In the year 1800 there were around one billion people on Earth. Today there are more than eight billion, and a baby is born roughly every second somewhere in the world. That astonishing climb is one of the biggest stories in geography — and it did not happen evenly.
The words you need
- Birth rate — the number of live births per 1,000 people per year.
- Death rate — the number of deaths per 1,000 people per year.
- Natural increase — birth rate minus death rate. When births outnumber deaths, the population grows even before anyone moves in or out.
- Life expectancy — the average number of years a newborn is expected to live.
| Measure (per 1,000/yr) | Country A | Country B |
|---|---|---|
| Birth rate | 34 | 11 |
| Death rate | 9 | 10 |
| Natural increase | +25 (fast growth) | +1 (nearly flat) |
The Demographic Transition Model
As a country develops, its birth and death rates change in a fairly predictable pattern. Geographers describe this with the Demographic Transition Model (DTM). In the earliest stage both rates are high, so the population barely grows. Better food, clean water and medicine then pull the death rate down first, and for a while births stay high — so the population booms. Later, as families choose to have fewer children (more education, women working, children no longer needed to farm), the birth rate falls too, and growth slows.
Reading a population pyramid
A population pyramid is a picture of a country's age structure. Ages run up the middle; males sit on the left, females on the right; the bar length shows how many people are in each group. A youthful country has a wide base (lots of children). An ageing country has a narrow base and a bulging top (many elderly people).