Why Should We Worry About What We Shouldn't? It would be a lot easier to enjoy your life if there weren't so many things trying to kill you every day. The problems start even before you're fully awake. There's the fall out of bed that kills 600 Americans each year. There's the early-morning heart attack, which is 40% more common than those that strike later in the day. There's the fatal plunge down the stairs, the bite of sausage that gets lodged in your throat, the tumble on the slippery sidewalk as you leave the house, the high-speed automotive pinball game that is your daily commute. Other dangers stalk you all day long. Will a cabbie's brakes fail when you're in the crosswalk? Will you have a violent reaction to bad food? And what about the risks you carry with you all your life? The father and grandfather who died of coronaries in their 50s probably passed the same cardiac weakness on to you. The tendency to take chances on the highway that has twice landed you in traffic court could just as easily land you in the morgue. Shadowed by peril as we are, you would think we'd get pretty good at distinguishing the risks likeliest to do us in from the ones that are statistical long shots. But you would be wrong. We agonize over avian flu, which to date has killed precisely no one in the U.S., but have to be cajoled into getting vaccinated for the common flu, which contributes to the deaths of 36,000 Americans each year. We wring our hands over the mad cow pathogen that might be (but almost certainly isn't) in our hamburger and worry far less about the cholesterol that contributes to the heart disease that kills 700,000 of us annually. We pride ourselves on being the only species that understands the concept of risk, yet we have a confounding habit of worrying about mere possibilities while ignoring probabilities, building barricades against perceived dangers while leaving ourselves exposed to real ones. Six Muslims traveling from a religious conference were thrown off a plane last week in Minneapolis, Minn., even as unscreened cargo continues to stream into ports on both coasts. Shoppers still look askance at a bag of spinach for fear of E. coli bacteria while filling their carts with fat-sodden French fries and salt-crusted nachos. We put filters on faucets, install air ionizers in our homes and lather ourselves with antibacterial soap. 'We used to measure contaminants down to the parts per million,' says Dan McGinn, a former Capitol Hill staff member and now a private risk consultant. 'Now it's parts per billion.' At the same time, 20% of all adults still smoke nearly 20% of drivers and more than 30% of backseat passengers don't use seat belts two-thirds of us are overweight or obese. We dash across the street against the light and build our homes in hurricane-prone areas and when they're demolished by a storm, we rebuild in the same spot. Sensible calculation of real-world risks is a multidimensional math problem that sometimes seems entirely beyond us. And while it may be tree that it's something we'll never do exceptionally well, it's almost certainly something we can learn to do better. Part of the problem we have with evaluating risk, scientists say, is that we're moving through the modem world with what is, in many respects, a prehistoric brain. We may think we've grown accustomed to living in a predator-free environment in which most of the dangers of the wild have been driven away or fenced off, but our central nervous system--evolving at a glacial pace--hasn't got the message. To probe the risk-assessment mechanisms of the human mind, Joseph LeDoux, a professor of neuroscience at New York University and the author of The Emotional Brain, studies fear pathways in laboratory animals. He explains that the jumpiest part of the brain--of mouse and man--is the amygdala, a primitive, almond-shaped clump of tissue that s