December 8, 2011
The English language is not especially kind to rats. We say we "smell a rat" when something doesn't feel right, refer to stressful competition as the "rat race," and scorn traitors who "rat on" friends. But rats don't deserve their bad rap. According to a new study in the December 9 issue of Science, rats are surprisingly selfless, consistently breaking friends out of cages—even if freeing their buddies means having to share coveted chocolate. It seems that empathy and self-sacrifice have a greater evolutionary legacy than anyone expected.
In 2007 neuroscientist Peggy Mason of the University of Chicago wrote about the neurobiology of empathy for Scientific American. Inbal Ben-Ami Bartal, a new PhD student in integrative neuroscience who worked across the street from Mason in a different lab, saw the article and proposed a collaboration. "Scientific American really brought us together," Mason says.
In the new study, Mason, Bartal and University of Chicago colleague Jean Decety placed pairs of rats in Plexiglass pens. One rat was trapped in a cage in the middle of the pen, whereas the other rat was free to run around. Most free rats circled their imprisoned peer, gnawing at the cage and sticking their paws, noses and whiskers through any openings. After a week of trial and error, 23 of the 30 rats in the experiment learned to open the cage and free their peers by head-butting the cage door or leaning their full weight against the door until it tipped over. (The door could only be opened from the outside.) At first the rats were startled by the noise of the toppling door. Eventually, however, they stopped showing surprise, which suggests that they fully intended to push the door aside. Further, the rodents showed no interest in opening empty cages or in those containing toy rats, indicating that a break out was their genuine goal.
In this first set of experiments, most rats seemed quite willing to help their peers, but Mason wanted to give them a tougher test. She placed rats in a Plexiglass pen with two cages: in one was another rat, in the other was a pile of five milk chocolate chips—a favorite snack of these particular rodents. The unrestricted rats could easily have eaten the chocolate themselves before freeing their peers or been so distracted by the sweets that they would neglect their imprisoned friends. Instead, most of the rats opened both cages and shared in the chocolate chip feast.
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