Excerpts from: Scientific American blog The Primate Diaries:
According to research published in the journal Animal Behaviour (pdf here), fairness is not only essential to the human social contract, it also plays an important role in the lives of nonhuman primates more generally. Sarah F. Brosnan and colleagues conducted a series of behavioral tests with a colony of chimpanzees housed at the University of Texas in order to find out how they would respond when faced with an unfair distribution of resources. A previous study in the journal Nature by Brosnan and Frans de Waal found that capuchin monkeys would refuse a food item when they saw that another member of their group had received a more desired item at the same time (a grape instead of a slice of cucumber). Some individuals not only rejected the food, they even threw it back into the researchers’ face. The monkeys seemed to recognize that something was unfair and they responded accordingly. This raised the provocative question: can the basis of the social contract be found in our evolutionary cousins?
Chimpanzees are known to be highly individualistic where food is concerned, so Brosnan and colleagues sought to determine whether these earlier results could be replicated in a more competitive species.
Perhaps unsurprisingly, chimpanzees behaved the same way that capuchins did and objected if they only received a carrot when their group mate was given a delicious grape for the same price. Out of 76 trials the chimpanzees were significantly more likely to refuse a carrot in these tests compared to times where both received the same low-value food reward (p = 0.004). Likewise, when both individuals received a carrot after first being shown a grape, they were significantly more likely to refuse than in cases where no expectation of a better reward had been presented. The bottom line was that if things weren’t fair a tantrum would ensue.
However, chimpanzees in this study went beyond the basic tenets of the social contract and demonstrated what could be considered the foundation of social solidarity.
As the authors reported:
We unexpectedly found that chimpanzees were more likely to refuse a high-value grape when the other chimpanzee got a lower-value carrot than when the other chimpanzee also received a grape. . . This reaction was not seen in previous studies of inequity in primates, either among chimpanzees or among capuchin monkeys.
Read the full article at Scientific American