Fraternal birth order correlates with sexual orientation

Viren tipped me off to this fascinating result that reinforces the idea that we really have no clue about what is happening in the earliest stages of neural development. This recent PNAS study found that the strongest predictor of a man being homosexual is the number of biological, older brothers. The effect is independent of non-biological brothers and still holds when the brothers are reared apart. As presented in the paper, the evidence suggests that the early development in the uterus might be different for later children.

Abstract after the jump.

Biological versus nonbiological older brothers and men’s sexual orientation
Anthony F. Bogaert


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