Aggression

I

Introduction

Aggression, form of animal behavior characterized by an assault or attack by one animal on another. Aggression can take two forms. One form of aggression is conflict between members of different species (interspecific aggression). It can include predatory aggression (food obtaining), defensive aggression, and aggression directed at competitors for resources such as food or water. Aggression of this sort typically does not involve emotions such as anger and can be regarded as a component of feeding and maintenance behavior.

A more significant kind of aggression involves attacks directed toward members of the same species (intraspecific aggression). Such fighting is observed in virtually all vertebrate species. Fish lock jaws and nip each other; birds attack one another, rats wrestle, kick, and occasionally bite; and steers, sheep, and goats butt their heads together. Animals fight in ways that are programmed by their genes—usually over some scarce resource. This kind of aggression exists because members of a given species have very similar needs and therefore find themselves in direct competition with one another for food, mates, and dwelling spaces. The form intraspecific aggression takes is determined in large part by the relative risks and potential benefits of the aggressive encounter. Some animals such as male sea elephants will fight to the death over possession of a breeding harem because defeat is equivalent to genetic suicide. Male American elk, on the other hand, engage in pushing contests with their antlers. When one becomes tired he retreats from the contest with the prospect that next year's mating season may bring better results. The antlers are not used to stab or wound and are shed at the end of the mating season. Most intraspecific aggression is of this sort and does not result in significant bodily harm.

II

Limiting Aggression

Because combat is dangerous and can lead to serious injury or death, evolutionary mechanisms tend to restrain the intensity of intraspecific aggressive behavior. One way aggression is minimized is through a genetically programmed tendency to establish territories. In this way conflicts are usually limited to occasional border skirmishes. The ritualization of aggressive behavior is another genetically programmed restraint on combat. Poisonous snakes wrestle without using their fangs; mountain sheep butt with well-armored heads without inflicting injury; some lizards make threat displays by expanding a skin fold in the throat; and apes shake branches, gesture, and shout fearsomely. The advantage of ritualization of combat is that even a sure winner has a great deal to lose if it becomes debilitated as a result of a fight. (The advantage to the probable loser in having the stronger animal not push its advantage is obvious.) An injured or exhausted victorious animal may not be able to defeat the next opponent and may become vulnerable to predation by other species. Therefore, most species have clear signals that indicate acceptance of defeat and terminate combat before injury occurs: A lizard will crouch; a cichlid fish will retract its fins; a stickleback will adopt a vertical posture; a dog will expose its unprotected belly; and a gull will offer the unguarded back of its neck to its opponent. Each of these maneuvers signals acceptance of defeat and immediately halts further aggression.

III

Aggression in Humans

Learned experience is an important determinant of aggressive behavior in humans. Elicitors of aggression such as personal insults, status threats, and the presence of weapons are all learned sources of aggressive behavior. Further, aggressive actions are often followed by rewards and are therefore likely to be repeated. Children learn that aggression can enable them to control resources such as toys and parental attention. Children also learn aggression by observing others behave aggressively. The violent behavior of some teenage gangs provides its younger members with aggressive role models. Children whose parents discipline with physical force tend to use more physical aggression when interacting with others, and parents who abuse their children were typically abused children themselves. The influence of the mass media, especially television, on promoting aggressive behavior is not yet well understood, but a growing body of research evidence indicates that watching violent entertainment is linked to subsequent aggression.

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See Animal Behavior; Sociobiology.

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