When I was seven years old, my father told me the Nazis had turned Jews into lampshades. Just one of those comments you hear once and the thought never goes away. To a child's mind – even to an adult's – these two types of thing just don't belong together. He also told me the Nazis turned Jews into bars of soap. It sounds so unbelievable, yet it is actually true. I knew our family was Jewish, so this image of turning people into objects felt a bit close to home.
Years later, I was teaching at St Mary's Hospital Medical School in London. I sat in on a lecture on physiology. The professor was teaching about human adaptation to temperature. He told the students the best data available on human adaptation to extreme cold had been collected by Nazi scientists performing "immersion experiments" on Jews and other inmates of Dachau concentration camp, who they put into vats of freezing water. They collected systematic data on how heartrate correlated with time, at zero degrees centigrade.
Hearing about this unethical research retriggered that same question in my mind: how can humans treat other people as objects? How do humans come to switch off their natural feelings of sympathy for a fellow human being who is suffering?
The standard explanation is that the Holocaust (sadly echoed in many cultures historically across the globe) is an example of the "evil" that humans are capable of inflicting on one another. 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. But, when you hold up the concept of evil to examine it, it is no explanation at all. For a scientist this is, of course, wholly inadequate.
As a scientist I want to understand the factors causing people to treat others as if they are mere objects. So let's substitute the term "evil" with the term "empathy erosion". Empathy erosion can arise because of corrosive emotions, such as bitter resentment, or desire for revenge, or blind hatred, or desire to protect. In theory these are transient emotions, the empathy erosion is reversible. But empathy erosion can be the result of more permanent psychological characteristics.
Unempathic acts are simply the tail end of a bell curve, found in every population on the planet. If we want to replace the term "evil" with the term "empathy", we have to understand empathy closely. The key idea is that we all lie somewhere on an empathy spectrum. People said to be "evil" or cruel are simply at one extreme of the empathy spectrum. We can all be lined up along this spectrum of individual differences, based on how much empathy we have. At one end of this spectrum we find "zero degrees of empathy".
Zero degrees of empathy means you have no awareness of how you come across to others, how to interact with others, or how to anticipate their feelings or reactions. It leaves you feeling mystified by why relationships don't work out, and it creates a deep-seated self-centredness. Other people's thoughts and feelings are just off your radar. It leaves you doomed to do your own thing, in your own little bubble, not just oblivious of other people's feelings and thoughts but oblivious to the idea that there might even be other points of view. The consequence is that you believe 100% in the rightness of your own ideas and beliefs, and judge anyone who does not hold your beliefs as wrong, or stupid.
Zero degrees of empathy does not strike at random in the population. There are at least three well-defined routes to getting to this end-point: borderline, psychopathic, and borderline personality disorders. I group these as zero-negative because they have nothing positive to recommend them. They are unequivocally bad for the sufferer and for those around them. Of course these are not all the sub-types that exist. Indeed, alcohol, fatigue and depression are just a few examples of states that can temporarily reduce one's empathy, and schizophrenia is another example of a medical condition that can reduce one's empathy.
Carol is 39 years old. I met her when she came to our diagnostic clinic in Cambridge. (I have disguised details of her life for reasons of confidentiality.) She has borderline personality disorder. For as long as she can remember, and certainly going back into early childhood, she has felt her life was "cursed". As she looks back on her stormy childhood, her unstable teens and her crisis-ridden adulthood, she contemplates her lifetime of depression. Her relationship with her parents has been punctuated by periods of years during which she did not speak to them at all. She is aware that she has a huge reservoir of hatred towards her parents, who she feels maltreated her and who were never really parents towards her. However nice people are to her, she feels she can never quench this simmering rage which even today can come out as hatred towards anyone she feels is disrespecting her. Often people she perceives as disrespecting her are simply people who disagree with her, and she senses that they are doing this in a confrontational way.
In this way, there is a distortion or a bias in how she reacts to others, assuming they are treating her badly when they are not. If her children don't do what she says, she screams and swears at them, saying: "How dare you treat me with such disrespect? You can just fuck off! I hate you. I never want to see you again. You can just look after yourselves. I'm through with the lot of you! You're evil, selfish bastards! I hate you! I'm going to kill myself! And I hope you're happy knowing you made me do it!" She will then storm out, slamming the door behind her.
Minutes later, she will drive to one of her friends and spend the evening having fun, leaving her children reeling with the impact of her hurtful words. When her hatred and anger bubble up, there is no chance of her stopping it coming out. It bursts forth with venom, designed to hurt whoever's ears the words land on. Her own feelings are so strong that there is no space in her mind to consider how her children might feel, being told by their mother that they are evil. The irony of Carol's behaviour is that, in accusing others of selfishness (because their will does not accord with hers), she herself behaves with absolute selfishness.
When Carol was a baby, her mother used to ignore her. She thought it would just spoil children to give them attention, that to show them affection was to "make a rod for your back", by which she meant that the child would then expect love and become clingy. She breastfed Carol for just one week after she was born, and then passed the baby to a nanny to feed by bottle, saying she was too busy to look after the baby. Carol was hit constantly if she didn't do what her mother ordered her to do. At the age of eight, Carol was sent to boarding school, where she felt lonely and was withdrawn and socially anxious. Her mother felt she had completed her maternal duty and that children needed to learn to stand on their own two feet. As a result, she grew up looking after herself, knowing her mother was never around to care for her. She would cook her own meals, clean the house and cry herself to sleep every night.
A well-known borderline was Marilyn Monroe (baptised Norma Jeane Baker). Despite her glamorous outward appearance, a volcano simmered within her. Elton John wrote his famous song "Candle in the Wind" to describe her, which succinctly summarises how impulsively changeable she was. Norma was born in 1926 and her parents divorced in 1928. She always claimed she didn't know who her real father was. Norma's mother Gladys, because of her mental health, gave her away for fostering to the Bolender family, where she lived until she was seven. Norma believed the Bolenders were her real parents until she was told the truth at this age. Gladys came back into her life and her daughter went to live with her again, but after Gladys was admitted to a psychiatric hospital, her mother's friend Grace became Norma's guardian. Grace married a man called Ervin Goddard when Norma was nine years old, so the young Norma was sent to the Los Angeles Orphan Home and a series of foster homes. Two years later she went back to live with Grace but was sexually molested by Goddard.
Norma was married three times, first to neighbour James Dougherty in 1942 when she was 16 years old. He agreed to marry her to avoid her being returned to the orphanage. The marriage lasted only three years. She then married again in 1954, to baseball player Joe DiMaggio, but this time the marriage lasted less than a year. Very soon after, in 1956, she married playwright Arthur Miller, who described her as follows: "She was a whirling light to me then, all paradox and enticing mystery, street-tough one moment, then lifted by a lyrical and poetic sensitivity that few retain past early adolescence." Throughout her life she hated being alone and was terrified of being abandoned. In adulthood she was in and out of psychiatric clinics, and attempted suicide at least three times. She finally succeeded in killing herself (overdosing on barbiturates) on 5 August 1962.
As we heard in both Carol's case and Marilyn Monroe's life, borderlines cannot tolerate being alone. For them, aloneness feels like abandonment, and to avoid that awful feeling the person will seek out other people, even relationships with strangers. But, whoever they are with, borderlines either feel suffocated (by someone getting close to them) or abandoned (by someone being distant from them). They cannot find a calm middle ground in which to enjoy a relationship comfortably. Instead they go through an unhealthy alternating sequence of pushing others away (with angry hate), or clinging desperately to them (with extreme gratitude).
Remarkably, despite the unstable behaviour of borderlines, or "Type Bs", scientists have managed to study their brains, which are definitely different in much of the empathy circuit. First, there is decreased binding of neurotransmitters to one of the serotonin receptors. Neuroimaging also reveals underactivity in the orbital frontal cortex and in the temporal cortex – all parts of the empathy circuit.
A novel approach has been to follow up people who were abused as children and scan their brains. It is novel because it is prospective rather than retrospective: the emotional damage was done in childhood and the scientific question is: "What happens to their brain?" Not all of them will be Type Bs, but a significant proportion will be. Such people again have abnormalities in the empathy circuit, such as having a smaller amygdala. This is also true of women who were sexually abused, who later show less grey matter in their left medial temporal cortex, compared to non-abused women. Smaller hippocampal volume is also found in people who experienced a trauma and went on to develop post-traumatic stress disorder (PTSD). One interpretation of all this evidence is that the early negative experiences of abuse and neglect change how the brain turns out. But the key point is that the zero degrees of empathy in borderlines arises from abnormalities in the empathy circuit of the brain.
Paul (not his real name, to protect his identity) is 28 years old and is currently detained in a secure prison after being found guilty of murder. He insisted he wasn't guilty because the man he stabbed had provoked him by looking at him from across the bar. Paul had gone over to the man and said, "Why were you staring at me?" The man had replied, I assume truthfully: "I wasn't staring at you. I was simply looking around the bar." Paul had felt incensed by the man's answer, believing it to be disrespectful, and felt he needed to be taught a lesson. He picked up a beer bottle, smashed it on the table and plunged the jagged end deep into the man's face.
Like me, the barrister at Paul's trial was shocked by the apparent lack of remorse and the self-righteousness of his plea of not guilty. Paul was adamant that he had simply defended himself. "He humiliated me in public. I had to show him I wasn't a doormat." I asked, "Do you believe you did anything wrong?" Paul replied, "People have treated me like shit all my life. I'm not taking it from no one no more. If someone shows me disrespect, they deserve what they get." I probed further: "Are you sorry that he died?" I waited to hear Paul's answer, holding my breath. He replied with anger in his voice: "Were the kids at school sorry when they bullied me? Was my boss sorry when he fired me? Was my neighbour sorry when he deliberately hit my car? And you ask me if I'm sorry that that piece of shit died? Of course I'm not sorry. He had it coming to him. No one's ever been sorry for how they've treated me. Why should I give a fuck about him?"
Paul's career of criminal behaviour had begun when he was as young as 13, when he had set fire to the school gym and sat in a tree across a field to watch it burn. He was expelled and from there went to three more schools, each time being expelled for aggression – starting fights in the playground, attacking a teacher who asked him to be quiet and even jumping on someone's head when they wouldn't let him join the football team.
Paul is clearly not the kind of guy you want to live near. Many would not hesitate to describe him as "evil". He is a psychopath – a Type P – though to give him the proper diagnostic label, he has antisocial personality disorder. He earns this label because he shows "a pervasive pattern of disregard for and violation of the rights of others that begins in childhood or adolescence, and continues into adulthood".
Clearly Type Ps differ in important ways to Type Bs, but they share the core feature of being zero-negative: their zero degrees of empathy can result in them doing cruel things to others. The Type P brain, too, shows lots of evidence of abnormalities in the empathy circuitry. Given the association with neglect and abuse in childhood, there is evidence that early stress affects how well the hippocampus functions, and how active the neural systems are that respond to threat. Prolonged exposure to stress isn't good for your brain. The amygdala is one of the brain regions that respond to stress or threat. When it does, it triggers the hypothalamus to trigger the pituitary gland to release a hormone called ACTH (adrenocorticotropic hormone). This is then carried by the blood from the brain down to the adrenal gland where it triggers the release of another hormone, cortisol. Cortisol is often called the "stress hormone" because it is a good indicator of when an animal is under stress. There are receptors for cortisol in the hippocampus that allow the animal to regulate the stress response. Remarkably, too much stress can damage and shrink your hippocampus, irreversibly. This is one more piece of evidence for the argument that instead of using the term "evil" we should talk about reduced (or even absent) empathy.
Empathy itself is the most valuable resource in our world. Given this assertion, it is puzzling that in the school curriculum empathy figures hardly at all, and in politics, business, the courts or policing it is rarely if ever on the agenda. We can see examples among our political leaders of the value of empathy, as when Nelson Mandela and FW de Klerk sought to understand and befriend each other, crossing the divide in Apartheid South Africa, but the same has not yet been achieved between Israel and Palestine, or between Washington and Iraq or Afghanistan. And, for every day that empathy is not employed in such corners of the world, more lives are lost.
I think we have taken empathy for granted, and thus to some extent overlooked it. Psychology as a science virtually ignored it for a century. Educators focusing on literacy and mathematics have also largely ignored it. We just assume empathy will develop in every child, come what may. We put little time, effort or money into nurturing it. Our politicians almost never mention it, despite the fact that they need it more than anyone. Until recently, neuroscientists hardly questioned what empathy is.
I sat in Alyth Gardens synagogue in Golders Green in north London last year. Two men went up on the stage. The first one spoke: "I am Ahmed, and I am a Palestinian. My son died in the Intifada, killed by an Israeli bullet. I come to wish you all Shabbat Shalom."
Then the other man spoke: "I am Moishe, and I am an Israeli. My son also died in the Intifada, killed by a homemade petrol bomb thrown by a Palestinian teenager. I come to wish you all Salaam Alaikum."
I was shocked: here were two fathers, from different sides of the political divide, united by their grief and now embracing each other's language. How had they met? Moishe had taken up the opportunity offered by a charity called The Parents Circle for Israelis and Palestinians to make free phone calls directly into each other's homes, to express their empathy to bereaved parents on the other side of the barbed-wire fence. Ahmed described how he had been at home in Gaza one day when the phone rang. It was Moishe, at that time a stranger in Jerusalem, who had taken that brave first step. They both openly wept down the phone. Neither had ever met or even spoken to someone from the other community, but both told the other they knew what the other was going through.
Empathy is like a universal solvent. Any problem immersed in empathy becomes soluble. It is effective as a way of anticipating and resolving interpersonal problems, whether this is a marital conflict, an international conflict, a problem at work, difficulties in a friendship, political deadlocks, a family dispute, or a problem with the neighbour. Unlike the arms industry that costs trillions of dollars to maintain, or the prison service and legal system that cost millions of dollars to keep oiled, empathy is free. And, unlike religion, empathy cannot, by definition, oppress anyone.
Zero Degrees of Empathy: a New Theory of Human Cruelty by Simon Baron-Cohen (Allen Lane, £20) is published on 7 April. To order a copy for £16 with free UK p&p, go to guardian.co.uk/bookshop or call 0330 333 6847
Simon Baron-Cohen is professor of psychology and psychiatry at Cambridge university