A new study involving 493,001 participants from the U.K., U.S., and Sweden — by far the most extensive of its kind — found that it is "effectively impossible to predict an individual’s sexual behavior from their genome."
The study found no single "gay gene" and concludes that the link between genetics, environment, and sexual orientation is extremely complicated, with thousands of genetic variants potentially having some degree of influence on behavior.
"Five genetic variants did appear significantly linked to sexual orientation, and thousands more also seemed involved to a lesser extent," Live Science explains. "In the end, the scientists could not find any genetic patterns that could be used, in any way, to identify a person's sexual orientation. Instead, the predisposition to same-sex sexual behavior appeared influenced by a complex mix of genetic and environmental influences."
"Same-sex sexual behavior is influenced by not one or a few genes but many," the study's conclusion reads. "Overlap with genetic influences on other traits provides insights into the underlying biology of same-sex sexual behavior, and analysis of different aspects of sexual preference underscore its complexity and call into question the validity of bipolar continuum measures such as the Kinsey scale. Nevertheless, many uncertainties remain to be explored, including how sociocultural influences on sexual preference might interact with genetic influences."
Ben Neale, a co-author of the study who is a statistical geneticist at the Broad Institute of MIT and Harvard, summarized the results of the sweeping research in comments to Live Science. "It's effectively impossible to predict an individual's sexual behavior from their genome," he said.
To conclude that sexuality is not influenced at all by genetics is "wrong," co-author and University of Queensland geneticist Brendan Zietsch told the outlet. However, it is also a "misinterpretation" of their findings to say that sexual preference is entirely determined by genes.
"We find that there are many, many genes that predispose one to same-sex sexual behavior. Each of them individually has a very small effect, but together they have a substantial effect," said Zietsch. "Another possible misinterpretation is to think that if same-sex preference is genetically influenced, it must therefore be totally genetically determined. That is not true. Genetically identical individuals — twins — often have different sexual orientations. We know there are non-genetic influences as well, but we don't understand these well, and our study does not say anything about them."
The study found that five genetic variants "were significantly associated with same-sex sexual behavior," including genes determining sex hormone regulation and sense of smell, but thousands of others may have some influence on orientation as well.
"These aggregate genetic influences partly overlapped with those on a variety of other traits, including externalizing behaviors such as smoking, cannabis use, risk-taking, and the personality trait 'openness to experience,'" reads the study's summary of results. "Additional analyses suggested that sexual behavior, attraction, identity, and fantasies are influenced by a similar set of genetic variants (rg > 0.83); however, the genetic effects that differentiate heterosexual from same-sex sexual behavior are not the same as those that differ among nonheterosexuals with lower versus higher proportions of same-sex partners, which suggests that there is no single continuum from opposite-sex to same-sex preference."