Let me tell you the story of the early bird and the night owl:
The early bird naturally wakes up by 8 a.m. every day. The early bird feels most productive during the beginning of the day, and likes to get into bed every night by 10 p.m.
The night owl, on the other hand, naturally wakes up each day by 12 noon. The night owl feels most productive during the evening hours, and likes to fall asleep around 2 a.m.
This isn’t one of Aesop’s fables, and this is based in reality. In this specific story, I am the early bird and my sister is the night owl. Even though we are from the same family, and we’re a family of predominantly early birds, my sister is the odd-one-out.
But it turns out this is a natural difference in sleep schedules, and one that can actually be explained with genetics.
What Is Your Sleep Chronotype?
We first need to explain the natural differences between sleep schedules among humans. This is something we’re all very familiar with because it is easy to recognize in both ourselves and others. But let’s break it down:
Our sleep cycle is predominantly controlled by two processes: circadian rhythm and sleep-wake homeostasis. Circadian rhythm is our internal biological clock, which is largely controlled by the light-dark cycle of the world around us. However, even in the absence of lightness or darkness, our circadian rhythm is always running.
Sleep-wake homeostasis is our desire to fall asleep. The longer we stay awake, the stronger our desire to sleep. This occurs because the organic compound adenosine continues to build-up throughout the day as we’re awake. Only when we sleep will our body “flush” itself of this built-up adenosine.
Even though these processes are always happening, especially our circadian rhythm, this doesn’t mean all humans are on the same sleep schedule. As my opening story described, some people are early birds, while others are night owls. And many people fall somewhere in between the two.
Our natural preference for when we sleep and when we feel most alert is known as our sleep chronotype. Individual sleep chronotypes vary from person-to-person, but there are three main categories of sleep chronotypes. About 40% of people have a morning preference (early birds), 30% of people have an evening preference (night owls), and the remaining 30% fall somewhere in between.
The Evolution Of Sleep Chronotype
Natural differences in humans are common. We have different heights, body shapes, hair colors, food preferences, and tons of other differences that separate us from one other. So it makes sense that we have a natural difference in sleep schedules. But there’s actually an evolutionary reason for this difference.
Humans are social creatures. We were not meant to sleep alone or as couples. Instead, humans slept in groups. This doesn’t mean a large group of people all slept in the same bed, but we slept surrounded by our tribe or community.
As humans worked their way up the evolutionary ladder, we needed a way to stay safe from nocturnal predators or rival tribes. The problem is if everyone in the tribe sleeps at the same time, the tribe is vulnerable for eight hours each night with no one standing guard.
But as always, we evolved. We naturally developed differences in our sleep schedules to promote tribe safety and survival. This way, we are vulnerable for less time. So if morning birds go to sleep at 9 p.m. and wake up at 5 a.m., the night owls go to sleep at 1 a.m. and wake up at 9 a.m.
This leaves the tribe vulnerable for only half the time (4 hours, between 1-5 a.m.), compared to when everyone shared the same sleep schedule.
This built-in safety measure is not needed so much in our modern society, but it is still very prevalent.
The Genetics Of Sleep Chronotype
This is where our differences in sleep schedules gets really fascinating. Our sleep chronotype is actually part of our DNA. This means our sleep preferences are part of our genetic code, and it is a trait that can be passed down from generation to generation.
If we remember back to our high school biology class, genes are a unit of heredity passed down from parents to their offspring. And there are dominant and recessive genes. We receive two versions of a gene, one from each parent. And if a dominant gene is present, we exhibit the dominant trait.
For example, brown eyes are dominant and blue eyes are recessive. If both of your parents have brown eyes, it is highly likely you will have brown eyes. But if both your parents carry one recessive blue eye gene, there is a small chance you will receive the recessive gene from both parents, giving you blue eyes.
It turns out our sleep chronotype is passed down in a similar way. Of course, sleep chronotype isn’t as simple as eye color, so this will be a huge over-simplification:
Let’s take my family, for example: my dad is an early bird. I am also an early bird, but not quite as early a riser as my dad. My mom prefers the morning, but does enjoy sleeping in until 10 a.m. or later on the weekends. And my sister, as described above, is a strong night owl.
And let’s say that being an early bird is a dominant gene, and being a night owl is a recessive gene. We can assume that both my parents carry the dominant and recessive genes, especially considering my mom falls into the in-between sleep chronotype. Therefore, with my morning preferences, I clearly carry the dominant gene.
But my sister is the odd-one-out in a family of mostly early birds. She clearly received the recessive gene from both my parents, and there was only a small chance this could happen. This is why she appears to be on a completely opposite schedule from the rest of us.
The Downside Of Being A Night Owl
Even though being a night owl is a completely natural occurrence, in our modern society it has many downsides.
The first downside is the stereotype that night owls are lazy. And it’s easy to see where this stereotype comes from. Our modern world shows a strong preference to early morning work hours, especially considering the typical work day beginning at 9 a.m. So when a night owl struggles to get up before 9 a.m., they are often perceived as lazy.
Furthermore, when a night owl works from 9 a.m. to 5 p.m., their most productive and alert hours are only beginning as the traditional work day is ending. This is yet another reason why night owls are often considered lazy, even unproductive.
Additionally, if a night owl works a typical 9-5, they may struggle to fall asleep early enough and achieve enough sleep needed to properly function the next day.
Night owls are constantly fighting between society’s clock and their internal biological clock. In fact, many night owls suffer the worst quality sleep because of this dilemma. And night owls are more likely to develop a caffeine dependence, melatonin supplement dependence, or even develop a sleep disorder because of the massive pressure they’re under.
As much as possible, night owls need to find ways to have their work and social schedules match their natural sleep preferences. This is difficult to do in our world, and something that still needs to be addressed on a larger scale.
I have to admit that this information was brand new to me. I knew people had sleep schedule preferences, but I had no idea it was part of our DNA.
And I also have to admit that, as an early bird, I would often consider night owls to be lazy. Knowing now that it’s a fundamental part of their genetics, I have to reconsider.