most assur’d,
His glassy essence, like an angry ape,
Plays such fantastic tricks before high heaven
As makes the angels weep.
—William Shakespeare, Measure for Measure
Two aspects of the decline of violence have profound implications for our understanding of human nature: (1) the violence; (2) the decline. The last six chapters have shown that human history is a cavalcade of bloodshed. We have seen tribal raiding and feuding that kills a majority of males, the disposal of newborns that kills a majority of females, the staging of torture for vengeance and pleasure, and killings of enough kinds of victims to fill a page of a rhyming dictionary: homicide, democide, genocide, ethnocide, politicide, regicide, infanticide, neonaticide, filicide, siblicide, gynecide, uxoricide, mariticide, and terrorism by suicide. Violence is found throughout the history and prehistory of our species, and shows no signs of having been invented in one place and spread to the others.
At the same time, those chapters contain five dozen graphs that plot violence over time and display a line that meanders from the top left to the bottom right. Not a single category of violence has been pinned to a fixed rate over the course of history. Whatever causes violence, it is not a perennial urge like hunger, sex, or the need to sleep.
The decline of violence thereby allows us to dispatch a dichotomy that has stood in the way of understanding the roots of violence for millennia: whether humankind is basically bad or basically good, an ape or an angel, a hawk or a dove, the nasty brute of textbook Hobbes or the noble savage of textbook Rousseau. Left to their own devices, humans will not fall into a state of peaceful cooperation, but nor do they have a thirst for blood that must regularly be slaked. There must be at least a grain of truth in conceptions of the human mind that grant it more than one part—theories like faculty psychology, multiple intelligences, mental organs, modularity, domain-specificity, and the metaphor of the mind as a Swiss army knife. Human nature accommodates motives that impel us to violence, like predation, dominance, and vengeance, but also motives that—under the right circumstances—impel us toward peace, like compassion, fairness, self-control, and reason. This chapter and its successor will explore these motives and the circumstances that engage them.
THE DARK SIDE
Before exploring our inner demons, I need to make the case that they exist, because there is a resistance in modern intellectual life to the idea that human nature embraces any motives that incline us toward violence at all.1 Though the ideas that we evolved from hippie chimps and that primitive people had no concept of violence have been refuted by the facts of anthropology, one still sometimes reads that violence is perpetrated by a few bad apples who do all the damage and that everyone else is peaceful at heart.
It is certainly true that the lives of most people in most societies do not end in violence. The numbers on the vertical axes of the graphs in the preceding chapters have been graduated in single digits, tens, or at most hundreds of killings per 100,000 people per year; only rarely, as in tribal warfare or an unfolding genocide, are the rates in the thousands. It is also true that in most hostile encounters, the antagonists, whether humans or other animals, usually back down before either of them can do serious damage to the other. Even in wartime, many soldiers do not fire their weapons and are racked by posttraumatic stress disorder when they do. Some writers conclude that the vast majority of humans are constitutionally averse to violence and that the high body counts are merely signs of how much harm a few psychopaths can do.
So let me begin by convincing you that most of us—including you, dear reader—are wired for violence, even if in all likelihood we will never have an occasion to use it. We can begin with our younger selves. The psychologist Richard Tremblay has measured rates of violence over the course of the life span and shown that the most violent stage of life is not adolescence or even young adulthood but the aptly named terrible twos.2 A typical toddler at least sometimes kicks, bites, hits, and gets into fights, and the rate of physical aggression then goes steadily down over the course of childhood. Tremblay remarks, “Babies do not kill each other, because we do not give them access to knives and guns. The question . . . we’ve been trying to