Sex and Relationships: Why do gay men often have older brothers? The Birth Order Effect Explained

In today's society, sexual orientation and gender identity are increasingly openly discussed, and scientists are constantly exploring the biological and psychological mechanisms behind these topics. A recent high-profile study has once again put the spotlight on an interesting phenomenon: having one or more older brothers may increase a man's chances of being gay.

According to Scott Semenyna, professor of psychology at Stetson University, this phenomenon, known as the "sibling birth order effect," has been documented not only in Canada and the U.S., but has been observed globally, including in Samoa, southern Mexico, Turkey and Brazil. This discovery challenges our traditional understanding of the formation of sexual orientation and triggers further exploration of the underlying biological mechanisms.

Prof. Semenina pointed out that researchers have noticed this phenomenon since the 1990s. Theoretically, the likelihood of a man being attracted to a man increases by about 331 TP3T for each additional brother he has, meaning that compared to a man with no brother, the chance of a man with one brother becoming homosexual is about 2.61 TP3T, and this increases to 3.51 TP3T for a man with two brothers, and for a man with five brothers, the chance increases to about For men with five brothers, the probability increases to about 81 TP3T.

The mechanisms behind this effect are not fully understood, but researchers have explored potential associations with parental chromosomes and possible biological factors.2022 A study published in the Journal of Sex Research found an even stronger correlation by looking at data from more than 9 million people in the Netherlands born between 1940 and 1990. Researchers at the University of Melbourne found that the likelihood of a man entering a same-sex relationship increased by 411 TP3T if he had three older brothers compared to men with three older sisters, and by 801 TP3T if this was compared to having three younger brothers.

Notably, this pattern was also observed in females, albeit to a relatively weak degree. This finding suggests that there may be some association that is at least partially driven by biological mechanisms.

However, experts emphasize that even if such a pattern exists, it affects only a small percentage of the population. The vast majority of people with multiple brothers are still attracted to the opposite sex. The study reminds us that the formation of sexual orientation is a complex process that is influenced by a variety of factors, including, but not limited to, genetics, biology, environment and personal experience.

As scientific research progresses, our understanding of the formation of sexual orientation will become more comprehensive. This will not only help us better understand gender diversity, but also provide a scientific basis for promoting inclusiveness and acceptance in society.