Simon Le Vay - INAH3 Research

INAH3 Research

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."