Overpopulation and the Vicious Circle Principle

March 19, 2012 • Daily Email Recap

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Craig Dilworth sent me the following essay of his, titled “Overpopulation and the Vicious Circle Principle”. The essay summarizes the treatment that population growth in receives in Mr. Dilworth’s book, Too Smart for Our Own Good. You can read a several short reviews on the book here: http://www.amazon.com/Too-Smart-our-Own-Good/dp/052176436X

Overpopulation and the Vicious Circle Principle

In my book Too Smart for Our Own Good, I present an ecological theory intended to explain human evolution and development, and I apply that theory to all major aspects of our actual evolution and development over the past 7 million years. In this paper, I shall summarise the treatment that population growth in particular receives in Too Smart.

The most fundamental determinants of a population’s behaviour are its species’ instincts. These instincts evolve with the species; and the species’ environment at the time the species first comes into existence is probably the one best suited to the species. It is on the basis of its instinctual behaviour that a species avoids extinction. When operating properly, instincts see to it that the species’ population stays in dynamic equilibrium with the other physical and biological systems making up its surroundings. Doing this will mean the species’ populations’ not becoming either too small or too large.

The earlier in a species’ evolution a type of instinct appears, the more basic instincts of that type are. Along these lines I distinguish three kinds of instinct: survival, sexual and social. The more sophisticated the species, the greater the number and sophistication of its instincts.

The most primitive instincts are the survival, which exist in all animals, and include consuming food, and avoiding being consumed. The ‘fight or flight’ response falls under the survival instincts.

Next are the sexual instincts, found in all sexually reproducing animals, first among them being to impregnate or get impregnated. In more-developed species they include the maternal and other parental instincts. The influence of parental instincts increases with the relative brain size of the members of the species, since infants will be progressively less mature when born and thus need more care. Both the survival and sexual instincts support the individual’s gene line (its genetic fitness); and it is in the context of sexual instincts in particular that individual territoriality arises.

Virtually all animals have individual territories, but social animals are characterised by having group territories. Social instincts arise in conjunction with group territory, and include those manifest in supporting one’s group by e.g. defending it against attack from other groups of the same species, or by killing one’s own offspring in times of overpopulation. Similar instincts exist in non-social animals, as manifest e.g. in lemming migrations and guppy cannibalism. Social species include primates, amongst whom group territoriality is manifest in combative behaviour between groups, keeping them apart, while individual territoriality is manifest as combative behaviour among males within the group, which works towards the determination of the group’s power structure and smooth organisation.

A general demarcation between more and less sophisticated species is recognised in the difference between r-selected and K-selected species. K-selected species are more sophisticated than are r-selected, and include most mammals and other animals that care for their young; r-selected species include e.g. insects and other classes whose members live less than a year. In being more primitive, r-selected species have only survival and sexual instincts, while some K-selected species have social instincts as well.

The instinct in K-selected species to acquire and protect individual territory is nevertheless more basic than that concerning group territory, since social species were preceded evolutionarily by non-social species. All social instincts are evolved from lower-level instincts (particularly sexual), just as all sexual instincts are evolved from survival instincts. For any social species however, groups must exist if the species is to exist, and social instincts are needed to support the gene line of the group in particular.

All three sorts of instinct exist so as to support the continuing existence of the species. Ultimately animals do not try to preserve their own lives ‘for the sake of’ their genetic fitness, but because through supporting their genetic fitness they are at the same time supporting the continuing existence of their species. The existence of the species is a precondition for the existence of its members, and the species’ survival takes precedence over the survival of individuals.

In most cases these three types of instinct work in concert. But in certain situations there can arise a ‘conflict of interest’ among them. In such a case the more-basic instincts have a tendency to override the less-basic (e.g. hunger takes precedence over the sexual drive), a phenomenon which, if it persists too far, can lead to disequilibrium and the demise of the species. In this regard, the social instincts differ from the survival and sexual instincts in that they may support the species’ existence at the expense of particular individuals’ gene lines, at least in the short term. Thus there can arise situations in which an individual’s supporting its own genetic fitness (sexual instincts) can reduce the fitness of the species – such as when a pair rears more than a replacement number of offspring in an overpopulated group. Infanticide, for example, is the result of the operation of a social instinct that helps maintain the health of the group. It is here, in the context of the manifestation of social instincts, that altruism and morals come into existence.

As regards human social instincts I cite Darwin:

We have now seen that actions are regarded by savages, and were probably so regarded by primeval man, as good or bad, solely as they obviously affect the welfare of the tribe. This conclusion agrees well with the belief that the so-called moral sense is aboriginally derived from the social instincts, for both relate at first exclusively to the community. (1874), p. 123.


[T]he social instincts which no doubt are acquired by man as by the lower animals for the good of the community, will from the first have given him some wish to aid his fellows, some feeling of sympathy, and have compelled him to regard their approbation and disapprobation. Such impulses will have served him at a very early period as a rude rule of right and wrong. (1874), p. 128.

The modern-human chromosomal structure or karyotype is such that it supported the continued existence of our species given the conditions when the species first came into existence, i.e. given the state of the physical and biological systems with which we interacted in Africa 200,000 years ago. As the subsequent development of our species has made clear, a central aspect of the human karyotype which allowed us to survive was the plasticity of behaviour it implied. In other words, the human karyotype, to a much greater extent than those of other organisms, favoured learning over instinct. This proclivity for learning provided us with a great ‘advantage’ over other species, both competitors and prey. Given our intellectual endowment, that the total population of the human species would become too small was not a problem; but that it would become too large certainly was.

What limits the growth of a population, preventing disequilibrium due to overpopulation, are various sorts of check. The most fundamental of these are external checks, though physically internal checks such as bodily aging are also fundamental. External checks stem from outside the population, and are typical of r-selected species. They can take the form of a limit of some kind – e.g. of food or breeding sites; or they can take the form of disease, or predators.

Malthus’ principle of population tells us that populations have a tendency to grow through the procreation of individuals beyond replacement level. This principle applies straightforwardly to r-selected species. Their populations have a constant tendency to grow, and are stopped by external checks.

Looking at population growth from a systems point of view, we can say that the population sizes of almost all species constantly vacillate about a mean, increasing and decreasing in cycles. As the population grows, its food consumption increases, which, unless some other check comes into play first, eventually leads to the population’s experiencing scarcity. This in turn necessitates reduced consumption, which leads to a reduction in the size of the population – paradigmatically through an increase in infant mortality – allowing the resource to recover. Such populations as continue indefinitely in this way are systems in equilibrium.

Whether systems in equilibrium grow or shrink largely depends on the availability of food and breeding sites and the prevalence of predators. But all species, to continue to exist, must maintain equilibrium with their surroundings. This means that in order to survive, a species’ total population must not become so large that, for example, it eliminates the species’ source of food, nor so small that, e.g., there is inbreeding. If equilibrium is not maintained, i.e. if the population grows or shrinks beyond certain limits, the species will go extinct.

In the case of K-selected species as distinct from r-selected, apart from external checks, there may also be internal checks, stemming from within the population. Though the sizes of such populations also vacillate about a mean, the population stops its own growth when it tends to lead to disequilibrium. (Such checks in the case of humans could be learned, but their basis would still be instinctual, i.e. stem from our karyotype.) In other words, there are biological mechanisms in the populations of such species that see to it that their members participate in the limitation or reduction of their own number when that number tends to become too large.Such internal population checks can take many forms, some somatic, such as the having of miscarriages, and some behavioural, such as infanticide and the excluding of particular individuals from food. In the case of humans, they include culturally reinforced checks, such as marriage, abortion (in primitive societies) and young men fighting (and dying) for their tribe or country. Internal checks to growth exist in virtually all vertebrates and even sea-anemones.

Temporary periods of scarcity occur naturally for all living organisms given the normally occurring changes in their environments, such as increases or decreases in temperature or rainfall. To survive as a species the populations that constitute the species must be able to live through such changes, which they do, given the changes are not too great, thanks to their adaptability. Predatory animals do not chronically depress their stocks of prey, nor do herbivores impair the regeneration of their food. The normal state of affairs for any species is one of dynamic equilibrium, where, for most of the time, hardship is not experienced by the vast majority. But if there is a severe or lengthy scarcity of food or breeding sites, the population size will diminish; and, of course, if it diminishes enough, the species will become extinct.

If, on the other hand, there is a surplus of food and breeding sites, the pioneering principle, a corollary to the population principle, tells us that there will be a tendency for the population to grow until it fills the new space.

The pioneering principle is that any increase in food or space, given a surplus of the other, will tend to be consumed or occupied by a population, with the result that the population grows.

For any population, a surplus of food tends to lead to population growth, given the availability of breeding sites; but when a certain density is reached, internal population checks (for those species which have them) are normally manifest. But if the surplus is large, lengthy or sudden, not only is the external check of starvation pushed back, but the social setting is destabilised. In practice this means that the survival and sexual instincts take precedence over the social instincts (which, in humans, are often culturally manifest). This is precisely what has happened and is happening in the case of the human species. Given the constantly increasing surplus humankind has experienced right from its inception, overpopulation has constantly been the case, and with it our species’ loss of equilibrium. More than this, from a systems-ecological point of view it would appear that the human population has gone beyond the limit at which dynamic equilibrium might possibly be regained. I would myself guess this limit to have been passed at the latest by 6000 years ago, when humans first became dependent on non-renewable resources.

A number of studies have been done of populations of mammals which, given a sudden and large surplus, have first increased drastically, after which a large proportion die off over a number of years, followed by an increase in the size of the population, but not to the same extent as previously. Eventually an equilibrium is reached, at which point the normally-functioning internal checks have once again become established. What happens in some cases however is that the species in question so badly abuses its environment that it no longer has any food, and goes extinct.

In 1912 or 1913 a few moose crossed over the ice from the Michigan mainland to Isle Royale in Lake Superior. This island is some 73 km long and 14 km wide, and the moose had no serious enemies there, with the result that by 1930 their numbers had risen to between 1000 and 3000. Numbers then fell sharply to about 200 in 1935, then rose gradually to 800 in 1948, then fell again, so that in 1950 there were only 500.

Similar phenomena have been witnessed with reindeer and mule or black-tailed deer, both of which over-exploited their habitats in response to a drastic weakening of external checks, and suffered marked die-back through starvation as a result, the reindeer dying out completely, while the mule deer continued to destroy the vegetation, and continued to fall in numbers, for more than ten years after their initial heavy decrease. We can see this as being partly the result of the reaction principle:

The reaction principle is that the members of any species will tend to react to their immediate environment.

Selection operates in the short term; as is implied by the reaction principle, species are selected for the immediate requirements of their environments. If environmental conditions change, a species’ attributes that were previously adaptive may no longer be so.

If the reaction principle is operative in a situation of a large or lengthy surplus, we get the overshoot principle:

The overshoot principle is that, given a pioneering situation, populations of slow-breeding animals will expand beyond the carrying capacity of their environment.

The reaction, pioneering and overshoot principles apply to humans as well as to other K-selected species. Their application to humans is special however, in that we are the only species to overcome periods of scarcity through technological innovation. In other words, we are the only species to use technology to create a pioneering situation. This brings us to the vicious circle principle, which applies only to humans:

The vicious circle principle

Humankind’s development consists in an accelerating movement from situations of scarcity, to technological innovation, to increased resource availability, to increased consumption, to popul­ation growth, to resource depletion, to scarcity once again, and so on.

The vicious circle principle (vcp) is both easy to understand and in keeping not only with modern science but also with common sense. Briefly put, it says that in the case of humans the experience of need, resulting e.g. from changed environmental conditions, sometimes leads to technological innovation, which becomes widely employed, allowing more to be taken from the environment, thereby promoting population growth, which leads back to a situation of need. Or, seeing as it is a matter of a circle, it could for example be expressed as: increasing population size leads to technological innovation, which allows more to be taken from the environment, thereby promoting further population growth; or as: technological innovation allows more to be taken from the environment, the increase promoting population growth, which in turn creates a demand for further technological innovation.

Human population checks, whether internal or external, operate so as to counteract the turning of the vicious circle. What we see with the expression of the vcp through the whole of our species’ development is a steady weakening of these checks. At the same time the constantly altering conditions and increasing complexity of human society lead to the checks’ taking new forms, or to certain forms manifesting themselves to a greater or lesser extent than earlier.

Technological innovation increases the potential for a particular area of land to support human habitation beyond the needs of its contemporary population, thereby constitut­ing a major factor in that population’s losing its incentive to control its own numbers. This loss of incentive may be manifest e.g. in a cultural shift condoning earlier marriages, or in increasing the convenience of having large families. And, given the surplus, which weakens internal checks, there is nothing to stop the population from once again becoming too large relative to what it is able to extract from its resource base, until external checks come into play. The way that this eventuality has been mitigated or avoided has been through the introduction of yet more efficient technology, allowing even more to be extracted from the resource base.

Humans’ development of technology distinguishes us from other life forms. It is what has made us the only species whose population has constantly grown from its inception. Not only has our population constantly grown, the rate at which it has grown has constantly increased: human population growth has always been accelerating.

Unlike other species, humans have invented and employed such devices as the hand-axe, fire, clothing, the bowl, spears, boats, the bow and arrow, the hoe, the plough, irrigation, watermills and windmills, sailboats, various petroleum-driven engines, and electricity generators operated by nuclear power. And this technology, paradigmatically, has had the effect of pushing back the limits to human population size, a phenomenon we do not see in other species.

Humans’ development of technology has been exponential, and has led to a corresponding exponential increase in our total resource consumption as well as in the size of our population – even before Homo sapiens came into existence. Most notable in this regard are early humans’ harnessing of fire some 1.5 million years ago, the horticultural revolution 10,000 years ago, the beginning of the mining of metals 6000 years ago, and the industrial revolution 250 years ago. But this process is going on all the time, with such apparently minor technological innovations as that of the stirrup or horseshoe, or ball-bearing or adjustable wrench, each contributing to the end result of increasing the number of humans that can occupy a given area of land.

There can be no human population growth beyond a certain limit without technological changes permitting more food to be provided per given unit of land. Population and technology have a feedback relationship: population growth provides the push, technological change the pull.

Humans must eat to survive, so an increase in the size of the population will mean an increase in its food requirement. Due to the presence of a surplus of food and breeding sites thanks to technological development (and in the latter case thanks to our adaptability), we humans, as would other animals in a similar situation, and as is suggested by the principle of population, tend to have more than a replacement number of offspring. And as suggested by the reaction principle, the inclination of the members of any species is naturally to react to their immediatesituation. Though our reason may tell us that an alternative mode of action is appropriate, in the main we follow our instincts, including our social instincts. And, again thanks to technological innovation and the surplus it provides, since at least some of the extra children we produce are not eliminated by internal or external checks, the result is the constant growth of the human population.

In terms of systems, technological development undermines the homeostasis of the human species; where there is no technological development, and resources are being used sustainably, homeostasis tends to assert or reassert itself. In terms of a thermostat analogy, the constant presence of a surplus of food and the diminution in the area necessary to raise a family lead to higher settings at which the thermostat controlling population growth clicks in.

According to the vcp, technology’s role in the growth of the human population is central, such that one may say that without technological development the population’s size would be miniscule as compared to what it is today. And technological development itself, together with the existence of resources to which it can be applied, constitutes the most important aspect of the vicious circle.

You could say that from the beginning we were not biologically equipped as a species to handle developing technology. This is clear from our using new technology (spears) to eradicate a huge proportion of the genera of the world’s large animals when we were still in our hunter-gatherer stage. If technological development were truly an aid to the survival of the human species, it would not have led to the elimination of a significant part of the population’s resource base, only to have it replaced by an inferior substitute. There is something wrong with the development of technology in the hands of humans – but then, you could say, something would be wrong with technological development in the ‘hands’ of any organism.

The next major revolution in the development of humankind after the industrial, namely the ecological, will be the first to result from a general decrease in available resources. That is to say, it will be the first and largest revolution involving the slowing down and eventual stopping of the vicious circle. The coming overshoot will not be that of just one turn of the vicious circle, but of the circle itself. The repercussions will be tremendous.

In systems terms, each new species in our development meant a change not only of structure but of organisation, i.e. there was a constant introduction of new systems. Each of these systems has been out of equilibrium with its environment (otherwise it wouldn’t have disappeared) – and each to an increasing degree.

With the reduction in resource availability, technology will no longer be able to provide a surplus that supports continued population growth, but will rather be fighting off a deficit that inflicts constantly increasing mortality. World peaks in population, standard of living, energy use, food production, trade, and rate of innovation will all be behind us. The social effects of reduced resource consumption will include an increase in experienced population pressure and consequent violence, including war.

From a biological/ecological point of view, the growth of the human population can be likened to that of lemming populations prior to their periodic migrations. Such a rate of growth is unprecedented in any large animal species. The global aggregate weight of humans is today ca. 350 million tons – well ahead of any other category except cattle. The human population is ‘swarming.’ We are behaving like an r-selected species.

Humankind’s ensnarement in the vcp works counter to our survival as a species, involving as it does constantly increasing consumption, population, and quantities of waste, all of which tend to move us further out of equilibrium with our surroundings, thereby increasing the likelihood of our becoming extinct. Key to this whole process is our constantly meeting vital needs through the application of new forms of technology to both renewable and non-renewable resources, combined with the fact that there have to date always existed resources amenable to that development.


Darwin, C. (1874) The Descent of Man, 2nd ed., Amherst, NY: Prometheus, 1998.

Dilworth, C. (2005) The selfish karyotype – An analysis of the biological basis of morals, Biology Forum 98: 125-154.

Dilworth, C. (2009) Too Smart for Our Own Good. The Ecological Predicament of Humankind, Cambridge: Cambridge University Press, 2010.

For information on Too Smart for Our Own Good, check out the link:


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