The myth of “pure evil” is a bad joke, resulting from and sustained by other unhelpful binaries: good and bad, right and wrong, normal and abnormal, and hot and cold.

How bad? How wrong? How abnormal or cold?

Science can speak to this question of degree and enrich our understanding of what “evil” might be. Specifically, the sciences of the mind have a variety of approaches to illuminate our understanding of natural phenomena like “evil” on a psychological and neurobiological level.

Take, for instance, the psychopath. The term “evil” is popularly equated with psychopathy, and together they readily evoke thoughts of ruthless dictators—Pol Pot, Stalin, and Hitler—and sadistic serial killers – Jack the Ripper, Jeffrey Dahmer, and Gary Ridgeway (the “Green River Killer”). While this subsample of infamous and sensationalized historical figures represents only a very narrow and conventional portrait of what people casually refer to as “evil,” psychopathology is generally understood as one of several other personality disorders that fall along a continuum of antisocial behaviours.

Antisocial Personality Disorder (ASPD) is characterized by chronic patterns of egotism, narcissistic grandiosity, as well as extreme manipulative and destructive behaviours towards others. Characterized by a lack of conscience and an inability to empathize with others, psychopaths are usually associated with a range of textbook behavioural and personality traits – for instance, a propensity for perpetrating cold-hearted, criminal acts of violence. The Psychopathy Checklist–Revised (PCL-R) is one of the standard clinical diagnostic tests used to determine psychopathy.

Currently in a clinical context the term ASPD is favoured over “psychopathy” and advocated for in the current version of the Diagnostic and Statistical Manual of Mental Disorders (DSM) produced by the American Psychiatric Association. In fact, there is an ongoing debate over how to differentiate psychopathy from other emotional dysfunctions along the antisocial disorder spectrum. However, several studies over the past few years have amassed evidence that provide a more definitive neuroscientific distinction for psychopathy as an independent brain disorder.

For example, a study published in 2010 by the psychologist Adrian Raine took magnetic resonance images (MRI) of the brains of around 90 individuals “at risk for antisocial personality disorder and psychopathy,” looking for signs of a damaged or underdeveloped  septum pellucidum – a structure in the limbic system of developing fetuses, which closes as the brain becomes fully formed.

Prenatal neural maldevelopment is associated with the pressence of a cavum septum pellucidum (CSP, a cavity in the septum pellucidum) and is suspected to result from exposing the fetus to alcohol. Raine et al. hypothesized and later confirmed via MRI that those who suffered from neurodevelopmental abnormalities in the “limbic and septal structures” (i.e., those with a CSP) were predisposed to ASPD and psychopathy.

Not discounting the role of environment, genetics and social circumstance at play, these findings basically mean those suffering from ASPDs and psychopathy were predisposed to these conditions by developmental biological forces beyond their control.

A related study published in May, 2012, by Sarah Gregory et al. aimed to quantify via MRI the difference in volume of gray matter (GM) between the brains of 60 men: “antisocial male violent offenders” suffering from ASPD and psychopathy, versus those simply suffering from some form of ASPD and those without any personality disorder at all. The result: “Reduced GM volume within areas implicated in empathic processing, moral reasoning, and processing of prosocial emotions such as guilt and embarrassment may contribute to the profound abnormalities of social behavior observed in psychopathy.”

A neuroscience of psychopathy only helps to de-stigmatize and demystify “evil.” It does not entail that we exonerate serial murderers across the board on the basis of them being issued a bad model of brain.