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Four Typical Shapes of Population
TERMS TO KNOW . . . Pyramids

population pyramid: A very useful graphic device for
comparing age and sex structure A population pyramid is a snapshot of a popula-
tion’s age and sex structure at a particular time, but
its shape also reveals past population changes that
large-scale, prolonged wars may reduce the male pop- resulted from major events, such as the introduction
ulation and lead to an imbalance in the sex ratio. The of medical technologies and sanitation methods (which
former Soviet Union suffered from such an imbalance reduce death rates), wars (which lead to significantly
for decades following World War II. fewer males in some cohorts), large-scale famine and
diseases (which lead to small cohorts), and baby booms
Consequences of Unbalanced Sex after wars (which lead to a “bulge” in the population).
Ratios By carefully examining a population pyramid, we can
learn how the population has been growing, identi-
The social and cultural ramifications of male-heavy pop- fy periods of baby boom or bust, determine whether
ulations are potentially profound. Men of marriageable the sex ratio is balanced at different age cohorts, cal-
age are increasingly unable to find female partners, a fact culate the country’s dependency ratio, and discover
that has led to an increase in human trafficking, sex traf- if the population is aging. We can also predict future
ficking, and the use of force, manipulation, or false prom- population trends.
ises of good jobs or romantic relationships to lure women Most population pyramids have one of four typical
into marrying men they barely know. In India, where men shapes that reveal rapid growth, slow growth, popula-
greatly outnumber women, girls have been kidnapped or tion stability, or population decline.
trafficked in from neighboring Nepal and Myanmar.
Rapid Growth The pyramid for a rapidly growing pop-
ulation has a wide base, resembling the classic stepped
8-4 What can a population pyramid be pyramid shape. Rapid population growth usually oc-
used for? curs in developing countries where birth rates are
relatively high and there is a large number of young
Population Pyramids people in the population. The population pyramid for
Tanzania in Figure 8.7 is a good example. Because peo-
A population pyramid is a very useful graphic device for ple in developing countries do not live as long as people
comparing age and sex structure in a country. A quick in developed countries, the sides of the pyramids may
look at a country’s population pyramid can speak vol- taper off relatively quickly to form a narrow top, re-
umes about the country’s past as well as its future. How flecting the small populations in advanced age groups.
many dependent people — the very old and the very Countries with a broad-based population pyramid may
young — live there? Has the country suffered the demo- face the challenges of educating the young and creating
graphic effects of major wars or disease epidemic? Are jobs. They also have the momentum for future growth
significantly more boys than girls being born? as the large number of young people grow into their re-
To create a population pyramid, we divide the productive years and start their own families, regard-
male and female populations into five-year age groups: less of how small those families may be compared to the
0–4 years, 5–9 years, 10–14 years, all the way up to 80+ families of earlier generations.
years. Next, we calculate the shares of all age-sex cohorts
in the total population. Finally, we plot the percentages Slow Growth When a country’s population growth
on a bar chart with the proportions on the horizontal slows down (the birth rate is just over death rate),
axis and the age cohorts on the vertical axis. We place its population pyramid will have a somewhat narrow
the male percentages on the left-hand side of the graph base, but it may still be slightly pyramid shaped or
and the female percentages on the right-hand side, but cylindrical. The graph for China in Figure 8.7, is a
absolute numbers of people may work too (Figure 8.7). good example of a slow-growth population pyramid.

30 Unit 2 Population and Migration Patterns and Process
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