Genes influence but do not determine sexual orientation. It is the main conclusion of an investigation with almost half a million people published in the journal Science and that represents the largest study carried out to date to find out the weight of genes in sexual behavior in the face of people of the same sex.
First exposed at a genetics conference in 2018, the study found five genetic variants associated with having a same-sex sexual partner, but those variants, called SNPs, do not predict people’s sexual behavior, the authors state.
“There is no gay gene that determines whether someone has same-sex partners,” says Andrea Ganna, a geneticist at the Broad Institute of MIT and Harvard and the University of Helsinki.
Family studies have suggested that genetics account for approximately 32% of the heritability of homosexual behavior; But each SNP, or single nucleotide polymorphism, has very little effect on whether someone has had a same-sex sexual partner, according to the new work.
Taking into account all the SNPs measured in the study, including those that were not statistically significantly associated with same-sex behavior, they explained only 8 to 25% of the heritability of same-sex behavior. When considering just those five statistically significant SNPs, that number drops to much less than 1%.
But those variants could point to biological processes that are involved in choosing sexual partners. For example, a variant identified in the study has been associated with male pattern baldness, and another with the ability to smell certain chemicals, which can affect sexual attraction.
Doubts regarding the investigation
Qazi Rahman, a psychologist and sexual orientation researcher at King’s College London, who was not involved in the study, is quite skeptical about the study.“I should be really excited about this.”, He says. But “despite being a fervent believer in the biological basis of sexuality, I found this study problematic, and I’m not entirely sure what was found and if it holds.”
Rahman points out what he sees asInconsistencies in the data and possible biases in the people who volunteered to participate in the study.The study attracted volunteers from two large genetic databases, theBiobanco from the UK and consumer DNA testing company23andMe,and three smaller studios. Participants answered questionnaires about how many sexual partners of each sex they had had. 23andMe clients also responded to questions about attraction, sexual identity, and fantasy.
Butonly 5.5% of UK Biobank participants and about 1.5% of 23andMe customers joined the study.These low participation rates could skew the results or point to genetic variants that make people more likely to enroll in a study. “What you get are genetic influences on self-selection in a study, not genetic influences on same-sex behavior,” Rahman clarifies.
The study was not designed to address sexual orientation or identity, but the same variants associated with same-sex behavior were also associated in 23and Me participants with attraction, sexual identity, and fantasies. The small contribution of genetics to sexual behavior is in line with genetic contributions to other behaviors, such as education level.
The authors do not disagree . The study underscores that elements of biology and the environment can play a role in shaping sexual behavior, says Benjamin Neale, a co-author of the work. Environmental influences can include a variety of developmental, social, and cultural factors that could affect behavior.
” We hope that our results help to reformulate the way in which sexual behavior is measured and that it is done in collaboration with the LGTBQ community and stakeholders,” concludes Andrea Ganna, leader of the study.
So does J. Fah Sathirapongsasuti, computational biologist at 23andMe in Mountain View, California; which is resounding in this regard: “just because it is not completely genetic or has an environmental component, it does not mean that it is an option.”
Referencia: Andrea Ganna et al. “Large-scale GWAS reveals insights into the genetic architecture of same-sex sexual behavior”. Science, 29 de agosto de 2019. DOI: 10.1126/science.aat7693.
