Many studies have shown that rats exhibit empathy and social behavior. In one, scientists trapped a rat in a tight plastic tube and observed as its free cagemate, distressed by the trapped rat's panicked squirming, maneuvered the latch to free it. But many critics attributed the free rat's behavior to a need for companionship, not sensitivity to a fellow rodent's distress. (Rats get lonely too, you know.)

But a new study published in Animal Cognition (the somewhat awkwardly titled "Rats demonstrate helping behavior toward a soaked conspecific") from Kwansei Gakuin University in Japan shows that a rat's empathy extends to rodents it's not motivated to socialize with. In the study, scientists set up a box with two compartments separated by a transparent wall. A rat was placed in each compartment. One side was filled with water, forcing the rat within to swim. (The rat wasn't at risk of drowning, but it wasn't having any fun either.) Meanwhile, the rat on the dry side witnessed the soaked rat's distress—and then opened a tiny door leading to its dry compartment so the wet rat could escape.

The dry rats repeatedly saved their struggling buddies. If there was no water in the box at all, the rats didn't open the door, which suggests the rats were motivated by empathy, not a need to socialize. Interestingly, rats that had previously experienced the wet side of the box were more likely to free their friends, showing they were very likely able to empathize.

For a final test, scientists threw a chocolate bribe into the mix. The dry rat now had to choose between two doors: one to the "soaked conspecific," and one to a tasty treat. Fifty to 80 percent of the time, the dry rat chose to save the wet rat. Rats seem to value friendship as much as they do food.

Scientists believe this behavior is learned, not innate. In another recent study, neurobiologists from the University of Chicago transferred albino rat babies into a black-patched rat group, which raised them. When these albino adoptees grew up, in experiments they would help black-patched rats, but not other albinos. This is further evidence that rats develop relationships based on social familiarity, not biology.

[h/t: Science Mag]