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Population
Bulletin Vol. 53 No. 3 September 1998 Table of Contents |
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Population: A Lively Introduction Population Composition
People have many characteristics with demographic dimensions—including their sex, age, race, ethnicity, occupation, education, religion, marital status, and living arrangements (see Box 5). A population has corresponding characteristics constructed from personal traits of individual members. The age composition of a population, for example, is determined from the collective ages of all its members. This Population Bulletin focuses on age, sex, race, and ethnicity because these characteristics are fashioned solely by the prime demographic forces of fertility, mortality, and migration. The age composition of a society can be depicted by a population pyramid, a figure that shows the proportion of the population in each age group. Notice in Figure 6, for instance, that about 16 percent of the population of Kenya is under age 5, while only about 3 percent is age 65 and older. The sum of the proportions in all age groups equals 100 percent of the population.
There are three general types of population pyramids: those depicting rapid growth, slow growth, and near- zero growth or decline. A rapid-growth population is the only one that really looks like a pyramid because each age cohort is larger than the one born before it. This pyramid shape results primarily from sustained high fertility. If couples in one generation average eight children, for example, their children's generation will be about four times larger than their own. The pyramid's base would be about four times as wide as its middle. The distinctive pyramid shape also results from declines in mortality. Because of high mortality in the past, older age groups have relatively few surviving members and occupy a small section of the pyramid. The base is broadened by the fact that mortality, particularly infant mortality, is declining. This increases the proportion of the younger birth cohort surviving to the next age group. Because the majority of people in rapid-growth societies are young, there is tremendous momentum for future growth because the large pool of young people are the parents of the future. Even if they only have four children apiece (the average for some less developed countries), their children's generation would be twice the size of their own. Kenya's population age structure is typical of a young, rapid-growth society. A population that is not growing, or is decreasing, produces a very different shape. The base of Italy's population "pyramid" is narrowing because its birth rate has been falling. The 1990-1994 birth cohort was barely one-half the size of the 1965-1969 cohort. If fertility remains below replacement, the pyramid's base will continue to constrict and Italy will undergo natural decrease. If Italy's TFR returns to the replacement level of 2.1, its age and sex structure would eventually assume a rectangular shape because similar numbers of births would occur each year. Because mortality is low, this shape will be maintained until the older ages, when mortality will eat away at the top bars. At the very top, the female bar is almost always longer because women live longer than men. A slow-growth population is generally in the process of changing from a rapid-growth to a near-zero growth shape in response to changes in fertility and mortality. The United States is typical of these "middle-age," slow-growth societies. Population pyramids also can be shaped by migration. Because migration is age selective, it alters the shape of age-sex pyramids in both the place of origin and destination. Migrants tend to be young adults; a steady migration stream is likely to make the place-of-origin population older, and the place-of-destination population younger. There are plenty of exceptions to this pattern. The population pyramid of the state of Florida, for example, has grown older because of the influx of retirees. Migration streams that are predominately male—as is labor migration to Middle Eastern countries—create an unbalanced pyramid, illustrated by Figure 8.
Pyramids also reflect historical events—wars, famines, baby booms or busts, and changes in immigration policies—that have affected one of the three demographic variables. Consider the tumultuous events portrayed in the pyramid for Germany in Figure 7. Births plummeted during the two world wars and a severe economic crisis, for example.
Median Age Population pyramids depict the general shape of a population's age structure, but they do not provide rates or measures that can be compared over time or with other populations. One such measure of age composition is the median age—the age at which exactly half the population is younger and half is older. In general, developing societies have rapidly growing populations with low median ages, while developed societies have slow-growing or declining populations with high median ages. Niger had a median age of 16 in 1995, compared with 38 for Sweden and Germany.52 Nearly four-fifths of the world's population lives in developing countries, and the world's overall age structure is young—about 26 years. The age structure of the United States looks more like a bowling pin than a pyramid (see Figure 6). This shape was created by drastic swings in the number of births—from the historic low of the 1930s, to the baby-boom peak of 1957, down to the baby-bust low of the mid-1970s, and back to the baby boomlet of the 1980s and early 1990s. The pyramid's middle-age bulge is composed of the baby-boom cohort, which has been likened to a swallowed pig moving through a python.53 The narrower base is made up of the baby-bust cohorts born since the late 1960s. Each year the U.S. population gets older, primarily because of the aging of the baby boomers and low fertility. Increases in average life expectancy also have contributed to the aging of the population. The U.S. median age was 34.9 in 1997, up from 27.9 in 1970. The U.S. median age could near 39 years in the 21st century.54 Effects of Age Composition The age structure of a society has a profound impact on its demographic and social character. Some of these impacts have been noted already—for example, the effect of age structure on population growth and on the average age of a society. But age structure is relevant to many seemingly unrelated social problems.55 The U.S. baby-boom generation provides a vivid example of the varied effects of changing age structure on society. The baby boomers, born between 1946 and 1964, are 78 million strong—much larger than the cohort that preceded them, and larger than the cohort that followed. They produced the bulge in the age pyramid for the United States in Figure 6. As they passed through each stage of the life cycle, the boomers faced shortages—in elementary schools, colleges, housing, and employment. The baby-boom generation often left excess supply in its wake because by the time enough schools or houses were built, teachers were trained, and colleges were expanded, the boomers no longer needed them. The 1980s found colleges scrambling to find students to fill slots created for the boomers. Real estate prices soared when baby boomers began to buy homes, then dropped as the boomers settled down to raise families. Some analysts see the age structure as responsible for many social changes that accelerated during the 1960s and 1970s when the baby boomers reached adulthood. Crime is also affected by age structure because young adults—ages 18 to 24—are most likely to be involved in crime. The aging of the U.S. population is one reason cited for a welcome decline in violent crime rates in the late 1990s. Young adults may be just as likely as ever to engage in crime, but crime rates have fallen because these youths make up a smaller share of the population. This illustrates how changes in age composition can alter the severity of a social problem even if there is no change in the underlying conditions. Similarly, aging increases the proportion of the population who are disabled or chronically ill. The aging of the large baby-boom population, along with the improvements in longevity, are expected to put increasing strains on the nation's health and pension systems over the next half century. Although the number of children is about the same in the late 1990s as it was during the baby boom (about 70 million under age 18), children now make up a smaller percentage of the population. The population under age 18 was about 26 percent of the 1997 U.S. population, compared with 36 percent of the 1960 population. Population pyramids also show the relative proportion of men and women in each age group. Small differences are difficult to discern, but some are obvious. Consider the bite out of the male side of Germany's pyramid for people ages 65 to 94 (see Figure 7). This indentation reflects the military casualties of World War I and World War II and the longer life expectancy for women than men at advanced ages. The sex composition of a population can be summarized by the sex ratio—the ratio of males to females. This ratio is usually expressed as the number of males for every 100 females. The world's sex ratio in the 1990s was 102, or 102 males for every 100 females. The ratio for developed countries was 95; for developing countries, 104. Sex ratios are determined by the now familiar forces—fertility, mortality, and migration. The influence of migration on the sex ratio is easy to assess. The unbalanced sex ratio of the United Arab Emirates (UAE) came about because the UAE brought in thousands of foreigners from Asia and other parts of the Middle East to work in the country's oil fields and construction sites. The majority of these labor migrants were men unaccompanied by their families. Women in the UAE and many other Moslem countries are less likely to work outside the home than women in Europe, for example. There were fewer jobs for women and relatively few women were recruited from abroad. Furthermore, the host governments did not want the immigrants to settle permanently and reasoned that the foreigners were less likely to stay if they had families waiting for them back home. The effects of this extremely unbalanced immigration pattern are evident in the population pyramid for the UAE shown in Figure 8. The sex ratio for the UAE was estimated at 179 in 1995. Mortality influences the sex ratio because males have higher death rates than females at nearly every age, be-ginning with conception. It is possible that as many as 150 male fetuses are conceived for every 100 female fetuses. But a large percentage of pregnancies spontaneously abort within the first few weeks, and a woman is more likely to miscarry a male fetus than a female fetus. By the time a pregnancy is carried to term, the ratio of males to females is down to about 105 (105 males to 100 females). In the United States, the ratio of men to women is about equal (a sex ratio of 100) between ages 25 and 34. The ratio declines to just below 95 by ages 50 to 54, and keeps falling. For the 85-and-older group, there are only 40 men for every 100 women. This preponderance of women at the older ages can be seen in the pyramids for Italy and the United States (Figures 6 and 7). Fertility affects the sex ratio by influencing the proportion of young people in a population. Any force that increases the relative proportion of young people in a society—as does a high fertility rate—raises the overall sex ratio of the society because the sex ratio is higher in the younger ages. A rapid drop in infant and child mortality, for example, in response to large-scale inoculation campaigns or the importation of modern medical technology, also contributes to the "younging" of a population. Conversely, any force that decreases the relative proportion of young people—such as high mortality or low fertility—lowers the overall sex ratio. In some nations cultural factors override the biological advantage that women usually have. In Indian society, for example, women are accorded low status. Girls receive less food, medical care, and familial attention than boys.56 This discrimination is reflected in the sex ratio of India—estimated at 107 in 1995. Sons are highly valued in many other Asian countries as well, often to the detriment of daughters. The sex ratio for all of South Central Asia was 106 in 1995, compared with 99 in Latin America. Effects of Sex Composition Why does the sex ratio matter? It affects the availability of marriage partners, for one thing. An unbalanced sex ratio in the young adult years—because of migration, fertility swings, or war casualties, for example—means that there may not be enough men or women for everyone to find a spouse. The scarcity of potential marriage partners is not merely a personal disappointment for individuals who really want to get married, it also affects the social and economic structure of a society.57 Marriage rates, childbearing practices, family stability, crime rates, and even the comparative status and power of women and men can be influenced by the sex ratio. In the United States, for example, the annual increases in the number of births during the baby boom created a "marriage squeeze" in the 1970s and 1980s by producing more women than men in the prime marrying ages. This phenomenon, along with the continued mortality gap between the sexes, has been linked to many of the changes in the American family since the 1960s—greater percentages of women remain single or delay marriage, get divorced, bear a child out of wedlock, or work outside the home.58 William Julius Wilson and other sociologists have speculated that a shortage of marriageable black males in ghetto areas may have fostered the dramatic increase in the proportion of births to unmarried women and in families headed by single women among African Americans in recent decades.59 In poor neighborhoods, the pool of black men who could support a family has been depleted by high rates of unemployment and incarceration, and by the high mortality rates of young black men. Similarly, the sex composition of immigrant groups has a bearing on the speed and ease with which they adjust to their new society. An immigrant group that contains more men than women, for instance, may compete with native men for marriage partners. This possibility, even if it does not happen, invites resentment against immigrants and even social disorganization. Also, men are far more likely than women to engage in crime, especially men in the young adult ages when most people migrate. Higher crime rates can create negative stereotypes that impair immigrants' relations with other Americans. 60 Many population characteristics are fluid. A person's age increases constantly, and educational attainment and marital status can change over time. Other characteristics are fixed at birth, like sex. Race and ethnicity appear to fall into the second category. An individual cannot change his or her ancestors; they are accidents of birth. But how societies evaluate and classify them is highly variable. Race and ethnicity are defined differently by different societies. These definitions, as well as their political and social significance, change over time. What are race and ethnicity? They are not scientific terms. There is no consensus about how many races there are or about exactly what distinguishes a race from an ethnic group. Many social scientists agree that, while race may have a biological or genetic component, it is defined primarily by society, not genetics. There are no universally accepted categories. Physical characteristics, such as facial features, hair texture, and skin color, are often used to identify racial groups, but these are highly subjective identifiers.61 Ethnicity is usually defined by cultural practices, language, cuisine, and traditions rather than biological or physical differences. In the United States, ethnicity often refers to the national origin of immigrant groups. The United Nations publishes data on ethnic composition reported by individual countries, but the UN warns that the categories are "not uniform in concept or terminology. They represent a variety of characteristics or attributes, variously designated by countries or areas as race, color, tribe, ethnic origin, ethnic group, ethnic nationality, and so forth…By the nature of the subject, these groups vary from country to country—no internationally relevant criteria can be recommended."62 The UN does not publish separate figures on "race." U.S. Race and Ethnic Categories The U.S. Census Bureau collects and publishes information by race and ethnicity in accordance with federal guidelines from the Office of Management and Budget (OMB). In 1997, OMB recommended that data be presented for five racial groups and two ethnic groups. The race groups are: (1) white, (2) black or African American, (3) Asian, (4) American Indian and Alaska Native, and (5) Native Hawaiian and Other Pacific Islander. The U.S. Census Bureau also includes an "Other Race" option for people who do not identify with the OMB categories. The two ethnic groups are Hispanics (or Latinos) and non-Hispanics. Hispanics are considered an ethnic group, not a race, but this distinction confuses many Americans. The Census Bureau classifies as Hispanic anyone who traces his or her ancestry to Spain, the Spanish-speaking countries of Latin America and the Caribbean, or any other Spanish culture. Hispanics may be of any race. Most report themselves as white, but a large number report their race as "other," which underscores the confusion about race and ethnic definitions. In the 1990 Census, 43 percent of Hispanics checked the "other" race box. A small number of Hispanics report themselves as black, Asian, or American Indian. Many Dominican Americans and Puerto Ricans have African ancestry, for example, and might choose black and Hispanic. Some Filipino Americans with Spanish surnames identify themselves as Hispanic but also as Asian. Many Americans have parents from different racial backgrounds—a white mother and a black father, for example, or an Asian mother and a white father. Previously, mixed-race Americans were asked to indicate the race they most closely identified with, thus rejecting the ancestry of one of their parents. People with one Hispanic parent faced the same dilemma. In accordance with the 1997 OMB decision, the 2000 Census form will, for the first time, allow Americans to check more than one race, but they still must choose one ethnic group. No one knows how many people will choose more than one race. Preliminary research by the U.S. Census Bureau suggests that about 2 percent of the U.S. population—more than 5 million Americans—may identify with more than one racial category in the census. The results are scheduled for release in 2002.63 Although exact definitions are elusive, race and ethnicity are important variables in the United States and most other countries. The relative size of individual groups sometimes determines their political power and socioeconomic status. Shifts in racial and ethnic composition can alter the social structure and foment prejudice and social unrest. Such problems often arise from a basic concern that some other group will grow faster than one's own and, consequently, increase its importance within the society. Changes in racial and ethnic composition come about through differences in the fertility, mortality, and migration of racial and ethnic groups. Major shifts in racial and ethnic composition are occurring in countries throughout the world. In South Africa, whites are becoming an ever-smaller minority, owing to a lower birth rate and a higher emigration rate than those for black or colored South Africans. In Israel, the Arab population is growing faster than the Jewish population and may become the majority in Israel early in the 21st century. And in many European countries, immigrant groups from developing countries are growing faster than their hosts, leading to anti-immigrant backlashes.64 Racial and ethnic diversity has been a hallmark of the United States since colonial times. Waves of immigrants from different parts of the globe, and different fertility and mortality rates among those groups than among native-born Americans, have kept the racial and ethnic composition in flux. This uneven growth continues, driven by the differences in fertility, mortality, and migration discussed earlier. In the 1990s, three of every four U.S. residents trace their ancestry to Europe. If present trends continue, one of every two residents will have European ancestry in 2050, while nearly half will trace theirs to Latin America, Asia, Africa, the Middle East, or the Pacific Islands. African Americans are the most numerous U.S. racial minority. But because of more immigration and higher fertility, Hispanics are projected to outnumber blacks early in the 21st century and become the nation's largest minority group. Asians will move from a trace element to a sizable minority. It is unlikely that any single racial or ethnic group will outnumber white non-Hispanics in the near future, but by 2100 white non-Hispanics may fall from being the majority group to being the largest of several large racial and ethnic minority groups. The evolving ethnic composition has a profound impact on almost every aspect of American society, from social values and culture to education, politics, and industry. More public schools than before teach non-English-speaking students from a wide variety of cultural backgrounds. In most big-city school districts, white non-Hispanics are already a racial minority. Because minorities have a younger age structure and higher fertility than non-Hispanic whites, minorities will make up an increasing share of the new job entrants in the U.S. labor force. By 2040, one-half of 18-year-olds are likely to be black, Hispanic, Asian, or American Indian.
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