From The New York Times:
Dr. Baron-Cohen, a professor of developmental psychology at the University of Cambridge and director of the university’s Autism Research Center, proposes that evil is more scientifically defined as an absence of empathy, exacerbated by negative environmental factors (usually parental, sometimes societal) and a genetic component. When these three exist in tandem they result in what he calls a Zero-Negative personality. Zero-Negative takes at least three forms (and possibly more), borrowing from terms used in psychiatry: Zero Type P (psychopathology), Zero Type B (borderline disorder) and Zero Type N (narcissism).
Whereas psychiatry groups these three loosely under the term “personality disorders,” Dr. Baron-Cohen proposes that they all share the characteristic of zero degrees of empathy. (His “empathy quotient” scale is available in the book or online, with an instant numerical score that is translated into degrees of empathy from zero to six, or super empathy.) Viewing these disorders in terms of empathy “has very different treatment implications,” he maintains. Psychopaths aside, people with low degrees of empathy can be taught empathy, as is done in schools concerned about bullying, and treated with standard psychiatric approaches.