This is something I've kicked around for a while as well (the whole post, not just B.W.'s comment). In order to dispense with the lenses of our belief systems that color our worldview, as well as our moral philosophizing if the two are distinguishable, I wanted to tear everything down to physical reality. Physical reality (simplified) says that the one who brings the most force or power to the conflict - and isn't all interaction with things other than ourselves conflict, much the way "collision" is defined in physics as two objects attempting to occupy the same space - wins the conflict. With sentient beings, a calculation of the odds and options is performed before entering too deeply into the conflict (as the consequences can become more grave as the conflict progresses) in order to preserve their existence. This calculation makes the appearance of force important.

When calculation of apparent force presents no clear winner, then collaboration and compromise become possible. (This obviously builds on many levels, and is just thinking out loud anyway). I think this is the point where moral systems develop and have effect ("Natural Rights" being part of a moral system). When the balance of power between entities appears to be nearly equal or not so biased as to reduce the risk of conflict then morals dictate the interaction. If that balance of power is skewed, the moral basis (rights and such) matters not.