Demographic shifts and populations | Demographic characteristics and processes | Psych/soc

Theories of demographic change

Malthusian

Thomas Malthus, an early 19th-century English clergyman, predicted that Earth’s population would eventually exceed its ability to sustain itself. He argued that three “positive checks”—war, famine, and disease—would naturally curb overpopulation by increasing mortality rates. These were balanced by “preventive checks,” such as birth control and celibacy, which reduced fertility rates. Malthus believed food production could not keep up with exponential population growth, leading to starvation, conflict, and repeated cycles of population decline.
However, his predictions did not come true. Advances in food production, medical innovations, and widespread contraception have helped sustain population growth. Still, some believe Malthus’ concerns remain relevant, warning that Earth’s resources may eventually be depleted.

Zero population growth

Paul Ehrlich, a neo-Malthusian researcher, expanded Malthus’ ideas by focusing on environmental degradation rather than food shortages. He warned that overpopulation, combined with resource depletion and pollution, could lead to environmental collapse. Ehrlich advocated for zero population growth (ZPG), where births and immigration equal deaths and emigration, stabilizing the population. While opinions on ZPG are mixed, it remains a debated solution to overpopulation concerns.

Cornucopian theory

Cornucopian theory rejects the idea that overpopulation will lead to catastrophe, arguing that human ingenuity can solve environmental and social challenges. Supporters believe that advancements in science and technology, such as agricultural innovations, will continue to meet growing needs, as they have for centuries.

Demographic transition theory

Demographic transition theory outlines four stages of population growth as societies evolve from pre-industrial to post-industrial.
- Stage 1: High birth, death, and infant mortality rates; short life expectancy (e.g., 1800s U.S.).
- Stage 2: Declining death and infant mortality rates, but high birth rates; life expectancy increases (e.g., Afghanistan).
- Stage 3: Birth rates decline, while life expectancy continues to rise; death rates remain low (e.g., Mexico).
- Stage 4: Low birth and death rates, longer life expectancy, and population stability or decline (e.g., Sweden).

Population growth and decline

Population composition provides an overview of a population’s demographic characteristics, including fertility, mortality, and migration rates. It also includes the sex ratio (the number of men for every hundred women). It helps sociologists analyze trends and predict social and economic challenges.

A population pyramid visually represents the distribution of a population by age and sex. This graphical tool is useful for understanding population trends, such as aging populations or youth-heavy societies, and assessing future societal needs.

Interpreting population pyramids:

Bottom-heavy → Indicates population growth with a high birth rate.
Top-heavy (“Upside down”) → Suggests population decline due to low birth rates and aging population.
Side-skewed → Reflects gender imbalance within the population.

How population projections are made

Population projections predict future population size and structure using demographic trends such as fertility, mortality, and migration rates.

Key steps in population projection:

Gathering data – Uses census records, birth/death rates, and migration statistics.
Analyzing birth rates – Determines how many people will be added.
Assessing death rates – Measures population loss and life expectancy.
Tracking migration – Accounts for immigration and emigration effects.
Applying statistical models – Uses methods like cohort-component analysis for forecasting.
Considering social & policy factors – Adjusts for healthcare, economic trends, and government policies.

Projection scenarios:

High growth – Higher birth rates and lower mortality.
Low growth – Declining fertility and aging population.
Stable/declining – Low fertility with longer life expectancy.

Though not exact, these projections help guide urban planning, resource management, and economic policies.

Fertility, migration, and mortality

Fertility and mortality rates (e.g., total, crude, age-specific)

Fertility rate measures the number of children born, while fecundity refers to the potential number of children a woman could have. Sociologists track fertility using the crude birth rate, which counts live births per 1,000 people per year.
Mortality rate measures deaths in a population, with the crude death rate indicating deaths per 1,000 people annually. Together, fertility and mortality rates help analyze population growth.
Migration refers to the movement of people in and out of an area. Immigration is moving into a new place, while emigration is leaving one. Voluntary migration is when a person is not under economic or political duress and chooses to move to a new place, involuntary migration is when a person needs to move to a new place under duress, such as during war or when a major natural disaster has made their hometown inhabitable, and forced migration, such as the historic transporting of slaves from Africa to the New World, the Trail of Tears, or modern-day human trafficking through kidnapping or under false pretenses.

The United Nations Population Fund (UNPF) classifies countries based on fertility rates:

High fertility (e.g., sub-Saharan Africa) – Population expected to triple by 2100.
Intermediate fertility (e.g., U.S., India, Mexico) – Growth projected at 26%.
Low fertility (e.g., China, Australia, Europe) – Population expected to decline by 20%.

Patterns in fertility and mortality

Developed nations typically experience low fertility and low mortality rates, resulting in slower population growth and aging populations.

Underdeveloped nations tend to have high fertility and high mortality rates, leading to rapid population growth but also higher infant and child mortality.

Push and pull factors in migration

Push factors are things causing your decision to leave. They could be societal issues like discrimination, persecution, high crime, or violence. These factors could also be natural disasters or famine. Economic factors like lack of jobs are also a common push.
Pull factors are the draw to a new place, like a safer environment, more stable climate, enough resources, plenty of jobs in an applicable sector, or societal acceptance.