Why has nothing evolved to not need sleep?

Wowbagger said:
I'm telling y'all: It is NOT the evolution of sleep we need to ask about. Sleep is the default position of life forms, and one that life forms will always try to revert to, as much as it can get away with. It is waking life that evolved: How we are able to become more aware of our surroundings, for some period of time, is the question to ask.

It might be wrong to assume staying awake all the time would be perfect evolution. What if sleeping all the time actually is, from nature's point of view?

Perhaps animals won't evolve to "not need sleep", simply because nature prefers them to sleep as much as possible, and only remain awake for what is necessary to survive.
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While I don't completely agree, as I mentioned above, there is much truth in this perspective.

The OP seems to originate in two basic assumptions -- that predator-prey relationships are THE driving force in evolution (which is wrong -- scarcity of resources is probably a MUCH more important issue and conservation of energy would therefore be more important than awareness), and that awareness of surroundings is THE way to avoid predation. I take issue with the second assumption as well, since animals without sophisticated nervous systems simply don't necessarily have a good means to suppress behaviors in certain situations and sleep is a definite (and relatively easy to acheive) means of suppressing certain types of behaviors in certain situations.

But, the larger issue is that the OP seems to assume that sleep performs a single function for all creatures. I think this is quite obviously wrong, and is probably wrong even for single individuals where it likely performs many different functions. It almost assuredly performed different functions in the earliest animals to adopt it as an active neurological state (as opposed to mere quiescence) than it does in animals alive today.

I could be very wrong in my speculations, but I think it also (keep in mind that we are discussing not quiescence but sleep, an active neurological state) permitted the development of complex neural networks as BenBurch argues. I simply think that it must have been in place for another reason, since there is always a chicken-egg problem with the what came first -- sleep or complicated neural networks.
 
Zeuzzz said:
I agree with that. 'Importance' isn't exactly a scientifically well defined term. So I shouldn't have worded it like that.

I mean that (and I'm not sure about this myself I need to give it more thought) evolution does an incredible job of refining animals to the best of their ability, but nothing has evolved to gain the advantages of being awake and alert all the time. Which, in a very general sense, means that sleep is more important, or rather that evolution seems incapable of reducing sleep and enabling animlas to experience the benefits of sleep without the periodic lack of/decrease in awareness of environmental stimuli that every animal on the planet experiences.
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Exactly. And what this should tell you is that sleeping provides more of an advantage than not sleeping. End of story. If getting rid of sleep resulted in more succesful animals, animals would have evolved to not need sleep. Since that has not happened, the only sensible conclusion is that your claim that sleep is a disadvantage is false.
 
Cuddles said:
And what this should tell you is that sleeping provides more of an advantage than not sleeping... the only sensible conclusion is that your claim that sleep is a disadvantage is false.
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But it doesn't explain why, and that's the real issue here, because the facts seem counterintuitive. It's not that "sleep is a disadvantage", but that "it seems as if sleep should be a disadvantage". When the way things actually work is different from the way it seems like they should on the face of it, that's always a good place to try to find out more about what's going on. That the answer is currently unknown doesn't make the question a bad one; it just makes the mystery more mysterious.
 
In case no one has seen it yet, I just found a new paper, published yesterday (August 26th, 2008) that deals with sleep. It can be found on PLoS Biology's website (which can be found by searching for "PLoS Biology" in google) if you search for the title of the article. The article itself is called "Is Sleep Essential?". I haven't read it in its entirety yet, but I will when I get home from work. It should prove to be an interesting read.

I am sorry I can't hyperlink it, I don't have enough posts to do so yet. If someone finds it, could they link it for me? Thanks.
 
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Cuddles said:
Exactly. And what this should tell you is that sleeping provides more of an advantage than not sleeping. End of story. If getting rid of sleep resulted in more succesful animals, animals would have evolved to not need sleep. Since that has not happened, the only sensible conclusion is that your claim that sleep is a disadvantage is false.
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Well, I think sleep is a disadvantageous and unavoidable result of something that is fantastically advantageous; A brain that can learn and efficiently process information.
 
I also think that the disadvantage to sleep, while there, is not very pronounced. How many prey animals get killed while asleep? Most animals can be woken from sleep by sound or changes in light. That seems to be sufficient to enable them to wake up in time to respond to predators.
 
Tortan said:
In case no one has seen it yet, I just found a new paper, published yesterday (August 26th, 2008) that deals with sleep. It can be found on PLoS Biology's website (which can be found by searching for "PLoS Biology" in google) if you search for the title of the article. The article itself is called "Is Sleep Essential?". I haven't read it in its entirety yet, but I will when I get home from work. It should prove to be an interesting read.

I am sorry I can't hyperlink it, I don't have enough posts to do so yet. If someone finds it, could they link it for me? Thanks.
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Very good find :) It pretty much deals with everything that has been discussed in this thread :thumbsup:

PLoS Biology - Is Sleep Essential?
Everybody knows that sleep is important, yet the function of sleep seems like the mythological phoenix: “Che vi sia ciascun lo dice, dove sia nessun lo sa” (“that there is one they all say, where it may be no one knows,” Wolfgang Amadeus Mozart and Lorenzo da Ponte [1790], Così fan tutte). But what if the search for an essential function of sleep is misguided? What if sleep is not required but rather a kind of extreme indolence that animals indulge in when they have no more pressing needs, such as eating or reproducing? In many circumstances sleeping may be a less dangerous choice than roaming around, wasting energy and exposing oneself to predators.
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Yep, I can see the point behind the part in italics. But the reason why non awareness is an essential aspect of sleep is still the bit that doesn't make much sense in a evolutionary sense to me, and why nothing has evolved to save energy while in an awake state. But this is more a mystery of sleep itself than evoultion I suppose, though you can approach it from an evolutionary perspective.

It goes on to discuss much of what had been said here, I'll quote a bit:



Animal Species in Which the Presence of Sleep and/or Its Homeostatic Regulation Have Been Called into Question

(See references [113–121]. SD, sleep deprivation.)

Coral reef teleosts showing sleep swimming have similarly been used as evidence that not all animals sleep (Figure 1). Two types of reef fish have been studied in terms of sleep; one is immobile at night and less responsive to alerting stimuli (stationary sleep [24]), and another [25] retreats to the coral at night, where it continues to move its fins even when holding a fixed position (called “sleep swimming”; possibly to avoid hypoxia [25]). The researchers who studied these teleosts defined sleep swimming as a state “equivalent to sleep.” They assumed that sensory information must still be processed to a certain extent during sleep swimming, because each individual remains in its swimming zone during the night. Yet, the fish at night loses the ability to respond to predators [25], and mortality due to predators' attacks is much higher at night, when the fish is sheltering in corals, than during the day, when it feeds in open waters[...........]

Sleep in Dolphins: A Difficult Case?

Dolphins and a few other species have developed unihemispheric (one-sided) sleep, a remarkable specialization strongly suggesting that sleep must have some essential function and cannot be eliminated [.........]

A function that cannot be provided by quiet wakefulness and that benefits from environmental disconnection.

If wakefulness were as good as sleep in fulfilling a fundamental biological function (or even nearly as good), is it likely that sleep would be so ubiquitous? Why would an animal choose to spend long periods of time not just immobile, but above all disconnected from the environment? [...........]

Conclusion

While there is still no consensus on why animals need to sleep, it would seem that searching for a core function of sleep, particularly at the cellular level, remains a worthwhile exercise. Especially if, as argued here, sleep is universal, tightly regulated, and cannot be eliminated without deleterious consequences. In the end, the burden of proof rests with those who are attempting not only to reject the null hypothesis, but to gather positive evidence for the elusive phoenix of sleep.[..........]
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All interesting stuff. I'll read it properly when I've more time.
 
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godless dave said:
I also think that the disadvantage to sleep, while there, is not very pronounced. How many prey animals get killed while asleep? Most animals can be woken from sleep by sound or changes in light. That seems to be sufficient to enable them to wake up in time to respond to predators.
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I would still maintain that overall it was, at one time, probably not a disadvantage at all, but probably an advantage. To call it a disadvantage we would need to see that the negatives outweigh the positives.

Since sleeping animals generally put themselves in protected environments, there is clearly an advantage there (not an overall positive for sleep itself, since torpid animals could do the same, but still). Couple this with your question -- how many animals are killed while asleep? My guess is -- few. Then ask, what is the alternative -- having animals awake and alert but in a state of torpor in their nests. That's all fine and good unless they do something stupid, like try to run out of the nest when they hear a predator, or something that they think might be a predator. The supposed advantage is that they can run if they need to, but what if running is the worst thing they could do in that situation, especially if they are at a relative visual disadvantage?

My guess would be that sleep would save more animals than a fight or flight reaction if a predator was knocking at the door. Digging an animal out of its burrow is a costly endeavor for a predator; I'm not sure it happens while animals are asleep all that often, and even if it did, how many predators would just give up? I think there is a reason why we have a particular image of predators hunting down their prey and not digging them out of their nests while they sleep.

Couple this with the probably greater issue: that scarcity of resources often plays a greater role in survival than predators do, and sleep does more than simple inactivity provides in terms of energy expenditures (body temperatures fall -- in fact, that is one of the theories of why REM sleep arose since body temps rise comparatively during REM in many animal species).

Couple this with the probable incorporation of sleep into the means by which more complex neural activity even became possible as you and BenBurch have argued.

I'm not sure I see the disadvantage of sleep.

Plus, I like it. I think I need to do it more often.
 
The dolphin solution seems to be the best we might hope for...shutting down one hemisphere at a time.

I wonder how its done?
 
The bottom line is that, as far as I know, we don't yet know why animals need to sleep. We only know that they do and can die from sleep deprivation, faster than they would die from food deprivation.

It is a very interesting subject in my view as we devote up to 1/3 of our life to this unexplained phenomena.
 
Delvo said:
But it doesn't explain why, and that's the real issue here, because the facts seem counterintuitive. It's not that "sleep is a disadvantage", but that "it seems as if sleep should be a disadvantage". When the way things actually work is different from the way it seems like they should on the face of it, that's always a good place to try to find out more about what's going on. That the answer is currently unknown doesn't make the question a bad one; it just makes the mystery more mysterious.
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Sure, but that's not the point I was addressing. I was arguing against the claim Zeuzzz has made that sleep absolutely is a disadvantage. Clearly, this is not true. The question of why it isn't true is an interesting one that we don't really know the answer to yet, but you can't even try to answer it until you recognise what you are actually trying to explain.

Essentially, Zeuzzz's argument seems to be:
"Sleep is bad, therefore we need to think of a way that it can get around evolution."
What it should be is:
"Sleep seems like it should be bad, therefore we need to think of a way it could still be selected for by evolution."
 
Creatures can not evelve a need to not sleep if neurons have to have a rest period to avoid spurious signals. If the base unit of complex neurological networks (the neuron) requires a rest period so they can function well, then you are going to be limited by that.

Evolution works on the material at hand, contingent history.


If as recent research has shown dolphins might sleep half the brain at a time, there is the sort of solution that natural selection can work on.

It is not survival of the fittest organisms. (So if one or two get eaten while asleep that is fine to natural selection, it might select for rousing traits)

It is about survival of some organisms to reproduce.

Not the 'perfect' model but the 'possible' model.
 
This is not definite in relation to people without epilepsy, it could be not significant for the control group and specific to people with epilepsy. i would also assume that the deprivation was not of the three day variety. I am thinking that maybe this sort of hyperexciation (Lowering thresholds ?) could be one possible (very tentative) reason that creatures need to sleep.

But it is a very far leap at this point:

http://www.ncbi.nlm.nih.gov/pubmed/17000971?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DiscoveryPanel.Pubmed_Discovery_RA&linkpos=1&log$=relatedarticles&logdbfrom=pubmed

It might involve the calcium channels of nueron membranes:

http://www.ncbi.nlm.nih.gov/pubmed/18571330

It might involve stabalization during REM and GABA:
http://www.ncbi.nlm.nih.gov/pubmed/...ez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum
 
Marquis de Carabas said:
In my opinion, you've got the mystery exactly backwards. In evolutionary terms, the only activity that really matters is reproducing. Why be awake any longer than it takes to do that?

Well, because an animal has to have some energy, so it has to wake up to go get food. And it doesn't want to become food itself, so it can't spend all its time still and unaware. So, you end up with a compromise; an animal sleeps as much as it can get away with sleeping.
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This last point is probably the answer, and explains why the lion - a super predator - sleeps much more than most animals. It can get away with it.

There appears to be numerous answers for why animals need sleep. It's more energy efficient, it improves brain function, and it has restorative advantages (affecting metabolism, healing, and the immune system, amongst others).

Perhaps a better question than "why haven't any animals evolved not to sleep?" is "why haven't any animals evolved to always be asleep?" since being able to breed and feed while asleep would be a much greater evolutionary advantage than not needing sleep.
 
Zeuzzz said:
I didn't say that, they dont! If you were a predator, would you prefer to pick a herd that where most the animals were sleeping and not aware of your presense, or a herd that was all awake and could see you coming?

The awake herd wins every time.
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Does it? You can’t say that unless you also asses the cost of being awake all the time, something you haven’t even attempted.

You are assuming that there are no tradeoffs and that every animal can evolve to be specialized in all things. In practice a generalist will not outperform a specialist in their specialty. If I as a predator have a choice between a herd where every animal is away vs one where only some are awake but the ones that do have their senses in overdrive and can wake the sleeping members I will go after the awake herd every time.

If there were no tradeoffs involved every animal would be as large as an elephant, as fast as a cheetah, survive months without eating like many reptiles and re-grow lost limbs, etc etc.
 
BenBurch said:
Well, I think sleep is a disadvantageous and unavoidable result of something that is fantastically advantageous; A brain that can learn and efficiently process information.
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I’m more inclined to think it’s like the feather. It evolved for one reason then got built on for something else that had advantages. Maybe there are other solutions for processing information, like resting half your brain at any time, but since sleep exists already for other reasons evolutions builds on it instead.
 
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