Are they not born, but become?
Scientists have determined the influence of genetics on people's sexual orientation
Yulia Vorobyova, Vesti
Is it possible to determine a person's sexual orientation based on the analysis of his genes? Definitely not. In fact, genetics can only explain up to 25% of non-heterosexual behavior.
This conclusion was made by an international team of scientists based on the results of the largest genetic study of people's sexual orientation to date. A scientific article based on the results of the work was published in the journal Science (Ganna et al., Large-scale GWAS reveals insights into the genetic architecture of same-sex sexual behavior).
Experts sought to understand whether there is a gene that makes a person homosexual, and how powerful a genetic factor has on people's orientation.
To find answers, experts studied the genetic data of 477 thousand people. The authors of the work clarified that this sample is about a hundred times larger than in previous studies on the same topic.
The information was obtained from the British base UK Biobank and from the base of the American biotechnology company 23andMe.
The authors studied the DNA markers of volunteers and the data of surveys about sexual behavior that they filled out. The team also consulted with behavioral psychologists and representatives of LGBT community advocacy groups.
As a result, scientists have found five genetic markers largely associated with same-sex sexual encounters. Two markers were common for men and women, two more were characteristic of men, and one was only for women.
In addition, thousands of other DNA markers have been found that also affect people's sexual preferences, but to a lesser extent.
It is noteworthy that one of the genetic variants was located in the region of the genome associated with male baldness and sex hormones such as testosterone. The other was in an area rich in olfactory genes that are associated with sexual attraction.
When the researchers combined all the data, they came to the conclusion that genetics can explain from 8% to 25% of non-heterosexual behavior. The rest, they say, is explained by the influence of the environment – from the effects of hormones in the womb to social factors in later human life. At the same time, the five most significant DNA markers explained less than 1% of cases of non-heterosexual behavior.
Thus, the team came to the conclusion that homosexuality is influenced by hundreds or even thousands of genes, each of which has its own very modest effect.
"For the first time, we can unequivocally conclude that some genes influence the propensity to have same–sex partners," said Michael Bailey from Northwestern University in the USA. He did not participate in this work, but earlier his team analyzed the genomes of 409 pairs of homosexual brothers and provided convincing evidence that attraction to members of their own sex has a biological basis.
However, the co-author of the new study, Benjamin Neale from Massachusetts General Hospital, emphasizes that there is not a single "homosexual gene", and a genetic test that a person will have a same-sex relationship is unlikely to be informative.
By the way, it is noted that earlier researchers also found that people with "markers of non-traditional orientation" are more open to new experiences, are more likely to use light drugs (marijuana) and have a higher risk of developing mental illnesses, such as depression. Researchers believe that representatives of sex minorities may be more susceptible to mental disorders due to pressure from society (in some countries, same-sex love is punishable, up to the death penalty).
The experts who commented on this work note that the results should be interpreted with caution, since in this case the "measure of evaluation of sexual orientation" was not clearly established. For example, even those people who declared only one same-sex sexual contact in the questionnaires were considered non-heterosexual. Some scientists believe that such an episode from the life of the participants does not necessarily indicate certain sexual preferences, but can only reflect how open a person is to a new experience.
The need to clearly indicate the measure of evaluation of sexual orientation, in particular, was stated by evolutionary biologist William Rice from the University of California at Santa Barbara. Earlier, his team suggested that homosexuality may be due to epigenetic changes in one of the parents, which are transmitted to the fetus. They do not affect the structure of genes, but manifest themselves in the process of their "inclusion" or work (in particular, the effect of testosterone on the embryo changes, which subsequently affects the work of the human brain and affects its behavior).
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