 In an earlier episode about overpopulation, I said so making an accurate demographic projection on the effects of life extension on the global population is beyond what we can do right now on this show anyway. Well, what do you know? A 2015 paper published in the journal Technological Forecasting and Social Change did precisely that. Actually, it did more than that. The paper is titled Opportunities and Challenges of a World with Negligible Cinescence, and as a matter of fact, it was among the sources I collected when I was working on the overpopulation episodes that we published some time back. Somehow, I managed to miss it entirely, so we're gonna talk about it right now. Welcome to Extend, your one-stop YouTube show for all things life extension. If you're new here, don't forget to click subscribe and hit the bell icon if you'd like to stay up to date with what science is doing to make aging a thing of the past. Today, we're going to see what might happen to our world if aging already were a thing of the past. The authors of that paper used a large-scale long-term modeling system to predict the effects of negligible senescence on our population, environment, economy, etc. If the term negligible senescence doesn't ring a bell, it's basically another way to say rejuvenation or life extension. More specifically, it refers to a situation in which senescence, that is, the aging of our bodies, has been made negligible, that is, pretty much undetectable. The forecasting system used by the researchers takes into account a number of different factors, such as education, demographics, energy, mortality, health, and so on, and the ways they affect each other to build models of what possible futures might look like. Before building any negligible senescence scenarios, the researchers built a baseline scenario to compare them to. All scenarios span all the way to 2100, but the baseline scenario assumes that science will only make modest progress against aging, managing to slow it down a little, without actually eliminating it. The negligible senescence scenarios, or NEG SENSE, all assume that rejuvenation therapies were already available in 2020 and would be phased in uniformly across the world over the course of 20 years. During this time, the researchers assumed that mortality by nearly all causes, including the chronic diseases of aging, would be driven down almost to zero. The only exception was mortality due to mental illness. The researchers assumed that mental illness would slowly accumulate with the passing of time, although they did place a limit on that. They also assumed that deaths due to accidents and injuries, too, would go down significantly. Their reasoning was that a society that managed to drive down age-related death would successfully try to do the same to other kinds of death, too. Another crucial assumption was that rejuvenation treatments would also preserve people's ability to have children at any age. So, what did their model say? In terms of population size, their baseline scenario behaved pretty much like the United Nations' medium-variant scenario. With population aging continuing to take its usual toll and slowing down population growth, this scenario predicted a population of 10.1 billion people by 2100. The next sense scenarios were divided into three variations, low, medium and high fertility. The medium fertility scenario assumed that the total fertility rate, or TFR, that is the average number of babies a woman will have in her life, would decline slowly to 1.9 babies in 2100, which is the same trend that we seem to be on right now. This led to a population of 14.8 billion by the end of the century. The low fertility scenario assumed that the TFR would go all the way down to one baby per woman well below a replacement rate, which produced a population of 11.6 billion in 2100. The high fertility scenario assumed a TFR of 3, higher than the current 2.4, and which the world hasn't seen since the early 90s. That kind of TFR would lead to a population of nearly 20 billion come 2100. Essentially, in the low and middle fertility scenarios, population went up fairly slowly because the average number of babies per woman was going down. In the high fertility scenario, both population size and fertility rate were going up, leading to a nightmare situation that, in practice, is not very likely. This emphasizes once more something we already knew. More than depopulation growth, longevity contributes to population size. A population won't grow at all if it doesn't reproduce, no matter how long individuals live. Population growth is driven by the fertility rate. Longevity slows down population shrinking, but it doesn't make populations grow per se. For comparison, the worst case approximations we saw in episode 2 of X10's Overpopulation series estimated a population of a little over 17 billion people on the assumption that age-related deaths disappeared overnight in 2021, and a little short of 19 billion people on the assumption that death in general disappeared overnight in 2021. Both these scenarios assumed an essentially declining fertility rate, though. The rest of the paper disregards the high fertility scenario, maybe because it's beyond unlikely or maybe because it's so catastrophic that it's not even worth going into. But anyway, the researchers then looked into the expected healthcare costs in their baseline and next-gen scenarios. The scenario with our rejuvenation predicts a gradual increase in healthcare spending related to disease and mortality between 2014 and 2050, from 10.6 to 12.4% of the global gross domestic product, or GDP, the total value of all good and services produced in a year. After that, global spending pretty much stabilizes around 11-something percent. To evaluate how much rejuvenation would cost to individual countries and the world, the researchers devised three more next-gen scenarios, low, middle, and high cost. In the middle-cost scenario, $100,000 worth of rejuvenation therapies grant 20 years of negligible senescence, after which they would have to be reapplied. This means that the cost of the year of negligible senescence would be $5,000 per person. In the low-cost scenario, the same $100,000 buy you 30 years of extra youth for the modest sum of $3,333 per person per year, while the high-cost scenario puts a year of rejuvenation at $10,000 per person, meaning that a $100,000 worth of therapies would buy you exactly 10 extra years of youth. The financial impact is different for different countries, depending on their level of income, but the global picture, including money transfers from rich countries to poor ones to help them afford rejuvenation, looks like this. At first, all next-gen scenarios cause a bump in health spending because of the cost of rejuvenation treatments, but they all eventually become far, far more economically convenient than the baseline. That's because other health and mortality expenditures all plummet, and also because the scenarios assume that annual rejuvenation costs would eventually go down to $1,250 per person. The low-cost next-gen scenario takes less than 20 years to become more convenient than the baseline. The middle cost takes a little over 20, while the high cost takes a good 40 years. Each and every cost assumption made by the researchers is of course up for debate, especially as they assumed that the effectiveness of rejuvenation therapies would always stay the same, but the assumption that not all countries would be able to afford rejuvenation right away is not at all far-fetched. That begs the question of whether rich countries would really be willing to destinate big chunks of their GDP to help poorer countries out. As the researchers note, that's already happening in the case of antiretrovirals for HIV, but it's not a given. When it comes to pensions, the simulated scenarios tinkered around with savings, government funds, labour force participation, and so on to try to close the gap between the consumption needs of retirees and the actual funds available for them. Things worked out okay in the baseline scenario, which assumed no rejuvenation, but not so okay in the next-sense scenarios. As a percentage of the GDP in 2100 the gap was only 1.1% in the baseline scenario, for the low and middle fertility next-sense, it was 30.5 and 43.6% respectively and no amount of playing around with parameters significantly reduced that gap. This led the researchers to the obvious conclusion that, without postponing a retirement age, rejuvenation therapies are probably not going to be affordable. This isn't just obvious, it's bleeding obvious. A growing, long-lived fraction of the population permanently leaving the workforce while keeping on consuming is economically suicidal. And in this case it's also fairly idiotic. Retirement as we know it exists only because eventually aging makes it hard for people to support themselves. If aging was no obstacle, as it isn't in the next-sense scenarios, people of whatever age would be perfectly capable of providing for themselves. In a situation like that, retirement has no reason to exist and no government in its right mind would ever keep handing out pensions forever to people who don't objectively need them. So the researchers tweaked the next-sense scenarios to allow retirement age to rise. The simulation gradually rose the retirement age of the low and medium fertility scenarios until it had 114 and 118 years respectively in 2100. This reduced the pension gap to levels comparable to the baseline scenario with a workforce participation of only around 43% in both next-sense scenarios. Of course, as the researchers observed, talking about retirement at that point makes little sense. In a world where we don't lose our health with age, work-pat-sense are bound to change significantly. People would probably drop out of work periodically to retrain or to rest, only to return to the workforce after a few years, depending on what their finances allow and how the job market will work in 2100 if there will even still be one. A very important thing to note is that in the next-sense scenarios, the world doesn't need to worry about how we're going to support older people, because older people can't support themselves just fine. This is the exact opposite of how our current system works, because it relies heavily on young people's work to support the retired elderly. In this sense, fertility rates didn't really matter in the next-sense scenarios. In the next-sense scenarios, the economies of the world got larger, which is good, but it does have its downsides. This is something that the researchers seem to be particularly concerned about. Their baseline model predicted that energy demand would rise by a factor of 5 between 2010 and 2100, even assuming dramatic increases in the energy efficiency of our economies. Our economies are getting more energy efficient, by the way, although not very fast. And this means essentially that producing one unit of GDP requires less energy over time. The baseline model also expects fossil fuel used to plateau in the 2030s and to steadily decline after 2040. According to the baseline, by 2192% of all our energy should come from non-fossil sources, which according to the researchers is a more optimistic forecast than others. The next-sense scenarios gave slightly different results depending on the fertility level. The low fertility next-sense scenario predicts our energy consumption will increase seven times, while in the middle fertility one it will increase eight times. The researchers also assumed that a larger population will make the transition to clean energy harder, and for that reason they considered two high-coal variations of the low and middle fertility scenarios, in which, by 2100, only 88% of our energy comes from sources other than fossil fuels. The bad news is that in all scenarios, next-sense or not, the amount of atmospheric carbon is well above the target threshold of 450 parts per million that scientists think is required to limit global warming. In this respect, normal next-sense scenarios perform only marginally worse than the baseline scenario, while all high-coal next-sense scenarios reach level as high as 800 parts per million and more, which is, well, really bad. The good news is, in all scenarios, we eventually wind up getting the vast majority of our energy from clean sources, and we should well hope that that will be the case. If the gods of nuclear fusion smile upon us, who knows? Before 2100 we might even ditch fossil fuels for good. Speaking of food availability in their paper, the researchers expressed concern that a world with negligible senescence might make it harder to curb undernourishment. In their baseline scenario, the global mean calories available per capita rise from 2800 in 2010 to almost 3300 in 2100, and undernourishment drops from 13 to 4%. In the medium fertility next-sense scenario, this improvement is less pronounced, as the number of available calories per capita is expected to almost not change at all, while in the low fertility scenario it will barely rise to a little over 2900. This means that if you take the total amount of calories produced in the world and divide it by the population size in 2100, each of us gets around 28 or 2900 calories per day. That sounds misleadingly good, because it's more than what the average person needs to survive, but the point is calorie distribution is unequal across the world. Some people get more than they need, and some get less. If this inequality dragged on to 2100, a lower average global amount of calories per person could result in undernourishment being reduced down only to 10% in the middle fertility next-sense scenario, or 9% in the low fertility one. It's worth noticing that the researchers might be a little too pessimistic in terms of technologies that may swoop in to save the day. You can learn more about that in our fourth overpopulation episode. There are some unclear points in the study, such as the age at which people in the simulation would receive rejuvenation treatments. It would be pointless to administer them to people in their 20s or younger, for example. If the researchers didn't take this into account, their estimated costs of life extension would be higher than it's reasonable to expect, because the model would assume that money was spent to give the treatments to people who didn't really need them. Another unclear point is why the researchers chose to assume that mental illness would slowly accumulate in the population over time. This isn't so much about whether rejuvenation would address mental illness, which is at least debatable, as it is about our ability to prevent and treat this kind of health problem in the future. The study had its limitations. For one, a uniform rollout of rejuvenation across the world right off the start is improbable, and so is the assumption that all rejuvenation therapies would be available at the same time rather than being developed over different periods of time. The study authors acknowledged these and other limitations, as well as the possibility that more people living longer and healthier lives might well be able to help us to more quickly find the solution to all the challenges that the study explored. In any case, studies like this one can help us be better prepared for the longevity revolution that is, hopefully, waiting for us a few decades down the line, so that we can all reap the pros of life extension without any cons getting in the way. By the way, the study we talked about is not paywalled, and there is a lot of it that didn't make it into this episode, so click the link in the description below if you want to go and read it for yourself. Thanks a bunch for watching this episode of X10, and thanks for all you do to support our show. If you have no idea what I'm talking about, Bob would like to head over to lifespan.io slash hero. You'll find instructions on how you can become a lifespan hero, and help us keep the show alive with a monthly donation. While you're at it, please do like and share this video if you found it interesting, and if you want to see more videos like this, I invite you to subscribe. 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