I'd be really curious to see what happened in a society where your social gender was determined by something else than your biological sex. Birth order, for instance. Odd male and even female, so that every family's first child is considered a boy and their second a girl. Or vice versa. No matter what the biology. (Presumably, there'd need to be some certain sign of the gender to tell the two apart, like all social females wearing a dress and no social males doing so.)