Everyone from Rudy Giuliani, to Malcolm Gladwell to Steven Levitt of Freakonomics have a theory on drop in violent crime in America and specially New York City. But nothing really conclusively explains what exactly led to such a rapid decline. Add to that another excellent research by Kevin Drum for Mother Jones.

The claim (corroborated by research and data) here, while not for the first time, is that drop in levels of Lead (or PB) when gasoline went unleaded lead to the rapid decline in crime. This is because even very low levels of lead in blood cause serious harm to parts of the brain that deal with control and judgement and the communication between them. Great read. Highly recommended.