Now it seems that increasing levels of antibodies in a mother’s immune system could play a role.
Anthony Bogaert at Brock University, Canada, and his team think that some women who are pregnant with boys develop antibodies that target a protein made by the Y chromosome. Our immune systems make antibodies to recognise foreign molecules, which have the potential to be from dangerous bacteria. But pregnant women sometimes also produce antibodies against fetal molecules – for example, if their fetus has a different blood group. Bogaert’s team wondered if maternal antibodies might play a role in shaping sexual orientation.
The team collected blood from 142 women, and screened it for antibodies to a particular brain protein that is only made in males.
They found that the mothers of gay sons with older brothers had the highest levels of antibodies against this protein, followed by the mothers of gay sons with no older brothers. Women who had straight sons had less of these antibodies, while women with no sons had the least.