Our bodies appear nearly the same. Only the marker of an adult, clothes, blankets and other man-made items, distinguish us. As we grow up, we learn to hate the other gender. They are different. They are to be treated so.
Girls hang out with girls.
Boys hang out with boys. When we mature, we find we must unlearn our bias against the other gender. Some of us go on to love and fantasize the other gender. Others chose to become the other gender. And finally, in death there is no discrimination.