Bullying Behavior: Blame It On Bad Genes?

This latest insight in the ongoing debate between nature and nurture was determined by a study involving about 1,500 pairs of Swedish and British twins, conducted by Thalia C. Eley, PhD, of the Institute of Psychiatry in London, Jim Stevenson, PhD, of the University of Southampton, and Paul Lichtenstein, PhD, of The Karolinska Institute, Sweden.

In the January-February issue of the journal, Child Development, they report what they say is the first to attempt to unravel and identify the degree of genetic and environmental influences in children and adolescents who combine both aggressive and non-aggressive antisocial behavior, as well as the first to test for the different sources in boys and girls of the two types of antisocial behavior.

They studied 1,022 pairs of Swedish twins and 501 pairs of British twins. About a third of the Swedish pairs and half of the British pairs are identical twins who share the same genetic inheritance. Fraternal twins, who develop from separate eggs, share about half of their genes.

"The most notable feature (of the study)," they write, "is the remarkable similarity between the results from the Swedish sample and the British sample. The initial finding is a double replication of the suggestion in the literature that aggressive and non-aggressive antisocial behavior have different etiologies."

Among the findings they report:

* Aggressive behavior can be inherited, but social environment plays a highly significant role in non-aggressive antisocial behavior.

* Boys learn non-aggressive antisocial behavior more from the environmental influences they encounter, while girls get it more from their genes.

* Combined aggressive and non-aggressive behavior is frequent in both boys and girls. In boys it is related mainly to environment effects that influence both kinds of behavior, whereas in girls the combined behaviors appear related primarily to genetic factors.

* Peer influences play a major role for both boys and girls and may be quite different for each member of a twin pair.

The authors of the study say their work will lead toward identification of specific genes associated with aggressive and non-aggressive antisocial behavior and the biological pathways involved. They cite the potential role of neurotransmitters such as serotonin and the enzymes that degrade them as possible mechanisms carrying these genetic effects.

The study was supported by grants from the Child Health Research Appeal Trust, Institute of Child Health, University of London, and Pennsylvania State University.