Discovering Human Sexuality, Fourth Edition

An evidence-based, accessible introduction to the study of sexuality and the diverse ways in which it brings joys and challenges to our lives. Now in its fourth edition, Discovering Human Sexuality has established itself as a popular and widely praised text that respects diversity both in the sexual world and among the students who read it. The backgrounds of the authors--in biology, sociology, teaching, and writing--have made possible a text that is multidisciplinary, authoritative, sex-positive, and a delight to read.

The scope of Discovering Human Sexuality ranges from homosexuality in ancient Greece to the recent Harvey Weinstein sexual harassment scandal while covering a stunningly diverse array of topics. Questions considered include: How does the menstrual cycle work? What's "splitting the bamboo"? Can premature ejaculation be treated? If a man has undetectable levels of HIV, can he have sex without condoms? Which sex offenders will repeat their crimes? Is there a gay gene? What's wrong with polygamy? Is emergeny contraception abortion? Which bathrooms should trans women use? This book gives factual answers to important questions and provides material for informed debate for issues without a single solution.

Simon LeVay, Ph.D is a British born neuroscientist turned science writer and teacher. He has served on the faculty of Harvard Medical School and the Salk Institute for Biological Studies, and has taught at Harvard, the University of California, and Stanford University. He is the author or coauthor of 11 books, including Gay, Straight, and the Reasn Why: The Science of Sexual Orientation. Janice Baldwin, Ph.D, and John Baldwin, Ph.D are sociologists at the University of Californina, Santa Barbara. They have been collaborators and writers on many papers and projects in the area of sex, sexuality, and sex education. The Baldwins co-teach a very dynamic undergraduate Human Sexuality course at UCSB, that has been regularly voted the Best Course there, and they have been named Best Professors multiple times. They also co-created--with their upper division students--a sex information website: SexInfoOnline.

Chapter 1. Sexuality: Pathways to Understanding
Sexuality Is a Broader Concept than Sex
Studying Sexuality Has Practical Benefits
Sexuality Has Changed over Time
Sexuality has been influenced by evolution
Society has changed sexuality
Box: Meet My Dads
Urbanization has been a curse and a blessing
Marriage has been transformed
Box: The Media: TV or Not TV?
Sex researchers followed diverse paths
Box: Freud and Hirschfeld: Contrasting Theories on Sexual Orientation
Sexuality Can Be Studied with a Wide Variety of Methods
Biomedical research focuses on the underlying mechanisms of sex
Psychology includes diverse approaches to sexuality
Cultural anthropology focuses on sexual diversity across cultures
Sociologists focus on the connection between sex and society
The economic approach weighs costs and benefits
Organizations promote sex research

Chapter 2. Women's Bodies
The Whole Body Is an Erogenous Zone
A Woman's Vulva Includes Her Mons, Labia, Vaginal Opening, and Clitoris
There is more to the clitoris than meets the eye
Box: Pubic Hair Removal
The appearance of the vaginal opening is variable
Box: Female Genital Cutting
The Vagina Is the Outermost Portion of the Female Reproductive Tract
The vagina undergoes changes during arousal
The G-spot is a controversial erogenous zone
The Anus Can Also Be a Sex Organ
Box: Genital Self-Examination
The Uterus Serves a Double Duty
Cancer can affect the cervix or the endometrium
Other uterine conditions include fibroids, endometriosis, abnormal bleeding, and prolapse
Should hysterectomy be so common?
The Oviducts Are the Site of Fertilization
The Ovaries Produce Ova and Sex Hormones
Box: The Feedback Loop That Controls Female Hormone Production
Menstruation Is a Biological Process with Cultural and Practical Aspects
The menstrual cycle has three phases
The cycle is driven by hormonal changes
Does the menstrual cycle influence sexuality?
Attitudes toward menstruation vary
Women use pads, tampons, or cups during menstruation
Box: Where Tampons Aren't an Option
Menstrual Problems Are Common but Treatable
Menstrual pain may or may not reflect underlying pelvic disease
Premenstrual syndrome has physical and psychological aspects
Menstruation stops during pregnancy--and for other reasons
Sex steroids affect more than the reproductive tract
The Breasts Have Both Erotic and Reproductive Significance
Breast Cancer Mortality Can Be Reduced
Many factors affect the risk of breast cancer
Clinical breast exams save lives
Treatment depends on the diagnostic findings and the woman's choice

Chapter 3. Men's Bodies
The Male External Genitalia Are the Penis and Scrotum
The penis combines erotic, reproductive, and urinary functions
Box: Male Circumcision
Some disorders affect penile function
Box: How Big Should a Penis Be?
Box: Diphallia
Penile Erection Involves Nerves, Blood, and Chemistry
Erection is the filling of the penis with blood
Muscles are also involved in erection
Erections occur during sleep
The scrotum regulates the temperature of the testicles
The Testicles Produce Sperm and Sex Hormones
Box: Declining Sperm Counts
Cancer and other disorders can affect the testicles
Other glands contribute secretions to the semen
What is semen?
Ejaculation Requires Coordination of Muscles and Glands
The testicles secrete sex hormones
Box: The Secret Life of Semen
The brain and pituitary gland regulate hormone levels
Box: Steroids and Sports
Nudity Is Culturally Regulated

Chapter 4. Sex Development and Diversity
Genes and Hormones Guide Sex Development
Female and male reproductive tracts develop from different precursors
Female and male external genitalia develop from the same precursors
The gonads descend during development
Puberty is sexual maturation
The brain also differentiates sexually
Sex Development Is Not Always Binary
Unusual sets of chromosomes affect growth and fertility
The gonads or genitals may be sexually ambiguous
Box: My Life with Androgen Insensitivity Syndrome
There Are Sex Differences in Many Mental Traits
Gender identity does not always match anatomical sex
Women and men differ in a variety of cognitive and personality traits
There are many differences in sexuality
Many sex differences arise early in life
Biological Factors Underlie Sex Differences
Evolutionary forces act differently on females and males
Box: Gendered Play in Primates
Experiments demonstrate a role for sex hormones
Life Experiences Mold Sex Roles
Girls and boys are socialized differently
Cognitive developmental models emphasize thought processes
Transgender People Challenge Society's Deepest Division
Box: The Boy Who Was Raised as a Girl
Transexual individuals are of more than one kind
Box: Trans Men and Women in Cross-Cultural Perspective
Changing sex is a multistage process
Many transgender people do not want surgery
Trans people struggle for awareness and acceptance
Box: Tempest in a Toilet

Chapter 5. Attraction, Arousal, and Response
Sexual Attraction: It Takes Two
Beauty is not entirely in the eye of the beholder
Culture influences the attractiveness of bodies
Box: Culture and Body Weight
Attractiveness involves senses besides vision
Behavior and personality influence sexual attractiveness
Familiarity may increase or decrease attraction
Perceived attractiveness varies around the menstrual cycle
Asexual women and men do not experience sexual attraction
Sexual Arousal Has Multiple Roots
Fantasy is a common mode of sexual arousal
Arousal occurs in response to a partner
Gonadal steroid hormones influence sexual arousability
Conditioning may influence arousal
Sexual Arousal Follows a Response Cycle
Box: Aphrodisiacs and Drugs
In the excitement phase, genital responses begin
In the plateau phase, arousal is maintained
Orgasm is the climax of sexual arousal
Box: Female Ejaculation
Brain imaging suggests where orgasm may be experienced
Box: Foot Orgasms
In the resolution phase, arousal subsides
The phases may be linked in different ways
Men experience a refractory period
Pituitary hormones influence the sexual response cycle
The Masters and Johnson cycle may be incomplete
People Derive Pleasure from Diverse Sexual Behaviors

Chapter 6. Sexual Behavior
Masturbation Is a Very Common Form of Sexual Expression
Box: Sex and Happiness
Negative attitudes toward masturbation are still prevalent
Several demographic factors influence masturbation
Women use more diverse techniques of masturbation than men
Gay people masturbate more than heterosexuals
The Kiss Represents True Love--Sometimes
Sexual Touching Takes Many Forms
Oral Sex Is Increasingly Popular
Fellatio is oral stimulation of the penis
Cunnilingus is oral stimulation of the vulva
Most Male-Female Sex Includes Coitus
Coitus can be performed in many different positions
Box: Progress in Coitus Research
The man-above position is a traditional favorite
The 1970s women's movement encouraged alternative positions
Anal Sex May Be a Part of Either Opposite-sex or Male Same-sex Behavior
Men and Women May Have Different Preferences for Sexual Encounters
Sex Toys Are Used to Enhance Sexual Pleasure
Sex May Be in Groups
Box: What Is "Great Sex"?
Sexual Behavior and Attitudes Vary Across Cultures
The Kama Sutra is the classic work on how to make love
Taoists recommended the avoidance of ejaculation
The Aka emphasize the importance of frequent sex
Box: Dry Sex
Many Disabled People Have Active Sex Lives
Many intellectually disabled people are competent to make sexual choices
Spinal cord injuries present a major challenge to sexual expression
Arthritis is the number one disability affecting sex
People Are Having Less Partnered Sex

Chapter 7. Sexual Relationships
Sexual Relationships Are Motivated by Many Factors
Demographic Factors Affect Sexual Attitudes
Box: Who May Marry?
Casual Sex Has More Appeal to Men than to Women
Hooking up--the new norm?
Box: Straight Women, Gay Sex
The hookup culture--some like it, some loathe it
Casual sex is more accepted in the gay male community
Negotiating sex involves flirting
Non-Cohabiting Relationships Are Often Short-Lived
Long-distance relationships can be very successful
Same-sex relationships have their own scripts
Non-cohabiting relationships may evolve rapidly
Love Cements Many Sexual Relationships
There are different kinds of love
Liking and reciprocal attraction precede falling in love
Researchers are probing the biological basis of love
Life Experiences Mold Our Sexual Relationships
Relationship styles are influenced by childhood attachments
Couples in relationships resemble each other
Communication Is a Key Factor in the Success of Relationships
Communication may be inhibited by upbringing or by the gender barrier
Marriage and relationship education teaches communication skills
How couples deal with conflict affects the stability of their relationships
In sexual relationships, sex matters
Box: Lasting Relationships: Gottman's Seven Principles
Love, Jealousy, and Infidelity Are Intertwined
Jealousy can have a positive function
Unrequited Love Is Painful for Both Parties
The rejector may experience guilt
Extra-Pair Relationships Have Many Styles and Motivations
Personal and evolutionary factors influence infidelity
Box: We Just Clicked
Extra-pair relationships are uncommon

Chapter 8. Fertility, Pregnancy, and Childbirth
Pregnancy and Childbirth Raise Major Health Concerns
The Fertilization of an Ovum Is Followed by Implantation
Box: Birth Facts
Pregnancy Is Confirmed by Hormonal Tests
Infertility Can Result from a Problem in the Woman or in the Man
A variety of factors can reduce sperm counts
Box: The Scent of an Ovum
Sperm can be donated
In vitro fertilization can circumvent many sperm problems
Abnormalities of the female reproductive tract may reduce fertility
Failure to ovulate can be dealt with by drugs or by egg donation
Box: Choosing Children's Sex
Surrogate mothers bear children for others
Adoption is limited by the supply of healthy infants
Fertility declines with age
Box: Commercial Gestational Surrogacy--An Ethical Minefield
Many Embryos Do Not Survive
Rh factor incompatibility can threaten second pregnancies
Ectopic pregnancy can endanger the mother's life
Pregnancy Is Conventionally Divided into Three Trimesters
The First Trimester Is a Period of Major Changes
Prenatal care provides health screening, education, and support
Adequate nutrition is vital to a successful pregnancy
Tobacco, alcohol, drugs, and radiation can harm the fetus
The Second Trimester Is the Easiest
Tests can detect fetal abnormalities
Sex during pregnancy is healthy
Moderate exercise during pregnancy is beneficial
The Third Trimester Is a Time of Preparation
A hospital is the best location for childbirth if complications are foreseen
Childbirth classes prepare parents for birth
The fetus also makes preparations for birth
Labor Has Three Stages
The first stage of labor is marked by uterine contractions and cervical dilation
The second stage is the delivery of the baby
Box: Pain-free Childbirth
The newborn child adapts quickly
The third stage is the expulsion of the placenta
Premature or delayed birth is hazardous
Box: Cesarean Section
The Period after Birth Places Many Demands on Parents
Postpartum depression may be accompanied by disordered thinking
Childbirth and parenthood affect sexuality
Breast-Feeding Is the Preferred Method of Nourishing the Infant
Lactation is orchestrated by hormones
The content of breast milk changes over time
Infant formula is an alternative to breast milk
Breast-feeding has many advantages and some drawbacks

Chapter 9. Contraception and Abortion
Birth Control Has a Long History
Feminists led the campaign to legalize contraception
Box: Margaret Sanger and the Birth Control Movement
Contraception has not yet solved the problem of unintended pregnancy
Different users have different contraceptive needs
Physical Methods Block Sperm Transport
Male condoms are reliable when properly used
Female condoms are relatively intrusive
Box: Male Contraceptives of the Future?
Diaphragms and cervical caps are inconvenient but have few side effects
Spermicides are not very reliable when used alone
Hormone-Based Methods Are Easy to Use
Combination pills offer health benefits
Continuous use of combination pills eliminates menstrual periods
Progestin-only pills have fewer side effects
Hormones Can Be Administered by Non-Oral Routes
Transdermal patches last a week
Vaginal rings last three weeks
Depo-Provera lasts three months
Implants are extremely reliable
Intrauterine devices require little attention
The Availability of Hormonal Contraceptives May Be Limited
Behavioral Methods Can Be Demanding
In fertility awareness methods, couples avoid coitus during the fertile window
The withdrawal method is simple but challenging
Noncoital sex can be used as a means of avoiding pregnancy
Combining long-acting methods and condoms makes sense
Box: Contraceptives and the Environment
There Are Contraceptive Options after Unprotected Coitus
Sterilization Is Highly Reliable
Vasectomy is a brief outpatient procedure
Tubal sterilization is more invasive and expensive
Disabled Persons Have Special Contraceptive Needs
Lack of Access to Contraception Is a Global Problem
Several Safe Abortion Procedures Are Available
Box: Abortion in the United States: Key Statistics
Vacuum aspiration is the standard first-trimester surgical method
Dilation and evacuation is used early in the second trimester
Induced labor and hysterotomy are performed late in the second trimester
Medical abortions are two-step procedures
Abortions do not cause long-lasting ill effects
Americans Are Divided on Abortion, but Most Favor Restricted Availability
The availability of abortion is decreasing
Box: Feticide

Chapter 10. Sexuality across the Life Span: From Birth to Adolescence
Some Forms of Childhood Sexual Expression Are Common
In contemporary Western culture, children are insulated from sex
Box: Talking with Children about Sex
Some children engage in solitary sexual activity
Sex with others can occur during childhood
Cultures vary in their attitudes toward childhood sexuality
Some Children Have Sexual Contacts with Adults
Most adult-child contacts involve older children and are single encounters
Some kinds of adult-child sex are more harmful than others
Box: Sex and Suggestibility
Strategies to prevent adult-child sex are quite effective
Preadolescence May Be Marked by an Increase in Sexual Interest
Preadolescent children segregate by sex
Strict gender norms may traumatize children who become gay or trans adults
Puberty Is a Period of Rapid Maturation
Puberty is marked by visible and invisible changes
Box: My First Period
Puberty occurs earlier in girls than boys
What drives puberty?
The body signals its readiness for puberty to the brain
Puberty may come too early or too late
Adolescence Is a Time of Sexual Exploration
Many cultures have puberty rites
There are social influences on teen sexual behavior
Box: Sex-ed--What Teens Say
Social media have risks and benefits
Males masturbate more than females
The sexual activity of American teens increased and then decreased
The meaning of "virginity loss" varies
Teen Sexuality Is Central to Identity Development
Teen relationships are often short-lived
Teen pregnancy is declining but is still too common

Chapter 11. Sexuality across the Life Span: Adulthood
In Young Adulthood, Conflicting Demands Influence Sexual Expression
Most young men and women have only a few sex partners
Dating relationships are short-lived
Cohabitation is an increasingly prevalent lifestyle
Cohabitation has diverse meanings
Cohabitation does not harm a subsequent marriage
Marriage Takes Diverse Forms
The formalization of sexual unions has social and personal functions
Many societies have permitted polygamy
Box: Mormon Polygamy
Polyamory includes a variety of nonmonogamous relationships
The Institution of Marriage Is Evolving
Companionate marriage makes the availability of divorce a necessity
Marriage is becoming a minority status
Relationship options have diversified
Most Long-Term Couples Are Satisfied with Their Sex Lives
The frequency of sex declines over the course of long-term relationships
Marital satisfaction declines during middle age
Box: You Know the Future of Your Marriage
A Variety of Factors Bring Relationships to an End
Several demographic factors increase the likelihood of a breakup
There are more personal reasons for breakups
Marital Disruption Can Have Negative and Positive Consequences
Divorced men and women can suffer psychological, physical, and economic damage
Divorce may be the start of a new life
Many divorced people remarry
Does marriage have a future?
Menopause Marks Women's Transition to Infertility
Menopause may be caused by depletion of ova
Women may experience a decline in sexual function at menopause
Decreased hormone levels affect a woman's physiology
Hormone therapy can reduce menopausal symptoms
Men's Fertility Declines Gradually with Age
Old People Face Challenges to Their Sex Lives--Often Successfully
Aging is accompanied by physiological changes in the sexual response
Medical conditions, drugs, and social factors can impair the sexuality of older people
Old age may be a time for romance
Box: Seniors on Sex

Chapter 12. Sexual Orientation
There Is a Spectrum of Sexual Orientations
Sexual Orientation Is Not an Isolated Trait
Box: Boys Will Be Girls
Diverse Theories Attempt to Explain Sexual Orientation
Freud proposed psychodynamic models
Sexual orientation has been attributed to socialization
Biological theories focus on prenatal hormones and genes
Box: Why Gay Genes?
The Gay Community Has Struggled for Equal Rights
The gay rights movement began in Germany
Box: Gay Martyrs
Gay rights are a global issue
Growing Up Gay Presents Challenges
Coming out is a lifelong process
Lesbians and gay men are well represented in certain occupations
Gay People Who Belong to Minorities Have Special Concerns
Gay Sex Has Its Own Style
Some same-sex couples differ in gender characteristics
Gay people aren't all of a kind
Box: Beyond Gay and Straight
Some gay people are parents
Changing One's Sexual Orientation Is Difficult or Impossible
Homophobia Has Multiple Roots
Cultural indoctrination transmits homophobia across generations
Gays are seen as rule breakers
Box: Born That Way? And Does It Matter?
Overcoming homophobia is a communal enterprise
Bisexual People Are Caught between Two Worlds
The prevalence of bisexuality depends on definitions
Bisexual people face prejudice
Lesbian, gay, straight, bi, other--more alike than different

Chapter 13. Atypical Sexuality
Sexual Variety Is the Spice of Life
Sadomasochism involves the infliction or receipt of pain or degradation
Box: In the Dungeon
Most fetishes are related to the body
People cross-dress for a variety of reasons
Box: Crush Fetishes
Box: Rubber Fetishism and the Internet
Some men are aroused by trans women
Adult babies reenact infancy
Furries wear animal costumes
Paraphilic Disorders Cause Distress or Harm Others
Exhibitionists expose themselves to nonconsenting persons
Obscene telephone calling is related to exhibitionism
Voyeurs are aroused by watching others
Frotteurism involves surreptitious physical contact
Box: Frotteurism: First-person Accounts
Some Adults Are Sexually Attracted to Children
Pedophilia and child molestation are not synonymous
"Child molestation" is a behavioral and legal term
Priests and others may molest children under their care
Some organizations support "minor-attracted people"
A Variety of Other Paraphilic Disorders Exist
Zoophiles are sexually attracted to animals
In necrophilia, nonresistance of the partner may be arousing
Sexual violence can be paraphilic
Box: Autoerotic Asphyxia
Sex Offenders Do Not Necessarily Repeat Their Offenses
There Are Numerous Theories of Paraphilic Disorders
Theories of Causation Have Suggested a Variety of Treatments
Conditioning is intended to change sexual desires
Cognitive therapy is aimed at preventing repeat offenses
The efficacy of psychological treatments is limited
Drug treatments interact with neurotransmitters or hormones
Castration is a treatment of last resort
Few "Kinks" Are Disorders

Chapter 14. Sexual Disorders
Sexual Disorders Are Common
A multidisciplinary approach to treatment is preferred
Box: Sensate Focus
Female Sexual Arousal Disorder Involves Insufficient Genital Response
There Are Many Reasons for Sexual Pain in Women
Vaginismus may make intercourse impossible
Box: Dyspareunia: A Case History
Difficulty in Reaching Orgasm Is Common among Women
Psychotherapy and directed masturbation may be helpful
Box: Kegel Exercises
Faked orgasms offer a questionable solution
Lack of Interest in Sex Is Not Necessarily a Problem
Estrogen or androgen treatment may improve sexual desire in women
Sex therapy may be helpful for low sexual desire in women
Alternative views on women's response cycles may influence treatment options
Premature Ejaculation Is Men's Number One Sex Problem
There are different kinds of premature ejaculation
Sex therapy helps some men
Drug treatment may be effective
Delayed Ejaculation Is Not Well Understood
Erectile Disorder Has Many Causes and Treatments
Erectile disorder can have physical or psychological causes
Simple measures may alleviate the problem
Psychological treatments may be useful
PDE5 inhibitors have become the leading treatments
Erectile disorder can be treated with devices and implants
Men May Have Little Interest in Sex
Sexual Pain Is Uncommon in Men
Too Much Interest in Sex Can Cause Problems
Treatment depends on theoretical models
LGBT People Have Special Concerns

Chapter 15. Sexually Transmitted Infections
Venereal Diseases Were Seen as Punishment for Sexual License
STIs Are Still a Major Problem in the United States
Lice and Mites Are More of an Annoyance Than a Danger
Pubic lice itch, and that's all they do
Scabies may be transmitted sexually or nonsexually
Trichomoniasis Is Caused by a Protozoan
Bacterial STIs Can Usually Be Treated with Antibiotics
Syphilis Is Down but Not Out
Untreated syphilis progresses through three stages
Syphilis has resisted elimination
Box: The Tuskegee Syphilis Study
Gonorrhea Can Lead to Infertility
Chlamydia Causes a Common Infection with Serious Complications
The Status of Bacterial Vaginosis as an STI Is Uncertain
Urethritis Can Be Caused by a Variety of Organisms
Box: Zika--The virus that came and went
Viral STIs Can Be Dangerous and Hard to Treat
Molluscum Contagiosum Is a Self-Limiting Condition
Genital Herpes Is a Lifelong but Not Life-Threatening Infection
Recurrent outbreaks are the rule
Drug treatment can shorten or prevent outbreaks
Human Papillomaviruses Can Cause Genital Warts--and Cancer
An HPV vaccine is available
Hepatitis Viruses Can Be Sexually Transmitted
AIDS Is Caused by the Human Immunodeficiency Virus
Sexual transmission is chiefly by coitus and anal sex
HIV infection progresses in a characteristic way
Antiretroviral drugs suppress but don't eliminate HIV
You Can Reduce Your STI Risks
Abstinence prevents STIs
Sexually active people can reduce their risk of STIs
Box: Partner Notification
Some sexual behaviors are riskier than others for STI transmission
Condoms are the mainstay of STI prevention
Not Everything Is an STI

Chapter 16. Sexual Assault, Harassment, and Partner Violence
What Is Sexual Assault?
Young women are the most frequent victims
Most sexual assaults are not reported
Box: It Happened to Me
Sexual Assaults in College Are Becoming Less Common
Many sexual assaults are committed by college athletes
Colleges must balance the rights of the accuser and the accused
The number one "date rape drug" is alcohol
Sexual Assault Can Have Severe Effects on the Victim
Box: Reducing the Risk of Sexual Assault
Services are available for rape victims
Rape can inflict long-lasting harm
Box: Ten Ways Men Can Prevent Sexual Violence
Male victims have special concerns
LGBT people are at high risk
Rape Laws Have Become More Protective of Victims
Reforms began in the 1970s
What happens to men who rape?
Repeat offending is common
Why Do Men Rape?
Rape may have evolutionary roots
Some characteristics distinguish rapists from nonrapists
Social forces influence the likelihood of rape
Box: Rape and War
Intervention Programs Are of Uncertain Value
Intimate Partner Violence Is a Crime with Many Names
Intimate partner violence follows an escalating cycle
Breaking up is hard to do
Help is available
Sexual Harassment Occurs in Many Environments
There are two kinds of workplace sexual harassment
Sexual harassment often begins early
Box: The Superstar Harasser
Sexual harassment harms its victims
Victims of sexual harassment can take steps to end it
There Are Three Kinds of Stalkers

Chapter 17. Sex Work
Sex Is an Industry
Prostitution Is on the Decline
Historically, prostitution was viewed as a necessary evil
There are moral and practical reasons for the decline
There Is a Hierarchy of Prostitution
Street prostitution has many risks
Box: The Economics of Prostitution
Female, male, and transgender streetwalkers have different experiences
Some prostitutes work out of massage parlors and strip clubs
Escort services are the main form of prostitution in the United States
Many prostitutes work for pimps
Box: Sugaring
Men who use escorts have liberal attitudes
Some women use male prostitutes
Juvenile prostitution is of special concern
Box:Juvenile Prostitutes in Portland, Oregon
Sex trafficking is a global business
There Are Conflicting Views on Prostitution
There are several options for legal reform
There Is More to Sex Work than Prostitution
Stripping is going mainstream
Phone sex has diversified
Pornography Has Always Been Part of Human Culture
Pornography has battled censorship
New technologies mean new kinds of pornography
Box: What's It Like to Be a Porn Star?
There is some pornography for women
There Are Conflicting Perspectives on the Value or Harm of Pornography
Research has not resolved the question of pornography's effects
Sex Is Part of the Mass Media
Sex sells, sometimes

Appendix A. Sex and Evolution
Rival Theories Offer Explanations for Sexual Reproduction
Sexual reproduction removes harmful mutations
Sexual reproduction may generate beneficial gene combinations
Why Are There Two Sexes?
Hermaphrodites combine male and female reproductive functions
Evolution Has Led to Diverse Methods of Sex Determination
In mammals, sex is determined by chromosomes
Sexual Selection Produces Anatomical and Behavioral Differences between Males and Females
Males and females follow different reproductive strategies
Females and males are exposed to different reproductive risks
Males often compete for access to females
Females often choose among males
Sometimes males make significant investments in reproduction
If males invest, sexual selection may work differently
Sexual selection protects against extinction
Diverse Relationship Styles Have Evolved
Social and sexual arrangements are not necessarily the same
Male promiscuity offers obvious evolutionary benefits
Why are females promiscuous?
Female promiscuity leads to adaptive responses by males
Males may copulate with females by force
Sometimes, Helping Relatives Reproduce Is a Good Strategy
Avoiding Incest Is an Evolved Behavior
Sex Has Acquired Other Functions beyond Reproduction
Female and male bonobos engage in nonreproductive sex
Bonobos use sex for conflict resolution and alliance formation

Appendix B. Sex and the Nervous System
Box: The Nervous System
Erection Can Be Mediated by a Spinal Reflex
Sensory innervation of the genitalia
The pudendal and pelvic nerves
Erectile Tissue Forms a Hydraulic System
Muscles Are Also Involved in Erection
The Brain Influences Erection and Ejaculation

Glossary
References
Author Index
Subject Index