Prenatal Influences on Human Sexual Orientation: Expectations versus Data

• Published in: Archives of sexual behavior Vol. 46; no. 6; pp. 1583 - 1592
• Main Author: Breedlove, S. Marc
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-08-2017; Springer Nature B.V
• Subjects: Androgens; Androgens - physiology; Behavioral Science and Psychology; Birth Order; Bisexuality; Female; Fingers - anatomy & histology; Gays & lesbians; Humans; Male; Mens health; Otoacoustic Emissions, Spontaneous; Pregnancy; Prenatal development; Prenatal Exposure Delayed Effects; Psychology; Public Health; Retrospective Studies; Sex Characteristics; Sex Differentiation - physiology; Sexual Behavior; Sexual Behavior - physiology; Sexual orientation; Social Learning; Social Sciences; Target Article; Testosterone - physiology; Testosterone; Androgens; Sexual orientation; Digit ratios; Otoacoustic emissions; Birth order
• ISSN: 0004-0002; 1573-2800
• DOI: 10.1007/s10508-016-0904-2

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.