There is an old saying in physics that “nature abhors a vacuum,” as the stuff around the vacuum would just fill in the vacuum and remove it. If a random cubic meter of air suddenly disappeared above Manhattan, the surrounding air would immediately fill it.
A variant of this saying appears in political history, that power abhors a vacuum. When you have some equilibrium and remove a powerful state or leader from the world and leave no one in charge, you create a power vacuum where surviving people rush (often violently) to seize control. (This is why I think despite having an inordinate amount of US taxpayer money going to the military, getting rid of it immediately would make the world even worse.)
But there is one more sense of the vacuum that I’m worried about and it’s that of population growth. It is the Malthusian worry but I would frame it in more abstract terms that also allow for extreme technological innovation. The idea is that for most of human history, the population grew at a slow rate, limited by disease and lack of technology. But as technology exploded in the last 300 years, so did population. Every time we innovated—every the population became capable of expanding—it did so.
The worry argument goes like this:
- The human population will always expand to its current carrying capacity based on current technology and environmental conditions. (Nature abhors a vacuum.)
- Technological growth will likely push the apparent carrying capacity higher than now. (However, it may have already slowed down significantly, i.e. will we have another Green Revolution?)
- There is some overall limit on the human population as determined by Earth’s finite resources.
- Eventually (if it has not already happened), (1) and (2) will raise the population to well above that of (3), and a global crisis may eventually follow.
Disclaimer: I’m a long-term optimist and this post represents more of a worry than a prediction.
The Green Revolution
In 1970 Norman Borlaug won the Nobel Peace Prize for breakthroughs in agricultural production. He is often credited with the saving of a billion lives.
But the cynical side asks: Did the Green Revolution actually save a billion people, or did it merely postpone and inflate a much bigger crisis? Did the human population simply increase to the new carrying capacity, leaving us back where we started? In fact, some people would argue we are now worse than where we started, due to environmental impact and loss of biodiversity.
Borlaug himself was very aware of this. In his Nobel speech:
The green revolution has won a temporary success in man’s war against hunger and deprivation; it has given man a breathing space. If fully implemented, the revolution can provide sufficient food for sustenance during the next three decades. But the frightening power of human reproduction must also be curbed; otherwise the success of the green revolution will be ephemeral only. Most people still fail to comprehend the magnitude and menace of the “Population Monster”…Since man is potentially a rational being, however, I am confident that within the next two decades he will recognize the self-destructive course he steers along the road of irresponsible population growth… (Nobel Lecture 1970)
Keynesian Leisure Society
I think this is also a reason we don’t live in the Keynesian dream of the “leisure society”. The Keynes argument goes, since productivity (since 1930) will increase by many many factors to now, by this time we should be working two days a week to obtain the same productivity and spending most of our time in leisure. Yet obviously, we still work the same hours as before.
There are some common answers to this including how people increase their wants as soon as they get what they want (which is sort of related to this topic), and relatedly that people care more about relative wealth than absolute. Another explanation is rising inequality (which will be mentioned later). But a third explanation is just population growth. The technology made the carrying capacity a lot higher, and the population filled in the vacuum. And the work required to sustain similar relative conditions might still be 5 days a week.
Why We Shouldn’t Be Worried (Objections)
I’ll go through a couple of objections.
- Earth doesn’t have a limited carrying capacity because technology will keep improving.
It’s true that technology will continue to improve for the foreseeable future. But eventually there must be a limit. Every time people have said this before, that the population couldn’t possibly double again. they were wrong, so I’ll make no claim about where that limit is. But eventually you can do some basic math on consumption requirements for a human at modern standard of living, and just multiply that by some number. I don’t know if the limit is 10 billion or 100 billion. But it’s there.
This is also a dangerous objection in that the potential problem becomes much worse as the population grows. If the Green Revolution did not happen, we could already be in a crisis, but it would be a crisis with 3 billion people. Now imagine the same crisis but with 20 billion.
- The world eventually reaches the demographic transition everywhere.
I’d be very happy if this happened. The demographic transition is the phenomenon that has occurred in most Western countries and some other industrialized countries like Japan, where the fertility rate (children born per woman) has started to approach the replacement rate of 2.1 and in some cases drop below it. In the long run, every country reaching 2.1 would mean a constant population.
There are still three concerns. One is that there is strong religious pressure in some places to not use contraception. If you imagine a world where nobody changes religions (not too unimaginable), and that certain religions have a higher fertility rate, then in the long run that religion will dominate the world population and we will have this problem again. Though, it’s not clear which effect is bigger between the demographic transition and “Be fruitful and multiply.”
A second concern is that high inequality could be partly keeping the population in check. That is, the US population is not growing as fast as it can, because many people are in poverty and don’t have enough resources, but once we solve inequality, the population increases rapidly again.
The third concern is that the demographic transition might not be the the complete phenomenon. We don’t know the future, and maybe beyond some point, the demographic transition reverses and the population rises again.
The negative association of fertility with economic and social development has therefore become one of the most solidly established and generally accepted empirical regularities in the social sciences. As a result of this close connection between development and fertility decline, more than half of the global population now lives in regions with below-replacement fertility (less than 2.1 children per woman). In many highly developed countries, the trend towards low fertility has also been deemed irreversible. Rapid population ageing, and in some cases the prospect of significant population decline, have therefore become a central socioeconomic concern and policy challenge. Here we show, using new cross-sectional and longitudinal analyses of the total fertility rate and the human development index (HDI), a fundamental change in the well-established negative relationship between fertility and development as the global population entered the twenty-first century. Although development continues to promote fertility decline at low and medium HDI levels, our analyses show that at advanced HDI levels, further development can reverse the declining trend in fertility. (Myrskylä 2009)
Finally, current projections of world population have the growth rate slowing down (United Nations Graphs). But I worry that this goes against basic intuitions of human nature and the vacuum. I worry it will keep increasing until it can’t.