It is commonly understood that humans need to sleep roughly about 7-9 hours each night. That of course is not a one size fits all, it varies with age – a newborn will be in the range of 11-19 hours, teens 7-11 hours, and the over 65 5-9 hours.
Have we always had one continuous sleep cycle?
Historian Roger Ekirch published a paper in 2001 that was the result of 16 years of research in which he suggested that there was heaps of historical data that pointed towards humans having a distinctly different sleep cycle, one that consisted of two periods with a break in between. If you surf on over to his website then you can find links and books he has published on it all, and it is indeed all quite interesting.
The PDF to the actual paper, “Sleep we have lost” is here.
The hypothesis is that having two periods of sleep with a break in between was once the standard human sleep pattern, but beginning in the late 17th century things began to change and starting with the upper urban classes there was a switch to one continuous cycle. That then filtered down to the rest of society until by about the 1920s any social memory that it was one like this was gone.
The evidence is a vast collection of various written sources that all make explicit references to the first and second sleep cycles, and these are not simply obscure sparse documents, you find it within well-known books …
- “He knew this, even in the horror with which he started from his first sleep, and threw up the window to dispel it by the presence of some object, beyond the room, which had not been, as it were, the witness of his dream.” Charles Dickens, Barnaby Rudge (1840)
- “Don Quixote followed nature, and being satisfied with his first sleep, did not solicit more. As for Sancho, he never wanted a second, for the first lasted him from night to morning.” Miguel Cervantes, Don Quixote (1615)
- “And at the wakening of your first sleepe You shall have a hott drinke made, And at the wakening of your next sleepe Your sorrowes will have a slake.” Early English ballad, Old Robin of Portingale
- The Tiv tribe in Nigeria employ the terms “first sleep” and “second sleep” to refer to specific periods of the night
This hypothesis is not without criticism.
In 2015 Jerome Siegel was part of a UCLA study on how hunter-gatherers sleep today in both Southern Africa and also in South America. So did they find this segmented sleep pattern?
They stay up late into the evening, average less than 6 1/2 hours of sleep and rarely nap.
The paper that sums it all up is …
How did humans sleep before the modern era? Because the tools to measure sleep under natural conditions were developed long after the invention of the electric devices suspected of delaying and reducing sleep, we investigated sleep in three preindustrial societies [ 1–3 ]. We find that all three show similar sleep organization, suggesting that they express core human sleep patterns, most likely characteristic of pre-modern era Homo sapiens. Sleep periods, the times from onset to offset, averaged 6.9–8.5 hr, with sleep durations of 5.7–7.1 hr, amounts near the low end of those industrial societies [ 4–7 ]. There was a difference of nearly 1 hr between summer and winter sleep. Daily variation in sleep duration was strongly linked to time of onset, rather than offset. None of these groups began sleep near sunset, onset occurring, on average, 3.3 hr after sunset. Awakening was usually before sunrise.
That comes across as very much like us today.
It also leads to a thought that turns the Ekirch hypothesis around. When you first read Ekirch’s impressive work you quite naturally leap to the conclusion that the norm was the bi-modal form of sleep he documents, hence our modern sleep pattern is not normal. However, Siegel’s work would appear to turn that on it’s head and suggest we we have returned to a more natural mode of sleep and what Ekirch discovered was a historical aberration that perhaps emerged as a result of humans making the transition from being hunter gatherers into agricultural driven societies.
Can you hack your sleep pattern?
It also does bring up another rather interesting question. We accept that having just one continuous sleep cycle every 24 hours is the ideal normal sleep pattern, but what if that is not the case, can we in fact hack our sleep patterns to be something distinctly different.
Marie Staver did just that. At 19, worried about getting all her collage work done, she developed a pattern in which she slept for just 20 minutes every 4 hours. The net effect was that she only slept for 2 hours total and so that left her with 22 hours per day. For the first week it was, as you might anticipate, deeply unpleasant (headaches, chills, etc…), but one month in she felt normal.
This however many not be a good idea because sleep researchers do also know a few things that should cause some concern. An example is that shift workers who sleep outside the normal pattern are at a high risk of numerous diseases. They also know that people who, on a regular basis, do not get enough sleep die younger, and so while you might indeed get five extra hours per day, you would end up potentially loosing years of life. It is also of course not practical to sleep for 20 minutes every 4 hours and so Staver has, for rather obvious practical reasons, given up that sleep pattern. It did however gain a lot of interest and so others have also experimented with it as well.
Sleep and Alzheimers?
One fascinating recent discovery is that a lack of proper sleep does appear to be very much linked to Alzheimers, and we are now beginning to understand why …
one reason why poor sleep may be linked to Alzheimer’s is that sleep may help to clear toxic molecules from the brain. Researchers at the University of Rochester Medical School found that when mice slept, the cells in their brains literally shrank, making more room for the flow of fluids through the brain. This increased flow of fluid acted something like the jet sprays in a dishwasher, flushing away harmful waste products like beta-amyloid.
“Sleep changes the cellular structure of the brain. It appears to be a completely different state,” said Dr. Maiken Nedergaard, a leader of the study, which was published in the journal Science. Similar results have been observed in other animal studies, and if these findings are shown to occur in people as well, they could explain how sleep may help to protect the brain.
Bottom Line: You need a good night’s sleep because it literally cleans your brain and helps to preserve your memory and thinking skills.
One Final Thought – Sleeping on MARS
She wears three watches, but if you work on Mars then you really do need to keep tabs on not just multiple, but also very different time zones.
When on shift they switch to working a Mars day, and that can be challenging because the length of a day on Mars is 40 minutes longer than the length of a day on Earth, so if you start work at say 8am on day 1, then on day 2 you start work at 8:40, and 9:20 on day 3, and so on … and as the days pass each and every working day starts 40 minutes later, so as you might imagine that can really bugger up your internal clock. Apparently they can sustain this pattern for about three months and then need to quit and stop this shift pattern.
If we ever did establish a colony on MARS, then this very small 40 minute time discrepancy could end up being one of the major challenges that humans face.