The hip bone is the ONLY gender specific bone in the human body. Until you manage to swap your hip bone, you're the same gender into which you were born. Any entity, to be recognizable and definable, must have a property or properties which are constant. You can't transition BETWEEN genders without having a hard or fixed definition of the genders themselves, i.e., you can't be gender fluid without being able to identify the genders being traversed, thus males and females OF A LOGICAL NECESSITY are different and distinct.