We don't expect animals to understand human "inventions" like economics (or pay scale, income inequality, or fairness). Surprisingly, they do.
This quick video showcases the emotional reaction of one Capuchin monkey when confronted with unequal pay for equal work. In this case, the work is giving a rock to a researcher in exchange for a treat. The monkey was perfectly happy trading a rock for a piece of cucumber – until a neighboring monkey gets a delicious grape for performing the same action.
See what happens next.