Canadian scientists have found that the more older male siblings a man has, the greater the chance he will be gay. In a series of studies reported in the UK Daily Mail Online, researchers discovered that each older brother raises a man’s odds of being a homosexual by a third.
"It’s likely to be a prenatal effect" said Anthony F. Bogeart back when his original findings were released in 2006. "This and other studies suggest that there is probably a biological basis for homosexuality."
The phenomenon is nature, not nurture, say docs from Brock University in Ontario. Rather than being attributed to any differences in the way a youngest son is raised, it has a biological basis.
Scientists say that a woman mounts an immune response in her womb while pregnant with a son. This increases with each male baby, "raising the odds of ’feminising’ the foetus’ developing brain.’"
A study of 1,000 men, including some who were adopted or brought up with stepsiblings, revealed that having many brothers raised a man’s odds of being gay. This correlation only occurred among blood brothers, however. Stepbrothers did not have an effect, but biological brothers who were brought up separately did. No similar link has been found between having many older sisters and becoming a lesbian. Full details of the study via Edge here!