This review of family, twin, and adoption studies on offender behaviors points to the importance of a genetic predisposition as a partial explanation for criminality in some populations. Twin and adoption studies show that criminality increases with the presence of criminality in biological relatives; the environmental effects of having a criminal adoptive parent also increase the risk of adoptee criminality. Delinquency is described developmentally as a fairly typical phase for many adolescents. Because of the high base rate for delinquency, any genetic predisposition for offense behaviors may be difficult to uncover in adolescence. Three groups are differentiated that may aid in this detection: continuous antisocials are delinquents who continue to be criminal as adults; transitory delinquents are delinquents but not criminals; and late bloomers are criminals but not delinquents.

In her review of the literature on the intergenerational transmission of violent behaviors, Widom (1989a) addressed the social issues but omitted all references to the relevant biological and genetic literature. This addition to her review introduces studies of criminality, delinquency, and violence from a behavioral genetic standpoint. There is clear evidence for a genetic role in criminality and for a physiological basis for violent behavior. The inclusion of such genetic and biological evidence is necessary for a more complete understanding of the transmission of violence from one generation to another.

Measures of infant cognitive development in 208 pairs of twins were evaluated at 7,8, and 9 months of age. Measures included Fagan's Test of Infant Intelligence (FTII), visual expectation measures of reaction time and anticipation, selected items from the Bayley Scales of Infant Development, variety of vocalizations, Bayley's Infant Behavior Record (IBR), and others. The midparent IQ scores were regressed on the infant measures to evaluate the likelihood of predicting later IQ. Significant predictors were the FTII, visual expectation, IBR, vocalizations, and a composite of selected Bayley items. These measures were also the best predictors of the infants' intelligence scores on the Bayley at 1 and 2 years of age and on the Stanford-Binet at 3 years of age.

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The present study examined the role of positive parenting on externalizing behaviors in a longitudinal, genetically informative sample. It often is assumed that positive parenting prevents behavior problems in children via an environmentally mediated process. Alternatively, the association may be due to either an evocative gene-environment correlation, in which parents react to children’s genetically-influenced behavior in a positive way, or a passive gene-environment correlation, where parents passively transmit a risk environment and the genetic risk factor for the behavioral outcome to their children. The present study estimated the contribution of these processes in the association between positive parenting and children’s externalizing behavior. Positive parenting was assessed via observations at ages 7, 9, 14, 24, and 36 months and externalizing behaviors were assessed through parent report at ages 4, 5, 7, 9, 10, 11, and 12 years. The significant association between positive parenting and externalizing behavior was negative, with children of mothers who showed significantly more positive parenting during toddlerhood having lower levels of externalizing behavior in childhood; however, there was not adequate power to distinguish whether this covariation was due to genetic, shared environmental, or nonshared environmental influences.