There is a significant correlation between the use of leaded gasoline and incidences of violent crime.
[L]ead emissions from automobiles explain 90 percent of the variation in violent crime in America. Toddlers who ingested high levels of lead in the ’40s and ’50s really were more likely to become violent criminals in the ’60s, ’70s, and ’80s.
Well, that explains a lot of my misspent youth.