What causes a person to be a sociopath?

Sociopathy/Psychopathy would be defined as a syndrome with strong behavioral features of impulsivity and fearlessness and a strong interpersonal domain comprised of aggressive social relations, manipulation, rebelliousness, self-centeredness, and a tendency to externalize blame.

One twin study suggests that psychopathy has a strong genetic component. The study demonstrates that children with anti-social behavior can be classified into two groups: those who were also callous acquired their behavior by genetic influences, and those who were not callous acquired it from their environment "The amygdala is crucial for stimulus-reinforcement learning and responding to emotional expressions, particularly fearful expressions that, as reinforcers, are important initiators of stimulus-reinforcement learning. Moreover, the amygdala is involved in the formation of both stimulus-punishment and stimulus-reward associations. Individuals with psychopathy show impairment in stimulus-reinforcement learning (whether punishment or reward based)and responding to fearful and sad expressions. It is argued that this impairment drives much of the syndrome of psychopathy.
There is a strong genetic link and much evidence to support the idea that psychopathy is passed down and is biological.

• Psychopaths don't have the same physiological responses to fear that constrain the behaviour of normal people, such as rapid heartbeat, sweating, dry mouth, trembling and muscle tension.
• Psychopaths don't have physiological responses to emotionally charged words such as "love" and "death" the way regular people do, suggesting that they process emotional stimuli differently.
• When one identical twin is psychopathic, the other is more likely to be psychopathic than those in the general population.
• Adoption studies indicate that children can inherit psychopathic traits from a psychopathic parent even when they are raised by different parents.
• When compared to non-psychopaths, differences have been found in a number of brain chemicals among psychopaths.

They are often reported as having an evil stare, sometimes with eyes that appear black rather then colored