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What Does Science Say?

I’ll outline the claims that have been made by the three most well-known scientific studies on homosexuality. The first study was conducted by Simon LeVay, whose research claimed to have found a “difference in hypothalamic structure between beterosexual and homosexual men.”

The second study was conducted by John M. Bailey and Richard Pillard, who studied the prevalence of homosexuality among biological twins and adopted brothers.

The third study was conducted by Dean Hamer, who claimed to have found a “linkage between DNA markers on the X chromosome and male sexual orientation.”

All of these researchers, except for Bailey, are self-identified gay men.

Simon LeVay

In 1991, Simon LeVay studied the brains of the cadavers of thirty-five men, nineteen of whom he believed were homosexuals and sixteen of whom he believed were heterosexuals. (LeVay told Science magazine that he had “assumed” the sexual orientation of some of his subjects.)

LeVay found a group of neurons in the hypothalamus that appeared to be twice as large in the heterosexual men as in the homosexual men. (The hypothalamus has been associated with the regulation of hormone release and reproductive behavior. It has been called the “most vital structure for motivation and emotion” in the human body.) He then suggested that the size of this group of neurons, called the INAH3, might have something to do with sexual orientation.

Note that LeVay never claimed to have found a genetic cause for homosexuality. LeVay said, upon completing his work, “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.”

Some of LeVay’s peers also questioned his research, noting that changes in brain structure could have been the result of homosexual behavior, rather than the cause. Dr. Kenneth Klivington of the Saulk Institute stated that there is a body of evidence that shows the brain’s neural networks reconfigure themselves in response to certain experiences. Therefore, the difference in homosexual brain structure may be a result of behavioral and environmental conditions.

In a study published in March of 2001, William Byne and a group of his colleagues attempted to replicate LeVay’s study but were not able to do so. The researchers said, “Although there was a trend for INAH3 to occupy a smaller volume in homosexual men than in heterosexual men, there was no difference in the number of neurons within the nucleus based on sexual orientation.”

Bailey and Pillard

J. Michael Bailey and Richard Pillard published a study in the Archives of General Psychiatry in December of 1991 on the prevalence of homosexuality among twins. They studied 56 pairs of identical twins, where at least one brother was homosexual, and found that 29 of them (52 percent) were both homosexual. They also found that 12 of 54 pairs of fraternal twins (22 percent) were both homosexual and 6 out of 57 pairs of adopted brothers (11 percent) were both homosexual. Bailey and Pillard, therefore, concluded that homosexuality has a genetic cause.

Biologist Anne Fausto-Stirling of Brown University, wasn’t so sure. She said, “In order for such a study to be at all meaningful, you’d have to look at twins raised apart.” Environmental factors such as a child’s relationship to his peers and sexual abuse or molestation can affect sexual development. Therefore, it would be impossible for Dr. Bailey and Dr. Pillard to determine whether it was genetics or environmental factors that caused the twins’ homosexuality unless the twins were separated. Furthermore, if it were genes and not environment that caused the twin’s homosexuality, one would expect 100 percent of the identical twins to both be homosexual instead of just 52 percent. Dr. Bailey seemed to agree. He wrote, “There must be something in the environment to yield the discordant twins.”

The most powerful refutation of this study, however, is the researcher’s inability to replicate his own work. In a study released in March of 2000, Dr. Bailey and a group of his colleagues used an Australian population of twins to conduct a similar twin study with even lower concordance numbers. The researchers studied the largest carefully ascertained twin sample ever assembled for such a study. They found that, for women, only 24 percent were both homosexual and, of the men they studied, only 20 percent were both homosexual.

Upon completing this study the researchers said, “Consistent with several studies of siblings, we found that sexual orientation is familial. In contrast to most prior twin studies of sexual orientation, however, ours did not provide statistically significant support for the importance of genetic factors for that trait. This does not mean that our results support heritability estimates of zero, though our results do not exclude them either.”

Dr. Warren Throckmorton, an associate professor of psychology at Grove City College who has done research on homosexuality, was taken aback by Bailey’s own admission that genetics may have no impact on sexual orientation at all. He said, “Heritability near zero? This is a pretty amazing statement! And one that no one has heard in the popular media.”

Dean Hamer

Dr. Dean Hamer of the National Cancer Institute studied forty pairs of homosexual brothers and found that thirty-three of the brothers had the same pattern at the top of the X chromosome known as the Xq28. Hamer estimated that this pattern was responsible for homosexual development in 64 percent of the brothers he studied.

As in the LeVay study, it is hard to determine whether these changes were the result of the cause of homosexual behavior.

George Ebers of the University of Western Ontario attempted to replicate Hamer’s study. He examined fifty-two pairs of gay brothers and found no connection between the pattern of the Xq28 and the homosexuality of his subjects.

Dr. Hamer himself wrote, “These genes do not cause people to become homosexuals… the biology of personality is much more complicated than that.”

What I find the most interesting about this particular study is that even after Hamer’s comments to the contrary, a few media outlets ran stories with headlines suggesting that a gay gene had been unmistakably discovered. The Wall Street Journal‘s headline read “Research Points toward a Gay Gene,” and the Associated Press wrote “Study Finds Genetic Link to Homosexuality.”

CHAD W. THOMPSON
Loving Homosexuals as Jesus Would (2004) Brazos Press: Grand Rapids, Michigan

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