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Kin Selection Plays Evolutionary Role
Evolutionarily speaking, male homosexuality doesn't make much sense (the article makes no mention of female homosexuality). If an organism's main biological goal is to make sure its genes are passed on to offspring, then what kind of advantage could this sexual orientation have? A possible explanation is what evolutionary psychologists call "kin selection hypothesis." Homosexuality may have an indirect benefit by enhancing the survival of closely related kin and relatives. In other words, they are "helpers in the nest."
Paul Vasey and Doug VanderLaan of the University of Lethbridge, Canada tested this idea on the Pacific island of Samoa. Samoa was chosen because it has another gender category beyond the female/male distinction called the fa'afafine, people considered "neither man nor woman," males that are exclusively attracted to adult males.
Past studies have shown that the fa'afafine are more altruistic towards their nieces and nephews than heterosexual Samoan men and women. They babysit, tutor, and help out financially far more often than others. Vasey and VanderLaan wanted to see if they were specifically nicer to their own kin, rather than just kids in general. They gave a mixed group of fa'afafine and heterosexual men and women questionnaires measuring their willingness to help their own nieces and nephews in various ways, and also their willingness to do the same for other, unrelated kids. The findings show that the fa'afafine showed a weaker link towards behaving altruistically for unrelated kids, but allocated their time and resources more efficiently and precisely towards their own kin.
According to Vasey, each fa'afafine would have to support the survival of two additional nieces or nephews to compensate for being childless. "The fa'afafine's avuncularity probably contributes to the evolutionary survival of genes for male same-sex sexual attraction, but is unlikely to entirely offset the costs of not reproducing."
Source: Science Daily