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Analysis of the Biological Studies Behind Homosexuality

By: Andres del Castillo

Homosexuality has been recorded and observed since the beginning of human civilization. Ancient Assyrian texts from Mesopotamia contain prayers blessing same-sex relationships, the ancient Hindu Kama Sutra discusses sexual rituals between homosexual males, and the Etero and Marind-anim people of the South Pacific celebrated homosexuality and viewed heterosexuality as sinful. This overarching theme of homosexuality throughout history poses an interesting question: What can we learn from homosexuality? What studies have been completed to find its meaning and purpose that lies in question?

After homosexuality was completely repealed in 1987 from the DSM-III-R, many scientists began to question what more could be found from the depths of human sexuality. Geneticist G Dörner from the Humboldt University of Berlin in 1988 wrote the scientific article titled "Neuroendocrine response to estrogen and brain differentiation in heterosexuals, homosexuals, and transsexuals” stating the hypothesis that male homosexuals have a cranial structure similar to a female brain.

However, a study by Dr. Swaab of the Netherlands Institute of Technology in 1990 refuted Dörner's hypothesis. Swaab and his team performed brain autopsies on 34 subjects who passed from AIDS, out of which ten identified as homosexual men and six identified as heterosexual men. A control group of six heterosexuals, with four being men and two being women who also died due to AIDS, was used. To reduce bias, only after all measurements were taken was it established through medical records whether the subject identified as heterosexual or as homosexual. Dr. Swaab and his team discovered a key difference between the size of the suprachiasmatic nucleus.

Swaab found that the homosexual group contained 2.4 times as many SCN cell numbers compared to the SCN cell numbers from the heterosexual group. Studies have found that females have significantly fewer SDNs than males. In Dr. Swaab's study, the SDN cell count was virtually identical between homosexuals and heterosexual subject groups, refuting Dörner's claim that homosexuality correlates with the female brain.

The long-standing issue of similarities between the homosexual neural anatomies to the heterosexual woman had been eliminated with Swaab's study, not only causing ripples in research terms but in societal terms. Swaab displays this conclusion towards the end of the article, tying both the study to the recent AIDS crisis and homosexuality.

Three years after the study by Swaab, a controversial article was posted by geneticist Dr. Dean Hamer in 1993, indicating the exact location on the X chromosome for the cause of homosexuality. Hamer conducted a study where pedigrees and analyses of 114 homosexual men and their families were used. Though the 114 homosexual men were used to find a sex-transmission linkage with homosexuality, only the 40 from the population that had gay brothers were chosen to conduct a DNA analysis of their X chromosome.

Hamer found that 33 out of the 40 subjects chosen were concordant with region Xq28 of the X chromosome. Hamer writes in the abstract of the lab report on the linkage between sexual orientation and region Xq28. All of this wraps the dawn of the sexual revolution, where scientists rushed to discover the secrets behind queerness, but in Hamer and Swaab's case, homosexuality in specific.

Scientists began to inch closer and closer to the "gay gene," and with Hamer making the shocking claim of having found the region of this gene with a 99% statistical confidence level, it seemed science had solved another mystery. But the turn of the century brought a sudden stop to this revolving door of opportunity.

In a study published in the American Association for the Advancement of Science (AAAS), Professor Mills discusses the results of the 2019 international study of 480,000 genetic profiles from homosexuals in the U.K. and the U.S. This was approximately 100 times larger than any previous study on this topic, making it the largest research effort of its kind. Mills' research team was able to pinpoint five specific genetic variants that could be associated with same-sex behaviors.

These different variants had little significance in same-sex behavior among the group of homosexuals studied. These five pinpoints found from the 480,000 gay men in the U.K and the U.S. are insignificant in terms of the complexity that human sexuality offers. Not only are these specific genes minimal in the tapestry of same-sex attraction, but they are also confusing in relative terms. One gene is located in the stretch of DNA with relation to the sense of smell, making the link of the sense of smell and sexual behavior unclear. Another of the five genes is located with genes related to male baldness, which could provide answers to hormone regulation in same-sex behaviors, but still stands as a puzzling discovery.

Throughout the last thirty-three years, the idea surrounding queerness has changed. Fortunately, due to the twentieth century thinking of Dörner, Swaab, and Hamer and the twenty-first-century findings of Mills and Ganna, societal and scientific views of the causes and importance of homosexuality in the threads of nature have shifted. But we must not mistake queerness in general as a new concept, as it is etched in ancient Mesopotamian texts, sung in the praises of the South Pacific winds, and read in Sanskrit in the Kama Sutra. Though we cannot pinpoint a single strand, gene, or loci as the cause of homosexuality, scientists must keep investigated and questioning, as all of history has waited to witness this moment.


1. Dean H. Hamer, Charles A. Thomas. A Linkage Between DNA Markers on the X Chromosome and Male Sexual Orientation. Science. 1933.

2. D.F. Swaab, M.A. Hofman. An enlarged suprachiasmatic nucleus in homosexual men. Brain Research. 1990.

3. Günter Dörner. Neuroendocrine response to estrogen and brain differentiation in heterosexuals, homosexuals, and transsexuals. Archives of Sexual Behavior. 1988.

4. Melinda C. Mills. How do genes affect same-sex behavior? Science. 2019.


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