Extracts from commentary by thinkers through the ages.
- Aristotle, philosopher (lived 384-322 BC)
- Nicolas Machiavelli, political theorist and philosopher (lived 1469-1527)
- Thomas Malthus, clergyman and scholar (lived 1766-1832)
- John Stuart Mill, philosopher (lived 1806-1873)
- Bertrand Russell, philosopher (lived 1872-1970)
- Aldous Huxley, writer (lived 1894-1963)
- Garrett Hardin, ecologist (lived 1915-2003)
- Paul Ehrlich, biologist (born 1932)
- Isaac Asimov, author (lived 1920-1992)
- John Gray, philosopher (born 1948)
- William Rees, academic (born 1943)
Aristotle, philosopher (lived 384-322 BC)
Politics — 350BC
[1265a] [In Plato’s Laws] it is also strange that although equalizing properties the writer does not regulate the number of the citizens, but leaves the birth-rate uncontrolled, on the assumption that it will be sufficiently leveled up to the same total owing to childless marriages, however many children are begotten, [1265b] because this seems to take place in the states at present.
But this ought to be regulated much more in the supposed case than it is now, for now nobody is destitute, because estates are divided among any number, but then, as division of estates will not be allowed, the extra children will necessarily have nothing, whether they are fewer in number or more.
And one might think that restriction ought to be put on the birth-rate rather than on property, so as not to allow more than a certain number of children to be produced, and that in fixing their number consideration should be paid to the chances of its happening that some of the children born may die, and to the absence of children in the other marriages; but for the matter to be left alone, as it is in most states, is bound to lead to poverty among the citizens, and poverty produces sedition and crime.
[1270a] It is better for a state’s male population to be kept up by measures to equalize property. The law in relation to parentage is also somewhat adverse to the correction of this evil. [1270b] For the lawgiver desiring to make the Spartiates as numerous as possible holds out inducements to the citizens to have as many children as possible: for they have a law releasing the man who has been father of three sons from military service, and exempting the father of four from all taxes. Yet it is clear that if a number of sons are born and the land is correspondingly divided there will inevitably come to be many poor men.
Nicolas Machiavelli, political theorist and philosopher (lived 1469-1527)
Titus Livius — 1517
As for the causes of oblivion which we may refer to Heaven, they are those which make havoc of the human race, and reduce the population of certain parts of the world to a very small number.
This happens by plague, famine, or flood, of which three the last is the most hurtful, as well because it is the most universal, as because those saved are generally rude and ignorant mountaineers, who possessing no knowledge of antiquity themselves, can impart none to those who come after them. Or if among the survivors there chance to be one possessed of such knowledge, to give himself consequence and credit, he will conceal and pervert it to suit his private ends, so that to his posterity there will remain only so much as he may have been pleased to communicate, and no more.
That these floods, plagues, and famines do in fact happen, I see no reason to doubt, both because we find all histories full of them, and recognize their effect in this oblivion of the past, and also because it is reasonable that such things should happen.
For as when much superfluous matter has gathered in simple bodies, nature makes repeated efforts to remove and purge it away, thereby promoting the health of these bodies, so likewise as regards that composite body the human race, when every province of the world so teems with inhabitants that they can neither subsist where they are nor remove elsewhere, every region being equally crowded and over-peopled, and when human craft and wickedness have reached their highest pitch, it must needs come about that the world will purge herself in one or another of these three ways, to the end that men, becoming few and contrite, may amend their lives and live with more convenience.
Thomas Malthus, clergyman and scholar (lived 1766-1832)
An Essay on the Principle of Population
The happiness of a country does not depend, absolutely, upon its poverty or its riches, upon its youth or its age, upon its being thinly or fully inhabited, but upon the rapidity with which it is increasing, upon the degree in which the yearly increase of food approaches to the yearly increase of an unrestricted population.
This approximation is always the nearest in new colonies, where the knowledge and industry of an old state operate on the fertile unappropriated land of a new one.
In other cases, the youth or the age of a state is not in this respect of very great importance. It is probable that the food of Great Britain is divided in as great plenty to the inhabitants, at the present period, as it was two thousand, three thousand, or four thousand years ago. And there is reason to believe that the poor and thinly inhabited tracts of the Scotch Highlands are as much distressed by an overcharged population as the rich and populous province of Flanders.
Were a country never to be overrun by a people more advanced in arts, but left to its own natural progress in civilization; from the time that its produce might be considered as an unit, to the time that it might be considered as a million, during the lapse of many hundred years, there would not be a single period when the mass of the people could be said to be free from distress, either directly or indirectly, for want of food.
In every state in Europe, since we have first had accounts of it, millions and millions of human existences have been repressed from this simple cause; though perhaps in some of these states an absolute famine has never been known.
Famine seems to be the last, the most dreadful resource of nature. The power of population is so superior to the power in the earth to produce subsistence for man, that premature death must in some shape or other visit the human race.
The vices of mankind are active and able ministers of depopulation. They are the precursors in the great army of destruction; and often finish the dreadful work themselves. But should they fail in this war of extermination, sickly seasons, epidemics, pestilence, and plague, advance in terrific array, and sweep off their thousands and ten thousands.
Should success be still incomplete, gigantic inevitable famine stalks in the rear, and with one mighty blow levels the population with the food of the world.
Limits to Growth — 1798
But to make the argument more general and less interrupted by the partial views of emigration, let us take the whole earth, instead of one spot, and suppose that the restraints to population were universally removed.
If the subsistence for man that the earth affords was to be increased every twenty-five years by a quantity equal to what the whole world at present produces, this would allow the power of production in the earth to be absolutely unlimited, and its ratio of increase much grater than we can conceive that any possible exertions of mankind could make it.
Taking the population of the world at any number, a thousand millions for instance, the human species would increase in the ratio of – 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, etc. and subsistence as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 etc.
In two centuries and a quarter, the population would be to the means of subsistence as 512 to 10: in three centuries as 4096 to 13, and in two thousand years the difference would be almost incalculable, though the produce in that time would have increased to an immense extent.
John Stuart Mill, philosopher (lived 1806-1873)
Principles of Political Economy (1848), Book IV, Chapter VI, §3, p. 516.
There is room in the world, no doubt, and even in old countries, for a great increase of population, supposing the arts of life to go on improving, and capital to increase. But even if innocuous, I confess I see very little reason for desiring it.
The density of population necessary to enable mankind to obtain, in the greatest degree, all the advantages both of co-operation and of social intercourse, has, in all the most populous countries, been attained. If the earth must lose that great portion of its pleasantness which it owes to things that the unlimited increase of wealth and population would extirpate from it, for the mere purpose of enabling it to support a larger but not a better or a happier population, I sincerely hope, for the sake of posterity, that they will be content to be stationary, long before necessity compels them to it…
The notion that it was possible to go further than this in removing the injustice — for injustice it is, whether admitting of a complete remedy or not — involved in the fact that some are born to riches and the vast majority to poverty, I then reckoned chimerical, and only hoped that by universal education, leading to voluntary restraint on population, the portion of the poor might be made more tolerable.
In short, I was a democrat, but not the least of a Socialist. We were now much less democrats than I had been, because so long as education continues to be so wretchedly imperfect, we dreaded the ignorance and especially the selfishness and brutality of the mass: but our ideal of ultimate improvement went far beyond Democracy, and would class us decidedly under the general designation of Socialists.
While we repudiated with the greatest energy that tyranny of society over the individual which most Socialistic systems are supposed to involve, we yet looked forward to a time when society will no longer be divided into the idle and the industrious; when the rule that they who do not work shall not eat, will be applied not to paupers only, but impartially to all; when the division of the produce of labour, instead of depending, as in so great a degree it now does, on the accident of birth, will be made by concert on an acknowledged principle of justice; and when it will no longer either be, or be thought to be, impossible for human beings to exert themselves strenuously in procuring benefits which are not to be exclusively their own, but to be shared with the society they belong to.
The social problem of the future we considered to be, how to unite the greatest individual liberty of action, with a common ownership in the raw material of the globe, and an equal participation of all in the benefits of combined labour.
We had not the presumption to suppose that we could already foresee, by what precise form of institutions these objects could most effectually be attained, or at how near or how distant a period they would become practicable. We saw clearly that to render any such social transformation either possible or desirable, an equivalent change of character must take place both in the uncultivated herd who now compose the labouring masses, and in the immense majority of their employers.
Both these classes must learn by practice to labour and combine for generous, or at all events for public and social purposes, and not, as hitherto, solely for narrowly interested ones. But the capacity to do this has always existed in mankind, and is not, nor is ever likely to be, extinct. Education, habit, and the cultivation of the sentiments, will make a common man dig or weave for his country, as readily as fight for his country.
True enough, it is only by slow degrees, and a system of culture prolonged through successive generations, that men in general can be brought up to this point. But the hindrance is not in the essential constitution of human nature. Interest in the common good is at present so weak a motive in the generality not because it can never be otherwise, but because the mind is not accustomed to dwell on it as it dwells from morning till night on things which tend only to personal advantage. When called into activity, as only self-interest now is, by the daily course of life, and spurred from behind by the love of distinction and the fear of shame, it is capable of producing, even in common men, the most strenuous exertions as well as the most heroic sacrifices.
The deep-rooted selfishness which forms the general character of the existing state of society, is so deeply rooted, only because the whole course of existing institutions tends to foster it; modern institutions in some respects more than ancient, since the occasions on which the individual is called on to do anything for the public without receiving its pay, are far less frequent in modern life, than the smaller commonwealths of antiquity.
Bertrand Russell, philosopher (lived 1872-1970)
The Impact of Science on Society — New York: Simon & Schuster, 1951 and 1953
I do not pretend that birth control is the only way in which population can be kept from increasing. There are others, which, one must suppose, opponents of birth control would prefer.
War, as I remarked a moment ago, has hitherto been disappointing in this respect, but perhaps bacteriological war may prove more effective. If a Black Death could be spread throughout the world once in every generation survivors could procreate freely without making the world too full.
There would be nothing in this to offend the consciences of the devout or to restrain the ambitions of nationalists. The state of affairs might be somewhat unpleasant, but what of that? Really high-minded people are indifferent to happiness, especially other people’s. (p. 26)
Aldous Huxley, writer (lived 1894-1963)
Brave New World Revisited — 1958
On the first Christmas Day the population of our planet was about two hundred and fifty millions — less than half the population of modern China. Sixteen centuries later, when the Pilgrim Fathers landed at Plymouth Rock, human numbers had climbed to a little more than five hundred millions.
By the time of the signing of the Declaration of Independence, world population had passed the seven hundred million mark. In 1931, when I was writing Brave New World, it stood at just under two billions.
Today, only twenty-seven years later, there are two billion eight hundred million of us.
And tomorrow — what?
Penicillin, DDT and clean water are cheap commodities, whose effects on public health are out of all proportion to their cost. Even the poorest government is rich enough to provide its subjects with a substantial measure of death control. Birth control is a very different matter.
Death control is something which can be provided for a whole people by a few technicians working in the pay of a benevolent government. Birth control depends on the co-operation of an entire people. It must be practiced by countless individuals, from whom it demands more intelligence and will power than most of the world’s teeming illiterates possess, and (where chemical or mechanical methods of contraception are used) an expenditure of more money than most of these millions can now afford.
Moreover, there are nowhere any religious traditions in favor of unrestricted death, whereas religious and social traditions in favor of unrestricted reproduction are widespread.
For all these reasons, death control is achieved very easily, birth control is achieved with great difficulty.
Death rates have therefore fallen in recent years with startling suddenness. But birth rates have either remained at their old high level or, if they have fallen, have fallen very little and at a very slow rate. In consequence, human numbers are now increasing more rapidly than at any time in the history of the species.
Garrett Hardin, ecologist (lived 1915-2003)
The Tragedy of the Commons — 1968
Population, as Malthus said, naturally tends to grow “geometrically,” or, as we would now say, exponentially.
In a finite world, this means that the per-capita share of the world’s goods must decrease. Is ours a finite world?
A fair defence can be put forward for the view that the world is infinite, or that we do not know that it is not. But, in terms of the practical problems that we must face in the next few generations with the foreseeable technology, it is clear that we will greatly increase human misery if we do not, during the immediate future, assume that the world available to the terrestrial human population is finite. “Space” is no escape.
A finite world can support only a finite population; therefore, population growth must eventually equal zero. (The case of perpetual wide fluctuations above and below zero is a trivial variant that need not be discussed.)
When this condition is met, what will be the situation of mankind? Specifically, can Bentham’s goal of “the greatest good for the greatest number” be realized?
No — for two reasons, each sufficient by itself.
The first is a theoretical one. It is not mathematically possible to maximize for two (or more) variables at the same time. This was clearly stated by von Neumann and Morgenstern,  but the principle is implicit in the theory of partial differential equations, dating back at least to D’Alembert (1717-1783).
The second reason springs directly from biological facts. To live, any organism must have a source of energy (for example, food). This energy is utilized for two purposes: mere maintenance, and work.
For man, maintenance of life requires about 1600 kilocalories a day (“maintenance calories”). Anything that he does over and above merely staying alive will be defined as work, and is supported by “work calories”, which he takes in.
Work calories are used not only for what we call work in common speech; they are also required for all forms of enjoyment, from swimming and automobile racing to playing music and writing poetry.
If our goal is to maximize population, it is obvious what we must do: We must make the work calories per person approach as close to zero as possible. No gourmet meals, no vacations, no sports, no music, no literature, no art … I think that everyone will grant, without argument or proof, that maximizing population does not maximize goods. Bentham’s goal is impossible.
In reaching this conclusion I have made the usual assumption that it is the acquisition of energy that is the problem. The appearance of atomic energy has led some to question this assumption. However, given an infinite source of energy, population growth still produces an inescapable problem. The problem of the acquisition of energy is replaced by the problem of its dissipation, as J. H. Fremlin has so wittily shown.  The arithmetic signs in the analysis are, as it were, reversed; but Bentham’s goal is unobtainable.
The optimum population is, then, less than the maximum. The difficulty of defining the optimum is enormous; so far as I know, no one has seriously tackled this problem. Reaching an acceptable and stable solution will surely require more than one generation of hard analytical work — and much persuasion.
Paul Ehrlich, biologist (born 1932)
The Population Explosion — 1990
The key to understanding overpopulation is not population density but the numbers of people in an area relative to its resources and the capacity of the environment to sustain human activities; that is, to the area’s carrying capacity.
When is an area overpopulated? When its population can’t be maintained without rapidly depleting nonrenewable resources (or converting renewable resources into nonrenewable ones) and without degrading the capacity of the environment to support the population.
In short, if the long-term carrying capacity of an area is clearly being degraded by its current human occupants, that area is overpopulated.
By this standard, the entire planet and virtually every nation is already vastly overpopulated. Africa is overpopulated now because, among other indications, its soils and forests are rapidly being depleted — and that implies that its carrying capacity for human beings will be lower in the future than it is now.
The United States is overpopulated because it is depleting its soil and water resources and contributing mightily to the destruction of global environmental systems.
Europe, Japan, the Soviet Union, and other rich nations are overpopulated because of their massive contributions to the carbon dioxide buildup in the atmosphere, among many other reasons.
Almost all the rich nations are overpopulated because they are rapidly drawing down stocks of resources around the world. They don’t live solely on the land in their own nations. Like the profligate son of our earlier analogy, they are spending their capital with no thought for the future.
Optimum Human Population Size — 1994
Although the tremendous size and rate of growth of the human population now influence virtually every aspect of society, rarely does the public debate, or even consider, the question of what would be an optimum number of human beings to live on Earth at any given time?
While there are many possible optima depending on both the criteria defining “optimum” and on prevailing biophysical and social conditions, there is a solid scientific basis for determining the bounds of possibilities. All optima must lie between the minimum viable population size, MVP (Gilpin & Soule, 1986; Soule, 1987) and the biophysical carrying capacity of the planet (Daily & Ehrlich, 1992).
At the lower end, 50-100 people in each of several groups, for a total of about 500, might constitute an MVP.
At the upper end, the present population of 5.5 billion, with its resource consumption patterns and technologies, has clearly exceeded the capacity of Earth to sustain it. This is evident in the continuous depletion and dispersion of a one-time inheritance of essential, non-substitutable resources that now maintains the human enterprise (e.g., Ehrlich & Ehrlich, 1991; Daily & Ehrlich 1992).
Numerous claims have been made that Earth’s carrying capacity is much higher than today’s population size. A few years ago, for example, a group of Catholic bishops, misinterpreting a thought exercise by Roger Revelle (1976), asserted that Earth could feed 40 billion people (Anonymous, 1988); various social scientists have made estimates running as high as 150 billion (Livi-Bacci, 1989). These assertions are based on preposterous assumptions, and we do not deal further with them here.
Nonetheless, we are left with the problem of determining an optimum within wide bounds. Above the minimum viable level and within biophysical constraints, the problem becomes a matter of social preference.
Community-level, national, and international discussions of such social preferences are critical because achieving any target size requires establishing social policies to influence fertility rates. Human population sizes have never, and will never, automatically equilibrate at some level. There is no feedback mechanism that will lead to perfectly maintained, identical crude birth and death rates.
Since prehistoric times, societies have controlled fertility and mortality rates to a substantial degree, through various cultural practices (Harris & Ross, 1987). In the future, societies will need to continue manipulating vital rates to reach desired demographic targets. Most important, societies must reach a rough consensus on what those targets should be as soon as possible because the momentum behind the growth of the present population ensures at least a doubling before any decline is possible (UNFPA, 1992).
Isaac Asimov, author (lived 1920-1992)
Interview with Bill Moyers — 1989
Bill Moyers: “What happens to the idea of the dignity of the human species if this population growth continues at its present rate?”
Isaac Asimov: “It will be completely destroyed.
“I like to use what I call my bathroom metaphor: If two people live in an apartment, and there are two bathrooms, then both have freedom of the bathroom. You can go to the bathroom anytime you want, stay as long as you want, for whatever you need. And everyone believes in Freedom of the Bathroom; It should be right there in the Constitution. But if you have twenty people in the apartment and two bathrooms, then no matter how much every person believes in Freedom of the Bathroom, there’s no such thing. You have to set up times for each person, you have to bang on the door, ‘Aren’t you through yet?’ And so on.
“Right now, most of the world is living under appalling conditions. We can’t possibly improve the conditions of everyone. We can’t raise the entire world to the average standard of living in the United States because we don’t have the resources and the ability to distribute well enough for that.
‘So right now, as it is, we have condemned most of the world to a miserable, starvation level of existence. And it will just get worse as the population continues to go up… Democracy cannot survive overpopulation. Human dignity cannot survive it. Convenience and decency cannot survive it.
“As you put more and more people into the world, the value of life not only declines, it disappears. It doesn’t matter if someone dies. The more people there are, the less one individual matters.”
John Gray, philosopher (born 1948)
Will Humans Be Left Alone? — 2002
According to Edward O Wilson, the greatest living Darwinian thinker, the earth is entering a new evolutionary era. We are on the brink of a great extinction the like of which has not been seen since the end of the Mesozoic Era, 65 million years ago, when the dinosaurs disappeared. Species are vanishing at a rate of a hundred to a thousand times faster than they did before the arrival of humans.
On present trends, our children will be practically alone in the world. As Wilson has put it, humanity is leaving the Cenozoic, the age of mammals, and entering the Eremozoic — the era of solitude.
The last mass extinction has not yet been fully explained. Many scientists believe it to have been the result of meteorites whose impact suddenly altered the global climate, but no-one can be sure. In contrast, the cause of the present mass extinction is not in doubt: human expansion. Homo sapiens are gutting the earth of biodiversity.
The lush natural world in which humans evolved is being rapidly transformed into a largely prosthetic environment. Crucially, in any time span that is humanly relevant, this loss of biodiversity is irreversible. True, life on earth recovered its richness after the last great extinction; but only after about 10 million years had passed. Unless something occurs to disrupt the trends under way, all future generations of human beings will live in a world that is more impoverished biologically than it has been for aeons.
Given the magnitude of this change, one would expect it to be at the centre of public debate.
In fact, it is very little discussed. Organizations such as the World Wildlife Fund press on with their invaluable work, and there are occasional reports of the destruction of wilderness; but for the most part, politics and media debates go on as if nothing is happening.
There are many reasons for this peculiar state of affairs, including the ingrained human habit of denying danger until its impact is imminent; but the chief reason is that it has become fashionable to deny the reality of overpopulation.
In truth, the root cause of mass extinction is too many people. As Wilson puts it in his book Consilience: “Population growth can justly be called the monster on the land.”
Yet, according to mainstream political parties and most environmental organizations, the despoliation of the environment is mainly the result of flaws in human institutions. If we are entering a desolate world, the reason is not that humans have become too numerous. It is because injustice prevents proper use of the earth’s resources. There is no such thing as overpopulation.
William Rees, academic (born 1943)
Avoiding Collapse — 2014
The overarching problem is one that the mainstream has yet to acknowledge: on a planet already in overshoot, there is no possibility of raising even the present world population to developed-country material standards sustainably, with known technologies and available resources.
By 2008, the world population had reached 6.7 billion (it hit 7.2 billion in 2014), with an average eco-footprint of approximately 2.7 global hectares (gha) per capita. However, there were only about 12 billion productive hectares on Earth or just 1.8 average hectares per capita — global overshoot has already topped 50 per cent.
We can refer to “1.8 average hectares per capita” as one’s equitable, or fair, “Earth share”. It represents the bio-capacity available to support each person, assuming the world’s productive ecosystems were distributed equally among the entire human population.
In this light, consider that average Europeans require the productive and carbon assimilative capacities of four to five gha per capita to support current levels of consumption. Thus, if everyone on Earth reached European material standards, aggregate demand would exceed 30 billion gha on a planet with a total of only 12 billion hectares of productive land and water. We would have a bio-capacity shortfall of almost two Earth-like planets.
The North American eco-footprint is seven gha/capita; to achieve North American levels of consumption and carbon emissions for everyone would demand at least three additional Earths (and we would still have to accommodate the material demands of the additional two billion people expected by 2050).
This already precarious situation is deteriorating because the fair Earth-share is a moving target, one that shrinks annually with increasing population and accelerating ecosystem degradation.
Even the arithmetically challenged should recognize that trying to grow our way out of poverty is ecologically naive, and ultimately disastrous for everyone.