The New York Times bestselling author of Genome and The Evolution of Everything revisits Darwin’s revelatory theory of mate choice through the close study of the peculiar rituals of birds, and how understanding this driver of evolution complicates our view of even how human mating evolved.

In all animals, mating is a deal. But few creatures behave as if sex is a simple, even mutually beneficial, transaction. Many more treat it with reverence, suspicion, angst, and violence. In the case of the Black Grouse, the bird at the center of Matt Ridley’s investigation, the males dance and sing for hours a day, for several exhausting months, in an arduous and even deadly ritual called a “lek.” To prepare for the ordeal, they grow, preen and display fancy, twisted, bold-colored feathers. When achieved, consummation with a female takes seconds. So why the months of practice and preparation that is elaborate, extravagant, exhausting and elegant?

The full answer remains a mystery. Evolutionary biologists can explain why males are generally the eager sellers, females the discriminating buyers. But they struggle to explain why, in some species, this extravagance goes beyond the mere gaudy, taking on bizarre shapes, postures, and behavior. And further, why these bird displays seem beautiful to us humans, a species with seemingly no skin in the game.

Using an early morning “lek" as his starting point, Ridley explores the scientific research into the evolution of bright colors, exotic ornaments, and elaborate displays in birds around the world. Charles Darwin thought the purpose of such displays was to "charm" females. Though Darwin’s theory was initially dismissed and buried for decades, recent scientific research has proven him newly right—there is a powerful evolutionary force quite distinct from natural selection: mate choice. In Birds, Sex, and Beauty, Ridley reopens the history of Darwin’s vexed theory, laying bare a century of disagreement about an idea so powerful, so weird, so wonderful, we may have yet to understand all of its implications.