But men and monkeys have a sense of fairness and an aversion to inequity. In a fascinating study, Sarah Brosnan and Frans de Waal showed that capuchin monkeys react negatively when another individual gets a better reward for the same or less effort on a specific task.
Pairs of brown capuchin monkeys (Cebus apella), were placed next to each other and trained to exchange a token with human handlers to receive a reward, in most cases, a piece of cucumber. Partners of capuchins who made the swap either received the same reward (a cucumber slice), or a better reward (a grape, a more desirable food), for the same amount of work or, in some cases, for performing no work at all. Capuchins who witnessed unfair treatment and failed to benefit from it often refused to conduct future exchanges, would not eat the cucumbers they received for their labors, and in some cases, threw food rewards at human researchers.
Like the Ultimatum Game in experimental economics, this experiment demonstrates inequity aversion. In the Ultimatum Game two parties interact anonymously and only once. The first player proposes how to divide a sum of money with the second party. If the second player rejects this division, neither gets anything. If the second accepts, the first gets what he proposed and the second gets the rest. Low offers are often rejected by the second party. Since an individual who rejects a positive offer is choosing to get nothing rather than something, that individual is not acting to maximize his economic gain.
In a study by Joseph Henrich et al., In Search of Homo Economicus: Behavioral Experiments in 15 Small-Scale Societies the researchers reported,
Recent investigations have uncovered large, consistent deviations from the predictions of the textbook representation of Homo Economicus: in addition to their own material payoffs, many experimental subjects appear to care about fairness and reciprocity and reward those who act in a cooperative manner while punishing those who do not even when these actions are costly to the individual…
We can summarize our results as follows. First, the canonical model is not supported in any society studied. Second, there is considerably more behavioral variability across groups than had been found in previous cross-cultural research, and the canonical model fails in a wider variety of ways than in previous experiments…
“Economic man” doesn’t exist. Neither, it seems, does “economic monkey”.
Update: See Joseph Henrich’s critique of Brosnan and de Waal here.