Darwin’s Finches

The study of the finches of Galapagos continues to reveal the mechanism by which natural selection operates

This year’s $500,000 Kyoto Prize in basic sciences—an award almost as prestigious as the Nobel—has been awarded for work in evolutionary biology. After all, the variety of life itself is the accumulated result of small changes.

Princeton biologists Peter and Rosemary Grant have spent 36 years studying ‘Darwin’s finches’ in the Galapagos Islands off the coast of Ecuador. They have studied the beak size and shape of 14 finch varieties, mainly on the Daphne Major island to examine the ways in which species evolve in response to environmental changes.

In 1831, travelling on board the ship Beagle, Darwin had observed these birds and had written that ‘in the 13 species of ground-finches, a nearly perfect gradation may be traced—from a beak extraordinarily thick, to one so fine—that it may be compared to that of the warbler…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 has been taken and modified for different ends.’ In a way, finches shaped Darwin’s work.

Thousands of years before Darwin’s visit, a few of the birds would have strayed onto these islands off the South American coast, and radiated in the way Darwin observed, to occupy various niches available for survival. The process is still underway, and is what the husband and wife team has been documenting. They have shown that a single millimetre of variation in the length or depth of the beak makes a difference to the finches’ survival because of the available food supply.

The finches eat seeds, and depending on the amount of rainfall and other climatic variables, seeds of one kind or the other are in preponderance. This in turn favours or disadvantages beaks of a particular length or depth. This slow accumulation of change in beak sizes has led to beaks that are very different in appearance. So much so that the few birds that strayed onto these islands have given rise to 13 different species.

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