Research
Comparative Analyses of Baboon Sociality
Natural selection favors traits that enable individuals to reproduce more successfully than other members of the population, and behavioral ecologists have devoted considerable effort to identifying the sources of variation in individual reproductive success. Much of this work has focused on the characteristics of individuals, such as their sex, age, parity, and physical condition. However, many animals live in social groups, and there is a growing body of evidence which demonstrates that the fitness of individuals depends at least in part on the outcome of their interactions with other group members. I have participated in analyses of data from longterm studies of yellow baboons in the Amboseli basin of Kenya and chacma baboons in the Okavango Delta of Botswana which show that females form strong, equitable, supportive, tolerant, and stable bonds with selected partners. The formation of close social bonds is associated with positive fitness outcomes for females---their infants are more likely to survive and females themselves are likely to live longer---and suggest that social bonds have adaptive value for individuals. We are now extending this work to a third species, olive baboons, in central Kenya. Like baboons in Moremi and Amboseli, female olive baboons also form strong ties to selected partners, particularly close kin. Olive baboons also form strong ties to particular adult males, and our analyses suggest that females' ties to males affect the strength of their ties to other females. Compared to yellow and chacma baboons, females seem to former weaker ties to maternal kin and unlike yellow and chacma baboons, female olive baboons do not preferentially associate with age mates. Ongoing analyses focus on the structure and function of male-female relationships and the effects of social bonds on female's reproductive performance.
The origin and ontogeny of prosocial preferences
Cooperation among unrelated individuals, who do not share direct genetic interests in offspring, is uncommon in nature but ubiquitous in human societies. How did the capacity for large scale cooperation and altruistic social preferences arise within human societies? There are three major hypotheses to account for the evolution of the extraordinary capacity for large scale cooperation and altruistic social preferences within human societies. One hypothesis is that human cooperation is built on the same evolutionary foundations as cooperation in other animal societies, and that fundamental elements of the social preferences that shape our species’ cooperative behavior are also shared with other closely related primates. Another hypothesis is that selective pressures favoring cooperative breeding have shaped the capacity for cooperation and the development of social preferences, and produced a common set of behavioral dispositions and social preferences in cooperatively breeding primates and humans. The third hypothesis is that humans have evolved derived capacities for collaboration, group-level cooperation, and altruistic social preferences that are linked to our capacity for culture. My colleagues and I have conducted a series of experiments, modeled after work in behavioral economics, to explore the social preferences of chimpanzees and children. These experiments suggest that chimpanzees are not consistently motivated to provide benefits to familiar partners and are tolerant of inequity. Parallel experiments conducted on children from a diverse set of societies shows that children behave very differently from other apes, and that the social preferences that underlie their behavior are influenced by both their age and the cultural context in which they live. Our most recent research explores the role that social norms play in shaping children's behavior. We find striking similarities in the development of sensitivity to normative information among children from diverse societies, suggesting that the psychology underlying norm acquisition is universal, while the content of norms varies considerably across cultures.
