to exchange gases with the water or air via their skin. To enable sufficient cutaneous respiration, the surface of their highly vascularised skin must remain moist to allow the oxygen to diffuse at a sufficiently high rate. Because oxygen concentration in the water increases at both low temperatures and high flow rates, aquatic amphibians in these situations can rely primarily on cutaneous respiration, as in the Titicaca water frog and the hellbender salamander. In air, where oxygen is more concentrated, some small species can rely solely on cutaneous gas exchange, most famously the plethodontid salamanders, which have neither lungs nor gills. Many aquatic salamanders and all tadpoles have gills in their larval stage, with some (such as the axolotl) retaining gills as aquatic adults. Reproduction For the purpose of reproduction most amphibians require fresh water although some lay their eggs on land and have developed various means of keeping them moist. A few (e.g. Fejervarya raja) can inhabit brackish water, but there are no true marine amphibians. There are reports, however, of particular amphibian populations unexpectedly invading marine waters. Such was the case with the Black Sea invasion of the natural hybrid Pelophylax esculentus reported in 2010. Several hundred frog species in adaptive radiations (e.g., Eleutherodactylus, the Pacific Platymantis, the Australo-Papuan microhylids, and many other tropical frogs), however, do not need any water for breeding in the wild. They reproduce via direct development, an ecological and evolutionary adaptation that has allowed them to be completely independent from free-standing water. Almost all of these frogs live in wet tropical rainforests and their eggs hatch directly into miniature versions of the adult, passing through the tadpole stage within the egg. Reproductive success of many amphibians is dependent not only on the quantity of rainfall, but the seasonal timing. In the tropics, many amphibians breed continuously or at any time of year. In temperate regions, breeding is mostly seasonal, usually in the spring, and is triggered by increasing day length, rising temperatures or rainfall. Experiments have shown the importance of temperature, but the trigger event, especially in arid regions, is often a storm. In anurans, males usually arrive at the breeding sites before females and the vocal chorus they produce may stimulate ovulation in females and the endocrine activity of males that are not yet reproductively active. In caecilians, fertilisation is internal, the male extruding an intromittent organ, the , and inserting it into the female cloaca. The paired Müllerian glands inside the male cloaca secrete a fluid which resembles that produced by mammalian prostate glands and which may transport and nourish the sperm. Fertilisation probably takes place in the oviduct. The majority of salamanders also engage in internal fertilisation. In most of these, the male deposits a spermatophore, a small packet of sperm on top of a gelatinous cone, on the substrate either on land or in the water.

The female takes up the sperm packet by grasping it with the lips of the cloaca and pushing it into the vent. The spermatozoa move to the spermatheca in the roof of the cloaca where they remain until ovulation which may be many months later. Courtship rituals and methods of transfer of the spermatophore vary between species. In some, the spermatophore may be placed directly into the female cloaca while in others, the female may be guided to the spermatophore or restrained with an embrace called amplexus. Certain primitive salamanders in the families Sirenidae, Hynobiidae and Cryptobranchidae practice external fertilisation in a similar manner to frogs, with the female laying the eggs in water and the male releasing sperm onto the egg mass. With a few exceptions, frogs use external fertilisation. The male grasps the female tightly with his forelimbs either behind the arms or in front of the back legs, or in the case of Epipedobates tricolor, around the neck. They remain in amplexus with their cloacae positioned close together while the female lays the eggs and the male covers them with sperm. Roughened nuptial pads on the male's hands aid in retaining grip. Often the male collects and retains the egg mass, forming a sort of basket with the hind feet. An exception is the granular poison frog (Oophaga granulifera) where the male and female place their cloacae in close proximity while facing in opposite directions and then release eggs and sperm simultaneously. The tailed frog (Ascaphus truei) exhibits internal fertilisation. The "tail" is only possessed by the male and is an extension of the cloaca and used to inseminate the female. This frog lives in fast-flowing streams and internal fertilisation prevents the sperm from being washed away before fertilisation occurs. The sperm may be retained in storage tubes attached to the oviduct until the following spring. Most frogs can be classified as either prolonged or explosive breeders. Typically, prolonged breeders congregate at a breeding site, the males usually arriving first, calling and setting up territories. Other satellite males remain quietly nearby, waiting for their opportunity to take over a territory. The females arrive sporadically, mate selection takes place and eggs are laid. The females depart and territories may change hands. More females appear and in due course, the breeding season comes to an end. Explosive breeders on the other hand are found where temporary pools appear in dry regions after rainfall. These frogs are typically fossorial species that emerge after heavy rains and congregate at a breeding site. They are attracted there by the calling of the first male to find a suitable place, perhaps a pool that forms in the same place each rainy season. The assembled frogs may call in unison and frenzied activity ensues, the males scrambling to mate with the usually smaller number of females.

The female takes up the sperm packet by grasping it with the lips of the cloaca and pushing it into the vent. The spermatozoa move to the spermatheca in the roof of the cloaca where they remain until ovulation which may be many months later. Courtship rituals and methods of transfer of the spermatophore vary between species. In some, the spermatophore may be placed directly into the female cloaca while in others, the female may be guided to the spermatophore or restrained with an embrace called amplexus. Certain primitive salamanders in the families Sirenidae, Hynobiidae and Cryptobranchidae practice external fertilisation in a similar manner to frogs, with the female laying the eggs in water and the male releasing sperm onto the egg mass. With a few exceptions, frogs use external fertilisation. The male grasps the female tightly with his forelimbs either behind the arms or in front of the back legs, or in the case of Epipedobates tricolor, around the neck. They remain in amplexus with their cloacae positioned close together while the female lays the eggs and the male covers them with sperm. Roughened nuptial pads on the male's hands aid in retaining grip. Often the male collects and retains the egg mass, forming a sort of basket with the hind feet. An exception is the granular poison frog (Oophaga granulifera) where the male and female place their cloacae in close proximity while facing in opposite directions and then release eggs and sperm simultaneously. The tailed frog (Ascaphus truei) exhibits internal fertilisation. The "tail" is only possessed by the male and is an extension of the cloaca and used to inseminate the female. This frog lives in fast-flowing streams and internal fertilisation prevents the sperm from being washed away before fertilisation occurs. The sperm may be retained in storage tubes attached to the oviduct until the following spring. Most frogs can be classified as either prolonged or explosive breeders. Typically, prolonged breeders congregate at a breeding site, the males usually arriving first, calling and setting up territories. Other satellite males remain quietly nearby, waiting for their opportunity to take over a territory. The females arrive sporadically, mate selection takes place and eggs are laid. The females depart and territories may change hands. More females appear and in due course, the breeding season comes to an end. Explosive breeders on the other hand are found where temporary pools appear in dry regions after rainfall. These frogs are typically fossorial species that emerge after heavy rains and congregate at a breeding site. They are attracted there by the calling of the first male to find a suitable place, perhaps a pool that forms in the same place each rainy season. The assembled frogs may call in unison and frenzied activity ensues, the males scrambling to mate with the usually smaller number of females.

The female takes up the sperm packet by grasping it with the lips of the cloaca and pushing it into the vent. The spermatozoa move to the spermatheca in the roof of the cloaca where they remain until ovulation which may be many months later. Courtship rituals and methods of transfer of the spermatophore vary between species. In some, the spermatophore may be placed directly into the female cloaca while in others, the female may be guided to the spermatophore or restrained with an embrace called amplexus. Certain primitive salamanders in the families Sirenidae, Hynobiidae and Cryptobranchidae practice external fertilisation in a similar manner to frogs, with the female laying the eggs in water and the male releasing sperm onto the egg mass. With a few exceptions, frogs use external fertilisation. The male grasps the female tightly with his forelimbs either behind the arms or in front of the back legs, or in the case of Epipedobates tricolor, around the neck. They remain in amplexus with their cloacae positioned close together while the female lays the eggs and the male covers them with sperm. Roughened nuptial pads on the male's hands aid in retaining grip. Often the male collects and retains the egg mass, forming a sort of basket with the hind feet. An exception is the granular poison frog (Oophaga granulifera) where the male and female place their cloacae in close proximity while facing in opposite directions and then release eggs and sperm simultaneously. The tailed frog (Ascaphus truei) exhibits internal fertilisation. The "tail" is only possessed by the male and is an extension of the cloaca and used to inseminate the female. This frog lives in fast-flowing streams and internal fertilisation prevents the sperm from being washed away before fertilisation occurs. The sperm may be retained in storage tubes attached to the oviduct until the following spring. Most frogs can be classified as either prolonged or explosive breeders. Typically, prolonged breeders congregate at a breeding site, the males usually arriving first, calling and setting up territories. Other satellite males remain quietly nearby, waiting for their opportunity to take over a territory. The females arrive sporadically, mate selection takes place and eggs are laid. The females depart and territories may change hands. More females appear and in due course, the breeding season comes to an end. Explosive breeders on the other hand are found where temporary pools appear in dry regions after rainfall. These frogs are typically fossorial species that emerge after heavy rains and congregate at a breeding site. They are attracted there by the calling of the first male to find a suitable place, perhaps a pool that forms in the same place each rainy season. The assembled frogs may call in unison and frenzied activity ensues, the males scrambling to mate with the usually smaller number of females.

There is a direct competition between males to win the attention of the females in salamanders and newts, with elaborate courtship displays to keep the female's attention long enough to get her interested in choosing him to mate with. Some species store sperm through long breeding seasons, as the extra time may allow for interactions with rival sperm. Life cycle Most amphibians go through metamorphosis, a process of significant morphological change after birth. In typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. Frogs, toads and salamanders all hatch from the egg as larvae with external gills. Metamorphosis in amphibians is regulated by thyroxine concentration in the blood, which stimulates metamorphosis, and prolactin, which counteracts thyroxine's effect. Specific events are dependent on threshold values for different tissues. Because most embryonic development is outside the parental body, it is subject to many adaptations due to specific environmental circumstances. For this reason tadpoles can have horny ridges instead of Teeth, whisker-like skin extensions or fins. They also make use of a sensory lateral line organ similar to that of fish. After metamorphosis, these organs become redundant and will be reabsorbed by controlled cell death, called apoptosis. The variety of adaptations to specific environmental circumstances among amphibians is wide, with many discoveries still being made. Eggs The egg of an amphibian is typically surrounded by a transparent gelatinous covering secreted by the oviducts and containing mucoproteins and mucopolysaccharides. This capsule is permeable to water and gases, and swells considerably as it absorbs water. The ovum is at first rigidly held, but in fertilised eggs the innermost layer liquefies and allows the embryo to move freely. This also happens in salamander eggs, even when they are unfertilised. Eggs of some salamanders and frogs contain unicellular green algae. These penetrate the jelly envelope after the eggs are laid and may increase the supply of oxygen to the embryo through photosynthesis. They seem to both speed up the development of the larvae and reduce mortality. Most eggs contain the pigment melanin which raises their temperature through the absorption of light and also protects them against ultraviolet radiation. Caecilians, some plethodontid salamanders and certain frogs lay eggs underground that are unpigmented. In the wood frog (Rana sylvatica), the interior of the globular egg cluster has been found to be up to warmer than its surroundings, which is an advantage in its cool northern habitat. The eggs may be deposited singly or in small groups, or may take the form of spherical egg masses, rafts or long strings. In terrestrial caecilians, the eggs are laid in grape-like clusters in burrows near streams. The amphibious salamander Ensatina attaches its similar clusters by stalks to underwater stems and roots. The greenhouse frog (Eleutherodactylus planirostris) lays eggs in small groups in the soil where they develop in about two weeks directly into juvenile frogs without an intervening larval stage. The tungara frog (Physalaemus pustulosus) builds a floating nest from foam to protect its eggs.

There is a direct competition between males to win the attention of the females in salamanders and newts, with elaborate courtship displays to keep the female's attention long enough to get her interested in choosing him to mate with. Some species store sperm through long breeding seasons, as the extra time may allow for interactions with rival sperm. Life cycle Most amphibians go through metamorphosis, a process of significant morphological change after birth. In typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. Frogs, toads and salamanders all hatch from the egg as larvae with external gills. Metamorphosis in amphibians is regulated by thyroxine concentration in the blood, which stimulates metamorphosis, and prolactin, which counteracts thyroxine's effect. Specific events are dependent on threshold values for different tissues. Because most embryonic development is outside the parental body, it is subject to many adaptations due to specific environmental circumstances. For this reason tadpoles can have horny ridges instead of Teeth, whisker-like skin extensions or fins. They also make use of a sensory lateral line organ similar to that of fish. After metamorphosis, these organs become redundant and will be reabsorbed by controlled cell death, called apoptosis. The variety of adaptations to specific environmental circumstances among amphibians is wide, with many discoveries still being made. Eggs The egg of an amphibian is typically surrounded by a transparent gelatinous covering secreted by the oviducts and containing mucoproteins and mucopolysaccharides. This capsule is permeable to water and gases, and swells considerably as it absorbs water. The ovum is at first rigidly held, but in fertilised eggs the innermost layer liquefies and allows the embryo to move freely. This also happens in salamander eggs, even when they are unfertilised. Eggs of some salamanders and frogs contain unicellular green algae. These penetrate the jelly envelope after the eggs are laid and may increase the supply of oxygen to the embryo through photosynthesis. They seem to both speed up the development of the larvae and reduce mortality. Most eggs contain the pigment melanin which raises their temperature through the absorption of light and also protects them against ultraviolet radiation. Caecilians, some plethodontid salamanders and certain frogs lay eggs underground that are unpigmented. In the wood frog (Rana sylvatica), the interior of the globular egg cluster has been found to be up to warmer than its surroundings, which is an advantage in its cool northern habitat. The eggs may be deposited singly or in small groups, or may take the form of spherical egg masses, rafts or long strings. In terrestrial caecilians, the eggs are laid in grape-like clusters in burrows near streams. The amphibious salamander Ensatina attaches its similar clusters by stalks to underwater stems and roots. The greenhouse frog (Eleutherodactylus planirostris) lays eggs in small groups in the soil where they develop in about two weeks directly into juvenile frogs without an intervening larval stage. The tungara frog (Physalaemus pustulosus) builds a floating nest from foam to protect its eggs.

There is a direct competition between males to win the attention of the females in salamanders and newts, with elaborate courtship displays to keep the female's attention long enough to get her interested in choosing him to mate with. Some species store sperm through long breeding seasons, as the extra time may allow for interactions with rival sperm. Life cycle Most amphibians go through metamorphosis, a process of significant morphological change after birth. In typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. Frogs, toads and salamanders all hatch from the egg as larvae with external gills. Metamorphosis in amphibians is regulated by thyroxine concentration in the blood, which stimulates metamorphosis, and prolactin, which counteracts thyroxine's effect. Specific events are dependent on threshold values for different tissues. Because most embryonic development is outside the parental body, it is subject to many adaptations due to specific environmental circumstances. For this reason tadpoles can have horny ridges instead of Teeth, whisker-like skin extensions or fins. They also make use of a sensory lateral line organ similar to that of fish. After metamorphosis, these organs become redundant and will be reabsorbed by controlled cell death, called apoptosis. The variety of adaptations to specific environmental circumstances among amphibians is wide, with many discoveries still being made. Eggs The egg of an amphibian is typically surrounded by a transparent gelatinous covering secreted by the oviducts and containing mucoproteins and mucopolysaccharides. This capsule is permeable to water and gases, and swells considerably as it absorbs water. The ovum is at first rigidly held, but in fertilised eggs the innermost layer liquefies and allows the embryo to move freely. This also happens in salamander eggs, even when they are unfertilised. Eggs of some salamanders and frogs contain unicellular green algae. These penetrate the jelly envelope after the eggs are laid and may increase the supply of oxygen to the embryo through photosynthesis. They seem to both speed up the development of the larvae and reduce mortality. Most eggs contain the pigment melanin which raises their temperature through the absorption of light and also protects them against ultraviolet radiation. Caecilians, some plethodontid salamanders and certain frogs lay eggs underground that are unpigmented. In the wood frog (Rana sylvatica), the interior of the globular egg cluster has been found to be up to warmer than its surroundings, which is an advantage in its cool northern habitat. The eggs may be deposited singly or in small groups, or may take the form of spherical egg masses, rafts or long strings. In terrestrial caecilians, the eggs are laid in grape-like clusters in burrows near streams. The amphibious salamander Ensatina attaches its similar clusters by stalks to underwater stems and roots. The greenhouse frog (Eleutherodactylus planirostris) lays eggs in small groups in the soil where they develop in about two weeks directly into juvenile frogs without an intervening larval stage. The tungara frog (Physalaemus pustulosus) builds a floating nest from foam to protect its eggs.

First a raft is built, then eggs are laid in the centre, and finally a foam cap is overlaid. The foam has anti-microbial properties. It contains no detergents but is created by whipping up proteins and lectins secreted by the female. Larvae The eggs of amphibians are typically laid in water and hatch into free-living larvae that complete their development in water and later transform into either aquatic or terrestrial adults. In many species of frog and in most lungless salamanders (Plethodontidae), direct development takes place, the larvae growing within the eggs and emerging as miniature adults. Many caecilians and some other amphibians lay their eggs on land, and the newly hatched larvae wriggle or are transported to water bodies. Some caecilians, the alpine salamander (Salamandra atra) and some of the African live-bearing toads (Nectophrynoides spp.) are viviparous. Their larvae feed on glandular secretions and develop within the female's oviduct, often for long periods. Other amphibians, but not caecilians, are ovoviviparous. The eggs are retained in or on the parent's body, but the larvae subsist on the yolks of their eggs and receive no nourishment from the adult. The larvae emerge at varying stages of their growth, either before or after metamorphosis, according to their species. The toad genus Nectophrynoides exhibits all of these developmental patterns among its dozen or so members. Frogs Frog larvae are known as tadpoles and typically have oval bodies and long, vertically flattened tails with fins. The free-living larvae are normally fully aquatic, but the tadpoles of some species (such as Nannophrys ceylonensis) are semi-terrestrial and live among wet rocks. Tadpoles have cartilaginous skeletons, gills for respiration (external gills at first, internal gills later), lateral line systems and large tails that they use for swimming. Newly hatched tadpoles soon develop gill pouches that cover the gills. The lungs develop early and are used as accessory breathing organs, the tadpoles rising to the water surface to gulp air. Some species complete their development inside the egg and hatch directly into small frogs. These larvae do not have gills but instead have specialised areas of skin through which respiration takes place. While tadpoles do not have true teeth, in most species, the jaws have long, parallel rows of small keratinized structures called keradonts surrounded by a horny beak. Front legs are formed under the gill sac and hind legs become visible a few days later. Iodine and T4 (over stimulate the spectacular apoptosis [programmed cell death] of the cells of the larval gills, tail and fins) also stimulate the evolution of nervous systems transforming the aquatic, vegetarian tadpole into the terrestrial, carnivorous frog with better neurological, visuospatial, olfactory and cognitive abilities for hunting. In fact, tadpoles developing in ponds and streams are typically herbivorous. Pond tadpoles tend to have deep bodies, large caudal fins and small mouths; they swim in the quiet waters feeding on growing or loose fragments of vegetation.

First a raft is built, then eggs are laid in the centre, and finally a foam cap is overlaid. The foam has anti-microbial properties. It contains no detergents but is created by whipping up proteins and lectins secreted by the female. Larvae The eggs of amphibians are typically laid in water and hatch into free-living larvae that complete their development in water and later transform into either aquatic or terrestrial adults. In many species of frog and in most lungless salamanders (Plethodontidae), direct development takes place, the larvae growing within the eggs and emerging as miniature adults. Many caecilians and some other amphibians lay their eggs on land, and the newly hatched larvae wriggle or are transported to water bodies. Some caecilians, the alpine salamander (Salamandra atra) and some of the African live-bearing toads (Nectophrynoides spp.) are viviparous. Their larvae feed on glandular secretions and develop within the female's oviduct, often for long periods. Other amphibians, but not caecilians, are ovoviviparous. The eggs are retained in or on the parent's body, but the larvae subsist on the yolks of their eggs and receive no nourishment from the adult. The larvae emerge at varying stages of their growth, either before or after metamorphosis, according to their species. The toad genus Nectophrynoides exhibits all of these developmental patterns among its dozen or so members. Frogs Frog larvae are known as tadpoles and typically have oval bodies and long, vertically flattened tails with fins. The free-living larvae are normally fully aquatic, but the tadpoles of some species (such as Nannophrys ceylonensis) are semi-terrestrial and live among wet rocks. Tadpoles have cartilaginous skeletons, gills for respiration (external gills at first, internal gills later), lateral line systems and large tails that they use for swimming. Newly hatched tadpoles soon develop gill pouches that cover the gills. The lungs develop early and are used as accessory breathing organs, the tadpoles rising to the water surface to gulp air. Some species complete their development inside the egg and hatch directly into small frogs. These larvae do not have gills but instead have specialised areas of skin through which respiration takes place. While tadpoles do not have true teeth, in most species, the jaws have long, parallel rows of small keratinized structures called keradonts surrounded by a horny beak. Front legs are formed under the gill sac and hind legs become visible a few days later. Iodine and T4 (over stimulate the spectacular apoptosis [programmed cell death] of the cells of the larval gills, tail and fins) also stimulate the evolution of nervous systems transforming the aquatic, vegetarian tadpole into the terrestrial, carnivorous frog with better neurological, visuospatial, olfactory and cognitive abilities for hunting. In fact, tadpoles developing in ponds and streams are typically herbivorous. Pond tadpoles tend to have deep bodies, large caudal fins and small mouths; they swim in the quiet waters feeding on growing or loose fragments of vegetation.

First a raft is built, then eggs are laid in the centre, and finally a foam cap is overlaid. The foam has anti-microbial properties. It contains no detergents but is created by whipping up proteins and lectins secreted by the female. Larvae The eggs of amphibians are typically laid in water and hatch into free-living larvae that complete their development in water and later transform into either aquatic or terrestrial adults. In many species of frog and in most lungless salamanders (Plethodontidae), direct development takes place, the larvae growing within the eggs and emerging as miniature adults. Many caecilians and some other amphibians lay their eggs on land, and the newly hatched larvae wriggle or are transported to water bodies. Some caecilians, the alpine salamander (Salamandra atra) and some of the African live-bearing toads (Nectophrynoides spp.) are viviparous. Their larvae feed on glandular secretions and develop within the female's oviduct, often for long periods. Other amphibians, but not caecilians, are ovoviviparous. The eggs are retained in or on the parent's body, but the larvae subsist on the yolks of their eggs and receive no nourishment from the adult. The larvae emerge at varying stages of their growth, either before or after metamorphosis, according to their species. The toad genus Nectophrynoides exhibits all of these developmental patterns among its dozen or so members. Frogs Frog larvae are known as tadpoles and typically have oval bodies and long, vertically flattened tails with fins. The free-living larvae are normally fully aquatic, but the tadpoles of some species (such as Nannophrys ceylonensis) are semi-terrestrial and live among wet rocks. Tadpoles have cartilaginous skeletons, gills for respiration (external gills at first, internal gills later), lateral line systems and large tails that they use for swimming. Newly hatched tadpoles soon develop gill pouches that cover the gills. The lungs develop early and are used as accessory breathing organs, the tadpoles rising to the water surface to gulp air. Some species complete their development inside the egg and hatch directly into small frogs. These larvae do not have gills but instead have specialised areas of skin through which respiration takes place. While tadpoles do not have true teeth, in most species, the jaws have long, parallel rows of small keratinized structures called keradonts surrounded by a horny beak. Front legs are formed under the gill sac and hind legs become visible a few days later. Iodine and T4 (over stimulate the spectacular apoptosis [programmed cell death] of the cells of the larval gills, tail and fins) also stimulate the evolution of nervous systems transforming the aquatic, vegetarian tadpole into the terrestrial, carnivorous frog with better neurological, visuospatial, olfactory and cognitive abilities for hunting. In fact, tadpoles developing in ponds and streams are typically herbivorous. Pond tadpoles tend to have deep bodies, large caudal fins and small mouths; they swim in the quiet waters feeding on growing or loose fragments of vegetation.

Stream dwellers mostly have larger mouths, shallow bodies and caudal fins; they attach themselves to plants and stones and feed on the surface films of algae and bacteria. They also feed on diatoms, filtered from the water through the gills, and stir up the sediment at bottom of the pond, ingesting edible fragments. They have a relatively long, spiral-shaped gut to enable them to digest this diet. Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles and fish. Young of the Cuban tree frog (Osteopilus septentrionalis) can occasionally be cannibalistic, the younger tadpoles attacking a larger, more developed tadpole when it is undergoing metamorphosis. At metamorphosis, rapid changes in the body take place as the lifestyle of the frog changes completely. The spiral‐shaped mouth with horny tooth ridges is reabsorbed together with the spiral gut. The animal develops a large jaw, and its gills disappear along with its gill sac. Eyes and legs grow quickly, and a tongue is formed. There are associated changes in the neural networks such as development of stereoscopic vision and loss of the lateral line system. All this can happen in about a day. A few days later, the tail is reabsorbed, due to the higher thyroxine concentration required for this to take place. Salamanders At hatching, a typical salamander larva has eyes without lids, teeth in both upper and lower jaws, three pairs of feathery external gills, a somewhat laterally flattened body and a long tail with dorsal and ventral fins. The forelimbs may be partially developed and the hind limbs are rudimentary in pond-living species but may be rather more developed in species that reproduce in moving water. Pond-type larvae often have a pair of balancers, rod-like structures on either side of the head that may prevent the gills from becoming clogged up with sediment. Some members of the genera Ambystoma and Dicamptodon have larvae that never fully develop into the adult form, but this varies with species and with populations. The northwestern salamander (Ambystoma gracile) is one of these and, depending on environmental factors, either remains permanently in the larval state, a condition known as neoteny, or transforms into an adult. Both of these are able to breed. Neoteny occurs when the animal's growth rate is very low and is usually linked to adverse conditions such as low water temperatures that may change the response of the tissues to the hormone thyroxine. Other factors that may inhibit metamorphosis include lack of food, lack of trace elements and competition from conspecifics. The tiger salamander (Ambystoma tigrinum) also sometimes behaves in this way and may grow particularly large in the process. The adult tiger salamander is terrestrial, but the larva is aquatic and able to breed while still in the larval state. When conditions are particularly inhospitable on land, larval breeding may allow continuation of a population that would otherwise die out.

Stream dwellers mostly have larger mouths, shallow bodies and caudal fins; they attach themselves to plants and stones and feed on the surface films of algae and bacteria. They also feed on diatoms, filtered from the water through the gills, and stir up the sediment at bottom of the pond, ingesting edible fragments. They have a relatively long, spiral-shaped gut to enable them to digest this diet. Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles and fish. Young of the Cuban tree frog (Osteopilus septentrionalis) can occasionally be cannibalistic, the younger tadpoles attacking a larger, more developed tadpole when it is undergoing metamorphosis. At metamorphosis, rapid changes in the body take place as the lifestyle of the frog changes completely. The spiral‐shaped mouth with horny tooth ridges is reabsorbed together with the spiral gut. The animal develops a large jaw, and its gills disappear along with its gill sac. Eyes and legs grow quickly, and a tongue is formed. There are associated changes in the neural networks such as development of stereoscopic vision and loss of the lateral line system. All this can happen in about a day. A few days later, the tail is reabsorbed, due to the higher thyroxine concentration required for this to take place. Salamanders At hatching, a typical salamander larva has eyes without lids, teeth in both upper and lower jaws, three pairs of feathery external gills, a somewhat laterally flattened body and a long tail with dorsal and ventral fins. The forelimbs may be partially developed and the hind limbs are rudimentary in pond-living species but may be rather more developed in species that reproduce in moving water. Pond-type larvae often have a pair of balancers, rod-like structures on either side of the head that may prevent the gills from becoming clogged up with sediment. Some members of the genera Ambystoma and Dicamptodon have larvae that never fully develop into the adult form, but this varies with species and with populations. The northwestern salamander (Ambystoma gracile) is one of these and, depending on environmental factors, either remains permanently in the larval state, a condition known as neoteny, or transforms into an adult. Both of these are able to breed. Neoteny occurs when the animal's growth rate is very low and is usually linked to adverse conditions such as low water temperatures that may change the response of the tissues to the hormone thyroxine. Other factors that may inhibit metamorphosis include lack of food, lack of trace elements and competition from conspecifics. The tiger salamander (Ambystoma tigrinum) also sometimes behaves in this way and may grow particularly large in the process. The adult tiger salamander is terrestrial, but the larva is aquatic and able to breed while still in the larval state. When conditions are particularly inhospitable on land, larval breeding may allow continuation of a population that would otherwise die out.

Stream dwellers mostly have larger mouths, shallow bodies and caudal fins; they attach themselves to plants and stones and feed on the surface films of algae and bacteria. They also feed on diatoms, filtered from the water through the gills, and stir up the sediment at bottom of the pond, ingesting edible fragments. They have a relatively long, spiral-shaped gut to enable them to digest this diet. Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles and fish. Young of the Cuban tree frog (Osteopilus septentrionalis) can occasionally be cannibalistic, the younger tadpoles attacking a larger, more developed tadpole when it is undergoing metamorphosis. At metamorphosis, rapid changes in the body take place as the lifestyle of the frog changes completely. The spiral‐shaped mouth with horny tooth ridges is reabsorbed together with the spiral gut. The animal develops a large jaw, and its gills disappear along with its gill sac. Eyes and legs grow quickly, and a tongue is formed. There are associated changes in the neural networks such as development of stereoscopic vision and loss of the lateral line system. All this can happen in about a day. A few days later, the tail is reabsorbed, due to the higher thyroxine concentration required for this to take place. Salamanders At hatching, a typical salamander larva has eyes without lids, teeth in both upper and lower jaws, three pairs of feathery external gills, a somewhat laterally flattened body and a long tail with dorsal and ventral fins. The forelimbs may be partially developed and the hind limbs are rudimentary in pond-living species but may be rather more developed in species that reproduce in moving water. Pond-type larvae often have a pair of balancers, rod-like structures on either side of the head that may prevent the gills from becoming clogged up with sediment. Some members of the genera Ambystoma and Dicamptodon have larvae that never fully develop into the adult form, but this varies with species and with populations. The northwestern salamander (Ambystoma gracile) is one of these and, depending on environmental factors, either remains permanently in the larval state, a condition known as neoteny, or transforms into an adult. Both of these are able to breed. Neoteny occurs when the animal's growth rate is very low and is usually linked to adverse conditions such as low water temperatures that may change the response of the tissues to the hormone thyroxine. Other factors that may inhibit metamorphosis include lack of food, lack of trace elements and competition from conspecifics. The tiger salamander (Ambystoma tigrinum) also sometimes behaves in this way and may grow particularly large in the process. The adult tiger salamander is terrestrial, but the larva is aquatic and able to breed while still in the larval state. When conditions are particularly inhospitable on land, larval breeding may allow continuation of a population that would otherwise die out.

There are fifteen species of obligate neotenic salamanders, including species of Necturus, Proteus and Amphiuma, and many examples of facultative ones that adopt this strategy under appropriate environmental circumstances. Lungless salamanders in the family Plethodontidae are terrestrial and lay a small number of unpigmented eggs in a cluster among damp leaf litter. Each egg has a large yolk sac and the larva feeds on this while it develops inside the egg, emerging fully formed as a juvenile salamander. The female salamander often broods the eggs. In the genus Ensatinas, the female has been observed to coil around them and press her throat area against them, effectively massaging them with a mucous secretion. In newts and salamanders, metamorphosis is less dramatic than in frogs. This is because the larvae are already carnivorous and continue to feed as predators when they are adults so few changes are needed to their digestive systems. Their lungs are functional early, but the larvae do not make as much use of them as do tadpoles. Their gills are never covered by gill sacs and are reabsorbed just before the animals leave the water. Other changes include the reduction in size or loss of tail fins, the closure of gill slits, thickening of the skin, the development of eyelids, and certain changes in dentition and tongue structure. Salamanders are at their most vulnerable at metamorphosis as swimming speeds are reduced and transforming tails are encumbrances on land. Adult salamanders often have an aquatic phase in spring and summer, and a land phase in winter. For adaptation to a water phase, prolactin is the required hormone, and for adaptation to the land phase, thyroxine. External gills do not return in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first time. Caecilians Most terrestrial caecilians that lay eggs do so in burrows or moist places on land near bodies of water. The development of the young of Ichthyophis glutinosus, a species from Sri Lanka, has been much studied. The eel-like larvae hatch out of the eggs and make their way to water. They have three pairs of external red feathery gills, a blunt head with two rudimentary eyes, a lateral line system and a short tail with fins. They swim by undulating their body from side to side. They are mostly active at night, soon lose their gills and make sorties onto land. Metamorphosis is gradual. By the age of about ten months they have developed a pointed head with sensory tentacles near the mouth and lost their eyes, lateral line systems and tails. The skin thickens, embedded scales develop and the body divides into segments. By this time, the caecilian has constructed a burrow and is living on land. In the majority of species of caecilians, the young are produced by viviparity. Typhlonectes compressicauda, a species from South America, is typical of these. Up to nine larvae can develop in the oviduct at any one time.

There are fifteen species of obligate neotenic salamanders, including species of Necturus, Proteus and Amphiuma, and many examples of facultative ones that adopt this strategy under appropriate environmental circumstances. Lungless salamanders in the family Plethodontidae are terrestrial and lay a small number of unpigmented eggs in a cluster among damp leaf litter. Each egg has a large yolk sac and the larva feeds on this while it develops inside the egg, emerging fully formed as a juvenile salamander. The female salamander often broods the eggs. In the genus Ensatinas, the female has been observed to coil around them and press her throat area against them, effectively massaging them with a mucous secretion. In newts and salamanders, metamorphosis is less dramatic than in frogs. This is because the larvae are already carnivorous and continue to feed as predators when they are adults so few changes are needed to their digestive systems. Their lungs are functional early, but the larvae do not make as much use of them as do tadpoles. Their gills are never covered by gill sacs and are reabsorbed just before the animals leave the water. Other changes include the reduction in size or loss of tail fins, the closure of gill slits, thickening of the skin, the development of eyelids, and certain changes in dentition and tongue structure. Salamanders are at their most vulnerable at metamorphosis as swimming speeds are reduced and transforming tails are encumbrances on land. Adult salamanders often have an aquatic phase in spring and summer, and a land phase in winter. For adaptation to a water phase, prolactin is the required hormone, and for adaptation to the land phase, thyroxine. External gills do not return in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first time. Caecilians Most terrestrial caecilians that lay eggs do so in burrows or moist places on land near bodies of water. The development of the young of Ichthyophis glutinosus, a species from Sri Lanka, has been much studied. The eel-like larvae hatch out of the eggs and make their way to water. They have three pairs of external red feathery gills, a blunt head with two rudimentary eyes, a lateral line system and a short tail with fins. They swim by undulating their body from side to side. They are mostly active at night, soon lose their gills and make sorties onto land. Metamorphosis is gradual. By the age of about ten months they have developed a pointed head with sensory tentacles near the mouth and lost their eyes, lateral line systems and tails. The skin thickens, embedded scales develop and the body divides into segments. By this time, the caecilian has constructed a burrow and is living on land. In the majority of species of caecilians, the young are produced by viviparity. Typhlonectes compressicauda, a species from South America, is typical of these. Up to nine larvae can develop in the oviduct at any one time.

There are fifteen species of obligate neotenic salamanders, including species of Necturus, Proteus and Amphiuma, and many examples of facultative ones that adopt this strategy under appropriate environmental circumstances. Lungless salamanders in the family Plethodontidae are terrestrial and lay a small number of unpigmented eggs in a cluster among damp leaf litter. Each egg has a large yolk sac and the larva feeds on this while it develops inside the egg, emerging fully formed as a juvenile salamander. The female salamander often broods the eggs. In the genus Ensatinas, the female has been observed to coil around them and press her throat area against them, effectively massaging them with a mucous secretion. In newts and salamanders, metamorphosis is less dramatic than in frogs. This is because the larvae are already carnivorous and continue to feed as predators when they are adults so few changes are needed to their digestive systems. Their lungs are functional early, but the larvae do not make as much use of them as do tadpoles. Their gills are never covered by gill sacs and are reabsorbed just before the animals leave the water. Other changes include the reduction in size or loss of tail fins, the closure of gill slits, thickening of the skin, the development of eyelids, and certain changes in dentition and tongue structure. Salamanders are at their most vulnerable at metamorphosis as swimming speeds are reduced and transforming tails are encumbrances on land. Adult salamanders often have an aquatic phase in spring and summer, and a land phase in winter. For adaptation to a water phase, prolactin is the required hormone, and for adaptation to the land phase, thyroxine. External gills do not return in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first time. Caecilians Most terrestrial caecilians that lay eggs do so in burrows or moist places on land near bodies of water. The development of the young of Ichthyophis glutinosus, a species from Sri Lanka, has been much studied. The eel-like larvae hatch out of the eggs and make their way to water. They have three pairs of external red feathery gills, a blunt head with two rudimentary eyes, a lateral line system and a short tail with fins. They swim by undulating their body from side to side. They are mostly active at night, soon lose their gills and make sorties onto land. Metamorphosis is gradual. By the age of about ten months they have developed a pointed head with sensory tentacles near the mouth and lost their eyes, lateral line systems and tails. The skin thickens, embedded scales develop and the body divides into segments. By this time, the caecilian has constructed a burrow and is living on land. In the majority of species of caecilians, the young are produced by viviparity. Typhlonectes compressicauda, a species from South America, is typical of these. Up to nine larvae can develop in the oviduct at any one time.

They are elongated and have paired sac-like gills, small eyes and specialised scraping teeth. At first, they feed on the yolks of the eggs, but as this source of nourishment declines they begin to rasp at the ciliated epithelial cells that line the oviduct. This stimulates the secretion of fluids rich in lipids and mucoproteins on which they feed along with scrapings from the oviduct wall. They may increase their length sixfold and be two-fifths as long as their mother before being born. By this time they have undergone metamorphosis, lost their eyes and gills, developed a thicker skin and mouth tentacles, and reabsorbed their teeth. A permanent set of teeth grow through soon after birth. The ringed caecilian (Siphonops annulatus) has developed a unique adaptation for the purposes of reproduction. The progeny feed on a skin layer that is specially developed by the adult in a phenomenon known as maternal dermatophagy. The brood feed as a batch for about seven minutes at intervals of approximately three days which gives the skin an opportunity to regenerate. Meanwhile, they have been observed to ingest fluid exuded from the maternal cloaca. Parental care The care of offspring among amphibians has been little studied but, in general, the larger the number of eggs in a batch, the less likely it is that any degree of parental care takes place. Nevertheless, it is estimated that in up to 20% of amphibian species, one or both adults play some role in the care of the young. Those species that breed in smaller water bodies or other specialised habitats tend to have complex patterns of behaviour in the care of their young. Many woodland salamanders lay clutches of eggs under dead logs or stones on land. The black mountain salamander (Desmognathus welteri) does this, the mother brooding the eggs and guarding them from predation as the embryos feed on the yolks of their eggs. When fully developed, they break their way out of the egg capsules and disperse as juvenile salamanders. The male hellbender, a primitive salamander, excavates an underwater nest and encourages females to lay there. The male then guards the site for the two or three months before the eggs hatch, using body undulations to fan the eggs and increase their supply of oxygen. The male Colostethus subpunctatus, a tiny frog, protects the egg cluster which is hidden under a stone or log. When the eggs hatch, the male transports the tadpoles on his back, stuck there by a mucous secretion, to a temporary pool where he dips himself into the water and the tadpoles drop off. The male midwife toad (Alytes obstetricans) winds egg strings round his thighs and carries the eggs around for up to eight weeks. He keeps them moist and when they are ready to hatch, he visits a pond or ditch and releases the tadpoles. The female gastric-brooding frog (Rheobatrachus spp.)

They are elongated and have paired sac-like gills, small eyes and specialised scraping teeth. At first, they feed on the yolks of the eggs, but as this source of nourishment declines they begin to rasp at the ciliated epithelial cells that line the oviduct. This stimulates the secretion of fluids rich in lipids and mucoproteins on which they feed along with scrapings from the oviduct wall. They may increase their length sixfold and be two-fifths as long as their mother before being born. By this time they have undergone metamorphosis, lost their eyes and gills, developed a thicker skin and mouth tentacles, and reabsorbed their teeth. A permanent set of teeth grow through soon after birth. The ringed caecilian (Siphonops annulatus) has developed a unique adaptation for the purposes of reproduction. The progeny feed on a skin layer that is specially developed by the adult in a phenomenon known as maternal dermatophagy. The brood feed as a batch for about seven minutes at intervals of approximately three days which gives the skin an opportunity to regenerate. Meanwhile, they have been observed to ingest fluid exuded from the maternal cloaca. Parental care The care of offspring among amphibians has been little studied but, in general, the larger the number of eggs in a batch, the less likely it is that any degree of parental care takes place. Nevertheless, it is estimated that in up to 20% of amphibian species, one or both adults play some role in the care of the young. Those species that breed in smaller water bodies or other specialised habitats tend to have complex patterns of behaviour in the care of their young. Many woodland salamanders lay clutches of eggs under dead logs or stones on land. The black mountain salamander (Desmognathus welteri) does this, the mother brooding the eggs and guarding them from predation as the embryos feed on the yolks of their eggs. When fully developed, they break their way out of the egg capsules and disperse as juvenile salamanders. The male hellbender, a primitive salamander, excavates an underwater nest and encourages females to lay there. The male then guards the site for the two or three months before the eggs hatch, using body undulations to fan the eggs and increase their supply of oxygen. The male Colostethus subpunctatus, a tiny frog, protects the egg cluster which is hidden under a stone or log. When the eggs hatch, the male transports the tadpoles on his back, stuck there by a mucous secretion, to a temporary pool where he dips himself into the water and the tadpoles drop off. The male midwife toad (Alytes obstetricans) winds egg strings round his thighs and carries the eggs around for up to eight weeks. He keeps them moist and when they are ready to hatch, he visits a pond or ditch and releases the tadpoles. The female gastric-brooding frog (Rheobatrachus spp.)

They are elongated and have paired sac-like gills, small eyes and specialised scraping teeth. At first, they feed on the yolks of the eggs, but as this source of nourishment declines they begin to rasp at the ciliated epithelial cells that line the oviduct. This stimulates the secretion of fluids rich in lipids and mucoproteins on which they feed along with scrapings from the oviduct wall. They may increase their length sixfold and be two-fifths as long as their mother before being born. By this time they have undergone metamorphosis, lost their eyes and gills, developed a thicker skin and mouth tentacles, and reabsorbed their teeth. A permanent set of teeth grow through soon after birth. The ringed caecilian (Siphonops annulatus) has developed a unique adaptation for the purposes of reproduction. The progeny feed on a skin layer that is specially developed by the adult in a phenomenon known as maternal dermatophagy. The brood feed as a batch for about seven minutes at intervals of approximately three days which gives the skin an opportunity to regenerate. Meanwhile, they have been observed to ingest fluid exuded from the maternal cloaca. Parental care The care of offspring among amphibians has been little studied but, in general, the larger the number of eggs in a batch, the less likely it is that any degree of parental care takes place. Nevertheless, it is estimated that in up to 20% of amphibian species, one or both adults play some role in the care of the young. Those species that breed in smaller water bodies or other specialised habitats tend to have complex patterns of behaviour in the care of their young. Many woodland salamanders lay clutches of eggs under dead logs or stones on land. The black mountain salamander (Desmognathus welteri) does this, the mother brooding the eggs and guarding them from predation as the embryos feed on the yolks of their eggs. When fully developed, they break their way out of the egg capsules and disperse as juvenile salamanders. The male hellbender, a primitive salamander, excavates an underwater nest and encourages females to lay there. The male then guards the site for the two or three months before the eggs hatch, using body undulations to fan the eggs and increase their supply of oxygen. The male Colostethus subpunctatus, a tiny frog, protects the egg cluster which is hidden under a stone or log. When the eggs hatch, the male transports the tadpoles on his back, stuck there by a mucous secretion, to a temporary pool where he dips himself into the water and the tadpoles drop off. The male midwife toad (Alytes obstetricans) winds egg strings round his thighs and carries the eggs around for up to eight weeks. He keeps them moist and when they are ready to hatch, he visits a pond or ditch and releases the tadpoles. The female gastric-brooding frog (Rheobatrachus spp.)

reared larvae in her stomach after swallowing either the eggs or hatchlings; however, this stage was never observed before the species became extinct. The tadpoles secrete a hormone that inhibits digestion in the mother whilst they develop by consuming their very large yolk supply. The pouched frog (Assa darlingtoni) lays eggs on the ground. When they hatch, the male carries the tadpoles around in brood pouches on his hind legs. The aquatic Surinam toad (Pipa pipa) raises its young in pores on its back where they remain until metamorphosis. The granular poison frog (Oophaga granulifera) is typical of a number of tree frogs in the poison dart frog family Dendrobatidae. Its eggs are laid on the forest floor and when they hatch, the tadpoles are carried one by one on the back of an adult to a suitable water-filled crevice such as the axil of a leaf or the rosette of a bromeliad. The female visits the nursery sites regularly and deposits unfertilised eggs in the water and these are consumed by the tadpoles. Genetics and genomics Amphibians are notable among vertebrates for their diversity of chromosomes and genomes. The karyotypes (chromosomes) have been determined for at least 1,193 (14.5%) of the ~8,200 known (diploid) species, including 963 anurans, 209 salamanders, and 21 caecilians. Generally, the karyotypes of diploid amphibians are characterized by 20–26 bi-armed chromosomes. Amphibians have also very large genomes compared to other taxa of vertebrates and corresponding variation in genome size (C-value: picograms of DNA in haploid nuclei). The genome sizes range from 0.95 to 11.5 pg in frogs, from 13.89 to 120.56 pg in salamanders, and from 2.94 to 11.78 pg in caecilians. The large genome sizes have prevented whole-genome sequencing of amphibians although a number of genomes have been published recently. The 1.7GB draft genome of Xenopus tropicalis was the first to be reported for amphibians in 2010. Compared to some salamanders this frog genome is tiny. For instance, the genome of the Mexican axolotl turned out to be 32 Gb, which is more than 10 times larger than the human genome (3GB). Feeding and diet With a few exceptions, adult amphibians are predators, feeding on virtually anything that moves that they can swallow. The diet mostly consists of small prey that do not move too fast such as beetles, caterpillars, earthworms and spiders. The sirens (Siren spp.) often ingest aquatic plant material with the invertebrates on which they feed and a Brazilian tree frog (Xenohyla truncata) includes a large quantity of fruit in its diet. The Mexican burrowing toad (Rhinophrynus dorsalis) has a specially adapted tongue for picking up ants and termites. It projects it with the tip foremost whereas other frogs flick out the rear part first, their tongues being hinged at the front. Food is mostly selected by sight, even in conditions of dim light. Movement of the prey triggers a feeding response.

reared larvae in her stomach after swallowing either the eggs or hatchlings; however, this stage was never observed before the species became extinct. The tadpoles secrete a hormone that inhibits digestion in the mother whilst they develop by consuming their very large yolk supply. The pouched frog (Assa darlingtoni) lays eggs on the ground. When they hatch, the male carries the tadpoles around in brood pouches on his hind legs. The aquatic Surinam toad (Pipa pipa) raises its young in pores on its back where they remain until metamorphosis. The granular poison frog (Oophaga granulifera) is typical of a number of tree frogs in the poison dart frog family Dendrobatidae. Its eggs are laid on the forest floor and when they hatch, the tadpoles are carried one by one on the back of an adult to a suitable water-filled crevice such as the axil of a leaf or the rosette of a bromeliad. The female visits the nursery sites regularly and deposits unfertilised eggs in the water and these are consumed by the tadpoles. Genetics and genomics Amphibians are notable among vertebrates for their diversity of chromosomes and genomes. The karyotypes (chromosomes) have been determined for at least 1,193 (14.5%) of the ~8,200 known (diploid) species, including 963 anurans, 209 salamanders, and 21 caecilians. Generally, the karyotypes of diploid amphibians are characterized by 20–26 bi-armed chromosomes. Amphibians have also very large genomes compared to other taxa of vertebrates and corresponding variation in genome size (C-value: picograms of DNA in haploid nuclei). The genome sizes range from 0.95 to 11.5 pg in frogs, from 13.89 to 120.56 pg in salamanders, and from 2.94 to 11.78 pg in caecilians. The large genome sizes have prevented whole-genome sequencing of amphibians although a number of genomes have been published recently. The 1.7GB draft genome of Xenopus tropicalis was the first to be reported for amphibians in 2010. Compared to some salamanders this frog genome is tiny. For instance, the genome of the Mexican axolotl turned out to be 32 Gb, which is more than 10 times larger than the human genome (3GB). Feeding and diet With a few exceptions, adult amphibians are predators, feeding on virtually anything that moves that they can swallow. The diet mostly consists of small prey that do not move too fast such as beetles, caterpillars, earthworms and spiders. The sirens (Siren spp.) often ingest aquatic plant material with the invertebrates on which they feed and a Brazilian tree frog (Xenohyla truncata) includes a large quantity of fruit in its diet. The Mexican burrowing toad (Rhinophrynus dorsalis) has a specially adapted tongue for picking up ants and termites. It projects it with the tip foremost whereas other frogs flick out the rear part first, their tongues being hinged at the front. Food is mostly selected by sight, even in conditions of dim light. Movement of the prey triggers a feeding response.

reared larvae in her stomach after swallowing either the eggs or hatchlings; however, this stage was never observed before the species became extinct. The tadpoles secrete a hormone that inhibits digestion in the mother whilst they develop by consuming their very large yolk supply. The pouched frog (Assa darlingtoni) lays eggs on the ground. When they hatch, the male carries the tadpoles around in brood pouches on his hind legs. The aquatic Surinam toad (Pipa pipa) raises its young in pores on its back where they remain until metamorphosis. The granular poison frog (Oophaga granulifera) is typical of a number of tree frogs in the poison dart frog family Dendrobatidae. Its eggs are laid on the forest floor and when they hatch, the tadpoles are carried one by one on the back of an adult to a suitable water-filled crevice such as the axil of a leaf or the rosette of a bromeliad. The female visits the nursery sites regularly and deposits unfertilised eggs in the water and these are consumed by the tadpoles. Genetics and genomics Amphibians are notable among vertebrates for their diversity of chromosomes and genomes. The karyotypes (chromosomes) have been determined for at least 1,193 (14.5%) of the ~8,200 known (diploid) species, including 963 anurans, 209 salamanders, and 21 caecilians. Generally, the karyotypes of diploid amphibians are characterized by 20–26 bi-armed chromosomes. Amphibians have also very large genomes compared to other taxa of vertebrates and corresponding variation in genome size (C-value: picograms of DNA in haploid nuclei). The genome sizes range from 0.95 to 11.5 pg in frogs, from 13.89 to 120.56 pg in salamanders, and from 2.94 to 11.78 pg in caecilians. The large genome sizes have prevented whole-genome sequencing of amphibians although a number of genomes have been published recently. The 1.7GB draft genome of Xenopus tropicalis was the first to be reported for amphibians in 2010. Compared to some salamanders this frog genome is tiny. For instance, the genome of the Mexican axolotl turned out to be 32 Gb, which is more than 10 times larger than the human genome (3GB). Feeding and diet With a few exceptions, adult amphibians are predators, feeding on virtually anything that moves that they can swallow. The diet mostly consists of small prey that do not move too fast such as beetles, caterpillars, earthworms and spiders. The sirens (Siren spp.) often ingest aquatic plant material with the invertebrates on which they feed and a Brazilian tree frog (Xenohyla truncata) includes a large quantity of fruit in its diet. The Mexican burrowing toad (Rhinophrynus dorsalis) has a specially adapted tongue for picking up ants and termites. It projects it with the tip foremost whereas other frogs flick out the rear part first, their tongues being hinged at the front. Food is mostly selected by sight, even in conditions of dim light. Movement of the prey triggers a feeding response.

Frogs have been caught on fish hooks baited with red flannel and green frogs (Rana clamitans) have been found with stomachs full of elm seeds that they had seen floating past. Toads, salamanders and caecilians also use smell to detect prey. This response is mostly secondary because salamanders have been observed to remain stationary near odoriferous prey but only feed if it moves. Cave-dwelling amphibians normally hunt by smell. Some salamanders seem to have learned to recognize immobile prey when it has no smell, even in complete darkness. Amphibians usually swallow food whole but may chew it lightly first to subdue it. They typically have small hinged pedicellate teeth, a feature unique to amphibians. The base and crown of these are composed of dentine separated by an uncalcified layer and they are replaced at intervals. Salamanders, caecilians and some frogs have one or two rows of teeth in both jaws, but some frogs (Rana spp.) lack teeth in the lower jaw, and toads (Bufo spp.) have no teeth. In many amphibians there are also vomerine teeth attached to a facial bone in the roof of the mouth. The tiger salamander (Ambystoma tigrinum) is typical of the frogs and salamanders that hide under cover ready to ambush unwary invertebrates. Others amphibians, such as the Bufo spp. toads, actively search for prey, while the Argentine horned frog (Ceratophrys ornata) lures inquisitive prey closer by raising its hind feet over its back and vibrating its yellow toes. Among leaf litter frogs in Panama, frogs that actively hunt prey have narrow mouths and are slim, often brightly coloured and toxic, while ambushers have wide mouths and are broad and well-camouflaged. Caecilians do not flick their tongues, but catch their prey by grabbing it with their slightly backward-pointing teeth. The struggles of the prey and further jaw movements work it inwards and the caecilian usually retreats into its burrow. The subdued prey is gulped down whole. When they are newly hatched, frog larvae feed on the yolk of the egg. When this is exhausted some move on to feed on bacteria, algal crusts, detritus and raspings from submerged plants. Water is drawn in through their mouths, which are usually at the bottom of their heads, and passes through branchial food traps between their mouths and their gills where fine particles are trapped in mucus and filtered out. Others have specialised mouthparts consisting of a horny beak edged by several rows of labial teeth. They scrape and bite food of many kinds as well as stirring up the bottom sediment, filtering out larger particles with the papillae around their mouths. Some, such as the spadefoot toads, have strong biting jaws and are carnivorous or even cannibalistic. Vocalization The calls made by caecilians and salamanders are limited to occasional soft squeaks, grunts or hisses and have not been much studied. A clicking sound sometimes produced by caecilians may be a means of orientation, as in bats, or a form of communication.

Frogs have been caught on fish hooks baited with red flannel and green frogs (Rana clamitans) have been found with stomachs full of elm seeds that they had seen floating past. Toads, salamanders and caecilians also use smell to detect prey. This response is mostly secondary because salamanders have been observed to remain stationary near odoriferous prey but only feed if it moves. Cave-dwelling amphibians normally hunt by smell. Some salamanders seem to have learned to recognize immobile prey when it has no smell, even in complete darkness. Amphibians usually swallow food whole but may chew it lightly first to subdue it. They typically have small hinged pedicellate teeth, a feature unique to amphibians. The base and crown of these are composed of dentine separated by an uncalcified layer and they are replaced at intervals. Salamanders, caecilians and some frogs have one or two rows of teeth in both jaws, but some frogs (Rana spp.) lack teeth in the lower jaw, and toads (Bufo spp.) have no teeth. In many amphibians there are also vomerine teeth attached to a facial bone in the roof of the mouth. The tiger salamander (Ambystoma tigrinum) is typical of the frogs and salamanders that hide under cover ready to ambush unwary invertebrates. Others amphibians, such as the Bufo spp. toads, actively search for prey, while the Argentine horned frog (Ceratophrys ornata) lures inquisitive prey closer by raising its hind feet over its back and vibrating its yellow toes. Among leaf litter frogs in Panama, frogs that actively hunt prey have narrow mouths and are slim, often brightly coloured and toxic, while ambushers have wide mouths and are broad and well-camouflaged. Caecilians do not flick their tongues, but catch their prey by grabbing it with their slightly backward-pointing teeth. The struggles of the prey and further jaw movements work it inwards and the caecilian usually retreats into its burrow. The subdued prey is gulped down whole. When they are newly hatched, frog larvae feed on the yolk of the egg. When this is exhausted some move on to feed on bacteria, algal crusts, detritus and raspings from submerged plants. Water is drawn in through their mouths, which are usually at the bottom of their heads, and passes through branchial food traps between their mouths and their gills where fine particles are trapped in mucus and filtered out. Others have specialised mouthparts consisting of a horny beak edged by several rows of labial teeth. They scrape and bite food of many kinds as well as stirring up the bottom sediment, filtering out larger particles with the papillae around their mouths. Some, such as the spadefoot toads, have strong biting jaws and are carnivorous or even cannibalistic. Vocalization The calls made by caecilians and salamanders are limited to occasional soft squeaks, grunts or hisses and have not been much studied. A clicking sound sometimes produced by caecilians may be a means of orientation, as in bats, or a form of communication.

Frogs have been caught on fish hooks baited with red flannel and green frogs (Rana clamitans) have been found with stomachs full of elm seeds that they had seen floating past. Toads, salamanders and caecilians also use smell to detect prey. This response is mostly secondary because salamanders have been observed to remain stationary near odoriferous prey but only feed if it moves. Cave-dwelling amphibians normally hunt by smell. Some salamanders seem to have learned to recognize immobile prey when it has no smell, even in complete darkness. Amphibians usually swallow food whole but may chew it lightly first to subdue it. They typically have small hinged pedicellate teeth, a feature unique to amphibians. The base and crown of these are composed of dentine separated by an uncalcified layer and they are replaced at intervals. Salamanders, caecilians and some frogs have one or two rows of teeth in both jaws, but some frogs (Rana spp.) lack teeth in the lower jaw, and toads (Bufo spp.) have no teeth. In many amphibians there are also vomerine teeth attached to a facial bone in the roof of the mouth. The tiger salamander (Ambystoma tigrinum) is typical of the frogs and salamanders that hide under cover ready to ambush unwary invertebrates. Others amphibians, such as the Bufo spp. toads, actively search for prey, while the Argentine horned frog (Ceratophrys ornata) lures inquisitive prey closer by raising its hind feet over its back and vibrating its yellow toes. Among leaf litter frogs in Panama, frogs that actively hunt prey have narrow mouths and are slim, often brightly coloured and toxic, while ambushers have wide mouths and are broad and well-camouflaged. Caecilians do not flick their tongues, but catch their prey by grabbing it with their slightly backward-pointing teeth. The struggles of the prey and further jaw movements work it inwards and the caecilian usually retreats into its burrow. The subdued prey is gulped down whole. When they are newly hatched, frog larvae feed on the yolk of the egg. When this is exhausted some move on to feed on bacteria, algal crusts, detritus and raspings from submerged plants. Water is drawn in through their mouths, which are usually at the bottom of their heads, and passes through branchial food traps between their mouths and their gills where fine particles are trapped in mucus and filtered out. Others have specialised mouthparts consisting of a horny beak edged by several rows of labial teeth. They scrape and bite food of many kinds as well as stirring up the bottom sediment, filtering out larger particles with the papillae around their mouths. Some, such as the spadefoot toads, have strong biting jaws and are carnivorous or even cannibalistic. Vocalization The calls made by caecilians and salamanders are limited to occasional soft squeaks, grunts or hisses and have not been much studied. A clicking sound sometimes produced by caecilians may be a means of orientation, as in bats, or a form of communication.

Most salamanders are considered voiceless, but the California giant salamander (Dicamptodon ensatus) has vocal cords and can produce a rattling or barking sound. Some species of salamander emit a quiet squeak or yelp if attacked. Frogs are much more vocal, especially during the breeding season when they use their voices to attract mates. The presence of a particular species in an area may be more easily discerned by its characteristic call than by a fleeting glimpse of the animal itself. In most species, the sound is produced by expelling air from the lungs over the vocal cords into an air sac or sacs in the throat or at the corner of the mouth. This may distend like a balloon and acts as a resonator, helping to transfer the sound to the atmosphere, or the water at times when the animal is submerged. The main vocalisation is the male's loud advertisement call which seeks to both encourage a female to approach and discourage other males from intruding on its territory. This call is modified to a quieter courtship call on the approach of a female or to a more aggressive version if a male intruder draws near. Calling carries the risk of attracting predators and involves the expenditure of much energy. Other calls include those given by a female in response to the advertisement call and a release call given by a male or female during unwanted attempts at amplexus. When a frog is attacked, a distress or fright call is emitted, often resembling a scream. The usually nocturnal Cuban tree frog (Osteopilus septentrionalis) produces a rain call when there is rainfall during daylight hours. Territorial behaviour Little is known of the territorial behaviour of caecilians, but some frogs and salamanders defend home ranges. These are usually feeding, breeding or sheltering sites. Males normally exhibit such behaviour though in some species, females and even juveniles are also involved. Although in many frog species, females are larger than males, this is not the case in most species where males are actively involved in territorial defence. Some of these have specific adaptations such as enlarged teeth for biting or spines on the chest, arms or thumbs. In salamanders, defence of a territory involves adopting an aggressive posture and if necessary attacking the intruder. This may involve snapping, chasing and sometimes biting, occasionally causing the loss of a tail. The behaviour of red back salamanders (Plethodon cinereus) has been much studied. 91% of marked individuals that were later recaptured were within a metre (yard) of their original daytime retreat under a log or rock. A similar proportion, when moved experimentally a distance of , found their way back to their home base. The salamanders left odour marks around their territories which averaged in size and were sometimes inhabited by a male and female pair. These deterred the intrusion of others and delineated the boundaries between neighbouring areas. Much of their behaviour seemed stereotyped and did not involve any actual contact between individuals.

Most salamanders are considered voiceless, but the California giant salamander (Dicamptodon ensatus) has vocal cords and can produce a rattling or barking sound. Some species of salamander emit a quiet squeak or yelp if attacked. Frogs are much more vocal, especially during the breeding season when they use their voices to attract mates. The presence of a particular species in an area may be more easily discerned by its characteristic call than by a fleeting glimpse of the animal itself. In most species, the sound is produced by expelling air from the lungs over the vocal cords into an air sac or sacs in the throat or at the corner of the mouth. This may distend like a balloon and acts as a resonator, helping to transfer the sound to the atmosphere, or the water at times when the animal is submerged. The main vocalisation is the male's loud advertisement call which seeks to both encourage a female to approach and discourage other males from intruding on its territory. This call is modified to a quieter courtship call on the approach of a female or to a more aggressive version if a male intruder draws near. Calling carries the risk of attracting predators and involves the expenditure of much energy. Other calls include those given by a female in response to the advertisement call and a release call given by a male or female during unwanted attempts at amplexus. When a frog is attacked, a distress or fright call is emitted, often resembling a scream. The usually nocturnal Cuban tree frog (Osteopilus septentrionalis) produces a rain call when there is rainfall during daylight hours. Territorial behaviour Little is known of the territorial behaviour of caecilians, but some frogs and salamanders defend home ranges. These are usually feeding, breeding or sheltering sites. Males normally exhibit such behaviour though in some species, females and even juveniles are also involved. Although in many frog species, females are larger than males, this is not the case in most species where males are actively involved in territorial defence. Some of these have specific adaptations such as enlarged teeth for biting or spines on the chest, arms or thumbs. In salamanders, defence of a territory involves adopting an aggressive posture and if necessary attacking the intruder. This may involve snapping, chasing and sometimes biting, occasionally causing the loss of a tail. The behaviour of red back salamanders (Plethodon cinereus) has been much studied. 91% of marked individuals that were later recaptured were within a metre (yard) of their original daytime retreat under a log or rock. A similar proportion, when moved experimentally a distance of , found their way back to their home base. The salamanders left odour marks around their territories which averaged in size and were sometimes inhabited by a male and female pair. These deterred the intrusion of others and delineated the boundaries between neighbouring areas. Much of their behaviour seemed stereotyped and did not involve any actual contact between individuals.

Most salamanders are considered voiceless, but the California giant salamander (Dicamptodon ensatus) has vocal cords and can produce a rattling or barking sound. Some species of salamander emit a quiet squeak or yelp if attacked. Frogs are much more vocal, especially during the breeding season when they use their voices to attract mates. The presence of a particular species in an area may be more easily discerned by its characteristic call than by a fleeting glimpse of the animal itself. In most species, the sound is produced by expelling air from the lungs over the vocal cords into an air sac or sacs in the throat or at the corner of the mouth. This may distend like a balloon and acts as a resonator, helping to transfer the sound to the atmosphere, or the water at times when the animal is submerged. The main vocalisation is the male's loud advertisement call which seeks to both encourage a female to approach and discourage other males from intruding on its territory. This call is modified to a quieter courtship call on the approach of a female or to a more aggressive version if a male intruder draws near. Calling carries the risk of attracting predators and involves the expenditure of much energy. Other calls include those given by a female in response to the advertisement call and a release call given by a male or female during unwanted attempts at amplexus. When a frog is attacked, a distress or fright call is emitted, often resembling a scream. The usually nocturnal Cuban tree frog (Osteopilus septentrionalis) produces a rain call when there is rainfall during daylight hours. Territorial behaviour Little is known of the territorial behaviour of caecilians, but some frogs and salamanders defend home ranges. These are usually feeding, breeding or sheltering sites. Males normally exhibit such behaviour though in some species, females and even juveniles are also involved. Although in many frog species, females are larger than males, this is not the case in most species where males are actively involved in territorial defence. Some of these have specific adaptations such as enlarged teeth for biting or spines on the chest, arms or thumbs. In salamanders, defence of a territory involves adopting an aggressive posture and if necessary attacking the intruder. This may involve snapping, chasing and sometimes biting, occasionally causing the loss of a tail. The behaviour of red back salamanders (Plethodon cinereus) has been much studied. 91% of marked individuals that were later recaptured were within a metre (yard) of their original daytime retreat under a log or rock. A similar proportion, when moved experimentally a distance of , found their way back to their home base. The salamanders left odour marks around their territories which averaged in size and were sometimes inhabited by a male and female pair. These deterred the intrusion of others and delineated the boundaries between neighbouring areas. Much of their behaviour seemed stereotyped and did not involve any actual contact between individuals.

An aggressive posture involved raising the body off the ground and glaring at the opponent who often turned away submissively. If the intruder persisted, a biting lunge was usually launched at either the tail region or the naso-labial grooves. Damage to either of these areas can reduce the fitness of the rival, either because of the need to regenerate tissue or because it impairs its ability to detect food. In frogs, male territorial behaviour is often observed at breeding locations; calling is both an announcement of ownership of part of this resource and an advertisement call to potential mates. In general, a deeper voice represents a heavier and more powerful individual, and this may be sufficient to prevent intrusion by smaller males. Much energy is used in the vocalization and it takes a toll on the territory holder who may be displaced by a fitter rival if he tires. There is a tendency for males to tolerate the holders of neighbouring territories while vigorously attacking unknown intruders. Holders of territories have a "home advantage" and usually come off better in an encounter between two similar-sized frogs. If threats are insufficient, chest to chest tussles may take place. Fighting methods include pushing and shoving, deflating the opponent's vocal sac, seizing him by the head, jumping on his back, biting, chasing, splashing, and ducking him under the water. Defence mechanisms Amphibians have soft bodies with thin skins, and lack claws, defensive armour, or spines. Nevertheless, they have evolved various defence mechanisms to keep themselves alive. The first line of defence in salamanders and frogs is the mucous secretion that they produce. This keeps their skin moist and makes them slippery and difficult to grip. The secretion is often sticky and distasteful or toxic. Snakes have been observed yawning and gaping when trying to swallow African clawed frogs (Xenopus laevis), which gives the frogs an opportunity to escape. Caecilians have been little studied in this respect, but the Cayenne caecilian (Typhlonectes compressicauda) produces toxic mucus that has killed predatory fish in a feeding experiment in Brazil. In some salamanders, the skin is poisonous. The rough-skinned newt (Taricha granulosa) from North America and other members of its genus contain the neurotoxin tetrodotoxin (TTX), the most toxic non-protein substance known and almost identical to that produced by pufferfish. Handling the newts does not cause harm, but ingestion of even the most minute amounts of the skin is deadly. In feeding trials, fish, frogs, reptiles, birds and mammals were all found to be susceptible. The only predators with some tolerance to the poison are certain populations of common garter snake (Thamnophis sirtalis). In locations where both snake and salamander co-exist, the snakes have developed immunity through genetic changes and they feed on the amphibians with impunity. Coevolution occurs with the newt increasing its toxic capabilities at the same rate as the snake further develops its immunity.

An aggressive posture involved raising the body off the ground and glaring at the opponent who often turned away submissively. If the intruder persisted, a biting lunge was usually launched at either the tail region or the naso-labial grooves. Damage to either of these areas can reduce the fitness of the rival, either because of the need to regenerate tissue or because it impairs its ability to detect food. In frogs, male territorial behaviour is often observed at breeding locations; calling is both an announcement of ownership of part of this resource and an advertisement call to potential mates. In general, a deeper voice represents a heavier and more powerful individual, and this may be sufficient to prevent intrusion by smaller males. Much energy is used in the vocalization and it takes a toll on the territory holder who may be displaced by a fitter rival if he tires. There is a tendency for males to tolerate the holders of neighbouring territories while vigorously attacking unknown intruders. Holders of territories have a "home advantage" and usually come off better in an encounter between two similar-sized frogs. If threats are insufficient, chest to chest tussles may take place. Fighting methods include pushing and shoving, deflating the opponent's vocal sac, seizing him by the head, jumping on his back, biting, chasing, splashing, and ducking him under the water. Defence mechanisms Amphibians have soft bodies with thin skins, and lack claws, defensive armour, or spines. Nevertheless, they have evolved various defence mechanisms to keep themselves alive. The first line of defence in salamanders and frogs is the mucous secretion that they produce. This keeps their skin moist and makes them slippery and difficult to grip. The secretion is often sticky and distasteful or toxic. Snakes have been observed yawning and gaping when trying to swallow African clawed frogs (Xenopus laevis), which gives the frogs an opportunity to escape. Caecilians have been little studied in this respect, but the Cayenne caecilian (Typhlonectes compressicauda) produces toxic mucus that has killed predatory fish in a feeding experiment in Brazil. In some salamanders, the skin is poisonous. The rough-skinned newt (Taricha granulosa) from North America and other members of its genus contain the neurotoxin tetrodotoxin (TTX), the most toxic non-protein substance known and almost identical to that produced by pufferfish. Handling the newts does not cause harm, but ingestion of even the most minute amounts of the skin is deadly. In feeding trials, fish, frogs, reptiles, birds and mammals were all found to be susceptible. The only predators with some tolerance to the poison are certain populations of common garter snake (Thamnophis sirtalis). In locations where both snake and salamander co-exist, the snakes have developed immunity through genetic changes and they feed on the amphibians with impunity. Coevolution occurs with the newt increasing its toxic capabilities at the same rate as the snake further develops its immunity.

An aggressive posture involved raising the body off the ground and glaring at the opponent who often turned away submissively. If the intruder persisted, a biting lunge was usually launched at either the tail region or the naso-labial grooves. Damage to either of these areas can reduce the fitness of the rival, either because of the need to regenerate tissue or because it impairs its ability to detect food. In frogs, male territorial behaviour is often observed at breeding locations; calling is both an announcement of ownership of part of this resource and an advertisement call to potential mates. In general, a deeper voice represents a heavier and more powerful individual, and this may be sufficient to prevent intrusion by smaller males. Much energy is used in the vocalization and it takes a toll on the territory holder who may be displaced by a fitter rival if he tires. There is a tendency for males to tolerate the holders of neighbouring territories while vigorously attacking unknown intruders. Holders of territories have a "home advantage" and usually come off better in an encounter between two similar-sized frogs. If threats are insufficient, chest to chest tussles may take place. Fighting methods include pushing and shoving, deflating the opponent's vocal sac, seizing him by the head, jumping on his back, biting, chasing, splashing, and ducking him under the water. Defence mechanisms Amphibians have soft bodies with thin skins, and lack claws, defensive armour, or spines. Nevertheless, they have evolved various defence mechanisms to keep themselves alive. The first line of defence in salamanders and frogs is the mucous secretion that they produce. This keeps their skin moist and makes them slippery and difficult to grip. The secretion is often sticky and distasteful or toxic. Snakes have been observed yawning and gaping when trying to swallow African clawed frogs (Xenopus laevis), which gives the frogs an opportunity to escape. Caecilians have been little studied in this respect, but the Cayenne caecilian (Typhlonectes compressicauda) produces toxic mucus that has killed predatory fish in a feeding experiment in Brazil. In some salamanders, the skin is poisonous. The rough-skinned newt (Taricha granulosa) from North America and other members of its genus contain the neurotoxin tetrodotoxin (TTX), the most toxic non-protein substance known and almost identical to that produced by pufferfish. Handling the newts does not cause harm, but ingestion of even the most minute amounts of the skin is deadly. In feeding trials, fish, frogs, reptiles, birds and mammals were all found to be susceptible. The only predators with some tolerance to the poison are certain populations of common garter snake (Thamnophis sirtalis). In locations where both snake and salamander co-exist, the snakes have developed immunity through genetic changes and they feed on the amphibians with impunity. Coevolution occurs with the newt increasing its toxic capabilities at the same rate as the snake further develops its immunity.

Some frogs and toads are toxic, the main poison glands being at the side of the neck and under the warts on the back. These regions are presented to the attacking animal and their secretions may be foul-tasting or cause various physical or neurological symptoms. Altogether, over 200 toxins have been isolated from the limited number of amphibian species that have been investigated. Poisonous species often use bright colouring to warn potential predators of their toxicity. These warning colours tend to be red or yellow combined with black, with the fire salamander (Salamandra salamandra) being an example. Once a predator has sampled one of these, it is likely to remember the colouration next time it encounters a similar animal. In some species, such as the fire-bellied toad (Bombina spp. ), the warning colouration is on the belly and these animals adopt a defensive pose when attacked, exhibiting their bright colours to the predator. The frog Allobates zaparo is not poisonous, but mimics the appearance of other toxic species in its locality, a strategy that may deceive predators. Many amphibians are nocturnal and hide during the day, thereby avoiding diurnal predators that hunt by sight. Other amphibians use camouflage to avoid being detected. They have various colourings such as mottled browns, greys and olives to blend into the background. Some salamanders adopt defensive poses when faced by a potential predator such as the North American northern short-tailed shrew (Blarina brevicauda). Their bodies writhe and they raise and lash their tails which makes it difficult for the predator to avoid contact with their poison-producing granular glands. A few salamanders will autotomise their tails when attacked, sacrificing this part of their anatomy to enable them to escape. The tail may have a constriction at its base to allow it to be easily detached. The tail is regenerated later, but the energy cost to the animal of replacing it is significant. Some frogs and toads inflate themselves to make themselves look large and fierce, and some spadefoot toads (Pelobates spp) scream and leap towards the attacker. Giant salamanders of the genus Andrias, as well as Ceratophrine and Pyxicephalus frogs possess sharp teeth and are capable of drawing blood with a defensive bite. The blackbelly salamander (Desmognathus quadramaculatus) can bite an attacking common garter snake (Thamnophis sirtalis) two or three times its size on the head and often manages to escape. Cognition In amphibians, there is evidence of habituation, associative learning through both classical and instrumental learning, and discrimination abilities. In one experiment, when offered live fruit flies (Drosophila virilis), salamanders chose the larger of 1 vs 2 and 2 vs 3. Frogs can distinguish between low numbers (1 vs 2, 2 vs 3, but not 3 vs 4) and large numbers (3 vs 6, 4 vs 8, but not 4 vs 6) of prey. This is irrespective of other characteristics, i.e. surface area, volume, weight and movement, although discrimination among large numbers may be based on surface area.

Some frogs and toads are toxic, the main poison glands being at the side of the neck and under the warts on the back. These regions are presented to the attacking animal and their secretions may be foul-tasting or cause various physical or neurological symptoms. Altogether, over 200 toxins have been isolated from the limited number of amphibian species that have been investigated. Poisonous species often use bright colouring to warn potential predators of their toxicity. These warning colours tend to be red or yellow combined with black, with the fire salamander (Salamandra salamandra) being an example. Once a predator has sampled one of these, it is likely to remember the colouration next time it encounters a similar animal. In some species, such as the fire-bellied toad (Bombina spp. ), the warning colouration is on the belly and these animals adopt a defensive pose when attacked, exhibiting their bright colours to the predator. The frog Allobates zaparo is not poisonous, but mimics the appearance of other toxic species in its locality, a strategy that may deceive predators. Many amphibians are nocturnal and hide during the day, thereby avoiding diurnal predators that hunt by sight. Other amphibians use camouflage to avoid being detected. They have various colourings such as mottled browns, greys and olives to blend into the background. Some salamanders adopt defensive poses when faced by a potential predator such as the North American northern short-tailed shrew (Blarina brevicauda). Their bodies writhe and they raise and lash their tails which makes it difficult for the predator to avoid contact with their poison-producing granular glands. A few salamanders will autotomise their tails when attacked, sacrificing this part of their anatomy to enable them to escape. The tail may have a constriction at its base to allow it to be easily detached. The tail is regenerated later, but the energy cost to the animal of replacing it is significant. Some frogs and toads inflate themselves to make themselves look large and fierce, and some spadefoot toads (Pelobates spp) scream and leap towards the attacker. Giant salamanders of the genus Andrias, as well as Ceratophrine and Pyxicephalus frogs possess sharp teeth and are capable of drawing blood with a defensive bite. The blackbelly salamander (Desmognathus quadramaculatus) can bite an attacking common garter snake (Thamnophis sirtalis) two or three times its size on the head and often manages to escape. Cognition In amphibians, there is evidence of habituation, associative learning through both classical and instrumental learning, and discrimination abilities. In one experiment, when offered live fruit flies (Drosophila virilis), salamanders chose the larger of 1 vs 2 and 2 vs 3. Frogs can distinguish between low numbers (1 vs 2, 2 vs 3, but not 3 vs 4) and large numbers (3 vs 6, 4 vs 8, but not 4 vs 6) of prey. This is irrespective of other characteristics, i.e. surface area, volume, weight and movement, although discrimination among large numbers may be based on surface area.

Some frogs and toads are toxic, the main poison glands being at the side of the neck and under the warts on the back. These regions are presented to the attacking animal and their secretions may be foul-tasting or cause various physical or neurological symptoms. Altogether, over 200 toxins have been isolated from the limited number of amphibian species that have been investigated. Poisonous species often use bright colouring to warn potential predators of their toxicity. These warning colours tend to be red or yellow combined with black, with the fire salamander (Salamandra salamandra) being an example. Once a predator has sampled one of these, it is likely to remember the colouration next time it encounters a similar animal. In some species, such as the fire-bellied toad (Bombina spp. ), the warning colouration is on the belly and these animals adopt a defensive pose when attacked, exhibiting their bright colours to the predator. The frog Allobates zaparo is not poisonous, but mimics the appearance of other toxic species in its locality, a strategy that may deceive predators. Many amphibians are nocturnal and hide during the day, thereby avoiding diurnal predators that hunt by sight. Other amphibians use camouflage to avoid being detected. They have various colourings such as mottled browns, greys and olives to blend into the background. Some salamanders adopt defensive poses when faced by a potential predator such as the North American northern short-tailed shrew (Blarina brevicauda). Their bodies writhe and they raise and lash their tails which makes it difficult for the predator to avoid contact with their poison-producing granular glands. A few salamanders will autotomise their tails when attacked, sacrificing this part of their anatomy to enable them to escape. The tail may have a constriction at its base to allow it to be easily detached. The tail is regenerated later, but the energy cost to the animal of replacing it is significant. Some frogs and toads inflate themselves to make themselves look large and fierce, and some spadefoot toads (Pelobates spp) scream and leap towards the attacker. Giant salamanders of the genus Andrias, as well as Ceratophrine and Pyxicephalus frogs possess sharp teeth and are capable of drawing blood with a defensive bite. The blackbelly salamander (Desmognathus quadramaculatus) can bite an attacking common garter snake (Thamnophis sirtalis) two or three times its size on the head and often manages to escape. Cognition In amphibians, there is evidence of habituation, associative learning through both classical and instrumental learning, and discrimination abilities. In one experiment, when offered live fruit flies (Drosophila virilis), salamanders chose the larger of 1 vs 2 and 2 vs 3. Frogs can distinguish between low numbers (1 vs 2, 2 vs 3, but not 3 vs 4) and large numbers (3 vs 6, 4 vs 8, but not 4 vs 6) of prey. This is irrespective of other characteristics, i.e. surface area, volume, weight and movement, although discrimination among large numbers may be based on surface area.

Conservation Dramatic declines in amphibian populations, including population crashes and mass localized extinction, have been noted since the late 1980s from locations all over the world, and amphibian declines are thus perceived to be one of the most critical threats to global biodiversity. In 2004, the International Union for Conservation of Nature (IUCN) reported stating that currently birds, mammals, and amphibians extinction rates were at minimum 48 times greater than natural extinction rates—possibly 1,024 times higher. In 2006, there were believed to be 4,035 species of amphibians that depended on water at some stage during their life cycle. Of these, 1,356 (33.6%) were considered to be threatened and this figure is likely to be an underestimate because it excludes 1,427 species for which there was insufficient data to assess their status. A number of causes are believed to be involved, including habitat destruction and modification, over-exploitation, pollution, introduced species, global warming, endocrine-disrupting pollutants, destruction of the ozone layer (ultraviolet radiation has shown to be especially damaging to the skin, eyes, and eggs of amphibians), and diseases like chytridiomycosis. However, many of the causes of amphibian declines are still poorly understood, and are a topic of ongoing discussion. With their complex reproductive needs and permeable skins, amphibians are often considered to be ecological indicators. In many terrestrial ecosystems, they constitute one of the largest parts of the vertebrate biomass. Any decline in amphibian numbers will affect the patterns of predation. The loss of carnivorous species near the top of the food chain will upset the delicate ecosystem balance and may cause dramatic increases in opportunistic species. In the Middle East, a growing appetite for eating frog legs and the consequent gathering of them for food was linked to an increase in mosquitoes. Predators that feed on amphibians are affected by their decline. The western terrestrial garter snake (Thamnophis elegans) in California is largely aquatic and depends heavily on two species of frog that are decreasing in numbers, the Yosemite toad (Bufo canorus) and the mountain yellow-legged frog (Rana muscosa), putting the snake's future at risk. If the snake were to become scarce, this would affect birds of prey and other predators that feed on it. Meanwhile, in the ponds and lakes, fewer frogs means fewer tadpoles. These normally play an important role in controlling the growth of algae and also forage on detritus that accumulates as sediment on the bottom. A reduction in the number of tadpoles may lead to an overgrowth of algae, resulting in depletion of oxygen in the water when the algae later die and decompose. Aquatic invertebrates and fish might then die and there would be unpredictable ecological consequences. A global strategy to stem the crisis was released in 2005 in the form of the Amphibian Conservation Action Plan. Developed by over eighty leading experts in the field, this call to action details what would be required to curtail amphibian declines and extinctions over the following five years and how much this would cost.

Conservation Dramatic declines in amphibian populations, including population crashes and mass localized extinction, have been noted since the late 1980s from locations all over the world, and amphibian declines are thus perceived to be one of the most critical threats to global biodiversity. In 2004, the International Union for Conservation of Nature (IUCN) reported stating that currently birds, mammals, and amphibians extinction rates were at minimum 48 times greater than natural extinction rates—possibly 1,024 times higher. In 2006, there were believed to be 4,035 species of amphibians that depended on water at some stage during their life cycle. Of these, 1,356 (33.6%) were considered to be threatened and this figure is likely to be an underestimate because it excludes 1,427 species for which there was insufficient data to assess their status. A number of causes are believed to be involved, including habitat destruction and modification, over-exploitation, pollution, introduced species, global warming, endocrine-disrupting pollutants, destruction of the ozone layer (ultraviolet radiation has shown to be especially damaging to the skin, eyes, and eggs of amphibians), and diseases like chytridiomycosis. However, many of the causes of amphibian declines are still poorly understood, and are a topic of ongoing discussion. With their complex reproductive needs and permeable skins, amphibians are often considered to be ecological indicators. In many terrestrial ecosystems, they constitute one of the largest parts of the vertebrate biomass. Any decline in amphibian numbers will affect the patterns of predation. The loss of carnivorous species near the top of the food chain will upset the delicate ecosystem balance and may cause dramatic increases in opportunistic species. In the Middle East, a growing appetite for eating frog legs and the consequent gathering of them for food was linked to an increase in mosquitoes. Predators that feed on amphibians are affected by their decline. The western terrestrial garter snake (Thamnophis elegans) in California is largely aquatic and depends heavily on two species of frog that are decreasing in numbers, the Yosemite toad (Bufo canorus) and the mountain yellow-legged frog (Rana muscosa), putting the snake's future at risk. If the snake were to become scarce, this would affect birds of prey and other predators that feed on it. Meanwhile, in the ponds and lakes, fewer frogs means fewer tadpoles. These normally play an important role in controlling the growth of algae and also forage on detritus that accumulates as sediment on the bottom. A reduction in the number of tadpoles may lead to an overgrowth of algae, resulting in depletion of oxygen in the water when the algae later die and decompose. Aquatic invertebrates and fish might then die and there would be unpredictable ecological consequences. A global strategy to stem the crisis was released in 2005 in the form of the Amphibian Conservation Action Plan. Developed by over eighty leading experts in the field, this call to action details what would be required to curtail amphibian declines and extinctions over the following five years and how much this would cost.

Conservation Dramatic declines in amphibian populations, including population crashes and mass localized extinction, have been noted since the late 1980s from locations all over the world, and amphibian declines are thus perceived to be one of the most critical threats to global biodiversity. In 2004, the International Union for Conservation of Nature (IUCN) reported stating that currently birds, mammals, and amphibians extinction rates were at minimum 48 times greater than natural extinction rates—possibly 1,024 times higher. In 2006, there were believed to be 4,035 species of amphibians that depended on water at some stage during their life cycle. Of these, 1,356 (33.6%) were considered to be threatened and this figure is likely to be an underestimate because it excludes 1,427 species for which there was insufficient data to assess their status. A number of causes are believed to be involved, including habitat destruction and modification, over-exploitation, pollution, introduced species, global warming, endocrine-disrupting pollutants, destruction of the ozone layer (ultraviolet radiation has shown to be especially damaging to the skin, eyes, and eggs of amphibians), and diseases like chytridiomycosis. However, many of the causes of amphibian declines are still poorly understood, and are a topic of ongoing discussion. With their complex reproductive needs and permeable skins, amphibians are often considered to be ecological indicators. In many terrestrial ecosystems, they constitute one of the largest parts of the vertebrate biomass. Any decline in amphibian numbers will affect the patterns of predation. The loss of carnivorous species near the top of the food chain will upset the delicate ecosystem balance and may cause dramatic increases in opportunistic species. In the Middle East, a growing appetite for eating frog legs and the consequent gathering of them for food was linked to an increase in mosquitoes. Predators that feed on amphibians are affected by their decline. The western terrestrial garter snake (Thamnophis elegans) in California is largely aquatic and depends heavily on two species of frog that are decreasing in numbers, the Yosemite toad (Bufo canorus) and the mountain yellow-legged frog (Rana muscosa), putting the snake's future at risk. If the snake were to become scarce, this would affect birds of prey and other predators that feed on it. Meanwhile, in the ponds and lakes, fewer frogs means fewer tadpoles. These normally play an important role in controlling the growth of algae and also forage on detritus that accumulates as sediment on the bottom. A reduction in the number of tadpoles may lead to an overgrowth of algae, resulting in depletion of oxygen in the water when the algae later die and decompose. Aquatic invertebrates and fish might then die and there would be unpredictable ecological consequences. A global strategy to stem the crisis was released in 2005 in the form of the Amphibian Conservation Action Plan. Developed by over eighty leading experts in the field, this call to action details what would be required to curtail amphibian declines and extinctions over the following five years and how much this would cost.

The Amphibian Specialist Group of the IUCN is spearheading efforts to implement a comprehensive global strategy for amphibian conservation. Amphibian Ark is an organization that was formed to implement the ex-situ conservation recommendations of this plan, and they have been working with zoos and aquaria around the world, encouraging them to create assurance colonies of threatened amphibians. One such project is the Panama Amphibian Rescue and Conservation Project that built on existing conservation efforts in Panama to create a country-wide response to the threat of chytridiomycosis. See also List of amphibians List of amphibian genera List of threatened reptiles and amphibians of the United States References Cited texts Further reading External links Amphibians – AnimalSpot.net ArchéoZooThèque : Amphibians skeletons drawings : available in vector, image and PDF formats Amphibian Specialist Group Amphibian Ark AmphibiaWeb Global Amphibian Assessment Amphibian vocalisations on Archival Sound Recordings Amphibious organisms Extant Late Devonian first appearances Taxa named by John Edward Gray

The Amphibian Specialist Group of the IUCN is spearheading efforts to implement a comprehensive global strategy for amphibian conservation. Amphibian Ark is an organization that was formed to implement the ex-situ conservation recommendations of this plan, and they have been working with zoos and aquaria around the world, encouraging them to create assurance colonies of threatened amphibians. One such project is the Panama Amphibian Rescue and Conservation Project that built on existing conservation efforts in Panama to create a country-wide response to the threat of chytridiomycosis. See also List of amphibians List of amphibian genera List of threatened reptiles and amphibians of the United States References Cited texts Further reading External links Amphibians – AnimalSpot.net ArchéoZooThèque : Amphibians skeletons drawings : available in vector, image and PDF formats Amphibian Specialist Group Amphibian Ark AmphibiaWeb Global Amphibian Assessment Amphibian vocalisations on Archival Sound Recordings Amphibious organisms Extant Late Devonian first appearances Taxa named by John Edward Gray

The Amphibian Specialist Group of the IUCN is spearheading efforts to implement a comprehensive global strategy for amphibian conservation. Amphibian Ark is an organization that was formed to implement the ex-situ conservation recommendations of this plan, and they have been working with zoos and aquaria around the world, encouraging them to create assurance colonies of threatened amphibians. One such project is the Panama Amphibian Rescue and Conservation Project that built on existing conservation efforts in Panama to create a country-wide response to the threat of chytridiomycosis. See also List of amphibians List of amphibian genera List of threatened reptiles and amphibians of the United States References Cited texts Further reading External links Amphibians – AnimalSpot.net ArchéoZooThèque : Amphibians skeletons drawings : available in vector, image and PDF formats Amphibian Specialist Group Amphibian Ark AmphibiaWeb Global Amphibian Assessment Amphibian vocalisations on Archival Sound Recordings Amphibious organisms Extant Late Devonian first appearances Taxa named by John Edward Gray

Alaska Alaska (; ; ; ; Yup'ik: Alaskaq; ) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., it borders the Canadian province of British Columbia and the territory of Yukon to the east and shares a maritime border with the Russian Federation's Chukotka Autonomous Okrug to the west, just across the Bering Strait. To the north are the Chukchi and Beaufort seas of the Arctic Ocean, while the Pacific Ocean lies to the south and southwest. Alaska is by far the largest U.S. state by area, comprising more total area than the next three largest states (Texas, California, and Montana) combined. It represents the seventh largest subnational division in the world. It is the third-least populous and the most sparsely populated state, but by far the continent's most populous territory located mostly north of the 60th parallel, with a population of 736,081 as of 2020—more than quadruple the combined populations of Northern Canada and Greenland. Approximately half of Alaska's residents live within the Anchorage metropolitan area. The state capital of Juneau is the second-largest city in the United States by area, comprising more territory than the states of Rhode Island and Delaware. The former capital of Alaska, Sitka, is the largest U.S. city by area. Alaska was occupied by various indigenous peoples for thousands of years before the arrival of Europeans. The state is considered the entry point for the settlement of North America by way of the Bering land bridge. The Russians were the first Europeans to settle the area beginning in the 18th century, eventually establishing Russian America, which spanned most of the current state. The expense and difficulty of maintaining this distant possession prompted its sale to the U.S. in 1867 for US$7.2 million (equivalent to $ million in ), or approximately two cents per acre ($4.74/km2). The area went through several administrative changes before becoming organized as a territory on May 11, 1912. It was admitted as the 49th state of the U.S. on January 3, 1959. While it has one of the smallest state economies in the country, Alaska's per capita income is among the highest, owing to a diversified economy dominated by fishing, natural gas, and oil, all of which it has in abundance. United States armed forces bases and tourism are also a significant part of the economy; more than half the state is federally owned public land, including a multitude of national forests, national parks, and wildlife refuges. The indigenous population of Alaska is proportionally the highest of any U.S. state, at over 15 percent. Close to two dozen native languages are spoken, and Alaskan Natives exercise considerable influence in local and state politics. Etymology The name "Alaska" () was introduced in the Russian colonial period when it was used to refer to the Alaska Peninsula.

Alaska Alaska (; ; ; ; Yup'ik: Alaskaq; ) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., it borders the Canadian province of British Columbia and the territory of Yukon to the east and shares a maritime border with the Russian Federation's Chukotka Autonomous Okrug to the west, just across the Bering Strait. To the north are the Chukchi and Beaufort seas of the Arctic Ocean, while the Pacific Ocean lies to the south and southwest. Alaska is by far the largest U.S. state by area, comprising more total area than the next three largest states (Texas, California, and Montana) combined. It represents the seventh largest subnational division in the world. It is the third-least populous and the most sparsely populated state, but by far the continent's most populous territory located mostly north of the 60th parallel, with a population of 736,081 as of 2020—more than quadruple the combined populations of Northern Canada and Greenland. Approximately half of Alaska's residents live within the Anchorage metropolitan area. The state capital of Juneau is the second-largest city in the United States by area, comprising more territory than the states of Rhode Island and Delaware. The former capital of Alaska, Sitka, is the largest U.S. city by area. Alaska was occupied by various indigenous peoples for thousands of years before the arrival of Europeans. The state is considered the entry point for the settlement of North America by way of the Bering land bridge. The Russians were the first Europeans to settle the area beginning in the 18th century, eventually establishing Russian America, which spanned most of the current state. The expense and difficulty of maintaining this distant possession prompted its sale to the U.S. in 1867 for US$7.2 million (equivalent to $ million in ), or approximately two cents per acre ($4.74/km2). The area went through several administrative changes before becoming organized as a territory on May 11, 1912. It was admitted as the 49th state of the U.S. on January 3, 1959. While it has one of the smallest state economies in the country, Alaska's per capita income is among the highest, owing to a diversified economy dominated by fishing, natural gas, and oil, all of which it has in abundance. United States armed forces bases and tourism are also a significant part of the economy; more than half the state is federally owned public land, including a multitude of national forests, national parks, and wildlife refuges. The indigenous population of Alaska is proportionally the highest of any U.S. state, at over 15 percent. Close to two dozen native languages are spoken, and Alaskan Natives exercise considerable influence in local and state politics. Etymology The name "Alaska" () was introduced in the Russian colonial period when it was used to refer to the Alaska Peninsula.

It was derived from an Aleut-language idiom, "alaxsxaq", meaning "the mainland" or, more literally, "the object towards which the action of the sea is directed". It is also known as "Alyeska", the "great land", an Aleut word derived from the same root. History Pre-colonization Numerous indigenous peoples occupied Alaska for thousands of years before the arrival of European peoples to the area. Linguistic and DNA studies done here have provided evidence for the settlement of North America by way of the Bering land bridge. At the Upward Sun River site in the Tanana Valley in Alaska, remains of a six-week-old infant were found. The baby's DNA showed that she belonged to a population that was genetically separate from other native groups present elsewhere in the New World at the end of the Pleistocene. Ben Potter, the University of Alaska Fairbanks archaeologist who unearthed the remains at the Upward Sun River site in 2013, named this new group Ancient Beringians. The Tlingit people developed a society with a matrilineal kinship system of property inheritance and descent in what is today Southeast Alaska, along with parts of British Columbia and the Yukon. Also in Southeast were the Haida, now well known for their unique arts. The Tsimshian people came to Alaska from British Columbia in 1887, when President Grover Cleveland, and later the U.S. Congress, granted them permission to settle on Annette Island and found the town of Metlakatla. All three of these peoples, as well as other indigenous peoples of the Pacific Northwest Coast, experienced smallpox outbreaks from the late 18th through the mid-19th century, with the most devastating epidemics occurring in the 1830s and 1860s, resulting in high fatalities and social disruption. The Aleutian Islands are still home to the Aleut people's seafaring society, although they were the first Native Alaskans to be exploited by the Russians. Western and Southwestern Alaska are home to the Yup'ik, while their cousins the Alutiiq ~ Sugpiaq live in what is now Southcentral Alaska. The Gwich'in people of the northern Interior region are Athabaskan and primarily known today for their dependence on the caribou within the much-contested Arctic National Wildlife Refuge. The North Slope and Little Diomede Island are occupied by the widespread Inupiat people. Colonization Some researchers believe the first Russian settlement in Alaska was established in the 17th century. According to this hypothesis, in 1648 several koches of Semyon Dezhnyov's expedition came ashore in Alaska by storm and founded this settlement. This hypothesis is based on the testimony of Chukchi geographer Nikolai Daurkin, who had visited Alaska in 1764–1765 and who had reported on a village on the Kheuveren River, populated by "bearded men" who "pray to the icons". Some modern researchers associate Kheuveren with Koyuk River.

It was derived from an Aleut-language idiom, "alaxsxaq", meaning "the mainland" or, more literally, "the object towards which the action of the sea is directed". It is also known as "Alyeska", the "great land", an Aleut word derived from the same root. History Pre-colonization Numerous indigenous peoples occupied Alaska for thousands of years before the arrival of European peoples to the area. Linguistic and DNA studies done here have provided evidence for the settlement of North America by way of the Bering land bridge. At the Upward Sun River site in the Tanana Valley in Alaska, remains of a six-week-old infant were found. The baby's DNA showed that she belonged to a population that was genetically separate from other native groups present elsewhere in the New World at the end of the Pleistocene. Ben Potter, the University of Alaska Fairbanks archaeologist who unearthed the remains at the Upward Sun River site in 2013, named this new group Ancient Beringians. The Tlingit people developed a society with a matrilineal kinship system of property inheritance and descent in what is today Southeast Alaska, along with parts of British Columbia and the Yukon. Also in Southeast were the Haida, now well known for their unique arts. The Tsimshian people came to Alaska from British Columbia in 1887, when President Grover Cleveland, and later the U.S. Congress, granted them permission to settle on Annette Island and found the town of Metlakatla. All three of these peoples, as well as other indigenous peoples of the Pacific Northwest Coast, experienced smallpox outbreaks from the late 18th through the mid-19th century, with the most devastating epidemics occurring in the 1830s and 1860s, resulting in high fatalities and social disruption. The Aleutian Islands are still home to the Aleut people's seafaring society, although they were the first Native Alaskans to be exploited by the Russians. Western and Southwestern Alaska are home to the Yup'ik, while their cousins the Alutiiq ~ Sugpiaq live in what is now Southcentral Alaska. The Gwich'in people of the northern Interior region are Athabaskan and primarily known today for their dependence on the caribou within the much-contested Arctic National Wildlife Refuge. The North Slope and Little Diomede Island are occupied by the widespread Inupiat people. Colonization Some researchers believe the first Russian settlement in Alaska was established in the 17th century. According to this hypothesis, in 1648 several koches of Semyon Dezhnyov's expedition came ashore in Alaska by storm and founded this settlement. This hypothesis is based on the testimony of Chukchi geographer Nikolai Daurkin, who had visited Alaska in 1764–1765 and who had reported on a village on the Kheuveren River, populated by "bearded men" who "pray to the icons". Some modern researchers associate Kheuveren with Koyuk River.

It was derived from an Aleut-language idiom, "alaxsxaq", meaning "the mainland" or, more literally, "the object towards which the action of the sea is directed". It is also known as "Alyeska", the "great land", an Aleut word derived from the same root. History Pre-colonization Numerous indigenous peoples occupied Alaska for thousands of years before the arrival of European peoples to the area. Linguistic and DNA studies done here have provided evidence for the settlement of North America by way of the Bering land bridge. At the Upward Sun River site in the Tanana Valley in Alaska, remains of a six-week-old infant were found. The baby's DNA showed that she belonged to a population that was genetically separate from other native groups present elsewhere in the New World at the end of the Pleistocene. Ben Potter, the University of Alaska Fairbanks archaeologist who unearthed the remains at the Upward Sun River site in 2013, named this new group Ancient Beringians. The Tlingit people developed a society with a matrilineal kinship system of property inheritance and descent in what is today Southeast Alaska, along with parts of British Columbia and the Yukon. Also in Southeast were the Haida, now well known for their unique arts. The Tsimshian people came to Alaska from British Columbia in 1887, when President Grover Cleveland, and later the U.S. Congress, granted them permission to settle on Annette Island and found the town of Metlakatla. All three of these peoples, as well as other indigenous peoples of the Pacific Northwest Coast, experienced smallpox outbreaks from the late 18th through the mid-19th century, with the most devastating epidemics occurring in the 1830s and 1860s, resulting in high fatalities and social disruption. The Aleutian Islands are still home to the Aleut people's seafaring society, although they were the first Native Alaskans to be exploited by the Russians. Western and Southwestern Alaska are home to the Yup'ik, while their cousins the Alutiiq ~ Sugpiaq live in what is now Southcentral Alaska. The Gwich'in people of the northern Interior region are Athabaskan and primarily known today for their dependence on the caribou within the much-contested Arctic National Wildlife Refuge. The North Slope and Little Diomede Island are occupied by the widespread Inupiat people. Colonization Some researchers believe the first Russian settlement in Alaska was established in the 17th century. According to this hypothesis, in 1648 several koches of Semyon Dezhnyov's expedition came ashore in Alaska by storm and founded this settlement. This hypothesis is based on the testimony of Chukchi geographer Nikolai Daurkin, who had visited Alaska in 1764–1765 and who had reported on a village on the Kheuveren River, populated by "bearded men" who "pray to the icons". Some modern researchers associate Kheuveren with Koyuk River.

The first European vessel to reach Alaska is generally held to be the St. Gabriel under the authority of the surveyor M. S. Gvozdev and assistant navigator I. Fyodorov on August 21, 1732, during an expedition of Siberian Cossack A. F. Shestakov and Russian explorer Dmitry Pavlutsky (1729–1735). Another European contact with Alaska occurred in 1741, when Vitus Bering led an expedition for the Russian Navy aboard the St. Peter. After his crew returned to Russia with sea otter pelts judged to be the finest fur in the world, small associations of fur traders began to sail from the shores of Siberia toward the Aleutian Islands. The first permanent European settlement was founded in 1784. Between 1774 and 1800, Spain sent several expeditions to Alaska to assert its claim over the Pacific Northwest. In 1789, a Spanish settlement and fort were built in Nootka Sound. These expeditions gave names to places such as Valdez, Bucareli Sound, and Cordova. Later, the Russian-American Company carried out an expanded colonization program during the early-to-mid-19th century. Sitka, renamed New Archangel from 1804 to 1867, on Baranof Island in the Alexander Archipelago in what is now Southeast Alaska, became the capital of Russian America. It remained the capital after the colony was transferred to the United States. The Russians never fully colonized Alaska, and the colony was never very profitable. Evidence of Russian settlement in names and churches survive throughout southeastern Alaska. William H. Seward, the 24th United States Secretary of State, negotiated the Alaska Purchase (also known as Seward's Folly) with the Russians in 1867 for $7.2 million. Russia's contemporary ruler Tsar Alexander II, the Emperor of the Russian Empire, King of Poland and Grand Duke of Finland, also planned the sale; the purchase was made on March 30, 1867. Six months later the commissioners arrived in Sitka and the formal transfer was arranged; the formal flag-raising took place at Fort Sitka on October 18, 1867. In the ceremony 250 uniformed U.S. soldiers marched to the governor's house at "Castle Hill", where the Russian troops lowered the Russian flag and the U.S. flag was raised. This event is celebrated as Alaska Day, a legal holiday on October 18. Alaska was loosely governed by the military initially, and was administered as a district starting in 1884, with a governor appointed by the United States president. A federal district court was headquartered in Sitka. For most of Alaska's first decade under the United States flag, Sitka was the only community inhabited by American settlers. They organized a "provisional city government", which was Alaska's first municipal government, but not in a legal sense. Legislation allowing Alaskan communities to legally incorporate as cities did not come about until 1900, and home rule for cities was extremely limited or unavailable until statehood took effect in 1959.

The first European vessel to reach Alaska is generally held to be the St. Gabriel under the authority of the surveyor M. S. Gvozdev and assistant navigator I. Fyodorov on August 21, 1732, during an expedition of Siberian Cossack A. F. Shestakov and Russian explorer Dmitry Pavlutsky (1729–1735). Another European contact with Alaska occurred in 1741, when Vitus Bering led an expedition for the Russian Navy aboard the St. Peter. After his crew returned to Russia with sea otter pelts judged to be the finest fur in the world, small associations of fur traders began to sail from the shores of Siberia toward the Aleutian Islands. The first permanent European settlement was founded in 1784. Between 1774 and 1800, Spain sent several expeditions to Alaska to assert its claim over the Pacific Northwest. In 1789, a Spanish settlement and fort were built in Nootka Sound. These expeditions gave names to places such as Valdez, Bucareli Sound, and Cordova. Later, the Russian-American Company carried out an expanded colonization program during the early-to-mid-19th century. Sitka, renamed New Archangel from 1804 to 1867, on Baranof Island in the Alexander Archipelago in what is now Southeast Alaska, became the capital of Russian America. It remained the capital after the colony was transferred to the United States. The Russians never fully colonized Alaska, and the colony was never very profitable. Evidence of Russian settlement in names and churches survive throughout southeastern Alaska. William H. Seward, the 24th United States Secretary of State, negotiated the Alaska Purchase (also known as Seward's Folly) with the Russians in 1867 for $7.2 million. Russia's contemporary ruler Tsar Alexander II, the Emperor of the Russian Empire, King of Poland and Grand Duke of Finland, also planned the sale; the purchase was made on March 30, 1867. Six months later the commissioners arrived in Sitka and the formal transfer was arranged; the formal flag-raising took place at Fort Sitka on October 18, 1867. In the ceremony 250 uniformed U.S. soldiers marched to the governor's house at "Castle Hill", where the Russian troops lowered the Russian flag and the U.S. flag was raised. This event is celebrated as Alaska Day, a legal holiday on October 18. Alaska was loosely governed by the military initially, and was administered as a district starting in 1884, with a governor appointed by the United States president. A federal district court was headquartered in Sitka. For most of Alaska's first decade under the United States flag, Sitka was the only community inhabited by American settlers. They organized a "provisional city government", which was Alaska's first municipal government, but not in a legal sense. Legislation allowing Alaskan communities to legally incorporate as cities did not come about until 1900, and home rule for cities was extremely limited or unavailable until statehood took effect in 1959.

The first European vessel to reach Alaska is generally held to be the St. Gabriel under the authority of the surveyor M. S. Gvozdev and assistant navigator I. Fyodorov on August 21, 1732, during an expedition of Siberian Cossack A. F. Shestakov and Russian explorer Dmitry Pavlutsky (1729–1735). Another European contact with Alaska occurred in 1741, when Vitus Bering led an expedition for the Russian Navy aboard the St. Peter. After his crew returned to Russia with sea otter pelts judged to be the finest fur in the world, small associations of fur traders began to sail from the shores of Siberia toward the Aleutian Islands. The first permanent European settlement was founded in 1784. Between 1774 and 1800, Spain sent several expeditions to Alaska to assert its claim over the Pacific Northwest. In 1789, a Spanish settlement and fort were built in Nootka Sound. These expeditions gave names to places such as Valdez, Bucareli Sound, and Cordova. Later, the Russian-American Company carried out an expanded colonization program during the early-to-mid-19th century. Sitka, renamed New Archangel from 1804 to 1867, on Baranof Island in the Alexander Archipelago in what is now Southeast Alaska, became the capital of Russian America. It remained the capital after the colony was transferred to the United States. The Russians never fully colonized Alaska, and the colony was never very profitable. Evidence of Russian settlement in names and churches survive throughout southeastern Alaska. William H. Seward, the 24th United States Secretary of State, negotiated the Alaska Purchase (also known as Seward's Folly) with the Russians in 1867 for $7.2 million. Russia's contemporary ruler Tsar Alexander II, the Emperor of the Russian Empire, King of Poland and Grand Duke of Finland, also planned the sale; the purchase was made on March 30, 1867. Six months later the commissioners arrived in Sitka and the formal transfer was arranged; the formal flag-raising took place at Fort Sitka on October 18, 1867. In the ceremony 250 uniformed U.S. soldiers marched to the governor's house at "Castle Hill", where the Russian troops lowered the Russian flag and the U.S. flag was raised. This event is celebrated as Alaska Day, a legal holiday on October 18. Alaska was loosely governed by the military initially, and was administered as a district starting in 1884, with a governor appointed by the United States president. A federal district court was headquartered in Sitka. For most of Alaska's first decade under the United States flag, Sitka was the only community inhabited by American settlers. They organized a "provisional city government", which was Alaska's first municipal government, but not in a legal sense. Legislation allowing Alaskan communities to legally incorporate as cities did not come about until 1900, and home rule for cities was extremely limited or unavailable until statehood took effect in 1959.

Alaska as an incorporated U.S. territory Starting in the 1890s and stretching in some places to the early 1910s, gold rushes in Alaska and the nearby Yukon Territory brought thousands of miners and settlers to Alaska. Alaska was officially incorporated as an organized territory in 1912. Alaska's capital, which had been in Sitka until 1906, was moved north to Juneau. Construction of the Alaska Governor's Mansion began that same year. European immigrants from Norway and Sweden also settled in southeast Alaska, where they entered the fishing and logging industries. During World War II, the Aleutian Islands Campaign focused on Attu, Agattu and Kiska, all which were occupied by the Empire of Japan. During the Japanese occupation, a white American civilian and two United States Navy personnel were killed at Attu and Kiska respectively, and nearly a total of 50 Aleut civilians and eight sailors were interned in Japan. About half of the Aleuts died during the period of internment. Unalaska/Dutch Harbor and Adak became significant bases for the United States Army, United States Army Air Forces and United States Navy. The United States Lend-Lease program involved flying American warplanes through Canada to Fairbanks and then Nome; Soviet pilots took possession of these aircraft, ferrying them to fight the German invasion of the Soviet Union. The construction of military bases contributed to the population growth of some Alaskan cities. Statehood Statehood for Alaska was an important cause of James Wickersham early in his tenure as a congressional delegate. Decades later, the statehood movement gained its first real momentum following a territorial referendum in 1946. The Alaska Statehood Committee and Alaska's Constitutional Convention would soon follow. Statehood supporters also found themselves fighting major battles against political foes, mostly in the U.S. Congress but also within Alaska. Statehood was approved by the U.S. Congress on July 7, 1958; Alaska was officially proclaimed a state on January 3, 1959. Good Friday earthquake On March 27, 1964, the massive Good Friday earthquake killed 133 people and destroyed several villages and portions of large coastal communities, mainly by the resultant tsunamis and landslides. It was the second-most-powerful earthquake in recorded history, with a moment magnitude of 9.2 (more than a thousand times as powerful as the 1989 San Francisco earthquake). The time of day (5:36 pm), time of year (spring) and location of the epicenter were all cited as factors in potentially sparing thousands of lives, particularly in Anchorage. Alaska oil boom The 1968 discovery of oil at Prudhoe Bay and the 1977 completion of the Trans-Alaska Pipeline System led to an oil boom. Royalty revenues from oil have funded large state budgets from 1980 onward. That same year, not coincidentally, Alaska repealed its state income tax. In 1989, the Exxon Valdez hit a reef in the Prince William Sound, spilling more than of crude oil over of coastline.

Alaska as an incorporated U.S. territory Starting in the 1890s and stretching in some places to the early 1910s, gold rushes in Alaska and the nearby Yukon Territory brought thousands of miners and settlers to Alaska. Alaska was officially incorporated as an organized territory in 1912. Alaska's capital, which had been in Sitka until 1906, was moved north to Juneau. Construction of the Alaska Governor's Mansion began that same year. European immigrants from Norway and Sweden also settled in southeast Alaska, where they entered the fishing and logging industries. During World War II, the Aleutian Islands Campaign focused on Attu, Agattu and Kiska, all which were occupied by the Empire of Japan. During the Japanese occupation, a white American civilian and two United States Navy personnel were killed at Attu and Kiska respectively, and nearly a total of 50 Aleut civilians and eight sailors were interned in Japan. About half of the Aleuts died during the period of internment. Unalaska/Dutch Harbor and Adak became significant bases for the United States Army, United States Army Air Forces and United States Navy. The United States Lend-Lease program involved flying American warplanes through Canada to Fairbanks and then Nome; Soviet pilots took possession of these aircraft, ferrying them to fight the German invasion of the Soviet Union. The construction of military bases contributed to the population growth of some Alaskan cities. Statehood Statehood for Alaska was an important cause of James Wickersham early in his tenure as a congressional delegate. Decades later, the statehood movement gained its first real momentum following a territorial referendum in 1946. The Alaska Statehood Committee and Alaska's Constitutional Convention would soon follow. Statehood supporters also found themselves fighting major battles against political foes, mostly in the U.S. Congress but also within Alaska. Statehood was approved by the U.S. Congress on July 7, 1958; Alaska was officially proclaimed a state on January 3, 1959. Good Friday earthquake On March 27, 1964, the massive Good Friday earthquake killed 133 people and destroyed several villages and portions of large coastal communities, mainly by the resultant tsunamis and landslides. It was the second-most-powerful earthquake in recorded history, with a moment magnitude of 9.2 (more than a thousand times as powerful as the 1989 San Francisco earthquake). The time of day (5:36 pm), time of year (spring) and location of the epicenter were all cited as factors in potentially sparing thousands of lives, particularly in Anchorage. Alaska oil boom The 1968 discovery of oil at Prudhoe Bay and the 1977 completion of the Trans-Alaska Pipeline System led to an oil boom. Royalty revenues from oil have funded large state budgets from 1980 onward. That same year, not coincidentally, Alaska repealed its state income tax. In 1989, the Exxon Valdez hit a reef in the Prince William Sound, spilling more than of crude oil over of coastline.

Alaska as an incorporated U.S. territory Starting in the 1890s and stretching in some places to the early 1910s, gold rushes in Alaska and the nearby Yukon Territory brought thousands of miners and settlers to Alaska. Alaska was officially incorporated as an organized territory in 1912. Alaska's capital, which had been in Sitka until 1906, was moved north to Juneau. Construction of the Alaska Governor's Mansion began that same year. European immigrants from Norway and Sweden also settled in southeast Alaska, where they entered the fishing and logging industries. During World War II, the Aleutian Islands Campaign focused on Attu, Agattu and Kiska, all which were occupied by the Empire of Japan. During the Japanese occupation, a white American civilian and two United States Navy personnel were killed at Attu and Kiska respectively, and nearly a total of 50 Aleut civilians and eight sailors were interned in Japan. About half of the Aleuts died during the period of internment. Unalaska/Dutch Harbor and Adak became significant bases for the United States Army, United States Army Air Forces and United States Navy. The United States Lend-Lease program involved flying American warplanes through Canada to Fairbanks and then Nome; Soviet pilots took possession of these aircraft, ferrying them to fight the German invasion of the Soviet Union. The construction of military bases contributed to the population growth of some Alaskan cities. Statehood Statehood for Alaska was an important cause of James Wickersham early in his tenure as a congressional delegate. Decades later, the statehood movement gained its first real momentum following a territorial referendum in 1946. The Alaska Statehood Committee and Alaska's Constitutional Convention would soon follow. Statehood supporters also found themselves fighting major battles against political foes, mostly in the U.S. Congress but also within Alaska. Statehood was approved by the U.S. Congress on July 7, 1958; Alaska was officially proclaimed a state on January 3, 1959. Good Friday earthquake On March 27, 1964, the massive Good Friday earthquake killed 133 people and destroyed several villages and portions of large coastal communities, mainly by the resultant tsunamis and landslides. It was the second-most-powerful earthquake in recorded history, with a moment magnitude of 9.2 (more than a thousand times as powerful as the 1989 San Francisco earthquake). The time of day (5:36 pm), time of year (spring) and location of the epicenter were all cited as factors in potentially sparing thousands of lives, particularly in Anchorage. Alaska oil boom The 1968 discovery of oil at Prudhoe Bay and the 1977 completion of the Trans-Alaska Pipeline System led to an oil boom. Royalty revenues from oil have funded large state budgets from 1980 onward. That same year, not coincidentally, Alaska repealed its state income tax. In 1989, the Exxon Valdez hit a reef in the Prince William Sound, spilling more than of crude oil over of coastline.

Today, the battle between philosophies of development and conservation is seen in the contentious debate over oil drilling in the Arctic National Wildlife Refuge and the proposed Pebble Mine. Geography Located at the northwest corner of North America, Alaska is the northernmost and westernmost state in the United States, but also has the most easterly longitude in the United States because the Aleutian Islands extend into the Eastern Hemisphere. Alaska is the only non-contiguous U.S. state on continental North America; about of British Columbia (Canada) separates Alaska from Washington. It is technically part of the continental U.S., but is sometimes not included in colloquial use; Alaska is not part of the contiguous U.S., often called "the Lower 48". The capital city, Juneau, is situated on the mainland of the North American continent but is not connected by road to the rest of the North American highway system. The state is bordered by Canada's Yukon and British Columbia to the east (making it the only state to border a Canadian territory); the Gulf of Alaska and the Pacific Ocean to the south and southwest; the Bering Sea, Bering Strait, and Chukchi Sea to the west; and the Arctic Ocean to the north. Alaska's territorial waters touch Russia's territorial waters in the Bering Strait, as the Russian Big Diomede Island and Alaskan Little Diomede Island are only apart. Alaska has a longer coastline than all the other U.S. states combined. At in area, Alaska is by far the largest state in the United States, and is more than twice the size of the second-largest U.S. state, Texas. Alaska is the seventh largest subnational division in the world, and if it was an independent nation would be the 16th largest country in the world, as it is larger than Iran. With its myriad islands, Alaska has nearly of tidal shoreline. The Aleutian Islands chain extends west from the southern tip of the Alaska Peninsula. Many active volcanoes are found in the Aleutians and in coastal regions. Unimak Island, for example, is home to Mount Shishaldin, which is an occasionally smoldering volcano that rises to above the North Pacific. The chain of volcanoes extends to Mount Spurr, west of Anchorage on the mainland. Geologists have identified Alaska as part of Wrangellia, a large region consisting of multiple states and Canadian provinces in the Pacific Northwest, which is actively undergoing continent building. One of the world's largest tides occurs in Turnagain Arm, just south of Anchorage, where tidal differences can be more than . Alaska has more than three million lakes. Marshlands and wetland permafrost cover (mostly in northern, western and southwest flatlands). Glacier ice covers about of Alaska. The Bering Glacier is the largest glacier in North America, covering alone. Regions There are no officially defined borders demarcating the various regions of Alaska, but there are six widely accepted regions: South Central The most populous region of Alaska, containing Anchorage, the Matanuska-Susitna Valley and the Kenai Peninsula.

Today, the battle between philosophies of development and conservation is seen in the contentious debate over oil drilling in the Arctic National Wildlife Refuge and the proposed Pebble Mine. Geography Located at the northwest corner of North America, Alaska is the northernmost and westernmost state in the United States, but also has the most easterly longitude in the United States because the Aleutian Islands extend into the Eastern Hemisphere. Alaska is the only non-contiguous U.S. state on continental North America; about of British Columbia (Canada) separates Alaska from Washington. It is technically part of the continental U.S., but is sometimes not included in colloquial use; Alaska is not part of the contiguous U.S., often called "the Lower 48". The capital city, Juneau, is situated on the mainland of the North American continent but is not connected by road to the rest of the North American highway system. The state is bordered by Canada's Yukon and British Columbia to the east (making it the only state to border a Canadian territory); the Gulf of Alaska and the Pacific Ocean to the south and southwest; the Bering Sea, Bering Strait, and Chukchi Sea to the west; and the Arctic Ocean to the north. Alaska's territorial waters touch Russia's territorial waters in the Bering Strait, as the Russian Big Diomede Island and Alaskan Little Diomede Island are only apart. Alaska has a longer coastline than all the other U.S. states combined. At in area, Alaska is by far the largest state in the United States, and is more than twice the size of the second-largest U.S. state, Texas. Alaska is the seventh largest subnational division in the world, and if it was an independent nation would be the 16th largest country in the world, as it is larger than Iran. With its myriad islands, Alaska has nearly of tidal shoreline. The Aleutian Islands chain extends west from the southern tip of the Alaska Peninsula. Many active volcanoes are found in the Aleutians and in coastal regions. Unimak Island, for example, is home to Mount Shishaldin, which is an occasionally smoldering volcano that rises to above the North Pacific. The chain of volcanoes extends to Mount Spurr, west of Anchorage on the mainland. Geologists have identified Alaska as part of Wrangellia, a large region consisting of multiple states and Canadian provinces in the Pacific Northwest, which is actively undergoing continent building. One of the world's largest tides occurs in Turnagain Arm, just south of Anchorage, where tidal differences can be more than . Alaska has more than three million lakes. Marshlands and wetland permafrost cover (mostly in northern, western and southwest flatlands). Glacier ice covers about of Alaska. The Bering Glacier is the largest glacier in North America, covering alone. Regions There are no officially defined borders demarcating the various regions of Alaska, but there are six widely accepted regions: South Central The most populous region of Alaska, containing Anchorage, the Matanuska-Susitna Valley and the Kenai Peninsula.

Today, the battle between philosophies of development and conservation is seen in the contentious debate over oil drilling in the Arctic National Wildlife Refuge and the proposed Pebble Mine. Geography Located at the northwest corner of North America, Alaska is the northernmost and westernmost state in the United States, but also has the most easterly longitude in the United States because the Aleutian Islands extend into the Eastern Hemisphere. Alaska is the only non-contiguous U.S. state on continental North America; about of British Columbia (Canada) separates Alaska from Washington. It is technically part of the continental U.S., but is sometimes not included in colloquial use; Alaska is not part of the contiguous U.S., often called "the Lower 48". The capital city, Juneau, is situated on the mainland of the North American continent but is not connected by road to the rest of the North American highway system. The state is bordered by Canada's Yukon and British Columbia to the east (making it the only state to border a Canadian territory); the Gulf of Alaska and the Pacific Ocean to the south and southwest; the Bering Sea, Bering Strait, and Chukchi Sea to the west; and the Arctic Ocean to the north. Alaska's territorial waters touch Russia's territorial waters in the Bering Strait, as the Russian Big Diomede Island and Alaskan Little Diomede Island are only apart. Alaska has a longer coastline than all the other U.S. states combined. At in area, Alaska is by far the largest state in the United States, and is more than twice the size of the second-largest U.S. state, Texas. Alaska is the seventh largest subnational division in the world, and if it was an independent nation would be the 16th largest country in the world, as it is larger than Iran. With its myriad islands, Alaska has nearly of tidal shoreline. The Aleutian Islands chain extends west from the southern tip of the Alaska Peninsula. Many active volcanoes are found in the Aleutians and in coastal regions. Unimak Island, for example, is home to Mount Shishaldin, which is an occasionally smoldering volcano that rises to above the North Pacific. The chain of volcanoes extends to Mount Spurr, west of Anchorage on the mainland. Geologists have identified Alaska as part of Wrangellia, a large region consisting of multiple states and Canadian provinces in the Pacific Northwest, which is actively undergoing continent building. One of the world's largest tides occurs in Turnagain Arm, just south of Anchorage, where tidal differences can be more than . Alaska has more than three million lakes. Marshlands and wetland permafrost cover (mostly in northern, western and southwest flatlands). Glacier ice covers about of Alaska. The Bering Glacier is the largest glacier in North America, covering alone. Regions There are no officially defined borders demarcating the various regions of Alaska, but there are six widely accepted regions: South Central The most populous region of Alaska, containing Anchorage, the Matanuska-Susitna Valley and the Kenai Peninsula.

Rural, mostly unpopulated areas south of the Alaska Range and west of the Wrangell Mountains also fall within the definition of South Central, as do the Prince William Sound area and the communities of Cordova and Valdez. Southeast Also referred to as the Panhandle or Inside Passage, this is the region of Alaska closest to the contiguous states. As such, this was where most of the initial non-indigenous settlement occurred in the years following the Alaska Purchase. The region is dominated by the Alexander Archipelago as well as the Tongass National Forest, the largest national forest in the United States. It contains the state capital Juneau, the former capital Sitka, and Ketchikan, at one time Alaska's largest city. The Alaska Marine Highway provides a vital surface transportation link throughout the area and country, as only three communities (Haines, Hyder and Skagway) enjoy direct connections to the contiguous North American road system. Interior The Interior is the largest region of Alaska; much of it is uninhabited wilderness. Fairbanks is the only large city in the region. Denali National Park and Preserve is located here. Denali, formerly Mount McKinley, is the highest mountain in North America, and is also located here. Southwest Southwest Alaska is a sparsely inhabited region stretching some inland from the Bering Sea. Most of the population lives along the coast. Kodiak Island is also located in Southwest. The massive Yukon–Kuskokwim Delta, one of the largest river deltas in the world, is here. Portions of the Alaska Peninsula are considered part of Southwest, with the remaining portions included with the Aleutian Islands (see below). North Slope The North Slope is mostly tundra peppered with small villages. The area is known for its massive reserves of crude oil and contains both the National Petroleum Reserve–Alaska and the Prudhoe Bay Oil Field. The city of Utqiaġvik, formerly known as Barrow, is the northernmost city in the United States and is located here. The Northwest Arctic area, anchored by Kotzebue and also containing the Kobuk River valley, is often regarded as being part of this region. However, the respective Inupiat of the North Slope and of the Northwest Arctic seldom consider themselves to be one people. Aleutian Islands More than 300 small volcanic islands make up this chain, which stretches more than into the Pacific Ocean. Some of these islands fall in the Eastern Hemisphere, but the International Date Line was drawn west of 180° to keep the whole state, and thus the entire North American continent, within the same legal day. Two of the islands, Attu and Kiska, were occupied by Japanese forces during World War II. Land ownership According to an October 1998 report by the United States Bureau of Land Management, approximately 65% of Alaska is owned and managed by the U.S. federal government as public lands, including a multitude of national forests, national parks, and national wildlife refuges. Of these, the Bureau of Land Management manages , or 23.8% of the state.

Rural, mostly unpopulated areas south of the Alaska Range and west of the Wrangell Mountains also fall within the definition of South Central, as do the Prince William Sound area and the communities of Cordova and Valdez. Southeast Also referred to as the Panhandle or Inside Passage, this is the region of Alaska closest to the contiguous states. As such, this was where most of the initial non-indigenous settlement occurred in the years following the Alaska Purchase. The region is dominated by the Alexander Archipelago as well as the Tongass National Forest, the largest national forest in the United States. It contains the state capital Juneau, the former capital Sitka, and Ketchikan, at one time Alaska's largest city. The Alaska Marine Highway provides a vital surface transportation link throughout the area and country, as only three communities (Haines, Hyder and Skagway) enjoy direct connections to the contiguous North American road system. Interior The Interior is the largest region of Alaska; much of it is uninhabited wilderness. Fairbanks is the only large city in the region. Denali National Park and Preserve is located here. Denali, formerly Mount McKinley, is the highest mountain in North America, and is also located here. Southwest Southwest Alaska is a sparsely inhabited region stretching some inland from the Bering Sea. Most of the population lives along the coast. Kodiak Island is also located in Southwest. The massive Yukon–Kuskokwim Delta, one of the largest river deltas in the world, is here. Portions of the Alaska Peninsula are considered part of Southwest, with the remaining portions included with the Aleutian Islands (see below). North Slope The North Slope is mostly tundra peppered with small villages. The area is known for its massive reserves of crude oil and contains both the National Petroleum Reserve–Alaska and the Prudhoe Bay Oil Field. The city of Utqiaġvik, formerly known as Barrow, is the northernmost city in the United States and is located here. The Northwest Arctic area, anchored by Kotzebue and also containing the Kobuk River valley, is often regarded as being part of this region. However, the respective Inupiat of the North Slope and of the Northwest Arctic seldom consider themselves to be one people. Aleutian Islands More than 300 small volcanic islands make up this chain, which stretches more than into the Pacific Ocean. Some of these islands fall in the Eastern Hemisphere, but the International Date Line was drawn west of 180° to keep the whole state, and thus the entire North American continent, within the same legal day. Two of the islands, Attu and Kiska, were occupied by Japanese forces during World War II. Land ownership According to an October 1998 report by the United States Bureau of Land Management, approximately 65% of Alaska is owned and managed by the U.S. federal government as public lands, including a multitude of national forests, national parks, and national wildlife refuges. Of these, the Bureau of Land Management manages , or 23.8% of the state.

Rural, mostly unpopulated areas south of the Alaska Range and west of the Wrangell Mountains also fall within the definition of South Central, as do the Prince William Sound area and the communities of Cordova and Valdez. Southeast Also referred to as the Panhandle or Inside Passage, this is the region of Alaska closest to the contiguous states. As such, this was where most of the initial non-indigenous settlement occurred in the years following the Alaska Purchase. The region is dominated by the Alexander Archipelago as well as the Tongass National Forest, the largest national forest in the United States. It contains the state capital Juneau, the former capital Sitka, and Ketchikan, at one time Alaska's largest city. The Alaska Marine Highway provides a vital surface transportation link throughout the area and country, as only three communities (Haines, Hyder and Skagway) enjoy direct connections to the contiguous North American road system. Interior The Interior is the largest region of Alaska; much of it is uninhabited wilderness. Fairbanks is the only large city in the region. Denali National Park and Preserve is located here. Denali, formerly Mount McKinley, is the highest mountain in North America, and is also located here. Southwest Southwest Alaska is a sparsely inhabited region stretching some inland from the Bering Sea. Most of the population lives along the coast. Kodiak Island is also located in Southwest. The massive Yukon–Kuskokwim Delta, one of the largest river deltas in the world, is here. Portions of the Alaska Peninsula are considered part of Southwest, with the remaining portions included with the Aleutian Islands (see below). North Slope The North Slope is mostly tundra peppered with small villages. The area is known for its massive reserves of crude oil and contains both the National Petroleum Reserve–Alaska and the Prudhoe Bay Oil Field. The city of Utqiaġvik, formerly known as Barrow, is the northernmost city in the United States and is located here. The Northwest Arctic area, anchored by Kotzebue and also containing the Kobuk River valley, is often regarded as being part of this region. However, the respective Inupiat of the North Slope and of the Northwest Arctic seldom consider themselves to be one people. Aleutian Islands More than 300 small volcanic islands make up this chain, which stretches more than into the Pacific Ocean. Some of these islands fall in the Eastern Hemisphere, but the International Date Line was drawn west of 180° to keep the whole state, and thus the entire North American continent, within the same legal day. Two of the islands, Attu and Kiska, were occupied by Japanese forces during World War II. Land ownership According to an October 1998 report by the United States Bureau of Land Management, approximately 65% of Alaska is owned and managed by the U.S. federal government as public lands, including a multitude of national forests, national parks, and national wildlife refuges. Of these, the Bureau of Land Management manages , or 23.8% of the state.

The Arctic National Wildlife Refuge is managed by the United States Fish and Wildlife Service. It is the world's largest wildlife refuge, comprising . Of the remaining land area, the state of Alaska owns , its entitlement under the Alaska Statehood Act. A portion of that acreage is occasionally ceded to the organized boroughs presented above, under the statutory provisions pertaining to newly formed boroughs. Smaller portions are set aside for rural subdivisions and other homesteading-related opportunities. These are not very popular due to the often remote and roadless locations. The University of Alaska, as a land grant university, also owns substantial acreage which it manages independently. Another are owned by 12 regional, and scores of local, Native corporations created under the Alaska Native Claims Settlement Act (ANCSA) of 1971. Regional Native corporation Doyon, Limited often promotes itself as the largest private landowner in Alaska in advertisements and other communications. Provisions of ANCSA allowing the corporations' land holdings to be sold on the open market starting in 1991 were repealed before they could take effect. Effectively, the corporations hold title (including subsurface title in many cases, a privilege denied to individual Alaskans) but cannot sell the land. Individual Native allotments can be and are sold on the open market, however. Various private interests own the remaining land, totaling about one percent of the state. Alaska is, by a large margin, the state with the smallest percentage of private land ownership when Native corporation holdings are excluded. Alaska Heritage Resources Survey The Alaska Heritage Resources Survey (AHRS) is a restricted inventory of all reported historic and prehistoric sites within the U.S. state of Alaska; it is maintained by the Office of History and Archaeology. The survey's inventory of cultural resources includes objects, structures, buildings, sites, districts, and travel ways, with a general provision that they are more than fifty years old. , more than 35,000 sites have been reported. Cities, towns and boroughs Alaska is not divided into counties, as most of the other U.S. states, but it is divided into boroughs. Delegates to the Alaska Constitutional Convention wanted to avoid the pitfalls of the traditional county system and adopted their own unique model. Many of the more densely populated parts of the state are part of Alaska's 16 boroughs, which function somewhat similarly to counties in other states. However, unlike county-equivalents in the other 49 states, the boroughs do not cover the entire land area of the state. The area not part of any borough is referred to as the Unorganized Borough. The Unorganized Borough has no government of its own, but the U.S. Census Bureau in cooperation with the state divided the Unorganized Borough into 11 census areas solely for the purposes of statistical analysis and presentation. A recording district is a mechanism for management of the public record in Alaska. The state is divided into 34 recording districts which are centrally administered under a state recorder.

The Arctic National Wildlife Refuge is managed by the United States Fish and Wildlife Service. It is the world's largest wildlife refuge, comprising . Of the remaining land area, the state of Alaska owns , its entitlement under the Alaska Statehood Act. A portion of that acreage is occasionally ceded to the organized boroughs presented above, under the statutory provisions pertaining to newly formed boroughs. Smaller portions are set aside for rural subdivisions and other homesteading-related opportunities. These are not very popular due to the often remote and roadless locations. The University of Alaska, as a land grant university, also owns substantial acreage which it manages independently. Another are owned by 12 regional, and scores of local, Native corporations created under the Alaska Native Claims Settlement Act (ANCSA) of 1971. Regional Native corporation Doyon, Limited often promotes itself as the largest private landowner in Alaska in advertisements and other communications. Provisions of ANCSA allowing the corporations' land holdings to be sold on the open market starting in 1991 were repealed before they could take effect. Effectively, the corporations hold title (including subsurface title in many cases, a privilege denied to individual Alaskans) but cannot sell the land. Individual Native allotments can be and are sold on the open market, however. Various private interests own the remaining land, totaling about one percent of the state. Alaska is, by a large margin, the state with the smallest percentage of private land ownership when Native corporation holdings are excluded. Alaska Heritage Resources Survey The Alaska Heritage Resources Survey (AHRS) is a restricted inventory of all reported historic and prehistoric sites within the U.S. state of Alaska; it is maintained by the Office of History and Archaeology. The survey's inventory of cultural resources includes objects, structures, buildings, sites, districts, and travel ways, with a general provision that they are more than fifty years old. , more than 35,000 sites have been reported. Cities, towns and boroughs Alaska is not divided into counties, as most of the other U.S. states, but it is divided into boroughs. Delegates to the Alaska Constitutional Convention wanted to avoid the pitfalls of the traditional county system and adopted their own unique model. Many of the more densely populated parts of the state are part of Alaska's 16 boroughs, which function somewhat similarly to counties in other states. However, unlike county-equivalents in the other 49 states, the boroughs do not cover the entire land area of the state. The area not part of any borough is referred to as the Unorganized Borough. The Unorganized Borough has no government of its own, but the U.S. Census Bureau in cooperation with the state divided the Unorganized Borough into 11 census areas solely for the purposes of statistical analysis and presentation. A recording district is a mechanism for management of the public record in Alaska. The state is divided into 34 recording districts which are centrally administered under a state recorder.

The Arctic National Wildlife Refuge is managed by the United States Fish and Wildlife Service. It is the world's largest wildlife refuge, comprising . Of the remaining land area, the state of Alaska owns , its entitlement under the Alaska Statehood Act. A portion of that acreage is occasionally ceded to the organized boroughs presented above, under the statutory provisions pertaining to newly formed boroughs. Smaller portions are set aside for rural subdivisions and other homesteading-related opportunities. These are not very popular due to the often remote and roadless locations. The University of Alaska, as a land grant university, also owns substantial acreage which it manages independently. Another are owned by 12 regional, and scores of local, Native corporations created under the Alaska Native Claims Settlement Act (ANCSA) of 1971. Regional Native corporation Doyon, Limited often promotes itself as the largest private landowner in Alaska in advertisements and other communications. Provisions of ANCSA allowing the corporations' land holdings to be sold on the open market starting in 1991 were repealed before they could take effect. Effectively, the corporations hold title (including subsurface title in many cases, a privilege denied to individual Alaskans) but cannot sell the land. Individual Native allotments can be and are sold on the open market, however. Various private interests own the remaining land, totaling about one percent of the state. Alaska is, by a large margin, the state with the smallest percentage of private land ownership when Native corporation holdings are excluded. Alaska Heritage Resources Survey The Alaska Heritage Resources Survey (AHRS) is a restricted inventory of all reported historic and prehistoric sites within the U.S. state of Alaska; it is maintained by the Office of History and Archaeology. The survey's inventory of cultural resources includes objects, structures, buildings, sites, districts, and travel ways, with a general provision that they are more than fifty years old. , more than 35,000 sites have been reported. Cities, towns and boroughs Alaska is not divided into counties, as most of the other U.S. states, but it is divided into boroughs. Delegates to the Alaska Constitutional Convention wanted to avoid the pitfalls of the traditional county system and adopted their own unique model. Many of the more densely populated parts of the state are part of Alaska's 16 boroughs, which function somewhat similarly to counties in other states. However, unlike county-equivalents in the other 49 states, the boroughs do not cover the entire land area of the state. The area not part of any borough is referred to as the Unorganized Borough. The Unorganized Borough has no government of its own, but the U.S. Census Bureau in cooperation with the state divided the Unorganized Borough into 11 census areas solely for the purposes of statistical analysis and presentation. A recording district is a mechanism for management of the public record in Alaska. The state is divided into 34 recording districts which are centrally administered under a state recorder.

All recording districts use the same acceptance criteria, fee schedule, etc., for accepting documents into the public record. Whereas many U.S. states use a three-tiered system of decentralization—state/county/township—most of Alaska uses only two tiers—state/borough. Owing to the low population density, most of the land is located in the Unorganized Borough. As the name implies, it has no intermediate borough government but is administered directly by the state government. In 2000, 57.71% of Alaska's area has this status, with 13.05% of the population. Anchorage merged the city government with the Greater Anchorage Area Borough in 1975 to form the Municipality of Anchorage, containing the city proper and the communities of Eagle River, Chugiak, Peters Creek, Girdwood, Bird, and Indian. Fairbanks has a separate borough (the Fairbanks North Star Borough) and municipality (the City of Fairbanks). The state's most populous city is Anchorage, home to 291,247 people in 2020. The richest location in Alaska by per capita income is Denali ($42,245). Yakutat City, Sitka, Juneau, and Anchorage are the four largest cities in the U.S. by area. Cities and census-designated places (by population) As reflected in the 2020 United States census, Alaska has a total of 355 incorporated cities and census-designated places (CDPs). The tally of cities includes four unified municipalities, essentially the equivalent of a consolidated city–county. The majority of these communities are located in the rural expanse of Alaska known as "The Bush" and are unconnected to the contiguous North American road network. The table at the bottom of this section lists the 100 largest cities and census-designated places in Alaska, in population order. Of Alaska's 2020 U.S. census population figure of 733,391, 16,655 people, or 2.27% of the population, did not live in an incorporated city or census-designated place. Approximately three-quarters of that figure were people who live in urban and suburban neighborhoods on the outskirts of the city limits of Ketchikan, Kodiak, Palmer and Wasilla. CDPs have not been established for these areas by the United States Census Bureau, except that seven CDPs were established for the Ketchikan-area neighborhoods in the 1980 Census (Clover Pass, Herring Cove, Ketchikan East, Mountain Point, North Tongass Highway, Pennock Island and Saxman East), but have not been used since. The remaining population was scattered throughout Alaska, both within organized boroughs and in the Unorganized Borough, in largely remote areas. Climate The climate in south and southeastern Alaska is a mid-latitude oceanic climate (Köppen climate classification: Cfb), and a subarctic oceanic climate (Köppen Cfc) in the northern parts. On an annual basis, the southeast is both the wettest and warmest part of Alaska with milder temperatures in the winter and high precipitation throughout the year. Juneau averages over of precipitation a year, and Ketchikan averages over . This is also the only region in Alaska in which the average daytime high temperature is above freezing during the winter months.The climate of Anchorage and south central Alaska is mild by Alaskan standards due to the region's proximity to the seacoast.

All recording districts use the same acceptance criteria, fee schedule, etc., for accepting documents into the public record. Whereas many U.S. states use a three-tiered system of decentralization—state/county/township—most of Alaska uses only two tiers—state/borough. Owing to the low population density, most of the land is located in the Unorganized Borough. As the name implies, it has no intermediate borough government but is administered directly by the state government. In 2000, 57.71% of Alaska's area has this status, with 13.05% of the population. Anchorage merged the city government with the Greater Anchorage Area Borough in 1975 to form the Municipality of Anchorage, containing the city proper and the communities of Eagle River, Chugiak, Peters Creek, Girdwood, Bird, and Indian. Fairbanks has a separate borough (the Fairbanks North Star Borough) and municipality (the City of Fairbanks). The state's most populous city is Anchorage, home to 291,247 people in 2020. The richest location in Alaska by per capita income is Denali ($42,245). Yakutat City, Sitka, Juneau, and Anchorage are the four largest cities in the U.S. by area. Cities and census-designated places (by population) As reflected in the 2020 United States census, Alaska has a total of 355 incorporated cities and census-designated places (CDPs). The tally of cities includes four unified municipalities, essentially the equivalent of a consolidated city–county. The majority of these communities are located in the rural expanse of Alaska known as "The Bush" and are unconnected to the contiguous North American road network. The table at the bottom of this section lists the 100 largest cities and census-designated places in Alaska, in population order. Of Alaska's 2020 U.S. census population figure of 733,391, 16,655 people, or 2.27% of the population, did not live in an incorporated city or census-designated place. Approximately three-quarters of that figure were people who live in urban and suburban neighborhoods on the outskirts of the city limits of Ketchikan, Kodiak, Palmer and Wasilla. CDPs have not been established for these areas by the United States Census Bureau, except that seven CDPs were established for the Ketchikan-area neighborhoods in the 1980 Census (Clover Pass, Herring Cove, Ketchikan East, Mountain Point, North Tongass Highway, Pennock Island and Saxman East), but have not been used since. The remaining population was scattered throughout Alaska, both within organized boroughs and in the Unorganized Borough, in largely remote areas. Climate The climate in south and southeastern Alaska is a mid-latitude oceanic climate (Köppen climate classification: Cfb), and a subarctic oceanic climate (Köppen Cfc) in the northern parts. On an annual basis, the southeast is both the wettest and warmest part of Alaska with milder temperatures in the winter and high precipitation throughout the year. Juneau averages over of precipitation a year, and Ketchikan averages over . This is also the only region in Alaska in which the average daytime high temperature is above freezing during the winter months.The climate of Anchorage and south central Alaska is mild by Alaskan standards due to the region's proximity to the seacoast.

All recording districts use the same acceptance criteria, fee schedule, etc., for accepting documents into the public record. Whereas many U.S. states use a three-tiered system of decentralization—state/county/township—most of Alaska uses only two tiers—state/borough. Owing to the low population density, most of the land is located in the Unorganized Borough. As the name implies, it has no intermediate borough government but is administered directly by the state government. In 2000, 57.71% of Alaska's area has this status, with 13.05% of the population. Anchorage merged the city government with the Greater Anchorage Area Borough in 1975 to form the Municipality of Anchorage, containing the city proper and the communities of Eagle River, Chugiak, Peters Creek, Girdwood, Bird, and Indian. Fairbanks has a separate borough (the Fairbanks North Star Borough) and municipality (the City of Fairbanks). The state's most populous city is Anchorage, home to 291,247 people in 2020. The richest location in Alaska by per capita income is Denali ($42,245). Yakutat City, Sitka, Juneau, and Anchorage are the four largest cities in the U.S. by area. Cities and census-designated places (by population) As reflected in the 2020 United States census, Alaska has a total of 355 incorporated cities and census-designated places (CDPs). The tally of cities includes four unified municipalities, essentially the equivalent of a consolidated city–county. The majority of these communities are located in the rural expanse of Alaska known as "The Bush" and are unconnected to the contiguous North American road network. The table at the bottom of this section lists the 100 largest cities and census-designated places in Alaska, in population order. Of Alaska's 2020 U.S. census population figure of 733,391, 16,655 people, or 2.27% of the population, did not live in an incorporated city or census-designated place. Approximately three-quarters of that figure were people who live in urban and suburban neighborhoods on the outskirts of the city limits of Ketchikan, Kodiak, Palmer and Wasilla. CDPs have not been established for these areas by the United States Census Bureau, except that seven CDPs were established for the Ketchikan-area neighborhoods in the 1980 Census (Clover Pass, Herring Cove, Ketchikan East, Mountain Point, North Tongass Highway, Pennock Island and Saxman East), but have not been used since. The remaining population was scattered throughout Alaska, both within organized boroughs and in the Unorganized Borough, in largely remote areas. Climate The climate in south and southeastern Alaska is a mid-latitude oceanic climate (Köppen climate classification: Cfb), and a subarctic oceanic climate (Köppen Cfc) in the northern parts. On an annual basis, the southeast is both the wettest and warmest part of Alaska with milder temperatures in the winter and high precipitation throughout the year. Juneau averages over of precipitation a year, and Ketchikan averages over . This is also the only region in Alaska in which the average daytime high temperature is above freezing during the winter months.The climate of Anchorage and south central Alaska is mild by Alaskan standards due to the region's proximity to the seacoast.

While the area gets less rain than southeast Alaska, it gets more snow, and days tend to be clearer. On average, Anchorage receives of precipitation a year, with around of snow, although there are areas in the south central which receive far more snow. It is a subarctic climate (Köppen: Dfc) due to its brief, cool summers. The climate of western Alaska is determined in large part by the Bering Sea and the Gulf of Alaska. It is a subarctic oceanic climate in the southwest and a continental subarctic climate farther north. The temperature is somewhat moderate considering how far north the area is. This region has a tremendous amount of variety in precipitation. An area stretching from the northern side of the Seward Peninsula to the Kobuk River valley (i.e., the region around Kotzebue Sound) is technically a desert, with portions receiving less than of precipitation annually. On the other extreme, some locations between Dillingham and Bethel average around of precipitation. The climate of the interior of Alaska is subarctic. Some of the highest and lowest temperatures in Alaska occur around the area near Fairbanks. The summers may have temperatures reaching into the 90s °F (the low-to-mid 30s °C), while in the winter, the temperature can fall below . Precipitation is sparse in the Interior, often less than a year, but what precipitation falls in the winter tends to stay the entire winter. The highest and lowest recorded temperatures in Alaska are both in the Interior. The highest is in Fort Yukon (which is just inside the arctic circle) on June 27, 1915, making Alaska tied with Hawaii as the state with the lowest high temperature in the United States. The lowest official Alaska temperature is in Prospect Creek on January 23, 1971, one degree above the lowest temperature recorded in continental North America (in Snag, Yukon, Canada). The climate in the extreme north of Alaska is Arctic (Köppen: ET) with long, very cold winters and short, cool summers. Even in July, the average low temperature in Utqiaġvik is . Precipitation is light in this part of Alaska, with many places averaging less than per year, mostly as snow which stays on the ground almost the entire year. Demographics The United States Census Bureau found in the 2020 United States census that the population of Alaska was 736,081 on April 1, 2020, a 3.6% increase since the 2010 United States census. According to the 2010 United States census, the U.S. state of Alaska had a population of 710,231, increasing from 626,932 at the 2000 U.S. census. In 2010, Alaska ranked as the 47th state by population, ahead of North Dakota, Vermont, and Wyoming (and Washington, D.C.). Estimates show North Dakota ahead . Alaska is the least densely populated state, and one of the most sparsely populated areas in the world, at , with the next state, Wyoming, at . Alaska is by far the largest U.S. state by area, and the tenth wealthiest (per capita income).

While the area gets less rain than southeast Alaska, it gets more snow, and days tend to be clearer. On average, Anchorage receives of precipitation a year, with around of snow, although there are areas in the south central which receive far more snow. It is a subarctic climate (Köppen: Dfc) due to its brief, cool summers. The climate of western Alaska is determined in large part by the Bering Sea and the Gulf of Alaska. It is a subarctic oceanic climate in the southwest and a continental subarctic climate farther north. The temperature is somewhat moderate considering how far north the area is. This region has a tremendous amount of variety in precipitation. An area stretching from the northern side of the Seward Peninsula to the Kobuk River valley (i.e., the region around Kotzebue Sound) is technically a desert, with portions receiving less than of precipitation annually. On the other extreme, some locations between Dillingham and Bethel average around of precipitation. The climate of the interior of Alaska is subarctic. Some of the highest and lowest temperatures in Alaska occur around the area near Fairbanks. The summers may have temperatures reaching into the 90s °F (the low-to-mid 30s °C), while in the winter, the temperature can fall below . Precipitation is sparse in the Interior, often less than a year, but what precipitation falls in the winter tends to stay the entire winter. The highest and lowest recorded temperatures in Alaska are both in the Interior. The highest is in Fort Yukon (which is just inside the arctic circle) on June 27, 1915, making Alaska tied with Hawaii as the state with the lowest high temperature in the United States. The lowest official Alaska temperature is in Prospect Creek on January 23, 1971, one degree above the lowest temperature recorded in continental North America (in Snag, Yukon, Canada). The climate in the extreme north of Alaska is Arctic (Köppen: ET) with long, very cold winters and short, cool summers. Even in July, the average low temperature in Utqiaġvik is . Precipitation is light in this part of Alaska, with many places averaging less than per year, mostly as snow which stays on the ground almost the entire year. Demographics The United States Census Bureau found in the 2020 United States census that the population of Alaska was 736,081 on April 1, 2020, a 3.6% increase since the 2010 United States census. According to the 2010 United States census, the U.S. state of Alaska had a population of 710,231, increasing from 626,932 at the 2000 U.S. census. In 2010, Alaska ranked as the 47th state by population, ahead of North Dakota, Vermont, and Wyoming (and Washington, D.C.). Estimates show North Dakota ahead . Alaska is the least densely populated state, and one of the most sparsely populated areas in the world, at , with the next state, Wyoming, at . Alaska is by far the largest U.S. state by area, and the tenth wealthiest (per capita income).

While the area gets less rain than southeast Alaska, it gets more snow, and days tend to be clearer. On average, Anchorage receives of precipitation a year, with around of snow, although there are areas in the south central which receive far more snow. It is a subarctic climate (Köppen: Dfc) due to its brief, cool summers. The climate of western Alaska is determined in large part by the Bering Sea and the Gulf of Alaska. It is a subarctic oceanic climate in the southwest and a continental subarctic climate farther north. The temperature is somewhat moderate considering how far north the area is. This region has a tremendous amount of variety in precipitation. An area stretching from the northern side of the Seward Peninsula to the Kobuk River valley (i.e., the region around Kotzebue Sound) is technically a desert, with portions receiving less than of precipitation annually. On the other extreme, some locations between Dillingham and Bethel average around of precipitation. The climate of the interior of Alaska is subarctic. Some of the highest and lowest temperatures in Alaska occur around the area near Fairbanks. The summers may have temperatures reaching into the 90s °F (the low-to-mid 30s °C), while in the winter, the temperature can fall below . Precipitation is sparse in the Interior, often less than a year, but what precipitation falls in the winter tends to stay the entire winter. The highest and lowest recorded temperatures in Alaska are both in the Interior. The highest is in Fort Yukon (which is just inside the arctic circle) on June 27, 1915, making Alaska tied with Hawaii as the state with the lowest high temperature in the United States. The lowest official Alaska temperature is in Prospect Creek on January 23, 1971, one degree above the lowest temperature recorded in continental North America (in Snag, Yukon, Canada). The climate in the extreme north of Alaska is Arctic (Köppen: ET) with long, very cold winters and short, cool summers. Even in July, the average low temperature in Utqiaġvik is . Precipitation is light in this part of Alaska, with many places averaging less than per year, mostly as snow which stays on the ground almost the entire year. Demographics The United States Census Bureau found in the 2020 United States census that the population of Alaska was 736,081 on April 1, 2020, a 3.6% increase since the 2010 United States census. According to the 2010 United States census, the U.S. state of Alaska had a population of 710,231, increasing from 626,932 at the 2000 U.S. census. In 2010, Alaska ranked as the 47th state by population, ahead of North Dakota, Vermont, and Wyoming (and Washington, D.C.). Estimates show North Dakota ahead . Alaska is the least densely populated state, and one of the most sparsely populated areas in the world, at , with the next state, Wyoming, at . Alaska is by far the largest U.S. state by area, and the tenth wealthiest (per capita income).

due to its population size, it is one of 14 U.S. states that still have only one telephone area code. Race and ethnicity The 2019 American Community Survey estimated 60.2% of the population was non-Hispanic white, 3.7% Black or African American, 15.6% American Indian or Alaska Native, 6.5% Asian, 1.4% Native Hawaiian and other Pacific Islander, 7.5% two or more races, and 7.3% Hispanic or Latin American of any race. At the survey estimates, 7.8% of the total population was foreign-born from 2015 to 2019. In 2015, 61.3% was non-Hispanic white, 3.4% Black or African American, 13.3% American Indian or Alaska Native, 6.2% Asian, 0.9% Native Hawaiian and other Pacific Islander, 0.3% some other race, and 7.7% multiracial. Hispanics and Latin Americans were 7% of the state population in 2015. From 2015 to 2019, the largest Hispanic and Latin American groups were Mexican Americans, Puerto Ricans, and Cuban Americans. The largest Asian groups living in the state were Filipinos, Korean Americans, and Japanese and Chinese Americans. The state was 66.7% White (64.1% non-Hispanic white), 14.8% American Indian and Alaska Native, 5.4% Asian, 3.3% Black or African American, 1.0% Native Hawaiian and other Pacific Islander, 1.6% from some other race, and 7.3% from two or more races in 2010. Hispanics or Latin Americans of any race made up 5.5% of the population in 2010. , 50.7% of Alaska's population younger than one year of age belonged to minority groups (i.e., did not have two parents of non-Hispanic white ancestry). In 1960, the United States Census Bureau reported Alaska's population as 77.2% White, 3% Black, and 18.8% American Indian and Alaska Native. Languages According to the 2011 American Community Survey, 83.4% of people over the age of five spoke only English at home. About 3.5% spoke Spanish at home, 2.2% spoke another Indo-European language, about 4.3% spoke an Asian language (including Tagalog), and about 5.3% spoke other languages at home. In 2019, the American Community Survey determined 83.7% spoke only English, and 16.3% spoke another language other than English. The most spoken European language after English was Spanish, spoken by approximately 4.0% of the state population. Collectively, Asian and Pacific Islander languages were spoken by 5.6% of Alaskans. Since 2010, a total of 5.2% of Alaskans speak one of the state's 20 indigenous languages, known locally as "native languages". The Alaska Native Language Center at the University of Alaska Fairbanks claims that at least 20 Alaskan native languages exist and there are also some languages with different dialects. Most of Alaska's native languages belong to either the Eskimo–Aleut or Na-Dene language families; however, some languages are thought to be isolates (e.g. Haida) or have not yet been classified (e.g. Tsimshianic). nearly all of Alaska's native languages were classified as either threatened, shifting, moribund, nearly extinct, or dormant languages. In October 2014, the governor of Alaska signed a bill declaring the state's 20 indigenous languages to have official status.

due to its population size, it is one of 14 U.S. states that still have only one telephone area code. Race and ethnicity The 2019 American Community Survey estimated 60.2% of the population was non-Hispanic white, 3.7% Black or African American, 15.6% American Indian or Alaska Native, 6.5% Asian, 1.4% Native Hawaiian and other Pacific Islander, 7.5% two or more races, and 7.3% Hispanic or Latin American of any race. At the survey estimates, 7.8% of the total population was foreign-born from 2015 to 2019. In 2015, 61.3% was non-Hispanic white, 3.4% Black or African American, 13.3% American Indian or Alaska Native, 6.2% Asian, 0.9% Native Hawaiian and other Pacific Islander, 0.3% some other race, and 7.7% multiracial. Hispanics and Latin Americans were 7% of the state population in 2015. From 2015 to 2019, the largest Hispanic and Latin American groups were Mexican Americans, Puerto Ricans, and Cuban Americans. The largest Asian groups living in the state were Filipinos, Korean Americans, and Japanese and Chinese Americans. The state was 66.7% White (64.1% non-Hispanic white), 14.8% American Indian and Alaska Native, 5.4% Asian, 3.3% Black or African American, 1.0% Native Hawaiian and other Pacific Islander, 1.6% from some other race, and 7.3% from two or more races in 2010. Hispanics or Latin Americans of any race made up 5.5% of the population in 2010. , 50.7% of Alaska's population younger than one year of age belonged to minority groups (i.e., did not have two parents of non-Hispanic white ancestry). In 1960, the United States Census Bureau reported Alaska's population as 77.2% White, 3% Black, and 18.8% American Indian and Alaska Native. Languages According to the 2011 American Community Survey, 83.4% of people over the age of five spoke only English at home. About 3.5% spoke Spanish at home, 2.2% spoke another Indo-European language, about 4.3% spoke an Asian language (including Tagalog), and about 5.3% spoke other languages at home. In 2019, the American Community Survey determined 83.7% spoke only English, and 16.3% spoke another language other than English. The most spoken European language after English was Spanish, spoken by approximately 4.0% of the state population. Collectively, Asian and Pacific Islander languages were spoken by 5.6% of Alaskans. Since 2010, a total of 5.2% of Alaskans speak one of the state's 20 indigenous languages, known locally as "native languages". The Alaska Native Language Center at the University of Alaska Fairbanks claims that at least 20 Alaskan native languages exist and there are also some languages with different dialects. Most of Alaska's native languages belong to either the Eskimo–Aleut or Na-Dene language families; however, some languages are thought to be isolates (e.g. Haida) or have not yet been classified (e.g. Tsimshianic). nearly all of Alaska's native languages were classified as either threatened, shifting, moribund, nearly extinct, or dormant languages. In October 2014, the governor of Alaska signed a bill declaring the state's 20 indigenous languages to have official status.

due to its population size, it is one of 14 U.S. states that still have only one telephone area code. Race and ethnicity The 2019 American Community Survey estimated 60.2% of the population was non-Hispanic white, 3.7% Black or African American, 15.6% American Indian or Alaska Native, 6.5% Asian, 1.4% Native Hawaiian and other Pacific Islander, 7.5% two or more races, and 7.3% Hispanic or Latin American of any race. At the survey estimates, 7.8% of the total population was foreign-born from 2015 to 2019. In 2015, 61.3% was non-Hispanic white, 3.4% Black or African American, 13.3% American Indian or Alaska Native, 6.2% Asian, 0.9% Native Hawaiian and other Pacific Islander, 0.3% some other race, and 7.7% multiracial. Hispanics and Latin Americans were 7% of the state population in 2015. From 2015 to 2019, the largest Hispanic and Latin American groups were Mexican Americans, Puerto Ricans, and Cuban Americans. The largest Asian groups living in the state were Filipinos, Korean Americans, and Japanese and Chinese Americans. The state was 66.7% White (64.1% non-Hispanic white), 14.8% American Indian and Alaska Native, 5.4% Asian, 3.3% Black or African American, 1.0% Native Hawaiian and other Pacific Islander, 1.6% from some other race, and 7.3% from two or more races in 2010. Hispanics or Latin Americans of any race made up 5.5% of the population in 2010. , 50.7% of Alaska's population younger than one year of age belonged to minority groups (i.e., did not have two parents of non-Hispanic white ancestry). In 1960, the United States Census Bureau reported Alaska's population as 77.2% White, 3% Black, and 18.8% American Indian and Alaska Native. Languages According to the 2011 American Community Survey, 83.4% of people over the age of five spoke only English at home. About 3.5% spoke Spanish at home, 2.2% spoke another Indo-European language, about 4.3% spoke an Asian language (including Tagalog), and about 5.3% spoke other languages at home. In 2019, the American Community Survey determined 83.7% spoke only English, and 16.3% spoke another language other than English. The most spoken European language after English was Spanish, spoken by approximately 4.0% of the state population. Collectively, Asian and Pacific Islander languages were spoken by 5.6% of Alaskans. Since 2010, a total of 5.2% of Alaskans speak one of the state's 20 indigenous languages, known locally as "native languages". The Alaska Native Language Center at the University of Alaska Fairbanks claims that at least 20 Alaskan native languages exist and there are also some languages with different dialects. Most of Alaska's native languages belong to either the Eskimo–Aleut or Na-Dene language families; however, some languages are thought to be isolates (e.g. Haida) or have not yet been classified (e.g. Tsimshianic). nearly all of Alaska's native languages were classified as either threatened, shifting, moribund, nearly extinct, or dormant languages. In October 2014, the governor of Alaska signed a bill declaring the state's 20 indigenous languages to have official status.

This bill gave them symbolic recognition as official languages, though they have not been adopted for official use within the government. The 20 languages that were included in the bill are: Inupiaq Siberian Yupik Central Alaskan Yup'ik Alutiiq Unangax Dena'ina Deg Xinag Holikachuk Koyukon Upper Kuskokwim Gwich'in Tanana Upper Tanana Tanacross Hän Ahtna Eyak Tlingit Haida Tsimshian Religion According to statistics collected by the Association of Religion Data Archives from 2010, about 34% of Alaska residents were members of religious congregations. Of the religious population, 100,960 people identified as evangelical Protestants; 50,866 as Roman Catholic; and 32,550 as mainline Protestants. Roughly 4% were Mormon, 0.5% Jewish, 0.5% Muslim, 1% Buddhist, 0.2% Baháʼí, and 0.5% Hindu. The largest religious denominations in Alaska was the Catholic Church with 50,866 adherents; non-denominational Evangelicals with 38,070 adherents; The Church of Jesus Christ of Latter-day Saints with 32,170 adherents; and the Southern Baptist Convention with 19,891 adherents. Alaska has been identified, along with Pacific Northwest states Washington and Oregon, as being the least religious states of the USA, in terms of church membership. The Pew Research Center in 2014 determined 62% of the adult population practiced Christianity. Protestantism was the largest Christian tradition, dominated by Evangelicalism. Mainline Protestants were the second largest Protestant Christian group, followed by predominantly African American churches. The Catholic Church remained the largest single Christian tradition practiced in Alaska. Of the unaffiliated population, they made up the largest non-Christian religious affiliation. Atheists made up 5% of the population and the largest non-Christian religion was Buddhism. In 1795, the first Russian Orthodox Church was established in Kodiak. Intermarriage with Alaskan Natives helped the Russian immigrants integrate into society. As a result, an increasing number of Russian Orthodox churches gradually became established within Alaska. Alaska also has the largest Quaker population (by percentage) of any state. In 2009, there were 6,000 Jews in Alaska (for whom observance of halakha may pose special problems). Alaskan Hindus often share venues and celebrations with members of other Asian religious communities, including Sikhs and Jains. In 2010, Alaskan Hindus established the Sri Ganesha Temple of Alaska, making it the first Hindu Temple in Alaska and the northernmost Hindu Temple in the world. There are an estimated 2,000–3,000 Hindus in Alaska. The vast majority of Hindus live in Anchorage or Fairbanks. Estimates for the number of Muslims in Alaska range from 2,000 to 5,000. The Islamic Community Center of Anchorage began efforts in the late 1990s to construct a mosque in Anchorage. They broke ground on a building in south Anchorage in 2010 and were nearing completion in late 2014. When completed, the mosque will be the first in the state and one of the northernmost mosques in the world. There's also a Baháʼí center. Economy As of 2016, Alaska had a total employment of 266,072. The number of employer establishments was 21,077.

This bill gave them symbolic recognition as official languages, though they have not been adopted for official use within the government. The 20 languages that were included in the bill are: Inupiaq Siberian Yupik Central Alaskan Yup'ik Alutiiq Unangax Dena'ina Deg Xinag Holikachuk Koyukon Upper Kuskokwim Gwich'in Tanana Upper Tanana Tanacross Hän Ahtna Eyak Tlingit Haida Tsimshian Religion According to statistics collected by the Association of Religion Data Archives from 2010, about 34% of Alaska residents were members of religious congregations. Of the religious population, 100,960 people identified as evangelical Protestants; 50,866 as Roman Catholic; and 32,550 as mainline Protestants. Roughly 4% were Mormon, 0.5% Jewish, 0.5% Muslim, 1% Buddhist, 0.2% Baháʼí, and 0.5% Hindu. The largest religious denominations in Alaska was the Catholic Church with 50,866 adherents; non-denominational Evangelicals with 38,070 adherents; The Church of Jesus Christ of Latter-day Saints with 32,170 adherents; and the Southern Baptist Convention with 19,891 adherents. Alaska has been identified, along with Pacific Northwest states Washington and Oregon, as being the least religious states of the USA, in terms of church membership. The Pew Research Center in 2014 determined 62% of the adult population practiced Christianity. Protestantism was the largest Christian tradition, dominated by Evangelicalism. Mainline Protestants were the second largest Protestant Christian group, followed by predominantly African American churches. The Catholic Church remained the largest single Christian tradition practiced in Alaska. Of the unaffiliated population, they made up the largest non-Christian religious affiliation. Atheists made up 5% of the population and the largest non-Christian religion was Buddhism. In 1795, the first Russian Orthodox Church was established in Kodiak. Intermarriage with Alaskan Natives helped the Russian immigrants integrate into society. As a result, an increasing number of Russian Orthodox churches gradually became established within Alaska. Alaska also has the largest Quaker population (by percentage) of any state. In 2009, there were 6,000 Jews in Alaska (for whom observance of halakha may pose special problems). Alaskan Hindus often share venues and celebrations with members of other Asian religious communities, including Sikhs and Jains. In 2010, Alaskan Hindus established the Sri Ganesha Temple of Alaska, making it the first Hindu Temple in Alaska and the northernmost Hindu Temple in the world. There are an estimated 2,000–3,000 Hindus in Alaska. The vast majority of Hindus live in Anchorage or Fairbanks. Estimates for the number of Muslims in Alaska range from 2,000 to 5,000. The Islamic Community Center of Anchorage began efforts in the late 1990s to construct a mosque in Anchorage. They broke ground on a building in south Anchorage in 2010 and were nearing completion in late 2014. When completed, the mosque will be the first in the state and one of the northernmost mosques in the world. There's also a Baháʼí center. Economy As of 2016, Alaska had a total employment of 266,072. The number of employer establishments was 21,077.

This bill gave them symbolic recognition as official languages, though they have not been adopted for official use within the government. The 20 languages that were included in the bill are: Inupiaq Siberian Yupik Central Alaskan Yup'ik Alutiiq Unangax Dena'ina Deg Xinag Holikachuk Koyukon Upper Kuskokwim Gwich'in Tanana Upper Tanana Tanacross Hän Ahtna Eyak Tlingit Haida Tsimshian Religion According to statistics collected by the Association of Religion Data Archives from 2010, about 34% of Alaska residents were members of religious congregations. Of the religious population, 100,960 people identified as evangelical Protestants; 50,866 as Roman Catholic; and 32,550 as mainline Protestants. Roughly 4% were Mormon, 0.5% Jewish, 0.5% Muslim, 1% Buddhist, 0.2% Baháʼí, and 0.5% Hindu. The largest religious denominations in Alaska was the Catholic Church with 50,866 adherents; non-denominational Evangelicals with 38,070 adherents; The Church of Jesus Christ of Latter-day Saints with 32,170 adherents; and the Southern Baptist Convention with 19,891 adherents. Alaska has been identified, along with Pacific Northwest states Washington and Oregon, as being the least religious states of the USA, in terms of church membership. The Pew Research Center in 2014 determined 62% of the adult population practiced Christianity. Protestantism was the largest Christian tradition, dominated by Evangelicalism. Mainline Protestants were the second largest Protestant Christian group, followed by predominantly African American churches. The Catholic Church remained the largest single Christian tradition practiced in Alaska. Of the unaffiliated population, they made up the largest non-Christian religious affiliation. Atheists made up 5% of the population and the largest non-Christian religion was Buddhism. In 1795, the first Russian Orthodox Church was established in Kodiak. Intermarriage with Alaskan Natives helped the Russian immigrants integrate into society. As a result, an increasing number of Russian Orthodox churches gradually became established within Alaska. Alaska also has the largest Quaker population (by percentage) of any state. In 2009, there were 6,000 Jews in Alaska (for whom observance of halakha may pose special problems). Alaskan Hindus often share venues and celebrations with members of other Asian religious communities, including Sikhs and Jains. In 2010, Alaskan Hindus established the Sri Ganesha Temple of Alaska, making it the first Hindu Temple in Alaska and the northernmost Hindu Temple in the world. There are an estimated 2,000–3,000 Hindus in Alaska. The vast majority of Hindus live in Anchorage or Fairbanks. Estimates for the number of Muslims in Alaska range from 2,000 to 5,000. The Islamic Community Center of Anchorage began efforts in the late 1990s to construct a mosque in Anchorage. They broke ground on a building in south Anchorage in 2010 and were nearing completion in late 2014. When completed, the mosque will be the first in the state and one of the northernmost mosques in the world. There's also a Baháʼí center. Economy As of 2016, Alaska had a total employment of 266,072. The number of employer establishments was 21,077.

The 2018 gross state product was $55 billion, 48th in the U.S.. Its per capita personal income for 2018 was $73,000, ranking 7th in the nation. According to a 2013 study by Phoenix Marketing International, Alaska had the fifth-largest number of millionaires per capita in the United States, with a ratio of 6.75 percent. The oil and gas industry dominates the Alaskan economy, with more than 80% of the state's revenues derived from petroleum extraction. Alaska's main export product (excluding oil and natural gas) is seafood, primarily salmon, cod, Pollock and crab. Agriculture represents a very small fraction of the Alaskan economy. Agricultural production is primarily for consumption within the state and includes nursery stock, dairy products, vegetables, and livestock. Manufacturing is limited, with most foodstuffs and general goods imported from elsewhere. Employment is primarily in government and industries such as natural resource extraction, shipping, and transportation. Military bases are a significant component of the economy in the Fairbanks North Star, Anchorage and Kodiak Island boroughs, as well as Kodiak. Federal subsidies are also an important part of the economy, allowing the state to keep taxes low. Its industrial outputs are crude petroleum, natural gas, coal, gold, precious metals, zinc and other mining, seafood processing, timber and wood products. There is also a growing service and tourism sector. Tourists have contributed to the economy by supporting local lodging. Energy Alaska has vast energy resources, although its oil reserves have been largely depleted. Major oil and gas reserves were found in the Alaska North Slope (ANS) and Cook Inlet basins, but according to the Energy Information Administration, by February 2014 Alaska had fallen to fourth place in the nation in crude oil production after Texas, North Dakota, and California. Prudhoe Bay on Alaska's North Slope is still the second highest-yielding oil field in the United States, typically producing about , although by early 2014 North Dakota's Bakken Formation was producing over . Prudhoe Bay was the largest conventional oil field ever discovered in North America, but was much smaller than Canada's enormous Athabasca oil sands field, which by 2014 was producing about of unconventional oil, and had hundreds of years of producible reserves at that rate. The Trans-Alaska Pipeline can transport and pump up to of crude oil per day, more than any other crude oil pipeline in the United States. Additionally, substantial coal deposits are found in Alaska's bituminous, sub-bituminous, and lignite coal basins. The United States Geological Survey estimates that there are of undiscovered, technically recoverable gas from natural gas hydrates on the Alaskan North Slope. Alaska also offers some of the highest hydroelectric power potential in the country from its numerous rivers. Large swaths of the Alaskan coastline offer wind and geothermal energy potential as well. Alaska's economy depends heavily on increasingly expensive diesel fuel for heating, transportation, electric power and light. Although wind and hydroelectric power are abundant and underdeveloped, proposals for statewide energy systems (e.g.

The 2018 gross state product was $55 billion, 48th in the U.S.. Its per capita personal income for 2018 was $73,000, ranking 7th in the nation. According to a 2013 study by Phoenix Marketing International, Alaska had the fifth-largest number of millionaires per capita in the United States, with a ratio of 6.75 percent. The oil and gas industry dominates the Alaskan economy, with more than 80% of the state's revenues derived from petroleum extraction. Alaska's main export product (excluding oil and natural gas) is seafood, primarily salmon, cod, Pollock and crab. Agriculture represents a very small fraction of the Alaskan economy. Agricultural production is primarily for consumption within the state and includes nursery stock, dairy products, vegetables, and livestock. Manufacturing is limited, with most foodstuffs and general goods imported from elsewhere. Employment is primarily in government and industries such as natural resource extraction, shipping, and transportation. Military bases are a significant component of the economy in the Fairbanks North Star, Anchorage and Kodiak Island boroughs, as well as Kodiak. Federal subsidies are also an important part of the economy, allowing the state to keep taxes low. Its industrial outputs are crude petroleum, natural gas, coal, gold, precious metals, zinc and other mining, seafood processing, timber and wood products. There is also a growing service and tourism sector. Tourists have contributed to the economy by supporting local lodging. Energy Alaska has vast energy resources, although its oil reserves have been largely depleted. Major oil and gas reserves were found in the Alaska North Slope (ANS) and Cook Inlet basins, but according to the Energy Information Administration, by February 2014 Alaska had fallen to fourth place in the nation in crude oil production after Texas, North Dakota, and California. Prudhoe Bay on Alaska's North Slope is still the second highest-yielding oil field in the United States, typically producing about , although by early 2014 North Dakota's Bakken Formation was producing over . Prudhoe Bay was the largest conventional oil field ever discovered in North America, but was much smaller than Canada's enormous Athabasca oil sands field, which by 2014 was producing about of unconventional oil, and had hundreds of years of producible reserves at that rate. The Trans-Alaska Pipeline can transport and pump up to of crude oil per day, more than any other crude oil pipeline in the United States. Additionally, substantial coal deposits are found in Alaska's bituminous, sub-bituminous, and lignite coal basins. The United States Geological Survey estimates that there are of undiscovered, technically recoverable gas from natural gas hydrates on the Alaskan North Slope. Alaska also offers some of the highest hydroelectric power potential in the country from its numerous rivers. Large swaths of the Alaskan coastline offer wind and geothermal energy potential as well. Alaska's economy depends heavily on increasingly expensive diesel fuel for heating, transportation, electric power and light. Although wind and hydroelectric power are abundant and underdeveloped, proposals for statewide energy systems (e.g.

The 2018 gross state product was $55 billion, 48th in the U.S.. Its per capita personal income for 2018 was $73,000, ranking 7th in the nation. According to a 2013 study by Phoenix Marketing International, Alaska had the fifth-largest number of millionaires per capita in the United States, with a ratio of 6.75 percent. The oil and gas industry dominates the Alaskan economy, with more than 80% of the state's revenues derived from petroleum extraction. Alaska's main export product (excluding oil and natural gas) is seafood, primarily salmon, cod, Pollock and crab. Agriculture represents a very small fraction of the Alaskan economy. Agricultural production is primarily for consumption within the state and includes nursery stock, dairy products, vegetables, and livestock. Manufacturing is limited, with most foodstuffs and general goods imported from elsewhere. Employment is primarily in government and industries such as natural resource extraction, shipping, and transportation. Military bases are a significant component of the economy in the Fairbanks North Star, Anchorage and Kodiak Island boroughs, as well as Kodiak. Federal subsidies are also an important part of the economy, allowing the state to keep taxes low. Its industrial outputs are crude petroleum, natural gas, coal, gold, precious metals, zinc and other mining, seafood processing, timber and wood products. There is also a growing service and tourism sector. Tourists have contributed to the economy by supporting local lodging. Energy Alaska has vast energy resources, although its oil reserves have been largely depleted. Major oil and gas reserves were found in the Alaska North Slope (ANS) and Cook Inlet basins, but according to the Energy Information Administration, by February 2014 Alaska had fallen to fourth place in the nation in crude oil production after Texas, North Dakota, and California. Prudhoe Bay on Alaska's North Slope is still the second highest-yielding oil field in the United States, typically producing about , although by early 2014 North Dakota's Bakken Formation was producing over . Prudhoe Bay was the largest conventional oil field ever discovered in North America, but was much smaller than Canada's enormous Athabasca oil sands field, which by 2014 was producing about of unconventional oil, and had hundreds of years of producible reserves at that rate. The Trans-Alaska Pipeline can transport and pump up to of crude oil per day, more than any other crude oil pipeline in the United States. Additionally, substantial coal deposits are found in Alaska's bituminous, sub-bituminous, and lignite coal basins. The United States Geological Survey estimates that there are of undiscovered, technically recoverable gas from natural gas hydrates on the Alaskan North Slope. Alaska also offers some of the highest hydroelectric power potential in the country from its numerous rivers. Large swaths of the Alaskan coastline offer wind and geothermal energy potential as well. Alaska's economy depends heavily on increasingly expensive diesel fuel for heating, transportation, electric power and light. Although wind and hydroelectric power are abundant and underdeveloped, proposals for statewide energy systems (e.g.

with special low-cost electric interties) were judged uneconomical (at the time of the report, 2001) due to low (less than 50¢/gal) fuel prices, long distances and low population. The cost of a gallon of gas in urban Alaska today is usually thirty to sixty cents higher than the national average; prices in rural areas are generally significantly higher but vary widely depending on transportation costs, seasonal usage peaks, nearby petroleum development infrastructure and many other factors. Permanent Fund The Alaska Permanent Fund is a constitutionally authorized appropriation of oil revenues, established by voters in 1976 to manage a surplus in state petroleum revenues from oil, largely in anticipation of the then recently constructed Trans-Alaska Pipeline System. The fund was originally proposed by Governor Keith Miller on the eve of the 1969 Prudhoe Bay lease sale, out of fear that the legislature would spend the entire proceeds of the sale (which amounted to $900 million) at once. It was later championed by Governor Jay Hammond and Kenai state representative Hugh Malone. It has served as an attractive political prospect ever since, diverting revenues which would normally be deposited into the general fund. The Alaska Constitution was written so as to discourage dedicating state funds for a particular purpose. The Permanent Fund has become the rare exception to this, mostly due to the political climate of distrust existing during the time of its creation. From its initial principal of $734,000, the fund has grown to $50 billion as a result of oil royalties and capital investment programs. Most if not all the principal is invested conservatively outside Alaska. This has led to frequent calls by Alaskan politicians for the Fund to make investments within Alaska, though such a stance has never gained momentum. Starting in 1982, dividends from the fund's annual growth have been paid out each year to eligible Alaskans, ranging from an initial $1,000 in 1982 (equal to three years' payout, as the distribution of payments was held up in a lawsuit over the distribution scheme) to $3,269 in 2008 (which included a one-time $1,200 "Resource Rebate"). Every year, the state legislature takes out 8% from the earnings, puts 3% back into the principal for inflation proofing, and the remaining 5% is distributed to all qualifying Alaskans. To qualify for the Permanent Fund Dividend, one must have lived in the state for a minimum of 12 months, maintain constant residency subject to allowable absences, and not be subject to court judgments or criminal convictions which fall under various disqualifying classifications or may subject the payment amount to civil garnishment. The Permanent Fund is often considered to be one of the leading examples of a basic income policy in the world. Cost of living The cost of goods in Alaska has long been higher than in the contiguous 48 states.

with special low-cost electric interties) were judged uneconomical (at the time of the report, 2001) due to low (less than 50¢/gal) fuel prices, long distances and low population. The cost of a gallon of gas in urban Alaska today is usually thirty to sixty cents higher than the national average; prices in rural areas are generally significantly higher but vary widely depending on transportation costs, seasonal usage peaks, nearby petroleum development infrastructure and many other factors. Permanent Fund The Alaska Permanent Fund is a constitutionally authorized appropriation of oil revenues, established by voters in 1976 to manage a surplus in state petroleum revenues from oil, largely in anticipation of the then recently constructed Trans-Alaska Pipeline System. The fund was originally proposed by Governor Keith Miller on the eve of the 1969 Prudhoe Bay lease sale, out of fear that the legislature would spend the entire proceeds of the sale (which amounted to $900 million) at once. It was later championed by Governor Jay Hammond and Kenai state representative Hugh Malone. It has served as an attractive political prospect ever since, diverting revenues which would normally be deposited into the general fund. The Alaska Constitution was written so as to discourage dedicating state funds for a particular purpose. The Permanent Fund has become the rare exception to this, mostly due to the political climate of distrust existing during the time of its creation. From its initial principal of $734,000, the fund has grown to $50 billion as a result of oil royalties and capital investment programs. Most if not all the principal is invested conservatively outside Alaska. This has led to frequent calls by Alaskan politicians for the Fund to make investments within Alaska, though such a stance has never gained momentum. Starting in 1982, dividends from the fund's annual growth have been paid out each year to eligible Alaskans, ranging from an initial $1,000 in 1982 (equal to three years' payout, as the distribution of payments was held up in a lawsuit over the distribution scheme) to $3,269 in 2008 (which included a one-time $1,200 "Resource Rebate"). Every year, the state legislature takes out 8% from the earnings, puts 3% back into the principal for inflation proofing, and the remaining 5% is distributed to all qualifying Alaskans. To qualify for the Permanent Fund Dividend, one must have lived in the state for a minimum of 12 months, maintain constant residency subject to allowable absences, and not be subject to court judgments or criminal convictions which fall under various disqualifying classifications or may subject the payment amount to civil garnishment. The Permanent Fund is often considered to be one of the leading examples of a basic income policy in the world. Cost of living The cost of goods in Alaska has long been higher than in the contiguous 48 states.

with special low-cost electric interties) were judged uneconomical (at the time of the report, 2001) due to low (less than 50¢/gal) fuel prices, long distances and low population. The cost of a gallon of gas in urban Alaska today is usually thirty to sixty cents higher than the national average; prices in rural areas are generally significantly higher but vary widely depending on transportation costs, seasonal usage peaks, nearby petroleum development infrastructure and many other factors. Permanent Fund The Alaska Permanent Fund is a constitutionally authorized appropriation of oil revenues, established by voters in 1976 to manage a surplus in state petroleum revenues from oil, largely in anticipation of the then recently constructed Trans-Alaska Pipeline System. The fund was originally proposed by Governor Keith Miller on the eve of the 1969 Prudhoe Bay lease sale, out of fear that the legislature would spend the entire proceeds of the sale (which amounted to $900 million) at once. It was later championed by Governor Jay Hammond and Kenai state representative Hugh Malone. It has served as an attractive political prospect ever since, diverting revenues which would normally be deposited into the general fund. The Alaska Constitution was written so as to discourage dedicating state funds for a particular purpose. The Permanent Fund has become the rare exception to this, mostly due to the political climate of distrust existing during the time of its creation. From its initial principal of $734,000, the fund has grown to $50 billion as a result of oil royalties and capital investment programs. Most if not all the principal is invested conservatively outside Alaska. This has led to frequent calls by Alaskan politicians for the Fund to make investments within Alaska, though such a stance has never gained momentum. Starting in 1982, dividends from the fund's annual growth have been paid out each year to eligible Alaskans, ranging from an initial $1,000 in 1982 (equal to three years' payout, as the distribution of payments was held up in a lawsuit over the distribution scheme) to $3,269 in 2008 (which included a one-time $1,200 "Resource Rebate"). Every year, the state legislature takes out 8% from the earnings, puts 3% back into the principal for inflation proofing, and the remaining 5% is distributed to all qualifying Alaskans. To qualify for the Permanent Fund Dividend, one must have lived in the state for a minimum of 12 months, maintain constant residency subject to allowable absences, and not be subject to court judgments or criminal convictions which fall under various disqualifying classifications or may subject the payment amount to civil garnishment. The Permanent Fund is often considered to be one of the leading examples of a basic income policy in the world. Cost of living The cost of goods in Alaska has long been higher than in the contiguous 48 states.

Federal government employees, particularly United States Postal Service (USPS) workers and active-duty military members, receive a Cost of Living Allowance usually set at 25% of base pay because, while the cost of living has gone down, it is still one of the highest in the country. Rural Alaska suffers from extremely high prices for food and consumer goods compared to the rest of the country, due to the relatively limited transportation infrastructure. Agriculture and fishing Due to the northern climate and short growing season, relatively little farming occurs in Alaska. Most farms are in either the Matanuska Valley, about northeast of Anchorage, or on the Kenai Peninsula, about southwest of Anchorage. The short 100-day growing season limits the crops that can be grown, but the long sunny summer days make for productive growing seasons. The primary crops are potatoes, carrots, lettuce, and cabbage. The Tanana Valley is another notable agricultural locus, especially the Delta Junction area, about southeast of Fairbanks, with a sizable concentration of farms growing agronomic crops; these farms mostly lie north and east of Fort Greely. This area was largely set aside and developed under a state program spearheaded by Hammond during his second term as governor. Delta-area crops consist predominantly of barley and hay. West of Fairbanks lies another concentration of small farms catering to restaurants, the hotel and tourist industry, and community-supported agriculture. Alaskan agriculture has experienced a surge in growth of market gardeners, small farms and farmers' markets in recent years, with the highest percentage increase (46%) in the nation in growth in farmers' markets in 2011, compared to 17% nationwide. The peony industry has also taken off, as the growing season allows farmers to harvest during a gap in supply elsewhere in the world, thereby filling a niche in the flower market. Alaska, with no counties, lacks county fairs. However, a small assortment of state and local fairs (with the Alaska State Fair in Palmer the largest), are held mostly in the late summer. The fairs are mostly located in communities with historic or current agricultural activity, and feature local farmers exhibiting produce in addition to more high-profile commercial activities such as carnival rides, concerts and food. "Alaska Grown" is used as an agricultural slogan. Alaska has an abundance of seafood, with the primary fisheries in the Bering Sea and the North Pacific. Seafood is one of the few food items that is often cheaper within the state than outside it. Many Alaskans take advantage of salmon seasons to harvest portions of their household diet while fishing for subsistence, as well as sport. This includes fish taken by hook, net or wheel. Hunting for subsistence, primarily caribou, moose, and Dall sheep is still common in the state, particularly in remote Bush communities. An example of a traditional native food is Akutaq, the Eskimo ice cream, which can consist of reindeer fat, seal oil, dried fish meat and local berries.

Federal government employees, particularly United States Postal Service (USPS) workers and active-duty military members, receive a Cost of Living Allowance usually set at 25% of base pay because, while the cost of living has gone down, it is still one of the highest in the country. Rural Alaska suffers from extremely high prices for food and consumer goods compared to the rest of the country, due to the relatively limited transportation infrastructure. Agriculture and fishing Due to the northern climate and short growing season, relatively little farming occurs in Alaska. Most farms are in either the Matanuska Valley, about northeast of Anchorage, or on the Kenai Peninsula, about southwest of Anchorage. The short 100-day growing season limits the crops that can be grown, but the long sunny summer days make for productive growing seasons. The primary crops are potatoes, carrots, lettuce, and cabbage. The Tanana Valley is another notable agricultural locus, especially the Delta Junction area, about southeast of Fairbanks, with a sizable concentration of farms growing agronomic crops; these farms mostly lie north and east of Fort Greely. This area was largely set aside and developed under a state program spearheaded by Hammond during his second term as governor. Delta-area crops consist predominantly of barley and hay. West of Fairbanks lies another concentration of small farms catering to restaurants, the hotel and tourist industry, and community-supported agriculture. Alaskan agriculture has experienced a surge in growth of market gardeners, small farms and farmers' markets in recent years, with the highest percentage increase (46%) in the nation in growth in farmers' markets in 2011, compared to 17% nationwide. The peony industry has also taken off, as the growing season allows farmers to harvest during a gap in supply elsewhere in the world, thereby filling a niche in the flower market. Alaska, with no counties, lacks county fairs. However, a small assortment of state and local fairs (with the Alaska State Fair in Palmer the largest), are held mostly in the late summer. The fairs are mostly located in communities with historic or current agricultural activity, and feature local farmers exhibiting produce in addition to more high-profile commercial activities such as carnival rides, concerts and food. "Alaska Grown" is used as an agricultural slogan. Alaska has an abundance of seafood, with the primary fisheries in the Bering Sea and the North Pacific. Seafood is one of the few food items that is often cheaper within the state than outside it. Many Alaskans take advantage of salmon seasons to harvest portions of their household diet while fishing for subsistence, as well as sport. This includes fish taken by hook, net or wheel. Hunting for subsistence, primarily caribou, moose, and Dall sheep is still common in the state, particularly in remote Bush communities. An example of a traditional native food is Akutaq, the Eskimo ice cream, which can consist of reindeer fat, seal oil, dried fish meat and local berries.

Federal government employees, particularly United States Postal Service (USPS) workers and active-duty military members, receive a Cost of Living Allowance usually set at 25% of base pay because, while the cost of living has gone down, it is still one of the highest in the country. Rural Alaska suffers from extremely high prices for food and consumer goods compared to the rest of the country, due to the relatively limited transportation infrastructure. Agriculture and fishing Due to the northern climate and short growing season, relatively little farming occurs in Alaska. Most farms are in either the Matanuska Valley, about northeast of Anchorage, or on the Kenai Peninsula, about southwest of Anchorage. The short 100-day growing season limits the crops that can be grown, but the long sunny summer days make for productive growing seasons. The primary crops are potatoes, carrots, lettuce, and cabbage. The Tanana Valley is another notable agricultural locus, especially the Delta Junction area, about southeast of Fairbanks, with a sizable concentration of farms growing agronomic crops; these farms mostly lie north and east of Fort Greely. This area was largely set aside and developed under a state program spearheaded by Hammond during his second term as governor. Delta-area crops consist predominantly of barley and hay. West of Fairbanks lies another concentration of small farms catering to restaurants, the hotel and tourist industry, and community-supported agriculture. Alaskan agriculture has experienced a surge in growth of market gardeners, small farms and farmers' markets in recent years, with the highest percentage increase (46%) in the nation in growth in farmers' markets in 2011, compared to 17% nationwide. The peony industry has also taken off, as the growing season allows farmers to harvest during a gap in supply elsewhere in the world, thereby filling a niche in the flower market. Alaska, with no counties, lacks county fairs. However, a small assortment of state and local fairs (with the Alaska State Fair in Palmer the largest), are held mostly in the late summer. The fairs are mostly located in communities with historic or current agricultural activity, and feature local farmers exhibiting produce in addition to more high-profile commercial activities such as carnival rides, concerts and food. "Alaska Grown" is used as an agricultural slogan. Alaska has an abundance of seafood, with the primary fisheries in the Bering Sea and the North Pacific. Seafood is one of the few food items that is often cheaper within the state than outside it. Many Alaskans take advantage of salmon seasons to harvest portions of their household diet while fishing for subsistence, as well as sport. This includes fish taken by hook, net or wheel. Hunting for subsistence, primarily caribou, moose, and Dall sheep is still common in the state, particularly in remote Bush communities. An example of a traditional native food is Akutaq, the Eskimo ice cream, which can consist of reindeer fat, seal oil, dried fish meat and local berries.

Alaska's reindeer herding is concentrated on Seward Peninsula, where wild caribou can be prevented from mingling and migrating with the domesticated reindeer. Most food in Alaska is transported into the state from "Outside" (the other 49 US states), and shipping costs make food in the cities relatively expensive. In rural areas, subsistence hunting and gathering is an essential activity because imported food is prohibitively expensive. Although most small towns and villages in Alaska lie along the coastline, the cost of importing food to remote villages can be high, because of the terrain and difficult road conditions, which change dramatically, due to varying climate and precipitation changes. The cost of transport can reach as high as 50¢ per pound ($1.10/kg) or more in some remote areas, during the most difficult times, if these locations can be reached at all during such inclement weather and terrain conditions. The cost of delivering a of milk is about $3.50 in many villages where per capita income can be $20,000 or less. Fuel cost per gallon is routinely twenty to thirty cents higher than the contiguous United States average, with only Hawaii having higher prices. Culture Some of Alaska's popular annual events are the Iditarod Trail Sled Dog Race from Anchorage to Nome, World Ice Art Championships in Fairbanks, the Blueberry Festival and Alaska Hummingbird Festival in Ketchikan, the Sitka Whale Fest, and the Stikine River Garnet Fest in Wrangell. The Stikine River attracts the largest springtime concentration of American bald eagles in the world. The Alaska Native Heritage Center celebrates the rich heritage of Alaska's 11 cultural groups. Their purpose is to encourage cross-cultural exchanges among all people and enhance self-esteem among Native people. The Alaska Native Arts Foundation promotes and markets Native art from all regions and cultures in the State, using the internet. Music Influences on music in Alaska include the traditional music of Alaska Natives as well as folk music brought by later immigrants from Russia and Europe. Prominent musicians from Alaska include singer Jewel, traditional Aleut flautist Mary Youngblood, folk singer-songwriter Libby Roderick, Christian music singer-songwriter Lincoln Brewster, metal/post hardcore band 36 Crazyfists and the groups Pamyua and Portugal. The Man. There are many established music festivals in Alaska, including the Alaska Folk Festival, the Fairbanks Summer Arts Festival the Anchorage Folk Festival, the Athabascan Old-Time Fiddling Festival, the Sitka Jazz Festival, and the Sitka Summer Music Festival. The most prominent orchestra in Alaska is the Anchorage Symphony Orchestra, though the Fairbanks Symphony Orchestra and Juneau Symphony are also notable. The Anchorage Opera is currently the state's only professional opera company, though there are several volunteer and semi-professional organizations in the state as well. The official state song of Alaska is "Alaska's Flag", which was adopted in 1955; it celebrates the flag of Alaska. Alaska in film and on television Alaska's first independent picture entirely made in Alaska was The Chechahcos, produced by Alaskan businessman Austin E. Lathrop and filmed in and around Anchorage.

Alaska's reindeer herding is concentrated on Seward Peninsula, where wild caribou can be prevented from mingling and migrating with the domesticated reindeer. Most food in Alaska is transported into the state from "Outside" (the other 49 US states), and shipping costs make food in the cities relatively expensive. In rural areas, subsistence hunting and gathering is an essential activity because imported food is prohibitively expensive. Although most small towns and villages in Alaska lie along the coastline, the cost of importing food to remote villages can be high, because of the terrain and difficult road conditions, which change dramatically, due to varying climate and precipitation changes. The cost of transport can reach as high as 50¢ per pound ($1.10/kg) or more in some remote areas, during the most difficult times, if these locations can be reached at all during such inclement weather and terrain conditions. The cost of delivering a of milk is about $3.50 in many villages where per capita income can be $20,000 or less. Fuel cost per gallon is routinely twenty to thirty cents higher than the contiguous United States average, with only Hawaii having higher prices. Culture Some of Alaska's popular annual events are the Iditarod Trail Sled Dog Race from Anchorage to Nome, World Ice Art Championships in Fairbanks, the Blueberry Festival and Alaska Hummingbird Festival in Ketchikan, the Sitka Whale Fest, and the Stikine River Garnet Fest in Wrangell. The Stikine River attracts the largest springtime concentration of American bald eagles in the world. The Alaska Native Heritage Center celebrates the rich heritage of Alaska's 11 cultural groups. Their purpose is to encourage cross-cultural exchanges among all people and enhance self-esteem among Native people. The Alaska Native Arts Foundation promotes and markets Native art from all regions and cultures in the State, using the internet. Music Influences on music in Alaska include the traditional music of Alaska Natives as well as folk music brought by later immigrants from Russia and Europe. Prominent musicians from Alaska include singer Jewel, traditional Aleut flautist Mary Youngblood, folk singer-songwriter Libby Roderick, Christian music singer-songwriter Lincoln Brewster, metal/post hardcore band 36 Crazyfists and the groups Pamyua and Portugal. The Man. There are many established music festivals in Alaska, including the Alaska Folk Festival, the Fairbanks Summer Arts Festival the Anchorage Folk Festival, the Athabascan Old-Time Fiddling Festival, the Sitka Jazz Festival, and the Sitka Summer Music Festival. The most prominent orchestra in Alaska is the Anchorage Symphony Orchestra, though the Fairbanks Symphony Orchestra and Juneau Symphony are also notable. The Anchorage Opera is currently the state's only professional opera company, though there are several volunteer and semi-professional organizations in the state as well. The official state song of Alaska is "Alaska's Flag", which was adopted in 1955; it celebrates the flag of Alaska. Alaska in film and on television Alaska's first independent picture entirely made in Alaska was The Chechahcos, produced by Alaskan businessman Austin E. Lathrop and filmed in and around Anchorage.

Alaska's reindeer herding is concentrated on Seward Peninsula, where wild caribou can be prevented from mingling and migrating with the domesticated reindeer. Most food in Alaska is transported into the state from "Outside" (the other 49 US states), and shipping costs make food in the cities relatively expensive. In rural areas, subsistence hunting and gathering is an essential activity because imported food is prohibitively expensive. Although most small towns and villages in Alaska lie along the coastline, the cost of importing food to remote villages can be high, because of the terrain and difficult road conditions, which change dramatically, due to varying climate and precipitation changes. The cost of transport can reach as high as 50¢ per pound ($1.10/kg) or more in some remote areas, during the most difficult times, if these locations can be reached at all during such inclement weather and terrain conditions. The cost of delivering a of milk is about $3.50 in many villages where per capita income can be $20,000 or less. Fuel cost per gallon is routinely twenty to thirty cents higher than the contiguous United States average, with only Hawaii having higher prices. Culture Some of Alaska's popular annual events are the Iditarod Trail Sled Dog Race from Anchorage to Nome, World Ice Art Championships in Fairbanks, the Blueberry Festival and Alaska Hummingbird Festival in Ketchikan, the Sitka Whale Fest, and the Stikine River Garnet Fest in Wrangell. The Stikine River attracts the largest springtime concentration of American bald eagles in the world. The Alaska Native Heritage Center celebrates the rich heritage of Alaska's 11 cultural groups. Their purpose is to encourage cross-cultural exchanges among all people and enhance self-esteem among Native people. The Alaska Native Arts Foundation promotes and markets Native art from all regions and cultures in the State, using the internet. Music Influences on music in Alaska include the traditional music of Alaska Natives as well as folk music brought by later immigrants from Russia and Europe. Prominent musicians from Alaska include singer Jewel, traditional Aleut flautist Mary Youngblood, folk singer-songwriter Libby Roderick, Christian music singer-songwriter Lincoln Brewster, metal/post hardcore band 36 Crazyfists and the groups Pamyua and Portugal. The Man. There are many established music festivals in Alaska, including the Alaska Folk Festival, the Fairbanks Summer Arts Festival the Anchorage Folk Festival, the Athabascan Old-Time Fiddling Festival, the Sitka Jazz Festival, and the Sitka Summer Music Festival. The most prominent orchestra in Alaska is the Anchorage Symphony Orchestra, though the Fairbanks Symphony Orchestra and Juneau Symphony are also notable. The Anchorage Opera is currently the state's only professional opera company, though there are several volunteer and semi-professional organizations in the state as well. The official state song of Alaska is "Alaska's Flag", which was adopted in 1955; it celebrates the flag of Alaska. Alaska in film and on television Alaska's first independent picture entirely made in Alaska was The Chechahcos, produced by Alaskan businessman Austin E. Lathrop and filmed in and around Anchorage.

Released in 1924 by the Alaska Moving Picture Corporation, it was the only film the company made. One of the most prominent movies filmed in Alaska is MGM's Eskimo/Mala The Magnificent, starring Alaska Native Ray Mala. In 1932, an expedition set out from MGM's studios in Hollywood to Alaska to film what was then billed as "The Biggest Picture Ever Made". Upon arriving in Alaska, they set up "Camp Hollywood" in Northwest Alaska, where they lived during the duration of the filming. Louis B. Mayer spared no expense in spite of the remote location, going so far as to hire the chef from the Hotel Roosevelt in Hollywood to prepare meals. When Eskimo premiered at the Astor Theatre in New York City, the studio received the largest amount of feedback in its history. Eskimo was critically acclaimed and released worldwide; as a result, Mala became an international movie star. Eskimo won the first Oscar for Best Film Editing at the Academy Awards, and showcased and preserved aspects of Inupiat culture on film. The 1983 Disney movie Never Cry Wolf was at least partially shot in Alaska. The 1991 film White Fang, based on Jack London's 1906 novel and starring Ethan Hawke, was filmed in and around Haines. Steven Seagal's 1994 On Deadly Ground, starring Michael Caine, was filmed in part at the Worthington Glacier near Valdez. The 1999 John Sayles film Limbo, starring David Strathairn, Mary Elizabeth Mastrantonio, and Kris Kristofferson, was filmed in Juneau. The psychological thriller Insomnia, starring Al Pacino and Robin Williams, was shot in Canada, but was set in Alaska. The 2007 film directed by Sean Penn, Into The Wild, was partially filmed and set in Alaska. The film, which is based on the novel of the same name, follows the adventures of Christopher McCandless, who died in a remote abandoned bus along the Stampede Trail west of Healy in 1992. Many films and television shows set in Alaska are not filmed there; for example, Northern Exposure, set in the fictional town of Cicely, Alaska, was filmed in Roslyn, Washington. The 2007 horror feature 30 Days of Night is set in Barrow, Alaska, but was filmed in New Zealand. Many reality television shows are filmed in Alaska. In 2011, the Anchorage Daily News found ten set in the state. Public health and public safety The Alaska State Troopers are Alaska's statewide police force. They have a long and storied history, but were not an official organization until 1941. Before the force was officially organized, law enforcement in Alaska was handled by various federal agencies. Larger towns usually have their own local police and some villages rely on "Public Safety Officers" who have police training but do not carry firearms. In much of the state, the troopers serve as the only police force available. In addition to enforcing traffic and criminal law, wildlife Troopers enforce hunting and fishing regulations.

Released in 1924 by the Alaska Moving Picture Corporation, it was the only film the company made. One of the most prominent movies filmed in Alaska is MGM's Eskimo/Mala The Magnificent, starring Alaska Native Ray Mala. In 1932, an expedition set out from MGM's studios in Hollywood to Alaska to film what was then billed as "The Biggest Picture Ever Made". Upon arriving in Alaska, they set up "Camp Hollywood" in Northwest Alaska, where they lived during the duration of the filming. Louis B. Mayer spared no expense in spite of the remote location, going so far as to hire the chef from the Hotel Roosevelt in Hollywood to prepare meals. When Eskimo premiered at the Astor Theatre in New York City, the studio received the largest amount of feedback in its history. Eskimo was critically acclaimed and released worldwide; as a result, Mala became an international movie star. Eskimo won the first Oscar for Best Film Editing at the Academy Awards, and showcased and preserved aspects of Inupiat culture on film. The 1983 Disney movie Never Cry Wolf was at least partially shot in Alaska. The 1991 film White Fang, based on Jack London's 1906 novel and starring Ethan Hawke, was filmed in and around Haines. Steven Seagal's 1994 On Deadly Ground, starring Michael Caine, was filmed in part at the Worthington Glacier near Valdez. The 1999 John Sayles film Limbo, starring David Strathairn, Mary Elizabeth Mastrantonio, and Kris Kristofferson, was filmed in Juneau. The psychological thriller Insomnia, starring Al Pacino and Robin Williams, was shot in Canada, but was set in Alaska. The 2007 film directed by Sean Penn, Into The Wild, was partially filmed and set in Alaska. The film, which is based on the novel of the same name, follows the adventures of Christopher McCandless, who died in a remote abandoned bus along the Stampede Trail west of Healy in 1992. Many films and television shows set in Alaska are not filmed there; for example, Northern Exposure, set in the fictional town of Cicely, Alaska, was filmed in Roslyn, Washington. The 2007 horror feature 30 Days of Night is set in Barrow, Alaska, but was filmed in New Zealand. Many reality television shows are filmed in Alaska. In 2011, the Anchorage Daily News found ten set in the state. Public health and public safety The Alaska State Troopers are Alaska's statewide police force. They have a long and storied history, but were not an official organization until 1941. Before the force was officially organized, law enforcement in Alaska was handled by various federal agencies. Larger towns usually have their own local police and some villages rely on "Public Safety Officers" who have police training but do not carry firearms. In much of the state, the troopers serve as the only police force available. In addition to enforcing traffic and criminal law, wildlife Troopers enforce hunting and fishing regulations.

Released in 1924 by the Alaska Moving Picture Corporation, it was the only film the company made. One of the most prominent movies filmed in Alaska is MGM's Eskimo/Mala The Magnificent, starring Alaska Native Ray Mala. In 1932, an expedition set out from MGM's studios in Hollywood to Alaska to film what was then billed as "The Biggest Picture Ever Made". Upon arriving in Alaska, they set up "Camp Hollywood" in Northwest Alaska, where they lived during the duration of the filming. Louis B. Mayer spared no expense in spite of the remote location, going so far as to hire the chef from the Hotel Roosevelt in Hollywood to prepare meals. When Eskimo premiered at the Astor Theatre in New York City, the studio received the largest amount of feedback in its history. Eskimo was critically acclaimed and released worldwide; as a result, Mala became an international movie star. Eskimo won the first Oscar for Best Film Editing at the Academy Awards, and showcased and preserved aspects of Inupiat culture on film. The 1983 Disney movie Never Cry Wolf was at least partially shot in Alaska. The 1991 film White Fang, based on Jack London's 1906 novel and starring Ethan Hawke, was filmed in and around Haines. Steven Seagal's 1994 On Deadly Ground, starring Michael Caine, was filmed in part at the Worthington Glacier near Valdez. The 1999 John Sayles film Limbo, starring David Strathairn, Mary Elizabeth Mastrantonio, and Kris Kristofferson, was filmed in Juneau. The psychological thriller Insomnia, starring Al Pacino and Robin Williams, was shot in Canada, but was set in Alaska. The 2007 film directed by Sean Penn, Into The Wild, was partially filmed and set in Alaska. The film, which is based on the novel of the same name, follows the adventures of Christopher McCandless, who died in a remote abandoned bus along the Stampede Trail west of Healy in 1992. Many films and television shows set in Alaska are not filmed there; for example, Northern Exposure, set in the fictional town of Cicely, Alaska, was filmed in Roslyn, Washington. The 2007 horror feature 30 Days of Night is set in Barrow, Alaska, but was filmed in New Zealand. Many reality television shows are filmed in Alaska. In 2011, the Anchorage Daily News found ten set in the state. Public health and public safety The Alaska State Troopers are Alaska's statewide police force. They have a long and storied history, but were not an official organization until 1941. Before the force was officially organized, law enforcement in Alaska was handled by various federal agencies. Larger towns usually have their own local police and some villages rely on "Public Safety Officers" who have police training but do not carry firearms. In much of the state, the troopers serve as the only police force available. In addition to enforcing traffic and criminal law, wildlife Troopers enforce hunting and fishing regulations.

Due to the varied terrain and wide scope of the Troopers' duties, they employ a wide variety of land, air, and water patrol vehicles. Many rural communities in Alaska are considered "dry", having outlawed the importation of alcoholic beverages. Suicide rates for rural residents are higher than urban. Domestic abuse and other violent crimes are also at high levels in the state; this is in part linked to alcohol abuse. Alaska has the highest rate of sexual assault in the nation, especially in rural areas. The average age of sexually assaulted victims is 16 years old. In four out of five cases, the suspects were relatives, friends or acquaintances. Education The Alaska Department of Education and Early Development administers many school districts in Alaska. In addition, the state operates a boarding school, Mt. Edgecumbe High School in Sitka, and provides partial funding for other boarding schools, including Nenana Student Living Center in Nenana and The Galena Interior Learning Academy in Galena. There are more than a dozen colleges and universities in Alaska. Accredited universities in Alaska include the University of Alaska Anchorage, University of Alaska Fairbanks, University of Alaska Southeast, and Alaska Pacific University. Alaska is the only state that has no institutions that are part of NCAA Division I. The Alaska Department of Labor and Workforce Development operates AVTEC, Alaska's Institute of Technology. Campuses in Seward and Anchorage offer one-week to 11-month training programs in areas as diverse as Information Technology, Welding, Nursing, and Mechanics. Alaska has had a problem with a "brain drain". Many of its young people, including most of the highest academic achievers, leave the state after high school graduation and do not return. , Alaska did not have a law school or medical school. The University of Alaska has attempted to combat this by offering partial four-year scholarships to the top 10% of Alaska high school graduates, via the Alaska Scholars Program. Beginning in 1998, schools in rural Alaska must have at least 10 students to retain funding from the state, and campuses not meeting the number close. This was due to the loss in oil revenues that previously propped up smaller rural schools. In 2015, there was a proposal to raise that minimum to 25, but legislators in the state largely did not agree. Transportation Roads Alaska has few road connections compared to the rest of the U.S. The state's road system, covering a relatively small area of the state, linking the central population centers and the Alaska Highway, the principal route out of the state through Canada. The state capital, Juneau, is not accessible by road, only a car ferry; this has spurred debate over decades about moving the capital to a city on the road system, or building a road connection from Haines. The western part of Alaska has no road system connecting the communities with the rest of Alaska. The Interstate Highways in Alaska consists of a total of .

Due to the varied terrain and wide scope of the Troopers' duties, they employ a wide variety of land, air, and water patrol vehicles. Many rural communities in Alaska are considered "dry", having outlawed the importation of alcoholic beverages. Suicide rates for rural residents are higher than urban. Domestic abuse and other violent crimes are also at high levels in the state; this is in part linked to alcohol abuse. Alaska has the highest rate of sexual assault in the nation, especially in rural areas. The average age of sexually assaulted victims is 16 years old. In four out of five cases, the suspects were relatives, friends or acquaintances. Education The Alaska Department of Education and Early Development administers many school districts in Alaska. In addition, the state operates a boarding school, Mt. Edgecumbe High School in Sitka, and provides partial funding for other boarding schools, including Nenana Student Living Center in Nenana and The Galena Interior Learning Academy in Galena. There are more than a dozen colleges and universities in Alaska. Accredited universities in Alaska include the University of Alaska Anchorage, University of Alaska Fairbanks, University of Alaska Southeast, and Alaska Pacific University. Alaska is the only state that has no institutions that are part of NCAA Division I. The Alaska Department of Labor and Workforce Development operates AVTEC, Alaska's Institute of Technology. Campuses in Seward and Anchorage offer one-week to 11-month training programs in areas as diverse as Information Technology, Welding, Nursing, and Mechanics. Alaska has had a problem with a "brain drain". Many of its young people, including most of the highest academic achievers, leave the state after high school graduation and do not return. , Alaska did not have a law school or medical school. The University of Alaska has attempted to combat this by offering partial four-year scholarships to the top 10% of Alaska high school graduates, via the Alaska Scholars Program. Beginning in 1998, schools in rural Alaska must have at least 10 students to retain funding from the state, and campuses not meeting the number close. This was due to the loss in oil revenues that previously propped up smaller rural schools. In 2015, there was a proposal to raise that minimum to 25, but legislators in the state largely did not agree. Transportation Roads Alaska has few road connections compared to the rest of the U.S. The state's road system, covering a relatively small area of the state, linking the central population centers and the Alaska Highway, the principal route out of the state through Canada. The state capital, Juneau, is not accessible by road, only a car ferry; this has spurred debate over decades about moving the capital to a city on the road system, or building a road connection from Haines. The western part of Alaska has no road system connecting the communities with the rest of Alaska. The Interstate Highways in Alaska consists of a total of .

Due to the varied terrain and wide scope of the Troopers' duties, they employ a wide variety of land, air, and water patrol vehicles. Many rural communities in Alaska are considered "dry", having outlawed the importation of alcoholic beverages. Suicide rates for rural residents are higher than urban. Domestic abuse and other violent crimes are also at high levels in the state; this is in part linked to alcohol abuse. Alaska has the highest rate of sexual assault in the nation, especially in rural areas. The average age of sexually assaulted victims is 16 years old. In four out of five cases, the suspects were relatives, friends or acquaintances. Education The Alaska Department of Education and Early Development administers many school districts in Alaska. In addition, the state operates a boarding school, Mt. Edgecumbe High School in Sitka, and provides partial funding for other boarding schools, including Nenana Student Living Center in Nenana and The Galena Interior Learning Academy in Galena. There are more than a dozen colleges and universities in Alaska. Accredited universities in Alaska include the University of Alaska Anchorage, University of Alaska Fairbanks, University of Alaska Southeast, and Alaska Pacific University. Alaska is the only state that has no institutions that are part of NCAA Division I. The Alaska Department of Labor and Workforce Development operates AVTEC, Alaska's Institute of Technology. Campuses in Seward and Anchorage offer one-week to 11-month training programs in areas as diverse as Information Technology, Welding, Nursing, and Mechanics. Alaska has had a problem with a "brain drain". Many of its young people, including most of the highest academic achievers, leave the state after high school graduation and do not return. , Alaska did not have a law school or medical school. The University of Alaska has attempted to combat this by offering partial four-year scholarships to the top 10% of Alaska high school graduates, via the Alaska Scholars Program. Beginning in 1998, schools in rural Alaska must have at least 10 students to retain funding from the state, and campuses not meeting the number close. This was due to the loss in oil revenues that previously propped up smaller rural schools. In 2015, there was a proposal to raise that minimum to 25, but legislators in the state largely did not agree. Transportation Roads Alaska has few road connections compared to the rest of the U.S. The state's road system, covering a relatively small area of the state, linking the central population centers and the Alaska Highway, the principal route out of the state through Canada. The state capital, Juneau, is not accessible by road, only a car ferry; this has spurred debate over decades about moving the capital to a city on the road system, or building a road connection from Haines. The western part of Alaska has no road system connecting the communities with the rest of Alaska. The Interstate Highways in Alaska consists of a total of .

One unique feature of the Alaska Highway system is the Anton Anderson Memorial Tunnel, an active Alaska Railroad tunnel recently upgraded to provide a paved roadway link with the isolated community of Whittier on Prince William Sound to the Seward Highway about southeast of Anchorage at Portage. At , the tunnel was the longest road tunnel in North America until 2007. The tunnel is the longest combination road and rail tunnel in North America. Rail Built around 1915, the Alaska Railroad (ARR) played a key role in the development of Alaska through the 20th century. It links north Pacific shipping through providing critical infrastructure with tracks that run from Seward to Interior Alaska by way of South Central Alaska, passing through Anchorage, Eklutna, Wasilla, Talkeetna, Denali, and Fairbanks, with spurs to Whittier, Palmer and North Pole. The cities, towns, villages, and region served by ARR tracks are known statewide as "The Railbelt". In recent years, the ever-improving paved highway system began to eclipse the railroad's importance in Alaska's economy. The railroad played a vital role in Alaska's development, moving freight into Alaska while transporting natural resources southward, such as coal from the Usibelli coal mine near Healy to Seward and gravel from the Matanuska Valley to Anchorage. It is well known for its summertime tour passenger service. The Alaska Railroad was one of the last railroads in North America to use cabooses in regular service and still uses them on some gravel trains. It continues to offer one of the last flag stop routes in the country. A stretch of about of track along an area north of Talkeetna remains inaccessible by road; the railroad provides the only transportation to rural homes and cabins in the area. Until construction of the Parks Highway in the 1970s, the railroad provided the only land access to most of the region along its entire route. In northern Southeast Alaska, the White Pass and Yukon Route also partly runs through the state from Skagway northwards into Canada (British Columbia and Yukon Territory), crossing the border at White Pass Summit. This line is now mainly used by tourists, often arriving by cruise liner at Skagway. It was featured in the 1983 BBC television series Great Little Railways. The Alaska Rail network is not connected to Outside. (The nearest link to the North American railway network is the northwest terminus of the Canadian National Railway at Prince Rupert, British Columbia, several hundred miles to the southeast.) In 2000, the U.S. Congress authorized $6 million to study the feasibility of a rail link between Alaska, Canada, and the lower 48. Some private companies provides car float service between Whittier and Seattle. Marine transport Many cities, towns and villages in the state do not have road or highway access; the only modes of access involve travel by air, river, or the sea. Alaska's well-developed state-owned ferry system (known as the Alaska Marine Highway) serves the cities of southeast, the Gulf Coast and the Alaska Peninsula.

One unique feature of the Alaska Highway system is the Anton Anderson Memorial Tunnel, an active Alaska Railroad tunnel recently upgraded to provide a paved roadway link with the isolated community of Whittier on Prince William Sound to the Seward Highway about southeast of Anchorage at Portage. At , the tunnel was the longest road tunnel in North America until 2007. The tunnel is the longest combination road and rail tunnel in North America. Rail Built around 1915, the Alaska Railroad (ARR) played a key role in the development of Alaska through the 20th century. It links north Pacific shipping through providing critical infrastructure with tracks that run from Seward to Interior Alaska by way of South Central Alaska, passing through Anchorage, Eklutna, Wasilla, Talkeetna, Denali, and Fairbanks, with spurs to Whittier, Palmer and North Pole. The cities, towns, villages, and region served by ARR tracks are known statewide as "The Railbelt". In recent years, the ever-improving paved highway system began to eclipse the railroad's importance in Alaska's economy. The railroad played a vital role in Alaska's development, moving freight into Alaska while transporting natural resources southward, such as coal from the Usibelli coal mine near Healy to Seward and gravel from the Matanuska Valley to Anchorage. It is well known for its summertime tour passenger service. The Alaska Railroad was one of the last railroads in North America to use cabooses in regular service and still uses them on some gravel trains. It continues to offer one of the last flag stop routes in the country. A stretch of about of track along an area north of Talkeetna remains inaccessible by road; the railroad provides the only transportation to rural homes and cabins in the area. Until construction of the Parks Highway in the 1970s, the railroad provided the only land access to most of the region along its entire route. In northern Southeast Alaska, the White Pass and Yukon Route also partly runs through the state from Skagway northwards into Canada (British Columbia and Yukon Territory), crossing the border at White Pass Summit. This line is now mainly used by tourists, often arriving by cruise liner at Skagway. It was featured in the 1983 BBC television series Great Little Railways. The Alaska Rail network is not connected to Outside. (The nearest link to the North American railway network is the northwest terminus of the Canadian National Railway at Prince Rupert, British Columbia, several hundred miles to the southeast.) In 2000, the U.S. Congress authorized $6 million to study the feasibility of a rail link between Alaska, Canada, and the lower 48. Some private companies provides car float service between Whittier and Seattle. Marine transport Many cities, towns and villages in the state do not have road or highway access; the only modes of access involve travel by air, river, or the sea. Alaska's well-developed state-owned ferry system (known as the Alaska Marine Highway) serves the cities of southeast, the Gulf Coast and the Alaska Peninsula.

One unique feature of the Alaska Highway system is the Anton Anderson Memorial Tunnel, an active Alaska Railroad tunnel recently upgraded to provide a paved roadway link with the isolated community of Whittier on Prince William Sound to the Seward Highway about southeast of Anchorage at Portage. At , the tunnel was the longest road tunnel in North America until 2007. The tunnel is the longest combination road and rail tunnel in North America. Rail Built around 1915, the Alaska Railroad (ARR) played a key role in the development of Alaska through the 20th century. It links north Pacific shipping through providing critical infrastructure with tracks that run from Seward to Interior Alaska by way of South Central Alaska, passing through Anchorage, Eklutna, Wasilla, Talkeetna, Denali, and Fairbanks, with spurs to Whittier, Palmer and North Pole. The cities, towns, villages, and region served by ARR tracks are known statewide as "The Railbelt". In recent years, the ever-improving paved highway system began to eclipse the railroad's importance in Alaska's economy. The railroad played a vital role in Alaska's development, moving freight into Alaska while transporting natural resources southward, such as coal from the Usibelli coal mine near Healy to Seward and gravel from the Matanuska Valley to Anchorage. It is well known for its summertime tour passenger service. The Alaska Railroad was one of the last railroads in North America to use cabooses in regular service and still uses them on some gravel trains. It continues to offer one of the last flag stop routes in the country. A stretch of about of track along an area north of Talkeetna remains inaccessible by road; the railroad provides the only transportation to rural homes and cabins in the area. Until construction of the Parks Highway in the 1970s, the railroad provided the only land access to most of the region along its entire route. In northern Southeast Alaska, the White Pass and Yukon Route also partly runs through the state from Skagway northwards into Canada (British Columbia and Yukon Territory), crossing the border at White Pass Summit. This line is now mainly used by tourists, often arriving by cruise liner at Skagway. It was featured in the 1983 BBC television series Great Little Railways. The Alaska Rail network is not connected to Outside. (The nearest link to the North American railway network is the northwest terminus of the Canadian National Railway at Prince Rupert, British Columbia, several hundred miles to the southeast.) In 2000, the U.S. Congress authorized $6 million to study the feasibility of a rail link between Alaska, Canada, and the lower 48. Some private companies provides car float service between Whittier and Seattle. Marine transport Many cities, towns and villages in the state do not have road or highway access; the only modes of access involve travel by air, river, or the sea. Alaska's well-developed state-owned ferry system (known as the Alaska Marine Highway) serves the cities of southeast, the Gulf Coast and the Alaska Peninsula.

The ferries transport vehicles as well as passengers. The system also operates a ferry service from Bellingham, Washington and Prince Rupert, British Columbia, in Canada through the Inside Passage to Skagway. The Inter-Island Ferry Authority also serves as an important marine link for many communities in the Prince of Wales Island region of Southeast and works in concert with the Alaska Marine Highway. In recent years, cruise lines have created a summertime tourism market, mainly connecting the Pacific Northwest to Southeast Alaska and, to a lesser degree, towns along Alaska's gulf coast. The population of Ketchikan for example fluctuates dramatically on many days—up to four large cruise ships can dock there at the same time. Air transport Cities not served by road, sea, or river can be reached only by air, foot, dogsled, or snowmachine, accounting for Alaska's extremely well developed bush air services—an Alaskan novelty. Anchorage and, to a lesser extent Fairbanks, is served by many major airlines. Because of limited highway access, air travel remains the most efficient form of transportation in and out of the state. Anchorage recently completed extensive remodeling and construction at Ted Stevens Anchorage International Airport to help accommodate the upsurge in tourism (in 2012–2013, Alaska received almost two million visitors). Regular flights to most villages and towns within the state that are commercially viable are challenging to provide, so they are heavily subsidized by the federal government through the Essential Air Service program. Alaska Airlines is the only major airline offering in-state travel with jet service (sometimes in combination cargo and passenger Boeing 737-400s) from Anchorage and Fairbanks to regional hubs like Bethel, Nome, Kotzebue, Dillingham, Kodiak, and other larger communities as well as to major Southeast and Alaska Peninsula communities. The bulk of remaining commercial flight offerings come from small regional commuter airlines such as Ravn Alaska, PenAir, and Frontier Flying Service. The smallest towns and villages must rely on scheduled or chartered bush flying services using general aviation aircraft such as the Cessna Caravan, the most popular aircraft in use in the state. Much of this service can be attributed to the Alaska bypass mail program which subsidizes bulk mail delivery to Alaskan rural communities. The program requires 70% of that subsidy to go to carriers who offer passenger service to the communities. Many communities have small air taxi services. These operations originated from the demand for customized transport to remote areas. Perhaps the most quintessentially Alaskan plane is the bush seaplane. The world's busiest seaplane base is Lake Hood, located next to Ted Stevens Anchorage International Airport, where flights bound for remote villages without an airstrip carry passengers, cargo, and many items from stores and warehouse clubs. In 2006, Alaska had the highest number of pilots per capita of any U.S. state. In Alaska there are 8,795 active pilot certificates as of 2020. Of these, there are 2,507 Private, 1,496 Commercial, 2,180 Airline Transport, and 2,239 Student. There are also 3,987 pilots with a Instrument rating and 1,511 Flight Instructors.

The ferries transport vehicles as well as passengers. The system also operates a ferry service from Bellingham, Washington and Prince Rupert, British Columbia, in Canada through the Inside Passage to Skagway. The Inter-Island Ferry Authority also serves as an important marine link for many communities in the Prince of Wales Island region of Southeast and works in concert with the Alaska Marine Highway. In recent years, cruise lines have created a summertime tourism market, mainly connecting the Pacific Northwest to Southeast Alaska and, to a lesser degree, towns along Alaska's gulf coast. The population of Ketchikan for example fluctuates dramatically on many days—up to four large cruise ships can dock there at the same time. Air transport Cities not served by road, sea, or river can be reached only by air, foot, dogsled, or snowmachine, accounting for Alaska's extremely well developed bush air services—an Alaskan novelty. Anchorage and, to a lesser extent Fairbanks, is served by many major airlines. Because of limited highway access, air travel remains the most efficient form of transportation in and out of the state. Anchorage recently completed extensive remodeling and construction at Ted Stevens Anchorage International Airport to help accommodate the upsurge in tourism (in 2012–2013, Alaska received almost two million visitors). Regular flights to most villages and towns within the state that are commercially viable are challenging to provide, so they are heavily subsidized by the federal government through the Essential Air Service program. Alaska Airlines is the only major airline offering in-state travel with jet service (sometimes in combination cargo and passenger Boeing 737-400s) from Anchorage and Fairbanks to regional hubs like Bethel, Nome, Kotzebue, Dillingham, Kodiak, and other larger communities as well as to major Southeast and Alaska Peninsula communities. The bulk of remaining commercial flight offerings come from small regional commuter airlines such as Ravn Alaska, PenAir, and Frontier Flying Service. The smallest towns and villages must rely on scheduled or chartered bush flying services using general aviation aircraft such as the Cessna Caravan, the most popular aircraft in use in the state. Much of this service can be attributed to the Alaska bypass mail program which subsidizes bulk mail delivery to Alaskan rural communities. The program requires 70% of that subsidy to go to carriers who offer passenger service to the communities. Many communities have small air taxi services. These operations originated from the demand for customized transport to remote areas. Perhaps the most quintessentially Alaskan plane is the bush seaplane. The world's busiest seaplane base is Lake Hood, located next to Ted Stevens Anchorage International Airport, where flights bound for remote villages without an airstrip carry passengers, cargo, and many items from stores and warehouse clubs. In 2006, Alaska had the highest number of pilots per capita of any U.S. state. In Alaska there are 8,795 active pilot certificates as of 2020. Of these, there are 2,507 Private, 1,496 Commercial, 2,180 Airline Transport, and 2,239 Student. There are also 3,987 pilots with a Instrument rating and 1,511 Flight Instructors.

The ferries transport vehicles as well as passengers. The system also operates a ferry service from Bellingham, Washington and Prince Rupert, British Columbia, in Canada through the Inside Passage to Skagway. The Inter-Island Ferry Authority also serves as an important marine link for many communities in the Prince of Wales Island region of Southeast and works in concert with the Alaska Marine Highway. In recent years, cruise lines have created a summertime tourism market, mainly connecting the Pacific Northwest to Southeast Alaska and, to a lesser degree, towns along Alaska's gulf coast. The population of Ketchikan for example fluctuates dramatically on many days—up to four large cruise ships can dock there at the same time. Air transport Cities not served by road, sea, or river can be reached only by air, foot, dogsled, or snowmachine, accounting for Alaska's extremely well developed bush air services—an Alaskan novelty. Anchorage and, to a lesser extent Fairbanks, is served by many major airlines. Because of limited highway access, air travel remains the most efficient form of transportation in and out of the state. Anchorage recently completed extensive remodeling and construction at Ted Stevens Anchorage International Airport to help accommodate the upsurge in tourism (in 2012–2013, Alaska received almost two million visitors). Regular flights to most villages and towns within the state that are commercially viable are challenging to provide, so they are heavily subsidized by the federal government through the Essential Air Service program. Alaska Airlines is the only major airline offering in-state travel with jet service (sometimes in combination cargo and passenger Boeing 737-400s) from Anchorage and Fairbanks to regional hubs like Bethel, Nome, Kotzebue, Dillingham, Kodiak, and other larger communities as well as to major Southeast and Alaska Peninsula communities. The bulk of remaining commercial flight offerings come from small regional commuter airlines such as Ravn Alaska, PenAir, and Frontier Flying Service. The smallest towns and villages must rely on scheduled or chartered bush flying services using general aviation aircraft such as the Cessna Caravan, the most popular aircraft in use in the state. Much of this service can be attributed to the Alaska bypass mail program which subsidizes bulk mail delivery to Alaskan rural communities. The program requires 70% of that subsidy to go to carriers who offer passenger service to the communities. Many communities have small air taxi services. These operations originated from the demand for customized transport to remote areas. Perhaps the most quintessentially Alaskan plane is the bush seaplane. The world's busiest seaplane base is Lake Hood, located next to Ted Stevens Anchorage International Airport, where flights bound for remote villages without an airstrip carry passengers, cargo, and many items from stores and warehouse clubs. In 2006, Alaska had the highest number of pilots per capita of any U.S. state. In Alaska there are 8,795 active pilot certificates as of 2020. Of these, there are 2,507 Private, 1,496 Commercial, 2,180 Airline Transport, and 2,239 Student. There are also 3,987 pilots with a Instrument rating and 1,511 Flight Instructors.

Other transport Another Alaskan transportation method is the dogsled. In modern times (that is, any time after the mid-late 1920s), dog mushing is more of a sport than a true means of transportation. Various races are held around the state, but the best known is the Iditarod Trail Sled Dog Race, a trail from Anchorage to Nome (although the distance varies from year to year, the official distance is set at ). The race commemorates the famous 1925 serum run to Nome in which mushers and dogs like Togo and Balto took much-needed medicine to the diphtheria-stricken community of Nome when all other means of transportation had failed. Mushers from all over the world come to Anchorage each March to compete for cash, prizes, and prestige. The "Serum Run" is another sled dog race that more accurately follows the route of the famous 1925 relay, leaving from the community of Nenana (southwest of Fairbanks) to Nome. In areas not served by road or rail, primary transportation in summer is by all-terrain vehicle and in winter by snowmobile or "snow machine", as it is commonly referred to in Alaska. Data transport Alaska's internet and other data transport systems are provided largely through the two major telecommunications companies: GCI and Alaska Communications. GCI owns and operates what it calls the Alaska United Fiber Optic system and, as of late 2011, Alaska Communications advertised that it has "two fiber optic paths to the lower 48 and two more across Alaska. In January 2011, it was reported that a $1 billion project to connect Asia and rural Alaska was being planned, aided in part by $350 million in stimulus from the federal government. Law and government State government Like all other U.S. states, Alaska is governed as a republic, with three branches of government: an executive branch consisting of the governor of Alaska and his or her appointees which head executive departments; a legislative branch consisting of the Alaska House of Representatives and Alaska Senate; and a judicial branch consisting of the Alaska Supreme Court and lower courts. The state of Alaska employs approximately 16,000 people statewide. The Alaska Legislature consists of a 40-member House of Representatives and a 20-member Senate. Senators serve four-year terms and House members two. The governor of Alaska serves four-year terms. The lieutenant governor runs separately from the governor in the primaries, but during the general election, the nominee for governor and nominee for lieutenant governor run together on the same ticket. Alaska's court system has four levels: the Alaska Supreme Court, the Alaska Court of Appeals, the superior courts and the district courts. The superior and district courts are trial courts. Superior courts are courts of general jurisdiction, while district courts hear only certain types of cases, including misdemeanor criminal cases and civil cases valued up to $100,000. The Supreme Court and the Court of Appeals are appellate courts.

Other transport Another Alaskan transportation method is the dogsled. In modern times (that is, any time after the mid-late 1920s), dog mushing is more of a sport than a true means of transportation. Various races are held around the state, but the best known is the Iditarod Trail Sled Dog Race, a trail from Anchorage to Nome (although the distance varies from year to year, the official distance is set at ). The race commemorates the famous 1925 serum run to Nome in which mushers and dogs like Togo and Balto took much-needed medicine to the diphtheria-stricken community of Nome when all other means of transportation had failed. Mushers from all over the world come to Anchorage each March to compete for cash, prizes, and prestige. The "Serum Run" is another sled dog race that more accurately follows the route of the famous 1925 relay, leaving from the community of Nenana (southwest of Fairbanks) to Nome. In areas not served by road or rail, primary transportation in summer is by all-terrain vehicle and in winter by snowmobile or "snow machine", as it is commonly referred to in Alaska. Data transport Alaska's internet and other data transport systems are provided largely through the two major telecommunications companies: GCI and Alaska Communications. GCI owns and operates what it calls the Alaska United Fiber Optic system and, as of late 2011, Alaska Communications advertised that it has "two fiber optic paths to the lower 48 and two more across Alaska. In January 2011, it was reported that a $1 billion project to connect Asia and rural Alaska was being planned, aided in part by $350 million in stimulus from the federal government. Law and government State government Like all other U.S. states, Alaska is governed as a republic, with three branches of government: an executive branch consisting of the governor of Alaska and his or her appointees which head executive departments; a legislative branch consisting of the Alaska House of Representatives and Alaska Senate; and a judicial branch consisting of the Alaska Supreme Court and lower courts. The state of Alaska employs approximately 16,000 people statewide. The Alaska Legislature consists of a 40-member House of Representatives and a 20-member Senate. Senators serve four-year terms and House members two. The governor of Alaska serves four-year terms. The lieutenant governor runs separately from the governor in the primaries, but during the general election, the nominee for governor and nominee for lieutenant governor run together on the same ticket. Alaska's court system has four levels: the Alaska Supreme Court, the Alaska Court of Appeals, the superior courts and the district courts. The superior and district courts are trial courts. Superior courts are courts of general jurisdiction, while district courts hear only certain types of cases, including misdemeanor criminal cases and civil cases valued up to $100,000. The Supreme Court and the Court of Appeals are appellate courts.

Other transport Another Alaskan transportation method is the dogsled. In modern times (that is, any time after the mid-late 1920s), dog mushing is more of a sport than a true means of transportation. Various races are held around the state, but the best known is the Iditarod Trail Sled Dog Race, a trail from Anchorage to Nome (although the distance varies from year to year, the official distance is set at ). The race commemorates the famous 1925 serum run to Nome in which mushers and dogs like Togo and Balto took much-needed medicine to the diphtheria-stricken community of Nome when all other means of transportation had failed. Mushers from all over the world come to Anchorage each March to compete for cash, prizes, and prestige. The "Serum Run" is another sled dog race that more accurately follows the route of the famous 1925 relay, leaving from the community of Nenana (southwest of Fairbanks) to Nome. In areas not served by road or rail, primary transportation in summer is by all-terrain vehicle and in winter by snowmobile or "snow machine", as it is commonly referred to in Alaska. Data transport Alaska's internet and other data transport systems are provided largely through the two major telecommunications companies: GCI and Alaska Communications. GCI owns and operates what it calls the Alaska United Fiber Optic system and, as of late 2011, Alaska Communications advertised that it has "two fiber optic paths to the lower 48 and two more across Alaska. In January 2011, it was reported that a $1 billion project to connect Asia and rural Alaska was being planned, aided in part by $350 million in stimulus from the federal government. Law and government State government Like all other U.S. states, Alaska is governed as a republic, with three branches of government: an executive branch consisting of the governor of Alaska and his or her appointees which head executive departments; a legislative branch consisting of the Alaska House of Representatives and Alaska Senate; and a judicial branch consisting of the Alaska Supreme Court and lower courts. The state of Alaska employs approximately 16,000 people statewide. The Alaska Legislature consists of a 40-member House of Representatives and a 20-member Senate. Senators serve four-year terms and House members two. The governor of Alaska serves four-year terms. The lieutenant governor runs separately from the governor in the primaries, but during the general election, the nominee for governor and nominee for lieutenant governor run together on the same ticket. Alaska's court system has four levels: the Alaska Supreme Court, the Alaska Court of Appeals, the superior courts and the district courts. The superior and district courts are trial courts. Superior courts are courts of general jurisdiction, while district courts hear only certain types of cases, including misdemeanor criminal cases and civil cases valued up to $100,000. The Supreme Court and the Court of Appeals are appellate courts.

The Court of Appeals is required to hear appeals from certain lower-court decisions, including those regarding criminal prosecutions, juvenile delinquency, and habeas corpus. The Supreme Court hears civil appeals and may in its discretion hear criminal appeals. State politics Although in its early years of statehood Alaska was a Democratic state, since the early 1970s it has been characterized as Republican-leaning. Local political communities have often worked on issues related to land use development, fishing, tourism, and individual rights. Alaska Natives, while organized in and around their communities, have been active within the Native corporations. These have been given ownership over large tracts of land, which require stewardship. Alaska was formerly the only state in which possession of one ounce or less of marijuana in one's home was completely legal under state law, though the federal law remains in force. The state has an independence movement favoring a vote on secession from the United States, with the Alaskan Independence Party. Six Republicans and four Democrats have served as governor of Alaska. In addition, Republican governor Wally Hickel was elected to the office for a second term in 1990 after leaving the Republican party and briefly joining the Alaskan Independence Party ticket just long enough to be reelected. He officially rejoined the Republican party in 1994. Alaska's voter initiative making marijuana legal took effect on February 24, 2015, placing Alaska alongside Colorado and Washington as the first three U.S. states where recreational marijuana is legal. The new law means people over 21 can consume small amounts of cannabis. The first legal marijuana store opened in Valdez in October 2016. Voter registration Taxes To finance state government operations, Alaska depends primarily on petroleum revenues and federal subsidies. This allows it to have the lowest individual tax burden in the United States. It is one of five states with no sales tax, one of seven states with no individual income tax, and—along with New Hampshire—one of two that has neither. The Department of Revenue Tax Division reports regularly on the state's revenue sources. The Department also issues an annual summary of its operations, including new state laws that directly affect the tax division. In 2014, the Tax Foundation ranked Alaska as having the fourth most "business friendly" tax policy, behind only Wyoming, South Dakota, and Nevada. While Alaska has no state sales tax, 89 municipalities collect a local sales tax, from 1.0 to 7.5%, typically 3–5%. Other local taxes levied include raw fish taxes, hotel, motel, and bed-and-breakfast 'bed' taxes, severance taxes, liquor and tobacco taxes, gaming (pull tabs) taxes, tire taxes and fuel transfer taxes. A part of the revenue collected from certain state taxes and license fees (such as petroleum, aviation motor fuel, telephone cooperative) is shared with municipalities in Alaska. The fall in oil prices after the fracking boom in the early 2010s has decimated Alaska's state treasury, which has historically received about 85 percent of its revenue from taxes and fees imposed on oil and gas companies.

The Court of Appeals is required to hear appeals from certain lower-court decisions, including those regarding criminal prosecutions, juvenile delinquency, and habeas corpus. The Supreme Court hears civil appeals and may in its discretion hear criminal appeals. State politics Although in its early years of statehood Alaska was a Democratic state, since the early 1970s it has been characterized as Republican-leaning. Local political communities have often worked on issues related to land use development, fishing, tourism, and individual rights. Alaska Natives, while organized in and around their communities, have been active within the Native corporations. These have been given ownership over large tracts of land, which require stewardship. Alaska was formerly the only state in which possession of one ounce or less of marijuana in one's home was completely legal under state law, though the federal law remains in force. The state has an independence movement favoring a vote on secession from the United States, with the Alaskan Independence Party. Six Republicans and four Democrats have served as governor of Alaska. In addition, Republican governor Wally Hickel was elected to the office for a second term in 1990 after leaving the Republican party and briefly joining the Alaskan Independence Party ticket just long enough to be reelected. He officially rejoined the Republican party in 1994. Alaska's voter initiative making marijuana legal took effect on February 24, 2015, placing Alaska alongside Colorado and Washington as the first three U.S. states where recreational marijuana is legal. The new law means people over 21 can consume small amounts of cannabis. The first legal marijuana store opened in Valdez in October 2016. Voter registration Taxes To finance state government operations, Alaska depends primarily on petroleum revenues and federal subsidies. This allows it to have the lowest individual tax burden in the United States. It is one of five states with no sales tax, one of seven states with no individual income tax, and—along with New Hampshire—one of two that has neither. The Department of Revenue Tax Division reports regularly on the state's revenue sources. The Department also issues an annual summary of its operations, including new state laws that directly affect the tax division. In 2014, the Tax Foundation ranked Alaska as having the fourth most "business friendly" tax policy, behind only Wyoming, South Dakota, and Nevada. While Alaska has no state sales tax, 89 municipalities collect a local sales tax, from 1.0 to 7.5%, typically 3–5%. Other local taxes levied include raw fish taxes, hotel, motel, and bed-and-breakfast 'bed' taxes, severance taxes, liquor and tobacco taxes, gaming (pull tabs) taxes, tire taxes and fuel transfer taxes. A part of the revenue collected from certain state taxes and license fees (such as petroleum, aviation motor fuel, telephone cooperative) is shared with municipalities in Alaska. The fall in oil prices after the fracking boom in the early 2010s has decimated Alaska's state treasury, which has historically received about 85 percent of its revenue from taxes and fees imposed on oil and gas companies.

The Court of Appeals is required to hear appeals from certain lower-court decisions, including those regarding criminal prosecutions, juvenile delinquency, and habeas corpus. The Supreme Court hears civil appeals and may in its discretion hear criminal appeals. State politics Although in its early years of statehood Alaska was a Democratic state, since the early 1970s it has been characterized as Republican-leaning. Local political communities have often worked on issues related to land use development, fishing, tourism, and individual rights. Alaska Natives, while organized in and around their communities, have been active within the Native corporations. These have been given ownership over large tracts of land, which require stewardship. Alaska was formerly the only state in which possession of one ounce or less of marijuana in one's home was completely legal under state law, though the federal law remains in force. The state has an independence movement favoring a vote on secession from the United States, with the Alaskan Independence Party. Six Republicans and four Democrats have served as governor of Alaska. In addition, Republican governor Wally Hickel was elected to the office for a second term in 1990 after leaving the Republican party and briefly joining the Alaskan Independence Party ticket just long enough to be reelected. He officially rejoined the Republican party in 1994. Alaska's voter initiative making marijuana legal took effect on February 24, 2015, placing Alaska alongside Colorado and Washington as the first three U.S. states where recreational marijuana is legal. The new law means people over 21 can consume small amounts of cannabis. The first legal marijuana store opened in Valdez in October 2016. Voter registration Taxes To finance state government operations, Alaska depends primarily on petroleum revenues and federal subsidies. This allows it to have the lowest individual tax burden in the United States. It is one of five states with no sales tax, one of seven states with no individual income tax, and—along with New Hampshire—one of two that has neither. The Department of Revenue Tax Division reports regularly on the state's revenue sources. The Department also issues an annual summary of its operations, including new state laws that directly affect the tax division. In 2014, the Tax Foundation ranked Alaska as having the fourth most "business friendly" tax policy, behind only Wyoming, South Dakota, and Nevada. While Alaska has no state sales tax, 89 municipalities collect a local sales tax, from 1.0 to 7.5%, typically 3–5%. Other local taxes levied include raw fish taxes, hotel, motel, and bed-and-breakfast 'bed' taxes, severance taxes, liquor and tobacco taxes, gaming (pull tabs) taxes, tire taxes and fuel transfer taxes. A part of the revenue collected from certain state taxes and license fees (such as petroleum, aviation motor fuel, telephone cooperative) is shared with municipalities in Alaska. The fall in oil prices after the fracking boom in the early 2010s has decimated Alaska's state treasury, which has historically received about 85 percent of its revenue from taxes and fees imposed on oil and gas companies.

The state government has had to drastically reduce its budget, and has brought its budget shortfall from over $2 billion in 2016 to under $500 million by 2018. In 2020, Alaska's state government budget was $4.8 billion, while projected government revenues were only $4.5 billion. Federal politics Alaska regularly supports Republicans in presidential elections and has done so since statehood. Republicans have won the state's electoral college votes in all but one election that it has participated in (1964). No state has voted for a Democratic presidential candidate fewer times. Alaska was carried by Democratic nominee Lyndon B. Johnson during his landslide election in 1964, while the 1960 and 1968 elections were close. Since 1972, however, Republicans have carried the state by large margins. In 2008, Republican John McCain defeated Democrat Barack Obama in Alaska, 59.49% to 37.83%. McCain's running mate was Sarah Palin, the state's governor and the first Alaskan on a major party ticket. Obama lost Alaska again in 2012, but he captured 40% of the state's vote in that election, making him the first Democrat to do so since 1968. The Alaska Bush, central Juneau, midtown and downtown Anchorage, and the areas surrounding the University of Alaska Fairbanks campus and Ester have been strongholds of the Democratic Party. The Matanuska-Susitna Borough, the majority of Fairbanks (including North Pole and the military base), and South Anchorage typically have the strongest Republican showing. Elections In a 2020 study, Alaska was ranked as the 15th hardest state for citizens to vote in. In the 2020 election cycle, Alaskan voters approved Ballot Measure 2. The measure passed by a margin of 1.1%, or about 4,000 votes. The measure requires campaigns to disclose the original source and any intermediaries for campaign contributions over $2,000. The measure establishes non-partisan blanket primaries for statewide elections (like in Washington state and California) and ranked-choice voting (like in Maine). Alaska is the third state with jungle primaries for all statewide races, the second state with ranked voting, and the only state with both. The first race to use the new system of elections will be the 2022 Senate election in which Lisa Murkowski will run for re-election. See also Index of Alaska-related articles Outline of Alaska Notes References External links Alaska's Digital Archives Alaska Inter-Tribal Council Who Owns/Manages Alaska? (map) Carl J. Sacarlasen Diary Extracts at Dartmouth College Library M.E. Diemer Alaska Photographs at Dartmouth College Library Alfred Hulse Brooks Photographs and Papers. Yale Collection of Western Americana, Beinecke Rare Book and Manuscript Library.

The state government has had to drastically reduce its budget, and has brought its budget shortfall from over $2 billion in 2016 to under $500 million by 2018. In 2020, Alaska's state government budget was $4.8 billion, while projected government revenues were only $4.5 billion. Federal politics Alaska regularly supports Republicans in presidential elections and has done so since statehood. Republicans have won the state's electoral college votes in all but one election that it has participated in (1964). No state has voted for a Democratic presidential candidate fewer times. Alaska was carried by Democratic nominee Lyndon B. Johnson during his landslide election in 1964, while the 1960 and 1968 elections were close. Since 1972, however, Republicans have carried the state by large margins. In 2008, Republican John McCain defeated Democrat Barack Obama in Alaska, 59.49% to 37.83%. McCain's running mate was Sarah Palin, the state's governor and the first Alaskan on a major party ticket. Obama lost Alaska again in 2012, but he captured 40% of the state's vote in that election, making him the first Democrat to do so since 1968. The Alaska Bush, central Juneau, midtown and downtown Anchorage, and the areas surrounding the University of Alaska Fairbanks campus and Ester have been strongholds of the Democratic Party. The Matanuska-Susitna Borough, the majority of Fairbanks (including North Pole and the military base), and South Anchorage typically have the strongest Republican showing. Elections In a 2020 study, Alaska was ranked as the 15th hardest state for citizens to vote in. In the 2020 election cycle, Alaskan voters approved Ballot Measure 2. The measure passed by a margin of 1.1%, or about 4,000 votes. The measure requires campaigns to disclose the original source and any intermediaries for campaign contributions over $2,000. The measure establishes non-partisan blanket primaries for statewide elections (like in Washington state and California) and ranked-choice voting (like in Maine). Alaska is the third state with jungle primaries for all statewide races, the second state with ranked voting, and the only state with both. The first race to use the new system of elections will be the 2022 Senate election in which Lisa Murkowski will run for re-election. See also Index of Alaska-related articles Outline of Alaska Notes References External links Alaska's Digital Archives Alaska Inter-Tribal Council Who Owns/Manages Alaska? (map) Carl J. Sacarlasen Diary Extracts at Dartmouth College Library M.E. Diemer Alaska Photographs at Dartmouth College Library Alfred Hulse Brooks Photographs and Papers. Yale Collection of Western Americana, Beinecke Rare Book and Manuscript Library.

The state government has had to drastically reduce its budget, and has brought its budget shortfall from over $2 billion in 2016 to under $500 million by 2018. In 2020, Alaska's state government budget was $4.8 billion, while projected government revenues were only $4.5 billion. Federal politics Alaska regularly supports Republicans in presidential elections and has done so since statehood. Republicans have won the state's electoral college votes in all but one election that it has participated in (1964). No state has voted for a Democratic presidential candidate fewer times. Alaska was carried by Democratic nominee Lyndon B. Johnson during his landslide election in 1964, while the 1960 and 1968 elections were close. Since 1972, however, Republicans have carried the state by large margins. In 2008, Republican John McCain defeated Democrat Barack Obama in Alaska, 59.49% to 37.83%. McCain's running mate was Sarah Palin, the state's governor and the first Alaskan on a major party ticket. Obama lost Alaska again in 2012, but he captured 40% of the state's vote in that election, making him the first Democrat to do so since 1968. The Alaska Bush, central Juneau, midtown and downtown Anchorage, and the areas surrounding the University of Alaska Fairbanks campus and Ester have been strongholds of the Democratic Party. The Matanuska-Susitna Borough, the majority of Fairbanks (including North Pole and the military base), and South Anchorage typically have the strongest Republican showing. Elections In a 2020 study, Alaska was ranked as the 15th hardest state for citizens to vote in. In the 2020 election cycle, Alaskan voters approved Ballot Measure 2. The measure passed by a margin of 1.1%, or about 4,000 votes. The measure requires campaigns to disclose the original source and any intermediaries for campaign contributions over $2,000. The measure establishes non-partisan blanket primaries for statewide elections (like in Washington state and California) and ranked-choice voting (like in Maine). Alaska is the third state with jungle primaries for all statewide races, the second state with ranked voting, and the only state with both. The first race to use the new system of elections will be the 2022 Senate election in which Lisa Murkowski will run for re-election. See also Index of Alaska-related articles Outline of Alaska Notes References External links Alaska's Digital Archives Alaska Inter-Tribal Council Who Owns/Manages Alaska? (map) Carl J. Sacarlasen Diary Extracts at Dartmouth College Library M.E. Diemer Alaska Photographs at Dartmouth College Library Alfred Hulse Brooks Photographs and Papers. Yale Collection of Western Americana, Beinecke Rare Book and Manuscript Library.

U.S. federal government Alaska State Guide from the Library of Congress Energy & Environmental Data for Alaska USGS real-time, geographic, and other scientific resources of Alaska US Census Bureau Alaska State Facts Alaska Statehood Subject Guide from the Eisenhower Presidential Library Alaska Statehood documents, Dwight D. Eisenhower Presidential Library Alaska state government State of Alaska website Alaska State Databases Alaska Department of Natural Resources, Recorder's Office Arctic Ocean Former Russian colonies States and territories established in 1959 States of the United States States of the West Coast of the United States U.S. states with multiple time zones 1959 establishments in the United States Western United States Northern America Enclaves and exclaves Beringia

U.S. federal government Alaska State Guide from the Library of Congress Energy & Environmental Data for Alaska USGS real-time, geographic, and other scientific resources of Alaska US Census Bureau Alaska State Facts Alaska Statehood Subject Guide from the Eisenhower Presidential Library Alaska Statehood documents, Dwight D. Eisenhower Presidential Library Alaska state government State of Alaska website Alaska State Databases Alaska Department of Natural Resources, Recorder's Office Arctic Ocean Former Russian colonies States and territories established in 1959 States of the United States States of the West Coast of the United States U.S. states with multiple time zones 1959 establishments in the United States Western United States Northern America Enclaves and exclaves Beringia

U.S. federal government Alaska State Guide from the Library of Congress Energy & Environmental Data for Alaska USGS real-time, geographic, and other scientific resources of Alaska US Census Bureau Alaska State Facts Alaska Statehood Subject Guide from the Eisenhower Presidential Library Alaska Statehood documents, Dwight D. Eisenhower Presidential Library Alaska state government State of Alaska website Alaska State Databases Alaska Department of Natural Resources, Recorder's Office Arctic Ocean Former Russian colonies States and territories established in 1959 States of the United States States of the West Coast of the United States U.S. states with multiple time zones 1959 establishments in the United States Western United States Northern America Enclaves and exclaves Beringia

Agriculture Agriculture is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to live in cities. The history of agriculture began thousands of years ago. After gathering wild grains beginning at least 105,000 years ago, nascent farmers began to plant them around 11,500 years ago. Pigs, sheep, and cattle were domesticated over 10,000 years ago. Plants were independently cultivated in at least 11 regions of the world. Industrial agriculture based on large-scale monoculture in the twentieth century came to dominate agricultural output, though about 2 billion people still depended on subsistence agriculture. The major agricultural products can be broadly grouped into foods, fibers, fuels and raw materials (such as rubber). Food classes include cereals (grains), vegetables, fruits, oils, meat, milk, eggs and fungi. Over one-third of the world's workers are employed in agriculture, second only to the service sector, although in recent decades, the global trend of a decreasing number of agricultural workers continues, especially in developing countries where smallholding is being overtaken by industrial agriculture and mechanization that brings an enormous crop yield increase. Modern agronomy, plant breeding, agrochemicals such as pesticides and fertilizers, and technological developments have sharply increased crop yields, but causing ecological and environmental damage. Selective breeding and modern practices in animal husbandry have similarly increased the output of meat, but have raised concerns about animal welfare and environmental damage. Environmental issues include contributions to global warming, depletion of aquifers, deforestation, antibiotic resistance, and growth hormones in industrial meat production. Agriculture is both a cause of and sensitive to environmental degradation, such as biodiversity loss, desertification, soil degradation and global warming, all of which can cause decreases in crop yield. Genetically modified organisms are widely used, although some are banned in certain countries. Etymology and scope The word agriculture is a late Middle English adaptation of Latin , from 'field' and 'cultivation' or 'growing'. While agriculture usually refers to human activities, certain species of ant, termite and beetle have been cultivating crops for up to 60 million years. Agriculture is defined with varying scopes, in its broadest sense using natural resources to "produce commodities which maintain life, including food, fiber, forest products, horticultural crops, and their related services". Thus defined, it includes arable farming, horticulture, animal husbandry and forestry, but horticulture and forestry are in practice often excluded. History Origins The development of agriculture enabled the human population to grow many times larger than could be sustained by hunting and gathering. Agriculture began independently in different parts of the globe, and included a diverse range of taxa, in at least 11 separate centres of origin. Wild grains were collected and eaten from at least 105,000 years ago. From around 11,500 years ago, the eight Neolithic founder crops, emmer and einkorn wheat, hulled barley, peas, lentils, bitter vetch, chick peas and flax were cultivated in the Levant.

Agriculture Agriculture is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to live in cities. The history of agriculture began thousands of years ago. After gathering wild grains beginning at least 105,000 years ago, nascent farmers began to plant them around 11,500 years ago. Pigs, sheep, and cattle were domesticated over 10,000 years ago. Plants were independently cultivated in at least 11 regions of the world. Industrial agriculture based on large-scale monoculture in the twentieth century came to dominate agricultural output, though about 2 billion people still depended on subsistence agriculture. The major agricultural products can be broadly grouped into foods, fibers, fuels and raw materials (such as rubber). Food classes include cereals (grains), vegetables, fruits, oils, meat, milk, eggs and fungi. Over one-third of the world's workers are employed in agriculture, second only to the service sector, although in recent decades, the global trend of a decreasing number of agricultural workers continues, especially in developing countries where smallholding is being overtaken by industrial agriculture and mechanization that brings an enormous crop yield increase. Modern agronomy, plant breeding, agrochemicals such as pesticides and fertilizers, and technological developments have sharply increased crop yields, but causing ecological and environmental damage. Selective breeding and modern practices in animal husbandry have similarly increased the output of meat, but have raised concerns about animal welfare and environmental damage. Environmental issues include contributions to global warming, depletion of aquifers, deforestation, antibiotic resistance, and growth hormones in industrial meat production. Agriculture is both a cause of and sensitive to environmental degradation, such as biodiversity loss, desertification, soil degradation and global warming, all of which can cause decreases in crop yield. Genetically modified organisms are widely used, although some are banned in certain countries. Etymology and scope The word agriculture is a late Middle English adaptation of Latin , from 'field' and 'cultivation' or 'growing'. While agriculture usually refers to human activities, certain species of ant, termite and beetle have been cultivating crops for up to 60 million years. Agriculture is defined with varying scopes, in its broadest sense using natural resources to "produce commodities which maintain life, including food, fiber, forest products, horticultural crops, and their related services". Thus defined, it includes arable farming, horticulture, animal husbandry and forestry, but horticulture and forestry are in practice often excluded. History Origins The development of agriculture enabled the human population to grow many times larger than could be sustained by hunting and gathering. Agriculture began independently in different parts of the globe, and included a diverse range of taxa, in at least 11 separate centres of origin. Wild grains were collected and eaten from at least 105,000 years ago. From around 11,500 years ago, the eight Neolithic founder crops, emmer and einkorn wheat, hulled barley, peas, lentils, bitter vetch, chick peas and flax were cultivated in the Levant.

Rice was domesticated in China between 11,500 and 6,200 BC with the earliest known cultivation from 5,700 BC, followed by mung, soy and azuki beans. Sheep were domesticated in Mesopotamia between 13,000 and 11,000 years ago. Cattle were domesticated from the wild aurochs in the areas of modern Turkey and Pakistan some 10,500 years ago. Pig production emerged in Eurasia, including Europe, East Asia and Southwest Asia, where wild boar were first domesticated about 10,500 years ago. In the Andes of South America, the potato was domesticated between 10,000 and 7,000 years ago, along with beans, coca, llamas, alpacas, and guinea pigs. Sugarcane and some root vegetables were domesticated in New Guinea around 9,000 years ago. Sorghum was domesticated in the Sahel region of Africa by 7,000 years ago. Cotton was domesticated in Peru by 5,600 years ago, and was independently domesticated in Eurasia. In Mesoamerica, wild teosinte was bred into maize by 6,000 years ago. Scholars have offered multiple hypotheses to explain the historical origins of agriculture. Studies of the transition from hunter-gatherer to agricultural societies indicate an initial period of intensification and increasing sedentism; examples are the Natufian culture in the Levant, and the Early Chinese Neolithic in China. Then, wild stands that had previously been harvested started to be planted, and gradually came to be domesticated. Civilizations In Eurasia, the Sumerians started to live in villages from about 8,000 BC, relying on the Tigris and Euphrates rivers and a canal system for irrigation. Ploughs appear in pictographs around 3,000 BC; seed-ploughs around 2,300 BC. Farmers grew wheat, barley, vegetables such as lentils and onions, and fruits including dates, grapes, and figs. Ancient Egyptian agriculture relied on the Nile River and its seasonal flooding. Farming started in the predynastic period at the end of the Paleolithic, after 10,000 BC. Staple food crops were grains such as wheat and barley, alongside industrial crops such as flax and papyrus. In India, wheat, barley and jujube were domesticated by 9,000 BC, soon followed by sheep and goats. Cattle, sheep and goats were domesticated in Mehrgarh culture by 8,000–6,000 BC. Cotton was cultivated by the 5th–4th millennium BC. Archeological evidence indicates an animal-drawn plough from 2,500 BC in the Indus Valley Civilisation. In China, from the 5th century BC there was a nationwide granary system and widespread silk farming. Water-powered grain mills were in use by the 1st century BC, followed by irrigation. By the late 2nd century, heavy ploughs had been developed with iron ploughshares and mouldboards. These spread westwards across Eurasia. Asian rice was domesticated 8,200–13,500 years ago – depending on the molecular clock estimate that is used – on the Pearl River in southern China with a single genetic origin from the wild rice Oryza rufipogon. In Greece and Rome, the major cereals were wheat, emmer, and barley, alongside vegetables including peas, beans, and olives. Sheep and goats were kept mainly for dairy products. In the Americas, crops domesticated in Mesoamerica (apart from teosinte) include squash, beans, and cacao.

Rice was domesticated in China between 11,500 and 6,200 BC with the earliest known cultivation from 5,700 BC, followed by mung, soy and azuki beans. Sheep were domesticated in Mesopotamia between 13,000 and 11,000 years ago. Cattle were domesticated from the wild aurochs in the areas of modern Turkey and Pakistan some 10,500 years ago. Pig production emerged in Eurasia, including Europe, East Asia and Southwest Asia, where wild boar were first domesticated about 10,500 years ago. In the Andes of South America, the potato was domesticated between 10,000 and 7,000 years ago, along with beans, coca, llamas, alpacas, and guinea pigs. Sugarcane and some root vegetables were domesticated in New Guinea around 9,000 years ago. Sorghum was domesticated in the Sahel region of Africa by 7,000 years ago. Cotton was domesticated in Peru by 5,600 years ago, and was independently domesticated in Eurasia. In Mesoamerica, wild teosinte was bred into maize by 6,000 years ago. Scholars have offered multiple hypotheses to explain the historical origins of agriculture. Studies of the transition from hunter-gatherer to agricultural societies indicate an initial period of intensification and increasing sedentism; examples are the Natufian culture in the Levant, and the Early Chinese Neolithic in China. Then, wild stands that had previously been harvested started to be planted, and gradually came to be domesticated. Civilizations In Eurasia, the Sumerians started to live in villages from about 8,000 BC, relying on the Tigris and Euphrates rivers and a canal system for irrigation. Ploughs appear in pictographs around 3,000 BC; seed-ploughs around 2,300 BC. Farmers grew wheat, barley, vegetables such as lentils and onions, and fruits including dates, grapes, and figs. Ancient Egyptian agriculture relied on the Nile River and its seasonal flooding. Farming started in the predynastic period at the end of the Paleolithic, after 10,000 BC. Staple food crops were grains such as wheat and barley, alongside industrial crops such as flax and papyrus. In India, wheat, barley and jujube were domesticated by 9,000 BC, soon followed by sheep and goats. Cattle, sheep and goats were domesticated in Mehrgarh culture by 8,000–6,000 BC. Cotton was cultivated by the 5th–4th millennium BC. Archeological evidence indicates an animal-drawn plough from 2,500 BC in the Indus Valley Civilisation. In China, from the 5th century BC there was a nationwide granary system and widespread silk farming. Water-powered grain mills were in use by the 1st century BC, followed by irrigation. By the late 2nd century, heavy ploughs had been developed with iron ploughshares and mouldboards. These spread westwards across Eurasia. Asian rice was domesticated 8,200–13,500 years ago – depending on the molecular clock estimate that is used – on the Pearl River in southern China with a single genetic origin from the wild rice Oryza rufipogon. In Greece and Rome, the major cereals were wheat, emmer, and barley, alongside vegetables including peas, beans, and olives. Sheep and goats were kept mainly for dairy products. In the Americas, crops domesticated in Mesoamerica (apart from teosinte) include squash, beans, and cacao.

Rice was domesticated in China between 11,500 and 6,200 BC with the earliest known cultivation from 5,700 BC, followed by mung, soy and azuki beans. Sheep were domesticated in Mesopotamia between 13,000 and 11,000 years ago. Cattle were domesticated from the wild aurochs in the areas of modern Turkey and Pakistan some 10,500 years ago. Pig production emerged in Eurasia, including Europe, East Asia and Southwest Asia, where wild boar were first domesticated about 10,500 years ago. In the Andes of South America, the potato was domesticated between 10,000 and 7,000 years ago, along with beans, coca, llamas, alpacas, and guinea pigs. Sugarcane and some root vegetables were domesticated in New Guinea around 9,000 years ago. Sorghum was domesticated in the Sahel region of Africa by 7,000 years ago. Cotton was domesticated in Peru by 5,600 years ago, and was independently domesticated in Eurasia. In Mesoamerica, wild teosinte was bred into maize by 6,000 years ago. Scholars have offered multiple hypotheses to explain the historical origins of agriculture. Studies of the transition from hunter-gatherer to agricultural societies indicate an initial period of intensification and increasing sedentism; examples are the Natufian culture in the Levant, and the Early Chinese Neolithic in China. Then, wild stands that had previously been harvested started to be planted, and gradually came to be domesticated. Civilizations In Eurasia, the Sumerians started to live in villages from about 8,000 BC, relying on the Tigris and Euphrates rivers and a canal system for irrigation. Ploughs appear in pictographs around 3,000 BC; seed-ploughs around 2,300 BC. Farmers grew wheat, barley, vegetables such as lentils and onions, and fruits including dates, grapes, and figs. Ancient Egyptian agriculture relied on the Nile River and its seasonal flooding. Farming started in the predynastic period at the end of the Paleolithic, after 10,000 BC. Staple food crops were grains such as wheat and barley, alongside industrial crops such as flax and papyrus. In India, wheat, barley and jujube were domesticated by 9,000 BC, soon followed by sheep and goats. Cattle, sheep and goats were domesticated in Mehrgarh culture by 8,000–6,000 BC. Cotton was cultivated by the 5th–4th millennium BC. Archeological evidence indicates an animal-drawn plough from 2,500 BC in the Indus Valley Civilisation. In China, from the 5th century BC there was a nationwide granary system and widespread silk farming. Water-powered grain mills were in use by the 1st century BC, followed by irrigation. By the late 2nd century, heavy ploughs had been developed with iron ploughshares and mouldboards. These spread westwards across Eurasia. Asian rice was domesticated 8,200–13,500 years ago – depending on the molecular clock estimate that is used – on the Pearl River in southern China with a single genetic origin from the wild rice Oryza rufipogon. In Greece and Rome, the major cereals were wheat, emmer, and barley, alongside vegetables including peas, beans, and olives. Sheep and goats were kept mainly for dairy products. In the Americas, crops domesticated in Mesoamerica (apart from teosinte) include squash, beans, and cacao.

Cocoa was being domesticated by the Mayo Chinchipe of the upper Amazon around 3,000 BC. The turkey was probably domesticated in Mexico or the American Southwest. The Aztecs developed irrigation systems, formed terraced hillsides, fertilized their soil, and developed chinampas or artificial islands. The Mayas used extensive canal and raised field systems to farm swampland from 400 BC. Coca was domesticated in the Andes, as were the peanut, tomato, tobacco, and pineapple. Cotton was domesticated in Peru by 3,600 BC. Animals including llamas, alpacas, and guinea pigs were domesticated there. In North America, the indigenous people of the East domesticated crops such as sunflower, tobacco, squash and Chenopodium. Wild foods including wild rice and maple sugar were harvested. The domesticated strawberry is a hybrid of a Chilean and a North American species, developed by breeding in Europe and North America. The indigenous people of the Southwest and the Pacific Northwest practiced forest gardening and fire-stick farming. The natives controlled fire on a regional scale to create a low-intensity fire ecology that sustained a low-density agriculture in loose rotation; a sort of "wild" permaculture. A system of companion planting called the Three Sisters was developed in North America. The three crops were winter squash, maize, and climbing beans. Indigenous Australians, long supposed to have been nomadic hunter-gatherers, practised systematic burning, possibly to enhance natural productivity in fire-stick farming. Scholars have pointed out that hunter-gatherers need a productive environment to support gathering without cultivation. Because the forests of New Guinea have few food plants, early humans may have used "selective burning" to increase the productivity of the wild karuka fruit trees to support the hunter-gatherer way of life. The Gunditjmara and other groups developed eel farming and fish trapping systems from some 5,000 years ago. There is evidence of 'intensification' across the whole continent over that period. In two regions of Australia, the central west coast and eastern central, early farmers cultivated yams, native millet, and bush onions, possibly in permanent settlements. Revolution In the Middle Ages, both in Europe and in the Islamic world, agriculture transformed with improved techniques and the diffusion of crop plants, including the introduction of sugar, rice, cotton and fruit trees (such as the orange) to Europe by way of Al-Andalus. After 1492 the Columbian exchange brought New World crops such as maize, potatoes, tomatoes, sweet potatoes and manioc to Europe, and Old World crops such as wheat, barley, rice and turnips, and livestock (including horses, cattle, sheep and goats) to the Americas. Irrigation, crop rotation, and fertilizers advanced from the 17th century with the British Agricultural Revolution, allowing global population to rise significantly. Since 1900 agriculture in developed nations, and to a lesser extent in the developing world, has seen large rises in productivity as mechanization replaces human labor, and assisted by synthetic fertilizers, pesticides, and selective breeding. The Haber-Bosch method allowed the synthesis of ammonium nitrate fertilizer on an industrial scale, greatly increasing crop yields and sustaining a further increase in global population.

Cocoa was being domesticated by the Mayo Chinchipe of the upper Amazon around 3,000 BC. The turkey was probably domesticated in Mexico or the American Southwest. The Aztecs developed irrigation systems, formed terraced hillsides, fertilized their soil, and developed chinampas or artificial islands. The Mayas used extensive canal and raised field systems to farm swampland from 400 BC. Coca was domesticated in the Andes, as were the peanut, tomato, tobacco, and pineapple. Cotton was domesticated in Peru by 3,600 BC. Animals including llamas, alpacas, and guinea pigs were domesticated there. In North America, the indigenous people of the East domesticated crops such as sunflower, tobacco, squash and Chenopodium. Wild foods including wild rice and maple sugar were harvested. The domesticated strawberry is a hybrid of a Chilean and a North American species, developed by breeding in Europe and North America. The indigenous people of the Southwest and the Pacific Northwest practiced forest gardening and fire-stick farming. The natives controlled fire on a regional scale to create a low-intensity fire ecology that sustained a low-density agriculture in loose rotation; a sort of "wild" permaculture. A system of companion planting called the Three Sisters was developed in North America. The three crops were winter squash, maize, and climbing beans. Indigenous Australians, long supposed to have been nomadic hunter-gatherers, practised systematic burning, possibly to enhance natural productivity in fire-stick farming. Scholars have pointed out that hunter-gatherers need a productive environment to support gathering without cultivation. Because the forests of New Guinea have few food plants, early humans may have used "selective burning" to increase the productivity of the wild karuka fruit trees to support the hunter-gatherer way of life. The Gunditjmara and other groups developed eel farming and fish trapping systems from some 5,000 years ago. There is evidence of 'intensification' across the whole continent over that period. In two regions of Australia, the central west coast and eastern central, early farmers cultivated yams, native millet, and bush onions, possibly in permanent settlements. Revolution In the Middle Ages, both in Europe and in the Islamic world, agriculture transformed with improved techniques and the diffusion of crop plants, including the introduction of sugar, rice, cotton and fruit trees (such as the orange) to Europe by way of Al-Andalus. After 1492 the Columbian exchange brought New World crops such as maize, potatoes, tomatoes, sweet potatoes and manioc to Europe, and Old World crops such as wheat, barley, rice and turnips, and livestock (including horses, cattle, sheep and goats) to the Americas. Irrigation, crop rotation, and fertilizers advanced from the 17th century with the British Agricultural Revolution, allowing global population to rise significantly. Since 1900 agriculture in developed nations, and to a lesser extent in the developing world, has seen large rises in productivity as mechanization replaces human labor, and assisted by synthetic fertilizers, pesticides, and selective breeding. The Haber-Bosch method allowed the synthesis of ammonium nitrate fertilizer on an industrial scale, greatly increasing crop yields and sustaining a further increase in global population.

Cocoa was being domesticated by the Mayo Chinchipe of the upper Amazon around 3,000 BC. The turkey was probably domesticated in Mexico or the American Southwest. The Aztecs developed irrigation systems, formed terraced hillsides, fertilized their soil, and developed chinampas or artificial islands. The Mayas used extensive canal and raised field systems to farm swampland from 400 BC. Coca was domesticated in the Andes, as were the peanut, tomato, tobacco, and pineapple. Cotton was domesticated in Peru by 3,600 BC. Animals including llamas, alpacas, and guinea pigs were domesticated there. In North America, the indigenous people of the East domesticated crops such as sunflower, tobacco, squash and Chenopodium. Wild foods including wild rice and maple sugar were harvested. The domesticated strawberry is a hybrid of a Chilean and a North American species, developed by breeding in Europe and North America. The indigenous people of the Southwest and the Pacific Northwest practiced forest gardening and fire-stick farming. The natives controlled fire on a regional scale to create a low-intensity fire ecology that sustained a low-density agriculture in loose rotation; a sort of "wild" permaculture. A system of companion planting called the Three Sisters was developed in North America. The three crops were winter squash, maize, and climbing beans. Indigenous Australians, long supposed to have been nomadic hunter-gatherers, practised systematic burning, possibly to enhance natural productivity in fire-stick farming. Scholars have pointed out that hunter-gatherers need a productive environment to support gathering without cultivation. Because the forests of New Guinea have few food plants, early humans may have used "selective burning" to increase the productivity of the wild karuka fruit trees to support the hunter-gatherer way of life. The Gunditjmara and other groups developed eel farming and fish trapping systems from some 5,000 years ago. There is evidence of 'intensification' across the whole continent over that period. In two regions of Australia, the central west coast and eastern central, early farmers cultivated yams, native millet, and bush onions, possibly in permanent settlements. Revolution In the Middle Ages, both in Europe and in the Islamic world, agriculture transformed with improved techniques and the diffusion of crop plants, including the introduction of sugar, rice, cotton and fruit trees (such as the orange) to Europe by way of Al-Andalus. After 1492 the Columbian exchange brought New World crops such as maize, potatoes, tomatoes, sweet potatoes and manioc to Europe, and Old World crops such as wheat, barley, rice and turnips, and livestock (including horses, cattle, sheep and goats) to the Americas. Irrigation, crop rotation, and fertilizers advanced from the 17th century with the British Agricultural Revolution, allowing global population to rise significantly. Since 1900 agriculture in developed nations, and to a lesser extent in the developing world, has seen large rises in productivity as mechanization replaces human labor, and assisted by synthetic fertilizers, pesticides, and selective breeding. The Haber-Bosch method allowed the synthesis of ammonium nitrate fertilizer on an industrial scale, greatly increasing crop yields and sustaining a further increase in global population.

Modern agriculture has raised or encountered ecological, political, and economic issues including water pollution, biofuels, genetically modified organisms, tariffs and farm subsidies, leading to alternative approaches such as the organic movement. Types Pastoralism involves managing domesticated animals. In nomadic pastoralism, herds of livestock are moved from place to place in search of pasture, fodder, and water. This type of farming is practised in arid and semi-arid regions of Sahara, Central Asia and some parts of India. In shifting cultivation, a small area of forest is cleared by cutting and burning the trees. The cleared land is used for growing crops for a few years until the soil becomes too infertile, and the area is abandoned. Another patch of land is selected and the process is repeated. This type of farming is practiced mainly in areas with abundant rainfall where the forest regenerates quickly. This practice is used in Northeast India, Southeast Asia, and the Amazon Basin. Subsistence farming is practiced to satisfy family or local needs alone, with little left over for transport elsewhere. It is intensively practiced in Monsoon Asia and South-East Asia. An estimated 2.5 billion subsistence farmers worked in 2018, cultivating about 60% of the earth's arable land. Intensive farming is cultivation to maximise productivity, with a low fallow ratio and a high use of inputs (water, fertilizer, pesticide and automation). It is practiced mainly in developed countries. Contemporary agriculture Status From the twentieth century, intensive agriculture increased productivity. It substituted synthetic fertilizers and pesticides for labour, but caused increased water pollution, and often involved farm subsidies. In recent years there has been a backlash against the environmental effects of conventional agriculture, resulting in the organic, regenerative, and sustainable agriculture movements. One of the major forces behind this movement has been the European Union, which first certified organic food in 1991 and began reform of its Common Agricultural Policy (CAP) in 2005 to phase out commodity-linked farm subsidies, also known as decoupling. The growth of organic farming has renewed research in alternative technologies such as integrated pest management, selective breeding, and controlled-environment agriculture. Recent mainstream technological developments include genetically modified food. Demand for non-food biofuel crops, development of former farm lands, rising transportation costs, climate change, growing consumer demand in China and India, and population growth, are threatening food security in many parts of the world. The International Fund for Agricultural Development posits that an increase in smallholder agriculture may be part of the solution to concerns about food prices and overall food security, given the favorable experience of Vietnam. Soil degradation and diseases such as stem rust are major concerns globally; approximately 40% of the world's agricultural land is seriously degraded. By 2015, the agricultural output of China was the largest in the world, followed by the European Union, India and the United States. Economists measure the total factor productivity of agriculture and by this measure agriculture in the United States is roughly 1.7 times more productive than it was in 1948.

Modern agriculture has raised or encountered ecological, political, and economic issues including water pollution, biofuels, genetically modified organisms, tariffs and farm subsidies, leading to alternative approaches such as the organic movement. Types Pastoralism involves managing domesticated animals. In nomadic pastoralism, herds of livestock are moved from place to place in search of pasture, fodder, and water. This type of farming is practised in arid and semi-arid regions of Sahara, Central Asia and some parts of India. In shifting cultivation, a small area of forest is cleared by cutting and burning the trees. The cleared land is used for growing crops for a few years until the soil becomes too infertile, and the area is abandoned. Another patch of land is selected and the process is repeated. This type of farming is practiced mainly in areas with abundant rainfall where the forest regenerates quickly. This practice is used in Northeast India, Southeast Asia, and the Amazon Basin. Subsistence farming is practiced to satisfy family or local needs alone, with little left over for transport elsewhere. It is intensively practiced in Monsoon Asia and South-East Asia. An estimated 2.5 billion subsistence farmers worked in 2018, cultivating about 60% of the earth's arable land. Intensive farming is cultivation to maximise productivity, with a low fallow ratio and a high use of inputs (water, fertilizer, pesticide and automation). It is practiced mainly in developed countries. Contemporary agriculture Status From the twentieth century, intensive agriculture increased productivity. It substituted synthetic fertilizers and pesticides for labour, but caused increased water pollution, and often involved farm subsidies. In recent years there has been a backlash against the environmental effects of conventional agriculture, resulting in the organic, regenerative, and sustainable agriculture movements. One of the major forces behind this movement has been the European Union, which first certified organic food in 1991 and began reform of its Common Agricultural Policy (CAP) in 2005 to phase out commodity-linked farm subsidies, also known as decoupling. The growth of organic farming has renewed research in alternative technologies such as integrated pest management, selective breeding, and controlled-environment agriculture. Recent mainstream technological developments include genetically modified food. Demand for non-food biofuel crops, development of former farm lands, rising transportation costs, climate change, growing consumer demand in China and India, and population growth, are threatening food security in many parts of the world. The International Fund for Agricultural Development posits that an increase in smallholder agriculture may be part of the solution to concerns about food prices and overall food security, given the favorable experience of Vietnam. Soil degradation and diseases such as stem rust are major concerns globally; approximately 40% of the world's agricultural land is seriously degraded. By 2015, the agricultural output of China was the largest in the world, followed by the European Union, India and the United States. Economists measure the total factor productivity of agriculture and by this measure agriculture in the United States is roughly 1.7 times more productive than it was in 1948.

Modern agriculture has raised or encountered ecological, political, and economic issues including water pollution, biofuels, genetically modified organisms, tariffs and farm subsidies, leading to alternative approaches such as the organic movement. Types Pastoralism involves managing domesticated animals. In nomadic pastoralism, herds of livestock are moved from place to place in search of pasture, fodder, and water. This type of farming is practised in arid and semi-arid regions of Sahara, Central Asia and some parts of India. In shifting cultivation, a small area of forest is cleared by cutting and burning the trees. The cleared land is used for growing crops for a few years until the soil becomes too infertile, and the area is abandoned. Another patch of land is selected and the process is repeated. This type of farming is practiced mainly in areas with abundant rainfall where the forest regenerates quickly. This practice is used in Northeast India, Southeast Asia, and the Amazon Basin. Subsistence farming is practiced to satisfy family or local needs alone, with little left over for transport elsewhere. It is intensively practiced in Monsoon Asia and South-East Asia. An estimated 2.5 billion subsistence farmers worked in 2018, cultivating about 60% of the earth's arable land. Intensive farming is cultivation to maximise productivity, with a low fallow ratio and a high use of inputs (water, fertilizer, pesticide and automation). It is practiced mainly in developed countries. Contemporary agriculture Status From the twentieth century, intensive agriculture increased productivity. It substituted synthetic fertilizers and pesticides for labour, but caused increased water pollution, and often involved farm subsidies. In recent years there has been a backlash against the environmental effects of conventional agriculture, resulting in the organic, regenerative, and sustainable agriculture movements. One of the major forces behind this movement has been the European Union, which first certified organic food in 1991 and began reform of its Common Agricultural Policy (CAP) in 2005 to phase out commodity-linked farm subsidies, also known as decoupling. The growth of organic farming has renewed research in alternative technologies such as integrated pest management, selective breeding, and controlled-environment agriculture. Recent mainstream technological developments include genetically modified food. Demand for non-food biofuel crops, development of former farm lands, rising transportation costs, climate change, growing consumer demand in China and India, and population growth, are threatening food security in many parts of the world. The International Fund for Agricultural Development posits that an increase in smallholder agriculture may be part of the solution to concerns about food prices and overall food security, given the favorable experience of Vietnam. Soil degradation and diseases such as stem rust are major concerns globally; approximately 40% of the world's agricultural land is seriously degraded. By 2015, the agricultural output of China was the largest in the world, followed by the European Union, India and the United States. Economists measure the total factor productivity of agriculture and by this measure agriculture in the United States is roughly 1.7 times more productive than it was in 1948.

Workforce Following the three-sector theory, the number of people employed in agriculture and other primary activities (such as fishing) can be more than 80% in the least developed countries, and less than 2% in the most highly developed countries. Since the Industrial Revolution, many countries have made the transition to developed economies, and the proportion of people working in agriculture has steadily fallen. During the 16th century in Europe, for example, between 55 and 75% of the population was engaged in agriculture; by the 19th century, this had dropped to between 35 and 65%. In the same countries today, the figure is less than 10%. At the start of the 21st century, some one billion people, or over 1/3 of the available work force, were employed in agriculture. It constitutes approximately 70% of the global employment of children, and in many countries employs the largest percentage of women of any industry. The service sector overtook the agricultural sector as the largest global employer in 2007. Safety Agriculture, specifically farming, remains a hazardous industry, and farmers worldwide remain at high risk of work-related injuries, lung disease, noise-induced hearing loss, skin diseases, as well as certain cancers related to chemical use and prolonged sun exposure. On industrialized farms, injuries frequently involve the use of agricultural machinery, and a common cause of fatal agricultural injuries in developed countries is tractor rollovers. Pesticides and other chemicals used in farming can be hazardous to worker health, and workers exposed to pesticides may experience illness or have children with birth defects. As an industry in which families commonly share in work and live on the farm itself, entire families can be at risk for injuries, illness, and death. Ages 0–6 May be an especially vulnerable population in agriculture; common causes of fatal injuries among young farm workers include drowning, machinery and motor accidents, including with all-terrain vehicles. The International Labour Organization considers agriculture "one of the most hazardous of all economic sectors". It estimates that the annual work-related death toll among agricultural employees is at least 170,000, twice the average rate of other jobs. In addition, incidences of death, injury and illness related to agricultural activities often go unreported. The organization has developed the Safety and Health in Agriculture Convention, 2001, which covers the range of risks in the agriculture occupation, the prevention of these risks and the role that individuals and organizations engaged in agriculture should play. In the United States, agriculture has been identified by the National Institute for Occupational Safety and Health as a priority industry sector in the National Occupational Research Agenda to identify and provide intervention strategies for occupational health and safety issues. In the European Union, the European Agency for Safety and Health at Work has issued guidelines on implementing health and safety directives in agriculture, livestock farming, horticulture, and forestry. The Agricultural Safety and Health Council of America (ASHCA) also holds a yearly summit to discuss safety. Production Overall production varies by country as listed.

Workforce Following the three-sector theory, the number of people employed in agriculture and other primary activities (such as fishing) can be more than 80% in the least developed countries, and less than 2% in the most highly developed countries. Since the Industrial Revolution, many countries have made the transition to developed economies, and the proportion of people working in agriculture has steadily fallen. During the 16th century in Europe, for example, between 55 and 75% of the population was engaged in agriculture; by the 19th century, this had dropped to between 35 and 65%. In the same countries today, the figure is less than 10%. At the start of the 21st century, some one billion people, or over 1/3 of the available work force, were employed in agriculture. It constitutes approximately 70% of the global employment of children, and in many countries employs the largest percentage of women of any industry. The service sector overtook the agricultural sector as the largest global employer in 2007. Safety Agriculture, specifically farming, remains a hazardous industry, and farmers worldwide remain at high risk of work-related injuries, lung disease, noise-induced hearing loss, skin diseases, as well as certain cancers related to chemical use and prolonged sun exposure. On industrialized farms, injuries frequently involve the use of agricultural machinery, and a common cause of fatal agricultural injuries in developed countries is tractor rollovers. Pesticides and other chemicals used in farming can be hazardous to worker health, and workers exposed to pesticides may experience illness or have children with birth defects. As an industry in which families commonly share in work and live on the farm itself, entire families can be at risk for injuries, illness, and death. Ages 0–6 May be an especially vulnerable population in agriculture; common causes of fatal injuries among young farm workers include drowning, machinery and motor accidents, including with all-terrain vehicles. The International Labour Organization considers agriculture "one of the most hazardous of all economic sectors". It estimates that the annual work-related death toll among agricultural employees is at least 170,000, twice the average rate of other jobs. In addition, incidences of death, injury and illness related to agricultural activities often go unreported. The organization has developed the Safety and Health in Agriculture Convention, 2001, which covers the range of risks in the agriculture occupation, the prevention of these risks and the role that individuals and organizations engaged in agriculture should play. In the United States, agriculture has been identified by the National Institute for Occupational Safety and Health as a priority industry sector in the National Occupational Research Agenda to identify and provide intervention strategies for occupational health and safety issues. In the European Union, the European Agency for Safety and Health at Work has issued guidelines on implementing health and safety directives in agriculture, livestock farming, horticulture, and forestry. The Agricultural Safety and Health Council of America (ASHCA) also holds a yearly summit to discuss safety. Production Overall production varies by country as listed.

Workforce Following the three-sector theory, the number of people employed in agriculture and other primary activities (such as fishing) can be more than 80% in the least developed countries, and less than 2% in the most highly developed countries. Since the Industrial Revolution, many countries have made the transition to developed economies, and the proportion of people working in agriculture has steadily fallen. During the 16th century in Europe, for example, between 55 and 75% of the population was engaged in agriculture; by the 19th century, this had dropped to between 35 and 65%. In the same countries today, the figure is less than 10%. At the start of the 21st century, some one billion people, or over 1/3 of the available work force, were employed in agriculture. It constitutes approximately 70% of the global employment of children, and in many countries employs the largest percentage of women of any industry. The service sector overtook the agricultural sector as the largest global employer in 2007. Safety Agriculture, specifically farming, remains a hazardous industry, and farmers worldwide remain at high risk of work-related injuries, lung disease, noise-induced hearing loss, skin diseases, as well as certain cancers related to chemical use and prolonged sun exposure. On industrialized farms, injuries frequently involve the use of agricultural machinery, and a common cause of fatal agricultural injuries in developed countries is tractor rollovers. Pesticides and other chemicals used in farming can be hazardous to worker health, and workers exposed to pesticides may experience illness or have children with birth defects. As an industry in which families commonly share in work and live on the farm itself, entire families can be at risk for injuries, illness, and death. Ages 0–6 May be an especially vulnerable population in agriculture; common causes of fatal injuries among young farm workers include drowning, machinery and motor accidents, including with all-terrain vehicles. The International Labour Organization considers agriculture "one of the most hazardous of all economic sectors". It estimates that the annual work-related death toll among agricultural employees is at least 170,000, twice the average rate of other jobs. In addition, incidences of death, injury and illness related to agricultural activities often go unreported. The organization has developed the Safety and Health in Agriculture Convention, 2001, which covers the range of risks in the agriculture occupation, the prevention of these risks and the role that individuals and organizations engaged in agriculture should play. In the United States, agriculture has been identified by the National Institute for Occupational Safety and Health as a priority industry sector in the National Occupational Research Agenda to identify and provide intervention strategies for occupational health and safety issues. In the European Union, the European Agency for Safety and Health at Work has issued guidelines on implementing health and safety directives in agriculture, livestock farming, horticulture, and forestry. The Agricultural Safety and Health Council of America (ASHCA) also holds a yearly summit to discuss safety. Production Overall production varies by country as listed.

Crop cultivation systems Cropping systems vary among farms depending on the available resources and constraints; geography and climate of the farm; government policy; economic, social and political pressures; and the philosophy and culture of the farmer. Shifting cultivation (or slash and burn) is a system in which forests are burnt, releasing nutrients to support cultivation of annual and then perennial crops for a period of several years. Then the plot is left fallow to regrow forest, and the farmer moves to a new plot, returning after many more years (10–20). This fallow period is shortened if population density grows, requiring the input of nutrients (fertilizer or manure) and some manual pest control. Annual cultivation is the next phase of intensity in which there is no fallow period. This requires even greater nutrient and pest control inputs. Further industrialization led to the use of monocultures, when one cultivar is planted on a large acreage. Because of the low biodiversity, nutrient use is uniform and pests tend to build up, necessitating the greater use of pesticides and fertilizers. Multiple cropping, in which several crops are grown sequentially in one year, and intercropping, when several crops are grown at the same time, are other kinds of annual cropping systems known as polycultures. In subtropical and arid environments, the timing and extent of agriculture may be limited by rainfall, either not allowing multiple annual crops in a year, or requiring irrigation. In all of these environments perennial crops are grown (coffee, chocolate) and systems are practiced such as agroforestry. In temperate environments, where ecosystems were predominantly grassland or prairie, highly productive annual farming is the dominant agricultural system. Important categories of food crops include cereals, legumes, forage, fruits and vegetables. Natural fibers include cotton, wool, hemp, silk and flax. Specific crops are cultivated in distinct growing regions throughout the world. Production is listed in millions of metric tons, based on FAO estimates. Livestock production systems Animal husbandry is the breeding and raising of animals for meat, milk, eggs, or wool, and for work and transport. Working animals, including horses, mules, oxen, water buffalo, camels, llamas, alpacas, donkeys, and dogs, have for centuries been used to help cultivate fields, harvest crops, wrangle other animals, and transport farm products to buyers. Livestock production systems can be defined based on feed source, as grassland-based, mixed, and landless. , 30% of Earth's ice- and water-free area was used for producing livestock, with the sector employing approximately 1.3 billion people. Between the 1960s and the 2000s, there was a significant increase in livestock production, both by numbers and by carcass weight, especially among beef, pigs and chickens, the latter of which had production increased by almost a factor of 10. Non-meat animals, such as milk cows and egg-producing chickens, also showed significant production increases. Global cattle, sheep and goat populations are expected to continue to increase sharply through 2050.

Crop cultivation systems Cropping systems vary among farms depending on the available resources and constraints; geography and climate of the farm; government policy; economic, social and political pressures; and the philosophy and culture of the farmer. Shifting cultivation (or slash and burn) is a system in which forests are burnt, releasing nutrients to support cultivation of annual and then perennial crops for a period of several years. Then the plot is left fallow to regrow forest, and the farmer moves to a new plot, returning after many more years (10–20). This fallow period is shortened if population density grows, requiring the input of nutrients (fertilizer or manure) and some manual pest control. Annual cultivation is the next phase of intensity in which there is no fallow period. This requires even greater nutrient and pest control inputs. Further industrialization led to the use of monocultures, when one cultivar is planted on a large acreage. Because of the low biodiversity, nutrient use is uniform and pests tend to build up, necessitating the greater use of pesticides and fertilizers. Multiple cropping, in which several crops are grown sequentially in one year, and intercropping, when several crops are grown at the same time, are other kinds of annual cropping systems known as polycultures. In subtropical and arid environments, the timing and extent of agriculture may be limited by rainfall, either not allowing multiple annual crops in a year, or requiring irrigation. In all of these environments perennial crops are grown (coffee, chocolate) and systems are practiced such as agroforestry. In temperate environments, where ecosystems were predominantly grassland or prairie, highly productive annual farming is the dominant agricultural system. Important categories of food crops include cereals, legumes, forage, fruits and vegetables. Natural fibers include cotton, wool, hemp, silk and flax. Specific crops are cultivated in distinct growing regions throughout the world. Production is listed in millions of metric tons, based on FAO estimates. Livestock production systems Animal husbandry is the breeding and raising of animals for meat, milk, eggs, or wool, and for work and transport. Working animals, including horses, mules, oxen, water buffalo, camels, llamas, alpacas, donkeys, and dogs, have for centuries been used to help cultivate fields, harvest crops, wrangle other animals, and transport farm products to buyers. Livestock production systems can be defined based on feed source, as grassland-based, mixed, and landless. , 30% of Earth's ice- and water-free area was used for producing livestock, with the sector employing approximately 1.3 billion people. Between the 1960s and the 2000s, there was a significant increase in livestock production, both by numbers and by carcass weight, especially among beef, pigs and chickens, the latter of which had production increased by almost a factor of 10. Non-meat animals, such as milk cows and egg-producing chickens, also showed significant production increases. Global cattle, sheep and goat populations are expected to continue to increase sharply through 2050.

Crop cultivation systems Cropping systems vary among farms depending on the available resources and constraints; geography and climate of the farm; government policy; economic, social and political pressures; and the philosophy and culture of the farmer. Shifting cultivation (or slash and burn) is a system in which forests are burnt, releasing nutrients to support cultivation of annual and then perennial crops for a period of several years. Then the plot is left fallow to regrow forest, and the farmer moves to a new plot, returning after many more years (10–20). This fallow period is shortened if population density grows, requiring the input of nutrients (fertilizer or manure) and some manual pest control. Annual cultivation is the next phase of intensity in which there is no fallow period. This requires even greater nutrient and pest control inputs. Further industrialization led to the use of monocultures, when one cultivar is planted on a large acreage. Because of the low biodiversity, nutrient use is uniform and pests tend to build up, necessitating the greater use of pesticides and fertilizers. Multiple cropping, in which several crops are grown sequentially in one year, and intercropping, when several crops are grown at the same time, are other kinds of annual cropping systems known as polycultures. In subtropical and arid environments, the timing and extent of agriculture may be limited by rainfall, either not allowing multiple annual crops in a year, or requiring irrigation. In all of these environments perennial crops are grown (coffee, chocolate) and systems are practiced such as agroforestry. In temperate environments, where ecosystems were predominantly grassland or prairie, highly productive annual farming is the dominant agricultural system. Important categories of food crops include cereals, legumes, forage, fruits and vegetables. Natural fibers include cotton, wool, hemp, silk and flax. Specific crops are cultivated in distinct growing regions throughout the world. Production is listed in millions of metric tons, based on FAO estimates. Livestock production systems Animal husbandry is the breeding and raising of animals for meat, milk, eggs, or wool, and for work and transport. Working animals, including horses, mules, oxen, water buffalo, camels, llamas, alpacas, donkeys, and dogs, have for centuries been used to help cultivate fields, harvest crops, wrangle other animals, and transport farm products to buyers. Livestock production systems can be defined based on feed source, as grassland-based, mixed, and landless. , 30% of Earth's ice- and water-free area was used for producing livestock, with the sector employing approximately 1.3 billion people. Between the 1960s and the 2000s, there was a significant increase in livestock production, both by numbers and by carcass weight, especially among beef, pigs and chickens, the latter of which had production increased by almost a factor of 10. Non-meat animals, such as milk cows and egg-producing chickens, also showed significant production increases. Global cattle, sheep and goat populations are expected to continue to increase sharply through 2050.

Aquaculture or fish farming, the production of fish for human consumption in confined operations, is one of the fastest growing sectors of food production, growing at an average of 9% a year between 1975 and 2007. During the second half of the 20th century, producers using selective breeding focused on creating livestock breeds and crossbreeds that increased production, while mostly disregarding the need to preserve genetic diversity. This trend has led to a significant decrease in genetic diversity and resources among livestock breeds, leading to a corresponding decrease in disease resistance and local adaptations previously found among traditional breeds. Grassland based livestock production relies upon plant material such as shrubland, rangeland, and pastures for feeding ruminant animals. Outside nutrient inputs may be used, however manure is returned directly to the grassland as a major nutrient source. This system is particularly important in areas where crop production is not feasible because of climate or soil, representing 30–40 million pastoralists. Mixed production systems use grassland, fodder crops and grain feed crops as feed for ruminant and monogastric (one stomach; mainly chickens and pigs) livestock. Manure is typically recycled in mixed systems as a fertilizer for crops. Landless systems rely upon feed from outside the farm, representing the de-linking of crop and livestock production found more prevalently in Organisation for Economic Co-operation and Development member countries. Synthetic fertilizers are more heavily relied upon for crop production and manure use becomes a challenge as well as a source for pollution. Industrialized countries use these operations to produce much of the global supplies of poultry and pork. Scientists estimate that 75% of the growth in livestock production between 2003 and 2030 will be in confined animal feeding operations, sometimes called factory farming. Much of this growth is happening in developing countries in Asia, with much smaller amounts of growth in Africa. Some of the practices used in commercial livestock production, including the usage of growth hormones, are controversial. Production practices Tillage is the practice of breaking up the soil with tools such as the plow or harrow to prepare for planting, for nutrient incorporation, or for pest control. Tillage varies in intensity from conventional to no-till. It may improve productivity by warming the soil, incorporating fertilizer and controlling weeds, but also renders soil more prone to erosion, triggers the decomposition of organic matter releasing CO2, and reduces the abundance and diversity of soil organisms. Pest control includes the management of weeds, insects, mites, and diseases. Chemical (pesticides), biological (biocontrol), mechanical (tillage), and cultural practices are used. Cultural practices include crop rotation, culling, cover crops, intercropping, composting, avoidance, and resistance. Integrated pest management attempts to use all of these methods to keep pest populations below the number which would cause economic loss, and recommends pesticides as a last resort. Nutrient management includes both the source of nutrient inputs for crop and livestock production, and the method of use of manure produced by livestock. Nutrient inputs can be chemical inorganic fertilizers, manure, green manure, compost and minerals.

Aquaculture or fish farming, the production of fish for human consumption in confined operations, is one of the fastest growing sectors of food production, growing at an average of 9% a year between 1975 and 2007. During the second half of the 20th century, producers using selective breeding focused on creating livestock breeds and crossbreeds that increased production, while mostly disregarding the need to preserve genetic diversity. This trend has led to a significant decrease in genetic diversity and resources among livestock breeds, leading to a corresponding decrease in disease resistance and local adaptations previously found among traditional breeds. Grassland based livestock production relies upon plant material such as shrubland, rangeland, and pastures for feeding ruminant animals. Outside nutrient inputs may be used, however manure is returned directly to the grassland as a major nutrient source. This system is particularly important in areas where crop production is not feasible because of climate or soil, representing 30–40 million pastoralists. Mixed production systems use grassland, fodder crops and grain feed crops as feed for ruminant and monogastric (one stomach; mainly chickens and pigs) livestock. Manure is typically recycled in mixed systems as a fertilizer for crops. Landless systems rely upon feed from outside the farm, representing the de-linking of crop and livestock production found more prevalently in Organisation for Economic Co-operation and Development member countries. Synthetic fertilizers are more heavily relied upon for crop production and manure use becomes a challenge as well as a source for pollution. Industrialized countries use these operations to produce much of the global supplies of poultry and pork. Scientists estimate that 75% of the growth in livestock production between 2003 and 2030 will be in confined animal feeding operations, sometimes called factory farming. Much of this growth is happening in developing countries in Asia, with much smaller amounts of growth in Africa. Some of the practices used in commercial livestock production, including the usage of growth hormones, are controversial. Production practices Tillage is the practice of breaking up the soil with tools such as the plow or harrow to prepare for planting, for nutrient incorporation, or for pest control. Tillage varies in intensity from conventional to no-till. It may improve productivity by warming the soil, incorporating fertilizer and controlling weeds, but also renders soil more prone to erosion, triggers the decomposition of organic matter releasing CO2, and reduces the abundance and diversity of soil organisms. Pest control includes the management of weeds, insects, mites, and diseases. Chemical (pesticides), biological (biocontrol), mechanical (tillage), and cultural practices are used. Cultural practices include crop rotation, culling, cover crops, intercropping, composting, avoidance, and resistance. Integrated pest management attempts to use all of these methods to keep pest populations below the number which would cause economic loss, and recommends pesticides as a last resort. Nutrient management includes both the source of nutrient inputs for crop and livestock production, and the method of use of manure produced by livestock. Nutrient inputs can be chemical inorganic fertilizers, manure, green manure, compost and minerals.

Aquaculture or fish farming, the production of fish for human consumption in confined operations, is one of the fastest growing sectors of food production, growing at an average of 9% a year between 1975 and 2007. During the second half of the 20th century, producers using selective breeding focused on creating livestock breeds and crossbreeds that increased production, while mostly disregarding the need to preserve genetic diversity. This trend has led to a significant decrease in genetic diversity and resources among livestock breeds, leading to a corresponding decrease in disease resistance and local adaptations previously found among traditional breeds. Grassland based livestock production relies upon plant material such as shrubland, rangeland, and pastures for feeding ruminant animals. Outside nutrient inputs may be used, however manure is returned directly to the grassland as a major nutrient source. This system is particularly important in areas where crop production is not feasible because of climate or soil, representing 30–40 million pastoralists. Mixed production systems use grassland, fodder crops and grain feed crops as feed for ruminant and monogastric (one stomach; mainly chickens and pigs) livestock. Manure is typically recycled in mixed systems as a fertilizer for crops. Landless systems rely upon feed from outside the farm, representing the de-linking of crop and livestock production found more prevalently in Organisation for Economic Co-operation and Development member countries. Synthetic fertilizers are more heavily relied upon for crop production and manure use becomes a challenge as well as a source for pollution. Industrialized countries use these operations to produce much of the global supplies of poultry and pork. Scientists estimate that 75% of the growth in livestock production between 2003 and 2030 will be in confined animal feeding operations, sometimes called factory farming. Much of this growth is happening in developing countries in Asia, with much smaller amounts of growth in Africa. Some of the practices used in commercial livestock production, including the usage of growth hormones, are controversial. Production practices Tillage is the practice of breaking up the soil with tools such as the plow or harrow to prepare for planting, for nutrient incorporation, or for pest control. Tillage varies in intensity from conventional to no-till. It may improve productivity by warming the soil, incorporating fertilizer and controlling weeds, but also renders soil more prone to erosion, triggers the decomposition of organic matter releasing CO2, and reduces the abundance and diversity of soil organisms. Pest control includes the management of weeds, insects, mites, and diseases. Chemical (pesticides), biological (biocontrol), mechanical (tillage), and cultural practices are used. Cultural practices include crop rotation, culling, cover crops, intercropping, composting, avoidance, and resistance. Integrated pest management attempts to use all of these methods to keep pest populations below the number which would cause economic loss, and recommends pesticides as a last resort. Nutrient management includes both the source of nutrient inputs for crop and livestock production, and the method of use of manure produced by livestock. Nutrient inputs can be chemical inorganic fertilizers, manure, green manure, compost and minerals.

Crop nutrient use may also be managed using cultural techniques such as crop rotation or a fallow period. Manure is used either by holding livestock where the feed crop is growing, such as in managed intensive rotational grazing, or by spreading either dry or liquid formulations of manure on cropland or pastures. Water management is needed where rainfall is insufficient or variable, which occurs to some degree in most regions of the world. Some farmers use irrigation to supplement rainfall. In other areas such as the Great Plains in the U.S. and Canada, farmers use a fallow year to conserve soil moisture to use for growing a crop in the following year. Agriculture represents 70% of freshwater use worldwide. According to a report by the International Food Policy Research Institute, agricultural technologies will have the greatest impact on food production if adopted in combination with each other; using a model that assessed how eleven technologies could impact agricultural productivity, food security and trade by 2050, the International Food Policy Research Institute found that the number of people at risk from hunger could be reduced by as much as 40% and food prices could be reduced by almost half. Payment for ecosystem services is a method of providing additional incentives to encourage farmers to conserve some aspects of the environment. Measures might include paying for reforestation upstream of a city, to improve the supply of fresh water. Crop alteration and biotechnology Plant breeding Crop alteration has been practiced by humankind for thousands of years, since the beginning of civilization. Altering crops through breeding practices changes the genetic make-up of a plant to develop crops with more beneficial characteristics for humans, for example, larger fruits or seeds, drought-tolerance, or resistance to pests. Significant advances in plant breeding ensued after the work of geneticist Gregor Mendel. His work on dominant and recessive alleles, although initially largely ignored for almost 50 years, gave plant breeders a better understanding of genetics and breeding techniques. Crop breeding includes techniques such as plant selection with desirable traits, self-pollination and cross-pollination, and molecular techniques that genetically modify the organism. Domestication of plants has, over the centuries increased yield, improved disease resistance and drought tolerance, eased harvest and improved the taste and nutritional value of crop plants. Careful selection and breeding have had enormous effects on the characteristics of crop plants. Plant selection and breeding in the 1920s and 1930s improved pasture (grasses and clover) in New Zealand. Extensive X-ray and ultraviolet induced mutagenesis efforts (i.e. primitive genetic engineering) during the 1950s produced the modern commercial varieties of grains such as wheat, corn (maize) and barley. The Green Revolution popularized the use of conventional hybridization to sharply increase yield by creating "high-yielding varieties". For example, average yields of corn (maize) in the US have increased from around 2.5 tons per hectare (t/ha) (40 bushels per acre) in 1900 to about 9.4 t/ha (150 bushels per acre) in 2001.

Crop nutrient use may also be managed using cultural techniques such as crop rotation or a fallow period. Manure is used either by holding livestock where the feed crop is growing, such as in managed intensive rotational grazing, or by spreading either dry or liquid formulations of manure on cropland or pastures. Water management is needed where rainfall is insufficient or variable, which occurs to some degree in most regions of the world. Some farmers use irrigation to supplement rainfall. In other areas such as the Great Plains in the U.S. and Canada, farmers use a fallow year to conserve soil moisture to use for growing a crop in the following year. Agriculture represents 70% of freshwater use worldwide. According to a report by the International Food Policy Research Institute, agricultural technologies will have the greatest impact on food production if adopted in combination with each other; using a model that assessed how eleven technologies could impact agricultural productivity, food security and trade by 2050, the International Food Policy Research Institute found that the number of people at risk from hunger could be reduced by as much as 40% and food prices could be reduced by almost half. Payment for ecosystem services is a method of providing additional incentives to encourage farmers to conserve some aspects of the environment. Measures might include paying for reforestation upstream of a city, to improve the supply of fresh water. Crop alteration and biotechnology Plant breeding Crop alteration has been practiced by humankind for thousands of years, since the beginning of civilization. Altering crops through breeding practices changes the genetic make-up of a plant to develop crops with more beneficial characteristics for humans, for example, larger fruits or seeds, drought-tolerance, or resistance to pests. Significant advances in plant breeding ensued after the work of geneticist Gregor Mendel. His work on dominant and recessive alleles, although initially largely ignored for almost 50 years, gave plant breeders a better understanding of genetics and breeding techniques. Crop breeding includes techniques such as plant selection with desirable traits, self-pollination and cross-pollination, and molecular techniques that genetically modify the organism. Domestication of plants has, over the centuries increased yield, improved disease resistance and drought tolerance, eased harvest and improved the taste and nutritional value of crop plants. Careful selection and breeding have had enormous effects on the characteristics of crop plants. Plant selection and breeding in the 1920s and 1930s improved pasture (grasses and clover) in New Zealand. Extensive X-ray and ultraviolet induced mutagenesis efforts (i.e. primitive genetic engineering) during the 1950s produced the modern commercial varieties of grains such as wheat, corn (maize) and barley. The Green Revolution popularized the use of conventional hybridization to sharply increase yield by creating "high-yielding varieties". For example, average yields of corn (maize) in the US have increased from around 2.5 tons per hectare (t/ha) (40 bushels per acre) in 1900 to about 9.4 t/ha (150 bushels per acre) in 2001.

Crop nutrient use may also be managed using cultural techniques such as crop rotation or a fallow period. Manure is used either by holding livestock where the feed crop is growing, such as in managed intensive rotational grazing, or by spreading either dry or liquid formulations of manure on cropland or pastures. Water management is needed where rainfall is insufficient or variable, which occurs to some degree in most regions of the world. Some farmers use irrigation to supplement rainfall. In other areas such as the Great Plains in the U.S. and Canada, farmers use a fallow year to conserve soil moisture to use for growing a crop in the following year. Agriculture represents 70% of freshwater use worldwide. According to a report by the International Food Policy Research Institute, agricultural technologies will have the greatest impact on food production if adopted in combination with each other; using a model that assessed how eleven technologies could impact agricultural productivity, food security and trade by 2050, the International Food Policy Research Institute found that the number of people at risk from hunger could be reduced by as much as 40% and food prices could be reduced by almost half. Payment for ecosystem services is a method of providing additional incentives to encourage farmers to conserve some aspects of the environment. Measures might include paying for reforestation upstream of a city, to improve the supply of fresh water. Crop alteration and biotechnology Plant breeding Crop alteration has been practiced by humankind for thousands of years, since the beginning of civilization. Altering crops through breeding practices changes the genetic make-up of a plant to develop crops with more beneficial characteristics for humans, for example, larger fruits or seeds, drought-tolerance, or resistance to pests. Significant advances in plant breeding ensued after the work of geneticist Gregor Mendel. His work on dominant and recessive alleles, although initially largely ignored for almost 50 years, gave plant breeders a better understanding of genetics and breeding techniques. Crop breeding includes techniques such as plant selection with desirable traits, self-pollination and cross-pollination, and molecular techniques that genetically modify the organism. Domestication of plants has, over the centuries increased yield, improved disease resistance and drought tolerance, eased harvest and improved the taste and nutritional value of crop plants. Careful selection and breeding have had enormous effects on the characteristics of crop plants. Plant selection and breeding in the 1920s and 1930s improved pasture (grasses and clover) in New Zealand. Extensive X-ray and ultraviolet induced mutagenesis efforts (i.e. primitive genetic engineering) during the 1950s produced the modern commercial varieties of grains such as wheat, corn (maize) and barley. The Green Revolution popularized the use of conventional hybridization to sharply increase yield by creating "high-yielding varieties". For example, average yields of corn (maize) in the US have increased from around 2.5 tons per hectare (t/ha) (40 bushels per acre) in 1900 to about 9.4 t/ha (150 bushels per acre) in 2001.

Similarly, worldwide average wheat yields have increased from less than 1 t/ha in 1900 to more than 2.5 t/ha in 1990. South American average wheat yields are around 2 t/ha, African under 1 t/ha, and Egypt and Arabia up to 3.5 to 4 t/ha with irrigation. In contrast, the average wheat yield in countries such as France is over 8 t/ha. Variations in yields are due mainly to variation in climate, genetics, and the level of intensive farming techniques (use of fertilizers, chemical pest control, growth control to avoid lodging). Genetic engineering Genetically modified organisms (GMO) are organisms whose genetic material has been altered by genetic engineering techniques generally known as recombinant DNA technology. Genetic engineering has expanded the genes available to breeders to use in creating desired germlines for new crops. Increased durability, nutritional content, insect and virus resistance and herbicide tolerance are a few of the attributes bred into crops through genetic engineering. For some, GMO crops cause food safety and food labeling concerns. Numerous countries have placed restrictions on the production, import or use of GMO foods and crops. Currently a global treaty, the Biosafety Protocol, regulates the trade of GMOs. There is ongoing discussion regarding the labeling of foods made from GMOs, and while the EU currently requires all GMO foods to be labeled, the US does not. Herbicide-resistant seed has a gene implanted into its genome that allows the plants to tolerate exposure to herbicides, including glyphosate. These seeds allow the farmer to grow a crop that can be sprayed with herbicides to control weeds without harming the resistant crop. Herbicide-tolerant crops are used by farmers worldwide. With the increasing use of herbicide-tolerant crops, comes an increase in the use of glyphosate-based herbicide sprays. In some areas glyphosate resistant weeds have developed, causing farmers to switch to other herbicides. Some studies also link widespread glyphosate usage to iron deficiencies in some crops, which is both a crop production and a nutritional quality concern, with potential economic and health implications. Other GMO crops used by growers include insect-resistant crops, which have a gene from the soil bacterium Bacillus thuringiensis (Bt), which produces a toxin specific to insects. These crops resist damage by insects. Some believe that similar or better pest-resistance traits can be acquired through traditional breeding practices, and resistance to various pests can be gained through hybridization or cross-pollination with wild species. In some cases, wild species are the primary source of resistance traits; some tomato cultivars that have gained resistance to at least 19 diseases did so through crossing with wild populations of tomatoes. Environmental impact Effects and costs Agriculture is both a cause of and sensitive to environmental degradation, such as biodiversity loss, desertification, soil degradation and global warming, which cause decrease in crop yield. Agriculture is one of the most important drivers of environmental pressures, particularly habitat change, climate change, water use and toxic emissions.

Similarly, worldwide average wheat yields have increased from less than 1 t/ha in 1900 to more than 2.5 t/ha in 1990. South American average wheat yields are around 2 t/ha, African under 1 t/ha, and Egypt and Arabia up to 3.5 to 4 t/ha with irrigation. In contrast, the average wheat yield in countries such as France is over 8 t/ha. Variations in yields are due mainly to variation in climate, genetics, and the level of intensive farming techniques (use of fertilizers, chemical pest control, growth control to avoid lodging). Genetic engineering Genetically modified organisms (GMO) are organisms whose genetic material has been altered by genetic engineering techniques generally known as recombinant DNA technology. Genetic engineering has expanded the genes available to breeders to use in creating desired germlines for new crops. Increased durability, nutritional content, insect and virus resistance and herbicide tolerance are a few of the attributes bred into crops through genetic engineering. For some, GMO crops cause food safety and food labeling concerns. Numerous countries have placed restrictions on the production, import or use of GMO foods and crops. Currently a global treaty, the Biosafety Protocol, regulates the trade of GMOs. There is ongoing discussion regarding the labeling of foods made from GMOs, and while the EU currently requires all GMO foods to be labeled, the US does not. Herbicide-resistant seed has a gene implanted into its genome that allows the plants to tolerate exposure to herbicides, including glyphosate. These seeds allow the farmer to grow a crop that can be sprayed with herbicides to control weeds without harming the resistant crop. Herbicide-tolerant crops are used by farmers worldwide. With the increasing use of herbicide-tolerant crops, comes an increase in the use of glyphosate-based herbicide sprays. In some areas glyphosate resistant weeds have developed, causing farmers to switch to other herbicides. Some studies also link widespread glyphosate usage to iron deficiencies in some crops, which is both a crop production and a nutritional quality concern, with potential economic and health implications. Other GMO crops used by growers include insect-resistant crops, which have a gene from the soil bacterium Bacillus thuringiensis (Bt), which produces a toxin specific to insects. These crops resist damage by insects. Some believe that similar or better pest-resistance traits can be acquired through traditional breeding practices, and resistance to various pests can be gained through hybridization or cross-pollination with wild species. In some cases, wild species are the primary source of resistance traits; some tomato cultivars that have gained resistance to at least 19 diseases did so through crossing with wild populations of tomatoes. Environmental impact Effects and costs Agriculture is both a cause of and sensitive to environmental degradation, such as biodiversity loss, desertification, soil degradation and global warming, which cause decrease in crop yield. Agriculture is one of the most important drivers of environmental pressures, particularly habitat change, climate change, water use and toxic emissions.

Similarly, worldwide average wheat yields have increased from less than 1 t/ha in 1900 to more than 2.5 t/ha in 1990. South American average wheat yields are around 2 t/ha, African under 1 t/ha, and Egypt and Arabia up to 3.5 to 4 t/ha with irrigation. In contrast, the average wheat yield in countries such as France is over 8 t/ha. Variations in yields are due mainly to variation in climate, genetics, and the level of intensive farming techniques (use of fertilizers, chemical pest control, growth control to avoid lodging). Genetic engineering Genetically modified organisms (GMO) are organisms whose genetic material has been altered by genetic engineering techniques generally known as recombinant DNA technology. Genetic engineering has expanded the genes available to breeders to use in creating desired germlines for new crops. Increased durability, nutritional content, insect and virus resistance and herbicide tolerance are a few of the attributes bred into crops through genetic engineering. For some, GMO crops cause food safety and food labeling concerns. Numerous countries have placed restrictions on the production, import or use of GMO foods and crops. Currently a global treaty, the Biosafety Protocol, regulates the trade of GMOs. There is ongoing discussion regarding the labeling of foods made from GMOs, and while the EU currently requires all GMO foods to be labeled, the US does not. Herbicide-resistant seed has a gene implanted into its genome that allows the plants to tolerate exposure to herbicides, including glyphosate. These seeds allow the farmer to grow a crop that can be sprayed with herbicides to control weeds without harming the resistant crop. Herbicide-tolerant crops are used by farmers worldwide. With the increasing use of herbicide-tolerant crops, comes an increase in the use of glyphosate-based herbicide sprays. In some areas glyphosate resistant weeds have developed, causing farmers to switch to other herbicides. Some studies also link widespread glyphosate usage to iron deficiencies in some crops, which is both a crop production and a nutritional quality concern, with potential economic and health implications. Other GMO crops used by growers include insect-resistant crops, which have a gene from the soil bacterium Bacillus thuringiensis (Bt), which produces a toxin specific to insects. These crops resist damage by insects. Some believe that similar or better pest-resistance traits can be acquired through traditional breeding practices, and resistance to various pests can be gained through hybridization or cross-pollination with wild species. In some cases, wild species are the primary source of resistance traits; some tomato cultivars that have gained resistance to at least 19 diseases did so through crossing with wild populations of tomatoes. Environmental impact Effects and costs Agriculture is both a cause of and sensitive to environmental degradation, such as biodiversity loss, desertification, soil degradation and global warming, which cause decrease in crop yield. Agriculture is one of the most important drivers of environmental pressures, particularly habitat change, climate change, water use and toxic emissions.

Agriculture is the main source of toxins released into the environment, including insecticides, especially those used on cotton. The 2011 UNEP Green Economy report stated that agricultural operations produced some 13 per cent of anthropogenic global greenhouse gas emissions. This includes gases from the use of inorganic fertilizers, agro-chemical pesticides, and herbicides, as well as fossil fuel-energy inputs. Agriculture imposes multiple external costs upon society through effects such as pesticide damage to nature (especially herbicides and insecticides), nutrient runoff, excessive water usage, and loss of natural environment. A 2000 assessment of agriculture in the UK determined total external costs for 1996 of £2,343 million, or £208 per hectare. A 2005 analysis of these costs in the US concluded that cropland imposes approximately $5 to $16 billion ($30 to $96 per hectare), while livestock production imposes $714 million. Both studies, which focused solely on the fiscal impacts, concluded that more should be done to internalize external costs. Neither included subsidies in their analysis, but they noted that subsidies also influence the cost of agriculture to society. Agriculture seeks to increase yield and to reduce costs. Yield increases with inputs such as fertilisers and removal of pathogens, predators, and competitors (such as weeds). Costs decrease with increasing scale of farm units, such as making fields larger; this means removing hedges, ditches and other areas of habitat. Pesticides kill insects, plants and fungi. These and other measures have cut biodiversity to very low levels on intensively farmed land. Effective yields fall with on-farm losses, which may be caused by poor production practices during harvesting, handling, and storage. Livestock issues A senior UN official, Henning Steinfeld, said that "Livestock are one of the most significant contributors to today's most serious environmental problems". Livestock production occupies 70% of all land used for agriculture, or 30% of the land surface of the planet. It is one of the largest sources of greenhouse gases, responsible for 18% of the world's greenhouse gas emissions as measured in CO2 equivalents. By comparison, all transportation emits 13.5% of the CO2. It produces 65% of human-related nitrous oxide (which has 296 times the global warming potential of CO2) and 37% of all human-induced methane (which is 23 times as warming as CO2.) It also generates 64% of the ammonia emission. Livestock expansion is cited as a key factor driving deforestation; in the Amazon basin 70% of previously forested area is now occupied by pastures and the remainder used for feedcrops. Through deforestation and land degradation, livestock is also driving reductions in biodiversity. Furthermore, the UNEP states that "methane emissions from global livestock are projected to increase by 60 per cent by 2030 under current practices and consumption patterns." Land and water issues Land transformation, the use of land to yield goods and services, is the most substantial way humans alter the Earth's ecosystems, and is the driving force causing biodiversity loss. Estimates of the amount of land transformed by humans vary from 39 to 50%.

Agriculture is the main source of toxins released into the environment, including insecticides, especially those used on cotton. The 2011 UNEP Green Economy report stated that agricultural operations produced some 13 per cent of anthropogenic global greenhouse gas emissions. This includes gases from the use of inorganic fertilizers, agro-chemical pesticides, and herbicides, as well as fossil fuel-energy inputs. Agriculture imposes multiple external costs upon society through effects such as pesticide damage to nature (especially herbicides and insecticides), nutrient runoff, excessive water usage, and loss of natural environment. A 2000 assessment of agriculture in the UK determined total external costs for 1996 of £2,343 million, or £208 per hectare. A 2005 analysis of these costs in the US concluded that cropland imposes approximately $5 to $16 billion ($30 to $96 per hectare), while livestock production imposes $714 million. Both studies, which focused solely on the fiscal impacts, concluded that more should be done to internalize external costs. Neither included subsidies in their analysis, but they noted that subsidies also influence the cost of agriculture to society. Agriculture seeks to increase yield and to reduce costs. Yield increases with inputs such as fertilisers and removal of pathogens, predators, and competitors (such as weeds). Costs decrease with increasing scale of farm units, such as making fields larger; this means removing hedges, ditches and other areas of habitat. Pesticides kill insects, plants and fungi. These and other measures have cut biodiversity to very low levels on intensively farmed land. Effective yields fall with on-farm losses, which may be caused by poor production practices during harvesting, handling, and storage. Livestock issues A senior UN official, Henning Steinfeld, said that "Livestock are one of the most significant contributors to today's most serious environmental problems". Livestock production occupies 70% of all land used for agriculture, or 30% of the land surface of the planet. It is one of the largest sources of greenhouse gases, responsible for 18% of the world's greenhouse gas emissions as measured in CO2 equivalents. By comparison, all transportation emits 13.5% of the CO2. It produces 65% of human-related nitrous oxide (which has 296 times the global warming potential of CO2) and 37% of all human-induced methane (which is 23 times as warming as CO2.) It also generates 64% of the ammonia emission. Livestock expansion is cited as a key factor driving deforestation; in the Amazon basin 70% of previously forested area is now occupied by pastures and the remainder used for feedcrops. Through deforestation and land degradation, livestock is also driving reductions in biodiversity. Furthermore, the UNEP states that "methane emissions from global livestock are projected to increase by 60 per cent by 2030 under current practices and consumption patterns." Land and water issues Land transformation, the use of land to yield goods and services, is the most substantial way humans alter the Earth's ecosystems, and is the driving force causing biodiversity loss. Estimates of the amount of land transformed by humans vary from 39 to 50%.

Agriculture is the main source of toxins released into the environment, including insecticides, especially those used on cotton. The 2011 UNEP Green Economy report stated that agricultural operations produced some 13 per cent of anthropogenic global greenhouse gas emissions. This includes gases from the use of inorganic fertilizers, agro-chemical pesticides, and herbicides, as well as fossil fuel-energy inputs. Agriculture imposes multiple external costs upon society through effects such as pesticide damage to nature (especially herbicides and insecticides), nutrient runoff, excessive water usage, and loss of natural environment. A 2000 assessment of agriculture in the UK determined total external costs for 1996 of £2,343 million, or £208 per hectare. A 2005 analysis of these costs in the US concluded that cropland imposes approximately $5 to $16 billion ($30 to $96 per hectare), while livestock production imposes $714 million. Both studies, which focused solely on the fiscal impacts, concluded that more should be done to internalize external costs. Neither included subsidies in their analysis, but they noted that subsidies also influence the cost of agriculture to society. Agriculture seeks to increase yield and to reduce costs. Yield increases with inputs such as fertilisers and removal of pathogens, predators, and competitors (such as weeds). Costs decrease with increasing scale of farm units, such as making fields larger; this means removing hedges, ditches and other areas of habitat. Pesticides kill insects, plants and fungi. These and other measures have cut biodiversity to very low levels on intensively farmed land. Effective yields fall with on-farm losses, which may be caused by poor production practices during harvesting, handling, and storage. Livestock issues A senior UN official, Henning Steinfeld, said that "Livestock are one of the most significant contributors to today's most serious environmental problems". Livestock production occupies 70% of all land used for agriculture, or 30% of the land surface of the planet. It is one of the largest sources of greenhouse gases, responsible for 18% of the world's greenhouse gas emissions as measured in CO2 equivalents. By comparison, all transportation emits 13.5% of the CO2. It produces 65% of human-related nitrous oxide (which has 296 times the global warming potential of CO2) and 37% of all human-induced methane (which is 23 times as warming as CO2.) It also generates 64% of the ammonia emission. Livestock expansion is cited as a key factor driving deforestation; in the Amazon basin 70% of previously forested area is now occupied by pastures and the remainder used for feedcrops. Through deforestation and land degradation, livestock is also driving reductions in biodiversity. Furthermore, the UNEP states that "methane emissions from global livestock are projected to increase by 60 per cent by 2030 under current practices and consumption patterns." Land and water issues Land transformation, the use of land to yield goods and services, is the most substantial way humans alter the Earth's ecosystems, and is the driving force causing biodiversity loss. Estimates of the amount of land transformed by humans vary from 39 to 50%.

Land degradation, the long-term decline in ecosystem function and productivity, is estimated to be occurring on 24% of land worldwide, with cropland overrepresented. Land management is the driving factor behind degradation; 1.5 billion people rely upon the degrading land. Degradation can be through deforestation, desertification, soil erosion, mineral depletion, acidification, or salinization. Eutrophication, excessive nutrient enrichment in aquatic ecosystems resulting in algal blooms and anoxia, leads to fish kills, loss of biodiversity, and renders water unfit for drinking and other industrial uses. Excessive fertilization and manure application to cropland, as well as high livestock stocking densities cause nutrient (mainly nitrogen and phosphorus) runoff and leaching from agricultural land. These nutrients are major nonpoint pollutants contributing to eutrophication of aquatic ecosystems and pollution of groundwater, with harmful effects on human populations. Fertilisers also reduce terrestrial biodiversity by increasing competition for light, favouring those species that are able to benefit from the added nutrients. Agriculture accounts for 70 percent of withdrawals of freshwater resources. Agriculture is a major draw on water from aquifers, and currently draws from those underground water sources at an unsustainable rate. It is long known that aquifers in areas as diverse as northern China, the Upper Ganges and the western US are being depleted, and new research extends these problems to aquifers in Iran, Mexico and Saudi Arabia. Increasing pressure is being placed on water resources by industry and urban areas, meaning that water scarcity is increasing and agriculture is facing the challenge of producing more food for the world's growing population with reduced water resources. Agricultural water usage can also cause major environmental problems, including the destruction of natural wetlands, the spread of water-borne diseases, and land degradation through salinization and waterlogging, when irrigation is performed incorrectly. Pesticides Pesticide use has increased since 1950 to 2.5million short tons annually worldwide, yet crop loss from pests has remained relatively constant. The World Health Organization estimated in 1992 that three million pesticide poisonings occur annually, causing 220,000 deaths. Pesticides select for pesticide resistance in the pest population, leading to a condition termed the "pesticide treadmill" in which pest resistance warrants the development of a new pesticide. An alternative argument is that the way to "save the environment" and prevent famine is by using pesticides and intensive high yield farming, a view exemplified by a quote heading the Center for Global Food Issues website: 'Growing more per acre leaves more land for nature'. However, critics argue that a trade-off between the environment and a need for food is not inevitable, and that pesticides simply replace good agronomic practices such as crop rotation. The Push–pull agricultural pest management technique involves intercropping, using plant aromas to repel pests from crops (push) and to lure them to a place from which they can then be removed (pull). Climate change Climate change and agriculture are interrelated on a global scale.

Land degradation, the long-term decline in ecosystem function and productivity, is estimated to be occurring on 24% of land worldwide, with cropland overrepresented. Land management is the driving factor behind degradation; 1.5 billion people rely upon the degrading land. Degradation can be through deforestation, desertification, soil erosion, mineral depletion, acidification, or salinization. Eutrophication, excessive nutrient enrichment in aquatic ecosystems resulting in algal blooms and anoxia, leads to fish kills, loss of biodiversity, and renders water unfit for drinking and other industrial uses. Excessive fertilization and manure application to cropland, as well as high livestock stocking densities cause nutrient (mainly nitrogen and phosphorus) runoff and leaching from agricultural land. These nutrients are major nonpoint pollutants contributing to eutrophication of aquatic ecosystems and pollution of groundwater, with harmful effects on human populations. Fertilisers also reduce terrestrial biodiversity by increasing competition for light, favouring those species that are able to benefit from the added nutrients. Agriculture accounts for 70 percent of withdrawals of freshwater resources. Agriculture is a major draw on water from aquifers, and currently draws from those underground water sources at an unsustainable rate. It is long known that aquifers in areas as diverse as northern China, the Upper Ganges and the western US are being depleted, and new research extends these problems to aquifers in Iran, Mexico and Saudi Arabia. Increasing pressure is being placed on water resources by industry and urban areas, meaning that water scarcity is increasing and agriculture is facing the challenge of producing more food for the world's growing population with reduced water resources. Agricultural water usage can also cause major environmental problems, including the destruction of natural wetlands, the spread of water-borne diseases, and land degradation through salinization and waterlogging, when irrigation is performed incorrectly. Pesticides Pesticide use has increased since 1950 to 2.5million short tons annually worldwide, yet crop loss from pests has remained relatively constant. The World Health Organization estimated in 1992 that three million pesticide poisonings occur annually, causing 220,000 deaths. Pesticides select for pesticide resistance in the pest population, leading to a condition termed the "pesticide treadmill" in which pest resistance warrants the development of a new pesticide. An alternative argument is that the way to "save the environment" and prevent famine is by using pesticides and intensive high yield farming, a view exemplified by a quote heading the Center for Global Food Issues website: 'Growing more per acre leaves more land for nature'. However, critics argue that a trade-off between the environment and a need for food is not inevitable, and that pesticides simply replace good agronomic practices such as crop rotation. The Push–pull agricultural pest management technique involves intercropping, using plant aromas to repel pests from crops (push) and to lure them to a place from which they can then be removed (pull). Climate change Climate change and agriculture are interrelated on a global scale.

Land degradation, the long-term decline in ecosystem function and productivity, is estimated to be occurring on 24% of land worldwide, with cropland overrepresented. Land management is the driving factor behind degradation; 1.5 billion people rely upon the degrading land. Degradation can be through deforestation, desertification, soil erosion, mineral depletion, acidification, or salinization. Eutrophication, excessive nutrient enrichment in aquatic ecosystems resulting in algal blooms and anoxia, leads to fish kills, loss of biodiversity, and renders water unfit for drinking and other industrial uses. Excessive fertilization and manure application to cropland, as well as high livestock stocking densities cause nutrient (mainly nitrogen and phosphorus) runoff and leaching from agricultural land. These nutrients are major nonpoint pollutants contributing to eutrophication of aquatic ecosystems and pollution of groundwater, with harmful effects on human populations. Fertilisers also reduce terrestrial biodiversity by increasing competition for light, favouring those species that are able to benefit from the added nutrients. Agriculture accounts for 70 percent of withdrawals of freshwater resources. Agriculture is a major draw on water from aquifers, and currently draws from those underground water sources at an unsustainable rate. It is long known that aquifers in areas as diverse as northern China, the Upper Ganges and the western US are being depleted, and new research extends these problems to aquifers in Iran, Mexico and Saudi Arabia. Increasing pressure is being placed on water resources by industry and urban areas, meaning that water scarcity is increasing and agriculture is facing the challenge of producing more food for the world's growing population with reduced water resources. Agricultural water usage can also cause major environmental problems, including the destruction of natural wetlands, the spread of water-borne diseases, and land degradation through salinization and waterlogging, when irrigation is performed incorrectly. Pesticides Pesticide use has increased since 1950 to 2.5million short tons annually worldwide, yet crop loss from pests has remained relatively constant. The World Health Organization estimated in 1992 that three million pesticide poisonings occur annually, causing 220,000 deaths. Pesticides select for pesticide resistance in the pest population, leading to a condition termed the "pesticide treadmill" in which pest resistance warrants the development of a new pesticide. An alternative argument is that the way to "save the environment" and prevent famine is by using pesticides and intensive high yield farming, a view exemplified by a quote heading the Center for Global Food Issues website: 'Growing more per acre leaves more land for nature'. However, critics argue that a trade-off between the environment and a need for food is not inevitable, and that pesticides simply replace good agronomic practices such as crop rotation. The Push–pull agricultural pest management technique involves intercropping, using plant aromas to repel pests from crops (push) and to lure them to a place from which they can then be removed (pull). Climate change Climate change and agriculture are interrelated on a global scale.

Global warming affects agriculture through changes in average temperatures, rainfall, and weather extremes (like storms and heat waves); changes in pests and diseases; changes in atmospheric carbon dioxide and ground-level ozone concentrations; changes in the nutritional quality of some foods; and changes in sea level. Global warming is already affecting agriculture, with effects unevenly distributed across the world. Future climate change will probably negatively affect crop production in low latitude countries, while effects in northern latitudes may be positive or negative. Global warming will probably increase the risk of food insecurity for some vulnerable groups, such as the poor. Animal husbandry is also responsible for greenhouse gas production of CO2 and a percentage of the world's methane, and future land infertility, and the displacement of wildlife. Agriculture contributes to climate change by anthropogenic emissions of greenhouse gases, and by the conversion of non-agricultural land such as forest for agricultural use. Agriculture, forestry and land-use change contributed around 20 to 25% to global annual emissions in 2010. A range of policies can reduce the risk of negative climate change impacts on agriculture, and greenhouse gas emissions from the agriculture sector. Sustainability Current farming methods have resulted in over-stretched water resources, high levels of erosion and reduced soil fertility. There is not enough water to continue farming using current practices; therefore how critical water, land, and ecosystem resources are used to boost crop yields must be reconsidered. A solution would be to give value to ecosystems, recognizing environmental and livelihood tradeoffs, and balancing the rights of a variety of users and interests. Inequities that result when such measures are adopted would need to be addressed, such as the reallocation of water from poor to rich, the clearing of land to make way for more productive farmland, or the preservation of a wetland system that limits fishing rights. Technological advancements help provide farmers with tools and resources to make farming more sustainable. Technology permits innovations like conservation tillage, a farming process which helps prevent land loss to erosion, reduces water pollution, and enhances carbon sequestration. Other potential practices include conservation agriculture, agroforestry, improved grazing, avoided grassland conversion, and biochar. Current mono-crop farming practices in the United States preclude widespread adoption of sustainable practices, such as 2-3 crop rotations that incorporate grass or hay with annual crops, unless negative emission goals such as soil carbon sequestration become policy. The International Food Policy Research Institute states that agricultural technologies will have the greatest impact on food production if adopted in combination with each other; using a model that assessed how eleven technologies could impact agricultural productivity, food security and trade by 2050, it found that the number of people at risk from hunger could be reduced by as much as 40% and food prices could be reduced by almost half. The food demand of Earth's projected population, with current climate change predictions, could be satisfied by improvement of agricultural methods, expansion of agricultural areas, and a sustainability-oriented consumer mindset.

Global warming affects agriculture through changes in average temperatures, rainfall, and weather extremes (like storms and heat waves); changes in pests and diseases; changes in atmospheric carbon dioxide and ground-level ozone concentrations; changes in the nutritional quality of some foods; and changes in sea level. Global warming is already affecting agriculture, with effects unevenly distributed across the world. Future climate change will probably negatively affect crop production in low latitude countries, while effects in northern latitudes may be positive or negative. Global warming will probably increase the risk of food insecurity for some vulnerable groups, such as the poor. Animal husbandry is also responsible for greenhouse gas production of CO2 and a percentage of the world's methane, and future land infertility, and the displacement of wildlife. Agriculture contributes to climate change by anthropogenic emissions of greenhouse gases, and by the conversion of non-agricultural land such as forest for agricultural use. Agriculture, forestry and land-use change contributed around 20 to 25% to global annual emissions in 2010. A range of policies can reduce the risk of negative climate change impacts on agriculture, and greenhouse gas emissions from the agriculture sector. Sustainability Current farming methods have resulted in over-stretched water resources, high levels of erosion and reduced soil fertility. There is not enough water to continue farming using current practices; therefore how critical water, land, and ecosystem resources are used to boost crop yields must be reconsidered. A solution would be to give value to ecosystems, recognizing environmental and livelihood tradeoffs, and balancing the rights of a variety of users and interests. Inequities that result when such measures are adopted would need to be addressed, such as the reallocation of water from poor to rich, the clearing of land to make way for more productive farmland, or the preservation of a wetland system that limits fishing rights. Technological advancements help provide farmers with tools and resources to make farming more sustainable. Technology permits innovations like conservation tillage, a farming process which helps prevent land loss to erosion, reduces water pollution, and enhances carbon sequestration. Other potential practices include conservation agriculture, agroforestry, improved grazing, avoided grassland conversion, and biochar. Current mono-crop farming practices in the United States preclude widespread adoption of sustainable practices, such as 2-3 crop rotations that incorporate grass or hay with annual crops, unless negative emission goals such as soil carbon sequestration become policy. The International Food Policy Research Institute states that agricultural technologies will have the greatest impact on food production if adopted in combination with each other; using a model that assessed how eleven technologies could impact agricultural productivity, food security and trade by 2050, it found that the number of people at risk from hunger could be reduced by as much as 40% and food prices could be reduced by almost half. The food demand of Earth's projected population, with current climate change predictions, could be satisfied by improvement of agricultural methods, expansion of agricultural areas, and a sustainability-oriented consumer mindset.

Global warming affects agriculture through changes in average temperatures, rainfall, and weather extremes (like storms and heat waves); changes in pests and diseases; changes in atmospheric carbon dioxide and ground-level ozone concentrations; changes in the nutritional quality of some foods; and changes in sea level. Global warming is already affecting agriculture, with effects unevenly distributed across the world. Future climate change will probably negatively affect crop production in low latitude countries, while effects in northern latitudes may be positive or negative. Global warming will probably increase the risk of food insecurity for some vulnerable groups, such as the poor. Animal husbandry is also responsible for greenhouse gas production of CO2 and a percentage of the world's methane, and future land infertility, and the displacement of wildlife. Agriculture contributes to climate change by anthropogenic emissions of greenhouse gases, and by the conversion of non-agricultural land such as forest for agricultural use. Agriculture, forestry and land-use change contributed around 20 to 25% to global annual emissions in 2010. A range of policies can reduce the risk of negative climate change impacts on agriculture, and greenhouse gas emissions from the agriculture sector. Sustainability Current farming methods have resulted in over-stretched water resources, high levels of erosion and reduced soil fertility. There is not enough water to continue farming using current practices; therefore how critical water, land, and ecosystem resources are used to boost crop yields must be reconsidered. A solution would be to give value to ecosystems, recognizing environmental and livelihood tradeoffs, and balancing the rights of a variety of users and interests. Inequities that result when such measures are adopted would need to be addressed, such as the reallocation of water from poor to rich, the clearing of land to make way for more productive farmland, or the preservation of a wetland system that limits fishing rights. Technological advancements help provide farmers with tools and resources to make farming more sustainable. Technology permits innovations like conservation tillage, a farming process which helps prevent land loss to erosion, reduces water pollution, and enhances carbon sequestration. Other potential practices include conservation agriculture, agroforestry, improved grazing, avoided grassland conversion, and biochar. Current mono-crop farming practices in the United States preclude widespread adoption of sustainable practices, such as 2-3 crop rotations that incorporate grass or hay with annual crops, unless negative emission goals such as soil carbon sequestration become policy. The International Food Policy Research Institute states that agricultural technologies will have the greatest impact on food production if adopted in combination with each other; using a model that assessed how eleven technologies could impact agricultural productivity, food security and trade by 2050, it found that the number of people at risk from hunger could be reduced by as much as 40% and food prices could be reduced by almost half. The food demand of Earth's projected population, with current climate change predictions, could be satisfied by improvement of agricultural methods, expansion of agricultural areas, and a sustainability-oriented consumer mindset.

Energy dependence Since the 1940s, agricultural productivity has increased dramatically, due largely to the increased use of energy-intensive mechanization, fertilizers and pesticides. The vast majority of this energy input comes from fossil fuel sources. Between the 1960s and the 1980s, the Green Revolution transformed agriculture around the globe, with world grain production increasing significantly (between 70% and 390% for wheat and 60% to 150% for rice, depending on geographic area) as world population doubled. Heavy reliance on petrochemicals has raised concerns that oil shortages could increase costs and reduce agricultural output. Industrialized agriculture depends on fossil fuels in two fundamental ways: direct consumption on the farm and manufacture of inputs used on the farm. Direct consumption includes the use of lubricants and fuels to operate farm vehicles and machinery. Indirect consumption includes the manufacture of fertilizers, pesticides, and farm machinery. In particular, the production of nitrogen fertilizer can account for over half of agricultural energy usage. Together, direct and indirect consumption by US farms accounts for about 2% of the nation's energy use. Direct and indirect energy consumption by U.S. farms peaked in 1979, and has since gradually declined. Food systems encompass not just agriculture but off-farm processing, packaging, transporting, marketing, consumption, and disposal of food and food-related items. Agriculture accounts for less than one-fifth of food system energy use in the US. Disciplines Agricultural economics Agricultural economics is economics as it relates to the "production, distribution and consumption of [agricultural] goods and services". Combining agricultural production with general theories of marketing and business as a discipline of study began in the late 1800s, and grew significantly through the 20th century. Although the study of agricultural economics is relatively recent, major trends in agriculture have significantly affected national and international economies throughout history, ranging from tenant farmers and sharecropping in the post-American Civil War Southern United States to the European feudal system of manorialism. In the United States, and elsewhere, food costs attributed to food processing, distribution, and agricultural marketing, sometimes referred to as the value chain, have risen while the costs attributed to farming have declined. This is related to the greater efficiency of farming, combined with the increased level of value addition (e.g. more highly processed products) provided by the supply chain. Market concentration has increased in the sector as well, and although the total effect of the increased market concentration is likely increased efficiency, the changes redistribute economic surplus from producers (farmers) and consumers, and may have negative implications for rural communities. National government policies can significantly change the economic marketplace for agricultural products, in the form of taxation, subsidies, tariffs and other measures. Since at least the 1960s, a combination of trade restrictions, exchange rate policies and subsidies have affected farmers in both the developing and the developed world. In the 1980s, non-subsidized farmers in developing countries experienced adverse effects from national policies that created artificially low global prices for farm products.

Energy dependence Since the 1940s, agricultural productivity has increased dramatically, due largely to the increased use of energy-intensive mechanization, fertilizers and pesticides. The vast majority of this energy input comes from fossil fuel sources. Between the 1960s and the 1980s, the Green Revolution transformed agriculture around the globe, with world grain production increasing significantly (between 70% and 390% for wheat and 60% to 150% for rice, depending on geographic area) as world population doubled. Heavy reliance on petrochemicals has raised concerns that oil shortages could increase costs and reduce agricultural output. Industrialized agriculture depends on fossil fuels in two fundamental ways: direct consumption on the farm and manufacture of inputs used on the farm. Direct consumption includes the use of lubricants and fuels to operate farm vehicles and machinery. Indirect consumption includes the manufacture of fertilizers, pesticides, and farm machinery. In particular, the production of nitrogen fertilizer can account for over half of agricultural energy usage. Together, direct and indirect consumption by US farms accounts for about 2% of the nation's energy use. Direct and indirect energy consumption by U.S. farms peaked in 1979, and has since gradually declined. Food systems encompass not just agriculture but off-farm processing, packaging, transporting, marketing, consumption, and disposal of food and food-related items. Agriculture accounts for less than one-fifth of food system energy use in the US. Disciplines Agricultural economics Agricultural economics is economics as it relates to the "production, distribution and consumption of [agricultural] goods and services". Combining agricultural production with general theories of marketing and business as a discipline of study began in the late 1800s, and grew significantly through the 20th century. Although the study of agricultural economics is relatively recent, major trends in agriculture have significantly affected national and international economies throughout history, ranging from tenant farmers and sharecropping in the post-American Civil War Southern United States to the European feudal system of manorialism. In the United States, and elsewhere, food costs attributed to food processing, distribution, and agricultural marketing, sometimes referred to as the value chain, have risen while the costs attributed to farming have declined. This is related to the greater efficiency of farming, combined with the increased level of value addition (e.g. more highly processed products) provided by the supply chain. Market concentration has increased in the sector as well, and although the total effect of the increased market concentration is likely increased efficiency, the changes redistribute economic surplus from producers (farmers) and consumers, and may have negative implications for rural communities. National government policies can significantly change the economic marketplace for agricultural products, in the form of taxation, subsidies, tariffs and other measures. Since at least the 1960s, a combination of trade restrictions, exchange rate policies and subsidies have affected farmers in both the developing and the developed world. In the 1980s, non-subsidized farmers in developing countries experienced adverse effects from national policies that created artificially low global prices for farm products.

Energy dependence Since the 1940s, agricultural productivity has increased dramatically, due largely to the increased use of energy-intensive mechanization, fertilizers and pesticides. The vast majority of this energy input comes from fossil fuel sources. Between the 1960s and the 1980s, the Green Revolution transformed agriculture around the globe, with world grain production increasing significantly (between 70% and 390% for wheat and 60% to 150% for rice, depending on geographic area) as world population doubled. Heavy reliance on petrochemicals has raised concerns that oil shortages could increase costs and reduce agricultural output. Industrialized agriculture depends on fossil fuels in two fundamental ways: direct consumption on the farm and manufacture of inputs used on the farm. Direct consumption includes the use of lubricants and fuels to operate farm vehicles and machinery. Indirect consumption includes the manufacture of fertilizers, pesticides, and farm machinery. In particular, the production of nitrogen fertilizer can account for over half of agricultural energy usage. Together, direct and indirect consumption by US farms accounts for about 2% of the nation's energy use. Direct and indirect energy consumption by U.S. farms peaked in 1979, and has since gradually declined. Food systems encompass not just agriculture but off-farm processing, packaging, transporting, marketing, consumption, and disposal of food and food-related items. Agriculture accounts for less than one-fifth of food system energy use in the US. Disciplines Agricultural economics Agricultural economics is economics as it relates to the "production, distribution and consumption of [agricultural] goods and services". Combining agricultural production with general theories of marketing and business as a discipline of study began in the late 1800s, and grew significantly through the 20th century. Although the study of agricultural economics is relatively recent, major trends in agriculture have significantly affected national and international economies throughout history, ranging from tenant farmers and sharecropping in the post-American Civil War Southern United States to the European feudal system of manorialism. In the United States, and elsewhere, food costs attributed to food processing, distribution, and agricultural marketing, sometimes referred to as the value chain, have risen while the costs attributed to farming have declined. This is related to the greater efficiency of farming, combined with the increased level of value addition (e.g. more highly processed products) provided by the supply chain. Market concentration has increased in the sector as well, and although the total effect of the increased market concentration is likely increased efficiency, the changes redistribute economic surplus from producers (farmers) and consumers, and may have negative implications for rural communities. National government policies can significantly change the economic marketplace for agricultural products, in the form of taxation, subsidies, tariffs and other measures. Since at least the 1960s, a combination of trade restrictions, exchange rate policies and subsidies have affected farmers in both the developing and the developed world. In the 1980s, non-subsidized farmers in developing countries experienced adverse effects from national policies that created artificially low global prices for farm products.

Between the mid-1980s and the early 2000s, several international agreements limited agricultural tariffs, subsidies and other trade restrictions. However, , there was still a significant amount of policy-driven distortion in global agricultural product prices. The three agricultural products with the most trade distortion were sugar, milk and rice, mainly due to taxation. Among the oilseeds, sesame had the most taxation, but overall, feed grains and oilseeds had much lower levels of taxation than livestock products. Since the 1980s, policy-driven distortions have seen a greater decrease among livestock products than crops during the worldwide reforms in agricultural policy. Despite this progress, certain crops, such as cotton, still see subsidies in developed countries artificially deflating global prices, causing hardship in developing countries with non-subsidized farmers. Unprocessed commodities such as corn, soybeans, and cattle are generally graded to indicate quality, affecting the price the producer receives. Commodities are generally reported by production quantities, such as volume, number or weight. Agricultural science Agricultural science is a broad multidisciplinary field of biology that encompasses the parts of exact, natural, economic and social sciences used in the practice and understanding of agriculture. It covers topics such as agronomy, plant breeding and genetics, plant pathology, crop modelling, soil science, entomology, production techniques and improvement, study of pests and their management, and study of adverse environmental effects such as soil degradation, waste management, and bioremediation. The scientific study of agriculture began in the 18th century, when Johann Friedrich Mayer conducted experiments on the use of gypsum (hydrated calcium sulphate) as a fertilizer. Research became more systematic when in 1843, John Lawes and Henry Gilbert began a set of long-term agronomy field experiments at Rothamsted Research Station in England; some of them, such as the Park Grass Experiment, are still running. In America, the Hatch Act of 1887 provided funding for what it was the first to call "agricultural science", driven by farmers' interest in fertilizers. In agricultural entomology, the USDA began to research biological control in 1881; it instituted its first large program in 1905, searching Europe and Japan for natural enemies of the gypsy moth and brown-tail moth, establishing parasitoids (such as solitary wasps) and predators of both pests in the USA. Policy Agricultural policy is the set of government decisions and actions relating to domestic agriculture and imports of foreign agricultural products. Governments usually implement agricultural policies with the goal of achieving a specific outcome in the domestic agricultural product markets. Some overarching themes include risk management and adjustment (including policies related to climate change, food safety and natural disasters), economic stability (including policies related to taxes), natural resources and environmental sustainability (especially water policy), research and development, and market access for domestic commodities (including relations with global organizations and agreements with other countries). Agricultural policy can also touch on food quality, ensuring that the food supply is of a consistent and known quality, food security, ensuring that the food supply meets the population's needs, and conservation.

Between the mid-1980s and the early 2000s, several international agreements limited agricultural tariffs, subsidies and other trade restrictions. However, , there was still a significant amount of policy-driven distortion in global agricultural product prices. The three agricultural products with the most trade distortion were sugar, milk and rice, mainly due to taxation. Among the oilseeds, sesame had the most taxation, but overall, feed grains and oilseeds had much lower levels of taxation than livestock products. Since the 1980s, policy-driven distortions have seen a greater decrease among livestock products than crops during the worldwide reforms in agricultural policy. Despite this progress, certain crops, such as cotton, still see subsidies in developed countries artificially deflating global prices, causing hardship in developing countries with non-subsidized farmers. Unprocessed commodities such as corn, soybeans, and cattle are generally graded to indicate quality, affecting the price the producer receives. Commodities are generally reported by production quantities, such as volume, number or weight. Agricultural science Agricultural science is a broad multidisciplinary field of biology that encompasses the parts of exact, natural, economic and social sciences used in the practice and understanding of agriculture. It covers topics such as agronomy, plant breeding and genetics, plant pathology, crop modelling, soil science, entomology, production techniques and improvement, study of pests and their management, and study of adverse environmental effects such as soil degradation, waste management, and bioremediation. The scientific study of agriculture began in the 18th century, when Johann Friedrich Mayer conducted experiments on the use of gypsum (hydrated calcium sulphate) as a fertilizer. Research became more systematic when in 1843, John Lawes and Henry Gilbert began a set of long-term agronomy field experiments at Rothamsted Research Station in England; some of them, such as the Park Grass Experiment, are still running. In America, the Hatch Act of 1887 provided funding for what it was the first to call "agricultural science", driven by farmers' interest in fertilizers. In agricultural entomology, the USDA began to research biological control in 1881; it instituted its first large program in 1905, searching Europe and Japan for natural enemies of the gypsy moth and brown-tail moth, establishing parasitoids (such as solitary wasps) and predators of both pests in the USA. Policy Agricultural policy is the set of government decisions and actions relating to domestic agriculture and imports of foreign agricultural products. Governments usually implement agricultural policies with the goal of achieving a specific outcome in the domestic agricultural product markets. Some overarching themes include risk management and adjustment (including policies related to climate change, food safety and natural disasters), economic stability (including policies related to taxes), natural resources and environmental sustainability (especially water policy), research and development, and market access for domestic commodities (including relations with global organizations and agreements with other countries). Agricultural policy can also touch on food quality, ensuring that the food supply is of a consistent and known quality, food security, ensuring that the food supply meets the population's needs, and conservation.

Between the mid-1980s and the early 2000s, several international agreements limited agricultural tariffs, subsidies and other trade restrictions. However, , there was still a significant amount of policy-driven distortion in global agricultural product prices. The three agricultural products with the most trade distortion were sugar, milk and rice, mainly due to taxation. Among the oilseeds, sesame had the most taxation, but overall, feed grains and oilseeds had much lower levels of taxation than livestock products. Since the 1980s, policy-driven distortions have seen a greater decrease among livestock products than crops during the worldwide reforms in agricultural policy. Despite this progress, certain crops, such as cotton, still see subsidies in developed countries artificially deflating global prices, causing hardship in developing countries with non-subsidized farmers. Unprocessed commodities such as corn, soybeans, and cattle are generally graded to indicate quality, affecting the price the producer receives. Commodities are generally reported by production quantities, such as volume, number or weight. Agricultural science Agricultural science is a broad multidisciplinary field of biology that encompasses the parts of exact, natural, economic and social sciences used in the practice and understanding of agriculture. It covers topics such as agronomy, plant breeding and genetics, plant pathology, crop modelling, soil science, entomology, production techniques and improvement, study of pests and their management, and study of adverse environmental effects such as soil degradation, waste management, and bioremediation. The scientific study of agriculture began in the 18th century, when Johann Friedrich Mayer conducted experiments on the use of gypsum (hydrated calcium sulphate) as a fertilizer. Research became more systematic when in 1843, John Lawes and Henry Gilbert began a set of long-term agronomy field experiments at Rothamsted Research Station in England; some of them, such as the Park Grass Experiment, are still running. In America, the Hatch Act of 1887 provided funding for what it was the first to call "agricultural science", driven by farmers' interest in fertilizers. In agricultural entomology, the USDA began to research biological control in 1881; it instituted its first large program in 1905, searching Europe and Japan for natural enemies of the gypsy moth and brown-tail moth, establishing parasitoids (such as solitary wasps) and predators of both pests in the USA. Policy Agricultural policy is the set of government decisions and actions relating to domestic agriculture and imports of foreign agricultural products. Governments usually implement agricultural policies with the goal of achieving a specific outcome in the domestic agricultural product markets. Some overarching themes include risk management and adjustment (including policies related to climate change, food safety and natural disasters), economic stability (including policies related to taxes), natural resources and environmental sustainability (especially water policy), research and development, and market access for domestic commodities (including relations with global organizations and agreements with other countries). Agricultural policy can also touch on food quality, ensuring that the food supply is of a consistent and known quality, food security, ensuring that the food supply meets the population's needs, and conservation.

Policy programs can range from financial programs, such as subsidies, to encouraging producers to enroll in voluntary quality assurance programs. There are many influences on the creation of agricultural policy, including consumers, agribusiness, trade lobbies and other groups. Agribusiness interests hold a large amount of influence over policy making, in the form of lobbying and campaign contributions. Political action groups, including those interested in environmental issues and labor unions, also provide influence, as do lobbying organizations representing individual agricultural commodities. The Food and Agriculture Organization of the United Nations (FAO) leads international efforts to defeat hunger and provides a forum for the negotiation of global agricultural regulations and agreements. Samuel Jutzi, director of FAO's animal production and health division, states that lobbying by large corporations has stopped reforms that would improve human health and the environment. For example, proposals in 2010 for a voluntary code of conduct for the livestock industry that would have provided incentives for improving standards for health, and environmental regulations, such as the number of animals an area of land can support without long-term damage, were successfully defeated due to large food company pressure. See also Aeroponics Agricultural aircraft Agricultural engineering Agricultural robot Agroecology Agrominerals Building-integrated agriculture Contract farming Corporate farming Crofting Ecoagriculture Hill farming List of documentary films about agriculture Pharming (genetics) Remote sensing Subsistence economy Vertical farming Vegetable farming References Cited sources External links Food and Agriculture Organization United States Department of Agriculture Agriculture material from the World Bank Group Agriculture Agronomy Food industry

Policy programs can range from financial programs, such as subsidies, to encouraging producers to enroll in voluntary quality assurance programs. There are many influences on the creation of agricultural policy, including consumers, agribusiness, trade lobbies and other groups. Agribusiness interests hold a large amount of influence over policy making, in the form of lobbying and campaign contributions. Political action groups, including those interested in environmental issues and labor unions, also provide influence, as do lobbying organizations representing individual agricultural commodities. The Food and Agriculture Organization of the United Nations (FAO) leads international efforts to defeat hunger and provides a forum for the negotiation of global agricultural regulations and agreements. Samuel Jutzi, director of FAO's animal production and health division, states that lobbying by large corporations has stopped reforms that would improve human health and the environment. For example, proposals in 2010 for a voluntary code of conduct for the livestock industry that would have provided incentives for improving standards for health, and environmental regulations, such as the number of animals an area of land can support without long-term damage, were successfully defeated due to large food company pressure. See also Aeroponics Agricultural aircraft Agricultural engineering Agricultural robot Agroecology Agrominerals Building-integrated agriculture Contract farming Corporate farming Crofting Ecoagriculture Hill farming List of documentary films about agriculture Pharming (genetics) Remote sensing Subsistence economy Vertical farming Vegetable farming References Cited sources External links Food and Agriculture Organization United States Department of Agriculture Agriculture material from the World Bank Group Agriculture Agronomy Food industry

Policy programs can range from financial programs, such as subsidies, to encouraging producers to enroll in voluntary quality assurance programs. There are many influences on the creation of agricultural policy, including consumers, agribusiness, trade lobbies and other groups. Agribusiness interests hold a large amount of influence over policy making, in the form of lobbying and campaign contributions. Political action groups, including those interested in environmental issues and labor unions, also provide influence, as do lobbying organizations representing individual agricultural commodities. The Food and Agriculture Organization of the United Nations (FAO) leads international efforts to defeat hunger and provides a forum for the negotiation of global agricultural regulations and agreements. Samuel Jutzi, director of FAO's animal production and health division, states that lobbying by large corporations has stopped reforms that would improve human health and the environment. For example, proposals in 2010 for a voluntary code of conduct for the livestock industry that would have provided incentives for improving standards for health, and environmental regulations, such as the number of animals an area of land can support without long-term damage, were successfully defeated due to large food company pressure. See also Aeroponics Agricultural aircraft Agricultural engineering Agricultural robot Agroecology Agrominerals Building-integrated agriculture Contract farming Corporate farming Crofting Ecoagriculture Hill farming List of documentary films about agriculture Pharming (genetics) Remote sensing Subsistence economy Vertical farming Vegetable farming References Cited sources External links Food and Agriculture Organization United States Department of Agriculture Agriculture material from the World Bank Group Agriculture Agronomy Food industry

Aldous Huxley Aldous Leonard Huxley (26 July 1894 – 22 November 1963) was an English writer and philosopher. He wrote nearly 50 books—both novels and non-fiction works—as well as wide-ranging essays, narratives, and poems. Born into the prominent Huxley family, he graduated from Balliol College, Oxford, with an undergraduate degree in English literature. Early in his career, he published short stories and poetry and edited the literary magazine Oxford Poetry, before going on to publish travel writing, satire, and screenplays. He spent the latter part of his life in the United States, living in Los Angeles from 1937 until his death. By the end of his life, Huxley was widely acknowledged as one of the foremost intellectuals of his time. He was nominated for the Nobel Prize in Literature nine times and was elected Companion of Literature by the Royal Society of Literature in 1962. Huxley was a pacifist. He grew interested in philosophical mysticism and universalism, addressing these subjects with works such as The Perennial Philosophy (1945)—which illustrates commonalities between Western and Eastern mysticism—and The Doors of Perception (1954)—which interprets his own psychedelic experience with mescaline. In his most famous novel Brave New World (1932) and his final novel Island (1962), he presented his vision of dystopia and utopia, respectively. Early life Huxley was born in Godalming, Surrey, England, in 1894. He was the third son of the writer and schoolmaster Leonard Huxley, who edited The Cornhill Magazine, and his first wife, Julia Arnold, who founded Prior's Field School. Julia was the niece of poet and critic Matthew Arnold and the sister of Mrs. Humphry Ward. Julia named him Aldous after a character in one of her sister's novels. Aldous was the grandson of Thomas Henry Huxley, the zoologist, agnostic, and controversialist ("Darwin's Bulldog"). His brother Julian Huxley and half-brother Andrew Huxley also became outstanding biologists. Aldous had another brother, Noel Trevenen Huxley (1889–1914), who took his own life after a period of clinical depression. As a child, Huxley's nickname was "Ogie", short for "Ogre". He was described by his brother, Julian, as someone who frequently "[contemplated] the strangeness of things". According to his cousin and contemporary, Gervas Huxley, he had an early interest in drawing. Huxley's education began in his father's well-equipped botanical laboratory, after which he enrolled at Hillside School near Godalming. He was taught there by his own mother for several years until she became terminally ill. After Hillside he went on to Eton College. His mother died in 1908, when he was 14 (his father later remarried). He contracted the eye disease Keratitis punctata in 1911; this "left [him] practically blind for two to three years". This "ended his early dreams of becoming a doctor". In October 1913, Huxley entered Balliol College, Oxford, where he studied English literature. He volunteered for the British Army in January 1916, for the Great War; however, he was rejected on health grounds, being half-blind in one eye. His eyesight later partly recovered.

Aldous Huxley Aldous Leonard Huxley (26 July 1894 – 22 November 1963) was an English writer and philosopher. He wrote nearly 50 books—both novels and non-fiction works—as well as wide-ranging essays, narratives, and poems. Born into the prominent Huxley family, he graduated from Balliol College, Oxford, with an undergraduate degree in English literature. Early in his career, he published short stories and poetry and edited the literary magazine Oxford Poetry, before going on to publish travel writing, satire, and screenplays. He spent the latter part of his life in the United States, living in Los Angeles from 1937 until his death. By the end of his life, Huxley was widely acknowledged as one of the foremost intellectuals of his time. He was nominated for the Nobel Prize in Literature nine times and was elected Companion of Literature by the Royal Society of Literature in 1962. Huxley was a pacifist. He grew interested in philosophical mysticism and universalism, addressing these subjects with works such as The Perennial Philosophy (1945)—which illustrates commonalities between Western and Eastern mysticism—and The Doors of Perception (1954)—which interprets his own psychedelic experience with mescaline. In his most famous novel Brave New World (1932) and his final novel Island (1962), he presented his vision of dystopia and utopia, respectively. Early life Huxley was born in Godalming, Surrey, England, in 1894. He was the third son of the writer and schoolmaster Leonard Huxley, who edited The Cornhill Magazine, and his first wife, Julia Arnold, who founded Prior's Field School. Julia was the niece of poet and critic Matthew Arnold and the sister of Mrs. Humphry Ward. Julia named him Aldous after a character in one of her sister's novels. Aldous was the grandson of Thomas Henry Huxley, the zoologist, agnostic, and controversialist ("Darwin's Bulldog"). His brother Julian Huxley and half-brother Andrew Huxley also became outstanding biologists. Aldous had another brother, Noel Trevenen Huxley (1889–1914), who took his own life after a period of clinical depression. As a child, Huxley's nickname was "Ogie", short for "Ogre". He was described by his brother, Julian, as someone who frequently "[contemplated] the strangeness of things". According to his cousin and contemporary, Gervas Huxley, he had an early interest in drawing. Huxley's education began in his father's well-equipped botanical laboratory, after which he enrolled at Hillside School near Godalming. He was taught there by his own mother for several years until she became terminally ill. After Hillside he went on to Eton College. His mother died in 1908, when he was 14 (his father later remarried). He contracted the eye disease Keratitis punctata in 1911; this "left [him] practically blind for two to three years". This "ended his early dreams of becoming a doctor". In October 1913, Huxley entered Balliol College, Oxford, where he studied English literature. He volunteered for the British Army in January 1916, for the Great War; however, he was rejected on health grounds, being half-blind in one eye. His eyesight later partly recovered.

He edited Oxford Poetry in 1916, and in June of that year graduated BA with first class honours. His brother Julian wrote: Following his years at Balliol, Huxley, being financially indebted to his father, decided to find employment. He taught French for a year at Eton College, where Eric Blair (who was to take the pen name George Orwell) and Steven Runciman were among his pupils. He was mainly remembered as being an incompetent schoolmaster unable to keep order in class. Nevertheless, Blair and others spoke highly of his excellent command of language. Huxley also worked for a time during the 1920s at Brunner and Mond, an advanced chemical plant in Billingham in County Durham, northeast England. According to the introduction to the latest edition of his science fiction novel Brave New World (1932), the experience he had there of "an ordered universe in a world of planless incoherence" was an important source for the novel. Career Huxley completed his first (unpublished) novel at the age of 17 and began writing seriously in his early twenties, establishing himself as a successful writer and social satirist. His first published novels were social satires, Crome Yellow (1921), Antic Hay (1923), Those Barren Leaves (1925), and Point Counter Point (1928). Brave New World (1932) was his fifth novel and first dystopian work. In the 1920s, he was also a contributor to Vanity Fair and British Vogue magazines. Contact with the Bloomsbury Set During the First World War, Huxley spent much of his time at Garsington Manor near Oxford, home of Lady Ottoline Morrell, working as a farm labourer. While at the Manor, he met several Bloomsbury Group figures, including Bertrand Russell, Alfred North Whitehead, and Clive Bell. Later, in Crome Yellow (1921), he caricatured the Garsington lifestyle. Jobs were very scarce, but in 1919, John Middleton Murry was reorganising the Athenaeum and invited Huxley to join the staff. He accepted immediately, and quickly married the Belgian refugee Maria Nys (1899-1955), also at Garsington. They lived with their young son in Italy part of the time during the 1920s, where Huxley would visit his friend D. H. Lawrence. Following Lawrence's death in 1930, Huxley edited Lawrence's letters (1932). Very early in 1929, in London, Huxley met Gerald Heard, a brilliant writer and broadcaster, philosopher and interpreter of contemporary science. Works of this period included important novels on the dehumanising aspects of scientific progress, most famously Brave New World, and on pacifist themes (for example, Eyeless in Gaza). In Brave New World, set in a dystopian London, Huxley portrays a society operating on the principles of mass production and Pavlovian conditioning. Huxley was strongly influenced by F. Matthias Alexander, and included him as a character in Eyeless in Gaza (1936). Beginning in this period, Huxley began to write and edit non-fiction works on pacifist issues, including Ends and Means (1937), An Encyclopedia of Pacifism, and Pacifism and Philosophy, and was an active member of the Peace Pledge Union.

He edited Oxford Poetry in 1916, and in June of that year graduated BA with first class honours. His brother Julian wrote: Following his years at Balliol, Huxley, being financially indebted to his father, decided to find employment. He taught French for a year at Eton College, where Eric Blair (who was to take the pen name George Orwell) and Steven Runciman were among his pupils. He was mainly remembered as being an incompetent schoolmaster unable to keep order in class. Nevertheless, Blair and others spoke highly of his excellent command of language. Huxley also worked for a time during the 1920s at Brunner and Mond, an advanced chemical plant in Billingham in County Durham, northeast England. According to the introduction to the latest edition of his science fiction novel Brave New World (1932), the experience he had there of "an ordered universe in a world of planless incoherence" was an important source for the novel. Career Huxley completed his first (unpublished) novel at the age of 17 and began writing seriously in his early twenties, establishing himself as a successful writer and social satirist. His first published novels were social satires, Crome Yellow (1921), Antic Hay (1923), Those Barren Leaves (1925), and Point Counter Point (1928). Brave New World (1932) was his fifth novel and first dystopian work. In the 1920s, he was also a contributor to Vanity Fair and British Vogue magazines. Contact with the Bloomsbury Set During the First World War, Huxley spent much of his time at Garsington Manor near Oxford, home of Lady Ottoline Morrell, working as a farm labourer. While at the Manor, he met several Bloomsbury Group figures, including Bertrand Russell, Alfred North Whitehead, and Clive Bell. Later, in Crome Yellow (1921), he caricatured the Garsington lifestyle. Jobs were very scarce, but in 1919, John Middleton Murry was reorganising the Athenaeum and invited Huxley to join the staff. He accepted immediately, and quickly married the Belgian refugee Maria Nys (1899-1955), also at Garsington. They lived with their young son in Italy part of the time during the 1920s, where Huxley would visit his friend D. H. Lawrence. Following Lawrence's death in 1930, Huxley edited Lawrence's letters (1932). Very early in 1929, in London, Huxley met Gerald Heard, a brilliant writer and broadcaster, philosopher and interpreter of contemporary science. Works of this period included important novels on the dehumanising aspects of scientific progress, most famously Brave New World, and on pacifist themes (for example, Eyeless in Gaza). In Brave New World, set in a dystopian London, Huxley portrays a society operating on the principles of mass production and Pavlovian conditioning. Huxley was strongly influenced by F. Matthias Alexander, and included him as a character in Eyeless in Gaza (1936). Beginning in this period, Huxley began to write and edit non-fiction works on pacifist issues, including Ends and Means (1937), An Encyclopedia of Pacifism, and Pacifism and Philosophy, and was an active member of the Peace Pledge Union.

He edited Oxford Poetry in 1916, and in June of that year graduated BA with first class honours. His brother Julian wrote: Following his years at Balliol, Huxley, being financially indebted to his father, decided to find employment. He taught French for a year at Eton College, where Eric Blair (who was to take the pen name George Orwell) and Steven Runciman were among his pupils. He was mainly remembered as being an incompetent schoolmaster unable to keep order in class. Nevertheless, Blair and others spoke highly of his excellent command of language. Huxley also worked for a time during the 1920s at Brunner and Mond, an advanced chemical plant in Billingham in County Durham, northeast England. According to the introduction to the latest edition of his science fiction novel Brave New World (1932), the experience he had there of "an ordered universe in a world of planless incoherence" was an important source for the novel. Career Huxley completed his first (unpublished) novel at the age of 17 and began writing seriously in his early twenties, establishing himself as a successful writer and social satirist. His first published novels were social satires, Crome Yellow (1921), Antic Hay (1923), Those Barren Leaves (1925), and Point Counter Point (1928). Brave New World (1932) was his fifth novel and first dystopian work. In the 1920s, he was also a contributor to Vanity Fair and British Vogue magazines. Contact with the Bloomsbury Set During the First World War, Huxley spent much of his time at Garsington Manor near Oxford, home of Lady Ottoline Morrell, working as a farm labourer. While at the Manor, he met several Bloomsbury Group figures, including Bertrand Russell, Alfred North Whitehead, and Clive Bell. Later, in Crome Yellow (1921), he caricatured the Garsington lifestyle. Jobs were very scarce, but in 1919, John Middleton Murry was reorganising the Athenaeum and invited Huxley to join the staff. He accepted immediately, and quickly married the Belgian refugee Maria Nys (1899-1955), also at Garsington. They lived with their young son in Italy part of the time during the 1920s, where Huxley would visit his friend D. H. Lawrence. Following Lawrence's death in 1930, Huxley edited Lawrence's letters (1932). Very early in 1929, in London, Huxley met Gerald Heard, a brilliant writer and broadcaster, philosopher and interpreter of contemporary science. Works of this period included important novels on the dehumanising aspects of scientific progress, most famously Brave New World, and on pacifist themes (for example, Eyeless in Gaza). In Brave New World, set in a dystopian London, Huxley portrays a society operating on the principles of mass production and Pavlovian conditioning. Huxley was strongly influenced by F. Matthias Alexander, and included him as a character in Eyeless in Gaza (1936). Beginning in this period, Huxley began to write and edit non-fiction works on pacifist issues, including Ends and Means (1937), An Encyclopedia of Pacifism, and Pacifism and Philosophy, and was an active member of the Peace Pledge Union.

Life in the United States In 1937, Huxley moved to Hollywood with his wife Maria, son Matthew Huxley, and friend Gerald Heard. He lived in the U.S., mainly in southern California, until his death, and also for a time in Taos, New Mexico, where he wrote Ends and Means (published in 1937). The book contains tracts on war, religion, nationalism, and ethics. Heard introduced Huxley to Vedanta (Upanishad-centered philosophy), meditation, and vegetarianism through the principle of ahimsa. In 1938, Huxley befriended Jiddu Krishnamurti, whose teachings he greatly admired. Huxley and Krishnamurti entered into an enduring exchange (sometimes edging on debate) over many years, with Krishnamurti representing the more rarefied, detached, ivory-tower perspective and Huxley, with his pragmatic concerns, the more socially and historically informed position. Huxley provided an introduction to Krishnamurti's quintessential statement, The First and Last Freedom (1954). Huxley also became a Vedantist in the circle of Hindu Swami Prabhavananda, and introduced Christopher Isherwood to this circle. Not long afterwards, Huxley wrote his book on widely held spiritual values and ideas, The Perennial Philosophy, which discussed the teachings of renowned mystics of the world. Huxley's book affirmed a sensibility that insists there are realities beyond the generally accepted "five senses" and that there is genuine meaning for humans beyond both sensual satisfactions and sentimentalities. Huxley became a close friend of Remsen Bird, president of Occidental College. He spent much time at the college, which is in the Eagle Rock neighbourhood of Los Angeles. The college appears as "Tarzana College" in his satirical novel After Many a Summer (1939). The novel won Huxley a British literary award, the 1939 James Tait Black Memorial Prize for fiction. Huxley also incorporated Bird into the novel. During this period, Huxley earned a substantial income as a Hollywood screenwriter; Christopher Isherwood, in his autobiography My Guru and His Disciple, states that Huxley earned more than $3,000 per week (approximately $50,000 in 2020 dollars) as a screenwriter, and that he used much of it to transport Jewish and left-wing writer and artist refugees from Hitler's Germany to the US. In March 1938, Huxley's friend Anita Loos, a novelist and screenwriter, put him in touch with Metro-Goldwyn-Mayer (MGM), which hired him for Madame Curie which was originally to star Greta Garbo and be directed by George Cukor. (Eventually, the film was completed by MGM in 1943 with a different director and cast.) Huxley received screen credit for Pride and Prejudice (1940) and was paid for his work on a number of other films, including Jane Eyre (1944). He was commissioned by Walt Disney in 1945 to write a script based on Alice's Adventures in Wonderland and the biography of the story's author, Lewis Carroll. The script was not used, however. Huxley wrote an introduction to the posthumous publication of J. D. Unwin's 1940 book Hopousia or The Sexual and Economic Foundations of a New Society.

Life in the United States In 1937, Huxley moved to Hollywood with his wife Maria, son Matthew Huxley, and friend Gerald Heard. He lived in the U.S., mainly in southern California, until his death, and also for a time in Taos, New Mexico, where he wrote Ends and Means (published in 1937). The book contains tracts on war, religion, nationalism, and ethics. Heard introduced Huxley to Vedanta (Upanishad-centered philosophy), meditation, and vegetarianism through the principle of ahimsa. In 1938, Huxley befriended Jiddu Krishnamurti, whose teachings he greatly admired. Huxley and Krishnamurti entered into an enduring exchange (sometimes edging on debate) over many years, with Krishnamurti representing the more rarefied, detached, ivory-tower perspective and Huxley, with his pragmatic concerns, the more socially and historically informed position. Huxley provided an introduction to Krishnamurti's quintessential statement, The First and Last Freedom (1954). Huxley also became a Vedantist in the circle of Hindu Swami Prabhavananda, and introduced Christopher Isherwood to this circle. Not long afterwards, Huxley wrote his book on widely held spiritual values and ideas, The Perennial Philosophy, which discussed the teachings of renowned mystics of the world. Huxley's book affirmed a sensibility that insists there are realities beyond the generally accepted "five senses" and that there is genuine meaning for humans beyond both sensual satisfactions and sentimentalities. Huxley became a close friend of Remsen Bird, president of Occidental College. He spent much time at the college, which is in the Eagle Rock neighbourhood of Los Angeles. The college appears as "Tarzana College" in his satirical novel After Many a Summer (1939). The novel won Huxley a British literary award, the 1939 James Tait Black Memorial Prize for fiction. Huxley also incorporated Bird into the novel. During this period, Huxley earned a substantial income as a Hollywood screenwriter; Christopher Isherwood, in his autobiography My Guru and His Disciple, states that Huxley earned more than $3,000 per week (approximately $50,000 in 2020 dollars) as a screenwriter, and that he used much of it to transport Jewish and left-wing writer and artist refugees from Hitler's Germany to the US. In March 1938, Huxley's friend Anita Loos, a novelist and screenwriter, put him in touch with Metro-Goldwyn-Mayer (MGM), which hired him for Madame Curie which was originally to star Greta Garbo and be directed by George Cukor. (Eventually, the film was completed by MGM in 1943 with a different director and cast.) Huxley received screen credit for Pride and Prejudice (1940) and was paid for his work on a number of other films, including Jane Eyre (1944). He was commissioned by Walt Disney in 1945 to write a script based on Alice's Adventures in Wonderland and the biography of the story's author, Lewis Carroll. The script was not used, however. Huxley wrote an introduction to the posthumous publication of J. D. Unwin's 1940 book Hopousia or The Sexual and Economic Foundations of a New Society.

Life in the United States In 1937, Huxley moved to Hollywood with his wife Maria, son Matthew Huxley, and friend Gerald Heard. He lived in the U.S., mainly in southern California, until his death, and also for a time in Taos, New Mexico, where he wrote Ends and Means (published in 1937). The book contains tracts on war, religion, nationalism, and ethics. Heard introduced Huxley to Vedanta (Upanishad-centered philosophy), meditation, and vegetarianism through the principle of ahimsa. In 1938, Huxley befriended Jiddu Krishnamurti, whose teachings he greatly admired. Huxley and Krishnamurti entered into an enduring exchange (sometimes edging on debate) over many years, with Krishnamurti representing the more rarefied, detached, ivory-tower perspective and Huxley, with his pragmatic concerns, the more socially and historically informed position. Huxley provided an introduction to Krishnamurti's quintessential statement, The First and Last Freedom (1954). Huxley also became a Vedantist in the circle of Hindu Swami Prabhavananda, and introduced Christopher Isherwood to this circle. Not long afterwards, Huxley wrote his book on widely held spiritual values and ideas, The Perennial Philosophy, which discussed the teachings of renowned mystics of the world. Huxley's book affirmed a sensibility that insists there are realities beyond the generally accepted "five senses" and that there is genuine meaning for humans beyond both sensual satisfactions and sentimentalities. Huxley became a close friend of Remsen Bird, president of Occidental College. He spent much time at the college, which is in the Eagle Rock neighbourhood of Los Angeles. The college appears as "Tarzana College" in his satirical novel After Many a Summer (1939). The novel won Huxley a British literary award, the 1939 James Tait Black Memorial Prize for fiction. Huxley also incorporated Bird into the novel. During this period, Huxley earned a substantial income as a Hollywood screenwriter; Christopher Isherwood, in his autobiography My Guru and His Disciple, states that Huxley earned more than $3,000 per week (approximately $50,000 in 2020 dollars) as a screenwriter, and that he used much of it to transport Jewish and left-wing writer and artist refugees from Hitler's Germany to the US. In March 1938, Huxley's friend Anita Loos, a novelist and screenwriter, put him in touch with Metro-Goldwyn-Mayer (MGM), which hired him for Madame Curie which was originally to star Greta Garbo and be directed by George Cukor. (Eventually, the film was completed by MGM in 1943 with a different director and cast.) Huxley received screen credit for Pride and Prejudice (1940) and was paid for his work on a number of other films, including Jane Eyre (1944). He was commissioned by Walt Disney in 1945 to write a script based on Alice's Adventures in Wonderland and the biography of the story's author, Lewis Carroll. The script was not used, however. Huxley wrote an introduction to the posthumous publication of J. D. Unwin's 1940 book Hopousia or The Sexual and Economic Foundations of a New Society.

On 21 October 1949, Huxley wrote to George Orwell, author of Nineteen Eighty-Four, congratulating him on "how fine and how profoundly important the book is". In his letter to Orwell, he predicted: In 1953, Huxley and Maria applied for United States citizenship and presented themselves for examination. When Huxley refused to bear arms for the U.S. and would not state that his objections were based on religious ideals, the only excuse allowed under the McCarran Act, the judge had to adjourn the proceedings. He withdrew his application. Nevertheless, he remained in the U.S. In 1959, Huxley turned down an offer to be made a Knight Bachelor by the Macmillan government without putting forward a reason; his brother Julian had been knighted in 1958, while another brother Andrew would be knighted in 1974. In the fall semester of 1960 Huxley was invited by Professor Huston Smith to be the Carnegie Visiting Professor of Humanities at the Massachusetts Institute of Technology (MIT). As part of the MIT centennial program of events organised by the Department of Humanities, Huxley presented a series of lectures titled, "What a Piece of Work is a Man" which concerned history, language, and art. Late-in-life perspectives Biographer Harold H. Watts wrote that Huxley's writings in the "final and extended period of his life" are "the work of a man who is meditating on the central problems of many modern men". Huxley had deeply felt apprehensions about the future the developed world might make for itself. From these, he made some warnings in his writings and talks. In a 1958 televised interview conducted by journalist Mike Wallace, Huxley outlined several major concerns: the difficulties and dangers of world overpopulation; the tendency towards distinctly hierarchical social organisation; the crucial importance of evaluating the use of technology in mass societies susceptible to persuasion; the tendency to promote modern politicians to a naive public as well-marketed commodities. In a December 1962 letter to brother Julian, summarizing a paper he had presented in Santa Barbara, he wrote, "What I said was that if we didn't pretty quickly start thinking of human problems in ecological terms rather than in terms of power politics we should very soon be in a bad way." Huxley's engagement with Eastern wisdom traditions was entirely compatible with a strong appreciation of modern science. Biographer Milton Birnbaum wrote that Huxley "ended by embracing both science and Eastern religion". In his last book, Literature and Science, Huxley wrote that "The ethical and philosophical implications of modern science are more Buddhist than Christian...." In "A Philosopher's Visionary Prediction," published one month before he died, Huxley endorsed training in general semantics and "the nonverbal world of culturally uncontaminated consciousness," writing that "We must learn how to be mentally silent, we must cultivate the art of pure receptivity.... [T]he individual must learn to decondition himself, must be able to cut holes in the fence of verbalized symbols that hems him in."

On 21 October 1949, Huxley wrote to George Orwell, author of Nineteen Eighty-Four, congratulating him on "how fine and how profoundly important the book is". In his letter to Orwell, he predicted: In 1953, Huxley and Maria applied for United States citizenship and presented themselves for examination. When Huxley refused to bear arms for the U.S. and would not state that his objections were based on religious ideals, the only excuse allowed under the McCarran Act, the judge had to adjourn the proceedings. He withdrew his application. Nevertheless, he remained in the U.S. In 1959, Huxley turned down an offer to be made a Knight Bachelor by the Macmillan government without putting forward a reason; his brother Julian had been knighted in 1958, while another brother Andrew would be knighted in 1974. In the fall semester of 1960 Huxley was invited by Professor Huston Smith to be the Carnegie Visiting Professor of Humanities at the Massachusetts Institute of Technology (MIT). As part of the MIT centennial program of events organised by the Department of Humanities, Huxley presented a series of lectures titled, "What a Piece of Work is a Man" which concerned history, language, and art. Late-in-life perspectives Biographer Harold H. Watts wrote that Huxley's writings in the "final and extended period of his life" are "the work of a man who is meditating on the central problems of many modern men". Huxley had deeply felt apprehensions about the future the developed world might make for itself. From these, he made some warnings in his writings and talks. In a 1958 televised interview conducted by journalist Mike Wallace, Huxley outlined several major concerns: the difficulties and dangers of world overpopulation; the tendency towards distinctly hierarchical social organisation; the crucial importance of evaluating the use of technology in mass societies susceptible to persuasion; the tendency to promote modern politicians to a naive public as well-marketed commodities. In a December 1962 letter to brother Julian, summarizing a paper he had presented in Santa Barbara, he wrote, "What I said was that if we didn't pretty quickly start thinking of human problems in ecological terms rather than in terms of power politics we should very soon be in a bad way." Huxley's engagement with Eastern wisdom traditions was entirely compatible with a strong appreciation of modern science. Biographer Milton Birnbaum wrote that Huxley "ended by embracing both science and Eastern religion". In his last book, Literature and Science, Huxley wrote that "The ethical and philosophical implications of modern science are more Buddhist than Christian...." In "A Philosopher's Visionary Prediction," published one month before he died, Huxley endorsed training in general semantics and "the nonverbal world of culturally uncontaminated consciousness," writing that "We must learn how to be mentally silent, we must cultivate the art of pure receptivity.... [T]he individual must learn to decondition himself, must be able to cut holes in the fence of verbalized symbols that hems him in."

On 21 October 1949, Huxley wrote to George Orwell, author of Nineteen Eighty-Four, congratulating him on "how fine and how profoundly important the book is". In his letter to Orwell, he predicted: In 1953, Huxley and Maria applied for United States citizenship and presented themselves for examination. When Huxley refused to bear arms for the U.S. and would not state that his objections were based on religious ideals, the only excuse allowed under the McCarran Act, the judge had to adjourn the proceedings. He withdrew his application. Nevertheless, he remained in the U.S. In 1959, Huxley turned down an offer to be made a Knight Bachelor by the Macmillan government without putting forward a reason; his brother Julian had been knighted in 1958, while another brother Andrew would be knighted in 1974. In the fall semester of 1960 Huxley was invited by Professor Huston Smith to be the Carnegie Visiting Professor of Humanities at the Massachusetts Institute of Technology (MIT). As part of the MIT centennial program of events organised by the Department of Humanities, Huxley presented a series of lectures titled, "What a Piece of Work is a Man" which concerned history, language, and art. Late-in-life perspectives Biographer Harold H. Watts wrote that Huxley's writings in the "final and extended period of his life" are "the work of a man who is meditating on the central problems of many modern men". Huxley had deeply felt apprehensions about the future the developed world might make for itself. From these, he made some warnings in his writings and talks. In a 1958 televised interview conducted by journalist Mike Wallace, Huxley outlined several major concerns: the difficulties and dangers of world overpopulation; the tendency towards distinctly hierarchical social organisation; the crucial importance of evaluating the use of technology in mass societies susceptible to persuasion; the tendency to promote modern politicians to a naive public as well-marketed commodities. In a December 1962 letter to brother Julian, summarizing a paper he had presented in Santa Barbara, he wrote, "What I said was that if we didn't pretty quickly start thinking of human problems in ecological terms rather than in terms of power politics we should very soon be in a bad way." Huxley's engagement with Eastern wisdom traditions was entirely compatible with a strong appreciation of modern science. Biographer Milton Birnbaum wrote that Huxley "ended by embracing both science and Eastern religion". In his last book, Literature and Science, Huxley wrote that "The ethical and philosophical implications of modern science are more Buddhist than Christian...." In "A Philosopher's Visionary Prediction," published one month before he died, Huxley endorsed training in general semantics and "the nonverbal world of culturally uncontaminated consciousness," writing that "We must learn how to be mentally silent, we must cultivate the art of pure receptivity.... [T]he individual must learn to decondition himself, must be able to cut holes in the fence of verbalized symbols that hems him in."

Association with Vedanta Beginning in 1939 and continuing until his death in 1963, Huxley had an extensive association with the Vedanta Society of Southern California, founded and headed by Swami Prabhavananda. Together with Gerald Heard, Christopher Isherwood and other followers, he was initiated by the Swami and was taught meditation and spiritual practices. In 1944, Huxley wrote the introduction to the "Bhagavad Gita: The Song of God", translated by Swami Prabhavananda and Christopher Isherwood, which was published by the Vedanta Society of Southern California. From 1941 until 1960, Huxley contributed 48 articles to Vedanta and the West, published by the society. He also served on the editorial board with Isherwood, Heard, and playwright John Van Druten from 1951 through 1962. Huxley also occasionally lectured at the Hollywood and Santa Barbara Vedanta temples. Two of those lectures have been released on CD: Knowledge and Understanding and Who Are We? from 1955. Nonetheless, Huxley's agnosticism, together with his speculative propensity, made it difficult for him to fully embrace any form of institutionalised religion. Psychedelic drug use and mystical experiences In the spring of 1953, Huxley had his first experience with the psychedelic drug mescaline. Huxley had initiated a correspondence with Doctor Humphry Osmond, a British psychiatrist then employed in a Canadian institution, and eventually asked him to supply a dose of mescaline; Osmond obliged and supervised Huxley's session in southern California. After the publication of The Doors of Perception, in which he recounted this experience, Huxley and Swami Prabhavananda disagreed about the meaning and importance of the psychedelic drug experience, which may have caused the relationship to cool, but Huxley continued to write articles for the society's journal, lecture at the temple, and attend social functions. Huxley later had an experience on mescaline that he considered more profound than those detailed in The Doors of Perception. Huxley wrote that "The mystical experience is doubly valuable; it is valuable because it gives the experiencer a better understanding of himself and the world and because it may help him to lead a less self-centered and more creative life." Eyesight Differing accounts exist about the details of the quality of Huxley's eyesight at specific points in his life. Circa 1939, Huxley encountered the Bates method, in which he was instructed by Margaret Darst Corbett. In 1940, Huxley relocated from Hollywood to a ranchito in the high desert hamlet of Llano, California, in northern Los Angeles County. Huxley then said that his sight improved dramatically with the Bates Method and the extreme and pure natural lighting of the southwestern American desert. He reported that, for the first time in more than 25 years, he was able to read without glasses and without strain. He even tried driving a car along the dirt road beside the ranch. He wrote a book about his experiences with the Bates Method, The Art of Seeing, which was published in 1942 (U.S.), 1943 (UK).

Association with Vedanta Beginning in 1939 and continuing until his death in 1963, Huxley had an extensive association with the Vedanta Society of Southern California, founded and headed by Swami Prabhavananda. Together with Gerald Heard, Christopher Isherwood and other followers, he was initiated by the Swami and was taught meditation and spiritual practices. In 1944, Huxley wrote the introduction to the "Bhagavad Gita: The Song of God", translated by Swami Prabhavananda and Christopher Isherwood, which was published by the Vedanta Society of Southern California. From 1941 until 1960, Huxley contributed 48 articles to Vedanta and the West, published by the society. He also served on the editorial board with Isherwood, Heard, and playwright John Van Druten from 1951 through 1962. Huxley also occasionally lectured at the Hollywood and Santa Barbara Vedanta temples. Two of those lectures have been released on CD: Knowledge and Understanding and Who Are We? from 1955. Nonetheless, Huxley's agnosticism, together with his speculative propensity, made it difficult for him to fully embrace any form of institutionalised religion. Psychedelic drug use and mystical experiences In the spring of 1953, Huxley had his first experience with the psychedelic drug mescaline. Huxley had initiated a correspondence with Doctor Humphry Osmond, a British psychiatrist then employed in a Canadian institution, and eventually asked him to supply a dose of mescaline; Osmond obliged and supervised Huxley's session in southern California. After the publication of The Doors of Perception, in which he recounted this experience, Huxley and Swami Prabhavananda disagreed about the meaning and importance of the psychedelic drug experience, which may have caused the relationship to cool, but Huxley continued to write articles for the society's journal, lecture at the temple, and attend social functions. Huxley later had an experience on mescaline that he considered more profound than those detailed in The Doors of Perception. Huxley wrote that "The mystical experience is doubly valuable; it is valuable because it gives the experiencer a better understanding of himself and the world and because it may help him to lead a less self-centered and more creative life." Eyesight Differing accounts exist about the details of the quality of Huxley's eyesight at specific points in his life. Circa 1939, Huxley encountered the Bates method, in which he was instructed by Margaret Darst Corbett. In 1940, Huxley relocated from Hollywood to a ranchito in the high desert hamlet of Llano, California, in northern Los Angeles County. Huxley then said that his sight improved dramatically with the Bates Method and the extreme and pure natural lighting of the southwestern American desert. He reported that, for the first time in more than 25 years, he was able to read without glasses and without strain. He even tried driving a car along the dirt road beside the ranch. He wrote a book about his experiences with the Bates Method, The Art of Seeing, which was published in 1942 (U.S.), 1943 (UK).

Association with Vedanta Beginning in 1939 and continuing until his death in 1963, Huxley had an extensive association with the Vedanta Society of Southern California, founded and headed by Swami Prabhavananda. Together with Gerald Heard, Christopher Isherwood and other followers, he was initiated by the Swami and was taught meditation and spiritual practices. In 1944, Huxley wrote the introduction to the "Bhagavad Gita: The Song of God", translated by Swami Prabhavananda and Christopher Isherwood, which was published by the Vedanta Society of Southern California. From 1941 until 1960, Huxley contributed 48 articles to Vedanta and the West, published by the society. He also served on the editorial board with Isherwood, Heard, and playwright John Van Druten from 1951 through 1962. Huxley also occasionally lectured at the Hollywood and Santa Barbara Vedanta temples. Two of those lectures have been released on CD: Knowledge and Understanding and Who Are We? from 1955. Nonetheless, Huxley's agnosticism, together with his speculative propensity, made it difficult for him to fully embrace any form of institutionalised religion. Psychedelic drug use and mystical experiences In the spring of 1953, Huxley had his first experience with the psychedelic drug mescaline. Huxley had initiated a correspondence with Doctor Humphry Osmond, a British psychiatrist then employed in a Canadian institution, and eventually asked him to supply a dose of mescaline; Osmond obliged and supervised Huxley's session in southern California. After the publication of The Doors of Perception, in which he recounted this experience, Huxley and Swami Prabhavananda disagreed about the meaning and importance of the psychedelic drug experience, which may have caused the relationship to cool, but Huxley continued to write articles for the society's journal, lecture at the temple, and attend social functions. Huxley later had an experience on mescaline that he considered more profound than those detailed in The Doors of Perception. Huxley wrote that "The mystical experience is doubly valuable; it is valuable because it gives the experiencer a better understanding of himself and the world and because it may help him to lead a less self-centered and more creative life." Eyesight Differing accounts exist about the details of the quality of Huxley's eyesight at specific points in his life. Circa 1939, Huxley encountered the Bates method, in which he was instructed by Margaret Darst Corbett. In 1940, Huxley relocated from Hollywood to a ranchito in the high desert hamlet of Llano, California, in northern Los Angeles County. Huxley then said that his sight improved dramatically with the Bates Method and the extreme and pure natural lighting of the southwestern American desert. He reported that, for the first time in more than 25 years, he was able to read without glasses and without strain. He even tried driving a car along the dirt road beside the ranch. He wrote a book about his experiences with the Bates Method, The Art of Seeing, which was published in 1942 (U.S.), 1943 (UK).

The book contained some generally disputed theories, and its publication created a growing degree of popular controversy about Huxley's eyesight. It was, and is, widely believed that Huxley was nearly blind since the illness in his teens, despite the partial recovery that had enabled him to study at Oxford. For example, some ten years after publication of The Art of Seeing, in 1952, Bennett Cerf was present when Huxley spoke at a Hollywood banquet, wearing no glasses and apparently reading his paper from the lectern without difficulty: "Then suddenly he faltered—and the disturbing truth became obvious. He wasn't reading his address at all. He had learned it by heart. To refresh his memory he brought the paper closer and closer to his eyes. When it was only an inch or so away he still couldn't read it, and had to fish for a magnifying glass in his pocket to make the typing visible to him. It was an agonising moment." Brazilian author João Ubaldo Ribeiro, who as a young journalist spent several evenings in the Huxleys' company in the late 1950s, wrote that Huxley had said to him, with a wry smile: "I can hardly see at all. And I don't give a damn, really." On the other hand, Huxley's second wife, Laura Archera, later emphasised in her biographical account, This Timeless Moment: "One of the great achievements of his life: that of having regained his sight." After revealing a letter she wrote to the Los Angeles Times disclaiming the label of Huxley as a "poor fellow who can hardly see" by Walter C. Alvarez, she tempered her statement: "Although I feel it was an injustice to treat Aldous as though he were blind, it is true there were many indications of his impaired vision. For instance, although Aldous did not wear glasses, he would quite often use a magnifying lens." Laura Huxley proceeded to elaborate a few nuances of inconsistency peculiar to Huxley's vision. Her account, in this respect, agrees with the following sample of Huxley's own words from The Art of Seeing: "The most characteristic fact about the functioning of the total organism, or any part of the organism, is that it is not constant, but highly variable." Nevertheless, the topic of Huxley's eyesight has continued to endure similar, significant controversy. American popular science author Steven Johnson, in his book Mind Wide Open, quotes Huxley about his difficulties with visual encoding: "I am and, for as long as I can remember, I have always been a poor visualizer. Words, even the pregnant words of poets, do not evoke pictures in my mind. No hypnagogic visions greet me on the verge of sleep. When I recall something, the memory does not present itself to me as a vividly seen event or object.

The book contained some generally disputed theories, and its publication created a growing degree of popular controversy about Huxley's eyesight. It was, and is, widely believed that Huxley was nearly blind since the illness in his teens, despite the partial recovery that had enabled him to study at Oxford. For example, some ten years after publication of The Art of Seeing, in 1952, Bennett Cerf was present when Huxley spoke at a Hollywood banquet, wearing no glasses and apparently reading his paper from the lectern without difficulty: "Then suddenly he faltered—and the disturbing truth became obvious. He wasn't reading his address at all. He had learned it by heart. To refresh his memory he brought the paper closer and closer to his eyes. When it was only an inch or so away he still couldn't read it, and had to fish for a magnifying glass in his pocket to make the typing visible to him. It was an agonising moment." Brazilian author João Ubaldo Ribeiro, who as a young journalist spent several evenings in the Huxleys' company in the late 1950s, wrote that Huxley had said to him, with a wry smile: "I can hardly see at all. And I don't give a damn, really." On the other hand, Huxley's second wife, Laura Archera, later emphasised in her biographical account, This Timeless Moment: "One of the great achievements of his life: that of having regained his sight." After revealing a letter she wrote to the Los Angeles Times disclaiming the label of Huxley as a "poor fellow who can hardly see" by Walter C. Alvarez, she tempered her statement: "Although I feel it was an injustice to treat Aldous as though he were blind, it is true there were many indications of his impaired vision. For instance, although Aldous did not wear glasses, he would quite often use a magnifying lens." Laura Huxley proceeded to elaborate a few nuances of inconsistency peculiar to Huxley's vision. Her account, in this respect, agrees with the following sample of Huxley's own words from The Art of Seeing: "The most characteristic fact about the functioning of the total organism, or any part of the organism, is that it is not constant, but highly variable." Nevertheless, the topic of Huxley's eyesight has continued to endure similar, significant controversy. American popular science author Steven Johnson, in his book Mind Wide Open, quotes Huxley about his difficulties with visual encoding: "I am and, for as long as I can remember, I have always been a poor visualizer. Words, even the pregnant words of poets, do not evoke pictures in my mind. No hypnagogic visions greet me on the verge of sleep. When I recall something, the memory does not present itself to me as a vividly seen event or object.

The book contained some generally disputed theories, and its publication created a growing degree of popular controversy about Huxley's eyesight. It was, and is, widely believed that Huxley was nearly blind since the illness in his teens, despite the partial recovery that had enabled him to study at Oxford. For example, some ten years after publication of The Art of Seeing, in 1952, Bennett Cerf was present when Huxley spoke at a Hollywood banquet, wearing no glasses and apparently reading his paper from the lectern without difficulty: "Then suddenly he faltered—and the disturbing truth became obvious. He wasn't reading his address at all. He had learned it by heart. To refresh his memory he brought the paper closer and closer to his eyes. When it was only an inch or so away he still couldn't read it, and had to fish for a magnifying glass in his pocket to make the typing visible to him. It was an agonising moment." Brazilian author João Ubaldo Ribeiro, who as a young journalist spent several evenings in the Huxleys' company in the late 1950s, wrote that Huxley had said to him, with a wry smile: "I can hardly see at all. And I don't give a damn, really." On the other hand, Huxley's second wife, Laura Archera, later emphasised in her biographical account, This Timeless Moment: "One of the great achievements of his life: that of having regained his sight." After revealing a letter she wrote to the Los Angeles Times disclaiming the label of Huxley as a "poor fellow who can hardly see" by Walter C. Alvarez, she tempered her statement: "Although I feel it was an injustice to treat Aldous as though he were blind, it is true there were many indications of his impaired vision. For instance, although Aldous did not wear glasses, he would quite often use a magnifying lens." Laura Huxley proceeded to elaborate a few nuances of inconsistency peculiar to Huxley's vision. Her account, in this respect, agrees with the following sample of Huxley's own words from The Art of Seeing: "The most characteristic fact about the functioning of the total organism, or any part of the organism, is that it is not constant, but highly variable." Nevertheless, the topic of Huxley's eyesight has continued to endure similar, significant controversy. American popular science author Steven Johnson, in his book Mind Wide Open, quotes Huxley about his difficulties with visual encoding: "I am and, for as long as I can remember, I have always been a poor visualizer. Words, even the pregnant words of poets, do not evoke pictures in my mind. No hypnagogic visions greet me on the verge of sleep. When I recall something, the memory does not present itself to me as a vividly seen event or object.

By an effort of the will, I can evoke a not very vivid image of what happened yesterday afternoon ..." Personal life Huxley married on 10 July 1919 Maria Nys (10 September 1899 – 12 February 1955), a Belgian epidemiologist from Bellem, a village near Aalter, he met at Garsington, Oxfordshire, in 1919. They had one child, Matthew Huxley (19 April 1920 – 10 February 2005), who had a career as an author, anthropologist, and prominent epidemiologist. In 1955, Maria Huxley died of cancer. In 1956, Huxley married Laura Archera (1911–2007), also an author, as well as a violinist and psychotherapist. She wrote This Timeless Moment, a biography of Huxley. She told the story of their marriage through Mary Ann Braubach's 2010 documentary, Huxley on Huxley. Huxley was diagnosed with laryngeal cancer in 1960; in the years that followed, with his health deteriorating, he wrote the Utopian novel Island, and gave lectures on "Human Potentialities" both at the UCSF Medical Center and at the Esalen Institute. These lectures were fundamental to the beginning of the Human Potential Movement. Huxley was a close friend of Jiddu Krishnamurti and Rosalind Rajagopal and was involved in the creation of the Happy Valley School, now Besant Hill School of Happy Valley, in Ojai, California. The most substantial collection of Huxley's few remaining papers, following the destruction of most in the 1961 Bel Air Fire, is at the Library of the University of California, Los Angeles. Some are also at the Stanford University Libraries. On 9 April 1962 Huxley was informed he was elected Companion of Literature by the Royal Society of Literature, the senior literary organisation in Britain, and he accepted the title via letter on 28 April 1962. The correspondence between Huxley and the society is kept at the Cambridge University Library. The society invited Huxley to appear at a banquet and give a lecture at Somerset House, London, in June 1963. Huxley wrote a draft of the speech he intended to give at the society; however, his deteriorating health meant he was not able to attend. Death On his deathbed, unable to speak owing to advanced laryngeal cancer, Huxley made a written request to his wife Laura for "LSD, 100 µg, intramuscular." According to her account of his death in This Timeless Moment, she obliged with an injection at 11:20 a.m. and a second dose an hour later; Huxley died aged 69, at 5:20 p.m. (Los Angeles time), on 22 November 1963. Media coverage of Huxley's death, along with that of fellow British author C. S. Lewis, was overshadowed by the assassination of American President John F. Kennedy on the same day, less than seven hours before Huxley's death.

By an effort of the will, I can evoke a not very vivid image of what happened yesterday afternoon ..." Personal life Huxley married on 10 July 1919 Maria Nys (10 September 1899 – 12 February 1955), a Belgian epidemiologist from Bellem, a village near Aalter, he met at Garsington, Oxfordshire, in 1919. They had one child, Matthew Huxley (19 April 1920 – 10 February 2005), who had a career as an author, anthropologist, and prominent epidemiologist. In 1955, Maria Huxley died of cancer. In 1956, Huxley married Laura Archera (1911–2007), also an author, as well as a violinist and psychotherapist. She wrote This Timeless Moment, a biography of Huxley. She told the story of their marriage through Mary Ann Braubach's 2010 documentary, Huxley on Huxley. Huxley was diagnosed with laryngeal cancer in 1960; in the years that followed, with his health deteriorating, he wrote the Utopian novel Island, and gave lectures on "Human Potentialities" both at the UCSF Medical Center and at the Esalen Institute. These lectures were fundamental to the beginning of the Human Potential Movement. Huxley was a close friend of Jiddu Krishnamurti and Rosalind Rajagopal and was involved in the creation of the Happy Valley School, now Besant Hill School of Happy Valley, in Ojai, California. The most substantial collection of Huxley's few remaining papers, following the destruction of most in the 1961 Bel Air Fire, is at the Library of the University of California, Los Angeles. Some are also at the Stanford University Libraries. On 9 April 1962 Huxley was informed he was elected Companion of Literature by the Royal Society of Literature, the senior literary organisation in Britain, and he accepted the title via letter on 28 April 1962. The correspondence between Huxley and the society is kept at the Cambridge University Library. The society invited Huxley to appear at a banquet and give a lecture at Somerset House, London, in June 1963. Huxley wrote a draft of the speech he intended to give at the society; however, his deteriorating health meant he was not able to attend. Death On his deathbed, unable to speak owing to advanced laryngeal cancer, Huxley made a written request to his wife Laura for "LSD, 100 µg, intramuscular." According to her account of his death in This Timeless Moment, she obliged with an injection at 11:20 a.m. and a second dose an hour later; Huxley died aged 69, at 5:20 p.m. (Los Angeles time), on 22 November 1963. Media coverage of Huxley's death, along with that of fellow British author C. S. Lewis, was overshadowed by the assassination of American President John F. Kennedy on the same day, less than seven hours before Huxley's death.

By an effort of the will, I can evoke a not very vivid image of what happened yesterday afternoon ..." Personal life Huxley married on 10 July 1919 Maria Nys (10 September 1899 – 12 February 1955), a Belgian epidemiologist from Bellem, a village near Aalter, he met at Garsington, Oxfordshire, in 1919. They had one child, Matthew Huxley (19 April 1920 – 10 February 2005), who had a career as an author, anthropologist, and prominent epidemiologist. In 1955, Maria Huxley died of cancer. In 1956, Huxley married Laura Archera (1911–2007), also an author, as well as a violinist and psychotherapist. She wrote This Timeless Moment, a biography of Huxley. She told the story of their marriage through Mary Ann Braubach's 2010 documentary, Huxley on Huxley. Huxley was diagnosed with laryngeal cancer in 1960; in the years that followed, with his health deteriorating, he wrote the Utopian novel Island, and gave lectures on "Human Potentialities" both at the UCSF Medical Center and at the Esalen Institute. These lectures were fundamental to the beginning of the Human Potential Movement. Huxley was a close friend of Jiddu Krishnamurti and Rosalind Rajagopal and was involved in the creation of the Happy Valley School, now Besant Hill School of Happy Valley, in Ojai, California. The most substantial collection of Huxley's few remaining papers, following the destruction of most in the 1961 Bel Air Fire, is at the Library of the University of California, Los Angeles. Some are also at the Stanford University Libraries. On 9 April 1962 Huxley was informed he was elected Companion of Literature by the Royal Society of Literature, the senior literary organisation in Britain, and he accepted the title via letter on 28 April 1962. The correspondence between Huxley and the society is kept at the Cambridge University Library. The society invited Huxley to appear at a banquet and give a lecture at Somerset House, London, in June 1963. Huxley wrote a draft of the speech he intended to give at the society; however, his deteriorating health meant he was not able to attend. Death On his deathbed, unable to speak owing to advanced laryngeal cancer, Huxley made a written request to his wife Laura for "LSD, 100 µg, intramuscular." According to her account of his death in This Timeless Moment, she obliged with an injection at 11:20 a.m. and a second dose an hour later; Huxley died aged 69, at 5:20 p.m. (Los Angeles time), on 22 November 1963. Media coverage of Huxley's death, along with that of fellow British author C. S. Lewis, was overshadowed by the assassination of American President John F. Kennedy on the same day, less than seven hours before Huxley's death.

In a 2009 article for New York magazine titled "The Eclipsed Celebrity Death Club", Christopher Bonanos wrote: This coincidence served as the basis for Peter Kreeft's book Between Heaven and Hell: A Dialog Somewhere Beyond Death with John F. Kennedy, C. S. Lewis, & Aldous Huxley, which imagines a conversation among the three men taking place in Purgatory following their deaths. Huxley's memorial service took place in London in December 1963; it was led by his elder brother Julian. On 27 October 1971, his ashes were interred in the family grave at the Watts Cemetery, home of the Watts Mortuary Chapel in Compton, Guildford, Surrey, England. Huxley had been a long-time friend of Russian composer Igor Stravinsky, who dedicated his last orchestral composition to Huxley. What became Variations: Aldous Huxley in memoriam was begun in July 1963, completed in October 1964, and premiered by the Chicago Symphony Orchestra on 17 April 1965. Awards 1939: James Tait Black Memorial Prize 1959: American Academy of Arts and Letters Award of Merit . 1962: Companion of Literature Film adaptations of Huxley's work 1950: Prelude to Fame based upon Young Archimedes 1968: Point Counter Point 1971: The Devils 1980: Brave New World 1998: Brave New World 2020: Brave New World Bibliography See also List of peace activists References Sources . Reprinted in Perspectives on Schoenberg and Stravinsky, revised edition, edited by Benjamin Boretz and Edward T. Cone. New York: W. W. Norton, 1972. Further reading Anderson, Jack. 4 July 1982. "Ballet: Suzanne Farrell in Variations Premiere". The New York Times. Atkins, John. Aldous Huxley: A Literary Study, J. Calder, 1956 Barnes, Clive. 1 April 1966. "Ballet: Still Another Balanchine-Stravinsky Pearl; City Troupe Performs in Premiere Here Variations for Huxley at State Theater". The New York Times, p. 28. Firchow, Peter. Aldous Huxley: Satirist and Novelist, U of Minnesota P, 1972 Firchow, Peter. The End of Utopia: A Study of Aldous Huxley's Brave New World, Bucknell UP, 1984 Huxley, Aldous. The Human Situation: Aldous Huxley Lectures at Santa Barbara 1959, Flamingo Modern Classic, 1994, Huxley, Laura Archera. This Timeless Moment, Celestial Arts, 2001, Meckier, Jerome. Aldous Huxley: Modern Satirical Novelist of Ideas, Firchow and Nugel editors, LIT Verlag Berlin-Hamburg-Münster, 2006, Morgan, W. John, 'Pacifism or Bourgeois Pacifism? Huxley, Orwell, and Caudwell', Chapter 5 in Morgan, W. John and Guilherme, Alexandre (Eds. ),Peace and War-Historical, Philosophical, and Anthropological Perspectives, Palgrave Macmillan, 2020, pp, 71–96. . Murray, Nicholas. Aldous Huxley, Macmillan, 2003, Poller, Jake. Aldous Huxley, Reaktion Critical Lives, 2021. . Poller, Jake. Aldous Huxley and Alternative Spirituality, Brill, 2019. . Rolo, Charles J. (ed.). The World of Aldous Huxley, Grosset Universal Library, 1947. Shaw, Jeffrey M. Illusions of Freedom: Thomas Merton and Jacques Ellul on Technology and the Human Condition. Eugene, Oregon: Wipf and Stock. 2014. . Shadurski, Maxim. The Nationality of Utopia: H. G. Wells, England, and the World State. New York and London: Routledge, 2020. (Chapter 5) Watt, Conrad (ed.).

In a 2009 article for New York magazine titled "The Eclipsed Celebrity Death Club", Christopher Bonanos wrote: This coincidence served as the basis for Peter Kreeft's book Between Heaven and Hell: A Dialog Somewhere Beyond Death with John F. Kennedy, C. S. Lewis, & Aldous Huxley, which imagines a conversation among the three men taking place in Purgatory following their deaths. Huxley's memorial service took place in London in December 1963; it was led by his elder brother Julian. On 27 October 1971, his ashes were interred in the family grave at the Watts Cemetery, home of the Watts Mortuary Chapel in Compton, Guildford, Surrey, England. Huxley had been a long-time friend of Russian composer Igor Stravinsky, who dedicated his last orchestral composition to Huxley. What became Variations: Aldous Huxley in memoriam was begun in July 1963, completed in October 1964, and premiered by the Chicago Symphony Orchestra on 17 April 1965. Awards 1939: James Tait Black Memorial Prize 1959: American Academy of Arts and Letters Award of Merit . 1962: Companion of Literature Film adaptations of Huxley's work 1950: Prelude to Fame based upon Young Archimedes 1968: Point Counter Point 1971: The Devils 1980: Brave New World 1998: Brave New World 2020: Brave New World Bibliography See also List of peace activists References Sources . Reprinted in Perspectives on Schoenberg and Stravinsky, revised edition, edited by Benjamin Boretz and Edward T. Cone. New York: W. W. Norton, 1972. Further reading Anderson, Jack. 4 July 1982. "Ballet: Suzanne Farrell in Variations Premiere". The New York Times. Atkins, John. Aldous Huxley: A Literary Study, J. Calder, 1956 Barnes, Clive. 1 April 1966. "Ballet: Still Another Balanchine-Stravinsky Pearl; City Troupe Performs in Premiere Here Variations for Huxley at State Theater". The New York Times, p. 28. Firchow, Peter. Aldous Huxley: Satirist and Novelist, U of Minnesota P, 1972 Firchow, Peter. The End of Utopia: A Study of Aldous Huxley's Brave New World, Bucknell UP, 1984 Huxley, Aldous. The Human Situation: Aldous Huxley Lectures at Santa Barbara 1959, Flamingo Modern Classic, 1994, Huxley, Laura Archera. This Timeless Moment, Celestial Arts, 2001, Meckier, Jerome. Aldous Huxley: Modern Satirical Novelist of Ideas, Firchow and Nugel editors, LIT Verlag Berlin-Hamburg-Münster, 2006, Morgan, W. John, 'Pacifism or Bourgeois Pacifism? Huxley, Orwell, and Caudwell', Chapter 5 in Morgan, W. John and Guilherme, Alexandre (Eds. ),Peace and War-Historical, Philosophical, and Anthropological Perspectives, Palgrave Macmillan, 2020, pp, 71–96. . Murray, Nicholas. Aldous Huxley, Macmillan, 2003, Poller, Jake. Aldous Huxley, Reaktion Critical Lives, 2021. . Poller, Jake. Aldous Huxley and Alternative Spirituality, Brill, 2019. . Rolo, Charles J. (ed.). The World of Aldous Huxley, Grosset Universal Library, 1947. Shaw, Jeffrey M. Illusions of Freedom: Thomas Merton and Jacques Ellul on Technology and the Human Condition. Eugene, Oregon: Wipf and Stock. 2014. . Shadurski, Maxim. The Nationality of Utopia: H. G. Wells, England, and the World State. New York and London: Routledge, 2020. (Chapter 5) Watt, Conrad (ed.).

In a 2009 article for New York magazine titled "The Eclipsed Celebrity Death Club", Christopher Bonanos wrote: This coincidence served as the basis for Peter Kreeft's book Between Heaven and Hell: A Dialog Somewhere Beyond Death with John F. Kennedy, C. S. Lewis, & Aldous Huxley, which imagines a conversation among the three men taking place in Purgatory following their deaths. Huxley's memorial service took place in London in December 1963; it was led by his elder brother Julian. On 27 October 1971, his ashes were interred in the family grave at the Watts Cemetery, home of the Watts Mortuary Chapel in Compton, Guildford, Surrey, England. Huxley had been a long-time friend of Russian composer Igor Stravinsky, who dedicated his last orchestral composition to Huxley. What became Variations: Aldous Huxley in memoriam was begun in July 1963, completed in October 1964, and premiered by the Chicago Symphony Orchestra on 17 April 1965. Awards 1939: James Tait Black Memorial Prize 1959: American Academy of Arts and Letters Award of Merit . 1962: Companion of Literature Film adaptations of Huxley's work 1950: Prelude to Fame based upon Young Archimedes 1968: Point Counter Point 1971: The Devils 1980: Brave New World 1998: Brave New World 2020: Brave New World Bibliography See also List of peace activists References Sources . Reprinted in Perspectives on Schoenberg and Stravinsky, revised edition, edited by Benjamin Boretz and Edward T. Cone. New York: W. W. Norton, 1972. Further reading Anderson, Jack. 4 July 1982. "Ballet: Suzanne Farrell in Variations Premiere". The New York Times. Atkins, John. Aldous Huxley: A Literary Study, J. Calder, 1956 Barnes, Clive. 1 April 1966. "Ballet: Still Another Balanchine-Stravinsky Pearl; City Troupe Performs in Premiere Here Variations for Huxley at State Theater". The New York Times, p. 28. Firchow, Peter. Aldous Huxley: Satirist and Novelist, U of Minnesota P, 1972 Firchow, Peter. The End of Utopia: A Study of Aldous Huxley's Brave New World, Bucknell UP, 1984 Huxley, Aldous. The Human Situation: Aldous Huxley Lectures at Santa Barbara 1959, Flamingo Modern Classic, 1994, Huxley, Laura Archera. This Timeless Moment, Celestial Arts, 2001, Meckier, Jerome. Aldous Huxley: Modern Satirical Novelist of Ideas, Firchow and Nugel editors, LIT Verlag Berlin-Hamburg-Münster, 2006, Morgan, W. John, 'Pacifism or Bourgeois Pacifism? Huxley, Orwell, and Caudwell', Chapter 5 in Morgan, W. John and Guilherme, Alexandre (Eds. ),Peace and War-Historical, Philosophical, and Anthropological Perspectives, Palgrave Macmillan, 2020, pp, 71–96. . Murray, Nicholas. Aldous Huxley, Macmillan, 2003, Poller, Jake. Aldous Huxley, Reaktion Critical Lives, 2021. . Poller, Jake. Aldous Huxley and Alternative Spirituality, Brill, 2019. . Rolo, Charles J. (ed.). The World of Aldous Huxley, Grosset Universal Library, 1947. Shaw, Jeffrey M. Illusions of Freedom: Thomas Merton and Jacques Ellul on Technology and the Human Condition. Eugene, Oregon: Wipf and Stock. 2014. . Shadurski, Maxim. The Nationality of Utopia: H. G. Wells, England, and the World State. New York and London: Routledge, 2020. (Chapter 5) Watt, Conrad (ed.).

Aldous Huxley, Routledge, 1997, External links Aldous Huxley full interview 1958: The Problems of Survival and Freedom in America Portraits at the National Portrait Gallery Raymond Fraser, George Wickes (Spring 1960). "Interview: Aldous Huxley: The Art of Fiction No. 24". The Paris Review. BBC discussion programme In our time: "Brave New World". Huxley and the novel. 9 April 2009. (Audio, 45 minutes) BBC In their own words series. 12 October 1958 (video, 12 mins) "The Ultimate Revolution" (talk at UC Berkeley, 20 March 1962) Huxley interviewed on The Mike Wallace Interview 18 May 1958 (video) Centre for Huxley Research Aldous Huxley Papers at University of California, Los Angeles Library Special Collections Online editions 1894 births 1963 deaths 20th-century English novelists 20th-century essayists Alumni of Balliol College, Oxford Anti-consumerists Bates method English emigrants to the United States 20th-century British short story writers Burials in Surrey Consciousness researchers and theorists Deaths from cancer in California Deaths from laryngeal cancer Duke University faculty English agnostics English essayists English expatriates in the United States English male novelists English male poets English male short story writers English pacifists English people of Cornish descent English satirists English science fiction writers English short story writers English travel writers Futurologists Human Potential Movement Aldous James Tait Black Memorial Prize recipients Male essayists Moral philosophers Mystics Neo-Vedanta People educated at Eton College People from Godalming Perennial philosophy Philosophers of culture Philosophers of ethics and morality Philosophers of literature Philosophers of mind Philosophers of technology Psychedelic drug advocates Writers from Los Angeles Writers from Taos, New Mexico 20th-century English philosophers Lost Generation writers

Aldous Huxley, Routledge, 1997, External links Aldous Huxley full interview 1958: The Problems of Survival and Freedom in America Portraits at the National Portrait Gallery Raymond Fraser, George Wickes (Spring 1960). "Interview: Aldous Huxley: The Art of Fiction No. 24". The Paris Review. BBC discussion programme In our time: "Brave New World". Huxley and the novel. 9 April 2009. (Audio, 45 minutes) BBC In their own words series. 12 October 1958 (video, 12 mins) "The Ultimate Revolution" (talk at UC Berkeley, 20 March 1962) Huxley interviewed on The Mike Wallace Interview 18 May 1958 (video) Centre for Huxley Research Aldous Huxley Papers at University of California, Los Angeles Library Special Collections Online editions 1894 births 1963 deaths 20th-century English novelists 20th-century essayists Alumni of Balliol College, Oxford Anti-consumerists Bates method English emigrants to the United States 20th-century British short story writers Burials in Surrey Consciousness researchers and theorists Deaths from cancer in California Deaths from laryngeal cancer Duke University faculty English agnostics English essayists English expatriates in the United States English male novelists English male poets English male short story writers English pacifists English people of Cornish descent English satirists English science fiction writers English short story writers English travel writers Futurologists Human Potential Movement Aldous James Tait Black Memorial Prize recipients Male essayists Moral philosophers Mystics Neo-Vedanta People educated at Eton College People from Godalming Perennial philosophy Philosophers of culture Philosophers of ethics and morality Philosophers of literature Philosophers of mind Philosophers of technology Psychedelic drug advocates Writers from Los Angeles Writers from Taos, New Mexico 20th-century English philosophers Lost Generation writers

Aldous Huxley, Routledge, 1997, External links Aldous Huxley full interview 1958: The Problems of Survival and Freedom in America Portraits at the National Portrait Gallery Raymond Fraser, George Wickes (Spring 1960). "Interview: Aldous Huxley: The Art of Fiction No. 24". The Paris Review. BBC discussion programme In our time: "Brave New World". Huxley and the novel. 9 April 2009. (Audio, 45 minutes) BBC In their own words series. 12 October 1958 (video, 12 mins) "The Ultimate Revolution" (talk at UC Berkeley, 20 March 1962) Huxley interviewed on The Mike Wallace Interview 18 May 1958 (video) Centre for Huxley Research Aldous Huxley Papers at University of California, Los Angeles Library Special Collections Online editions 1894 births 1963 deaths 20th-century English novelists 20th-century essayists Alumni of Balliol College, Oxford Anti-consumerists Bates method English emigrants to the United States 20th-century British short story writers Burials in Surrey Consciousness researchers and theorists Deaths from cancer in California Deaths from laryngeal cancer Duke University faculty English agnostics English essayists English expatriates in the United States English male novelists English male poets English male short story writers English pacifists English people of Cornish descent English satirists English science fiction writers English short story writers English travel writers Futurologists Human Potential Movement Aldous James Tait Black Memorial Prize recipients Male essayists Moral philosophers Mystics Neo-Vedanta People educated at Eton College People from Godalming Perennial philosophy Philosophers of culture Philosophers of ethics and morality Philosophers of literature Philosophers of mind Philosophers of technology Psychedelic drug advocates Writers from Los Angeles Writers from Taos, New Mexico 20th-century English philosophers Lost Generation writers

Ada Ada may refer to: Places Africa Ada Foah or Ada, Ghana, a town Ada (Ghana parliament constituency) Ada, Osun, a town in Osun State, Nigeria Asia Adeh, Urmia, also known as Ada, a village in West Azerbaijan Province Ada, Karaman, a village in Karaman Province, Turkey Australia and New Zealand Ada River (disambiguation), three rivers Europe Ada, Bosnia and Herzegovina, a village Ada, Croatia, a village Ada, Serbia, a town and municipality Ada Ciganlija or Ada, a river island artificially turned into a peninsula in Belgrade, Serbia North America United States Ada, Alabama, an unincorporated community Ada County, Idaho Ada, Kansas, an unincorporated community Ada Township, Michigan Ada, Minnesota, a city Ada Township, Dickey County, North Dakota Ada, Ohio, a village Ada, Oklahoma, a city Ada, Oregon, an unincorporated community Ada Township, Perkins County, South Dakota Ada, West Virginia, an unincorporated community Ada, Wisconsin, an unincorporated community Outer space 523 Ada, an asteroid Film and television Ada TV, a television channel in the Turkish Republic of Northern Cyprus Ada (1961 film), a 1961 film by Daniel Mann Ada (2019 film), a short biopic about Ada Lovelace Ada... A Way of Life, a 2008 Bollywood musical by Tanvir Ahmed Ada (dog actor), a dog that played Colin on the sitcom Spaced Ada, one of the main characters in 1991 movie Armour of God II: Operation Condor Biology Ada (plant), a genus of orchids Adenosine deaminase, an enzyme involved in purine metabolism Ada (protein), an enzyme induced by treatment of bacterial cells Computer science Ada (programming language), programming language based on Pascal Ada (computer virus) Air travel Ada Air, a regional airline based in Tirana, Albania Ada International Airport or Saipan International Airport, Saipan Island, Northern Mariana Islands Aerolínea de Antioquia, a Colombian airline Airline Deregulation Act, a 1978 US bill removing governmental control from commercial aviation Schools Ada, the National College for Digital Skills, a further education college in Tottenham Hale, London Ada High School (Ohio), Ada, Ohio Ada High School (Oklahoma), Ada, Oklahoma People Ada (name), a feminine given name and a surname, including a list of people and fictional characters Ada Lovelace (1815–1852), computer scientist sometimes regarded as the first computer programmer Other uses List of tropical storms named Ada Ada (food), a traditional Kerala delicacy Ada, the cryptocurrency of the Cardano blockchain platform Ada Bridge, Belgrade, Serbia , a cargo vessel built for the London and South Western Railway Ada (ship), a wooden ketch, wrecked near Newcastle, New South Wales, Australia Ada or Ardor: A Family Chronicle, novel by Vladimir Nabokov Dangme language, spoken in Ghana (ISO 639-2 and 639-3 code "ada") Ada Health GmbH, a symptom checker app See also ADA (disambiguation) Ada regulon, an Escherichia coli adaptive response protein Adah (disambiguation) Adha (disambiguation) Ada'a, a woreda in the Oromia Region of Ethiopia Ade (disambiguation) USS Little Ada (1864), a steamer captured by the Union Navy during the American Civil War

Ada Ada may refer to: Places Africa Ada Foah or Ada, Ghana, a town Ada (Ghana parliament constituency) Ada, Osun, a town in Osun State, Nigeria Asia Adeh, Urmia, also known as Ada, a village in West Azerbaijan Province Ada, Karaman, a village in Karaman Province, Turkey Australia and New Zealand Ada River (disambiguation), three rivers Europe Ada, Bosnia and Herzegovina, a village Ada, Croatia, a village Ada, Serbia, a town and municipality Ada Ciganlija or Ada, a river island artificially turned into a peninsula in Belgrade, Serbia North America United States Ada, Alabama, an unincorporated community Ada County, Idaho Ada, Kansas, an unincorporated community Ada Township, Michigan Ada, Minnesota, a city Ada Township, Dickey County, North Dakota Ada, Ohio, a village Ada, Oklahoma, a city Ada, Oregon, an unincorporated community Ada Township, Perkins County, South Dakota Ada, West Virginia, an unincorporated community Ada, Wisconsin, an unincorporated community Outer space 523 Ada, an asteroid Film and television Ada TV, a television channel in the Turkish Republic of Northern Cyprus Ada (1961 film), a 1961 film by Daniel Mann Ada (2019 film), a short biopic about Ada Lovelace Ada... A Way of Life, a 2008 Bollywood musical by Tanvir Ahmed Ada (dog actor), a dog that played Colin on the sitcom Spaced Ada, one of the main characters in 1991 movie Armour of God II: Operation Condor Biology Ada (plant), a genus of orchids Adenosine deaminase, an enzyme involved in purine metabolism Ada (protein), an enzyme induced by treatment of bacterial cells Computer science Ada (programming language), programming language based on Pascal Ada (computer virus) Air travel Ada Air, a regional airline based in Tirana, Albania Ada International Airport or Saipan International Airport, Saipan Island, Northern Mariana Islands Aerolínea de Antioquia, a Colombian airline Airline Deregulation Act, a 1978 US bill removing governmental control from commercial aviation Schools Ada, the National College for Digital Skills, a further education college in Tottenham Hale, London Ada High School (Ohio), Ada, Ohio Ada High School (Oklahoma), Ada, Oklahoma People Ada (name), a feminine given name and a surname, including a list of people and fictional characters Ada Lovelace (1815–1852), computer scientist sometimes regarded as the first computer programmer Other uses List of tropical storms named Ada Ada (food), a traditional Kerala delicacy Ada, the cryptocurrency of the Cardano blockchain platform Ada Bridge, Belgrade, Serbia , a cargo vessel built for the London and South Western Railway Ada (ship), a wooden ketch, wrecked near Newcastle, New South Wales, Australia Ada or Ardor: A Family Chronicle, novel by Vladimir Nabokov Dangme language, spoken in Ghana (ISO 639-2 and 639-3 code "ada") Ada Health GmbH, a symptom checker app See also ADA (disambiguation) Ada regulon, an Escherichia coli adaptive response protein Adah (disambiguation) Adha (disambiguation) Ada'a, a woreda in the Oromia Region of Ethiopia Ade (disambiguation) USS Little Ada (1864), a steamer captured by the Union Navy during the American Civil War

Aberdeen (disambiguation) Aberdeen is a city in Scotland, United Kingdom. Aberdeen may also refer to: Places Africa Aberdeen, Sierra Leone Aberdeen, Eastern Cape, South Africa Asia Hong Kong Aberdeen, Hong Kong, an area and town on southwest Hong Kong Island Aberdeen Channel, a channel between Ap Lei Chau (Aberdeen Island) and Nam Long Shan on the Hong Kong Island in Hong Kong Aberdeen Country Park, a country park in Hong Kong Island Aberdeen floating village, at Aberdeen Harbour, containing approximately 600 junks, which house an estimated 6,000 people Aberdeen Harbour, a harbour between Aberdeen, Hong Kong and Ap Lei Chau (Aberdeen Island) Aberdeen Tunnel, a tunnel in Hong Kong Island Aberdeen Tunnel Underground Laboratory, an underground particle physics laboratory in Hong Kong Island Ap Lei Chau or Aberdeen Island, an island of Hong Kong Aberdeen (constituency), a constituency of Southern District Council India Aberdeen Bazaar, a shopping centre in Port Blair, South Andaman Island Sri Lanka Aberdeen Falls, a waterfall in Sri Lanka Australia Aberdeen, New South Wales Aberdeen, South Australia, one of the early townships that merged in 1940 to create the town of Burra Aberdeen, Tasmania, a suburb of the City of Devonport Caribbean Aberdeen, Jamaica, a town in Saint Elizabeth, Jamaica Europe Aberdeen (Parliament of Scotland constituency) Aberdeen (UK Parliament constituency) 1832-1885 Aberdeen Burghs (UK Parliament constituency) 1801-1832 Aberdeen Central (Scottish Parliament constituency) Aberdeen Central (UK Parliament constituency) Aberdeen Donside (Scottish Parliament constituency) County of Aberdeen, a historic county of Scotland whose county town was Aberdeen Old Aberdeen, a part of the city of Aberdeen in Scotland North America Canada Aberdeen, community in the township of Champlain, Prescott and Russell County, Ontario Aberdeen, Abbotsford, a neighbourhood in the City of Abbotsford, British Columbia Aberdeen Centre, a shopping mall in Richmond, British Columbia Aberdeen, Grey County, Ontario Aberdeen, Kamloops, an area in the City of Kamloops, British Columbia Aberdeen Lake (Nunavut), a lake in Kivalliq Region, Nunavut, Canada Aberdeen, Nova Scotia, part of the Municipality of Inverness County, Nova Scotia Aberdeen Parish, New Brunswick Rural Municipality of Aberdeen No.

Aberdeen (disambiguation) Aberdeen is a city in Scotland, United Kingdom. Aberdeen may also refer to: Places Africa Aberdeen, Sierra Leone Aberdeen, Eastern Cape, South Africa Asia Hong Kong Aberdeen, Hong Kong, an area and town on southwest Hong Kong Island Aberdeen Channel, a channel between Ap Lei Chau (Aberdeen Island) and Nam Long Shan on the Hong Kong Island in Hong Kong Aberdeen Country Park, a country park in Hong Kong Island Aberdeen floating village, at Aberdeen Harbour, containing approximately 600 junks, which house an estimated 6,000 people Aberdeen Harbour, a harbour between Aberdeen, Hong Kong and Ap Lei Chau (Aberdeen Island) Aberdeen Tunnel, a tunnel in Hong Kong Island Aberdeen Tunnel Underground Laboratory, an underground particle physics laboratory in Hong Kong Island Ap Lei Chau or Aberdeen Island, an island of Hong Kong Aberdeen (constituency), a constituency of Southern District Council India Aberdeen Bazaar, a shopping centre in Port Blair, South Andaman Island Sri Lanka Aberdeen Falls, a waterfall in Sri Lanka Australia Aberdeen, New South Wales Aberdeen, South Australia, one of the early townships that merged in 1940 to create the town of Burra Aberdeen, Tasmania, a suburb of the City of Devonport Caribbean Aberdeen, Jamaica, a town in Saint Elizabeth, Jamaica Europe Aberdeen (Parliament of Scotland constituency) Aberdeen (UK Parliament constituency) 1832-1885 Aberdeen Burghs (UK Parliament constituency) 1801-1832 Aberdeen Central (Scottish Parliament constituency) Aberdeen Central (UK Parliament constituency) Aberdeen Donside (Scottish Parliament constituency) County of Aberdeen, a historic county of Scotland whose county town was Aberdeen Old Aberdeen, a part of the city of Aberdeen in Scotland North America Canada Aberdeen, community in the township of Champlain, Prescott and Russell County, Ontario Aberdeen, Abbotsford, a neighbourhood in the City of Abbotsford, British Columbia Aberdeen Centre, a shopping mall in Richmond, British Columbia Aberdeen, Grey County, Ontario Aberdeen, Kamloops, an area in the City of Kamloops, British Columbia Aberdeen Lake (Nunavut), a lake in Kivalliq Region, Nunavut, Canada Aberdeen, Nova Scotia, part of the Municipality of Inverness County, Nova Scotia Aberdeen Parish, New Brunswick Rural Municipality of Aberdeen No.

373, Saskatchewan Aberdeen, Saskatchewan Aberdeen Bay, a bay between southern Baffin Island and north-eastern Hector Island in the Nunavut territory Aberdeen Township, Quebec, until 1960 part of Sheen-Esher-Aberdeen-et-Malakoff, now part of Rapides-des-Joachims, Quebec Aberdeen River, a tributary of rivière aux Castors Noirs in Mauricie, Québec New Aberdeen, Nova Scotia United States Aberdeen, Arkansas Aberdeen, Florida Aberdeen, Georgia Aberdeen, Idaho Aberdeen, Ohio County, Indiana Aberdeen, Porter County, Indiana Aberdeen, Kentucky Aberdeen, Maryland Aberdeen Proving Ground, a United States Army facility located near Aberdeen, Maryland Aberdeen, Massachusetts, a neighborhood of Brighton, Boston Aberdeen, Mississippi Aberdeen Lake (Mississippi), a lake in northeast Mississippi on the Tennessee-Tombigbee Waterway, close to Aberdeen, Mississippi Aberdeen Township, New Jersey Aberdeen, North Carolina Aberdeen Historic District (Aberdeen, North Carolina) Aberdeen, Ohio Aberdeen, South Dakota Aberdeen Historic District (Aberdeen, South Dakota) Aberdeen, Texas Aberdeen (Disputanta, Virginia) Aberdeen Gardens (Hampton, Virginia) Aberdeen, Washington Aberdeen Gardens, Washington Aberdeen, West Virginia Business Abrdn, formerly Standard Life Aberdeen Aberdeen Asset Management Education Aberdeen Business School Aberdeen College, formerly one of the largest further education colleges in Scotland, merged with Banff & Buchan College to form North East Scotland College Aberdeen Grammar School, Aberdeen, Scotland Aberdeen Hall, a university-preparatory school in Kelowna, British Columbia, Canada Aberdeen High School (disambiguation) King's College, Aberdeen University of Aberdeen, a public research university in the city of Aberdeen Entertainment Aberdeen (2000 film), a 2000 Norwegian-British film directed by Hans Petter Moland, starring Stellan Skarsgård and Lena Headey Aberdeen (2014 film), a 2014 Hong Kong film starring Louis Koo Aberdeen (band), an American rock band Aberdeen (song), a song by Cage The Elephant Aberdeen City (band), Boston based indie/alternative rock band Other transportation Aberdeen Airport (disambiguation) Aberdeen Lock and Dam, one of four lock and dam structures on the Tennessee-Tombigbee Waterway Rail Aberdeen, Carolina and Western Railway, a short-line railroad operating in North Carolina Aberdeen and Rockfish Railroad, a short-line railroad operating in North Carolina Aberdeen Corporation Tramways Aberdeen Line (disambiguation) Aberdeen station (disambiguation) Dundee and Perth and Aberdeen Junction Railway, a later name of the Dundee and Perth Railway Shipping Aberdeen Line, a British shipping company founded in 1825 , one of several ships by that name , a sloop of the British Royal Navy that served between 1936 and 1948 , a merchant ship operated during the latter stages of World War II, later commissioned as the USS Altair Sports Aberdeen Dad Vail Regatta, the largest regular intercollegiate rowing event in the United States, named after its sponsor, Aberdeen Asset Management Aberdeen F.C. (disambiguation) Aberdeen GSFP RFC, an amateur rugby union club based in Aberdeen Aberdeen IronBirds, a minor league baseball team affiliated with the Baltimore Orioles Aberdeen L.F.C., a women's football team affiliated with Aberdeen F.C.

373, Saskatchewan Aberdeen, Saskatchewan Aberdeen Bay, a bay between southern Baffin Island and north-eastern Hector Island in the Nunavut territory Aberdeen Township, Quebec, until 1960 part of Sheen-Esher-Aberdeen-et-Malakoff, now part of Rapides-des-Joachims, Quebec Aberdeen River, a tributary of rivière aux Castors Noirs in Mauricie, Québec New Aberdeen, Nova Scotia United States Aberdeen, Arkansas Aberdeen, Florida Aberdeen, Georgia Aberdeen, Idaho Aberdeen, Ohio County, Indiana Aberdeen, Porter County, Indiana Aberdeen, Kentucky Aberdeen, Maryland Aberdeen Proving Ground, a United States Army facility located near Aberdeen, Maryland Aberdeen, Massachusetts, a neighborhood of Brighton, Boston Aberdeen, Mississippi Aberdeen Lake (Mississippi), a lake in northeast Mississippi on the Tennessee-Tombigbee Waterway, close to Aberdeen, Mississippi Aberdeen Township, New Jersey Aberdeen, North Carolina Aberdeen Historic District (Aberdeen, North Carolina) Aberdeen, Ohio Aberdeen, South Dakota Aberdeen Historic District (Aberdeen, South Dakota) Aberdeen, Texas Aberdeen (Disputanta, Virginia) Aberdeen Gardens (Hampton, Virginia) Aberdeen, Washington Aberdeen Gardens, Washington Aberdeen, West Virginia Business Abrdn, formerly Standard Life Aberdeen Aberdeen Asset Management Education Aberdeen Business School Aberdeen College, formerly one of the largest further education colleges in Scotland, merged with Banff & Buchan College to form North East Scotland College Aberdeen Grammar School, Aberdeen, Scotland Aberdeen Hall, a university-preparatory school in Kelowna, British Columbia, Canada Aberdeen High School (disambiguation) King's College, Aberdeen University of Aberdeen, a public research university in the city of Aberdeen Entertainment Aberdeen (2000 film), a 2000 Norwegian-British film directed by Hans Petter Moland, starring Stellan Skarsgård and Lena Headey Aberdeen (2014 film), a 2014 Hong Kong film starring Louis Koo Aberdeen (band), an American rock band Aberdeen (song), a song by Cage The Elephant Aberdeen City (band), Boston based indie/alternative rock band Other transportation Aberdeen Airport (disambiguation) Aberdeen Lock and Dam, one of four lock and dam structures on the Tennessee-Tombigbee Waterway Rail Aberdeen, Carolina and Western Railway, a short-line railroad operating in North Carolina Aberdeen and Rockfish Railroad, a short-line railroad operating in North Carolina Aberdeen Corporation Tramways Aberdeen Line (disambiguation) Aberdeen station (disambiguation) Dundee and Perth and Aberdeen Junction Railway, a later name of the Dundee and Perth Railway Shipping Aberdeen Line, a British shipping company founded in 1825 , one of several ships by that name , a sloop of the British Royal Navy that served between 1936 and 1948 , a merchant ship operated during the latter stages of World War II, later commissioned as the USS Altair Sports Aberdeen Dad Vail Regatta, the largest regular intercollegiate rowing event in the United States, named after its sponsor, Aberdeen Asset Management Aberdeen F.C. (disambiguation) Aberdeen GSFP RFC, an amateur rugby union club based in Aberdeen Aberdeen IronBirds, a minor league baseball team affiliated with the Baltimore Orioles Aberdeen L.F.C., a women's football team affiliated with Aberdeen F.C.

373, Saskatchewan Aberdeen, Saskatchewan Aberdeen Bay, a bay between southern Baffin Island and north-eastern Hector Island in the Nunavut territory Aberdeen Township, Quebec, until 1960 part of Sheen-Esher-Aberdeen-et-Malakoff, now part of Rapides-des-Joachims, Quebec Aberdeen River, a tributary of rivière aux Castors Noirs in Mauricie, Québec New Aberdeen, Nova Scotia United States Aberdeen, Arkansas Aberdeen, Florida Aberdeen, Georgia Aberdeen, Idaho Aberdeen, Ohio County, Indiana Aberdeen, Porter County, Indiana Aberdeen, Kentucky Aberdeen, Maryland Aberdeen Proving Ground, a United States Army facility located near Aberdeen, Maryland Aberdeen, Massachusetts, a neighborhood of Brighton, Boston Aberdeen, Mississippi Aberdeen Lake (Mississippi), a lake in northeast Mississippi on the Tennessee-Tombigbee Waterway, close to Aberdeen, Mississippi Aberdeen Township, New Jersey Aberdeen, North Carolina Aberdeen Historic District (Aberdeen, North Carolina) Aberdeen, Ohio Aberdeen, South Dakota Aberdeen Historic District (Aberdeen, South Dakota) Aberdeen, Texas Aberdeen (Disputanta, Virginia) Aberdeen Gardens (Hampton, Virginia) Aberdeen, Washington Aberdeen Gardens, Washington Aberdeen, West Virginia Business Abrdn, formerly Standard Life Aberdeen Aberdeen Asset Management Education Aberdeen Business School Aberdeen College, formerly one of the largest further education colleges in Scotland, merged with Banff & Buchan College to form North East Scotland College Aberdeen Grammar School, Aberdeen, Scotland Aberdeen Hall, a university-preparatory school in Kelowna, British Columbia, Canada Aberdeen High School (disambiguation) King's College, Aberdeen University of Aberdeen, a public research university in the city of Aberdeen Entertainment Aberdeen (2000 film), a 2000 Norwegian-British film directed by Hans Petter Moland, starring Stellan Skarsgård and Lena Headey Aberdeen (2014 film), a 2014 Hong Kong film starring Louis Koo Aberdeen (band), an American rock band Aberdeen (song), a song by Cage The Elephant Aberdeen City (band), Boston based indie/alternative rock band Other transportation Aberdeen Airport (disambiguation) Aberdeen Lock and Dam, one of four lock and dam structures on the Tennessee-Tombigbee Waterway Rail Aberdeen, Carolina and Western Railway, a short-line railroad operating in North Carolina Aberdeen and Rockfish Railroad, a short-line railroad operating in North Carolina Aberdeen Corporation Tramways Aberdeen Line (disambiguation) Aberdeen station (disambiguation) Dundee and Perth and Aberdeen Junction Railway, a later name of the Dundee and Perth Railway Shipping Aberdeen Line, a British shipping company founded in 1825 , one of several ships by that name , a sloop of the British Royal Navy that served between 1936 and 1948 , a merchant ship operated during the latter stages of World War II, later commissioned as the USS Altair Sports Aberdeen Dad Vail Regatta, the largest regular intercollegiate rowing event in the United States, named after its sponsor, Aberdeen Asset Management Aberdeen F.C. (disambiguation) Aberdeen GSFP RFC, an amateur rugby union club based in Aberdeen Aberdeen IronBirds, a minor league baseball team affiliated with the Baltimore Orioles Aberdeen L.F.C., a women's football team affiliated with Aberdeen F.C.

See also Aberdeen Act Aberdeen Angus, a Scottish breed of small beef cattle Aberdeen Central (disambiguation) Aberdeen Gardens (disambiguation) Aberdeen Historic District (disambiguation) Aberdeen Hospital (disambiguation) Aberdeen Quarry, a granite quarry in Colorado Battle of Aberdeen (disambiguation) Diocese of Aberdeen and Orkney, one of the seven dioceses of the Scottish Episcopal Church Etymology of Aberdeen Marquess of Aberdeen and Temair, a title in the Peerage of the United Kingdom

See also Aberdeen Act Aberdeen Angus, a Scottish breed of small beef cattle Aberdeen Central (disambiguation) Aberdeen Gardens (disambiguation) Aberdeen Historic District (disambiguation) Aberdeen Hospital (disambiguation) Aberdeen Quarry, a granite quarry in Colorado Battle of Aberdeen (disambiguation) Diocese of Aberdeen and Orkney, one of the seven dioceses of the Scottish Episcopal Church Etymology of Aberdeen Marquess of Aberdeen and Temair, a title in the Peerage of the United Kingdom

See also Aberdeen Act Aberdeen Angus, a Scottish breed of small beef cattle Aberdeen Central (disambiguation) Aberdeen Gardens (disambiguation) Aberdeen Historic District (disambiguation) Aberdeen Hospital (disambiguation) Aberdeen Quarry, a granite quarry in Colorado Battle of Aberdeen (disambiguation) Diocese of Aberdeen and Orkney, one of the seven dioceses of the Scottish Episcopal Church Etymology of Aberdeen Marquess of Aberdeen and Temair, a title in the Peerage of the United Kingdom

Algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular microalgae, such as Chlorella, Prototheca and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga which may grow up to in length. Most are aquatic and autotrophic (they generate food internally) and lack many of the distinct cell and tissue types, such as stomata, xylem and phloem that are found in land plants. The largest and most complex marine algae are called seaweeds, while the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example, Spirogyra and stoneworts. No definition of algae is generally accepted. One definition is that algae "have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells". Likewise, the colorless Prototheca under Chlorophyta are all devoid of any chlorophyll. Although cyanobacteria are often referred to as "blue-green algae", most authorities exclude all prokaryotes from the definition of algae. Algae constitute a polyphyletic group since they do not include a common ancestor, and although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria. Diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a wide range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids (leaf-like structures) of bryophytes, rhizoids of nonvascular plants, and the roots, leaves, and other organs found in tracheophytes (vascular plants). Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some unicellular species of green algae, many golden algae, euglenids, dinoflagellates, and other algae have become heterotrophs (also called colorless or apochlorotic algae), sometimes parasitic, relying entirely on external energy sources and have limited or no photosynthetic apparatus. Some other heterotrophic organisms, such as the apicomplexans, are also derived from cells whose ancestors possessed plastids, but are not traditionally considered as algae. Algae have photosynthetic machinery ultimately derived from cyanobacteria that produce oxygen as a by-product of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfur bacteria. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago. Because of the wide range of types of algae, they have increasing different industrial and traditional applications in human society. Traditional seaweed farming practices have existed for thousands of years and have strong traditions in East Asia food cultures.

Algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular microalgae, such as Chlorella, Prototheca and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga which may grow up to in length. Most are aquatic and autotrophic (they generate food internally) and lack many of the distinct cell and tissue types, such as stomata, xylem and phloem that are found in land plants. The largest and most complex marine algae are called seaweeds, while the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example, Spirogyra and stoneworts. No definition of algae is generally accepted. One definition is that algae "have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells". Likewise, the colorless Prototheca under Chlorophyta are all devoid of any chlorophyll. Although cyanobacteria are often referred to as "blue-green algae", most authorities exclude all prokaryotes from the definition of algae. Algae constitute a polyphyletic group since they do not include a common ancestor, and although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria. Diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a wide range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids (leaf-like structures) of bryophytes, rhizoids of nonvascular plants, and the roots, leaves, and other organs found in tracheophytes (vascular plants). Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some unicellular species of green algae, many golden algae, euglenids, dinoflagellates, and other algae have become heterotrophs (also called colorless or apochlorotic algae), sometimes parasitic, relying entirely on external energy sources and have limited or no photosynthetic apparatus. Some other heterotrophic organisms, such as the apicomplexans, are also derived from cells whose ancestors possessed plastids, but are not traditionally considered as algae. Algae have photosynthetic machinery ultimately derived from cyanobacteria that produce oxygen as a by-product of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfur bacteria. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago. Because of the wide range of types of algae, they have increasing different industrial and traditional applications in human society. Traditional seaweed farming practices have existed for thousands of years and have strong traditions in East Asia food cultures.

More modern algaculture applications extend the food traditions for other applications include cattle feed, using algae for bioremediation or pollution control, transforming sunlight into algae fuels or other chemicals used in industrial processes, and in medical and scientific applications. A 2020 review, found that these applications of algae could play an important role in carbon sequestration in order to mitigate climate change while providing valuable value-add products for global economies. Etymology and study The singular is the Latin word for 'seaweed' and retains that meaning in English. The etymology is obscure. Although some speculate that it is related to Latin , 'be cold', no reason is known to associate seaweed with temperature. A more likely source is , 'binding, entwining'. The Ancient Greek word for 'seaweed' was (), which could mean either the seaweed (probably red algae) or a red dye derived from it. The Latinization, , meant primarily the cosmetic rouge. The etymology is uncertain, but a strong candidate has long been some word related to the Biblical (), 'paint' (if not that word itself), a cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the eastern Mediterranean. It could be any color: black, red, green, or blue. Accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used. The name fucus appears in a number of taxa. Classifications The committee on the International Code of Botanical Nomenclature has recommended certain suffixes for use in the classification of algae. These are -phyta for division, -phyceae for class, -phycideae for subclass, -ales for order, -inales for suborder, -aceae for family, -oidease for subfamily, a Greek-based name for genus, and a Latin-based name for species. Algal characteristics basic to primary classification The primary classification of algae is based on certain morphological features. The chief among these are (a) pigment constitution of the cell, (b) chemical nature of stored food materials, (c) kind, number, point of insertion and relative length of the flagella on the motile cell, (d) chemical composition of cell wall and (e) presence or absence of a definitely organized nucleus in the cell or any other significant details of cell structure. History of classification of algae Although Carolus Linnaeus (1754) included algae along with lichens in his 25th class Cryptogamia, he did not elaborate further on the classification of algae. Jean Pierre Étienne Vaucher (1803) was perhaps the first to propose a system of classification of algae, and he recognized three groups, Conferves, Ulves, and Tremelles. While Johann Heinrich Friedrich Link (1820) classified algae on the basis of the colour of the pigment and structure, William Henry Harvey (1836) proposed a system of classification on the basis of the habitat and the pigment. J. G. Agardh (1849–1898) divided algae into six orders: Diatomaceae, Nostochineae, Confervoideae, Ulvaceae, Floriadeae and Fucoideae. Around 1880, algae along with fungi were grouped under Thallophyta, a division created by Eichler (1836).

More modern algaculture applications extend the food traditions for other applications include cattle feed, using algae for bioremediation or pollution control, transforming sunlight into algae fuels or other chemicals used in industrial processes, and in medical and scientific applications. A 2020 review, found that these applications of algae could play an important role in carbon sequestration in order to mitigate climate change while providing valuable value-add products for global economies. Etymology and study The singular is the Latin word for 'seaweed' and retains that meaning in English. The etymology is obscure. Although some speculate that it is related to Latin , 'be cold', no reason is known to associate seaweed with temperature. A more likely source is , 'binding, entwining'. The Ancient Greek word for 'seaweed' was (), which could mean either the seaweed (probably red algae) or a red dye derived from it. The Latinization, , meant primarily the cosmetic rouge. The etymology is uncertain, but a strong candidate has long been some word related to the Biblical (), 'paint' (if not that word itself), a cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the eastern Mediterranean. It could be any color: black, red, green, or blue. Accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used. The name fucus appears in a number of taxa. Classifications The committee on the International Code of Botanical Nomenclature has recommended certain suffixes for use in the classification of algae. These are -phyta for division, -phyceae for class, -phycideae for subclass, -ales for order, -inales for suborder, -aceae for family, -oidease for subfamily, a Greek-based name for genus, and a Latin-based name for species. Algal characteristics basic to primary classification The primary classification of algae is based on certain morphological features. The chief among these are (a) pigment constitution of the cell, (b) chemical nature of stored food materials, (c) kind, number, point of insertion and relative length of the flagella on the motile cell, (d) chemical composition of cell wall and (e) presence or absence of a definitely organized nucleus in the cell or any other significant details of cell structure. History of classification of algae Although Carolus Linnaeus (1754) included algae along with lichens in his 25th class Cryptogamia, he did not elaborate further on the classification of algae. Jean Pierre Étienne Vaucher (1803) was perhaps the first to propose a system of classification of algae, and he recognized three groups, Conferves, Ulves, and Tremelles. While Johann Heinrich Friedrich Link (1820) classified algae on the basis of the colour of the pigment and structure, William Henry Harvey (1836) proposed a system of classification on the basis of the habitat and the pigment. J. G. Agardh (1849–1898) divided algae into six orders: Diatomaceae, Nostochineae, Confervoideae, Ulvaceae, Floriadeae and Fucoideae. Around 1880, algae along with fungi were grouped under Thallophyta, a division created by Eichler (1836).

More modern algaculture applications extend the food traditions for other applications include cattle feed, using algae for bioremediation or pollution control, transforming sunlight into algae fuels or other chemicals used in industrial processes, and in medical and scientific applications. A 2020 review, found that these applications of algae could play an important role in carbon sequestration in order to mitigate climate change while providing valuable value-add products for global economies. Etymology and study The singular is the Latin word for 'seaweed' and retains that meaning in English. The etymology is obscure. Although some speculate that it is related to Latin , 'be cold', no reason is known to associate seaweed with temperature. A more likely source is , 'binding, entwining'. The Ancient Greek word for 'seaweed' was (), which could mean either the seaweed (probably red algae) or a red dye derived from it. The Latinization, , meant primarily the cosmetic rouge. The etymology is uncertain, but a strong candidate has long been some word related to the Biblical (), 'paint' (if not that word itself), a cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the eastern Mediterranean. It could be any color: black, red, green, or blue. Accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used. The name fucus appears in a number of taxa. Classifications The committee on the International Code of Botanical Nomenclature has recommended certain suffixes for use in the classification of algae. These are -phyta for division, -phyceae for class, -phycideae for subclass, -ales for order, -inales for suborder, -aceae for family, -oidease for subfamily, a Greek-based name for genus, and a Latin-based name for species. Algal characteristics basic to primary classification The primary classification of algae is based on certain morphological features. The chief among these are (a) pigment constitution of the cell, (b) chemical nature of stored food materials, (c) kind, number, point of insertion and relative length of the flagella on the motile cell, (d) chemical composition of cell wall and (e) presence or absence of a definitely organized nucleus in the cell or any other significant details of cell structure. History of classification of algae Although Carolus Linnaeus (1754) included algae along with lichens in his 25th class Cryptogamia, he did not elaborate further on the classification of algae. Jean Pierre Étienne Vaucher (1803) was perhaps the first to propose a system of classification of algae, and he recognized three groups, Conferves, Ulves, and Tremelles. While Johann Heinrich Friedrich Link (1820) classified algae on the basis of the colour of the pigment and structure, William Henry Harvey (1836) proposed a system of classification on the basis of the habitat and the pigment. J. G. Agardh (1849–1898) divided algae into six orders: Diatomaceae, Nostochineae, Confervoideae, Ulvaceae, Floriadeae and Fucoideae. Around 1880, algae along with fungi were grouped under Thallophyta, a division created by Eichler (1836).

Encouraged by this, Adolf Engler and Karl A. E. Prantl (1912) proposed a revised scheme of classification of algae and included fungi in algae as they were of opinion that fungi have been derived from algae. The scheme proposed by Engler and Prantl is summarised as follows: Schizophyta Phytosarcodina Flagellata Dinoflagellata Bacillariophyta Conjugatae Chlorophyceae Charophyta Phaeophyceae Rhodophyceae Eumycetes (Fungi) The algae contain chloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circular DNA like that in cyanobacteria and are interpreted as representing reduced endosymbiotic cyanobacteria. However, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. The table below describes the composition of the three major groups of algae. Their lineage relationships are shown in the figure in the upper right. Many of these groups contain some members that are no longer photosynthetic. Some retain plastids, but not chloroplasts, while others have lost plastids entirely. Phylogeny based on plastid not nucleocytoplasmic genealogy: Linnaeus, in Species Plantarum (1753), the starting point for modern botanical nomenclature, recognized 14 genera of algae, of which only four are currently considered among algae. In Systema Naturae, Linnaeus described the genera Volvox and Corallina, and a species of Acetabularia (as Madrepora), among the animals. In 1768, Samuel Gottlieb Gmelin (1744–1774) published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the then new binomial nomenclature of Linnaeus. It included elaborate illustrations of seaweed and marine algae on folded leaves. W. H. Harvey (1811–1866) and Lamouroux (1813) were the first to divide macroscopic algae into four divisions based on their pigmentation. This is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: red algae (Rhodospermae), brown algae (Melanospermae), green algae (Chlorospermae), and Diatomaceae. At this time, microscopic algae were discovered and reported by a different group of workers (e.g., O. F. Müller and Ehrenberg) studying the Infusoria (microscopic organisms). Unlike macroalgae, which were clearly viewed as plants, microalgae were frequently considered animals because they are often motile. Even the nonmotile (coccoid) microalgae were sometimes merely seen as stages of the lifecycle of plants, macroalgae, or animals. Although used as a taxonomic category in some pre-Darwinian classifications, e.g., Linnaeus (1753), de Jussieu (1789), Horaninow (1843), Agassiz (1859), Wilson & Cassin (1864), in further classifications, the "algae" are seen as an artificial, polyphyletic group. Throughout the 20th century, most classifications treated the following groups as divisions or classes of algae: cyanophytes, rhodophytes, chrysophytes, xanthophytes, bacillariophytes, phaeophytes, pyrrhophytes (cryptophytes and dinophytes), euglenophytes, and chlorophytes. Later, many new groups were discovered (e.g., Bolidophyceae), and others were splintered from older groups: charophytes and glaucophytes (from chlorophytes), many heterokontophytes (e.g., synurophytes from chrysophytes, or eustigmatophytes from xanthophytes), haptophytes (from chrysophytes), and chlorarachniophytes (from xanthophytes). With the abandonment of plant-animal dichotomous classification, most groups of algae (sometimes all) were included in Protista, later also abandoned in favour of Eukaryota.

Encouraged by this, Adolf Engler and Karl A. E. Prantl (1912) proposed a revised scheme of classification of algae and included fungi in algae as they were of opinion that fungi have been derived from algae. The scheme proposed by Engler and Prantl is summarised as follows: Schizophyta Phytosarcodina Flagellata Dinoflagellata Bacillariophyta Conjugatae Chlorophyceae Charophyta Phaeophyceae Rhodophyceae Eumycetes (Fungi) The algae contain chloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circular DNA like that in cyanobacteria and are interpreted as representing reduced endosymbiotic cyanobacteria. However, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. The table below describes the composition of the three major groups of algae. Their lineage relationships are shown in the figure in the upper right. Many of these groups contain some members that are no longer photosynthetic. Some retain plastids, but not chloroplasts, while others have lost plastids entirely. Phylogeny based on plastid not nucleocytoplasmic genealogy: Linnaeus, in Species Plantarum (1753), the starting point for modern botanical nomenclature, recognized 14 genera of algae, of which only four are currently considered among algae. In Systema Naturae, Linnaeus described the genera Volvox and Corallina, and a species of Acetabularia (as Madrepora), among the animals. In 1768, Samuel Gottlieb Gmelin (1744–1774) published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the then new binomial nomenclature of Linnaeus. It included elaborate illustrations of seaweed and marine algae on folded leaves. W. H. Harvey (1811–1866) and Lamouroux (1813) were the first to divide macroscopic algae into four divisions based on their pigmentation. This is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: red algae (Rhodospermae), brown algae (Melanospermae), green algae (Chlorospermae), and Diatomaceae. At this time, microscopic algae were discovered and reported by a different group of workers (e.g., O. F. Müller and Ehrenberg) studying the Infusoria (microscopic organisms). Unlike macroalgae, which were clearly viewed as plants, microalgae were frequently considered animals because they are often motile. Even the nonmotile (coccoid) microalgae were sometimes merely seen as stages of the lifecycle of plants, macroalgae, or animals. Although used as a taxonomic category in some pre-Darwinian classifications, e.g., Linnaeus (1753), de Jussieu (1789), Horaninow (1843), Agassiz (1859), Wilson & Cassin (1864), in further classifications, the "algae" are seen as an artificial, polyphyletic group. Throughout the 20th century, most classifications treated the following groups as divisions or classes of algae: cyanophytes, rhodophytes, chrysophytes, xanthophytes, bacillariophytes, phaeophytes, pyrrhophytes (cryptophytes and dinophytes), euglenophytes, and chlorophytes. Later, many new groups were discovered (e.g., Bolidophyceae), and others were splintered from older groups: charophytes and glaucophytes (from chlorophytes), many heterokontophytes (e.g., synurophytes from chrysophytes, or eustigmatophytes from xanthophytes), haptophytes (from chrysophytes), and chlorarachniophytes (from xanthophytes). With the abandonment of plant-animal dichotomous classification, most groups of algae (sometimes all) were included in Protista, later also abandoned in favour of Eukaryota.

Encouraged by this, Adolf Engler and Karl A. E. Prantl (1912) proposed a revised scheme of classification of algae and included fungi in algae as they were of opinion that fungi have been derived from algae. The scheme proposed by Engler and Prantl is summarised as follows: Schizophyta Phytosarcodina Flagellata Dinoflagellata Bacillariophyta Conjugatae Chlorophyceae Charophyta Phaeophyceae Rhodophyceae Eumycetes (Fungi) The algae contain chloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circular DNA like that in cyanobacteria and are interpreted as representing reduced endosymbiotic cyanobacteria. However, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. The table below describes the composition of the three major groups of algae. Their lineage relationships are shown in the figure in the upper right. Many of these groups contain some members that are no longer photosynthetic. Some retain plastids, but not chloroplasts, while others have lost plastids entirely. Phylogeny based on plastid not nucleocytoplasmic genealogy: Linnaeus, in Species Plantarum (1753), the starting point for modern botanical nomenclature, recognized 14 genera of algae, of which only four are currently considered among algae. In Systema Naturae, Linnaeus described the genera Volvox and Corallina, and a species of Acetabularia (as Madrepora), among the animals. In 1768, Samuel Gottlieb Gmelin (1744–1774) published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the then new binomial nomenclature of Linnaeus. It included elaborate illustrations of seaweed and marine algae on folded leaves. W. H. Harvey (1811–1866) and Lamouroux (1813) were the first to divide macroscopic algae into four divisions based on their pigmentation. This is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: red algae (Rhodospermae), brown algae (Melanospermae), green algae (Chlorospermae), and Diatomaceae. At this time, microscopic algae were discovered and reported by a different group of workers (e.g., O. F. Müller and Ehrenberg) studying the Infusoria (microscopic organisms). Unlike macroalgae, which were clearly viewed as plants, microalgae were frequently considered animals because they are often motile. Even the nonmotile (coccoid) microalgae were sometimes merely seen as stages of the lifecycle of plants, macroalgae, or animals. Although used as a taxonomic category in some pre-Darwinian classifications, e.g., Linnaeus (1753), de Jussieu (1789), Horaninow (1843), Agassiz (1859), Wilson & Cassin (1864), in further classifications, the "algae" are seen as an artificial, polyphyletic group. Throughout the 20th century, most classifications treated the following groups as divisions or classes of algae: cyanophytes, rhodophytes, chrysophytes, xanthophytes, bacillariophytes, phaeophytes, pyrrhophytes (cryptophytes and dinophytes), euglenophytes, and chlorophytes. Later, many new groups were discovered (e.g., Bolidophyceae), and others were splintered from older groups: charophytes and glaucophytes (from chlorophytes), many heterokontophytes (e.g., synurophytes from chrysophytes, or eustigmatophytes from xanthophytes), haptophytes (from chrysophytes), and chlorarachniophytes (from xanthophytes). With the abandonment of plant-animal dichotomous classification, most groups of algae (sometimes all) were included in Protista, later also abandoned in favour of Eukaryota.

However, as a legacy of the older plant life scheme, some groups that were also treated as protozoans in the past still have duplicated classifications (see ambiregnal protists). Some parasitic algae (e.g., the green algae Prototheca and Helicosporidium, parasites of metazoans, or Cephaleuros, parasites of plants) were originally classified as fungi, sporozoans, or protistans of incertae sedis, while others (e.g., the green algae Phyllosiphon and Rhodochytrium, parasites of plants, or the red algae Pterocladiophila and Gelidiocolax mammillatus, parasites of other red algae, or the dinoflagellates Oodinium, parasites of fish) had their relationship with algae conjectured early. In other cases, some groups were originally characterized as parasitic algae (e.g., Chlorochytrium), but later were seen as endophytic algae. Some filamentous bacteria (e.g., Beggiatoa) were originally seen as algae. Furthermore, groups like the apicomplexans are also parasites derived from ancestors that possessed plastids, but are not included in any group traditionally seen as algae. Relationship to land plants The first land plants probably evolved from shallow freshwater charophyte algae much like Chara almost 500 million years ago. These probably had an isomorphic alternation of generations and were probably filamentous. Fossils of isolated land plant spores suggest land plants may have been around as long as 475 million years ago. Morphology A range of algal morphologies is exhibited, and convergence of features in unrelated groups is common. The only groups to exhibit three-dimensional multicellular thalli are the reds and browns, and some chlorophytes. Apical growth is constrained to subsets of these groups: the florideophyte reds, various browns, and the charophytes. The form of charophytes is quite different from those of reds and browns, because they have distinct nodes, separated by internode 'stems'; whorls of branches reminiscent of the horsetails occur at the nodes. Conceptacles are another polyphyletic trait; they appear in the coralline algae and the Hildenbrandiales, as well as the browns. Most of the simpler algae are unicellular flagellates or amoeboids, but colonial and nonmotile forms have developed independently among several of the groups. Some of the more common organizational levels, more than one of which may occur in the lifecycle of a species, are Colonial: small, regular groups of motile cells Capsoid: individual non-motile cells embedded in mucilage Coccoid: individual non-motile cells with cell walls Palmelloid: nonmotile cells embedded in mucilage Filamentous: a string of nonmotile cells connected together, sometimes branching Parenchymatous: cells forming a thallus with partial differentiation of tissues In three lines, even higher levels of organization have been reached, with full tissue differentiation. These are the brown algae,—some of which may reach 50 m in length (kelps)—the red algae, and the green algae. The most complex forms are found among the charophyte algae (see Charales and Charophyta), in a lineage that eventually led to the higher land plants. The innovation that defines these nonalgal plants is the presence of female reproductive organs with protective cell layers that protect the zygote and developing embryo. Hence, the land plants are referred to as the Embryophytes.

However, as a legacy of the older plant life scheme, some groups that were also treated as protozoans in the past still have duplicated classifications (see ambiregnal protists). Some parasitic algae (e.g., the green algae Prototheca and Helicosporidium, parasites of metazoans, or Cephaleuros, parasites of plants) were originally classified as fungi, sporozoans, or protistans of incertae sedis, while others (e.g., the green algae Phyllosiphon and Rhodochytrium, parasites of plants, or the red algae Pterocladiophila and Gelidiocolax mammillatus, parasites of other red algae, or the dinoflagellates Oodinium, parasites of fish) had their relationship with algae conjectured early. In other cases, some groups were originally characterized as parasitic algae (e.g., Chlorochytrium), but later were seen as endophytic algae. Some filamentous bacteria (e.g., Beggiatoa) were originally seen as algae. Furthermore, groups like the apicomplexans are also parasites derived from ancestors that possessed plastids, but are not included in any group traditionally seen as algae. Relationship to land plants The first land plants probably evolved from shallow freshwater charophyte algae much like Chara almost 500 million years ago. These probably had an isomorphic alternation of generations and were probably filamentous. Fossils of isolated land plant spores suggest land plants may have been around as long as 475 million years ago. Morphology A range of algal morphologies is exhibited, and convergence of features in unrelated groups is common. The only groups to exhibit three-dimensional multicellular thalli are the reds and browns, and some chlorophytes. Apical growth is constrained to subsets of these groups: the florideophyte reds, various browns, and the charophytes. The form of charophytes is quite different from those of reds and browns, because they have distinct nodes, separated by internode 'stems'; whorls of branches reminiscent of the horsetails occur at the nodes. Conceptacles are another polyphyletic trait; they appear in the coralline algae and the Hildenbrandiales, as well as the browns. Most of the simpler algae are unicellular flagellates or amoeboids, but colonial and nonmotile forms have developed independently among several of the groups. Some of the more common organizational levels, more than one of which may occur in the lifecycle of a species, are Colonial: small, regular groups of motile cells Capsoid: individual non-motile cells embedded in mucilage Coccoid: individual non-motile cells with cell walls Palmelloid: nonmotile cells embedded in mucilage Filamentous: a string of nonmotile cells connected together, sometimes branching Parenchymatous: cells forming a thallus with partial differentiation of tissues In three lines, even higher levels of organization have been reached, with full tissue differentiation. These are the brown algae,—some of which may reach 50 m in length (kelps)—the red algae, and the green algae. The most complex forms are found among the charophyte algae (see Charales and Charophyta), in a lineage that eventually led to the higher land plants. The innovation that defines these nonalgal plants is the presence of female reproductive organs with protective cell layers that protect the zygote and developing embryo. Hence, the land plants are referred to as the Embryophytes.

However, as a legacy of the older plant life scheme, some groups that were also treated as protozoans in the past still have duplicated classifications (see ambiregnal protists). Some parasitic algae (e.g., the green algae Prototheca and Helicosporidium, parasites of metazoans, or Cephaleuros, parasites of plants) were originally classified as fungi, sporozoans, or protistans of incertae sedis, while others (e.g., the green algae Phyllosiphon and Rhodochytrium, parasites of plants, or the red algae Pterocladiophila and Gelidiocolax mammillatus, parasites of other red algae, or the dinoflagellates Oodinium, parasites of fish) had their relationship with algae conjectured early. In other cases, some groups were originally characterized as parasitic algae (e.g., Chlorochytrium), but later were seen as endophytic algae. Some filamentous bacteria (e.g., Beggiatoa) were originally seen as algae. Furthermore, groups like the apicomplexans are also parasites derived from ancestors that possessed plastids, but are not included in any group traditionally seen as algae. Relationship to land plants The first land plants probably evolved from shallow freshwater charophyte algae much like Chara almost 500 million years ago. These probably had an isomorphic alternation of generations and were probably filamentous. Fossils of isolated land plant spores suggest land plants may have been around as long as 475 million years ago. Morphology A range of algal morphologies is exhibited, and convergence of features in unrelated groups is common. The only groups to exhibit three-dimensional multicellular thalli are the reds and browns, and some chlorophytes. Apical growth is constrained to subsets of these groups: the florideophyte reds, various browns, and the charophytes. The form of charophytes is quite different from those of reds and browns, because they have distinct nodes, separated by internode 'stems'; whorls of branches reminiscent of the horsetails occur at the nodes. Conceptacles are another polyphyletic trait; they appear in the coralline algae and the Hildenbrandiales, as well as the browns. Most of the simpler algae are unicellular flagellates or amoeboids, but colonial and nonmotile forms have developed independently among several of the groups. Some of the more common organizational levels, more than one of which may occur in the lifecycle of a species, are Colonial: small, regular groups of motile cells Capsoid: individual non-motile cells embedded in mucilage Coccoid: individual non-motile cells with cell walls Palmelloid: nonmotile cells embedded in mucilage Filamentous: a string of nonmotile cells connected together, sometimes branching Parenchymatous: cells forming a thallus with partial differentiation of tissues In three lines, even higher levels of organization have been reached, with full tissue differentiation. These are the brown algae,—some of which may reach 50 m in length (kelps)—the red algae, and the green algae. The most complex forms are found among the charophyte algae (see Charales and Charophyta), in a lineage that eventually led to the higher land plants. The innovation that defines these nonalgal plants is the presence of female reproductive organs with protective cell layers that protect the zygote and developing embryo. Hence, the land plants are referred to as the Embryophytes.

Turfs The term algal turf is commonly used but poorly defined. Algal turfs are thick, carpet-like beds of seaweed that retain sediment and compete with foundation species like corals and kelps, and they are usually less than 15 cm tall. Such a turf may consist of one or more species, and will generally cover an area in the order of a square metre or more. Some common characteristics are listed: Algae that form aggregations that have been described as turfs include diatoms, cyanobacteria, chlorophytes, phaeophytes and rhodophytes. Turfs are often composed of numerous species at a wide range of spatial scales, but monospecific turfs are frequently reported. Turfs can be morphologically highly variable over geographic scales and even within species on local scales and can be difficult to identify in terms of the constituent species. Turfs have been defined as short algae, but this has been used to describe height ranges from less than 0.5 cm to more than 10 cm. In some regions, the descriptions approached heights which might be described as canopies (20 to 30 cm). Physiology Many algae, particularly members of the Characeae species, have served as model experimental organisms to understand the mechanisms of the water permeability of membranes, osmoregulation, turgor regulation, salt tolerance, cytoplasmic streaming, and the generation of action potentials. Phytohormones are found not only in higher plants, but in algae, too. Symbiotic algae Some species of algae form symbiotic relationships with other organisms. In these symbioses, the algae supply photosynthates (organic substances) to the host organism providing protection to the algal cells. The host organism derives some or all of its energy requirements from the algae. Examples are: Lichens Lichens are defined by the International Association for Lichenology to be "an association of a fungus and a photosynthetic symbiont resulting in a stable vegetative body having a specific structure". The fungi, or mycobionts, are mainly from the Ascomycota with a few from the Basidiomycota. In nature they do not occur separate from lichens. It is unknown when they began to associate. One mycobiont associates with the same phycobiont species, rarely two, from the green algae, except that alternatively, the mycobiont may associate with a species of cyanobacteria (hence "photobiont" is the more accurate term). A photobiont may be associated with many different mycobionts or may live independently; accordingly, lichens are named and classified as fungal species. The association is termed a morphogenesis because the lichen has a form and capabilities not possessed by the symbiont species alone (they can be experimentally isolated). The photobiont possibly triggers otherwise latent genes in the mycobiont. Trentepohlia is an example of a common green alga genus worldwide that can grow on its own or be lichenised. Lichen thus share some of the habitat and often similar appearance with specialized species of algae (aerophytes) growing on exposed surfaces such as tree trunks and rocks and sometimes discoloring them. Coral reefs Coral reefs are accumulated from the calcareous exoskeletons of marine invertebrates of the order Scleractinia (stony corals).

Turfs The term algal turf is commonly used but poorly defined. Algal turfs are thick, carpet-like beds of seaweed that retain sediment and compete with foundation species like corals and kelps, and they are usually less than 15 cm tall. Such a turf may consist of one or more species, and will generally cover an area in the order of a square metre or more. Some common characteristics are listed: Algae that form aggregations that have been described as turfs include diatoms, cyanobacteria, chlorophytes, phaeophytes and rhodophytes. Turfs are often composed of numerous species at a wide range of spatial scales, but monospecific turfs are frequently reported. Turfs can be morphologically highly variable over geographic scales and even within species on local scales and can be difficult to identify in terms of the constituent species. Turfs have been defined as short algae, but this has been used to describe height ranges from less than 0.5 cm to more than 10 cm. In some regions, the descriptions approached heights which might be described as canopies (20 to 30 cm). Physiology Many algae, particularly members of the Characeae species, have served as model experimental organisms to understand the mechanisms of the water permeability of membranes, osmoregulation, turgor regulation, salt tolerance, cytoplasmic streaming, and the generation of action potentials. Phytohormones are found not only in higher plants, but in algae, too. Symbiotic algae Some species of algae form symbiotic relationships with other organisms. In these symbioses, the algae supply photosynthates (organic substances) to the host organism providing protection to the algal cells. The host organism derives some or all of its energy requirements from the algae. Examples are: Lichens Lichens are defined by the International Association for Lichenology to be "an association of a fungus and a photosynthetic symbiont resulting in a stable vegetative body having a specific structure". The fungi, or mycobionts, are mainly from the Ascomycota with a few from the Basidiomycota. In nature they do not occur separate from lichens. It is unknown when they began to associate. One mycobiont associates with the same phycobiont species, rarely two, from the green algae, except that alternatively, the mycobiont may associate with a species of cyanobacteria (hence "photobiont" is the more accurate term). A photobiont may be associated with many different mycobionts or may live independently; accordingly, lichens are named and classified as fungal species. The association is termed a morphogenesis because the lichen has a form and capabilities not possessed by the symbiont species alone (they can be experimentally isolated). The photobiont possibly triggers otherwise latent genes in the mycobiont. Trentepohlia is an example of a common green alga genus worldwide that can grow on its own or be lichenised. Lichen thus share some of the habitat and often similar appearance with specialized species of algae (aerophytes) growing on exposed surfaces such as tree trunks and rocks and sometimes discoloring them. Coral reefs Coral reefs are accumulated from the calcareous exoskeletons of marine invertebrates of the order Scleractinia (stony corals).

Turfs The term algal turf is commonly used but poorly defined. Algal turfs are thick, carpet-like beds of seaweed that retain sediment and compete with foundation species like corals and kelps, and they are usually less than 15 cm tall. Such a turf may consist of one or more species, and will generally cover an area in the order of a square metre or more. Some common characteristics are listed: Algae that form aggregations that have been described as turfs include diatoms, cyanobacteria, chlorophytes, phaeophytes and rhodophytes. Turfs are often composed of numerous species at a wide range of spatial scales, but monospecific turfs are frequently reported. Turfs can be morphologically highly variable over geographic scales and even within species on local scales and can be difficult to identify in terms of the constituent species. Turfs have been defined as short algae, but this has been used to describe height ranges from less than 0.5 cm to more than 10 cm. In some regions, the descriptions approached heights which might be described as canopies (20 to 30 cm). Physiology Many algae, particularly members of the Characeae species, have served as model experimental organisms to understand the mechanisms of the water permeability of membranes, osmoregulation, turgor regulation, salt tolerance, cytoplasmic streaming, and the generation of action potentials. Phytohormones are found not only in higher plants, but in algae, too. Symbiotic algae Some species of algae form symbiotic relationships with other organisms. In these symbioses, the algae supply photosynthates (organic substances) to the host organism providing protection to the algal cells. The host organism derives some or all of its energy requirements from the algae. Examples are: Lichens Lichens are defined by the International Association for Lichenology to be "an association of a fungus and a photosynthetic symbiont resulting in a stable vegetative body having a specific structure". The fungi, or mycobionts, are mainly from the Ascomycota with a few from the Basidiomycota. In nature they do not occur separate from lichens. It is unknown when they began to associate. One mycobiont associates with the same phycobiont species, rarely two, from the green algae, except that alternatively, the mycobiont may associate with a species of cyanobacteria (hence "photobiont" is the more accurate term). A photobiont may be associated with many different mycobionts or may live independently; accordingly, lichens are named and classified as fungal species. The association is termed a morphogenesis because the lichen has a form and capabilities not possessed by the symbiont species alone (they can be experimentally isolated). The photobiont possibly triggers otherwise latent genes in the mycobiont. Trentepohlia is an example of a common green alga genus worldwide that can grow on its own or be lichenised. Lichen thus share some of the habitat and often similar appearance with specialized species of algae (aerophytes) growing on exposed surfaces such as tree trunks and rocks and sometimes discoloring them. Coral reefs Coral reefs are accumulated from the calcareous exoskeletons of marine invertebrates of the order Scleractinia (stony corals).

These animals metabolize sugar and oxygen to obtain energy for their cell-building processes, including secretion of the exoskeleton, with water and carbon dioxide as byproducts. Dinoflagellates (algal protists) are often endosymbionts in the cells of the coral-forming marine invertebrates, where they accelerate host-cell metabolism by generating sugar and oxygen immediately available through photosynthesis using incident light and the carbon dioxide produced by the host. Reef-building stony corals (hermatypic corals) require endosymbiotic algae from the genus Symbiodinium to be in a healthy condition. The loss of Symbiodinium from the host is known as coral bleaching, a condition which leads to the deterioration of a reef. Sea sponges Endosymbiontic green algae live close to the surface of some sponges, for example, breadcrumb sponges (Halichondria panicea). The alga is thus protected from predators; the sponge is provided with oxygen and sugars which can account for 50 to 80% of sponge growth in some species. Lifecycle Rhodophyta, Chlorophyta, and Heterokontophyta, the three main algal divisions, have lifecycles which show considerable variation and complexity. In general, an asexual phase exists where the seaweed's cells are diploid, a sexual phase where the cells are haploid, followed by fusion of the male and female gametes. Asexual reproduction permits efficient population increases, but less variation is possible. Commonly, in sexual reproduction of unicellular and colonial algae, two specialized, sexually compatible, haploid gametes make physical contact and fuse to form a zygote. To ensure a successful mating, the development and release of gametes is highly synchronized and regulated; pheromones may play a key role in these processes. Sexual reproduction allows for more variation and provides the benefit of efficient recombinational repair of DNA damages during meiosis, a key stage of the sexual cycle. However, sexual reproduction is more costly than asexual reproduction. Meiosis has been shown to occur in many different species of algae. Numbers The Algal Collection of the US National Herbarium (located in the National Museum of Natural History) consists of approximately 320,500 dried specimens, which, although not exhaustive (no exhaustive collection exists), gives an idea of the order of magnitude of the number of algal species (that number remains unknown). Estimates vary widely. For example, according to one standard textbook, in the British Isles the UK Biodiversity Steering Group Report estimated there to be 20,000 algal species in the UK. Another checklist reports only about 5,000 species. Regarding the difference of about 15,000 species, the text concludes: "It will require many detailed field surveys before it is possible to provide a reliable estimate of the total number of species ..." Regional and group estimates have been made, as well: 5,000–5,500 species of red algae worldwide "some 1,300 in Australian Seas" 400 seaweed species for the western coastline of South Africa, and 212 species from the coast of KwaZulu-Natal. Some of these are duplicates, as the range extends across both coasts, and the total recorded is probably about 500 species. Most of these are listed in List of seaweeds of South Africa.

These animals metabolize sugar and oxygen to obtain energy for their cell-building processes, including secretion of the exoskeleton, with water and carbon dioxide as byproducts. Dinoflagellates (algal protists) are often endosymbionts in the cells of the coral-forming marine invertebrates, where they accelerate host-cell metabolism by generating sugar and oxygen immediately available through photosynthesis using incident light and the carbon dioxide produced by the host. Reef-building stony corals (hermatypic corals) require endosymbiotic algae from the genus Symbiodinium to be in a healthy condition. The loss of Symbiodinium from the host is known as coral bleaching, a condition which leads to the deterioration of a reef. Sea sponges Endosymbiontic green algae live close to the surface of some sponges, for example, breadcrumb sponges (Halichondria panicea). The alga is thus protected from predators; the sponge is provided with oxygen and sugars which can account for 50 to 80% of sponge growth in some species. Lifecycle Rhodophyta, Chlorophyta, and Heterokontophyta, the three main algal divisions, have lifecycles which show considerable variation and complexity. In general, an asexual phase exists where the seaweed's cells are diploid, a sexual phase where the cells are haploid, followed by fusion of the male and female gametes. Asexual reproduction permits efficient population increases, but less variation is possible. Commonly, in sexual reproduction of unicellular and colonial algae, two specialized, sexually compatible, haploid gametes make physical contact and fuse to form a zygote. To ensure a successful mating, the development and release of gametes is highly synchronized and regulated; pheromones may play a key role in these processes. Sexual reproduction allows for more variation and provides the benefit of efficient recombinational repair of DNA damages during meiosis, a key stage of the sexual cycle. However, sexual reproduction is more costly than asexual reproduction. Meiosis has been shown to occur in many different species of algae. Numbers The Algal Collection of the US National Herbarium (located in the National Museum of Natural History) consists of approximately 320,500 dried specimens, which, although not exhaustive (no exhaustive collection exists), gives an idea of the order of magnitude of the number of algal species (that number remains unknown). Estimates vary widely. For example, according to one standard textbook, in the British Isles the UK Biodiversity Steering Group Report estimated there to be 20,000 algal species in the UK. Another checklist reports only about 5,000 species. Regarding the difference of about 15,000 species, the text concludes: "It will require many detailed field surveys before it is possible to provide a reliable estimate of the total number of species ..." Regional and group estimates have been made, as well: 5,000–5,500 species of red algae worldwide "some 1,300 in Australian Seas" 400 seaweed species for the western coastline of South Africa, and 212 species from the coast of KwaZulu-Natal. Some of these are duplicates, as the range extends across both coasts, and the total recorded is probably about 500 species. Most of these are listed in List of seaweeds of South Africa.

These animals metabolize sugar and oxygen to obtain energy for their cell-building processes, including secretion of the exoskeleton, with water and carbon dioxide as byproducts. Dinoflagellates (algal protists) are often endosymbionts in the cells of the coral-forming marine invertebrates, where they accelerate host-cell metabolism by generating sugar and oxygen immediately available through photosynthesis using incident light and the carbon dioxide produced by the host. Reef-building stony corals (hermatypic corals) require endosymbiotic algae from the genus Symbiodinium to be in a healthy condition. The loss of Symbiodinium from the host is known as coral bleaching, a condition which leads to the deterioration of a reef. Sea sponges Endosymbiontic green algae live close to the surface of some sponges, for example, breadcrumb sponges (Halichondria panicea). The alga is thus protected from predators; the sponge is provided with oxygen and sugars which can account for 50 to 80% of sponge growth in some species. Lifecycle Rhodophyta, Chlorophyta, and Heterokontophyta, the three main algal divisions, have lifecycles which show considerable variation and complexity. In general, an asexual phase exists where the seaweed's cells are diploid, a sexual phase where the cells are haploid, followed by fusion of the male and female gametes. Asexual reproduction permits efficient population increases, but less variation is possible. Commonly, in sexual reproduction of unicellular and colonial algae, two specialized, sexually compatible, haploid gametes make physical contact and fuse to form a zygote. To ensure a successful mating, the development and release of gametes is highly synchronized and regulated; pheromones may play a key role in these processes. Sexual reproduction allows for more variation and provides the benefit of efficient recombinational repair of DNA damages during meiosis, a key stage of the sexual cycle. However, sexual reproduction is more costly than asexual reproduction. Meiosis has been shown to occur in many different species of algae. Numbers The Algal Collection of the US National Herbarium (located in the National Museum of Natural History) consists of approximately 320,500 dried specimens, which, although not exhaustive (no exhaustive collection exists), gives an idea of the order of magnitude of the number of algal species (that number remains unknown). Estimates vary widely. For example, according to one standard textbook, in the British Isles the UK Biodiversity Steering Group Report estimated there to be 20,000 algal species in the UK. Another checklist reports only about 5,000 species. Regarding the difference of about 15,000 species, the text concludes: "It will require many detailed field surveys before it is possible to provide a reliable estimate of the total number of species ..." Regional and group estimates have been made, as well: 5,000–5,500 species of red algae worldwide "some 1,300 in Australian Seas" 400 seaweed species for the western coastline of South Africa, and 212 species from the coast of KwaZulu-Natal. Some of these are duplicates, as the range extends across both coasts, and the total recorded is probably about 500 species. Most of these are listed in List of seaweeds of South Africa.

These exclude phytoplankton and crustose corallines. 669 marine species from California (US) 642 in the check-list of Britain and Ireland and so on, but lacking any scientific basis or reliable sources, these numbers have no more credibility than the British ones mentioned above. Most estimates also omit microscopic algae, such as phytoplankton. The most recent estimate suggests 72,500 algal species worldwide. Distribution The distribution of algal species has been fairly well studied since the founding of phytogeography in the mid-19th century. Algae spread mainly by the dispersal of spores analogously to the dispersal of Plantae by seeds and spores. This dispersal can be accomplished by air, water, or other organisms. Due to this, spores can be found in a variety of environments: fresh and marine waters, air, soil, and in or on other organisms. Whether a spore is to grow into an organism depends on the combination of the species and the environmental conditions where the spore lands. The spores of freshwater algae are dispersed mainly by running water and wind, as well as by living carriers. However, not all bodies of water can carry all species of algae, as the chemical composition of certain water bodies limits the algae that can survive within them. Marine spores are often spread by ocean currents. Ocean water presents many vastly different habitats based on temperature and nutrient availability, resulting in phytogeographic zones, regions, and provinces. To some degree, the distribution of algae is subject to floristic discontinuities caused by geographical features, such as Antarctica, long distances of ocean or general land masses. It is, therefore, possible to identify species occurring by locality, such as "Pacific algae" or "North Sea algae". When they occur out of their localities, hypothesizing a transport mechanism is usually possible, such as the hulls of ships. For example, Ulva reticulata and U. fasciata travelled from the mainland to Hawaii in this manner. Mapping is possible for select species only: "there are many valid examples of confined distribution patterns." For example, Clathromorphum is an arctic genus and is not mapped far south of there. However, scientists regard the overall data as insufficient due to the "difficulties of undertaking such studies." Ecology Algae are prominent in bodies of water, common in terrestrial environments, and are found in unusual environments, such as on snow and ice. Seaweeds grow mostly in shallow marine waters, under deep; however, some such as Navicula pennata have been recorded to a depth of . A type of algae, Ancylonema nordenskioeldii, was found in Greenland in areas known as the 'Dark Zone', which caused an increase in the rate of melting ice sheet. Same algae was found in the Italian Alps, after pink ice appeared on parts of the Presena glacier. The various sorts of algae play significant roles in aquatic ecology. Microscopic forms that live suspended in the water column (phytoplankton) provide the food base for most marine food chains.

These exclude phytoplankton and crustose corallines. 669 marine species from California (US) 642 in the check-list of Britain and Ireland and so on, but lacking any scientific basis or reliable sources, these numbers have no more credibility than the British ones mentioned above. Most estimates also omit microscopic algae, such as phytoplankton. The most recent estimate suggests 72,500 algal species worldwide. Distribution The distribution of algal species has been fairly well studied since the founding of phytogeography in the mid-19th century. Algae spread mainly by the dispersal of spores analogously to the dispersal of Plantae by seeds and spores. This dispersal can be accomplished by air, water, or other organisms. Due to this, spores can be found in a variety of environments: fresh and marine waters, air, soil, and in or on other organisms. Whether a spore is to grow into an organism depends on the combination of the species and the environmental conditions where the spore lands. The spores of freshwater algae are dispersed mainly by running water and wind, as well as by living carriers. However, not all bodies of water can carry all species of algae, as the chemical composition of certain water bodies limits the algae that can survive within them. Marine spores are often spread by ocean currents. Ocean water presents many vastly different habitats based on temperature and nutrient availability, resulting in phytogeographic zones, regions, and provinces. To some degree, the distribution of algae is subject to floristic discontinuities caused by geographical features, such as Antarctica, long distances of ocean or general land masses. It is, therefore, possible to identify species occurring by locality, such as "Pacific algae" or "North Sea algae". When they occur out of their localities, hypothesizing a transport mechanism is usually possible, such as the hulls of ships. For example, Ulva reticulata and U. fasciata travelled from the mainland to Hawaii in this manner. Mapping is possible for select species only: "there are many valid examples of confined distribution patterns." For example, Clathromorphum is an arctic genus and is not mapped far south of there. However, scientists regard the overall data as insufficient due to the "difficulties of undertaking such studies." Ecology Algae are prominent in bodies of water, common in terrestrial environments, and are found in unusual environments, such as on snow and ice. Seaweeds grow mostly in shallow marine waters, under deep; however, some such as Navicula pennata have been recorded to a depth of . A type of algae, Ancylonema nordenskioeldii, was found in Greenland in areas known as the 'Dark Zone', which caused an increase in the rate of melting ice sheet. Same algae was found in the Italian Alps, after pink ice appeared on parts of the Presena glacier. The various sorts of algae play significant roles in aquatic ecology. Microscopic forms that live suspended in the water column (phytoplankton) provide the food base for most marine food chains.

These exclude phytoplankton and crustose corallines. 669 marine species from California (US) 642 in the check-list of Britain and Ireland and so on, but lacking any scientific basis or reliable sources, these numbers have no more credibility than the British ones mentioned above. Most estimates also omit microscopic algae, such as phytoplankton. The most recent estimate suggests 72,500 algal species worldwide. Distribution The distribution of algal species has been fairly well studied since the founding of phytogeography in the mid-19th century. Algae spread mainly by the dispersal of spores analogously to the dispersal of Plantae by seeds and spores. This dispersal can be accomplished by air, water, or other organisms. Due to this, spores can be found in a variety of environments: fresh and marine waters, air, soil, and in or on other organisms. Whether a spore is to grow into an organism depends on the combination of the species and the environmental conditions where the spore lands. The spores of freshwater algae are dispersed mainly by running water and wind, as well as by living carriers. However, not all bodies of water can carry all species of algae, as the chemical composition of certain water bodies limits the algae that can survive within them. Marine spores are often spread by ocean currents. Ocean water presents many vastly different habitats based on temperature and nutrient availability, resulting in phytogeographic zones, regions, and provinces. To some degree, the distribution of algae is subject to floristic discontinuities caused by geographical features, such as Antarctica, long distances of ocean or general land masses. It is, therefore, possible to identify species occurring by locality, such as "Pacific algae" or "North Sea algae". When they occur out of their localities, hypothesizing a transport mechanism is usually possible, such as the hulls of ships. For example, Ulva reticulata and U. fasciata travelled from the mainland to Hawaii in this manner. Mapping is possible for select species only: "there are many valid examples of confined distribution patterns." For example, Clathromorphum is an arctic genus and is not mapped far south of there. However, scientists regard the overall data as insufficient due to the "difficulties of undertaking such studies." Ecology Algae are prominent in bodies of water, common in terrestrial environments, and are found in unusual environments, such as on snow and ice. Seaweeds grow mostly in shallow marine waters, under deep; however, some such as Navicula pennata have been recorded to a depth of . A type of algae, Ancylonema nordenskioeldii, was found in Greenland in areas known as the 'Dark Zone', which caused an increase in the rate of melting ice sheet. Same algae was found in the Italian Alps, after pink ice appeared on parts of the Presena glacier. The various sorts of algae play significant roles in aquatic ecology. Microscopic forms that live suspended in the water column (phytoplankton) provide the food base for most marine food chains.

In very high densities (algal blooms), these algae may discolor the water and outcompete, poison, or asphyxiate other life forms. Algae can be used as indicator organisms to monitor pollution in various aquatic systems. In many cases, algal metabolism is sensitive to various pollutants. Due to this, the species composition of algal populations may shift in the presence of chemical pollutants. To detect these changes, algae can be sampled from the environment and maintained in laboratories with relative ease. On the basis of their habitat, algae can be categorized as: aquatic (planktonic, benthic, marine, freshwater, lentic, lotic), terrestrial, aerial (subaerial), lithophytic, halophytic (or euryhaline), psammon, thermophilic, cryophilic, epibiont (epiphytic, epizoic), endosymbiont (endophytic, endozoic), parasitic, calcifilic or lichenic (phycobiont). Cultural associations In classical Chinese, the word is used both for "algae" and (in the modest tradition of the imperial scholars) for "literary talent". The third island in Kunming Lake beside the Summer Palace in Beijing is known as the Zaojian Tang Dao, which thus simultaneously means "Island of the Algae-Viewing Hall" and "Island of the Hall for Reflecting on Literary Talent". Cultivation Seaweed farming Bioreactors Uses Agar Agar, a gelatinous substance derived from red algae, has a number of commercial uses. It is a good medium on which to grow bacteria and fungi, as most microorganisms cannot digest agar. Alginates Alginic acid, or alginate, is extracted from brown algae. Its uses range from gelling agents in food, to medical dressings. Alginic acid also has been used in the field of biotechnology as a biocompatible medium for cell encapsulation and cell immobilization. Molecular cuisine is also a user of the substance for its gelling properties, by which it becomes a delivery vehicle for flavours. Between 100,000 and 170,000 wet tons of Macrocystis are harvested annually in New Mexico for alginate extraction and abalone feed. Energy source To be competitive and independent from fluctuating support from (local) policy on the long run, biofuels should equal or beat the cost level of fossil fuels. Here, algae-based fuels hold great promise, directly related to the potential to produce more biomass per unit area in a year than any other form of biomass. The break-even point for algae-based biofuels is estimated to occur by 2025. Fertilizer For centuries, seaweed has been used as a fertilizer; George Owen of Henllys writing in the 16th century referring to drift weed in South Wales: Today, algae are used by humans in many ways; for example, as fertilizers, soil conditioners, and livestock feed. Aquatic and microscopic species are cultured in clear tanks or ponds and are either harvested or used to treat effluents pumped through the ponds. Algaculture on a large scale is an important type of aquaculture in some places. Maerl is commonly used as a soil conditioner. Nutrition Naturally growing seaweeds are an important source of food, especially in Asia, leading some to label them as superfoods.

In very high densities (algal blooms), these algae may discolor the water and outcompete, poison, or asphyxiate other life forms. Algae can be used as indicator organisms to monitor pollution in various aquatic systems. In many cases, algal metabolism is sensitive to various pollutants. Due to this, the species composition of algal populations may shift in the presence of chemical pollutants. To detect these changes, algae can be sampled from the environment and maintained in laboratories with relative ease. On the basis of their habitat, algae can be categorized as: aquatic (planktonic, benthic, marine, freshwater, lentic, lotic), terrestrial, aerial (subaerial), lithophytic, halophytic (or euryhaline), psammon, thermophilic, cryophilic, epibiont (epiphytic, epizoic), endosymbiont (endophytic, endozoic), parasitic, calcifilic or lichenic (phycobiont). Cultural associations In classical Chinese, the word is used both for "algae" and (in the modest tradition of the imperial scholars) for "literary talent". The third island in Kunming Lake beside the Summer Palace in Beijing is known as the Zaojian Tang Dao, which thus simultaneously means "Island of the Algae-Viewing Hall" and "Island of the Hall for Reflecting on Literary Talent". Cultivation Seaweed farming Bioreactors Uses Agar Agar, a gelatinous substance derived from red algae, has a number of commercial uses. It is a good medium on which to grow bacteria and fungi, as most microorganisms cannot digest agar. Alginates Alginic acid, or alginate, is extracted from brown algae. Its uses range from gelling agents in food, to medical dressings. Alginic acid also has been used in the field of biotechnology as a biocompatible medium for cell encapsulation and cell immobilization. Molecular cuisine is also a user of the substance for its gelling properties, by which it becomes a delivery vehicle for flavours. Between 100,000 and 170,000 wet tons of Macrocystis are harvested annually in New Mexico for alginate extraction and abalone feed. Energy source To be competitive and independent from fluctuating support from (local) policy on the long run, biofuels should equal or beat the cost level of fossil fuels. Here, algae-based fuels hold great promise, directly related to the potential to produce more biomass per unit area in a year than any other form of biomass. The break-even point for algae-based biofuels is estimated to occur by 2025. Fertilizer For centuries, seaweed has been used as a fertilizer; George Owen of Henllys writing in the 16th century referring to drift weed in South Wales: Today, algae are used by humans in many ways; for example, as fertilizers, soil conditioners, and livestock feed. Aquatic and microscopic species are cultured in clear tanks or ponds and are either harvested or used to treat effluents pumped through the ponds. Algaculture on a large scale is an important type of aquaculture in some places. Maerl is commonly used as a soil conditioner. Nutrition Naturally growing seaweeds are an important source of food, especially in Asia, leading some to label them as superfoods.

In very high densities (algal blooms), these algae may discolor the water and outcompete, poison, or asphyxiate other life forms. Algae can be used as indicator organisms to monitor pollution in various aquatic systems. In many cases, algal metabolism is sensitive to various pollutants. Due to this, the species composition of algal populations may shift in the presence of chemical pollutants. To detect these changes, algae can be sampled from the environment and maintained in laboratories with relative ease. On the basis of their habitat, algae can be categorized as: aquatic (planktonic, benthic, marine, freshwater, lentic, lotic), terrestrial, aerial (subaerial), lithophytic, halophytic (or euryhaline), psammon, thermophilic, cryophilic, epibiont (epiphytic, epizoic), endosymbiont (endophytic, endozoic), parasitic, calcifilic or lichenic (phycobiont). Cultural associations In classical Chinese, the word is used both for "algae" and (in the modest tradition of the imperial scholars) for "literary talent". The third island in Kunming Lake beside the Summer Palace in Beijing is known as the Zaojian Tang Dao, which thus simultaneously means "Island of the Algae-Viewing Hall" and "Island of the Hall for Reflecting on Literary Talent". Cultivation Seaweed farming Bioreactors Uses Agar Agar, a gelatinous substance derived from red algae, has a number of commercial uses. It is a good medium on which to grow bacteria and fungi, as most microorganisms cannot digest agar. Alginates Alginic acid, or alginate, is extracted from brown algae. Its uses range from gelling agents in food, to medical dressings. Alginic acid also has been used in the field of biotechnology as a biocompatible medium for cell encapsulation and cell immobilization. Molecular cuisine is also a user of the substance for its gelling properties, by which it becomes a delivery vehicle for flavours. Between 100,000 and 170,000 wet tons of Macrocystis are harvested annually in New Mexico for alginate extraction and abalone feed. Energy source To be competitive and independent from fluctuating support from (local) policy on the long run, biofuels should equal or beat the cost level of fossil fuels. Here, algae-based fuels hold great promise, directly related to the potential to produce more biomass per unit area in a year than any other form of biomass. The break-even point for algae-based biofuels is estimated to occur by 2025. Fertilizer For centuries, seaweed has been used as a fertilizer; George Owen of Henllys writing in the 16th century referring to drift weed in South Wales: Today, algae are used by humans in many ways; for example, as fertilizers, soil conditioners, and livestock feed. Aquatic and microscopic species are cultured in clear tanks or ponds and are either harvested or used to treat effluents pumped through the ponds. Algaculture on a large scale is an important type of aquaculture in some places. Maerl is commonly used as a soil conditioner. Nutrition Naturally growing seaweeds are an important source of food, especially in Asia, leading some to label them as superfoods.

They provide many vitamins including: A, B1, B2, B6, niacin, and C, and are rich in iodine, potassium, iron, magnesium, and calcium. In addition, commercially cultivated microalgae, including both algae and cyanobacteria, are marketed as nutritional supplements, such as spirulina, Chlorella and the vitamin-C supplement from Dunaliella, high in beta-carotene. Algae are national foods of many nations: China consumes more than 70 species, including fat choy, a cyanobacterium considered a vegetable; Japan, over 20 species such as nori and aonori; Ireland, dulse; Chile, cochayuyo. Laver is used to make laver bread in Wales, where it is known as ; in Korea, . It is also used along the west coast of North America from California to British Columbia, in Hawaii and by the Māori of New Zealand. Sea lettuce and badderlocks are salad ingredients in Scotland, Ireland, Greenland, and Iceland. Algae is being considered a potential solution for world hunger problem. Two popular forms of algae are used in cuisine: Chlorella: This form of alga is found in freshwater and contains photosynthetic pigments in its chloroplast. It is high in iron, zinc, magnesium, vitamin B2 and Omega-3 Fatty acids. Furthermore, it contains all nine of the essential amino acids the body does not produce on its own Spirulina: Known otherwise as a cyanobacterium (a prokaryote, incorrectly referred to as a "blue-green alga"), contains 10% more protein than Chlorella as well as more thiamine and copper. The oils from some algae have high levels of unsaturated fatty acids. For example, Parietochloris incisa is very high in arachidonic acid, where it reaches up to 47% of the triglyceride pool. Some varieties of algae favored by vegetarianism and veganism contain the long-chain, essential omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Fish oil contains the omega-3 fatty acids, but the original source is algae (microalgae in particular), which are eaten by marine life such as copepods and are passed up the food chain. Algae have emerged in recent years as a popular source of omega-3 fatty acids for vegetarians who cannot get long-chain EPA and DHA from other vegetarian sources such as flaxseed oil, which only contains the short-chain alpha-linolenic acid (ALA). Pollution control Sewage can be treated with algae, reducing the use of large amounts of toxic chemicals that would otherwise be needed. Algae can be used to capture fertilizers in runoff from farms. When subsequently harvested, the enriched algae can be used as fertilizer. Aquaria and ponds can be filtered using algae, which absorb nutrients from the water in a device called an algae scrubber, also known as an algae turf scrubber. Agricultural Research Service scientists found that 60–90% of nitrogen runoff and 70–100% of phosphorus runoff can be captured from manure effluents using a horizontal algae scrubber, also called an algal turf scrubber (ATS). Scientists developed the ATS, which consists of shallow, 100-foot raceways of nylon netting where algae colonies can form, and studied its efficacy for three years.

They provide many vitamins including: A, B1, B2, B6, niacin, and C, and are rich in iodine, potassium, iron, magnesium, and calcium. In addition, commercially cultivated microalgae, including both algae and cyanobacteria, are marketed as nutritional supplements, such as spirulina, Chlorella and the vitamin-C supplement from Dunaliella, high in beta-carotene. Algae are national foods of many nations: China consumes more than 70 species, including fat choy, a cyanobacterium considered a vegetable; Japan, over 20 species such as nori and aonori; Ireland, dulse; Chile, cochayuyo. Laver is used to make laver bread in Wales, where it is known as ; in Korea, . It is also used along the west coast of North America from California to British Columbia, in Hawaii and by the Māori of New Zealand. Sea lettuce and badderlocks are salad ingredients in Scotland, Ireland, Greenland, and Iceland. Algae is being considered a potential solution for world hunger problem. Two popular forms of algae are used in cuisine: Chlorella: This form of alga is found in freshwater and contains photosynthetic pigments in its chloroplast. It is high in iron, zinc, magnesium, vitamin B2 and Omega-3 Fatty acids. Furthermore, it contains all nine of the essential amino acids the body does not produce on its own Spirulina: Known otherwise as a cyanobacterium (a prokaryote, incorrectly referred to as a "blue-green alga"), contains 10% more protein than Chlorella as well as more thiamine and copper. The oils from some algae have high levels of unsaturated fatty acids. For example, Parietochloris incisa is very high in arachidonic acid, where it reaches up to 47% of the triglyceride pool. Some varieties of algae favored by vegetarianism and veganism contain the long-chain, essential omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Fish oil contains the omega-3 fatty acids, but the original source is algae (microalgae in particular), which are eaten by marine life such as copepods and are passed up the food chain. Algae have emerged in recent years as a popular source of omega-3 fatty acids for vegetarians who cannot get long-chain EPA and DHA from other vegetarian sources such as flaxseed oil, which only contains the short-chain alpha-linolenic acid (ALA). Pollution control Sewage can be treated with algae, reducing the use of large amounts of toxic chemicals that would otherwise be needed. Algae can be used to capture fertilizers in runoff from farms. When subsequently harvested, the enriched algae can be used as fertilizer. Aquaria and ponds can be filtered using algae, which absorb nutrients from the water in a device called an algae scrubber, also known as an algae turf scrubber. Agricultural Research Service scientists found that 60–90% of nitrogen runoff and 70–100% of phosphorus runoff can be captured from manure effluents using a horizontal algae scrubber, also called an algal turf scrubber (ATS). Scientists developed the ATS, which consists of shallow, 100-foot raceways of nylon netting where algae colonies can form, and studied its efficacy for three years.

They provide many vitamins including: A, B1, B2, B6, niacin, and C, and are rich in iodine, potassium, iron, magnesium, and calcium. In addition, commercially cultivated microalgae, including both algae and cyanobacteria, are marketed as nutritional supplements, such as spirulina, Chlorella and the vitamin-C supplement from Dunaliella, high in beta-carotene. Algae are national foods of many nations: China consumes more than 70 species, including fat choy, a cyanobacterium considered a vegetable; Japan, over 20 species such as nori and aonori; Ireland, dulse; Chile, cochayuyo. Laver is used to make laver bread in Wales, where it is known as ; in Korea, . It is also used along the west coast of North America from California to British Columbia, in Hawaii and by the Māori of New Zealand. Sea lettuce and badderlocks are salad ingredients in Scotland, Ireland, Greenland, and Iceland. Algae is being considered a potential solution for world hunger problem. Two popular forms of algae are used in cuisine: Chlorella: This form of alga is found in freshwater and contains photosynthetic pigments in its chloroplast. It is high in iron, zinc, magnesium, vitamin B2 and Omega-3 Fatty acids. Furthermore, it contains all nine of the essential amino acids the body does not produce on its own Spirulina: Known otherwise as a cyanobacterium (a prokaryote, incorrectly referred to as a "blue-green alga"), contains 10% more protein than Chlorella as well as more thiamine and copper. The oils from some algae have high levels of unsaturated fatty acids. For example, Parietochloris incisa is very high in arachidonic acid, where it reaches up to 47% of the triglyceride pool. Some varieties of algae favored by vegetarianism and veganism contain the long-chain, essential omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Fish oil contains the omega-3 fatty acids, but the original source is algae (microalgae in particular), which are eaten by marine life such as copepods and are passed up the food chain. Algae have emerged in recent years as a popular source of omega-3 fatty acids for vegetarians who cannot get long-chain EPA and DHA from other vegetarian sources such as flaxseed oil, which only contains the short-chain alpha-linolenic acid (ALA). Pollution control Sewage can be treated with algae, reducing the use of large amounts of toxic chemicals that would otherwise be needed. Algae can be used to capture fertilizers in runoff from farms. When subsequently harvested, the enriched algae can be used as fertilizer. Aquaria and ponds can be filtered using algae, which absorb nutrients from the water in a device called an algae scrubber, also known as an algae turf scrubber. Agricultural Research Service scientists found that 60–90% of nitrogen runoff and 70–100% of phosphorus runoff can be captured from manure effluents using a horizontal algae scrubber, also called an algal turf scrubber (ATS). Scientists developed the ATS, which consists of shallow, 100-foot raceways of nylon netting where algae colonies can form, and studied its efficacy for three years.

They found that algae can readily be used to reduce the nutrient runoff from agricultural fields and increase the quality of water flowing into rivers, streams, and oceans. Researchers collected and dried the nutrient-rich algae from the ATS and studied its potential as an organic fertilizer. They found that cucumber and corn seedlings grew just as well using ATS organic fertilizer as they did with commercial fertilizers. Algae scrubbers, using bubbling upflow or vertical waterfall versions, are now also being used to filter aquaria and ponds. Polymers Various polymers can be created from algae, which can be especially useful in the creation of bioplastics. These include hybrid plastics, cellulose-based plastics, poly-lactic acid, and bio-polyethylene. Several companies have begun to produce algae polymers commercially, including for use in flip-flops and in surf boards. Bioremediation The alga Stichococcus bacillaris has been seen to colonize silicone resins used at archaeological sites; biodegrading the synthetic substance. Pigments The natural pigments (carotenoids and chlorophylls) produced by algae can be used as alternatives to chemical dyes and coloring agents. The presence of some individual algal pigments, together with specific pigment concentration ratios, are taxon-specific: analysis of their concentrations with various analytical methods, particularly high-performance liquid chromatography, can therefore offer deep insight into the taxonomic composition and relative abundance of natural algae populations in sea water samples. Stabilizing substances Carrageenan, from the red alga Chondrus crispus, is used as a stabilizer in milk products. Additional images See also AlgaeBase AlgaePARC Eutrophication Iron fertilization Marimo algae Microbiofuels Microphyte Photobioreactor Phycotechnology Plant Toxoid – anatoxin References Bibliography General . Regional Britain and Ireland Australia New Zealand Europe Arctic Greenland Faroe Islands . Canary Islands Morocco South Africa North America External links – a database of all algal names including images, nomenclature, taxonomy, distribution, bibliography, uses, extracts EnAlgae Endosymbiotic events Polyphyletic groups

They found that algae can readily be used to reduce the nutrient runoff from agricultural fields and increase the quality of water flowing into rivers, streams, and oceans. Researchers collected and dried the nutrient-rich algae from the ATS and studied its potential as an organic fertilizer. They found that cucumber and corn seedlings grew just as well using ATS organic fertilizer as they did with commercial fertilizers. Algae scrubbers, using bubbling upflow or vertical waterfall versions, are now also being used to filter aquaria and ponds. Polymers Various polymers can be created from algae, which can be especially useful in the creation of bioplastics. These include hybrid plastics, cellulose-based plastics, poly-lactic acid, and bio-polyethylene. Several companies have begun to produce algae polymers commercially, including for use in flip-flops and in surf boards. Bioremediation The alga Stichococcus bacillaris has been seen to colonize silicone resins used at archaeological sites; biodegrading the synthetic substance. Pigments The natural pigments (carotenoids and chlorophylls) produced by algae can be used as alternatives to chemical dyes and coloring agents. The presence of some individual algal pigments, together with specific pigment concentration ratios, are taxon-specific: analysis of their concentrations with various analytical methods, particularly high-performance liquid chromatography, can therefore offer deep insight into the taxonomic composition and relative abundance of natural algae populations in sea water samples. Stabilizing substances Carrageenan, from the red alga Chondrus crispus, is used as a stabilizer in milk products. Additional images See also AlgaeBase AlgaePARC Eutrophication Iron fertilization Marimo algae Microbiofuels Microphyte Photobioreactor Phycotechnology Plant Toxoid – anatoxin References Bibliography General . Regional Britain and Ireland Australia New Zealand Europe Arctic Greenland Faroe Islands . Canary Islands Morocco South Africa North America External links – a database of all algal names including images, nomenclature, taxonomy, distribution, bibliography, uses, extracts EnAlgae Endosymbiotic events Polyphyletic groups

They found that algae can readily be used to reduce the nutrient runoff from agricultural fields and increase the quality of water flowing into rivers, streams, and oceans. Researchers collected and dried the nutrient-rich algae from the ATS and studied its potential as an organic fertilizer. They found that cucumber and corn seedlings grew just as well using ATS organic fertilizer as they did with commercial fertilizers. Algae scrubbers, using bubbling upflow or vertical waterfall versions, are now also being used to filter aquaria and ponds. Polymers Various polymers can be created from algae, which can be especially useful in the creation of bioplastics. These include hybrid plastics, cellulose-based plastics, poly-lactic acid, and bio-polyethylene. Several companies have begun to produce algae polymers commercially, including for use in flip-flops and in surf boards. Bioremediation The alga Stichococcus bacillaris has been seen to colonize silicone resins used at archaeological sites; biodegrading the synthetic substance. Pigments The natural pigments (carotenoids and chlorophylls) produced by algae can be used as alternatives to chemical dyes and coloring agents. The presence of some individual algal pigments, together with specific pigment concentration ratios, are taxon-specific: analysis of their concentrations with various analytical methods, particularly high-performance liquid chromatography, can therefore offer deep insight into the taxonomic composition and relative abundance of natural algae populations in sea water samples. Stabilizing substances Carrageenan, from the red alga Chondrus crispus, is used as a stabilizer in milk products. Additional images See also AlgaeBase AlgaePARC Eutrophication Iron fertilization Marimo algae Microbiofuels Microphyte Photobioreactor Phycotechnology Plant Toxoid – anatoxin References Bibliography General . Regional Britain and Ireland Australia New Zealand Europe Arctic Greenland Faroe Islands . Canary Islands Morocco South Africa North America External links – a database of all algal names including images, nomenclature, taxonomy, distribution, bibliography, uses, extracts EnAlgae Endosymbiotic events Polyphyletic groups

Analysis of variance Analysis of variance (ANOVA) is a collection of statistical models and their associated estimation procedures (such as the "variation" among and between groups) used to analyze the differences among means. ANOVA was developed by the statistician Ronald Fisher. ANOVA is based on the law of total variance, where the observed variance in a particular variable is partitioned into components attributable to different sources of variation. In its simplest form, ANOVA provides a statistical test of whether two or more population means are equal, and therefore generalizes the t-test beyond two means. History While the analysis of variance reached fruition in the 20th century, antecedents extend centuries into the past according to Stigler. These include hypothesis testing, the partitioning of sums of squares, experimental techniques and the additive model. Laplace was performing hypothesis testing in the 1770s. Around 1800, Laplace and Gauss developed the least-squares method for combining observations, which improved upon methods then used in astronomy and geodesy. It also initiated much study of the contributions to sums of squares. Laplace knew how to estimate a variance from a residual (rather than a total) sum of squares. By 1827, Laplace was using least squares methods to address ANOVA problems regarding measurements of atmospheric tides. Before 1800, astronomers had isolated observational errors resulting from reaction times (the "personal equation") and had developed methods of reducing the errors. The experimental methods used in the study of the personal equation were later accepted by the emerging field of psychology which developed strong (full factorial) experimental methods to which randomization and blinding were soon added. An eloquent non-mathematical explanation of the additive effects model was available in 1885. Ronald Fisher introduced the term variance and proposed its formal analysis in a 1918 article The Correlation Between Relatives on the Supposition of Mendelian Inheritance. His first application of the analysis of variance was published in 1921. Analysis of variance became widely known after being included in Fisher's 1925 book Statistical Methods for Research Workers. Randomization models were developed by several researchers. The first was published in Polish by Jerzy Neyman in 1923. Example The analysis of variance can be used to describe otherwise complex relations among variables. A dog show provides an example. A dog show is not a random sampling of the breed: it is typically limited to dogs that are adult, pure-bred, and exemplary. A histogram of dog weights from a show might plausibly be rather complex, like the yellow-orange distribution shown in the illustrations. Suppose we wanted to predict the weight of a dog based on a certain set of characteristics of each dog. One way to do that is to explain the distribution of weights by dividing the dog population into groups based on those characteristics.

Analysis of variance Analysis of variance (ANOVA) is a collection of statistical models and their associated estimation procedures (such as the "variation" among and between groups) used to analyze the differences among means. ANOVA was developed by the statistician Ronald Fisher. ANOVA is based on the law of total variance, where the observed variance in a particular variable is partitioned into components attributable to different sources of variation. In its simplest form, ANOVA provides a statistical test of whether two or more population means are equal, and therefore generalizes the t-test beyond two means. History While the analysis of variance reached fruition in the 20th century, antecedents extend centuries into the past according to Stigler. These include hypothesis testing, the partitioning of sums of squares, experimental techniques and the additive model. Laplace was performing hypothesis testing in the 1770s. Around 1800, Laplace and Gauss developed the least-squares method for combining observations, which improved upon methods then used in astronomy and geodesy. It also initiated much study of the contributions to sums of squares. Laplace knew how to estimate a variance from a residual (rather than a total) sum of squares. By 1827, Laplace was using least squares methods to address ANOVA problems regarding measurements of atmospheric tides. Before 1800, astronomers had isolated observational errors resulting from reaction times (the "personal equation") and had developed methods of reducing the errors. The experimental methods used in the study of the personal equation were later accepted by the emerging field of psychology which developed strong (full factorial) experimental methods to which randomization and blinding were soon added. An eloquent non-mathematical explanation of the additive effects model was available in 1885. Ronald Fisher introduced the term variance and proposed its formal analysis in a 1918 article The Correlation Between Relatives on the Supposition of Mendelian Inheritance. His first application of the analysis of variance was published in 1921. Analysis of variance became widely known after being included in Fisher's 1925 book Statistical Methods for Research Workers. Randomization models were developed by several researchers. The first was published in Polish by Jerzy Neyman in 1923. Example The analysis of variance can be used to describe otherwise complex relations among variables. A dog show provides an example. A dog show is not a random sampling of the breed: it is typically limited to dogs that are adult, pure-bred, and exemplary. A histogram of dog weights from a show might plausibly be rather complex, like the yellow-orange distribution shown in the illustrations. Suppose we wanted to predict the weight of a dog based on a certain set of characteristics of each dog. One way to do that is to explain the distribution of weights by dividing the dog population into groups based on those characteristics.

A successful grouping will split dogs such that (a) each group has a low variance of dog weights (meaning the group is relatively homogeneous) and (b) the mean of each group is distinct (if two groups have the same mean, then it isn't reasonable to conclude that the groups are, in fact, separate in any meaningful way). In the illustrations to the right, groups are identified as X1, X2, etc. In the first illustration, the dogs are divided according to the product (interaction) of two binary groupings: young vs old, and short-haired vs long-haired (e.g., group 1 is young, short-haired dogs, group 2 is young, long-haired dogs, etc.). Since the distributions of dog weight within each of the groups (shown in blue) has a relatively large variance, and since the means are very similar across groups, grouping dogs by these characteristics does not produce an effective way to explain the variation in dog weights: knowing which group a dog is in doesn't allow us to predict its weight much better than simply knowing the dog is in a dog show. Thus, this grouping fails to explain the variation in the overall distribution (yellow-orange). An attempt to explain the weight distribution by grouping dogs as pet vs working breed and less athletic vs more athletic would probably be somewhat more successful (fair fit). The heaviest show dogs are likely to be big, strong, working breeds, while breeds kept as pets tend to be smaller and thus lighter. As shown by the second illustration, the distributions have variances that are considerably smaller than in the first case, and the means are more distinguishable. However, the significant overlap of distributions, for example, means that we cannot distinguish X1 and X2 reliably. Grouping dogs according to a coin flip might produce distributions that look similar. An attempt to explain weight by breed is likely to produce a very good fit. All Chihuahuas are light and all St Bernards are heavy. The difference in weights between Setters and Pointers does not justify separate breeds. The analysis of variance provides the formal tools to justify these intuitive judgments. A common use of the method is the analysis of experimental data or the development of models. The method has some advantages over correlation: not all of the data must be numeric and one result of the method is a judgment in the confidence in an explanatory relationship. Classes of models There are three classes of models used in the analysis of variance, and these are outlined here. Fixed-effects models The fixed-effects model (class I) of analysis of variance applies to situations in which the experimenter applies one or more treatments to the subjects of the experiment to see whether the response variable values change. This allows the experimenter to estimate the ranges of response variable values that the treatment would generate in the population as a whole. Random-effects models Random-effects model (class II) is used when the treatments are not fixed.

A successful grouping will split dogs such that (a) each group has a low variance of dog weights (meaning the group is relatively homogeneous) and (b) the mean of each group is distinct (if two groups have the same mean, then it isn't reasonable to conclude that the groups are, in fact, separate in any meaningful way). In the illustrations to the right, groups are identified as X1, X2, etc. In the first illustration, the dogs are divided according to the product (interaction) of two binary groupings: young vs old, and short-haired vs long-haired (e.g., group 1 is young, short-haired dogs, group 2 is young, long-haired dogs, etc.). Since the distributions of dog weight within each of the groups (shown in blue) has a relatively large variance, and since the means are very similar across groups, grouping dogs by these characteristics does not produce an effective way to explain the variation in dog weights: knowing which group a dog is in doesn't allow us to predict its weight much better than simply knowing the dog is in a dog show. Thus, this grouping fails to explain the variation in the overall distribution (yellow-orange). An attempt to explain the weight distribution by grouping dogs as pet vs working breed and less athletic vs more athletic would probably be somewhat more successful (fair fit). The heaviest show dogs are likely to be big, strong, working breeds, while breeds kept as pets tend to be smaller and thus lighter. As shown by the second illustration, the distributions have variances that are considerably smaller than in the first case, and the means are more distinguishable. However, the significant overlap of distributions, for example, means that we cannot distinguish X1 and X2 reliably. Grouping dogs according to a coin flip might produce distributions that look similar. An attempt to explain weight by breed is likely to produce a very good fit. All Chihuahuas are light and all St Bernards are heavy. The difference in weights between Setters and Pointers does not justify separate breeds. The analysis of variance provides the formal tools to justify these intuitive judgments. A common use of the method is the analysis of experimental data or the development of models. The method has some advantages over correlation: not all of the data must be numeric and one result of the method is a judgment in the confidence in an explanatory relationship. Classes of models There are three classes of models used in the analysis of variance, and these are outlined here. Fixed-effects models The fixed-effects model (class I) of analysis of variance applies to situations in which the experimenter applies one or more treatments to the subjects of the experiment to see whether the response variable values change. This allows the experimenter to estimate the ranges of response variable values that the treatment would generate in the population as a whole. Random-effects models Random-effects model (class II) is used when the treatments are not fixed.

A successful grouping will split dogs such that (a) each group has a low variance of dog weights (meaning the group is relatively homogeneous) and (b) the mean of each group is distinct (if two groups have the same mean, then it isn't reasonable to conclude that the groups are, in fact, separate in any meaningful way). In the illustrations to the right, groups are identified as X1, X2, etc. In the first illustration, the dogs are divided according to the product (interaction) of two binary groupings: young vs old, and short-haired vs long-haired (e.g., group 1 is young, short-haired dogs, group 2 is young, long-haired dogs, etc.). Since the distributions of dog weight within each of the groups (shown in blue) has a relatively large variance, and since the means are very similar across groups, grouping dogs by these characteristics does not produce an effective way to explain the variation in dog weights: knowing which group a dog is in doesn't allow us to predict its weight much better than simply knowing the dog is in a dog show. Thus, this grouping fails to explain the variation in the overall distribution (yellow-orange). An attempt to explain the weight distribution by grouping dogs as pet vs working breed and less athletic vs more athletic would probably be somewhat more successful (fair fit). The heaviest show dogs are likely to be big, strong, working breeds, while breeds kept as pets tend to be smaller and thus lighter. As shown by the second illustration, the distributions have variances that are considerably smaller than in the first case, and the means are more distinguishable. However, the significant overlap of distributions, for example, means that we cannot distinguish X1 and X2 reliably. Grouping dogs according to a coin flip might produce distributions that look similar. An attempt to explain weight by breed is likely to produce a very good fit. All Chihuahuas are light and all St Bernards are heavy. The difference in weights between Setters and Pointers does not justify separate breeds. The analysis of variance provides the formal tools to justify these intuitive judgments. A common use of the method is the analysis of experimental data or the development of models. The method has some advantages over correlation: not all of the data must be numeric and one result of the method is a judgment in the confidence in an explanatory relationship. Classes of models There are three classes of models used in the analysis of variance, and these are outlined here. Fixed-effects models The fixed-effects model (class I) of analysis of variance applies to situations in which the experimenter applies one or more treatments to the subjects of the experiment to see whether the response variable values change. This allows the experimenter to estimate the ranges of response variable values that the treatment would generate in the population as a whole. Random-effects models Random-effects model (class II) is used when the treatments are not fixed.

This occurs when the various factor levels are sampled from a larger population. Because the levels themselves are random variables, some assumptions and the method of contrasting the treatments (a multi-variable generalization of simple differences) differ from the fixed-effects model. Mixed-effects models A mixed-effects model (class III) contains experimental factors of both fixed and random-effects types, with appropriately different interpretations and analysis for the two types. Example: Teaching experiments could be performed by a college or university department to find a good introductory textbook, with each text considered a treatment. The fixed-effects model would compare a list of candidate texts. The random-effects model would determine whether important differences exist among a list of randomly selected texts. The mixed-effects model would compare the (fixed) incumbent texts to randomly selected alternatives. Defining fixed and random effects has proven elusive, with competing definitions arguably leading toward a linguistic quagmire. Assumptions The analysis of variance has been studied from several approaches, the most common of which uses a linear model that relates the response to the treatments and blocks. Note that the model is linear in parameters but may be nonlinear across factor levels. Interpretation is easy when data is balanced across factors but much deeper understanding is needed for unbalanced data. Textbook analysis using a normal distribution The analysis of variance can be presented in terms of a linear model, which makes the following assumptions about the probability distribution of the responses: Independence of observations – this is an assumption of the model that simplifies the statistical analysis. Normality – the distributions of the residuals are normal. Equality (or "homogeneity") of variances, called homoscedasticity — the variance of data in groups should be the same. The separate assumptions of the textbook model imply that the errors are independently, identically, and normally distributed for fixed effects models, that is, that the errors () are independent and Randomization-based analysis In a randomized controlled experiment, the treatments are randomly assigned to experimental units, following the experimental protocol. This randomization is objective and declared before the experiment is carried out. The objective random-assignment is used to test the significance of the null hypothesis, following the ideas of C. S. Peirce and Ronald Fisher. This design-based analysis was discussed and developed by Francis J. Anscombe at Rothamsted Experimental Station and by Oscar Kempthorne at Iowa State University. Kempthorne and his students make an assumption of unit treatment additivity, which is discussed in the books of Kempthorne and David R. Cox. Unit-treatment additivity In its simplest form, the assumption of unit-treatment additivity states that the observed response from experimental unit when receiving treatment can be written as the sum of the unit's response and the treatment-effect , that is The assumption of unit-treatment additivity implies that, for every treatment , the th treatment has exactly the same effect on every experiment unit. The assumption of unit treatment additivity usually cannot be directly falsified, according to Cox and Kempthorne. However, many consequences of treatment-unit additivity can be falsified.

This occurs when the various factor levels are sampled from a larger population. Because the levels themselves are random variables, some assumptions and the method of contrasting the treatments (a multi-variable generalization of simple differences) differ from the fixed-effects model. Mixed-effects models A mixed-effects model (class III) contains experimental factors of both fixed and random-effects types, with appropriately different interpretations and analysis for the two types. Example: Teaching experiments could be performed by a college or university department to find a good introductory textbook, with each text considered a treatment. The fixed-effects model would compare a list of candidate texts. The random-effects model would determine whether important differences exist among a list of randomly selected texts. The mixed-effects model would compare the (fixed) incumbent texts to randomly selected alternatives. Defining fixed and random effects has proven elusive, with competing definitions arguably leading toward a linguistic quagmire. Assumptions The analysis of variance has been studied from several approaches, the most common of which uses a linear model that relates the response to the treatments and blocks. Note that the model is linear in parameters but may be nonlinear across factor levels. Interpretation is easy when data is balanced across factors but much deeper understanding is needed for unbalanced data. Textbook analysis using a normal distribution The analysis of variance can be presented in terms of a linear model, which makes the following assumptions about the probability distribution of the responses: Independence of observations – this is an assumption of the model that simplifies the statistical analysis. Normality – the distributions of the residuals are normal. Equality (or "homogeneity") of variances, called homoscedasticity — the variance of data in groups should be the same. The separate assumptions of the textbook model imply that the errors are independently, identically, and normally distributed for fixed effects models, that is, that the errors () are independent and Randomization-based analysis In a randomized controlled experiment, the treatments are randomly assigned to experimental units, following the experimental protocol. This randomization is objective and declared before the experiment is carried out. The objective random-assignment is used to test the significance of the null hypothesis, following the ideas of C. S. Peirce and Ronald Fisher. This design-based analysis was discussed and developed by Francis J. Anscombe at Rothamsted Experimental Station and by Oscar Kempthorne at Iowa State University. Kempthorne and his students make an assumption of unit treatment additivity, which is discussed in the books of Kempthorne and David R. Cox. Unit-treatment additivity In its simplest form, the assumption of unit-treatment additivity states that the observed response from experimental unit when receiving treatment can be written as the sum of the unit's response and the treatment-effect , that is The assumption of unit-treatment additivity implies that, for every treatment , the th treatment has exactly the same effect on every experiment unit. The assumption of unit treatment additivity usually cannot be directly falsified, according to Cox and Kempthorne. However, many consequences of treatment-unit additivity can be falsified.

This occurs when the various factor levels are sampled from a larger population. Because the levels themselves are random variables, some assumptions and the method of contrasting the treatments (a multi-variable generalization of simple differences) differ from the fixed-effects model. Mixed-effects models A mixed-effects model (class III) contains experimental factors of both fixed and random-effects types, with appropriately different interpretations and analysis for the two types. Example: Teaching experiments could be performed by a college or university department to find a good introductory textbook, with each text considered a treatment. The fixed-effects model would compare a list of candidate texts. The random-effects model would determine whether important differences exist among a list of randomly selected texts. The mixed-effects model would compare the (fixed) incumbent texts to randomly selected alternatives. Defining fixed and random effects has proven elusive, with competing definitions arguably leading toward a linguistic quagmire. Assumptions The analysis of variance has been studied from several approaches, the most common of which uses a linear model that relates the response to the treatments and blocks. Note that the model is linear in parameters but may be nonlinear across factor levels. Interpretation is easy when data is balanced across factors but much deeper understanding is needed for unbalanced data. Textbook analysis using a normal distribution The analysis of variance can be presented in terms of a linear model, which makes the following assumptions about the probability distribution of the responses: Independence of observations – this is an assumption of the model that simplifies the statistical analysis. Normality – the distributions of the residuals are normal. Equality (or "homogeneity") of variances, called homoscedasticity — the variance of data in groups should be the same. The separate assumptions of the textbook model imply that the errors are independently, identically, and normally distributed for fixed effects models, that is, that the errors () are independent and Randomization-based analysis In a randomized controlled experiment, the treatments are randomly assigned to experimental units, following the experimental protocol. This randomization is objective and declared before the experiment is carried out. The objective random-assignment is used to test the significance of the null hypothesis, following the ideas of C. S. Peirce and Ronald Fisher. This design-based analysis was discussed and developed by Francis J. Anscombe at Rothamsted Experimental Station and by Oscar Kempthorne at Iowa State University. Kempthorne and his students make an assumption of unit treatment additivity, which is discussed in the books of Kempthorne and David R. Cox. Unit-treatment additivity In its simplest form, the assumption of unit-treatment additivity states that the observed response from experimental unit when receiving treatment can be written as the sum of the unit's response and the treatment-effect , that is The assumption of unit-treatment additivity implies that, for every treatment , the th treatment has exactly the same effect on every experiment unit. The assumption of unit treatment additivity usually cannot be directly falsified, according to Cox and Kempthorne. However, many consequences of treatment-unit additivity can be falsified.

For a randomized experiment, the assumption of unit-treatment additivity implies that the variance is constant for all treatments. Therefore, by contraposition, a necessary condition for unit-treatment additivity is that the variance is constant. The use of unit treatment additivity and randomization is similar to the design-based inference that is standard in finite-population survey sampling. Derived linear model Kempthorne uses the randomization-distribution and the assumption of unit treatment additivity to produce a derived linear model, very similar to the textbook model discussed previously. The test statistics of this derived linear model are closely approximated by the test statistics of an appropriate normal linear model, according to approximation theorems and simulation studies. However, there are differences. For example, the randomization-based analysis results in a small but (strictly) negative correlation between the observations. In the randomization-based analysis, there is no assumption of a normal distribution and certainly no assumption of independence. On the contrary, the observations are dependent! The randomization-based analysis has the disadvantage that its exposition involves tedious algebra and extensive time. Since the randomization-based analysis is complicated and is closely approximated by the approach using a normal linear model, most teachers emphasize the normal linear model approach. Few statisticians object to model-based analysis of balanced randomized experiments. Statistical models for observational data However, when applied to data from non-randomized experiments or observational studies, model-based analysis lacks the warrant of randomization. For observational data, the derivation of confidence intervals must use subjective models, as emphasized by Ronald Fisher and his followers. In practice, the estimates of treatment-effects from observational studies generally are often inconsistent. In practice, "statistical models" and observational data are useful for suggesting hypotheses that should be treated very cautiously by the public. Summary of assumptions The normal-model based ANOVA analysis assumes the independence, normality and homogeneity of variances of the residuals. The randomization-based analysis assumes only the homogeneity of the variances of the residuals (as a consequence of unit-treatment additivity) and uses the randomization procedure of the experiment. Both these analyses require homoscedasticity, as an assumption for the normal-model analysis and as a consequence of randomization and additivity for the randomization-based analysis. However, studies of processes that change variances rather than means (called dispersion effects) have been successfully conducted using ANOVA. There are no necessary assumptions for ANOVA in its full generality, but the F-test used for ANOVA hypothesis testing has assumptions and practical limitations which are of continuing interest. Problems which do not satisfy the assumptions of ANOVA can often be transformed to satisfy the assumptions. The property of unit-treatment additivity is not invariant under a "change of scale", so statisticians often use transformations to achieve unit-treatment additivity. If the response variable is expected to follow a parametric family of probability distributions, then the statistician may specify (in the protocol for the experiment or observational study) that the responses be transformed to stabilize the variance. Also, a statistician may specify that logarithmic transforms be applied to the responses, which are believed to follow a multiplicative model.

For a randomized experiment, the assumption of unit-treatment additivity implies that the variance is constant for all treatments. Therefore, by contraposition, a necessary condition for unit-treatment additivity is that the variance is constant. The use of unit treatment additivity and randomization is similar to the design-based inference that is standard in finite-population survey sampling. Derived linear model Kempthorne uses the randomization-distribution and the assumption of unit treatment additivity to produce a derived linear model, very similar to the textbook model discussed previously. The test statistics of this derived linear model are closely approximated by the test statistics of an appropriate normal linear model, according to approximation theorems and simulation studies. However, there are differences. For example, the randomization-based analysis results in a small but (strictly) negative correlation between the observations. In the randomization-based analysis, there is no assumption of a normal distribution and certainly no assumption of independence. On the contrary, the observations are dependent! The randomization-based analysis has the disadvantage that its exposition involves tedious algebra and extensive time. Since the randomization-based analysis is complicated and is closely approximated by the approach using a normal linear model, most teachers emphasize the normal linear model approach. Few statisticians object to model-based analysis of balanced randomized experiments. Statistical models for observational data However, when applied to data from non-randomized experiments or observational studies, model-based analysis lacks the warrant of randomization. For observational data, the derivation of confidence intervals must use subjective models, as emphasized by Ronald Fisher and his followers. In practice, the estimates of treatment-effects from observational studies generally are often inconsistent. In practice, "statistical models" and observational data are useful for suggesting hypotheses that should be treated very cautiously by the public. Summary of assumptions The normal-model based ANOVA analysis assumes the independence, normality and homogeneity of variances of the residuals. The randomization-based analysis assumes only the homogeneity of the variances of the residuals (as a consequence of unit-treatment additivity) and uses the randomization procedure of the experiment. Both these analyses require homoscedasticity, as an assumption for the normal-model analysis and as a consequence of randomization and additivity for the randomization-based analysis. However, studies of processes that change variances rather than means (called dispersion effects) have been successfully conducted using ANOVA. There are no necessary assumptions for ANOVA in its full generality, but the F-test used for ANOVA hypothesis testing has assumptions and practical limitations which are of continuing interest. Problems which do not satisfy the assumptions of ANOVA can often be transformed to satisfy the assumptions. The property of unit-treatment additivity is not invariant under a "change of scale", so statisticians often use transformations to achieve unit-treatment additivity. If the response variable is expected to follow a parametric family of probability distributions, then the statistician may specify (in the protocol for the experiment or observational study) that the responses be transformed to stabilize the variance. Also, a statistician may specify that logarithmic transforms be applied to the responses, which are believed to follow a multiplicative model.

For a randomized experiment, the assumption of unit-treatment additivity implies that the variance is constant for all treatments. Therefore, by contraposition, a necessary condition for unit-treatment additivity is that the variance is constant. The use of unit treatment additivity and randomization is similar to the design-based inference that is standard in finite-population survey sampling. Derived linear model Kempthorne uses the randomization-distribution and the assumption of unit treatment additivity to produce a derived linear model, very similar to the textbook model discussed previously. The test statistics of this derived linear model are closely approximated by the test statistics of an appropriate normal linear model, according to approximation theorems and simulation studies. However, there are differences. For example, the randomization-based analysis results in a small but (strictly) negative correlation between the observations. In the randomization-based analysis, there is no assumption of a normal distribution and certainly no assumption of independence. On the contrary, the observations are dependent! The randomization-based analysis has the disadvantage that its exposition involves tedious algebra and extensive time. Since the randomization-based analysis is complicated and is closely approximated by the approach using a normal linear model, most teachers emphasize the normal linear model approach. Few statisticians object to model-based analysis of balanced randomized experiments. Statistical models for observational data However, when applied to data from non-randomized experiments or observational studies, model-based analysis lacks the warrant of randomization. For observational data, the derivation of confidence intervals must use subjective models, as emphasized by Ronald Fisher and his followers. In practice, the estimates of treatment-effects from observational studies generally are often inconsistent. In practice, "statistical models" and observational data are useful for suggesting hypotheses that should be treated very cautiously by the public. Summary of assumptions The normal-model based ANOVA analysis assumes the independence, normality and homogeneity of variances of the residuals. The randomization-based analysis assumes only the homogeneity of the variances of the residuals (as a consequence of unit-treatment additivity) and uses the randomization procedure of the experiment. Both these analyses require homoscedasticity, as an assumption for the normal-model analysis and as a consequence of randomization and additivity for the randomization-based analysis. However, studies of processes that change variances rather than means (called dispersion effects) have been successfully conducted using ANOVA. There are no necessary assumptions for ANOVA in its full generality, but the F-test used for ANOVA hypothesis testing has assumptions and practical limitations which are of continuing interest. Problems which do not satisfy the assumptions of ANOVA can often be transformed to satisfy the assumptions. The property of unit-treatment additivity is not invariant under a "change of scale", so statisticians often use transformations to achieve unit-treatment additivity. If the response variable is expected to follow a parametric family of probability distributions, then the statistician may specify (in the protocol for the experiment or observational study) that the responses be transformed to stabilize the variance. Also, a statistician may specify that logarithmic transforms be applied to the responses, which are believed to follow a multiplicative model.

According to Cauchy's functional equation theorem, the logarithm is the only continuous transformation that transforms real multiplication to addition. Characteristics ANOVA is used in the analysis of comparative experiments, those in which only the difference in outcomes is of interest. The statistical significance of the experiment is determined by a ratio of two variances. This ratio is independent of several possible alterations to the experimental observations: Adding a constant to all observations does not alter significance. Multiplying all observations by a constant does not alter significance. So ANOVA statistical significance result is independent of constant bias and scaling errors as well as the units used in expressing observations. In the era of mechanical calculation it was common to subtract a constant from all observations (when equivalent to dropping leading digits) to simplify data entry. This is an example of data coding. Logic The calculations of ANOVA can be characterized as computing a number of means and variances, dividing two variances and comparing the ratio to a handbook value to determine statistical significance. Calculating a treatment effect is then trivial: "the effect of any treatment is estimated by taking the difference between the mean of the observations which receive the treatment and the general mean". Partitioning of the sum of squares ANOVA uses traditional standardized terminology. The definitional equation of sample variance is , where the divisor is called the degrees of freedom (DF), the summation is called the sum of squares (SS), the result is called the mean square (MS) and the squared terms are deviations from the sample mean. ANOVA estimates 3 sample variances: a total variance based on all the observation deviations from the grand mean, an error variance based on all the observation deviations from their appropriate treatment means, and a treatment variance. The treatment variance is based on the deviations of treatment means from the grand mean, the result being multiplied by the number of observations in each treatment to account for the difference between the variance of observations and the variance of means. The fundamental technique is a partitioning of the total sum of squares SS into components related to the effects used in the model. For example, the model for a simplified ANOVA with one type of treatment at different levels. The number of degrees of freedom DF can be partitioned in a similar way: one of these components (that for error) specifies a chi-squared distribution which describes the associated sum of squares, while the same is true for "treatments" if there is no treatment effect. See also Lack-of-fit sum of squares. The F-test The F-test is used for comparing the factors of the total deviation. For example, in one-way, or single-factor ANOVA, statistical significance is tested for by comparing the F test statistic where MS is mean square, is the number of treatments and is the total number of cases to the F-distribution with , degrees of freedom.

According to Cauchy's functional equation theorem, the logarithm is the only continuous transformation that transforms real multiplication to addition. Characteristics ANOVA is used in the analysis of comparative experiments, those in which only the difference in outcomes is of interest. The statistical significance of the experiment is determined by a ratio of two variances. This ratio is independent of several possible alterations to the experimental observations: Adding a constant to all observations does not alter significance. Multiplying all observations by a constant does not alter significance. So ANOVA statistical significance result is independent of constant bias and scaling errors as well as the units used in expressing observations. In the era of mechanical calculation it was common to subtract a constant from all observations (when equivalent to dropping leading digits) to simplify data entry. This is an example of data coding. Logic The calculations of ANOVA can be characterized as computing a number of means and variances, dividing two variances and comparing the ratio to a handbook value to determine statistical significance. Calculating a treatment effect is then trivial: "the effect of any treatment is estimated by taking the difference between the mean of the observations which receive the treatment and the general mean". Partitioning of the sum of squares ANOVA uses traditional standardized terminology. The definitional equation of sample variance is , where the divisor is called the degrees of freedom (DF), the summation is called the sum of squares (SS), the result is called the mean square (MS) and the squared terms are deviations from the sample mean. ANOVA estimates 3 sample variances: a total variance based on all the observation deviations from the grand mean, an error variance based on all the observation deviations from their appropriate treatment means, and a treatment variance. The treatment variance is based on the deviations of treatment means from the grand mean, the result being multiplied by the number of observations in each treatment to account for the difference between the variance of observations and the variance of means. The fundamental technique is a partitioning of the total sum of squares SS into components related to the effects used in the model. For example, the model for a simplified ANOVA with one type of treatment at different levels. The number of degrees of freedom DF can be partitioned in a similar way: one of these components (that for error) specifies a chi-squared distribution which describes the associated sum of squares, while the same is true for "treatments" if there is no treatment effect. See also Lack-of-fit sum of squares. The F-test The F-test is used for comparing the factors of the total deviation. For example, in one-way, or single-factor ANOVA, statistical significance is tested for by comparing the F test statistic where MS is mean square, is the number of treatments and is the total number of cases to the F-distribution with , degrees of freedom.

According to Cauchy's functional equation theorem, the logarithm is the only continuous transformation that transforms real multiplication to addition. Characteristics ANOVA is used in the analysis of comparative experiments, those in which only the difference in outcomes is of interest. The statistical significance of the experiment is determined by a ratio of two variances. This ratio is independent of several possible alterations to the experimental observations: Adding a constant to all observations does not alter significance. Multiplying all observations by a constant does not alter significance. So ANOVA statistical significance result is independent of constant bias and scaling errors as well as the units used in expressing observations. In the era of mechanical calculation it was common to subtract a constant from all observations (when equivalent to dropping leading digits) to simplify data entry. This is an example of data coding. Logic The calculations of ANOVA can be characterized as computing a number of means and variances, dividing two variances and comparing the ratio to a handbook value to determine statistical significance. Calculating a treatment effect is then trivial: "the effect of any treatment is estimated by taking the difference between the mean of the observations which receive the treatment and the general mean". Partitioning of the sum of squares ANOVA uses traditional standardized terminology. The definitional equation of sample variance is , where the divisor is called the degrees of freedom (DF), the summation is called the sum of squares (SS), the result is called the mean square (MS) and the squared terms are deviations from the sample mean. ANOVA estimates 3 sample variances: a total variance based on all the observation deviations from the grand mean, an error variance based on all the observation deviations from their appropriate treatment means, and a treatment variance. The treatment variance is based on the deviations of treatment means from the grand mean, the result being multiplied by the number of observations in each treatment to account for the difference between the variance of observations and the variance of means. The fundamental technique is a partitioning of the total sum of squares SS into components related to the effects used in the model. For example, the model for a simplified ANOVA with one type of treatment at different levels. The number of degrees of freedom DF can be partitioned in a similar way: one of these components (that for error) specifies a chi-squared distribution which describes the associated sum of squares, while the same is true for "treatments" if there is no treatment effect. See also Lack-of-fit sum of squares. The F-test The F-test is used for comparing the factors of the total deviation. For example, in one-way, or single-factor ANOVA, statistical significance is tested for by comparing the F test statistic where MS is mean square, is the number of treatments and is the total number of cases to the F-distribution with , degrees of freedom.

Using the F-distribution is a natural candidate because the test statistic is the ratio of two scaled sums of squares each of which follows a scaled chi-squared distribution. The expected value of F is (where is the treatment sample size) which is 1 for no treatment effect. As values of F increase above 1, the evidence is increasingly inconsistent with the null hypothesis. Two apparent experimental methods of increasing F are increasing the sample size and reducing the error variance by tight experimental controls. There are two methods of concluding the ANOVA hypothesis test, both of which produce the same result: The textbook method is to compare the observed value of F with the critical value of F determined from tables. The critical value of F is a function of the degrees of freedom of the numerator and the denominator and the significance level (α). If F ≥ FCritical, the null hypothesis is rejected. The computer method calculates the probability (p-value) of a value of F greater than or equal to the observed value. The null hypothesis is rejected if this probability is less than or equal to the significance level (α). The ANOVA F-test is known to be nearly optimal in the sense of minimizing false negative errors for a fixed rate of false positive errors (i.e. maximizing power for a fixed significance level). For example, to test the hypothesis that various medical treatments have exactly the same effect, the F-test's p-values closely approximate the permutation test's p-values: The approximation is particularly close when the design is balanced. Such permutation tests characterize tests with maximum power against all alternative hypotheses, as observed by Rosenbaum. The ANOVA F-test (of the null-hypothesis that all treatments have exactly the same effect) is recommended as a practical test, because of its robustness against many alternative distributions. Extended logic ANOVA consists of separable parts; partitioning sources of variance and hypothesis testing can be used individually. ANOVA is used to support other statistical tools. Regression is first used to fit more complex models to data, then ANOVA is used to compare models with the objective of selecting simple(r) models that adequately describe the data. "Such models could be fit without any reference to ANOVA, but ANOVA tools could then be used to make some sense of the fitted models, and to test hypotheses about batches of coefficients." "[W]e think of the analysis of variance as a way of understanding and structuring multilevel models—not as an alternative to regression but as a tool for summarizing complex high-dimensional inferences ..." For a single factor The simplest experiment suitable for ANOVA analysis is the completely randomized experiment with a single factor. More complex experiments with a single factor involve constraints on randomization and include completely randomized blocks and Latin squares (and variants: Graeco-Latin squares, etc.). The more complex experiments share many of the complexities of multiple factors. A relatively complete discussion of the analysis (models, data summaries, ANOVA table) of the completely randomized experiment is available.

Using the F-distribution is a natural candidate because the test statistic is the ratio of two scaled sums of squares each of which follows a scaled chi-squared distribution. The expected value of F is (where is the treatment sample size) which is 1 for no treatment effect. As values of F increase above 1, the evidence is increasingly inconsistent with the null hypothesis. Two apparent experimental methods of increasing F are increasing the sample size and reducing the error variance by tight experimental controls. There are two methods of concluding the ANOVA hypothesis test, both of which produce the same result: The textbook method is to compare the observed value of F with the critical value of F determined from tables. The critical value of F is a function of the degrees of freedom of the numerator and the denominator and the significance level (α). If F ≥ FCritical, the null hypothesis is rejected. The computer method calculates the probability (p-value) of a value of F greater than or equal to the observed value. The null hypothesis is rejected if this probability is less than or equal to the significance level (α). The ANOVA F-test is known to be nearly optimal in the sense of minimizing false negative errors for a fixed rate of false positive errors (i.e. maximizing power for a fixed significance level). For example, to test the hypothesis that various medical treatments have exactly the same effect, the F-test's p-values closely approximate the permutation test's p-values: The approximation is particularly close when the design is balanced. Such permutation tests characterize tests with maximum power against all alternative hypotheses, as observed by Rosenbaum. The ANOVA F-test (of the null-hypothesis that all treatments have exactly the same effect) is recommended as a practical test, because of its robustness against many alternative distributions. Extended logic ANOVA consists of separable parts; partitioning sources of variance and hypothesis testing can be used individually. ANOVA is used to support other statistical tools. Regression is first used to fit more complex models to data, then ANOVA is used to compare models with the objective of selecting simple(r) models that adequately describe the data. "Such models could be fit without any reference to ANOVA, but ANOVA tools could then be used to make some sense of the fitted models, and to test hypotheses about batches of coefficients." "[W]e think of the analysis of variance as a way of understanding and structuring multilevel models—not as an alternative to regression but as a tool for summarizing complex high-dimensional inferences ..." For a single factor The simplest experiment suitable for ANOVA analysis is the completely randomized experiment with a single factor. More complex experiments with a single factor involve constraints on randomization and include completely randomized blocks and Latin squares (and variants: Graeco-Latin squares, etc.). The more complex experiments share many of the complexities of multiple factors. A relatively complete discussion of the analysis (models, data summaries, ANOVA table) of the completely randomized experiment is available.

Using the F-distribution is a natural candidate because the test statistic is the ratio of two scaled sums of squares each of which follows a scaled chi-squared distribution. The expected value of F is (where is the treatment sample size) which is 1 for no treatment effect. As values of F increase above 1, the evidence is increasingly inconsistent with the null hypothesis. Two apparent experimental methods of increasing F are increasing the sample size and reducing the error variance by tight experimental controls. There are two methods of concluding the ANOVA hypothesis test, both of which produce the same result: The textbook method is to compare the observed value of F with the critical value of F determined from tables. The critical value of F is a function of the degrees of freedom of the numerator and the denominator and the significance level (α). If F ≥ FCritical, the null hypothesis is rejected. The computer method calculates the probability (p-value) of a value of F greater than or equal to the observed value. The null hypothesis is rejected if this probability is less than or equal to the significance level (α). The ANOVA F-test is known to be nearly optimal in the sense of minimizing false negative errors for a fixed rate of false positive errors (i.e. maximizing power for a fixed significance level). For example, to test the hypothesis that various medical treatments have exactly the same effect, the F-test's p-values closely approximate the permutation test's p-values: The approximation is particularly close when the design is balanced. Such permutation tests characterize tests with maximum power against all alternative hypotheses, as observed by Rosenbaum. The ANOVA F-test (of the null-hypothesis that all treatments have exactly the same effect) is recommended as a practical test, because of its robustness against many alternative distributions. Extended logic ANOVA consists of separable parts; partitioning sources of variance and hypothesis testing can be used individually. ANOVA is used to support other statistical tools. Regression is first used to fit more complex models to data, then ANOVA is used to compare models with the objective of selecting simple(r) models that adequately describe the data. "Such models could be fit without any reference to ANOVA, but ANOVA tools could then be used to make some sense of the fitted models, and to test hypotheses about batches of coefficients." "[W]e think of the analysis of variance as a way of understanding and structuring multilevel models—not as an alternative to regression but as a tool for summarizing complex high-dimensional inferences ..." For a single factor The simplest experiment suitable for ANOVA analysis is the completely randomized experiment with a single factor. More complex experiments with a single factor involve constraints on randomization and include completely randomized blocks and Latin squares (and variants: Graeco-Latin squares, etc.). The more complex experiments share many of the complexities of multiple factors. A relatively complete discussion of the analysis (models, data summaries, ANOVA table) of the completely randomized experiment is available.

There are some alternatives to conventional one-way analysis of variance, e.g. : Welch's heteroscedastic F test, Welch's heteroscedastic F test with trimmed means and Winsorized variances, Brown-Forsythe test, Alexander-Govern test, James second order test and Kruskal-Wallis test, available in onewaytests R It is useful to represent each data point in the following form, called a statistical model: where i = 1, 2, 3, …, R j = 1, 2, 3, …, C μ = overall average (mean) τj = differential effect (response) associated with the j level of X; this assumes that overall the values of τj add to zero (that is, ) εij = noise or error associated with the particular ij data value That is, we envision an additive model that says every data point can be represented by summing three quantities: the true mean, averaged over all factor levels being investigated, plus an incremental component associated with the particular column (factor level), plus a final component associated with everything else affecting that specific data value. For multiple factors ANOVA generalizes to the study of the effects of multiple factors. When the experiment includes observations at all combinations of levels of each factor, it is termed factorial. Factorial experiments are more efficient than a series of single factor experiments and the efficiency grows as the number of factors increases. Consequently, factorial designs are heavily used. The use of ANOVA to study the effects of multiple factors has a complication. In a 3-way ANOVA with factors x, y and z, the ANOVA model includes terms for the main effects (x, y, z) and terms for interactions (xy, xz, yz, xyz). All terms require hypothesis tests. The proliferation of interaction terms increases the risk that some hypothesis test will produce a false positive by chance. Fortunately, experience says that high order interactions are rare. The ability to detect interactions is a major advantage of multiple factor ANOVA. Testing one factor at a time hides interactions, but produces apparently inconsistent experimental results. Caution is advised when encountering interactions; Test interaction terms first and expand the analysis beyond ANOVA if interactions are found. Texts vary in their recommendations regarding the continuation of the ANOVA procedure after encountering an interaction. Interactions complicate the interpretation of experimental data. Neither the calculations of significance nor the estimated treatment effects can be taken at face value. "A significant interaction will often mask the significance of main effects." Graphical methods are recommended to enhance understanding. Regression is often useful. A lengthy discussion of interactions is available in Cox (1958). Some interactions can be removed (by transformations) while others cannot. A variety of techniques are used with multiple factor ANOVA to reduce expense. One technique used in factorial designs is to minimize replication (possibly no replication with support of analytical trickery) and to combine groups when effects are found to be statistically (or practically) insignificant. An experiment with many insignificant factors may collapse into one with a few factors supported by many replications.

There are some alternatives to conventional one-way analysis of variance, e.g. : Welch's heteroscedastic F test, Welch's heteroscedastic F test with trimmed means and Winsorized variances, Brown-Forsythe test, Alexander-Govern test, James second order test and Kruskal-Wallis test, available in onewaytests R It is useful to represent each data point in the following form, called a statistical model: where i = 1, 2, 3, …, R j = 1, 2, 3, …, C μ = overall average (mean) τj = differential effect (response) associated with the j level of X; this assumes that overall the values of τj add to zero (that is, ) εij = noise or error associated with the particular ij data value That is, we envision an additive model that says every data point can be represented by summing three quantities: the true mean, averaged over all factor levels being investigated, plus an incremental component associated with the particular column (factor level), plus a final component associated with everything else affecting that specific data value. For multiple factors ANOVA generalizes to the study of the effects of multiple factors. When the experiment includes observations at all combinations of levels of each factor, it is termed factorial. Factorial experiments are more efficient than a series of single factor experiments and the efficiency grows as the number of factors increases. Consequently, factorial designs are heavily used. The use of ANOVA to study the effects of multiple factors has a complication. In a 3-way ANOVA with factors x, y and z, the ANOVA model includes terms for the main effects (x, y, z) and terms for interactions (xy, xz, yz, xyz). All terms require hypothesis tests. The proliferation of interaction terms increases the risk that some hypothesis test will produce a false positive by chance. Fortunately, experience says that high order interactions are rare. The ability to detect interactions is a major advantage of multiple factor ANOVA. Testing one factor at a time hides interactions, but produces apparently inconsistent experimental results. Caution is advised when encountering interactions; Test interaction terms first and expand the analysis beyond ANOVA if interactions are found. Texts vary in their recommendations regarding the continuation of the ANOVA procedure after encountering an interaction. Interactions complicate the interpretation of experimental data. Neither the calculations of significance nor the estimated treatment effects can be taken at face value. "A significant interaction will often mask the significance of main effects." Graphical methods are recommended to enhance understanding. Regression is often useful. A lengthy discussion of interactions is available in Cox (1958). Some interactions can be removed (by transformations) while others cannot. A variety of techniques are used with multiple factor ANOVA to reduce expense. One technique used in factorial designs is to minimize replication (possibly no replication with support of analytical trickery) and to combine groups when effects are found to be statistically (or practically) insignificant. An experiment with many insignificant factors may collapse into one with a few factors supported by many replications.

There are some alternatives to conventional one-way analysis of variance, e.g. : Welch's heteroscedastic F test, Welch's heteroscedastic F test with trimmed means and Winsorized variances, Brown-Forsythe test, Alexander-Govern test, James second order test and Kruskal-Wallis test, available in onewaytests R It is useful to represent each data point in the following form, called a statistical model: where i = 1, 2, 3, …, R j = 1, 2, 3, …, C μ = overall average (mean) τj = differential effect (response) associated with the j level of X; this assumes that overall the values of τj add to zero (that is, ) εij = noise or error associated with the particular ij data value That is, we envision an additive model that says every data point can be represented by summing three quantities: the true mean, averaged over all factor levels being investigated, plus an incremental component associated with the particular column (factor level), plus a final component associated with everything else affecting that specific data value. For multiple factors ANOVA generalizes to the study of the effects of multiple factors. When the experiment includes observations at all combinations of levels of each factor, it is termed factorial. Factorial experiments are more efficient than a series of single factor experiments and the efficiency grows as the number of factors increases. Consequently, factorial designs are heavily used. The use of ANOVA to study the effects of multiple factors has a complication. In a 3-way ANOVA with factors x, y and z, the ANOVA model includes terms for the main effects (x, y, z) and terms for interactions (xy, xz, yz, xyz). All terms require hypothesis tests. The proliferation of interaction terms increases the risk that some hypothesis test will produce a false positive by chance. Fortunately, experience says that high order interactions are rare. The ability to detect interactions is a major advantage of multiple factor ANOVA. Testing one factor at a time hides interactions, but produces apparently inconsistent experimental results. Caution is advised when encountering interactions; Test interaction terms first and expand the analysis beyond ANOVA if interactions are found. Texts vary in their recommendations regarding the continuation of the ANOVA procedure after encountering an interaction. Interactions complicate the interpretation of experimental data. Neither the calculations of significance nor the estimated treatment effects can be taken at face value. "A significant interaction will often mask the significance of main effects." Graphical methods are recommended to enhance understanding. Regression is often useful. A lengthy discussion of interactions is available in Cox (1958). Some interactions can be removed (by transformations) while others cannot. A variety of techniques are used with multiple factor ANOVA to reduce expense. One technique used in factorial designs is to minimize replication (possibly no replication with support of analytical trickery) and to combine groups when effects are found to be statistically (or practically) insignificant. An experiment with many insignificant factors may collapse into one with a few factors supported by many replications.

Associated analysis Some analysis is required in support of the design of the experiment while other analysis is performed after changes in the factors are formally found to produce statistically significant changes in the responses. Because experimentation is iterative, the results of one experiment alter plans for following experiments. Preparatory analysis The number of experimental units In the design of an experiment, the number of experimental units is planned to satisfy the goals of the experiment. Experimentation is often sequential. Early experiments are often designed to provide mean-unbiased estimates of treatment effects and of experimental error. Later experiments are often designed to test a hypothesis that a treatment effect has an important magnitude; in this case, the number of experimental units is chosen so that the experiment is within budget and has adequate power, among other goals. Reporting sample size analysis is generally required in psychology. "Provide information on sample size and the process that led to sample size decisions." The analysis, which is written in the experimental protocol before the experiment is conducted, is examined in grant applications and administrative review boards. Besides the power analysis, there are less formal methods for selecting the number of experimental units. These include graphical methods based on limiting the probability of false negative errors, graphical methods based on an expected variation increase (above the residuals) and methods based on achieving a desired confidence interval. Power analysis Power analysis is often applied in the context of ANOVA in order to assess the probability of successfully rejecting the null hypothesis if we assume a certain ANOVA design, effect size in the population, sample size and significance level. Power analysis can assist in study design by determining what sample size would be required in order to have a reasonable chance of rejecting the null hypothesis when the alternative hypothesis is true. Effect size Several standardized measures of effect have been proposed for ANOVA to summarize the strength of the association between a predictor(s) and the dependent variable or the overall standardized difference of the complete model. Standardized effect-size estimates facilitate comparison of findings across studies and disciplines. However, while standardized effect sizes are commonly used in much of the professional literature, a non-standardized measure of effect size that has immediately "meaningful" units may be preferable for reporting purposes. Model confirmation Sometimes tests are conducted to determine whether the assumptions of ANOVA appear to be violated. Residuals are examined or analyzed to confirm homoscedasticity and gross normality. Residuals should have the appearance of (zero mean normal distribution) noise when plotted as a function of anything including time and modeled data values. Trends hint at interactions among factors or among observations. Follow-up tests A statistically significant effect in ANOVA is often followed by additional tests. This can be done in order to assess which groups are different from which other groups or to test various other focused hypotheses. Follow-up tests are often distinguished in terms of whether they are "planned" (a priori) or "post hoc."

Associated analysis Some analysis is required in support of the design of the experiment while other analysis is performed after changes in the factors are formally found to produce statistically significant changes in the responses. Because experimentation is iterative, the results of one experiment alter plans for following experiments. Preparatory analysis The number of experimental units In the design of an experiment, the number of experimental units is planned to satisfy the goals of the experiment. Experimentation is often sequential. Early experiments are often designed to provide mean-unbiased estimates of treatment effects and of experimental error. Later experiments are often designed to test a hypothesis that a treatment effect has an important magnitude; in this case, the number of experimental units is chosen so that the experiment is within budget and has adequate power, among other goals. Reporting sample size analysis is generally required in psychology. "Provide information on sample size and the process that led to sample size decisions." The analysis, which is written in the experimental protocol before the experiment is conducted, is examined in grant applications and administrative review boards. Besides the power analysis, there are less formal methods for selecting the number of experimental units. These include graphical methods based on limiting the probability of false negative errors, graphical methods based on an expected variation increase (above the residuals) and methods based on achieving a desired confidence interval. Power analysis Power analysis is often applied in the context of ANOVA in order to assess the probability of successfully rejecting the null hypothesis if we assume a certain ANOVA design, effect size in the population, sample size and significance level. Power analysis can assist in study design by determining what sample size would be required in order to have a reasonable chance of rejecting the null hypothesis when the alternative hypothesis is true. Effect size Several standardized measures of effect have been proposed for ANOVA to summarize the strength of the association between a predictor(s) and the dependent variable or the overall standardized difference of the complete model. Standardized effect-size estimates facilitate comparison of findings across studies and disciplines. However, while standardized effect sizes are commonly used in much of the professional literature, a non-standardized measure of effect size that has immediately "meaningful" units may be preferable for reporting purposes. Model confirmation Sometimes tests are conducted to determine whether the assumptions of ANOVA appear to be violated. Residuals are examined or analyzed to confirm homoscedasticity and gross normality. Residuals should have the appearance of (zero mean normal distribution) noise when plotted as a function of anything including time and modeled data values. Trends hint at interactions among factors or among observations. Follow-up tests A statistically significant effect in ANOVA is often followed by additional tests. This can be done in order to assess which groups are different from which other groups or to test various other focused hypotheses. Follow-up tests are often distinguished in terms of whether they are "planned" (a priori) or "post hoc."

Associated analysis Some analysis is required in support of the design of the experiment while other analysis is performed after changes in the factors are formally found to produce statistically significant changes in the responses. Because experimentation is iterative, the results of one experiment alter plans for following experiments. Preparatory analysis The number of experimental units In the design of an experiment, the number of experimental units is planned to satisfy the goals of the experiment. Experimentation is often sequential. Early experiments are often designed to provide mean-unbiased estimates of treatment effects and of experimental error. Later experiments are often designed to test a hypothesis that a treatment effect has an important magnitude; in this case, the number of experimental units is chosen so that the experiment is within budget and has adequate power, among other goals. Reporting sample size analysis is generally required in psychology. "Provide information on sample size and the process that led to sample size decisions." The analysis, which is written in the experimental protocol before the experiment is conducted, is examined in grant applications and administrative review boards. Besides the power analysis, there are less formal methods for selecting the number of experimental units. These include graphical methods based on limiting the probability of false negative errors, graphical methods based on an expected variation increase (above the residuals) and methods based on achieving a desired confidence interval. Power analysis Power analysis is often applied in the context of ANOVA in order to assess the probability of successfully rejecting the null hypothesis if we assume a certain ANOVA design, effect size in the population, sample size and significance level. Power analysis can assist in study design by determining what sample size would be required in order to have a reasonable chance of rejecting the null hypothesis when the alternative hypothesis is true. Effect size Several standardized measures of effect have been proposed for ANOVA to summarize the strength of the association between a predictor(s) and the dependent variable or the overall standardized difference of the complete model. Standardized effect-size estimates facilitate comparison of findings across studies and disciplines. However, while standardized effect sizes are commonly used in much of the professional literature, a non-standardized measure of effect size that has immediately "meaningful" units may be preferable for reporting purposes. Model confirmation Sometimes tests are conducted to determine whether the assumptions of ANOVA appear to be violated. Residuals are examined or analyzed to confirm homoscedasticity and gross normality. Residuals should have the appearance of (zero mean normal distribution) noise when plotted as a function of anything including time and modeled data values. Trends hint at interactions among factors or among observations. Follow-up tests A statistically significant effect in ANOVA is often followed by additional tests. This can be done in order to assess which groups are different from which other groups or to test various other focused hypotheses. Follow-up tests are often distinguished in terms of whether they are "planned" (a priori) or "post hoc."

Planned tests are determined before looking at the data, and post hoc tests are conceived only after looking at the data (though the term "post hoc" is inconsistently used). The follow-up tests may be "simple" pairwise comparisons of individual group means or may be "compound" comparisons (e.g., comparing the mean pooling across groups A, B and C to the mean of group D). Comparisons can also look at tests of trend, such as linear and quadratic relationships, when the independent variable involves ordered levels. Often the follow-up tests incorporate a method of adjusting for the multiple comparisons problem. Study designs There are several types of ANOVA. Many statisticians base ANOVA on the design of the experiment, especially on the protocol that specifies the random assignment of treatments to subjects; the protocol's description of the assignment mechanism should include a specification of the structure of the treatments and of any blocking. It is also common to apply ANOVA to observational data using an appropriate statistical model. Some popular designs use the following types of ANOVA: One-way ANOVA is used to test for differences among two or more independent groups (means), e.g. different levels of urea application in a crop, or different levels of antibiotic action on several different bacterial species, or different levels of effect of some medicine on groups of patients. However, should these groups not be independent, and there is an order in the groups (such as mild, moderate and severe disease), or in the dose of a drug (such as 5 mg/mL, 10 mg/mL, 20 mg/mL) given to the same group of patients, then a linear trend estimation should be used. Typically, however, the one-way ANOVA is used to test for differences among at least three groups, since the two-group case can be covered by a t-test. When there are only two means to compare, the t-test and the ANOVA F-test are equivalent; the relation between ANOVA and t is given by . Factorial ANOVA is used when there is more than one factor. Repeated measures ANOVA is used when the same subjects are used for each factor (e.g., in a longitudinal study). Multivariate analysis of variance (MANOVA) is used when there is more than one response variable. Cautions Balanced experiments (those with an equal sample size for each treatment) are relatively easy to interpret; unbalanced experiments offer more complexity. For single-factor (one-way) ANOVA, the adjustment for unbalanced data is easy, but the unbalanced analysis lacks both robustness and power. For more complex designs the lack of balance leads to further complications. "The orthogonality property of main effects and interactions present in balanced data does not carry over to the unbalanced case. This means that the usual analysis of variance techniques do not apply. Consequently, the analysis of unbalanced factorials is much more difficult than that for balanced designs."

Planned tests are determined before looking at the data, and post hoc tests are conceived only after looking at the data (though the term "post hoc" is inconsistently used). The follow-up tests may be "simple" pairwise comparisons of individual group means or may be "compound" comparisons (e.g., comparing the mean pooling across groups A, B and C to the mean of group D). Comparisons can also look at tests of trend, such as linear and quadratic relationships, when the independent variable involves ordered levels. Often the follow-up tests incorporate a method of adjusting for the multiple comparisons problem. Study designs There are several types of ANOVA. Many statisticians base ANOVA on the design of the experiment, especially on the protocol that specifies the random assignment of treatments to subjects; the protocol's description of the assignment mechanism should include a specification of the structure of the treatments and of any blocking. It is also common to apply ANOVA to observational data using an appropriate statistical model. Some popular designs use the following types of ANOVA: One-way ANOVA is used to test for differences among two or more independent groups (means), e.g. different levels of urea application in a crop, or different levels of antibiotic action on several different bacterial species, or different levels of effect of some medicine on groups of patients. However, should these groups not be independent, and there is an order in the groups (such as mild, moderate and severe disease), or in the dose of a drug (such as 5 mg/mL, 10 mg/mL, 20 mg/mL) given to the same group of patients, then a linear trend estimation should be used. Typically, however, the one-way ANOVA is used to test for differences among at least three groups, since the two-group case can be covered by a t-test. When there are only two means to compare, the t-test and the ANOVA F-test are equivalent; the relation between ANOVA and t is given by . Factorial ANOVA is used when there is more than one factor. Repeated measures ANOVA is used when the same subjects are used for each factor (e.g., in a longitudinal study). Multivariate analysis of variance (MANOVA) is used when there is more than one response variable. Cautions Balanced experiments (those with an equal sample size for each treatment) are relatively easy to interpret; unbalanced experiments offer more complexity. For single-factor (one-way) ANOVA, the adjustment for unbalanced data is easy, but the unbalanced analysis lacks both robustness and power. For more complex designs the lack of balance leads to further complications. "The orthogonality property of main effects and interactions present in balanced data does not carry over to the unbalanced case. This means that the usual analysis of variance techniques do not apply. Consequently, the analysis of unbalanced factorials is much more difficult than that for balanced designs."

Planned tests are determined before looking at the data, and post hoc tests are conceived only after looking at the data (though the term "post hoc" is inconsistently used). The follow-up tests may be "simple" pairwise comparisons of individual group means or may be "compound" comparisons (e.g., comparing the mean pooling across groups A, B and C to the mean of group D). Comparisons can also look at tests of trend, such as linear and quadratic relationships, when the independent variable involves ordered levels. Often the follow-up tests incorporate a method of adjusting for the multiple comparisons problem. Study designs There are several types of ANOVA. Many statisticians base ANOVA on the design of the experiment, especially on the protocol that specifies the random assignment of treatments to subjects; the protocol's description of the assignment mechanism should include a specification of the structure of the treatments and of any blocking. It is also common to apply ANOVA to observational data using an appropriate statistical model. Some popular designs use the following types of ANOVA: One-way ANOVA is used to test for differences among two or more independent groups (means), e.g. different levels of urea application in a crop, or different levels of antibiotic action on several different bacterial species, or different levels of effect of some medicine on groups of patients. However, should these groups not be independent, and there is an order in the groups (such as mild, moderate and severe disease), or in the dose of a drug (such as 5 mg/mL, 10 mg/mL, 20 mg/mL) given to the same group of patients, then a linear trend estimation should be used. Typically, however, the one-way ANOVA is used to test for differences among at least three groups, since the two-group case can be covered by a t-test. When there are only two means to compare, the t-test and the ANOVA F-test are equivalent; the relation between ANOVA and t is given by . Factorial ANOVA is used when there is more than one factor. Repeated measures ANOVA is used when the same subjects are used for each factor (e.g., in a longitudinal study). Multivariate analysis of variance (MANOVA) is used when there is more than one response variable. Cautions Balanced experiments (those with an equal sample size for each treatment) are relatively easy to interpret; unbalanced experiments offer more complexity. For single-factor (one-way) ANOVA, the adjustment for unbalanced data is easy, but the unbalanced analysis lacks both robustness and power. For more complex designs the lack of balance leads to further complications. "The orthogonality property of main effects and interactions present in balanced data does not carry over to the unbalanced case. This means that the usual analysis of variance techniques do not apply. Consequently, the analysis of unbalanced factorials is much more difficult than that for balanced designs."

In the general case, "The analysis of variance can also be applied to unbalanced data, but then the sums of squares, mean squares, and F-ratios will depend on the order in which the sources of variation are considered." ANOVA is (in part) a test of statistical significance. The American Psychological Association (and many other organisations) holds the view that simply reporting statistical significance is insufficient and that reporting confidence bounds is preferred. Generalizations ANOVA is considered to be a special case of linear regression which in turn is a special case of the general linear model. All consider the observations to be the sum of a model (fit) and a residual (error) to be minimized. The Kruskal–Wallis test and the Friedman test are nonparametric tests, which do not rely on an assumption of normality. Connection to linear regression Below we make clear the connection between multi-way ANOVA and linear regression. Linearly re-order the data so that -th observation is associated with a response and factors where denotes the different factors and is the total number of factors. In one-way ANOVA and in two-way ANOVA . Furthermore, we assume the -th factor has levels, namely . Now, we can one-hot encode the factors into the dimensional vector . The one-hot encoding function is defined such that the -th entry of is The vector is the concatenation of all of the above vectors for all . Thus, . In order to obtain a fully general -way interaction ANOVA we must also concatenate every additional interaction term in the vector and then add an intercept term. Let that vector be . With this notation in place, we now have the exact connection with linear regression. We simply regress response against the vector . However, there is a concern about identifiability. In order to overcome such issues we assume that the sum of the parameters within each set of interactions is equal to zero. From here, one can use F-statistics or other methods to determine the relevance of the individual factors. Example We can consider the 2-way interaction example where we assume that the first factor has 2 levels and the second factor has 3 levels. Define if and if , i.e. is the one-hot encoding of the first factor and is the one-hot encoding of the second factor. With that, where the last term is an intercept term. For a more concrete example suppose that Then, See also ANOVA on ranks ANOVA-simultaneous component analysis Analysis of covariance (ANCOVA) Analysis of molecular variance (AMOVA) Analysis of rhythmic variance (ANORVA) Explained variation Linear trend estimation Mixed-design analysis of variance Multivariate analysis of covariance (MANCOVA) Permutational analysis of variance Variance decomposition Expected mean squares Footnotes Notes References Pre-publication chapters are available on-line. Cohen, Jacob (1988). Statistical power analysis for the behavior sciences (2nd ed.). Routledge Cox, David R. (1958). Planning of experiments. Reprinted as Freedman, David A.(2005). Statistical Models: Theory and Practice, Cambridge University Press. Lehmann, E.L. (1959) Testing Statistical Hypotheses. John Wiley & Sons.

In the general case, "The analysis of variance can also be applied to unbalanced data, but then the sums of squares, mean squares, and F-ratios will depend on the order in which the sources of variation are considered." ANOVA is (in part) a test of statistical significance. The American Psychological Association (and many other organisations) holds the view that simply reporting statistical significance is insufficient and that reporting confidence bounds is preferred. Generalizations ANOVA is considered to be a special case of linear regression which in turn is a special case of the general linear model. All consider the observations to be the sum of a model (fit) and a residual (error) to be minimized. The Kruskal–Wallis test and the Friedman test are nonparametric tests, which do not rely on an assumption of normality. Connection to linear regression Below we make clear the connection between multi-way ANOVA and linear regression. Linearly re-order the data so that -th observation is associated with a response and factors where denotes the different factors and is the total number of factors. In one-way ANOVA and in two-way ANOVA . Furthermore, we assume the -th factor has levels, namely . Now, we can one-hot encode the factors into the dimensional vector . The one-hot encoding function is defined such that the -th entry of is The vector is the concatenation of all of the above vectors for all . Thus, . In order to obtain a fully general -way interaction ANOVA we must also concatenate every additional interaction term in the vector and then add an intercept term. Let that vector be . With this notation in place, we now have the exact connection with linear regression. We simply regress response against the vector . However, there is a concern about identifiability. In order to overcome such issues we assume that the sum of the parameters within each set of interactions is equal to zero. From here, one can use F-statistics or other methods to determine the relevance of the individual factors. Example We can consider the 2-way interaction example where we assume that the first factor has 2 levels and the second factor has 3 levels. Define if and if , i.e. is the one-hot encoding of the first factor and is the one-hot encoding of the second factor. With that, where the last term is an intercept term. For a more concrete example suppose that Then, See also ANOVA on ranks ANOVA-simultaneous component analysis Analysis of covariance (ANCOVA) Analysis of molecular variance (AMOVA) Analysis of rhythmic variance (ANORVA) Explained variation Linear trend estimation Mixed-design analysis of variance Multivariate analysis of covariance (MANCOVA) Permutational analysis of variance Variance decomposition Expected mean squares Footnotes Notes References Pre-publication chapters are available on-line. Cohen, Jacob (1988). Statistical power analysis for the behavior sciences (2nd ed.). Routledge Cox, David R. (1958). Planning of experiments. Reprinted as Freedman, David A.(2005). Statistical Models: Theory and Practice, Cambridge University Press. Lehmann, E.L. (1959) Testing Statistical Hypotheses. John Wiley & Sons.

In the general case, "The analysis of variance can also be applied to unbalanced data, but then the sums of squares, mean squares, and F-ratios will depend on the order in which the sources of variation are considered." ANOVA is (in part) a test of statistical significance. The American Psychological Association (and many other organisations) holds the view that simply reporting statistical significance is insufficient and that reporting confidence bounds is preferred. Generalizations ANOVA is considered to be a special case of linear regression which in turn is a special case of the general linear model. All consider the observations to be the sum of a model (fit) and a residual (error) to be minimized. The Kruskal–Wallis test and the Friedman test are nonparametric tests, which do not rely on an assumption of normality. Connection to linear regression Below we make clear the connection between multi-way ANOVA and linear regression. Linearly re-order the data so that -th observation is associated with a response and factors where denotes the different factors and is the total number of factors. In one-way ANOVA and in two-way ANOVA . Furthermore, we assume the -th factor has levels, namely . Now, we can one-hot encode the factors into the dimensional vector . The one-hot encoding function is defined such that the -th entry of is The vector is the concatenation of all of the above vectors for all . Thus, . In order to obtain a fully general -way interaction ANOVA we must also concatenate every additional interaction term in the vector and then add an intercept term. Let that vector be . With this notation in place, we now have the exact connection with linear regression. We simply regress response against the vector . However, there is a concern about identifiability. In order to overcome such issues we assume that the sum of the parameters within each set of interactions is equal to zero. From here, one can use F-statistics or other methods to determine the relevance of the individual factors. Example We can consider the 2-way interaction example where we assume that the first factor has 2 levels and the second factor has 3 levels. Define if and if , i.e. is the one-hot encoding of the first factor and is the one-hot encoding of the second factor. With that, where the last term is an intercept term. For a more concrete example suppose that Then, See also ANOVA on ranks ANOVA-simultaneous component analysis Analysis of covariance (ANCOVA) Analysis of molecular variance (AMOVA) Analysis of rhythmic variance (ANORVA) Explained variation Linear trend estimation Mixed-design analysis of variance Multivariate analysis of covariance (MANCOVA) Permutational analysis of variance Variance decomposition Expected mean squares Footnotes Notes References Pre-publication chapters are available on-line. Cohen, Jacob (1988). Statistical power analysis for the behavior sciences (2nd ed.). Routledge Cox, David R. (1958). Planning of experiments. Reprinted as Freedman, David A.(2005). Statistical Models: Theory and Practice, Cambridge University Press. Lehmann, E.L. (1959) Testing Statistical Hypotheses. John Wiley & Sons.

Moore, David S. & McCabe, George P. (2003). Introduction to the Practice of Statistics (4e). W H Freeman & Co. Rosenbaum, Paul R. (2002). Observational Studies (2nd ed.). New York: Springer-Verlag. Further reading Cox, David R. & Reid, Nancy M. (2000). The theory of design of experiments. (Chapman & Hall/CRC). Freedman, David A.; Pisani, Robert; Purves, Roger (2007) Statistics, 4th edition. W.W. Norton & Company Tabachnick, Barbara G. & Fidell, Linda S. (2007). Using Multivariate Statistics (5th ed.). Boston: Pearson International Edition. External links SOCR ANOVA Activity Examples of all ANOVA and ANCOVA models with up to three treatment factors, including randomized block, split plot, repeated measures, and Latin squares, and their analysis in R (University of Southampton) NIST/SEMATECH e-Handbook of Statistical Methods, section 7.4.3: "Are the means equal?" Analysis of variance: Introduction Design of experiments Statistical tests Parametric statistics