A widely publicized study comparing the brains of gay and heterosexual men led to a debate over the nature of same-gender attraction and the role of biological studies in understanding sexuality.
The end of the twentieth century saw an explosion of interest in the cognitive, genetic, and neurologic bases of complex behaviors like language, reasoning, and human sexuality. In the midst of this interest came one the first contemporary studies on possible biological correlates of same-gender attraction and affection.
In 1991, Simon LeVay, a neuroscientist who earlier had been affiliated with the Salk Institute for Biological Studies in San Diego, California, published an article in the journal Science reporting on a postmortem analysis of the sizes of the hypothalamuses
One of the structures within the hypothalamus, the medial preoptic region (MPR), appears to be associated with male-typical sexual behavior in rats and monkeys. Studies have shown that hormone levels influence the structure and function of the MPR throughout development, including during fetal development in utero. These studies have also shown that the size of the MPR differs as a function of sex: females have a smaller MPR than males.
LeVay conducted a postmortem analysis of the size of the MPR in three groups of people: heterosexual men, gay men, and women whose sexual orientations were unknown. LeVay found that the size of gay men’s MPR was smaller than that of heterosexual men and comparable in size to that of women. LeVay interpreted this as an indication that same-gender attraction in men has a biological basis. Specifically, he argued that his finding was broadly consistent with theories of sexual orientation that posit that gay men had experienced different hormonal levels while in utero. These hormone levels influence the structure and function of different areas of the brain, including the MPR, which could lead to same-gender attraction in adulthood.
The reaction to LeVay’s findings was mixed. Some people reacted positively, claiming that LeVay’s finding was evidence that same-gender attraction and affection were inevitable and should therefore not be judged as morally or ethically deviant lifestyle “choices.” Others applauded LeVay for extending biological research to include studies of sexual diversity and for formulating explicit hypotheses about the nature of sexual orientation that could be tested with data that had been collected in controlled, experimental settings.
Considerable negative reaction followed LeVay’s study as well. Many people felt that LeVay’s findings ran strongly contrary to their personal experience of having overtly and consciously chosen same-gender attraction. Other people criticized LeVay for having what they perceived to be the motive of reducing diversity in human behaviors to simple genetic differences and, in doing so, discounting a large body of literature suggesting that social identities are actively constructed. Still others criticized LeVay’s methodology. All of the gay men and many of the heterosexual men in LeVay’s sample had died of AIDS. People questioned whether this sample was sufficiently representative of the entire population of gay and heterosexual men to draw general conclusions about the nature of same-gender attraction.
The years since Simon LeVay’s original finding have seen an increase in research quantifying the relative contribution of biological and social factors in same-gender attraction. Although not in direct response to LeVay’s research, these studies have continued many of the debates that LeVay’s study began.
For example, later studies purport to have found further support for the hypothesis that same-gender attraction is related to prenatal hormonal levels. Research has found differences as a function of sexual orientation in the way that the inner ear responds to sound. These responses, called otoacoustic emissions, are related to hormonal levels. Books by Joan Roughgarden and Bruce Bagemihl have proposed alternative accounts of same-gender attraction in the context of biological diversity. In particular, these works have sought to show that same-gender attraction is not an aberrant condition that results from atypically high hormone levels but is instead a natural consequence of sexual diversity within organisms and communities.
Much of the criticism of LeVay’s study has occurred during a time when older debates on whether “nature” or “nurture” predominates in development have been replaced by newer theories in which complex behaviors are seen to emerge as the consequence of interactions among biological and social conditions as well as cognitive abilities. Ultimately, these theories provide a framework in which to understand sexuality as the product of input and experience in conditions of diverse biological and cognitive predispositions.
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Bagemihl, Bruce. Biological Exuberance: Animal Homosexuality and Natural Diversity. New York: St. Martin’s Press, 1998. -
Eisenberg, Leon. “The Social Construction of the Human Brain.” American Journal of Psychiatry 152 (1995): 1563-1575. -
Elman, Jeffrey L., Elizabeth A. Bates, Mark H. Johnson, Annette Karmiloff-Smith, Domenico Parisi, and Kim Plunkett. Rethinking Innateness: A Connectionist Perspective on Development. Cambridge, Mass.: MIT Press, 1996. -
LeVay, Simon. “A Difference in Hypothalamic Structure Between Heterosexual and Homosexual Men.” Science 253 (1991): 1034-1037. -
_______. The Sexual Brain. Cambridge, Mass.: MIT Press, 1993. -
McFadden, Dennis, and Edward D. Pasanen. “Spontaneous Otoacoustic Emissions in Heterosexuals, Homosexuals, and Bisexuals.” Journal of the Acoustical Society of America 105 (1999): 2403-2413. -
Roughgarden, Joan. Evolution’s Rainbow: Diversity, Gender, and Sexuality in Nature and People. Berkeley: University of California Press, 2004.
May 6, 1868: Kertbeny Coins the Terms “Homosexual” and “Heterosexual”
1869: Westphal Advocates Medical Treatment for Sexual Inversion
1897: Ellis Publishes Sexual Inversion
May 14, 1897: Hirschfeld Founds the Scientific-Humanitarian Committee
1905: Freud Rejects Third-Sex Theory
1906: Friedlaender Breaks with the Scientific-Humanitarian Committee
1908: Carpenter Publishes The Intermediate Sex
1929: Davis’s Research Identifies Lesbian Sexuality as Common and Normal
1948: Kinsey Publishes Sexual Behavior in the Human Male
1952: APA Classifies Homosexuality as a Mental Disorder
1953: Kinsey Publishes Sexual Behavior in the Human Female
1953-1957: Evelyn Hooker Debunks Beliefs That Homosexuality is a “Sickness”
June 5 and July 3, 1981: Reports of Rare Diseases Mark Beginning of AIDS Epidemic
Spring, 1984: AIDS Virus Is Discovered