The Bell Curve

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The Bell Curve is a best-selling and controversial 1994 book by Harvard University psychologist Richard J. Herrnstein (deceased before the book was released) and American Enterprise Institute political scientist Charles Murray. Its central argument was that intelligence (as measured by intelligence quotient (IQ) testing) is substantially influenced by both genetics and environment and a strong predictor of many personal outcomes, including financial income, job performance, chance of unwanted pregnancy, and involvement in crime. The book also argued that those with high intelligence, the "cognitive elite", are becoming separated from those of average and below-average intelligence, and that this is a dangerous social trend, with the United States moving towards a more divided society, similar to that in Latin America.

Much of the controversy concerned the parts of the book in which the authors wrote about racial differences in intelligence and discussed the implications of those differences. The authors were reported throughout the popular press as arguing that these IQ differences are due genetics, and they did indeed write in chapter 13: "It seems highly likely to us that both genes and the environment have something to do with racial differences." The introduction to the chapter more cautiously stated, "The debate about whether and how much genes and environment have to do with ethnic differences remains unresolved."

The book's title comes from the bell-shaped normal distribution of intelligence quotient (IQ) scores in a population.

Shortly after publication, many people rallied both in criticism and defense of the book. A number of critical texts were written in response to the book.

A frequent misrepresentation is that The Bell Curve made many new and controversial claims, which had never been made before, implying that they were new and fringe views with little support. Instead, much of the contents of the book consisted of citing an extensive existing academic literature on IQ and group differences. The book differed from this academic literature by being written for the general public, by making certain policy recommendations, and by becoming a bestseller.


The Bell Curve contained 941 pages in the first printing and 879 in the revised paperback. Much of its material is technical and academic, but the book's statistical explanations are styled to appeal to a general audience. There are extensive notes, graphs, and tables. The Bell Curve is divided into four sections.

Part I argues that social stratification on the basis of intelligence has been increasing since the beginning of the twentieth century.
Part II presents original research showing significant correlations between intelligence and various social and economic outcomes. For instance, based on data as of 1989, this section showed that among non-Hispanic whites, intelligence level (cognitive class) is a better predictor of poverty than parents' socioeconomic class.
Part III, by far the most controversial, examined what role IQ plays in contributing to social and economic differences between ethnic groups in the United States.
Part IV discussed the implications of the findings for education and social policy in the United States.

The book argued that:

  1. Intelligence exists and is accurately measurable across racial, language, and national boundaries.
  2. Intelligence is one of, if not the most, important factors correlated to economic, social, and overall success in the United States, and its importance is increasing.
  3. Intelligence is largely (40% to 80%) genetically heritable.
  4. No one has so far been able to manipulate IQ to a significant degree through changes in environmental factors—except for child adoption—and in light of these failures, such approaches are becoming less promising.
  5. The USA has been in denial of these facts. A better public understanding of the nature of intelligence and its social correlates is necessary to guide future policy decisions.

The book extensively cited earlier research but also provided new evidence from an analysis of data compiled from the National Longitudinal Study of Youth (NLSY), a study conducted by the United States Department of Labor's Bureau of Labor Statistics, tracking thousands of Americans starting in the 1980s. All participants in the NLSY took the Armed Services Vocational Aptitude Battery (ASVAB), a battery of ten tests taken by all who apply for entry into the armed services. Four of those tests comprise the Armed Forces Qualification Test, a measure of cognitive ability comparable to an IQ test. (Some had taken an IQ test in high school, and the median correlation of the AFQT and those tests was .81.) Participants were later evaluated for social and economic outcomes. In general, IQ/AFQT scores were a better predictor of life outcomes than social class background. Similarly, after statistically controlling for differences in IQ, many outcome differences between racial-ethnic groups disappeared.

The book stated that the average measured IQ of African Americans is 85; Latinos 89; Whites 103; Asians 106; and Jews 113.


IQ and associations
with social outcomes
Countries and intelligence:
Associations with other variables
Countries and intelligence:
Within-country regions
Dysgenics: Pessimism regarding
the future of Western civilization
Effects of race mixing:
Latin America
Intelligence quotient:
Social outcomes
Race and intelligence:
Historical societies
Race and intelligence:
Modern societies
Smart fraction
The Bell Curve: Tables
Relation between IQ and economic and social variables in the U.S. Values are the percentage of each IQ group, fitting each descriptor, among non-Hispanic whites only.
IQ group <75 75-90 90-110 110-125 >125
% of US population distribution 5 20 50 20 5
Lives in poverty 30 16 6 3 2
High school dropout 55 35 6 0.4 0
Out of labor force more than 1 month out of year (men) 22 19 15 14 10
Unemployed more than 1 month out of year (men) 12 10 7 7 2
Married by age 30 72 81 81 72 67
Divorced in 5 years 21 22 23 15 9
Had a child outside marriage (mothers) 32 17 8 4 2
% who beomce chronic welfare recipients (mothers) 31 17 8 2 0
% of their children with IQ in bottom decile (mothers) 39 17 6 7 -
% of their toddlers with a "Friendliness Index" temperament ranking in the bottom decile (mothers) 12 11 5 3 -
Ever convicted (young men, self-report) 14 21 15 7 3
Ever incarcerated (young men, self-report) 7 7 3 1 0
Herrnstein & Murray (1994) pp. 132, 146, 158, 163, 171, 174, 180, 194, 230, 247, respectively.
Average IQ per level of contact with the criminal justice system, among young White males, self-report (p. 246).
Level Incarcerated Booked but not convicted Stopped by police but not booked Convicted but not incarcerated No contact
Average IQ 93 100 101 103 106

Murray's later follow-up on effects of IQ on life outcomes

From a 1997 article by Murray in the journal Public Interest

Relation between IQ and earnings in the U.S.
IQ <75 75–90 90–110 110–125 >125
Age 18 2,000 5,000 8,000 8,000 3,000
Age 26 3,000 10,000 16,000 20,000 21,000
Age 32 5,000 12,400 20,000 27,000 36,000
Values are the average earnings (1993 US Dollars) of each IQ sub-population.[1]

Murray responded to specific criticisms of the analysis of the practical importance of IQ compared to socio-economic status (Part II of The Bell Curve) in the 1998 book Income Inequality and IQ. To circumvent criticisms surrounding the Bell Curve's use of a statistical control for socioeconomic status (SES), Murray adopted a sibling design. Rather than statistically controlling for parental SES, Murray compared life outcome differences among full sibling pairs who met a number of criteria, in which one member of the pair has an IQ in the "normal" range and the other siblings has an IQ in a higher or lower IQ category. According to Murray, this design controls for all aspects of family background (full siblings share the same family background, growing up together in the same home and the same community).[2]

Relation between IQ and life outcomes in the U.S. among sibling pairs
IQ <75 75–90 90–110 110–125 >125
Mean years of education 11.4 (10.9) 12.3 (11.9) 13.4 (13.2) 15.2 (15.0) 16.5 (16.5)
Percentage obtaining B.A. 1 (1) 4 (3) 19 (16) 57 (50) 80 (77)
Mean weeks worked 35.8 (30.7) 39.0 (36.5) 43.0 (41.8) 45.1 (45.2) 45.6 (45.4)
Mean earned income 11,000 (7,500) 16,000 (13,000) 23,000 (21,000) 27,000 (27,000) 38,000 (36,000)
Percentage with a spouse who has earned income 30 (27) 38 (39) 53 (54) 61 (59) 58 (58)
Mean earned family income 17,000 (12,000) 25,000 (23,400) 37,750 (37,000) 47,200 (45,000) 53,700 (53,000)
Percentage children born out of wedlock 49 (50) 33 (32) 14 (14) 6 (6) 3 (5)
Fertility to date 2.1 (2.3) 1.7 (1.9) 1.4 (1.6) 1.3 (1.4) 1.0 (1.0)
Mother's mean age at birth 24.4 (22.8) 24.5 (23.7) 26.0 (25.2) 27.4 (27.1) 29.0 (28.5)
Values are "Utopian sample" ("Full sample"). Earning values are the 1993 US Dollars.[2]

Policy recommendations

The book argued the average genetic IQ of the United States is declining, due to the tendency of the more intelligent to have fewer children than the less intelligent, for the generation length to be shorter for the less intelligent, and through the large scale immigration to the United States of those with low intelligence.

The United States will become increasingly like Latin America, with high IQ whites and Asians living in fortified enclaves, protected by high fences and armed guards from "the menace of the slums" below.

In a discussion of the future political outcomes of an intellectually stratified society, they stated that they "fear that a new kind of conservatism is becoming the dominant ideology of the affluent - not in the social tradition of an Edmund Burke or in the economic tradition of an Adam Smith but 'conservatism' along Latin American lines, where to be conservative has often meant doing whatever is necessary to preserve the mansions on the hills from the menace of the slums below".[3] Moreover, they feared that increasing welfare will create a "custodial state" in "a high-tech and more lavish version of the Indian reservation for some substantial minority of the nation's population." They also predict increasing totalitarianism: "It is difficult to imagine the United States preserving its heritage of individualism, equal rights before the law, free people running their own lives, once it is accepted that a significant part of the population must be made permanent wards of the states".[4]

Herrnstein and Murray recommended the elimination of welfare policies that encourage poor women to have babies:

We can imagine no recommendation for using the government to manipulate fertility that does not have dangers. But this highlights the problem: The United States already has policies that inadvertently social-engineer who has babies, and it is encouraging the wrong women. "If the United States did as much to encourage high-IQ women to have babies as it now does to encourage low-IQ women, it would rightly be described as engaging in aggressive manipulation of fertility." The technically precise description of America's fertility policy is that it subsidizes births among poor women, who are also disproportionately at the low end of the intelligence distribution. We urge generally that these policies, represented by the extensive network of cash and services for low-income women who have babies, be ended. The government should stop subsidizing births to anyone rich or poor. The other generic recommendation, as close to harmless as any government program we can imagine, is to make it easy for women to make good on their prior decision not to get pregnant by making available birth control mechanisms that are increasingly flexible, foolproof, inexpensive, and safe.[5]

This claim spurred later research in economics and sexology, which considered that welfare programs for women had a doubly negative effect on aggregate IQ within the transfer group, by allowing the female partner to forgo a full consideration of the male's ability to serve as a provider of familial resources, instead placing greater emphasis on desirable physical or social characteristics (presumed to be not as positively correlated with IQ). Neither of these claims, as originally embodied in text and the follow-on research, dealt with race as such, but rather demonstrated concern that large numbers of minorities were positioned as recipients, leading to a continual worsening of the measured divergence in intelligence. However, two years later, the 1996 U.S. welfare reform substantially cut these programs.

The book also argued for reducing immigration into the US, which was argued to lower the average national IQ. It also recommended against policies of affirmative action.


The Bell Curve became a bestseller and caused a large debate. Not surprisingly, the not politically correct book was intensely attacked. Many articles and several books were written in response. The books arguments regarding IQ as a measure of intelligence, effects of IQ, race and IQ, and the policy recommendations were criticized.

A large number of professors, all experts in intelligence and allied fields, in response to the debate signed a statement titled "Mainstream Science on Intelligence". Its prologue stated "Since the publication of "The BELL CURVE," many commentators have offered opinions about human intelligence that misstate current scientific evidence. Some conclusions dismissed in the media as discredited are actually firmly supported. This statement outlines conclusions regarded as mainstream among researchers on intelligence, in particular, on the nature, origins, and practical consequences of individual and group differences in intelligence. Its aim is to promote more reasoned discussion of the vexing phenomenon that the research has revealed in recent decades. The following conclusions are fully described in the major textbooks, professional journals and encyclopedias in intelligence."[6]

The American Psychological Association with a similar motivation' established a special task force that published a report titled "Intelligence: Knowns and Unknowns".[7]

In a 2005 article titled "The Inequality Taboo", Murray wrote "When the late Richard Herrnstein and I published The Bell Curve eleven years ago, the furor over its discussion of ethnic differences in IQ was so intense that most people who have not read the book still think it was about race. Since then, I have deliberately not published anything about group differences in IQ, mostly to give the real topic of The Bell Curve--the role of intelligence in reshaping America's class structure--a chance to surface... ...In the autumn of 1994, I had watched with dismay as The Bell Curve's scientifically unremarkable statements about black IQ were successfully labeled as racist pseudoscience... ...The Orwellian disinformation about innate group differences is not wholly the media's fault. Many academics who are familiar with the state of knowledge are afraid to go on the record. Talking publicly can dry up research funding for senior professors and can cost assistant professors their jobs. But while the public's misconception is understandable, it is also getting in the way of clear thinking about American social policy." He continued the article by describing more current research regarding differences between men and women and between races.[8] (See external links below for a link to the article).

In a 2014 interview he stated "the roof is about to crash in on those who insist on a purely environmental explanation of all sorts of ethnic differences, not just intelligence. Since the decoding of the genome, it has been securely established that race is not a social construct, evolution continued long after humans left Africa along different paths in different parts of the world, and recent evolution involves cognitive as well as physiological functioning... ...We’re not talking about another 20 years before the purely environmental position is discredited, but probably less than a decade."[9]

External links

Charles Murray

Reports and statements



  1. Murray, C. (1997). IQ and economic success. Public Interest, 128, 21–35.
  2. 2.0 2.1 Murray, C. (1998). Income Inequality and IQ. Washington: AEI Press.
  3. p. 518.
  4. p. 526.
  5. pp. 548-549.
  6. See: Linda Gottfredson (1997) "Mainstream Science on Intelligence", Intelligence, 24(1), pages 13-23.
  7. Ulric Neisser (Chair) et al. (1996) "Intelligence: Knowns and Unknowns", American Psychologist, 51(2), pages 77-101.
  8. "The Inequality Taboo", Commentary Magazine. Charles Murray.
  9. ‘The Bell Curve’ 20 Years Later: A Q&A with Charles Murray. AEI Ideas, October 16, 2014.
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