Human Population Growth

11 Key excerpts on "Human Population Growth"

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  eBook - ePub

  Human Biological Diversity

  • Daniel E. Brown(Author)
  • 2019(Publication Date)
  • Routledge

    (Publisher)

  Chapter 9

  Demography

  Populations, reproduction, and mortality

  Demography is the study of human population size, distribution, and structure, and how these change with time. Human demography deals with issues of profound importance to our world, such as global Human Population Growth, the increase in elderly people as a proportion of the population in developed countries, and localized problems caused by population change in specific regions. An example of the latter would be the effect on rural villages of the migration of young men to urban areas to engage in wage labor.

  Evolutionary biologists and ecologists often use population size and growth rate as crude measures of a species’ relative success in adapting to its environment, with larger and/or more rapidly growing populations indicative of better success. Thus the large, rapidly growing human population could be seen as a gauge of our species’ remarkable evolutionary success. On the other hand, the rapid population growth of our species clearly has negative aspects as well.

  Population ecology

  Ecologists study population size and composition in various plant, animal, and microbial populations. The means by which they do this is applicable to the study of human populations, although traditionally there have been some methodological differences associated with human demographic studies. Population ecology considers general characteristics of population growth and its regulation.

  Population growth

  Demographers define population growth as the change in numbers of individuals over time. Growth may impact populations, causing difficulties with finding resources or space for the increased numbers of individuals, or conversely causing difficulties in finding enough “warm bodies” if growth is negative. The impact of population growth can be due to factors other than absolute numbers, depending on circumstances. For instance (and very hypothetically), one may imagine how different a growth rate of one million people per year would be for the population of China versus that of a small city in the United States. In the case of China, that growth rate would represent a welcome respite from the normally much higher growth rates. However, for the small U.S. city, the increase of one million people in a single year would represent a catastrophic situation with which the society must cope, finding housing, food, space, and utilities for the burgeoning populace. The issue in this hypothetical situation is one of scale.

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  The Environment

  Science, Issues, and Solutions

  • Mohan K. Wali, Fatih Evrendilek, M. Siobhan Fennessy(Authors)
  • 2009(Publication Date)
  • CRC Press

    (Publisher)

  215 Topics Introduction Forces Driving Human Population Growth Rapid Growth in Numbers Means Greater Consumption Biophysical Controls over Population Growth Increasing Consumption and Decreasing Natural Resources Uneven Access to Natural Capital Threatens Global Security Environmental Refugees Overall Assessment of Increasing Human Numbers 11 Human Population Growth Introduction The factors, phenomena, and principles that govern the numbers of all naturally occurring animal and plant populations, despite their many manifestations, apply to human numbers as well. Biotic potential, equilibration with the carrying capacity of the environ-ment, density-dependent and density-independent relationships, and the competitive phenomena discussed in Chapter 8 apply to the human population as well. To begin, it may be worthwhile to consider a discourse on the potential of burgeoning human numbers relative to constrained environmental resources as visualized by the Reverend Thomas Malthus in 1798, now a landmark in environment literature. Malthus wrote: “Taking the earth as a whole, … the human species would increase as the numbers, 1, 2, 4, 8, 16, 32, 64, 128, 256, and subsistence as 1, 2, 3, 4, 5, 6, 7, 8, 9.” Further, “1. Population is necessarily limited by the means of subsistence; 2. Population invariably increases where the means of subsis-tence increase, unless prevented by some very powerful and obvious checks.” As noted in Chapter 1, these postulates—an exponential increase in population numbers, but a linear growth in available resources—are referred to as Malthusian. The consequences of resource constraints encountered by vastly expanding animal and plant populations are now well documented in population ecology. Despite that, it is intriguing that this essay—now over 200 years old—continues to evoke a strong denunciation (see, for example, Trewavas 2002).

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  Biology Today

  An Issues Approach

  • Eli Minkoff, Pamela Baker(Authors)
  • 2003(Publication Date)
  • Garland Science

    (Publisher)

  In addition, even in the face of a global population increase, there has also been increasing research on the biology of infertility, in part because an increasing number of couples who are not able to conceive their own children seek these reproductive therapies. Both global population growth and individual fertility and infertility raise ethical questions. We have seen earlier (Chapter 1) that the boundaries between the individual good and the social good are one of the subjects of ethics. Biology can inform ethical debate by assessing, for different scenarios, the biological risks to the individual and to society. The Population Explosion 9 Demography Helps to Predict Future Population Size The study of the biological factors that affect the sizes of populations is called population ecology ; the study of human populations in numeri-cal terms is known as demography . Recall that a population is defined as a set of potentially interbreeding individuals in a certain geographical location at a certain time (see also Chapter 5, p. 151). Our ability to understand population growth depends on our ability to make predic-tions, based on both population ecology and demography. Because popu-lations are large aggregates, we need mathematical models to make these predictions and to study the factors that might influence and possibly curb population growth. These mathematical models were initially devel-oped from the study of bacterial populations, but they pertain to the growth of all other species, including humans. Mathematical models of population growth begin with the gathering of census data. A census is, at minimum, a head count of all the individ-uals living in a specified area, usually within recognized political bound-aries. Early censuses of human populations were often inaccurate, and the opposition of the censused populations (who did not want to be taxed) only compounded the inaccuracy.

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  Biology Trending

  A Contemporary Issues Approach

  • Eli Minkoff, Jennifer K. Hood-DeGrenier(Authors)
  • 2023(Publication Date)
  • CRC Press

    (Publisher)

  In addition, even in the face of a global population increase, there has also been increasing research on the biology of infertility, in part because an increasing number of couples who are not able to conceive their own children seek these reproductive therapies. Both global population growth and individual fertility and infertility raise ethical questions. We have seen in Chapter 1 that the boundaries between the individual good and the social good are one of the subjects of ethics. Biology can inform ethical debate by assessing the biological risks to the individual and to society in different scenarios. 9.1 DEMOGRAPHY HELPS TO PREDICT FUTURE POPULATION SIZE The study of the biological factors that affect the sizes of populations is called population ecology ; the study of human populations in numerical terms is known as demography. Recall that a population is defined (Section 5.4.1) as a set of potentially interbreeding individuals in a certain geographical location at a certain time. Our ability to understand population growth depends on our ability to make predictions based on both population ecology and demography. Because populations are large aggregates, we need mathematical models to make these predictions and to study the factors that might influence and possibly curb population growth. These mathematical models were initially developed from the study of bacterial populations, but they pertain to the growth of all other species, including humans. Mathematical models of population growth begin with the gathering of census data. A census is, at minimum, a head count of all the individuals living in a specified area, usually within recognized political boundaries. Early censuses of human populations were often inaccurate, and the opposition of the censused populations (who did not want to be taxed) only compounded the inaccuracy

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  Exploring Environmental Issues

  An Integrated Approach

  • David D. Kemp(Author)
  • 2004(Publication Date)
  • Routledge

    (Publisher)

  4 Demography and World Population Growth

      After reading this chapter you should be familiar with the following concepts and terms:

  age-specific fertility rate	exponential growth	population
  (ASFR)	family planning	population planning
  agricultural revolution	fecundity	population projections
  arithmetic progression	fertility	r-strategists
  baby boom	fuelwood	rate of natural increase
  birth control	general fertility rate (GFR)	(RNI)
  carrying capacity	geometric progression	renewable resources
  contraceptive pill	gestation	replacement fertility rate
  crude birth rate (CBR)	immigration	(RFR)
  crude death rate (CDR)	industrial revolution	replacement migration
  demographic transition	K-strategists	total fertility rate (TFR)
  model	migration	zero population growth
  doubling time	mortality	(ZPG)
  emigration	non-renewable resources

  POPULATION ECOLOGY

  A population is a group of individuals, usually of the same species, occupying a specific area. In the case of the human species the area involved is effectively the entire earth, but human population distribution is uneven. Although humans have developed a remarkable ability to adapt to different environmental conditions and to manipulate environments to meet their ends, some regions remain largely unpopulated. Empty spaces such as those in the Arctic and Antarctic, the deserts of Africa and Asia and the mountainous regions of all the continents, for example, are not unaffected by human activities, but in population numbers they contrast sharply with adjacent more populous regions.

  CARRYING CAPACITY

  In these parts of the earth thinly populated by humans, the population of other species tends to be low also, reflecting the limited resources available to support life. In ecological terms, the carrying capacity of these areas is low. This concept, linking population numbers with the availability of natural resources, originated in ecology, but it is now considered too simplistic for many ecological situations. It continues to be used in conservation ecology and ecological economics, however, and in consideration of relationships between society and the environment (Turner II and Keys 2002). Carrying capacity is a measure of the maximum number of organisms that can be supported in a particular environment, and under natural conditions it represents a theoretical equilibrium state within a dynamic system. If the species in an area are below carrying capacity, for example, populations will tend to increase until some form of balance is reached with the resources available. If the carrying capacity is exceeded, because of the rapid growth in the number of organisms in the ecosystem, for example, there will be insufficient resources to support the excess population, and numbers will decline until equilibrium between the resource base and the population is re-established. Typically, the population fluctuates above and below the level of the carrying capacity before it eventually approaches equilibrium again (Figure 4.1

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  Population Geography

  Social Justice for a Sustainable World

  • Helen D. Hazen, Heike C. Alberts, Kazimierz J. Zaniewski(Authors)
  • 2023(Publication Date)
  • Routledge

    (Publisher)

  CHAPTER 4 Population growth and change

  DOI: 10.4324/9781003143253-4

  After reading this chapter, a student should be able to:

  1. describe major changes in population size over time;
  2. discuss some of the key factors driving rapid population growth using the example of India;
  3. explain major theories of population growth and change associated with Malthus, Marx, and the demographic transition model.

  Population growth has been one of the enduring trends of human population dynamics for much of human history. Although populations have fluctuated over short timescales, particularly in early human eras, in more recent centuries the human story has been one of population growth, with global population hitting 8 billion in November 2022. The environmental implications of this are profound, as more and more of the Earth’s land surface and energy have been appropriated for human use. In recent decades this trend has begun to slow, however, as many human populations have begun to limit fertility, leading us to a potential turning point—will human population size finally stabilize and even decline in the coming decades?

  PART I: POPULATION GROWTH OVER TIME

  A short history of population growth

  Most of us have seen graphs alerting us to the dramatic growth in human population experienced over the past 200 years. Population growth was indeed dramatic from the late 1700s onwards, with an almost eight-fold increase in global population size between 1800 and 2020 (figure 4.1 , inset graph). Prior to the 1700s, the story of human population was still of overall growth but in much more gradual and variable terms (figure 4.1

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  The Ecological World View

  • Charles Krebs(Author)
  • 2008(Publication Date)
  • CSIRO PUBLISHING

    (Publisher)

  Cohen 1995 , Appendix 3.)

  Any discussion of carrying capacity must involve the concept of sustainability, which refers to the use of resources in a manner that can be continued indefinitely in the future. Sustainability is a critical issue for this century because humans are running into limits that are set by the biological resources of Earth. We will consider sustainability further in Chapter 21.

  Like all populations, human populations are subject to the rule that critical resources limit population growth sooner or later. The next four chapters explore how these limitations operate in plant and animal populations.

  SUMMARY

  Populations change over time, and a variety of population growth models have been proposed to quantify these changes. The most basic model describes geometric growth, which can occur for only a short time. Therefore, most realistic models account for regulated population growth. The most surprising result of population models is that a great variety of population changes—from stability to unpredictable fluctuations—can arise from very simple assumptions. Data from natural populations illustrate that few populations are stable and wide fluctuations are common.

  No population can increase without limits. Many studies have analyzed the environmental factors that stop population growth and cause population decline. Reproduction, death, immigration and emigration are all involved in changing population size. Pest control and the conservation of declining species are two practical examples of the need to understand the causes of changes in populations in size over time.

  The human population is increasing rapidly, and this increase must come to an end during this century, because humans are not exempt from ecological laws. Sustainability is essential for all populations, including humans. The carrying capacity of Earth for humans may already have been exceeded, and the transition from a growing human population to a stable one is one of the most important problems of this century.

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  A First Course in Systems Biology

  • Eberhard Voit(Author)
  • 2017(Publication Date)
  • Garland Science

    (Publisher)

  3 ]. Thus, throughout recorded history, population growth has been measured, documented, predicted, and analyzed.

  This chapter takes a very broad view of populations. While we might immediately think of the human world population or the population growth in our home town, populations may also consist of free-living bacteria, viruses, and healthy or tumor cells. One might even include unconventional populations, such as the alleles of a gene within a human or animal population [4 ] or a population of molecules that is converted into a population of different molecules by the action of an enzyme.

  POPULATION GROWTH

  The earliest rigorous mathematical descriptions of population sizes and their trends are often attributed to the British clergyman and economist Thomas Robert Malthus [5 ], who formulated the law of exponential growth, and to the Belgian mathematician Pierre-François Verhulst [6 ], who proposed the sigmoidal logistic growth function that we often encounter in microbial populations (see Chapter 4 ). An enormous number of other growth functions were subsequently proposed for diverse populations, ranging from humans, animals, and plants to bacteria, cells, and viruses, and the literature on growth functions is huge. Most of these are relatively simple nonlinear functions, some discrete, some continuous, while others can be represented as the solutions of differential equations [1 ]. One might find it odd that population sizes, which are clearly discrete integers, are often modeled with differential equations, which could predict something like 320.2 individuals. The simple rationale for this strategy is that differential equations are often easier to set up and analyze than the corresponding discrete models. The situation is in reality even more complicated, because processes like growth that evolve over a long time period are almost always affected by stochastic

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  From Malthus' Stagnation to Sustained Growth

  Social, Demographic and Economic Factors

  • Bruno Chiarini, Paolo Malanima, Gustavo Piga(Authors)
  • 2012(Publication Date)
  • Palgrave Macmillan

    (Publisher)

  Population, Earth Carrying Capacity and Economic Growth 145 2. - Population Growth and Earth’s Carrying Capacity The carrying capacity of an ecosystem for a living species is normally defined as the maximum number of individuals which the ecosystem can support by means of the resources it generates for them. Indeed, it is a very “Malthusian” concept, even though Malthus never used it explicitly. Malthus recognised geometric progression as the natural trend of Human Population Growth when it is not braked by land fertility, that is the power of land to generate subsistence for human beings (Malthus, 1970). This concept of “subsistence” is really strictly connected with that of carrying capacity used in modern ecological sciences, because it is related to all the resources necessary for the survival of a given human population. Without technological progress, in Malthus’ analysis there is a limit to the human population level determined by the land productivity or, in a more general sense, by the potential flow of goods and services produced by the ecosystem in each period of time. Human beings can increase the land product by means of their labour, but only with decreasing returns (Malthus, 1970). When the population grows, the product does not grow proportionally, so that per capita incomes decrease, cutting down the birthrate and raising the death rate until the growth rate falls to zero. Even though not formalised, the original Malthusian model had a more complex dynamics than its successive mathematical “vulgate”. Today, Malthus’s original intuition is always formalised by means of the fol- lowing differential equation: (1) where: N(t) is the number of human individuals at time t; b is birthrate; d is death rate; n is population growth rate; Thus, the time path of population is an exponential function, as follows: (2)

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  The History of Human Populations

  Volume I, Forms of Growth and Decline

  • P. M. G. Harris(Author)
  • 2001(Publication Date)
  • Praeger

    (Publisher)

  In this fresh formulation, the nature of demographic dynamics themselves, what has been called the “hard mathematical core” of demography (Coleman and Schofield 1986, “Introduction,” 5), shapes how both populations and their environments evolve. In such reinterpretation, population theory is elevated from a passive, mostly reactive junior partner among the social sciences to a primal explanation of how and why, and with what consequences, changes in all aspects of the collective life of humankind exhibit repeated forms. How populations grow, for what reasons they grow, and what consequences their growth generates were already central concerns as the classical early modern population debate began to take shape two and a half centuries ago, in the Page 4 1750s. They remain so today, permeating and shaping all the social sciences. Indeed, views first posited in the 18th and early 19th centuries still structure much of the theory to be found in contemporary population studies and related discussions in disciplines like economics and sociology. At least since Benjamin Franklin’s “Observations on the Increase of Mankind” and Adam Smith’s Wealth of Nations, the response of populations to the fruitfulness of their environments has provided a central core of issues about how populations grow and what difference that makes (Franklin 1751, 227–34; Smith 1776, 74–85). The most famous, and the most bleak, formulation was of course offered by Thomas Robert Malthus in his 1798 Essay on the Principle of Population, which recently experienced its bicentennial anniversary. Compared with other participants in the evolving international debate, Malthus judged that significantly fewer and less pleasant options were all that was available for bringing the explosive and virtually unlimited power of human multiplication into balance with the quite restricted potential that existed for expanding the resources that are required to make life possible, let alone enjoyable.

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  Dynamical System Models in the Life Sciences and Their Underlying Scientific Issues

  • Frederic Y M Wan(Author)
  • 2017(Publication Date)
  • WSPC

    (Publisher)

  Part 1

  Growth of a Population

  Passage contains an image

  Chapter 2

  Evolution and Equilibrium

  2.1 Growth without Immigration

  2.1.1 Population size dependent growth rates

  As indicated earlier, the goal here is to use a simple problem to begin illustrating the mathematical modeling process. We do so by modeling the familiar growth of human population on Earth. Typically, mathematical modeling is prompted by the modeler’s quest for some information about a phenomenon. The human population on Earth has grown from 4 billions in 1974 to 7 billions by 2011. Naturally, we are concerned about future growth and want to know how the population size will change with time.

  To quantify the evolution of the human population, let y(t) be the population size at time t. Size may be measured by the number of individuals or tonnage of total biomass. Time may be measured in seconds, minutes, hours, days or years from some reference time. To answer by mathematical modeling the question how does the population size evolves with time, we need to formulate some mathematical relation(s) about y(t) on the basis of known scientific principle (such as Newton’s law in physics for motion of mass particles). Unfortunately, there is no equivalence of Newton’s law in biology that governs and regulates population growth. In that case, the modeler would have to adopt some reasonable assumptions (postulates) for the phenomenon on hand based on available data and general observations. For a first model, we wish to avoid plunging into highly technical area of statistical analysis of available data or the complex relations of birth and death processes. Instead, we start with a simple phenomenological model of population growth.

  For this simple first model, we should not (and cannot) make assumptions on the size of the population at any future time y(t), since that is what we want to deduce from the model. This forces us to focus on the next level of observable, the change of the population with time. With the human population on Earth changing in fractions of a second (as can be seen from the U.S. Department of Commerce website on the U.S. and World population clock [31 ]), it is not unreasonable to think of the two variables y and t as continuous variables if we measure time in years and size in tons of biomass or billions of individuals. In that case, we may work with the instantaneous rate of change of the Earth’s (human) population dy/dt in developing our mathematical model. In fact, this volume is concerned mainly with phenomena that can be modeled by relations involving instantaneous rates of change. When the rate of change involved is with respect to time, such models are known as dynamical systems

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