We now turn our attention to the specific factors we will emphasize in subsequent chapters

Intelligence and Crime

The study of intelligence and crime has a long history. McGloin, Pratt, and Maahs (2004) describe how “Criminologists have treated the relationship between IQ and delinquent behavior with a curious mixture of faith, indifference, and contempt” (p. 601). Early discussions (e.g., Davenport, 1915; Dugdale, 1877 as cited by McGloin et al., 2004) unabashedly linked intellectual “inferiority” or “feeblemindedness” and offending (Richmond, 1931) and authors believed the relationship to be causal and linear (McGloin et al., 2004). Interest in “biological” explanations for criminality was supplanted in the early 20th century by social theories, though some researchers continued to collect data on intelligence. Glueck and Glueck (1934) reported on the low intelligence of their Boston delinquents. Reports from Project Metropolitan, begun in 1953, show prospective associations between IQ in childhood and later criminal activity (H0gh & Wolf, 1983). Hirschi and Hindelang (1977) are credited with resurrecting the issue in the 1970s, reviewing the literature and estimating that there is a one-standard-deviation difference in intelligence between delinquents and nondelinquents. This point was emphasized in subsequent work by Wilson and Herrnstein (1985) and, most famously, by Herrnstein and Murray (1994) in The Bell Curve. Studies continue to find intelligence deficits in serious violent offenders. In recent years, the low intelligence of imprisoned offenders has become a cause celebre for some, because of ethical concerns. Cunningham and Vigen (2002) reviewed studies of death row inmates and conclude that they are “intellectually limited and academically deficient” (p. 194). A significant minority in several studies had IQ scores in the mentally retarded range, or bordered that range.

Intelligence and related factors (e.g., executive functioning, verbal abilities) have been associated with aggression and criminality in many studies, across contexts and samples (Moffitt, Caspi, Silva, & Stouthamer-Loeber, 1995). We touch on some of the literature here and treat it more systematically in Chapter 4. It is likely that the idea first came to light from observations of offender populations in which low intelligence is frequently evident. Contemporary observers find this as well. A Canadian study reports that 19% of men in a pre-trial holding center, who agreed to participate in their study, had a probable intellectual disability (Crocker, Cote, Toupin, & St-Onge, 2007). Nearly one third were in the borderline IQ range. These individuals had concomitant problems such as not completing high school and substance use disorders. Talbot and Jacobson (2010) write that it is “generally recognised [sic]” that about 7% of the prison population in the United Kingdom have an IQ below 70, and an additional 25% have an IQ between 70 and 79. Moffitt has reported the association in her New Zealand sample (Moffitt et al., 1995). Fazel, Xenitidis, and Powell (2008) examined published reports from four countries and concluded that the number of prisoners diagnosed with intellectual disabilities, was “considerable.”

A plethora of studies and reviews have found that intellectual and cognitive deficits are associated with aggressive behavior (e.g., Bennett, Farrington, & Huesmann, 2005; Donnellan, Ge, & Wenk, 2000; Seguin, Assaad, Nagin, & Tremblay, 2004; Seguin, Parent, Tremblay, & Zelazo, 2009). Related studies using measures of intelligence and school grades support the idea that cognitive abilities are inversely associated with violence in older children and adolescents.

More recently, “neuropsychological deficits” feature prominently in Moffitt’s dual taxonomy of persistent offending. Low intellectual ability, reading difficulties, and poor scores on neuropsychological test of memory have been differentially associated with life-course-persistent offending in her data (Moffitt, 2006). Substantial evidence of an association between deficits in intellectual function and chronic offending has accrued in other data sets as well (e.g. Cottle, Lee, & Heilbrun, 2001; Denno, 1990; Farrington, 2000b; Farrington & West, 1993; Ge, Donnellan, & Wenk, 2001; Maughan & Rutter, 1998; Piquero & White, 2003; Raine, Loeber, Stouthamer-Loeber, Moffitt, Caspi, & Lynam, 2005; Sampson & Laub, 2003). While life-course-persistent offending is not completely synonymous with violent offending, the two are highly correlated.

The reasoning for an association between low intelligence and violence relies mainly on indirect effects. Those with low intelligence are less likely to learn to employ problem solving to avoid violence. They are less likely to generate multiple ideas for how to carry themselves in social situations. They may be less likely to learn the cognitive aspects of theory of mind and empathy.

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