Tragic events like the shootings at Columbine High School capture public attention and concern, but are not typical of youth violence. Most adolescent homicides are committed in inner cities and outside of school. They most frequently involve an interpersonal dispute and a single victim. On average, six or seven youths are murdered in this country each day. Most of these are inner-city minority youths. Such acts of violence are tragic and contribute to a climate of fear in schools and communities.

Research findings are identifying factors in the development of aggressive and antisocial behavior from early childhood to adolescence and into adulthood. Prospective longitudinal and intervention studies have identified major correlates for the initiation, escalation, continuation, and cessation of serious violent offending.

Many studies indicate that a single factor or a single defining situation does not cause child and adolescent antisocial behavior. Rather, multiple factors contribute to and shape antisocial behavior over the course of development. Some factors relate to characteristics within the child, but many others relate to factors within the social environment (e.g., family, peers, school, neighborhood, and community contexts) that enable, shape, and maintain aggression, antisocial behavior, and related behavior problems.

The research on risk for aggressive, antisocial, and violent behavior includes multiple aspects and stages of life, beginning with interactions in the family. Such forces as weak bonding, ineffective parenting (poor monitoring, ineffective, excessively harsh, or inconsistent discipline, inadequate supervision), exposure to violence in the home, and a climate that supports aggression and violence puts children at risk for being violent later in life. This is particularly so for youth with problem behavior, such as early conduct and attention problems, depression, anxiety disorders, lower cognitive and verbal abilities, etc. Outside of the home, one of the major factors contributing to youth violence is the impact of peers. In the early school years, a good deal of mild aggression and violence is related to peer rejection and competition for status and attention. More serious behavior problems and violence are associated with smaller numbers of youths who are failing academically and who band together, often with other youth rejected by prosocial peers. Successful early adjustment at home increases the likelihood that children will overcome such individual challenges and not become violent. However, exposure to violent or aggressive behavior within a family or peer group may influence a child in that direction.

Types and Severity of Antisocial Behavior

The types and severity of antisocial behaviors exhibited by youths vary greatly and include lying, bullying, truancy, starting fights, vandalism, theft, assault, rape, and homicide. As a rule, the older the age of onset, the fewer the number of antisocial youths who will engage in seriously aggressive and violent behavior. Longitudinal studies show that many children who engage in antisocial behavior in childhood continue to do so at least through adolescence.

Longitudinal research has identified types of youth who progress to adolescent antisocial behavior, multiple pathways through which it develops and persists, and the multiple factors that shape this risk. This research has identified two types of life course trajectories: life course persistent, which is viewed as a form of psychopathology, and adolescence limited, which is identified only in select social situations. The distinction between these two types of individuals is very useful, both as a way of thinking about developmental knowledge and as a tool for targeting the right interventions for antisocial youth.

Research in this area has generated evidence for this way of thinking about how adolescents grow and has investigated the relationship between adolescent problem behavior and cognitive deficits. Life course persistent individuals begin antisocial behavior early in childhood and continue into adulthood, after their adolescence limited counterparts stop. Life course persistent behavior has been correlated with neurological deficits and pathological behaviors, (e.g., impulsivity) which are exacerbated when they are combined with stressful home situations. In one study of 13 year olds, individual differences�such as deficits in sensory, perceptual, and cognitive abilities, including the use of language were shown to predict participation in crime 5 years later. For instance, boys with poorer verbal functioning initiated delinquent behavior at younger ages. It has also been demonstrated that boys with poorer neuropsychological functioning, especially verbal functioning at age 13, were more likely to have committed crimes at age 18 than were their counterparts with better neuropsychological functioning at age 13.

Gender Differences

From about 4 years of age on, boys are more likely than girls to engage in both aggressive and nonaggressive antisocial behavior. Much remains to be learned about the causes of gender differences in antisocial behavior, but based on what is known, it is suspected that antisocial behavior might need to be defined somewhat differently for the two genders. In contrast to overt aggression, which inflicts harm through physical damage or the threat of such damage more common in boys, social aggression by girls harms through damage to peer relationships; study of this form of aggression may be crucial to understanding the aggressive development of girls. The NIMH is currently funding research on the antecedents and consequences of aggression for girls, as well as for boys, knowledge that can be used to develop empirically-based interventions for aggressive children of both sexes.

Antisocial Behavior Co-Occurring with Child Psychopathology

There is strong evidence for the co-occurrence of two or more syndromes or disorders among children with behavioral and emotional problems. Many people think that children either act out or turn their feelings inward, but the truth is more complex. The obviously angry adolescent has other conditions such as anxiety disorders and depression (as seen in the quiet withdrawn young person) more often than would occur by chance. Research in this area indicates that very young children with conduct problems and anxiety disorders or depression display more serious aggression than youths with only conduct problems. It is not entirely clear whether depression precipitates acting out, whether impairments and predispositions for acting out lead to depression, or whether there are underlying causal factors that are responsible for the joint display of such problems.

It is very common for youth with conduct problems to also display symptoms of attention deficit hyperactivity disorder (ADHD), the most commonly diagnosed behavioral disorder of childhood. The diagnosis is made by the presence of persistent age-inappropriate inattention and impulsivity, often coexisting with hyperactivity. This co-occurrence is often associated with an early onset of aggression and impairment in personal, interpersonal, and family functioning. Furthermore, academic underachievement is common in youth with early onset conduct problems, ADHD, and adolescents who display delinquent behavior.

Individual Liability and Genetic Factors

Identifying numerous genes that may play a role in any complex disorder is a formidable task and is only the first step in understanding how a gene or genes affect an individual. Genes act by producing specific proteins that may contribute to a particular biological or behavioral trait. Every human carries between 80,000 and 100,000 genes; the products of these genes acting together and in combination with the environment help shape every human characteristic. It has become clear that the genetics of vulnerability to certain behaviors or mental disorders is complex. We still do not know how many different genes might contribute to vulnerability for any personality trait or specific mental disorder, nor do we know the nature of the nongenetic effects (such as environmental factors) that convert vulnerability into illness.

Our understanding of the nature of genetic influences on antisocial behavior is similarly incomplete. However, research on differences in the magnitude of genetic and environmental influences on different kinds of conduct problems is providing a key to understanding the developmental origins of antisocial behavior. Many twin and adoption studies indicate that child and adolescent antisocial behavior is influenced by both genetic and environmental factors, suggesting that genetic factors directly influence cognitive and temperamental predispositions to antisocial behavior. These predisposing child factors and socializing environments, in turn, influence antisocial behavior.

Research suggests that for some youth with early onset behavior problems, genetic factors strongly influence temperamental predisposition, particularly oppositional temperament, which can affect experiences negatively. When antisocial behavior emerges later in childhood or adolescence, it is suspected that genetic factors contribute less, and such youths tend to engage in delinquent behavior primarily because of peer influences and lapses in parenting. The nature of the child's social environment regulates the degree to which heritable early predisposition results in later antisocial behavior. Highly adaptive parenting is likely to help children who may have a predisposition to antisocial behavior. Success in school and good verbal ability tend to protect against the development of antisocial behavior, pointing to the importance of academic achievement.

Parent and Family Factors

Research has demonstrated that youths who engage in high levels of antisocial behavior are much more likely than other youths to have a biological parent who also engages in antisocial behavior. This association is believed to reflect both the genetic transmission of predisposing temperament and the maladaptive parenting of antisocial parents.

The importance of some aspects of parenting may vary at different ages. For example, inadequate supervision apparently plays a stronger role in late childhood and adolescence than in early childhood. There is evidence from many studies that parental use of physical punishment may play a direct role in the development of antisocial behavior in their children. In longitudinal studies, higher levels of parental supervision during childhood have been found to predict less antisocial behavior during adolescence. Other researchers have observed that parents often do not define antisocial behavior as something that should be discouraged, including such acts as youths bullying or hitting other children or engaging in "minor" delinquent acts such as shoplifting.

Research examining the mental health outcomes of child abuse and neglect has demonstrated that childhood victimization places children at increased risk for delinquency, adult criminality, and violent criminal behavior. Findings from early research on trauma suggest that traumatic stress can result in failure of systems essential to a person's management of stress response, arousal, memory, and personal identity that can affect functioning long after acute exposure to the trauma has ended. One might expect that the consequences of trauma can be even more profound and long lasting when they influence the physiology, behavior, and mental life of a developing child or adolescent.

Peer Influences

Antisocial children with earlier ages of onset tend to make friends with children similar to themselves. Consequently, they reinforce one another's antisocial behavior. Children with ADHD are often rejected due to their age-inappropriate behavior, and thus are more likely to associate with other rejected and/or delinquent peers. The influence of delinquent peers on late-onset antisocial behavior appears to be quite strong. Association with antisocial peers has been shown to be related to the later emergence of new antisocial behavior during adolescence among youths who had not exhibited behavior problems as children.

Less adult supervision allows youths to spend more time with delinquent peers. Thus, improving parental supervision may be an important way to reduce the effects of delinquent peer influence. Ongoing research is examining how neighborhood effects on antisocial behavior are mediated by the willingness of neighbors to supervise youths and possibly reduce the likelihood of association with delinquent peers in the neighborhood.

Socioeconomic Factors

An inverse relationship of family income and parental education with antisocial behavior has been found in many population-based studies. Across gender and ethnicity, much of the inverse relationship between family income and antisocial behavior is accounted for by less parental monitoring at lower levels of socioeconomic status.