In sixteenth-century Paris, a popular form of entertainment was cat-burning, in which a cat was hoisted in a sling on a stage and slowly lowered into a fire. According to historian Norman Davies, "[T]he spectators, including kings and queens, shrieked with laughter as the animals, howling with pain, were singed, roasted, and finally carbonized." Today, such sadism would be unthinkable in most of the world. This change in sensibilities is just one example of perhaps the most important and most underappreciated trend in the human saga: Violence has been in decline over long stretches of history, and today we are probably living in the most peaceful moment of our species' time on earth.
In the decade of Darfur and Iraq, and shortly after the century of Stalin, Hitler, and Mao, the claim that violence has been diminishing may seem somewhere between hallucinatory and obscene. Yet recent studies that seek to quantify the historical ebb and flow of violence point to exactly that conclusion.
Some of the evidence has been under our nose all along. Conventional history has long shown that, in many ways, we have been getting kinder and gentler. Cruelty as entertainment, human sacrifice to indulge superstition, slavery as a labor-saving device, conquest as the mission statement of government, genocide as a means of acquiring real estate, torture and mutilation as routine punishment, the death penalty for misdemeanors and differences of opinion, assassination as the mechanism of political succession, rape as the spoils of war, pogroms as outlets for frustration, homicide as the major form of conflict resolution--all were unexceptionable features of life for most of human history. But, today, they are rare to nonexistent in the West, far less common elsewhere than they used to be, concealed when they do occur, and widely condemned when they are brought to light.
At one time, these facts were widely appreciated. They were the source of notions like progress, civilization, and man's rise from savagery and barbarism. Recently, however, those ideas have come to sound corny, even dangerous. They seem to demonize people in other times and places, license colonial conquest and other foreign adventures, and conceal the crimes of our own societies. The doctrine of the noble savage--the idea that humans are peaceable by nature and corrupted by modern institutions--pops up frequently in the writing of public intellectuals like Jose Ortega y Gasset ("War is not an instinct but an invention"), Stephen Jay Gould ("Homo sapiens is not an evil or destructive species"), and Ashley Montagu ("Biological studies lend support to the ethic of universal brotherhood"). But, now that social scientists have started to count bodies in different historical periods, they have discovered that the romantic theory gets it backward: Far from causing us to become more violent, something in modernity and its cultural institutions has made us nobler.
To be sure, any attempt to document changes in violence must be soaked in uncertainty. In much of the world, the distant past was a tree falling in the forest with no one to hear it, and, even for events in the historical record, statistics are spotty until recent periods. Long-term trends can be discerned only by smoothing out zigzags and spikes of horrific bloodletting. And the choice to focus on relative rather than absolute numbers brings up the moral imponderable of whether it is worse for 50 percent of a population of 100 to be killed or 1 percent in a population of one billion.
Yet, despite these caveats, a picture is taking shape. The decline of violence is a fractal phenomenon, visible at the scale of millennia, centuries, decades, and years. It applies over several orders of magnitude of violence, from genocide to war to rioting to homicide to the treatment of children and animals. And it appears to be a worldwide trend, though not a homogeneous one. The leading edge has been in Western societies, especially England and Holland, and there seems to have been a tipping point at the onset of the Age of Reason in the early seventeenth century.
At the widest-angle view, one can see a whopping difference across the millennia that separate us from our pre-state ancestors. Contra leftist anthropologists who celebrate the noble savage, quantitative body-counts--such as the proportion of prehistoric skeletons with axemarks and embedded arrowheads or the proportion of men in a contemporary foraging tribe who die at the hands of other men--suggest that pre-state societies were far more violent than our own. It is true that raids and battles killed a tiny percentage of the numbers that die in modern warfare. But, in tribal violence, the clashes are more frequent, the percentage of men in the population who fight is greater, and the rates of death per battle are higher. According to anthropologists like Lawrence Keeley, Stephen LeBlanc, Phillip Walker, and Bruce Knauft, these factors combine to yield population-wide rates of death in tribal warfare that dwarf those of modern times. If the wars of the twentieth century had killed the same proportion of the population that die in the wars of a typical tribal society, there would have been two billion deaths, not 100 million.
President Bush, touting his successful environmental policy, holds up the last remaining piece of Greenland.
Political correctness from the other end of the ideological spectrum has also distorted many people's conception of violence in early civilizations--namely, those featured in the Bible. This supposed source of moral values contains many celebrations of genocide, in which the Hebrews, egged on by God, slaughter every last resident of an invaded city. The Bible also prescribes death by stoning as the penalty for a long list of nonviolent infractions, including idolatry, blasphemy, homosexuality, adultery, disrespecting one's parents, and picking up sticks on the Sabbath. The Hebrews, of course, were no more murderous than other tribes; one also finds frequent boasts of torture and genocide in the early histories of the Hindus, Christians, Muslims, and Chinese.
At the century scale, it is hard to find quantitative studies of deaths in warfare spanning medieval and modern times. Several historians have suggested that there has been an increase in the number of recorded wars across the centuries to the present, but, as political scientist James Payne has noted, this may show only that "the Associated Press is a more comprehensive source of information about battles around the world than were sixteenth-century monks." Social histories of the West provide evidence of numerous barbaric practices that became obsolete in the last five centuries, such as slavery, amputation, blinding, branding, flaying, disembowelment, burning at the stake, breaking on the wheel, and so on. Meanwhile, for another kind of violence--homicide--the data are abundant and striking. The criminologist Manuel Eisner has assembled hundreds of homicide estimates from Western European localities that kept records at some point between 1200 and the mid-1990s. In every country he analyzed, murder rates declined steeply--for example, from 24 homicides per 100,000 Englishmen in the fourteenth century to 0.6 per 100,000 by the early 1960s.
On the scale of decades, comprehensive data again paint a shockingly happy picture: Global violence has fallen steadily since the middle of the twentieth century. According to the Human Security Brief 2006, the number of battle deaths in interstate wars has declined from more than 65,000 per year in the 1950s to less than 2,000 per year in this decade. In Western Europe and the Americas, the second half of the century saw a steep decline in the number of wars, military coups, and deadly ethnic riots.
Zooming in by a further power of ten exposes yet another reduction. After the cold war, every part of the world saw a steep drop-off in state-based conflicts, and those that do occur are more likely to end in negotiated settlements rather than being fought to the bitter end. Meanwhile, according to political scientist Barbara Harff, between 1989 and 2005 the number of campaigns of mass killing of civilians decreased by 90 percent.
The decline of killing and cruelty poses several challenges to our ability to make sense of the world. To begin with, how could so many people be so wrong about something so important? Partly, it's because of a cognitive illusion: We estimate the probability of an event from how easy it is to recall examples. Scenes of carnage are more likely to be relayed to our living rooms and burned into our memories than footage of people dying of old age. Partly, it's an intellectual culture that is loath to admit that there could be anything good about the institutions of civilization and Western society. Partly, it's the incentive structure of the activism and opinion markets: No one ever attracted followers and donations by announcing that things keep getting better. And part of the explanation lies in the phenomenon itself. The decline of violent behavior has been paralleled by a decline in attitudes that tolerate or glorify violence, and often the attitudes are in the lead. As deplorable as they are, the abuses at Abu Ghraib and the lethal injections of a few murderers in Texas are mild by the standards of atrocities in human history. But, from a contemporary vantage point, we see them as signs of how low our behavior can sink, not of how high our standards have risen.
The other major challenge posed by the decline of violence is how to explain it. A force that pushes in the same direction across many epochs, continents, and scales of social organization mocks our standard tools of causal explanation. The usual suspects--guns, drugs, the press, American culture--aren't nearly up to the job. Nor could it possibly be explained by evolution in the biologist's sense: Even if the meek could inherit the earth, natural selection could not favor the genes for meekness quickly enough. In any case, human nature has not changed so much as to have lost its taste for violence. Social psychologists find that at least 80 percent of people have fantasized about killing someone they don't like. And modern humans still take pleasure in viewing violence, if we are to judge by the popularity of murder mysteries, Shakespearean dramas, Mel Gibson movies, video games, and hockey.
What has changed, of course, is people's willingness to act on these fantasies. The sociologist Norbert Elias suggested that European modernity accelerated a "civilizing process" marked by increases in self-control, long-term planning, and sensitivity to the thoughts and feelings of others. These are precisely the functions that today's cognitive neuroscientists attribute to the prefrontal cortex. But this only raises the question of why humans have increasingly exercised that part of their brains. No one knows why our behavior has come under the control of the better angels of our nature, but there are four plausible suggestions.
The first is that Hobbes got it right. Life in a state of nature is nasty, brutish, and short, not because of a primal thirst for blood but because of the inescapable logic of anarchy. Any beings with a modicum of self-interest may be tempted to invade their neighbors to steal their resources. The resulting fear of attack will tempt the neighbors to strike first in preemptive self-defense, which will in turn tempt the first group to strike against them preemptively, and so on. This danger can be defused by a policy of deterrence--don't strike first, retaliate if struck--but, to guarantee its credibility, parties must avenge all insults and settle all scores, leading to cycles of bloody vendetta. These tragedies can be averted by a state with a monopoly on violence, because it can inflict disinterested penalties that eliminate the incentives for aggression, thereby defusing anxieties about preemptive attack and obviating the need to maintain a hair-trigger propensity for retaliation. Indeed, Eisner and Elias attribute the decline in European homicide to the transition from knightly warrior societies to the centralized governments of early modernity. And, today, violence continues to fester in zones of anarchy, such as frontier regions, failed states, collapsed empires, and territories contested by mafias, gangs, and other dealers of contraband.
Payne suggests another possibility: that the critical variable in the indulgence of violence is an overarching sense that life is cheap. When pain and early death are everyday features of one's own life, one feels fewer compunctions about inflicting them on others. As technology and economic efficiency lengthen and improve our lives, we place a higher value on life in general.
A third theory, championed by Robert Wright, invokes the logic of non-zero-sum games: scenarios in which two agents can each come out ahead if they cooperate, such as trading goods, dividing up labor, or sharing the peace dividend that comes from laying down their arms. As people acquire know-how that they can share cheaply with others and develop technologies that allow them to spread their goods and ideas over larger territories at lower cost, their incentive to cooperate steadily increases, because other people become more valuable alive than dead.
Then there is the scenario sketched by philosopher Peter Singer. Evolution, he suggests, bequeathed people a small kernel of empathy, which by default they apply only within a narrow circle of friends and relations. Over the millennia, people's moral circles have expanded to encompass larger and larger polities: the clan, the tribe, the nation, both sexes, other races, and even animals. The circle may have been pushed outward by expanding networks of reciprocity, a la Wright, but it might also be inflated by the inexorable logic of the golden rule: The more one knows and thinks about other living things, the harder it is to privilege one's own interests over theirs. The empathy escalator may also be powered by cosmopolitanism, in which journalism, memoir, and realistic fiction make the inner lives of other people, and the contingent nature of one's own station, more palpable--the feeling that "there but for fortune go I."
Whatever its causes, the decline of violence has profound implications. It is not a license for complacency: We enjoy the peace we find today because people in past generations were appalled by the violence in their time and worked to end it, and so we should work to end the appalling violence in our time. Nor is it necessarily grounds for optimism about the immediate future, since the world has never before had national leaders who combine pre-modern sensibilities with modern weapons.
But the phenomenon does force us to rethink our understanding of violence. Man's inhumanity to man has long been a subject for moralization. With the knowledge that something has driven it dramatically down, we can also treat it as a matter of cause and effect. Instead of asking, "Why is there war?" we might ask, "Why is there peace?" From the likelihood that states will commit genocide to the way that people treat cats, we must have been doing something right. And it would be nice to know what, exactly, it is.
Steven Pinker is Johnstone Professor of Psychology at Harvard and the author of The Stuff of Thought.