Was just listening to Terri Gross, Fresh Air…talking to an animal emotions researcher; seems that most primates have a sense of fairness. Put two Capuchin monkeys in side by side cages where they can see each other, give both a piece of cucumber, no problem, both a grape (yum) no problem, give one cucumber one grape, big problems. The one shorted will refuse the cucumber, protest, maybe throw a tantrum, the one with the grape might refuse as well until treats are equalized. Hope I’m as fair as a Capuchin;)