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Chapter 9-1 Slide 2 Study of populations, usually human Demographers study historical size and makeup of various world populations to make predictions about Growth Economics Social Structure Demographers have categorized countries into two categories Developed Nations higher average incomes, slower population growth and diverse industrial economies Developing Nations lower average incomes, simple agriculture-based economies and rapid population growth Slide 3 Human population growth was in a lag phase until the 1800s From the 1800s on, the human population went into an exponential growth phase Humans are reproducing much faster than dying Likely due to: Increase food production Increased hygiene and medical care Industrial and Scientific Revolutions It is unlikely we can stay in this phase much longer, however, it is nearly impossible to predict when we will hit Earths carrying capacity Slide 4 Slide 5 Age Structure refers to the distribution of ages in a specific population If the population has more young than old, the population will likely increase as the young grow up and have kids Graphs are called population pyramids Survivorship refers to the predicted percent of a population to survive until any given age Type I curve means most people live until old age Developed nations Type II means similar death rate at any age Type III curve means most of the population dies as children Usually developing nations Slide 6 Fertility Rates the number of babies born each year per 1,000 women in a population Total fertility rate is the average number of children a woman gives birth to in her lifetime Replacement level is the average number of children each parent must have to replace themselves in the population We dropped below this in 1972 but are current above again Migration movement of individuals between areas Emigration is movement out of an area Immigration is movement into an area Many of us are 2 nd and 3 rd generation immigrants to the US Slide 7 The death rate of humans has dropped dramatically in the last 200 years, likely due to: Adequate food and water, safe sewage disposal, medicines Life Expectancy average number of years an individual is expected to survive In 1900, this was about 40 years old and there was a high infant mortality rate By 2000, the infant mortality dropped to almost 1/3 of what it was and global life expectancy has increased to about 67 Developed nations have high life expectancy, usually 80 or older Infant mortality is affected by parents education, food, fuel and clean water Slide 8 Demographic transition is a model that describes how economic and social changes affect population growth rates Stages of Transition Lag phase : birth and death are high but equal and the population is stable in size Exponential Growth phase : population explodes due to education, hygiene, nutrition etc. Stabilizing phase : growth slows as the birth rate decreases and becomes close to the death rate again, however, the population is much larger than it was in the lag phase Some developed countries have populations 4x larger now than in 1900 Death phase : population decreases because the birth rate drops below replacement level, however, the population does not totally decline Slide 9 The number one factor in the decline of birth rate is an increase in education and economic independence for women In some countries where women do not work as much, children are assets by working at a young age to support the family and helping to take care of the elderly In other communities, children are a financial burden if the mother is working away from home and must pay for child care, additionally if the mother is financially stable, working children are not necessary Elderly may also be financially independent or taken care of by other means Fertility Rate Developed Nations: 1.6 children per woman Fertility Rate Developing Nations: 3.1 children per woman Slide 10 1. Describe how the size and growth rate of the human population has changed in the last 200 years 2. Define four properties that scientists use to predict population sizes 3. Explain what we can predict about a populations likely growth rates based on its current age structure 4. Describe the four stages of demographic transition 6. Evaluating theories: Do you think that all countries will follow the pattern of the demographic transition?