Psychological Experiments That Reveal Humanity’s Darkest Sides

We like to think of ourselves as rational, independent people who are not prone to inexplicable cruelty or indifference. In reality, this is far from the truth—under certain circumstances, Homo sapiens can surprisingly easily abandon their “humanity.” Here are five psychological experiments that expose the darker aspects of human nature.

1. The Asch Conformity Experiment (1951)

This study focused on group conformity. Student volunteers were invited under the pretense of a vision test. The subject was placed in a group with seven actors whose answers were not counted in the results. Participants were shown a card with a vertical line, then another card with three lines, and asked to identify which line matched the first card. The subject was always asked last.

This procedure was repeated 18 times. In the first two rounds, the actors gave correct answers, as the matching lines were obvious. But then, they unanimously began to choose the wrong answer. Sometimes, one or two actors were instructed to give the correct answer 12 times. Despite this, the real subjects felt extreme discomfort when their opinion differed from the majority.

In the end, 75% of students conformed to the group at least once, choosing the wrong answer despite the clear visual mismatch. 37% of all responses were incorrect, and only one person in the control group of 35 made a single mistake. When the group was not unanimous or when there were two independent subjects, the likelihood of error dropped fourfold.

What does this say about us?
People are highly influenced by the opinions of the group they are in. Even if the group’s view contradicts common sense or personal beliefs, it doesn’t mean we can resist it. As long as there’s even a faint threat of social disapproval, it’s often easier to silence our inner voice than to stand our ground.

2. The Good Samaritan Experiment (1973)

The parable of the Good Samaritan tells of a traveler who selflessly helped an injured and robbed man while others passed by. Psychologists Daniel Batson and John Darley decided to test how much such moral imperatives influence behavior in stressful situations.

One group of seminary students was told the parable and then asked to give a sermon about it in another building. The second group was asked to prepare a speech about job opportunities. Some participants were told to hurry to the audience. On the way, students encountered a person lying on the ground, clearly in need of help.

It turned out that students preparing the Good Samaritan sermon reacted to the emergency just like the second group—their decision was influenced only by time pressure. Only 10% of those told to hurry stopped to help, even if they had just heard a lecture about the importance of helping others in need.

What does this say about us?
We can easily abandon religion or any ethical imperatives when it suits us. People tend to justify their indifference with phrases like “it’s not my business,” “I can’t help anyway,” or “someone else will handle it.” This happens most often not during disasters, but in everyday life.

3. The Bystander Effect Experiment (1968)

In 1964, a woman was attacked twice within half an hour and died on her way to the hospital. More than a dozen people witnessed the crime (though Time magazine sensationally reported 38), yet no one responded appropriately. Inspired by these events, John Darley and Bibb Latané conducted their own psychological experiment.

Volunteers were invited to participate in a discussion on sensitive topics, communicating remotely via intercom. During the conversation, one participant (an actor) simulated an epileptic seizure, which was clearly audible. When the conversation was one-on-one, 85% of subjects responded and tried to help. But when the subject believed four others were also listening, only 31% attempted to intervene. The rest assumed someone else would take responsibility.

What does this say about us?
If you think being surrounded by many people makes you safer, think again. Crowds can be indifferent to others’ misfortunes, especially when marginalized individuals are involved. As long as someone else is present, we’re happy to shift responsibility onto them.

4. The Stanford Prison Experiment (1971)

The U.S. Navy wanted to better understand the nature of conflicts in its correctional facilities, so it funded behavioral psychologist Philip Zimbardo’s experiment. Zimbardo converted the basement of Stanford University into a mock prison and recruited male college students to play the roles of guards and prisoners.

Participants passed health and psychological screenings and were randomly assigned to two groups of 12—guards and prisoners. Guards wore military-style uniforms, carried wooden batons, and wore mirrored sunglasses. Prisoners wore uncomfortable clothing without underwear and rubber sandals, were referred to only by numbers, and had small chains on their ankles as a constant reminder of their confinement. Prisoners were “arrested” at home by real police, fingerprinted, photographed, and stripped before being assigned numbers.

Guards worked in shifts, but many volunteered for extra hours. All participants were paid $15 a day (about $85 in 2012 dollars). Zimbardo acted as the prison superintendent. The experiment was supposed to last four weeks, with guards instructed only to maintain order without using force.

By the second day, prisoners staged a rebellion, barricading themselves and taunting the guards, who responded with fire extinguishers. Soon, guards forced prisoners to sleep naked on bare concrete, and access to showers became a privilege. Sanitation deteriorated—prisoners were denied bathroom breaks and punished by not being allowed to empty their waste buckets.

One in three guards displayed sadistic tendencies, humiliating prisoners and forcing some to clean toilets with their bare hands. Two prisoners were so traumatized they had to be removed. A replacement prisoner was so shocked he went on a hunger strike and was placed in solitary confinement as punishment. Other prisoners were given the choice to give up their blankets or leave the striker in solitary all night—only one chose to sacrifice his comfort. About 50 observers monitored the experiment, but only Zimbardo’s girlfriend, who came to interview participants, objected to what was happening. The experiment was shut down after six days. Many guards regretted that it ended early.

What does this say about us?
People quickly adopt assigned social roles and can become so absorbed by their own power that the boundaries of acceptable behavior toward others vanish rapidly. The Stanford participants were not sadists—they were ordinary people. Higher education and sound mental health did not prevent them from abusing those under their authority.

5. The Milgram Experiment (1961)

During the Nuremberg Trials, many convicted Nazis justified their actions by claiming they were just following orders. Yale psychologist Stanley Milgram wanted to see how far people would go in harming others if it was part of their job.

Volunteers were recruited for a small fee, none of whom raised concerns for the researchers. At the start, the subject and an actor drew lots for the roles of “teacher” and “learner,” but the subject was always the teacher. The “learner” was strapped to a chair with electrodes, and the teacher was given a sample 45V shock before being seated at a generator with 30 switches ranging from 15 to 450 volts. Under the supervision of an experimenter in a lab coat, the teacher tested the learner’s memory of word pairs, administering a shock for each mistake, increasing the voltage each time. The final switches were labeled “Danger: Severe Shock” and “XXX.” The teacher and learner were separated by a wall.

If the teacher hesitated, the experimenter, without threatening, would urge them to continue. At 300 volts, the learner would bang on the wall and then stop responding. Silence for 10 seconds was treated as a wrong answer, and the teacher was told to increase the shock. In another version, the learner warned of heart problems and cried out at 150 and 300 volts, then refused to continue and screamed when shocked further. After 350 volts, the learner stopped responding entirely, but the teacher was told to keep going. The experiment ended when the teacher administered the maximum shock three times.

65% of subjects went all the way to the highest voltage, stopping only when the experimenter told them to. Only 12.5% stopped after the first time the learner banged on the wall; the rest continued even after the learner stopped responding. The experiment was repeated in various countries and settings, with or without payment, with men and women—if the basic conditions were the same, at least 60% of subjects went to the end, despite their own stress and discomfort.

What does this say about us?
Even when deeply distressed, the vast majority of people were willing to administer potentially lethal shocks to a stranger simply because an authority figure told them to. Most people are surprisingly willing to obey authority, even when it leads to destructive or tragic outcomes.