What Is Demography?
Demography is the study of the size, distribution, and composition of populations. A population is defined as the total number of inhabitants of a given area, such as a city or country. Demography considers human populations. Demographers look at the size of populations as well as population growth, the change in the number of people in a certain area during a certain period of time. Positive population growth means that the number of people is increasing. Negative population growth means that the number of people is decreasing.Three factors determine population growth: fertility, mortality, and migration. Fertility refers to the number of live birth in a given population, which can be affected by numerous factors including education and migration. Demographers use several tools to measure fertility, such as crude birth rate and general fertility rate. The crude birth rate is the number of live births per 1,000 people in a population in a given year. It is based on total population and does not factor in other information, such as sex or age. The general fertility rate is the number of live births per 1,000 women of childbearing age (15 to 44) in a population in a given year. The fertility rates of a country or a community can be influenced by many factors, including culture, access to health care, and economic trends. Most high-income, industrial, or postindustrial countries have relatively low fertility rates compared to lower-income countries. This may be linked to access to education and birth control, norms related to gender and family, and cultural values. Fertility rates can also be affected by environmental factors, such as air and water quality.
Global Birth Rates: Births per 1,000 People (2017)
Migration is the movement of people into and out of specific areas. Migration includes in-migration, or immigration (movement into an area) and out-migration, or emigration (movement out of an area). Migration is a permanent move; people who migrate take up permanent residence in a different location. Migration can take place across national borders or within a country's national borders. In addition to population size, demographers look at population composition, the demographic profile of a population. It includes statistics on the age, sex, ethnicity, race, and other characteristics of the people who make up that population. As population compositions changes, the needs and concerns of a society tend to change as well. Migration can also affect the fertility and mortality rates and age distribution of a population.
Population Growth and Overpopulation
For over 200 years many people around the world have worried about overpopulation. In 1798 English clergyman and economist Thomas Malthus outlined what is known at the Malthusian theory, asserting that without restraint, the population will increase at a greater rate than its food supply. Malthus argued that while population growth is exponential, the growth of food production is linear. He asserted that population is controlled through positive checks—war, famine, disease—and preventive checks—measures to reduce fertility. He warned that to avoid mass starvation, people must control fertility, specifically by marrying later and becoming more celibate.
In the last 200 years, world population has surged, but not at the rate Malthus predicted. In fact, the rate of increase has slowed, especially in industrialized countries. According to demographic transition theory, population growth occurs in four stages, based on levels of industrialization:
- Stage 1 occurs in preindustrial societies, where birth, death, and infant mortality rates are high, life expectancy is short, and the population is stable.
- Stage 2 occurs as societies begin to industrialize. Birth rates remain high, while death and infant mortality rates decrease, life expectancy increases, and the population soars.
- Stage 3 occurs in industrialized societies. Death and infant mortality rates decrease and life expectancy continues to increase, but birth rates decrease and the population becomes more stable.
- Stage 4 occurs in postindustrial societies, where birth, death, and infant mortality rates remain low, life expectancy is high, and population growth is stable or in decline.
In 1968 American biologist Paul Ehrlich (b. 1932) proposed a goal of zero population growth to combat concerns about mass starvation and damage to the environment. Zero population growth means maintaining the population at a constant level by limiting births so that the number of people born in a year is equal to the number of people who die. (In looking at a particular community or society, zero population growth can also take into account numbers of people who immigrate and emigrate, as well as the numbers of people who are born and who die). Ehrlich did not believe the planet could withstand the pollution and depletion of natural resources brought about by a larger population. Ehrlich advocated population control, including social policies such as the elimination of tax benefits for people who had more than the permitted number of children. His less controversial proposals focused on environmental issues and how patterns of consumption threaten to use up natural resources needed to sustain human life. Ehrlich's critics argue that free markets function to pressure societies to use resources in certain ways. For example, when oil prices rise, people use less oil. However, social policies can also create these types of pressure.