Calling someone a rat isn't a compliment about their character – but a new study suggests that maybe it should be.
Rats that see another rat struggling in a pool of water will open a door to rescue it, even if they could open a different door to get a chocolate treat instead.
Rats that knew what it was like to be wet and struggling in the pool were even quicker to help.
"Our findings suggest that rats can behave prosocially and that helper rats may be motivated by empathy-like feelings towards their distressed cage mate," Nobuya Sato, lead author of a study, said in a statement.
The study was published this week in the journal Animal Cognition.
Sato and his team at Kwansei Gakuin University in Japan designed experiments involving pairs of rat cage mates, either two males or two females.
The two were placed in separate compartments separated by a transparent wall and door – one compartment that was dry and empty, and one filled with a deep pool of water and sheer walls that made it impossible to climb out. The door could be opened by the rat on the dry side, allowing the other rat to climb out of the pool.
Motivated by helping
Rats on the dry side of the cage were quick to open the door if they saw their cage mates struggling in the water, but not if the pool was empty or contained a stuffed toy rat. If no water was in either compartment, they also didn't open the door. That suggested that they were motivated by helping and not just opening the door for fun.
The researchers reversed the roles and found that rats were quicker to learn to open the door and rescue their cage mate if they had previously experienced a similar struggle in the pool.
"This modulation of learning by prior experience suggests that the helping behaviour observed in the present study might be based on empathy," they wrote.
In another experiment, rats in the dry compartment could choose between two different doors.
- One that allowed them to rescue their cage mate from the pool.
- Another that provided access to a chocolate cereal treat.
More than half the time, rats chose to rescue the other rat first – especially if they were trained to open the door in a similar rescue scenario rather than being trained to open the door in order to access a food treat.
"These results suggest that for all rats, helping a distressed cage mate has a higher value than obtaining a food reward," the researchers wrote.
The results are similar to those in a previous experiment by different researchers, in which rats rescued other rats trapped in an acrylic tube. Still, there has some debate about whether this type of helping behaviour exists among animals other than primates such as monkeys and humans.