Population increases rapidly in places where more people are born than die, and it declines in places where deaths outnumber births. The population of a place also increases or decreases as people move in or out. This element of population change—migration—is discussed in Chapter 3. For most of human history, Earth’s population was unchanged at perhaps a half-milliOn. In contrast, about 85 million people are now being added to the population of the world annually.
Key Issue 2: Why is Population Increasing
A. Natural Increase
Natural increase rate (NIR)
a. percentage by which population growth in a year
b. excludes migration
Population Growth in History
a. doubling time—number of years to double a population assuming a constant rate of
natural increase
B. Births & Deaths
Fertility
a. crude birth rate—total number of life births in a year for every
b. total fertility rate—average number of children a woman will have throughout her
childbearing years
Mortality
a.infant mortality rate—annual number of deaths of infants under one year of age
compared with total live births
b. crude death rate—total number of deaths per year per 1,000 people term in an activity
C. The Demographic Transition—process of change in a society’s population
Stage 1—low growth
a. very high CBR
b. very high CDR
Stage 2—high growth
a. high CDR
b. rapidly declining CDR
c. Industrial Revolution—improvements in manufacturing goods and delivering them to
market
d. medical revolution—medical technology and improved practices eliminated traditional
causes of death in developing countries
3. Stage 3—moderate growth
a. rapidly declining CBR
b. moderate declining CDR
4. Stage 4—low growth
a. very low CBR
b. low or slightly increasing CDR
c. zero population growth
*indicates information specific to the text and is not in the AP Human Geography course
**indicates information is background or foundational to building further understanding and development
Key Issue 2: Why Is Population Increasing?
Natural Increase The natural increase rate (NIR) is the percentage by which a population grows in a year, excluding growth by migration.
Population Growth in History For the several hundred-thousand-year occupancy of Earth, the NIR was essentially zero. While the world NIR peaked at 2.1 percent in the 1960s and has been in decline since the 1990s, the NIR during the second half of the twentieth century was considerably high by historical standards. The number of people added annually has decreased from a historic peak of 93 million in 1988 to the present level of 85 million people. This drop is less acute than the drop in NIR as the world population base is larger now than in the past. World population increased from 3 to 4 billion in 14 years, from 4 to 5 billion in 13 years, from 5 to 6 billion in 12 years, and from 6 to 7 billion in 12 years.
The NIR affects the doubling time, which is the number of years required to double a population, assuming a steady rate of natural increase. If the present rate of 1.2 percent per year holds, world population would double in approximately 58 years.
Births and Deaths Population increases rapidly in locations where more people are born than die, and it decreases in locations where more people die than are born.
Fertility The crude birth rate (CBR) is the total number of live births in a year per thousand people alive in society. The highest CBRs are concentrated in Africa and Southwest Asia.
The total fertility rate (TFR) is the average number of children a woman will have throughout her childbearing years (ages 15–49). The average world TFR is 2.4 with a TFR in sub-Saharan Africa of 4.9 and a 1.6 TFR in Europe.
Mortality Infant mortality rate (IMR) is the annual number of deaths of infants under one year of age per 1,000 live births. The highest IMRs are in sub-Saharan Africa and the lowest in Europe.
The crude death rate (CDR) is the total number of deaths in a year for every thousand people in society. The CDR is usually higher in developed countries.
The Demographic Transition The demographic transition is a model of population change where high birth rates and death rates transition to low birth rates and death rates. It is divided into four stages. Some demographers are anticipating a fifth stage.
Stage 1: Low Growth In stage 1, crude birth and death rates are both high, resulting in a low rate of natural increase. For most of this period, people depended on hunting and gathering for food. When food was easily obtained, a region’s population increased, but it declined when people were unable to locate enough animals or vegetation nearby. There are no countries presently in stage 1.
Stage 2: High Growth The move to stage 2 is caused by a rapid decline in crude death rates. Crude birth rates remain high, leading to rapid population growth. Developed regions such as Europe and North America entered stage 2 as a part of the Industrial Revolution. Many less developed countries entered stage 2 much later as a result of the diffusion of medical technologies and knowledge into the less developed world (the medical revolution).
Stage 3: Moderate Growth Stage 3 is marked by a decrease in fertility, which brings down the crude birth rate and decreases the natural increase rate. A society enters stage 3 when people have fewer children. The decision to have fewer children is partly a reaction to a decline in mortality. The crude death rate in stage 3 societies continues to fall but not as rapidly as the crude birth rate.
Stage 4: Low Growth Stage 4 is marked by a nearly equal low crude birth and death rates, and roughly zero natural increase. This condition is called zero population growth (ZPG), a term often applied to stage 4 countries. Stage 4 resembles stage 1 in terms of growth, but otherwise is very different. Total population of a country is much higher in stage 4 than in stage 1. Also, instead of high crude birth and death rates, both are low. Life expectancies are much longer in stage 4.
2.2 Key Terms
Age/sex ratio Comparison of the numbers of males and females of different ages
Contraception Methods of preventing pregnancy
Crude Birth Rate (CBR) The number of live births per one thousand people in the population
Crude Death Rate (CDR) The number of deaths per one thousand people in the population
Demographic Transition Model (DTM) A model that helps explain how countries throughout the world tend to proceed through a similar process in term of CBR, CDR, and population
Doubling time The time period it takes for a population to double in size
Fecundity Fancy word for fertility
Fertility The number of live births occuring in a population
Industrial Revolution Economic and social changes resulting from technology changes that started in England in 1760 - moving away from hand tools to power-driven machines
Infant mortality rate (IMR) The number of children who don't survive their first year of life per 1000 live births in a country
Replacement-fertility level When a population is neither growing or shrinking but staying about the same (an NIR of 0 or TFR of 2.1)
Total fertility rate (TFR) The average number of children a woman is predicted to have in her child bearing (fecund) years
Rate of Natural Increase (RNI) (also known as NIR) An increase of (birth rate - death rate)/10 - a positive NIR means a population is growing and a negative NIR means a population is shrinking