4.1.1: History of Human Population Growth - Biology

4.1.1: History of Human Population Growth - Biology

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The human population is growing rapidly. For most of human history, there were fewer than 1 billion people on the planet. During the time of the Agricultural Revolution, 10,000 B.C., there were only 5-10 million people on Earth - which is basically the population of New York City today. In 1800, when the Industrial Revolution began, there were approximately 1 billion people on Earth. Continued agricultural expansion and extraction of fossil fuels and minerals led to rapid global economic growth and, in turn, population growth in the 19th century. We’ve added over 6 billion people to the human population in just a little over 200 years (figure (PageIndex{a})). As of August 2020, the global human population is around 7.8 billion people.

The fundamental cause of the acceleration of growth rate for humans in the past 200 years has been the reduced death rate due to changes in public health and sanitation. Clean drinking water and proper disposal sewage has drastically improved health in developed nations. Also, medical innovations such as 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 one hundred million people. Naturally, infectious disease continues to have an impact on human population growth, especially in poorer nations. For example, life expectancy in sub-Saharan Africa, which was increasing from 1950 to 1990, began to decline after 1985 largely as a result of HIV/AIDS mortality. According to a 2016 study by Marcus et al., The reduction in life expectancy caused by HIV/AIDS was estimated to be 8 years for 2016.

Figure (PageIndex{a}): Human population growth since 1000 AD is exponential (dark blue line). Notice that while the population in Asia (yellow line), which has many economically underdeveloped countries, is increasing exponentially, the population in Europe (light blue line), where most of the countries are economically developed, is growing much more slowly.

Although global population size continues to increase, the rate of human population growth has decreased. This means that the population size is not increasing as quickly as it did in the past (figure (PageIndex{b})).

Figure (PageIndex{b}): Global population growth rate from 1950-2010 and projections through 2050. Image by U.S. Census (public domain).

Human technology and particularly our harnessing of the energy contained in fossil fuels have caused unprecedented changes to Earth’s environment, altering ecosystems to the point where some may be in danger of collapse. Changes on a global scale including depletion of the ozone layer, desertification and topsoil loss, and global climate change are caused by human activities.


Marcus, J. L., Chao, C. R., Leyden, W. A., Xu, L., Quesenberry, C. P., Jr, Klein, D. B., Towner, W. J., Horberg, M. A., & Silverberg, M. J. (2016). Narrowing the Gap in Life Expectancy Between HIV-Infected and HIV-Uninfected Individuals With Access to Care. Journal of acquired immune deficiency syndromes (1999), 73(1), 39–46.

Human Population Growth: The Effects on Biodiversity

“The massive growth in the human population through the 20th century has had more impact on biodiversity than any other single factor.” –Sir David King, science advisor to the UK government.

We all know that the population is expanding. However how often is it that we really think about the effects? How many times have we even seen the effects with our own eyes?

It can be a tough subject to pinpoint exactly, but one of the ways we can begin to do that is through investigating one of the ways that human population growth affects the planet most visibly: through the plant’s biodiversity, and through the lives of species other than our own. In fact, the growth of the human species is the main factor in the mass animal extinctions that we have experienced over the recent years.

Today, our population is over 7 billion. Before we had gotten to the 6 billion mark, humans alone were already using over 40 percent of the global NPP number. NPP is the term used to describe the process of species utilizing the sun’s energy for the sustaining of life. What’s interesting (and alarming) to note about this is the fact that humans have been on this earth for far less time than the majority of the earth’s species. In fact, we are a relatively young group – while our ancestors lived as many as 6 million years ago, the modern form of the human as we know it today has only been in existence for around 200,000 years. The oldest animal fossil to date, on the other hand, is around 560 million years old.

Thus, human population growth arguably affects other species even more than it does our down. Humans share the earth’s resources with countless other species (the majority of which also most likely haven’t even been discovered yet!). A primary issue that lies in this is the fact that as humans, we don’t exactly seem to know how to share very well at all. Rapid growth of the human population has resulted in the increase of human need for earth’s natural resources – food, water, the materials for shelter, etc. Because of this, we are increasingly cutting into resources that other species must use in order to survive. We have hindered, or even ended the lives, of numerous species. Today, 99% of the species still remaining on this planet are at risk because of human activity alone.

For example, exploitation and habitat loss through human activity has resulted in the loss of approximately 93% of the world’s tigers. Today, there could be as few as 3,000 tigers left on the planet.

5 species of rhinos have recently gone extinct because of humans, as well. According to Huffington Post, the west African black rhino (the most recent species of rhino to go extinct) was officially declared extinct because of habitat loss, as well as an increase in poaching for rhino horns.

The passenger pigeon one made up as much as 40 percent of the world’s bird population. Today, there are no passenger pigeons left.

According to the Discovery Channel, as of 2014 humans have directly caused 322 animal extinctions over the past 500 years alone. All of this has occurred while, simultaneously, the human population has grown exponentially.

It’s easy to wonder how the numbers have grown to be so extreme on both ends of the spectrum. The truth is, it’s an inverse relationship – as human population, demands, the need for resources goes up the number of species and their quality of life goes down. And we were the ones to take it to the extreme measures that we see today.

The existence of species other than our own is crucial for the health of the planet – and that seems like an obvious statement.

So what is it then that we’ve done? Do we truly need all of the resources that we are continuing to exploit? Or do we just have a lack of willpower that we can’t seem to get over?

Human Population Growth and extinction

We're in the midst of the Earth&rsquos sixth mass extinction crisis. Harvard biologist E. O. Wilson estimates that 30,000 species per year (or three species per hour) are being driven to extinction. Compare this to the natural background rate of one extinction per million species per year, and you can see why scientists refer to it as a crisis unparalleled in human history.

The current mass extinction differs from all others in being driven by a single species rather than a planetary or galactic physical process. When the human race &mdash Homo sapiens sapiens &mdash migrated out of Africa to the Middle East 90,000 years ago, to Europe and Australia 40,000 years ago, to North America 12,500 years ago, and to the Caribbean 8,000 years ago, waves of extinction soon followed. The colonization-followed-by-extinction pattern can be seen as recently as 2,000 years ago, when humans colonized Madagascar and quickly drove elephant birds, hippos, and large lemurs extinct [1].

The first wave of extinctions targeted large vertebrates hunted by hunter-gatherers. The second, larger wave began 10,000 years ago as the discovery of agriculture caused a population boom and a need to plow wildlife habitats, divert streams, and maintain large herds of domestic cattle. The third and largest wave began in 1800 with the harnessing of fossil fuels. With enormous, cheap energy at its disposal, the human population grew rapidly from 1 billion in 1800 to 2 billion in 1930, 4 billion in 1975, and over 7.5 billion today. If the current course is not altered, we&rsquoll reach 8 billion by 2020 and 9 to 15 billion (likely the former) by 2050.

No population of a large vertebrate animal in the history of the planet has grown that much, that fast, or with such devastating consequences to its fellow earthlings. Humans&rsquo impact has been so profound that scientists have proposed that the Holocene era be declared over and the current epoch (beginning in about 1900) be called the Anthropocene: the age when the "global environmental effects of increased human population and economic development" dominate planetary physical, chemical, and biological conditions [2].

  • Humans annually absorb 42 percent of the Earth&rsquos terrestrial net primary productivity,30 percent of its marine net primary productivity, and 50 percent of its fresh water [3].
  • Forty percent of the planet&rsquos land is devoted to human food production, up from 7 percent in 1700 [3].
  • Fifty percent of the planet&rsquos land mass has been transformed for human use [3].
  • More atmospheric nitrogen is now fixed by humans that all other natural processes combined [3].

The authors of Human Domination of Earth's Ecosystems, including the current director of the National Oceanic and Atmospheric Administration, concluded:

"[A]ll of these seemingly disparate phenomena trace to a single cause: the growing scale of the human enterprise. The rates, scales, kinds, and combinations of changes occurring now are fundamentally different from those at any other time in history. . . . We live on a human-dominated planet and the momentum of human population growth, together with the imperative for further economic development in most
of the world, ensures that our dominance will increase."

Predicting local extinction rates is complex due to differences in biological diversity, species distribution, climate, vegetation, habitat threats, invasive species, consumption patterns, and enacted conservation measures. One constant, however, is human population pressure. A study of 114 nations found that human population density predicted with 88-percent accuracy the number of endangered birds and mammals as identified by the International Union for the Conservation of Nature [4]. Current population growth trends indicate that the number of threatened species will increase by 7 percent over the next 20 years and 14 percent by 2050. And that&rsquos without the addition of global warming impacts.

When the population of a species grows beyond the capacity of its environment to sustain it, it reduces that capacity below the original level, ensuring an eventual population crash.

"The density of people is a key factor in species threats," said Jeffrey McKee, one of the study&rsquos authors. "If other species follow the same pattern as the mammals and birds. we are facing a serious threat to global biodiversity associated with our growing human population." [5].

So where does wildlife stand today in relation to 7.5 billion people? Worldwide, 12 percent of mammals, 12 percent of birds, 31 percent of reptiles, 30 percent of amphibians, and 37 percent of fish are threatened with extinction [6]. Not enough plants and invertebrates have been assessed to determine their global threat level, but it is severe.

Extinction is the most serious, utterly irreversible effect of unsustainable human population. But unfortunately, many analyses of what a sustainable human population level would look like presume that the goal is simply to keep the human race at a level where it has enough food and clean water to survive. Our notion of sustainability and ecological footprint &mdash indeed, our notion of world worth living in &mdash presumes that humans will allow for, and themselves enjoy, enough room and resources for all species to live.

Human Population Growth and Climate Change

The largest single threat to the ecology and biodiversity of the planet in the decades to come will be global climate disruption due to the buildup of human-generated greenhouse gases in the atmosphere. People around the world are beginning to address the problem by reducing their carbon footprint through less consumption and better technology. But unsustainable human population growth can overwhelm those efforts, leading us to conclude that we not only need smaller footprints, but fewer feet.

Portland, Oregon, for example, decreased its combined per-capita residential energy and car driving carbon footprint by 5 percent between 2000 and 2005. During this same period, however, its population grew by 8 percent.

Scientists warn we must reduce atmospheric CO2 to 350 ppm in order to avoid global catastrophe.
Sign the People's Petition to Cap Carbon at 350 Parts Per Million today.

A 2009 study of the relationship between population growth and global warming determined that the “carbon legacy” of just one child can produce 20 times more greenhouse gas than a person will save by driving a high-mileage car, recycling, using energy-efficient appliances and light bulbs, etc. Each child born in the United States will add about 9,441 metric tons of carbon dioxide to the carbon legacy of an average parent. The study concludes, “Clearly, the potential savings from reduced reproduction are huge compared to the savings that can be achieved by changes in lifestyle.”

One of the study’s authors, Paul Murtaugh, warned that: “In discussions about climate change, we tend to focus on the carbon emissions of an individual over his or her lifetime. Those are important issues and it's essential that they should be considered. But an added challenge facing us is continuing population growth and increasing global consumption of resources. . . . Future growth amplifies the consequences of people's reproductive choices today, the same way that compound interest amplifies a bank balance."

The size of the carbon legacy is closely tied to consumption patterns. Under current conditions, a child born in the United States will be responsible for almost seven times the carbon emissions of a child born in China and 168 times the impact of a child born in Bangladesh.

The globalization of the world economy, moreover, can mask the true carbon footprint of individual nations. China, for example, recently surpassed the United States to become the world’s leading greenhouse gas emitter. But a large portion of those gases is emitted in the production of consumer goods for the United States and Europe. Thus a large share of “China’s” greenhouse gas footprint is actually the displaced footprint of high-consumption western nations.

The United States has the largest population in the global north, and is the only high-income nation experiencing significant population growth: Its population may double before the end of the century. Its 300 million inhabitants produce greenhouse gases at a per-capita rate that is more than double that of Europe, five times the global average, and more than 10 times the average of the global south. The U.S. greenhouse gas contribution is driven by a disastrous combination of high population, significant growth, and massive (and rising) consumption levels, and thus far, lack of political will to end our fossil-fuel addiction.

More than half of the U.S. population now lives in car-dependent suburbs. Cumulatively, we drive 3 trillion miles each year. The average miles traveled per capita is increasing rapidly, and the transportation sector now accounts for one-third of all U.S. carbon emissions.

Another one-fifth of U.S. carbon emissions comes from the residential sector. Average home sizes have increased dramatically in recent decades, as has the accompanying footprint of each home. Suburban sprawl contributes significantly to deforestation, reducing the capacity of the planet to absorb the increased CO2 we emit. Due to a dramatic decrease in household size, from 3.1 persons per home in 1970 to 2.6 in 2000, homebuilding is outpacing the population growth that is driving it. More Americans are driving farther to reach bigger homes with higher heating and cooling demands and fewer people per household than ever before. All of these trends exacerbate the carbon footprint inherent in the basic energy needs of a burgeoning U.S. population.

Globally, recent research indicates that assumptions regarding declining fertility rates used by the Intergovernmental Panel on Climate Change to develop future emissions scenarios may be overly optimistic. While fertility rates have generally declined over the past few decades, progress has slowed in recent years, especially in the global south, largely due to cutbacks in family planning assistance and political interference from the United States. And even if fertility rates are reduced to below replacement levels, population levels will continue to climb steeply for some time as people live longer and billions of young people mature and proceed through their reproductive years. Per-capita greenhouse gas emissions may drop, but the population bulge will continue to contribute to a dangerous increase in greenhouse gases in the atmosphere.

Time is short, but it is not too late to stop the climate crisis. Economy-wide reduction of greenhouse gas emissions to a level that brings atmospheric CO2 back from 386 parts per million to 350 or less, scaling back global north consumption patterns, and long-term population reduction to ecologically sustainable levels will solve the climate change crisis and move us to toward a healthier, more stable, post-fossil fuel, post-growth addicted society.

When is R an appropriate maximand?

The expected lifetime number of offspring, commonly denoted by R, is often used as a maximand in life history theory. Hawkes et al.’s model [3], for example, relies heavily on the theory developed by Charnov (e.g. [17]), which is based on R as a maximand. Kaplan et al.’s model [1], which I reanalyze below, uses R to develop a general theory of human life history evolution. R is commonly used outside of anthropology many examples can be found in [8, 9] and [10]. An important problem, then, is to determine the conditions under which R can be used in optimality models. I show here that the conditions are more limiting than some authors appear to appreciate.

It is frequently claimed that R is a correct fitness measure under zero population growth. This is true in the sense that it determines the rate of gene frequency change over a short period when r = 0 [13]. As such, R is an appropriate dynamical measure of fitness under such conditions. In particular, R is a useful dynamical measure of fitness in density-dependent populations because, over evolutionary time, the population will usually be near carrying capacity at which r = 0 (assuming no cyclic or chaotic dynamics). Maximization methods, however, treat long-term evolutionary questions: they assume that enough time has passed for all possible strategies to invade, and for selection to bring the optimal strategy to high frequency (see [18] for a discussion of timescale in models of natural selection). As a fitness maximand, R generally fails, even in density-dependent populations with zero growth. The reason is that, under density dependence, a strategy does not have a single number R. Rather, R becomes a function of population size. Without a single number by which to compare different strategies, one cannot use a maximization procedure. One could choose an arbitrary N at which to evaluate R, but this has no justification in general—especially because the ordering of R across strategies may vary with N. In fact, the theory of the previous section shows that the single number of interest is N ^ , a strategy’s carrying capacity.

  1. Density dependence only affects expected fertility via the same multiplier for all strategies, independently of age. Survival is not density-dependent.
  2. Density dependence only affects the probability of survival to reproductive ages via the same multiplier for all strategies. Fertility is not density-dependent.
  3. Density dependence affects both fertility and survival via the mechanisms in (1) and (2), only.

It is easy to imagine plausible cases where these conditions do not hold. For example, suppose that the D’s are not equal for A and B—in other words, one strategy is more affected by crowding than the other. Then the exponential terms in Equation (6) would not cancel, allowing the possibility for the ordering of R’s to vary by N. Another possibility is to imagine a simple form of density-dependent survival: suppose the probability of survival at each age is affected by a simple exponential multiplier, similar to above. Because the probability of surviving to age x is the product of survival probabilities at each previous age, the exponential term now contains x in the exponent: (8) If we suppose fertility is density independent, then the ratio RA/RB is (9) Now the term involving N is age dependent (i.e., it includes x), so it cannot be removed from the integral and canceled. The relative orderings of R will not necessarily be independent of N, and therefore we cannot use R to deduce the optimal strategy.

The three conditions noted above do not appear to be well appreciated, especially among anthropologists. There is no mention of these strict conditions by Kaplan et al. [1], for example. This is probably because life history theorists have not always been clear about demographic assumptions in the classic models. For example, Hawkes et al. [3] rely on Charnov’s R-based models, including a paper in which Charnov claims that R is “a Darwinian fitness measure appropriate for a nongrowing population,” and uses it as a maximand [19]. We have seen that this is incorrect in general. Fortunately, Charnov’s models frequently assume the second density-dependence case listed above (see, e.g., [20, 17]), for which R is appropriate. Unfortunately, this form of density dependence is not mentioned in the articles cited by [3] it is not surprising, then, that they do not state restrictions themselves. The three conditions are also not noted influential life history textbooks [8, 10, 9].

The broad conclusion here is that one cannot study the evolution of a density-dependent population in general by maximizing a density-independent function of R. Further, the assumption of zero population growth alone does not justify R as a maximand. R is only appropriate under the specific forms of density dependence listed above. Whether these conditions are accurate for human populations is largely unknown certainly they have not been justified by anthropologists.

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.

With a 2012 rate of natural increase in Mexico of 1.5%, its population would be expected to double in 46 years (0.69/0.015 = 46) from its 116.1 million people now to some 232 million in 2058. Will it?

No one knows for certain. What actually happens to population growth depends on a number of factors. Some of these can be estimated with some confidence, some cannot.

  • the age structure of the population and
  • the total fertility rate (TFR).

Total Fertility Rate (TFR)

The total fertility rate is the average number of children that each woman will have during her lifetime. The TFR is an average because, of course, some women will have more, some fewer, and some no children at all.

Theoretically, when the TFR = 2, each pair of parents just replaces itself.

Actually it takes a TFR of 2.1 or 2.2 to replace each generation &mdash this number is called the replacement rate &mdash because some children will die before they grow up to have their own two children. In countries with low life expectancies, the replacement rate is even higher (2.2&ndash3).

Age Structure of Populations

But even a TFR of 2.1 may not ensure zero population growth (ZPG). If at one period a population has an unusually large number of children, they will &mdash as they pass through their childbearing years &mdash increase the r of the population even if their TFR goes no higher than 2.

Most childbearing is done by women between the ages of 15 and 49. So if a population has a large number of young people just entering their reproductive years, the rate of growth of that population is sure to rise.

These pyramids compare the age structure of the populations of France and India in 1984. The relative number (%) of males and females is shown in 5-year cohorts. Almost 20% of India's population were children &mdash 15 years or less in age &mdash who had yet to begin reproduction. When the members of a large cohort like this begin reproducing, they add greatly to birth rates. In France, in contrast, each cohort is about the size of the next until close to the top when old age begins to take its toll.

  • with high birth rates
  • low life expectancies (where many people die before reaching old age)
  • advances in public health have recently reduced infant and childhood mortality.

The U.S. Baby Boom

The TFR in the United States declined from more than 4 late in the nineteenth century to less than replacement in the early 1930s.

However, when the small numbers of children born in the depression years reached adulthood, they went on a childbearing spree that produced the baby-boom generation. In 1957 more children were born in the United States than ever before (or since).

These population pyramids show the baby-boom generation in 1970 and again in 1985 (green ovals).

Profound changes (e.g. enrollments in schools and colleges) have occurred &mdash and continue to occur &mdash in U.S. society as this bulge passes into ever-older age brackets.

The baby boomers seem not to be headed for the high TFRs of their parents. They are marrying later and having smaller families than their parents. So it looks as though the TFR for the baby-boom generation will not exceed replacement rate.

But this is not the same as zero population growth. Even with the current TFR of 1.7, this large cohort of people will keep the U.S. population growing during their reproductive years (current value for r = 0.3%).

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.

Global Problems of Population Growth

This survey course introduces students to the important and basic material on human fertility, population growth, the demographic transition and population policy. Topics include: the human and environmental dimensions of population pressure, demographic history, economic and cultural causes of demographic change, environmental carrying capacity and sustainability. Political, religious and ethical issues surrounding fertility are also addressed. The lectures and readings attempt to balance theoretical and demographic scale analyzes with studies of individual humans and communities. The perspective is global with both developed and developing countries included.

This Yale College course, taught on campus twice per week for 75 minutes, was recorded for Open Yale Courses in Spring 2009.


This survey course introduces students to the important and basic material on human fertility, population growth, the demographic transition and population policy. Topics include: the human and environmental dimensions of population pressure, demographic history, economic and cultural causes of demographic change, environmental carrying capacity and sustainability. Political, religious and ethical issues surrounding fertility are also addressed. The lectures and readings attempt to balance theoretical and demographic scale analyzes with studies of individual humans and communities. The perspective is global with both developed and developing countries included.

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There are two midterm examinations and a final. Each 75 minute midterm (25% of final grade each) will cover material on the preceding third of the course. The first half of the final exam (75 minutes) will cover the material from the last third of the course (25% of final grade). The second half of the final (also 75 minutes) will contain comprehensive questions (25% of final grade). Students have the option of submitting a paper of 10-20 pages (double spaced) in lieu of taking the second half of the final (25% of final grade).

Midterm examination 1: 25%
Midterm examination 2: 25%
Final examination: 50%

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.

Watch the video: Human Population Growth (July 2022).


  1. Rhoecus

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  2. Tynan

    it seems to me, you are right

  3. Dearg

    I see, thank you for your help in this matter.

  4. Yozshugami

    let's take a look

  5. Upton

    Sorry, I thought, and deleted the sentence

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