Unlike hunger, sexual drive does not motivate people to fulfill a basic biological need. A lack of food leads to death; a lack of sex, on the other hand, does not. Both biological and psychological factors strongly influence sexual drive.
One of the first researchers to give a modern account of human sexuality wasAlfred Kinsey. In the 1940s, he and his colleagues interviewed more than 18,000 U.S. men and women about their sexual behavior and attitudes. In his comprehensive reports about human sexuality, Kinsey denounced the repressive social attitudes of his time, which he said bore little relation to actual sexual practices. Kinsey provided statistics showing that sexual practices varied widely and that even in the 1940s there was a high prevalence of masturbation and premarital sex. These statistics shocked many people of his day.
Critics of Kinsey’s research maintained three arguments:
- Kinsey’s sample was not random. Instead, it consisted largely of well-educated, white city dwellers.
- Kinsey and his colleagues used questionable methods to gather their data, especially asking leading questions when interviewing subjects.
- Kinsey may have let his own beliefs influence his results.
Masters and Johnson’s Studies
Other pioneers of sexual research were William Masters and Virginia Johnson. In the 1960s, they studied several hundred male and female volunteers who agreed to either masturbate or have intercourse in a laboratory. Masters and Johnson hooked up the volunteers to instruments that measured various physiological indicators during sexual activity. Using the results of these studies, they described the sexual response cycle.
The Sexual Response Cycle
Masters and Johnson divided the human sexual response cycle into four phases:
- Excitement phase: Physiological arousal increases quickly. Muscle tension, heart rate, blood pressure, and breathing rate increase. In men, the penis gets erect and the testes swell. In women, the clitoris hardens and swells, the vaginal lips open, and the vagina lubricates.
- Plateau phase: Physiological arousal continues. In women, the clitoris retracts under the clitoral hood. Men may secrete a small amount of fluid from the penis.
- Orgasm phase: Physiological arousal peaks. Men ejaculate seminal fluid. Both men and women experience muscular contractions in the pelvic area, along with a sensation of pleasure.
- Resolution phase: Physiological responses return to normal levels. Men then go through a refractory period that can vary in length, during which they are not responsive to stimulation. The refractory period tends to get longer as men age.
Critics of Masters and Johnson’s research maintained two arguments:
- Masters and Johnson studied a biased sample of people. The sample included only people who were both willing and able to perform sexual acts in a laboratory setting.
- Masters and Johnson didn’t pay attention to individual differences. In reality, people’s sexual responses vary according to factors such as age, amount of sexual experience, and cultural background.
Psychological Factors in Sexual Motivation
Hormones alone cannot cause sexual arousal. Psychological factors are also highly influential.
- Erotic stimuli: Both men and women can become sexually aroused by external and internal erotic stimuli. External erotic stimuli include sexually exciting material that is read, heard, or seen. Internal erotic stimuli include thoughts, fantasies, and memories of past sexual experiences. What is considered erotic varies according to the individual, historical period, and cultural context.
- Desires: People have an infinite number of desires that influence the motivation for sex, including to procreate, to express love, to have physical enjoyment, to cope with difficult situations and emotions, to validate one’s desirability, and to do what peers do.
- Cultural context: Having a strong influence on sexual behavior, cultures inform people about sexual scripts, or implicit rules that allow a person to judge the appropriate sexual behavior for a given situation. For example, people follow sexual scripts when deciding whether they should initiate sexual activity or wait to receive a partner’s advances.
A culture’s social and economic structure determines the gender roles that men and women adopt. These gender roles in turn determine people’s attitude toward sexual activity. In some cultures, for instance, women need marriage to get access to status and wealth. In such cultures, a woman is less likely to be interested in sex for its own sake, since casual sex can damage her reputation and reduce her chances of marriage.
Gender Differences in Sexual Behavior and Partner Choice
Many researchers have found that some differences exist between men and women in sexual behavior and partner choice, though all men and all women do not behave the same way or feel the same things.
|More interested in sex; initiate and think about sex more often||Less interested in sex|
|Want sex with more partners||Not as interested in sex with many partners|
|Desire sex without emotional commitment||Desire sex with emotional commitment|
|Focus on youth and physical attractiveness when choosing a sex partner||Focus on social and economic status when choosing a sex partner|
|Feel more jealous when partner is physically unfaithful||Feel more jealous when partner is emotionally unfaithful|
Some theorists use evolutionary theory to explain these gender differences. Their explanations are generally based on Robert Trivers’s idea that men and women make different parental investments in order to produce offspring. From a biological standpoint, men invest no more than the energy required for intercourse. Women, on the other hand, invest time and energy in pregnancy and breast feeding. Because of these biological differences, females can produce only a limited number of offspring, whereas males can potentially produce virtually unlimited offspring.
Males can increase their reproductive success by producing as many offspring as possible. Evolutionary theory predicts that men tend to choose attractive, youthful partners because these qualities imply good health and an ability to reproduce successfully. Females increase their reproductive success by being highly discriminating when choosing mates. They try to select males who have the most access to material resources, because such males can contribute the most to caring for offspring.
Furthermore, men must contend with paternity uncertainty—they can never be certain that they are the fathers of their partners’ offspring. Evolutionary theorists predict that men would therefore tend to have concerns about their partners’ sexual infidelity. Women, on the other hand, can be certain that their offspring are their own, though they cannot be certain that their partners will provide for their offspring. Therefore, they are more likely to be concerned about the emotional fidelity of their partners.
Problems with Evolutionary Explanations
Many people criticize the use of evolutionary explanations of gender differences in sexual behavior. Some critics argue that alternative explanations can account equally well for the observed gender differences. For example, women’s history of social and economic subservience may have taught them to place a high value on their partners’ access to material resources. Men’s preferences and behaviors may likewise be a product of socialization. See page 43 for more information on problems with evolutionary explanations.
Sexual orientation is such a controversial subject that people cannot even agree about how the term sexual orientation should be defined. Some people argue over whether it refers to sexual behavior, sexual attraction, emotional attraction, or all three.
Researchers define sexual orientation in a variety of ways, which means there is no clear idea about what proportion of the population is homosexual. Researchers also have many different opinions regarding how much biological and environmental factors contribute to sexual orientation.
Possible Biological Factors
Researchers have many ideas about the possible biological factors of homosexuality:
- Hormones: Some researchers have suggested that homosexuals and heterosexuals have different levels of various hormones in the blood. However, research in this area has failed consistently to find hormonal variations that could account for differences in sexual orientation.
- Genes: Others have proposed that there is a genetic basis for predisposition to homosexuality. To investigate the possibility of a genetic basis, researchers have studied the sexual orientations of the identical, fraternal, and adoptive siblings of homosexual people. This research has shown that the identical twins of homosexuals are much more likely to be homosexual than the fraternal twins of homosexuals. In turn, the fraternal twins of homosexuals are more likely to be homosexual than the adoptive siblings of homosexuals.
- Prenatal factors: Some researchers have focused on prenatal environment. These researchers believe that the level of hormones present during a critical period in prenatal development can affect the organization of the brain, which in turn can influence sexual orientation. Research shows that women who were exposed to high prenatal levels of androgens are more likely to be homosexual. Critics point out that not all women who were exposed to prenatal androgens became homosexual and that many homosexual women were not exposed to androgens prenatally.
- Brain differences: One researcher, Simon LeVay, examined anatomical differences in the brains of homosexual and heterosexual men. He found that a specific area of the hypothalamus tended to be smaller in homosexual men and in heterosexual women than in heterosexual men.
Many researchers believe biological factors alone can’t explain the origin of homosexuality. For example, there is only about a 50 percent chance that the identical twins of homosexual men will also be homosexual. Therefore, some other factor must make the other 50 percent heterosexual. Although this other factor remains unknown, researchers have proposed a number of environmental situations that might influence sexual orientation:
- An ineffectual, distant father and an overly close, domineering mother
- Seduction in childhood by a homosexual adult
- Same-sex sexual play as children
Many of these proposals lack empirical support.
At this time, no one knows exactly what determines sexual orientation. Possibly, men and women develop homosexual orientations through various pathways. It is also possible that the cause of homosexual orientation differs from individual to individual.