Human Populations
Chapter 6
After this lecture, you will be able to:
Perceive the scope of human population growth
Evaluate how human population, affluence and technology affect the environment
Explain and apply the fundamentals of demography
Understand demographic transition
Describe how wealth and poverty, the status of women and family planning affect
population growth
Central Case Study: China’s One-Child Policy
In 1970, China’s 790 million people faced starvation
The government instituted a one-child policy
The growth rate plummeted
The policy is now less strict
but has unwanted consequences:
Killing of female infants
Black-market trade in teenaged girls
Our world at seven billion
Populations continue to rise in most countries, particularly in poverty-stricken developing
nations
Although the rate of growth is slowing, we are still increasing in numbers
Counting to 1 billion (1/second) would take 31 years—it would take 221 years to count to 7
billion!
The human population is growing rapidly
Growth rates vary
At today’s 1.2% global growth rate, the population will double in 58 years
Is there a limit to population growth?
Technology, sanitation, medication, and food increase population
Death rates drop, but not birth rates
Earth’s carrying capacity for people?
2 billion prosperous people
33 billion very poor people
Thomas Malthus’ An Essay on the Principles of Population (1798)
War, disease, starvation will reduce populations
Different views on population growth
Paul Ehrlich’s The Population Bomb (1968) predicted that population growth would lead to
famine and conflict
But intensified food production fed more people
Many economists think depleted resources will be replaced or new resources created
But many resources (e.g., species) cannot be replaced
Quality of life will suffer with unchecked growth
Population growth: causes and consequences
Several factors affect the environment
The IPAT model: I = P  A  T
Our total impact (I) on the environment results from:
Population (P)
Affluence (A)
Technology (T)
Further model refinements include the effects of education, laws, and ethics on the formula
Demography
Demographers study:
Population size
Density and
distribution
Age structure
Sex ratio
Birth, death, immigration, and emigration rates
Population size and density
The UN predicts 9 billion humans by 2050
If women have just 0.5 children fewer than the medium scenario, there will be 8, not 9.15,
billion by 2050
Population distribution
Age structure affects population size
Many populations are aging
The global mean age is now 28—in 2050, it will be 38
Factors in population change
Rates of birth, death, and migration determine whether a population grows, shrinks, or
remains stable
Birth and immigration add individuals
Death and emigration remove individuals
Technological advances cause decreased deaths
The increased gap between birth and death rates resulted in population expansion
Natural rate of population change is the change due to birth and death rates alone,
excluding immigration and emigration
Eighty million added per year despite falling growth rates
Factors affecting total fertility rate
Total fertility rate (TFR) is the average number of children born to each female during her
lifetime
Replacement fertility is the TFR that keeps the size of a population stable (about 2.1)
Causes of decreasing TFR:
Medical care reduces infant mortality
Urbanization increases childcare costs
Children go to school instead of working
Social Security supports the elderly
Educated women enter the labor force
Life expectancy is increasing
People live longer in countries with good sanitation, health care, and food
Urbanization, industrialization, and personal wealth increases life expectancy (the time a
person can expect to live) and decreases infant mortality
Demographic transition is a model of economic and cultural change
Explains the declining death and birth rates in industrializing nations
The demographic transition
As they industrialize, nations move from a stable pre-industrial state of high birth and death
rates to a stable post-industrial state of low birth and death rates
Industrialization decreases mortality rates
Death rates fall before birth rates
Resulting in temporary population growth
4 stages of demographic transition
Pre-industrial stage: low population growth
High death (disease, starvation, few medicines) and birth (compensation for mortality) rates
Transitional stage: industrialization, increased food and medical care reduce mortality rates
High birth rates cause population to surge
Industrial stage: women get jobs and use birth control
Post-industrial stage: low birth and death rates stabilize populations
Is demographic transition universal?
It has occurred in Europe, the U.S., Canada, Japan, and other nations over the past 200–300
years
But it may or may not apply to developing nations
The transition could fail:
If the population is too large to allow the transition
In cultures that place greater value on childbirth or grant women fewer freedoms
Family planning is the key to controlling growth
Birth control reduces the frequency of pregnancy
Contraception is the deliberate prevention of pregnancy through a variety of methods
Hindered by religious and cultural influences
Rates range from 10% (Africa) to 86% (China)
Empowering women reduces fertility rates
A nation’s fertility rates drop when women gain access to contraceptives, family planning
programs, and educational opportunities
Educating women reduces fertility rates, delays childbirth, and gives them a voice in
reproductive decisions
A woman controls her reproductive window
Jobs or school delays the birth of a first child
Contraceptives space births
The window is “closed” after the desired number of kids
Family planning reduces fertility rates
Poverty and population growth are related
Poor societies have higher population growth rates
Poverty and population growth make each other worse
Projected population growth
Wealth also impacts the environment
Affluent societies have enormous resource consumption
One American has as much environmental impact as 3.5 Chinese or 9 Indians or 13 Afghans
We must reduce population growth and consumption