This paper presents historical evidence on marriage patterns in ancient Sparta, Rome, Early Christianity, and the Early Middle Ages. Monogamy occurred in all of these societies but there is a great deal of diversity in origin and function of monogamous mating arrangements. In the case of Sparta, monogamy arose as part of an intensively egalitarian, racially homogenous social structure which fostered intense cooperation and altruism within the group. In the case of Rome monogamy coexisted with pronounced social, political, and economic inequalities, and there was much more ethnic diversity at Rome than at Sparta. The case of early Christianity involved the spread of a more radical ideology of monogamy and sexual restraint among the lower and middle classes of the Roman Empire, but the crucial event in the Christianization of the West was the apparently chance conversion of a single powerful individual, the Emperor Constantine. In the case of the Christianization of barbarian Europe, the movement was spearheaded by a powerful institution and the acceptance among the aristocracy of Christian ideology. The revolution thus proceeded from the top of the society downward. These findings are related to a model of cultural evolution that emphasizes the irreducibility of social controls and ideology in maintaining egalitarian mating practices.