Altruism in which one organism provides a benefit to another in the expectation of future reciprocation. It would only be expected to evolve in the presence of a mechanism to identify and punish "cheaters".
An example of reciprocal altruism is blood-sharing in the vampire bat[?].
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... the village the population is spread out with 27.6% under the age of 18, 6.2% from 18 to 24, 17.7% from 25 to 44, 36.0% from 45 to 64, and 12.5% who are 65 years of age or ...