Out all day shopping for that perfect gift for your bestie?  Relish in the joys of reciprocal altruism this holiday season.  Reciprocal altruism occurs when unrelated individuals give each other some sort of benefit, such as food, a festively wrapped item of clothing, or maybe even cash (insert hint to friends here).

Robert Trivers developed the theory of reciprocal altruism in the early 70s in an attempt to explain why organisms help each other when there is no genetic relatedness between them.  The basic idea is “you give to me, and at some point I will give you back even more in return.”   Reciprocal altruism occurs under certain conditions: when two organisms have the ability to remember each other, and these two individuals can interact repeatedly over long periods of time. In general, the cost of the gift is lower than the ultimate benefit received from sharing.

Many primates are capable of displaying reciprocity.  This makes a lot of sense because primates tend to live in social groups where individuals are not always related, and social interactions occur at frequent rates.  In vervet monkeys (Cercopithecus aethiops), females can form friendships with unrelated individuals.  However, females in the group do not always get along (gasp!).  When fights between females break out, the female combatants begin calling loudly for back-up.  Who shows up when there’s about to be a girl fight?  Primarily the females’ relatives, but friends that were recently groomed by the fighters may also get involved to lend assistance. A little gift of grooming to a friend can guarantee big benefits when support is needed most.

Chimpanzee males sometimes share highly prized food items such as meat with unrelated individuals.  Food sharing can solidify alliances, guarantee later reciprocal gifts of food, or even secure mating privileges.

Below is a video of a male chimpanzee securing a papaya from a tree and sharing it with an unrelated female.

Happy holidays to you, your kin, and all your social acquaintances!

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Sources: Seyfarth, R.M. & Cheney, D.L. 1984. Grooming, alliances, and reciprocal altruism in vervet monkeys. Nature 308, 541-543.

Hockings KJ, Humle T, Anderson JR, Biro D, Sousa C, et al. (2007) Chimpanzees Share Forbidden Fruit. PLoS ONE 2(9): e886. doi:10.1371/journal.pone.0000886