Some of my ancestors floating in the Great Salt Lake around 1926. The guy in the back was a family friend. People use to take the train out to the Great Salt Lake for a day at the Saltair resort, therefore the matching swimsuits. No implication of anyones sexuality implied, I just enjoyed the photo of brothers.

As the oldest child this doesn’t apply to me, but the more older brothers a boy has, the higher the chance a boy will be gay. Younger brothers and sisters of any age have no correlation.

We don’t know why, but there’s an interesting theory. When a mother has a series of boys, and becomes pregnant with another male, her body may have an immune system response that affects fetal development, including sexual differentiation of the brain. This could be a reaction of her female body reacting to a series of male embryos or it could be an evolutionary adaptation to ensure there is a feminized boy in the family if girls fail to appear.

A later study validated the results, and added the calculation that each older brother increases the chances the next son is homosexual by 33%. At an average rate of homosexual orientation of 4%, it would take 9-10 older brothers to reach a 50-50 chance of being gay.


  • Gay Men: The more older brothers, the more likely a son is gay.
  • Lesbians: No sibling effect observed.


  • R. Blanchard and A.F. Bogaert, Proportion of homosexual men who owe their sexual orientation to fraternal birth order: an estimate based on two national probability samples, Am. J. Hum. Biol. 16 (2004), pp. 151–157.
  • R. Blanchard, Quantitative and theoretical analyses of the relation between older brothers and homosexuality in men, J. Theor. Biol. 230 (2004), pp. 173–187.