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The Human Population
Miss Napolitano & Mrs. RodriguezEnvironmental Science
The Human Population Over Time
Demography: the study of human populations
Includes size, makeup, & growth
Developed countries: higher average incomes, slower population growth, diverse industrial economies
Developing countries: lower average incomes, agriculture-based economies, & rapid population growth
The Human Population Over Time
Human population began to grow rapidly in 1800s
Growing exponentially – growth rates increased during each decade
Growth rate due to increases in food production & hygiene
Unlikely to be able to sustain current growth rate for much longer
Age Structure
Age structure: distribution of ages in a specific population at a certain time
Ex: population has more young people population size will increase
Graphed in a population pyramid
High growth rates have more young people
Slow/no growth rates have even distribution
Fewer young people when parents have fewer children
Age Structure Diagrams
Survivorship
Survivorship: percentage of members of a group that are likely to survive at any given age
Notes when members of a population die
Type I: more people survive to old age
Developed countries
Type II: similar death rate at all ages
Type III: many children die young
Developing countries
Fertility Rates
Fertility rate: number of babies born each year per 1,000 women
Total fertility rate: average number of children a woman gives birth to in her lifetime
Replacement level: average number of children each parent must have in order to “replace” themselves
~2.1 because not all born will survive to reproduce
Fertility level of US dropped below replacement level for first time in 1972
Migration
Migration: movement of individuals between areas
Emigration: movement out of an area
Immigration: movement into an area
Populations might be decreasing if not for immigration in many developed countries
Life Expectancy
Death rates have declined drastically due to access to adequate food, clean water, safe sewage disposal, & vaccines
Life expectancy: average number of years a person is likely to live
Affected by infant mortality (death rate of infants)
Average life expectancy around the world is ~67 years
Increased to almost 80 in developed countries
More people means more diseases like HIV and TB
The Demographic Transition
Demographic transition: describes how populations have stopped growing in developed countries
Industrial development causes economic and social progress that then affects population growth rates
4 Stages of Transition
Stage 1:Birth & death rates both high, population stable
Stage 2: Population explosion
Hygiene, nutrition & education improve, leading to lower death rates
Stage 3: Population slows & starts to stabilize
Due to birth rate decrease
Stage 4: Birth rate drops below replacement level
Population starts to decrease
Problems of Rapid Growth
Shortage of fuel wood
Unable to boil water & cook food in many countries
Unsafe water
Drinking, washing, sewage disposal
Causes diseases & parasites
Negative impacts on land
Shortage of land for crops, housing, or natural habitats
Causes urbanization (moving to cities) or suburban sprawl (cities become crowded, move to suburbs)
Demographically Diverse World
Not all countries fit the terms “developed” or “developing”
Some mix between the two – ex: modern industries with low incomes
Focus is on least developed countries
Few signs of development, increasing death rates, high birth rates
Populations are relatively stable in Europe, the US, Canada, Russia, South Korea, Thailand, China, Japan, Australia, & New Zealand
Populations growing rapidly in less developed regions (mostly in Asia)
Managing Population Growth
Some governments tried to reduce birth rates
China, Thailand, & India created campaigns to reduce fertility rates of citizens
Campaigns include advertising, family planning, economic incentives, or legal punishments
Currently, fertility rates have declined since 1970
Rates still higher in less developed regions
UN projects population will be between 8 billion & 11 billion by 2050, depending on fertility rates