Re: Does our circadian cycle provide evidence we originated elsewhere?

Dave-
You pose an interesting question. As a general answer, I think it would be hard to causally relate a discrepancy in circadian rhythms to an idea that shows we did not evolve here on earth. Even if we did have really different circadian cycles than most animals, that observation could be explained by a lot of different things other than ontogeny from extraterrestrial origins.

That being said, it looks like we have similar circadian cycles to many other animals. Most mammals appear to have a basic circadian ‘cycle’ of between 23-25 hours. The amazing thing about a circadian pacemaker is that it can be reset (“entrained”) by environmental cues, such as light. It’s as though the system is engineered to have a little slop; it gets in the ballpark, but utilizes the rise of the sun to make sure it’s truly on the 24 hour scale.

But what does the pacemaker do if there’s no cue like light to reset the rhythm each morning? Several people have looked at this, and have found some striking results. In the absence of light, animals (monkeys, mice, and men) all stray a bit from the 24 hour day. For most mammals, the internal clock runs closer to 25 hours (23 in some mice). After long periods of no cues, the clock can run longer, maybe up to 30 hours at times (but it generally varies between 25-30 hours).

So now enters the length of the day – which is generally increasing as years pass (as you pointed out). However, the increase is pretty slow – the day increases by 2.2 seconds every 100,000 years! But animals have been on earth for a pretty long time, so this could still be a significant change over the course of life on earth. So we do a little math:

Mammals first appeared on earth about 225 million years ago and we know how fast the day’s length changes:
   225,000,000 years
    x 2.2 sec/100,000 years
------------------- -----------
Equals: 4950 seconds

Exactly why the clock is a little slower than a day for most animals is a good question. Perhaps animals in the past were able to detect that days are getting a little longer and have overcompensated. Or perhaps severe, climate-changing events (such as volcanic eruptions) occurred during a large part of particularly sensitive time during evolution; it might be dark for days on end with all the ash in the sky. If only we could go back in time and look at animals millions of years ago to see how long their bodies thought a day should be!

I hope this sheds some light on the topic. I’ve included a few scientific papers and websites where I got my info.

cheers,
Alex

References

Society for Research on Biological Rhythms: http://www.srbr.org/

A page on Biological Clocks with some nice links: http://www.oikos.w arwick.ac.uk/~bioar/circad.html

Siffre, Michael. "Six Months Alone in a Cave." National Geographic, March 1975; 426-435.

R.A. Wever (1979) The circadian system of man: results of experiments under temporal isolation.

Pittendrigh & Daan, A Functional Analysis of Circadian Pacemakers in Nocturnal Rodents, J of Comparative Physiology , 106 (1976), 223 - 252

Sulzman FM, Fuller CA, Moore-Ede MC, Environmental synchronizers of squirrel monkey circadian rhythms, J Appl Physiol 1977 Nov 43:5 795-800