CONCEPTS IN BIOLOGY
PART VI. PHYSIOLOGICAL PROCESSES
27. Human Reproduction, Sex, and Sexuality
27.3. Components of Human Sexual Behavior
The primary biological goal of sexual intercourse (coitus, mating) is the union of sperm and egg to form offspring. However, in humans and some other animals, sexual intercourse between willing partners usually is enjoyable and is an important part of the social and psychological aspects of life. Sexuality is a complex interaction that involves distinct components.
Sexual attraction involves many factors, but sight and smell are probably the most important. How one person appears to another is usually what catches the other’s attention. If we find a person pleasing in appearance, we say he or she is “attractive”; that is, we want to be closer. Like many other organisms, humans release chemicals that act as attractants. These chemicals are called pheromones. The existence of pheromones in humans has been well-documented even though we usually are not aware of their actions. The cosmetic and fashion industries are founded on these fundamentals of sexual attraction (figure 27.3). After the initial attraction, the couple will usually talk. The conversation will better acquaint the two, present the idea that there is an attraction, and may suggest that they are interested in sexual intercourse. This period is often called courtship and may be brief or develop into a long-term relationship depending on how the two respond to one another. However, ultimately, sexual intercourse occurs or the relationship ends.
FIGURE 27.3. Sexual Attraction
Both males and females find appearance to be of primary importance in mate selection.
Foreplay is the term used to describe sexual stimulation that precedes sexual intercourse. Hugging, kissing, and fondling (petting) arouse sexual excitement and desire. This leads to changes in the levels of certain hormone production and an increase blood flow in both male and female genitals. In males, tissues in the penis become engorged with blood, causing the penis to stiffen or become erect. In females, the clitoris becomes erect and the labia become swollen. In addition, lubricating fluids are released from male and female reproductive tracts. Throughout arousal, the heart rate increases, breathing quickens, and blood pressure increases.
Sexual intercourse involves inserting the erect penis into the vagina. Once the penis is inside the vagina, pelvic movements result in stimulation of both the male and female and usually results in ejaculation by the male. Ejaculation is the release of semen, which contains sperm and other fluids, from the penis. It occurs with a pulsating of smooth muscle in the tubes that lead from the testes to the penis. This release is generally accompanied by a sensation called orgasm. Orgasm is the pleasurable climax of sexual activity. In addition to the muscles of sex organs (vagina, uterus, and male sex organs), muscles throughout the body begin to spasm. Following orgasm, blood, which had accumulated and caused erection of the penis or clitoris and swelling of labia, leaves and these organs return to normal. This period is typically associated with a period of complete relaxation.
Two other forms of sexual intercourse practiced are anal (penis in anus) and oral (penis in mouth or oral stimulation of vagina or clitoris). These two variations may also be part of the arousal phase of a sexual encounter.
Long-term relationships usually involve a conscious decision by the two partners to live together and make joint decisions about many aspects of their lives. However, an important part of maintaining such relationships is paying attention to the sexual aspects of the relationship. Maintaining an active, enjoyable sex life in a long-term relationship requires the same amount of effort that was extended at the beginning of the relationship. Things that can interfere include work (time away, lack of free time, tiredness), family problems (kids, relatives), physical exhaustion (work, sports), affairs, emotions (depression, anger, jealousy), and a person’s overall health (overweight, strength, pain, long-term illness). The use of alcohol, street drugs, or certain prescription medications can lead to a reduction of sex drive and may include erectile dysfunction (ED). Since sight plays an initial and important role in sexual attraction and self-image, changes in a person’s anatomy can also dampen sexual activity; for example, changes such as a mastectomy due to cancer or disfigurement due to an accident. In addition, acquiring a sexually transmitted disease can place limits on sexual activity in socially responsible individuals.
27.3. CONCEPT REVIEW
5. What is the primary biological function of sexuality?
6. Describe changes in the body that are associated with foreplay and orgasm.