Population growth and demographic change can be measured in many ways and ascribe to different theories that postulate changes in demographics over time and its impact on the social interactions of the population.

Demography is the study of population statistics and its changing effect on populations over time. Three of the most important components that affect the demographics are fertility, mortality, and migration.

The fertility rate of a society is a measure of the number of children born.

The mortality rate is a measure of the number of people who die.

Migration is a measure of the movement of people in and out of a country

These three components can be measured and can provide a snapshot of the changes to a population. Using these measures, theories of population growth and demographic change can be formulated to inform social interactions in populations.

There are four key theories in the study of populations growth and change:

Malthusian theory:  According to Malthusian theory, three factors would control the human population that exceeded the earth’s carrying capacity, or how many people can live in a given area considering the number of available resources. Malthus identified these factors as war, famine, and disease. He termed them “positive checks” because they increase mortality rates, thus keeping the population in check. They are countered by “preventive checks,” which also control the population but by reducing fertility rates; preventive checks include birth control and celibacy. Thinking practically, Malthus saw that people could produce only so much food in a given year, yet the population was increasing at an exponential rate. Eventually, he thought people would run out of food and begin to starve. They would go to war over increasingly scarce resources and reduce the population to a manageable level, and then the cycle would begin anew.

Zero population growth theory: the environment, not specifically the food supply, will play a crucial role in the continued health of the planet’s population. The theory postulates that the human population is moving rapidly toward complete environmental collapse, as privileged people use up or pollute a number of environmental resources such as water and air. This theory advocates for a goal of zero population growth (ZPG), in which the number of people entering a population through birth or immigration is equal to the number of people leaving it via death or emigration.

Cornucopian theory: Asserts that human ingenuity can resolve any environmental or social issues that develop. As an example, it points to the issue of the food supply. If we need more food, the theory contends, agricultural scientists will figure out how to grow it, as they have already been doing for centuries.

Demographic transition theory: suggests that future population growth will develop along with a predictable four-stage model. In Stage 1, birth, death, and infant mortality rates are all high, while life expectancy is short. As countries begin to industrialize, they enter Stage 2, where birthrates are higher while infant mortality and the death rates drop. Life expectancy also increases. Stage 3 occurs once a society is thoroughly industrialized; birthrates decline, while life expectancy continues to increase. Death rates continue to decrease. In the final phase, Stage 4, we see the postindustrial era of society. Birth and death rates are low, people are healthier and live longer, and society enters a phase of population stability.

Practice Questions

Khan Academy

MCAT Official Prep (AAMC)

Online Flashcards Sociology Question 17

Section Bank P/S Section Question 51

Key Points

• Demography is the study of populations  and changes to populations over time through birth rates, mortality rates, and migration
• Theories of sociology can be ascribed to population growth to postulate what changes happen within a society and why due to growth

Key Terms

• Carrying capacity: how many people can live in a given area considering the number of available resources.
• Industrialized: develop industries in (a country or region) on a wide scale.
• Zero population growth: is a condition of demographic balance where the number of people in a specified population neither grows nor declines