A lynching took place recently outside an ironmonger’s shop in Nairobi … It was close to one of the city’s fancier shopping centres, early in the morning, with commuters streaming down the road on foot. A man had his mobile phone stolen but managed to lay a hand on the thief just long enough for the crowd to close in. His two accomplices waded in to rescue their man but the mob engulfed them. Stones rained down. Boulders crushed their heads and chests. Then the crowd moved on, became commuters once more, and the police removed three bodies.

This scene of mob violence, casually reported in The Economist two years ago, is common in Kenya. Could it just as easily happen on the streets of London or New York? The politically correct reply is yes. The truth is no. Steven Pinker’s The Better Angels of Our Nature explains why.

Pinker, a renowned evolutionary psychologist at Harvard, offers a 800-page tale of how humanity, led by the West, has collectively tamed the beast of violence. The result is that the post-1945 period is probably the least bloody sixty-five-year patch in the history of our species. Indeed, our chance of meeting