Serotonin and Impulsive Aggression: Not So Fast

Joel Wallman

This article appeared in The Biology of Aggression, the Spring 1999 edition of The HFG Review, a Harry Frank Guggenheim Foundation publication that examined topics of violence in depth.

The quest to root violent criminality in organic shortcomings has a long and, viewed with the wisdom of hindsight, sometimes silly history. Lombroso’s diagnostic taxonomy of criminal physical features, the phrenology of Gall, Kretschmer’s body typing and, more recently, the attempt to link the XYY or “supermale” genetic constitution to criminality are textbook cases of fruitless efforts to explain bad behavior as the outcome of bad biology.

Contemporary endeavors are, on the whole, far more sound in their scientific methods, if thus far not much more compelling. Studies linking persistent impulsive aggression to deficits or excesses of various juices of the brain (dopamine, GABA, MAOA), the nether regions (testosterone, estrogen), or parts in between (adrenal steroids) have yielded occasionally suggestive but generally equivocal findings. The same applies to research on areas of the brain, the most traveled in this search being the frontal and temporal lobes, amygdala, and hypothalamus.

One promising exception is the neurotransmitter serotonin. Dozens of studies have found that people with documented histories of impulsive violence have, on the average, a reduction in function of the serotonin system relative to people without such a profile. This has been found whether serotonin function is assessed by lumbar spinal tap of cerebrospinal fluid to determine the quantity of serotonin’s metabolic byproduct or by less direct measures, such as the magnitude of biochemical response to ingestion of a substance that increases serotonin production.

These and other methods are quite removed from direct assay of serotonin function in the brain, but the correlation between serotonin deficit and impulsive violence, both self- and other-directed, is a recurrent finding nonetheless. Moreover, studies in non-human animals in which serotonin levels were experimentally reduced through chemical intervention found an increase in aggressive behavior (compared to control animals subjected to identical delivery of an inert substance), suggesting that the correlation found in human research reflects a true causal relationship.

In the serotonin deficit, then, we seem to have a constitutional flaw underlying the syndrome of impulsive violent behavior. If serotonin abnormalities are truly linked in a specific way to aggression as opposed to behavior problems more generally, then we have a window into not just pathologies of aggression but the normal neurobiology of aggression as well. This discovery also provides a basis for intelligent conjecture about the selective forces governing the evolution of both serotonin and aggression in animals in general, primates more specifically, and humans in particular.

Yet one needn’t be a student of neurotransmitters to wonder about the specificity of the connection between serotonin and aggression. A regular reader of New York Times articles on human behavior and health, for example, might well be troubled in attempting to collate the implicit claim that serotonin is the “aggression chemical” with reports that underactive serotonin circuits are also the cause of migraines (July 24, 1996, section C, p. 8), extreme shyness (May 18, 1999, section C, p. 1), obsessive-compulsive disorder (February 16, 1997, section 13CN, p. 3), anxiety and pessimism (November 29, 1996, section A, p. 1), and “restless leg” syndrome (night cramps) (April 10, 1996, section C, p. 10). A survey of popular books on the virtues of keeping one’s serotonin up will reveal that a deficit of this substance is responsible for craving and hence addiction to gambling, drugs, sex, and food (The Craving Brain, Ronald Ruden and Marcia Byalick); that, in addition to controlling emotion, serotonin is in charge of “intellect” (Naturally Slim & Powerful, Philip Lipetz and Jean Zevnik); and that serotonin is the culprit in insomnia (5-HTP: The Natural Way to Boost Serotonin and Overcome Depression, Obesity and Insomnia, Michael T. Murray). Combine this litany of affliction with the knowledge that tens of millions of people are being prescribed Prozac, a serotonin enhancer, on the apparently well-established medical belief that depression derives from—yes—a serotonin deficit, and, unless all of these reports and claims are dismissed as baseless, one is justified in concluding that a serotonin shortage manifests itself in a congeries of emotional and behavioral problems, including but by no means limited to aggression.

That conclusion is certainly consonant with the fact that serotonergic neurons, which reside in the brainstem, project their axons into many and functionally diverse regions of the brain, including the amygdala, hypothalamus, hippocampus, cerebellum, and temporal and prefrontal regions of the cerebral cortex. It would be surprising, given this wide ramification, if abnormalities of the serotonin system affected aggression in a specific way.

Just how sound are the numerous studies reporting a specific association between diminished serotonin function and violent behavior? A meta-analysis of this literature by Balaban and colleagues (1996) is illuminating. From 70 studies, Balaban chose 39 that provided sufficient information for an analysis employing the variables Balaban thought pertinent to answering the question. The subjects in these studies fall into three categories: violent psychiatric patients, nonviolent psychiatric or neurological patients, and normal, healthy control subjects. Not all studies employed all three groups, but a typical finding of those that did was reduced serotonin in the violent psychiatric group compared to both the nonviolent patients and normal controls, with no difference between the latter two, indicating that serotonin deficiency is associated specifically with violent psychiatric conditions rather than with serious psychiatric problems in general.

However, there are non-psychiatric sources of variability in serotonin level, and few of the serotonin studies take them into account (i.e., statistically control for them) in all subject categories used. In particular, serotonin (actually 5-HIAAA, its main break-down product) measured at the lumbar level through spinal tap is lower in males, goes up with age, and declines with stature. (Serotonin diffuses out of the brain into the cerebrospinal fluid. From there, most of it is transported to the bloodstream; the fraction making it down as far as the lumbar region decreases with increasing spinal length).

Using those studies in the set of 39 that provided information on height, age, and sex of normal controls, Balaban computed the effects of those variables alone on serotonin level. These values were then used to adjust the measured serotonin levels in all studies for all subject categories for which mean height and age and male-female ratio were published. Because the three subject categories happened to consistently differ in these traits, correcting for these non-psychiatric determinants of serotonin level yields results that are quite different from what is typically reported: violent psychiatric patients do indeed have somewhat lower levels than normal controls, but so do the non-violent psychiatric and neurological patients, and the psychiatric groups do not differ from each other. In short, people with a history of being in an institution or under psychiatric or neurological treatment have lower levels of serotonin than normal nonpatients.

In addition to the reasons adduced above for questioning the usefulness of low serotonin as a marker for impulsive aggression, there are reports in the scientific literature that, while far from refuting the claim that low serotonin increases impulsive aggression, contradict it and thus warrant weighing in the balance. These are not simply studies that fail to find a relationship between low serotonin and aggression—unless the relationship were extremely strong in a statistical sense, one would expect a certain number of studies to come up empty by chance even if the relationship were generally valid. One kind of contradictory finding is the observation in at least two studies that highly aggressive children evince not a reduction but an increase in serotonin function (Castellanos et al. 1994; Halperin et al. 1994). And there is the much-cited discovery in a large Dutch family of an association between a genetic deficiency of the enzyme MAOA and impulsive violent behavior (Brunner et al. 1993). What has gone unremarked on in the discussion of this finding (which, predictably, was heralded in the non-technical media as the revelation of a “gene for aggression”) is the problem it poses for the other major putative organic cause of abnormal aggression, serotonin. For MAOA is the enzyme that, among other functions, breaks down serotonin, which means that the affected men in this group would, arguably, have an excessively high level of serotonin. And, finally, the same primate experiments mentioned earlier, which showed that altering serotonin level affects behavior, also provide evidence that serotonin is equally a result of behavior. If the dominant male is removed from a group of vervet monkeys, an aggressive contest for dominance results. The male that ascends to top rank will experience an increase in serotonin level, and the exiled alpha male, if not returned to its group, will undergo a serotonin drop (McGuire and Troisi 1998). To the extent that it is legitimate to extrapolate to humans, this observation calls into question the assumption that serotonin abnormality precedes the behavioral problems with which it has been linked.

The correct inference from all of the foregoing is not that anyone low on the serotonin scale should be a dangerous, depressed, and overweight compulsive gambler, torn between shyness and nymphomania, who would be kept awake at night by their headaches and restless legs even if they didn’t suffer from insomnia. It is rather that serotonin is not a very discriminating marker for violence and that the neurophysiological and neurochemical characteristics that accompany low serotonin—whether as causes, consequences, or both—are not limited to brain regions that govern aggression.

But what if there were no ambiguity about the serotonin-aggression relationship? If it were clearly established that underactive serotonin circuits increased the risk for serious aggressive behavior, and only that risk, what insight would be gained into human violence? Would it help us understand the shocking increase in youth homicide in the United States beginning in the middle 1980s or the decrease of recent years? Would it clarify why the rate of violent crime has declined in New York, Los Angeles, and Tampa but increased in New Orleans and Richmond, why Nevada’s murder rate is 10 times higher than South Dakota’s, or why the U.S. rate is 15 times higher than Britain’s?

The explanation of these facts will come not from research in neurobiology but from understanding economic forces, variation in cultural mores regarding the acceptability of violence, diversity in the kinds and efficacy of means of informal and formal social control, and availability of firearms. A reasonable response to this assertion would be to suggest that individual differences in serotonin could explain why this person rather than the next succumbs to the distinctive mix of violence-promoting influences impinging on a given neighborhood, ethnic group, class, or nation. I am rather pessimistic about the potential of this approach, however. But that may just be the serotonin talking.


  1. Balaban, E., J. S. Alper, and Y. L. Kasamon. 1996. Mean genes and the biology of aggression: A critical review of recent animal and human research. J. Neurogenetics 11: 1-43.
  2. Brunner, H. G., M. Nelen, X. O. Breakefield, H. H. Ropers, and B. A. van Oost. 1993. Abnormal behavior associated with a point mutation in the structural gene for monoamine oxidase A. Science 262: 578-80.
  3. Castellanos, F. X., J. Elia, M. J. Kruesi, C. S. Gulotta, I. N. Mefford, W. Z. Potter, G. F. Ritchie, and J. L. Rapopor. 1994. Cerebrospinal fluid monoamine metabolites in boys with attention-deficit hyperactivity disorder. Psychiatry Research 52: 305-16.
  4. Halperin, J. M., V. Sharma, L. J. Siever, S. T. Schwartz, K. Matier, G. Wornell, and J. H. Newcorn. 1994. Serotonergic function in aggressive and nonaggressive boys with attention deficit hyperactivity disorder. Am J Psychiatry 151: 243-8.
  5. McGuire, M. and A. Troisi. 1998. Darwinian Psychiatry. New York: Oxford University.

Some Things Psychologists Think They Know About Aggression and Violence

Clark McCauley

Professor of Psychology, Bryn Mawr College; Co-Director, Solomon Asch Center for the Study of Ethnopolitical Conflict, University of Pennsylvania; HFG grantee

This article appeared in Teaching About Violence, the Spring 2000 edition of The HFG Review, a Harry Frank Guggenheim Foundation publication that examined topics of violence in depth.

There are two distinctions that are crucial in the psychology of aggression and violence. The first is impulsive vs. instrumental aggression, and the second is individual vs. group aggression. Conveying these fundamental concepts to students is essential for teaching the psychology of intergroup conflict and genocide, where the costs of human aggression are highest.

Impulsive Aggression Is Different from Instrumental Aggression

Psychologists understand aggression to be behavior aimed at harming another member of the same species, and most psychologists distinguish between impulsive and instrumental aggression. Impulsive aggression (also known as irritable, angry, or expressive aggression) is marked by strong emotion, especially anger, and is aimed at hurting another. Instrumental aggression is cooler and the hurt delivered to another is not an end in itself but only the means to some other end. Aggression in a mugging, for instance, is aimed at getting the victim’s money; aggression against Saddam Hussein’s Iraq is aimed at repelling an aggressor.

Of course a particular instance of aggression may involve both impulsive and instrumental aggression, as when a parent spanks a child for going into the street. The spanking may be aimed at keeping the child out of the street in the future (instrumental aggression), but it may at the same time express the parent’s fear and anger in reaction to the child’s danger and disobedience (impulsive aggression). Although pure cases of impulsive or instrumental aggression may be rare, it is often useful to ask about a particular case of aggression whether it is predominantly impulsive or instrumental. Studies of aggression in children, for instance, have found it useful to distinguish reactive (impulsive) from proactive (instrumental) aggression.

Sociologists and criminologists studying violent crime are also beginning to use this distinction. Psychopaths are individuals with defective emotions; they do not experience normal levels of shame, guilt, or fear. Possibly as a result of this defect, they also have weak and transitory social attachments; they treat other people as objects. Psychopaths show predominantly instrumental aggression, as they use aggression coldly, as a means of controlling others. They are likely to continue aggressive acts despite conviction and punishment, and they are over-represented in prison populations.

Compared with instrumental aggression, impulsive aggression may be more easily deterred, or at least recidivism is less for crimes involving anger. A man who kills in anger in a bar brawl is less likely to kill again than a man who kills in the conduct of a robbery. Similarly, it appears that men who assault their female partners or their children in anger are more likely to quit than those who use aggression coldly, as a means of controlling those around them. There is also evidence that impulsive aggression, but not instrumental aggression, is related to low levels of serotonin in the brain.

If impulsive aggression looks like the lesser of two evils, it may be because anger, like shame and guilt, is a moral emotion. Aristotle said that anger is a reaction to insult—a specific form of moral violation. Modern frustration-aggression theory says that anger is a reaction to any noxious experience, including frustration. However, frustration-aggression theory recognizes the importance of moral violation as justifying the expression of anger and aggression. Further indication of the importance of moral violation in anger and aggression is provided by survey data indicating that the most common occasions of anger are perceived infringements of authority or independence, or other threats to positive self-image. Aristotle and modern psychology are agreed in seeing moral violation at the center of anger and impulsive aggression.

Group Violence Is Different from Individual Violence

The psychology of individual aggression is importantly different from the psychology of intergroup conflict. In general terms, it is the least socialized who are disproportionately involved in individual violence, whereas it is often the best socialized who are involved in intergroup violence.

Individual violence is represented in the statistics of violent crime: murder, robbery, assault, and rape. Although violence associated with organized crime groups and youth gangs makes some contribution to these statistics, the overwhelming majority of violent crime offences are individual offences. Violent crimes are committed disproportionately by individuals of lower socioeconomic status—individuals poorer and less educated than average. These are often individuals who do not accept the larger societal norms that give to the state a monopoly of the use of violence. Their weak socialization may be more cultural than personal, that is, the individual may be part of a deviant subculture in which violence is more acceptable than it is in the dominant culture. Still, from the point of view of the state and its norms, violent crime is predominantly a problem of undersocialized individuals.

In contrast, intergroup violence depends upon the leadership and example of well-socialized individuals. The prototype of intergroup violence is the violence of interstate war, and studies of U.S. and Israeli soldiers show consistently that the best soldiers are above average in civilian qualifications. Despite the many films based on a “dirty dozen” of career criminals forged into an effective combat team, the reality is that success in modern war depends on soldiers with middle-class levels of intelligence and education, multiplied by entrepreneurial virtues of initiative and cooperation. As war becomes more complex, success depends more on having good people up front.

The crucial role of well-socialized individuals is evident particularly in the extent to which good people do bad things in the name of the state. It was not the worst but some of the best of American boys who dropped firebombs on Dresden, Hamburg, and Tokyo and atom bombs on Hiroshima and Nagasaki. It was no less obvious then than now that, in time of war, city bombing is killing mostly noncombatants—old people, women, and children. Similarly, studies of police and military torturers reveal these individuals to be unremarkable except perhaps for a stronger-than-ordinary sense of duty and respect for authority.

Thus it is the least socialized who are disproportionately involved in individual violence, whereas the best socialized are the foundation of intergroup violence. The distinction is important because the origins of individual violence are mostly to be found in individual differences that tell us little about group conflict. Rather the origins of group conflict are in the power of group dynamics, and the origins of genocide are in the power of the state.

Government Is the Big Killer

The twentieth century has seen unprecedented accomplishments in killing, and government is the big killer. In a century of two world wars and many smaller ones, including civil wars, about 40 million men have died in uniform. But governments also kill non-combatants, and the total of these deaths for the twentieth century is approximately 150 million. Mao killed class enemies of the people; Stalin killed class enemies and nationalities; Hitler killed Jews and gypsies; Pol Pot killed class enemies and “non-Cambodian” minorities. To these official target groups must be added those who did not accede to state power—liberal elements, former allies, personal enemies of state leaders. The striking aspect of this killing is that it is within rather than across state boundaries: Chinese killing Chinese, Soviets killing within the U.S.S.R., Hitler killing within Germany and German-occupied territories, Pol Pot killing Cambodians.

Some cases of state killing are often hidden under the label of “ethnic conflict”: Turks killing Armenians, Hutus killing Tutsi, Serbs killing Albanians. In these cases we do not have a name to hitch to the killing: no Mao, no Stalin, no Hitler, no Pol Pot. Without a name to blame, we may find it easy to ascribe the killing to “ancient enmities” of tribe or ethnic group. “Ancient enmities” implies mass hatred—most people of one group hating another group, most of one group rising up to kill the most they can of the hated group. In fact, however, mass killing typically involves relatively small groups of killers.

In Rwanda, it is estimated that only about one percent of Hutus actually participated in killing Tutsi. The Hutu elite prepared the population to accept genocide with months of radio broadcasts about Tutsi plans for domination; the killers were prepared with prioritized lists of those, Hutu as well as Tutsi, who were to be killed. The fact that the killing employed mostly low-tech weapons like machetes and clubs does not mean it was not organized. Similarly it seems likely that no more than one percent of Turks participated in killing and transporting Armenians, and no more than one percent of Serbs participated in ethnic cleansing in Kosovo.

The fact that killers are a small minority in ethnic cleansing is inconsistent with ancient-enmities explanations of ethnic conflict and genocide. Mass killing involves not a mass of individuals boiling with hate or fear, but massive organization and planning. Individual hatreds make exceptions for friends and neighbors, and individual killers get tired or run out of victims. Mass killing requires prioritizing victims, transporting and supplying killers, transporting and disposal of those to be killed. Mass killing requires the industrialization of killing with the power of the state—not impulsive aggression by the many but instrumental aggression by a few.

In contrast to government killing, terrorist killing is relatively small. A terrorist group aims to bring down the state by threatening and killing those who support the state. Since World War II, only a handful of terrorist groups have succeeded in replacing the state they were fighting: in Palestine, Algeria, and South Africa; perhaps in South Vietnam and Northern Ireland. Although states have for several decades been concerned about nuclear, biological, and chemical attacks in which terrorists would kill millions, thus far terror from below has not come close to the killing accomplished by state power—terror from above.

Intergroup Violence Is Normal Group Psychology, Not Individual Pathology

The psychology of state violence is twofold. There is the psychology of leaders who plan and order the violence, and there is the psychology of those who perpetrate the violence.

It is tempting to say that anyone who can order millions of innocent people killed must be crazy. The usual specification of the craziness is psychopathy, the diagnostic category described earlier as associated with use of instrumental aggression. Unfortunately for this comfortable view of evil as distant from normality, there is no evidence that leaders such as Mao, Stalin, Hitler, or Pol Pot were psychopaths. Indeed, it is unlikely that a psychopath, with typically impoverished social relations, could develop the relationships and loyalties required for effective leadership. The mega-killers are normal men who devoted their lives to gaining power for themselves and for an idea that justifies killing—often an ideology of class or race advancement.

Similarly, it is tempting to say that anyone who can perpetrate violence against civilians—anyone who can kill old people, women, and children—must be a psychopath. But, as noted above, some of America’s best have been capable of this kind of violence. Individual motives and individual pathology cannot explain intergroup violence; state killers and those who direct them can only be understood at the level of group psychology.

People care about groups, even groups they are not part of, like sports teams and famine victims. Research indicates that group attachments are a better predictor of political opinions than individual self-interest. White support for school desegregation, for instance, is not related to having school-age children but is related to sympathy for blacks. Voters are not asking “What’s in it for me?” but “What’s in it for the groups I care about?” This is what is meant by group identification: caring about what happens to a group. In positive identification, we want good things to happen to a group; in negative identification, we want bad things to happen. Theory and research from a number of perspectives can illuminate the ways in which group identification affects our behavior.

According to terror-management theory, our attachment to important cultural groups is our buffer against mortality. Humans are the only animals that know they are going to die. The human answer to mortality is participation in a group that will not die when the individual dies. Larger groups with longer histories and more glorious futures offer better reassurance against mortality, so family, ethnic, religious, and national groups offer more reassurance than neighborhood, recreational, and occupational groups. Terror-management theory answers the question of why individuals should be willing to die for their national or ethnic group: dying for a cultural group gives meaning to life and an answer to death.

TMT is an extension of group-dynamics theory in relation to the social-reality function of groups. As science is grounded in replication, so individual perceptions are validated by the agreement of others. If someone says she can see a star where I see none, I am ready to admit the star and my weak eyes when a third person says she can see the star.

The central concept of group-dynamics theory is cohesion, the attractiveness of the group to its members. As emphasized by TMT, cohesion is increased by the degree to which group consensus offers an antidote to uncertainty about issues of meaning and value. Cohesion is also increased by more mundane membership rewards, such as congeniality, status, and accomplishment of group goals.

High cohesion leads to strong pressures for uniformity on issues relevant to the group. This is basically a homeostatic prediction, in which differences of opinion that would get in the way of a social-reality consensus or pursuit of group goals must be controlled if members are to experience the rewards that attract them to the group. For group members, higher cohesion thus leads to greater acceptance of group norms, more rejection of deviates, and greater respect for and obedience to group leaders.

Although developed in studies of small face-to-face groups (primary groups), the predictions of group-dynamics theory can be scaled up to apply as well to larger collectivities, such as ethnic and national groups, that are so large that most members cannot be known personally (secondary groups). Identification with secondary groups is equivalent to cohesion in primary groups, and the consequences of primary-group cohesion can be predicted as well from identification with secondary groups. More identification should lead to greater acceptance of ethnic or national group norms, more rejection of those who deviate from these norms, and more respect for ethnic or national leaders.

The power of the group and the consequences of cohesion are explicated in some of the classic experiments in social psychology. In Solomon Asch’s experiments on conformity, 75% of college students denied the evidence of their own eyes to give an incorrect judgment of line length when seven other students (confederates of the experimenter) unanimously gave the incorrect judgment. This power was increased by greater uncertainty (more difficult line discriminations) and decreased by any break in the unanimity of the majority (if even one confederate gave the objectively correct judgment). If the subjects could make their judgments privately rather than aloud, conformity was cut by two thirds.

One clear implication of these results is that group influence depends partly on group power to reward conformers and punish deviates; when the group could not hear the subject’s judgment, conformity was decreased. The conformity remaining with private judgment shows a different kind of group influence, influence based on subjects accepting the judgments of others as valid information about reality. Group power to define reality is even stronger on issues of value, where there is no source of certainty except group consensus.

Both kinds of group power contribute to killing in intergroup conflict. Killers are controlled by the rewards and punishments of their group, and by their acceptance of group norms and the social reality defined by group consensus. In time of war, every state depends on coercion to make men fight: prison or death for refusing conscription, prison or death for desertion, prison or death for disobeying an order. Terrorist killers are probably less controlled by coercion than by the social-reality power of their group, inasmuch as terrorist groups only wish they had the reward and punishment powers of the state.

Even for soldiers, however, the controlling group norms tend to be more the values of the combat group than the values of the state. Research with American soldiers in particular has shown that, in the stress of combat, most soldiers fight less for cause or country or hatred of the enemy than for their buddies. The half dozen or dozen men who share the loneliness of the battlefield are closer than brothers; they fight because to do less is to endanger the group on which they are totally dependent. One of the great lessons of social psychology is that group power is maximized when group members have no other group to turn to. In combat groups as in terrorist groups, the individual’s social world has contracted to just the few around him.

A similar account has been offered for genocidal killing. Christopher Browning describes how middle-aged German men in uniform came to participate in killing Jews. The Reserve Police were sent to Poland, separated from family, friends, and previous occupations in a foreign land where their only home was their unit. Their officers had orders to kill Jews, but, at least initially, did not threaten much coercion against men who could not or would not. In this situation, it is not individual motives of anti-semitism that explain the killing. Browning points instead to the cohesion of “ordinary men,” for whom the best reason to kill Jews was that those who did less put more burden on their fellows.

Browning puts considerable emphasis also on desensitization and routinization of killing in explaining how men slowly escalated their participation in killing. This is the psychology of commitment, much studied in research on dissonance theory. In its modern version, dissonance is a theory of rationalization in which individuals sucked into stupid or sleazy behavior will change their opinions to justify and make sense of their behavior. Probably the paradigm case of this psychology is another classic study, Milgrams’s research on obedience.

Milgram showed that the majority of normal individuals will give a supposed “learner” increasing levels of shock, up to a maximum 450-volt shock labeled “XXX DANGER STRONG SHOCK.” Part of the power of this paradigm is the slow, graded nature of the shocks, which begin at only 15 volts and increase 15 volts with every mistake the “learner” makes. So close is the grading of shock levels that, at each level, to recognize something wrong with giving the next level must imply something wrong with the level already administered. Slow escalation of hurting others is a slippery slope in which each act of aggression becomes a reason for more aggression.

Taken together, group dynamics and the psychology of escalating commitment go a long way toward explaining how normal people can do awful things. Throw in the reward and punishment power of the state, a power that needs move only a small number of people to do the dirty work against a target class or race, and even genocide begins to be comprehensible.

Clark McCauley is Professor of Psychology at Bryn Mawr College and Co-Director of the Solomon Asch Center for the Study of Ethnopolitical Conflict at the University of Pennsylvania. He is an HFG grantee.

Suggested Reading

  1. Averill, J. R. 1982. Anger and Aggression: An Essay on Emotion. New York: Springer.
  2. Berkowitz, L. 1989. Frustration-aggression hypothesis: Examination and reformulation. Psychological Bulletin 106: 59-73.
  3. Browning, C. R. 1992. Ordinary Men: Reserve Police Battalion 101 and the Final Solution in Poland. New York: HarperCollins.
  4. Duckitt, J. 1989. Authoritarianism and group identification: A new view of an old construct. Political Psychology 10: 63-84.
  5. Dodge, K. A. 1991. The structure and function of reactive and proactive aggression. In D. J. Pepler and K. H. Rubin (eds.) The Development and Treatment of Childhood Aggression. Hillsdale: Erlbaum.
  6. Holmes, R. 1985. Acts of War: The Behavior of Men in Battle. New York: Free Press.
  7. Kinder, D. R. 1998. Opinion and action in the realm of politics. In D. T. Gilbert, S. T. Fiske, and G. Lindzey (eds.) Handbook of Social Psychology, vol. 2. New York: McGraw-Hill.
  8. McCauley, C. (ed.) 1991. Terrorism Research and Public Policy. London: Cass.
  9. Pyszczynski, T., J. Greenberg, and S. Solomon. 1997. Why do we need what we need? A terror management perspective on the roots of human social motivation. Psychological Inquiry 8: 1-20.
  10. Rummel, R. J. 1996. Death by Government. New Brunswick, N.J.: Transaction Publishers.
  11. Smith, D. N. 1998. The psychocultural roots of genocide: Legitimacy and crisis in Rwanda. American Psychologist 53: 743-753.
  12. Williamson, S., R. D. Hare, and S. Wong. 1987. Violence: Criminal psychopaths and their victims. Canadian Journal of Behavioral Science 19: 454-462.

A Political Science Perspective on Teaching about Violence

Steven I. Wilkinson

This article appeared in Teaching About Violence, the Spring 2000 edition of TheHFG Review, a Harry Frank Guggenheim Foundation publication that examined topics of violence in depth.

Political scientists who teach about violence nearly all recognize the value of incorporating readings from other disciplines. In my own courses, for example, I frequently include extracts from The Nature of Prejudice, Gordon Allport’s classic social psychology text, to spark discussions of whether diversity programs based on the “contact hypothesis” can reduce ethnic tensions and conflict. But despite our increasing openness to multi-disciplinary approaches to violence, political scientists inevitably pay greater attention to some issues than do our colleagues in psychology, history, sociology, and anthropology. What distinguishes political science from these other disciplines, in my view, is the central importance we attach to the role of the state in causing violence, and in failing to prevent it where it takes place.

First, we are interested in how the state shapes the identities (e.g., region, class, caste, tribe, and ethnicity) and the inequalities of economic resources and power that lead to violence. Second, we want to understand how and why some states do a much better job of preventing violence than others. We recognize, for example, that mass ethnic violence like that in Rwanda or Bosnia rarely takes place unless the state allows it to happen. So we try to identify what it was about the Rwandan and Yugoslav states that led their leaders to promote ethnic violence at one moment, rather than another. Third we want to influence policy. We use comparative analysis and statistical analysis to identify the policies that have been most successful in reducing violence. Once we identify the “right” policies, we then try to persuade politicians, NGOs, and governments to adopt them.

I think that in a semester-long course on violence, it makes sense to treat each of these three issues in sequence. In my own course on ethnic violence, I begin with readings that make students recognize that some of the solid ethnic categories and ethnic conflicts they may be used to thinking about are in large part the result of state categorization and discrimination. To emphasize that this process is not new, I use several books that look at the construction of ethnicity and how state-inspired ethnic categories affected the level of violence in the pre-modern period: Robert Bartlett’s The Making of Europe: Conquest, Colonization and Cultural Change, 950-1350, David Nirenberg’s Communities of Violence: Persecution of Minorities in the Middle Ages, and Richard Eaton’s The Rise of Islam and the Bengal Frontier, 1204-1760). Robert Bartlett, for instance, describes how the medieval state decided who could be counted as a German or Slav, and how in the early middle ages it was relatively easy to cross from the status of “Slav” to the more privileged “German” class. He also shows how, as the shortage of manpower on the German frontier began to diminish, merchants and artisans developed a biological view of race that allowed them to block economic competitors who were Slav. By the end of the thirteenth century, entrants to the German guilds had to prove that they had German ancestors going back several generations. Medieval states discriminated between members of different ethnic and religious groups in ways that encouraged violence. In Spain, for example, the law required the confiscation of property and death for a Muslim who killed a Christian, but only a fine and exile for a Christian who killed a Muslim.

After establishing that state categorization and discrimination is not new, I complete the first section of my course with readings that show students how these processes have been intensified in the nineteenth and twentieth centuries, especially as a result of the western colonization of much of Africa and Asia. Donald Horowitz’s Ethnic Groups in Conflict is a useful text here, because it demonstrates how colonial rule strengthened some ethnic identities (such as Malay in Malaysia, Ashanti in Ghana) and favored some ethnic groups (Kikuyu in Kenya, Hawiye in Somalia) over others. Horowitz also shows how this process of colonial categorization and discrimination led to conflicts after decolonization, as favored groups such as the Kikuyu sought to hold on to their privileges in the face of sometimes violent protests by their rivals.

In the second section of my course, I explore the ways in which governments have tried to deal with ethnic tensions and ethnic violence. There is great variation in state responses to ethnic demands. Some, such as China, use a combination of occasional concessions and repression. Others respond by creating new federal units, decentralizing political institutions, and recognizing ethnic differences through policies such as ethnic preferences in government and employment. The comparative method allows us to explore how these policies affect the probability of ethnic violence in very different political and cultural environments. One book I like very much is Myron Weiner and Mary Katzenstein’s India’s Preferential Policies, which explores the issue of whether ethnic preferences have the capacity to resolve ethnic tensions by comparing their effects in India, the U.S., and Malaysia.

In the third part of my course, I use books such as Arend Lijphart’s Democracy in Plural Societies: A Comparative Exploration and Horowitz’s Ethnic Groups in Conflict and A Democratic South Africa? to introduce students to the toolkit of policies that can be used to solve ethnic conflicts. Lijphart identifies four policies—an inclusive “grand coalition,” a minority veto, cultural autonomy, and ethnic proportionality—that together he believes have prevented violence in states such as Malaysia and Switzerland, and that can prevent ethnic violence elsewhere. Horowitz, on the other hand, believes that Lijphart’s policies underestimate the degree to which ethnic identities are constantly changing. In Ethnic Groups in Conflict, he identifies several electoral and constitutional mechanisms, such as the alternative vote system, that he thinks are more likely to moderate ethnic conflicts and encourage inter-ethnic cooperation.

Although the suggestions I have offered here relate to a course on ethnic violence, the course framework I suggest—analyze the identities, see how the state has made things better or worse, and then choose policies to make things better—can easily be adapted for courses that deal with other types of violence. In a course examining violent crime, for example, it seems natural to start with books that lay out general theories of violence, such as David Courtwright’s Violent Land, which offers a gendered explanation for the prevalence of violence on the American frontier and in inner cities. In the second part of the course we could then move on to such works as Dane Archer and Rosemary Gartner’s Violence in Cross-National Perspective, which present comparative data that tends to undermine the simple theories presented in the first part of the course. Finally, in the third segment of the course I might assign James Q. Wilson’s Thinking about Crime, which emphasizes the importance of city-level policing and sentencing policies in explaining why similar cities have very different levels of violence.

In teaching about violence, my objective is always to give my students a sense that violence is not normal, and that the conflicts they see reported on TV or in the press are not a permanent feature of human existence, but the result of political processes that can and ought to be changed. I get this point across partly by making every course I teach explicitly comparative and historical, so that students can see that the same social problems lead to violence in some countries at some times, but not in others. But the best way of getting students to think creatively about the causes of violence, I have found, is to ask them to write a term paper in which they diagnose and “solve” their own violent conflict. In my course on ethnic conflict, I ask my students to write a 25-page paper in which they can analyze any ethnic conflict they choose. My only requirement is that they: a) describe the role of the state in creating the groups that are involved in violence; b) assess the ways in which the state has, historically, intensified or helped resolve the conflict; c) put forward and justify their own recommendations on how best to solve the conflict in question, using the toolkit of policies covered in the third part of the course. Many of my students are immigrants, or the children of immigrants, and one of the most rewarding aspects of teaching has been to see them re-examine conflicts in their countries of origin using new and more hopeful lenses that they have acquired in the class.

Steven Wilkinson, Assistant Professor of Political Science at Duke University, is an HFG grantee.


  1. Allport, Gordon W. 1954. The Nature of Prejudice. Reading, Mass.: Addison Wesley.
  2. Archer, Dane, and Rosemary Gartner. 1984. Violence and Crime in Cross-National Perspective. New Haven: Yale University Press.
  3. Bartlett, Robert. 1993. The Making of Europe: Conquest, Colonization and Cultural Change, 950-1350. Princeton: Princeton University Press.
  4. Courtwright, David. 1996. Violent Land: Single Men and Social Disorder from the Frontier to the Inner City. Cambridge, Mass.: Harvard University Press.
  5. Eaton, Richard. 1993. The Rise of Islam and the Bengal Frontier, 1204-1760. Delhi: Oxford University Press.
  6. Horowitz, Donald L. 1985. Ethnic Groups in Conflict. Berkeley: University of California Press.
  7. Horowitz, Donald L. 1992. A Democratic South Africa?: Constitutional Engineering in a Divided Society. Berkeley: University of California Press.
  8. Katzenstein, Mary, and Myron Weiner. 1981. India’s Preferential Policies: Migrants, the Middle Classes, and Ethnic Equality. Chicago: University of Chicago Press.
  9. Lijphart, Arend. 1977. Democracy in Plural Societies: A Comparative Exploration. New Haven: Yale University Press.
  10. Nirenberg, David. 1996. Communities of Violence: Persecution of Minorities in the Middle Ages. Princeton: Princeton University Press.
  11. Wilson, James Q. 1985. Thinking about Crime. 2nd ed. New York: Vintage.

What Do Historians Have to Say About Violence?

Jeffrey S. Adler and Thomas W. Gallant

This article appeared in Teaching About Violence, the Spring 2000 edition of The HFG Review, a Harry Frank Guggenheim Foundation publication that examined topics of violence in depth.

On May 24, 1885, a Boston policeman, walking his beat near Cottage Farm, noticed a small object on the bank of the Charles River. Moving closer to investigate, he found the body of a newborn infant. This was not an unusual occurrence. Each year in Boston, as in other cities, policemen, sewer workers, and others municipal employees came across dozens of dead infants. Patrolman Hall followed a familiar procedure and carried the body to the city morgue, where a medical examiner would perform an autopsy in order to determine the cause of death. The following day a physician performed the autopsy on the body of the infant, estimated to have been three days old at the time of death. The medical examiner discovered that the body had been badly mutilated. “All of the sexual organs,” he recorded in the official log book, had been “removed and retained. The abdomen had then been closed up and sewn with a brick inside to sink the body.” “No sign of violence,” he concluded. The cause of death, according to the medical examiner, was “probably still-birth.” Thus, the case of the “white new-born child (sex unknown)” was closed, and local law enforcers saw no reason to investigate the death or to treat it as a homicide.1

In most respects, this case was not unusual. Although medical examiners seldom encountered infants whose genitalia had been “removed,” policemen and physicians were accustomed to dealing with dead infants and to dismissing such obvious murders without further thought or investigation. But Bostonians during the 1880s were neither particularly violent nor especially insensitive toward aggression. Rather, they devoted increasing attention to domestic abuse, criminalizing forms of family violence that had long been accepted as “natural.” Moreover, by the standards of nineteenth-century America, Boston had little serious violence. Compared to late twentieth-century America, Boston in 1885 was remarkably peaceful, enjoying a homicide rate roughly one-fourth that of the city’s modern rate.2 Yet, late-nineteenth-century Bostonians, loath as they were to engage in drunken brawls or street fights, simply did not consider the intentional murder of a newborn infant to be a form of violence, except in very unusual circumstances.

Infanticide in late nineteenth-century Boston challenges many widely held—modern—assumptions about the causes of violence. “Family values” flourished in Boston a century ago. Children lived at home much longer than today, and grandparents, uncles, aunts, and cousins typically lived close at hand and assumed crucial roles in child rearing, providing moral and financial support as well as playing central roles in all of the ritual and celebrations through the life cycle. Nor did late-nineteenth-century Bostonians forsake religion. Rather, these city dwellers structured their lives around religious practice and belief. In short, in the world in which the murder of a “white new-born child (sex unknown)” was discovered but ignored, strong religious belief, loving family ties, and cohesive neighborhood life were compatible with the commonplace and even sadistic murder of very young children.

Three other vignettes from the past also illustrate potential problems with our models for understanding violence and aggression. From our modern perspective, late nineteenth-century cities, such as Chicago, should have been awash in blood. Chicago’s population exploded during this period, nearly tripling between 1870 and 1890, as the great metropolis of the Middle West became a major industrial center and the second largest city in the United States. Density in the city a century ago dramatically exceeded that of modern Chicago, and some behavioral researchers, often working with rodents, suggest a correlation between high density and aggression. The Illinois metropolis was also far more heterogeneous that it is today; 41 percent of the city’s residents in 1890 were foreign born, and peasant farmers from Bohemia, Italy, Greece, Poland, Russia, and a score of other nations as well as African-American farmers from the Deep South poured into the city. Social, religious, and political tensions were more explicit and raw than today, and conflict relating to the labor movement was far more volatile than in modern America, producing some of the worst labor unrest in the nation’s history, including the 1886 Haymarket bombing and the 1894 strike at the Pullman car works. In short, Chicago during the closing decades of the last century seemed to possess all of the ingredients for violence: the city was experiencing explosive, jarring growth; its residents were poor, densely packed in slums, and deeply divided along ethnic, religious, and racial lines; the local housing stock could not keep pace with demand; public health institutions were inadequate; and municipal government was rife with corruption. Yet, Chicago had little violence. The city’s homicide rate was approximately one-fifth the current rate, and muggings and armed robberies were virtually unheard-of events.3

Meanwhile, on the other side of the Atlantic ocean, similar processes of urban growth produced astronomically high levels of interpersonal violence. Until the 1870s, Athens, Greece, was a modestly sized, relatively affluent city, befitting its role as the capital of the new country. Though an ancient city, the modern incarnation of Athens dates only to 1832, when the Greeks obtained their independence from the Ottoman Empire. From the 1830s to the 1870s, Athens manifested exceedingly low levels of violence. As Greek countrymen began to flock to the city during the 1870s and 1880s, however, that changed dramatically. Rates of violence skyrocketed as poor young men migrated to the city and encountered wretched housing conditions, high levels of unemployment, and widespread poverty. By 1890, Athens had become the murder capital of the western world, as poor young men stabbed, shot, and bludgeoned each other to death with only the slightest provocation. But by 1920, the Athenian homicide rate had fallen to one of the lowest levels among the world’s cities, and Athens has remained one of the least violent cities to this day.4 Thus, in late nineteenth-century Chicago, high density, heterogeneity, and poverty did not produce high levels of violence, whereas in Athens, where the population was culturally, ethnically, and religiously homogeneous, rates of violence soared. In short, historical evidence demonstrates that there is no inevitable or natural correlation between, for example, high density or even poverty and violence.

Our point is that the past was neither peaceful and harmonious nor a time when life was necessarily “nasty, brutish, and short.” The relatively low levels of violence in late nineteenth-century American cities, however, should cause modern scholars to reassess popular explanations for violence in late twentieth-century society. The history of Athens shows as well just how rapidly changing conditions can influence violence—for good or ill. Similarly, some of our modern ideas about the social conditions that reduce violence also need to be reevaluated in light of recent historical scholarship. Medieval England, for example, blended many of the crucial elements modern observers associate with nonviolence. This was a rural society in which the population was stable, family ties were strong, and religious belief framed daily life and bound individuals to one another and to communal institutions. Families and neighbors sustained each other during hard times and shared the bounty during flush times. Likewise, this society had scant diversity; nearly everyone had common ethnic and racial roots, and the church’s teaching instilled a common ethical and moral order. These English farmers, as a matter of course, venerated their elders and deferred to their religious leaders. This was also a world with few deadly weapons; medieval farmers, for instance, did not possess firearms. Yet, for all of this rural harmony and for all of the powerful social, religious, and communal bonds that linked these people to one another, medieval England proved to be one of the most violent societies in recorded history.5 As striking as the prevalence of violence in this world was the casualness of violence. One fourteenth-century English farmer, for instance, spied a neighbor walking across his field. He set his dog to chase the trespasser away. An hour later, the wayward wanderer returned and stabbed his neighbor through the eye. Similarly, a fourteenth-century candlestick maker refused to hand over his product until a customer showed him the money; enraged that the vendor questioned his word, the purchaser “struck him in the front part of the head so that his brains flowed forth and he died forthwith.”6 Reflecting the same quick and casual resort to violence, a matron “of good name” suspected that her husband had been unfaithful. So, she identified the suspected adulteress to her kinsmen, who then seized the woman, held her to the ground, and sliced off her nose.7 Clearly, violence was not necessarily considered deviant in this world; although modern social psychologists often posit that poorly socialized individuals are particularly prone to violent behavior, in medieval Europe the opposite was more often true; medieval men and women often viewed violent behavior as appropriate and as a crucial source of social stability.

Research on both city and countryside in the past, therefore, challenges common beliefs about violence. The mean streets of modern New York, for example, are a great deal safer than were the pastoral fields of thirteenth-century York. Similarly, for nearly all of the last seven hundred years, the countryside has been far deadlier than the city, and for most of the twentieth century New York was safer than the overall nation.8 Likewise, the scenic hills of nineteenth-century Corsica and the picturesque mountains of Greece were more violent than the crowded streets of London, Paris, or Berlin—by factors of at least twenty.9 Such evidence suggests, again, that generalizations about the relationship between violence and density or heterogeneity or poverty or religious intensity or family life need to be questioned.10

Although historical research challenges timeless explanations, historical perspectives on violence do not provide easy “lessons.” Instead, this scholarship points to the complexity of the wellsprings of violent behavior. Understanding why nineteenth-century Japan had extraordinary low levels of most kinds of violent behavior but extraordinarily high levels of infanticide is revealing about the social and cultural roots of aggression, but it does not suggest simple policy solutions. Historical research especially calls into question universalist models. Even important work on the biochemical roots of aggression needs to consider the historical variability of violent behavior. Whereas levels of testosterone or neurotransmitters may help to explain why some individuals are more prone to aggressive behavior than others, such research does not explain why some eras have had higher rates of violence than others or why violent tendencies may wax and wane over time among the same group of people—such as the young men of Athens, discussed earlier. Biochemical research is unlikely to explain why the homicide rate in early twentieth-century Memphis, for example, was fourteen times higher than that of Philadelphia, twenty-five times higher than that of Berlin, and fifty-nine times higher than the homicide rate of London or why South Carolina had more homicides in 1878 than the combined totals of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, Michigan, and Minnesota.11

Historical research on aggression, however, does not merely serve to debunk overly broad modern theories. With the benefit of hindsight, historians undertake research that provides important clues about the social, cultural, and economic conditions that have generated—or discouraged—aggression. Late nineteenth-century New York, for instance, has captured the attention of historians of violence. In 1890, for instance, the city had “as many Germans as Hamburg, twice as many Irish as Dublin, and two and a half times as many Jews as Warsaw.”12 Moreover, these newcomers were disproportionately clustered in the city’s Lower East Side, which had the highest residential density in the history of mankind. Despite such crowding and diversity, New York had an extremely low homicide rate, and the level of violence fell during this era.13 Historians have undertaken research to determine the conditions at work in New York City that blunted the inclination toward violent behavior during this period of jarring growth. What has accounted for sharp decreases in violence in the past? Similarly, other historians have found that Vermont has been one of the least violent states in the nation for two hundred years.14 What social or cultural forces account for this enviable record? The question is particularly interesting because other rural states, with comparable levels of population density and per capita income, have been considerably more violent. A large body of historical scholarship has explained the ways in which industrialization and urbanization have discouraged aggressive behavior in both Europe and the United States.15 The history of domestic violence has commanded the attention of historians as well. Recent work, for example, has revealed that lethal violence between acquaintances has often decreased during eras when lethal violence toward family members increased.16 What does such a pattern reveal about the sources of domestic violence? Historians have also focused considerable attention on the relationship between race and violence, and they have found that the gap between African-American and white homicide rates has fluctuated dramatically over the course of the last century.17 Understanding what conditions accompanied the narrowing of this gap should be of great interest to policy makers grappling with modern inner-city violence. Recent studies have also documented the relationship between collective violence and interpersonal violence over the last two centuries.18 It seems self-evident, for example, that it would be valuable to know if riots tended to occur during periods of rising or falling violence or during eras when domestic violence was increasing or decreasing. Other historians are undertaking equally fascinating research that helps to explain fundamental shifts in the level and the character of violence. Recent work on nineteenth- and twentieth-century Greece, for instance, explains how and why violence can become ritualized, revealing why Greek peasants were quick to maim or disfigure one another with knives but increasingly loath to kill.19 Historians of violence focusing on the construction of class and gender identities offer important insights into modern hate groups and trends in violence toward women.20

In short, historians explore eras with much bloodshed in order to determine the cluster of forces that account for increased violence, just as they study periods of falling levels of violence to help to understand when and why societies reject the use of violence and effectively discourage aggressive behavior. The insights from such research do not offer any kind of magic bullet. Rather, historical research provides an understanding of the social and cultural contexts that have generated (and may continue to generate) high levels—or low levels or particular kinds of—violence. For although violence is a complex issue, it is not a new issue, and a fuller understanding of the source of violence and the reasons for shifts in levels of violence during the last thousand years provides a crucial foundation for understanding modern—and future—violence.

Jeffrey S. Adler is Associate Professor of History and Criminology at the University of Florida. Thomas W. Gallant is Associate Professor of History at the University of Florida. Both are HFG grantees.


  1. Medical Examiner’s Returns. 1885. Unpublished ledger:239. Boston: Massachusetts State Archives; Boston Globe. 1885. (May 25).
  2. Waldo E. Cook. 1893. Murder in Massachusetts. Proceedings of the American Statistical Association 3 (September): 357-78; Theodore N. Ferdinand. 1967. The criminal patterns of Boston since 1849. American Journal of Sociology 73 (July): 84-99; Roger Lane. 1968. Crime and criminal statistics in nineteenth-century Massachusetts. Journal of Social History 2 (Winter): 156-63.
  3. Department of Health. 1931. Report of the Department of Health of the City of Chicago for the Years 1926-1930 Inclusive: 1138. Chicago; Jeffrey S. Adler. Forthcoming. “Halting the slaughter of the innocents”: The civilizing process and the surge in violence in turn-of-the-century Chicago. Social Science History.
  4. Thomas W. Gallant. 1998. Murder in a mediterranean city: Homicide trends in Athens, 1850-1936. Journal of the Hellenic Diaspora 24(1): 1-24.
  5. James Buchanan Given. 1977. Society and Homicide in Thirteenth-Century England. Stanford: Stanford University Press; Barbara A. Hanawalt. 1976. Violent death in fourteenth- and early fifteenth-century England. Comparative Studies in History and Society 18(July): 297-320.
  6. Hanawalt (note 5), 312.
  7. Valentin Groebner. 1995. Losing face, saving face: Noses and honour in the late medieval town. History Workshop 40: 1-15.
  8. Eric Monkkonen. 1997. Homicide over the centuries. In Lawrence M. Friedman and George Fisher (ed.) The Crime Conundrum. Boulder: Westview Press, 163-170.
  9. Stephen Wilson. 1988. Feuding, conflict and banditry in nineteenth-century Corsica. Cambridge: Cambridge University Press; Gallant in note 4, and forthcoming. Long hair and burning blood: The vendetta in Greek society. In Clive Emsley (ed.) Vendetta.
  10. Ted Robert Gurr. 1989. Historical trends in violent crime: Europe and the United States. In Ted Robert Gurr (ed.) Violence in America. New bury Park, Cal.: Sage; Roger Lane. 1977. Murder in America. Columbus: Ohio State University Press.
  11. Frederick L. Hoffman. 1925. The Homicide Problem. Newark: The Prudential Press, 22-25; Horace V. Redfield. 1880. Homicide, North and South. Philadelphia: Lippencott, 12.
  12. Charles N. Glaab and A. Theodore Brown. 1967. A History of Urban America. London: Macmillan, 139; Raymond A. Mohl. 1985. The New City. Arlington Heights: H. Davidson, 51.
  13. Eric H. Monkkonen. 1995. Homicide over the centuries. Social Science History 19(Summer): 168; Monkkonen. 1995. New York City homicides. Social Science History 19(Summer): 201-14.
  14. Randolph Roth. 1998. The long decline in homicide: New England, 1630-1830. Paper presented at the Twenty-Third Annual Meeting of the Social Science History Association, Chicago, November 21.
  15. For example, see Eric A. Johnson and Eric H. Monkkonen (eds.) 1996. The Civilization of Crime. Urbana: University of Illinois Press; Johnson. 1995. Urbanization and Crime. New York: Cambridge University Press.
  16. Jeffrey S. Adler. 1997. “My mother-in-law is to blame, but I’ll walk on her neck yet”: Homicide in late nineteenth-century Chicago. Journal of Social History 31(Winter): 253-76; Pieter Spierenburg. 1994. Faces of violence: Homicide trends and cultural meanings. Journal of Social History 27: 701-16.
  17. Roger Lane. 1986. Roots of Violence in Black Philadelphia. Cambridge, Mass.: Harvard University Press; Eric H. Monkkonen. 1995. Racial factors in New York City homicides, 1800-1874. In Darnell F. Hawkins (ed.) Ethnicity, Race, and Crime. Albany: State University of New York Press. 99-120.
  18. For example, see Christopher Waldrep. 1998. Roots of Disorder. Urbana: University of Illinois Press.
  19. Thomas W. Gallant. forthcoming. Honor, masculinity, and ritual knife-fighting in nineteenth-century Greece. American Historical Review.
  20. For example, see Mary E. Odem. 1999. Cultural representations and social contexts of rape in the early twentieth century. In Michael A. Bellesiles (ed.) Lethal Imagination. New York: New York University Press, 353-70; Angus McLaren. 1997. The Trials of Masculinity. Chicago: University of Chicago Press; Martin J. Wiener. 1998. The Victorian criminalization of men. In Pieter Spierenburg (ed.) Men and Violence. Columbus: Ohio State University Press, 197-212.

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