A new study seems to firmly bury the idea of a so-called “gay gene.” Scientists looked at the genes of nearly a half million people and couldn’t find any genetic variations that could reliably predict someone’s same-sex behaviour. Rather, they argue, our sexual preferences are influenced by a complex mix of our genes, environment, and life experiences.
The international research team, which includes scientists from Sweden, Denmark, the UK and the U.S., looked at genetic data collected from earlier studies and projects, including from the consumer DNA testing company 23andMe. In total, just over 470,000 people were included.
The researchers performed a type of analysis known as a genome-wide association study. These studies sweep through the genomes of people and look for any variations in genes — also called markers — that could be linked to whatever other variables they’re testing for. In this study, that variable was whether a person had reported ever having sex with someone of the same sex.
“This study is the largest and most thorough investigation into the genetics of same sex sexual behaviour to date,” said study author Ben Neale, director of genetics in the Stanley Centre for Psychiatric Research at the Broad Institute of MIT and Harvard University, in a press conference on Wednesday. The study was published Thursday in Science.
All told, there were five markers that were “significantly” associated with same-sex behaviour. That means that these genetic markers were found often enough in people with a history of same-sex behaviour that they could be a relevant contributor. But if even someone had all these markers at birth, the authors estimated, they would be less than 1 per cent more likely to someday report same-sex behaviour than someone born without them.
Neale and his team’s research doesn’t suggest that genes play no role in our sexual orientation, though. There are likely thousands of other common genetic markers that might affect sexuality, they noted. But the influence is so small on an individual level that it would take studying many more people to find them.
The authors estimated that all of these markers — the five found in their study and the many more still unknown — could account for 8 to 25 per cent of the variation found in whether someone will engage in same-sex behaviour.
But according to Neale, the findings “also underscore an important role for the environment in shaping human sexual behaviour and perhaps most importantly [that] there is no single gay gene but rather the contribution of many small genetic effects scattered across the genome.”
The authors and their respective institutions took great pains to make sure their study would be carried out responsibly. 23andMe, for instance, asked customers for consent to be included in this specific dataset, separate from the permission asked for general research purposes. The nature of the study, which involves de-identified data and confidential surveys, should also mean that no one can figure out the identity of a volunteer or their stated sexual orientation.
The authors also corresponded with LGBTQ alliance and advocacy groups before publication, which led them to emphasise some important caveats to their study.
Because they only relied on self-reported sexual behaviour, for instance, they might be missing some people attracted to the same sex but who have never acted on it or who don’t feel comfortable disclosing that history. And while someone may have had sex with someone of the same sex, that doesn’t necessarily mean they identify as gay or lesbian, so the authors refrained from using those sorts of terms.
Another limitation of the study is that it only includes people whose assigned-at-birth sex and self-reported gender match, meaning there’s nothing these results can say about people who are transgender or non-binary. The data is also drawn entirely from people of European ancestry, so there’s no telling whether the same specific mix of genetics and environment would play out among other groups when it comes to sexual orientation.
These qualifications aside, the study might upturn another common narrative about sexual behaviour. Some of the datasets let them look at more specific behaviours, such as how many partners people had of either sex. And the authors found that there was little overlap between the genetic influences behind whether someone had ever engaged in same-sex behaviour and the degree to which they had same-sex partners (i.e, having sex mostly or exclusively with the same sex).
In other words, the authors said, there’s no evidence on a genetic level that “the more someone is attracted to the same sex, the less they are attracted to the opposite sex.” Common measures of sexual orientation, such as the Kinsey Scale, rely on that simple continuum, but the findings seem to show our sexual preferences are more complicated than that.
And while genes may only be part of the puzzle, the authors did find some connection between sexual orientation and other personal aspects that merit further study.
In men, for instance, some of the markers found also seem to influence their chances of baldness, which indicates that sex hormones could play a role in both traits. Another marker was linked to sense of smell, though it’s less clear what that connection could mean. And only around 50 per cent of the markers, such as those linked to risk-taking, were found in both men and women, suggesting that different genetic influences affect different genders.
All of these leads are worth exploring in the future. But the most important takeaway from the study is that it should further dispel the harmful narrative of same-sex behaviour being an aberration to be identified and presumably cured—one that’s been fuelled by flawed or cherrypicked genetic research. Like so many things about people, the authors noted, our sexuality is nuanced and influenced by everything that surrounds us. But it’s also perfectly human.
“So overall, these findings reinforce the importance of diversity as a key aspect of sexual behaviour,” Neale said.