Past research found that carriers of a particular gene slept for about 2 hours less than non-carriers. They also found short sleepers who did not carry this gene but had another mutation that appeared to be linked with short sleep.
Natural short sleepers don't seem to suffer health problems associated with getting too little sleep. But it could be that short sleepers are really efficient sleepers.
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Perhaps sleep arose to group the body's processes, ensuring that specific processes don't conflict with one another.
It is not genetics that determines whether you are an 'early riser' or an 'evening owl'. It is mostly habitual and environmental.
Early research found a connection between night owls and developing schizophrenia later in life. On average, owls also have lower wellbeing and are more likely to develop depression. It could be that owls are experiencing constant jet lag, which may put their bodies under stress.
While even experts haven’t reached a consensus explanation for why we sleep, numerous indicators support the view that it serves an essential biological function.
In adults, a lack of sleep has been associated with a wide range of negative health consequences including cardiovascular problems, a weakened immune system, higher risk of obesity and type II diabetes, impaired thinking and memory, and mental health problems like depression and anxiety.
About 80% of our sleeping is of the SWS variety, identified by slow brain waves, relaxed muscles and deep breathing.
Deep sleep is important for the consolidation of memories. New experiences get moved to long-term storage and less important experiences from the previous day get cleared out.