January 28, 2016 6:04 AM EST

The reports of mobs of men sexually assaulting women in Germany on New Year’s Eve–and the mobs of rioters targeting Pakistani and Syrian immigrants–have left many wondering how so many people could commit such horrific acts. Some blame cultural differences. But there’s another factor at play: the crowds themselves.

Being part of a group changes how people think and behave. Training with a team, for example, can drive athletes to push their physical limits.

But crowds can also be dangerous, in part because they promote a so-called mob mentality. When acting with others, individuals often feel more anonymous and less responsible for their actions, including acts of aggression. Sometimes they may even commit wrongdoing knowingly to seek the approval of those around them. In our own research, we found evidence suggesting that being swept up in the excitement of a crowd can also make people lose touch with their personal moral code–and, in turn, more likely to violate it.

Of course, this in no way diminishes the responsibility of the New Year’s Eve attackers. It does suggest, though, that it may actually be more, rather than less, likely for larger numbers of people to commit wrongdoing–if those people come together as a group.

Cikara, a Harvard psychology professor, and Jenkins, a postdoctoral researcher at the University of California, are the authors of a prominent study on mob mentality

This appears in the February 08, 2016 issue of TIME.

Contact us at letters@time.com.

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