Downloaded by [New York University] at 06:51 14 August 2016 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. Downloaded by [New York University] at 06:51 14 August 2016 This page intentionally left blank Downloaded by [New York University] at 06:51 14 August 2016 THE TROUBLE WITH TWIN STUDIES A Reassessment of Twin Research in the Social and Behavioral Sciences Jay Joseph Downloaded by [New York University] at 06:51 14 August 2016 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 Downloaded by [New York University] at 06:51 14 August 2016 IN MEMORY OF MY PARENTS, MARJORIE H. JOSEPH AND JAMES H. JOSEPH Downloaded by [New York University] at 06:51 14 August 2016 This page intentionally left blank Downloaded by [New York University] at 06:51 14 August 2016 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 Downloaded by [New York University] at 06:51 14 August 2016 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 Downloaded by [New York University] at 06:51 14 August 2016 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 Downloaded by [New York University] at 06:51 14 August 2016 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 PREFACE Many people have read that twin studies provide conclusive evidence that hereditary factors strongly influence IQ, personality, socially disapproved behavior, depression, schizophrenia, and most other types of behavior. Some people are undoubtedly skeptical of such claims, yet lack the argu- ments to be able to counter them. Based on my extensive knowledge of the twin studies of behavior literature, I decided to write this book to help supply such arguments in the context of the failure to discover genes for behavior at the molecular level. While working on my dissertation on the genetics of schizophrenia in the late 1990s, I noticed that there weren’t many critical writings on twin research. This was surprising, since it seemed obvious to me that genetic interpretations of twin studies were based on theoretical assumptions that were not true, even as most textbooks reported that they provided solid evidence in favor of genetics. I also became aware that twin research had been used in the past in support of harmful and unjust social and political policies. This provided additional motivation to examine twin research and other types of genetic studies very closely, which has resulted in two books and various other publications since 1998. In this book I bring the total twin research critical analysis together in one place and in much greater detail, with a special emphasis on reared-apart twin studies, and I incorporate new and updated perspectives, analyses, arguments, and evidence. I am a clinical psychologist examining the methods and publications of academic research from the outside looking in. Although many psycho- Downloaded by [New York University] at 06:51 14 August 2016 therapists are influenced by behavioral genetic research, most lean towards “environmentalism” because they witness the harmful effects of having experienced adverse environmental experiences every day in their clinical work. Although I am not a twin researcher by trade, the twin research critique is based largely on logic and statistics, on an understanding of human psychology and human societies, and on the lives and psychologi- cal makeup of twins growing up and living in these societies. Like most readers, I have encountered twins in daily life and have observed how x PREFACE they interact with each other, and how they are treated. The key assump- tions of twin research run counter to what most people intuitively under- stand about twins, their relationship with each other, and their social environments. My original intention had been to write a book that could be under- stood by a larger audience, but as the work progressed I realized that this would be a more difficult task than I first imagined. At the same time, I have tried to cover the main topics and controversies as simply as possible. I have done my best to review and analyze the twin research literature and the molecular genetic literature in a manner that can be followed and understood by people unfamiliar with these fields. This is a book about the fallacies of twin studies and the failure to discover genes for human behavioral differences, and the relationship between the two. Jay Joseph Downloaded by [New York University] at 06:51 14 August 2016 xi ACKNOWLEDGMENTS Many people provided important assistance while I was writing this book. I have especially benefitted from the knowledge, wisdom, advice, and updates from the members of a critical genetics e-mail group, unofficially known as “The Forum.” In addition, I want to thank Ken Richardson and M. C. Jones for reading and commenting on several key chapters. I would also like to thank Claudia Chaufan, David Cohen, Galina Gerasimova, David Jacobs, Andrew Kimbrell, Richard M. Lerner, Journal of Mind and Behavior Editor Raymond C. Russ, William H. Tucker, the Editors of GeneWatch magazine, and Stephanie Welch for their help and sup- port. I also thank Routledge and the Taylor & Francis Group for their willingness to publish a controversial book such as this one, and I thank George Zimmar and Elizabeth Lotto of Routledge for their support and assistance.