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Every so often, the FBI releases its crime statistics. When the statistics show that crime rates are going up, I hear a collective sigh of relief as pundits reach for familiar bromides to explain the troubling rise in murder and burglaries: They blame decaying cities, recessions, Republicans for cutting social services, Democrats for being soft on crime etc.
In recent years, however, the stats have generally shown crime rates going down. This is bad news for the let's-frighten-people-so-they-will-(Pick one: vote-for-us, fund-our-cause, buy-our-crime-fighting-gizmo). But it also leaves pundits scratching their heads, as in this recent update from the Associated Press. How can crime be falling in the midst of a recession? Among the various theories propounded are the graying of the population, better policing techniques and (my favorite) more people working from home leaving fewer unpopulated homes vulnerable to burglars.
A very good investigative reporter once told me the most important question a journalist could ask is, "How do you know that?" Put another way, whenever we hear an intriguing theory, we should say, "that's a nice theory, but where's the evidence to support it?" Has crime always fallen in lockstep with demographic aging? Has anyone systematically studied whether burglary fluctuates inversely with telecommuting? Is there evidence that areas which have had the largest increase in telecommutters in the past few months have shown the largest declines in crime?
The most convincing evidence I have seen to explain the drop in crime is something much less sexy and much more rigorously studied -- and also studiously ignored. Systematic research across several countries shows that as lead poisoning rates fall -- by phasing out lead in gasoline, removing lead from household paint, and making it mandatory to de-lead homes where young children are living -- the crime rate falls about 18 years later. There are intersecting lines of evidence here: Lead is a potent neurotoxin, known to increase aggression and impulsive behavior, and studies have found significantly higher lead levels in the brains of juvenile offenders than among random youngsters from the same community who are not in trouble with the law. Lead is mostly ingested by toddlers, but its effects on crime show up when the toddlers are adolescents -- hence the 18 year gap between poisoning and its effects on crime.
The most convincing aspect of the research, which I wrote about some time ago, is the cross-national data. Since different countries have phased out lead at different points in time, this gives us a nice experimental framework to test the lead-crime theory. If the theory were true, rates in the different countries ought to fall at different times. Researchers have shown that this is indeed the case -- a little under two decades after lead starts to get eliminated from the environment, you start to see steady drops in crime, regardless of country, culture, abortion rates etc. (Unlike the much celebrated abortion-crime theory, the lead-crime theory works as you move through time in different countries, and is not just a snapshot of a single country in a single cross-section of time.)
One of the perennial themes I return to in The Hidden Brain is our society's inability or unwillingness to take evidence and data seriously. We believe crime goes up when the economy goes down, and that the best way to fight bad guys is to give the good guys bazookas. Maybe the researchers studying the connection between lead-and-crime should try calling their next peer-reviewed scientific paper, Die Hardest?
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