Why do we sleep?

Eric Mintz mintz at orchid.UCSC.EDU
Thu Feb 17 15:15:58 EST 1994

In article <9402171428.AA50438 at polywog.biology.uofs.edu> greuelb1 at jaguar.uofs.edu (Brian T. Greuel) writes:
>I would like to ask a related question that I have often wondered about:
>Why do we sleep?  Is there something that builds up in our bodies that gives 
>us a feeling of fatigue and that during sleep gets metabolized somehow so 
>that we feel refreshed upon waking?

The idea that something builds up in the body or brain which causes sleepiness
and then gets metabolized during sleep is known as the restorative theory
of sleep.  The theory has several problems with it.  The main problem
is that after years and years of looking, no one has been able to find
anything that would serve this function, and that is not for a lack of 
trying.  In addition, there is at least one animal, the pigeon, which 
can be sleep deprived indefinitely without showing any ill effects,  and
when the sleep-depriving stimulus (continuous light) is removed, they
show no sleep "rebound."

An alternative theory is that sleep evolved as a mechanism for energy 
conservation.  Sleep involves a reduction in metabolic rate that can
yield significant energy savings.  This does not preclude the possibility
that a restorative function evolved afterward in some species.

Eric Mintz
mintz at orchid.ucsc.edu

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