17.1 Growth of Human Populations

What will stop population growth?

It took all of human history until 1802 for the human population to reach its first billion. It took just 12 years for it to acquire its most recent billion. Although the growth rate is predicted to slow later this century, there's no end to population growth in sight. Yet, the population can't continue to grow forever. How will it stop?

Human Population Numbers

Human population growth over the past 10,000 years has been tremendous (Figure below). The entire human population was estimated to be

• 5 million in 8000 B.C.
• 300 million in A.D. 1
• 1 billion in 1802
• 3 billion in 1961
• 7 billion in 2011

As the human population continues to grow, different factors limit population in different parts of the world. What might be a limiting factor for human population in a particular location? Space, clean air, clean water, and food to feed everyone are limiting in some locations.

The Rate of Growth

Not only has the population increased, but the rate of population growth has increased (Figure below). The population was estimated to reach 7 billion in 2012, but it did so in 2011, just 12 years after reaching 6 billion.

Although population continues to grow rapidly, the rate that the growth rate is increasing has declined. Still, a recent estimate by the United Nations estimates that 10.1 billion people will be sharing this planet by the end of the century. The total added will be about 3 billion people, which is more than were even in existence as recently as 1960.

Summary

• The human population is growing more than exponentially.
• The human population is increasing, the rate of human population growth is increasing, but the rate at which the rate of growth is increasing has declined.
• The United Nations estimates a population of 10.1 billion by the end of the century yet that is much less than the number we would expect if 1 billion people were being added every 12 years.

Review

1. What does it mean that the human population growth rate is increasing?
2. What does it mean that the rate that the growth rate is increasing has declined?
3. What factors may someday limit human population growth?

Explore More

Use this resource to answer the questions that follow.

1. What is exponential growth in a population?
2. What happened in 1650?
3. What was the population in 1650? 1850? 1930? 1975? What is the population now?
4. What has the human population of the planet done in the past 80 years?
5. What does R versus K selection theory compare? What does that have to do with reproduction?
6. Which organisms tend to be R and which K? What population size do K organisms tend to have?
7. Why are humans considered to be K animals?
8. How have humans managed to go 350 years with a population growth curve that looks more like an R animal? Describe the reasons.
9. What is the estimated carrying capacity of humans on Earth?
10. How do ecologists now try to determine what the carrying capacity is? Why is this not the same for everyone on Earth?
11. What happens as we take up more space and resources?
12. What does it mean that the rate of human population growth peaked in 1962? Is population still growing?
13. Why is the rate of population growth decreasing and how can we make the rate decrease further?