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This lecture will help you understand:

  • Human population growth
  • Population, affluence, and technology’s effects
  • Demography
  • Demographic transition
  • Factors affecting 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

  • Our population grows by over 80 million each year
  • It took until 1800 to reach 1 billion
  • We added 6 more billion in 130 years
  • We added the most recent billion in 12 years
  • Because of exponential growth (increase by a fixed %), even if the growth rate remains steady, population will continue to grow

Growth rates vary from region to region

  • At today’s 1.2% global growth rate, the population will double in 58 years (70/1.2 = 58)
  • If China’s rate had continued at 2.8%, it would have had 2 billion people within 25 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
    • Less space, food, wealth per person
  • Population growth is a problem if it depletes resources, stresses social systems, and degrades the environment

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): individuals need space and resources
    • Affluence (A): per capita resource use
    • Technology (T): increases use of, or protects, resources
  • Sensitivity (S): a fourth factor showing how sensitive an area is to human pressure
  • Further model refinements include the effects of education, laws, and ethics on the formula

China is an example of the IPAT formula

  • Elements of the IPAT equation can combine
    • Causing tremendous impact in a very short time
  • Modern China’s rapid development is causing unprecedented environmental challenges
    • Intensive agriculture is eroding farmland
    • Overuse has dried up the mighty Yellow River
    • Increasing vehicles are causing urban pollution and massive traffic jams
  • China shows us what the rest of the world can become

Human population growth and regulation-Effects of human activity

Human population growth and regulation-Carrying capacity

  • Animation: Population Growth Regulation
  • Right-click slide / Select “Play”


  • Demographers study:
    • Population size
    • Density and distribution
    • Age structure
    • Sex ratio
    • Birth, death, immigration, and emigration rates
  • Demography: applying the principles of population ecology to the study of change in human populations

Population size and density

  • The UN predicts 9 billion humans by 2050
  • Highest density: temperate, subtropical, tropical biomes
    • Coasts, rivers, cities
  • Lowest density: extreme climates (desert, rainforest, tundra)
    • Also, areas away from water
  • If women have just 0.5 child fewer than the medium scenario, there will be 8, not 9.15, billion by 2050

Population distribution

  • Humans are unevenly distributed around the globe
    • Many unpopulated areas (e.g., deserts, arid grasslands) are environmentally sensitive
      • High S value in the modified IPAT equation
      • Vulnerable to humans (agriculture, ranching, etc.)

Age structure affects population size

  • Age structure: describes relative numbers of individuals in each age class
    • Shown by age structure diagrams (population pyramids)
  • Wide base: has many young that haven’t reproduced yet
    • Population will soon grow rapidly
  • Even age distribution:
    • Remains stable
    • Births = deaths

Age structures: Canada vs. Madagascar

  • Canada’s age structure is balanced (growth rate = 0.4%)
  • Madagascar’s age structure is heavily weighted toward the young (growth rate = 2.9%)

Many populations are aging

  • The global mean age is now 28—in 2050, it will be 38
  • China’s age structure is changing
    • In 1970, the median age was 20
    • By 2050, it will be 45
    • Although fewer people will be working to support social programs, the elderly can remain productive

Sex ratios affect population dynamics

  • Human sex ratios at birth slightly favor males
  • Chinese females are selectively aborted
    • 120 boys were reported for 100 girls
  • The undesirable social consequences?
    • Many single Chinese men
    • Teenaged girls are kidnapped and sold as brides

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: change due to birth and death rates alone, excluding migration

Falling growth rates do not mean fewer people

  • Despite falling growth rates, the population continues growing by adding 80 million people each year

Factors affecting total fertility rate

  • Total fertility rate (TFR): the average number of children born to each female during her lifetime
  • Replacement fertility: 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 reduces rates of infant mortality
    • Which increases life expectancy (the time a person can expect to live)
  • Demographic transition: 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
    • So there is less need for large families
    • Parents invest in quality of life, not quantity of kids
  • Death rates fall before birth rates
    • Resulting in temporary population growth

Human population growth and regulation-Death rate

  • Animation: Population Growth Regulation
  • Right-click slide / Select “Play”

The 4 stages of the 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
    • Kids do not need to help get food
  • Post-industrial stage: low birth and death rates stabilize populations

The demographic transition’s four stages

  • Population growth is seen as a temporary phenomenon

Is the 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
  • For people to attain the material standard of living of North Americans, we would need the natural resources of 4.5 more Earths

Family planning: key to controlling growth

  • Family planning: efforts to plan the number and spacing of children
    • The greatest single factor slowing population growth
    • Clinics offer advice, information, and contraceptives
  • Birth control: controlling the number of children born by reducing the frequency of pregnancy
  • Contraception: 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
  • Women need control over their reproductive window:
    • The time in their lives when they can become pregnant
  • 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

Human population growth and regulation-Slowing the growth rate

  • Animation: Population Growth Regulation
  • Right-click slide / Select “Play”

Human population growth and regulation-Decreasing births per woman

  • Animation: Population Growth Regulation
  • Right-click slide / Select “Play”

Policies and family planning work

  • Funding and policies that encourage family planning lower population growth rates in all nations
  • Thailand’s education-based approach to family planning reduced its growth rate from 2.3% to 0.6%
    • Brazil, Mexico, Iran, Cuba, and other developing countries have active programs
  • 1994’s UN population conference in Cairo, Egypt, called for universal access to reproductive health care
    • Offer education, health care, and address social needs
    • Global funding has fallen 33%, slowing progress

Family planning reduces fertility rates

  • Blue: with family planning
  • Red: without family planning

Poverty and population growth are correlated

  • Poor societies have higher population growth rates
  • Poverty and population growth make each other worse
  • 99% of the next billion people added will be born in poor, less developed regions that are least able to support them

Poverty causes environmental degradation

  • Population growth in poor nations increases environmental degradation
    • Farming degrades soil in arid areas (Africa, China)
    • Poor people cut forests, deplete biodiversity, and hunt endangered species

Wealth also impacts the environment

  • Affluent societies have enormous resource consumption
    • With severe, far-reaching environmental impacts
    • Ecological footprints are huge
  • One American has as much environmental impact as 3.5 Chinese or 9 Indians or 13 Afghans

We must reduce population growth and consumption

  • Our global ecological footprint is 50% more than the Earth can support
  • For a high standard of living and quality of life for all, developing nations must slow their population growth
    • Their consumption is also increasing
  • Developed nations must slow their consumption


  • The human population is larger than it has ever been
  • Rates are decreasing but populations are still rising
  • Most developed nations have passed through the demographic transition
  • Expanding women’s rights slows population growth
  • How will the population stop rising?
    • The demographic transition, governmental intervention, or disease and social conflict?
  • Sustainability requires a stabilized population to avoid destroying natural systems

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