«Abstract This paper aims to characterise the aggressive behaviour of great apes: the orang‑utan, the gorilla, the chimpanzee and the bonobo. We ...»
Are great apes aggressive?
A cross‑species comparison
Cláudia Sousa1,2,, Catarina Casanova3,4,5,
1Department of Anthropology, Faculty of Social and Human Sciences, New University of Lisbon, Portugal;
2CRIA – Centre for Research in Anthropology, Portugal; 3 ISCSP – Advanced Institute of Social and Political Sciences,
Technical University of Lisbon,Portugal;4 CAPP – Center of Administration and Public Policies,Technical University of Lisbon,
Portugal; 5CBA – Environmental Biology Center,University of Lisbon,Portugal; 6APP – Portuguese Primatological Society firstname.lastname@example.org
This paper aims to characterise the aggressive behaviour of great apes:
the orang‑utan, the gorilla, the chimpanzee and the bonobo. We start by discussing the lack of consensual definitions for terms such as violence, aggression and ago‑ nistic behaviour. Secondly, we describe the evidence of aggression in each species.
Finally we describe several referential models developed to explain the way of life and aggressive behaviour of the first hominins through insights provided from the behaviour of non‑human primates.
Key words Aggression; great apes; models.
Resumo O presente artigo tem como objectivo caracterizar o comportamento agressivo dos grandes símios: orangotango, gorila, chimpanzé e bonobo. Come‑ çamos por discutir a falta de definições consensuais para termos como violência, agressão e comportamento agonístico. Posteriormente são descritas as evidências de agressão para cada espécie. Por fim, são descritos vários modelos referenciais desenvolvidos para explicar a forma de vida e o comportamento agressivo dos pri‑ meiros hominínios, através de evidências vindas do comportamento dos primatas não‑humanos.
Palavras‑chave Agressão; grandes símios; modelos.
“When I asked Samoan informants about the feeling of alofa ‘love’ which exists between parents and children, I was surprised to learn that many of them believed a father’s beating was an appropriate sign of his love” (Gerber, 1985:131).
Antropologia Portuguesa 22/23, 2005/2006: 71-118 Cláudia Sousa, Catarina Casanova Conceptual framework: aggression, violence and dominance In the past, aggression was seen by psychologists as “a socially negative tendency that poses serious problems to society” (de Waal, 1996b:159), i.e., an anti‑social behaviour resulting from both internal and external factors on the individual.
The term ‘aggression’ has proven remarkably difficult to define in a manner pleasing or useful to all disciplines. Between primatologists and ethologists in general, there is little or no agreement regarding the definition of aggression (Fedigan, 1992; Silverberg and Gray, 1992; Casanova, 2003).
According to Hinde and Groebel (1989), behaviour directed towards causing physical injuryto another individual is labelled as aggressive.
Silverberg and Gray (1992) note that aggression is used in the behavioural domain as a synonym for an intense assault against some object(s) or some other being(s). Thus, aggression could be defined as “any behaviour directed toward the goal of harming or injuring another living being who is motivated to avoid such treatment” (Baron, 1977: 7), or as “one of the means (of a party) to test and to provoke the other, and to make each party’s interest clear” (de Waal, 1996b: 162). To Wilson (1975: 577), aggression is a “physical act or threat of action by one individual that reduces the freedom or genetic fitness of another”. Siann (1985: 12), on the other hand, distinguishes aggression from violence by stating that while aggression “involves the intention to hurt or emerge superiors to others, but does not necessarily involve physical injury, violence involves the use of great physical force or intensity and, while it is often impelled by aggressive motivation, may occasionally be used by individuals in a mutual interaction which is regarded by both parties as intrinsically rewarding”.
The difficulty in defining the term aggression lies in the heterogeneous nature of a collection of terms that bear a family resemblance to the concept (e.g. forcefulness, ferocity, conflict, force, violence, combativeness, etc.).
Hinde and Groebel (1989) distinguish between conflict, conflict resolution, aggression, attack, violence, competition, and even war. To these authors, violence implies inflicting of physical harm to another individual (or object).
The harm inflicted is usually intended to be severe, although it may not be.
As for the term conflict, Hinde and Groebel (1989) refer to it, in a broad sense, as a disagreement over status or the allocation of feeding or social resources. A conflict may occur between individuals or groups, and usually Are great apes aggressive? A cross‑species comparison 73 implies that the individuals involved perceive the situation as one that can be won or lost. Thus, when a resource is limited, there is competition over it. While competing, participants may not be aware of the conflict since both parts may, for example, search for food independently. Finally, war is defined as a special type of aggression: it involves aggressive groups in which the individuals are in some degree organized towards achieving a common goal. It is usually institutionalized (although not always), with individuals occupying distinct roles (Hinde and Groebel, 1989). According to Silverberg and Gray (1992), aggression is used in different domains: the social domain (an intersocietal situation that is characterized by such violence); in the communicative domain (for a suggestion or equivalent of violence); and in the psychic domain (for an emotional discharge). Thus, the term is used to characterize the acts of individuals and social groups and is applied both to acts and to the readiness to initiate an act.
While for many purposes it is convenient to group together as aggressive behaviour all instances in which individuals or groups direct their behaviour so as to harm others, this category conceals considerable internal heterogeneity (Hinde and Groebel, 1989). This is reflected in the numerous attempts that have been made to classify aggressive acts into distinct sub‑categories. When referring to childhood aggression, both Feshbach (1964) and Manning and colleagues (1978) define aggression by relating the term to its underlying
1) instrumental or specific aggression (concerned with obtaining or retaining particular objects or positions or access to desirable activities);
2) hostile or teasing aggression (directed primarily towards annoying or injuring another individual);
3) defensive or reactive aggression (provoked by the actions of others), and
4) games aggression (involving deliberate attempts to inflict injury escalating out of physical games).
Tinklenberg and Ochberg (1981) classified aggressive violence in adolescents into 5 categories: instrumental, emotional, felonious, bizarre, and dissocial. These and other attempts to categorize aggression often provide additional clarification. Still, no typological system is wholly satisfactory (Hinde and Groebel, 1989). It is difficult to find a cross‑cultural valid Cláudia Sousa, Catarina Casanova “etic” definition of violence such that its use can command considerable inter‑observer reliability (Silverberg and Gray, 1992). The problem may not only lie in the fact that authors use different conceptual frameworks, but these same authors (and respective frameworks) are also influenced by the culture in which they live (Costa, 2004; Casanova, 2006). Thus, what can be labelled violent and aggressive in one culture may not be classified the same way by a different culture.
Aggressive behaviour involves behaviour by individuals, and thus necessarily depends on behavioural mechanisms within individuals (Hinde and Groebel, 1989). Episodes of aggression may involve an interaction between 2 (or more) individuals and an interaction refers to a series of exchanges occurring within a limited span of time (Hinde and Groebel, 1989). The nature of each interaction will be affected by the features of both individuals involved. If two individuals often interact aggressively, we may say that they have an aggressive relationship. The nature of any particular relationship depends on the nature and patterning of the interactions of which it is composed. Simultaneously, the nature of a relationship affects the nature of its constituent interactions, because the individuals concerned guide their behaviour according to their experience within and expectations for that relationship. And, in the longer term, the behaviour individuals can show is affected by the relationships they have experienced. Relationships are a set within networks of other relationships such as family groups and work mates, among others. Each relationship is affected by the nature of the group, and the nature of the group depends upon the constituent relationships (Hinde and Groebel, 1989). Thus, according to Hinde and Groebel (1989) it is useful to consider a succession of levels of social complexity: individuals, interactions, relationships and groups, all with a two‑way causal relationships between them.
Ethological studies have demonstrated that emotional displays of anger most commonly serve to reduce the likelihood of aggression between two organisms. This means that a connection between anger and inflicting harm is not an automatic one: the primary adaptive function of anger is expressive and is not to inflict harm. The expression of anger serves as a warning signal to others (Feshbach, 1989). As stated by Hinde (1974) aggressive behaviour is that directed to cause physical injury in other individuals. “In primatology the term (…) is frequently applied to all sorts of self‑assertive behaviour – displays, supplantation (…) and yet as Barnett (1968) notes, the intent of Are great apes aggressive? A cross‑species comparison 75 these signals may not be to cause physical injury, but to induce withdrawal of another animal” (Fedigan, 1992: 73). This means that individuals may behave aggressively without engaging with opponents in attacks (but by inducing withdrawal). Thus an animal may exhibit agonistic behaviour without physically attacking his/her target. Sometimes, agonistic behaviour may have the purpose of avoiding violence between individuals, which may have high costs (Casanova, 2003). Agonism does not equate with violence since violence is its most extreme form, but not the most common (de Waal, 1989b). In order to constitute agonism, the action must be composed of several specific behaviour patterns [like chasing and biting (de Waal, 1989b)]. Aggression can be seen as non‑vocal threats (attacks and displays), and aggressive and submissive behaviour (Chapais, 1991). Aggressive behaviour develops during infancy, when infants join their mothers and siblings in their acts (Chism, 1991). Thus, there are scaling acts along a continuum of violence ranging from anti‑violent, through non‑violent and to violent. Hinde and Groebel (1989) also point out the fact that there is a mosaic of elements of attack and threat. An attack on another individual usually involves risk of injury for the attacker. The attack is associated with self‑protective and withdrawal responses. Because of the close association between the elements that constitute the mosaic, many authors lump together attack, threat, submissive and withdrawal behaviour as agonistic behaviour, even though some types of behaviour in this category are clearly aggressive and others are not (de Waal, 1989b; Hinde and Groebel, 1989). To Fedigan (1992) a working definition/operational term such as ‘agonistic behaviour’ is suitable.
Dominance has typically been associated with aggression and competition, although primates often compete without being aggressive towards each other (Walters and Seyfarth, 1987). Although hierarchies of dominance are constructed mainly on rank interactions (formal or ritualised), which may be peaceful, disruptive or aggressive (de Waal, 1989a,b), dominance rank may not be synonymous with aggression and violence (or agonism). According to Lee and Johnson (1992: 392), dominance “is defined either by the ability of one animal to take a resource from another, or by its ability to make another avoid or submit during an approach or aggression.