i. Psychological AspectsLeonard Berkowitz
ii. International AspectsFrederick L. Schuman
The study of aggression—here regarded as any behavior whose goal is the injury of some person or thing (cf. Dollard et al. 1939)—has long been governed by philosophical preconceptions and clouded by hopes and fears. Writers have accounted for aggressive behavior in strikingly different ways: as the manifestation of an innate destructive drive, as an inborn reaction to frustrations, or as a learned way of responding to particular situations. Many of these interpretations have clearly been influenced more by metatheoretical beliefs regarding the nature of man or religiophilosophical hopes as to what human beings should be like than by carefully controlled and precise observations. Freud, as an example, at first had maintained that aggression was a “primordial reaction” to the blocking of pleasure-seeking or pain-avoiding strivings. However, partly because of his pessimism growing out of World War i, he revised his formulation and postulated the existence of an instinctive force of destruction and death (1920). Other psychologists have advanced entirely different conceptions. Some were predisposed to deny or minimize the role of innate factors in human behavior, while for others the notion of inherent aggressiveness was incompatible with their view of man as being basically good. Whatever the exact nature of their analysis, all too often their general theoretical or philosophical assumptions resulted in a relatively extreme stand in which some factors were given very heavy emphasis and others were played down or denied altogether.
The Freudian “death instinct.”
In Freud’s post-1920 discussion of aggressive behavior, the dominant tendency in all organic life was held to be the effort to reduce nervous excitation to the lowest possible level (1920). Just as all pleasure-seeking was supposedly oriented toward tension reduction, all organic life presumably sought death, for to die was to be free from stimulation. (Freud also proposed that death was often sought violently rather than quietly and peacefully.) But this initial striving for active self-annihilation did not find fulfillment, Freud maintained, because the death instinct, Thanatos, was opposed by the life instinct, Eros, which diverted the destructive drive from the self to others. Thus, in attacking other people the person found a release for pressures that otherwise would impel him to seek his own death.
Empirical evidence provides little support for Freud’s analysis of aggressive behavior (cf. Berkowitz 1962). To cite just one difficulty, research clearly indicates that organisms do not seek the complete elimination of excitation. There are many situations in which human beings, as well as lower animals, work for an increase in stimulation (White 1959). Death is not necessarily the inherent aim of all organic life.
Other instinct doctrines
A number of biologists as well as orthodox psychoanalysts have accounted for aggression solely in terms of some inner force. The ethologist Konrad Lorenz (1952) has suggested, for example, that excitation is built up in each instinctive center within the central nervous system and is then dissipated when the instinctive act is performed. If an animal did not engage in aggressive behavior, “action-specific energy” would supposedly accumulate within the instinctive center controlling aggression. When enough energy is built up the action pattern presumably would go off by itself, that is, there would be “vacuum activity.” In contrast to this notion of spontaneous aggression, others (for example, Scott 1958) have maintained that there is no evidence of a spontaneous stimulation for fighting arising within the body. Actual fighting, which usually involves males belonging to the same species, is relatively rare in nature; in most cases the opponents display threat ceremonies instead of coming to blows.
Exteroceptive cues. In contrast to the model based on notions of energy accumulation, many students prefer to analyze instincts as species-specific behavior patterns governed by exteroceptive stimuli, which activate and terminate the actions. External stimuli are thus considered to be important contributors to aggressive behavior. Fighting behavior in many species varies with the nature of the antagonist—whether the animal’s opponent is from its own or some other species, and if the latter, whether it is a predator or some prey (EiblEibesfeldt 1963). More than determining merely the form of the response, external cues often appear to be necessary for eliciting any kind of hostile actions. Tinbergen (1951) observed that the male stickleback fish attacked a dummy with a red spot on its belly but ignored a detailed replica of the stickleback that did not have this characteristic of the breeding male or that had the red spot on its back.
Fighting arising from competition for dominance, food, sexual partners, or territory clearly attests to the role of external stimulation in animal aggression. The aggressive activity in these cases is the product of some perceived obstacle to the attainment of a desirable goal state. Even apparently noncompetitive fighting may be explained in these terms; the combat may have been instigated in order to achieve such things as dominance or undisturbed possession of living space (cf. Berkowitz 1962, p. 17).
Internal conditions. The efficacy of external stimuli in evoking aggressive behavior, however, is probably contingent upon the presence of some suitable internal condition. In the case of the stickleback fish the necessary internal prerequisite seems to be the production of the hormones involved in reproduction. Given the required internal state, a particular stimulus evokes the aggressive response. As yet another illustration of this principle, von Holst and von Saint Paul (1962) have shown that electrical stimulation of a certain region of the fowl brain results in recognizable aggressive actions only in the presence of relevant cues, “an enemy real or artificial.” Applying this formulation to competitive fighting, we can say that the rivalry produces an emotional state creating a readiness to engage in aggressive activity and that the competitor then provides the cue that releases (or evokes) the aggression.
The frustration–aggression hypothesis
The principle just advanced is a version of the “frustration-aggression hypothesis,” which has long been used to account for aggressive behavior. Independently espoused by such writers as Freud (prior to World War I) and McDougall (1908), the hypothesis was spelled out most clearly by Dollard, Doob, Miller, Mowrer, and Sears in a now-classic monograph published in 1939. Briefly, these psychologists maintained that a frustration—“an interference with the occurrence of an instigated goal-response at its proper time in the behavior sequence”—arouses an instigation to aggression (Dollard et al. 1939, p. 7). Since this formulation has been criticized frequently, some additional points should be made clarifying and defending it. First, Dollard and his colleagues did not claim that frustration had no consequences other than aggression. A thwarting will produce instigations to many different kinds of responses. Some of these other response tendencies may be stronger than the instigation to aggression, and the aggression is not revealed openly (Miller 1941). Moreover, although the hypothesis did say that all aggressive actions presuppose the existence of frustration, a person does not have to be frustrated in order to engage in aggressive actions (Bandura & Walters 1963). A contemporary revision of the frustration-aggression hypothesis must be less sweeping and all-explanatory than the original version.
This is not to say, however, that the hypothesis must be discarded altogether, as a number of writers have insisted (e.g., Buss 1961). While we cannot deal here with all of the criticisms (cf. Berkowitz 1962 for a more complete discussion), several of the arguments against the hypothesis can be answered.
Do only some frustrations produce aggression?
To begin, several psychologists have contended that only certain kinds of frustrations give rise to aggressive responses. Threats or attacks upon the self produce aggressive tendencies, they say, but mere deprivations supposedly lead to other consequences. In a similar vein, other critics have suggested that arbitrary or unexpected thwartings lead to aggression, while less arbitrary or expected frustrations presumably do not.
Two comments can be offered in rebuttal. Dollard et al. (1939) proposed that the strength of the instigation to aggression resulting from a frustration is in direct proportion to the strength of the thwarted drive. Since the desire for self-enhancement is typically fairly strong in our society, we would expect attacks upon the self to lead to stronger aggressive reactions than, say, interference with the performance of some unimportant task. Attacks upon the self then may lead to overt aggression, while the hostile responses produced by the interruption of a task that is not relevant to the self may be too weak to be apparent. But the frustration need not even be a direct attack on the self in order to produce aggression. Buss (1963) has demonstrated that college students who were prevented by a peer from attaining a desirable goal (such as a money prize) tended to display more intense open aggression toward the peer than did a nonfrustrated control group. The thwarting was not an arbitrary one, and the allowable aggression was not instrumental to the attainment of other ends, but there was a definite aggressive reaction, if only a weak one.
The second comment deals with the matter of deprivations and arbitrary frustrations. According to the definition employed by Dollard and his colleagues, a frustration is the blocking of some on-going, goal-directed activity. A person thoroughly engrossed in his work is not frustrated just because he has been without food for a number of hours. He may be deprived of food, but there are no ongoing eating response sequences, either in his thoughts or his overt activity, that are prevented from reaching completion. His failure to eat at his regular mealtime will therefore not produce an aggressive reaction. But what if this person had been prepared to eat at a certain time and had been thinking of the food he was soon going to enjoy? Suppose his employer unexpectedly gives him a sudden job that keeps him working late at night and causes him to miss his meal. We would now expect him to become angry. Whereas some psychologists would say he has now experienced an arbitrary or unexpected frustration, in contrast to an expected frustration, the present writer maintains that only now is he frustrated, whereas formerly, before he had anticipated eating, he was not. Only now is an ongoing response sequence prevented from reaching completion at its anticipated time (cf. Berkowitz 1962, pp. 36–42).
The innate nature of the aggressive reaction
American psychologists are characteristically reluctant to refer to instinctive or innate mechanisms in accounting for human behavior. Some of the objections to the frustration–aggression hypothesis seem to be dictated by this prejudice against the notion of innate reaction patterns.
Animals and humans can be trained to respond nonaggressively to situations that ordinarily produce hostile responses. For that matter, they can also learn to act aggressively in situations where formerly they had displayed little violence. In an experiment with school children, for example, Davitz (1952) rewarded one group of youngsters for acting aggressively and competitively, while another group was rewarded for cooperative and constructive behavior. After several training sessions all of the children were frustrated when a movie they were seeing stopped and, at the same time, their candy was taken away. Observations showed that the aggressively trained group exhibited more aggression in a free-play period immediately afterwards and that the constructively trained youngsters reacted more constructively to the thwarting. Scott (1958), after reviewing several of his animal experiments that had obtained essentially similar results, concluded that aggression was the product of previous learning. Taking much the same position, others (Bandura & Walters 1963) have argued that frustration produces a heightened motivational state that enhances the strength of whatever responses the individual has learned to make in the given situation; these may or may not be aggressive in nature.
Yet the experiments just mentioned do not really invalidate the frustration-aggression hypothesis. They demonstrate that previous experience can enhance or reduce the likelihood of aggressive behavior, but they do not prove that aggression will not occur under suitable conditions in the absence of any aggression training. Indeed, several experiments indicate that animals reared in isolation, and who had not previously learned to be aggressive, can react aggressively to arousing stimuli (Eibl-Eibesfeldt 1963, p. 11). In another demonstration that prior learning is not necessary for aggressive reactions, Seay and Harlow at the University of Wisconsin Primate Laboratory thwarted some infant monkeys by separating them from their mothers (1963). Six of the eight young animals subsequently displayed some aggression against a peer-playmate—but primarily when the previously frustrated infants were in their mothers’ presence. Two aspects of this finding are noteworthy. First, and most important, monkeys of the species used (rhesus) rarely show any aggression at all during the first year of life, and these particular infants had never before been observed to act aggressively. It is very unlikely, then, that they had learned aggressive actions earlier. Second, and we shall return to this point later, the aggressive response to a frustration is clearly revealed only under certain conditions.
Inflicting injury as a goal response
Another criticism of the frustration-aggression hypothesis as advanced by Dollard and others stems from a particular philosophy of science embraced by some psychologists. In saying that aggression was a behavioral sequence whose goal was the injury of the person to whom the activity was directed, the authors of the 1939 monograph implied that this behavior was purposive or intentional. Some writers, taking the position of Watsonian behaviorists, object to the inclusion of intentionality in the definition of aggression. Intentionality usually has to be inferred, and these critics prefer to confine themselves to a strict operationism having little room for inferences. While we cannot here debate the merits and demerits of this approach, there is reason to believe that aggressive frustration reactions are frequently purposive in nature. Hokanson and his students have shown that provoked subjects who are permitted to aggress against their tormentor often display a drop in systolic blood pressure that brings their pressure level close to that exhibited by a nonaroused control group. Systolic pressure does not decline as much, however, when the angered people can carry out some activity, but do not believe they have inflicted injury on their frustrater (even though the activity is physically comparable to the aggressive response), or when the aggression is directed against someone other than the person who had provoked them (cf. Hokanson et al. 1963). If the decrease in systolic blood pressure is a sign of physiological relaxation brought about by the performance of a goal response, engaging in mere activity or aggressing against just anyone does not seem to be sufficient to produce this tension reduction; the frustrated person (who wants, and is prepared, to attack his frustrater) may be primarily concerned with injuring the person who had provoked him.
A revised frustration–aggression hypothesis
Elsewhere (Berkowitz 1962) I have suggested that the original version of the frustration-aggression hypothesis should be modified in three ways. First, I would contend that a frustration—preventing the occurrence of some goal response at its proper time in an ongoing response sequence— arouses, among other things, an emotional state, anger, that creates a readiness for aggressive acts. (The arousal state produced by a thwarting also increases the strength of the ongoing responses, whether these are aggressive or not.)
Second, it is important to make explicit what was only implicit in the formulation advanced by Dollard and his coworkers. Aggressive responses do not occur, even given this readiness, in the absence of suitable cues—stimuli associated with the present or previous anger instigators. These cues, in other words, evoke aggressive responses from a person who is “primed” to make them. The strength of the aggressive response resulting from a frustration presumably is a function of the intensity of the aroused anger and the degree of association between the available stimuli and past and present anger instigators.
By suggesting that cues are necessary to elicit aggressive actions, we can explain two propositions advanced by Dollard and his coworkers: In the absence of inhibitions, the strongest hostile responses supposedly are directed toward the perceived source of the frustration; and progressively weaker aggressive responses theoretically are evoked by objects having less and less similarity to the frustrater. In both cases, the more direct the association with the anger instigator the stronger is the aggressive reaction that is elicited.
A third necessary revision of the frustration-aggression hypothesis restricts the extent to which thwartings are employed as an explanation of aggression. Instead of maintaining that all aggression “presupposes the existence of frustration,” we now recognize that (a) suitable cues may lead to aggressive behavior by arousing previously acquired aggressiveness habits and (b) such habits may be formed through learning—for example, by observing the behavior of some adult model—without involving a thwarting (Bandura & Walters 1963). To repeat, the revised hypothesis now would claim only that frustrations create a readiness for aggressive behavior.
The revised formula discussed above has some important implications for such phenomena as displacement and “scapegoating.” In the scapegoat theory of prejudice the victim is said to be attacked primarily because he is a visible and safe target for pent-up hostility within the prejudiced individual. The aggressive “drive” supposedly “pushes” aggressive acts onto safe, available targets. Contrary to such a view, the present position contends that a target with appropriate stimulus qualities “pulls” (evokes) aggressive responses from a person who is ready to engage in such actions either because he is angry or because particular stimuli have acquired cue value for aggressive responses from him.
Several experiments by the writer and his students offer support for this analysis of hostility displacement. In one study (Berkowitz & Green 1962) it was shown that subjects who were deliberately provoked by the experimenter subsequently exhibited greater hostility toward a person who had angered them some time earlier than toward someone else who had not provoked them. By having angered the subjects previously, the former person had acquired the cue value that now enabled him to evoke hostile responses from them when they were later thwarted by the frustrater. The writer suggests that those minority groups that frequently are the victims of displaced hostility, such as Negroes and Jews, are capable of eliciting aggressive responses from thwarted people because these groups are strongly disliked, that is, they had previously aroused anger. The dislike could arise from learning that the groups have unpleasant qualities as well as from prior frustrating experiences with them.
According to this reasoning, most explanations of social prejudice are too one-sided. Typically they either explain why some people are ready to act aggressively, or they provide reasons why certain minority groups are disliked. The present formulation attempts to integrate the two sets of explanations: we have to know both (a) why some people are “primed” to act aggressively and (b) what stimulus qualities are possessed by certain groups which enable them to evoke hostile responses from the people having a readiness to behave aggressively.
Comprehensive analyses of scapegoating must deal with those people who characteristically display relatively strong hostility toward minority groups. Recent research (Berkowitz 1959) indicates that highly ethnocentric college students typically have a strong tendency to attack other people when frustrated by someone else. It is not altogether clear, however, whether this tendency is due to (a) previously acquired aggressiveness habits; (b) a proclivity to establish broad categories, especially when under stress, so that in essence the immediate frustrater is not sharply differentiated from the others; (c) intense emotional arousal; or (d) some combination of these factors.
Inhibiting aggressive reactions
When an angered person displaces hostility, he presumably does so because fear or anxiety inhibits direct aggression against the frustrater. The analysis presented here helps explain why the displaced aggression is frequently quite intense. Miller’s (1948) translation of the psychoanalytic formulation maintains, as I indicated earlier, that stimulus objects increasingly removed from the frustrater on some appropriate generalization dimension would evoke weaker and weaker aggressive responses from the angered person. Attacks upon some bystander should thus be relatively weak and never stronger than the aggression that would be directed against the anger source. At least two studies, however, have obtained a substantial departure from this prediction. In one experiment (Pepitone & Reichling 1955), angered men whose inhibitions were presumably lowered by placing them in the company of others they liked exhibited the expected aggression gradient: much stronger attacks upon their tormentor than upon other associated stimuli. However, a more strongly inhibited group of men did not show this difference; the aggression they directed against the associated stimuli was practically as intense as the aggression against the anger instigator. Essentially similar findings have been obtained in other studies. Where members of a less inhibited group generally directed the strongest aggression against the source of their anger, most of the men in a more inhibited condition actually were more hostile toward the associated stimuli than toward the anger source (Berkowitz et al. 1963).
This last finding can be explained readily by noting that the inhibition of an aggressive response is a frustration. The emotional reaction produced by the thwarting should increase the strength of the individual’s aggressive proclivities. Since there is a restraint against a direct attack on the frustrater, attacks evoked by other stimuli should be strengthened. (Dollard and his colleagues had made this prediction in their 1939 monograph.)
Expectations to aggress
Anger arousal does not in itself necessarily lead to an instigated aggressive response sequence. Stimuli associated with the anger instigator must also be present. These cues may be provided either by the external environment or the individual’s thought processes. If a person is thinking of injuring his tormentor, the aggression goal (his frustrater) is symbolically represented in his thoughts. This symbolic representation serves as a cue setting an aggressive sequence into operation, if only internally. Preventing him from attacking his frustrater would then be an additional thwarting. Suppose, on the other hand, that the angered person does not see his tormentor, or any associated stimuli, and, for that matter, does not even think of “getting even.” There would be no ongoing aggressive sequence, and an inability to attack the anger source would not be a frustration.
Berkowitz and Luehrig have obtained data consistent with this reasoning (Berkowitz 1964a), demonstrating that angered male college students who had expected to be able to attack their frustrater but were prevented from doing so subsequently exhibited a high level of aggression toward him at the end of the session. The aggression they displayed toward him was stronger than that shown by other provoked people who had been able to attack this person earlier with electric shock or who, although not having been given this earlier opportunity, had not previously expected to be able to attack him. It is not enough just to say that a “set” or expectation had been thwarted in the former group without explaining the meaning of “set.” “Set” may consist of an implicit but nevertheless ongoing chain of responses. In the present case the implicit response sequence was activated by the anticipation of the aggressive opportunity, and the inability to satisfy this expectation was thus frustrating.
Since the time of Aristotle, social science folklore has contended that an individual can be “purged” of his emotions by displaying his feelings. Aggressive behavior should therefore weaken the instigation to further aggression (unless he is frustrated again) and should somehow make the person feel better. But although such a proposition is almost universally accepted, empirical evidence regarding this catharsis hypothesis is far from unequivocal. We cannot be sure that catharsis takes place as readily and frequently as many people seem to assume.
There are manifold problems confronting research in this area. One difficulty is that observers have often regarded the intensity of the overt aggression following an initial attack as being a good indicator of the strength of the remaining “aggressive drive.” They forget that inhibitions produced by guilt or anxiety arising from the initial aggression may weaken any subsequent expressions of hostility. But even in the absence of such inhibitions, diminutions in aggressive tendencies following an intervening experience are also not necessarily due to a cathartic drainage of aggressive “energy.” An angered person who then watches a movie or a football game may calm down and become friendlier to his frustrater, not because he has discharged his anger vicariously but because he has been so distracted by the movie or game that he does not think of the thwarting he has experienced and ceases to stir himself up. Since he does not stimulate himself, his anger dissipates. To mention one other problem, the catharsis hypothesis is frequently tested by comparing an angered group that is permitted to aggress against someone with a similarly provoked group not given this aggressive opportunity. However, as we have already seen, if measurements obtained later should suggest there is a greater level of residual hostility in the latter (nonaggressing) condition, this difference may not be due to a catharsis in the group permitted to aggress; the angered people in the nonaggressing condition may have been frustrated —assuming they had wanted to, and had been prepared to, attack the anger source—and, so, they became more strongly aroused.
Clearly, given such difficulties, we cannot definitely say now that the free expression of aggression will automatically reduce the likelihood of subsequent aggression. Indeed, several studies of children in situations similar to play therapy suggest that the expression of aggression under such permissive conditions frequently serves to increase the probability of later violence (cf. Berkowitz 1962). The permissive situation may weaken inhibitions, and the performance of aggressive actions can strengthen aggressiveness habits. Nor does the observation of other people engaging in violence generally reduce aggressive tendencies. (1) The person who watches others acting aggressively often learns to behave aggressively through modeling himself after these others. (2) The witnessed hostility may provide cues activating previously acquired aggressiveness habits. (3) The witnessed hostility may affect the observer’s judgment of the propriety of his own aggressive desires.
To demonstrate this last-mentioned possibility, in three separate experiments Berkowitz (1964b) and his students showed a filmed prize fight scene to deliberately angered college men. In some cases the aggression they watched was made to appear justified (in that a villain received his “comeuppance”), while for other men the witnessed aggression was made to appear less warranted. Since the justified fantasy aggression lowered inhibitions against aggression—as indicated by several measures—the catharsis hypothesis would predict that the angered men in this group would participate vicariously in the filmed violence and, thus, would purge themselves of their anger. But contrary to this expectation, the angered men in this justified fantasy-aggression condition later displayed stronger aggression against their frustrater than did the similarly provoked group shown the less justified aggression. If aggression was warranted on the screen, the former may have thought, it was all right to attack the villain in their own lives.
Performing an aggressive act may well be a goal response completing an ongoing aggressive response sequence, but satisfactory completion is apparently attained only to the extent that (a) the angered person himself (or perhaps someone the person associates with himself) does the attacking and (b) the frustrater (or perhaps someone associated with him) is injured. Further, we are not altogether certain as to what the effects of this completion would be. It may well produce a feeling of tension reduction, especially if the angered person had wanted to, and had been prepared to, aggress against the anger instigator but, for some reason, had not been able to do so right away. Whether the tension reduction signifies a decreased likelihood of subsequent aggression is not altogether clear, however. The aggressive act may lessen the thwarted person’s anger at the moment, and thus may lower the probability of aggression at this time. But this frustrater has also acquired cue value for aggressive responses. Much like a red flag waved in front of a bull, under appropriate conditions (such as another thwarting experience) this individual may again evoke aggressive responses from the aroused person, whether or not he was the cause of the thwarting.
The reasoning just advanced obviously differs sharply from the “drainage” conception of aggressive behavior. Contrary to the notion of a free-floating aggressive energy that may be released through many different activities (for example, attempting to master others), or in attacking a wide variety of objects, available evidence suggests that the catharsis hypothesis must be restricted in scope. Moreover, if the view given here is correct, it is not necessary to provide substitute activities in order to “drain” a supposed reservoir of pent-up emotion. Unless the thwarted person is kept aroused or is rearoused, his anger probably will dissipate with time, and the probability of aggression will decline. But even if he is angry or has developed aggressiveness habits, aggressive behavior presumably will not occur unless appropriate cues are present.
[Directly related are the entries Conflict; War. Other relevant material may be found in Instinct; Psychoanalysis; Stress.]
Bandura, Albert; and Walters, R. H. 1963 Social Learning and Personality Development. New York: Holt.
Berkowitz, Leonard 1959 Anti-Semitism and the Displacement of Aggression. Journal of Abnormal and Social Psychology 59:182–187.
Berkowitz, Leonard 1962 Aggression: A Social Psychological Analysis. New York: McGraw-Hill.
Berkowitz, Leonard 1964a Aggressive Cues in Aggressive Behavior and Hostility Catharsis. Psychological Review 71:104–122.
Berkowitz, Leonard 1964b The Effects of Observing Violence. Scientific American 210, February:35–41.
Berkowitz, Leonard; Corwin, R.; and Heironimus, M. 1963 Film Violence and Subsequent Aggressive Tendencies. Public Opinion Quarterly 27:217–229.
Berkowitz, Leonard; and Green, J. A. 1962 The Stimulus Qualities of the Scapegoat. Journal of Abnormal and Social Psychology 64:293–301.
Buss, Arnold H. 1961 The Psychology of Aggression. New York: Wiley.
Buss, Arnold H. 1963 Physical Aggression in Relation to Different Frustrations. Journal of Abnormal and Social Psychology 67:1–7.
Davitz, Joel R. 1952 The Effects of Previous Training on Postfrustration Behavior. Journal of Abnormal and Social Psychology 47:309–315.
Dollard, John et al. 1939 Frustration and Aggression. Yale University Institute of Human Relations. New Haven: Yale Univ. Press.
Eibl-Eibesfeldt, IrenÄus 1963 Aggressive Behavior and Ritualized Fighting in Animals. Pages 8–17 in Jules H. Masserman (editor), Violence and War: With Clinical Studies. Academy of Psychoanalysis, Science and Psychoanalysis, Vol. 6. New York: Grune & Stratton.
Freud, Sigmund (1920) 1950 Beyond the Pleasure Principle. Authorized translation from the 2d ed., by C. J. M. Hubback. International Psycho-analytic Library, No. 4. New York: Liveright. → First published under the title Jenseits des Lustprinzips. A paperback edition, translated by James Strachey, was published in 1959 by Bantam Books.
Hokanson, J. E.; Burgess, M.; and Cohen, M. F. 1963 Effects of Displaced Aggression on Systolic Blood Pressure. Journal of Abnormal and Social Psychology 67:214–218.
Holst, Erich von; and Saint paul, Ursula von 1962 Electrically Controlled Behavior. Scientific American 206, March: 50–59.
Lorenz, Konrad 1952 King Solomon’s Ring: New Light on Animal Ways. New York: Crowell; London: Methuen.
Mcdougall, William (1908) 1936 An Introduction to Social Psychology. 23d ed., enl. London: Methuen. → A paperback edition was published in 1960 by Barnes and Noble.
Miller, Neal E. 1941 The Frustration-Aggression Hypothesis. Psychological Review 48:337–342.
Miller, Neal E. 1948 Theory and Experiment Relating Psychoanalytic Displacement to Stimulus-Response Generalization. Journal of Abnormal and Social Psychology 43:155–178.
Pepitone, Albert; and Reichling, George 1955 Group Cohesiveness and the Expression of Hostility. Human Relations 8:327–337.
Scott, John P. 1958 Aggression. Univ. of Chicago Press.
Seay, B. M.; and Harlow, Harry F. 1963 Personal communication.
Tinbergen, Nikolaas 1951 The Study of Instinct. Oxford: Clarendon.
White, Robert W. 1959 Motivation Reconsidered: The Concept of Competence. Psychological Review 66:297–333.
Power holders and decision makers in the parochial sovereignties into which mankind has been habitually divided have repeatedly resorted to armed violence against neighboring communities in pursuit of political objectives. Every such resort to force has invariably been regarded as aggression (hence as unjustified, illegal, and immoral) by its victims and, also invariably, been deemed moral, legal, and justified by the alleged “aggressors” on the grounds of “self-defense,” “preservation of the balance of power,” “national honor,” or some other plausible formula for rationalizing recourse to war.
Aggression as a concept or abstraction poses, therefore, a semantic and psychological problem rather than a problem admitting of solution by reference to traditional criteria of international law, diplomatic practice, military science, or international organization. In our time, aggression is a term of disapproval, usually limited to acts of military violence by “enemy” states whose purposes must be resisted. It is a prime article of faith, in the cult of nationalism, that aggression is always a crime committed by enemy governments and never a sin of one’s own nation-state. The obvious falsity of this dichotomy has had little or no effect on the behavior of those committed to its fallacies.
The problem is not so simple, however, as these introductory comments suggest. Whether, the propensity of human beings to resort to violence against other human beings is attributable to “instinct” or to “culture” has long been debated inconclusively. Some hold, with Sigmund Freud, that the human psyche is afflicted with a “death instinct,” which avoids suicide only by a triumph of Eros over Thanatos, or, more commonly, by deflection of aggression against the self to aggression against others. Others, along with Bronislaw Malinowski, hold that aggression is not innate but is a product of the frustration of other human aspirations.
The issue in international law
In the realm of interstate relations many people, and policy makers, confronted with the recurring tragedies of worldwide violence in the twentieth century, have earnestly striven to outlaw war and to forbid aggression by international agreement. All such efforts have thus far failed.
The “outlawry of war” was anticipated in many late medieval and early modern treaties whereby sovereignties solemnly pledged themselves to perpetual peace. Since such pledges had no discernible effect on the subsequent decisions of statesmen, the formula was abandoned in the nineteenth century. It was revived in the twentieth by the shock of World War i. The League to Enforce Peace, 1915-1919, championed American membership in a league of nations in which “aggression” was to be met with such overwhelming economic and military force that it would not be attempted.
The League of Nations Covenant of 1919 forbade recourse to war, with qualifications. The Kellogg-Briand Pact of 1928, which pledged its signatories to renounce war as an instrument of national policy, save in “self-defense,” was largely vitiated by the numerous national interpretations and reservations. Other bilateral and multilateral treaties of the 1930s reiterated the same goal. The Charter of the United Nations bound its members “to ensure, by the acceptance of principles and the institution of methods, that armed force shall not be used save in the common interest” and, further, “to maintain international peace and security, and to that end to take effective collective measures … for the suppression of acts of aggression or other breaches of the peace” (art. 1).
The assumption of the framers of the charter at San Francisco in the spring of 1945 was that a concert of powers, cooperating for common purposes, would guarantee peace and halt aggression by collective action, provided that the great powers with permanent seats on the Security Council would act unanimously on all measures of “enforcement” (cf. art. 27, the “veto” article of the UN Charter). The assumption proved false with the advent of the cold war in 1945/1946. Common action against aggression was henceforth impossible, with each contestant using real or alleged “aggression” by others as a weapon of propaganda, diplomacy, and strategy against the “enemy.”
Within the context of the logic of international law, aggression consists in resort to war or to measures of armed coercion short of formal war, undertaken in violation of treaty obligations not to resort to war or to other acts of force. In the years that followed the signing of the Kellogg-Briand Pact, national policy makers, with the support of all patriots, paid no attention to the legal duties they or their predecessors had assumed whenever prevailing concepts of “national interest” dictated an opposite course. Law is an effective guide to conduct only in organized communities whose members accept its purposes as paramount. The Western state system is not such a community.
The totalitarian states have provided numerous examples of violations of treaty obligations forbidding aggression—for example, the fascist conquest of Ethiopia in 1935-1936; the Nazi seizure of Austria and Czechoslovakia in 1938–1939; Axis intervention in Spain in 1936-1939; Hitler’s invasion of Poland in 1939; the Japanese assaults on China in 1931 and 1937 and on the United States in 1941; Stalin’s partition of Poland with Hitler in 1939; the Soviet attack on Finland in 1939-1940 and conquest of the Baltic states in 1940. However, the democracies have no better record. Witness, among recent instances, the abortive Anglo-French-Israeli attack on Egypt in 1956; India’s seizure by force of Hyderabad and Goa and attempted seizure by force in 1962 of territories in dispute between New Delhi and Peking; and the U.S. “spy flights” over the U.S.S.R. by U-2 planes (1955-1960), the Bay of Pigs invasion of Cuba in April 1961, and the “quarantine” of Cuba in October 1962. Other instances of resort to force come readily to mind, with each side accusing the other of “aggression”: the U.S. war on North Vietnam, launched February 7, 1965; the U.S. intervention in the Dominican Republic, April 28, 1965; the India-Pakistan war over Kashmir, September 1965.
The problem of definition
It is evident that decision makers in sovereign states do not abide by treaty obligations when “security” or “defense” or ambition dictates contrary conduct. This circumstance has led diplomats and legalists to cultivate the illusion that obedience to law could somehow be assured if only a more precise definition of aggression could be formulated and generally accepted. Laborious efforts at Geneva in the 1920s in the name of the League of Nations were devoid of operational results. Similar efforts by the United Nations since 1946 have been equally in vain. The most notable, albeit futile, attempt to define aggression was made by Maxim Litvinov, foreign minister of the U.S.S.R., at the London Economic Conference of 1933. On July 4 of that year he signed a “Convention for the Definition of Aggression” with envoys of Rumania, Yugoslavia, and Turkey (a few other states subsequently adhered). The signatories to this convention agreed to define the aggressor in an international conflict as that state which is the first to commit any of the following actions: (1) declaration of war upon another state; (2) invasion by its armed forces, with or without a declaration of war, of the territory of another state; (3) attack by its land, naval, or air forces, with or without a declaration of war, on the territory, vessels, or aircraft of another state; (4) naval blockade of coasts or ports of another state; (5) provision of support to armed bands formed on its territory which have invaded the territory of another state, or refusal, notwithstanding the request of the invaded state, to take on its own territory all the measures in its power to deprive those bands of all assistance or protection (art. 2). Furthermore, it was stipulated that no political, military, economic, or other considerations could serve as an excuse or justification for such acts of aggression (art. 3).
No better definition of aggression has been formulated since 1933. The futility of the enterprise is shown by the fact that Soviet policy makers in their “winter war” against Finland in 1939–1940 violated all the obligations they had so recently assumed. Other instances of violations of pledged words are innumerable in the diplomatic and military history of the twentieth century.
The premise of all efforts to outlaw war and to define and forbid aggression by bilateral or multilateral accords among sovereignties is that national policy makers will be deterred from misbehavior by their promises and by threats of action against them from the entire community of nations. In practice, the promises are frequently ignored, for reasons pointed out by Machiavelli more than four centuries ago. As for the efficacy of threats against aggressors in the name of collective security, the verdict of experience thus far is negative. National policy makers, dedicated to the pursuit of the national interest, whether this is defined in terms of power, pride, profit, or prestige, can always be relied upon, whatever their rationalizations, to ignore their commitments to refrain from aggression whenever they believe that resort to force will serve their purposes.
Aggression can probably never be prevented by legalistic formulae or by the artifacts of international organization and collective security, so long as the state system remains an arena of international anarchy among polities possessed of unlimited national sovereignty. Aggression will cease only when mankind reluctantly accepts the necessity of a drastic alteration of values and purposes in international relations and gives operational meaning to the ideal of world government. This goal is remote because of the universal disposition of Homo sapiens to cling to ancient ways in the face of new circumstances calling for new thought and threatening disaster if rethinking is resisted. In the absence of significant progress toward this objective, aggression in interstate relations will continue in the future, as in the past, with potentially catastrophic consequences—and all efforts to define, outlaw, and forbid recourse to force by one state against another must inevitably fail of their purpose.
Frederick L. Schuman
Boggs, Marion William 1941 Attempts to Define and Limit Aggressive Armament in Diplomacy and Strategy. Columbia: Univ. of Missouri Press.
Langer, Robert; and Schuman, Frederick L. 1947 Seizure of Territory: The Stimson Doctrine and Related Principles in Legal Theory and Diplomatic Practice. Princeton Univ. Press.
Litvinov, Maxim 1939 Against Aggression. New York: International Publishers. → Speeches, together with texts of treaties and of the Covenant of the League of Nations.
Research in International Law, Harvard Law School 1939 Draft of Conventions Prepared for the Codification of International Law. Concord, N.H.: Rumford Press. → Also published as a supplement to Volume 33 of the American Journal of International Law, 1939.
Stone, Julius 1958 Aggression and World Order: A Critique of United Nations Theories of Aggression. Berkeley: Univ. of California Press.
"Aggression." International Encyclopedia of the Social Sciences. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/social-sciences/applied-and-social-sciences-magazines/aggression
"Aggression." International Encyclopedia of the Social Sciences. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/social-sciences/applied-and-social-sciences-magazines/aggression
Distinctions have been made between different types of aggression, largely on the basis of the context in which it occurs or the stimuli that provoke it: (i) inter-male, or inter-female (territorial, social conflict, etc.); (ii) maternal; (iii) self defence; and (iv) infanticide. Aggression towards members of the same species has been divided more simply into ‘offence’ and ‘defence’. Predation, the hunting of other species, is sometimes included in discussions of aggressive behaviour, but is more properly classed as feeding behaviour.
Human aggression has been separated into ‘emotional’ aggression, carried out by people with the main intention of harming someone, and ‘instrumental’ aggression, with some other objective, such as to obtain something rewarding, rather than specifically to injure a victim. In general, both the form of the aggressive act and the context in which it occurs have to be taken into account.
Social factorsMost species, including human beings, live in social groups whose structure affects access by individuals to items in short supply — such as food, mates, or shelter. Direct aggressive confrontation may be used to determine which individual has priority, but it is more usual that animals come to know, through a process of social learning, who is likely to win in such an encounter. This determines their strategy, and also gives the group its dominance structure. Animals, or people, low in the hierarchy may not challenge those higher in the scale, presumably because of the cost in terms of potential injury. This mechanism of social control, based on previous aggressive interactions, functions to reduce aggression; but it does have potent effects on individuals. If it is to be effective, social control by hierarchy requires extremely sophisticated neural processing; indeed, there are those who claim that the primary function of the human brain is to facilitate social interaction.
Gender influencesThere are marked individual and gender-related differences in aggression. In most mammalian species aggression is more common between males than between females. Exposure of the brain to testosterone in the womb may alter infant behaviour: young males show more aggressive-like play than females. Testosterone may also sensitize the individual to the later effects of the same hormones: for example, increasing the likelihood of adult aggressive behaviour, particularly in the context of competition for desirable, but limited, resources. However, giving excess testosterone to men has had rather inconspicuous effects on their aggressive behaviour or tendencies (including thoughts), though levels of testosterone in the saliva have been shown to correlate positively with violent crimes in male prison inmates. But social status also alters testosterone, so the relation between individual differences in aggressivity and testosterone may be indirect. A variety of studies, in both human and non-human primates, has shown that social ‘stress’ (that is, demands made by the social or working environment) lowers testosterone and that ‘dominant’ males have higher levels. However, injecting ‘subordinate’ monkeys with testosterone does not improve their position in the hierarchy, or make them more aggressive.
Aggression is not a male prerogative. It also occurs in females, particularly when they need to defend their young. For example, lactating rats are highly aggressive to intruding males (rather than females). In this context, different hormones may play a role. This aggressive reaction seems to depend upon suckling, and has the obvious biological function of protecting the young. Testosterone given to lactating females actually reduces their aggressive reaction to males.
Are specific parts of the brain involved in aggression?Since much of aggression in the biological world is part of another behaviour, it is difficult to separate those areas of the brain responsible for the underlying behaviour (getting food, winning mates, etc.) from those associated with the particular behavioural strategy of aggression to achieve these ends. It has been known for many years that damage to a part of the brain called the amygdala results in ‘tameness’ and reduced aggression. The amygdala is part of the limbic system, a set of brain structures particularly concerned with survival, adaptation, and the defence of the body against the metabolic or social demands that constitute stress. The amygdala is closely involved in the ability of the brain to classify stimuli in a motivationally and emotionally meaningful way. Its role is not, therefore, restricted to aggression, but this along with many other behaviours is dependent on proper functioning of this part of the brain. Human cases are known in which disturbances of the amygdala have led to inappropriate or excessive aggression.
Another area of the brain implicated in aggression is the hypothalamus. Lesions or stimulation in several areas of the hypothalamus have altered aggressive interactions. The hypothalamus is implicated in other behaviours. For example, part of it has well-established roles in sexual and maternal behaviour, and it is prominently involved in the regulation of feeding and drinking. Bearing in mind the relation between aggression and other categories of adaptive behaviour, it is clear that there is still uncertainty about the exact role of the hypothalamus in aggression, and whether this can be truly separated from its other adaptive and homeostatic functions. Nevertheless, there are well-documented cases describing humans with tumours in the particular parts of the hypothalamus who became highly aggressive, responding with aggression to stimuli they would have previously considered only annoying. ‘Sedative’ surgical interventions, involving the hypothalamus, have been used in the treatment of aggressive patients.
We have seen that aggression forms an important part of social regulation and social interaction. This is known to involve the cortex of the frontal lobes of the brain. The frontal cortex is also intimately connected with both the amygdala and the hypothalamus and is therefore in a position to influence these other brain centres that control aggression. This behaviour can occur as a feature of frontal lobe damage in man. Patients with damage in one region of the frontal cortex react impulsively, without planning or taking into account the consequences of their behaviour; they are irritable and have short tempers, responding to minor provocation. But the frontal cortex is a complex area of the brain, and it is still not very clear whether particular parts may have distinct roles in aggression.
Are there specific aggression-related chemicals in the brain?The brain is a chemical machine, and the recognition that different parts can be defined by the chemical transmitters that they use offers a different perspective. In humans, changes in the level and metabolism of serotonin have been correlated with affective behaviour in general and more specifically with aggressive behaviour. Serotonin has become the major focus of biological studies of suicidal behaviour (defined as ‘self-aggression’) and impulsive aggressive behaviour in humans. An association has been reported between low serotonin concentration in the brain and impulsive, destructive behaviours, particularly when aggression and violence are involved. Studies in animals show that a wide range of aggressive behaviours are sensitive to manipulations of the serotonergic system. Depletion of brain serotonin increases aggression. Conversely, serotonergic-enhancing drugs, such as the specific serotonin-uptake inhibitors (SSRIs), reduce aggression. A class of drugs acting on serotonin are known as ‘serenics’; these reduce aggression.
But serotonin is not the only neurochemical implicated in aggression. Animal studies suggest that increasing brain dopamine activity creates a state in which they are more prepared to respond aggressively to stimuli in the environment. Antagonists of dopamine receptors are the most frequently used therapeutic agents in the management of violent patients. However, dopamine has important roles in generalized behavioural categories such as reward or punishment; this may be the real reason why it contributes to the display of aggression.
Hyperactivity of noradrenaline in the brain has been found to correlate with aggressive behaviour in humans, and noradrenergic receptor blockade is clinically useful in its treatment. This is supported by the effects on aggressive behaviours in isolated mice of drugs that modify noradrenaline activity in the brain.
Many peptides are found in the brain, particularly in the limbic system, that act as neurotransmitters. One of these, corticotrophin releasing factor, is present throughout the limbic system. It has an important role in organizing the co-ordinated response to stress; this includes behaviour, hormones, and the emergency systems regulating the cardiovascular and other autonomic responses. It may also increase aggression. Vasopressin (first known as a pituitary hormone) is another peptide found in the limbic system, and microinjections of this into the hypothalamus and amygdala increased offensive aggression in rodents. Although alterations in several peptides, as well as other substances, are known to change aggression, no single one so far has been specifically associated with this behaviour. Clearly, given the current preoccupation with understanding and controlling aggression in man, the existence of such compounds, should they be proved, would be most important.
The complexity of aggression — the behaviour pattern, the contexts in which it occurs, and the uses to which it is put — means that there can never be a single, definable system underlying it. Nevertheless, attempts should continue to define aggression more precisely, since this offers not only greater understanding of the relation between this behaviour and others but also direct help to those who try to control undesirable aggression in either animals or humans.
Albert, D. J.,, Walsh, M. L.,, and and Jonik, R. H. (1993). Aggression in humans: what is its biological foundation? Neuroscience and Biobehavioural Reviews, 17, 405–25.
Archer, J. (1988). Behavioural biology of aggression. Cambridge University Press.
Valzellli, L. (1981). Psychobiology of aggression and violence. Raven Press Books, New York.
See also hormones; peptides; serotonin; violence.
"aggression." The Oxford Companion to the Body. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/aggression
"aggression." The Oxford Companion to the Body. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/aggression
Because members of a population have a common niche, there is a strong potential for conflict. Agonistic behavior is displayed when there is a contest that will determine which competitor gains access to a particular resource—for example, food or a mate. The encounter involves both threatening and submissive behavior, and may also involve tests of strength. More often, the contestants engage in threat displays that make them look large or fierce, usually through exaggerated posturing and vocalizations. Eventually one animal will stop threatening and end with a display of submission or appeasement, in effect calling an end to the fight.
Much agonistic behavior includes ritual activity so that serious harm does not occur to either combatant. In many circumstances, escalated violence over ownership of a mate or commodity is less an adaptive behavior than it is an exchange of signals, whether threatening or submissive. The agonistic signals provide information about the likely intentions and levels of commitment of the senders, as well as the relative fighting ability if escalation occurs. Any future interactions between the same two animals is usually settled much more quickly and in favor of the original victor.
Aggression can be used in a number of different interactions, such as those concerning territorial defense, potential mates, parent-offspring communication, social integration, and food. Conflict resolution usually occurs at short sender-receiver distances. The senders perform actions with tactical and signal functions, and the receivers make decisions based on all the information pooled from the cues and all secondary sources.
Intra- and Interspecific Competition
Conflicts usually arise between two more or less equal individuals who need the same resources to secure or increase their fitness. Both would like to obtain the resource with minimal fighting, so both want the other individual to back down. However, the two opponents are rarely of equal fighting ability or resource-holding potential. Each combatant wants to convey that it is the superior fighter and so uses displays of aggression. However, each one must also assess the other's fighting ability relative to its own. Thus both individuals are senders and receivers simultaneously. The number of signals and tactical acts, and the truthfulness in the information being conveyed, must have something to do with the resolution of the conflict.
Types of Conflict
When the conflict is intraspecific , between members of the same species, dominance hierarchies come into consideration. For example, placing several hens together that are unfamiliar with each other results in pecking and skirmishing. Eventually, a pecking order is established in which the most dominant hen, the alpha hen, controls the behavior of all the other hens, mostly through threat rather than actual pecking. The beta (second-ranked) hen does the same and so on to the lowest hen, the omega. The advantage of the top hens is that they are assured access to food resources. There is an advantage for the lower-ranked hens as well, because the system ensures that they will not waste energy or risk injury in futile combat.
In the event that two or more species in a community rely on similar resources, they may be subject to interspecific competition. Actual fighting between members of two different species is termed interference competition, whereas the use or consumption of the "shared" resources is called exploitative competition. As population densities increase and resources such as food or nesting sites decrease, there is bound to be an increase in competition between the species. The same tactics of agonistic signaling apply here despite the variation in numbers and types of signals among the different species.
Strategies for Victory
Individuals in conflict can employ a number of strategies when assessing their opponent and the minimal level of aggression necessary to be the victor.
Hawk vs. Dove.
One theory, termed "hawk versus dove," helps explain why two animals do not always fight over the commodity that is sure to increase the fitness of the winner. Assuming the contestants are equal, there are two clear choices regarding the sought-after commodity: fight (as an aggressive hawk would do) or exhibit peaceable displays (as a dove would be more apt to do). When two hawks meet, they immediately fight over the commodity, with the loser suffering fight injuries as well as the cost of having lost the resource. Because the contest is assumed to be symmetric, each hawk wins half of its battles with other hawks. When a hawk meets a dove, the hawk becomes aggressive and the dove flees. Two doves will both use some costless exchange of displays to decide who gets the commodity and who leaves peacefully.
The take game.
Another contest that has been observed is a take game, which again involves two strategies: to be passive or to cheat. The passive animal minds its own business. The cheat, however, increases its own fitness at the expense of the fitness of others. The fishing activity of gulls and terns offers a good example. Some (passive) birds will concentrate solely on catching their own fish. Others (the cheats) will give up some of their own fishing time to monitor the success of other birds. When another bird catches a fish, the cheat will chase after the bird until the fish is dropped and then steal the fish. There is an advantage to cheating only if the bird can steal more fish than it would catch on its own.
The significance of this game is that once any cheats appear, the population will become most stable once all the organisms cheat. Evolution will have therefore lowered the average fitness of the population, a nonintuitive outcome given the assumption that evolution generally improves the average fitness of populations. It is only where evolution models a more passive approach to the acquisition of resources that populations enjoy improvements in their average fitness. However, many evolutionary models lead to lower average fitness, and this simply reflects the costs of competition.
The war of attrition.
Certain games employ strategies drawn from a continuous range of possibilities. A classic example is the war of attrition, in which two opponents compete by selecting an amount of strategic investment to be played during the particular confrontation. Neither opponent knows before the confrontation what level of investment the other has chosen. During the confrontation, the opponent that chose a larger investment wins. The investment might be the amount of time each is prepared to display to the other, or it might be how much energy the players put into the display.
It is unlikely that many animals meet the conditions for a symmetric war of attrition, where all players suffer the same cost of display and would obtain the same benefit in winning. Usually the rate at which costs accumulate will not be the same for any two players. Also, the commodity over which they are fighting is likely to have different fitness values for each player. The critical issue thus becomes which player stands to gain the most from the commodity and lose the least while trying to win it. If the two animals knew at the outset which one was on superior footing, then there would be no confrontation and the animal that stood to lose the most would leave immediately.
However, such complete and accurate information is rarely available as two opponents face each other. The "game" that is then played is called an asymmetric war of attrition. A player that suspects it has the winner role will likely select a higher investment, while a player that suspects it has the inferior role will likely select a lower investment. Of course, it is possible that both players will decide they occupy the same role. These considerations emphasize the uncertainty inherent in this game. Depending on the presumptions of both animals, the confrontation may brief—or it may prove to be a long and vigorous fight.
see also Behavior; Behavioral Ecology; Dominance Hierarchy; Social Animals.
Bradbury, Jack W., and Sandra L. Vehrencamp. Principles of Animal Communication. Sunderland, MA: Sinauer, 1998.
Campbell, Neil A. Biology, 3rd ed. San Francisco, CA: Benjamin/Cummings Publishing Company, 1993.
Maynard Smith, J. Evolution and the Theory of Games. Cambridge, U.K.: Cambridge University Press, 1982.
"Aggression." Animal Sciences. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/science/news-wires-white-papers-and-books/aggression
"Aggression." Animal Sciences. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/news-wires-white-papers-and-books/aggression
Aggression is defined as behavior that is intended to harm others and that is perceived as harmful by the victim. Because aggression is such a broad phenomenon, subtypes of aggression have been proposed to reconcile discrepant research findings—for example, that not all aggression is angry. Subtypes of aggression abound, but two classifications are most important: reactive versus proactive aggression, and physical versus social aggression.
Reactive aggression is angry, impulsive, and typically occurs in response to provocation, whereas proactive aggression (sometimes called instrumental aggression ) is more cool and deliberate and is deployed to achieve a social goal. Although reactive and proactive aggression are highly correlated, they seem to be related to different correlates and developmental outcomes (Coie and Dodge 1998). Reactive aggression is related to overattributing hostility in social interactions, whereas proactive aggression is related to expecting that physical aggression will have positive outcomes. Reactive aggression is associated with parental abuse, behavior problems in the classroom, and peer rejection and victimization. Proactive aggression is related to friendship similarity and leadership, and also predicts future antisocial behavior.
Because hurtful behavior can take nonphysical forms, perhaps especially for girls, other important subtypes to consider are physical and social aggression. Social aggression is behavior that hurts others by harming their social status or friendships. This form of aggression includes malicious gossip, friendship manipulation, and verbal and nonverbal forms of social exclusion (Underwood 2003). Social aggression is sometimes called indirect or relational aggression, but the construct of social aggression acknowledges that harm to relationships can be both direct and indirect, and that social exclusion can be both verbal and nonverbal. Here again, children’s propensities to engage in social and physical aggression are highly correlated. Both social and physical aggression may take reactive or proactive forms.
Across almost all cultures that have been studied, boys and men are more physically aggressive than girls and women are. However, evidence for gender differences is much less clear for social aggression. Because base rates for girls’ physical aggression are so low, without a doubt girls are more socially aggressive than they are physically aggressive. However, this does not necessarily mean that girls are more socially aggressive than boys are, and research findings conflict. Future research should examine whether social aggression unfolds differently in girls’ groups than in boys’ groups.
Physical aggression emerges in the first two years of life (Tremblay et al. 2005) and may have biological correlates. Experts disagree as to whether there is a strong genetic component for physical aggression, but genes likely underlie temperamental qualities that have been shown to be related to aggression in childhood, which appears in such forms as impulsivity, negative emotionality, and reactivity. Although testosterone has long been thought to be related to physical aggression, the relation between this hormone and physical fighting is complex and at best indirect. Elevations in testosterone are more related to social ascendance than aggression specifically.
Socialization experiences may relate to a child’s propensity for physical aggression. Children who experience harsh, abusive parenting may develop a bias toward interpreting ambiguous social cues as hostile, which leads them to be sensitive to slights and prone to reactive aggression. Children whose parents have an authoritarian style (punitive and low on warmth) may be more likely to have behavior and peer problems. Children who engage in coercive cycles with parents, in which the child’s behavior escalates until the parent gives in, thereby reinforcing the highly noncompliant behavior, are more prone to a number of antisocial behaviors that may include physical aggression. Children may also become increasingly aggressive as a result of exposure to media violence on television or in video games, although the direction of causation is difficult to disentangle because physically aggressive children may be more drawn to violent media content.
Physical aggression is associated with a number of adjustment problems, in childhood and beyond. Children who fight are at risk for peer rejection and academic difficulties; as adolescents, they are at risk for dropping out of school, delinquency, and substance use. Although fewer girls than boys fight physically, those that do are just as much at risk for these negative outcomes (Putallaz and Bierman 2004). For girls, physical aggression in childhood is associated with adolescent childbearing, and these adolescent mothers who were aggressive as children are at heightened risk for having children with health and behavioral problems.
Although much less is known about the developmental origins of social aggression, interesting hypotheses are emerging. Children may learn the power of social aggression by watching their parents resolve marital conflicts in ways that involve triangulating others and threatening relationship harm, or by watching how parents refrain from open conflict with friends but instead malign others behind their backs. Children may also learn social aggression by observing peers or siblings, or perhaps even by seeing relationship manipulation and malicious gossip gleefully depicted in television and movies, not only those aimed at children and adolescents but also adult programming.
Engaging in high levels of social aggression and chronically being victimized are both associated with psychological maladjustment for children. Children, especially girls, who are frequently victimized report elevated levels of depression, loneliness, anxiety, and low self-concept. In addition, children who frequently perpetrate social aggression are disliked by peers, and they report feeling lonely and anxious. In young adult women, being nominated by peers as high on social aggression has been shown to be related to bulimia and borderline personality disorder. As suggested by Nicki Crick and Carolyn Zahn-Waxler (2003), high levels of social aggression may be associated with the psychological problems to which girls and women are most vulnerable.
Future research should examine how physical and social aggression are related and unfold together in both real and developmental time. Promising strategies to reduce physical aggression involve training parents to respond strategically to their children by rewarding positive behavior and not reinforcing aggression, and teaching children skills that will help them regulate emotions and form relationships. Some of these same strategies may be helpful for reducing social aggression, and adding components that address social aggression may enhance the effectiveness of violence prevention programs.
Coie, John D., and Kenneth A. Dodge. 1998. Aggression and Antisocial Behavior. In Handbook of Child Psychology, ed. William Damon. Vol. 3, Social, Emotional, and Personality Development, ed. Nancy Eisenberg, pp. 779-862,. New York: Wiley.
Crick, Nicki R., and Carolyn Zahn-Waxler. 2003. The Development of Psychopathology in Females and Males: Current Progress and Future Challenges. Development and Psychopathology 15, 719-742.
Putallaz, Martha, and Karen L. Bierman. 2004. Aggression, Antisocial Behavior, and Violence Among Girls: A Developmental Perspective. New York: Guilford.
Tremblay, Richard E., Willard W. Hartup, and John Archer. 2005. Developmental Origins of Aggression. New York: Guilford.
Underwood, Marion K. 2003. Social Aggression Among Girls. New York: Guilford.
Marion K. Underwood
"Aggression." International Encyclopedia of the Social Sciences. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/social-sciences/applied-and-social-sciences-magazines/aggression-0
"Aggression." International Encyclopedia of the Social Sciences. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/social-sciences/applied-and-social-sciences-magazines/aggression-0
Aggression is behavior or a behavioral urge with the object of threatening or harming primarily members of one's own species. Several theories attempt to explain aggression.
Theories of aggression
The theory of instinct in ethology, as proposed by Konrad Lorenz (1903–1989), supposes that humans, like other biological creatures, are so constituted that they either continuously or periodically produce physiological energies that must seek outlet in certain kinds of species-specific aggressive behavior. Other ethologists argue that although innate genetic codes, as well as neural and hormonal processes, account for an aggressive disposition, there is no reason to assume the existence of aggressive energies. All ethologists agree, however, that aggression has arisen in the course of evolution and serves the same basic functions in animals and humans in regulating the intercourse between members of a species, although the regulation involves more psychological and cultural aspects with humans than with other animals.
This assumption is endorsed by sociobiology, first systematized by Edward O. Wilson (1929–), which studies the social behavior of humans using evolutionary methods. Like ethologists, sociobiologists presume an innate aggressive disposition in humans, but sociobiologists define innateness as the measurable probability that aggressiveness will develop in a species within a specified set of environments, not the certainty that it will develop in all kinds of environments.
The psychoanalytic drive theory of Sigmund Freud (1856–1939) resembles the instinct theory of Lorenz in the assumption that innate drives represent physiological energies. Freud departs from Lorenz, however, by assuming that the activity of the drives does not result in species-specific behavior patterns. Freud concluded that two drive complexes embodied in human beings constitute the basic sources of all human behavior; these were the life-building Eros and the life-demolishing Thanatos, with aggression, directed both outwards against others and inwards against oneself, as its central feature.
The theory of needs by Henry Murray (1893–1988) put forward a list of about twenty presumably universal human needs, among them aggression. In need theory there is no place for physiological energies. If a certain need, such as aggression, is dominant within a person in many different situations, it also appears as a personality trait.
The frustration theory, first presented by John Dollard (1900–1980) and his colleagues, explains aggression in a different way. Although aggression probably is a universal human disposition, aggressive behavior arises only as a reaction to incidents where purposeful behavior is blocked. Because this theory can only explain some kinds of aggression, it was modified by Leonard Berkowitz (1926–), who argued that aggression might still be a basic reaction to frustration.
The theory of learning proposed by Albert Bandura (1925–) and others places the origin of aggression solely in the social environment in assuming that aggressive behavior is learned during life history. Aggression is learned either because it is rewarded, or at least not sanctioned, and thereby reinforced. It may also be learned by observing aggressive behavior at home, on the streets, or from the media and entertainment industries, which show that aggression is worthwhile because it gets results, with aggressive people becoming models for imitation.
There might be elements of truth in all the theories, depending on which kind of aggression is in question in which kind of context: physical or mental, intended or reactive, instrumental or spontaneous, hostile or teasing, assaulting or defending, directed toward others or toward oneself, status demonstration, group conflict, sex, age, personality, and so on. Innumerable circumstances may influence the causes of aggression and aggressive behavior may involve a wide spectrum of explanations.
Aggression as evil
Anger is a faithful partner to aggression. For medieval Christians wrath was one of the seven deadly sins. Only God could pass judgment on righteous and unrighteous deeds, and in many cases anger arises when an offense is experienced as unjust. This tenet might have left deeper marks on culture than people are aware of, showing up in the widespread condemnation of anger and aggression. While moderate anger can instigate constructive action, blind anger often leads to destructive aggression. Yet to psychology and biology even furious anger and aggression cannot in itself be sinful, let alone evil. Because aggression is probably an unavoidable human trait, be it conceived of as innate or acquired, from a scientific point of view the very occurrence of aggression cannot be malice, and the absence of aggression cannot be kindness. For conceptions of good and evil to make scientific sense, evil must be viewed as the absence of an attempt to control aggression, thus preventing love to prevail.
In the animal kingdom human beings alone are able to curb their natural impulses and their learned habits, at least to some extent, and to listen to the voice of conscience, moral qualities that can be learned and even taught using psychological techniques. The attempt to curb aggressive behavior might not succeed, which in itself is not evil because it is bound to happen now and then. Evil is only the absence of the attempt to curb aggression, and the absence of remorse at not doing so. In psychological terms, such remorse could be called guilt in a more general sense than the concrete failure of the attempt, due to the conscience, which in its innermost voice tells a person that every concrete failure is a sin against the general good or a sin against love understood as the basic source of bonding and attachment in personal and social life. In this way, the concrete failure to curb aggression makes a person guilty against humankind, not only against the victim of the concrete failure. If a person grasps this idea of aggressive behavior, and yet in defiance and pride does not attempt to control aggression or seek atonement for the sin of failing to control it, then this person might be called evil. If so, probably all people are evil now and then, and many are evil fairly often. However, control can take the shape of inhibition and aggression can be turned inwards, which is not always mentally healthy either.
see also altruism; evil and suffering; psychology; sociobiology
bandura, albert. aggression: a social learning analysis. englewood cliffs, n.j.: prentice-hall, 1973.
berkowitz, leonard. aggression: its causes, consequences, and control. new york: mcgraw-hill, 1993.
dollard, john; doob, leonard w.; miller, neal e.; mowrer, orval hobart; and sears, robert r. frustration and aggression. new haven, conn.: yale university press, 1939.
freud, sigmund. beyond the pleasure principle (1920), trans. c. j. m. hubback. london: hogarth press, 1953.
lorenz, konrad. on aggression (1963), trans. margaret kerr wilson. new york: harcourt, 1966.
murray, henry a., et al. explorations in personality: a clinical and experimental study of fifty men of college age. new york: oxford university press, 1938.
wilson, edward o. sociobiology. cambridge, mass.: harvard university press, 1975.
"Aggression." Encyclopedia of Science and Religion. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/education/encyclopedias-almanacs-transcripts-and-maps/aggression
"Aggression." Encyclopedia of Science and Religion. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/education/encyclopedias-almanacs-transcripts-and-maps/aggression
Any act that is intended to cause pain, suffering, or damage to another person.
Aggressive behavior is often used to claim status, precedent, or access to an object or territory. While aggression is primarily thought of as physical, verbal attacks aimed at causing psychological harm also constitute aggression. In addition, fantasies involving hurting others can also be considered aggressive. The key component in aggression is that it is deliberate—accidental injuries are not forms of aggression.
Theories about the nature and causes of aggression vary widely in their emphases. Those with a biological orientation are based on the idea that aggression is an innate human instinct or drive. Sigmund Freud explained aggression in terms of a death wish or instinct (Thanatos) that is turned outward toward others in a process called displacement. Aggressive impulses that are not channeled toward a specific person or group may be expressed indirectly through safe, socially acceptable activities such as sports, a process referred to in psychoanalytic theory as catharsis . Biological theories of aggression have also been advanced by ethologists, researchers who study the behavior of animals in their natural environments. Several have advanced views about aggression in humans based on their observations of animal behavior. The view of aggression as an innate instinct common to both humans and animals was popularized in three widely read books of the 1960s—On Aggression by Konrad Lorenz , The Territorial Imperative by Robert Ardrey, and The Naked Ape by Desmond Morris. Like Freud's Thanatos, the aggressive instinct postulated by these authors builds up spontaneously—with or without outside provocation— until it is likely to be discharged with minimal or no provocation from outside stimuli.
Today, instinct theories of aggression are largely discredited in favor of other explanations. One is the frustration-aggression hypothesis first set forth in the 1930s by John Dollard, Neal Miller, and several colleagues. This theory proposes that aggression, rather than occurring spontaneously for no reason, is a response to the frustration of some goal-directed behavior by an outside source. Goals may include such basic needs as food, water, sleep , sex, love, and recognition. Contributions to frustration-aggression research in the 1960s by Leonard Berkowitz further established that an environmental stimulus must produce not just frustration but anger in order for aggression to follow, and that the anger can be the result of stimuli other than frustrating situations (such as verbal abuse).
In contrast to instinct theories, social learning theory focuses on aggression as a learned behavior. This approach stresses the roles that social influences, such as models and reinforcement , play in the acquisition of aggressive behavior. The work of Albert Bandura , a prominent researcher in the area of social learning, has demonstrated that aggressive behavior is learned through a combination of modeling and reinforcement. Children are influenced by observing aggressive behavior in their parents and peers, and in cultural forms such as movies, television, and comic books. While research has shown that the behavior of live models has a more powerful effect than that of characters on screen, film and television are still pervasive influences on behavior. Quantitative studies have found that network television averages 10 violent acts per hour, while on-screen deaths in movies such as Robocop and Die Hard range from 80 to 264. Some have argued that this type of violence does not cause violence in society and may even have a beneficial cathartic effect. However, correlations have been found between the viewing of violence and increased interpersonal aggression, both in childhood and, later, in adolescence . In addition to its modeling function, viewing violence can elicit aggressive behavior by increasing the viewer's arousal, desensitizing viewers to violence, reducing restraints on aggressive behavior, and distorting views about conflict resolution .
As Bandura's research demonstrates, what is crucial in the modeling of violence—both live and on screen—is seeing not only that aggressive behavior occurs, but also that it works. If the violent parent, playmate, or superhero is rewarded rather than punished for violent behavior, that behavior is much more likely to serve as a positive model: a child will more readily imitate a model who is being rewarded for an act than one who is being punished. In this way, the child can learn without actually being rewarded or punished himself—a concept known as vicarious learning.
The findings of social learning theory address not only the acquisition, but also the instigation, of aggression. Once one has learned aggressive behavior, what environmental circumstances will activate it? The most obvious are adverse events, including not only frustration of desires but also verbal and physical assaults. Modeling, which is important in the learning of aggression, can play a role in instigating it as well. Seeing other people act in an aggressive manner, especially if they are not punished for it, can remove inhibitions against acting aggressively oneself. If the modeled behavior is rewarded, the reward can act vicariously as an incentive for aggression in the observer. In addition, modeled aggression may serve as a source of emotional arousal.
Some aggression is motivated by reward: aggressive behavior can be a means of obtaining what one wants. Another motive for aggression is, paradoxically, obedience. People have committed many violent acts at the bidding of another, in both military and civilian life. Other possible motivating factors include stressors in one's physical environment , such as crowding, noise, and temperature, and the delusions resulting from mental illness . In addition to the acquisition and instigation of aggression, various types of reinforcement, both direct and vicarious, help determine whether aggression is maintained or discontinued.
Researchers have attempted to learn whether certain childhood characteristics are predictors of aggression in adults. Traits found to have connections with aggressive behavior in adulthood include maternal deprivation, lack of identification with one's father, pyromania , cruelty to animals, and parental abuse. A 22-year longitudinal study found patterns of aggression to be established by the age of eight—the aggressive behavior of both boys and girls at this age was a strong predictor of their future aggression as adults. Other factors cited in the same study include the father's upward social mobility, the child's degree of identification with parents, and preference for violent television programs.
See also Television and aggression
Aggression and Peacefulness in Humans and Other Primates. New York: Oxford University Press, 1992.
Aggressive Behavior: Current Perspectives. New York: Plenum Press, 1994.
Bandura, Albert. Aggression: A Social Learning Analysis. New York: Prentice-Hall, 1973.
Of Mice and Women: Aspects of Female Aggression. New York: Academic Press, 1992.
"Aggression." Gale Encyclopedia of Psychology. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/aggression-0
"Aggression." Gale Encyclopedia of Psychology. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/aggression-0
aggression, a form of behavior characterized by physical or verbal attack. It may appear either appropriate and self-protective, even constructive, as in healthy self-assertiveness, or inappropriate and destructive. Aggression may be directed outward, against others, or inward, against the self, leading to self-destructive or suicidal actions. It may be driven by emotional arousal, often some form of frustration, or it may be instrumental, when it is used to secure a reward.
Sigmund Freud postulated (1920) that all humans possessed an aggressive drive from birth, which, together with the sexual drive, contributed to personality development, and found expression in behavior. Austrian ethologist Konrad Lorenz suggested that aggression was innate, an inherited fighting instinct, as significant in humans as it was in other animals. He contended that the suppression of aggressive instincts, common among human societies, allows these instincts the chance to build up, occasionally to the point where they are released during instances of explosive violence. Many psychoanalysts have argued against these theories, which see aggression as a primary drive, offering the possibility that aggression may be a reaction to frustration of primary needs. In the late 1930s, John Dollard argued that any sort of frustration inevitably led to an aggressive response.
More recently, Albert Bandura has performed studies that indicated that aggression is a learned behavior. Using children in his studies, Bandura demonstrated that, by watching another person act aggressively and obtain desirable rewards or by learning through personal experience that such behavior yields rewards, aggression can be learned. Leonard Berkowitz has contended that all animals learn the most effective response to an aversive occurence (one where the expected reward is denied), whether it be attack or flight. A number of psychologists contend that children and adolescents are vulnerable to media portrayals of violence, particularly in film and television. Popular media tends to depict violence as relatively common, and generally effective. Anonymity may facilitate aggression: when an individual is part of a large group, he may be more likely to elicit aggressive behavior, in a process known as deindividuation.
Recent research on the biological basis of aggression has sought to show that genetic factors may be responsible for aggressive behavior. In the 1970s it was suggested that men who were born with an extra Y chromosome were likely to display more episodes of aggressive behavior than men who were not born with this extra chromosome. Still, conclusive proof has yet to be found for a genetic theory of aggression.
Other factors, including learning difficulties, minimal brain damage, brain abnormalities—such as temporal lobe epilepsy—and such social factors as crowding and poverty have been suggested to have contributed in certain cases to exaggeratedly aggressive behavior. Psychological investigation into aggressive behavior continues, with significant corrolary studies being performed in endocrinology—to determine whether hormonal imbalances have an impact on behavior—and in primate research. Each theory may be accurate in part, since aggression is believed to have a number of determining factors.
See J. Archer and K. Brown, ed., Human Aggression (1988); R. A. Baron and D. R. Richardson, Human Aggression (1991).
"aggression." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/aggression
"aggression." The Columbia Encyclopedia, 6th ed.. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/aggression
However, most sociological theories of aggression root it not in the biological substructure or psychological superstructure of the individual, but in his or her relationship to the social environment. Probably the most popular of these is the so-called frustration-aggression hypothesis or theory, which states that aggressive behaviour results when purposeful activity is interrupted (see the classic statement in J. Dollard et al. , Frustration and Aggression, 1939
). Thus, for example, children may attack other children who take their toys from them. This theory has, however, been criticized for its inability to explain the circumstances under which frustration leads to outcomes other than aggression. (Some children may simply sulk quietly under these circumstances.) The frustration-aggression thesis has also been identified with the earlier work of Sigmund Freud, who argued that frustration—the blocking of pleasure-seeking or pain-avoiding activities—always leads to aggression, either towards the perceived source of interference, or (if inhibited) displaced on to another object. (Freud later postulated that aggression was the product of the death instinct—Thanatos.)
A third group of theories—learning theories—view violence as the result of successful socialization and social control. That is, aggressive behaviour in general and violent behaviour in particular occur where they are expected, even in the absence of frustration. For example, members of a subculture may learn to behave in accordance with norms of violence which have been presented to them as socially desirable, as in cases where the use of force (such as fist-fighting) is associated with masculinity. Similarly, soldiers at the front and teenagers in a gang may feel violence is acceptable and the done thing, because they have been brought up to believe this to be the case, expect to win approval and prestige if they fight well, and wish to avoid censure should they ‘chicken out’. See also DIFFERENTIAL ASSOCIATION.
"aggression." A Dictionary of Sociology. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/social-sciences/dictionaries-thesauruses-pictures-and-press-releases/aggression
"aggression." A Dictionary of Sociology. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/social-sciences/dictionaries-thesauruses-pictures-and-press-releases/aggression
"aggression." A Dictionary of Biology. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/aggression-1
"aggression." A Dictionary of Biology. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/aggression-1
ag·gres·sion / əˈgreshən/ • n. hostile or violent behavior or attitudes toward another; readiness to attack or confront: territorial aggression between individuals of the same species. ∎ the action of attacking without provocation, esp. in beginning a quarrel or war. ∎ forceful and sometimes overly assertive pursuit of one's aims and interests.
"aggression." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/aggression
"aggression." The Oxford Pocket Dictionary of Current English. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/aggression
Unjustified planned, threatened, or carried out use of force by one nation against another.
The key word in the definition of aggression is "unjustified"—that is, in violation of international law, treaties, or agreements. It was the basic charge leveled against Nazi Germany at the nuremberg trials in 1946.
"Aggression." West's Encyclopedia of American Law. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/law/encyclopedias-almanacs-transcripts-and-maps/aggression
"Aggression." West's Encyclopedia of American Law. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/law/encyclopedias-almanacs-transcripts-and-maps/aggression
So aggressive XIX; perh. after F.
"aggression." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/aggression-0
"aggression." The Concise Oxford Dictionary of English Etymology. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/aggression-0
"aggression." A Dictionary of Ecology. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/aggression
"aggression." A Dictionary of Ecology. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/aggression
"aggression." A Dictionary of Zoology. . Encyclopedia.com. (April 22, 2017). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/aggression-0
"aggression." A Dictionary of Zoology. . Retrieved April 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/aggression-0