Where does human savagery come from? The animal behaviorist Marc Bekoff, writing in Psychology Today after last month's awful events in Newtown, Conn., echoed a common view: It can't possibly come from nature or evolution. Harsh aggression, he wrote, is "extremely rare" in nonhuman animals, while violence is merely an odd feature of our own species, produced by a few wicked people. If only we could "rewild our hearts," he concluded, we might harness our "inborn goodness and optimism" and thereby return to our "nice, kind, compassionate, empathic" original selves.
What makes humans special is not our occasional propensity to kill strangers when we think we can do so safely. Our unique capacity is our skill at engineering peace. Within societies of hunter-gatherers (though only rarely between them), neighboring groups use peacemaking ceremonies to ensure that most of their interactions are friendly. In state-level societies, the state works to maintain a monopoly on violence. Though easily misused in the service of those who govern, the effect is benign when used to quell violence among the governed.
Under everyday conditions, humans are a delightfully peaceful and friendly species. But when tensions mount between groups of ordinary people or in the mind of an unstable individual, emotion can lead to deadly events. There but for the grace of fortune, circumstance and effective social institutions go you and I. Instead of constructing a feel-good fantasy about the innate goodness of most people and all animals, we should strive to better understand ourselves, the good parts along with the bad.
—Ms. Goodall has directed the scientific study of chimpanzee behavior at Gombe Stream National Park in Tanzania since 1960. Mr. Wrangham is the Ruth Moore Professor of Biological Anthropology at Harvard