Tille Human Population and Its Impact

Applyin.g Population Ecology: TIlle Human Population and Its Impact

ers it is the number of people in developed countries E CASE STUDY such as the United States where high resource con- e World Overpopulated? sumption rates magnify the environmental impact of each person (Figure 1-7, P: 13 and Figure 1-14, bot- orld's human population is projected to in- tom, p. 20). efram 6.6 to 9.2 billion or more between 2006 Those who do not believe the world is overpopu- 050 (Figure 1-1, P: 6), with much of this growth lated point out that the average life span of the ring in several rapidly developing countries world's 6.6 billion people is longer today than at any as India and China (Figure 9-1). Are there too time in the past and is projected to increase. According ypeople on the earth? to them, the world can support billions more people :Some argue that the planet has too many people as a result of human technological ingenuity in pro- iectively degrading the earth's natural capital. To viding food and other resources. They also see more p;e the problem is the sheer number of people in people as the world's most valuable resource for solv- ~yeloping countries (Figure 1-14, top, P: 20). To oth- ing environmental and other problems and for stimu- lating economic growth by increasing the number of consumers. Some view any form of population regulation as a violation of their religious or moral beliefs. Others see it as an intrusion into their privacy and personal freedom to have as many children as they want. Some developing countries and some members of minorities in developed countries regard population control as a form of genocide to keep their numbers and political power from growing. Proponents of slowing and eventually stopping population growth ask if we cannot or will not pro- vide basic support for about one of every five people-about 1.4 billion people today, how will we be able to do so for the projected 2.6 billion more people by 2050? They also warn that if we do not sharply lower birth rates, the death rate may increase because of declining health and environmental conditions in some areas, as is already happening in parts of Africa. They also warn that resource use and environmental degra- dation may intensify as more consumers increase their already large ecological footprint in developed countries and in rapidly developing countries, such as China and India. This debate over interactions among population growth, economic growth, politics, and moral beliefs is one of the most important and controversial issues in environmental science.

Figure 9-1 Crowded street in China. Together, China and India QY-I f/Ot//f!l/O{/LD YO{/ VOTE? Should the population of the have 37% of the world's population and the resource use per country where you live be stabilized as soon as possible? person in these countries is projected to grow rapidly as they Cast your vote online www.thomsonedu.com/biology/miller. become more modernized (Case Study, p. 15). ------Tlu: proincm: io be faced O(C vast and comptex, b!!{"come there are 6.6 billion of us. It took from the time we ar- do~;./n .\;- [,.i;.j.'.j,' 5.6 billion people ate iJreeding exponcntiati». The rived until about 1927 to add the first 2 billion people procrss /illt]iling their wants atul neeii: is stripping eortl: o( to the planet; less than 50 years to add the next 2 billion iis biotic capacity to produce lire; a climactic burst ofcon- (by 1974); and just 25 years to add the next 2 billion (by sumprior: by (j single species is cverwhelmi.ig the skies, earth. 1999)-an illustration of the power of exponential waters, a:id [auna. growth. Such growth raises the question of whether ,., the earth is overpopulated (Core Case Study, p. 171).

This chapter looks at the factors that affect the growth and decline of the human population. It addresses the Population Growth Today: Slowing but Still following questions: Growing (Science and Economics) The rate or po~:n~~IZitiong~,~0V\/t~1.:1215 slewed but is still !II What is the history of human population growth, gro';,vlng ~·Ci.pidly, and how many people are likely to be here by 2050? During 2006, about 81 million people were added to the world's population-79.5 million in developing l!I How is population size affected by birth, death, countries and 1.2 million in developed countries. At fertility, and migration rates? this exponential growth rate of 1.23% a year, we share

I1J How is population size affected by the percentages the earth and its resources with about 222,000 more of males and females at each age level? people each day and 2.4 more people every time your heart beats. 18 How can we slow population growth? An exponential growth rate of 1.23% may seem IB What success have India and China had in slowing small, but compare the 81 million people added to the population growth? world's population in 2006 to the 69 million added in tII What are the major impacts of human activities on 1963, when the world's population growth reached its the world's natural ecosystems? peak. This increase of 81 million people per year is roughly equal to adding another New York City (USA) every month or another Germany every year. Also, there is a big difference between population HUMAN POPULATION GROWTH: growth rates in developed and developing countries. A BRIEF HISTORY In 2006, the population of developed countries was growing exponentially at a rate of 0.1% per year. That Population Growth in the Past (Science of the developing countries was 1.5% per year-15 and Economics) times faster. VVehave kept the 11111.J.12f1 population gr()yving Thus, population growth in recent decades is a re- by expanding into ecosystems throughout the sult of keeping more people alive by increasing life ex- world and using technologica! innovations to pectancy and reducing death rates. This is a good thing. expand the food supply and lower death rates, But coupled with increased resource consumption per For most of history, the human population grew slowly person this can to lead increased environmental degra- (Figure 1-1, left part of curve, p. 6). But for the past 200 dation as the human ecological footprint spreads across years, the human population has experienced rapid ex- the.planet (Figure 1-7, p. 13, and Figure 3 on pp. S12-513 ponential growth reflected in the characteristic [-curve. in Supplement 4). To those arguing that both developed (Figure 8-3, left side, p. 163 and Figure 1-1, right part of and developing countries are overpopulated, the solu- curve, p. 6). tion is to focus on sharply reducing birth rates. Three major factors explain this population increase. First, humans developed the ability to expand Where Are We Headed? (Science, Economics, into diverse new habitats and different climate zones. and Politics) Second, the emergence of early and modern agriculture allowed more people to be fed per unit of land area. "VVedo not know how long live CC'!Xlcontinue ir:.cE·(:::~~,~,ii}.1g..... Third, we developed sanitation systems, antibi- the earth' 5 carrying capacity for bl.UT!.3~:'S. otics, and vaccines to help control infectious disease Scientific studies of populations of other species, agents, and we tapped into concentrated sources of en- (Chapter 8), tell us that no population can continue gl'OW--' ergy (mostly fossil fuels, Case Study, P: 42). As a result, ing indefinitely. How long can we continue increasing. death rates dropped sharply below birth rates. the earth's carrying capacity for our species by side-. About 10,000 years ago when agriculture began stepping many of the factors that sooner or later lirnit: there were about 5 million humans on the planet; now the growth of any population? .

172 CHAPTER 9 Applying Population Ecology: The Human Population and Its Impact rfii_iiiiii~-:------.

(The debate over this important question has been vide an adequate standard of living for the medium projec- g on since 1798 when Thomas Malthus, a British tion of 8.9 billion people in 2050 without causing wide- rtornist, hypothesized that the human population spread environmental damage?" In other words, how ds to increase exponentially, while food supplies many people can the earth support indefinitely? Some d to increase more slowly at a linear rate. So far, say about 2 billion. Others say as many as 30 billion. 'tthus has been proven wrong. Food production has Some analysts believe this is the wrong question. 'wn at an exponen~ial rate instead of at a linear rate Instead, they say, we should ask what the optimum ;'cause of genetic and technological advances in in- sustainable population of the earth might be, based on "strialized food production. the planet's cultural carrying capacity. Such an opti- '. No one knows how close we are to the environ- mum level would allow most people to live in rea- -ntallimits that sooner or later will control the popu- sonable comfort and freedom without impairing the ~tion size of the human species, but the evidence is ability of the planet to sustain future generations. (See 'rowing that we are steadily degrading the natural the Guest Essay by Garrett Hardin on this topic on apital that keeps us and other species alive and sup- the website for this chapter.) There is disagreement on :orts our economies-one of the arguments support- what the optimum sustainable population size for the ,fig the idea that the world is overpopulated (Core world is. 'C-aseStudy, p. 171). .' How many of us are likely to be here in 2050? An- ~ l2J rfllNKING A80tIT POP(JLAriON GROlfffl What do you . swer: 7.2-10.6 billion people, depending mostly on '} think is (a) the maximum human population size and (b) the optimum human population size? How do your answers reflect >'projections about the average number of babies your position on whether the world is overpopulated (Core women are likely to have. The medium projection is Case Study, p. 171) and your environmental worldview 8.9 billion people (Figure 9-2). About 97% of this (pp. 22-23)7 growth is projected to take place in developing countries, where acute poverty (living on less than $1 per day) is a way of life for about 1.4 billion people. During this century the human population may level off as it moves from a J-shaped curve of exponential growth to an S-shaped curve of logistic growth ' (Figure 8-3, p. 163). FACTORS AFFECTING HUMAN '., The key question, as raised in the Core Case Study POPULATION SIZE :";> . at the beginning of this chapter, is, "Can the world pro- Birth Rates and Death Rates: Entrances and Exits (Science) 12

11 ill11;~jgr(i~~_:.c::(1~-; ~,cdcc~: -ep..s'2:;t.hJ.~cL-~ghdeaths ?r;{~ ~ High 2n1 i.gr-~ticr.. 10 ~ Medium Human populations grow or decline through the inter- if) 9 ~Low c play of three factors: births (fertility), deaths (mortality), 9 8 and As pointed out in Chapter 8, we can cal- :0 migration. c 7 culate population change by subtracting the number 0 ~ of people leaving a population (through death and '3 6 Q emigration) from the number entering it (through 0 Q 5 birth and immigration) during a specified period of 4 time (usually one year):

3 ~ rg: cPopUhangleation = (S'lrthi's + mrruqratroionn) - (D eat hss +f- Ernmigrationion) 2 L--L __ ~ __ L--L __ J- __ L--L __ ~~ __ -Y 1950 1960 1970 1980 1990200020102020203020402050 Year When births plus immigration exceed deaths plus emigration, population increases; when the reverse is Figure 9-2 (;HGf:lz;, G,:,nllbcikms: UN world population projec- true, population declines. tions, assuming that by 2050 women have an average of 2.5 Instead of using the total numbers of births and children (high), 2.0 children (medium), or 1.5 children (low) The most likely projection is the medium one-8.9 billion by 2050. deaths per year, population experts (demographers) (Data from United Nations, World Population Prospects. The use the birth rate, or crude birth rate (the number of 2001 Revision, 2002) live births per 1,000 people in a population in a given

.tncmsonedu.ecm/utoloqy/mtner 173

------CJ Average crude birth rate ~ Average crude death rate Fertility is the number of children born to a woman during her lifetime, Two types of fertility rates affect a World _"9'~",,,~nJb21 country's population size and growth rate. The first type, replacement-level fertility, is the All developed countries number of children a couple must bear to replace themselves, It is slightly higher than two children per All developing countries couple (2,1 in developed countries and as high as 25 in some developing countries), mostly because some Developing countries children die before reaching their reproductive years. (w/o China) Does reaching replacement-level fertility bring an immediate halt in population growth? No, because so many future parents are alive, If each of today's cou- ples had an average of 2.1 children and their children Africa ~;'~t" ""'"~_h''''''',,",,''',..~ 38 also had 2.1 children, the world's population would continue to grow for 50 years or more (assuming death Latin and rates do not rise), Central America .''6'" >,.,~~.•"'~."'''',''~ 21 The second type of fertility rate, the total fertility Asia 20 rate (TFR) is the average number of children a woman _'7'~.".'"~.~" typically has during her reproductive years. Today, the Oceania _'7"'"_K_"~17 average woman in the world has half as many children as her counterpart in 1972. In 2006, the average global United TFR was 2.7 children per woman: 1.6 in developed States _'8~",~14 countries (down from 25 in 1950) and 2.9 in develop- North ing countries (down from 65 in 1950), Although the America iii'S=Eh14 decline in TFR in developing countries is impressive, it Europe iiiii~1 is still far above the replacement level of 2,1. Figure 9-3 GiD0Zd ,comv.'!Gl:O:im;: average crude birth and China death rates for various groupings of countries in 2006. (Data ~~"~~illion from Population Reference Bureau) India ~,0~.4billion

USA 00 million year), and the death rate, or crude death rate (the 349 million number of deaths per 1,000 people in a population in a Indonesia given year). Figure 9-3 shows the crude birth and death rates for various groupings of countries in 2006. Brazil What five countries had the largest numbers of people in 2006? Number 1 is China with 1.3 billion Pakistan people, or one of every five people in the world. Num- ber 2 is India with 1.1 billion people, or one of every Bangladesh 47 million six people, Together China and India have 37% of the' 190 million world's population. The United States, with 300 mil- Russia 142 million lion people in 2006-has the world's third largest pop- 130 million ulation but only 4,5% of its people. Nigeria ~35million Can you guess the next two most populous coun- 199 million tries? What three countries are expected to have the Japan iJ 128 million most people in 2025? Look at Figure 9-4 to see if your , 121 million answers are correct. 02006 ~2025

Declining Fertility Rates: Fewer Babies per Figure 9-4 G',.'D::1i ·~(li':Fi",;!:k)'!;.i: the world's 10 most populOUS: Woman (Science and Economics) countries in 2006, with projections of their population size in .~ 2025. In 2006, more people lived in China than in all of Europe..: The Cl.\rerage number of children tha~ 3. V/ClI":;~r~b.:;?~~"S Russia, North America, Japan, and Australia combined By' has dropped sharply. but is not low ,2P..:J:"l.:SL-: to 2050, India is expected to have a larger population than China,:' s~:2.oilize the world's :JDG"L:12.cic:nir: .he .:.;f::ZJ' ;L~tE:·~2. (Data from World Bank and Population Reference Bureau) .

174 CHAPTER 9 Applying Population Ecology: The Human Population and Its Impact

-- ---.-- Study: fertin:ft1l:yand Bh-th Rates country's population is still growing faster than that of ii~United States (Science and any other developed country and is not close to level- , odes) ing off. ~?tion ~-:;';- ~:-!E-'Jj_-:i:-~~'-=S~ t~~test~c;s:-,fC; J.,l2-:: Nearly 3,0 million people were added to the Us. population in 2006, About 56% of this growth occurred is hot clo'"",',',: ':i"". because births outnumbered deaths; the rest came ':p~pulation of the United States has grown from from legal and illegal immigration. ':'llion in 1900 to 299 million in 2006, despite oscil- According to the US, Census Bureau, the US. , :hs in the country's TFR (Figure 9-5) and birth population is likely to increase from 300 million in 2006 (Figure 9-6). The period of high birth rates be- to 420 million by 2050 and then to 571 million by 2100. n 1946 and 1964 is known as the baby-boom pe- In contrast, population growth has slowed in other ; This added 79 million people to the Us. popula- major developed countries since 1950, most of which . In 1957, the peak of the baby boom, the TFR are expected to have declining populations after 2010. ched 3.7 children per woman, Since then it has Because of a high per capita rate of resource use, each fterally declined, remaining at or below replace- addition to the us. population has an enormous envi- ent level since 1972. The baby bust that followed the ronmental impact (Figure 1-7, p. 13, and Figure 4 on ,1Jy boom (Figure 9-6) was due in large part to de- pp. 514-S15 in Supplement 4 at the end of this book), layed marriage, widespread contraceptive use, and In addition to the almost fourfold increase in pop- abortion. ulation growth, some amazing changes in lifestyles , The drop in the TFR has led to a decline in the rate took place in the United States during the twentieth pf population growth in the United States, But the century (Figure 9-7, P: 176), which led to dramatic increases in per capita resource use and a much larger Us. ecological footprint, Here are a few more changes during the last century In 1905, the three leading causes of death in the c E 30 United States were pneumonia, tuberculosis, and diar- ~ 2.5 rhea; 90% of US. doctors had no college education; ~ 2,1"1:-_~~----\:~;;;;;;!~;::;;.-1 l!i 2.0r one out of five adults could not read or write; the aver- J!! 1,5 . Baby boom Replacement age US, worker earned $200-400 per year and the av- ~ 1.0 (1946-64) level erage daily wage was 22 cents per hour; there were 0,5 only 9,000 cars in the US., and only 232 kilometers (144 miles) of paved roads; a 3-minute phone call from o 1920 1930 1940 1950 1960 1970 1980 199020002010 Denver, Colorado, to New York City cost $11; only 30 Year people lived in Las Vegas, Nevada; and most women washed their hair only once a month. Figure 9-5 Total fertility rates for the United States between 1917and 2006, Use this figure to trace changes in total fertility l.2f the --- rates dUring your lifetime, QUESTION: How many children do you IH;;;KING.4BO~O~;POP(/LArION-D~~~ink plan to have? (Data from Population Reference Bureau and US United States, or the country where you live, is overpopulated? Census Bureau) Explain .------

Figure 9-6 Birth rates in the United States. 1910-2006.Use this figure to trace changes in crude birth rates durinq your lifetime. (Data from U,S, Bureau of Census and US. Commerce Department)

.tncrnsunedu.com/btotegp/mrtler 175 - Figure 9-7 Some major changes that took place in the United States be- life expectancy 11111•••••••• 77 years tween 1900 and 2000. QUESTION: Which two of these changes do you think were the most important? (Data Married women working from U.S. Census Bureau and Depart- outside the home 81% ment of Commerce)

Homes with flush toilets 98%

Homes with electricity 99%

Living in suburbs 52% E:j1900

Hourly manufacturing job .2000 wage (adjusted for inflation) $15

Homicides per 100,000 people 5.8

in rural areas, where children are often needed to per- Factors Affecting Birth Rates and Fertility form essential tasks. Rates (Science and Economics) Another important factor is the educational and em- "Thenumber of children womenhave is affected ployment opportunities availablefor women. TFRs tend to by the cost of raising and educating children. be low when women have access to education and availability of pensions, urbanization, educational paid employment outside the home. In developing and employment opportunities for women. infant countries, women with no education generally have deaths, marriage Clge, and availability of more children than women with a secondary school contraceptives and abortions. education. In Brazil, for example, illiterate women on Many factors affect a country's average birth rate and average have more than six children compared to two TFR. One is the importance of children as a part of the la- children for literate women. bor force. Proportions of children working tend to be Another 'factor is the infant mortality rate. In areas higher in developing countries-especially in rural ar- with low infant mortality rates, people tend to have eas, where children begin working to help raise crops fewer children because not as many children die at an at an early age. early age. Another economic factor is the cost of raising and Average age at marriage (or, more precisely, the av- educating children. Birth and fertility rates tend to be erage age at which women have their first child) also lower in developed countries, where raising children plays a role. Women normally have fewer children is much more costly because they do not enter the la- when their average age at marriage is 25 or older. bor force until they are in their late teens or twenties. Birth rates and TFRs are also affected by the avail- In the United States, it costs about $250,000 to raise a ability of legal abortions. Each year about 190 million middle-class child from birth to age 18. women become pregnant. The United Nations and the The availability of private and public pension systems World Bank estimate that 46 million of these women can affect a couple's decision on how many children to get abortions-26 million of them legal and 20 million have. Pensions reduce a couple's need to have many illegal (and often unsafe). children to help support them in old age. The availability of reliable birth control methods al- Urbanization plays a role. People living in urban lows women to control the number and spacing of the areas usually have better access to family planning ser- children they have. Religious beliefs, traditions, and cul- vices and tend to have fewer children than those living tural norms also playa role. In some countries, these

176 CHAPTER9 Applying Population Ecology: The Human Population and Its Impact actorS favor large families and strongly oppose abor- 21,000 mostly unnecessary infant deaths per day. This tion and some forms of birth control. is equivalent to 55 jumbo jets, each loaded with 400 infants younger than age 1, crashing each day with no Learning more a;;~ut how these and 'r[Ji;;EAR;;;;"j;O~IrIE;' survivors! other factors interact and affect birth and fertility rates ~ .-~--.------.- The U.S. infant mortality rate declined from 165 in 1900 to 6.7 in 2006. This sharp decline was a major factor in the marked increase in U.S. average life ex- .Factors Affecting Death Rates (Science and pectancy during this period. Still, some 46 countries Economics) (most in Europe) had lower infant mortality rates than ~~'-Deathrates have declined because of increased food the United States had in 2006. If the U.S. infant mortal- .~.suppli.(~S;better nutrition, advances in medicine, ity rate was as low as that of Singapore (ranked no. 1) improved sanitation and personal hygiene; and Seder in 2006, this would have saved the lives of 18,900 water sc:pplies. American children. The rapid growth of the world's population over the Three factors have helped keep the U.S. infant past 100 years is not the result of a rise in the crude birth mortality rate higher than it could be: inadequate health rate. Instead, it has been caused largely by a decline in carefor poor women during pregnancy and for their babies crude death rates, especially in developing countries. after birth, drug addiction among pregnant women, and a More people started living longer and fewer in- high birth rate among teenagers. fants died because of increased food supplies and distribution, better nutrition, medical advances such as Case Study: U.S. Immigration (Economics immunizations and antibiotics, improved sanitation, and Politics) and safer water supplies (which curtailed the spread . ,~ of many infectious diseases). Immigration has played, and continues to play, a Two useful indicators of overall health of people major role in the grovlth and cultured diversity of the in a country or region are life expectancy (the average LIS. population. number of years a newborn infant can expect to live) The third factor in population change is migration: the and the infant mortality rate (the number of babies out movement of people into (immigration) and out of (emi- of every 1,000 born who die before their first birthday). gration) a specific geographic area. Only five coun- Great news. Between 1955 and 2006, the global life tries-the United States, Canada, Australia, New expectancy increased from 48 years to 67 years (77 Zealand, and Israel-have official policies to encour- years in developed countries and 65 years in develop- age immigration. ing countries). It ranges from a low of 34 in Botswana Most migrants seek jobs and economic improve- to a high of 82 in Iceland. Average life expectancy is ment. But some are driven by religious persecution, projected to reach 74 in developing countries by 2050. ethnic conflicts, political oppression, wars, and envi- Between 1900 and 2006, life expectancy in the United ronmental degradations such as water shortages, soil States increased from 47 to 78 years and is projected to erosion, deforestation, desertification, population pres- reach 82 years by 2050. sures, and severe poverty. According to a UN study, Bad news. In the world's poorest countries, life ex- there were about 19.2 million environmental refugees in pectancy is 49 years or less. In many African countries, 2005 and the number could reach 50 million by 2010. In life expectancy is expected to fall further because of a globally warmed world the number could soar to 250 rising numbers of deaths from AIDS. million or more. Infant mortality is viewed as the best single mea- Since 1820, the United States has admitted almost sure of a society's quality of life because it reflects a twice as many immigrants and refugees as all other country's general level of nutrition and health care. A countries combined! However, the number of legal im- high infant mortality rate usually indicates insufficient migrants (including refugees) has varied during dif- food (undernutrition), poor nutrition (malnutrition), ferent periods because of changes in immigration laws and a high incidence of infectious disease (usually and rates of economic growth (Figure 9-8, p. 178). Cur- from contaminated drinking water and weakened dis- rently, legal and illegal immigration account for about ease resistance from undernutrition and malnutrition). 44% of the country's annual population growth. Good news. Between 1965 and 2006, the world's in- Between 1820 and 1960, most legal immigrants to fant mortality rate dropped from 20 (per 1,000 live the United States came from Europe. Since 1960, most births) to 6.3 in developed countries and from 118 to 59 have come from Latin America (53%) and Asia (25%), in developing countries. followed by Europe (14%). In 2006, Latinos (67% of Bad news. Annually, at least 7.6 million infants them from Mexico) made up 14% of the U.S. popula- (most in developing countries) die of preventable tion and by 2050 are projected to make up 25% of the .~ . ~' causes during their first year of life-an average of population.

., '.ihomsonedu.com/bioiogy/miller 177 r------_.. 2,000 I======;(£']~ world's poor and oppressed. In addition, legal and illegal immigrants pay taxes, take many menial and ~ 1,800 c low-paying jobs that most other Americans shun, open ill 1,600 businesses, and create jobs. And according to the U.S. ::> o 2- 1,400 1907 Census Bureau, after 2020 higher immigration levels / (j) 1914 will be needed to supply enough workers as baby ~ 1,200 / New laws boomers retire. 0, restrict E 1,000 immigration .~ 00 !fO/lf/!lf/O(/LD (0(/ t/ors? Should legal immigration into the

.ill0 400 E ~ 200 ..-: '.':0 o 1820184018601880190019201940196019802000 ·2010 POPULATION AGE STRUCTURE

Year Age Structure Diagrams (Science and Figure 9-8 Legal immigration to the United States, 1820-2003. The Economics) large increase in immigration since 1989 resulted mostly from the The number of people in young, middle, and older Immigration Reform and Control Act of 1986, which granted legal status to illegal immigrants who could show they had been living in age groups determines 110"\1'1/ fast populations grovv or the country for several years. (Data from U.s. Immigration and decline. Naturalization Service and the Pew Hispanic Center) As mentioned earlier, even if the replacement-level fertility rate of 2.1 children per woman were magically achieved globally tomorrow, the world's population In 1995, the U.S. Commission on Immigration would keep growing for at least another 50 years (as- Reform recommended reducing the number of legal suming no large increase in death rates). This results . immigrants from about 1,000,000 to 700,000 peryear for mostly from the age structure: the distribution of a transition period and then to 550,000 per year. Some males and females in each age group in the world's analysts want to limit legal immigration to 20% of the population. country's annual population growth. They would ac- Demographers construct a population age struc- cept new entrants only if they can support themselves, ture diagram by plotting the percentages or numbers of arguing that providing immigrants with public services males and females in the total population in each of makes the United States a magnet for the world's poor. three age categories: prereproductive (ages 0-14), repro- In 2006, there were about 35.2 million foreign- ductive (ages 15-44), and posireproductioe (ages 45 and born legal immigrants-roughly one of every eight up). Figure 9-9 presents generalized age structure dia- Americans-living in the United States. Add to this grams for countries with rapid, slow, zero, and nega- about 11-12 million illegal immigrants-81% of them tive population growth rates. from Latin America and 56% from Mexico. According to a 2006 poll, 75% of Americans believe that illegal Effects of Age Structure on Population immigrants should be able to earn citizenship and fa- Growth: Teenagers Rule (Science and vor guest-worker registration for those already here. Economics) Proponents of reducing legal immigration argue that it would allow the United States to stabilize its The number of people youJ:1ger than age 15 is the population sooner and help reduce the country's enor- major factor determining a country's future mous environmental impact. Polls show that almost population gro'iJ\lth. 60% of the u.s. public strongly supports reducing le- Any country with many people younger than age 15 gal immigration. (represented by a wide base in Figure 9-9, left) has a There is also strong public support for sharply powerful built-in momentum to increase its popula- reducing illegal immigration. But some people are tion size unless death rates rise sharply. The number of concerned that a crackdown on the country's illegal births will rise even if women have only one or twq· immigrants can also lead to discrimination against children, because a large number of girls will soon be some of the country's legal immigrants. moving into their reproductive years. - Others oppose reducing current levels of legal im- What is perhaps the world's most important pOR, migration. They argue that it would diminish the his- ulation statistic? Twenty-nine percent of the people on t • torical role of the u.s. as a place of opportunity for the planet were under 15 years old in 2006. These 1.9 billio

178 CHAPTER 9 Applying Population Ecology: The Human Population and Its Impact Female

l- i I ~ I: ( I i· I Expanding Rapidly Expanding Slowly Stable Declining i I' Guatemala United States Spain Germany Nigeria Australia Portugal Bulgaria i Saudi Arabia Canada Greece Italy I Ell Prereproductive ages 0-14 D Reproductive ages 15-44 f!&~l!I Postreproductive ages 45-85+ I ThomsonNOVi{' Active Figure 9-9 Generalized population age Developed Countries structure diagrams for countries with rapid (1.5-3%), slow (0.3-1.4%), zero (0-0.2%), and negative population growth 85+ rates (a declining population). Populations with a large propor- 80-85 tion of its people in the prereproductive ages of 1-14 (at left) 75-79 Male Female 70-74 have a large potential for rapid population growth. QUESTION: 65-69 Which of these diagrams best represents the country where you 60-64 live? See an animation based on this figure and take a short 55-59 quiz on the concept. (Data from Population Reference Bureau) 50-54 :g, 45-49 < 40-44 35-39 30-34 25-29 20-24 15-19 young people are poised to move into their prime re- 10-14 5-9 productive years. In developing countries the number 0-4 is even higher: 32% (with 42% in Africa), compared 300 200 100 0 100 200 300 with 17% in developed countries. We live in a demo- graphically divided world, as shown in Figure 9-10. Population (millions) The youthful age structure of most developing countries contributes to an unemployment crisis. Developing Countries In parts of Asia, Africa, and Latin America with 85+ rapid population growth and youthful age structures 80-85 20-50% of the 15-24 age group is unemployed. This 75-79 70-74 provides a tinderbox for social unrest and recruits for 65-69 terrorist activities. 60-64 55-59 Rapid population growth and cultural and reli- 50-54 :g, 45-49 gious conflicts can also lead to political tensions and -c 40-44 armed conflict within countries such as the African 35-39 30-34 country of Rwanda. Between 1950 and 1993, its popu- 25-29 lation tripled. By 1991, the demand for firewood was 20-24 15-19 twice the sustainable yield of local forests. As trees dis- 10-14 appeared, crop residues were burned for heat and 5-9 0-4 cooking. This reduced soil fertility and decreased crop 300 200 100 0 100 200 300 productivity. Desperation for food and land grew and when a Population (millions) 1994 plane crash killed the country's president, an or- Figure 9·10 Gbfx;i ccnnections: population structure by ganized attack by Hutus led to an estimated 800,000 age and sex in developing countries and developed countries, deaths of Tutsi people within 100 days with the Hutus 2006. (Data from United Nations Population Division and claiming precious plots of land. Population Reference Bureau)

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Using Age Structure Diagrams to Make of seniors with the needs of the rest of the population, Population and Economic Projections at levels of taxation that don't strangle the economy. (Science, Economics, and Politics) In other respects, the baby-bust generation should have an easier time than the baby-boom generation. Changes iI1 the distribution of a country's age Fewer people will be competing for educational op- groups have long-lasting sconornic and social portunities, jobs, and services. Also, labor shortages impacts, may drive up their wages, at least for jobs requiring Between 1946 and 1964, the United States had a baby education or technical training beyond high school. boom that added 79 million people to its population, However, this may not happen if many American- Over time, this group looks like a bulge moving owned companies operating at the global level (multi- up through the country's age structure, as shown in national companies) continue to export many low- and Figure 9-11. high-paying jobs to other countries. ...~ Today baby boomers make up nearly half of all Members of the baby-bust group may find it diffi- adult Americans, As a result, they dominate the popu- cult to get job promotions as they reach middle age be- lation's demand for goods and services and play in- cause members of the much larger baby-boom group creasingly important roles in deciding who gets will occupy most upper-level positions. And many elected and what laws are passed, Baby boomers who baby boomers may delay retirement because of im- created the youth market in their teens and twenties proved health, the need to accumulate adequate retire- are now creating the 50-something market and will ment funds, or extension of the retirement age at soon move on to create a 60-something market. After which they can collect Social Security. 2011, when the first baby boomers will turn 65, the number of Americans older than age 65 will grow .jhornsorr Examine how the baby boom affects the /' i\~O~'VjU,S, age structure over several decades at sharply through 2029. ~~~~y:¥ ..• ThomsonNOW. According to some analysts, the retirement of baby boomers is likely to create a shortage of workers in the United States unless immigrant workers replace Stable Populations in Some Countries some of them. Retired baby boomers are also likely to (Science and Economics) use their political clout to force the smaller number of About 13~/oof the world's people live ill. countries people in the baby-bust generation (Figure 9-6) to pay with stabilized or declining populations, higher income, health-care, and Social Security taxes, An important U.S. public policy question is how In 2006, about 884 million people lived in 41 countries the country will balance the needs of growing numbers with essentially stable (annual growth rates at or be-

Age Age Age Age

Females Females Males Females Males

1955

ThomsonNOW' Active Figure 9-11 Tracking the baby-boom generation in the United States, See an animation based on this figure and take a short quiz on the concept, (Data from Population Reference Bureau and U,S, Census Bureau)

180 CHAPTER 9 Applying Population Ecology: The Human Population and Its Impact