Listener Questions #39

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

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Daniel Whiteson?

  This is an iHeart Podcast. Guaranteed Human.

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• 1:43Kelly Weinersmith?

  Promotions I've done many times. I barely have to think. This is kinda nuts. How do my mind and muscles sync?

• 1:52Daniel Whiteson?

  Will Star Trek-style sonic showers replace the rinse and spray? Or will a clever mist just fake it while we still need water anyway?

• 2:01Kelly Weinersmith?

  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.

• 2:12Daniel Whiteson?

  Whatever questions keep you up at night, Daniel and Kelly's answers will make it all right.

• 2:18Kelly Weinersmith?

  Welcome to Listener Questions, episode number 39.

• 2:34Daniel Whiteson?

  Hi, I'm Daniel. I study particles and aliens and I'd give my left hand to be ambidextrous.

• 2:41Kelly Weinersmith?

  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.

• 2:51Daniel Whiteson?

  And do you have any left-handed children?

• 2:53Kelly Weinersmith?

  Uh, you know, it's hard to say. So our oldest is definitely right-handed and our youngest is ambidextrous, maybe? Uh, it's, we're not quite sure. His handwriting is a little sloppy with either hand. So hard to say.

• 3:15Daniel Whiteson?

  Well, I've always been amazed watching lefties do a lot of stuff, like writing, for example. It feels like a very unnatural motion to me, though I know to a lefty, of course, it must feel very natural.

• 3:26Kelly Weinersmith?

  Yeah, that's right. I, but I think if I was a left-handed person, I would get really tired of all of the, the jokes and the, you know, being called a southpaw or whatever, or like every time you reach for a scissor, being like, no, these weren't made for me. That's, I can imagine that being frustrating.

• 3:42Daniel Whiteson?

  Yeah, the world is definitely built by and for right-handed people.

• 3:45Kelly Weinersmith?

  That's right.

• 3:46Daniel Whiteson?

  And whichever side of your brain you use, if you're right-brained or left-brained, 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.

• 4:00Kelly Weinersmith?

  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, uh, which, you know, I think is something that I pretty much say every time. So, uh, let's go ahead and hear Adrian's question.

• 4:22Speaker 06

  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, the bin. And I was wondering, how did I do that? I didn't think about it. I didn't have the calculations going on. And then I extended that to even in sport when you're catching a ball and somehow you manage 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.

• 5:02Daniel Whiteson?

  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 did 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.

• 5:27Kelly Weinersmith?

  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.

• 5:45Daniel Whiteson?

  What?

• 5:46Kelly Weinersmith?

  I know. What?

• 5:47Daniel Whiteson?

  Muscles actually might have memories?

• 5:49Kelly Weinersmith?

  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 of 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.

• 6:31Daniel Whiteson?

  Hmm. 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.

• 6:42Kelly Weinersmith?

  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.

• 6:53Daniel Whiteson?

  Well, then you got the wrong co-host if you don't want to have a philosophical conversation.

• 6:57Kelly Weinersmith?

  And you know, 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, to mean stuff like this.

• 7:09Daniel Whiteson?

  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, you know, like work in physics and work in life are two totally separate concepts. 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.

• 7:34Kelly Weinersmith?

  Okay.

• 7:34Daniel Whiteson?

  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.

• 7:43Kelly Weinersmith?

  That's right. Okay. Yes. And so, 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.

• 8:20Daniel Whiteson?

  Okay.

• 8:21Kelly Weinersmith?

  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.

• 8:38Daniel Whiteson?

  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. 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?

• 9:15Kelly Weinersmith?

  All right. Well, I'm going to forgive you for asking a question that's way outside the bounds of what I

• 9:20Daniel Whiteson?

  Not at all.

• 9:22Kelly Weinersmith?

  What I have on my outline, but, but, okay. So, all right. So FMRI studies, yeah, they have some problems. In fact, there was this like classic study where they put dead trout in an FMRI machine and asked them questions and there were some like parts of their brains that lit up and they, anyway, so that 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.

• 10:05Daniel Whiteson?

  Right.

• 10:05Kelly Weinersmith?

  Now we even have things we can do where we can like, gosh, I don't, 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.

• 10:32Daniel Whiteson?

  Right.

• 10:33Kelly Weinersmith?

  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.

• 10:55Daniel Whiteson?

  Okay.

• 10:55Kelly Weinersmith?

  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.

• 11:26Daniel Whiteson?

  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.

• 11:54Kelly Weinersmith?

  Okay, well, and I'm gonna, I'm gonna step us back again because I'm always pushing back against your, your desire to keep us on track. But, 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, on non-human animals where we feel a little bit more comfortable.

• 12:13Daniel Whiteson?

  Yeah.

• 12:14Kelly Weinersmith?

  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.

• 12:22Daniel Whiteson?

  Yeah.

• 12:22Kelly Weinersmith?

  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, 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 the soccer ball, but I'm pretty sure it involves your leg.

• 12:49Daniel Whiteson?

  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?

• 13:07Kelly Weinersmith?

  I don't know who this messy fella is, but it sounds to me like he should clean his room. But, uh, no, no, the motor cortex, or she should clean her room. Uh, but, but anyway, uh, 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, uh, and you need to be paying more attention to the wind next time.

• 13:47Kelly Weinersmith?

  And so it tries to help your motor cortex coordinate better so that next time you do a better job. And so if messy gets out there and practices every day, which your face is telling me that I should know who messy is, so messy probably has practiced a lot. And so.

• 14:03Daniel Whiteson?

  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?

• 14:14Kelly Weinersmith?

  Yes.

• 14:15Daniel Whiteson?

  Okay. All right.

• 14:17Kelly Weinersmith?

  He married a Spice Girl.

• 14:18Daniel Whiteson?

  Cristiano Ronaldo?

• 14:20Kelly Weinersmith?

  Nope. Renodo.

• 14:23Daniel Whiteson?

  You never heard of Pele?

• 14:27Kelly Weinersmith?

  No.

• 14:28Daniel Whiteson?

  Wow. Okay. Wow. I didn't know where to go from there.

• 14:32Kelly Weinersmith?

  Well, I, 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 like how well coordinated a behavior is, uh, 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.

• 15:17Kelly Weinersmith?

  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.

• 16:02Daniel Whiteson?

  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 learn 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 realize, 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

• 16:46Daniel Whiteson?

  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.

• 17:08Kelly Weinersmith?

  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.

• 17:16Daniel Whiteson?

  Yeah.

• 17:16Kelly Weinersmith?

  With for the car thing, I feel like I, I think maybe I shouldn't be autopiloting. When I'm driving, uh, cause even if I subconsciously know the route, I should probably be alert for things that are changing, uh, you know, like the kid who might be running across the road.

• 17:31Daniel Whiteson?

  Yeah.

• 17:32Kelly Weinersmith?

  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 cause you're like, oh, I've done this enough. I don't need to think about anymore. Activate the driving to the grocery store pathway.

• 17:46Daniel Whiteson?

  Right.

• 17:46Kelly Weinersmith?

  But you should still be trying to pay attention when you're activating the going to the grocery store pathway.

• 17:51Daniel Whiteson?

  But it feels like we can describe that, but I'm not sure that we understand how that works. Right?

• 17:55Kelly Weinersmith?

  Yes, I would say that that is fair and that that this was Kelly's best attempt at trying to understand how this all works. Uh, and I, 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.

• 18:11Daniel Whiteson?

  Mm hmm.

• 18:12Kelly Weinersmith?

  And this is just sort of like our best guess of what's happening at the moment.

• 18:15Daniel Whiteson?

  Sure.

• 18:16Kelly Weinersmith?

  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, uh,

• 18:49Daniel Whiteson?

  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.

• 18:57Kelly Weinersmith?

  All right. Well, you, you managed to marry one of the Spice Girls. And so, uh, 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.

• 19:26Daniel Whiteson?

  What?

• 19:26Kelly Weinersmith?

  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 like 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.

• 20:00Daniel Whiteson?

  Wow.

• 20:01Kelly Weinersmith?

  10 centimeters long.

• 20:02Daniel Whiteson?

  That's crazy.

• 20:03Kelly Weinersmith?

  That's a long cell.

• 20:04Daniel Whiteson?

  This is something I usually think about as like microscopic.

• 20:07Kelly Weinersmith?

  Yeah, right. You could see, you can see that in a dissection lab. And it can contain something like 3,000 nuclei.

• 20:13Daniel Whiteson?

  Wow, that's incredible.

• 20:14Kelly Weinersmith?

  Yeah.

• 20:15Daniel Whiteson?

  3,000 nuclei. So like, who's making the decisions?

• 20:18Kelly Weinersmith?

  That's a good question. I don't know. Maybe they're all sharing. So 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, haha, 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.

• 20:59Daniel Whiteson?

  Oh.

• 21:00Kelly Weinersmith?

  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 gonna take a whole month. And then he doesn't exercise for a month and then he gets back to it.

• 21:28Daniel Whiteson?

  Yeah, that is a very unrealistic scenario.

• 21:32Kelly Weinersmith?

  Well, you know, I don't know anything about sports, so. When he gets back to it, he's got all these extranuclei 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 extranuclei 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.

• 22:16Daniel Whiteson?

  I see.

• 22:17Kelly Weinersmith?

  So I thought that was interesting.

• 22:18Daniel Whiteson?

  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 he going to be fitter faster because he's got these muscle cells with their extranuclei, but he's got the pathways to remember like how to kick the ball around the defenders, et cetera, et cetera. Right?

• 22:44Kelly Weinersmith?

  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 extranuclei stick around. We think it's a long time, but you know, this, this science area is, is pretty new.

• 23:02Daniel Whiteson?

  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?

• 23:15Kelly Weinersmith?

  Yeah, I think that's more about what's happening in your brain. Uh, 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.

• 23:26Daniel Whiteson?

  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.

• 23:40Kelly Weinersmith?

  Please don't send me more muscle physiology questions. I don't know the answers.

• 23:45Daniel Whiteson?

  But let's send this back to Adrian to hear if it answers his question.

• 23:49Speaker 06

  Thanks, Daniel, 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.

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• 26:07Daniel Whiteson?

  Okay, we're back and we're answering questions from listeners today about how to stay fit and how to stay clean.

• 26:14Kelly Weinersmith?

  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.

• 26:27Speaker 06

  Hi, Daniel and Kelly. My name is Bruce from the UK. My girlfriend recently asked me, when are they 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.

• 27:00Kelly Weinersmith?

  Yeah, so I'll be out. This was, 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?

• 27:19Kelly Weinersmith?

  That question lands a little different, I guess, depending on your cultural background.

• 27:23Daniel Whiteson?

  Right. Yeah, a little Schindler's List energy there.

• 27:25Kelly Weinersmith?

  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?

• 27:38Daniel Whiteson?

  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? Showers 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 inflowing 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.

• 28:23Daniel Whiteson?

  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.

• 28:31Kelly Weinersmith?

  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 details 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?

• 28:52Daniel Whiteson?

  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.

• 29:16Kelly Weinersmith?

  All right, moving on.

• 29:18Daniel Whiteson?

  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 associate it 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.

• 30:03Daniel Whiteson?

  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 blanks. So it would be like W blank, blank, H or S H blank, 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 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.

• 30:44Daniel Whiteson?

  That's why it's called the Lady Macbeth effect, you know, out, out damn 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.

• 31:08Kelly Weinersmith?

  I mean, like, 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.

• 31:29Daniel Whiteson?

  Yep.

• 31:29Kelly Weinersmith?

  But, you know, I can also imagine for other people, it'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.

• 31:52Daniel Whiteson?

  Right. Yeah. Well, this study was published in Science, so got a lot of press, but then faced some replication issues.

• 31:59Kelly Weinersmith?

  Okay.

• 32:00Daniel Whiteson?

  People tried to reproduce it, didn't get the same results. So, you know, is it pee hacking? We don't really know.

• 32:05Kelly Weinersmith?

  Okay.

• 32:06Daniel Whiteson?

  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?

• 32:14Kelly Weinersmith?

  Daniel and Kelly presenting science we don't necessarily stand by since 2024.

• 32:21Kelly Weinersmith?

  All right. What else?

• 32:22Daniel Whiteson?

  Well, then I found a paper from 2018 that did a randomized controlled trial comparing routine immersion bathing, where you 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 was better at 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 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

• 33:08Daniel Whiteson?

  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.

• 33:22Kelly Weinersmith?

  Yeah. Well, and water just like feels nice.

• 33:25Daniel Whiteson?

  Yeah, exactly. It does. But that doesn't mean that we couldn't get clean without water, right? And I think that's what Bruce's question is about is 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

• 34:08Daniel Whiteson?

  showers. And so they have all sorts of strategies for dealing with this. Kelly, tell us a little bit about how astronauts stay clean.

• 34:15Kelly Weinersmith?

  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 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 hiney to make sure that that like 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

• 34:57Kelly Weinersmith?

  your hair. And then you kind of 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.

• 35:15Daniel Whiteson?

  This coffee tastes like Kelly.

• 35:19Kelly Weinersmith?

  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.

• 35:28Daniel Whiteson?

  It's like space kombucha. Yum. Who knows what's in it?

• 35:31Kelly Weinersmith?

  So neither one of the, oh, hey, watch it, buddy. Kombucha's great. But neither one of those sounds very relaxing.

• 35:37Daniel Whiteson?

  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. And this is what Bruce asks about. And ultrasound cleaning is a technology we have already today for cleaning like jewelry and medical devices. And ultrasound just means sound at a frequency above the range you can hear. Infrared 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

• 36:20Daniel Whiteson?

  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 and 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 could never reach. So that's why it's very effective. The forces are really, really tiny, but they're very, very local.

• 37:03Daniel Whiteson?

  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 like shake off all the really hard to get to stuff. That's like the current use of ultrasonic cleaning.

• 37:39Kelly Weinersmith?

  Well, 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.

• 37:55Daniel Whiteson?

  Yeah, exactly. So it can make your bath more efficient. Exactly. Shake all those things off without need to like find them and scrub them and like get that, you know, sponge into that corner.

• 38:06Kelly Weinersmith?

  Without needing to enjoy the bath at all. Okay.

• 38:10Daniel Whiteson?

  It can suck all the pleasure out of the experience for you.

• 38:13Kelly Weinersmith?

  Excellent.

• 38:13Daniel Whiteson?

  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.

• 38:57Daniel Whiteson?

  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.

• 39:12Kelly Weinersmith?

  So after I muck the goat stalls, I should not use electrostatic dust removal. I will be no cleaner.

• 39:19Daniel Whiteson?

  No, exactly. Another direction is to use the water more efficiently. And so there's a technology called mist based showers. So a 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.

• 40:02Daniel Whiteson?

  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, mm, 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.

• 40:33Kelly Weinersmith?

  Messy people need showers. Yeah.

• 40:35Daniel Whiteson?

  There you go. That was.

• 40:36Kelly Weinersmith?

  That's right.

• 40:37Daniel Whiteson?

  That's an obvious joke. I can't believe you didn't see that.

• 40:41Kelly Weinersmith?

  I thought that's why you picked messy.

• 40:45Daniel Whiteson?

  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 leader over and over again.

• 41:21Kelly Weinersmith?

  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.

• 41:41Daniel Whiteson?

  No, it's always a trade off, 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? Blast 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,

• 42:25Daniel Whiteson?

  maybe a mild ultrasound where you could like step into it very quickly, get pretty clean with low water use.

• 42:32Kelly Weinersmith?

  Okay, yeah, I can see that being good for the planets, but less relaxing. Trade offs.

• 42:39Daniel Whiteson?

  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.

• 42:51Speaker 06

  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 liked Kelly's point about how showers are just nice. But I honestly think my girlfriend would prefer a 10-second dip in an ultrasonic bath than a three-minute shower. It seems like water isn't crucial, but makes cleaning so much easier. So it's unlikely we will be replacing our regular showers for ultrasonic mist instant filtration showers anytime soon. Thanks again.

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• 45:20Daniel Whiteson?

  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?

• 45:29Kelly Weinersmith?

  Are you kidding me? No. Moving on. All right, Ben from Connecticut. Thank you for writing in with your question. And let's hear what Ben had to ask about.

• 45:43Speaker 06

  Hi, Kelly and Daniel. This is Ben from Connecticut. When I was a teenager, someone once told me that there is no left-handed gene. The dominant allele is right-handed. And if you're 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 for the podcast.

• 46:14Kelly Weinersmith?

  All right. So Ben is asking about handedness, which is why we were talking about South Paws at the beginning of the episode. Daniel, but 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?

• 46:30Daniel Whiteson?

  Hmm, 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 10.

• 46:43Kelly Weinersmith?

  Okay, it's about 10%, but it varies a lot. And one of the reasons that it varies depended, 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.

• 46:58Daniel Whiteson?

  Yeah.

• 46:59Kelly Weinersmith?

  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 70s and the 80s where they found that children in China, only about 3.5% 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.

• 47:33Daniel Whiteson?

  You don't think that's the influence of the left-wing media?

• 47:36Kelly Weinersmith?

  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

• 48:20Kelly Weinersmith?

  or a righty in one direction or another. But again, none of them make the decision 100%. 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 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.

• 48:56Daniel Whiteson?

  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.

• 49:06Kelly Weinersmith?

  Yes, yeah, to some extent, yeah.

• 49:08Daniel Whiteson?

  Okay.

• 49:08Kelly Weinersmith?

  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.

• 49:16Daniel Whiteson?

  Depends on how much NPR they listen to, right?

• 49:19Kelly Weinersmith?

  Okay, all right, all right. Calm down, Daniel.

• 49:23Daniel Whiteson?

  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.

• 49:43Kelly Weinersmith?

  Yeah.

• 49:43Daniel Whiteson?

  It's amazing and tragic, but also really interesting.

• 49:47Kelly Weinersmith?

  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.

• 50:11Daniel Whiteson?

  That makes sense.

• 50:12Kelly Weinersmith?

  There's also a term called mixed handedness, where you preferentially use different hands for different tasks.

• 50:20Daniel Whiteson?

  Maybe you bat right-handed and pitch left-handed, to use a familiar sports analogy.

• 50:26Kelly Weinersmith?

  Yeah. Does Messi also play baseball? Or is that unclean?

• 50:31Daniel Whiteson?

  I don't know, but he can score with both feet. I do know that.

• 50:34Kelly Weinersmith?

  Oh, hey, I think you use 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 ago, I saw a talk that absolutely blew my mind. Okay, so it was a talk on blind cavefish. 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.

• 51:19Kelly Weinersmith?

  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 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, alright, 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.

• 52:04Kelly Weinersmith?

  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.

• 52:13Daniel Whiteson?

  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 cave fish actually have a preference.

• 52:23Kelly Weinersmith?

  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. And like, 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, the way the room has changed.

• 52:50Daniel Whiteson?

  Right.

• 52:50Kelly Weinersmith?

  But they don't have eyes because they're blind. They're blind cave fish. And so the way that they see the room is by moving and feeling the water bounce off the Legos and hit the side of their body.

• 53:02Daniel Whiteson?

  Amazing.

• 53:03Kelly Weinersmith?

  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.

• 53:12Daniel Whiteson?

  Yeah.

• 53:12Kelly Weinersmith?

  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 tends 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?

• 53:51Daniel Whiteson?

  Yeah, they respond to the use. Yeah.

• 53:54Kelly Weinersmith?

  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, 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 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.

• 54:34Daniel Whiteson?

  We think maybe data, data, fMRI stuff, yes.

• 54:37Kelly Weinersmith?

  Yeah, yeah, yeah, exactly. Right, brains are comp- 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 skills need to be connected.

• 55:21Kelly Weinersmith?

  Maybe that's just a stronger part of the brain. If somebody wants to explain that to me, that would be great.

• 55:26Daniel Whiteson?

  Well, do Italians gesture more with their dominant hand, or is it equal?

• 55:32Kelly Weinersmith?

  I did not research that.

• 55:34Daniel Whiteson?

  Wow.

• 55:35Kelly Weinersmith?

  Yeah. But, but it's an interesting question. But there's some arguments and parrots that like, they, 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.

• 56:18Daniel Whiteson?

  So, basically, specialization is good, right? Like, the way, your body's 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 or the other, and that's more effective than having everything be able to do everything.

• 56:37Kelly Weinersmith?

  Yeah, that sounds good.

• 56:38Daniel Whiteson?

  Okay.

• 56:39Kelly Weinersmith?

  Yeah.

• 56:39Daniel Whiteson?

  And how long have we been doing this, though? Like, do we know how far back in our history we've been mostly righties?

• 56:45Kelly Weinersmith?

  Yeah, good question. So you had a bit of a segment on questionable science. Let's keep that going. And so, so, 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.

• 57:16Daniel Whiteson?

  And we diverged from Neanderthals, what, a few hundred thousand years ago?

• 57:20Kelly Weinersmith?

  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 all into all that again. But we won't. So Homo habilis, we found a skeleton that's 1.8 million years old.

• 57:38Daniel Whiteson?

  Amazing.

• 57:39Kelly Weinersmith?

  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?

• 57:57Daniel Whiteson?

  Okay.

• 57:57Kelly Weinersmith?

  All right, so here, 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.

• 58:38Daniel Whiteson?

  All right, so I'm like a caveman soccer ball maker, right? And 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?

• 58:49Kelly Weinersmith?

  Yes.

• 58:49Daniel Whiteson?

  I see. Okay. And occasionally slip and slam the rock into my face.

• 58:54Kelly Weinersmith?

  Yes. And, and so if you do that, or, or if you are the students who are 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

• 59:35Kelly Weinersmith?

  marks on the teeth that have been used 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, are you convinced?

• 1:00:11Daniel Whiteson?

  There's a lot of leaps there. Yeah, I don't know.

• 1:00:14Kelly Weinersmith?

  That's what I thought.

• 1:00:15Daniel Whiteson?

  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?

• 1:00:31Kelly Weinersmith?

  Yeah. Yep. I mean, I thought it was a very clever thought experiment.

• 1:00:35Daniel Whiteson?

  Yeah.

• 1:00:35Kelly Weinersmith?

  But like, what if they really liked fighting with each other and like the other caveman had like a rock in his left hand and he was like

• 1:00:42Daniel Whiteson?

  Yeah.

• 1:00:43Kelly Weinersmith?

  jabbing it at their teeth with their left hand or something that might've made the same marks. That would have been a left-handed person making those marks on the, you know, somebody else's face.

• 1:00:53Daniel Whiteson?

  Hmm. Yeah. Or maybe while they watched the caveman World Cup, you know, caveman Messi. 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 activities of these prehistoric folks.

• 1:01:11Kelly Weinersmith?

  It's it's true, but I will 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 got to say, I don't feel like it's a slam dunk. But on the other hand, it's a clever scenario, clever way to indirectly like try to make use of, you know, skeletons where like, man, you know, are we ever going

• 1:01:56Kelly Weinersmith?

  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.

• 1:02:06Daniel Whiteson?

  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 got to be creative and do the best you can. It's just important that we try to assess the level at which like 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.

• 1:02:31Kelly Weinersmith?

  Yeah, right. And two, two quick things to say in favor of the authors is one, they 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 they did try to create a clever experiment where they had people put in those mouthguards 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.

• 1:03:01Daniel Whiteson?

  Very cool.

• 1:03:02Kelly Weinersmith?

  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.

• 1:03:11Daniel Whiteson?

  And I really enjoyed hearing about it. Thanks for doing all that research.

• 1:03:14Kelly Weinersmith?

  Yeah, my pleasure.

• 1:03:15Speaker 06

  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 mixed-handed. I have different preferences for different activities. Thanks so much for the podcast.

• 1:03:48Daniel Whiteson?

  All right. Thank you to everybody who wrote in with their questions. And thanks to everybody who engages. We really do want to hear from you. Don't be shy. Write to us to [email protected]. Share your questions, share your curiosity, share your thoughts.

• 1:04:01Kelly Weinersmith?

  We look forward to hearing from you.

• 1:04:09Daniel Whiteson?

  Thanks, everybody, for listening. Please go and do us a favor and rate the show on whatever podcast app you're using. It really helps people find us.

• 1:04:17Kelly Weinersmith?

  Daniel and Kelly's Extraordinary Universe is edited by the amazing Matt Kesselman.

• 1:04:22Daniel Whiteson?

  He really is a wizard. You can also find us online on Blue Sky, Instagram, and X, D and K Universe. Come engage with us.

• 1:04:32Kelly Weinersmith?

  You can email us at [email protected]. We really do want to hear from you.

• 1:04:37Daniel Whiteson?

  And you can find our website, www.danielandkelly.org, where you'll also find an invitation to join our Discord, where everybody comes and talks about the amazing universe.

• 1:04:49Kelly Weinersmith?

  And we also have the most amazing moderators. This is an iHeart Podcast. Thanks for joining us.

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