Cooperation and competition in chimpanzees: current understanding and future challenges

Two goals in the study of evolutionary anthropology are to determine the factors that make humans unique and to reconstruct the evolution of our behavior. As humans ’ closest living relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) have always been of special interest in this regard. Because of their close evolutionary relationship to us, these animals provide the requisite comparative data to evaluate claims made about human uniqueness. In addition, knowledge of the dif-ferences among chimpanzees, bonobos, and us furnishes important insights into the changes that occurred during human evolution. Given these circumstances, studies of chimpanzees and bonobos remain high priorities for research. The volatile political situation in the Democratic Republic of the Congo, home to bonobos, has made long-term study of their behavior difficult, if not impossible. In contrast, field research on chimpanzees, initiated by Jane Goodall1 and Toshisada Nishida2 nearly 50 years ago, continues to grow and thrive. While past and ongoing field work has added enormously to our understanding of the behavior of chimpanzees,3–8 gaps in knowl-edge persist. In this paper, I summarize some of these gaps, giving special emphasis to male cooperation and female competition. Cooperation and competition gener-ate considerable theoretical interest and remain prominent issues in the study of evolutionary biology. Dar-win’s9,10 twin theories of natural selec-tion and sexual selection furnish the basis for our current understanding of cooperation and competition in the bi-ological world. Cooperation, defined as behavior that increases the fitness of others,11 poses a problem because it is not immediately clear why organisms might help others in the face of selec-tion operating to produce organic structures and behaviors ‘‘solely by and for the good of each.’’9 Why males cooperate poses an additional puzzle because these individuals typically compete to fertilize females, who are neither easily divided nor shared. As a result, extensive research has been devoted to attempting to explain the evolution of cooperation during the past 50 years.11–20 After having been virtually ignored for 100 years after its publication i