Some people awake naturally at the break of dawn greeting the early beams of lights with authentic smiles of gratitude and enthusiastic cheerfulness towards the day’s quests. They are known as early birds or larks (the little brown bird known for its early tunes). Larks have been described by several studies as happier and more flexible than their counterparts, night owls. The latter category, in contrast, feels at its best from dusk onwards, and has been shown to be smarter, more adventurous and extraverted. Why is the human race divided between these two opposed lifestyle inclinations? Is this categorization reversible?
What does it mean to be an early riser or a night owl?
Each individual has a chronotype, which describes a person’s natural inclination towards times of day to sleep, or, conversely, be alert and energetic. Your chronotype reflects a circadian system, a biological 24h clock that encompasses all the physiological processes and variations that take place in your organism within the day. These processes involve regulating body temperature, secreting appropriate hormones (melatonin before bedtime, dopamine after waking up), and will dictate when you feel tired, hungry or awake.
Circadian rhythms tend to be synchronized with external factors such as cycles of light and dark and ambient temperature. This partially explains why different countries are characterized by different clocks (a Spanish nap can take place during a Swedish dinner), or why people have more energy in the summertime, or why staring at the lights of a computer delays one’s desire to sleep.
These rhythms are also, however, largely genetically determined. The interplay of a myriad of genes controls one’s personal circadian rhythm. Back in 2003, researchers discovered a major player, called the Period 3 or “clock” gene. Early birds were more often found to have a longer version of the gene. More recently, Nature published in 2016, a genome-wide association study (GWAS) using the DNA of nearly 90,000 people who’d submitted their genetic material. The researchers discovered 15 genetic patterns associated with being a lark. This evidence suggests that if one tends to wake up early it is most likely a predisposition passed on from previous generations rather than sheer ‘will-power’.
The diagram above depicts the circadian patterns typical of a lark who rises early in the morning, eats lunch around noon, and sleeps at night (10 p.m.).
Why are humans divided into these two categories?
It has long been unknown why genetics separates humans into larks and owls. The first rational explanation was laid out by Frederick Snyder in 1966, who intelligently observed that for many social animals safe sleep could only be possible if other members remained awake to ward off external threats. This theory, known as the sentinel hypothesis, has for logic that sentinel behaviour resulting from varied chronotypes made early human groups safer as different members had different peaks in alertness. This meant that the group is safe at night (thanks to night owls), and cognitively prepared for whatever the day will bring (thanks to early birds), and overall more capable of protecting young offspring whom need more sleep to develop properly.
Thus, different chronotypes are testimony of solidaristic rather than individualistic behaviour within a species because having a different sleep pattern from your neighbour helps you protect him and vice-versa. Snyder’s theory has gained much more scientific ground as studies conducted last year over a Tanzanian hunter-gatherer tribe validated its reasoning.
Above, picture of the Hadza tribe of Tanzania (courtesy of Survival International)
The study published in Proceedings of the Royal Society B followed the Hadza a tribe that lives in groups of 20 to 30 people spending their days finding berries, tubers, and meat in the savanna woodlands and nights sleeping outside next to the fire or indoors within woven-grass huts. Importantly, they sleep on the ground without artificial lighting or climate control making their environment close to that of early pre-agricultural humans.
The study concluded that over a period out of 10 days with more than 220 hours of observation there were only 18 minutes where all 33 participants were asleep at the same time. On average, more than a third of the group was awake at any given time.
Snyder’s theory also offers some explanation as to why your circadian rhythm can change over your lifetime. As in fact, school-age children are generally early birds, while teenagers tend to be night owls, and then as they age, adults gradually transition back into morning people, with elderly people known to be major larks (find out about the grandmother hypothesis in this BBC article).
This study also has the benefit of showing us that one shouldn’t feel guilty for being an early riser or a night bird as social jetlags make sure we can keep an eye on each other.
What about you? Are you a lark or an owl? Leave us a comment below 🙂