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Why Do We Sleep

Subject: Science

Description: Instead of making New Year resolutions to stop drinking, smoking and losing weight maybe we should improve our sleep and by doing so improve our minds and bodies.

Posted by David Caldwell on 09/01/14 at 13:03

How our Primate Ancestors Slept

Our primate ancestors slept in trees and therefore had to be light sleepers to avoid falling from their nests. 

Most of us experience a feeling of falling when we are entering light sleep and react by awakening with a start.  This is called a ‘Hypnic Jerk’ which may be a regressive reaction to prevent our primate ancestors entering deep sleep paralysis which would lead to them falling out of their trees.

Our hominid ancestors such as Homo erectus chose like modern chimps to sleep in ground nests. 

Why they abandoned the safety of the trees to sleep on the ground where the nocturnal predators’ roam is unknown but the change in sleeping arrangements gave an evolutionary advantage as they could now enter the deep phase of sleep called REM.  

REM aided the cognitive development of this species and enabled them to evolve into our clever flavour of the ape.

Segmented Sleep

In pre-industrialised societies, the majority of humans indulged in segmented sleep.  At dusk the population would take to their beds and have their first sleep which lasted typically four hours.  They would then wake for an hour or two and spend the time reading or in quiet restful contemplation. 

They would then have their second or morning sleep for another four hours and arise to face another day.  This segmented sleep is believed to be a natural pattern and is seen when researchers remove volunteers from external stimuli.  The quiet time between sleeps is also thought to be how our ancestors resolved stress which now the blight of our modern society.

Many insomniacs experience waking up in the middle of the night as a medical condition to be cured but wakefulness in between sleeps could just be a regression to a natural sleeping pattern.

Industrial Revolution

During the Industrial Revolution advances in technology led to improved lighting in streets and homes which meant the populace and workers could lead active and productive lives well into the hours of darkness. People were encouraged to work longer and sleep less the act of sleeping was seen to be idle indulgence in a controllable force of nature which Thomas Edison called a waste of time.

People are now expected to have a single sleep lasting 7 to 8 hours.

How Much Sleep do we need?

Adults require 7 to 8 hours to function normally, children need up to 11.5 and teenagers require up to 9.25 hours.  It is a myth that the elderly need more sleep (it is their ability to sleep which is impaired) adults require the same amount of sleep no matter what the age.

Why do we Sleep?

Nobody knows but like all living things we have an innate circadian rhythm which lasts for the duration of an earth day (24 hours) this governs periods of wakefulness, feeding and periods of sleep.  The powerhouse behind our circadian cycle is the chemical Melatonin whose build up after dark makes us feel sleepy and morning decrease leads us to wakefulness.

It appears that sleep has a restorative effect and we can see this in how certain genes are switched on when we are asleep.  Sleep improves cognitive function and consolidates memory.

What happens if we don’t Sleep?

Statistics show that the majority of us are suffering from sleep deprivation.  This manifests in tiredness, irritability,  lack of concentration and even hallucinations but the more profound effects of sleep are not just skin deep.

Lack of sleep reduces the production of growth hormone.  We are prone to depression and anxiety.  Our skin ages as the production of cortisol increases which damages collagen and makes the skin thinner and less elastic.

Sleep deprivation affects the production of the peptide leptin which decreases energy expenditure and increases appetite this means that there is a link between lack of sleep and obesity and to compound matters makes us crave sugary and fatty foods.

Getting less sleep leads to the increased use of stimulants such as caffeine, nicotine, and alcohol.   Reduced sleep is a contributing factor in mental illness.  Studies have revealed that night shift workers have a higher risk of cancers than the less sleep-deprived day workers.


Instead of making New Year resolutions to stop drinking, smoking and losing weight maybe we should improve our sleep and by doing so improve our minds and bodies.

Keywords: benefits of sleep, sleep, sleep deprivation, health