How deeply did lead's toxicity affect society? Well, economist Rick Nevin believes it might just be a major underlying cause of the recent global crime decline.
Nevin studied the criminal histories of nine countries and found that in each case he could link significant crime drops with that country's campaign to eliminate childhood lead poisoning. In his own words, "65 to 90 percent or more of the substantial variation in violent crime in all these countries was explained by lead." You could say that the timing was just coincidence, but each country Nevin studied conducted those campaigns at different points in time, and in every case, 20 years after lead poisoning rates fell, crime started to fall. Another study in 1990 showed that U.S. counties with high lead levels had four times the murder rate of counties with low lead exposure.
Shotgun victims are also very likely to have high lead exposure.
Now, as with every entry on this list, we'll never know for sure how true this was -- you could just as easily say that the type of country or era that is advanced enough to successfully deal with environmental problems is also capable of fighting crime. Still, it makes us wonder what stuff we're all being exposed to right now that will turn out to have been making us crazy. We're imagining a future earth in chaos, roving bands of savages driven mad by a decade of iPhone fumes.
If not the iPhones themselves.