- Circadian rhythm variation in humans developed as an evolutionary response for survival and reproduction.
- Sleep patterns are normally distributed, with about 30% of people on the extremes of the spectrum and about 70% concentrated toward the middle.
- Circadian rhythms of night owls are out of sync with the world as we’ve shaped it, but it does not mean that they are lazy.
- There is a socially ascribed miscalculation of how we should function in time as a society on the whole.
The generic 9-to-5 workday schedule (or what has become the 24/7 or 996 work culture) is a human-constructed paradigm that goes against the natural inter-individual variation in sleep patterns ("biological clock" in the vernacular) among the human species.
Circadian rhythms are a 24-hour, cyclically driven biological sequence. From an evolutionary standpoint, humans developed variation in circadian rhythms, that is, morningness and eveningness chronotypes, for survival and reproduction. Specifically, to facilitate short-term mating and to ensure the longest period of protection over a 24-hour period.
Put another way, the period of highest risk from predators is when the "village" sleeps. So, we have a good reason for night owls, early birds (aka morning larks), and everyone in between. Each is equally necessary. The biological clock of one is merely set to an earlier hour than the other.
Yet, in all our infinite wisdom (sarcasm at its best), we continue to label night owls "lazy." "Irresponsible." We punish them for their daily brawl with sunrise timekeeping, with preference and accolades given to morning birds without legitimate rationale.
Owls, birds, and everything between
The reality is that sleep patterns among the population are normally distributed, with approximately 30 percent sitting on the extremes of the spectrum and approximately 70 percent concentrated across the epicenter.
Early birds, or morning-types, prefer early wake and sleeping times—if they are anything like me, they annoy those around them with joyous singing, laughter, and pleasantness at 5 a.m. in the morning, excited for the day ahead of them. But they reach maximum alertness soon after waking, with cognitive peaks in performance early during the day. They struggle to stay up late and become increasingly more miserable as day becomes night.
In contrast, night owls, or evening-types, are more alert and dynamic at night. They prefer late wake and night times—typically after midnight and approaching midday. This tends to evoke feelings of frustration in those around them because they struggle to conform to the socially constructed timelines, particularly for school and then work. They become active in the evening, with cognitive peaks in performance late in the day.
Night owls aren't lazy.
While the circadian rhythms of night owls are out of sync with the world as we have fashioned it, it does not mean they are lazy. Instead, it reflects a socially ascribed miscalculation, as these diurnal differences can be leveraged for the betterment of society on the whole.
The lifecycle lark-owl transition
Changes to chronotype are experienced non-linearly across the lifespan. This is because preadolescent children tend to be early birds, with a natural shift to eveningness as they transition into adolescence. Then, by increasing age, the proportion of early birds in adulthood becomes larger.
This non-linear transition across the lifecycle should inform the timing of activities such as school. Teens with later school times, for example, are known to perform better than those forced into an early start. Whereas young children tend to cope better with early start times and ebb early in the day.
The battle of the sexes
Curiously, though not highly observable before puberty, the eveningness chronotype is overrepresented in men. This is because chronotypes are sexually dimorphic, reflecting a systematic difference between the sexes. However, to be noted, gender differences do become less perceptible as we age because morningness progressively declines in women post-menopause.
Let's get it on.
Interestingly, night owls are said to be more promiscuous. No judgment, and granted, there are always exceptions to the rule. But women are said to be less socially sexually restricted, and men report greater numbers of sexual partners than early birds, while both men and women tend to experience shorter-term romantic relationships. However, this could conceivably be because of the social intolerance we generally exhibit toward night owls.
A split of personalities
These differences in behavior have been attributed, in part, to contrasts in personality between night owls and early birds. A greater proportion of night owls have been found to exhibit traits of extraversion, narcissism, Machiavellism, impulsivity, novelty-seeking, and risk-taking. Meanwhile, we tend to think of early birds in terms of being conscientious, disciplined, and emotionally stable.
But one would expect early birds to be all those things and more (creative, productive, and engaged, for instance), merely because they are sleeping functionally, at times that are optimal to their natural diurnal rhythm. Whereas novelty-seeking or risk-taking, for example, tend to increase in people who are sleep-deprived, with reductions seen in attention, judgment, caution, and restraint.
It is heritable.
The mechanisms underlying human circadian rhythmicity are largely unknown. But chronotypes are known to be heritable; some report heritability as high as approximately 50 percent. As demonstrated through twin studies, chronotypes are further determined by interactions between both genes and the environment.
Therefore, while not impossible, the amount of control that we can exercise over our chronotype is limited without compromising biological integrity. It comes as no surprise, then, that chronotype is thought to be a fairly immutable biological character across adulthood, where no sleep pathology exists. Others have described chronotype variation as a genetic variation, similar to differences seen in eye color, blood type, height, personality, etc.
Let them sleep.
Although morningness and eveningness are both associated with sleep disorders, morningness is more closely related to a difficulty in sleep maintenance and sleep phase-advance syndrome, which is a difficulty in returning to sleep in the early hours of the morning once awake. You know, when you wake up at 3 a.m. and, frustratingly, can't fall back asleep, despite having to get up at 6 a.m. in preparation for a 9 a.m. presentation.
While eveningness is more closely associated with sleep initiation and morning drowsiness—dragging oneself sluggishly from the bed, begrudgingly opening one eyelid at a time, having hit the snooze button for the umpteenth time—for night owls, this can be the daily equivalent to that 3 a.m. wake. Ultimately, it is important to overall health that we let people sleep to their natural rhythms.
The hidden health burden
As compared to morningness, eveningness has been associated with worse mental health, cardiovascular diseases, type 2 diabetes, eating disorders, respiratory disorders, and even spinal disease. This may plausibly be because they are forced to conform to wake-sleep schedules that contradict their natural diurnal rhythms. So, we see this chronic misalignment between natural chronotype sleep timing and externally imposed timing of work and social activities, leading to morbidity and all-cause mortality.
Sleepless nights. Stressful days.
Not only is the quality of sleep worse for night owls forced to adapt to artificially manufactured sleep schedules, but eveningness is associated with a greater stress response, and so we see a deleterious reciprocal cycle between stress and sleep and changes seen beneath the skin.
Why burn candles at both ends?
This natural chronotype variation can be advantageous to society in a number of ways. It can extend the number of hours we are productive as a society by sharing the load and responsibility between night owls, early birds, and everyone in between. As Arthur Baer mockingly said: "His insomnia was so bad, he couldn't sleep during office hours." Why have night owls burn candles at both ends, when early birds can start early and finish early, then "tag" those in between for the regular 9 to 5, and then they can "tag" night owls into the game for a later finish? It is clear that the typical 9 to 5 does not work for everyone, leaving many struggling with sleep deprivation and daytime fatigue.
An evolutionary perspective
Let us be strategically pragmatic about this. A partnership between a night owl and an early bird, for example, does not have to be antagonistic. Equally, a fusion of night owls and early birds, with everyone in between, can be advantageous to organizations and society on the whole. Perhaps it's idealistic, but consider all the things that could be gained by operating as a "village": splitting the load into elected shifts that compliment chronotype—childcare arrangements and the working day, to name two, could be much more equitably distributed among the population.
This post was informed, in part, by Ponzi and colleagues (2015) and Merikanto and colleagues (2021).
Merikanto, I., Kantojärvi, K., Partonen, T., Pesonen, A.-K., & Paunio, T. (2021). Genetic variants for morningness in relation to habitual sleep-wake behavior and diurnal preference in a population-based sample of 17,243 adults. Sleep Medicine, 80, 322–332. https://doi.org/10.1016/j.sleep.2021.01.054
Ponzi, D., Henry, A., Kubicki, K., Nickels, N., Wilson, M. C., & Maestripieri, D. (2015). The slow and fast life histories of early birds and night owls: Their future- or present-orientation accounts for their sexually monogamous or promiscuous tendencies. Evolution and Human Behavior, 36(2), 117–122. https://doi.org/10.1016/j.evolhumbehav.2014.09.008