This Podcast Will Kill You - Ep 198 Sleep Part 1: Sleeping with one eye open

Episode Date: January 20, 2026

Sleep is a universal experience. It’s not just the lion that sleeps tonight - it’s also the butterfly, the chicken, the jellyfish, the dog, the snake, the worm, and of course the human. What is this widespread physiological process whose spell we are all under? What purpose (or purposes) does it serve? Why do we sleep the way we do? These are just some of the questions we’re going to get into in this week’s episode, the first half of our two-parter on sleep. We break down the different components of sleep in humans before diving deep into how animals sleep and what drives the different patterns we see. Night owl or daybird? Light sleeper or deep slumberer? Frequent naps or one big chunk? One eye open or both eyes closed? Tune in as we unravel some of the mysteries of sleep. Support this podcast by shopping our latest sponsor deals and promotions at this link: https://bit.ly/3WwtIAuSee omnystudio.com/listener for privacy information.

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Janice Torres here. And I'm Austin Hankwitz. We host the podcast, Mind the Business, Small Business Success Stories, produced by Ruby Studio, in partnership with Intuit QuickBooks. We're back for season four to talk to some incredible small business owners. The big thing about working at tech is that it's ever evolving, ever changing. everyone's a rookie. That's how fast the industry is changing. So what I'm really excited about is to be part of that change. So listen on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hey, everyone, it's Stephen Ray Morris. I'm here to tell you a little bit about

sleep paralysis and lucid dreaming and where the two meet in the middle, which is me. Sleeping has always been, especially lately, has been pretty difficult. But for most of my life, I've had pretty like stressful dreams to the point where I feel like sleep isn't very restful for me. I was younger, it used to be really easy for me to fall asleep, but then the actual dreams and things themselves wouldn't be very restful. And that I think, like a common theme in my dreams is that I have to do a task in the limited amount of time and there's an obstacle getting in the way. And some of my favorite examples of this are I am like a manager at a brothel Christmas party. and I have to make sure everybody gets their gifts, but all the gifts are unlabeled. I have to catch a train,

but I keep running into people I haven't seen in a long time. So, oh, hey, nice to see. I actually got to catch that train. And then I run into somebody else. In college, I started getting sleep paralysis. I still do from time to time, but it was really bad where, you know, it's your brain is awake, but your body is asleep. So there's usually some sort of demon, like Nasgol, Dementor-style thing in the corner of the room. And it just causes this intense fear and terror. And so I usually wake up, like everyone I've ever, is whatever, spent the night with, have always had to deal with me waking up and screaming from these forces. In college, I met my roommate, my buddy Evan, who's from the Bay Area. And, you know, we all watched waking life.

And in that movie, they talk about lucid dreaming, which is, you know, the ability to, be aware that you're dreaming and control your dreaming, et cetera, et cetera. The two main things that I took away from it are, you know, like AI, look at your hands or look at clocks because dreams can't represent either of those things very well. So if you see them, that means you know you're dreaming. So I'd started continuing these dreams where just this intense fear, as this dark figure, is looming in the corner. And I, after all this lucid dreaming training or whatever, I started to like wriggle a little bit,

you know, because I was so scared that I like was really trying to get away. And then one night as it got right over my bed was looming down at me, I just remember this feeling of, you know, like full like superhero movie like that strain. And I reached my hand out and grabbed this sleep process demon by the wrist. And then I woke up and I didn't have sleep process again for a few years. I still remember this so clearly like it was yesterday, even though this was maybe like, I don't know, almost 20 years ago. The sleep process still happens every once in a while, but I think my lucid dreaming training still serves me well occasionally. So I'm prepared, basically, anytime sleep paralysis demons come at me. Stephen. Stephen. I mean, first of all,

terrifying, but also secondly, what a joy to hear your voice. Thank you so much for sharing your sleep and sleep dreams, sleep paralysis stories with us. It is so scary. I've had sleep paralysis just a few times in my life and I truly thought I was dying. I know. I don't know that I've ever had it, but all of the stories that I hear are like really terrifying. Yeah. Yeah. Yeah. Oh. Ha ha ha ha. So, thank you. Thank you. Thank you. Hi. I'm Aaron Welsh. And I'm Aaron Olman Upday. And this is, this podcast will kill you. Welcome to the exactly right studios. Yes. Where we will be discussing in two episodes, sleep. I'm excited for this.

Very much so. What are we going to be talking about? There's a lot that we're going to cover and a lot that we will not cover. So we are going to be talking to this first episode, we're focusing on what sleep is essentially. Like what does it entail? What is your brain doing? A little bit about why sleep is important or what we think sleep is important for. I'm going to be talking about sleep in animals.

I'm so excited. A lot. I'm really excited about that. I'm excited about it too. I did not know where it was going to go. Right. And then next episode, we're going to talk about some of the consequences of sleep deprivation. And also we're going to be talking about the history of human sleep. I'm really excited about that too. I think the second episode is going to be a lot of interesting discussion about how we think about sleep today. I think so too. I personally felt a lot better about sleep. Oh, good. Yeah. That's great. At the end of it. Happy to hear it. Thank you. Thank you. Hopefully everyone else will too.

But not this week. No. This week you'll just learn a lot about sleep. Yeah. I'm excited. And you'll also have a really delicious beverage to go along with it because it's quarantine time. It is. In this case, it's placebo-rita time because alcohol, spoiler alert, makes you sleep badly.

It's not good for your sleep. Even though lots of people use it as a sleep aid or an anxiolytic, it's not good for either of those. I mean, alcohol is not good for anything, period. It's not good for your body. Yeah. There's no safe amount. Anyway, so we're doing a placebo rita. Our placebo rita is basically like a really nice version of a chamomile tea.

But what is it called, Erin? It's called Pillow Talk. Yeah. The long pause of me trying to remember. Well, because we had a few different options. We did. There was also bedtime story. Yeah.

It's a great one. It's a great one. Yeah. Pillow talk. Yeah. It's a camomile tea plus ginger honey syrup. Yum. So good.

And a little bit of lemon in there. Yeah. Kind of wish we had that to drink. Does sound nice. Sounds good for your throat. Yeah. Yeah. Anyways.

But you can make one and drink along with us. We'll post the full recipe on our social media channels for sure. Maybe on our website. Erin, walk us through the website. Oh, the website. Sorry for throwing it at you. What a treat. Yeah.

The website is a real joy to discover. You can find things like. transcripts. You can find things like the sources for each and every one of our episodes. You can find links to our bookshop.org affiliate page, Goodreads list, merch, some pretty sweet merch. You can find links to Music by Bloodmobile, to a contact us form, a first-hand account form, and probably some other things. There's an About Us page, too. There is. It's got like four lines. Yep. It does not contain a lot of information.

Oh, so check that out. Check it out. Make sure you are rated. rate it. Make sure you are rate. Make sure you have subscribed. And if you'd like to rate and review the podcast, we would appreciate that. We're doing great. We're really killing it today. Yeah. And if you are a fan of watching things, we're on YouTube on the exactly right network channel. So you can see some sweet PJs that we're wearing. We're pretty excited about this. I really like, I really like yours. It's very beetle juice. I love yours too. It is very beetle juice. I love it. We took a long time picking these out, everyone. So we did.

Well, with that, Erin, shall we take a break? Business completed? Business complete. Let's move on to learning about sleep. Love it. Okay. Dinner shows up every night, whether you're prepared for it or not. And with Blue Apron, you won't need to panic order takeout again.

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Order now at blueapron.com. Get 50% off your first two orders plus free shipping with code this point. Podcast 50. Terms and conditions apply. Visit blue apron.com slash terms for more information. Anyone who works long hours knows the routine. Wash, sanitize, repeat. By the end of the day, your hands feel like they've been through something. That's why O'Keefe's working hands hand cream is such a relief. It's a concentrated hand cream that is specifically designed to relieve extremely dry, cracked hands caused by constant hand washing and harsh conditions. Working hands creates a protective layer on the skin that locks in moisture. It's non-greasy, unscented,

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The fit is amazing, and they come in a bunch of different washes, so I'm about to go order some more. Refresh your wardrobe with quince. Go to quince.com slash this podcast to get free shipping on your order and 365-day returns, now available in Canada, too. That's Q-U-I-N-C-E dot com slash this podcast to get free shipping and 365-day returns. Quince.com slash this podcast. We all sleep. All of us, humans. And Erin, I know that you are going to walk us through some of the many different ways that animals sleep, which I'm quite excited about like what does that mean in animals.

What does it mean? And there's such a variety there. What does it mean in humans? Well, let me tell you about it. And that's an interesting question. It's because like because we all sleep, I think that we all know what it means to sleep. One could even go so far as to say, much like the super. Supreme Court Justice, Potter Stewart said in 1964 when trying to define hardcore pornography, I know it when I see it. You know it when you see it. Yeah. Yeah.

We all know what sleep is. But what is sleep if we're trying to put like a label on it? What are our brains doing when we sleep? And these are the questions that I'm going to try and answer today. But the biggest question is one that we cannot. really answer with what we know. And that is why. Do we sleep? Exactly. Why do we sleep? We don't really know truly the function of sleep. But we do have a lot of thoughts and hypotheses which have various levels of support. So we'll get into some of that as well. And then next week, like we said,

we'll talk more about what makes good sleep good and what makes bad sleep bad. It's so, and then what about like the quantities of sleep and all of that stuff? And the architecture of sleep. Oh, yeah. Oh, yeah. Okay. So what? So what? And then what? And then. So, what? And the consequences. And the architecture of sleep. Oh, yeah. Oh, yeah. Okay. So what is sleep? If we define it. Sure. A simplified definition is like a reduced state of voluntary motor activity. So you're not moving. You've got a decreased response to stimulation. And in general, there's a stereotypic posture associated with sleep. I know you'll talk more about that, Aaron. No, I just love the thought of the stereotypical posture. I know, right? It's very cute. In humans, we lay down, right? Yeah. That's what we do for sleep. And in contrast to other states that,

that might be similar to sleep, like say a coma, sleep is easily reversible. Okay. But in reality, in medicine, we have defined sleep based on specific patterns of electrical activity in our brains. EEGs. EGs. So let's get into it. We talked about EEGs or electroencephalograms in our epilepsy episode. Oh, gosh, that was a long time ago. It was a while back. And at that time, I was just like, I don't want to get into it. Goodbye. And we just didn't talk about it. We'll do it someday. Today is that day. Today's the day. So EEGs measure the electrical activity happening in our brains. And the readouts of EEGs, when you see them on paper or on a computer, are these wave patterns.

Kind of like if you've ever edited like a sound file, you see these little wave patterns. They look very similar to that. And waves, if anyone hasn't taken physics in a long time, are measured by two main measurements. And that is amplitude, which is the height of the waves. and frequency, which is the number of waves per second or per unit of time. Right. Okay. So the higher the frequency, that means the faster the waves, the closer together the waves are.

And we call that a high frequency. Uh-huh. And then lower frequency are slower waves. Okay. So longer, wavelength, longer frequency. Okay. Depending on what our brain is doing, our EEG makes a number of kind of predictable patterns. Some of which we only see when we're awake and some of which we only really see when we're asleep.

So when we're awake, our EEG pattern shows these fast frequency, low amplitude waves. Fast frequency, low amplitude. Yeah, yeah, yeah. So they're like close together waves and they're not, they're just little baby waves. And the most common two types of waveforms are called alpha waves and beta waves. There's a few others, too. Alpha rhythms are like calm, eyes closed, like meditation type of vibes. And then beta waves are what we see more with like activity of the brain.

Sorry. So we're talking about these are sleep. Awake. Oh, these are awake. Okay. This is what we're doing right now. Yeah, yeah. We're probably beta waving to each other.

We're definitely beta waving. Not calm at all. But during sleep, our EEG patterns change. And we can measure more than. just the brain electricity, actually. So when we're measuring sleep, there's three main sets of measurements that we're looking at. The EEG, which is your brain electrical activity, the EMG, or electromagnogram, which records activity in our skeletal muscles. Okay.

And then the EOG, or electrooculogram. Yes. Which is measuring rapid eye movement. Yes, horizontal eye movement. And if we put all three of these together, they result in what's called a polysomel. or PSG. So you can look up a picture of a PSG, but it's like a lot of wires all over. Yeah. And sometimes there's more if you're measuring like your pulse ox and your heart rate and things like that. Okay. I've always wondered this about sleep study things. Yeah. I feel like I would sleep terribly. I know. It's a valid

concern. I don't have an answer for it. Okay. So like how, okay, another question then. How many nights will you sleep with wires, et cetera, to get like a good model of. what your sleep is like. That's a great question. I don't know. A lot of times it might just be one night. Just one night. Yeah, but it totally depends on like what the scenario is, what the study is, and like what

information they get from that kind of a thing. I find that so interesting because I feel like sleep is so variable. Oh, it's so variable, Aaron. It can totally be so variable. Yeah. So I don't have a great answer to that. Okay. Yeah.

Yeah. Totally depends on the study and what they're doing, what they're looking for. But based on. these PSG readings, what we've done over the years and studying many people for longer periods and in the lab, etc. We now can divide sleep into two main phases. There's REM sleep. Just two? Well, two main like divisions. Yeah, yeah, yeah. There's faces within these. But the two main divisions are REM or rapid eye movement sleep and non-REM or non-rapid eye movement sleep. Yeah. Within non-REM sleep, there are three different faces, sometimes four, sometimes stage three. three and four are separated.

And this is just depending on classification, not like... Yeah. The older literature kind of says there's four stages of non-REM, and the newer literature is like, realistically, deep sleep is all deep sleep. We'll just call it phase three. Oh, interesting. Yeah. So anyways, it doesn't really matter.

But let's walk through what a night of sleep looks like together because we fall asleep in relatively predictable patterns. And as we fall asleep, our brain waves kind of gives. kind of get slower and slower as we go. So like I said before, as we're awake and relaxed, our brain is in this alpha wave pattern, which is low amplitude, relatively high frequency waves. Then as we fall into stage one sleep, which is one of the stages of non-REM, we call it kind of drowsiness, we'll slip into this pattern called theta waves, which is slightly lower frequency.

still low amplitude. Slightly lower frequency. So a little longer wavelength and a little longer frequency than the alpha waves. But still low amplitude. Okay. Little just chilling down there. Muscle wise, you might have these little like twitches or muscle jerks, as we all know. Why?

I don't know. Okay. And then stage two is when you start to truly fall asleep. This is when conscious awareness is gone. Your muscle activity decreases substantially. And your brain waves will continue in this theta wave pattern. But then we see them punctuated by these really weird little bursts of activity, these short little bursts of super high frequency events that are called spindles,

followed by what's called a K complex, which is this very, it's a low frequency, high amplitude, just like one-two punch. the high amplitude. So like wide. Yeah. And tall. Weird. But there's one. And that's a K complex.

Okay. And that's like stage two. So we see this mostly like slightly chiller pattern than awake and then little bursts of. Yeah. Like a heart. Almost like a heartbeat kind of. Yeah. Sure.

We'll say sure. Yeah. And then after stage two, we fall into deep sleep or slow wave sleep. Stage three of not. So I'm guessing frequency goes down. Yes. Tell me about amplitude. Amplitude goes up.

So we see this high amplitude, low, low frequency, slow waves that we call delta waves. What is what does it mean to have high amplitude? You know? Yeah. So the waves are created essentially by this like activity of our neurotransmitters happening all at once. Okay. And so really it's that the activity patterns in various parts of our brain have. have slowed down, essentially, is what we're seeing.

For the frequency. Right. And what about the amplitude? I don't know the answer about amplitude. Yeah, I really don't. This is why I'm like not an EEG expert. And maybe someone who is can let us know. Because I don't.

But that is deep sleep or slow wave sleep. So we'll stay in that sleep for a period of time. Don't know how long. Depends on you. And then we pop up quickly to stage two. We pass through that pretty quickly, and then we enter our first REM sleep of the night. So deep sleep is one. That's stage – that's the first thing that we encounter?

No, we go stage one, stage two, stage three, which is deep sleep. Oh, okay. We'll stay there for a little while. And then we'll go stage two, REM. Got it. Okay. And in contrast to all these other sleep patterns where waves are getting longer and in REM sleep, your brain EEG pattern looks like you're awake.

Right. It is an awake beta wave, so not even like a calm alpha wave pattern. It's like a beta wave zz-z-z-z-z-a type of pattern. Like we're recording an episode in our sleep. In our sleep. And REM sleep is also characterized by like an more awake type of physiology. Our blood pressure is higher. Our heart rate is higher.

Our respiratory rate is higher compared to non-REM sleep. What about our temperature, our body temp? Oh, that's a good question. I think our body temperature goes up as well, too. Still probably not quite as high as it is, because in general, our body temperature falls with sleep. But it's going to go up compared to deep sleep. Okay. However, we have two weird things happening in REM sleep that we do not see when we're awake.

And that is these rapid horizontal eye movements that happen. And our skeletal muscle activity is essentially atonic. We really do not move. So we move even less than we do in our falling asleep. sleep twitchy. Correct. Yeah. You might still have occasional muscle twitches.

Right. But in general, your skeletal muscles, so like arms and legs are not really moving. I know that this is all foundational so that someday we will talk about sleep disorders in more detail. Yes. But it is making me want to ask 1001 questions. Yeah. About like what happens when sleepwalking. Anyway, we, yeah.

Yeah. Sleepwalking is something you'd see more in the deep sleep. In the deep sleep. Right. Because you're, again, in REM sleep, your muscles are not moving. Right. So in REM sleep, we can see things like sleep paralysis. We think that that's like your...

In REM sleep. Yeah, because you can't move. You're having basically REM sleep muscle activity, but with an awake brain where you actually do wake up. And that's what we think is happening in sleep paralysis. And that's all I'm going to talk about when it comes to dreams. Yeah. FYI. Yeah.

So in a night of sleep, we cycle through both non-REM and REM sleep in a pretty typical pattern. We go from stage one to two to three, that quick pick stop at two and then back up to REM. And that, once we end that REM cycle, is considered one sleep cycle. And in adults, a sleep cycle lasts between like 90 and 100 or so minutes. Okay. So depending on how long you sleep at night, we might go through like four or five or more of these cycles. Okay. I have a question about the REM.

The REM, like deep sleep. So I remember reading that deep sleep happens early on in the night. Correct. Yes. Why? But REM sleep happens throughout. We tend to have more deep sleep early in the night. And then like shorter periods of REM sleep earlier in the night and longer periods of REM sleep later in the night.

And then it's possible that you might not like later in the night drop all the way down to that deep sleep like stage three. N-REM, you might maybe just go to stage two, then up to REM a couple of times in your later sleep cycles. Yes, that is true. Why? I don't know, Erin. It's also really interesting because, like, the amount of deep sleep that you get also correlates to how much sleep you got, say, the night before. So if you are sleep deprived and you're running off of like sleep debt, as they sometimes call it, then your next night of sleep will likely have more of that slow wave or deep sleep, compared to the night before. Recovery sleep, kind of. So in terms of the breakdown of, like, I'm,

the sleep cycle, not even like the number, but just the proportion overall, I'm getting ahead of things. You are, yeah. But I'm like, what proportion of sleep, quote unquote, should be REM, should be deep sleep, should be whatever, stage two. Yeah, it depends on your age and your stage of life and things like that. So babies have like a lot more REM sleep than adults. They've got like over, over 40% REM sleep. Adults, it's usually 20 to 30% is considered typical. And then 20, I think it's like 15 to 20%. It's in my notes from next episode. So we'll get more into it. But yeah, it's usually like 15 to 20% or so is deep sleep. Oh, wow. Or should be deep sleep. Typical deep sleep. Oh my gosh. I mean. And then the rest is that like stage two type of sleep. Yeah. Or bouncing between, you know, stage one and stage two. Sort of like, which is not, I mean, I feel like deep sleep and REM are like the stars of the show. Yeah, they get the cred, even though they're not the majority of your sleep.

Right, which is also important. It is, it is. Yeah. But that is like how your sleep cycle goes throughout the night. And it is going to depend how much time you spend in each one of these from night to night, from person to person. And anybody who has one of those rings or one of those watches that's monitoring your sleep knows that these things are going to vary night to night. Yeah. So speaking of which, I just wanted to.

Good. Yeah. I'm glad you're talking about this. Just wanted to talk about these real quick because there is so much out there right now that's like you need one of these rings to monitor your sleep and you need to be monitoring your sleep. And these are, this one is the best one to be monitoring it, etc. I found a paper that was not sponsored by the manufacturer of any of these devices. Just the one. Just one. There's a lot of other papers that are sponsored by, that were like funded by the manufacturing of these. things who will say like, oh, these are like 75 to 80 percent accurate compared to PSGs. Like these are super, super accurate. Yeah. So I found one paper that was comparing a number of different rings. It wasn't as much looking at the watches that was trying to figure out, could these be as good as PSGs that we do in clinic, which is really important because especially to diagnose a lot

of sleep disorders, like you do need this data. And it's like accessibility and ease and all of these things. Right. So it's like if we could use these clinically, that would be really awesome. Right. And then you're not having to wear all of these tubes that make you sleep poorly. And then you're like, you're a terrible sleeper. You need all these things. And it's like I was just had hooked up to wires all night. Well, and like the ability to be able to do it at home is so, yeah. So there's so much that would be great if these things were really great. The problem is that they're not. And it's not that they're not decent. Yeah. But I will quote here because I think that this quote kind of summarizes. at all. What they said was that even the ones that correlate very strongly with the PSGs, who, like, on average agree with what the PSG readings are, they said that, quote, this agreement masks

substantial individual level inaccuracies, prohibiting their use in clinical sleep medicine as accurate assessment of individual nights, including both nights with exceptionally low or high quality and quantity, is essential for patient care. So like on average, if you're just looking like population wide, sure they decently, they do decently well. But on a night to night basis, there's a lot of variability in how well it's capturing you as an individual. That makes sense. So you can't wake up in the morning and go, how was last night? Right. Oh, yeah. I see what happened. Yes. Yeah, yeah, yeah. Like we did this morning. Like we did. Like we've been doing the last couple of weeks. So, yeah. So that's just what I want to say about those. It's like they're not. I have heard that like, so they're not great at distinguishing between among the stages of sleep. Correct. But they are okay at distinguishing awake and sleep. Yes. So like to get like total duration, they're pretty decent. Right. But again, if you're.

trying to like understand, especially like quality, what we call quality, and like differentiating between the different stages and things like that. Or even if you're trying to, and this paper was specifically more looking at people who have, say, like obstructive sleep apnea or some other kind of sleep disorder where you really want to be able to get that fine detail. They weren't going to be effective for that. And most of the studies funded by the manufacturers are looking at like the general population. So like healthy people without any diagnosed sleep disorders or anything. So it's also a different population level that we're looking at. Right, right.

So yeah, so that's what we know about those devices. Moving on, before I get too deep into like why, what is happening, we know now what our brains are doing as we monitor them. But before we get into the maybe why of it, I want to touch base really quickly on kind of how we sleep. Like what is driving our sleep. Okay. Sleep drive. Sleep drive. That's the answer.

We did talk a little bit about this in our circadian rhythm episode. Yes. Because our circadian rhythm is one of the drivers of our sleep. So as a recap, so that you don't have to listen to that episode again, there's a collection of cells deep in like the center front of our brain behind our eyes deep in our brain. That's called the superchaismatic nucleus that is the clock of our brain. The SCN. The SCN. The SCN.

Yep. And it basically generates this close to 24-hour rhythm. All of our cells. do this to one degree or another. Which is really cool. It's so cool. But this is like the master clock that keeps all of our body functions in sync, mostly using signals from light and dark from the sun, right? And this circadian clock of ours drives things like hormone production, among many other things that help to promote sleep and awake at the right times of day and night for us as diurnal creatures. But our brain also has other mechanisms aside from just the circadian

clock that helped to promote both sleep and wakefulness or what's called arousal in the literature. Yeah. And it's mostly parts of our brain stem. Right. And our brain stem is like the deep back part of our brain that connects to our spinal cord. The stem. The stem. And parts of our brain stem release a whole bunch of neurotransmitters that are involved mostly in promoting wakefulness.

In wakefulness. Right. So promoting us being awake and active during the day. These are things like histamine, dopamine, noradrenaline, serotonin, all of these types of things that act in other parts of our brain to be like, go do things, be awake. Yeah. That's what I imagine they're saying. And we think that sleep ends up happening from a couple things changing in our brain. One is that there's other parts of our brain closer towards the front of it that send signals to start to inhibit.

those awake signals. So like at some point in the day, other parts of our brain will send signals and be like, hey, listen, histamine, chill out a little bit. You've done enough today. So they'll start to inhibit the release of histamine or orexin or other signals that are saying be awake, be awake, right? And so, okay. And then the other part, I'll wait. The other part is that, and this I think is really interesting. We also, during the day, like just with our normal metabolism, how our brain is functioning all day long, we are making a bunch of stuff. And some of those things we think act as like sleepy substances, where as they build up in our brains throughout the day, as the concentration of this substance or these substances really accumulate in our body tissues, including our brain, they increase sleep pressure. Yeah.

One of the classic ones of these is adenosine. And adenosine, we produce just as a byproduct of metabolism. But as we produce that and it builds up in our brain, it makes us more sleepy. Caffeine, which we talked about. I was just about to ask about caffeine. Caffeine inhibits the adenicene receptors. So it tricks our brain into thinking that we don't have a buildup of this sleepy substance. Right.

When we actually do. And that's how it works to keep us awake. What about like morning, though, because if we're starting, are we starting the day fresh, things cleared out. Tell me again about caffeine. It's been way too long since that episode. So caffeine basically, like we, because we're making adenosine just like from metabolism, we break down ATP that we make adenosine. So throughout the day, it's just going to build up, build up, build up, build up. And it's going to bind to these receptors that do inhibition stuff that's like, go to sleep, go to sleep. Caffeine binds to those receptors. So it doesn't

matter how much adenosine you have. There's nothing for them to bind to. Got it. Because caffeine is blocking them. And so it tricks our brain into being like, there's no adenis here. I don't need to go to sleep. And it is quite effective. Like there's so many studies on like caffeine helping to alleviate sleepiness. I think that like what is so interesting, okay, speaking for myself. Yeah. I feel like when, if I am sleepy during the day or in the evening or whatever, just at any point in the day, I'm like I didn't get good sleep.

I'm really tired. And I feel like I expect that if to get really good sleep or getting really good sleep, makes me have no sleep drive. And that's the ideal. Oh, that's so interesting. You know what I mean? Yeah, yeah. Like you shouldn't ever be sleepy if you're getting asleep. I shouldn't be sleepy until it's right before bed. And now I just lay it back, close my eyes, and I'm out. And I'm like, that would be great. That would be great. But like, it's not realistic. It's not realistic. So sleep drive is so important is what I'm saying. Well, and it's also, it's interesting too, because there is this, there's like a buildup of our sleep drive versus our circadian rhythm. And so

sometimes those kind of cross paths are a weird time where we can get more sleepy than we expect in like the middle afternoon or something like that. Yeah. And so that's part of why we might feel sleepy at times of day where we think, like, I don't understand why I feel sleepy right now. Right. And it's just maybe because things are, you know, it hasn't overlapped in exactly the right way today kind of a thing. But it doesn't necessarily mean that your sleep was terrible the night before. Right. So it is really interesting. And I'm probably not doing it justice. But there's obviously a lot. And it's not just. adenosine, right? There's a lot of other substances that we think are involved in this. So there's a lot that goes into when and how we're sleepy. And some of it too is genetics. So we know that some of our sleep drive and a lot of our circadian rhythm, like whether we are a night owl or a morning bird. Morning lark. Morning lark. Like some of that is genetics. There's also some genetic markers that we think are associated with like very short sleep where people sleep very little but are totally. fine. Oh, yeah. Right? And our need for and our pattern of sleep also changes drastically over our lifetime. It does. My favorite example of this are tiny babies. Oh, yeah. Because even though fetuses sleep when they are still in utero, they do that like mostly in sync with the human who's housing them. But once a baby is born, they do not have a well-defined circadian clock. It's a mess. It is a disaster.

Yeah. Their circadian clock is much less than 24 hours. And their sleep pattern, like I said, a sleep cycle is like 90 minutes. It's much shorter in babies. So they're also cycling through a whole cycle of sleep in much less time. Yep. And their sleep pattern is totally random. Yeah. Completely random. And they'll sleep up to like 16 hours a day. Like a dog. And not in any pattern that's compatible with adult sleep pattern. And it's not until the first like six to 12 months of life that they start to consolidate their sleep into these 24-hour patterns. And because I fell into what is very common these days of being very obsessive about my infant sleep when my first child was born, I have data that you can check out if you're watching the YouTube of my kid's sleep pattern when he was an infant. And you can see that it is literally all over the place.

I don't think anyone listening is surprised that you collected data for how many months of your first kids' life. So many months. So many. I mean, the first probably 15 months. And that's just one aspect of it. I had all of the data. I remember, too. There was so much.

Yeah. Yeah. The second one I didn't do any of that. But you can then see that by 11 or 12 months, even though sleep wasn't great, you can see this 24-hour pattern emerge where there's like a nap in the middle of the day or maybe two naps. But then the majority of sleep is happening over the night. nighttime period. And that is because that's how long it really takes for infants to develop this 24-hour pattern, which I think is just so interesting. And then the amount of sleep that we need over our lifetime changes too. Kids need a lot more sleep. Teenagers we talked about in our circadian rhythm episode do actually have a shift in their circadian rhythm towards night owl tendencies. Yeah. And so they tend to sleep later and wake up later. And that can put them out of sync with our modern society. And then as adults, especially older adults, a lot of times we don't need quite as much sleep. So the amount of sleep that we actually need varies.

So why do we need this much sleep? Like, why? I'm asking you, but I'm not. It's a rhetorical question that I'm going to try an answer. We're asking the room? We're asking, does anybody know? Does anyone know? We still, like, we still don't really know.

We don't. exactly what our brains are doing in terms of the function of our sleep. Like we know what happens, we know there are bad things that happen when we don't get enough sleep. Correct. And that's what guides a lot of our assumptions about why sleep is important. Yes. And like what our brains are really like doing during sleep. Yeah. So we do see and one of the, one of the hypotheses, I'll kind of walk through the biggest ones. One of the hypotheses is that it is kind of energy conservation during sleep. And that is because we do see a relative decrease. in metabolism during sleep. However. Not really.

Not really. Yeah. Yeah. Especially if you're looking at total body metabolism. Like during REM sleep, our metabolism is essentially the same as when we're awake. Our brain metabolism does decrease substantially, especially during non-REM sleep. But again, that's only a portion of our total sleep. Right.

And it's nothing like our sleep is nothing like hibernation or torpor or something where we're truly decreasing metabolism. Yeah. So that's clearly not the whole story. Could be part of it. There is a lot of evidence that we see changes in things like gene expression. So like certain things turn on and certain things turn off when we're asleep that only happens when we're asleep. So we think that must be important.

But why exactly we don't know? I mean, yeah. Because I talked about these like sleepy substances and things like that, we do think that there's sort of like a clean out of the buildup of these neurotransmitters that happens during the day. Detox. Yeah, brain detox. I hate that word. It's not accurate. But we do see like an increase of cerebral spinal fluid flow during sleep and things like that. Washes over the brain is how I've just heard it described. Yeah. Getting rid of all these neurotransmitters and replenishing others as well. It's very, like, it's a very satisfying image to think about. Just like, whoosh, just like a gentle washing of the brain.

That's what you're hearing as you fall asleep. Anyways. Great white noise. How much of is that the function of sleep? Maybe. Yeah. And then one of the biggest hypotheses is that sleep is required for consolidation of our memory. Memory consolidation. Why do we have to whisper? I don't know.

And we do know there's something called sleep-dependent memory processing where there's done a bunch of studies where if you give humans or animals a task and then deprive them of sleep, they never really learn that task to the same degree that they would if you let them sleep after it. But even this, the data is a little, it's a little bit controversial still. That like, is this truly the function of sleep? Especially because it's like we're trying to compare human brains to like, well, we don't have like lots of animals sleep that don't, we don't know anything about their memory. Oh, you'll get to it. You'll get to it with those eyebrows. Sorry. I love it.

But, but yeah, that's, that is one of the kind of big hypotheses that like sleep really is essential for our memory. I what can okay but like I don't understand why that's controversial only in that if it's overstated that this is the function that's what it is okay that's what it is it's that like we know that it's essential it is a function it is a function but I think I think that it's just that people are so obsessed with this idea that there is like a reason for things nah it's just sorry but that's true right like we're not going to get to oh oh like right this like this like this Like, enlightening will not arrive. It's a bunch of different things happen when we sleep.

I know. It's not as satisfying as we found it. Here is the answer. The reason for sleep. Right. The singular function of sleep. Yeah. That's ridiculous.

We sleep for a bunch of different reasons. And as we'll see in next episode, if we don't, there's a problem. A lot of different things happen. A bunch of problems. Beyond memory. But that's for next episode. So, Aaron, what I'd like to know from you, please, is like, obviously I know my dog sleeps. My cat, all he does is sleep.

Yeah. Do all animals sleep? Oh, do they? Do they? Do they? I'll tell you. Okay. Anyone who works long hours knows the routine.

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No code, no gimmicks. Just real fresh food. In 1971, renowned sleep research. Alan Rekshaufen wrote that, quote, if sleep does not serve an absolute vital function, then it is the biggest mistake the evolutionary process has ever made, end quote. I love that. Right? Yeah. Okay, so let's break that statement down.

First, why would sleep be a mistake? It leaves us vulnerable to predators and bugs and parasites transmitted by bugs. And it takes up precious time that we could be using to do something else, like for. or mate or socialize or read a book or do your taxes or play with your kids or exercise or cook a nice meal or work more hours at the office. So true. So many things. I know that many tech bros view sleep as a mistake. Oh, yeah.

You don't even need it. You don't need it. You could just wake up at 3 a.m. Sorry. Wow. I think something just happened there. Something I flipped. I liked it.

But, I mean, that aside, though, I do think that most of us have at one point in our lives wish that we didn't have. to sleep as much as we did. Because, like, we could get so much more done. I know that I have wished that. Like, gosh, I could just, if I didn't have to sleep as much, I could do things I wanted to do. It is undeniable that sleep is costly. But it would only be a mistake if we didn't get anything out of it. Right. Okay. So second, does sleep serve a vital function? From what you just told us, Erin, it serves multiple vital functions. We may not know precisely how sleep helps us and the pathways that it works along. But we know from experimental and observational research that sleep deprivation is harmful and that when we lose out on sleep, our body compensates

by increasing sleep. There's like sleep homeostasis kind of. Totally. Okay. So now why would sleep be the biggest mistake that the evolutionary process ever made? Because sleep is ubiquitous across the animal kingdom. Love this. At this point, in our understanding of sleep, it would be much harder to prove that an animal doesn't sleep, then determine that it does. Okay. Even cavefish species like the Mexican blind cavefish, which has lost eyes and pigmentation and much of their circadian rhythm patterns. Because they're in the complete black darkness.

Complete darkness. Yeah. They still retain some sleep. Wow. It's reduced as much as like 80%. But still, there are indications of sleep. What does indications of sleep mean? Especially in a fish.

I know. Okay. So for us to recognize and measure sleep. in non-human animals, we have to step outside of our human box. Right. So for one, there's a logistical challenge of recording an EEG on a Mexican blind cave fish. Like that's, can you do it? Can you do it?

I don't know. It's pretty difficult, challenging. Sure. And then for two, we want to be able to observe sleep in more natural settings. And for three, it's important to step back from our tendency to make humans like the ideal, the norm, right? Like, oh, if you don't sleep like a human, are you sleeping? Are you sleeping at all? So we can measure sleep electrophysiologically using EEGs, and we have done that for a number of animal species.

And we can measure it behaviorally. So researchers use five criteria to say that an animal sleeps. Number one, and it's very similar, like you mentioned some of these. Number one, prolonged behavioral quiescence. Basically, stop doing stuff. You're not doing stuff. You're not doing it. Okay.

Number two, reversible upon stimulation, unlike, like you said, torpor or a coma. Okay. Three, a species-specific posture. It's not just humans, like laying down or tucking your antenna away. And then I have a picture of my dog in bagel formation, which is a very... He's one of his favorites. Number four, increased arousal threshold.

So you need a louder or, like, more substantial stimulus, like a noise to get you to respond that if you're awake. Decreased response to stimulation. Same idea. You may be, like, whispering like, hey, wake up now. Could you please roll over? Right. Might not do it. You're snoring. So like your senses are dulled. Right.

And number five, rebound. After being sleep deprived, you sleep more. And so these are the things that we can use to say that animal is sleeping. Okay. Because it's doing all these things. Okay. And so using these criteria, we can describe and define sleep in a huge array of species like pond snails, octopus, cuddlefish, which may even exhibit REM sleep. Sorry. Snails. Snails. Oh, it gets even more extreme. Lobsters, mice, armadillos, flies. And funnily enough, whether animals truly sleep is kind of a more recent question.

Ancient scholars like Aristotle fully believed that animals sleep. You're like, of course. And there's an adorable quote I'm going to read to you from an 1865 book called Yearbook of Facts. Quote, an insect composes itself to sleep with its antenna folded. Some of the beetles adjust them to their breast. the butterfly seeks some particular aspect of a tree and folds vertically its wings, throws back the antennae, and remains motionless and insensible to all external circumstances. When caterpillars, which are insatiable feeders, are observed resting immovable with their heads down, they are asleep.

I love it. Isn't that cute? They're like, we don't need an EEG, bro. Just look at the bugs. Look at their little antennae. They're all feet, boop. Yeah. And you can hear them quietly snoring.

Oh, yeah. So sweet. So cute. But it's still helpful to have these specific standards for what counts the sleep because we can then also try to trace the genetic basis and neurological pathways of sleep. Okay. Okay. So for example, C. Elegance, the research world's favorite worm contains a mere 302 neurons. Wow.

Compared to an adult fruit fly, which has 250,000. Wow. Okay. So, right? And since C. Elegance sleeps, we can map out the neural pathway of sleep, at least in that critter because there are so few neurons. Wow, that's really cool. Okay, really cool, but what's even more amazing is that this isn't the quote unquote like simplest creature to sleep. Okay. Using those behavioral criteria, researchers concluded that the upside down jellyfish in the genus

Cassiopeia sleep. Jellyfish. Jellyfish. Unlike sea elegans, these jellyfish, they don't have a central nervous system, just a nerve net, like rings of neurons. And so, some of, Scientists observed that when the jellyfish is active, their nerve net contracts and causes pulsing behavior that lets them feed and get nutrients. But at night, the pulsing behavior reduces and they become less responsive to external stimuli. And then when you disrupt their resting time, like you keep splashing them with water or waves or whatever, they will pulse even less the next day indicative of sleep rebound. Oh, my gosh. Right? I love it.

Isn't that wild? Yes. And so this means that sleep likely evolved before a central nervous system. That is so interesting. Huge, huge. Especially the context of memory and stuff like that. Well, I mean, okay, yeah. Okay.

Yeah, yeah, yeah. But like, this is an ancient and widespread thing. And so given how ancient and widespread it is, it doesn't really seem like sleep is a mistake. No. And as far as, I mean, sleep doesn't get fossilized because it's a behavior. But as far as we can tell, no species has entirely lost the capacity for sleep, meaning that it is still so vital to continued existence. Yeah. Yeah.

Sleep disturbances or a lack of sleep can have profound effects on health and overall performance, vulnerability to infections, attentiveness, reaction time, memory formation. Mollusks that have been deprived of sleep cannot form new memories. So like it goes deep. How do you measure a mollusk's memory? I don't know. I didn't go that deep. Now I need to. Oh, I will find the paper for you and send it your right.

And then there are a few gruesome experiments where rats that were completely deprived of sleep for like a long period of time died. Oh my gosh. They died. Yeah. The world record for no sleep, sleep deprivation in a human is 11 days. I heard that. 264 hours held by a San Diego teenager named Randy Gardner, who in 1965 played basketball throughout the night. to stay awake. But apparently, like, I think in, I don't know how they determined this,

but they were discovering that he was taking, like, micro-naps. Of course he was. And so was it truly 264 hours? You know, yeah. I mean, his brain was falling asleep. He just did not know it. He didn't know it. And no one else knew that he was. Yeah. But in any case, that's like a do not try that at home situation. No. Mm-hmm. Yeah. So even though we all sleep in some capacity, we don't all sleep the same. Elephants sleep about half the time that humans do, four hours compared to our eight, which is really more like six to seven. Brown bats sleep about 19 hours a day, similar to armadillos. Koalas sleep even longer, 20 to 22 hours.

Meanwhile, donkeys sleep about three hours. Cats sleep 12 and a half hours a day, which seems like an underestimate. Absolutely an underestimate. Goats, 5.3 on average. Guinea pigs, 9.4. I mean, just to show you, it's all over the map. Yeah. And really many of these sleep duration estimates, we do have to take with a grain of salt because we're measuring sleep in the lab. And so there tends to be a bias towards like longer sleep because they're like, I don't have to worry about predators.

Yeah. I've got food here. Yeah. I've got water. I'm chilling. Might as well take a nap. Might as well just nap all the time. But even still, we do have this huge variation in how much sleep different species need.

But duration is just one component of sleep as we talked about. There's also whether you sleep in one big chunk or multiple times throughout the day or throughout the night. Like monophasic sleep is one big chunk, which is what humans usually do, big asterisk on that. Bifasic sleep, which is two chunks, which is what humans maybe used to do, asterisk on that. Or polyphasic sleep, like multiple chunks like my dog who sleeps constantly. The cat. Yeah. Whether you tend to sleep during the nighttime or during the day is another.

big component of this, like a red-tailed hawk versus a barn owl, for instance, if we're talking birds. And not all owls are nocturnal. A lot are crepuscular. So it took me a while to find one that I was like, is a barnal? I love corpuscular. Yeah, it's very good. There's also whether or not you have REM sleep. So generally speaking, mammals and birds are the only animals with REM sleep, except for maybe the cuttlefish. That's so weird. I know, I know. And not all mammals have REM sleep. Really? Yeah.

Okay. So side note, REM sleep evolved after non-REM sleep as far as we can tell. And it's thought to have emerged in mammals and birds independently. Oh, that's interesting. Yeah. Which indicates that it might be really important for cognitive activities or warm bloodedness, like, aka endothermia. Oh, interesting. Okay.

Cuddlefish, I don't know. Who knows? Cuddlefish are weird ones. They are. I love them. They're so cute. But if you do have REM sleep, you know how long are your sleep cycles between REM and non-REM? So, for instance, you said human is 90 minutes or so.

The chinchilla is six minutes. Six minutes? They go through a whole sleep cycle in six minutes. Oh, my gosh. They're like, done. And up. There's also whether you sleep with all of your brain or half of it. That's, I think, one of my favorite facts I learned in a children's book accidentally before we were.

It was called sleep. And that is where I learned about unihemispheric sleep. Ne hemispheric sleep. Yep. It's a real thing sleeping with one eye open. It was a real thing. Aquatic mammals like whales, dolphins, and seals, as well as some bird species, especially those that are undergoing like long migrations.

Oh, like the, what's the one that never touches the land for like? Albatross. Yeah. Is that it? Oh, gosh. I don't know. Ooh. Sorry.

Sorry ornithologists. But yeah, unihemispheric sleep. And we've got a little thing here that shows like the EEG of what it looks like when you have like one part of the brain. So it's like part of your brain is on and part of your brain is off. Yeah. Oh my gosh. That's so interesting. It's amazing.

In the right and the left. Wow. And what's even weirder about this is that whales, dolphins, and porpoises who do this unihemispheric sleep, they don't seem to have REM sleep. Or if they do, it's not in a form that we recognize. Oh, that's so interesting. Yeah. So it's like, did they lose REM sleep? Right. When they went back to the oceans.

Right. I don't know. I don't know. Okay, but why do aquatic mammals sleep with just one half of their brain? I mean. There's a few different possible reasons, right? So one is because they need to breathe. Right. And so they need to be able to come up and have that more active thing. Another is to reduce heat loss, apparently. It's supposed to help with like thermogeneration. Interesting. And a third is to be on the lookout for predators. And a fourth is to stay close to one another because you can really drift apart because of the water. If you're just drifting. Yeah. Yeah.

Like, have you seen those amazing videos of sperm whales all sleeping vertical in like a forest of sperm whales? Yeah. Sea otters, of course, hold hands when they sleep, which is just, oh, it's so cute. You know how I feel about sea whales. Yep. And unlike terrestrial mammals, newborn dolphins and orca whales are on the move from the first moment. And unlike human babies, which sleep, like you said, so much, so randomly all over the place. these baby dolphins and orca whales are continuously active for like four weeks.

Like no sleep. They don't sleep at all? No sleep, along with mom, yeah. Fascinating. Yep, yep. And it's only after those weeks that sleep gradually returns. And this might be because it's just a really vulnerable time for those babies. They can't afford it.

Yeah. Huh. And even when sleeping, these aquatic mammals are moving quite a bit. So dolphins make counterclockwise circles, regardless of which half of the brain is sleeping. Counterclockwise circles? Mm-hmm. Why? Great question.

I do not know. I do not know. Counter-clockwise circles, regardless of which part of their brain is sleeping. Yeah. That is so interesting. I know. Do they sleep, sorry, I'm going to ask more details. Do they sleep, like, obviously it's one half at a time, but is it like consolidated, like at night time?

They're going to like, okay, 40 minutes on this half and then 40 minutes on this half or whatever? That's a good question. I don't know. I don't know. Okay, I'm so curious. I can say there's a really great paper. that I have, I'll shout out at the end. That has like a lot more information on this.

And even like pictures of dolphins sleeping at the bottom of like enclosures and whales and stuff like that. Yeah. Yeah. I love it. Okay, fur seals, listen to this description. It's very cute. When fur seals sleep in water, they usually float on their sides, holding one front and two hind flippers in the air. The front flipper in the water constantly paddles.

Isn't that cute? And the rest are just like up in the air. One eye is open and the other is closed. Wow. Fur seals also are one of these creatures that spend some time on land. And guess what their sleep is like on land? Like a dog. Like any other terrestrial mammal.

But when they're in the water, they're unihemispheric? They're unihemispheric sleep. What? And when they're on land, both eyes are closed and they cycle through REM and non-REM. But when they're in the water, they don't. Nope. Oh, that is so interesting. I know.

I know. Oh, wow. It makes me, like, I never, I mean, I have, like, thought about sleep, mostly in, like, a very selfish, like, am I sleeping enough? Oh, my gosh, my sleep kind of a way. But this is maybe more interested in REM sleep than, like, ever. Yeah. Yeah, same. Yeah. I did not know any of that. Yep. Me either. How interesting. It's amazing. Yeah. Okay, so that, but the fact that sleep comes in all shapes and sizes across the animal kingdom and is even variable, like you said, within. in an individual's life, it shows us that sleep is not random, right? How a species sleeps is the outcome of millennia of adaptations, nor is sleep rigid, right? There may be times when we need to go with less sleep than we, you know, ideally like to have migration, midterms, having a newborn. Migration or midterms. Equal. I love it. Socializing stress. You know, there's a lot of different reasons that might affect our sleep duration. And we can do that. We can sleep with, we can have less sleep than we'd like for a limited, like a certain amount of time. And then our bodies know to

recover from that sleep dead. So if the way that we sleep is not random, what determines how species sleep? Why is a chinchilla have a six minute? That I can't answer that. I don't know about that. But it is a great question overall. And we don't exactly know. And so there are some general patterns that I'll take you through, but to every pattern, there's an exception. So if we take all that we know about sleep in animals and we look for similarities after controlling for how related they are, a few strong drivers emerge. Predation, metabolism, immune function, gestation length, brain mass, and neuroanatomical regions like the amygdala.

So these are all the parts of things that are contributing to how long and how an animal is sleeping? Um, mostly, I would say like how long and the polyphasic versus... Got it. Yeah. Yeah. Monophasic, et cetera. Okay. And I don't, like, there are some aspects of REM and non-REM, but like that seems, I mean,

it's just like it's really difficult to draw any sort of, like, parallels. Well, and I feel like it's so interesting because one of the books that I read, it was like how you define sleep in animals, like with this behavioral thing, then also affects how we think about and look at the why of sleep, right? If you define it in slightly different ways, then you might come to a different conclusion as to the function of sleep. It's a little bit of a guiding hypothesis kind of a thing. Yeah. And you're like, well, if REM is really, the questions that you're asking are driving that, yeah, how you're looking for data. If you're only counting REM sleep as sleep, then your conclusions are going to be totally different versus if you. Or is like, is more REM sleep

better? Right. Yeah. It's so interesting. It's really interesting. Okay. So let's talk about some of these, some of these different factors. When you're sleeping, you are in a vulnerable state. Yeah. Your senses are dulled, so you can't hear that twig snap and you're laying there motionless looking like a nice, tasty snack for that tiger that's, you know, just caught your scent and creeping away from the, creeping towards you, actually. Creeping away would be great. But so you might be a little better off if you had like a burrow or a tree hole to nestle into, but if you just plop down in an exposed area, you're playing a very risky, very risky game. Yeah. And so to lower that risk, you might sleep less. Okay. And that is what we tend to see.

Prey species or species that sleep in more vulnerable locations, like on the ground as opposed to like in the tree, they tend to have shorter sleep durations. Interesting. And in one experiment, rats that encountered a predator got less sleep afterwards, both REM and non-RE. They were like, on edge. You're just on edge. You've got to be like, you're in lighter sleep, I guess. Yeah. Some researchers actually suggest that light sleepers and people with insomnia might have those predator or biting insect vigilance mechanisms on overdrive. Oh, that's interesting. So if you're like someone who was really hard time getting into like your wake at the drop of like just a little rustle. Yeah. Maybe that's fine. It's just evolution. It's adaptive. Yeah. Not anymore though. You won't get eaten. It once was adaptive. Yeah. And so sleeping in larger groups, like larger social groups, that might have. help counteract some of the vulnerability to predators while you're sleeping. But then there's also the tradeoff of social disturbances and parasite transmission because you're just like all together.

Yeah. But so it's like sleep alone and be easier prey or sleep in a group and get less sleep, not necessarily worse, but like, and maybe it's more efficient sleep, but it does seem like sometimes it's shorter sleep. Okay. Interesting. Or you could sleep while your predators also sleep. Okay. And predators tend to get more sleep on average. like, it's fine, bro. Right. Like, I'm chilling. And metabolism might also play a role in that when it comes to predators versus prey because herbivores, which are more generally, more often prey, they need to eat more frequently because they have faster metabolisms or like their food is less calorically dense. And so they have to spend a good chunk of their time foraging, especially if their food is,

their preferred food is dispersed across the landscape. Like, oh, I have to get fruit trees and I have to go far to find them. And so you're like, your commute is long. Got it. And you're like, I got to get back to my little burrow. Yes. Yeah. Animals with faster metabolisms relative to body size also sleep less. And smaller animals tend to sleep throughout the day. They're polyphasic sleepers. Interesting. Immune function. So we all know that not getting enough sleep leaves us more vulnerable to infections. And some studies suggest that species with longer sleep durations have higher white blood cell counts and are less likely to be parasitized. Interesting.

I think this is a very big generality. Exactly. Yeah. And finally, oh, there's also gestation length. So longer gestations are associated with shorter sleep. So that's why like elephants, you said, get only four hours. Yeah. That's really weird, though.

Why? Maybe it's just a correlation. Yeah. Could be. They're all down to metabolites. I don't know. I mean, that's like a lot. This is like a very much an I don't know episode.

Yeah, yeah, yeah. How interesting, though. And then finally, bigger brains per body size. Per body size, yeah. In proportion of body size equals a bigger chunk of time spent in REM sleep. In REM sleep specifically. Okay. But again, this is all messy.

So there was a cool paper, though, I read that showed how vastly different sleep could be for two closely related species and how similar it could be for distantly related species. So, for instance, the domestic cat and its relative the genet, a cat, gets around 12 and a half hours of sleep, like I said, a day with 3.2 hours REM. And it gets about half that 6.3 hours with 1.3 hours REM. And those are like closely related species. Yeah. Yeah. And is that just like because domestic cats are just chilling. They might be just domestic cats. Yeah. But then there's also a golden mantled ground squirrel. Okay. And a day goo. Again, closely related. The squirrel's 15.9 hours of sleep with three and REM.

And 7.7 for the day goo with point. nine in REM. How interesting. So it's not just about like domestication, although I'm assuming that is a decent part of it for the cat. Yeah. Then take a guinea pig and a baboon, not closely related, but their sleep architecture is, or they're not architecture. Their sleep like duration and REM proportion is very similar. They each get about 9.4 hours of sleep and one of REM. That's so interesting. And in case you were wondering for humans, humans, we humans get the same amount of sleep as an Eastern American mole. We get seven to eight hours and we both have about two hours sleep REM.

Oh my gosh. Interesting. Isn't that funny? Yeah. It's really funny. But among primates, though, humans are the exception. We are at the very extreme end of sleep duration with some of the shortest sleeps of all primate species. Oh, interesting.

The shortest sleep of all primates. Yeah. Huh. Yeah. On the other end of the spectrum are owl or night monkeys. owl monkeys or night monkeys, which sleep about 17 hours, but they get the same amount of REM sleep as humans. That is so interesting. Yeah. Oh, I do want to look so much more into REM now. I know. Right? What is up with that? I know. What is up with that? Sleep. What is up with that?

Yeah. Based on our human body size, brain size, body mass, predation, risk, foraging needs, sexual selection dynamics, diet, and what we know, about other primates. Like, researchers have kind of compiled this model to be like, how should we expect humans to sleep based on what we know about all other primates? And that comes out to nine and a half hours a night. That's how much we should be getting based on these. That is not. But we, on average, it's six to seven hours for humans.

And this does not mean that we should all be sleeping nine and a half hours. It's just what the model predicts based on other primates. So it shows that we are weirdos. Yes. Because evidence, I mean, evidence points to. six to seven is normal sleep or six to eight is normal sleep in humans. And it might just be that we somehow squeezed our sleep into a shorter duration like we're more efficient or intense sleepers. Interesting. Other great apes sleep a bit more than humans, but less than like night

monkeys. And like chimpanzees get about 10 hours with similar REM as humans. And gorilla's sleep about 12. Orangetans sleep about nine, slightly less than humans. But when it comes to humans, and other great apes, we do share other characteristics. So we have this high proportion of REM sleep, and we have nesting behavior, which I just think is adorable. Many of the over 400 primates species that exist, sleep in trees, whether that's in tree holes or on bare branches, just like balancing up there. Even if they spend much of their waking time on the ground, they will sleep up in the trees. And this might help with like predator avoidance probably. Other species might sleep individually or they might sleep in groups or they might sleep on bare ground or on cliffs like baboons, sleep on cliffs and on bare grounds.

And some build nests mostly in trees. In fact, all great apes build nests, all of them. I did not know that. Yeah, me either. Yeah. And so this suggests that the behavior emerged about 14 to 18 million years ago. Interesting. They are built individually.

they take between one to seven minutes to construct, and they're usually built every night with occasional reuse. So they just make their own new nest every night? They make their own new nest, yeah, with a bunch of different materials. There is so much more about nest building and I have a paper too. And so why did we start to build nests? It's thought that as body size got bigger in these great ape species, they probably helped to make sleeping more comfortable overall and to protect against damage if you fell out of a tree than like your body. was just like, you got a little cushion there? You got some cushion. So like, yeah, it makes it

more comfortable. And so this also helped to avoid predation. So research suggests that chimpanzees build nests higher and in closer proximity to each other in places when there are more predators. And also thermoregulation. So you can decide, okay, is your nest placement going to be higher up or lower down? Do I need more insulation? Do I need to pack in some more leaves? Is it a cold night? Is it a chilly night? You know, like I want to get a breeze up in there. Yeah. And finally, nests may also help to deter biting insects. So researchers found that some orangutans built their nests near naturally mosquito repellent tree species when mosquitoes were abundant. I love this so much. I know. I mean, if you think about, nest building is an incredible behavior and there are some researchers that categorize it under tool use, which would make it the most pervasive among great apes. Wow. Yeah. It's environmental

problem solving when it comes down to it. Did great apes build nests because they were smart? Or did building nests help evolve smartness, evolve enhanced cognition? Such an interesting question. Yeah, chicken or egg? I don't know. I don't know. So like I mentioned, most of these nests are in trees, but humans have long slept on the ground, despite the ground making us more vulnerable to predators. And some researchers have suggested that this ground sleeping, with its more stable surface, would have enabled, even deeper sleep, which then allowed us to sleep more intensely. Because we're not going to fall out of a tree.

Right. We don't have to have that increased vigilance as much. And so that's what maybe allowed us to shorten our sleep duration. And then once humans developed the ability to control fire, that would have cut down on the risk of predators and biting insects and it would have increased our thermoregulation capacities while allowing us longer hours to socialize into the night, exchanging ideas and storytelling, maybe even promoting the evolution of language. And so in short, sleeping on the ground helped to make us become human. Oh, my gosh. Right?

Once we made it there on the ground, what happened then? Did we just stick to our six to eight hours a night with no breaks? Or is the story slightly more complicated than that? I'm leaving you on a cliffhanger, so you'll have to tune in next next. week to find out. But I hope you liked this little hodgepodge of a tour through animal kingdom sleep. I loved it. It's not a mistake. No. Sleep is not a mistake. Sleep is not an evolutionary mistake. I think that was mostly said tongue-in-shake. I totally sounded like it. Yeah, yeah, yeah. Oh, that was really fun, and it made me really excited to find out what humans did with our sleep.

I can't wait to tell you. Because obviously, I mean, I don't sleep on the floor. I don't sleep on the floor. I have slept on floors. Many times. Yeah. Or on... Airport benches. It's horrible. So I can't wait to hear what we did with sleep. Well, in the meantime, there's a lot more reading that you can do. Shall we tell the people where to read? Let us tell them. I have many sources, many sources for this one. I can't wait. Because I just kept going down rabbit holes. I loved them all. We didn't even talk about rabbits.

We didn't. But I actually did have a section where I went through each of the animals on my PJs to be like, You can sleep this amount. Possum sleep this amount. My favorite animal, besides the Tasmanian devil, squirrels, etc. And I cut it because I was like, it's way too many animals. Okay. You can find more information. There's a book about a lot of animal sleep called Evolution of Sleep, Phylogenetic and Functional Perspectives by McNamara at All from 2010. Then there's a great paper I loved from 2008 called Unerthing the Phylogenetic Routes of Sleep by Alata and Siegel. from 2008. I think I already said 2008 multiple times. By Lyman at at all from 2008 as well, Cetation Sleep, an unusual form of mammalian sleep. And finally, by

Fruth and Stewart Sleep and Nesting Behavior in Primates, a review. Love it. Great stuff. I had most of this information that I shared came from a book from 2012 that was called Sleep, a very short introduction from Oxford University

Press. It is It covers all the bases. But I also enjoyed a paper from physiological reviews from also 2012. That's weird. That was called Control of Sleep and Wakefulness by Brown at all. And then the paper that was not funded by industry about the wearable finger tracker ring sleep measures was from scientific reports published this year, 2025. Trying so hard not to say any brand names. I know.

You know the ones. I guess 2025 is last year by the time this. comes out. Doesn't matter. Anyways, it was by Herberger at all, and it was titled Performance of Wearable Finger Ring Trackers for Diagnostic Sleep Measurement in the Clinical Context. But I have other ones as well to you and so many more papers, so you can read them all and find them all on our website. This podcast will kill you.com. We will post them all there. Stephen Ray Morris. Thank you again. What an absolute delight. It was really, thank you so much for sharing your story. Also, sorry that you've had sleep

paralysis. I know. We're not saying your sleep paralysis. This was a delight. No. Hearing your voice. It's always a delight. It was wonderful. Thank you. And thank you also to Bloodmobile

for providing the music for this episode and all of our episodes. Thank you, thank you. Thank you to everyone here at exactly right. Studios, as well as everyone who helps make this podcast possible. Yes. Including you listeners.

Thank you for listening. Patrons. Thank you for patroning. Your patronage. Your patronage. That feels. Yeah. Thank you for everything.

Thank you. Wow. Until next time, wash your hands. You feel the animals? This is Bethany Frankel from Just Be with Bethany Frankel. Listen, I have a bone to pick with these dog food brands calling themselves fresh, natural, healthy. Sounds great, but a lot of these quote-unquote fresh dog foods in your fridge are not even 100% human grade, which is why feed your babies just food for dogs.

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