How much sleep do humans and fish need?

A tiny tropical fish called the anableps has eyes that work just like a pair of bifocals. The upper half of each eye is focused for water-surface vision, the lower half for underwater sight.

Gasoline has no definite freezing point. Ordinary gas will solidify only under temperatures of between 180 and 240 degrees below zero—a temperature which has never been reached on this planet outside the laboratory.

Slumberland

How much sleep does one need? Answer: Anywhere from five to ten hours. Science has come up with no explanation as to why one individual requires more sleep than another. An infant sleeps most of the day because he is growing at a faster pace than at any other period in his life.

As we age, the quality of our sleep tends to gradually deteriorate. The sleep of older people is sometimes so fragmented that it is little more than a series of catnaps.

Winston Churchill managed to turn his handicap into an advantage. He took short snoozes throughout the day to rejuvenate himself; and he insisted that his daily nap in the afternoon turned one day, in effect, into two.

Still, medical evidence suggests that sustained sleep is more helpful; "to sleep like a baby" is an apt description of ideal slumber.

However, not even the sleep of infants is always tranquil. In the 1950s, psychologists Eugene Aserinsky and Nathaniel Kleitman observed a regular pattern in the sleep of infants: intervals of quiet slumber alternated with periods of body activity.

Extending their discovery to a study of adult sleep, these scientists noticed recurring periods of rapid eye movements (REMs) beneath the closed lid, alternating with periods of peaceful sleep. These REMs, the psychologists learned, signaled the onset of dreams.

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