In his book "Beasts: What animals can tell us about human nature," Jeffrey Moussaeiff Masson writes that "if we engaged in a fair comparison of animals and humans, we would gain a deeper understanding of where our own species has gone wrong. We can learn, too, what can be done about it, even at this late hour." Masson's idea of a perfect world would be one in which humans stop eating, wearing, experimenting on, and generally exploiting animals.
He realizes that's not likely to happen, but in this thoughtful, provocative book, he presents valid arguments pertaining to the origins of violence in humankind, and the lack of similar behavior in wild animals. Instances where animals in the wild have demonstrated what could be called psychopathic tendencies (vengeful killing, rape, cannibalism) have all been traced to some sort of negative human intervention. In essence, we have not only nearly killed off some species, but we've driven a few individuals crazy.
The question of why humans seem so bent on violence takes us back 10,000 years to the advent of agriculture. The domestication of animals for the sole purpose of food, the fencing of territory, and the concern with protecting one's own family against someone else's tribe resulted, eventually, in war.