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Nature or Nurture? Professor Says Both Contribute to Crime

Portnoy Studies Links Among Biology, Environment and Aggression

UMass Lowell Asst. Prof. of Criminology Jill Portnoy studies the interaction of physiological and social factors in crime Photo by K. Webster
Asst. Prof. of Criminology Jill Portnoy studies how biology and social environment interact to produce impulsive and aggressive behavior.

07/24/2018
By Katharine Webster

Are criminals born or made? 

Both, says Jill Portnoy, an assistant professor in the School of Criminology and Justice Studies

Portnoy studies biological and social factors that interact to explain and predict aggressive, impulsive and risky behavior – to help figure out effective ways to intervene before anti-social behavior escalates into crime. 

This fall, Portnoy will offer Internship in Criminal Justice as a class for 12 undergraduates, who will earn credit for learning about the research process through direct involvement in one of her projects: measuring life stresses, heart rate and criminal behavior among adults in the community. She also involves graduate students, honors students and an undergraduate Emerging Scholar in her research. Recently, she sat down with us to talk about her work.

Q: How did you get interested in this particular area of criminal justice research?

A: I’ve always been interested in the criminal brain: Why do people do it? For a long time, the argument was “nature versus nurture” – whether people have something in their physiological makeup that predisposes them to a life of crime, or whether social factors like abusive parents or living in an impoverished neighborhood cause criminal behavior.

Of course, it’s both. Biology and social environment interact in complex ways that we’re just beginning to figure out. Before we can design effective interventions, we need to do research to understand what’s happening.

Q: Can you give me an example from your own research?

A: We had known for a while that people with a low resting heart rate tend to engage in more anti-social behavior, but we really didn’t know why. There’s a prominent theory that a low heart rate is unpleasant, so people with lower-than-average heart rates seek out stimulation to raise their heart rates. 

Working with Prof. Adrian Raine at the University of Pennsylvania, I found support for this theory in data collected for a long-term study: the Pittsburgh Youth Study, which followed hundreds of boys in the Pittsburgh public schools over many years. We looked at 335 boys and their heart rates at rest, as well as during cognitive and stressful tasks. 

Then we looked at whether there was a correlation between resting heart rate and their answers to questions measuring sensation-seeking, like whether they would enjoy getting lost in a new place or doing something “crazy” just for fun. Those with lower resting heart rates were more likely to answer “yes.” They were also more likely to self-report anti-social behavior. This supported the idea that people with low heart rates engage in anti-social behaviors as a form of sensation-seeking.  

UMass Lowell Asst. Prof. of Criminology Jill Portnoy plugs in sensors used to measure skin conductance and heart rate Photo by K. Webster
Portnoy plugs in sensors used to measure heart rate and skin conductance.
Q: Yet surely there are harmless ways to increase your heart rate, like playing competitive sports. What makes someone act out in an anti-social way?

A: The social environment is likely a factor, too. Low heart rate may be especially problematic for people living in social environments that have few options for positive forms of stimulation.

But environment doesn’t explain everything, either. Another study I did looked at students in a very different social environment: a private university in the Northeast. It found that those with lower resting heart rates were more likely to report that they’d cheated on tests, plagiarized or committed other forms of academic dishonesty.   

Q: What’s your latest research project in this area?

A: The undergraduates who intern with me this fall will be helping with the Health, Stress and Behavior Study, which is funded by a $10,000 internal seed grant. It involves healthy adults age 18 and up who are living in the community. We will measure their heart rate and the electrical conductivity of their skin – another measure of physiological arousal in response to stimulation – in a resting state and then again while they perform a stressful task, such as trying to solve a set of math problems. We will also ask them to report stressful events across their entire lives, as well as aggressive and criminal behavior.

My theory is that a low resting heart rate might be an acquired, adaptive trait: If you are subjected to chronic or frequent stress as a child, you adapt by lowering your heart rate. The lower heart rate protects you by blunting your reaction to stressful events, but it can also lead to stimulation-seeking behavior. In other words, a stressful environment may cause physiological changes that lead to an increase in aggressive and impulsive behavior, in addition to causing the behavior directly.

Q: Why study healthy adults living in the community?

A: There’s a continuum of criminal behavior. Nearly all of us break the law in small ways – for example, by driving over the speed limit. I’m interested in people who are behaving aggressively but not yet reaching the level of criminal behavior, or maybe they’re committing more serious crimes like theft or assault, but haven’t been caught. They’re still exacting a toll on society. And if we want to design more general social interventions, like teaching people healthier ways to adapt to stress, then we shouldn’t just study those who get caught.

Q: Speaking of effective interventions, you’ve found a fascinating relationship between omega-3 fatty acid supplements for children and intimate partner aggression between their parents or other adult caretakers. Can you talk more about that?

A: Previous research has found lower levels of disruptive behavior by children taking omega-3 fatty acid supplements. Our study bore this out, and also found that the children’s better behavior had a beneficial effect on their parents, who were less likely to argue with each other or engage in other forms of psychological intimate partner aggression, such as name-calling. 

We also thought that since the children were behaving better, supplementation might reduce aggressive behavior by the parents toward their children – but it didn’t. We’re not sure why not. Our research was based on data gathered in Mauritius as part of another long-term study into child health. Now we need to do the same study in the United States to see whether we get the same results, or whether different cultural norms might produce different results.

This is a promising line of research, because omega-3 fatty acids are thought to improve brain health in several ways in children and adults. If we can improve people’s health and improve their behavior in the process, that’s a really big plus.