Cycling one morning over the East Bay Hills, Professor Dacher Keltner had a near-death experience. “I was riding my bike to school,” he recalls, “and I came to a four-way intersection. I had the right of way, and this black Mercedes just barrelled through.” With two feet to spare before impact, the driver slammed on his brakes. “He seemed both surprised and contemptuous, as if I was in his more important way.” Keltner’s first response was a mixture of anger and relief: no Berkeley psychology professor with surfer-dude hair had been smeared over the Californian tarmac that day. His second was more academic. Was there, he wondered, a measurable difference between the behaviour of Mercedes owners and those of other cars? Cars that didn’t cost twice the average annual income of an American middle-class family? Had the guy who nearly killed him bought something else, along with $130,000-worth of German engineering?

The professor put a group of students on the case; sent them out with clipboards to loiter on the traffic islands of Berkeley. They monitored vehicle etiquette at road junctions, kept notes on models and makes. They observed who allowed pedestrians their right of way at street crossings; who pretended not to see them and roared straight past. The results couldn’t have been clearer. Mercedes drivers were a quarter as likely to stop at a crossing and four times more likely to cut in front of another car than drivers of beaten-up Ford Pintos and Dodge Colts. The more luxurious the vehicle, the more entitled its owner felt to violate the laws of the highway.

What happened on the road also happened in the lab. In some experiments Keltner and his collaborators put participants from a variety of income brackets to the test; in others, they “primed” subjects to feel less powerful or more powerful by asking them to think about people more or less powerful than themselves, or to think about times when they felt strong or weak. The results all stacked the same way. People who felt powerful were less likely to be empathetic; wealthy subjects were more likely to cheat in games involving small cash stakes and to dip their fists into a jar of sweets marked for the use of visiting children. When watching a video about childhood cancer they displayed fewer physiological signs of empathy.

Similar results occurred even when the privilege under observation had no meaning beyond the experiment room. Rigged games of Monopoly were set up in which one player took a double salary and rolled with two dice instead of one: winners failed to acknowledge their unfair advantage and reported that they had triumphed through merit. In another study, volunteers were divided into bosses and workers and set to work on an administrative task. When a plate of biscuits was brought into the room, the managers reached for twice as many as the managed. “Power tends to corrupt, and absolute power corrupts absolutely,” said Lord Acton in 1887. Here was the evidence, lab-tested, that it also awakened the Cookie Monster within.

Acton’s pronouncement on power was a response to a specific 19th-century event – the Vatican’s decision, in 1870, to adopt the doctrine of papal infallibility. When 20th-century social scientists began studying the moral conduct of powerful people, they did it in reaction to the absolutism of their own age. In 1956 the sociologist C. Wright Mills published “The Power Elite”, an account of American society that shocked a generation: partly because it suggested the country was controlled by self-sustaining cliques of military, political and corporate men; partly because Mills modelled his work on an earlier study of the social and political hierarchies of Nazi Germany. Three years later, Pitirim Sorokin, founder of Harvard’s sociology department and a refugee from Lenin’s Russia, published “Power and Morality”, which proposed that the individuals described by Mills were not just self-interested, but sick. “Taken as a whole,” he wrote, “the ruling groups are more talented intellectually and more deranged mentally than the ruled population.”

Sorokin’s pathological language may seem intemperate, but the idea of power as a disease or disorder was infectious. In 1959, Eugene Jennings, the founder of business psychology and nobody’s idea of a dangerous radical, quizzed 162 American executives about their ethical lives. While in the office, he discovered, most professed that they treated colleagues with suspicion, regarded friendship as a weakness and allowed self-interest to govern their behaviour. At the weekends, however, they were Mr Nice Guys who played with their children and invited their neighbours over for barbecues. “Typical executive possesses Jekyll-Hyde Strain”, said the headlines. The implication was that these men were born with it: that unethical behaviour was a trait of the powerful, not a side-effect of being in charge.

A study conducted at the beginning of the 1970s, however, rewrote that assumption, and popularised a new idea – that the moral character of an individual mattered less than that of the social environment. The Stanford Prison Experiment made the reputation of its creator, Philip Zimbardo – one that is elevated but ambiguous, as befits a man who begins lectures by performing air-guitar to Santana’s “Evil Ways”, and was played by Billy Crudup in the movie of his life. In 1971, Zimbardo created a jail-like environment in the basement of the psychology building at Stanford. For a period of two weeks, a group of 24 male students was divided into prisoners and guards, and given uniforms and props that reinforced those roles. Over a CCTV link, Zimbardo watched as the guards became nastier and the prisoners more submissive. The characters of the participants seemed barely relevant. The situation had made this happen – and, after six days, it had got brutally out of hand. By the end, Zimbardo had harvested videotape imagery of hooded captives and club-waving guards that captured the troubled American 1970s as effectively as Nixon’s goodbye from the White House lawn or the crowbarred Watergate filing cabinets now on display in the Smithsonian.

The methodology of the Stanford Prison Experiment was so questionable that many psychologists do not regard it as a true experiment. But the issues it raised are now being studied in more carefully controlled conditions by a new generation of academics which includes Keltner, and whose work tends to support his view that the powerful behave worse than the powerless. In 2015 a project at Iowa State University watched its boss figures bearing false witness against their fellow participants in exchange for tiny bribes. (It was published under the glorious title, “Throwing You Under the Bus: High Power People Knowingly Harm Others When Offered Small Incentives”.) This year, two Berkeley psychologists shared the results of an experiment that examined the collaborative skills of powerful individuals. When asked to work together, leaders proved less efficient, creative and productive than the people beneath them, partly because they spent too much time squabbling about who should be in charge. The more positive effects of wielding power have also been studied – it reduces stress levels and sensitivity to pain – but this research has yet to generate headlines as eye-catching as “Science Proves Rich People are Jerks”.

Not everyone likes these conclusions. “We got a lot of pushback when we said that poorer people in the US share more of their wealth and are more compassionate,” says Keltner. “I had hate mail like you wouldn’t believe.” He was, said one writer, “a Berkeley communist”. Didn’t he know that the world only progressed through the efforts of superior people? “To put it in strong terms,” Keltner says, “there are a lot of people who are committed to the idea that the powerless are mentally deficient.” His response has come in the form of “The Power Paradox”, a handbook for those seeking to mitigate the negative effects of power. He also lectures, telling companies and government departments that too much power is bad for individuals, bad for society, bad for commerce. They’re not always pleased to hear it. “When you meet a group of venture capitalists and start telling them how inequality is damaging our nervous systems,” he says, “it’s like walking into a room full of atheists and talking to them about intelligent design. They prickle.”

Prickly venture capitalists, however, are not the only ones to express unease, and not every critique has been written in green ink. When Keltner and his colleagues published an influential paper on the subject in 2010, three European academics, Martin Korndörfer, Stefan Schmukle and Boris Egloff, wondered if it would be possible to reproduce the findings of small lab-based experiments using much larger sets of data from surveys carried out by the German state. The idea was to see whether this information, which documented what people said they did in everyday life, would offer the same picture of human behaviour as results produced in the lab. “We simply wanted to replicate their results,” says Boris Egloff, “which seemed very plausible to us and fine in every possible sense.” The crunched numbers, however, declined to fit the expected patterns. Taken cumulatively, they suggested the opposite. Privileged individuals, the data suggested, were proportionally more generous to charity than their poorer fellow citizens; more likely to volunteer; more likely to help a traveller struggling with a suitcase or to look after a neighbour’s cat.

Egloff and his colleagues wrote up their findings and sent them to the Journal of Personality and Social Psychology, which had also published Keltner’s work. “We thought,” says Egloff, “naive as we were, that this might be interesting for the scientific community.” The paper was rejected. They extended their analysis to data from America and other countries, and felt confident that they had identified several more pieces that didn’t fit the jigsaw being assembled by their American peers. They argued that psychology’s consensus view on social status and ethical behaviour did not exist in other disciplines, and concluded with a quiet plea for more research in this area. Their paper was rejected again. Last July, it eventually found a home in a peer-reviewed online journal.

Egloff has been doing research since 1993 and is used to the bloody process of peer review. But he was shocked by the hostility towards his work. “I am not on a crusade,” he says. “I am not rich. My family is not rich. My friends are not rich. We never received any money from any party for doing this research. Personally I would have loved the results of the Berkeley group to be true. That would be nice and would provide a better fit to my personal and political beliefs and my worldview. However, as a scientist…” The experience of going against this particular intellectual grain was so painful that Egloff vows never to study the topic of privilege and ethics again.

Who, then, is right? Are powerful people nicer or nastier than powerless ones? How can we explain the disparate answers yielded by these two sets of data?

It may be that rich people are better at disguising their true nature than poor people. If being generous in public brings rewards, then rich people might be more inclined to help old ladies across roads. Selfish driving is consistent with this idea: the anonymity of the road means that aggressive petrolheads need not worry about damaging their reputations. And Keltner points out that the data come from people’s accounts of their own charitable giving, and not from watching them in the act. “We know from other studies that the wealthy are more likely to lie and exaggerate about ethical matters,” he says. “Survey self-report data in economics and face-to-face data in psychology capture different processes. What I say I do in society versus how I behave with actual people.”

But it is also possible that the problem lies not with the survey data but with the psychological experiments. Over the past year, this possibility has become the subject of bitter debate. In August 2015, the journal Science reported that a group of 270 academics, led by Brian Nosek, a respected professor of psychology at the University of Virginia, had attempted to reproduce the results of 100 psychological studies. Ninety-seven of the original studies had produced statistically significant results. Only 36 of the replications did the same. Those numbers threatened to undermine the entire discipline of experimental psychology, for if a result cannot be replicated then it must be in doubt. In March 2016 a panel of luminaries claimed to have detected serious shortcomings in the methodology of Nosek’s paper. The inquiry was led by Dan Gilbert, a Harvard professor with a history of hostility to the replicators. (“Psychology’s replication police prove to be shameless little bullies,” he tweeted in 2014, defending another researcher whose work was questioned.) When a journalist from Wired magazine asked Gilbert if his defensiveness might have influenced his conclusions, he hung up on them. Psychology’s “Replication Crisis” might not yet be over.

In September 2015, five social psychologists and a sociologist published a paper in the Journal of Behavioral and Brain Sciences that suggested why psychology might show privileged people in a bad light. Left-wing opinion, contended Jonathan Haidt and his co-authors, was over-represented in psychology faculties. This, they suspected, might be distorting experimental findings – as well as making campus life difficult for researchers with socially conservative views. “The field of social psychology is at risk of becoming a cohesive moral community,” they warned. “Might a shared moral-historical narrative in a politically homogeneous field undermine the self-correction processes on which good science depends? We think so.” So does Boris Egloff. “It was a great and timely paper,” he says. “I congratulate them on their courage.” But it came too late for him. “We spoilt the good guys’ party,” he says.

A few weeks after first talking to Keltner, I have lunch with him in London. He is visiting the city to promote his book. He likes talking to British people about power. It was in Britain that he first became interested in the subject, when, at the age of 15, he was transported from the foothills of the Sierra Nevada Mountains to a suburb of Nottingham, where he stuck out like a sore Californian thumb and attracted the attention of “Clockwork Orange-type bullies”. The British class system, he thinks, has ensured that citizens of the United Kingdom are sensitive to the workings of power; unlike Americans, they don’t overestimate the meritocratic nature of their society.

Keltner points out that plenty of his experiments have been replicated, and is comfortable defending himself against those who are sceptical of his message. “Look,” he begins, imagining a roomful of hostile faces. “Here is what power does to just about every human being. It’s going to make you not pay attention to people as well as you used to pay attention to them. You may find yourself swearing at a colleague or telling them that their work is horseshit. You will be a little less careful in the language you use. You will be a little less thoughtful about how things look from their perspective. So just practise a little gratitude. Listen empathetically. It shouldn’t be that difficult.” Keltner smiles a lot, and is persuasive. I can picture him giving this speech to Marie Antoinette.

We finish our lunchtime fish and chips in a Sherlock Holmes-themed pub near Trafalgar Square. The day is bright and warm, and Keltner intends to spend the afternoon walking in Hyde Park. Minutes after we have gone our separate ways, something happens that makes me want to run back down the street to find him. I am waiting at a pedestrian crossing, and just as the lights are changing from amber to red, a car bowls through. It is a black Mercedes.■