Darwin's Finches - Darwin's Theory

Darwin's Theory

During the survey voyage of HMS Beagle, Darwin had no idea of the significance of the birds of the Galápagos. He had learned how to preserve bird specimens while at the University of Edinburgh and had been keen on shooting, but he had no expertise in ornithology and by this stage of the voyage concentrated mainly on geology. In Galápagos he mostly left bird shooting to his servant Syms Covington. Nonetheless, these birds were to play an important part in the inception of Darwin's theory of evolution by natural selection.

On the Galápagos Islands and afterward, Darwin thought in terms of "centres of creation" and rejected ideas of transmutation of species. From Henslow's teaching he was interested in geographical distribution of species, particularly links between species on oceanic islands and on nearby continents. On Chatham Island he recorded that a mockingbird was similar to those he had seen in Chile, and after finding a different one on Charles Island he carefully noted where mockingbirds had been caught. In contrast he paid little attention to the finches. When examining his specimens on the way to Tahiti Darwin noted that all the mockingbirds on Charles Island were of one species, those from Albemarle of another, and those from James and Chatham Islands of a third species. As they sailed home about nine months later this, together with other facts including what he'd heard about Galápagos tortoises, made him wonder about the stability of species.

Following his return from the voyage, Darwin presented the finches to the Geological Society of London at their meeting on 4 January 1837, along with other mammal and bird specimens he had collected. The bird specimens, including the finches, were given to John Gould, the famous English ornithologist, for identification. Gould set aside his paying work and at the next meeting on 10 January reported that birds from the Galápagos Islands which Darwin had thought were blackbirds, "gross-beaks" and finches were in fact "a series of ground Finches which are so peculiar an entirely new group, containing 12 species." This story made the newspapers.

Darwin had been in Cambridge at that time. In early March he met Gould again and for the first time got a full report on the findings, including the point that his Galápagos "wren" was another closely allied species of finch. The mockingbirds Darwin had labelled by island were separate species rather than just varieties. Gould found more species than Darwin had anticipated, and concluded that 25 of the 26 land birds were new and distinct forms, found nowhere else in the world but closely allied to those found on the South American continent. Darwin now saw that if the finch species were confined to individual islands, like the mockingbirds, this would help to account for the number of species on the islands, and he sought information from others on the expedition. Specimens had also been collected by Captain Robert FitzRoy, FitzRoy’s steward Harry Fuller and Darwin's servant Covington, who had labelled them by island. From these, Darwin tried to reconstruct the locations where he had collected his own specimens. The conclusions supported his idea of the transmutation of species.