Historian of science Frank J. Sulloway of the University of California, Berkeley, has highlighted Darwin's dogged genius in his own tenacious efforts to force the truth of how Darwin actually pieced together the theory of evolution. The iconic myth is that Darwin became an evolutionist in the Galpagos when he discovered natural selection operating on finch beaks and tortoise carapaces, each species uniquely adapted by food type or island ecology. The notion is ubiquitous, appearing in everything from biology textbooks to travel brochures, the latter inveigling potential travelers to visit the mecca of evolutionary theory and walk in the tracks of St. Darwin the Divine.
In June 2004 Sulloway and I did just that, spending a month retracing some of Darwin's fabled footsteps. Sulloway is one sagacious scientist, but I had no idea he was such an intrepid field explorer until we hit the lava on San Cristbal to reconstruct the famous naturalist's explorations there. Doggedness is the watchword here: with a sweltering equatorial sun and almost no freshwater, it is not long before 70-pound water-loaded packs begin to buckle knees and strain backs. Add hours of daily bushwhacking through dry, dense, scratchy vegetation, and the romance of fieldwork quickly fades.
Yet the harder it got, the more resolute Sulloway became. He actually seemed to enjoy the misery, and this gave me a glimpse into Darwin's single-mindedness. At the end of one particularly grueling climb through a moonscapelike area Darwin called the "craterized district" of San Cristbal, we collapsed in utter exhaustion, muscles quivering, and sweat pouring off our hands and faces. Darwin described a similar excursion as "a long walk."
Death permeates these islands. Animal carcasses are scattered hither and yon. The vegetation is coarse and scrappy. Dried and shriveled cacti trunks dot a bleak lava landscape so broken with razor-sharp edges that moving across it is glacially slow. Many people have died, from stranded sailors of centuries past to wanderlust-struck tourists of recent years. Within days I had a deep sense of isolation and of life's fragility. Without the protective blanket of civilization, none of us is far from death. With precious little water and even less edible foliage, organisms eke out a precarious living, their adaptations to this harsh environment selected for over millions of years. These critters are hanging on by the skin of their adaptive radiations. A lifelong observer of, and participant in, the creation-evolution controversy, I was struck by how clear the solution is in these islands: creation by intelligent design is absurd. Why, then, did Darwin depart the Galpagos a creationist?
Darwin ate his data on the voyage home.
The Darwin Galpagos legend is emblematic of a broader myth that science proceeds by select "eureka!" discoveries followed by sudden revolutionary revelations, whereupon old theories fall before new facts. Not quite. Paradigms power perceptions. Sulloway discovered that nine months after departing the Galpagos, Darwin made this entry in his ornithological catalogue about his mockingbird collection: "When I see these Islands in sight of each other, & possessed of but a scanty stock of animals, tenanted by these birds, but slightly differing in structure & filling the same place in Nature, I must suspect they are only varieties." That is, similar varieties of fixed kinds, rather than the myth that he already knew that evolution was responsible for the creation of separate species. Darwin was still a creationist! This quotation explains why Darwin did not even bother to record the island locations of the few finches he collected (and in some cases mislabeled) and why, as Sulloway has pointed out, these now famous "Darwin finches" were never specifically mentioned in On the Origin of Species.
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 Galpagos 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 Galpagos 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 Galpagos 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 Galpagos: "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.