fraternal birth order https://en.wikipedia.org/wiki/Fraternal_birth_order_and_male_sexual_orientation https://www.wikidata.org/wiki/Q3543404 A theoretical concept which posits that the more older brothers a man has from the same mother, the greater the probability is that he will be gay. Not all studies, including some with large, nationally representative samples, have been able to replicate the fraternal birth order effect. Some did not find any statistically significant difference in the sibling composition of gay and straight men; this includes the National Longitudinal Study of Adolescent to Adult Health, the largest study in the United States with relevant data on the subject. Furthermore, at least one study, on the familial correlates of joining a same-sex union or marriage in a sample of two million people in Denmark, found that the only sibling correlate of joining a same-sex union among men was having older sisters, not older brothers. fraternal birth order and male sexual orientation fraternal birth order effect olrder brother effect birth order