When a mother gives birth to her first son, she may create antibodies in response to the foreign male proteins of her baby. The leading biological theory is the maternal immunization hypothesis, which suggests that something changes with each son a mother conceives. 'My study adds to that - it adds another fairly strong piece to the biological puzzle that underlies, at least in part, men's sexual orientation.' 'Most studies indicate there is probably a biological basis to men's sexual orientation,' Bogaert said.
