Psychopathy—it’s biological

Researchers have found the biological explanation for psychopaths after studying the brains of psychopaths who attempted murder, manslaughter, rape
and/or false imprisonment. It was found that the psychopath brain has a structural deficiency—a significant reduction of a white matter tract
which connects the amygdale (the area associated with emotions, fear and aggression) and the orbitofrontal cortex (the area responsible for decision
making). The study offers evidence that psychopathy has a biological basis—and is not a byproduct of societal forces on the individual. "The suggestion of a clear structural deficit in the brains of psychopaths has profound implications for clinicians, research scientists and the criminal justice system," says author of the study Dr. Michael Craig, from the Institute of Psychiatry at King’s College London.
Science Daily
http://www.sciencedaily.com/releases/2009/08/090804090946.htm