The Mentalities of Gorillas and Orangutans

ANIMAL BEHAVIOUR, 2000, 59, 657–663 doi:10.1006/anbe.1999.1336, available online at http://www.idealibrary.com on

Book Reviews the social conditions (high density of population such that each individual will have ample opportunities to observe and learn about tool use throughout its life). Although this may explain the data from wild populations the question remains why this happens so often in captivity. The ‘human caretaker environment’, in which ample opportunities exist to observe the use of tools, and the ‘ecological’ conditions, in which ample opportunities and leisure time exist to invent tools, may be contributing factors (chapter by Boysen et al.). This is an interesting area of research. In any case it is clear that individual gorillas and orang-utans do have the capacity to develop tools. To what extent they devote this capacity to other purposes under other conditions and why this is the case remain to be determined. The chapters on communication are basically chapters about communication with humans using either (American) sign language (ASL) or ‘visual symbolic language’ (VSL). A most interesting chapter is that by Tanner & Byrne in which the development of gestural communication in a group of zoo-living lowland gorillas is explored. One question about ASL is whether it moulds on an ability that is present but rarely used or whether it needs a close enculturation with humans and thereby may create a new capacity, in which case the gestures become part of living in the ‘human created niche’. According to Tanner & Byrne these gorillas do develop iconic and deictic gestures among themselves under these zoo conditions. The question still arises to what extent this is specific for such conditions. The last part of the book, on social cognition, is a collection of different topics such as mirror selfrecognition, deception, imitation, teaching and the development of play. The chapter on mirror selfrecognition by Swartz et al. is clearly directed at putting the gorillas and orang-utans alongside chimpanzees. Swartz et al. present a table of all studies on mirror self-recognition to show that no significant differences (chi-square test) exist between species as to the percentages of animals with positive scores, e.g. mark test (percentages, number of animals): chimpanzee 43%, 97; bonobo ?, no data; orang-utan 50%, 6; gorilla 31%, 13. However such tables are sensitive to whether all data are included (e.g. Kitchen et al. 1996 is missing (six of six chimpanzees showed a positive score)) or whether new data appear (e.g. none out of two gorillas in Shillito et al. 1999). Furthermore, and more importantly, as we have discussed (de Veer & van den Bos 1999) such comparisons are justified only when the data are not confounded by for example differences in rearing conditions. For instance, in contrast to chimpanzees, it appears that only home-reared gorillas reliably show evidence of mirror self-recognition. In both the preface and the epilogue the editors give yet another reason for this book: to demonstrate the usefulness of the cladistic approach of comparative data. Begun’s chapter on this topic nicely explains the principles underlying this methodology. Cladograms are trees built on changes in character states in species of interest

The Mentalities of Gorillas and Orangutans. Comparative Perspectives. Edited by SUE TAYLOR PARKER, ROBERT W. MITCHELL & H. LYN MILES. Cambridge: Cambridge University Press (1999). Pp. x+419. Price £50.00. This book is the fourth edited volume of a series on cognition in great apes and deals specifically with mental life in gorillas and orang-utans. It has four sections: (1) comparative evolutionary and developmental perspectives on gorillas and orang-utans (three chapters); (2) cognition and tool use (six chapters); (3) communication (four chapters); and (4) social cognition (five chapters) in gorillas and orang-utans. In the epilogue the editors attempt to bring the information in these sections together into a coherent comparative perspective. In the preface the editors set out their aim: to move away from the chimpocentric approach to the study of cognition; that is, much attention has been given to, and much comparative work has been done using, chimpanzees (and bonobos) at, what the editors believe, the expense of gorillas and orang-utans. They attribute this imbalance to (1) the greater number of captive chimpanzees creating a large pool of study subjects, (2) the greater number of detailed field chimpanzee studies and (3) the appeal that chimpanzees have because of their ‘humanlike’ social (e.g. warfare) and cognitive (e.g. tool use) capacities. Whether these reasons hold on closer scrutiny is of less relevance than the fact that in general there is indeed a strong bias towards chimpanzees in the great ape behaviour database. For instance, in Swartz et al.’s chapter on mirror self-recognition the numbers of study subjects are (in declining order): 163 (79.1%) chimpanzees, 21 (10.2%) gorillas, 16 (7.8%) bonobos and six (2.9%) orang-utans. So, strictly speaking this book should have included bonobos, although the editors themselves seem to include them within this chimpocentric view anyway. Given de Waal & Lanting’s (1997) book Bonobos: The Forgotten Ape, this hardly seems justified. In similar vein one could argue that gibbons and siamangs should have been included. The behaviour of these lesser apes may put the behaviour of both great apes and Old World monkeys in perspective. So, the chapters are all directed at exploring the mentalities of gorillas and orang-utans. The chapters on tool use reveal that both use tools. However, clear differences exist as to the conditions under which they do so. Both gorillas and orang-utans have been observed to use tools regularly in captivity but rarely in the wild despite extensive observations (the same seems to apply to bonobos). However, in their chapter Fox et al. describe tool use in a wild orang-utan population living at the Suaq Balimbing Research Station, Sumatra, Indonesia. To account for their findings, they suggest a complex interaction between the likelihood of inventing tools per se (low) and maintaining the invention in the population, which is dependent on the ecological conditions (density of items that can be obtained with a tool and the success of tool-foraging effort per tool-manufacturing effort) and 0003–3472/00/030657+07 $35.00/0

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(the ingroup) compared with a closely related set of species (the outgroup). The characters should be informative, that is they should be able to differentiate between species. So characters that are only absent in the ingroup and present in the outgroup are not informative for the relationships between the ingroup species. Several independent cladograms can be used to construct phylogenetic trees, which give an indication of the way species have evolved. Characters and their states can also be plotted on existing phylogenetic trees to reveal their state changes. This is not similar to creating cladograms. In both cases characters and their respective states have to be defined beforehand. The editors use the plotting technique but unfortunately they do not use this method to its fullest extent in their comparative approach. They combine the data on great apes to produce tables or statements of what is present or absent in these apes in captivity or the wild and discuss whether the trait (deception, self-recognition, etc.) is present or absent in their common ancestor. Implicitly they seem to assume that the trait is absent in the common ancestor of the great apes and lesser apes or the common ancestor of apes and Old World monkeys. Implicitly therefore their analysis often reduces these traits to characters with only two states: present (1) or absent (0). In their attempt to put gorillas and orangutans on the stage the editors have eliminated the possibility of differences between great ape species. They have not defined characters and the states thereof beforehand and sufficiently well to use a plotting technique. Their cladistic approach often leads to a set of noninformative characters for the ingroup under study, namely the great apes, since the character states do not give any information about possible differences between the species involved. The question arises whether more than one character state exists for the different characters. So, rather than suggesting that there is no difference between species, it would have been more interesting and appropriate to determine whether and how a character might differ between species. Finally, the book contains a chapter by Semendeferi on the frontal lobes and cognitive processes of great apes with a focus on gorillas and orang-utans. Indeed, analysing the differences in the neural network that supports the cognitive capacities of apes is crucial for understanding the differences between species in terms of hardware. We have shown how the cladistic approach can be fruitfully applied to reveal such patterns in the neural organization underlying theory of mind in primates (van den Bos et al. 1998). In sum this book contains much valuable information on gorillas’ and orang-utans’ mental life but is not well organized from a comparative perspective. RUUD VAN DEN BOS MONIQUE DE VEER Animal Welfare Centre, Utrecht University, Yalelaan 17, NL-3584 CL Utrecht, The Netherlands References van den Bos, R., Nolten, C. & Van Veller, M. 1998. Phylogenetic reconstruction of a neural network underlying Theory of Mind in primates. European Journal of Neuroscience, Supplement 10, 10, 197.

Kitchen, A., Denton, D. & Brent, L. 1996. Self-recognition and abstraction abilities in the common chimpanzee studied with distorting mirrors. Proceedings of the National Academy of Sciences U.S.A., 93, 7405–7408. Shillito, D. J., Gallup, G. G. Jr & Beck, B. B. 1999. Factors affecting mirror behaviour in western lowland gorillas, Gorilla gorilla. Animal Behaviour, 57, 999–1004. de Veer, M. W. & van den Bos, R. 1999. A critical review of methodology and interpretation of mirror self-recognition research in nonhuman primates. Animal Behaviour, 58, 459–468. de Waal, F. & Lanting, F. 1997. Bonobos: The Forgotten Ape. Berkeley: University of California Press.

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Mammalian Social Learning: Comparative and Ecological Perspectives. Edited by HILARY O. BOX & KATHLEEN R. GIBSON. Cambridge: Cambridge University Press (1999). Pp. xiv+424. Price £60.00. This volume is often about what we do not know rather than what we do. Around half of the 21 chapters describe the natural history of a species or group of species with particular attention to their social organization. Each author then discusses the likely opportunities for the animals to learn from their conspecifics, presenting field studies and anecdotes that may be highly suggestive of social learning but fall short of providing definitive evidence for it. The chapters by Lee & Moss on elephants and by Gilbert on bears exemplify this approach. The observations reported are the fruits of persistent and ingenious fieldwork, but the reader is nevertheless left with a sense of how much more needs to be done before we really understand social learning in that animal. Some chapters review both field observations and controlled experiments, and these contributions lead to a more fleshed-out picture. For example, Kitchener’s chapter, on young learning from their mothers among the Felidae, integrates field observations of big cats with experimental work on domestic cats. Kitchener establishes that social learning is important in allowing young cats to identify appropriate prey species and to perfect their killing techniques. A few chapters describe original, well-constructed experiments that really pin down an instance of social learning. Laland’s chapter describes a series of transmission chain experiments using rats, and establishes that a novel foraging technique can be passed along a sequence of animals. Hudson, Schaal & Bilko´ look at the ways in which young European rabbits learn food preferences from their mothers, and show that multiple mechanisms exist: transmission occurs in utero, through suckling, and via faecal pellets. The first four chapters of the book are theoretical or position pieces, including Box’s argument that individual differences in temperament will mean different opportunities for social learning, and a piece by Sibly applying some rudimentary cost–benefit results from signalling games to the social learning case. The editors are aware that humans, hominids and apes are mammals too, and the book covers these groups in the concluding four chapters. For example, Byrne discusses the ability of apes to imitate behavioural programmes, and Mithen makes the surprising claim that the archaeological record, 

2000 The Association for the Study of Animal Behaviour