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biology
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2. 5-3 Human Population Growth
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Historical Overview
How has the size of the human population changed over time?
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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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6. Human Population Growth
Historical Overview
With these advances, the human population experienced exponential growth.
Human Population Growth
The size of the human population has increased over time. After a long, slow start, the worldwide population grew exponentially following improvements in medicine, sanitation, agriculture, energy use, and technology.
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7. 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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8. Patterns of Population Growth
Why do population growth rates differ in countries throughout the world?
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9. Patterns of Population Growth
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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10. Patterns of Population Growth
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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11. Patterns of Population Growth
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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12. Patterns of Population Growth
The demographic transition is complete when the birthrate falls to meet the death rate, and population growth stops.
Birthrates, death rates, and the age structure of a population help predict the rate of population growth. Birthrates and death rates fall during the demographic transition. In Stage I, both the birthrate and death rate are high. During Stage II, the death rate drops while the birthrate remains high. Finally, in Stage III, the birthrate also decreases.
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13. Patterns of Population Growth
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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14. Patterns of Population Growth
U.S. Population
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.
80+
Males
Females
60–64
Age (years)
40–44
This graph shows the age structure of the U.S. population.
20–24
0–4
Percentage of Population
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15. Patterns of Population Growth
Rwandan Population
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+
Males
Females
60–64
Age (years)
40–44
This graph shows the age structure of the Rwandan population.
20–24
0–4
Percentage of Population
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16. 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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17. Future Population Growth
This table, based on actual and projected data from the U.S. Census Bureau, International Database, shows data on world population.
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18. Future Population Growth
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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5-3
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5-3
The size of the human population began to increase exponentially after the
bubonic plague.
development of plowing and irrigation.
Industrial Revolution.
development of the first cities.
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5-3
Which of the following is NOT a potential limiting factor of human population growth?
famine
medicine
war
disease
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5-3
After the demographic transition is complete, a population
grows rapidly.
grows slowly.
begins a period of rapid decline.
stays about the same size as time passes.
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5-3
An age-structure diagram shows a breakdown of a population by
location and age group.
age group and gender.
birthrate and death rate.
age group and emigration rate.
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5-3
Since the mid-1960s, the average annual growth rate of the human population has
remained about the same.
failed to show a consistent pattern.
increased.
decreased.
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25. END OF SECTION