Empathy was thought to be an emotion reserved to higher mammals such as primates. But a new experiment with rats is proving that theory wrong.
Rats, when faced with the choice of eating a bunch of chocolate all by themselves, or freeing a caged pal and then splitting the sweets with them, will take what, to the human eye, looks like the less selfish course.
This experiment shows that, from an evolutionary perspective, traits like empathy developed earlier than originally thought. The study also has implications for neuroscience, indicating that rats can be used to study pro-social behaviors, such as those found in humans.
“There are a lot of ideas in the literature showing that empathy is not unique to humans, and it has been well demonstrated in apes, but in rodents it was not very clear,” study co-author Jean Decety, a psychiatry and psychology professor at the University of Chicago, told Popular Science. “We put together in one series of experiments evidence of helping behavior based on empathy in rodents, and that's really the first time it's been seen.”
The experiment was simple: two rats would share a cage for two weeks. Then, one rat would be placed into a tight capsule cage that could be opened from the outside. That capsule cage would then be placed inside a larger cage, in which the second rat would be placed, free to roam.
The free rat would be agitated, squeaking ultrasonic alarm calls, when its cagemate was stuck in the capsule cage, which the researchers say shows that the rat felt "emotional contagion," a type of empathy in which animals share the distress of another. It would then examine the container, claw at it and spend time near it, sometimes even reaching through the holes to touch (or possibly comfort?) the other rat inside.
The researchers did a few variations to make sure that the free rat's interest in the box had to do with the fact that its cagemate was in there and not some associated reason. For instance, they placed the box in the cage by itself without a rat inside to ensure that the free rat was not merely intrigued by the box. But the rats ignored the box when it was empty.
They also separated the rats after the liberation -- to prevent the initially free rat from enjoying the reward of getting to socialize with its newly freed its partner. Even when they knew that they were not going to get more than companionship, the rats still would work until the cage opened.
The last version of this involves chocolate: The free rat was placed in a cage with two containers -- one containing its cagemate and the other pieces of chocolate. It would open both containers equally as often, showing the "the value of freeing a trapped cagemate is on par with that of accessing chocolate chips.”
But more than half the time, they saved half the chocolate chips for their liberated cagemates. Now, that's sweet.