In the world, there are 4 billion happy, healthy Humans. In this case, thanks to the power of magic, it's safe to assume that they also live long, happy lives. Just like we do today! An Evil Villain Bad Guy has grown tired of them, though. He casts a terrible curse on Humanity- they are all sterile! Even those still in the womb!

This is obviously quite terrible, but how terrible?

The humans can fix this. It won't be permanent so long as they work fast enough on a counter-spell. Humanity will work towards fixing this as soon as possible of course.

How much time do they have to develop a cure before the species is irrevocably doomed?

  • $\begingroup$ until the last man standing, or two - Adam and Eve, version 2. $\endgroup$
    – MolbOrg
    Commented Oct 5, 2017 at 14:15
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    $\begingroup$ Reminder to close-voters: the OP can't fix problems if he is not aware of them. @Onyz Welcome to WorldBuilding Onyz! Can you please clarify what you mean? Are all humans forever sterilized and therefore doomed if they don't have any eggs/sperm frozen somewhere? Or do you wish for calculations on when humanity would irrevocably be too few in numbers to get back to a healthy population if they suddenly were not sterile again by the might of your magic? If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$
    – Secespitus
    Commented Oct 5, 2017 at 14:27
  • $\begingroup$ Ah sorry, I tried to imply that it was something the Humans could (and were trying to) fix. I was hoping for calculations on when they would "be too few in numbers to get back to a healthy population if they were suddenly not sterile again". Thank you for the help... $\endgroup$
    – Onyz
    Commented Oct 5, 2017 at 14:54
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    $\begingroup$ Onyz, if you could clarify what you're asking for in the question, I think would be an acceptable question. Without clarification, the naive answer is "You've got 20 to 30 years before all the current infants exit their peak fertility years." $\endgroup$
    – Green
    Commented Oct 5, 2017 at 15:05
  • $\begingroup$ As anon and elemtilas have pointed out 40-50 years is the limit on female fertility but also if you're anything over 30 years you will severely damage the quality of your male breeders contributions as well. The quality of sperm produced by men decreases as they age and starts to drop badly past the age of 25. It might not kill the population but it could hurt future fertility badly. $\endgroup$
    – Ash
    Commented Oct 5, 2017 at 15:06

10 Answers 10


Assumption #1:

Somewhere between 40 and 50 years. Any girl babies just conceived before the Curse was thrown down will have somewhere between 40 and 50 years before menopause sets in and they will no longer be able to easily bear children once the Curse is lifted.

Here I assume that Evil Villain Bad Guy was smart enough to include cryogenically preserved eggs and sperm in his Curse.

Assumption #2:

No worries! (Well, not many worries!) If Evil Villain Bad Guy is unaware of the cryo-preservation industry, then it would just be a matter of choosing high quality brood-mothers to be implanted with viable and unaffected fertilised embryos.

The earlier this programme can be implemented, the better chance there will be of allowing civilisation in general to continue. Due to the great expense and the high technology of this industry, it goes without saying that broad swathes of Earth will be utterly uninhabited within 100 years.


This programme is the biggest crap shoot in history.

We all know that IVF type technology doesn't always work --- success rates are not that high. And once a given facility's stocks of embryos are used up, well, that's the end of the programme in that region. There certainly won't be enough new humans to keep civilisation going after the Great Death; and there may not be enough to even restart anything like civilisation as we know it.

The assumption here is that about half of the approximately 400000 preserved embryos in the US will be born. This is barely enough people to form a good sized city.

You will need to institute a very serious programme of placement, education and indoctrination for every single one of those 200k children. A cradle of new civilisation will have to be located --- one with a reasonable climate and fertile soil. Once settled there, they will have to be educated in a very wide variety of sciences and technical arts --- they will need chemists and electrical engineers and nurses and doctors and civic planners. But they will also need to be educated in social and cultural arts as well. Keep in mind that most of the world will be depopulated and all those cultures and histories will die with those people. An awareness and respect for those past cultures must also be inculcated in the new civilisation.

I would also suggest that, under this assumption, the Doomed should also create a programme of shutting down, securing and cleaning up the mess that will soon be generated by their gradual departure from the Earth.

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    $\begingroup$ Add to this the development of a comprehensive program to handle the Great Death. 200K+new births can't handle the load of dealing with 4Bil. people and the disease, etc. created when they die. What happens when there's no one to staff the assisted living centers, mortuaries, etc? People would need to willingly go someplace to die and be buried by buldozer. Euthanasia would be a welcome relief to the survivors and an entire new social view of death would develop. $\endgroup$
    – JBH
    Commented Oct 5, 2017 at 16:28
  • $\begingroup$ More like 7bil, but yeah, excellent points! I didn't want to get into that aspect of the programme for the Doomed. I guess that would be part of shutting down and clearing up! Towards the end, I suspect there's just going to be a number of unburied bodies lying about as the last of the Doomed finally leave the stage. ~~ Also, I wouldn't burden the 200k with all that. Let the dead bury the dead. That's why they've been separated and placed in a new community of their own. They should be pretty effectively sealed off from the rest of society. By the time they go exploring, it will all be ruins. $\endgroup$
    – elemtilas
    Commented Oct 5, 2017 at 18:32
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    $\begingroup$ @JBH, infectious dead bodies is a myth. There are very few diseases that can be transmitted through contact with cadavers. The only serious risk is water contamination by a huge number of rotting corpses. $\endgroup$
    – Olga
    Commented Oct 5, 2017 at 18:55
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    $\begingroup$ @Olga, I did not know about those reports, thanks! $\endgroup$
    – JBH
    Commented Oct 5, 2017 at 18:59
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    $\begingroup$ What happens when all the embryos are used up? My interpretation of the curse is that those kids would grow up to be sterile as well. Have we just prolonged the inevitable by one generation? $\endgroup$ Commented Oct 6, 2017 at 13:05


It is possible to create new animals by cloning. This technology has never been developed in humans because of severe ethical issues, but faced with extinction, it'd likely be up and running within a decade. The core principles are all understood.

However, this assumes the mechanism of infertility allows implantation of embryos. Even if not it is possible humanised animals could be used for incubation.

To address some objections raised in the comments:

Cloning technology is imperfect: this is certainly true, however it is already the case that cloning is commercially viable. There is a biotechnology company in China that is producing 500 cloned pigs a year, while the cloning process itself involves a high degree of technical sophistication, none of the steps are prohibatively expensive or difficult in themselves. Faced with global infertility, vast sums of money will be made available for research, and enormous pressure placed on elected officials to remove legislative barriers. Under these circumstances we should expect viable cloning techniques to become routinely available in the developed world within a decade, probably faster. Cloning should be inherently about as expensive as IVF but with the extraordinary levels of demand we should expect economies of scale to drop prices fast. I would expect reproductive cloning to be available at around $1000 dollars pretty soon. Too expensive to be routinely available in the developing world, but no problem for developed countries with universal healthcare.

Cloning suffers from the same problems as IVF: IVF is only performed on clients who have exhibited problems conceiving the old fashioned way and are typically older. Accordingly success rates are far lower than we should expect from people who do not have these problems and thus success rates should be closer to the far higher rates observed with egg donation.

Telomere shortening: while this was a concern, it turns out not to be a problem. Even if it was a problem, it should be possible to develop a solution by temporary activation of the telomarases that naturally restore telomeres during normal reproduction.

Accumulation of mutations: cloning will inevitably accumulate mutations. This could be mitigated by long term storage of DNA from the original source but even this would be imperfect since the DNA is likely to slowly degrade even under ideal storage conditions. However, the accumulation of mutations is unlikely to render the process non-viable for a great many generations (plants and animals that self are known to survive for 100s of generations without apparent loss of viability, although cloning methods may induce higher mutation rates so an exact comparison is not possible), and there are a range of existing techniques that could developed to repair (e.g. CRISPR) or screen embyros (e.g. shotgun sequencing) and prevent transmission of harmful mutations. Moreover, in the hundreds of years available to humanity, the development of in vitro techniques to restore crossing-over and mixture of genes as per natural sexual reproduction seems much more likely than not.

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    $\begingroup$ It can't be indefinitely because once every human is dead, no one can do the actual cloning. $\endgroup$ Commented Oct 5, 2017 at 17:09
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    $\begingroup$ The curse doesn't need to be lifted, to start cloning $\endgroup$
    – Christian
    Commented Oct 5, 2017 at 17:57
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    $\begingroup$ @A.C.A.C. the clones can make more clones themselves $\endgroup$ Commented Oct 5, 2017 at 18:05
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    $\begingroup$ Not indefinitely. Cloning technology is nowhere close to perfect. Very few clones have ever been successfully born. Add to this the difficulties of IVF as already discussed. Society will almost certainly collapse and as the technology breaks down and no one is left to sort it out, that will spell the end. $\endgroup$
    – elemtilas
    Commented Oct 5, 2017 at 18:37
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    $\begingroup$ Given the existence of magic, I think most of these objections are moot. $\endgroup$ Commented Oct 8, 2017 at 9:03

The time will depend on your definition of 'irrevocably doomed'. Based on your wording, it seems that you are focusing mostly on the biological survival of the species. However, there is also a cultural/civilisational aspect. In some sense, the loss of civilisation is also an extinction.

Biological survival: 50 years to infinity till the humanity is doomed

Biological survival means that the species do not go extinct. However, it does not guarantee retaining culture and civilisation.

The conservative estimate assumes:

  • no serious medical advances are made in the near future;
  • sterility means not only sterility of eggs and sperm but also inability to carry a baby to a term;
  • frozen eggs, sperm, and embryos were rendered infertile.

As others noted, modern women in developed societies are capable of bearing children till the age of 50. Some women do not experience menopause till their 60s, but childbearing is extremely risky at this age.

Minimal viable population for the survival of species is approximately 4200 individuals. This has to be local, not global, population. Considering that 1) it is much harder to get pregnant and successfully deliver a baby for mature women; 2) babies are at much higher risk of genetic disorders (both parents age is a contributing factor here), the latest time when the curse must be lifted is when about 10,000 women are still fertile. Children and mothers must be transported to a single location with the mild climate and fertile land to ensure the species survival.

The optimistic estimate can be achieved through:

  • human cloning and genetic engineering (sexual reproduction is overrated anyway :) ):
    • only cloning can be enough if we develop a way to create perfect copies (no mutations), but humanity will be unable to adapt to changing environment;
    • genetic engineering solves the problem of imperfect clones, it also allows to imitate evolution;
  • eternal life and youth:
    • the species does not have to have babies in order to survive if they are immortal.

Cultural survival: this is a bit tricky

Civilisation and technology heavily rely on population size. It is not possible to keep the modern level of development with just 10,000 people. I saw estimates ranging from hundreds of millions to billions of people. So, if we are optimistic, the curse must be lifted when it is still possible to deliver, grow, and educate about half a billion of babies. This gives probably 10-20 years. In a pessimistic scenario, the time shortens to a couple of years (maybe a decade, but not longer).

A possible workaround for the population size problem is total robotisation. If everything (including robots' repairs) is fully automated you only need to take care of the biological survival.

Another possibility is abandoning biological survival altogether. The entire world population can be digitised and uploaded to the servers. Of course, total robotisation is a must for this plan to succeed.

You also must take into consideration the effects of total infertility on society. This was addressed, for example, in The Children of Men.

  • $\begingroup$ If the MVP is ~4k, why does your cutoff (10k women) more than quadruple the total population (20k men and women)? Safety margin? Also, note that it's an estimate. Others project anywhere from 100 to way over 100k. There's no way to know until we find out. $\endgroup$
    – Mazura
    Commented Oct 6, 2017 at 0:21
  • $\begingroup$ @Mazura, first of all 10,000 men aren’t needed to impregnate 10’000 women. Also we are talking mature first-time mothers, hence, the probability of a difficult pregnancy is very high. Some women will miscarry, some women will give birth to children with genetic diseases, some women will die in childbirth. It’s better to err on a safe side. To address MVP, here we are talking only probability of the biological survival of the species. You can avoid inbreeding with fewer individuals, but a small population has a high risk of dying off due to infection, diseases, natural disasters, etc. . $\endgroup$
    – Olga
    Commented Oct 6, 2017 at 1:55
  • $\begingroup$ "eternal life and youth" as long as no one ever dies in an accident (or gets murdered)... $\endgroup$
    – WernerCD
    Commented Oct 6, 2017 at 4:43
  • $\begingroup$ @WernerCD, truly immortal beings cannot die or be killed. This world has magic, true immortality is possible :) $\endgroup$
    – Olga
    Commented Oct 6, 2017 at 6:48
  • $\begingroup$ @Olga "True" immortality has different aspects... I doubt you're truly immortal if your hands are tied and you are buried in concrete... or "accidentally" fall into the ocean... $\endgroup$
    – WernerCD
    Commented Oct 6, 2017 at 14:54

The curse actually contains more questions than it initially appears. It would strongly influence our sexuality, behavior and even global economy.

In a scenario where people wouldn't worry about babies, surely the STDs consequences would accelerate our extinction even more, due unprotected sexual relations.

We also have to observe that having children is beneficial to living longer, as you create affectional bonds which make most of people adopt a more responsible and even more conservative lifestyle - you tend to drink less alcohol and drive more carefully, or to avoid risky hobbies, such as mountain climbing, for example.

Surely, the main factor which contributes to our extinction is the zero population replacement rate caused by the curse, but this process would be faster than 40-50 years, because of our new sexual behavior - possibly more exposed to STDs - and our new lifestyle originated from the lack of family links.

Although it is hard to estimate, I would say it is at least 10% faster, then 35-45 years.

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    $\begingroup$ I really like your answer because it brings up a lot of complications the highest answer doesn't take into account- and implies that there are more as well- but it isn't self-contained (understandable) so I've selected the other one. Thank you though! :) $\endgroup$
    – Onyz
    Commented Oct 9, 2017 at 12:59
  • $\begingroup$ And think about the economic consequences: nobody will have children, so no heritages or savings for your children's university and it would inject a huge amount of money on the economy. Crazy! $\endgroup$
    – Victor F
    Commented Nov 27, 2017 at 19:01

Magic aside, the question is how was the sterility achieved? Would the sterility continue with the next generation if we bypassed reproduction?

Already we have advancements in cloning, generating sperm or eggs from skin cells, IVF and artificial wombs.

Even if it could never be reversed, humanity has almost achieved the ability to reproduce without reproduction. If an event like this happened I almost doubt they would look for a counterspell but would actually leave it in place as a means of control.

Investment would be put into artificial reproduction because suddenly the industry would be worth trillions world wide. With investment of that level, would the powers that be want people being able to reproduce for free anymore?

Biologically 30 years would be the point of no return. After that point there wouldn't be the population of breeding age people to rescue humanity from the collapse of society.

Up to 50 years society would need to rebuild almost from scratch. After 50 it's too late.

Technology would more than likely have a solution within 10 years when it would have all the best minds and unlimited budget.


Answer 1: never, if you sterilize all of humanity then the race is doomed because no one can ever reproduce.

Answer 2: if you mean temporary sterilization, then, women (on average) can roughly remain fertile till the age of 40 (plus or minus). So you have roughly 40 years to reverse the curse or humanity is doomed.


If everyone is sterile, then the species is already de facto extinct. Once all the living people die, they are gone forever.

If there is a way to reverse it (say, with scientific reasearch), the amount of time you have is that which consists of the productive life span of the researchers. If the researchers don't solve the problem before they retire and die, then the species is doomed.

I don't think that issues like the maximum age of female fertility and such enter into the picture so much because that assumes a particular solution to the problem. The solution could arise from cloning from non-reproductive cells.

(Any solution to the problem which is rooted in a re-start of regular female fertility will no longer be workable once the last person who is currently a baby has aged past reproductive age. But anyway, that estimate is only within a few decades of the one based on the last person who is currently a baby no longer being able to conduct research into the problem.)

We also have to consider that children have to be raised; it can't just be that the last few people somehow manage to produce fertile offspring and then die.

However, there is a completely different possibility.

The exinct human species could be resurrected in the far future by a different intelligent race, using preserved cells. Under this possibility, the time limit is much, much more generous.

Another possibility.

Humanity develops AI, which continues the search for the solution after the last human dies. When AI succeeds in making human babies (which are capable of reproduction upon maturity), AI also raises those babies. The AI-raised babies then bootstrap a resurgence of humanity.

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    $\begingroup$ "I don't think that issues like the maximum age of female fertility and such enter into the picture so much because that assumes a particular solution to the problem." The question is worded in such a way, "...without causing extinction", that there will be a reversal of the Curse. So yes, the maximum age of female fertility is very much at the heart of the matter. That's the terminus ad quem. If you wait until the youngest people alive are 78 year olds, then extinction is guaranteed. If the Curse is lifted while there are still some 47year old women out there, then they'd better get busy!! $\endgroup$
    – elemtilas
    Commented Oct 5, 2017 at 18:55
  • $\begingroup$ @elemtilas You're assuming that the solution to the extinction curse requires women under 50. I.e. that some octagenarian researchers cannot produce a baby "just using science": create an embryo and gestate it without starting with sex cells and without using a womb. $\endgroup$
    – Kaz
    Commented Oct 5, 2017 at 19:22
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    $\begingroup$ @elemtilas (By the way, the ~47 limitation is on the women being fertile with their own eggs. Women a bit past fifty can be pregnant with a donor egg (though not without lowered risks of a successful pregnancy and delivery, and complications). This leads to the imaginary scenario that scientists have produced some embryos by some means, and some group of 55 year-old-women (the youngest available by then) are able to bring some of them to term. $\endgroup$
    – Kaz
    Commented Oct 5, 2017 at 19:23
  • $\begingroup$ Well, the basic assumption is that we're trying to avoid extinction. I was reading that during past near-extinction crises there were as few as maybe 5k to 10k individuals. Some of these will be children, some will be old, some injured or sick. You might have 2k to 5k people healthy enough to successfully mate and stave off extinction. You can probably do it with a few thousand fifty year old women. I just don't think that a few octogenarian scientists can lab create enough unaffected people to make for a successful stopgap. $\endgroup$
    – elemtilas
    Commented Oct 5, 2017 at 20:38
  • $\begingroup$ @elemtillas The question is about the "longest time", and so that is the worst case scenario, in which humanity escapes extinction by a hair's breadth, so to speak. In the worst case scenarios in which humans themselves still solve the problem, it is inescapable that everyone has gotten as old as possible without missing the last possible deadline. $\endgroup$
    – Kaz
    Commented Oct 5, 2017 at 20:56

The existing answers ignore the effects of aging. Yes, some women can bear children into their 40's and 50's but there are two factors to consider:

  • fertility declines as you age. More women than ever are having late-in-life children, but many of them are doing it with medical intervention. You haven't actually stated the technology of your world, but it's very rare in fiction to see high technology (cloning, in-vitro) co-exist with magic (curses) so I'm going to assume that that medical intervention isn't available in your world

  • genes degrade as you age, and this is true for both women and men. Your extinction question implies that after the curse is broken, humanity will not just resume breeding, but that that breeding will produce a healthy, viable population that can bounce back from the population slump. So you really don't want a high incidence of things like Down's Syndrome, &etc.

These factors mean that you don't have 40-50 years to break the curse. You probably really want to get this done in 20 to 30 to have the best chance of recovery.

  • $\begingroup$ Actually, age is at the heart of the answer! Keep in mind that the scenario asks for the time frame beyond which humanity will be "irrevocably doomed"; not the last ideal time-frame for resolution with the least number of difficulties. (Because the answer to that question will be "five minutes after the Curse was pronounced, they found the cure!") There are certainly risks involved for 40 and 50 year old mothers. But the alternative is extinction. $\endgroup$
    – elemtilas
    Commented Oct 8, 2017 at 1:48
  • $\begingroup$ @elemtilas I'm not talking about the risks to the mother; I'm talking about genetic risks to the children. $\endgroup$ Commented Oct 9, 2017 at 14:59

Short answer: Around 50 years.

Long answer:

If the humans live the same age of our world, then you must consider that the maximum reproductive age of women. According to wikipedia, "The oldest mother to date to conceive, was 71 years, and the youngest mother, 5 years old". So, since currently there are children in your world, they can become pregnant until around the age of 70, but with risks. The ideal pregnancy is to happen before 50 years old, and it can vary from woman to woman, so it is not safe to trust new births to woman after 50 (they may not be fertile anymore).

But this answer can vary depending of what kind of magic is possible. Since it's possible to avoid newborns with magic, is it possible to conceive a baby with magic? Or at least ensure that the mother and the children won't die on advanced ages (like 70).

Once new children are able to born, if there are enough new children and adults, the continuity of humanity is ensured. But in terms of extinction, if a small group of 2 men and 2 women (all able to reproduce) survive, then humanity is, technically saved, since will be possible to reproduce without incest.

However, other things must be considered on a world where everybody is sterile, like wars, new religions (which may also include fanatic people who believes that this is the fate of humanity and start hunting pregnant woman and also those who are trying to revert the curse), economic depression (since the population will start falling), slavery and even sexual diseases. They all can shorten the time humanity have to find its cure. The more time passes, the worst becomes the scenario.


If all are sterile, then the length of that generation. The odds on finding reversible answer decrease as time goes on - as experts get older and die off, but the last born would have to get up to speed on the current research which takes research prospects away from researching (but not all people are great researchers). Depending on the reversal and the length of time it takes, it has to be done within the fertility period of the females, and also enough females to retain a genetically viable population base.

Also there would be factors such as old age care (with the imminent disaster do we expect the elderly to execute themselves to save resources for the research and cure? But also we no longer lose productivity to child raising, and after a few years teachers, carers, and producers of young people items would be freed up to do more productive work), although those same freed up people would be also aging along with the rest of the population.

The other side effect is our current financial economy would completely collapse as it is based on exploiting a continuous supply of active, ignorant, young people to keep it afloat. (schools, universities, anywhere with low skill/low pay workers would go out of business as their current low level employees skilled up but couldn't be replaced)

  • $\begingroup$ You seem to have missed the question. How long is that generation? How long is the fertility period of the as yet unborn women? How many of them are needed to be genetically viable? $\endgroup$
    – Brythan
    Commented Oct 8, 2017 at 2:51

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