Darwin similarly botched his tortoise observations. Later, he recalled a conversation he had had while in the islands with the vice governor Nicholas O. Lawson, who explained that for the tortoises Lawson "could with certainty tell from which island any one was brought. I did not for some time pay sufficient attention to this statement, and I had already partially mingled together the collections from two of the islands." Worse, as Sulloway recounts humorously, Darwin and his mates ate the remaining tortoises on the voyage home. As Darwin later confessed: "I never dreamed that islands, about fifty or sixty miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a nearly equal height, would have been differently tenanted."

Through careful analysis of Darwin's notes and journals, Sulloway dates Darwin's acceptance of the fact of evolution to the second week of March 1837, after a meeting Darwin had with the eminent English ornithologist John Gould, who had been studying his Galápagos bird specimens. With access to museum ornithological collections from areas of South America that Darwin had not visited, Gould corrected a number of taxonomic errors Darwin had made (such as labeling two finch species a "Wren" and an "Icterus") and pointed out to him that although the land birds in the Galápagos were endemic to the islands, they were notably South American in character.

Darwin left the meeting with Gould, Sulloway concludes, convinced "beyond a doubt that transmutation must be responsible for the presence of similar but distinct species on the different islands of the Galápagos group. The supposedly immutable 'species barrier' had finally been broken, at least in Darwin's own mind." That July, Darwin opened his first notebook on Transmutation of Species, in which he noted: "Had been greatly struck from about Month of previous March on character of S. American fossils--and species on Galapagos Archipelago. These facts origin (especially latter) of all my views." By 1845 Darwin was confident enough in his data to theorize on the deeper implications of the Galápagos: "The archipelago is a little world within itself, or rather a satellite attached to America, whence it has derived a few stray colonists, and has received the general character of its indigenous productions.¿ Hence both in space and time, we seem to be brought somewhat near to that great fact--that mystery of mysteries--the first appearance of new beings on this earth."

For a century and a half, Darwin's theory has steadfastly explained more disparate facts of nature than any other in the history of biology; the process itself is equally dogged, as Darwin explained: "It may be said that natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers." Doggedly so.

This article was originally published with the title It's Dogged as Does It.

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