1 Introduction</h5> Circadian rhythms are widespread across organisms, from bacteria to animals, have evolved independently multiple times, and have adaptive value that is bound to the cyclical variation of stimuli and resources necessary for survival and reproduction ( DeCoursey, 2004 ). In humans there is considerable inter-individual variation in behavioral circadian rhythms, and such variation can be reliably identified with self-reported measures of diurnal activity patterns, such as wake/sleep times and the timing of peak cognitive performance ( Horne & Östberg, 1976, 1977 ). Using this approach it has been shown that people's sleep patterns are normally distributed, with approximately 30% of individuals falling at the two extremes ( Adan et al., 2012 ). At one extreme of the distribution, morning-types (or early birds) prefer early wake-up and sleeping times, reach maximum alertness soon after waking up, and have cognitive performance peaks early during the day. At the other extreme, evening-types (or night owls) are characterized by late wake-up and sleeping times and by their preference for being active in the evening. In a given population, approximately 70% of individuals have sleep pattern preferences intermediate between those of early birds and night owls (see Adan et al., 2012
Evolution and Human Behavior – Elsevier
Published: Mar 1, 2015
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