Announcements
• First exam next Tuesday
– Bring a number two pencil (and a spare)
• Today: Human population growth
• End of lecture today: Exam review
Thomas Malthus (economist)
• 1798: Essay on the Principle of
Population as it Affects the
Future Improvement of Society
– Population growth tends to
outstrip the means of
subsistence
– Food increases arithmetically
whereas population increases
geometrically (exponentially)
– The poor can be kept alive by
charity, but since they would
then propagate, this is
cruelty in disguise.
...democracy cannot survive overpopulation.
Human dignity cannot survive it.
Convenience and decency cannot survive it.
As you put more and more people into the
world, the value of life not only declines, it
disappears. It doesn't matter if someone dies.
The more people there are, the less one
individual matters. – Isaac Asimov
Paul Ehrlich (Stanford Ecologist)
1968: The Population Bomb
• “The battle to feed all of
humanity is over.
• In the 1970s the world
will undergo famines—
• Hundreds of millions of
people are going to starve
to death”
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World population growth
World population growth
• Human populations have increased at
greater than exponential rates - Why?
• Has this lead to, humanitarian, economic
and environmental disaster?
• What are the implications of this kind of
human population growth?
Review of population concepts
• Populations grow exponentially
• But, as populations approach carrying
capacity, growth slows due to resource
limitation, density-dependent mortality
• These phenomena can be quantified using
exponential and logistic growth models
• Do human populations follow the same
rules?
Consequences of Exploding
Populations (Brown 2009)
Larger population
with high rates
of resource
consumption
•deforestation
•groundwater depletion
•loss of agricultural land
•resource depletion
•reduced biodiversity
•disease
•pest resistance
•fossil fuel consumption
•pollution
•population migration
•conflict
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Machakos
in sub-Saharan Africa
More people = less erosion?
Population quadrupled
Consequences of exploding
populations
Labor force increased
WWII brought new technology
1930s – 250,000 people
Land was terraced, irrigated, fertilized
Nearby Nairobi grew and provided
market for farm products
Soil conditions improved
Food stability, increased income led to
better education and lower birth rates
1990s – >1 million people
What made Machakos different than
expected?
Populations and age structure
Perspective 1 (economic gloom):
Overuse and degradation of resources, environmental
degradation, famine, suffering and conflict
Perspective 2 (economic boom):
Increased labor, increased ideas and innovation, increased
economic growth, solutions to environmental problems,
increased carrying capacity
Age-structure in China
1982
After reaching replacement fertility,
China continued growth due to
“population momentum”
Often requires 2 generations (~ 50 y)
to slow population growth.
Nigeria
158
5.7
47
75
500,000
Country
Population (millions)
Fertility rate
Life expectancy
Infant death rate
Infant deaths per year
Japan
127
1.4
83
2.6
2830
2000
Baby boom “echo”
2010 statistics, UNPD
3
China’s “missing girls”
Resources and human fertility
Total fertility rate and income (2007)
8
Demographic dividend
Resources
and human
fertility rates
7
Fertility Rate
6
• Plot from Baerlocher
(2007) Canadian Medical
Association Journal
5
4
3
2
1
0
0
10000
20000
30000
40000
Per capita income ($)
50000
Data from WHO, World Health Statistics 2009
4
Global patterns in fertility
Projected population growth
Literacy, income and fertility
Geographical patterns of female illiteracy
Total fertility rate and literacy (2007)
8
Fertility Rate
7
6
5
4
3
2
R 2 = 0.66
1
0
20
40
60
80
Adult literacy (%)
100
Data from WHO, World Health Statistics 2009
5
Education and fertility in the US
Availability of contraceptives
9
Fertility Rate
7
6
R² = 0.7
5
4
US Census Bureau data 2006
2,000
1,500
1,000
Graduate or
professional
degree
Bachelors
degree
Associate
degree
Some
college, no
degree
0
High school,
4 years
500
Incentives for high fertility
•
•
•
•
8
2,500
Not a high
school
graduate
Children born per 1000 women
What do the literacy data suggest?
High infant mortality rates
Economic benefits of children
Improves future security
Women’s status
3
2
1
0
0
20
40
60
80
100
• Motherhood in developing countries starts ~ 17 y
• Average marriage age in developed world: 25-27y
Contraceptive use (%)
Data from WHO, World Health Statistics 2009
6
Declining death rates and
population growth rates
•
•
•
•
•
•
Causes of disease recognized
Improvements in nutrition
Discovery of antibiotics
Improvements in medicine
Increase in # of women who reach child-bearing age
Short generation times in some countries
Demographic transition
Fertility
transition
Epidemiologic
transition
Summary: Continued high birth rates and short generation times
with declining mortality rates lead to rapid population growth
Primitive stability
Epidemiologic transition
Fertility transition
Modern stability
Time
Demographic transition in India
Regions in transition
Figure from Wright (2005)
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Sustainable development
• Developed countries helping developing nations to improve living
conditions without sacrificing resources of future generations
• Principles:
1: Education (literacy)
2: Health: nutrition, hygiene
3: Family planning
4: Enhance income
5: Resource management: sustainable use
• One expected result: Reduced population growth rates by moving
nations through the demographic transition
Sustainable development and the
World Bank
• Loans money to developing countries to start moneymaking programs
• Idea: Lend money → start a development project.
Project makes money → repay the loan.
• Problems:
– If project fails, country’s debt increases.
– If corrupt officials steal the money, debt increases.
– If programs are not sustainable (e.g., cutting down
rain forest for ranching), debt increases and natural
resources diminish.
• One solution: micro loans
Complications to sustainable development
Big Challenges
Population growth rates and
HIV/AIDS (2006)
• Poverty
• War
• Corruption
• Hunger
• HIV
HIV infection rate in Swaziland: 26% (2011)
Life expectancy: < 50 y
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What can you do to affect
population growth rates?
Projecting the future
• Support sustainable development programs
• Support women’s rights and family services
worldwide
• Problems to consider:
–
–
–
–
Dark side of large-scale sustainable development
Coercion as family planning
Differences in values
Problems are complex and unfamiliar
Asimov
Malthus
Ehrlich
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