It's theorized that prenatal hormone exposure can alter the neonate brain a bit. Also, conditioning by a bad parent can warp a kid. My younger brother says he thinks he's gay, but he was pretty normal growing up. However, our mother conditioned him to have female emotional reactions and she warped him in the years after I left home. I think he's maybe straight - he asks me questions about women - but got socially conditioned into being screwed up. We had weak stepfather - lousy role model - but I rebelled and was way hetero but my brother was stuck at home in that f'ed up environment.