AP® Environmental Science review sheet from Aim for Five (aimforfive.com/enviro/units/3/3-9)
Unit 3 · Topic 3.9
3.9 Demographic Transition
The demographic transition model describes how birth and death rates change as a country industrializes. Death rates fall first, causing rapid population growth, and later birth rates fall too, so growth slows as the country moves through four stages.
Key terms
- demographic transition model
- pre-industrial stage
- transitional stage
- industrial stage
- post-industrial stage
The four stages
The gap between the birth rate and death rate is the rate of natural increase, so growth is fastest in stage 2 and early stage 3, when that gap is widest.
| Stage | Birth rate | Death rate | Population growth | Why |
|---|---|---|---|---|
| 1. Pre-industrial | High | High | Slow, with ups and downs | Limited food, poor sanitation and little medicine keep deaths high; families have many children |
| 2. Transitional | High | Falling quickly | Rapid | Better food supply, clean water, sanitation and medicine cut deaths, especially of children, while birth rates stay high |
| 3. Industrial | Falling | Low | Growth slows | Cities grow, children cost more, women gain education and jobs, and contraception spreads |
| 4. Post-industrial | Low | Low | Very slow, stable or slightly declining | Small families are the norm; the population ages |
Why death rates fall first
Lowering the death rate doesn't require people to change personal choices. When a country gets cleaner water, sewers, vaccines, antibiotics and a more reliable food supply, fewer people die, especially infants and children. These changes can happen within a few decades.
Birth rates depend on family decisions shaped by culture, economics, education and expectations. Those take longer to change, often a generation or more. In the meantime, the population grows very fast. Much of the world's huge population growth in the 1900s happened because many countries entered stage 2.
Where countries are today
No country today is in stage 1. Many countries in sub-Saharan Africa are in stage 2 or early stage 3, with high birth rates and falling death rates. Many countries in Latin America and South Asia are in stage 3. Most of Europe, the U.S., Canada, Japan and South Korea are in stage 4. Less developed countries also tend to have higher infant mortality and more children working, often on family farms, than developed countries.
Some versions of the model add a stage 5, where birth rates fall below death rates and the population shrinks, as in Japan and parts of Eastern Europe. You may see it in some sources, but the four stages above are the core of the model.
Death rates can rise a little again in stage 4, because an aging population has more older people dying each year, even though health care is excellent.
Limits of the model
The model is based on the history of Europe and North America, so it doesn't fit every country. Some countries moved through the stages much faster with modern medicine. Others have seen birth rates stall in stage 3 for cultural or economic reasons. Migration, which the model ignores, can change population size a lot. Use the model as a general pattern, not a strict rule.
Worked examples
Try each one yourself first, then open the solution.
- Example 1Calculator allowed
Placing a country in a stage
Country X has a crude birth rate of 38 per 1,000 and a crude death rate of 12 per 1,000. Its death rate has fallen sharply over the last 30 years, while its birth rate has barely changed. Identify its stage and calculate its growth rate and doubling time.
Show the solutionHide the solution
- Step 1: A high birth rate with a recently falling death rate is the signature of stage 2 (transitional).
- Step 2: Growth rate = (38 − 12) ÷ 10 = 2.6% per year.
- Step 3: Doubling time ≈ 70 ÷ 2.6 = 26.9 years.
Answer: Stage 2; growth rate 2.6% per year; doubling time about 27 years.
- Example 2
Explaining a shift between stages
A country's birth rate has fallen from 40 to 22 per 1,000 over 25 years, while its death rate has stayed near 7. Which stage transition is happening, and give two reasons birth rates might be falling.
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- Step 1: The death rate is already low and the birth rate is now falling, which describes stage 3 (industrial).
- Step 2: Reason 1: more people move to cities, where children cost more to raise and don't contribute farm labor.
- Step 3: Reason 2: more education and job opportunities for women and wider access to contraception lead to smaller families.
- Step 4: Lower infant mortality also means parents don't need extra children to make sure some survive.
Answer: The country is in stage 3. Birth rates are falling because of urbanization and the higher cost of children, plus more education for women and access to family planning.
Common mistakes
- Saying birth rates fall first. Death rates fall first; that gap causes rapid growth in stage 2.
- Putting the fastest growth in stage 4. Stage 4 has slow or no growth; stage 2 is fastest.
- Thinking stage 4 death rates must keep falling. They may rise slightly as the population ages.
On the exam
- Expect birth and death rate data or a described graph and a question about which stage a country is in. Use both rates and the trend in your answer.
- Link stages to age structure diagrams: stage 2 has a wide-based pyramid, stage 4 a column or narrow base.
Connected topics
Videos
Check yourself
4 questions on 3.9 Demographic Transition. Pick an answer to see if you got it, and why.
In the industrial stage of the demographic transition, birth rates fall. Which change best explains this?
| Country | Crude birth rate (per 1,000) | Crude death rate (per 1,000) |
|---|---|---|
| J | 44 | 40 |
| K | 38 | 12 |
| L | 18 | 9 |
| M | 9 | 11 |
Hypothetical data
Which country is most likely in the transitional stage (Stage 2) of the demographic transition model?
What is the rate of natural increase for Country K?
Which statement best explains why death rates usually fall before birth rates as a country develops?
0 of 4 answered