Calling someone a rat may be complimentary. According to a study published in the December 9, 2011, issue of Science, rats can be surprisingly selfless.

University of Chicago neuroscientist Peggy Mason and psychologists Inbal Ben-Ami Bartal and Jean Decety placed pairs of rats in pens. One rat was caged in the middle of the pen, whereas the other was free to run around. In this experi­ment, 23 of 30 rats liberated their peers by head butting the cage door or leaning against the door until it tipped over.
To actually test the rodents’ selflessness, Mason placed rats in pens with two cages: in one was another rat; in the other was a pile of chocolate chips. The unhindered rats could easily have eaten the chocolate themselves. Instead most of the rodents opened both cages and shared the sweets. “In rat land, that is big,” Mason says. This is the first study to show altruistic behavior in rodents.

McGill University psychologist Jeffrey Mogil was impressed with Mason’s study, but both he and Mason point out that the jailbreaking rats might only be trying to silence their cohorts’ distressing alarm calls. Mason thinks the alarm calls are not frequent enough to motivate the rats; Mogil is not so sure.

Mason’s new study is just one in a series of recent experiments that have changed how scientists think about empathy and altruism—namely, that such characteristics are not limited to people, as they once thought. It now seems that many animals have evolved instincts to help others, even at a cost to themselves, and that we inherited these same instincts. “The bottom line,” Mason says, “is that helping an individual in distress is part of our biology.”

This article was published in print as "Will You Rat Me Out?"