Natural increase as a component of population change

Welcome to Human Geography!

In this chapter, we are going to look at one of the most fundamental parts of Geography: how and why the number of people on our planet changes. While people moving from place to place (migration) is important, today we are focusing on Natural Increase. This is simply the balance between babies being born and people passing away. By the end of these notes, you’ll understand the "math" behind populations and why different countries have such different population "shapes." Don't worry if some of the terms look new; we will break them down step-by-step!

1. The Basics: Births, Deaths, and Natural Increase

To understand how a population grows or shrinks naturally, we look at two main "engines": the Birth Rate and the Death Rate.

Key Definitions

Crude Birth Rate (CBR): The number of live births per 1,000 people in a population in a year.

Crude Death Rate (CDR): The number of deaths per 1,000 people in a population in a year.

Natural Increase Rate (NIR): This is the rate at which a population grows (or shrinks) based only on births and deaths. We calculate it using this simple formula:

\( \text{Natural Increase} = \text{Birth Rate} - \text{Death Rate} \)

The Bathtub Analogy

Think of a population like a bathtub. The faucet (Birth Rate) lets water in, and the drain (Death Rate) lets water out. If the faucet is running faster than the drain, the water level (the population) rises. This is Natural Increase. If the drain is faster than the faucet, the water level falls. This is Natural Decrease.

Quick Review: Remember that "natural" means we are ignoring migration for now. We are only looking at what happens "naturally" within the population through life and death.

Memory Aid: Just remember "B" before "D". Births minus Deaths = Natural Change.

2. Fertility and Infant Mortality

Geographers also look at more specific measurements to understand the health and future of a country.

Fertility Rate

The Total Fertility Rate (TFR) is the average number of children a woman is expected to have during her lifetime.
Did you know? A TFR of about 2.1 is called Replacement Level Fertility. This is the magic number needed for a population to exactly replace itself from one generation to the next without growing or shrinking.

Infant Mortality Rate (IMR)

The Infant Mortality Rate is the number of children who die before their first birthday, per 1,000 live births. This is a vital "health check" for a country. If the IMR is high, it usually suggests that the country struggles with clean water, nutrition, or medical care.

Key Takeaway: High Fertility Rates often lead to rapid natural increase, while high Infant Mortality Rates are usually a sign of poverty or lack of healthcare.

3. Why Do These Rates Change? (SEEP Factors)

Why do some countries have ten babies per family while others have only one? We can group the reasons into Social, Economic, Environmental, and Political factors (SEEP).

Social Factors

• Role of Women: In places where women have access to education and careers, they often choose to have fewer children and have them later in life.
• Religion and Culture: Some religions or traditions encourage large families or discourage the use of contraception.

Economic Factors

• Children as Assets: In poorer, farming-based societies, children are "extra hands" to help work the land. They are also the "pension plan" for parents in old age.
• Cost of Living: In wealthy countries, raising a child is very expensive (schooling, housing, etc.), which often leads people to have fewer children.

Environmental Factors

• Disease and Health: In areas with poor sanitation or high rates of diseases like Malaria or HIV/AIDS, death rates can be very high.
• Climate and Food: Frequent droughts or famines can increase death rates, especially among the very young and the elderly.

Political Factors

• Government Policy: Some governments try to increase the birth rate (Pro-natalist) by giving tax breaks for babies, while others try to decrease it (Anti-natalist) like China’s former One-Child Policy.

Common Mistake to Avoid: Don't assume that a high death rate always means a country is "poor." Some very wealthy countries have rising death rates simply because they have a lot of very elderly people!

4. Population Structure: The Age/Sex Pyramid

To visualize all this data, Geographers use Age/Sex Structure Diagrams, also known as Population Pyramids.

How to Read a Pyramid

• The Vertical Axis (Up/Down): Shows age groups (usually in 5-year gaps like 0-4, 5-9).
• The Horizontal Axis (Left/Right): Shows the number or percentage of people. Usually, males are on the left and females are on the right.

What the Shape Tells You

1. Wide Base: This means a high birth rate. There are lots of babies being born.

2. Narrowing Sides (Triangle Shape): This means a high death rate or lower life expectancy. People are passing away as they move into older age groups.

3. Straight Sides (Chimney Shape): This means low birth rates and most people living to an old age (found in many HICs - High-Income Countries).

4. Bulges or Indents: An indent might show a war (where many young men died) or a famine. A bulge might show a "baby boom" or a lot of young migrants moving in for work.

Quick Review: If the pyramid looks like a true triangle, it's a growing population. If it looks like a vase (narrow at the bottom), the population is likely shrinking.

5. Dependency and the Dependency Ratio

A population is divided into two groups: those who work and those who "depend" on the workers.

Who are the Dependents?

• Young Dependents: Children aged 0–14.
• Elderly Dependents: Seniors aged 65 and over.
• The Working Population: People aged 15–64 who pay taxes and support the dependents.

The Dependency Ratio

This formula tells us how much pressure there is on the working population:

\( \text{Dependency Ratio} = \frac{\text{Number of Dependents (0-14 and 65+)}}{\text{Working Age Population (15-64)}} \times 100 \)

Example: If the ratio is 80, it means for every 100 workers, there are 80 dependents to look after. That’s a heavy load!

Key Takeaway: High youth dependency is common in LICs (Low-Income Countries) and requires spending on schools. High elderly dependency is common in HICs and requires spending on healthcare and pensions.

Final Summary Table

Use this table as a quick reference for your revision!

Term: Natural Increase
What it is: Population growth when Births > Deaths.

Term: Fertility Rate
What it is: Average number of children per woman.

Term: Infant Mortality Rate
What it is: Babies dying before age 1 (per 1,000 births).

Term: Dependency Ratio
What it is: The balance between workers and non-workers.

Don't worry if this seems like a lot to memorize! Focus on the "why" behind the numbers—like why a parent might want more children or why a government might want fewer—and the math will start to make much more sense.