The Chimpanzees of the Tai Forest: Behavioural Ecology and Evolution

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Summary: Tai Chimps
Review: The Chimpanzees of the Tai Forest is a fascinating analysis of chimpanzee behaviour based on a fifteen year study in the West African jungle of the Cote d'Ivoire. The authors engage with some of the fundamental questions in regards to the evolutionary relationship between primates, with a specific focus on the affinity between chimpanzees and humans. They combine rigorous scientific data, often in the form of statistical tables, with personal anecdotal descriptions. These lines of evidence are presented together, to create an authoritative and yet picturesque account of Chimpanzee behaviour.
In the first chapter the authors provide an orientation to the Tai Chimpanzee project by situating it within other data from prominent studies of wild chimpanzees of varying duration. In the second chapter the authors explain how the Tai chimpanzee community has gone through many demographic changes but has remained, for the entire study period, within the same area in the Tai forest. In the third chapter, on female life histories, they explain that dominant females have interbirth intervals 26 months longer for male than for female offspring, which results in a higher survival rate for males. In contrast, subdominant females invest 12 months more in daughters, which does not result in a higher a survival rate. In chapter four the authors suggest that at Tai, the males' life history is strongly influenced by their mother's investment. High-ranking mothers invest more in male infants who, as a result, become more interested in acquiring rank and have greater reproductive success than low ranking males. Thus, they suggest that reproductive strategies used by males are influenced by male-male competition as well as female choice. In chapter five the authors document the social structure of the Tai chimpanzees indicating that the inter-population variations of the fission-fusion system is influenced by the demographic factors of community size and adult sex ratio. In chapter six they show how social interactions are distributed within a community with strong associations between its members. This chapter offers a discussion of how chimpanzees show capacities for cooperation, reciprocal interaction and coalition behaviour and how these alliances are created through explicit social strategies. In chapter seven the authors argue that chimpanzees' inter-group aggression possesses several features considered typical for human warfare such as a group enterprise of large coalitions concentrated against neighbour groups. They also suggest that the Tai chimpanzees possess strategies for attack, which involve anticipation of possible outcomes. In chapter eight the authors describe how Tai chimpanzees hunt very regularly and have developed a system of reciprocity in which hunters are rewarded for their contribution which involves a system of individual recognition, temporary memory of recent actions and social enforcement of values. In chapter nine the authors explain that tool use among the Tai chimpanzees, especially in the context of nut cracking, involves elaborate planning and a long term learning phase that can persist for several years. They also discuss how nut cracking and food sharing intermingle in a manner that effects many aspects of social life. In chapter ten the authors review the cognitive abilities of wild chimpanzees and conclude that they show highly developed faculties relating to mental representations, the notion of causality and a theory of mind. They also argue that wild chimpanzees show a more developed understanding of causality than has been shown in captive chimpanzees. In the eleventh and final chapter of the book, the authors put forth a model of evolution of chimpanzees that attempts to account for the presence of their behaviorally similar characteristic to humans. Specifically, they argue that three characteristics, which are common to all chimpanzee populations, select for higher cognitive abilities related to causality and of third party attention. These characteristics are the fission-fusion social system, hunting behaviour in trees and flexible and numerous types of tool use. They propose that these characteristics were slowly elaborated in a synergistic manner that may have begun before the divergence between the chimpanzee and human lineage.
The book documents chimpanzee behaviour in such a way to reveal its striking diversity. In each chapter the authors attempt comparisons between the different chimpanzee populations to delineate the factors in the environment and in the social life of chimpanzees that generate the variations observed across sites. Additionally, they situate their observations within the broader context of research in behavioural ecology and compare their own data with other prominent work on chimpanzee populations. There is frequent reference to important studies by Jane Goodall and Toshisada Nishida.
The authors also adopt a perspective informed by feminist methodology, arguing that the view of chimpanzees as a purely male-oriented society does not reflect the social life of Tai chimpanzees. This is apparent in their discussion of the stronger role of female choice in reproductive strategies in chapter four and in the importance of female friendship discussed in chapter five. Their argument for the Tai chimpanzee society being bi-sexually bonded is also evident in the authors' contention that females have a dominant position in gaining access to meat (Chapter 8) and their discussion of female chimpanzees' greater involvement in territorial defense (Chapter 7).
In the last two chapters of the book a clear agenda emerges. The authors argue against a basic discontinuity between humans and other animal species and do so by portraying the affinity between apes and chimpanzees. To a large extent, this view is also about securing basic rights for chimpanzees. At points, their agenda becomes sufficiently transparent to undermine the authority of their data. This is particularly obvious in the degree of anthropomorphizing in anecdotal accounts throughout the later chapters of the book. However, overall the purity of the authors' intentions redeems them for these momentary indulgences in their own motivations. The authors argue that the limiting factor in the quest for human and chimpanzee identity is their survival. And it is this fight that the authors contend, should be our utmost priority.