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Why ‘Nature Versus Nurture’ Often Doesn’t Matter

• August 22, 2014 • 4:00 AM

(Photo: abstract/Shutterstock)

Sometimes it just doesn’t make any sense to try to separate the social and the biological.

Every Friday this month we’re taking a look at the relationship between the social and the biological—specifically, how and why the former becomes the latter. Check back next week for the final installment.

When it comes to understanding ourselves, we tend to be splitters: mind and body, nature and nurture, or genes and environment. We take such a split for granted when we ask how the social becomes biological, but sometimes it’s not so useful to dichotomize the world into society and biology. Instead of looking for distinct social and biological influences (and believing that we can change one but not the other), we should recognize that the factors that drive our social behavior can, like a Zen koan, be two things at once.

Take the case of teen alcohol abuse. In a study published last week, an international team of researchers reported the “neuropsychosocial” factors that identify teens who are likely to abuse alcohol. The word “neuropsychosocial” does away with the common nature/nurture divide, and so did the researchers. Rather than asking whether teens abuse alcohol because of social influences or innate biology, the scientists looked at those variables that could be measured, regardless of whether the variables were social, biological, or a mix of both.

We often approach a social problem by splitting it into its social and biological root causes, and assuming that we can change the social ones while working around the supposedly irreversible biological ones. But when it comes to human behavior, this is often not very useful or informative.

The study is part of a long-term European project called IMAGEN, established to understand the “biological and environmental factors that might have an influence on mental health in teenagers.” The project enrolled 2,000 14-year-olds, from whom were collected several types of data, including personal histories, psychological assessments of behavior, brain images, and genetic data. The researchers asked theses teens about their alcohol consumption at the beginning of the study, and then again at age 16. Armed with this data and a relatively large sample size, the scientists set out to answer the question: What neuropsychosocial factors identify teens who abuse alcohol?

In one analysis, the researchers looked for the factors that identified “current” drinkers, 14-year-olds who were already abusing alcohol when the study data were collected. They compared “binge drinkers” (defined as having been drunk at least three times by age 14) to non-drinkers (teens who drank no more than twice before age 16). In a second analysis, they attempted to identify future alcohol abusers—teens who were not drinking at age 14, but went on to get drunk multiple times by age 16. For each of these analyses, they built a computer model that used the measured neuropsychosocial variables to classify teens as drinkers or non-drinkers. The first model correctly identified 82 percent of current binge-drinking teens and 89 percent of non-drinking teens. The second model, predicting future drinkers, didn’t fare quite as well: 66 percent of drinkers and 73 percent of non-drinkers were correctly classified.

The most important identifying factors of current and future alcohol abusers were an inseparable mix of the social and the biological. A look at those factors shows how teasing out distinct social and biological causes would be an analytical nightmare: the different genetic, neurological, and life history variables are linked together in a thicket of feedback connections. For example, a history of romantic or sexual relationships strongly predicted current and future binge drinking behavior. But teen sexual behavior is surely influenced by other variables the researchers measured, like personality (which has a substantial genetic component), and “reward anticipation” or “emotional reactivity,” which were measured using brain imaging. It’s important to keep in mind that the study was not designed to discover which factors cause teen drinking, a much more difficult task. Instead, the researchers focused on what they could measure—an approach that, while it has its limits, is one of science’s most successful strategies.

What are the neuropsychosocial factors that best identify current and future teen drinkers? Some predictive traits include the volume and activity level of certain brain areas: “Future binge drinkers had reduced grey matter volume but increased activity when receiving a reward in the superior frontal gyrus compared to controls.” A personality trait characterized by “searching for, and feeling rewarded by, novel experiences” predicts both current and future teen drinkers. Other factors, like disruptive family events and more developed pubertal status identify current (but not future) drinkers, while “anxiety sensitivity” predicts only future drinkers. Notably, one set of factors that are not very predictive are specific genetic variants associated with alcohol dependence. This isn’t surprising because the individual effect of any one gene on a behavior like alcohol abuse is likely to be small.

With these results, we can we say about the biological basis for the social phenomenon of teen alcohol abuse? Not much more than, “it’s complicated.” And anyway, framing the question like this is a mistake.

We often approach a social problem by splitting it into its social and biological root causes, and assuming that we can change the social ones while working around the supposedly irreversible biological ones. But when it comes to human behavior, this is often not very useful or informative. As the authors write, their data “speak to the multiple causal factors for alcohol misuse,” and, in fact, any one variable, taken in isolation, had a small influence in their study. The predictive power of their computer model came from combining variables that were measurable—regardless of whether they could be neatly categorized as social or biological—into a single risk profile. This profile offers clues for how to find and help at-risk teens, and the most effective interventions may turn out to have little to do with directly treating some key social or biological cause of alcohol abuse. As we think about the connection between our social behavior and our biology, we should, like good scientists, be pragmatic, and abandon the distinction between society and biology when it’s not useful.

Michael White
Michael White is a systems biologist at the Department of Genetics and the Center for Genome Sciences and Systems Biology at the Washington University School of Medicine in St. Louis, where he studies how DNA encodes information for gene regulation. He co-founded the online science pub The Finch and Pea. Follow him on Twitter @genologos.

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