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13.2: Agriculture and Human Population Growth

Difficulty Level: At Grade Created by: CK-12
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What's your vision of a chicken farm?

In many nations, farming today is industrial, growing the maximum amount of food for the minimum price, often without much thought as to the long-term social or environmental consequences. These industrial food production plants are a long way from the farms of the past.

Advances in Agriculture and Population

Every major advance in agriculture has allowed global population to increase. Early farmers could settle down to a steady food supply. Irrigation, the ability to clear large swaths of land for farming efficiently, and the development of farm machines powered by fossil fuels allowed people to grow more food and transport it to where it was needed.

Hunters and Gatherers

What is Earth’s carrying capacity for humans? Are humans now exceeding Earth’s carrying capacity for our species? Many anthropologists say that the carrying capacity of humans on the planet without agriculture is about 10 million (Figure below). This population was reached about 10,000 years ago. At the time, people lived together in small bands of hunters and gatherers. Typically men hunted and fished; women gathered nuts and vegetables.

In a hunter-gatherer society, people relied on the resources they could find where they lived.

Obviously, human populations have blown past this hypothetical carrying capacity. By using our brains, our erect posture, and our hands, we have been able to manipulate our environment in ways that no other species has ever done. What have been the important developments that have allowed population to grow?


About 10,000 years ago, we developed the ability to grow our own food. Farming increased the yield of food plants and allowed people to have food available year round. Animals were domesticated to provide meat. With agriculture, people could settle down, so that they no longer needed to carry all their possessions (Figure below). They could develop better farming practices and store food for when it was difficult to grow. Agriculture allowed people to settle in towns and cities.

(a) Like early farmers, subsistence farmers today grow only enough food for their families, with perhaps a bit extra to sell, barter, or trade. (b) More advanced farming practices allowed a single farmer to grow food for many more people.

When advanced farming practices allowed farmers to grow more food than they needed for their families (Figure below), some people were then able to do other types of work, such as crafts or shop keeping.

Farming has increasingly depended on machines. Such advanced farming practices allow one farmer to feed many more people than in the past.

The Industrial Revolution

The next major stage in the growth of the human population was the Industrial Revolution, which started in the late 1700s (Figure below). This major historical event marks when products were first mass-produced and when fossil fuels were first widely used for power.

Early in the Industrial Revolution, large numbers of people who had been freed from food production were available to work in factories.

The Green Revolution

The Green Revolution has allowed the addition of billions of people to the population in the past few decades. The Green Revolution has improved agricultural productivity by:

  • Improving crops by selecting for traits that promote productivity; recently, genetically engineered crops have been introduced.
  • Increasing the use of artificial fertilizers and chemical pesticides. About 23 times more fertilizer and 50 times more pesticides are used around the world than were used just 50 years ago (Figure below).
  • Agricultural machinery: plowing, tilling, fertilizing, picking, and transporting are all done by machines. About 17% of the energy used each year in the United States is for agriculture.
  • Increasing access to water. Many farming regions depend on groundwater, which is not a renewable resource. Some regions will eventually run out of this water source. Currently about 70% of the world’s fresh water is used for agriculture.

Rows of a single crop and heavy machinery are normal sights for modern day farms.

The Green Revolution has increased the productivity of farms immensely. A century ago, a single farmer produced enough food for 2.5 people, but now a farmer can feed more than 130 people. The Green Revolution is credited for feeding 1 billion people that would not otherwise have been able to live.

The Future

The flip side to this is that for the population to continue to grow, more advances in agriculture and an ever increasing supply of water will be needed. We’ve increased the carrying capacity for humans by our genius: growing crops, trading for needed materials, and designing ways to exploit resources that are difficult to get at, such as groundwater. And most of these resources are limited.

The question is, even though we have increased the carrying capacity of the planet, have we now exceeded it (Figure below)? Are humans on Earth experiencing overpopulation?

Manhattan is one of the most heavily populated regions in the world.

There is not yet an answer to that question, but there are many different opinions. In the eighteenth century, Thomas Malthus predicted that human population would continue to grow until we had exhausted our resources. At that point, humans would become victims of famine, disease, or war. This has not happened, at least not yet. Some scientists think that the carrying capacity of the planet is about 1 billion people, not the 7 billion people we have today. The limiting factors have changed as our intelligence has allowed us to expand our population. Can we continue to do this indefinitely into the future?


  • Hunters and gatherers lived off the land, with no agriculture, and reached a total population of no more than around 10 million.
  • Farming allowed people to settle down and allowed populations to grow.
  • The Green Revolution and the Industrial Revolution are heavily dependent on fossil fuels.


Use this resource to answer the questions that follow.


1. Who was Thomas Malthus?

2. What did Malthus think would happen as population increased?

3. What did Malthus think would limit population?

4. What is the Malthusian limit?

5. What is happening to population growth in some developed countries today?

6. Malthus didn't account for what in his theory?

7. What country is close to the Malthusian limit today?


1. Link major advances in agriculture and industry with changes in the human population.

2. What is carrying capacity? Has the human population exceeded Earth's carrying capacity for humans? If so, how could this have happened?

3. What is the Green Revolution? How has it affected human population?

4. What do you think of Thomas Malthus' prediction? Have we proven Malthus wrong or have we just not gotten to that point yet?


Green Revolution

Green Revolution

Changes in the way food is produced since World War II that have resulted in enormous increases in production.
Industrial Revolution

Industrial Revolution

A time when mass production and fossil fuel use started to grow explosively.


When the population of an area exceeds its carrying capacity or when long-term harm is done to resource availability or the environment.


A chemical that kills a certain pest that would otherwise eat or harm plants that humans want to grow.

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Difficulty Level:
At Grade
Date Created:
Feb 24, 2012
Last Modified:
Mar 23, 2016
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