The term “chronotype” is used to characterize a person's sleep patterns. There are three main chronotypes: morning, evening, and mid-range. In addition to influencing someone's sleep patterns, one's chronotype also appears to have a role in a person's more general physiology. For example, depending on whether one is a morning or evening person, sleep reduction can have different effects. Many sleep researchers are very interested in the differences between people with different chronotypes, ranging from creative ability to average body temperature.
People first became interested in sleep on a scientific level in the early 1900s, and the various chronotypes were one of the first things that people identified. Morning people, sometimes called larks, tend to get up much earlier than the general population, and they also go to sleep earlier. Evening people or owls, on the other hand, stay up late and therefore sleep in later. People who are indifferent or mid-range can vary their circadian rhythms, or they fall into an average sleeping and waking pattern which is between the two possible extremes.
Around 40% of people appear to be strong larks or owls, which can be both an advantage and a disadvantage, depending on the type of lifestyle they lead. For example, some owls have trouble in school, because they cannot wake up early enough for classes, and forcing themselves to take up results in a disruption of their circadian rhythms, but they do very well on night shift jobs. Larks, on the other hand, do not cope well with late shifts at work, although they can get up for early classes without difficulty.
Studies of the various chronotypes have illustrated that they persist despite race, gender, socioeconomic background, education, and other factors. This suggests that the chronotype is in a sense hardwired. For people who are extremely rigid morning or evening people, this can represent a problem, as it is easy to disrupt their circadian rhythm. Many larks, for example, struggle with social obligations which require them to stay up late, while people with a mid-range chronotype can adjust their schedules to accommodate a few late nights on occasion.
Learning one's chronotype can help to get to the bottom of some sleep-related problems. People who disrupt their circadian rhythms enough may find themselves experiencing profound sleep disorders, which can be addressed in a variety of ways, ranging from hyponosis to changing a work schedule. By being aware of one's chronotype, it is also possible to know one's limits when it comes to things like getting up early, staying up late, or making other schedule adjustments.