This undated handout photo obtained July 8, 2020, courtesy of the University of Chicago, shows a rat trapped in a restrainer,as…
This undated handout photo obtained July 8, 2020, courtesy of the University of Chicago, shows a rat trapped in a restrainer, as a free rat opens the restrainer door to liberate the trapped rat.

A new study using rats suggests that how a person decides whether to step in and help another person who is in distress may be more a factor of biology than psychology and may show why some people show empathy and others do not.

A long-held social-psychological concept holds that people in a group are less likely to help someone in need than if those individuals were alone. The idea, known as “the bystander effect,” is often explained by suggesting a larger group “diffuses responsibility.” In other words, an individual might feel less personally responsible for helping.

But the study, conducted at the University of Chicago and published Wednesday in the Journal of Science Advances, shows rats, making decisions based purely on biological instincts and not any concept of right or wrong, reacted in a similar way while part of a group.

Led by neurobiologist Peggy Mason, the researchers used a small device to restrain a single rat. They then created a group of rats categorized as "bystanders," giving them an anti-anxiety drug, similar to Valium, to ensure that these rats would not help the one in distress. The goal was to see if a nondrugged rat would still jump in and help the rat in distress, despite guaranteed inactive bystanders.

The experiment revealed that when “bystanders” were unhelpful, the nondrugged rats were less likely to help the restrained rat.

Mason maintained this showed that the tendency is not a human cultural phenomenon. "This is part of our mammalian inheritance," she said.   

Mason noted that when the “bystander” rats were tested alone and without drugs, they offered aid. "It’s the indifference of these other rats that changes the experience for them,” she added.