One Finite Planet

My Journey To Understanding Population.

First Published:

Table of Contents

Population is a complex area. To arrive at my current point of understanding, it took me a number of light bulb moments over the years since 2013, with many realisations shattering some of my previous beliefs, and sometimes taking years to be ready to take the next step.

Here is a recap of my journey, and if you can move quickly from step to step, then you can absorb information faster than I can, but perhaps this information will inspire others on their own journey.



My very first posts on this site reflected my initial fears, that many of our problems the world faces stem from overpopulation, and something must be done to limit the population growth which seemed to be in our nature.

This page is intended to into context the pages I have created over the years while on the journey to understanding just how many of my initial ideas and beliefs were so wrong.

I now, almost 10 years later, feel the full analysis results in a very thorough set of insights on population, and human population levels, that already, have provided better predictions of future trends than those available from the UN official data. Although they have recently adjusted their forecasts to be a closer match to mine.

Previous versions of the UN World Population Prospects showed a significant slowdown in population growth, with very slow growth – almost reaching a plateau – by the end of the century. In its previous release, it projected that the world population would be around 10.88 billion in 2100, and would not yet have peaked.

In this new release, the UN projects that the global population will peak before the end of the century – in 2086 at just over 10.4 billion people

With each step on the journey, I include links to the pages that enabled that step.

Overpopulated: David Suzuki and The Petri Dish doom!

David Suzuki: 2010.

Yes, I started with the David Suzuki petri dish analogy, and that if we are not existing sustainably, then we are already overpopulated.

Watching David Suzuki, it becomes clear that while economists insist that perpetual exponential growth is essential for a thriving economy, perpetual exponential growth is impossible in the natural world.

A look at any graph of human population shows almost flat line … almost flat line ..  almost flat line and then WHAM, population takes off soon after the year 1700, or around the start of the industrial revolution.  From year 1 to the start of the industrial revolution over 17 centuries the population merely doubled.

Then in less than 300 years it multiplied by a factor of 14.

It looks clear. Humanity has entered a phase of a seemingly unprecedent rate exponential population growth. and clearly exponential growth will lead to our doom. Every year the population increases, and this has to stop.

It is easy to believe that greed will lead to our downfall, and perhaps it will, but it turns outs, despite continuing population growth, the dire predictions of the 60s and 70s have not come true, because somewhat unexpectedly, we humans have dramatically reduced the rate of growth, avoiding the 13 billion we would have already, had the peak growth rate continued.

While I posted my original concern about population growth in 2014, I had already been researching and a few months after that page, I came to realise that although principles describe by David Suzuki are relevant and important part of the journey, the picture is more complex and these principles are just a starting step.

Step 1 is: “already overpopulated, and exponential population growth is out of control, we are doomed”!

Further pages:

Growth is Slowing, ‘Births per Woman’ is falling: There is Hope?

Population Growth is slowing.

By 2015, I had learnt that exponential growth was no longer the pattern playing out, as the exponent was decreasing.

Rather than continuing the accelerating exponential growth seen up to the 1960s and 1970s, and discussed by David Suzuki, the population growth rate was now slowing. Even such authorities as the UN projected population growth was now on trajectory towards a peak population, and that after that, population levels could even fall.

I posted “Population: Brace, the slow down has started!” in early 2015, and there were comments from people who strongly believed “this is wrong, we are all having too many children and will perish as a result”. Beliefs are powerful and it is hard to change beliefs in a short time by new information in response to new information.

Too many children? If so, then of course population would still be growing. What is “too many children”? The best measure available is ‘births per woman’, also referred to as fertility rate, and rather than 2.0 being zero growth, complexity of measurement and other factors mean that around 2.3 population stability.

Clearly, births per woman has been falling, but regardless of the predictions by the UN, the data so far still has the worlds population rising.

Growth ending is only a projection.

And population growth may appear to be slowing according to the UN data, but slowing, is not necessarily stopping.

Birth rates have fallen and are still falling, the rate of growth is slowing, and this slowing growth is already is a huge change. If even the rate of population growth is slowing, then our entire economic system which has evolved to be centred on significant population growth, is in for a severe shock.

But population growth slowing is not an end to population growth, and that is where step 2 leads.

Step 2 is: Population growth is slowing, but despite declining birth rates, population growth continues and it is hard to have faith population growth will ever be sufficiently constrained.

The Trend is better than it looks: Hans Rosling, Peak Child, and Population Pipeline.

The population pipeline, means

In fact, I reached step 3 had been exploring the population pipeline, even before I discovered the talks by Hans Rosling.

The realisation came that despite that the population is still rising, growth was indeed set to halt. We are still seeing a rise now, because there is a lag between birth rate changes, and what happens with population growth. It took me several explorations such as ‘brace‘ and ‘population lag‘ before being confident enough this was reality.

Now years later there are many more sources of this news, and by 2020 even the BBC was predicting a total population crash, even while the population is still growing.

However, watching Videos by Hans made it far easier to feel comfortable with this step, and his videos, including Ted Talks, and Gapminder videos, are recommended watching.

Peak Child, and then, peak population: earlier than predicted, and likely by 2055.

Professor Hans Rosling.

Hans Rosling explains that birth rates have already fallen to the level that results in “peak child“, and that this will, given time, result in the end of population growth.

On first hearing about ‘peak child’ it can seem unbelievable, given the global population is still rising. You would think peak child should immediately result in an end to population growth, but it turns out there is a delay, due to the “population pipeline” which result in a a full life span (around 80 year) wait between peak child and “peak population“.

Hans was somewhat of an optimist, with belief that although population levels are already a challenge for sustainable existence, it is inevitable that having reached peak child, population will stabilise and it will then be manageable. However there were two limitations to the model by Hans:

  1. Economists, billionaires and politicians pursuing perpetual growth is essential, will try to intervene.
  2. While Hans Rosling had ideas as to why population growth was slowing, even these theories did not fit with the data.

These two points are essential to future outcome. Will the rich an powerful manage to directly change the outcome? And, what is driving the outcome in the first place.

My own explorations at this point strongly supported that birth rates would keep falling beyond the level for population stability in many countries, and result in a population peak as early as 2055.

Step 3 is: An understanding that peak child arrives prior to peak population, and that population pipeline will mean changes to birth rates will take up to a lifetime to fully be reflected in population growth trends. But there is still a nagging doubt, that something could result in population growth continuing.

Explosion: Understanding 250 Years Of Unprecedented Growth.

It is natural to assume that the pattern of population growth seen by our parents, grand parents and great-grand parents has been as things have always been. But no, while ‘peak child’ and generations a similar size to that of their parents, is how things were for tens of thousands of year and all of history until the last few hundred years.

The growth from less than 1 billion people in 1801, to almost 8 billion people, a sixteen fold population increase, has happened in just close to 200 years. Homo-sapiens date back 300,000 years, and population growth from 2 homo-sapiens 300,000 years ago to 1 billion in 1801 would be an annual growth of below 0.007% and see the population double only once every 10,000 years. Not 100x faster growth of almost 7x more people in just 200 years which is 1.0% population growth every year!

Looking back at the UN data with the predictions above, it is quite clear that until around 250 years ago, population levels had been relatively stable for a long time. This rapid population growth, is specific to the last 250 years.

Why was population growth so much slower throughout history, even when people have had families with an average of well over 2 children per family. We have all heard of families of 10 or even 20 children, but of course there were also families with no children, but still the historical average has been 6 children per family.

Hans Rosling gives his answer to why there was population stability prior to the ‘population explosion’:

Why did the worlds population grow so slowly before 1800? Throughout history, all historical records show that on average, 2 parents got more or less 6 children. But that looks, as a very fast population growth. So why didn’t it grow? Because 1.. 2.. 3.. 4.. of the the children died before growing up to be children themselves. People in the past never lived in ecological balance with nature, they died in ecological balance with nature. It was utterly tragic!

Hans Rosling:,historical families sizes allow for children dying.

Step 4 is: Understanding that population growth as seen in the 19th and 20th centuries is not only unsustainable, but also unprecedented.

What Caused the Explosion? Could It Happen Again?

Realising we have had one explosion raises the question, how can we be sure there won’t be another population explosion, unless we know what caused this last population explosion? If we had an explosion once, perhaps the same will happen again?

The Cause.

It turns out, that, as explained by Hans, the explosion was caused not by larger families, but by children surviving.

But with the industrial revolution, this changed. Better wages, more food, tapped water, better sanitation, soap, medical advances…. So from all these advances, why did population grow? Was it because they got more children? No! In 1963, when I was at school [the peak of population growth], actually the number of children per woman had decreased a little in the world, to 5. And the reason for the fast population growth was the improved children survival, 4 survived at that time. But still 1 out of 5 died, that was still terrible.

Hans Rosling: Children stopped dying due to improved health.

It is clear early in any analysis, that the population explosion between 1650 and 2000 represented exceptional, and from all records, unprecedented population growth. It was indeed a population explosion.

Again, what caused this period of exceptional population growth?

  • Increased family sizes.
  • Increased food production.
  • Reduced infant mortality.

Comparing family sizes before and during the explosion, children born per family was lower during the explosion than before the explosion. Food production may have enabled avoiding famines as a result of the population increase, but it was not more births, but slightly less births with greatly reduced infant mortality that triggered the increase. Prior to the explosion, while food was always great quality, population was not constrained by available food, and family sizes did not increase their number of children in response to more food, as clearly, families did increase the number of children being born.

Clearly the explosion was driven by the reduction in infant mortality, as explained in more detail here.

There is no question that reduced infant mortality triggered the explosion, and progressing to this step only requires reviewing the evidence and waiting for the answer to sink in.

Could It Happen Again?

We have very much solved infant mortality. There are still child deaths, but these are now in sufficiently low numbers that even eradicating all remaining deaths will have insignificant further impact on population. Therefore the exact same problem will not reoccur, however there medical advances that result in longer lives would increase the number of people alive at any one time. As the elderly do no currently reproduce, the impact is a one time increase, rather that ongoing population growth, however if these secret of living indefinitely is ever revealed, then we reach a whole new overpopulation problem.

Step 5 is: Understanding we have experienced an explosion, and it was clearly driven by the reduction of infant mortalities.

The population explosion is ending: Peak Population.

The explosion is ending? Really?

Fact is, I had seen population growth was slowing even before I understood the explosion, but now this is supported by real world data, as referenced in the ‘peak child’ page, and it is very clear the explosion is ending. The big question now, is why?

Why is the explosion ending? Solving The mystery of Falling Birth rates.

Understanding that the population explosion was ended by falling birth rates raises a huge, and unanswered question:

What caused the fall in birth rates that brought an end the population explosion?

It is huge because without an answer, the future is dangerously unpredictable. It is unanswered, not because there is no answer, but because people are not agreed on a correct reason to be the answer.

Unlike a boom caused by a temporary increase in birth rates, a boom caused by increased child survival cannot happily end by having things return to how they were before. We do no wish to return to high infant mortality to end a population explosion. Falling birth rates is a better solution, but a puzzling one. Now we have two changes. Reduced infant mortality and reduced birth rates, but the reduced infant mortality was intentional, while for the most part, reduced birth-rates occurred without specific intent or even necessarily obvious reasons.

There are several suggested reasons including:

  • Family Planning programs and measures by governments to reduce population.
  • The availability of birth control.
  • The education and changing role of women in society.

I discuss each of these in Why are birth rates falling?

Generally, the answers have problems. Yes, some countries, notably China, took steps to reduce birth rates, but most countries took no steps, and still have falling birth-rates, so steps to reduce birth rates are at best a partial explanation relevant only in some cases.

The most commonly accepted explanation is that factors not planned to lower birth rates, and not directly linked to the population growth explosion, are central to returning population growth back to historically normal levels.

The other possibility would seem to be that the reproductive instincts of humans, like other animals, is a drive designed by evolution to produce a sustainable population. We seem to think there is some logic that makes humans decide to have a specific number of children, or to fall in love in the first place, and even to love our children. In reality, surely these are not logic, but things we have evolved to be driven to do. And if so, it would seem logical that we are driven to produce an appropriate number of children.

That such factors play a role, is the only explanation for throughout history people having an appropriate number of children.

Full Planet: Population increase always comes at a cost.

  • No Vacancy: For every increase in human population, other species decrease.

We live in a society where the virtues of ‘growth’ are heavily promoted. We also live in a society that has just experienced a population explosion. All this combines to create an illusion of a world where growth is the normal, and population growth is the normal.

But if population growth is the normal, the in the past, the population of life on Earth must have been much smaller. The Earth should have spent most of its history almost barren of life, with the amount of life gradually increasing to the current level, and continually increasing from this point forward.

Yet, most of the story of the Earth does not match that story of growth.

Prior to around 400 million years ago the Earth did have basically no life on land, but that was because the lack of protection from radiation and lack of a breathable atmosphere made life on land impossible. It turns out that within a short time of life appearing on land, there was as much life on land as there is today.

For the past 300 million years, new living things have bloomed in population, but only by replacing previous living things.

Same with humans. We can keep increasing our numbers, but only by decreasing the number of other living things we sharing the planet.

Optimal Population: We Evolved to Reach A Population Plateaux.

The next step for me what a light bulb moment arising from thinking again about those historical levels of growth, that for so much of human history had to be close to stability. Then comparing this with what happens in nature.

Gorillas in the mist tells the story of a population of gorillas that appears to have been stable for thousands of generations. Yes species, including gorillas are capable of population growth that would over time result in incredible numbers, but instead seem to quickly reach a ‘population plateaux’ or stable level.

Just three children per family surviving to have their own family would result in population growth sufficient for a population doubling every 50 years. Clearly while this has happened during the last 200 years, historically humans rarely average 3 children living to have their own families, because if just this rate continued for just 3,000 years of the 300,000 years humans have existed, we would have 9,223,372,036,854,775,808 humans, which is over 18,000 humans for every square metre of the surface of the Earth.

On a finite planet that is even 500,000 years old, every species on the planet has had sufficient time to completely overrun the planet. This means every species has way more time than need to reach it resource constraints, and for those that can exceed sustainable constraints, to exceed constraints and reach a catastrophic level of overpopulation.

If it was human nature to populate ourselves out of existence, you would think we would have already done so by now. Since almost all animals can exceed sustainable constraints and exterminate their food sources, there has to be a way animals naturally limit reproduction.

Conclusion and Where Next.

In a reversal of the situation back in 2015 when people questioned that population growth would end, we now have stories like this one from the BBC:

The world is ill-prepared for the global crash in children being born which is set to have a “jaw-dropping” impact on societies, say researchers.

Falling fertility rates mean nearly every country could have shrinking populations by the end of the century.

And 23 nations – including Spain and Japan – are expected to see their populations halve by 2100.

Countries will also age dramatically, with as many people turning 80 as there are being born.

Fertility rate: ‘Jaw-dropping’ global crash in children being born, BBC 15 July 2020

While these stories do echo the words of those motivated by big population, neither an ‘ageing population‘ nor contracting populations, are nearly as worrying as an overcrowded Earth where people have no place to live.

There are many predictions of population numbers up to 2100, when China, Italy, and Japan will all halve in population and Nigeria will have more people than China. The risk with these projections is do they project based on current trends, or do they predict future trends? The data seems to be the former.

What will happen next? If the ‘optimal population‘ concept is correct, then while the population may fall for a time, it will only continue to fall if that is what appears the right solution for humanity. I guess the next step is to further explore just would the right solution for humanity be.