Listener Questions #39

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28:03Okay, 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, 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.

28:40How 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. 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?

29:16That 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? Wow. 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?

29:50Water 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. 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.

30:28I 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? 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.

31:06And 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, it's just restorative. And there's this famous paper from 20 years ago about the Lady Macbeth effect. If humans have this 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.

31:50And 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 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.

32:28They would say things like wish or shaker. And so this is supposed to probe whether thinking about bad things puts you in a mindset where you think about flowing water or washing yourself. That's why it's called the Lady Macbeth effect, 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 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.

33:08Like, 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, 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.

33:40It'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 it 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 P hacking? We don't really know. Okay. 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.

34:17All right. What else? Well, then I found a paper from 2018 that did a randomized control trial comparing routine immersion bathing, where you get all the way in the water, to just showering. And one of them has more water contact than the other, but both of them make you feel clean and refreshed, though bathing was better at treating 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 that humans do have some connection to water. You know, there's a reason people want to live by the beach.

34:57And there is a reason 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. And water just feels nice. Yeah, exactly. It does. But that doesn't mean that we couldn't get clean without water. 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?

35:33And so what exists today is that you can take what's called a dry shower 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 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 step one. And I know that folks out in space, for example, where water is really at a premium, can 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.

36:11Yeah, 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. 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 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.

36:42And 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 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. 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.

37:22So 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. Kombucha is 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 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.

38:00Infra 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.

38:39So 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?

39:15And 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. 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.

39:51Yeah, exactly. So it can make your bath more efficient. Huh? Right. Exactly. I can shake all those things off without needing to find them and scrub them and get that 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 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.

40:29So 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 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.

41:09So 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 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.

41:49And the advantage of mist is that it has a higher surface area per volume. 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 high-speed, super tiny, misty droplets can deliver kinetic energy enough to knock stuff off of your body. And so that's very cool. I don't think that it feels as nice. It doesn't provide the like, I'm washing away my bad day kind of a sense. I'm Lionel Messi and I missed five goals and I want to wash that away.

42:30Messi people need showers. Yeah. There you go. That's right. That's an obvious joke. I can't believe I didn't see that. I thought that's why you picked Messi. 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. 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.

43:09So 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 lever 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 trade-off, right? The simplest thing is to like stand under a really high volume of water and get clean.

43:44And that feels good. 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, blast some of the stuff off of you just using air. I think that overall, without some new, totally revolutionary technology where you use 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.

44:28Okay. Yeah. I can see that being good for the planets, but less relaxing. Trade-offs. And this could definitely help reduce water consumption. 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 bath than a three-minute shower.

45:06It 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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48:39All right, we're back and we're talking about showers and biology. Kelly, 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 writing 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 you're homozygous recessive, you have the potential to be ambidextrous and essentially choose at a young age which hand you prefer.

49:18I'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. All right. So Ben is asking about handedness, which is why we were talking about southpaws at the beginning of the episode. Daniel, 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.

49:55So that's probably over-representative. I would have guessed, you know, maybe one in five or one in ten. Okay, it's about 10%, 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 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.

50:33But 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 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?

51:17And 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%. 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.

51:58And 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 percent 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. Okay. 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.

52:35Depends 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?

53:12Because 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 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.

53:52I do know that. 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 cave fish. Okay. And blind cave fish 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.

54:38Right. 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, all right, I got it. And so if you take them out and 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.

55:23And 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 cave fish 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.

55:51This 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 way the room has changed. Right. 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. 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.

56:32They'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.

57:10Does 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 if you slice our brain down the center, it would look like both sides are sort of the same.

57:48But we do have different regions of our brains that specialize in different things. We think maybe dot-dot-dot-fmri stuff, yes. Yeah, yeah, yeah, yeah. Exactly. Right. Brains are 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.

58:32And 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. 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 it equal? I did not research that. Wow. Okay. 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.

59:11And 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 or the other.

59:52And 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? 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.

1:00:35And 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.

1:01:14And you tell me what you think of it. OK. OK. 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.

1:01:57All 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? 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.

1:02:39And 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 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 of right-handedness.

1:03:20And 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. That's 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. But what if they really liked fighting with each other and the other caveman had a rock in his left hand and he was jabbing it at their teeth with their left hand or something?

1:04:05That might have made the same marks. That would have been a left-handed person making those marks on somebody else's face. Yeah, or maybe while they watch 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. It's true, but I will note, so like, 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.

1:04:42And 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 i gotta 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 like 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 uh i don't know i thought it was a clever experiment but again i I didn't leave thinking Homo habilis was definitely right-handed.

1:05:25No, 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 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.

1:05:57They 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 mouth guards 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.

1:06:31And 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 learned 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.

1:07:02I have different preferences for different activities. Thanks so much for the podcast. All right. Thank you to everybody who wrote in with our questions. And thanks to everybody who engages. We really do want to hear from you. Don't be shy. Write to us to questions at danielandkelly.org. Share your questions. Share your curiosity. Share your thoughts. We look forward to hearing from you.

1:07:29Thanks, 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. Daniel and Kelly's Extraordinary Universe is edited by the amazing Matt Kesselman. He really is a wizard. You can also find us online on Blue Sky, Instagram, and XDNKUniverse. Come engage with us. You can email us at questions at danielandkelly.org. We really do want to hear from you. 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.

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