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Re: Evolution of sleep



--- Dann Pigdon <dannj@alphalink.com.au> wrote:
> don ohmes wrote:
> > 
> > To expand the question:
> > Assuming sleep correlates with sharply reduced
> > alertness/awareness, what is the across-the-board
> > selective advantage of unconsciousness that
> prevents
> > at least some vertebrate animals from evolving
> always
> > on status relative to mental awareness? Or if
> there
> > are some, why are they rare?
> 
> Sleep may simply be a way of conserving precious
> energy while an animal
> is inactive. Few vertebrates are able to do what
> they do best 24 hours a
> day. A species with poor eyesight and no other keen
> senses to fall back
> on (like us apes) will be virtually useless on a
> dark night. To remain
> active during those hours when they can't forage for
> food would burn up
> energy uselessly. Remaining still in a safe place
> may also reduce the
> chances of a predator discovering you at a time when
> your senses aren't
> at their best.

Granted. But the question was why can't we rest/be
still/remain safe without being unconscious.


> Us larger-brained vertebrates may also sleep more
> than other species due
> to the tremendous amounts of data our brains have to
> process. Go for too
> long with out sleep and information may start to
> back up, forcing the
> brain to take cognitive shortcuts in order to deal
> with the back log
> (hence the halucinations).

Excellent point. It may be a defrag thing. IMO, we
might all be surprised how far down the evolutionary
ladder this goes. I guess that whatever it is that
processes sensory stimuli just has to shut down
periodically, a basic limitation of the animal
kingdom. Or a pathway taken so long ago that selection
can't reach it anymore. It appears from what I read on
the list that the best extant animals can do is
arrange for a partial shutdown. 

> Dolphins (and probably whales) can't breath
> automatically, so complete
> unconsciousness would lead to drowning. Hence they
> rest in a state of
> semi-unconsciousness, where half the brain is still
> active enough to
> keep breathing and stay at the surface, while
> reducing brain activity
> enough to prevent 'cognitive burnout' (a
> halucinating dolphin would be
> an interesting sight, though!).
> 
> -- 
>
___________________________________________________________________
> 
> Dann Pigdon
> GIS / Archaeologist        
> http://www.geocities.com/dannsdinosaurs
> Melbourne, Australia       
> http://heretichides.soffiles.com
>
___________________________________________________________________
>