Rats exhibit empathy

From an article in Science, reported at Live Science:

The act of helping others out of empathy has long been associated strictly with humans and other primates, but new research shows that rats exhibit this prosocial behavior as well.

In the new study, laboratory rats repeatedly freed their cage-mates from containers, even though there was no clear reward for doing so. The rodents didn't bother opening empty containers or those holding stuffed rats...

The researchers then conducted other tests to make sure empathy was the driving force in the rats' behavior. In one experiment, they rigged the container so that opening the door would release the captive rat into a separate arena. The free rat repeatedly set its cage-mate free, even though there was no reward of social interaction afterwards...

"Helping is our evolutionary inheritance," Mason told LiveScience. "Our study suggests that we don't have to cognitively decide to help an individual in distress; rather, we just have to let our animal selves express themselves."

Via Reddit, where a surprising number of rat owners contributed to the discussion.