What evolutionary value could male homosexuality have, without any discernible reproductive advantage? One possible explanation is the “kin selection hypothesis.” By acting altruistically toward nieces and nephews, homosexual men would perpetuate the family genes, including some of their own. Paul Vasey and Doug VanderLaan of the University of Lethbridge, Canada, tested this idea in Samoa with a group of fa’afafine — a distinct Samoa ngender category of males who prefer men as sexual partners. They recently recruited a large sample of fa’afafine, and comparable samples of women and heterosexual men, then gave them all a series of questionnaires measuring their willingness to help their nieces, nephews, and unrelated children in various ways — caretaking, gifts, teaching. Compared to Samoan women and heterosexual men, fa’afafine showed a much weaker link between their avuncular (or uncle like) behavior and their altruism toward kids generally. This cognitive dissociation, the scientists argue, allows the fa’afafine to allocate their resources more efficiently and precisely to their kin and, thus, enhance their own evolutionary prospects.
Vasey, P., & VanderLaan, D. (February 2010). An adaptive cognitive dissociation between willingness to help kin and nonkin in Samoan fa’afafine. Psychological Science.