Raine: There’s no question whatsoever that genetic influences play a very significant role in shaping crime and violence. That can no longer be disputed. What can be debated is what specific genes are involved – and in what way. The gene that codes for the enzyme MAOA does seem to be involved at some level, but there’s still a long way to go in the hunt for genes that predispose to violence.
There’s also an explosion of brain imaging research. The most replicable finding so far is dysfunction to the prefrontal cortex, the “guardian angel” in the brain that controls our impulsive behavior and regulates our emotions. Damage that emergency brake on behavior, and explosive violence is not far away.
But you know, the neurobiology of violence is far from simple. We’re clearly going to find that it’s enormously complex. At the end of the day we’ll find that multiple brain systems are in on the act. One prime suspect in shaping psychopathic behavior is the amygdala – the seat of emotion. Psychopaths have a core emotional deficit – they lack conscience, remorse, and guilt. They just don’t feel feelings the way we do. Several studies are documenting volume reductions in this brain structure in psychopaths. The amygdala is also less activated in psychopaths when they contemplate moral dilemmas. It’s as if psychopaths don’t have the feeling for what is right and wrong – even if they know it at a cognitive level. Still, we are just at the very beginning of a long journey into understanding the brain basis to violence. We have a very long way to go.
What else at the biological level? Lots of things. At a psychophysiological level something as simple as low resting heart rate is probably the best-replicated biological correlate of antisocial and aggressive behavior in children and adolescents. We think it’s a marker for fearlessness and impulsive stimulation-seeking. High testosterone and low cortisol are hormonal candidates. In terms of neurotransmitters, low serotonin is a well-replicated correlate of impulsive violence.
But health factors are really important too, and in a way the seeds of sin are sown pretty early on in life. Mothers who smoke or drink during pregnancy are much more likely to have babies who grow up to become violent offenders. Poor nutrition during pregnancy also raises the odds of later offending. Even birth complications – especially when combined with social risk factors like the maternal neglect – raises the odds of adult violence. And let’s not forget environmental toxins like lead. They damage the brain, and not surprisingly are associated with antisocial behavior.
Cook: What do you think of the argument put forward by Steven Pinker in The Better Angels of Our Nature, suggesting that violence has dropped dramatically as our social structures have changed?
Raine: The Better Angels of Our Nature was a masterful thesis that to my mind was right on the mark in its main argument – violence has indeed dropped over time. Sure, social structures that provide order and help contain violence have surely been a part of this, but the idea I particularly resonated to in Pinker’s book is the idea that thinking and reasoning has been one of our better angels. We’ve become smarter, more educated, and better able to reason, and partly for that reason we’ve moved away from violence.
And that’s really why I wrote The Anatomy of Violence. I want more people to understand why people commit crime. I want them to know the brain mechanisms behind these acts, and what factors, including environmental influences, shape the brain processes that predispose to violence.