Some currents of Psychology collect how the order of birth influences some aspects of personality or character. Even scientific studies have obtained results about how this fact interferes with health, the structure of the brain and, even, intelligence. Now, science supports this effect in relation to sexual orientation, through a discovery published in 2017 by the prestigious journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).
Although the number of older siblings had previously been linked to sexual orientation, science had not been able to explain this phenomenon until now: the article details how the level of certain antibodies in the mother’s immune system could play a role on the sexual orientation of male children.
Specifically, it is a protein that targets the Y chromosome of the embryo during pregnancy. According to the researchers, some mothers develop antibodies against this protein, essential in the development of the male brain, an effect that occurs with increasing probability with each male pregnancy, altering the brain structures underlying sexual orientation in their children.
In other words, the more male children a woman has, the more likely it is that the latter are homosexual. Or, what is the same, the probability that a homosexual child is born increases with the number of pregnancies.
The key is in maternal antibodies
The researchers, belonging to various Canadian universities, started from an initial observation: that gay men have more older brothers than heterosexual men. And they developed the hypothesis that the mother’s immune system is involved in this fact.
For the study, immunological assays were developed targeting two proteins linked to the Y chromosome, which is what determines the male sex in the embryo and shapes the male brain. This protein is essential in brain development. Specifically: protocarin 11 linked to Y (PCDH11Y) and neuroligin 4 linked to Y (NLGN4Y).
Subsequently, the plasma of various women, about half of whom had a homosexual child, was analyzed along with a control group (women with heterosexual children or no male children) for specific antibodies to male proteins.
The results indicated that mothers of homosexual children, particularly those with more older children, had significantly higher levels of NLGN4Y than the rest of mothers with heterosexual children or no male children.
Therefore, the results suggest an association between the maternal immune response to NLGN4Y and subsequent sexual orientation in male offspring.
The biological origin of homosexuality, a source of controversy
The biological origin of human sexual orientation is a topic that generates controversy in society, but no less scientific interest.
Be that as it may, this study is an important advance in understanding the origins of sexual orientation in men, as it provides support for a biological mechanism, which had been theorized but never experimentally studied: a maternal immune response to a important protein in the development of the male fetal brain.
At the same time, it provides an explanation for one of the events most closely related to male homosexuality for years: the number of older brothers.
References: ‘Male homosexuality and maternal immune responsivity to the Y-linked protein NLGN4Y’. Anthony F. Bogaerta, Malvina N, Skorskab, Chao Wangd, José Gabriea, Adam J. MacNeila, Mark R. Hoffarthb, Doug P. VanderLaanc, e, Kenneth J. Zuckerf, and Ray Blanchardf. (2017) PNAS. D oi: 10.1073 / pnas.1705895114
