"It's pretty bad science to observe the rats in one cage, and then assume that their behavior must be a perfect representation of all rats that have/will ever exist(ed)."

This is it. Human 'nature' cannot properly be observed when we have collectively existed within artificial constructs of people outside of our awareness for generations. The existence of governments, media, and control systems of all kinds creates a hostile environment driven by artificial scarcity and competition.

Attempting to ascertain a degree of certainty when it comes to what constitutes human nature is a bit frivolous in this regard.

Of course if we put humans in a cage with limited pieces of cheese, we're going to rip each other to shreds to survive. That's not 'human nature', that's disconnection from nature.