reciprocal altruism

n. A form of relationship in which one individual helps in a way that is more beneficial to the individual receiving help than it is detrimental to the individual giving help and is extended only if the individual expects the other to help him or her in a similar situation at a later time. If the other fails to reciprocate, this failure is identified by the group, and then altruistic cooperation is withdrawn and the nonreciprocator is punished in some way. Thus, in vampire bats, a bat that has had a good feeding will sometimes regurgitate some of the blood it has drunk for another member of the colony that has not been able to feed. If the bat receiving blood does not reciprocate to other members of the colony when it has drunk plenty of blood, then the other bats expel it from the community.