Prenatal Influences on Human Sexual Orientation: Expectations versus Data
- 2.9k Downloads
In non-human vertebrate species, sexual differentiation of the brain is primarily driven by androgens such as testosterone organizing the brains of males in a masculine fashion early in life, while the lower levels of androgen in developing females organize their brains in a feminine fashion. These principles may be relevant to the development of sexual orientation in humans, because retrospective markers of prenatal androgen exposure, namely digit ratios and otoacoustic emissions, indicate that lesbians, on average, were exposed to greater prenatal androgen than were straight women. Thus, the even greater levels of prenatal androgen exposure experienced by fetal males may explain why the vast majority of them grow up to be attracted to women. However, the same markers indicate no significant differences between gay and straight men in terms of average prenatal androgen exposure, so the variance in orientation in men cannot be accounted for by variance in prenatal androgen exposure, but may be due to variance in response to prenatal androgens. These data contradict several popular notions about human sexual orientation. Sexual orientation in women is said to be fluid, sometimes implying that only social influences in adulthood are at work, yet the data indicate prenatal influences matter as well. Gay men are widely perceived as under-masculinized, yet the data indicate they are exposed to as much prenatal androgen as straight men. There is growing sentiment to reject “binary” conceptions of human sexual orientations, to emphasize instead a spectrum of orientations. Yet the data indicate that human sexual orientation is sufficiently polarized that groups of lesbians, on average, show evidence of greater prenatal androgen exposure than groups of straight women, while groups of gay men have, on average, a greater proportion of brothers among their older siblings than do straight men.
KeywordsSexual orientation Testosterone Androgens Birth order Digit ratios Otoacoustic emissions
This article was funded by NIH Grant R21MH104780.
Compliance with Ethical Standards
Conflict of interest
The author declares no conflict of interest.
- Blanchard, R. (1997). Birth order and sibling sex ration in homosexual versus heterosexual males and females. Annual Review Sex Research, 8, 27–67.Google Scholar
- Bogin, B. (1997). Evolutionary hypotheses about human childhood. Yearbook of Physical Anthropology, 40, 60–89.Google Scholar
- Cohen, J. (1988). Statistical power analysis for the behavioral sciences (2nd ed.). Hillsdale, NJ: Erlbaum Associates.Google Scholar
- Colapinto, J. (1997, 11 December). The true story of John/Joan. Rolling Stone, pp. 54–97.Google Scholar
- Colapinto, J. (2000). As nature made him: The boy who was raised as a girl. New York, NY: Harper Collins.Google Scholar
- Diamond, L. M. (2008b). Sexual fluidity: Understanding women’s love and desire. Cambridge, MA: Harvard University Press.Google Scholar
- Golombok, S., & Fivush, R. (1994). Gender development. New York: Cambridge University Press.Google Scholar
- Hiraishi, K., Sasaki, S., Shikishima, C., & Ando, J. (2012). The second to fourth digit ratio (2D:4D) in a Japanese twin sample: Heritability, prenatal hormone transfer, and association with sexual orientation. Archives of Sexual Behavior, 41(3), 711–724. doi: 10.1007/s10508-011-9889-z.CrossRefPubMedGoogle Scholar
- LeVay, S. (2016). Gay, straight, and the reason why: The science of sexual orientation. New York: Oxford University Press.Google Scholar
- Meyer-Bahlburg, H. F. L., Dolezal, C., Baker, S. W., & New, M. I. (2008). Sexual orientation in women with classical or non-classical congenital adrenal hyperplasia as a function of degree of prenatal androgen excess. Archives of Sexual Behavior, 37(1), 85–99. doi: 10.1007/s10508-007-9265-1.CrossRefPubMedGoogle Scholar
- Money, J., & Ehrhardt, A. A. (1972). Man & woman, boy & girl: Differentiation and dimorphism of gender identity from conception to maturity. Baltimore: Johns Hopkins University Press.Google Scholar
- Nedoma, K., & Freund, K. (1961). Somatosexual findings in homosexual men. Ceskoslovenska Psychiatre, 57, 100–103.Google Scholar
- Prior, L., Bordet, S., Trifiro, M. A., Mhatre, A., Kaufman, M., Pinsky, L., … Liao, S. (1992). Replacement of arginine 773 by cysteine or histidine in the human androgen receptor causes complete androgen insensitivity with different receptor phenotypes. American Journal Human Genetics, 51, 143–155.Google Scholar
- Roselli, C. E., Larkin, K., Resko, J. A., Stellflug, J. N., & Stormshak, F. (2004). The volume of a sexually dimorphic nucleus in the ovine medial preoptic area/anterior hypothalamus varies with sexual partner preference. Endocrinology, 145(2), 478–483. doi: 10.1210/en.2003-1098.CrossRefPubMedGoogle Scholar
- Sanders, A. R., Martin, E. R., Beecham, G. W., Guo, S., Dawood, K., Rieger, G., … Bailey, J. M. (2015). Genome-wide scan demonstrates significant linkage for male sexual orientation. Psychological Medicine, 45(7), 1379–1388. doi: 10.1017/S0033291714002451.
- Tortorice, J. L. (2002). Written on the body: Butch vs. femme lesbian gender identity and biological correlates of low digit ratio. New Brunswick, NJ: Rutgers University.Google Scholar
- Williams, T. J., Pepitone, M. E., Christensen, S. E., Cooke, B. M., Huberman, A. D., Breedlove, N. J., … Breedlove, S. M. (2000). Finger–length ratios and sexual orientation. Nature, 404(6777), 455–456.Google Scholar
- Wudy, S. A., Dorr, H. G., Solleder, C., Djalali, M., & Homoki, J. (1999). Profiling steroid hormones in amniotic fluid of midpregnancy by routine stable isotope dilution/gas chromatography–mass spectrometry: Reference values and concentrations in fetuses at risk for 21-hydroxylase deficiency. Journal of Clinical Endocrinology and Metabolism, 84(8), 2724–2728.PubMedGoogle Scholar