Paris (AFP) - Gene sequencing of Galapagos Island finches first studied by Charles Darwin have found the birds have a traceable evolutionary history going back two million years, scientists said on Wednesday.
Arguably the most famous community of birds in the world, the finches came to Darwin's attention when he visited the islands in 1831.
Darwin was struck by the archipelago's extraordinary wide range of finch species.
He theorised they had derived from a single species which had been "taken and modified" -- and with it, he set in place a cornerstone theory of evolution.
The 15 species today -- collectively known as Darwin's finches or Galapagos finches -- are closely monitored for clues about how a niche habitat forces evolutionary change.
In a study in the journal Nature, a team from Uppsala University in Sweden and Princeton University, New Jersey, said they had unravelled the genetic code from 120 birds, with samples from all 15 species plus two close relatives.
The common ancestor of the birds arrived on the Galapagos about two million years, they estimated.
Interbreeding between the various bird communities played an important part in the evolutionary saga, providing a broad gene pool from which to draw.
"Hybridisation has played a critical role in the evolution of the finches and has contributed to maintaining their genetic diversity," said Princeton's Peter Grant.
The birds' key feature is their beak, which evolves in size and shape in order to exploit local food resources, be it insects, seeds, nectar from cactus flowers or even blood from iguanas.
The gene that largely determines the beak shape is called ALX1 -- and, intriguingly, it also plays a part in the development of the face and skull in humans.