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Monday, August 4, 2014

Alfred Russel Wallace and Evolution

Alfred Russel Wallace

Condensed from Wikipedia, the free encyclopedia
Alfred Russel Wallace
Born(1823-01-08)8 January 1823
Usk, Monmouthshire, Wales
Died7 November 1913(1913-11-07) (aged 90)
Broadstone, Dorset, England
FieldsExploration, evolutionary biology, zoology, biogeography, and social reform
Known forCo-discovery of natural selection
Pioneering work on biogeography
Wallace Line
Wallace effect
Notable awardsRoyal Medal (1868)
Darwin Medal (1890)
Copley Medal (1908)
Gold Medal of the Société de Géographie (1870)
Founder's Medal (1892)
Linnean Medal) (1892)
Darwin-Wallace Medal (Gold, 1908)
Order of Merit (1908)
Author abbrev. (botany)Wallace

Alfred Russel Wallace OM FRS (8 January 1823 – 7 November 1913) was a British naturalist, explorer, geographer, anthropologist, and biologist. He is best known for independently conceiving the theory of evolution through natural selection; his paper on the subject was jointly published with some of Charles Darwin's writings in 1858.[1] This prompted Darwin to publish his own ideas in On the Origin of Species. Wallace did extensive fieldwork, first in the Amazon River basin and then in the Malay Archipelago, where he identified the faunal divide now termed the Wallace Line, which separates the Indonesian archipelago into two distinct parts: a western portion in which the animals are largely of Asian origin, and an eastern portion where the fauna reflect Australasia.

He was considered the 19th century's leading expert on the geographical distribution of animal species and is sometimes called the "father of biogeography".[2] Wallace was one of the leading evolutionary thinkers of the 19th century and made many other contributions to the development of evolutionary theory besides being co-discoverer of natural selection. These included the concept of warning colouration in animals, and the Wallace effect, a hypothesis on how natural selection could contribute to speciation by encouraging the development of barriers against hybridisation.

Wallace was strongly attracted to unconventional ideas (such as evolution). His advocacy of spiritualism and his belief in a non-material origin for the higher mental faculties of humans strained his relationship with some members of the scientific establishment. In addition to his scientific work, he was a social activist who was critical of what he considered to be an unjust social and economic system in 19th-century Britain. His interest in natural history resulted in his being one of the first prominent scientists to raise concerns over the environmental impact of human activity.

Wallace was a prolific author who wrote on both scientific and social issues; his account of his adventures and observations during his explorations in Singapore, Indonesia and Malaysia, The Malay Archipelago, is regarded as probably the best of all journals of scientific exploration published during the 19th century.

Wallace had financial difficulties throughout much of his life. His Amazon and far-eastern trips were supported by the sale of specimens he collected and, after he lost most of the considerable money he made from those sales in unsuccessful investments, he had to support himself mostly from the publications he produced. Unlike some of his contemporaries in the British scientific community, such as Darwin and Charles Lyell, he had no family wealth to fall back on, and he was unsuccessful in finding a long-term salaried position, receiving no regular income until he was awarded a small government pension, through Darwin's efforts, in 1881.

Theory of evolution

Early evolutionary thinking

Unlike Darwin, Wallace began his career as a travelling naturalist already believing in the transmutation of species. The concept had been advocated by Jean-Baptiste Lamarck, Geoffroy Saint-Hilaire, Erasmus Darwin, and Robert Grant, among others. It was widely discussed, but not generally accepted by leading naturalists, and was considered to have radical, even revolutionary connotations.[56][57]

Prominent anatomists and geologists such as Georges Cuvier, Richard Owen, Adam Sedgwick, and Charles Lyell attacked it vigorously.[58][59] It has been suggested that Wallace accepted the idea of the transmutation of species in part because he was always inclined to favour radical ideas in politics, religion and science,[56] and because he was unusually open to marginal, even fringe, ideas in science.[60]

He was also profoundly influenced by Robert Chambers' work Vestiges of the Natural History of Creation, a highly controversial work of popular science published anonymously in 1844 that advocated an evolutionary origin for the solar system, the earth, and living things.[61] Wallace wrote to Henry Bates in 1845:
I have a rather more favourable opinion of the 'Vestiges' than you appear to have. I do not consider it a hasty generalization, but rather as an ingenious hypothesis strongly supported by some striking facts and analogies, but which remains to be proven by more facts and the additional light which more research may throw upon the problem. It furnishes a subject for every student of nature to attend to; every fact he observes will make either for or against it, and it thus serves both as an incitement to the collection of facts, and an object to which they can be applied when collected.[60]
In 1847, he wrote to Bates:
I should like to take some one family [of beetles] to study thoroughly, principally with a view to the theory of the origin of species. By that means I am strongly of opinion that some definite results might be arrived at.[62]
Wallace deliberately planned some of his field work to test the hypothesis that under an evolutionary scenario closely related species should inhabit neighbouring territories.[56] During his work in the Amazon basin, he came to realise that geographical barriers—such as the Amazon and its major tributaries—often separated the ranges of closely allied species, and he included these observations in his 1853 paper "On the Monkeys of the Amazon".[63] Near the end of the paper he asks the question "Are very closely allied species ever separated by a wide interval of country?"

In February 1855, while working in Sarawak on the island of Borneo, Wallace wrote "On the Law which has Regulated the Introduction of New Species", a paper which was published in the Annals and Magazine of Natural History in September 1855.[64] In this paper, he discussed observations regarding the geographic and geologic distribution of both living and fossil species, what would become known as biogeography. His conclusion that "Every species has come into existence coincident both in space and time with a closely allied species" has come to be known as the "Sarawak Law". Wallace thus answered the question he had posed in his earlier paper on the monkeys of the Amazon river basin. Although it contained no mention of any possible mechanisms for evolution, this paper foreshadowed the momentous paper he would write three years later.[65]

The paper shook Charles Lyell's belief that species were immutable. Although his friend Charles
Darwin had written to him in 1842 expressing support for transmutation, Lyell had continued to be strongly opposed to the idea. Around the start of 1856, he told Darwin about Wallace's paper, as did Edward Blyth who thought it "Good! Upon the whole! ... Wallace has, I think put the matter well; and according to his theory the various domestic races of animals have been fairly developed into species." Despite this hint, Darwin mistook Wallace's conclusion for the progressive creationism of the time and wrote that it was "nothing very new ... Uses my simile of tree [but] it seems all creation with him." Lyell was more impressed, and opened a notebook on species, in which he grappled with the consequences, particularly for human ancestry. Darwin had already shown his theory to their mutual friend Joseph Hooker and now, for the first time, he spelt out the full details of natural selection to Lyell. Although Lyell could not agree, he urged Darwin to publish to establish priority. Darwin demurred at first, then began writing up a species sketch of his continuing work in May 1856.[66]

Natural selection and Darwin

By February 1858, Wallace had been convinced by his biogeographical research in the Malay Archipelago of the reality of evolution. As he later wrote in his autobiography:
The problem then was not only how and why do species change, but how and why do they change into new and well defined species, distinguished from each other in so many ways; why and how they become so exactly adapted to distinct modes of life; and why do all the intermediate grades die out (as geology shows they have died out) and leave only clearly defined and well marked species, genera, and higher groups of animals?[67]
According to his autobiography, it was while he was in bed with a fever that Wallace thought about Thomas Malthus's idea of positive checks on human population growth and came up with the idea of natural selection.[68] Wallace said in his autobiography that he was on the island of Ternate at the time; but historians have questioned this, saying that on the basis of the journal he kept at the time, he was on the island of Gilolo.[69] From 1858 to 1861 he rented a house on Ternate from the Dutchman M.D. van Renesse van Duivenbode. He used this house as a base camp for expeditions to other islands such as Gilolo.[70]

Wallace describes how he discovered natural selection as follows:
It then occurred to me that these causes or their equivalents are continually acting in the case of animals also; and as animals usually breed much more quickly than does mankind, the destruction every year from these causes must be enormous in order to keep down the numbers of each species, since evidently they do not increase regularly from year to year, as otherwise the world would long ago have been crowded with those that breed most quickly. Vaguely thinking over the enormous and constant destruction which this implied, it occurred to me to ask the question, why do some die and some live? And the answer was clearly, on the whole the best fitted live ... and considering the amount of individual variation that my experience as a collector had shown me to exist, then it followed that all the changes necessary for the adaptation of the species to the changing conditions would be brought about ... In this way every part of an animals organization could be modified exactly as required, and in the very process of this modification the unmodified would die out, and thus the definite characters and the clear isolation of each new species would be explained.[71]
The Darwin–Wallace Medal was issued by the Linnean society on the 50th anniversary of the reading of Darwin and Wallace's papers on natural selection.

Wallace had once briefly met Darwin, and was one of the correspondents whose observations Darwin used to support his own theories. Although Wallace's first letter to Darwin has been lost, Wallace carefully kept the letters he received.[72] In the first letter, dated 1 May 1857, Darwin commented that Wallace's letter of 10 October which he had recently received, as well as Wallace's paper "On the Law which has regulated the Introduction of New Species" of 1855, showed that they were both thinking alike and to some extent reaching similar conclusions, and said that he was preparing his own work for publication in about two years time.[73] The second letter, dated 22 December 1857, said how glad he was that Wallace was theorising about distribution, adding that "without speculation there is no good and original observation" while commenting that "I believe I go much further than you".[74] Wallace trusted Darwin's opinion on the matter and sent him his February 1858 essay, "On the Tendency of Varieties to Depart Indefinitely From the Original Type", with the request that Darwin would review it and pass it on to Charles Lyell if he thought it worthwhile.[1] Although Wallace had sent several articles for journal publication during his travels through the Malay archipelago, the Ternate essay was in a private letter. On 18 June 1858, Darwin received the essay from Wallace. While Wallace's essay obviously 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 very similar to the theory that Darwin had worked on for twenty years, but had yet to publish. Darwin sent the manuscript to Charles Lyell with a letter saying "he could not have made a better short abstract! Even his terms now stand as heads of my chapters ... he does not say he wishes me to publish, but I shall, of course, at once write and offer to send to any journal."[75] Distraught about the illness of his baby son, Darwin put the problem to Charles Lyell and Joseph Hooker, who decided to publish the essay in a joint presentation together with unpublished writings which highlighted Darwin's priority. Wallace had not asked for publication of his essay, and indeed, doing so probably contravened the copyright law of the time. Wallace's essay was presented to the Linnean Society of London on 1 July 1858, along with excerpts from an essay which Darwin had disclosed privately to Hooker in 1847 and a letter Darwin had written to Asa Gray in 1857.[76]

Communication with Wallace in far-off Malay was impossible without months of delay, so he was not part of this rapid publication. Fortunately, Wallace accepted the arrangement after the fact, happy that he had been included at all, and never expressed public or private bitterness. Darwin's social and scientific status was far greater than Wallace's, and it was unlikely that, without Darwin, Wallace's views on evolution would have been taken seriously. Lyell and Hooker's arrangement relegated Wallace to the position of co-discoverer, and he was not the social equal of Darwin or the other prominent British natural scientists. However, the joint reading of their papers on natural selection associated Wallace with the more famous Darwin. This, combined with Darwin's (as well as Hooker's and Lyell's) advocacy on his behalf, would give Wallace greater access to the highest levels of the scientific community.[77] The reaction to the reading was muted, with the president of the Linnean remarking in May 1859 that the year had not been marked by any striking discoveries;[78] but, with Darwin's publication of On the Origin of Species later in 1859, its significance became apparent. When Wallace returned to the UK, he met Darwin. Although some of Wallace's iconoclastic opinions in the ensuing years would test Darwin's patience, they remained on friendly terms for the rest of Darwin's life.

Over the years, a few people have questioned this version of events. In the early 1980s, two books, one written by Arnold Brackman and another by John Langdon Brooks, even suggested not only that there had been a conspiracy to rob Wallace of his proper credit, but that Darwin had actually stolen a key idea from Wallace to finish his own theory. These claims have been examined in detail by a number of scholars who have not found them to be convincing.[79][80][81] Research into shipping schedules has shown that, contrary to these accusations, Wallace's letter could not have been delivered earlier than the date shown in Darwin's letter to Lyell.[82] [83]

Defence of Darwin and his ideas

After the publication of Darwin's On the Origin of Species, Wallace became one of its staunchest defenders on his return to England in 1862. In one incident in 1863 that particularly pleased Darwin, 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 rebuke a paper by a professor of geology at the University of Dublin that had sharply criticised Darwin's comments in the Origin on how hexagonal honey bee cells could have evolved through natural selection.[84]

An even lengthier defence of Darwin's work was "Creation by Law", a review Wallace wrote in 1867 for The Quarterly Journal of Science of the book The Reign of Law, which had been written by George Campbell, the 8th Duke of Argyll, as a refutation of natural selection.[85] After an 1870 meeting of the British Association, Wallace wrote to Darwin complaining that there were "no opponents left who know anything of natural history, so that there are none of the good discussions we used to have."[86]

Differences between Darwin's and Wallace's ideas on natural selection

Historians of science have noted that, while Darwin considered the ideas in Wallace's paper to be essentially the same as his own, there were differences.[87] Darwin emphasised competition between individuals of the same species to survive and reproduce, whereas Wallace emphasised environmental pressures on varieties and species forcing them to become adapted to their local conditions, leading populations in different locations to diverge.[88][89] Some historians, including Peter J. Bowler, have suggested the possibility that in the paper he mailed to Darwin Wallace was not discussing selection of individual variations at all but rather group selection.[90]

Others have noted that another difference was that Wallace appeared to have envisioned natural selection as a kind of feedback mechanism keeping species and varieties adapted to their environment.[91] They point to a largely overlooked passage of Wallace's famous 1858 paper:
The action of this principle is exactly like that of the centrifugal governor of the steam engine, which checks and corrects any irregularities almost before they become evident; and in like manner no unbalanced deficiency in the animal kingdom can ever reach any conspicuous magnitude, because it would make itself felt at the very first step, by rendering existence difficult and extinction almost sure soon to follow.[1]
The cybernetician and anthropologist Gregory Bateson would observe in the 1970s that, though writing it only as an example, Wallace had "probably said the most powerful thing that'd been said in the 19th Century".[92] Bateson revisited the topic in his 1979 book Mind and Nature: A Necessary Unity, and other scholars have continued to explore the connection between natural selection and systems theory.[91]

Warning colouration and sexual selection

In 1867, Darwin wrote to Wallace about a problem he was having understanding how some caterpillars could have evolved conspicuous colour schemes. Darwin had come to believe that sexual selection, an agency to which Wallace did not attribute the same importance as Darwin did, explained many conspicuous animal colour schemes. However, Darwin realised that this could not apply to caterpillars. Wallace responded that he and Henry Bates had observed that many of the most spectacular butterflies had a peculiar odour 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 colour 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 coloured caterpillars that supported Wallace's idea. Warning colouration was one of a number of contributions Wallace made in the area of the evolution of animal colouration in general and the concept of protective colouration in particular.[93] It was also part of a lifelong disagreement Wallace had with Darwin over the importance of sexual selection. In his 1878 book Tropical Nature and Other Essays, he wrote extensively on the colouration of animals and plants and proposed alternative explanations for a number of cases Darwin had attributed to sexual selection.[94] He revisited the topic at length in his 1889 book Darwinism. In 1890, he wrote a critical review in Nature of his friend Edward Bagnall Poulton's The Colours of Animals which supported Darwin on sexual selection, attacking especially Poulton's claims on the "æsthetic preferences of the insect world".[95]

Wallace effect

In 1889, Wallace wrote the book Darwinism, which explained and defended natural selection. In it, he proposed the hypothesis that natural selection could drive the reproductive isolation of two varieties by encouraging the development of barriers against hybridisation. Thus it might contribute to the development of new species. He suggested the following scenario. When two populations of a species had diverged beyond a certain point, each adapted to particular conditions, hybrid offspring would be less well-adapted than either parent form and, at that point, natural selection will tend to eliminate the hybrids. Furthermore, under such conditions, natural selection would favour the development of barriers to hybridisation, as individuals that avoided hybrid matings would tend to have more fit offspring, and thus contribute to the reproductive isolation of the two incipient species.
This idea came to be known as the Wallace effect.[96] Wallace had suggested to Darwin that natural selection could play a role in preventing hybridisation in private correspondence as early as 1868, but had not worked it out to this level of detail.[97] It continues to be a topic of research in evolutionary biology today, with both computer simulation and empirical results supporting its validity.[98]

Application of theory to humans, and role of teleology in evolution

An illustration from the chapter on the application of natural selection to humans in Wallace's 1889 book Darwinism shows a chimpanzee.

In 1864, 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 humankind. Darwin had not yet publicly addressed the subject, although Thomas Huxley had in Evidence as to Man's Place in Nature. He explained the apparent stability of the human stock by pointing to the vast gap in cranial capacities between humans and the great apes. Unlike some other Darwinists, including Darwin himself, he did not "regard modern primitives as almost filling the gap between man and ape".[99] He saw the evolution of humans in two stages: achieving a bipedal posture freeing the hands to carry out the dictates of the brain, and the "recognition of the human brain as a totally new factor in the history of life. Wallace was apparently the first evolutionist to recognize clearly that ... with the emergence of that bodily specialization which constitutes the human brain, bodily specialization itself might be said to be outmoded."[99] For this paper he won Darwin's praise.

Shortly afterwards, Wallace became a spiritualist. At about the same time, he began to maintain that natural selection cannot account for mathematical, artistic, or musical genius, as well as metaphysical musings, and wit and humour. He eventually said that something in "the unseen universe of Spirit" had interceded at least three times in history. The first was the creation of life from inorganic matter.
The second was the introduction of consciousness in the higher animals. And the third was the generation of the higher mental faculties in humankind. He also believed that the raison d'être of the universe was the development of the human spirit.[100] These views greatly disturbed Darwin, who argued that spiritual appeals were not necessary and that sexual selection could easily explain apparently non-adaptive mental phenomena. While some historians have concluded that Wallace's belief that natural selection was insufficient to explain the development of consciousness and the human mind was directly caused by his adoption of spiritualism, other Wallace scholars have disagreed, and some maintain that Wallace never believed natural selection applied to those areas.[101][102] Reaction to Wallace's ideas on this topic among leading naturalists at the time varied. Charles Lyell endorsed Wallace's views on human evolution rather than Darwin's.[103][104] Wallace's belief that human consciousness could not be entirely a product of purely material causes was shared by a number of prominent intellectuals in the late 19th and early 20th centuries.[105] However, many, including Huxley, Hooker, and Darwin himself, were critical of Wallace.[106] As the historian of science Michael Shermer has stated, Wallace's views in this area were at odds with two major tenets of the emerging Darwinian philosophy, which were that evolution was not teleological (purpose driven) and that it was not anthropocentric (human-centred).[107] Much later in his life Wallace returned to these themes, that evolution suggested that the universe might have a purpose and that certain aspects of living organisms might not be explainable in terms of purely materialistic processes, in a 1909 magazine article entitled The World of Life, which he later expanded into a book of the same name;[108] a work that Shermer said anticipated some ideas about design in nature and directed evolution that would arise from various religious traditions throughout the 20th century.[105]

Assessment of Wallace's role in history of evolutionary theory

In many accounts of the development of evolutionary theory, Wallace is mentioned only in passing as simply being the stimulus to the publication of Darwin's own theory.[109] In reality, Wallace developed his own distinct evolutionary views which diverged from Darwin's, and was considered by many (especially Darwin) to be a leading thinker on evolution in his day, whose ideas could not be ignored. One historian of science has pointed out that, through both private correspondence and published works, Darwin and Wallace exchanged knowledge and stimulated each other's ideas and theories over an extended period.[110] Wallace is the most-cited naturalist in Darwin's Descent of Man, often in strong disagreement.[111] Wallace remained an ardent defender of natural selection for the rest of his life. By the 1880s, evolution was widely accepted in scientific circles, but Wallace and August Weismann were nearly alone among prominent biologists in believing that natural selection was the major driving force behind it.[112][113] In 1889, Wallace published the book Darwinism as a response to the scientific critics of natural selection.[114] Of all Wallace's books, it is the most cited by scholarly publications.[115]

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