Violent crime began trending down in the 1990's after the highs of the 1970's and 80's,
The Christian Science Monitor reported that in 2012, the national rate of serious crimes was at its lowest since 1963.

Researchers have developed many theories about why the crime rate unexpectedly dropped. Some credit tough-on-crime policies. Others credit the rise and fall of crack. One team of researchers famously — or infamously, depending on your view — argued that legalized abortion helped reduce the crime rate.

But there's another theory I wasn't aware of until last night, when I came across an article on Mother Jones' website called "America's Real Criminal Element." The article pulls together several studies citing lead exposure as a factor in the crime rate. When exposure increased, so did crime levels. When lead was banned from things like gasoline and paint, crime rates fell.

The article pays particular attention to a study linking leaded gasoline to crime levels.