What Does Science Say

About Homosexuality?

Some theories on sexual development claim that homosexuality is developed after birth as a result of a person’s environment. Environmental factors such as a child's relationship to his same-sex parent or peers, and the presence of sexual abuse or molestation can affect sexual development (See Questions & Answers). While other theories have suggested that homosexuality is genetic and can be traced to a specific gene.

Most researchers, by this time, have come to the conclusion that sexual orientation is likely determined by a complex interaction between a person’s genetic make-up and their environment. However, there are still some who claim that science has found a “gay gene.” Let’s take a look at the research that’s been done to try and find a genetic cause for homosexuality.

The three most well-known scientific studies were conducted by Simon LeVay, whose study claimed to have found a “difference in hypothalamic structure between heterosexual and homosexual men”2; Bailey and Pillard, who studied the prevalence of homosexuality among biological twins and adopted brothers3; and Dean Hamer, who claimed to have found a “linkage between DNA markers on the X chromosome and male sexual orientation.”4 Interestingly, all of these researchers, except 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.5)

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. He then suggested that the size of this group of neurons, called the INAH3, might have something to do with sexual behavior. However, he 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.6

Some of LeVay’s peers questioned his research, noting that changes in brain structure could be the result of homosexual behavior, rather than the cause. Dr. Kenneth Klivington stated:

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 behavior and environmental conditions.7

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.

As we mentioned above, environmental factors can can impact sexual development. Therefore it would be impossible for Dr. Bailey and Dr. Pillard to determine whether it was genetics or environment that caused the twins’ homosexuality unless the twins were separated. In fact, biologist Anne Fausto-Stirling of Brown University stated: “In order for such a study to be at all meaningful, you’d have to look at twins raised apart.”8

Furthermore, if it was, in fact, genes and not environment which caused the twins homosexuality, one would expect 100% of identical twins to both be homosexual, instead of 52%.

Dr. Bailey seemed to agree, he wrote:

There must be something in the environment to yield the discordant twins.9

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% were both homosexual and, of the men they studied, only 20% 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.”10

Dean Hamer

Dean Hamer of he National Cancer Institute studied forty pairs of homosexual brothers and found that thirty-three of the brothers had the same pattern at the tip 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.

Like the Simon LeVay study, it is hard to determine whether the changes in brain structure were the result of homosexual behavior, or the cause.

George Ebers of the University of Western Ontario attempted to replicate Hamers 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.11

Dr. Hamer, upon completing his study, wrote:

These genes do not cause people to become homosexuals…the biology of personality is much more complicated than that.12

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,13 and the Associated Press wrote Study Finds Genetic Link to Homosexuality.14

The American Psychiatric Association

The Diagnostic and Statistical Manual, also known as the DSM, is the official list of mental disorders that all mental health professionals refer to when diagnosing patients.

The first version, released in 1952, listed homosexuality as a sociopath personality disturbance. In 1968, the second version (DSM II) reclassified homosexuality as a sexual deviancy. Soon afterward, gay protestors began picketing at the APA’s annual conventions, demanding that homosexuality be removed from the list completely. In 1973, after intensive debate and numerous disturbances by gay activists, the APA decided to remove homosexuality from it’s next manual (DSM IV) completely.

What followed was a swarm of outrage from psychiatrists within the APA who disagreed with the decision and demanded that the issue be reconsidered. In 1974, a referendum was called and approximately 40 percent of the APA’s membership voted to put homosexuality back into the DSM IV. Since a majority was not achieved to reverse the decision, homosexuality remains omitted from the APA’s Diagnostic and Statistical manual.

Many in the scientific community have criticized the APA’s decision to remove homosexuality from the DSM IV, claiming it’s motives were more political than scientific. Dr. Ronald Bayer, author of the book, Homosexuality and American Psychiatry writes:

The entire process, from the first confrontation organized by gay demonstrators to the referendum demanded by orthodox psychiatrists, seemed to violate the most basic expectations about how questions of science should be resolved. Instead of being engaged in sober discussion of data, psychiatrists were swept up in a political controversy. The result was not a conclusion based on an approximation of the scientific truth as dictated by reason, but was instead an action demanded by the ideological temper of the times.15

Along these same lines, a recent radio documentary on the subject of homosexuality revealed that the President-elect of the APA in 1973, Dr. John P. Speigel, was a “closeted homosexual with a very particular agenda.”16

Some have exaggerated or misrepresented these studies in attempt to prove that homosexuality is genetic. Others insist that homosexuality is developed after birth as a response to one’s environment. The truth is that we have no conclusive replicable research to prove either conclusion. However, most researchers have come to the conclusion that sexual orientation is likely determined by a complex interaction between a person’s genetic make-up and their environment.

Even the American Psychological Association asserts that:

There are numerous theories about the origins of a person's sexual orientation; most scientists today agree that sexual orientation is most likely the result of a complex interaction of environmental, cognitive and biological factors. In most people, sexual orientation is shaped at an early age.17 (emphasis added).

And the American Psychiatric Association wrote:

Currently there is a renewed interest in searching for biological etiologies for homosexuality. However, to date there are no replicated scientific studies supporting any specific biological etiology for homosexuality.18

Whatever the case, we know from the personal testimonies of thousands that homosexuality is a changeable condition. Stanton Jones, who is Chair of Psychology at Wheaton College states: “Every secular study of change has shown some success rate...”19

2 “A Difference in Hypothalamic Structure Between Heterosexual and Homosexual Men,” Science, August 30, 1991, p. 1034. 3 Archives of General Psychiatry #48, 1991, p. 1089. 4 Science, 261, July 16, 1993, p. 321. 5 “A Difference in Hypothalamic Structure Between Heterosexual and Homosexual Men,” Science, August 30, 1991, p. 1034. 6 “Sex and the Brain” Discover, March 1994, Vol. 15, No. 3, p. 64. 7 “Born or Bred?” Newsweek, February 24, 1992, Vol. 119, no. 8, p. 46. 8 “What Causes People to Be Homosexual?” Newsweek, September 9, 1991, vol. 118, no. 11, p. 52. 9 “Born or Bred?” Newsweek, February 24, 1992, Vol. 119, no. 8, p. 46. 10 www.drthrockmorton.com. 11 Scientific American, November 1995. 12 “The Personality Genes,” Time, April 27, 1998, Vol.151, no. 16, p. 60. 13 “Research Points Toward a Gay Gene,” The Wall Street Journal, July 16, 1993, p. B1. 14 “Study Finds Genetic Link to Homosexuality,” Des Moines Register, July 16, 1993, p. 6A. 15 Ronald Bayer, Homosexuality and American Psychiatry: The Politics of Diagnosis (New York: Basic Books, 1981), pp. 3-4. 16 Alix Spiegel, 81 Words, radio production for National Public radio. 17 From the APA's booklet, "Answers to Your Questions About Sexual Orientation and Homosexuality." 18 American Psychiatric Association Fact Sheet, May 2000. 19 “The Loving Opposition: Speaking the truth in a climate of hate,” Christianity Today, July 19, 1993, Vol. 37, no. 8, p. 18.

Last Updated 4-4-06

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