One of the biggest challenges in studying psychological disorders is that they often result from a complex mix of physical and social factors, and psychopathy is no exception. An analysis of identical twins in Minnesota suggests that the disorder is at least 60 percent determined by genetics, though other sources peg the number closer to 50 percent [sources: Brogaard, Kiehl and Buckholtz]. Either way, it's clear that both factors play an important role.
Identifying social factors has proven to be a difficult task for researchers. Studies have shown that absent fathers and physical neglect in childhood are strongly associated with psychopathic characteristics in adults, but there's no proof that these factors actually cause the disorder. In fact, many of the United States' most notorious psychopathic serial killers — including Ted Bundy and Dennis Rader — grew up in healthy, supportive households. The challenge of positively identifying social factors is that it's difficult to isolate them from physical ones. For example, a psychopath may have been neglected by his father, but it's hard to tell whether the neglect caused his disorder or was an indicator that his father was also a psychopath [sources: Wallisch, Brogaard].
Clearly, social factors can only explain so much. So what's actually going on in the physical structure of a psychopath's brain? Like many questions about the brain, the answer is complicated. Scientists first suspected damage to the frontal lobe, which among other things processes risk, reward and punishment [sources: Kiehl and Buckholtz, Brogaard].
More recent research, however, has shifted to the brain region known as the paralimbic system. These new findings came about thanks to a technology called functional magnetic resonance imaging, or fMRI, which allows researchers to see to what extent different parts of the brain are being used. As it turns out, psychopathic brains show significantly less activity in the paralimbic system than normal brains, which means it's underdeveloped. So why is this important? The paralimbic region controls moral reasoning, emotional memories and inhibition — in other words, exactly the kinds of characteristics lacking in psychopathic behavior [source: Kiehl and Buckholtz].