The Better Angels of Our Nature: The Decline of Violence in History and its Causes, By Steven Pinker

There has never been a better time to bet on dying in bed. Judging by the shattered remains of fossil human bones, in prehistory the chances of dying by another's hand were 15 per cent on average, rising as high as 60 per cent. Studies of societies without states, an imperfect but suggestive guide to the way our distant ancestors lived, show annual war death-rates averaging 500 per 100,000 people. Despite the world wars, genocides, insurgencies and post-colonial power struggles of the 20th century, the global rate of death from war and other political conflicts was about 3 per cent, or 60 per 100,000. That looks like progress.

Click here to get money off this book from at Independent's bookshop

The big picture is drawn over and over again in the cascade of graphs that the psychologist Steven Pinker uses to demonstrate the decline of violence over the course of human history. People's odds of avoiding violent death were improved by the imposition of state power, although states themselves dealt out death and cruelty in abundance. In the past few centuries, states have pacified themselves significantly. Most established ones now get along without the executions, massacres and torture once assumed necessary to the maintenance of order. Pinker has taken up the idea of what sociologist Norbert Elias called the "civilising process" and put figures to it.

The result is a salutary reality-check for the pessimism induced by looking back at the 20 century, and the self-absorption that treats terrorism as a threat even remotely comparable to those which faced the world in that era of global conflict. For most people, the world is a far ore peaceful place than it was for any of their ancestors - though as populations grow, the actual number of victims may multiply even though the percentages fall. Pinker's suggestion that the 20th century may not have been the bloodiest in history "when one adjusts for population size" discounts the dreadful toll from 20th-century conflicts given in a table: they approach 150 million.

His interpretation of the great historical decline in violence turns upon the two dominant themes in his understanding of human psychology. On the one hand, human nature is a package of evolved traits; on the other, humans have cognitive faculties that enable them to do things very different from what their psychology originally induced them to do. As he once put it, "if my genes don't like it, they can go jump in the lake".

Human nature is a package of capacities on which people can draw as necessary, like tools in a toolbox. Contrary to the popular "hydraulic" metaphor, violence is not like a fluid that inexorably wells up in a man's psyche and has to be discharged or channelled. If violence is not needed, not provoked and not admired, it will rarely be used.

The trick is to arrange society so that violence pays less than other means to pursue interests. In asserting a monopoly on violence, a state reduces the incentives for individuals to kill those whom they feel have done them wrong, by assuming the burden of justice, removing the pressure to use force to uphold reputation, and imposing penalties for taking the law into one's own hands. Nations can prosper more by engaging in "gentle commerce" than by plunder. One of the great heroes of the reduction of human conflict is the repeat customer.

Democracy is another pacifying arrangement, though there are no masses or common people discernible in Pinker's vision. For him it is a means to improve the circulation of information, allowing aspiring elites such as "financiers, lawyers, writers, publishers, and well-connected merchants" to challenge established authority. If society is sufficiently open to the circulation of ideas, Pinker believes, then reason will speak peace to power.

"With enough scrutiny by disinterested, rational, and informed thinkers," practices such as slavery, judicial torture and the execution of heretics "cannot be justified indefinitely." Rational inquiry forces thinkers to Enlightenment positions in the same way, he contends, that biochemical research forced scientists to conclude that DNA has four bases.

Reason cannot prevail without passion, though. It isn't the liberals trying to pick their way between "on the one hand" and "on the other" who force through change; it's the people who pour onto the streets unhampered by doubt that one side is right and the other wrong. And in general the passions tend not to be friends of the Enlightenment.

The psychologist Jonathan Haidt argues that conservatism taps into more wellsprings of moral passion than liberalism, which gives the Right a powerful electoral advantage. Although Pinker discusses Haidt's model, he doesn't pick up that point. Better Angels represses its demons rather than wrestling with them. All the shades of unenlightenment, from quiet patriotism and bedrock faith to paranoid nationalism and grandiose fundamentalism, remain invisible. If it were a map of America, it would show the two coasts but not the part in between.

Pinker also turns a blind eye to passion, even when on the side of his better angels. He devotes considerable attention to the 1960s, partly because he prefers quoting pop songs to philosophers, and partly because the Sixties pose a problem for his argument. Violence graphs show an uptick beginning in the 1960s and persisting into the 1990s. An analysis rooted in evolutionary psychology might consider whether changes in sexual mores were at work here. The old system in which men exercised monopolies over their wives was destabilised: perhaps this instability led to an increase in the competition between men that underlies so much of human aggression.

Pinker keeps things simple, though. He is inclined to blame the bad examples set by musicians, and a general abandonment of the self-control he identifies as a key factor in the decline of violence. But it is not clear that "Sympathy for the Devil" outweighed "Give Peace A Chance" in a counter-culture whose symbol was, after all, the peace sign. And if he believes that the historical trend towards increasing self-control has reasserted itself, he should take a walk down a British high street on a Friday night. Alternatively, figures for current levels of consumer debt may cast a less garish but wider light on the state of impulse control today.

Pinker himself is a model of restraint when it comes to the future. "Optimism requires a touch of arrogance," he remarks, nicely distancing himself from the current wave of conviction optimists who insist that the current order, liberal in economics and morality, will sustain us onwards and upwards. Here, perhaps, those great unacknowledged concentrations of unenlightenment hold him back. He declines to argue that because he finds the liberal order good, it must endure and continue its pacifying work. Instead, he commends a handful of better angels to us, in the hope that we will recognise what an immense achievement the reduction of violence has been, and see how to build upon it further.

Better Angels is itself a great liberal landmark. It has its conceits and is not as universal as it likes to think – but that's true of all great liberals. And few of them are as readable as this book, whose 700 pages of exposition almost turn themselves.

Marek Kohn's latest book is 'Turned Out Nice' (Faber & Faber)