I'm fairly sure most anthropologists would argue aggression, and thus it various expressions, are natural to anything living.
IMHO, most anthropologist would agree that the human species has evolved so far from any thing close to nature or natural that only the social anthropologist would study us.
I will check with my colleagues, but I am fairly sure they will say there has always been the warriors of any clan/tribe, but they were the exception, not the rule. But its their exploits that were valued and recorded, meaning they stood out from the others, which could support that they were not the norm, but the elite.
Guess we haven't evolved that far have we?
Are we all capable of violence/killing? Yes, but few will every actually realize that capability.
Are we all capable of love and peace? Yes, and many more will actually realize that.