Chronotype (morningness/eveningness) is associated with preference for the timing of many types of behavior, most notably sleep; also associated with aspects of personality, like prosocial behavior

The impact of chronotype on prosocial behavior. Natalie L. Solomon, Jamie M. Zeitzer. PLOS, April 30, 2019. https://doi.org/10.1371/journal.pone.0216309

Abstract
Introduction: Chronotype (morningness/eveningness) is associated with preference for the timing of many types of behavior, most notably sleep. Chronotype is also associated with differences in the timing of various physiologic events as well as aspects of personality. One aspect linked to personality, prosocial behavior, has not been studied before in the context of chronotype. There are many variables contributing to who, when, and why one human might help another and some of these factors appear fixed, while some change over time or with the environment. It was our intent to examine prosocial behavior in the context of chronotype and environment.

Methods: Randomly selected adults (N = 100, ages 18–72) were approached in a public space and asked to participate in a study. If the participants consented (n = 81), they completed the reduced Morning-Eveningness Questionnaire and the Stanford Sleepiness Scale, then prosocial behavior was assessed.

Results/Conclusions: We found that people exhibited greater prosocial behavior when they were studied further from their preferred time of day. This did not appear to be associated with subjective sleepiness or other environmental variables, such as ambient illumination. This suggests the importance of appreciating the differentiation between the same individual’s prosocial behavior at different times of day. Future studies should aim at replicating this result in larger samples and across other measures of prosocial behavior.

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Introduction

Individual differences in the time at which people prefer to do particular behaviors, most notably sleep, are referred to as chronotype. In essence, chronotype describes whether someone is a “morning” person or an “evening” person. While many (50%) individuals identify somewhere between the extremes of chronotype, around 30% of individuals identify as morning type and 20% identify as evening type [1,2]. An individual’s chronotype is likely created by an interaction between the endogenous circadian pacemaker and its responses to light [3,4] and can be modulated by factors such as age [2,5,6] and life circumstance (e.g., needing to get to work early over years may shift preference towards earlier hours). There are a variety of physiologic events that vary by chronotype (e.g., timing of melatonin [7], core temperature [8], and cortisol [9]), as well behaviors that vary by chronotype (e.g., cognition, mood, susceptibility to stress and personality traits) [10,11]. A meta-analysis examining the association between chronotype and personality, as described by the Big Five Personality Model [12], found that conscientiousness is the personality dimension that relates most to morningness. Agreeableness is also related to morningness, although to a lesser degree, and openness to experience, extraversion and neuroticism, contribute a very small degree [12].
Another variable linked to both agreeableness and conscientiousness, prosocial behavior, has received little attention in terms of its potential modulation by chronotype. Prosocial behavior, or an action that is done for the benefit of another human or society as a whole, is regulated by both situational and dispositional variables [13]. The study of situational determinants of prosocial behavior was the focus of most early investigation. Among the situational variables that could influence prosocial behavior are setting (rural settings eliciting more prosocial behavior than urban settings) [14,15], other behaviors (e.g., cell phone use) [16], amount of sunlight [17], and weather [18]. Noise has also been found to be negatively correlated with prosocial behavior, with high noise levels interfering more with verbal help than with physical help [19]. Opportunities in which the situation is viewed as uncontrollable, such as a medical emergency, are likely to evoke more prosocial behavior [20], while the presence of bystanders reduces prosocial behavior [21]. More recently, however, there has been increasing interest in examining how dispositional (trait) variables relate to prosocial behavior. Agreeableness and conscientiousness are the personality traits most correlated with prosocial behavior [22–24]. Other variables associated with prosocial behavior include sex [25] and age [26,27].
As both chronotype and prosocial behavior are linked to agreeableness, conscientiousness, and other aspects of personality, we wanted to explore whether chronotype is linked to prosocial behavior. One previous study examining adolescents found morningness to be correlated positively with prosocial behavior, and negatively with behavioral problems [28]. We specifically hypothesized that individuals would be more likely to engage in prosocial behavior if asked to do so when closer to their preferred time of day. We secondarily hypothesized that sleepiness, a common occurrence in many adults that can be associated with chronotype [29] and impacts many aspects personality [30], would be negatively associated with prosocial behavior.

Materials and methods

Participants (N = 100) were approached at the Mountain View Caltrain Station in Mountain View, California. This location was chosen because many people waiting at the station may have some extra time and may not be immediately headed somewhere. Participants were approached when a train was not scheduled to depart from the platform within the next eight minutes. The same researcher (NS) approached all individuals. The researcher approached every third person on the platform to reduce the likelihood that the researcher was biasing their choice of participant. If the next participant was within earshot of the last participant, the researcher would move on to the next person on the platform who was out of earshot of the last participant.
To control for the effects of socializing and peer influence, only individuals standing alone were sampled. Individuals with others standing nearby were approached while individuals clearly traveling with another were not. Children (individuals who appeared to be less than 17 years old), people on crutches, people with heavy packages or others who might not be fully capable of filling out the questionnaires were excluded.
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When the participant finished the survey, the researcher thanked them and employed a sidewalk interview method [14,18,31,32] by saying the following script, which was adapted from the sociology department of the University of Minnesota [18]: “We are also conducting a second study related to sleep. Although the survey is 80 questions long, you do not have to answer all of the questions. How many questions would you be willing to answer to help me?” [...]