How are gene variants associated with same-sex sexual behaviour maintained in the gene pool? New study suggests that the same variants, when found in individuals who don't engage in SSSB behavior, are associated with having more sexual partners

Genomic evidence consistent with antagonistic pleiotropy may help explain the evolutionary maintenance of same-sex sexual behaviour in humans. Brendan P. Zietsch, Morgan J. Sidari, Abdel Abdellaoui, Robert Maier, Niklas Långström, Shengru Guo, Gary W. Beecham, Eden R. Martin, Alan R. Sanders & Karin J. H. Verweij. Nature Human Behaviour, August 23 2021. https://www.nature.com/articles/s41562-021-01168-8

Abstract: Human same-sex sexual behaviour (SSB) is heritable, confers no immediately obvious direct reproductive or survival benefit and can divert mating effort from reproductive opportunities. This presents a Darwinian paradox: why has SSB been maintained despite apparent selection against it? We show that genetic effects associated with SSB may, in individuals who only engage in opposite-sex sexual behaviour (OSB individuals), confer a mating advantage. Using results from a recent genome-wide association study of SSB and a new genome-wide association study on number of opposite-sex sexual partners in 358,426 individuals, we show that, among OSB individuals, genetic effects associated with SSB are associated with having more opposite-sex sexual partners. Computer simulations suggest that such a mating advantage for alleles associated with SSB could help explain how it has been evolutionarily maintained. Caveats include the cultural specificity of our UK and US samples, the societal regulation of sexual behaviour in these populations, the difficulty of measuring mating success and the fact that measured variants capture a minority of the total genetic variation in the traits.

Popular version: Genetic patterns offer clues to evolution of homosexuality. Sara Reardon. Nature News, Aug 23 2021. https://www.nature.com/articles/d41586-021-02312-0