The first explanation of why we need to sleep is coherent with the theory of evolution and survival. Hibernation, which is like a very deep sleep in winter for some animals, has been studied extensively by biologists. It is an adaptive survival mechanism enabling certain animals to survive long snowy winters; without it, many of these animals would face extinction. The hibernating animals do not need food during the winter months, at a time when food may be scarce or unavailable. Just before winter comes, they have built up a great deal of body fat. When winter arrives, they automatically go into extremely low activity and so can survive solely on their fat reserves. There is very little movement, the body temperature is very low, the metabolism is minimal, and the breathing is slow and shallow. The brain waves of these hibernating animals are nearly silent and are in distinct contrast to those of sleep. Normally, during hibernation, the animals cannot be aroused, even if given a good shake.

Hibernation has been studied in laboratory conditions. The animals are kept inside in the warm with plenty of food throughout the winter. However, they still go into hibernation, as if there is a need for them to do so. Hibernation is an innate mechanism in these animals; they do not have to learn how to hibernate. Hence the mechanism could have been handed down from one generation to the next through the genes.

What about sleep? Sleep is distinct from hibernation. This is shown by the different brain wave pattern and the fact that an animal can always be aroused from sleep but not from hibernation. Sleep is possibly another evolutionary adaptation to survival. The earth rotates once every 24 hours and any one point on the surface is in darkness nearly half of this time. Man has been walking on the planet Earth for over a million years. Remember that artificial light such as candles, oil lamps, and electric lights are inventions only of the last few thousand years. During the long dark night, primitive man had nothing to do. In fact it could be dangerous to move around in the dark. Man could injure himself easily by tripping over in the rugged country or through meeting some vicious animal. Hence he withdrew, stayed put, closed his eyes, and slept.

The need to sleep at night not only withdraws us from a dangerous environment, but also allows us to rest and restore our energy. Sleep is an innate biological function like hibernation, and has been studied under laboratory conditions. Even if the room is continuously brightly lit without the cue of what time of day or night it is, we still feel the need to sleep once every 24 hours or so. Here, the need to sleep is very similar to the need to hibernate—an evolutionary adaptation for survival.


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