Are Chimpanzees Fair?

Originally posted by Jane Goodall Institute of Canada’s Change Is In You Blog

Humans care about fairness.  I know for me personally, if there are a limited number of resources (e.g., food, shelter), I would feel bad making a decision that gave me more resources at the expense of a close friend or family member.  Of course, that is an anecdotal example of human fairness, but it has been studied scientifically!

Researchers have studied this scientifically by designing “the ultimatum game.”  This game tests whether humans always act in their material self-interest.  In the game, one person must decide how to divide a sum of money and/or resources between two people.  The first person (proposer) makes a proposal, and the second player (responder) either accepts or rejects the proposal.  If the responder rejects the proposal, both players receive nothing.  When human adults play this game, they typically split the resources equally.  This demonstrates that humans are sensitive to fairness.  However, primatologists are still unsure of whether our closest relatives, chimpanzees and bonobos, behave in the same way.

In order to find out, researchers from the University of London decided teach a modified ultimatum game to chimpanzees and bonobos (Kaiser, I. et al., 2012).  Individual apes were exposed to two different food resources: their own, and another individual’s.  In each scenario, one ape had to make a decision of whether to eat their own food, or to eat their own food and steal the other individual’s food.  The team found that neither chimpanzees nor bonobos cared about fairness in this experiment and generally stole a portion of food.  They concluded that “our sense of fairness” must be a derived trait (meaning that it was absent in the human/chimp/bonobo common ancestor).

Open and shut case right?  Perhaps not.

A team of researchers at Yerkes National Primate Center led by primatologists Darby Proctor and Frans de Waal decided to design their own ultimatum game to re-test the hypothesis that our sense of fairness is derived (Procotor & de Waal, 2013).  The study was conducted with six adult chimpanzees and the ultimatum game was much more similar to the human-version of the ultimatum game when compared to the Kaiser et al. study.  The chimpanzees had to choose between coloured tokens that could be exchanged for food rewards.  One token offered equal rewards to both players.  However, a second token would give more resources to the player proposing the deal, at the expense of resources allocated to the second player.  No food reward would be given until both individuals agreed to use one of the two coloured tokens.

So what did the results show?  Chimpanzees behaved in the same way adult humans do.  When a partner’s cooperation was required, they would allocate resources fairly.  So it seems that Kaiser et al. may have prematurely concluded that fairness is a derived behaviour for modern humans.  In retrospect, it shouldn’t be surprising that chimpanzees display empathy and act fairly to one another.  All chimpanzee groups live in highly social groups, and antisocial behaviour would be detrimental to prolonged group cohesion.  In fact, wild behavioural studies have shown that chimpanzees do have a tendency to distribute various foods equally among kin (e.g., Pruetz & Lindshield, 2011).  Western chimpanzees in Senegal have been observed to share plant food, honey, meat, and tools based on elaborate hierarchies that have yet to be fully understood.

In the future more wild behavioural research may need to be conducted to better understand how sharing behaviours function with a chimpanzee community, and how their sense of fairness relates to our human sense of fairness.  So although we do not have all the answers yet, it seems likely that our common ancestor with chimpanzees had a similar sense of fairness in regards to resource allocation.  And we should feel lucky that that is the case because that means our sense of fairness is a deeply ingrained aspect of what it means to be fair.

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Kaiser, I., et al.  2012.  Theft in an ultimatum game: chimpanzees and bonobos are insensitive to unfairness.  Biology Letters, DOI: 10.1098/rsbl.2012.0519

Proctor, D & de Waal, F..  2013.  Gambling and Decision-Making Among Primates: The Primate Gambling Task.  Proceedings of the National Academy of Sciences.

Pruetz, J.D. & Lindshield, S.  2011.  Plant-food and tool transfer among savanna chimpanzees at Fongoli, Senegal.  Primates, DOI: 10.1007/s10329-011-0287-x


About Cadell Last
Hello. I'm probably drinking coffee and reading.

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