# Population growth

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# Population Growth

Population growth refers to change in the size of a populationwhich can be either positive or negativeover time, depending on the balance of births and deaths. If there are many deaths, the world's population will grow very slowly or can even decline. Population growth is measured in both absolute and relative terms. Absolute growth is the difference in numbers between a population over time; for example, in 1950 the world's population was 4 billion, and in 2000 it was 6 billion, a growth of 2 billion. Relative growth is usually expressed as a rate or a percentage; for example, in 2000 the rate of global population growth was 1.4 percent (or 14 per 1,000). For every 1,000 people in the world, 14 more are being added per year.

For the world as a whole, population grows to the extent that the number or rate of births exceeds the number or rate of deaths. The difference between these numbers (or rates) is termed "natural increase" (or "natural decrease" if deaths exceed births). For example, in 2000 there were 22 births per 1,000 population (the number of births per 1,000 population is termed the "crude birth rate") and 9 deaths per 1,000 population (the "crude death rate"). This difference accounts for the 2000 population growth rate of 14 per 1,000, which is also the rate of natural increase. In absolute numbers, this means that approximately 78 million peopleor about the population of the Philippinesare added to the world each year. For countries, regions, states, and so on, population growth results from a combination of natural increase and migration flows. The rate of natural increase is equivalent to the rate of population growth only for the world as a whole and for any smaller geographical units that experience no migration.

Populations can grow at an exponential rate, just as compound interest accumulates in a bank account. One way to assess the growth potential of a population is to calculate its doubling timethe number of years it will take for a population to double in size, assuming the current rate of population growth remains unchanged. This is done by applying the "rule of seventy"; that is, seventy divided by the current population growth rate (in percent per year). The 1.4 percent global population growth rate in 2000 translates into a doubling time (if the growth rate remains constant) of fifty-one years.

## History of Global Population Growth

As can be seen in Figure 1, the world's population grew very slowly until about 1750. There was a long period of stationary growth (no growth) until 1000 b.c.e., when the world's population was approximately 300 million; this was followed by a period of slow growth from 1000 b.c.e. to approximately 1750, at which time global population was an estimated 800 million. Until this time, the world's population was kept in check by high death rates, which were due to the combined effects of plagues, famines, unsanitary living conditions, and general poverty. After 1750, the world's population grew substantially; by 1950 it had tripled to around 2.5 billion. In this 200-year period, the doubling time was 122 years. Growth from 1950 to 1985 was even more dramatic; by 1985, the human population was 5 billion. World population had doubled in thirty-five years. By 2000 global population was 6 billion and is projected to be 9 billion in 2050.

Population growth did not become exponential until around 1750. Before that, high mortality counterbalanced the high fertility needed by agrarian parents. Death rates were high and life expectancy was low; life expectancy at birth was in the range of twenty to forty years (most likely around thirty years) until the middle of the eighteenth century. This high mortality was a function of several factors, including poor nutrition, which led directly to deaths through starvation and indirectly through increasing susceptibility to disease; epidemics; and, quite possibly, infanticide and geronticide, especially during times of food shortage.

Starting in the middle of the eighteenth century, the mortality rate began to decline in the West, the first place in the world where the natural balance between births and deaths was altered by humans. This decline in deaths occurred not because of major medical breakthroughs (e.g., penicillin was first used only in the 1940s) but rather because of improvements in food availability, housing, water cleanliness, personal hygiene, and public sanitation. Later, in the twentieth century, medical advances, particularly vaccinations against infectious diseases, accelerated mortality decline. Western mortality decline was relatively slow, paralleling socioeconomic development, and it occurred in a global context in which European population "surplus" (arising from gaps between lowering mortality and more slowly lowering fertility) was able to migrate to new areas (e.g., the United States, Canada, and Australia) that were very sparsely populated by Aboriginal peoples (whose numbers were reduced even more by contagious diseases brought by Europeans).

Mortality decline in less developed countries followed a different path. First, mortality decreases did not begin until around 1950, much later than in the West. Second, in many less developed countries, substantial mortality reductions occurred in a short period of time. A classic example is Ceylon (now Sri Lanka), where the death rate was halved in less than a decade, starting in the early 1950s. (In the West, a comparable reduction typically took around one century.) In these less developed countries, mortality decreases were not matched by fertility decreases, where they produce population growth rates much greater than those experienced in the West. So the demographic transition that took two centuries to unfold in the West occurred (or is occurring) within the span of a single life. Third, mortality decline did not parallel economic development. Rather, the impetus behind third world mortality reductions originated, for the most part, in factors external to the society. For example, the speedy mortality decline in Ceylon was due to the importation of American technology (pesticides and the airplanes for spraying them) that killed the mosquitoes that were responsible for malaria, the leading cause of death. During the cold war, it was not uncommon for the United States to provide nonaligned countries with such assistance in the hopes of wooing them away from the Soviet Union and a communist development model.

As a result, the world witnessed unprecedented rapid population growth between 1950 and 1985, owing, in large part, to third world increases. Further, the phenomenal increase in human numbers over the past 250 years is largely the consequence of mortality declinesnot fertility increases. The first deaths to be reduced were those due to infectious diseases, the victims of which were most often children. The old killers of the past were to be replaced by chronic and degenerative diseases; the primary victims shifted from the young to the old.

## Population Growth 1950–2050

The rate of global population growth has declined significantly from its 1970s highs (see Figure 2). Current estimates anticipate a continued decline to about 0.5 percent in 2050. This corresponds to a doubling time of 140 years, a rate that has fostered concern about how the world will cope with 18 billion people in 2190.

It is in the less developed countries that the continued growth in population will occur in the twenty-first century. Even though mortality is much higher in less developed countries (e.g., life expectancy at birth in 2000 was 75 years in the more developed countries and 62 to 64 years in the less developed countries), fertility remains even higher, thus accounting for relatively high growth in the third world. However, projections are not guarantees. Population may grow more slowly if, optimistically, fertility declines more quickly than experts expect (e.g., between just 1965 and 1987 the average number of children born to Thai women dropped from 6.3 to 2.2) or, pessimistically, if mortality increases, especially in light of the persistence of HIV/AIDS pandemic and other communicable diseases.

## Theories of Population Growth

While theories about population growth first appeared in ancient Greece, the English clergyman and economist Thomas Malthus (17661834) is considered to be the pioneering theorist of the modern age. Malthus formulated a "principle of population" that held that unchecked population grows more quickly than the means of subsistence (food and resources) to sustain it. Population will be controlled either by preventive checks (lowering the number of births, particularly by postponement of marriage age) or by positive checks (increasing deaths as a result of famines, plagues, natural disasters, war). Given a morally based preference for preventive checks, later followers of Malthus (neo-Malthusians) have supported family planning and contraception even though Malthus himself felt that contraception was unacceptable. Other neo-Malthusians have focused upon the claimed negative effects of rapid population growth: war, violence, and environmental degradation.

Karl Marx's views on population were directly opposed to those of Malthus. Marx disagreed with the Malthusian idea of a universal principle of population that applied to all societies. For Marx, population growth depended upon the economic base of society. Thus, capitalist society is characterized by its own population principle, which Marx termed the "law of relative population surplus." He argued that capitalism creates overpopulation (i.e., a surplus of people relative to jobs), leading to increased unemployment, cheap labor, and poverty. Also, capitalism requires unemployment in order to ensure a docile, low-paid class of laborers. Marx envisioned that overpopulation would not occur in postcapitalist, communist society.

In the middle of the twentieth century, demographic transition theory became the dominant theory of population growth. Based on observed trends in Western European societies, it argues that populations go through three stages in their transition to a modern pattern. Stage One (pretransition) is characterized by low or no growth, and high fertility is counterbalanced by high mortality. In Stage Two (the stage of transition), mortality rates begin to decline, and the population grows at a rapid pace. By the end of this stage, fertility has begun to decline as well. However, because mortality decline had a head start, the death rate remains lower than the birth rate, and the population continues to experience a high rate of growth. In Stage Three (posttransition), the movement to low fertility and mortality rates is complete, producing once again a no-growth situation. The theory of demographic transition explains these three stages in terms of economic development, namely industrialization and urbanization. Since about 1980, demographic transition theory has been criticized on a number of grounds, including its assumption that the demographic experience of non-Western societies will inevitably follow that of the West; its failure to consider cultural variables; and its hypothesized relationship between population growth and economic development. Indeed, all three theories above contain assumptions about population growth and economic development; however, there is mounting evidence that this relationship is complex and varies from context to context. As the twenty-first century begins, the attempt to erect a general theory of population growth has been abandoned, signaling for some an alarming trend in population studies.

See also: Causes of Death; Demographics and Statistics; Life Expectancy; Malthus, Thomas; Social Functions of Death; Technology and Death

## Bibliography

Brown, Lester R., Gary T. Gardner, and Brian Halweil. Beyond Malthus: Nineteen Dimensions of the Population Challenge. New York: W. W. Norton, 1999.

Coale, Ansley J. "The History of the Human Population." Scientific American 231 (1974):4051.

Ehrlich, Paul R., and Anne H. Erhlich. The Population Explosion. New York: Simon and Schuster, 1990.

Furedi, Frank. Population and Development: A Critical Introduction. Cambridge, England: Polity Press, 1997.

Homer-Dixon, Thomas. Environment, Scarcity, and Violence. Princeton, NJ: Princeton University Press, 1999.

Keyfitz, Nathan. "Population Theory and Doctrine: A Historical Survey." In Alex Inkeles and Masamichi Sasaki eds., Comparing Nations and Cultures: Readings in a Cross-Disciplinary Perspective. Englewood Cliffs, NJ: Prentice-Hall, 1996.

Livi-Bacci, Massimo. Population and Nutrition: An Essay on European Demographic History. Cambridge: Cambridge University Press, 1991.

McKeown, Thomas. The Origins of Human Disease. Oxford: Basil Blackwell, 1988.

McKeown, Thomas. The Modern Rise of Population. London: Edward Arnold, 1976.

Overbeek, Johannes. History of Population Theories. Rotterdam, Netherlands: Rotterdam University Press, 1974.

Petersen, William. From Birth to Death: A Consumer's Guide to Population Studies. New Brunswick, NJ: Transaction Publishers, 2000.

Population Reference Bureau. World Population Data Sheet, 2000. Washington, DC: Author, 2000.

United Nations. Population Growth, Structure and Distribution: The Concise Report. New York: United Nations, Department of Economic and Social Affairs, 1999.

ELLEN M. GEE

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# Population Growth

BIBLIOGRAPHY

Population growth (positive or negative) is caused exclusively by the operation of fertility, mortality, and migration. Regarding the population growth of countries and other national populations, the effect of migration is normally not as influential as the effects of fertility and mortality, usually considered to be the major factors directly causing national population growth (Hinde 1998). However, regarding the population growth of the subareas (states, provinces, counties) of national populations, migration is the single most important of the three demographic processes. Differences in birthrates and death rates in subareas of the same country are typically small compared to differences between the subareas in migration. Migration is thus the major method for redistributing the population within a country.

Fertility is a source of population growth because the number of births indicates whether a population is in a growing pattern (Hinde 1998). If a fertility rate, say the total fertility rate (TFR), is above 2.0, this indicates that on average a woman has more than two children in her lifetime. If the TFR is above 2.1, it means that the woman on average has above replacement fertility, allowing the population to grow via fertility. Mortality is also important given that the death rate determines the number of people who will no longer be able to contribute to the growth of the population. Controlling fertility, countries with high age-specific death rates in infancy and childhood are more likely to have fewer people to give birth to children and thus slower and sometimes negative rates of population growth. Constant fertility and mortality rates typically produce constant population growth rates (Hinde 1998).

The rate of population growth is not only a demographic phenomenon, it also has a broad impact on the society and peoples lives. For instance, researchers have found relationships between population growth and economic growth (Barlow 1994; Blanchet 1992; Coale 1986). Robin Barlow (1994) has argued that in a relatively short period of time, an increase in fertility tends to have a negative effect on the economy, while in the long run the opposite relationship is true. Population growth can also lead to a rising demand for food. Problems of instability in food production are particularly difficult for some developing countries with high population growth rates and low technological changes in agriculture (Mellor 1982). In addition rapid population growth tends to impact the interactions between human beings and their environment. An increasing number of people in the population leads to pressures on land resources, which limits the amount of arable agricultural land and tends to worsen the situation of food supply and human reproduction (Shaw 1976). Furthermore a high rate of population growth is likely to increase population density in certain geographic areas, particularly urban settings. As a result overcrowding, unemployment, and poverty are likely to lead to social problems in some localities (Sibly and Hone 2002).

From a microperspective, the population growth rate also has significant influences on an individuals life. Researchers have found that population pressures tend to affect individuals social reactions. They either force individuals to withdraw from social life as methods of escape or protection due to social overload (Baum and Koman 1976; Evans et al. 2000), or they provoke competition for resources, which tends to amplify peoples aggressive behaviors (Calhoun 1962; Lorenz 1967). The latter reaction is often used to explain deviant social behavior in overly crowded areas (Regoeczi 2002). Residential overcrowding has also been found to have an effect on individual well-being and family relations. Children in crowded households have sometimes been observed to have difficulties in behavioral adjustment at school, to perform poorly in academic settings, and to have vulnerable relationships with their parents (Evans et al. 1998). Highly populated households have been shown to increase marital instability and result in the more frequent disciplining of children (Fuller et al. 1993). Previous research has also noted that the impacts of overcrowding on individuals often vary among different subgroups. High-density homes with mothers, children, or low-status individuals are more likely to be problematic compared to other subgroups, and they tend to report more health complaints than other subgroups (Baldassare 1981). All the above effects of high population density on individuals are considered largely mediated by psychological stress (Fuller et al. 1993, p. 410). Individuals, however, are not only passively affected by the condition of crowdedness, they can also be adaptive to the social context. Residential overcrowding has been considered a well-known feature of the immigrant experience in the United States, especially in Southern California. Researchers find such an overcrowding situation has been reduced due to the growth of immigrants incomes, although patterns of decline in overcrowding vary significantly among different racial groups (Myers and Lee 1996). This phenomenon provides an example of how individuals improve the situation of overcrowdedness.

Even though psychological stress is treated as the major mediator shaping the manner in which crowding impacts individuals, other factors have been found to play a role through interaction with psychological pressures. These factors include social support for children and parents, gender, and interactions among individuals. Social support is important because individuals in crowded families are often associated with deteriorating social support structures, which may intensify an individuals psychological pressure (Evans et al. 1998). Gender is often related to the level of stress and an individuals behavior. It has been found that stress is more marked among males than among females in high-density locations (Evans et al. 1998; Freedman et al. 1972; Paulus 1988). Moreover interaction among household members tends to determine the way individuals handle psychological stress (Evans et al. 1998). Thus providing social support for crowded families, especially for males, and strengthening parent-child interaction and family members communication may reconcile the problems in overcrowded households.

At the societal level many countries and places with rapid population growth rates and high population densities have developed a number of strategies to slow down their population growth. China, the country with the largest population in the world (almost 1.3 billion people in 2005) has made considerable efforts to reduce its fertility and control its population growth. These efforts include the later, longer, and fewer policy (later marriage, longer intervals between births, and fewer children) in the early 1970s (Qian 1983) and the nationwide one-birth policy announced in 1979. Consequently, along with social and economic developments, China has experienced a remarkable decline in fertility since the 1970s (Poston 2000), and this has led to considerable population control in China. These programs, however, have also raised demographic and social concerns. One of them is the unbalanced sex ratio at birth (SRB) in China. Due to the strong tradition of son preference and the policy constraints of one birth per couple, the selective abortion of female fetuses and the underreporting of female babies have led to extremely high SRBs in China since the 1980s (Zeng et al. 1993); that is, there are more boys born every year than girls. It is estimated that between the years of 2000 and 2025, there will be more than 31.6 million marriage-age Chinese males who will not be able find Chinese brides. There will not be enough Chinese women in the marriage market for them to marry. These bare branches may possibly result in increases in sexual crimes owing to forced marriages, girls stolen for wives, bigamy, prostitution, rape, and adultery (Poston and Zhang 2007). The surplus boys could eventually threaten national stability and international security. Thus it is crucial to strategically coordinate the population growth rate, resources, and social and economic development.

SEE ALSO Demography; Economic Growth; Fertility, Human; Migration; Morbidity and Mortality; Population Control

## BIBLIOGRAPHY

Baldassare, Mark. 1981. The Effects of Household Density on Subgroups. American Sociological Review 46: 110118.

Barlow, Robin. 1994. Population Growth and Economic Growth: Some More Correlations. Population and Development Review 20: 153165.

Baum, Andrew, and Stuart Koman. 1976. Differential Response to Anticipated Crowding: Psychological Effects of Social and Spatial Density. Journal of Personality and Social Psychology 34: 526536.

Blanchet, Didier. 1992. Reversal of the Effects of Population Growth on Economic Growth since the End of the 1970s: Reality or Artefact? Paper prepared for the Population Division, Department of Economic and Social Development, United Nations.

Calhoun, John B. 1962. Population Density and Social Pathology. Scientific American 206: 139148.

Coale, Ansley J. 1986. Population Trends and Economic Development. In World Population and U.S. Policy: The Choices Ahead, ed. Jane Menken, 96104. New York: Norton.

Evans, Gary W., Stephen J. Lepore, B. R. Shejwal, and M. N. Palsane. 1998. Chronic Residential Crowding and Childrens Well-Being: An Ecological Perspective. Child Development 69: 15141523.

Evans, Gary W., Eunju Rhee, Camille Forbes, et al. 2000. The Meaning and Efficacy of Social Withdrawal as Strategy for Coping with Chronic Residential Crowding. Journal of Environmental Psychology 20: 335342.

Freedman, Jonathan L., A. S. Levey, R. W. Buchanan, and J. Price. 1972. Crowding and Human Aggressiveness. Journal of Experimental Social Psychology 8: (6): 528548.

Fuller, Theodore D., John N. Edwards, Sairuee Vorakitphokatorn, and Santhat Sermsri. 1993. Household Crowding and Family Relations in Bangkok. Social Problems 40: 410430.

Hinde, Andrew. 1998. Demographic Methods. New York: Oxford University Press.

Lorenz, Konrad. 1967. On Aggression. Trans. Marjorie Latzke. London: Methuen.

Mellor, John W. 1982. The World Development: Food, Employment, and Growth Interactions. American Journal of Agricultural Economics 64: 304311.

Myers, Dowell, and Seong Woo Lee. 1996. Immigration Cohorts and Residential Overcrowding in Southern California. Demography 33: 5165.

Paulus, Paul B. 1988. Prison Crowding: A Psychological Perspective. New York: Springer-Verlag.

Poston, Dudley L., Jr. 2000. Social and Economic Development and Fertility Transition in Mainland China and Taiwan. Population and Development Review 26: 4060.

Poston, Dudley L., Jr., and Li Zhang. 2007. How Many Extra Boys Have Been Born in China? In Gender and Sexually Transmitted Infections in China, eds. X. Zheng, Dudley L. Poston, and B. Gu, 5076. Beijing: Beijing University Press.

Qian, Xinzhong. 1983. Chinas Population Policy: Theory and Methods. Studies in Family Planning 14: 295301.

Regoeczi, Wendy C. 2002. The Impact of Density: The Importance of Nonlinearity and Selection on Flight and Fight Responses. Social Forces 81: 505530.

Shaw, R. Paul. 1976. Government Perceptions of Population Growth. Population Studies 30: 7786.

Sibly, Richard M., and Jim Hone. 2002. Population Growth Rate and Its Determinants: An Overview. Philosophical Transactions: Biological Sciences 357: 11531170.

Zeng, Yi, Ping Tu, Baochang Gu, et. al. 1993. Causes and Implications of the Recent Increase in the Reported Sex Ratio at Birth in China. Population and Development Review 19: 283302.

Li Zhang

Dudley L. Poston Jr .

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## population growth

population growth The increase in a population that occurs when the birth rate is higher than the death rate, or when immigration exceeds emigration, or when a combination of these factors is present. A growth curve, obtained by plotting population size against time, is typically S-shaped (sigmoid) or J-shaped (see graph). A sigmoid growth curve shows an initial phase of exponential growth. The curve levels off when the environment has reached its carrying capacity, i.e. when food, space, and other conditions can support a given number of individuals without an increase in population numbers. A J-shaped growth curve shows an initial phase of exponential growth that ceases abruptly, with a sudden decrease in population numbers. This decrease may be caused by a number of factors, such as the end of the life cycle of the prey or any other factor contributing to environmental resistance that may suddenly take effect. See also bacterial growth curve.

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# POPULATION GROWTH

Populations increase as people are born or immigrate into a country, and decrease as people die or emigrate. Rates of population growth, usually expressed as a percentage, vary greatly. In the late twentieth century, growth rates in many European nations were extremely low, and in some parts of Eastern Europe and the former Soviet Union the growth rate was negativethat is, populations were declining in number. On the other hand, in some African and Latin American nations, the growth rate was around 4 percent, which is a doubling time of less than twenty years. The United States, as of the year 2000, had a growth rate of about 1 percent per annum.

John M. Last

(see also: Demography; Doubling Time; Population Density; Population Forecasts; Population Policies; Zero Population Growth )

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## population explosion

population explosion(population eruption) A sudden rapid increase in size of the population of a species or genus. The most violent explosions occur when a species is introduced into a new locality where it finds unexploited resources of suitable food, shelter, etc., and a lack of negative controls such as predators or parasites. Examples include the population explosions of the prickly pear (Opuntia) and of Rhododendron ponticum following the introduction of these species into Australia and Britain respectively. See r-selection.

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## population explosion

population explosion (population eruption) The sudden rapid increase in size of the population of a species or genus. The most violent explosions occur when a species is introduced into a new locality where it finds unexploited resources of suitable food, shelter, etc., and a lack of negative controls such as predators or parasites. Examples include the population explosions of the prickly pear and of Rhododendron ponticum following the introduction of these species into Australia and Britain respectively.

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## population explosion

population explosion (population eruption) A sudden rapid increase in size of the population of a species or genus. The most violent explosions occur when a species is introduced into a new locality where it finds unexploited resources of suitable food, shelter, etc., and a lack of negative controls such as predators or parasites. See r-SELECTION.