Monday, June 18, 2007

Et In Circadia Ego

Mammals evolved on a planet with a day that is 24 hours long, or thereabouts. So it should come as no surprise that genes are finely tuned to Earth's daily cycle.
"New research from Colorado State University shows that the function of all genes in mammals is based on circadian -- or daily -- rhythms. The study, refutes the current theory that only 10 percent to 15 percent of all genes were affected by nature's clock. While scientists have long known that circadian rhythms regulate the behavior of the living, the study shows that daily rhythm dominates all life functions and particularly metabolism." (Here.)
The fact that the Earth's 24-hour "daily rhythm dominates all life functions" has got to have implications for long-term human settlement of other planets in our Solar System.

Mars has a day that is about 40 minutes longer than 24 hours. Some JPL Rover scientists and engineers lived on Mars time early in the mission and the experiment played havoc with their lives. Some of that can be attributed to what was, in essence, trying to live on two planets at once. (Here.) But other research has shown that living non-Earth standard days harms human health and productivity and leads to "jet lag in space." (Here.)

Research by Brigham and Women’s Hospital’s (BWH) Division of Sleep Medicine has shown that humans can function in a longer day by resetting their circadian rhythms through modulation of the brightness of artificial light over the course of a day. (Here.) But the purpose of the BWH research was to find measures that would allow humans to work effectively in a non-Earth standard day on missions with a defined length.

How will humans cope with living non-standard days for their entire lives? And if every single life function down to the genetic level is tuned to Earth's 24-hour daily rhythm, how will humanity change once new generations are born and die off-Earth?


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This sounds like one more reason to prefer O'Neill style space colonies over living on planets other than earth. In space colonies it's easier to duplicate earth gravity & light-dark cycles.

However, mammals, including humans do OK in the high arctic where there are months of continuous light or dark, so the effects of a different light dark cycle can't be too terrible.
Thanks for your comment, Jim. For the very reason you give, I'm starting to wonder if maybe living in free space might be the way to go for humans off-Earth. You make an interesting point about the high Arctic. But the Seasonal Affected Disorder suffered by many people living in northern latitudes is real-world evidence of the effect of extreme day-night cycles. I wonder if the fact that the extremes of long days and nights in the Arctic are seasonal would make a difference compared to the extra 40 minutes on Mars every day forever. That being said, you're right that people and animals thrive in the northern latitudes. So perhaps the answer for humans on Mars, for instance, will be as simple as modulated lighting or medication. Or some good Martian vodka!
Going totally Sci-fi, we could use moving space colonies which (on their journey to the destination planet) slowly adapt the living conditions to that of the planet. Over the generations required to reach said planet, the resulting humans would either be a perfect match for the living conditions or, in a more probably scenario, be deformed and inbred or entirely wiped out due to a lack of telephone sanitisers.
I'm not sure the "high latitudes" argument is a good one. Even if the day or night is longer, the entire cycle stays at 24 hrs. I'm not sure the 24.6 hr rythym, regardless of the day/night cycle, is the same thing.
I expect that if a generation ship did an interstellar voyage, the people who arrived would just build more space colonies to continue to live in the way they were accustomed. After a few generations of building space colonies & exploratory expeditions onto planets in the new solar system then settlement of the planets might start, possibly with genetically engineered settlers.

Months of continuous light or dark such as we get when well above the arctic circle doesn't much resemble a 24 hour cycle. There do seem to be psychological problems with lack of daylight, so the 24.6 hour cycle might also cause problems.
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