Empathy is a human trait, but it isn't unique to humans. Our closest relatives, primates, will help each other out. Elephants bury their dead and giraffe moms who lost a calf are often flanked with other giraffe females during her time of grief. So, how far down the food chain does this trait go?

We prefer not to think about rats as related to us, but our common ancestor might have been around a few millions of years ago, according to the BBC. They aren't that much like us... but a new study shows that rats will save their rat buddies from drowning.

Researchers at the Kwansei Gakuin University in Japan used water, rats and chocolate treats for their study. "Helping behavior is a prosocial behavior whereby an individual helps another irrespective of disadvantages to him or herself," study authors wrote. "In the present study, we examined whether rats would help distressed, conspecific rats that had been soaked with water. In Experiment 1, rats quickly learned to liberate a soaked cagemate from the water area by opening the door to allow the trapped rat into a safe area. Additional tests showed that the presentation of a distressed cagemate was necessary to induce rapid door-opening behavior. In addition, it was shown that rats dislike soaking and that rats that had previously experienced a soaking were quicker to learn how to help a cagemate than those that had never been soaked."

When one rat was soaking, another rats learned that operating a lever would save his distressed mate. The rats even ignored food - delicious chocolate - to help their comrade in trouble. If the savior rat had a similar past experience, he demonstrated empathy when operating the lever to save the wet rat.

To make sure the rats weren't just pressing the lever without purpose, another experiment was conducted. When there were no distressed rats, the rats no longer operated the lever. The study, published in the journal Animal Cognition, suggests that rats are able to recognize the suffering of others and want to help alleviate it.

Understanding the level of empathy in rats could extend to an understanding of empathy at a neural level - which could lead to physiological breakthroughs for humans.