As that video demonstrates (a Capuchin who was happy to perform a simple task in order to get a piece of cucumber goes crazy when another monkey is introduced who gets a grape for the same task) this notion of fairness is so basic, it is pre-human. According to the video, it's even been replicated with dogs and birds.
https://www.youtube.com/watch?v=meiU6TxysCg
As that video demonstrates (a Capuchin who was happy to perform a simple task in order to get a piece of cucumber goes crazy when another monkey is introduced who gets a grape for the same task) this notion of fairness is so basic, it is pre-human. According to the video, it's even been replicated with dogs and birds.