A new study has, demonstrated the existence of empathy-driven behavior in laboratory rats.

In an experiment carried out by University of Chicago neuroscientists, pairs of rats that normally shared a cage were placed in a special area, where one was confined to a closed tube with a door that could be opened from the outside while the other remained able to roam around freely. The researchers observed that "the free rat acted more agitated when its cagemate was restrained, compared to its activity when the rat was placed in a cage with an empty restrainer."

This kind of "emotional contagion" had been observed previously in tats -- but what happened next was more unexpected. As described by Science Daily, "After several daily restraint sessions, the free rat learned how to open the restrainer door and free its cagemate. Though slow to act at first, once the rat discovered the ability to free its companion, it would take action almost immediately upon placement in the test arena."

"We are not training these rats in any way," one of the designers of the experiment explained. "These rats are learning because they are motivated by something internal. We're not showing them how to open the door, they don't get any previous exposure on opening the door, and it's hard to open the door. But they keep trying and trying, and it eventually works."

Further variations on the experiment appeared to confirm that the rats were acting out of pure empathy. For example, they would not bother to open the door when a toy rat was placed in the tube. However, they would open it even if it released their companion into a separate area, meaning they were not just looking for company.

And not only that, but when the rats were offered two tubes -- one of which contained their companion and the other a pile of chocolate chips -- they were as likely to free the other rat first as they were to start by gobbling all the chocolate. There were also cases in which the rat retrieved the chocolate chips first but didn't eat them until after freeing the other and sharing the chocolate with them.

There was, however, one significant gender-based difference. Females were more consistent than males both in learning how to open the door and in using this skill to free a trapped companion.

This video is from the University of Chicago, uploaded to YouTube December 9, 2011.