Human beings have been around for hundreds of thousands of years. For the vast majority of that time, the total population of humans has been quite small.
Then, quite suddenly, at least in the grand sweep of history, the population of humanity exploded.
Now, it appears that humans might be on the cusp of a new era of demographics, the likes of which we haven’t experienced before.
Learn more about the global population since the dawn of humanity and what is in store in the future on this episode of Everything Everywhere Daily.
Trying to estimate the population of humanity throughout history is a very difficult task. Taking a census is a rather recent phenomenon, historically speaking.
Even when ancient empires took a census of their population, the results were probably lost to history.
So, we are left with having to create estimates of what historical human population levels were.
That being said, even though it is necessary to make estimates of what populations were, we have a lot of evidence that we can use to make educated estimates.
For example, through archeological evidence, we know how people lived. We know how they fed themselves, and we know what size communities they lived in.
Through the study of human remains, we know at what age people died and approximately how many children they had.
We can start the population discussion at the very dawn of human history, going back 4,000,000 to 200,000 years ago when humans and their hominid ancestors lived on the African savanna.
Many of our ancestors who lived at this time wouldn’t even be considered modern humans, but knowing their numbers are still insightful.
The estimates for the total population of hominids or humans during this period at any given time would be somewhere in the range of 10,000 to 100,000 people.
That estimate spans a full order of magnitude, indicating the difficulty in making such estimates. However, populations of any creature will naturally rise and fall over time, so it is entirely possible that, at some point, both the high and low estimates might have been true.
The average human life expectancy, and again not all of these people might have been modern humans, was about 20 years old. This age factors in infant mortality, which is always something you have to consider.
Our ancestors at this time probably began reproducing almost as soon as they were physically capable, meaning that the average age of having a first child might have been extremely low, perhaps as young as 12 or 13.
Several theories have proposed that early human populations may have experienced several bottlenecks, where the population may have decreased to dangerously low levels.
These bottlenecks reduced the genetic diversity of the surviving population. It isn’t known how many such bottlenecks might have occurred in human history, but there must have been at least a few.
One of the problems was that all the humans were living in Africa. Basically, our species was like a really important document you were creating on your computer, and you didn’t have a backup. If some natural catalyst occurred in Africa, it could have wiped out the species.
The event which changed human population levels was human migrations out of Africa.
When this first happened, and how many times it happened, has been the subject of debate and will be the subject of a future episode. What is certain is that sometime around 300,000 to 150,000 years ago, one or more waves of humans left the African continent.
Humanity now had its first backup, and we became a multi-continental species.
As humans spread, they were able to inhabit more ecological niches in different places, and populations of humans were able to grow as they migrated.
Next, let’s lump together the period from 200,000 years ago to 10,000 years ago. This is a long period of time that covers much greater change than did the previous several million years.
Humanity spread throughout Asia, Europe, and Australia. Towards the end of this period, humans also managed to finally migrate to the Americas and the New World.
The average global human population during this period was probably between one million and 10 million, with more people obviously near the end of this period 10,000 years ago.
There would have been some bottlenecks during this period as well. One proposed bottleneck was the Toba explosion about 75,000 years ago, which probably caused a massive global dieoff of many species.
Likewise, when humans first entered the Americas, some estimates put the number in the initial group as low as 70 people. Again, as with the African migration, there isn’t a consensus yet on how many migrations into the Americas occurred or when the first one occurred.
The migration of humans to the western hemisphere was sort of like having an off-site backup for our species.
Once we get beyond approximately 10-11,000 years ago, things begin to change rapidly.
The glaciers retreated, and humans moved from being mostly nomadic to agricultural. The rise of agriculture allowed for the creation of complex civilizations and a division of labor where some people would engage in pursuits that didn’t involve procuring food.
The rise of agriculture was actually a mixed bag for humanity, although you seldom hear of it discussed that way. While it allowed many more calories to be consumed, it also resulted in diseases, large-scale wars, and probably a reduction in human life spans, at least initially, due to shifting to a heavily grain-based diet.
I’ll leave the downsides of the agricultural revolution to another episode, but there was one overwhelming upside. It allowed for much larger populations.
More food meant more people.
For the next approximately 9,000 years, there was a gradual, linear increase in the global population.
By linear, I certainly don’t mean that it was perfectly linear. There were enormous events that resulted in the deaths of millions of people, usually from pandemics.
The first major recorded pandemic was the Plague of Justinian, of which I previously did an episode. Somewhere between a quarter to half of the population in Europe and the Middle East might have died.
Nonetheless, large population centers developed in China, India, Mesopotamia, and the Mediterranean.
By the year 1,000 BC, estimates place the global population between 50 to 100 million people. Again, these estimates have a large margin of error, but at this point, we are only talking about a factor of 2 rather than a factor of 10, as we did 10,000 years ago.
One thousand years later, in the year 1, estimates put the total number of humans on Earth between 150 to 300 million people. By this time, we have large empires in China, Europe, and India, and humans have expanded to even remote islands and arctic regions.
By the year 1,000, the global population has not increased by much. Estimates now are between 250 to 310 million.
Around the year 1,200, things start to change. The global population hits around 400 million people.
Trade increases between regions increases, and technology starts slowly improving. The global population kept slowly climbing despite the black death and Mongol invasions.
By the year 1600, the global population had reached 550 million people. It took about 600 years to approximately double the world’s population.
Europeans had now made contact with the people in the Americas who had been isolated for thousands of years. Pre-Columbian population estimates in the Americas vary widely but range from about 10 million to 110 million people.
The result of European contact with the Americans resulted in one of the greatest mortality events in world history, mostly due to disease.
In the 17th century, new crops from the Americans had found their way back to Europe and were getting introduced in their colonies in Asia and Africa.
These new crops allowed for yet more food to be produced.
According to most estimates, the 17th century saw close to a doubling of the Earth’s population. The first time that such a thing happened in a span as short as a century.
Most estimates place humanity passing the billion mark sometime around the beginning of the 18th century. However, other estimates place that date around the start of the 19th century.
Regardless when humanity hit the 1 billion mark, 19th-century physics vastly outstripped 19th-century biology and medicine.
People were still dying of communicable diseases, as I’ve mentioned in several episodes, the germ theory of disease still wasn’t prevalent, and infant mortality was still high.
Before I get into what happened during the 20th century, it is important to understand what is underlying population numbers.
As should be pretty obvious, population growth is a function of birth rates and death rates.
For most of human history, it was not uncommon for women to have between 5 to 8 children. The problem was that it was also not uncommon only to have a few of those children reach adulthood.
Infant mortality was extremely high, as was death during childbirth. Infant mortality was the biggest reason why life expectancy was so low before the 20th century. It wasn’t that most adults died at the age of 40, it was that so many people never even reached adulthood.
Having a large number of children was a response to the high rates of infant mortality. If you knew that only a quarter to half of your children would reach adulthood, then the solution was just to have more children.
Also, at the dawn of the 20th century, the vast majority of people still lived in rural areas. As you’ll see in just a bit, this is extremely important.
The 20th century saw remarkable improvements in health care and child mortality. Many communicable diseases either became preventable once the causes were known, aka cholera, or were easily treated like the bubonic plague.
The dramatic changes to infant mortality and life expectancy didn’t result in changes to the fertility rate right away. Although the number of children did drop, people were still having large families as they did when infant mortality was high.
If you look at a graph of the world population over time, everything is basically flat until the 20th century, when it suddenly becomes vertical.
Humanity passed 2 billion people around 1927 and kept climbing.
Three billion people was reached in 1959, 4 billion in 1975, 5 billion in 1987, 6 billion in 1999, and 7 billion in 2012.
The 8th billionth person on Earth was probably born in late 2022.
You might have noticed that the time between every billion people was decreasing, with the last billion having taken just ten years. At such a growth rate, it might seem that we could hit 20 billion people by the end of this century.
However, that is almost certainly not going to happen. In fact, we probably may never hit 11 billion, and quite possibly even 10 billion.
That is because there has been a radical change in fertility rates around the world.
The number of children required to maintain a population is 2.1 children per couple. The 0.1 is there to capture things such as early deaths, infertility, and other issues which might occur.
If you have a fertility rate below 2.1, then your population will eventually start decreasing. This is exactly what has been happening all over the world.
The reason why the population has been increasing is that the older generation is still living and hasn’t died off yet. To put it in terms of a metaphor, imagine climbing a hill in a car and before you reach the peak of the hill, you take your foot off the gas. The car will keep moving forward over the hill even though you are no longer accelerating.
That is the phase we are in right now in terms of world population growth.
In every developed country in the world and most developing countries, the birth rate is now at or below replacement level. It has dropped in half in the last 50 years.
For example, the fertility rate in South Korea is now 0.89. When a fertility rate is at 1, it means that the next generation will be half the size of the current one.
China used to have a one-child policy, which resulted in a dramatic reduction in its fertility rate. They recently removed the policy, but fertility rates kept dropping.
It is estimated that the population of China will only be half the size it is today by the year 2100 and possibly will reach that level several decades sooner.
In Japan, the number of births in 2021 was the lowest number they have seen since the 19th century.
The population of Russia has been decreasing every year since the start of the 21st century.
India has reached replacement level, which surprised many demographers by how fast it occurred.
Every country in Europe has a fertility rate below the replacement level.
The only part of the world with fertility rates significantly above replacement level is sub-Saharan Africa. Niger and Somalia still have rates over six and Nigeria is still over 5.
It is estimated that by the year 2100, Nigeria might be one of the top two populous countries in the world, and Lagos might be world’s largest city?
Sub-Saharan Africa has lagged behind the rest of the world in terms of fertility rates, but it seems that they will get there as well as fertility rates have been dropped quickly.
There have been several reasons for the decrease in fertility rates. The biggest has been urbanization and the increase in women in the workforce.
When you live in a city, it is more expensive to have children, and when women work, they tend to put off having children until later, which decreases the total number of children.
I have read estimates that say the largest number of children the world will ever see…is right now.
When the world population is going to peak is a subject of debate amongst demographers. Past estimates of population growth over the last several decades have overestimated what the actual population has been.
This has mostly been due to how fast the unexpected drop in fertility rates has been.
The big question going forward is how low fertility rates will drop, and how quickly fertility rates will drop in sub-Saharan Africa.
There are estimates which show peak human population as early as 2040 and some place it around the year 2100.
If the 20th century was the century of population growth, the 21st century will probably be the century of population transition, and the 22nd century might be the century of population decline.
Your great-grandchildren may very well live in a world where the biggest problem is sustaining and increasing human populations, not trying to decrease them.
The population of humanity has seen enormous changes over the last 200 years and based on the demographic data currently available, we should see a continued dramatic change, albeit it in the other direction, over the next 200 years.
Everything Everywhere Daily is an Airwave Media Podcast.
The executive producer is Darcy Adams.
The associate producers are Thor Thomsen and Peter Bennett.
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Thank you for doing these podcasts. I love learning new fun facts and all you episodes are perfect for that. very happy to have discovered them. Good luck!
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