With a few liberating swipes of their paws, a group of research rats freed trapped labmates and raised anew the possibility that empathy isn’t unique to humans and a few extra-smart animals, but is widespread in the animal world.

Though more studies are needed on the rats’ motivations, it’s at least plausible they demonstrated “empathically motivated pro-social behavior.” People would generally call that helpfulness, or even kindness.

“Rats help other rats in distress. That means it’s a biological inheritance,” said neurobiologist Peggy Mason of the University of Chicago. “That’s the biological program we have.”

In a study published Dec. 7 in Science, Mason and University of Chicago psychologists Jean Decety and Inbal Ben-Ami Bartal describe their rat empathy-testing apparatus: An enclosure into which pairs of rats were placed, with one roaming free and the other restrained inside a plastic tube. It could only be opened from the outside, which is exactly what the free rats did — again and again and again, seemingly in response to their trapped companions’ distress.

The experiment built on research conducted several years ago by geneticist Jeff Mogil at McGill University, where mice were shown capable of “emotional contagion” — a slightly scary-sounding term denoting a tendency to become upset when cagemates were in pain. This might not seem surprising, but anecdotes from wild animal observations don’t pass academic scrutiny, and it hadn’t before been shown in captive mice. It hinted at unexpectedly sophisticated cognition: Mice were supposed to feel pain, but not each other’s, at least not outside children’s stories.

At the time, ethologist Frans de Waal of Emory University, whose work has helped redefine what’s known about thoughts and feelings in chimpanzees and dolphins and elephants, said Mogil’s experiment “justifies speaking of ‘empathy’” — the ability to both put oneself in the shoes, or paws, of another, and to become emotionally involved in their situation. Sure, mice almost certainly weren’t so empathic as humans, but maybe they had the seeds of it. Maybe empathy wasn’t the result of some high-powered cognitive process, as most biologists and psychologists preferred to think, but a relatively simple phenomenon.

Wrote de Waal in Scientific American, “This mouse experiment suggests that the emotional component of this process is at least as old as the mammals and runs deep within us.”

Still, it was hard to know what to think, and emotional contagion didn’t equal empathy. Maybe the mice were simply fearful for themselves. But the possibility was open for investigation. And around the same time as the McGill studies, Bartal — then researching cancer in Israel — noticed rats at her lab becoming distressed when surgeries were performed on other rats. She couldn’t shake the feeling that empathy was involved. When she read about a rat bringing food to a trapped rat, she again thought about empathy.

Bartal went to the University of Chicago, where she joined with Decety, a leading scholar on empathy and prosocial behavior, and Mason, who’d been intrigued by Mogil’s work. Together they designed the new study — and not only did they find what might be empathy, but the rats acted on it.

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