Professor Philip Corbet

Human Overpopulation

Version of 21 November 2007

Population Matters (very much indeed)

By Professor Philip S. Corbet


I ask your indulgence this evening if I read most of this talk. I do this to preserve the continuity of ideas and because I cannot reliably remember all the dates and quotations I shall be including. Also, to economise on time, I shall be presenting my interpretation of the human predicament as though it is the only one, but this is to save time. I shall be emphasising the almost universal importance of carrying capacity in population-related matters, but I am conscious of the warning attributed to Epicurus (341-270 BC) that one should beware of trying to attribute all phenomena to a single cause! This talk will be presented in six sections:

Carrying capacity.
How did we reach our present position?
Chronology of awareness of overpopulation.
My own involvement.

1. Carrying capacity

I am a qualified zoologist, specialising in ecology. My professional career has been in entomological research – pure and applied – in research management; and in teaching, research and management at university level, in Uganda, Canada, New Zealand and the United Kingdom. In all these activities I have had to be aware of the ecological principle of carrying capacity. This principle states that, for any resource base (usually an area of land or sea) there is a maximum number of individuals of a given species that can be supported there on a sustainable basis. By definition, if this number is exceeded, the numbers soon fall back to the carrying capacity, or below it, while the resource base and the animal population recover (if possible) from the stresses that they have endured by the imbalance that has been experienced. Or it may be that, after a population exceeds its carrying capacity, a new equilibrium is established, characterised by a lower population and a lower carrying capacity. When the numbers of a species are increasing rapidly, and as the carrying capacity is approached, certain compensatory effects start to operate. Typically these are:
Depletion of the essential resource base.
Intraspecific conflict.

1 Amplified version of a talk to Cornwall Humanists, Chasewater, Cornwall on 16 October 2007.
2 Emeritus Professor of Zoology, University of Dundee; Honorary Professor, University of Edinburgh.

These consequences of overpopulation are well known in non-human animal populations; but what is seldom acknowledged is that human populations are no exception. Because the numbers of Homo sapiens are increasing geometrically, and because our species depends on a finite resource base, it is obvious that our populations, if not already doing so, will very soon experience these compensatory effects. Indeed, unless humans recognise this and plan accordingly, their populations will be liable to experience, with increasing severity, the effects of exceeding their carrying capacity. In such ways are all animal populations adjusted to their carrying capacity under natural conditions. Food and space have special significance for adjusting the size of a population, although other factors may play a role. Factors involved include:

Availability of food – its quantity and quality.
Frequency of encounters with other individuals (a measure of stress)
Level of pollution of living space by the products or artefacts of other individuals, and
Accessibility of sites for reproduction.

Almost all animals have evolved behavioural traits that counter these consequences of overpopulation, and humans are no exception. However, expression of these traits lowers the quality of life for all individuals and often lowers the birth rate and post-natal survival rate as well. In the case of human populations we already see these consequences expressed in increased incidence of famine, pestilence and war, all of which we claim that we wish to minimise. In short, such consequences reduce our quality of life, which leads to one definition of an optimum population for man, namely:

“the maximum number that can be maintained indefinitely
without detriment to the health of individuals,
from pollution or from social or nutritional stress.”

In my opinion this definition is flawed in a way that reveals a weakness in human nature. Why, for goodness’ sake, should the optimum population have to be the maximum number? I sense the not-too-subtle influence of mainstream economists here, and their commitment to growth. Another reason for specifying the maximum is, I suggest, that natural selection has endowed humans with the urge to produce as many offspring as possible. In this respect, knowing what we do about the merits of stabilising our population, we are still struggling against the incubus of maximum reproduction, fixed on us in the course of evolution. (Sir Richard Southwood, in 1970, suggested, tongue in cheek, that this primeval urge to reproduce as fast as possible may equate to “original sin”!)

A term which is much used nowadays when human pressures on the environment are being discussed is ‘Environmental Impact.’ This concept is closely relevant to carrying capacity because, as a population grows, so does its Environmental Impact. It is agreed among ecologists (e.g. Ehrlich & Holdren 1971; Southwood 1972) that Environmental Impact (I) can be realistically defined as follows:

I = P x E x N

Where I is the environmental impact

P is the size of the human population

E is the amount of energy consumed per capita

and N is the proportion of this energy that is
(a) derived by modifying an ecosystem so that in future its production of energy will be less (e.g. resource depletion) and
(b) used for the production of materials that are not immediately and harmlessly recycled in the ecosystem (e.g. pollution).

This formula may appear rather weighty but it’s actually straightforward. Recently some authors have chosen to express it in a slightly different way, as I = P x A x T, where A = affluence and T = technology, but the implications of both formulae are virtually identical.
Understanding this formula is absolutely central to any discussion of population size because it highlights the key role played by human numbers in determining the intensity of I and in acting as a multiplier for all the other terms, which express the nature and extent of resource consumption and their effects on the environment. So it highlights the inverse relationship between population size and the quality of life.

Today, people in the so-called ‘developed nations’ continue to use the earth’s precious, finite resources in an almost frivolous way, by indulging in pastimes such as speedboat racing or using electric bread-knives. This led Kenneth Boulding (1966) to observe that:

“In the West, our desire to conquer nature often means simply
that we diminish the probability of small inconveniences
at the cost of increasing the probability of very large disasters.”

The carrying capacity of man’s environment has, since our hunter-gatherer days, increased greatly through technological change. This may have given some people the illusion that such changes can somehow lessen the effects of intra-specific stress and aggressive behaviour. Ironically, however, our greatly increased density has obliged a higher and higher proportion of us to live tightly packed in huge conurbations where the inhabitants are becoming increasingly vulnerable to stress and face the increasing prospect of mass mortality from warfare and disease. Already we live in a world where intertribal and international belligerence are increasing, and where weapons of mass destruction are being contemplated as possible ways of resolving conflict. It is obvious that, as populations continue to grow on what is becoming a diminishing resource base, these symptoms can only become more pronounced.

2. How did we get to where we are today?

It is generally accepted that the earliest Homo sapiens existed as hunter-gatherers, living within the earth’s carrying capacity. Since then, by the application of ingenuity, our species has raised the earth’s carrying capacity (for humans) by exploiting portions of the biosphere that had been supporting other forms of life, or by tapping into its capital (as distinct from its income). These takeovers were accomplished by major cultural developments, prominent among which were:

Control of fire and development of hafted weapons.
Agriculture and pastoralism.
Use of tokens for trade and the accumulation of monetary wealth.
Hygiene and medicine.
High-energy technology.

The control of fire enabled our hunter-gatherer ancestors to move into areas where winter would have been unendurable had they not learnt how to release, through wintertime combustion, supplies of solar energy stored in wood by summertime photosynthesis. This development increased the world’s human population to perhaps 5 million, which can reasonably be regarded as the Earth’s carrying capacity for Homo sapiens as a hunter-gatherer (Ehrlich 1985). Also, the development of hafted weapons will have made it possible for hunters to secure the healthiest prey animals instead of those most debilitated by parasites. This will have reduced infant mortality among humans from parasitic diseases. Next, discovery of techniques of plant cultivation and grain storage, about 10,000 years ago, enabled humans to appropriate for human food areas of land that would otherwise have been occupied by humanly inedible plants and the animals dependent on them. As a result, our species became about 50 times as numerous over the next ten thousand years (Ehrlich 1985). Agricultural man made further technological changes to agriculture that enabled him to increase the productivity of additional tracts of land, allowing him to boost his numbers still further – all at the expense of other species. All these developments had a significant impact on the environment, as did, of course, the resulting increase in human numbers. By 1775, shortly before the Industrial Revolution, the world population had increased massively, to perhaps 750 million (Bligh 2004; Ponting 2007).

Industrialisation was a breakthrough of a different kind. The resulting addition to the world population of about 1-2 billion people (Howard 1969) represented a clear case of overshoot. The 750 million or so that the earth supported by preindustrial agriculture may be an approximate measure of the earth’s carrying capacity for man, simply as a result of displacement of competitors. Industrialisation enlarged the illusory (i.e. temporary) carrying capacity for humans by exploiting the planet’s geological savings deposits in the form of coal and other fossil fuels. These energy-rich deposits are, as we know, the product of millions of years of photosynthesis and of course are not being replaced at anything like the rate at which they are being consumed. The rate at which we use up the earth’s finite reserves of capital has now been accelerated by three other cultural developments: (1) the development of economics, based on the use of tokens and surplus food as a medium for trade; this led directly to the commitment to growth and the accumulation of wealth, measured by money, which encourages consumption rather than conservation; (2) the development of preventive medicine; which reduces the death-rate without making compensating adjustments to the birth-rate; and (3) the development of a high-energy technology based on fossil fuels. We may note that these developments have all been extremely recent, having taken place in less than 1% of man’s time on this planet. This has been too short a time to allow humans to make the cultural changes needed to deal with the huge transformation that has occurred in their interaction with the biosphere.

The biological equipment that humans have acquired through natural selection and brought to their present existence is that of the hunter-gatherer. Man is of course an animal, unique only in that he has recently (by the exercise of ingenuity) been able to free himself to a large extent from normal ecological control and from the processes of natural selection, but not from his evolved attributes or their consequences (Morris 1967).

As the product of natural selection, humans retain certain strong drives:

The urge to reproduce and to maximise the number and fitness of their descendants;
The drive to defend the land from which they derive their livelihood; and
Tribalism, which drives them to be suspicious of, and belligerent towards, other potential competitors, be they tribes or nations, that might appropriate their resources.

These characteristics remain with us as biological norms and they do not provide a suitable recipe for living in harmony with other humans in an overpopulated world where competition for essential resources is acute and worsening. It’s useless to debate the morality of our self-interest because we are programmed this way. Our natural tendency to reproduce, greatly in excess of survivability, is still the basic cause of tribal conflict and accordingly is a major source of human misery. Only when this is understood can we agree on population limitation and cease to quarrel over food-producing land. The only way out of this trap is to modify the expression of human instincts by the influences of reason and the resultant application of social constraints. On the other hand, if we are unable to overcome our servitude to uncritical genetic command, we must consider the possibility that we shall fail to rescue ourselves from ultimate self-destruction.

3. Chronology of awareness of overpopulation

Humans began seriously to overshoot their carrying capacity only at the dawn of the industrial era and it seems that the first formal recognition of this fact was when the much- maligned Thomas Malthus published his famous Essay on the Principle of Population (1798). Malthus was a distinguished mathematician and a Fellow of the Royal Society of London. Curiously, he was also a theologian (perhaps so that he could hold down a job!). Malthus pointed out that because, with unrestrained reproduction, human numbers increase geometrically, whereas food resources only ever increase arithmetically, in the absence of birth control humans will always outstrip their food supply, resulting in starvation and misery. Malthus insisted that he had reached this conclusion from applying reason, as distinct from emotion or wishful thinking, and that, in any case, it was intuitively obvious. There were, and still are, powerful vested interests in opposition to his conclusion, especially among mainstream economists, who advocate continual growth in order to boost the economy. It is also fashionable to discredit Malthus simply because widespread starvation did not immediately follow his pronouncement. An example is a recent statement by the journalist Andrew Marr (1998) who wrote:

“We all know that Malthus got it wrong. Malthus’s explanation
of the coming poverty, environmental decay
and social collapse……has gone down as one of history’s
great failed predictions – not just wrong, but hilariously wrong.”

Marr’s statement, which one might call not just hilariously wrong, but sadly and pathetically wrong, is typical of commentators who follow the fashionable trend without the application of reason. Those wishing to discredit Malthus derived strength from the fact that the famines he predicted did not occur promptly, or at least not in countries his critics were concerned about. This was not because Malthus was wrong, but only because the world’s food supply increased enormously, in a manner that could not have been foreseen, partly as a result of the cultivation of new land, for example in the Americas and Australia, and partly as a result of improved technology. In the longer term, and today for instance (when there is widespread poverty in the world), Malthus was of course absolutely right, and it’s a great pity this was not recognised sooner. Instead, for at least 200 years it proved fashionable to dismiss what he said. Of course there were distinguished exceptions. As the Committee on Resources and Man of the U.S. National Academy of Sciences and National Research Council (Cloud 1969) put it:

“The Malthusian limits are more likely to be extended
by recognising their validity and doing something
about them than by uninformed ridicule.”

Indeed, the Committee’s leading recommendation for general policy was:

“That efforts to limit population increase in the nation and the world
be intensified by whatever means are practicable,
working towards a goal of zero rate of growth by the end of the century.”

Their amplifying comment was that:

“population control is the absolute primary essential
without which all other efforts are nullified.”

Contemplating the present laissez-faire attitude in the United States towards population growth, it is difficult to believe that this recommendation was ever made.

I may have overlooked some allusions to the need for a population policy in Britain, but the next noteworthy event known to me is the publication of the satirical novel, Brave New World, by Aldous Huxley (1932) where he postulated a surreal society in which the imbalance between human numbers in relation to natural resources had been resolved by the existence of an all-powerful totalitarian state. In his sequel, Brave New World Revisited, Huxley (1959) made overpopulation his central theme, expanding on the urgency of addressing it if societies were going to retain any prospect of avoiding severely restrictive regimes. He stressed that man faced a “double crisis”, identifying the imbalance between the world population and the available food supplies as the fundamental issue that underlies all the better-recognised social and political considerations, and the effects of which will inevitably lead to widespread loss of individual freedoms. A few years earlier the UK Government, perhaps in a fit of absent-mindedness, had established the Royal Commission on Population which recommended in 1949: (1) that our numbers should be stabilized; and (2) that the Government should make an official body responsible for maintaining a continuous watch over population movements and their bearing on national policies. The Commission noted also: first, that it would be impossible for any policy to be neutral because over a wide range of affairs, policy and administration have a continuous influence on family size, and second, that the control by men and women over the numbers of their offspring is one of the first conditions of their own and the community’s welfare.

Had the Commission’s recommendations been heeded and implemented, we might be living in a very different country today. But all were ignored, and no action was taken. The Labour MP, Douglas Houghton, remarked (1970) that political parties fight shy of these matters and find them extremely distasteful. Such matters, he said, are bad for party unity and are supposedly vote losers. Houghton noted further that in 40 years the Labour Party had debated birth control only twice, in 1927 and 1940; and the Conservative Party not at all. Perhaps it need not surprise us that, almost immediately after Mr Houghton had made these statements, the Labour Party dissociated itself from his remarks. This denial persists: in a recent article Jack Parsons, the author of Population versus liberty (1971) bewails the fact that: “The BBC has been systematically excluding virtually all material on the question of basic population policy.”

In today’s society the forces opposed to population limitation are nothing short of formidable. Ehrlich and Holdren (1969) identify them as follows:

“growth-minded economists and businessmen,…
nationalistic statesmen,…zealous religious leaders
and the myopic and well-fed of every description.”

It is worth noting that in 1968 322 MPs signed a motion demanding that there be an official population policy. I understand, from an article by Jon Tinker (1969), that, in secret, some action was taken: evidently an interdepartmental committee of civil servants was set up to advise Government how legislative and administrative acts could be made to further a policy of population stabilization. Predictably, the existence of this committee was kept secret (though fortunately not from Jon Tinker!). So, apparently, has any outcome of their deliberations.

The World Population Congress, held under the auspices of the United Nations in 1954, reported that no policy could be agreed upon because some countries had ‘doctrinal objections’ to birth control. No prizes can be expected for guessing which countries these were! In the mid-70s I attended an International Conference on Population Matters in Wellington, New Zealand. There again, it was found impossible to achieve unanimity on the need for population limitation. One country that voted against any policy of population limitation was Argentina, whose delegate declared that her country wanted more people, not fewer!

The tradition of committed ostrich-like denial by the UK Government persists. It was only about three years ago that the then Home Secretary, David Blunkett, went on public record as declaring that there was “no limit to the number of people that Britain could accommodate.” Such a statement must have been swiftly followed by Thomas Malthus and Aldous Huxley (among others) turning in their respective graves. Likewise, very recently, the former Prime Minister (Tony Blair) admitted that his Government had no policy on population (Jones ca 2005). Outside Government, however, there is overt concern that continued population growth will put enormous pressure on Britain’s essential services (Randall 2007). I am reminded of Douglas Houghton’s observation in 1970 that, to the British politician, “population increase in Britain is thought of as something to be provided for, not something to be stopped.” “

The distinguished economist, John Maynard Keynes, (1883-1946), addressed the matter of overpopulation by posing the following question:

“Is not a country overpopulated when its standards are
lower than they would be if the numbers were fewer?”

I find Keynes’ approach much more fruitful than trying to identify the ‘optimum population’. In 1970 the Institute of Biology, commendably in my view, mounted a symposium under the title “The optimum population for Britain” (Taylor 1970). The contributions to the Symposium, from a distinguished slate of international speakers, were uniformly excellent, but I regretted the choice of the words ‘optimum population’ in the title. This is because, even at that time, the most urgent need by far was to achieve a reduction in Britain’s population. To spend time and resources trying to identify (and agree upon) an optimum seemed to me to represent a serious distraction from what should have been the main objective. In a talk that I and a colleague gave in Canada soon after this Symposium (Corbet & Smith 1973), we illustrated this view by posing the following analogy. If a man is in a small rowing boat drifting towards the top of the Niagara Falls, his strategy should not be to try to calculate precisely where on the bank he wished to disembark but to devote all his energies to reaching the bank as soon as possible. And later, in 1977, I concluded an article thus:

“Time devoted to discussing whether this or that size of population
is to be preferred is wasted time or worse.
“Our overwhelming priority is clearly to reduce the rate of increase
and then the size of the population as soon as is humanly, humanely, possible.”

The unorthodox economist, Kenneth Boulding, wrote in 1959 that

“without birth control, the equilibrium between resources and population
is only maintainable by the misery of starvation and premature death,
or by the human vice of genocide, as individuals, families or tribes (i.e. nations)
seek to supply their own needs at any other individual’s or tribe’s expense.”

Boulding saw three probable causes of lack of birth control:

1. Religious teachings.
2. The prevailing view that “God will provide.”
3. The view that, as economies grow, the birth rate will fall (the so-called ‘demographic transition.’).

With regard to resource use, Boulding pointed out that mankind today lives in what can only be a brief phase of enjoying free access to the planet’s capital – its rich but finite store of fossil sunlight. To have any chance of future stability, our policy should be to use this precious resource not in ways that make us increasingly reliant on it, but in ways that enable us to do without it. The planet’s stocks of accessible fossil fuels cannot last much longer. Our present treatment of them can be likened to someone burning down his house in order to keep warm.

Ever-popular agricultural ‘self-help’ schemes are useless (except as conscience-relievers) unless accompanied by birth control (Hardin 1974; Corbet 2006; Duguid 2007). The food aid supplied through ‘Band Aid’ 20 years ago now has to be repeated annually, as populations continue to increase on an impoverished resource base. On the other hand, where women are effectively enfranchised and enabled to realise their preference for two or three children, there is a realistic prospect of stabilising or even reducing the population. Sadly this consideration seldom features in the agenda of aid charities, often because they fear that to do so will alienate donors. If suffering in undernourished populations is to be relieved, attention would be much better directed primarily towards the goal of reducing births.

A seminal essay by the biologist-philosopher Garrett Hardin appeared in 1968. It drew attention to the so-called ‘Tragedy of the Commons’ and its lesson for population limitation. Hardin pointed out that any resource to which all members of a community have free access will inevitably be destroyed because each user puts his own short-term interest before that of the community, namely the sustainability of the resource. Hardin saw this principle as applying to man’s urge to reproduce, and showed that, only by mutually agreed coercion (to limit family size), could overpopulation and resource destruction be averted. In this context he defined true freedom as the ‘recognition of necessity.’ Many years earlier, the philosopher Edmund Burke (1729-1797), a contemporary of Thomas Malthus, had put it this way:

“Men are qualified for civil liberty in exact proportion to their disposition
to put moral chains upon their own appetites……
Society cannot exist unless a controlling power upon will
and appetite be placed somewhere, and the less there is of it within,
the more there must be without. It is ordained in the eternal constitution
of things that men of intemperate minds cannot be free.
Their passions forge their fetters.”

And, more succinctly, in his Letter to the Sheriffs of Bristol:

“Liberty, too, must be limited in order to be possessed.”

The take-home message from both Hardin and Burke is that a democracy is fundamentally unsuited to achieve population limitation.

In 1972 the journal The Ecologist devoted a whole number to its “Blueprint for Survival”. This was a publishing milestone. Signed by several distinguished scientists, it laid out the path that Britain would be advised to follow if the consequences of overpopulation and resource depletion were to be avoided. Prominent among the measures it advocated was population limitation. The British ‘Establishment’ reacted promptly and angrily to the “Blueprint.” John Maddox, the then Editor of the journal Nature, devoted an editorial to trying to discredit the “Blueprint” under the title “A case of hysteria” (Anon. 1972). Immediately after Maddox’s diatribe had appeared, a letter signed by about 20 senior biologists appeared in The Times saying that they approved in principle of the “Blueprint” and had only withheld their signatures for trivial reasons. Maddox’s editorial was not closely reasoned and merely accused the authors of the “Blueprint” of being “alarmist”, which, for Maddox, seemed to be sufficient justification for ignoring the message they were trying to convey.

In 1966, the distinguished Australian immunologist and Nobel Laureate, Sir Macfarlane Burnet, when reflecting on man’s treatment of the environment, remarked that:

“There are three imperatives: to reduce war to a minimum;
to stabilize human population;
and to prevent progressive destruction of the earth’s irreplaceable resources.”

Later, in 1970, he declared that:

“man suffers from a surfeit of knowledge and a deficiency of understanding.”

He amplified this by saying that man lacks understanding of a few central notions that apply to his treatment of global resources.

Not long afterwards Chris O’Neill (1976), a sociologist, warned that “What’s done now, or not done, must be lived with for a long time.”

In 1989, the Duke of Edinburgh used the Dimbleby Lecture to highlight the effect that human numbers were having on the biosphere, speaking primarily as a conservationist, but also as someone concerned with what human population growth was doing to the biosphere. He said:

“In the end it is up to us as procreators, predators, manipulators, exploiters and consumers to realise that we have to live off the limited land of our planet.”


“We have to learn to accept that any further growth
in the human population…..[is] bound
to cause very serious problems for the [future] generations”

And three years later, the Prince of Wales (1992) urged that the topic of runaway population growth should be seriously addressed and should find prominence on the agenda of the Earth Summit Conference in Rio.

In a refreshingly forthright interview earlier this year, Chris Rapley, the newly appointed Director of the Science Museum, chose to focus on the need for population stabilisation in Britain (Clover 2007). Rapley identified this as an issue that must be addressed although “no one will talk about it.” In regard to the matter of environmental impact, he stated that “the country needs fewer people, not greener ones!” He stressed that we face problems that will not be solved by technology alone, but only by a change in social attitudes.

From this abbreviated review of pronouncements on the population problem since Malthus had his say, I draw the following conclusions.

Man’s powerful, innate drives towards unconstrained reproduction and resource consumption have led to a serious imbalance between the size of the human population and the ability of the biosphere to support it on a sustainable basis.
This imbalance, which grows more pronounced by the day, is already causing widespread hunger and premature death and can only result in the collapse, of numbers and of social order, if stern countermeasures are further postponed.
Although respected scientists and a few unorthodox economists have been publicising the need for countermeasures for at least 50 years, there is a widespread reluctance among society’s leaders, including the Government, to address this issue and to formulate remedial action.
This being so, human society as we know it faces imminent destabilisation.

4. My own involvement

It was when I was a 23-year-old PhD student at the University of Cambridge in 1952 that my perception of the human condition underwent a sudden transformation and gave me a focus of intense concern that has remained with me ever since. In brief, I became acutely aware that the world’s human population was increasing without control and that, unless governments acted robustly to check its increase, disaster lay ahead. What alerted me to this realisation was hearing on the radio the Presidential Address to the British Association for the Advancement of Science delivered by the distinguished biophysicist A.V. Hill under the title “The Ethical Dilemma of Science” (Hill 1952). The dilemma that Professor Hill identified was the morality of using science primarily to save lives when there were already so many people on the planet that famine and infant mortality were rife.

From that time onwards I resolved to try to publicise the fact of human overpopulation whenever opportunity offered. In practice, because people are so averse to discussing this matter, opportunity hardly ever did offer, until, that is, I acquired what I would call a ‘power base’. This happened when in 1967 I was appointed Director of a large agricultural research institute in Canada. I find this sad to relate, but I found that, while I held that position, what I said (e.g. in a committee or advisory group) was listened to because of my position, rather than because of what I said. This was a depressing realisation but I exploited it to the full. During the rest of my professional career I always had a power base of some kind and so was able to pursue my aim of publicising the need for a population policy. In committees I could do this by introducing a motion that would lead to action of some kind, or at least oblige other members to respond to a question which would then be recorded in the minutes of the meeting. The case for a population policy was so compelling, especially to biologists, that I often received support, even though none of my associates was willing to raise the matter independently. For example, in Canada I served as President of one of the largest scientific Societies in the country and from that position, via a motion passed by the Council and then at an Annual General Meeting, I arranged that an open letter be sent to the Canadian Government asking for its population policy to be stated and publicised (Corbet 1971). Interestingly, and significantly, there was only one dissenting member of the Society’s Council. He was a Roman Catholic, and the obligatory member from the Province of Quebec. He may have feared for his prospects in the Hereafter! There were other opportunities: as a member of Council of the newly-formed Committee of Heads of Canadian University Biology Departments, I proposed that the first statement on the Committee’s manifesto be to call for a national population policy. A general meeting supported this unanimously, which gave it strength. And in 1971, with a senior colleague, I orchestrated an open letter from 25 senior biologists to the Prime Minister (Corbet & Leroux 1972), asking that Canada formulate a national population policy. We received an answer (we had to!) but predictably it was a bland one which effectively sidelined the issue. These are only a few examples. Suffice to say, I used any opportunity that came my way to use my influence towards this end.

When in New Zealand, between 1974 and 1980, I had better opportunities to expose the issue of overpopulation. I jumped at the chance to direct a two-year MSc course in resource management that had been newly established there by the University of Canterbury and Lincoln Agricultural College. This was because the relationship between the numbers of people and New Zealand’s carrying capacity is so straightforward. It can be easily explained in terms of the country’s simple agricultural economy and its dependence on imported fossil fuels. Put simply, New Zealand depends on its agricultural production to earn the foreign exchange with which it purchases the fossil fuels which, in turn, it needs to underwrite its agriculture. This circular dependency, which is easy to grasp, shows that per-capita prosperity in New Zealand will diminish as its human population increases. I was able to raise the population issue in a number of forums, while serving on bodies such as the New Zealand Environmental Council, the newly-formed Demographic Society (which I helped to establish) and the New Zealand Club of Rome, and when making population the main topic for discussion at an annual conference of the New Zealand Mensa Association. Two incidents deserve mention. The first occurred within a few days of my arrival in the country. The United Nations was to hold a World Population Conference to address the topic of demography world-wide and had invited each nation to submit a position paper outlining its population policy. Wishing to participate, the New Zealand Government set up an Inter-Departmental Committee on Population Questions to prepare a paper for submission to the United Nations. This Committee invited submissions from the public, to be collated and summarised by the New Zealand Commission for the Environment. Of course I submitted a contribution; it included the recommendation that the New Zealand Government’s policy should be to adopt

“measures to ensure that population size would become
progressively adjusted to a level at which an acceptable standard of living
and quality of life can be sustained for future generations
with the resources available to New Zealand in the long term.”

As it happened, I knew the Commissioner for the Environment well and I was aware that, although he was a civil servant, he was also a senior scientist who, predictably, shared my views on environmental concerns. Anyway, the Interdepartmental Committee must have allowed their attention to wander while preparing the final submission because my exact words appeared in the eventual position paper for New Zealand. So, thereafter, whenever I wished to advocate a population policy, I could honestly say that the official position of the New Zealand Government on the matter of a population policy “is as follows” and quote my own words! Another opportunity came when I was serving on a quango, the New Zealand Fact-Finding Group on Nuclear Power. This group, appointed to advise the New Zealand Government in 1975, comprised six members, plus support staff, and was chaired by the President of the Royal Society of New Zealand. Each member was assigned duties by the Chairman. When it came to producing the final Report, I was delighted to be given the task of writing the summary. This gave me the opportunity to stress the need for New Zealand to live within its means, in other words to tailor demand to the resources available in the long term. I gave this statement prominence by putting it in a free-standing Epilogue at the end of the Report so that it would be the message that readers would take away with them. Of course a message like this was not what mainstream economists and members of the Establishment wanted to hear. As time passed, I began to think I had got away with it without having to defend my position when late one evening the Chairman ‘phoned me at my home to say that the Epilogue would have to be changed. He tried to persuade me to water it down but I asked if instead I could come round to his home and talk about it. He graciously allowed me to do this and the upshot was that the statement remained in the final Report unchanged. I was gratified by this outcome because the Report (1977) was adopted by the New Zealand Government as the country’s position statement on nuclear power.

I have mentioned a few selected examples of the opportunities that exist for advancing awareness about population matters if one can command a power base, however modest. However, the defence mechanisms of the establishment and governments are more than equal to any progress that individuals or quangos can make towards reform, and I have to say that, for all my efforts on this front, I have detected no change in national policy as a result. I think it will be clear from parts 3 and 4 of this talk how determined and effective governments can be when trying to block any discussion of the topic of population policy.

I have reviewed the attempts by individuals, and sometimes associations, to publicise the need for a population policy, and their consistent lack of success. This brings us to the present, in a world where the human population continues to increase and the inevitable consequences of this, namely pollution, famine and conflict, continue to worsen. It is now appropriate to examine the prospects that face the world’s human population in 2007.

Part 5. Prospects

I shall begin by quoting what Aldous Huxley, the author of “Brave New World”, wrote in 1959. He said:

“Overpopulation is the grim background
against which the drama is being played out.
The choices are between famine, pestilence and war on the one hand,
birth control on the other.”

When one looks for any recognition of this scenario among governments during the intervening years, one encounters only a consistent resolve to ignore Huxley’s warning. Indeed there are still influential people willing to dismiss such warnings as the utterances of so-called ‘Doomsayers’, evidently believing that merely to use this term will invalidate any warnings of impending catastrophe.

My own view comes close to the wry statement in a book by the American novelist, James Branch Cabell, published in 1926. He wrote:

“The optimist proclaims that we live in the best of all possible worlds,
and the pessimist fears this is true.”

When one reflects on the known consequences of a species exceeding its carrying capacity when there is no prospect of its avoiding these consequences, one has to face the fact that the environment we enjoy today, especially in a protected, privileged, resource-rich country like Britain, is anomalous and acutely temporary. We live in a world struggling under the burden of inequitable distribution of resources essential for survival and health. Today’s human population is starkly partitioned between the ‘haves’ and the ‘have-nots’. As we well know, the world’s food resources nowadays go to those people who can afford them, not to those who most need them. This inequity originated in, and persists as a legacy of, the economic arrangements put in place by the western nations who, because of their advanced technology (Diamond 1997), were able to colonise Third-World countries, especially during the 18th and 19th Centuries. When contemplating or trying to maintain this inequity, we should be well advised to reflect that it is unlikely to persist unchallenged for long. As a species we have been programmed by natural selection to respond to resource shortage in ways that will swiftly increase the likelihood of civil disturbance, conflict and social unrest. As Bligh (2004) has pointed out, we have the latent ability to consider how best to serve mankind in perpetuity and not just how to serve ourselves during our own lifetimes. To do that, he says:

“we must strive to sustain and strengthen that thin veneer of humanity
by which we seek to subdue our animal inheritances
and ensure, to the best of our ability, that we leave the world
in a fit state for our successors. The only way to stand any chance
of achieving this is to institute birth control.”

This is a pronouncement by a thoughtful expert whose only aim is to make a measured and sober prognosis of human prospects.

The question can be fairly put: given our biological inheritance, can we avoid ultimate self-destruction? The ‘green’ economist, Colin Price, writing in 1993, and contemplating the pattern of our resource depletion, predicted that:

“The human species is destined to have a very short tenure
in the history of life on Earth because it cannot help
but use up the energy resources that it evolved to exploit.”

As I see it, although the time to avert disaster is now critically short, any hope that humankind has to do so depends absolutely on using our power of reason to suppress our instinctive behaviour. In other words, on marshalling the will to change our ways. As Robert Socolow has said (Kolbert 2007):

“Whether it’s still practical depends on how much we give a damn.”

In 2007, as I contemplate the human population’s response to the need to arrest global warming (among other environmental threats), I see no convincing sign that we ‘give a damn.’ On the contrary, in matters of reproduction, resource consumption and production of waste products, our policy is ‘BAU’, or ‘Business As Usual.’ Elizabeth Kolbert (2007), after projecting existing trends towards climate change, and noting the failure of governments to act effectively towards mitigating or offsetting these trends, concludes by saying:

“It may seem impossible to imagine that a technologically advanced society
could choose, in essence, to destroy itself,
but that is what we are now in the process of doing.”

Or, as Bligh (2004) speculates:

“Someone will visit the earth in a few million years
and find that there were some intelligent beings who lived
here for a while, but they just couldn’t handle the transition
from being hunter-gatherers to high technology.”


I’ve reviewed the evidence that overpopulation is the most serious problem facing mankind. I shall end this talk by summarising the facts as I see them.

The integrity and stability of the biosphere – that delicate envelope around the planet on which all life depends – are under threat from the outbreak of the human population and the inevitable consequences of this, namely resource depletion, pollution and climate change. These impacts are merely symptoms of one primary cause – overpopulation. Although the destructive effects of unrestrained population growth were clearly enunciated more than 200 years ago, and although many respected advocates have urged, in the intervening years, that remedial policies be put in place for reducing population growth, the appointed leaders of almost all nations have steadfastly refused to recognise or address the problem, even though it is clear that, the longer action is delayed, the worse the ensuing crisis will be, and the more draconian any countermeasures will have to be.

The (sustainable) carrying capacity of the biosphere for humans is probably less than 1 billion, this being the approximate size of the population just before the Industrial Revolution. Since then the human population has increased geometrically, to reach about 6.5 billion, a situation powered by the instinctive urge to reproduce, and exacerbated by adoption of a high-energy technology that has greatly increased the effectiveness of food production, disease prevention and death control, as well as the rate of resource consumption and pollution. Those developments have relied to a huge extent on access to the planet’s finite stock of fossilised sunlight, accumulated over many millions of years. Despite our almost total dependence on these reserves, their exhaustion is now in sight, whereas virtually no contingency plans exist to maintain our present way of life without them. As with the need to arrest population growth, governments are not developing effective ways of managing modern civilisations without a massive subsidy from fossil fuels.

A continuing feature of human civilisation is the very inequitable distribution of resources, a situation maintained and exacerbated by commitment to economic goals based on the manipulation of money. In practice this results in the planet’s resources, including food, flowing primarily to people who can afford them, rather than to those who most need them – a legacy from the economic arrangements put in place and imposed by the more technologically advanced, colonizing nations two to three Centuries ago (Diamond 1997; Ponting 2007).

The insatiable thirst for economic growth and the acquisition of wealth continually exacerbate the effects of population growth, bringing ever closer the time when the symptoms of overpopulation will cause collapse of civilisations as we know them. These symptoms include global warming (causing desertification and rising sea levels), widespread famine, premature mortality, pestilence, and civil and international conflict.

In their steadfast refusal to address the problem of overpopulation, mankind’s so-called leaders have exhibited stupidity, timidity or denial, or a combination of these failings. Because only they can generate the coercive policies needed to limit population growth, by their neglect these individuals will have denied future generations the opportunity to enjoy a fruitful existence, having enriched themselves at their descendants’ expense. The ethics of our present state are well described by Catton (1976) when he remarks that:

“Our numbers and our technology have locked us into stealing from the future.”


These are undoubtedly very dismal prognoses. Remedial action has been postponed for so long that, whatever action is now taken, it will be impossible to avoid, at the worst, universal chaos, and, at the best, draconian curbs on individual freedoms under totalitarian regimes. Nevertheless, even at this late stage, there may be ways of mitigating this grim scenario and perhaps of salvaging some of our self-respect.

It is clear that a democratic system is not equipped to devise and implement policies involving curbs on individual freedoms, such as reproduction or resource consumption. This being so, a way forward might be for all political parties in each country to be persuaded that, for the sake of human civilisation, they must form a coalition (as in wartime) and act in concert on the issues of overpopulation and climate change. The only route by which I could see this happening in Britain (remotely unlikely though it may be) is for the President of the Royal Society of London, with the unanimous support of the Fellowship, to convince Government of the gravity and urgency of the need, and to request that they adopt this course.

Small though the chances of success might be, I cannot see continued inaction as a moral alternative for people who take seriously their obligations to future generations.



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