Chapter 20. Population, Urbanization, and the Environment

20.1 Demography and Population

Shoulder to shoulder crowd on a city boulevard at night.
Figure 20.4 Earth’s population, which recently grew to 8 billion in November 2022, could reach 9.7 billion by 2050 (UN, 2022). (Photo courtesy of Scott Cresswell/Flickr.) CC BY 2.0

Humanity recently hit a population milestone of 8 billion humans on Earth’s surface (UN, 2022). The planet added 1 billion people since 2010 and 2 billion since 1998 — or 1 billion people every 12 years. In short, the planet is filling up. It is estimated to grow from 8 billion to 9.7 billion in 2050, and could peak at nearly 10.4 billion in the mid-2080s. How will that population be distributed? Where is population growth the highest? Where is it slowing down? Where will people live? What are the implications of population pressures for institutions, employment, risk management, environmental stresses, housing, and political conflict?

To explore these questions, sociologists turn to demography, or the study of populations. Demography is sociology at its most predictive; predicting future social outcomes based on current variables. Three of the most important variables affecting the issues above are rates of fertility, mortality, and migration.

The fertility rate of a society is a measure describing the number of children born per unit of time. Sociologists often measure fertility using the total fertility rate, which describes the average number of live births per woman through the duration of their reproductive period. For example, replacement-level fertility in G7 counties is approximately 2.1 births per woman, the level of child-bearing at which a new generation exactly replaces the previous one in terms of size. The total fertility rate is calculated based on the crude birthrate (the number of live births per 1,000 people per year).

Just as fertility measures child-bearing, the mortality rate is a measure of the number of people who die. The crude death rate is a number derived from the number of deaths per 1,000 people per year. When analyzed together, fertility and mortality rates help researchers understand the growth occurring in a population. If more people are born than die, the population is expanding. If more people die than are born, the population is contracting.

Another key element in studying populations is the movement of people into and out of an area. This movement is called migration. Migration may take the form of immigration, which describes movement into an area to assume permanent residence, or emigration, which refers to movement out of an area to another place of permanent residence. Migration might be voluntary (as when university students study abroad), involuntary (as when Somalians left the drought and famine-stricken portion of their nation to stay in refugee camps), or forced (as when many First Nations were removed from the lands they had lived in for generations).

Population growth rate equals current minus initial all divided by the initial and multiplied by 100
Figure 20.5 Population growth rate (Image courtesy of Sydney Brown/Khan Academy.) CC BY-NC-SA 2.0

The growth rate of a population, or how the population of a defined area grows or shrinks in a specific time period, is therefore a function of the number of births and deaths, as well as the number of people migrating to and from a country. It is calculated as the current population minus the initial population (at the beginning of the time period) divided by the initial population (then multiplied by 100). This gives the percentage increase relative to the initial population.

For example, Canada’s growth rate in 2022 was 2.7%, the highest among the G7 countries (as has been the case for several years), and highest since 1957 when the growth rate was 3.3% (Statistics Canada, 2023a). The reason for population growth was much different than in 1957. In 1957, the record high growth rate was due to the increased number of births during the post-war baby boom, as well as the immigration of Hungarian refugees following the Hungarian Revolution of 1956. In 2022, immigration was the sole cause of population growth, with 95.9% of the growth due to the arrival of approximately one million international immigrants. Canada is otherwise a low fertility country, with a record low of 1.40 children per woman in 2020 — far below replacement level (Statistics Canada, 2022). Canada’s population hit 40 million people in 2023 (Statistics Canada, 2023b).

Population Growth

The UN Population Division (2023) estimates that more than half of the projected increase in global population up to 2050 will be concentrated in just eight countries: the Democratic Republic of the Congo, Egypt, Ethiopia, India, Nigeria, Pakistan, the Philippines and the United Republic of Tanzania. On the other hand, Europe and Northern America are projected to reach their peak size and begin to decline before 2100.

Changing fertility, mortality, and migration rates make up the total population composition, a snapshot of the demographic profile of a population. This number can be measured for societies, nations, world regions, or other groups. The population composition includes the sex ratio (the number of men for every hundred women) as well as a population pyramid (a picture of population distribution by sex and age). See figures 20.5 and 20.6 for the pyramids of Canada and he Democratic Republic of the Congo.

A pyramid graph depicting the 2020 population of Canada, grouped by age and sex. The graph is relatively even for each age 5 year age range until beginning to taper off after age 70.
Figure 20.6 This population pyramid shows the breakdown of the 2020 Canadian population according to age and sex. (Graph courtesy of


A pyramid graph depicting the 2020 population of the Democratic Republic of Congo, grouped by age and sex. The graph is sharply tapered (like a pyramid) from largest percent of population aged 0-4 at the bottom to a tiny percentage of population at the top (age 70 and above).
Figure 20.7 This population pyramid shows the breakdown of the 2020 population of the Democratic Republic of the Congo according to age and sex. (Graph courtesy of

The population pyramid provides an interesting graphic representation of the population tendencies of different countries by showing the distribution of population by age group and sex. When a population grows due to high fertility rates, it forms a steep pyramid, with the largest percentage of the population in the 0–4 age category, as is the case with the Democratic Republic of Congo (Figure 20.6). When fertility rates are low, or below replacement, it begins to take the form of a kite or oval, because there is a proportional decrease in younger age groups compared to older age groups, as is the case with the aging population of Canada. The pyramids are also useful for visualizing the future dynamics of a population. In Canada, the bulge of the baby boom generation (55 and older in 2020) is reaching retirement age, indicating issues concerning the costs of pension plans and health care, as well as issues of labour scarcity as the baby boomers leave the work force.

Table 20.1. Varying Fertility, Mortality, Migration by Country.  [Skip Table]
Country Populations (in millions) Total fertility rate (children per woman) Mortality Rate/1000 Net migration rate (migrants/1000) Sex Ratio Male to Female Population Growth rate
Congo (DRC) 111.8* 5.56 7.74 -0.63 1 3.13
India 1,399.2 2.07 9.65 0.12 1.06 0.7
Sweden  10.5 1.67 9.5 3.79 1.01 0.5
United States 339.7 1.84 8.42 3.01 0.97 0.68
Canada  38.5 1.57 8.17 5.37 0.98 0.73

*Note. Reason for discrepancy between the CIA data and UN data used in the population pyramid above (Figure 20.6) is unclear. (Chart data courtesy of CIA World Factbook 2023)

As Table 20.1 illustrates, countries vary greatly in fertility rates, mortality rates and net migration rates — the components that make up a population composition and population growth rate. Comparing these four countries reveals that in India, there are more men than there are women, whereas the reverse is true in Canada and the United States. The Congo has significantly higher fertility rates than any of the other four countries but has lower mortality rates. Why? Are these statistics surprising? How does the population makeup impact the political climate and economics of the different countries? What factors lead to a sex ratio in which men outnumber women? What factors lead to higher fertility rates?

Demographic Theories

Sociologists have long looked at population dynamics as central to being able to predict future outcomes and issues for societies. Four theories about population have informed sociological thought: Malthusian, zero population growth, cornucopian, and demographic transition theories.

Malthusian Theory

Black and white drawing of 68 year old Thomas Malthus from 1834 sitting and facing the viewer with book on lap.
Figure 20.8 Thomas Malthus (1766-1834) by John Linnell (1834) (Image courtesy of Wellcome Collection Library/Wikimedia Commons.) CC BY 4.0

Thomas Malthus (1766–1834) was an English clergyman who made dire predictions about Earth’s ability to sustain its growing population. According to Malthusian theory, three factors would prevent human population from exceeding the earth’s carrying capacity, or how many people can live in a given area considering the limited amount of available resources. He identified these factors as war, famine, and disease (Malthus 1798). He termed these “positive checks” because they increased mortality rates, thus keeping the population in check, so to speak. He contrasts these with “preventive checks,” including birth control and celibacy, which also seek to control the population, but by reducing fertility rates.

In his Essay on the Principle of Population, (1798) Malthus argued that the production of food could only increase arithmetically (ie., 2, 4, 6, 8…) , while, unchecked, the population would increase at an exponential rate (ie., 2, 4, 16, 132…). Eventually, this meant that people would run out of food and begin to starve. They would go to war over the increasingly scarce resources, reduce the population to a manageable level, and the cycle would begin anew.

Of course, this has not exactly happened. The human population has continued to grow long past Malthus’s predictions. So, what happened? Sociologists suggest three reasons for the continued expansion of the population of our planet. First, technological developments in food production have increased both the amount and quality of calories produced per person. Second, scientific advances have developed new medicines to curtail death from disease. Finally, the development and widespread use of contraception and other forms of family planning decreased the speed at which the population increased. But what about the future? The thesis that catastrophic overpopulation will exceed the carrying capacity of the planet is still based on the Malthusian theory. In this model, ample resources to support the Earth’s population will soon run out, leading to a dismal apocalyptic future of war, famine, and disease.

Zero Population Growth

A Neo-Malthusian researcher named Paul Ehrlich brought Malthus’s predictions into the 20th century. However, according to Ehrlich, it is the environment, not specifically the food supply, that will play a crucial role in the continued health of planet’s population (Ehrlich 1968). His ideas suggest that the human population is moving rapidly toward complete environmental collapse, as privileged people use up or pollute a number of environmental resources, such as water and air. He advocated for a goal of zero population growth (ZPG), in which the number of people entering a population through birth or immigration is equal to the number of people leaving it via death or emigration. While support for this concept is mixed, it is still considered a possible solution to global overpopulation.

Cornucopian Theory

Of course, some theories are less focused on the pessimistic hypothesis that the world’s population will meet a detrimental challenge to sustaining itself. Cornucopian theory scoffs at the idea of humans wiping themselves out; it asserts that human ingenuity can resolve any environmental or social issues that develop. As an example, it points to the issue of food supply. If the population needs more food, the theory contends, agricultural scientists will figure out how to grow it, as they have already been doing for centuries. In this perspective, human ingenuity has been up to the task for thousands of years and there is no reason for that pattern not to continue (Simon 1981).

Demographic Transition Theory

Other sociologists argue there are clear patterns that can be seen in population growth that show that rapid or exponential population growth is a temporary phenomenon. Modernization theorists argue that societies develop along a predictable continuum as they evolve from unindustrialized to postindustrial societies. Following the modernization thesis, demographic transition theory suggests that future population growth will develop along a predictable five-stage model (Caldwell and Caldwell 2006) .


The five stages of demographic transition are shown in two graphs. The top graph shows the transition from high birth rates and high death rates to low birth rates and deth rates. The bottom graph shows five population pyramids that go from pyramidal form to oval form.
Figure 20.9 The five stages of the demographic transition. In the top graph, high birth and death rates with a low population total represent Stage 1. High death rates cancel out high birth rates, and the population remains low and stable. As demographic transition occurs, death rates decline due to the introduction of modern medicine and public health measures, while birth rates remain high, leading to rapid population growth. As birth rates decline to match lower death rates, population growth stops or declines. This is represented in the population pyramid shapes, which go from steep pyramidal, based on a high ratio of children to adults, to oval, based on similar population levels at each age range until around 70. (Figure courtesy of Max Roser/Wikipedia Commons.) CC BY-SA 4.0

In Stage 1, birth, death, and infant mortality rates are all high, while life expectancy is short. An example of this stage is 19th century North America. As countries begin to industrialize, they enter Stage 2, where birth rates are higher, and infant mortality and death rates drop. Life expectancy also increases. The Congo is currently in this stage. Stage 3 occurs once a society is thoroughly industrialized; birth rates decline, while life expectancy continues to increase. Death rates continue to decrease. Mexico’s population is at this stage. Stage 4 is the postindustrial era of a society. Birth and death rates are low, people are healthier and live longer, and society enters a phase of population stability or even decline. Sweden and Canada are considered Stage 4. Stage 5 projects future demographic transition as uncertain. Some predict continued declining populations, but others note a slight uptick in fertility rates in post-industrial societies, coupled with potential leaps in life expectancy due to advances in medical technology.

Current Global Population Trends

As mentioned earlier, the Earth’s population is over 8 billion. That number might not seem particularly jarring on its own. But consider the fact that the human population grew very slowly for most of its existence, then doubled in only half a century to reach 6 billion in 1999. Now, just over twenty years later, it has added another two billion. The latest projections by the United Nations suggest that the global population could grow to around 8.5 billion in 2030, 9.7 billion in 2050 and 10.4 billion in 2100 (UN Population Division, 2023).

A look at the graph of projected population indicates that while the actual growth rate has been falling, the total global population will continue to grow. This is driven by the momentum of past increases that are embedded in the youthful (child-bearing) age structure of the fastest growing populations (UN Population Division, 2023). 


Graph showing a decline in global population growth rate from the mid 1960s to the present and projecting a continued decline up to 2050, while global population size has steadily increased from approximately 2 billion in 1950 to 8 billion in 2023, to a projected 10 billion in 2050.
Figure 20.10 Global population has steadily increased since 1950 and will continue to do so, even as the population growth rate has declined. “Given that most population increase until 2050 will be driven by the momentum of past growth, further actions by Governments aimed at reducing fertility would do little to slow the pace of growth between now and mid-century, beyond the gradual slowdown indicated by the projections presented here” (Graph courtesy of UN Population Division, 2023.)

The United Nations Population Fund (2008) categorizes nations as high fertility, intermediate fertility, or low fertility. It anticipates a triple population growth between 2011 and 2100 in high-fertility countries, which are currently concentrated in sub-Saharan Africa (see Figure 20.11). For countries with intermediate fertility rates (the United States, India, and Mexico all fall into this category), growth is expected to be about 26%. Low-fertility countries like China, Australia, and most of those in Europe will actually see population declines of approximately 20%. Figures 20.11 and 20.12 illustrate this trend.


The graph shows that population grown in African countries will triple by 2100.
Figure 20.11 Projected Population in Africa. This graph shows the population growth of countries on the African continent, many of which have high fertility rates. (Graph courtesy of USAID, 2010.) Public Domain
A graph predicting the growing population of Canada.
Figure 20.12 Projected Population in Canada. Canada has a low fertility rate, and therefore, a comparatively moderate projected population growth. (Graph courtesy of USAID, 2010.) Public Domain
This chart grows that population growth may actually decrease in Europe.
Figure 20.13 Projected Population in Europe. This chart shows the projected population growth of Europe for the remainder of this century. (Graph courtesy of USAID, 2010.) Public Domain

It would be impossible to discuss population growth and trends without addressing access to family planning resources and birth control. As the stages of population growth indicate, more industrialized countries see birth rates decline as families limit the number of children they have. Today, many people — over 200 million — still lack access to safe family planning, as reported by USAID (2010). According to its report, this need is growing, with demand projected to increase by 40% in the next 15 years. Many social scholars would assert that until women are able to have only the children they want and can care for, the poorest countries would always bear the worst burden of overpopulation.

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Introduction to Sociology – 3rd Canadian Edition by William Little is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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