Are there physical differences in the brain structure of heterosexual and homosexual people?
Kenneth M. Cohen, PhD, Lecturer in Human Development at Cornell University, in his 2002 article, "Relationships Among Childhood Sex-Atypical Behavior, Spatial Ability, Handedness, and Sexual Orientation in Men," published in the Archives of Sexual Behavior, that:
"A growing body of empirical literature suggests that the brains of gay males are less masculinized than those of heterosexual males, reflected in visual-spatial task performance -- a measure of cerebral masculinazation and one in which heterosexual males usually surpass females.
Several studies report that the cognitive performance of gay males is more typical of heterosexual females than heterosexual males.
Furthermore, the brain waves of gay males while performing verbal and spatial tasks are more similar to heterosexual females than males or significantly different from both."
Dick Swaab, MD, PhD, former Director of the Netherlands Institute for Brain Research, et al., published a 1995 research study, "Brain Research, Gender, and Sexual Orientation," in the Journal of Homosexuality, that stated:
"[I]n a sample of brains of homosexual men we did find that an area of the hypothalamus called the suprachiasmatic nucleus (SCN) contains twice as many cells as the SCN of a heterosexual group...
It appears very unlikely that homosexual behavior as such would increase the neuronal number in any brain structure. Yet the development of SCN cell numbers suggest that the explanation for the large SCN in homosexual men most likely may be found in early brain development.
At birth, the SCN contains only 13-20% of the adult number of cells, but in the postnatal period development is rapid. Cell counts reach a peak around 13-16 months after birth. The SCN cell numbers found in adult homosexual men were in the same order of magnitude as found around 13-16 months after birth. The normal pattern is that the cell numbers decline to the adult value of about 35% of the peak values.
In homosexual men, therefore, this postnatal cell death in the SCN seems to have been curtailed."
Laura S. Allen, PhD, Assistant Researcher, and Roger A. Gorski, PhD, Professor, in the Laboratory of Neuroendocrinology at the David Geffen School of Medicine at the University of California at Los Angeles (UCLA), wrote in their 1992 article "Sexual Orientation and the Size of the Anterior Commissure in the Human Brain," published in the Proceedings of the National Academy of Sciences:
"The anterior commissure, a fiber tract that is larger in its midsagittal area [the vertical plane that divides the brain into two halves] in women than in men, was examined in 90 postmortem brains from homosexual men, heterosexual men, and heterosexual women. The midsagittal plane of the anterior commissure in homosexual men was 18% larger than in heterosexual women and 34% larger than in heterosexual men."
William Byne, MD, PhD, Director of the Laboratory of Neuroanatomy and Morphometrics at Mount Sinai School of Medicine, wrote in his 1995 article "Science and Belief: Psychobiological Research on Sexual Orientation," published in the Journal of Homosexuality, that:
"The search for anatomical sex differences in the brain has a long history of producing results that were consistent with the researchers' biases but were ultimately discredited by their inability to be replicated...
Even though reports of structural sex differences abound, the only structural sex difference in the human brain that has proven to be consistently replicable is the dimorphism in its overall size, which is large in men; the extent to which this difference is simply in proportion to the sex difference in body size is controversial."
Joe Sartelle, Webmaster for the Office of Undergraduate and Interdisciplinary Studies (UGIS) at the University of California at Berkeley, wrote in his May 14, 1994 article, "Rejecting the Gay Brain (and Choosing Homosexuality)," in the magazine Bad Subjects, that:
"The most famous of all the 'gay brain' studies must surely be the research of Simon LeVay, who claimed that he discovered a modest but significant difference in the size of an already tiny section of the brain, the hypothalamus, in a group of dead straight and gay men...
The many serious flaws in LeVay's research and conclusions have been pointed out repeatedly, as have the tentative and problematic nature of the other work that has been done on identifying the biological causes of homosexuality. For example, there was no way to tell from the brains LeVay studied whether the differences in brain structure were the cause or the effect of homosexual behavior.
Moreover, there was no verifiable way to determine the men's actual sexual behavior, since they were dead by the time the research was done -- the assumption was simply made that the ones who died from HIV infection were homosexuals..."
Neil Whitehead, PhD, Scientific Research Consultant, wrote on his website "Homosexuality and Science: A Scientific Look at Homosexuality" (accessed Jan. 26, 2006), that:
"Scientists have barely been able to distinguish between the microstructure of male and female brains in adults, let alone between male homosexual and female brains. Attempts to prove such a similarity have been unconvincing.
Male and female brains appear identical at birth, and the only consistently replicable difference, from about age two or three, is their size. Most of the development of the human brain takes place after birth in response to stimuli, learning, and experience. The brain changes so much in response to learning and repeated human behaviors that this could probably account for any differences between homosexual and heterosexual brains which might be ultimately discovered."