Being too cheap to travel to the Galápagos on my own, I’ve wished for years for an invitation to go there as an “expert.” That’s about to come true, as I embark Thursday for a ten-day trip to the islands, courtesy of The Aspen Institute and the folks at Lindblad. This is a “Darwin Year” voyage, complete with readings, discussions, and panels on evolution. (The other “experts” are Olivia Judson and Mark Plotkin). I’ll try to do some postings from the islands, though internet access is limited.
Over the last few weeks I’ve been rereading Darwin and others (especially Frank Sulloway) on the islands and their effect on Darwin’s formulation of 1859. What is most striking from these readings is that the islands did not, as is often assumed, constitute a “eureka moment” for Darwin: he did not hit upon, nor even begin to formulate, his theory of “transmutation” until several years thereafter.
True, the Galápagos did constitute important evidence for the biogeographic chapters of The Origin, but this came as much from the plants (and Joseph Hooker’s analysis of them) as from the finches. Indeed, “Darwin’s finches” are not even mentioned in The Origin! This may be because Darwin botched his collections there, failing to put the island source on the collecting labels. He was forced to reconstruct the biogeography of the finches (which at first he didn’t recognize as a group of close relatives) using specimens collected — and properly labelled — by Darwin’s manservant and by Captain Fitzroy himself. Darwin’s failure to mention finches in The Origin may reflect his continuing uncertainty about the nature of the evidence. He knew by 1859 that the 14 species were indeed closely related (ornithologist John Gould had determined that for him), but the uncertainty about their biogeography led to confusion about what role geographic isolation played in the origin of species.
Darwin’s plant collections, on the other hand, were properly labeled, for pressing plants on the spot is more conducive to accurate recording of localities. And it was Joseph Hooker’s identification of the plants, their affinity, and especially the uniqueness of many species to specific islands, that helped convince Darwin he was on the right track.
Here, from Chapter 12, is the most famous mention of the Galápagos in The Origin. Notice Darwin’s clever use of rhetorical questions to attack creationism. How could a Victorian reader fail to be convinced by arguments like this?
The most striking and important fact for us in regard to the inhabitants of islands, is their affinity to those of the nearest mainland, without being actually the same species. Numerous instances could be given of this fact. I will give only one, that of the Galapagos Archipelago, situated under the equator, between 500 and 600 miles from the shores of South America. Here almost every product of the land and water bears the unmistakeable stamp of the American continent. There are twenty-six land birds, and twenty-five of those are ranked by Mr Gould as distinct species, supposed to have been created here; yet the close affinity of most of these birds to American species in every character, in their habits, gestures, and tones of voice, was manifest. So it is with the other animals, and with nearly all the plants, as shown by Dr. Hooker in his admirable memoir on the Flora of this archipelago. The naturalist, looking at the inhabitants of these volcanic islands in the Pacific, distant several hundred miles from the continent, yet feels that he is standing on American land. Why should this be so? why should the species which are supposed to have been created in the Galapagos Archipelago, and nowhere else, bear so plain a stamp of affinity to those created in America? There is nothing in the conditions of life, in the geological nature of the islands, in their height or climate, or in the proportions in which the several classes are associated together, which resembles closely the conditions of the South American coast: in fact there is a considerable dissimilarity in all these respects. On the other hand, there is a considerable degree of resemblance in the volcanic nature of the soil, in climate, height, and size of the islands, between the Galapagos and Cape de Verde Archipelagos: but what an entire and absolute difference in their inhabitants! The inhabitants of the Cape de Verde Islands are related to those of Africa, like those of the Galapagos to America. I believe this grand fact can receive no sort of explanation on the ordinary view of independent creation; whereas on the view here maintained, it is obvious that the Galapagos Islands would be likely to receive colonists, whether by occasional means of transport or by formerly continuous land, from America; and the Cape de Verde Islands from Africa; and that such colonists would be liable to modifications; the principle of inheritance still betraying their original birthplace.