In a study from (1998), Gale and Martyn presented research aimed at investigating the validity of Benjamin Franklin’s adage “early to bed and early to rise makes a man healthy, wealthy and wise”. They found no evidence to support any differences between morning and evening people in their measured socioeconomic, health and cognitive variables and argued that this maxim rested on little more than traditional authority. This review aims to briefly reiterate historical findings within the field of chronobiology, specifically focusing on human chronotypes, circadian rhythms, personality traits and behavioural characteristics. These findings are discussed alongside more recent findings with the aim of seeing how the traditional perception of the two chronotypes of morning and evening people have changed, if at all, and whether current research supports these perceptions.
Chronotypes refer to the differences seen in individual human beings regarding at what time during the day their physical and cognitive characteristics change in activity and ability. Some people naturally wake up early in the morning; some seem to be at their best in the evening and wake up later. In one of the first studies on the subject, morning people (larks, or M-types) display morningness; they rose and retired significantly earlier when compared to evening people (owls, or E-types) (Horne & Östberg, 1975; 1977). Further research using the same questionnaire revealed that larks in general were more stable in their sleeping patterns (Webb & Bonnet, 1978). This study also found that larks had less variation in when they woke up and took shorter naps. This group also scored higher on self-reported health, and less on rumination during the night.
M-types were later found to perform better on a rejection task in the morning (Horne, Brass, & Petitt, 1980), compared to E-types who performed better in the evening. The results additionally suggested that M-types’ performance declines over the day, whereas the opposite was found for E-types. More recent research has investigated the impact of being either M- or E-type on emotional attention, which would have impacts on relationships and social interactions. In a study from 2014 Antúnez, Navarro and Adan showed that there are differences in emotional intelligence between larks and owls, but that this also is related to gender. Morning type men have lower emotional attention than evening types. The authors concluded that this is a protective trait to maintain health and well-being. In contrast, they also found that there was a “neither-type”, or intermediate type, which seems to be susceptible to psychological problems.
Roenneberg, Wirz-Justice and Merrow (2003) stated that human beings are controlled by three types of clocks: the solar clock, the social clock and the biological clock. These are intrinsically connected, with the solar clock activating the biological clock, for example, by activating so called “clock-genes” (Young & Kay, 2001) or light reaching the rods and cones of the eye and photoreceptors (Roenneberg & Merrow, 2002). For the purpose of this review the focus will be on the biological clock, sometimes also referred to as the circadian rhythm, which spans over approximately 24 hours. The human circadian cycle is diurnal, with the majority of individuals being preferentially active during daylight hours. Several of the early studies on chronotypes found differences in some of the functions associated with circadian rhythms. Specifically the daily variations in body temperature differed between larks and owls, with owls reporting a higher body temperature in the evening. This trend was not reported by the larks (Horne & Östberg, 1977; Horne et al., 1980; Kerkhof, Korving, Geest, & Rietveld, 1980; Foret, Benoit, & Royant-Parola, 1982). It is now well established that larks and owls show reliable differences in their circadian rhythms (Kerkhof, 1985; Tankova, Adan, & Buela-Casal, 1994). Circadian rhythms show differences depending on countries and populations, with more M-types reported in more temperate climates (Smith et al., 2002). Waking up in the morning is partly controlled by the cortisol awakening response, where free cortisol is found in a higher concentration body immediately after awakening. In M-types the level of free cortisol was found to be higher immediately after awakening, when compared to E-types (Randler & Schaal, 2010). However, recent study found no difference in salivary cortisol between morning and evening types, only a difference in salivary α-amylase (Toda, Kawai, Takeo, Rokutan, & Morimoto, 2012).
In an effort to disentangle the circadian rhythm from habitual tendencies, Kerkhof and Van Dongen (1996) showed that there were significant differences in the body temperature and alertness between M- and E-types, suggesting that chronotypes are different by nature. Research has found that the time difference between the two chronotypes is approximately two hours, e.g. their body temperature peaks at this interval, as well as the time of going to bed and getting up are approximately two hours apart. It also takes longer for E-types to feel sleepy which could explain why their alert preferences are at a later time than M-types (Taillard, Philip, Coste, Sagaspe, & Bioulac, 2003).
Personality traits and behavioural characteristics
The theories around the differences between larks and owls are many and span over the last decades. The five conventional personality traits in psychological research are agreeableness, conscientiousness, extraversion, neuroticism and openness. A few of the early studies considered the connection between extraversion, introversion and the M/E-types, and while a few studies found that the owls were slightly more extraverted than the larks, others found the evidence to be inconclusive (Horne & Östberg, 1977; Jackson and Gerard, 1996). Several researchers have investigated differences between M/E-types and found pronounced statistically significant differences in conscientiousness, self-esteem and locus of control. Additionally, in Jackson and Gerard (1996), M-types scored higher on both conscientiousness and self-esteem, and their locus of control appeared to more internal, when compared to E-types. Mecacci and Rocchetti (1998) administered a large set of personality and psychopathological questionnaires; Eyseneck Personalities, Beck Depression Inventory, Bortner’s Scale, Jenkins Activity Survey and Strelau Temperament Inventory, to name a few. They found significant correlations between the specific types of M/E-types and the individual questionnaire scores. These results reflected a significant difference in personalities, mental health and coping mechanisms for stress. M-types reported less psychological problems and fewer difficulties in coping with instances of social and environmental stress. There is evidence of differences in the way larks and owls think and deal with information presented or sought out, how they organise their thinking patterns and how they interact socially and relate to other individuals. (Díaz-Morales, 2007; Giampietro and Cavallera, 2007). Research has also been presented which is based on the FFM and meta-traits showing that morning people are “stable people”, compared to evening types. With “stable” the authors 0- (DeYoung, Hasher, Djikic, Criger, & Peterson, 2007). Additionally, larks were found to have a more positive and energetic attitude than owls, and this held to be true despite age differences between older and younger adults (Biss & Hasher, 2012). As morningness is a trait found more often in older individuals, the authors suggested that there might be an interaction with the positive attitude found in older adults, when compared to younger adults, which has the effect of greater well-being. One recent study (Vollmer & Randler, 2012) showed that the two chronotypes differ in how they consider the values around them. M-types showed a greater acceptance of social values, whereas E-types were more inclined to accept individual values.
In a recent experiment chronotypes were tested in driving vigilance during morning or evening sessions. While E-types displayed decreased vigilance during the morning session of driving, the M-types were unaffected by the time of day (Correa, Molina, & Sanabria, 2014). Some researchers attribute differences in planning and task orientation to rising late or early (Nowack & van der Meer, 2013). Others have recently presented links between M/E-types and task orientation to additional differences between the two types in self-control (Milfont & Schwarzenthal, 2014). M-types have been found to score higher on leftside-thinking tasks, compared to other chronotypes, e.g. E-types and intermediates. Conversely, E-types scored higher on rightside-thinking tasks (Fabbri et al., 2007).
Some additional notable behavioural differences include an effect on E-type adults (as opposed to adolescents) with regards to changing sleep-wake behaviour through work patterns, which is not seen to the same extent in M-types (Mecacci & Zani, 1983). In a study aimed at investigating a link between chronotypes and consumption of alcohol and stimulants, E-types were reported to consume more of these substances than M-types (Adan, 1994). The difference in patterns of substance use was investigated further more recently. Prat & Adan, (2011) found that E-types consumed more legal and illegal drugs than M-types. E-types also showed more problems associated with overconsumption of alcohol, such as hangover symptoms. The authors concluded that the E-type circadian preference is a risk factor for substance abuse problems. E-types have also been found to be more sensitive to pain, regardless of what time of the day the stimulus was delivered (Jankowski, 2013).
The last decade has seen research on larks and owls with regards to academic achievement. Goldstein, Hahn, Hasher, Wiprzycka, and Zelazo (2007) tested maladaptive behavioural patterns and academic performance in adolescents. The maladaptive performance patterns were more common for E-types. This type also showed poor academic performance more often. Interestingly, the same was seen in adolescents who were tested at the time of day they considered to be non-optimal. In a study from 2011 (Beşoluk, Önder, & Deveci, 2011) showed that academic performance was impacted by at what time the teaching lessons and test started. This study also showed that M-types generally achieved higher scores than other chronotypes.
These studies prove that the differences between larks and owls are many and complex. The differences in behaviour between larks and owls ultimately feed back into how they appreciate the surrounding environment and how this affects their behaviour in future situations. This review has only focused on the morning and evening types, primarily due to word length limitations. However, there is research supporting the existence of intermediate, or neither-types (Koskenvuo, Hublin, Partinen, Heikkilä, & Kaprio, 2007)(Antúnez et al., 2014). There are also the aspects of length of sleep, sleep quality and time of sleep to take into account when considering the traits of larks and owls. Sleep research has indicated that length of sleep is irrelevant unless the time of sleep is taken into account, e.g. there is an optimal time period for sleep during our 24 hour clock. This has not been covered in this review.
One important point to make here is that our society is designed in most aspects to benefit an individual with morning preference the most. On top of this there is social reinforcement to foster the morning type personality, and it is not uncommon to hear of anecdotal evidence where individuals who have evening type personalities are considered less reliable and ambitious. It could thus be a case of which came first, the chicken or the egg, e.g. are different chronotypes an inherent trait or is it a consequence of social nurturing. It is also unclear if these traits exist to the same extent in children and how they are affected by developmental factors. Additional research is needed to investigate these matters and the social impact of this. The ideal study of investigation of the link between chronotypes and a defined variable of success would be a causal effect study, however, in reality this would be nearly impossible to achieve. As with many psychological traits and studies, there are a multitude of factors that could potentially affect the measure outcome variable, and it is hard to control for all of these.
In conclusion, while there is evidence that larks and owls do exists and present differences in personality and behaviour, as well as physiological characteristics, it is not clear as to what extent the evidence can be used to confirm Benjamin Franklin’s old maxim with certainty. While the assumed research consensus might be that M-types are more likely to succeed in our current society (partly because it is constructed to reinforce this trait) it is rational to assume that there are benefits to having E-type preferences. Hence, the stereotypes still exist, much in the same form, but the role of social nurture is not clear. The maxim in itself poses a complex set of personality questions that will most likely require further research in several different directions, to be linked to the diurnal variations in biology. Nonetheless, the differences presented so far provide solid evidence that there are distinctions in the physical and mental health implications for larks and owls. Further research is needed to investigate additional correlations between the psychology of owls and larks, the implications of these preferences and their subsequent behavioural patterns on life choices and health conditions.
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