Human Populations
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Outline:
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Population Growth
 Limits to Growth
Human Demography
 Fertility and Mortality
 Life Span and Expectancy
Population Growth - Opposing Factors
Demographic Transition
Family Planning
Future of Human Populations
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
POPULATION GROWTH
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Until the Middle Ages, human populations
were held in check by diseases, famines and
wars, and thus grew very slowly.
 It took all of human history to reach 1 billion.
 150 years to reach 3 billion
 12 years to go from 5 to 6 billion (1999)
- Population 3x during 20th c.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Human Population History
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
LIMITS TO GROWTH
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Thomas Malthus (1798) argued human
populations tend to increase exponentially
while food production is plentiful.
 Humans inevitably outstrip food supply and
eventually collapse.
- Human population only stabilized by
positive checks.
- Humans are too lazy and immoral to
voluntarily reduce birth rates.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Malthus Theory of “Overpopulation”
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Social Justice Perspective
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Population growth is a symptom rather than
a root cause of poverty and other social
problems.
 Real causes of these problems are
exploitation and oppression.
- The way to slow population growth and
alleviate many social problems is
through social justice.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Population Perspectives Today
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Neo-Malthusians - Believe we are
approaching, or have already surpassed, the
Earth’s carrying capacity.
 We should make over-population issues
our first priority.
Social Justice - Believe eliminating
oppression and poverty through social justice
is the only solution to the population problem.
 Wealth and resource distribution must be
addressed.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
The Role of Technology
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Technological optimists argue that Malthus
was wrong in his predictions because he
failed to account for scientific progress.
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Current burst of growth was stimulated by
the scientific and industrial revolutions.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Can More People be Beneficial ?
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More people mean larger markets, more
workers, and increased efficiency due to
mass productions.
Greater numbers also provide more
intelligence and enterprise to overcome
problems.
 Human ingenuity and intelligence.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
DEMOGRAPHY
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Vital statistics
about people
Births, deaths,
distribution, and
population size.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Population Density (persons / square km)
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Two Demographic Worlds
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Periphery is poor, young, and rapidly
growing.
- Contain 80% of world population, and
will account for 90% of projected growth.
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Core is wealthy, old, and mostly shrinking.
- Average age is about 40.
- Populations expected to decline.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Estimated Human Population Growth
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Fertility Rate
(# children per woman of childbearing age)
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Population growth
in Periphery:
Cause or symptom
of poverty and
environmental
degradation?
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Ehrlich Theory of “Population Bomb”
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Population growth would deplete resources
 Can be true on local/national level
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Treats population as cause
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Core responsibility for Periphery growth
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Core consumes far more resources
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Demands cheap, unskilled young labor
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Population growth as a symptom of poverty
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Why parents in Periphery have kids
Better chance for one kid to survive
Bring in the crops and income
Help parents in old age
Women often lack power to not have kids
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Fertility declines, real and projected
Developing
Children per Woman
(2.1 = no population growth)
7
6
Developed
5
Africa
4
Asia
3
2
South and
Central
America
1
1950
1965
1980
1995
2010
2025
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
2040
Women’s empowerment:
Contraception Rates
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Policies to lower birth rate
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Forced
 One-child policy (China)
 Coercive “population control”
Voluntary
 Availability of birth control
 Incentives for small families
•Social
–Empowerment of women
–Better health care and education
–End to child labor
–Social security
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Fertility and Birth Rates
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Crude Birth Rate - Number of births in a year
per thousand. (Not adjusted for population
characteristics)
Total Fertility Rate - Number of children born
to an average woman in a population during
her life.
Zero Population Growth - Occurs when births
plus immigration in a population just equal
deaths plus emigration.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Mortality and Death Rates
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Crude Death Rate - Number of deaths per
thousand persons in a given year.
 Poor countries average about 20 while
wealthier countries average about 10.
- Some rapidly growing countries have
very low crude death rates compared to
slower growing countries, due to a
higher proportion of young people in the
population.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Population Growth Rates
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Natural Increase
 (Crude Birth Rate - Crude Death Rate)
Total Growth Rate
 Includes immigration and emigration
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Life Span and Life Expectancy
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Life Expectancy - Average age a newborn
can expect to attain in any given society.
 Declining mortality is the primary cause of
most population growth in last 300 years.
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Worldwide, average has risen from 40 to
65.5 over the past century.
- Greatest progress has been in
developing countries.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Demographic Implications of Living Longer
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A population growing rapidly due to natural
increase has more young people than a
stationary population.
 Both rapidly and slowly growing countries
can have a problem with dependency ratio.
- The number of non-working compared to
working individuals in a population.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Germany (effect of wars)
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Canada, 1971-2006
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Russia, 1990-2006
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Emigration and Immigration
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Emigration and Immigration play a large role
in human population dynamics.
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Developed regions expect 2 million
immigrants a year for next 50 years.
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Locals complain immigrants take away
jobs and overload social services.

Sierra Club debate over immigation.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
POPULATION GROWTH, OPPOSING
FACTORS
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Pronatalist Pressures
 Factors that increase the desire for children.
- Source of pleasure, pride, comfort.
- Source of support for elderly parents.
- Current source of family income.
- Social Status
- Replace members in society as they die.
 Boys frequently valued more than girls.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Birth Reduction Pressures
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Higher education and personal freedom for
women often result in decisions to limit
childbearing.
 When women have more opportunities to
earn a salary, they are less likely to have
children.
 Education and socioeconomic status are
usually inversely related to fertility in
wealthier countries.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Birth Reduction Pressures
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In developing countries, higher income often
means families can afford more children,
thus fertility often increases.
In less-developed countries, adding another
child to a family usually does not cost much,
while in developed countries, raising an
additional child can carry significant costs.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
United States Birth Rate
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
DEMOGRAPHIC TRANSITION
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Model of falling death rates and birth rates
due to improved living conditions
accompanying economic development.
 Pre-Modern Society - Poor conditions keep
death rates high, thus birth rates are
correspondingly high.
 Economic Development brings better
conditions and standard of living thus
death rates fall. Birth rates stay constant or
even rise.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Demographic Transition
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Eventually, birth rates begin to fall.
 Populations grow rapidly in time between
death rates and birth rates fall.
Developed Countries - Transition is complete
and both death and birth rates are low and
population is in equilibrium.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Demographic Transition
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Optimism or Pessimism
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Some demographers believe the
Demographic Transition is already taking
place in developing countries, and world
population should stabilize during the next
century.
Others argue that many poorer countries are
trapped in the middle phase of transition, and
that their populations are growing so rapidly
that human demands exceed sustainable
resource yields.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Social Justice
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Still other demographers believe that in order
for the Demographic Transition model to
work, resources must be distributed more
equitably.
 The world has enough natural resources,
but inequitable social and economic
systems cause maldistribution.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
FAMILY PLANNING
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Family Planning allows couples to determine
the number and spacing of their children.
Birth Control - Any method used to reduce
births.
 Traditional Methods
- Long breast-feeding, taboos against
intercourse while breast-feeding,
celibacy, folk medicines, abortion,
infanticide.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
FUTURE OF HUMAN POPULATIONS
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Most demographers believe the world
population will stabilize sometime during the
next century.
 Projections of maximum population size:
- Low
8
billion
- Medium
9.3 billion
- High
13 billion
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.