"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."
A newer version of the argument notes that women who are related to gay men have more children on average than women who are not related to gay men. This may be because gay men end up being helpers, but it may also be that both share a common genetic heritage that predisposes them to more frequent sex, thus resulting in more children among women. According to this hypothesis, gay men may simply be a side effect of the evolutionarily advantageous genes - though of course it is not necessarily one or the other. It could be that both effects reinforce each other.