By way of summary I can’t do better than Pinker’s own opening paragraph: “This book is about what may be the most important thing that has ever happened in human history. Believe it or not—and I know that most people will not—violence has declined over long stretches of time, and today we may be living in the most peaceable era in our species’ existence. The decline, to be sure, has not been smooth; it has not brought violence down to zero; and it is not guaranteed to continue. But it is an unmistakable development, visible on scales from millennia to years, from waging of wars to the spanking of children.”

Yes, the 20^th century was gored with horrific violence and mass murder perpetrated by Hitler, Stalin, Mao, Pol Pot, and lesser monsters, and Pinker’s not denying this; he’s just saying things used to be even worse, and he devotes a large part of this lengthy book (700-some pages of texts and graphs plus 100 or so of notes, references, and an index) to presenting evidence to back that up.

For example, examination of the remains of prehistoric humans reveals that about 15 percent of them died as a result of violence, very little different from the fraction of persons killed in local wars and raids in hunter-gatherer societies today. In the 20^th century, deaths attributable not just to warfare itself but also to genocide, war-related disease, and mass starvation caused by Stalin, Mao, et al, amounted to around 3 percent of all deaths.

Pinker offers an interesting table compiled by Matthew White listing the allegedly worst things humans have ever done to each other, as measured by loss of life. The 20^th century shows up only three places in the top 10. True, the very top two spots are held by World War II (55 million deaths including the Holocaust) and Mao Zedong (40 million, mostly from policies that caused starvation). Stalin (20 million) trails way back in 8^th place.

But adjusted for the size of the world population at the time, World War II is the only 20^th century slaughter to make the top 10, and that just barely, at position 9. In terms of the fraction of all humans killed, the deadliest bloodbath of all time resulted from General An Lushan’s takeover of China in the year 755, which cost some 36 million lives in a remarkably brief period, the equivalent of 429 million in the mid-20^th century. (See necrometrics.com for more.)

It isn’t just war-related deaths that have declined. For instance, from a sampling of historical written records and a comparison with modern data from the same locations, it appears that circa 1300 the murder rate (the annual number of homicides per 100,000 persons) in Western Europe was about 30 times as high as it is today.

Pinker suggests that the decline of violence is likely due to a succession of overlapping developments, starting with the appearance of civilizations and central governments, which even if disposed to external war and conquest have typically found it in their interest to enforce peace within their borders. That idea goes back at least to Thomas Hobbes, who argued in Leviathan (1651) that in a state of prehistoric anarchy violence was a rational choice, a way of obtaining wealth and women, destroying potentially dangerous opponents, and making others afraid to attack. Only a strong neutral third party able to enforce the rule of law—a government, the “Leviathan”—could make men behave.

Another development was what Pinker calls the Humanitarian Revolution, the spread of learning that slowly led to the beginnings of empathy and the notion that other people aren’t so different from ourselves, a process that clearly still has a long way to go.

Society has become less barbaric in other ways as well, doing away with corporal punishment for criminals, then for schoolchildren. (I don’t recall Pinker’s remarking on it, but if you think about it, that ordering is odd.) Slavery still exist but is everywhere illegal. In advanced countries homosexuals are no longer treated as criminals (only a few years too late to save Alan Turing) and in a rapidly growing number of places same-sex couples, like mixed-race couples before them, are no longer denied the fundamental human right to marry.

Steven Pinker is a Harvard psychology professor, and as one might expect he spends a lot of time talking about the anatomy of the brain as it relates to violence. While interesting, this is only peripherally related to the subject of the book, since obviously brain anatomy itself hasn’t changed very much over the time span in question. A little more relevant is his excursion into behavioral economics and game theory, showing how various developments have altered the payoff matrix that otherwise would have made violence the optimal choice.

While I think Pinker could have made his point more succinctly, he is a good writer and the book manages to stay interesting despite its length, and it is full of fascinating facts. For just one surprising example, a study of terrorism in recent decades found not one instance in which terrorists who primarily targeted civilians achieved their stated goals.

Anyway, it’s nice to read something positive about the world for a change!

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