Summer 2009
He never knew it at the time, but Darwin had stepped into an evolutionary laboratory
Tortoises, sunflowers, mockingbirds, or finches? Which of these gave Charles Darwin a eureka moment—that flash of inspiration when it suddenly dawned on him that plants and animals radically change over time?
On his famous, five-year voyage on HMS Beagle Darwin spent less than six weeks in 1835 in the Galapagos Islands, a volcanic archipelago lying astride the equator about 600 miles due west of Ecuador on the South American continent. Brief though it was, Darwin's visit to the Galapagos ultimately changed everything scientists thought they knew about how nature works. For 150 years, scientists have speculated about what single discovery may have triggered Darwin's eureka moment about the origins of species.
Stopping on only four of the larger islands, Darwin busied himself collecting plants and animals and talking with the local inhabitants in the most fascinating place he'd ever seen. During his stay on James Island, he visited a low crater with a shallow briny lake in its center from which locals were procuring salt. There among the bushes yet lay the skull of a sealing-vessel captain who had been murdered by his shipmates a few years previously. Camping nearby, Darwin recorded oppressive heat, but at higher elevations, a "green and flourishing vegetation."
He never knew it at the time, but Darwin had stepped into an evolutionary laboratory unmatched anywhere on the planet, except possibly the Hawaiian Islands, which also sit atop a moving oceanic crustal hotspot. Like all volcanic islands, the Galapagos offer scientists some powerful clues about the rate of evolution of species because they are easily datable by geologists. The oldest island which Darwin visited first,
Chatham, is estimated to be about 5 million years old; the youngest, Narborough, is a veritable youngster at a paltry one million.
Darwin was intrigued by everything he saw. He collected as many specimens of animals and plants as he could during the short time he had on the islands. It was only after John Gould , a famous ornithologist, analyzed his bird skins back in England that finches took their place in Darwin's thinking about the evolution of species. (Gould informed Darwin that he had found no less than 14 species new to science—every single one of them a finch, and every one only found in the Galapagos Islands.)
But even though his name has been famously associated with finches, the tiny birds weren't likely the source of any "eureka moment" Darwin may have had. In Voyage of the Beagle, published in 1839, here's what Darwin had to say about the birds that are now famously known as Darwin's Finches: "Unfortunately most of the specimens of the finch tribe were mingled together...."
In other words, his first encounter with Galapagos finches didn't figure into his thoughts on the evolution of species. That all changed, of course, with the publication of his seminal work 20 years later, On the Origin of Species, in 1859.
More plausibly, Darwin 's eureka moment-if indeed he ever had one—might have come while contemplating the three species of mockingbirds he collected on different islands. These abundant songbirds captured his imagination and he wrote of them: "My attention was first thoroughly aroused, by comparing together the numerous specimens, shot by myself and several other parties on board, of the mocking-thrushes, when, to my astonishment, I discovered that all those from Charles Island belonged to one species (Mimus trifasciatus); all from Albemarle Island to M. parvulus; and all from James and Chatham Islands...belonged to M. melanotis."
Even plants might claim to have been the inspiration that got Darwin to question the dogma of the time that species were never-changing. Darwin wrote: "...thus, Scalesia, a remarkable arborescent genus of the Compositae, is confined to the archipelago: it has six species: one from Chatham, one from Albemarle, one from Charles Island, two from James Island, and the sixth from one of the three latter islands...not one of these six species grows on any two islands."
As it turns out, a "Mr. Lawson"—a British official who oversaw Galapagos affairs for the Ecuadorian government—may have planted the first kernel of evidence of evolution in Darwin's mind:
"I have not as yet noticed by far the most remarkable feature in the natural history of this archipelago; it is, that the different islands to a considerable extent are inhabited by a different set of beings. My attention was first called to this fact by the Vice-Governor, Mr. Lawson, declaring that the tortoises differed from the different islands, and that he 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. I never dreamed that islands, about 50 or 60 miles apart, and most of them in sight of each other…would have been differently tenanted...."
Four years after his Galapagos visit and with ample time for reflection, Darwin mused in Voyage: "But it is the circumstance, that several of the islands possess their own species of the tortoise, mocking-thrush, finches, and numerous plants, these species having the same general habits, occupying analogous situations, and obviously filling the same place in the natural economy of the archipelago, that strikes me with wonder."
And he was clearly fast on the track of his seminal idea: "Hence, both in space and time, we seem to be brought somewhat near to that great act—that mystery of mysteries—the first appearance of new beings on earth..."
Truth is, Darwin may never have had a true eureka moment at all. After Voyage was published, he spent the ensuing 20 years mulling over his original observations bolstered with information supplied him by various specialists who studied his collections.
In all likelihood, instead of being struck with the proverbial eureka moment, the "Father of Evolution" arrived at his theory of natural selection after slow and careful deliberation—a practice befitting the greatest biologist—and some would argue scientist—of all time.
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