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Population
The World's Human Population is now:
A population pyramid is a tool used in demography to study the changes in population over time. It is a horizontal compound bar graph. The horizontal axis shows the percent of the popualtion (male or female). The vertical axis shows the population by age groups (usually 5 years intervals). A population pyramid represents the age-sex structure of the population which is dependent on the birth and death rates of the population over time. It is a visual representation of the important demographic events over the past 80 years in a particular population. Changes can be readily seen in the graph such as the impacts of immigration/emigration, wars and famines, and changes in birth and death rates.
Below are 3 example Population pyramids (from the Population Reference Bureau) showing very different shapes.
The pyramid from Kenya shows that its population is growing at a very fast rate. Its base is wide and its top is very narrow. This would be an example of an EXPANSIVE Graph where a high proportion of their population is in the younger age groups. This type of structure is the result of a rapidly declining death rate and an unchanging or slowly declining birth rate. When death rates fall, it is most dramatic in the infant and child mortality rates since inoculations and other basic medical technology can cause these rates to fall rapidly. Consequently a much higher proportion of babies survive and the number of people in the younger age groups increases, creating the concave shape to the pyramid.
The pyramid for the United States is an example of a STATIONARY Graph where the age groups are relatively the same size until the oldest age groups. This type of population pyramid evolves under conditions of low death rates and replacement level birth rates. Death rates of 10-15 per thousand and total fertility rates of less than 2 must exist for at least 20 years to produce this type of pyramid. This kind of pyramid exists in most developed countries with high standards of living, long life expectancies and low growth rates.
The pyramid for Germany shows a structure where the population growth rate is negative. This happens when the death rates exceed the birth rates for an extended time. There will be a narrowing at the base of the pyramid and the middle and older age groups are similar to a stationary graph.
It is also noteworthy to observe the Baby Boom generation in both the Germany and United States graphs. The increase in birth rates during those age groups can be readily seen.
