As you watch your six-year-old daughter having a tantrum because she lost her favourite hair slide, it's easy to wonder: where does that rage come from? And where might it lead? Equally, when you watch her blithely crush snails underfoot or deliberately pinch her little brother, you find yourself thinking: how come she is so apparently unfeeling? Is it something we, as parents, have done?
Rare is the parent with a child so saintly that she has never asked herself these questions. But there is little need to worry. Young children get angry. They jump on snails and squash flies. And at six, your daughter will still be developing a conscience - moral awareness coupled with what psychologists call "theory of mind": the ability to imagine what other people might be thinking and feeling. She's still finding her way socially and emotionally, and the fact that you're even reading an article like this means you care about how she turns out.
In this respect she is lucky. Less fortunate children, their development having been derailed at a crucial stage by abuse, neglect or the loss of a parent, can go on to have troubled lives marked by an inability ever to learn theory of mind. Such children may, in extreme cases, display the sort of behaviour we find it convenient to call "evil" when we witness it in obviously disturbed children such as the killers of the British toddler James Bulger. But as a remarkable new book shows, this word doesn't really tell us anything, let alone suggest ways in which these children can be (or could have been) helped.
Simon Baron-Cohen is an expert in autism and a professor of developmental psychopathology at Cambridge University. For him, the word "evil" is not just unhelpful but unscientific. As he puts it in his book Zero Degrees of Empathy: A New Theory of Human Cruelty, "Evil is treated as incomprehensible, a topic that cannot be dealt with because the scale of the horror is so great that nothing can convey its enormity." He suggests we substitute "empathy erosion", which gives a more accurate picture of what is happening neuropsychologically when people behave cruelly.
As Baron-Cohen sees it, we all lie somewhere on the empathy spectrum, from six degrees at one end to zero at the other. At six degrees, people are highly empathetic - that is, they identify with what someone else is thinking or feeling to such a degree that their altruism borders on self-neglect. But at zero they are psychopathic. A "chip in their neural computer" is missing, which leaves them unable to socialise properly. Worse, they see other people simply as objects who can be manipulated. (An interesting hallmark of psychopaths is that they never learn to fear punishment.)
In some cases there might be positive aspects to having zero empathy. Baron-Cohen places in the "zero positive" category sufferers from autism who have special skills in the areas of music, art or memory. But most empathy-deficient people will be "zero negative": "borderline" (volatile and impulsive, switching from extreme love to extreme hate); narcissistic (believing they are special and have a right to be treated well no matter what); or psychopathic (prepared to do whatever it takes to advance themselves - a sub-group is the scheming, lying, every-office-has-one "high Machiavellian").
Empathy is generated when at least 10 interconnected regions of the brain click into action, among them the medial prefrontal cortex (a hub for social information processing) and the inferior frontal gyrus, which handles emotion recognition. Baron-Cohen calls this "the empathy circuit". The sobering revelation of Zero Degrees of Empathy is that, while there is a genetic component to zero negativity, nothing causes the empathy circuit to fail like bad parenting. The upside being, of course, the potential good you could do in the world by doing right by your children.