Organizational Effects of Gonadal Hormones on Human Sexual Orientation

Purpose: Sexual attraction to males or females is perhaps the largest behavioral sex difference across animal species. Experiments in laboratory mammals show that prenatal androgens mediate this sex difference, but ethical considerations preclude such experimentation in humans. Multiple lines of converging correlational evidence are therefore needed to demonstrate such mediation in humans. Methods: We review available data linking human sexual orientation to endocrine action, including research on endocrine disorders and biomarkers of early sex hormones. We also perform a meta-analysis across 13 studies comprising 56,804 individuals to investigate a possible link between non-heterosexuality and polycystic ovary syndrome (PCOS), an endocrine condition associated with elevated androgens in females. Results and conclusions: We find converging evidence that prenatal gonadal hormones influence the development of human sexual orientation and orchestrate its sexual differentiation primarily by regulating patterns of gene expression in the developing brain. Evidence is particularly strong that androgens increase sexual attraction to females. In our meta-analysis, PCOS was more common in non-heterosexual females (r = 0.18, p < 0.001). Some evidence also indicates that estrogens increase sexual attraction to males. We discuss why data may be less clear regarding variation in sexual orientation among males, including the possible existence of subgroups characterized by distinct biological pathways that contribute to same-sex sexual orientation. Moving forward, we propose that multiple measures and/or markers be considered together to better characterize early hormonal action on human sexual orientation.