Chapter 9 The Human Population Section 9 1
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Chapter 9 The Human Population Section 9. 1
Studying Human Populations l l Demography is the study of populations, but most often refers to the study of human populations. Countries with similar population trends are grouped into two general categories. l Developed countries have higher average incomes, slower population growth, and stronger social support systems. l Developing countries have lower average incomes, simple and agriculture-based economies, and rapid population growth.
The Human Populations Over Time l After growing slowly for thousands of years, the human population grew rapidly in the 1800 s. l These increases were mostly due to increased food production and improvements in hygiene that came with the industrial and scientific revolutions. l It is unlikely that the Earth can sustain this growth for much longer.
Forecasting Population Size l Age structure is the distribution of ages in a specific population at a certain time. l Age structure can be graphed in a population pyramid, a type of doublesided bar graph.
Survivorship l Survivorship is the percentage of members of a group that are likely to survive to any given age.
Fertility Rates l The number of babies born each year per 1, 000 women in a population is called the fertility rate. l Replacement level is the average number of children each parent must have in order to “replace” themselves in the population.
Migration l The movement of individuals between areas is called migration. l Movement into an area is immigration and movement out of an area is called emigration.
Declining Death Rates l The dramatic increase in Earth’s human population in the last 200 years happened because death rates have declined more rapidly than birth rates. l Death rates have declined mainly because more people now have access to adequate food, clean water, and safe sewage disposal. l The average number of years a person is likely to live is that person’s life expectancy.
The Demographic Transition l The demographic transition is a model that is based on observations of the history of many developed countries. l There are four stages which demographers use to compare expected trends in birth rate, death rate, and population size.
Stages of the Transition l Stage 1: a society is in a preindustrial condition. The birth and death rates are at high levels and the population size is stable. l Stage 2: a population explosion occurs. Death and birth rates decline as hygiene, nutrition, and education improve. During this stage, the population could double in less than 30 years. l Stage 3: population growth slows because the birth rate decreases. l Stage 4: the birth rate drops below replacement level, so the size of the population begins to decrease.
Women and Fertility l The factors most clearly related to a decline in birth rates are increasing education and economic independence for women.
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