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Why are we gay?


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Most of us started wondering why we are actually different in our sexual orientation.


This thread is not supposed to discuss, what we personally think or what bizarre reasons we or society has given to explain homosexuality but is shall be a rapport of the latest explanation or scientific basis on why there are people who are homosexual.


Science itself is contradicting on this topic.


I will place some first articles here as a starting point.


But my "research" on the net is not exhaustive and surely it would be helpful if some experts from the science are able to contribute if they have better access to researches.



Edited by singalion
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  • NEWS
  • 29 August 2019

Nature Portfolio

No ‘gay gene’: Massive study homes in on genetic basis of human sexuality

Nearly half a million genomes reveal five DNA markers associated with sexual behaviour — but none with the power to predict the sexuality of an individual.

The largest study1 to date on the genetic basis of sexuality has revealed five spots on the human genome that are linked to same-sex sexual behaviour — but none of the markers are reliable enough to predict someone’s sexuality.


The findings, which are published on 29 August in Science and based on the genomes of nearly 500,000 people, shore up the results of earlier, smaller studies and confirm the suspicions of many scientists: while sexual preferences have a genetic component, no single gene has a large effect on sexual behaviours.


“There is no ‘gay gene’,” says lead study author Andrea Ganna, a geneticist at the Broad Institute of MIT and Harvard in Cambridge, Massachusetts.


Ganna and his colleagues also used the analysis to estimate that up to 25% of sexual behaviour can be explained by genetics, with the rest influenced by environmental and cultural factors — a figure similar to the findings of smaller studies.


“This is a solid study,” says Melinda Mills, a sociologist at the University of Oxford, UK, who studies the genetic basis of reproductive behaviours.


But she cautions that the results may not be representative of the overall population — a limitation that the study authors acknowledge. The lion’s share of the genomes comes from the UK Biobank research programme and the consumer-genetics company 23andMe, based in Mountain View, California. The people who contribute their genetic and health information to those databases are predominantly of European ancestry and are on the older side. UK Biobank participants were between 40 and 70 years old when their data were collected, and the median age for people in 23andMe’s database is 51.


The study authors also point out that they followed convention for genetic analyses by dropping from their study people whose biological sex and self-identified gender did not match. As a result, the work doesn’t include sexual and gender minorities (the LGBTQ community) such as transgender people and intersex people.

A need for more data

Scientists have long thought that someone’s genes partly influenced their sexual orientation. Research from the 1990s2 showed that identical twins are more likely to share a sexual orientation than are fraternal twins or adopted siblings. Some studies suggested that a specific part of the X chromosome called the Xq28 region was associated with the sexual orientation of people who were biologically male — although subsequent research cast doubt on those results.


But these studies all had very small sample sizes and most focused on men, says Mills. This hampered scientists’ ability to detect many variants associated with sexual orientation.


In the recent study, Ganna and his colleagues used a method known as a genome-wide association study (GWAS) to look at the genomes of hundreds of thousands of people for single-letter DNA changes called SNPs. If lots of people with a trait in common also share certain SNPs, chances are that the SNPs are related in some way to that characteristic.


The researchers split their study participants into two groups — those who reported having had sex with someone of the same sex, and those who didn’t. Then the researchers performed two separate analyses. In one, they evaluated more than one million SNPs and looked at whether people who had more SNPs in common with each other also reported similar sexual behaviours. The scientists found that genetics could explain 8–25% of the variation in sexual behaviour.


For their second analysis, Ganna and his colleagues wanted to see which particular SNPs were associated with same-sex sexual behaviours, and found five that were more common among those individuals. However, those five SNPs collectively explained less than 1% of the variation in sexual behaviour.


This suggests that there are a lot of genes that influence sexual behaviour, many of which researchers haven’t found yet, says Ganna. An even larger sample size could help to identify those missing variants, he says.


But Ganna cautions that these SNPs can’t be used to reliably predict sexual preferences in any individual, because no single gene has a large effect on sexual behaviours.

It’s complicated

Although the researchers have identified some of the SNPs involved in same-sex sexual behaviour, they aren’t sure what the genetic variants do. One is near a gene related to smell, which Ganna says has a role in sexual attraction. Another SNP is associated with male-pattern baldness — a trait influenced by levels of sex hormones, which suggests that these hormones are also linked to same-sex sexual behaviour.


The results demonstrate the complexity of human sexuality, says Ganna. They also presented a challenge to the study researchers, who knew that explaining nuanced findings on such a sensitive topic to the general public would be tricky.



To ensure that their results are not misinterpreted, the study researchers worked with LGBTQ advocacy groups and science-communication specialists on the best way to convey their findings in the research paper and to the public. Their efforts included the design of a website that lays out the results — and their limitations — to the public, using sensitive, jargon-free language.


Ewan Birney, a geneticist and director of EMBL European Bioinformatics Institute near Cambridge, UK, applauds that effort. “It’s a communications minefield,” he says.

Although some researchers and LGBTQ advocates might question the wisdom of conducting this kind of research, Birney says that it’s important. There has been a lot of sociological research on same-sex sexual behaviours, he says, but this is an incredibly complicated topic. It’s time to bring a strong, biologically based perspective to the discussion, Birney says.



Nature 573, 14-15 (2019)

doi: https://doi.org/10.1038/d41586-019-02585-6


  1. Ganna, A. et al. Science 365, eaat7693 (2019).

    Article  Google Scholar 

  2. Pillard, R. C. & Bailey, J. M. Hum. Biol. 70, 347–365 (1998).

    PubMed  Google Scholar 


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Scientific american


Massive Study Finds No Single Genetic Cause of Same-Sex Sexual Behavior

Analysis of half a million people suggests genetics may have a limited contribution to sexual orientation

By Sara Reardon on August 29, 2019



Few aspects of human biology are as complex—or politically fraught—as sexual orientation. A clear genetic link would suggest that gay people are “born this way,” as opposed to having made a lifestyle choice. Yet some fear that such a finding could be misused “cure” homosexuality, and most research teams have shied away from tackling the topic.


Now, a new study claims to dispel the notion that a single gene or handful of genes make a person prone to same-sex behavior. The analysis, which examined the genomes of nearly half a million men and women, found that although genetics are certainly involved in who people choose to have sex with, there are no specific genetic predictors. Yet some researchers question whether the analysis, which looked at genes associated with sexual activity rather than attraction, can draw any real conclusions about sexual orientation.


“The message should remain the same that this is a complex behavior that genetics definitely plays a part in,” said study co-author Fah Sathirapongsasuti, a computational biologist at genetic testing company 23andMe in Mountain View, Calif., during a press conference. The handful of genetic studies conducted in the past few decades have looked at only a few hundred individuals at most—and almost exclusively men. Other studies have linked sexual orientation with environmental factors such as hormone exposure before birth and having older brothers.


In the new study, a team led by Brendan Zietsch of the University of Queensland, Australia, mined several massive genome data banks, including that of 23andMe and the UK Biobank (23andMe did not fund the research). They asked more than 477,000 participants whether they had ever had sex with someone of the same sex, and also questions about sexual fantasies and the degree to which they identified as gay or straight.


The researchers found five single points in the genome that seemed to be common among people who had had at least one same-sex experience. Two of these genetic markers sit close to genes linked to sex hormones and to smell—both factors that may play a role in sexual attraction. But taken together, these five markers explained less than 1 percent of the differences in sexual activity among people in the study. When the researchers looked at the overall genetic similarity of individuals who had had a same-sex experience, genetics seemed to account for between 8 and 25 percent of the behavior. The rest was presumably a result of environmental or other biological influences. The findings were published Thursday in Science.


Despite the associations, the authors say that the genetic similarities still cannot show whether a given individual is gay. “It’s the end of the ’gay gene,’” says Eric Vilain, a geneticist at Children’s National Health System in Washington, D.C., who was not involved in the study.


The research has limitations: almost all of the participants were from the U.S. or Europe, and the individuals also tended to be older—51 years old on average in the 23andMe sample and at least 40 in the UK Biobank sample.


Still, researchers welcome the data. “A lot of people want to understand the biology of homosexuality, and science has lagged behind that human interest,” says William Rice, an evolutionary geneticist at the University of California, Santa Barbara, who also was not involved in the work. “It’s been a taboo topic, and now that we’re getting information I think it’s going to blossom.”


The study will not be the last word on the vexing question of what causes homosexuality, however. In 1993 geneticist Dean Hamer of the U.S. National Cancer Institute and his colleagues published a paper suggesting that an area on the X chromosome called Xq28 could contain a “gay gene.” But other studies, including the new paper, found no such link, and Sathirapongsasuti says that the new study is the final nail in the coffin for Xq28 as a cause of same-sex attraction.


But Hamer, now retired, disagrees. His study, which analysed the genomes of 40 pairs of gay brothers, looked exclusively at people who identified as homosexual. He sees the new paper as an analysis of risky behavior or openness to experience, noting that participants who engaged in at least one same-sex experience were also more likely to report having smoked marijuana and having more sexual partners overall. Hamer says that the findings do not reveal any biological pathways for sexual orientation. “I’m glad they did it and did a big study, but it doesn’t point us where to look.”


Rice and Vilain agree that the conclusion is unclear. A more detailed questionnaire that looks at more aspects of sexuality and environmental influences would allow the researchers to better pinpoint the roots of attraction.


The authors say that they did see links between sexual orientation and sexual activity, but concede that the genetic links do not predict orientation. “I think it’s true we’re capturing part of that risk-taking behavior,” Sathirapongsasuti says, but the genetic links still suggested that same-sex behavior is related to attraction.


Nevertheless, Hamer and others praise the new contribution to a field that suffers from a dearth of good studies. “I hope it will be the first of many to come.”




Sara Reardon is a freelance journalist based in Bozeman, Mont. She is a former staff reporter at Nature, New Scientist and Science and has a master's degree in molecular biology.


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Nature Portfolio


  • NEWS
  • 23 August 2021

Genetic patterns offer clues to evolution of homosexuality

Massive study finds that genetic markers associated with same-sex encounters might aid reproduction. But some scientists question the conclusions.


To evolutionary biologists, the genetics of homosexuality seems like a paradox. In theory, humans and other animals who are exclusively attracted to others of the same sex should be unlikely to produce many biological children, so any genes that predispose people to homosexuality would rarely be passed on to future generations. Yet same-sex attraction is widespread in humans, and research suggests that it is partly genetic.


In a study of data from hundreds of thousands of people, researchers have now identified genetic patterns that could be associated with homosexual behaviour, and showed how these might also help people to find different-sex mates, and reproduce. The authors say their findings, published on 23 August in Nature Human Behaviour1, could help to explain why genes that predispose people to homosexuality continue to be passed down. But other scientists question whether these data can provide definitive conclusions.




Evolutionary geneticist Brendan Zietsch at the University of Queensland in Brisbane, Australia, and his colleagues used data from the UK Biobank, the US National Longitudinal Study of Adolescent to Adult Health and the company 23andMe, based in Sunnyvale, California, which sequence genomes and use questionnaires to collect information from their participants. The team analysed the genomes of 477,522 people who said they had had sex at least once with someone of the same sex, then compared these genomes with those of 358,426 people who said they’d only had heterosexual sex. The study looked only at biological sex, not gender, and excluded participants whose gender and sex did not match.


In earlier research, the researchers had found that people who’d had at least one same-sex partner tended to share patterns of small genetic differences scattered throughout the genome2. None of these variations seemed to greatly affect sexual behaviour on its own, backing up previous research that has found no sign of a ‘gay gene’. But the collection of variants seemed to have a small effect overall, explaining between 8% and 25% of heritability.


Next, the researchers used a computer algorithm to simulate human evolution over 60 generations. They found that the array of genetic variations associated with same-sex behaviour would have eventually disappeared, unless it somehow helped people to survive or reproduce.

Overlapping genes

Zietsch and his team decided to test whether these genetic patterns might provide an evolutionary edge by increasing a person’s number of sexual partners. They sorted the participants who had only had heterosexual sex by the number of partners they said they had had, and found that those with numerous partners tended to share some of the markers that the team had found in people who had had a same-sex partner.


The researchers also found that people who’d had same-sex encounters shared genetic markers with people who described themselves as risk-taking and open to new experiences. And there was a small overlap between heterosexual people who had genes linked to same-sex behaviour and those whom interviewers rated as physically attractive. Zietsch suggests that traits such as charisma and sex drive could also share genes that overlap with same-sex behaviour, but he says that those traits were not included in the data, so “we’re just guessing”.




The authors acknowledge many limitations of the study. All of the participants lived in the United Kingdom or United States, and were of European descent. And the databases’ questionnaires asked about sexual behaviour, not sexual attraction. Most of the participants were born during a time when homosexuality was either illegal or culturally taboo in their countries, so many people who were attracted to others of the same sex might never have actually acted on their attraction, and could therefore have ended up in the wrong group in the study.


Julia Monk, an ecologist and evolutionary biologist at Yale University in New Haven, Connecticut, thinks that these caveats are so important that the paper can’t draw any real conclusions about genetics and sexual orientation. Sexual behaviour and reproduction, she says, occupy a different place in modern societies than they did for human ancestors, so it’s difficult to infer their role in our evolution. For instance, people might engage with more sexual partners now that sexually transmitted diseases can be cured. And the existence of birth control and fertility treatments negates many of the reproductive advantages that genes might provide. “It’s clear that people’s behaviour when it comes to sex and reproduction is highly culturally informed, and maybe digging into genetics is next to impossible,” Monk says.


Weak linkages

Qazi Rahman, a psychologist at King’s College London, thinks that the study was well-conducted, but he is sceptical of some of the conclusions. He says the data sets are too biased towards people who were willing to reveal their sexual behaviour to researchers, which could itself be considered a risky behaviour that could be reflected in the genetic data. He adds that once the data are broken down into men and women, and into those who had only had same-sex partners versus those who had encounters across sexes, the number of people in each group becomes so small that the genetic linkages are very weak.


Dean Hamer, a retired geneticist in Haleiwa, Hawaii, who published some of the first studies on the genetics of sexual orientation, is disappointed with the study. Defining sexual orientation on the basis of a single same-sex encounter is not a useful way of categorizing people, he says, because many people who identify as heterosexual have experimented with a same-sex partner. “You’re not even asking the right people the right question,” Hamer says. Instead, he thinks the researchers have found genetic markers associated with openness to new experiences, which could explain the overlap between people who have had a homosexual partner and heterosexual people who have had many partners.


Zietsch says that risk-taking can explain only part of the statistical link between markers associated with same-sex encounters and those associated with number of partners. And he admits that using a single homosexual experience as an indication of sexual orientation isn’t ideal, but says that the UK Biobank didn’t provide data on attraction. Zietsch’s previous research on data from 23andMe showed a strong genetic overlap between people who reported same-sex sexual experiences and those who reported same-sex attraction, suggesting that the same genes controlled both factors.


Hamer acknowledges that linking a complex behaviour to genetics is extremely difficult, but says he is glad the team is researching sexual orientation. “It’s vastly understudied considering it’s a driving force for the human race,” he says. “It’s a good question, they just didn’t find an answer.”


Nature 597, 17-18 (2021)

doi: https://doi.org/10.1038/d41586-021-02312-0


  1. Zietsch, B. P. et al. Nature Hum. Behav. https://doi.org/10.1038/s41562-021-01168-8 (2021).

    Article  Google Scholar 

  2. Ganna, A. et al. Science 365, eaat7693 (2019).



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