Genetics and Crime

criminal behavior is not exactly new. Perhaps most convincingly, several adoption studies in the 1970s and 1980s provided powerful evidence that having an incarcerated birth parent raised one’s own risk of earning a criminal conviction as an adult, even if reared by pro-social, law-abiding – but genetically unrelated – foster parents. This remarkable finding was replicated in adoptive cohorts across cultures, including two Scandinavian studies (Cloninger et al., 1982; Mednick et al., 1984) as well as in the United States (Cadoret et al., 1983). Based on these adoption studies, the genetic effect on criminal outcomes appears important for both sexes, although individual genetic risk is typically more extreme for female than male offenders (Baker et al., 1989). Heritable influences also differ in these studies according to the type of crimes committed, with petty, non-violent offending showing larger genetic influence than violent offenses (Mednick et al., 1984). Most importantly, however, these early adoption studies shared one other remarkable and profound result, which is that the genetic risk for criminal behavior could be exacerbated by adverse environmental circumstances, such as coming from a low socioeconomic background (Van Dusen, 1983), or being raised in a family with at least one criminal adoptive parent (Cloninger et al., 1982; Mednick et al., 1984). Such effects fall under the realm of genotype by environment (GxE) interactions, and highlight the complexity of the genetic and environmental effects in criminal outcomes. The provocative findings from these early adoption studies have since sparked numerous lines of research attempting to replicate and further refine our understanding of both genetic and environmental causes of crime and violence. A plethora of twin and adoption studies subsequently confirmed the genetic effect on criminal outcomes, and on the wider constructs of antisocial behavior (see Rhee and Waldman, 2002) and externalizing behavior disorders. Although dozens of studies have replicated the genetic effect in antisocial behavior across a variety of cultures, the genetic 1