AGGRESSIVE BEHAVIOUR

any action of an animal that serves to injure an opponent or prey animal or to cause an opponent to retreat. The term is used in many different ways, however, and no single definition can possibly cover all of its meanings. When considering human aggression, for example, some psychiatrists consider any act that has destructive consequences (including suicide) to be aggressive. (For a discussion of aggressive behaviour in man, see emotion.) Thus, the role of aggression in behaviour has beenand continues to bedebated by psychologists and ethologists, as is the meaning of the term itself. Frequently, aggressive behaviour encompasses both attack and defense. Other investigators exclude food-gathering behaviour, though it may involve attack on another animal. In order to avoid these ambiguities of definition, a distinction must be made between causation, function, and description of observed behaviour. It is frequently assumed that a single motivational system (aggression) causes all recognizably aggressive behaviour in higher animals. This assumption is certainly invalid for invertebrates and for most higher vertebrates, in which a variety of motivational bases appear to exist. A motivational definition of aggression is thus difficult. The only possible rigorous approach is to list patterns of behaviour, usually held on both functional and causative grounds to be aggressive. Because aggressive behaviour has been most studied in mammals, mammalian behaviour will be examined here first as a basis for comparison with other animals. any action of an animal that serves to injure an opponent or prey animal or to cause an opponent to retreat. Animals develop their aggressive tendencies over time. Young animals often engage in play fighting with each other, mimicking adults in all but the finaland hurtfulsteps. A kitten playing with an inanimate object is another example of a young animal rehearsing for more serious activity to come. Sexual maturity is brought on by the secretion of sex hormones within the body, some of which are also associated with aggressive behaviour. Although many females are capable of aggressionto protect their young and to huntmale sex hormones (androgens) are more closely associated with aggression. For example, red deer stags given the androgen testosterone at any time of the year will return to their regular mating grounds and will lose the velvet covering on their antlers in preparation for territorial battles, even in the absence of females. An aggressive act may be caused by various stimuli. Within its own group, an animal must display aggressive postures to maintain its position within the hierarchy. The mere threatmanifested by ruffled feathers or teeth revealed in a snarlis usually sufficient to maintain an already established social order. The pecking order of chickens is a well-known example of a hierarchy maintained where many animals share the same territory. If family groups are smaller, the boundaries of neighbouring territories may be established by bird calls or scent marking, but these would be insufficient if they could not be reinforced with a physical threat to keep out intruders. Conspecific hostility (fighting with a member of one's own species) is also found just before the mating season, when males win their choice of females and territory. As in juvenile play fighting, the interests of the species are not served by actual combat, so that most animals in conspecific disputes have developed distinct postures that signify submission. The exposed throat of a dog, for example, will immediately inhibit attack; among some baboons, a male will indicate submission by assuming the receptive posture of a female in heat. Humans also have signs of submission, ranging from weeping in the face of an enemy to the formal presentation of one's neck to a sovereign's sword, but none of these measures brings about an instinctive halt to aggression as it does with other animals. Additional reading S.A. Barnett, A Study in Behaviour (1963), is a general work with particularly useful sections on aggression. Konrad Lorenz, On Aggression (1966; originally published in German, 1963), is a highly readable account. Silvio Garattini and E.B. Sigg (eds.), Aggressive Behaviour (1969), discusses modern theories and experiments on aggressive behavioral responses of animals. Bruce B. Svare (ed.), Hormones and Aggressive Behavior (1983), is an overview intended mainly for graduate students and beginning researchers. Kevin J. Flannelly, Robert J. Blanchard, and D. Caroline Blanchard (eds.), Biological Perspectives on Aggression (1984), deals mostly with aggression in rodents and is readable by experimental psychologists, biologists, and others who already have some familiarity with the subject of aggression in animals.