Researchers have gone and thrown a giant, fascinating, lead brick into the "broken windows" theory. Over the years since the ongoing dramatic drop in crime across the country began in the '90s, folks have been poking holes in the popular theory—in which larger crimes are prevented by systematically stopping smaller ones—but this month a piece by Kevin Drum in Mother Jones makes a very compelling argument that windows have little to do with the drop. Using a number of researchers' work, Drum argues that the real reason for the dramatic rise and drop in crime in the second half of the 20th century was...drum roll please...lead. Specifically tetraethyl lead in gasoline.
While better crime prevention practices certainly have also helped make cities much safer in the past two decades, the research Drum collects argues that when you follow the post-war introduction and later banning of gasoline with lead—thanks for that, General Motors!—it matches up shockingly well with the rise and fall of crime roughly twenty years later. And this isn't just a national argument, it turns out it appears to hold up on a local level:
During the '70s and '80s, the introduction of the catalytic converter, combined with increasingly stringent Environmental Protection Agency rules, steadily reduced the amount of leaded gasoline used in America, but [Jessica Wolpaw] Reyes discovered that this reduction wasn't uniform. In fact, use of leaded gasoline varied widely among states, and this gave Reyes the opening she needed. If childhood lead exposure really did produce criminal behavior in adults, you'd expect that in states where consumption of leaded gasoline declined slowly, crime would decline slowly too. Conversely, in states where it declined quickly, crime would decline quickly. And that's exactly what she found.
Further, it even seemed to match up on a neighborhood level:
Just this year, Tulane University researcher Howard Mielke published a paper with demographer Sammy Zahran on the correlation of lead and crime at the city level. They studied six US cities that had both good crime data and good lead data going back to the '50s, and they found a good fit in every single one. In fact, Mielke has even studied lead concentrations at the neighborhood level in New Orleans and shared his maps with the local police. "When they overlay them with crime maps," he told me, "they realize they match up."
Of course, showing a correlation between lead in the air and crime only makes a difference if you can also show that lead consumption can cause violent behavior later on. And what do you know! Research shows that it can. Looking into a connection between the two, scientists have found that:
One set of scans found that lead exposure is linked to production of the brain's white matter—primarily a substance called myelin, which forms an insulating sheath around the connections between neurons. Lead exposure degrades both the formation and structure of myelin, and when this happens, says Kim Dietrich, one of the leaders of the imaging studies, "neurons are not communicating effectively." Put simply, the network connections within the brain become both slower and less coordinated.
A second study found that high exposure to lead during childhood was linked to a permanent loss of gray matter in the prefrontal cortex—a part of the brain associated with aggression control as well as what psychologists call "executive functions": emotional regulation, impulse control, attention, verbal reasoning, and mental flexibility. One way to understand this, says Kim Cecil, another member of the Cincinnati team, is that lead affects precisely the areas of the brain "that make us most human."
And just as interesting, "Although both sexes are affected by lead, the neurological impact turns out to be greater among boys than girls."
Pretty fascinating, no? Really, the whole article is worth a read. Especially as it isn't like all the lead released by those cars in the last century suddenly went away. Not a bit of it:
As it turns out, tetraethyl lead is like a zombie that refuses to die. Our cars may be lead-free today, but they spent more than 50 years spewing lead from their tailpipes, and all that lead had to go somewhere. And it did: It settled permanently into the soil that we walk on, grow our food in, and let our kids play around.
