Two Sleeps: the hidden history of Biphasic Sleep

In my five decades of life, the art of physical displacement is one I’ve learned to practice with little effort. Many of my phases of travel were stimulated by a displacement trigger: if only I could get some quiet time away from here to finish this essay, this work, this editing. A mid-life crisis Masters degree found me alone high in the hills above the Ronda Valley in Spain, displaced from a noisy university library and hiking a particularly unstable pathway. My lack of climbing skills led to a minor slip and a twisted shoulder, albeit “nothing that sleep and hydration cannot good health”, according to the doctor’s Google Translate.

Awkward Questions 

These middle years have led me to a lot of questions, an unpicking of my own assumptions.  For example, as I travel a lot, I like this simple question about movement: what happens when you move X from Place A to Place B? It’s an adaptable kind of question, e.g., what happens when you move the Irish Border (X) from a land border (A) to the Irish Sea (B)? That question provided me with a thesis topic.  What happens when you move an Irishman (X) from Belfast (A) to Ronda (B)? It turns out he gets a twisted shoulder. 

When I left college the first time round, I missed the daily arguments in the tutorial room. In corporate life, fewer people ask ‘why?’.  Back at Queen’s University in Belfast in my 40s, a lecturer mistook my grey hair for knowledge, distinguishing the style of teaching Bachelors vs Masters students as “delivering the orthodoxy before you unpick it”.  There are many advantages to taking a questioning stance, even in everyday life.  If you critically analyse orthodoxy (what everyone accepts to be true), you might destabilise a lot of norms, but you create a space to rethink the world, which opens up a space to ask how things became this version of normal. 

Spanish Siesta

With a small handful of painkillers and a big bottle of water, I got back to my hotel in the searing Spanish evening. Only 50km from the Costa del Sol’s hectic traffic, Ronda is steeped in Andalusian traditions with its whitewashed buildings and traditional siesta. Although it’s changing form in the cities, the siesta persists here as shops and cafes still close for the afternoon.  The term siesta derives from “hora sexta” in Latin, the sixth hour, describing the original timing of a second sleep at 12 noon, six hours after waking.  

Culture Memory 

Despite the meds, I couldn’t quite make it into deep sleep and woke at intervals to hear the night sounds of a Spanish summer evening: glasses clinking, happy laughter, the equine clop of stilettos on the tiles. At 4am, I gave up and pressed the espresso machine into use, lamenting the lack of UHT milk in Spanish hotel rooms.  I opened the floor-length shutters, letting in the rosiness of dawn and the gentle swooshing of a street cleaning machine. 

Given my own predilection for structure and schedules, I planned a post-lunch siesta to catch up on sleep. I’ve always assumed a siesta to be a sensible way to manage afternoon heat, a quirk of Spanish culture alongside air-dried jamon and powerful aftershaves. But why did I assume that?  The stories we tell ourselves, our cultural narratives, tell us how things are and what they mean (Wang 2022). Culture relies on an important factor: memory.   We remember that this feels culturally normal and that feels alien, because of shared culture-memory. The Spanish siesta feels alien to me as an Irishman because Irish people tend to sleep in one long chunk of 6-8 hours, not in two phases, one at night and one in the day.  What if a siesta is more than just a heat-based cultural anomaly, splitting sleep into two segments? 

Three ‘phasic’ forms of sleep

With my first coffee brewed, I fired up my laptop to explore the idea of sleep. It’s a world with its own language.  Monophasic sleep describes one long chunk of sleep; biphasic refers to two separate sleep phases and polyphasic to more than two phases.  The bulk of research links sleep to physical and psychological health, e.g., polyphasic sleep can be symptomatic of underlying health problems.  However, my question is tied more closely to the cultural genealogy of norms of sleep. There are traces of evidence everywhere from ancient Greek philosophy to poetry and court records. While I enjoyed articles by the BBC and CNN, I could see that the research of historian, Roger Ekirch, had collated evidence to suggest an important theory: human sleep norms were once more biphasic than monophasic, a fact erased from our cultural memories, I.e., humans used to thrive on two sleeps. 

History of biphasic sleep

The normalcy of monophasic sleep is deeply embedded in our modern minds, bodies and schedules. It feels almost inevitable. We can imagine the historical traces of how we wake for work: the cockerel replaced by a monastery bell, the alarm and ultimately your phone. Our morning lives are scheduled from the moment of waking, from our coffee rituals to our work timetables. 

That sense of inevitability is simply not true. However, Ekirch found that monophasic sleep was simply not the norm in many pre-industrial societies from Europe to Oman to Australia. He writes: “French priest André Thevet, on traveling to Rio de Janeiro, Brazil in 1555, reported that the Tupinamba Indians ate whenever they had an appetite, ‘even at night after their first sleep they get up to eat then return to sleep’.”  Earlier, ancient Greek writer Plutarch wrote that Egyptians took leisure hours between two sleeps. The history of biphasic is long: later, segmented sleep persisted into living memory in populations less affected by modernity in Surinam, Australia and parts of Africa. 

The key evolutionary changes causing the shift to one block of sleep include the Industrial Revolution, which demanded the availability of workers at set hours.  Artificial light made an impact, lengthening the ‘awake hours’ of populations and technology has embedded the norm for monophasic sleep in calendars, alarms and wellness apps.  

Is biphasic sleep healthy? 

Medical writers have a lot to say about biphasic sleep, but whether it’s “better” for us or not is beyond my ken.  In a world where the paleo diet is sold as evolutionarily optimal, it’s inevitable that attention should be paid to biphasic norms of sleep. To be fair, there IS some evidence that biphasic sleep might be beneficial for some people.  It’s claimed segmented sleep might aid productivity and creativity, improve mood and recharge the brain.  For some, two sleeps could lower blood pressure or reduce the risk of heart attacks and strokes. But on this, I’m no expert. 

We have lost the memory of what people did between sleeps and if that contributed to our personal and social health. We can imagine that people did tasks possible in low light, when the temperatures were cooler: stoking the fire, playing with children, caring for the elderly.  In the Aeneid, Virgil mentions a ‘careful housewife’ who spins flax after her first sleep (Ekirch, 2018). In medieval court records, a witness reports that her mother goes out after her first sleep, only to be murdered (Gorvett, 2022).  The pressures of rising for prayer or going to work has erased our collective memory of intra-sleep activities and even biphasic sleeping might feel like an oddity to us where it persists, such as in Spain. 

In 2011, researchers chose an unnamed monastery to question whether a sleep segmented into two phases by a 1,000 year old prayer schedule had deleterious effects on the body (Arnulf et al, 2011).  The monastic tradition of those studied punctuated the day and night with prayer, meaning monks arose at midnight for 2-3 hours of Matins (morning prayer).  Measures showed body temperature rose in anticipation of waking (before any alarm clock), but that monks experienced poor daytime focus or even hallucinations. My reading of the research showed the modern body can adapt from monophasic to biphasic sleep, but not without serious consequences for some of those studied. 

The shifting sands of sleep

Shifting patterns of sleep are a long episodic story in which changes in work patterns, technology and artificial light effect changes that become so normal that alternative ways of sleeping have faded from our collective culture memory. Only traces, like the Spanish siesta persist because it serves an ongoing climatic purpose.  Sleep has evolved to match work patterns, but as AI starts to displace work norms, sleep might further evolve alongside the changing shape of our schedules. 

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