Population Growth

Implications of Different Rates of Growth

Different rates of growth can lead to overpopulation or underpopulation, both of which have potential consequences.

Learning Objectives

Discuss the implications both overpopulation and underpopulation can have for society

Key Takeaways

Key Points

  • When the fertility rate is at the replacement level, a population will remain stable, neither growing nor shrinking.
  • Fertility rates above the replacement level will cause the population to grow; fertility rates below the replacement level will cause the population to shrink.
  • Overpopulation is judged relative to carrying capacity and can have deleterious effects. When the population is too large for the available resources, famine, energy shortages, war, and disease can result.
  • Recently, in some countries, sub-replacement fertility rates have led to underpopulation. This can lead to economic decline, the aging of the population, and poverty.

Key Terms

  • fertility rate: The average number of children that would be born to a woman over her lifetime if she followed the current average pattern of fertility among a given group of women and survived through her reproductive years; used as an indicator of strength of population growth.
  • Replacement level: Regarding fertility, refers to the number of children that a woman must have in order to replace the existing population.
  • gross domestic product: (GDP) The market value of all officially recognized final goods and services produced within a country in a year; often used as an indicator of a country’s material standard of living.
  • carrying capacity: The number of individuals of a particular species that an environment can support.

Fertility rates refer to the rates of birth per 1,000 women of reproductive age in a given population. When the fertility rate is at the replacement level, a population will remain stable, neither growing nor shrinking. However, when the fertility rate deviates from the replacement level, the size of the population will change. Fertility rates above the replacement level will cause the population to grow; fertility rates below the replacement level will cause the population to shrink.

The population reached 6 billion people around 1999, and increased to around 7 billion by 2012. However, in some countries the birth rate is falling while the death rate is not, leading to a decline in the population growth rate. The population growth rate has been decreasing in higher income countries; however the number of people added to the global population each year continues to increase due to increasing growth rates in lower income countries.

Overpopulation

High fertility rates lead to population growth, which, under certain circumstances, can cause a condition known as “overpopulation. ” Overpopulation is not a function of the number or density of individuals, but rather the number of individuals compared to the resources they need to survive. In other words, it is a ratio: population to resources. Humans are not unique in their capacity for overpopulation; in general terms, overpopulation indicates a scenario in which the population of a living species exceeds the carrying capacity of its ecological niche.

When estimating whether an area is overpopulated, resources to be taken into account include clean water, food, shelter, arable land, and various social services (such as jobs, money, education, fuel, electricity, medicine, proper sewage and garbage management, and transportation).

Overpopulation can have deleterious effects. When population outstrips available resources, calamity can result, including famine, shortages of energy sources and other natural resources, rapid and uncontrolled spread of communicable diseases in dense populations, and war over scarce resources, such as land. Dense populations may also settle available land and crowd out other land uses, such as agriculture.

Different rates of growth

Presently, every year the world’s human population grows by approximately 80 million. However, that population growth is not distributed evenly across all countries. Most population growth comes from developing countries, where birthrates remain high. Meanwhile, about half the world lives in nations with sub-replacement fertility. In some of these countries, the population has actually begun to shrink (e.g., Russia). All of the nations of East Asia – with the exceptions of Mongolia, the Philippines, and Laos – have fertility rates below replacement level. Russia and Eastern Europe are dramatically below replacement fertility. Western Europe also is below replacement. In the Middle East Iran, Tunisia, Algeria, Turkey, and Lebanon are below replacement. Some countries still have growing populations due to high rates of immigration, but have native fertility rates below replacement: Canada, Australia, and New Zealand are similar to Western Europe, while the United States is just barely below replacement with about 2.0 births per woman.

A new fear for many governments, particularly those in countries with very low fertility rates, is that a declining population will lead to underpopulation and will reduce the gross domestic product (GDP) and economic growth of the country, as population growth is often a driving force of economic expansion. To combat extremely low fertility rates, some of these governments have introduced pro-family policies that include incentives, such as payments to parents for having children and extensive parental leave for parents.

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Slums in Mumbai: Rapid population growth in Indian cities has resulted in vast slums as populations have exceeded available land and housing.

Three Demographic Variables

The basics of demographic population growth depend on the rate of natural increase (births versus deaths) and net migration.

Learning Objectives

Explain how population growth is calculated

Key Takeaways

Key Points

  • Demography is the statistical study of human populations. It encompasses the study of the size, structure, and distribution of these populations, and spatial and/or temporal changes in them in response to birth, migration, aging, and death.
  • Population change depends on the rate of natural increase and net migration.
  • Natural increase is calculated by the fertility rate minus the mortality rate.
  • Net migration depends on in-migration and out-migration.

Key Terms

  • Natural increase: Population growth that depends on the fertility rate and the mortality rate.
  • Net migration: The difference of immigrants and emigrants of an area in a period of time, divided (usually) per 1,000 inhabitants (considered on midterm population). A positive value represents more people entering the country than leaving it, while a negative value mean more people leaving than entering it.
  • demography: The study of human populations and how they change.
  • mortality rate: The number of deaths per given unit of population over a given period of time.

Demography is the statistical study of human populations. It can be a very general science that can be applied to any kind of dynamic living population, or one that changes over time or space. It encompasses the study of the size, structure, and distribution of these populations, and spatial and/or temporal changes in them in response to birth, migration, aging, and death.

Human population growth depends on the rate of natural increase, or the fertility rate minus the mortality rate, and net migration. The basics of demography can be reduced to this formula:

(Births – Deaths) +/- ((In-Migration) – (Out Migration)) = Population Change.

As this equation shows, population change depends on three variables: (1) the natural increase changes seen in birth rates, (2) the natural decrease changes seen in death rates, and (3) the changes seen in migration. Changes in population size can be predicted based on changes in fertility, mortality, and migration rates.

Natural increase refers to the increase in population not due to migration, and it can be calculated with the fertility rate and the mortality rate. Net migration is the mathematical difference between those migrating into a country and those migrating out of a country.

This basic equation can be applied to populations and subpopulations. For example, the population size of ethnic groups or nationalities within a given society or country is subject to the same sources of change as the national population. However, when dealing with ethnic groups, “net migration” might have to be subdivided into physical migration and ethnic re-identification (assimilation). Individuals who change their ethnic self-labels or whose ethnic classification in government statistics changes over time may be thought of as migrating or moving from one population subcategory to another. More generally, while the basic demographic equation holds true by definition, the recording and counting of events (births, deaths, immigration, emigration) and the enumeration of the total population size are subject to error. Allowance needs to be made for error in the underlying statistics when any accounting of population size or change is made.

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US Fertility Rate: The US fertility rate has leveled off at about 2.0, which is nearly equal to the replacement level. This means that population growth in the US is due to inward migration, rather than a high birthrate.

Problems in Forecasting Population Growth

Population growth is difficult to predict because unforeseen events can alter birth rates, death rates, migration, or resource limitations.

Learning Objectives

Explain the various ways sociologist try to estimate the rate of population growth, such as through fertility, birth and death rates

Key Takeaways

Key Points

  • Population forecasts try to estimate the rate of population growth. However, unpredictable factors can change fertility rates, mortality rates, or migration rates, which can cause difficulty in forecasting.
  • Certain government policies are making it easier and more socially acceptable to use contraception and abortion methods. Likewise, some countries are instituting pro-natalist policies to encourage fertility.
  • Malthusian catastrophe refers to a scenario where overpopulation would compromise global food security, leading to mass starvation.
  • In the future, food production be increased by innovations such as genetically modified crops, more efficiently employing agricultural technology, and aquaculture. This would raise the limit on the number of people the world can support.

Key Terms

  • Green Revolution: Green Revolution refers to a series of research, development, and technology transfer initiatives, occurring between the 1940s and the late 1970s, that increased agriculture production around the world, beginning most markedly in the late 1960s
  • Birth rates: The birth rate is typically the rate of births in a population over time. The rate of births in a population is calculated in several ways: live births from a universal registration system for births, deaths, and marriages; population counts from a census, and estimation through specialized demographic techniques.
  • forecast: An estimation of a future condition.

Forecasts try to estimate the rate of population growth, but this is understandably difficult to predict. For example, the UN has issued multiple projections of future world population, based on different assumptions. From 2000 to 2005, the UN consistently revised these projections downward, until the 2006 revision, issued on March 14, 2007, revised the 2050 mid-range estimate upwards by 273 million. The UN now estimates that, by 2050, world population will reach 9 billion people. However, this forecast, like all population forecasts, is subject to change.

Population growth is difficult to predict because unforeseen events can alter birth rates, death rates, migration, or the resource limits on population growth. Birth rates may decline faster than predicted due to increased access to contraception, later ages of marriage, the growing desire of many women in such settings to seek careers outside of child rearing and domestic work, and the decreased economic “utility” of children in industrialized settings. Countries may also choose to undertake mitigation measures to reduce population growth. For example, in China, the government has put policies in place that regulate the number of children allowed to each couple. Other societies have already begun to implement social marketing strategies in order to educate the public on overpopulation effects. Certain government policies are making it easier and more socially acceptable to use contraception and abortion methods.

Such policies could have a significant effect on global fertility rates. Worldwide, nearly 40% of pregnancies are unintended (some 80 million unintended pregnancies each year). An estimated 350 million women in the poorest countries of the world either did not want their last child, do not want another child or want to space their pregnancies, but they lack access to information, affordable means and services to determine the size and spacing of their families. In the United States, in 2001, almost half of pregnancies were unintended. Fertility rates could be significantly reduced by providing education about overpopulation, family planning, and birth control methods, and by making birth-control devices like male/female condoms, pills, and intrauterine devices easily available. At the same time, other countries may roll back access to contraception, as has happened recently in Afghanistan. Or they may implement pro-natalist policies, like those seen in much of Europe where governments are concerned with sub-replacement fertility. Any of these changes could affect fertility rates and therefore alter forecasts of population growth.

At the same time, other factors could affect mortality rates, which would also alter population forecasts. Death rates could fall unexpectedly due to advances in medicine or innovations that stretch resources so population can continue to grow past what seemed like intractable resource limits. For example, in the mid-20th century, the Green Revolution in agriculture dramatically increased available food by spreading farming technology like fertilizer and increasing efficiency in agriculture. In the future, production might be increased by innovations such as genetically modified crops, more efficiently employing agricultural technology, and aquaculture.

At the same time, death rates can also increase unexpectedly due to disease, wars, and other mass catastrophes. According to some scenarios, disasters triggered by the growing population’s demand for scarce resources will eventually lead to a sudden population crash, or even a Malthusian catastrophe, where overpopulation would compromise global food security and lead to mass starvation.

Population Growth Forecasts: This video uses commonly cited statistics about population growth predictions to advocate for population control. The problem with activism surrounding population growth is that forecasts cannot predict unexpected changes in fertility and mortality rates.

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The Green Revolution: The Green Revolution was a period of rapid technological innovation in agricultural, which made food resources more widely available than expected and thus reduced the global mortality rate. This type of unanticipated change can reduce the accuracy of population forecasts.

Malthus’ Theory of Population Growth

Malthus believed that if a population is allowed to grow unchecked, people will begin to starve and will go to war over increasingly scarce resources.

Learning Objectives

Discuss Malthus’s controversial theory on population growth, in terms of the concept of “moral restraint”

Key Takeaways

Key Points

  • Thomas Malthus warned that without any checks, population would theoretically grow at an exponential rate, rapidly exceeding its ability to produce resources to support itself.
  • Malthus argued that an exponentially growing population will self-correct through war, famine, and disease.
  • Malthus cautioned that in order to avoid catastrophe such as famine and war, people should enact deliberate population control, such as birth control and celibacy.
  • Malthusian catastrophes refer to naturally occurring checks on population growth such as famine, disease, or war.
  • These Malthusian catastrophes have not taken place on a global scale due to progress in agricultural technology. However, many argue that future pressures on food production, combined with threats such as global warming, make overpopulation a still more serious threat in the future.

Key Terms

  • carrying capacity: The number of individuals of a particular species that an environment can support.
  • exponential growth: The growth in the value of a quantity, in which the rate of growth is proportional to the instantaneous value of the quantity; for example, when the value has doubled, the rate of increase will also have doubled. The rate may be positive or negative.
  • Malthusian catastrophes: Malthusian catastrophes are naturally occurring checks on population growth such as famine, disease, or war.

Early in the 19th century, the English scholar Reverend Thomas Malthus published “An Essay on the Principle of Population.” He wrote that overpopulation was the root of many problems industrial European society suffered from— poverty, malnutrition, and disease could all be attributed to overpopulation. According to Malthus, this was a mathematical inevitability. Malthus observed that, while resources tended to grow arithmetically, populations exhibit exponential growth. Thus, if left unrestricted, human populations would continue to grow until they would become too large to be supported by the food grown on available agricultural land. In other words, humans would outpace their local carrying capacity, the capacity of ecosystems or societies to support the local population.

As a solution, Malthus urged “moral restraint. ” That is, he declared that people must practice abstinence before marriage, forced sterilization where necessary, and institute criminal punishments for so-called unprepared parents who had more children than they could support. Even in his time, this solution was controversial.

According to Malthus, the only alternative to moral restraint was certain disaster: if allowed to grow unchecked, population would outstrip available resources, resulting in what came to be known as Malthusian catastrophes: naturally occurring checks on population growth such as famine, disease, or war.

Over the two hundred years following Malthus’s projections, famine has overtaken numerous individual regions. Proponents of this theory, Neo-Malthusians, state that these famines were examples of Malthusian catastrophes. On a global scale, however, food production has grown faster than population due to transformational advances in agricultural technology. It has often been argued that future pressures on food production, combined with threats to other aspects of the earth’s habitat such as global warming, make overpopulation a still more serious threat in the future.

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Overpopulated Urban Slums: Malthusians would cite epidemics and starvation in overpopulated urban slums, like this one in Cairo, as natural checks on growing populations that have exceeded the carrying capacities of their local environments.

Demographic Transition Theory

Demographic transition theory outlines five stages of change in birth and death rates to predict the growth of populations.

Learning Objectives

Break down the demographic transition model/theory into five recognizable stages based on how countries reach industrialization

Key Takeaways

Key Points

  • Demographic transition theory suggests that populations grow along a predictable five-stage model.
  • In stage 1, pre-industrial society, death rates and birth rates are high and roughly in balance, and population growth is typically very slow and constrained by the available food supply.
  • In stage 2, that of a developing country, the death rates drop rapidly due to improvements in food supply and sanitation, which increase life spans and reduce disease.
  • In stage 3, birth rates fall due to access to contraception, increases in wages, urbanization, increase in the status and education of women, and increase in investment in education. Population growth begins to level off.
  • In stage 4, birth rates and death rates are both low. The large group born during stage two ages and creates an economic burden on the shrinking working population.
  • In stage 5 (only some theorists acknowledge this stage—others recognize only four), fertility rates transition to either below-replacement or above-replacement.

Key Terms

  • demographic transition theory: Describes four stages of population growth, following patterns that connect birth and death rates with stages of industrial development.

Whether you believe that we are headed for environmental disaster and the end of human existence as we know it, or you think people will always adapt to changing circumstances, we can see clear patterns in population growth. Societies develop along a predictable continuum as they evolve from unindustrialized to postindustrial. Demographic transition theory (Caldwell and Caldwell 2006) suggests that future population growth will develop along a predictable four- or five-stage model.

Stage 1

In stage one, pre-industrial society, death rates and birth rates are high and roughly in balance. An example of this stage is the United States in the 1800s. All human populations are believed to have had this balance until the late 18th century, when this balance ended in Western Europe. In fact, growth rates were less than 0.05% at least since the Agricultural Revolution over 10,000 years ago.

Population growth is typically very slow in this stage, because the society is constrained by the available food supply; therefore, unless the society develops new technologies to increase food production (e.g. discovers new sources of food or achieves higher crop yields), any fluctuations in birth rates are soon matched by death rates.

Stage 2

In stage two, that of a developing country, the death rates drop rapidly due to improvements in food supply and sanitation, which increase life spans and reduce disease. Afghanistan is currently in this stage.

The improvements specific to food supply typically include selective breeding and crop rotation and farming techniques. Other improvements generally include access to technology, basic healthcare, and education. For example, numerous improvements in public health reduce mortality, especially childhood mortality. Prior to the mid-20th century, these improvements in public health were primarily in the areas of food handling, water supply, sewage, and personal hygiene. Another variable often cited is the increase in female literacy combined with public health education programs which emerged in the late 19th and early 20th centuries.

In Europe, the death rate decline started in the late 18th century in northwestern Europe and spread to the south and east over approximately the next 100 years. Without a corresponding fall in birth rates this produces an imbalance, and the countries in this stage experience a large increase in population.

Stage 3

In stage three, birth rates fall. Mexico’s population is at this stage. Birth rates decrease due to various fertility factors such as access to contraception, increases in wages, urbanization, a reduction in subsistence agriculture, an increase in the status and education of women, a reduction in the value of children’s work, an increase in parental investment in the education of children and other social changes. Population growth begins to level off. The birth rate decline in developed countries started in the late 19th century in northern Europe.

While improvements in contraception do play a role in birth rate decline, it should be noted that contraceptives were not generally available nor widely used in the 19th century and as a result likely did not play a significant role in the decline then.

It is important to note that birth rate decline is caused also by a transition in values; not just because of the availability of contraceptives.

Stage 4

During stage four there are both low birth rates and low death rates. Birth rates may drop to well below replacement level as has happened in countries like Germany, Italy, and Japan, leading to a shrinking population, a threat to many industries that rely on population growth. Sweden is considered to currently be in Stage 4.

As the large group born during stage two ages, it creates an economic burden on the shrinking working population. Death rates may remain consistently low or increase slightly due to increases in lifestyle diseases due to low exercise levels and high obesity and an aging population in developed countries.

By the late 20th century, birth rates and death rates in developed countries leveled off at lower rates.

Stage 5 (Debated)

Some scholars delineate a separate fifth stage of below-replacement fertility levels. Others hypothesize a different stage five involving an increase in fertility.

The United Nations Population Fund (2008) categorizes nations as high-fertility, intermediate-fertility, or low-fertility. The United Nations (UN) anticipates the population growth will triple between 2011 and 2100 in high-fertility countries, which are currently concentrated in sub-Saharan Africa.

For countries with intermediate fertility rates (the United States, India, and Mexico all fall into this category), growth is expected to be about 26 percent. And low-fertility countries like China, Australia, and most of Europe will actually see population declines of approximately 20 percent.

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Demographic Transition Overview

Conclusions

As with all models, this is an idealized picture of population change in these countries. The model is a generalization that applies to these countries as a group and may not accurately describe all individual cases. The extent to which it applies to less-developed societies today remains to be seen. Many countries such as China, Brazil and Thailand have passed through the Demographic Transition Model (DTM) very quickly due to fast social and economic change. Some countries, particularly African countries, appear to be stalled in the second stage due to stagnant development and the effect of AIDS.