Violence

As historical and cross-cultural records demonstrate, our evolutionary history is laced with examples of violence. Indeed, paleontological data reveal a rather continuous stream of human violence dating back thousands of years. It is clear that violence is not restricted to early historical periods or particular cultural groups. Despite recent concerns in the United States and elsewhere over spiraling violence rates, available data suggest that there is actually less violence now than in ancient times. From an evolutionary perspective, human violence may represent a context-sensitive solution to particular problems of social living that may ebb and flow in accordance with changing conditions. In reviewing these adaptive functions, Buss and Shackelford describe seven problems for which violence may have evolved as a solution: (1) co-opting the resources of others; (2) defending against attack; (3) inflicting costs on same-sex rivals; (4) negotiating status and power hierarchies; (5) deterring rivals from future aggression; (6) deterring males from sexual infidelity; and (7) reducing resources expended on genetically unrelated children.

Against a backdrop of adaptive violence, there are still many other factors that play a role in the ontogeny of violence and help explain variations in violence across individuals and social groups. In most cases, a number of different factors converge to increase the likelihood of violent behavior. These factors can be divided into roughly three groups: (1) innate factors; (2) socialization factors; and (3) situational factors.

Innate factors. Early efforts to unveil differences between violent and nonviolent individuals began with attempts to assign precise neural locations to a range of behaviors including violence. Known as phrenology, this approach assigned high priority to the innate and presumably defective aspects of individual makeup. The idea that behaviors are linked to physical characteristics also drove some of the first criminological efforts to understand the etiology of violence. Perhaps the most well-known work is that of nineteenth-century Italian criminal anthropologist Cesare Lombroso, who popularized the notion that violent individuals possessed distinct physical features indicative of primitive or inferior development, known as atavisms.

A concern over physical features gave way to the far more powerful influence of genetics. Although there was much resistance toward biology-as-destiny approaches, more and more geneticists were taking over the reigns of biology. However, much of the early writing on the genetic underpinnings of violence failed to pinpoint the precise causal mechanisms. The lack of a genetic road map did not unravel efforts to search for the innate determinants of aggression. Support for the idea that aggression was hard-wired from birth came from a number of different encampments.

Beginning in the early part of the twentieth century, ethologists saw aggression and violence as a response to the call of internal mechanisms or instincts. This emphasis found good company in the Freudian psychoanalysts. They saw aggression as derived from an inborn tendency to destroy. Like all instincts, it builds up over time and must ultimately be discharged in either acceptable or unacceptable ways. This pressure is made worse by frustration. The idea that aggression and violence are linked to frustration had a significant impact on the field and was followed by models emphasizing the frustration-aggression connection (Dollard et al.). Although still grounded in a drive model of behavior, this work also provided evidence that violence can be learned. Still, innate drive theories persisted and were later popularized by the writings of Konrad Lorenz. According to Lorenz, aggression was not simply a response to an instinct but was itself an innate driving force, notable for both its spontaneity and centrality to species preservation.

But drive theories found themselves caught up in an empty vessel. There was little evidence to indicate that aggressive energy builds up until it is released. Further, while the notion of drive or instinct may have some descriptive utility, it offered little in the way of specifying the precise internal mechanisms that underlie violence and ran the risk of engendering a pessimistic attitude about prevention. Fortunately, scientific advances in understanding neuranatomy, brain chemistry, and genetic transmission allowed for increasingly greater precision in understanding the biology of violence, leading us farther from the notion of violence as inevitable instinct. The role of key areas of the brain in regulating emotion and behavior is now well established. Violence has also been associated with some kinds of brain damage from birth trauma, tumors, or head injury. However, rather than acting alone, the biological and social environments seem to exert reciprocal influences.

For example, threat perceptions involve neurotransmitters that partially determine an individual's sensitivity to environmental stimuli—some more reactive, others less so. But environmental exposure to violence, danger, or abuse during the early years can quickly overload the brain's alarm system, creating adolescents who are hypervigilant to stress and overreact to environmental cues (Pynoos, Steinberg, and Ornitz). Hypervigilance to threats may also explain some of the inconclusive findings linking testosterone and aggression. It appears that testosterone is linked to specific types of aggression, notably the tendency to "fight back" in a more defensive or reactive fashion related to heightened threat perception rather than the tendency to start fights or engage in offensive aggression (Olweus, Mattson, and Low).

Socialization factors. Not only does the social environment serve as a trigger for biological development, it also provides a context for learning appropriate behaviors. Whatever propensity for violence is written on an individual's biological birth certificate, it is clearly molded and shaped through interactions with others. There is a sizable body of evidence showing that early socialization across multiple contexts accounts for much of the individual differences in later violent behavior.

Different mechanisms have been implicated in the learning of violence. Early theories stressed the importance of reinforcement. A young child wants a toy, but his playmate will not relinquish it. The boy pushes and grabs the toy and the playmate relents. Aggression works. If followed by reinforcement, both mild aggression and serious violence are likely to increase. Such reinforcement is not limited to tangible objects; it can include outcomes such as attention, status, and advantageous positioning in the peer status hierarchy, similar to some of the adaptive functions of aggression discussed previously.

In addition to the role of reinforcement, early formulations of social learning theory emphasized the role of observational learning (Bandura). Individuals who see others use and obtain rewards for violence, especially others whom they admire, are more likely to imitate them and behave violently under similar circumstances. As a psychological mechanism, modeling can also explain variation in violence levels across different social groups and cultures. As violence becomes more legitimate in a social group, it is more likely that members will conform to these emerging group norms. Some observers have described a "code of violence" that characterizes the behavior of many inner-city males. Status is associated with willingness to use violence, and children emulate the toughness and violence of older male role models.

Much of the concern about the links between exposure to media to violence and aggression derives from social learning theory. Research with children has clearly demonstrated a correlation with exposure to media violence and aggressive behavior. Children who watch more violent movies and television are more likely to engage in similar behaviors both as children and adults. Long-term exposure to media violence fosters later violence through several mechanisms. In addition to teaching aggressive attitudes and behaviors, it also seems to desensitize viewers to violence, making it more acceptable. People who watch a lot of televised violence also show exaggerated fears of violence, perhaps making them more hypervigilant and susceptible to reactive outbursts.

The media is but one socialization context that can promote the learning of violence. Research has shown that both parents and peers can be a powerful force in shaping children's behavior. Lack of attention to children's behavior and inconsistent parental discipline and monitoring of activities have been consistently related to the development of aggressive and violent behavior patterns. Extremely harsh and abusive parenting has also been linked to later aggression. Stated simply, "violence begets violence." Equally important is the failure of positive encouragement for prosocial and nonviolent behaviors. Many parents ignore children's efforts at solving conflicts peacefully or managing frustration. Oversights such as these may inadvertently teach children that aggressive acts alone are worthy of notice.

Peers also exert an influence from an early age, but seem to become most important during adolescence. Perhaps one of the most robust findings in the delinquency literature is that anti-social and violent peers tend to gravitate toward one another. Delinquents associate with each other and this association stimulates greater delinquency. Nowhere is this more apparent than in the actions of gangs. Not only is violent behavior accepted, it is required. Members must be "jumped in" via violent victimization; the same procedure is followed for those who want to leave the gang.

The environment also operates to influence the learning of violence. Some studies of environmental influences have focused on the effects of poverty and disadvantage. Poverty itself does not cause violence. Rather, being poor affects one's life experiences in several ways conducive to violence. Individuals living in poor neighborhoods have few resources and supports for healthy development and are more likely to experience multiple stressors. In some neighborhoods, there are few legitimate routes to financial success and social status, which may also engender feelings of relative deprivation in contrast to middle-class society. Those who have little also have little to lose. Thus, low social and economic status may contribute to heightened risk-taking behavior, an idea that finds some support in psychological studies showing that artificially lowering an individual's self-esteem gives rise to higher levels of risky or rule-breaking behavior.

In urban settings, poverty often produces situational factors, such as overcrowding, that are linked to violence. Indeed, the highest rates of violence typically are found among the urban poor (Dahlberg). Drive-by shootings and random violence have come to characterize some of the most distressed, inner-city communities. As violence increases and neighborhoods become more dangerous, the use of force may be seen as normal and even necessary for self-protection. A subculture of violence can emerge wherein violence is legitimized as an acceptable behavior within certain groups. The idea that degree of violence is related to the prevailing social norms about its acceptability can also shed light on cross-cultural differences. Countries where violence is considered non-normative such as Japan have low homicide rates; countries where violence has become almost a way of life such as El Salvador and Guatemala have homicide rates over one hundred times higher (Buvinic, Morrison, and Shifter).

These different contextual factors can serve as a training ground for violence via their influence on children's learning. However, beyond a focus on how individuals learn violent behavior through socialization, recent efforts have highlighted the importance of cognitive processes that help shape and control behavior—what might be called the software of the brain. Studies have shown that more aggressive and violent individuals have different ways of processing information and thinking about social situations. They tend to interpret ambiguous cues as hostile, think of fewer nonviolent options, and believe that aggression is more acceptable (Crick and Dodge). Once these cognitions crystallize during socialization, they are more resistant to change.

Situational factors. Both innate factors and socialization experiences mold an individual's propensity to violence. But this is not the whole story. It appears that situational catalysts can also lead to violence and increase the seriousness of such behavior. Almost any aversive situation can provoke violence. Frustrating situations are linked to heightened aggression, although frustration does not always produce aggression and is certainly not the only instigating mechanism. Other aversive experiences such as pain, foul odors, smoke, loud noises, crowding, and heat portend heightened aggressiveness, even when such behavior cannot reduce or eliminate the aversive stimulation (Berkowitz).

The influence of pain on violent behavior has been widely studied. Pain-instigated aggression is often cited as one of the clearest examples of aversively generated aggression. Further, the likelihood of overt aggression increases as the pain becomes greater and the ability to avoid it decreases. However, it is not necessarily the pain, per se, that causes aggression. Indeed, investigations of people suffering from intense pain have documented higher levels of anger and hostility and speculate that subsequent aggression may be due to the agitated negative affect that accompanies pain rather than the pain itself. Along these lines, any type of aversive experience that results in heightened negative affect should increase the likelihood of subsequent aggression.

Alcohol has also been shown to promote violence. In studies of alcohol and domestic violence, alcohol use typically is implicated in more than half of all incidents. Similarly, both homicide victims and perpetrators are likely to have elevated blood alcohol levels. Although a relation has been established, the precise mechanisms by which alcohol increases violence are unclear. It is likely that these effects are related to its impact on how an individual evaluates social situations and decides on an appropriate response. For example, some alcohol-violence studies suggest that ingestion of alcohol makes normal social interactions extremely difficult, heightening the likelihood of a range of inappropriate responses including violence.

Situational cues that suggest violence are also likely to increase violence by priming violencerelated thoughts, feelings, and behaviors. Street fights engender more violence because they cue violent responses in observers. The presence of guns can also make violence more likely to occur when they are associated with an aggressive meaning and positive outcomes. For instance, the presence of a hunting rifle will not promote hostile and violent behavior in those who disapprove of aggression toward others. It is not just the weapon but the meaning and anticipated consequences of its use that promote violence. Even the picture of a gun or weapon in a room can increase the chance of an aggressive act. This effect is of particular concern because guns make violence more deadly. For example, the rise in murders of juveniles in the United States during the late 1980s and early 1990s was entirely firearm-related. Firearms are now the leading cause of death among children and youth in many places (Snyder and Sickmund).

Even nonviolent individuals can turn violent when they are part of a violent crowd. Group violence seems to make individuals feel less personally responsible for their behavior, acting in ways they would never do alone. Violence becomes an act of the group with no one person being held responsible. In some groups, violence emerges as a necessary strategy for defense against enemies—as seen in gang warfare, terrorist organizations, and political violence. At the other end of the spectrum, isolation also breeds violence. Different mechanisms to account for the influence of isolation have been proposed. These range from psychological changes akin to delusions of grandeur to disturbances in the balance of neurochemical pathways critical to the control of emotional and stressful responses.