The concept of intelligence and its perception in society at large has often been at odds with the state of scientific knowledge on the issue. This can be seen from perusal of popular literature on the topic, including even such reputable works as Scientific American. This argument was brought to the forefront of public debate by the 1994 publication of the controversial best seller The Bell Curve. Shortly after the publication of The Bell Curve, many attempts were made to refute the findings and even the scientific basis of the book. (The most notable of these was Stephen Jay Gould's scathing review of the book in The New Yorker.)

The vast majority of these reviews and attacks were based on "knowledge" that was and is contradictory to the knowledge of the scientific community on these topics. This upset many leaders in the fields of psychology, who are normally reclusive from the public eye. Fifty-two experts in psychology and "allied fields" wrote and signed a statement entitled "Mainstream Science on Intelligence", which was published in The Wall Street Journal on December 13, 1994. This statement provided a full endorsement of every major finding of The Bell Curve, including its controversial six assertions in the book's introduction. The work is in the public domain and is reprinted here for the reader's convenience.

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

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

                The Meaning and Measurement of Intelligence

  1. Intelligence is a very general mental capability that, among other
     things, involves the ability to reason, plan, solve problems, think
     abstractly, comprehend complex ideas, learn quickly and learn from
     experience. It is not merely book learning, a narrow academic skill, or
     test-taking smarts. Rather, it reflects a broader and deeper capability
     for comprehending our surroundings--"catching on," "making sense" of
     things, or "figuring out" what to do.

  2. Intelligence, so defined, can be measured, and intelligence tests
     measure it well. They are among the most accurate (in technical terms,
     reliable and valid) of all psychological tests and assessments. They do
     not measure creativity, character personality, or other important
     differences among individuals, nor are they intended to.

  3. While there are different types of intelligence tests, they all measure
     the same intelligence. Some use words or numbers and require specific
     cultural knowledge (like vocabulary). Others do not, and instead use
     shapes or designs and require knowledge of only simple, universal
     concepts (many/few, open/closed, up/down).

  4. The spread of people along the IQ continuum, from low to high, can be
     represented well by the bell curve (in statistical jargon, the "normal
     curve"). Most people cluster around the average (IQ 100). Few are
     either very bright or very dull: About 3% of Americans score above IQ
     130 (often considered the threshold for "giftedness"), with about the
     same percentage below IQ 70 (IQ 70-75 often being considered the
     threshold for mental retardation).

  5. Intelligence tests are not culturally biased against American blacks or
     other native-born, English-speaking peoples in the U.S. Rather, IQ
     scores predict equally accurately for all such Americans, regardless of
     race and social class. Individuals who do not understand English well
     can be given either a nonverbal test or one in their native language.

  6. The brain processes underlying intelligence are still little
     understood. Current research looks, for example, at speed of neural
     transmission, glucose (energy) uptake, and electrical activity of the
     brain, uptake, and electrical activity of the brain.

                                Group Differences

  7. Members of all racial-ethnic groups can be found at every IQ level. The
     bell curves of different groups overlap considerably, but groups often
     differ in where their members tend to cluster along the IQ line. The
     bell curves for some groups (Jews and East Asians) are centered
     somewhat higher than for whites in general. Other groups (blacks and
     Hispanics) ale centered somewhat lower than non-Hispanic whites.

  8. The bell curve for whites is centered roughly around IQ 100; the bell
     curve for American blacks roughly around 85; and those for different
     subgroups of Hispanics roughly midway between those for whites and
     blacks. The evidence is less definitive for exactly where above IQ 100
     the bell curves for Jews and Asians are centered.

                               Practical Importance

  9. IQ is strongly related, probably more so than any other single
     measurable human trait, to many important educational, occupational,
     economic, and social outcomes. Its relation to the welfare and
     performance of individuals is very strong in some arenas in life
     (education, military training), moderate but robust in others (social
     competence), and modest but consistent in others (law-abidingness).
     Whatever IQ tests measure, it is of great practical and social

 10. A high IQ is an advantage in life because virtually all activities
     require some reasoning and decision-making. Conversely, a low IQ is
     often a disadvantage, especially in disorganized environments. Of
     course, a high IQ no more guarantees success than a low IQ guarantees
     failure in life. There are many exceptions, but the odds for success in
     our society greatly favor individuals with higher IQs.

 11. The practical advantages of having a higher IQ increase as life
     settings become more complex (novel, ambiguous, changing,
     unpredictable, or multifaceted). For example, a high IQ is generally
     necessary to perform well in highly complex or fluid jobs (the
     professions, management): it is a considerable advantage in moderately
     complex jobs (crafts, clerical and police work); but it provides less
     advantage in settings that require only routine decision making or
     simple problem solving (unskilled work).

 12. Differences in intelligence certainly are not the only factor affecting
     performance in education, training, and highly complex jobs (no one
     claims they are), but intelligence is often the most important. When
     individuals have already been selected for high (or low) intelligence
     and so do not differ as much in IQ, as in graduate school (or special
     education), other influences on performance loom larger in comparison.

 13. Certain personality traits, special talents, aptitudes, physical
     capabilities, experience, and the like are important (sometimes
     essential) for successful performance in many jobs, but they have
     narrower (or unknown) applicability or "transferability" across tasks
     and settings compared with general intelligence. Some scholars choose
     to refer to these other human traits as other "intelligences."

                 Source and Stability of Within-Group Differences

 14. Individuals differ in intelligence due to differences in both their
     environments and genetic heritage. Heritability estimates range from
     0.4 to 0.8 (on a scale from 0 to 1), most thereby indicating that
     genetics plays a bigger role than does environment in creating IQ
     differences among individuals. (Heritability is the squared correlation
     of phenotype with genotype.) If all environments were to become equal
     for everyone, heritability would rise to 100% because all remaining
     differences in IQ would necessarily be genetic in origin.

 15. Members of the same family also tend to differ substantially in
     intelligence (by an average of about 12 IQ points) for both genetic and
     environmental reasons. They differ genetically because biological
     brothers and sisters share exactly half their genes with each parent
     and, on the average, only half with each other. They also differ in IQ
     because they experience different environments within the same family.

 16. That IQ may be highly heritable does not mean that it is not affected
     by the environment. Individuals are not born with fixed, unchangeable
     levels of intelligence (no one claims they are). IQs do gradually
     stabilize during childhood, however, and generally change little

 17. Although the environment is important in creating IQ differences, we do
     not know yet how to manipulate it to raise low IQs permanently. Whether
     recent attempts show promise is still a matter of considerable
     scientific debate.

 18. Genetically caused differences are not necessarily irremediable
     (consider diabetes, poor vision, and phenal keton uria), nor are
     environmentally caused ones necessarily remediable (consider injuries,
     poisons, severe neglect, and some diseases). Both may be preventable to
     some extent.

                Source and Stability of Between-Group Differences

 19. There is no persuasive evidence that the IQ bell curves for different
     racial-ethnic groups are converging. Surveys in some years show that
     gaps in academic achievement have narrowed a bit for some races, ages,
     school subjects and skill levels, but this picture seems too mixed to
     reflect a general shift in IQ levels themselves.

 20. Racial-ethnic differences in IQ bell curves are essentially the same
     when youngsters leave high school as when they enter first grade.
     However, because bright youngsters learn faster than slow learners,
     these same IQ differences lead to growing disparities in amount learned
     as youngsters progress from grades one to 12. As large national surveys
     continue to show, black 17- year-olds perform, on the average, more
     like white 13-year-olds in reading, math, and science, with Hispanics
     in between.

 21. The reasons that blacks differ among themselves in intelligence appear
     to be basically the same as those for why whites (or Asians or
     Hispanics) differ among themselves. Both environment and genetic
     heredity are involved.

 22. There is no definitive answer to why IQ bell curves differ across
     racial-ethnic groups. The reasons for these IQ differences between
     groups may be markedly different from the reasons for why individuals
     differ among themselves within any particular group (whites or blacks
     or Asians). In fact, it is wrong to assume, as many do, that the reason
     why some individuals in a population have high IQs but others have low
     IQs must be the same reason why some populations contain more such high
     (or low) IQ individuals than others. Most experts believe that
     environment is important in pushing the bell curves apart, but that
     genetics could be involved too.

 23. Racial-ethnic differences are somewhat smaller but still substantial
     for individuals from the same socioeconomic backgrounds. To illustrate,
     black students from prosperous families tend to score higher in IQ than
     blacks from poor families, but they score no higher, on average, than
     whites from poor families.

 24. Almost all Americans who identify themselves as black have white
     ancestors-the white admixture is about 20%, on average--and many
     self-designated whites, Hispanics, and others likewise have mixed
     ancestry. Because research on intelligence relies on self-
     classification into distinct racial categories, as does most other
     social-science research, its findings likewise relate to some unclear
     mixture of social and biological distinctions among groups (no one
     claims otherwise).

                          Implications for Social Policy

 25. The research findings neither dictate nor preclude any particular
     social policy, because they can never determine our goals. They can,
     however, help us estimate the likely success and side effects of
     pursuing those goals via different means.

The following professors-all experts in intelligence and allied fields-have
signed this statement:

     Richard D. Arvey,        University of Minnesota
     Thomas J. Bouchard, Jr., University of Minnesota
     John B. Carroll,         U.N.C. at Chapel Hill
     Raymond B. Cattell,      University of Hawaii
     David B. Cohen,          U.T. at Austin
     Rene W. Dawis,           University of Minnesota
     Douglas K. Detterman,    Case Western Reserve U.
     Marvin Dunnette,         University of Minnesota
     Hans Eysenck,            University of London
     Jack Feldman,            Georgia Institute of Technology
     Edwin A. Fleishman,      George Mason University
     Grover C. Gilmore,       Case Western Reserve U.
     Robert A. Gordon,        Johns Hopkins University
     Linda S. Gottfredsen,    University of Delaware
     Richard J. Haier,        U.C. Irvine
     Garrett Hardin,          U.C. Berkeley
     Robert Hogan,            University of Tulsa
     Joseph M. Horn,          U.T. at Austin
     Lloyd G. Humphreys,      U.Ill. at Champaign-Urbana
     John E. Hunter,          Michigan State University
     Seymour W. Itzkoff,      Smith College
     Douglas N. Jackson,      U. of Western Ontario
     James J. Jenkins,        U. of South Florida
     Arthur R. Jensen,        U.C. Berkeley
     Alan S. Kaufman,         University of Alabama
     Nadeen L. Kaufman,       Cal. School of Prof. Pshch., S.D.
     Timothy Z. Keith,        Alfred University
     Nadine Lambert,          U.C. Berkeley
     John C. Loehlin,         U.T. at Austin
     David Lubinski,          Iowa State University
     David T. Lykken,         University of Minnesota
     Richard Lynn,            University of Ulster at Coleraine
     Paul E. Meehl,           University of Minnesota
     R. Travis Osborne,       University of Georgia
     Robert Perloff,          University of Pittsburg
     Robert Plomin,           Institute of Psychiatry, London
     Cecil R. Reynolds        Texas A&M University
     David C. Rowe            University of Arizona
     J. Philippe Rushton      U. of Western Ontario
     Vincent Sarich,          U.C. Berkeley
     Sandra Scarr,            University of Virginia
     Frank L. Schmidt         University of Iowa
     Lyle F. Schoenfeldt,     Texas A&M University
     James C. Sharf,          George Washington University
     Julian C. Stanley,       Johns Hopkins University
     Del Theissen,            U.T. at Austin
     Lee A. Thompson,         Case Western Reserve U.
     Robert M. Thorndike,     Western Washington University
     Philip Anthony Vernon,   U. of Western Ontario
     Lee Willerman,           U.T. at Austin

It is important to note that while referring to a statement such as this could be called an appeal to authority, or some other logical fallacy, in reality, all people must rely, at least in part, on the research of scientific professionals in their chosen fields. If we as society choose to reject the findings of legitimate science (such as this paper) based on our feelings or beliefs, we risk a return to the Dark Ages. That is something I doubt any of us desire.


Richard Herrnstein, Charles Murray. The Bell Curve. New York City: Simon & Schuster, 1994.

"Mainstream Science on Intelligence." The Wall Street Journal. New York City: Dow Jones & Company, 1994. (Public Domain Work.)

Upstream. Accessed: 11/24/02.

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