Endocrine Aspects of Aggression and Dominance in Chimpanzees

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This study will be the first to document how the concentrations of two hormones, testosterone and cortisol, are related to the social behavior and nutritional plane of wild chimpanzees. We will study two wild populations of chimpanzees (in Kibale National Park, Uganda; and Gombe National Park, Tanzania), living in habituated communities that each contain about 10 adult males. In each site we will collect urine from individuals in trees and freeze it for later analysis. We will also make systematic observations of the social behavior of adult chimpanzees, including rates of aggression and submission, sexual behavior, and alliances. We will then find out whether (as in our pilot study) testosterone and dominance are consistently related to each other among adult male chimpanzees, and if so, how both are also related to the frequency of aggression. We will also establish how levels of sexual behavior are related to both hormones, how hormonal levels change in response to group composition, and how they are related to seasonal fluctuations in food supply. By analyzing the relationship between hormones and aggression in wild chimpanzees, this study will contribute to understanding the evolution and function of the parallel system in humans.