It’s all the rage these days to worry about the growing gap between rich and poor. Our fretting was fuelled by Capital in the 21st Century, by the French economist Thomas Piketty, which claims to show that over time this gap will grow inexorably. But we’ve been agonising about equality for aeons, and for aeons arriving at the same stand-off between rich and (relatively) poor.

Here’s how the argument goes: those who don’t feel rich begin by saying that it’s disgusting how much of the world’s total wealth is owned by a small minority. Globally, the richest 10 per cent hold close to 90 per cent of the world’s assets. It’s just wrong, they say.

To which the rich, aggrieved, reply: ‘Why? What’s wrong per se with being wealthy? Look how much tax we pay! We pay for public hospitals and schools we don’t even use, so let’s have some gratitude, please, or we’ll up-sticks for the UAE.’ The rich have a point. In the UK the richest 5 per cent may own 40 per cent of the total wealth, but they pay 48 per cent of total tax. Even so, say the fretters, something is amiss. It’s not healthy, this gap — and here’s where the debate ends, in a disgruntled stalemate. Everybody’s right and everybody’s unhappy, as they say in Russia.

But what if the problem isn’t so much a financial one as a sociological or moral one? What if the unease people feel isn’t about inequality of wealth so much as in-equality of behaviour? We don’t pay them much heed these days, but Christianity, literature, folklore, myth and history all warn us repeatedly: money and power corrupt. Perhaps that’s what we’re really antsy about, and if so, science is on our side. Paul K. Piff, a sociologist at the University of California, studies the rich in the way Dian Fossey once did gorillas. Over the last few years he has set up a number of tests to examine the effects of money and status on behaviour, and the results are pretty terrifying: they read like an experimental proof of the New Testament.

In one of Piff’s scenarios, his researchers posed as pedestrians and waited at a crossroads to see what sort of cars would let them pass. Cars are required to give way to pedestrians in California, but what Piff discovered was that only people driving the cheapest cars, the old bangers, actually obeyed the law consistently. The more expensive the car, the more likely it was to zoom by, and the worst offenders were BMW owners. Pleasingly, Prius drivers were almost as bad; Piff ascribes this to a phenomenon he calls ‘moral licensing’. Because drivers had done a ‘good deed’ in choosing an eco car, they gave themselves licence to run over passers-by.

In test after test, Piff found that those who saw themselves as richer or more powerful than the average man (meaning, at times, you and me) behaved in a way we’d all agree was worse. For one thing, they were more miserly. When given ten bucks and told they could keep it or share it with a stranger, participants who earned under $25,000 a year gave nearly away nearly 50 per cent more than those who made over $200,000. Blessed are the poor.

More surprising than the tightfistedness of the rich was their relative lack of compassion. In one experiment, volunteers were left waiting beside a bowl of sweets, which they were told explicitly was reserved for children participating in a trial nearby. Poorer volunteers left the bowl alone, but at least half of the rich tucked in. Did they consciously realise they were taking candy from kids? I’m sure not. There’s evidence to suggest that those who feel powerful become past masters at inventing excuses for themselves which they quickly accept as true. Think of that bowl of sweets as a pot of taxpayers’ money, and the rich volunteer as an MP, and you begin to see why politicians, light-headed with self-regard, get into hot water over expenses.

But using Piff’s research to sneer at the rich or at politicians would be to miss the point. The wealthy aren’t a separate breed: power and money will corrupt us all. Piff’s most telling experiment involves 200 strangers, randomly selected and then paired up in the lab to play Monopoly. Before beginning, each pair flips a coin which selects one of them as the ‘rich’ player. Play then continues as normal, except that the ‘rich’ player is showered with unfair advantage. He begins with twice as much money, receives twice as much after passing ‘Go’, and is allowed to roll two dice where his opponent only rolls one. It doesn’t take long for the ‘rich’ player to start winning, and as he hauls in money and property, so his behaviour begins to change. He talks louder, say more aggressive things. He’s ruder and keener to flash his cash in front of the losing chap. A film of the Monopoly game shows ‘winning’ players bragging uncontrollably: ‘I have so much money. You’re going to lose all your money. I’m going to buy out this whole board’, all the while stuffing great handfuls of pretzels into their faces. When asked to explain why they won, players were all noticeably reluctant to ascribe their success to anything but skill. Instead of mentioning the rigged game, they discussed their brilliant strategies and said that they deserved to win.

See how the weasel mind turns luck into a well-earned triumph? It’s pretty depressing. Civilisation gives us the freedom to strive for success; but if we end up on top, we whip round and attack the things civilisation holds dear: compassion, empathy, humility. You have to be a saint to survive great riches.

But I can see an upside to the Monopoly experiment. If an average Joe can become sociopathic so quickly, then presumably the rich and powerful can, if nudged, undo their lack of concern. The hedge-fund manager Jonathan Ruffer wrote a moving piece for this magazine two years ago in which he proposed a solution to the stand-off. If the poor attack the rich, said Jonathan, the rich will believe (probably rightly) that it’s down to envy. It has to be the rich leading the rich — by giving money away. ‘This sounds as much fun as a Methodist sermon,’ he wrote, ‘but believe me, it’s the most wonderfully releasing thing — life as a colour film after black and white. If this sounds strange, remember that wealth has the character of a bully: whack it away and it turns out to be a very insipid adversary.’