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.

人类同性性行为 (SSB) 是可遗传的，不会立即带来明显的直接生殖或生存益处，并且可以转移交配努力以减少生殖机会。这提出了一个达尔文悖论：为什么 SSB 在明显的选择反对的情况下仍被保留？我们表明，与 SSB 相关的遗传效应可能在仅从事异性性行为的个体（OSB 个体）中赋予交配优势。利用最近一项关于 SSB 的全基因组关联研究和一项关于 358,426 人异性性伴侣数量的新全基因组关联研究的结果，我们表明，在 OSB 个体中，与 SSB 相关的遗传效应与拥有更多异性性伴侣。计算机模拟表明，与 SSB 相关的等位基因的这种交配优势可以帮助解释它是如何在进化上得以维持的。注意事项包括我们的英国和美国样本的文化特异性、这些人群中性行为的社会规范、测量交配成功的难度以及测量的变异捕获性状总遗传变异的一小部分这一事实。