Few things come more naturally to us than sex—or so it would seem. Yet to a chimpanzee, the sexual practices and customs we take for granted would appear odd indeed. He or she might wonder why we bother with inconveniences like clothes, why we prefer to make love on a bed, and why we fuss so needlessly over privacy. Evolution and Human Sexual Behavior invites us into the thought-experiment of imagining human sex from the vantage point of our primate cousins, in order to underscore the role of evolution in shaping all that happens, biologically and behaviorally, when romantic passions are aroused.