What makes humans different, and enables long term growth?
Other species don’t experience population growth over such a long term. Our population growth differentiates us from other species, and anything that differentiates us from other species, tells us something about ourselves.
A key factor, is that we continue to advance. With other species, while they can evolve over time, that evolution, or those ‘upgrades’, results in a new, physically different species.
With humans, the homo sapiens of 30,000 years ago were the same species as humans today. Already basically physically the same as modern humans, yet given a picture of humans 30,000 years ago and one of humans today, the difference is very obvious.
Take a picture of even our nearest relatives, chimpanzees, bonobos or gorillas in their environment 30,000 years ago and I suggest it would be very hard to spot the difference.
The pictures of humans, reflect their societies, and human society has managed to evolve, while the societies of those nearest relative species have remained very much the same.
Societies have managed to evolve far more than us as individuals of the species have evolved, and logically if this is biggest progression, it is this evolution of our societies that has been the key enabling humans to continue to better adapt to an increasing variety of environments, and out compete other species, and thus increase our population.
This continual advancement, both enables long term population growth, and regulates and determines the rate of that growth.
The principle of ‘optimum population‘ is that any species can grow to a population such that is would ‘carpet the planet’ in less than 10,000 years, but instead, successful species can maintain their optimum population within environmental carrying capacity. For any species there is an optimal population, which will rise of fall due either a change in environment, or advancement of the species.
We haven’t simply ‘carpeted the planet’ because as an advanced species, our rates of reproduction do normally reflect building a population supported by the environment. However, unlike other species, we don’t remain at one long term stable population, because we keep advancing from generation to generation. We change both the environment, and out species.
This still leaves questions on how we keep improving as a species, and how far population growth can still continue, given the fact that the planet is finite, and thus all growth has a limit.
The history of human population growth.
The recent explosion.
In the period between 1650 and 2020, world population experienced an explosion. This population explosion was not a result of people having more children, but due to the reduction in children dying.
The fertility rate was commonly higher than 6 children per woman on average, as we discuss here. A fertility rate of 4 children per woman would imply a doubling of the population size each generation; a rate of 6 children per woman would imply a tripling from one generation to the next. But instead population barely increased: From 10,000 BCE to 1700 the world population grew by only 0.04% annually. A high number of births without a rapid increase of the population can only be explained by one sad reality: a high share of children died before they could have had children themselves.
Our world in Data: Child Mortality in the past
Clearly, prior to the population explosion, the human population level was relatively stable. But why not actually stable? The 0.04% in the quote is slow growth, but over time, as can be seen in the graph at the top of this page, and the actual data behind it, from 10,000 BCE to 1650 CE, the population rose from only 2.5* million to 500 million, which while slow growth, over such a long time adds up and is still an increase to 200x as many people!
As examined in detail in ‘Optimum Population‘, humans had ample time to reach our maximum possible population well before 10,000 BCE, which suggest that if in 10,000 BCE, the population of 2.5 million was at that time, the maximum possible, and thus the limit of the carrying capacity of the planet for humans.
This raises a two part question: What enabled the planet to move from a 2.5 million carrying capacity in 10,000 BCE, to a 200x larger carrying capacity of 500 million by 1650, even before the population explosion, and what produced the population growth to utilise the increased capacity?
The expansion that was happening even before the recent Explosion.
Limits to Data prior to 10,000 BCE.
There is an interesting pattern. The further back in time, the slower the overall growth of human population. What becomes less and less clear is what conditions were like. Calculating uniform growth over a long term growth over a time span only requires estimates of population estimates for population at the start and finish.
growth rate = e(log(finish/start)/years)-1
The “subtract 1” converts from multiplier to rate of increase. Multiply by 100 to make it a percent.
The oldest population figures I have are estimate for 10,000 BCE, which range from 1 to 10 million, although estimates which appear to have the best research put the number between 2 and 4 million.
The oldest human remains are currently the Jebel Irhoud Skulls, which date as over 300,000 years old and suggests humans were already widespread at that time. To ascertain the upper limit of early growth, use the lowest possible starting number, and highest possible ending number. So starting with just 100 people, and ending the outlier high estimate of 10 million after 300,000 years, still gives a growth rate of only 0.0038%. So even the highest possible rate of growth, was still really very low.
But it may be an underestimate. The problem is, what if the population grew fast, but suffered setbacks or collapses and catastrophes during the time interval, rather than being smooth slow growth? A higher rate could have masked by catastrophes. In those 300,000 years of time there have been glacial periods, earthquakes and volcanoes. Specifically, the most recent known major catastrophe, the Toba volcanic eruption of just over 70,000 years ago, is widely thought to have dramatically lowered the human population at that time, to as low as 3,000 individuals. It would be more prudent to largely ignore population growth that was largely wiped out, and just calculate growth from the 70,000 years after Toba. So a starting population, again using low starting estimates, of three thousand (3,000) to that 10 million(10,000,000) high end estimate, and the rate jumps up to 0.0116% as the highest value calculated from estimates for oldest period where there is any confidence in the data.
Still not definitive, by strong evidence that early growth rates were overall very low. What we still don’t know is how evenly the growth was distributed. Such low rates are probably evidence of long periods of stable population, broken by break throughs in advances in stone age tools, but there is not sufficient data to be certain.
Trends from 10,000 BCE to the industrial age.
For further calculations, as 10,000 BCE is now to be used as a starting time and not an ending time, I move from using the highest of estimates, to working with the estimates as used in the graph from Wikipedia as used in the page header graphic. This is value of a 4 million population for 10,000 BCE, as estimated by the Gapminder Foundation of the late Hans Rosling, likely the most accurate of more recent estimates.
Overall, that data shows population from 4 million in 10,000 BCE rising:
- rising at 0.011% to 5 million by 8,000 BCE
- then stable at 5 million until 5,000 BCE
- rising at 0.0337% to 7 million by 4,000 BCE
- rising at 0.066% to 50 million by 1,000 BCE
- maintaining just above the same underlying trend of 0.066% growth until 1650 but including:
- a surge until 300 BCE: the time of Alexander The Great
- surge offset by subsequent low to very low growth between 200 BCE to around 1000 CE.
This means that prior to the “population explosion”, there had already been a more gradual, but still very significant long term population expansion taking place, which was preceded by a 3 thousand year period of population stability.
In practice, history tells us much of what happened over most of this time frame. Some key events are:
- 10,000 BCE, The Neolithic revolution, and beginning of the the agricultural period.
- 5,000 BCE The copper age.
- 3,500 BCE Beginning of written history.
- 3,300 BCE Bronze age
- 1,200 BCE Iron age (start varies with location to as late as 800 AD)
- 500 CE, Middle ages (Early or ‘Dark to 1000CE, High to 1300 and Late)
- 1400 CE Early Modern Period
- 1500 CE Renaissance.
- 1600 CE Age of Enlightenment.
- 1760 CE Industrial age.
Analysis
Rates of growth.
- 0.004% prior to copper age,
- 0.004% Average from first humans though to copper age.
- 0.004% Neolithic average prior to copper age but with periods of growth others and of stability.
- 0.066% From the copper age to industrial revolution.
- 0.75% from the industrial revolution until 21st century (with a peak of over 2.0%) .
Looking at the historical population graph again, is quite flat until around the copper age, begins a climb until the industrial age around 1650, then takes off again.
Key points from history.
1: The evolution of tools enabled the growth.
I was expecting to find that the development of literacy had the most notable impact, but it turns out the strongest correlation to the development of tools. Turns out the people who named ages ‘paleolithic’, ‘neolithic’ etc. knew what they were doing. Agriculture and the first civilization, both came very soon after the start of the neolithic, but the population increases correlate best with the advances in the tools themselves rather than the agriculture the tools enabled.
Time differences in tool development between different areas also shows a strong correlation to when populations surged in different areas.
In many ways, the differences between the abilities of people in different eras, comes down to their tools that were developed in those areas, and more importantly spread to those areas from elsewhere.
2: It is unclear whether, increased births, or reduced deaths, drove population growth.
The differences in growth between iron age, bronze age etc, are so small that it would require very precise data to determine whether prosperity ever so slightly increase desire or willingness to have more children, or whether improved nutrition improved survival rates.
If we assume an average age per generation of 25 years, the number of children surviving to have their own families would be:
- 2.002 per woman until the copper age.
- 2.033 from the copper age until the industrial revolution
- 2.410 during the industrial revolution
Yet we know that during the industrial revolution, births per woman numbers, which number total of children as opposed to number who survive to have their own families, did not rise as these numbers suggest, but fell significantly. This is because births overall track amazingly close the exact number for a stable population, even though historically, that required around 7 children per woman.
Even in the extreme of the population explosion, per generation numbers on average and amazingly close to stable.
3: Societies can have the characteristics of subspecies.
Groups such as the Ancient, Greeks, the Egyptians, the Mayans or Aztecs develop distinct behaviours and other differences to an extent that does not occur in nature without being regarded as subspecies, despite all individuals of these groups having no significant genetic differences.
Why humans are different: the evolution of tools and societies that use them.
Intergenerational memory: transfer of information or learnings from one generation to another.
In the early days of the theory of evolution, there was a proposal by Lamarck that physical characteristics acquired by an individual, could be passed on to their descendants. An often quoted example is a giraffe acquiring a longer neck by constant stretching. The problem with the theory, was that that there was no mechanism for physical characteristics to be transferred to offspring. New individuals are created from genes, as the genes themselves have not acquired the characteristics.
The only traits which can be genetically inherited by an individual, are those contained with genes. As genes are basically ‘blueprints’ on the design of a species, evolution through genes is limited to which blueprints are ‘fittest’ and thus have the best survival rate. Feedback from characteristics acquired later and not part of the design blueprint, could only affect subsequent generations if there a some mechanism for intergenerational transfer beyond the genetic blueprints.
It turns out, humans societies, have developed successful intergeneration transfer which allows a form of Lamarckian inheritance, and thus evolution of the society, without genetic evolution of the individuals. No other species has achieved this Lamarckian inheritance, or evolution with genetic evolution, because no other species has managed a mechanism of intergenerational memory, where the next generation can learn study what was leant by previous generations. This is what makes humans different.
Individuals, tools and societies with tools: only humans show Lamarckism inheritance of tools.
Humans are not unique in making use of tools. Octopus have been observed to use coconut shells as tools for protection, and chimpanzees to use twigs as tools to access ants. However, there is no mechanism for intergenerational memory that allows these tool building skills, having been learnt, to be passed onto subsequent generations, and to be improved on by subsequent generations.
The damns of beavers, and the nest of bees could also be considered tools. However, as far we know, no beaver, or bee, has ever managed to pass on a skill they acquired in terms of building their dams or nests.
A beaver has no ability to pass on acquired dam building skill, which means an improvement in dam building relies mutations that result in beavers innately building better dams, and thus restricts evolution to the slower and more restrictive Darwinian evolution.
It is unlikely Darwinian evolution would ever have resulted in a human who innately went about making a sword. Building that first sword required some means of accessing knowledge gained by previous generations, in order to improve what they did previously.
The mechanisms of intergenerational memory.
Humans have to mechanisms of transferring knowledge to future generations:
- direct communication.
- written communication
- artifacts.
Prior to examining actual history, I expected written communication to play the most significant role the evolution of societies, but the data suggest that the combination of direct communication and the artifacts or examples provided by previous tools themselves seems to have played the major role. Even after the invention of written records literacy rates were extremely low the mid 1700s, and the start of the population explosion, which means most individuals in society learnt from direct communication and the examination of examples of things they wished to build.
Evolution of societies through evolution of tools.
Population growth seems to corelate more precisely with the development of the tools that enabled population growth than with the techniques such as farming that were enabled by the tools. For example population growth was higher from 10,000 BCE (12, thousand years ago), to 8,000 BCE, which was neolithic revolution in tools, than from 8,000 BCE to 5,000 BCE during the expansion of agriculture that was enabled by the newer tools. As there are so many other possible factor that could have affected growth it is advisable to cautious with conclusions, but there is little evidence that the growth was as much as result of the agriculture itself as I would have expected.
Education enables the evolution of tools.
It seems very likely that prior to formal education literacy, tools, together with direct training provided major mechanisms of passing knowledge from generation to generation.
Though much of western human history, there was a strong connection between religion and education.
Contemporary access to schooling – a solid pathway to educational attainment – depends on a country’s educational infrastructure. In many instances, the foundations of that infrastructure are based on facilities originally built by religious leaders and organizations to promote learning and spread the faith.
How religion may affect educational attainment: scholarly theories and historical background
While there were times prior to the industrial revolution when engineering was studied, such as in Ancient Rome, there were also times when academic studies were largely funded by religions, which would have meant the vast majority of the working population and trades people had no formal eduation other than working in their trade.
This would have meant the evolution of tools was very often based on using previous tools as a source of inspiration and knowledge.
Conclusion: Societal evolution.
It is very clear that the change from a group of paleolithic humans to a group of modern humans, is far greater than seen between two groups of any other species separated by a similar timespan.
This is because human societies can exhibit their own, new form of evolution, an evolution even without any evolution of the genes of individual humans. A Lamarckism form of evolution where learned characteristics can be passed on to future generations, because many of those characteristics take the form of tools, with human without any ‘accessories’ or tools being considered ‘naked’, which is the normal situation for any other species. That is what, so far, separates humans from all other species, and allows humans societies to grown in population.
The planet is finite; therefore, the rules of exponential growth make it clear the planet was fully populated hundreds of millions of years ago, which means this continued evolution of human societies that has enabled the population to not only grow, but the growth to accelerate, will not end simply end simply because the current population explosion is ending.
The ability to continue to increase the percentage of live on Earth that is either human, or food for humans will continue until either:
- The reduction in biodiversity and reduction in numbers of other species creates results in a less habitable planet, cause a collapse in the human population.
- or
- Humanity decides biodiversity is desirable and the is a point at which the cost to the environment of continuing growth of the human population, is reducing the quality of life, even if it is still possible.
The rapid change in child mortality, and the resulting huge shift required to restabilise population levels has almost certainly resulting is a overpopulation problem or ‘sustainability problem’ as we prefer to label it, which rules out further population growth until current problems are solved, but sooner or later, we need to decide how many people we want to have on this one finite planet.
Hopefully by something other than just let’s keep growing until everything breaks.
Updates.
- 2022 August 15: First published.