The Role of Adaptive Psychology in Violence

I should have disambiguated earlier between a rational theory of violence where people are acting in what they perceive to be their own self-interest and an adaptive theory of violence. What I'm really talking about is sort of proximate motivational psychology. So what is the person feeling? The assumption is that there are ultimate causes that are driven by adaptive reasons, but that in the proximate psychology of the perpetrator, they're not necessarily doing the kind of cost benefit calculation of their actions.