Gay, straight, and the reason why : the science of sexual orientation PDF
Preview Gay, straight, and the reason why : the science of sexual orientation
i Gay, Straight, and the Reason Why ii iii Gay, Straight, and the Reason Why The Science of Sexual Orientation SECOND EDITION SIMON LeVAY 1 iv 3 Oxford University Press is a department of the University of Oxford. It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide. Oxford is a registered trade mark of Oxford University Press in the UK and certain other countries. Published in the United States of America by Oxford University Press 198 Madison Avenue, New York, NY 10016, United States of America. © Oxford University Press 2011, 2017 First issued as an Oxford University Press paperback, 2012 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, by license, or under terms agreed with the appropriate reproduction rights organization. Inquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above. You must not circulate this work in any other form and you must impose this same condition on any acquirer. Library of Congress Cataloging- in- Publication Data Names: LeVay, Simon, author. Title: Gay, straight, and the reason why : the science of sexual orientation / Simon LeVay. Description: Second edition. | Oxford ; New York : Oxford University Press, [2017] | Includes bibliographical references and index. Identifiers: LCCN 2016006377 (print) | LCCN 2016014053 (ebook) | ISBN 9780190297374 (pbk. : alk. paper) | ISBN 9780190297381 (UPDF) | ISBN 9780190297398 (EPUB) Subjects: LCSH: Sexual orientation. | Sex (Psychology) | Sex (Biology) Classification: LCC BF692 .L476 2017 (print) | LCC BF692 (ebook) | DDC 155.3/4—dc23 LC record available at http://lccn.loc.gov/2016006377 This material is not intended to be, and should not be considered, a substitute for medical or other professional advice. Treatment for the conditions described in this material is highly dependent on the individual circumstances. And, while this material is designed to offer accurate information with respect to the subject matter covered and to be current as of the time it was written, research and knowledge about medical and health issues is constantly evolving and dose schedules for medications are being revised continually, with new side effects recognized and accounted for regularly. Readers must therefore always check the product information and clinical procedures with the most up-to-date published product information and data sheets provided by the manufacturers and the most recent codes of conduct and safety regulation. The publisher and the authors make no representations or warranties to readers, express or implied, as to the accuracy or completeness of this material. Without limiting the foregoing, the publisher and the authors make no representations or warranties as to the accuracy or efficacy of the drug dosages mentioned in the material. The authors and the publisher do not accept, and expressly disclaim, any responsibility for any liability, loss, or risk that may be claimed or incurred as a consequence of the use and/ or application of any of the contents of this material. 1 3 5 7 9 8 6 4 2 Printed by Sheridan Books, Inc., United States of America v CONTENTS Preface to the Second Edition vii Introduction ix 1. What Is Sexual Orientation? 1 2. Why We Need Biology 15 3. The Outline of a Theory 25 4. Childhood 39 5. Characteristics of Gay and Straight Adults 51 6. The Role of Sex Hormones 67 7. The Role of Genes 85 8. The Brain 105 9. The Body 123 10. The Older- Brother Effect 135 11. Beyond Gay and Straight 147 12. Conclusions 163 Notes 179 Glossary 193 Bibliography 199 Author Index 235 Subject Index 237 v vi vii PREFACE TO THE SECOND EDITION The five years that have passed since the publication of the first edition of this book have seen considerable progress in our understanding of how sexual ori- entation develops. Molecular geneticists have come closer to identifying “gay genes.” Brain scientists have probed deeper into the neural wiring that under- lies sexual attraction. Psychologists have given us a clearer view of the cogni- tive and personality traits that distinguish gay people from straight people. They have also helped us better understand how a trait as counterintuitive as homosexuality can persist over the generations and why it exists in most human cultures. To cover these advances I have added mention of over 170 research papers that have appeared since I wrote the first edition. In general, the recent studies strengthen the idea that gay people differ from straight people in more than the direction of their sexual feelings. There is great diversity among lesbians and gay men, to be sure, but in general ho- mosexuality is part of a collection of gender- atypical traits, just as heterosex- uality is part of a collection of gender- typical traits. These different “packages” arise because the sexual differentiation of the brain goes forward differently in individuals destined to become gay adults as compared with their same- sex heterosexual peers. Differences in genes, sex hormones, and their interactions with the developing brain are what cause this divergence. Some of the recent findings are pointing in interesting new directions, however. There is increasing evidence, for example, that sexual orientation is affected by epigenetic processes. These are processes that involve chemical alterations to the genome but not to the DNA base sequence itself— the “let- ters” of the genetic code. Another area of active inquiry is the “older- brother effect”— the observation that boys with older brothers have an increased likeli- hood of becoming gay men. Canadian researchers believe that they are homing in on the biological basis for this effect. Perhaps most significantly, it’s becoming obvious that there is much more to sexual attraction than “gay” and “straight.” Bisexuality, asexuality, attraction vii viii viii Preface to different age groups,and the various kinds of gay sexuality indicated by the colloquial terms “butch,” “femme,” “top,” and “bottom”— all these have begun to attract the attention of biologically oriented researchers. So has transexual- ity, which has some features in common with homosexuality. I have added a new chapter, titled “Beyond Gay and Straight” (Chapter 11), that is devoted to these other important aspects of sexuality and gender. The University of Lethbridge, Alberta, hosts a conference every few years under the title “The Puzzle of Sexual Orientation.” The 2015 conference, organ- ized by Paul Vasey, Kelly Suschinksy, and Jean- Baptiste Leca, attracted many of the leading researchers in the field. In this book I mention some of the re- search findings presented at the conference. It is expected that most of these presentations will be published in a special edition of Archives of Sexual Behavior sometime in 2016. ix INTRODUCTION In August of 1991, when I was a neuroscientist working at the Salk Institute for Biological Studies in San Diego, I published a short research paper in the journal Science. The article was titled “A Difference in Hypothalamic Structure Between Heterosexual and Homosexual Men.” It attracted a great deal of in- terest from the media, the general public, and the scientific community, and it helped trigger a wave of new research into an age- old question: What makes people straight or gay? The hypothalamus* is a small region at the base of the brain that helps reg- ulate several of our instinctual drives, including our sex drive. In my study, I took specimens of the hypothalamus from men and women who had died and were undergoing autopsy. About half of the men were gay. I focused on a region at the front of the hypothalamus that is known to be involved in regulating the sexual behaviors typically shown by males. Within this region lies a rice- grain- sized collection of nerve cells named INAH3, which is usually larger in men than in women. I confirmed this basic sex difference. In addition, however, I found that INAH3 was significantly smaller, on average, in the gay men than in the straight men. In fact, there was no difference in size between INAH3 in the gay men and the women in my sample. I interpreted this finding as a clue that biological processes of brain development may influence a man’s sexual orientation. I was certainly not the first person to have thought about sexual orientation from a biological perspective. A hundred years ago a German physician and sex researcher, Magnus Hirschfeld, proposed that brain development followed different paths in fetuses destined to become gay adults and those destined to become straight. Just a year before I published my study, a Dutch group re- ported that another cluster of cells in the hypothalamus, the suprachiasmatic * Most technical terms are italicized at first mention and are defined in the Glossary. ix
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