4.2.6: Human Population Growth
- Page ID
- 105425
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Unit 4.2.6 - Human Population Growth
- Please read and watch the following Learning Resources
- Reading the material for understanding, and taking notes during videos, will take approximately 1 hour.
- Optional Activities are embedded.
- Bolded terms are located at the end of the unit in the Glossary. There is also a Unit Summary at the end of the Unit.
- To navigate to the Unit Glossary and Summary, use the Contents menu at the top of the page OR the right arrow on the side of the page.
- If on a mobile device, use the Contents menu at the top of the page OR the links at the bottom of the page.
- Discuss how human population growth can be exponential
- Explain how humans have expanded the carrying capacity of their habitat
- Relate population growth and age structure to the level of economic development in different countries
- Discuss the long-term implications of unchecked human population growth
Introduction
Concepts of animal population dynamics can be applied to human population growth. Humans are not unique in their ability to alter their environment. For example, beaver dams alter the stream environment where they are built. Humans, however, have the ability to alter their environment to increase their carrying capacity sometimes to the detriment of other species (e.g., via artificial selection for crops that have a higher yield). Earth’s human population is growing rapidly, to the extent that some worry about the ability of the Earth’s environment to sustain this population, as long-term exponential growth carries the potential risks of famine, disease, and large-scale death.
Although humans have increased the carrying capacity of their environment, the technologies used to achieve this transformation have caused unprecedented changes to Earth’s environment, altering ecosystems to the point where some may be in danger of collapse. The depletion of the ozone layer, erosion due to acid rain, and damage from global climate change are caused by human activities. More is discussed in Unit 5. The ultimate effect of these changes on our carrying capacity is unknown. As some point out, it is likely that the negative effects of increasing carrying capacity will outweigh the positive ones—the carrying capacity of the world for human beings might actually decrease.
The world’s human population is currently experiencing exponential growth even though human reproduction is far below its biotic potential (Figure \(\PageIndex{1}\)). To reach its biotic potential, all females would have to become pregnant every nine months or so during their reproductive years. Also, resources would have to be such that the environment would support such growth. Neither of these two conditions exists. In spite of this fact, human population is still growing exponentially.
A consequence of exponential human population growth is the time that it takes to add a particular number of humans to the Earth is becoming shorter. Figure \(\PageIndex{2}\) shows that 123 years were necessary to add 1 billion humans in 1930, but it took only 24 years to add two billion people between 1975 and 1999. As already discussed, at some point it would appear that our ability to increase our carrying capacity indefinitely on a finite world is uncertain. Without new technological advances, the human growth rate has been predicted to slow in the coming decades. However, the population will still be increasing and the threat of overpopulation remains.
In this 4-minute video, you will explore the historical pace of human population growth.
Questions after watching: Do we have an ethical obligation to limit human population growth? Why? If so, how might we do it ethically? If not, how should we distribute dwindling resources for the growing population?
In this 6-minute video of the American Museum of Natural History, you will follow human population and distribution on a world map for the past 200,000 years.
Question after watching: In watching this video, what appears to have contributed to sharp rises in the human population throughout history?
Humans have altered their own carrying capacity. Explain how humans have changed their carrying capacity and the consequences of this change.
- By limiting their own carrying capacity, humans have enabled their population to grow rapidly.
- By decreasing their own carrying capacity, humans have enabled their population to grow slowly.
- By stabilizing their own carrying capacity, humans have enabled their population to grow steadily.
- By increasing their own carrying capacity, humans have enabled their population to grow exponentially.
- Answer
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d. By increasing their own carrying capacity, humans have enabled their population to grow exponentially.
Overcoming Density-Dependent Regulation
Humans are unique in their ability to alter their environment with the conscious purpose of increasing its carrying capacity. This ability is a major factor responsible for human population growth and a way of overcoming density-dependent growth regulation. Much of this ability is related to human intelligence, society/culture, and communication. Humans can construct shelters to protect them from the elements and have developed agriculture and domesticated animals to increase their food supplies. In addition, humans use language to communicate this technology to new generations, allowing them to improve upon previous accomplishments.
Other factors in human population growth are migration and public health. Humans originated in Africa, but have since migrated to nearly all inhabitable land on Earth. Public health, sanitation, and the use of antibiotics and vaccines have decreased the ability of infectious disease to limit human population growth. In the past, diseases such as the bubonic plague of the fourteenth century killed between 30 and 60 percent of Europe’s population and reduced the overall world population by as many as 100 million people. Today, the threat of infectious disease, while not gone, is certainly less severe. Compared to some of the epidemics of the past, the percentage of the world's population killed by infectious diseases between 1993 and 2002 decreased from 0.30 percent of the world's population to 0.24 percent. It appears that the influence of infectious diseases on human population growth is becoming less significant, although the SARS-CoV-2 pandemic may be a harbinger of things to come due to globalization and anti-vaccination movements.
Age Structure, Population Growth, and Economic Development
The age structure of a population is an important factor in population dynamics. Age structure is the proportion of a population at different age ranges. Age structure allows better prediction of population growth, plus the ability to associate this growth with the level of economic development in the region. Countries with rapid growth have a pyramidal shape in their age structure diagrams, showing a preponderance of younger individuals, many of whom are of reproductive age or will be soon (Figure \(\PageIndex{3}\)). This pattern is most often observed in underdeveloped countries where individuals do not live to old age because of sub-optimal living conditions such as Mali (Stage 1). Age structures of areas with slow growth, including some developed countries such as Canada, still have a pyramidal or even arched structure, but with many fewer young and reproductive-aged individuals and a greater proportion of older individuals (Stages 2-3) (Figure \(\PageIndex{4}\)). Other developed countries, such as Italy and Japan, have zero or even negative population growth. The age structure of these populations is more conical, with more middle-aged and older individuals than young people. The actual growth rates in different countries are shown in Figure \(\PageIndex{5}\), with the highest rates tending to be in the less economically developed countries within Africa and Asia.
Figure \(\PageIndex{4}\): This graph compares the age structure of the 1998 and the 2018 population of Canada at July 1st in relative value. The left side shows males and the right side shows females. The horizontal axis shows the population in relative value and the vertical axis shows age. (Copyright 2018 Statistics Canada)
In this 5-minute TED-Ed video, you will explore population statistics applied to human populations and learn to interpret the population pyramid.
Question after watching: Now that you have learned more about how to interpret a population pyramid, explain what is happening in a Stage 4 structure diagram. Which is the diagram portrayed in Figure 4.2.6.3 does Canada's population fit?
Figure \(\PageIndex{3}\): Age structure diagrams for rapidly growing, slow growing and stable populations are shown in stages 1 through 3. What type of population change do you think stage 4 represents?
- Answer
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Stage 4 represents a population that is decreasing.
Long-Term Consequences of Exponential Human Population Growth
Many dire predictions have been made about the world’s population leading to a major crisis called the “population explosion.” In the 1968 book The Population Bomb, biologist Dr. Paul R. Ehrlich wrote, “The battle to feed all of humanity is over. In the 1970s hundreds of millions of people will starve to death in spite of any crash programs embarked upon now. At this late date, nothing can prevent a substantial increase in the world death rate.”1 While many critics view this statement as an exaggeration, the laws of exponential population growth are still in effect, and unchecked human population growth cannot continue indefinitely. In turn, the planet may be able to support larger numbers of humans that live with less of a collective ecological footprint. However, more and more individuals around the world have adopted consumerist lifestyles, and the Earth may not be able to support as many humans as it once might have been able to due to resource depletion, pollution, etc.
In this 11-minute video, you will explore in more depth human population growth.
Questions after watching: Water and oil are listed as essential resources for humans, over which populations fight. Would you agree that each of these is an essential resource for human populations; that they have the potential to limit population growth? Why?
In spite of population control policies in some countries, nearly all of which have now been phased out, the human population continues to grow. At some point, food supplies may be increasingly scarce because of the subsequent need to produce more and more food to feed our population, even more challenging with the crisis of climate change. The United Nations estimates that future world population growth may vary from 6 billion (a decrease) to 16 billion people by the year 2100. There is no way to know whether human population growth will moderate to the point where the crisis described by Dr. Ehrlich will be averted.
Another result of population growth is the endangerment of the natural environment. Many countries have attempted to reduce the human impact on climate change by reducing their emissions of greenhouse gases like carbon dioxide. However, these treaties have not been ratified by every country, and many underdeveloped countries trying to improve their economic condition may be less likely to agree with such provisions if it means slower economic development. Furthermore, the role of human activity in causing climate change (Unit 5.3) has become a hotly debated socio-political issue in some developed countries. Thus, we enter the future with considerable uncertainty about our ability to curb human population growth and protect our environment.
In this 10-minute video, you will learn how population geographers view human population growth.
Question after watching: In this video, you learned that many countries are encouraging populations to increase their birth rate, which is at odds with some of the data about humans having exceeded our carrying capacity on this planet. What is driving these seemingly contradictory messages?
Predict and explain the effects of the human population on biodiversity many years in the future.
- Biodiversity will decline as human population increases because of habitat loss, increased pollution, and climate change.
- Biodiversity will decline as human population increases because of enhanced food supplies, medical advances, and development of renewable energy sources.
- Biodiversity will increase as human population increases because of habitat loss, increased pollution, and climate change.
- Biodiversity will increase as human population increases because of enhanced food supplies, medical advances, and development of renewable energy sources.
- Answer
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a. Biodiversity will decline as human population increases because of habitat loss, increased pollution, and climate change.
In this 4.5-minute video, you will continue to explore population dynamics. You will learn about birth and death rates and how they impact the population as a whole.
Questions after watching: This video mentions that the growth rate = births - deaths. What is another factor that can impact growth rates? Why is this factor particularly important in Canada?
Footnotes
- 1 Paul R. Erlich, prologue to The Population Bomb, (1968; repr., New York: Ballantine, 1970).