Social and Behavioral Sciences Commons^™

Cross-Cousin Marriage Among The Yanomamö Shows Evidence Of Parent–Offspring Conflict And Mate Competition Between Brothers, Napoleon A. Chagnon, Robert F. Lynch, Mary K. Shenk, Raymond Hames, Mark V. Flinn

Department of Anthropology: Faculty Publications

Marriage in many traditional societies often concerns the institutionalized exchange of reproductive partners among groups of kin. Such exchanges most often involve cross-cousins—marriage with the child of a parent’s opposite-sex sibling—but it is unclear who benefits from these exchanges. Here we analyze the fitness consequences of marrying relatives among the Yanomamo¨ from the Amazon. When individuals marry close kin, we find that (i) both husbands and wives have slightly lower fertility; (ii) offspring suffer from inbreeding depression; (iii) parents have more grandchildren; and (iv) siblings, especially brothers, benefit when their opposite-sex siblings marry relatives but not when their same-sex siblings …