Lesson 2: Human Population Growth Big Question Why Is Human Population Growth the Underlying...

Lesson 2: Human Population Growth

Big QuestionWhy Is Human Population Growth the Underlying Environmental

Problem?

Lesson 2 / ESRM100 / University of Washington

The Prophecy of Malthus

“the power of population growth” is “greater than the power of Earth to

produce subsistence.”


Thomas Malthus: Essay on the Principle of Overpopulation-1798

• Malthus was the first to notice the issue of there

being more people than could be supported by the

food supply.• He noticed farming improvements could raise

food production by a certain amount each year –

in an arithmetic rate of increase..1, 2, 3, 4, 5,

6…… • Whereas population tends to increase at a

‘exponential rate’ with each generation…1, 2, 4, 8,

16, 32……. So he concluded there must come a

point when there are too many people for the

available food supply.


The Malthusian Dilemma

• Malthus believed that when the population

level rose above the food supply – then

nature would regulate population growth

by responding with: PESTILENCE,

PLAGUE, FAMINE, WAR

• Malthus suggested that population growth

should be limited by people marrying later

– and abstinence until marriage. (he

basically wanted to cut the birth rate of the

poorer classes)


Exponential Growth

• Growth is exponential when it occurs at a constant rate per time

period.• Exponential growth produces a J-shaped growth curve.• The human population has mostly grown exponentially.


Reaching the Carrying Capacity

• Malthus believed that the earth would reach it’s

carrying capacity if populations continued to grow

exponentially. • The maximum number of organisms of a species

that can be supported indefinitely in a given

environment.• Once capacity had been reached equilibrium would

be thrown off and natural and human disasters

would occur.


Esther Boserup (1965) / Julian Simons (1981): Belief in human ingenuity.

• These two theorists claim that rising populations are not a problem.

In fact, Boserup suggested that it was at times when there were

food shortages following periods of population growth, that people

were forced to come up with better ways of producing food in order

to survive. Summed up best by the phrase : Necessity is the

mother of invention.• Julian Simons supported this approach and suggested that

governments should NOT try to influence populations. As resources

become scarce, humans use their brain power to develop new

technologies, substitute materials, or more efficient ways of using

resources – so they don’t run out. As a result, mankind is better off

after periods of resource shortage as we develop better ways – or

‘innovation’.


Which theorist do you most agree with and why?


Major Periods of Human History

• The early period of hunters and gatherers - less than a few million people• The rise of agriculture - first major increase in the human population• The Industrial Revolution - improvements in the food supply and health

care led to a rapid population growth• Today -growth has slowed in industrialized nations but is increasing

rapidly in many less developed nations


Population Change, cont.

• Kenya has pyramid shape with many young people – rapid growth• United States has column shape – slow growth• Italy is slightly top-heavy – slow/negative growth


The Demographic Transition

• Stage I - birth and death rates are high until industrialization

reduces death rates• Stage II - gap between birth and death rates results in high

population growth• Stage III - birth rate drops toward death rate and population growth

declines


The Demographic Transition, cont.

• Some nations are slow to move from stage II to stage III• Medical advances can affect the demographic transition by

decreasing death rates


Longevity and Its Effect on Population Growth

• The maximum lifetime (longevity) is

the genetically determined maximum

possible age to which an individual

can live.

• Life expectancy is the average

number of years an individual can

expect to actually live.

• The human population has grown

despite little or no change in

longevity.


Limiting Factors to Population Growth

• Short-term factors: drought, disruption to energy supply, disease

• Intermediate-term factors: desertification, pollutants, disruption to

supply of non-renewable resources

• Long-term factors: Soil erosion, groundwater, climate change


Quality of Life and the Human Carrying Capacity of the Earth

• What is the human carrying capacity of Earth?• Logistic curve predictions• Packing space• Deep Ecology – moral imperative to preserve the biosphere by

limiting human population• The higher the quality of life, the lower the Earth’s carrying

capacity


How Can We Achieve Zero Population Growth?

• Raise the age of first childbearing

• Social pressures to delay marriage

• Birth control• Breast feeding• Family planning


National Programs to Reduce Birth Rates

• The first country to adopt an official population

policy was India in 1952.• Many countries now have a family-planning

program.• China has one of the oldest and most effective

family-planning programs:• encourages couples to have only one child.• relies on education, family planning control,

and a system of rewards and penalties.• Should governments force people to limit family

size?


How Many People Can Earth Support?Estimates range from 2.5 billion to 40 billion.

Critical factors are• Food supply• Land and soil resources• Water resources• Population density• Technology

Chapter 2: Human Population Growth

Questions? E-mail your TA. [email protected]

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