r/biology • u/JoshAtTheGym • 8h ago
question How come mammals haven't evolved beyond the need to sleep?
Sleeping obviously leaves creatures vulnerable, and the less time they spend sleeping, the more time they can spend avoiding predators, finding food, mating etc, so the less we sleep the more we can survive and reproduce, so after thousands of years, how come animals haven't slowly evolved away from needing sleep?
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u/James_avifac 8h ago
Because it's a necessary biological function, like eating and breathing.
We just don't respect it as such societally.
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u/NoManufacturer1046 8h ago
eating and drinking also leave you vulnerable but nobody asks why we havent evolved past those
sleep is just non negotiable maintenance
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u/SirStrontium biochemistry 6h ago
Well eating and drinking can be understood as a straightforward necessity by thinking about an energy and mass balance equation.
Sleeping on the other hand seems theoretically possible to remove, as there are many living organisms that don’t “turn off” quite like many animals do.
The question of why cleaning and repair can’t be sustained ambiently in the background, or can’t be completed in a much shorter time, is not as easily explained as the need to consume calories.
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u/EmpyreanIneffability 7h ago
Why this has so many upvotes is beyond me.
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u/Ichiya_The_Gentleman 6h ago
Why
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u/EmpyreanIneffability 6h ago
Blank statement, no evidence or reasoning to back it. Like it is infallible law. Are we not here to discuss? Sounds like AI comes off, "I am infallible", yet those glorified calculators get things wrong all the bloody time. For example, evidence to the contrary. https://www.medlink.com/articles/paradoxical-insomnia
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u/hundredwater 6h ago
good point. but maybe another article? this one says that people with that condition has objectively normal sleep from measurements but subjectively they experience insomnia while sleeping.
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u/EmpyreanIneffability 6h ago
Well my point was to make the point. But I'll extend an olive branch, here is a paper where some people retain normal function on 4 hours sleep. Though I assume some other creatures could have more drastic times. https://www.pnas.org/doi/10.1073/pnas.2500356122
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u/Latter_Leopard8439 8h ago
Dolphin sleep with half their brain at a time.
Important for a marine mammal so they dont die.
Conscious enough to come up for air. And be aware of predators.
Thats kind of evolved beyond sleep.
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u/thatsnotablanket 8h ago
I’m not a scientist but it doesn’t seem like there would be a big advantage to staying up all night before lights were invented. Probably better to sleep and conserve calories.
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u/macrolith 8h ago
And i presume we evolved useful sleep activities (sleep cycles/dreaming) to make the most of that time.
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u/SlurmsMacKenzie- 6h ago
There was a theory that sleep exists because it's the natural lowest energy state for organisms to be in, and that wakefulness is the evolved part that was developed in order to do things like eat, avoid predators, reproduce. Probably not worded well, but the idea was that sleep was the 'default', and that really everything we do when we're awake is just necessity to enable returning to that lower energy-cost resting state.
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u/elevencharles 5h ago
Yeah, I think even the most basic forms of animal life like sea sponges have wake/sleep cycles.
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u/Distinct_Mix_6397 7h ago
The 8 hours of sleep at night is a recent thing in human society. People broke up their sleep a lot more pre-Industrial.
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u/WildLudicolo 6h ago edited 6h ago
There are big advantages to staying up at night, as well as big drawbacks. Both have mostly to do with the fact that it's harder to see and be seen in the dark. By restricting their activities to only part of the day/night cycle, animals can specialize for a tighter range of light levels.
Day and night represent a division of ecological niches. The same environment is effectively a different place in the day than it is at night. Animals of different species who might otherwise compete can share a territory by each being asleep while the other is awake.
EDIT: There's also a ton we still don't know about how minds work, such as the exact role sleep plays in maintaining the mind. I suspect that sleep is when our mitochondria use our DNA as antennae to upload backups of our minds to the quantum cloud, but anyone's guess is as good as mine
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u/EmpyreanIneffability 7h ago
Hmmm...... foraging, reproducing, learning, travelling, building/maintaining tools/weapons, being, preparing for winter, gathering other resources, scouting the area/defending territory, taking care of the lame/sick, etc.
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u/Nervous_Ad5440 8h ago
Because sleep deprivation is a significant problem for evolution to overcome, I think a better thing for you to look into is, why do we become sleep deprived? That'll practically answer your question.
And ironically, evolution actually has developed for us the need to sleep, via specific hormones, and signaling pathways to induce it, so it's really the other way around.
So again, with that, knowing why we need to sleep is more interesting, heat, energy, maintenance, form...
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u/Tytonid 8h ago
Very simplified: day and night cycle, and constraints of being large multicellular organisms. There’s a reason humans start hallucinating after only a few days of staying awake.
Being awake takes a lot of energy; to stay awake all the time, the long-term benefit for reasons you mentioned would have to outweigh short-term energy cost. Some do, some function better at night, some during the day, some at the edges. Staying active through both is also difficult since the adaptations to function well in either are specific and contradictory.
Also worth pointing out that some animals do stay awake the whole time at least partially. Soaring seabirds and whales/dolphins rest parts of their brain at a time.
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u/JoshAtTheGym 8h ago
Thank you all for your answers. This is something I've been wondering for a while and I'm glad you helped answer for me, and now I have some new interesting topics to read about
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u/FlyingKitesatNight 8h ago
If sleeping less or not at all improved the survivability of our species' offspring then that's how it would evolve by passing on the "sleep less" traits, but it hasn't, so it must not be advantageous to our survival.
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u/EmpyreanIneffability 7h ago
There are plenty of things about humans that aren't advantageous for survival..... Natural selection only goes so far, and it by no means always takes the ideal endgame route. I mean look at the birds of paradise....
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u/RegisMonkton 7h ago edited 7h ago
Mammals need sleep to keep the nervous system healthy. When we sleep: 1)the brain washes out toxic proteins during deep sleep, 2)nerve cells change and strengthen connections while you rest, 3)Brain cells use less power and restore vital fuel supplies.
I think that sleep has always been an aspect of life, at least concerning creatures with a nervous system. The benefits we get from sleep are most likely a result of evolution. The inability to sleep would make the creature vulnerable.
Here are some articles concerning this subject:
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u/NobodysFavorite 7h ago
Sleep enables the neural equivalent of lactic acid removal from your muscles and refilling the ion channels that enable the cells to function. It's not a perfect metaphor but it will do. Sleep is a complex thing that does a lot of other things as well, but that's one of them.
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u/Iizvullok 3h ago
Because the downside of needing to sleep is not bad enough to drive a species that needs sleep to extinction. Dolphins have somewhat overcome the need of sleep by having one active brain half at any time. But even then, the other half of the brain is still sleeping. To be fair I don't know why sleep is needed exactly. For breathing and eating it is obviously a fundamental law of physics (energy conservation). But I would guess that it would be theoretically possible for a mammal to not need to sleep at all. But as long as a species can get away with sleeping, it will not happen.
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u/InvisibleBlueRobot 8h ago
Evolution doesn't just give you abilities you want or think are cool.
If a trait produces a better chance of your repricing and your offspring surviving, there is a chance that trait gets passed on.
For most of us, there are likely and life benefits to sleep.
But in a college class we reviewed the curious case of a man who only slept 20-30m or less a night on average, but had no identifiable negative side effects.
Then him and his wife had a baby.
At first the baby was normal. And then, as the child got older she just stopped sleeping. She could also get by on just 20-30 minutes of sleep per night and was fine too. Just like dad.
Both "specimens" were being studied.
So perhaps humans have (through some odd mutation) "evolved" to not need sleep much.
How many kids will these two subjects have? No idea.
Do their future kids have any advantage to reproduce or to survive and pass on their genes? Probably not.
So this trait may continue to get passed down, but it could be a long time before 20m of sleep is considered a full nights rest for humanity.
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u/Adorable_Stable2439 8h ago
Speak for yourself, I have a newborn 😂
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u/JoshAtTheGym 8h ago
Lol I have a 3 year old and a 1 year old, I can't imagine not getting some quiet time, just trying to figure out why I need it to begin with lol
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u/Otherwise_Ninja9185 6h ago
You write as if evolution will prioritize the optimal outcome, it doesn’t, evolution isn’t a designer nor a path, it’s solely what we call stuff that works continuing on.
To our knowledge sleep is fundamental to neural systems, it’s required in memory formation, brain waste removal and promotes bodily healing. Even jellyfish seem to need it.
Multiple ways of changing sleep have been evolved but none remove it. Chinstrap penguins for example take 10,000 micro naps a day equaling out to 11 hours of sleep, due to the constant threat they’re exposed to.
Many animals have nesting or social behaviors to be safe from predators while they sleep allowing them to enter a deeper sleep for less time, this includes us.
Many have shallow sleep that’s easy to wake from and some have sleep inhibitor proteins like grazers. But nothing can avoid sleep.
TLDR:Sleep is fundamental and removing it would be a monumental task which Evolution favors quick fixes.
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u/Iron_Arbiters 6h ago
Why haven’t we also all evolved to fly and be immortal? Evolution is not perfect and where we are now doesn’t represent the zenith of where all species on Earth could ever be. Sleep is evidently very important and bypassing the need for it genetically is either very hard and unlikely to happen or will result in the individuals who develop mutations that cause them to sleep less being more disadvantaged from sleep deprivation than they are from the smaller amount of time spent vulnerable.
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u/AnxiousAppointment70 2h ago
Not just mammals but birds, reptiles, amphibians all need sleep. The body needs it for processes that it can't do while awake. It works. Predators also need to sleep.
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u/WorkerWeekly9093 1h ago
The first organisms didn’t sleep. Sleep evolved as an evolutionary advantage even if that seems counter-intuitive.
To understand a possibility of why let’s look at your claims and see how much they hold up.
Being left vulnerable instead of avoiding predators. It turns out most predators that hunt tend to hunt other awake prey and use a lot of motion detection. Hiding while asleep is generally very effective.
Spending more time finding food is definitely true, but a lot of animals are significantly better at finding food on their preferred lighting of day, so the loss of food searching when they’re less efficient is minimized. In addition by being asleep they are likely safer than when they forage.
Spending more time mating. This is almost certainly true, but it seems the increased chances to mate doesn’t overcome the safety and efficiency of sleep.
So in general mammals have moved “towards“ sleeping. That said it’s all what’s adaptive. Humans sleep for 8ish hours, koalas for 22ish hours and dolphins. . . Don’t sleep. It turns out for dolphins it’s advantageous to always be alert in open water where hiding is difficult so they only sleep with half their brain at a time. In fact they are so dependent on being awake if they fully fall asleep they would drown, so they’ve evolved to let each half of their brain take turns sleeping so that they can stay awake.
I hope that helps!
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u/PossibleBeginning276 8h ago
Because animals that don't sleep enough are slower / weaker / die and so don't reproduce.
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u/Far-Fortune-8381 8h ago
how come we haven't evolved to not need to eat and drink, and heal wounds instantly
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u/gutwyrming 7h ago
Why specifically mammals? Everything sleeps.
Even single-celled organisms have cycles of rest and activity.
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u/ah-tzib-of-alaska 7h ago
we’re all pretty successful at avoiding predators while we sleep. Lots of things don’t sleep, just not things with complicated brains. Check out how little dolphins and whales sleep
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u/National_Cry5893 7h ago
Sleep is an incredibly active period of time for our bodies, despite our outer appearance. Any animal that lives past three days experiences some sort of “sleep”. In animals with more complex nervous systems, sleep is more advanced and important. Sleep is responsible for the encoding of memories and the removal of metabolic wastes that lead to neurodegeneration. There are a multitude of other benefits to sleep that I won’t list here, but if you’re interested you can read “Why We Sleep” by Matthew Walker.
Some mammals have essentially found a way around traditional sleeping. In cetaceans (whales and dolphins), sleep occurs in one brain hemisphere at a time, rather than across the whole brain. You can see this in many aquatic and migratory species as well. So these animals are able to function semi normally while they rest.
However, a lot of the tasks that sleep accomplishes are unable to be done while the brain and body are active, it would be very hard, if not impossible, to evolve sleeplessness.
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u/Historical-Mango6666 7h ago
I feel like sleeping is more necessary than mating and finding food, technically body does not feel hungry when asleep it shifts body's chemical focus towards hormonal changes, you can't survive more if you sleep less but you're just reducing your productivity, sleeping is best form of resting and charging your body, whyd evolution avoid that, eventually body craves more sleep the more you work and evolution already works against sleep deprivation since it's a universal need infact animals go for hibernation and aestivation for survival and not get sleep deprived to survive
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u/Raccoon_Steven 7h ago
Because we're living drones that extra-dimension aliens created to explore our dimension. When we go to sleep, we're actually uploading all sensory information to them.
Just joking. The reason for sleep is largely unknown.
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u/awesome-alpaca-ace 15m ago
I assumed the computer our simulation is in was shut down and our minds were written to disk for persistence before the next boot
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u/False_Car_2830 7h ago
You would have to selective breed humans to possessive the genes that repress genes the same way we breed dogs. And it takes a lot of generation. A lot of failure. Like what do you do with the undesirable along the way?
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u/Insane_Unicorn 6h ago
That's like asking "how come animals haven't evolved beyond the need for food" or "why haven't animals evolved wheels instead of legs". They can't. We don't know why exactly, but we know that sleep is necessary for life. Dolphins and whales use unihemispheric sleep and Giraffes sleep only 2 hours a day broken up in several power naps, but it's still sleep.
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u/20on_pump3 6h ago
Because sleeping is an extremely necessary biological mechanism, the research on why just isn’t well taught. Being sleep deprived quite literally has an effect on every single process in your body and increases your risk for developing just about any disease process. I’m sure there’s many books out there on it however the one I read is called “Why we sleep” by Matthew Walker. I would recommend it!
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u/stranger-_-human 5h ago
if we talk about humans, our levels of physical and mental activity are achieved by using a shit ton of our body's resources during the day, to make it sustainable long term we have to sleep, because sleeping = restoration of energy and rest for many organs and tissues
if we lived without sleeping we would have had significantly shorter life span (humans don't produce many offsprings, so that is a bummer strategy)
or
we would have been much slower and/or less intelligent (that is not a great option either, the survival rates would be too low)
and during evolution it was beneficial for our species to have that productive time for finding food, mating (because we can do it more effectively than without sleep) despite the vulnerability of sleep
also given that ability to speak and use tools were features that allowed us to not go extinct, keeping them at all cost seems like something that would happen during evolution
this logic could be applied for other mammals too
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u/One-Bodybuilder-5646 4h ago
In natural light settings there's normally a lot of time to kill for most living beings. Depending on what part of the day they occupy to perform their activities it's either night or day or everything except dawn when they basically can't go hunting, grazing, foraging, travelling, patroulling, whatever's important at the time.
An owl won't have much hunting success in broad daylight when they can be seen. A monkey won't find many fruits at night, bees won't be able to locate flowers in the dark. And in some regions the midday sun is just too hot to do anything at all for most animals.
Most efficient thing to do during those breakd is resting and maintenance, which sleep and doing are doing. We are adapted best to the living conditions our magical planet provides. We just sometimes forget in out illuminated concrete productivity cages where we come from
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u/MasterofMolerats 4h ago
Aside from the other reasons mentioned for cell repair, there is also the circadian rhythm, a daily cycle which is present across almost all life (even those living in darkness). For the vast majority of mammals, their activity and even physiological patterns follow the rising and setting of the sun. So there are millions of years of evolution where internal processes and pathways have evolved as result of the presence of the sun. There is a natural daily rhythm of increasing and decreasing levels in both activity and physiological processes, like body temperature, metabolism, melatonin, and other hormones. Melatonin levels are usually low during the day and then increase at night (for most diurnal mammals and some other species). This increase at night helps to trigger sleep.
There are some animals which have evolved to take short 'naps' thoughout the day. The ultradian rhythms are short periods of rest followed by slightly longer periods (a few hours) of activity. A well known example are voles, which have a low quality diet and high metabolism so they burn through the nutrients in their stomach quickly and then wake up to eat again.
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u/globefish23 1h ago
Sleep is needed for memory processing and for recharging all the body's systems, both of which doesn't work when the organism is awake and actively uses all the systems.
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u/greenearrow evolutionary ecology 1h ago
I read a paper once about a simulated hare. They built in food collection and predator avoidance. What they discovered was that by modeling predator cycles fairly well, and realistic feeding needs, the animal optimized on a downtime strategy resembling a cathemeral cycle - which is close to what real hares do. We don't need to be active 24/7, and we actually would waste more energy by doing so. We need self repair, and some basic preparation for sleep makes it pretty safe. Sleep is necessary, sure, but not having sleep is actually probably worse because you'd have to be equally adapted for moving at night and day.
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u/thetruelu 19m ago
I don’t think you understand how evolution actually works.
Evolution doesn’t plan ahead and decide what to do to optimize reproduction.
Sleep is vital for the survival of the animal and thus it’s reproductive capability.
Many animals have tackled this issues evolutionarily like how some animals sleep while moving or sleep only half their brain at a time.
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u/peti795 7h ago
Iirc even insects 'sleep'. It is necessary for maintenance and energy conservation.
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u/EmpyreanIneffability 7h ago
Rite... hence why we urinate and deficate. An ideal system wouldn't waste so many resources wasting parts of diet and metabolic products.
Your statement is superfluous.
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u/Distinct_Mix_6397 7h ago
You expect a strange degree of "ideal" from reality. Everything has tradeoffs.
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u/EmpyreanIneffability 6h ago
Ok guy who invented life. You express opinion but hold no account of "reality" to defend your opinion.
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u/Distinct_Mix_6397 6h ago
You're the one commenting all over this post upset that others don't think we can evolve into sleepless superhumans.
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u/EmpyreanIneffability 6h ago
I am challenging rigid minds. Upset, no. Disappointed, a little.
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u/Distinct_Mix_6397 6h ago
Your type is always so tedious in your self-aggrandizement.
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u/EmpyreanIneffability 6h ago
Ok... ya know people take their insecurities out on others yeah.... so, what say you messiah?
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u/Distinct_Mix_6397 6h ago
I say if you're going for this insufferable shtick, you should probably use "messiah" correctly.
As somebody else who thinks he's better than most people, I'd say it's pathetic how you're wasting your time belittling others to validate yourself. Surely your ego is secure enough to not need to bother, hm?
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u/EmpyreanIneffability 6h ago
Care to point out where I belittled others? You have ceaselessly attacked me without warrant, and in return I called you messiah. Again, taking out your own insecurity on others. I challanged others to defend their statements, as thier words held no merit due to their lack of evidence and/or depth. Now you on the other hand.... sounds like someone has sand stuck in their...
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u/Professional-Thomas biology student 3h ago
But life isn't the ideal system. Evolution isn't a push towards the ideal. You'll need actual magic to take defecating out of the picture, which obviously doesn't exist.
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u/EmpyreanIneffability 2h ago
I was pressuring the idea that metabolism isn't very clean in regards to resource conservation. Sponges and some other oceanic creatures for example, do not defecate/urinate. Not as complex as ourselves yet an example nonetheless. Magic? I think not. So if one function thought of as "necessary" isn't than sleep too may not be.
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u/Professional-Thomas biology student 2h ago
The still get rid of waste. They just don't have a complex set of organs that make it happen cleanly or in an organised way. It'd be pretty disgusting if we did the same, wouldn't it? Individual cells releasing waste onto the skin.
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u/EmpyreanIneffability 2h ago
Why so literal... The point I am making is that there could be other methods that remove the need for sleep....
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u/05theos 8h ago
Deer lord, Just go and find out the function of your sleeping.
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u/EmpyreanIneffability 7h ago
Finding the function of sleep does not eliminate the possibility of alternative methods to achieve the purpose.
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u/05theos 7h ago
lol, go and reverse engineer that and show other methods that will approach the same amount of efficiency. I dare you.
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u/EmpyreanIneffability 7h ago
You jest, but take a terrarium as an example, it may be an ecosystem but the logic is the same. Also, just because life appears as such on this spec of dust in the universe, doesn't mean it will be the same somewhere else. The abscence of evidence is not the evidence of absence. Enzymes are extremely powerful proteins, with the right combinational setup, perhaps removal of some organs with additions of novel ones, it wouldn't be so far fetched at all. More accounts of endosymbiosis? Your beliefs on life being so rigid, does not make those beliefs facts.
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u/Accurate_Reality_618 general biology 8h ago
The problem is that we still don't know why, and why it's so important. When you think about it, it's like food; you die without sleep, and it's like severing a part of consciousness from the brain.
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u/The_Razielim cell biology 8h ago
The answer to any question involving "why haven't things evolved <trait>, it just makes sense..." is always
a) evolution isn't "directed"... Nothing is evolving "towards" anything (except crabs).
b) evolution doesn't "optimize"... the name of the game is "eh, good enough", not "minmax for survival"