News > Research confirms same-sex attraction has a biological basis and your siblings matter

Research confirms same-sex attraction has a biological basis and your siblings matter

New research shows having a greater number of older brothers increases the probability of a person entering a same-sex union at some point in their lives.

The “fraternal birth order effect” is one of the most well-documented patterns supporting a biological origin of human sexual orientation. This longstanding hypothesis proposes men’s propensity for homosexuality increases with the number of older biological brothers they have.