The Bell Curve: Intelligence and Class Structure in American Life

by Richard J. Herrnstein

  Theories nearer the psychological pole were more common earlier in the history of criminology and have lately regained acceptance among experts. Here, the emphasis shifts to the characteristics of the offender rather than to his circumstances. The idea is that criminals are distinctive in psychological (perhaps even biological) ways. They are deficient, depending on the particular theory, in conscience or in self-restraint. They lack normal attachment to the mores of their culture, or they are peculiarly indifferent to the feelings or the good opinion of others. They are overendowed with restless energy or with a hunger for adventure or danger. In a term that was in common use throughout the nineteenth and early twentieth centuries, chronic offenders may be suffering from “moral insanity.”5 In other old-fashioned vocabularies, they have been called inhumane, atavistic, demented, monstrous, or bestial—all words that depict certain individuals as something less than human. In their most extreme form, psychological theories say that some people are born criminal, destined by their biological makeup to offend.

  We are at neither of these theoretical poles. Like almost all other students of crime, we expect to find explanations from both sociology and psychology. The reason for calling attention to the contrast between the theories is that public discussion has lagged; it remains more nearly stuck at the sociological pole in public discourse than it is among experts. In this chapter, we are interested in the role that cognitive ability plays in creating criminal offenders. This by no means requires us to deny that sociology, economics, and public policy might play an important part in shaping crime rates. On the contrary, we assume that changes in those domains are likely to interact with personal characteristics.

  Among the arguments often made against the claim that criminals are psychologically distinctive, two are arguments in principle rather than in fact. We will comment on these two first, because they do not require any extensive review of the factual evidence.

  Argument 1 : Crime rates have changed in recent times more than people’s cognitive ability or personalities could have. We must therefore find the reason for the rising crime rates in people’s changing circumstances.

  When crime is changing quickly, it seems hard to blame changing personal characteristics rather than changing social conditions. But bear in mind that personal characteristics need not change everywhere in society for crime’s aggregate level in society to change. Consider age, for example, since crime is mainly the business of young people between 15 and 24.6 When the age distribution of the population shifts toward more people in their peak years for crime, the average level of crime may be expected to rise. Or crime may rise disproportionately if a large bulge in the youthful sector of the population fosters a youth culture that relishes unconventionality over traditional adult values. The exploding crime rate of the 1960s is, for example, partly explained by the baby boomers’ reaching adolescence.7 Or suppose that a style of child rearing sweeps the country, and it turns out that this style of child rearing leads to less control over the behavior of rebellious adolescents. The change in style of child rearing may predictably be followed, fifteen or so years later, by a change in crime rates. If, in short, circumstances tip toward crime, the change will show up most among those with the strongest tendencies to break laws (or the weakest tendencies to obey them).8 Understanding those tendencies is the business of theories at the psychological pole.

  Argument 2: Behavior is criminal only because society says so. There cannot be psychological tendencies to engage in behavior defined so arbitrarily.

  This argument, made frequently during the 1960s and 1970s and always more popular among intellectuals than with the general public, is heard most often opposing any suggestion that criminal behavior has biological roots. How can something so arbitrary, say, as not paying one’s taxes or driving above a 55 mph speed limit be inherited? the critics ask. Behavior regarding taxes and speed limits certainly cannot be coded in our DNA; perhaps even more elemental behaviors such as robbery and murder cannot either.

  Our counterargument goes like this: Instead of crime, consider behavior that is less controversial and even more arbitrary, like playing the violin. A violin is a cultural artifact, no less arbitrary than any other man-made object, and so is the musical scale. Yet few people would argue that the first violinists in the nation’s great orchestras are a random sample of the population. The interests, talents, self-discipline, and dedication that it takes to reach their level of accomplishment have roots in individual psychology—quite possibly even in biology. The variation across people in any behavior, however arbitrary, will have such roots. To that we may add that the core crimes represented in the violent crime and property crime indexes—murder, robbery, and assault—are really not so arbitrary, unless the moral codes of human cultures throughout the world may be said to be consistently arbitrary in pretty much the same way throughout recorded human history.

  But even if crime is admitted to be a psychological phenomenon, why should intelligence be important? What is the logic that might lead us to expect low intelligence to be more frequently linked with criminal tendencies than high intelligence is?9

  One chain of reasoning starts from the observation that low intelligence often translates into failure and frustration in school and in the job market. If, for example, people of low intelligence have a hard time finding a job, they might have more reason to commit crimes as a way of making a living. If people of low intelligence have a hard time acquiring status through the ordinary ways, crime might seem like a good alternative route. At the least, their failures in school and at work may foster resentment toward society and its laws.

  Perhaps the link between crime and low IQ is even more direct. A lack of foresight, which is often associated with low IQ, raises the attractions of the immediate gains from crime and lowers the strength of the deterrents, which come later (if they come at all). To a person of low intelligence, the threats of apprehension and prison may fade to meaninglessness. They are too abstract, too far in the future, too uncertain.

  Low IQ may be part of a broader complex of factors. An appetite for danger, a stronger-than-average hunger for the things that you can get only by stealing if you cannot buy them, an antipathy toward conventionality, an insensitivity to pain or to social ostracism, and a host of derangements of various sorts, combined with low IQ, may set the stage for a criminal career.

  Finally, there are moral considerations. Perhaps the ethical principles for not committing crimes are less accessible (or less persuasive) to people of low intelligence. They find it harder to understand why robbing someone is wrong, find it harder to appreciate the values of civil and cooperative social life, and are accordingly less inhibited from acting in ways that are hurtful to other people and to the community at large.

  With these preliminaries in mind, let us explore the thesis that, whatever the underlying reasons might be, the people who lapse into criminal behavior are distinguishable from the population at large in their distribution of intelligence.

  THE LINK BETWEEN COGNITIVE ABILITY AND CRIMINAL BEHAVIOR: AN OVERVIEW

  The statistical association between crime and cognitive ability has been known since intelligence testing began in earnest. The British physician Charles Goring mentioned a lack of intelligence as one of the distinguishing traits of the prison population that he described in a landmark contribution to modern criminology early in the century.10 In 1914, H. H. Goddard, an early leader in both modern criminology and the use of intelligence tests, concluded that a large fraction of convicts were intellectually subnormal.11

  The subsequent history of the study of the link between IQ and crime replays the larger story of intelligence testing, with the main difference being that the attack on the IQ/crime link began earlier than the broader attempt to discredit IQ tests. Even in the 1920s, the link was called into question, for example, by psychologist Carl Murchison, who produced data showing that the prisoners of Leavenworth had a higher mean IQ than that of enlisted men in World War I.12
Then in 1931, Edwin Sutherland, America’s most prominent criminologist, wrote “Mental Deficiency and Crime,” an article that effectively put an end to the study of IQ and crime for half a century.13 Observing (accurately) that the ostensible IQ differences between criminals and the general population were diminishing as testing procedures improved, Sutherland leaped to the conclusion that the remaining differences would disappear altogether as the state of the art improved.

  The difference, in fact, did not disappear, but that did not stop criminology from denying the importance of IQ as a predictor of criminal behavior. For decades, criminologists who followed Sutherland argued that the IQ numbers said nothing about a real difference in intelligence between offenders and nonoffenders. They were skeptical about whether the convicts in prisons were truly representative of offenders in general, and they disparaged the tests’ validity. Weren’t tests just measuring socioeconomic status by other means, and weren’t they biased against the people from the lower socioeconomic classes or the minority groups who were most likely to break the law for other reasons? they asked. By the 1960s, the association between intelligence and crime was altogether dismissed in criminology textbooks, and so it remained until recently. By the end of the 1970s, students taking introductory courses in criminology could read in one widely used textbook that the belief in a correlation between low intelligence and crime “has almost disappeared in recent years as a consequence of more cogent research findings,”14 or learn from another standard textbook of “the practical abandonment of feeblemindedness as a cause of crime.”15

  It took two of the leading criminologists of another generation, Travis Hirschi and Michael Hindelang, to resurrect the study of IQ and criminality that Sutherland had buried. In their 1977 article, “Intelligence and Delinquency: A Revisionist View,” they reviewed many studies that included IQ measures, took into account the potential artifacts, and concluded that juvenile delinquents were in fact characterized by substantially below-average levels of tested intelligence.16 Hirschi and Hindelang’s work took a while to percolate through the academy (the author of the 1982 edition of one of the textbooks quoted above continued to make no mention whatever of IQ),17 but by the end of the 1980s, most criminologists accepted not just that an IQ gap separates offenders and nonoffenders, but that the gap is genuinely a difference in average intellectual level or, as it is sometimes euphemistically called, “academic competence,” Criminology textbooks now routinely report the correlation between crime and intelligence, and although some questions of interpretation are still open, they are narrower than they used to be because the correlation itself is no longer in dispute.18

  The Size of the IQ Gap

  How big is the difference between criminals and the rest of us? Taking the literature as a whole, incarcerated offenders average an IQ of about 92, 8 points below the mean. The population of nonoffenders averages more than 100 points; an informed guess puts the gap between offenders and nonoffenders at about 10 points.19 More serious or more chronic offenders generally have lower scores than more casual offenders.20 The eventual relationship between IQ and repeat offending is already presaged in IQ scores taken when the children are 4 years old.21

  Not only is there a gap in IQ between offenders and nonoffenders, but a disproportionately large fraction of all crime is committed by people toward the low end of the scale of intelligence. For example, in a twenty-year longitudinal study of over 500 hundred boys in an unidentified Swedish community, 30 percent of all arrests of the men by the age of 30 were of the 6 percent with IQs below 77 (at the age of 10) and 80 percent were of those with IQs below 100.22 However, it stands to reason (and is supported by the data) that the population of offenders is short of very low-scoring persons—people whose scores are so low that they have trouble mustering the competence to commit most crimes.23 A sufficiently low IQ is, in addition, usually enough to exempt a person from criminal prosecution.24

  Do the Unintelligent Ones Commit More Crimes—or Just Get Caught More Often?

  Some critics continue to argue that offenders whose IQs we know are unrepresentative of the true criminal population; the smart ones presumably slipped through the net. Surely this is correct to some degree. If intelligence has anything to do with a person’s general competence, then it is not implausible that smart criminals get arrested less often because they pick safer crimes or because they execute their crimes more skillfully.25 But how much of a bias does this introduce into the data? Is there a population of uncaught offenders with high IQs committing large numbers of crimes? The answer seems to be no. The crimes we can trace to the millions of offenders who do pass through the criminal justice system and whose IQs are known account for much of the crime around us, particularly the serious crime. There is no evidence for any other large population of offenders, and barely enough crime left unaccounted for to permit such a population’s existence.

  In the small amount of data available, the IQs of uncaught offenders are not measurably different from the ones who get caught.26 Among those who have criminal records, there is still a significant negative correlation between IQ and frequency of offending.27 Both of these kinds of evidence imply that differential arrests of people with varying IQs, assuming they exist, are a minor factor in the aggregate data.

  Intelligence as a Preventative

  Looking at the opposite side of the picture, those who do not commit crimes, it appears that high cognitive ability protects a person from becoming a criminal even if the other precursors are present. One study followed a sample of almost 1,500 boys born in Copenhagen, Denmark, between 1936 and 1938.28 Sons whose fathers had a prison record were almost six times as likely to have a prison record themselves (by the age of 34-36) as the sons of men who had no police record of any sort. Among these high-risk sons, the ones who had no police record at all had IQ scores one standard deviation higher than the sons who had a police record.29

  The protective power of elevated intelligence also shows up in a New Zealand study. Boys and girls were divided on the basis of their behavior by the age of 5 into high and low risk for delinquency. High-risk children were more than twice as likely to become delinquent by their mid-teens as low-risk children. The high-risk boys or girls who did not become delinquent were the ones with the higher IQs. This was also true for the low-risk boys and girls: The nondelinquents had higher IQs than the delinquents.30

  Children growing up in troubled circumstances on Kauai in the Hawaiian chain confirm the pattern. Several hundred children were followed in a longitudinal study for several decades.31 Some of the children were identified by their second birthday as being statistically “vulnerable” to behavioral disorders or delinquency. These were children suffering from two or more of the following circumstances: they were being raised in troubled or impoverished families; had alcoholic, psychologically disturbed, or unschooled (eight years or less of schooling) parents; or had experienced prenatal or perinatal physiological stress. Two-thirds of these children succumbed to delinquency or other psychological disturbances. But how about the other third, the ones who grew up without becoming delinquents or disturbed psychologically? Prominent among the protective factors were higher intellectual ability scores than the average for the vulnerable group.32

  THE LINK BETWEEN COGNITIVE ABILITY AND CRIMINAL BEHAVIOR: WHITE MEN IN THE NLSY

  In the United States, where crime and race have become so intertwined in the public mind, it is especially instructive to focus on just whites. To simplify matters, we also limit the NLSY sample to males. Crime is still overwhelmingly a man’s vice. Among whites in the sample, 83 percent of all persons who admitted to a criminal conviction were male.

  The Rest of the Story

  The statistically distinguishable personal characteristics of criminals go far beyond IQ. There is, for example, the enormous difference between the levels of male and female criminality, which cannot be explained by intellectual differences between the sexes. Accounts of the rapidly expanding literature on the
psychological and biological correlates of criminality, which has become highly informative about everything from genes to early childhood precursors, may be tracked in numerous scientific journals and books.33 Probably as much could be learned about individual differences beyond intelligence that characterize the chronically unemployed, unmarried mothers, neglectful parents, and others who have been the subjects of the other chapters in Part II. But that is just surmise at this point. The necessary research has either not been done at all or has been done in only the sketchiest way.34

  Interpreting Self-Report Data

  In the 1980 interview wave, the members of the NLSY sample were asked detailed questions about their criminal activity and their involvement with the criminal justice system. These data are known as self-report data, meaning that we have to go on what the respondent says. One obvious advantage of self-reports is that they presumably include information about the crimes of offenders whether or not they have been caught. Another is that they circumvent any biases in the criminal justice system, which, some people argue, contaminate official criminal statistics. But can self-report data be trusted? Criminologists have explored this question for many years, and the answer is yes, but only if the data are treated gingerly. Different racial groups have different response patterns, and these are compounded by differences between the genders.35 Other issues are discussed in the note.36