¨ The human population is growing at a rate of nearly 3 people per
second.
Historical Overview
¨ For most of human existence, the population grew slowly.
¨ Limiting factors kept population sizes low.
Ø
Life was harsh
Ø
Food was scarce
Ø
Incurable diseases were rampant
· Only half the children in the world survived to adulthood so families had many
children to make sure some would survive.
· Agriculture and industry made life easier and safer.
· Improved sanitation, medicine and health care reduced the death rate and increased
longevity.
· With these advances, the human population experienced exponential growth.
Patterns of Population
Growth
¨ The human population cannot keep growing exponentially forever,
because Earth and its resources are limited.
¨ Today, scientists have identified a variety of social and economic
factors that can affect human populations.
¨ Demography is the scientific study of human populations.
¨ 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.
The Demographic
Transition
¨ Over the past century, population growth in the United States,
Japan, and much of Europe has slowed dramatically.
¨ These countries have completed a demographic
transition which is a dramatic change in birth
and death rates.
¨ Due to many advances in society, the death rate is lower thus the
demographic transition has begun.
¨ How does this work?
Ø When the death rate first begins to fall, birthrates remain high.
So, population increases rapidly.
· This happened between 1790 and 1910 in the U.S.
· Many parts of South America, Africa, and Asia
are still in this phase.
Ø With modernization, higher education and an increase in the standard
of living, families have fewer children. So, as the birthrate falls, population
growth slows.
Ø The demographic transition is complete when the birthrate falls
to meet the death rate, and population growth stops.
¨ Most people live in countries that have not yet completed the demographic
transition.
¨ Most of the population growth today is contributed by only 10 countries
with India and China
in the lead.
Age Structure
¨ Population growth depends on how many people of different ages make
up a given population.
¨ Age-structure diagrams graph the numbers of people in different age groups in the population.
Future Population Growth
¨ To predict how the world’s population will grow, demographers
must consider many factors:
Ø The age structure of each country
Ø The prevalence of life-threatening diseases
¨ Current projections suggest the population will reach 9 billion
in 2050.
¨ The growth rate may level off or even decrease if countries that
are currently growing rapidly move toward the demographic transition.
¨ In 2050, the growth rate is projected to be .43%.
¨ The peak growth rate of 2.19% was reached in the early 1960’s.