234 Lesson 2

THE NUMBER OF PEOPLE sharing Earth and its resources is getting bigger and bigger by the minute. Right now, assuming moder-ate population growth, scientists project that the human population may increase to more than 9 billion people by 2050. Some scientists project that it could reach 10.5 billion people by then! That’s a lot of people—and a big difference in projections. So, what information do demographers use to make these predictions?

Fertility Rate Fertility rate helps demographers predict the rates at which

populations will grow in the future.

At the most basic level, the factors that affect human population growth are the same as those that affect the populations of other organisms. Births add individuals to the global population and deaths remove them. Immigration and emigration affect the population size of particular regions. To get a clear picture of a population’s potential for growth, demographers look at many characteristics of a particular population.

Reading Strategy Before you read, make an outline using the blue and green headings in this lesson. As you read, fill in key phrases or sentences about each heading.

Vocabulary total fertility rate, replacement fertility, demographic transition

• Describe total fertility rates and replacement fertility.• Explain how the age structure and sex ratio of a

population define its potential for growth.• Describe the demographic transition.• Discuss social factors that affect population growth.

Guiding Question: How might the human population’s growth rate change in the future?

Predicting Population GrowthLE

SSO

N 2

Figure 7 Collecting Data Around the world, demographers collect data in similar ways, such as these census workers in Ecuador (a) and the United States (b).

(a)

(b)

FOCuS Have students form small groups. Ask each group to develop a prediction of how the human popu-lation growth rate might change in the next 100 years. Have each group share its prediction and two state-ments supporting its prediction with the class. Use students’ predic-tions to launch a class discussion on information demographers use to predict population growth rates.

GUIDING QUESTION

8.2 LESSON PLAN PREVIEWDifferentiated instruction English language learners dis-tinguish between total fertility rate and replacement fertility.inquiry A simple demonstra-tion helps students visualize the demographic transition’s affect on population growth.real World Students discuss social factors that affect a nation’s population growth and resource use.

8.2 RESOURCESIn Your Neighborhood Activity, Using Census Data • Paper and Pencil Activity, Interpreting Age Structure • Graph It, Age Pyramids and Popula-tion Growth • Lesson 8.2 Worksheets • Lesson 8.2 Assessment • Chapter 8 Overview Presentation

What Doyou think?

What Doyou think?

Trends in China’s Population Growth

Total fertility rate

Rate of natural population increase (% per year)

Doubling time (years)

Population (billions)

5.8

1.9

37

0.55

5.8

2.6

27

0.83

2.2

1.4

50

1.14

1.6

0.5

140

1.32

Measure 1950 1970 1990 2007

Data from China Population Information and Research Center; and Population Reference Bureau. 2007. 2007 World population data sheet.

Human Population 235

Total Fertility Rate One key statistic that demographers examine is total fertility rate. The average number of children a female member of a population has during her lifetime is the population’s total fertility rate.

Various factors influence total fertility rate. Historically, people tended to have many children to ensure that at least some would survive child-hood. On farms, people also had more children so that they had help with farm work. And, as parents got older, they could rely on their children to support them.

Recently, total fertility rates have started to drop in many nations, which indicates that most women are having fewer children. There are many reasons for this trend. In China the trend can be partly attributed to the one-child policy (Figure 8). In many other nations, parents feel less pressure to have many children because almost all children survive childhood. Also, many governments now have programs to help support older adults. Because every child requires food, clothing, and shelter, par-ents may feel that they can better provide for smaller families. However, although fertility rates are dropping, it’s important to remember that the human population is still increasing.

Replacement Fertility The total fertility rate for a nation that would keep its population size stable is called replacement fertility. This rate dif-fers from nation to nation depending on its death rate. In many nations, the replacement fertility is about 2.1. If a nation’s total fertility rate climbs above 2.1, then the population will most likely increase over time. If it falls below 2.1, then the population will most likely decrease over time. As of 2009, seventy-two nations had fallen below the total fertility rate of 2.1. In nations that have a higher than average death rate, replacement fertility is greater than 2.1.

Age Structure and Sex Ratios Age structure and sex ratios define a population’s potential

for growth.

Total fertility rate helps demographers predict if a population’s size will increase, decrease, or stay the same. But the statistic does not tell the whole story. Age structure and sex ratios can also help demographers predict how a population might change.

In the United States, Canada, and many European nations, the total fertility rate has fallen below the replacement rate. What economic and social consequences do you think might result from below-replacement fertility rates?

FiguRe 8 Trends in China The data show that the population growth rate in China has declined since the establishment of the one-child policy. Natural population increase refers to the balance of births and deaths, but does not include changes due to immigration or emigration. Interpret Tables Do the data in this table indicate that China’s population size is decreasing?

ANSWERS

Figure 8 No, the growth rate is de-creasing, but not the population size.What Do You Think? Answers will vary, but should reflect an under-standing of the consequences of below-replacement fertility rates, such as a reduced work force.

Age Structure of Canada in 2010 Age Structure of Madagascar in 2010

Reproductive agePost-reproductive agePre-reproductive age Reproductive age

Post-reproductive agePre-reproductive age

Data from U.N. Population Division

Male Female Male Female

90100

8070605040302010

0

Age

90100

80

70605040302010

0

Age

Population (millions)Population (millions)0 1 212 2 1 0 1 2

236 Lesson 2

Age Structure Populations consist of individuals of different ages. Age structure describes the relative numbers of organisms of each age within a population and is often represented by a graph called an age structure diagram. Age structure diagrams also show how many males and females there are in each age group.

Age structure shows the proportion of individuals currently of repro-ductive age, and those who could reproduce in the future. This informa-tion helps demographers predict how the size of a population will change over time. A population with many young people compared to older peo-ple could likely experience rapid population growth as the young people mature and have children. A population with fewer younger people will likely decrease in the future.

Look at the age structure diagrams for Canada and Madagascar shown in Figure 9. The pyramid shape of Madagascar’s diagram indicates that it has a greater population growth rate than Canada. In fact, its annual growth rate is 2.9 percent, while Canada’s is only 0.4 percent.

The pattern of population aging seen in Canada is occurring in many nations, including the United States. Older populations present new chal-lenges for many nations, as increasing numbers of older people require the care and financial assistance of relatively fewer working-age citizens. But, healthy older citizens can also be very productive as volunteers in their communities and caregivers to grandchildren. Nations undergoing rapid growth, such as Madagascar, face different challenges as they try to provide education, roads, and other resources to support a rapidly grow-ing population.

ReadingCheckpoint

Do you think that an age structure diagram representing China’s population would look more like Canada’s or more like Madagascar’s? Explain.

Figure 9 Age Structure Diagrams Canada’s age structure is relatively balanced. This indicates that there will be fewer people of reproductive age in future decades than there are now. In Madagascar, however, there are many more young people than older people.

Age Pyramids and Population Growth

ANSWERS

reading Checkpoint China’s age structure graph would likely look more like Canada’s because China’s growth rate has slowed.Quick Lab1. The Hispanic or Latino population,

the shape of the age structure graph indicates greater projected growth.

2. Yes; by comparing the proportion of reproductive-age women and the number of children in each age structure diagram, you could compare the total fertility rates of the two populations.

3. Hispanic or Latino population: 39%; white population: 25%. This indicates that the Hispanic or Latino population should grow at a greater rate.

Under 5

5–9

10–14

15–19

20–24

25–29

30–34

35–39

40–44

45–49

50–54

55–59

60–64

65–69

70–74

75–79

80–84

85 and over

Total

5,747,742

6,321,695

6,623,228

6,530,937

5,865,075

6,038,628

6,723,177

7,835,996

8,058,013

7,410,884

6,669,501

5,151,858

4,079,327

3,578,792

3,267,502

2,603,467

1,597,046

1,054,863

95,157,731

5,446,604

5,982,208

6,259,312

6,228,997

5,729,667

5,952,235

6,642,233

7,829,977

8,077,349

7,497,327

6,809,448

5,393,811

4,402,685

4,072,035

4,060,120

3,703,906

2,687,860

2,619,269

99,395,043

1,817,543

1,771,795

1,546,227

1,483,090

1,534,288

1,559,188

1,456,837

1,350,696

1,125,604

888,473

696,699

503,868

402,998

331,169

271,575

191,263

111,619

101,091

17,144,023

1,900,431

1,851,885

1,617,185

1,688,556

1,875,139

1,826,146

1,668,064

1,474,462

1,178,548

886,695

664,236

456,165

347,409

268,184

205,691

135,463

67,919

49,617

18,161,795

White Male

White Female

Hispanic or Latino Female

Hispanic or Latino Male

Age

Source: U.S. Census 2000

Population Size of Two Subgroups in the U.S.

Human Population 237

Sex Ratios Age structure diagrams also show the sex ratio for each age group. Sex ratio is the number of males compared to females in a popula-tion. At birth, the naturally occurring sex ratio of humans has slightly more males. For every 100 females born, about 106 males are born (sex ratio of 1.06 to 1). This phenomenon may be an evolutionary adaptation because males are slightly more likely to die during any given year of life. Therefore, having more male children in a population tends to ensure that the sex ratio is about equal when they reach reproductive age.

Human activities can skew the sex ratio one way or another. Some regions may have more females than males because many males emigrate to find work. Other areas may have more males than females. For exam-ple, in a culture that values sons more than daughters, daughters may not be given the same quality of care.

Build and Compare Age Structure DiagramsAlthough the United States’ popula-tion as a whole is aging, not every subset of the population is follow-ing the same pattern. The data in the table are from the 2000 U.S. Census. Use the data to make age structure diagrams for these two populations. Then use the diagrams to answer the questions. 1. Predict Which of these two

populations will likely grow at the greater rate over the next thirty years? Explain.

2. Interpret Diagrams Could you use age structure diagrams to compare total fertility rates of two populations? Explain.

3. Calculate Calculate the per-centage of the white popula-tion and the Hispanic or Latino population that was younger than 20 years old in 2000. Does your answer follow the predic-tion you made in Question 1? Explain.

MATH SUPPORT For help calculating with percentages, see the Math Handbook.

Adapted from Kent, M.M. and K.A. Crews. 1990. World population: Fundamentals of growth. Population Reference Bureau.

Demographic Transition

Time

Populationincrease

Gro

wth

rat

e

Birthrate anddeath rateare high

Birthrate anddeath rateare low

Pre-industrialstage

Post-industrialstage

Industrialstage

Transitionalstage

Death ratedeclines dueto increasedfood productionand improvedmedical care

Death rate

Birthrate

Birthrate declinesdue to increasedopportunities forwomen and accessto birth control

238 Lesson 2

The Demographic Transition The demographic transition may explain the reason that some

industrialized nations have experienced a large drop in birthrates and death rates.

In nations with good sanitation, effective healthcare, and reliable food supplies, people are living longer lives. In fact, over the past half-century, worldwide average life expectancy has increased from 46 to 68 years. Also, infant mortality rates have fallen in many regions. Societies going through these changes are generally those that have undergone the shift from rural life to urban life and industrialization, and that have generated personal wealth for their citizens.

To make sense of these trends, demographers use a concept called the demographic transition. The demographic transition is a model that explains the change from high birthrates and death rates to a condition of low birthrates and death rates. A demographic transition is the result of economic growth that has led to social changes. As shown in Figure 10, the demographic transition is a four-stage process.

The Pre-Industrial Stage The first stage, or the pre-industrial stage, is characterized by conditions that have defined most of human history. For pre-industrial societies, both death rates and birthrates are high. Death rates are high because of widespread disease, poor medical care, and unreliable food and water supplies. Birthrates are high because people want larger families or they don’t have access to family planning methods. Infant mortality is likely to be high during this stage, and hav-ing many children increases the chance that some of them will survive. Populations in the pre-industrial stage are not likely to experience much growth. This may explain why the human population was relatively stable until the Industrial Revolution.

Figure 10 Demographic Transition During the demographic transition, birthrates and death rates start high. Death rates fall first, followed by birthrates.

Human Population 239

The Transitional Stage Industrialization starts the transitional stage of the demographic transition. In this stage, death rates decline as food production increases and medical care improves. Because people have not adjusted to the new economic and social conditions, birthrates remain high. Population growth increases because births exceed deaths.

The Industrial Stage The third stage in the demographic transition is the industrial stage. Industrialization increases job opportunities outside the home, particularly for women. Couples may choose to have fewer children in part because there is less fear of losing them to disease or famine. Birthrates fall, closing the gap with death rates. In turn, the rate of population growth also falls.

The Post-Industrial Stage In the final stage, the post-industrial stage, both birthrates and death rates fall to low and stable levels. Population sizes stabilize or decline slightly but are much higher than they were at the pre-industrial stage. The society enjoys the benefits of industrializa-tion without the threat of runaway population growth.

The demographic transition has occurred in many nations over the past 200 to 300 years. For example, many European nations, the United States, Canada, and Japan have all undergone this transition. But social scientists cannot predict whether every nation will eventually follow the same pattern.

ReadingCheckpoint

Briefly describe the four stages of the demographic transition.

FIgure 11 Japan and India (a) Japan has already gone through the demographic transition, which means that many couples have only one or two children. (b) No one knows if population growth in other nations, such as India, will follow the demographic transition pattern.

(a)

(b)

ANSWERS

reading Checkpoint Check that students have accurately described the characteristics of the pre-indus-trial stage, transitional stage, industrial stage, and the post- industrial stage.

How does the human population affect the environment?Application After students have read the information about the four stages of the demographic transi-tion, refer them back to the Big Question. Discuss each of the four stages of the demographic transi-tion in turn. For each, have students describe how population trends as-sociated with that stage would affect the environment.

BIG QUESTION

Distribution of World Population

Year

Glo

bal p

opul

atio

n (b

illio

ns)

1950 1975

8

6

4

2

02000 2025 2050

Developing nationsDeveloped nations

Data from U.N. Population Division.

240 Lesson 2

Social Factors Social factors, such as wealth and education, affect a nation’s

population growth and its resource use.

Predicting population growth is not just a numbers game. People live in complex societies that influence population growth and their impact on the environment. Factors such as poverty, wealth, and education levels affect population size.

Developing Nations The term developing nation refers to nations with moderate or low income and includes China and Mexico as well as all the nations of Africa, Central America, South America, Indonesia, and eastern Europe. Worldwide, more people live in developing nations than live in developed nations. Developed nations are high-income nations including the United States, Canada, western European nations, Australia, New Zealand, Japan, and some Arab states.

Compared to developed nations, developing nations tend to have higher fertility rates, infant mortality rates, and death rates. Life expectancy is also typically lower. In some areas, crowded conditions, poor sanitation, poor nutrition, and lack of health education lead to higher frequency of diseases such as AIDS and tuberculosis that can spread from person to person.

Despite these difficulties, the population growth of developing nations as a whole surpasses population growth in developed nations as shown in Figure 12. This affects distribution of people on the planet. In 1950, 68 percent of the world’s population lived in developing nations. By 2009, 82 percent of the world’s population lived in these nations. Population growth in developing regions presents many challenges. Will there be enough jobs for people to support themselves? Will there be enough resources to support a quickly growing population?

▶ National Policies Many developing nations experiencing rapid population growth have programs to encourage citizens to have smaller families. China’s program is an extreme example. Other rapidly grow-ing nations have implemented less restrictive programs. For example, Thailand relies on an education-based approach to family planning. In the 1960s, Thailand’s growth rate was about 3 percent. Now it is about 0.6 percent.

In 1994, the United Nations hosted a conference in Cairo on popula-tion and development. The conference urged governments to offer better education and healthcare and to address social needs that influence population size. Since then Brazil, Mexico, Iran, Cuba, and other nations have instituted programs that involve economic incentives, education, free contraception, and reproductive healthcare.

Figure 12 Distribution of Future growth Almost all of the next 1 billion people added to Earth’s population will reside in less developed, poorer parts of the world. The dashed lines indicate projected future trends.

Human Population 241

1. Infer Assuming there is no emigration, would you expect the total fertility rate of a declining popula-tion to be more or less than 2.1? . Explain.

2. Explain How does age structure help us predict population growth?

3. Apply Concepts A population that is industrial-ized is experiencing a drop in death rates. However, the birthrate remains high. Could it be undergoing the demographic transition? Explain.

4. Review How does population growth compare between poorer and wealthier societies?

5. A nation has a total fertility rate of 2.5. The age structure of this popu-lation is fairly balanced. Recently people from a neighboring nation have been arriving in masses to escape a civil war. Do you think this population will likely increase or decrease in the near future? Explain your answer.

2

▶ Empowering Women Better educational opportunities for women are closely tied to declining fertility rates. Studies show that in societies in which women are freer to decide whether and when to have children, fertility rates fall. Many social scientists and policymakers recognize that for population growth to slow and stabilize, women need to achieve equal education and power with men. But there is a long way to go. Over two thirds of the world’s people who cannot read and 60 percent of those liv-ing in poverty are women.

Developed Nations Beyond the actual number of people, it’s also important to consider the amount of resources a particular popula-tion uses and the amount of waste it produces. Just as population size is distributed unevenly around the globe, so are wealth and rate of resource consumption. As explained in Figure 13, people in nations such as the United States typically use far more resources compared to people in developing nations. In this sense, the addition of one American has as much environmental impact as the addition of five Chinese or thirteen Pakistanis. As more and more nations become industrialized, whether or not they go through the demographic transition, their consumption rates will also rise.

FIguRE 13 uneven Consumption Rates The amount of resources needed to supply a food market is a sign of uneven consumption rates. (a) The U.S. market needs fossil fuels for shipping, materials for packaging, and electricity that the (b) Sengalese market does not. Although the United States does have open-air markets where locally grown produce is sold, they are not common.

(a) (b)

ANSWERS

Lesson 2 Assessment

1. Less than; replacement fertility is 2.1. Declining populations likely have a TFR that is less than 2.1.

2. Age structure shows the number of people who are at or near repro-ductive age.

3. Yes; it is likely in the transitional stage of the demographic transi-tion in which death rates drop but birthrates remain high.

4. Poorer societies tend to have higher population growth rates than wealthier ones.

5. Increase; the total fertility rate is likely above the replacement level and immigrants are joining the population. A balanced age struc-ture shows that there are some people who will be at reproductive age currently or in the near future.