Vol. 5, No. 3, 1999 Page 1&6 
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Vol. 5, No. 3, 1999 Page 1&6 |
What makes a child a bully? According to a new study, the answer, in large part, is genetic.
Thalia Eley and colleagues studied more than 1,500 pairs of Swedish and British twins to determine the causes of antisocial behavior beginning early in life. The researchers examined two types of antisocial behavior, aggressive (e.g., bullying and fighting) and non-aggressive (e.g., truancy and stealing). To distinguish between environmental and hereditary influences, they compared identical (monozygotic) twins with fraternal (dizygotic) twins.
The researchers found that "variance in individual differences in aggressive symptoms was primarily due to additive genetic factors in both sexes"-that is, that genes play a powerful role in whether or not a child is aggressive. In contrast, environmental factors appeared to play a predominant role in non-aggressive antisocial behavior in boys, while such behavior was strongly genetically influenced in girls.
"The most notable feature (of the study data)," the researchers say, "is the remarkable similarity between the results from the Swedish sample and the British sample." Data from both countries show, they say, that "aggressive and non-aggressive antisocial behavior have different etiologies."
Identifying these etiologies is important, Eley et al. say, because childhood antisocial behavior is one of the strongest predictors of adult antisocial behavior and criminality. The researchers say future investigations should focus in part on identifying specific genes associated with aggressive antisocial behavior. "These are likely to involve the monoamine neurotransmitters such as serotonin and enzymes involved in the degradation of these monoamines such as monoamine oxidase-A," they say, "as variation in these is highly heritable and is significantly associated with aggressive antisocial behavior."
"Sex differences in the etiology of aggressive and nonaggressive antisocial behavior: results from two twin studies," Thalia C. Eley, Paul Lichtenstein, and Jim Stevenson, Child Development, Vol. 70, No. 1, Jan./Feb. 1999, pp. 155-168. Address: Thalia C. Eley, Social, Genetic and Dev. Psychiatry Research Centre, Institute of Psychiatry, 111 Denmark Hill, De'Crespigny Park, London SE5 8AF, U.K.