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LIVING IN THE ENVIRONMENT, 18e G. TYLER MILLER • SCOTT E. SPOOLMAN
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6 The Human Population and Its
Impact
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• The evolution of Homo sapiens and a total
population of 2 billion has taken 200,000
years
• It has taken less than 50 years to reach
the second 2 billion
• It took 25 years to add the third 2 billion
• Twelve years later, the population topped
7.1 billion
• What is a sustainable human population?
Core Case Study: Planet Earth: Population
7 Billion
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Fig. 6-1, p. 122
Hunting and
gathering
Agricultural revolution Industrial
revolution
Billio
ns o
f peo
ple
1800 (1 billion)
2011 (7 billion) 1999 (6 billion) 1987 (5 billion)
1974 (4 billion)
1960 (3 billion)
1930 (2 billion)
Core Case Study: Planet Earth: Population 7 Billion
Time
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• The continuing rapid growth of the human
population and its impacts on natural
capital raise questions about how long the
human population can keep growing
6-1 How Do Environmental Scientists
Think about Human Population Growth?
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• Rate of population growth has slowed in
recent decades
• Human population growth is unevenly
distributed geographically
• People are moving from rural to urban
areas
Human Population Growth Shows Certain
Trends
Annual Growth Rate of World Population,
1950-2010
Fig. 6-2, p. 123
Where Population Growth Occurred, 1950-
2010
Fig. 6-3, p. 123
Population in less-developed countries
Wo
rld
po
pu
lati
on
(in
bil
lio
ns)
Population in more-developed countries
Year
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• As the human population grows, so does
the global total human ecological footprint
• Cultural carrying capacity
– Total number of people who could live in
reasonable freedom and comfort indefinitely,
without decreasing the ability of the earth to
sustain future generations
Human Population Growth Impacts Natural
Capital
Natural Capital Degradation
Altering Nature to Meet Our Needs
Reducing biodiversity
Increasing use of net primary
productivity
Increasing genetic resistance in
pest species and disease-
causing bacteria
Eliminating many natural
predators
Introducing harmful species into
natural communities
Using some renewable resources
faster than they can be replenished
Disrupting natural chemical
cycling and energy flow
Relying mostly on polluting and
climate-changing fossil fuels
Fig. 6-4, p. 125
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• Population size increases through births
and immigration, and decreases through
deaths and emigration
• The average number of children born to
women in a population (total fertility rate)
is the key factor that determines
population size
6-2 What Factors Influence the Size of the
Human Population?
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• Population change =
(births + immigration) – (deaths +
emigration)
• Crude birth rate
– The number of live births/1000/year
• Crude death rate
– The number of deaths/1000/year
The Human Population Can Grow,
Decline, or Remain Fairly Stable
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• Fertility rate
– Number of children born to a woman during
her lifetime
• Replacement-level fertility rate
– Average number of children a couple must
have to replace themselves
– Approximately 2.1 in developed countries
– Up to 2.5 in developing countries
Women Are Having Fewer Babies, But the
World’s Population Is Still Growing
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• Total fertility rate (TFR)
– Average number of children born to women in
a population
– Between 1955 and 2012, the global TFR
dropped from 5 to 2.4
– However, to eventually halt population growth,
the global TFR will have to drop to 2.1
The World’s Population Is Still Growing
(cont’d.)
Total Fertility Rate Total Fertility Rates
Baby boom
(1946–64)
Replacement
level
Bir
ths
pe
r w
om
an
Fig. 6-5, p. 127
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• Population still growing and not leveling off
– 76 million in 1900
– 314 million by 2012
• Drop in TFR in U.S.
– Rate of population growth has slowed
• What have been some changes in lifestyle
in the U.S. during the 20th century?
Case Study: The U.S. Population – Third
Largest and Growing
77 years Life expectancy 47 years
1900
2000
Married women working
outside the home 8%
81%
High school
graduates
15%
83%
Homes with flush
toilets
10%
98%
Homes with
electricity 2%
99%
Living in
suburbs
10%
52%
Hourly manufacturing job
wage (adjusted for inflation) $3
$15
Homicides per
100,000 people
1.2
5.8 Stepped Art
Fig. 6-7, p. 132
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• Immigration
– U.S. has admitted almost twice as many
immigrants and refugees as all other
countries combined
Case Study: The U.S. Population – Third
Largest and Growing (cont’d.)
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Fig. 6-6, p. 127
Nu
mb
er
of
leg
al im
mig
ran
ts (
tho
usan
ds)
1907
1914
New laws
restrict
immigration
Great
Depression
Year
Legal Immigration to the United States
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• Children as part of the labor force
• Cost of raising and educating children
• Availability of private and public pension
• Urbanization
• Educational and employment opportunities
for women
Several Factors Affect Birth Rates and
Fertility Rates
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• Average age of a woman at marriage
• Availability of legal abortions
• Availability of reliable birth control methods
• Religious beliefs, traditions, and cultural
norms
Several Factors Affect Birth Rates and
Fertility Rates (cont’d.)
Several Factors Affect Birth Rates and
Fertility Rates (cont’d.)
Fig. 6-9, p. 129
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• Life expectancy
• Infant mortality rate
– Number of live births that die in first year
• High infant mortality rate indicates:
– Insufficient food
– Poor nutrition
– High incidence of infectious disease
Several Factors Affect Death Rates
Several Factors Affect Death Rates (cont’d.)
Fig. 6-10, p. 129
Less-developed
countries
World
Infa
nt
mo
rtali
ty r
ate
(death
s p
er
1,0
00 l
ive b
irth
s)
More-developed
countries
Year
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• Migration
– The movement of people into and out of
specific geographic areas
• Causes:
– Economic improvement
– Religious and political freedom
– Wars
• Environmental refugees
Migration Affects an Area’s Population Size
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• The numbers of males and females in
young, middle, and older age groups
determine how fast a population grows or
declines
6-3 How Does a Population’s Age
Structure Affect Its Growth or Decline?
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• Age structure categories
– Prereproductive ages (0-14)
– Reproductive ages (15-44)
– Postreproductive ages (45 and older)
• Seniors are the fastest-growing age group
A Population’s Age Structure Helps Us
Make Projections
A Population’s Age Structure Helps Us
Make Projections (cont’d.)
Fig. 6-11, p. 131
Male Female Male Female Male Female Male Female
Expanding Rapidly
Guatemala Nigeria
Saudi Arabia
Expanding Slowly
United States
Australia China
Stable Japan
Italy Greece
Declining Germany
Bulgaria Russia
Prereproductive ages
0–14
Reproductive ages
15–44
Postreproductive ages 45–85+
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A Population’s Age Structure Helps Us
Make Projections (cont’d.)
Fig. 6-12, p. 132
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• 79 million people added from 1946-1964
– 36% of adults
• Affect politics and economics
• Now becoming senior citizens
– Graying of America
Case Study: The American Baby Boom
Case Study: The American Baby Boom
(cont’d.)
Fig. 6-13, p. 132
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• Slow decline
– Manageable
• Rapid decline
– Economic problems
• Proportionally fewer young people working
• Labor shortages
Populations Made Up of Mostly Older
People Can Decline Rapidly
Fig. 6-14, p. 133
Some Problems with Rapid
Population Decline
Can threaten economic growth
Labor shortages
Less government revenues with fewer
workers
Less entrepreneurship and new
business formation
Less likelihood for new technology
development
Increasing public deficits to fund higher
pension and health-care costs
Pensions may be cut and retirement age
increased
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• AIDS has killed more than 30 million
people
• Many young adults die – loss of most
productive workers
• Sharp drop in life expectancy
• International community
– Reduce the spread of HIV through education
and health care
– Financial assistance and volunteers
Populations Can Decline due to a Rising
Death Rate: The AIDS Tragedy
The AIDS Tragedy (cont’d.)
Fig. 6-15, p. 134
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• We can slow human population growth by
reducing poverty, elevating the status of
women, and encouraging family planning
6-4 How Can We Slow Human Population
Growth?
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• Demographic transition
– As countries become industrialized
• First death rates decline
• Then birth rates decline
• Four stages
– Preindustrial
– Transitional
– Industrial
– Postindustrial
The First Step Is to Promote Economic
Development
Death rate
Total population
Birth rate
Population grows rapidly
because birth rates are high and
death rates drop because of
improved food production and
health
Decreasing
Stage 2
Transitional
Increasing Very high
Stepped Art
Population growth
levels off and then
declines as birth
rates equal and
then fall below
death rates
Stage 4
Postindustrial
Negative Zero
Population
grows very
slowly because
of a high
birth rate
(to compensate
for high infant
mortality) and a
high death rate
Stage 1
Preindustrial
Growth rate over time
80
70
60
50
40
30
20
10
0
Bir
th r
ate
an
d d
ea
th r
ate
(nu
mb
er
pe
r 1
,00
0 p
er
ye
ar)
Low
Population growth
slows as both birth
and death rates
drop because of
improved food
production, health,
and education
Stage 3
Industrial
Low
Fig. 6-16, p. 135
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• Factors that decrease total fertility rates:
– Education
– Paying jobs
– Ability to control fertility
• Women:
– Do most of the domestic work and child care
– Provide unpaid health care
– 2/3 of all work for 10% of world’s income
– Discriminated against legally and culturally
Empowering Women Can Slow Population
Growth
Empowering Women Can Slow Population
Growth (cont’d.)
Fig. 6-17, p. 135
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• Family planning in less-developed
countries
– Responsible for a 55% drop in TFRs
– Financial benefits – money spent on family
planning saves far more in health, education
costs
Family Planning Can Provide Several
Benefits
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• Two problems
– 42% pregnancies unplanned, 26% end with
abortion
– Many couples do not have access to family
planning
• How can family planning programs be
expanded?
Family Planning Can Provide Several
Benefits (cont’d.)
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• Population: 1.26 billion people in 2012
• Problems
– Poverty, malnutrition, and environmental
degradation
• Causes
– Bias toward having male children
– Poor couples want many children
– Only 47% of couples use family planning
Case Study: Slowing Population
Growth in India
Case Study: Slowing Population
Growth in India (cont’d.)
Fig. 6-20, p. 137
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• World’s most populous country
• Threat of mass starvation in the 1960s
• Government established a strict family
planning and birth control program
– Reduced number of children born per woman
from 5.7 to 1.5
Case Study: Slowing Population Growth in
China: A Success Story