These sources include individual pathology, lack of accountability, Machiavellian leadership that condones tyranny, and a combination of other factors. The studies reviewed show that people who typically act rationally and morally under normative conditions committed evil acts as individuals or a group when confronted with various experimental conditions. The most surprising finding was that when exposed to such behavior, so few people resisted or acted humanely in response. In a study conducted in 1961 by Yale University psychology professor Stanley Milgram, participants were randomly divided into two groups: the "teachers," who were the actual subjects of the experiment, and the "learners," who were instructed to act in a certain way in response to "teacher" actions. The teachers were instructed to read a list of words to the "learners" (whom they could not see), and to administer an electric "shock" to a "learner" (none was actually given) when the "learner" made a mistake. Repeated mistakes were to be followed by shocks of increasing intensity. The study found that each "teacher" was willing to shock a "learner" up to 300 volts, and two-third of the "teachers" gave the maximum shock of 450 volts. This was done despite "learner" screams and claims they had heart conditions. A 1971 study by Philip Zimbardo focused on the dynamics that developed within and between groups in a simulated prison setting. The "guards" repeatedly depersonalized the "prisoners" and engaged in degrading punishments of the "prisoners" for errors or disobedience. A 1979 Australian study tested correctional guards' treatment of inmates under varying prison policy and training scenarios, finding that guards' treatment of inmates varied in accordance with prison policies and training. 15 references