There’s an interesting article in the Washington Post about a very strong correlation between lead exposure and crime rates.

The theory offered by the economist, Rick Nevin, is that lead poisoning accounts for much of the variation in violent crime in the United States. It offers a unifying new neurochemical theory for fluctuations in the crime rate, and it is based on studies linking children’s exposure to lead with violent behavior later in their lives.

What makes Nevin’s work persuasive is that he has shown an identical, decades-long association between lead poisoning and crime rates in nine countries.

“It is stunning how strong the association is,” Nevin said in an interview. “Sixty-five to ninety percent or more of the substantial variation in violent crime in all these countries was explained by lead.”

How can that be? I’ll let hilzoy explain, since she’s a better writer than I’ll ever be.

If a chemical alters your brain in such a way as to make it less likely that you will stop and think about what you’re doing, it increases the odds that you will do something stupid, like, say, committing a crime. This is why I would expect that people are more likely to commit impulsive crimes (as opposed to, say, a very carefully planned bank robbery) when they’ve been drinking. If there were a chemical that heightened impulsivity permanently, not just for several hours after you drink a beer, then it makes total sense that it would be associated with increases in the crime rate.

For consideration of the social/policy implications, I direct readers to the rest of hilzoy’s post.