Why So Little Sleep?

     In the reading from Lockley and Foster, there is a lovely chart that depicts the average percent of the day each mammal sleeps.  (Here is a link to refresh your memory) It is stated in the book that there are three ideas to why animals sleep: cellular respiration, energy conservation, and the consolidation of memory and learning (Lockney & Foster, 49).  Each of these theories are examined scientifically and either discredited or praised.  What I am going to attempt is to make the case for logic as to why the Giraffe- the least sleeping animal mentioned, only sleeping at most two hours a day, sleeps so little.  First off, it is good to get rid of the convention image that most people have of a giraffe.  They are not the docile animals we see in zoos.  We need to think about the ones that still live in the wild. These animals are out there to survive.  A huge animal such as the giraffe needs lots of food to stay active and healthy.  Most of their day is consumed by well, consuming.  It is said that "a giraffe may eat more than 75 pounds (34 kilograms) of food each day," (Bradford, 1).  The average giraffe weights about 600 pounds.  If all day the animal is eating to maintain its health, sleep might just be the compromise. Also it is needed to look at the actual risks of sleep. Below is a picture of an average size giraffe.  Its neck is six foot seven inches long.  This creates quite a hassle when the giraffe has to lay down for REM sleep, and has to rest it on a tree for NREM sleep.  This though for a short time is time that the animal is fully exposed to the other predators.  It is survival out in the wild and sleeping is a calculated risk. It takes the giraffe a full minute to get up from the ground when in REM sleep.  Also another fact to consider is that when in REM the animals body is paralyzed leaving them openly vulnerable. Here is a link to a video of the process of a giraffe getting up. The video is sped up for your convenience.  This can be a logical reason as to why humans can and do sleep more.  We live in an environment for the most part where we are not looking over our shoulder all the time waiting to be attacked. We feel safe and sleep because we can.  Other animals that sleep more than humans like bats are able because they for the most part have few predators that can get them.  Sleep is a biological need, but is sometimes compromised for safety and protection.

Image and information are from:

http://www.livescience.com/27336-giraffes.html