Humans evolved to live in small hunter-gatherer groups that did not possess such things as hand guns. The US has by far the highest murder rate in developed world (barring only South Africa which is a special case) and roughly half of all these murders go unsolved. Although it is easy enough to kill someone using a hammer or knife or whatever impliment is handy guns account for the vast majority of these murders. Other countries that have outlawed possession of hand guns might have similar numbers of serious assualts involving weapons, but much lower murder rates. Thus the idea that murder is something common that humans have evolved to commit is not supported by the facts. Modern murder rates are by and large a result of extreme social circumstances and/or the availability and common possession of hand guns.

The overwhelming majority of murders are crimes of passion committed in the heat of the moment by friends and relatives of the deceased. Just as many wild animals will impulsively strike out at each other on occation, people do the same. However, in nature such attacks are seldom fatal and rarely last more than a few moments. Tempers may flare, but die down equally rapidly. It is the introduction of modern weapons that causes such fits of temper to become fatal more often.