Explanations for modern human behavior rooted in evolutionary psychology have come under particularly strong attack lately. (See, e.g., here.)
With that caveat in mind, I direct your attention to this article in the L.A. Times by David Buss, a well-known evolutionary psychologist, who claims that "we all have the capacity to become murderers." Here's an excerpt:
The unfortunate fact is that killing has proved to be a disturbingly effective solution to an array of adaptive problems in the unforgiving evolutionary games of survival and reproductive competition: preventing injury, rape or death; protecting one's children; eliminating a crucial antagonist; acquiring a rival's resources; securing sexual access to a competitor's mate; preventing an interloper from appropriating one's own mate; and many others. The logic of evolutionary struggle is all about reproductive competition. Those strategies that lead to greater reproductive success are selected for, over eons of evolution, and come to characterize our species.
. . . .
If we all have mental mechanisms designed for murder, why don't more of us kill? For one thing, killing is so costly for victims that natural selection has fashioned finely honed defenses — anti-homicide strategies — designed to damage those who attempt to destroy us. We kill to prevent being killed, so attempting murder is a dangerous strategy indeed. Second, we live in a modern world of laws, judges, juries and jails, which have been extremely effective in raising the cost of killing. Homicide rates among traditional cultures lacking written laws and professional police forces are far higher than those in modern Western cultures. Among the Yanomamo of Venezuela and the Gebusi of Africa, for example, more than 30% of men die by being murdered.
It may be disturbing to think of killing as evolutionarily adaptive and part of human nature, but this does not mean approval or acceptance of murder. I would suggest instead that those who create myths of a peaceful human past, who blame killing on the contemporary ills of modern culture and who cling to single-variable theories that have long outlived their scientific warrant are the ones who tread on dangerous moral ground. The problem of murder cannot be solved by wishing away undesirable aspects of human nature.
(Thanks to Mind Hacks for a pointer to the L.A. Times article.)