Intelligence and Crime


Many early criminologists maintained that many delinquents and criminals’ behavior is a result of below-average intelligence and that low IQ is a cause of their criminality. Criminals were believed to have inherently substandard intelligence, and thus, they seemed naturally inclined to commit more crimes than more intelligent persons. This article will shed light on the link between intelligence (low IQ) and crime, and examine some prevention programs and criticism.

Research conducted by Social scientists on a group of subjects in juvenile training schools and penal institutions on IQ and its influence on crime. The correlation between IQ and crime by testing adjudicated offenders. Thus, inmates of penal institutions were used as a test group around which numerous theories about intelligence were built, leading ultimately to the nature-versus-nurture controversy that is still going on today. 

Nature Theory of Crime 

Nature theorists argue that intelligence is largely determined genetically, that ancestry determines IQ, and that low intelligence, as demonstrated by low IQ, is linked to criminal behavior. When the newly developed IQ tests were administered to inmates of prisons and juvenile training schools, the nature position gained support because a very large proportion of the inmates scored low on the tests. During his studies, Henry Goddard found that many institutionalized persons were what he considered “feebleminded”; he concluded that at least half of all juvenile delinquents were mental defectives. William Healy and Augusta Bronner tested groups of delinquent boys in Chicago and Boston and found that 37 percent were subnormal in intelligence. They concluded that delinquents were five to ten times more likely to be mentally deficient than normal boys.

These and other early studies were embraced as proof that low IQ scores identified potentially delinquent children and that a correlation existed between innate low intelligence and criminal behavior. IQ tests were believed to measure the inborn genetic makeup of individuals, and many criminologists accepted the idea that individuals with substandard IQs were predisposed toward delinquency and adult criminality.

Nurture Theory of Crime

The rise of culturally sensitive explanations of human behavior in the 1930s led to the nurture school of intelligence. Nurture theory states that intelligence must be viewed as partly biological but primarily sociological. Because intelligence is not inherited, low-IQ parents do not necessarily produce low-IQ children. Nurture theorists discredited the notion that people commit crimes because they have low IQs. Instead, they postulated that environmental stimulation from parents, relatives, social contacts, schools, peer groups, and innumerable others create a child’s IQ level and that low IQs result from an environment that also encourages delinquent and criminal behavior. Thus, if low IQ scores are recorded among criminals, these scores may reflect criminals’ cultural background, not their mental ability.

Studies challenging the natural assumption that people automatically committed criminal acts because they had below-average IQs began to appear. John Slawson studied 1,543 delinquent boys in New York institutions and compared them with a control group of New York City boys. Slawson found that although 80 percent of the delinquents achieved lower scores in abstract verbal intelligence, delinquents were about normal in mechanical aptitude and nonverbal intelligence. These results indicated the possibility of cultural bias in portions of the IQ tests. He also found that there was no relationship between the number of arrests, the types of offenses, and IQ.

In 1931, Edwin Sutherland evaluated IQ studies of criminals and delinquents, he  noted significant variation in the findings, which disproved Goddard’s notion that criminals were “feebleminded.”Goddard attributed discrepancies to testing and scoring methods rather than to differences in the mental ability of criminals. Sutherland’s research put an end to the belief that crime was caused by “feeblemindedness”; the IQ-crime link was forgotten in the criminological literature.

The Re-emergence  of  IQ and Criminality

 The alleged IQ-crime link was dismissed by mainstream criminologists, but it once again became an important area of study when respected criminologists Travis Hirschi and Michael Hindelang published a widely read paper linking the two variables. After re-examining existing research data, Hirschi and Hindelang concluded that the weight of evidence is that IQ  is a more important factor than race and socioeconomic class for predicting criminal and delinquent involvement. They concluded that major differences exist between criminals and noncriminals within similar racial and socioeconomic class categories. They proposed the idea that low IQ increases the likelihood of criminal behavior through its effect on school performance. That is, youths with low IQs do poorly in school, and school failure and academic incompetence are highly related to delinquency and later to adult criminality.

Hirschi and Hindelang’s inferences have been supported by research conducted by both U.S. and international scholars. Some studies have found a direct  IQ-delinquency link among samples of adolescent boys. When Alex Piquero examined violent behavior among groups of children in Philadelphia, he found that scores on intelligence tests were the best predictors of violent behavior and could be used to distinguish between groups of violent and nonviolent offenders.

In the book “ Crime and Human Nature”, James Q. Wilson and Richard Herrnstein find that the IQ-crime link is an indirect one: Low intelligence leads to poor school performance, which enhances the chances of criminality. They conclude, “A child who chronically loses standing in the competition of the classroom may feel justified in settling the score outside, by violence, theft, and other forms of illegality.” 

Cross-National Studies

The IQ-crime relationship has also been found in cross-national studies. A significant relationship between low IQ and delinquency has been found among samples of youth in Denmark. Researchers found that children with a low IQ tend to engage in delinquent behaviors because their poor verbal ability was a disability in the school environment. Research by Canadian neural psychologist Lorne Yeudall and his associates found samples of delinquents possessed IQs about 20 points less than nondelinquent control groups on one of the standard 1Q tests, the Wechsler Adult Intelligence Scale. An IQ-crime link was also found in a study of Swedish youth; low IQ measures taken at age 3 were significant predictors of later criminality over the life course.

IQ and Crime Reconsidered 

The Hirschi-Hindelang research increased interest and research on the association between IQ and crime, but the issue is far from settled and is still a matter of significant debate. Some recent studies find that IQ level has a negligible influence on criminal behavior. Also, a recent evaluation of existing knowledge on intelligence conducted by the American Psychological Association concluded that the strength of an IQ-crime link was”very low. ” 

In contrast, The Bell Curve, Richard Herrnstein, and Charles Murray’s influential albeit controversial book on intelligence, comes down firmly for an IQ-crime link. Their extensive review of the available literature shows that people with lower IQs are more likely to commit crimes, get caught, and be sent to prison. Conversely, kids with higher IQs seem to be protected from becoming criminals by their superior ability to succeed in school and social relationships. Taking the scientific literature as a whole, Herrnstein and Murray conclude that criminal offenders have an average IQ of 92, about 8 points below the mean; chronic offenders score even lower than the “average” criminal.

To those who suggest that the IQ-crime relationship can be explained by the fact that only low-IQ criminals get caught, they counter with data showing little difference in IQ scores between self-reported and official criminals. This means that even criminals whose activities go undetected by the authorities have lower IQs than the general public; the IQ-crime relationship cannot be explained away by the fact that slow-witted criminals are the ones most likely to be apprehended by the police.


 The well-documented criticisms suggesting that IQ tests are race and class-biased would certainly influence the testing of the criminal population who are besieged with a multitude of social and economic problems. Even if it can be shown that known offenders have lower IQs than the general population, it is difficult to explain many patterns in the crime rate: Why are there more male than female criminals? (Are females three times smarter than males?) Why do crime rates vary by region, time of year, and even weather patterns? Why does aging occur? IQs do not increase with age, so why should crime rates fall?

Prevention Programs 

 prevention programs that seek to treat personal problems before they manifest themselves as crime. To this end, thousands of family therapy organizations, substance abuse clinics, and mental health associations operate throughout the United States. Teachers, employers, relatives, welfare agencies, and others make referrals to these facilities. These services are based on the premise that if a person’s problems can be treated before they become overwhelming, some future crimes will be prevented. Secondary prevention programs provide treatment such as psychological counseling to youths and adults who are at risk for law violation. Tertiary prevention programs may be a requirement of a probation order, part of a diversionary sentence, or aftercare at the end of a prison sentence.

Biological Prevention Program

Biologically oriented therapy is also being used in the criminal justice system. Programs have altered diets, changed lighting, compensated for learning disabilities, treated allergies, and so on. Another practice that has elicited concern is the use of psychosurgery (brain surgery) to control antisocial behavior. Surgical procedures have been used to alter the brain structure of convicted sex offenders to eliminate or control their sex drives. Results are still preliminary, but some critics argue that these procedures are without scientific merit.

Numerous psychologically based treatment methods range from individual counseling to behavior modification. For example, treatment based on how people process information takes into account that people are more likely to respond aggressively to provocation if thoughts intensify the insult or otherwise stir feelings of anger. Cognitive therapists attempt to teach explosive people to control aggressive impulses by viewing social provocations as problems demanding a solution rather than retaliation. Therapeutic interventions designed to make people better problem solvers may involve measures that enhance; Coping and problem-solving skills, Relationships with peers, parents, and other adults; Conflict resolution and communication skills, and methods for resisting peer pressure related to drug use and violence; Consequential thinking and decision-making abilities, Prosocial behaviors, including cooperation with others, self-responsibility, respect for others, and public-speaking efficacy; and Empathy.


While there is a correlation between intelligence and crime, it is important to approach this topic with caution. Intelligence alone does not determine criminal behavior, as there are various other factors at play, such as socioeconomic status and environmental influences. It is crucial to consider the complex interplay of these factors when studying the relationship between intelligence and crime. Further research is needed to gain a deeper understanding of this topic and to develop effective strategies for crime prevention and intervention.

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