Human Population SizeHuman Population Size

Questions for Today:Questions for Today:

• What are the Major Factors that affect Human Population Size?

• How are fertility rates analyzed?

• What are the factors that affect Birth and Fertility Rates?

• What are factors that affect Death Rates?

• What factors affect Migration?

Factors that affect Population Factors that affect Population SizeSize

• There are three factors that affect population size:• Births (fertility)• Death (mortality)• Migration

• Remember the formula to calculation Population Change:

Pop. Change = (B + I) – (D + E)

Population ChangePopulation Change

• For most of human history, the human population roughly grew at a slow pace.

• Within the past 200 years, that rate has increased significantly.• Our current rate is roughly, 1.22%

• 82 million people were added to the world in 2008.

• An Average of 225,000 people are added daily• 2.4 people are added every time your heart beats.

• http://www.worldometers.info/

Population ChangePopulation Change• Three major factors account for this major increase:

• Our ability to invade new ecosystems and adapt fast.

• The Agricultural Revolution

• Led to food surpluses and civilization

• The Industrial Revolution and modern medicine

• The development of sanitation, antibiotics, and vaccines.

• Longer life spans and decreased infant mortality

Fig. 6-3, p. 126

Make sure that you know at least the top 5!

Factors that affect Population SizeFactors that affect Population Size

• Demographers use the crude birth and crude death rate to calculate population change:

• Crude rates are determined by looking at the number of births and deaths per 1,000 people in a population per year.

• An estimated and extrapolated number.

Fertility RatesFertility Rates

• Demographers also take in consideration Fertility Rates when calculating Population Statistics.• Fertility rates are the number of children born

to a woman during her lifetime.• Two types of fertility rates:

• Replacement-level fertility rate• Total Fertility rates

Replacement Level FertilityReplacement Level Fertility

• The average number of children per woman necessary to sustain a population size.

• Ideally would be 2 children per woman, one to replace the mother and one to replace the father.

• Ranges from 2.1 in developed countries (low infant mortality rates and good medical care) to 2.5 in developing countries (high infant mortality rates and medical care not as good).

Total Fertility RateTotal Fertility Rate

• The average number of children born to women in a population during their reproductive years.• The average world wide is 2.6 children

per women.• 1.6 in developed• 2.8 in developing

Factors that Affect Birth and Factors that Affect Birth and Fertility RatesFertility Rates

• There are 10 factors that affect Fertility rates:1. Child Labor (higher for developing)2. Cost of raising and Education (causes decrease

in rates for developed countries)3. Availability of private and public pension

systems (reduces the need to have many children for support)

4. Urbanization (Urban areas typically provide more access to family planning services)

5. Educational and employment opportunities for women (Increased opportunities tend to lower rates).

Factors that Affect Birth and Factors that Affect Birth and Fertility RatesFertility Rates

6. Infant Mortality Rate7. Average age of marriage (Typically fewer

children when avg. age of marriage is higher)8. Availability of legal abortions9. Reliable Birth Control 10. Religious Beliefs and Cultural Norms (For

example, these factors may favor large families and strongly oppose abortion and some forms of birth control).

Factors that affect Death RateFactors that affect Death Rate

• The boom in Human population growth is not primarily caused by the birth rate.

• Our Death (Mortality) Rate has significantly dropped.• Death Rates have dropped due to:

• Increased Food Supply• Better nutrition• Medical Advances• Improved Sanitation• Availability of Clean Water

Factors that affect the Death RateFactors that affect the Death Rate

• Two statistics used by Demographers as indicators of the overall health of people in a country or region:

• Life Expectancy (the avg. number of years a newborn infant can expect to live)

• 1955: 48 2008: 68 2050: 74

• Worldwide

• In the US, the Life Expectancy is 78

• Infant Mortality Rate (number of babies out of every 1,000 born who die before first birthday)

Life ExpectancyLife Expectancy

• Two major factors that affect Life Expectancy in the US:

• Healthcare across the Nation

• Obesity

Infant MortalityInfant Mortality

• Infant Mortality is one of the best measures of a society’s quality of life• Reflects general nutrition and pediatric health

care• Three factors affect Infant Mortality Rates in the

US:• Health Care• Drug addictions among pregnant women• High Teen Birth Rates

MigrationMigration

• Migration is affected by the economic and social problems of other countries.

• Most people leave countries to pursue better opportunities in another.• Jobs• Healthcare• Political Opposition• Religious Intolerance

Population Doubling TimePopulation Doubling Time

• Refers to the number of years that it takes for a population to double

• Can be estimated with the “rule of 70”

• Doubling time = 70/the percentage growth rate

• For example, at a growth rate of 2% annually:

• Doubling time = 70/2% (keep whole number)

• The number of years required for this population to double is 35.