[A] reasonable summary is that, when it comes to male homosexuality, there is almost certainly a direct influence, although probably not strict control, by one or more alleles. Ditto for female homosexuality, although the genetic mechanism(s), and almost certainly the relevant genes themselves, differ between the sexes.
Beyond the suggestive but inconclusive search for DNA specific to sexual orientation, other genetic evidence has emerged. Gay-lesbian differences in those outcomes further support the idea that the genetic influence upon homosexuality differs somewhat, somehow, between women and men. Other studies confirm that the tendency to be lesbian or gay has a substantial chance of being inherited.
Consider, too, that across cultures, the proportion of the population that is homosexual is roughly the same. We are left with an undeniable evolutionary puzzle: What maintains the underlying genetic propensity for homosexuality, whatever its specific manifestations? Unlike most mystery stories, in which the case is typically solved at the finish, this one has no ending: We simply do not know.
View the original article here: The Evolutionary Mystery of Homosexuality