The Truth About Morning and Night People
Little-known science that could change how you see yourself
When I was a teenager, I used to dream about the day when scientists finally proved that some people are biologically wired to be night owls. On school mornings, I would wake up to my alarm in a murderous mood, praying I wouldn’t bump into any family members on my way to the bathroom. I would brush my teeth and imagine a future in which the whole world no longer marched to a morning person’s drum.
A good friend of mine in college had the opposite frustration: on weekends, she would be up for hours before any of her housemates stirred. She was ready to go out and have fun, if only they would finally wake up! By 10 p.m., when they were getting ready for a night out on the town, she was getting ready for bed.
Was I really just lazy, and was she just boring? Or are there two fundamentally different kinds of people in the world: morning people and night people?
As it turns out, scientists have been studying the phenomenon of “morningness” and “eveningness” in humans since the 1970s, and in the 80s, the term “chronotype” first appeared in the scientific literature.  A person’s chronotype is whether they are a “lark”, that is, a morning person (M-type), or an “owl” meaning a night person (E-type for evening). Some people fall somewhere in the middle and are called N-types for “neither”. To date, over 500 scientific articles have been published on the subject of chronotype and its relationship to our health, lifestyle, and performance.
As it turns out, being a morning person or a night person (or somewhere in-between) isn’t just a matter of discipline or habit. There are some clear biological differences between chronotypes:
- Body Temperature
Each person’s core body temperature varies in a cyclical fashion throughout the day, typically dropping to the lowest values at night while we sleep. However, in people who consider themselves “evening people”, the lowest body temperature occurs about two hours later on average than in self-described “morning people”. 
Is this simply a result of the “evening people” keeping a later schedule, forcing their bodies to adjust accordingly? Apparently not. Even when subjects are forcibly put on the same sleep schedule, E-types still experience the lowest body temperature an hour later than M-types. As a result, their core body temperature is lower when they are woken up, and they are less alert than M-types.  Conversely, if they go to bed at the same time, E-types will be less sleepy than M-types because their body temperature is still too high. Of course, a 1-hour difference may not seem like a big deal — but note that the extreme representatives of “larks” and “owls” may be as much as 12 hours apart in their physiological rhythms! 
2. Melatonin Production
Melatonin is the body’s own “sleeping pill”, a hormone that helps regulate our sleep-wake cycle. It’s secreted by the pineal gland, a small structure inside the brain.  The pineal gland responds to decreasing outside light (such as during sunset) by producing more melatonin, which, in turn, affects our “internal clock” and makes us sleepy.  Although we all experience this effect, the increase in melatonin happens earlier in morning people than in night people, thus triggering them to go to bed earlier. 
3. Cortisol Production
Cortisol is a hormone which is released by the adrenal gland. It is necessary for making energy available to the body’s cells and for managing stress . Interestingly, in the first hour after waking up, morning chronotypes have higher cortisol levels than evening chronotypes.  In a sense, rising cortisol levels prepare us for the trials of the day, so M-types’ bodies are ready to tackle their tasks earlier than those of E-types.
So what causes these biological differences?
I’ve already mentioned our “internal clock”. Where exactly in the body does this clock live? Well, as you might guess, it’s in the brain — specifically, in a part of the brain called the hypothalamus , which is buried right in the center of your skull, almost directly behind your eyes. Inside is a bundle of neurons called the suprachiasmatic nucleus (a mouthful, so usually abbreviated to SCN) which controls the circadian rhythms of the entire body. 
We actually have two SCNs, just to the right and left of the middle of the brain.  Each one is tiny, about 0.0002 of an inch  — but it contains all we need to keep internal time. The neurons in the SCN regulate the activities of many other parts of the brain as well as the release of many hormones, ensuring that our body functions run on a consistent internal schedule from day to day. 
So why is a morning person’s internal clock different than a night person’s? With recent advances in molecular biology, scientists have finally been able to study whether there are genetic differences between morning and night people. An article published this year reveals that 22 genes are currently known to affect a person’s chronotype  — and there are probably more yet to be discovered. In other words, you were probably born a morning person or a night person!
There is a large group of European researchers currently working on a method of testing individuals’ biological chronotype.  Perhaps, in the near future, a simple cheek swab to test for different clock genes will allow researchers to quickly tell you which type you are. Indeed, there are already some promising pilot studies attempting to do just that! 
For now, you can confirm your probable chronotype by completing this questionnaire from the Center of Environmental Therapeutics: link. Note that this tool will be most useful if you have some control over your bedtime and wake-up time on at least some days of the week.
So, now you know your chronotype. Now what?
The good news is that the European research group I mentioned earlier is also working on making a computer model which will devise an optimal schedule for each individual based on their chronotype and sleep needs. [12, 13] Unfortunately, for now, many of us are probably stuck with schedules which are far from optimal because of work, school, family obligations, and various other constraints. Because of this, many of us may be chronically suffering from what leading chronobiologist Till Roenneberg calls “social jet lag” — the discrepancy between our internal clocks and the schedules dictated by our social environment. 
Still, if we are aware of the very real biological diversity of chronotypes in our population, we can make a conscious effort to accommodate different schedules.
For example, you are surely familiar with sayings like, “The early bird catches the worm” and “Early to bed and early to rise makes a man healthy, wealthy, and wise”. These may seem like quaint expressions, but research shows that all things being equal, employers perceive employees who arrive at work earlier as better workers than those who start later, even if their total number of hours worked, productivity, etc. is the same.  Furthermore, supervisors who are themselves morning people tend to exhibit this prejudice more strongly and show this bias in their employees’ performance evaluations.  By recognizing that chronotype is largely genetically determined, such workplace discrimination can be avoided.
Although there are practical limitations to accommodating each individual’s preferred schedule, there are some changes we can make to reduce social jetlag for large segments of the population. For instance, there seems to be a biological basis to the fact that most teenagers prefer to go to bed late and wake up late. [4, 15] This may sound contradictory given the genetic basis of chronotype — but in fact, everyone in adolescence simply shifts to later schedules relative to where they started.  This has led some experts to propose moving start times in middle school and high school to later in the morning to ensure that students are better rested and able to perform better. [4, 16] Conversely, there is a shift toward a morning chronotype as we approach old age , so it makes sense to schedule events aimed at the elderly earlier in the day.
On a personal level, you can maximize your own performance and sense of well-being by working in harmony with your chronotype. For example, morning-person athletes experience a workout done in the evening as being significantly harder than an identical workout in the morning.  So don’t schedule your run with your owl training buddy if you are a lark. There is also a large body of evidence that evening types tend to exhibit poorer performance in school compared to morning types, largely because typical school days start early.  If you are a late chronotype student or the parent of one, opt for classes with later meeting times if you can.
So the next time someone calls you lazy for not getting up at 8 a.m. on Sunday, or boring because you can’t stay up past midnight, remember: your chronotype is real and largely innate. It’s time we all recognized that.
 As determined by a Pubmed (https://www.ncbi.nlm.nih.gov/pubmed) search of scholarly articles using the search terms “morningness”, “eveningness”, and “chronotype”
 Baehr, E.K. et al. (2000). Individual differences in the phase and amplitude of the human circadian temperature rhythm: with an emphasis on morningness-eveningness. Journal of Sleep Research 9: 117–127
 Bailey, S.L. and M.M. Heitkemper. (2001). Circadian rhythmicity of cortisol and body temperature: morningness-eveningness effects. Chronobiology International 18(2):249–61
 Roenneberg, T. (2012). Internal time: Chronotypes, social jet lag, and why you’re so tired. London, England: Harvard University Press.
 Campbell, N.A. et al. (2008). Biology (8th ed.). New York, NY: Pearson Benjamin Cummings.
 Duffy, J.F. et al. (1999). Relationship of endogenous circadian melatonin and temperature rhythms to self-reported preference for morning or evening activity in young and older people. Journal of Investigative Medicine 47(3):141–50
 Silverthorn, D. (2010). Human physiology: An integrated approach. New York, NY: Pearson.
 Kudielka, B.M. et al. (2006). Morningness and eveningness: the free cortisol rise after awakening in “early birds” and “night owls”. Biological Psychology 72(2):141–6
 Howard Hughes Medical Institute. (2016). The human suprachiasmatic nucleus. Retrieved from: http://www.hhmi.org/biointeractive/human-suprachiasmatic-nucleus
 Hofman, M.A. et al. (1988). Morphometric analysis of the suprachiasmatic and paraventricular nuclei in the human brain: sex differences and age-dependent changes. Journal of Anatomy 160: 127–143
 Novakova, M. et al. (2013). Human chronotype is determined in bodily cells under real-life conditions. Chronobiology International 30(4):607–17
 Phillips, M.L. (2009). Of owls, larks and alarm clocks. Nature 458: 142–144
 Centre for Chronobiology at Ludwig-Maximilians-University Munich Institute for Medical Psychology (2013). Euclock. Retrieved from: http://www.euclock.org/
 Yam, K.C. et al. (2014). Morning employees are perceived as better employees: employees’ start times influence supervisor performance ratings. Journal of Applied Psychology 99(6):1288–99
 Waterhouse, J. et al. (2012). Daily rhythms of the sleep-wake cycle. Journal of Physiological Anthropology 31:5
 Barnes, C.M. and C.L. Drake. (2015). Prioritizing sleep health: public health policy recommendations. Perspectives on Psychological Science 10(6): 733–737
 Kunorozva, L. et al. (2013). Perception of effort in morning-type cyclists is lower when exercising in the morning. Journal of Sports Science 32(10):917–25
 Tonetti, L. et al. (2015). Association between circadian preference and academic achievement: A systematic review and meta-analysis. Chronobiology International 32(6):792–801