Table Of ContentARTHUR R. JENSEN
Genetics and Education
1817
HARPER & ROW, PUBLISHERS
New York, Evanston, San Francisco, London
To my wife Barbara
genetics and education. Copyright © 1972 by Arthur R. Jensen. All rights
reserved. Printed in the United States of America. No part of this book may be
used or reproduced in any manner whatsoever without written permission
except in the case of brief quotations embodied in critical articles and reviews.
For information address Harper & Row, Publishers, Inc., 10 East 53rd Street,
New York, N.Y. 10022.
FIRST U.S. EDITION
STANDARD BOOK NUMBER: 06-012192-0
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CONTENTS
Acknowledgements page vi
Preface 1
How Much Can We Boost IQ and Scholastic Achievement? 69
A Theory of Primary and Secondary Familial
Mental Retardation 204
Estimation of the Limits of Heritability of Traits
by Comparison of Monozygotic and Dizygotic Twins 294
IQs of Identical Twins Reared Apart 307
Genetic Research on Human Mental Abilities: Ethical Issues 327
A Note on Why Genetic Correlations Are Not Squared 333
References 336
Bibliography (1) Articles about ‘How Much Can We
Boost IQ and Scholastic Achievement?’ 356
Bibliography (2) Articles on Genetics and Individual
Differences by A. R. Jensen 365
Author Index 370
Subject Index 374
v
Acknowledgements
For permission to reprint articles in this volume the author and
publisher would like to thank the following: the President and
Fellows of Harvard College for ‘How Much Can We Boost IQ and
Scholastic Achievement?’ {Harvard Educational Review, 1969, 39,
1-123); the Academic Press, Inc. for ‘A Theory of Primary and
Secondary Familial Retardation’ {International Review of Research
in Mental Retardation, 1970, 4, 33-105); the National Academy of
Sciences for ‘Estimation of the Limits of Heritability of Traits by
Comparison of Monozygotic and Dizygotic Twins’ {Proceedings of
the National Academy of Science, 1967, 58, 149-156); the Editor of
Behavior Genetics for ‘IQs of Identical Twins Reared Apart’
{Behavior Genetics, 1970, 1, 133-148); the Editor of The Humanist
for ‘Genetic Research on Human Mental Abilities: Ethical Issues’
{The Humanist, January-February 1972, 5-6); the American
Psychological Association for ‘A Note on Why Genetic Correlations
are not Squared’ {Psychological Bulletin, 1971, 75, 223-224).
Additional footnotes to the articles, made for this book, are
distinguished from the original footnotes by an asterisk, instead
of a numeral.
vi
Preface
A little more than three years have now passed since the original
publication of my article ‘How Much Can We Boost IQ and Scho
lastic Achievement?’ in the Harvard Educational Review (Winter,
1969). The storm of ideologically, often politically, motivated pro
tests, misinterpretations, and vilifications prompted by this article
has by now fortunately subsided, with most encouraging signs of
being displaced in professional journals and conferences (and now
to a large extent even in the popular press) by rational and sober
consideration of the educational and societal implications of the
important issues raised in this article. The heat and smoke have
largely abated, which is all to the good; yet the concerned interest
of the kind I had originally hoped my article would stimulate has
continued to grow. Since its publication, reprint requests num
bering in the thousands have been received, which of course I could
not personally fill; and they are still coming in, merely to be
answered by a form letter. Judging from my mail, many college
courses in education, psychology, biology, and genetics throughout
the country have devoted a substantial part of their discussion to
my article, and in a number of departments that have come to my
attention whole courses and seminars have been built around it.
I have in my files hundreds of term papers which students have
written on the article in a variety of courses (including a few from
high school classes), sent to me by the students who wrote them or
by their teachers. The handling of the volume of mail resulting
from this publication and its attendant publicity was for many
months practically a full-time job for my wife, whose superior
capabilities for organization and diplomacy have considerably
1
2 Genetics and Education
relieved the burden on me, making it possible, unstintingly, to
continue my research on some of the problems that were high
lighted in my article.
Because of the continued and growing interest in these topics
among educators and workers in the biological, behavioral, and
social sciences, I heartily welcomed the suggestion to reprint
the article, making it more accessible to a wider, more international
audience. Also, some of the most typical inquiries I have received
from readers of the original publication, it turns out, are answered
in detail in several of my other closely related publications. In
attempting to answer these inquiries, I soon ran out of my supply
of reprints of the most relevant articles. The few most germane and
frequently requested of these articles have been included in the
present volume. Two of them go into the study of twins in con
siderable detail. The first deals with the estimation of the heritabi-
lity of intelligence (and other traits) by means of comparing iden
tical and fraternal twins. The second is a re-analysis of all the
existing major studies of the IQs of identical twins who were
separated early in life and reared apart. Then, since most psycho
logists who have studied statistics as a part of their formal training
were taught that the proportion of variance accounted for in one
variable by another variable is given by the rz, that is, the square of
the coefficient of correlation between the two variables, many
psychologists wrote to me in puzzlement as to why I had not
squared the correlations between identical twins in order to obtain
the estimate of the proportion of IQ variance attributable to genetic
factors. This is a point which has never bothered geneticists, to my
knowledge, probably because they have been brought up on it, so
to speak, and have used correlations for somewhat different pur
poses than those for which psychologists typically think about the
meaning of a correlation coefficient. The article ‘Why Genetic
Correlations Are Not Squared’ is my answer to these inquiries. It is
essential that the reader not be puzzled on this point if he is to
understand the quantitative logic of heritability estimation based
on kinship correlations. Also, I have received many inquiries from
workers in the fields of special education and mental retardation
concerning the relationship of problems in these fields to the so-
called nature-nurture controversy and to the conspicuous connec
tion between social class and the frequency of milder forms of
Preface 3
mental retardation and scholastic backwardness. The problems here
are so diverse that one cannot even begin to tackle all the questions
that are posed. But the gist of the directions which my thinking and
research have taken in this area, making no claim to comprehensive
ness, are presented in ‘A Theory of Primary and Secondary Fami
lial Mental Retardation’. My research in the two years since this
article originally appeared has led to some revisions of my theory,
particularly regarding the degree of functional dependence of Level
II (intelligence) ability upon Level I (memory and rote learning)
ability, and these new points are summarized in the Addendum to
the article on familial mental retardation. Finally, questions are
frequently raised concerning the ethical and moral problems
involved in the public discussion of the genetic aspects of individual
and especially social class and racial group differences in socially and
educationally valued traits such as intelligence. Major symposia
have been devoted to discussion of these moral and ethical issues.
The essence of my statements in two such symposia in which I was
an invited participant is given in the last selection in this volume.
For readers who may wish to delve into commentary aroused
by my Harvard Educational Review (henceforth abbreviated HER)
article, I have included a bibliography of commentary on the HER
article. The list is as complete as I can make it by the time this
volume goes to press. Some of these items are quite worth reading,
many are trivial, and some are plainly misinformed. I have made
no attempt to select them, but have simply aimed to make the list
as complete as possible. It would have been practically impossible
and scarcely worth while for me to have responded individually to
each of these items. I have replied to critics only in those instances
where the criticism has dealt with scientific (rather than ideological)
issues or when the facts have been seriously misrepresented in
reputable scholarly journals with a large readership and therefore
should not be allowed to go unchallenged. I have generally not
bothered with articles in the popular press.
In all the published criticisms and in the personal correspondence
I have received, several errors in the original publication have been
turned up, all minor points and mostly typographical. These have
all been corrected in this edition. In all but the most trivial instances,
I have footnoted the changes. The claims of some of my overly
zealous critics that there exists a large number of errors or
4 Genetics and Education
misinterpretations in this work simply have not held up under
examination. In a subsequent issue of the HER, for example, one
critic stated:
I should like to make it clear at the outset, however, that in Jensen’s
article I found many erroneous statements, misinterpretations, and
misunderstandings of the nature of intelligence, intelligence tests,
genetic determination of traits, education in general, and compen
satory education in particular. A colleague reports coming across 17
such errors in a casual perusal. . . . Perhaps so large a number of
errors would not be remarkable were it not for the fact that Jensen’s
previous work has contained so few, and, more malignant, all the
errors referred to are in the same direction: maximizing differences
between blacks and whites and maximizing the possibility that such
differences are attributable to hereditary factors.
This critic was informed many months ago that all errors were
to be corrected in this new edition of the article and that he could
perform a service by specifically pointing out all the errors he
claimed existed. But he has been unable to point to anything that
by any stretch of the imagination could be called an error except
one obvious misprint (which the printers had already corrected
in all printings subsequent to the first, along with two other
obvious typographical errors that occurred in the first printing).
The attempts to discredit the main substance of my article have
been most intemperate in some circles, ultimately to the discredit
and embarrassment of the critics. On the other hand, I have cor
rected all actual errors in this edition that were noted by critics
or were brought to my attention by various knowledgeable corre
spondents.
Another class of questioning that has often been addressed to me
concerning the HER article has to do not with the substantive
issues but with my reasons for writing the article - the history of
the whole affair, including the tumultuous reactions that followed
its publication. This is probably as appropriate a place as any to
chronicle these events briefly and to set the record straight in those
instances where attempts have been made to misrepresent the true
chain of events.
As a psychological researcher, how did I go from the rather
esoteric research on theoretical problems in serial rote learning to
Preface 5
research on the inheritance of mental abilities and its implications
for education? Upuntil about 1961,all of my psychological research
was conducted in the laboratory, as is true of most investigators in
the psychology of human learning, and all of my experimental
subjects were university undergraduates. The details of the prob
lems I was researching in an attempt to achieve an adequate theory
of certain serial learning phenomena - one of the classical topics of
human learning research — are unimportant in the present context.
The point is that they were about as far removed from the topics of
the present volume as one could get and still be working in the field
of psychology. While I was engrossed in my research on serial
learning, one of my graduate students who worked as a school
psychologist brought to my attention what appeared to be a chal
lenging problem for a researcher on human learning. Besides, it
was a part of my personal philosophy that a scientist should try to
bring his technical expertise to bear on practical as well as theore
tical problems; and here, it seemed, was a worthy practical problem.
My student said he was looking for a good culture-free or culture-
fair test of intelligence and had not been able to find one. All the
tests he used, whether they were claimed to be culture-fair or not,
were in considerable agreement with respect to children diagnosed
as educationally mentally retarded (EMR), by which they were
assigned to special small classes offering a different instructional
program from that in the regular classes. To qualify for this special
treatment, children had to have IQs below 75 as well as lagging far
behind their age-mates in scholastic performance. My student, who
had examined many of these backward pupils himself, had gained
the impression that the tests were quite valid in their assessments
of white middle-class children but not of minority lower-class
children. Many of the latter, despite IQs below 75 and markedly
poor scholastic performance, did not seem nearly as retarded as the
white middle-class children with comparable IQs and scholastic
records. Middle-class white children with IQs in the EMR range
generally appeared more retarded than the minority children who
were in special classes. Using nonverbal rather than verbal tests
did not appreciably alter the problem. I confirmed my student s
observations for myself by observing EMR children in their classes
and on the playground and by discussing their characteristics with
a number of teachers and school psychologists. My student’s
6 Genetics and Education
observations proved reliable. EMR children who were called ‘cult
urally disadvantaged’, as contrasted with middle-class EMR chil
dren, appeared much brighter socially and on the playgound, often
being quite indistinguishable in every way from children of normal
IQ except in their scholastic performance and in their scores on a
variety of standard IQ tests. Middle-class white children diagnosed
as EMR, on the other hand, though they consituted a much smaller
percentage of the EMR classes, usually appeared to be more men
tally retarded all round and not just in their performance in
scholastic subjects and IQ tests. I asked myself, how could one
devise a testing procedure that would reveal this distinction so that
it could be brought under closer study and not depend upon casual
observations and impressions.
It appeared to me that most of the item content of traditional IQ
tests called for information and skills that the testee was expected
to have had the opportunity to acquire before taking the test. In
short, most IQ tests assessed what the subject had learned outside
the testing situation. If it could be assumed that all subjects had
had roughly equal opportunities for learning prior to being tested,
their scores could well be an accurate reflection of their learning
ability. But in cases where this assumption could not be made, as
in the case of children with a quite different cultural background, it
struck me that perhaps the best way to assess a child’s learning
ability (which at that time I more or less equated with intelligence)
was not to test what the child had learned at some time prior to the
test situation but to measure his rate of learning something new,
right in the testing situation itself. This I called a ‘direct learning
test’. I devised several such tests, using the simplest possible
materials. What we found in our first studies was that EMR chil
dren who were ‘culturally disadvantaged’, meaning they were from
low socioeconomic status (SES) homes, performed much better on
our direct learning tests relative to middle-SES EMR children of
the same low IQ. In short, direct learning tests reflected important
behavioral and cognitive differences between low-SES and middle-
SES EMR children which were not at all reflected in scores on the
usual IQ tests or in scholastic achievement. In fact, on the learning
tests many of the EMR children performed as well as children of
average IQ and some even performed as well as children at the
so-called ‘gifted’ level of IQ (i.e., IQs above 130 or 140).
