The Bell Curve

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The Bell Curve: Intelligence and Class Structure in American Life is a controversial work published in 1994 by political scientist Charles Murray and psychology professor Richard Herrnstein of Harvard University . The title refers to the bell curve of the intelligence test scores. Among other things, the authors analyzed the data from a comprehensive longitudinal study of the life courses of American adolescents from 1979 to 1990 (the National Longitudinal Survey of Youth , NLSY for short). They described the results of their analyzes in this book.


The bell curve of the intelligence test values ​​gave the book its name.

The book deals with the relationships between socio-economic class, intelligence and the genetic factor . In the authors' opinion, intelligence is largely hereditary. In their work, the authors point out that belonging to socio-economic classes is remarkably closely related to intelligence. They describe, for example, that white Americans who score in the bottom five percent on intelligence tests are 15 times more likely to be in the “poor” category than those who score in the top five on the tests % achieved.

In the course of the book, several such examples are given, only with other references (e.g. intelligence and unemployment or intelligence and upbringing ) to show how intelligence (or its non-existence) affects living conditions in different areas of society affects.

The book is divided into four parts:

  1. In the first part, the authors propose that in the USA intelligence plays an important role in determining which class a person belongs to. Intelligent people would move up to higher layers, less intelligent people would move down to lower layers. The IQ is more important than the class of his parents for the stratum of an American non-Hispanic white person in adulthood.
  2. In the second part, the authors propose that many social problems in the USA can be explained by a low IQ. This is how they explain unemployment, school failure, poverty , maternity of minors , illegitimate births, neglect of children and other problems, including a low IQ.
  3. In the third part, the authors propose that in the USA different ethnic groups differ in their average IQ. For example, Asians are on average more intelligent than whites, while they are on average more intelligent than blacks. The authors also discuss the causes of the IQ difference of about 15 points between black and white Americans. In doing so, they come to the conclusion that both genes and the environment play a role without committing to any percentage. The third part also examines the relationship between intelligence and the birth rate.
  4. In the fourth part the authors make political demands. The demand that American social policy should be changed has been particularly controversial, as it leads to people with low IQ having more children than people with high IQ.


Herrnstein and Murray put forward various theses in the course of describing the genetic factor.

One of these theses says that intelligence between 40% and 80% is genetically determined, but also that different ethnic groups have different levels of intelligence or that qualitative differences in cognitive abilities can be identified.

The work addresses various dimensions of intelligence: its genetic factor, its different level in the ethnic groups, its social effects and especially their connections with one another. From the interplay of these connections, the authors derive one of the central theses of the work: In the course of intelligence tests it was found that black Americans have an IQ that is around 15 points lower on average than whites. Herrnstein and Murray attribute these differences to their genes and environmental influences. In addition, due to all the effects that intelligence has on a person, these people are trapped in a cycle that they cannot break because the level of intelligence can only be increased insignificantly through schooling, for example.

Herrnstein and Murray have also come under fire for their political demands.

In their book, they suggested that aid for single mothers should be abolished, as this would lead to below average intelligent women financially worthwhile having children:

“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. "

Reception of the book

American Psychological Association (APA) Response

The Bell Curve sparked a bitter controversy, especially in the United States. At the height of the conflict, a working group (made up of Ulric Neisser and Robert Sternberg ) was set up by the American Psychological Association .

The statements of the APA (as of 1995/1996) are briefly presented below

IQ and academic success

The APA suggests a connection between IQ and academic success. The correlation between IQ and school grades is around 0.5. The thesis postulated in The Bell Curve that there is a connection between intelligence and academic success is thus supported by the APA.

IQ and length of school education

The APA also points to a relationship between IQ and length of schooling. The correlation in this case is 0.55. Many other factors have an influence on the length of school education, but the intelligence test values ​​are the most explanatory.

IQ, occupation, social status and income

According to the APA, IQ scores in childhood and later occupation show a significant correlation, even if other explanatory variables such as education and family background are eliminated. To this extent, Murray and Herrnstein's theses are supported.

According to the APA, it is difficult to say exactly what influence a person's IQ has on their social status, because this is correlated with the social class of their parents, which also has an influence on a person's socio-economic status (the correlation of status of Parental home and IQ is 0.33, according to White from 1982, "The relationship between socioeconomic status and academic achievement").

The American Psychological Association refers to a study by Jencks (1979; "Who get's ahead? The determinants of economic success in America"), which tries to separate the two influencing factors. One way to look at the relationship is to start with the socio-economic status of the parental home. This explains 1/3 of the variance in the social status of young Americans (or in simpler words: one third of the social status of young adults can be explained by that of their parents) and explains 1/5 of the variance in income. However, half of these effects can be explained by differences in the IQ of young people due to the class of origin. The other way around, one can also look at the connection starting with the IQ. Differences in IQ explain a quarter of the variance in socioeconomic status and 1/6 the variance in income among young Americans. If the effects of social origin are factored out, only a quarter of the explanation of the variance is eliminated.

Race and intelligence

The APA does not completely reject the connection between race and intelligence postulated by Herrnstein and Murray, but takes a more differentiated position in this regard. In particular, the APA notes that IQ scores for blacks in the United States have risen in recent decades. According to the APA, other observations also cast doubts on the close relationship between race and intelligence postulated in The Bell Curve .

Further criticisms

The Bell Curve has been criticized by parts of the professional world as being methodologically unclean. Herrnstein and Murray, however, received support from the Jensen tradition of psychometric intelligence research. Many of these scientists were among the 52 signatories of the mainstream Science on Intelligence , written by Linda S. Gottfredson , which supported the central theses of The Bell Curve . The Institute for the Study of Academic Racism then accused Gottfredson of scientific racism.

Among other things, the following criticism was specifically raised.


Michael Nunley, professor of anthropology at the University of Oklahoma, accused Herrnstein and Murray of deliberate public disinformation and farmer trapping. He said Herrnstein and Murray were misleading statistically inexperienced readers with controversial statistics. He referred to her as "Pied Piper" (the English name of the Pied Piper of Hamelin ). He called the book a scam:

“I believe this book is a scam; that its writers must have known it was a scam when they wrote it, and that Charles Murray must still know it was a scam as he is now defending it. By 'fraud' I mean an intentional, deliberately misleading presentation of the facts. After careful reading, I cannot believe that its authors should not have been clear about what they used and what they left out, and how they falsified what they used. "

Leon J. Kamin accused Herrnstein and Murray of abusing science for racist purposes.

These allegations were compounded as the very conservative Bradley Foundation and the right-wing Pioneer Fund were major financiers of this book. Murray even received bomb threats as a result of the discussion and criticism of The Bell Curve .


In their study, Herrnstein and Murray found that the IQ of American blacks is 15 points lower than that of American whites. This agrees with the results of other studies. The authors described the cause of the lower IQ as an allegedly worse genetic predisposition in black Americans than in whites.

The African-born IQ researcher John Ogbu accused Herrnstein and Murray of racism for this implication. Critics like Jeanne Brooks-Gunn and Pamela Klebanov accused Herrnstein and Murray of having overlooked important factors. For example, there is the fact that black children in the USA are more likely to grow up in poverty . 40% of all black children, but only 5% of all white children in the US live in poverty. In addition, even if they are not poor, black children often grow up in problem areas. The parents of black children are also more likely to be single parents, they are more often minors and more often unemployed. All of these can have a negative impact on IQ.

Martin Seligman believes that learned helplessness leads to lower IQ scores in black people. He notices:

“Both IQ and school performance can be lowered through helplessness. [Successful cognitive performance is] dependent on two conditions: adequate cognitive skills and achievement motivation. To the extent that a child is convinced that they are helpless and that success is independent of their willful reactions, they become less likely to engage in such cognitive performances - such as B. feel your memory or add up in your mind - be ready, which would lead to high IQ values ​​and successful school performance. "

Right-wing extremist and eugenic motivations

The authors and their supporters have been accused of right-wing extremist and eugenic motivations by a number of scholars and journalists . Critics have pointed to the fact that of the 17 authors cited in the book, several have written for the controversial journal Mankind Quarterly . The journal has come under fire for right-wing texts and has received funding from the controversial Pioneer Fund . Steven Fraser accuses Herrnstein and Murray of having eugenic motivations: “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 " .

Claim that there is only one intelligence

The claim that there is only one intelligence has been criticized by numerous scientists, including Stephen Jay Gould . Herrnstein and Murray only went into the logical-analytical intelligence and this was wrong. As Gould put it, “ The Bell Curve is nothing new. This 800-page manifesto is nothing more than a long elaboration of the strong version of Spearman's g - the theory of a unified, genetically based, unalterable thing in the head that can be ranked. ”Gould called this opinion false . He is of the opinion that people have a wide variety of cognitive abilities that cannot be measured with an IQ test. In their criticism of the book, many scholars refer to Robert Sternberg's triarchic theory of intelligence and Howard Gardner's theory of multiple intelligences .

Heredity of intelligence

Heredity estimates within a group must not be used to interpret group differences

The opinion held by Murray and Herrnstein that general intelligence is hereditary was criticized by Leon J. Kamin, among others.

Critics of the authors often refer to Richard Lewontin . According to Lewontin, a certain percentage of the IQ differences within a stratum could be genetic, but this does not mean that the differences between two strata must also be genetic.

Lewontin cites adoption studies as evidence of his thesis, for example those by Skodak and Skeels and the Minnesota Transracial Adoption Study, and refers to the success of intervention programs ( compensatory education ). Lewontin tries to illustrate this with a parable:

“Imagine having a sack full of wheat grains. Divide this sack in half at random. One half would be sown in fertile soil that was well watered and fertilized. The other half is thrown into a barren field. If you now look at the first field, you will notice that the ears of wheat are of different sizes. One can trace this back to the genes, because the environment was the same for all ears. If you look at the second field, you will be able to attribute the variation within the field to the genes. But it will also be noticeable that there are big differences between the first field and the second field. In the first field the differences are 100% genetic, in the second field the differences are 100% genetic, but that does not mean that the differences between field 1 and field 2 are also genetic. "

Turkheimer differentiates social classes with regard to a genetic heredity from intelligence. While intelligence in the middle class is largely hereditary, it is not so in the lower class . The reason: The poor environmental conditions in the lower class meant that the children could not develop their genetically given potential. On a scale from 0.00 to 1.00, the IQ in the middle class is 0.72 determined by genes, but only 0.10 in the lower class, according to Turkheimer.

Criticism of the methodology

These research results have not gone unchallenged. Jay Zagorsky from the Center for Human Resource Research at Ohio State University analyzed the same data and came to the conclusion that there was no connection between IQ and financial success. He summarized his results with "Your IQ has really no relationship to your wealth. And being very smart does not protect you from getting into financial difficulty " together. The NLSY's survey methods were also criticized (for example by Stephen Jay Gould in the expansion of his book The Mismeasure of Man ).

See also

Web links


  1. ^ Herrnstein, Richard, Murray Charles (1994): The Bell Curve - Intelligence and Class Structure in America , Freepress, ISBN 0-02-914673-9 , p. 548
  2. ^ All data are from: American Psychological Association. February 1996 [1] (PDF; 673 kB). American Psychologist
  3. Report of a Task Force established by the Board of Scientific Affairs of the American Psychological Association: Intelligence: Knowns and Unknowns , first version published in August 1995, second version slightly modified version: [2] (PDF; 673 kB) American Psychologist, Feb 1996
  4. Gottfredson, Linda (December 13, 1994). Mainstream Science on Intelligence. Wall Street Journal, p. A18 and
  5. Institute for thev study of scientific racism: Linda Susanne Gottfredson ( Memento from January 5, 2006 in the Internet Archive ) accessed on January 3, 2008
  6. "I believe this book is a fraud, that its authors must have known it was a fraud when they were writing it, and that Charles Murray must still know it's a fraud as he goes around defending it. By" fraud, "I mean a deliberate, self-conscious misrepresentation of the evidence. After careful reading, I cannot believe its authors were not acutely aware of what they were including and what they were leaving out, and of how they were distorting the material they did include. " You've got to be taught to hate and fear ... Downloaded December 31, 2007
  7. Leon J. Kamin, “Lies, Damned Lies and Statistics,” R. Jacoby & N. Glauberman (Eds.), The Bell Curve Debate: History, Documents, Opinions. (New York: Times Books, 1995) pp. 81-105
  8. Northwestern study finds that poverty and early learning opportunities - not race - account for the gap in IQ scores between blacks and whites Download on December 31, 2007
  9. Northwestern study finds that poverty and early learning opportunities - not race - account for the gap in IQ scores between blacks and whites Download on December 31, 2007
  10. Martin Seligman: Learned helplessness . Weinheim and Basel 1999, Beltz Taschenbuch, p. 155
  11. ^ Steven Fraser (1995): The Bell Curve Wars: Race, Intelligence, and the Future of America . Basic Books
  12. ^ Gould, 1996, p. 35
  13. How Heritability Misleads about race. The Boston Review, XX, no 6, January, 1996, pp. 30–35 [3]
  14. Not in Our Genes: Biology, Ideology and Human Nature (with Steven Rose and Leon J. Kamin ) (1984)
  15. Weiss, Rick: Genes' Sway Over IQ May Vary With Class . In: The Washington Post , September 2, 2003; Page A01, accessible online at Genes' Sway Over IQ May Vary With Class , accessed January 3, 2008.
  16. You don't have to be smart to be rich ( Memento of the original from June 21, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Downloaded January 3, 2008 @1@ 2Template: Webachiv / IABot /