Re: [LEAPSECS] building consensus

From: Rob Seaman <>
Date: Wed, 7 Jun 2006 10:03:49 -0700

On Jun 7, 2006, at 2:01 AM, Clive D.W. Feather wrote:

> Actually, the evidence from experiments is that the "natural" sleep-
> wake
> cycle is about 27 hours long, but force-locked to the day-night
> cycle (it's
> easier to synchronise a longer free-running timer to a shorter
> external
> signal than vice-versa).

References for this? Your explanation makes a lot of sense and I'm
prepared to be convinced, but have been skeptical of experimental
design as applied to questions of human behavior since participating
in studies as a requirement of undergraduate psychology coursework.
And if this cycle is inferred from the behavior of undergraduates,
I'm even more skeptical :-)

> So humans will cope until the solar day is about
> 27 (present) hours long, after which we'll probably start to move to a
> system of two sleep-wake cycles per day.

Well, "cope" isn't the right word if this cycle is as you describe.
Also hard to imagine how one gracefully transitions from one to two
sleep cycles a day. It would simply appear that the underlying
mechanism evolved to rely on a slightly longer free-running timer
synchronized to length-of-day. As the day lengthens, Darwin would
predict that our intrinsic cycle would also lengthen. This is
similar to arms races leading to other periodic natural behavior such
as prime number 13 and 17 year locusts. (Non-primes would allow
locust predators to emerge more frequently while locking into the
phase, thus gaining an advantage.)

Also, whether or not one believes that humans have somehow escaped
the grip of evolution, it is hard to imagine our continued sojourn on
Mother Earth half a billion years hence :-)

Obvious lines of research for further sleep period investigations
would be to examine similar cycles in other animals. One imagines
this is some function of the nervous system, so one might also
contrast strategies pursued by plants and animals without. Also -
how is this intrinsic cycle inferred? Could signatures of this
intrinsic cycle be preserved in the fossil or DNA record? All sorts
of other cycles are. Could such signatures be correlated with length-
of-day at various epochs?

Just another mechanism tying our species to time-of-day.

Received on Wed Jun 07 2006 - 10:04:23 PDT

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