The science of sexual orientation

Can genes explain sexuality? Should we even try to know?


There’s nothing new about being gay, but that hasn’t stopped scientists from trying to understand it.

Over the past two decades, many researchers have become focused on the notion of a “gay gene” — biological proof that one was “born this way.”

It makes sense: Our genes can influence who we are, and psychologists contend sexual orientation is not a conscious choice. It theoretically stands to reason there might be genetic underpinnings to who we become sexually attracted to.

But more recent research has both confirmed and debunked the notion of a genetic basis for sexual orientation. Instead of just one gene (or one marker on one gene) that determines sexual orientation, there are many genes with markers related to attraction to the same sex.

For example, in 2019, the researchers studying those markers and same-sex attraction told Inverse: “This finding suggests that on a genetic level, there is no single dimension from opposite-sex to same-sex preference.”

But that’s just part of the story.

Two new studies published Monday, one in Nature Human Behavior and the other in Scientific Reports, further illuminate the complexities of sexual orientation and how fraught scientific study of the subject is. They also highlight three key factors:

  1. Our own sexual orientation may be much more fluid than we thought.
  2. The same cluster of genes that may be associated with same-sex sexual behavior may confer some evolutionary advantage.
  3. There are inherent dangers in focusing on genetics in relation to sexual orientation.

Genes and sexual behavior — First author Brendan Zietsch, an associate professor of psychology at the University of Queensland in Australia, and colleagues attempted to discover why the genes associated with same-sex sexual behavior continue to flourish. Their study was published in Nature Human Behavior.

In a statement, the study authors report:

“Because [same-sex sexual behavior] SSB confers no immediately obvious direct reproductive or survival benefit and can divert mating effort away from reproductive opportunities, its widespread occurrence across the animal kingdom and human cultures raise questions for evolutionary biology.”

Using information from the UK Biobank, and questionnaire responses about sexual behavior from hundreds of thousands of individuals, the study team analyzed the genome of 477,522 people in the United Kingdom and the United States who had only had same-sex interactions.

They compared that data set to the genome of 358,426 people in the same countries who had only had opposite-sex encounters.

The team found the genes linked to same-sex behavior are also found in straight people. This gene profile across groups is associated with having more sexual partners.

A man waves an LGBTQ flag in front of the Bosnian parliament.Getty

The authors posit that the number of opposite-sex sexual partners could be advantageous from an evolutionary perspective, as it could lead to more children.

In turn, they argue their results help explain why same-sex sexual behavior has persisted throughout the evolution of the human species: These genetic effects may have been favored by evolution as they are associated with more children.

Ultimately and critically, the authors claim, the genes may less have to do with sexual preference and more to do with sexual openness/willingness.

The ethical debate — Other scientists caution against extrapolating information about sexual preference or behavior from genes.

In a commentary piece published alongside the study, ethicists Julian Savulescu, Brian D. Earp, and Udo Schuklenk distill the debate around whether or not this kind of research will lead to societal abuse.

They write:

“One can imagine technologically advanced repressive regimes where homosexuality is outlawed requiring genetic testing of embryos and foetuses, destroying those disposed to SSB, or testing children early in life for their propensities. Others will respond that the world (or at least some parts of it) has become more accepting of homosexuality, so perhaps these worries are overblown.”

What matters, they argue, is creating a society in which this kind of genetic research can’t be abused to further harm anyone, much less already marginalized groups.

They write: “Genes shape, limit, and provide opportunities for who we are and who we can be, both as individuals and as members of communities. To prepare for further research into polygenic behavioral traits including SSB, we must reshape society.”

Ilan Dar-Nimrod, a researcher and professor at The University of Sydney’s School of Psychology, tells Inverse “genes are taking oversize agency” in the minds of sexual behavior researchers.

“Genes code for properties,” he explains. “And although they can predict a lot of things, many people have this one-to-one view: if you have the gene, you’re going to be that and you can’t change it.”

That’s simply not in line with what we know about the science of genetics, he says.

On Monday, Dar-Nimrod and his colleagues also published a study looking at sexual preferences, this one in Scientific Reports. This study’s results support his assertion about preferences being more malleable than genes would suggest.

Sexuality is a spectrum

In their study, Dar-Dimrod and colleagues asked 420 cisgender people ranging in age from 18 to 83 to read literature. The study participants identified as exclusively heterosexual.

“We’ve just changed how they look at it.”

One group read literature about sexual preferences as a fluid spectrum. For example, one of the articles discussed gradations of sexual attraction towards men and women and noted that people can fall anywhere along the continuum. Another article explained that sexual orientation can change over time, shifting throughout one’s life instead of being fixed. The control group read unrelated articles.

After reading the literature about sexual fluidity:

  • Twenty-eight percent of the participants in the experimental group were more likely to identify as non-exclusively heterosexual.
  • Nineteen percent indicated they would be more likely to be willing to engage in same-sex sexual activities.

The rate of participants identifying as “non-exclusive heterosexual” more than quadrupled after the experiment.

In contrast, in the control group, only 8 percent of the participants identified as “non-exclusively heterosexual” after reading the literature unrelated to sexual preferences.

Dar-Nimrod says there were several results that surprised him:

  • How many people in the experimental group identified as “non-exclusively heterosexual” following the experiment
  • People actually expressed a willingness to engage in same-sex activities following the experiment
  • That even when balanced with literature refuting the idea of sexual preference as a spectrum — one of the articles argued that sexual orientation is indeed fixed — participants still gave more credence to the literature that discussed a sexual spectrum

Dar-Nimord doesn’t believe the literature he had the experimental group read actually changed who the participants were attracted to.

“We haven’t changed the underlying orientation,” he says. “We’ve just changed how they look at it.”

While our genes may predispose us to certain traits and conditions, when it comes to behavior, our society, environment, and relationships all play a huge role in how we behave.

“Do we really need to suggest that [queer people] were born with a certain gene to accept them and their relationships with other consenting adults?” Dar-Nimord says. “I don’t think so.”

Once we realize we’re not in fixed, black and white boxes, we have the freedom to explore the gray area to which most of us belong. At least, that’s what science really can show.

Nature Human Behavior abstract: Human same-sex sexual behaviour (SSB) is heritable, confers no immediately obvious direct reproductive or survival benefit and can divert mating effort from reproductive opportunities. This presents a Darwinian paradox: why has SSB been maintained despite apparent selection against it? We show that genetic effects associated with SSB may, in individuals who only engage in opposite-sex sexual behaviour (OSB individuals), confer a mating advantage. Using results from a recent genome-wide association study of SSB and a new genome-wide association study on number of opposite-sex sexual partners in 358,426 individuals, we show that, among OSB individuals, genetic effects associated with SSB are associated with having more opposite-sex sexual partners. Computer simulations suggest that such a mating advantage for alleles associated with SSB could help explain how it has been evolutionarily maintained. Caveats include the cultural specificity of our UK and US samples, the societal regulation of sexual behaviour in these populations, the difficulty of measuring mating success and the fact that measured variants capture a minority of the total genetic variation in the traits.
Scientific Reports abstract: We examined whether heterosexual individuals’ self‐reported sexual orientation could be influenced experimentally by manipulating their knowledge of the nature of sexual orientation. In Study 1 (180 university students, 66% female) participants read summaries describing evidence for sexual orientation existing on a continuum versus discrete categories or a control manipulation, and in Study 2 (460 participants in a nationally representative Qualtrics panel, 50% female) additionally read summaries describing sexual orientation as fluid versus stable across the life‐course. After reading summaries, participants answered various questions about their sexual orientation. In Study 1, political moderates and progressives (but not conservatives) who read the continuous manipulation subsequently reported being less exclusively heterosexual, and regardless of political alignment, participants reported less certainty about their sexual orientation, relative to controls. In Study 2, after exposure to fluid or continuous manipulations heterosexual participants were up to five times more likely than controls to rate themselves as non‐exclusively heterosexual. Additionally, those in the continuous condition reported less certainty about their sexual orientation and were more willing to engage in future same‐sex sexual experiences, than those in the control condition. These results suggest that non‐traditional theories of sexual orientation can lead heterosexuals to embrace less exclusive heterosexual orientations.