To Sleep Perchance... Twice

Zaria Gorvett has an intriguing piece on BBC Future on the history of sleep. Gorvett assembled a substantial amount of evidence that the most common sleep pattern in pre-industrial times was biphasic; where sleep was broken into two periods separated by several hours of wakefulness usually starting from 23:00 to 01:00. This was so common that it was seldom even referred to. People used this period to do pretty much anything, from doing the chores to socializing and, as one would imagine, no small amount of sex.

This is backed up by a a remarkable study by Thomas Wehr, that has not gotten as much attention as it deserves. In the study participants were deprived of artificial light for 10 hours and then confined to a bedroom with no lights or windows and were not allowed to exercise or play music. After four weeks their sleeping patterns began to changed. They no longer sleep continuously until morning, but sleep naturally broke into two roughly equal periods with a 1-3 hour period of wakefulness in between.

Most of the evidence Gorvett assembled was from northern temperate climates where nights are very long in winter and days are equally long in summer. This makes nights intolerable during summer months because they are too short for anything to cool down before sunrise. What people from northern climate don't realize is that the tropics may be far hotter than what they are used to but every night is 10-12 hours long. No matter how hot it gets during the day, by dawn the next day everything is quite comfortable and it takes half the morning for things to heat up again. The worst of the heat is usually over by 17:00 and by 19:00 or 20:00 it is quite comfortable again.

When I was living along the Thai-Laos border it was common for men to light small fires many evenings on days that had reached 40C. The fires were not for heat but for light, keeping biting insects at bay and cooking the occasional looser of that day's cock fight. The men would sit around the fire, drink beer and sing songs while the women would congregate back in the house with the children running amok everywhere. Every so often a wife would stick her head out the door or wander over to briefly check that their spouse wasn't too drunk or things weren't getting out of hand.

Even today, this pattern of low afternoon activity is quite common. In the university where I live, almost all classes are held in the morning with some classes starting as early 07:30 and most classes are finished for the day before noon. The campus is a ghost town in the afternoons. Most Western foreigners who visit the school, annoyingly, come in the afternoon and wonder why there are no students. Noel Coward nailed it in his 1931 song "Mad Dogs and Englishmen":

In tropical climes there are certain times of day
When all the citizens retire
To take their clothes off and perspire
It's one of those rules the greatest fools obey
Because the sun is far too sultry
And one must avoid its ultry-violet ray

The natives grieve when the white men leave their huts
Because they're obviously, definitely nuts!

This is why the siesta was, and in places still is, a common practice in the tropics. People in hot climes are typically early risers, work in the morning when it is cool, sleep through the worst of the afternoon heat and then a very active again late into the evening.

In recent years the siesta has been reinvented as the nap which has undergone all of the obsessive innovative pointlessness that Westerners devote to diets. The nap was transformed into what psychologist James Maas coined the power nap. Some credit the invention of the power nap to Thomas Edison who would hold several ball bearings in his hand when he took a nap in a chair. When he began to doze off his hand would relax and the balls would crash to the floor waking him up. The idea is that most of the short term restorative benefits from napping take place before entering deep sleep, also known as SWS (slow-wave sleep). To be fair, there credible studies that back up the case for short naps.

Replace the ball bearings with caffeine and you get the coffee nap or caffeine nap or (sigh) nappuccino. This is supposed to work because the time it takes for the caffeine to hit your nervous system is long enough to squeeze in a brief nap. I am not convinced. Falling asleep can not be reliably set on a timer, especially a chemical timer which can't be turned off. In my case I never fell asleep before the caffeine kicked in and I was left both jittery and tired.

There are now napping rooms in offices, and napping pods in universities. More recently naps and sleep have been sucked into the all-singing-and-dancing mindfulness and meditation vortex and instantaneously fetishized and commodified into countless books, blogs, apps and sundry subscription services.

This is a shame because when rest is no longer so natural that no one would think to comment on it, it becomes a mediated activity, a self-conscious act of social signaling which defeats its purpose. Rest and sleep should allow us to take a break from such silliness.

Further Reading: I highly recommend Rest: Why You Get More Done When You Work Less by Alex Soojung-Kim Pang.