Why rats don’t rat on other rats

Friends help each other and that goes for rats too, surprisingly. In fact, rats that know each other will release one another from a simple tube structure that can only be opened from the outside but what about rats that don't know each other and they're strangers, or rats that look totally different from each other because they're from a different strain for example? Peggy Mason from the University of Chicago helped to answer this...

Peggy - When we first saw that they opened for strangers, we were very surprised. And so what we wanted to do was then to test them with a different strain. So what we did was we decided to use the Long-Evans strain and Long-Evans strain is not an albino rat. It's this quite attractive rat that has a white coat background and then it has a black cape, and they're very attractive. We did two conditions. We did one where the white rat lived with the black caped rat, and one where the white rat had never seen a black caped rat before and was exposed to 12 different black caped strangers. When they were cage mates, the white rat opened for the black caped rat. No problem. When they were strangers, they did not open. It was really remarkable.

Chris - So just to crystalise that for a second. So you've got a situation where this rat can clearly recognise a different strain of rat and if it knows it, it lets it out. If it doesn't know it and has never seen that strain before, it's suspicious and doesn't let it out.

Peggy - That was our hunch but there was one other possibility which could be something more complicated, which is that if it's not your strain, then you have to know the individual. That would also explain the results. But along the way, this incredible serendipitous event occurred. What happened was that in the cage mates, the white rat that was living with the black caped rat, one of the black caped rats got a tumour in its liver and he died. So what we did was, with the surviving white rat, we housed him with another white rat and then we exposed him to the strangers. And this was just a one off. We weren't going to publish this, this was just to see what would happen. And what happened was this guy helped every stranger. He was a tremendous opener helper. And what that tells you is that all it takes is familiarity with the type of rat but not with the individual, that the individual rat does not matter whether it's your own strain or a different strain, it doesn't matter. The only thing that matters is that you have to have been exposed to that type of rat.

Chris - So I suppose one way to explore that then would be what would happen if you took a baby, let's call it a baby white rat and you put it into a family of caped rats which look totally different, so it's the odd one out, but it thinks that that mother is it's real mother. It'll grow up with litter mates that look grossly different to it. What happens then?

Peggy - And that's exactly the experiment we did. We wanted to know whether the white rat innately knew that it was a white rat and would therefore grow up to help other white rats. So we put that to the test. On the day they were born, we took the white rats and we put them into black caped litters. So they had a black caped mom and black caped litter mates. And when they were adults, we tested half of them with black caped rats and as you may imagine, they helped the black caped rats. That's who they've lived with their entire lives. But the real question was, would they help the albino rats, which is what they are? But they've never seen another one. And the answer was, no, they did not. And that is really remarkable. It tells you that genetics does not inform a rat who they are and who they should help. What informs them is who they experience, who they interact with as they are growing up. 

Chris - What do you think the importance and implication of this is?

Peggy - I think that this is another one of the ways in which social cohesion is built. It's very important that animals that live in a group function well in a group. Groups hunt better, group protect themselves better, you're more likely to succeed and reproduce if you're in a cohesive group where you can gain, not only from your own actions but from other's actions as well. And we can even go a step further, and I will go a step further. Humans are mammals and I think that this not only tells us something about rats and other non-human animals but it also tells us about humans. Biology is part of empathy. Biology is part of how we react to others who are in distress and it's part of how we decide that we're going to help this individual in distress and then perhaps maybe not that individual in distress. It tells us that, as in the rats, a diverse environment is more likely to lead to extended helping of different types of individual.

Chris - So, it's official. Rats are racist. At least, until they make friends with each other.