A country's population pyramid has a very wide base (ages 0-14) that narrows rapidly at older ages. What can you infer about this population's likely position in the demographic transition?
AStage 4 — the wide base reflects a past baby boom, not current high fertility
BStage 2 or early Stage 3 — high fertility is producing large young cohorts, while mortality may still be elevated at older ages
CStage 1 — both fertility and mortality are high, producing the wide base
DThe pyramid shape alone cannot indicate anything about the demographic transition
A wide base with rapid narrowing is the classic expansive pyramid shape, indicating high current fertility producing large young cohorts. This is characteristic of Stage 2 (mortality declining, fertility still high) or early Stage 3 (fertility beginning to decline but still high). Stage 1 populations would show more irregular shapes due to mortality crises, and the pyramid alone cannot distinguish Stage 1 from Stage 2 without trend data. Stage 4 populations have narrow or contracting bases.
Question 2 True / False
Each horizontal bar of a population pyramid represents people currently alive at that age — it tells you nothing about past demographic events.
TTrue
FFalse
Answer: False
Each bar represents a birth cohort that has been shaped by three historical forces: fertility at the time they were born (determining initial cohort size), cumulative mortality since birth (reducing cohort size), and net migration at various ages. An indentation at ages 75-80 might reflect low fertility during a depression or war losses. A bulge at ages 30-35 might reflect a baby boom or immigration wave. Reading a pyramid is reading demographic history.
Question 3 Short Answer
Explain why a country with below-replacement fertility can still have an expansive (wide-base) population pyramid, and what this implies for future growth.
Think about your answer, then reveal below.
Model answer: If a country recently transitioned from high to below-replacement fertility, the large cohorts born during the high-fertility era are now of reproductive age. Even though each woman has fewer than 2.1 children on average, there are so many women in the childbearing ages that total births still exceed deaths, maintaining a relatively wide base. This is population momentum — the age structure inherited from past high fertility continues to drive growth even after fertility falls below replacement. The pyramid will gradually shift from expansive to constrictive as the large cohorts age out of reproductive years.
This is one of the most important concepts in applied demography. India, for example, reached near-replacement fertility but will continue growing for decades because its age structure is young. Momentum can account for a substantial fraction of projected global population growth — not because fertility is high, but because the echo of past high fertility reverberates through the age structure.