Male homosexuality has stumped evolutionary biologists and psychologists for decades. According to evolutionary theory, the highest goal is to pass on one’s genes, yet homosexual males will father no direct offspring without the help of surrogates. Moreover, homosexuality seems to be at least partially heritableand is relatively common in developed societies. Why would such an evolutionarily costly trait be so prevalent?
Past studies have suggested that genes related to homosexuality might confer a mating advantage to heterosexuals expressing them, and that female relatives of homosexual males may receive a boost to fecundity. Evidence supporting those notions remains sparse, however.
A study published in August to PLoS ONE provides support for the former contention. Lead author Julien Barthes, along with his counterparts Pierre-André Crochet and Michel Raymond, suggest that a sexually-transmitted gene on the X chromosome may yield higher femininity or attractiveness in women, and thus signal increased levels of fertility. But, as a side effect, when this gene is expressed in a male on his single X chromosome, it can increase the odds that he will be homosexual.