Dr. Frans B. M. de Waal Proposal # IOS-0718010 Social Modification of Primate Behavior
For social animals to react appropriately to each other they need to know about each others'' gender, social status, and the state they are in (such as whether they are hungry, distressed, fearful, or aggressive). This project seeks to establish what brown capuchin monkeys (Cebus apella) know about their group mates. It asks them to indicate, on the basis of portraits projected on a computer screen, which individual monkey belongs to their group. It asks them to rate calls as either aversive or attractive, dependent on the identity of the caller (for example, does a female find the distress calls of her own offspring more aversive than such calls by unrelated juveniles?). And it will ask monkeys to share food with others based on what they know about their hunger state to see if they take the needs of others into account. Available are 30 capuchin monkeys, kept in indoor/outdoor enclosures, trained for temporary separation for experiments. The proposed study will illuminate basic social cognition that is often taken for granted. The laboratory at the Yerkes Primate Center serves the education of a great many undergraduate and graduate students, who obtain valuable training in combination with classes they take. Through his popular books and lectures, the Principal Investigator is at the forefront in communicating findings in animal behavior to a wider public, both academic and nonacademic.
We are interested in how monkeys make social decisions, how they achieve cooperation, and what they know about each other. This is relevant to human behavior, because if monkeys decide to help each other or share food we assume they use the same psychology (motivations, emotions, knowledge) as our own species given that we are closely related to monkeys and have very similar brains (the human brain is obviously larger, but does not contain any structures that we do not find in a monkey brain). For example, we have found for example that monkeys are just as sensitive to (un)fairness as humans in that they react with protest to receiving less rewards for the same task than a companion. Such data is important because of the implication that our own responses go back far in our ancestral history and have been shaped by the same evolutionary pressures. For this purpose we work with about 30 brown capuchin monkeys, which live indoors and outdoors in two large social groups. Most of the time they socialize, but we invite them into an experimental room about once per day to conduct studies. After experiments, the monkeys are released back into their group. The studies usually involve cooperation, food sharing, or some computer task for which they receive rewards. To offer three main findings from these projects: 1 - Face recognition: Monkeys not only are excellent at face recognition, but they are even capable of picking out of an array of faces the ones they know (individuals they live with in the same group) versus ones they do not know. This means that they connect two-dimensional images of faces with actual individuals, which is a capacity that we take for granted in our own species, but was never demonstrated before in other primates. The monkeys use holistic information to process faces as demonstrated by the fact that they show the same inversion effect (they have trouble recognizing upside-down faces) as humans. This confirms the similarity in face processing between humans and other primates. 2 - Prosocial tendencies: As opposed to the general speculation that only humans are altruistic, we conducted experiments in which monkeys could do each other favors. Capuchins are prepared to seek rewards for others, such as when we place two of them side by side, while one of them barters with us with differently colored tokens. One token rewards only the monkey itself, whereas the other rewards both monkeys. Soon, the monkeys prefer the "prosocial" token. This is not out of fear, because dominant monkeys (who have least to fear) turn out to be the most generous. 3 - Sense of fairness: Monkeys are aversive to unequal reward distributions, and react similarly to human children in that they protest receiving lesser rewards (cucumber) than another individual for the same task (who receives grapes). This inequity experiment has become very popular in the media (more than a million internet users have watched it), and has been replicated by other scientists, including on quite different species such as dogs and crows. A brief video can be seen here: www.youtube.com/watch?v=HK8Mp3OJYjk Overall, these studies support the view that there is evolutionary continuity in the social cognition of humans and other primates and illuminates certain processes, such as face recognition and prosociality, by inspiring techniques to study these that can be applied across many different species. Findings from our studies have been published 16 peer-reviewed journal articles, and are also featuredin popular books by the principal investigator.
