Paradox: Why Is The Population Explosion Ending? Why are birth rates falling?

Births per woman from a sample group of countries.

Surprisingly, humanity is at ‘peak child‘ and looks to be heading to population stability. We are still are left with an overpopulated planet, following the population explosion, but it is ending. Human ‘births’ per woman has fallen from over 6 prior to 1900, to 4.7 by around 1950, and to around 2.3 in 2021. There are countless studies of population trends, but in the end, most explanations for the fall in population contain contradictions. Three main types of explanations for the decline in birth rates coming just when it was needed are explored here.

  • Background
  • Explanations categories:
    1. One or more Planned Responses to solve overpopulation.
    2. The Pill“.
    3. Luck: A Lucky Coincidence, or lucky bonus while pursuing another goal.
      • 3a. Pure Luck: The birth rate happened to fall when we need it to.
      • 3b. Mostly Luck, but with a reason why were lucky.
        • Empowering women etc
    4. Nature, an instinctive reduction of birth-rates.
  • Conclusion: The Paradox.


The explosions starts as an unfortunate side-effect of improved medicine.

Humanity has just experienced a population explosion. While there are various factors that enabled the explosion to continue, there is one single clear reason why the explosion happened. It was not increased birth rates, which actually fell during the population explosion. Birth rates fell, and at no time during the explosion reached pre-explosion birth-rates, even during ‘baby-booms’.

The difference between the time of population explosion, and the time before, is that previously over half of all children died before growing up to have their own families. Once we solved the huge historic problem of half of all children dying before becoming adults, almost all children then went on to have their own families.

There are people who explore theories such as how improved farming allowed supporting an increased population, and factors such of these explain how managed to sustain the increased population, but it not the cause of the increased population. Given that birth rates did not increase, it is clear that is the advances in medicine that caused the explosion.

Humans reduced infant mortality to end the tragic loss of life, and the population explosion was an unfortunate side effect.

The population explosion was an unfortunate, accidental side effect of saving children’s lives. It is an ‘accident’ in the sense that we did not pre-plan the population explosion, it was just a side effect that, without something bring the resulting growth rate to an end, could have ended civilization.

The explosion ends due to decreased ‘births-per-woman’, another side effect?

At peak 20th century growth rates of 2.1% annually, or 42 times the average of the previous 12,000 years. At that rate, the same increase in population as occurred over 12,000 years, would happen in just 200 years. Such a rate of increase would quickly completely overrun the planet if continued, but now births per woman has startlingly fell levels similar to those previous 12,000 years, for population growth back to the historic normal.

Births per woman, which has already began falling prior to 1960, in the 60 years to 2020, fell from over 5.0 to around 2.3. Why did the births per woman then fall? Was it another ‘accidental’ side affect of something else as with the start of the explosion?

Just in Time?

How many times in movies is the bomb diffused with just moments to spare before there would have been a disaster?

The ending of the population explosion in some ways seems just like those movies. In the 1970s, at the peak of population growth, many people were already predicting disaster unless something was done.

If, instead of this fall in birth-rates taking place, growth at the rate of the 1970s had continued, there would be 18 billion people today (2021), in place of the less than 8 billion people we actually have. If population had grown to 18 billion, what would the world now be like? Imagine CO2 levels now in a world with double the population. Plus accelerated deforestation to access resources for over twice the number of people, and all those mouths to feed.

How did the fall happen just in time?

1. Planned Responses to solve overpopulation.

Some of the explanations listed above, did directly target a reduction in birth rates. There were specifically designed to reduce birth rates, but they cannot explain global trends, and many countries where birth rates have fallen have had no such measures. Measures include:

While these measures are certainly not a full explanation for global trends the include countries where no measures were adopted, planned responses have contributed to the global reduction.

There is a full spectrum possible between trying to educate people on the advantages of less children, through to the one child policy of China which went as far as mandatory contraception and sterilization in some cases for women who already had two children. In between education and the more drastic measures are financial and employment based incentives and limitations.

Certainly there were place in the world that took steps some time after 1960 in order to reduce birth rates.

  • China introduced the one child policy in 1979 after around 10 years of an earlier two child policy.
  • Various countries introduced public campaigns to encourage parents to only have 2 children, including:
    • Vietnam (1960s), Hong Kong (1970), Singapore(1980).
  • Some countries including India (2019), have introduced incentives for less children, and others (UK, 2012) have contemplated such measures,
  • Other countries have had ‘family planning’ programs, and education programs encouraging parents to have less children.
    • see Bangladesh example in Hans Rosing video here.


The one child policy was introduced in China in 1979, when world population growth rate was still close to the 1972 peak, but there is another story, which requires considering the population pyramid for China in 1978. Looking at the pyramid, at first it looks like two child policy introduced 10 years earlier , partly in response to the great famine, was starting to work, The 0-4 year population was for the 1st time in a long time, smaller now than it was 5 years ago (the now 5-9 band). But, now consider that each five year band represents the children born to the population four bars, or around 20 years earlier. The children in the 0-4 band, were mostly born to the 20-24 band, and therefore, still represented an increase relative to their parents, and as each of the next two groups to become 20-24 in 5, and then 10 years, were even larger populations, on trend, the population would again be growing. They felt they needed more!

Hence the move to a ‘one child’ policy. The pyramid of 20 years later shows there was logic to moving to the even stricter ‘on child’ policy and even despite this, and the peak years (5-9, 10-14) were again peak years 20 years later, but the pyramid is no longer so “bottom heavy”. The world population in 1978 was 4.3 billion and increased 40% to almost 6 billion by 1998. The 31% increase in China from 0.97 in 1978 billion to 1.27 billion is below that world average. At world average, China would have reached. So how many less people than the world trend in China after ten years of 2 child policy followed by 20 years of 1 child policy?

world_increase_rate x china_in_78 - china_in_98 = (6/4.3)x.97-1.27 = 0.083 billion

Today, as the population pyramid of China has been transformed from that of 1978. The people over 50, were all born before ‘child policies’, and the top of the pyramid is still the traditional shape of from the 1960s and earlier. But from age 50 down, the shape is no longer a pyramid, but the straight sided shape of a stable population, and almost half, 48%, of the population are over 40.

Overall, from 1978 until now, the population of China grew by 48% from 0.97 billion to 1.44 billion, while the world population grew 81% from 4.3 billion to 7.79 billion. If China had increased population at the rate of the rest of the world, China would have 317 million extra people. Considering growth in China was over world average before the two child policy, perhaps China could kept growing beyond the world average? It is hard to project exactly what would have happened had China not introduced the policy. Would an extra 317 million people, or more, been able to survive? If such a population had been able to survive, would would the environment of China look like as a result, and how would having so many people have damaged the economy?

Just looking at averages, the fall in birth-rates since 1972 globally have spared the world needing to support at least 3.2 billion more people. The efforts by China have outperformed the rest of the world, and that contribution by China meant that the rest of the world had to find around 10% less reduction. Without China, there could be 317 million extra people on Earth today.

The result is significant, but only explains around 10% of the world reduction in population growth. Perhaps the policy of Bangladesh and other countries can account for another 5% of the impact, but that still leaves over 85% of the reduction in birth rates down to measures not targeted at reducing birth rates. Why effective the entire rest of the world also reduced birth-rates is down to conjecture, but what is clear is there was no world-wide deliberate program as in China.

It is not even in the same category as the way the population explosion started, where although the goal of eliminating child mortality clear was not targeted at increasing population growth, it is certain that more people alive must be a consequence. Measures such as ’empowerment of women’ do may logically be a reason for less children, but does not with certainly preclude women having the same number of children. As a cause of decrease in birth-rates, it is feasible, but untestable explanation.

The biggest conundrum with all explanations that did not deliberately seek to address birth-rates, is just how co-incidental it is that these events not only produced the lucky result of reducing birth-rates, but took place and had the effect just when we needed birth-rates to be reduced.

Worldwide, the birth-rate (Niger and some other countries in Africa excepted) birth-rates fell dramatically without intervention as implemented in China, or strong education programs as with Bangladesh. Why? Is this just luck? Or something more?

2. “The Pill”.

Did the availability of the “pill” cause the fall?

Note that the fall in birth rates from 6.0 in 1900, to 4.7 in 1950, is the similar to

There were many charts at one time showing the strong correlation between the availability of the pill in the USA and a strong correlation to decline birth rates. The correlation was stronger in earlier years but as birth rate decline was significant after market saturation reduced slowed increase in usage of the pill lead people moving their focus to other explanations. Note a similar correlation exists for the USA between the uptake of colour television and decline in birth rates, plus a similar timeline for the decline in birth rates occurred in some other countries where the contraceptive pill was restricted or the introduction delayed.

The pill was not invented by a company planning to solve the worlds population crisis. It was also not invented with a primary goal of reducing family sizes, although a reduction in family sizes on average is a logical outcome of the invention of the pill. Interestingly, prior to the population explosion, humans had almost the exact balance of children required to be in balance with parents, once infant mortality took its toll. This means that had the pill been available prior to the reduction of infant mortality, and the pill did achieve a reduction in children at that time, the human population would have declined following the introduction of the pill.

During the population explosion, there was certainly a market for the pill. Perhaps during this time there was an increased appetite to also reduce family sizes? How much the pill has changed when people have children compared to how many children, is hard to know.

Overall it is clear not all reduction was due to the pill, but the introduction did very likely accelerate the process.

Given the invention was not in response to population growth, then to whatever extend the pill has reduced family sizes and population growth, the pill becoming available at the right time was certainly lucky. Much earlier, and there was no reduction in family sizes needed, much later and overpopulation could be far more serious.

3. Luck: A Lucky Coincidence, or lucky bonus while pursuing another goal.

3a. Pure Luck: Are We Just The Lucky Ones?

Perhaps it was pure luck the birth-rates happened to start falling when we desperately needed them to fall?

If there is only one planet in this galaxy of over 100 billion stars with an advanced intelligent life form, what are the odds of being born on that planet? Incredibly low, but since only and advanced intelligent life form would contemplate those odds, the only people thinking about the odds, have already won that very lottery. In other words, unlikely as any event may be, if the event is required for our survival, that event must have happened, because we are here to think about it. So anything required for us to be alive, no matter how unlikely, happened in our past, because in order to think about what happened, we have to be on a planet where it did happen.

The same principle could be applied to the fall in birth rate. Perhaps it just happened randomly, despite it being incredibly unlikely. The only reason we are still able to contemplate those odds, is that it did happen, which enabled us to still live in a civilized society. All the people on planets were the birth rate did not fall, at a similar point in their society on their planet, died from overpopulation, and this is just another reason why we are not seeing other advanced civilizations.

Summary: It is possible that the reduction in birth rates just happened almost randomly, and just as there is no point in a lottery winner wondering ‘why me’, there is no point in wondering about birth rates, it is just chance. That we are on the planet where the lucky event happened, enables us to wonder about it all.

3b. Mostly Luck, but with a reason why were lucky.

People have looked at the falling birth rate, and in retrospect formed explanations as to why the number of children per woman has decreased.

Most explanations assume something done for other reasons reduced birth rates as a side effect, which makes the reduction in birth rates just when humanity needed it a lucky bonus.

E.g. It is proposed increasing education for women resulted in reduced birth-rates, yet it is clear the primary goal of educating women was greater equality, improving womens educations was not planned as a solution to birth-rates.

Here is a list from ‘our world in data on factors linked to the change in the number of children women have?

Empowerment of women
Women’s labor force participation
Increasing well being and status of children
Increasing prosperity and structural transformation of the economy
Culture and norms
Family planning (Untargeted)
Religion and fertility
Family planning (Targeting having less children as in Bangladesh)
Coercive policy interventions
Fertility is first falling with development – and then rising with development


Note none of the top entries were measures targeting reduction of birth-rates. This section is targeted at those reasons, and yes, there are measures directly designed to target birth rates in the list, but these are discussed further in ‘planned responses’.

This is not my list, but the list from ‘our world in data’. I would change ’empowerment of women’ to ‘education and empowerment of women’, although when I follow the link, it does become clear they do associate ’empowerment’ and ‘education’.

These ‘explanations’, can be divided into three categories:

  1. Actions specifically intended to reduce birth-rates. (see planned responses)
    • Family planning (Targeting having less children as in Bangladesh), Contraception as part of targeted programs, government programs to reduce births.
  2. Changes/actions which target other outcomes but do also anticipate reducing birth-rates, or sometimes are targeting birth rate reductions.
    • Family planning (Untargeted), Religion and fertility, Contraception (simply providing a method for avoiding unwanted children together with sexual freedom)
  3. Changes/actions with no intent to change to birth-rates an not the intent, and are not a planned outcome, but may be a bonus.
    • eg, Women’s labour force participation, Increasing well being and status of children, Increasing prosperity and structural transformation of the economy, Culture and norms

As already covered, the vast majority of countries have not taken any steps intended to reduce birth-rates, so the first two classes of explanations have already been ruled out as a universal explanation. Coercive policy interventions as applied in China, family planning that also targets population growth, as practiced in Bangladesh, can have an impact, but there are too many counties with no such measures for these to explain it all. Improved contraception has also had an impact, but again simply does not explain the extent of the change.

This leave only class number three, factors not are not designed to reduce birth rates, as the only explanations capable of applying in most countries where birth rates have fallen.

It has nothing to do with sperm counts or the usual things that come to mind when discussing fertility.

Instead it is being driven by more women in education and work, as well as greater access to contraception, leading to women choosing to have fewer children.

In many ways, falling fertility rates are a success story.

BBC- Fertility rate: ‘Jaw-dropping’ global crash in children being born

This quote from the BBC represents a typical attempt to explain the falling birth-rates. A combination of factors, but with changes to society, not at all intended to reduce birth-rates at least partially responsible for a “success story”.

Birth-rates having been reduced by side-effects, puts the reduction of birth-rates into the same category as the reducing child mortality triggering population growth: a predicable but unplanned accident.

The implication is that if we had a society where, if religion or some other factor delayed the globalisation of education of women for years, or we had not invented the pill at the time we did, our society we would probably have collapsed due to overpopulation.

If, as is generally proposed, changes/actions which predominantly did not have reducing birth-rates as a primary goal, have played a critical role in preventing a catastrophe, then we have been saved at least in part by luck.

Summary: So, all explanations that are in not way linked to efforts to lower birth-rates still amount to luck that birth rates fell when needed, as above. While these explanation provide more detailed analysis, all of them share the concept that some change to society just happened to result in a reduction in birth-rates.

4. Nature: an instinctive reduction of birth-rates.

The one possible factor not explored in material I have found so far, is what if humans naturally reduce birth-rates when they need to? The need to have children is hard-wired into humanity, just as reproduction is hard-wired into all living things. Might that hard-wiring be more sophisticated than we give credit, and the need to have children in terms of number of children?

Consider our nearest relatives, chimpanzees and gorillas. They seem to have stable populations, without accidentally having population explosions that are unsustainable. Just perhaps, our basic instinct to have children, is also to have children in balance.

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 point by Hans, is that the birth rate only produced a balance once deaths were also considered. But it was in balance. Historically, humans produced the right amount of children such that, overall there was balance. Now consider, what if the system takes time to adjust, but in fact humans have now simply adjusted to this new lower death-rate, by naturally having a lower-birth rate?

Historical population levels reveal that human population grew very slowly. Requiring almost exact balance between births and deaths. Population level rose as civilization evolved to be able to displace nature further and further, and as human spread over the globe, but population never grew beyond the means of society. Despite that even at moderate growth levels, humans have had time to completely overrun the planet.

What if, the measures introduced in China were only required while people adjusted, and are no longer necessary? What if the explosion occurred because the change in infant mortality was so sudden that we humans needed time to adapt, but we are now adapting to our changed situation?

To me this seems possible. However, perhaps the instincts that while in the jungle or the savanna, could pick up signals to trigger people to having more or less children in order to maintain the balance, have difficulty adapting to pick up the signals in our modern city environments?

The attraction of this hypothesis is that, instead of requiring a belief that it was only coincidence that birth rates happened to fall the right amount, just when they needed to fall, it requires only a belief that it is our nature to find balance.

Sure other factors affect birth rate, but perhaps regardless of other factors, humans will find a birth rate balance, at least provided nothing interferes to a level beyond our ability to adjust.

On this basis, that fall in birth rate is in response to the fall in infant mortality. There is a lag, and modern society may make us slow at picking up cues, but if this is true countries with low infant mortality will find balance sooner or later.

Yes, there is correlation with many factors such as education of women, but these factors also have a strong correlation with reduction in infant mortality.

There is a lot to explore before declaring everything adds up. How the signals could work in society? Wouldn’t it be logical if people are responding to environment for people in crowded areas to have less children? So many questions that a dedicated exploration make sense.

But, just perhaps, that is NOT coincidence.

Conclusion: The Paradox.

Programs to reduce birth-rates played a role in ending the population explosion, but on all evidence contributed not more than around 15% of the reduction globally. The paradox for current explanations for the other 85% of the reduction, is that none explain the birth-rate reduction alone, requiring a co-incidence of several factors that just happen have a side-effect of reducing birth-rates, all occurring right at the time when humanity requires birth-rates to fall.

It would seem far more logical that some underlying drive for lower birth-rates was able to be accelerated by working with some of these factors, than they all happened to cause the desired result at the right time.

Either a co-incidence, or an underlying factor yet to be further explored.

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