Actually I think there is an evolutionary basis for human beings being civil and cooperative with each other .... we never would've survived as a species in the wild if we were constantly killing each other.
We had to survive in a group/tribe culture to hunt, raise children, and protect each other. I think this is especially true of humans because physically we're not anything special ... put a human in a cage with a tiger or a lion and we're not lasting very long. We needed to be in group and to be able to think and communicate to be able to do things like hunt in a more cerebral way, since physically we're relatively on the weak end of the natural kingdom.
I think the natural human "equilibrium" is actually to be in a relatively peaceful state with the person next to you. It's advantageous to human survival, a person who's running around like a nutcase, killing and raping etc. at will would be counter productive in an evolutionary sense and could put the tribe/group at risk.
Feeling "bad" or guilty when you've done something awful very well may be an evolutionary "reflex", which eventually we came to rationalize as morality.







