Have you ever been deep into a Netflix true crime binge-watch and thought “wow, seems like there were A LOT of serial killers in the 70s and 80s in the United States?” Well, you’re not alone and researchers have a very interesting theory as to why this is: chronic lead exposure.
This Lead-Crime Hypothesis sets to link the amount of lead in the atmosphere to a spike in crime rates. The theory hypothesizes that the chronic low-to-moderate exposure of lead that children ingested post WWII (lead paint, leaded gas, and/or contaminated soil) caused them to be slowly poisoned. This affected their brain development (specifically the frontal cortex), and essentially made them more likely to commit criminal offences.
This is because when lead exposure happens chronically (slowly, over time) the neural pathways in the growing brain can be significantly affected. Specifically, it's the calcium molecules that are affected. Calcium is essential for our brains to develop correctly, but when lead is present those molecules take over the spots “assigned” for calcium. This replacement disrupts the formation of the neural pathways responsible for cognitive development, most notably in the brains frontal cortex. Chronic exposure to lead can lead to a child having:
Permanent intellectual and learning disabilities
Slow development of normal childhood behaviours (such as talking)
Issues with inhibition and emotional regulation (which can manifest as social aggression)
Increased risk for attention disorders
Lack of understanding of their own actions
Increased risk for substance abuse problems later in life
(We do want to emphasize that just because a child exhibits such behaviours, DOES NOT MEAN that they will become a violent offender. Rather, these (and countless other factors) MAY lead to criminal behaviour.)
For those exposed, this poisoning compounded year after year creating the boom of crime rates we saw in the 70s and 80s. This widespread exposure has been confirmed by researchers who studied the concentrations of lead in bone marrow and brain scans over these decades.
One study looked at levels of lead in children (living in the highly contaminated areas of rural Cincinnati) and associated brain scans, then repeated the study when the children became adults (19-24 yrs of age). It found that there was significant volume loss in the frontal cortex, particularly in men. This supported the idea that those born in the US during the late 1940’s, and beyond, accumulated lead in their brains and were therefore were more likely to commit violent crimes than the generations before them.
“Ok” we hear you saying “so what, that doesn’t prove anything”. And you would be right! However, the very interesting thing is that once lead was phased out in the 1990’s these crime rates suddenly, and dramatically, plummeted, and have been continuing to decrease ever since.
In 1971, the United States government passed the Lead Poisoning Prevention Act however, not all jurisdictions were quick to adopt it. Although lead was still prevalent until the 1990’s in some areas, it has been shown that the faster an area got rid of lead, the faster their crime rates dropped. While correlation doesn't equal causation when it comes to the Lead Crime Hypothesis, there are dozens of studies that ultimately combine to support it, and give the theory serious legitimacy.
And while we do find this theory fascinating, it’s not the only one out there. Some of these alternative reasons for why this phenomenon occurred include:
Economic inequality in the 70s and 80s
Introduction, and eventual decrease, of crack cocaine
Gun ownership discouraging crime
Increased incarceration rates and police in the 90s-present
Realistically, we think it was a combination of several economic, social and political factors. While we were researching we also learned that the Age of Enlightenment in the 18th century coincided with the French starting to drink tea and coffee rather than their usual beer or wine. (A brain on a stimulant, rather than on a depressant.) So maybe it is possible that ingesting specific substances can influence behaviours that ripple through time.
But...we really just like the idea of a Clue (1985) remake where Tim Curry exclaims “It was Mrs. White in the billiard room, because of lead poisoning!”
For more information about the Lead Crime Hypothesis check out our references:
The Lead-Crime Hypothesis:
Cecil KM, Brubaker CJ, Adler CM, Dietrich KN, Altaye M, Egelhoff JC, et al. (2008) Decreased Brain Volume in Adults with Childhood Lead Exposure. PLoS Med 5(5): e112. https://doi.org/10.1371/journal.pmed.0050112
The Lead Poisoning Prevention Act of 1971: