Introduction to Population Processes

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Introduction to Population Processes

• Stevan Harrell
• EARTH II
• 1 March 2005

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What do we Need to Know about Population?

• What determines population growth?
• What drives population growth?
• How has the worlds population grown through
  history?
• How do population growth and density vary in
  different kinds of societies?
• How does population growth affect the
  environment?
• What does the future look like?

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What determines population growth?

• Fertility a measure of births per population per
  year
• Crude birth rate number of births per total
  population per year
• Age specific fertility rate number of births per
  woman of a specified age (e.g. 20-24) per year
• Total fertility rate the average number of
  children born per woman sum of ASFR for all ages
• Net Reproduction Rate The Average number of
  daughters a woman bears in her lifetime

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What determines population growth?
Age structure of a population
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Age-Specific Fertility and TFR
Note that TFR, as a sum of age-specific rates,
does not vary directly with CBR A simple way to
think of it CBR (TFR) (p15-44)
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Determinants of Age-specific Fertility

• Proportion married at each age
• Nuptiality rate
• Age at marriage
• Ratio of marital and non-marital fertility
• Parity progression
• Birth intervals
• Age-specific mortality

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Parity Progression Ratios
Note As part of overall fertility decline,
ratios at higher parities also decline.
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What determines population growth?

• Mortality A measure of deaths per population per
  year
• Crude death rate the number of deaths per total
  population per year
• Age specific mortality rate the number of deaths
  per population of a particular age (e.g.1-4 or
  70-74) per year
• Life expectancy the average number of years one
  can expect to live at a particular age

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Life Expectancy and Life Span
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Life Table
Note right hand column is nex, life expectancy
at age x. Couldnt get it to copy.
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Age-specific mortality
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Population growth
Very simple Population growth CBR-CDR The
devil is in the details. Some exercises
Assume the same CBR for the two countries what
will population growth look like?
Assume the same TFR for the two countries. What
will CBR look like?
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Population growth
Very simple Population growth CBR-CDR The
devil is in the details. Some exercises
Assume a NRR of 0.9 for each country. What will
the age structure look like in 20 years?
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How has the worlds population grown through
history?
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How has the worlds population grown through
history?
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How do population growth and density vary in
different kinds of societies?
Density of population
Nomadic hunter-gatherers (foragers)
lt1/mi2 Shifting cultivators
20-30/mi2 Agrarian civlizations 1000/mi2 Indu
strial societies 2000/mi2
Maximum growth rate
Nomadic hunter-gatherers (foragers)
lt.02/yr Shifting cultivators Agrarian
civilizations .5/yr Industrial
societies gt2/yr
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What drives population growth?Measures

• Rising fertility
• Earlier maturation
• Shorter birth interval
• Declining mortality at reproductive age
• Declining mortality
• Control of infectious diseases, particularly in
  infancy
• Assured food supply
• Medical care??

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What Drives Population Growth Theories

• Mortality driven
• Invention of new technologies allows lowered
  mortality and excess of births over deaths
• People will reproduce until they come up against
  positive checks (Malthus)
• Fertility driven
• Population growth forces people to create new
  technologies to accommodate the extra people
• People are capable of limiting their fertility

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What Drives Population Growth Theories

• Malthuss Main Points
• Growth of population and growth of agricultural
  production
• Population grows geometrically
• Production grows arithmetically
• This will eventually lead to a crisis, if
  unchecked
• Two kinds of checks
• Positive checks
• Preventive checks

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What Drives Population Growth Theories

• Malthuss view of different societies
• England related by preventive checks moral
  restraint
• Late marriage
• Non-universal marriage
• China regulated by positive checks
• Early marriage
• Universal marriage
• Lets look at some of the
• Ethical and cultural assumptions
• Demographic assumptions

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How has the worlds population grown through
history?
Chinas population, 1000-1850
From Kent J. Deng, Unveiling Chnas True
Premodern Population Statstics, Population
Review, 2004
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How has the worlds population grown through
history?
World population, 1900-2000
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How has the worlds population grown through
history?
World population, 1900-2000
From Haines, Modern Mortality
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How has the worlds population grown through
history?
World population, 1900-2000
From Haines, Modern Mortality
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How has the worlds population grown through
history?
World population, 1900-2000
From Livi-Bacci, A Concise History of World
Population
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Effects of Population Growth
Effects of increasing population density
Larger group size Increased pressure on local
resources Increased infectious disease
morbidity Possibilities for increased division
of labor
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Effects of Population Growth
Effects of faster population growth
Younger age structure More complex families
Higher rates of migration Higher rates of
conflict?
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What Drives Population GrowthDemographic
Transition
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The first half of the Demographic
TranstionMortality Decline
Causes of Death
From Haines, Modern Mortality
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The first half of the Demographic
TranstionMortality Decline
Mortality Rates
From Haines, Modern Mortality
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Mortality from Tuberculosis
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Mortality from Infectious Diseases
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U.S. Life Expectancy
Fertility and Mortality Expectation of
Lifea Year White Blackb 1800 1810 1820 1830
1840 1850 38.9 1860 40.9c 1870 44.1 1880 39
.6 1890 45.7 1900 49.6 1910 51.9 1920 57.4 47.
0 1930 60.8 48.5 1940 65.0 53.9 1950 69.1 60.8 196
0 70.7 63.6 1970 71.7 65.2 1980 74.4 68.1
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Current world life expectancy and infant mortality
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The Second Half of the Demographic Transition
Fertility
Some representative Total Fertility Rates
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The Second Half of the Demographic Transition
Fertility
U.S. Birth RatesFertility and Mortality
Birthratea Year White Blackb 1800 55.0 1810 54.3
1820 52.8 1830 51.4 1840 48.3 1850 43.3 58.6c
1860 41.4 55.0d 1870 38.3 55.4e 1880 35.2 51.9f 18
90 31.5 48.1 1900 30.1 44.4 1910 29.2 38.5 1920 26
.9 35.0 1930 20.6 27.5 1940 18.6 26.7 1950 23.0 33
.3 1960 22.7 32.1 1970 17.4 25.1 1980 14.9 22.1
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The Second Half of the Demographic Transition
Fertility

• What drives fertility decline?
• Mortality decline
• Declining value of children with
• Urbanization
• Professionalization
• Cost of Education
• Womens education
• Contraceptive availability

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Pre-and Post-Transition Populations
High fertility High mortality
High fertility Low mortality
Low fertility Low mortality
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AIDS and Mortality
Sam Clarks Gwembe Tonga Study
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AIDS and Mortality
Sam Clarks Gwembe Tonga Study
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AIDS and Mortality
Sam Clarks Gwembe Tonga Study
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AIDS and Mortality
Sam Clarks Gwembe Tonga Study
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How does population growth affect the environment?
Some adverse affects, all else being equal
Decreased habitat for other species Resource
depletion - Changes in land cover -
Deforestation and loss of carbon sinks -
Extinction of prey species Pollution -
Nitrogen from fertilizers and wastes - Sulfur
from combustion
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How does population growth affect the environment?
But all else is never equal
I PAT Impact population x affluence x
technology
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How does population growth affect the environment?
But all else is never equal
Ecological footprint The amount of land it takes
to support one person (in hectares)
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What does the future look like?
Some representative Total Fertility Rates
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What does the future look like?
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What does the future look like?
I PAT
The effects of population growth on the
environment will be magnified by increases in the
affluence of world populations
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What does the future look like?
An aging population
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What does the future look like?
If the world population levels off at 10 billion
mid-century
And global TFR declines to 1.9 and stays there,
population in 3000 will be 2.14B, around the 1950
level
And global TFR declines to 1.7 and stays there,
population in 3000 will be 76M, probably about
the 2000 B.C.E. level
And global TFR declines to 1.3 and stays there,
population in 3000 will be 24K