Is tibetan polyandry adaptive?

This paper addresses methodological and metatheoretical aspects of the ongoing debate over the adaptive significance of Tibetan polyandry. Methodological contributions include a means of estimating relatedness of fraternal co-husbands given multigenerational polyandry, and use of Hamilton’s rule and a member-joiner model to specify how inclusive fitness gains of co-husbands may vary according to seniority, opportunity costs, and group size. These methods are applied to various data sets, particularly that of Crook and Crook (1988). The metatheoretical discussion pivots on the critique by evolutionary psychologists of adaptationist accounts of polyandry. Contrary to this critique, I argue that valid adaptationist explanations of such practices do not necessitate cognitive mechanisms evolved specifically to produce polyandry, nor that there must have been exact equivalents of Tibetan agricultural estates and social institutions in human evolutionary history. Specific issues raised when one posits either kin selection or cultural evolution to explain the adaptive features of Tibetan polyandry are also discussed.