I just picked these noticeable acute periods from the _continuous_ history of human violence as mere illustrative examples.

While only few practice medicine, majority of the people do have ideas about what "valid and just" violence can be applied to what group of other people, and as result they either directly participate or support violence performed on their behalf. So in my view, major combined reasoning activity of human species brains, ie. performed activity integrated over participants (think "top" command), is the reasoning supporting the various acts of violence.

Vs. the actual consequences - my numbers look differently than yours. May be one Einstein or Mozart resulted in even more lives saved than medicine. It doesn't change the fact that for each hour of Mozart's brain developing music there are several orders of magnitude more hours cumulatively spent by others at the same time reasoning for violence.

An the reason being here is that human species got evolutionary advantage by being able to strike first with overwhelming power. Lions don't try to exterminate hyenas and hyenas doesn't try to exterminate lions. They peacefully coexist until paths of specific lions and hyenas cross over specific zebra. Humans are unique in their ability to reason that exterminating others they would potentially have more zebras to themselves and that the "others" may have the same reasoning, and thus "either we or they". Thus we have, again just for mere example, tutsi and hutu.