Other chimpanzees


The Chimpanzees of the Taï Forest: Behavioural Ecology and Evolution. By C. Boesch and H. Boesch-Achermann. Oxford University Press, Oxford, 2000. viii + 316 pp. Price £19.95. ISBN 0 19 850507 8.

Had Darwin known more about chimpanzees, he surely would have referred to them, rather than baboons, when he wrote in one of his notebooks (after triumphantly proclaiming ‘Origin of man now proved’): ‘Metaphysics must flourish. – He who understands baboon would do more towards metaphysics than Locke.’ However, until a few decades ago, the behaviour of wild primates, including chimpanzees, was the stuff of fables and legend.

Chimpanzees are our closest living relatives. Decades of patient observation of wild chimpanzees in East African woodlands have upturned many a cherished belief about human uniqueness. It is difficult to believe that only 40 years ago we still thought that humans were the only creatures in the natural world to use and manufacture tools, to wage war on neighbouring groups, to hunt co-operatively, or to kill and subsequently cannibalize conspecifics, including babies. Articles in glossy magazines and especially films have seen to it that these insights are now part of our popular culture.

The book by Christophe and Hedwige Boesch-Achermann reports on similar studies of West African chimpanzees, based on 20 years of study of a rainforest population in Côte d’Ivoire. Their work has made an essential contribution to a more recent and equally surprising finding, namely that chimp behaviour varies from site to site, with no apparent link to habitat or geography. Is this just because they are better studied than any other organism, and would we find equally impressive variability if we did detailed comparisons among populations of squirrels, sparrows or sharks? Closer scrutiny reveals that the variation among chimpanzee populations is largely due to socially transmitted local traditions, rather than genetic differences. The discovery of culture in great apes is opening yet another window onto our origins.

All the peculiarities of the West African chimps are brought together in this book: the endless and incredibly skilful nut cracking with stone tools that the chimps may have carried to the site from far away in the dense forest; the intricately choreographed co-operative hunting of red colobus monkeys, followed by meat sharing based not on dominance but on the contribution to the success of the hunt; the blood-curdling attacks on unsuspecting parties of neighbours, but without the killing seen elsewhere; the consistent gregariousness and unparalleled co-ordination of travel by subgroups.

Whenever the data are available, the contrasts with the results of chimpanzee studies elsewhere are documented in fine detail. This analysis makes it possible to describe chimpanzee universals, as well as to detect a pattern among the differences. The Taï chimps are at the tolerant end of the chimpanzee spectrum, showing remarkable respect for possession of meat or tools. Most important is the greater social influence of the females, made possible by their consistent gregariousness, and accompanied by longer sexual swellings and more frequent sexual activity. Mothers push their sons on their climb to the top of the hierarchy. Evidently, the Taï chimps are the perfect intermediate between the patriarchic eastern chimpanzee and the female-dominated bonobos of the Congo basin. Various hypotheses can be entertained; the one presented by the Boesches remains to be tested in detail.

The detailed comparisons make this book extremely valuable, but that does not mean it is perfect. The writing is often imprecise, typographic errors abound, methods are often left unexplained, some statistical tests are inappropriate, graphical representations tend to be unconventional, and most graphs lack an indication of variance or even sample sizes. Many readers will be irked by the authors’ tendency to blur the distinction between description and interpretation: virtually every aspect of the chimps’ behaviour is cast in anthropomorphic terms and is considered cognitively complex by default. For instance, when yields from tool use or hunting increase with age, long-term learning is simply presupposed, whereas a critical reader would first like to see a rejection of the simpler alternative explanation invoking maturation of strengths or motor co-ordination. A related shortcoming is the ‘chimpocentrism’, indicated by sparse referencing to studies of other animals, even other primates. The interpretations of chimp behaviour do not really take into account that hunting roles among lions are just as cleverly co-ordinated, that monkey males have equally intricate coalitions, and that tool use by orang-utans or New Caledonian crows is every bit as flexible. Thus, phenomena thought to be unique to chimpanzees may be more widespread, and, consequently, explanations may likewise have to be more general than suggested by the authors.

Yet, in the end, such critical notes seem largely pedantic. I believe the authors’ claims about chimpanzee cognition will emerge largely vindicated, even if we will quibble about details for years to come and other taxa may be found to reach similar levels. This conclusion is not based on convincing analyses of a small set of common phenomena, but rather on the sheer weight of observations of rare and unusual behaviours. The plankroot drumming by the leader male signalling rest bouts and direction changes; the extraordinary care for the injured indicative of a high level of empathy; the occasional instances where mothers actively teach their infants how to use tools; rapid changes in one male’s pant-hoot calls following the disappearance of another. These, and many other, observations are difficult to replicate, let alone test experimentally. But if we may believe them, they support the cognitively rich interpretation of the authors that assumes chimpanzees attribute beliefs and knowledge to others, use behaviours hierarchically to reach goals as if they were subroutines in a computer program, have an understanding of causality that goes beyond contingency, and communicate symbolically.

These glimpses into the complexities of the wild chimps’ mind as compared to what has so far been brought out in most captive animals imply that the role of conditions during development is even more critical for the full realization of cognitive capacity than most of us thought. While this conclusion should not be surprising, it raises questions about the extent to which so-called enculturated chimps are exposed to similar socializing influences as wild ones, and may help us to devise ways of raising chimpanzees kept in confined housing to create equally rich chimpanzee minds.

In sum, this book will infuriate some, delight others, and bore nobody. It is essential and inspiring reading for those who use primate behavioural ecology to inform reconstructions of human evolution and explorations of human nature.

There are yet other chimps out there, no doubt holding more surprises, but in West Africa old-growth forests are all but gone, and the bushmeat trade is turning the remaining forests elsewhere into hollow shells. Or, in the Boeschs’ own words: ‘the limiting factor in our quest for human and chimpanzee identity is their survival. The fight for the survival of the chimpanzees in nature should more than ever become an absolute priority.’