This is the same curve of crime statistics that economist Steven Levitt, of Freakonomics fame, attributed to the legalization of abortion. Levitt's theory was that, after Roe v. Wade, there were fewer unwanted babies born into dire circumstances and, thus, fewer people to grow up on the path to criminal behavior. Levitt matched the rise in abortion rates to the decrease in crime, but frankly, there are a lot of things that you can correlate to the decrease in crime.

What makes the lead theory interesting is that correlations match not just at the national level, but at regional, and even neighborhood levels. Increases in lead relate to increases in crime — usually a couple of decades later. Likewise decreases in lead relate to later decreases in crime. What's more the same correlations exist in countries all over the world. Meanwhile, we know that lead has big impacts on growing bodies — it affects brain function, it's linked to hyperactivity, difficulty managing aggression, and lowered IQ.

Correlation isn't causation. But in this case they definitely seem to be winking suggestively at one another. Kevin Drum has an excellent piece on this at Mother Jones, working through a decade worth of research by multiple scientists that supports this disturbing conclusion. It really is possible that we, as a society, damaged a generation of children and caused a crime wave (not to mention the ongoing damage to kids that live in high-lead neighborhoods today).