6 Billion™ - The Game Of The New Millennium

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External Links:
Zero Population Growth
Negative Population Growth organisation
The Voluntary Human Extinction Movement
Exponential Growth and The Rule Of 70
- by EcoFuture 
World Overpopulation Awareness
The Living Universe Foundation
Natural Selection and Differential Reproduction - from Replicators: Evolutionary Powerhouses

The Cassandra Prediction - Exploding The ZPG Myth
(This is background information only - you do not need to know this to play "6 Billion™")

Note: The title of this page was changed from The Cassandra Prophecy to The Cassandra Prediction. This is due to prior copyright of the phrase The Cassandra Prophecy - see web site www.caspro.com for more. Board Not Bored Games Pty Ltd has no association or affiliation with the the book "The Cassandra Prophecy" by Ian Gurney.


This article introduces the Cassandra Prediction, which is intimately tied to explaining what ZPG is, and why it is a myth. The structure of this article is therefore as follows: 

  1. What is ZPG?
  2. What is the effect of a growth rate?
  3. So Why Is ZPG a Holy Grail?
  4. But Surely Technology Will Save Us?
  5. So What's Going To Happen Now?
  1. Replacement Rates
  2. Suppose Some People Refuse?
  3. Sociological Change
  4. Scientific Progress
  5. China and Human Rights
  6. The Natural Order Of Things
  7. Biospheres
  8. The Exponentialist Argument
  9. Nanotechnology
  10. Colonising Space
  11. An End To Limits?
  12. Hooray For Negative Growth?
  13. Catastrophe
  14. Reverend Malthus and Christian Morality
  15. History
  1. Why Cassandra?

  2. 6 Billion™

  3. Doris Day

What is ZPG?

ZPG stands for Zero Population Growth, but what does it actually mean? Typically, the unscientific media focus on what is called the replacement rate of 2 children per family. This is an inaccurate definition and sadly misleading, as I will show below. Nonetheless, because they read it in the press, people believe it and thus sleep soundly in their beds at night. 

To all of these people I say "Here is the nightmare, come to sit on your chest in the dead of night.

To attain ZPG, a population must have the death rate (per 1,000 people) equal to the birth rate (per 1,000 people). Suppose you live in Utopia, with a population of 1 million people. Your death rate averages out at 18 people per 1,000 and your birth rate averages out at 18 people per 1,000. This means, each year, 18,000 people die and 18,000 people are born. What makes this vision Utopian is that your population stays at 1 million people. 

A growth rate is usually presented by demographers in percentage terms. Thus our Utopia has a growth rate of zero per cent, hence the phrase zero population growth. You have achieved ZPG, the Holy Grail of governments and demographers the world over!

What is the effect of a growth rate?

Let us go back to Utopia, and introduce something (improved medical care, better road safety, safer aeroplanes - what ever you decide) which permanently reduces the death rate. After all, this is meant to be Utopia! 

You are delighted to find the death rate drop from 18 per 1,000 to just 8 per 1,000. Now only 8,000 people a year die, thanks to you. This means, each year, you have saved 10,000 people a year! Great - next year we'll find a way to do something else wonderful and humane! You are a hero!

So, to recap, the birth rate is now 18 per 1,000 but the death rate is only 8 per 1,000. Therefore, there is a net gain of 10 people per thousand in your population (a growth rate of 1%). With a starting population of  1 million, you will therefore gain 10,000 people in the first year, 10,100 in the second, 10,201 in the third ...and so on. Well, given that you live in Utopia, it's going to be pretty darned easy to accommodate just 10,000 or so people a year. But why are your demographers shaking their heads in sadness?

At a 1% growth rate a population doubles roughly every 70 years (see Population Doubling Mechanism). This is because of the accumulative effect of any positive growth rate (in banking this is referred to as variable compound interest). 

So what? People are not numbers, and nor are they the same as money in a bank account! Well, I'm sorry to say that you will have to face up to reality. The mathematical effect is the same whether we are discussing money in a bank account, breeding bacteria, or human beings. 

Now, if a population doubles every 70 years then after 700 years at the same growth rate your population will double as follows (figures are millions):

1  2  4  8  16  32  64  128  256  512  1024

Oh dear, now there are over 1 billion people in Utopia! Do you think these people will regard you as a hero now, despite all your good intentions?

So why is ZPG a Holy Grail?

There are lots of arguments in favour of zero population growth and sustained development. To me, these arguments are self-evident and do not need to be explained further by me. However, protagonists of ZPG and sustained development are in a constant struggle with various fools around the planet who just don't seem to get it. Governments and cultures around the globe often resent the suggestion that they should adopt birth control measures, and educate people in family planning methods. 

If you don't understand why ZPG is so important, try these links to various population orientated web sites.

I fully endorse all humane efforts to achieve ZPG globally. This includes contraception, moral restraint and women's suffrage. I fully endorse all efforts to protect the Earth (and all life on Earth) from the damage caused by sheer human numbers in the developing world, and high-consumption lifestyles in the developed world. However, my argument is that ZPG is a myth. I do not intend that my argument should lessen any efforts towards achieving ZPG, but I want people to understand that ZPG is simply a stop-gap measure which can only buy humanity (and this planet) time. Personally, I do not think it is possible for humanity as a whole to achieve ZPG, but I consider it vital that we try to get as close as possible and do so as quickly as possible. Otherwise, the consequences for humanity and for all life on Earth will be extremely ugly and possibly terminal.

But surely technology will save us?

When Thomas Malthus wrote of humanity's impending doom in "On The Principle Of Population" in 1798, the world's population was 1 billion people. Now we are 6 billion. 

When the Club Of Rome published "The Limits To Growth" in 1972 their assessment of mankind's predicament proved to be naive. 

Both books failed to take true account of scientific progress. The general consensus is that technology and human ingenuity (through scientific progress) did indeed "save us". In fact, this combination is so successful that the human population doubling rate peaked in the 1960's, prompting books such as Paul Erhlich's "The Population Explosion". 

The argument continues to rage as to whether technology can "save us" again and, more significantly, whether it should. Perhaps we should let nature take its course, and reduce our numbers the old-fashioned way? The Four Riders Of The Apocalypse (War, Famine, Pestilence & Death) have never really deserted us, and I'm quite sure they would be extremely effective in doing Nature's dirty work. Is this what we want? 

So what's going to happen now?

Many have a blind faith in technology and our own ingenuity to find solutions in the coming decades and are confident we can avoid catastrophic population losses. Some might welcome such losses as the most humane solution, in the end. 

Myself, I am optimistic of emerging technologies based on nanotechnology, advanced computing (including artificial intelligence, DNA computers, quantum computers and nano-computers), genetic engineering, cloning, and biotechnologies generally. Of course, these then come with a host of ethical problems, the most disturbing of which is that we might be forging our own doom in the new workshops of today's scientists. The risk is certainly there, but again I am optimistic. There is a difference between blind faith and optimism. For a start, I read about this stuff all the time. I ensure I read pessimistic and optimistic assessments of future technologies and trends, to ensure balance. Then I decide for myself. Those with blind faith simply believe what they read in the press, and rarely read the source material. Even if they do read the source material, they only read the optimistic assessments. Also, those with blind faith refuse to admit that they can be wrong. I'm happy to state here and now that my optimistic assessment of our future technologies could be wrong. Things could be better, or worse, than I imagine.

However, I believe technology and human ingenuity (and hopefully AI ingenuity) will buy us a little more time.

Our current global growth rate is about 1.26% and dropping (US Census Bureau, mid-point for 2000). This is good news. The consensus prediction for our population is that it will "stabilise" around 9 to 10 billion around the year 2050. Most realists would see a continued growth of perhaps 0.5 % beyond that. If this new growth rate was sustained then our population would continue to double every 140 years. The hope is that during those 140 years we can bring that rate down to zero, and achieve the dream of ZPG.

ZPG and sustained development fans point to the negative population growth of most European countries, Russia, and soon Japan. Many see China's controversial One Child Policy leading to ZPG for China this century.

Despite these facts and trends (which I do not dispute) I believe that the dream of global ZPG cannot be realised. Even if it was realised, and we finally achieved global ZPG, the moment would only be fleeting. 

The Cassandra Prediction

The Cassandra Prediction is that long-term Zero Population Growth is a myth. The long-term trend for any species (from bacteria to humanity) is always for population doubling, for as long as a species exists. Moral restraint and virtue, together with human ingenuity and scientific progress, can only buy humanity time. 

If humanity does not colonise space soon then we will slowly erode life on this planet, and humanity will slowly become extinct. If humanity does not colonise space soon then perhaps one of our creations will do so in our place. Either way, humanity is the loser. Either way, humanity will have destroyed many of the living species on Earth through our failure to recognise the true implications of exponential growth.

Time is running out.

Exponential growth is a natural attribute of all living creatures. Exponential growth means population doubling. Hence, we should prepare for a future where population doubling is possible, or accept the consequences. We must colonise space. In fact, the colonisation of space needs no other argument. It is imperative that we do so, otherwise we will have no choice but to face the consequences.

The consequences of not accepting this principle are that we will become extinct and destroy much of the life on this planet in the process. It will be a slow and painful end, our numbers will rise and fall like floodwaters washing over the face of the Earth. There will be many valiant attempts to save one dying species after another. They will all fail. In the end, humanity will have slowly drowned its own promise by refusing to accept reality. Some will never know why they had to drown, and some will hold their own heads above the waters as they push down murderously upon the heads of those below. Some will not admit that to keep their crying baby safe and dry they had to stand upon the corpses of whole species. 

This pessimistic vision is summed up in my poem "Drowning Children Beneath The Stars" published by The Millennial Foundation (now The Living Universe Foundation). It was also made available with copies of 6 Billion™.

Humanity is the only Earth species ever to dream of colonising space (if the term colonise offends you, well then pick another). We have a duty to all life on this planet. We must not destroy it all, and we must not destroy ourselves. We must accept the stewardship of all life on the Earth, and take that life with us to the stars. This is a noble goal, and hopefully an inspirational one. If you agree with this goal, then you must fight for it. Otherwise you are drowning children beneath the stars.

OK, so why is ZPG a myth?

So far all I have offered are hints of my argument against long-term ZPG. I have come up against people who clearly believe in ZPG and sustainable development. Their belief is almost spiritual. It is blind faith. I commend their efforts, I applaud their good intentions, but I question their scientific reasoning. In the end, it is their lack of scientific reasoning which could spell our doom and destroy much of life on Earth.

Replacement Rates

The common assumption that if a woman has 2 children you get ZPG is incorrect. Also, replacement rates are generally too imprecise. For example, a 16 year old girl can have children. Assume she has 2 daughters. When they are 16 they each have 2 daughters etc. This is quite different to the same scenario, but the woman has children when she is 32 (and her children have theirs at 32 etc). I ignore the men, and just count the women.

First Scenario - 16 year old mothers -  total people (number of elapsed years, age of original mother):

1 (beginning of scenario so year zero), 3 (16 years, original mother now 32), 7 (32 years, original mother now 48) etc

Second Scenario - 32 year old mothers - total people (number of elapsed years, age of original mother):

1 (beginning of scenario so year zero), 3 (32 years, original mother now 64), 7 (64 years, original mother now 96) etc

If we apply the same death rate to either scenario, it is obvious that the 16 year old mothers will cause Earth's population to increase at a faster rate. So, the age of the mother must be taken into account.

The replacement rate figure of 2 children per woman, commonly accepted by gullible (non-sceptical) people, only really applies to countries in the developed world. Even then, it would result in slight negative growth and not ZPG. In fact, even a country like the USA would require a replacement rate of 2.1 children (to allow for those children that dies before reproductive age). Countries like India, with higher infant mortality rates, would require a replacement rate of 2.4 children per woman. A higher infant mortality rate means a higher replacement rate. 

Even if your population has reached replacement rate, you will not achieve ZPG until the generation after death rates catch up with birth rates. This only happens in populations where the average age of the population has increased (as death occurs mainly amongst the old).

If all of this sounds complicated then forget about replacements rates altogether - they simply confuse the gullible. Concentrate on what ZPG actually means - birth rate equals death rate. Or, to put it simply, ZPG means that the number of people that are born each year is matched by the number of people who die.

Suppose some people refuse?

Can we assume that all 6 billion people agree with the policy of ZPG? This would be the first time in recorded history that all people agreed about anything so significant. Very, very unlikely. Still, let's be extremely optimistic. Let's assume that 5 billion are taken in by the new ideology of ZPG, and 1 billion refuse.

5 Billion at ZPG. Regardless of how much time passes, there are still 5 billion. This is what ZPG would mean for them. I'm sure they would be feeling smug in knowing that their sacrifice has saved humanity.

1 billion at 1% growth rate (even though they disagree with the wiser majority, they are persecuted like people in China who have more than there allotted 1 child. Hence, they feel they shouldn't overdo things and so their rate is 1%). 2% is quite easy to achieve, so 1%  is extremely modest and may be optimistic. This means that their doubling rate is roughly 70 years. And off they go...

1  2  4  8  16  32  64  128  256  512  1024 

Obviously, I do not propose that it is possible to sustain their growth rate if we stay on Earth. A catastrophic Malthusian disaster would strike long before then. Nonetheless, the trend towards population doubling is proven mathematically

So, after 10 doublings (700 years) at a modest 1% growth rate we would have 1024 billion anti-ZPG people, and 5 billion pro-ZPG people. Get it? Any majority decision to go with ZPG will soon make the ZPG population the minority. Long-term ZPG is a myth, requiring people to agree about something as incredibly personal as reproductive rights forever. What do you think 1024 billion anti-ZPG people would have to say to the 5 billion pro-ZPG people about that (in the year 2,700)? 

"So long guys, we're off to the stars! You can have the planet. Oh, sorry we wrecked it for you...losers!"

Sociological Change

OK, by some miracle, lets assume everyone goes with the ZPG dogma/doctrine/ideology. 100 years pass. Do they still agree? Are we in space yet? Another 100 years pass. Do they still agree? Are we in space yet? As time passes, societies change. Plus, we get scientific and technological progress. Both of these will destroy the ZPG myth. 

No ideology survives for ever. Even in China, the strong central government  is struggling to maintain full control. There are sure signs that the controls in China are slowly and quietly being relaxed. If the Chinese government can't impose its will, what chance does India (the world's biggest democracy) have? What chance does Africa have?

Scientific Progress

If the centuries pass, and the ZPG ideology somehow survives (thus proving me wrong), what affect do you think scientific progress will have? To be sure, any limitlessly strong and brutal regime could enforce ZPG for some time. If that time duration was centuries, would they also repress scientific progress? Suppose we include technological progress in with scientific progress. The Gutenberg printing press, the telephone, television and the internet are all inventions which enable the sharing of knowledge and ideas. The trend here is towards more effective methods for sharing knowledge and ideas, so I find it highly unlikely that any society could ever stop scientific progress (though some have tried).

Moore's Law, which states that computers double in capacity and processing power every 18 months, is a good example of how technology can emulate life in adhering to Malthus's Principle Of Population.

It is no coincidence that the most explosive period of growth for the human species has occurred during our period of greatest scientific progress. Scientific progress was the cause of our exponential population growth in our past, is the cause of our exponential growth today, and will always be the cause of our exponential growth in our future. 

It is true that, today, the fashion is to control and restrict growth. Virtually every Web page about population cries out the same message, over and over. There is good reason for this, as I stated earlier. Alongside all the efforts to slow population growth, scientists and others in the secular world are :-

All of the above, and more besides, will have the opposite effect to slowing population growth - each will allow us to support greater populations whilst at the same time attempting to minimise our impact on the environment. 

China and human rights

I do not intend to state my opinion of human rights in China in this article. However, I am aware that in China some families practice infanticide on female babies (like many human cultures around the world) to favour the sex of their only child being male. Plus, today's abortion vacuum pump was invented in China.

Ask yourselves, if we are to reach ZPG, what measures will be necessary? If you think it can all be done nicely and voluntarily well...you are deluding yourself. 

The Natural Order Of Things

The problem with the ZPG argument (and I include sustainable development here) is that it assumes it has the moral high ground. In fact, it is a moral quagmire. Many ZPG protagonists argue that nature is in favour of ZPG. On Earth, as we have seen, it is obvious that population doubling cannot be allowed to continue. But the mistake that ZPG protagonists make is that they assume ZPG must be natural, because it is good for nature. ZPG is not natural. Population doubling and exponential growth are natural. 

Nature has a way of balancing population doubling and exponential growth. This state of dynamic equilibrium is popularly termed "the survival of the fittest". It's a contentious phrase (not invented by Darwin, by the way, but by Herbert Spencer). In real terms, it must mean that we are the fittest. It is neither virtuous nor sinful to be the fittest. My definition of "the fittest" is:

"Whichever species best adapts to changes in its environment, learns to dominate and manipulate other species to the greatest effect and to its own benefit."

Sometimes this means finding your own quiet little niche on an island somewhere, and eking out a living. Sometimes it means out-breeding other species to their detriment and for the benefit of your own species. Our own recent "success" doesn't make humanity clever, or better. It simply results in more of us, at the expense of other species. The success of species such as pigs, sheep, cattle, dogs, cats, lab rats and so on is because we use them for our purposes. The same goes for wheat, corn, barely, rice etc.  Their numbers benefit from their alliance (however one-sided and dubious) with humanity. Species for which we have little use, or sometimes too much use too quickly (e.g. the dodo), tend to go extinct. This trend will continue for as long as we remain Earth bound. Yes, we will still use life for our own purposes. Certain viruses and bacteria might flourish as the human monoculture grows exponentially. This is the natural order of things, though humanity will hopefully continue to defy Nature and keep the microbes in check.

We can reverse this trend by colonising space and taking life with us, and nurturing life. 


The high morals of ZPG protagonists are usually also directed against "wasteful and extravagant" expenditures in support of space colonisation. These same people will condemn scientists for the potential  unforseen consequences of "tampering with nature" or "playing God". They do not realise that they are on the same side as the scientists they so frequently condemn. ZPG protagonists and many scientists are both simply buying us time. If we do not use that time to colonise space then there is no hope for humanity. If there is no hope for humanity then all the high hopes and aspirations of ZPG forever, and sustainable development, will sink inexorably into a quagmire of their own making. It may take some time,  but if we fail to colonise space then we will take many of the species from Earth's biosphere down into that Hell with us.

One of the more famous grand experiments relating to space colonisation is the apparent failure of Biosphere II. These were self-contained, artificial habitats in the middle of the Arizona desert. They were designed to study closed ecologies. "What a waste of money!" people cried. What they fail to realise is that, putting aside any arguments in favour of colonising space, if we can't manage those simple closed ecologies then what hope do we ever have of managing the Earth's extremely complex biosphere? 

We are a long way from even naming all of the species on this planet, so let's not pretend that we can  assume our efforts will lessen the damage our larger future population will do. Let's stop fooling ourselves. We don't know what we're doing. All we do know is that humanity will use Earth's ecology to its own end. Some will sooth their guilt by valiantly saving the odd species here and there. I applaud them, but their efforts are doomed by Malthus's mathematical Principle Of Population. 

Whatever mistakes we made with Biosphere II will prove useful in our attempts to colonise space, as well as our attempts to manage the Earth's biosphere. 

See Biospheres and Solar System Exploration by Thomas O. Paine, Ph.D. (Administrator of NASA, 1968-70; Chairman, National Commission on Space, 1984-86) for a great presentation on this topic.

The Exponentialist Argument

What is an exponentialist? It's a new word, and here's my definition:

"An exponent of the exponent, with particular reference to the natural processes of replication."

Note that the first use of the word exponent does not mean the same as "proponent". Exponent means "someone who explains". Proponent means "someone in favour". The second use of the word exponent relates to exponential growth. Using the standard 'scientific notation', 23 = 8 (this is 2 x 2 x 2). 103 = 1,000 (this 10 x 10 x 10). In both cases, the 3 is the exponent. 

Hence, an exponentialist explains the significance of exponential growth and emphasises that it is part of the natural order of the universe for all populations of living things to tend towards population doubling. 

I use the word "replication" in recognition of the work done by British zoologist Richard Dawkins in "The Selfish Gene", "The Extended Phenotype" and "A River Out Of Eden". In the latter work, Dawkins recognises the significance of humanity's role of enabling the "replication bomb" of life to "reverberate through deep space" from its fragile beginning on Earth.

Replication is also the word Eric Drexler ("Engines Of Creation") uses for the Holy Grail of  nanotechnology  - a self-replicating assembler. Potentially, a new form of life. 

Even without nanotechnology, John von Neumann postulated long ago what has become known as the von Neumann machine. Any self-replicating machine, whether endowed with artificial intelligence or not. 

For a definition of Dawkins' replicators, see What is A Replicator? from Replicators: Evolutionary Powerhouses. I would add the growth rate for a given time span as an attribute of any replicator, such as 1% per annum, or 2% per day. Given that any population of replicators can be said to have a replication rate (or birth rate) and a death rate, it follows that all populations of replicators can only ever be in one of 3 states: 

It is worth repeating that Positive Population Growth leads to exponential growth, which allows us to calculate population doubling times. Similarly, Negative Population Growth rates allow us to calculate population halving times. 

Positive Growth Rate

1% 2% 3% 4% 5% 6% 7%
Doubling Period 70 35 23.3 17.5 14 11.6 10

Negative Growth Rate

1% 2% 3% 4% 5% 6% 7%
Halving Period 70 35 23.3 17.5 14 11.6 10

Table A: Approximate doubling and halving periods derived using the Law Of 70.

Clearly, for a given rate, the period is the same regardless of whether the rate is positive or negative. For human populations, the time unit normally used is one year. For bacteria, the time unit is typically an hour or less. Hence, 35  would be 35 years for a human population, or 35 hours for a bacterial population which doubles every hour.

A replicator should (literally speaking) only produce replicas (identical copies) whereas Natural Selection works due to mutation and non-identical copies. A true replicator would have a fidelity of 100% (all copies are identical), making most species poor replicators (with fidelities between 99 and 100%). Still, Dawkins' introduction of the generic term replicator does not assume that humanity will colonise space and remain the dominant life-form, and nor does it exclude the possibility that we might. It also allows for von Neumann machines, or life-forms based on nanotechnology, to assume the mantle of stewardship for all life. So, from a population perspective, humanity can be described as a population of replicators (or, as Dawkins might describe it, a population of replicator vehicles). 

Exponential growth drives Natural Selection and drives Differential Reproduction. Differential Reproduction (or Differential Replication, as I prefer to call it) is the principle of the comparative success of replicator populations. See Natural Selection and Differential Reproduction - from Replicators: Evolutionary Powerhouses. From a population perspective, the dynamics of Differential Replication will work whether you are describing human populations, virus populations, bacterial populations...in fact, any population of replicators whatsoever. If you don't like the use of the word replication with regard to human populations, then by all means stick with reproduction. It makes little difference to Differential Replication..

So, if humanity itself does not continue Life's "Grand Plan" into space, some of our creations might. The trend of population doubling and exponential growth can continue without us, and again long-term ZPG will prove to be no more than a myth.


Originally, this argument came under the same argument as Scientific Progress. However, nanotechnology has the potential to re-write all the rules and deserves an argument all of its own.

Nanotechnology offers the greatest hope of the ultimate recycling technology. Matter could be reconstituted at the molecular level,  deconstructed molecule by molecule then rebuilt molecule by molecule. With such a technology, there might be no such thing as "waste". All matter, from the animate to the inanimate, becomes a resource made from molecules. Everything could be used to help make food or fresh clean water! The environment could be restored as we see fit!

Such technology is not available today, but if the full promise of nanotechnology is realised then the human populations that it could support (even if restricted to Earth) could be truly staggering. But nanotechnology would be capable of redefining humanity itself (see Nanomedicine Web page), and all life. Imagine a super intelligent nano bloom, or nano swarm. Or see Robert Bradbury's Matrioshka Brain Web page for a Solar System sized brain which could be built using nanotechnology, or my own ideas on Nano Cells, Nano Sails and Heliovores. Other people have used the term Unnatural Selection to describe genetic engineering and cloning. I prefer to extend this term to include nanotechnology, artificial intelligence, and all future forms of artificial life. 

Exponential growth will also be the driving force behind Unnatural Selection when it takes up the reins from Natural Selection. Potentially, nanotechnology could create true replicators with 100% fidelity. Evolution does not occur for such hypothetical species, though Differential Replication will still apply to populations of such creatures as they compete for their slice of the pie.

Nanotechnology replicators could have population doubling times comparable with bacteria (which double, on average, every 20 minutes). Such replicators would be capable of massive and rapid growth on an unprecedented scale. So, whilst on the one hand nanotechnology could sustain massive populations through becoming the ultimate recycling and eco-friendly technology ever imagined, it could also be the cause of growth rates higher than ever before achieved by humanity.

If nanotechnology is fully realised, the only question will be whether we will use nanotechnology to colonise space (first our solar system, then other stars), or whether AI-enabled nanotechnology will use humanity to step up and beyond us into space (leaving us far behind). 

Colonising Space

Let's assume the worst, and the ZPG zealots of planet Earth round up all the trouble-maker scientists and atheists. These guys are always raging against the wisdom of society, and the doctrine of ZPG and sustainable development. Suppose there are just 1 million of them. Get rid of them!. But it's out of fashion to torture and burn the atheists, or place the scientists under house arrest! Don't worry, it can be done humanely. Scientific progress enables these trouble-makers to colonise space, so you exile them there. Earth is too good for them!

People generally think life is impossible without Earth-like planets. They don't understand the resources available even in our own Solar System. Take water, for example. A common misperception is the lack of water in space. If all the Earth's oceans and seas is one Ocean Mass, a conservative estimate (ignoring the icy and extensive Oort cloud) of all the ice in the Solar System is 180 Ocean Masses (from Adrian Berry, "The Next 500 Years"). 

Even without nanotechnology, the resources in our own solar system are so vast that these gallant few would be hard-pressed to prevent a positive population growth rate (a modest assumption of 2% growth would mean population doubling roughly every 35 years). So you exile the 1 million radicals, and off we go again...

1  2  4  8  16  32  64  128  256  512  1024  - making over 1 billion, in space, in 350 years. 

Then, in billions...

1  2  4  8  16  32  64  128  256  512  1024  - making over 1 trillion, in space, in the next 350 years.

And so on...

On Earth - the zealot population is still 6 Billion at ZPG (the 1 million newly available birth-slots would be quickly filled). 

Without nanotechnology, these Earth-bound zealots might enjoy their own personal man-made Hell. Of course, the Earth scientists might will lessen the pain for while, and prolong the myth of ZPG. 

With fully realised nanotechnology, our solar system can be seen as a vast store of useful molecules bathed in energy from the Sun. Our 1 million exiles could almost certainly experience faster growth rates, whilst at the same time redefining humanity and all life. They could fully harness the energy of the Sun, and use the matter from the planets, moons, asteroids and comets as they choose.  

If fully realised nanotechnology were used by the ZPG zealots on Earth (and I doubt that they would welcome it), it could comfortably sustain a population of 6 billion indefinitely on Earth. But throughout the Solar System, evolution would be passing them by as the descendants of our exiles head off for other solar systems to fully exploit. What would be the point of such self-sacrifice on the altar of Earth? Life on Earth would become a mere sideshow...

An End To Limits?

So colonising space solves the problem of exponential population growth?

No. Malthus got this bit right - it is the nature of life to always tend towards exponential population growth (see Reverend Malthus and Christian Morality). This has always been the case, is the case now, and will always be the case. 

It's a pity Malthus didn't know Soviet astronomer Nikolai Kardashev (see Kardashev in my article Per Ardua Ad Astra), who simply and clearly stated the true "limits to growth" for any space-faring civilisation - home planet, home solar system, home galaxy.

At each level, life will reach a limit. With each planet, each star, each galaxy - life will face limits.

The challenge for humanity now is to reach Kardashev Level 1 without destroying life on Earth in the process, and soon after begin the struggle towards Kardashev Level 2 (thus taking life with us into the Solar System).

Hooray For Negative Growth?

Isn't there anything we can cheer about? After all, Europe, Russia and Japan now all have slightly negative growth. Doesn't that balance out against the 1% growth rate of China, the 2% growth rate of India and the 3% growth rate of Africa? In short, no.

Let's be generous, and lump the negative growth countries into a 1 billion person mass. Let's be even more generous, and assume a negative growth rate for them of negative 1% (halving every 70 years).

Let's allow for 4 billion people at ZPG, and the remaining 1 billion at positive 1% (a very conservative vision of Africa and India's combined growth). 

1 billion - negative growth of 1%. Such a rate of negative growth is a 'slow' route to extinction. For example, after 300 years they'd be down to around 5% of the original 1 billion which is 50 million. In time their population will disappear in a puff of despair. 

"Bugger", the last poor soul was heard to say.

4 billion at ZPG - always at 4 billion.

"You should have listened to us! We're all doomed!" is their parrot-like refrain. And they're right, too, in a way.

1 billion at 1%. Here they go again...

1   2   4   8   16   32   64   128   256   512   1024

So, in just 10 doublings (700 years), nobody will remember Europe, Russia & Japan. But there will be 1024 billion Africans and Indians to laugh at, or take pity on, the 4 billion still preaching ZPG. 

Notice that the complete lack of balance between the 1 billion with negative growth and the 1 billion with positive growth. Notice also the total marginalisation of the 4 billion ZPG protagonists - they are irrelevant. The only significant population is the one descended from the original 1 billion growing at 1%. This is Differential Replication, and evolution, at work.

Even if we take 5 billion with negative growth of 1%, and 1 billion with positive growth of 1%, the message is the same.

Nature does not favour populations with negative growth. They either die out, or resort to population doubling as soon as resources allow. 

This is neatly summed up in "From So Simple A Beginning - The Book Of Evolution" (p. 182) by Philip Whitfield (1993):

"The extinction of a species does not usually involve the sudden death of all its individual members. Rather, it is a function of the dynamics between rates of birth and death. Species will persist when their overall birth rate equals or exceeds their death rate. But if the latter exceeds the birth rate for a long enough period, replacement of one generation by the next ceases to exist. If no new factor intervenes then the species will go extinct."

Dynamic Equilibrium

Some people optimistically believe that humanity can achieve Zero Population Growth through a cycle of Negative Growth and Positive Growth, or population halving and population doubling. This is known as dynamic equilibrium. If you believe that this is realistic, ask yourself these questions:

Perhaps the only realistic way for a human population to achieve a state of dynamic equilibrium is to let Nature take its course. 


Hopefully, everyone is now familiar with the unlikely but deadly threat posed by an asteroid strike on the Earth. Other pessimistic visions abound, including nearby supernovas, alien invasions, super plagues, nuclear war (followed by nuclear winter), enormous volcanic eruptions and so on. Surely any one of these will lessen the burden of humanity upon the Earth's fragile biosphere?

Assume a major catastrophe occurs and 2 billion people die, leaving 4 billion. A modest sustained annual growth rate of 1% will result in that population doubling every 70 years

4   8   16   32   64   128

and so in just 350 years (5 doublings) the Earth would have 128 billion people. In fact, it only takes 1 double (to 8 billion) to surpass our current 6 billion. So whilst the threat of catastrophe is real, and the loss of life would be substantial, exponential growth can quickly compensate for such events. The history of mass extinctions on Earth (refer "The Sixth Extinction" by Richard Leakey and Roger Lewin) teaches us that life will go on (even if we don't)...

Reverend Malthus and Christian Morality

Malthus deserves recognition as one of the first men in history to understand the basic mathematical Principle Of Population (the natural tendency of populations towards exponential growth). This is simply illustrated through the Mechanism Of Population Doubling. Malthus also understood clearly the constant, unavoidable and miserable consequences of this for humanity. The Reverend Thomas Malthus was the first exponentialist, followed closely by Charles Darwin.

However, in assuming the moral high-ground for Christianity, Malthus obscures the true significance of his own work. The first edition of his essay offered a stark view, offering no real hope. By amending that view in subsequent editions, he now reinforces the delusion that ZPG is an achievable and sustainable goal (perhaps through "moral restraint") even though he didn't really believe it himself.


Throughout the history of Homo sapiens sapiens, humanity has experienced both regional and global population doubling. Occasionally, local populations decline, but the global trend is always towards population doubling. The long slow climb to the first billion, and our rapid growth since, are described in my Brief Demographic History Of Humanity.

As our global population reached the current limits to growth throughout our demographic history, so our exponential population graph takes on the classic S curve. Then, as science and technology pushed back the limits to growth on Earth through the Agricultural and Industrial Revolutions, so our demographic history reflects new bursts of human population growth across the globe. Nanotechnology, and other advanced technologies, will create the next burst of growth... on Earth and beyond. 

As it was in the past, so it will be in the future, for as long as there is a human race.


Why Cassandra?

Cassandra is a figure from Greek mythology. Loved by Apollo, he gave her the gift of prophecy. When it became clear that she felt that she owed him nothing for this gift (including her virginity), he cursed her. The effect of this curse was that nobody believed her prophecies, even though they were true. I'll bet she didn't dream up this one!

People think I was playing at prophecy with the boardgame 6 Billion™. Wrong, I was just trying to provide an optimistic (and both possible and feasible) alternative to the real prophecy. 

But I'm not a prophet, I just like stating the obvious. I find some simple mathematics and common sense helps. Oh yes, one other thing, I tend to steer clear of blind faith.

6 Billion™

The 6 Billion™ boardgame assumes population doubling each game turn. The reason why this assumption is valid is because a game turn represents the amount of time it takes for population of the Solar System to double. This could take anything from decades to centuries, but they will double.

Negative growth leads to the extinction of the population in question (be they Europeans, or the entire human race), whereas evolution (through Differential Replication) favours populations capable of sustaining positive growth. Evolution is a numbers game, and so is the 6 Billion™ boardgame. Evolution favours populations that double (see Natural Selection and Differential Reproduction - from Replicators: Evolutionary Powerhouses), and so does 6 Billion™. 

Sustained ZPG is a myth (reinforcing the assumption of population doubling), and human populations are destined to continue to overcome limits and keep doubling into the distant future. 6 Billion™ dates the first game turn as starting 12th October, 1999 (The United Nations dubbed this "The Day Of 6 Billion"). We now have the beginnings of a permanent human settlement in space - the International Space Station. The human exploration of Mars will begin in just a decade or two away. The first game turn is under way...

I describe 6 Billion™ as an optimistic vision because 6 Billion™ assumes that humanity survives the challenges to our future. 6 Billion™ assumes that, for the duration of the game (roughly 10 population doubles), it is still valid to count human populations as we will remain essentially human. Perhaps we will live alongside far more advanced intelligences of our own making. 6 Billion™ only counts the humans, though it is fun to imagine that each player's faction might represent a bifurcation of humanity into related species...

If you believe humanity will be surpassed by artificial intelligences, or advanced descendants of the human species, then play 6 Billion™ again but imagine the existing human species as the Neutral faction with the players representing populations of advanced species...

In time, intelligent life from Earth will view the entire Solar System as their home. Earth will always be special as the original source of that intelligence, but will also fade to nothing more than an evolutionary and demographic sideshow. One day, the people of the future will say that the Solar System is getting too crowded. Then the long-cherished dream of colonising the stars will gain enormous impetus as the next wave of evolution pushes out from our Solar System.

Doris Day

"The future's not ours to see. 
Que Sera Sera, whatever will be, will be." 

So sings Doris Day, neatly summing up many people's attitude to the future. 

Good luck,

David A. Coutts

PS - Has anyone got a ticket to Mars?

Related pages include Per Ardua Ad Astra, 6 Billion - A Demographic History, The Design and Production of 6 Billion™ and The Planets And The Asteroid Belt

For a list of articles by me, see the Articles page.

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Last modified: 27 August, 2012