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Genes Can’t Predict Same-sex Sexual Behavior, Large-Scale Study Shows

Senior author Ben Neale discusses the key takeaways from the Science study. | Broad Institute of MIT and Harvard

A person's genetic makeup cannot be used to predict whether they will engage in same-sex sexual behavior, according to an August 30 Science report — the largest, most thorough analysis into the genetics underlying same-sex sexual behavior to date.

Instead, same-sex sexual behavior — similar to what's seen for most other human traits — is influenced by a complex mix of genetics and environment, with genes playing a relatively smaller role.

"This study shows there is no single 'gay gene,'" said author Ben Neale, a member of the Broad Institute, and an associate professor in the Analytic and Translational Genetics Unit at Massachusetts General Hospital. "To the extent that sexuality is influenced by genetics, it is more likely that hundreds or thousands of genetic variants are involved, each with a small effect. These variants, together with the environment and experiences, shape outcomes like same-sex sexual behavior."

Previous research exploring whether same-sex sexual behavior is heritable have found some evidence to support this idea. However, these studies have had too few participants and looked at too few DNA markers to draw reliable, reproducible conclusions, some researchers suggest.

The genetics of same-sex sexual behavior "is a largely understudied area of scientific research," the authors of the Science study write on a website they developed to communicate their study results, after including feedback from LGBTQ outreach and advocacy groups. "[We] have unique opportunities to contribute to the field."

The authors' opportunities came in part through access to a large amount of crowd-sourced data, provided by nearly half a million research participants who had answered questions about their sexual behavior, from platforms including 23andMe, Inc., a personal genetics company founded in 2006, and the U.K. Biobank, a large long-term study in the United Kingdom begun in the same year.

Because of the sensitivity of the topic, 23andMe, for example, asks participants in the sexual behavior survey to sign a secondary consent form, in addition to the main consent document. "The purpose [of the second form] is to specifically outline the additional benefits and potential risks associated with the survey," said author Fah Sathirapongsasuti, senior scientist at 23andMe. "We note, for example, that scientific applications of genetic associations with a specific behavior may change the way these behaviors are perceived by the public."

Sathirapongsasuti added that one of the top requests 23andMe gets from customers relates to understanding how genetics influences sexual orientation and sexual behavior.

The data he and colleagues studied came from individuals who self-reported as having engaged in same-sex sexual behavior, which is related to, but not the same as, sexual orientation and identity, the authors emphasized after their talks with LGBTQ advocacy groups.

Using genetic marker data from these individuals, the researchers performed genome-wide association studies, or analyses of differences in genes, looking for differences closely associated with same-sex sexual behavior.

Though they could not find any patterns that could be used to meaningfully predict or identify a person's sexual behavior, Neale and colleagues do report five genetic variants that were "significantly" associated with same-sex sexual behavior. However, these variants, along with thousands more, had only small overall effects on same-sex sexual behavior — under 1% collectively.

"[T]he effects are so small that this genetic score could not be reliably used to predict same-sex sexual behavior of an individual," writes Melinda Mills, the Nuffield Professor of Sociology at the University of Oxford, in a related Perspective.

The genes they found here to play a role in same-sex sexual behavior correlated with several other traits, including openness to experience and risk-taking behavior. The authors also found genetic overlap with some health-related behaviors such as smoking and cannabis use and overlap with risks for certain psychiatric conditions such as schizophrenia, bipolar disorder and major depression.

"[W]e need to be cautious about how we interpret these results, as the social environment likely has much to do with the overlap we observe," the authors write. "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."

Neale said environmental, non-genetic factors that influence behavior can range "from in utero influences to who you stand beside on the tube in the morning."

Sathirapongsasuti highlighted 23andMe's commitment to understanding biological differences among humans as part of this work. "We are committed to diversity, and sexual diversity is a part of that," he said. "We hope that this study marks the beginning of more research on this important topic."

Sathirapongsasuti, Neale and colleagues said they were motivated to do this study because the data were publicly available and they believe "it is important to do this line of work in as rigorous a way as possible."

To achieve this, the team brought together researchers across many disciplines.

"We also engaged with alliance and advocacy groups about how we could communicate this work as thoughtfully as possible to individuals who might be affected by these results," said Neale.

The authors did allude to limitations of the study, namely a focus on individuals with European ancestry, and perhaps some bias among those who opted in.

While focusing on genetics in their study, the authors emphasized that non-genetic factors are an important part of same-sex sexual behavior.

In the end, the authors say their study doesn't change the message about same-sex sexual behavior being a complex behavior. But it does underscore that there's an element of biology and one of environment, too, with the latter encompassing influences of culture, society, family or individual experiences.

"This [interplay] is a natural part of our species," said Neale. "There's no way to get away from the idea that both matter in this space."