The dogma holds that Darwin's theory of natural selection explains every branch on the tree of life, but can it really account for everything we see in nature? Yale ornithologist Richard Prum doesn't think so, and he cites astonishing examples in the courtship rituals of club-winged manakins and great argus pheasants. To explain this, he dusts off Darwin's long-neglected theory of sexual selection in which the act of choosing a mate for purely aesthetic reasons—for the mere pleasure of it—is an independent engine of evolutionary change. Most crucially, Prum offers insights into the evolution of human sexuality, particularly the ways in which female preferences have changed male bodies, and even maleness itself, through evolutionary time.