In Search of the ‘Gay gene’: The Genetic Components of Sexual Orientation

The phenomena of homosexual attraction have puzzled theologians, philosophers, and scientists for centuries. For decades, scientists were of the opinion that sexual orientation was a pattern of behavior that developed through interaction with one's social environment. Psychoanalyst thinkers attributed homosexual ‘deviance’ to the absence of a father figure, or overattachment to one’s mother during childhood. Others, who were of the belief that homosexuality was a learned trait, maintained that it could be ‘unlearned’ through proper interventions like aversion therapy. However, the collective failure of such conversion therapies has shown that sexual orientation is an innate trait that persists throughout one’s lifetime. But if the true cause of sexual orientation does not lie in one’s upbringing or environment, then how does it come about? This question has led researchers to assume that there is a gene that determines sexual orientation.

Dean Hamer, a geneticist working at the U.S National Cancer Institute, was interested in solving the puzzle of whether sexual orientation was shaped by nature or nurture. Earlier, a psychologist by the name of J. Micheal Bailey had attempted to demonstrate a genetic cause for homosexuality by recruiting 110 male twin pairs in which at least one twin was gay. Bailey’s hypothesis was rather simple- if he could show that more identical twins were concordant for homosexuality than fraternal twins, he could prove that homosexuality was an inherited trait. The results were largely in his favor- nearly 52 percent of monozygotic twins were concordant for homosexuality.

Inspired by the study, Hamer would soon conduct his own. By collecting the information of family members of nearly 114 gay participants and by constructing elaborate family trees, Hamer was able to observe that gay men tended to have maternal uncles who were gay, but no paternal ones. For a geneticist like Hamer, this implied that the gene which determined homosexuality had to be carried by the X chromosome. In other words, male homosexual orientation was an X-linked trait. By conducting genetic linkage analysis, Hamer was able to narrow down the location of this gene to a stretch of the X chromosome called Xq28.

While Hamer’s findings received enormous media attention, he did not exactly discover the gay gene. Rather, he merely demonstrated that one of the many genes that played a role in the development of male homosexuality was located somewhere on the X chromosome. Additionally, further studies reveal that multiple genes are involved in sexual orientation. For instance, a study conducted in 2019 by researchers at the Broad Institute of MIT and Harvard analyzed the DNA of nearly 500,000 participants from the UK Biobank and found five genetic variants associated with same-sex sexual behaviour. However, these genetic variants only accounted for a small percentage of the overall variation in sexual behaviour and did not predict sexual behaviour with great accuracy.

Another limitation of these studies is that they fail to take epigenetic factors into consideration. Epigenesis means development resulting from ongoing, bidirectional exchanges between heredity and all levels of the environment. The degree to which certain genes find expression is dependent on environmental factors. Scientists posit prenatal androgen as a potential cofactor in the development of sexual orientation as it has been repeatedly linked to sex-typed behaviours in infants.

But perhaps the most staggering limitation is the lack of scientific literature on the nature and development of female homosexuality.

So what do we know so far about sexual orientation?

While we are yet to discover the exact genes responsible for homosexual orientation, we do know for a fact that a major part of it is genetically determined. As a result, sexual orientation is immutable- it cannot be changed. It is written into the very biology of the individual. The current consensus within the scientific community is that sexual orientation is the result of a complex interplay of genetic and environmental factors.

References:

1. Dean Hamer. (n.d.). Wikipedia. Retrieved April 14, 2023, from https://en.wikipedia.org/wiki/Dean_Hamer

2. Colapinto, J. (2006). As Nature Made Him: The Boy Who Was Raised as a Girl. HarperCollins.

3. Mukherjee, S. (2016). The Gene: An Intimate History. Scribner.

4. Mullen, J. (n.d.). Prenatal hormones and sexual orientation. Wikipedia. Retrieved April 14, 2023, from https://en.wikipedia.org/wiki/Prenatal_hormones_and_sexual_orientation