The Trouble with Twin Studies: A Reassessment of Twin Research in the Social and Behavioral Sciences

337 Pages·2014·1.284 MB·English

by  Jay Joseph

THE TROUBLE WITH
TWIN STUDIES
The Trouble with Twin Studies questions popular genetic explanations
of human behavioral differences based upon the existing body of twin
research. Psychologist Jay Joseph outlines the fallacies of twin studies
in the context of the ongoing decades-long failure to discover genes for
human behavioral differences, including IQ, personality, and the major
psychiatric disorders. This volume critically examines twin research, with
a special emphasis on reared-apart twin studies, and incorporates new
and updated perspectives, analyses, arguments, and evidence.
Jay Joseph, PsyD., is a licensed psychologist practicing in the San Francisco
Bay Area. Since 1998 he has published two books, several book chap-
ters, and many articles in peer-reviewed journals, where he has presented
a critical appraisal of genetic theories and research in psychiatry and
psychology.
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THE TROUBLE WITH
TWIN STUDIES
A Reassessment of Twin Research in the
Social and Behavioral Sciences
Jay Joseph
First published 2015
by Routledge
711 Third Avenue, New York, NY 10017
and by Routledge
27 Church Road, Hove, East Sussex BN3 2FA
Routledge is an imprint of the Taylor & Francis Group, an
informa business
© 2015 Jay Joseph
The right of Jay Joseph to be identified as author of this work has
been asserted by him in accordance with sections 77 and 78 of the
Copyright, Designs and Patents Act 1988.
All rights reserved. No part of this book may be reprinted
or reproduced or utilized in any form or by any electronic,
mechanical, or other means, now known or hereafter invented,
including photocopying and recording, or in any information
storage or retrieval system, without permission in writing from the
publishers.
Trademark notice: Product or corporate names may be
trademarks or registered trademarks, and are used only for
identification and explanation without intent to infringe.
Library of Congress Cataloging-in-Publication Data
Joseph, Jay.
The trouble with twin studies : a reassessment of the research/
Jay Joseph.
pages cm
Includes bibliographical references and index.
1. Twins. 2. Twins—Psychology. I. Title.
HQ777.35.J67 2015
306.875—dc23
2014024510
ISBN: 978-1-138-81306-9 (hbk)
ISBN: 978-1-315-74838-2 (ebk)
Typeset in Sabon
by Swales & Willis Ltd, Exeter, Devon, UK
IN MEMORY OF MY PARENTS,
MARJORIE H. JOSEPH AND JAMES H. JOSEPH
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CONTENTS
List of Illustrations ix
Preface x
Acknowledgments xii
List of Abbreviations xiii
PART I
Studies of Reared-Apart Twins: Scientific Proof or
Scientific Illusion? 1
1 Introduction 3
2 Studies of Reared-Apart Twins: Origins,
Publications, and Scandal 17
3 Studies of Reared-Apart Twins:
The Critics Respond 61
4 Studies of Reared-Apart Twins: Basic Assumptions
and Potential Fallacies 75
5 The Minnesota Study of Twins Reared Apart I:
Biases, Assumptions, and Other Problem Areas 102
6 The Minnesota Study of Twins Reared
Apart II: IQ and Personality Studies 128
PART II
Studies of Reared-Together Twins 151
7 The MZT–DZT Equal Environment Assumption:
The Achilles Heel of the Classical Twin Method 153
vii
CONTENTS
8 Twin Research in Psychiatry 179
PART III
Approaching a Post-Behavioral-Genetics Era? 205
9 Molecular Genetic Research: The Ultimate Test
of Genetic Interpretations of Twin Studies 207
10 The Crumbling Pillars of Behavioral Genetics 222
11 A Human Genetics Parable 236
12 Summary and Conclusions 247
Appendix A: The Funding of MISTRA 253
Appendix B: A Little-Known Behavioral Genetic
Adoption Study Whose Results Contrast with
the MISTRA Personality Findings 259
Appendix C: List of Quotations from Twin
Researchers and Others Invoking the “Twins
Create Their Own Environment” Argument A
in Defense of the MZT–DZT Equal Environment
Assumption of the Twin Method: 1954–2014 267
Glossary 273
References 279
Index 308
viii
ILLUSTRATIONS
Figures
7.1 Circular Reasoning Used Since the 1950s in Support
of the Twin Method: Twin Researchers’ Argument A 159
Tables
1.1 Four Types of Pairs Studied in Twin Research 16
2.1 Environmental Similarities, Contact, and Relationship
of “Reared-Apart” MZA Twin Pairs: Information on All
19 Pairs Reported in the 1937 Newman, Freeman, and
Holzinger Study 25
2.2 Environmental Similarities, Contact, and Relationship
of “Reared-Apart” MZA Twin Pairs: Information on All
44 Pairs Reported in the 1962 Shields Study 31
2.3 Environmental Similarities, Contact, and Relationship
of “Reared-Apart” MZA Twin Pairs: Information on All
12 Pairs Reported in the 1965/1980 Juel-Nielsen Study 45
3.1 Summary of Problem Areas in TRA Studies as
Identified by the Critics 73
4.1 Environmental Influences Shared by Reared-Apart
Monozygotic Twin Pairs (MZAs) 96
4.2 Correlated Environments: Ascending Potential
Shared Environmental Influences Experienced by
Reared-Apart Monozygotic Twin Pairs (MZAs) 98
5.1 MISTRA Sample Sizes: 1981–2000 105
5.2 Some Implicit and Explicit MISTRA Assumptions 108
7.1 Environmental Dissimilarity among MZT and
DZT Twin Pairs: Levels of Identity Confusion and
Attachment 166
7.2 Behavioral Genetic and Psychiatric Genetic
Interpretations of Research Findings: Family
Studies versus the Twin Method 170
ix