Earlier it was believed by researchers that sleep is not a good thing as it does not allow an organism to stay alert all the time due to which there are high chances of such organism being consumed by other organism. However, with the discovery of theory of evolution, it is now believed that sleep has also evolved. Its evolution allows an organism to save energy and conserve it.
Evolved sleep has helped decrease synaptic strength which allows a person to preserve memories and function well during the day time. REM sleep in the early morning makes brain metabolically active even while sleeping and hence, dream comes.
