An analysis of nearly half a million people has found there is no single ‘gay gene’ associated with same-sex relationships. Instead sexuality is influenced by a mix of genetic, social and environmental factors.
The study found genetic factors account for, at most, one quarter of same-sex behaviour across the whole population. But only when the entire genetic makeup of an individual is considered.
So does this mean environmental factors have more of a role to play than your genetic makeup? Has the study finally answered whether it is nature or nurture which determines who we are attracted to? Here we dig into the research a littler further.
What did the study look at?
The study by researchers from Harvard and MIT, published in Science, used data from 409,000 people signed up to the UK Biobank project and 68,500 registered with the genetics company 23andMe.
It asked participants to self-report whether they had ever had sex with someone of the same sex – about 4% of men and nearly 3% of women said they had done (the researchers stress they did not focus on identity or orientation and did not include transgender people).
Once they understood people’s sexual history they scanned their genomes (the unique DNA sequence).
What did the study find?
The researchers found five specific genetic variants that were particularly associated with same-sex behaviour, including one linked to the biological pathway for smell and others to those for sex hormones. The variants only partially overlapped between men and women.
But these five variants, taken together, only accounted for under 1% of same-sex behaviour.
Due to the fact they are such a small quantity the researchers say they cannot, and should not, be used to try and meaningfully establish a pattern to predict a person’s sexual orientation or behaviour.
Benjamin Neale, associate professor at Massachusetts General Hospital who worked on the study, said: “Genetics is less than half of this story for sexual behaviour, but it’s still a very important contributing factor.
“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. It’s effectively impossible to predict an individual’s sexual behaviour from their genome.”
“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..."”
They concluded, from these findings, that genetics could account for between 8-25% of same-sex behaviour across the population, when the entire genome is taken into consideration.
Their findings indicate that, as with personality and other complex human traits, sexual behaviour is influenced by a combination of genetic and environmental factors. They compared this to your height, which although partially determined by genes, is also dependent on environmental factors.
Zeke Stokes, from the LGBTQ media advocacy organisation GLAAD, said the study confirmed “no conclusive degree to which nature or nurture influenced how a gay or lesbian person behaves.”
Dr Brendan Zietsch, co-author of the research from the University of Queensland in Australia, said although it is a mixture of factors it does not mean it is all to do with environmental factors such as upbringing or culture. It could still be nature rather than nurture.
“It is thought that non-genetic factors before birth, such as the hormonal environment in the womb, also play an important role,” he told the Guardian.
So where did the ‘gay gene’ idea come from?
The idea that genetics might play a role in same-sex attraction was put in the spotlight in 1993 when a scientist at the US National Cancer Institute, Dean Hamer, found links between DNA markers on the X chromosome and male sexual orientation.
The findings caused considerable controversy, with the finding being dubbed the “gay gene” by the media.
Since Hamer’s findings nearly 30 years ago, subsequent research has thrown up mixed results, but most have put the genetic influence figure at around 30-50%.
Unlike Hamer’s work, the latest Harvard and MIT study does not show any special importance of the X chromosome.
What has the reaction been?
Fah Sathirapongsasuti, senior scientist at 23andMe, said that seeing some genetic influence on sexual behaviour should stop the notion that gayness can be “cured” by treatments.
“This is a natural and normal part of the variation in our species and that should also support precisely the position that we shouldn’t try and develop gay ‘curism’. That’s not in anyone’s interest,” Sathirapongsasuti said.
Are there any limitations to the study?
The pool of participants in this study is far larger than the previous studies but it is still based on people mainly of European ancestry and the age range of participants does not fully reflect that of the wider population.
It also relied on self-reported evidence of sexual behaviour.