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6.21: Human Population

Difficulty Level: At Grade Created by: CK-12
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How do humans adapt to their environment?

It could be said that the human population does not have to adapt to its environment, but forces the environment to change to suit us. We can live practically anywhere we want, eat all types of food, and build all types of housing. Because of all of these "adaptations," our population has grown, after a slow start, considerably fast.

The Human Population

Humans have been called the most successful "weed species" Earth has ever seen. Like weeds, human populations are fast growing. They also disperse rapidly. They have colonized habitats from pole to pole. Overall, the human population has had a pattern of exponential growth, as shown in Figure below. The population increased very slowly at first. As it increased in size, so did its rate of growth.

Growth of the Human Population. This graph gives an overview of human population growth since 10,000 BC. It took until about 1800 AD for the number of humans to reach 1 billion. It took only a little over 100 years for the number to reach 2 billion. The human population recently passed the 7 billion mark! Why do you think the human population began growing so fast?

Early Population Growth

Homo sapiens arose about 200,000 years ago in Africa. Early humans lived in small populations of nomadic hunters and gatherers. They first left Africa about 40,000 years ago. They soon moved throughout Europe, Asia, and Australia. By 10,000 years ago, they had reached the Americas. During this long period, birth and death rates were both fairly high. As a result, population growth was slow. Humans invented agriculture about 10,000 years ago. This provided a bigger, more dependable food supply. It also let them settle down in villages and cities for the first time. The death rate increased because of diseases associated with domestic animals and crowded living conditions. The birth rate increased because there was more food and settled life offered other advantages. The combined effect was continued slow population growth.


  • Early humans lived in small populations of nomadic hunters and gatherers. Both birth and death rates were fairly high. As a result, human population growth was very slow.
  • The invention of agriculture increased both birth and death rates. The population continued to grow slowly.


Use this resource to answer the questions that follow.

  1. What was the human population 2,000 years ago? Where did most people live?
  2. Describe the growth rate over the next 1,000 years.
  3. What was the population around the year 1800? Where did most people live?
  4. When did the population reach 2 billion?
  5. What changed in the mid-1900s that profoundly affected the growth rate?
  6. How long did it take the population to grow from 2 billion to 3 billion people?
  7. How long did it take the population to grow from 3 billion to 4 billion people? Why?
  8. As of 1999, what percentage of the population lived in Asia?
  9. What will the population be like in 2050?


1. Describe human population growth rates.

2. How did the invention of agriculture affect human birth and death rates? How did it affect human population growth?

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Homo sapiens The only living species in the Homo genus; humans.

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Difficulty Level:
At Grade
Date Created:
Feb 24, 2012
Last Modified:
Aug 28, 2016
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