Is evil just in the eye of the beholder? At the beginning of this book, the criminal psychologist author cites Nietzsche’s claim that “thinking evil means making evil” – though Hamlet got there first with “there is nothing either good or bad, but thinking makes it so”, and the Stoics long before him. But what about murderers?

It turns out, Julia Shaw wants to argue, that we all have the capacity to commit murder and other heinous acts, and it boils down to a matter of moral luck that most of us have the impulse control that prevents us acting out our dark fantasies. “I regularly feel like I want to kill people,” she admits disarmingly, “you know, just a little bit.” Look more closely at the context of a crime – or inside a person’s head – and you will not fail to find extenuating circumstances. Shaw recounts the sad case of a man who stabbed his father to death because he had been convinced by an alcoholism counsellor that his substance abuse problems must have been caused by sexual abuse in his childhood. Meanwhile, it may be the case that an absence of empathy, of the kind characteristic of psychopaths and killers, is neurologically determined at birth. Can it be anyone’s fault to be born with such a brain?

For such reasons, Shaw argues that we do wrong when we label people with villainous nouns on the basis of a single act – “Murderer. Rapist. Thief. Liar” – or use what might be genetic conditions as terms of disapprobation: “Psychopath. Paedophile.” This linguistic habit, she says, tends to convince us that “some people should not be empathised with”. But we are all somewhere on the spectrum of dark behaviours. We are all, for example, potential sadists – even if I was alarmed to learn about “a type of aggression that you have probably felt but never understood: a weird feeling that you want to hurt tiny, fluffy animals”. Not me, guv. (This, Shaw suggests, is – at least in some people – the brain’s self-defence mechanism against being overloaded by cuteness.)

The book is warmly, chattily written, and its preference for “realistic harm reduction” over wanton vilification of others is laudably humane, though it is not to be relied on as an etymological source. (“Have you ever noticed that ‘devil’ is just the word ‘evil’ with the letter ‘d’ attached to the front of it?” Well, not really: the words have entirely different roots.) Shaw draws knowledgeably on psychological and neuroscientific research, even if the latter can often be peculiarly unilluminating. (“All types of moral decision-making involve increased activation of the left middle temporal gyrus, medial frontal gyrus and cingulate gyrus.” Cool. But so what?) She also makes use of more dubious findings – the famous Stanford prison experiment, for example, when volunteers were separated into guards and inmates and the guards began acting sadistically, allegedly saw more interference and coaching than was at first admitted. (“I believed that I was doing what the researchers wanted me to,” one of the guards told the reporter Ben Blum last year.)

But her main argument – that there is no such thing as evil – is one that science can’t settle one way or the other. And she seems to shy away from pursuing the implications of her position to their logical conclusion. Having persuaded the reader that, given the right circumstances, we might all be killers, creeps, deviants, cyberbullies, slave-owners and accomplices to torture or genocide, Shaw is careful to point out that she does not subscribe to “moral relativism”, and that some things just are wrong. Indeed, she concludes: “Just because we can see how circumstances influence us in profound ways does not mean that we are justified in behaving badly … I believe that intentionally causing pain and suffering is inexcusable.”

At this point, arguably, the semantic difference between “inexcusable” and “evil” seems negligible in context, and whether you call it one or the other is moot. “I challenge you to go through life without resorting to calling actions or people evil,” she suggests, which seems like a decent idea; but is calling them inexcusable not just as bad, if not worse? (Theologically speaking, at least evil can be excusable.) Whichever term you choose, the point is one of absolute condemnation. Yet the strong implication of the way Shaw uses empirical evidence throughout the book is that one day, when we can analyse the brain carefully enough, we will find physiological causes for “inexcusable” behaviour from which the subject was in no sense free to resile. At which point it would be a hard person indeed who refused to say: tout comprendre, c’est tout pardonner.

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