NATURAL BODY CLOCK
Why do we have a biological clock? It has been suggested that, during the course of evolution, organisms have maximized their use of the environment so as to maximize their chances of survival. It has been shown that man’s efficiency varies during the 24 hour period. We perform best between 7 a.m. and 11 a.m. in the morning, and worst at 3 a.m. at night when most of us are sleeping. Hence, for man, sleep coincides with the time of lowest efficiency, which is at night. A phase map can be constructed for each bodily process within the 24 hour period. The phase map for body temperature shows that temperature is highest in the day and lowest at night. It has been suggested that the phase map of sleep coincides with the reduction of body temperature at night Dr Charles Czeisler of the Harvard Medical School claims that he can shift a person’s circadian rhythm quickly by exposing them to strong light and thus resetting the body block.
What about a natural body clock? Do we have one that is not under the influence of the sun? In one experiment, conducted in 1972, a French cave explorer, Michel Siffre, lived underground in a Texas cave for seven months, away from all noises and civilization. He was not permitted to have any watches, clocks, radios, or televisions. In other words, his external cues for time were removed completely. Under these experimental conditions, without an external time cue, the body clock was free running. After a period of days the natural body clock would emerge. It was found that under free running conditions the human body clock was about 25 hours.
However, once he returned to the natural environment, the body clock was reset to 24 hours again. This resetting of the biological dock depends on external cues, the strongest being the change from dark to light.
Experiments have also shown that if we are placed in an artificially lit day of 19 hours and an artificially dark night of 9 hours, we can be trained to live in a 28 hour clock. In this case the biological clock gradually becomes a 28 hour clock instead of a 24 hour clock, and the phase map of temperature shows a maximum once every 28 hours instead of once every 24.
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