http://en.wikipedia.org/wiki/Birth_order#Sexuality: That's odd, I didn't think birth order affected that kind of stuff... As the youngest in the family, I was disappointed with this study so I decided to call myself a "functional first born". I'm not doing worse in life than my sister (I hope).The fraternal birth order effect is the name given to the observation that the more older brothers a man has, the greater the probability is that he will have a homosexual orientation. The fraternal birth order effect is the strongest known predictor of sexual orientation, with each older brother increasing a man's odds of being gay by approximately 33%. Even so, the fraternal birth order effect only accounts for a maximum of one seventh of the prevalence of homosexuality in men. There seems to be no effect on sexual orientation in women, and no effect of the number of older sisters.