Male Homosexual Desire: Neurological Investigations and Scientific Bias

MALE HOMOSEXUAL DESIRE: NEUROLOGICAL INVESTIGATIONS AND SCIENTIFIC BIAS MICHAEL R. GORMAN* Introduction In December 1990, Swaab and Hofman reported in Brain Research that the volume of the suprachiasmatic nucleus (SCN) of the hypothalamus was 1.7 times larger and contained 2.1 times as many cells in homosexual than heterosexual men [I]. Eight months later, LeVay indicated in Science the volume of the third interstitial nucleus of the anterior hypothalamus (INAH 3) was 50 percent smaller in homosexual than heterosexual men [2]. These demonstrations of morphological differences in brain structure between homosexual and heterosexual men were heralded by the media as proof of a biological basis of homosexuality, but the two studies were not equally celebrated. In the Nexis database of newspapers and nonspecialist magazines, Swaab's name appears in only three stories between December 1990 and March 1993, whereas LeVay is mentioned in more than 100. Moreover, all of the references to Swaab appeared in stories principally about LeVay's work. Among academic publications covered by the Science Citation Index, by February 1993 Swaab and Hofman's paper was referenced six times by other investigators, compared to twenty-two references to LeVay. Social Sciences Citation Index lists three references to Swaab and Hofman and twelve to LeVay as of December 1992. Why should two articles reporting the same type of seemingly earthshaking findings warrant such different receptions? The two studies employed similar subject populations, reported results of comparable Preparation of this manuscript was supported in part by NIH Grant HD-02982 and a Berkeley Predoctoral Fellowship. The author thanks Irving Zucker, Martha McClintock, Kim Wallen, Ellen Zucker, and Howard Bern for their helpful comments on an earlier draft of this manuscript. *Department of Psychology, University of California, Berkeley, California 94720.© 1994 by The University of Chicago. AU rights reserved. 0031-5982/94/3801-0893$01.00 Perspectives in Biology andMedicine, 38, 1 ¦ Autumn 1994 | 61 magnitude and statistical significance, and were published in respected journals. LeVay, in a footnote, questioned the significance of the Swaab/ Hofman findings on the grounds that the SCN is not known to regulate sexual behavior beyond its control of circadian rhythms. Yet LeVay distances himself from the conclusion that the INAH 3 regulates sexual orientation, suggesting that "the results do not allow one to decide if the size of INAH 3 in an individual is the cause or consequence of that individual's sexual orientation, or if the size of INAH 3 and sexual orientation covary under the influence of some third, unidentified variable ." Rather he concludes that "discovery that a nucleus differs in size between heterosexual and homosexual men illustrates that sexual orientation in humans is amenable to study at the biological level." Surely, the same conclusion is no less supported by Swaab and Hofman's paper. The differing responses to these studies, I suspect, reflect the papers' deeper messages. The INAH 3 is reportedly larger in men unselected for sexual orientation (presumed heterosexual) than in women (also presumed heterosexual). Not only do homosexual men have smaller INAH 3's than do heterosexual men, but the INAH 3's of homosexual men do not differ in size from those of heterosexual women. In contrast, the size of the SCN does not differ between men and women unselected for sexual orientation. Thus, Swaab and Hofman showed that homosexual men's brains differed distinctly from those of heterosexual men but did not resemble those of heterosexual women. LeVay's, but not Swaab and Hofman's, results lent superficial credence to the ubiquitously held conviction that homosexuality represents "femininity" in men, and "masculinity" in women.1 Science progresses, however, not merely by demonstrations in support of popular prejudices . Francis Bacon, in Novum Organum, warns against four "idols" or classes of error which hamper scientific progress [4]. First among these are the "idols of the tribe," which include the tendency to support a preconceived idea by affirmative examples and to ignore or dismiss contradictions , and the tendency to attend too much to the senses, which can be deceiving. Adherence to Bacon's scientific method, in which alternative hypotheses are defined, critically tested against one another, and discarded by disproof, protects against these errors. In the remainder of...