In 1991 Dr. LeVay, a neuro-scientist at the Salk Institute of La Jolla, California, examined the brains of 41 cadavers: 19 allegedly homosexual men, 16 allegedly heterosexual men, and 6 allegedly heterosexual women. His study focused on a group of neurons in the hypothalamus structure called the interstitial nuclei of the anterior hypothalamus, or the INAH3.
He reported this region of the brain to be larger in heterosexual men than in homosexuals; likewise, he found it to be larger in heterosexual men than in the women he studied. For that reason, he postulated homosexuality to be inborn, the result of size variations in the INAH3, and his findings were published in Science in August of 1991.[19] This is the study most often quoted when people insist homosexuality has been "proven" to be inborn.
Response: This argument is exaggerated and misleading for six reasons:
First, LeVay did not prove homosexuality to be inborn; his results were not uniformly consistent. On the surface it appears all of LeVay's homosexual subjects had smaller INAH3's than his heterosexual ones; in fact, three of the homosexual subjects actually had larger INAH3's than the heterosexuals. Additionally, three of the heterosexual subjects had smaller INAH3's than the average homosexual subject. Thus, six of LeVay's 35 male subjects (17% of his total study group) contradicted his own theory.[20]
Second, LeVay did not necessarily measure the INAH3 properly. The area LeVay was measuring is quite small-smaller than snowflakes, according to scientists interviewed when his study was released. His peers in the neuroscientific community cannot agree on whether the INAH3 should be measured by its size/volume or by its number of neurons.[21]
Third, it's unclear whether brain structure affects behavior or behavior affects brain structure. Dr. Kenneth Klivington, also of SALK Institute, points out that neurons can change in response to experience. "You could postulate," he says, "that brain change occurs throughout life, as a consequence of experience."[22] In other words, even if there is a significant difference between the brain structures of heterosexual and homosexual men, it is unclear whether the brain structure caused their homosexuality, or if their homosexuality affected their brain structure.
In fact, one year after LeVay's study was released, Dr. Lewis Baxter of UCLA obtained evidence that behavioral therapy can produce changes in brain circuitry, reinforcing the idea that behavior can and does affect brain structure.[23] Therefore, even if differences do exist between the INAH3's of homosexual and heterosexual men, it is possible that the diminished size of the homosexual's is caused by his behavior, rather than his behavior being caused by the INAH3's size.
Fourth, LeVay was not certain which of his subjects were homosexual and which were heterosexual. Dr. LeVay admits this represents a "distinct shortcoming" in his study. Having only case histories on his subjects to go by (which were by no means guaranteed to provide accurate information about the patient's sexual orientation), he could only assume that, if a patient's records did not indicate he was gay, he must have been heterosexual.
Yet 6 of the 16 reportedly heterosexual men studied had died of AIDS, increasing the chances their sexual histories may have been incompletely recorded.[24] If it is uncertain which of LeVay's subjects were heterosexual and which were homosexual, how useful can his conclusions about "differences" between them really be?
Fifth, LeVay did not approach the subject objectively. Dr. LeVay, who is openly homosexual, told Newsweek that, after the death of his lover, he was determined to find a genetic cause for homosexuality or he would abandon science altogether. Furthermore, he admitted, he hoped to educate society about homosexuality, affecting legal and religious attitudes towards it.[25] None of which diminishes his credentials as a neuroscientist. But his research can hardly be said to have been unbiased.
Sixth, the scientific community did not by any means unanimously accept Dr. LeVay's study. Comments from other scientists in response to LeVay's work are noteworthy. Dr. Richard Nakamura of the National Institute of Mental Health says it will take a "larger effort to be convinced there is a link between this structure and homosexuality."[26] Dr. Anne-Fausto Sterling of Brown University is less gentle in her response:
My freshman biology students know enough to sink this study.[27]
Dr. Rochelle Klinger, at Psychiatrist at Medical College of Virginia, doubts we will "ever find a single cause of homosexuality."[28] And Scientific American sums up the reason many professionals approach the INAH3 theory with caution:
LeVay's study has yet to be fully replicated by another researcher.[29]
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