The country has made unprecedented strides in the fight against crime. Both violent and non-violent crime are way down from their highs in decades past. This is great news, of course, but the success could easily lull us into a false sense of security, believing that we have the problem solved. Indeed, what if much of what we know about the causes of crime is either deeply flawed or flat out wrong?
Imagine the trial of a new drug for an ailment that is as intractable as it is lethal. Researchers find 100 people with the disease and give the new drug to the first 50 patients who show up to the clinic. The next 50 trial participants are placed into a control group and given no treatment. The drug has a truly shimmering success rate.
As you may have guessed, problems abound with this experimental design. For starters, because it isn’t randomized and because preexisting differences among the participants aren’t taken into account, the study can’t answer the question: Did the new drug cause anyone to get better? Such a study would be laughed out of the medical research community. And yet much of the knowledge concerning the causes of crime (as well as a host of other issues in the social sciences) stems from designs that aren’t much better than the poorly executed drug trial example.
Social scientists generally, and criminologists especially, often lack the ability (usually due to both ethical and practical concerns) to perform randomized controlled trials, the gold standard of research. We might expect, for instance, that having low levels of self-control is a cause of criminal behavior. In fact, some of the most powerful explanations of crime have been built on this idea, and there is much evidence to support it. We might also hypothesize that bad parenting causes children to develop low levels of self-control. Yet we can’t randomly assign people to have different levels of self-control, and we most assuredly can’t randomly assign kids to parents. All of this is to say that criminologists may never know for sure whether parenting causes self-control and whether, in turn, self-control causes crime.
While criminologists typically can’t use randomized trials, they do use a variety of statistical methods to study parenting and self-control, and self-control and crime. They attempt to rule out the most likely alternative explanations for why bad parenting leads to less self-control and why less self-control leads to criminal behavior. This research has consistently revealed that parenting styles correlate with self-control development in children, and self-control in childhood predicts a variety of important outcomes, including criminal behavior. Criminologists make their living uncovering precisely these types of associations.
Yet these studies will never achieve the accuracy of a randomized controlled trial, because all of those factors, like self-control, delinquent peer affiliation, etc., are also, to some degree, heritable.
Ah, heritability. A term that is much maligned in disciplines like criminology and often serves as a wellspring of confusion. Humans differ in height, weight, personality style, and behavioral tendencies — not everyone is nice and outgoing, just like not everyone is as tall as a professional basketball player. But here’s the important part, heritability has to do with the origins of these differences. To say that something is heritable is to say that genetic differences play a role in creating observable differences.
Variety in our gene pool matters when we seek to understand why some people can dunk a basketball or compose a sonnet, and why some people persistently break the law. The effects of genetic differences make some people more impulsive and shortsighted than others, some people more healthy or infirm than others, and, despite how uncomfortable it might be to admit, genes also make some folks more likely to break the law than others.
The hypothetical drug trial didn’t do a good job of accounting for everything that might explain differences between the treatment and control group participants, which opened the door to alternative explanations for why participants in the treatment group got better. In a similar vein, the finding that most human outcomes are heritable means that studies of behavior should account for heritability in order to rule it out as an alternative explanation.
Imagine that you’re curious whether certain parenting styles influence self-control in children. It’s not hard to find evidence that the way parents treat their children is associated with the child’s level of self-control later in life. But parents don’t just pass on life lessons for learning self-control to their kids, they also pass along their genetic material. Half of your genetic material was inherited from Mom and half came from Dad. If you ignore the element of genetic transmission, you might falsely attribute any correlation between parent and child as being due to social transmission.
The way parents treat children is, in part, a product of their own personality and temperament. Personality is partly heritable, so the observation that parents and children tend to have similar levels of self-control could be due to social transmission, genetic transmission, or both.
Most of the evidence about the causes of crime overlooks genetic transmission. Yet, some research has found that once you account for genetic influences on self-control, previously identified social transmission effects (read: parenting) on the child’s self-control become unstable. In other words, when you control for genetic transmission (the alternative explanation that most criminologists overlook), the effect of parenting on self-control diminishes or goes away entirely.
Consider another type of parenting effect — one that shows up in the news frequently — spanking. Not long ago, we examined the relationship between spanking and behavioral problems in children. Once we controlled for genetic transmission, there was no spanking effect in the way that most scholars think about spanking effects. Put another way, our evidence did not support the conclusion that spanking causes behavioral problems in the sense that most psychologists would argue.
The conundrum of heritability transcends parenting. For instance, it’s obvious that crime isn’t randomly distributed across neighborhoods. It seems to be a relatively stable factor that defines an area over many generations. Equally nonrandom, though, is the process by which people sort themselves into neighborhoods. People cluster into areas based on a host of factors, including the primary factor of income. Here’s the kicker, if any of the traits that affect residential choices are heritable and you ignore that influence, your findings regarding the impact of neighborhood factors on crime could be in jeopardy.
A remarkable study in Sweden recently found that highly disadvantaged neighborhoods had more crime. Yet that neighborhood effect disappeared when risk factors concentrated within certain families were taken into account. Once again, social transmission effects weakened (and, in this case disappeared) when other factors like genetic transmission were controlled for. Does this finding guarantee that similar results will emerge in other samples around the world? No. But criminologists rarely consider the possibility that their own studies could be polluted by hidden genetic effects.
The more technical term for this phenomenon is genetic confounding, and there is reason to believe that it is endemic to much of the research coming out of the social sciences in general, and criminology in particular. Our own research into the issue suggests that even a modest amount of unmeasured genetic influence can pollute and infect your findings. As a result, much of what we think we know about the causes of crime could be overstated or just flat wrong.
Our goal here is not to pick on social scientists; after all, we are social scientists. But social scientists in general, and criminologists in particular, should embrace research designs that allow one to account for genetic confounding. To do so, it will be necessary to adopt designs capable of pulling apart genetic and environmental factors. This translates into a need to analyze data from relatives.
Sampling one child, from one family — as social scientists typically do — is similar to performing a weak drug trial. For decades, behavior geneticists have been analyzing sibling data (mostly twins), which is one of the most powerful methods for probing the relationship between two variables.
Yet most criminologists do not utilize these designs. Not for any good methodological reason, at least none of which we are aware. Instead, it seems that the word “gene” makes social scientists nauseated. Not long ago, in fact, the top journal in the field of criminology published an article calling for an end to twin studies. Let that resonate a moment. There was an actual call to remove a perfectly good research technique from the field, one that also happens to be exceedingly valuable when trying to rule out widespread problems like genetic confounding.
If criminology and the social sciences wish to continue maturing into powerful scientific enterprises, we must stop conducting studies like they are bad drug trials.
Brian Boutwell is an associate professor of criminology and criminal justice at St. Louis University. J.C. Barnes is an associate professor of criminal justice at the University of Cincinnati.