An excerpt from Why Women Have Sex: Understanding Sexual Motivations from Adventure to Revenge (and Everything in Between) by Cindy M. Meston and David M. Buss.

Introduction

Inside the Sexual Mind

Why women have sex is an extraordinarily important but surprisingly little-studied topic. One reason for its neglect is that scientists and everyone else have assumed that the answers are already obvious— to experience pleasure, to express love, or— at the very heart of the biological drive to have sex— to reproduce. So, more than five years ago, we decided to undertake an intensive research project, involving more than three thousand individuals, to uncover the mysteries of women’s sexuality.

When our scientific article “Why Humans Have Sex” was published in the August 2007 issue of Archives of Sexual Behavior, it generated an avalanche of interest. What that media coverage revealed, however, was just the tip of the iceberg. In that original study, we identified 237 distinct sexual motivations that covered an astonishing variety of psychological nuance. These motives ranged from the mundane (“I was bored”) to the spiritual (“I wanted to get closer to God”), from altruistic (“I wanted my man to feel good about himself”) to vengeful (“I wanted to punish my husband for cheating on me”). Some women have sex to feel powerful, others to debase themselves. Some want to impress their friends; others want to harm their enemies (“I wanted to break up a rival’s relationship by having sex with her boyfriend”). Some express romantic love (“I wanted to become one with another person”); others express disturbing hate (“I wanted to give someone else a sexually transmitted disease”). But none of these reasons conveyed the “why” that hid behind each motive.

Through statistical procedures, we clustered the motivations into natural groupings. We then set out to explore women’s sex lives in richer detail in a new study designed specifically for this book. And we integrated our research with all the latest scientific findings—from our labs and from the labs of other scientists throughout the world— to present what we believe is one of the richest and deepest understandings of women’s sexuality yet achieved.

Why Women Have Sex brings these insights to life with detailed descriptions of women’s actual sexual encounters; the motives that impel women to have sex; and the theory behind why each of those motives exists in women’s sexual psychology. Although human sexuality has been the primary focus of our scientific research for many years, this project proved to be more illuminating about women’s sexuality than we ever expected.

How did we end up collaborating on this extraordinary project? As it happens, we have offices right next door to each other in the psychology department at the University of Texas at Austin, where we are both professors. Given our shared professional interests, we’ve had many conversations about human sexuality. The topic of conversation turned one day to sexual motivation, and we started discussing a simple question: Why do people have sex?

As coauthors, we combine uniquely complementary domains of expertise. One of us, Cindy M. Meston, is a clinical psychologist and one of the world’s leading experts on the psychophysiology of women’s sexuality. The other, David M. Buss, is an evolutionary psychologist and one of the world’s scientific experts on strategies of human mating. Our collaboration allowed us to develop a deeper understanding of women’s sexuality than either of us could have achieved working alone.

Viewed from both clinical and evolutionary perspectives, women’s sexuality poses interesting questions. Why do women desire some qualities in a mate, yet are repulsed by others? What tactics do women use to attract their preferred sex partners? Why do some women fuse love and sex psychologically? Why are erotic romance novels so much more appealing to women than to men? Why do some women have sex to keep a mate, whereas other women use sex to get rid of an unwanted mate?

The scientific study of sex, or “sexology,” is a multifaceted field spanning the disciplines of psychology, sociology, anthropology, evolutionary biology, and medicine. For the past several decades, sexology has focused on three core issues: defining and understanding what sexual behaviors, attitudes, and relationships are normal or healthy; ascertaining how biological factors, life events, and personal preferences or circumstances shape our sexual identities and desires; and discovering how human sexuality affects, and is affected by, social relationships. Clinical psychologists are especially interested in the extent to which a person’s sexual choices and responses can be modified or improved. Evolutionary psychologists study adaptive functions of the components of human sexual psychology, as well as why sexual motivations sometimes malfunction in the modern environment.

Since the late nineteenth century, sex researchers have primarily used three scientific methodologies for investigating human sexual behavior: case studies, questionnaires and surveys, and behavioral observation and assessment. The case-study method involves careful, in- depth description of individuals with sexual problems or anomalies. For example, early sexologist Richard von Krafft-Ebing (1840–1902) observed a high prevalence of masturbation among his patients, which led him to conclude (erroneously) that masturbation was the source of all sexual variation. Based on case studies, psychologist Sigmund Freud (1856–1939) theorized that childhood erotic drives shaped adult sexual behavior.

The forerunner of survey research was Havelock Ellis (1859–1939), who emphasized the vast individual diversity in sexual behavior— and wrote a memoir detailing his “open marriage” to a self- identified lesbian. In the 1940s and ’50s, Alfred C. Kinsey (1894–1956) and his collaborators Wardell B. Pomeroy, Paul H. Gebhard, and Clyde E. Martin redefined the way Americans viewed their sex lives with the publication of two reports describing the sexual activities of men and women. Kinsey and his team fashioned a standardized interview that they used to gather the detailed sex histories of approximately 18,000 men and women across the United States— the largest survey ever of human sexual practices. Kinsey personally recorded 7,985 of the histories.

Robert Latou Dickinson (1861–1950), a practicing gynecologist in New York, pioneered the laboratory observation of women’s sexuality with his development of a glass observation tube to view and document women’s internal sexual anatomy. Kinsey also used direct observational techniques to study sexual response, but the current era of laboratory sex research began with the work of William H. Masters (1915–2001) and Virginia E. Johnson (b. 1925), who were married from 1971 until 1992. In contrast to the limited observations made by their predecessors, Masters and Johnson recruited nearly seven hundred men and women to participate in studies at their lab, where they documented the physiological changes that occur with sexual arousal and orgasm. They uncovered the role of vaginal lubrication in sexual arousal, the physiology of multiple orgasms, and the similarity between vaginal and clitoral orgasms in women.

Since the publication in 1966 of Masters and Johnson’s landmark book The Human Sexual Response, a relatively distinct branch of lab research has emerged: sexual psychophysiology. Studies in sexual psychophysiology investigate the complex interplay between the psychological (feelings, emotions and thought processes) and the physiological (hormones, brain chemicals, genital engorgement, and lubrication) in human sexual behavior.

Psychological sexual arousal is typically measured using questionnaires that ask how “turned on” or “turned off” a person feels in a certain context and whether his or her mood is positive, negative, relaxed, or anxious. In the early days of sexual psychophysiology, researchers interested in measuring human physiological arousal with adapted devices used in other species. For instance, penile erection monitors for men can be traced to machines used by horse breeders in the late nineteenth century to prevent masturbation in stud horses! In the early 1970s, two doctors developed a probe that could be used to mea sure thermal conductance in sheep vaginas. They claimed the device “caused no discomfort for the waking sheep” during the experiments, which lasted up to four hours. Although the device proved too cumbersome and invasive for use in women, its design is not terribly different from modern vaginal probes.

Today, researchers mea sure physiological sexual responses, particularly genital blood flow, using a number of techniques. In women, studies involve vaginal photoplethysmography (a light- sensing device), pulsed wave Doppler ultrasonography, pelvic magnetic resonance imaging, sensors that mea sure changes in the temperature of the vagina or labia, and thermal imaging of thighs and genitals. In addition, sexual psychophysiologists often record changes in heart rate, respiration rate, body temperature, blood pressure, and sweat gland activity. While these nongenital measures can provide information about a person’s physiological state during sexual arousal, they do not specifically indicate sexual response, since emotions such as anger, fear, anxiety, and even laughter can also trigger these changes. More recently, researchers have turned to functional magnetic resonance imaging (fMRI) to identify the areas of the brain involved in human sexual response and behavior.