A good long article on sleep

There's a good post on sleep on a blog called circadiana. Here's the link and excerpts from the post:

Everything You Always Wanted To Know About Sleep (But Were Too Afraid To Ask)

Until not long ago, just about until electricity became ubiquitous, humans used to have a sleep pattern quite different from what we consider "normal" today. At dusk you go to sleep, at some point in the middle of the night you wake up for an hour or two, then fall asleep again until dawn. Thus there are two events of falling asleep and two events of waking up every night (plus, perhaps, a short nap in the afternoon). As indigenous people today, as well as people in non-electrified rural areas of the world, still follow this pattern, it is likely that our ancestors did, too.The bimodal sleep pattern was first seen in laboratory animals (various birds, lizards and mammals) in the 1950s, 60s and 70s, i.e, before everyone moved their research to mice and rats who have erratic (un-consolidated) sleep patterns. The research on humans kept in constant conditions, as well as field work in primitive communities (including non-electrified rural places in what is otherwise considered the First World) confirmed the bimodality of sleep in humans, particularly in winter.

One thing I noticed upon arriving to the States is that nobody here seems to have any notion of "sleep manners". I have seen (and experienced) many times people barging into the room containing a sleeping person, switching on the lights and TV, talking, even talking to the sleeping person, all the while not being even aware that this is a Big No-No, very inconsiderate, and extremely rude. When confronted, the response is usually very defensive, stressing the person's individual right to do whatever he/she wants and not bother about being considerate about some lazy bum who is sleeping at an inappropriate time. Whoa! Stop right there!

It has been known for a while that adolescents are quite extreme "owls" no matter what their chronotype may be earlier and later in life (and fortunately, school districts are starting to recognize this). This has been attributed to the surge of sex hormones in early adolescence. Responsiveness of the circadian clock to sex hormones has not been studied much (virtually not at all, though I should be able to publish my data within a year or so, sorry for not being able to divulge more detailed information yet), yet most people in the field believe this to be the case, even if no details are available yet.

There is a continuum of individual sleep patterns ranging from extreme "larks" who fall asleep at the first inkling of dusk but wake up before dawn, all the way to the extreme "owls" who stay up quite late and wake up once the day is in full swing, and of course everything in between. No matter where you are on this continuum, you tend to sleep more during the winter long nights than during the short summer nights.