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The Neurobiology of Evil

September 8, 2010, 12:00 AM

Is a person's propensity toward evil a matter of malfunctioning synapses and neurons?

Michael Stone, professor of clinical psychiatry at Columbia University and author of “The Anatomy of Evil,” says it is.  Ever-more-detailed brain scans are revealing the biological origins of psychological issues in "evil" people, from those who are mildly antisocial to serial murderers.

Under each brain’s wrinkly cortex lies the limbic system, an evolutionary heirloom controlling emotion and motivation, among other functions.  Within this limbic system is the amygdala, an almond-shaped cluster of nuclei that processes our feelings of fear and pleasure.

Murderers and other violent criminals have been shown to have amygdalae that are smaller or that don’t function properly, explains Stone.  One recent study concluded that individuals who exhibit a marker of “limbic neural maldevelopment” have “significantly higher levels of antisocial personality, psychopathy, arrests and convictions compared with controls.” 

The amygdala is important because, among its other functions, it allows an individual to respond to the facial expressions of others.  When a person has an abnormal amygdala—one that doesn't process the facial expressions of emotion—they can have an inability to register the fear and suffering of a victim, says Stone.  This lack of response to the emotions of others predisposes an individual to antisocial, even criminal, behavior.

Under normal development, empathy from a full-functioning amygdala pairs with a moral “braking system” in the brain’s higher-functioning cortex.  This connection halts deep-rooted urges from our neural-narcissistic lizard brain, keeping each of us morally and socially in step. However, if that connection is not operating properly, says Stone, "the person may go ahead and do the unspeakable crime, which otherwise he would have put the brakes on or maybe even not even contemplated doing it in the first place.”  

A biological predisposition to antisocial behavior is not a sentence to criminality, but research shows a significant population of antisocial personality disorder among people in prison.  A 2002 review of 62 studies sampling 2,300 prisoners found that almost half—47%—had antisocial personality disorder, which can be linked to or aggravated by developmental issues with the prefrontal cortex and with other parts of the brain.

This link between criminality and the brain has generated interest in where neurology and the law meet.  Neurolaw—and more generally neuroethics—is a hot topic in universities, law schools and, increasingly, the judicial system.  The newest brain-scanning technology is leading academics, lawyers, judges and scientists to reevaluate or reinforce laws that have been based on the culpability of the person, not of the brain. Legal defenses that blame the brain while exonerating the "person" have not flooded the courts, yet the attention among academics is undeniable, with papers, foundation-organized seminars, blogs and courses proliferating.  In 2007, for example, more than two dozen universities were awarded a share of a $10 million MacArthur project specifically to study this intersection of law and neuroscience. 

The implications don't end there.  Brains are built from the blueprints encoded in our DNA, a fact which is leading the newest research to seek out specific genes that predispose people toward antisocial—even "evil"—behavior.  According to a review of recent research, at least seven specific genes have been identified that both are linked to antisocial or aggressive behavior and are thought to organize how brain growth is structured.  These seven—MAOA, 5HTT, BDNF, NOTCH4, NCAM, tlx, and Pet-1-ETS—are the usual suspects for neuroscientists looking beyond brain anatomy to the genetic origins of "evil". 


Thanks to MRI and PET brain scans, we now know more than ever about how deficiencies in certain parts of the brain may underlie "evil" behavior.  These scans show antisocial, rule-breaking populations who prone to criminality have structurally impaired sections of the brain, such as the amygdala.

The implications of a brain-based origin for "evil" potentially open up testing for predisposition to antisocial, even psychopathic, behavior early in a life.  A study published in November by the American Journal of Psychiatry suggests that amygdala dysfunction in children as young as three can cause a lacking response to fear that precedes criminality in adulthood.

Learn More

— Gao, Yu, et al. “Association of Poor Childhood Fear Conditioning and Adult Crime.”

— Davidson, R. et al. “Dysfunction in the Neural Circuitry of Emotion Regulation — A Possible Prelude to Violence.”

— Raine, A., and Yang, Y. “Neural foundations to moral reasoning and antisocial behavior.”

— DeLisi, M., et al. “The Criminology of the Amygdala.”

— Raine, A., et al. “A neurodevelopmental marker for limbic maldevelopment in antisocial personality disorder and psychopathy.”

— Raine, A. “From genes to brain to antisocial behavior. Current Directions in Psychological Science.”


The Neurobiology of Evil

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