Re: Does the time of day you were born makeyou a 'morning person' or night owl

Morgan-

     That's a great question! To get to an answer, let me first discuss why people sleep at night and stay awake during the day. Then we can ask some questions about how early or late a person decides to stay up.

     When we talk about the waking and sleeping schedule a person keeps, we call it a circadian cycle. This circadian cycle is set to about 24 hours - so that a person sleeps each night, and is awake during the day. While it's set to a little over 24 hours, exposure to light resets it each morning, so that we're always in rhythm with the sun. More on that can be found here.

     But as you pointed out, some people like to get up earlier than others, but some people like to sleep in later (and stay up later) than others. So there definitely is some way to fine tune this cycle! So you asked a really good question - "Does the time of day you were born make you a 'morning person' or night owl?" This is a very reasonable hypothesis.

     However, I haven't been able to find any evidence that a person birth time that influences our sleep preference. Actually, when babies are born, they don't have the same rhythm as adults do. (and they tend to keep their parents up, as a result!) But as they get older, they begin to have a normal cycle, like everyone else. But the point is: since they don't really have a cycle when they are born, it's not likely that their bodies "remember" what time they were born when they finally have a cycle.

     Interestingly, the Season in which a person was born may influence his or her early or late tendencies. A preliminary study found that people born in autumn and winter were more likely to be morning people than people born during the summer. This isn't a hard and fast rule, but the general trend.
     What does the season matter? Well, as you've undoubtedly noticed, days are a lot shorter in the winter than the summer. Perhaps people who are born when the days are short are more sensitive to light - it's like when they were young, they got used to trying to get as much sun as they possibly could! The people who did this study think it's because the hormone melatonin, which increases or decreases with the length of the day (and thus with the seasons), sets up the circadian cycle for future use.

     Also, some people have suggested that some genes might be responsible for differences between people.

     But really, more work is needed in this area. We can only sit and wait for scientists (like you!) to tackle these questions!

-Alex G
cgoddard@fas.harvard.edu

P.S. - the words in bold are important ones. You may want to look them up if you are interested!

some links

Some info on our natural clock, or circadian rhythm: http://www.bio.warwick.ac.uk/andrewM/Jo%20Selwood% 20site/index.htm

Some research on influences of our genes on our sleep schedule: http://www.stanford.edu/~dement/early.html

One of the papers that talks about the relationship between sleep schedule and season http://www.ncbi.nlm.nih.gov/entrez/query.fcgi? cmd=Retrieve&db=PubMed&list_uids=12566 940&dopt=Abstract (this one is kind of hard to read, so you might want to ask your parents or teacher to read it with you!)