Steven Pinker is a professor of psychology at Harvard University, the author of several magnificent books about the human mind, and one of the most influential scientists on earth. He is also my friend, an occasional mentor, and an adviser to my nonprofit foundation.

Steve’s new book is The Better Angels of Our Nature: Why Violence Has Declined. Reviewing it for The New York Times Book Review, the philosopher Peter Singer called it “a supremely important book.” I have no doubt that it is, and I very much look forward to reading it. In the meantime, Steve was kind enough to help produce a written interview for this blog.

I suspect that when most people hear the thesis of your book—that human violence has steadily declined—they are skeptical: wasn’t the 20th century the most violent in history?

Probably not. Data from previous centuries are far less complete, but the existing estimates of death tolls, when calculated as a proportion of the world’s population at the time, show at least nine atrocities before the 20th century (that we know of) that may have been worse than World War II. They arose from collapsing empires, horse tribe invasions, the slave trade, and the annihilation of native peoples, with wars of religion close behind. World War I doesn’t even make the top 10.

Also, a century comprises 100 years, not just 50, and the second half of the 20th century was host to a Long Peace among great powers and developed nations (the subject of one of the book’s chapters) and more recently, to a New Peace in the rest of the world (the subject of another chapter), with unusually low rates of warfare.

Need I remind you that the “atheist regimes” of the 20th century killed tens of millions of people?

This is a popular argument among theoconservatives and critics of the new atheism, but for many reasons it is historically inaccurate.

First, the premise that Nazism and communism were “atheist” ideologies makes sense only within a religiocentric worldview that divides political systems into those that are based on Judeo-Christian ideology and those that are not. In fact, 20th-century totalitarian movements were no more defined by a rejection of Judeo-Christianity than they were defined by a rejection of astrology, alchemy, Confucianism, Scientology, or any of hundreds of other belief systems. They were based on the ideas of Hitler and Marx, not David Hume and Bertrand Russell, and the horrors they inflicted are no more a vindication of Judeo-Christianity than they are of astrology or alchemy or Scientology.

Second, Nazism and Fascism were not atheistic in the first place. Hitler thought he was carrying out a divine plan. Nazism received extensive support from many German churches, and no opposition from the Vatican. Fascism happily coexisted with Catholicism in Spain, Italy, Portugal, and Croatia.

Third, according to the most recent compendium of history’s worst atrocities, Matthew White’s Great Big Book of Horrible Things (Norton, 2011), religions have been responsible for 13 of the 100 worst mass killings in history, resulting in 47 million deaths. Communism has been responsible for six mass killings and 67 million deaths. If defenders of religion want to crow, “We were only responsible for 47 million murders—communism was worse!,” they are welcome to do so, but it is not an impressive argument.

Fourth, many religious massacres took place in centuries in which the world’s population was far smaller. Crusaders, for example, killed 1 million people in world of 400 million, for a genocide rate that exceeds that of the Nazi Holocaust. The death toll from the Thirty Years War was proportionally double that of World War I and in the range of World War II in Europe.

When it comes to the history of violence, the significant distinction is not one between theistic and atheistic regimes. It’s the one between regimes that were based on demonizing utopian ideologies (including Marxism, Nazism, and militant religions) and secular liberal democracies that are based on the ideal of human rights. I present data from the political scientist Rudolph Rummel showing that democracies are vastly less murderous than alternative forms of government.

Your claim that violence has declined depends on comparing rates of violence relative to population size. Is that really a fair measure? Should we give ourselves credit for being less violent just because there has been population growth?

You can think about it in a number of ways, but they all lead to the conclusion that it is the proportion, rather than the absolute number, of deaths that is relevant. First, if the population grows, so does the potential number of murderers and despots and rapists and sadists. So if the absolute number of victims of violence stays the same or even increases, while the proportion decreases, something important must have changed to allow all those extra people to grow up free of violence.

Second, if one focuses on absolute numbers, one ends up with moral absurdities such as these: (a) it’s better to reduce the size of a population by half and keep the rates of rape and murder the same than to reduce the rates of rape and murder by a third; (b) even if a society’s practices were static, so that its rates of war and violence don’t change, its people would be worse and worse off as the population grows, because a greater absolute number of them would suffer; (c) every child brought into the world is a moral evil, because there is a nonzero probability that he or she will be a victim of violence.

As I note in the book, “Part of the bargain of being alive is that one takes a chance at dying a premature or painful death, be it from violence, accident, or disease. So the number of people in a given time and place who enjoy full lives has to be counted as a moral good, against which we calibrate the moral bad of the number who are victims of violence. Another way of expressing this frame of mind is to ask, If I were one of the people who were alive in a particular era, what would be the chances that I would be a victim of violence? [Either way, we are led to] the conclusion that in comparing the harmfulness of violence across societies, we should focus on the rate, rather than the number, of violent acts.”

Where did you get your data?

It depends. For the contrast between nonstate and state societies, I used data from forensic archeology and from quantitative ethnography. For the history of homicide in Europe, data from coroners and town records go back centuries. Western governments today keep good data on homicides (the violent crime of choice, because a dead body is hard to explain away), and several of them conduct crime victimization surveys for other crimes (which avoid the distortion of how willing victims are to report crimes to the police). For wars large and small, and other kinds of armed conflict since 1946, we have the Uppsala Conflict Data Project/Human Security Report Project and the Peace Research Institute of Oslo. For larger wars since 1816, I used datasets from the Correlates of War Project. Some historians and political scientists (such as Pitirim Sorokin, Quincy Wright, Peter Brecke, and Jack Levy) have tried to quantify war deaths in earlier periods, and “atrocitologists” such as Matthew White and Rudolph Rummel have done so for genocides, deliberate famines, and other kinds of mass violence. And of course in recent decades almost no aspect of life has gone unquantified by pollsters, government bureaucrats, and social scientists.

Haven’t we just been lucky? If Churchill hadn’t stood up to Hitler, if Stalin hadn’t been willing to sacrifice tens of millions of Russians, if German scientists had succeeded in their nuclear program, then most of the world would be living under the horrors of the Third Reich.

True, but these counterfactuals go both ways. As John Mueller has put it, “Had Adolf Hitler gone into art rather than politics, had he been gassed a bit more thoroughly by the British in the trenches in 1918, had he, rather than the man marching next to him, been gunned down in the Beer Hall Putsch of 1923, had he failed to survive the automobile crash he experienced in 1930, had he been denied the leadership position in Germany, or had he been removed from office at almost any time before September 1939 (and possibly even before May 1940), Europe’s greatest war would most probably never have taken place.”

One could argue that in fact the world has just emerged from a run of stupendous bad luck, one in which three extraordinarily bloodthirsty men—Hitler, Stalin, and Mao—managed to take over powerful states and were responsible for a majority of the deaths from war and genocide in the 20th century. Many historians have argued as follows: no Hitler, no Holocaust; no Stalin, no Purge; no Mao, no Great Leap Forward and Cultural Revolution.

I repeat: Haven’t we just been lucky? On a number of occasions, such as the Cuban Missile Crisis, the world seems to have come dangerously close to nuclear annihilation.

According to the most recent analyses of documents from the Cuban Missile Crisis (see, e.g., Max Frankel’s High Noon in the Cold War), both the U.S. and U.S.S.R. desperately tried to get out of the crisis, avoiding unnecessary provocations and offering greater concessions than they had to. Other allegedly just-this-close brushes with Armageddon, such as the Vietnam and Yom Kippur wars, were even less perilous. As Mueller puts it, the metaphor of an escalator, in which one misstep could have carried leaders up and away to all-out nuclear war, is misleading. A better metaphor is a ladder: each rung made leaders increasingly acrophobic, and in every case they nervously sought a way to step back down.

You attribute a part of the decline of violence to the forces of modernity and enlightenment. Yet Germany before the Nazi takeover was the most cultured, advanced, and cosmopolitan society in the world. Doesn’t this show that cultural and intellectual sophistication are no protection against barbarism?

It’s misleading to essentialize an entire society as if it were a single mind. Weimar Germany did have subcultures that were sophisticated and cosmopolitan. But it also had subcultures, both elite and grassroots, that loathed secular modernity and Enlightenment universalism and signed on to Counter-Enlightenment sentiments of romantic militarism and nationalism—the valorization of blood and soil. The problem was that members of the second subculture murdered the members of the first. In a section called “Ideology” I discuss social psychology experiments showing how the silencing of dissenting views can result in the takeover of a society by a belief system that few of its individual members hold individually—the phenomenon of “extraordinary popular delusions and the madness of crowds.”

Have there been times in history when violence has increased? If so, couldn’t it happen again?

Of course. Examples of increases of violence I discuss include a rise in the concentration of destructiveness of European wars up until World War II, the heyday of genocidal dictators in the middle decades of the 20th century, the rise of crime in the 1960s, and the bulge of civil wars in the developing world following decolonization. Yet every one of these developments has been systematically reversed.

The decline of violence isn’t a steady inclined plane from an original state of maximal and universal bloodshed. Technology, ideology, and social and cultural changes periodically throw out new forms of violence for humanity to contend with. The point of Better Angels is that in each case humanity has succeeded in reducing them. I even present some statistical evidence for this cycle of unpleasant shocks followed by sadder-but-wiser recoveries.

As to whether violence might increase in the future: of course it might. My argument is not that an increase in violence in the future is impossible; it’s that a decrease in violence has taken place in the past. These are different claims.

Most people seem to think that wars erupt over scarce resources? Is this true?

Most wars are not fought over shortages of resources such as food and water, and most shortages of resources don’t lead to war. The Dust Bowl of the 1930s did not lead to an American civil war; nor did the tsunamis of 2003 and 2011 lead to war in Indonesia or Japan. And several statistical studies of recent armed conflicts have failed to find a correlation between drought or other forms of environmental degradation and war. Climate change could produce a lot of misery and waste without necessarily leading to large-scale armed conflict, which depends more on ideology and bad governance than on resource scarcity.

Are you willing to make any predictions about violence in the future?

I think that the humanitarian movements that have gathered momentum since the Enlightenment will continue to make progress. The burning of heretics, gruesome executions, blood sports, slavery, debtors’ prisons, foot-binding, eunuchism, and wars between developed states won’t make a comeback any time soon. Most likely capital punishment, violence against women, human trafficking, the beating and bullying of children, and the persecution of homosexuals will continue to decline, albeit bumpily and unevenly, over a span of decades. I’m willing to go out on this limb because international moral shaming campaigns in the past (such as those against piracy, whaling, and slavery) have generally succeeded over the long term. I think there is also a non-negligible chance that within the next 25 to 50 years there will be fewer bloodthirsty despots, and that nuclear weapons could be abolished. But terrorist attacks, civil war, and wars involving nondemocracies are too capricious to predict, since they depend so much on the actions of individuals. Also, crime rates have defied every expert prediction, and it would be foolish to say that they could not go back up.

One of my great concerns is that technology is making it easier for one person to harm vast numbers of other people. It is certainly conceivable that one event—a hugely successful act of bioterrorism, for instance—could suddenly displace us from this historical trend toward pacifism that you describe. And, as Jonathan Glover pointed out in his fine book Humanity, technology has made it so that those things that are most harmful are not necessarily most disturbing. Thus, if waging war becomes increasingly like playing a video game, the gamer-soldiers of the future might be appalled by the brutality of a bar fight but capable of annihilating whole populations by remote control with a clear conscience. There is also the worry that the most destructive technologies will find their way into the hands of people who have not had their moral intuitions tuned by modernity—think Mongols with nuclear weapons. I’m wondering to what degree you share these concerns.

Yes, I discuss all of them. It’s an interesting question—almost a philosophical question—whether a single kook with a nuke, or a small number of fanatics with other weapons of mass destruction would count as displacing the world from its historical trend toward pacifism, if the vast majority of the world were appalled by the destruction and continued its pacific trajectory. A large number of deaths from a single renegade perpetrator would be a misleading indicator of the state of the world. But more to the point, I don’t think that it’s inevitable, or even particularly likely, that a terrorist group will get its hands on a loose nuke or build a garage nuke, nor that it would engineer an epidemic-scale pathogen.

I also admire Glover’s Humanity (I wrote a glowing review of it for The New York Times when it came out), but I don’t think that the transition from face-to-face to remote-control styles of killing has led to an increase in deaths. In past centuries, men with swords, spears, daggers, bows and arrows, pikes, bayonets, and muskets could kill people by the millions, while today’s drones are targeted to take out enemies in the single digits—and when an errant drone in Afghanistan killed 10 civilians (which would have been a rounding error in previous wars), it was an international incident that brought out profuse apologies. I argue in the book that weaponry is overrated as a driver of violence—human intentions are vastly more important. And while it’s true that people have an aversion to causing direct bodily harm to a stranger, this skittishness is easily set aside, or even inverted into a ferocious savagery, under a variety of circumstances, including vengeance, panic, and sadism.

To read more of Sam Harris’s writing, check out his blog.