On the flip side, when two unrelated chimps put side by side were presented with a tasty grape and a less tasty carrot, the chimp with the grape sometimes threw it away. "I would say that the most likely cause was either fear of retribution or just general discomfort about being around an individual getting less than you," says Brosnan. Differences in the social hierarchy also played a role, she says. Dominant chimps were angrier when they were on the receiving end of a lesser reward than those lower in the pecking order.As you can see, fairness is the rich anthropomorphic explanation, but there are also leaner explanations.
The results among the chimps are indicative of highly cooperative societies, where relying on someone else is especially crucial. This may be why chimpanzees and humans will avoid inequity, Brosnan suggests, to have long-term cooperation from friends.
However, she cautions against calling it fairness exactly: "Fairness is a social ideal" she says. ... [The animals] don't have social ideals in the same sense [that people do]." Her research reveals behaviors that may look like a push for fairness; but that doesn't mean strategic, higher-order thinking is driving it. The explanation may be much simpler, based more on emotion, Brosnan says: "When my social partner gets upset, I give them something that makes them happy."
People often talk about chimps and other primates as being social like humans, but they are not at all. It is true that they often live in groups, but they do not cooperate on tasks as humans do, so they are not really social.