Men who have a brother have a higher chance of becoming gay
First, homosexual men do tend to have a higher birth order than heterosexual men, and this higher birth order is attributed to homosexual men having greater number of older brothers. [8][9] According to several studies, each older brother increases a male child's naturally occurring odds of having a homosexual orientation by 28–48%. [7][ The fraternal birth order effect is the tendency for older brothers to increase the odds of homosexuality in later-born males. This study compared the strength of the effect in subjects from small versus large families and in homosexual subjects with masculine versus feminine gender identities.
Men with older brothers are more likely to be gay, suggesting
Studies worldwide show that queer people tend to have more older brothers than other kinds of siblings. Justin Torres, a queer novelist and the youngest of three brothers, asks: Should it matter?. This is a preview of subscription content, log in via an institution to check access. Institutional subscriptions. Why gay men often have older brothers
Researchers are further exploring the notion that having an older brother increases a man's chances of being gay. It's called fraternal birth order effect. Men with an older brother are more likely to become gay and the cause of the problem is formed before birth. There are many different factors that need to be considered to determine someone's sexual orientation. 
Fraternal birth order and male sexual orientation
The proteins enter the mother’s bloodstream and trigger the production of antibodies that influence the sexual development of subsequent children. These maternal antibodies accumulate over successive pregnancies with male foetuses, which means men with more older brothers are more likely to experience same-sex sexual attraction. .
Men with older brothers are more likely to be gay, study suggests
The fraternal birth order effect is the tendency for older brothers to increase the odds of homosexuality in later-born males. This study compared the strength of the effect in subjects from small versus large families and in homosexual subjects with masculine versus feminine gender identities. Meta . .
Having older brothers increases a man’s chances of being gay
Having older brothers increases a man’s chances of being gay. Known since the s as the "fraternal birth order effect," it has been theorized that men have roughly a 33% increased probability of being attracted to men for every older brother they have. . Recent Findings on Fraternal Birth Order and Homosexuality in
The fraternal birth order effect (FBOE) is the finding that greater numbers of older brothers are statistically associated with greater odds of homosexuality in later-born males. The reliability of this effect has recently been confirmed in separate meta-analyses of 30 convenience samples (Blanchard, a) and six probability samples (Blanchard, b), together totaling homosexual males. . Fraternal Birth Order, Family Size, and Male Homosexuality
Previously, there was a study that yielded similar results, a man with the probability of becoming gay and attracted to other men was higher if there were many brothers. In , a study showed that the proportion of a gay man would increase by about one-third if there was an older brother, but then scientists could not explain this phenomenon. .