Is there a gay scale

Genes and homosexualityThere is no such thing as a gay or lesbian gene

Genes and sexuality - keywords that motivate researchers and the public. Studies with 80 participants make the headlines.

Andrea Ganna: "In most cases the results could not be confirmed. So we put together an international team and collected the data from half a million people. That is a hundred times more than was previously available."

The data comes from the UK Biobank in Great Britain and the American company 23andMe. On the other hand, if you want to collect as much data as Andrea Ganna from the European Molecular Biology Laboratory in Helsinki, you have to compromise on the exact description of the behavior that is involved. Sexuality in particular has many forms. In this study it was reduced to one question: "Have you ever had sex with someone of the same sex?"

The genetic makeup is important, the environment is more important

This includes self-confessed homosexuals as well as people who have experimented with the same sex in adolescence. Thanks to this simplification, however, the authors were able to achieve clear results. The first is that genetic differences explain about a third of the differences in sexual orientation. The genetic makeup is important, but the environment is more important. It is completely unclear what these environmental factors are. As far as the genetic component is concerned, the researchers were able to identify some locations in the genome.

Andrea Ganna: "We examined the entire genome and found five variants that have something to do with whether someone has ever had sex with a same-sex person. These variants are very common in the population, but they only have a small effect. Together they explain less than one percent of the differences in sexual behavior. "

Deeper understanding of sexual behavior

So these are certainly not gay or lesbian genes. It is like many other behaviors: The influence of DNA is apparently distributed over hundreds, maybe thousands, of very small effects. So it is hardly possible to construct a genetic test for homosexuality. This message was also important to those affected, who are still struggling with discrimination in many countries and with whom the researchers worked closely. For science, however, the small effects are quite interesting, they can lead to a deeper understanding of sexual behavior, says Andrea Genna.

"One variant lies next to several genes that influence the sense of smell. And that is important for sexual attraction. Another variant has something to do with hair loss and thus with sex hormones. So here there could be a connection between the regulation of sex hormones and same-sex sexual behavior. "

It is also interesting that gay and lesbian love are presented differently at the level of genes. This could be related to the hormones or to the social environment that treated women and men differently.

Sex is complex

In general, Andrea Ganna and his colleagues emphasize how complex sexuality is. In a further analysis, they looked for genetic differences between bisexual and purely homosexual people. Here again completely different variants were noticeable. On the genetic level, sexual behavior shows many different facets. One-dimensional psychological scales such as that of Alfred Charles Kinsey therefore fall short. For Ben Neale of the Broad Institute in Cambridge, USA, this is the most important finding from the new study.

Ben Neale: "We have learned that there is a lot more diversity out there, as the genetic analysis shows. These increasingly longer abbreviations in the LGBTQIA + community really do exist, we can prove it."

Or rather, give first hints. After all, even this huge study was still too small and the questions posed to the participants were not specific enough.

* Editor's note: The original headline was "There is no such thing as a gay or lesbian gene". In order to rule out any misunderstanding, we have made the heading more precise.