You enter a room with two cages. One contains a friend, who is clearly distressed. The other contains a bar of chocolate, which clearly isn’t. What do you do? While a few people would probably go for the chocolate first (and you know who you are), most would choose to free the friend. And so, it seems, would a rat. Inbal Ben-Ami Bartal from the University of Chicago found that rats will quickly learn to free a trapped cage-mate, even when they get nothing in return, or when there’s a tasty chocolate distraction around. Bartal thinks that the rats conduct their prison breaks because they empathise with one another. This ability to understand and share the feelings of another individual is found in humans, apes, elephants, dolphins and other intelligent animals. It seems that rats belong in this club too. This is either a surprise or a retelling of old news, depending on how far back your memory goes. In 1959, the psychologist Russell Church trained a rat to press a lever for food. Then, he connected the lever to the electrified floor of a cage containing another rat. If the first rat pressed the lever, the second one would get a painful shock. That’s not what happened – when the first rat saw what was going on, it forfeited its food and avoided the lever. Church’s published his results in a provocative paper called "Emotional reactions of rats to the pain of others”, which sparked a flurry of similar studies throughout the 1960s. But the time wasn’t right. Psychologists were mostly interested in what animals did rather than what they felt, and the dominant view of nature red in tooth and claw left little room for cuddly feelings of empathy or altruism. “No one knew what to do with the studies, and they were forgotten,” says Frans de Waal, who studies how animals think. In later years, the taboo on animal empathy began to lift and people became happier to ascribe it to the wider animal kingdom. In 2006, Dale Langford from McGill University returned to Church’s work and produced more evidence that rats can feel empathy. She showed that mice become more sensitive to pain when they see their cagemates in it. It seemed that rats are sensitive to each other’s emotions, ‘catching’ them from one another. But Bartal wanted to know if this “emotional contagion” would actually motivate rats to help one another. Would empathy lead to action? Arguably, Church showed as much back in 1959, but psychologists have wondered whether the rats stopped pressing the levers out of concern for their fellows, or out of fear that their own floors would be electrified. Bartal needed a new experiment. She kept her rats in pairs for two weeks, and then placed one of them in a cage. The trapped rats were clearly stressed – Bartal used a bat detector to show that they were occasionally making high-pitched alarm calls. Their partners could free them by pushing against a restraining door and tipping it over. That’s what they did, although most took a week to learn how. Bartal found that the rats spent more time exploring the cage, and were more likely to open it, when there was another rat inside. It didn’t matter if the liberated rat got nothing in return. When Bartal changed the set-up so the only exit from the cage led to a different arena, the free rat still opened the door for its colleague, who promptly scurried away. Even when the rats were faced with a second cage containing delicious chocolate chips, they freed their cage-mate as often as they went for the food. They even shared their chocolate bounty with their liberated pals. “Empathy is a truly powerful motivator, on a par with the desire for chocolates!” says de Waal. Stephanie Preston, who works on animal emotions, says that Bartal has strengthened the case made by the studies from the 50s and 60s. “As shown previously, the rodents were not only empathically aroused by the emotion of [another rat], they took direct action to help. This is the definition of empathy,” she says. There are alternative explanations, but none of them are strong. They weren’t just trying to silence the grating alarm calls from their trapped peers, because such calls were too rare to be a potent motivator. They weren’t just curious about the trapped rat, because they still opened the cages if they were very familiar with the animal inside. And they weren’t just looking for something to do for the door mechanism is difficult. The only explanation that really fits the rodents’ actions is that they were trying to end the distress of the trapped rat, or perhaps their own distress at seeing their cage-mate’s plight. “The study is truly ground-breaking,” adds de Waal. It shows that rodents are not just affected by the emotions of others, but that empathy motivates altruism. Instead of explaining altruism by a cost/benefit calculation, as biologists and economists like to do, we are now entering a distinctly psychological realm of emotions and reactions to the emotions of others. This is where most human altruism finds its motivation and where, as this study suggests, animal altruism does too. In fact, the cost/benefit analysis was carried out long ago by evolution.” De Waal suggests that the rats’ behaviour is the result of ancient neural circuits that allow mammals to “make the situation of others their own to some degree, thus offering them an emotional stake in it.” These circuits underlie the behaviour of apes, dolphins, elephants, rats, and probably more. De Waal thinks that they originated from the care that mammal mothers offered towards their young, which might explain why female rats (like female chimps and female humans) seem to be more empathic than male ones. In Bartal’s experiment, all the female rats opened doors for a trapped individual, compared to just three-quarters of the males. Reference: Bartal, Decety & Mason. 2011. Empathy and Pro-Social Behavior in Rats. 2011. Science http://dx.doi.org/10.1126/science.1210789