Scientists in Bern have shown that animals other than humans can reciprocate an action by exchanging two different social services, in their case food and grooming. 

Many examples exist in nature of tit-for-tat cooperation between animals, for example the sharing of food among bees and ants or mutual grooming among birds or apes. However, this cooperation was always thought to follow the principle of “you scratch my back and I’ll scratch yours”, in other words one would be repaid in kind. Being repaid in another commodity or service was thought to be unique to humans. 

Now, Manon Schweinfurth and Michael Taborsky at the Institute of Ecology and EvolutionExternal link at the University of Bern have shown how brown rats (Rattus norvegicus) apply direct reciprocity rules when exchanging two different social services: food provisioning and allogrooming (social grooming between members of the same species). 

“Focal rats were made to experience partners either cooperating or non-cooperating in one of the two commodities. Afterwards, they had the opportunity to reciprocate favours by the alternative service,” they wrote in their paperExternal link “Reciprocal Trading of Different Commodities in Norway Rats” published in the journal Current Biology. 

“Test rats traded allogrooming against food provisioning, and vice versa, thereby acting by the rules of direct reciprocity.” 

Schweinfurth and Taborsky noted this might indicate that reciprocal altruism among non-human animals was much more widespread than currently assumed.

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