"Aggression" is a familiar term in common parlance, as well as a key concept in the study of human behavior. In conversation, we may use the word "aggressive" to define a person assaulting another, a carnivorous animal seeking prey, even a storm wreaking havoc on the earth it passes. For our purposes, the more narrow definition used in psychology is most appropriate. Aggression is behavior whose intent is to harm another. More specifically, aggression is defined as "any sequence of behavior, the goal response to which is the injury of the person toward whom it is directed." You may notice that this definition, even on the surface, poses a conceptual challenge: How do we know the intent of the actor?
While the definition of aggression varies somewhat from author to author, I find it helpful to look at theories of aggression by dividing them into three schools: those that consider aggression as an instinct, those that see it as a predictable reaction to defined stimuli, and those that consider it learned behavior. The three schools form a continuum along which, at one end, aggression is seen as a consequence of purely innate factors and, at the other end, of external factors. In fact, much of the debate on aggression might be framed as a more general "nature vs. nurture" debate.
A prominent psychologist associated with the aggression-as-instinct school is Sigmund Freud. He considered aggression to be a consequence of a more primary instinct he called...
Thanatos, an innate drive toward disintegration that Freud believed was directed against the self. If he was right, how is it that we all don't commit suicide? In part, it is because of a struggle between Thanatos and Eros [our innate drive toward life], which, luckily for us, Eros usually wins. But it is also because displacement redirects our self-destructive energies outward; we aggress against others to avoid aggressing against ourselves.
How, then, do people manage to avoid wreaking terrible violence upon one another? The answer, according to Freud, is catharsis: Watching violent events or engaging in mild displays of anger diminishes the aggressive urge and leaves us emotionally purified and calmed. 
A great many people think of aggression as instinctual. This is the case even though the public-at-large has not read Freud on the subject and probably would not accept his notion of a death instinct, even if they were to become familiar with it. On a popular level, aggression is not seen so much as an outward displacement of an innate internally-directed destructive drive, but rather as a universal externally directed drive, possibly connected to a survival instinct, which unites humankind with the animal world. Many go farther in assuming that we can look to the non-human animal world to gain a clearer understanding of human aggression.
And that is what a number of scientists -- particularly ethologists and socio-biologists -- have done. Chief among them is Konrad Lorenz, whose 1966 book On Aggression made a major impact. Its cover offers quotations that are suggestive of this impact. The New York Times heralded it as "one of the most important works of our age," expressing hope that it "be read not only by natural scientists but by Rand Corporation thinkers, members of the Pentagon, pacifists, and presidents...."
Lorenz defines aggression as "the fighting instinct in beast and man which is directed against members of the same species." He relates it to Darwin's notion of the "struggle for existence": "the struggle Darwin was thinking of and which drives evolution forward is the competition between near relations." At least it does so under "natural -- or rather pre-cultural -- conditions... [because] it is always favorable for the species if the stronger of two rivals takes possession of the territory or of the desired female."
Lorenz' own study is based largely on his careful research of a variety of animal species, particularly fish and birds and to a lesser extent, non-primate mammals. In these varied species, he notes a shared instinct to defend territory from encroachment by an animal of the same species, to defeat a rival for a desired female and to protect the young and defenseless of the species. He finds that such aggression serves the animal kingdom well in that it brings about a "balanced distribution of animals of the same species over the available environment", assures that the gene pool is continually modified toward strength, and enhances the likelihood of the young of a species growing to adulthood. In these three ways, aggression helps to preserve the species, regularly improving it to make it more adaptive to the environment. Beyond this, Lorenz attributes to aggression a role in developing the social structure due to its critical role in clarifying the rank ordering of the members of a group. Lorenz sees this as a necessity for developing an advanced social life. Lorenz also attributes to the aggressive drive a range of other functions under the general rubric of "motivation."
The presumption is that the primary functions of aggression accrued to humankind in its pre-cultural state. The problem is that cultural and technological advances have outstripped the inhibitory capacities of the human aggressive instinct. To illustrate this in an extreme form, two male mammals fighting over territory or a female do not fight to the death; the stronger backs off when the weaker acknowledges his loss by exposing a vulnerable body part. Humankind, however, has produced and perfected lethal weapons delivered at a great distance from those being attacked. Sometimes, the attacked do not even know of the attack until the fatal blow has already been struck. Thus they are unable to capitulate and stave off destruction. The babies in the day care center at the federal building in Oklahoma City could hardly have had the opportunity to display their defenselessness to the bomber. Our inhibitory mechanisms were presumably sufficient to allay intra-specific killing when our weapons were limited to our hands and feet, but they were not designed to offset the utilization of something even so low-tech as a handgun.
Aggression-as-instinct theorists tend to ascribe a cathartic effect to expressions of aggression. Empirical research, however, tends to cast doubt on this function:
Unfortunately, such predictions [of catharsis] turn out to be wrong. Couples who argue the most are those who are the most likely to become violent. Husbands who push their wives are those most likely to move on to slapping and punching. The best predictor of an individual's likelihood of criminal violence this year is his criminal violence last year. Violence seems to beget violence rather than decrease it. 
The second theory of aggression moves from innate predispositions to external stimuli as sources of aggression. The central supposition is that aggression is a predictable reaction to defined stimuli, the defined stimuli being frustration. In their classic treatise on the subject, Dollard and his colleagues make the bold two-part assertion at the outset, that "the occurrence of aggressive behavior always presupposes the existence of frustration" and that the "existence of frustration always leads to some form of aggression."
The reason that I classify the correlated presumptions as bold is the use of the word "always." Human behavior is complicated and multi-faceted; to assume that any variable always leads to a specific behavior and that, furthermore, that behavior is always preceded by that variable, is unusual and daring. And, in fact, Dollard et al. were open to criticism on this score from the beginning. Even the co-authors were soon writing articles, which suggested exceptions to the general guideline (e.g., Doob & Sears, 1939; Miller, 1941; Mowrer, 1960; Sears, 1941). Nonetheless, the book has had a significant impact in scholarly circles; "most authorities today regard aggression as originating ultimately in response to some frustration."
Dollard and his colleagues define frustration as "an interference with the occurrence of an instigated goal-response at its proper time in the behavioral sequence." While we ourselves may not be familiar with language like "instigated goal response," it is easy to draw on our own experience with conflict for examples that meet the definition: the husband that comes home from work to find dinner not awaiting him, the employee who does not get a promotion she feels she deserves, the child who's excluded from a game on the school playground. Examples abound, but the question we ask is whether the husband, the employee, and the child always engage in a "sequence of behavior, the goal response to which is the injury of the person toward whom it is directed?" Does every husband, employee and child who finds him or herself in such a predicament engage in aggressive behavior? Is every aggressive act engaged in by a spouse, worker, or child precipitated by a frustration?
Berkowitz asks these questions in a more general form: "Is all aggression the result of frustration? ; and "Does every frustration lead to some form of aggression?" He concludes by supporting "the essential validity of the Dollard et al. formulation with some modifications." In order to shed light on these modifications, he utilizes two intervening variables: anger and interpretation. He proposes that "every frustration increases the instigation to aggression, but this instigation is here termed anger" and that anger will only lead to aggression when "there are appropriate cues or releasers." Here, Berkowitz allows that individuals may learn that expressing anger by aggressing is inappropriate and therefore be less likely to aggress even when the frustrating stimulus is intense. Additionally, "[o]ne of the ways in which learning might operate to alter the response probabilities is through affecting the individual's interpretation of the thwarting situation." A person, for example, may focus on other components of the frustrating stimulus than the frustration.
An example of this occurs to me, which helps me make these abstractions more concrete. I arrived home late one night to find the back door of my house open. I was immediately concerned that someone might be in the house and I knew it wasn't anyone with whom I lived, since they were away. I knew I couldn't get to sleep, fearful that someone was in the house, so I proceeded to check the house to ascertain I was alone (calling 911 would probably have been a wiser choice, but that's not what I did). After I was sure the house was secure, I went to bed. Immediately upon waking, I knew that my stereo had been stolen the night before. I went downstairs and, as I expected, my stereo and several other easily hocked items were missing. Since I was living on the below-subsistence wages of a graduate assistant, I could not afford to replace the stereo for a long time and every time I wanted to hear some music, I was reminded of the theft. But as soon as I would begin to feel angry, I would begin to feel grateful. In not having even thought about the stereo until the morning after the break-in and having been only concerned about my personal safety, I had learned what was important to me in a very clear and deep way. So while the event was a frustration, it was also a learning experience I prized. For the most part, I interpreted the events of that night more as something to value than as a loss.
Given Berkowitz' reference to the role of learning, this could be an appropriate place to move on to the social learning school of aggression, but I want to add an additional segment on the frustration-aggression school before leaving it. The frustration-aggression theory is a psychological one which attempts to explain individual behavior. Can it be used to explain aggression and violence on a group or societal level? Ted Robert Gurr answers this question with a firm yes in Why Men Rebel (1970).
[T]he primary source of the human capacity for violence appears to be the frustration-aggression mechanism. Frustration does not necessarily lead to violence, and violence for some men is motivated by expectations of gain. The anger induced by frustration, however, is a motivating force that disposes men to aggression, irrespective of its instrumentalities. If frustrations are sufficiently prolonged or sharply felt, aggression is quite likely, if not certain to occur.... The frustration-aggression mechanism is in this sense analogous to the law of gravity: men who are frustrated have an innate disposition to do violence to its source in proportion to the intensity of their frustration, just as objects are attracted to one another in direct proportion to their relative masses and inverse proportion to their distance. A number of other variables influence the behavior of men, and of objects, in such circumstances: for men, their beliefs, inhibitions, and social environment; for objects in a gravitational field, their energies, configuration, and the properties of the medium in which they are situated. But it seems even less feasible to account for political violence without reference to the properties of men that dispose them to violence than it is to construct a theory of flight without reference to the law of gravitation.
And so, Gurr constructs a tightly woven, comprehensive theory of collective political violence based squarely on the frustration-aggression hypothesis. He brings the concept of frustration to the socio-political plane with his concept of relative deprivation which is defined as "actors' perception of discrepancy between their value expectations and their value capacities. Value expectations are the goods and conditions of life to which people believe they are rightfully entitled. Value capabilities are the goods and conditions they think they are capable of getting and keeping." Gurr's first hypothesis, which forms the foundation of the rest of the book, is that
The potential for collective violence varies strongly with the intensity and scope of relative deprivation among members of a collectivity. 
It is noteworthy here that Gurr does not look to a more absolute or objective indicator of deprivation as the source of political violence. People can become inured to a bad state of affairs, even one that offers so little access to life-sustaining resources that members of the group are starving or dying of remediable diseases or exposure. If, however, there is a significant discrepancy between what they think they deserve and what they think they will get, there is a likelihood of rebellion. Gurr posits this to be the case even if there is no question that their basic needs will be met. The first situation may be a desperate one, but it is the second that is frustrating. And, according to Gurr, just as frustration produces aggressive behavior on the part of an individual, so too does relative deprivation predict collective violence by social groups.
To return to the individual as the unit of analysis, we turn to our final school of theories of aggression; the one that begins by presuming that aggression is learned behavior. This school argues does not accept that aggression is the naturally dominant response to frustration, but rather that aggression is largely a learned behavior. Adherents of this school point out both that there are many societies in which aggression is largely absent, and that aggressive behavior will be imitated even when there is no frustrating stimulus.
Learning theory advocates point to the work of a number of anthropologists as totally debunking the aggression-as-instinct school and largely undermining the frustration-aggressions hypothesis. Reviewing the work of Margaret Mead and several other anthropologists, Erich Fromm (1973) concludes that only six of thirty primitive societies studied were "destructive," i.e., "characterized by much interpersonal violence, destructiveness, aggression, and cruelty". He categorizes the majority as "life-affirmative (societies in which "there is a minimum of hostility, violence or cruelty among people, no harsh treatment, hardly any crime, and the institution of war is absent or plays an exceedingly small role") or "non-destructive aggressive societies." If aggression is instinctual, it must be universal, and if it is universal, every society would have aggressive indicators not found in many of these societies. Furthermore, it is hard to conceive that frustrating events would be so absent from entire societies as to result in such low levels of aggression. There must be another explanation.
Albert Bandura is a major researcher, theorist and exponent of the social learning theory of aggression. His experimentation has shown, for example, that children who observe aggressive adult models reproduce the same behavior even in a new situation while a control group of children does not , and that this same type of imitation will occur when the model is on film. He and Walters report many other such studies in Social Learning and Personality Development (1963). The conclusion of this school of thought on aggression has been summed up: "Human aggression is a learned conduct that, like other forms of social behavior, is under stimulus, reinforcement, and cognitive control."
How do people learn not to be aggressive? One model is provided by Patricia Draper in her consideration of the child rearing practices of the !Kung of the Kalahari Desert. Draper indicates at least three aspects of the learning environment of children which discourages aggressive responses:
1. "When two small children argue or begin to fight, adults don't punish or lecture them; they separate them and physically carry each child off in an opposite direction. The adult tries to soothe and distract the child and to get him interested in other things." A similar interventionist strategy is used with older children by calling the ringleader away or by adults joining the group.
2. "[P]arents do not use physical punishment, and ...aggressive postures are avoided by adults and devalued by the society at large." 
3. "Adults consistently ignore a child's angry outburst when it does not inflict harm. A child's frustration at such times is acute, but he learns that anger does not cause an adult to change his treatment of the child, and the display of anger does not get the adult's attention or sympathy."
What impact does such child-rearing practices have on a society? In Draper's observation,
the !Kung were extraordinarily successful in discouraging harmful and malicious behavior in young people. During the twelve months in which I lived with different camps... there were no conflicts between adults, which led to serious injuries or homicides.
In other words, she found the!Kung to be a relatively non-aggressive society and attributed this, in large degree, to their non-aggressive child rearing practices.
Just as the modified version of the frustration-aggression hypothesis allows for some impact of learning in mediating the way in which a person responds to aggression, so do the social learning theorists allow for an impact of frustration in making it more likely that the person who has learned aggressive responses will use them. Basically, they see frustration as one possible instigator of aggressive behavior, but insist that aggression is socially learned behavior rather than an automatic response to aggression or any other stimulus.
 Dollard, John., Doob, Leonard.W., Miller, Neal E., Mowrer, O.H., and Sears, Robert R. Frustration and Aggression. New Haven:Yale University Press, 1939.
 Campbell, Anne. Men, Women and Aggression. New York: Basic Books, 1993, p. 8. <http://www.amazon.com/Men-Women-Aggression-Anne-Campbell/dp/0465044506>
 Lorenz, Konrad. On Aggression. (Marjorie Kerr Wilson, Trans.) New York: Harcourt, Brace & World, Inc., 1966, p. ix.
 Lorenz, 1966, p. 20.
 Lorenz, 1966, p. 27.
 Lorenz, 1966, p.40.
 Campbell, 1993, p. 8.
 Dollard, J., Doob, L.W., Miller, N.E., Maurer, O.H., and Sears, R.R. Frustration and Aggression. New Haven: Yale University Press, 1939, p.8.
 Berkowitz, L. The Frustration-Aggression Hypothesis. In R. A. Falk and S. S. Kim, (Eds.), The War System: An Interdisciplinary Approach. Boulder, CO: Westview Press, 1980, p.116.
 Dollard, et. al. 1939, p.7.
 Berkowitz, 1980, p. 119.
 Berkowitz, 1980, p. 126.
 Berkowitz, 1980, p. 135.
 Berkowitz, 1980, p. 136.
 Berkowitz, 1980, p. 122.
 Gurr, Ted R. Why Men Rebel. Princeton, N.J: Princeton University Press, 1970, p.37.
 Gurr, 1970, p. 24.
 Gurr, 1970, p. 24.
 Fromm, Erich. The Anatomy of Human Destructiveness. Greenwich, CT: Fawcett Crest, 1973, p.17. Edition of 2013 of this book available at: http://books.google.com/books?id=vZ2Ja6D9cxcC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
 Fromm, 1973, p.20.
 Bandura, Albert, Ross, D., and Ross, S.A. Transmission of Aggression Through Imitation of Aggressive Models. Journal of Abnormal and Social Psychology. 63, 575-582, 1961. <http://psychclassics.yorku.ca/Bandura/bobo.htm>
 Bandura, Albert and Walters, R. H. Social Learning and Personality Development. New York: Holt, Rinehart & Winston, 1963.
 Bandura, Albert. The Social Learning Theory of Aggression. In R. A. Falk and S. S. Kim, (Eds.), The War System: An Interdisciplinary Approach. Boulder, CO: Westview Press, 1980, p.146.
 Draper, P. The Learning Environment for Aggression and Anti-social Behavior Among the !Kung. In A. Montagu (Ed.), Learning Non-aggression: The Experience of Non-literate Societies. New York: Oxford University Press, 1978, p.36. <http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1011&context=anthropologyfacpub>
 Draper, 1978, p. 37.
 Draper, 1978, p. 37-38
Use the following to cite this article:
Dugan, Máire A.. "Aggression." Beyond Intractability. Eds. Guy Burgess and Heidi Burgess. Conflict Information Consortium, University of Colorado, Boulder. Posted: July 2004 <http://www.beyondintractability.org/essay/aggression>.