Chapter 7

The Human Population

I. Background InfoA. Earth is ~4.6 billion years old

B. Modern humans have been on Earth

~200,000 yrs

C. For most of human history, limiting factors

kept population levels low (scarce food,

disease, etc)

D. High human birth and death rates

E. History of Human Population Growth:

1. Early period of hunter/gatherers• Total population < a few million

2. Rise of agriculture• Allowed for increase in population density and increase in human

population3. Industrial revolution

• Improvements in medicine, sanitation and agriculture led to rapid increase in population

4. Today• Rate of growth slow in industrialized nations but high in less

developed nations

Agriculturebegins

Plowingand

irrigation

Bubonicplague

IndustrialRevolution

begins

II. Factors That Influence Human Population Growth

Demography = study of human populations and their trends

A. Changes in Population Size1. View population as system with inputs and outputs

a. If inputs > outputs = growth rate is positiveb. If inputs < outputs = growth rate is negative

2. Crude birth rate (CBR)= the number of births per

1,000 individuals per year

3. Crude death rate (CDR)= the number of deaths per

1,000 individuals per year

4. Global population growth rate = (CBR - CDR) / 10

a. In 2009 there were 20 births per 8 deaths = %?

5. National population growth rate =

(CBR + immigration) - (CDR + emigration) / 10

6. Doubling time is # of years it takes for population to

double = 70 / growth rate (if growth rate remains

constant)

Examples of Doubling Time

• Nicaragua w/ a growth rate of 2.7%, doubling time = 26 yrs

• US w/ a growth rate of 0.6%, doubling time = 117 yrs

• Northern Europe w/ a growth rate of 0.2%, doubling time = 350

yrs

B. Fertility

1. Total fertility rate (TFR) = estimate of the average number of

children that each woman in a population will bear

a. Current TFR for women in US is 2.06

2. To gauge changes in population size, look at replacement level

fertility (RLF) = TFR required to offset the average number of

deaths in a population and for the current population size to

remain stable

In developed countries RLF is typically 2.1 (one child to

replace each parent)

In developing countries RLF is above 2.1

a. Low levels of industrialization

b. Income of <$3/day

c. High mortality among young (TFR needs to be higher than 2.1 to achieve RLF)

d. Uneducated (especially women)

3. When TFR = RLF and immigration = emigration, a country’s

population is stable (zero population growth)

Projected World Population Growth

The 12 Most Populous Countries in the World

C. Life Expectancy

1. Average number of years that an infant born in a particular year in a particular country can be expected to live, given the current average life span and death rate of that country

2. Generally higher in countries with better health care

3. Good predictor of high resource consumption rates and environmental impacts

4. Infant and Child Mortality Rates

a. Determined by access to health care, good nutrition and potable water, and exposure to environmental pollutants

b. Infant mortality rate = # of deaths under age 1 per 1,000 live births

c. Child mortality rate = # of deaths under age 5 per 1,000 live births

d. In 2009, global infant mortality rate 46; Europe was 2.5-3.6; U.S. 6.6; Bolivia 50, Liberia 99

5. Aging and Disease

a. Dependent upon standard of living

b. Disease is important regulator of human populations

a. According to World Health Organization (WHO), infectious diseases are the 2nd biggest killer worldwide after heart disease

b. e.g. HIV, AIDS, malaria and tuberculosis

D. Age Structure

1. Population growth depends upon number of people of different ages

2. Age-structure diagram (population pyramids) = displays a population by ages, used to predict future growth

E. Migration

1. Country with low CBR, but high immigration rate may still experience population growth

a. U.S. is estimated to grow 44% by 2050

2. Net migration rate = difference between immigration and emigration per year/per 1,000 people

a. U.S. gains about 1 million people per year with current population of 300 million = 3.3 per 1,000

b. Canada = 7 per 1,000 people

3. Movement of people around the world affects ecological footprint, and humanitarian and health issues (if displaced)

III. Demographic TransitionA. As a country moves from a subsistence economy to

industrialization and increased affluence, it undergoes a predictable shift in population growth.

B. Stages of Demographic Transition

Phase 1: Slow population growth because there are high birth rates and high death rates which offset each other.

Phase 2: Rapid population growth because birth rates remain high but death rates decline due to better sanitation, clean drinking water, increased access to food and goods, and access to health care.

Phase 3: Stable population growth as the economy and educational system improves and people have fewer children.

Phase 4: Declining population growth because the relatively high level of affluence and economic develop encourage women to delay having children.

Affluence and Fertility

IV. Zero Population Growth – can it be achieved?

A. Possible approaches1. Delay age of first child bearing – simplest

and most effectivea. Higher 1st reproduction age = fewer

childrenb. In South Asia and Sub-Saharan Africa, 50%

of women marry between 15-19; Bangladesh average age is 16; Sri Lanka average age is 25

c. World Bank estimates that if Sri Lanka model were used, families would average 2.2 fewer children

2. Family Planning a. Regulating the number and spacing of offspring

through the use of birth controlb. Increase education of women = increase women’s

incomes = decreased birth rates

3. National programs to reduce birth ratesa. Information (education)b. Increase access to birth control

V. Population Size and Consumption, Impact the Enviroment

A. Human impact on the environment is a result of several factors:

1. Number of people

2. Amount of resources each person uses

a. Each person has an impact on the environment by eating, drinking, producing waste, consuming products, etc. = “Ecological footprint”

3. Affluence

a. More affluence = more environmental impact

b. Gross domestic product (GDP) = the value of all products and services produced in a year in that country.

3. Made up of consumer spending, investments, government spending, and exports minus imports.

c. A countries GDP often correlates with its pollution levels.

B. IPAT Equation

1. To estimate the impact of human lifestyles on Earth we can use the IPAT equation:

Impact = Population x Affluence x Technology

2. Modern technology increases the use of resources and enables us to affect the environment in new ways (CFC’s, cars, etc)

3. (T = P x I) equation reveals irony: Improving standard of living increases P, countering the benefits of declining I

VI. Human Carrying CapacityA. Background Info

1. Every 5 days, the global population increases by about 1 million people

2. In 1798, Thomas Malthus proposed:

a. Human population grows exponentially, while food supply grows linearly

b. Humans will eventually exceed food supply

c. Consequences will be famine, disease, massive human die-off

B. How many people can the Earth support?

1. Limiting Factors

a. Short Term - affect population immediately (food shortages)

b. Intermediate Term - affect population for 1-10 years (e.g. desertification, dispersal of pollutants, etc.)

c. Long Term - effects not apparent until after 10 years (e.g. soil erosion, decline in groundwater supply, climate change)

2. Earth’s long term carrying capacity

a. Wood production peaked in 1967

b. Fish production peaked in 1970

c. Beef and cereal crop production peaked in 1977

2. Estimation methods

a. Extrapolation from past growth (assuming populations follow S-curve)

b. Packing problem approach – how many people can be packed onto the Earth? (50 billion!)

c. Deep Ecology – sustaining the biosphere (few million people)

d. Depends on the quality of life people desire and are willing to accept