An image representing attraction and diversity among individuals. [Credit: Francesca Cattaneo]

Is Sexual Orientation Encoded In Our DNA?

No ‘gay gene’ or genetic signature for same-sex sexual behavior found in the largest human study of its kind

What determines a person’s sexual orientation? Is it passed down from generation to generation? Or does ‘nurture’ prevail over ‘nature’ with life’s experiences forming our preferred sexual behaviors?

As if the social and political aspects weren’t complicated enough, the hereditary and environmental determinants of sexual orientation have also been the subject of debate for years. This is partly due to hints that sexual preferences may be somewhat genetically hardwired.

Yet, studies trying to pin down the inherited information tied to this have proved to be superficial and insubstantial. Gaining insights into linkages between genetic makeup and behavior usually requires studying very large populations.

Now, a new study in Science analyzing data from roughly half a million people, by far the largest research project of its kind, shows that there may be evidence of variations in human DNA linked to same-sex sexual behavior, adding to the complexity of human sexuality.

The combined effects, however, are so small that this alone cannot conjure an individual’s sexual orientation. In other words, there is no genetic signature for same-sex sexual behavior.

“As a teenager trying to understand myself and understand my sexuality, I looked at the internet for the ‘gay gene’…This paper has basically disproved that.”

— Fah Sathirapongsasuti, Ph.D.

This work rejects the use of genetic results for prediction, intervention, or a supposed ‘cure’ for sexual orientation, let alone discrimination against sexual minority groups, such as people who identify as LGBTQIA.

Above all else, this study provides further evidence that there is no ‘gay gene’ and that diverse sexual behaviors and orientations are a natural part of the human spectrum.

Across human societies, people engage in sexual intercourse with same-sex partners either exclusively or in addition to those of the opposite sex. Although the hereditary determinants for sexual preference are largely unknown, a few observations point to some heritable influences.

Notably, same-sex sexual behavior appears to run in families, and it lines up more often in twins that are genetically identical (monozygotic) than in twin pairs that are not genetically identical (fraternal) or siblings.

However, genetics is not the only factor influencing sexual behavior, identity, or orientation. Like other human traits, human sexuality is influenced by a continuously stirring cauldron of heritable and environmental influences.

This raises questions about the genetic influences of sexual orientation: what is the hereditary information involved in sexual behavior, attraction, and identity, and what processes does it affect?

Cataloging spots of DNA that are tightly linked to same-sex sexual behavior could enable exploration of the biological processes involved in the development of sexual orientation.

To test these questions, a group of scientists from universities, research institutes, and genetic analysis companies from all over the world collaboratively searched for pieces of DNA that were associated with same-sex sexual behavior.

Using massive datasets, the international team, led by Brendan Zietsch, Ph.D., a member of the Faculty of Health and Behavioural Sciences from the University of Queensland, Australia, matched the self-reported sexual history of people to the millions of hereditary units across participants’ genomes.

This included information from the UK Biobank study — comprising a sample of around half a million UK residents aged 40 to 70 years — and the commercial genetic analysis company 23andMe that provides individuals with detailed information about ancestry, relatives, and predisposition to traits and diseases.

“Just to give you a sense of the scale of the data, this is approximately 100 times bigger than the previous studies on this topic,” describes lead author Andrea Ganna, Ph.D., a research fellow at the Analytical and Translational Genetic Unit at Massachusetts General Hospital and Harvard Medical School.

So, what did Dr. Ganna and his colleagues find? “Well, we scanned the entire human genome and found a handful, five to be precise, locations in the human genome that are clearly associated with whatever a person reports in engaging in same-sex sexual behavior,” he continued.

Each of these locations has a very small effect individually and distinctly dependent on the person’s sex; that is, each contributes very little to a person’s sexual orientation and may act differently for males and females.

“These [genetic] variants are common in the population and they have a very small effect,” explains Dr. Ganna. “So, there is no gauge that determines whether someone has a same-sex partner. Same-sex sexual behavior is, in fact, very polygenic, meaning there is a lot of variants that contribute to these traits and this is very similar to many other behavioral traits.”

This is not unusual for complex human outcomes, as alterations in DNA common on the population level often contribute only a tiny amount to the overall variation of a trait.

“Genetics is less than half of the story for sexual behavior, but it’s still a very important contributing factor. So, overall, these findings reinforce the importance of diversity as a key aspect of sexual behavior.”

— Benjamin Neale, Ph.D.

The work reveals that the underlying genetics for sexual orientation is highly intricate and has no single determinant. Instead, many DNA bits with individually small effects spread across an individual’s entire genetic blueprint, contribute to singular differences in predisposition to same-sex sexual behavior.

“It also underscores an important role for the environment in shaping human sexual behavior and perhaps most importantly there is no single gay gene but rather the contribution of many small genetic effects scattered across the genome,” says senior author Benjamin Neale, Ph.D., Associate Professor in the Analytic and Translational Genetics Unit at Massachusetts General Hospital.

These sexual orientation related DNA fragments together explain only part of the heritability at the population level and do not allow meaningful prediction of an individual’s sexual preference.

Fah Sathirapongsasuti, Ph.D., Senior Computational Biologist at 23andMe and an author of the study relates, “As a teenager trying to understand myself and understand my sexuality, I looked at the internet for the ‘gay gene’…This paper has basically disproved that.”

How an individual bit of DNA ties back to an actual trait can be complicated. In fact, this can be one of the most challenging tasks in human genetics.

But Dr. Ganna and colleagues did find two interesting connections. These identified regions provide scientists a starting place for follow-up work on how our DNA influences sexual orientation on a biological level.

One of the locations identified associated with balding, which suggests that sex hormone regulation may be involved in the biology of same-sex sexual behavior.

Dr. Ganna postulates, “This might suggest a relationship between sex hormone regulation and same-sex sexual behavior, but really more research is needed because we need to try to better understand the biological mechanism. These are just statistical associations.”

Another one of the identified DNA regions tied to same-sex sexual behavior also relates to our sense of smell. This is interesting because while odors are important for sexual attraction we don’t yet understand how this might be related to sexual behavior.

Although the underlying mechanism at this piece of DNA is unclear, a connection between smell and reproduction has previously been established. In particular, people with Kallmann syndrome always have both delayed or absent puberty and an impaired sense of smell.

There’s still a lot to learn about the genetics of sexual orientation and behavior. The findings by this global research group highlight that there is not a single genetic component from opposite-sex to same-sex preference like in the Kinsey scale — a widely accepted and used research tool for measuring sexual orientation.

“We discovered that the Kinsey Scale, which really places individuals on a continuum from basically exclusively opposite-sex partners to exclusively same-sex partners is really an oversimplification of the diversity of sexual behavior in humans,” states Dr. Neale.

Another measure, the Klein Grid, uses the same premise but separately measures sexual attraction, behavior, fantasies, and identification as well as nonsexual preferences. However, these sexual measures are influenced by genetic factors.

“There is no gauge that determines whether someone has a same-sex partner.”

— Andrea Ganna, Ph.D.

Overall, this suggests that the most popular measures for guessing sexual behavior are based on a misconception of how sexual orientation forms and may need to be rethought.

“We also found that it’s effectively impossible to predict an individual’s sexual behavior from their genome,” states Dr. Neale. “Genetics is less than half of the story for sexual behavior, but it’s still a very important contributing factor. So, overall, these findings reinforce the importance of diversity as a key aspect of sexual behavior.”

At this juncture, we don’t know how this research applies to people around the world. Are these same-sex sexual behavior linked DNA fragments similar in different parts of the world?

Since this study was limited to participants of European ancestry and from a few Western countries, future studies with larger and more diverse samples are needed to see how these findings apply across different socio-cultural contexts.

Dr. Neale speculates that this research moves our understanding to a slightly deeper and more nuanced place where we see there is more complexity out there that we’re capturing in our very simplistic measures. He says, “That complexity is an important part of ourselves.”

That said, the study’s results overwhelmingly point toward the richness and diversity of human sexuality and refute a role for discrimination based on sexual identity or attraction.

These insights into the biological underpinnings of same-sex sexual behavior also underscore the importance of resisting unfounded conclusions especially considering the long history of misusing genetic results for social purposes.

Along these lines, Dr. Sathirapongsasuti deduces that this applies to many other human behaviors. “Similarly depression or happiness has genetic components but also non-genetic components, and none of these is necessarily a choice.”

In the end, the words of the Pulitzer Prize and Academy Award-winning Armenian-American novelist, short-story writer, and playwright William Saroyan have never rung more true, “Remember that every man is a variation of yourself.”



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Jonathan D. Grinstein, PhD

Jonathan D. Grinstein, PhD

Science writer reporting on brains, genes, and biotechnology.