Humans sleep more then nearly any other creature (true sleep, not low-activity like cats and sloths), and are some of the only true sapient species on earth. Many other intelligent, or nearly sapient, species similarly have much higher degrees of sleep. Clearly we find sleep to be useful.

Of course, sleep has its downsides. we spend 1/3 of our life in a state where we can not do anything to take care of ourselves. While sleeping were not producing or finding food, nor are we raising young, finding mates, achieving dominance, higher social status, or more territory, or any of the other things that animals need to do for survival of the fittest. Plus were more vulnerable when asleep. Clearly if humans, or other sapience, could achieve our brain power without dedicating so much time to sleep this would be preferable. The question is rather or not we can.

Thus the question, Can a sapient species evolve that does not require sleep, or requires far less sleep?

Lets narrow the question scope some though, since I may ask follow up questions for certain aspects of sleep and don't want to repeat answers. For this questions I'm specifically looking at sleep as related to brain power alone (which probably means mostly REM parts of sleep). Sleep serves uses in physical healing and other functions as well, but there are other approaches to addressing the body maintenance aspect of sleep and I may ask about them in separate question. Feel free to touch on that aspect if relevant, but mostly I want to focus on just the part of sleep mandated by sapience.

I'm asking in terms of any species, not just species evolved on earth-like planets, this may include planets without a standard day-night structure. However, lets focus on species that would be at least recognizable to humans, carbon based, human-like sapience, basically not completely alien (yes I said not completely-alien aliens, I'm invoking some poetic license here; they need to be similar enough to earth species for audiences to be able to understand them).

I may ask a follow up question on what alternative sleep-like approaches may evolve in place of sleep, if something sleep-like is required, as a follow up question. For now I'm more focused on rather sleep specifically is required, or generally what parts of sleep may be required if not sleep specifically.


6 Answers 6


The dolphin is actually a good animal that possesses a lot of intelligence but also sleeps in a very different way. It's called unihemispheric slow-wave sleep.

Half of its brain becomes dormant while the other half remains alert. It allows it to react to its surroundings and survive predators, which is something that any animal would need until it develops the ability to build shelter where its predator evasion becomes less important.

You could conceive of an animal that's of human intelligence or higher that relied on phenomena like this in order to survive without what we need, which is rapid eye movement sleep. There isn't a high barrier evolution-wise, since it's a feature of the organism which doesn't have a too extreme environmental catalyst. The dolphin does it because it consciously breathes.

There also isn't a very good reason for the feature to be lost. If the species can continue to procreate and the feature does not prohibit it, it's likely to stay. I'm imagining a human-intelligence-or-higher animal that also consciously breathes. Perhaps it lives in a colder environment where it still needs to have more muscle movement and have more heat.

This is in contrast to our slower metabolism, lower body temperature, and restriction of our muscles so we don't act out the dreams we experience in REM.

Its biology has to abate the need for rapid eye movement sleep for restorative function like maintenance of its immune system. If that's in conflict then it's likely won't evolve into it.

  • $\begingroup$ hmm. I would imagine "high order" thought, real sapience, would be disabled whenever either hemisphere is sleeping though? $\endgroup$
    – dsollen
    Dec 17, 2015 at 22:08
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    $\begingroup$ Since there are humans with only one hemisphere, I imagine it is not impossible for an organism to still be rather capable. baltimore.cbslocal.com/2015/07/10/… $\endgroup$ Dec 17, 2015 at 22:12
  • $\begingroup$ that's cheating, the brain healing back from injury is different then default behavior :P. Just judging from my evolutionary knowledge I suspect dolphin's are mostly instinctual, or at least less 'intelligent' during slow wave sleep, if that were true then it would likely be evolved away in favor of 'normal' sleep once there was no longer a need to sleep "with one eye open". However, this is a guess. I tried to find research on long-sleep and adaptivity while sleeping before to confirm my guess but never had much luck. $\endgroup$
    – dsollen
    Dec 17, 2015 at 22:19
  • $\begingroup$ yeah dolphins during their "sleep" phases are not capable of a whole hell of a lot, they are basically like sleep walkers they can swim slowly and surface for air, and that's about it. $\endgroup$
    – John
    Jan 1, 2017 at 6:57

There are are several species which engage in Unihemispheric slow-wave sleep in which the animal lets one hemisphere fall asleep while the other hemisphere monitors the environment and keeps the animal functioning. For example, some birds with high numbers of predators will do this during long migration flights.

Sure, they're sleeping in the most technical sense of the word. But I think the fact that they're freaking flying while they do it may be good enough =)


Genetic components & environmental pressures define sleep cycle.

It is an interesting question, and as a cell biologist, I am convinced that the key point to answer it lies within the genetic component of the circadian rhythm and the "environment" that constraint the night/day cycle. If I may add, sleep do help the body to "take care of ourselves" (even we find it useless and unproductive!) and that brainwaves is maybe not the good answer to your question.

Dsollen in your question you rightly introduce some results/consequence of sleep on evolutionary and social aspects (producing or finding food, raising young, finding mates, achieving dominance, higher social status, or more territory, vulnerability when asleep. nature of source of the sleep), but you must not forget that sleep is a long-evolved process which takes roots billions years ago during cell evolution - which evolution is based on night/day cycle as primary (and most stable) selection pressure. Billions of years after, this result in a fine-regulated circadian clock present within each of our cells.

As you probably know, the circadian clock is encoded by genetic factors: the "core" genes working driving this circadian clock are now well known, and the network they define is quite intricate and complex. There is a lot of research going on about this topic, most of them rely on using engineered cells and mutants which possess a rather similar clock than human. The crucial point is that these genes drive the expression of many cell functions and biological processes, including: blood cell activity, immunology, cell migration, dna repair (thus tissue organization/regeneration), etc. I don't know any good scientific that review all of that at once-its in fact many papers-, but you may start with google scholar. In particular, I recommend the publications of Pierre Baldi, a research scientist of UC Irvine university I meet this year in conference in Japan. His research focuses on the molecular aspect of the circadian clock. For example, see this paper http://www.pnas.org/content/109/14/5541.short

These deep molecular and physiological implications I briefly introduced above apply at various scale within any species, and this will undoubtedly constrain the answer to your question.

The putative evolution of shorter sleep in a sapient-like species is possible with specific mutations (as said above it was shown in humans), but evidence to say that there is no counter-effects are in my opinion still lacking, because it these research do not cover all physiological aspects and molecular levels (i.e., these people may have some defect at levels not measured yet, such as immunological resistance or tissue regeneration)

Therefore, to shorten the sleep cycle also means increasing the risk of developing cancer and diseases: http://www.nature.com/nrg/journal/v9/n10/abs/nrg2430.html but also may change the ability of this species to answer to pathogens and infections: http://www.pnas.org/content/109/14/5541.short

As it took millions of years for this system to evolve in simple then more complex organisms, with various complexity and scale, I can't conceive that we could suddenly (or over few years) "suppress sleep". Rather than that, I imagine that, in a putative fiction world or close future, that sleep may be "optimized" through appropriate genetic treatments and methods, assuming we got a better knowledge of the molecular processes at work by then. But in a naturally-evolved process, it may well take millions of year to evolve it to a more optimized circadian clock (and assuming the day/night cycle is not changed and still of importance).

You may also imagine that in a world where the night/day cycle have very short nights, then you have about 100% chance that single-cells, then multi-cellular species will evolve in response to this environmental condition in their own specific way.

Hope my answer is helpful, Best, Arno


Yes, in fact with the line of sapience getting blurred, it may already exist.

@The Anathema had some good points on dolphins, but I have some things I'd like to add. Recently Koko the gorilla has blurred the line between what we consider sapient and sentient. Despite being a member of a species we count as sentient, she seems to be self-aware. What does this have to do with sleep, you ask? Well if a gorilla can be sapient, then animals we consider to be smarter than gorillas could also be sapient. Dolphins are one of the animals we consider extremely intelligent and if they are sapient, then your wish is granted.

Now the reason the dolphins sleeps with half its brain at a time can also be applied to an alien. The dolphin sleeps in the way it does because it prevents them from drowning to death. The same reason sleeping fish evolved the swim bladder. If you species is a land animal that evolved to live underwater, similar to whales, then they'd likely have a similar, if not the same, mechanism to survive underwater.


If the theory of evolution is accurate, the answer is almost certain to be a genetic mutation.

In fact, there is mutation or for a clinical article that appears to reduce the normal 8 hour sleep requirement to about 6 hours.

The important aspect is that the mutated people suffer no apparent ill effects from what would typically be sleep deprivation and recover more quickly in actual sleep deprivation experiements.

As the article notes, who knows what other genetic variation could impact sleep requirements.

It is also well-documented that a small percentage of the population (1% or so) are considered to required comparatively sleep - reports of 3-5 hours per night are common in the group, although people do not self report sleep with great accuracy.

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    $\begingroup$ unless you mistaken (purposely?) the definition of theory, evolution is a fact! $\endgroup$
    – user31616
    Jan 6, 2017 at 23:40
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    $\begingroup$ @ArnoGermond - The scientific basis for the mechanics of the theory of evolution has been modified a number of times over the years and will continue to be modified as there are quite of issues that are not satisfactory. Mutation has in recent years been deemed insufficient explanation in some cases, requiring epigenetic modifications to explain some variation. For an example discussion of evolutions problems, a mix of expert and amateur opinions. Evolution theory accuracy is not beyond question. $\endgroup$ Jan 7, 2017 at 6:03
  • $\begingroup$ Evolution does not happen through random mutations. It happens through intentional adaptation to the environment necessitating changes in the organism needed for survival. Animals evolve in order to cope with changing environmental circumstances. Mutations are random, negligible occurrences. Nature leaves nothing to chance. Putting the survival of your species to chance in a harsh food chain environment is foolish. $\endgroup$
    – Galaxy
    Jul 12, 2020 at 0:00

Humans already have the ability to minimize their sleep dramatically: polyphasic sleep.

There's a lot of experimentation with taking more frequent sleep breaks, each one for a short time. While there are many critics as to how little sleep one could ultimately require, there are some proponents who claim that it's possible to need only 2 hrs of sleep daily. (One of the most famous people to do this was Buckminster Fuller, relying on a 30 minute nap every six hours.)

When I spoke with a proponent of this approach, he claimed that polyphasic sleep works because a person trains their body to slip right into REM mode, and right out. He personally followed the approach of sleeping for 3 hours in the middle of the night, and then 3 20-minute naps every 6 hours, for a total of 4 hours daily. He had been doing it for 5 years and had no health problems, though he had to adjust his diet to fit his new energy requirements.

If this idea already exists in our society today, it should be very plausible to tweak it a bit for your world to make it even less. Perhaps a 15 minute nap every 4 hours, which would only total 1 1/2hrs of sleep daily.


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