Chimps' Sense of Justice Found Similar to Humans'

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SciAm.com
January 26, 2005

Chimps' Sense of Justice Found Similar to Humans'

Inequities big and small can lead people to believe that life is indeed not
fair. But how humans respond to unfair situations depends on the social
circumstances: inequality among friends and family is less disturbing than
it is among strangers, for instance. The results of a new study indicate
that the same is true for chimpanzees, a finding that sheds light on how our
sense of fairness evolved.

In the fall of 2003, Sarah Brosnan and Frans de Waal of the Yerkes National
Primate Research Center in Atlanta determined that capuchin monkeys don't
like being subjected to treatment they deem unjust. In the new work, the
researchers tested the reactions of pairs of chimpanzees to exchanges of
food that varied in quality. The animals received either a grape, which they
coveted, or a less appealing cucumber and they could see what their partner
obtained. In pairs of chimps that had lived together since birth, the
individual given the cucumber was less likely to react negatively to the
situation than was the short-changed member of a pair that did not know each
other as well. Indeed, chimps in the short-term social groups refused to
work after their partner received a better reward for the same job. "Human
decisions tend to be emotional and vary depending on the other people
involved," Brosnan says. "Our findings in chimpanzees implies this
variability in response is adaptive and emphasizes there is not one best
response for any given situation but rather it depends on the social
environment at the time."

Further experiments to investigate reactions to unfair situations are
ongoing at the center in the hopes of understanding why we humans make the
decisions we do. "Identifying a sense of fairness in two closely-related
nonhuman primate species implies it could have a long evolutionary history,"
Brosnan remarks. The findings will be published in the February 7 edition of
the Proceedings of The Royal Society B: Biological Sciences. --Sarah Graham