Biological Research on Women's Sexual Orientations: Evaluating the Scientific Evidence

Journal of Social Issues, Summer, 2000 by Rosemary C. Veniegas, Terri D. Conley

Evaluating the Biological Research on Women's Sexual Orientations

This section reviews and evaluates scientific evidence about biological influences on women's sexual orientation. Early this century, the inversion theories of sexologists such as Richard von Krafft-Ebing (1908/1950) asserted that heterosexuality is the biological norm. Consequently they proposed that homosexuality results from a biological abnormality creating gender-atypical ("inverted") sexual attractions and personality traits. Heterosexual women were believed to have feminine physical attributes and lesbians to have masculine physical characteristics (see Peplau, Spalding, Conley, & Veniegas, 1999). Krafft-Ebing (1908/1950, p. 399) wrote that the most extreme type of lesbians were women "whose frame, pelvis, gait, appearance, coarse masculine features, rough deep voice, etc., betray rather the man than the woman." Researchers such as the Committee for the Study of Sex Variants (Henry, 1948) carefully measured the anatomical and physiological features of lesbians in a fruitless search for distinctive mas culine attributes. The results of later studies of women's body build were inconclusive and often contradictory, prompting researchers to abandon the hypothesis that women's sexual orientation is linked to anatomical features (A. Ellis, 1963; Terry, 1990). Griffiths et al. (1974, p. 550) concluded "it is clear that there is no such thing as a Lesbian physique."

A subsequent line of research tested the hypothesis that women's sexual orientation is affected by their levels of circulating sex hormones (estrogens and androgens). The prediction was that lesbians would have more masculine patterns of hormones than would heterosexual women. Several small studies found differences between lesbians and heterosexual women (Gartrell, Loriaux, & Chase, 1977; Loraine, Adamopoulos, Kirkham, Ismail, & Dove, 1971; Loraine, Ismail, Adamopoulos, & Dove, 1970). In contrast, three more recent studies comparing carefully matched samples of lesbians and heterosexual women failed to find significant differences on multiple hormonal measures (Dancey, 1990; Downey, Ehrhardt, Schiffman, Dyrenfurtli, & Becker, 1987; Griffiths et al., 1974). [1] In a review of the hormonal evidence Byne (1996, p. 133) concluded, "This hypothesis is no longer viewed favorably because an overwhelming majority of studies failed to demonstrate a correlation between sexual orientation and adult hormonal constituti on."

Today, two lines of biological research are being actively pursued. The first analyzes the impact of prenatal hormones and the second investigates genetics.

The Neuroendocrine Theory of Women's Sexual Orientations

The prevailing neuroendocrine theory about sexual orientation predicts that prenatal exposure to atypically high levels of so-called male hormones "masculinizes" brain structures and influences women's sexual orientation (Collaer & Hines, 1995; L. Ellis, 1996). The hypothesis is that "if a female fetus is exposed to high levels of testosterone in the latter half of gestation, her brain will function as a male brain. Following puberty, one manifestation of this male brain functioning will be a preference for female sex partners" (L. Ellis, 1996, p. 22).