Genetic, family or environmental factors that influence sexual orientation have been the subject of scientific study for decades and no definitive conclusion has been reached . As it is a multicausal phenomenon, it is not easy to isolate variables that usually appear together and decide which ones weigh the most as an explanatory factor.
Two recent studies focus on a possible cause unsuspected until recently to explain male homosexuality: the number of older brothers . The first, led by Ray Blanchard, Professor of Psychiatry at the University of Toronto (Canada), is a meta-analysis of previous research. Their conclusion is that there are more homosexuals among men who have more older brothers . The two variables – older and male – had been identified in previous studies, but Blanchard applied statistical methodology and found that they must go together for a connection to be established.
The second study was led by another Canadian expert, the psychologist Anthony Bogaert, who participated in Blanchard’s study and concluded that there was a prenatal cause in this matter, because he had found that having more older male siblings does not influence whether they are adopted . That idea prompted him to undertake his own research, which argues that the maternal immune response to NLGN4Y, a protein linked to the Y chromosome , could be closely related to the sexual orientation of males .
Mothers of gay boys – especially those with older siblings – had significantly higher levels of NLGN4Y. These experiments have their detractors, such as Michael Bailey, a psychologist at the University of the Northwest (USA), who has criticized the design and the unrepresentative nature of these samples. According to him, publication bias, that is, the tendency to publish significant results before inconclusive ones, could have led these two authors to reach these seemingly picturesque conclusions.
