Do genes influence sexuality?
Studies of the families of gay men show they are more likely to have gay brothers, uncles and cousins than are heterosexual men – especially on their mother's side of the family. Studies of twins also point to a genetic influence on sexuality. In 2008 the world's largest study of twins concluded that sexuality is shaped by both genetic and random environmental factors (but unlikely to be things like family influences). The results suggested that genetics accounted for around 35% of the differences between men and 18% of those between women in homosexual behaviour.