There is no one “gay gene” that influences our sexual preferences. Rather, a wide host of genetic variants – coupled with environmental and social influences – determine which biological sex we are attracted to.
Sexual behavior is highly complex and cannot be simplistically defined by any single factor, according to the results of the largest study on the genetics of sexual behavior. Evidence suggests that some same-sex behavior is partly inherited and some is also influenced by a mix of genetics, environmental factors, and life experiences.
In order to determine the role of genetics in shaping sexual behavior, an international team of scientists reviewed existing DNA data from more than 500,000 research participants who had submitted their information to databases like UK Biobank and 23andMe, Inc. Using a genome-wide association study (GWAS), the team analyzed people's self-reported sexual history and – for those who had previously had sex with a person of the same sex, gender, or orientation – compared it against millions of genetic markers across entire genomes to determine which of the four DNA bases (A, C, G, and T) were present at common locations.
Though self-reported sexual behaviors may not always be honest and they could not control for differences in interpretation or definition, the researchers were able to identify certain genetic markers associated with same-sex behaviors. These markers both influence human sexual behavior and other mental and physical traits, including psychiatric, personality, and reproductive characteristics. Five genetic markers, in particular, were associated with sexual behavior. Individually each of these markers has a small effect on a person’s sexual behavior, but they can be shaped by hundreds of thousands of genetic variants that are influenced by a person’s environment and life experience.
“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,” write the authors.
These genetic markers were also associated with other biological traits. For example, one marker identified was linked with balding, suggesting that sex hormone regulation may somehow be involved in same-sex sexual behavior. Links to openness to experience and risk-taking behavior, like smoking or cannabis use, and certain psychiatric conditions were present, which could be explained by social environments. A member of the LGBTQ community may experience discrimination because of their orientation, which could, in turn, lead to certain behaviors or mental health issues.
Interestingly, just 40 percent of genetic influences were shared by both sexes while the other 60 percent were unique to each sex. Genetic overlap between males and females for most traits is usually “much higher”, a feature the authors suggest could be described as the result of different gendered and social constructs for each sex.
The authors are quick to caution that their work is in no way meant to “identify” or “predict” whether a person will be interested in their same sex, but rather helps to understand the complexity of sexual orientation, genetic differences between males and females, behavior, attraction, and identity.
A number of limitations were listed in the study, including demographic data that may have been constrained in the previous studies reviewed. Furthermore, differences in gender identity and biological sex may not have been accurately represented.
The results are published in the journal Science.