Slide 1 of 24 Copyright Pearson Prentice Hall 5-3 Human Population Growth.

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Copyright Pearson Prentice Hall

5-3 Human Population Growth


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Historical Overview

Historical Overview

Like the populations of many other living organisms, the size of the human population tends to increase with time.

For most of human existence, the population grew slowly.

Limiting factors kept population sizes low.


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Historical Overview

About 500 years ago, the human population began growing more rapidly.

Life was made easier and safer by advances in agriculture and industry.

Death rates were dramatically reduced due to improved sanitation, medicine, and healthcare, while birthrates remained high.


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Historical Overview

With these advances, the human population experienced exponential growth.

Human Population Growth


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Patterns of Population Growth


The scientific study of human populations is called demography.

Demography examines the characteristics of human populations and attempts to explain how those populations will change over time.


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Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly.


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The Demographic Transition

Over the past century, population growth in the United States, Japan, and much of Europe has slowed dramatically.

According to demographers, these countries have completed the demographic transition, a dramatic change in birth and death rates.


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The demographic transition has three stages.

In stage 1, there are high death rates and high birthrates.

In stage 2, the death rate drops, while the birthrate remains high. The population increases rapidly.

In stage 3, the birthrate decreases, causing population growth to slow.


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The demographic transition is complete when the birthrate falls to meet the death rate, and population growth stops.


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Age Structure

Population growth depends, in part, on how many people of different ages make up a given population.

Demographers can predict future growth using models called age-structure diagrams.

Age-structure diagrams show the population of a country broken down by gender and age group.


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In the United States, there are nearly equal numbers of people in each age group.

This age structure diagram predicts a slow but steady growth rate for the near future.

Males Females

8 6 4 2 0 2 4 6 8

Percentage of Population

80+

60–64

20–24

0–4

40–44A

ge

(yea

rs)

U.S. Population


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In Rwanda, there are many more young children than teenagers, and many more teenagers than adults.

This age structure diagram predicts a population that will double in about 30 years.

80+

60–64

20–24

0–4

Ag

e (y

ears

)

Males Females

Rwandan Population

40–44

Percentage of Population


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Future Population Growth


To predict human population growth, demographers must consider the age structure of each country, as well as the prevalence of life-threatening diseases.

If growing countries move toward the demographic transition, growth rate may level off or decrease.


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Ecologists suggest that if growth does not slow down, there could be serious damage to the environment and global economy.

Economists assert that science, technology, and changes in society may control the negative impact of population growth.


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A survivorship curve is a graph showing the number or proportion of individuals surviving at each age for a given species or group (e.g. males/females).

Survivorship curves can be constructed for a given cohort (a group of individuals of roughly the same age) based on a life table.

Survivorship curves tell us something about how long individuals survive in a population. There are basically three types of survivorship curves:


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Type I survivorship curves are for species that have a high survival rate of the young, live out most of their expected life span and die in old age.

Ex. Human

Type II survivorship curves are for species that have a relatively constant death rate throughout their life span. Death could be due to hunting or diseases.

Ex. coral, squirrels, honey bees, birds, and many reptiles.

Type III survivorship curves are found in species that have many young, most of which die very early in their life.

Ex. Plants, oysters and sea urchins


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Slide 1 of 24 Copyright Pearson Prentice Hall 5-3 Human Population Growth.

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