Thread: Why Do We Sleep?

There was a documentary on the Beeb last night about sleep, and it was pretty cool to see that Stephen LaBerge and his lucidity research was featured in the last ten minutes or so; it's probably on the net somewhere if you wanna watch it (it was a Horizon program I think). He seems like a pretty cool guy.

Anyway, the main thing that hit me during watching it was the following fact; every night, for about 8 hours - a whole third of our day - we go into a state of unconscious paralysis; and we consider it completely normal, even though we have absolutely no idea why it happens. Isn't that utterly bizarre?

There is still no accepted hypothesis for the function of sleep at all, which is really quite ironic considering how much we have learnt about the most obscure workings of the the universe, completely detached from human experience.

Even more mysterious is how anomalous this is in the context of natural selection. For an entire third of the day, mammals become completely unresponsive. The ability for the organism to find food, reproduce, and defend itself, is effectively decreased by a 1/3. This is a huge disadvantage. The fact that it hasn't been weeded out shows that there is something extremely crucial to the process.

But what? The only explanations I've heard so far are extremely weak. For example; 'we need it to form long term links between experiences'. Not particularly; don't we do that to a large extent during waking anyway? This also fails to explain why mental function completely collapses without sleep for a long time, and seems completely inadequate to sacrifice an entire 1/3 of the organism's ability to create offspring. The same applies to an even greater extent to theories such as 'we heal a bit faster' (not remotely worth 1/3, and why exactly do we need to switch off our brains to perform what must be a simple metabolic function?), etcetera.

Personally I think the reason could be much more profound, relating to the inner workings of the neural network of the cerebral cortex, which are so far completely unknown. I'm completely open to other ideas though.

to me it almost feels like its simply a way for my brain to recoup from all the information being blasted on me and the stress being put on my body. Maybe because we pick up SO much information on a daily basis we need more respite from it?

Originally Posted by Xei

Even more mysterious is how anomalous this is in the context of natural selection. For an entire third of the day, mammals become completely unresponsive. The ability for the organism to find food, reproduce, and defend itself, is effectively decreased by a 1/3.

That's not true at all. When sleeping, mammals are responsive, hence why they wake up when threatened. Also, most mammals in the wild don't sleep a full 8 hours, or at least not in a single chunk. And of course, they don't just fall asleep no matter what; the process of falling asleep requires the perception of a perfectly safe surrounding.

Originally Posted by Xei

This is a huge disadvantage. The fact that it hasn't been weeded out shows that there is something extremely crucial to the process.

It's clearly an advantage since evolution positively favours it.

Originally Posted by Xei

But what? The only explanations I've heard so far are extremely weak. For example; 'we need it to form long term links between experiences'. Not particularly; don't we do that to a large extent during waking anyway?

No. Numerous studies have shown that sleep is necessary for the formation of long term memories.

Originally Posted by Xei

This also fails to explain why mental function completely collapses without sleep for a long time,

I don't understand this comment. If the hypothesis is that sleep helps form memory, then that alone would explain mental collapse.

Originally Posted by Xei

and seems completely inadequate to sacrifice an entire 1/3 of the organism's ability to create offspring.

Since evolution favours sleep, this 1/3 figure is obviously blatantly wrong.

Originally Posted by Xei

The same applies to an even greater extent to theories such as 'we heal a bit faster' (not remotely worth 1/3, and why exactly do we need to switch off our brains to perform what must be a simple metabolic function?), etcetera.

You don't think being immobile for 8 hours might make wounds heal faster? Um...

Constant sensory input would hinder our ability to organize and compartmentalize the sensory input we've already received. Most people have experienced working on a problem, absorbing all of the information about that problem but have been unable to come up with a solution until after a good night's rest. Sleep allows for a period of introspection to reorganize sensory input into a useful combination.

Not to mention the fact that our bodies need a certain amount of rest per day to recuperate from activity, repair muscles torn microscopically in exercising, etc.. Nor does the human body absolutely require a full eight hours of sleep (which is more like seven and a half to nine, anyway, due to 90-minute sleep cycles by and large) every night; biphasic and polyphasic sleep schedules must be taken into account. The latter is not recommended for active people such as athletes or heavy laborers, however, due to the body's need for rest in Delta (I believe) sleep.

Also, sleep deprivation stunts growth. No sleep=shortness despite genetics.

Originally Posted by Black_Eagle

Also, sleep deprivation stunts growth. No sleep=shortness despite genetics.

Makes sense. Gravity and all that.