An observation on evolutionary psychology
I’m generally sceptical about sociobiology/evolutionary psychology, on the grounds that, since we know almost nothing about the conditions under which we evolved (hunter-gatherer societies that survived into the 20th century are necessarily exceptional, and therefore unrepresentative), it’s very hard to see how we can make any useful inferences.
But the simple fact that our ancestors were hunters enables us to make one kind of inference with high reliability. Encounters with other*, armed, humans must have been a frequent occurrence
Two things follow, both of which have been remarked on, but typically by different people.
First, if even a modest proportion of such encounters led to armed combat, our ancestors would have wiped each other out
Second, if even a tiny proportion of such encounters led to armed combat, the death rate from violence would far exceed that associated with modern warfare.
(Do an example, and you can substitute your own values for “modest” and “tiny”)
From the first point, it follows that there must have existed some combination of cultural and genetic constraints that ensured that the vast majority of encounters between armed humans passed off peacefully. From the second, it follows that any cultural or genetic characteristic that increased an individual’s probability of surviving such encounters would yield substantial survival benefits.
If you emphasise either one of these in isolation, you can derive strong, and seemingly compelling hypotheses about genetic constraints on human behavior. But taking the two together, the picture is a lot more complex.
*The most frequent encounters would have been with close kin, but on any plausible assumption about the organisation of hunting there must have been plenty of encounters with distantly related or unrelated individuals (or social constructs such as territorial boundaries that acted to reduce the frequency of such encounters).