In a provocative story for Mother Jones, Kevin Drum suggests that atmospheric lead may be a more important determinant of crime than policing, incarceration, or any of the other factors usually mentioned in policy debates.
It's well worth reading Drum's entire essay for a sense of the strength of the evidence for the thesis that exposure to lead can cause criminality. But this one graph Drum presents, taken from data from a study by Rick Nevin, shows a correlation that immediately commands attention:
The level of lead from gasoline maps very closely to the level of crime lagged about 20 years. The unavoidable takeaway is that childhood exposure to lead might make a person more likely to be a criminal later on in life. Drum musters more evidence to suggest that this is more than a mere correlation, so read the whole piece.