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This article appeared in Volume 3 (1) of The Semiotic Review of Books.
Chimpanzees of the Mahale Mountains. Sexual And Life History Strategies. Edited by Toshisada Nishida. Tokyo: U. of Tokyo Press. 1990. (ISBN: 4-13-068153-2)
This study provides a fascinating comparison to Jane Goodall work on the Gombe chimpanzees. For at least 25 years the two studies ran in parallel in similar habitats, less than 200 kilometres apart on the shores of Lake Tanganyika. Together they provide us with a broad spectrum of information allowing us to ascertain and assess the similarities and differences between two chimpanzee populations. This is important because we are learning that in spite of underlying similarity of demographic pattern and environmental exploitation, there are important differences between populations in their biocultural relationships with each other and their habitat.
Since Goodall's work was mainly published in English and has received support from organizations promoting the use of film, such National Geographic, most people are much more aware of her work than they are of the Japanese research program. Nishida's book is an effort to collect and make available in English a comparable set of data on the male chimpanzees. All the articles have been written especially for this book, but they refer to material previously published in a wide variety journals, dircting the reader to sources describing work earlier in detail.
The eleven authors who are represented in this collection are not all of those who have conducted work at Mahale Mountains. Chapters 4 through 15 were very specific studies well bolstered with statistical support for the questions examined. These covered a wide range, from age differences in consumption of ants, sex differences in ranging patterns, sperm competition, and mating behaviours, to adult male social relations with adult females.
Among the more fascinating chapters is the material on demographic and reproductive profiles which can only come from a long term study of known animals, and is so important for our understanding of life history patterns and conservation. The information that over a 10 year period in one group of these chimpanzees deaths equalled births (74) in a population which is not hunted for food and living in a National Park, reinforces the realization that chimpanzee populations are basically in a no growth stage. Of 107 animals born in 22 years, 56, or 52% died before weaning of a combination of disease, aggression, death of mother and unknown causes. As a matter of fact, chimpanzee intra-species aggression, particularly infanticide by males, was responsible for 18% of the deaths, and may be a major factor in holding the population size constant. A confounding factor in determining precise population size is emigration of females, often at about age 11 ± 1.5 years and the return immigration of other females of unknown age. Because of this there are no known ages at first birth. Although these can be closely estimated, one notable difference between this population and the situation at Gombe, is that a number of natal females remained in the Gombe population to breed, and had their first live offspring at 13-14 years of age. The information from Mahale suggests that it takes immigrant females an average of about 3 years to become pregnant. They must establish relationships with males, learn a foraging area and develop relationships with other animals. During this period they run the risk of being attacked by females, disease, exhausted by stress, failure to consort and the possibility that they will leave this community, and go through the same process in attempting to move into another one. As a result the estimated age at first birth is about 14-15 years -- range 12 to 20.
The median number of births per female was 3 with a median number surviving to reproduction of 2 offspring per female. It is also not clear that if the females who disappear from a group survive long enough to establish themselves in a new group, so the death rate may be even higher than estimated. These figures reinforce the information of stable population size from Gombe, even though there is an argument that human disease (polio) disrupted the normal demographic pattern at Gombe. The mounting tide of statistics on population size is clearly relevant in decisions about "harvesting" wild chimpanzees for use in medical and behaviourial research. Nishida does not comment on this problem.
However, the overview of chimpanzee behaviour at Mahale in the first chapter by Nishida is a fine summary and will permit easy comparison with other material on chimpanzees. Nishida notes some of the most salient comparisons with material from Gombe and the Budongo forest such as material on incest, tool use and greeting gestures. The primate background to mother-son, brother-sister and father-daughter mating has long been an interesting focus for those investigating the human condition. Many aspects of group formation are considered to be adaptations to prevent serious levels of inbreeding in primates. These include offspring dispersal in monogamous forms, male emigration in multi-male groups, periodic male replacement in single male groups, and, among chimpanzees, female emigration. The most clearly recognizable incest is between mothers and sons, since in most cases fathers of offspring are not known with accuracy. Mother-son mating does occur with pre and post post-weaning offspring, both in chimpanzees and rhesus macaques (Fedigan 1982). Nishida reports pairs of mothers and immature sons in which he says mating was often seen, but that in the only case of a mature son mounting his mother, she threw him out of the tree, and he didn't try it again. Goodall in contrast, reported some episodes of mothers mating with mature sons (1986). This behaviour may have had other relevance than reproductive. For example it may have allowed the son the opportunity to assert himself over a female in the presence of other males. Brother-sister and father-daughter mating was not seen in Mahale because all natal females emigrated as late adolescents. In Gombe, Fifi was seen to scream and attempt to fight off her brothers when they tried to mate with her, even though she persistently solicited mating from all the other males. These observations of a persistent, but not universal avoidance of incest, and its variability by age suggest that the inhibitors tend to be social rather than biological factors which come into play when the relations between adult males and females are confounded by the relations between mothers and offspring.
Another area in which comparisons with the Gombe material are interesting is the variability in subsistence activities. Of particular interest is the difference in ant fishing techniques and the species of ants eaten. Gombe chimps eat driver ants which they fish for using a long stick. Mahale chimps eat a number of species of Camponotus and Crematogaster ants which they lick up after chewing into nests. However, Mahale chimps occasionally use long sticks for extracting a nesting bird from a hole in a tree. Differences in culturally transmitted behaviours such as these are indicative of the behaviourial plasticity of chimpanzees, but the uniformity of prey species and extraction techniques within communities, suggests a basic conservation. Nishida notes that in spite of the thousands of hours of chimpanzee observation, the adoption of a new habit has not been seen. New foods have been added to the food list after humans were translocated, leaving cultigens behind. In some cases adult females were observed to initiate their use, unlike the patterns reported for some macaques.
Greeting and grooming gestures also show some differences between the two populations. The mutual grooming hand clasp is an unusual behaviour seen among Mahale chimpanzees, and not seen among other groups. Other aspects of coupleship behaviour such as a leaf clipping display were also used in different contexts among Mahale chimpanzees. These comparisons help us to understand where areas of variability occur in the behaviourial template of chimpanzees. However a more organized presentation of these areas of comparison, with input from all available studies of free ranging chimpanzees would have turned some very interesting comparisons into a truly valuable tool to explore the ranges of labile behaviours.
The only summarizing essay, after the background of the study and the ecological parameters of the region are explored, is the final piece on deception in chimpanzees, which brought together some of the anecdotal material involving deception seen by various researchers over the years and compared them with some other published accounts. In this I feel that the book has not lived up to the exhortation by Itani "not to forget the Kyoto University African Primatological Expedition tradition of extensive study from a "birds eye view" (Preface). It is Goodall's ability to move back and forth from the specific to the general which makes her work so readable to the non-specialist. Nishida's book is very valuable in the detail and insight provided in discussing particular research questions, but it lacks the overview from a population perspective. A concluding chapter which referred to the studies presented in the book and summarized their content, drawing general insights into Mahale chimpanzee behaviour would have been very useful it would have permitted rapid comparison to be drawn between this population and others which have been studied, and contributed to a general understanding of chimpanzee behaviour.
Nonetheless this book provides an excellent compilation of material some of which was previously unavailable to western researchers. The history of establishing the study site is a clear example of how perseverance can eventually result in longterm success. The major advantage of this material is its long time span which allows comparisons to be drawn with both the type of data short studies provide and other long term ape research.
The tables, photographs and maps included also contribute substantially to the overall appeal and usefulness of this book. It will serve as a valuable addition to the resources of those engaged in studying primates' social life and communication.
Fedigan, L. (1982) Primate Paradigms. Montreal: Eden Press
Goodall, J. (1986) The Chimpanzees of Gombe. Cambridge: Beinap Press of Harvard University Press.Anne Zeller is an Associate Professor in the Department of Anthropology at the University of Waterloo (Canada). She has recently been conducting fieldwork in Indonesia (Kalimantan) on the adult-infant social relations in Macaca fascicularis (crab-eating macaque). She is the author of a study of visual and vocal communication in Macaca sylvanus in Primates: recherches actuelles. J.J. Roeder and J.R. Anderson (eds.) Paris: Masson (1990). Among her other publications are: "Comparison of component patterns in threatening and friendly gestures in Macaca sylvanus of Gibraltar", in Current Perspectives in Primate Social Dynamics. D.M. Taub and F.A. King (eds.) New York: Van Nostrand Reinhold Press, 1986. (487-504), "Primate Facial Gestures: A Study of Communication" in International Journal of Human Communication (1980) 13.4: 565-606.