How hybrids have upturned evolutionary theory

IN 1981 PETER and Rosemary Grant, a husband-and-wife team of evolutionary biologists, spotted something odd on Daphne Major. Every year for the previous decade they had travelled from Princeton University to this island in the Galápagos, to study its three endemic tanager species, part of a group known colloquially as “Darwin’s finches”. On this occasion their eyes were drawn to an unusual male that sported dark feathers and sang a unique song. Genetic analysis later identified him as a large cactus finch, probably blown in from Española, another part of the archipelago that is over 100km away.