Alfred Russel Wallace : biography
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. 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.
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.Desmond & Moore Darwin 1991, p. 438; Browne Charles Darwin: Voyaging pp. 537–46.
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?Wallace My Life p. 361.
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.Slotten pp. 144–45. 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.Slotten p. 144. 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.Heij, dr. C.J., 2011. Biographical Notes of Antonie Augustus Bruijn (1842–1890). IBP Press, Bogor. ISBN 978-979-493-294-0.
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.Wallace My Life pp. 361–62.