Older siblings affect chances of younger brother being born

A recent study found that younger siblings are more likely to be gay.

Researchers at the University of Melbourne have provided new insights into the relationship between sibling order and sexual orientation, the Daily Mail reports.

Previous research has identified a link between having older brothers and an increased chance of male homosexuality, but this study is the first to find a similar link among people with older sisters, The Washington Post reported in April.

The findings showed that men with siblings were more likely to identify as gay, and that the likelihood increased with the number of older brothers.

For example, having at least one older brother increases the odds of being gay by about 10%, while having a sister increases the odds by 5%.

However, men with three older brothers were a staggering 41% more likely to be gay, while men with five older brothers were 8% more likely, four times as likely as the average man.

The researchers also found that this correlation did not hold true for lesbians and older siblings or for bisexuals.

However, the study did reveal a link between the number of siblings and asexuality: People without siblings were more likely to report not experiencing sexual attraction.

Data for this study were taken from UK Biobank, a comprehensive study monitoring the health and lifestyle of a large UK population over time.

This finding is consistent with a previous survey conducted in the Netherlands, which also highlighted the relationship between the number of older brothers and the probability of homosexuality.

The reason for this link has not been proven, but one leading theory is the “maternal immunity hypothesis.”

The theory claims that after a mother gives birth to a boy, the protein enters her bloodstream and triggers the production of antibodies that may affect the boy’s subsequent sexual development.

As a mother gives birth to more sons, these antibodies accumulate and may affect personality traits, which may lead to differences in sexual orientation.

This hypothesis is supported by a 2017 study that showed that mothers of gay sons had more antibodies against a male-specific protein than mothers of straight sons. However, this explanation doesn’t explain the newfound connection with her sister.

Despite these findings, the researchers stressed the need for more research into why sibling order affects sexual behavior.