Genetics may play a role in sexuality

 

A new study has found that there is no “single gay gene”. Instead, researchers suggest there are thousands of genetic variants linked to the trait, that when combined only contribute to one per cent of the genetic variation.

The researchers also suggest that same-sex sexual behaviour is influenced, like most other human traits, by a mix of genetic and environmental factors.

Researcher Ben Neale from the Broad Institute and Massachusetts General Hospital says that the study shows just how complex genetics are.

“This study is the largest and most thorough investigation into the genetics of same-sex sexual behaviour to date and it really provides the clearest glimpse yet into the genetic underpinnings of same-sex sexual behaviour.”

“It highlights both the importance of the genetics as well as the complexity of the genetics, but [also that] genetics is not this whole story,” he says.

“Our findings should not in any way be interpreted so as to imply that the experiences of LGBTQ individuals are “wrong” or “disordered”,” the authors write.

“In fact, this study provides further evidence that diverse sexual behaviour is a natural part of overall human variation.”

Five genetic markers were discovered

An international team of researchers, including from the University of Queensland, examined the genetics of over 470,000 individuals who self-reported whether they had ever engaged in same-sex behaviour.

The researchers used five datasets for the genome-wide association study, including information from commercial genetics company 23andMe.

“We scanned the entire human genome and found a handful, five to be precise, locations in the human genome that are clearly associated with whatever a person reports in engaging in same-sex, sexual behaviour,” says lead author Andrea Ganna from the Institute of Molecular Medicine in Finland, and the Massachusetts General Hospital.

Five genetic markers were found but are thought to comprise less than one per cent of the variation.

This led researchers to find that there were no patterns among the genetic variations, nor any single variation that could be used to determine a person’s sexual behaviour. They suggest that thousands appear to also be involved, but when put together these variants only had small effects on a person’s sexual behaviour.

“This common variance accounts somewhere between eight per cent and 25 per cent of the variance in self-reported same-sex sexual behaviour,” Ganna says, meaning any commonalities only reflected a small percentage of the those who had engaged in same-sex sexual behaviour.

However, they do highlight that while the variance is small, it “could hint at some biological pathways that might be involved in same-sex sexual behaviour”.

The element of environmental factors

The researchers do highlight that it is hard to say how a genetic marker ties back to the biology of a trait. Like with many traits, such as height in humans, there is no single marker.

Neale says the study underscores that there is an element of environmental factors in same-sex sexual behaviour from anything in utero to who you stand next to on the train in the morning.

“That’s all potentially environmental factors that can have some influence on complex traits and so… we can’t say what those environmental factors are, it’s more that we have a sense they exist because we put bounds on the extent to which the genetics is really influencing the trait.”

“Both things matter. That’s the sort of take-home message. Yes, there’s some biology and yes, there’s likely some environment, but beyond that we can’t specify,” says Neale.

The researchers also note that the study relied on self-reporting, excluded non-binary genders, and only involved people from the UK and US.

This research isn’t the final answer

Neale highlights that this study is just the beginning for understanding the spectrum of human sexuality, and merely opens the door to more research on the topic.

“I wouldn’t describe this research as the final answer. I think what this research does is it moves our understanding to a slightly deeper and more nuanced place where we see there is more complexity out there than we’re capturing in our very simplistic measures,” says Neale.

Melinda Mills, a molecular genetics and demography expert from Oxford University who was not involved in the study, cautioned against misconstruing the data. “The effects are so small (under 1%) that this genetic score could not be reliably used to predict same-sex sexual behavior of an individual.”

She adds that “using these results for prediction, intervention or a supposed ‘cure’ is wholly and unreservedly impossible.”

The full findings are published in the journal Science.

Video courtesy of Francesca Cattaneo, Miriam Palopoli, Alessandro Nepote Vesin, Andrea Ganna

This article was first published on Australia’s Science Channel, the original news platform of The Royal Institution of Australia.