Brilliant_ The Evolution of Artificial Light - Jane Brox [113]
There is one stirring hour unknown to those who dwell in houses, when a wakeful influence goes abroad over the sleeping hemisphere, and all the outdoor world are on their feet. It is then that the cock first crows, not this time to announce the dawn, but like a cheerful watchman speeding the course of night. Cattle awake on the meadows; sheep break their fast on dewy hillsides, and change to a new lair among the ferns; and houseless men, who have lain down with the fowls, open their dim eyes and behold the beauty of the night.... At what inaudible summons, at what gentle touch of Nature are all these sleepers thus recalled in the same hour to life?...Even shepherds and old country-folk, who are deepest read in these arcana, have not a guess as to the means or purpose of this nightly resurrection. Towards two in the morning they declare the thing takes place.
Given a chance, many humans will fall back into that medieval pattern of sleep, which may have been the way even the first humans slept. When Dr. Thomas Wehr and researchers at the National Institute of Mental Health attempted to replicate prehistoric sleep conditions by imposing on a group of men a daylight time of ten hours—what people in the middle latitudes during the dead of winter experience—he found that they
slept only about an hour more than normal, but the slumber was spread over about a 12-hour period. They slept for about four to five hours early on, and another four to five hours or so toward morning, the two sleep bouts separated by several hours of quiet, distinctly nonanxious wakefulness in the middle of the night. The early evening sleep was primarily deep, slow-wave sleep and the morning episode consisted largely of REM, or rapid eye movement, sleep characterized by vivid dreams. The wakeful period, brain wave measurement indicated, resembled a state of meditation.
"We think Thomas Edison had a bigger effect on the human body clock than anyone realized," remarked Dr. Czeisler. Edison, who favored catnaps on his laboratory tables, would have loved to think so, for he once commented, "Everything which decreases the sum total of man's sleep, increases the sum total of man's capabilities. There is really no reason why men should go to bed at all." Few would now agree with Edison, for although we may not yet know why we need to sleep, most people now understand it to be essential. As researchers look more deeply into sleep, they increasingly discover the true toll its lack takes on the physiological and psychological well-being of humans. Sleep-deprived people are more prone to elevated blood pressure and blood glucose levels. Lack of sleep depresses the immune system, affects memory and brain function, and shifts levels of the hormone leptin, which controls appetite, so it may also contribute to obesity.
We humans can alleviate the way artificial light creates havoc with our biological clocks: sleep institutes, sleep programs, sleep doctors all prescribe a regimen that re-creates ancient life. In addition to advising insomniacs to get daily exercise, avoid stimulants, and slow down in the evening, experts suggest that they avoid bright light at night, go to bed in a dark room, and sleep until daylight. But other creatures adversely affected by our light can do little more than suffer its effects or adapt to it. Nocturnal animals hunting in the dark, as well as those abroad in daylight that sleep at night—standing up, or with one eye open, or in hiding—are at its mercy, and human light not only affects their circadian rhythms; it can also compromise their chances for survival and even alter their evolutionary trajectories.
As with humans, the