Scientists and sociologists have long debated and puzzled over two seemingly unrelated facts: continually rising IQ rates, and continually falling crime rates. We may have had the explanation in front of us for over decades: lead.

partial lead pipe replacementA “partial replacement” of lead piping – one way to make your children less intelligent and more violent.

Despite what doomsday pundits might tell you, we’re living in one of the safest periods in history. Crime has been falling steadily since the end of prohibition, homicide is down, and violent crimes are pretty much down across the board. The problem was that no one could really prove why, but there were no shortage of theories. Like any unexplained boon, everyone stepped in to take the credit. The police patted themselves on the back for being tough (and sometimes “brutal”) on crime.  Politicians, economists, and pro-choice advocates took credit for the diminishing violence in America.

During the same period, IQ rates have been rising steadily, much to the bewilderment of psychologists. Students from 2013 taking the 1970 IQ test will score significantly better on the test. The wider the gap, the greater the difference. The phenomenon of rising IQ has been dubbed the Flynn Effect, and it is vexing to psychologists because average intelligence is supposed to stay relatively stable – it’s not supposed to fluctuate wildly over time. It took us millions of years to evolve to this point – there’s no way that almost non-existent evolutionary pressures has created a rise in intelligence in a mere 70 years.  Some suggest that the Flynn Effect is a result of better national education. The most popular hypothesis today is that the environment around us is more intellectually stimulating. All of these hypotheses seem possible, but generally lack a foundation of solid data.

Perhaps because sociologists and criminologists study crime rates, the most commonly accepted causes are explanations that make sociologists comfortable. Similarly, the primary scientists studying rising intelligence are psychologists, and they tend to be most accepting of developmental explanations.

As it turns out, we’ve known that lead lowers IQ and causes changes in the pre-frontal cortex for at least 40 years. Lead poisoning has been linked to cognitive deficiencies in the areas known to control inhibitions. Despite only recently developing the neurological explanation of lead’s toxic function in the brain, the danger of lead has been known for far longer than 40 years. The Greek philosopher and physician Dioscorides said that lead caused the mind to “give way” before 100 AD. Some have claimed that lead may have contributed to the fall of the Roman Empire, as they used it heavily in pipes, drinking vessels, and as a wine additive. While impossible to prove, it’s interesting to consider that lead may have been a contributor to the violence of ancient Rome.

Awareness for the hazards of lead surged with the recently piece in Mother Jones by Kevin Drum that suggests that lead may account for up to 90% of America’s crime rates. That claim seemed absolutely crazy to me at first. It seemed absolutely mad that 90% of a complex thing like human crime trends could be explained by a simple little molecule. Researchers like Rick Nevin has shown that our diminished use of lead has caused IQ rates to rebound to their natural level while making us less violent.

Simple lead – what a fascinating and horribly sad potential explanation of two parallel mysteries.