In the last chapter of his eminently readable exploration of our allegedly dangerous world, Daniel Gardner describes a cemetery in Ontar­io where a headstone com­mem­or­ates the six children of one couple, all killed by diphtheria within less than a week in 1902. Far from marking a freakish occurrence, the headstone is a reminder of the vast toll contagious illnesses took on children in the dark days before vaccines all but eradicated such diseases in the industrialized world. It is the final proof of what Gardner argues throughout 

: The world we have inherited is in many ways the ­safest—­least risky to the individual and the ­species—­that has ever ­existed.

So why, he asks, are we afraid of so many things? Why do homicides, abductions, and other statistically unlikely threats (Gardner includes terrorism among these) occupy an inordinate amount of our attention and consume resources that could be spent protecting us from statistically far more significant threats, such as preventable illnesses? Gardner’s answer is that evolution has equipped us with a brain superbly suited to tell us what to do when we spot a large brown thing in the long grass: recognize it for a lion, get scared, and run like hell; once safe, tell everybody about what happened to the slowest one. But our brains are ill equipped to ­process—­at that same speed, and based on the same need-to-know premise—the more subtle dangers coming our way.

The brain Homo sapiens possessed as early as 200,000 years ago has remained unchanged in the blink of an eye that constitutes the span of modern history. This brain consists of subcon­scious and conscious, or what Gardner calls “Gut” and “Head.” Once, Gut (feeling) kept people alive by rapidly, intuitively differentiating between safe and dangerous, and by prompting ­life-­saving actions based on its ­split-­second verdict. Head (reason)—the ability to use logic, analyze, do the ­math—­was not useful, given the ­conditions.

Gut brought the species far, by instinctively following a set of rules. Gardner, a Canadian journalist, draws on a wealth of academic research to catalog these rules and show how necessary they were for making the world intelligible and survivable for prehistoric humankind. And he convincingly argues that they can thoroughly mislead ­us—­and are used by manipulators of all stripes to do so. (What better way to sell us software X or burglar alarm Y than by frightening us with inflated numbers of Internet predators or crimes we’re unlikely to become victims of?)

Take, for instance, “the Example Rule”: Gut tells us that the more easily we recall an event, the more likely it is to happen again. In an environment where information is local, the example of one member of the tribe being eaten by a lion plants in the other members a ­vivid—­hence, easy to ­recall—­memory of the very real danger of lions and places frequented by lions. In an environ­ment where information propagates rapidly, and a hundred million of us find out, through the media, about one gruesome homi­cide, the example, processed by Gut in the same way, does little or nothing to make us safer. But it does raise the national anxiety level and make us more easily persuaded to allocate funds for more prisons or to support the death ­penalty.

Gardner puts into context half a dozen other such rules. All of them share their immense usefulness for the survival of hunters and gatherers. And all of them share the unfortunate potential to make us bark up the wrong light pole in environments where light poles out­number ­trees.

His analysis suggests that for the sake of our survival, one fear ought to become stronger: that of being afraid of the wrong things. He may not succeed in shutting up Gut when it says “Lock the doors or risk being murdered,” but he pre­sents compelling evidence that unfounded fears pose real dangers. Only by recognizing these dangers will we be ready to give Head a chance and to fight wasteful and foolish measures proposed to keep us safe from what we needn’t fear.

, a lecturer at Stanford University, is the author of 

and four novels. She is at work on a book about the natural history of fear.

The Science of Fear: Why We Fear the Things We Shouldn't—and Put Ourselves in Greater Danger

 by Daniel Gardner, Dutton, 339 pp, 2008.

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Writing about Daniel Gardner's The Science of Fear, Evelin Sullivan concludes that "for the sake of our survival, one fear ought to become stronger: that of being afraid of the wrong things."