Hydras suggest that sleep evolved before brains | Hacker News Reader

Hydras suggest that sleep evolved before brains

quantamagazine.org

298 pointstheafh135 comments

The article describes how sleep has been found in simpler and simpler animals. But I wonder if you could go further: do plants sleep? It seems like an absurd idea, but on the other hand there was an article a few months ago, "Anesthesia works on plants too, and we don’t know why".

https://news.ycombinator.com/item?id=25591443

I don't know if you could call it "sleep" per se, but there are certainly plenty of plants that need a daily period of darkness to grow properly. This comes up when growing indoor plants when people say you shouldn't run a grow light 24/7.

Plants increase their respiration at night and stop photosynthesizing.

https://www.bbc.co.uk/bitesize/guides/zxtcwmn/revision/1

It seems kind of like sleeping to me.

Although without sunlight, they have no choice but to stop photosynthesizing.

Then we have plants like the dracaena fragans, whose flowers remain closed at day, but open and release their delicious fragrance all night. I'm not sure how sleep would work for her.

https://en.wikipedia.org/wiki/Dracaena_fragrans

Daytime sleeping is not unheard of.

Nitpicking: "stop photosynthesizing" is just a direct consequence of the lack of ambient light. People stop getting sunburn at night, that's not part of "sleeping".

Other than that: +1.

Well, you raise a non-trivial point that is more than just a semantic issue, viz what do we mean by "sleep"?

Plants physiology changes significantly during the night, so it's not just "no more photosyntheses without Sun"... respiration rates at night are strongly correlated with the amount of stored carbon and sucrose in the leaf tissue, which is probably related to the fact that plants also grow faster at night.

Maybe not.

Plants have two sources of nutrition: uptake via their roots and photosynthesis. My general understanding is that photosynthesis is what provides them energy whereas uptake via roots provides water and some essential nutrients they can't synthesize.

The details will vary and some plants, for example, grow in total darkness or feed parasitically on other plants. But I think photosynthesis is roughly the equivalent of humans eating carbs for energy.

So it's a little like saying "One defining characteristic of sleep is that animals stop eating." And, in fact, hibernation through the winter when food is in very limited supply is a known mechanism of survival for some species in harsh climates: They sleep instead of eating.

In fact, my understanding is that to some degree eating and sleeping are substitutable. If you can't sleep, you can eat to help keep yourself functional while awake on a long shift.

I think they do this on episodes of Deadliest Catch: feed people more when they are pulling a long shift and going to be awake for 24 hours straight.

I mean, that's like 99.9999....% expected, since they all evolved with a big light signal in the sky that operates on a 24 hr cycle. Plants, even more than animals, should be optimized to function that way (do mostly resource production at day, do mostly maintenance at night).

One difference at night is that it is cooler, so less water may be lost when the stomata are opened for gas exchange. Many plants (separately) evolved a photosynthesis cycle where gases need only be exchanged at night and the stomata may be closed during the day.[1] While the actual photosynthesis reaction happens during the day, the nighttime preparation is needed, and should perhaps be counted towards the effort.

https://en.m.wikipedia.org/wiki/Crassulacean_acid_metabolism

According to this plants can tell time.

https://youtu.be/CA-YsWXRSHU?t=453

Plants also have nyctinasty which isn't sleep but is interesting: https://www.livescience.com/34569-why-flowers-close-at-night...

The book Why We Sleep mentioned an experiment. Some plants obviously change during day or night, extending leaves during the day and letting them droop at night, something like that from what I remember. People thought the plant was just reacting to the sunlight, until they put the plant in total darkness for several days and observed it going through the same cycles. The plant was not only responding to light, but also to an internal timer. Depending on how you define sleep, this is sleep. Granted plants don't use sleep for all the same purposes as animals.

If you find that article, I'd love to see it. I know a bit about plant hormones, but most of what I remember is some of the growth hormones degrade in sunlight, which can cause the apparent growth toward the sun. So if you have a stem and the light is coming from the right, the cells on the right side don't divide or elongate as quickly as the cells on the left side in the shade, which causes the stem to bend to the right. This is also the cause of etiolation, or legginess, in plants that aren't getting enough sun. Those cells have plenty of the hormone as it's not being degraded by the sunlight, causing them to elongate more quickly than a plant getting adequate light.

"In 1729, French scientist Jean-Jacques d'Ortous de Mairan conducted the first experiment designed to distinguish an endogenous clock from responses to daily stimuli. He noted that 24-hour patterns in the movement of the leaves of the plant Mimosa pudica persisted even when the plants were kept in constant darkness."

https://en.wikipedia.org/wiki/Circadian_rhythm#History second paragraph

Awesome! Thanks!

There was a paper, I think it was also linked on HN via quanta magazine, where some researchers seemed to have pinpointed the reason why sleep is necessary to live, at least for animals and insects.

However, it seemed too good to be true (I can only wait to see if there is a Nobel prize) and it's not clear to me what to make of it.

The gist of it was that the fundamental damage from lack of sleep actually originates in the gut, not the brain, across rather different species, (mice and fruit flies) where "reactive oxygen species" (iirc) cause cumulative damage that is eventually fatal.

The researchers claimed they had confirmed causality by reversing the shortened lifespan in fruit flies deprived of sleep by feeding them antioxidants.

I have never seen a paper that seemed to so thoroughly eliminate the possibility of a misleading correlation, but the sticking point for me is, if it is so simple to avoid the need for sleep, why hasn't it been eliminated by evolution in the first place?

(Sleep Loss Can Cause Death through Accumulation of Reactive Oxygen Species in the Gut Vaccaro, Alexandra et al. Cell, Volume 181, Issue 6, 1307)

Anesthesia works on humans too, and we still don’t know why.

The evolution of sleep may or may not predate the evolution of brains. It might have evolved twice, once in predecessors of hydras and once in predecessors of beings with brains.

agreed, divergent evolution is very common

The upthread suggestion is actually of convergent, not divergent, evolution.

thats funny because I googled it before I wrote it and still wrote the wrong one

It's amazing how bad our brains can be, even after a few million years of evolution. They're capable of flying a helicopter on Mars and cranking out a vaccine within months, as well as developing vast machines containing zettabytes of information -- and still can't retain a word for 15 seconds.

All the amazing capabilities you mention are the result of cooperation between dozens, hundreds or even thousands of humans. Without doubt, individual people made millions of errors in the process, and each time some other contributor caught it.

Single brains can only do that much, great things are the product of cooperation between humans.

Hydras, like c. elegans, cockroaches, fruit flies, humans, sponges and all the other animals named in TFA are eukaryotes.

What about prokaryotes? Do they sleep?

Here is something on cyanobacteria showing sleep-like behaviour during which they do not divide.

https://phys.org/news/2010-03-cell-division-cyanobacteria-ki...

I mean, they're all animals. Prokaryotes are far less related to animals than e.g. fungi or plants would be.

You would know that eukaryotes evolved from prokaryotes.

So, the interesting point of the question is whether sleep is something that occurs at the cellular level or the organism level.

See the article linked to in the comment above, about cyanobacteria.

> Cyanobacteria maintain their circadian rhythms even when isolated from the naturally occurring daily light-dark cycles of the sun, just as humans do. The researchers found that under conditions of moderate constant light, the cyanobacteria undergo cell division about once per day, and the divisions take place mostly at the midpoint of the 24-hour cycle.

Sleep occurs at both the cellular and organism level. Sleep is probably like getting a car serviced and cleaned. Sleep isn't just blowing up the tires, or changing the oil or cleaning the screen, it's all of it.

Can you please be specific when you say sleep occurs at cellular level. Definitely bodily systems (circulatory, respiratory etc.) don't go to sleep, even when we are sleeping.

Strictly speaking insects are not animals AFAIK

Insects are animals:

https://en.wikipedia.org/wiki/Grasshopper

Infobox on the right-> Kingdom: Animalia, Phylum: Arthropoda, Class: Insecta.

There are even microscopic single-celled animals, such as Amoeba:

https://en.m.wikipedia.org/wiki/Amoebozoa

Currently that Wikipedia page has an inexplicable (hillarious?) image of a bush turkey on it, can't really see the connection.. but didn't try to find out how it got there either.

Amoeba are not animals. Animals (metazoa) are multicellular organisms.

Yep you're totally right! Apologies.. I had always thought the 'zoa' on the end meant they were animal. TIL about metazoa! thanks!

Thank you for the correction. My impression rose from the fact that insect experiments need no ethical approval, whereas experiments with vertebrates do.

That probably tells us more about humans than it does about insects.

I feel like this article touches a lot more on the definition of what sleep is, rather than what people commonly refer to as sleep. I mean, what really defines sleep? I would've thought it is the temporary absence of consciousness in an otherwise conscious being. Or something along those lines. Of course that wouldn't make a lot of sense with medical comas and such.

So maybe sleep is just a, perhaps regular, phase in which an organism is 'inactive', that is, doesn't perform a lot of actions or waste energy. Energy is limited after all. From an evolutionary perspective, it might make sense to have an organism not be dependent on a permanently available power source. It'd be better to alternate between using a lot of energy and using less energy, because permanent sources of energy are rare or even non-existing. Depending on such a permanent source would starve the organism to death and hence it wouldn't evolve. So you get those intervals and they'll naturally evolve to synchronize to the phases of their energy source. And that's supposedly the sleep cycle?

I wouldn't be surprised if sleep is an aspect of a nervous system in general. Last year an article came out about how even artificial neural networks benefited from sleep. Perhaps it's the nature of the beast.

https://news.ycombinator.com/item?id=24018131

Man, working from home has the advantage of a power nap, or a "coffee power nap", which basically makes you feel like it's the second morning of the day.

https://www.vox.com/2014/8/28/6074177/coffee-naps-caffeine-s...

Coffee, by itself, doesn't affect me much. Could this be the secret to making it work?

Most of the effect is because it's addictive. This does work, but of course it's better to get enough sleep at night.

This gives additional evidence to my personal hypothesis that the normal state of living beings is sleeping. The awake state only appeared as a survival strategy, to better adapt to the natural environment.

What do you mean by "the normal state of living beings"?

Surely you understand that most people consider being awake to be our default state and sleeping is just something that we need to do sometimes

The way you phrased is reminded me how blindly we walk through life, doing things that our body forces us to do, because despite all our bravado about how smart we are... we really have no clue what we do and why we do it most of the time.

It means that being aware of surroundings with continual sensory input and influence is the aberration.

This matches some other theories as well, where humans and a few other always awake organisms are the extreme, due to selective pressures. For example, humans "feel bored" because having nothing pressing to do for survival is usually the wrong option. Whereas that isn't true for many other organisms and they likely wouldn't have an opinion about staying still in the same place for prolonged periods of time.

This is basically what Matthew Walker (https://en.wikipedia.org/wiki/Matthew_Walker_(scientist)) sort of alludes to in his book, "Why we sleep". It's a good book. He specifically mentions hydras as well (iirc)... he's a neuroscientist who is a crazy maniac about sleep and he cites newest research and delivers a very clear message of urgency.

Lots of fascinating stuff there, highly recommend if you're interested.

What is his clear message of urgency?

In my view (of his view) - that in many cultures we see today, we've come to vastly underestimate the importance of sleep. For example, we've removed afternoon naps from workday routine (with field evidence showing effects on health such as heart disease (against comparative groups who haven't stopped taking naps - but not lab-controlled I think) etc.) We sleep less.[2]

We shouldn't be asking what's the purpose of this pesky thing called sleep (which evolution turns to always incorporate into animal life, however inconvenient it is[1]; to route around the inconveniences as it were, rather than the other way around). We should rather be asking, is there a single function which isn't improved by sleep (Walker thinks no). End of preach rant :)

[1]: e.g.: some birds appear to sleep in patterns such as when there's a row of birds sleeping, the two birds at each end sleep with one hemisphere each - but opposite ones - so that the field of vision is maximised. At midpoint in time however they swap places. The rest of the birds sleep with both hemispheres. That sounds pretty cool.

[2]: though apparently there's criticism directed at Walker re: this, and re: him not mentioning that mortality appears to increase beyond the 7 hour mark (but I'm just learning this, so basically, just a fair warning not to take all of this at face value, there's nuance).

Ah, I align with him then.

Regarding mortality and the 7 hour mark, this is such unfortunate bullshit, that keeps being propagated by people who should know better. Ill people sleep more (even if you catch a cold, once you get past the peak, you sleep more for a few days) because their body requires more recovery.

In chronically ill people this continues for a long time and the body never is able to catch up to the problem it's trying to solve.

But despite all the "correlation not causation" mantras repeated by everyone, we keep citing this as if we decide to sleep a bit more that'll make it more likely to die, which is nonsense.

Ah okay, so basically you're saying that the mortality vs > 7 hour sleep time correlation claim hasn't normalized / accounted for other parent causes (e.g. chronic illness and other things affecting / disturbing sleep quality)? I'm a noob here, but if that is the case, that is very unfortunate and frustrating.

I've not seen a single study to demonstrate causative link, or conclusively eliminate other variables (which is frankly quite impossible anyway).

Unfortunately a lie repeated a thousand times (by media) becomes truth. And it's just too juicy of a news to say "sleeping too much bad for health". Especially managers, they love that kind of news ;-)

BTW my frustration is pointed at general media and society, not you in particular, I wasn't clear.

Regarding naps. Pretty much every sleep expert I heard or talked to is against naps during the day. Mostly because it disturbs night sleep.

In toddlers and in very elderly, the sleep-wake cycle can no longer be full 24 hours due to decreased/lower abilities of your body to “buffer” for that amount of time. So a single well defined afternoon sleep can be good.

I wouldn’t call that “naps”. That’s not what it is.

Important to note there has been pushback on Matthew Walker's writing. Feel free to read more from Alexey Guzey [1] or Andrew Gelman [2].

[1]https://guzey.com/books/why-we-sleep/ [2]https://statmodeling.stat.columbia.edu/2020/03/24/why-we-sle...

Hey, thanks, I'll check it out! Haven't gotten around to reading critique of Walker, but I should. Thank you

P.S. are you familiar with Walker's response as well? https://sleepdiplomat.wordpress.com/2019/12/19/why-we-sleep-... I'll familiarize myself later, and thank you again

Depends what you focus on as your definition of "living beings". If you look at our cells, they behave more naturally while we sleep. While we sleep, they're "awake". So yes, that's their natural state.

But the "multicellular organism" mode they switch while we're awake is necessary for them to be more than a pile of cells. Which indeed is very important for our survival, as complex behaviors that only multicellular organisms have, are crucial to our ability to adapt.

> the normal state of living beings is sleeping

This is reminiscent of the claim that zebras are black with white stripes (or is it the other way around?)

A fascinating idea.

For your hypothesis to work, and I think this is what you mean by the article supporting it, sleep would have had to evolve very early. Because being awake activates a great deal of a modern organism’s complexity, and that complexity wouldn’t have evolved in an always-sleeping organism that doesn’t benefit from it. So either the predecessors were awake, or sleep came before all the complexity that is now activated only when awake.

For the first wakers, then, being awake was little more than a period of increased activity. A boost mode. And indeed we’ve already seen the utility of boost modes across a variety of technology, from CPUs to cars to high output flashlights.

But does that make the predecessors really asleep? To use a very HN analogy, were pre-boost CPUs always idling?

It doesn't seem like too far of a stretch to guess that the earliest life forms would have been pretty passive, absorbing nutrients directly from their "primordial soup" and somehow replicating whenever they've stored up enough. I imagine "life" would have gone on for quite some time before "waking up" and evolving the ability respond to their environment by doing things like relocating to a more nutrient rich area or away from danger.

> But does that make the predecessors really asleep?

Well, not directly, but we can certainly talk about the appearance a distinct state, which would now be called awake state in comparison to previous organisms that had a single state. After this appearance it makes sense to talk about previous life forms as "sleeping".

> The awake state only appeared as a survival strategy, to better adapt to the natural environment.

Well. Given that "awake" creatures react to stimuli, that might not be too far off the truth. If we could passively survive and not have to forage or hunt for food, what's the point of 'waking up'?

Sleeping is advantageous (less energy use). Efficiency is usually selected for, unless there's some other kind of environmental pressure.

Maybe that's why we haven't found other civilizations. They are all 'sleeping'. Maybe consciousness is also unnecessary (on that front, I love https://rifters.com/real/Blindsight.htm)

While Peter Watts' writing feels like he enjoys being intentionally abstruse, his books are very thought provoking. I still get reminded about the concepts in Blindsight from time to time, years after I read it.

Only awake beings can reproduce.

That we know of, yes.

In the earth animal kingdom, yes.

But what if there was some king of being that "shed" their spawn in a totally passive manner, perhaps using all that surplus energy from not needing to be awake most of the time?

"Normal" is arbitrary, but since most animals need to be awake to reproduce it's hard to envision enough of them always sleeping for it to be the default.

By the time complex animals evolved, the awake state would already be the norm for survival. So, I guess everything we now assign to complex animals is already dependent on the appearance of an awake state.

This is the most weird and interesting hypothesis I've heard in a LONG time !

coliveira, you have obviously given this some thought. Any further nuances?

I'm not a biologist, so I consider this just my pet theory. But the idea is that one key element of evolution was the appearance of an alert state, which we now call wakefulness. The normal for all organisms was what we now call sleep. Organisms that developed this awake state were obviously able to better adapt to the environment.

Like in many other cases, we can take clues from embryonic development. We know for example that fetuses spend at least 95% of their time sleeping. So we know from pretty early stage that sleeping seems to be the norm. Sleeping is also the most efficient, energy-wise, state for an organism. Even nowadays certain animals are able to hibernate for months. Humans can do this too in extreme situations, it is called comma.

So, when we go to sleep we're not just "recharging". We're going to our normal state, and while it is possible to stay that way for long periods, I never heard of anyone staying awake for more than a few days.

This is evidence in favor of the hypothesis that consciousness happens in microtubules. https://en.wikipedia.org/wiki/Orchestrated_objective_reducti...

Sleep might have helped to maintain the first sleeper’s rudimentary nervous system, but it could just as easily have been for the benefits of its metabolism or digestion. “Before we had a brain, we had a gut,” he said.

I will note that the nervous system of the human gut is so complex that some people speak of it as "a second brain" and there is growing evidence that the gut biome and what we eat significantly impact brain chemistry.

If jellyfish sleep, that suggests sleep may have evolved more than 1 billion years ago

This is sort of off topic.

When me and my adult sons were first homeless, we spent a month in Port Aransas. While we were there, there was a big storm and this storm left a lot of jellyfish stranded on the beach.

My oldest son set out to rescue some of them. He would take a plastic container and plastic utensils and flip them into the container so they couldn't sting him. He would get five or six of them into the container and in his first attempt, he just walked out into the water and dropped them in the water and then he had to get the hell out of the way so they wouldn't wash into his legs and sting his legs.

So he began walking out onto the jetty so he could drop them into the water while standing on a rock. That way he was in no danger of being stung because he wasn't standing in the water he was dropping them into. The other reason he began going out onto the jetty is because they were getting washed back up onto the beach. He felt it wasn't working at all.

And he told me that the jellyfish stranded on the beach all closed themselves up as best they could, as if trying to conserve water while on dry land in hopes of surviving long enough to wash back out to sea.

He reads really fast and has always been interested in science. He knows more about science than I ever will and he told me he had never read anything like that about jellyfish behavior.

Once he dumped them in the water, they "uncurled" and began to pump immediately. So perhaps they were sort of "asleep" or hibernating while on land and once they were in water and safe from this harsh environment that was threatening to be the death of them, they would revive and resume pumping.

He went on a bit about that. He thought it was really exciting and interesting stuff.

I think he saved a few dozen jellyfish over the course of about three days.

Edited for accuracy after fact checking with my son.

In talking with him, he said that at first he thought it was coincidence that they were kind of closed up. But after seeing them all immediately open up and start pumping, he decided "No, I think this is deliberate."

Additional update:

He quit trying to rescue ones that were flat and a different color because he concluded they were dead. Those didn't pump when they went back in the water. The ones that were curled up were still alive.

(Read by my son, edited in accordance with his wishes and signed off by him as an acceptable telling of the story. There should be no further edits after this.)

Thank you for sharing this story. Really interesting. If this isn’t part of the literature, hopefully some jellyfish experts will take note!

I hope so. I did my best to make it as accurate as possible because I don't think it is part of the literature, so I want it to be as useful as possible as a scientific note in case someone does want to pursue this further.

My son told me today that it was a big deal to him precisely because the seemingly intentional nature of the behavior ran completely counter to everything he had read about jellyfish. So all of his reading had "anti prepared" him for what he was seeing. (That's in quotations because that's the actual expression he used today in conversation with me.)

Sleep is a whole-body process of repair and optimization. Many cultures chastise sleepers as lazy, but every time you sleep, it's like a big reconstruction process in your body.

I think that sleep and allowing adequate time for it is the lowest hanging fruit for most people's health. Us site readers usually get enough to eat, and sometimes more, yet when was the last time you allowed yourself to sleep as much as you want to, without limit?

> when was the last time you allowed yourself to sleep as much as you want to, without limit?

I was told premature optimization was the root of all evil.

> Many cultures chastise sleepers as lazy, but every time you sleep, it's like a big reconstruction process in your body.

The morning alarm is society telling you "stop reconstructing yourself, start working on our problems."

Not using an alarm clock 90% of the time is one of the greatest privileges I experience in life. One which I wish more people were fortunate to share.

As a parent of a young child, I'd welcome the routine tyranny of an alarm clock

Oh man. You aren’t kidding.

Eventually the human alarm clocks do grow up.

Part of the problem is that children occupy a lot of your time. After you get them in bed, it's tempting to stay up later than one usually would in order to have some personal time. This doesn't change the time that the human alarm clocks go off, though, and it can quickly spiral out of control.

It gets better. When they are older you can include them into your passion projects, or whatever sort of hobbies you have. This part is great because you are both teaching them and having fun at the same time.

I say this all the time because it showcases how little time you have with them, but you only have about 1,000 weekends with them until they are adults. It all happens so fast. I enjoy the time that I spent with them, especially over the last year when we were all together as a family for so many months. I, myself, am nearing the end of those 1,000 weekends with my oldest and I miss some of those human alarm clock days when they were up early and just wanted to play together.

On a similar note:

"It turns out that when I graduated from high school, I had already used up 93% of my in-person parent time."

https://waitbutwhy.com/2015/12/the-tail-end.html

Even if you just have a pet, many of them are very excited for you to get up in the morning and feed them. And worse, they don't even understand DST!

A lot of us get a taste of this on weekends or days off, but what have you personally noticed the difference to be? Maybe in terms of productivity, fatigue, mood, health, etc.

I went from waking up at 6AM every day for 6 years (US mil) to not setting an alarm in the last 6 (remote employee). The main thing I notice in the rare event where I have to set an alarm these days is this 15-30 minutes of heavy brain fog after waking up. In my experience it feels very similar to the sensation in your head shortly after you've taken a dose of melatonin, which I guess makes sense. It's hard to put into words but obviously we've all experienced it. I don't ever experience this sensation waking up naturally.

The end result is early morning grumpiness, in my case. I'm just in a foul mood for the first hour or two after being ripped from sleep via an alarm. I otherwise don't feel more productive or healthy.

I'm curious why this is; I assume it has to do with the natural sleep cycle. Do those chemicals metabolize in some way shortly before you wake up naturally vs waking up by an alarm where they're still present?

I find it to be almost universally positive. I'm a freelancer and I work practically "full time" but I don't start work until I naturally wake up unless I happen to have a meeting scheduled.

One of first things I noticed is hunger. When I wake up to an alarm I generally feel sluggish and immediately hungry. If I wake up to my alarm at 8 then I need to eat almost immediately. If I naturally wake up at 9 I might potter about and eat breakfast at 10 without thinking much about it. Alarms seem to induce stress and stress induces hunger.

I generally find that only having weekends alarm free provides just enough respite and replenishment for taking on the work week but not enough to reduce mental stress across the board. Being able to have a lay in on any given day that requires it makes a world of difference to mid week slumps.

Do you find your sleep skews? Any longer (2-3 week) vacations I've taken I've found that my waking up time keeps skewing even if I'm not going to bed later. Maybe I've never seen the end where it stabilizes.

My wake up time is a 2 hour window between 7:30 and 9:30 but usually around the middle of that. It varies day to day. Whether it's earlier or later mostly depends on how much exercise I do the day before. My training has large spikes where I go out rock climbing all day and then have multiple "rest" days so I let my body get whatever sleep it needs.

My waking times definitely skew, but for me I think it happens because my bed time pushes it later and later until my night owl habits and my guilt over sleeping late reach an equilibrium.

When I was in college I'd pretty quickly drift to a 4:00AM to noon sleep schedule on holidays. Even today (in my mid 20's) I find I'm happiest sleeping from roughly 2:00AM to 10:00AM.

At the beginning of the pandemic, no one in our family had any fixed time obligations other than my afternoon meetings, so we basically stopped enforcing any bedtimes or wake up times for the kids (and ourselves).

Pre-pandemic we were all waking around 8am to get my daughter to pre-school. Within a week of foregoing bedtimes, we were all going to bed between 2am and 4am and waking up around 11am. So the kids still got their 9 hours and the adults got their 7, but it did stabilize.

(Not the parent)

My sleep cycle naturally drifts infinitely by some 30 minutes a day on average.

It makes life strange at times, especially on this latitude. Imagine waking up at night through a whole winter, not seeing the Sun for months.

I've tried to hold steady cycle but I just grow more and more tired every day until finally the alarm fails to wake me. School was hell. Was absent a lot simply for sleeping.

I was exactly the same, a lot of reading about sleep and strict sleep hygiene fixed it. There are lots you can do but briefly just go out for a jog when you wake up. You need the exposure to blue light to help set your circadian rhythm. The exercise increases body temp which helps bring forward your circadian rhythm. Basically your habits are probably shifting your circadian rhythm back 30min a day, and if not you can have habits which bring forward your circadian rythm

There are so many variables involved, once you start listening, the schedule will never be a schedule again.

Sometimes I want to sleep a few extra hours. Sometimes I'm so excited for the day, I get up early and go to sleep late. Sometimes I need to stay up for a while, and next time I sleep it's for 20 hours straight. Sometimes it's just a nap here and there for a few days.

The most important thing I've learned is to listen to my tiredness level, and not get too carried away with productivity.

Isn't it the case that physical height growth occurs during sleep? That's more evidence that sleep is a whole body process.

That part in particular is as simple as... you get higher because you're laying down, so there's no vertical pressure on your back.

Not the nightly half-inch, but like your growth from 18" to 6' over the course of your life happens while you sleep.

How would you measure 8 hours of that?

I think the basic answer to that is: by measuring height before and after, controlling for laying down still but not sleeping, perhaps also with some intermediate measurements.

If most of human height growth occurs in the first 20 years of life, that's about 200 microns per 24 hours. Can you measure that accurately? What sort of fluctuating errors would be introduced by for example, temperature and hydration?

That may be the average, but it happens in spurts, and you can probably get some decent measurements if you put your mind to it.

Ah yeah, growth occurs mostly during sleep. Vast majority of it. Growth hormone is actually released mostly during sleep.

When a cell has to function as part of a higher-level system, "dividing" is kind of disruptive. So this happens while we sleep.

Sleep is basic resource management: it takes too much resources to both run all macro systems, and also all microsystems (on cellular level). So they take turns and interleave through the sleep/wake cycle. As you say, microsystems take over during sleep.

From a cell's perspective, they sleep while "we" are awake.

This means sleep is advantageous to all multicellular organisms, unless there's great pressure for them to evolve hybrid alternatives (such as sleeping dolphins or migrating birds).

It's a bit discouraging that in the mainstream we keep asking "but why sleep tho" or even worse, we keep propagating the wrong answers, when the principles lay before our eyes.

It's not just resource management. In humans, during sleep there is a cleanup program that gets rid of waste in your brain. My pet theory is that this is because running cleanup during the day would impair the function of the tissue too much, so it's ran during the sleep phase.

Yes. Basically we're 2-in-1, we have two modes (macro and micro, or from macro perspective: operation and maintenance), and they're largely incompatible together for many reasons, but both are needed in order for the organism to exist within parameters.

This pattern emerges in complex artificial systems as well. "Stop the world" garbage collection in some programming languages.

Or the fact most stores prefer to not be open 24/7 not simply to save on salaries and power bills, but also to restock, reorganize shelves etc.

The workweek/weeekend cycle is another trivial example. And so on.

It's a bit like an OS that distributes time-slices of a single CPU core between a set of "background services" and "the main application".

Your reduction is, I think, too simplistic. Some bacteria appear to also have some basic passive/active cycle, for example. It's really fascinating and there's tons of functions interleaved.

edit it's not just multi/unicellular modes - REM is very close to awake state, cell activity wise (looking from PoV of brain waves emerging), with source of sensory input being switched to internal; and in deep sleep NREM, large parts of the brain (depends on the animal, hemispheres take turns in some) are in a sort of slow-mo sine wave "sync" (kinda amazing!) Etc. etc.

My reduction strives to drive home the core of an idea that extends both at higher levels (i.e. we have passive/active cycles as a society as well, the most simple example being workweek/weekend), and lower levels, like your bacteria example.

And yes, it's not about "one cell" vs. "all the cells", more generally it's about "higher-level systems" vs. "lower-level systems" where also some functionality serendipitously adapts/fits/evolves into one of those modes without specific regard about where it semantically sits in this hierarchy of complexity.

Regarding REM sleep, I think our methodology and terminology is a bit too crude, electrical "activity" means very little about the state of the brain. For ex. you have no access to most of your memories while in REM sleep, you can't even determine you're sleeping most of the time, and when you do, you usually forget in a minute or two, your cognitive function is that low.

Honestly the way you described REM sleep, it started sounding a bit like unit testing (inputs/outputs come from the repository, not from the user, and this process goes through the entire brain in order). :-) Which... actually might not be far from truth (in some aspects of it).

> where also some functionality serendipitously adapts/fits/evolves into one of those modes without specific regard about where it semantically sits in this hierarchy of complexity.

That did make sense, I oversimplified your reduction on first pass :D yea, I agree, nice generalization. And I like this idea re: it not caring where it sits. edit how to even place it on a linear complexity scale anyway...

> it started sounding a bit like unit testing

In the book I mentioned elsewhere in the thread (Why we sleep), there are some interesting theories related to this... sifting through memories, colliding them together, decisions being made on what to keep, and so on. I sometimes wonder if REM sleep as we experience it is, in part, the phenomenological perception of a kind of encoding and compression process, looking from the inside, as it were. Well, in a way I didn't say much I guess, because you can model so many things as a type of compression :D but anyway. Yea, cool stuff...

I slept for 10 hours last night and felt great today. It really is a great way to stay healthy (or regain health). I burned the candle a bit much last year building a side project and now I decided not to launch it because it really messed me up health wise and I can’t commit to day job, family AND side project without it making me ill.

> Sleep is a whole-body process of repair and optimization.

This is what I felt when I watched the Netflix documentary "My Octopus Teacher".

At some point, the octopus was vigorously attacked by a shark, which cost her a tentacle. She was bleeding and retreated to her den.

The attack made her very weak. She could no more change colors, nor get out of the den, even to get food.

After a week or so in the den, presumably sleeping, she started recovering and her arm started to regenerate.

My question is whether ctenophores sleep. These are the critters we used to call "comb jellies", and thought they were related to jellyfish. But it appears, according to some biologists, that they invented nerves independently of the other animals; they use different molecules for the job, controlled by different genes.

For an eye-opening introduction to ctenophores, look up some youtube sequences of Beroe eating other ctenophores.

https://www.youtube.com/watch?v=1xkNPp6mzzI , e.g., at 37s in, or https://www.youtube.com/watch?v=eDS_NMrPPKc at 2:50.

I don't know if anybody has studied ctenophore sleep. You could be the first!

I always thought sleep didn't make sense evolutionarily speaking - I mean wouldn't carnivores be selected for learning how to function with no sleep, to prey on the sleeping herbivores? I mean I would assume carnivores because herbivores have to spend a long time eating - but a carnivore just needs one lucky break, and the likelihood skyrockets with a diminishing sleep schedule.

Well, clearly there are negative aspects to getting less sleep, so there is no (or insufficient compared to the benefits) evolutionary pressure in that direction.

Your are describing nocturnal animals.

Shout out to the beautiful design of this web. The loop video of the hydra at the beginning is meaningful and super informative!

I came here to say this as well. The video is so crisp and detailed that it is mesmerising. And being able to view it from the comfort of my iPad screen? Wow. Technology really is amazing. It’s funny (and maybe sad) that it took something as small as a quality video loop for me to really appreciate all of the things involved in the process of me being able to view that video.

Interesting that sleep has functionality for resting the body as well as then brain. Off topic, sorry, but: hydras and rotifers were my favorite pond creatures to look at under my microscope when I was a little kid. Hydras were much more difficult to find.

This is not surprising, for consciousness to awaken, it has to be asleep first !

> She distilled a set of behavioral criteria to identify sleep without the EEG. A sleeping animal does not move around. It is harder to rouse than one that’s simply resting. It may take on a different pose than when awake, or it may seek out a specific location for sleep. Once awakened it behaves normally rather than sluggishly. ... A sleeping animal that has been disturbed will later sleep longer or more deeply than usual, a phenomenon called sleep homeostasis.

When you define "sleep" this way, without reference to the brain or consciousness, it's not all that surprising that animals without brains can "sleep".

If you take out the criteria having to do with locomotion, so as not to exclude organisms that don't need it, plants probably sleep too...

Really? Certainly it's not surprising that animals without brains might go without movement for periods of time, but why would you expect them a priori to have a state that meets all these criteria?

Everyone is wondering how sleep serves life. Maybe it's the other way around: the purpose of being awake is to find nutrients and a safe place to enable sleeping.

I mean, that's a fun and trippy idea. But we're vessels for propagating genes. Can't do that while you're sleeping, so one would have to construct an exceedingly strange model of the universe to make sleeping central to our existence.

Given that the default state of being is "not awake" it's reasonable to suppose that sleep evolved first, and then wakefulness.

They do not seem to have considered convergent evolution, like the article about trees that was on the front page a few days ago.

The simplest universe is a repeating binary sequence. Night and day. The simplest intelligence learns to predict this pattern and switches on/off to maximize its energy input and minimize its energy output. So, a sleeping brain is probably the simplest brain there is.

Every complex mechanism requires some form of downtime for maintenance

I mean, do you want to live in a world where no one ever sleeps?

I would rather say all forms of combustion produces pollutant that needs to be dealt with.

proof -> evidence

Evolution has reinvented many things in different ways.

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