Scientists might be getting closer to finding the genetic source for homosexuality, after a team announced it had identified gene regions that appeared to be linked to the sexual orientation — but not everyone is buying it.
A study published in the journal Scientific Reports highlights genes that have previously been shown to be crucial for brain development and thyroid gland function. It specifically points to two genes called SLITRK5 and SLITRK6 that reside on the 13th chromosome. SLITRK6 is especially active in the diencephalon, an area in the brain that includes the hypothalamus, which is “a region previously reported as differing in size in men by sexual orientation,” the study notes. According to the research, genes that are linked to neurodevelopment and to traits related to the nervous system “are also of potential relevance to behavioral phenotypes such as sexual orientation.”
Another chunk of DNA the researchers identified was the TSHR gene on chromosome 14, which is linked to the thyroid.
Some scientists have previously suggested that thyroid hormones, including those produced by a pregnant mother, can affect sexual orientation.
The researchers identified those genes when they compared the DNA of about 1,000 gay and 1,200 straight men, most of whom had European ancestry.
Although previous investigation has suggested a genetic link to sexual orientation, this study pinpoints specific pieces of the genetic code that could be involved in the development of that orientation.
It was unclear whether the results could extend to lesbians and straight women, as the scientists did not analyze female DNA in this study. It was also unclear how the findings relate to orientations other than homosexuality, such as bisexuality and asexuality.
Some experts, however, were skeptical that the findings could even have significance for gay men.
“Like nearly every complex human trait we study, the genetics of sexual orientation will be multifactorial, meaning that hundreds (or likely thousands) of genetic differences will each contribute in a tiny way to sexual orientation,” Dr. Jeffrey Barrett, from the genetics research group Wellcome Trust Sanger Institute, said in a statement from the British organization Science Media Centre. “What this means is that to study traits like this requires looking at the genomes of tens of thousands (or even hundreds of thousands) of people. This study is way, way, way too small to draw any meaningful conclusion.”
He called the ideas about the SLITRK6 and TSHR genes “utter speculation.”
Alan Sanders, a researcher on the new genetic investigation from Illinois’ North Shore University, acknowledged that there could be multiple genes connected to homosexuality, among environmental influences, and simply carrying some of those genes doesn’t mean a man will be gay.
“There will be men who have the form of gene that increases the chance of being gay, but they won’t be gay,” he told New Scientist.
Conclusive identification of genes that are linked to homosexuality, if possible, could be controversial due to social and political factors, such as stigma against sexual orientation.
As medical science has advanced, for example, doctors have been able to give expectant parents more information about birth defects. A screening can now tell mothers the likelihood that their babies will be born with Down syndrome, raising the question of whether it is ethical to for people to use that information when deciding whether to abort a pregnancy or deliver the baby. Technology allowing scientists to edit people’s DNA, with the goal of removing harmful genes and replacing them with ones that function normally, is also constantly advancing. Critics of that technology have spoken against the possibility that parents would use it to design babies of certain heights, eye colors and other physical traits.