Monkeys appear to have an innate sense of when they are being treated unfairly, read here. Capuchin monkeys will refuse beneficial exchanges, if they see another monkey getting a better deal. Sound familiar? Similar results are found in the literature on experimental economics for humans, as Robert Frank notes at the link.
Here is one summary from The Washington Times, the only paper I can find in today’s Virginia power blackout, they don’t yet have the link on-line:
When both monkeys were given a cucumber slice after handing over the token, they completed the trade 95 percent of the time.
But when one was given the tastier grape for the same amount of work, the rate of cooperation from the other monkey fell to 60 percent…The refusal to make the exchange increased as the experiment continued…The scientists concluded that capuchins apparently measure rewards in relative terms…the tropical forest-dwelling capuchins were chosen for the experiment because they often share food.
One commentator on the study, a Charles Janson of SUNY, suggests that the behavior of the monkeys might have been learned in captivity (again, cited in The Washington Times).