The Bell Curve


The Bell Curve: Intelligence and Class Structure in American Life is a 1994 book by the psychologist Richard J. Herrnstein and the political scientist Charles Murray in which the authors argue that human intelligence is substantially influenced by both inherited and environmental factors and that it is a better predictor of many personal outcomes, including financial income, job performance, birth out of wedlock, and involvement in crime, than is an individual's parental socioeconomic status. They also argue that those with high intelligence, the "cognitive elite", are becoming separated from those of average and below-average intelligence, and that this separation is a source of social division within the United States.
The book has been, and remains, highly controversial, especially where the authors discussed purported connections between race and intelligence and suggested policy implications based on these purported connections. The authors claimed that average intelligence quotient differences between racial and ethnic groups are at least partly genetic in origin, a view that is now considered discredited by mainstream science. Many of the references and sources used in the book were advocates for racial hygiene, whose research was funded by the white supremacist organization Pioneer Fund and published in its affiliated journal Mankind Quarterly. Because of this, many critics have dismissed the book and its purported findings as pseudoscience.
Shortly after its publication, many people rallied both in criticism and in defense of the book. A large number of critical texts by psychologists, cognitive scientists, and anthropologists were written in response to it. Several criticisms were collected in the book The Bell Curve Debate.

Synopsis

The Bell Curve, published in 1994, was written by Richard Herrnstein and Charles Murray to explain the variations in intelligence in American society, warn of some consequences of that variation, and propose social policies for mitigating the worst of the consequences. The book's title refers to the bell-shaped normal distribution of IQ scores observed in large populations.

Introduction

The book starts with an introduction that appraises the history of the concept of intelligence from Francis Galton to modern times. Spearman's introduction of the general factor of intelligence and other early advances in research on intelligence are discussed along with a consideration of links between intelligence testing and racial politics. The 1960s are identified as the period in American history when social problems were increasingly attributed to forces outside the individual. This egalitarian ethos, Herrnstein and Murray argue, cannot accommodate biologically based individual differences.
The introduction states six of the authors' assumptions, which they claim to be "beyond significant technical dispute":
  1. There is such a difference as a general factor of cognitive ability on which human beings differ.
  2. All standardized tests of academic aptitude or achievement measure this general factor to some degree, but IQ tests expressly designed for that purpose measure it most accurately.
  3. IQ scores match, to a first degree, whatever it is that people mean when they use the word intelligent, or smart in ordinary language.
  4. IQ scores are stable, although not perfectly so, over much of a person's life.
  5. Properly administered IQ tests are not demonstrably biased against social, economic, ethnic, or racial groups.
  6. Cognitive ability is substantially heritable, apparently no less than 40 percent and no more than 80 percent.
At the close of the introduction, the authors warn the reader against committing the ecological fallacy of inferring things about individuals based on the aggregate data presented in the book. They also assert that intelligence is just one of many valuable human attributes and one whose importance among human virtues is overrated.

Part I. The Emergence of a Cognitive Elite

In the first part of the book Herrnstein and Murray chart how American society was transformed in the 20th century. They argue that America evolved from a society where social origin largely determined one's social status to one where cognitive ability is the leading determinant of status. The growth in college attendance, a more efficient recruitment of cognitive ability, and the sorting of cognitive ability by selective colleges are identified as important drivers of this evolution. Herrnstein and Murray propose that the cognitive elite has been produced by a more technological society which offers enough high skill jobs for those with a higher intelligence to fill. They also propose that by removing race, gender or class as criteria the main criterion of success in academic and professional life is cognitive ability. Increased occupational sorting by cognitive ability is discussed. They maintain that cognitive ability is the best predictor of worker productivity.
Herrnstein and Murray argue that due to increasing returns to cognitive ability, a cognitive elite is being formed in America. They argue that this elite is getting richer and progressively more segregated from the rest of society.

Part II. Cognitive Classes and Social Behavior

The second part describes how cognitive ability is related to social behaviors: high ability predicts socially desirable behavior, low ability undesirable behavior. The argument is made that group differences in social outcomes are better explained by intelligence differences rather than socioeconomic status, a perspective, the authors argue, that has been neglected in research.
The analyses reported in this part of the book were done using data from the National Longitudinal Survey of Labor Market Experience of Youth, a study conducted by the United States Department of Labor's Bureau of Labor Statistics tracking thousands of Americans starting in the 1980s. Only non-Hispanic whites are included in the analyses so as to demonstrate that the relationships between cognitive ability and social behavior are not driven by race or ethnicity.
Herrnstein and Murray argue that intelligence is a better predictor of individuals' outcomes than parental socioeconomic status. This argument is based on analyses where individuals' IQ scores are shown to better predict their outcomes as adults than the socioeconomic status of their parents. Such results are reported for many outcomes, including poverty, dropping out of school, unemployment, marriage, divorce, illegitimacy, welfare dependency, criminal offending, and the probability of voting in elections.
All participants in the NLSY took the Armed Services Vocational Aptitude Battery, a battery of ten tests taken by all who apply for entry into the armed services.. Participants were later evaluated for social and economic outcomes. In general, Herrnstein and Murray argued, IQ/AFQT scores were a better predictor of life outcomes than social class background. Similarly, after statistically controlling for differences in IQ, they argued that many outcome differences between racial-ethnic groups disappeared.
IQ<7575–9090–110110–125>125
US population distribution52050205
Married by age 307281817267
Out of labor force more than 1 month out of year 2219151410
Unemployed more than 1 month out of year 1210772
Divorced in 5 years212223159
% of children w/ IQ in bottom decile 391767–
Had an illegitimate baby 3217842
Lives in poverty3016632
Ever incarcerated 77310
Chronic welfare recipient 3117820
High school dropout553560.40
Scored "Yes" on "Middle Class Values Index"1630506774

Values are the percentage of each IQ sub-population, among non-Hispanic whites only, fitting each descriptor.

Part III. The National Context

This part of the book discusses ethnic differences in cognitive ability and social behavior. Herrnstein and Murray report that Asian Americans have a higher mean IQ than white Americans, who in turn outscore black Americans. The book argues that the black–white gap is not due to test bias, noting that IQ tests do not tend to underpredict the school or job performance of black individuals and that the gap is larger on apparently culturally neutral test items than on more culturally loaded items. The authors also note that adjusting for socioeconomic status does not eliminate the black–white IQ gap. However, they argue that the gap is narrowing.
According to Herrnstein and Murray, the high heritability of IQ within races does not necessarily mean that the cause of differences between races is genetic. On the other hand, they discuss lines of evidence that have been used to support the thesis that the black–white gap is at least partly genetic, such as Spearman's hypothesis. They also discuss possible environmental explanations of the gap, such as the observed generational increases in IQ, for which they coin the term Flynn effect. At the close of this discussion, they write:
The authors also stress that regardless of the causes of differences, people should be treated no differently.
In Part III, the authors also repeat many of the analyses from Part II, but now compare whites to blacks and Hispanics in the NLSY dataset. They find that after controlling for IQ, many differences in social outcomes between races are diminished.
The authors discuss the possibility that high birth rates among those with lower IQs may exert a downward pressure on the national distribution of cognitive ability. They argue that immigration may also have a similar effect.
At the close of Part III, Herrnstein and Murray discuss the relation of IQ to social problems. Using the NLSY data, they argue that social problems are a monotonically decreasing function of IQ, in other words at lower IQ scores the frequency of social problems increases.