Sleep 100%

Lack of inactivity that results from sleep may have helped animals to survive according to evolutionary perspectives. As a result, they weren't as exposed to danger, which increased their chances of surviving. The adaptive-inactivity theory of sleep posits that sleep is a product of continuous evolution. The theory states that humans need to sleep now because it was advantageous for them to have slept in the distant past. Humans slept at night because they were safer asleep in one spot during the night than if they had been hunting for food in the day, especially since their eyesight at night was so poor.

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The sleep cycle has five stages: stages 1-4 and the REM (rapid eye motion) sleep stage. Stages 1-4 are also known as NREM or non-REM sleep. During stage 1 sleep, the brain is dominated by theta waves. The sleeper is in a very light sleep with closed eyes, but the sleep is very light and it is easy to be woken up. Indeed, sometimes a person wakes up with a start in a phenomenon called a hypnic jerk. During stage 2 sleep, the sleeper's muscles begin to slowly contract and relax as the sleeper twitches. The body begins to slow: heart rate, breathing pattern, and body temperature all fall during this stage. The brain continues to be dominated by theta waves, but it will begin to contain deeper delta waves. Stages 3 and 4 sleep are very similar. Usually, scientists differentiate the two categories by stating that during stage 3, less than 50 percent of brain waves are delta waves, and during stage 4, more than 50 percent of brain waves are delta. Some scientists are even beginning to classify these groups together into one stage 3 category dominated by delta waves. It is during these stages of sleep that the sleeper is most deeply asleep and is receiving the most intense physical and psychological recovery. The last stage of sleep is known as REM sleep, so named because of the rapid eye movements that accompany its occurrence. During this stage of sleep, the sleeper's brainwave pattern begins to show much more activity. In fact, the brain waves of this stage closely resemble the alpha or beta wave pattern of an awakened person. It is during this stage that a person will experience dreams.

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A dolphin's sleep cycle is very different from that of a human being. A dolphin's unique biological situation (conscious breather, aquatic animal) makes it so that sleep, which rests the entire brain and is occasioned by the loss of conscious behavior, would be fatal. Instead, dolphins sleep with only one half of their brain at a time, and they regularly come to the surface for breath during one of their sleep cycles.

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