Darwin's Finches Evolve Before Scientists' Eyes

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The large ground finch (Geospiza magnirostis) on Daphne Major Island, Galapagos. (Image credit: B. Rosemary Grant)

For the first time scientists have observed in real-time evolutionary changes in one species driven by competition for resources from another.

In a mere two decades, one of Charles Darwin's finch species, Geospiza fortis, reduced its beak size to better equip itself to consume small sized seeds, scientists report in the July 14 issue of the journal Science.

"When there is a severe drought on a small island, natural selection occurs," said study co-author Peter Grant of Princeton University.

The new larger species ate the larger and harder seeds on the island, food that the biggest members of the native finch clan normally ate.

"The recent immigrant species had almost eaten the supply of food themselves, so they almost went extinct," Grant said. "The resident species, the species that was there before the new species arrived, underwent a large shift toward small size in beaks."

Typically, the small members of the species can't crack the larger seeds. But with the depletion of the larger seeds, the small-beaked population, which could reach the smaller feed and needed less food to meet its daily energy needs, had a better survival rate.

This type of evolutionary change is known as character displacement.

"It's a very important one in studies of evolution because it shows that species interact for food and undergo evolutionary change, which minimizes further evolution," Grant said. 'It has not been possible to observe the whole process from start to finish in nature."

Sara Goudarzi
Sara Goudarzi
Sara Goudarzi is a Brooklyn writer and poet and covers all that piques her curiosity, from cosmology to climate change to the intersection of art and science. Sara holds an M.A. from New York University, Arthur L. Carter Journalism Institute, and an M.S. from Rutgers University. She teaches writing at NYU and is at work on a first novel in which literature is garnished with science.