for context: an apocalypse has happened. Everyone dies with the exception of this one man. Assume that this man is able to stumble upon a cloning machine. Said machine can hold up to 10 babies. We assume that this man is able to back build this machine and he's a master in machinery and we assume he has access to a disk full of useful information.

added context (an edit):

  • while he's the only human, there's still plenty of livestock left.

  • we assume that this machine is located in a bunker in Kansas, so is the disk and plenty of other necessary things to build civilization.

  • the drawback: he's unable to find other DNA and as such the babies will be his own clones.

main question:

How much a population growth would be able to grow in 100 years?

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    $\begingroup$ this question is unanswerable as posed right now. A lot of information is missing. $\endgroup$
    – L.Dutch
    Feb 25, 2022 at 11:49
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    $\begingroup$ 1304 men, less those who have died of old age or other causes. Cloning men won't get you any women or natural population increase. $\endgroup$
    – Monty Wild
    Feb 25, 2022 at 12:38
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    $\begingroup$ How long does the clone machine take to produce a clone? Can we safely assume that every human will get their survival and developmental needs met? As written this looks like an underspecified math problem not a real worldbuilding question. $\endgroup$
    – sphennings
    Feb 25, 2022 at 15:13
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    $\begingroup$ Heh heh. This story has been done by Red Dwarf. youtube.com/watch?v=38oui1hfRwk $\endgroup$
    – Dan
    Feb 25, 2022 at 18:47
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    $\begingroup$ Does this answer your question? How many people are required for a healthy re-population of the Earth (Post-Apocalypse)? $\endgroup$
    – Mazura
    Feb 25, 2022 at 20:08

4 Answers 4


What does "back build" mean? Do you mean he can duplicate the machine?

If he cannot duplicate the machine, and can only keep it in good repair, then his capacity to care for children is the bottleneck, along with capacity of the one machine to produce clones.

Presuming a batch of infants every nine months, humans are not able to be independent at all until the age of two or three (24-36 months) and not fully independent until the age of 5 (60 months) , which is going to mean about 30 infants he has to care for, feed clothe and dress, without any help, and possible 70 kids (63 months) before he has any fellow babysitters to help.

More likely, he is going to have to wait until the first batch is about four before he begins a second batch, and in general will have to start slow and ramp up. After about 20 years, he can probably run the cloning machine at full capacity with enough caregivers to not exhaust himself, so there is 80 years of full capacity. That is 960 months, about 107 rounds, of ten children each, for 1070 kids. In the first 20, batches are probably 3 years apart, maybe 70 kids, half of them at least 10 years old, so 35 kids to care and provide for 10 infants and 10 children. That sounds difficult but possible.

I'd say a population of 1100 to 1200.

If he can reproduce the machine, the population can grow much larger, possibly doubling every 10 years after the ramp-up period (still 20 years). Then you'd have 2^8 = 512x the initial population of about 70, roughly 35,000.

I hope I have provided enough detail for you to make your own estimates. I would spreadsheet this year by year, if I were you.

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    $\begingroup$ There's a possible twist here that could alter some of that, he's male, so he has both X and Y chromosomes, so with adequate expertise and the right tech available (and if he has a cloning machine and the ability to use it and build more then he presumably has, 🤔 probably) he could potentially switch out the Y chromosome for a copy of his X chromosome in some of those clones 😁 $\endgroup$
    – Pelinore
    Feb 25, 2022 at 15:56

Realistically, he can get the population up to 10 or 12 and no more.

Assuming the bunker is well-stocked and it has generators and vast quantities of fuel to power the electronics for the cloning vat, he can realistically power this up for months at a time. Then he needs to take a newborn infant out on a cross country trek to find more fuel. The fuel itself is degrading, but we'll handwave it away and say that this isn't a 2018 Audi, and that the generators back at the bunker can run off of it.

Even then, he is limited to the reagents for the cloning vat. Whatever stockpile they provided is everything he will ever have. He's not going to go on a journey across the country to some biotech startup's headquarters in Portland, read through their paper documentation (hah! they didn't even keep that crap digitally), and work their boutique pharma factory for a year to get 20 more gallons of I-Can't-Believe-It's-Not-Amniotic-FluidTM.

All the meanwhile, the cloning vat's electronics are going to crap do to tiny-little microfilaments growing out of its solder joints because the now extinct world mandated lead-free soldering in electronics several decades ago.

A colony of 500 couldn't manage to keep this magical machine up to its minimal maintenance standards or feed it the endless quantities of consumables that it requires to run. Let alone one man.

If this machine allows any sort of ad hoc editing, he'd do much better to conserve the supplies and see if he can duplicate the X chromosome in one or more of the first zygotes.


Assuming the babies grow at a rate of 10 children per 9 months, and he has enough food and such to feed them all, he can make a maximum of 1330 people. If he lives that long, 1331.

It'll be hard to raise children in the first few years. Assuming all his children are exceptional geniuses like him, and that they respond well to a training program, by the time they're four or five they can help with rapid reproduction.

There will also be accidents, death to diseases, death from other things. Assume a population of about a 1000 by the time a hundred years have passed.


I don't buy it

Max 1-250 men will die happily everafter, for lack of spare parts and specialized expertise

Even if this man is a genious, he won't ever be able to reconstruct this advanced medical device on its own. Suppose he he can repair and maintain it, a single machine won't produce relevant offspring. Life expectancy for an ECG machine is usually 10 to 11 years, compare your machine in complexity, in the optimal case not needing spare parts during that period, you'd have 20-25 goes. But take into account your guy must be an absolute universal genious, all experts are gone.. and damage will occur at random: expected lifetime between service and recalibration etc is only 3-4 months. Two times per year you'll need some service, requiring specific knowledge. This is not a measuring device, so it may last a bit longer, however only if you are lucky, it can sit out the 9 months you require without malfunction. If you can't repair and replace the machine anymore by lack of spare parts, population growth will stop.


Even if the machine keeps working, it will take quite a while!

This single survivor can't possibly take care of all these little boys.. say he manages to keep that machine on for 18 months, he'll got 20 little kids to take care of now. If he's a good parent, he'd need to leave his darling machine and take a break for 11-12 years, every time, until the next generation.


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