Discovering Human Sexuality THIRD EDITION

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important anatomy and terminology.

Companion Website

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WEB ACTIVITIES The following activities are available on the site.

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ADDITIonAL fEATurES Chapter outlines & Summaries provide a thorough review of each chapter.

Learning objectives in the form of short-answer questions help you focus on the important topics in each chapter.

Quizzes with multiple choice and essay questions allow you to test your comprehension of each chapter and synthesize and apply the concepts you have learned. (Instructors must register in order for their students to be able to take the quizzes.)

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2.1 The Vulva . . . . . . . . . . . . . . . . . . 22

2.2 Internal Anatomy of the Vulva. . . . . . . . . . . . . . . . . . . . . . . . 29

2.3 The Female Reproductive Tract, Part 1. . . . . . . . . . . . . . . 30

2.4 The Female Reproductive Tract, Part 2. . . . . . . . . . . . . . . 30

2.5 The Pap Test. . . . . . . . . . . . . . 34

2.6 Ovarian and Uterine Cycles . . . . . . . . . . . . 38, 42, 43

2.7 Main Processes of the Menstrual Cycle . . . . . . . . . . 43

2.8 The Reproductive Years . . . . . . . . . . . . . . . . . . . . . . . 44

2.9 Internal Structure of the Lactating Breast. . . . . . . . . . 51

_____________________________________

3.1 The Male External Genitalia . . . . . . . . . . . . . . . . . . . 62

3.2 Internal Structure of the Erect Penis and the Urethra . . . . . . . . . . . . . . . . . . . . . 65

3.3 The Mechanism of Erection . . . . . . . . . . . . . . . . . . . . 69

3.4 The Scrotum and Its Contents. . . . . . . . . . . . . . . . . . . 71

3.5 Internal Structure of the Testicle and Epididymis. . . . . . . . . . . . . . . . . 73

3.6 The Male Reproductive Tract . . . . . . . . . . . . . . . . . . . . . . . . 74

3.7 Anatomy of the Prostate. . . . . . . . . . . . . . . . . . . . 76

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4.1 Development of the Male and Female Reproductive Tracts. . . . . . . . . . . . . . . . . . . . . . . 89

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7.1 Definitions of Sexual Relationships . . . . . . . . . . . 192

7.2 Sternberg’s Seven Types of Love . . . . . . . . . . . . . . . . . . . 209

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8.1 How a Home Pregnancy Test Works . . . . . . . . . . . . . . 229

8.2 In Vitro Fertilization. . . . . 232 _____________________________________

9.1 Vasectomy . . . . . . . . . . . . . . 291

9.2 Tubal Sterilization . . . . . . 292 _____________________________________

15.1 Milestones in the Global HIV/AIDS Pandemic . . . 480

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a.1 Mitosis . . . . . . . . . . . . . . . . . . . 552

a.2 Mitosis Time-Lapse Video . . . . . . . . . . . . . . . . . . . . . 552

a.3 Meiosis. . . . . . . . . . . . . . . . . . . 552

a.4 Differences and Similarities between Meiosis and Mitosis . . . . . . . . . . . . . . . . . . . 552

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Discovering Human Sexuality

third edition

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Sinauer Associates, Inc.  Publishers Sunderland, Massachusetts U.S.A.

Discovering Human Sexuality

third edition

Simon LeVay west hollywood, california

Janice Baldwin university of california

santa barbara

John Baldwin university of california

santa barbara

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Discovering Human Sexuality, Third Edition Copyright © 2015 by Sinauer Associates, Inc. All rights reserved. This book may not be reproduced in whole or in part without permission from the publisher.

For information or to order, address: Sinauer Associates P.O. Box 407 Sunderland, MA 01375 USA Fax: 413-549-1118 E-mail: publish@sinauer.com Internet: www.sinauer.com

Library of Congress Cataloging-in-Publication Data

LeVay, Simon. Discovering human sexuality / Simon LeVay, West Hollywood, CA, Janice Baldwin, University of California, Santa Barbara, John Baldwin, University of California, Santa Barbara. — Third edition. pages cm ISBN 978-1-60535-275-6 (alk. paper) 1. Sex (Psychology) 2. Sex (Biology) 3. Sex–Social aspects. I. Baldwin, Janice I. II. Baldwin, John D., 1941- III. Title. BF692.L47 2015 306.7–dc23 2014044757

Printed in the USA 5 4 3 2 1

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Simon LeVay, PhD is a British-born neuroscientist turned writer and teacher. He has served on the faculties of Harvard Medical School and the Salk Institute for Biologi- cal Studies and has taught at Harvard; the University of California, San Diego; and Stanford University. He is best known for a 1991 study that described a difference in brain structure between heterosexual and homosexual men; this study helped spark a wealth of new research on the biology of sexual orientation. LeVay is the author or coauthor of 11 books, the most recent of which is a historical novel, The Donation of Constantine (Lambourn, 2013).

Janice Baldwin, PhD and John Baldwin, PhD are sociologists at the University of California, Santa Barbara. They have been collaborators in numerous studies and coauthored many articles in the areas of play, creativity, sexuality, and sex educa- tion, as well as the textbook Behavior Principles in Everyday Life (Prentice Hall). John Baldwin’s latest book is Ending the Science Wars (Paradigm, 2008). The Baldwins co- teach an undergraduate human sexuality course that is regularly voted best course at UCSB. They also teach an advanced seminar course on the same topic. Their students run a sex-ed website, SexInfoOnline (www.SexInfoOnline.com).

About the Authors

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chapter 1 Sexuality: Pathways to Understanding 3

chapter 2 Women’s Bodies 21

chapter 3 Men’s Bodies 61

chapter 4 Sex, Gender, and Transgender 87

chapter 5 Attraction, Arousal, and Response 123

chapter 6 Sexual Behavior 155

chapter 7 Sexual Relationships 191

chapter 8 Fertility, Pregnancy, and Childbirth 227

chapter 9 Contraception and Abortion 265

chapter 10 Sexuality across the Life Span: From Birth to Adolescence 305

chapter 11 Sexuality across the Life Span: Adulthood 335

chapter 12 Sexual Orientation 365

chapter 13 Atypical Sexuality 401

chapter 14 Sexual Disorders 431

chapter 15 Sexually Transmitted Infections 461

chapter 16 Sexual Assault, Harassment, and Partner Violence 493

chapter 17 Sex as a Commodity 523

appendix a Sex and Evolution 551

appendix b Sex and the Nervous System 573

Brief Contents

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Contents

Sexuality Is a Broader Concept than Sex 4

Studying Sexuality Has Practical Benefits 4

Sexuality Has Changed over Time 4 Sexuality has been influenced by evolution 5

Society has changed sexuality 5

Box 1.1 Meet My Dads 6

Marriage has been transformed 8

Sex has become a topic of social discourse 9

Social movements have affected sexuality 10

Box 1.2 Freud and Hirschfeld: Contrasting Theories on Sexual Orientation 11

Sexuality Can Be Studied with a Wide Variety of Methods 12

Biomedical research focuses on the underlying mechanisms of sex 12

Psychology includes diverse approaches to sexuality 13

Sociologists focus on the connection between sex and society 15

The economic approach weighs costs and benefits 16

Chapter 1 Sexuality: Pathways to Understanding 3

A Woman’s Vulva Includes Her Mons, Labia, Vaginal Opening, and Clitoris 22

There is more to the clitoris than meets the eye 24

Box 2.1 Female Genital Cutting 26

The appearance of the vaginal opening is variable 27

The Vagina Is the Outermost Portion of the Female Reproductive Tract 29

The vagina undergoes changes during arousal 31

The G-spot is a controversial erogenous zone 31

The Anus Can Also Be a Sex Organ 32

The Uterus Serves a Double Duty 32 Box 2.2 Genital Self-Examination 33

Cancer can affect the cervix or the endometrium 34

Other uterine conditions include fibroids, endometriosis, abnormal bleeding, and prolapse 35

Should hysterectomy be so common? 36

The Oviducts Are the Site of Fertilization 36

The Ovaries Produce Ova and Sex Hormones 37

Box 2.3 The Feedback Loop that Controls Female Hormone Production 38

Menstruation Is a Biological Process with Cultural and Practical Aspects 40

Box 2.4 Menstrual Synchrony: Reality or Myth? 41

The menstrual cycle has three phases 42

The cycle is driven by hormonal changes 43

Does the menstrual cycle influence sexuality? 44

Attitudes toward menstruation vary 44

Box 2.5 Attitudes toward Menstruation 45

Women use pads, tampons, or cups during menstruation 46

Menstrual Problems Are Common but Treatable 48

Menstrual pain may or may not reflect underlying pelvic disease 48

The premenstrual syndrome has physical and psychological aspects 48

Menstruation stops during pregnancy—and for many other reasons 49

Sex steroids affect systems in women besides the reproductive tract 50

The Breasts Have Both Erotic and Reproductive Significance 50

Chapter 2 Women’s Bodies 21

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x CONTENTS

Breast cancer mortality can be reduced 51

Many factors affect the risk of breast cancer 52

Early detection is important 54

Box 2.6 Breast Self-Examination 55

Treatment depends on the diagnostic findings and the woman’s choice 56

Most women with breast cancer return to an active sex life 56

The Male External Genitalia Are the Penis and Scrotum 62

The penis combines erotic, reproductive, and urinary functions 63

Box 3.1 Male Circumcision 64

Box 3.2 How Big Should a Penis Be? 67

Box 3.3 Diphallia 68

Penile Erection Involves Nerves, Blood, and Chemistry 68

Erection is filling of the penis with blood 69

Muscles are also involved in erection 70

Erections occur during sleep 70

The scrotum regulates the temperature of the testicles 70

The Testicles Produce Sperm and Sex Hormones 71

Other glands contribute secretions to the semen 73

What is semen? 74

Box 3.4 Disorders of the Testicles 75

Box 3.5 Disorders of the Prostate Gland 76

Ejaculation Requires Coordination of Muscles and Glands 77

The testicles secrete sex hormones 78

Box 3.6 Designer Steroids 80

The brain and pituitary gland regulate hormone levels 80

Nudity Is Culturally Regulated 81

Chapter 3 Men’s Bodies 61

Genes and Hormones Guide Sex Development 88

Female and male reproductive tracts develop from different precursors 88

Female and male external genitalia develop from the same precursors 89

The gonads descend during development 91

Puberty is sexual maturation 92

The brain also differentiates sexually 92

Sex Development May Go Awry 93 Chromosomal anomalies affect growth and fertility 93

The gonads or genitals may be sexually ambiguous 95

Box 4.1 My Life with Androgen Insensitivity Syndrome 96

Gender Is a Central Aspect of Personhood 97 Gender identity might not match anatomical sex 97

Women and men differ in a variety of cognitive and personality traits 98

There are Many Sex Differences in Sexuality 99

Many gender differences arise early in life 101

Biological Factors Influence Gender 102

Evolutionary forces act differently on females and males 102

Box 4.2 Gendered Play in Primates 103

Experiments demonstrate a role for sex hormones 103

Life Experiences Influence Gender 105 Gender is molded by socialization 105

Cognitive developmental models emphasize thought processes 108

Gender Development Is Interactive 108 Box 4.3 The Boy Who Was Raised as a Girl 109

Transgender People Cross Society’s Deepest Divide 110

Box 4.4 Trans Men and Women in Cross- Cultural Perspective 111

Transexual individuals are of more than one kind 112

Changing sex is a multistage process 113

Some transgender people do not want surgery 115

Box 4.5 How Should We Treat Gender- Dysphoric Children? 116

Trans people struggle for awareness and acceptance 118

Chapter 4 Sex, Gender, and Transgender 87

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CONTENTS xI

Sexual Attraction: It Takes Two 124 Beauty is not entirely in the eye of the beholder 124

Culture influences the attractiveness of bodies 126

Attractiveness involves senses besides vision 129

Behavior and personality influence sexual attractiveness 130

Box 5.1 Sex Pheromones 131

Familiarity may increase or decrease attraction 133

Perceived attractiveness varies around the menstrual cycle 135

Judgments of attractiveness change as people get to know each other 136

Asexual women and men do not experience sexual attraction 136

Sexual Arousal Has Multiple Roots 137 Fantasy is a common mode of sexual arousal 138

Arousal occurs in response to a partner 139

Hormones influence sexual arousability 140

Conditioning may influence arousal 141

Box 5.2 Aphrodisiacs and Drugs 142

Sexual Arousal Follows a Response Cycle 143

In the excitement phase, genital responses begin 143

In the plateau phase, arousal is maintained 144

Orgasm is the climax of sexual arousal 145

Box 5.3 Female Ejaculation 146

Brain imaging suggests where orgasm may be experienced 147

Box 5.4 Foot Orgasms 148

In the resolution phase, arousal subsides 149

The phases may be linked in different ways 149

Some people experience multiple orgasms 150

Men experience a refractory period 151

The Masters and Johnson cycle may be incomplete 151

Chapter 5 Attraction, Arousal, and Response 123

People Derive Pleasure from Diverse Sexual Behaviors 156

Masturbation Is a Very Common Form of Sexual Expression 156

Box 6.1 Sex and Happiness 157

Negative attitudes toward masturbation are still prevalent 158

Several demographic factors influence masturbation 158

Women use more diverse techniques of masturbation than men 160

Gay people masturbate more than heterosexuals 161

Different cultures have different attitudes toward masturbation 161

The Kiss Represents True Love— Sometimes 162

Sexual Touching Takes Many Forms 163

Oral Sex Is Increasingly Popular 164 Fellatio is oral stimulation of the penis 164

Cunnilingus is oral stimulation of the vulva 165

Most Heterosexual Sex Includes Coitus 166 Coitus can be performed in many different

positions 166

The man-above position is a traditional favorite 167

The women’s movement encouraged alternative positions 168

Box 6.2 Progress in Coitus Research 169

Box 6.3 Sex and the Seasons 171

Anal Sex May Be a Part of Either Heterosexual or Male Homosexual Behavior 172

Men and Women May Have Different Preferences for Sexual Encounters 173

Sex Toys Are Used to Enhance Sexual Pleasure 174

Sex May Be in Groups 177 Box 6.4 What Is “Great Sex”? 178

Sexual Behavior and Attitudes Vary among Cultures 179

The Kama Sutra is the classic work on how to make love 179

The Aka emphasize the importance of frequent sex 181

Many Disabled People Have Active Sex Lives 181

Box 6.5 On Seeing a Sex Surrogate 182

Many intellectually disabled people are competent to make sexual choices 183

Spinal cord injuries present a major challenge to sexual expression 184

Arthritis is the number one disability affecting sex 186

Chapter 6 Sexual Behavior 155

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xII CONTENTS

Sexual Relationships Are Motivated by Many Factors 192

Moral Judgments about Sex Depend on Its Context 192

Demographic factors affect sexual attitudes 192

Box 7.1 Who May Marry? 194

Americans’ Attitudes Have Changed over Time 195

Casual Sex Has More Appeal to Men than to Women 196

Hooking up—the new norm? 196

Box 7.2 Straight Women, Gay Sex 197

Hookups can be pleasurable or abusive 198

Hookups can have positive or negative consequences 200

Casual sex is more accepted in the gay male community 200

Negotiating sex involves flirting 201

Box 7.3 Flirting Styles 202

Non-Cohabiting Relationships Are Often Short-Lived 203

Same-sex relationships have their own scripts 205

Non-cohabiting relationships may evolve rapidly 205

Love Cements Many Sexual Relationships 206

There are different kinds of love 206

Being in love may be the justification for marriage or sex 206

Liking and reciprocal attraction precede falling in love 206

Researchers are probing the biological basis of love 207

One theory proposes that love has three components 208

Unrequited Love Is Painful for Both Parties 210

Box 7.4 Love Stories 211

The rejector may experience guilt 212

Life Experiences Mold Our Sexual Relationships 213

Relationship styles are influenced by childhood attachments 213

Couples in relationships resemble each other 213

Communication Is a Key Factor in the Success of Relationships 214

Communication may be inhibited by upbringing or by the gender barrier 214

Relationship and marriage education teaches communication skills 215

How couples deal with conflict affects the stability of their relationship 216

Love, Jealousy, and Infidelity Are Intertwined 218

Jealousy can have a positive function 218

Extra-Pair Relationships Have Many Styles and Motivations 219

Personal and evolutionary factors influence infidelity 220

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