An older sibling can affect a younger sibling’s chances of being gay – new study finds how

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

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

Previous research had already established a link between having older brothers and an increased chance of male homosexuality, The Post reported in April, but this study is the first to identify a similar link for those with older sisters.

The findings showed that men with older siblings are more likely to identify as gay, with the probability increasing with the number of older siblings they have.

For example, having at least one older brother increases the odds of being gay by approximately 10%, while having older sisters is associated with a 5% increase.

However, men with three older brothers have a shocking 41% higher chance of being gay, and those with five older brothers face an 8% chance – four times more than the average man.

The researchers also found that this correlation does not extend to lesbians and older siblings or bisexuality.

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

Data for this research was obtained from the UK Biobank, a comprehensive study that monitors the health and lifestyle of a large British population over time.

The findings are consistent with a previous investigation conducted in the Netherlands, which also highlighted the relationship between the number of older siblings and the probability of being gay.

The reason for this connection is still unconfirmed, but a leading theory is the “maternal immune hypothesis”.

This theory claims that after a mother gives birth to a boy, proteins enter her bloodstream and stimulate the production of antibodies that can affect the sexual development of subsequent male children.

As a mother has more sons, these antibodies accumulate and can affect personality traits, potentially leading to changes in sexual orientation.

A 2017 study supports this hypothesis by showing that mothers of gay sons have more antibodies targeting male-specific proteins compared to mothers of straight sons. However, this explanation does not take into account the newfound bond with older sisters.

Despite these findings, the researchers stress the need for more research into why sibling order affects sexuality.