Virtually everybody is capable of the abuse committed by American soldiers at Abu Ghraib prison in Baghdad, psychologists said yesterday.

The degrading treatment of Iraqi prisoners of war was not the result of particular cruelty or evil on the part of the abusers, but was more heavily influenced by social processes to which all of us are susceptible.

An expert analysis of the scandal, in which naked prisoners were beaten, forced to simulate sex and in one case paraded on a dog’s leash, has indicated that the perpetrators of such crimes are rarely psychopathic or even particularly sadistic.

Evidence from more than 25,000 studies involving eight million participants shows that almost anybody is capable of performing acts of apparently inexplicable cruelty when the conditions are right.

Most people can be persuaded to take part in activities they would normally find morally repugnant by a combination of peer pressure, the influence of authority figures, stress and the portrayal of the enemy as a dehumanised “outgroup”.

“Abu Ghraib resulted in part from ordinary social processes, not just extraordinary evil,” the report concluded.

In an article for the leading journal Science, Susan Fiske, Lasana Harris and Amy Cuddy, of Princeton University, said that while individuals such as Private Lynndie England have to bear responsibility for their actions, their behaviour can be explained by known psychological phenomena.

Nobody can be confident that they would not have done the same thing under similar circumstances. Professor Fiske said: “Could any average 18-year-old have tortured these prisoners? I would have to answer, ‘Yes, just about anyone could have — unfortunately’.”

The researchers drew particularly on the findings of a set of experiments conducted by Stanley Milgram in the 1960s, in which students were asked to administer electric shocks of increasing severity to people in the next room.

They continued to turn up the voltage when the victims (in reality actors) began to scream, and even when they fell silent, suggesting they were unconscious or dead.

Other research that has shown how easily people can resort to abuse includes the Stanford Prison Experiment, conducted by Philip Zimbardo in 1971, which had to be stopped after students playing the role of guards began abusing volunteers assigned as prisoners.

The researchers said that many of the characteristic factors that can turn normal, non-violent individuals into abusers were present at Abu Ghraib.

“The situation of the 800th Military Police Brigade guarding Abu Ghraib prisoners fits all the social conditions known to cause aggression,” they said.

“The soldiers were certainly provoked and stressed, at war, in constant danger, taunted and harassed by some of the very citizens they were sent to save, and their comrades were dying daily and unpredictably.

“Their morale suffered, they were untrained for the job, their command climate was lax, their return home was a year overdue, their identity as disciplined soldiers was gone and their own amenities were scant. Heat and discomfort also doubtless contributed.” The attitude of superior officers and peers, who either encouraged or turned a blind eye to the abuse, was particularly critical.

“Ordinary people can engage in incredibly destructive behaviour if so ordered by legitimate authority,” the scientists said. “Subordinates not only do what they are ordered to do, but what they think their superiors would order them to do, given their understanding of the authority’s overall goals.”

The situation was exacerbated by the way in which US soldiers came to see Iraqis as “interchangeable members” of a contemptible and alien group.

Strong leadership and giving soldiers access to semi-independent figures such as chaplains, to whom they could raise concerns, were suggested as the best ways of avoiding a recurrence.

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