In my setting there are large floating islands and much smaller floating islands that flow in random directions. Smaller ones sometimes contain mini ecosystems or ore veins that are extremely useful to larger islands. Battles and skirmishes are fought over these or even other larger islands between differing floating islands. Sometimes humans are fighting each other, other times non human entities need to be wiped out to secure an island or defend the home island.

There exists a class of medicine and drugs that greatly helps the human body fight internal diseases and bodily issues. It also makes the human body more capable of surviving on a floating island in the first place as well. Things like cancers, heart attacks, tumors/ general organ ware are curable so long as the issue didn't originate from an outside source. This means that even with a limited pool of people on the island, genetic disease or issues that you would normally see with an extremely homogeneous group are practically non existent. Genetic diversity doesn't rear the ugly head it does when you have a smaller sample size because of the medicine/ drug. This is important because things like a famine or lack of resources (such as water), might kill a great deal of people. But the population can recover without issue.

The drug mainly works on genetics and stopping bodily issues when it can start fixing the issue when its not terrible or out of control. Outside sources of infection or issue can cause rapid degeneration of the human body if not treated well enough in time. In that situation it has limited use there, but modern medicine and general medical practices can step in to save lives.

I.e someone isn't going to be able to survive sudden acute radiation poisoning since the drug works on prevention, mitigation and repair over a period of time. Trying to fix an issue after it happens isn't going to yield helpful results. An analogy is like being shot, but doing medical procedures to late. While the procedures are sound, they only work when done asap.

Because its a floating island, this drug is useful for keeping a population alive. It also means that older people are still able to function greatly as their bodies aren't ageing or being damaged at the rate humans in our world are. But at the same time this poses an issue, if the purpose of this drug is to help keep people alive and useful on the islands for longer, why is overpopulation not an issue? With that many older people in great shape on a floating island with limited resources compared to a country, after a few generations the population will explode and keep continuing to grow.

Limiting the drug on the population simply isn't an option (actually its a plot point for a different island, so for the main island its out).

Some ideas that I've considered are:

  1. Procreation means a total incompatibility with the drug and any medical practices that use the drug as a basis. Problem is, what's to stop a selfish society from deciding that they don't want kids. At that point you're practically signing up for death, even if it means you can have kids. Encouraging people to have children brings up the issue of a baby boom.

  2. The setting is so violent, each citizen past a certain age is required to commit X amount of service years every so often. Past a certain age people get the option of retiring or having longer breaks between their next tour of duty. There are a few issues that I have with this. One is that the military would want to hold onto veterans to train new soldiers. Second, an extremely elite cadre of veterans could basically live forever if they don't die in the service. Third, in order to get to this point of artificial culling, a lot of young people would have to die for this to make sense.

  3. Compatibility is a range, some are more tuned than others. Therefore the drug/medicine works better on some people than others. This immediately sets up a hierarchical issue whereby people can selectively choose partners so that offspring can live longer. Down the line the problem gets worse.

Essentially I need to have the ability to increase the lifespan of people without it causing everyone on the island to live for a long long time. People should have the potential to live long and be useful, but it shouldn't be the widespread norm to the point that it strains resources. The older people need to be able to fight and do day to day activities in life without much assistance. They cannot be stuck in nursing homes. Ideally I'd like to avoid eugenics or saying that past a certain age, people are executed (seems ripe for a revolution) or restricting it from the general population. Simply getting rid of it isn't an option as its a central resource that many islands and non human entities fight over. Basically if people aren't dying en masse to disease or the body deteriorating anymore, they have to be dying to something else.

At present I am considering rolling the above three points together and changing a few things. But I would like to hear some other arguments since I am not totally satisfied with the arguments above.

  • $\begingroup$ What is the technology level of your world? $\endgroup$ Jul 27, 2022 at 15:23
  • $\begingroup$ There are some real questions on how your drugs work. It works at a genetic level, but the drugs aren't introducing DNA, are they? The body only knows how to make what it is told to, so how are genetic disorders overcome? $\endgroup$
    – DWKraus
    Jul 27, 2022 at 18:05
  • $\begingroup$ @GiantSpaceHamster 1980s-1990s but there's far more digitization. The issue for the island isn't having the technology, its mass producing it and having the resources and space for major scientific breakthrough. As a result, things like microprocessors aren't widespread or as developed. The military and air force usually get the brunt of resource allocation, followed by hospitals/sanitation/farming. Civilian/general population are the last people to get these technologies. So, people aren't living at the technology level on an everyday level despite the island having access to the technology. $\endgroup$
    Jul 27, 2022 at 20:57
  • $\begingroup$ @DWKraus I'm not a biologist so I probably couldn't come up with a genuine/real reason that it makes sense or is plausible. From a computer science point of view, maybe assume it's like a vaccine that can be trained on a set of viruses, genetic diseases, human borne cancers/tumors etc. Train in this sense like how you would train an AI/ML model. But the reason it doesn't work on all bodily issues from external sources is because maybe the drug can't do it. Or just pure handwavium reasons. $\endgroup$
    Jul 27, 2022 at 21:13
  • $\begingroup$ That's fine, I AM a biologist. I left an answer with a set of solutions all compatible with biology. We'll leave the drug mechanics to handwavium, except as listed in the answers. $\endgroup$
    – DWKraus
    Jul 27, 2022 at 21:28

9 Answers 9


Many Polynesian Islands had this already, no need for drugs.

Population was limited by endemic warfare and blood feuds. Families with 10+ children were common. Sickness was almost unknown until the great unwashed Europeans introduced it.

All the kids were trained to fight in the knowledge that they may need to fight to the death at any time. No one formally declared war, you just assumed your neighbours wanted to kill you and you got them first if you had a chance.

Large areas of some islands have never been cultivated, it wasn't overpopulation in the sense of not enough resources that drove the main Polynesian expansion.

Peaceful visits from other islands would normally be treated very well as they were a source of stories, dance, trade and gene flow.

  • 4
    $\begingroup$ Ah yes, the natural solution to overpopulation. $\endgroup$
    – user253751
    Jul 27, 2022 at 20:25

Decreased Libido:

The drugs are affecting the desire of the people using them. People simply have less sex, and the levels keep going down over time. By around age 50, there is really no particular sex drive left. It is POSSIBLE to have sex, but without the impulse or enjoyment, it's just going through the motions for reproduction.


The drugs make you feel great - like, REALLY great. So much so, that as the users get older, they only feel any real pleasure from the drugs. Getting more drugs becomes their chief preoccupation, and sex is simply not of any great interest anymore (unless it is exchanged for drugs).


Your drugs are able to control when a woman ovulates. A woman must take a specific drug to go through a cycle. Since a woman must consciously choose to reproduce, there is no accidental conception. Given a choice, would you take the drug and go through unpleasant cycles if you weren't specifically trying to get pregnant?


Your drugs boost the immune system. But babies are seen by the immune system as foreign parasites. So like RH factor, eventually after one or two pregnancies, every woman will develop antibodies that cause pregnancies to spontaneously abort.

Underlying genetics:

While your drugs can treat the symptoms of genetic disorders, they don't have the ability to tell what good or bad genes are. Any trait that is lethal before birth causes fetuses to die before they are born. Sure you can magically cure any disease, but if 90+% of pregnancies never make it to term, birth rates will be extremely low.

Lowered metabolism:

The drugs slow down the metabolism, and as a result pregnancies are also slowed. So much so, in fact, that it can take a baby six or seven years to be born. This is 6-7 years of constant discomfort, and many women do all they can to avoid this long and unpleasant process.

Social Pressure:

All those oldsters don't want to compete with young people for resources. When resources become scarce, folks having new babies are ostracized and exiled. Abortion, widespread infanticide, and execution for petty childhood offences mean that few children if any become adults. Citizenship is only given to those who live to over 100.


All youth, at about age 16, are required to leave home. The must go out into the world and find a way to be successful. If they live long enough, they can come home and claim citizenship. This makes for a large number of youth who fail and die, or find a place elsewhere.


There is only so much drug supply to go around. It is expensive, and the sources of the drugs are some of the main sources of conflict. Successful groups with plenty of drugs must constantly fight to maintain their sources. This naturally means societies either restrict reproduction to match supplies, constantly fight to gain bigger supplies, or give up and live natural lives without the drugs.


The drugs cause 99+% of your population to only desire same-sex partners. While people can grudgingly have heterosexual sex for reproduction, it is an unpleasant chore.


The drug helps preventing aging related diseases and deaths, but does nothing to avoid fall related deaths.

And if you live on a floating island, exposed to winds which will be stronger than at ground level and with no restrains on its edges, it's a matter of time before somebody goes pluff, falling into the void and plunging to their demise.

In particular if the islands are small, the chances of being close to their edges are higher, and so the chance of falling. It can be so common that is considered as a matter of life.

Those deaths will help avoiding overpopulation.


If the drug drastically lowers infant mortality then population growth will halt naturally.

we see this in countries where infant mortality drops low enough, people have fewer children. Evolutionarily speaking this happens because when the chances of children dying is high people unconsciously have more children and invest less time and energy in each child because that is more successful in getting your genes into the next generation, once infant mortality is low the opposite is true your best bet evolutionarily is having only a few children and investing as much time and energy as possible into them.

population booms really only happen when a place is transitioning from one to the other. We see this over and over again in populations, infant morality drops and population growth drops a generation later.

enter image description here

Alternatively, keeping the elderly alive helps prevent population growth naturally.

The elderly don't produce children so the more of your population skews to the elderly the fewer children their are, your population can't grow quickly because most of your population cannot reproduce. This wil not stop population growth but it will drastically slow it.

  • $\begingroup$ I have questions about the first part, but the second part definitely sounds incorrect. Unless the old people are competing with the young for scarce resources -- and thereby raising rates of mortality and infertility among the young -- the survival of old people will not reduce the rate of population growth. You can get the impression of slowing growth if you're careless about which factors you hold constant, but if you take two identical, separate groups, A and B, then give B medicine that keeps people alive from 50 to 100, B's population will be greater than A's from then on. $\endgroup$
    – Beta
    Jul 28, 2022 at 1:35
  • $\begingroup$ @Beta in most societies there are limited resources so skewing the population towards the elderly slows population growth. It is not nearly as effective as infant mortality but the effect is measurable. $\endgroup$
    – John
    Jul 28, 2022 at 2:53
  • 1
    $\begingroup$ I've seen several hypotheses that the change to allow humans to live past menopause is one reason why we expanded so much compared to chimps. Grandmothers increase population as they help forage food for the grandchildren. Grandfathers actually cause more problems as they are still competing for reproductive rights. $\endgroup$
    – David R
    Jul 28, 2022 at 14:28
  • 1
    $\begingroup$ It appears that I have utterly failed to convey my point. $\endgroup$
    – Beta
    Jul 28, 2022 at 22:37
  • $\begingroup$ @beta your point fails because you assume the behavior of humans does not change as the population changes, its like saying if nothing else changes a growing population will grow until it starves to death, the hypothetical may be true but it is basically irrelevant because the underlying assumption is so far from what actually happens. There are measurable repeatable changes in how human populations have children based on the environment they grow up in. low infant mortality and elderly populations both trigger a switch to more K strategy behavior. $\endgroup$
    – John
    Jul 29, 2022 at 2:44

The drug makes people sterile.

Most people can have their first few children before they need the drug, but once they take it for the first time, they are sterile for the rest of their lives.

Pair that with your reason No 3 and you can't breed for compatibility for the drug anymore. As you can't select the ones that are highly compatible for breeding. (once you know they are, it is too late).

If you are afraid people might be too selfish to procreate anymore, make having kids a social goal. People want to have kids and they do, but sooner or later everybody needs the drug and can't procreate anymore.

Then there are still accidents to make sure your population does not overshoot and even a very long life ends sometime.


I think your questions answers your question. Twice

By famine

This is important because things like a famine or lack of resources (such as water),

Or by sword

Simply getting rid of it isn't an option as its a central resource that many islands and non human entities fight over. Basically if people aren't dying en masse to disease or the body deteriorating anymore, they have to be dying to something else.

emphasis added

No need for complicated explanations, your population stays low because there is only so much food to go around and that scarcity leads to famine or bloody conflict. Either of which will keep the population down.


I think no special reason is needed

If your world is technologically in 1980's-1990's this is close to modern technology level. Currently in most first world countries the birth rates are close to or in some cases below replacement - see this, it wasn't so different back in the 80's - 90's. As long as education level is similar to modern and contraceptives are available, population will not balloon naturally anyway.

The drug will make people age slower and thus stay fertile for longer, but if a couple does not want to have more than 2-3 kids anyway this will not lead to an uncontrolled population growth.

Additional factors are, it sounds like there is a lot of warfare in your setting, which will lead to people dying. Also, since people are living on islands there will be a shortage of space which will make families even more reluctant to have a lot of children.


Sausage party

Dudes, dudes, dudes. It is the island of ever-young dudes. They play the sports, argue about the rules, make wars on other islands, grill, and generally engage in never-getting-senile dudely activities. Valhalla!

There are many fantastic scenarios where all characters are dudes. For some reason Wind in the Willows comes to mind. Mr Toad! Especially in days past the lack of females was not explained. In more recent fiction, creators feel a need to increase the visibility and agency of female characters - the movie version of Lord of the Rings is an example.

Your island of spry old dudes is just that. Where did the ladies go? Did they decamp to some other island? Does the medicine not work for them? Were there no ladies in the first place? Grist for the prose mill.

  • 1
    $\begingroup$ Basically any software company. $\endgroup$
    – Tom
    Jul 28, 2022 at 23:44

The drug eventually drives people to death

The drug builds up in a person's body over time. This can then become a problem in two ways:

  • skipping a dose of the drug has bad consequences; or
  • maintaining a high concentration has bad consequences.

In either case, the effect I like is that the individual starts to have breaks with reality, brief spells during which they lose their sense of place or self. These spells become longer and more powerful, until the person has some fatal misadventure while spaced-out. They step off the island while hallucinating, or try to hug a warrior who is attacking them, or eat handfuls of dirt from the garden.

Essentially, long-term use of the drug substantially increases the risk of accidental death. This will lower the average life expectancy across the board.

It's also a pretty standard theme in fiction that anything which seems "too good to be true" is revealed to have secret negative consequences that more than compensate for the obvious benefits.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .