In contrast to the neurological and endocrinological correlates of homosexuality, genetic studies that have attempted to find “sexual orientation genes” are less conclusive and straightforward (Bogaert 2018). Although many experiments have identified multiple potential loci, no single one is a compelling predictor of homosexuality. Although the present website highlights on this inconclusiveness and claims that it disproves any theory of biological origin, the outcomes from these genetic experiments are not at all unusual, and are somewhat expected given the incredibly complex nature of sexual development espoused in other experiments.
Most likely, there is a complicated, polygenetic interaction between several genes and environmental factors that lead to multiple phenotypic expressions of homosexuality and bisexuality (Bogaert 2018). In such a system, one would not expect to uncover a single, responsible gene in genetic surveys of different populations.
“The largest GWAS (over 23,000 subjects) of sexual orientation was performed by scientists at 23andme in 2012. The data were presented at the American Society of Human Genetics annual meeting in San Francisco, showing that there were no loci associated with sexual orientation, including Xq28 on the X chromosome (Drabant, et al. 2012).”
The website cites this 2012 GWAS, with no significant findings, as the most comprehensive genetic study on sexual orientation to date. While the sample size (23,000) seems large, this is actually the total number of participants including controls, and only 1,380 participants identified as homosexual, a relatively small sample size. Additionally, the author states “These analyses are preliminary; we have not checked for outliers or confounders beyond what is listed in the methods" Drabant et al. 2012).
Although never mentioned on the website, larger more comprehensive GWAS’s have been conducted since this one in 2012, and did find significant loci associations. In the 2019 article, “Large-scale GWAS reveals insights into the genetic architecture of same-sex sexual behavior” the genotypes of ~500,000 participants (11,000-17,000 of which were homosexual depending on the particular analysis) were analyzed for loci associated with same-sex sexual behavior. The authors concluded
“we identified five SNPs whose association with same-sex sexual behavior reached genome-wide significance . . . there is certainly no single genetic determinant; many loci with individually small effects, spread across the whole genome and partly overlapping in females and males, additively contribute to individual differences in predisposition to same sex sexual behavior" (Ganna et al. 2019).
Furthermore, "Follow-up of these loci suggested links to biological pathways that involve sex hormone regulation and olfaction” which is consistent with previous literature that describe endocrinological origins and others that show olfactory differences between sexual orientations in the processing of sexual pheromones (Ganna et al. 2019).
Several other GWAS and genetic linkage studies have made conclusive findings; regions on 11 different autosomal chromosomes and
particularly on the X chromosome in women have been identified as having a statistically significant association with same-sex attraction. Many GWAS have shown heritability of homosexuality from 10%-40%, including 8%-25% in the aforementioned 2019 GWAS (Bogaert 2018). In regards to these studies, the website states that
“Attempts to identify specific genes related to male homosexual orientation have failed to consistently identify such genes and have often been contradictory. The best predictor of genetic association is through the new technique of GWAS, which have also failed to confirm any specific genetic associations with homosexual orientation.”
While it is correct that these studies have yet to identify a single, compelling gene, other disciplines of science have demonstrated that human sexual orientation is incredibly complex, and one could not logically expect to find a single “homosexuality gene” across all populations and cultures.
It is instead more likely that numerous genes interact in a polygenetic way to influence sexual orientation, a conclusion reached by many genetic studies (Bogaert 2018).
Furthermore, as mentioned in previous posts, many proposed biological mechanisms of homosexuality involve random variations in the prenatal environment that cannot be attributed to the fetus’ genes, and therefore would fall under the category of “environmental factors.” Additionally, these prenatal differences are largely the result of changes in the mother’s physiology, whether genetically-based or random. Therefore, if these differences did have a genetic origin, then the loci that determines an individual’s sexual orientation would be found in the mother’s genome and not necessarily in the individual’s genome. Lastly, the website claims that:
“If a gene or genes were ever identified, it would be arduous to resolve how it could persist within the population, given the severely reduced reproductive capacity of homosexuals.”
Although this may hold true for simple, single-gene phenotypes, the genetic expression of sexual orientation is so complex that many of these proposed loci can exist in the individuals without actually resulting in homosexuality, and thus, can easily persist throughout generations.
In summary, the modest evidence for a genetic basis of sexual orientation is not by any means discouraging. Rather, it is expected, and even if a large portion of variability is attributable to environmental factors (which can include prenatal environment), the consistent findings of even a few genetic correlates in each of these studies seem to prove that there does exist some biological bases for sexual orientation.
1. Bogaert, Anthony F., and Malvina N. Skorska. "A short review of biological research on the development of sexual orientation." Hormones and Behavior 119 (2020): 104659.
2. Deem, Richard. “Genetics and Homosexuality: Are People Born Gay? The Biological Basis for Sexual Orientation by Richard Deem, MSc.” Are People Born Gay? The Biological and Genetic Basis for Homosexuality, Godandscience.org, 2017, www.godandscience.org/evolution/homosexuals_born_gay.html#frisch.
3. Drabant, EM, et al. 2012. "Genome Wide Association Study of Sexual Orientation in a Large, Web-Based Cohort." https://blog.23andme.com/wp-content/uploads/2012/11/Drabant-Poster-v7.pdf.
4. Ganna, Andrea, et al. "Large-scale GWAS reveals insights into the genetic architecture of same-sex sexual behavior." Science 365.6456 (2019): eaat7693.