Violent crime has fallen in the US for years, but why? Experts have floated theories ranging from police techniques to the "crack epidemic" to the legalizing of abortion, but none quite fit the facts. One, however, does: lead poisoning. In Mother Jones, Kevin Drums reports that the rise and fall of leaded gasoline directly mimics the arc of violent crime in America, on a 23-year time lag. In fact, studies show the same correlation in countries around the world, six US cities, and even a New Orleans neighborhood. "When they overlay [lead concentrations] with crime maps," says one researcher, "they realize they match up."
The science fits, too: Many studies link lead intake with lower IQs, delayed development, and a propensity to commit crimes later in life. Of course millions of children who inhaled lead from car tailpipes between the 1940s and the 1970s didn't become criminals, but those on the margin "were pushed over the edge from being merely slow or disruptive to becoming part of a nationwide epidemic of violent crime," writes Drums. The clincher: Lead molecules still lurk in our soil and an estimated 16 million US houses. Cleaning them up would cost billions, but save far more in the long run, Drums writes: It "could turn out to be the cheapest, most effective crime prevention tool we have. And we could start doing it tomorrow." (Read more lead poisoning stories.)