So, why's this sleep thing still a mystery?

[Half_Man_Half_Wit]

Every know and then, you stumble across an article about alleged ‘n things science can’t explain’, such as this recent one on Cracked. More often than not, one of those things will be sleep; various theories will be noted (restoration, memory processing, ‘training’ of newly developed neural pathways), but by and large, sleep researchers worldwide are being portrayed as wearing large question marks upon blank faces on heads supported by shoulders constantly cramped from perpetual shrugging. Similarly, there’ve been numerous threads here on the dope, and Cecil himself weighed in, managing not to tilt the scales one iota one way or the other.

All the while, I just keep thinking: but isn’t it, you know, obvious? And obviously, this means I’m missing something obvious. To me, it looks just like: there’s a cycle of activity and relative inactivity every living thing goes through. There’s a cycle of plentiful versus relatively scarce available energy (that whole thing with it’s warmer when the sun is up, etc.). So shouldn’t the most natural hypothesis be that the two are linked? That, when there’s less energy to consume, there’s less possibility for activity, and evolution takes it from there? I mean, we still see the same thing on a yearly basis: numerous animals, when the weather gets cold and resources become scarce, go to sleep for prolonged periods of time. Why shouldn’t daily sleep, at least in origin, have the same explanation?

Of course, technically, many animals (including yours truly) aren’t really all that dependent on the sun as energy source any more, but evolution is nothing if not opportunistic, so at the point sleep wasn’t necessary any more just for reasons of energy economy, it had already been co-opted by all sorts of other processes the body could perform during the mandatory downtime, which is were the restoring, brain-path reinforcing, and other functions of sleep may stem from. So getting rid of sleep wasn’t feasible any more, and since everybody suffered from the same or similar handicaps, unnecessary as well, so it stayed.

So what throws a spanner in the works of this idea?

[Musicat]

Sites like that delight in twisting words to make the unknown appear more mysterious than it really is. Looking at the article about astronomy, rather than saying “one proposed explanation is…” they say, “science is baffled!” or “scientists say this MUST be the explanation, and that’s too weird to be true!”

It’s all about journalism, not science.

[Half_Man_Half_Wit]

Yes, but those lists were just an example – sleep is considered unexplained by more reputable sources, such as Cecil, for instance.

[Sailboat]

Haven’t been able to find it via searches, but a while back there was some article or study suggesting the possibility that sleep serves to moderate predator activity. Animals that have a lot of impact on their prey sleep a lot, apparently, and those with less impact sleep less (as a generalization).

My understanding of what I read is roughly:

[ul]
[li]A given prey population can only support so many predators[/li][li]If those predators are less active, the prey population can support more individual predators[/li][li]More individuals permits greater genetic diversity and also serves as insurance against catastrophe, thus being an evolutionary advantage[/li][li]Thus sleep is advantageous to the predator population[/li][/ul]

[ultrafilter]

@Sailboat

Haven’t been able to find it via searches, but a while back there was some article or study suggesting the possibility that sleep serves to moderate predator activity. Animals that have a lot of impact on their prey sleep a lot, apparently, and those with less impact sleep less (as a generalization).

My understanding of what I read is roughly:

[ul]
[li]A given prey population can only support so many predators[/li][li]If those predators are less active, the prey population can support more individual predators[/li][li]More individuals permits greater genetic diversity and also serves as insurance against catastrophe, thus being an evolutionary advantage[/li][li]Thus sleep is advantageous to the predator population[/li][/ul]

Sleep-like behavior is found in worms, so it’s very likely not a predator-prey thing.

[Sailboat]

@ultrafilter

Sleep-like behavior is found in worms, so it’s very likely not a predator-prey thing.

I may have exaggerated the predator-prey aspect; what i recall reading admitted sleep occurs in most animals, but hypothesized that limiting activity was useful in reducing strain on resources generally.

[dracoi]

The problem with energy conservation, heat conservation and predator-prey explanations is they all ignore one simple observation: someone who rests while not sleeping is achieving all three goals and yet sleep deprivation still causes them to go insane eventually. (I’m using insane as a shorthand for the various mental symptoms of sleep deprivation).

Sleep clearly fulfills some mental process. Since we have a very poor understanding of other basic brain processes like learning, memory-formation, emotions and depression, it isn’t surprising that we also do not understand how sleep works in this sense.

[Der_Trihs]

@Half_Man_Half_Wit

All the while, I just keep thinking: but isn’t it, you know, obvious? And obviously, this means I’m missing something obvious. To me, it looks just like: there’s a cycle of activity and relative inactivity every living thing goes through. There’s a cycle of plentiful versus relatively scarce available energy (that whole thing with it’s warmer when the sun is up, etc.). So shouldn’t the most natural hypothesis be that the two are linked? That, when there’s less energy to consume, there’s less possibility for activity, and evolution takes it from there? I mean, we still see the same thing on a yearly basis: numerous animals, when the weather gets cold and resources become scarce, go to sleep for prolonged periods of time. Why shouldn’t daily sleep, at least in origin, have the same explanation?

For one thing, it doesn’t explain why animals that are active at all times still need sleep. Like dolphins, which can’t ever fall unconscious or they’ll drown; rather than not sleeping, they instead sleep one brain hemisphere at a time. And as said, when creatures cannot sleep they go insane and eventually die; an extreme case being fatal familial insomnia.

[Sage_Rat]

@dracoi

The problem with energy conservation, heat conservation and predator-prey explanations is they all ignore one simple observation: someone who rests while not sleeping is achieving all three goals and yet sleep deprivation still causes them to go insane eventually. (I’m using insane as a shorthand for the various mental symptoms of sleep deprivation).

Sleep clearly fulfills some mental process. Since we have a very poor understanding of other basic brain processes like learning, memory-formation, emotions and depression, it isn’t surprising that we also do not understand how sleep works in this sense.

If a bear is kept from hibernating, does it do alright or does it experience super sleep deprivation?

[dracoi]

@Sage_Rat

If a bear is kept from hibernating, does it do alright or does it experience super sleep deprivation?

Is hibernation the same as sleep?

[runcible_spoon]

@Der_Trihs

For one thing, it doesn’t explain why animals that are active at all times still need sleep. Like dolphins, which can’t ever fall unconscious or they’ll drown; rather than not sleeping, they instead sleep one brain hemisphere at a time. And as said, when creatures cannot sleep they go insane and eventually die; an extreme case being fatal familial insomnia.

Well, given that dolphins evolved from land mammals, it’s certainly not unreasonable to guess that at that point, sleep was already established as a need (by whatever brain processes make it so), and the adaptation that came up was the half-brain sleeping thing instead of getting rid of sleep altogether. Same reason why cetaceans didn’t re-evolve gills - at that point, it’s evolutionarily simpler to adapt than restart.

Mind you, that’s all WAG, but seems reasonable. What’s the simplest creature we know of that sleeps? Seems like that might be a clue to the origin, at least.

[Half_Man_Half_Wit]

@runcible_spoon

Mind you, that’s all WAG, but seems reasonable.

That’s kind of where I stand with the OP, too…

What’s the simplest creature we know of that sleeps?

Well, it’s difficult to exactly determine what counts as ‘sleep’ in extremely simple organisms – you can’t really monitor brain activity, or see them close their eyes. The simplest organism I know of where it’s unambiguously known is the nematode (worm) C. Elegans. And of course, we all know that even plants have dormant states, which only makes sense, as they depend on the Sun’s energy far more immediately than animals do.

In a certain sense, all chemicals ‘sleep’ at night: the chemical activity in a warm pond will be higher than in a nightly cooled one, so it’s to my mind not unreasonable that sleep just takes off from there, right along with the creation of life.