A new study suggests that the more biological older brothers a man has, the more likely he is to be gay, which researchers say supports the "nature-over-nurture" theory, or more commonly known as "born this way."
The claim, by scientists at Brock University in Ontario, is that women's bodies mount an immune responses whenever pregnant with a male child which produce antibodies that affect the part of the fetus' brain linked to sexual orientation. It's believed that with each pregnancy, the immune response increases. (No link was found between a girl having more older sisters and being a lesbian.)
As part of the study, researchers collected data from 1,000 men including those who were adopted. Having older stepbrothers or older adopted brothers raised in the same household did not seem to have the same affect on sexuality as having older biological brothers, even if they weren't raised in the same household.