I'm putting together a scenario where in a post-disaster earth, most environments are so toxic that humans tend not to live beyond their early twenties.

This would be through unavoidable health complications, rapidly onsetting cancers or similar. Although if most people dont make it to adulthood then medical knowledge would take somewhat of a nosedive so causes can be vague.

What implications on day to day activites would having no aged population bring up?

  • $\begingroup$ Quite aside from the fact that, as @MontyWild made clear, because people are not dying suddenly but from illnesses and health complications, they'd never be healthy enough to do anything, almost all of the roles involved in maintaining modern society (including education!) require a course of education that stretches into the early twenties. Leaving aside the illnesses incapacitating the entire population and leading to universal death by starvation, everything would fall apart and you'd be reduced to an agrarian society but with no one strong enough to maintain even that. $\endgroup$
    – jdunlop
    Commented Sep 15, 2023 at 1:39
  • $\begingroup$ If you want a society where people are healthy but die early, look at en.wikipedia.org/wiki/Logan%27s_Run $\endgroup$
    – Monty Wild
    Commented Sep 15, 2023 at 1:41
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    $\begingroup$ You'll see in the help center that "what if X happened" questions are ruled out here. This is because they are both too broad and looking for opinions (answers tend to be equal), both things this site is bad at. $\endgroup$ Commented Sep 15, 2023 at 2:29
  • $\begingroup$ It would look bad, because there was a toxic disaster and everyone is dying. What answer are you looking for? What would colleges look like? What would restaurants look like? What would dating look like? What would the military look like? You have just asked infinite questions. This is fine, but each one has to be posted separately. You'll have to break this down, I have to vote to close per policy. $\endgroup$
    – Vogon Poet
    Commented Sep 15, 2023 at 4:49
  • $\begingroup$ At least all the first world problems would disappear. $\endgroup$
    – elemtilas
    Commented Sep 16, 2023 at 4:49

4 Answers 4


If somehow they can miraculously sustain the population, ie. they are not dying out, they would probably regress to stone age. Without elders, long-term cultural memory is gone, and harsh conditions make people concentrate on keeping their own people alive at the expense of everything else.

Every time people die so young, the population tends to switch to r selection. It means that they make as many babies as possible. As a result, for every capable adult, there is going to be lot of children under 10, and many adolescents. If there were too few babies, the population would die out soon, so r selection is the only viable choice.

In this situation, it is nigh impossible to take care of the youngest, feed the people, maintain shelters, maintain some kind of order and peace (many adolescents, and many of them completely without parents!), and educate the next generation at the same time.

Of these, investing on human capital (culture, education etc.) provides the least survival benefit. If life is so short, and majority of people would die before they enter puberty anyway, most of it would never be put into use nor tested in practice, and passing it onto next generation would just eat up resources for nothing... and resources are already limited.

Everything that is more sophisticated than stone age tech would be soon too complex to create and maintain, and all information pertaining to it will be forgotten or too corrupt to be of any use.

Eventually, the remaining human capital is just that which can be most effectively channeled to survival and taught reliably to the next generation. In time, even making and handling iron, bronze and other metals can be more or less out of reach (lack of resources, lack of adults doing the work, and lack of education is a tough combination), and existing tools are going to break sooner or later.

If just one generation (remember: there are no elders!) loses even a single piece of pivotal information about something complex, all related information can become completely useless. Rinse and repeat: stone age awaits.

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    $\begingroup$ Thanks, this was the sort of input I was looking for, instead I got the "akshually your question is bad, I'm so happy I got to vote this closed" $\endgroup$
    – NotADog
    Commented Sep 15, 2023 at 10:45
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    $\begingroup$ Following up, the population would crash as people in this situation could survive only in places where a lot of food is easily available. In the first 2 decades of life, we need a lot of food, and we don't have the skills, strength, and knowledge to gather / hunt that much food when conditions vary from year to year. The human species grew bigger when grandparents survived to help feed and train the second generation. $\endgroup$
    – David R
    Commented Sep 15, 2023 at 14:18
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    $\begingroup$ @NotADog "Akshually," we close off-topic high concept questions for good reasons. It's so rare to get an answer that has a specific, studied response like Jani's does that you frankly got lucky. And 99.9% of the time, when answers sneak in before closure, they are of the basic tenor of Jani's (your idea can't work because...). But critiquing ideas isn't what Stack Exchange or this Stack want to to. We appreciate people who take the time to understand Stack Exchange and our Stack, and work with our rules and policies. $\endgroup$
    – JBH
    Commented Sep 15, 2023 at 15:31

This wouldn't look like a society at all. This would look like a bunch of sick kids dying slowly in a polluted landscape. There would be negative population growth, and a viable live birth would be a rarity, and such a child would be unlikely to survive to adulthood, given that it and its parents would be dying from all the toxins in the environment.

I hate to say it, but life would be nasty, brutish and short.

  • $\begingroup$ Miri $\endgroup$
    – elemtilas
    Commented Sep 16, 2023 at 4:48

20 years life expectancy means that on average one would become orphan before hitting puberty, at an age that in the Western world would see them still in primary school, and would likewise have no grandparents or older people around.

This would be a dramatic hit on the transfer of knowledge across generations, throwing the population in a real dark age, with nothing more than day to day survival struggle.

Incidentally it is believed that when life expectancy of mankind rose to the point of allowing 3 generations to live together, it allowed a jump forward in knowledge transfer, because the elders could teach the juniors while the parents were busy finding food.


There have been locales at times that were similar.

Kids married early, got pregnant young and did what they could to survive. Nowadays we expect a long learning period of adolescence, but in the third World you get children who are basically thinking like adults by 10 years old out of necessity. Their play time is long over.

Education is less formal and concentrates on survival strategies for their environment rather than science and maths. These children are not stupid though, they 'learn' to learn and can pick things up very quickly, their minds are sharpened by hunger.

So this is what you'd end with in your scenario, except since you have a sickly population they might all die off.


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