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Original Articles
Introduction
An important question in understanding the origins of pathological human violence is to clarify the nature, origins and magnitude of familial-environmental contributions to individual differences. Genetic epidemiological research has addressed this issue through an examination of criminality using a variety of methodological designs (Lange, 1929; Rosanoff et al. 1934). Twin and adoption studies have suggested that genetic factors contribute substantially to the etiology of a range of antisocial behaviors (Rhee & Waldman, 2002) and particularly criminal offending (Lange, 1929; Rosanoff et al. 1934; Crowe, 1972; Christiansen, 1974; Dalgard & Kringlen, 1976; Bohman, 1978; Gabrielli & Mednick, 1984; Mednick et al. 1984). In their meta-analysis, Rhee & Waldman (2002) estimated that 16% of the variance in liability to antisocial behaviors resulted from environmental influences shared by siblings. In a recent national Swedish adoption study of violent criminal behavior (VCB), we found that genetic risk, indexed by VCB and other externalizing disorders in biological parents, and familial environmental risk, indexed by divorce, death and low educational status of the adoptive parents, both contributed meaningfully to risk for VCB in the adoptee (Kendler et al. 2013a ).
Studies using self-report survey data from the general population (Rowe & Britt, 1991; Rowe & Gulley, 1992; Rowe et al. 1992; Lauritsen, 1993; Takahashi & Miczek, 2013) have reported similarity in criminal offending among siblings. Lauritsen (1993) notes that most of these studies report correlations of delinquency involvement among sibling pairs between 0.20 and 0.40. Slomkowski et al. (2001) examined similarity in sibling self-reported delinquency across four time points. Using data from 164 male and female same-sex sibling pairs, they found significant similarity in self-reported delinquency for both male and female sibling pairs. They also examined the impact of the older sibling's delinquency on the probability of the younger sibling's delinquency and found, for both males and females, evidence that older sibling delinquency predicted delinquency in the younger sibling. They did not examine if this finding held for mixed-sex sibling pairs. Sibling similarity in delinquency and criminal offending has also been found in studies using official measures of criminal offending, such as criminal convictions (Rowe & Farrington, 1997). Using data from the Cambridge Study in...