One of the traits that make humans different from other animals is their sense of fairness. Humans are willing to make sacrifices for the sake of fair play. Ironically, this behavior appears to have evolved for selfish reasons. Two scientists arrived at this conclusion after conducting a series of studies with animals starting with an experiment with monkeys, which are among the closest known animal relatives of humans.
For the new study published in the journal Science on Sept. 18, Sarah Brosnan, from the Neuroscience Institute and Language Research Center of Georgia State University in Atlanta and Frans de Waal, from the Yerkes National Primate Research Center and Psychology Department of the Emory University in Atlanta, reviewed their own research on how primates respond to inequity as well as other animal studies to better understand the sense of fairness among humans.
In a 2003 study on monkeys entitled "Monkeys Reject Unequal Pay," the two researchers found that brown capuchin monkeys became distressed and refused to do a task after a partner received better reward for doing the same task, indicating the sense of equality in these animals. The experiment was followed by other studies on inequity response in nine other species of primates including humans.
The researchers observed that animals tend to only respond to inequity when they routinely cooperated with strangers not related to them. Of the animals studied, however, Brosnan and de Waal found that only humans and chimpanzees possess the willingness to give up benefit for the sake of equal outcome and foster a cooperative relationship.
"We hypothesize that lots of species respond negatively to getting less than a partner, which is the first step in the evolution of fairness, but only a few species are able to make the leap to this second step, which leads to a true sense of fairness," Brosnan said.
It also appears that the motivation to seek for equality despite disadvantaging oneself also has something to do with selfish motivations. Inequality, for instance, could result in conflict and loss of beneficial cooperative relationship.
"This reaction probably reflects an attempt to forestall partner dissatisfaction with obtained outcomes and its negative impact on future cooperation, the researchers wrote. "It is the evolution of this response that allowed the development of a complete sense of fairness in humans, which aims not at equality for its own sake but for the sake of continued cooperation."
