"Early to bed, early to rise makes a man healthy, wealthy, and wise." - Benjamin Franklin
"There is a romance about all those who are abroad in the dark hours." - Robert Louis Stevenson
Researchers have long recognized that many biological processes correspond to a (roughly) 24-hour cycle.
These circadian rhythms (from the Latin circa, meaning about, and diem, meaning day), have been widely observed in humans, plants, animals, insects, and even single-celled organisms. Examples include our natural eating and sleeping patterns, hormone production, brain wave changes, and even leaf movements in many plants.
While these rhythms are endogenous, or determined by our basic biology, external cues such as sunlight, temperature, and availability of food can often be used to "reset" the body's internal clock through a process known as entrainment. This is what allows us to overcome jet lag whenever we travel across time zones and our bodies adapt to new sleeping and waking schedules.
This entrainment process can also lead to enormous individual variations in terms of our basic sleep-wake patterns and the time of day during which we are most active. Usually referred to as circadian preferences, they seem to be relatively fixed in most people, and twin studies suggest that genetics play a strong role in how these preferences develop.
The most common examples are the early risers who are most mentally and physically active during the morning hours and the "night owls" who are more alert at night and prefer to sleep in most mornings. There are even psychometric tests that have been developed to measure these preferences, including the Morningness Eveningness Questionnaire (MEQ), the Composite Circadian Scale, and the Composite Scale of Morningness.
Granted, "pure" morning or evening types are pretty rare. According to research, only about 10 to 15 percent of people fall within one of those two types. The rest of us tend to be a mixture of the two types and the preference for morning or evening activities can change over the course of our lifespans. While most children are morning-oriented, this gradually shifts as they grow and mature. By late adolescence or early adulthood (around the age of 20), people tend to be more evening-oriented, a preference that only begins shifting again as they reach middle age. After age 50, morningness starts to increase again.There are also some evidence for a gender difference, with women being more morning-oriented than men, but the relationship seems to be fairly weak.
But how does morningness or eveningness relate to other factors such as intelligence or personality? Interestingly enough, while correlations have been found between eveningness and higher intelligence, it is the morning people who often excel academically. Even when factors such as daytime sleepiness and cognitive ability are taken into account, studies show evening people have lower grade-point averages than morning people.
The question of how morning and evening people differ in terms of personality can be harder to answer though. While Hans Eysenck proposed that extraverts are more likely to be evening-oriented than introverts, no consistent evidence for this has even been found. Most recent personality research looking at circadian preferences focus on the Big Five Personality traits (extraversion, agreeableness, openness, conscientiousness, and neuroticism) and how they are linked to morningness versus eveningness.
Of all the Big Five traits examined so far, conscientiousness appears to have the strongest association with morningness. People high in conscientiousness show a strong tendency towards self-discipline, vigilance, and systematic behavior. The average correlation between measures of conscientiousness and a preference for morning activities to be fairly moderate (r = .27) while its relationship with eveningness seems weaker (r= .17). Other studies have also found a low but significant correlation between morningness and agreeableness (tendency towards social harmony and being considerate) though no consistent findings have been identified for the other Big Five traits.
A recent study published in the Journal of Personality and Social Psychology presents the results of one of the most comprehensive overviews of research linking circadian preferences to Big Five personality traits. Conducted by Anastasiya A. Lipnevich of the City University of New York's Graduate Centre and a team of co-researchers, the findings combined the results of 44 prior studies and data for 16,647 participants. All of the studies used accepted measures of morningness and eveningness (either as separate factors or combined on a single morningness-eveningness dimension) and standardized Big Five personality measures such as the NEO Personality Inventory and the Big Five Inventory.
As expected, the strongest relationship was between conscientiousness and morningness and a smaller negative relationship with eveningness. Extraversion, on the other hand, showed a strong correlation with eveningness but didn't appear to correlate that strongly with morningness. Other traits, including openness and agreeableness didn't seem to correlate strongly with any circadian preference though there was a small but significant negative correlation between neuroticism and morningness.
As Lipnevich and her co-authors suggest in discussing their findings, the link between conscientiousness and circadian preference seems especially important considering the role that being conscientious plays in academic success. Research has already shown that conscientiousness is a strong predictor of academic achievement, whether at the preschool, high school, or postsecondary school level. Even when grades and SAT scores are taken into account, people high in conscientiousness tend to perform strongly. As for morningness and eveningness, the authors found a significant relationship with academic success even when the Big Five personality traits were taken into account (with morningness being a positive predictor while eveningness was a negative predictor).
While personality traits and circadian preferences can certainly change over the course of our lifespan, it is important to recognize how important morningness and eveningness can be in shaping the way we act and behave in work and school. Though personality testing is often used in employment settings to determine the suitability of job candidates, factors such as circadian preference have been relatively ignored up to now. But as we can see from studies such as this one, circadian preference may be an important predictor of success in many jobs that require mental alertness or energy, especially at specific times of the day, whether in the morning or evening.
So spare a thought to your own inner clock and what it can mean for your long-term success in work or school. Tailoring your personal schedule to take your own circadian preferences in account can yield powerful dividends.
Lipnevich, A. A., Credè, M., Hahn, E., Spinath, F. M., Roberts, R. D., & Preckel, F. (2017). How distinctive are morningness and eveningness from the Big Five factors of personality? A meta-analytic investigation. Journal of Personality and Social Psychology, 112(3), 491-509.