And it has dropped steeply since the Middle Ages. Oxford in the 1300s, Pinker tells us, was 110 times more murderous than it is today.
With a nod to the German sociologist Norbert Elias, Pinker calls this movement away from killing the "civilising process". He challenges several enduring myths. It's not true, says Pinker, that man in primitive societies, being at one with his environment, was less inclined towards violent struggle. Nor was the church-focused village a more peaceful environment than the model that replaced it, the impersonalised cities of the Industrial Revolution. In short, the book is a corrective to the widely held belief that humanity is locked into some sort of moral decline.
The notion that life is measurably improving is about as unfashionable in educated circles as the conviction that Western culture is in any sense civilising.
To be tagged as a credulous optimist is one thing, yet Pinker also risks being condemned as a scientific racist. His graphs on the incidence of murder show present-day tribal and hunter-gatherer cultures to be far more homicidal than even the most lethally armed developed nation - a fact that is bound to bring censure from those Pinker derides as the "anthropologists of peace".
The subject of evolutionary psychology is often viewed as a form of biological determinism that repeats the mistakes of discredited sciences of human nature by lending credence to discriminatory prejudices. Others feel it reduces human beings to gene robots, governed by impulses over which we have no control.
For his part, Pinker points out that genetic predisposition does not rule out individual free will. The thrice-married professor believes that it's preposterous "that because I believe that the male desire for multiple sexual partners has an evolutionary explanation ... I am excusing or apologising for men who sleep around". By the same token, while he promotes the Darwinian hypothesis that, like all species, we are compelled to reproduce, he made the decision not to have children. As he wrote in How The Mind Works, if his genes don't like it, "they can take a running jump".
Pinker appears to have become more emboldened with each new book. And while he is not overtly political in the sense of occupying a defined position on the left or right, his subject matter has become steadily more political in the sense of its potential divisiveness.
Born in Montreal in 1954, Pinker grew up in a middle-class, secular, Jewish household. His father was a manufacturing salesman who retrained as a lawyer, and his mother a homemaker who later became the deputy principal of a school.
"The way to explain the decline in violence," he writes, "is to identify the changes in our cultural and material milieu that have given our peaceable motives the upper hand."
Inspired by Noam Chomsky's revolutionary theory of universal grammar, Pinker argued in his 1994 book The Language Instinct that the facility for language was innate to humans, and humans alone, and the product of natural selection. With The Blank Slate: The Modern Denial of Human Nature, he plunged into the more popular territory that is the nature versus nurture quagmire. The book was an argument against what Pinker saw as an intellectual tendency to dismiss any discussion of human nature as inherently racist, sexist and reactionary.
Perhaps Pinker was on to something when he wrote in The Blank Slate: "The strongest argument against totalitarianism may be a recognition of a universal human nature; that all humans have innate desires for life, liberty and the pursuit of happiness. The doctrine of the blank slate ... is a totalitarian's dream."
It's this vision of our common humanity, what Abraham Lincoln called "the better angels of our nature", that animates Pinker's latest work. The good news for the professor is that it's not all good news. "If it bleeds, it leads," is the modern media maxim. There should be plenty of blood across the review pages and, as a result, no shortage of publicity for the book.
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