I did some googling and found a Harvard Medical page called Healthy Sleeping: Changes in Sleep with Age. It includes the usual stuff about how many hours of sleep we need, but also says a little about *when* we sleep:
In the beginning, as all new parents discover, a newborn's sleep is sporadic: the need to sleep and the need to eat cycle across the day and night, with little time for anything else. After three or four months, infants begin to develop a pattern in which sleep becomes consolidated into longer periods. Older infants and young children typically obtain their sleep during a solid nighttime session plus two or more daytime naps. Generally speaking, through the toddler years, naps become fewer in number and shorter in duration, and sleep becomes more consolidated during the night. By the age of six or seven, many children have stopped taking naps entirely. Their sleep is experienced much as it will be through adulthood: in a single consolidated block, most often at night.
So sleeping in a single block may be healthy and normal for adults. Then again – and I didn’t know this – napping practices vary by culture and even by latitude:
In many cultures, napping continues to be a normal part of daily life for both young and old. This practice, which in Spanish-speaking countries is called a siesta, tends to be more common in the tropics than in more temperate latitudes. Naps in these cultures typically take place in mid-afternoon and coincide with the hottest time of day, as well as a lull in the brain's alerting signal that works to counteract the drive to sleep.
As a consequence of these regular daytime naps, nighttime sleep is often shifted to a later hour than it is for societies or individuals that don't nap during the day.
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I also googled for how our ancient ancestors slept, and here is a bit from an article called Trouble sleeping? The solution could lie in our ancestors' lifestyle and taking rests like a caveman:
Our ancient ancestors were programmed to rest at regular intervals throughout the day rather than sleep for eight hours every night.
'Passing out for hours at a time may not have been conducive to our safety and survival, so throughout the day we rested in short phases, whenever we could, to build our energy for hunting and gathering and to maintain our wellbeing. Rest became a substitute for sleep.'
These days it is widely accepted that human sleep patterns are governed by the 'circadian rhythm' - the 24-hour cycle of being awake and active and then, when it becomes dark, resting and sleepy.
'However, built into this 24-hour pattern is a series of shorter cycles of about 90 minutes - called the "ultradian rhythm". This explains the smaller peaks and troughs of energy at throughout the day.'
Dr Ramlakhan believes this ultradian rhythm is a throwback to our hunter-gatherer years.
And while we tend to pay much more attention to the 24-hour cycle than the 90-minute one, Dr Ramlakhan believes the body works best when we move with these natural ultradian rhythms, building in pauses, stopping and resting, so continually renewing our energy.
So maybe napping is the way to go. I’ll just remind you: Don’t worry about it too much.
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Gabe also shared two interesting links on polyphasic sleep.
In the first, Dustin Curtis reminds us that sleep is still largely a mystery:
A lot of people believe sleep has been proven to repair or rehabilitate the brain and body, but this is not necessarily true. We don’t really know much about sleep. There’s no clearly defined biological reason for it, and it is intuitively an evolutionary disadvantage.
Given that, he seems a little too sure of himself regarding the benefits of polyphasic sleep, which he says works by "hacking" your brain to get just the good REM stuff and skip the fluff. Yay, productivity hacks! More free time! (In case you can't discern sarcasm, I'm skeptical.)
But I did like the graphic presenting the five types of polyphasic sleep:
The other link was much less annoying, and was Steve Pavlina's account of why he stopped polyphasic sleep and returned to a normal routine. The gist: Because everyone else does it.
The #1 reason I decided to call it quits is simply that the rest of the world is monophasic. If most of the world was polyphasic, I probably would have stuck with it. Obviously when you go polyphasic, you fall out of sync with the way other people live. You’re awake most of the night while everyone is asleep. If you sleep like most people, then the hours you’ll gain from polyphasic sleep will come in the middle of the night. And as I gradually learned, nighttime hours are not the same as daytime hours when you live in a monophasic world.
At first I rather liked the novelty of this new way of living. I enjoyed having all that alone time. It was great for writing, since I’d never be interrupted. But after several months, it began to wear on me. Although I gained those nighttime hours, I also lost about 90 minutes during the daytime because of my naps. So that meant less time to interact with people while they were awake. There were times when that wasn’t such a desirable trade-off.
If I can convince another woman to hang out with me, I'll probably return to a "normal" routine, too. Either that or I'll drag her into The Siesta routine with me.
