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HUMAN POPULATION

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Nt+1

= Nt+ Births – Deaths + Immigration – Emigration

Populations can be described with simple models

reindeer, marine algae, or humans.…for reindeer, marine algae, or humans, the same rules apply

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•  Population growth and distribution

•  Effect of migration on population growth

•  Population age structure

•  Patterns of world urbanization

•  The status of women

•  World health

•  Human relationships with the environment

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Nt+1 = Nt + Births – Deaths

Global population: why were there so few of us?

•  Predators,

parasites,pathogens

•  Famine &dependence on

found food

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Population distribution is not even, globally

Source: United Nations Population Division, Briefing Packet, 1998 Revision of 

World Population Prospects. 

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The world's population distribution has notchanged much over time

•  In 1800, 86% of the world's population resided in Asia and Europe,65% in Asia alone; currently Asia still represents nearly 60%.

•  1900, Europe's population represented 25% of the world, fueled bythe Industrial Revolution. Some of this spilled over to the Americas.

•  After World War II, growth accelerated as less developed countriesbegan to increase dramatically.

•  A billion people were added between 1960 and 1975. Another billionwere added between 1975 and 1987.

•  Human population entered the 20th century with 1.6 billion peopleand left the century with 6.1 billion. 

•  1789, Thomas Malthus studied population growth in Europe. Heobserved that populations grow geometrically (1, 2, 4, 8 …), rather thanarithmetically (1, 2, 3, 4 …), like food production. He feared eventualglobal starvation.

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Population growth rates are not even, either

Why are some countries declining, others stable orincreasing in population?

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Rate of Natural Increase

Rate of Natural Increase: Rate at which a population isincreasing (or decreasing) in a given year due to a surplus(or deficit) of births over deaths.

• 1700s start of

the modern era ofpopulation growth 

• 1850-1900:annual globalgrowth ratereached 0.5%.

• mid-1960s:surged to 2.0%;

• mid-1980s:dropped to 1.7% 2000 down to

~1.4%.

Drop inbirthrate, late20th century.

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Crude birth rate - The average annual number of live births during a year per 1,000 population

Crude death rate - The average annual number of deaths during a yearper 1,000 population

Global population isgrowing, but not evenlyaround the world.

In some countries,

death > birth (Belgium,Finland)

In many countries,birth < death (developingcountries, e.g. Cameroon)

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•  Population growth and distribution

•  Effect of migration on population growth

•  Population age structure

•  Patterns of world urbanization

•  The status of women

•  World health

•  Human relationships with the environment

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Source: U.S. Census Bureau, Current Population Reports .

Nt+1 = Nt + Births – Deaths + Immigration – Emigration

Percentage of U.S. PopulationGrowth from Migration 

• Most Americans, Australians,and Brazilians are immigrants or descendants of immigrants

• 2/3 of United Statespopulation growth is fromnatural increase and 1/3 isfrom immigration andinternational migration.

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Source: Immigration and Naturalization Service, 1998 Statistical Yearbook .

Nt+1 = Nt + Births – Deaths + Immigration – Emigration

Regional Origins of Immigrants to the United States 

People move for economic (agriculture, labor), political, and religious reasons.

Current immigration to the U.S. isestimated at ~100-500K per year

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• 

Population growth and distribution

•  Effect of migration on population growth

•  Population age structure

•  Patterns of world urbanization

•  The status of women

•  World health

•  Human relationships with the environment

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Ages 0-14 Ages 15-44 Ages 45-85+

Male FemaleMale Female

Rapid GrowthCameroon

Nigeria

Saudi Arabia

Slow GrowthUnited States

China

Canada

Zero GrowthSweden

Austria

Germany

Negative GrowthEstonia

Latvia

Russia

Population Age Structure

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100

10

1

0

Age

Population age structure viewed a different way:

Survival rates vary with age among human populations just as they do among other animal species

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Age 

Fem. Males

Age 

Females Males

2416

8448

1620

Millions 2416

8448

16

Millions 

Age  Age 

Females Males Females Males

20 168 4 

4 8 16 20 

Millions  2416

8448

1624

Millions 

1955 1985 2015 2035

Age structures can change through time

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• 

Population growth and distribution

•  Effect of migration on population growth

•  Population age structure

•  Patterns of world urbanization

•  The status of women

•  World health

•  Human relationships with the environment

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Largest urban agglomerations through time

More developed nations: 76% urban; Less developed nations: 40% urban

2015: 23 cities expected >10 million people; 19 in less developed countries.2030: 60% of the world population is expected to be urban.

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• 

Population growth and distribution

•  Effect of migration on population growth

•  Population age structure

•  Patterns of world urbanization

•  The status of women

•  World health

•  Human relationships with the environment

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Women’s age at first reproduction and family size

Source: Demographic and Health Surveys , 1991–1999; and Carl Haub andDiana Cornelius, 2000 World Population Data Sheet (Washington, DC:

Population Reference Bureau, 2000).

strong relationship betweenage at first reproductionand # children.

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Assuming births > deaths, shorter generation times result in fasterpopulation growth

P1 + P2

G1 G2 G3 G4

K2K1

15

15

15

P1 + P2

K2K1

25

25

Descendants by age 65:

630

Nt+1

= Nt

+ Births – Deaths

Women’s age at first reproduction and population growth

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Women’s education and family size

Source: Demographic and Health Surveys , 1991–1999.

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• 

Population growth and distribution

•  Effect of migration on population growth

•  Population age structure

•  Patterns of world urbanization

•  The status of women

•  World health

•  Human relationships with the environment

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Life expectancy has increased through time 

Source: World Bank, Demographic Trends and Prospects

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Life expectancy remains uneven, globally:a different view

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Infant mortality is a sensitive measure of a nation’s health

Source: World Bank, World Development Indicators 2002 .

Source: UNICEF, The State of the 

World's Children, 1998. 

Mortality sources under 5 years-1995 

Less developed countries  

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AIDS is causing decreased life expectancy in many countries

Source: UNAIDS, Report on Global HIV/AIDS Epidemic, 2000  

Source: World Bank, World Development Indicators, 2004

Percent of world's HIV/AIDScases, 1999

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• 

Population growth and distribution

•  Effect of migration on population growth

•  Population age structure

•  Patterns of world urbanization

•  The status of women

•  World health

•  Human relationships with the environment

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Global impacts of humans,…on humans!

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Replacement reproduction

Replacement reproduction – replacement of a couple with the samenumber of people (an average of one boy and one girl).

It can also be defined as (an average of) one daughter born to eachmother (red line).

A fertility rate of ~ 2.1 or 2.2 children/couple is the replacement rate thatallows a constant population.

Nt+1 = Nt + Births – Deaths

Replacement reproductiondepends on both birth anddeath rates