LYNN NEARY, host:
A new study shows that a mouse can sense another mouse's pain. It's evidence that some form of empathy exists in all mammals. NPR's Jon Hamilton reports.
JON HAMILTON reporting:
Jeffrey Mogil sees a lot of mice in varying degrees of discomfort. It's part of his job as a pain researcher at McGill University in Montreal. Mogil hopes that by studying mice, he'll find new ways to relieve the suffering of people with painful diseases like arthritis and cancer. One day, while reviewing a series of mouse studies, Mogil and his team noticed something odd.
Dr. JEFFREY MOGIL (Professor of Pain Studies, McGill University, Montreal): It appeared that the order in which you tested mice for pain from a cage of mice had an effect on their pain sensitivity.
HAMILTON: The first mouse experienced less pain than the ones who went later. Mogil's team wondered why. They considered factors like stress.
Dr. MOGIL: And, one by one, all the alternate explanations fell by the wayside and the only explanation that really explained the data was empathy.
HAMILTON: Empathy: the ability to be effected by another creature's situation. Mogil says that for the mice, waiting to be tested was like sitting in a dentist's lobby and seeing one patient after another emerge in obvious pain.
But mice aren't supposed to have this sort of empathy. So Mogil's team decided to test their hypothesis. They injected mice with a substance that causes a mild stomachache. This sets the stage for what pain researchers call a writhing test, though Mogil says that's not actually what the mice do.
Dr. MOGIL: The mouse looks like it's stretching itself out. In fact, some people call it the stretching test; maybe that's a better name.
HAMILTON: The more often a mouse stretches, the higher its pain score. In the new experiment - published in the journal, Science - Mogul studied pairs of mice placed in a clear plastic tube. Mogul says sharing the space with another mouse in pain had no effect if the mice were strangers.
Dr. MOGIL: But when they were cage-mates - and when I say cage-mates, I mean they needed to be housed together in the same cage for two to three weeks - in that condition, then both of them writhed more often than they would have, tested alone.
HAMILTON: The mice who'd lived together were sensitized by seeing their cage-mate's discomfort, a crude form of empathy. Frans de Waal, a primatologist at Emory University, says humans aren't very different.
Dr. FRANS DE WAAL (Professor of Primate Behavior, Emory University): We empathize more with individuals who are either very similar to you or very close to you.
HAMILTON: De Waal says people can also empathize with others who aren't similar, or aren't even in the same species. And he says there's growing evidence that animals, from mice to dogs to dolphins, all possess some ability to empathize. That's easy to see in animals like chimpanzees.
De Waal says he was at a zoo once where zookeepers were trying to retrieve a monkey who'd escaped and climbed a tree. They'd tranquilized the monkey with a dart and were holding a net under the tree to catch him when he fell. De Waal says a group of chimpanzees were observing the drama.
Dr. DE WAAL: I still remember that one of the males who was watching it, he gave a little yelp and he held the hand of another chimp when the monkey fell out of the tree and into the net. So he was completely identifying with the monkey, so to speak.
HAMILTON: De Waal says it makes sense that mammals would have empathy. After all, they give birth to babies who are nearly defenseless.
Dr. DE WAAL: Originally, it was very important for females to be in tune with every little emotion of their offspring; every little distress, or when they were cold or when they were hungry she had to respond to. So, it's basically -empathy is a survival strategy, if you look at it at that level.
HAMILTON: Baby mice probably wouldn't survive without a little maternal empathy. And De Waal says that may explain why all mice can feel another mouse's pain. Jon Hamilton, NPR News.
NEARY: This is NPR News. Transcript provided by NPR, Copyright NPR.
