Pinker attributes the decline of violence to numerous mutually reinforcing factors that are likely to sound familiar. At the top of the list is the rise of the modern state, which suppresses the violence of citizens and adjudicates disputes by means of police and courts. What is more, democracies rarely if ever fight against each other; over the past century the percentage of humanity living under democratic regimes has surged from 12 to over 60 percent. The growing empowerment of women has played an important role; when women gain access to birth control violence tends to subside along with population growth. The rise of international trade, which makes nations increasingly dependent on each other, has helped, too. So have mass media and the spread of literacy, which promote empathy for others beyond our family, tribe, nation, and even species.
Pinker keeps coming back to reason as the key to our ongoing pacification. Reason helps us see the destructive consequences of submitting to our violence-perpetuating "demons," notably our desire for power and vengeance. Through reason we can understand the destructive consequences of violence, even against those whom we fear, and we can appreciate the benefits of cooperation. Reason has propelled the growing, global recognition of the rights of women, children, homosexuals, racial and religious minorities, and other often-abused groups.
I have one major disagreement with Pinker. True to his tragic view of human nature, he subscribes to what I call the deep-roots theory of war, which holds that lethal group aggression, and not just violence per se, is an evolutionary adaptation reaching back millions of years. As evidence, he notes that chimpanzees, our closest genetic relatives, have been observed engaging in deadly group raids. So have tribal societies such as the Yanomamo, whose behavior supposedly resembles that of our pre-state ancestors. Archaeological relics—skeletons with hack marks and spear heads embedded in them, rock drawings depicting battles and walls and other fortifications—also reveal that pre-state societies engaged in group violence.
Critics have raised many objections to the deep-roots theory. Chimp raids are rare, and may be a response to recent human encroachment. Some modern tribal people, such as the Semai of Malaysia and the !Kung of Africa, are quite peaceful. As for the archaeological evidence of warfare, it extends back only about 12,000 years, and excavations have revealed that some pre-state societies thrived for centuries or longer without leaving significant signs of violence.
You don’t have to be prone to dangerously utopian views to be persuaded, as I am, by a different theory of war’s origins, first advanced by Margaret Mead in 1940 and favored by anthropologists such as Sarah Blaffer Hrdy, Douglas Fry, and Brian Ferguson. War, Mead proposed, is not a biological adaptation but a cultural "invention"—like music, art, cooking, and religion—that emerged relatively recently in human prehistory. War is an especially infectious meme, because if one society starts attacking its neighbors, their only options are to surrender, flee, or fight. Societies in a warlike region have a strong incentive to boost their fighting capability, by inventing new tactics and weapons, and to carry out pre-emptive strikes against neighbors. In this way, the whole world rapidly became militarized, armed and dangerous. For millennia, we have been struggling to overcome this cultural contagion, and we're still struggling, in spite of our recent gains. Just in the last decade, the United States, arguably the most advanced civilization in history, has invaded two countries, and it now routinely assassinates without trial many suspected enemies around the world.
The debate over how war began is important, because those who reject the possibility of a radical, permanent reduction of state-sponsored violence often cite the claim that war is deeply rooted in our prehistory and genes: War, if it is ancient and innate, must also be inevitable. I wish that Pinker had repudiated the deep-roots theory, or at least acknowledged the abundant counterevidence. Still, Better Angels is a monumental achievement. His book should make it much harder for pessimists to cling to their gloomy vision of the future. Whether war is an ancient adaptation or a pernicious cultural infection, we are learning how to overcome it.