The scruffy dweller of sewers and rubbish dumps will help a brother in distress.
Nobuya Sato and his team at Kwansei Gakuin University divided a box into two compartments separated by a transparent partition. Water was poured into one of the compartments while the other remained dry. A rat, placed in the water, could be seen by another from the dry side of the partition. The wet individual had to tread water to stay afloat but it wasn’t in danger of drowning; there was a ledge to which it could cling. It could only leave the water, however, if the observing rat opened a door in the partition. Rats placed on the dry side soon learned how to do this and released their wet companions.
This is not the first experiment to reveal what seems to be altruism in rats. Four years ago, scientists at the University of Chicago, placed a rat in a small cage. Rats outside the cage soon figured out how to open the door of the cage and liberate the prisoner. In a refinement of the experiment, access to chocolate was also provided. Rats usually opted to free the trapped individual before gorging themselves on the chocolate. This, the experimenters claimed, demonstrated altruism but not all scientists agreed. Rats are social creatures, they objected, and the trapped individual was not distressed. The liberators might just be seeking companionship.
Sato’s team got around that difficulty by placing their subjects in a genuinely distressing situation. When they repeated their experiment with no water in the box, the rat on the other side of the partition didn’t bother to open the door. Clearly, the liberating behaviour was a response to the wet animal’s distress. Moreover, rats which had been in the water on a previous occasion responded more quickly to a distressed neighbour than ones which hadn’t. Did memories of that unpleasant experience render their sympathetic feelings more intense?
As in the Chicago experiment, the Japanese rats were placed in a box with two doors. Opening one door released a victim swimming in the water; the other door gave access to a piece of chocolate. Most of the rats released their wet colleague before going for the chocolate.
“Our findings suggest that rats can behave pro-socially and that helper rats may be motivated by empathy-like feelings towards their distressed cage-mate,” says Sato.
How altruistic behaviour evolved is difficult to explain. An individual is programmed to act only in the interests of its genes. A mother, in risking her life to defend her young, appears altruistic but she is actually protecting her genetic legacy. An aunt bestows favours on nieces or nephews. With a quarter of their DNA common to hers, she is as close a relative as their granny. The celebrated geneticist JBS Haldane famously remarked that he would sacrifice his life for two of his brothers or four of his cousins. As Don Corleone observed in the Godfather, “it’s stupid to risk your life for strangers”.
A creature working, or sacrificing, itself for other than a close relative is digging its own genetic grave. Neglecting to promulgate its own genes, the ones promoting the unselfish behaviour won’t be passed on to succeeding generations.
But altruistic tendencies had to evolve before complex social groups became possible. Many primates, particularly apes, help each other; some of the altruistic propensities of humans must have been inherited from our common ancestors. Our line diverged from that of our nearest relatives, the chimps, between six and seven million years ago. That empathic behaviour is present in rodents, whose evolutionary line split from ours seventy million earlier, suggests the neural basis of social behaviour may be very old indeed.