TWIN STUDY TRACES ROOTS OF PSYCHOPATHIC BEHAVIOR

Psychopaths make up a minority of criminals, but the damage they cause far outweighs their numbers. Nearly two- thirds of psychopathic offenders commit another crime within three years of release from prison, compared to only one- quarter of non-psychopathic prisoners, and psychopaths released from prison are far more likely than other former inmates to commit a violent crime.

Because there is evidence that heredity plays a role in psychopathy, several research groups are focusing on teasing out the effects of genes on different facets of psychopathic behavior. A recent study by Jeanette Taylor and colleagues sought to determine the influence of genes on two trait dimensions that define psychopathy: impulsive/antisocial behavior, and callous/unemotional personality.

The researchers studied two separate groups of teenaged male twins. One group included 142 identical (monozygotic) and 70 fraternal (dizygotic) twin pairs, while the other included 128 identical and 58 fraternal twin pairs. All of the teens completed the Minnesota Temperament Inventory (MTI), a questionnaire that includes subsets assessing antisocial traits and detachment.

The researchers say their results indicate a significant influence of genes on each trait dimension, and a common genetic influence on these two trait dimensions. The latter, they say, is "consistent with the notion of common biological substrates for impulsivity/antisocial behavior and emotional detachment." Slightly more than half of the co-variation between the two trait dimensions was associated with genetic factors, while slightly less than half was associated with non-shared environmental factors (differences in peer groups and other non-familial factors).

Taylor et al. say their findings indicate that psychopathic traits are present prior to adulthood, and stem to a significant degree from genetic factors. "The results of this study also suggest that shared environmental factors are not particularly salient in the development of psychopathy traits," they say.

"Genetic and environmental influences on psychopathy trait dimensions in a community sample of male twins," Jeanette Taylor, Bryan R. Loney, Leonardo Bobadilla, William G. Iacono, and Matt McGue, Journal of Abnormal Child Psychology, Vol. 31, No. 6, December 2003, 633-45. Address: Jeanette Taylor, Department of Psychology, Florida State University, Tallahassee, FL 32306-1270, taylor@psy.fsu.edu.