GIVE AND RECEIVE

There are two routes to cooperation. First, it can pay to help genetically similar, close relatives. Second, you can forge a reciprocal relationship in which you trade favours for favours.

In which case, close relatives might be particularly keen to form reciprocal alliances. But new research on brown rats suggests otherwise. In fact, individuals seem more willing to share food mutually with unrelated individuals.

According to Manon Schweinfurth of the University of St Andrews, it may be a product of rats’ social organisation. “Rats under natural conditions form subgroups within colonies and probably it is the kin that clusters. Hence, kin compete more intensively over the same mating partners, food and nesting sites,” she says.

Then again, relatedness might become more important when the stakes are high when one rat must make a big sacrifice to save another.

“That is really speculation,” says Schweinfurth. “Although rats live near us, we know surprisingly little about their natural social behaviour.”

Rats don’t just rely on their family for favours.