Why monkeys (and humans) are wired for fairness

This was the first paper to show that individuals of another species care when someone else gets more than they do. We tested whether capuchin monkeys would respond if their partners got a more preferred reward — a grape compared to a piece of cucumber — than they did for doing the same task (returning a token to the experimenter). Our monkeys were more likely to refuse to participate for a piece of cucumber when their partner got a grape than when they both got the cucumber piece, suggesting that they did indeed notice — and care — if another monkey got a better reward than they did for doing the same work. This paper set the stage for subsequent research showing the same response in different species of primates as well as dogs, wolves and several species of birds.

Ten years later, we assessed the advances in the field since that original paper. We found that species that routinely cooperated with non-kin were more likely to respond to inequity than those that did not typically cooperate. Moreover, chimpanzees reacted if they got more than their partner. We hypothesized that any species that cooperates needs to be able to identify good partners — that is, those who treat them equitably — and that noticing when they get less helps them to do so. Some species, including humans, chimpanzees and, likely, other highly social, intelligent species, then evolved to respond when they benefitted. Doing this shows that they "play fair" and are therefore a good partner, which should pay off in the long run by attracting long-term cooperative partners.

What is the nature of the hierarchy in humans? Christopher Boehm, an anthropologist who has worked in the field with both chimpanzees and humans, argues that the answer lies in our extreme flexibility, which allows for our continuum from dominance to egalitarianism. He highlights "reverse hierarchies," in which those at the bottom band together to prevent those at the top from taking advantage of them. To track the evolution of egalitarianism, Boehm traces these tendencies through the other apes and a variety of different human cultures. The result is both fascinating and thought-provoking.

Frans de Waal has written several fantastic books on primate behavior, but this is one of my favorites. He documents a fateful year in the life of a group of chimpanzees at Berger's Zoo in Arnhem, the Netherlands, as the three dominant males scheme and maneuver for power. Ultimately, he shows the importance of their coalitions and alliances as they negotiate their social world — and the critical consequences when coalitions collapse. This highly readable account will give you a new appreciation for the complexity and intelligence of ape society.

Is a fair society really a better one? This provocative book, by two epidemiologists, explains how every facet of our lives, from our personal health to societal well-being, is influenced not by the wealth or political system of the society in which we live, but by how equal it is. They concretely show just how bad inequality is for all of us, whether we're at the top or the bottom, and convincingly demonstrate that there are very good reasons indeed to care if you are not getting your fair share.

Did you ever wonder why you just did that? In this comprehensive book, Robert Sapolsky has an answer. He starts the book at the moment at which a behavior occurs in the brain and then moves back in time, from the effects of the nervous and endocrine systems minutes to days prior through the impact of genes, development, ecology, culture and society, and, ultimately, the evolutionary history of the behavior. Sapolsky then considers what this all means for the good and the bad of being human. Although much covered in this book is technical, Sapolsky is a gifted writer who conveys this information clearly and engagingly to non-experts.