Rem sleep is also called because the brain is aroused and active while the person remains nonresponsive and asleep.

The answer to this question is Paradoxical sleep. Paradoxical sleep is the stage of sleep where in the person’s muscles are relaxed and this is the stage that is called a dreaming sleep. In this stage of sleep the person is in deep sleep state.    

clumped distribution, because you'de have all of the population gathered in a relatively small are.

it's the most common because it provides protection and a mate for reproduction

example: humans, seeweed, cattles, etc.

what's the question ?