The Bell Curve: Intelligence and Class Structure in American Life is a 1994 book by psychologist Richard J. Herrnstein and political scientist Charles Murray, in which they argue that human intelligence is substantially influenced by both inherited and environmental factors and is a better predictor of many personal dynamics, including financial income, job performance, birth out of wedlock, and involvement in crime than are an individual's parental socioeconomic status, or education level. They also argue that those with high intelligence, the "cognitive elite", are becoming separated from those of average and below-average intelligence. The book was controversial, especially where the authors wrote about racial differences in intelligence and discussed the implications of those differences.
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 work.
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 comes from the bell-shaped normal distribution of intelligence quotient (IQ) scores in a population.
Many of the arguments put forth by the authors were controversial, ranging from the relationships between low measured intelligence and anti-social behavior, to a genetic component of the low observed test scores for African-American (compared to whites). The book was heavily publicized as it was released, just after the death of Herrnstein. In the first several months of its release, 400,000 copies of the book were sold around the world. The Bell Curve argues that:
- Intelligence exists and is accurately measurable across racial, language, and national boundaries.
- 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.
- Intelligence is largely (40% to 80%) heritable.
- 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 the light of these failures, future successful manipulations are unlikely.
- The United States 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's argument is based on the authors' analysis of data compiled in 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. (Some had taken an IQ test in high school, and the median correlation of the Armed Forces Qualification Test (AFQT) scores and those IQ test scores 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.
|US population distribution||5||20||50||20||5|
|Married by age 30||72||81||81||72||67|
|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|
|Divorced in 5 years||21||22||23||15||9|
|% of children w/ IQ in bottom decile (mothers)||39||17||6||7||-|
|Had an illegitimate baby (mothers)||32||17||8||4||2|
|Lives in poverty||30||16||6||3||2|
|Ever incarcerated (men)||7||7||3||1||0|
|Chronic welfare recipient (mothers)||31||17||8||2||0|
|High school dropout||55||35||6||0.4||0|
|Scored "Yes" on "Middle Class Values Index"||16||30||50||67||74|
|Values are the percentage of each IQ sub-population, among non-Hispanic whites only, fitting each descriptor. Herrnstein & Murray (1994) pp. 171, 158, 163, 174, 230, 180, 132, 194, 247-248, 194, 146, 264 respectively.|
- According to Murray and Herrnstein (pp. 263–64), the "Middle Class Values Index" was intended "to identify among the NLSY population, in their young adulthood when the index was scored, those people who are getting along with their lives in ways that fit the middle-class stereotype." To score "Yes" on the index, a NLSY subject had to meet all four of the following criteria:
- Received at least a high-school diploma
- Never interviewed while incarcerated
- Still married to one's first spouse
- Men only: In the labor force, even if not employed
- Women only: Never gave birth outside of marriage
Herrnstein and Murray argued the average genetic IQ of the United States is declining, owing to the tendency of the more intelligent to have fewer children than the less intelligent, the generation length to be shorter for the less intelligent, and the large-scale immigration to the United States of those with low intelligence. Discussing a possible future political outcome of an intellectually stratified society, the authors 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." Moreover, they fear 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."
The authors 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.
The Bell Curve received a great deal of media attention. The book was not distributed in advance to the media, except for a few select reviewers picked by Murray and the publisher, which delayed more detail critiques for months and years after the book's release. Stephen Jay Gould, reviewing the book in The New Yorker, said that the book "contains no new arguments and presents no compelling data to support its anachronistic social Darwinism" and said that the "authors omit facts, misuse statistical methods, and seem unwilling to admit the consequence of their own words."
A 1995 article by Fairness and Accuracy in Reporting writer Jim Naureckas criticized the media response, saying that "While many of these discussions included sharp criticisms of the book, media accounts showed a disturbing tendency to accept Murray and Herrnstein's premises and evidence even while debating their conclusions".
After reviewers had more time to review the book's research and conclusions more significant criticisms begin to appear. Nicholas Lemann, writing in Slate, said that later reviews showed the book was "full of mistakes ranging from sloppy reasoning to mis-citations of sources to outright mathematical errors." Lemann said that "Unsurprisingly, all the mistakes are in the direction of supporting the authors' thesis."
Herrnstein and Murray were criticized for not submitting their work to peer review before publication, despite presenting it as a scholarly work. Many scholarly reviews of the book arrived later. Richard Lynn (1999) wrote that "The book has been the subject of several hundred critical reviews, a number of which have been collected in edited volumes".
"Mainstream Science on Intelligence"
Fifty-two professors, most of them researchers in intelligence and related fields, signed an opinion statement titled "Mainstream Science on Intelligence" endorsing a number of the views presented in The Bell Curve. The statement was written by psychologist Linda Gottfredson and published in The Wall Street Journal in 1994 and subsequently reprinted in Intelligence, an academic journal. Of the 131 who were invited by mail to sign the document, 100 responded, with 52 agreeing to sign and 48 declining. Eleven of the 48 dissenters claimed that the statement or some part thereof did not represent the mainstream view of intelligence.
APA task force report
In response to the controversy surrounding The Bell Curve, the American Psychological Association's Board of Scientific Affairs established a special task force to publish an investigative report on the research presented in the book. In their final report, titled Intelligence: Knowns and Unknowns, some of the task force's findings supported or were consistent with statements from The Bell Curve. They agreed that:
- IQ scores have high predictive validity for individual differences in school achievement.
- IQ scores have predictive validity for adult occupational status, even when variables such as education and family background have been statistically controlled.
- There is little evidence to show that childhood diet influences intelligence except in cases of severe malnutrition.
Regarding Murray and Herrnstein's claims about racial differences and genetics, the APA task force stated:
There is certainly no such support for a genetic interpretation...It is sometimes suggested that the Black/White differential in psychometric intelligence is partly due to genetic differences (Jensen, 1972). There is not much direct evidence on this point, but what little there is fails to support the genetic hypothesis.
Regarding statements about other explanations for racial differences, the APA task force stated:
The differential between the mean intelligence test scores of Blacks and Whites (about one standard deviation, although it may be diminishing) does not result from any obvious biases in test construction and administration, nor does it simply reflect differences in socio-economic status. Explanations based on factors of caste and culture may be appropriate, but so far have little direct empirical support. There is certainly no such support for a genetic interpretation. At present, no one knows what causes this differential.
The APA journal that published the statement, American Psychologist, subsequently published eleven critical responses in January 1997.
Criticism of assumptions made in book
- Intelligence must be reducible to a single number.
- Intelligence must be capable of rank ordering people in a linear order.
- Intelligence must be primarily genetically based.
- Intelligence must be essentially immutable.
According to Gould, if any of these premises are false, then the entire argument disintegrates.
Similarly, anthropologist C. Loring Brace suggests that The Bell Curve made six basic assumptions at the start and argued that there are faults in every one of these assumptions:
- Human Cognitive ability is a single general entity, depictable as a single number.
- Cognitive ability has a heritability of between 40 and 80 percent and is therefore primarily genetically based.
- IQ is essentially immutable, fixed over the course of a life span.
- IQ tests measure how "smart" or "intelligent" people are and are capable of rank ordering people in a linear order.
- IQ tests can measure this accurately.
- IQ tests are not biased with regard to race, ethnic group or socioeconomic status.
The Nobel-Memorial-Prize-winning economist James Heckman considers two assumptions made in the book to be questionable: that g accounts for correlation across test scores and performance in society, and that g cannot be manipulated. Heckman's reanalysis of the evidence used in The Bell Curve found contradictions:
- The factors that explain wages receive different weights than the factors that explain test scores. More than g is required to explain either.
- Other factors besides g contribute to social performance, and they can be manipulated.
In response, Murray argued that this was a straw man and that the book does not argue that g or IQ are totally immutable or the only factors affecting outcomes.
In a 2005 interview, Heckman praised The Bell Curve for breaking "a taboo by showing that differences in ability existed and predicted a variety of socioeconomic outcomes" and for playing "a very important role in raising the issue of differences in ability and their importance" and stated that he was "a bigger fan of [The Bell Curve] than you might think." However, he also maintained that Herrnstein and Murray overestimated the role of heredity in determining intelligence differences.
Criticism of statistical methodologies and methods
Claude S. Fischer, Michael Hout, Martín Sánchez Jankowski, Samuel R. Lucas, Ann Swidler, and Kim Voss in the book Inequality by Design recalculated the effect of socioeconomic status, using the same variables as The Bell Curve, but weighting them differently. They found that if IQ scores are corrected, as Herrnstein and Murray did, to eliminate the effect of education, the ability of IQ to predict poverty can be made to look dramatically overstated, by as much as 61 percent for whites and 74 percent for blacks. According to the authors, Herrnstein and Murray's finding, that IQ predicts poverty much better than socioeconomic status does, is substantially a result of the way they handled the statistics.
In August 1995, National Bureau of Economic Research economist Sanders Korenman and Harvard University sociologist Christopher Winship found errors in Herrnstein's methodology. Korenman and Winship concluded:"... there is evidence of substantial bias due to measurement error in their estimates of the effects of parents' socioeconomic status. In addition, Herrnstein and Murray's measure of parental socioeconomic status (SES) fails to capture the effects of important elements of family background (such as single-parent family structure at age 14). As a result, their analysis gives an exaggerated impression of the importance of IQ relative to parents' SES, and relative to family background more generally. Estimates based on a variety of methods, including analyses of siblings, suggest that parental family background is at least as important, and may be more important than IQ in determining socioeconomic success in adulthood."
In the book Intelligence, Genes, and Success: Scientists Respond to The Bell Curve, a group of social scientists and statisticians analyzes the genetics-intelligence link, the concept of intelligence, the malleability of intelligence and the effects of education, the relationship between cognitive ability, wages and meritocracy, pathways to racial and ethnic inequalities in health, and the question of public policy. This work argues that much of the public response was polemic, and failed to analyze the details of the science and validity of the statistical arguments underlying the book's conclusions.
Criticism of use of AFQT
William J. Matthews writes that part of The Bell Curve's analysis is based on the AFQT "which is not an IQ test but designed to predict performance of certain criterion variables". The AFQT covers subjects such as trigonometry.
Heckman observed that the AFQT was designed only to predict success in military training schools and that most of these tests appear to be achievement tests rather than ability tests, measuring factual knowledge and not pure ability. He continues:
Ironically, the authors delete from their composite AFQT score a timed test of numerical operations because it is not highly correlated with the other tests. Yet it is well known that in the data they use, this subtest is the single best predictor of earnings of all the AFQT test components. The fact that many of the subtests are only weakly correlated with each other, and that the best predictor of earnings is only weakly correlated with their "g-loaded" score, only heightens doubts that a single-ability model is a satisfactory description of human intelligence. It also drives home the point that the "g-loading" so strongly emphasized by Murray and Herrnstein measures only agreement among tests—not predictive power for socioeconomic outcomes. By the same token, one could also argue that the authors have biased their empirical analysis against the conclusions they obtain by disregarding the test with the greatest predictive power.
Janet Currie and Duncan Thomas presented evidence suggesting AFQT scores are likely better markers for family background than "intelligence" in a 1999 study:
Herrnstein and Murray report that conditional on maternal "intelligence" (AFQT scores), child test scores are little affected by variations in socio-economic status. Using the same data, we demonstrate their finding is very fragile.
Charles R. Tittle and Thomas Rotolo found that the more that written, IQ-like examinations are used as screening devices for occupational access, the stronger the relationship between IQ and income. Thus, rather than higher IQ leading to status attainment because it indicates skills needed in a modern society, IQ may reflect the same test-taking abilities used in artificial screening devices by which status groups protect their domains.
Min-Hsiung Huang and Robert M. Hauser write that Herrnstein and Murray provide scant evidence of growth in cognitive sorting. Using data from the General Social Survey, they tested each of these hypotheses using a short verbal ability test which was administered to about 12,500 American adults between 1974 and 1994; the results provided no support for any of the trend hypotheses advanced by Herrnstein and Murray. One chart in The Bell Curve purports to show that people with IQs above 120 have become "rapidly more concentrated" in high-IQ occupations since 1940. But Robert Hauser and his colleague Min-Hsiung Huang retested the data and came up with estimates that fell "well below those of Herrnstein and Murray." They add that the data, properly used, "do not tell us anything except that selected, highly educated occupation groups have grown rapidly since 1940."
In 1972, Noam Chomsky questioned Herrnstein's idea that society was developing towards a meritocracy. Chomsky criticized the assumptions that people only seek occupations based on material gain. He argued that Herrnstein would not want to become a baker or lumberjack even if he could earn more money that way. He also criticized the assumption that such a society would be fair with pay based on value of contributions. He argued that because there are already unjust great inequalities, people will often be paid, not for valuable contributions to society, but to preserve such inequalities.
In 1995, Chomsky directly criticized the book and its assumptions on IQ. He takes issue with the idea that IQ is 60% heritable saying, the "statement is meaningless" since heritability doesn't have to be genetic. He gives the example of women wearing earrings:
To borrow an example from Ned Block, "some years ago when only women wore earrings, the heritability of having an earring was high because differences in whether a person had an earring was due to a chromosomal difference, XX vs. XY." No one has yet suggested that wearing earrings, or ties, is "in our genes," an inescapable fate that environment cannot influence, "dooming the liberal notion."
He goes on to say there is almost no evidence of a genetic link, and greater evidence that environmental issues are what determine IQ differences.
Race and intelligence
One part of the controversy concerned the parts of the book which dealt with racial group differences on IQ and the consequences of this. The authors were reported throughout the popular press as arguing that these IQ differences are genetic, 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 states, "The debate about whether and how much genes and environment have to do with ethnic differences remains unresolved."
In an article praising the book, economist Thomas Sowell criticized some of its aspects, including some of its arguments about race and the malleability of IQ:
When European immigrant groups in the United States scored below the national average on mental tests, they scored lowest on the abstract parts of those tests. So did white mountaineer children in the United States tested back in the early 1930s. ... Strangely, Herrnstein and Murray refer to "folklore" that "Jews and other immigrant groups were thought to be below average in intelligence." It was neither folklore nor anything as subjective as thoughts. It was based on hard data, as hard as any data in The Bell Curve. These groups repeatedly tested below average on the mental tests of the World War I era, both in the army and in civilian life. For Jews, it is clear that later tests showed radically different results—during an era when there was very little intermarriage to change the genetic makeup of American Jews.
Columnist Bob Herbert, writing for The New York Times, described the book as "a scabrous piece of racial pornography masquerading as serious scholarship." "Mr. Murray can protest all he wants," wrote Herbert; "his book is just a genteel way of calling somebody a nigger."
In 1996 Stephen Jay Gould released a revised and expanded edition of his 1981 book The Mismeasure of Man, intended to more directly refute many of The Bell Curve's claims regarding race and intelligence, and arguing that the evidence for heritability of IQ did not indicate a genetic origin to group differences in intelligence. This book has in turn been criticized.
Psychologist David Marks has suggested that the ASVAB test battery used in the analyses of The Bell Curve correlates highly with measures of literacy, and argues that the ASVAB test in fact is not a measure of general intelligence but of literacy.
Melvin Konner, professor of anthropology and associate professor of psychiatry and neurology at Emory University, called Bell Curve a "deliberate assault on efforts to improve the school performance of African-Americans":
This book presented strong evidence that genes play a role in intelligence but linked it to the unsupported claim that genes explain the small but consistent black-white difference in IQ. The juxtaposition of good argument with a bad one seemed politically motivated, and persuasive refutations soon appeared. Actually, African-Americans have excelled in virtually every enriched environment they have been placed in, most of which they were previously barred from, and this in only the first decade or two of improved but still not equal opportunity. It is likely that the real curves for the two races will one day be superimposable on each other, but this may require decades of change and different environments for different people. Claims about genetic potential are meaningless except in light of this requirement.
In 1995, Noam Chomsky criticized the book's accusations about race, saying that there is little evidence that IQ is genetic but that it is influenced by the environment. He goes on to criticize the notion that Blacks and people with lower IQs having more children is even a problem and criticized solutions the authors propose to stop it:
There's an easy solution to the problem: simply bring here millions of peasants driven from the countryside in China...and radically reduce Browne's income...while Black mothers are placed in Manhattan high rises and granted every advantage. Then the Asian influx will raise the IQ level; and as serious inquiry demonstrates, the fertility rate of Blacks is very likely to drop while that of the children of the journalistic elite, Harvard psychology professors, and associates of the American Enterprise Institute will rapidly rise. The problem is solved.
Rutledge M. Dennis suggests that through soundbites of works like Jensen's famous study on the achievement gap, and Herrnstein and Murray's book The Bell Curve, the media "paints a picture of Blacks and other people of color as collective biological illiterates—as not only intellectually unfit but evil and criminal as well," thus providing, he says "the logic and justification for those who would further disenfranchise and exclude racial and ethnic minorities."
Charles Lane pointed out that 17 of the researchers whose work is referenced by the book have also contributed to Mankind Quarterly, a journal of anthropology founded in 1960 in Edinburgh, which has been viewed as supporting the theory of the genetic superiority of the whites.
The Bell Curve Wars: Race, Intelligence, and the Future of America is a collection of articles published in reaction to the book. Edited by Steven Fraser, the writers of these essays do not have a specific viewpoint concerning the content of The Bell Curve, but express their own critiques of various aspects of the book, including the research methods used, the alleged hidden biases in the research and the policies suggested as a result of the conclusions drawn by the authors. Fraser writes that "by scrutinizing the footnotes and bibliography in The Bell Curve, readers can more easily recognize the project for what it is: a chilly synthesis of the work of disreputable race theorists and eccentric eugenicists".
Allegations of racism
Since the book provided statistical data supporting the assertion that blacks were, on average, less intelligent than whites, some people have feared that The Bell Curve could be used by extremists to justify genocide and hate crimes. Much of the work referenced by The Bell Curve was funded by the Pioneer Fund, which aims to advance the scientific study of heredity and human differences, and has been accused of promoting scientific racism.
Evolutionary biologist Joseph L. Graves described The Bell Curve as an example of racist science, containing all the types of errors in the application of scientific method that have characterized the history of scientific racism:
- claims that are not supported by the data given
- errors in calculation that invariably support the hypothesis
- no mention of data that contradict the hypothesis
- no mention of theories and data that conflict with core assumptions
- bold policy recommendations that are consistent with those advocated by racists.
Some of the books that were written in reply include The Bell Curve Debate (1995).
|Values are the average earnings (1993 US Dollars) of each IQ sub-population.|
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 a 1998 book Income Inequality and IQ. To circumvent criticisms surrounding their 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).
|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.|