An international team of researchers set out to determine whether people truly are "born this way," studying genetic markers predisposing us to certain sexual behavior. What they found is that there's no one, on-and-off switch for heterosexuality, and that instead, thousands of small variants can be linked to sexuality.
In particular, there are five specific markers most closely associated with sexuality. None of them had a significant impact, but in total, those markers are thought to contribute a small amount to an individual's sexual orientation. What's more, the research team says, behavior is further impacted by personal environment and experiences. Essentially, they claim sexuality is both nature and nurture.
"This study provides further evidence that diverse sexual behavior is a natural part of overall human variation," the researchers write.
The research was inspired, in part, by previous studies indicating that same-sex sexual behavior is partly heritable, at levels comparable to personality traits like extroversion or how many years someone spends in school.
This study also calls into question the validity of the Kinsey scale: the idea that sexuality can be linearly graded on a 0 to 6 scale.
"The genetics suggest that it is an oversimplification to assume that the more someone is attracted to the same sex, the less they are attracted to the opposite sex," the research team writes. "There is not a single dimension of sexuality."
Researchers acknowledge some limitations to the study. They used self-reporting to determine same-sex activity in participants, a method that poses a risk of misreporting. The study also looked exclusively at biologically assigned sex, rather than gender identity, and at least one dataset excluded trans and nonbinary people.
In addition, another of the more problematic elements of the study is that the half-million people whose records were examined were all of European descent; researchers claimed genetic data from other groups is lacking.
The study was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development. Findings were derived from records covering nearly half a million individuals, supplied by organizations like 23andMe and Biobank, as well as research projects like the National Longitudinal Study of Adolescent to Adult Health and Molecular Genetic Study of Sexual Orientation.
Researchers employed a method known as "genome-wide association study" to test for particular DNA bases across millions of markers.
"Our findings provide insights into the biological underpinnings of same-sex sexual behavior," the study concludes, "but [they] also underscore the importance of resisting simplistic conclusions because the behavioral phenotypes are complex, because our genetic insights are rudimentary, and because there is a long history of misusing genetic results for social purposes."