likes to challenge conventional , as he does in his book The Better Angels of Our Nature: Why Violence Has Declined. The subtitle relays the counterintuitive thesis right up front, stopping us in our tracks: Violence has declined? Anyone who pays knows that violence is occurring constantly in America and around the world. Stories of senseless human are a predictable part of the day’s events, every day in virtually every geographic region. Doesn't Pinker watch the news?

Pinker, however, citing extensive research and statistical evidence, argues quite convincingly that, despite what the live television reporter from today's scene may be suggesting, we are living in what may be the most peaceful period of human history. Disputes among rival neighbors, violence toward women and children, military conflicts, hostile treatment of racial and ethnic minorities—in virtually every category, the chances of violence today are lower than in previous eras.

For numerous and varied reasons—the rise of nation-states and their ability to impose order, the expansion of commerce and its tendency to make distant peoples trading partners instead of warring enemies, increased literacy and the that it instills, the dissemination of knowledge and the accompanying wider appreciation of reason, and many other factors—the human animal in recent centuries has been driven steadily, if imperfectly, toward more peaceful societies.

Strangely, however, even as I consider how lucky I am to live in modern suburban Boston rather than in the path of Attila the Hun, a nagging sense of insecurity persists, not so much for myself, but for the wider human family. This feeling can perhaps best be explained by a formula invented by another Harvard man, the distinguished jurist Learned Hand.

In laying out a legal formula for determining whether a party was negligent, Hand suggested the following calculation: we must factor the probability of harm resulting from one’s actions by the degree of harm that will result from those actions, and then weigh that result against the burden of taking adequate precautions to prevent the harm. If the probability (P) factored by the degree (D) is greater than the burden (B), then the action in question breaches one’s duty of care.

Pinker has set forth a compelling thesis that the probability of harm today may be lower than ever, and Better Angels is already recognized as an authoritative work and necessary read for anyone interested in that topic. In considering the modern world, however, our ongoing concern might be the second factor above—the degree of harm. After all, nuclear weapons weren’t available to Genghis Khan, or, for that matter, Hitler. In comprehensively assessing risk today, the decline in the probability of violence could arguably be offset by a great increase in the degree of harm that will occur if and when the rare event happens.

This, in turn, leaves us considering the third element in Hand’s formula: what are the adequate precautions that can be taken? Arguments can be made for various courses of action to prevent a future nuclear catastrophe, from the pacifist approach on one hand to a preemptive militaristic strategy on the other. Whatever the ultimate approach, it seems that this issue is key as humanity moves forward. Eventually, before too long, the human family’s in-group must be global. As technological advancement accelerates, the degree of potential harm will always be great even if the probability diminishes, so each generation will live with a serious burden to take adequate precautions.

David Niose on Twitter: @ahadave

David Niose's Nonbeliever Nation: The Rise of Secular Americans is available here.

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