Darwin and the finches: what actually happened

What almost everyone gets wrong

The version in circulation goes like this: a young Darwin steps ashore in the Galápagos, notices that the finches have different beaks on different islands, realises they must have descended from a common ancestor, and evolution is born.

Almost none of that is true. It is a story assembled later, largely by textbook writers, and it is repeated on most Galápagos websites including several run by people who should know better. The real sequence is slower, more human and considerably more interesting.

What actually happened

1. 15 Sept 1835 The Beagle reaches San Cristóbal. Darwin is 26. His first impression is of somewhere like hell — black lava, stunted scrub, heat. He is more interested in the geology than the birds.
2. 24 Sept On Floreana, the acting governor Nicholas Lawson mentions in passing that he can tell which island a tortoise came from by the shape of its shell. Darwin writes it down and does not act on it. He will call this, much later, one of the observations that first unsettled him.
3. 8 Oct Nine days ashore on Santiago — his longest stay. He collects heavily, including finches, and labels them carelessly.
4. 20 Oct 1835 The Beagle leaves. Five weeks in total. Darwin has no theory of evolution and does not think he is carrying anything revolutionary in the hold.
5. Oct 1836 The Beagle returns to England, having gone the long way round the world.
6. Jan 1837 The turning point. The ornithologist John Gould examines the specimens and reports that the assorted "blackbirds, grosbeaks and finches" are in fact twelve species of closely related ground finches, all new to science. Darwin had not seen it. And now he needs to know which island each came from — and his own labels do not say.
7. 1837 He reconstructs the island data from the collections of Captain FitzRoy and two other shipmates, who had labelled theirs properly. In July he opens his first notebook on the transmutation of species.
8. 1859 On the Origin of Species is published — twenty-four years after the visit. It mentions the Galápagos finches only briefly, and does not use them as the central argument at all.

It was the mockingbirds, not the finches

Here is the part that gets left out. While still aboard the Beagle, before England, before Gould, Darwin noticed something about the mockingbirds: the ones from Floreana, San Cristóbal and Isabela were visibly different from each other. And unlike the finches, he had labelled the mockingbirds by island.

In his ornithological notes he wrote that if there was any substance to the differences, then "such facts would undermine the stability of Species" — the closest he came to the idea while still at sea. It is the mockingbirds that made him uneasy. The finches only became the famous example a century later, because they make a neater diagram.

You can see this for yourself. The Española mockingbird is bold enough to land on your bag, and looks nothing like the one on Santa Cruz. The Floreana mockingbird — the one that started it — is now critically endangered and survives on two offshore islets, extinct on Floreana itself since the nineteenth century.

The finches, properly

They descend from a single ancestral population that arrived from South America roughly two million years ago, and they have radiated into around 18 recognised species. The differences are mostly in the beak, and the beak maps onto the food:

The woodpecker finch is worth pausing on: it is one of very few birds anywhere that uses a tool, holding a cactus spine in its beak to lever grubs out of bark. Nobody taught it. It is not closely related to any other tool-using bird.

The experiment that is still running

The best evidence for natural selection anywhere on Earth is not in a museum. It is on Daphne Major, a small islet north of Santa Cruz, where Peter and Rosemary Grant spent forty years catching, measuring and releasing every finch on the island.

What they recorded is this. In a drought year the small soft seeds run out first. Birds with deeper beaks can crack the big hard ones; birds with smaller beaks starve. Average beak depth in the surviving population rises measurably within a single generation — and falls back when the rains return and small seeds are plentiful again.

Darwin assumed evolution was too slow to watch. The Grants watched it, repeatedly, and wrote down the numbers. They also documented the emergence of what appears to be a new breeding lineage from a single immigrant bird, within about three generations.

Where you see this yourself

Daphne Major is closed to visitors — it is a research site. But the finches are not rare, and the archipelago itself is the argument:

• Santa Cruz highlands — the easiest finch watching in the islands. Several species around one feeding area, and the Charles Darwin Research Station at the edge of town.
• Española — the bold endemic mockingbird, and the red-and-green marine iguanas found on no other island. Island-by-island difference, standing in front of you.
• Floreana — where Lawson told Darwin about the tortoise shells, and where the mockingbird that unsettled him is now clinging on offshore.
• The tortoises — domed shells on wet highland islands where food grows low, saddle-backed shells on dry islands where it grows high. This is the clearest visible case in the archipelago, and it was Lawson's point in 1835.

An honest warning about the finches themselves. They are small, brown, and genuinely hard to tell apart — the species boundaries are still argued over by people who do this for a living, and some of them interbreed. If a guide identifies every finch instantly and with total confidence, be a little sceptical. The difficulty is not a failure of the guide. It is the actual scientific situation, and it is more interesting than a clean answer.

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