It probably has to do with sex or something. Because women carry and give birth to babies, that automatically makes them weak or something, maybe it has to do with something stupider like penetration and the penetrated is always the weaker one so it just carried onto gender norms. It's rather stupid either way - to base something off of primitive antics every other animal does. [ she sighs, a bit irritated at memories of being shafted because she was a kunoichi and not a medic nin ): ]