Leaded gasoline and the 20th-century crime wave

Scientists are amassing evidence that suggests exposure to tetraethyl lead — the additive once used in almost all the gasoline sold in the United States — could account for the dramatic increase in crime that happened in this country between the 1960s and 1980s. As leaded gasoline was phased out, they say, children were exposed to less lead, leading to the decline in crime that began to really kick in in the 1990s.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).