Photograph from the collection of Stephen Rutledge
If you are guy and you have older brothers, there is a better chance that you are gay. It has something to with what is called ”Fraternal Birth Order Effect”. This is rather dry, but stick with me. According to an article just published in the journal Proceedings of the National Academy of Sciences in the United State of America (PNAS), scientists have noticed this in previous research, but now they think they have a biological explanation as to why. It starts before birth.
At Brock University, Anthony Bogaert and his research team say that some women who are pregnant with boys develop antibodies that target a protein made by the Y chromosome (which women do not have). The immune systems make antibodies to recognize foreign molecules that could be dangerous bacteria. Pregnant women produce antibodies against fetal molecules, such as their fetus having a different blood group.
The researchers say this may be at least one of the biological reasons some men are gay. They noticed a pattern that may be linked to something that happens in the womb. It’s possible that when a woman gets pregnant with her first boy, this Y-linked protein gets into her bloodstream. The mother’s body recognizes the protein as a foreign substance, and her immune system responds, creating antibodies. If enough of these antibodies build up in the woman’s body and if she becomes pregnant with another a boy, they can cross the placental barrier and enter the brain of the second male fetus.
They found that the mothers of gay sons with older brothers had the highest levels of antibodies against this protein, followed by the mothers of gay sons with no older brothers. Women who had straight sons had less of these antibodies, while women with no sons had the least.
The team suggests these antibodies build up in some women’s bodies with every male baby they have. At higher concentrations, it is possible that the effect of these antibodies on the protein they target leads to changes in brain development that have an influence on sexual orientation.
The protein targeted by the antibodies is called NLGN4Y. It sounds like an Internet acronym or a Star Wars character, but it is thought to play a role in how brain cells connect to each other. These antibodies affect the wiring of the fetal brain, and that might explain why each subsequent son is more likely to be gay.
Earlier research had shown that the more older brothers a boy has, the more of a chance that boy will be attracted to other guys. A study in 2006 showed that with each brother, the chance that a man will be gay goes up by about a third.
The researchers tested 142 women and 12 men, from 18 to 80-years-old, and found a higher concentration of NLGN4Y in blood samples from women than from men. They found the highest concentration of antibodies to the protein in women with gay younger sons who had older brothers, compared with women who had no sons or who had given birth to only straight boys.
The study builds on work Bogaert and his team have been researching for more than 20 years. Their initial research noted the phenomenon happens even across cultures. They found that a man’s chances of being gay increased even if he was raised apart from his older brother.
Researchers did not see a similar pattern in families with adopted brothers, so scientists started to think there must be some sort of a maternal developmental explanation. Their research did not bring a biological explanation for why some men are bisexual or for gay only children, gay oldest sons, or lesbians. I am not a scientist, but there must be an explanation for girls who like girls, perhaps the mother was listening to Indigo Girls at conception.
I hope that this research will lead to an understanding the being gay is innate and not environmental, and that the antibodies can’t be fiddled with invitro, because the world needs more gays.
