The Human Population and Its
Impact
Chapter 6

Core Case Study: Are There Too
Many of Us?
 1.6 million people added to world each WEEK
• Estimated increase from 6.7 billion to 9.3 billion by 2050
 Are there too many people already?
• 82% world ’ s population in developing countries
 Will technological advances overcome environmental resistance that populations face?

Core Case Study: Are There Too
Many of Us?
 Will growing populations cause increased environmental stresses?
• Infectious diseases
• Biodiversity losses
• Water shortages
• Traffic congestion
• Pollution of the seas
• Climate change

Crowded Street in China

Human Population Growth Continues but It Is Unevenly Distributed
 Reasons for human population increase
• Movement into new habitats and climate zones
• Early and modern agriculture methods
• Control of infectious diseases through
• Sanitation systems
• Antibiotics
• Vaccines

Human Population Growth Continues but It Is Unevenly Distributed
 Population growth in developing countries is increasing 15 times faster than developed countries
• World population increasing by 1.22% per year
 By 2050, 97% of growth will be in developing countries

Global Connections: UN World
Population Projections by 2050

No Population Can Grow Indefinitely:
J-Curves and S-Curves
 Exponential growth – population that increases at a fixed rate
 Logistic growth – rapid exponential population growth followed by a steady decrease in population growth

Population Growth
 Exponential Growth
 No regulation of population size
 No predation, disease, illness,
 Unlimited resources
 The larger the population gets, the faster it grows

No Population Can Grow Indefinitely:
J-Curves and S-Curves
 Biotic potential – capacity for population growth under ideal conditions
• Larger organisms tend to have low potential
 Intrinsic rate of increase (r) – rate the population of a species would grow if it had unlimited resources

No Population Can Grow Indefinitely:
J-Curves and S-Curves
 Individuals in populations with high r
• Reproduce early in life
• Have short generation times
• Can reproduce many times
• Have many offspring each time they reproduce

Unlimited resources?
 With NO controls a species of bacteria that reproduces every 20 minutes would generate enough offspring to form a layer 1 foot deep over the entire surface of the earth in…
• 36 hours!

No Population Can Grow Indefinitely:
J-Curves and S-Curves
 Environmental resistance – combination of all factors that act to limit the growth of a population
 Carrying capacity (K) – maximum population of a given species that a habitat can sustain indefinitely without being degraded

No Population Can Continue to Increase in Size Indefinitely

Phases of Logistic Growth Curve
1.
Lag Phase – little initial growth.
2.
Rapid Growth Phase
3.
Stable Phase – stabilizing factors limit growth

Human Population Growth Continues but It Is Unevenly Distributed
 Should the optimum sustainable population be based on cultural carrying capacity ?
• Optimum level that would allow most people to live in reasonable comfort and freedom without impairing the ability of the planet to sustain future generations

Populations Can Grow, Shrink, or
Remain Stable
 Population size governed by
• Births
• Deaths
• Immigration
• Emigration
 Population change =
(births + immigration) – (deaths + emigration)

Calculating population growth…
 Rule of 70
 Doubling time = 70/annual growth rate (in %)
 Example: If a population is growing at a rate of
4%, how long will it take for the population to double?
 Doubling time = 70/4 = 17.5 years

Natural Capital Degradation: Altering
Nature to Meet Our Needs

6.3

Populations Made Up Mostly of Young
People Can Grow Rapidly
 Age structure – distribution of males and females among age groups in a population
• Prereproductive ages (0-14)
• Reproductive ages (15-44)
• Postreproductive ages (45+)
 Nearly 28% of the people on the planet were under 15 years old in 2008
• 41% in Africa!

Generalized Population Age Structure
Diagrams

We Can Use Age-Structure Information to
Make Population and Economic Projections
 Baby boomers now make up half of all adult Americans
• Influences elected officials and laws
 Job market will increase when they retire
• Shortage of workers
• Argument to support immigration

Tracking the Baby-Boom Generation in the United States

Populations Made Up of Mostly Older
People Can Decline Rapidly
 Slow decline
• Manageable
 Rapid decline
• Severe economic problems; How?
• Severe social problems
• Example: Japan

Populations Made Up of Mostly Older
People Can Decline Rapidly
 Japan
• World ’ s highest proportion of elderly people
• Strain on government budget
• Lowest proportion of young people
• 128 million in 2008
• 96 million by 2050

Some Problems with Rapid Population
Decline

Populations Can Decline from a Rising
Death Rate: The AIDS Tragedy
 25 million killed by 2008
 Many young adults die: loss of most productive workers
 Sharp drop in life expectancy
 International community called upon to
• Reduce the spread of HIV through education and health care
• Financial assistance and volunteers

6.2

The Human Population Can Grow,
Decline, or Remain Fairly Stable
 Population change
• Births: fertility
• Deaths: mortality
• Migration
 Population change =
(births + immigration) –
(deaths + emigration)

The Human Population Can Grow,
Decline, or Remain Fairly Stable
 Crude birth rate – number of live births per 1,000 people in a population in a given year
 Crude death rate number of deaths per 1,000 people in a population in a given year

Global Connections: The World ’ s 10
Most Populous Countries in 2008

Women Having Fewer Babies but Not
Few Enough!
 Fertility rate – number of children born to a woman during her lifetime
• Replacement-level fertility rate – average number of children a couple must bear to replace themselves (2.1 – 2.5)

Women Having Fewer Babies but Not
Few Enough!
 Fertility rate – number of children born to a woman during her lifetime
• Total fertility rate
(TFR) – average number of children born to women in a population during reproductive years
(1.6 – 2.8 still too high)

Baby Boom: 1946-1964
 79 million people were added to the
U.S. population
• Previously took 139 years to add 100 million people!
 Peak 1957
• TFR = 3.7 children per woman

US and immigration
 Fourfold increase in population growth since 1900
 US has highest population rate of any developed country
• TFR decreasing but immigration increasing
 Some migrating to the
US ever 32 seconds
 Previous leading causes of death
• Pneumonia
• Tuberculosis
• Diarrhea
• Untrained doctors

TFR Rates for the U.S. between 1917 and 2008

Birth Rates in the U.S. from 1910 to 2008

Some Major Changes That Took Place in the U.S. between 1900 and 2000

Several Factors Affect Birth Rates and
Fertility Rates
 Children as part of the labor force
• Higher in developing countries
 Cost of raising and educating children
• $290,000 B  18

Several Factors Affect Birth Rates and
Fertility Rates
 Availability of private and public pension
• Reduce need for financial support of children
 Urbanization
• Better access to family planning
 Educational and employment opportunities for women

Several Factors Affect Birth Rates and
Fertility Rates
 Infant mortality rate – number of children per
1,000 births who die before one year of age
• Age of a woman at birth of first child
• Availability of abortions
(25% of all pregnancies)
• Availability of reliable birth control methods
• Religious beliefs, traditions, and cultural norms

Several Factors Affect Death Rates
 Life expectancy – average number of years a newborn infant can expect to live
• 77 years in developed countries
• 67 years in developing countries
 Infant mortality rate – number of babies out of very 1,000 born who die before their first birthday
• Indicator of societies quality of life (reflects nutrition and health care)

Migration Affects an Area ’ s Population
Size
 Economic improvement
 Religious freedom
 Political freedom
 Wars
 Environmental refugees

Case Study: The United States: A Nation of Immigrants
 Since 1820 US has admitted almost twice as many immigrants and refuges as all countries combined
 Legal and illegal immigration account for about 40% of the country ’ s annual population growth

6.4 Part 2

Planning for Babies Works
 Family Planning
• Responsible for a 55% drop in TFRs
• Developing countries 42% are unplanned and
26% result in abortion
 Slow and stabilize population growth
• Invest in family planning
• Reduce poverty
• Elevate the social and economic status of women

Thailand: Reducing TFRs
 Used family planning to cut annual population growth rate from 3.2% to
0.5%
• Reduced TFR from 6.4 to 1.6 children per family

Empowering Women Can Slow
Population Growth
 Educated women
 Paying jobs
 Human rights without suppression
 “ For poor women the only holiday is when you are asleep ”

Women from a Village in Burkina Faso
Returning with Fuelwood
 Globally women account for two-thirds of all hours worked but receive only 10% of the world ’ s income and own less than 2% of land

Case Study: Slowing Population Growth in China: the One-Child Policy
 1972-2008 cut birth rate in half
• TFR decreased from 5.7 to 1.6
• Discourages premarital sex
• Gender imbalance
• Preference for loyal males
• Females high commodity
• Fast-growing economy
• 47% struggle to live on $2 per day
• Face serious resource and environmental problems

Case Study: Slowing Population Growth in China: the One-Child Policy
 Why only one?
• Married couples with one child receive:
• More food
• Larger pensions
• Better housing
• Free health care
• Salary bonuses
• Free school tuition for their child
• Preferential employment opportunities for their child

6.4

As Countries Develop, Their
Populations Tend to Grow More Slowly
 Demographic transition hypothesis as countries become industrialized death rates and then birth rates decline
 Four stages
• Preindustrial
• Transitional
• Industrial
• Postindustrial
 See handout…

Four Stages of the Demographic
Transition

Active Figure: Demographic transition model