# 8.8: Population

$$\newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$

$$\newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$$

$$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$

( \newcommand{\kernel}{\mathrm{null}\,}\) $$\newcommand{\range}{\mathrm{range}\,}$$

$$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$

$$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}[1]{\| #1 \|}$$

$$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$

$$\newcommand{\Span}{\mathrm{span}}$$

$$\newcommand{\id}{\mathrm{id}}$$

$$\newcommand{\Span}{\mathrm{span}}$$

$$\newcommand{\kernel}{\mathrm{null}\,}$$

$$\newcommand{\range}{\mathrm{range}\,}$$

$$\newcommand{\RealPart}{\mathrm{Re}}$$

$$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$

$$\newcommand{\Argument}{\mathrm{Arg}}$$

$$\newcommand{\norm}[1]{\| #1 \|}$$

$$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$

$$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\AA}{\unicode[.8,0]{x212B}}$$

$$\newcommand{\vectorA}[1]{\vec{#1}} % arrow$$

$$\newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow$$

$$\newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$

$$\newcommand{\vectorC}[1]{\textbf{#1}}$$

$$\newcommand{\vectorD}[1]{\overrightarrow{#1}}$$

$$\newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}}$$

$$\newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}}$$

$$\newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$

$$\newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$$

$$\newcommand{\avec}{\mathbf a}$$ $$\newcommand{\bvec}{\mathbf b}$$ $$\newcommand{\cvec}{\mathbf c}$$ $$\newcommand{\dvec}{\mathbf d}$$ $$\newcommand{\dtil}{\widetilde{\mathbf d}}$$ $$\newcommand{\evec}{\mathbf e}$$ $$\newcommand{\fvec}{\mathbf f}$$ $$\newcommand{\nvec}{\mathbf n}$$ $$\newcommand{\pvec}{\mathbf p}$$ $$\newcommand{\qvec}{\mathbf q}$$ $$\newcommand{\svec}{\mathbf s}$$ $$\newcommand{\tvec}{\mathbf t}$$ $$\newcommand{\uvec}{\mathbf u}$$ $$\newcommand{\vvec}{\mathbf v}$$ $$\newcommand{\wvec}{\mathbf w}$$ $$\newcommand{\xvec}{\mathbf x}$$ $$\newcommand{\yvec}{\mathbf y}$$ $$\newcommand{\zvec}{\mathbf z}$$ $$\newcommand{\rvec}{\mathbf r}$$ $$\newcommand{\mvec}{\mathbf m}$$ $$\newcommand{\zerovec}{\mathbf 0}$$ $$\newcommand{\onevec}{\mathbf 1}$$ $$\newcommand{\real}{\mathbb R}$$ $$\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}$$ $$\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}$$ $$\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}$$ $$\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}$$ $$\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}$$ $$\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}$$ $$\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}$$ $$\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}$$ $$\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}$$ $$\newcommand{\laspan}[1]{\text{Span}\{#1\}}$$ $$\newcommand{\bcal}{\cal B}$$ $$\newcommand{\ccal}{\cal C}$$ $$\newcommand{\scal}{\cal S}$$ $$\newcommand{\wcal}{\cal W}$$ $$\newcommand{\ecal}{\cal E}$$ $$\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}$$ $$\newcommand{\gray}[1]{\color{gray}{#1}}$$ $$\newcommand{\lgray}[1]{\color{lightgray}{#1}}$$ $$\newcommand{\rank}{\operatorname{rank}}$$ $$\newcommand{\row}{\text{Row}}$$ $$\newcommand{\col}{\text{Col}}$$ $$\renewcommand{\row}{\text{Row}}$$ $$\newcommand{\nul}{\text{Nul}}$$ $$\newcommand{\var}{\text{Var}}$$ $$\newcommand{\corr}{\text{corr}}$$ $$\newcommand{\len}[1]{\left|#1\right|}$$ $$\newcommand{\bbar}{\overline{\bvec}}$$ $$\newcommand{\bhat}{\widehat{\bvec}}$$ $$\newcommand{\bperp}{\bvec^\perp}$$ $$\newcommand{\xhat}{\widehat{\xvec}}$$ $$\newcommand{\vhat}{\widehat{\vvec}}$$ $$\newcommand{\uhat}{\widehat{\uvec}}$$ $$\newcommand{\what}{\widehat{\wvec}}$$ $$\newcommand{\Sighat}{\widehat{\Sigma}}$$ $$\newcommand{\lt}{<}$$ $$\newcommand{\gt}{>}$$ $$\newcommand{\amp}{&}$$ $$\definecolor{fillinmathshade}{gray}{0.9}$$

## Population

##### Learning Objectives
1. Describe the central concepts of the study of demography.
2. Understand demographic transition theory and how it compares with the views of Thomas Malthus.
3. Explain why some experts feel that world hunger does not result from overpopulation.
4. Provide examples of how US history is marked by anti-immigrant prejudice.

Population change often has weighty consequences throughout a society. As we think about population change, we usually think about and worry about population growth, but population decline is also a concern. Consider the experience of Michigan (Dzwonkowski, 2010).Dzwonkowski, R. (2010, September 19). New leaders can’t shrink from Michigan realities. Detroit Free Press, p. 2A. Like several other northern states, Michigan has lost population during the past few decades. Its birth rate has declined by 21 percent from 1990, and elementary school populations dropped as a result. Several schools lost so many students that they had to close, and others are in danger of closing. In addition, many more people have been moving out of Michigan than moving in. Because many of those moving out are young, college-educated adults, they take with them hundreds of millions of dollars in paychecks away from Michigan’s economy and tax revenue base. They also leave behind empty houses and apartments that help depress the state’s real estate market. Because of the loss of younger residents from the declining birth rate and out-migration, Michigan’s population has become older on the average. This shift means that there is now a greater percentage of residents in their older years who need state services.

Among other consequences, then, Michigan’s population decline has affected its economy, educational system, and services for its older residents. While Michigan and other states are shrinking, states in the southern and western regions of the nation are growing, with their large cities becoming even larger. This population growth also has consequences. For example, schools become more crowded, pressuring communities to hire more teachers and either enlarge existing schools or build new ones. The population growth also strains hospitals, social services, and many other sectors of society.

This brief discussion of US cities underscores the various problems arising from population growth and decline. These are not just American problems, as they play out across the world. The remainder of this section introduces the study of population and then examines population problems in greater depth.

## The Study of Population

We have commented that population change is an important source of other changes in society. The study of population is so significant that it occupies a special subfield within sociology called demography. To be more precise, demography is the study of changes in the size and composition of population. It encompasses several concepts: fertility and birth rates, mortality and death rates, and migration. Let’s look at each of these briefly.

## Fertility and Birth Rates

Fertility refers to the number of live births. Demographers use several measures of fertility. One measure is the crude birth rate, or the number of live births for every 1,000 people in a population in a given year. We call this a “crude” birth rate because the population component consists of the total population, not just the number of women or even the number of women of childbearing age (commonly considered 15–44 years).

A second measure is the general fertility rate (also just called the fertility rate or birth rate), or the number of live births per 1,000 women aged 15–44 (i.e., of childbearing age). The US general fertility rate for 2010 was about 64.7 (i.e., 64.7 births per 1,000 women aged 15–44) (Sutton & Hamilton, 2011).Sutton, P. D., & Hamilton, B. E. (2011). Recent trends in births and fertility rates through 2010. Washington, DC: Centers for Disease Control and Prevention.

A third measure is the total fertility rate, or the number of children an average woman is expected to have in her lifetime (taking into account that some women have more children and some women have fewer or no children). This measure often appears in the news media and is more easily understood by the public than either of the first two measures. In 2010, the US total fertility rate was about 1.93 (or 1,930 births for every 1,000 women) (Hamilton, Martin, & Ventura, 2011).Hamilton, B. E., Martin, J. A., & Ventura, S. J. (2011). Births: Preliminary data for 2010. National Vital Statistics Reports, 60(2), 1–14.

As Figure 15.1 indicates, the US general fertility rate has changed a lot since 1920, dropping from 101 (per 1,000 women aged 15–44) in 1920 to 70 in 1935, during the Great Depression, before rising afterward until 1955. (Note the very sharp increase from 1945 to 1955, as the post–World War II baby boom began.) The fertility rate then fell steadily after 1960 until the 1970s but has remained rather steady since then, fluctuating only slightly between 65 and 70 per 1,000 women aged 15–44.

Figure US General Fertility Rate, 1920–2010

Sources: Data from Hamilton, B. E., Martin, J. A., & Ventura, S. J. (2011). Births: Preliminary data for 2010. National Vital Statistics Reports, 60(2), 1–13; Martin, J. A., Hamilton, B. E., Sutton, P. D., Ventura, S. J., Menacker, F., Kirmeyer, S., & Mathews, T. J. (2009). Births: Final data for 2006. National Vital Statistics Reports, 57(7), 1–102; US Census Bureau. (1951). Statistical abstract of the United States: 1951. Washington, DC: US Government Printing Office.

Fertility rates differ around the world and are especially high in poor nations (see Figure 15.2). Demographers identify several reasons for these high rates (Weeks, 2012).Weeks, J. R. (2012). Population: An introduction to concepts and issues (11th ed.). Belmont, CA: Wadsworth.

Figure Crude Birth Rates around the World, 2008 (Number of Births per 1,000 Population)

First, poor nations are usually agricultural ones. In agricultural societies, children are an important economic resource, as a family will be more productive if it has more children. This means that families will ordinarily try to have as many children as possible. Second, infant and child mortality rates are high in these nations. Because parents realize that one or more of their children may die before adulthood, they have more children to make up for the anticipated deaths.

A third reason is that many parents in low-income nations prefer sons to daughters, and, if a daughter is born, they try again for a son. Fourth, traditional gender roles are often very strong in poor nations, and these roles include the belief that women should be wives and mothers above all. With this ideology in place, it is not surprising that women will have several children. Finally, contraception is uncommon in poor nations. Without contraception, many more pregnancies and births certainly occur. For all these reasons, then, fertility is much higher in poor nations than in rich nations.

Poor nations have higher birth rates for several reasons. One reason is the agricultural economies typical of these nations. In these economies, children are an important economic resource, and families will ordinarily try to have as many children as possible.

Image courtesy of R. Kalden, Voice of America, http://commons.wikimedia.org/wiki/File:Children_near_renovation_of_Jawaharlal_Nehru_Stadium_in_New_Delhi_2010-02-24.JPG

## Mortality and Death Rates

Mortality is the flip side of fertility and refers to the number of deaths. Demographers measure it with the crude death rate, the number of deaths for every 1,000 people in a population in a given year. We call this a “crude” death rate because the population component consists of the total population and does not take its age distribution into account. All things equal, a society with a higher proportion of older people should have a higher crude death rate. Demographers often calculate age-adjusted death rates that adjust for a population’s age distribution.

## Migration

Another important demographic concept is migration, the movement of people into and out of specific regions. Since the dawn of human history, people have migrated in search of a better life, and many have been forced to migrate by ethnic conflict or the slave trade.

Several classifications of migration exist. When people move into a region, we call it in-migration, or immigration; when they move out of a region, we call it out-migration, or emigration. The in-migration rate is the number of people moving into a region for every 1,000 people in the region, while the out-migration rate is the number of people moving from the region for every 1,000 people. The difference between the two is the net migration rate (in-migration minus out-migration). Recalling our earlier discussion. Michigan has had a net migration of less than zero, as its out-migration has exceeded its in-migration.

Migration can also be either domestic or international in scope. Domestic migration happens within a country’s national borders, as when retired people from the northeastern United States move to Florida or the Southwest. International migration happens across national borders. When international immigration is heavy, the effect on population growth and other aspects of national life can be significant, as can increased prejudice against the new immigrants. Domestic migration can also have a large impact. The great migration of African Americans from the South into northern cities during the first half of the twentieth century changed many aspects of those cities’ lives (Wilkerson, 2011).Wilkerson, I. (2011). The warmth of other suns: The epic story of America’s great migration New York, NY: Vintage Books. Meanwhile, the movement during the past few decades of northerners into the South and Southwest also had quite an impact: The housing market initially exploded, for example, and traffic increased.

## Population Growth and Decline

Now that you are familiar with some basic demographic concepts, we can discuss population change in more detail. Three of the factors just discussed determine changes in population size: fertility (crude birth rate), mortality (crude death rate), and net migration. The natural growth rate is simply the difference between the crude birth rate and the crude death rate. The US natural growth rate is about 0.6 percent (or 6 per 1,000 people) per year. When immigration is also taken into account, the total population growth rate has been almost 1.0 percent per year (Rosenberg, 2012).Rosenberg, M. (2012). Population growth rates. Retrieved from http://geography.about.com/od/populationgeography/a/populationgrow.htm.

Figure 15.3 depicts the annual population growth rate (including both natural growth and net migration) of all the nations in the world. Note that many African nations are growing by at least 3 percent per year or more, while most European nations are growing by much less than 1 percent or are even losing population, as discussed earlier. Overall, the world population is growing by about 80 million people annually (Population Reference Bureau, 2012).Population Reference Bureau. (2012). World population growth, 1950–2050. Retrieved February 4, 2012, from http://www.prb.org/Educators/TeachersGuides/HumanPopulation/PopulationGrowth.aspx.

Figure International Annual Population Growth Rates (%), 2005–2010

To determine how long it takes for a nation to double its population size, divide the number 70 by its population growth rate. For example, if a nation has an annual growth rate of 3 percent, it takes about 23.3 years (70 ÷ 3) for that nation’s population size to double. As you can see from the map in Figure 15.3, several nations will see their population size double in this time span if their annual growth continues at its present rate. For these nations, population growth will be a serious problem if food and other resources are not adequately distributed.

Demographers use their knowledge of fertility, mortality, and migration trends to make projections about population growth and decline several decades into the future. Coupled with our knowledge of past population sizes, these projections allow us to understand population trends over many generations. One clear pattern emerges from the study of population growth. When a society is small, population growth is slow because there are relatively few adults to procreate. But as the number of people grows over time, so does the number of adults. More and more procreation thus occurs every single generation, and population growth then soars in a virtual explosion.

We saw evidence of this pattern when we looked at world population growth. When agricultural societies developed some 12,000 years ago, only about 8 million people occupied the planet. This number had reached about 300 million about 2,100 years ago, and by the fifteenth century it was still only about 500 million. It finally reached 1 billion by about 1850; by 1950, only a century later, it had doubled to 2 billion. Just fifty years later, it tripled to more than 6.8 billion, and it is projected to reach more than 9 billion by 2050 (see Figure 15.4) and 10 billion by 2100 (Gillis & Dugger, 2011).Gillis, J., & Dugger, C. W. (2011, May 4). UN forecasts 10.1 million by century’s end. New York Times, p. A1.

Source: Data from US Census Bureau. (2012). Statistical abstract of the United States: 2012. Washington, DC: US Government Printing Office. Retrieved from http://www.census.gov/compendia/statab.

Eventually, however, population growth begins to level off after exploding, as explained by demographic transition theory, discussed later. We see this in the bottom half of Figure 15.4, which shows the average annual growth rate for the world’s population. This rate has declined over the last few decades and is projected to further decline over the next four decades. This means that while the world’s population will continue to grow during the foreseeable future, it will grow by a smaller rate as time goes by. As Figure 15.3 suggested, the growth that does occur will be concentrated in the poor nations in Africa and some other parts of the world. Still, even in these nations the average number of children a woman has in her lifetime dropped from six a generation ago to about three today.

Past and projected sizes of the US population appear in Figure 15.5. The US population is expected to number about 440 million people by 2050.

Figure Past and Projected Size of the US Population, 1950–2050 (in Millions)

Source: Data from US Census Bureau. (2012). Statistical abstract of the United States: 2012. Washington, DC: US Government Printing Office. Retrieved from http://www.census.gov/compendia/statab.

8.8: Population is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.