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The most important finding of the large new study, says Benjamin Neale, a geneticist at the Broad Institute of MIT and Harvard University, “is there is no single gay gene.”
Neale and a team of researchers, who published their results in the journal Science on Thursday, scanned the genomes of roughly half a million people for differences that might form the genetic foundation for same-sex sexual behavior.
Neale says their findings confirmed something that researchers had long believed: Sexual behavior is a trait like most human characteristics such as height, skin tone, intelligence and personality.
All of these traits arise from an ensemble of thousands of genes, each exerting a minute influence on the individual, and the “environment,” a vague catch-all term for anything that’s not genetic. This can include a person's social circle, where a person grew up, and things that may have happened in the womb.
The study isn’t the first time scientists have searched for a biological underpinning for same-sex sexual behavior, though this line of research has always generated controversy. Some members of the LGBTQ community have argued that the work should not be conducted at all.
“There is only a short distance between understanding the genetic or environmental origins of sexual variation and the possibility of intervention – [in] medical terms, ‘cure,’ ” wrote Douglas Futuyma, an evolutionary biologist who is openly gay, in an essay in 2005.
Inside the Broad Institute, similar concerns have been raised about this study. In a letter posted on the organization's website at the same time that the findings were released, geneticist Steven Reilly questioned whether the study should have been published.
“At best, our understanding remains essentially the same," he said. "At worst, the public will be misinformed and confused about why scientists would study this trait over thousands of serious diseases, all while a historically marginalized group has been left more vulnerable."
To conduct the research, the study's authors used two sources of data: the commercial genome testing company 23andMe and the UK Biobank, a genetic research database of roughly half a million United Kingdom residents between the ages of 40 and 70.
All of the participants in the study were asked a few questions about their sexual history — including whether they had ever had a sexual experience with someone of the same sex, and what proportion of their sexual partners had been of the same sex. The researchers then used these responses to look for variations in the genome that might be associated with same-sex sexual behavior.
Their analysis found five genetic variations related to having at least one sexual experience with a same-sex partner. Two of these gene variants exist in men only. One exists in women only, and two are in both men and women.
“Together, they account for a very small fraction — much less than 1% — of the variation between people,” Neale says. When the researchers looked at differences across the entire genome, they found that genetics accounted for roughly 8 to 25% of the variation between people.
That means that while these genes are statistically associated with same-sex sexual behavior, they do not predict that someone has, or will have, a same-sex sexual partner, he says.
“Thousands of [genes] scattered across the genome each have a small influence on same-sex sexual behavior,” Neale says. “That implies it will be effectively meaningless to predict an individual’s same-sex sexual behavior from genetics. We just won’t be able to do that.”
“I could make a list of a thousand diseases and traits that I would want to spend my time understanding first, because I know that this might be able to help someone. But [same-sex sexual behavior] isn’t a disease."Steven Reilly
That does not allay the concerns of the study's critics, who fear the results could be misused in an attempt to predict sexual orientation.
“You can have people who just misconstrue this,” says Reilly, at the Broad Institute. “And you get to extreme examples of companies trying to sell products to choose an embryo based on these genetics or offering [gene] editing for fetuses. It’s not scientifically feasible, but it doesn’t mean someone might not try. There’s already examples of companies that test for IQ or eye color.”
Scientists have always known that sexual behavior is a complex trait that likely involved thousands of genes, Reilly says. This study simply confirms that.
“I could make a list of a thousand diseases and traits that I would want to spend my time understanding first, because I know that this might be able to help someone,” he says. “But [same-sex sexual behavior] isn’t a disease. When we live in a world that has discrimination against vulnerable populations, we have to ask who does this research potentially benefit and who does it potentially hurt?"
The authors of the study say they understand these criticisms, but they believe their work can benefit the LGBTQ community.
“I didn’t do this to understand myself better, but because better understanding of things like same-sex sexual behavior can lead to stigma reduction.”Benjamin Neale
“I didn’t do this to understand myself better, but because better understanding of things like same-sex sexual behavior can lead to stigma reduction,” says Neale, who is gay. For instance, Neale says, the results suggest same-sex sexual behavior is a natural part of human biology and diversity.
“It’s natural and normal, and there’s no genetic test for this,” he says.
The findings might strengthen legal protections for people in the LGBTQ community, says Melinda Mills, a social sciences and genetics researcher at the University of Oxford, who did not work on the study.
“If this behavior is something that we are hard-wired to engage in and there’s nothing we can do, then it could enhance [human] rights,” she says. “That is one take you can have on this, but we have to be careful. So many other factors play a role as well.”
The research also can’t be used to say anything definitive about sexual identity, says Jeremy Yoder, an evolutionary biologist at California State University Northridge, who was not involved in the study. He points out that the findings are tied only to whether participants had at least one same-sex sexual experience, which is different from identifying as gay or queer.
Sexuality is something you define for yourself, Yoder says. “It’s a very personal thing. It’s about what your experience is. Some of it is genetic, but some of it is your personal history. It’s what you actually do, who you connect with, and how you end up living your life.”
This segment aired on August 30, 2019.
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