I was brainstorming with a bunch of friends about a story with more than one sapient species on a planet. The idea was to have different lifespans for each species as part of their differences.

I thought about having the usual humans with a standard 70 years lifespan and other species with ten (10) or a hundred (100) times longer lifespans but then the idea of a species with a shorter lifespan came up.

These species are supposed to be able to create a fully functional civilization with culture and some technology and given that most cultural and intellectual endeavors and most skills, blacksmithing, for example, take a lot of time to developed I worried that if we made their average lifespan too short they would not be able to form any sort of civilization.

My question is: what do you think is the minimal lifespan that would allow a species to develop a functional human-like civilization? By this I mean they have some sort of culture like music and religion and technology, like metalworking or masonry, academic pursuits like mathematics and science, and functioning governments and economies et cetera.

Also these species are also as smart as humans, if they are super geniuses then the question is pointless. And lack magic or superpowers that could let them transplant knowledge from other individuals into themselves. Basically they cannot cheat to learn stuff

  • $\begingroup$ You said there were multiple species of intelligent life on this planet, right? So each could adopt culture from the others, along with technological developments? Or am I misunderstanding? Once one intelligent species developed culture, the others could simply copy (as long as the body plan/environment were reasonably close; dolphins show no sign of becoming "civilized") $\endgroup$
    – DWKraus
    Jun 24, 2020 at 2:48
  • $\begingroup$ intelligence is a messy affair, sea turtle are born with inert ability to track ocean current but human on the other hand have to learn the skill and develops equipment just to best the turtle. So you need a mechanism to develop complex behavior to compensate for the shorter time frame ;D $\endgroup$
    – user6760
    Jun 24, 2020 at 2:55
  • $\begingroup$ Consider genetic memory $\endgroup$
    – DKNguyen
    Jun 24, 2020 at 14:45
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    $\begingroup$ "And lack magic or superpowers that could let them transplant knowledge from other individuals into themselves." Are written language and books allowed? Because that's how a lot of humans do transplanting of knowledge from other individuals. $\endgroup$ Jun 24, 2020 at 17:44

8 Answers 8


The defining quantity for cultural creature lifespan is generation-to-generation data transfer ratio.

Culture is something to be taught, non-instinct part of a behavior. This means that cultural creature needs to have enough lifetime to:

  1. Be taught
  2. Apply knowledge to support those who are on stage 1 and 3
  3. Teach the next generation

The ratio between these periods varies greatly on the type of civilization. For ancient times (Sparta - Rome) stage 1 was about 10-15 years, stage 2 was about 20 years (since very low productivity) and stage 3 was about 3-5 years (on average - one teacher teaches 3-5 students). For modern time ratio is 20-25 (up to 30-40 for top tech) / 20-30 / 0,001 - 1 (one teacher teaches up to thousand students in their lifetime).

It means that for an ancient civilization minimum average lifespan should be no less than 30-40 years and for modern - no less than 40-55 years.

Lesser lifespans would prevent knowledge from passing through generations and thus culture would simplify and degrade.

But this is true for humans. For, say, cyborg civilization teaching process might be much shorter - about days, and cyborg-years to support cyborg infrastructure be quite small (due to automation) - about, say, 5 years per cyborg. This would give us that 5 years is enough to support and 10 years enough to support and progress this cyborg culture.

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    $\begingroup$ I think this is the key concept indeed. This is not so much lifetime, as much as the ratio between lifetime and learning rate. If the species live 10x faster (accelerated time bubble) or 10x slower (decelerated time bubble) then civilization still progresses even though the lifetimes, from the outside, are 10x shorter or 10x longer. $\endgroup$ Jun 24, 2020 at 14:44
  • $\begingroup$ The average ages of having their first and last children also factor into this. $\endgroup$
    – cowlinator
    Jun 24, 2020 at 22:53
  • $\begingroup$ Also, have enough time to generate new knowledge $\endgroup$
    – Plinth
    Jun 25, 2020 at 2:43
  • $\begingroup$ @cowlinator, no, that is not a factor. In period of intensive use of child labor common practice was older workers (10-12y) were teaching newbies (5-7y). Since all ages are present at any given time the only demand is that breeding is enough to sustain population numbers $\endgroup$
    – ksbes
    Jun 25, 2020 at 6:07
  • $\begingroup$ @Plinth, this is exactly what happening at stage 2 (among the other things) $\endgroup$
    – ksbes
    Jun 25, 2020 at 6:08

I think the lifespan should be such that 3 generations can coexist at any time, allowing the grandparents to help the parents in raising the children.

This would allow for a more efficient transmission of knowledge through the generations and resource collection, since the parents can dedicate more time to it instead of chasing the babies.

Thus, if sexual maturity is reached at X years of age, the lifespan should be at least 3X.

  • 2
    $\begingroup$ As I tried to write my own answer, nearly all of the issues I brought up are a reflection of L.Dutch's answer. The species must be capable of learning quickly enough to establish the beginnings of a vocation or career by X years of age. For humans that's 18-30 leading to a lifespan of 54-90. That's the only thing I'd add. The OP's species can be as short-lived as they want so long as they can cram for the test in that first third of their life. If they can't do that, they'll stop at the highest tech level they can train for (and maybe a hair beyond, but that's it). $\endgroup$
    – JBH
    Jun 24, 2020 at 17:10

3 years. But their ancestors lived a lot longer.

In the remote past your species was much like humans, and developed science and arts (and war, and medicine) as we did. These skills were usually passed in the family.

Individuals who were better adapted to their skill had access to more resources and so had better genetic fitness and reproduced more. Evolution can happen faster with shorter generation times and so time to reproductive maturity grew shorter. These things grew up and had kids fast. A consequent is that they died fast too.

The result now is a caste system, whereby strains of this species are adapted for the skills they perform, like ant castes.

ant castes

This is true for the artisans and craftsmen, the leader / scientists, and especially the warriors who are capable of frighteningly fast reproduction when their kind is needed.

Selective pressure on the physicians went the other way and the doctors are functionally immortal.

Concepts lifted liberally from The Mote in God's Eye. If you like high science fiction do not read the wikipedia article (spoilers!); just order the book. It should be required reading for would-be worldbuilders.

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    $\begingroup$ +1 for recommending Mote. It (and its sequel) should be required reading for worldbuilding. $\endgroup$ Jun 24, 2020 at 17:59

Tl;dr: The lifespan is not the issue. The real question is how long it takes an individual to develop from perception to maturity and life span only balances the drawbacks of a long childhood. And there is no minimal life span/ childhood for the way a society functions will change gradually with this or any other factor to the point that one can meet any single condition with any lifespan as long as the rest is built accordingly.

Your mistake is to assume their civilizations function in (at least basically) the same way as ours. Them having the same habits as we do is quite unlikely and becomes even more improbable the greater the difference in any given attribute and any given direction is.

A functioning society can easily be established with a lifespan of just a month - it just would not look and function like our own. Workers of social insects don't usually live long (usually months, rarely years) but the hive can still learn. Any ant- or beekeeper can tell you that each people has it's own personality and it is not unheard of that an ant people learns stuff over the cause of several worker's lifespans. The individual might be less intelligent than a human but they have a really strong connection to one another and for reasons still unknown to us, even existing social insects can create structures and solve problems that would be a real challenge for us. It is less of a far fetch to assume that a species like that would be able to evolve a literal hive mind or that the individuals become more intelligent (still far less than humans) but keep their hive connection and compete with us on equal terms that way than to assume that any civilization with considerably less life span would function similar to ours. The more time and energy is consumed by an individual before they contribute to their society, the more they have to return later on in order to make it work. A species that is fully grown and developed after a year or two does not have to be as smart as we are and even if it is, it won't be able to develop craftsmanship in the few years before it dies. Take cuttlefish for example. They can manipulate objects at least as keenly as we can, their intelligence rivals our own, in captivity, they show boredom, do juggle, solve puzzles and so on but they do not craft nor do they create a society.

On the other hand, species that have even longer development than we do are going to live far longer and need to learn the heck out of their environment and create machines, computers, and the next big things just to stay in business.

Rivaling humans while making choices and forming one's habitat as a society can be done with reproduction times down to hours e.g. with adapting information in the DNA.

If you insist on a human-like system, the most important trait is that parents care for their young until they have profound skills in their profession so an individual must be strong and able for at least a bit longer than the entire childhood of their children. Given there are several children per year and couple (if couples exist) we can assume that after maturing, two years suffice for mating and childbirth, and then we need the development time from conception to adulthood a second time (parenting). How long do they grow? If they are small but smart, three years should be ample. The most extreme human-like beings would need about eight years of "safe" live. Make it more extreme and have older children teach the young (similar to some forms of military organizations or schools of martial arts) and you can trim it down to five years. We could go on and make it less human like with shorter lifespans until we are down to Schätzing's hive-minded bacteria.


On Earth, there is one species which is known or believed (by its members) to be intelligent and to be civilized.

There are a number of other species of large brained mammals which might possibly be intelligent beings, though none of them are civilized.

If in the future ways to communicate with those species on equal terms are invented, it might be possible for humans to teach them how to develop advanced technology. In such a case the number of civilized species on Earth would rise from one to a higher number, perhaps as high as about a hundred.

I note that a majority of the potentially intelligent species on Earth are cetaceans, and they lack limbs useful for manipulating their environment, and also live in the sea where making fire to smelt metals would be a problem.

In Larry Niven's story "The Handicapped" a company sells artificial limbs to "Handicapped" species such as dolphins and Bandersnatchi, and a representative of the company arrives on the planet Down to investigate whether the sessile Grogs are intelligent and potential customers.


Thus it seems likely that the various species of possibly intelligent beings on Earth are more likely to become members of human civilization instead of developing separate civilizations on their own.

And possibly that may be the pattern for habitable planets in real life, that a number of different species of intelligent beings evolve at the same time, and one of them develops civilization and the others eventually become part of that civilization.

Of course the unified civilization of all intelligent species which might hypothetically develop might later splinter into separate civilizations for each separate species.

In any case, it might be a good idea to investigate the life spaces of the various possibly intelligent, though not (yet) civilized, species on Earth to see how much variation in lifespan there is among potentially intelligent species on Earth, and perhaps use that as model for your fiction.

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    $\begingroup$ "For instance, on the planet Earth, man had always assumed that he was more intelligent than dolphins because he had achieved so much—the wheel, New York, wars and so on—whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man—for precisely the same reasons." (THGTTG) $\endgroup$ Jun 24, 2020 at 18:02
  • $\begingroup$ Oh, and don't forget the Mice. $\endgroup$ Jun 24, 2020 at 18:02

An Alternative Approach

Most answers here focus on teaching, generations and degeneration from an earlier state. I'd like to turn these, all be it fascinating and functional, concepts on the head. The deeper issue most answers touch on is teaching. Teaching and even the concept of civilisation are at their roots about the accretion, discovery and optimization of memetic ideas. Memetic ideas are rather abstract in human civilisation and are transmitted via the many flavors of teaching between generations. What if ideas take a more physical "hardware" form?

Enter Turritopsis dohrnii, the Immortal Jellyfish.

enter image description here

Like most other hydrozoans, T. dohrnii begin their life as tiny, free-swimming larvae known as planulae. As a planula settles down, it gives rise to a colony of polyps that are attached to the sea-floor. All the polyps and jellyfish arising from a single planula are genetically identical clones. The polyps form into an extensively branched form, which is not commonly seen in most jellyfish. Jellyfish, also known as medusae, then bud off these polyps and continue their life in a free-swimming form, eventually becoming sexually mature. When sexually mature they have been known to prey on other jellyfish species at a rapid pace. If a T. dohrnii jellyfish is exposed to environmental stress or physical assault, or is sick or old, it can revert to the polyp stage, forming a new polyp colony. It does this through the cell development process of transdifferentiation, which alters the differentiated state of the cells and transforms them into new types of cells. - Wikipedia

The key thing to understand here is that Turritopsis Dohrnii reverts to an earlier stage, beginning its life cycle anew. This is an example of intergenerational data transfer. True, Turritopsis Dohrnii only transmits genetic information, but what if it were more complex and could genetically alter some special sequences of its genome? Everything a member of this species knows gets not only saved in long term memory, but also in a genetic data storage organ.

As soon as a member of your species dies or is hurt badly, it commits suicide. The data from the genetic storage organ is then mixed with the seeds the dying one turns into. This might offer a really interesting reproductive cycle and has fascinating social implications. The species might be entirely asexuell or hermaphroditic, though an aproch to sexual reproduction is also conceivable.

If it is asexuell it might be a quite solitary species of lone geniuses, somewhat like the Jaghut from the Malazan series. They might live in symbiosis with viruses to use horizontal gene transfer to compete with or even outcompete the adaptability of sexual reproduction. They will probably have a very alien sense of self, as their memories have lived through a thousand bodies. Apperence and physical attributes might matter very little to them and concepts like childhood and age would be utterly alien to them.

If they are hermaphrodites or sexual, they'll most likely just exchange sperm packs like octopuses do and be done with it. Even the idea of relationships and marriage would be utterly rediculess to them, given that they would have a very long view of the world and would perceive all partnerships as necessarily temporary.

So, here are my ideas. I hope that you find them useful as what I'm suggesting might be a bit more alien than you bargained for.

PS: One could argue that this species isn't short lived at all but biologically immortal. This depends on what information is passed down the next generation. This could range from just factual knowledge, a database and nothing more, to biological mind uploading. Depending on where they are on this scale, they are either short lived of effectively immortal.


My answer is a modification of L.Dutch's, but I see other answers making similiar assumptions about the parents alone raising children.

The first and third generation do not need to overlap. Rather, lifespans need to be long enough that the oldest children in the extended family can care for the youngest while the parents resume their civilization-building activities. If older generations overlap it is undeniably a bonus, but not strictly necessary for the minimal lifespan.

From the Paleolithic to Bronze and Iron Ages, human life expectancy hovered around 30 years, ±3. Menarche began, as it does today, between the ages of 7 and 13 or 25-50% into the lifespan. This gives us a narrow window of just a few years in which children are physically capable of helping to raise younger children before they set off to start families of their own. Assuming age 10 for the first successful pregnancy and one successful birth every two years, by age 16 the first child (age 6) will be capable of basic assistance with the third; by age 18 the first and second child will be capable of minding the third and fourth for most of the day.

So, that leaves us with two key variables to work with: the age an individual is physically mature enough to help care for others, but not have children of its own, and the immature share of the lifespan prior to that. In humans I'd argue at a minimum the latter is 5 years, and the former (based on the above) is 5–8 years. Combined this is 33%+ of the lifespan, implying by the 10th child (using the above assumption) of the first generation, the second generation is already several children along itself, at or near the point they can begin to help their aunts and uncles raise their cousins and siblings.

It would seem trivial then to say the solution is to minimize the immature stage and maximize the mature but pre-childbearing stage, so long as the two combined do not exceed the length of the third, childbearing, stage. If you hold to the human-like constraints, this puts the minimum lifespan around 20, with little room to compensate for death and disease.

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    $\begingroup$ No. You're mixing up life expectancy with how long people lived. In a society such as ours there is a reasonable correspondence, but your Paleolithic guy didn't generally die at 30. Rather, a lot died young. Plenty of people lived well past 30, but a lot died in infancy. $\endgroup$ Jun 25, 2020 at 0:40
  • $\begingroup$ I don't see what any of that has to do with answering the question or how I arrived at this answer. Paleohumans who lived to 50, 70 or 110 have nothing to contribute to a question of minumum lifespan. It's entirely about maximizing the utility of youth. $\endgroup$
    – rek
    Jun 25, 2020 at 18:10

Firstly, lifespan doesn't matter in isolation, as pointed out by other answers. What matters is lifespan should be long enough for learning to take place from parent to child.

How quickly this learning takes place could be anything. There could be an option to acquire the entire brain of the parent. Alternatively the species as a whole might share a brain (like if corals or banyan trees had brains). Or maybe children share their brain with just their parents, and branch off (like plant offshoots). If learning must take place via outside media, how about it being chemical? We use oral and non-verbal communication which is relatively slow, direct chemical communication could be much faster.

The parent need not be alive for the children to learn. Mammals have a take-care-of-young-for-long principle, most species don't. Parents could leave non-living remnants for children to study in their own time. (For instance if your parent taught you basic reading skills then died - leaving you the knowledge of the internet; not a perfect example cause we have emotional needs but what if we didn't). Survival skills can be genetically coded instead of having to be learnt from parents (like with most species except mammals), everything else can be learnt via a non-living medium such as written text.


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