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Will Solving Ageing Cause Overpopulation?

Posted on 10 May 2023

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We may soon have the ability to slow down the ageing process in humans. But should we? In such discussions, overpopulation is usually among the first concerns to be raised as a reason why we might not want to delay the ageing process. Overpopulation is often thought of as one of humanity’s biggest challenges, and it’s going to get worse, regardless of whether we are successful in slowing ageing. It is often blamed for many of the world’s problems, such as poverty, environmental degradation, conflict, and disease. Yet while anti-ageing technology could make overpopulation worse by allowing people to live longer, it may be necessary in order to solve an much bigger problem.

What is overpopulation?

Everyone knows what overpopulation is: it’s when there are too many people. But how many is too many? Overpopulation is relative: it occurs when there are more people than can be sustained by resources in a given area. We typically think of food or water shortages when we think of overpopulation, but insufficient materials or space could also result in a territory being overpopulated.

Thus, overpopulation is not a simple matter of ‘more people is a bad thing’. Less developed territories with low agricultural productivity will have a lower threshold for what is considered overpopulation. Keep this in mind when we consider how the population is predicted to grow and, later, how rejuvenation technology will affect us.

Population growth this century: a grim prediction?

Whether the population grows or falls over a given period of time depends mostly on the number of births and the number of deaths during that period. Since everyone will die eventually, a population will ultimately grow if the fertility rate is higher than the replacement level, which is the fertility rate required to keep the population stable. If everyone reproduced, then the replacement level would be 2 children per woman. In practice, some people will die before they have children, generally resulting in a replacement level of 2.1 (the exact number depends mainly on infant mortality).

So, if we want to predict population growth in the future, we need to predict fertility rates, and one of the best ways to do that is to look at the development state of a country. Fertility rates tend to be higher in less developed countries. A large part of this is due to poor access to contraception and lower levels of education for girls (educated women tend to marry later and have fewer children).

This introduces some uncertainty into the calculation, because history has shown us that fertility can fall very rapidly as a country develops. In South Korea, it took only 18 years for the fertility rate to fall from over 6 births to fewer than 3 births per woman, while in Iran it only took 10.

Because Sub-Saharan Africa will be the largest contributor to population growth over the coming decades, development in this region will have a large impact on how much the global population actually grows. However, you can see from the graph below that the Earth is likely to keep getting more populous for at least the next 50 years, and that this trend could continue past the turn of the century. Most predictions place the global population at around 11 billion by 2100. That means that today’s population of 8 billion, which many people already believe is too many, will grow by over a third. However, we need to ask ourselves an important question: is this necessarily overpopulation?

Previous and future global population predictions by the UN as of 2019. The red line indicates the most likely prediction, while there is an 80% chance that population will fall within the orange zone, and a 95% chance it will fall within the yellow zone. The probability that the population will stop growing before the turn of the century is about 27%.
World Population Prospects 2019

Not in terms of space: if everyone lived in cities with a similar population density to New York, 11 billion people would occupy about 1.1 million square kilometres, about the size of three US states. That’s a lot of space to be covered in a city, but the Earth still looks fairly roomy under this scenario, even if only half the population are living in cities (as is the case today).

What about food? While it is true that developing countries with high population growth are more likely to suffer from food scarcity, this is not an issue of global overpopulation or global food shortage. Globally, there are more deaths related to overeating than undernourishment, which makes it fairly obvious that the problem is the way food is distributed, not how much of it is being produced. Even when global population growth peaked half a century ago, food production kept up with demand and no major upheavals occurred as a result of population growth. With advances in technologies like GM crops and lab-grown meat, we could sustainably support an additional 3 billion humans by 2100.

Keep in mind that all of the above refers to the global population as a whole. Many developed countries are already experiencing a population decline and will be joined by many more over the coming decades.

So, while overpopulation is a threat, there are clear steps that we could take to prevent it, even if the population grows as rapidly as projected. Unfortunately, there’s another problem related to population growth that we need to solve soon, and one that leaves us with far fewer options.

Population age this century: a grim reality

These graphs hide a key piece of information, which is the age distribution among the population. When fertility rates increase, the average age of the population tends to decrease, and vice versa. 

To illustrate this with a simplified scenario, imagine a country that has been maintaining a consistent fertility rate of 4.2 – about twice the replacement level. This means that each subsequent generation is about twice the size of the previous generation. If you picked someone at random from such a country, you would be more likely to pick a member of the youngest generation, since they are the most numerous. Imagine that, for some reason, the fertility rate suddenly fell down to the replacement level. Now each generation is about the same size as the last. By the time the last generation before the drop has died off, the oldest generation will be just as numerous as the youngest – the population will have aged. If the fertility rate then fell below the replacement level, each subsequent generation would be smaller than the last – the population will age further, and it will also shrink.

Now look at the graph above showing the global fertility rate: even as the population was experiencing its most rapid growth, the global fertility rate was undergoing its most rapid decline. This has led to a very skewed age distribution in many affected countries.

Elderly people generally require more resources to support, due to worsening health and disability. This statement should not be confused for a suggestion that the elderly are less valuable than younger people – everyone contributes to society and deserves to be given back to later in life. Unfortunately, a greater proportion of elderly people means that a greater proportion of the working age population are required to support them – more healthcare expenditure and more healthcare workers are needed. This problem is already affecting most of the Northern hemisphere, and will soon affect most of the world. It’s also going to get worse in the countries already affected due to falling fertility rates, with many countries expected to experience massive population decline. China, for example, is predicted to lose about half of its population by 2100.

Unlike overpopulation, there are few palatable options available to us when it comes to dealing with population ageing. Hopefully, most people will agree that culling humans à la Logan’s Run is off the table. We could encourage people to have more children, but this strategy generally doesn’t work very well. Even if fertility rates did increase, they would need to remain high in order to keep the population young. Thus, the best approach to preventing population ageing is arguably to delay the ageing process itself.

Rejuvenation solves population ageing

There’s a common misconception that the main goal of rejuvenation or anti-ageing research is to make humans live longer. While extended lifespan may be a welcome side effect of slowing down the ageing process, the primary goal is to extend healthspan – the period of time spent in good health. 

Before modern medicine, people were relatively unlikely to reach their 60s. Death before this age was mostly the result of infectious diseases, which killed fairly indiscriminately. After developments like antibiotics and vaccination, most people could expect to grow old, and so age-related diseases became the main cause of death (and consequently a major focus of modern medicine). Unfortunately, even though we have become pretty good at keeping people with age related diseases alive, we haven’t become much better at curing them. A 65 year-old who gets heart disease today can expect to live much longer than they would have 100 years ago, but they will still be living with heart disease for the remainder of that time.

Possible outcomes of rejuvenation technology.

A true anti-ageing treatment should make the body of a 65 year-old behave like that of a younger person, and therefore the onset of ageing and age-related diseases should be delayed. In an ideal scenario, they would experience negligible senescence, which means they would essentially display no signs of ageing at all (not even an increased mortality rate) right up until their death. Negligible senescence is a natural occurrence in several species. If humans became negligibly senescent, it would mean that only a tiny fraction of the population would require geriatric care at any one time, while significantly improving quality of life and allowing older people to contribute to society and to the economy in the same way that they did when they were younger. Negligible senescence in humans is probably a long way off, but any slowing in the rate of ageing, even if slight, would have a significant impact.

But won’t rejuvenation also increase the population?

We don’t know whether rejuvenation technology will increase the maximum age to which a human can live, but it’s very likely to increase the average length of life (life expectancy) because it will delay the onset of age related diseases that are the main cause of mortality globally. 

This should favour population growth, but it’s very hard to predict how much of an effect it will have. Not only would it depend on the effectiveness of the rejuvenation, but also who gets access to the technology. Prominent scientists in the field argue that rejuvenation technology will be provided free of charge by state health services. That’s because even if the technology is expensive, it’s unlikely to cost the state more than treating and caring for an ageing population.

With all this in mind, let’s take a look at some possible outcomes for a developed country currently experiencing population decline (Sweden) adopting rejuvenation technology. Both of the following graphs come from a paper entitled Demographic consequences of defeating aging. The first graph shows a fairly extreme scenario: in 2035, the entire population of Sweden becomes negligibly senescent after age 60. This means that from age 60 onwards, there is no further increase in mortality. This would result in a median lifespan of 134 years for men and 180 years for women.

Projection of the Swedish population until year 2105, assuming negligible senescence from age 60.
Demographic Consequences of Defeating Aging

In this scenario, the country would be rescued from population decline, and would instead experience a 22% growth in population by the time 100 years have passed since population decline began. This is hardly catastrophic population growth considering the extent of rejuvenation. In order for the population to grow, new humans still need to be born, and Sweden’s fertility rate is already very low (1.6) and declining. What’s more, a high life expectancy doesn’t change the fact that everyone will die eventually. As the new negligibly senescent population starts to reach the new life expectancy, the population will begin to plateau and will even start to decline again if the fertility rate is still below the replacement level.

Now for a more realistic scenario: only 10% of the population gain access to negligible senescence in 2035, with an additional 1% gaining access each following year. It’s also assumed that, for whatever reason, 5% of the population decide not to adopt rejuvenation technologies.

Population projection for Sweden if the population gains negligible senescence gradually over time.
Demographic Consequences of Defeating Aging

In this scenario, the population would still decline, but the decline would be more gradual. More importantly, most of that population would be in good health, avoiding the scenario of catastrophic population ageing.

It’s about half a century too late to be worrying about overpopulation – between 1960 and 1974, the World went from having 3 billion people to 4 billion. Yet this massive growth did not cause any global disaster. We started this article by stating that population growth is one of humanity’s most pressing challenges. While that may be true, it is clearly one that can be solved.

Population ageing is a new problem to which solutions are more limited. Everyone agrees that we should improve treatments for cancer, heart disease and Alzheimer’s, despite the fact that this will make people live longer and grow the population, while simultaneously leaving people in poor health for a longer proportion of their lives. It makes little sense, then, not to support rejuvenation when the rewards are greater and the drawbacks are lesser.

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    Title image by Elton Sa, Unsplash


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