A body of recent work demonstrates that sociality enhances the fitness of females in two species of savanna baboons, Papio cynocephalus and Papio ursinus. Females that are more fully integrated into their groups and have stronger social bonds have higher survivorship among their infants and live longer than other females. I have recently begun research on a third species of savanna baboons, Papio anubis, in the Laikipia Plateau of Kenya in collaboration with Eila Roberts (postdoctoral fellow, ASU) and Shirley Strum (UCSD, Director Uaso Ngiro Baboon Project). There are several reasons to think the form and function of female-female bonds may be somewhat different in P. anubis than in the other savanna baboon species. Current evidence suggests that P. anubis females form more enduring relationships with males than P. cynocephalus and P. ursinus females do, and this may influence both the form and utility of female-female bonds. Our work on anubis baboons is part of a larger collaborative project to compare the nature of social relations among multiple baboons species, including geladas and guinea baboons, with researchers using common protocols and methods for analysis.
The ontogeny of prosocial preferences
Humans differ from all other organisms in our capacity for large-scale cooperation that is not based on kinship or reciprocity. However, there is substantial variation in the nature of cooperation across societies. It seems likely that these differences are maintained by learned cultural beliefs that are transmitted from one individual to another within societies. These sets of beliefs, norms, and values may have been shaped by cultural evolution to maintain group-level cooperation. Although cross-cultural differences in the cooperative behavior of adults have been documented, there is little systematic information about the developmental trajectory that underlies this variation. How and when does the cooperative behavior of children begin to resemble the behavior of adults from their own societies? To address this gap, my colleagues and I examined the ontogeny of culturally-specific patterns of generosity among children and adolescents in five small scale societies and one urban western populations. Our work suggests that middle childhood (6-8 years of age) marks the time when children begin to acquire the culturally-specific beliefs and values that influence altruistic preferences. We are beginning a second round of experiments to extend and verify these findings.
The evolutionary roots of prosocial behavior
Altruistic behavior is well-documented in nonhuman primates, but the range of altruistic behaviors is much more limited than it is in humans. Moreover, when altruism does occur among other primates, it is typically limited to familiar group members—close kin, mates, and reciprocating partners. This suggests that there may be fundamental differences in the social preferences that motivate altruism in humans and other primates. However, it is difficult to assess that preferences that motivate animals to cooperate in natural settings. Do chimpanzees share food because they prefer outcomes that benefit others, because they have received food from their partner in the past, or because it is easier to share than to put up with persistent harassment? To gain insight about social preferences, I have worked on a a body of experimental studies designed to examine the nature of prosocial preferences. This work suggests that chimpanzees have, at best, weak preferences for outcomes that benefit others, and that the structure of tasks affects chimpanzees behavior.