One defining characteristic of humans is their unusually cooperative nature, which is unparalleled among animals. An important goal for anthropology is to understand the nature and evolution of this "altruistic" behavior. This doctoral dissertation project will investigate cooperative exchanges among free-ranging rhesus macaques in order to test predictions from several competing evolutionary hypotheses about altruism. Studying cooperative exchanges among rhesus macaques will provide a comparative model for understanding the behavioral evolution of humans and our ancestors. The broader impacts of this project include the support of science education and outreach, through valuable field experience for research assistants, data analysis experience for undergraduates, and presentation of research results in various public formats, including local zoos and conferences.
This study will observe grooming interactions among 50 adult female rhesus macaques from three social groups at Cayo Santiago, Puerto Rico, using focal animal sampling methodology, for eleven months (spanning both mating and birth seasons). Specifically, the project will examine how well reciprocal grooming exchanges resemble those predicted by several competing theoretical hypotheses (kin selection, reciprocal altruism, biological markets theory, and social bond investment), in one comprehensive and integrated analysis, via AIC model ranking. These exchanges will be examined across multiple time scales and across groups of variable sizes. Additionally, there will be a more detailed investigation of biological markets theory. By focusing on exchanges of grooming for mates or infant handling, this study will test a key prediction that such exchanges conform to supply and demand relationships. The extent to which apparent supply and demand relationships may be artifacts of, or mediated by, stress responses will be examined, with stress measured both behaviorally and via fecal glucocorticoid metabolite assays.
