A systematic, comparative account of how human marriage systems arise and change, combining ethnographic evidence and evolutionary reasoning. It examines biological antecedents of mating and parental care, proposes a past seasonality in human pairing, and analyses the psychological and social roots of incest prohibitions. The study surveys variations in conjugal forms, residence rules, mate exchange, and sexual selection, and argues that marital institutions are rooted in family relationships and shaped by both natural and social selection. Chapters interweave data, hypotheses, and methodological discussion to explain persistence and transformation of marriage customs.