The science behind sexuality: is there a gay gene?

Matthew King explores the research behind sexuality's origins

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When I first realised I liked both men and women, I remember scouring the internet for what it all meant. Was I sick? Were my feelings normal? I recall taking a questionnaire to help me find the answer to all these questions. Alas, I never found any. To this day, I still find defining my sexuality difficult. Some small part of this has been the debate of nature versus nurture – are people born gay or is it picked up when growing up? Despite having absolutely no scientific background except two A’s in Science GCSE, I firmly believe that people are born the way they are; love cannot be learnt (as romcom-like as that sounds!) Despite my own beliefs, I will look into some recent and past studies around this to hopefully shed some light on this issue.

Whilst the strive for more acceptance of the LGBTQ+ community has happened more recently in our history, the majority of research concerning homosexuality’s nature or nurture debate happened in the late 20th century. As set out in science, one such study from 1993 used a genetic analysis of 40 pairs of gay brothers to uncover a zone on the X chromosone that could contain a gene or genes for homosexualty. Dean Halmer, and the rest of his team, researched specifically male homosexuality. They recruited 76 men and compared their genes with their family’s history of homosexuality. Interestingly, when the researchers looked deeper into the family trees of the men, they found that there were more gay relatives on the mothers’ side of the family and that homosexuality was more common among maternal uncles and cousins from the mothers’ side. This could suggest that you’re gay because of your mother’s side of the family, which could mean that the ‘gay gene’ is found on the X chromosone, which is inherited excluisively from your mother.

To study this further, the researchers underwent gene linkage analysis on the 40 pairs of brothers. They did this because, on average, each pair of brothers will have about half their DNA on their X chromosomes in common. If men are gay because of a gene inherited from the mother, then this must lie in the shared sections of the chromosome which this type of analysis can find. If a shared section is found, then it could contain the ‘gay’ gene. When the researchers did this, they found that 33 out of 40 pairs shared a set of five markers located in the X chromosome – the shared areas which may contain the gene behind homosexuality. The researchers stated that it is unlikely that this is due to merely chance and that the linkage has a technical measure off 99.5 percent certainty that there is a gene or genes in this area that predisposes a man to be gay. Hamer stated that this cannot explain all homosexuality, however, as he saw some traits which were passed paternally and some brothers did not share the set of genes on their X chromosome. Therefore, he concluded that homosexuality seems to have a “variety of causes, genetic and perhaps environmental as well.”

A similar study to Hamer’s, by Michael Bailey of Northwestern University, had similar findings with the comparative study of brothers. He found that half of the identical twins of gay men were also gay themselves, which could further suggest that homosexuality is coded into family genetics, not environmental factors.

However, these studies do have their weaknesses, such as small sample sizes, and that they are almost 30 years old now. Additionally, their approach to this question seems to be plagued with homophobic undertones, with the article in question comparing the study of genetic disorders with the genetic makeup of sexuality.

Despite their age, and potentially damaging implications, these studies are reinforced by some more recent research. Again, as published in Science, Andrea Ganna, a research fellow with the Broad Institute in Cambridge, Massachusetts and Harvard Medical School in Boston, examined hundreds of thousands of DNA samples and behavioural information. Their study analysed the DNA markers of those who answered ‘yes’ to the question: ‘have you ever had sex with someone of the same sex?’ Overall, 450,939 people said their sexual encounters had been solely heterosexual and 26,890 people reported at least one homosexual experience.

After they had this information, the researchers performed a genome-wide association study to look for specific variations in DNA that were common in those who had answered ‘yes’ to the previous question. They found four variants on chromosomes seven, 11, 12 and 15. Interestingly, one variant on chromosome 11 sits in a region rich with the receptors that register smell, which Ganna suggested may play a role in sexual attraction. This study was more thoughtful than Hamers’, as the team behind it regularly met and consulted with members of the LGBTQ+ community. Despite this, there are still worries that such studies of homosexuality could lead to further stigmatisation of homosexuality, with Nicole Ferraro and Kameron Rodrigues from Stanford University arguing that “ the study didn’t do enough to explore the nuances of how one’s sexual identity differs from sexual behavior ”.

Overall, Ganna’s findings emphasise the fact that human sexual behaviour is a complex issue which cannot be attributed to one single ‘gay gene’. Instead, Ganna argues that ‘“nonheterosexuality” is in part influenced by many tiny genetic effects.

From the the small number of studies I have explored here, I think it is safe to say that no one knows where homosexuality comes from – perhaps this is a good thing. To begin to disseminate and reduce LGBTQ+ individuals to genes and chromosomes leads to further alienating us from the rest of humanity. What these studies show is that, even the most intelligent among us conclude that, there is no one thing which makes up a person –  we are all made up of millions of different components. So, whether being gay is nature or nurture, some things will always be the same. Gay people exist and cannot be reduced to their sexuality.

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