Calling someone a rat should no longer be considered an insult. The often maligned rodents go out of their way to liberate a trapped friend, a gregarious display that’s driven by empathy, researchers conclude in the Dec. 9 Science.
“As humans, we tend sometimes to have this feeling that there’s something special about our morals,” says neuroscientist Christian Keysers at the Netherlands Institute for Neuroscience in Amsterdam, who was not involved in the study. “It seems that even rats have this urge to help.”
As many pet rat owners know, rats are highly social animals, says study coauthor Inbal Ben-Ami Bartal, a psychologist at the University of Chicago. Bartal and colleagues wanted to see whether rats would take action to ease the suffering of a cage mate. The team put one rat inside a clear cage that could be sprung from the outside, and left another rat to roam free outside the cage for an hour at a time.
Initially, the free rat would circle the cage, digging and biting at it. After about seven days of encountering its trapped friend, the roaming rat learned how to open the cage and liberate the trapped rat. “It’s very obvious that it is intentional,” Bartal says. “They walk right up to the door and open the door.” The liberation is followed by a frenzy of excited running.
The rats would selectively take action when another rat was in distress: Empty cages didn’t inspire rats to learn how to open the door nearly as well as those who were motivated to rescue a trapped rat. By the end of the experiment, only five of 40 rats learned to open an empty cage, while 23 of 30 rats learned to open the cage to free an occupant. (And trapped stuffed animals fared no better than empty cages.)
“If I open the door, that rat’s distress goes away and my distress goes away,” psychologist Matthew Campbell of Yerkes National Primate Research Center at Emory University in Atlanta, who studies empathy in chimpanzees. “They are affected by what the other is experiencing, and that alone is remarkable.”
To push the limits of the rats’ goodwill, Bartal and her team pitted a trapped rat against trapped chocolate, forcing a rat to choose which one to release. “These rats adore their chocolate,” she says. The results astonished Bartal: The rats were equally likely to free a rat in distress as they were to free the sweets. To a rat, a fellow rodent’s freedom was just as sweet as five chocolate chips.
And the niceness doesn’t stop there: “The most shocking thing is they left some of the chocolate for the other rat,” Bartal says. The hero rat left a chocolate chip or two for its newly free associate in more than half of the trials. On purpose. “It’s not like they missed a chocolate,” Bartal says. “They actually carried it out of the restrainer sometimes but did not eat it.”