Population change and composition

The essentials

Population changes through three components: births, deaths and migration. The crude birth rate (CBR) is the number of live births in a year per thousand people; the crude death rate (CDR) is the number of deaths in a year per thousand people.

Migration is the movement of people from one place to another. The place of origin loses population and the place of destination gains it. Push factors (unemployment, poor living conditions, political unrest, natural disasters, epidemics) make people leave; pull factors (jobs, better living conditions, peace, security, pleasant climate) attract them.

The demographic transition theory describes how a society moves from high births and high deaths to low births and low deaths. In the first stage both rates are high and growth is slow. In the second, death rates fall quickly while birth rates stay high, so population expands rapidly. In the third, both rates are low and population becomes stable or grows slowly.

Key points

• Sex ratio is the ratio between females and males. In India it is expressed as number of females per thousand males; many countries express it as males per hundred females.
• Age structure divides people into children, working age (15–59 years) and the aged (60+).
• Age-sex pyramid shapes: expanding (wide base, triangular – high birth rate, as in many less developed countries), constant (bell-shaped – birth and death rates almost equal) and declining (narrow base – low birth rate, as in Japan).
• Rural-urban composition, literacy and occupational structure (primary, secondary, tertiary, quaternary) are other aspects of composition.
• Thomas Malthus (1798) argued that population grows faster than food supply.

Exam tips

Identify pyramid types by the base: wide base = high births; narrow base = falling births.

Common mistakes

In the second stage of demographic transition, it is the death rate that falls first – not the birth rate.