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Tuesday March 9 1:35 PM ET

Bullying may have genetic roots

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NEW YORK, Mar 09 (Reuters Health) -- Aggressive, bullying behavior may have genetic causes, especially in boys, according to a report in a recent issue of the journal Child Development.

The results of a study in twins ``support the hypothesis that aggressive behavior is heritable,'' write a team of British and Swedish researchers led by Dr. Thalia Eley of the Institute of Psychiatry in London, UK.

They studied the behaviors of over 1,500 pairs of twins. Approximately one third of the pairs were identical twins.

The authors found that ``aggressive behavior'' -- bullying or fighting -- ``was highly inheritable,'' especially among boys.

On the other hand, the causes of non-aggressive, antisocial behaviors -- such as theft or truancy -- seemed to vary by gender, with ``environment having a greater role for boys and genetic effects having a greater influence on girls.''

Eley and colleagues point out that genes help regulate the function of various neurotransmitters -- chemicals that carry messages in the brain. Among these is serotonin, which is ''specifically associated with physical aggression'' but not linked with non-aggressive behaviors such as theft. The tendency toward violent or aggressive behavior seems to begin very early in childhood development, they add, indicating a 'pre-set' genetic origin for bullying, violent behaviors.

On the other hand, studies have suggested that environmental influences -- especially family life and peer groups -- may be strongly linked to later indulgence in non-aggressive antisocial behaviors, especially in boys. Eley's group speculate that ''boys (may) experience these influences more often than girls, resulting in their higher... levels of antisocial behavior.''

The researchers also found that children of either gender were more likely to exhibit delinquent, antisocial behaviors if they already exhibited aggressive personalities. This pairing of the two types of behavior seemed to be linked to ``both genetic and... environmental influences'' among boys, but to genetic factors alone in girls, the authors conclude.

SOURCE: Child Development 1999;70.