The social and biological influences contribute to risks involving the child's temperament and cognitive competence. These include, for example, impulsiveness, hyper-activity, attention deficits, emotional lability, verbal problems and below-average intelligence (Farrington, 1998; Hawkins et al., 1998; Lipsey and Derzon, 1998). Deficits in executive brain functions impact on abstract thinking, planning, goal-directed behaviour and self-control (Moffitt and Henry, 1991). Again, one should not overemphasize one single risk factor. For example, even the attention-deficit-hyperactivity-disorder syndrome shows only a moderate correlation with later criminality (Loeber and Stouthamer-Loeber, 1998). The personality dispositions may also have a different impact on various delinquent pathways. Frick (1998), for example, distinguishes between two causal pathways of antisocial development. The first results primarily from poor parental socialization and low intelligence. The second is mainly due to callous, unemotional, and other traits of psychopathy (see Hare, 2001). It should also not be forgotten that some aggressive offenders are not impulsive and hyperactive, but more inhibited. Such over-controlled hostile individuals (Megargee, 1996;
White and Heilbrun, 1995) often exhibit other psychological problems and act violently when conflicts escalate under strong affects.
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