Question

Discuss the components of population change.

Hint:

Write the formula \(\Delta P=(B-D)+(I-E)\), then devote a short paragraph each to fertility, mortality, and migration. Close with demographic transition and population momentum to make the answer exam-ready.

Answer 1

Core idea
Population change is governed by just three components: fertility (births), mortality (deaths) and migration. In symbols for a region and period,
\[ \Delta P = (B - D) + (I - E) $\Rightarrow$ r \approx (CBR - CDR) + \text{Net migration rate} \] where \(B,D\) are births and deaths; \(I,E\) are in- and out-migrants; \(CBR, CDR\) are crude rates (per 1000).
1) Fertility
Measures: Crude Birth Rate (CBR), General Fertility Rate, Age-Specific Fertility Rate (ASFR), and Total Fertility Rate (TFR—average births per woman).
Determinants: Child survival and health services; female education and labour force participation; age at marriage; cultural norms and son preference; access to contraception; income, housing and childcare costs; social security/pensions.
Implications: High fertility sustains youthful age structure and rapid growth; once fertility falls below replacement (\(\approx 2.1\)), ageing begins unless offset by migration.
2) Mortality
Measures: Crude Death Rate (CDR), Infant and Under-5 Mortality Rates (IMR/U5MR), Life Expectancy at birth, and cause-specific death rates.
Determinants: Nutrition and food security; safe water and sanitation; vaccination and primary care; epidemics/pandemics; wars and disasters; occupational and traffic risks; age structure.
Mortality decline—via clean water, antibiotics, immunisation—usually precedes fertility decline and triggers a period of rapid growth (demographic transition).
3) Migration (internal and international)
Forms: Rural–urban, urban–urban, seasonal, long-term; international labour and refugee flows.
Drivers (push–pull): Wage gaps and jobs; education; marriage; safety; environmental stress; policies/visas.
Selectivity: Migrants are often young adults—lower death rates but, depending on sex ratio, may raise or lower local births.
Effects: Redistributes population geographically; can rejuvenate ageing regions (through net immigration) or depopulate origins; remittances influence fertility choices and human capital.
Demographic transition frame for synthesis
Stage I (high birth–high death) \(\rightarrow\) Stage II (death declines) \(\rightarrow\) Stage III (births decline) \(\rightarrow\) Stage IV/V (low birth–low death, sometimes below-replacement). Fertility and mortality shape natural increase; migration modifies local totals.
Population momentum (bonus concept)
Even after fertility falls to replacement, a youthful age structure can keep numbers growing for decades because many people are entering childbearing ages. This is a structural component arising from past fertility, not high current TFR.
Policy levers
Maternal–child health and sanitation reduce mortality; girls' education, contraception access and gender equity lower fertility; managed migration addresses labour shortages and ageing; social security affects desired family size.