The specific cause or causes of antisocial personality disorder (ASP) are unknown. Like many mental health issues, evidence points to inherited traits. But dysfunctional family life also increases the likelihood of ASP. So although ASP may have a hereditary basis, environmental factors contribute to its development.

Researchers have their own ideas about ASP’s cause. One theory suggests that abnormalities in development of the nervous system may cause ASP. Abnormalities that suggest abnormal nervous system development include learning disorders, persistent bedwetting and hyperactivity.

A recent study showed that if mothers smoked during pregnancy, their offspring were at risk of developing antisocial behavior. This suggests that smoking brought about lowered oxygen levels with may have resulted in subtle brain injury to the fetus.

Yet another theory suggests that people with ASP require greater sensory input for normal brain function. Evidence that antisocials have low resting pulse rates and low skin conductance, and show decreased amplitude on certain brain measures supports this theory. Individuals with chronically low arousal may seek out potentially dangerous or risky situations to raise their arousal to more optimal levels to satisfy their craving for excitement.

Brain imaging studies have also suggested that abnormal brain function is a cause of antisocial behavior. Likewise, the neurotransmitter serotonin has been linked with impulsive and aggressive behavior. Both the temporal lobes and the prefrontal cortex help regulate mood and behavior. It could be that impulsive or poorly controlled behavior stems from a functional abnormality in serotonin levels or in these brain regions.

The Environment

Social and home environments also contribute to the development of antisocial behavior. Parents of troubled children frequently show a high level of antisocial behavior themselves. In one large study, the parents of delinquent boys were more often alcoholic or criminal, and their homes were frequently disrupted by divorce, separation, or the absence of a parent.

In the case of foster care and adoption, depriving a young child of a significant emotional bond could damage his ability to form intimate and trusting relationships, which may explain why some adopted children are prone to develop ASP. As young children, they may be more likely to move from one caregiver to another before a final adoption, thereby failing to develop appropriate or sustaining emotional attachments to adult figures.

Erratic or inappropriate discipline and inadequate supervision have been linked to antisocial behavior in children. Involved parents tend to monitor their child’s behavior, setting rules and seeing that they are obeyed, checking on the child’s whereabouts, and steering them away from troubled playmates. Good supervision is less likely in broken homes because parents may not be available, and antisocial parents often lack the motivation to keep an eye on their children. The importance of parental supervision is also underscored when antisocials grow up in large families where each child gets proportionately less attention.

A child who grows up in a disturbed home may enter the adult world emotionally injured. Without having developed strong bonds, he is self-absorbed and indifferent to others. The lack of consistent discipline results in little regard for rules and delayed gratification. He lacks appropriate role models and learns to use aggression to solve disputes. He fails to develop empathy and concern for those around him.

Antisocial children tend to choose similar children as playmates. This association pattern usually develops during the elementary school years, when peer group acceptance and the need to belong start to become important. Aggressive children are the most likely to be rejected by their peers, and this rejection drives social outcasts to form bonds with one another. These relationships can encourage and reward aggression and other antisocial behavior. These associations may later lead to gang membership.

Child abuse also has been linked with antisocial behavior. People with ASP are more likely than others to have been abused as children. This is not surprising since many of them grow up with neglectful and sometimes violent antisocial parents. In many cases, abuse becomes a learned behavior that formerly abused adults perpetuate with their own children.

It has been argued that early abuse (such as vigorously shaking a child) is particularly harmful, because it can result in brain injury. Traumatic events can disrupt normal development of the central nervous system, a process that continues through the adolescent years. By triggering a release of hormones and other brain chemicals, stressful events could alter the pattern of normal development.