“Most [evolutionary biologists] see outrageous sexual traits” – say, beautiful plumage and elaborate mating rituals in birds – “as reliable advertisements. The logic goes that only the fittest manakins could coordinate their movements just so. Only the healthiest peacocks could afford to carry such a cumbersome tail. Their displays and dances hint at their good genes, allowing females to make adaptive decisions. But [ornithologist Richard] Prum says that view is poorly supported by years of research, and plainly makes no sense when you actually look at what birds do.”