6315 Thirty-six years ago, an unfamiliar schnoz popped up on Daphne Major. Over the past four decades, Rosemary and Peter Grant have identified and banded every finch that lives on this tiny, dog-bowl-shaped isle in the heart of the Galapagos archipelago. So, in 1981, when a member of their research team noticed a young male with an imposing beak and a strange song, the Princeton University scientists instantly knew it was out of place. A blood sample confirmed their hunch: The bird was an Española Cactus-Finch, and it had crossed miles of ocean to mingle with the local Medium Ground-Finches. And that’s how the latest, most bizarre case of finch evolution began: with a wanderer and then a bang. The exotic male from Española island quickly mated with a native female, giving rise to a group of stocky-beaked finches that biologists dubbed the “Big Bird” lineage. After just three generations, the Big Birds started pairing up with hybrids exclusively, and are now on their...