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The Demographic Transition Model (DTM) is one of the most frequently tested concepts in AP Human Geography because it connects population dynamics, economic development, urbanization, and cultural change into a single framework. You're not just being asked to memorize birth and death rates—you're being tested on your ability to explain why populations change and how those changes ripple through every aspect of human geography, from migration patterns to urban land use to political stability.
Understanding the DTM means understanding the mechanisms behind population change: industrialization, healthcare access, women's empowerment, and economic restructuring. When you see an FRQ asking about population pyramids, dependency ratios, or policy responses to aging, the DTM is your anchor. Don't just memorize which stage has high or low rates—know what forces drive the transitions and what consequences follow for societies at each stage.
Before modernization, populations existed in a precarious equilibrium where high fertility barely offset high mortality. Disease, famine, and lack of medical knowledge kept death rates unpredictable and life expectancy short.
The key mechanism here is asymmetric change—death rates plummet while birth rates stay high, creating rapid population growth. This lag between mortality and fertility decline is the engine of population booms.
Compare: Stage 2 vs. Stage 3—both show population growth, but Stage 2 growth comes from falling death rates while Stage 3 growth comes from demographic momentum even as birth rates fall. If an FRQ asks why population keeps growing after fertility drops, momentum is your answer.
Once both birth and death rates reach low levels, populations stabilize—but new challenges emerge. Aging populations, shrinking workforces, and changing dependency ratios reshape economies and policies.
Compare: Stage 1 vs. Stage 4—both have stable populations, but for opposite reasons. Stage 1 stability comes from high rates canceling out; Stage 4 stability comes from low rates in equilibrium. This distinction is a classic multiple-choice trap.
Some scholars identify a fifth stage where birth rates fall below death rates, creating natural decrease. Economic pressures, changing gender roles, and delayed family formation drive fertility below replacement.
Compare: Stage 4 vs. Stage 5—Stage 4 maintains replacement fertility and population stability, while Stage 5 sees fertility collapse below replacement. Countries like Japan and Germany (Stage 5) face workforce crises that France and the U.S. (Stage 4) have largely avoided through immigration and family policy.
| Concept | Best Examples (Stages) |
|---|---|
| High mortality from infectious disease | Stage 1, early Stage 2 |
| Population explosion / highest RNI | Stage 2 |
| Epidemiological transition begins | Stage 2 |
| Fertility transition / declining CBR | Stage 3 |
| Demographic momentum | Stage 3, early Stage 4 |
| Replacement-level fertility | Stage 4 |
| Aging population / elderly dependency | Stage 4, Stage 5 |
| Below-replacement fertility / natural decrease | Stage 5 |
Which two stages have relatively stable populations, and what fundamentally different mechanisms produce that stability?
A country has a rapidly growing population but birth rates have started declining—which stage is it in, and what factors typically cause fertility to drop?
Compare the population pyramids you would expect in Stage 2 versus Stage 5. What shapes would each have, and why?
An FRQ asks you to explain why a country's population continues growing even after TFR drops to 2.1. Which concept explains this, and in which stage transition does it occur?
A government implements pro-natalist policies and relaxes immigration restrictions. Based on these policies, what stage is the country likely in, and what demographic challenges is it trying to address?