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)