With the San Bernardino shootings we’re being exposed to another spate of articles about gun violence. One point that occasionally jumps out of these news bits is that gun violence has actually substantially declined in over the past 20 years. You’d think this would be a fact people would celebrate but it’s all but ignored. Most people couldn’t be blamed for thinking gun violence is getting worse. (This is an example of one of my beefs with the news—good news does’t sell.)

It would be interesting to figure out why gun violence has gone down. Well, The Washington Post takes a shot (ha – get it?) at it in this article: We’ve had a massive decline in gun violence in the United States. Here’s why.

Some reasons are not too surprising: more cops, better policing etc. But some do seem unexpected. Americans are drinking less alcohol. And, a drop in exposure to lead could make people less violent.

Besides alcohol, lead is another substance that has been shown to make humans more aggressive. Lead is toxic, and it can affect the behavior of children who are exposed to the metal while their brains are still developing. After the passage of the Clean Air Act in 1970, refiners were required to sell unleaded gasoline. Jessica Reyes, an economist at Amherst College, has argued that the children born after that law took effect breathed in less lead from car exhaust and that their brains were healthier as a result. She has estimated that the removal of lead reduced violent crime by no less than 56 percent.

This idea was the gist of a Mother Jones piece a few years back and while I approached the article dubiously, it made a strong case.