The act of trying to measure intelligence has a disturbing history in the United States and beyond. One of the first official measures of intelligence, the IQ or intelligence quotient test, originated with French psychologists Alfred Binet and Theodore Simon in 1905. They were tasked with ascertaining whether there was a link between mental capacity and behavioral issues in school children. IQ was determined by dividing actual age by mental age and then multiplying by 100. A score of 100, give or take 15 points, was considered average. If someone scored higher than 115, they were considered to be very smart. If someone fell below 85, they were considered unintelligent and were eventually labeled as problematic and having a disability. When mapped out (figure 4.9), IQ scores create a shape known as a bell curve.

Although the initial intentions were good, and Binet believed that IQ could be increased through training and education, the IQ test took a different shape in the United States. Henry Goddard, whom we discussed earlier in Learn More: Degeneracy in the Family Tree, began his notorious work with the French Binet-Simon IQ test, translated it, and modified it for his own purposes in the United States in the early 1900s. Goddard advocated for isolating, incarcerating, institutionalizing, or sterilizing people he deemed to be “mental defectives.” He used his updated IQ test to support these beliefs. In 1912, he published the study titled The Kallikak Family: A Study in the Heredity of Feeble-Mindedness, which was discussed earlier. Goddard, having spent time with youth who had committed offenses, claimed that at least half of all criminals are mentally defective. In this manner, he created the supposed link between intelligence and crime. Goddard later admitted that his study was deeply flawed, but this was after the results had already influenced future research and even policy.

In 1929, American psychiatrist M.H. Erickson conducted a large study and discovered a link between IQ and crime, but his research showed that some crimes require a greater IQ than others. However, Erickson believed that the link between IQ and crime was indirect and that intelligence did not appear to be a causal factor in producing criminals in society. Further challenging the relationship between IQ and criminality, sociologist Edwin Sutherland published a study in 1931 that contradicted the possible connection between IQ and crime. Sutherland compared the IQ scores of adults who had committed offenses to those of army draftees and found that the two groups had nearly identical IQ levels. The army draftees represented the general population, which is something the previous studies had failed to measure and compare. Sutherland argued that if the average IQ of the general population was not known, then it would be impossible to claim it has any effect on human behavior. He concluded that intelligence was not a generally important cause of delinquency (Sutherland, 1931). In spite of Sutherland’s research, the debate over the link between IQ and crime continued for the next 40 years.

IQ, Criminality, and Racism

In 1961, psychologist Arthur Jensen divided intelligence into two different categories: associative learning and conceptual learning. Associative learning is the simple retention of input or the memorization of facts and skills, such as when you study for an exam and memorize facts you know will be on the test. Conceptual learning is the ability to manipulate and transform information input or problem-solving, such as when that same test has open-ended questions that ask you to think critically about a challenge and offer up possible solutions.

Jensen tested children of color in the 1960s and reached two conclusions. First, Jensen concluded that 80% of intelligence is genetic, and the remaining 20% is due to environmental factors. This claim spoke directly to the “nature versus nurture” debate, with Jensen arguing that nature (genetics) has more influence on intelligence than nurture (the environment in which a child is raised). Second, he claimed that while all races were equal in terms of associative learning, conceptual learning occurred with a significantly higher frequency in white children than in Black children. This research led Jensen to incorrectly conclude that white people were inherently more able to engage in conceptual learning than Black people. Similarly, Nobel laureate and physicist William Shockley (1967) stated that the difference between Black American and European American IQ scores was due to genetics. He claimed that genetics might also explain the variable poverty and crime rates in society.

In 1994, psychologist Richard Hernstein and political scientist Charles Murray published The Bell Curve: Intelligence and Class Structure in American Life, which soon became controversial. In the book, they conclude that low IQ is a risk factor for criminal behavior. In particular, they claim the more experience white men have in the criminal justice system, the lower their IQ. Hernstein and Murray suggest that low intelligence can lead to criminal behavior by being associated with the following experiences:

• lack of success in school and the job market
• lack of foresight and a desire for immediate gains
• unconventionality and insensitivity to pain or social rejection
• failure to understand the moral reasons of law conformity

They argue that it is cognitive disability rather than economic or social disadvantage that creates crime. Because of this, they state that policy should focus on cognitive problems instead of social problems, such as unemployment and poverty.

Hernstein and Murray’s study received criticism because of their outdated views of intelligence and their claim that it is difficult to increase IQ scores, despite there being evidence to the contrary. They also explained high crime among Black Americans as being due to inherited intellectual inferiority. What Hernstein and Murry failed to consider were alternative criminogenic risk factors, such as the impact of systemic racism on school quality. By portraying people who committed offenses as criminals because of cognitive disadvantage, their research justified repressive crime policies that focused primarily on the individual and not the environment.

It is important to note the research and theories making claims about intelligence and race have been disproven and determined to be both racist and misleading (figure 4.10). These claims are part of the scientific racism ideology that “appropriates the methods and legitimacy of science to argue for the superiority of white Europeans and the inferiority of non-white people whose social and economic status have been historically marginalized” (National Human Genome Research Institute, 2022). Nonetheless, we look at IQ testing in a book on criminology because these factors were used in deciding whether or not someone was a criminal. This label not only led to people being incarcerated or institutionalized, but it also led to their murder. For example, in Virginia it was legal to forcibly sterilize someone with a low IQ score, and in Nazi Germany, it was legal to murder children with scores below average. All of this horror was part of the eugenics movement (discussed in the next section) in which the criminal justice system and criminologists played a key role.

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Licenses and Attributions for Crime and Intelligence

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“Crime and Intelligence” by Curt Sobolewski, Taryn VanderPyl, and Jessica René Peterson is licensed under CC BY 4.0.

“Crime and Intelligence Question Set” was created by ChatGPT and is not subject to copyright. Edits for relevance, alignment, and meaningful answer feedback by Colleen Sanders are licensed under CC BY 4.0.

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Figure 4.9. “IQ curve” by Alessio Damato and Mikhail Ryazanov is licensed under CC BY-SA 3.0.

Figure 4.10. “The Dark History of IQ Tests” by TED-Ed is licensed under the Standard YouTube License.

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“Scientific Racism” definition from National Human Genome Research Institute is included under fair use.