This page explores how, despite all other complex organisms on earth reaching a ‘normal population’ level, humanity seems to continue population growth.
- The Population: “Missing Puzzle Piece”.
- Growth Cycles In Nature: The Concept of ‘Normal Population’.
- Did wild animal populations keep growing before humans?
- The Mechanism of ‘Normal Population‘.
- The Human Body As A Model: Growth Stops at Maturity, unless repairs are needed.
- Mechanisms of Population Control at the Cellular Level: Contact inhibition of proliferation.
- Mechanisms of Population Control in Animals: Kangaroos as an example.
- Alternatives Explanations to ‘Normal Population’:
- Population Growth from A Human Perspective:
- Can’t we keep growing?
- Don’t We Notice “Normal Populations” in Nature?
- So how have we kept growing so far?
- Human Population: Continuous Growth, or ‘Normal Population’?
- Looks like Resource Constrained Continuous Growth: But its not!
- Full Human Population History: The Reality Of Human Population Growth.
- Population and The Evolution Of Human Societies.
- Recent Population Explosion: The Breaking of ‘Normal Population’
- The End Of The Population Explosion: ‘Normal Population’ Resumed?
- The Mechanisms Of Stability and ‘Normal Population’.
- Mechanisms In Nature.
- When Mechanisms Fail: From ‘Normal Population’, to Plagues and Population Explosions.
- Has the Explosion Exceeded ‘Normal Population’?
- The Recent Population Explosion in Perspective.
- The Environment Always Recovers From Plagues In Nature, So No Problem?
- Conclusion: A Return To Normal For the Many, Or Greed Of The Few?
Normal Population in a nutshell.
The concept of a ‘Normal’ population is that the entire population of each species follows a similar growth pattern to an individual animal.
The normal growth pattern for an individual is for each individual to experience a growth phase, until reaching an adult size, and then to remain at approximately the same size from that time. Every individual animal is also a ‘colony of cells’, and continues making new cells for its entire life, but the population of cells reaches a point of stability at the end of the growth phase, and while new cells continue to be produced, for most of the individuals life there is a stable population of cells. From maturity the number of cells in the animal remains at a ‘normal’ population: cell population stability. New cells are always being produced, but once mature, this happens only fast enough to continue the stable population. The average cell in a human is around 7 years old, even if the human is 70 years old. The same ‘person’ even though almost all the cells are new. When there is damage, there can be more rapid grown, just as when we lose skin cells, but once the damage is repaired, cancer aside, cell reproduction goes back to just the rate required for population stability.
The population grows to ‘normal population’, and then cell production naturally drops to the level required to achieve population stability, just as cells populations do in an individual adult. If the population is temporality reduced, the population will recover and again stabilize.
The concept of normal population, is that the entire species can also be considered as a living organism that grows the population of individuals until maturity when ‘normal population’ is reached, and then there is population stability.
Real World Example: Humpback Whales.
As an example, consider humpback whales. The population of humpbacks in the south Atlantic ocean fell from an estimated 23,000 to 34,000 in 1830 to 440 by in the late 1950s, and has since recovered to an estimated 99% of their previous population. This is 5.7 doublings of population is less than 70 years, or one doubling every 12 years. Despite their ability to double the population once every 12 years, and having existed in the Earths oceans without any significant predators prior to whaling for well over 1 million years, which is enough time to double in population 83,000 times, their population stopped doubling after within 15 doublings even if there were only 2 whales 1 million years ago. Clearly there is a normal whale population, and as these whales have not decimated their plankton food source and there there an not whales continually dying of starvation, the ‘normal’ population is not a result of deaths of whales or running out of food. Some natural process results in an whales growing in population up to an optimum number, as also happens with elephants, lions, or any other animal.
Despite every animal on Earth having had more than enough time to overpopulation many times over, most animals reach a ‘natural’ population level, at which point they only reproduce at a level that results in a stable population.
The Population: “Missing Puzzle Piece”.
Researching the history of human population uncovers a puzzle, and normal population finally provides a solution to that puzzle.
I have been exploring the state of global population since 2014, as outlined in the my population journey. Initially motived by the passionate sound of alarm by David Suzuki, I soon had my first surprise on learning that rather than follow a path towards annihilation as highlighted by David Suzuki, population growth rates had fallen towards a level of population stability.
I then learnt that the recent population explosion was an aberration, and the human population over time is normally remarkably stable. In the words of the great medical researcher and statistician Hans Rosling:
People in the past never lived in ecological balance with nature, they died in ecological balance with nature. It was utterly tragic!Hans Rosling (see video, 19m)
The puzzle emerged: how did people manage to be born in appropriated numbers to match deaths for that ecological balance.
Doing the maths, it becomes obvious that for any animal in nature, exponential growth is impossible, because the timescales are too long. Just 63 population doublings in population takes any species from 2 individuals, to 9,223,372,036,854,775,808 individuals, which for anything beyond microscopic life, would fully cover the surface of all land and oceans of the Earth.
On a planet billions of years old, every living thing has had more than enough time for way, way beyond 64 doublings, and no species exists in the numbers that would result from continual doubling in population at even a fraction of the rate that species can double in population. Clearly, exponential growth over any significant time is impossible, and all life has some mechanism for population stability.
Plants, and some other organisms are resource constrained, which makes overpopulation impossible for those organisms. But for a huge range of species, from the bacteria in David Suzuki’s petri dish, through to humanity, population growth beyond a sustainable level is not only possible, but inevitable without some mechanism limit reproduction to exist in “ecological balance with nature”.
The missing puzzle becomes: how is it possible that most organisms can exist in a state of population stability?
Growth Cycles In Nature: The Concept of ‘Normal Population’.
Observations of nature: Did Elephant or other wild animal populations keep growing before humans?
I existed my entire life until recently, assuming that reproduction just blindly produced offspring in some fixed ratio relative to the parents my entire live until stopping and considering the alternative.
If we look at the populations of animals such as elephants in areas where there was not habitat destruction of poaching by humans, all evidence is the populations are stable. This is the same from whales in the ocean pre-whaling, through to polar bears and penguins. Plants and animals have flourished in natural habitats without constant population growth, and give the length of time these organisms have existed, if there was population growth then every habitat would be overrun. The reality is we see that population growth is not ubiquitous in nature, and at least almost all species manage a stable population when the environment is stable. This suggests either all species are resource constrained, or that there are natural mechanisms that control population growth.
The Mechanism for ‘Normal Population’.
Observation suggests that most living things tune their rate of reproduction to produce a stable population level.
The proposal is that evolution has resulted in many living things having evolved the ability to regulated their population at a desired ‘normal’ level.
How could this work? In practice, achieving a stable population would requires a feedback mechanism, so that when the population is below the ‘normal’ level, reproductive rate increases, and when the population exceeds the ‘normal’ level, reproductive rate falls. So for this idea to be reality, there must be examples in nature of mechanisms to control growth rates.
The Human Body As A Model: Growth Stops at Maturity, unless repairs are needed.
Consider how an individual experiences growth. For the first few years, growth is rapid, and then during teenage years, we stop growing, and spend the entire rest of our lives without further growth. It is not as simple as we stop growing, because while it seems possible for brain cells to last our entire lives, even bone cells only last 20 years, many other cells only last days. Our bodies are a population of cells from a series of generations. Cell production is continuous, takes place at varying rates for different cell types, but once we are adults, manages to produce cells at just the right rate for a stable population.
Further, consider what happens with skin cells when the skin is damaged. New skin cells are produced at an accelerated rate. If the accelerated rate continued, there would be excess growth around the wound, but once the wound heals, the growth rate returns to normal.
Mechanisms of Population Control at the Cellular Level: Contact inhibition of proliferation.
Some mechanisms of population control at the cellular level are well known. Contact inhibition of proliferation, a clear and simple example of population control, is where the density of cells in a given region controls the speed at which cells reproduce, with signalling between cells playing a key role. Although we are still learning all the details of ‘contact inhibition’, including having learnt that actual contact is not required, it is clear that population density can directly inhibit population growth at a cellular level.
Just as too many organisms endangers the entire colony, too many cells also endangers the entire organism, and without a mechanism to stop cell reproduction, our bodies would have cancer like growths or actual cancers.
Contact inhibition of proliferation, that is, the phenomenon that cells stop proliferating upon contact formation has been described several decades ago (Fisher and Yeh, 1967), but the underlying mechanisms are only now emerging. Importantly, loss of contact inhibition is a hallmark of cancer.Science Direct
As discussed in ‘life in the colonies‘, in fact we are all colonies of cells and what happens at a cellular level normally propagates even to the level of societies.
Mechanisms of Population Control in Animals: Kangaroos as an example.
Today in Australia the population of kangaroos is a problem for farmers, however it should be considered that, despite kangaroos in Australia having had 24 million years to grow their populatio , the Europeans did not arrive to a country overrun by kangaroos. While there are now more kangaroos than desired by farmers, that is partly as farmers raise not kangaroos, but sheep and cattle, and they all eat the same food.
In fact, the kangaroo population manages to reduce to a ‘drought normal’ in response to drought, and return to ‘non-drought normal’ when droughts end, without any assistance from humans.
Periods of extreme drought may delay the onset of maturity in female kangaroos and lead to suppression of their fertility cycles. At the same time most fertile females cease to breed. As a drought worsens, fewer and fewer females have joeys either at foot or in their pouches.
After two years of drought a population may include females aged three years or more which have never produced young, while none of the kangaroos in the area would be younger than two, the precise duration of the drought.Australia’s Amazing Kangaroos and the Birth of Their Young
That droughts last several years in Australia allows kangaroos to provide a clear example of how large mammals can not only maintain a ‘normal’ population, but even adjust to a ‘different normal’, in this case for the duration of a drought, and then return to ‘regular normal’ when the drought ends:
Following rainfall and growth of new herbage, kangaroos come into breeding condition almost immediately. However, it can take as long as eight years for kangaroos, even though prolific breeders, to reach their pre-drought numbers again.Australia’s Amazing Kangaroos and the Birth of Their Young
Alternatives to ‘Normal Population’: Predation and Resource Constraint.
It sounds simple, the number of organisms is limited by available resources. In fact, this simple model does appear to apply for some living organisms.
Recall the original “bacteria in a petri dish” by David Suzuki? This example highlights both that the bacteria do demonstrate resource constraint, and the limitations of relying on resource constraint for population control. Unless the constrained resources can be renewed from zero, like new sunlight each day, population will continue to increase exponentially until the constraint is reached, completely exhausting the resource. Then there will be the catastrophe of maximum population and zero resource. Relying on resource constraint for population control is often going to be a path to extinction.
Consequently, observation reveals most complex organisms have evolved population control that avoids the problems of relying on resource constraint. Even ignoring the fact that relying on resource constraint will completely devastate the critical resource, we simply do not see animals where the population is control mechanism is a significant number of deaths by starvation due to lack of resources. If population control was a result of only resource constraint work, there would always be too many lions in a safari park and a given percentage would always be dying of starvation, and when we went into a national park, we would see a percentage of dying starving animals. Further, the lions would continue to populate unsustainably devouring all their prey.
What we actually see is that, as with the kangaroos, animals seem to manage their reproduction to produce only the number of offspring that the resources will sustainably support.
Constraint by Predation.
One alternative to a species controlling its own population would be external control from predation. Certainly for many animals, a reduction in the number of predators will see population numbers increase, which suggests at least two possible explanations for this observation:
- The species is has no population control mechanism other than predation.
- The range of reproductive rates of the species has evolved to allow for predation.
The first explanation has three problems. Firstly, it is natural that the species would evolve before predators for their species exist, so they would have nothing to prevent catastrophic population growth prior to predators appearing. Secondly, while predation would slow growth, there is no way it would automatically result in a stable population, as any time the population of the species grows, survival rate from predation would increase, resulting in even more population growth, and a decline in population would result in a higher rate of predation leading to extinction. Thirdly, this mechanism breaks down with apex predators, for whom predation provides no population control, and so apex predators would continue population growth until the wipe out all of their prey.
The second explanation seems far more likely. That species do have another mechanism of population control that when combined with predation produces a stable result, but that other mechanisms may not be sufficient when predator numbers change dramatically.
Population Growth from a human Perspective.
Why Can’t We As Individuals Keep Growing?
Imagine a human growing up without any adults as a reference. Year after year this human gets larger. Why would this person assume that at a certain age they will stop growing? I can imagine it would be disturbing for such an individual, having experienced year after year of increased growth, to observe their growth decrease and eventually stop. In such a situation, would you wonder if you were dying? Or worry if something was wrong with you to stop you growing?
Or perhaps, this lone individual human would notice that it seems normal for other animals to reach a ‘normal’ size at maturity, and then exist at that same size for the rest of their life?
Don’t We Notice “Normal Populations” in Nature?
Or maybe the human wouldn’t learn from what happens with other animals. Humans have habit of assuming we are beyond the rest of nature, and can seem that we have not learnt about population growth from observing other animals. We don’t expect the populations of other living things to just keep growing, and we don’t expect their lack of population growth to be result of significant starvation, yet it is not common to consider what this means for humanity.
When I walk though a national park, I have never even though about the fact that the number of lizards in that park has remained basically the same for millions years, because I assumed that like us humans have lately, all animals must always increase in population. Of course when you think about it, clearly it is impossible for these species to have been increasing in number for millions of year, but I never thought about it.
But I had also not thought about the fact that when I enter a national park, there is no abundance of animals dead from starvation as a consequence animals having too many young. When there are fires or other disasters naturalists all talk of populations recovering, but as humans we don’t think about how these populations reach a ‘normal’ level and then remain at that level.
Somehow, we have animals all around us with ‘normal populations’, without it occurring to us to ask “do we have a normal population?”
Human Population: Continuous Growth, or ‘Normal Population’.
It Can Look like Resource Constrained Continuous Growth: But its not!
There is that David Suzuki model of population growth like bacteria in a petri dish, which looks a lot like t human population growth of 1960, or even 1980. Human population growth has been at 2% per year a rate of doubling every 34 years! Clearly unsustainable, unrestrained growth that will soon result in all resources being decimated!
But then, stepping back, doubling every 34 years would produce 64 doubling in just over 2,000 year, so we would expect at least 9,223,372,036,854,775,808 humans by now, even if there were only two humans just over 2,000 years ago! We should have at least 18,000 humans per square metre of the entire earth!
It turns out, through most of history, population growth was almost non-existent, and then we have a had a recent explosion.
This seems the exact opposite of what is expected. Instead of growth before reaching a ‘normal population’, humanity had a boost of growth long after reaching ‘normal population’.
Full Human Population History: The Reality Of Human Population Growth.
If we consider humans as a species that evolved around 300,000 years ago, we should have been able to reach our ‘normal’ population within at most 10,000 years.
Yet, although normally very gradual, there has been continued population growth. Discounting the recent population explosion since 1801 for the moment, to go from two humans as to around 1 billion humans in 1801 would be an annual growth rate of only 0.007% per annum. That is assuming continuous homogenous growth, which seems unlikely. But there is still a long term trend of very gradual growth, and that can’t happen with every species, or the world would be getting fuller and fuller, and it is not.
An increase in population of one species would normally occur following a step in evolution, and result a decline in the population of other species displaced by the new improved more evolved species. With humans, it is not the species that has continued to evolve, but the societies of people that have evolved.
Looking more closely, human societies have driven population increases due to changes:
- Increased range due to migration.
- Improved tools in the progression from Palaeolithic age to Neolithic age.
- The invention of farming.
- The rise of civilizations.
- Continual introduction of of new technology.
- Propagation of new technology societies.
So to put all of this together, the history of human population is linked to the evolution of not the human species, but instead evolution of human society. The pattern is that human populations:
- Are completely static for most of human history.
- Exhibit very slow growth are evolution of society increases range and slowly improves technologies.
- Has seen bursts of growth following major society evolution such as the introduction of farming.
- Saw unprecedented growth during the population explosion from around 1800 to year 2000.
Population And The Evolution of Human Societies.
Normal population should see a ‘normal population’ quickly achieved, followed by population stability until evolution results in a new species.
People have not really evolved, but society certainly has evolved. In many ways, rather than the species ‘homo sapiens’ being the organism, the organism is the society. Practices adopted by each society changes both the ability to compete with other species for resources, and ‘normal population’ that can be sustainably supported within a given environment. The entire basis of ‘normal population’ is that the control of population evolved to protect the organism that is the colony. Just as individuals stop growing at maturity, societies stop growing at maturity.
But when a society evolves into a new society, just as when an individual gives birth to offspring, the limitation of growth is reset, and the society grows to a new maturity, just as would an individual baby.
As the evolved society grows to a new ‘normal’ people can increase family sizes, lifting population levels. Still, in all the more recent human history where we have statistics, population levels were remarkably stable up until the recent population explosion. In fact, population levels have been so stable, that either it has just been an amazing coincidence, or humans also have some mechanism that has ensured births are in balance with deaths.
Historically, we can see over time the human population has grown at specific times, but the long term stability suggests long periods of population stability. As a ‘colony’ or society, there has been major evolution, sometimes gradually, and sometimes in great leaps. Population ‘normal’ does seem to increase incredibly gradually when society evolves gradually, and move ahead in leaps with breakthroughs to society like the introduction of farming.
Population Explosion: The Breaking of ‘Normal Population’.
An initial assessment could be that the industrial revolution must be an evolution of society that triggered a new, higher ‘normal population’ for human beings, so in response the population expanded. Improved farming techniques able to support a larger population, either reduced deaths from starvation, or triggered people to have more children.
Reality is, deaths from starvation were not reduced during the explosion, and instead, some countries experiencing a population boom, such as China and Bangladesh experienced famines, as a result of increased population. There is a link for the population boom causing starvation, and no link for a reduction in starvation causing a population boom.
Further, analysis of birth rates shows that birth rates declined during the population explosion. An increased ‘normal population’ effect, should trigger increased birth rates. Perhaps there rare locations where birth rates rose somewhat, but if so, this was more than offset by almost all of the world experiencing reduced birth rates.
All evidence is that that main driver for increased population, was the reduction of infant mortality. The goal in almost eliminating infant mortality, is the reduction of suffering, and the resulting population explosion was a side effect, not a motivation. This means that the previous balance of population was broken by improved an improved medical system, and that the population explosion was not humanity adjusting to a new level of ‘normal population’.
The End Of The Population Explosion: ‘Normal Population’ Resumed?
With infant mortality largely eradicated, far less children are required for births to be in balance with deaths. It does seem that birth rates are adjusting downward, to restore ‘normal population’, and generate birth rates that are again produce a population in balance.
What we have seen, is that when families needed 6.0 (six) children to maintain the population due mostly to infant mortality, families had 6.0 (six) children. Now, with infant mortality down to a level where only 2.3 children are required for a stable population, families globally are having only 2.3 children. Is this a new coincidence? Or is this evidence of a mechanism for ‘normal population’ in humans?
The Mechanisms Of Stability and ‘Normal Population’.
Mechanisms In Nature.
Kangaroos do not get together and debate “drought headed this way, we all should agree to hold off having children”. Instead, the reduction in offspring is the result of instincts. Many plants an animals reproduce either only, or predominantly in spring. Their biology could allow them to reproduce throughout the year, but they are ‘triggered’ to reproduce only when there is the greatest chance of survival of their offspring. Reproduction does not just happen all the time as with the bacteria, sophisticated animals and even plants reproduce in response to stimuli. It also logically follows that they reproduce not at the optimum time, but in the optimum number. Any animal that reproduces in numbers that would destroy the environment soon becomes extinct.
Are Humans Beyond Nature?
Are we humans really that much different? Isn’t our desire to have children also driven by instinct? Yes, following those instincts may lead to some of the greatest joys in life, but it still makes sense that these are instincts. Instincts that in just over 100 years have result in our joy being fulfilled by giving birth to far less children than in all of previous history.
I can see three possible factors altering the number of children people have:
- The number of children people feel the instinct to want to have.
- Sperm counts in males.
- Conception rates in females.
What is the reason an increasing number of people choose to be child-free? Is the instinct to have children influenced by environment? Perhaps there is more to the global decline in male sperm rates than some people have considered. The most popular theory is the decline is due to chemicals in the environment, but I am not the first to consider it could at least in part be due to a natural response to being above ‘normal’ population?
When Mechanisms Fail: From ‘Normal Population’ to Plagues and Population Explosions.
Population stability results from a balance between births and deaths. Deaths are mostly determined by environment, with the species in question needing to adjust births to match deaths, over which the species itself normally has no control. Disease, predation, and natural disasters can all impact deaths, and as adjusting births takes time, there can be near extinction events or population explosions and plagues, but over time, populations return to normal, and the environment recovers.
Has the Human Explosion Exceeded ‘Normal Population’?
The Recent Population Explosion in Perspective.
To recap, humanity has just experienced the greatest population ever. The industrial revolution is often given credit for supporting this population explosion, but data clearly shows rather than a rise in birth rates in response to people being motivated to have more children, people had less children during the population explosion.
Perhaps the advances of the industrial revolution caused birth rates to fall more slowly as we adjusted to the ‘new normal’ of almost all children surviving, but the increase in population was all a result of birth rates not falling quickly enough to adjust to the new smaller number of children required. The medical advances were rapid, and resulted in saving lives of children already born that would have perished without these advances. It would be impossible for people to adjust the number of children they had in anticipation of medical advances.
Clearly, even if there was no basis for an increase in population, solving the problem of infant mortality would result in an huge lift in population whether desirable or not, as people adjust to the new ‘normal’ number of children.
Statistics on birth rates show we are again at ‘peak child’ and population stability has returned, but now we have an increased population, that, for the first time, was not increased by human birth rates in response to a readiness for a population increase.
Now we are faced with this hugely increased population, whether society is ready for it or not, and the result is that we are currently not able to exist sustainably. The definition of carrying capacity is the number of a species that can exist sustainably. Clearly, we are currently over carrying capacity, and thus we have overpopulation.
You would never trade sustainability for saving all those infants from death. Solving infant mortality was worth the price of resultant overpopulation. But now we are in a race to change our society so that the current population is sustainable, before the damage to the environment is too great.
The Environment Always Recovers From Plagues In Nature, So No Problem?
The human population explosion is unusual as humans it was largely a result of improvements in medicine, but nature also gets out of balance and can produce population explosions, and populations normalise, and the environment recovers. Every time. Locust plague, mouse plague, whatever, the population normalises, and the environment recovers.
On that basis, the human population should normalise to a level that ends the damage to the environment, and then the environment will recover. But there are two potential problems:
- Humans are now a global society, so this is global population explosion, and the environmental damage is global.
- Humanity is not ready to accept solving the problem with through population reduction, and in reality, in this case, population reduction alone is most likely not a viable solution anyway.
The reality is the problem of a global overpopulation of humans is complex, and there is already significant focus on solving some of the most pressing problems. However, further interference with nature to exacerbate the root cause of many environmental problems. overpopulation, is an ongoing risk.
Conclusion, and Where Next?
The evidence for ‘normal population’ is compelling, as is the evidence that humanity had a population explosion that breaks the rules of ‘normal population’.
The planet needs a solution to us having broken with ‘normal population’. We either need to find a way to bring or ‘normal population’ up in number to match the number of people we have, or just manage things hoping ‘normal population’ will see the number of humans naturally return to an appropriate population. Or perhaps, some combination of both.
What we do not need, is economic greed of the few who would benefit, driving a push for further population increases with a total disregard for nature.