Aggression is usually defined as behaviour intended to injure another person (either physically or verbally) or to destroy property.
The key word is intent, if I accidentally step on your toes in a crowded elevator and immediately apologize, you are not likely to label my behaviour, aggressive. If I walk up as you sit at your desk studying and stomp my foot down on yours, you are apt to respond with outrage at such a blatantly aggressive act.
But it is also clear that even intentional aggressive acts can serve goals other then inflicting injury.
Any specific act can satisfy a wide range of possible motives. Power, wealth, and status are only a few of the ends that can be attained by aggressive means.
Some psychologists distinguish between:
(1) hostile aggression, the sole aim of which is to inflict injury; and
(2) instrumental aggression, which is aimed at obtaining rewards other than the victim’s suffering. Instrumental aggression would include such behaviour as assault during a robbery, batting to defend the rights of an undergo, or fighting to prove one’s strength and power. But the distinction is not clear cut.
Freud viewed aggression as one of two basic instincts. The energy of the death instinct build up within the organism until it must be discharged, either outwardly through overt aggression or inwardly in the form of self-destructive acts. Freud was pessimistic about the possibility of ever eliminating aggression.
Later theorists in the Freudian tradition rejected the idea that aggression was an innate drive or instinct and proposed that it was a frustration-produced drive.
The frustration-aggression hypothesis assumes that thwarting a person’s efforts to reach a goal induces an aggressive drive which, in turn motivates behaviour designed to injure the person or object causing the frustration (Dollard and others, 1939).
The expression of aggression reduces the drive. Aggression is the dominant response to frustration, but other responses can occur if aggression has been punished in the past. By this formulation, aggression is not inborn; but, since frustration is a fairly universal condition, it is still a drive that must find an outlet.
Some support for a biologically based aggressive drive comes from studies showing that aggressive behaviour can be elicited in animals by mild electrical stimulation of a specific region of the hypothalamus.
When a cat’s hypothalamus is stimulated via implanted electrodes, the animal hisses, its hair bristles, its pupils dilate, and at will strike out at a rat or other object placed in its cage. Stimulation of a slightly different area of the hypothalamus produced quite different behaviour; the cat shows none of the above “rage” responses but, instead will coldly stalk a rat and kill it.
In higher mammals such instinctive aggressive patterns are more under the control of the cortex and thus more influenced by experience.
Monkeys living in groups establish a dominance hierarchy with one or two males as leaders and the other at various levels of subordination.
Remote-control electrical stimulation of the hypothalamus of a monkey who assumes a dominant role in the group instigates attacks on subordinate males but not females. The same stimulation of a monkey low in rank elicits covering and submissive behaviour. Thus aggression is not automatically elicited by stimulation of the hypothalamus.
The hypothalamus may send a message to the cortex indicating that its “aggression centre” has been activated, but the cortex, in choosing the response it will initiate, considers what is going on in the environment and its memory of past experiences.
Like the lower animals, we have the neurological mechanisms that enable us to behave aggressively.
But the activation of these mechanisms is under much more cognitive control. Some brain-damaged individuals may react aggressively to stimulation that normally would be ineffections; in these cases cortical control is impaired.
One study reports a high incidence of neurological defects in persons who are repeatedly violent and assaultive (Mark and Ervin, 1970). But in normal individuals the frequency with which aggressive behaviour is expressed, the forms it takes, and the situations in which it is displayed are determined largely by learning and social influences.