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Demographic Transition & Population Growth Factors
- 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 4 Lecture Outline
- 2. Learning Outcomes After studying this chapter, you should be able to answer the following questions: • Why are we concerned about human population growth? • Will the world’s population double again as it did between 1965 and 2000? • What is the relationship between population growth and environmental impact? • Why has the human population grown so rapidly since 1800? • How is human population growth changing in different parts of the world? • How does population growth change as a society develops? • What factors slow down or speed up human population growth? 4-2
- 3. For every complex problem there is an answer that is clear, simple, and wrong. –H. L. Mencken 4-3
- 4. 4.1 Past and Current Population Growth Are Very Different • Every second, on average, four or five children are born, somewhere on the earth. In that same second, two other people die. • The U.S. Census Bureau estimates the mid- 2008 world population to be about 6.7 billion people and growing at 1.15 percent per year. 4-4
- 5. Human populations grew slowly until recently 4-5
- 6. Human populations throughout history 4-6
- 7. 4.2 Perspectives on Population Growth • Does environment or culture control human population growth? • Technology increases carrying capacity for human beings. • Population growth could bring benefits, such as economic growth. 4-7
- 8. 4.3 Many Factors Determine Population Growth • Terminology – Demography encompasses vital statistics about people, such as births, deaths, and where they live, as well as total population size. – Fecundity is the physical ability to reproduce, while fertility is the actual production of offspring. – The total fertility rate is the number of children born to an average woman in a population during her entire reproductive life. – Zero population growth (ZPG) occurs when births plus immigration in a population just equal deaths plus emigration. 4-8
- 9. 4.3 Many Factors Determine Population Growth continued… • Factors affecting population growth –Fertility varies among cultures and at different times –Mortality offsets births –Life expectancy is rising worldwide –Living longer has profound social implications 4-9
- 10. Fertility varies among cultures and at different times • Fertility rates have declined dramatically in every region of the world except Africa over the past 50 years. 4-10
- 11. Life expectancy • Life span is the oldest age to which a species is known to survive. • Life expectancy is the average age that a newborn infant can expect to attain in any given society. 4-11
- 13. People want children for many reasons • Factors that increase people’s desires to have babies are called pronatalist pressures. • Children may be the only source of support for elderly parents in countries without a social security system. • Often children are valuable to the family not only for future income but even more as a source of current income and help with household chores. • Society also has a need to replace members who die or become incapacitated. 4-13
- 14. Education and income affect the desire for children • Highly developed countries. – Higher education and personal freedom affect women to not have children. – The desire to spend time and money on other priorities limits the number of children. • Less-developed countries – Feeding and clothing is minimally expensive, adding one more child is negligible. 4-14
- 15. 4.5 A Demographic Transition Can Lead to Stable Population Size • Demographic transition is a typical pattern of falling death rates and birth rates due to improved living conditions that usually accompanies economic development. 4-15
- 16. Stage II • Economic and social conditions change mortality and births – Stage I in figure 4.13 represents the conditions in a premodern society. 4-16
- 17. Stage II • Economic development in Stage II brings better jobs, medical care, sanitation, and a generally improved standard of living, and death rates often fall very rapidly. 4-17
- 18. Stage III • Note that populations grow rapidly during Stage III when death rates have already fallen but birth rates remain high. 4-18
- 19. Stage IV • Stage IV represents conditions in developed countries, where the transition is complete and both birth rates and death rates are low, often a third or less than those in the predevelopment era. 4-19
- 20. 4-20
- 21. The following factors help stabilize populations: • Growing prosperity and social reforms that accompany development reduce the need and desire for large families in most countries. • Technology is available to bring advances to the developing world much more rapidly than was the case a century ago. • Less-developed countries have historic patterns to follow. • Modern communications (especially television) have caused a revolution of rising expectations that act as stimuli to spur change and development. 4-21
- 22. Two ways to complete the demographic transition • The Indian states of Kerala and Andra Pradesh exemplify two approaches to population growth. – Social justice strategy: In Kerala, providing a fair share of social benefits to everyone was the key to completing the demographic transition. – Birth control strategy: Andra Pradesh adopted a strategy of aggressively promoting birth control, rather than social justice 4-22
- 23. Improving women’s lives helps reduce birth rates • A broad consensus reached by the 180 participating countries agreed that : – responsible economic development, – education and empowerment of women, and – high-quality health care (including family planning services) must be accessible to everyone if population growth is to be slowed. 4-23
- 24. Total fertility declines as women’s education increases 4-24
- 25. 4.6 Family Planning Gives Us Choices • Family planning allows couples to determine the number and spacing of their children. • Birth control usually means any method used to reduce births. 4-25
- 26. The major categories of birth control techniques (1) avoidance of sex during fertile periods (for example, celibacy or the use of changes in body temperature or cervical mucus to judge when ovulation will occur) (2) mechanical barriers that prevent contact between sperm and egg (for example, condoms, spermicides, diaphragms, cervical caps, and vaginal sponges) (3) surgical methods that prevent release of sperm or egg (for example, tubal ligations in females and vasectomies in males) (4) hormone-like chemicals that prevent maturation or release of sperm or eggs or that prevent embryo implantation in the uterus (for example, estrogen plus progesterone, or progesterone alone, for females; gossypol for males) (5) physical barriers to implantation (for example, intrauterine devices) (6) abortion. 4-26
- 27. 4-27
- 28. 4.7 What Kind of Future Are We Creating Now? • Most demographers believe that world population will stabilize sometime during the twenty-first century. • When we reach that equilibrium, the total number of humans is likely to be somewhere around 8 to 10 billion. 4-28
- 29. 4-29
- 30. Practice Quiz 1. About how many years of human existence passed before the world population reached its first billion? What factors restricted population before that time, and what factors contributed to growth after that point? 2. Describe the pattern of human population growth over the past 200 years. What is the shape of the growth curve (recall chapter 3)? 3. Define ecological footprint. Why is it helpful, but why might it also be inaccurate? 4. Why do some economists consider human resources more important than natural resources in determining a country’s future? 4-30
- 31. Practice Quiz continued… 5. In which regions of the world will most population growth occur during the twenty-first century? What conditions contribute to rapid population growth in these locations? 6. Define crude birth rate, total fertility rate, crude death rate, and zero population growth. 7. What is the difference between life expectancy and life span? Why are they different? 8. What is the dependency ratio, and how might it affect the United States in the future? 9. What factors increase or decrease people’s desire to have babies? 10. Describe the conditions that lead to a demographic transition. 4-31
Editor's Notes
- Every second, on average, four or five children are born, somewhere on the earth. In that same second, two other people die. This difference between births and deaths means a net gain of roughly 2.3 more humans per second in the world’s population. The U.S. Census Bureau estimates the mid-2008 world population to be about 6.7 billion people and growing at 1.15 percent per year. This means we are adding roughly 75 million more people per year. Humans are now one of the most numerous vertebrate species on the earth. We also are more widely distributed and manifestly have a greater global environmental impact than any other species. For the families to whom these children are born, each birth may be a joyous and long-awaited event (fig. 4.2). But is a continuing increase in humans good for the planet in the long run?
- For most of our history, humans were not very numerous, compared with other species. Studies of hunting and gathering societies suggest that the total world population was probably only a few million people before the invention of agriculture and the domestication of animals around 10,000 years ago. The agricultural revolution produced a larger and more secure food supply and allowed the human population to grow, reaching perhaps 50 million people by 5000 b.c. For thousands of years, the number of humans increased very slowly. Archaeological evidence and historical descriptions suggest that only about 300 million people were living at the time of Christ (table 4.1).
- As you can see in figure 4.3, human populations began to increase rapidly after about a.d. 1600. Many factors contributed to this rapid growth. Increased sailing and navigating skills stimulated commerce and communication among nations. Agricultural developments, better sources of power, and better health care and hygiene also played a role. We are now in an exponential, or J curve, pattern of growth, described in chapter 3.
- Since the time of the Industrial Revolution, when the world population began growing rapidly, individuals have argued about the causes and consequences of population growth. In 1798 Thomas Malthus (1766–1834) wrote An Essay on the Principle of Population, changing the way European leaders thought about population growth. Malthus marshaled evidence to show that populations tended to increase at an exponential, or compound, rate while food production either remained stable or increased only slowly. Eventually human populations would outstrip their food supply and collapse into starvation, crime, and misery. He converted most economists of the day from believing that high fertility increased gross domestic output to believing that per capita output actually fell with rapidly rising population. Several decades later, the economist Karl Marx (1818–1883) presented an opposing view, that population growth resulted from poverty, resource depletion, pollution, and other social ills. Optimists argue that Malthus was wrong in his predictions of famine and disaster 200 years ago because he failed to account for scientific and technical progress. In fact, food supplies have increased faster than population growth since Malthus’ time. Think of the gigantic economic engine that China is becoming as it continues to industrialize and its population becomes more affluent. More people mean larger markets, more workers, and efficiencies of scale in mass production of goods. Moreover, adding people boosts human ingenuity and intelligence that will create new resources by finding new materials and discovering new ways of doing things. Economist Julian Simon (1932–1998), a champion of this rosy view of human history, believed that people are the “ultimate resource” and that no evidence suggests that pollution, crime, unemployment, crowding, the loss of species, or any other resource limitations will worsen with population growth. In a famous bet in 1980, Simon challenged Paul Ehrlich, author of The Population Bomb, to pick five commodities that would become more expensive by the end of the decade. Ehrlich chose metals that actually became cheaper, and he lost the bet.
- Fertility rates have declined dramatically in every region of the world except Africa over the past 50 years (fig. 4.6). In the 1960s, total fertility rates above 6 were common in many countries. The average family in Mexico in 1975, for instance, had 7 children. By 2005, however, the average Mexican woman had only 2.6 children. According to the World Health Organization, 61 of the world’s 190 countries are now at or below a replacement rate of 2.1 children per couple. The greatest fertility reduction has been in Southeast Asia, decades. Contrary to what many demographers expected, some of the poorest countries in the world have been remarkably successful in lowering growth rates. Bangladesh, for instance, reduced its fertility rate from 6.9 in 1980 to only 3.0 children per woman in 2005. China’s one-child-per-family policy decreased the fertility rate from 6 in 1970 to 1.8 in 1990 (fig. 4.7). This policy, however, along with a strong preference for sons, has sometimes resulted in abortions, forced sterilizations, and even infanticide. It also has been so successful that the government is now worried about a shortage of workers. By mid century, at least one-third of the Chinese population will be retirees, if current trends continue.
- For most of human history, life expectancy in most societies probably has been 35 to 40 years. This doesn’t mean that no one lived past age 40 but, rather, that many people died at earlier ages (mostly early childhood), which balanced out those who managed to live longer. The twentieth century saw a global transformation in human health unmatched in history. This revolution can be seen in the dramatic increases in life expectancy in most places (table 4.3). Worldwide, the average life expectancy rose from about 40 to 67.2 years over the past 100 years.
- A population growing rapidly by natural increase has more young people than does a stationary population. One way to show these differences is to graph age classes in a histogram, as figure 4.9 shows. In Niger, which is growing at a rate of 3.5 percent per year, 47.8 percent of the population is in the prereproductive category (below age 15). Even if total fertility rates fell abruptly, the total number of births, and the population size, would continue to grow for some years as these young people entered reproductive age. This phenomenon is called population momentum. By contrast, a country with a relatively stable population will have nearly the same number in most cohorts. Notice that females outnumber males in Sweden’s oldest group because of differences in longevity between sexes. A rapidly declining population, such as Singapore’s, can have a pronounced bulge in middle-age cohorts as fewer children are born than in their parents’ generation. Both rapidly growing countries and slowly growing countries can have a problem with their dependency ratio, or the number of nonworking compared with working individuals in a population. In Niger, for example, each working person supports a high number of children. In the United States, by contrast, a declining working population is now supporting an ever larger number of retired persons.
- Children can be a source of pleasure, pride, and comfort. They may be the only source of support for elderly parents in countries without a social security system. Where infant mortality rates are high, couples may need to have many children to ensure that at least a few will survive to take care of them when they are old. Where there is little opportunity for upward mobility, children give status in society, express parental creativity, and provide a sense of continuity and accomplishment otherwise missing from life. Often children are valuable to the family not only for future income but even more as a source of current income and help with household chores. In much of the developing world, small children tend domestic animals and younger siblings, fetch water, gather firewood, help grow crops, or sell things in the marketplace (fig. 4.11). Parental desire for children rather than an unmet need for contraceptives may be the most important factor in population growth in many cases. Society also has a need to replace members who die or become incapacitated. This need often is codified in cultural or religious values that encourage bearing and raising children. Some societies look upon families with few or no children with pity or contempt. The idea of deliberately controlling fertility may be shocking, even taboo. Women who are pregnant or have small children have special status and protection. Boys frequently are more valued than girls because they carry on the family name and are expected to support their parents in old age. Couples may have more children than they really want in an attempt to produce a son. Male pride often is linked to having as many children as possible. In Niger and Cameroon, for example, men, on average, want 12.6 and 11.2 children, respectively.
- In more highly developed countries, many pressures tend to reduce fertility. Higher education and personal freedom for women often result in decisions to limit childbearing. A desire to spend time and money on other goods and activities offsets the desire to have children. When women have opportunities to earn a salary, they are less likely to stay home and have many children. In less-developed countries, where feeding and clothing children can be a minimal expense, adding one more child to a family usually doesn’t cost much.
- In 1945 demographer Frank Notestein pointed out that a typical pattern of falling death rates and birth rates due to improved living conditions usually accompanies economic development. He called this pattern the demographic transition from high birth and death rates to lower birth and death rates. Figure 4.13 shows an idealized model of a demographic transition. This model is often used to explain connections between population growth and economic development.
- Stage I in figure 4.13 represents the conditions in a premodern society. Food shortages, malnutrition, lack of sanitation and medicine, accidents, and other hazards generally keep death rates in such a society around 30 per 1,000 people. Birth rates are correspondingly high to keep population densities relatively constant.
- Economic development in Stage II brings better jobs, medical care, sanitation, and a generally improved standard of living, and death rates often fall very rapidly. Birth rates may actually rise at first as more money and better nutrition allow people to have the children they always wanted. In a couple of generations, however, birth rates fall as people see that all their children are more likely to survive and that the whole family benefits from concentrating more resources on fewer children.
- Note that populations grow rapidly during Stage III when death rates have already fallen but birth rates remain high. Depending on how long it takes to complete the transition, the population may go through one or more rounds of doubling before coming into balance again. Many of the most rapidly growing countries in the world, such as Kenya, Yemen, Libya, and Jordan, now are in Stage III of this demographic transition. Their death rates have fallen close to the rates of the fully developed countries, but birth rates have not fallen correspondingly. In fact, both their birth rates and total population are higher than those in most European countries when industrialization began 300 years ago. The large disparity between birth and death rates means that many developing countries now are growing at 3 to 4 percent per year.
- Stage IV represents conditions in developed countries, where the transition is complete and both birth rates and death rates are low, often a third or less than those in the predevelopment era. The population comes into a new equilibrium in this phase, but at a much larger size than before. Most of the countries of northern and western Europe went through a demographic transition in the nineteenth or early twentieth century similar to the curves shown in figure 4.13. In countries such as Italy, where fertility levels have fallen below replacement rates, there are now fewer births than deaths, and the total population curve has started to decline. A huge challenge facing countries in the final stage of the demographic transition is the imbalance between people in their most productive years and people who are retired or in their declining years. The debate in the U.S. Congress about how to fund the social security system is due to the fact that, when this program was established, the United States was in the middle of the demographic transition, with a large number of young people relative to older people. In ten to fifteen years, that situation will change, with many more elderly people living longer, and fewer younger workers to support them.
- Growing prosperity and social reforms that accompany development reduce the need and desire for large families in most countries. Technology is available to bring advances to the developing world much more rapidly than was the case a century ago, and the rate of technology exchange is much faster than it was when Europe and North America were developing. Less-developed countries have historic patterns to follow. They can benefit from the mistakes of more-developed countries and chart a course to stability relatively quickly. Modern communications (especially television) have caused a revolution of rising expectations that act as stimuli to spur change and development.
- The Indian states of Kerala and Andra Pradesh exemplify two approaches to population growth (see What Do You Think? p. 88). In Kerala, providing a fair share of social benefits to everyone was the key to completing the demographic transition. This social justice strategy assumes that the world has enough resources for everyone, but inequitable social and economic systems cause maldistributions of those resources. Hunger, poverty, violence, environmental degradation, and overpopulation are symptoms of a lack of justice, rather than a lack of resources. Although overpopulation exacerbates other problems, a focus on overpopulation alone encourages racism and hatred of the poor. Proponents of the social justice view argue that people in the richer nations should recognize their excess consumption levels and the impact that this consumption has on others (fig. 4.14). The leaders of Andra Pradesh, on the other hand, adopted a strategy of aggressively promoting birth control, rather than social justice. This strategy assumes that better access to birth control is the key to reducing populations, and that social justice is an unrealistic goal.
- Family planning allows couples to determine the number and spacing of their children. It doesn’t necessarily mean fewer children—people could use family planning to have the maximum number of children possible—but it does imply that the parents will control their reproductive lives and make rational, conscious decisions about how many children they will have and when those children will be born, rather than leaving it to chance. As the desire for smaller families becomes more common, birth control often becomes an essential part of family planning. In this context, birth control usually means any method used to reduce births, including celibacy, delayed marriage, contraception, methods that prevent embryo implantation, and induced abortions.
- The United Nations Population Division projects four population scenarios (fig. 4.16). The optimistic (low) projection suggests that world population might stabilize by about 2030 and then drop back below current levels. This is not likely. The medium projections suggest that growth could continue until at least 2050, at which point the total world population could be 11 to 13 billion.