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1.4.18.13: Human Population Growth - Biology

1.4.18.13: Human Population Growth - Biology


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Learning Objectives

  • Discuss how the human population has changed over time

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 its 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. 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 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 2 shows that 123 years were necessary to add 1 billion humans in 1930, but it only took 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.

Click through this interactive view of how human populations have changed over time.

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, and communication. Humans can construct shelter 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 the 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 plaque 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. According to the World Health Organization, global death from infectious disease declined from 16.4 million in 1993 to 14.7 million in 1992. To compare to some of the epidemics of the past, the percentage of the world’s population killed between 1993 and 2002 decreased from 0.30 percent of the world’s population to 0.24 percent. Thus, it appears that the influence of infectious disease on human population growth is becoming less significant.

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 3). This pattern is most often observed in underdeveloped countries where individuals do not live to old age because of less-than-optimal living conditions. Age structures of areas with slow growth, including developed countries such as the United States, still have a pyramidal structure, but with many fewer young and reproductive-aged individuals and a greater proportion of older individuals. Other developed countries, such as Italy, have zero population growth. The age structure of these populations is more conical, with an even greater percentage of middle-aged and older individuals. The actual growth rates in different countries are shown in Figure 4, with the highest rates tending to be in the less economically developed countries of Africa and Asia.

Practice Question

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?

[practice-area rows=”2″][/practice-area]
[reveal-answer q=”115181″]Show Answer[/reveal-answer]
[hidden-answer a=”115181″]Stage 4 represents a population that is decreasing.[/hidden-answer]

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.” 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.

Efforts to control population growth led to the one-child policy in China, which used to include more severe consequences, but now imposes fines on urban couples who have more than one child. Due to the fact that some couples wish to have a male heir, many Chinese couples continue to have more than one child. The policy itself, its social impacts, and the effectiveness of limiting overall population growth are controversial. In spite of population control policies, the human population continues to grow. At some point the food supply may run out because of the subsequent need to produce more and more food to feed our population. 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 emission of the greenhouse gas 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 has become a hotly debated socio-political issue in some developed countries, including the United States. Thus, we enter the future with considerable uncertainty about our ability to curb human population growth and protect our environment.

Learning Objectives

The world’s human population is growing at an exponential rate. Humans have increased the world’s carrying capacity through migration, agriculture, medical advances, and communication. The age structure of a population allows us to predict population growth. Unchecked human population growth could have dire long-term effects on our environment.

This video tells us the specifics of why and how human population growth has happened over the past hundred and fifty years or so, and how those specifics relate to ecology.

A YouTube element has been excluded from this version of the text. You can view it online here: pb.libretexts.org/bionm2/?p=570


Population: Definition, Attributes and Growth | Biology

Population is a set of individuals of a particular species, which are found in a particular geographical area.

The population that occupies a very small area, is smaller in size, such a population is called local population. A group of such a closely related local population is called meta-population.

Population ecology is an important area of ecology because it links ecology to the population genetics and evolution. Natural selection operates at a levels of population.

Population Attributes:

A population has certain attributes that an individual organism does not have.

Some of them are given below:

(i) Population Size or Density:

It is the number of individuals of a species per unit area or volume

(ii) Birth Rate (Natality):

It is the rate of production (birth rate) of new individuals per unit of population per unit time. For example, if in a pond, there are 20 lotus plants last year and through reproduction, 8 new plants are added, taking the current population to 28. Then, birth rate = 8/20 = 0.4 offspring per lotus per year.

(iii) Death Rate (Mortality):

It is the rate of loss of individuals (death rate) per unit time due to death or due to the different environmental changes, competition, predation, etc. For example, if individuals in a laboratory population of 40 fruit flies died during a specified time interval. Then, the death rate = 4/40 = 0.1 individuals per fruit fly per week.

An individual is either a male or a female but a population has a sex ratio like 60% of the population are females and 40% are males.

Population at any given time is composed of individuals of different ages. When the age distribution (per cent individuals of a given age or age group) is plotted for the population, this is called age pyramid.

The age pyramids of human population generally shows the age distribution of males and females in a combined diagram.

The growth status of the population is reflected by the shape of the pyramids.

Population Growth:

The size of a population for any species is not a static parameter, it keeps changing with time.

It depends on the following factors:

The density of a population in a given habitat during a given period, fluctuates due to the four basic processes:

(a) Natality refers to the number of births during a given period in the population that are added to initial density.

(b) Mortality is the number of deaths in the population during a given period.

(c) Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.

(d) Emigration is the number of individuals of population who left the habitat and moved elsewhere during a given period of time.

Out of these four, natality and immigration contribute an increase in population density while mortality and emigration contribute to the decrease in population density.

So, if N is the population density at time t, then its density at time t +1 is

Where, N = Population density

From the above equations, we can see that population density will increase if, (B + I) is more than (D + E).

Studying about the behaviour and pattern of different animals can help us to learn a lesson on how to control the human population growth.

There are following two models of population growth:

Exponential Growth:

Availability of resources (food and space) is essential for the growth of population. The unlimited availability results in population exponential. The increase or decrease in population density (N) at a unit time period (t) is calculated as (dN/dt)

Where, N is population size, b is birth per capita

d is death per capita, t is time period

and r is intrinsic rate of natural increase.

r, is an important parameter that assess the effects of biotic and abiotic factors on population growth. It is different for different organisms.

It is 0.015 for Norway rat and 0.12 for flour beetle. The above equation results in J-shaped curve as shown in graph.

Integral form of exponential growth is Nt = N0ert

Nt = Population density after time t,

N0 = Population density at time zero (beginning),

r = Intrinsic rate of natural increase,

e = Base of natural logarithms (2.71828).

Any species growing exponentially under unlimited resource conditions, without any checks can reach enormous population densities in a short time.

Logistic Growth:

Practically, no population of any species in nature has unlimited resources at its disposal. This leads to competition among the individuals and the survival of the fittest. Therefore, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible.

This is called the carrying capacity (K) for that species in that habitat. When N is plotted in relation to time t, the logistic growth show sigmoid curve and is also called Verhulst-Pearl Logistic Growth and is calculated as

Where, N is population density at time t K is carrying capacity and r is intrinsic rate of natural increase.

This model is more realistic in nature because no population growth can sustain exponential growth indefinitely as there will be completion for the basic needs.

Human population growth curve will become S-shaped, if efforts are being made throughout the world to reduce the rate of population growth and make it stationary.

Human population growth curve is not J-shaped.

Life History Variations:

Darwinian fitness (high ‘r’ value) states that the population evolve to maximise their reproductive fitness in the habitat where they live. Under particular set of selection pressures, organisms evolve towards the most efficient reproductive strategy.

The rate of breeding varies from species to species:

a. Some species breed only once in their life time (Pacific salmon fish and bamboo), while some breed many times in their life time (birds and mammals).

b. Some produce large number of small sized offsprings (oysters), whereas other produce small number of large sized offsprings (birds and mammals).

c. Life history traits of organisms have evolved in relation to the constraints imposed by the biotic and abiotic components of habitats in which they live.


The Demographic Transition

Slowly declining birth rates following an earlier sharp decline in death rates are today characteristic of most of the less-developed regions of the world.

The shift from high birth and death rates to low birth as well as death rates is called the demographic transition.

This graph (based on data from the Population Reference Bureau) shows that the demographic transition began much earlier in Sweden than in Mexico and was, in fact, completed by the end of the nineteenth century. The spike in deaths in the interval between 1901 and 1926 was caused by the worldwide influenza pandemic of 1918&ndash1919.

The birth rate in Sweden is now (2018) 11.3/1000 the death rate 9/1000, giving a rate of natural increase (r) of


Growth of Human Population | Ecology

The north and south poles are free of human habitation mainly because they are extremely cold and also agriculturally unproductive. Human settlements occur in places where adequate sources of water are available.

The fertility of the soil for farming is another important determinant of population distribution. For instance, the main basis of the highly dense populations in the Indus valley and Indo-Gangetic plains is the alluvial nature of the soils in these regions.

In certain places both iron ore and coal and other fossil energy sources are located close together. Industrial cities based around steel plants have come up in Jamshedpur, Bokaro, Durgapur, Bhilai and Rourkela.

Means of transportation have played an important role in the redistribution of population. This made it possible for the first time for persons to live far away from the source of produce or of goods required for living. Transportation by water is cheaper than by land or air and this is probably the main basis for the coastal location of most big cities such as Kolkata, Mumbai, London, New York and Tokyo.

2. Socio-Economic Factors:

The size of population, and birth and death rates has great significance on the standard of living of the people, their aspirations, and their economic and social development.

The birth rate of human population is regulated more by socio-economic factors than biological factors. These factors may be social status of women, age of women at marriage, family structure, education, acceptability of family planning practices, and religious beliefs.

Prosperity in the cities is the basic cause of continued urban growth. Some important consequences of increasing urbanization are-overcrowding, leading to problems of sanitation and sewage disposal transportation and associated traffic problems environmental pollution generated by industrial activities and automobiles noise pollution and various socio-economic and cultural changes and problems related to juvenile delinquency and crime.

Urbanization involves progressive increase in the use of our fertile agricultural lands for housing new industries, factories, government offices, schools, hospitals and residential quarters.

3. Demographic Factors:

The birth-rate, death-rate, and the rate of natural increase are called vital rates because any change in these parameters will determine the overall pattern of population density.

The study of trends in human population growth and the prediction of future development make a special branch of knowledge called demography. Such studies involve parameters, that is, the number and proportion of different age-groups requiring education, training and employment.

Countries with a wide gap between birth rate and death rate tend to have a population age structure in which a higher percentage of its population consists of pre-school and school-going rate of a narrow gap between birth and death rates would contain relatively much lower proportion of pre­school and school-going age groups.

Data of age distribution and economic status of different social groups are also needed for economic and social welfare planning.

The human population is increasing at an enormous rate. However, the rate of growth is not uniform in all countries. It may vary even is different groups of the same country. Unlimited population growth leads to over-crowding, has adverse environmental implications, especially in urban areas It tends to reduce food, water, fuel, land and other natural resources.

It is a fact that the growth of human population is more stable in the developed countries, i.e., both the birth rates and death rates are low.

When the birth rate of a population is high, the population increases, and on the other hand when the death rate is high the population decreases. In the United States of America, France and Germany, the population growth is more stable than in the developing countries like Pakistan, Bangladesh, India and China.

Usually, the relationship between population growth rate and the level of industrial development and education is inversely proportional. Such relationship is also found among different groups of the people in the same country.


Impact of Population Growth

It is more important now than ever to talk about population. What will we do if we continue to grow at exponential rates? What are ethical, viable strategies to decrease population?

This is a blog in the MAHB ‘Let’s Talk About Population’ Blog Series.

Complacency concerning this component of man’s predicament is unjustified and counterproductive.

The interlocking crises in population, resources, and environment have been the focus of countless papers, dozens of prestigious symposia, and a growing avalanche of books. In this wealth of material, several questionable assertions have been appearing with increasing frequency. Perhaps the most serious of these is the notion that the size and growth rate of the U.S. population are only minor contributors to this country’s adverse impact on local and global environments (1, 2). We propose to deal with this and several related misconceptions here, before persistent and unrebutted repetition entrenches them in the public mind—if not the scientific literature. Our discussion centers around five theorems which we believe are demonstrably true and which provide a framework for realistic analysis:

  1. Population growth causes a disproportionate negative impact on the environment.
  2. Problems of population size and growth, resource utilization and depletion, and environmental deterioration must be considered jointly and on a global basis. In this context, population control is obviously not a panacea—it is necessary but not alone sufficient to see us through the crisis.
  3. Population density is a poor measure of population pressure, and redistributing population would be a dangerous pseudosolution to the population problem.
  4. “Environment” must be broadly construed to include such things as the physical environment of urban ghettos, the human behavioral environment, and the epidemiological environment.
  5. Theoretical solutions to our problems are often not operational and sometimes are not solutions.

We now examine these theorems in some detail.

Population Size and Per Capita Impact

In an agricultural or technological society, each human individual has a negative impact on his environment. He is responsible for some of the simplification (and resulting destabilization) of ecological systems which results from the practice of agriculture (3). He also participates in the utilization of renewable and nonrenewable resources. The total negative impact of such a society on the environment can be expressed, in the simplest terms, by the relation

where P is the population, and F is a function which measures the per capita impact. A great deal of complexity is subsumed in this simple relation, however. For example, F increases with per capita consumption if technology is held constant, but may decrease in some cases if more benign technologies are introduced in the provision of a constant level of consumption. (We shall see in connection with theorem 5 that there are limits to the improvements one should anticipate from such “technological fixes.’’)

Pitfalls abound in the interpretation of manifest increases in the total impact I. For instance, it is easy to mistake changes in the composition of resource demand or environmental impact for absolute per capita increases, and thus to underestimate the role of the population multiplier. Moreover, it is often assumed that population size and per capita impact are independent variables, when in fact they are not. Consider, for example, the recent article by Coale (1), in which he disparages the role of U.S. population growth in environmental problems by noting that since 1940 “population has increased by 50 percent, but per capita use of electricity has been multiplied several times.” This argument contains both the fallacies to which we have just referred.

First, a closer examination of very rapid increases in many kinds of consumption shows that these changes reflect a shift among alternatives within a larger (and much more slowly growing) category. Thus the 760 percent increase in electricity consumption from 1940 to 1969 (4) occurred in large part because the electrical component of the energy budget was (and is) increasing much faster than the budget itself. (Electricity comprised 12 percent of the U.S. energy consumption in 1940 versus 22 percent today.) The total energy use, a more important figure than its electrical component in terms of resources and the environment, increased much less dramatically—140 percent from 1940 to 1969. Under the simplest assumption (that is, that a given increase in population size accounts for an exactly proportional increase in consumption), this would mean that 38 percent of the increase in energy use during this period is explained by population growth (the actual population increase from 1940 to 1969 was 53 percent). Similar considerations reveal the imprudence of citing, say, aluminum consumption to show that population growth is an “unimportant” factor in resource use. Certainly, aluminum consumption has swelled by over 1400 percent since 1940, but much of the increase has been due to the substitution of aluminum for steel in many applications. Thus a fairer measure is combined consumption of aluminum and steel, which has risen only 117 percent since 1940. Again, under the simplest assumption, population growth accounts for 45 percent of the increase.

The “simplest assumption” is not valid, however, and this is the second flaw in Coale’s example (and in his thesis). In short, he has failed to recognize that per capita consumption of energy and resources, and the associated per capita impact on the environment, are themselves functions of the population size. Our previous equation is more accurately written

displaying the fact that impact can increase faster than linearly with population. Of course, whether F (P) is an increasing or decreasing function of P depends in part on whether diminishing returns or economies of scale are dominant in the activities of importance. In populous, industrial nations such as the United States, most economies of scale are already being exploited we are on the diminishing returns part of most of the important curves,

As one example of diminishing returns, consider the problem of providing nonrenewable resources such as minerals and fossil fuels to a growing population, even at fixed levels of per capita consumption, As the richest supplies of these resources and those nearest to centers of use are consumed, we are obliged to use lower-grade ores, drill deeper, and extend our supply networks. All these activities increase our per capita use of energy and our per capita impact on the environment. In the case of partly renewable resources such as water (which is effectively nonrenewable when groundwater supplies are mined at rates far exceeding natural recharge), per capita costs and environmental impact escalate dramatically when the human population demands more than is locally available. Here the loss of free-flowing rivers and other economic, esthetic, and ecological costs of massive water-movement projects represent increased per capita diseconomies directly stimulated by population growth.

Diminishing returns are also operative in increasing food production to meet the needs of growing populations. Typically, attempts are made both to overproduce on land already farmed and to extend agriculture to marginal land. The former requires disproportionate energy use in obtaining and distributing water, fertilizer, and pesticides. The latter also increases per capita energy use, since the amount of energy invested per unit yield increases as less desirable land is cultivated. Similarly, as the richest fisheries stocks are depleted, the yield per unit effort drops, and more and more energy per capita is required to maintain the supply (5). Once a stock is depleted it may not recover—it may be nonrenewable.

Population size influences per capita impact in ways other than diminishing returns. As one example, consider the oversimplified but instructive situation in which each person in the population has links with every other person—roads, telephone lines, and so forth. These links involve energy and materials in their construction and use. Since the number of links increases much more rapidly than the number of people (6), so does the per capita consumption associated with the links.

Other factors may cause much steeper positive slopes in the per capita impact function, F(P). One phenomenon is the threshold effect. Below a certain level of pollution trees will survive in smog. But, at some point, when a small increment in population produces a small increment in smog, living trees become dead trees. Five hundred people may be able to live around a lake and dump their raw sewage into the lake, and the natural systems of the lake will be able to break down the sewage and keep the lake from undergoing rapid ecological change. Five hundred and five people may overload the system and result in a “polluted” or eutrophic lake. Another phenomenon capable of causing near-discontinuities is the synergism. For instance, as cities push out into farmland, air pollution increasingly becomes a mixture of agricultural chemicals with power plant and automobile effluents. Sulfur dioxide from the city paralyzes the cleaning mechanisms of the lungs, thus increasing the residence time of potential carcinogens in the agricultural chemicals. The joint effect may be much more than the sum of the individual effects. Investigation of synergistic effects is one of the most neglected areas of environmental evaluation.

Not only is there a connection between population size and per capita damage to the environment, but the cost of maintaining environmental quality at a given level escalates disproportionately as population size increases. This effect occurs in part because costs increase very rapidly as one tries to reduce contaminants per unit volume of effluent to lower and lower levels (diminishing returns again!). Consider municipal sewage, for example. The cost of removing 80 to 90 percent of the biochemical and chemical oxygen demand, 90 percent of the suspended solids, and 60 percent of the resistant organic material by means of secondary treatment is about 8 cents per 1000 gallons (3785 liters) in a large plant (7). But if the volume of sewage is such that its nutrient content creates a serious eutrophication problem (as is the case in the United States today), or if supply considerations dictate the reuse of sewage water for industry, agriculture, or groundwater recharge, advanced treatment is necessary. The cost ranges from two to four times as much as for secondary treatment (17 cents per 1000 gallons for carbon absorption 34 cents per 1000 gallons for disinfection to yield a potable supply). This dramatic example of diminishing returns in pollution control could be repeated for stack gases, automobile exhausts, and so forth.

Now consider a situation in which the limited capacity of the environment to absorb abuse requires that we hold man’s impact in some sector constant as population doubles. This means per capita effectiveness of pollution control in this sector must double (that is, effluent per person must be halved). In a typical situation, this would yield doubled per capita costs, or quadrupled total costs (and probably energy consumption) in this sector for a doubling of population. Of course, diminishing returns and threshold effects may be still more serious: we may easily have an eightfold increase in control costs for a doubling of population. Such arguments leave little ground for the assumption, popularized by Barry Commoner (2, 8) and others, that a 1 percent rate of population growth spawns only 1 percent effects.

It is to be emphasized that the possible existence of “economies of scale” does not invalidate these arguments. Such savings, if available at all, would apply in the case of our sewage example to a change in the amount of effluent to be handled at an installation of a given type. For most technologies, the United States is already more than populous enough to achieve such economies and is doing so. They are accounted for in our example by citing figures for the largest treatment plants of each type. Population growth, on the other hand, forces us into quantitative and qualitative changes in how we handle each unit volume of effluent—what fraction and what kinds of material we remove. Here economies of scale do not apply at all, and diminishing returns are the rule.

Global Context

We will not deal in detail with the best example of the global nature and interconnections of population resource and environmental problems—namely, the problems involved in feeding a world in which 10 to 20 million people starve to death annually (9), and in which the population is growing by some 70 million people per year. The ecological problems created by high-yield agriculture are awesome (3, 10) and are bound to have a negative feedback on food production. Indeed, the Food and Agriculture Organization of the United Nations has reported that in 1969 the world suffered its first absolute decline in fisheries yield since 1950. It seems likely that part of this decline is attributable to pollution originating in terrestrial agriculture.

A second source of the fisheries decline is, of course, overexploitation of fisheries by the developed countries. This problem, in turn, is illustrative of the situation in regard to many other resources, where similarly rapacious and shortsighted behavior by the developed nations is compromising the aspirations of the bulk of humanity to a decent existence. It is now becoming more widely comprehended that the United States alone accounts for perhaps 30 percent of the nonrenewable resources consumed in the world each year (for example, 37 percent of the energy, 25 percent of the steel, 28 percent of the tin, and 33 percent of the synthetic rubber) (11). This behavior is in large part inconsistent with American rhetoric about “developing” the countries of the Third World. We may be able to afford the technology to mine lower grade deposits when we have squandered the world’s rich ores, but the underdeveloped countries, as their needs grow and their means remain meager, will not be able to do so. Some observers argue that the poor countries are today economically dependent on our use of their resources, and indeed that economists in these countries complain that world demand for their raw materials is too low (1). This proves only that their economists are as shortsighted as ours.

It is abundantly clear that the entire context in which we view the world resource pool and the relationships between developed and underdeveloped countries must be changed, if we are to have any hope of achieving a stable and prosperous existence for all human beings. It cannot be stated too forcefully that the developed countries (or, more accurately, the overdeveloped countries) are the principal culprits in the consumption and dispersion of the world’s nonrenewable resources (12) as well as in appropriating much more than their share of the world’s protein. Because of this consumption, and because of the enormous negative impact on the global environment accompanying it, the population growth in these countries must be regarded as the most serious in the world today.

In relation to theorem 2 we must emphasize that, even if population growth were halted, the present population of the world could easily destroy civilization as we know it. There is a wide choice of weapons—from unstable plant monocultures and agricultural hazes to DDT, mercury, and thermonuclear bombs. If population size were reduced and per capita consumption remained the same (or increased), we would still quickly run out of vital, high-grade resources or generate conflicts over diminishing supplies. Racism, economic exploitation, and war will not be eliminated by population control (of course, they are unlikely to be eliminated without it).

Population Density and Distribution

Theorem 3 deals with a problem related to the inequitable utilization of world resources. One of the commonest errors made by the uninitiated is to assume that population density (people per square mile) is the critical measure of overpopulation or underpopulation. For instance, Wattenberg states that the United States is not very crowded by “international standards” because Holland has 18 times the population density (13). We call this notion “the Netherlands fallacy.” The Netherlands actually requires large chunks of the earth’s resources and vast areas of land not within its borders to maintain itself. For example, it is the second largest per capita importer of protein in the world, and it imports 63 percent of its cereals, including 100 percent of its corn and rice. It also imports all of its cotton, 77 percent of its wool, and all of its iron ore, antimony, bauxite, chromium, copper, gold, lead, magnesite, manganese, mercury, molybdenum, nickel, silver, tin, tungsten, vanadium, zinc, phosphate rock (fertilizer), potash (fertilizer), asbestos, and diamonds. It produces energy equivalent to some 20 million metric tons of coal and consumes the equivalent of over 47 million metric tons (14).

A certain preoccupation with density as a useful measure of overpopulation is apparent in the article by Coale (1). He points to the existence of urban problems such as smog in Sydney, Australia, “even though the total population of Australia is about 12 million in an area 80 percent as big as the United States,” as evidence that environmental problems are unrelated to population size. His argument would be more persuasive if problems of population distribution were the only ones with environmental consequences, and if population distribution were unrelated to resource distribution and population size. Actually, since the carrying capacity of the Australian continent is far below that of the United States, one would expect distribution problems—of which Sydney’s smog is one symptom—to be encountered at a much lower total population there. Resources, such as water, are in very short supply, and people cluster where resources are available. (Evidently, it cannot be emphasized enough that carrying capacity includes the availability of a wide variety of resources in addition to space itself, and that population pressure is measured relative to the carrying capacity. One would expect water, soils, or the ability of the environment to absorb wastes to be the limiting resource in far more instances than land area.)

In addition, of course, many of the most serious environmental problems are essentially independent of the way in which population is distributed. These include the global problems of weather modification by carbon dioxide and particulate pollution, and the threats to the biosphere posed by man’s massive inputs of pesticides, heavy metals, and oil (15). Similarly, the problems of resource depletion and ecosystem simplification by agriculture depend on how many people there are and their patterns of consumption, but not in any major way on how they are distributed.

Naturally, we do not dispute that smog and most other familiar urban ills are serious problems, or that they are related to population distribution. Like many of the difficulties we face, these problems will not be cured simply by stopping population growth direct and well-conceived assaults on the problems themselves will also be required. Such measures may occasionally include the redistribution of population, but the considerable difficulties and costs of this approach should not be underestimated. People live where they do not because of a perverse intention to add to the problems of their society but for reasons of economic necessity, convenience, and desire for agreeable surroundings. Areas that are uninhabited or sparsely populated today are presumably that way because they are deficient in some of the requisite factors. In many cases, the remedy for such deficiencies—for example, the provision of water and power to the wastelands of central Nevada—would be extraordinarily expensive in dollars, energy, and resources and would probably create environmental havoc. (Will we justify the rape of Canada’s rivers to “colonize” more of our western deserts?)

Moving people to more “habitable” areas, such as the central valley of California or, indeed, most suburbs, exacerbates another serious problem— the paving-over of prime farmland. This is already so serious in California that, if current trends continue, about 50 percent of the best acreage in the nation’s leading agricultural state will be destroyed by the year 2020 (16). Encouraging that trend hardly seems wise.

Whatever attempts may be made to solve distribution-related problems, they will be undermined if population growth continues, for two reasons. First, population growth and the aggravation of distribution problems are correlated—part of the increase will surely be absorbed in urban areas that can least afford the growth. Indeed, barring the unlikely prompt reversal of present trends, most of it will be absorbed there. Second, population growth puts a disproportionate drain on the very financial resources needed to ’combat its symptoms. Economist Joseph Spengler has estimated that 4 percent of national income goes to support our 1 percent per year rate of population growth in the United States (17). The 4 percent figure now amounts to about $30 billion per year. It seems safe to conclude that the faster we grow the less likely it is that we will find the funds either to alter population distribution patterns or to deal more comprehensively and realistically with our problems.

Meaning of Environment

Theorem 4 emphasizes the comprehensiveness of the environment crisis. All too many people think in terms of national parks and trout streams when they say “environment.” For this reason many of the suppressed people of our nation consider ecology to be just one more “racist shuck” (18). They are apathetic or even hostile toward efforts to avert further environmental and sociological deterioration, because they have no reason. to believe they will share the fruits of success (19). Slums, cockroaches, and rats are ecological problems, too. The correction of ghetto conditions in Detroit is neither more nor less important than saving the Great Lakes—both are imperative.

We must pay careful attention to sources of conflict both within the United States and between nations. Conflict within the United States blocks progress toward solving our problems conflict among nations can easily “solve” them once and for all. Recent laboratory studies on human beings support the anecdotal evidence that crowding may increase aggressiveness in human males (20). These results underscore long-standing suspicions that population growth, translated through the inevitable uneven distribution into physical crowding, will tend to make the solution of all of our problems more difficult.

As a final example of the need to view “environment” broadly, note that human beings live in an epidemiological environment which deteriorates with crowding and malnutrition—both of which increase with population growth. The hazard posed by the prevalence of these conditions in the world today is compounded by man’s unprecedented mobility: potential carriers of diseases of every description move routinely and in substantial numbers from continent to continent in a matter of hours. Nor is there any reason to believe that modern medicine has made widespread plague impossible (21). The Asian influenza epidemic of 1968 killed relatively few people only because the virus happened to be nonfatal to people in otherwise good health, not because of public health measures. Far deadlier viruses, which easily could be scourges without precedent in the population at large, have on more than one occasion been confined to research workers largely by good luck [for example, the Marburg virus incident of 1967 (22) and the Lassa fever incident of 1970 (21, 23)].

Solutions: Theoretical and Practical

Theorem 5 states that theoretical solutions to our problems are often not operational, and sometimes are not solutions. In terms of the problem of feeding the world, for example, technological fixes suffer from limitations in scale, lead time, and cost (24). Thus potentially attractive theoretical approaches—such as desalting seawater for agriculture, new irrigation systems, high-protein diet supplements—prove inadequate in practice. They are too little, too late, and too expensive, or they have sociological costs which hobble their effectiveness (25). Moreover, many aspects of our technological fixes, such as synthetic organic pesticides and inorganic nitrogen fertilizers, have created vast environmental problems which seem certain to erode global productivity and ecosystem stability (26). This is not to say that important gains have not been made through the application of technology to agriculture in the poor countries, or that further technological advances are not worth seeking. But it must be stressed that even the most enlightened technology cannot relieve the necessity of grappling forthrightly and promptly with population growth [as Norman Borlaug aptly observed on being notified of his Nobel Prize for development of the new wheats (27)].

Technological attempts to ameliorate the environmental impact of population growth and rising per capita affluence in the developed countries suffer from practical limitations similar to those just mentioned. Not only do such measures tend to be slow, costly, and insufficient in scale, but in addition they most often shift our impact rather than remove it. For example, our first generation of smog-control devices increased emissions of oxides of nitrogen while reducing those of hydrocarbons and carbon monoxide. Our unhappiness about eutrophication has led to the replacement of phosphates in detergents with compounds like NTA—nitrilotriacetic acid—which has carcinogenic breakdown products and apparently enhances teratogenic effects of heavy metals (28). And our distaste for lung diseases apparently induced by sulfur dioxide inclines us to accept the hazards of radioactive waste disposal, fuel reprocessing, routine low-level emissions of radiation, and an apparently small but finite risk of catastrophic accidents associated with nuclear fission power plants. Similarly, electric automobiles would simply shift part of the environmental burden of personal transportation from the vicinity of highways to the vicinity of power plants.

We are not suggesting here that electric cars, or nuclear power plants, or substitutes for phosphates are inherently bad. We argue rather that they, too, pose environmental costs which must be weighed against those they eliminate. In many cases the choice is not obvious, and in all cases there will be some environmental impact. The residual per capita impact, after all the best choices have been made, must then be multiplied by the population engaging in the activity. If there are too many people, even the most wisely managed technology will not keep the environment from being overstressed.

In contending that a change in the way we use technology will invalidate these arguments, Commoner (2, 8) claims that our important environmental problems began in the 1940’s with the introduction and rapid spread of certain “synthetic” technologies: pesticides and herbicides, inorganic fertilizers, plastics, nuclear energy, and high-compression gasoline engines. In so arguing, he appears to make two unfounded assumptions. The first is that man’s pre-1940 environmental impact was innocuous and, without changes for the worse in technology, would have remained innocuous even at a much larger population size. The second assumption is that the advent of the new technologies was independent of the attempt to meet human needs and desires in a growing population. Actually, man’s record as a simplifier of ecosystems and plunderer of resources can be traced from his probable role in the extinction of many Pleistocene mammals (29), through the destruction of the soils of Mesopotamia by salination and erosion, to the deforestation of Europe in the Middle Ages and the American dustbowls of the 1930’s, to cite only some highlights. Man’s contemporary arsenal of synthetic technological bludgeons indisputably magnifies the potential for disaster, but these were evolved in some measure to cope with population pressures, not independently of them. Moreover, it is worth noting that, of the four environmental threats viewed by the prestigious Williamstown study (15) as globally significant, three are associated with pre-1940 technologies which have simply increased in scale [heavy metals, oil in the seas, and carbon dioxide and particulates in the atmosphere, the latter probably due in considerable part to agriculture (30)]. Surely, then, we can anticipate that supplying food, fiber, and metals for a population even larger than today’s will have a profound (and destabilizing) effect on the global ecosystem under any set of technological assumptions.

John Platt has aptly described man’s present predicament as “a storm of crisis problems” (31). Complacency concerning any component of these problems—sociological, technological, economic, ecological—is unjustified and counterproductive. It is time to admit that there are no monolithic solutions to the problems we face. Indeed, population control, the redirection of technology, the transition from open to closed resource cycles, the equitable distribution of opportunity and the ingredients of prosperity must all be accomplished if there is to be a future worth having. Failure in any of these areas will surely sabotage the entire enterprise.

In connection with the five theorems elaborated here, we have dealt at length with the notion that population growth in industrial nations such as the United States is a minor factor, safely ignored. Those who so argue often add that, anyway, population control would be the slowest to take effect of all possible attacks on our various problems, since the inertia in attitudes and in the age structure of the population is so considerable. To conclude that this means population control should be assigned low priority strikes us as curious logic. Precisely because population is the most difficult and slowest to yield among the components of environmental deterioration, we must start on it at once. To ignore population today because the problem is a tough one is to commit ourselves to even gloomier prospects 20 years hence, when most of the “easy” means to reduce per capita impact on the environment will have been exhausted. The desperate and repressive measures for population control which might be contemplated then are reason in themselves to proceed with foresight, alacrity, and compassion today.

This article was originally published in Science on March 26, 1971. To review the sources, please download the article here.


244 Human Population Growth

By the end of this section, you will be able to do the following:

  • Discuss exponential human population growth
  • 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

Population dynamics can be applied to human population growth. 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. 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. 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 world’s carrying capacity for human beings might actually decrease.

The human population is currently experiencing exponential growth even though human reproduction is far below its biotic potential ((Figure)). 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 a reduction in time that it takes to add a particular number of humans to the Earth. (Figure) shows that 123 years were necessary to add 1 billion humans in 1930, but it only took 24 years to add two billion people between 1975 and 1999. As already discussed, our ability to increase our carrying capacity indefinitely my be limited. 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.


Click through this interactive view of how human populations have changed over time.

Overcoming Density-Dependent Regulation

Humans are unique in their ability to alter their environment with the conscious purpose of increasing 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, and communication. Humans can construct shelter 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 the 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 plaque 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. According to the World Health Organization, global death from infectious disease declined from 16.4 million in 1993 to 14.7 million in 1992. To compare to some of the epidemics of the past, the percentage of the world’s population killed between 1993 and 2002 decreased from 0.30 percent of the world’s population to 0.24 percent. Thus, infectious disease influence on human population growth is becoming less significant.

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)). This pattern is most often observed in underdeveloped countries where individuals do not live to old age because of less-than-optimal living conditions. Age structures of areas with slow growth, including developed countries such as the United States, still have a pyramidal structure, but with many fewer young and reproductive-aged individuals and a greater proportion of older individuals. Other developed countries, such as Italy, have zero population growth. The age structure of these populations is more conical, with an even greater percentage of middle-aged and older individuals. The actual growth rates in different countries are shown in (Figure), with the highest rates tending to be in the less economically developed countries of Africa and Asia.


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?


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 experts view this statement as incorrect based on evidence, the laws of exponential population growth are still in effect, and unchecked human population growth cannot continue indefinitely.

Several nations have instituted policies aimed at influencing population. Efforts to control population growth led to the one-child policy in China, which is now being phased out. India also implements national and regional populations to encourage family planning. On the other hand, Japan, Spain, Russia, Iran, and other countries have made efforts to increase population growth after birth rates dipped. Such policies are controversial, and the human population continues to grow. At some point the food supply may run out, but the outcomes are difficult to predict. The United Nations estimates that future world population growth may vary from 6 billion (a decrease) to 16 billion people by the year 2100.

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 emission of the greenhouse gas carbon dioxide. However, these treaties have not been ratified by every country. The role of human activity in causing climate change has become a hotly debated socio-political issue in some countries, including the United States. Thus, we enter the future with considerable uncertainty about our ability to curb human population growth and protect our environment.

Visit this website and select “Launch movie” for an animation discussing the global impacts of human population growth.

Section Summary

The world’s human population is growing at an exponential rate. Humans have increased the world’s carrying capacity through migration, agriculture, medical advances, and communication. The age structure of a population allows us to predict population growth. Unchecked human population growth could have dire long-term effects on our environment.

Visual Connection Questions

(Figure) 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?

(Figure) Stage 4 represents a population that is decreasing.

Review Questions

A country with zero population growth is likely to be ________.

  1. in Africa
  2. in Asia
  3. economically developed
  4. economically underdeveloped

Which type of country has the greatest proportion of young individuals?

  1. economically developed
  2. economically underdeveloped
  3. countries with zero population growth
  4. countries in Europe

Which of the following is not a way that humans have increased the carrying capacity of the environment?

  1. agriculture
  2. using large amounts of natural resources
  3. domestication of animals
  4. use of language

Critical Thinking Questions

Describe the age structures in rapidly growing countries, slowly growing countries, and countries with zero population growth.

Rapidly growing countries have a large segment of the population at a reproductive age or younger. Slower growing populations have a lower percentage of these individuals, and countries with zero population growth have an even lower percentage. On the other hand, a high proportion of older individuals is seen mostly in countries with zero growth, and a low proportion is most common in rapidly growing countries.

Since the introduction of the Endangered Species Act the number of species on the protected list has more than doubled. Describe how the human population’s growth pattern contributes to the rise in endangered species.


Population growth is defined as the percentage increase in a population over a given time period.

First, the initial population must be determined. For this example, the initial population size is estimated to be 10,000.

Next, you must calculate or estimate the growth rate. This is typically a growth rate per year in percent, but it can be any period length the problem calls for. For this problem, the growth rate is found to be 12% per year.

Next, you must determine the total number of years or periods that the growth occurs for. In this example, the growth occurs for 5 consecutive years.

Finally, the final population amount can be calculated using the formula above. Plugging in the information from the steps above, the final population is calculated to be 17958.56. Sometimes these numbers are rounded to the closest integer because you can have half a person.

In this next problem, we will look at a case in which the population grows on a shorter time scale of a month.

The initial population is given as 10,000. the growth rate is 15% per month, and the length of growth is 20 months.

Using the same formula as before, the growth of the population is found to be 163,666. In this problem, we can really see the effect of compound growth.

Population growth is the increasing growth of a population due to reproducing.

A population growth rate is a rate at which a population increase every year, or per time period that is being analyzed.

Typically population growth is exponential, however, at some point, all populations hit a tipping point where they cant support their growth rate any longer due to many factors including health and food supply.


Human Population Growth Lesson Plans:

In this lesson students learn about population pyramids, which show the age distribution of individuals in a country. The shape of the pyramid can tell us if the population is growing or shrinking, or if there are particular problems in the country, such as an AIDS epidemic. Having students compare population pyramids for various countries will help them learn about the value of these diagrams.

Students explore factors that change human population growth in a biology simulation for seven countries including the United States, China, Egypt, Germany, Italy, India, and Mexico. Factors such as age at which women begin having children, fertility rate and death rate are examined.

Students explore population growth, discuss potential issues associated with the world's growing population, evaluate public policy in the area of population growth, and create population pyramids.

Students examine the changes in the population in Idaho over a specific amount of time. In groups, they use a digital atlas to identify the trends in the population and describe why and how they exist. To end the lesson, they compare and contrast human population growth limits from the past and today.

Students use this lesson to focus on population growth and the threat of overpopulation. In groups, they analyze the world birth and death rates to determine the growth rate of the population. As a class, they discuss the causes and consequences of a growing population on the land space and resources available. They pretend with a partner to have a discussion about adding a new baby to their family and how it would affect Connecticut as a whole. This could be adapted for use with any geographic region.

Students examine the changes in the population in Idaho over a specific amount of time. In groups, they use the digital atlas to identify the trends in the population and describe why and how they exist. To end the lesson, they compare and contrast the human population growth limits from the past and today.

Students make a variety of mathematical calculations designed to illustrate the current size and growth rate of the human population. They analyze a graph that shows human population growth over time.


Definitions for population growth pop·u·la·tion growth

In biology or human geography, population growth is the increase in the number of individuals in a population. Many of the world's countries, including many in Sub-Saharan Africa, the Middle East, South Asia and South East Asia, have seen a sharp rise in population since the end of the Cold War. The fear is that high population numbers are putting further strain on natural resources, food supplies, fuel supplies, employment, housing, etc. in some of the less fortunate countries. For example, the population of Chad has ultimately grown from 6,279,921 in 1993 to 10,329,208 in 2009, further straining its resources. Vietnam, Mexico, Nigeria, Egypt, Ethiopia, and the DRC are witnessing a similar growth in population. Global human population growth amounts to around 83 million annually, or 1.1% per year. The global population has grown from 1 billion in 1800 to 7.616 billion in 2018. It is expected to keep growing, and estimates have put the total population at 8.6 billion by mid-2030, 9.8 billion by mid-2050 and 11.2 billion by 2100. Many nations with rapid population growth have low standards of living, whereas many nations with low rates of population growth have high standards of living.

Freebase (3.16 / 36 votes) Rate this definition:

Population growth is the change in a population over time, and can be quantified as the change in the number of individuals of any species in a population using "per unit time" for measurement. In biology, the term population growth is likely to refer to any known organism, but this article deals mostly with the application of the term to human populations in demography. In demography, population growth is used informally for the more specific term population growth rate, and is often used to refer specifically to the growth of the human population of the world. Simple models of population growth include the Malthusian Growth Model and the logistic model. The world population grew from 1 billion to 7 billion from 1800 to 2011. During the year 2011, according to estimates, 135 million people were born and 57 million died, for an increase in population of 78 million.

U.S. National Library of Medicine (3.95 / 27 votes) Rate this definition:

Increase, over a specific period of time, in the number of individuals living in a country or region.


Free Response

Describe the age structures in rapidly growing countries, slowly growing countries, and countries with zero population growth.

Rapidly growing countries have a large segment of the population at a reproductive age or younger. Slower growing populations have a lower percentage of these individuals, and countries with zero population growth have an even lower percentage. On the other hand, a high proportion of older individuals is seen mostly in countries with zero growth, and a low proportion is most common in rapidly growing countries.


Watch the video: Global population growth. Environment. Biology. FuseSchool (July 2022).


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