"Male homosexuality doesn't make complete sense from an evolutionary point of view. It appears that the trait is heritable, but because homosexual men are much less likely to produce offspring than heterosexual men, shouldn't the genes for this trait have been extinguished long ago? What value could this sexual orientation have, that it has persisted for eons even without any discernible reproductive advantage?"
"One possible explanation is what evolutionary psychologists call the "kin selection hypothesis." What that means is that homosexuality may convey an indirect benefit by enhancing the survival prospects of close relatives. Specifically, the theory holds that homosexual men might enhance their own genetic prospects by being "helpers in the nest." By acting altruistically toward nieces and nephews, homosexual men would perpetuate the family genes, including some of their own."
"Kin selection hypothesis" may explain homosexuality from an evolutionary point of view. (2010). Retrieved February 17, 2016, from http://www.news-medical.net/news/20100205/Kin-selection-hypothesis-may-explain-homosexuality-from-an-evolutionary-point-of-view.aspx