Researchers started by housing 30 rats together in pairs, each duo sharing the same cage for two weeks. Then, they moved them to a new cage where one rat was held in a restraining device while the other could roam free.
The free rat could see and hear his (or her — six of the rats were female) trapped buddy, and appeared more agitated while the entrapment was going on.
The door to the trapping enclosure was not easy to open, but most rats figured it out within three to seven days. Once they knew how, they went straight to the door to open it every time they were put in the cage.
To test the rats’ true bond to their cagemates, researchers also ran the experiment with toys in the restraint to see if the rats would free the fake stuffed rats like they did their comrades. They did not.
“We are not training these rats in any way,” said first author Inbal Ben-Ami Bartal.
“These rats are learning because they are motivated by something internal. We’re not showing them how to open the door, they don’t get any previous exposure on opening the door, and it’s hard to open the door. But they keep trying and trying, and it eventually works.”
Even when researchers rearranged the experiment so that the trapped rat would be set free into another enclosure, away from his hero friend, the rats still opened the door, indicating they were not motivated by companionship.
“There was no other reason to take this action, except to terminate the distress of the trapped rats,” Bartal said. “In the rat model world, seeing the same behavior repeated over and over basically means that this action is rewarding to the rat.”
In one final test to truly measure the resolve of the rats, scientists presented them with a pile of chocolate chips in the cage. The rats were not hungry, and in prior experiments showed they liked chocolate because they would eat it instead of rat chow given the chance.
Still, free rats tended to act benevolently. Even if they munched on a few chips first, they would then free their pal and allow him to eat the remaining chips.
“It said to us that essentially helping their cagemate is on a par with chocolate. He can hog the entire chocolate stash if he want(s) to, and he does not. We were shocked,” said co-author Peggy Mason, a professor of neurobiology.
It makes sense that social species would have some innate inclination to help one of their own, since our individual survival is dependent on the group’s well-being (we depend on each other’s cooperation to thrive). Furthermore, this suggests that morality does indeed have some natural origin, given that empathy of the kind demonstrated in this experiment underpins all moral actions.