Natural selection can sometimes work one gene at time, a new study of Darwin’s finches suggests.
Variants of one gene had a major effect on rapid changes in beak size after a drought, researchers report in the April 22 Science. The finding may help explain how Darwin’s finches evolved into 18 species in an evolutionarily speedy 1 million to 2 million years.
A drought that struck the Galápagos island of Daphne Major in 2004 and 2005 put adaptation of some of Darwin’s iconic finches on fast-forward. Competition for scarce seeds pitted medium-sized ground finches (Geospiza fortis) with big beaks against large ground finches (G. magnirostris) with big beaks. Big-beaked medium ground finches lost that contest. They died, but medium ground finches with small beaks survived by eating small seeds. As a result, medium ground finches on the island tended to have smaller beaks after the drought than before.