There have been many debates about homosexuality, from whether it’s a choice to whether it can be passed on through family genes.
Now, however, studies have found that men with older brothers are more likely to be gay, particularly if you have a number of them.
In a phenomenon known as the ‘fraternal birth order effect,’ boys who have a bunch of older male siblings will be more prone to be gay.
According to research, an antibody in mothers increases after a certain amount of births, making their child more likely to be interested in the same sex.
In the Proceedings of the National Academy of Sciences, a study was published explaining how this comes to be possible. They were searching for a factor common to mothers who had multiple sons, as well as at least one gay child in the family. They attempted to correlate these factors and find common ground for them.
In their research, the researchers found that there was a common factor in women with multiple male offspring – they discovered that when they’re pregnant with a male child, they produce an antibody known as NLGN4Y.
This protein is produced by the Y chromosome and has a role in brain development. For that reason, it stood out against all other factors available to the researchers.
NLG4Y has the power to change a brain in the womb, which could affect a child’s sexuality.
As the researchers looked deeper into the protein, they concluded that the influence it had centered in the section of the brain where sexual attraction is processed.
NLGN4Y seemed to get to work there in each of the pregnancies, and so the more boys a female conceives, the more of the protein she produces. The exposure the babies have to NLGN4Y makes them more likely to have same-sex attraction.
Of the 142 women studied, the ones with gay sons and no or few older brothers had lesser amounts of the NLGN4Y antibody. On the other hand, the women who had birthed a lot of male children had gay sons with high levels of NLGN4Y in their bloodstream, which means men with older brothers are more likely to be gay.
The correlation is therefore strong and indicates that the older brothers you have, the more likely you are to have high levels of NLGN4Y, as well as more of a disposition to be homosexual.
Furthermore, women who had no sons or heterosexual children produced much less NLGN4Y. Also, men have less of this antibody present in their brains as a general rule.
However, despite substantial evidence, this study has yet to be tested on a larger scale. While it may seem conclusive that the protein is relevant in sexuality, it could merely be coincidence too.
It has also only been found to be true of 15% of gay men that the protein effects.
The question of the origin of sexuality is more complex, too. The study doesn’t take into account why lesbians are attracted to one another, and it also doesn’t explain those who have attractions to multiple sexes.
The more you think about it, the less likely it seems that a conclusion has been discovered. However, it’s an interesting scientific addition to studies about sexuality and attraction.
