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MCAT Content / Demographic Shifts And Social Change / Population Growth And Decline

Population Growth and Decline

Topic: Demographic Shifts And Social Change

Demography is the study of statistics such as births and deaths to understand the changing structure of human populations.

To explore questions about human populations, we turn to demography. Three of the most important components that affect demographics are fertility, mortality, and migration.

The fertility rate of a society is a measure noting the number of children born. The fertility number is generally lower than the fecundity number, which measures the potential number of children that could be born to women of childbearing age. Sociologists measure fertility using the crude birthrate (the number of live births per 1,000 people per year). Just as fertility measures childbearing, the mortality rate is a measure of the number of people who die. The crude death rate is a number derived from the number of deaths per 1,000 people per year. When analyzed together, fertility and mortality rates help researchers understand the overall growth occurring in a population.

Another key element in studying populations is the movement of people into and out of an area. Migration may take the form of immigration, which describes movement into an area to take up permanent residence, or emigration, which refers to movement out of an area to another place of permanent residence. Migration might be voluntary (as when college students study abroad), involuntary (as when Syrians evacuated war-torn areas), or forced (as when many Native American tribes were removed from the lands they’d lived in for generations).

Changing fertility, mortality, and migration rates make up the total population composition, a snapshot of the demographic profile of a population. This number can be measured for societies, nations, world regions, or other groups. The population composition includes the sex ratio, the number of men for every hundred women, as well as the population pyramid, a picture of population distribution by sex and age. Population projections predict changes in populations by examining current data.


Practice Questions

Khan Academy


MCAT Official Prep (AAMC)

Section Bank P/S Section Question 50

Practice Exam 2 P/S Section Passage 2 Question 6

Key Points

• Demography is the study of populations and population numbers and composition and how it is affected by mortality rates, fertility rates, and migration

• A population pyramid is a graphical representation of the distribution of age groups and sex in a population

• Population projection can be done by assessing the different factors that affect population numbers and using this and assumptions to predict the growth or decline of a population in the future

Key Terms

Demography: the study of population

Fertility rate: a measure noting the actual number of children born

Mortality rate: a measure of the number of people in a population who die

Population composition: a snapshot of the demographic profile of a population, based on fertility, mortality, and migration rates

Population pyramid: a graphic representation that depicts population distribution according to age and sex

Sex ratio: the ratio of men to women in a given population

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