"Human biological clock makes a turn in a cycle of about 25 hours when there is no clue to know the passage of time. However, the earth rotates in a cycle of 24 hours, repeating light and darkness. " (http://www.societies.cam.ac.uk/cujif/ABSTRACT/020825.htm)
"For most of evolution humans have slept clustered together with friends, animals, parents and children. In traditional societies, according to Worthman, communal sleep is considered safer since there is always someone there to help in case of an emergency. In these societies people find that group sleeping reduces the risk of spirit loss, which is especially common when a person dreams.Recently, studies have shown that this type of sleeping, called co-sleeping to contrast it from the solitary sleeping patterns of people in modern societies, has real physiological benefits. James McKenna of the University of Notre Dame reports that babies in many countries outside the United States sleep next to or in the same room as their parents. He notes that infants who sleep alone slip into abnormal patterns of very deep sleep which prevents them from waking during an episode of apnea. " (http://findarticles.com/p/articles/mi_m0ISW/is_2002_July/ai_87719989)
"Recent research suggests that sleep patterns vary significantly across human cultures. The most striking differences are between societies that have plentiful artificial light and ones that do not. Cultures without artificial light have more broken-up sleep patterns. For example, people in these cultures might go to sleep far more quickly after the sun sets, but then wake up several times throughout the night, sometimes staying awake for several hours. The boundaries between sleeping and waking are blurred in these societies. Some observers[attribution needed]slow sleep believe that sleep in these societies is most often split into two main periods, the first characterised primarily by "" and the second by REM sleep. This is called segmented sleep, which led to expressions such as "first sleep," "watch," and "second sleep" which appear in literature from all over the world." (http://en.wikipedia.org/wiki/Sleep)
I have to say that this last quote from wikipedia is fascinating and somehow appealing to me. I love the way my house feels when I walk around it in the middle of the night and everything is peaceful and sleepy. I love how close everybody feels on my block when it's late on a still night. I can lean off my balcony and and talk to my neighbor halfway down the block almost without raising my voice. I love the intimacy of talking in the middle of the night. What I wonder is how the different sleep patterns affect the relationships between people. Obviously, without artificial light, people aren't really doing anything when they're up in the middle of the night except maybe talking and thinking, maybe walking or small tasks that can be done by the light of moon or fire.
I have to clarify that I don't like to have to get up in the middle of the night. I *do* enjoy an unbroken night of sleep...yet, on the nights when I've been up for a while in the middle of the night there's something appealing about it...not when I have to be up, but when I am just up.
Also, I need to clarify that the last quote is from wikipedia, and I'm still looking for more scholarly sources. If anybody out there knows books or resources about the anthropology of sleep, I'd be interested.
Here's an interesting sleep project:
"The Uberman's sleep schedule revolves around forcing yourself to rely on six twenty to thirty minute naps spread throughout the day for your daily dose of sleep. I stuck to thirty minute naps, currently having them starting roughly at 2 AM, 6 AM, 10 AM, 2 PM, 6 PM, and 10 PM every day."
Ok...here's something other than Wikipedia saying the same thing:
"Indigenous cultures that do not rely on artificial light differ greatly in their sleep patterns from those that do, according to Prof. Roger Ekirch, author of At Day's Close: A History of Night-time. They have what's called "segmented sleep" patterns where they wake several times during the night, sometimes for long periods at a time. Ekirch theorizes that artificial light's influence on sleep cycles has contributed largely to the rise of sleeping disorders in industrialized nations." (http://shl.stanford.edu:3455/TenThings/1735)