Humans are one of the few species of animals that can sense and protest to injustice. For a long time, our self-righteousness made us believe that we were the only ones able to do this. We also considered ourselves as the only ones capable of feelings and altruistic behavior, but that too was proven false. Now, another one of the things that supposedly made humans unique appears in other species of animals as well. Granted, birds still can't sense it, but capuchin monkeys surely can. The research that proved that again showed that the primates, like humans, only militate for fairness out of self-interest.

In our species, this is clearly visible in protests. Only poor people and those in the middle class militate against the inequities of society. Those in the upper classes, who benefit from the status-quo, are never seen protesting against receiving the large sums of money they receive. Moving past being fair or unfair, no one can honestly blame them for not wanting to change things. But consider the next situation, in which a worker making minimum wage comes across a lot of money, and becomes a member of the upper class.

As soon as this happens, he or she opposes to the same ideals of social fairness he or she has been previously fighting for. This proves that members of society look for justice only in the instances when this benefits their personal interest. And it would appear that, evolutionarily speaking, this type of behavior is a lot older than formerly thought. It may even have originated well before humans broke off from other primates, millions of years ago. Scientists have identified the self-interested behavior in capuchin monkeys, which have been analyzed in a lab setting.

“Our monkeys have not reached the point at which their sense of fairness stretches beyond egocentric interests – for example, the one who gets the grape never levels the outcome by giving it to the other - but in cooperative human societies, such as those in which men hunt large game, anthropologists have found great sensitivity to equal distribution,” explains Frans de Waal. He is the Charles Howard Candler professor of Primate Behavior in the Psychology Department of the Emory University, and also a member of the National Academy of Sciences, in the US and the Netherlands.

“Sometimes, successful hunters aren't even allowed to carve up their own kill to prevent them from favoring their family. Without ever having heard calls for equality, these cultures are nevertheless keenly aware of the risk that inequity poses to the social fabric of their society,” he concludes, in an article posted on NewScientist.