While studying the distribution and changes of living organisms, Alfred Russel Wallace developed an explanation involving natural selection. His paper led to a joint presentation with Darwin's material in 1858.
Wallace also studied animal geography in Southeast Asia, and the Wallace Line bears his name. Joint publication does not mean that their views and research experiences were identical.
Natural selection and Darwin
By February 1858, Wallace had been convinced by his biogeographical research in the Malay Archipelago that evolution was real. He later wrote in his autobiography that the problem was of how species change from one well-marked form to another. He stated that it was while he was in bed with a fever that he thought about Malthus's idea of positive checks on human population, and had the idea of natural selection. His autobiography says that he was on the island of Ternate at the time; but the evidence of his journal suggests that he was in fact on the island of Gilolo. From 1858 to 1861, he rented a house on Ternate from the Dutchman Maarten Dirk van Renesse van Duivenbode, which he used as a base for expeditions to other islands such as Gilolo.
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 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.
Communication with Wallace in the far-off Malay Archipelago involved months of delay, so he was not part of this rapid publication. Wallace accepted the arrangement after the fact, happy that he had been included at all, and never expressed bitterness in public or in private. 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. All the same, 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.
The reaction to the reading was muted, with the president of the Linnean Society remarking in May 1859 that the year had not been marked by any striking discoveries; 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 opinions in the ensuing years would test Darwin's patience, they remained friends and frequent correspondents 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 by Arnold Brackman and another by John Langdon Brooks, 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 and found unconvincing by a number of scholars. Shipping schedules show that, contrary to these accusations, Wallace's letter could not have been delivered earlier than the date shown in Darwin's letter to Lyell.