Evolutionary Basis for Sleep?
Posted on: December 21, 2008 - 6:56pm
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Evolutionary Basis for Sleep?
My psych textbook said that the evolutionary basis for sleep is still unknown, but it must serve some function as people die without sleep for 6-7 days and if it were possible a non-sleeping evolved organism would quickly outcompete a sleeping evolved organism.
I was wondering if my text was out-of-date or oversimplified. It said something about it being used for memory consolidation, but lack of memory consolidation wouldn't cause death after a week.
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As far as I know, there's no "official" answer yet, but here's a link to some new research compilations. I don't know how far you want to dig to find available papers, but this would be a good place to start:
http://www.bu.edu/phylogeny/projects/index.html
Here's a link to several PDFs available online:
http://www.bu.edu/phylogeny/publications/index.html
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I don't have a textbook answer for you, so I thought instead I'd just toss in some more random speculation: I think sleep itself is more likely a metabolic adaptation than a neurological one. Dreaming I think is the neurological one that aids memory. Dreaming comes later, after sleep had already evolved.
Imagine you're a predator. You've just caught lunch and need to digest it. There's no point hunting for more food, since your stomach is already full. No need to hunt, means less need to be alert and moving around. In fact, you may be wounded from the hunt, and it would be a good time to rest and heal a little bit. This scenario paints a picture of a lifestyle that would benefit from two distinct metabolic modes: one highly alert and active mode for hunting (or foraging, or whatever), and another less-active, less-alert, more regenerative mode for when food has already been eaten (or if energy just needs to be conserved, such as at night when there's not enough light to hunt or whatever). Given these two modes, it seems reasonable to speculate that genetic adaptations that supported the two modes would be advantageous.
Even full loss of consciousness might be useful to perform regenerative functions in the brain, which builds up stress as the more alert awake mode progresses throughout the day. In essence, I see this as a trade-off: I'll let you be even *more* active and alert during the wakeful mode (advantageous for hunting/foraging/whatever), but this causes a build up of stress, so you'll need to turn off that consciousness for a while so the sleeping mode and clean up the mess (stress hormones, etc. in the brain). There is a similar trade-off in being warm blooded: I'll let you move faster and for longer periods of time, but in return you'll have to eat more food during that time.
In fact, (another speculation) it may be that deeper sleep is an adaptation to being warm-blooded. Since wakefulness uses up so much energy, keep the metabolism as low as possible during the restful periods.
It also seems reasonable to speculate that some varieties of animals (say, mammals) became dependent on the continuous alternation of these modes, such that the sleep mode was necessary to perform basic regenerative functions in the body. So, as evolution progressed, sleep went from being optional to being mandatory. Thus, disrupting this cycle could actually lead to a build up of metabolic 'damage' (whether it be stressed out cells, build up of toxins in bloodstream, or whatever) which over time can actually lead to death.
However, I don't think they yet know the actual cause of death when it's caused by sleep deprivation. The person just drops dead after a while. I heard of a guy who was so caught up playing online video games that he just up and died from lack of sleep. Pretty crazy when you think about it.
(Side note: Dreaming appears to be more about re-wiring the brain than about metabolic maintenance. It's like putting your consciousness in a protective box (the dream) while the workmen come in to rennovate your brain. I think it's just a convenience that dreaming happens during sleep more often than in wakefulness. They complement each other that way. There have been studies that show that dreaming is involved in long-term memory and skill learning. Sleep without dreaming does not convey the same benefits.)
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There's a theory that the sleep and dreaming is necessary to sort out an experiences of the day, so we can manage with them better. In fact, we tend to have in our dreams a lot of what we do or think when we are awake. For example, when my co-worker at a car factory worked all the day along the cars, then she did the same in her dreams, until she got accustomed to this boring work.
I also have ocassionally this kind of dream sequences, but they're actually a minority. The vast majority of my dreams is always similar in some sense. It is about
Being in some place - tropical islands, river areas, industrial complexes, cities, villages, schools, or a combination of these things, or any imaginable place like that. And a few of the unimaginable.
Doing something - there's always some sort of quest, task, or errand which I have to do. I never remember what it is, because it's different almost every time. For example, being a guide to someone entrusted to me.
With someone - there are people with me, who I don't know and I have to lead them somewhere through some area, for example. There are also people I don't know in real life, but I'm very familiar with them in a dream. I also remember talking with them about some things, and I remember they sometimes didn't know what I'm talking about, though I expected them to know. These companions behaves as my friends, co-workers, teachers, or strangers I have to deal with. About what, I don't know, it's always obvious there.
How? - the actions usually doesn't involve flying. I had a dreams about flying, but in these kinds of dreams I just walk or run. Or run away. There seems to be sometimes not very friendly fauna. However, this doesn't scare me much, it belongs to the routine of the work.
"There" I recognize no thematic parallels to my real life. "There" I behave as a man at work, doing what I'm probably not bad at, but it's a working routine nonetheless. It's not always ideal, there's a lot of dark places, nicer places, completely normal places, ocassionally some monsters which spices up the action a bit, it's like a second life, different, but normal. Except I saw there a lot of things which I didn't understand, either there, or after I woke up... I mean, it's like a second world, not perfect just like ours, but also not much worse or better. Yes, there are sequences of very obvious memory catharsis, but they doesn't fit in the general scheme. This general scheme is described by more people, it seems almost like an objective phenomenon.
My favorite theory to explain this is based on books of Robert Allan Monroe. One of my life goals is to achieve the so-called permanent consciousness, so I can remember perfectly my dream sequences as they all will become a lucid dreaming. I already remember my dreams better than a majority of people.
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The fact is that just about everything above single-celled organisms sleeps. Sharks swim in a state of reduced brain function. As you suggest there would likely be an advantage that comes with not sleeping. That something is an advantage does not mean it will evolve. The only thing evolution "guarantees" is that harmful mutations will be eliminated. There is no quarantee that a beneficial mutation will arise, the Mutationmaker is blind.
But death in a week for humans is false. The voluntary record is longer than that but forget what it is. Google Guiness records. As it is a modern fun form of torture one assumes the involuntary record is longer than the voluntary one.
What is common among people who have not slept for over three days is personality changes. The DJ fad of staying awake was followed up and all those who were married were divorced soon after with 'a different person' being complaint.
There are guesses but no one knows what sleep is for. In Psych it is amusing it does not lead to the obvious observation that Freud was a fraud as dream analysis was a conerstone of his methodology. He was an MD and one can say that if he did not know his methods were helping no one then he was incompetent. But he was followed by an army of MDs getting into the business. They had to know they were not helping their patients and the methods did not work.
I propose they all be prosecuted for fraud because they are all knowing criminals.
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