Aggression

Field of study: Human genetics and social
issues Significance: Aggression refers to behavior directed toward causing harm to others. Aggressive antisocial behavior is highly heritable, and antisocial behavior (ASB) during childhood is a good predictor of ASB in adulthood and crime. Physical acts of aggression are sometimes distinguished from the more context-sensitive “covert” ASBs, including theft, truancy, and negative peer interactions.
Key terms
antisocial behavior (ASB): behavior that violates rulesorconventions ofsociety and/or personal rights
impulsivity: a tendency to act quickly without planning or a clear goal in mind
irritability: atendency to overreact tominor stimuli; short-temperedness or volatility
liability: the riskofexhibitinga behavior; the higher one’s score for a measure of liability, the greater is one’s the risk of exhibiting the behavior
serotonin: aneurotransmitter, 5-hydroxytryp-tamine (5-HT), present in blood platelets, the gastrointestinal tract, and certain regions of the brain, which plays role in initiating sleep, blood clotting, and stimulating the heartbeat, and levels of which have been correlated with aggressive behavioraswell as depression and panic disorder
Aggression and Related Behaviors
Aggression or agonistic behavior in animals is usually an adaptive response to specific environmental situations during competition for resources, as in establishing dominance and a territory or in sexual competition. Rat and mice studies indicate it is partly genetic, because selective breeding produces strains that differ in levels of aggression. Human aggression can also represent a variety of natural responses to challenging situations. Measures of aggression vary, but of greatest concern are antisocial behaviors (ASBs) such as crime and delinquency and whether some individuals are more likely to engage in these behaviors than others.
The earliest evidence for a genetic contribution to these complex behaviors comes from twin and adoptee studies. Genes also increase the liability for many clinical conditions that include aggressive behaviors, suchasconduct disorder (physically aggressive acts such as bullying or forced sexual activity) and antisocial personality disorder (persistent violation of social norms, including criminal behavior) and for personality traits that often accompany aggression, such as impulsivity and irritability. Differences in measuring ASBs partly account for the variability in heritability estimates, which range from 7 to 81 percent, but many studies indicate a heritability for genetic influences of 0.40-0.50, a minor influence of shared environment, and a much more significant influence of nonshared environment (environment unique to the individual).
Aggression and Human Development
Aggressive behavior develops in children through a complex interaction of many environmental and biological factors. Also increasing liability for aggression and perhaps criminality are such factors as low socioeconomic status and parental psychopathology. A consistent finding is that the measure of the activity of the central nervous system’s serotonin correlates inversely with levels of lifetime aggression, tendency to physically assault, irritability, and impulsivity. Some of the implicated genes regulate serotonin synthesis, release, and reuptake as well as metabolism and receptor activation, and vary from individual to individual. Seroto-nergic dysfunction is also noted in alcoholism with aggression and in suicide attempters and completers. Brain injuries can also exacerbate tendencies to exhibit ASBs.
Some aggression, however, is a normal part of development. Thus, Terrie Moffitt and colleagues distinguish between “adolescent-limited aggression”—times when most adolescents are rebelling against adult authority—and “life-course persistent” ASB, which likely reflects neuropsychological deficits and specific temperaments that are often exacerbated in un-supportive family settings. Genetic factors play a smaller role in adolescent delinquency and are consistent with aggression at this age as a developmental response to social context.
Sex Differences
A significant feature of ASB is a marked difference between the sexes. Males exhibit higher levels of physical aggression and violence at every age in all situations except in the context of partner violence (where females exceed males). More males than females are diagnosed with conduct disorderateveryage. More males than females begin actsoftheft and violenceat every age. Males also exhibit higher rates of risk factors, suchas impaired neurocognitive status, increased hyperactivity, and difficulties with peers. Females are rarely identified with the life-course persistent form of ASB; the male:female sex ratio is 10:1. Antisocial male and female adolescents tend to associate and often marry and reproduce at younger ages. The role that hormones, particularly testosterone, may play in these differences is not clear.
Social Significance
There is much controversy surrounding the efforts to identify genes associated with aggression or crime, especially now that genome sequencing is easier than ever. Many demand that the privacy of individuals be protected because the presence of specific genes does not dictate behavioral outcomes: Genes do not determine socially defined behaviors but only act on physiological systems.Inaddition, what constitutes acceptable or unacceptable behavior for individuals is culturally defined. Biological and environmental risk factors may increase an individual’s liability to commit an act of aggression or crime, but the behavior must be interpreted within its specific context. Criminal law presumes that behavior is a function of free will, and most attempts to use genes as a mitigating factor in the courtroom have been unsuccessful. Efforts to prevent crime and violence must include consideration of all factors. Family milieu and parental competence are just as important as impaired cognitive mechanisms suchasreduced serotonin activity.Anim-balance in brain chemistry leading to impul-sivity or aggression may be ameliorated by a
supportive home setting, by medication, or by adequate nutrition.
—Joan C. Stevenson See also: Aging; Behavior; Biological Determinism; Criminality; DNA Fingerprinting; Forensic Genetics; Sociobiology; Steroid Hormones; XYY Syndrome.
Further Reading
Bock, Gregory R., and Jamie A. Goode. Genetics of Criminal and Antisocial Behaviour. New York: John Wiley & Sons, 1996. This symposium was held at the Ciba Foundation in London in 1995 and includes a representative sample of the research foci in this arena, followed by discussions.
Fishbein, Diana H., ed. The Science, Treatment, and Prevention of Antisocial Behaviors: Application to the Criminal Justice System. Kingston, N.J.: Civic Research Institute, 2000. An excellent set of reviews on aggression and the many associated behaviors and mental disorders.
Lesch, Klaus Peter, and Ursula Merschdorf. “Impulsivity, Aggression, and Serotonin: A Molecular Psychobiological Perspective.” Behavioral Sciences and the Law 18, no. 5 (2000): 581-604. A wonderful review of all the interacting factors, including all the elements of the serotonin system.
Moffitt, Terrie E., Avshalom Caspi, Michael Rutter, and Phil A. Silva. Sex Differences in Antisocial Behaviour: Conduct Disorder, Delinquency, and Violence in the Dunedin Longitudinal Study. New York: Cambridge University Press, 2001. Sex differences are documented as children grow up.
Roush, Wade. “Conflict Marks Crime Conference.” Science 269, no. 5232 (1995): 1808-1809. An excellent description of the pros and cons of genetic research on ASB.