New Research Sheds Light on the Biological Factors That Influence Sexuality

For decades, scientists have been trying to figure out which biological factors determine sexuality. One of the more inexplicable discoveries in this arena is that homosexuality is more common in men who have older brothers, known as the "older brother effect". Up until now, it’s been unclear why that is.

New research from Brock University in Canada suggests that women who give birth to boys multiple times progressively build up antibodies that will affect their future sons in utero. The researchers argue that these antibodies, formed in response to proteins present in male brains, may lead to changes in brain development that influence sexual orientation.

“It seems that some women during their first male pregnancy, or just after their first male birth, begin to detect this foreign substance (the NLGN4Y protein) and start to develop an immune response. And then later, with further male pregnancies, the high levels of antibodies directed toward this substance may change brain development in these later born males,” says lead researcher Tony Bogaert in a media release.

While the study has yet to be replicated by another research team, it suggests that the older brother effect is rooted in prenatal factors. In other words, this is yet more evidence that sexual orientation has a biological basis, a point that has long been contested by anti-gay types.

“The implications of this study, especially if and when it is replicated by an independent team, are profound,” explains Bogaert. “Along with more deeply understanding the exact origin of the older brother effect, it helps solidify the idea that, at least in men, there’s a strong biological basis to sexual orientation. “This is the culmination of more than 20 years of research where we started looking at the older brother, or fraternal birth order, effect. The current study adds to the growing scientific consensus that homosexuality is not a choice, but rather an innate predisposition.”

There's no single factor determining whether a person is gay or not, but research like this continues to support the theory that sexual orientation is at the very least influenced by biological factors. Considering that anti-gay groups still push the notion that being gay is a choice that can be fixed with harmful conversion therapy and the like, this area of research is truly valuable.

This story has been updated.