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.