INTRODUCTION

Chimpanzees (Pan troglodytes) and bonobos (P. paniscus) have a similar social structure (patrilineal multi-male and multi-female social unit; Itani, 1985). However, bonobos exhibit quite different copulatory activities from other non-human primates, including chimpanzees: (1) bonobos copulate more often than other anthropoid apes (Kano, 1989); (2) bonobos copulate in varied postures (Savage-Rumbaugh & Wilkerson, 1978); (3) copulationlike behavior often occurs in other social contexts (Kano, 1980; de Waal, 1989); (4) female bonobos exhibit lengthy estrus (Dahl, 1986); (5) suckling mothers resume sexual cycling within a year after giving birth (Kano, 1992). Some authors (e.g. Blount, 1990) have discussed these features in connection with the evolution of the sexuality of human females.

However, how different is the sexual behavior of bonobos from that of chimpanzees in the wild? Here, we compare the copulatory behavior of these two species, based on previous reports and on our field studies.

BACKGROUND

In the Mahale Mountains National Park, Tanzania, the chimpanzees of M group have been observed since 1965. The group contained about 100 individuals in 1981 (see table 3 in Nishida et al., 1990). The adult sex ratio (10 : 39) was significantly skewed toward females compared with the expected ratio of 1 : 1 (Chi-squared = 17.2, df = 1, p < 0.001; for discussion of this tendency, see Hiraiwa-Hasegawa et al., 1984; Nishida et al., 1990).

INTRODUCTION

Why do animals live in groups? Generally, animals are thought to live in groups in order to increase their survival and reproductive success. But group living incurs costs, mainly in terms of higher intraspecific competition and higher risks of parasite transmission. Therefore, the discussion has focused around the benefits that could make possible the evolution of sociality. Three main benefits have been proposed; group living decreases predator pressure (van Schaik, 1983; Dunbar, 1988), allows better exploitation and protection of food resources (Wrangham, 1980; Krebs & Davies, 1993), or results from the need for cooperative behavior, like hunting or communal breeding (Caraco & Wolf, 1975; Emlen, 1991). For more specific situations, other factors have been proposed such as rearing strategies (e.g. lions; Packer et al., 1990). In most cases, observers study animals that already live in groups, making it difficult to investigate the factors that were originally responsible for the appearance of social groups. However, we can study the factors that affect the social groups that we observe in the wild.

Predation pressure has been shown to have a large impact on group size in many animals including species of fish, birds, ungulates and primates (Pulliam & Caraco, 1984; Kummer et al., 1985; Cheney & Wrangham, 1987; Dunbar, 1988; Krebs & Davies, 1993). Similarly, seasonal variation in food supply has been shown to have a marked influence in the fragmentation of hamadryas, olive and gelada baboons and of spider monkeys (Kummer, 1971; Dunbar, 1988; Chapman et al., 1995).

INTRODUCTION

Many animals, both primates and non-primates, are characterized by permanent associations between individuals with partly conflicting interests. While the existence of these associations must mean that the parties gain from them, this does not imply that competition has disappeared. Often, animals continue to compete over resources, such as food and mates, despite association and cooperation.

For such an arrangement to work, aggressive conflict needs to be controlled and regulated so that it does not undermine relationships. Paralleling interspecific symbiosis and mutualism, individual members of groupliving species appear to enter ‘social contracts’ that optimally represent their respective interests. No doubt, some of these compromises have been worked out at the genetic level, in the course of evolution, but negotiations about the terms of a relationship may also take place as a social process. The present paper seeks to lay out a heuristic framework from which to conduct research in this area.

In order to do so, I will first critically review the current state of two approaches to social conflict: one by psychologists and social scientists, the other by evolutionary biologists. Traditionally, these frameworks have neglected the contractual perspective: not because the idea of compromise and negotiation is alien to these fields of science, but because of continued adherence to a dichotomy between aggressive competition and sociality.

INTRODUCTION

Although the great apes, as our nearest relatives, are a valuable subject for cognitive research, it remains difficult to gain insights into their mental abilities. Some of the problems are reflected in a debate between Kummer et al. (1990) and de Waal (1991) over the question of at what stage of research (anecdotal, correlational or experimental) anthropomorphic labels for behavior are allowable, if ever. Whereas de Waal uses these terms deliberately throughout his writings, Kummer and his co-authors argue that such terms should not be used unless more parsimonious alternative hypotheses are excluded by experimental evidence.

Although this discussion lays bare some of the difficulties in cognitive primatological research, it does not attack its central problem: how to go beyond anthropomorphic labeling by generating meaningful alternative hypotheses. The central thesis of the present paper is that adopting a view based on self-organization provides us with a tool to generate such alternatives.

Thinking in terms of self-structuring asks for a different way of thinking about complexity. By convention it is believed that a complex system can be understood by taking it apart and studying the pieces. This analytic procedure, also known as the ‘top-down’ or reductionist approach, boils down to a static description of the system. Supporters of the self-structuring view, however, advocate an opposite route: by studying interactions on a lower level, the emergence of a macrostructure on a higher level is perceived and therefore better understood (Hogeweg, 1988).

INTRODUCTION

Chimpanzee intelligence can be studied from two very different points of view. One is the experimental analysis of the cognitive skills of captive chimpanzees. The other is the field observation of behavioral patterns in wild chimpanzees. This paper aims to form a new bridge between the two separate fields by presenting a synthesized view of chimpanzee intelligence through research in both the laboratory and the wild.

People have believed that human beings are a unique species (Sebeok & Umiker–Sebeok, 1980; Lieberman, 1991). In comparison with other animals, humans seem to have special features: language, tools, culture and so on. These human traits have been attributed to our species' unique intelligence based on a highly developed neocortex. Are we really so unique? If so, how and why has such a unique creature evolved? What is the ultimate difference between humans and other creatures? To answer these questions, one should look not only at humans but also at the species with whom we last shared a common ancestor in our evolutionary history. Chimpanzees are the most appropriate species, because they are the closest relative of humans.

My approach may be described as Comparative Cognitive Science (CCS). This new discipline aims to understand human cognition from an evolutionary perspective. The research method is characterized by the comparison of the performance of different species based on an unified objective scale.

INTRODUCTION

The view that male–male sexual competition is lower in bonobos than in chimpanzees has recently been proposed (e.g. Ihobe, 1992; Kano, 1992). This view is based on the estimation that more estrous females are available to a male bonobo than to a male chimpanzee. (1) Maximal or semi-maximal perineal tumescence in adult females lasts for more than 20 days for bonobos at Wamba (Kano, 1992), whereas average durations of maximal tumescence for adult female chimpanzees are 9.6 and 12.5 days at Gombe and Mahale, respectively (Nishida & Hiraiwa-Hasegawa, 1987; Takahata et al., Chapter 11). There is no marked difference in cycle length, and in both species most copulations occur when females show sexual swelling (Takahata et al., Chapter 11). Hence, the sexually receptive proportion of each cycle is greater in bonobo females than in their chimpanzee counterparts. (2) Young nulliparous immigrant females of bonobos show continual estrus and the highest copulation rates (Kano, 1989). Although chimpanzee adolescent females also show semi-continuity or irregularity in genital swelling (Tutin & McGrew, 1973), they mate much less frequently with adult males (Goodall, 1968). This implies that male bonobos are attracted to adolescent swellings, while male chimpanzees are not. (3) Females of both species experience estrous cycles after conception, but sexual receptivity in pregnant bonobos appears to last longer.

Introduction

Numerous authors writing under the influence of Pavlov's (1928) seminal contribution have stressed the importance of individual differences in personality (or “temperament”) to the explanation of OCD and other dysthymic disorders (for example, neurotic depression, phobias, etc.). Most notable among these authors is Eysenck, through whose work (e.g., 1952, 1979) this personality theory approach is linked to the behavioural/learning account of OCD and phobias (see Chapter 2). A brief outline of this approach, along with some points of general relevance to it, will be followed by more detailed discussions of two recent contributions from this school – those of Gray (1982) and Claridge (1985) – and, in particular, the accounts these authors offer of OCD.

Eysenck's account, and suggested modifications of it

As discussed in Section 2.1, Eysenck considers OCD and phobias to result from the operation of conditioning mechanisms. Consistent with this, he holds that those people who are most inclined to develop conditioned responses (argued to be those who tend toward neurotic introversion) are those in whom these disorders are most likely to be observed.

Gray (1970) suggests, among other modifications of Eysenck's account, that it may only be in settings involving signals of “frustrative non-reward” or punishment that neurotic introverts are more inclined to develop conditioned responses.

Gray (1979, 1982) also denies, as does (to some extent) Claridge (1985), that it is the hypothesised greater inclination among neurotic introverts to develop conditioned responses that explains most cases of OCD and phobias.

Introduction

The standard diagnostic criteria for OCD have been challenged, and an alternative analysis has been proposed that suggests that no single feature or collection of features is both common and peculiar to all instances of the disorder. Consistent with this position, it was also argued that there is no single way in which OCD may be distinguished either from phobias or from delusional states; and various ways in which OCD may be so distinguished were presented.

The difficulties encountered by the theoretical approaches to OCD that have been reviewed are perhaps more striking than their successes, at least if one attempts to regard any of these approaches as providing a full explanation of the disorder. Nonetheless, some of the accounts that have been considered certainly offer observations and suggestions that concern some OCD patients and that may well be of importance to any valid account of these patients’ psychopathology that eventually emerges. The following observations have been presented as being of possible theoretical importance to an explanation of OCD:

1. OBSERVATION (1) Evolutionary influences may have a role in selecting the content of some OCD symptoms (stressed by some behavioural writers and some of the Pavlovian personality theorists).

2. OBSERVATION (2). The basal ganglia (among other possible biological factors) may have a role in producing at least some cases of OCD.

3. OBSERVATION (3). A neurotic temperament is displayed by many OCD patients (stressed by the Pavlovian personality theorists).

4. OBSERVATION (4). OCD is co-morbid with certain other disorders (stressed by both the Pavlovian personality theorists and Janet's account).

5. […]

Introduction

An increase of interest has recently been shown in biological approaches to OCD, and there are available a number of reviews/discussions of the findings from genetic, neuroanatomical, neurophysiological, neuropsychological and biochemical studies of OCD, as well as from studies of what have been presented as animal models of the disorder (for example, Turner, Beidel and Nathan, 1985; Rapoport and Wise, 1988; Insel, 1988; Pitman, 1989). This chapter will attempt to offer neither detailed comments on the quality of these biological findings, nor a comprehensive review of them. Instead, some of what have been claimed to be the most important of these findings will be briefly outlined, along with some of the suggestions biological theorists have offered regarding the psychological processes at work in OCD. Discussion will then focus on how powerful an argument in favour of a biological account of OCD these findings, if sound, could sustain.

Given the use of supposed animal models of OCD in some biological research, a few remarks concerning such models are in order here. (Animal models of OCD are also offered in other types of research – for example, de Silva, 1988, pp. 206–7). Reed (1985, p. 11) objects to the use of animal models in the study of OCD on the basis of his belief that the defining criteria for the disorder are phenomenological – for a thought or action to be symptomatic of the disorder, according to Reed, it must be experienced as senseless and be resisted, and it is unclear, in the case of any animal behaviour, on what grounds it could be argued that such behaviour has been experienced in this way (although see de Silva, 1988, p. 207).

An outline of the model

The behavioural/learning account of OCD (e.g., Eysenck and Rachman, 1965) is based on Mowrer's (1939,1960) “two factor” theory of learning. This approach provides very similar accounts of both OCD and phobic states. The preoccupations of OCD patients are held by this approach to concern feared stimuli that have acquired anxiety-producing properties by a process of classical conditioning. The behavioural/learning account suggests that the compulsions provoked by these feared stimuli are escape or avoidance behaviour. According to this account, this behaviour reduces or prevents anxiety and is thus reinforced by a process of instrumental conditioning. De Silva (1988) suggests that “the model is essentially one of learned anxiety reduction”. In the case of OCD, as in the case of phobias, the avoidance behaviour may be passive (for example, not approaching objects thought to be contaminated) or active (for example, checking for contamination [Gray, 1982, p. 440]). An example of an OCD escape behaviour is cleaning to remove what is thought to be some contamination.

The model is not substantially altered by the recognition that it is not only anxiety but also other forms of mood disturbance, subsumed under the vaguer term “discomfort” (Rachman and Hodgson, 1980), that is reported by some OCD patients. The maintenance of compulsions is then attributed to learned discomfort reduction (de Silva, 1988).

Consistent with this account, Rachman and his co-workers (e.g., Hodgson and Rachman, 1972; Rachman, de Silva, and Roper, 1976; Rachman and Hodgson, 1980) have shown that compulsions are indeed often provoked by environmental cues, and that when OCD patients are exposed to these cues they experience an increase in anxiety or discomfort.

Introduction

Janet's classic contribution to the literature on OCD (1903) has still not been translated into English. Fortunately, Pitman has provided a highly readable synopsis of Janet's work (1984) as well as an interesting review/commentary (1987a), which will be used as the basis of the discussion here. In his review/commentary, Pitman presents a summary of Janet's ideas in three segments, each of which will be considered in turn here; the points Pitman himself offers will be considered in the course of commenting on Janet's work. Havens (1966) also provides an interesting account of Janet's contribution, some points from which will be briefly discussed in what follows, as will some of Reed's (1985) comments on Janet.

Janet on the clinical stages of psychasthenic illness

Janet includes OCD, among other conditions, in the category he terms psychasthenic illness. He divides this category into three stages, these being, from the least to the most severe, the psychasthenic state, forced agitations, and obsessions and compulsions. According to Janet, patients develop the less severe stages of the illness before the more severe and, similarly, lose the more severe stages of the illness before they lose the less severe.

The first stage of the illness – the psychasthenic state – involves the patient's feeling that actions have been unsatisfactorily or incompletely performed. Incompleteness in “perceptions” is also present, consisting of such experiences as derealisation and depersonalisation. Indecision, amnesia, poor control of thoughts, and “emotional insufficiencies” (that is, an inability to experience emotions fully) are reported by patients.