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What makes a human population grow, and how do birth, death and migration rates combine to set its growth rate?

Topic 3.7 Human Population Dynamics: explain the factors that influence human population size and growth, and calculate growth rate from crude birth, death and migration rates.

A focused answer to APES Topic 3.7, covering crude birth and death rates, immigration and emigration, the factors driving human population change, infant mortality and life expectancy, and how to calculate population growth rate, with worked math.

Generated by Claude Opus 4.811 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this topic is asking
  2. What changes a population
  3. What drives birth and death rates
  4. The calculation
  5. Why this matters
  6. Try this

What this topic is asking

The College Board (Topic 3.7) wants you to explain what drives human population change and to calculate growth rate from crude birth, death and migration rates. This is a quantitative topic.

What changes a population

The natural increase of a population (ignoring migration) is the birth rate minus the death rate. Net migration (immigration minus emigration) is then added to get the total change. A population can therefore grow even when births and deaths are balanced, if more people move in than out, and it can shrink despite a positive natural increase if emigration is large enough.

What drives birth and death rates

These indicators also reveal a country's stage of development. A high crude death rate, high infant mortality and low life expectancy point to a less-developed country, while low death rates, very low infant mortality and high life expectancy point to a more-developed one. Tracking how these rates change over time shows whether a country is moving through the demographic transition (Topic 3.8) and lets demographers compare the trajectories of different nations using the same measurable numbers.

The calculation

Why this matters

Human population dynamics ties Unit 3 to real policy. It depends on total fertility rate (Topic 3.6), shows up in the age structure (Topic 3.5), and is the mechanism behind the demographic transition (Topic 3.8). It also sets the demand side of every resource topic in Units 5 to 9: more people, growing faster, place more pressure on land, water, energy and the atmosphere.

Try this

Q1. Identify the indicator measured as deaths under age 1 per 1,000 live births. [1 point]

  • Cue. The infant mortality rate.

Q2. Calculate the natural growth rate of a country with a CBR of 30 per 1,000 and a CDR of 10 per 1,000. [1 point]

  • Cue. 30−101,000×100%=2.0%\frac{30 - 10}{1{,}000} \times 100\% = 2.0\% per year.

Exam-style practice questions

Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

AP 2021 (style)4 marksSection II (FRQ, quantitative). A country has a crude birth rate of 22 per 1,000 and a crude death rate of 9 per 1,000, with negligible migration. (a) Calculate the annual percentage growth rate. (b) Use the rule of 70 to estimate the doubling time. (c) Describe one factor that lowers a country's crude death rate. (d) Explain how net migration can change a country's growth rate even if births and deaths are balanced.
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A 4-point quantitative FRQ on human population dynamics.

(a) Calculate (1 point): growth rate =22−91,000×100%=131,000×100%=1.3%= \frac{22 - 9}{1{,}000} \times 100\% = \frac{13}{1{,}000} \times 100\% = 1.3\% per year.
(b) Calculate (1 point): doubling time =70/1.3≈54= 70 / 1.3 \approx 54 years.
(c) Describe (1 point): improved healthcare, sanitation, clean water, nutrition or vaccination lowers the death rate.
(d) Explain (1 point): if more people immigrate than emigrate (positive net migration), the population grows even when births equal deaths; net emigration would shrink it.

Markers reward subtracting death rate from birth rate and converting to a percentage, the correct rule-of-70 division, a valid death-rate factor, and net migration as an independent driver.

AP 2020 (style)1 marksSection I (multiple choice). A country has a crude birth rate of 14 per 1,000 and a crude death rate of 8 per 1,000, with no migration. What is its annual growth rate? (A) 0.6% (B) 6% (C) 22% (D) 0.06%. Justify your choice.
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A 1-point quantitative MCQ. The answer is (A).

Growth rate =14−81,000×100%=61,000×100%=0.6%= \frac{14 - 8}{1{,}000} \times 100\% = \frac{6}{1{,}000} \times 100\% = 0.6\% per year. Option (B) forgets to divide by 1,000 properly; (C) adds the rates; (D) misplaces the decimal. The trap is the per-1,000 basis: subtract the rates, then divide by 1,000 and multiply by 100 to get a percentage.

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