I was looking at my bed the other morning, just staring at the rumpled sheets, and it hit me how much of our modern identity is wrapped up in this single, monolithic eight-hour block of unconsciousness. We treat sleep like a shift at a factory. You clock in at eleven, you clock out at seven, and if you wake up in the middle of it, you feel like a broken machine. But what if the machine isn't broken? What if we just forgot how to use it? Today's prompt from Daniel is about exactly that, the history and physiology of biphasic sleep. He wants us to look at whether that old-school first sleep and second sleep model actually has biological perks over our modern monophasic standard.
It is a massive topic, Corn, and honestly, one of the most misunderstood areas of human biology. I am Herman Poppleberry, by the way, for anyone joining us for the first time. Daniel's prompt is incredibly timely because we are seeing this huge cultural pivot right now in March of twenty-twenty-six. After years of people trying to use every gadget imaginable to optimize their sleep, we are seeing a move toward what people are calling sleep simplicity. The American Academy of Sleep Medicine actually just put out a case study on March thirteenth regarding the risks of this sleepmaxxing trend, where people are so obsessed with hitting specific metrics that they are actually causing circadian misalignment.
It is the classic case of over-engineering a natural process. We have been talking about sleep on this show for years, but the idea that our ancestors didn't just crash for eight hours straight is still wild to a lot of people. I remember we touched on the midday rest in episode eleven sixty when we looked at those high-tech nap pods, but Daniel is asking about something much more fundamental. He is talking about the segmented sleep pattern that was the global norm before the Industrial Revolution.
The foundational research here comes from a historian named A. Roger Ekirch. He spent years combing through thousands of historical documents, diaries, court records, and medical manuals. What he found was that before artificial lighting became cheap and ubiquitous, humans almost everywhere followed a biphasic pattern. You would have your first sleep, which usually started a couple of hours after dusk. That would last for about four hours. Then, you would wake up for an hour or two of what people called the watch. After that, you would have your second sleep until dawn.
The watch. That sounds so much more intentional than just lying there staring at the ceiling wishing you were asleep. It was not considered insomnia, right? It was just a scheduled part of the night.
It was completely normal. People would stay in bed and pray, or they would read by candlelight, or even get up and visit neighbors. There is this beautiful new historical analysis that was just published on March tenth in the journal REMO. It suggests that this watch period was characterized by elevated levels of prolactin. Now, prolactin is a hormone we usually associate with nursing, but in this context, it creates a state of quiet wakefulness. It is a meditative, serene feeling that is totally different from the high-cortisol, frantic alertness we feel when we wake up in the morning and realize we are late for work.
So the brain was in a different gear entirely. Instead of fighting the wakefulness, they were leaning into this chemically induced calm. That makes me wonder about the physiological architecture of it all. If you split your sleep into two four-hour chunks, how does that change the way you cycle through Rapid Eye Movement and Slow Wave Sleep? Because we are told you need those long, uninterrupted cycles to get the good stuff.
That is the core of the debate. When you sleep in a single eight-hour block, your brain prioritizes Slow Wave Sleep, which is the deep, restorative physical rest, in the first half of the night. Rapid Eye Movement sleep, which is for emotional processing and memory consolidation, mostly happens in the second half. When you move to a biphasic model, you are essentially creating two opportunities for the brain to navigate those cycles. In a siesta model, which is the other common biphasic form where you have a shorter night sleep and a long midday nap, you can actually get a very efficient burst of Slow Wave Sleep during that afternoon dip.
The post-prandial dip. The classic afternoon slump after lunch.
That is the one. Our internal clocks actually have a natural dip in alertness in the early afternoon, usually around eight hours after we wake up. Aligning a ninety-minute nap with that dip can be incredibly powerful. A ninety-minute sleep is key because that is roughly the length of one full sleep cycle. You get the deep sleep and the dreaming sleep, and you wake up at the end of the cycle so you don't feel that groggy sleep inertia.
I have always felt like the afternoon slump was a design flaw, but you are saying it is actually a feature we are just ignoring. If you have the luxury of a flexible schedule, is there a measurable cognitive boost to doing this?
There absolutely is. Splitting the sleep reduces what we call homeostatic sleep pressure. Think of it like a balloon filling with air throughout the day. The longer you stay awake, the more pressure builds up. That pressure is caused by the accumulation of adenosine in the brain. When you take a significant midday nap, you are essentially letting some of the air out of that balloon. This can lead to much higher levels of alertness in the evening and potentially better cognitive performance across the whole sixteen hours of wakefulness.
It is interesting that you mention evening alertness, because that leads us into the Karachi study that Daniel mentioned. This was published just a couple of months ago, in January of twenty-twenty-six. They looked at four hundred adults in Karachi, and the findings were fascinating. They found that while about forty percent were monophasic, nearly forty-two percent were naturally biphasic. But they split those biphasic sleepers into two groups: the siesta sleepers and the dawn sleepers.
The dawn sleepers are the ones who really caught the researchers' attention. These are people who wake up very early for prayer or work, stay awake for a while, and then go back for a second sleep before starting their main day. The study found that these biphasic-dawn sleepers had the lowest levels of daytime sleepiness on the Epworth Sleepiness Scale. Their average score was seven point eighteen, which is remarkably low.
That is a concrete data point that flies in the face of the idea that interrupted sleep is always bad sleep. These people are intentionally interrupting their sleep, yet they are more alert during the day than the people who try to power through in one go. It makes me think about the people who struggle with chronic insomnia. About ten percent of the population deals with that, and a lot of the stress comes from the fear of waking up at three in the morning. If we reframe that three a.m. wake-up as the watch, does the pathology of insomnia just... evaporate?
For some people, yes. There is a whole movement within sleep therapy right now looking at segmented sleep as a treatment for certain types of insomnia. If you stop fighting the wakefulness and treat it as a natural period of reflection, your stress levels drop, your cortisol stays low, and you are much more likely to fall into a high-quality second sleep. The problem is that our modern society isn't built for the watch. We have bright LED lights, smartphones, and the constant hum of the internet, all of which suppress melatonin and mess with that prolactin-heavy state of quiet wakefulness.
We have traded the watch for the scroll. Instead of quiet reflection, we are feeding our brains a firehose of information at three in the morning, which is basically the opposite of what the brain needs in that state. But we have to talk about the extreme end of this, because Daniel also asked about polyphasic sleep. This was huge a few years ago with the whole productivity hacker crowd. People trying the Uberman schedule, where you take six twenty-minute naps every four hours and only sleep two hours total per day. Herman, is anyone actually doing that successfully in twenty-twenty-six?
The short answer is no. Not sustainably, anyway. The July twenty-twenty-five report from the Sleep Foundation was pretty definitive on this. They looked at the long-term metabolic and cognitive effects of these extreme polyphasic schedules and the results were grim. When you try to compress your sleep into tiny twenty-minute bursts, your brain never gets enough time to complete the necessary cycles. You end up in a state of permanent sleep deprivation. Your reaction times slow down, your immune system takes a hit, and your emotional regulation goes out the window.
It is the ultimate expression of the sleepmaxxing mindset. Trying to treat the body like a piece of software you can just patch. But humans do adopt polyphasic sleep in some contexts, right? Infants are the obvious one.
Infants are naturally polyphasic until they are about three months old because their circadian rhythms haven't fully developed yet. Their bodies are just responding to immediate needs like hunger and growth. The other group is people in extreme environments, like solo offshore sailors or certain military units. They use polyphasic schedules out of pure necessity. If you are sailing a boat alone across the Atlantic, you can't sleep for eight hours or you might hit something. So you sleep in twenty-minute increments. But those sailors will tell you, it is not a hack. It is a survival strategy, and it takes a massive toll on their mental clarity over time.
So it is not a natural state for an adult human. Which brings up an interesting counter-argument Daniel mentioned. There was a study back in twenty-fifteen that looked at equatorial hunter-gatherer groups like the Hadza in Tanzania and the San in Namibia. The researchers expected to find these groups using biphasic sleep, but they were actually largely monophasic. They slept in one block from a few hours after sunset until just before dawn.
That study is the main piece of evidence used by people who argue that biphasic sleep isn't some universal biological mandate, but rather an adaptation to specific environments. The theory is that in places with long, cold winter nights, like Northern Europe, humans had to spend sixteen hours in the dark. You can't sleep for sixteen hours, so the sleep naturally segmented. But in equatorial regions where the day-night cycle is more consistent and the nights are shorter, monophasic sleep might be more efficient.
So maybe it is not that one is natural and the other is artificial. Maybe the human brain is just incredibly plastic and can adapt its sleep architecture to whatever the environment demands. If you are a hunter-gatherer in a warm climate, you sleep in one block. If you are a medieval peasant in a cold climate, you split it up. And if you are a modern office worker, you try to cram it all into eight hours so you can be at your desk by nine.
That plasticity is our greatest strength, but it is also why we are in this mess. We have used technology to create an environment that is totally disconnected from any natural cycle. We have artificial light that mimics the sun at midnight, and we have social pressures that demand we be alert and productive during the very hours when our biology is telling us to rest. The American Academy of Sleep Medicine is actually pushing for a move to permanent Standard Time for this exact reason. They want our social clocks to align better with the sun, which would help our internal circadian rhythms stay in sync.
It feels like we are at a crossroads. We have all these gadgets and apps telling us exactly how we slept, but we feel more tired than ever. Maybe the takeaway from Daniel's prompt isn't that we all need to start waking up at two a.m. to pray, but that we need to stop being so rigid. If you wake up in the middle of the night, maybe don't panic. Maybe realize that you are just experiencing a version of the watch.
I think that is a very healthy way to look at it. The goal shouldn't be to force a specific pattern, but to understand the mechanisms at play. If you have the flexibility, experimenting with a ninety-minute midday nap could be life-changing for your energy levels. If you find yourself waking up early and feeling refreshed after a few hours, maybe that is your natural biphasic-dawn pattern kicking in. The Karachi study showed us that those people are some of the most alert people on the planet.
It is about listening to the biology instead of the metrics. We did a deep dive on the science of restorative rest back in episode five forty, and the big takeaway there was that sedation isn't sleep. The same applies here. Forcing yourself to stay in bed for eight hours when your brain wants to be in the watch isn't rest, it is just frustration.
And that frustration is what drives people toward these extreme sleepmaxxing hacks that usually backfire. The best thing most people can do is simplify. Get the lights down low in the evening, stop the high-intensity blue light exposure, and if you wake up in the night, just let it be a quiet, peaceful time. Use that prolactin-induced calm for what it is.
It is funny to think that the most high-tech thing we can do for our sleep in twenty-twenty-six is to act more like someone from the year sixteen hundred. Just minus the wooden pillows and the straw mattresses.
I will keep my memory foam, thank you very much. But the schedule? The schedule might be worth a second look.
Definitely. This has been a great dive into the history of how we rest. If you are struggling with your own sleep, maybe take a look at our archives. Episode six sixteen goes deep into why the timing of your sleep might matter more than the total duration. You can find all of those at myweirdprompts dot com.
We should also give a big thanks to our producer, Hilbert Flumingtop, for keeping the gears turning behind the scenes. And a huge thank you to Modal for providing the GPU credits that power the generation of this show. They make this whole collaboration possible.
If you are finding these deep dives helpful, a quick review on your podcast app really does help us reach more people who are looking for substance over surface-level takes.
We will be back soon with another prompt. This has been My Weird Prompts.
Sleep well, however you choose to do it.
Goodbye.
