Forensic Behavioral Analysis
In her article addressing the transmission of abusive or antisocial behaviors from one generation to another, Widom (1989a) accurately pointed out the need for “a comprehensive and critical assessment of the existing empirical literature on the ‘violence begets violence’ hypothesis” (p. 4). Her review of the literature, however, explored the relevant environmental studies but lacked reference to any studies with a genetic or biological bent. There is a sufficiently large body of evidence related to the biological bases of criminal behavior for Widom’s review of the violence literature to be incomplete without reference to genetic studies. The intergenerational transmission of violent or abusive behaviors quite likely has a genetic or biological component worth exploring.
In reviewing transmission of violence, the child abuse, delinquency, and criminality literature all are relevant. Widom allocated most of her review to critiquing the child abuse literature, for which there have not been any genetic studies. However, there have been numerous genetic studies on criminality and a few on delinquency, which add an important aspect to her review, especially given the comorbidity between child abuse and other diagnoses such as antisocial personality (Oliver, 1985, 1988). These are summarized here following a brief explanation of the logic behind twin and adoption studies. The present article is offered as a “friendly amendment” and is concerned only with studies of a genetic or biological bent.
Genetic Research Methodology
Three types of samples are used traditionally for genetic research—nuclear families, twins, and adoptees. The idea behind them is to be able to separate genetic and environmental components of variance. Hence, calling this “genetic research” is only half of the story; these designs are equally useful in examining the role of the environment in the variables of interest. A brief description of each method follows.
Family studies are useful in that family members share both genes and environment. If there were no relationship between family members for a certain behavior, it could be deduced that there is no genetic or shared environmental influence for that behavior. However, if a relationship does exist between family members, there is no way to determine whether that relationship is a function of genes, environment, or both, although an estimate of the upper limit of heritability can be established (Plomin, DeFries, & McClearn, 1989). The twin and adoption methods are necessary in order to disentangle the influences of genes and environment.
The twin design makes use of the fact that monozygotic (MZ) twins share 100% of their genes and dizygotic (DZ) twins share on average 50% of their genes. Thus, a comparison of concordance rates between the two types of twins provides a handle on the extent of environmental influence.
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