Genes associated with homosexual behaviour are, in heterosexuals, associated with greater mating success; genes that predispose to homosexual behaviour may have been evolutionarily maintained in the population because they confer a mating advantage to heterosexual carriers

The evolutionary genetics of homosexuality. Brendan Zietsch, Andrea Ganna, Karin Verweij, Felix Day, Michel Nivard, Robert Maier, Robbee Wedow, Abdel Abdellaoui, Benjamin Neale, John Perry. Human Behavior and Evolution Society, 30t Annual Meeting, July 2018. http://www.hbes.com/conference/hbes2018/

Abstract: Homosexual behaviour in humans is genetically influenced and is associated with having fewer offspring. This presents a Darwinian paradox: why have genes that predispose to homosexual behaviour been maintained in the population despite apparent selection against them? Here we show that genes associated with homosexual behaviour are, in heterosexuals, associated with greater mating success. In in a genotyped sample of more than 400,000 individuals from the UK and USA, we for the first time found genomewide-significant association of specific variants with ever having had a same-sex partner, and hundreds of additional variants were significantly associated in aggregate. Among men and women who had never had a same-sex partner, these same aggregate genetic effects were significantly associated with having more lifetime sexual partners and, in an independent sample, with being judged more physically attractive. Our results suggest that genes that predispose to homosexual behaviour may have been evolutionarily maintained in the population because they confer a mating advantage to heterosexual carriers.