Alfred Russel Wallace, OM, FRS (January 8, 1823 – November 7, 1913) was a British naturalist, explorer, geographer, anthropologist and biologist. He independently proposed a theory of natural selection which prompted Charles Darwin to publish his own more developed and researched theory sooner than he had intended. Wallace is sometimes called the "father of biogeography".
Wallace was born at Usk, Monmouthshire in Wales. He was the eighth of nine children of Thomas Vere Wallace and Mary Anne Greenell. He attended grammar school in Hertford until financial ruin forced his family to withdraw him in 1836. After a stint as an apprentice builder in London, he began to work as a surveyor with his older brother William. Between 1840 and 1843, he spent his time surveying in the west of England and Wales. In 1844, he was hired as a master at the Collegiate School in Leicester. After the death of his brother William in 1845, Wallace left his teaching position to assume control of his brother's firm.
Wallace, inspired by the chronicles of earlier traveling naturalists including Alexander von Humboldt, Charles Darwin, and William Henry Edwards, decided that he wanted to travel abroad as a naturalist as well.
In 1848, Wallace, together with another naturalist, Henry Walter Bates (whom he had met in Leicester), left for Brazil to collect specimens in the Amazon Rainforest, with the intention of selling them to collectors back in England, and the hope of gathering facts in order to solve the riddle of the origin of species. Unfortunately, a large part of his collection was destroyed when his ship caught fire and sank while returning to Britain in 1852.
From 1854 to 1862, he travelled through the Malay Archipelago or East Indies (now Malaysia and Indonesia), to collect specimens for sale and to study nature. His observations of the marked zoological differences across a narrow zone in the archipelago led to his hypothesis of the zoogeographical boundary now known as the Wallace line. One of his better known species descriptions during this trip is the gliding tree frog Rhacophorus nigropalmatus, Wallace's flying frogs. His studies there were eventually published in 1869 as The Malay Archipelago.
Unlike Darwin, Wallace started his career as a traveling naturalist already believing in the transmutation of species. He had come to this belief because of a natural and life long inclination in favor of radical ideas in politics, religion and science,  and because he had been profoundly influenced by Robert Chambers work Vestiges of the Natural History of Creation, a work of popular science published in 1844 that advocated an evolutionary origin for the solar system, the earth, and living things. Wallace hoped to find evidence that supported the ideas found in that extremely controversial book.  Wallace deliberately planned some of his field work to try and test the hypothesis that under an evolutionary scenario closely related species should inhabit neighboring territories.  During his work in the Amazon basin he came to realize that geographical barriers, such as the Amazon and its major tributaries, often separated the ranges of closely related species and he included these observations in the paper On the Monkeys of the Amazon published in 1853.  Near the end of the paper he asks the question Are very closely allied species ever separated by a wide interval of country?
In 1855, Wallace published a paper, On the Law Which has Regulated the Introduction of Species based on his pioneering work at Mount Santubong, Sarawak, in which he gathers and enumerates general observations regarding the geographic and geologic distribution of species (biogeography), and concludes that "Every species has come into existence coincident both in space and time with a closely allied species." The paper, also known as the Sarawak Law (named after the state of Sarawak, located on the island of Borneo) was a foreshadowing of the momentous paper he would write three years later.
Wallace had once briefly met Darwin, and was one of Darwin's numerous correspondents from around the world, whose observations Darwin used to support his theories. Wallace knew that Darwin was interested in the question of how species originate, and trusted his opinion on the matter. Thus, he sent him his essay, On the Tendency of Varieties to Depart Indefinitely From the Original Type, and asked him to review it. On 18 June 1858 Darwin received the manuscript from Wallace. While Wallace's essay did not employ Darwin's term natural selection, it did outline the mechanics of an evolutionary divergence of species from similar ones due to environmental pressures. In this sense, it was essentially the same as the theory that Darwin had worked on for twenty years, but had yet to publish. Darwin wrote in a letter to Charles Lyell: "he could not have made a better short abstract! Even his terms now stand as heads of my chapters!" Although Wallace had not requested that his essay be published, Charles Lyell and Joseph Hooker decided to present the essay, together with excerpts from a paper that Darwin had written in 1844, and kept confidential, to the Linnean Society of London on 1 July 1858, highlighting Darwin's priority.
Wallace accepted the arrangement after the fact, grateful that he had been included at all. Darwin's social and scientific status was at that time far greater than Wallace's, and it was unlikely that Wallace's views on evolution would have been taken as seriously. However he pointed out, in a largely overlooked passage of the 1858 paper that "The action of this principle is exactly like that of the centrifugal governor". The cybernetician and anthropologist Gregory Bateson observed though seeing it only as an illustration Wallace had "probably said the most powerful thing that’d been said in the 19th. Century". Though relegated to the position of co-discoverer, and never the social equal of Darwin or the other elite British natural scientists, Wallace was granted far greater access to tightly-regulated British scientific circles after the advocacy on his part by Darwin. When he returned to England, Wallace met Darwin and the two remained friendly afterwards.
After the publication of Darwin’s Origin of Species Wallace became one of its staunchest defenders. In one incident that particularly pleased Darwin in 1863, Wallace published the short paper Remarks on the Rev. S. Haughton's Paper on the Bee's Cell, And on the Origin of Species in order to utterly demolish a paper by a professor of geology at the University of Dublin that had sharply criticized Darwin’s comments in the Origin on how hexagonal honey bee cells could have evolved through natural selection. 
In 1867 Darwin wrote to Wallace about a problem he was having understanding how some caterpillars could have evolved very conspicuous color schemes. Darwin had come to believe that sexual selection, an idea Wallace didn’t accept, explained many conspicuous animal color schemes, but he realized there was no way it could apply to caterpillars. Wallace responded that he and Henry Bates had observed that many of the most spectacular butterflies had a peculiar odor and taste, and that he had been told by John Jenner Weir that birds would not eat a certain kind of common white moth because they found it unpalatable. Now, as the white moth is as conspicuous at dusk as a coloured caterpillar in the daylight, Wallace wrote back to Darwin that it seemed likely that the conspicuous color scheme served as a warning to predators and thus could have evolved through natural selection. Darwin was impressed by the idea. At a subsequent meeting of the Entomological Society Wallace asked for any evidence anyone might have on the topic. In 1869 Weir published data from experiments and observations involving brightly colored caterpillars that supported Wallace’s idea. Warning coloration would prove to be one of a number of contributions Wallace would make in the area of the evolution of animal coloration.  It was also part of a life long disagreement Wallace would have with Darwin over the importance of sexual selection. In his 1878 book Tropical Nature and Other Essays he wrote extensively on the coloration of animals and plants and proposed alternative explanations for a number of cases Darwin had attributed to sexual selection. 
In 1889 Wallace wrote the book Darwinism which explained and defended natural selection. In it he proposed the hypothesis that when two populations of a species had diverged beyond a certain point, hybrid offspring would be less fit than either parent form, and at that point natural selection will tend to eliminate the hybrids, contributing to the reproductive isolation of the populations. This idea came to be known as the Wallace effect.
In a letter to a relative in 1861, Wallace wrote: "I think I have fairly heard and fairly weighed the evidence on both sides, and I remain an utter disbeliever in almost all that you consider the most sacred truths... I can see much to admire in all religions... But whether there be a God and whatever be His nature; whether we have an immortal soul or not, or whatever may be our state after death, I can have no fear of having to suffer for the study of nature and the search for truth...."
In 1864, before Darwin had publicly addressed the subject—though others had—Wallace published a paper, The Origin of Human Races and the Antiquity of Man Deduced from the Theory of 'Natural Selection', applying the theory to mankind. Wallace subsequently became a spiritualist, and later maintained that natural selection cannot account for mathematical, artistic, or musical genius, as well as metaphysical musings, and wit and humor; and that something in "the unseen universe of Spirit" had interceded at least three times in history: 1. The creation of life from inorganic matter. 2. The introduction of consciousness in the higher animals. 3. The generation of the above-mentioned faculties in mankind. He also believed that the raison d'Ítre of the universe was the development of the human spirit. (See Wallace (1889)). These views greatly disturbed Darwin in his lifetime, who argued that spiritual appeals were not necessary and that sexual selection could easily explain such apparently non-adaptive phenomena. Wallace was also an enthusiast of phrenology , and early in his career he experimenteted with hypnosis then known as mesmerism. He used some of his students in Leicester as subjects. 
In many accounts of the history of evolution, Wallace is relegated to a role of simply being the "stimulus" to Darwin's own theory. In reality, Wallace developed his own distinct evolutionary views which diverged from Darwin's, and was considered by many (especially Darwin) to be a chief thinker on evolution in his day whose ideas could not be ignored. He is among the most cited naturalists in Darwin's Descent of Man, often in strong disagreement.
Wallace's very public advocacy of spiritualism and his repeated defense of spiritualist mediums against allegations of fraud in the 1870’s did do damage to his scientific reputation. It strained his relationships with previously friendly scientists such as Henry Bates, Thomas Huxley, and even Darwin who felt he was overly credulous. Others such as the physiologist William Benjamin Carpenter (formerly a friend of Wallace), and zoologist Edwin Ray Lankester became openly and publicly hostile to Wallace over the issue. Wallace and other scientists, notably William Crookes, who defended spiritualism, were subject to much criticism from the press, with the Lancet, the leading English medical journal of the time, being particularly harsh. The controversy would affect the public perception of Wallace’s work for the rest of his career.  When Darwin first tried to rally support among naturalists for getting Wallace awarded a Civil pension in 1879, Joseph Hooker responded:
Hooker would eventually relent and agree to support the pension request. 
In 1872, at the urging of many of his friends including Darwin, Philip Sclater, and Alfred Newton, Wallace began research for a general review of the geographic distribution of animals, but did not make much progress in part because classification systems for many types of animals were in flux at the time.  He was able to resume the work in earnest in 1874 thanks to the publication of a number of new works on classification.  He was able to extend the system developed by Sclater, which divided the earth into 6 separate geographic regions for describing the geographical distribution of birds, to cover mammals, reptiles and insects as well. The resulting system is the basis for the ecozones still in use today. He discussed all of the factors then known to influence the current and past geographic distribution of animals within each geographical region, including the effects of the appearance and disappearance of land bridges (such as the one currently connecting North America and South America), and the effects of periods of increased glaciation. He provided maps that displayed factors, such as elevation of mountains, depths of oceans, and the character of regional vegetation, that effected the distribution of animals. He also summarized all the known families and genera of the higher animals and listed their known geographic distributions. He organized the text so that it would be easy for a traveler to use to learn what animals could be found in a particular location. The resulting 2 volume work, The Geographical Distribution of Animals, was published in 1876 and would serve as the definitive text on biogeography for the next 80 years. 
In 1880 Wallace published the book Island Life as a sequel to The Geographical Distribution of Animals. It surveyed the distribution of both animal and plant species on islands. Wallace classified islands into 3 different types. Oceanic islands, such as the Galapagos and Hawaiian Islands (then known as the Sandwich Islands) formed in mid ocean and had never been part of any large continent. Such islands were characterized by a complete lack of terrestrial mammals and amphibians, and their inhabitants (with the notable exceptions of migratory birds and species introduced by human activity) were the typically the result of accidental colonization and subsequent evolution. He divided continental islands into to 2 separate classes depending on whether they had recently been part of a continent (like Britain) or much less recently (like Madagascar) and discussed how that difference affected the flora and fauna. He talked about how isolation affected evolution and how that could result in the preservation of classes of animals, such as the Lemurs of Madagascar that were remnants of once widespread continental faunas. He extensively discussed how changes climate, particularly periods of glaciation, may have affected the distribution of flora and fauna on some islands. Island Life was considered a very important work at the time of its publication, and was discussed extensively in scientific circles both in published reviews and in private correspondence. 
Wallace’s interest in biogeography made him acutely aware of the effects of human activities on the environment. In Tropical Nature and Other Essays, which he published in 1878, he warned about the dangers of deforestation and soil erosion especially in tropical climates prone to heavy rain fall. Noting the complex interactions between vegetation and climate, he warned that the extensive clearing of rain forest for coffee cultivation in Ceylon and India would adversely impact the climate in those counties and lead to their eventual impoverishment due to soil erosion.  In Island Life Wallace again talked about deforestation and also the impact of invasive species. He wrote the following about the impact of European colonization on the island of St. Helena:
During his time as an apprentice builder in London, starting in 1836, he was exposed, mainly through lectures and books at the London Mechanics' Institute, to radical reformist political ideas that had a profound and lasting influence on his thinking. He was particularly influenced by the ideas of Robert Owen and Thomas Paine.  His deep sympathy for what he considered to be an oppressed working class and his discomfort with class conscious English society would always separate him from a British scientific establishment that in the 19th century was dominated by members of the upper class.  In 1889 Wallace would read Looking Backward by Edward Bellamy and thereafter he would refer to himself as a socialist. 
These ideas would lead him to oppose both Social Darwinism and Eugenics, ideas supported by other prominent 19th century evolutionary thinkers, on the grounds that contemporary society was too corrupt and unjust to allow any reasonable determination of who was fit or unfit. 
One of the political causes to which Wallace devoted a significant amount of time to was land reform. He believed that rural land should be owned by the state and leased to people who would make the use of it that benefited the most people, thus breaking the often abused power of wealthy land owners in English society. In 1881 Wallace was elected as the first president of the Land Nationalization Society. Later that year he wrote a book Land Nationalization on the topic.  Another topic on which he wrote and spoke at length was the negative affects of international trade on the lives of working class people. 
In 1884 Wallace was drawn into the debate over mandatory smallpox vaccination. Wallace was originally saw the issue as a matter of personal liberty, but after studying some of the statistics provided by anti-vaccination activists he began to question the efficacy of vaccination. At the time the germ theory of disease was very new and far from universally accepted, and no one knew enough about the human immune system to understand why vaccination worked. When Wallace did some research he discovered some cases where questionable statistics had been used by supporters of vaccination. Always suspicious of authority, Wallace became convinced that reductions in the incidence of smallpox that had been attributed to vaccination were in fact due to better hygiene and sanitation, and that physicians had a vested interest in promoting vaccination. In 1889 Wallace gave evidence before a royal commission investigating the controversy. When the commission examined the material he submitted to support his testimony they found a number of errors including some questionable statistics. The Lancet pointed out that Wallace and the other anti-vaccination activists were being highly selective in their choice of statistics to present, ignoring large quantities of data inconsistent with their position. The commission found that smallpox vaccination was effective and should remain compulsory, though they did recommend some changes in procedures to improve safety and that the penalties for people who refused to comply be made less severe. Wallace would write a pamphlet attacking the commission’s findings, which was in turn attacked by the Lancet, which pointed out that it contained many of the same errors as his evidence given to the commission.
In 1907 Wallace wrote the short book Is Mars Habitable? to criticize the claims made by Percival Lowell that there were Martian canals built by intelligent beings. Among other things Wallace pointed out that spectroscopic analysis had shown no signs of water vapor in the Martian atmosphere.
In 1866 Wallace married Annie Mitten. Wallace had been introduced to Mitten by Richard Spruce a botanist and explorer who had become a close friend of Wallace in Brazil and who was also a good friend of Annie Mitten's father, William Mitten, an expert in mosses. They would have 3 children, Herbert (1867-1874), who died in childhood, Violet(1869-1945), and William(1871-1951).
Wallace had previously been engaged to a woman that he would only identify as Miss L. in his autobiography. She had broken off the engagement, to Wallace's considerable dismay.
Among the many awards presented to Wallace were the Order of Merit (1908), the Royal Society's Copley Medal (1908), the Royal Geographical Society's Founder's Medal (1892) and the Linnean Society's Gold Medal (1892).
Elected head of the anthropology section of the British Association in 1866.
Elected president of the Entomological Society of London in 1870.
Elected head of the biology section of the British Association in 1876.
Asked to chair the International Congress of Spiritualists (which was meeting in London) in 1898.
In 1881, in large part due to lobbying by Darwin and Huxley, the British government awarded Wallace a civil pension of £200 a year in recognition of his many contributions to science.
In 1928, a house at Richard Hale School was named for Wallace. Wallace attended Richard Hale as a student from 1828-1836
He died in Broadstone and was buried near there but two years later in November 1, 1915, a medallion with his name on it was placed in Westminster Abbey.
He is also honored by having craters on Mars and the Moon named after him. Having sometimes been referred to as "Darwin's Moon" it is amusing that Wallace has a crater on the Moon named after himself.
A center for biodiversity research in Sarawak named in his memory was proposed in 2005 .