Evolution of Sleep         Sleep in humans is defined scientifically on the basis of particular brain- wave patterns. But what about animals? Some scientists seem to think that sleep, as opposed to rest or inactivity, is a relatively recent evolutionary development. Some researchers will insist that to have true sleep the animal must have the same types of brain waves that humans do, namely, slow-wave sleep and rapid eye movement. This is the equivalent to saying that before we conclude that an animal can think, it must have the human capacity for language. For this reason, some researchers have used more relaxed definitions of sleep in different species (Coren). FIGURE 2 TYPICAL DAILY SLEEP TIMES FOR VARIOUS COMMON SPECIES OF MAMMALS (Rounded Off to the Nearest Hour) Source: Stanley Coren. Sleep Thieves. New York: Free Press Paperbacks, 1997,  p. 42.                 All mammals seem to show patterns of sleep. Animals that tend to graze like sheep, cattle, deer, etc… are always at risk from predators. Their only defense is to flee at the sight of danger. This is why grazing animals tend to only sleep for about 3-4 hours a day (Coren).         An amazing development in the realm of sleep is the very complex physical mechanisms that some animals use to get a little sleep. A fascinating example is the northern fur seal. This animal spends several days away from the shore on fishing expeditions. Sleep becomes a problem because this is an air-breathing animal. If it fell asleep it would sink to the bottom of the ocean and drown. In order to prevent this, the seal has developed a complex system. Its brain is structured like the human brain; two hemispheres, the left side of the brain controls the right side of the body and vice versa. The fur seal will gently flap its right flipper, using its left side of the brain, just enough to keep his little nose above water. Meanwhile the unused right side of the brain will rest. Then in about 20 minutes the seal will flip over and rest the other half of its brain! This mechanism is also found in some species of dolphins (Coren). Marine mammals in general have very peculiar sleeping habits. The Indus dolphin never stops swimming. If it did it would risk injury from strong currents and debris. Scientists were shocked to learn that this animal sleeps for seven hours a day. The trick is that it doesn’t sleep for seven hours all at once. It takes short naps, with the longest around 60 seconds and the shortest around 4 seconds (Coren). Birds show sleeping patterns that are related to mammals, too. They have slow-pattern brain-waves and active REM sleep (except the owl must have some other indication of active sleep, as it can’t move its eyes!) The amount of sleep that birds get seems to be directly related to the amount of light in a typical day. As the days grow longer the birds tend to sleep less, although the minimum is not usually below 7 hours (Coren). The complicated animals are reptiles and fish, lower end animals that do not have readable EEG patterns to suggest different brain-wave levels. These animals can be observed as being more so or less active. Their sleeping patterns suggest that anything that can be called “sleep” is active sleep, with almost no slow-wave sleep (Coren).          Many flying insects have active periods during the day and less active periods at night. Bees for example are very active during the day and calm at night in a hive where they become less sensitive to stimulation. Moths and sea slugs (however unrelated) also wedge themselves in places during the night, and do not move for several hours suggesting behaviors of sleep patterns (Coren).         Dr. Allan Rechtschaffen of the University of Chicago so elegantly put it, “If sleep does not serve an absolutely vital function then it is the biggest mistake the evolutionary process has ever made,” Well, the fact that sleep is as pervasive as it is, across so many different species and so many different levels of physical and neurological complexity, suggests that it is performing a useful and vital function. “Certainly, the complex procedures adopted by certain species to get some sleep and the fact that evolution is willing to sacrifice anywhere from 20-70 percent of the animal’s active life to this activity testify to its [sleep] importance,” (Coren). These seem to suggest that we may be risking grave harm to ourselves, from a biological perspective, if we ignore the evolutionary imperative to sleep and instead try to extend our active conscious lives.