Biology 2014-2015

Section 5-3: Human Population Growth
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¨       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.