July 16, 2006

Darwin's Finchs Evolutionary Update

In 1995, a marvelous book called The Beak of The Finch: A Story of Evolution in Our Time won the Pulitzer Prize for science writing. In it, Jonathan Weiner told the story of Peter and Rosemary Grant in their long study of Darwin's Finches on Daphne Major, an uninhabited island in the Galapagos and he used their studies to illuminate the story of how Darwin came about his theory of evolution.

Well, this month, the Grants have published an update to the remarkable tale of the finches. In the last period of drought in 2003 and 2004, they observed how the larger beaked medium-beaked finches had very tough competition from the large-beaked finches for the extremely hard Tribulus seed. The competition meant that the medium beaked finches with smaller beaks were more successful in surviving the drought because they could eat smaller seeds.

"Small-beaked birds survived better than the large-beaked birds, to a strong extent, during the drought," says Peter Grant. And that trait was then passed down to the next generation.

In 2004 and 2005, the Grants observed a strong shift towards smaller beak size among the medium ground finch. The birds' feeding patterns changed too: they went for the large seeds only half as often as in previous years.

This kind of evolution, in which a characteristic of two similar species diverges due to competition over resources, is called character displacement. The idea has become widely accepted thanks to a number of well-detailed studies, says Jonathan Losos, a biologist at Washington University, St Louis.

People have inferred character displacement," says Jeffrey Podos, an associate professor of biology at the University of Massachusetts, Amherst. "But to actually see it as it happens is quite a triumph. To be in the right place at the right time to observe something like this is really just incredible."

So, through careful observation, another leg of evolutionary theory has been shown to be a fact. What a remarkable study the Grants have undertaken, and how much we've learned from their observations over the more than three decades they've conducted this study.

Last year, I wrote about my visit to Daphne Major, the island of the Grant's studies.

Posted by Mary at July 16, 2006 12:22 AM | Science | Technorati links |