The crude view of evolution is often stark: a struggle for life in the wilderness, dominated by the strong, the cunning, the fierce, or the exquisitely camouflaged. And yet, who thrives today? Dogs.

Modern dog breeds come in a mind-boggling array of shapes and sizes—from Chihuahua to Great Dane, corgi to greyhound, pug to German shepherd. In fact, the domestic dog, Canis familiaris, shows more ...