In zoology the word chronotype refers to the time of the sleep and regular activities of an animal. Nocturnal animals are active at night, for instance. Humans are diurnal – active in the day and at sleep at night. However, in sleep research and sleep science as applied to humans, chronotype refers to the people’s regular rising and bedtimes. Some people are morning larks and rise early and are more active in the morning. Others are night owls and sleep late, being more active in the evenings and late nights. These are people at the poles; there are other variations such as people who rise early but do not become active until mid-morning, etc. Night owls also tend to sleep more on weekends, apparently having built up a sleep debt during the week more than larks do.
When these tendencies are very strong and interfere with the person’s daily life, the person can be said to have a circadian rhythm sleep disorder. Advanced sleep phase syndrome (ASPS) and delayed sleep phase syndrome (DSPS) are the most common types. Does it sound like a somewhat artificial line between a tendency (e.g. morning lark) and a disorder (ASPS)? It is. But lots of medicine is like this. Chronotype behavior isn’t seen in just sleep times, but in level of activity and vigilance during waking periods, and even body temperature, serum cortisol levels, and blood pressure.
The physiology of chronotypes isn’t understood and it is surely very complicated. It is known that morning larks experience an earlier circadian rhythm temperature peak than night owls so it is apparent that the entire cycle is shifted. Chronotypes definitely have a genetic component. They run in families. A New Zealand study found they are "largely independent of ethnicity, gender, and socioeconomic position" based on a survey.
In popular morality, there is the notion that early birds are more moral than late risers. This prejudice appears to be slowly on the decline as we move further from an agricultural society.
"To rise with the lark, and go to bed with the lamb." - Nicholas Breton
Scientists attempt to more formally measure chronotypes with a Morning-Eveningness Scale. However, this classification has not yet found widespread use and has not produced much of use. An attempt to find a correlation between the onset of melatonin blood serum increases and the decline in slow-wave brain activity - and therefore a relationship between the circadian and homeostatic cycles - in morning people vs evening people, was unsuccessful. Some Russian scientists recently proposed expanding the number of definitive chronotypes from two to four.
Nature Article: Circadian rhythms: Of owls, larks and alarm clocks
Can you change from a morning lark to a night owl or vice versa? No. You can’t really change the underlying biological predilection to a chronotype. Over time your body may change. Lots of people find themselves turning into morning people as they age. But it’s not possible to make this happen. You can do things like use exposure to bright light to attempt to reset your circadian clock. And you can use a drug like melatonin or (perhaps in the future) one of the new drugs in the emerging field of chronobiotics. But this probably isn’t a good long term solution. Talk to a doctor. Most doctors will tell you to avoid staying on drugs for long periods unless necessary.
If you lived on your own with no interactions with others, you wouldn’t have problems with your chronotype. Tension comes in when you have to live and work with others. This is rarely a serious problem, though. You learn to live with family members who are different from you. You learn to get to work at the time your employer demands and when social activities with others are scheduled. The disconnect can be termed social jet lag but unlike real jet lag, the social form is chronic.
Scientific American had an article on the difference between how caffeine affects morning larks and night owls. The short answer: daytime caffeine disrupts night sleep more in morning people than in evening people. Scientists have also determined at least part of the genetic basis of larkiness. This is of little practical use, but it is further proof that the tendency is in-born, not a product of habit or morality.
German scientists studying the circadian cycle and how it shifts through our lifetime suggest that a marker for the end of adolescence may be the end of the forward shift in the cycle that most teens experience. When people stop sleeping late and adopt an adult pattern, they have become adults. This definition has not gained currency but it is an interesting idea.
Spanish: A quien madruga, Dios le ayuda - "God helps those who get up early."
German: Morgenstund hat Gold im Mund – “Morning-hours have gold in the mouth."
Italian: Chi dormi non piglia pesci – “He who sleeps doesn't catch any fish.”