Population, urbanisation and migration

Sociology · Structure, order and change. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Demography studies the size, structure and movement of population. Population changes through three processes only: fertility (births), mortality (deaths) and migration.

Malthus (1798) warned that population grows faster than food supply and is held down by checks. The demographic transition describes what actually happened in industrial countries: death rates fell first, birth rates fell later, and population grew fast in between.

Urbanisation is the rise in the share of people living in towns and cities. It is fed by rural to urban migration, and when it is rapid it brings slums, pressure on services, congestion and weaker informal control.

Rules to remember

Malthus: population grows geometrically (1, 2, 4, 8), food arithmetically (1, 2, 3, 4). Positive checks raise deaths (famine, disease, war); preventive checks lower births (late marriage, moral restraint).
Demographic transition: stage 1 high birth and death rates; stage 2 death rate falls, rapid growth; stage 3 birth rate falls; stage 4 both low, slow growth.
Crude birth rate and crude death rate: live births or deaths per 1,000 population per year.
Rate of natural increase (%) = (crude birth rate − crude death rate) ÷ 10.
Infant mortality rate: deaths under age one per 1,000 live births. Fertility = actual births; fecundity = biological capacity.
Replacement-level fertility is about 2.1 children per woman.
Push factors drive people out (no jobs, drought); pull factors attract (work, schools). Immigration = moving in; emigration = moving out.

Common mistake

Birth and death rates are per 1,000 but growth is quoted per cent. Subtract the rates and then divide by 10; forgetting this gives an answer ten times too large.

Worked example

A country has a crude birth rate of 42 per 1,000 and a crude death rate of 12 per 1,000. Ignoring migration, find the rate of natural increase and say which stage of the demographic transition this suggests.

Natural increase = 42 − 12 = 30 per 1,000.
As a percentage: 30 ÷ 10 = 3.0 per cent a year.
The birth rate is still high while the death rate has fallen well below it, so growth is rapid.
A falling death rate with a birth rate that is still high is the mark of stage 2.

Answer: 3.0 per cent a year; stage 2.

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