The Relationship Between Morningness–Eveningness, Psychosocial Variables, and Cortisol Reactivity to Stress From a Life History Perspective

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Consistent with the hypothesis that some of the psychological, behavioral, and physiological characteristics of morning- and evening-types may represent adaptations to slow and fast life histories, respectively, this study investigated variation in time perspective (i.e., being present- vs. future-oriented), impulsivity, cooperation and competition, self-perceived social status, and cortisol and testosterone concentrations in baseline conditions and in response to psychosocial stress in relation to morningness–eveningness. Study participants were 60 male and 60 female young adults, mostly college students. Questionnaires were used to collect demographic information and to assess morningness–eveningness, impulsivity, time perspective, and self-perceived social status. Cooperative and competitive tendencies were assessed with an Ultimatum Game, an iterated Prisoner’s Dilemma Game, and a Prosocial Risk-Taking Task. Half of the study participants underwent a standardized procedure that elicits psychosocial stress (the Trier Social Stress Test) and half served as controls. Three saliva samples were obtained before and after the TSST or the control condition and later assayed for testosterone and cortisol concentrations. Consistent with our hypotheses, morning-types were more future-oriented, more cooperative in the Prisoner’s dilemma (men, not women), and perceived themselves to be of lower social status than evening-types. Furthermore, morning-types had a significantly greater cortisol response to stress than evening-types. Some of our findings support the functional interpretation of morningness–eveningness from a life history perspective. In particular, higher physiological reactivity to psychosocial stress among morning-types may be associated with their reported lower extraversion and be one of the factors contributing to some aspects of their slow life history strategy, including their avoidance of short-term mating strategies, lower sexual competitiveness, and lower social status.

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