The Social Foraging Niche of the Mbendjele Bayaka

This thesis addresses the question of how a population of modern hunter-gatherers, the Mbendjele BaYaka, utilise social behaviours to exploit high quality but difficult to acquire foods. In contrast to other primates, the human diet contains a high proportion of meat, tubers and honey which have in common not only a very high calorific density but also considerable acquisition costs. The theory that human cognition coevolved with a transition to a diet specialising in these resources is far from novel. However, the underlying proximate mechanisms that allow hunter-gatherers to exploit these foods is poorly understood. It is widely accepted that food sharing by hunter-gatherers acts as a form of reciprocal altruism, reducing the risk inherent to high variability foods such as large game. However, the underlying mechanism which maintain the reciprocity are often ignored, simply assuming humans have the capacity to calculate and act upon inequalities. Similarly, a long-standing theory explaining the extended period of juvenile dependence in humans argues that it provides the opportunity to acquire the skills and knowledge necessary to hunt and gather difficult to acquire foods, yet we still no relatively little about how hunter-gatherer children learn and develop. In this this thesis I address not only the well-worn question of the ultimate explanations for sharing and childhood, but also examine the proximate mechanisms underlying cooperation and social learning. I make use of a range of data on three contemporary Mbendjele camps, which offer varying social structures and levels of market integration, and compare this to previously published data on the Mbendjele as well as data on a contemporary population of fisher-gatherers, the Agta of the Philippines. The Mbendjele in this study live within a logging concession, an area that in recent years has undergone rapid development. This provides an opportunity to study the impact changes in economy have had on foraging and food sharing. In combination with analyses that make use of recent innovations in remote sensing technology and social network analysis to examine how kin and social relations facilitate cooperation, I find evidence that food sharing serves multiple functions in this society, one of which is risk reduction, but also that attitudinal reciprocity rather than calculated reciprocity may be the underlying mechanism. By observing how Mbendjele children spend their time and how this differs with both age and sex I find evidence that learning is a primary motivator of children’s activity. However, I challenge the assumption that direct experiential learning of male specific foraging is the main mode of learning for Mbendjele boys, suggesting that either learning is indirect and reliant on horizontal pathways, or that this type of learning is not the primary cause for the evolution of the extended juvenile period in humans. The key findings of this thesis highlight the important role played, not only by social behaviours, but also social structures in the hunter-gatherer economy. Affiliative relationships stabilise cooperation and facilitate social learning, and a greater understanding of the proximate mechanisms surely offers a pathway to a better understanding of human evolution