INTELLIGENCE SECOND EDITION NATHAN BRODY Department of Psychology Wesleyan University Middletown, Connecticut ACADEMIC PRESS, INC. Harcourt Brace Jovanovich, Publishers San Diego New York Boston London Sydney Tokyo Toronto This bookis printed on acid-free paper. Copyright © 1992, 1976 by ACADEMIC PRESS,INC. All Rights Reserved. No part of this publication may be reproducedor transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Academic Press,Inc. San Diego, California 92101 United Kingdom Edition published by Academic Press Limited 24-28 Oval Road, London NW1 7DX Library of Congress Cataloging-in-Publication Data Brody, Nathan. Intelligence / Nathan Brody.-- 2nd ed. p. cm. Includes bibliographical references and index. ISBN 0-12-134251-4 1. Intellect. 2. Intelligence tests. 3. Nature and nuture. BF431.B6844 1992 153.9--dc20 91-30772 CIP PRINTEDIN THE UNITED STATES OF AMERICA 92 93 94 95 96 HA 98765432 1 CONTENTS Preface ix ] HISTORICAL BACKGROUND Spearman’s 1904 Paper Binet and Simon’s Test of Intelligence Binet and Spearman Thomson and Spearman Spearman and Thurstone — OOmONNWN 2 THE STRUCTURE OF INTELLECT The Theory of Fluid and Crystallized Ability 18 Guttman’s Radex Theory 26 Guilford’s Theory 28 Gardner’s Theory of Multiple Intelligence 34 Conclusion 40 3 g AND BASIC INFORMATION- PROCESSINGSKILLS: THE SEARCH FOR THE HOLY GRAIL Reaction TimeandIntelligence 50 Inspection Time 62 Infant Habituation 71 Conclusion 77 v1 CONTENTS 4 MULTIPLE AND COMPLEX CORRELATES OF INTELLIGENCE Multiple Cognitive Correlates of Intelligence 80 The Complex Correlates of Intelligence 97 Componential Analysis 103 Conclusion 124 5 BEHAVIOR GENETICS OF INTELLIGENCE Introduction 126 Twin Studies 128 Family Studies 137 Quantitative Estimates 150 Developmental Behavior Genetics 158 Special Abilities 164 Conclusion 167 6 ENVIRONMENTAL DETERMINANTS OF INTELLIGENCE Between-Family Environmental Effects 168 Interventionsto Increase Intelligence 174 Changesin Intelligence Attributable to Education 186 Within-Family Environmental Influences 196 The Biological EnvironmentandIntelligence 206 Conclusion 214 7 BIOLOGICAL CORRELATES OF INTELLIGENCE Anatomical and Physical Correlates of Intelligence 217 Functional Properties of the Nervous System andIntelligence 220 Conclusion 226 CONTENTS Vii 8 CONTINUITY AND CHANGE IN INTELLIGENCE Is Intelligence Fixed? 228 Life-Span Change 234 Conclusion 249 9 CORRELATES OF INTELLIGENCE Intelligence and Education 252 Intelligence and Occupations 272 OtherCorrelates of Intelligence 274 Conclusion 279 10 GROUP DIFFERENCES IN INTELLIGENCE Black—White Differences 280 The Intelligence of Japanese and Chinese Groups 310 Gender Differencesin Intelligence 317 11 BEYONDIQ: SOCIAL INTELLIGENCE AND PERSONALITY Social Intelligence 329 Personality and Intelligence 342 12 EPILOGUE: THE FUTURE OF INTELLIGENCE Research 349 The Future of Tests 350 Literature Cited 357 Index 383 PREFACE Science, politics, and ideology are linked in the study of intelligence. Beliefs aboutracial and genderdifferences in intelligence, the heritability of intelligence, declinesin intelligence amongthe aged,the relationships between intelligence and schooling, and the modifiability of intelligence seem to be influenced by a complex mixture of ideology and science.If this is true, it is not unreasonable to expect someone writing a volume about intelligence to explicate his or her political and ideological posi- tion. I will do so but not without a sense of reluctance. I prefer scientific anonymity and its implicit stance of objective neutrality. Myinterest in the field of intelligence began some twenty odd years ago. My wife, Erness, was teaching Educational Psychology at Rutgers University, and she read Arthur Jensen’s article in which he suggested that racial differences in intelligence might have a genetic basis. She knew that I had becomeinterested in the behaviorgenetics of personality and she asked me whatI thoughtof the article. I read the article and answeredhertruthfully that I knewlittle or nothing about the field of intelligence. This was a curious omission in my knowledge since I was writing a book about personality, and I thought of myself as an individual difference psychologist. I had a course in graduate school devoted to the administration of tests of intelligence. The information about intelli- genceI received in the course was often wrong andlargely irrelevant to an understandingof the natureof intelligence. I was disturbed about my lack of knowledge aboutintelligence. It seemed to me that this was an impor- tant dimension of individual differences about which I should know something. Erness and I decided to learn as much as we could about intelligence. We were motivated by a desire to demonstrate that Jensen was wrong. Ourcollaboration led to the publication of a book by Academic Press in 1976 Intelligence: Nature, Determinants, and Consequences. If the world were as I would like it to be, what I think I have learned aboutintelligence would notbetrue.I think that individual differencesin intelligence, as assessed by standardizedtests, relate to what individuals ix xX PREFACE learn in schools and to their social mobility. And I think that scores on such tests are related, albeit weakly related, to race and social class background. In addition, I think we do not know howto substantially modify or eliminate individual differences in intelligence or the relation- ship between individual differences in intelligence and whatis learned in schools. As long as this is true, individual differences in intelligence will relate to various importantsocial outcomes.In my utopia, children would be equally capable of learning and everyone would be well educated. Dif- ferences in status associated with different occupations would be mini- mized or eliminated. Individual differences, in whatever would be analo- gous to intelligence in such a world, would beof little relevance. That world is not the world in which welive. In our world, individual differ- ences in intelligence as assessed by standardized tests are important. I have tried to understand these differences and to write about them in whatI hopeis an objective and honest way. I have two beliefs that influence what I have written in this volume. First, the study of “traditional” issues surrounding individual differences in intelligence remains important despite recent efforts to change the field by renewed emphasis on theories and methods derived from cogni- tive experimental psychology. I try to sketch someof the ways in which the traditional study of individual differences relates to the new experi- mental approach. Second, I believe that scientific analysis is capable of leading us to an approximation of whatis “true.” I hope that mycritics will discover the errors in what is written in this book and lead us to a better understanding of individual differences in intelligence. There are eleven chapters in this volume. Thefirst two chapters describe the structure of intellect. Chapter 1 is historical and deals with the works of Binet and Spearman, amongothers. Chapter 2 deals with contemporary psychometric analyses of the structure of intellect and includes a discus- sion of Gardner’s theory of multiple intelligence. Chapters 3 and 4 deal with the experimental studyof intelligence. Chapter 3 is concerned with attempts to relate general intelligence to elementary cognitive processes, and Chapter 4 deals with more complex viewsof the basisof intelligence and includesa discussion of componential analysis. Chapters 5 and 6 deal with the behavior genetics of individual differences in intelligence. Chap- ter 5 focuses on genetic influences, and Chapter 6 is concerned with environmental influences. Chapter 7 contains a brief discussion of re- search on the biological basis of intelligence. Chapter 8 deals with sta- bility and changein intelligence over the life span. The three remaining chapters in the volume may be thought of as a discussion of socially relevant issues related to intelligence. Chapter 9 explicitly considers the relationship between intelligence and socially relevant outcomes, includ- ing the relationship betweenintelligence and education. Chapter 10 deals with race and gender differences in IQ. Chapter 11 considers dimensions other than IQ that are related to social competence. PREFACE X1 It is a pleasure for me to acknowledge someof the debts I accrued while writing this book. Bob Sternberg and Tony Vernonsent meprepublication manuscripts of books they are editing. Howard Ehrlichman and John Sim- monsread an earlier version of Chapter 10 and provided valuable com- ments. I benefited from discussions with a numberof colleagues about various issues; Ian Deary wasespecially helpful. Santina Scalia has been wonderfully patient and hard working in dealing with my inadequacies as a typist and word processor. I am grateful for the good grace with which she typed and retyped manypages of this manuscript. And, finally, a special expression of love and gratitude to Erness who first interested mein this field and taught me morethingsthanI will ever know—both about intelligence and many other far more important things. It is to her that I dedicate this book. 1 HISTORICAL BACKGROUND In the last two decadesof the nineteenth century, psychologists in Amer- ica, England, France, and Germanyattempted to measure individualdif- ferences in intelligence. In England,