At the very least, the new experiment reported in Science is going to make people think differently about what it means to be a “rat.” Eventually, though, it may tell us interesting things about what it means to be a human being.

In a simple experiment, researchers at the University of Chicago sought to find out whether a rat would release a fellow rat from an unpleasantly restrictive cage if it could. The answer was yes.

The free rat, often hearing distress calls from its compatriot, learned to open the cage and did so with greater efficiency over time. It would release the other animal even if there wasn’t the payoff of a reunion with it. Astonishingly, if given access to a small hoard of chocolate chips, the free rat would usually save at least one treat for the captive – which is a lot to expect of a rat.

The researchers came to the unavoidable conclusion that what they were seeing was empathy and, apparently, selfless behavior driven by that mental state.

“There is nothing in it for them except for whatever feeling they get from helping another individual,” said neurobiologist Peggy Mason, who conducted the experiment with graduate student Inbal Ben-Ami Bartal and fellow researcher Jean Decety.

The idea that animals have emotional lives and are capable of detecting emotions in others has been gaining ground for decades.

Empathic behavior has been observed in apes and monkeys, and testified to by umpteen pet owners (especially dog owners). Recently, scientists demonstrated “emotional contagion” in mice, a situation in which one animal’s stress worsens another’s. But empathy that leads to helping activity – what psychologists term “pro-social behavior” – hasn’t been formally shown in non-primates until now.

If this experiment holds up under scrutiny, it will give neuroscientists a method to study empathy and altruism in a rigorous way.

Do age and sex affect empathic behavior? Will a rat free a rat it doesn’t know? Is more help offered to individuals an animal is related to, either directly or as a member of the same genetic tribe? What are the genes, and their variants, that determine whether one animal helps another and how much? Answering those questions becomes possible now that there is an animal “model” for this behavior.

Another major question that needs to be answered next is whether the free rat liberates the captive one to relieve its own stress or the stress of the other animal.