The Demographic Saturation Theory
by Wolfgang G. Gasser / 1997-1998


Most remarkable aspects of the postwar world demographic evolution are:

1.      Rapid demographic transition (mortality decline, followed after a variable interval by fertility decline) not only in the developed countries but meanwhile even in many of the poorest countries.

2.      Postwar baby booms in the OECD, followed by very low fertility after 1970.

3.      Population decline in many East European countries after the collapse of the 'communist system' because of high mortality, low fertility and migration (for example to Germany, Israel and to the U.S.A.).

4.      Globally speaking, rates of population growth much lower than expected with the highest rates of growth in the poorest countries.


Demographic projections over more than 10 years were often shown to be worthless.

1.      The projections for the developed countries of the 1960s were refuted by the rapid fertility decline. Instead of exponential growth it came to astonishingly constant population figures.

2.      In the 1970s hardly any demographer did predict the already beginning fertility decline in China. It was generally accepted that government interventions cannot have much influence on fertility.

3.      As late as in 1992 the UN projected that the population of the (former) Soviet Union would continue to grow until 416 million (according to the 'medium variant', the most probable scenario). But the last years revealed that this prediction is pure speculation.

4.      The ongoing fertility decline even in the poorest countries refutes projections made few years ago.

5.      The population decrease which was predicted for some Euopean countries as Germany did not take place. Instead the populations of the respective countries increased because of migration.

A basic premise of modern demography is that the worldwide fertility decline depends exclusively (or at least at a large degree) on conscious decisions of man and women.


Modern demography, as Charles Darwin's evolution theory, is based in many respects on the philosophy of Robert Malthus: <The size of a species is limited only by external factors like food and habitat. A species, which evolved in a limited habitat with space and food for at most one million individuals, can increase in size by a factor of 1000, as soon as the habitat increases by the same factor.>

According to the saturation thesis, which is relevant not only to humans but to all organisms, at least in the short term the species could not increase substantially beyond the original number. In the long term however, the species could increase at the expense of other related (extinct) species.


The strongest argument against the saturation thesis seems to be the demographic evolution of mankind. There are even estimates, that more people are alive today than ever have died. But apart from the problem, when the human species first appeared, such estimates are based on untenable assumptions.

Until not too long ago (in western society) all human beings were thought to descend from one single couple, which lived several thousands years ago (a modern variant: Mitochondrial Eve). The idea of an ever growing world population is deeply rooted.

The theory of evolution of Charles Darwin excludes a continuous evolution of larger populations (despite the fact that such continuous evolutions occur) and for this reason supports the thesis of a little starting population of mankind (and of the races).

The last fifty years show on the one hand that an annual rate of population growth of 3% is not exceptional, if surviving conditions are favourable. They show on the other hand, how fast growth rates can change by increasing or decreasing. An annual growth rate of about 3% leads to a population 20 times as large in one century and to a population 3 million times as large in only 5 centuries.

For this reason it is, in principle, impossible to find the past evolution of world population by means of projections. (Such projections have to assume average rates of growth close to zero, which is not very realistic.) The argument that only agriculture and other technological progress made possible an earth's carrying capacity of more than for example 100 million people, has no scientific basis at all.

Bangladesh, for example, with less than 0.1% of the Earth's land surface has a population of more than 100 million. Thousands of years ago the Sahara was fertile. A very fertile Sahara could feed the current world population.

There are no methods to calculate the population densities using archaeological data such as bones, manufactured objects or other traces.


The population figures of the recent past which are thought as valid are often based on figures of historic documents, whose reliability cannot be out of question, considering the problems of census even in the age of computers and modern means of transport.

If the proportion of the registered population raises from 65% to 95%, this alone seems to be a population increase of almost 50%. After registration of births and deaths became compulsory in many countries, certainly births were more likely reported than the deaths of not registered persons.

In the same way as the temporarily strong increase in 'HIV-positiveness' in many regions also has been caused by an increase in HIV-testing, a major part of the 'increase in world population' before 1950 and a smaller part after 1950 only has been the result of better census and estimates.

It is much more likely to underestimate than to overestimate the size of a population. Because too low figures of past estimates can always be explained by the expected population growth, there has never been any reason to doubt theses figures.

Even if in Africa the registered population of conurbations grows very fast, one must not overlook that the not registered population of the huge hinterland can decrease at the same time.


Many demographers suppose that fertility will level out everywhere at 2.1 births per woman. They argue that only this fertility can guarantee a constant population and it is an empirical fact that after the so-called demographic transition the population of a country or a region remains rather constant (without migration). This reasoning is strange, because after demographic transition, fertility rate is much lower than 2.1 births per woman in most countries despite a constant population.

The European countries show that the number of birth correlates much stronger with the number of deaths than with the number of women in reproductive age. The more women in reproductive age and the less deaths, the lower is fertility. Just the countries with the high birth rates in the 1960s and 1970s such as Spain, Italy and Germany have now very low fertility, while fertility in Scandinavian countries (a steady population pyramid with a high proportion of old people) is relatively high.

In 1997, Sweden had 10.8 deaths and 11.4 births per 1000 persons (U.S. Census Bureau) and a fertility rate of 1.7, while Spain had a rate of 9.5 deaths and 9.4 births, but a fertility rate of only 1.2. In 1995, in the European Union the number of births surpassed the number of deaths by just under 300'000 and the population grew by just under 0.1% (without immigration). Despite this slight population increase the fertility rate was only 1.4 births per woman.


Every classification of people into groups such as races, nations or social groups is in some respect arbitrary. Nevertheless for the correct presentation of the demographic saturation theory it is useful to classify mankind into not exactly specified populations, which are more or less related. In principle a saturation value can be attributed to all these populations.

A saturation value of 30% means that 30 percent of the individuals of the corresponding population are physically existent or that the souls attributed to this population are alive on average 30 out of 100 years. The question whether life begins at procreation, at birth or at some other time shall be left open. For the populations of Europe, North America, Japan and some other countries, the saturation value meanwhile amounts to almost 100 percent. These populations can increase further only at the expense of other populations.

The population of the USA increases because of immigration and an excess of births over deaths. It increases at the expense of Latin American and East European populations. As the Latin American population is not yet saturated, the out-migration of a part of the population is not noticeable. But as the East European population is saturated, the out-migration (of physical persons and human souls) can be noticed by declining population figures.

For the partially large excesses of deaths over births in Eastern Europe there are further reasons: 1) Collapse of the public health sector, which reduces the saturation value. 2) The desire for children is generally weakened by pessimism.

To sum up: <In the short term human populations cannot grow beyond a saturation value of 100%. In the medium term they can grow at the expense of other (related) populations and maybe in the long term even at the expense of ape species.>

Still at the turn of the last millennium, the Arabian area was leading in science, philosophy and culture. While the European population was increasing, deserts were expanding in North Africa and South East Asia.

An indicator of near saturation of a population is a decline in birth number despite an increase in women in reproductive age.

If one knows the respective saturation values for all regions of the world, it is possible to calculate the limit, up to which world population can grow (in the short and medium term). The saturation values can be estimated by considering population pyramids and other demographic data in comparison with the data of yet saturated populations. If the calculations resulted in a saturation value of 77% for the 1997 world population, it would follow a maximum number of 7.5 billion humans.

During the millions of years of human evolution, human population regionally as well as globally alternated between growth and decline. It could be the first time in history that human population is saturated in many regions of the world, by which the limitation of human souls becomes obvious. It is quite probable that the current saturation value is the highest ever reached.


In Europe the demographic transition lasted for several centuries. The survival rate increased by technological and social progress (above all in health care). The saturation value was increasing more or less continuously (apart from wars and other catastrophic events).

Many developing countries got the benefit of social and medical progress only after the reconstruction after World War II. A country whose saturation value has been oscillating at about 30% for centuries can reach saturation in less than half a century by reducing mortality. After having reached saturation, fertility reaches a minimum, because a high proportion of women in reproductive age is confronted with very low mortality.

In many of the poorest countries the decline in fertility will follow the decrease in mortality with higher velocity and intensity than it was observed in Europe and some Asian and South American countries. And if life expectancy continues to rise, fertility after saturation will become extremely low.

The relationship between poverty and fertiliy (which is no longer well established) is not direct but indirect. The poorer and less educated populations are, the higher is their mortality and the lower their saturation value. Because they are the last who get the benefit of the technological and medical progress, they are the last who reach saturation. Also in Europe, fertility among the poorest groups was the last to decline.

The population of a country is composed of groups which have different saturation values or have reached saturation at different times. The groups having reached saturation at first, are the first with very low (sub-replacement) fertility, but they will also be the first whose fertility will increase again because of population aging. For this reason, in some countries with low fertility, more educated groups with higher incomes should have higher fertility than less educated groups with lower incomes.


The saturation thesis is relevant not only to humans but to all organisms. It can hardly be denied that many animal populations remain rather constant in size without Malthusian struggles for survival. There are also limits on animal breeding and plant cultivation.

There is even a saturation for pathogens like bacteria and viruses. A pathogen of a local epidemic cannot be a threat to mankind, nor can genetically engineered pathogens.

New methods to fight pests become possible: On the one hand the pests are fought where they are harmful, and on the other hand they are bred to saturation in places where they don't do any harm.


Ten Years into the Demographic Saturation Model (June 2007)


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