The Galapagos holds a special place in the history of evolution, but the story of how the island’s wildlife influenced Darwin’s thought is often misconstrued. Many people imagine the young Charles Darwin bounding off the Beagle, taking a good look at the animals and plants of the islands and suddenly leaping to an understanding of the process of Natural Selection. This isn’t true, there was no ‘Eureka!’ moment. It wasn’t until after some hard work, by Darwin and other biologists he employed to help with the Beagle specimens, that he realised what he had observed.
What really happened on the Galapagos?
The Galapagos islands sit 600 miles west of South America, on the equator. There are ten main islands, and some smaller ones, all formed from a volcanic rock called basalt. Darwin arrived on the 15th September 1835, the Beagle landing on Chatham Island. Over the next 5 weeks the crew passed through a number of Islands, Darwin doing his thing: collecting specimens, making notes and thinking about what he observed.
The most famous fauna of the islands of course are the iguanas, giant tortoises and finches. On Charles Island, their second stop, Darwin was told by the local prisoners that each island had its own peculiar tortoise. These are huge beasts weighing up to and over 90kg, big enough for Charles and others to ride like a horse, and the staple meat for the islanders and visitors alike. They seemed to live an age as well; he was informed that ‘the old ones seem generally to die from accidents, as from falling down precipices’ and dead animals were never found without an ‘evident cause’. Darwin though let this local wisdom pass him by, thinking at the time that the tortoises were originally imported by man.
Likewise he seemed little impressed by the iguanas, not realising these ‘disgusting clumsy Lizards’ were unique to the island chain. But he observed their habits closely and his Journal of Researches has some lovely stories of what he saw:
‘I watched one for a long time, till half its body was buried; I then walked up and pulled it by the tail; at this it was greatly astonished, and soon shuffled up to see what was the matter; and then stared me in the face, as much as to say, “What made you pull my tail?”’
The Finches that don’t Flinch
He also initially missed the evolutionary clues hidden in the Finches, finding them very hard to tell apart – indeed he was not even aware that they were all finches at all – the different species flock together when eating and drinking. He was more interested in how tame they were; they had obviously only recently encountered man, and didn’t yet have the instinctive fear for people. Charles found he could even prod them with his gun and many would still sit still.
The mocking birds caught Darwin’s eye. He noticed that some of these were different on different islands, but also all similar to mocking birds of the mainland, and collected specimens from each island, labelling them separately. Although he collected many finches, unlike his usual thoroughness, he didn’t label them by island. Fortunately for his later studies, FitzRoy and Syms Covington were keeping more meticulous records. On the final island they visited a local told Charles that many of the plants and trees, just like the tortoises, were unique on each island… you can imagine he felt pretty disappointed with his poor labelling as after leaving the islands he seems to have put two and two together ‘each variety (of mocking bird) is constant in its own island. – This is a parallel fact to the one mentioned about the Tortoises’. But still the significance of this find didn’t sink in; he wrote in a later edition his Journal:
‘I never dreaned that islands, abouty fifty or sixty miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a similar climate, rising to a nearly equal height, would have been differently tenanted’
As the Beagle set sail for Tahiti, the crew ate their fill of tortoise meat, disposing of their shells overboard.
On second thoughts…
It was not until the Beagle returned to England, and Darwin set about sorting his specimens, that he figured things out. He needed help to classify all his many specimens and these experts often spotted what Darwin missed. From them he learned that each island had its own finch species. The iguanas too came in more than one form; there was a marine and a land iguana that were unique in the world. Darwin managed to decipher the marine iguana’s unique ecology from his observations, correctly concluding (without ever witnessing) that they feed on seaweed at the bottom of the sea around the coast. Joseph Hooker confirmed much of the Galapagos plant life was unique to the island chain, and many species unique to individual islands.
And then there were the birds. Their sorting was offered to John Gould. Gould concluded that, what Darwin thought were varieties of mockingbirds and finches were in fact individual species! After calling in Covington’s and FitzRoy’s more carefully labelled specimens he could see that each island had its own unique species, some endemic to particular islands, all with unique bill shapes and sizes. Darwin concluded in his Journal:
‘Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends’.
So much for species being fixed entities! Why so many closely related species, with highly similar ecologies? And why did they bare a wider similarity to South American Species? Darwin was beginning to formulate the answers. Read on...
Written by Stephen Montgomery
References & Further Reading
The Autobiography of Charles Darwin
by Charles Darwin (Edited by Francis Darwin), The Thinker's Library: 1929
by Cyril Aydon, Robinson: 2003
by John van Wyhe, Andre Deutsch: 2009
by Adrian Desmond & James Moore, Penguin: 1991
Darwin: Discovering the Tree of Life
by Niles Eldredge, WW Norton & Co.: 2005
by Peter Nichols, Profile Books LTD: 2003
Journal of Researches
by Charles Darwin, 1839 (any edition)
The Life of Charles Darwin
by Francis Darwin, Senate: 1995 (1902)