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The next time Giuliani tries to take credit for the decrease in violence during his tenure as NYC’s mayor, send him this chart.

The NY Times shines some light on Jessica Reyes’ excellent work linking decreased lead exposure to a drop in violent crime in the US. The decreased lead exposure, of course, was from the phase-out of leaded gasoline from the American market. BTW, Nascar still uses leaded gasoline in its cars, nice going, guys.

The answer, according to Jessica Wolpaw Reyes, an economist at Amherst College, lies in the cleanup of a toxic chemical that affected nearly everyone in the United States for most of the last century. After moving out of an old townhouse in Boston when her first child was born in 2000, Reyes started looking into the effects of lead poisoning. She learned that even low levels of lead can cause brain damage that makes children less intelligent and, in some cases, more impulsive and aggressive (Emphasis Added).

Lead exposure at an early age (2-3 years) is especially significant as this is an age where personality development occurs and any interference in neuron development and apoptosis (death!) can cause permanent changes in personality. This excellent review article summarizes the effects of lead on neuronal development.

Reyes’ research mentions that while decreased lead exposure was very well correlated with violent crime (accounting for 56% of the reduction in crime), no correlation was found to property crimes (such as theft). This of course makes intuitive sense. A property crime is usually premeditated whereas violence is usually impulsive (excluding serial killers, of course). It is more likely that a budding criminal sets out to steal a car than to beat somebody to pulp. It is when the crime goes wrong that the probability of a violent crime increases. An individual with damaged impulse control is then more likely to seek a violent way out of the bad situation.

Our society (like most) views violent crime as a moral issue, a matter of good and evil that is determined by your “character”. So, a simple chemical correlator to violent crime that can explain a majority of the commission of violent acts goes a long way in undermining this whole notion of morality and crime. Of course, there are other sociological factors at play which need to be addressed. But it is heartening to know that beyond all the complicated and recalcitrant social issues that underly crime, there’s a ubiquitously evil pollutant lurking that can be eliminated. I am guessing that this line of reasoning is not going to be very popular among the “tough on crime” types that perpetrate our political airwaves these days.

Reference

Reyes, Jessica Wolpaw (2007) “Environmental Policy as Social Policy? The Impact of Childhood Lead Exposure on Crime,” The B.E. Journal of Economic Analysis & Policy: Vol. 7 : Iss. 1 (Contributions), Article 51.