I just started reading The Science of Evil by Simon Baron-Cohen, the autism researcher who also wrote Mindblindness. The subtitle of the Science of Evil is, On Empathy and the Origins of Cruelty. Baron-Cohen’s thesis is: cruelty exists when empathy fails.
Baron-Cohen’s definition of empathy
First part of definition:
“Empathy occurs when we suspend our single-minded focus of attention and instead adopt a double-minded focus of attention.” 
In other words, having empathy means that one has consideration for another’s frame of mind in addition to one’s own. Someone focused only on his or her own needs and desires, is not empathetic by this definition.
Baron-Cohen suggests that there is a spectrum of empathy, in the same way that there is a spectrum of severity of autism. Furthermore, he says that the distribution of empathy among the population takes the form of a bell-shaped distribution. In other words, there are those on the low end of the curve with little or no empathy and those on the high end who are totally empathetic; the rest of us lie somewhere in between. One’s place on the curve isn’t static. For example, a person distracted with one’s own problems may, for the moment not have the capacity for empathy with another. It is also possible that an event may trigger a higher degree of empathy in a person normally at the low end of the empathy spectrum.
Second part of definition:
“Empathy is our ability to identify what someone else is thinking or feeling and to respond to their thoughts and feelings with appropriate emotion.” 
Therefore, in addition to recognizing another’s state of mind, one must be able to respond in a way that shows understanding of the other’s condition. The implication is that one must somehow be aware that there are other minds, different from one’s own. One therefore must be capable of having a Theory of Mind. Theory of Mind “is the ability to attribute mental states—beliefs, intents, desires, pretending, knowledge, etc.—to oneself and others and to understand that others have beliefs, desires, and intentions that are different from one’s own.” 
Neurological foundations of empathy
I am fascinated by the brain mechanisms that somehow mediate behavior and emotions. This is another aspect of empathy covered by Baron-Cohen in The Science of Evil. I must leave the discussion of this aspect of empathy for another post.
Implications of absence of empathy
The Science of Evil gives examples of failure of empathy in individuals who commit horrendous crimes and notes the wholesale failure of empathy in Nazi German.
The book, Inventing the Feeble Mind  details the treatment and characterization of the mentally ill and mentally handicapped throughout American history. I wonder if American Society’s place on the bell curve of empathy tracks with the public policy and attitudes toward those who have lesser mental abilities. That is, does poor treatment of the mentally disabled correspond with an America that is self absorbed and unable to have a double-minded focus of attention?
In future posts, I would like to: 1) determine if empathy is scaleable from an individual to a society; 2) if so, investigate whether societal empathy tracks with the treatment of the mentally handicapped.