The question has puzzled criminologists for decades: Why did violent crime rates start to soar across the U.S. from the 1960s, before beginning “a spectacular decline” in the 1990s—a decline that’s continued ever since? Theories abound, from improved policing strategies to the end of the crack epidemic. But a more likely possibility is a molecule, said Kevin Drum in Mother Jones, and that molecule is lead. Research has provided strong evidence that lead exposure damages the brain, lowering IQ and impulse control and leading to violent behavior. As automobile ownership soared beginning in the 1950s, millions of children in car-choked urban centers breathed in fumes from leaded gasoline. Those kids, research indicates, were more likely to grow up and “become violent criminals in the ’60s, ’70s, and ’80s.” And when the U.S. began phasing out leaded gas, the crime epidemic began to ebb. Lead exposure data over decades, scientists have found, are strongly correlated with crime rates in individual cities—right down to the neighborhood level. Cutting lead pollution, it seems, is the “most effective crime prevention tool we have.”
Lead exposure probably did play a role in the crime epidemic, said Jim Manzi in NationalReview.com. But let’s not get carried away. The research that Drum cites found that while lead exposure was associated with higher violent crime rates, it didn’t have a statistically significant effect on property crime or murder. Why would a lead-damaged brain make me more likely to assault someone, but not more likely to kill them or rob their home? As any scientist will tell you, “correlation is not causation,” said Ronald Bailey in Reason.com. The fact that crime rates fell in line with lead pollution doesn’t mean you can dismiss other factors. Extra funding for police, more incarceration, and increased concealed-carry rates all likely helped America become a safer place.
The lead data is pretty convincing to me, said Tim Worstall in Forbes.com. And if it turns out that crime is largely “a result of the stupidity brought on by environmental poisoning,” it would challenge everything we know about crime. Conservatives would have to stop blaming culture and broken families. Liberals would have to stop bleating that crime is a consequence of poverty and inequality. “When the facts change,” an honest man changes his mind—and we all have some new facts to consider about crime.