📈 High fertility
Several countries in sub-Saharan Africa, such as Niger, have fertility rates of about 6 children per woman. Populations grow quickly.
Population Growth and Decline » Why Populations Grow and Shrink
What you'll learn this session
Study time: 30 minutes
Cambridge spec: 6.1.2
- What birth rate, death rate, natural increase and fertility rate mean, and how to calculate them
- How migration adds to or takes away from a country's population
- Why birth rates and death rates are high in some countries and low in others
- How to explain why a population grows or declines
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Unlock This CourseThe ingredients of population change
A country's population changes for two reasons: people are born and die (this is natural change), and people move in or out (this is migration). Put them together and you can explain why a population grows or shrinks. Remember from World Population Growth that some countries are growing fast while others are stable or falling. This lesson explains why.
Key terms:
- Birth rate: the number of live births per 1,000 people in the population per year.
- Death rate: the number of deaths per 1,000 people in the population per year.
- Natural increase: the birth rate minus the death rate, when births are higher than deaths. The population grows without any migration.
- Natural decrease: the birth rate minus the death rate, when deaths are higher than births. The population falls without any migration.
- Fertility rate: the average number of children born to each woman in a country.
- Replacement level: the fertility rate needed to keep the population steady, about 2.1 children per woman. It is a little over 2 because not every child survives to have children of their own.
- Migration: the movement of people from one place to live in another.
- Net migration: the number of people arriving to live in a country (immigrants) minus the number leaving it (emigrants). It can be positive or negative.
Calculating natural increase
Birth rate and death rate are both given per 1,000 people per year. This makes it fair to compare a small country with a huge one. To find natural increase, subtract.
Worked example 1: natural increase
Country A (made-up) has a birth rate of 24 per 1,000 and a death rate of 8 per 1,000.
Natural increase = 24 − 8 = 16 per 1,000 per year.
To change this to a percentage, divide by 10: 16 per 1,000 = 1.6% a year.
Worked example 2: natural decrease
Country B (made-up) has a birth rate of 9 per 1,000 and a death rate of 12 per 1,000.
9 − 12 = −3 per 1,000 per year. This is a natural decrease of 0.3% a year. The population is falling even before we think about migration.
Worked example 3: from raw numbers
Country C (made-up) has 2,000,000 people. In one year there are 36,000 births and 24,000 deaths.
Birth rate = 36,000 ÷ 2,000,000 × 1,000 = 18 per 1,000.
Death rate = 24,000 ÷ 2,000,000 × 1,000 = 12 per 1,000.
Natural increase = 18 − 12 = 6 per 1,000, or 0.6%.
Adding migration
Natural change is only half the story. Net migration is immigrants minus emigrants. It can be positive (more arrive than leave) or negative (more leave than arrive).
Worked example 4: total change
In Country C (above), 10,000 immigrants arrive and 4,000 emigrants leave in the same year.
Net migration = 10,000 − 4,000 = +6,000.
Natural increase in people = 36,000 − 24,000 = 12,000.
Total population change = 12,000 + 6,000 = +18,000.
A country can have a natural decrease and still grow if net migration is high enough. A country with a natural increase can still shrink if many people emigrate. Who migrates and why is taught in Types of Migrant and Why People Migrate.
The fertility rate
Fertility rate looks at the choices women make about family size. If it is above about 2.1, each generation is bigger than the last. If it is below 2.1, the population will eventually shrink unless migrants arrive.
📉 Low fertility
South Korea has a fertility rate below 1, and Japan and many European countries are also below replacement level. Populations age and often decline.
Why birth rates are high or low
Birth rates fall when families choose, or are able, to have fewer children. Look for the reason in each group of factors:
| Factor | Why the birth rate is HIGH | Why the birth rate is LOW |
|---|---|---|
| Social | Girls leave school early and marry young. Large families are seen as normal. | Women are educated, marry later and have careers, so they have fewer children. |
| Religion and culture | Some beliefs encourage large families or oppose contraception. | Where religious influence is weaker or contraception is accepted, families are smaller. |
| Health | Little access to contraception. Many children die young, so parents have extra children to be safe. | Contraception is easy to get. Fewer children die, so parents plan smaller families. |
| Political | Government laws that support or encourage large families, or little protection of women's rights. | Government laws that limit family size, or that protect women's rights and education. These policies are covered in Pro-Natalist and Anti-Natalist Policies. |
| Economic | Children work on the farm or earn money (child labour). There is no pension, so children care for parents in old age. | Children are expensive: schooling, housing, food. Child labour is banned. Pensions mean parents do not rely on their children. |
Why death rates are high or low
🏥 Lower death rates
Good healthcare and vaccination, clean water and sanitation, enough food, and peace. These stop people dying from infectious disease, hunger and violence.
⚠️ Higher death rates
Poor healthcare, dirty water, disease, famine, war and conflict (a political factor), or an old population where many people are in their final years.
That last point surprises students. A rich country such as Japan has excellent healthcare, yet its death rate is not very low, because so many of its people are elderly. This is one reason Japan has more deaths than births.
Common mistakes
- Writing "population increase" when the question asks about natural increase. Natural increase ignores migration.
- Forgetting that birth rate and death rate are per 1,000, not per cent. Divide by 10 for a percentage.
- Mixing up birth rate (births per 1,000 people) with fertility rate (children per woman). They are different measures.
- Giving only a factor with no explanation. Always say how it changes the birth rate or death rate.
Exam-style question
Fig. 1.1 shows made-up data for two countries.
| Country | Birth rate (per 1,000) | Death rate (per 1,000) | Fertility rate | Net migration (per 1,000) |
|---|---|---|---|---|
| P | 35 | 9 | 4.6 | −2 |
| Q | 8 | 11 | 1.3 | +5 |
(a) Calculate the natural increase for Country P. [1 mark]
(b) Define the term fertility rate. [1 mark]
(c) Describe how the population of Country Q is changing. Use figures from Fig. 1.1. [3 marks]
(d) Explain how education of women, the cost of children and the availability of pensions may cause the birth rate in a country to fall. [6 marks]
Model answer
(a) 35 − 9 = 26 per 1,000 (1).
(b) The average number of children born to each woman in a country (1).
(c) Country Q has a natural decrease (1) because the birth rate of 8 is lower than the death rate of 11, a fall of 3 per 1,000 (1). Net migration of +5 per 1,000 is higher than the natural decrease, so the total population is still growing slightly, by about 2 per 1,000 (1).
(d) Level 3 (5-6 marks): a full explanation of all three factors. Educated women stay in school longer, marry later and have careers, so they have fewer years to have children and want smaller families (1) (1). When children are expensive, with costs for schooling, food and housing, parents choose fewer children (1) (1). Where there are pensions, parents do not need many children to look after them in old age, so families become smaller (1) (1). Together these cause the birth rate and fertility rate to fall.
Exam tip
In part (c), use both natural change and net migration, and quote at least two figures. Marks go to answers that do the arithmetic, not just copy the table.