Mainstream Science on Intelligence
50 professors at Universities throughout the U.S.,
Canada, and Britain have signed the following
statement concerning the generally accepted
science of intelligence and inter-race differences
in intelligence.
You will be surprised at many of the conclusions
and at the number and identity of the signers, all
of whom are listed at the end of the article.
Dec. 13, 1994 Wall Street Journal p A18
Mainstream Science on Intelligence
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.
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 importance.
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 thereafter.
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
intodistinct 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 an 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 Universit
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
50 professors at Universities throughout the U.S.,
Canada, and Britain have signed the following
statement concerning the generally accepted
science of intelligence and inter-race differences
in intelligence.
You will be surprised at many of the conclusions
and at the number and identity of the signers, all
of whom are listed at the end of the article.
Dec. 13, 1994 Wall Street Journal p A18
Mainstream Science on Intelligence
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.
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 importance.
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 thereafter.
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
intodistinct 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 an 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 Universit
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
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