Friday, 13 July 2007

Rats influenced by the kindness of strangers

reposted from


Thanks to Ian for the link.

Reposted from:

If rats benefit from the kindness of strangers they are more likely to assist an unfamiliar rat in future. In doing so, they provide the first evidence of an unusual form of altruism that appears to violate evolutionary theory.

Claudia Rutte and Michael Taborsky of the University of Berne, Switzerland, trained rats to pull a lever that released food for their partner in the next cage. If the rats subsequently received snacks released by lever-pulling strangers in neighbouring cages, they were more likely to lever-pull and so feed another unfamiliar rat in the future. In other words, the rats became altruistic in response to a general level of cooperation in the population.

Theoretically, such "generalised reciprocity" shouldn't exist. In large groups, dirty rats will take advantage of helpful strangers and offer nothing in return.

It persists, says Taborsky, because exploited animals move away. "An animal is more likely to leave the group if it didn't receive cooperation in the past," he says. "This leads to cooperative and uncooperative groups in a population." If cooperative groups are better at exploiting the environment, generalised reciprocity remains in the population (PLoS Biology, DOI: 10.1371/journal.pbio.0050196).

Author Summary

The evolution of cooperation is based on four general mechanisms: mutualism, where an action benefits all partners directly; kin selection, where related individuals are supported; “green beard” altruism that is based on a genetic correlation between altruism genes and respective markers; and reciprocal altruism, where helpful acts are contingent upon the likelihood of getting help in return. The latter mechanism is intriguing because it is prone to exploitation. In theory, reciprocal altruism may evolve by direct, indirect, “strong,” and generalized reciprocity. Apart from direct reciprocity, where individuals base their behavior towards a partner on that partner's previous behavior towards themselves, and which works under only highly restrictive conditions, no other mechanism for reciprocity has been demonstrated among conspecifics in nonhuman animals. Here, we tested the propensity of wild-type Norway rats to help unknown conspecifics in response to help received from other unknown partners in an instrumental cooperative task. Anonymous receipt of help increased their propensity to help by more than 20%, revealing that nonhuman animals may indeed show generalized reciprocity. This mechanism causes altruistic behavior by previous social experience irrespective of partner identity. Generalized reciprocity is hence much simpler and therefore more likely to be important in nature than other reciprocity mechanisms.

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