More fragmented sleep, with people talking in the night, etc. I guess that's different from the low, unnatural, rumbles of cars and aeroplanes the majority of people have to put up with.
> Some emerging research suggests Earth’s magnetism matters, as well. Being barefoot on the ground versus 30 stories high in a downtown skyscraper puts you in a completely different magnetic environment.
Really? My instinctive reaction to this statement is that it's quackery. Would be very interested to see headlines appear about this if it's true.
People already live in different altitudes, ie with vastly different amounts of rock between themselves and the bits of the earth that produce her magnetic field.
So colour me skeptical of this claim as well.
And while I like going barefoot for other reasons, I don't think it makes much of a difference to the magnetic fields.
It's definitely quackery. There's way more "natural" magnetic variation between two different cities than between a ground floor apartment and a 30th floor apartment (see magnetic declination maps), and that's even before you get into the way-more-powerful magnetic fields generated or present in a home.
This is called "grounding" or "earthing" and Wikipedia doesn't pull punches in dismissing it [0]. You can buy grounding wires for your mattress or copper rivets for your shoes.
From my tissue engineering class in undergrad my 2 cents is this is maybe 95% supplements quackery and 5% genuine mystery. You can find papers that claim EM fields have cellular interactions [1]. I don't think serious scientists will touch conventional earthing, though.
I would not jump to such conclusions, I would assume is not fully known and needs to be further understood.
on the other side, do you know we have polarized and non-polarized cells? do you know they can be affected by electromagnetism?
this two things already establish the existence of a relationship and effects between them. If we then consider that cells mechanism work based on differential of electrical or chemical potentials, and that they continuously use that for their functions, reactions or environmental compensations well...
I just think they are related and we need to understand better.
Fascinating, but polarization is a red herring. Magnetism is famously the wildly-unreactive half of electromagnetism; copper is REALLY sensitive to electricity and REALLY insensitive to magnetism.
> Sleep is critical to human functioning, and yet, we sleep fewer total hours than any other ape, and are still arguably the most evolutionarily successful of the primates
> humans are weird outliers—we’re the shortest sleeping primates, yet we pack in the most REM sleep relative to this short duration
Isn't that sort of the point? Sleep is a detrimental necessity and the more efficient an organism is in needing less of it, the more effective it can be because it simply has more time to get ahead of the others?
It's still very odd that no species has ended up evolving a continuous maintenance system that can run while conscious, the benefits when hunting other animals that need sleep would be enormous, so there has to be significant evolutionary push for it. I suppose the single hemisphere sleep some marine mammals do is part of the way there, but it is at most a lazy workaround. Practically all other organs have evolved to run 24/7 for up to a century without a single break, what makes brains so universally different?
The fact they electrically signal via chemical analogs fuelled by immersion in nutrient bearing fluid that also accretes waste products, yet is kept separate from the primary loop of the cardiovascular system by the blood-brain barrier?
> It's still very odd that no species has ended up evolving a continuous maintenance system that can run while conscious
Great point. Afaik, our bodies do preserve energy when we sleep/rest. A few questions that needs to answered first:
- will gains of 24/7 hunting/foraging offset the extra energy costs? Lions sleep 16-20 hours a day, according to the internet.
- do continuous maintenance systems imply duplicate systems? If so, I have a hunch that even a mere 40% increase in energy expenditure would quickly undo the gains in waking hours.
> It's still very odd that no species has ended up evolving a continuous maintenance system that can run while conscious, the benefits when hunting other animals that need sleep would be enormous, so there has to be significant evolutionary push for it.
I disagree. Endurance hunters walk an animal down throughout a single day. Sleep isn't the bottleneck. Efficient bipedalism and sweat are enough.
Unihemispheric sleep has been used by cults for mind control because it puts you in a vulnerable mental state (for example https://zizians.info/#unihemispheric-sleep). So anybody reading this and interested in trying it, ensure you’ve done sufficient research first.
> It's still very odd that no species has ended up evolving a continuous maintenance system that can run while conscious, the benefits when hunting other animals that need sleep would be enormous, so there has to be significant evolutionary push for it.
This is actually quite a conundrum.
Animals as simple as flies have been observed sleeping (diminished brain activity while resting). It is highly conserved, so it must be incredibly important.
They're probably also less confronted with articles/videos/social media posts telling them they're doing it wrong and how they should sleep instead. Sometimes ignorance (or rather, not overthinking things) is bliss...
If they have no frame of reference then it seems like their general contentedness is being measured (or as another commenter indicated, their willingness to gripe.)
True. But the article mentions that the amplitude of their circadian rhythm is higher (which tells you how much a relevant measure like the amount of melatonin or body temperature varies in a 24 hour cycle), so that is an indication of better sleep. A low amplitude means less difference between sleeping and being awake.
This interview feels weird to me, maybe because there's lots of places where I'm thinking there's an obvious idea that isn't raised.
Like, it seems obvious to me that sleep has a higher opportunity cost in humans than most other animals. So naturally there's more evolutionary pressure in humans to sleep more efficiently.
Is this actually true? Dunno! But it was really weird that it doesn't get brought up.
> untangle what he calls the sleep paradox: Sleep is critical to human functioning, and yet, we sleep fewer total hours than any other ape
Instead of going to Tanzania you could’ve asked a sleep scientist. Sleep length has no known correlation to brain size and is known for drastic within family variation. What’s more sleep has a high within species variation too, some sleepers can survive 4 hours, others need 8. Collectively we used to sleep 9 hours in the 20th century, but it appears shorter sleep is fine too.
TLDR: no one has any idea why sleep length varies and he won’t find his answers in antrophological studies in Tanzania, though luck, buddy
>“No way. They’re partying all night.” But they can, because there’s no top-down pressure to go into the office at 8 a.m. They’re free to catch supplemental sleep as needed throughout the 24-hour period.
This feels like the key point to me. These societies follow their body and go to sleep when they are tried, while us in the west have to sleep at a specific time to fit our schedules.
But the article discussed here also points in that direction when it mentions the importance of people on the lookout at night. The article also mentions primitive tribes partying all night, so that is yet another direction.
My boy when very young (just months) went thru a phase where in the middle of the night he would suddenly sit bolt upright, swivel his head to scan the room, and then conk out again. This was not caused by noises.
I found this reassuring and slightly amazing, that he is wired to do his part as a nighttime lookout.
Assuming you are not jesting, I am not certain I would qualify that behavior as any indication of being wired for some sort of nighttime patrol duty based on those details alone.
Fascinating. Also, not that you implied this by any means, but I was not trying to say "you are wrong, I'm right." Rather, who knows? Do all behaviors happen for a reason? Idk.
We have evidence that during the medieval period people did take two-sleeps. Whether this is the more "natural" organization is debatable. But it made sense for that time.
> Historical texts and recent research suggest an alternative view: that sleep can be naturally segmented into two periods across the 24h cycle – a pattern known as biphasic sleep
I would also imagine a single block of sleep is relatively new due a host of various factors. Especially when considering untreatable medical conditions, chronic pain, parasites (bed bugs, lice, etc.), lack of comfortable bedding, cohabitation with others, and plenty of other factors all had major impacts.
>while us in the west have to sleep at a specific time to fit our schedules.
This does seem to work great at group level. Considering we're in a competitive setup and all that.
I also recognize I personally benefit from others having this schedule. It would quickly go sideways if the firefighter felt like he wanted to sleep a bit more, or the police officer didn't really feel like it whenever is an emergency.
Firefighters and police are quite strange examples to choose, since they both have to offer 24hr support. Surely they could benefit from sporadic sleeping and shift work?
For example if they're able to have some firefighters napping at the station, whilst others keep watch for alerts, that would seem better than enforcing strict wakefulness for the whole squad so they are all tired if the call comes in at the end of a night shift?
Obviously there would have to be some communication and understanding about who stays awake and who takes a rest, but I could see it working.
That was the low hanging fruit, after I set the stage for the real state of things. Again, we are in a competitive setup, globally, which imposes a certain gameplay. If we're not organized we're not as efficient. Or functional for that matter. You are either putrid rich and can afford to pay others to keep it together for you, or you need to do what you don't really enjoy, but must be done. As always basically.
In the past we were facing famine mostly, so we had to do what we had to do. There were times for partying but we always had to do what we do not enjoy doing. It's nothing new really, it's just the way we're doing it that's different.
So coming back, what would be your solution? Because you cannot simply ignore the global competition for resources and basically power. If you slack you get taken over. As in, slacking might work for a while, sure. But that will inevitably be seen somewhere, in some numbers, statistics, resources etc. Sooner or later. What do you do then? One just needs to look at some current wars footage to get a sense of how bad it can be.
Also don't get me wrong, I'm all for world peace and all that. Very hard feat though, considering human nature.
The article title is "Where human sleep went wrong" but then the entire article is about how we sleep the best we ever have, we have the most high quality sleep, and all the fearmongering about sleep is basically wrong.
I think people in HN (and in general) have to remember the central axes of evolution before digesting this kind of article. I've already seen comments like it's "odd that no species has ended up evolving a continuous maintenance system" and "sleep has a higher opportunity cost in humans" in this comments section.
This is a common, but poor framing of evolution. Remember: the only real rule with evolution is "did this evolutionary change mean they survived / reproduced more"? Evolution is not a local or global maxima solving function. I find this kind of attempt at interpreting selection common with engineers, programmers, etc.
> "did this evolutionary change mean they survived / reproduced more"
You're just renaming the terms. More/less is a fitness gradient, and the thing that lives there is called an optimizer.
Evolution is a tunable-scale optimizer. It's not perfectly local, because it shotguns to avoid local optimums on a fitness landscape. If you tune the 'shot pattern' really wide (infinite copies with infinite variation), you'd genuinely get a one-shot global optimizer at the limit. But that's not efficient nor realistic, so typically it's somewhere in between.
Uh, compare maze solvers: you've got your greedy direct route (gets stuck in the first corner) , Dijkstra (finds all the answers but takes ages), and then stuff like A, which is a happy medium. Evolutionary algos can be used to solve mazes just the same. I think it's a bit heavier on resources than A, but well suited to embarrassingly parallel optimization.
I tried to imitate japanese people in the public transport when i was there, meaning I managed to kinda sleep/nap with eyes closed for 10-15minutes between rides and it was astonishing.
while I understand might be a more known thing, it was surprising to try it and feel very rested after that. I'm still surprised and I wonder why not the whole world does it.
of course without the music at the stops would not be possible :P
>18 degrees Celsius is considered optimal for sleep depth
I'm instantly skeptical of anyone making universal statements like this, because they're certainly not true for everyone, and having looked into these and similar (f/x "ideal room/office temperature"), are based on many entangled assumptions. Most of the time I expect it's just people making after-the-fact justification for doing (or imposing) what they most prefer.
When statements like this are made usually it’s because studies would have been done comparing sleep depth at different temperatures and there would have been a statistically significant increase in sleep depth at 18 degrees Celsius in the tested group compared to groups sleeping at other temperatures.
I have no idea if that was actually done here but that’s usually how these statements are justified.
Of course we are all individuals so it may not apply to everyone but you can say that for everything in medicine. Only thing we can do is look for statistically significant differences between groups in double blind controlled studies after controlling for all other factors.
yeah probably lot of study measurements and data confirming that, I'm not skeptical about it, to me it feels like something scientifically measured proven since quite some time already. of course genetics and outliers still need to be considered.
also do you know that the body temperature decreases during sleep? based on that I simply deduce and assume the more the difference between body and room temperature the more side effects arises for sleep, of course simplifying without ignoring all the rest.
And every time I hear about an optimum, I think of the Bathtub Curve.
As I imagine the curve, I use a real bathtub. Where is the water deepest? At the drain, which is typically just under the faucet. Where is the optimal place to sit? Well, pretty much anywhere except there, because "deepest" (an optimum) isn't enough to accurately gauge "best place". But even if you can swing the faucet out of the way... where is the optimal place? Anywhere on the bottom, a broad, slow curve, as opposed to the steep walls or rim.
So, if 18 degrees C is the optimum, what's the standard deviation? I bet it's not 0.1 degrees. Could be 2 degrees - and that would mean concentrating on 18 degrees is a distraction, not a goal.
This is something evolutionary discussions don't address well, either. If a gene line (species) has a pressure to change, it can "settle" for any place on the bathtub floor (when the solution is shaped like that). This is another example of evolution not seeking an optimum; merely avoiding a pessimum (a word I just googled, and like!).
In fact, it doesn't even matter if it's a bathtub curve. Maybe it's a slope, like the amount of capsaicin a pepper plant carries to fight off fungus. More better - but it costs something to make, so just make enough to ensure survival. More fungus? Increase capsaicin production. There's no floor to this bathtub; it's a linear slant all the way down to maximum possible capsaicin content (which, amazingly, is about 10% by weight of the fruit cells!!!).
18C is more like the maximum OK temperature. But then I also gotta sleep without PJs when its that hot. Still a blanket for comfort.
Best sleep from my experience? It's usually about 5C at the thermostat, which is farthest from the window, by the time I wake up. The cold air coming in will be 0C and colder and I sleep next to the window. Winter is my happy sleep time.
If you are wearing clothing or any covering, clearly it isn’t your optimal temperature. I’m not trying to be glib here; I understand the appeal of being warm in a cool or even chilly room with air that keeps you from overheating. But that’s not sleeping at the optimal temperature; it’s choosing the sleeping setting you like.
And there are huge swaths of the world where the temperature basically never gets that low (18 C is the lowest temperature ever recorded in Kingston, Jamaica; 16 along the coast of west Africa, 18.9 in Jakarta). Even here in the southeastern US it is normal for temperatures to stay above 20 C at all times for three full months of the year (late June through early September).
Nothing wrong with liking to sleep in cold air, but it’s a preference.
Your feeling might be different. But for me, body temperature and feeling is way different from the air I'm breathing.
I can be, actually want to be toasty warm under the blanket. But I want the air I am breathing to be fresh and cold. That is when I feel comfortable and "at peace".
I will often stick out my feet from under the blanket because it's way too toasty but the rest of my body needs to be warm.
Sure, when it's 25C I'll essentially just lay there without anything but a sheet across the chest to "feel safe" but anything else will just make me way too warm and the air I'm breathing will feel restricting.
What is really great in 25C+ temps is to be outside in a hammock without an underquilt, which cools things down considerably. But I've also slept comfortably at 0F (-18C) in a hammock. With two underquilts and a 0C sleeping bag as well as a winter tarp with doors and snow cover all around, weighing down the tarp sides (wind does suck at that temp ;)).
I was really responding to the article’s odd claim of 18 C being the perfect sleeping temp, and your comment was so extreme in the make-it-cold direction that it seemed to be a good spot to reply. If we’re talking about “optimum” sleep temp as though such a thing has meaning beyond personal preference, then clearly it must not be cluttered with cultural detritus like depth of blankets, etc.
My wife wants it to be 20 C or lower and sleep under two blankets. I pointed out that 23 with a fan and a sheet is less energy-intensive and gives equivalent results, and she said stuff it. Not a battle worth fighting at home, but on the internet…
(Of note, the one of our dogs that loves me but worships her still sleeps next me every night, under covers, because she’s a Chihuahua and gets cold easily, and unlike my wife I sleep like a dead log.)
For you, and that's kind of my point. For me, my preferred temperature would be about 28C with no blanket or a light sheet. Something like 18C can be tolerable with blankets for me, but it's certainly not "maximum comfort", even with blankets. There is too much variation and too many things that wouldn't be controlled for, like number/thickness of coverings, and other such things. Having some "best" universal temperature is just not something generalizable like this.
If you want a tried and tested heuristic it should be cold enough to make you retreat to hibernate under a mountain of blankets roughly equivalent to or exceeding the warmth of a polar bear's coat.
> Most importantly, when we measured their circadian function directly, small-scale communities had much higher amplitude circadian rhythms than global north populations, which I think is why they report being happy with their sleep even though it’s more fragmented.
This could explain why I feel more rested when I wake up if I take glycine before going to bed, even though I don't sleep more.
"we’re the shortest sleeping primates, yet we pack in the most REM sleep relative to this short duration."
Nothing surprising here. We sleep in cozy comfortable beds in a locked and secure location. Of course we'd can get int REM sleep. Compare to other primates who sleep outside with the critters and predators, deep sleep could mean the end of them.
My understanding is that REM isn't particularly deep. Quick web searches aren't actually defining it as more like light or deep sleep, but many of our systems are more active than other stages[1][2]. Still I don't think it's super surprising that we spend more time in REM since our brains are uniquely complex and we spend a lot of energy on perception and interpretation, which REM seems to help with [1][3]. And I would be willing to be safety and comfort also play a decent role in it as well!
Probably the only primates where a significant portion spent tens of thousands of years isolated up in the Arctic during prehistoric times.
Where the sun doesn't go down every single day anyhow, and you may need to trudge across the tundra routinely for more than 24 hours at a stretch to get almost anywhere, without ever worrying about it at all.
Then they later came down and intermixed with (not) everyone else, so you never know who is going to be less tired than "normal" when they work a 36-hour day.
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[ 3.9 ms ] story [ 83.9 ms ] threadReally? My instinctive reaction to this statement is that it's quackery. Would be very interested to see headlines appear about this if it's true.
So colour me skeptical of this claim as well.
And while I like going barefoot for other reasons, I don't think it makes much of a difference to the magnetic fields.
https://www.pbs.org/newshour/science/dogs-poop-in-alignment-...
but then again maybe not
https://www.sciencedirect.com/science/article/abs/pii/S15587...
From my tissue engineering class in undergrad my 2 cents is this is maybe 95% supplements quackery and 5% genuine mystery. You can find papers that claim EM fields have cellular interactions [1]. I don't think serious scientists will touch conventional earthing, though.
[0]: https://en.wikipedia.org/wiki/Energy_medicine#Earthing
[1]: https://pubmed.ncbi.nlm.nih.gov/38068954/
on the other side, do you know we have polarized and non-polarized cells? do you know they can be affected by electromagnetism?
this two things already establish the existence of a relationship and effects between them. If we then consider that cells mechanism work based on differential of electrical or chemical potentials, and that they continuously use that for their functions, reactions or environmental compensations well...
I just think they are related and we need to understand better.
https://news.ycombinator.com/item?id=49360307
even mechanical of course :)
I agree ideas shouldn't be dismissed out-of-hand.
> humans are weird outliers—we’re the shortest sleeping primates, yet we pack in the most REM sleep relative to this short duration
Isn't that sort of the point? Sleep is a detrimental necessity and the more efficient an organism is in needing less of it, the more effective it can be because it simply has more time to get ahead of the others?
It's still very odd that no species has ended up evolving a continuous maintenance system that can run while conscious, the benefits when hunting other animals that need sleep would be enormous, so there has to be significant evolutionary push for it. I suppose the single hemisphere sleep some marine mammals do is part of the way there, but it is at most a lazy workaround. Practically all other organs have evolved to run 24/7 for up to a century without a single break, what makes brains so universally different?
- will gains of 24/7 hunting/foraging offset the extra energy costs? Lions sleep 16-20 hours a day, according to the internet.
- do continuous maintenance systems imply duplicate systems? If so, I have a hunch that even a mere 40% increase in energy expenditure would quickly undo the gains in waking hours.
I disagree. Endurance hunters walk an animal down throughout a single day. Sleep isn't the bottleneck. Efficient bipedalism and sweat are enough.
This is actually quite a conundrum.
Animals as simple as flies have been observed sleeping (diminished brain activity while resting). It is highly conserved, so it must be incredibly important.
And why wouldn't they? This is (presumably) the only kind of sleep they know.
Even in your example, you propose an individual could know multiple kinds of after-sleep feelings.
Also, we humans can get used to a lot of things and just be okay with it. For an extreme example, look at domestic abuse victims...
Like, it seems obvious to me that sleep has a higher opportunity cost in humans than most other animals. So naturally there's more evolutionary pressure in humans to sleep more efficiently.
Is this actually true? Dunno! But it was really weird that it doesn't get brought up.
Instead of going to Tanzania you could’ve asked a sleep scientist. Sleep length has no known correlation to brain size and is known for drastic within family variation. What’s more sleep has a high within species variation too, some sleepers can survive 4 hours, others need 8. Collectively we used to sleep 9 hours in the 20th century, but it appears shorter sleep is fine too. TLDR: no one has any idea why sleep length varies and he won’t find his answers in antrophological studies in Tanzania, though luck, buddy
This feels like the key point to me. These societies follow their body and go to sleep when they are tried, while us in the west have to sleep at a specific time to fit our schedules.
I found this reassuring and slightly amazing, that he is wired to do his part as a nighttime lookout.
That doesn't mean they didn't sleep all night, typically.
https://www.sciencedirect.com/science/article/pii/S138994572...
This does seem to work great at group level. Considering we're in a competitive setup and all that.
I also recognize I personally benefit from others having this schedule. It would quickly go sideways if the firefighter felt like he wanted to sleep a bit more, or the police officer didn't really feel like it whenever is an emergency.
For example if they're able to have some firefighters napping at the station, whilst others keep watch for alerts, that would seem better than enforcing strict wakefulness for the whole squad so they are all tired if the call comes in at the end of a night shift?
Obviously there would have to be some communication and understanding about who stays awake and who takes a rest, but I could see it working.
So coming back, what would be your solution? Because you cannot simply ignore the global competition for resources and basically power. If you slack you get taken over. As in, slacking might work for a while, sure. But that will inevitably be seen somewhere, in some numbers, statistics, resources etc. Sooner or later. What do you do then? One just needs to look at some current wars footage to get a sense of how bad it can be. Also don't get me wrong, I'm all for world peace and all that. Very hard feat though, considering human nature.
This is a common, but poor framing of evolution. Remember: the only real rule with evolution is "did this evolutionary change mean they survived / reproduced more"? Evolution is not a local or global maxima solving function. I find this kind of attempt at interpreting selection common with engineers, programmers, etc.
You're just renaming the terms. More/less is a fitness gradient, and the thing that lives there is called an optimizer.
Evolution is a tunable-scale optimizer. It's not perfectly local, because it shotguns to avoid local optimums on a fitness landscape. If you tune the 'shot pattern' really wide (infinite copies with infinite variation), you'd genuinely get a one-shot global optimizer at the limit. But that's not efficient nor realistic, so typically it's somewhere in between.
Uh, compare maze solvers: you've got your greedy direct route (gets stuck in the first corner) , Dijkstra (finds all the answers but takes ages), and then stuff like A, which is a happy medium. Evolutionary algos can be used to solve mazes just the same. I think it's a bit heavier on resources than A, but well suited to embarrassingly parallel optimization.
while I understand might be a more known thing, it was surprising to try it and feel very rested after that. I'm still surprised and I wonder why not the whole world does it.
of course without the music at the stops would not be possible :P
I'm instantly skeptical of anyone making universal statements like this, because they're certainly not true for everyone, and having looked into these and similar (f/x "ideal room/office temperature"), are based on many entangled assumptions. Most of the time I expect it's just people making after-the-fact justification for doing (or imposing) what they most prefer.
I have no idea if that was actually done here but that’s usually how these statements are justified.
Of course we are all individuals so it may not apply to everyone but you can say that for everything in medicine. Only thing we can do is look for statistically significant differences between groups in double blind controlled studies after controlling for all other factors.
also do you know that the body temperature decreases during sleep? based on that I simply deduce and assume the more the difference between body and room temperature the more side effects arises for sleep, of course simplifying without ignoring all the rest.
As I imagine the curve, I use a real bathtub. Where is the water deepest? At the drain, which is typically just under the faucet. Where is the optimal place to sit? Well, pretty much anywhere except there, because "deepest" (an optimum) isn't enough to accurately gauge "best place". But even if you can swing the faucet out of the way... where is the optimal place? Anywhere on the bottom, a broad, slow curve, as opposed to the steep walls or rim.
So, if 18 degrees C is the optimum, what's the standard deviation? I bet it's not 0.1 degrees. Could be 2 degrees - and that would mean concentrating on 18 degrees is a distraction, not a goal.
This is something evolutionary discussions don't address well, either. If a gene line (species) has a pressure to change, it can "settle" for any place on the bathtub floor (when the solution is shaped like that). This is another example of evolution not seeking an optimum; merely avoiding a pessimum (a word I just googled, and like!).
In fact, it doesn't even matter if it's a bathtub curve. Maybe it's a slope, like the amount of capsaicin a pepper plant carries to fight off fungus. More better - but it costs something to make, so just make enough to ensure survival. More fungus? Increase capsaicin production. There's no floor to this bathtub; it's a linear slant all the way down to maximum possible capsaicin content (which, amazingly, is about 10% by weight of the fruit cells!!!).
Best sleep from my experience? It's usually about 5C at the thermostat, which is farthest from the window, by the time I wake up. The cold air coming in will be 0C and colder and I sleep next to the window. Winter is my happy sleep time.
And there are huge swaths of the world where the temperature basically never gets that low (18 C is the lowest temperature ever recorded in Kingston, Jamaica; 16 along the coast of west Africa, 18.9 in Jakarta). Even here in the southeastern US it is normal for temperatures to stay above 20 C at all times for three full months of the year (late June through early September).
Nothing wrong with liking to sleep in cold air, but it’s a preference.
I can be, actually want to be toasty warm under the blanket. But I want the air I am breathing to be fresh and cold. That is when I feel comfortable and "at peace".
I will often stick out my feet from under the blanket because it's way too toasty but the rest of my body needs to be warm.
Sure, when it's 25C I'll essentially just lay there without anything but a sheet across the chest to "feel safe" but anything else will just make me way too warm and the air I'm breathing will feel restricting.
What is really great in 25C+ temps is to be outside in a hammock without an underquilt, which cools things down considerably. But I've also slept comfortably at 0F (-18C) in a hammock. With two underquilts and a 0C sleeping bag as well as a winter tarp with doors and snow cover all around, weighing down the tarp sides (wind does suck at that temp ;)).
My wife wants it to be 20 C or lower and sleep under two blankets. I pointed out that 23 with a fan and a sheet is less energy-intensive and gives equivalent results, and she said stuff it. Not a battle worth fighting at home, but on the internet…
(Of note, the one of our dogs that loves me but worships her still sleeps next me every night, under covers, because she’s a Chihuahua and gets cold easily, and unlike my wife I sleep like a dead log.)
For you, and that's kind of my point. For me, my preferred temperature would be about 28C with no blanket or a light sheet. Something like 18C can be tolerable with blankets for me, but it's certainly not "maximum comfort", even with blankets. There is too much variation and too many things that wouldn't be controlled for, like number/thickness of coverings, and other such things. Having some "best" universal temperature is just not something generalizable like this.
Then its good night, Irene
This could explain why I feel more rested when I wake up if I take glycine before going to bed, even though I don't sleep more.
Nothing surprising here. We sleep in cozy comfortable beds in a locked and secure location. Of course we'd can get int REM sleep. Compare to other primates who sleep outside with the critters and predators, deep sleep could mean the end of them.
1: https://www.healthline.com/health/how-much-deep-sleep-do-you... 2: https://www.health.harvard.edu/healthy-aging-and-longevity/r... 3: https://www.sleepfoundation.org/stages-of-sleep/rem-sleep
Where the sun doesn't go down every single day anyhow, and you may need to trudge across the tundra routinely for more than 24 hours at a stretch to get almost anywhere, without ever worrying about it at all.
Then they later came down and intermixed with (not) everyone else, so you never know who is going to be less tired than "normal" when they work a 36-hour day.