Modern-day replications of one of history’s most disturbing social psychology experiments, the Milgram study, reveal what makes ordinary people obey an immoral order – and how to resist.

“One of the main factors that distinguishes rescuers from genocide perpetrators is the presence of role models in their early childhood,” [Emilie Caspar, a professor in experimental psychology at Ghent University in Belgium] says, based on her team’s research. “So, for instance, rescuers are more likely to have witnessed their parents or other relatives helping other human beings.”

Refusing to demonise a group of people, and cultivating a belief in shared humanity, may help fight persecution in those early stages, she says.