Daniel and Kelly’s Extraordinary Universe - Listener Questions #39

Episode Date: May 21, 2026

Daniel and Kelly answer questions about muscle memory, water-less showers, and why everyone can't be ambidextrous.See omnystudio.com/listener for privacy information.

This is an I-Hart podcast. Guaranteed Human. Hey, guys, it's us. The Jonas Brothers. I'm Joe. I'm Kevin. And I'm Nick. And guess what? We created our own podcast called,

Hey, Jonas. Nice. We invented a podcast? Well, we didn't invent it. We just contributed to it. We're the first people to do podcasts. We get to ask other people questions because we're sick and tired of being asked questions.

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Is it just me or does every woman my age want to look at Pinterest instead of having sex sometimes? They say we can't polish a turd, but we're sure going to try. So let's get blunt with laughs, tears or tears of laughter. Listen to How Hard Can It Be with Deanna Maria Riva on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Will Ferrell's Big Money Players and IHeart Podcasts presents soccer moms. So I'm Leanne. Yeah.

This is my best friend, Janet. Hey. And we have been joined at the hips since high school. Absolutely. A redacted amount of years later, we're still joined at the hip. Just a little bit bigger hips. This is a podcast. We're recording it as we tailgate our youth soccer games in the back of my Honda Odyssey.

with all the snacks and drinks. Why did you get hard seltzer instead of beer? Oh, they hit a bogo. Well, then you got it. Listen to soccer moms on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Promotions I've done many times. I barely have to think. This is kind of nuts.

How do my mind and muscles sink? Will Star Trek-style sonic showers replace the rinse and spray? Or will a clever mist just fake it while we see? still need water anyway. Is there only one gene that determines if I use my left hand or my right? And what gives evolution? Ambidextrous would be way better in a fight. Whatever questions keep you up at night, Daniel and Kelly's answers will make it all right.

Welcome to listener questions episode number 39. Hi, I'm Daniel. I study particles and aliens and I'd give my left hand to be ambidextrous. Hi, I'm Kelly Weiner-Smith. I study parasites and space, and I married a left-handed person. And it hasn't caused that many problems in our marriage. And do you have any left-handed children? You know, it's hard to say. So our oldest is definitely right-handed, and our youngest is ambidextrous maybe.

We're not quite sure. His handwriting is a little slugly. with either hand. It's so hard to say. Well, I've always been amazed watching lefties do a lot of stuff. Like writing, for example, it feels like a very unnatural emotion to me, though I know to a lefty, of course, and must feel very natural. Yeah, that's right. But I think if I was a left-handed person, I would get really tired of all of the jokes and the, you know, being called a Southpaw or whatever.

Or like, every time you reach for a scissor being like, nope, these weren't made for me. I can imagine that being frustrating. Yeah, the world is definitely built by and for right-handed people. That's right. And whichever side of your brain you use, if you're right-brained or left-brain, we want to hear about the questions that you have about the universe. We want to know which parts of it fit into your mind and which parts of it need a little bit of Daniel and Kelly help.

And we are always here to help and add a little bit of levity to the questions as well. And today we have a really great question to start the day off with from Adrian. about muscle memory. And this one went in a direction I totally didn't expect in the research, which, you know, I think is something that I pretty much say every time. So let's go ahead and hear Adrian's question.

Hi, Daniel and Kelly. Love the show. This is Adrian from Brighton in the UK. And my question is around muscle memory. So this morning I was making a cup of tea. Took the tea bag out of the cup, threw it across the room, and it went straight into the bin.

And I was wondering, how did I do that? I didn't think about it. I didn't have any calculations going on and then I extended that to even in sport when you're catching a ball and somehow you managed to judge the trajectory, the wind, the spin, the position of your body, all in no time at all. So if you could tell me, how am I doing that? That would be great. I love this question. I want to know the answer to this question. I think about this all the time when I watch my kids ride a bike or when I jump over a puddle or something. And I think about how I don't need to know the details of the mechanics here. How do my neural network just like figure out how to manage this? I can just think like, let's go in this direction and

something does a bunch of processing and figures out how to control the muscles to make that happen. It's amazing. Yeah. No, it's absolutely amazing. And you know, you might not be surprised that the answer to some extent is, we're not totally sure, but some of it is happening in the brain. And then recently, we've started to think that actually some of muscle memory is happening at the level of the muscle. What? I know. What? Muscles actually might have memories? Well, okay, hold on, hold on. Okay, so first, let's deal with the word memory. So, you know, when we hear the word memory, we think something happening with the brain or like something stored on a computer. But scientists use the word memory for a couple different things. So, for example,

we talk about our immune systems having a memory. And for that, what we mean is like, maybe you've been exposed to the miracle that is a vaccine, which means that your immune system has seen, like, I don't know, part of a virus. And it has components that will now remember what that virus looks like so that the next time part of that virus is in your body, it can be attacked immediately. It's immediately recognized as an invader. And scientists will refer to that as immune system memory. That doesn't really feel like memory to me. You know, that's just like it's been changed.

You know, like if I throw a rock at the wall and leave a dent, you wouldn't say that the wall has like a memory of the rock. Sure. But I guess I was saying that more to just lay out that this is how scientists use the word memory as opposed to have a philosophical discussion about what memory should really mean. Well, then you've got the wrong co-host if you don't want to have a philosophical conversation. I'm totally on board with having the philosophical conversation. But whatever you and I decide isn't going to change the fact that other scientists use the word memory to mean stuff like this.

Yeah. And of course, in science, we often use common words in a particular and precise way and co-opt those words and give them new technical meanings without really being clear about the fact that it means something different. Like work in physics and work in life are two totally separate concepts. So we use the same word. So I have no high ground to criticize. Anybody else's use of words, I just want to be clear for the listeners. All right. Okay. So you're saying immune systems have memory in that sense, but they don't, like, experience it. They're not, like, traumatized by the memory of when you got the flu or something.

That's right. Okay. Yes. And so when we say muscle memory, the first thing that we really mean is something that is essentially stored in your brain. So let's start with that. Okay. So muscle memory starts by just doing an action.

And when you do an action, we're usually talking about what's happening in your motor cortex. So your motor cortex is a squiggly part of your brain. So like, I'm at, shut your eyes and picture your brain. It's got all of those squiggly bits. One of those squiggly bits starts kind of near where your ear is and it moves upwards towards the top of your head. Okay. That squiggle is the motor cortex. And what it does is it sends messages to your spinal cord and then to your skeletal muscle to tell it to move.

So your motor cortex controls motor movements. Amazingly, every once in a while we have a term that sort of kind of is intuitive. All right, but this touches on something I've always wanted to understand, which is you hear a lot about how like this part of your brain does that. This part of your brain does this other thing. And I always wonder like, how do we really know that since we don't really know how the brain works? And it feels to me like it relies on these like fMRI studies where they're like somebody pick your nose and then we'll watch which part of your brain has more blood, flow and they're like, oh, that's the nose-picking part of the brain. And it feels like there's a lot of assumptions there, like, just because this blood flow here doesn't mean that, like, that's where

those decisions are happening or this part of your brain is good at picking your nose or something. How well do we really understand which part of your brain does what? All right. Well, I'm going to forgive you for asking a question that's way outside the bounds of what I've... Not at all. What I have on my outline, but... Oh, good. But, okay. So, all right, so fMRI studies, yeah, they have some problems.

In fact, there was this classic study where they put dead trout in an fMRI machine and ask them questions. And there were some like parts of their brains that lit up. And they, anyway, so that like made the news for a while. There have been lots and lots and lots of fMRI studies that have said the exact same thing, which increases our confidence in the results. But there have also been a lot of studies in, for example, rodents where you can do things like you can, you know, dissect out a part of the brain and then see, oh, the rodent, that can't pick its nose anymore, and it could before. Now we even have things we can do where we can like, gosh, I don't know a lot about this technique, but you can essentially get certain neurons to light up when they're being used.

And so you can say, oh, man, there's a light on in that part of the mouse's brain only when it's picking its nose. And as soon as it pulls its paw out of its nose, those lights go off. And you can turn those lights on through methods. Again, I don't really understand. And then the mouse sticks its paw right back up its nose. And so we have a lot more ways to study and manipulate brains that are much more, I guess, invasive is the honest answer. But like much more cause and effect than observational. So, you know, you were talking about going into an fMRI machine.

That's like observational. We can get our hands a lot dirtier doing mouse experiments. Okay. And we can also take advantage, unfortunately, of situations where somebody has an accident. And for example, you know, if a spike goes through a certain part of someone's head, and I'm thinking of a famous example where a spike went through someone's head and went through a particular part of their brain and then they watched to see how that person's personality changed. And so, you know, you can take advantage of horrible situations where people have had brain damage and then keep track of what happened. You know, of course, for ethical reasons, you can never permanently hurt someone's brain, or at least you ought not to. So anyway, we've got pretty good data for some of this stuff.

All right. And I don't mean to sound like I'm criticizing neuroscience. I know this is a really hard problem, and it's amazing what they've been able to do. I just feel like sometimes we tackle a hard problem by doing the best thing we can, the only thing we can, and we don't always carry along with us into analyzing the conclusions, our memory of the limitations of our techniques. But anyway, so let's say we know which part of the brain is in charge of this motor cortex, trying to get us back on track here. Okay.

And I'm going to step us back again because I'm always pushing back against your desire to keep us on track. But that's kind of why I started with. We don't really know because, like, we do have data on this. We have been able to do studies on non-human animals where we feel a little bit more comfortable, you know, doing experiments on the brain directly. But at the end of the day, we don't understand this in a very, like, deep way. You know, this is like our best understanding at the moment, but there's still a lot that we don't know. Brains are really complicated, and like this is the best that we know as of today.

Okay, so motor cortex, part of the brain that we think is responsible for, you know, if you're kicking a soccer ball, this is the part of your brain that's sending the message to your leg that says, you know, kick your leg. And I'm not very good at kicking a soccer ball, but I'm pretty sure it involves your leg. And does that mean it's doing the bit where it tells your leg to move? And it's also doing the bit where it tells your leg, like, how to move in this certain moment when the ball is coming at this angle and the wind is at that angle. Does Lionel Messi's motor cortex know how to play soccer or is that like more upstream? I don't know who this messy fella is, but it sounds to me like he should clean his room. But no, no, the motor cortex or she should clean her room. But anyway, the motor cortex is saying.

contract your leg muscle because you need to kick something. And then the cerebellum, so this is like a lump on the bottom part of your brain that's kind of near your spinal cord. And the cerebellum is essentially telling your motor cortex how good of a job you did. So like if you totally whiffed, your cerebellum is like,

hey, messy, you totally missed the ball and you need to be paying more attention to the wind next time. And so it tries to help your motor cortex coordinate better so that next time you do a better job. And so if Messi gets out there and practices every day, which your face is telling me that I should know who Messi is, so Messi probably has practiced a lot. And so.

Oh, my gosh, Kelly. Hold on. We have to stop here. Let's just do a quick quiz. How calibrated is Kelly? So never heard of Lionel Messi. You ever heard of David Beckham? Yes.

Okay. All right. He married a spice girl. All right. Cristiano Ronaldo? Nope. Renodo. You never heard of Pele?

Pan No. Wow. Okay. Wow. I don't know where to go from there. Well, I shouldn't have picked soccer, but I did. It was a mistake. I should have gone with playing the guitar or something.

And then we could have talked about 90s-era grunge bands. But here we are. Mired in a sport I know nothing about. But anyway, all right. So your cerebellum's job is to try to figure out, how well-coordinated a behavior is, and talk to your motor cortex. And as you do this more and more and more times,

as you practice more and more, your cerebellum plays a role in helping to make sure that these behaviors can happen like at a subconscious level, that they can happen without you thinking about them when you've done enough practice. And part of that is because you're creating neuronal pathways that involve other parts of your brain.

So, you know, if you're talking about being able to play the guitar, while singing, you have to practice playing the guitar a bunch of times, and that information might get stored in a different part of your brain than what happens when you're playing soccer, and you need to also be calculating like wind speed. And so this is where we're, you know, getting into really not understanding what's happening. But anyway, so muscle memory is some combination of your motor cortex telling your body what to do, your cerebellum helping with coordination, and that information getting stored somewhere in your brain, and eventually you've created neuronal pathways that have been sort of like solidified that you're just kind of like

turning on when you do the behavior and you don't have to think too hard about it because your cerebellum has helped to make sure that it's like in there in a coordinated way. Yeah, that's fascinating. I feel like there's two separate questions there. One is like, how do you learn to do this kind of stuff? And that part makes a lot of sense to me. Like I had a toddler. I saw this toddler, like, learned to use their arms. And the first few times they like, hit themselves in the face. And they were like, hey, who was that who hit me in the face? And then they realized, oh, that's me. And if I do this and I can do that. And it's like watching somebody learn how to ride a bike. You know, they explore this feedback there. They learn. That makes a lot of sense to me.

But there's this second piece where you can do it without thinking about it, which seems much more complicated because it connects to this question of like your experience and your consciousness. Like I think we've all had the experience of like driving somewhere familiar getting there and realizing, I don't remember a moment of that driving, but I'm pretty sure I was paying attention and I didn't run over any pedestrians, et cetera, et cetera. And it's terrifying because you're like, I hope I was paying attention, but you can't remember it. Does that mean that you were aware of it and you forgot about it and that's what consciousness is? Anyway, I feel like that's a whole other rabbit hole that's much fuzzier. I feel like you've brought us back to philosophy, which is great.

I love philosophy. But yeah, I don't really know that I have the answer to that. Yeah. With for the car thing, I feel like I think maybe I shouldn't be autopiloting when I'm driving. Because even if I subconsciously know the route, I should probably be alert for things that are changing. You know, like the kid who might be running across the road. Yeah. This time, but didn't last time. But yeah. So, I mean, I think you do something long enough and your brain essentially like creates pathways that you can just like activate.

Because you're like, oh, I've done this enough. I don't need to think about it anymore. Activate the driving to the grocery store pathway. Right. but you should still be trying to pay attention when you're activating the going to the grocery store pathway. But it feels like we can describe that, but I'm not sure that we understand how that works, right? Yes, I would say that that is fair. And that this was Kelly's best attempt at trying to understand how this all works.

And I hope that I've done a good job of clarifying the areas that are the murkiest for us. But I do think it's fair to say that a lot of this is murky for us. And this is just sort of like our best guess at what's happening at the moment. Sure. And let's go into real quick this idea that our muscles might have memory also. So here's a little bit of new science. And this, I should say, super speculative. Most of this we've seen in animals.

We don't know if this is happening in humans. But there's this idea that's pretty exciting, which is essentially, you know, say you kick a ball like a bunch. You're Lionel Messi and you are, you've been like strength training to do soccer for a really long time. Daniel knows who you are. you're that good. And I am not a huge soccer fan. So, like, you don't have to be a huge soccer fan to have heard of these, like, global superstars.

But anyway, it's cool on. You managed to marry one of the spice girls. And so the idea here is that if you get really strong at one point, you've sort of primed your muscles to, like, remember that they were strong so that they're more likely to get strong or it's easier to get strong again in the future. And here's the idea for how that happens. So first of all, most of the cells in your body have one nucleus, but your muscle cells have more than one, which is something I had forgotten.

But this makes sense, right? Because your nuclei direct protein synthesis. So they essentially have the instructions for the proteins, and then they send instructions out to the main part of yourself for proteins that need to be made. And when you're exercising, your muscles need to be generating proteins. and stuff. So you'd want more than one nucleus so that you can like keep up with the protein synthesis that needs to happen. Plus, your muscle cells are much longer than most of your other cells. So for example, a single bicep muscle fiber is 10 centimeters long. Whoa. 10 centimeters long.

That's crazy. That's a long cell. This is something I usually think about is like microscopic. Yeah, right. You could see, you can see that in a dissection lab. And it can contain something like 3,000 nuclei. Wow, that's incredible. Yeah. 3,000 nuclei. So, like, who's making the decisions? That's a good question. I don't know.

Maybe they're all sharing. And they're about equidistant apart from one another. Okay, so when you go to exercise, you know, essentially building a muscle involves, like, tearing some muscles. And so when you are exercising, you tear some muscle fibers. And then we think what happens. And again, this is super speculative. A decade from now, we might be like, ha, ha, it's cute that we thought that. But anyway, satellite cells come in to try to patch up the damage.

Satellite cells, one of the things that they might be doing, is patching up the damage and then giving the muscle fibers in the area their nuclei when they're done. Oh. Yeah, right. So muscle fibers that have been worked out pick up more nuclei so that the next time you start exercising, they are more prepared to get bigger, faster because they've got more machinery that can then help them bulk up when you start exercising again. And so even if you've taken a bit of a break from exercising,

like, Messi is like, I need to clean my house. And he's like, it's going to take a whole month. And then he doesn't exercise for a month. And then he gets back to it. Yeah, that is a very unrealistic scenario. Okay. Well, you know, I don't know anything about sports. So when he gets back to it,

he's got all these extra nuclei that are prepared to help him rebuild muscle when he starts to get back to it. And so folks in the field of like exercise physiology are calling this muscle memory because you exercise your muscles and they remember that you were once super fit once and they've got these extra nuclei to help you get there again faster the next time.

And folks are also arguing that this is why it's important when you're young to exercise and muscle train because when you get older, you know, if you like hurt something and then you need to try to get strong again, you'll still have these nuclei and it will help you to get strong again faster after, you know, something bad happens. So I see.

I thought that was interesting. That is very interesting. But like, let's say that Messi takes a break and doesn't play soccer for a few years to the point where he's like as bad at soccer as Daniel is. But then we both devote ourselves to soccer and practice full time. He's going to be better faster. Not only is going to be fitter faster because he's got these muscle cells with their extra nuclei, but he's got the pathways to remember like,

how to kick the ball around the defenders, et cetera, et cetera, right? Yes, he's got the, like, quote, muscle memory, end quote, you know, like coming from two ends, from the muscles and from the brain. He's got the benefits in both of those places. And I should say, again, with the muscle memory, we're not, like, totally clear on how long those extra nuclei stick around. We think it's a long time. But, you know, this science area is pretty new.

And so do you think this scientific understanding, as imperfect as it is, validates the old adage, like, you don't forget how to ride a bike? Like, do we know now why you don't forget how to ride a bike? It's because you still have those pathways in your brain. Yeah, I think that's more about what's happening in your brain. And yeah, I do think that that is why you can still jump on a bike years later and you still know how to ride it. It's still you still have those neural pathways up there. Well, thanks for giving us that cutting edge, if imperfect understanding of what's going on in our brains and in the muscles of the world's premier athletes.

This is not turned into an exercise physiology podcast. Please don't send me more muscle physiology questions. I don't know the answers. But let's send this back to Adrian to hear if it answers his question. Thanks, Daniel and Kelly for the answer. The combination between cerebellum and motor cortex makes a lot of sense. I guess there's still a lot of unknowns, but that doesn't surprise me. The biggest shock is that Kelly didn't know who Lionel Messi was.

Shocking. But thanks again. And love the show. please keep it up Hey it's us the Jonas Brothers And guess what? We have some big news What's the news? Huge news.

We created our own podcast called Hey Jonas. We invented a podcast? Well, we didn't invent it. We just contributed to it. We're the first people to do podcasts. Pretty wide range of podcasts. We're starting a trend.

But this one's extra special. So how do we actually come up with a name Hey Jonas, guys? I honestly don't remember I think it was on a call about what we should call it And we were thinking I'm originally calling it One of the early names of our band

Before Jonas Brothers This is how you guys remember it going down Yes I have a very different memory of this We were talking about a thing A bit for the podcast For people could call in and say hey Jonas And then I wrote down on my little

Notepad Hey Jonas And offered it up as a potential title For the podcast But thanks for remembering that guys listen to hey jonas on the iheart radio app apple podcasts or wherever you get your podcast just listen we don't care where you hear it another podcast from some s nl late night comedy guy not quite unhumor me with robert smigel and friends me and hilarious guests from bob odenkirk to david letterman help make you funnier this week my guess s nl's mikey day and head writer streeter sidel

help an acapella band with their between songs banter where does your group perform we do some retirement homes. Those people are starving for banter. Listen to humor me with Robert Smigel and friends on the I-Heart Radio app, Apple Podcasts, or wherever you get your podcasts. The story I've told myself about love or relationships can then shape my behavior, and that can lead me to sabotage the possibility of connection. This Mental Health Awareness Month, tune into the podcast deeply well with Debbie Brown and explore the journey of healing, self-discovery, and returning to yourself.

We explore higher consciousness, emotional well-being, and the practices that help you find clarity, peace, and self-mastery in a world that can feel overwhelming. The world is becoming lonelier. We're not becoming more social and connected. We're becoming more individualized, but we actually meet people in connection. If you've been searching for a soft place to land while doing the work to become whole. This podcast is for you. To hear more, listen to deeply well with Debbie Brown from the Black Effect Podcast Network on the Iheart Radio app, Apple Podcasts, or wherever you get your podcast.

Hey, I'm George Adano. You might know me as that loud guy who yells out, help on the internet. Help! Somebody! Please! But there's so much more to me than me. I'm an actor. I'm a comedian. And recently, I've become quite the helper myself. And on my new podcast, hope from a hypocrite, I'll be changing lives, helping people in need with my sage advice and thoughtful solutions. Sike, I'm a comedian. I'm not qualified to give good advice. Join me and my comedian friends as we riff rant and recommend some of the most legally

dubious advice known to man. If I'm calling you, even if you're on your phone, let it ring twice. One ring is too scary. Oh, cream of chicken suit. A cream. Cream a chicken suit. This is Help from a Hypocrite, the worst advice from the dumbest people you know. Listen to Help from Hypocrite as part of the Mike Coutura Podcast Network available on the IHart Radio app, Apple Podcasts, or wherever you get your podcasts.

Okay, we're back and we're answering questions from listeners today about how to stay fit and how to stay clean. Oh, love it. Yeah, so we've got the next question is from Bruce from the UK, or really from Bruce's girlfriend from the UK. And this is a fantastic question, so let's go ahead and hear it. Hi, Daniel and Kelly. My name is Bruce from the UK. My girlfriend recently asked me, one of the going to invent showers that don't use water?

And I thought it might be a good question for you both. I know that in Star Trek, all the crew clean themselves using sonic showers, which seem to require no water. How plausible is it that waterless showers are somewhere in our future? Is water a critical part of the definition of being clean? if some media is required, could a gas be used instead? Could waterless showers help save water and allow for more drinking water around the world? Thank you.

Yeah, so I'll be honest. This question was a bit of an emotional roller coaster. On the one hand, I got excited because I was like, oh, this is such an interesting question. And, like, backpackers around the world are like, I need to know the answer to this. On the other hand, you know, the idea of, oh, can I step into a shower and can we use gas? that question lands a little different, I guess, depending on your cultural background. Right. Yeah, a little Schindler's List energy there.

That's right. That's right. But anyway, okay, obviously, that's not the direction this question is going in. This is a good, clean question. And so, yeah, Daniel, why do we use water in a shower? Well, didn't realize we were going to be talking about the Holocaust today. But let's talk about why water does make a good shower because it does, right? Shows are fun. They feel good. You feel clean afterwards. From a chemical point of view,

soap and water is a very effective way to clean yourself, right? Water is very good at removing a bunch of stuff, anything that can dissolve in water, for example, water can help you remove it. famously, oil doesn't dissolve in water and doesn't mix very well with water, and that's why we use soap. Soap has this amazing chemical property. One end binds to water, the other end binds to oils. and if you have an in-flowing water, it can grab those oils and clean you up. So it's a really nice experience. It can also carry away like dirt and microbes.

So the combination of like dissolving a bunch of stuff, carrying away the oils, the mechanical force of it, all that works to make you clean. I have a question for you. So now Katrina being a huge microbe fan, how does she feel about all those microbes being carried away? Now I'm not asking for the detail. of Katrina's shower routine, but does she feel like we should shower maybe less than daily

because we're losing good microbes? Or where does she stand on this? That's a great question. And I know that there's a big controversy in the field about the hygiene hypothesis. You know, like, are we too clean? The fact that we like try to keep our kids out of the dirt is that the reason we now have allergies. And I know that that was a popular hypothesis for a while. And then there was pushback against it. And I think we should have her back on the podcast to talk about that exact question because I don't feel qualified to answer it. All right, moving on. But there is beyond the actual getting clean, there's the psychological feeling of being clean.

Something about immersing yourself in water, like, it's just restorative, you know. And there's this famous paper from like 20 years ago about the Lady Macbeth effect. if humans have this like mental connection to water and associated with being clean. And they did this hilarious study, which I never would have thought to try this. But essentially what they did is they took a bunch of people and they split them into two groups. And they said, group one, think about something unethical, something like bad you did in your life, something you're like feeling ashamed of or embarrassed about. and the other group think about something good you did.

All right. So unethical group and ethical group. Then they put some words in front of them with blinks. So it would be like W-blank-blank-H or S-H-blank-E-R. And the folks who thought about like some bad deeds they had done were more likely to fill in those blanks to spell wash or shower. And the ones that had thought about something good they had done in their life weren't as likely to say wash or shower. They would say things like wish or a shaker. And so this is supposed to probe whether like thinking about bad things puts you in a mindset where you think about flowing water, right?

Or washing yourself. That's why it's called the Lady Macbeth effect, you know, out-out-dam spot sort of a situation. And the conclusions of this paper is that water is linked to feeling clean or that if you're feeling dirty, mentally dirty, you want water to like cleanse you of your guilt. And y'all can't see Kelly's facial expression, but she looks very skeptical of these conclusions. I mean, like, so I can imagine there's a cultural connection there. Like, you know, I'm Catholic. I was raised Catholic. And, you know, we get baptism.

You get some, like, water put on your head. And now you can go into heaven. And so there's this connection between water and being able to get into heaven. And so I can imagine that there is this cultural connection. But, you know, I can also imagine for other people that's just like, Oh man, you know, when I think about that thing that I did in my past that was bad, now I feel bad. And when I feel bad, what I really want is to like relax. And so I just want to get into like a shower.

And it's not like I'm washing away my sins. It's just like now I want to do my like lazy day feel better routine, which is, you know, like, I don't know, maybe includes a shower and a glass of wine or something. I don't know. Right. Yeah. Well, this study was published in science, so got a lot of press. But then faced some replication issues. Okay.

People tried to reproduce it, didn't get the same results. So, you know, is it peahacking? We don't really know. So I'm not going to stand by this study, but it's out there as part of the conversation on these issues of like, can you feel clean without water? Daniel and Kelly presenting science. We don't necessarily stand by since 2024. All right. What else?

Well, then I found a paper from 2018 that did a randomized control trial comparing routine immersion bathing, where you're like, get all the way in the water to just showering. And, you know, one of them has more water contact than the other, but both of them make you feel like clean and refreshed, though bathing with better treating like fatigue and stress and pain and improved your skin condition. And like, all right, so you hang out in a bath for a while, it's good for you. That's not really a very controversial conclusion. But you're right.

I think the humans do have some connection to water. You know, there's a reason people want to live by the beach. beach and there is a reason that it's nice to go for a walk by a river and wash your face. And you're right that many religions have water purification rituals, wash your feet before you go in or take a water bath or, you know, holy water, right? So it's definitely been a part of our existence for a long, long time and woven itself into our culture. Yeah. Well, and water just like feels nice. Yeah, exactly. It does. But that doesn't mean that we couldn't get clean without water, right? And And I think that's what Bruce's question is about.

It's like, what are the other options? What can we do? How close are we to accomplishing this? And so, you know, what exists today is that you can take some what's called a dry shower, like using dry shampoo. And that's essentially just like a powder, which can absorb oil. And so you can rub it on your skin. It'll absorb some of the oils. Then you can brush it off.

The way that you can like clean something with sand, right? Rub something in the sand and a lot of the stuff that sticks to your skin can come off. So that's like step one. And I know that folks out in space, for example, where water is really at a premium can't take long, luxurious showers. And so they have all sorts of strategies for dealing with this. Kelly, tell us a little bit about how astronauts stay clean. Yeah, so they'll like, you know, rub some, like, soap on themselves with a bit of a slightly wet rag. They did have a shower in Skylab, I think it was, for example.

But, like, you need to essentially make a tube. And you have to be very careful to make sure that the water doesn't end up in, like, like a bubble that ends up around your face and then you drown in space, which would be very embarrassing. And it's just like a huge pain in the hyeney to make sure that the bubbles of water don't end up in your equipment and then short your equipment. And so they ended up deciding that actually showers are like way too much of a pain. And so now they do these like, you know, wet rag. You wipe yourself down with like a soapy water concoction. And then you kind of wipe it all off. And then you put a little bit of shampoo and stuff in your hair. And then you kind

know, rinse it off a little bit, you get like a little bottle with some water, and then you just kind of like try to get it all out with the towel, and then you put the towel out to dry so that the equipment can then absorb that moisture again, and they can clean it out, and you can use it for coffee the next day. This coffee tastes like Kelly. Yeah, they actually, they call the water yesterday's coffee because, you know, the urine also gets cleaned for drinking water. So hooray for space.

It's like space kombucha. Yum. Who knows what's in it. So neither one of the, oh, hey, watch it, buddy. Cambocha's great. But neither one of those sounds very relaxing. Wow. Katrina's not even here to defend kombucha, and she doesn't even have to be. Look at that. Big kombucha has bought you off. All right. So there are other technologies you can use to get clean without any water, like sonic showers. This is what Bruce asks about. And ultrasound cleaning is the technology we have already today for cleaning like jewelry and medical devices. is an ultrasound just means sound at a frequency above the range you can hear. Infra means low and ultra means high, which is like ultraviolet light is light above the violet

that we can see. Ultrasonic just means frequencies we can't hear. So we're talking like 200 to 400 kilohertz. These are just pressure waves, right? Sound is just a pressure wave. And having really high frequency sound creates high and low pressure regions and it forms bubbles. And so the bubbles form in the low pressure regions, and then they collapse in the high pressure regions. This is called cavitation. And the way the bubbles collapse creates super high speed, very, very small jets with local heat and pressure spikes. So the bubbles don't collapse completely uniformly. So you get these like collapse in this direction, in that direction.

And those are like little cleaning jets. And it gets into really tiny little spaces and it can clean all sorts of stuff. you can never reach. So that's why it's very effective. The forces are really, really tiny, but they're very, very local, right? So the magnitude of the force is not high, but the area is very, very small so the pressure can be high. And that's the good news. The bad news is that ultrasonic cleaning works best in a liquid because you need pressure waves, right? And liquid is better at transmitting this stuff than air is. So this is like a way to make water more effective. It's not really a great way to replace water.

So you can put it in like a water bath and then use ultrasound and to like shake off all the really hard to get to stuff. That's like the current use of ultrasonic cleaning. Okay. So like if I was really busy and I was like, I need to get really clean in like 10 seconds. I could like lay in a bath and be like, hit me with the ultrasonic stuff. And it would like take all of the dirt and oil off and then I could get out in 10 seconds and I'd be totally clean. Yeah, exactly. So you can make your bath more efficient.

Right? Exactly. I can shake all those things off without need to like find them and scrub them and like get that, you know, sponge into that corner. Without needing to enjoy the bath at all. Okay. Exactly. It can suck all the pleasure out of the experience for you. Excellent.

Another thing you can do is electrostatic dust removal. Right. So some particles, if they're not really tightly bound to a surface, you want to like lift them off very, very gently. like the surface itself is something you want to protect. Then you can use this technique. The idea is to use an electric field to lift those particles off. So first you ionize them using like ultraviolet light to ionize some of the atoms or just ionized air, which binds to them. And then you apply an electric field and it'll lift off like dry dust or debris, anything very, very lightly adhered.

And this is the kind of technique they use in semiconductor fabrication, like places where they want it super duper clean because they're making, you know, the next chips for the AI that's going to take over the world, they use electrostatic dust removal quite often. So it's good for that, but if you are not a silicon chip, then it's not great for you because it's not great for oils or like coffee stains or, you know, mud on your toddler's face or anything that's very strongly adhered. So after I muck the goat stalls, I should not use electrostatic dust removal. I will be no cleaner. No, exactly. Another direction is to use the water more efficiently. And so there's a technology called mist-based showers.

So normal shower uses a lot of water. It's pouring over you. You use tens of liters of water in even a fairly short shower. So instead of pouring the water over you, spray the water onto you using tiny droplets. So replace the really big droplets of water from your rain shower with really tiny small droplets like microns across that are suspended in the air. So that's what mist is. And the advantage of mist is that it has a higher surface area per volume, right?

As you shrink the droplets, the volume drops faster than the surface area. So you get more surface area per volume, and so you're getting more contact with your skin. And these can still be fairly high speed. They don't just have to float there. You have like high speed, super tiny, misty droplets can deliver, like, kinetic energy enough to like knock stuff off of your body. And so that's very cool. I don't think that it feels as nice. You know, it doesn't provide the like, I'm washing away my bad day kind of a sense.

You know, I'm Lionel Messi and I missed five goals and I want to wash that away. Messy people need showers, yeah. There you go. That's right. That's an obvious joke. I can't believe we didn't see that. I thought that's why you picked messy. So it probably doesn't feel as good.

It's also much more complicated to build these mist-based showers. It's more expensive. It's more parts, et cetera. It's just not as simple as flowing. Another technology you can use to reduce the water cost is to recycle the shower water instantly. So instead of like the water flows down and then you purify it and then tomorrow you use it to make coffee, you instantly filter and sterilize it and back up to the top of the shower and reuse it in real time. So instead of using a large volume of water, you can now have a shower with a much smaller volume of water because you're reusing the same leaf.

over and over again. That sounds complicated because, I mean, saying filter and sterilize sounds easy, but like to have a really good filter, you need to push the water through that filter. And now it's a complicated system. And if you're going to sterilize it with like a UV sterilizer, now you've got like extra energy you're putting into the system. And that doesn't sound easy, Daniel. No, it's always a tradeoff.

Right. The simplest thing is to like stand under a really high volume of water and get clean. And that feels good, right? and that just uses a lot of water. And whenever you're reducing the water usage, you're adding complications. Another thing you can do to stay clean is to use air jets, right? Blasts some of the stuff off of you just using air. I think that overall, without some like new totally revolutionary technology

where you use like high energy particles and AI to target dirt specifically or something, what we're likely to see is like a compressed optimized shower, like you use a high efficiency mist rinse, maybe together with dry or foaming agents, maybe a mild ultrasound where you could like step into it very quickly get pretty clean with low water use. Okay. Yeah. I can see that being good for the planets, but less relaxing.

Tradeoffs. And this could definitely help reduce water consumption, you know, if that's an important thing, if you're in a low water environment. All right. let's send this over to Bruce and his girlfriend and hear what they have to say. Hi, thanks so much for your answers. They were fascinating. The Lady Macbeth effect sounds so interesting, but I also understand Kelly's skepticism. I like Kelly's point about how showers are just nice, but I honestly think my girlfriend would prefer a 10-second dip in an ultrasonic

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or wherever you get your podcast. All right, we're back and we're talking about showers and biology. Kelly, a question for you, which hand do you use to clean yourself in the shower? Are you kidding me? No. Moving on. All right, Ben from Connecticut. Thank you for in with your question and let's hear what Ben had to ask about. Hi Kelly and Daniel. This is Ben from Connecticut.

When I was a teenager, someone once told me that there's no left-handed gene. The dominant allele is right-handed. And if your homozygous recessive, you have the potential to be ambidextrous and essentially choose at a young age which hand you prefer. I've traced this trait through my family and the genetics seem to track.

However, I haven't dug through the literature to find out if this is true. Relatedly, I'm wondering, why is handedness an evolutionary advantage at all? Wouldn't it be advantageous to be ambidextrous? Thanks to the podcast. All right. So, Ben is asking about handedness, which is why we were talking about Southpaws at the beginning of the episode. Daniel, you know, maybe you've already looked at the outline to see the answer here,

but what percent of the population would you guess are left-handed people? That's a good question. I have a left-handed brother and an ambidextrous mother. So that's probably over representative. I would have guessed, you know, maybe one in five or one in ten. Okay. It's about 10 percent, but it varies a lot. And one of the reasons that it varies depends a bit on culture.

And so one of the things that surprised me when I was looking and doing the reading is the extent to which left-handed people have been sort of discriminated against over time. Yeah. Yeah. So I think the idea is that you're supposed to be right-handed. And so, for example, we found that there were these studies in the same. 70s and the 80s, where they found that children in China, only about three and a half percent of them, were, like, admitting to being left-handed. But if you look at Chinese children who were

born and raised in the United States, a much higher percent of them were left-handed. And the idea was just that it was slightly more acceptable in the United States to be left-handed. And so it sort of depends on, you know, how acceptable it is in your culture, the extent to which you're willing to say that you're left-handed. You don't think that's the influence of the left-wing media. Oh, we're staying away from politics. Anyway, so the question from Ben was, is there a dominant gene that controls handedness? And the answer is no.

So there have been some studies that have been done that have looked to see, like, is there a gene that determines if you are left or right-handed? And it looks like when you look at the entire genome, so all of the sequences in the human genome. There's about 48 different spots in the genome that contribute to whether or not you'll be left or right-handed, but none of them are definitive. And so they sort of like inch the percent probability that you end up being a lefty or righty in one direction or another. But again, none of them make the decision 100 percent. And so there's a little bit of genetic impact. It looks like there's a little bit of environmental impact where things like birth weight or a season

of birth or birth year can play a role. And as we've mentioned, there's some cultural impacts that can play a role. And so it looks like whether or not you're right or left-handed is a complicated trait, but genetics or heritability contributes about 24% of whether or not you end up being left or right-handed. All right. So we can't identify an individual gene. but we do see a trend between generations, meaning lefties are more likely to have lefty babies. Yes. Yeah, to some extent. Yeah.

Yeah, yeah. But it's not a slam dunk. Like, if you are a lefty and you marry another lefty, you're not definitely going to have a lefty baby. Depends on how much NPR they listen to, right? Okay. All right. All right. Calm down, Daniel.

I think this is super fascinating, especially the interplay with culture. As you mentioned earlier, it's hard to measure things. that society discriminates against because people don't always want to admit it. And sometimes people like force their kids to learn to write right-handed, even though they're obviously lefty. And I think there's terrible stories about people being forced to write right-handed. Yeah. It's amazing and tragic.

But also really interesting. Yep. Totally agree. And so then Ben's next question was, why not be ambidextrous? Because wouldn't it be better to be able to use both hands equally well? Great question. And so first I'll note that there are. more terms related to handedness than I had realized when I jumped into the literature. So ambidextrous

means you're equally skilled at using both hands for fine motor tasks like writing. That makes sense. There's also a term called mixed handedness where you preferentially use different hands for different tasks. Maybe you're bat right-handed and pitch left-handed to use a familiar sports analogy. Yeah. Does Messi also play baseball? Or is that unclean? I don't know, but he can score with both feet. I do know. I think he's hands for baseball, Daniel.

Okay, so anyway, why not be ambidextrous? I'm not totally sure that we know, but I do think it's really interesting to note that having a preference for one side over another is seen in loads of vertebrates and even in some invertebrates. So, like, I remember when I was an undergrad, and so this was like two decades. decades ago, I saw a talk that absolutely blew my mind. Okay, so it was a talk on blind cavefish.

Okay. And blind cavefish have a preference for exploring the world with one side of their body or another. So they have these like sensors on the side of their body that can detect like the flow of water. Right. And so if you put them in a bowl and you put like Lego bricks around the bowl, they will swim around the bowl with one side of their bowl. body facing the bricks to detect the different things in their environment. And eventually they'll build a picture in their mind of like what is where in their environment. Then you take them out and you put them in the next day and they'll move very slowly around their environment because

they know where everything is and they're like, all right, I got it. And so if you take them out, you put them back in on like day three, but you've moved everything around, they'll detect that something is different and they'll put that, like, their preferred side of their body towards the Legos, and they'll quickly move around the environment trying to figure out what has changed and update their mental map of the environment. And some of the fish are lefties, and some of the fish are righties. And they have a preferred side. If you do this over and over again,

they always explore the environment with their preferred side. This is like if you go into a maze and you want to find every corner, you just like always turn left or follow the left wall, and you're saying you could do left or right, and these kfish actually have a preference. Well, so your thing is different. Yours is like the trick for getting out of the maze is if you always have your hand on that side of the wall,

you will always make it out of the maze. This is not a maze. This is just like there's a tower here and a tower there. It's just the environment has changed. And the way, so like if you lived in a room that changed every fifth day, you would just walk around and use your eyes to see where the way the room has changed. Right. But they don't have eyes because they're blind.

They're blind K-Fish. And so the way that they say, see the room is by moving and feeling the water bounce off the Legos and hit the side of their body. Amazing. And they have a side of their body that they prefer to get that information on. And so they will move around with that side facing the Lego so they can collect that information. Yeah. They've also done experiments on elephants.

And elephants have tusks that have different weights when they get really big, which suggests that they're using one of their tusks. more to fight and explore the environment. And over time, that one's getting worn away more. And so they have asymmetrical tusks. And in humans, you can figure out which arm or which hand we prefer if you look at a skeleton because our right side, our arms and stuff tend to be bigger and stronger because we use that side more. And that causes those bones to get bigger.

And so if you look at a skeleton, our right arm bones are bigger than our left arm bones. Does that make sense? Yeah. They respond to the use. Yeah. Yeah, that's right. So all over the animal kingdom, even parrots, like, parrots will have a foot that they prefer to explore the world with. So you have left-footed parrots and right-footed parrots. And so anyway, the point is having a preference seems very, very common. And maybe that's because it's just you can't be good at everything, right? You have to sort of specialize and get good with one thing. But there's also this idea called lateralization. So, all right, you look at our brains and, you look at our brains, and, you have to be good at everything. And you have to specialize. You have to specialize. You have to specialize. You have to, you have if you slice our brain down the center, it would look like both sides are sort of the same. But we do have different regions of our brains that specialize in different things.

We think maybe dot-a-tah-farmera stuff, yes. Yeah, yeah, yeah, yeah, exactly. Right, brains are stupid, super-duper complicated. And for your brain, the part of the brain that controls the right side of your body is the left side of your brain. and the right side of your brain controls the left side of your body. In the human species, which tends to be right-handed, I'm under the impression that our fine motor skill part of the brain is in the left side of our brain. And so we tend to be right-handed.

There's also some argument that that's where the language part of our brain tends to be, and so there's some connection between those things. To be honest, I find that argument really confusing. I don't know why the language and the fine motor-spects. skills need to be connected. Maybe that's just a stronger part of the brain. If somebody wants to explain that to me, that would be great. Well, do Italians gesture more with their dominant hand or is equal? I did not research that. Wow. But it's an interesting question. But there's some arguments in parrots that like they tend to have a preference for their, I think it's their right

foot and the left side of their brain tends to be the like stronger side of their brain for a variety of different reasons. And so that's why we think that they tend to have the left foot preference. But the good news for me is that Ben didn't ask about brain lateralization. Ben asked, why not be ambidextrous? And the answer seems to just be, we're not 100% sure, but throughout the animal kingdom, we see this preference. And it could just be because our brains can't handle being equally good on both sides for the most part. So basically specialization is good, right? Like the way your body is not just a big blob of cells that all do everything, you have a liver and you have organs, parts of your brain develop specializations like mental organs that are good at this or that at the other,

and that's more effective than having everything be able to do everything. Yeah, that sounds good. Okay. Yeah. And how long have we been doing this, though? Like, do we know how far back in our history we've been mostly righties? Yeah, good question. So you had a bit of a segment on questionable science. Let's keep that going. And so let's start with some sort of less questionable science. So, you know, we talked about Neanderthals in a not too distant episode.

We have pretty good evidence from Neanderthal skeletons that they have right arms that are bigger than left arms, which suggests that Neanderthals also had a right hand or right arm preference. just like we tend to see in humans today. And we diverged from Neanderthals, what, a few hundred thousand years ago? Don't have that written down. But, you know, we were interbreeding with them, so we overlapped. And you could argue that some people argue we're the same species because we produced viable offspring. We can get into all that again. Right.

But we won't. So, Homo habilis, we found a skeleton that's 1.8 million years old. Amazing. And we weren't lucky enough to find a left and a right arm. so that we could compare arm bones to see if they were right or left handed. But we found their teeth and we have this indirect evidence from their teeth. And you tell me what you think of it, okay? Okay.

All right. So here's the evidence. The front teeth have marks on the teeth that go in a certain direction that are indented in a certain direction. And so here's what they think is happening. Imagine they have some item that they want to cut. And let's just imagine it's leather, right? So they hold the leather in their teeth on one side. And then they've got their left hand pulling it out on the other side.

And then they have a cutting tool in their right hand. And they are trying to cut it while they're holding it with their teeth. But every once in a while, they miss and they slam the rock into their teeth. All right. So I'm like a caveman soccer ball maker. right? I'm taking a piece of leather to repair for like Caveman World Cup. And I'm using my mouth as one of my tools, right? Yes.

I see. Okay. And occasionally slip and slam the rock into my face. Yes. And so if you do that, or if you are the students who were recruited for this experiment and you're wearing the mouth guard and then you slam the instrument into the mouth guard and it makes this same indentation, these indentations in the teeth and in the mouth guards go in one direction if you're a right-handed person using the tool in your right hand and holding the leather in your left hand, and they go in the opposite direction if you're a left-handed person who's holding the tool in your left hand and holding the leather in your right hand. And so this fossil and other fossils we've seen have these very distinctive marks on the teeth that have been used. And,

as indirect evidence that homo habilis was right-handed. And we also, I believe Neanderthal, we found similar marks on the teeth that we've used to say, hey, not only are the bones suggesting that they're right-handed, but we're also seeing the striations on their teeth going in the same direction. So that's, you know, probably more evidence that of right-handedness. And so maybe our homo ancestors, 1.8 million years ago, are showing evidence of right-handedness, and we're indirectly seeing it through the teeth. Are you convinced? There's a lot of leaps there.

Yeah, I don't know. As what I thought. I mean, they had to invent this whole activity that they're suspecting, maybe they're doing. And in the context of that hypothetical activity, there's potentially this sensitivity to handedness. But they don't even really know if these guys ever did that thing, right? Yeah.

Yep. I mean, I thought it was a very clever thought experiment. Yeah. But, like, what if they really liked fighting with, other and like the other caveman had like a rock in his left hand and he was like jabbing it at their teeth with their left hand or something that might have made the same marks that would have been a left handed person making those marks on the you know somebody else's face yeah or maybe while they watched the caveman world cup you know caveman messy scoring the final goal they like to

sit there and like chew on gravel and toss it into their mouth with their right hand or their left hand or who knows what like we're speculating about like cultural of these prehistoric folks. It's true, but I will note so, like, they, you only see these marks on the, like, front teeth. You don't see these marks on the, like, back teeth where you would expect them to be chewing on things. And so it's in a very, like, the front part of the front teeth where you wouldn't expect a lot of, like, marks related to chewing. And so it's probably from some other activity. And so, you know, I like the amount of time.

people have clearly spent staring at these teeth and thinking about it and coming up with scenarios. I've got to say, I don't feel like it's a slam dunk. But on the other hand, it's a clever scenario, a clever way to indirectly try to make use of, you know, skeletons where like, man, you know, are we ever going to get any better evidence, hopefully, but maybe not. And I don't know. I thought it was a clever experiment. But again, I didn't leave thinking homo habilis was definitely right-handed. No, definitely props to the scientists here. I mean, lots of areas of science, you're very limited amount of data you have. You can't create new data. You can't run these experiments. You don't know.

And so you've got to be creative and do the best you can. It's just important that we try to assess the level at which we're imposing our own cultural biases on this small amount of data and wondering whether we can trust our conclusions at all. But it's definitely creative research. Yeah, right. And two quick things to say in favor of the authors is one, they added caveats. to like how confident you could be about these results. They weren't like, bam, slam dunk. Also, N of one, doesn't matter. And then the other thing was, I thought they did try to create a clever experiment

where they had people put in those mouth guards and then they looked to see what kind of markings ended up on the mouthguards and compare them to what's on the teeth. So like, you know, they tried to do some experiments to, like, validate their hypothesis. But anyway, yes, all of the caveats that you just said, I agree with. Very cool. So let's see what Ben thinks of this sort of, all over the place answer I came up with, but I really enjoyed researching this topic.

And I really enjoyed hearing about it. Thanks for doing all that research. Yeah, my pleasure. Hi, Kelly. Thanks for doing all that research for me. Like a lot of biology, it's a lot more complicated than what we learn in high school. Also makes me wonder what sort of environment I need to set up to make sure that my kids are left-handed. I buy the argument that specialization can be an evolutionary advantage. I understand learning to do things one way and sticking with it. I also appreciate having a new term to describe myself. I've always been told that I'm left-handed because I write with my left hand, but I would actually describe myself as mix-handed. I have different preferences for different activities. Thanks so much for the podcast. All right. Thank you to everybody who wrote in with our

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