It’s obvious we need food, water, and sleep to survive. But where does sex fit into the needs hierarchy? “Sex may be studied as a purely physiological need,” according to Maslow, “[but] ordinarily sexual behavior is multi-determined” (Maslow, 1943, p. 381). In other words, there are many forces motivating us to engage in sexual activity. These include the need for affection and love, and that means “both giving and receiving love” (p. 381). Every person is different, of course. There is tremendous variability in human sexuality—that is, our sexual activities, attitudes, and behaviors.

To grasp the complexity of human sexuality, we must understand the basic physiology of the sexual response. Enter William Masters and Virginia Johnson and their pioneering laboratory research, which included the study of approximately 10,000 distinct sexual responses of 312 male and 382 female participants (Masters & Johnson, 1966).

LO 9 Describe the human sexual response as identified by Masters and Johnson.

HUMAN SEXUAL RESPONSE CYCLE Masters and Johnson began their research in 1954, not exactly a time when sex was thought to be an acceptable subject for dinner conversation. Nevertheless, almost 700 people volunteered to participate in their study, which lasted a little more than a decade (Masters & Johnson, 1966). Using a variety of instruments to measure blood flow, body temperature, muscular changes, and heart rate, they discovered that most people experience a similar physiological sexual response, which can result from oral stimulation, manual stimulation, vaginal intercourse, or masturbation. Men and women tend to follow a similar pattern or cycle: excitement, plateau, orgasm, and resolution (Figure 9.3). These phases vary in duration for different people.

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Sexual arousal begins during the excitement phase. This is when physical changes start to become evident. Muscles tense, the heartbeat quickens, breathing accelerates, the nipples become firm, and blood pressure rises a bit. In men, the penis becomes erect, the scrotum constricts, and the testes pull up toward the body. In women, the vagina lubricates and the clitoris swells (Levin, 2008).

Next is the plateau phase. There are no clear physiological signs to mark the beginning of the plateau, but it is the natural progression from the excitement phase. During the plateau phase, the muscles continue to tense, breathing and heart rate increase, and the genitals begin to change color as blood fills the area. This phase is usually quite short-lived, lasting only a few seconds to minutes.

The shortest phase of the sexual response cycle is the orgasm phase. As the peak of sexual response is reached, an orgasm occurs, which is a powerful combination of extremely gratifying sensations and a series of rhythmic muscular contractions. When men and women are asked to describe their orgasmic experiences, it is very difficult to differentiate between them. Brain activity observed via PET scans is also quite similar (Georgiadis, Reinders, Paans, Renken, & Kortekaas, 2009; Mah & Binik, 2001).

The final phase of the sexual response cycle, according to Masters and Johnson, is the resolution phase. This is when bodies return to a relaxed state. Without further sexual arousal, the blood flows out of the genitals, and blood pressure, heart rate, and breathing return to normal. Men lose their erection, the testes move down, and the skin of the scrotum loosens. Men will also experience a refractory period, an interval during which they cannot attain another orgasm. This can last from minutes to hours, and typically the older a man is, the longer the refractory period lasts. For women, the resolution phase is characterized by a decrease in clitoral swelling and a return to the normal labia color. Women do not experience a refractory period, and if sexual stimulation continues, some are capable of having multiple orgasms.

Masters and Johnson’s landmark research has led to further studies of the physiological aspects of the sexual response cycle, and although their basic model is viewed as valid, research suggests there may be the need for “correction or modification, or additional explanation” (Levin, 2008, p. 2). As mentioned, sex is different for every person, and not everyone fits neatly into the same model. This idea applies not only to the physical experience of sex, but to all aspects of sexuality, including sexual orientation.

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LO 10 Define sexual orientation and summarize how it develops.

Sexual orientation is the “enduring pattern” of sexual, romantic, and emotional attraction that individuals exhibit toward the same sex, opposite sex, or both sexes (APA, 2008). When attracted to members of the opposite sex, sexual orientation is heterosexual. When attracted to members of the same sex, sexual orientation is homosexual, commonly referred to as “lesbian” for women and “gay” for men (APA, 2008). When attracted to members of the same sex and members of the opposite sex, sexual orientation is bisexual, although most people tend to prefer one sex or the other. Those who do not feel sexually attracted to others are asexual. Lack of interest in sex does not necessarily prevent a person from maintaining relationships with spouses, partners, or friends, but little is known about the impact of asexuality because research on the topic is scarce.

WHAT’S IN A NUMBER? What percentage of the population is heterosexual? How about homosexual and bisexual? These questions may seem straightforward, but they are not easy to answer, partly because there are no clear-cut criteria for classifying people this way. Sexual orientation represents a vast spectrum; at one end are people who are “exclusively heterosexual” and at the other end are those considered “exclusively homosexual.” Between these two poles is considerable variation (Kinsey, Pomeroy, & Martin, 1948; Figure 9.4). Some people might be exploring their sexuality, but not necessarily exhibiting a particular orientation, and this adds to the variability of rates. Estimates are available, but definitions of sexual orientation vary across cultures, and findings can be inconsistent as a result of differing survey designs: data collection in different years, the use of different age groups, different wording of questions, and so forth (Mosher, Chandra, & Jones, 2005, September 15). According to one estimate, 8 million people in the United States, or 3.5% of the adult population, are homosexual or bisexual (Gates, 2011).

We are not sure how sexual orientation develops, although most research supports biological factors. Among professionals in the field, there is near agreement that human sexual orientation is not a matter of choice. Research has focused on everything from genetics to culture, but there is no strong evidence that sexual orientation is determined by one particular factor (or set of factors). Instead, it appears to result from an interaction between nature and nurture, but this is still under investigation, and may never be fully determined or understood (APA, 2008).

GENETICS AND SEXUAL ORIENTATION To determine the influence of biology in sexual orientation, we turn to twin studies, which are commonly used to examine the degree to which nature and nurture contribute to psychological traits. Since monozygotic twins share 100% of their genetic make-up, we expect them to share more genetically influenced characteristics than dizygotic twins, who only share about 50% of their genes. In a large study of Swedish twins, researchers explored the impact of genes and environment on “same-sex sexual behavior” (2,320 monozygotic twin pairs, 1,506 dizygotic twin pairs). In their sample, the monozygotic twins were moderately more likely than the dizygotic twins to have the same sexual orientation. They also found that same-sex sexual behavior for monozygotic twins had heritability estimates around 34–39% for men, and 18–19% for women (Långström, Rahman, Carlström, & Lichtenstein, 2010). These findings highlight two important factors: Men and women differ in terms of the heritability of same-sex sexual behavior, and the influence of the environment is substantial.

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Researchers have searched for specific genes that might influence sexual orientation. Some have suggested that genes associated with male homosexuality might be transmitted by the mother. In one key study, around 64% of male siblings who were both homosexual had a set of several hundred genes in common, and these genes were located on the X chromosome (Hamer, Hu, Magnuson, Hu, & Pattatucci, 1993). But critics suggest this research was flawed, and no replications of this “gay gene” finding have been published since the original study (O’Riordan, 2012). Despite numerous attempts to identify genetic markers for homosexuality, researchers have had very little success (Dar-Nimrod & Heine, 2011). Some suggest that the search for genes underlying homosexuality is misguided. Why do we spend so much time and money seeking biological explanations for a “valid alternative lifestyle” (Jacobs, 2012)?

THE BRAIN AND SEXUAL ORIENTATION Researchers have also studied the brains of people across sexual orientations, and their findings are interesting. Neuroscientist Simon LeVay (1991) discovered that a “small group of neurons” in the hypothalamus of homosexual men was almost twice as big as that found in heterosexual men. He did not suggest this size difference was indicative of homosexuality, but he did find it intriguing. LeVay also noted that these differences could have been the result of factors unrelated to sexual orientation. More recently, researchers using MRI technology found the corpus callosum to be thicker in homosexual men (Witelson et al., 2008).

HORMONES AND SEXUAL ORIENTATION How do such differences arise in the brain? They may emerge before birth; hormones (estrogen and androgens) secreted by the fetal gonads play a role in the development of reproductive anatomy. One hypothesis is that the presence of androgens (the hormones secreted primarily by the male gonads) influences the development of a sexual orientation toward women. This would lead to heterosexual orientation in men, but homosexual orientation in women (Mustanski, Chivers, & Bailey, 2002). Because it would be unethical to manipulate hormone levels in pregnant women, researchers rely on cases in which hormones are elevated because of a genetic abnormality or medication taken by a mother. For example, high levels of androgens early in a pregnancy may cause girls to be more “male-typed,” and promote the development of a homosexual orientation (Berenbaum, Blakemore, & Beltz, 2011; Jordan-Young, 2012).

Interestingly, having older brothers in the family seems to be associated with homosexuality in men (Blanchard, 2008). Why is this so? Evolutionary theory would suggest that the more males there are in a family, the more potential for “unproductive competition” among the male siblings. A homosexual younger brother would present less competition for older brothers in terms of securing mates and resources to support offspring.

BIAS Although differences in sexual orientation are universal and have been evident throughout recorded history, individuals identified as members of the nonheterosexual minority have been subjected to stereotyping, prejudice, and discrimination. Nonheterosexual people in the United States, for example, have been, and continue to be, subjected to harassment, violence, and unfair practices related to housing and employment.

EVOLUTIONARY PSYCHOLOGY AND SEX What is the purpose of sex? Evolutionary psychology would suggest that humans have sex to make babies and ensure the survival of the species (Buss, 1995). But if this were the only reason, then why would so many people choose same-sex partners? Some researchers believe it has something to do with “kin altruism,” which suggests that homosexual men and women support reproduction in the family by helping relatives care for their children. Homosexual individuals may not “spend their time reproducing,” but they can nurture the reproductive efforts of their “kin” (Erickson-Schroth, 2010).

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There are other reasons to believe that there is more to human sex than making babies. If sex were purely for reproduction, we would expect to see sexual activity occurring only during the fertile period of the female cycle. Obviously, this is not the case. People have sex throughout a woman’s monthly cycle and long after she goes through menopause. Sex is for feeling pleasure, expressing affection, and forming social bonds.

It is only natural for us to wonder if what we are doing between the sheets (or elsewhere) is typical or healthy. Is it normal to masturbate? Is it normal to fantasize about sex with strangers? The answers to these types of questions depend somewhat on cultural context. Most of us unknowingly learn sexual scripts, or cultural rules that tell us what types of activities are “appropriate” and don’t interfere with healthy sexual intimacy. In some cultures, the sexual script suggests that women should have minimal, if any, sexual experience before marriage, but men are expected to explore their sexuality, or “sow their wild oats.” Of course, not everyone follows the sexual scripts they are assigned.

KINSEY BREAKS GROUND When did researchers begin exploring sexuality in a systematic way? Alfred Kinsey and colleagues were among the first to try to scientifically and objectively examine human sexuality in America (Kinsey, Pomeroy, & Martin, 1948; Kinsey, Pomeroy, Martin, & Gebhard, 1953). Using the survey method, Kinsey and his team collected data on the sexual behaviors of 5,300 White males and 5,940 White females. Their findings were surprising; both men and women masturbated, and participants had experiences with premarital sex, adultery, and sexual activity with someone of the same sex. Perhaps more shocking was the fact that so many people were willing to talk about their personal sexual behavior in post–World War II America. At that time, people generally did not talk openly about sexual topics.

The Kinsey study was groundbreaking in terms of its data content and methodology, which included accuracy checks and assurances of confidentiality. The data have served as a valuable reference for researchers studying how sexual behaviors have evolved over time. However, Kinsey’s work was not without limitations. For example, Kinsey and colleagues (1948, 1953) utilized a biased sampling technique that resulted in a group of participants that was not representative of the population. It was a completely White sample, with an overrepresentation of well-educated Protestants (Potter, 2006; Wallin, 1949). Another criticism of the Kinsey study is that it failed to determine the context in which orgasms occurred. Was a partner involved? Was the orgasm achieved through masturbation (Potter, 2006)?

SEXUAL ACTIVITY IN RELATIONSHIPS Subsequent research has been better designed, using samples that are more representative of the population (Herbenick et al., 2010; Michael, Laumann, Kolata, & Gagnon, 1994). Some of the findings may surprise you, others probably not. Around 77% of adults in the United States report they engaged in intercourse by age 20, regardless of cultural background or ethnicity. By the age of 44, 95% of adults have had intercourse. And the overwhelming majority did not wait for marriage (Finer, 2007). However, married people do have more sex than those who are unmarried (Laumann, Gagnon, Micheal, & Michaels, 1994). According to a large study of Swedish adults, the frequency of penile–vaginal intercourse is associated with sexual satisfaction, as well as satisfaction with relationships, mental health, and life in general. Other sexual activities, such as masturbation, were found to have an inverse relationship with a variety of measures of satisfaction (Brody & Costa, 2009). Many studies indicate not only psychological benefits, but also physiological benefits of penile–vaginal intercourse. Correlations are apparent between the frequency of penile–vaginal intercourse and greater life expectancy, lower blood pressure, slimmer waistline, and lower prostate and breast cancer risk (Brody, 2010).

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SEXUAL ACTIVITY AND GENDER DIFFERENCES As stereotypes might suggest, men think about sex more often than women (Laumann et al., 1994), and they consistently report a higher frequency of masturbation (Peplau, 2003; see Table 9.3 for reported gender differences in frequency of sexual activity). Men in the United States tend to be more tolerant than women when it comes to casual sex before marriage, as well as more permissive in their attitudes about extramarital sex (Laumann et al., 1994). But these attitude differences are not apparent in heterosexual teenagers and young adults (Garcia, Reiber, Massey, & Merriwether, 2012). For these young people, attitudes about casual sex are apparent in their “hookup” behavior (Table 9.4).

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SEX EDUCATION One way to learn about this relatively new phenomenon of sexting—or any sexual topic, for that matter—is through sex education in the classroom. School is the primary place where American children get information about sex (Byers, 2011), yet it is somewhat controversial. Many parents are afraid that some types of sex education essentially condone sexual activity among young people. Until 2010, Title V federal funding was limited to states that taught abstinence only (Chin et al., 2012). Yet, research suggests that programs promoting abstinence are associated with more teenage pregnancies: States with a greater emphasis on abstinence (as reflected in state laws and policies) have higher teenage pregnancy and birth rates (Stanger-Hall & Hall, 2011).

Teenagers who are provided a thorough education on sexual activity, including information on how to prevent pregnancy, are less likely to become pregnant (or get someone pregnant). Research shows that formal sex education increases safe-sex practices, reducing the likelihood of disease transmission (Kohler, Manhart, & Lafferty, 2008; Stanger-Hall & Hall, 2011). Sex education clearly impacts the behaviors of teenagers and young adults.

SEXUAL ACTIVITY AND AGE Now let’s look at some data comparing the sexual behaviors of people at various stages of life. Would you expect to see major differences among people young, old, and in-between? According to a large cross-sectional survey of Americans ages 14 to 94, masturbation is more common than partnered sexual activities among adolescents and people over the age of 70. The same study found that more than half of those aged 18 to 49 had engaged in oral sex in the past year, with a lower proportion of the younger and older age groups engaging in this activity. Penetrative sex (vaginal and anal) was most common among adults ages 20 to 49 (Herbenick et al., 2010). In another large study (57- to 85-year-olds), researchers reported that aging did not seem to adversely affect interest in sexual activity. In fact, through the age of 74, the frequency of sexual activity remained steady, even with a high proportion of “bothersome sexual problems.”

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across the WORLD

When there is a “significant disturbance” in the ability to respond sexually or to gain pleasure from sex, we call this sexual dysfunction (American Psychiatric Association, 2013). In the National Health and Social Life Survey, researchers found 43% of women and 31% of men suffered from some sort of sexual dysfunction (Laumann, Paik, & Rosen, 1999). Temporary sexual difficulties may be caused by everyday stressors or situational issues but can be resolved once the stress or the situation has passed. Longer-term sexual difficulties stem from a variety of issues, including beliefs about sex, ignorance about sexual practices, and even performance expectations. Health conditions can also give rise to sexual difficulties. The biopsychosocial perspective is invaluable for helping to untangle the roots of sexual problems. Sexual dysfunction may result from problems with desire, arousal, orgasm, and pain, but these are not mutually exclusive categories.

DESIRE Situational issues such as illness, fatigue, or frustration with one’s partner can lead to temporary problems with desire. In some cases, however, lack of desire is persistent and distressing. Although either sex can be affected, women tend to report desire problems more frequently than men (Brotto, 2010; Heiman, 2002).

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AROUSAL Problems with arousal occur when the psychological desire to engage in sexual behavior is there, but the body does not cooperate. Men may have trouble getting or maintaining an erection, or they may experience a decrease in rigidity, which is called erectile disorder (American Psychiatric Association, 2013). More than half of all men report they have occasionally experienced problems with erections (Hock, 2012). Women can also struggle with arousal. Female sexual interest/arousal disorder is apparent in reduced interest in sex, lack of initiation of sexual activities, reduced excitement, or decreased genital sensations during sexual activity (American Psychiatric Association, 2013).

ORGASM Female orgasmic disorder is diagnosed when a woman is consistently unable to reach orgasm, has reduced orgasmic intensity, or does not reach orgasm quickly enough during sexual activity (American Psychiatric Association, 2013). Men who experience frequent delay or inability to ejaculate might have a condition known as delayed ejaculation (American Psychiatric Association, 2013; Segraves, 2010). With this disorder, the ability to achieve orgasm and ejaculate is inhibited or delayed during partnered sexual activity. Men who have trouble controlling when they ejaculate (particularly during vaginal sex) may suffer from premature (early) ejaculation (American Psychiatric Association, 2013).

PAIN Women typically report more problems with intercourse-related pain than men. Genito-pelvic pain/penetration disorder refers to four types of co-occurring symptoms specific to women: difficulty having intercourse, pain in the genitals or pelvis, fear of pain or vaginal penetration, and tension of the pelvic floor muscles (American Psychiatric Association, 2013). Up to 15% of women in North America report frequent pain during intercourse, and issues related to pain are associated with reduced desire and arousal.

LO 11 Identify the most common sexually transmitted infections.

Although sex is pleasurable and exciting for most, it is not without risks. Many people carry sexually transmitted infections (STIs)—diseases or illnesses passed on through sexual activity (Centers for Disease Control and Prevention [CDC], 2012f). There are many causes of STIs, but most are bacterial or viral (see Table 9.5, below for data on their prevalence). Bacterial infections such as syphilis, gonorrhea, and chlamydia often clear up with antibiotics. Viral infections like genital herpes and human papillomavirus (HPV) have no cure, only treatments to reduce symptoms.

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We have now explored many facets of motivation, from basic physiological drives to transcendent needs for achievement. As you may have guessed from the title of this chapter, motivations are intimately tied to emotions. In the sections to come, we will explore the complex world of human emotion, with a focus on fear and happiness.

Question 1

1. excitement, plateau, orgasm, and resolution.

2. plateau, excitement, orgasm, and relaxation.

3. excitement, plateau, and orgasm.

4. excitement, orgasm, and resolution.

Question 2

Question 3

1. Syphilis; gonorrhea

2. Pelvic inflammatory disease; herpes

3. Human papillomavirus; herpes

4. Syphilis; acquired immune deficiency syndrome