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Homosexuality is not a disease or a lifestyle. Our orientation is rooted in our biology. However, when it comes to the question of where it really comes from, researchers are unable to give a clear answer. One theory is that a certain genetic mutation is responsible for homosexuality. Yet another relates him to the number of siblings he has, especially brothers. How much truth is there in these theories?
The researchers at NorthShore University in Illinois decided to look for the relationship between genes and orientation. Scientists have identified gene variants that are more common in homosexual men than in heterosexual men. Research on DNA samples from 1231 heterosexual men and 1077 homosexual men suggests that specific genes may determine sexual orientation.
Researchers identified two genes: SLITRK6, located on chromosome 13, and TSHR, on chromosome 14. The first one influences the functioning of the diencephalon, an area that previous studies have shown has a different volume in heterosexual and homosexual men. The latter gene is mainly related to the functioning of the thyroid gland, although it also influences the brain via a thyroid stimulating protein.
– The results of these studies have not met with any special recognition from the scientific world. Several thousand samples were tested for genes that would determine whether someone is heterosexual or homosexual. But in fact, no significant correlation could be found. However, it does not change the fact that genes may contain an answer to the question of where does sexual orientation come from: research on identical twins suggests this. If one of the twins is gay, the probability that the other is also gay is much higher than that of male fraternal twins. However, this probability is not 100%, so there are other factors besides genes. Some hypotheses assume that the environment in which we grow up, how we are brought up, can translate into our orientation. The results of studies in which brain scans were compared, it turned out that the brains of homosexual people are different from the brains of heterosexual people. But whether such a change is an effect or a cause is not known.
It must be remembered that looking for answers to why we are heterosexual or homosexual is not easy, it consists of many factors, in the current state of knowledge it cannot be said that one of them is more decisive. Certainly, research based on comparing the sequence of genes is a new and very interesting direction, but it is still too early for it to be considered a solution to the problem, says Prof. Piotr Stępień from the Institute of Genetics and Biotechnology of the University of Warsaw and IBB PAN.
Tell me how many brothers you have and I’ll tell you who you are
According to prof. Stępnia, the research conducted by Canadian researchers seems to be much more interesting. The researchers most likely managed to explain the reason for the relationship between the number of older brothers and the incidence of homosexual orientation in younger siblings (the so-called fraternal birth order effect). The effect is that the more older brothers someone has, the more likely they are to be gay. The effect of fraternal birth order may be responsible for the development of homosexuality in approx. 15% of people. men of this orientation. A similar phenomenon has not been observed in homosexual women.
Specialists from Brock University examined blood samples of 142 women, mothers of adult children. 16 of the study participants had daughters alone, 72 women had sons who were heterosexual, 31 women were mothers of homosexual men without male siblings, and 23 were homosexual sons who also had older brothers.
In the blood of women, antibodies were searched for the protein NLGN4Y, which is only found in men and is formed in the brain in utero. It is involved in the formation of connections between neurons in the fetal brain. If NLGN4Y comes into contact with the mother’s bloodstream (e.g. during childbirth), her immune system will make specific antibodies. In the next pregnancy, they may pass to the fetus and affect its brain development.
It turned out that the highest levels of anti-NLGN4Y antibodies are found in the blood of women whose one of the younger sons is homosexual. Slightly lower was found in women whose only son is gay, even lower in mothers of only heterosexual men, and the lowest in women who had never had a male child. These results suggest that the mother’s immune system is responsible for the fraternal birth order effect.
This is a very interesting result, comments prof. Stępień. However, it requires confirmation by other laboratories and in a larger number of cases. To conclusively confirm this theory, animal studies would have to be conducted. Preferably on mice or sheep, since the latter are known to have permanent homosexual orientation in males. Females would need to circulate the animal NLGN4Y protein into the bloodstream, thereby causing the formation of antibodies, and assessing whether the offspring would prefer more often the same sex. If one wanted to find out if a theory was actually true in humans, such research would have to last at least twenty years.