Crime Causation: Biological Theories

The importance of gene-environment interactions are illustrated in several adoption studies. For example, the effects of socioeconomic status (SES) on inhibiting or promoting the expression of the genetic vulnerability to criminality have been examined in two large-scale adoption studies, the Danish and Swedish adoption studies. Cloninger and others (1982) and Van Dusen and others (1983) have reported that adoptive parent SES appears to interact with genetic vulnerability for criminality. Specifically, the risk of criminality among adoptees of criminal biological parents was significantly reduced if they were adopted into middle to high SES adoptive homes. Conversely, low adoptive parent socioeconomic status interacted with criminality in the biological parents to increase the adoptee's risk of criminality.

Other adverse environmental influences, such as adoptive parental registrations for alcohol and crime, and later age of placement, were found to interact with the genetic risk for criminal behavior. Crowe (1975) found that adoptees who had a criminal biological mother and spent longer time in an orphanage or foster placement had the highest rates of criminal conviction. In a separate series of adoption studies carried out by Cadoret and colleagues, evidence for the importance of gene-environment interactions in the development of antisocial problems in adoptees has been presented. Cadoret and others (1983) reported in a Missouri adoption sample (n = 108) that adoptees with an alcoholic or anti-social biological parent who were placed in an adoptive home at a later age had the highest rate of adolescent antisocial problems. In an Iowan adoption study (n = 246 male and female adoptees), Cadoret and Cain found that the presence of alcohol or antisocial symptoms in the biological parents interacted with adverse environmental conditions, such as the presence of alcohol and antisocial problems in the adoptive parents, time spent in foster care, and divorced status of the adoptive parents, to produce a marked increase in the incidence of adolescent antisocial behavior. Cadoret and others (1995) reported that a biological background of antisocial problems interacted with adverse environmental conditions, such as the presence of a psychiatric condition in the adoptive family, separation or divorce of the adoptive parents, adoptive parent alcohol or drug abuse, to increase the risk of childhood conduct disorder and adolescent aggressivity. Taken together, these studies demonstrate the utility of the gene-environmental model to our understanding of the etiological correlates of criminal behavior.