Males and females of a number of animal species divide labor and provide jointly for offspring. Males may provide food, for example, while females protect defenseless young. This exchange is unlikely, however, unless a prior partnership has been established in which a female practices fidelity in exchange for a male’s provisioning activity. The formation of the trading partnership is itself an exchange, and economic theory can help explain when and why there are mutual gains from trading fidelity for resources. Environmental (...) factors determine the potential gains from trade while evolved psychological mechanisms influence the extent to which gains are realized. (shrink)

Natural experiments wherein preferred marriage partners are co-reared play a central role in testing the Westermarck hypothesis. This paper reviews two such hitherto largely neglected experiments. The case of the Karo Batak is outlined in hopes that other scholars will procure additional information; the case of the Oneida community is examined in detail. Genealogical records reveal that, despite practicing communal child-rearing, marriages did take place within Oneida. However, when records are compared with first-person accounts, it becomes clear that, owing to (...) age- and gender-segregating practices, most endogamously marrying individuals probably did not share a history of extensive propinquity. (shrink)