Abstract: This article revisits the old controversy concerning the relation of the mother’s brother and sister’s son in patrilineal societies in the light both of anthropological criticisms of the very notion of kinship and of evolutionary and epidemiological approaches to culture. It argues that the ritualized patterns of behavior discussed by Radcliffe-Brown, Goody, and others are to be explained in terms of the interaction of a variety of factors, some local and historical, others pertaining to general human dispositions. In particular, an evolved disposition to favor relatives can contribute to the development and stabilization of these behaviors not by directly generating them but by making them particularly “catchy” and resilient. In this way, it is possible to recognize both that cultural representations and practices are specific to a community at a time in its history (rather than mere tokens of a general type) and that they are, in essential respects, grounded in the common evolved psychology of human beings.