No single gay gene linked to same-sex behavior, says study

Same-sex sexual behavior is similar to other personilty traits such as one’s height and is shaped by a combination of multiple factors such as genes, environment, and culture

                            No single gay gene linked to same-sex behavior, says study
(Getty Images)

There is no single gene that can predict whether a person will be gay or not, a study has found. An international group of scientists examined whether there are any connections between our genetics, same-sex sexual behavior, and other human traits like personality. They found that same-sex sexual behavior is similar to other traits such as height, in that there are many different factors that play important roles. In other words, it is not going to possible to predict an individual’s same-sex sexual behavior through genetics.

The researchers could not find any patterns among genetic markers - also called variants, they are bits of DNA that vary from person to person - that could be used to meaningfully predict or identify a person’s sexual behavior.

“There is no single gay gene that is linked to same-sex behavior,” says the study published in Science.

The team found about a third of the differences between people in their sexual behavior could be explained by inherited genetic factors, but the environment also plays a significant role in shaping these differences. The findings suggest same-sex sexual behavior is influenced by a complex mix of genetic and environmental influences, similar to what is seen for most other human traits. 

Among the millions of genetic markers, the researchers were able to identify, for the first time, five genetic markers, that they could link with high confidence to sexual behavior.

However, they say, since there are so many genetic markers, each with small effects, it is impossible to predict from someone’s DNA who they will be attracted to. At the same time, says the team, it is also clear from the study that sexuality is not a choice, and that it is both biology and environment working together in ‘incredibly’ complicated ways. 

According to Benjamin Neale, Institute Member at the Broad Institute of MIT and Harvard, what this study does is disprove the notion that there is a so-called gay gene, and disproves the notion that sexual behavior is a choice.

“There is no single gay gene, and we cannot predict whether someone will have a same-sex partner. We find that diversity of sexual behavior is a part of normal variation in people. It is shaped by our genes, our culture, and our environment. Five genes reach statistical significance, but they capture only a tiny fraction of the variation. At the same time, it is also clear that being gay is not a choice. Genetics absolutely plays an important role. Many genes are involved, and altogether they capture perhaps a quarter of same-sex sexual behavior. That means genetics is not even half the story. The rest is likely environmental, but even there, it is not simple at all,” says Neale.

The reseaechers say that if people were worried that something like genetic testing or genome editing might one day be a threat to the LGBTQ community, the study is reassuring.

“The genetics are just too complicated, and biology and environment are both involved. In that sense, what we are reporting here is evidence that the biology and environmental factors all work together to contribute to sexual diversity,” says Neale.

Why this study?

The study was done by a group of scientists from universities and research institutes in the UK, the US, the Netherlands, Australia, Sweden, and Denmark, who were interested in studying the genetics of sexuality. They designed this study to better understand the diverse set of factors that may contribute to sexual behavior.

The researchers wanted to find genetic markers associated with same-sex sexual behavior. They used information from nearly half a million research participants who contributed DNA and answered questions about their sexual behavior to several large-scale research projects or direct-to-consumer genetic companies.

“Some people are attracted to men, some people are attracted to women, and some are attracted to both. So why do we differ? We tried to answer this question by looking at the role of genetics in shaping sexual behavior. We combined several large studies which included 477,522 individuals and millions of genetic markers. Participants in the study answered questions like - "Have you ever had sex with someone of the same sex?” or “To whom are you sexually attracted?” The responses were then connected to genetic markers, via a method called a genome-wide association study or GWAS,” say the researchers.

They add: “Ours is not the first study to look for genetic markers of same-sex sexual behavior or orientation. However, past studies had too few people participating and often looked at too few DNA markers to draw any reliable and reproducible conclusions. This is the largest and most thorough investigation into the genetics of same-sex sexual behavior to date and it really provides the clearest glimpse yet into the genetic underpinnings of same sex sexual behavior.”

What did the study find?

While the researchers discovered five genetic markers that were associated with same-sex sexual behavior, thousands more appear to also be involved. Further, each marker has a very small effect individually - that is, each contribute very little to a person’s sexual behavior. Hence, genetic variants alone do not define someone’s sexual behavior, says the team. 

“This is not unusual for complex human outcomes. Common genetic variants (typically defined as variants that appear in at least 1% of the population) often contribute only a tiny amount to the variation in the overall outcome,” says the study.

It says, “Behavioral traits, like sexual behavior and orientation, are only partially genetic in nature. They are shaped by hundreds or thousands of genetic variants, each with a minimal effect, yet they are also shaped in large part by a person’s environment and life experiences. We can, therefore, say with confidence that there is neither a single genetic determinant of nor single gene for same-sex sexual behavior or sexual orientation. To the extent that sexuality is influenced by genetics, it is more likely that hundreds or thousands of genetic variants are involved. These variants, together with the environment and experiences, shape outcomes like same-sex sexual behavior.” 

The team says when they analyze all common genetic markers together, they capture between 8 and 25% of the individual differences in same-sex sexual behavior. These results suggest that more markers will be discovered with larger sample sizes.

While many of the same genetic markers influence same-sex sexual behavior in females and males, the study also found some markers with sex-specific effects. “40% of the genetic influences on same-sex sexual behavior were shared by both sexes, and approximately 60% were unique for each sex. This may reflect differences in the biology of same-sex sexual behavior in females and males or maybe the result of the different gendered and socialized contexts for expressing sexuality for females and males. However, this is a noteworthy finding, as the genetic overlap between females and males for most traits is usually much higher than this,” says the study.

Are the researchers concerned the findings may be misinterpreted? 

According to Neale, it is likely that some people will misunderstand or even deliberately twist their findings. “There is a long history of people using genetics in harmful ways, to advance their own misguided agendas. As a gay man, I have experienced homophobia, and I felt both hurt and isolated by it,” he says.

The researchers are particularly worried that people will misrepresent our findings about mental health. Results show that genes that play a role in same-sex sexual behavior partly overlap with those for several other traits, including openness to experience and risk-taking behavior. 

The researchers also found genetic overlap with some health-related behaviors, for example,  smoking, cannabis use, and with risks for certain psychiatric conditions - schizophrenia, bipolar disorder, and major depression.

“We found evidence of genetic overlap between same-sex sexual behavior and some mental illnesses, including depression and bipolar disorder. But one does not cause the other. In fact, there is evidence that as society becomes more welcoming, mental health improves for members of the LGBTQ community, and that is really encouraging,” says Neale. 

The results, caution the researchers, in no way, promote or justify discrimination based on sexual identity, attraction, or behavior. “Our findings should not, in any way, be interpreted so as to imply that the experiences of LGBTQ individuals are “wrong” or “disordered.” In fact, this study provides further evidence that diverse sexual behavior is a natural part of overall human variation. Our research is intended to improve our understanding of the genetic basis of same-sex sexual behavior. It should not be misconstrued to disparage LGBTQ people,” say the researchers.

The team explains that there are reasons why same-sex sexual behavior and other traits may share genetic markers. For example, it could be that one trait leads to another through the influences of environmental factors. “For instance, a member of the LGBTQ community may experience prejudice and discrimination based on their sexual orientation and behavior, which would increase their risk for depression. In that case, what might appear to be a genetic association is actually one that is driven by the environment,” the findings state. 

The findings, say the researchers, provides further evidence that diverse sexual behavior is a natural part of overall human variation. (Getty Images)

For the study, the researchers engaged with the LGBTQ community and advocacy groups. According to the team, these interactions changed the way that they approached the study, and the way they communicated their findings.

“Not everyone thinks this research was a good idea. I totally understand that. We heard from a lot of people who raised valid concerns. We felt like these connections were going to be drawn soon anyway, and it is important that we tried to get the science and the community engagement right. A key takeaway is that engaging with the community strengthens the quality of research, affirming that science should not be done in isolation,” says Neale. 

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