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From: cosell@bbn.com (Bernie Cosell)
Newsgroups: sci.bio,sci.misc
Subject: Re: 25 hr day
Message-ID: <58173@bbn.BBN.COM>
Date: 13 Jul 90 12:14:23 GMT
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arrizzo@cbnewsl.att.com (anthony.r.rizzo) writes:

}In article <33843@ut-emx.UUCP> tmca@emx.UUCP (The Anarch) writes:
}#OK, I gotta question:
}#
}#	I'm told, through various reputable sources, which I can't remember
}#just this minute, that the majority of the human race lives on a 25 hr 
}#schedule, and some on as long as a 27 hr schedu
}#... Now this is all very well, and would
}#explain admirably why I can't get up of a morning, but, being a scientist
}#'n'all, I can't help but think that there ought to be some good reason
}#for this. After all, the Earth has been running on a 24 hr day for quite
}#some time now, and I'd've thought that we'd have caught up by now. Anyone
}#got any ideas?


}I agree with you.  There must be some good reason for the mismatch,
}and it must be evolutionary in nature.  Here's my idea:
}the 25 hr to 27 hr cycle is observed only in the laboratory.
}Individuals eventually reverse their sleep/waking periods
}completely if their bodies are not permitted the luxury of
}some form of clock or time reference, such as the sun.
}However, outside of the laboratory such a time reference
}is inevitable.  We're usually awakened by sunlight and
}animal noises, in the absence of a timepiece.  Therefore,
}outside of the laboratory, such as in the wild millions
}of years ago as well as now, the body's cycle is reset
}each morning.  I suggest that the longer cycle ensured
}a necessary degree of alertness at dusk, when most
}predators go hunting....

Actually, I have a simpler conjecture.  Just try to figure out how YOU
would design such a cycle.  It is obviously important for the body
functions to stay in sync with the sun, and so you need some kind of
fairly stable cycle.  Well, about the simplest mechanism I can think of
to do that is to have a simple positive-sync mechanism, and then have
the natural cycle be just a bit too long.   Thus, the animal would
sleep through the night, and the rising of the sun (for diurnal
animals) would 'sync' the cycle and start it up.  And so you'd have
nice feedback and the cycle would stay in sync.  What happens if the
cycle is too short?  Well, your body would start its new day too early,
and then an hour or so later the 'sync' would come but what should your
body do then?  Things have been going already, your body temp has
changed, the metabolism sped up, and it is real hard to see how the
body would use the hour-late sync [and more importantly, when you wake
up ANOTHER hour earlier the next day, the sync comes *two* hours late,
and it is hard to see how the feedback would work].

On the other hand, mostly the body is idling through the night and
having the sync-pulse kick off the start of that day's rhythms works
perfectly --- and all it takes is to have the *natural* cycle be just a
bit too long, so that when the sync comes you're still on 'overnight'
and _just_ about to kick the new-day systems in.

As a meta comment, there were some studies [by the Air Force I think,
it was written up in one of those books about how to beat jet lag].  It
bascially said that the onset-of-daylight was the *primary* mechanism
for regulating the circadian cycles.  And so their recommended jet-lag
procedure was that prior to your trip you work fairly hard to mess up
your rhythms [e.g., you avoid going out in broad daylight, you change
your eating habits, etc] The idea is to give you body as little
syncing-feedback as you possibly can, and to actually interfere with
the cycles as much as you can.  This is all orchestrated so that it
builds to a climax on the day of your trip:  the idea is that while
you're on the airplane winging your way to whereever, you want the
buildup to have resulted in your body being *totally* confused an
de-synced.  There won't be much of anything to resync it on the plane,
of course.  And then you arrive at your destination and the theory is
that your bod will almost-instantly sync up to the new cues.  Dunno if
it works or not --- I never had the patience to follow through with the
whole two-week-before-the-trip plan.

  /Bernie\