Why, why, why do people continue to ignore this simple rule–including people who presumably know better but who invoke a correlation as a lazy rhetorical device?
In The Atlantic this month, neuroscientist David Eagleman writes about biological bases for criminal behavior. The article is interesting and thoughtful in several respects. But after describing a few examples in which biological anomalies were direct causes of anti-social behavior, he launches into a paean to genetic determinism, bracketed by this assertion:
If you think genes don’t affect how people behave, consider this fact: if you are a carrier of a particular set of genes, the probability that you will commit a violent crime is four times as high as it would be if you lacked those genes. You’re three times as likely to commit robbery, five times as likely to commit aggravated assault, eight times as likely to be arrested for murder, and 13 times as likely to be arrested for a sexual offense. The overwhelming majority of prisoners carry these genes; 98.1 percent of death-row inmates do. … By the way, as regards that dangerous set of genes, you’ve probably heard of them. They are summarized as the Y chromosome. If you’re a carrier, we call you a male.
To observe a correlation is to discover a question, not an answer. This particular question–why are males in the U.S. incarcerated at higher rates than females?–has many possible answers. To claim that male genes cause criminal behavior requires additional proof: say, demonstration of a causal mechanism, or a controlled study to establish the likelihood that such a mechanism exists. Perhaps the genes on the Y chromosome really do trigger brain structures or processes that create a greater tendency toward criminal behavior. But perhaps people with Y chromosomes tend to be socialized differently. Eagleman jumps directly from correlation to his preferred causal explanation, asserting that males and females must be genetically different “in terms of drives and behaviors” that lead to crime.
Why does he perpetuate this error, even though elsewhere in the article he emphasizes the complex ways in which genes and environment interact to produce observed behavior?
Partly, when he talks about “environment,” Eagleman seems to be thinking mostly of physical injuries–tumors, drug-abusing pregnant women, lead-based paint–rather than a social environment. The article promotes the view that we are our genes, unless we get poisoned or knocked on the head along the way.
In addition, the correlation between Y chromosomes and criminality fits neatly with a set of evolutionary/pop-psychology just-so stories that we tell ourselves about sex differences. Sex differences therefore function as a convenient ace up the sleeve of anyone trying to argue that biology is destiny. Eagleman can count on most of his readers accepting a genetic explanation for sex differences without noticing the slippage from correlate to cause.
This sort of sloppy argument is dangerous for several reasons. In this context, the primary one is that sex is not the only social category that correlates with incarceration. Do the genes that influence skin color, like those that influence maleness, also cause different “drives and behaviors” that lead to criminality? I assume that Eagleman would say no, and would point to other explanations for the racial disparities in our prison system. I can only assume, however, because Eagleman has somehow managed to write an entire article about biological bases for crime without addressing the racial implications of his argument. Perhaps he addresses this issue in his book, from which the article is excerpted. But one would think that, when publishing a lengthy article in a national magazine that promotes a biological view of crime, one would go out of one’s way to avoid encouraging readers to draw genetic, causal conclusions from current disparities in incarceration rates among demographic groups.