A recent study on fruit flies has found that not only does same-sex sexual behavior seem to be heritable, but females with a genetic makeup that is associated with this trait actually display higher reproductive rates, which happens to be an evolutionary advantage.
Natural selection helps get rid of traits and behaviors that are detrimental to the reproductive success of an organism, which has scientists wondering why so many species (currently more than 1,500) exhibit same-sex sexual behavior (SSB).
The two main hypothesis for SSB are over dominance and sexual antagonism. IFL Science explains:
“The former proposes that SSB could persist in the population if genes for this behavior confer a harmonizing reproductive advantage in individuals only possessing one copy of the gene, or heterozygotes, as opposed to those in possession of two (homozygotes). The latter suggests that a gene that is detrimental to fitness in one sex could be maintained so long as it is beneficial to the other sex.”
Scientists used a combination of genetic and behavioral tests to try and determine which theory prevailed. Although data leaned slightly more to the over dominance hypothesis, they actually found that both options could be contributing to SSB in the gene pool.
Perhaps even more interesting, however, is the finding that males displaying high levels of SSB are producing female offspring with higher rates of reproduction. This suggests that genes associated with SSB, despite being reproductively harmful to males, could be persisting in nature because of the reproductive advantages they provide to females.