Andrea Ganna, lead author and European Molecular Biology Laboratory group leader at the Institute of Molecular Medicine in Finland, said the research reinforces the understanding that same-sex sexual behavior is simply “a natural part of our diversity as a species.” The new study, published in August, 2019 in the journal Science, is not the first to explore the link between genetics and same-sex behavior, but it is the largest of its kind, and experts say it provides one of the clearest pictures of genes and sexuality.
Ganna, who is also an instructor at Massachusetts General and Harvard, and an international team of scientists examined data from more than 470,000 people in the United States and the United Kingdom to see whether certain genetic markers in their DNA were linked to their sexual behavior. Specifically, the researchers used data from the UK Biobank study and from the private genomics company 23andMe, which included their DNA data and responses to questions about sexual behaviors, sexual attraction and sexual identity. More than 26,000 participants reported at least one sexual encounter with someone of the same sex. Earlier studies, the researchers said, weren’t large enough to reveal the subtle effects of individual genes.
Two brothers are identical twins, they were raised together, and as they grew up they remained physically similar, but their tastes and interests began to diverge. One became interested in dance and academia, while the other preferred sports. The most surprising difference between the brothers is that one is gay. They were raised by the same parents in the same household, sharing the same environment at a crucial time in their personal development.
Gay Twin Brothers
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In the general population the chance of someone being gay is less than 5%, unless you have a gay twin, here the chances are much higher. If you’re fraternal sharing half your genes, there’s nearly a 25% chance that you will also be gay. If you’re identical sharing all your genes, there’s roughly a 50% chance that you will also be gay. This suggests that there must be some genetic component to our sexuality. However, it can’t be all down to genes, otherwise all identicals would be either both be gay, or both straight. Some other factor must be at play.
The researchers were able to find five genetic variants that were statistically associated with same-sex sexual behaviors, but none had a large effect and none could itself predict same-sex behaviors. One of the variants was found in a stretch of DNA that includes several genes related to the sense of smell. And another one of the genes is related to male pattern baldness, which the authors said could suggest that sex hormone regulation may somehow be involved.
These variants, along with thousands of others in the human genome that have even smaller effects, together accounted for 8 to 25 percent of variation in same-sex sexual behavior, the analysis showed. Some of the variants were correlated with same-sex sexual behavior in men, others in women, and some in both. Eric Vilain, director of the Center for Genetic Medicine Research at Children’s National Health System, said the study marks the end of “the simplistic concept of the ‘gay gene.’ ” “It just shows us that same-sex sexual behavior is much more complex than this idea of having just one gene influencing it all,” said Vilain, who was not involved in the study. “It shows that there are genetic factors, which we had suspected long ago ... but it also shows those genetic factors do not tell the whole story.”
Discrimination: Science Magazine notes, “Attributing same-sex orientation to genetics could enhance civil rights or reduce stigma. Conversely, there are fears it provides a tool for intervention or “cure.” Same-sex orientation has been classified as pathological and illegal and remains criminalized in more than 70 countries, some with the death penalty”. The discovery of sexuality by genetics could go a long way to ensure that legal equality is mandated by law. Many people still believe that sexuality is a choice, made into a “sin” by the major religions of the world. The genetic factor could help make lawmakers give consideration to equality when confronted with scientific evidence that sexuality is in nature, not nurture.
Previous studies have suggested that sexual orientation and same-sex behaviors may be, at least in part, genetic. For instance, research has shown patterns in families with multiple men in the same family identifying as gay. There is some evidence of a correlation between left-handedness and same-sex attraction, and left-handedness has both genetic and environmental influences. Environmental effects may be a factor for some people; for instance, having older brothers increases the odds that younger brothers will be gay, which researchers suspect may have to do with changes to the mother’s immune system in response to the earlier pregnancies.
Zeke Stokes, chief programs officer for GLAAD, said in a statement that the new research on the genetics “provides even more evidence that being gay or lesbian is a natural part of human life, a conclusion that has been drawn by researchers and scientists time and again. The identities of LGBTQ people are not up for debate. This new research also reconfirms the long established understanding that there is no conclusive degree to which nature or nurture influence how a gay or lesbian person behaves.”
There are limitations to the new research. Vilain, chair of the Department of Genomics and Precision Medicine at George Washington University, noted that the study’s authors placed all participants who had reported even one same-sex sexual event into the same group. “The problem with this is that it might dilute the efficiency of a search for genetic factors that may be present only in individuals who have exclusive same-sex attraction throughout their lives,” he said. That said, Vilain added, “it does capture the complexity of same-sex attraction. It captures real-life experiences rather than trying to put people into bins that are always arbitrary.” Also, Vilain said the study, which includes mostly European-American participants, lacks key diversity. “It’s missing out on what’s going on in other populations,” he said.
Dr. Lisa Diamond is Professor of Psychology and Gender Studies at the University of Utah. She studies the expression of sexual attractions and sexual identity over the lifetime, and the influences of early life experiences on later sexual development. Dr. Diamond is known for her research on sexual fluidity, which describes the capacity for individuals to experience shifts in their pattern of same-sex and other-sex attractions over time. Dr. Diamond is co-editor of the APA Handbook of Sexuality and Psychology and is a fellow of two divisions of the APA. Dr. Diamond has published over 100 articles and book chapters, and has been invited to present her research all over the world. She has received awards from the Developmental Psychology and LGBT Psychology Divisions of the APA, the American Association of University Women, the International Association for Relationship Research, the Society for the Scientific Study of Sexuality, and the Society for the Psychological Study of Social Issues.