No individual gene alone makes a person gay, lesbian or bisexual, a major study has found. Instead, thousands of genes likely influence only a part of sexual behaviour.
The new international study, published in journal Science and the largest of its kind, looked at genetic markers predisposing us to sexual attraction.
The study identified five genetic variants found to be closely associated with same-sex sexual behaviour. One comes from a region of DNA containing genes related to sense of smell. Another relates to male-pattern baldness.
But University of Queensland researcher Brendan Zietsch, who was involved in the study, said there were many – possibly thousands – more.
“Individually, each of these genes has only a very small effect, but their combined effect is substantial,” he wrote in The Conversation.
“We could also tell with high confidence that there are hundreds or thousands of other locations that also play a role, although we couldn’t pinpoint where they all are.”
Overall, the findings suggested genetics could account for between 8 and 25 percent of a person’s sexual desires. This was when taking into account the entire genome.
Researcher Ben Neale said same-sex attraction is “a natural and normal part of variation in our species” but was impossible to predict.
“It’s effectively impossible to predict an individual’s sexual behavior from their genome,” Neale said.
“There is no single gay gene, and a genetic test for if you’re going to have a same-sex relationship is not going to work.
“Genetics is less than half of this story for sexual behaviour, but it’s still a very important contributing factor.”
Researchers warn against ‘simplistic conclusions’
The study, published today by journal Science, is the largest study of same-sex sexual behavior.
It relied on genetic testing and survey responses on sexual behaviour from nearly half a million US and UK participants.
Zietsch said finding genes associated with sexuality among millions of parts of DNA is “like finding a needle in a haystack.”
He said the study reinforced “the extreme complexity” of the biology underlying sexual orientation and there were no “black-and-white answers.”
“Sexual preference is influenced by genes but not determined by them,” he said.
“Even genetically identical twins often have completely different sexual preferences.
“We have little idea, though, what the non-genetic influences are. Our results say nothing about this.”
But one limitation was the study’s focus on sexual behavior, and not sexual identity or orientation. Other limitations included the use of self-reporting of same-sex activity by participants.
Researchers only examined biologically-assigned sex, and excluded transgender and non-binary people from the study.
“Our findings provide insights into the biological underpinnings of same-sex sexual behavior,” the study concludes.
“But [the results] also underscore the importance of resisting simplistic conclusions.
“The behavioral phenotypes are complex, our genetic insights are rudimentary, and there is a long history of misusing genetic results for social purposes.”
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