CONCEPTS IN BIOLOGY

PART VI. PHYSIOLOGICAL PROCESSES

27. Human Reproduction, Sex, and Sexuality

Are Sperm Counts Falling?

Environmental factors could be involved.

In recent years there have been several studies that suggest that sperm counts have been falling. One British study suggests that sperm counts have fallen by 29% in 12 years. Another study found that men with higher levels of certain pesticides in their blood had lower sperm counts. There are many critics of the various studies, who question the way the data were collected or the conclusions reached. For example, some data were collected at fertility clinics where men might be expected to have low sperm counts. Other studies had very small sample sizes or had other problems with the way the study was designed and carried out.

Regardless of the quality of the data, people with particular views have used these studies to support their concerns about environmental chemicals—pesticides, chemicals in plastics—the use of birth control pills, consumption of high amounts of beef, and a variety of other environmental factors. Some have even suggested that tight pants or the heat from laptop computers could raise the temperature of the testes and reduce sperm counts.

• Could environmental factors affect sperm production?

• Is fertility falling?

• Should a well-designed, worldwide study of sperm counts be done?

ü  Background Check

Concepts you should already know to get the most out of this chapter:

• The nature of meiosis and gamete production (chapter 9)

• The fundamentals of genetics (chapter 10)

• The basic structure and function of the endocrine system (chapter 26)

27.1. Sexuality from Various Points of View

Probably nothing interests people more than sex and sexuality. Sex is the nature of the biological differences between males and females. By sexuality, we mean all the factors that contribute to one’s female or male nature. A person’s sexuality includes the structure and function of the sex organs, sexual behavior, and the ways in which culture influences sexual behavior. Males and females have different behavior patterns for a variety of reasons. Some behavioral differences are learned (e.g., patterns of dress, the use of facial makeup), whereas others appear to be less dependent on culture (e.g., degree of aggressiveness, the frequency of sexual thoughts).

There are several ways of looking at human sexuality. The behavioral sciences tend to focus on the behaviors associated with being male and female and what is considered appropriate or inappropriate sexual behavior. Psychologists consider sexual behavior to be a strong drive, appetite, or urge. They describe the sex drive as a basic impulse to satisfy a biological, social, or psychological need. Other social scientists, such as sociologists and cultural anthropologists, are interested in sexual behavior as it occurs in various cultures. When a variety of cultures are examined, it becomes very difficult to classify various kinds of sexual behavior as normal or abnormal. What is considered abnormal in one culture may be normal in another. For example, public nudity is considered abnormal in many cultures, but not in others (figure 27.1).

FIGURE 27.1. Culture and Sexuality

In the culture of Papua New Guinea, tradition patterns of dress typically involve partial nudity. This would be unacceptable in many Muslim cultures, which regards exposure of skin as immodest. In both cultures there are differences in the dress of men and women.

Biologists have studied the sexual behavior of nonhuman animals for centuries. They have long considered the function of sexuality in light of its value to the population or species. Sexual reproduction results in new combinations of genes, which are important in the process of natural selection. Many biologists are attempting to look at human sexual behavior from an evolutionary perspective and speculate on why certain sexual behaviors are common. The behaviors of courtship, mating, the raising of the young, and the division of labor between the sexes are complex in all social animals, including humans, as demonstrated in the elaborate social behaviors surrounding picking a mate and forming a family. It is difficult to draw the line between the biological development of sexuality and the social customs related to the sexual aspects of human life. However, the biological mechanism that determines whether an individual will develop into a female or a male has been well documented.

27.1. CONCEPT REVIEW

1. Define the term sexuality.

2. How do psychologists, biologists, and anthropologists differ in how they view sexuality?