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Genes play a significant role in the development of psychopathy. However socialization and other environmental factors interact with genetics, so genes are not the only determinant in whether one has psychopathic traits. Studies on the heritability of psychopathy have focused primarily on identical twins (100% shared genes) and fraternal twins (50% shared genes). One study (Larsson, Andershed, & Lichtenstein, 2006) which examined the heritability of psychopathy in twins reported that genetics accounted for approximately half of the variation in the features of psychopathy (as assessed by a self-report measure, the Youth Psychopathic Traits Inventory). Other studies have also reported substantial heritability to psychopathic traits when these are assessed using self-report measures (Blonigen, Hicks, Krueger, Patrick, & Iacono, 2005; Brook, Panizzon, Kosson, Sullivan, Lyons, Franz, Eisen, & Kremen, 2010).
The finding that about 50% of individual differences in psychopathic traits are genetic suggests that a fair amount of variance in psychopathic features is environmental. (It is worth noting that approximately 40-60% of the variance in many personality traits and in several other disorders also appears to reflect genetic factors. Thus, psychopathy is similar to other personality traits and disorders in which genetic factors are important, yet do not explain everything.) Although specific genes relevant to psychopathy have not yet been identified, most people believe there are probably multiple genes which contribute to psychopathy, just as there are multiple genes involved in most clinical conditions which are partly heritable. (Thus, there is not usually just one gene that by itself leads to a clinical disorder or condition.)
Furthermore, there is increasing evidence that genetic and environmental factors interact, and psychopathy may reflect an interaction between these two factors. The aforementioned study (Larsson et al., 2006) examined the influence of shared environmental factors and non-shared environmental factors in psychopathic traits. Shared environmental factors are those aspects of the environment that tend to make people more like each other, such as parents and growing up in a particular neighborhood. To the extent that the parents behave the same way with all their children, any consequences of being around those parents should have the effect of making two twins more similar to each other. An example of non-shared environmental factors discussed by Larsson and his colleagues would be peer relationships. Since each individual in a twin pair is likely to form different friendships outside of the home, the consequences of associating with different peers can contribute to observed differences between twins. After the contribution of genetic factors was accounted for in the study, the role of environmental effects was examined. Findings showed that the contribution of non-shared environmental effects was fairly large, while shared environmental effects were negligible. Since it appears that environmental factors may influence the expression of genetic risk for psychopathy, we encourage all parents of at-risk children to seek the advice of mental health professionals if children show signs of poor impulse control or antisocial behavior.
Additional reading (note: The resources listed here are written with an academic focus and may be too technical for many readers): For people who are interested in reading more about genetics and psychopathy, the chapters “Genetic and Environmental Influences on Psychopathy and Antisocial Behavior” (pp. 205-228) and “Family Background and Psychopathy” (pp. 229-250) in C.J. Patrick’s Handbook of Psychopathy (2007), and the chapters “Genetics of Childhood and Adolescent Psychopathy (pp.113-134)” and “Environmental Influences on Child and Adolescent Psychopathy” (pp. 202-232)” in Salekin and Lynam’s Handbook of Childhood and Adolescent Psychopathy (2010) provide good overviews of studies examining the role of genes and environment on psychopathy.
Blonigen, D.M., Hicks, B.M., Krueger, R.F., Patrick, C.J., & Iacono, W.G. (2005). Psychopathic personality traits: Heritability and genetic overlap with internalizing and externalizing psychopathology. Psychological Medicine: A Journal of Research in Psychiatry and the Allied Sciences, 35, 637-648.
Brook, M., Panizzon, M. S., Kosson, D. S., Sullivan, E. A., Lyons, M. J., Franz, C. E., Eisen, S. A., & Kremen, W. S. (2010). Psychopathic personality traits in middle-aged male twins: A behavior genetic investigation. Journal of Personality Disorders, 24, 473-486.
Farrington, D.P., Ullrich, S., & Salekin, R.T (2010). Environmental influences on child and adolescent psychopathy. In R.T. Salekin & D.R. Lynam (Eds.), Handbook of Childhood and Adolescent Psychopathy (pp. 113-134). New York: The Guilford Press.
Viding, E. & Larsson, H. (2010). Genetics of childhood and adolescent psychopathy. In R.T. Salekin & D.R. Lynam (Eds.), Handbook of Childhood and Adolescent Psychopathy (pp. 113-134). New York: The Guilford Press.
Waldman, I.D. & Rhee, S.Y. (2007). Genetic and environmental influences on psychopathy and antisocial behavior. In C.J. Patrick (Ed.), Handbook of Psychopathy (pp. 229-250). New York: The Guilford Press.