1. Module 15
Human Sexuality
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2. Human Sexuality: The Physiology of Sex Hormones and Sexual Behavior
15-1: HOW DO HORMONES INFLUENCE HUMAN SEXUAL MOTIVATION?
Asexuality is having no sexual attraction to others.
Sex hormones are one of the forces that drive sexual behavior.
Testosterone: Most important male sex hormone
In both males and females, but the additional testosterone in males stimulates growth of the male sex organs during fetal period, and development of the male sex characteristics during puberty
Estrogens: The estrogens sex hormones, such as estradiol, are secreted in greater amounts by females than by males and contribute to female sex characteristics
In nonhuman female mammals, estrogen levels peak during ovulation, promoting sexual receptivity

3. Human Sexuality: The Physiology of Sex Hormones and Sexual Behavior
Large hormonal surges or declines tend to occur at two predictable points in life span
Pubertal stage surge triggers development of sex characteristics and sexual interest
In later life, hormone levels fall, with women experiencing menopause and men a more gradual change
A third point sometimes occurs
For some, surgery or drugs may cause hormonal shifts

4. Human Sexuality: The Physiology of Sex The Sexual Response Cycle
15-2: WHAT IS THE HUMAN SEXUAL RESPONSE CYCLE, AND HOW DO SEXUAL DYSFUNCTIONS AND PARAPHILIAS DIFFER?
The sexual response cycle identifies four stages of sexual responding as identified by William Masters and Virginia Johnson (1966):
Excitement
Plateau
Orgasm
Resolution

5. Human Sexuality: The Physiology of Sex The Sexual Response Cycle
Excitement
The Sexual Response Cycle (Masters and Johnson)
Resolution
Plateau
Orgasm

6. Human Sexuality: The Physiology of Sex Sexual Dysfunctions and Paraphilias
Impair sexual arousal or functioning
Often involve sexual motivation, especially sexual motivation and arousal
Include erectile disorder and premature ejaculation (males)
Include female orgasmic disorder and female sexual interest/arousal disorder (females)
Sometimes involve paraphilias (sexual desire directed in unusual ways; e.g., pedophilia, exhibitionism)

7. Human Sexuality: The Physiology of Sex Sexual Dysfunctions and Paraphilias
Problem that consistently impairs sexual arousal or functioning
Erectile disorder
Inability to develop or maintain an erection due to insufficient bloodflow to the penis
Premature ejaculation
Sexual climax that occurs before the man or his partner wishes

8. Human Sexuality: The Physiology of Sex Sexual Dysfunctions and Paraphilias
Female orgasmic disorder
Distress due to infrequently or never experiencing orgasm
Paraphilias
Sexual arousal from fantasies, behaviors, or urges involving nonhuman objects, the suffering of self or others, and/or non-consenting persons

9. Human Sexuality: The Physiology of Sex Sexual Dysfunctions and Paraphilias
American Psychological Association (2013)
Only classifies people as disordered who experience sexual desire in unusual ways if:
Person experiences distress from unusual sexual interest or
It entails harm or risk of harm to others
Paraphilias include necrophilia, exhibitionism, and pedophilia

10. Human Sexuality: The Physiology of Sex Sexually Transmitted Infections
15-3: HOW CAN SEXUALLY TRANSMITTED INFECTIONS BE PREVENTED?
Sexually transmitted infection (STI)
Also called sexually transmitted disease (STD)
Every day, more than 1 million people worldwide acquire an STI
AIDS (acquired immune deficiency syndrome)
Is life-threatening, sexually transmitted infection
Caused by the human immunodeficiency virus (HIV)
Depletes immune system and leaves person vulnerable to infections

11. Human Sexuality: The Physiology of Sex Sexually Transmitted Infections
CDC report: 14- to 19-year-old U.S. females found 39.5 percent had STIs.
Condom use effectiveness varies by infection (80 percent effectiveness against transmission of HIV when used with infected partner; less effective with skin-to-skin STIs such as herpes).
Significant link between oral sex and STIs, such as HPV; most HPV infections can now be prevented with a vaccination administered before sexual contact.
Worldwide, women’s AIDs rates are increasing fastest, partly because the virus is passed from man to woman much more often than woman to man.

12. Human Sexuality: The Psychology of Sex
15-4: HOW DO EXTERNAL AND IMAGINED STIMULI CONTRIBUTE TO SEXUAL AROUSAL?
Levels of Analysis for Sexual Motivation
Our sexual motivation is influenced by biological factors, but psychological and social-cultural factors play an even bigger role.

13. Human Sexuality: The Psychology of Sex External Stimuli
Our sophisticated brain allows us to experience sexual arousal both from what is real and from what is imagined
External stimuli
People may find sexual arousal from erotic materials either pleasing or disturbing; repeated exposure often habituates emotional response
Men tend to be more aroused when erotic material aligns with personal sexual interest
Pornography may increase rape acceptance, and decrease evaluation of and sexual satisfaction with own partner

14. Human Sexuality: The Psychology of Sex Imagined Stimuli
Sexual desire and arousal can be imagined; our brain has been said to be our most significant sex organ
People with spinal-cord injury reported feeling sexual desire
95 percent of people report having sexual fantasies
Male fantasies tend to be more frequent, more physical, and less romantic than those of women

15. Human Sexuality: The Psychology of Sex Teen Pregnancy
15-5: WHAT FACTORS INFLUENCE TEENAGERS’ SEXUAL BEHAVIORS AND USE OF CONTRACEPTIVES?
Compared with European teens, American teens have higher rates of STIs and teen pregnancy
Environmental factors that influence a higher teen pregnancy rate:
Minimal communication about birth control
Guilt related to sexual activity
Alcohol use
Mass media norms of unprotected promiscuity; media help write the social scripts that affect our perceptions and actions

16. Human Sexuality: The Psychology of Sex Teen Pregnancy
Later sex may pay emotional dividends, with those who had later first sex reporting greater relationship satisfaction
Factors that predict sexual restraint:
High intelligence
Religious engagement
Father presence
Participation in service learning programs

17. Human Sexuality Sexual Orientation
15-6: WHAT HAS RESEARCH TAUGHT US ABOUT SEXUAL ORIENTATION?
Sexual orientation is our enduring sexual attraction toward
members of one’s own sex (homosexual orientation)
the other sex (heterosexual orientation)
or both sexes (bisexual orientation)
In all cultures, heterosexuality has prevailed but homosexuality has existed. Where same-sex relationships are illegal, the prevalence of people who are lesbian, gay, or bisexual is no different.

18. Human Sexuality Sexual Orientation: The Numbers
Survey results vary by survey methods and population; less open response in less tolerant places
Exclusively homosexual: 3 to 4 percent in men and 2 percent in women
Actively bisexual: Reported by fewer than 1 percent—for example, 12 out of 7076 people in a Dutch survey
5 percent of men and 13 percent of women in U.S. report some same-sex sexual contact during their lives
APA (2009) reports efforts to change sexual orientation are unlikely to be successful and involve some risk of harm
Women’s sexual orientation tends to be less strongly felt and potentially more fluid; sexual activity level also varies more

19. Human Sexuality: Sexual Orientation Origins of Sexual Orientation
Homosexuality is not linked with problems in parent-child relationships, does not involve a fear or hatred of the other sex, and isn’t significantly linked to childhood sexual victimization
There is a lack of evidence for environmental causes of homosexuality
Instead, homosexuality seems to have biological influences, as investigated in studies of same-sex behavior in other species, gay-straight brain differences, genetic influences, and prenatal influences

20. Human Sexuality: Sexual Orientation Origins of Sexual Orientation
Same-sex attraction in other species
Same-sex behavior has been observed in several hundred species (swans, penguins, grizzlies, gorillas, monkeys, flamingos, and owls).
Gay-straight brain differences
Gay-straight brain differences where one hypothalamic cell cluster is smaller in women and gay men than in straight men
Anterior commissure is larger in gay men than in straight men.
Gay men’s hypothalamus reacts as do straight women’s to the smell of sex-related hormones.

21. Human Sexuality: Sexual Orientation Origins of Sexual Orientation
Genetic influences
Shared sexual orientation is higher among identical twins than among fraternal twins.
Sexual attraction in fruit flies can be genetically manipulated.
Male homosexuality often appears to be transmitted from the mother’s side of the family.

22. Human Sexuality: Sexual Orientation Origins of Sexual Orientation
Prenatal Influences
Altered prenatal hormone exposure may lead to homosexuality in humans and other animals.
Men with several older biological brothers are more likely to be gay, possibly due to a maternal immune-system reaction.
The consistency of the brain, genetic, and prenatal findings clearly leads to a biological explanation of sexual orientation.

23. Human Sexuality: Sexual Orientation Origins of Sexual Orientation
The fraternal birth-order effect
Researcher Ray Blanchard (2008a) offers these approximate curves depicting a man’s likelihood of homosexuality as a function of his number of older brothers. This correlation has been found in several studies, but only among right-handed men (as about 9 in 10 men are).

24. Human Sexuality: Sexual Orientation Origins of Sexual Orientation Gay-Straight Trait Differences
Research indicates that homosexuals and heterosexuals differ in the following traits
spatial abilities
age of onset of puberty in males
fingerprint ridge counts
birth size and weight
auditory system development
sleep length
handedness
physical aggression
occupational preferences
walking style
relative finger lengths
gender nonconformity
See Table On average (the evidence is strongest for males), results for gays and lesbians fall between those of straight men and straight women. Three biological influences—brain, genetic, and prenatal—may contribute to these differences.

25. An Evolutionary Explanation of Human Sexuality: Male-Female Differences in Sexuality
15-7: HOW MIGHT AN EVOLUTIONARY PSYCHOLOGIST EXPLAIN MALE-FEMALE DIFFERENCES IN SEXUALITY AND MATING PREFERENCES?
Cross-culturally, men think more than women about sex, and men are more likely to think that casual sex is acceptable.
See Table 15.2, which shows questions researchers have asked samples of U.S. adults whether they agreed or disagreed with; students can predict the number of males and females who agreed with each statement.
Why might natural selection have resulted in greater male promiscuity?

26. An Evolutionary Explanation of Human Sexuality: Male-Female Differences in Sexuality
Compared with lesbians, gay men (like straight men) report more interest in uncommitted sex, more responsiveness to visual sexual stimuli, and more concern with their partner’s physical attractiveness.
Gay male couples report having sex more often than do lesbian couples.
Men who had the trait of promiscuity were more likely to have their genes continue, and even spread, in the next generation. There is little cost to spreading their genes.
For women, a trait of promiscuity would not greatly increase the number of babies, and it would have greater survival costs. Pregnancy was often life-threatening.

27. An Evolutionary Explanation of Human Sexuality: Natural Selection and Mating Preferences
Men prefer women with signs of future fertility (narrow waist and fuller figure; age of peak fertility). Women prefer men with loyal behavior and physical/social power and resources.
Why might natural selection have resulted in mating preferences?
Male choices optimized the chance of producing offspring.
Female choices optimized offspring survival.
Men chose widely; women chose wisely!

28. Human Sexuality Critiquing the Evolutionary Perspective
15-8: WHAT ARE THE KEY CRITICISMS OF EVOLUTIONARY EXPLANATIONS OF HUMAN SEXUALITY, AND HOW DO EVOLUTIONARY PSYCHOLOGISTS RESPOND?
Most psychologists agree that natural selection prepares humans for survival and reproduction. But critics of evolutionary psychology research note these limitations:
Evolutionary psychology starts with and effect and works backward to explain what happened
More immediate explanations better understood through social learning theory (including social scripts) than decisions made by our distant ancestors
Social consequences of evolutionary explanation are problematic
Some traits and behaviors are difficult to explain by natural selection

29. Human Sexuality Social Influences on Human Sexuality
15-9: WHAT ROLE DO SOCIAL FACTORS PLAY IN OUR SEXUALITY, AND HOW DO NATURE, NURTURE, AND OUR OWN CHOICES INFLUENCE GENDER ROLES AND SEXUALITY?
Human sexuality research does not aim to define personal meaning of sex, but one significance of such intimacy is its expression of our profoundly social nature.
For both men and women, but especially for women, orgasm occurs more often when sex happens in a committed relationship rather than a sexual hookup.
Sex is a socially significant act. Achieving orgasm alone is less satisfying, and with much less of a surge in the prolactin hormone associated with sexual satisfaction and satiety, than after sex with a loved one.
Thanks to overlapping brain reward areas, sexual desire and love feed each other.

30. Reflections on the Nature and Nurture of Sex, Gender, and Sexuality
Our ancestral history helped form us as a species; where there is variation, natural selection, and heredity, there will be evolution. But our culture and experiences also form us.
Human nature is formed by:
Our genes
Our culture and experiences
In many modern cultures, gender roles are merging. There have been swift changes in gender roles and sexual attitudes since 1960; biology does not fix gender roles.
We can’t excuse our failings by blaming them solely on bad genes or bad influences. In reality, we are both the creatures and creators of our worlds.