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.

The authors claimed that average intelligence quotient (IQ) differences between racial and ethnic groups are at least partly genetic in origin, a view that is now considered discredited by mainstream science.

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 (via the establishment of free primary education and the prohibition of discrimination) the main criterion of success in academic and professional life is cognitive ability.

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.

At the close of this discussion, they write:[5] If the reader is now convinced that either the genetic or environmental explanation has won out to the exclusion of the other, we have not done a sufficiently good job of presenting one side or the other.

[5] 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.

As an antidote to this prognosis, they offer a vision of society where differences in ability are recognized and everybody can have a valued place, stressing the role of local communities and clear moral rules that apply to everybody.

"[9] 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."

[12] 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.

[21][22][20][23][24][25] In response to the controversy surrounding The Bell Curve, the American Psychological Association's Board of Scientific Affairs established a special task force chaired by Ulric Neisser to publish an investigative report focusing solely on the research presented in the book, not the policy recommendations that it made.

[26] Regarding explanations for racial differences, the APA task force stated: The cause of that differential is not known; it is apparently not due to any simple form of bias in the content or administration of the tests themselves.

In short, no adequate explanation of the differential between the IQ means of Blacks and Whites is presently available.American Psychologist subsequently published eleven critical responses in January 1997.

[29] 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.

[34] Canadian psychologist Sidney Segalowitz concurs with Block that twin studies fail to draw conclusions about heritability, and as a result Murray's work is methodologically flawed.

[35] 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.

[36] In August 1995, National Bureau of Economic Research economist Sanders Korenman and Harvard University sociologist Christopher Winship argued that measurement error was not properly handled by Herrnstein and Murray.

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.

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.

"[42] Charles R. Tittle [de] and Thomas Rotolo found that the more the written, IQ-like, examinations are used as screening devices for occupational access, the stronger the relationship between IQ and income.

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."

[49][50] 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.

[51]The 2014 textbook Evolutionary Analysis by Herron and Freeman[52] devoted an entire chapter to debunking what they termed the "Bell Curve fallacy", saying that "Murray and Herrnstein's argument amounts to little more than an appeal to personal incredulity" and that it is a mistake to think that heritability can tell us something about the causes of differences between population means.

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".

[53] 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 white people.

[55] In his afterword to the 1996 Free Press edition of The Bell Curve, Murray responded that the book "draws its evidence from more than a thousand scholars" and among the researchers mentioned in Lane's list "are some of the most respected psychologists of our time and that almost all of the sources referred to as tainted are articles published in leading refereed journals".

[57] 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".

[58] Since the book provided statistical data making the assertion that blacks were, on average, less intelligent than whites, some people have argued that The Bell Curve could be used by extremists to justify genocide and hate crimes.

By never spelling out a reason for reporting on these differences in the first place, the authors transmit an unspoken yet unequivocal conclusion: Race is a helpful indicator as to whether a person is likely to hold certain capabilities.

"[67] Columnist Bob Herbert, writing for The New York Times, described the book as "a scabrous piece of racial pornography masquerading as serious scholarship".