Evolution happens through
natural selection. (continued)
Suitably, one of the most striking
examples of natural selection in action concerns the very Galapagos finches
that Darwin made famous. Since 1973, biologists Peter and Rosemary Grant,
working on the tiny island of Daphne Major in the Galapagos, have studied a
species of finch called Geospiza fortis
(upper right in illustration, which appeared in Darwin's 1839 book about
his five-year journey aboard the Beagle). After a drought in 1977 devastated plants bearing small seeds, more
than 1,000 of the 1,200 G. fortis
finches on the island died. The Grants discovered that larger G.
fortis, which could break open larger seeds
than smaller G. fortis could,
survived better. The survivors mated in 1978, and, on average, their offspring
had beaks 4 percent larger than those of the previous generation. Following
another drought in 2003, G. fortis
with smaller beaks survived better, in part because of stiff competition for
bigger seeds after a larger finch species, G. magnirostris, settled the island. Between 2003 and 2005, the
Grants found, G. fortis beaks
shrank by 5 percent.