When a few people break the rules, bad behavior spreads quickly - Other Sciences - Social Sciences - Political science

Experimental task and main results. Credit: Proceedings of the Royal Society B: Biological Sciences (2026). DOI: 10.1098/rspb.2026.1940

The old saying that one bad apple spoils the barrel suggests that an individual behaving badly can have a negative influence on the entire group. The idea now has some fresh scientific backing.

Researchers at the University of Amsterdam, led by Lucas Molleman, wanted to test whether seeing someone break a rule makes people copy them or go even further.

So before the 2024 presidential election in the United States, the team recruited 750 participants, roughly evenly split between Republicans and Democrats, to take part in an online experiment.

Each participant watched an animation of a shooting star zip across a screen divided into 100 squares. Clicking on the square that lit up most intensely was the rule of the game, and it earned them a real monetary reward.

So far, so straightforward. But the researchers added a little temptation to the mix. Participants could pocket some extra cash if they selected squares farther to the right. This created a clear conflict between following the rule and helping themselves.

Then came the twist. After making their initial selection, volunteers were shown how a previous participant had acted and whether they had followed the rule, broken it slightly or committed a major violation. They were also shown the political affiliation of this anonymous person before being asked to make a second choice.

The contagious nature of bad behavior

So did people play it straight or indulge in a little rule-breaking?

The study, published in Proceedings of the Royal Society B: Biological Sciences, found that nearly a quarter of initial choices (23%) involved breaking the rule to earn more cash. But things soon took a turn for the worse.

Bad behavior proved contagious. Watching someone commit a major rule violation caused a substantial increase in rule-breaking, especially when that rule-breaker belonged to the participant's own political party.

However, observing someone play strictly by the rules did almost nothing to inspire better behavior. Good behavior had very little influence.

Small violations become bigger ones

When volunteers saw a minor violation, many followed suit. But in about 4% of cases, participants went even further to grab a bigger payout.

To see how some of this might play out in larger groups, the team ran computer simulations testing a range of scenarios. When they built in the tendency to occasionally escalate small violations, things quickly got out of hand, with limited infractions turning into widespread, collective rule-breaking.

"Our data suggest that minor violations invite imitation and can sometimes trigger escalation," said the study authors.

But even knowing how small infractions can lead to more widespread rule-breaking, the researchers caution against stamping them out completely. "However, this should not be taken to imply that all minor violations should be suppressed."

They note that breaking conventions can be beneficial, often fostering creativity and learning. 

by Paul Arnold, Phys.org

edited by Gaby Clark, reviewed by Robert Egan 

Source: When a few people break the rules, bad behavior spreads quickly