An amoeba can do an unusual mathematical trick: It multiplies by dividing. After it has grown to a certain size, the amoeba’s single cell divides in half to produce two amoebas. In about a day, the two amoebas have grown to the point at which they are ready to divide and form four; the day after that, there are eight amoebas, and so forth. How many amoebas will there be at the end of the week?

The institution of the foreign migrant worker appears around the world when a relatively rich country is near a relatively poor one and there is access between them. Mexican farm workers in the United States, Algerian farm workers in France, Turkish laborers in Germany, and Ethiopian domestic servants in Kuwait are all examples. Each example shows the combined effects of overpopulation and unequal distribution of employment opportunity and wealth. In all cases, there are dangers that migrant workers will be exploited by local employers who recognize their vulnerability and that they will be resented by local workers who see them as competitors. Cesar Chavez (1927–1994) organized the United Farm Workers union in California in response to such problems in 1962 and after a multiyear strike was able to obtain better wages and working conditions for grape pickers. Similar unions have developed in many places around the world.

Drama languished in Europe after the fall of Rome during the fifth and sixth centuries. From about A.D. 400 to 900 almost no record of dramatic productions exists except for those of minstrels and other entertainers, such as acrobats and jugglers, who traveled through the countryside. The Catholic church was instrumental in suppressing drama because the theater—represented by the excesses of Roman productions— was seen as subversive. No state-sponsored festivals brought people together in huge theaters the way they had in Greek and Roman times.

One form of distraction is imagery. Creating a vivid mental image can help control pain or other unpleasant physical symptoms. Usually people create a pleasant and progressive scenario, such as walking along the beach, hiking in the mountains, or enjoying a gathering of friends. Aggressive or arousing imagery can also be useful, such as imagining a heated argument, fighting off an enemy, or driving a race car at high speeds. Whatever imaginary scenario you use, try to visualize all the different sensations involved, including the sights, sounds, aromas, touches, and tastes. The goal is to become so absorbed in your fantasy that you distract yourself from the pain sensations.

Before the twentieth century, women had a single role, that of wife and mother. Occasionally accidents of royal succession placed a woman in a position of great power, and the eighteenth century saw two amazingly long-lasting cases: Catherine the Great, Empress of Russia, who ruled from 1762 to 1796, and Maria Theresa, de facto [in fact] empress of the Austrian Empire from 1740 to 1780. But what we now think of as “careers” were simply not open to women, with very few exceptions.

In 1985, scientists discovered that the high-altitude ozone layer, which shields organisms from harmful ultraviolet radiation, had thinned greatly over Antarctica. Ozone (O3) is produced by the action of sunlight on atmospheric oxygen (O2) in tropical regions and is transported to high latitudes, where it is destroyed. Chlorine compounds, produced mainly by humans, appear to be the main cause of the unusually high rates of ozone destruction. Ozone is now seriously depleted at very high latitudes, where conditions favor its destruction.

Anger is prompted by a person’s reactions to frustrating or provocative situations, not by the situations themselves. People make themselves angry by thinking angering thoughts. By challenging these thoughts, they can learn to turn down their anger alarm, avoid hostile confrontations, and save wear and tear on their cardiovascular systems.

Make a loud noise and infants only minutes old will startle and may even cry. They will also turn their heads toward the source of the noise, an indication that they perceive sound as roughly localized in space. Yet newborns’ hearing is not so acute for some parts of the sound spectrum as it will be when they are older. Sensitivity to sound improves dramatically in infancy and then more slowly until the age of 10, when it reaches adult levels.

Most mass media evolve through various stages, which are initiated not only by the diligence of great inventors, such as Thomas Edison, but by social, cultural, political, and economic circumstances. For instance, both telegraph and radio developed as new industrialized nations sought to expand their control over colonies and to transmit information more quickly. The phonograph, too, emerged because of the social and economic conditions of a growing middle class with more money and leisure time. Today, the information highway is a contemporary response to similar sets of concerns: transporting messages more rapidly while appealing to middle- and upper-middle-class consumers.

Meditation is not easy to define. In general, meditation refers to a group of techniques that induce an altered state of focused attention and heightened awareness. Meditation takes many forms, and has been used for thousands of years as part of religious practices throughout the world. Virtually every major form of religion has a rich tradition of meditative practices—whether Hindu, Taoist, Buddhist, Jewish, Christian, or Muslim. However, many people practice meditation independent of any religious tradition or spiritual context. Some forms of psychotherapy also include meditative practice as a component of the overall therapy.