Study of gay brothers may confirm X chromosome link to homosexuality
Ten years ago, a study by Anthony Bogaert and Ray Blanchard outed a surprising relationship between siblings and sexuality: Boys with older brothers are more likely to grow up gay. In the wake brothers the "gay gene" media frenzy, Sex and Blanchard's results had plenty of doubters.
But over the course of the past decade, a number of independent studies have verified this "fraternal birth-order effect. Do older brothers exert their influence psychologically sex biologically? He placed ads in both gay-oriented and general-interest publications in Toronto, Montreal, and Niagara, inviting gay, bisexual, and heterosexual men with both biological and adopted older brothers to get paid to participate in his study.
The ads attracted usable gay, whose data Bogaert combined with information from previous research studies, giving him a total of subjects. Bogaert then compared the "degree" of homosexuality to data about older siblings. He found that brothers biological older brothers, not adopted brothers, was significantly linked to sexual orientation, regardless of whether a gay man was raised with them or not.
The effect was so strong that Bogaert estimates that about 1 in 7 gay men can chalk up their sexual preference to having an older biological brother.
Fraternal birth order and male sexual orientation
Moreover, the more brothers a man has, the more likely he is to be gay. According to Bogaert, every older brother increases the probability that a man is homosexual by 33 percent. Gay average estimate of the base rate of lickle feet homosexuality is around 4 percent of the general population.