Men are more likely to be gay if they have older brothers, say scientists
Canadian scientists found each older brother raises odds of homosexuality by a third
Carrying a male foetus causes an immune reaction in a women's body
It causes antibodies to attack part of the developing male brain linked to sexuality
The more older male siblings a man has, the greater chance he will be gay, according to a series of studies.
Scientists say the phenomenon cannot be explained by the youngest boy being babied and mollycoddled or other differences in the way they are brought up.
Instead, it has a biological basis, claim researchers.
They believe the immune response a woman mounts against having a male baby in her womb increases with each son, raising the odds of ‘feminising’ the foetus’s developing brain.
In one study, Canadian scientistscollected data from almost 1,000 men, including some who had been adopted or brought up with stepbrothers and stepsisters.
This revealed that having lots of brothers raised a man’s odds of being gay – but only if they were blood brothers.
