In his landmark new book, the Harvard professor argues we are much less violent than our ancestors. It could lead to much academic bloodletting

Human nature is a highly contested concept, but whatever it may amount to, it doesn't seem to involve a thirst for good news. Which may be a problem for Steven Pinker, who has dedicated much of his academic life to the study of human nature, because his latest book is full of good news.

In The Better Angels of Our Nature: The Decline of Violence in History and Its Causes, the celebrated evolutionary psychologist and bestselling author argues that we – the human race – are becoming progressively less violent. To the consumer of 24-hour news, steeped in images of conflict and war, that may sound plain wrong. But Pinker supports his case with a wealth of data.

Drawing on the work of the archaeologist Lawrence Keeley, Pinker recently concluded that the chance of our ancient hunter-gatherer ancestors meeting a bloody end was somewhere between 15% and 60%. In the 20th century, which included two world wars and the mass killers Stalin and Hitler, the likelihood of a European or American dying a violent death was less than 1%.

Pinker shows that, with notable exceptions, the long-term trend for murder and violence has been going down since humans first developed agriculture 10,000 years ago. And it has dropped steeply since the Middle Ages. It may come as a surprise to fans of Inspector Morse but 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".

In so doing, 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.

Nowadays, the notion that life is measurably improving – and there can be no more profound improvement than not being killed or tortured – is about as unfashionable in educated circles as the conviction that western culture is in any sense civilising.

As both conservative pessimists, such as the philosopher John Gray, and postmodern relativists dismiss the post-Enlightenment understanding of progress as pure folly, Pinker is likely to stand accused of Panglossian naivety. Indeed, he says that when he told colleagues what he was writing, they said he reminded them of the man who jumped off the roof of a tall building and halfway down observed: "It looks good so far."

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 Canadian-American Harvard academic is hardly a newcomer to controversy. A couple of years back, he entered into a public spat with the New Yorker writer Malcolm Gladwell that managed to get extremely heated over the question of quarterback recruitment in American football. On top of which the whole subject of evolutionary psychology is often viewed as a form of biological determinism that repeats the mistakes of earlier 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. Many feminists, for instance, reject out of hand the idea that "female" behaviour is fundamentally hard-wired.

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 (I997), if his genes don't like it "they can take a running jump".

Although he is no quick-sell contrarian, 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.

At the age of 13, he declared himself an atheist and an anarchist, but dropped the anarchism a couple of years later after witnessing the effects of a police strike in Montreal. The strife and chaos he saw apparently changed his perception of human nature. "I was a Rousseauian then." he later recalled. "Now I'm a Hobbesian."

Rousseau believed that modern society corrupted human nature, whereas for Hobbes modern society was a necessary protection from human nature. It's Pinker's contention that without the pacifying influence of a commonly recognised state, we are prone to make life the nasty, brutish and short experience that Hobbes described.

But which mode of behaviour reflects our true nature? Killing each other or organising a state? For Pinker, it's not a matter of either/or. "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."

Pinker's cultural milieu has remained firmly located within prestigious centres of academic study. He started out studying psychology at McGill University and completed his PhD at Harvard, going on to become a star academic at MIT, where he quickly gained a media-friendly reputation with his prog-rocker haircut and spark-ling clarity of thought. By the time he left MIT in 2003 to return to Harvard, where he is a professor of psychology, he was regularly named in magazine lists of top intellectuals and thinkers.

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. The thesis has its critics, not least the late palaeontologist Stephen Jay Gould, but the disputes it engendered were mostly concerned with arcane areas of evolutionary debate.

As such, linguistics was always going to be too narrow a field for the promiscuously curious Pinker to plough. Whereas Chomsky maintained a clear distance between his work in linguistics and his interest in politics, Pinker has in a sense tried to bridge the gap, bringing together recondite academic research and larger social issues in lively and accessible prose.

With The Blank Slate: The Modern Denial of Human Nature (2002), 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.

His presentation of the science in The Blank Slate was characteristically clear-eyed and carefully argued, but he ran into trouble with some of his claims about the evolutionary causes of enlightened society. As writer and academic Louis Menand put it in an excoriating review in the New Yorker: "Either human beings spent 10,000 years denying their own nature by slavishly obeying the whims of the rich and powerful, cheerfully burning heretics at the stake, and arranging their daughters' marriages (which would imply a pretty effective system of socialisation), or modern liberal society is largely a social construction. Which hypothesis seems more plausible?"

This is the problem with defining human nature: it can seem like a post-facto explanation of social phenomena that are essentially historical accidents. At its most crude, it becomes teleological, ascribing a pattern and an ultimate end to random events. Yet it's also fair to say that a reluctance to suffer and die is part of the human condition and it's only natural that we should seek ways of limiting suffering and death. Perhaps in this respect 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. By that standard, there should be plenty of blood across the review pages and, as a result, no shortage of publicity for the book.