In my psychology texts, and in other writings (such as here for the faith community), I have explained the growing evidence that sexual orientation is a natural, enduring disposition (most clearly so for males). The evidence has included twin and family studies indicating that sexual orientation is influenced by genes—many genes having small effects. One recent genomic study, led by psychiatrist and behavior geneticist Alan Sanders, analyzed the genes of 409 pairs of gay brothers, and identified sexual orientation links with parts of two chromosomes.
Today, Nature will be releasing (through its Scientific Reports) a follow-up genome-wide association study by the Sanders team that compares 1,077 homosexual and 1,231 heterosexual men. They report genetic variants associated with sexual orientation on chromosomes 13 and 14, with the former implicating a “neurodevelopmental gene” mostly expressed in a brain region that has previously been associated with sexual orientation. On chromosome 14 they identified a gene variant known to influence thyroid functioning, which also has been associated with sexual orientation.
Although other factors, including prenatal hormonal influences, also help shape sexual orientation, Sanders et al. conclude that “The continued genetic study of male sexual orientation should help open a gateway to other studies focusing on genetic and environmental mechanisms of sexual orientation and development.” The science of sexual orientation (for females as well) marches on.