In 1991, LeVay published "A difference in hypothalamic structure between heterosexual and homosexual men" in Science. This article reported a difference in average size between the third Interstitial Nucleus of the Anterior Hypothalamus (INAH3) in the brains of heterosexual men and homosexual men: INAH3 was more than twice as large in heterosexual men as in homosexual men. The INAH3 size of homosexual men was the same as that of women. LeVay wrote that "This finding indicates that INAH is dimorphic with sexual orientation, at least in men, and suggests that sexual orientation has a biological substrate." LeVay added, "The existence of 'exceptions' in the present sample (that is, presumed heterosexual men with small INAH 3 nuclei, and homosexual men with large ones, hints at the possibility that sexual orientation, although an important variable, may not be the sole determinant of INAH 3 size. It is also possible, however, that these exceptions are due to technical shortcomings or to misassignment of subjects to their subject groups."
LeVay's finding was widely reported in the media. LeVay cautioned against misinterpreting his findings in a 1994 interview: "It’s important to stress what I didn’t find. I did not prove that homosexuality is genetic, or find a genetic cause for being gay. I didn’t show that gay men are born that way, the most common mistake people make in interpreting my work. Nor did I locate a gay center in the brain. The INAH3 is less likely to be the sole gay nucleus of the brain than a part of a chain of nuclei engaged in men and women's sexual behavior." Some critics of LeVay questioned the accuracy and appropriateness of his measurements, saying that the structures are difficult to see in tissue slices and that he measured in volume rather than cell count. Nancy Ordover wrote in her 2003 book American Eugenics that LeVay has been criticized for "his small sample size and for compiling inadequate sexual histories."
The Sexual Brain
The Sexual Brain, published in 1993, was LeVay's first book. It discussed brain mechanisms involved in sexual behavior and feelings.
LeVay wrote in the introduction that his INAH3 study was his only publication on sex to that date, and that most of his previous research had been on the visual areas of the cerebral cortex. LeVay explained the circumstances that led to his taking an interest in sexuality: "As a teenager and young adult I accepted the Freudian line [on sexual orientation], according to which a young child's relations with his or her parents play a decisive role...it seemed to be borne out in my own family experience: I remembered my mother as having been very close and possessive, and my father as distant, even hostile...when I came to read Freud I was swept away by his eloquence and the sheer audacity of his theories."
LeVay added, however, "Later...I began to have serious doubts. First, as I got to know large numbers of gay men and lesbian women, it became harder and harder to see them, or myself, as the products of defective parenting; we just seemed too normal. Second, as I became trained in the methods of science I became more and more skeptical that there was anything scientific about Freud's ideas, even though he repeatedly asserted that they were so. And finally, discoveries were being made in the area of sexual biology that were pointing in all kinds of new and exciting directions; Freudianism, on the other hand, seemed to have become a fossilized immovable dogma."
Queer Science
Queer Science, published in 1996, was a survey of sexual orientation research. It discussed the work of pioneering sexologists such as Karl Heinrich Ulrichs and Magnus Hirschfeld, Sigmund Freud and his followers, behaviorism, and LeVay's own research on INAH3 and its possible implications.
In the sixth chapter, The Brain, LeVay mentioned his research on INAH3. He wrote that, "The findings on INAH3 fit very well with the model put forward by Hirschfeld nearly a century ago, and in my view they greatly strengthen the notion that the development of sexual orientation, at least in men, is closely tied in with the prenatal sexual differentation of the brain. But it is important to stress several limitations of the study. The observations were made on adults who had already been sexually active for a number of years. To make a really compelling case, one would have to show that these neuroanatomical differences existed early in life - preferably at birth. Without such data, there is always at least the theoretical possibility that the structural differences are actually the result of differences in sexual behavior - perhaps on the 'use it or lose it' principle. Furthermore, even if the differences in the hypothalamus arise before birth, they might still come about from a variety of causes, including genetic differences, differences in stress exposure, and many others. It is possible that the development of INAH3 (and perhaps other brain regions) represents a 'final common path' in the determination of sexual orientation, a path to which innumerable prior factors may contribute.
Another limitation arises because most of the gay men whose brains I studied died of complications of AIDS. Although I am confident that the small size of INAH3 in these men was not an effect of the disease, there is always the possibility that gay men who die of AIDS are not representative of the entire population of gay men. For example, they might have a stronger preference for receptive anal intercourse, the major risk factor for acquiring HIV infection. Thus, if one wished, one could make the argument that structural differences in INAH3 relate more to actual behavioral patterns of copulation rather than to sexual orientation as such. It will not be possible to settle this issue definitively until some method becomes available to measure the size of INAH3 in living people who can be interviewed in detail about their sexuality."
In the twelfth chapter, Science and the Law, LeVay criticized Dean Hamer's argument that genetic studies have proven that homosexuality is not a choice. LeVay wrote, referring to Colorado's Amendment 2 case, "...the pressures of the trial drove the expert witnesses to take somewhat more extreme or simplified positions than they might otherwise have done. Hamer, for example, said at one point: "Since people don't choose their genes, they couldn't possibly choose their sexual orientation. The same goes for the question about changing. People can't change their genes. So that part of sexuality that is genetically influenced, of course, cannot be easily changed." This goes beyond the data in two respects. First, it seems to deny any possibility of choice even if the genetic influence is only partial. Yet it is possible to construct a hypothesis whereby both "gay genes" and a desire to be homosexual are necessary for a person actually to become homosexual. Second, it equates genetic loading with immutability, a connection that is open to challenge."
In the fourteenth chapter, Conclusions, LeVay discussed the issues of motivation and bias. LeVay wrote, "Because my own research on the hypothalamus drew so much public attention, I have myself been the target of many accusations of bias. These accusations have come from several different directions. According to one school of thought, typified by Jack Wesoky, the defending attorney in the Colorado Amendment 2 case, my findings are not to be believed because I am gay. According to another school, my very engagement in biological research on homosexuality proves that I am secretly out to eliminate gay people. This is the point of view of Jonathan Tolins, as expressed in Twilight of the Golds."
Albrick's Gold
Albrick's Gold, published in 1997, was a science fiction novel, whose main character, Roger Cavendish, is partially based on Simon LeVay.
Gay, Straight, and the Reason Why: The Science of Sexual Orientation
Gay, Straight, and the Reason Why: The Science of Sexual Orientation, published in 2010, details findings from over 650 studies on sexual orientation, including findings he had not considered. “I didn’t expect the avenue of research about birth order, that gay men tend to be late born in families, and that women aren’t as fixed in their sexual orientation as are men.”
Other Books
LeVay has also co-authored a textbook on human sexuality and books on earthquakes, volcanoes, Parkinson's disease, and extraterrestrial life. Human Sexuality (now in its third edition) was described in one review as "an exceptional book that addresses nearly every aspect of sexuality from multiple theoretical, historical, and cultural perspectives."
