Finally, although this was a cross-sectional study and firm conclusions about causal pathways are not possible, the results suggest that the path to heroin and multiple substance dependence may be different for males and females. A meta-analysis of studies examining genetic and environmental influences on antisocial behaviour (ASB) concluded that the heritable liability was the same for both sexes (Rhee, et al., 2002). The polygenic multiple threshold model suggests that females may need a greater liability to express antisocial behaviour, thus explaining the lower prevalence of ASB amongst females (Rhee, et al., 2002). Other studies have found that there are genetic effects on an individual’s tendency to seek out deviant peers and high risk environments (McGue, Iacono, & Krueger, 2006; Rowe & Rodgers, 1984). This is referred to as active gene-environment correlation, where it is the child’s genes which influence their liability to seek out particular environmental circumstances (Rutter, et al., 2006). This study’s results are consistent with a more passive gene-environment correlation for females than for males. Passive gene-environment correlation refers to the parents’ genetic liability for ASB which
