What Is This Thing We Call Sleep

Historically, sleep has been considered a time of mere inactivity for the mind and body to rejuvenate itself. Some philosophers have even considered it a complete waste of time. However, 20 century scientific and medical research into the phenomenon of sleep has revealed that these simplistic views of sleep are not at all accurate. Human and animal sleep is actually a complex series of different 

These questions go on and on and have plagued scientists and philosophers alike for decades, if not centuries. The answer 

Species Average sleep Time (total hours per day) 

As you can see, the amount of sleep a particular species needs is not directly proportional to obvious things like its size, number of legs, or whether or not it is nocturnal or diurnal. So, why does a bat need 20 hours of sleep while a giraffe only 2 Your guess is as good as any. 

SLEEP NEEDS CHANGE THROUGHOUT THE LIFE SPAN 

---