You Don't Exist For One Third Of Your Life

14:15Hannah Fry:So there are I mean, before ethics committees got involved and sleep deprivation now, by the way, does count as torture. The UN has, since what happened after 9-11, has changed its ruling on that and says that the deliberate destruction of sleep architecture is torture, full stop. Back in the day, before those kind of rulings, before ethics committees, there were researchers who would deliberately deprive themselves of sleep. Two in particular, this is in 1896, Patrick and Gilbert, they're called. And they managed to stay awake for 90 hours, which is just under four days. and they documented their own mental decline.

14:55Hannah Fry:So by hour 24, their attention span decreased. By hour 48, they were having trouble with really simple arithmetic. And then it goes downhill very quickly. By hour 60, hallucinations are beginning. By hour 72, they can barely think straight. And then by hour 90, they describe themselves as barely human, which is an incredibly quick decline. I think I've stayed up for a bit over 48 hours. That's my longest ever, which was when I had my daughter. Maybe into the 50s, but I was really broken by the end. Wow.

15:33Michael Stevens:Yeah, you'd be really broken. I stayed up maybe for about 40 hours in a row when I flew back from New Zealand. I did one of those, and this was just last week. I did one of those day flights that's 12 hours long. So I just read the whole time, never slept. And then I arrive in L.A. and it's the middle it's morning and I had to fly from there to Colorado. And I was I was nodding off on that flight, but I couldn't I couldn't sleep. So I kept like jumping back up and it made me increasingly hot and uncomfortable and really, really angry and short tempered. Then I was like, well, what do I do? Do I just stay up until a regular time to go to sleep in the mountain time zone?

16:12Michael Stevens:And I did. But man, I was so loopy. I was like unable to judge, you know, what was important and what. It was a bad position to be in.

16:21Hannah Fry:The last election in the UK, I was part of the election coverage, which runs through the night.

16:29Michael Stevens:Oh, what were you doing? Were you doing like the data of the votes coming in? I was the numbers girl.

16:35Hannah Fry:The numbers girl. It was honestly so much fun. It was so much fun. With Alistair and Rory from The Rest is Politics, actually. You actually start off quite early because you're preparing all of your notes. It's all of your, you know, you have to also prepare all of the, when the exit poles close, you have to prepare your packages for that. You start off maybe 10 o 'clock in the morning and you run through on air till the following 10 a.m. And it definitely comes in waves. So your tiredness, I would say once it gets to about two o 'clock in the morning, that sort of, that zone between two and six a.m.

17:11Hannah Fry:is really tough. But once you get past that, the next wave is actually okay. But it is quite entertaining to watch some of those broadcasts and to compare the image of anyone who's on TV for that long from the moment they arrive as the program starts to the moment they leave and just how much more disheveled they look. It's quite a thing.

17:33Michael Stevens:Oh, I know. When I did the Minefield show, all of the interstitials were shot on the roof of a building at night. And so we had to do all night recordings for a week. So I'd have to sleep during the day. And then from like 8 p.m. until maybe 6 in the morning, we would film. And by the end of those, I would get so dizzy and so unable to focus. It was a good experience to learn like what happens to me when I haven't slept. But it's really bad. So what do we know about what's actually causing all of these negative effects?

18:07Hannah Fry:I think the astonishing thing about this is just how quickly you see these negative effects. I mean, we're talking these examples that we're describing are when you lose one night's sleep, when you lose two nights sleep. The study done by Patrick and Gilbert was 90 hours. But I mean, there are some people who have pushed this further than that, right?

18:26Michael Stevens:Well, yeah, and not voluntarily. There's, for example, a condition known as fatal insomnia. It's often called fatal familial insomnia because it is inheritable. If your parents have it, you most likely have it. We know exactly what it's caused by, a genetic mutation of the PRNP gene, which is on chromosome 20 in position P13. And what this means is that your body produces proteins incorrectly. incorrectly and over time, like over quite a while, up until you're like 30s, you might not even know anything's wrong. But then suddenly you start to be unable to sleep. It's just it's insomnia, right? Maybe you're stressed about something.

19:07Michael Stevens:Maybe you're worried. But as it turns out, these incorrectly produced proteins are actually affecting your thalamus, which is a part of the brain that regulates a lot of automatic behavior, not just sleeping, but also your heart rate, your digestion. But the things that we notice first are the inability to sleep. It begins few weeks of just not really being able to sleep. And then suddenly you can't sleep at all. Let me give you a timeline here. Fatal insomnia has four stages. It begins with not just worsening insomnia, but panic attacks, paranoia, and new phobias for about four months. And then for another five months after that, you start to have hallucinations and really extreme panic attacks.

19:51Michael Stevens:A hallucination means you're seeing things that aren't there. And then for about three months after that, you have a complete inability to sleep and you rapidly lose weight. And then over the next six months, you develop dementia and die. Wow. It all just kind of suddenly happens. Wow.

20:09Hannah Fry:Okay, but if this is genetic, you know this is in your future. So when you're in your 20s or whatever it is, you know that you don't know how long you have left, but you know this is coming.

20:20Michael Stevens:If your parents or someone in your family was diagnosed with fatal insomnia, you may or may not have that same mutation. You're not guaranteed to, but there is a just astonishing documentary about two women who are sisters whose parents had this. And they each have, you know, like a 50 % chance of having it too. And the big question is, should we go get tested? We're not old enough now for the symptoms to start beginning, but they may or they may not do. We want to know. And it's the documentary is very much about that debate. I think one of them decides to get tested. The other just doesn't want to know.

21:00Michael Stevens:It's incredible.

21:02Hannah Fry:Which side would you fall on? If I could tell you for sure which day you would die, would you want to know? If I had a piece of paper with it written down would you want to know man i don't know i mean i'm

21:14Michael Stevens:assuming that there's like there's no way around it it's like somehow or another it's going to happen because otherwise i'm going to get distracted by thinking oh well then i will avoid it but famously in all the like ancient stories about this kind of thing you can never avoid it it always happens like the way you try to avoid it causes it to happen right so let's assume that i cannot escape it uh like it's an execution basically and i know it's coming at this very specific date.

21:41Michael Stevens:I don't think I'd want to know. Yeah, I think that that would make me use my life better. If I just knew that it was coming like a thief in the night, I would not be prepared. I would I would work harder. I would love harder. I would spend more time with people. But if I knew that it was, you know, in 2057, I'd be like, nah, I'm going to procrastinate.

22:03Hannah Fry:I got a lot of time to I've got time to waste. I've got time to waste.

22:06Michael Stevens:Yeah, but if I didn't know, it could be tomorrow. So I would carpe the diem better. What about you?

22:14Hannah Fry:I think I would not want to know. I think I'm quite comfortable with the idea of dying. Not completely comfortable. I don't think you're ever completely comfortable. But I think I am not resistant to it in the same way as I was when I was younger.

22:32Michael Stevens:Well, when you were younger, if you don't mind, when did things change?

22:37Hannah Fry:So for actually, so today is I was at the hospital today and it's my five year cancer free. I get, you know, they don't give you a little badge. No, congratulations. Today, in fact, today's the day. So I had a quite serious run in with cancer five years. And that was the switch. I think when you are when you are really staring down your own mortality, I think it does change your view of death. And I like to think that I would be much more sanguine about it. But at the same time, I think it's different to say it is a theoretical question. Would you want to know? But the reason why I said a piece of paper is because I think if it were literally in front of me, if the piece of paper were literally there, I would struggle to resist turning it over.

23:25Hannah Fry:And I think that your DNA is that version of that. It is written, particularly in this example of something like fatal familial insomnia. It really is written your future. And I would find that difficult not to turn over the piece of paper.

23:43Michael Stevens:Difficult not to look at. Have you read When Breath Becomes Air?

23:47Hannah Fry:Yes, it's beautiful.

23:49Michael Stevens:It's beautiful. I very much recommend that to those listening who aren't familiar with it. It's about a brain surgeon who is diagnosed with lung cancer. And he starts writing a book about kind of just figuring out what am I? Or rather, what will I have been once I'm gone? And I love that title, When Breath Becomes Air. When does that happen? When is my breath just back to the universe? For me, and again, this is not really about sleep anymore, but I think everything's about sleep in a way, you know, and the rest is science. But the point is, for me, I haven't had any direct confrontation with my own mortality.

24:30Michael Stevens:But I've had the indirect kind where when my daughter was born, I started to be like, oh, wait a second, all the boxes are checked. I graduated college, got married, had a kid. The next one is die. And that gave me a real existential crisis for a few years where I really struggled as I went to bed. And for some reason, I'm not as scared now. I don't know. I think brain chemistry changes as you grow up. Who knows?

24:55Hannah Fry:But I think you also just get used to the idea a bit more. I do think that there is something about that, about just getting used to the idea.

25:04Michael Stevens:That's right. You get used to it. You know, you spend enough sleepless nights worrying about your own mortality and eventually you get bored of it and you move on and you go play some back game. or something and you have a fun time, you know?

25:15Hannah Fry:Go back to eating some more grass. Okay, so here's the thing though, right? We can't change when we're going to die, but maybe we can change how much life we have between now and then because I'm still on this mission to find out what can prevent us from needing to sleep. And after the break, when we come back, I think we're going to talk about what sleeplessness does to the body and why we need sleep. And maybe that will give us a clue as to why we have not yet found a way to solve the sleep problem.

25:46Michael Stevens:Yeah, we'll solve sleep and then we can solve death. Sure. Easy peasy.

26:04Michael Stevens:This episode is brought to you by Cancer Research UK.

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26:46Michael Stevens:And early studies suggest that speed could make a real difference. Flash radiotherapy may cause up to 50 % less damage to healthy cells.

26:55Hannah Fry:But scientists don't yet know why healthy cells seem to be spared. So Cancer Research UK are working to answer that. understanding it could be key to reducing side effects in the future.

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28:23Michael Stevens:All right, so welcome back. We're going to talk about what more specifically is going on that causes all these terrible symptoms from sleep deprivation. What is sleep doing for us or at least what happens while we sleep that is so important?

28:38Hannah Fry:OK, so I've got a couple of things here. They are based on experiments that have been done with animals that actually give us, I think, some very important clues, even though the experiments themselves are not very nice. So just as a little bit of a heads up that these are not the nicest of experiments. So back in the 80s, there was a famous researcher called Rektschaffen. This is in Chicago. And he wanted to study the effects of extended sleep deprivation. So he had some rats. He kept them awake indefinitely. It was the same as the fatal familial insomnia. It's not just that they got sick or that they had hallucinations, that the rats ended up dying after about 15 to 20 days of sleep deprivation this was.

29:23Hannah Fry:But the really strange thing was that up until this point, everybody believed this idea that sleep was all about the brain, that it was about clearing toxins from the brain, that it was about our cognitive shuffling, really sort of filtering through the experiences of the day and making your brain more efficient. But when they performed these autopsies, what was bizarre was that, I mean, they were expecting the rats' brains to be total mush, really, after this time. But the brains were structurally fine. So, in fact, no major organs had this kind of definitive anatomical cause of death associated with them.

30:02Hannah Fry:All that had happened was in advance that the rats had eaten twice as much food but lost loads of weight, as you described with the FFI, fatal familial insomnia. They also lost their ability to regulate their body temperature. They've got very strange skin lesions. And then they just died of this catastrophic system failure. But it was all this really strange mystery. People knew that too much sleep deprivation or not enough sleep, rather, would kill you, but no one really understood the mechanism. And then only very, very recently, this is 2020, there was a neuroscientist from Harvard who decided to look at this problem without assuming that the brain was the culprit of the death.

30:53Hannah Fry:So their team, they got fruit flies and they had mice and they kept them up for days and days on end. And they systematically scanned every tissue in the bodies of the animals as this was going on, looking for cellular damage. And they found the smoking gun. They found what was causing the problem. And it wasn't in the nervous system.

31:13Michael Stevens:It was in the intestines, which is so strange.

31:17Hannah Fry:Like, why would it be that it would be your digestive system that would cause this problem? and it turns out when you deprive an animal of sleep their gut fills up with these toxic levels of something called reactive oxygen species or ROS and these are these unbelievably reactive molecules that you actually find naturally during metabolism they're kind of produced naturally and at normal levels they're fine your body can hound on them but when you stop the animals from sleeping this ROS and their small and large intestines builds up builds up builds up and causes this massive oxidative stress, which is essentially, it's like rust, but the biological version.

32:00Hannah Fry:And all of this excess RIS, it started shredding the DNA, shredding the fats, the proteins inside the gut, which explains the weight loss, despite the additional eating. So, you know, this wasn't brain failure. They died because their intestines were being biologically incinerated from the inside by these toxic molecules.

32:25Michael Stevens:Do we know what causes or what connection there is between lack of sleep and the ROS elevation?

32:32Hannah Fry:Yeah. So this was, that was in 2020. And that was still the big question, exactly as you've described. So in November 2023, this is like less than, you know, three years ago, this was a study published in Cell, it's a very prestigious journal from Peking University. And it looks like we finally worked out what was going on. So they had some mice that were kept awake almost continuously, so 96 % of the time. And mice normally sleep, it was 50-50, wasn't it?

33:03Michael Stevens:Half the time, yeah.

33:04Hannah Fry:And sadly, 80 % of these mice died, 20 % of them survived. So as these mice are kept awake, the brain is like frantically producing this sleep-promoting molecule. It's called progress the land in D2 or PGD2. Sounds like a robot from Star Wars. Anyway, normally this PGD2, it builds up, you get sleepy, you fall asleep and then the brain clears out. You're fine, it's done. But because you force these mice to stay awake, the brain ends up pumping out so much of this molecule that the system starts overflowing. It breaches the containment. physically leaks across the blood brain barrier, spills out into the body's main circulatory system.

33:48Hannah Fry:And then what happens is the immune system detects this flood of this molecule all over the place and is like, whoa, emergency. This is like a catastrophic situation. Triggers this gigantic immune response, specifically called a cytokine storm, which you may remember from COVID, which was the thing that really caused problems with COVID. So all of these white blood cells, they swarm the tissue. The body is just flooded with these inflammatory signals. The immune system goes into this blind rage. And, well, we think that that is what has triggered that fatal explosion of ROS in the gut, the rust, essentially, that the Harvard team found.

34:32Michael Stevens:Wow. So is this part of that glymphatic system I've been reading about, the system of toxins or just chemicals, let's say, in general, that build up during waking hours that then need to be flushed and can seemingly only be flushed during a sleep cycle.

34:51Hannah Fry:Exactly. Exactly right. Exactly right. PGD2 is precisely one of those. Just to be sure that the PGD2 was the thing that was causing all of this, the researchers then ran the experiment, but where they blocked the PGD2 pathway. So they stopped it from affecting the mice, either genetically or by literally removing the receptor or with drugs. And they found that these sleep-deprived mice still didn't sleep because they were preventing them from sleeping, but they didn't die. They didn't get the inflammation and they lived. So this is, I think, a very big clue, In mice, at least, this particular molecule is a key part of what is causing this attack of the body on itself.

35:43Hannah Fry:But I think crucially, what's interesting here is that death by sleep deprivation, nothing to do with the brain, despite your brain feeling the effects of it. It's actually death by friendly fire. It's your own immune system that ends up burning your organs to the ground.

35:57Michael Stevens:So does this mean that we could be, there could be a path, maybe it'll take a long time, but in the future for us to figure out ways to counteract all of these problems. We can say, look, normally sleep fixes this, but we found a medicine that does it faster while you're awake and slowly we whittle away at the amount of sleep we need.

36:17Hannah Fry:You can just flush out the PGD2 and you're done.

36:20Michael Stevens:Yeah, flush it out. That would be nice. Rather than taking eight hours to do it, can we do it in like 10 minutes? Like a bathroom break, but it's a brain flush break.

36:31Hannah Fry:I mean, I think it's going to be a bit more complicated than that, unfortunately. And the reason why I think it's a bit more complicated than that is because time is literally built into all of the cells in our body. This isn't a preference. It's this coordinated thing. This is some work by Russell Foster, a very good friend of mine. He's written this amazing book on sleep, by the way, called Lifetime. it's it's just fantastic and uh one of the ways i think to describe it is that every cell in your body every single cell in your body has uh this this process in it you can kind of imagine it like a protein factory so when you wake up there's a couple of genes in your dna that turn on and start manufacturing this specific protein and during the day these proteins they pile up inside your cell and the pile i mean you can sort of imagine the piles gets higher and higher and higher and after 12 hours the pile of proteins is so massive that it physically blocks the factory doors so the genes can't make it anymore so the factory shuts down and then during the night shift over the next 12 hours you get the reverse process that pile of proteins breaks down slowly slowly slowly and dissolves and right around the the 24 hour mark the proteins are gone and the process starts all over again.

37:52Hannah Fry:So this, I mean, this is one of the reasons why jet lag is so painful because you have, you have this cell time, you know, it's these, these cellular clocks in, in all of the cells in your body, but your brain is sort of like the master conductor that is trying to synchronize everything all together because all of these cells have their own clocks because every organ also has its own clock. You know, your stomach knows when it's time to digest, your liver knows when it's time to process sugar. They need this conductor to keep them in sync. Otherwise, you know, you'll be biological chaos. And the conductor is called the suprachiasmatic nucleus, which is this little cluster of neurons that's sitting right above your optic nerve, takes in light from the sun, acts like the atomic clock for the rest of your body.

38:42Hannah Fry:and what happens with jet lag is that it's it's not just that you're tired it's not just that you're tired from traveling is that the clock in your brain has shifted because it's it's doing that based on light but the clocks in your in your liver and your kidneys and your stomach they're still operating on on yesterday's time you know you've got this this temporal desynchronization basically they're playing they're completely out of rhythm with one another So I don't know. I don't know. I think that if you are, I don't think it's going to be quite as simple as just putting in a drug that blocks this one particular protein of PGD2.

39:17Hannah Fry:I think you're going to have to worry about all of the other little clocks that are going on in your body.

39:22Michael Stevens:That's right. Yeah. Like it sounds like there's a constellation of probably a hundred different things that sleep is helping us do that would have to be replaced with new medical procedures or drugs. and ultimately you know as I've surfed around and asked people about like curing sleep another thing they mention is that they wouldn't want it done away with because they like it it is so pleasurable at the end of a hard or a long day to rest it is so comfortable to wake up and see that you have another couple hours before you have to be up and to get to sleep more it's not like smallpox where everyone's like get rid of it I don't care it's It's like, I don't know, I kind of like it.

40:08Michael Stevens:I mean, yeah, I'd be more productive, but do I want to be more productive? Maybe there's only so much grass you can eat. I mean, humans actually sleep a lot less than you would expect, apparently. There's a great study I was reading this morning that looked at how long should humans sleep. We're a primate. We're a kind of primate. So let's compare ourselves to gorillas and bonobos and chimpanzees. and looking at all the different measures that there are, like an alien scientist would expect a human to sleep for something like, actually, I've got the numbers right here, 10.3 hours. That's where we should fall.

40:47Michael Stevens:But humans don't sleep that long. And it's not just because of televisions and smartphones and electric lights. In the ethnographic research that looks at people who have no electricity, I'm talking about people like the traditional Maligay on Madagascar. They sleep about six and a half hours a night. Not the eight that we often talk about. I need my solid eight. Well, the Hadza hunter-gatherers, 6.2 hours per night. There are three other hunter-gatherers that were quoted about six and a half hours. Haitian non-electric sleepers, meaning they don't have any electricity, nothing to keep them up, seven hours.

41:23Michael Stevens:And so Western populations are also around seven, but it does not seem like modern life has caused sleep amount to go down. Our relationship to it and the quality of that sleep might be different. Our sleep hygiene might be worse, but it doesn't seem like a human, like a paleo human, you know, slept a lot.

41:44Hannah Fry:I do sort of wonder about this, though. It kind of goes back to what you were saying right at the beginning. The idea that evolution would select for something that left you so vulnerable is weird. I mean, what are the theories about that?

42:03Michael Stevens:Okay. So here's the thing. Obviously, you can talk about sleep as a vulnerability. At the same time, you can think of it mathematically and you can say, well, what's better for reproductive success? me being at the same energy and focus level every hour of the day for 24 hours, or if I sacrifice some focus and ability some of the time, and I reserve that for like a short period of activity, maybe I can be stronger and faster and smarter than my conspecifics and my predators, than my threats. Now that works if you can safely have lower activity and awareness levels, so you can store up. And if you live in the trees, like you're a chimpanzee, it's pretty easy.

42:52Michael Stevens:But Homo sapiens came down from the trees for some reason. Okay, our species did not live in the trees, we sleep on the ground. And that opens you up to being a lot more vulnerable when you sleep. And so that's one of the hypotheses the researchers have for why Homo sapiens sleep so much less than predicted. Another one is that we are so social. And our lives depend so much on trading stories and skills. Sleep is an opportunity cost in that case. If I'm sleeping, I'm not sharing and teaching skills to others. I'm not being social. I'm not forming relationships. In some weird ways, it feels like sleep isn't necessarily that human of a thing.

43:35Michael Stevens:And the reason I'm even saying this is that when I went into this episode, I thought, you know what? But I bet REM sleep, especially like dreams that are just so they're so abstract and metaphorical. Surely human creativity and imagination is like somehow interlinked to our REM sleeping. Like maybe that's what sleep is about. It's about consolidating memories, which it kind of is. But there must be a connection between what makes us characteristically human and our sleeping. But it does not feel that way. It feels almost like we've had to give up some sleep to become human. But then you might think maybe it's the kind of sleep because sleep has these two forms.

44:13Michael Stevens:You've got the non-REM sleep and the REM sleep. REM stands for rapid eye movement. During a rapid eye movement phase in your sleep, which you have multiple through a night, your eyes rapidly move and your brain is very much awake. Its activity levels are really high. During the rest of your sleep, it's really low. and it's during REM cycles that your dreams occur. My first thought was humans must have way more REM sleep than anything else, but that's not true either. We sleep seven hours a night and we get about two of those seven are in a REM cycle. The platypus sleeps about 14 hours a day, so twice as much as we do, but gets four times as much REM sleep, eight hours a night.

45:00Hannah Fry:I mean, are you surprised the platypus are having wacky dreams? I mean, are you? I know.

45:05Michael Stevens:Look, they're a wacky animal, but you can look this up. Other non-wacky animals are the same. They might sleep more than us, but they have a disproportionately large amount of REM sleep. And none of these animals are out there writing books about differential topology or building rockets or debating justice. Or trying to categorize platypi. Or yeah, they're not worrying about is it platypuses or platypi, but we are. So I don't think the REM sleep has anything to do with it. And then beyond that, you don't necessarily seem to even need REM sleep. A lot of medications remove REM sleep from a person's life.

45:45Michael Stevens:And this could happen for years and they have no cognitive decline. They don't seem to be any different. In fact, I read a paper that argued that REM sleep might be more about thermoregulation than any deeper creative or emotional reason. That basically the brain has to like cool down. It needs to have something has to happen to the cells in the brain perhaps in order for them to like not get stuck and hallucinate. But if it slows down too much for too long, it literally gets too cold and cannot be. It's not ready to be rapidly awoken in the case of an emergency, a predator, a problem, a natural disaster.

46:31Michael Stevens:And so periodically during our sleep every night, it has to warm itself back up. And that's all REM sleep is. It's just warming the brain back up.

46:39Hannah Fry:That's amazing.

46:41Michael Stevens:And it works really well because our muscle tone is so diminished when we sleep that the brain can go. And our eyes go crazy and we dream, but yet we don't move. So we don't hurt ourselves. We don't hurt other people, but it needs to warm itself up. And then it's warm enough and we go back into that slow wave sleep where we're like very much not there. But then I got to warm up again. So that blew my mind because I had always lived my life thinking that REM sleep was this important thing that was key to consciousness and the human condition. and it just might not be. But I want to caveat all of this by saying that all these things, we're learning this stuff now.

47:24Michael Stevens:This is new. A lot of this is new research. Yeah, this is proper cutting edge. Yeah, we're finding that sleep is not the same as a virus. It's not like, oh, kill the virus, problem solved. Sleep is a thousand different viruses that are all necessary. And so we just have to live with it. We just have to take a nap.

47:43Hannah Fry:Take a nap, exactly.

47:44Michael Stevens:So in the paper, I loved this. They said that REM sleep might just be the brain's way of shivering. Periodically, it has to warm itself up. But we think that it's some, oh my gosh, the dreams told me something about the future or my relationship with my mother. And you know what? Maybe they weren't trying to, but maybe if it makes you think about that relationship or that interview you have tomorrow, it can lead to insights. I'm totally pro dream. Don't paint me as an anti-dream guy. But if that's not the advantage of sleeping, what is? If we go really far back and we look at even single celled organisms, there can be rhythms, temporal rhythms can be found in them, too.

48:27Michael Stevens:And so my favorite argument here is that sleep may have began because if you are a life form on Earth, you've got to find a niche. OK, and you want to exploit that niche and thrive in it. But you cannot find a single niche on this darned planet because it's spinning. We have night and day. So even if you're a little orchid that needs to live only within this like five meter radius or you'll die, you still have night and day. And so here's the deal. How about during one of those cycles, I just turn off. I turn off so that I don't have to be fit during that period. I don't have evolutionary pressures for living in the day and the night.

49:08Michael Stevens:And so if that was the beginning of sleep, then it could have been co-opted by later organisms in the history of evolution for doing things like cleaning out neurons, for cleaning out and consolidating and defragging memories. And that seems to be what we use it for.

49:24Hannah Fry:That's absolutely fascinating. I like that idea also because when you look at marine animals, I mean, I'm thinking about dolphins here, for example, dolphins, whales, sharks, they don't have the same relationship with sleep that we do. There's not this sort of transition for the nighttime. It's like dolphins, for example, can sleep with half of their brain at a time. They kind of have to. Yeah. Yeah.

49:51Michael Stevens:Like they can't just turn off the way we can and stop evolving, stop having threats like they need. They still need to clean out the brain or whatever they're doing. But, yeah, they have to just put one half of their brain asleep at a time, keep the other half ready so that they stay alive. So what I love about the theory is that it's kind of like maybe sleep began not because there was nothing to do in the night, but so that we wouldn't fall in love with the night. So we wouldn't become this creature that had to expend energy being fit all the time.

50:31Hannah Fry:Your take on things, Michael, never ceases to amuse and amaze me. why why would we be unconscious though i mean sure right i accept i accept this idea i like this idea of there being the adaptation towards a particular environment rather than two simultaneously i like that a lot but i don't know why it would cause unconsciousness like you can rest you know you can you like the rest in front of the tv you can rest while reading a book why I, this sort of feels a bit wild that you would add that in.

51:05Michael Stevens:I know. Does it have to be that way? Does sleep have to involve me, myself, my consciousness, completely checking out for a while? I mean, on the one hand, it feels like, well, if it must, then maybe it's because there's also some evolutionary pressures on consciousness, on the way I think. Do I think differently at night, though? I mean, it's also been shown that the memory problems caused by sleep deprivation can be somewhat alleviated by simply resting. Just sit quietly in a chair and don't take in any more information. Your brain is still trying to consolidate short-term into long-term memories.

51:43Michael Stevens:And you perform better at memory tasks. So, I mean, that is some good news, by the way, if you struggle sometimes to sleep and you're just laying in bed and you're not asleep and it's making you more and more anxious. The Mythbusters even showed this. It's fine. You're still resting.

51:57Hannah Fry:Yeah. You're still resting. And you're still doing a lot of the good stuff.

52:00Michael Stevens:If you're just laying there in the dark, that's still better than getting up.

52:05Hannah Fry:I think you can also end up dreaming about sleeping. It's actually quite hard to know precisely unless you're sort of, you know, using a sleep tracker, which generally if you are struggling to sleep, I wouldn't. It just makes you more anxious. Exactly.

52:19Michael Stevens:Exactly. Just let your body do its thing. You're just along for the ride.

52:23Hannah Fry:And maybe we should say, I mean, we've spoken a little bit about proteins. We've spoken a little bit about cell time and the various, the sort of oxidation that happens in the gut. But I think it's also important to say the profound impact that sleep does have on the brain or rest at least. You know, your synapses are pruned and recalibrated. Your memories are consolidated, which can happen when you rest. Your metabolic waste is cleared via glymphatic flow, which you were describing earlier. You know, your immune signaling is regulated, your cellular stress responses are resolved, your circadian gene expression cycles are coordinated.

53:01Hannah Fry:There's like there's an unbelievable amount of stuff that is happening. And if we are looking for a cure, if we're looking to solve this, I think there's going to be a long time coming. There's quite a lot of complex stuff going on there.

53:14Michael Stevens:Yeah, there is. So, I mean, that basically answers the question of why we haven't cured sleep yet. why we still need it, why we still need it to function properly. On that note, I was just watching a video this morning from University of California television. Charles Dunn at Duke University gave a talk about a paper that he worked on where he talked about that glymphatic system, all of this mental brain neural stuff that is helped, that's basically cleaned out of toxins while we sleep. And I guess whatever mechanism is responsible for our sentient awareness, like just has to be off for that cleaning to happen.

53:57Michael Stevens:You know, for a long time, we never saw Alzheimer's in other animals. I mean, a lot of that is changing, but it's still an open question to what extent the cognitive decline that humans see later in life, but also humans sleep a lot less than we predict that they should. So the trade-off for being more social and more productive. Maybe that our brains don't get cleaned through our lifetimes enough. And then you wind up with all these things, especially amyloid beta, which is part of the process that we think leads to Alzheimer's disease. However, I want to also point out that studies have not shown that sleeping longer is good.

54:36Michael Stevens:In fact, if people sleep a lot more or a lot less than seven hours a night, bad longevity, bad health.

54:44Hannah Fry:Right. But then I wonder how much of that is about the lifestyle that's associated with sleeping too much or too little. Exactly.

54:50Michael Stevens:Right. Like if you're sleeping a lot, it's probably not because you've chosen to. Yeah. It could be that there's a lot of other stuff going on in your life that's making you stay in bed and vice versa. If you're not sleeping a lot, there's probably a lot of stressors in your life.

55:03Hannah Fry:But then this idea that Alzheimer's, which, you know, is at least in part down to a buildup of this particular protein, is this disease of complex intelligence and sleep failure and extreme aging all at once.

55:20Michael Stevens:Yeah.

55:21Hannah Fry:Yeah. When the sort of nightly wash cycle can't keep pace.

55:23Michael Stevens:Yeah. And that wash cycle is not simple. It's not like, I mean, compared to digestion, it is so much more complicated that we still don't understand how it all works. And all we know is that sleep is doing something very, very complicated and very, very important.

55:44Hannah Fry:So I guess then our big conclusion is have fun with your 52 years of being awake because that's all you're getting.

55:50Michael Stevens:That's all you're, can you, isn't that wild? Like I can say, oh, you know, here's how much time I have left in my life. But then I got to, I got to subtract a third of it. Because unless I don't, unless I take an attitude of, but sleeping is something I love doing. I'm glad that I get to spend a third of my remaining years on earth asleep.

56:09Hannah Fry:Yeah. I mean, it's just, I like going to sleep a lot. I like the feeling of having slept a lot. there's definitely some times where it feels like a a very big waste of time for me i i never have

56:25Michael Stevens:disliked sleep i get sleepy pretty early like i'd say by 10 p.m i'm like all right i'm done but i wake up really early and i love waking up early not feeling tired i don't use an alarm clock and then i just am able to work and read um i'm i'm finally reading the lord of the rings look at this tome this is not just a book this is a finger workout like try to read this in bed you can't fall asleep it's gonna fall in your eyeball and cut it out i mean this is and and look how look how far through it i am there there's my little bookmark ribbon i'm just on chapter 250 pages already what time do you wake up in the morning then i usually wake up around like 450 or five But I go to bed at 10.

57:10Michael Stevens:So how many hours is that? That's like seven, right?

57:14Hannah Fry:Six and a half.

57:15Michael Stevens:I'm fine. Yeah, I mean, I'm feeling fine.

57:16Hannah Fry:I think, Michael, you should do your own version of I wake up at 430. The first thing I do is I do a finger workout. Then I, you know, like the bros.

57:27Michael Stevens:I know. I know. I see. That's why I don't really talk about this too much. By 6 a.m. I've had a whole work day. I think that I hate that kind of stuff. The like, I wake up at three and then I journal and then I work out. And I'm like, no, I wake up and I read The Lord of the Rings and I drink vanilla Coke and I browse Reddit. I mean, I need an intake phase in my life, you know, and then later on when everyone else is up, I can output.

57:54Hannah Fry:So there we go. I think that's our big conclusion. Elephants were born to eat grass. Bats were born to sleep. Michael was born to browse Reddit.

58:03Michael Stevens:Well, I want to I want to say I also heard something really, really cool from Charles Nunn's talk. We can link that down in the description as well. He was like, you know, a lot of the studies we do on human sleep and animal sleep, we hope to learn a lot about improving human health from these studies. But we have to keep in mind that animals and people who are from cultures that don't have electric devices, I mean, they're not necessarily sleeping in a way that evolution prepared for them so that they are healthier. Evolution and natural selection operates on reproductive success, not health and longevity.

58:43Michael Stevens:And so we have a lot still to learn about what kind of sleep is healthy. What's natural, paleo sleep schedules might not actually be the thing that gives you the best life. It's what means that your descendants survive and there's a lot of them.

59:00Hannah Fry:But wait, hang on. Explain what you mean by that.

59:03Michael Stevens:What I mean is the more we learn about how humans should be sleeping, the more we have to answer the question, what does should mean? Does it mean what sleep does for us? Does it mean how we would sleep if there were no distractions? Does it mean what feels good? Does it mean what allows us to be more productive? We just we don't know. And by studying the history of sleep in medieval times, there's a lot of talk about people sleeping twice, having two sleeps in the night.

59:34Hannah Fry:And waking up for food in the middle.

59:36Michael Stevens:I had my first sleep, woke up at about three, did some work and then had my second sleep. Is that more? Is that healthier? or is the way, you know, Neanderthals slept or prehistoric people slept or people from tribal cultures with no phones or electric lights, are those healthier ways of sleeping or are they ways that just led to better reproductive success?

1:00:01Hannah Fry:What I'm hearing from you, Michael, is that after all this time, it might be that Salvador Dali was correct. Maybe, maybe the best way to sleep of all is with a key and a plate in your hand. And on that note, it's quite late here in the UK. I'm going to go to bed. You better. Yeah. Yeah. Cleanse your brain. Cleanse your gut. I will. Sleep it off. So sorry, everybody who was hoping for a miracle cure. You're going to be sadly disappointed.

1:00:29Michael Stevens:I won't lose any sleep over it. It's a hard problem, guys. We're not even close to solving it. So for now, enjoy your rest.

1:00:38Hannah Fry:Well, that's all for today. Join us on Thursday for our episode of Field Notes and again on Tuesday for our main episode.

1:00:45Michael Stevens:And if you'd like to ask us a question, which we may answer on an episode of Field Notes, send your questions to the rest is science at goal hanger dot com. The rest resting resting is a mystery. The rest is science. The rest is necessary. There's something there. The editors can turn that into some brilliant like like philosophical thought and promo for the show. Send us your ideas. Send us your ideas. Until then, good night. Good night.