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Vampire bat food sharing (explained by David Attenborough)

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Reciprocal altruism, as described by Robert Trivers (Trivers, 1971), is a behavior whereby one individual decreases its fitness temporarily to increase the fitness of another.  This behavior is expected to be reciprocated to the altruist at a later time.

Examples of Reciprocal Altruism[]

This concept is used to explain the food sharing behavior in vampire bats.   As highlighted by Okasha (2013) article, vampire bats have been observed to exhibit blood-sharing behaviors in which individuals will “donate” blood through regurgitation to other group members that failed to feed during a particular night.  Because vampire bats can die after only a few nights of not feeding, obliviously the blood donation offers huge service to the recipient by averting starvation.  Additionally, since vampire bats live in relatively small groups and interact with the same individuals over extended periods of time, the likeliness of the service at some point being return appears to be relatively high, inferring that there is also most likely benefit to the donator (Okasha, 2013). Interestingly, studies also indicate that the more “giving” individuals may actually derive greater long term benefit because the bats were more likely to blood-share with individuals that recently donated to them (Okasha, 2013).

Reciprocal alturism can also be observed in many anti-predator behaviors like alarm calling in birds, primates, and mammals. 


Carter, G. G., & Wilkinson, G. S. (2013). Food sharing in vampire bats: reciprocal help predicts donations more than relatedness or harassment.Proceedings of the Royal Society B: Biological Sciences280(1753).

Okasha, S. (2013, Fall). Biological altruism. The Stanford Encyclopedia of Philosophy. Retrieved from: http://plato.stanford.edu/archives/fall2013/entries/altruism-biological/.

Trivers, R. L. (1971). The evolution of reciprocal altruism. Quarterly review of biology, 35-57.