Decades after a notorious experiment, scientists have found test subjects are still willing to inflict pain on others - if told to by an authority figure.
US researchers repeated the famous "Milgram test", with volunteers told to deliver electrical shocks to another volunteer - played by an actor.
Even after faked screams of pain, 70% were prepared to increase the voltage, the American Psychology study found.
Both may help explain why apparently ordinary people can commit atrocities.
Yale University professor Stanley Milgram's work, published in 1963, recruited volunteers to help carry out a medical experiment, with none aware that they were actually the subject of the test.
A "scientist" instructed them to deliver a shock every time the actor answered a question wrongly.
When the pretend 150-volt shock was delivered, the actor could be heard screaming in pain, and yet, when asked to, more than eight out of ten volunteers were prepared to give further shocks, even when the "voltage" was gradually increased threefold.
Some volunteers even carried on giving 450-volt shocks even when there was no further response from the actor, suggesting he was either unconscious or dead.
Dr Jerry Burger, of Santa Clara University, used a similar format, although he did not allow the volunteers to carry on beyond 150 volts after they had shown their willingness to do so, suggesting that the distress caused to the original volunteers had been too great.
Again, however, the vast majority of the 29 men and 41 women taking part were willing to push the button knowing it would cause pain to another human.
Even when another actor entered the room and questioned what was happening, most were still prepared to continue.
He told Reuters: "What we found is validation of the same argument - if you put people in certain situations, they will act in surprising and maybe often even disturbing ways."
He said that it was not that there was "something wrong" with the volunteers, but that when placed under pressure, people will often do "unsettling" things.
Even though it was difficult to translate laboratory work to the real world, he said, it might partly explain why, in times of conflict, people could take part in genocide.
Dr Abigail San, a chartered clinical psychologist, has recently replicated the experiment for a soon-to-be-aired BBC documentary - all the way up to the 450-volt mark, again finding a similar outcome to Professor Milgram.
"It's not that these people are simply not good people any more - there is a massive social influence going on."
She said that the volunteers were being asked to carry out a complex task in aid of scientific research, and became entirely focused on it, with "little room" left for considering the plight of the person receiving the shock.
"They tend to identify massively with the 'experimenter', and become very engaged and distracted by the research.
"There's no opportunity for them to say 'What's my moral stand on this?'"