The Evolution Of Sleep

That raises the question of what makes us tired. How do we know/recognise when we are tired? What triggers it? Is it some sort of chemical/hormone?Can we learn anything about the biological nature of sleep from studying narcoleptics and insomniacs?

Yes. Adenosine: it builds up while we are awake and dgreades when we are asleep. We do, but sleep disorders are often not normal sleep so it's harder to generalise from.Edited by Larni, : No reason given.

I'm not sure if this applies generally to predator/prey relationships (although I suspect it does), but since you're talking cheetahs, grazers on the African plains tend to sleep much, much less than the hunters. Whereas hunters will happily spend more than half the day asleep (lions average something silly like 16 hours a day), antelope only sleep a few hours, and this they do in short naps, whilst standing up, and are easily startled awake by loud noises.I imagine the antelope are pushing the limits of what you can get away with; and it probably makes more sense from an energy efficiency point of view for the lions to not directly compete on the sleep front, instead conserving energy for as long as possible between meals. If they catch sufficient meals in their few hours of wakefulness anyway, why increase your energy demands by only sleeping a quarter as often?Edited by caffeine, : No reason given.

But even when awake it is possible to have very vivid hallucinations and visions (I'm not knowingly prone to such things but I have experienced my share of recreational drugs). And if I close my eyes I can very clearly imagine the face of my son (for example) who I last saw a couple of hours ago.So I don't think such clarity is necessarily a feature of dreams specifically.

But here you are talking about two different things: sleep and dreams.The act of being asleep can have more than one function.

I agree. I'm just not convinced by GDR's idea that images within dreams are necessarily superior.I suspect the main difference is that when we dream it seems more real because we are not consciously aware that we are dreaming and that it isn't real.Or something like that.

If they evolved to their places after sleep had already evolved, it could still... but yeah, I doubt the circadian rhythm is the entire explanation. Energy regulation should be a big factor too. But fish do have a more primitive form of sleep. I'm still not seeing what's so bizarre about it? Seems like a good idea to me... Well, my computer does have a sleep mode (although nothing really happens during it). Don't most of the droids in Sci-Fi have it too? Is there any reason to think that we wouldn't? Nothing runs forever and everything wears down, so it makes sense to delay the inevitable with a sleep mode. Wouldn't they? You said it right there, even with an ultimate result of escalation, the whole thing is kept in blance through graduality. If having a sleep state means having to spend less energy, then that benefit could be the selective pressure away from an arms race to sleeplessness. I suppose they could, but then, what kind of energy input is that going to require? How much would you need if you had to do all your repair work while you were running at full speed? Would that be sustainable? So instead of sleeping at night, you just have to be eating the whole time? Would that really be better? Shit, now I got to get another job to pay for all this extra food I need, or I could just shut down instead. Would you want an engine that you never had to turn off but that you had to change the oil in on your way to work? Is your question why the oil doesn't just work longer? Or why there's no perfect engine?

Oh I don't know. It just occurred to me how odd sleep is in an evolutionary context. Apparently I find it more odd than most. Although some googling around suggests that the question of why exactly we sleep is at least deemed an interesting scientific question that we have yet to fully answer.The fact that all complex lifeforms do seem to sleep and that it seems to have evolved at least twice independently (to our knowledge) suggests that there is something rather fundamental about it.I suppose what I am asking (to put it into geek speak) is why it is that despite all our seeming biological refinements we are more like Windows operating systems than UNIX. Windows needs to rebooted all the blasted time whilst my record for a UNIX box is seven years and counting.But now I am just letting my work frustrations infringe on the far more important activity of internet foruming......

Where did we establish that it evolved independently in deuterostomes and protostomes? Catholic Scientist threw it out there, but I can't find any evidence anywhere for the idea. If sleep is so widespread even in quite simple animals, a single origin seems the default assumption to me.

Fair point.In my own ignorance I took CS's speculations to be more authoritative than even he probably intended. I can't find any support for this claim either.And I agree that it seems more likely that the origin lies in a common ancestor to both. Which makes sleep something that arose very very very early in our evolutionary past.So where does that leave us on the 'Would evolved aliens also likely sleep?' question?

I don't actually have a point in all of this except that I find it strange. I can look at a face, close my eyes and create a mental picture. The mental picture I get is a memory of what I was just looking at.In my dreams however, it is much more like what I experience when I'm awake with my eyes open and in some cases I dream of things and people of which I have no memory.With a bit of circular reasoning I think that it has something to do with the consciousness or mind being a reality that isn't a physical reality. That however is JMHO. I think dreams have a lot to do with needing sleep and so I think that discussing dreams is consistent with the theme of this thread. I thought I’d add that before some sharp eyed admin tells me I’m off topic.

Why do you find it so odd?Anything besides the pred-prey relationship? Life evolved on a planet that was dark half the time... Sounds like the creationist musings on why evolution didn't give us eagle vision...There's lots of "issues" like that because you only have to evolve to be good enough.

The apparent inefficiency of it. The vulnerable state it leaves us in. The fact that a whole mechanism for allowing our imagination to run wild (i.e. dreaming) whilst restricting us from acting out these fantasies (we apparently undergo a sort of mild induced form of paralysis whilst REM sleeping) has evolved. The fact that despite all of us all doing it (along with practically every other complex living thing on the planet) scientists still don't really understand why we do it or how exactly it works. The strangeness of phenomena like sleepwalking (people have apparently sent emails and even cooked whilst asleep!!!), narcolepsy and insomnia. The lack of rhyme or reason in how much sleep is needed (a giraffe needs less than 2 hours of sleep a day and an elephant about 3 - Why? I would have thought size would make sleep more necessary). Etc. etc. etc.In general it just seems to be a very strange and interesting phenomenon. It just made me think - How the hell did that evolve? Apart from anything else with a five year old and one year old it is something which I am desperately short of and something which is much on my mind. LinkLinkEdited by Straggler, : No reason given.

Whilst the mind body problem is a fascinating topic in itself (maybe I'll start a thread at some point) but let's not explicitly go there here. But on that note....You must admit that physical things (e.g. drugs) can induce dream like states, hallucinations and all of the other things that you seem to consider non-physical. Isn't sleep (and dreaming) just bio-chemistry at the end of the day? Well if I have any say as the starter of the topic I would like to agree with you in a bid to keep those sharp eyed admins at bay.

If I were a creationist looking for a gap I think the whole issue of sleep and dreaming would be rife with opportunity. No obvious evolutionary explanation agreed upon by science as a whole and lots of opportunity for subjective mysticism regarding dreams and the like.This isn't an invite. Just an observation.