Guys who have older brothers have higher chances of being gay, according to scientists.
There have been previous studies showing this pattern, and researchers now believe there is a biological explanation for this, which begins before children are even born, CNN reports. If these findings can be replicated, then there might be a concrete reason to explain why some men are gay.
Many factors contribute to a person’s sexual orientation, but researchers in Canada determined a pattern that may be associated with something that happens in a mother’s womb. This is related to a protein linked to the Y chromosome, and is vital to brain development in males.
When a woman gets pregnant with her first boy, researchers think it’s possible that this Y-linked protein enters her bloodstream. The mother’s body thinks that the protein is a foreign substance, and the immune system reacts accordingly by producing antibodies. If enough of these antibodies build up, and the woman gets pregnant with a second boy, the antibodies can cross the placenta into the brain of the next male fetus.
Anthony Bogaert, a Canadian psychologist and professor in the departments of psychology and community health sciences at Brock University, lead author on the study, said,
That may alter the functions in the brain, changing the direction of how the male fetus may later develop their sense of attraction.
Some studies have shown that the more older brothers a boy has, the greater the chances that he will be attracted to men. In 2006, research revealed that with the addition of each brother, the chances that a man will be gay goes up by one-third. However, the researchers did not explain why.
Bogaert and colleagues have been investigating the subject for over 20 years. Their initial findings noted the trend, and other studies have detected the phenomenon, even in instances where the brothers were raised apart. The same did not hold true for adopted brothers, which made scientists believe a biological explanation.
The study was published in the journal PNAS.
