AP® Human Geography review sheet from Aim for Five (aimforfive.com/geo/units/2/2-6)
Unit 2 · Topic 2.6
2.6 Malthusian Theory
Thomas Malthus argued that population would outgrow food supply and lead to disaster. His theory was wrong in key ways, but the debate it started about population and resources is still alive.
Key terms
- Malthusian theory
- exponential (geometric) growth
- arithmetic (linear) growth
- neo-Malthusian
What Malthus argued
In 1798 the English economist Thomas Malthus published An Essay on the Principle of Population. He argued that, if nothing stopped it, population grows exponentially (geometrically), doubling again and again: 1, 2, 4, 8, 16. Food supply, he said, grows only arithmetically (linearly), adding the same amount each time: 1, 2, 3, 4, 5. So population would eventually outrun food.
Malthus said two kinds of checks would hold population down. Positive checks raise the death rate: famine, disease and war. Preventive checks lower the birth rate: delaying marriage and having fewer children, which he called moral restraint.
| Period | Population (geometric) | Food supply (arithmetic) |
|---|---|---|
| Start | 1 | 1 |
| 1 | 2 | 2 |
| 2 | 4 | 3 |
| 3 | 8 | 4 |
| 4 | 16 | 5 |
Why critics say he was wrong
- Technology raised food output far faster than he predicted. Mechanization, fertilizers, irrigation and the Green Revolution's high-yield seeds (topic 5.5) multiplied harvests. World population grew from about 1 billion around 1800 to more than 8 billion (the UN marked 8 billion in November 2022), and food production per person rose over that time.
- Birth rates fell as countries became wealthier and more urban, as the demographic transition describes. Population didn't keep doubling.
- Hunger today is mostly about poverty, conflict and unequal distribution, not a global shortage of food. The economist Amartya Sen showed that many famines happened when people lost the ability to buy or grow food, even when food existed nearby.
- The economist Ester Boserup argued the reverse of Malthus: population pressure pushes farmers to invent ways to grow more on the same land.
Scale matters here too
At the global scale, food supply has kept up with population. At regional and local scales the picture is mixed. Places with fast population growth, poor soils, frequent drought or ongoing conflict can still face hunger, and in those places population pressure is one factor among several. When you use Malthus on the exam, say which scale you're talking about, and remember that conflict, poverty and distribution usually explain modern famines better than population alone.
Neo-Malthusians
Neo-Malthusians are modern thinkers who share Malthus's concern but widen it. They argue that population growth, combined with rising consumption, strains not only food but also water, soil, fisheries, forests and the climate. Paul Ehrlich's 1968 book The Population Bomb predicted mass famines that mostly didn't happen, which critics point to. Neo-Malthusians reply that environmental limits are real even if their timing is hard to predict.
On the exam, you should be able to explain the theory, give at least one critique, and explain the neo-Malthusian view.
Worked examples
Try each one yourself first, then open the solution.
- Example 1
Evaluating Malthus with evidence
Explain one reason why Malthus's prediction of widespread famine did not come true on a global scale.
Show the solutionHide the solution
- Step 1: Restate the prediction briefly: food supply would grow too slowly to keep up with exponential population growth.
- Step 2: Give a specific reason: agricultural technology, such as the Green Revolution's high-yield seeds, fertilizers and irrigation, sharply increased food output.
- Step 3: Connect it to the prediction: food supply grew faster than the arithmetic rate Malthus assumed, so it kept pace with population.
Answer: Malthus assumed food would grow only arithmetically, but new farm technology like the Green Revolution's high-yield seeds, fertilizer and irrigation greatly increased yields, so global food supply kept up with population growth.
Common mistakes
- Reversing the growth types. Population grows exponentially (geometrically) in Malthus's theory; food grows arithmetically.
- Saying Malthus was simply right or simply wrong. He underestimated technology, but resource limits are still debated.
- Forgetting the checks. Malthus named positive checks (more deaths) and preventive checks (fewer births).
On the exam
- Expect multiple-choice questions on the difference between exponential and arithmetic growth, and on who a neo-Malthusian is.
- If a question asks for a critique, technology and falling birth rates are the clearest, strongest answers.
Connected topics
Videos
Check yourself
4 questions on 2.6 Malthusian Theory. Pick an answer to see if you got it, and why.
"Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio. A slight acquaintance with numbers will shew the immensity of the first power in comparison of the second."
Thomas Malthus, An Essay on the Principle of Population, 1798
Which of the following best summarizes Malthus's argument in the passage?
Suppose a population doubles every 25 years while food supply increases by the same fixed amount every 25 years. If food and population start in balance, what would their ratio be after 100 years, according to Malthus's reasoning?
Which development since 1798 most weakens Malthus's prediction?
A neo-Malthusian writing today would most likely argue that
0 of 4 answered