Throughout history humans have been fascinated with incest. Stories, fables, literature, philosophers, church officials, and scientists have explored this mysterious topic. The taboo is critical to human survival, as incest threatens the species and patterns of human social organization. Drawing upon the rich legacy of theory, empirical data, and speculation about the origins of the incest taboo, this book develops a new explanation for not only the emergence of the taboo in hominid and human evolutionary history but also for the varying strength of the taboo for the incestuous dyads of the nuclear family, the different rates of incest of these dyads, and the dramatic differences of the psychological pathology of incest on its younger victims. Synthesizing findings from biology, sociobiology, neurology, primatology, clinical psychology, anthropology, and sociology, the authors weave together a scenario of how natural selection initially generated mechanisms of sexual avoidance; and then, as the nuclear family emerged in hominid and human evolution, how sociocultural selection led to the development of the incest taboo.