Student ID: 4314752
Why Do Organisms Sleep?
Organisms cannot live without 3 major components: food, water and oxygen. After this, there is
sleep. Whilst not listed as an initial component for survival, extreme sleep deprivation will
almost definitely kill an organism if continued for long enough. This would lead one to believe
that sleep has a fairly if not equally vital role (of which researchers are still yet to discover
entirely) in organisms’ survival. Proving the vitality of sleep further, the average person spends
36% of their life asleep, meaning if a person lives to 90, they will spend 32 years of their life
asleep. (Foster, 2018)
The simplified answer to why organisms sleep is derived from two possible theories researchers
have produced: ‘Recuperation Theory’ versus ‘Evolutionary Theory’.
Recuperation theory states we need sleep because it restores our homeostasis and energy
levels, whilst being awake disrupts our homeostasis. Evolutionary theories, however, state that
sleep in not a reaction to homeostatic disruption. Sleep is believed to have evolved in humans
to prevent accidents and predation at night, we don’t need it to survive but are still motivated
to have it. Furthermore, the evolutionary theory proposes that mammals, at some point,
evolved to have extended REM episodes of sleep, therefore having more sleep that would
promote memory restricting as opposed to memory stabilisation.
The need for sleep varies between all mammals and birds, and is reflected through the number
of hours of sleep each organism has per day. Many believe this variation Is due to lifestyle, size
or activity of the organism. Surprisingly though, figures prove this entirely wrong. For example,
, Student ID: 4314752
a giant sloth needs 20 hours of sleep day, despite having a very ‘lazy’ lifestyle and hardly
moving around at all. On the other hand, a horse only requires 2 hours sleep out of a 24-hour
day and is still a large animal, and is far more likely to exert more energy through more exercise
than a sloth. (Haselgrove, 2018) Thus, hours of sleep required cannot be related to body size or
lifestyle alone. These figures contradict the recuperation theory because a sloth for example,
sleeps for 20 hours a day despite being large and so not needing to conserve energy. Similarly,
rabbits sleep 8 hours (the same as humans) despite being at high risk of predation, so this
would be seemingly contradicting the evolutionary theory as it is not beneficial to their survival
and evolution.
From an evolutionary stance, it seems to almost not make sense that animals sleep, as it leaves
them unconscious, significantly more vulnerable to predation than when they are awake.
“Whatever functions sleep performs, they must be so fundamentally important that they far
outweigh the obvious vulnerability associated with being asleep.” (Barras, 2018) The fact that
natural selection did not suppress sleep proves this point further.
Some researchers argue that sleep is a good way to conserve energy (recuperation theory), as
mammalian core body temperatures often drop during some stages of sleep. However,
Matthew Walker of the University of California challenges this: “The amount of energy humans
save by falling asleep, versus simply lying on the couch, is about what you find in a slice of
brown bread,”. He goes on to explain: “Losing consciousness just isn’t worth saving 120
Why Do Organisms Sleep?
Organisms cannot live without 3 major components: food, water and oxygen. After this, there is
sleep. Whilst not listed as an initial component for survival, extreme sleep deprivation will
almost definitely kill an organism if continued for long enough. This would lead one to believe
that sleep has a fairly if not equally vital role (of which researchers are still yet to discover
entirely) in organisms’ survival. Proving the vitality of sleep further, the average person spends
36% of their life asleep, meaning if a person lives to 90, they will spend 32 years of their life
asleep. (Foster, 2018)
The simplified answer to why organisms sleep is derived from two possible theories researchers
have produced: ‘Recuperation Theory’ versus ‘Evolutionary Theory’.
Recuperation theory states we need sleep because it restores our homeostasis and energy
levels, whilst being awake disrupts our homeostasis. Evolutionary theories, however, state that
sleep in not a reaction to homeostatic disruption. Sleep is believed to have evolved in humans
to prevent accidents and predation at night, we don’t need it to survive but are still motivated
to have it. Furthermore, the evolutionary theory proposes that mammals, at some point,
evolved to have extended REM episodes of sleep, therefore having more sleep that would
promote memory restricting as opposed to memory stabilisation.
The need for sleep varies between all mammals and birds, and is reflected through the number
of hours of sleep each organism has per day. Many believe this variation Is due to lifestyle, size
or activity of the organism. Surprisingly though, figures prove this entirely wrong. For example,
, Student ID: 4314752
a giant sloth needs 20 hours of sleep day, despite having a very ‘lazy’ lifestyle and hardly
moving around at all. On the other hand, a horse only requires 2 hours sleep out of a 24-hour
day and is still a large animal, and is far more likely to exert more energy through more exercise
than a sloth. (Haselgrove, 2018) Thus, hours of sleep required cannot be related to body size or
lifestyle alone. These figures contradict the recuperation theory because a sloth for example,
sleeps for 20 hours a day despite being large and so not needing to conserve energy. Similarly,
rabbits sleep 8 hours (the same as humans) despite being at high risk of predation, so this
would be seemingly contradicting the evolutionary theory as it is not beneficial to their survival
and evolution.
From an evolutionary stance, it seems to almost not make sense that animals sleep, as it leaves
them unconscious, significantly more vulnerable to predation than when they are awake.
“Whatever functions sleep performs, they must be so fundamentally important that they far
outweigh the obvious vulnerability associated with being asleep.” (Barras, 2018) The fact that
natural selection did not suppress sleep proves this point further.
Some researchers argue that sleep is a good way to conserve energy (recuperation theory), as
mammalian core body temperatures often drop during some stages of sleep. However,
Matthew Walker of the University of California challenges this: “The amount of energy humans
save by falling asleep, versus simply lying on the couch, is about what you find in a slice of
brown bread,”. He goes on to explain: “Losing consciousness just isn’t worth saving 120
