What does it mean to be human? The human body is rich with evidence of how we evolved in the distant past. Why do the males of many primate species practice infanticide? Is sexual jealousy natural and inevitable? Were our prehistoric ancestors naturally monogamous or is polygamy more likely? Can modern genetic techniques determine whether early human kinship was matrilineal, patrilineal or some combination of these? In the past, scientists could only make guesses on such topics, but today we are beginning to discover some answers.