Sleep — Designed for Our Good
The other day, when I awoke from a restful sleep, the thought occurred to me that sleep, as an important part of our physical lives, holds some deep evidence of design.
In reviewing research on sleep, I found that a common but somewhat surprising result is the acknowledgement of how incomplete our understanding is of why we sleep in the first place.
Despite the fact that it’s been a universal of human experience for our entire existence as a species, it remains one of science’s greatest mysteries.1
Although it is apparent that humans need sleep, the current understanding of precisely why sleep is an essential part of life is still yet to be determined. We might suggest that the primary value of sleep is to restore natural balances among neuronal centers, which is necessary for overall health. However, the specific physiological functions of sleep remain a mystery and are the subject of much research.2
Darwinian evolution credits animal traits such as strength, speed, flight, and prowess to the selective mechanism of survival of the fittest (never mind how those complex functions arose in the first place), but survival of the unconscious? How reasonable is that?
Surely natural selection would weed out the unfit who fall prey in sleep and would favor those able to stay awake, wouldn’t it? Yet that is not the case in insects, reptiles, birds, mammals or humans.3
An Obstacle to Understanding
I would suggest that the evolutionary mindset operates as a major obstacle to the scientific understanding of sleep. In presupposing that all animals evolved from a common ancestor and that the universal biological need for the sleep-wake cycle evolved along with all organisms, two unsupported assumptions are exposed. One is that “survival of the fittest” has selected for the counterintuitive process of regularly going unconscious, and the other is that Darwinian mechanisms have the capacity to generate the high levels of information within the designed systems inherent in the process of sleep.
…if sleep doesn’t serve some vital function, it is the biggest mistake evolution ever made.4
Debate rages over why all but the simplest of animals have evolved to spend so much of their lives unconscious. One idea is that sleep conserves energy, but studies have shown we burn almost as many calories snoozing as we do when we are awake, so that seems unlikely.
Unfortunately, however, evolutionary theories are hard to prove, so for the moment we are left wondering how sleep emerged in the first place.5
Various studies have yielded some clues as to why we need sleep, based on physiological processes that occur during sleep.
Researchers discovered that cells in the brains of sleeping mice shrink, allowing cerebrospinal fluid — the colourless liquid that circulates in the brain and spinal cord — to flow more easily, sweeping away debris that builds up around active cells during the day. This is carried to lymph glands and flushed out of the body. So perhaps sleep is vital because without it, these toxic by-products build up in the brain. The idea that sleep cleans up our brains is hard to test…6
Organisms without brains also exhibit evidence of a rhythm of sleep, revealing that even simple nerve responses to external stimuli may overtax the body without some regular period of respite.7
But although creatures with more primitive nervous systems don’t sleep quite the same way as more complex animals, they do in fact display regular sleeping behaviors.8
To Sleep, Perchance to Dream
Psychological studies reveal that our brains utilize the sleeping state to organize sensory information and thoughts received during waking hours.
During sleep, our brains sort through information taken in during the day, decide what to store, and make connections between new facts and memories. It is possible that dreams help with this…9
“Dropping off,” as we sometimes call going to sleep, involves a cascade of physiological modifications within our bodies that belies the seeming simplicity of the act of closing our eyes for a rest.
Sleep is an extremely complicated process that consists of more than simply closing one’s eyelids and counting sheep. It is an active state of unconsciousness produced by the body where the brain is in a relative state of rest and is reactive primarily to internal stimulus. The exact purpos
An abbreviated description of just a few of the necessary processes for regulating sleeping and wakefulness are presented below. Sleep stages are distinguished by rapid-eye movement (REM) and non-REM stages.
Sleep-Promoting Processes
GABA [Gamma-aminobutyric acid] is the primary inhibitory neurotransmitter of the central nervous system, and it has been well established that activation of GABA-a receptors favors sleep. Sleep-promoting neurons in the anterior hypothalamus release GABA, which inhibits wake-promoting regions in the hypothalamus and brainstem. Adenosine also promotes sleep by inhibiting wakefulness-promoting neurons localized to the basal forebrain, lateral hypothalamus, and tuberomammillary nucleus.11
Wakefulness-Promoting Processes
Neurochemicals such as acetylcholine (Ach), dopamine, norepinephrine, serotonin (5-HT), histamine, and the peptide hypocretin maintain the waking state. Cortical ACh release is greatest during waking and REM sleep and lowest during NREM sleep…. The noradrenergic cells of the [locus coeruleus] inhibit REM sleep, promote wakefulness, and project to various other arousal-regulating brain regions, including the thalamus, hypothalamus, basal forebrain, and cortex.
Circadian rhythms, which begin to develop in humans at 2-3 months of age, follow a 24-hour cycle and affect several biological functions, including sleeping and waking.
The sleep cycle is regulated by the circadian rhythm, which is driven by the suprachiasmatic nucleus (SCN) of the hypothalamus. GABAergic sleep-promoting nuclei are found in the brainstem, lateral hypothalamus, and preoptic area.12
Transitions between sleep and wake states are orchestrated by multiple brain structures, which include:
Hypothalamus: controls onset of sleep
Hippocampus: memory region active during dreaming
Amygdala: emotion center active during dreaming
Thalamus: prevents sensory signals from reaching the cortex
Reticular formation: regulates the transition between sleep and wakefulness
Pons: helps initiate REM sleep. The extraocular movements that occur during REM are due to the activity of PPRF (paramedian pontine reticular formation/conjugate gaze center).13
As Steve Laufmann and Howard Glicksman lucidly describe in their recent book, Your Designed Body, a “push-pull principle” dominates in the proper regulation of many critically important bodily systems. Our body’s sleep-wake cycle exhibits this type of complex engineering design.
The mechanism through which sleep is generated and maintained is more of a balance between two systems located within the brain: the homeostatic processes, which are functionally the body’s “need for sleep” center, and the circadian rhythm which is an internal clock for the sleep-wake cycle.
Since the regulatory processes producing sleep and the return to wakefulness involve the coordinated activity of multiple brain structures and numerous neurotransmitters, calling it all irreducibly complex seems like quite the understatement. If getting to sleep is necessary for survival, returning to wakefulness is undeniably more so. All aspects of the process of sleeping and waking need to be in full operation before this “evolutionary mystery” could impart any survival advantage. For sleep to be able to accomplish its function of restoration and refreshment for body and mind, without leaving us to languish in the “land of nod,” is evidence of an intelligent designer whose purposes work for our blessing.14
Notes
“The Mystery of Sleep,” Penn Medicine News.
Aakash K. Pate, Vamsi Reddy, Karlie R. Shumway, John F. Araujo, “Physiology, Sleep Stages” (September 7, 2022).
“Sleep on It: Design in the Subconscious Brain,” Evolution News.
“Why do we sleep?” BBC Science Focus Magazine.
“The mysteries of sleep: everything we don’t know about why we snooze,” BBC Science Focus Magazine.
“Why do we sleep?” BBC Science Focus Magazine.
“The Simplest of Slumbers,” Elizabeth Pennisi, Science.
“The Mystery of Sleep,” Penn Medicine News.
“Why do we sleep?” BBC Science Focus Magazine.
Joshua E. Brinkman, Vamsi Reddy, Sandeep Sharma, “Physiology of Sleep” (April 3, 2023).
Aakash K. Pate, Vamsi Reddy, Karlie R. Shumway, John F. Araujo, “Physiology, Sleep Stages” (September 7, 2022).
Ibid.
Ibid.
“In peace I will both lie down and sleep; for you alone, O Lord, make me dwell in safety.” (Psalm 4:8 ESV)
