Population Studies: Demographics, Theories, and Pyramids
In sociology and biology, a population is a group of people or organisms of a species that live in a specific geographical area or space. The number of people is normally determined by a census. Demography is the statistical study of human populations. Several aspects of human behavior in populations are studied in sociology, economics, and geography, especially in population geography. The study population is usually governed by the laws of probability, and the conclusions of the studies may not always be applicable to some individuals, groups, or countries. These are theories to explain the patterns of population growth in many countries worldwide.
According to Sidney H. Coontz[1], population theories can be classified into three groups:
Biological Theories
These theories suggest that humans are like any living being. They include all those who believe that the laws governing the growth of the human species are the same as those that regulate the growth of animals and plants. The thesis that food availability correlates with population growth is a clear example of a biological theory applicable to both humans and other living things. According to this thesis, there are alternating periods in which the number of inhabitants is below or above the level of food resources, which determines a decrease or increase in mortality, respectively. Biological theories might include those of Malthus[2] and Josué de Castro[3]. Malthus studied population growth without relating it to cultural factors. For Malthus, population growth had a higher evolutionary rate than food production: the number of inhabitants grew following a geometric progression, whereas food availability increased at an arithmetic progression.
Economic Theories
Based on the theories of Marx-Lenin, these theories imply that population growth is a result of the demand for labor. Much of the economic theories are no longer valid due to technological development in industry, resulting in a reduced need for manpower over time. They refer to the second half of the nineteenth century. The film How Green Was My Valley[4] shows this theory in practice, depicting the life of a small village where the discovery of a coal mine creates employment for all men and children in mining tasks. The film also illustrates the tremendous impact of the Industrial Revolution on rural migration to cities.
Population Pyramids
- Expansive Pyramid: A wide base and narrow top are typical of late-developing countries with high birth rates and mortality rates and high natural growth. These countries are dominated by youth.
- Stationary Pyramid: A smaller base. They are typical of aging countries in which youth and adults are dominant.
- Regressive Pyramid: A narrow base, center, and relatively broad peak. They are typical of developed countries with low birth rates and reduced mortality, and low natural growth. In these countries, the adult and elderly populations are dominant.
Population density is the total number of inhabitants divided by the number of square kilometers of area, region, or country. It is measured by dividing the number of individuals by the area of the region where they live. Countries with greater population density are microstates: Monaco, Singapore, Vatican City, and Malta. Among larger countries, Bangladesh has the highest population density. Expressed in relative terms (inhabitants per km²), population density is used to compare the demographics of different countries, regions, or parts of the world. A population distribution by year and sex of a given population, nation, or region is usually represented by a population pyramid. This histogram or bar graph represents the portions of the population by age group and sex on the horizontal (X) axis, with age groups in 5-year increments on the vertical (Y) axis. The male population is represented on the left vertical axis and the female population on the right.
The economically active population (EAP) is a term coined by economic science to describe, within a defined universe of people, those who are able to work and work. It refers to the fraction of the population belonging to the workforce (also called the economically active population or EAP) who are working at the time of the census. The inactive population is made up of people who are unemployed due to their age—typically children under 15 and people over 65 (the most common retirement age in most countries). This is the most common situation worldwide, although there are some differences between countries regarding labor laws. However, there are countries, and above all individual situations, that go beyond this age limit: children under 15 who work throughout the world, especially in rural areas, and many over 65 who also work. The trend, however, is towards ever earlier retirement, because technology often eliminates sources of employment, and private companies are advancing different retirement ages to employ more people with lower salaries.