Deep Time and Evolutionary History

You're listening to the Skeptic's Guide to the Universe. Your esc ape to real ity . Hello and welcome to the Skeptic's Guide to the Universe. Today is Thursday, May 21st , 2026, and this is your host, Steven Novella. Joining me this week are Bob Novella. Hey everybody. Kara Santa Maria. Howdy. Jay Novella. Hey guys. And Evan Bernstein. Good afternoon, everyone. Is everybody set to go to Australia , New Zealand? Got all your things that you need? Well I got reminders about the things I still need. Right. How is it almost already June? Right. And you know it's after June. July. July, and that's when we're going. Like holy crap. Steve, you know that's a loaded question for me because I have an incredible you know, like my I'm not just thinking like baggage and you know, what's my plane seat gonna be like I'm like I'm I had the whole thing on my head so but I'm things are going good I'm like in a in a mad uh swag ordering phase right now but I also you know anytime we do any kind of trip I verify everything, you know, meaning like I check that our hotel rooms rooms, our cars, you know. Hundreds of points to check. Hundreds. Yeah. Which is why we need the constant reminders that we get, thank goodness. And you're very good about that. I appreciate it. And uh yeah, so apparently you need a passport to leave the country. Who knew? No, I I I'm kidding. Not fair. It's good. And you need an entry visa to get into these other countries. Yep. But but I don't have a visa credit card. You need a visa credit card to shop at Costco . It's weird. Should we say at this point, should we just like say we're Canadian or something? Will that help? I think they also need visas. Maybe not actually. Do you have a Canadian visa Bob? No, but I just don't, you know. No, then it's more trouble than it's worth, Bob. Hand them your American passport. Bob, just when you show it to them, just put your thumb over the country. Say, hey, there it is. See, see that's me. This is the number. I'm good. But trust me, all this stuff that feels annoying now, which actually isn't annoying, it's like five minutes of work, makes it so that when you get to the country you just walk right in. You don't have to wait in those really long cues. Even and not even walk. You could potentially even just waltz, you know, just sachet. Yes, I should saunter. Yeah. Saunter. Lower. Here I can't tell you how many times you know we um with all the years that we've traveled where we use the global entry and we get into like this really short line to get through customs and you look at the 3,000 people that are in that queue and and it it's such a's like, oh my god, like thank God. It's not even and now it's like it's not even a line at global entry. You don't even use the key you remember you used to have to use the kiosks since the passport and they give you the ticket. Now you just look at the camera and they just and then you just walk forward. Look at it. It's so fast. I love it. All right, Jay. We're gonna dive right in. Tell us about sleep and aging. Yeah, so guys, do you have any idea on how many hours of sleep you need to feel fully rested? Yeah. In general for humans. No, my own perception. Oh well. Yeah, you know. I seem I think I function normally at a minimum of six hours. Before I was diagnosed and medicated for idiopathic hypersomnia, I would say twelve to thirteen and I still didn't ful feel rested. But now awful six to eight. Yeah, it's good. I'm in that sweet spot, six to eight. Yeah, for me, I mean it's about eight hours. Do you ever get a good eight hours? No. No, I don't I wake up in the middle of the night frequently or um or just straight up like you know, I'll I'll go to sleep around ten o'clock and um you know, I'll just wake up at four in the morning and I'm uh So I should stop calling you at three thirty and okay, got it. But the you know these are good questions and good things for people to think about because sleep, of course, is incredibly important to our overall health. You know, your mental health is affected by your sleep as well for a lot of people. So I I chose this uh item to talk about because it dig s into a study that did a what I think is a very good job at studying um sleep patterns and you know how much time do people need. Um and it and it gets into some real biological outcomes if you don't get enough sleep or if you get too much sleep. So this study was published in Nature, and they were looking at, like I said, you know, sleep duration and biological aging and if there's a connection between the two. So you know it wasn't just a is sleep good for you study. Like they really they really were asking whether different amounts of sleep are linked to any measurable signs that parts of your body are aging faster or slower. You know, what impact does sleep overall have on your physiology? So they compared it was the self-reported sleep duration with 23 biological aging clocks that they came up with, which I'll explain. The basic idea is that these clocks estimate whether a tissue or organ system appears biologically older or younger than a person's actual age, right? Steve, you and I were just talking about this, right? You could, you know, Steve was telling me and Bob about how you know he's tracked patients over the the course of his his entire career where he could look at them and and be like okay that person looks to be about 50 and then he'll open up their chart and they're actually 30. And then of course he finds out, well, they've been smoking since they were teenagers or they've been drinking alcohol or whatever. Well, sleep is kind of like that, right? Sleep has that kind of effect. So the clocks were built basically from MRI imaging, blood proteins, metabolites, you know, these small molecules that are involved in metabolism. So they're that's what they're tracking. So as a cool example here, like two people might both be 60 years old, but one person's brain and liver and their immune system or their metabolic profile might look older than the others. And that that difference is called a biological age gap. And the findings that they came had what's called a U-shaped relationship between sleep duration and biological aging. So people who reported sleeping too little tended to show more signs of biological aging, which we would expect. But so did people who reported sleeping too much? You know, in my world, Kara, and you know what I'm about to say, there is no too much sleeping. It's amazing. We were uh opposite. Right? Because I was that person. I remember talking to my neurologist, because I take a hardcore drug every night. And I was like, what is the long term effect of people taking this drug every night? And he was like, we don't really have a lot of data on that. But what I can say is that the long term effect of sleeping 12 hours a night and napping three hours a day is not good. Yeah. It's very bad. Yeah. So I still know it's better. I was still going to be able to health position now with that medication. Absolutely. So the lowest biological age gaps were generally seen in the middle range, right ? So 6.4 to 7.8 hours of sleep. And this also depended on the organ system, the sex, and specific aging clock. So this is like a generalization, but between those sleep times, 6.4 and 7.8 hours. That's where they found the optimal health of all the people that they studied. Meaning that if people were sleeping within those with within that range, they were biologically younger than people who slept less or more than that. And it's important to point out, this doesn't mean there's a magic sleep number that works for everyone. It is the opposite of that, if anything. You know, optimal sleep dur ations, of course, they vary from person to person. And this is why we have to pay attention to our own bodies and try to come up with a good understanding of what we need and what's working. And you know, it's one thing to say, hey, I'm not getting enough sleep, so I'm going to go to bed a little bit earlier or prioritize carving out the right amount of time that I need to be undisturbed and all that stuff. But I think a lot of people don't don't think of oversleeping as a problem. Um the point here is that the relationship is not linear. So more sleep was not always better and less sleep was not harmless. And the healthiest looking range, at least by the biological aging aging measures that they did in this study, they were always in the middle. The researchers know that self-reported sleep is imperfect, right? Anybody that's self-reporting basically on anything is going to have their own perspective and SKU and they're you know there's going to be they're not gonna make good estimations exactly on how long they slept. It's all just too subjective. But what they felt was that the data set was so large and it was a very large data set that they they there was enough data there to look for patterns across all these biological systems, meaning that even with the errors in self-reporting, there were consistencies that showed connections to good or bad health. And they tested uh 23 different aging clocks, and nine of them showed the same basic pattern. People at either end of the sleep range look biologically older than people in the middle. And these involve systems connected to the brain , uh, you know, the lungs, the liver, immune system, skin, endocrine system, adipose, tissue, and pancreas. And so, you know, these are all very important things, right? As a human, you want these functioning well. I like my pancreas. Me too. You do? Yeah, and how often do you really think about it? Like, how's my pancreas doing? Yeah, mine's kind of annoying. I think about it when I hear about people who get pancreatic cancer of the world. Of course. The worst of the worst. Oh, that's when I think about it. The study doesn't prove that sleeping too little or too much directly causes accelerated aging. It just shows the an association between too much sleep or too little sleep with you know being biologically older, right? But they didn't find the exact causes of why that this was functioning. So this is like the very beginning of them going into deeper studies to get more details. Short sleep could plausibly contribute to worse health. I think it's pretty well established at this point. Chronic sleep restriction can