There are a lot of physical, mental, and emotional reasons to sleep. But, is there any reasons why some organisms don't have to completely sleep, while others have to completely sleep? When I say completely sleep, I mean that most of the brain is not active. An example is when a human is in "deep sleep" and how most of it's brain is not active. The shark on the other hand, doesn't have to completely sleep. In fact, it turns half of it brain "off" while it keeps the other half "on" so it can stay alive. This gives it the ability to stay awake 24/7.
The title of this post, "Is sleep really needed?", is also questioning, do humans need sleep? Most of our body is active while we sleep so we stay alive. Also, if you look back at the other Kingdoms, you will see that onle the animal kingdom holds organisms that sleep; the others don't. If humans don't need sleep, then what makes us want to go to sleep. What caused a change in our evolution to make us need to sleep while others don't need this "necessity"? And is it possible for humans to evolve so we don't need sleep? Or any other mammal for that matter?