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This lesson examines how and why populations grow and decline over time. You will study the Demographic Transition Model (DTM), crude birth and death rates, natural increase, and population pyramids. These concepts are central to AQA A-Level Geography Paper 2, Section C — Population and the Environment.
Before analysing population change, it is essential to understand the measures used:
| Measure | Definition | Formula |
|---|---|---|
| Crude Birth Rate (CBR) | Number of live births per 1,000 population per year | (Live births / Total population) × 1,000 |
| Crude Death Rate (CDR) | Number of deaths per 1,000 population per year | (Deaths / Total population) × 1,000 |
| Rate of Natural Increase (RNI) | Difference between CBR and CDR, expressed as a percentage | (CBR − CDR) / 10 |
| Total Fertility Rate (TFR) | Average number of children born to a woman during her lifetime | Calculated from age-specific fertility rates |
| Infant Mortality Rate (IMR) | Number of deaths of infants under 1 year per 1,000 live births per year | (Infant deaths / Live births) × 1,000 |
| Life Expectancy | Average number of years a newborn is expected to live | Derived from mortality tables |
Key Definition: Replacement-level fertility is the TFR at which a population exactly replaces itself from one generation to the next — approximately 2.1 in developed countries (slightly above 2 to account for mortality before reproductive age).
World population reached approximately 8 billion in November 2022 (UNFPA). Growth has not been steady — it took roughly 200,000 years for the global population to reach 1 billion (around 1804), but only 11 years to grow from 7 to 8 billion.
| Year | World Population | Time to add 1 billion |
|---|---|---|
| 1804 | 1 billion | ~200,000 years |
| 1927 | 2 billion | 123 years |
| 1960 | 3 billion | 33 years |
| 1974 | 4 billion | 14 years |
| 1987 | 5 billion | 13 years |
| 1999 | 6 billion | 12 years |
| 2011 | 7 billion | 12 years |
| 2022 | 8 billion | 11 years |
The rate of growth is now slowing. The UN projects a peak population of approximately 10.4 billion by the 2080s before a gradual decline begins.
Exam Tip: When discussing population growth, always distinguish between the rate of growth (which has been declining since the late 1960s) and absolute growth (which continued to rise until recently). The peak annual growth rate was about 2.1% in 1968; by 2023 it was approximately 0.9%.
The Demographic Transition Model was first proposed by Warren Thompson (1929) and later developed by Frank Notestein (1945). It describes how populations transition from high birth and death rates to low birth and death rates as a country develops economically.
graph LR
S1["Stage 1<br/>High Stationary<br/>High CBR, High CDR<br/>Low growth"] --> S2["Stage 2<br/>Early Expanding<br/>High CBR, Falling CDR<br/>Rapid growth"]
S2 --> S3["Stage 3<br/>Late Expanding<br/>Falling CBR, Low CDR<br/>Slowing growth"]
S3 --> S4["Stage 4<br/>Low Stationary<br/>Low CBR, Low CDR<br/>Stable/slow growth"]
S4 --> S5["Stage 5<br/>Declining<br/>Very low CBR, Low CDR<br/>Natural decrease"]
| Stage | CBR | CDR | Natural Increase | Example Countries | Characteristics |
|---|---|---|---|---|---|
| 1: High Stationary | High (35-50) | High (35-50) | Low/Zero | No countries today; pre-industrial societies | No contraception, high infant mortality, disease, famine |
| 2: Early Expanding | High (35-50) | Falling (15-35) | Rapid growth | Afghanistan, Niger, Chad | Improved sanitation, medicine, food supply; cultural lag in fertility decline |
| 3: Late Expanding | Falling (15-35) | Low (10-15) | Moderate growth | India, Brazil, Mexico | Urbanisation, education (especially female), access to contraception |
| 4: Low Stationary | Low (10-15) | Low (10-15) | Low/Zero | UK, France, USA, Australia | Post-industrial economy, high cost of child-rearing, career priorities |
| 5: Declining | Very low (<10) | Low (10-15) | Negative | Japan, Germany, Italy, South Korea | Ageing population, sub-replacement fertility, pension crises |
Falling Death Rates (Stage 2):
Falling Birth Rates (Stage 3):
Exam Tip: The DTM is a descriptive model, not a predictive one. It was based on the historical experience of Western Europe. Many LICs may not follow the same trajectory — for example, some countries have rapidly urbanised without industrialising (e.g., sub-Saharan Africa). Always evaluate the model's limitations.
Population pyramids (age-sex structure diagrams) provide a visual snapshot of a population's structure at a given point in time. They display age groups on the vertical axis and population (often in thousands or millions, split by sex) on the horizontal axis.
| Shape | DTM Stage | Characteristics | Example |
|---|---|---|---|
| Wide base, narrow top (triangular) | Stage 2 | High CBR, high CDR, low life expectancy, large young population | Niger (median age 15.4) |
| Narrowing base, bulge in middle | Stage 3 | Falling CBR, improving life expectancy, growing working-age population | India (median age 28.7) |
| Column/barrel shape | Stage 4 | Low CBR, low CDR, roughly even age distribution | UK (median age 40.7) |
| Inverted triangle / top-heavy | Stage 5 | Very low CBR, ageing population, shrinking workforce | Japan (median age 48.6) |
Japan illustrates the challenges of Stage 5 of the DTM:
Exam Tip: When using case studies in essays, always include specific data (dates, percentages, population figures). A well-evidenced case study demonstrates AO2 (application) skills and can significantly improve your mark.
Governments intervene in population change through policies designed to increase or decrease fertility:
| Policy Type | Examples | Case Study |
|---|---|---|
| Pro-natalist | Childcare subsidies, parental leave, tax benefits for families, baby bonuses | France: generous childcare provision, three-year parental leave; TFR of 1.80 (2022), among the highest in Europe |
| Anti-natalist | Family planning programmes, education campaigns, economic incentives for smaller families | China: One-Child Policy (1979–2015) — reduced TFR from 5.9 (1970) to 1.6 (2000), but caused gender imbalance, forced abortions, ageing population; now reversed to three-child policy (2021) |
France has long pursued pro-natalist policies and maintains one of the highest TFRs in Europe:
Evaluation Point: France's relatively high fertility is also attributable to cultural factors, higher rates of cohabitation, and immigration. It is difficult to isolate the effect of policy from these broader social trends.