It is now well-understood that lead in the bloodstream, even at levels once thought negligible, harms people, especially children. Discovery, in the mid-2010s, of dangerous lead levels in the water of Flint, Michigan, brought this home to many Americans. Even as the United States purged paint and gasoline of lead and closed lead-emitting smelting plants, lead residues in millions of older homes, in the soil near high-traffic roads, and, as in the case of Flint, in many water pipes persisted.
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Lead poisoning is a story of environment and health; it is also a story of environment and behavior. Although lead was a known poison when it was first added to gasoline nearly a century ago, only in recent decades have studies pointed to lead poisoning as a cause of problematic social behavior ranging from underperforming in school to teen pregnancy to murder. Such findings enrich sociologists’ understanding, but it also makes them nervous about biology’s role in explaining social phenomena. Should it?
Bad Stuff
In a 2018 review paper, Berkeley sociologist Christopher Muller and Harvard sociologists Robert Sampson and Alix Winter explain that lead in the bloodstream damages regions of the brain that govern the executive function critical to concentrating and to controlling impulses. Impaired executive function raises the risk of low test scores, high impulsivity, and criminal behavior. Variations in the level of lead in a population partly explain variations in social outcomes such as rates of early pregnancy and rates of violence.
Here are examples of studies that substantiate this summary. Some establish lead effects in individuals, for example:
* This year, several psychologists reported a study that followed over 500 New Zealand children for more than 30 years, regularly assessing them in clinical interviews. Higher lead levels predicted higher chances of psychopathology in adulthood (even though New Zealand has had relatively modest overall levels of lead poisoning).
* This year as well, economists Anna Aizer and Janet Currie reported a study of 125,000 Rhode Island students whose lead levels had been tested in preschool from 1990 to 2004. Those levels, holding race and class constant, predicted higher odds of boys years later getting suspended from school and or being put in juvenile detention. Overall lead levels declined over those years and the authors conclude that “reductions in blood lead can explain one-third of the 72% decline in [school] suspensions over the fifteen-year period.”
Other studies establish a connection between population levels of lead and social outcomes, for example:
* Christopher Muller and Boston University economist James Feigenbaum showed that in the 1920s and ‘30s communities that used lead water pipes had higher homicide rates than did communities that used iron pipes, holding constant many other aspects of the communities.
* The best-known such studies have look at the association across communities and across recent decades between lead use in gasoline and crime rates. Data journalist Kevin Drum has for years promoted the argument that the traumatic boom in crime from the 1960s through the 1980s and then the puzzling bust in crime from the 1990s to now are best explained by the rise and fall of gasoline-produced lead levels about 20 years earlier when the perpetrators were infants. The surge of lead from increased motor vehicle traffic after World War II explains the rise of violent crime and the required phasing out of lead from gasoline starting in the 1970s explains the fall of violent crime. In a recent update, Drum lists newer studies. For example, the São Paulo state of Brazil experienced an unusual 50 percent drop in homicides during the 2000s. That followed by about 20 years a major shift from leaded gasoline to ethanol in São Paulo.
It is likely that the biological effects of lead were multiplied by social effects, that the more youths there were who acted impulsively because of lead poisoning, the more influenced their un-poisoned peers were to do the same.
This account places biological processes right in the middle of sociological analyses.
Uncomfortable
In “The Potential Relevances of Biology to Social Inquiry,” 2003, sociologists Jeremy Freese, Jui-Chung Allen Li, and Lisa Wade wrote that “few things provoke sociologists as easily or strongly as the perceivedly improper invocation of ‘biology’ as an explanatory device, especially when done on sociologists’ own turf” (and they included me as an example of such a provoked sociologist). They are correct. Some criminologists and sociologists have noted the findings about lead and behavior but have done so with some hesitation, suggesting serious discomfort.
For example, in a 2013 web essay on the post-1990 crime drop, University of Minnesota sociologists Chris Uggen and Suzy McElrath reviewed six possible “social sources” for that drop but did not include the lead poisoning hypothesis. When asked about that by a commentator, Uggen agreed that the correlations of lead with crime are “intriguing” but wrote that he didn’t “feel comfortable making strong claims about a lead-crime relationship.” Even in the review essay about lead that I started this post with, sociologists Muller et al are careful to say “that these causes [of lead poisoning] are fundamentally social. This means that they require social solutions.” Require? Maybe not. Direct medical interventions, vaccines so to speak, also work. At least one study has shown that lead abatement can reduce children’s behavioral problems, even as the social origins of their lead poisoning–for example, their poor housing–remain unaddressed.
The Larger Frame
Sociologists’ aversion to biology is unfortunate and unnecessary. Others have argued this before, such as Jeremy Freese, cited above, but largely to promote evolutionary psychology and behavioral genetics, which comprise but one corner of biology–a corner I still consider problematic. Nonetheless, human biology more broadly understood is an important intermediate mechanism in explaining how, often, social facts produce social facts.
This is how Muller, Sampson, and Winter, introduced at the top, discuss lead poisoning: Broad social factors such as the extent of industrialization and the nature of the technology, more immediate social factors such as the distribution of chemical plants, highways, and housing, and very specific social factors, such as regulations and their enforcement determine exposure to lead. That black and poor children in the 1960s had unusually high lead levels cannot be explained by their biology but instead mainly by housing segregation, gasoline production, and ineffective regulation. The biology of lead in the brain then connected social conditions of the 1960s to behavior in the 1980s.
This is a more general point. Biological factors rarely matter by themselves in explaining social outcomes. Perhaps in cases like pestilence, a biological “accident” can restructure society. (Feigenbaum and Muller, along with Deidre Bloom, show in another paper that boll weevil infestation in the South about a century ago undercut black family formation.) Much more often, however, biological dynamics are intermediate mechanisms between a social cause and a social effect, even pestilence–the result, for example, of new trade routes or techniques of water storage. At the individual level, fear, love, avarice, and anger operate in social conflict, parenting, work, and crime. All sorts of neurological processes turn a social cause into a social effect. The apparent violation of a racial norm, say, turns into a race riot in part because people are aroused. Even supposedly “cold” cognitive processes, such as perception, evaluation and calculation, are shaped chemically, as we saw with lead; affected individuals weigh their decisions less carefully than they would otherwise.
Sometimes, on the other hand, biological mechanisms add little to our understanding. Take the centuries-long decline in interpersonal violence in the West–a history recently popularized by Steven Pinker in his 2011 book, The Better Angels of Our Nature (my review is here). If the decline in mayhem and brutality is explained by the rise of law enforcement powers or by cultural trends, there is not much of a role for a biological mechanism. If, on the other hand, it is explained by improvements in nutrition producing greater frontal cortex growth and that, in turn, strengthening executive functioning–this is one of Pinker’s suggestions–then biology is a major intervening factor between agricultural productivity and social order.
The story of lead and behavior is one explanation that does place biological processes right in the middle of social ones. And sociologists should be fine with that if the data suggest it. We know that typically, as in the story of lead and behavior, the biological process is socially framed and triggered.
Update, June 30, 2021
Here is a recent, 2021, report on the lead-behavior connections. It cites a few of the studies cited here and some more.
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