The different beak shapes of these Galapagos Finches helped inspire Darwin's theory of evolution. The beak of the G. difficilis (top), also known as the 'vampire finch,' was sharp enough for the bird to peck a seabird and drink its blood. Later beak modifications helped , for example, G. magnirostris (middle) to crack open seeds, and G. conirostris (bottom) to eat cactus flowers. A 2004 study suggests that a change in when and how intensely the gene Bmp4 is turned on can account for all the beak differences. The right-hand column shows the underlying structure of each beak and highlights the activity of Bmp4; the gene is most active in magnirostris and least in difficilis, fuliginosa and scandens. (Source: Arhat Abzhanov/Harvard Medical School)

From Boston Globe, March 13, 2006, p. C4 (see article for more info.)