Chimpanzees and fairness.

Sometimes, ethologists find behaviors in animals that evoke similarities with behaviors that were previously thought unique to humans. Those cases are interesting in two ways; they can show us that we underestimate what animals can do, and sometimes they also suggest that we might be overestimating the complexity of what we do as humans. Frans de Waal is one of the researchers who has pioneered the study of cooperation and aggressive behaviors in non-human animals. His works and books have shed light on animal social behaviors using approaches that were more akin to politics and sociology than what most ethologists would have classically allowed themselves to do. His research in macaques, bonobos and chimpanzees have opened a window over the vast and complex behavioral repertoire of social animals, including how they form alliance, share food and care about others. He his one of the authors on a study by Darby Proctor, Rebecca A. Williamson, himself and Sarah F. Brosnan from Georgia State University that looks further into whether chimpanzees can play fair in a game context.

Whoever tries to study social behaviors in animals faces a problem of complexity. Scientists are used to experimental paradigms that reduce to the minimum the conditions under which we can observe behaviors. The typical approach consists in removing any feature of an experiment that is unnecessary. If you want to understand how subjects view colors for instance, a dark room with a computer screen displaying different colors is the best setup. Social behaviors are somewhat of an exception: the contexts are harder to reduce. Often, they require the presence of someone else, or a group of individuals to interact with. This is necessary to study how subjects socially interact but it also brings in confounding factors as you might lose some of the control you have over the experiment. What if the other subjects you bring in your experiment behave differently every day? What if people adopt different attitudes toward different people? Those are not reasons to give up studying social behaviors; their understanding will be crucial to gain insight on important social phenomenons including neuropsychiatry, politics and morality. We do, instead, have to find ways to reduce the number of variables by putting groups of subjects in simple environments where they can interact, like games, and attempt to reproduce those experiments with many different subjects.

Young chimpanzees playing.

A pair of young chimpanzees playing.

Photo by Delphine Bruyere, released under the Creative Commons License.

The recent study from Georgia State University reports that pairs of chimpanzees play fair in a game that was previously thought to trigger fair decisions only in humans1. The game is called the Ultimatum game. It is a reduced test designed to evaluate whether subjects can behave in a fair or cooperative way. One subject is offered a choice: how much of 10$ do you want to keep for yourself and how much do you want to give to a partner? The partner, seeing the offer, can either reject the whole trial (nobody gets anything), or accept the share (the two subjects get the split chosen by the first subject). The key with these games is to convince the second partner to accept the offer and not tempt him to punish you. The game was attempted before in chimpanzees, with food instead of money, and it was shown that chimpanzees tend to be selfish – not seeking the fair offers, and not rejecting unfair offers2,3.

The newer study seeked to design a more chimp-friendly version of the ultimatum game. The authors argued that perhaps the mechanical apparatus used to distribute food in the other studies were not understood by the chimpanzees and that a simpler version might reveal fair behavior. To make sure that their new setup was also working with humans, they made kids play the game as well. Here tokens exchangeable for food were used for chimpanzees whereas kids were rewarded with stickers.

The results of the study indicate that in the ultimatum game, chimpanzees as well as kids use fair offers. The chimpanzees, for instance, were very often choosing the highest amount of food when no interacting partner was present, but within the first trials where a partner was introduced, inverted their preferences and sacrificed tokens to let their partner have some. Some might think that this is due to learning during the experiment – perhaps, after all, the chimpanzees being punished by their partner end up choosing the fair option not because they have a preference for it but simply because they get less food due to partner punishment. However this does not seem to be the case as the authors point out that within all the trials, there is no case where the partner has rejected an offer – the chimpanzees and kids systematically accepted the offer, it is thus unlikely that the proposers learn to use fair offers through punishment within the game itself.

One of the possibilities to explain those results is that the partners might have influenced the proposer’s choices. The authors noticed that on some rare occasions the partner communicated with the proposer. Kids, for instance, said “You got more stickers than me”. Chimpanzees occasionally threatened their partner. This sort of social “punishment” might have driven part of the fair decisions adopted by chimpanzees and humans.

Although there should not be much disagreement about the results reported in the study, I suspect that, as is often the case with cooperation research, there will be intense controversy on the interpretation of the results. The first question to address is what, of the difference between this study and the previous ones, made the results end up so differently. The other is whether or not it is the communication between the subjects that influenced fair decisions – what are the behaviors by which one chimpanzee can influence the other? A few are reported in the study, but are there also others, more subtle, that were harder to observe by the experimenter?

Then, there is the question of interpretation. Should we think of chimpanzees as cooperative, fair? Although it might seem intuitive for non-scientists to think that some animals might have feelings and might be aware of the outcomes of others, there is still an important part of the scientific community that is reluctant to using those concepts to describe animal behavior. There is, also, the risk of anthropomorphism. Those words are to be kept for describing humans as they are human attributes, some scientists think. I personally lie in a sort of third position. I think that behaviors are to be observed for what they are – here, a group of chimpanzees chose an option instead of another. Thinking that this necessarily reveals some fundamental aspect of the inner working of their mind might be too advanced for our current level of knowledge of their cognition and their brain. On the other hand, I am reluctant to swipe away those behaviors with a simple explanation that appeals to what we currently know, such as how animals learn through reinforcement. Sometimes, the impatience of researchers to explain any observation with what we currently know constitutes the most efficient

break to discovery as it creates the illusion that we know everything. And we don’t.

At the opposite of anthropomorphism lies anthropocentrism – the belief that humans are a completely unique and exceptional creature that has nothing in common with the other animals. That, I think, is at least as dangerous as anthropomorphism, as it blinds us to the similarities that our behaviors and our brains might share with those animals with who we share a common ancestor. Perhaps the discoveries of the last decade concerning how animals behave similarly to humans in some game contexts is a good occasion to reflect about what terms like cooperation, fairness and generosity really mean and how these behaviors are controlled by the brain – both in humans and non-human animals.


1. Proctor D, Williamson RA, de Waal FB, Brosnan SF. (2013) Chimpanzees play the ultimatum game. Proceedings of the National Academy of Sciences of the United States of America. Jan 14. Epub.

2. Jensen K, Call J, Tomasello M (2007) Chimpanzees are rational maximizers in an ultimatum game. Science 318:107–109.

3. Kaiser I, Jensen K, Call J, Tomasello M (2012) Theft in an ultimatum game: Chimpanzees and bonobos are insensitive to unfairness. Biology Letters 8:942–945.

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