The English-language historiography of early modern sexual mores places great emphasis on the role of ideologies in shaping “gendered” behavior. Close analysis of relations between the sexes in a typical Tuscan village, however, reveals the importance of human evolutionary universals in sexual relations. The strategic decisions made by males and females in Montefollonico about marriage and fidelity suggest that ideology and social custom were ultimately at the mercy of biological imperatives, regardless of their strength.