Straight science? Homosexuality is a problem for evolutionary theory. How does a non- reproductive sexual preference survive? There is increasing evidence for a biological basis to homosexuality, not least the discovery in 1993 of markers for a gay gene. Yet Darwinism, the most widely accepted evolutionary theory, emphasises successful reproduction and the ‘survival of the fittest’. How do we explain a lifetime preference for non-reproductive sex? What does evolutionary theory make of a behaviour that seems to be positively selected yet produces fewer children? Surely homosexuality defies evolutionary explanation? Is there an evolutionary advantage to homosexuality? Straight Science? examines the latest research and considers these questions from an evolutionary perspective. While social constructivism offers explanations in terms of social learning and cultural preferences, the body of evidence for a genetic predisposition to homosexuality grows. The implication of adopting the social constructivist view of homosexual sex is that such sex is merely misdirected and therefore futile, but far from dying out it continues through the ages and across cultures. Jim McKnight provides a comprehensive summary of the research on the biology of homosexuality, including twin studies; hormonal assays; anatomical, functional and molecular biology differences; and the search for a gay gene. The book considers biological and social evolutionary theories of the causation of homosexuality, and puts forward a model of the most likely causes. It concludes with an overview of the adequacy of social constructivist challenges to a biosocial perspective on homosexuality. Jim McKnight is Chair of the Psychology Department at the University of Western Sydney, Macarthur, and author of six books including Social Psychology (1994) (with J.E.Sutton). Straight science? Homosexuality, evolution and adaptation Jim McKnight London and New York First published 1997 by Routledge 11 New Fetter Lane, London EC4P 4EE This edition published in the Taylor & Francis e-Library, 2005. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.” Simultaneously published in the USA and Canada by Routledge 29 West 35th Street, New York, NY 10001 © 1997 Jim McKnight All rights reserved. No part of this book may be reprinted or reproduced or utilised 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. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data A catalogue record for this book has been requested ISBN 0-203-36047-8 Master e-book ISBN ISBN 0-203-37303-0 (Adobe eReader Format) ISBN 0-415-15772-2 (hbk) ISBN 0-415-15773-0 (pbk) For Des Crawley, who defended this work, ad utrumque paratus Contents List of figures and tables viii Preface ix 1 Is male homosexuality adaptive? 1 Homosexuality, futile sex? 3 Orientation or preference? 5 How many gay men and just what is homosexuality anyway? 6 What do we know and what do we want to know about 7 homosexuality? Explaining homosexuality? 8 Is evolution social? 14 Where to from here? 17 2 A biology of homosexuality 19 Homosexuality, a sexual inversion? 22 Does genetic inversion model homosexuality? 24 A chemical imbalance: the de-androgenised foetus theories 27 An anatomical difference? 39 Functional differences? 41 A genetic variation? 44 Discovering a difference: familial studies 45 A world of difference? Xq28 53 A typology of homosexuality 59 So where are we now? 62 3 Homosexuality as physical evolution 65 vi Is homosexuality really adaptive? 65 Models of balance polymorphism: a balanced superior 76 heterozygotic fitness Models of balance polymorphism: sperm competition 92 Models of balance polymorphism: density and frequency- 98 dependent selection Models of balance polymorphism: frequency-dependent sexual 102 selection Homosexuality as an evolutionary byproduct 115 Models of evolutionary futility: an overloving effect 117 Models of evolutionary futility: homosexuality—a continuously 120 occurring mutation? 4 Homosexuality as social evolution 125 Kin selection 128 Kin selection for a homosexuality gene 129 Kin selection for genes other than homosexuality 136 Kin selection and a social preference for homosexuality 140 Parental manipulation 145 A social adjustment 150 The central theoretical problem of sociobiology 156 5 The seven deadly sins of sociobiology 163 The first deadly sin: we are animals 164 The second deadly sin: explaining homosexuality is unnecessary 167 and misguided The third deadly sin: trivial pursuits 170 The fourth deadly sin: a creeping reductionism 172 The fifth deadly sin: sly determinism 177 The sixth deadly sin: sociobiology is morally bankrupt 178 The seventh deadly sin: sociobiology is sexist 180 Conclusions 184 vii Glossary 189 Bibliography 195 Author index 213 Subject index 219 Figures and Tables FIGURES 2.1 Changes in LH in response to a single injection of Premarin 35 3.1 Types of natural selection 71 3.2 Proportion of 1881 generation in subsequent generation 86 3.3 Mean values for lowest acceptable intelligence and involvement 110 level 3.4 Double-matings, contraceptive use, and fertility 111 4.1 Population penetrance of direct versus indirect inclusive fitness 134 4.2 Reproductive success of bisexual and heterosexual women 152 TABLES 2.1 Maternal and paternal line gay relatives of homosexual men 55 3.1 Comparative content of fantasy material: frequency of 80 occurrence 3.2 Equilibrium in simulated selection experiment due to rare-male 100 advantage in Drosophila pseudoobscura 4.1 Reproductive success and descendants via kin selection and 133 direct reproduction Preface At the risk of entirely blowing my credibility at the outset, let me start this speculative look at male homosexuality by saying that it is written by a straight researcher who is less interested in explaining homosexuality, or in passing comment on it as a lifestyle, than in the perspective of a theorist confronted with an enormous difficulty threatening the tidy order of his theoretical universe. Homosexuality is a major problem for those like myself who believe that Darwinism is the great unifying force which social theory, particularly psychology, so desperately needs for internal coherence. Unfortunately, few would agree and there are many challenges to a Darwinistic view of the social order. Perhaps one of the cleverest challenges to confront evolutionary theory is homosexuality. Homosexuality seems to be a tailor-made rebuttal of the great evolutionary credo—survival of the fittest. How do we explain what is often a lifelong preference for non- reproductive sex? Surely homosexuality defies evolutionary explanation? This is a clever criticism. While far from being a life against nature, homosexuality seems to contradict the Darwinian logic of individual reproductive success. Yet any number of surveys tell us that there are many homosexuals, and history attests to homosexuality’s antiquity. If homosexuality is ‘futile’ sex, why are gay men still with us? Despite the weight of a historical bad press, which sees homosexuality as a pathological inversion of normal heterosexuality, its continuance suggests it is an adaptive feature of evolution. What selective advantages might homosexuals enjoy? How is such a widespread social behaviour to be explained? In this book we set out to answer these and other questions from an evolutionary perspective. While many would argue that Darwinism adds little to our understanding of homosexuality, nevertheless, causation is an intriguing puzzle and, if a diverse gay literature is any guide, is often a source of confusion for homosexuals themselves. Apart from being a purely intellectual puzzle, these questions also touch on much broader issues about the nature of biosocial research. If the genesis of a book arises from dissatisfaction, mine was professional. Whatever the truth about homosexuality, as a social psychologist I came to see that social constructivism, my profession’s dominant paradigm, had