When we try to explain acts of human cruelty, there is no scientific value in the term 'evil' but there is scientific value in using the term 'empathy erosion'. The key claim in my book is that when people commit acts of cruelty, a specific circuit in the brain ("the empathy circuit") goes down. This might be temporarily (for example, when we are stressed) or in a more enduring way. For some people, this empathy circuit never developed in the first place, for reasons of environmental neglect and/or for genetic reasons. Whatever the reason this circuit in the brain did not develop in the usual way, or is not functioning in the usual way, it is the very same circuit that is involved.
The functioning of the empathy circuit determines how much empathy a person has, and empathy is "normally distributed" in the population: from zero degrees at the low end through to six degrees at the high end. Most of us are somewhere in the middle, and in my book I explore the different routes that can lead a person to end up at zero degrees of empathy. There are some medical/psychiatric conditions that cause this outcome and most are negative (Zero Negative). These include the personality disorders, such as psychopaths and people with Borderline Personality Disorder.
But one is surprisingly positive (autism spectrum conditions) because although people with autism struggle with empathy, they do so because they have a mind that is highly tuned to spot patterns (rules) in the world. I call this "systemizing", and in people with autism or Asperger Syndrome the "systemizing mechanism" is tuned to an extreme degree. This can have remarkable advantages when trying to figure out how a system works (hence Zero Positive), but leads to disability when applied to the world of people and emotions, because people and emotions are hard (if not impossible) to systemize.
Whilst acts of cruelty always entail zero degrees of empathy, it is not a symmetric relationship: zero degrees of empathy does not necessarily lead to acts of cruelty. In the case of people with autism spectrum conditions, their low empathy usually leads them to avoid other people because they find other people confusing. Their low empathy doesn't lead them to commit acts of cruelty any more than anyone else in the population, but it does often lead them to feel socially isolated, with the risk of depression.
The key difference between autism and psychopaths seems to be that in psychopaths the 'cognitive' component of empathy is intact but the 'affective' component is not. In autism, both components may be impaired, and in Asperger Syndrome just the cognitive component is impaired. In addition, their strong systemizing leads them, through logic, to develop a moral code based on 'fairness' and 'justice'. People with autism spectrum conditions often end up as 'super-moral', developing a set of rules they expect people to live up to consistently (such as honesty), arriving at the conclusion that one should 'treat others as you would have others treat you' because it is the most logical approach.
Whilst even adults with Asperger Syndrome may have difficulties figuring out why someone else's remark was considered funny, or why their own remark was considered rude, or may judge others as liars when they simply are inconsistent in not doing what they said they would do, they may nevertheless have a highly developed emotional empathy, caring about how someone feels and not wanting to hurt them. If they do hurt them it is often unintentional and they feel mortified when it is pointed out, and want to rectify this. In this respect, they do have some of the components of empathy.
For the criminal justice system to work, it is vital to hold onto the notion of people being responsible for their actions. We ask the defendant to plead guilty or not guilty. I am not trying to upturn this principle of the legal system as I think it provides a valuable method for society to decide how to deal with someone who has broken a law. But, if someone who is Zero Negative is violent or abusive because of how the empathy circuit in their brain currently functions, or because of the empathy circuit in their brain did not develop in the usual way, then perhaps we should see such behaviour not as a product of individual choice or responsibility, but as a product of the person's neurology.
We do not hold someone with schizophrenia responsible for having a hallucination, just as we don't hold someone with diabetes responsible for their increased thirst. In the case of the person with diabetes, we 'blame' the person's low levels of insulin, or the person's cells for not responding normally to insulin. That is, we recognize the biomedical causes of the behaviour. Equally, if someone's behaviour is the result of their low empathy, which itself stems from the underactivity of the brain's empathy circuit, and which ultimately is the result of their genetic make-up and/or their early experience, in what sense is the 'person' responsible?
These are complex medico-ethical issues. We need to keep our socio-legal framework since it serves many valuable functions, including recognizing the victim or their family want to see justice done; but those with low empathy who end up in the criminal justice system also warrant our compassion, and may even warrant treatment within the health service.
My book has an optimistic message, namely, that empathy can be increased. For some people it is simply a matter of waiting for development, and gaining experience. For others it may be a matter of either education or therapy. Imaginative approaches are being taken in many fields to facilitate empathy, and I do believe in the idea that people can change - because the evidence supports this.