Divergence from exclusive heterosexual orientation is commonly observed in women. Understanding this phenomenon requires exploring it from an evolutionary perspective, which in turn entails knowledge of human evolutionary history, particularly with respect to mating patterns. The anthropological and historical records indicate that during most of the human evolutionary time, mate choice was regulated, with parental and social control being directed predominantly toward women. Strong control over mating, along with less emphasis placed on intimacy, male–male competition, and male tolerance toward female same-sex attractions, result in weak selection pressures exercised on alleles that predispose for deviations from exclusive heterosexual orientation. These pressures are weak over small deviations, but become increasingly stronger when such deviations tend toward exclusive homosexual orientation. As a consequence, a distribution of sexual orientation arises with many women having nonexclusive heterosexual orientation, and few women having bisexual and homosexual orientation. Further predictions are derived from this hypothesis, which are matched to available evidence.