Why Feet Are Weirder Than You Think

Compared with almost every other animal on Earth, our feet seem strangely specialised. They can't grip branches, they're full of arches and joints, and for some reason we're the only species that regularly puts shoes on them. Hannah and Michael explore how millions of years of evolution transformed ape like feet into powerful biological springboards, uncovering a surprising connection between human walking, pizza slices, and one of mathematics' most beautiful ideas. After the break, they ask why feet attract so much attention from WikiFeet ratings to one of the most common fetishes on Earth. ------------------- For more information about Cancer Research UK, their research, breakthroughs and how you can support them, visit https://www.cancerresearchuk.org/our-research/rest-is-science Cancer Research UK is a registered charity in England and Wales (1089464), Scotland (SC041666), the Isle of Man (1103) and Jersey (247). A company limited by guarantee. Registered company in England and Wales (4325234) and the Isle of Man (5713F). Registered address: 2 Redman Place, London, E20 1JQ. ------------------- Find The Rest Is Science all over the internet by ⁠⁠clicking here.⁠⁠ ------------------- Video Producer: Adam Thornton + Oli Oakley + Jack Meek Animator: Sam Benson Video & Social: Bex Tyrrell Assistant Producer: Lucy Lipscombe Producer: Simona Rata Senior Producer: Lauren Armstrong-Carter Head Of Digital: Samuel Oakley Exec Producer: Neil Fearn Learn more about your ad choices. Visit podcastchoices.com/adchoices

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

• 0:01Hannah Fry?

  Welcome to The Rest Is Science. I'm Hannah Fry.

• 0:02Michael Stevens?

  And I'm Michael Stevens.

• 0:04Hannah Fry?

  Here's a question for you, Michael. What is going on with feet?

• 0:07Michael Stevens?

  With my feet?

• 0:09Hannah Fry?

  Yeah. Not just yours, but also yours.

• 0:12Michael Stevens?

  Okay. No one knows what's going on with my feet because I never show them off.

• 0:16Hannah Fry?

  Do you not?

• 0:16Michael Stevens?

  Okay, I guess I did once when I stepped on Legos, like, for a bit to get views. But when I was a small child, like a child, I had hairy feet. Yes. And I was walking around barefoot one day and my dad's friend, whose name was Al, like, I'm not afraid to name and shame. He looked at me and he goes to my dad, he goes, "Whoa, your son's feet have a lot of hair on them."

• 0:39Hannah Fry?

  Wait, how old were you at this point?

• 0:40Michael Stevens?

  Okay, in my mind, I'm like four, but I'm sure, I'm sure I was like a teenager.

• 0:45Hannah Fry?

  Are we talking about like, sort of, soft, downy children hair? Or are we talking about like, thick man hair?

• 0:50Michael Stevens?

  No, we're talking about, like, look at my beard and then imagine toes coming out of it. It's, it's almost like that. Even at home, I've been married to my wife for 10 years now. I still just wear socks all the time so she won't go, "Ugh," whenever she sees me.

• 1:05Hannah Fry?

  Are they still hairy?

• 1:06Michael Stevens?

  Well, yeah, I haven't shaved them.

• 1:09Hannah Fry?

  Wow.

• 1:09Michael Stevens?

  But this episode is not about me.

• 1:11Hannah Fry?

  Okay.

• 1:11Michael Stevens?

  This episode is about our entire species.

• 1:14Hannah Fry?

  It is about our entire species.

• 1:16Michael Stevens?

  And I hadn't really thought about it until you mentioned it, but they are a bit weird.

• 1:20Hannah Fry?

  They are very weird. They're very different to other animals' feet. And that is what we're going to get into it. But, listeners, don't worry. We're going to come back to Michael's feet as well because I've got more questions. I've got more questions about that.

• 1:32Michael Stevens?

  I have no more answers. Or do I?

• 1:41Michael Stevens?

  This episode is brought to you by Cancer Research UK.

• 1:44Hannah Fry?

  Scientists have found that cancer risks usually increase with age and size, but some species defy the odds.

• 1:51Michael Stevens?

  For example, deep-sea Greenland sharks. They can grow over six meters long, weigh more than a small car, and yet, live for up to 400 years.

• 2:01Hannah Fry?

  Now, understanding how Greenland sharks' cellular repair and immune systems seem to have managed to keep them cancer-free for centuries, that could open up exciting research pathways.

• 2:13Michael Stevens?

  Essentially, over millions of years, evolution has been running the world's most successful cancer-prevention trial. And sometimes, breakthroughs can be found in unusual places.

• 2:23Hannah Fry?

  So by exploring the unexpected, Cancer Research UK scientists are uncovering new ways to tackle over 200 types of cancer. Their work has helped to double survival in the UK over the last 50 years and continues to save and improve lives around the world.

• 2:39Michael Stevens?

  For more information about Cancer Research UK, their research and breakthroughs and how you can support them, visit cancerresearchuk.org/the rest is science.

• 2:50Speaker 02

  Hi, this is Gary Lineker from Goalhangers, The Rest Is Football. This episode is brought to you by Wise. It's only when you start moving money between currencies that you really think about the exchange rate, the fee, and what might be hidden away in the small print. Whether you're living abroad, paying someone overseas, or just trying to manage your money across borders, you want a fair exchange rate, an easy transfer, and no surprises along the way. Wise keeps things simple. Wise is a smart way to move the currencies you need around the globe. It works in more than 160 countries and with over 40 currencies, most transfers arrive instantly. Wise uses the mid-market exchange rate, like the one you see on Google, with no markups or hidden fees. So when money

• 3:35Speaker 02

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• 3:48Hannah Fry?

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• 4:33Hannah Fry?

  an infection, flu-like symptoms, or need a vaccine. Explore what's possible. Ask your doctor about Tremfya today. Call 1-800-526-7736 to learn more, or visit tremfyaradio.com.

• 4:54Hannah Fry?

  So I was in Cambridge the other day, having lunch, and I ended up chatting to a colleague of mine called Shreya Smanrey. He raised this question with me, I'm like, why are human feet so weird compared to every other creature that exists? Okay? If you think about it, the same solution has evolved over and over again in the form of hooves and trotters.

• 5:15Michael Stevens?

  What's a trotter?

• 5:17Hannah Fry?

  A trotter.

• 5:17Michael Stevens?

  Like a paw?

• 5:18Hannah Fry?

  It's like a, it's on a pig, you know?

• 5:21Michael Stevens?

  Oh, okay.

• 5:21Hannah Fry?

  It's got a split, it's got kind of like toes.

• 5:23Michael Stevens?

  But it's different than a hoof. Pigs don't have hooves, do they?

• 5:26Hannah Fry?

  It's sort of halfway between, it's slightly softer than a hoof.

• 5:29Michael Stevens?

  See, I'm not afraid to admit what I don't know.

• 5:31Hannah Fry?

  Do you know, I'm also now worried about the limits of my own knowledge of trotter versus hoof.

• 5:36Michael Stevens?

  Is anyone Jewish here? Because they would know. They've got that whole rule about you can't eat a hoofed animal unless it choose cud.

• 5:44Hannah Fry?

  Really?

• 5:45Michael Stevens?

  Yeah.

• 5:46Hannah Fry?

  Do you know what? I think trotter might be a kitchen word.

• 5:48Michael Stevens?

  Yeah, because if you look up pig trotter, pig trotter on Wikipedia, it's a culinary dish. And the picture is pretty...

• 5:56Hannah Fry?

  Grim.

• 5:56Michael Stevens?

  Grim. Like, it's good, it illustrates the trotter.

• 6:01Hannah Fry?

  That's what you needed.

• 6:02Michael Stevens?

  It does not look appetizing.

• 6:03Hannah Fry?

  It does not, it does not.

• 6:04Michael Stevens?

  It looks quite undignified.

• 6:06Hannah Fry?

  I would not want to be that pig, put it that way.

• 6:09Michael Stevens?

  Okay, but here's... Hold on. If you're gonna be a pig who's going to be slaughtered, you could do worse than being the pig whose trotter gets pictured on Wikipedia for eternity. You're immortalized.

• 6:21Hannah Fry?

  I don't think I would care that much about legacy as a...

• 6:24Michael Stevens?

  Oh, I would. I'm like, I'm in it, I'm in it for, for the legacy, for the fame.

• 6:30Hannah Fry?

  Yeah.

• 6:31Michael Stevens?

  Yeah, for the photos.

• 6:32Hannah Fry?

  The immortality of my trotter.

• 6:35Michael Stevens?

  My little trotter, my little trotters.

• 6:37Hannah Fry?

  Okay, here's the thing, right? Hooves make really good mechanical sense, you know? You've got, you want to be a fast, heavy runner, you evolve hooves, right? You're not damaging the ground. If you want to sprint and hunt, then you evolve paws, these are much softer, they're like squishy jelly bean pads. If you want to climb, then you evolve a kind of second pair of hands, which is what you get with monkeys. Feet, what what is going on with them?

• 7:03Michael Stevens?

  Right, it's kind of halfway between climbing and not climbing.

• 7:07Hannah Fry?

  Right.

• 7:08Michael Stevens?

  It can't grasp, but but monkeys have much more opposable toes.

• 7:13Hannah Fry?

  They do.

• 7:14Michael Stevens?

  In fact, my daughter has a book about human evolution and it's got all these artist renderings of early hominids. And they all have like hand feet. So, yeah, well, not only is that different, but also Homo sapiens are the only animals on this planet that wears shoes.

• 7:31Hannah Fry?

  Right.

• 7:32Michael Stevens?

  Now, we put them on horses.

• 7:33Hannah Fry?

  Sure.

• 7:34Michael Stevens?

  When they're doing labor for us, we'll put them on dogs, but only when the dog is going to be walking on something we made, like asphalt or concrete. By the way, do you say asphalt or asphalt?

• 7:43Hannah Fry?

  Asphalt.

• 7:44Michael Stevens?

  Oh, you said felt.

• 7:45Hannah Fry?

  I don't know. It doesn't come up that often in my world, I'll be honest.

• 7:49Michael Stevens?

  Well, anyway, and so why, what's going on there? Our feet are weird.

• 7:53Hannah Fry?

  They are weird. They are weird, but I think the shape of them in particular. When people first started trying to make robots, okay, the first time that you sort of needed to like construct a foot to see how it could work. And they tried to make these these like flat feet. It's just like kind of moving like this, right? Which is, maybe that's how our feet have evolved. Maybe it was that we were previously climbing trees and then they just became slightly flatter, slightly less able to grip around the the trunk of a tree and slightly more attuned to to going on the ground.

• 8:22Michael Stevens?

  To walking, yeah.

• 8:24Hannah Fry?

  So when people first start building robots, they they made these perfectly flat feet and it was a total disaster. Because what that means is if if your feet are completely flat, you can't roll forwards.

• 8:34Michael Stevens?

  Right.

• 8:34Hannah Fry?

  So instead, like the early robots like Asimo, which is, you know, a particularly famous one. They have to, if you look at them, they have to stand essentially with their knees permanently bent in order to be able to to move forward, right? It's really, really energy intensive to like kind of lift your feet up this way. And if you look at an ape walking, that's essentially what they're having to do.

• 8:55Michael Stevens?

  Oh, really?

• 8:56Hannah Fry?

  Because their their feet are so flexible.

• 8:59Michael Stevens?

  Right.

• 9:00Hannah Fry?

  That when they are down on the ground, boof, they have them very flat. And so their knees and their hips are continually having to be bent in order for them to propel themselves forward. It's like really. Energy intensive, they don't like doing it at all, would much rather be in the trees.

• 9:14Michael Stevens?

  And so a firmer foot that's less flexible, like a human foot is better for walking.

• 9:20Hannah Fry?

  Right, you sort of want the rigidity in order to be able to kind of press off, but you also don't want it to be flat.

• 9:27Michael Stevens?

  Right.

• 9:27Hannah Fry?

  Because the flat obviously takes a lot of energy.

• 9:29Michael Stevens?

  It needs to be somewhere in between.

• 9:30Hannah Fry?

  Yeah, but then here's a question, okay, you don't want it to be flat, you want it to be rigid. Why isn't it shaped like a rocking chair? That would help you propel forwards.

• 9:38Michael Stevens?

  Oh, yeah.

• 9:39Hannah Fry?

  I mean, that would make way more sense.

• 9:40Michael Stevens?

  I mean, it needs to be, I need to be able to move it, like I need my toes to be able to sometimes give more or less resistance to the rocking motion.

• 9:48Hannah Fry?

  Agreed, but like this kind of, this effect of like rolling forwards, and yet our feet are arched exactly the opposite way.

• 9:55Michael Stevens?

  They are, aren't they? Yeah.

• 9:56Hannah Fry?

  So this was a genuine puzzle. Why is it that our feet are arched that way around rather than the other way around?

• 10:01Michael Stevens?

  Can I make a guess or I I would guess that it's like architectural for support, that that arch, just like an arch in architecture, holds weight better than like a saggy rocking chair type foot.

• 10:13Hannah Fry?

  I don't think that's the primary reason.

• 10:15Michael Stevens?

  So what other reason is there?

• 10:17Hannah Fry?

  It's probably because standing still would be really difficult if our foot, if our feet were bent like a rocking chair.

• 10:23Michael Stevens?

  Oh.

• 10:24Hannah Fry?

  And people have tried this with robots as well.

• 10:26Michael Stevens?

  Right.

• 10:26Hannah Fry?

  So the sort of next generation of robots had had rocking chair type feet. But then standing still would require you to continually tense yourself. You'd have to like permanently be locked in place.

• 10:39Michael Stevens?

  Yeah.

• 10:40Hannah Fry?

  And so it just doesn't work either. So instead with the arch the other way, it means that you can kind of create a triangle between the big toe, sort of pinky side of the foot and your heel, and you're kind of sitting on a little tripod, right?

• 10:53Michael Stevens?

  Little tubular tripods, yeah.

• 10:55Hannah Fry?

  Kind of be in a, in a relaxed state. But in the nineteen fifties, people were like, this does still really not make a lot of sense. Like, why have we got this? Maybe the foot arch is there for, for structure, but you know, it makes sense why we don't have these flat feet. But what is going on? Like, why are our feet in this particular shape? So in the nineteen fifties, this English orthopedic surgeon, he was like, guys, I've cracked this, I've worked it out. He was kind of looking. At the human foot. And he knew it couldn't be a rocking chair. But he also knew that if it was just this fluffy, fluffy bag of joints.

• 11:28Michael Stevens?

  Yeah.

• 11:28Hannah Fry?

  You know, this insane number of bones.

• 11:30Michael Stevens?

  Like a monkey foot.

• 11:31Hannah Fry?

  Like a monkey foot, then we wouldn't be able to push off and it would be really, really difficult. So he was like, right, there must be this kind of structure that's going on in here. This is the explanation that he managed to come up with. Okay.

• 11:43Michael Stevens?

  Oh, you've got a cardboard model.

• 11:45Hannah Fry?

  I do.

• 11:45Michael Stevens?

  Looks like you built it yourself.

• 11:46Hannah Fry?

  I did, in the car on the way here.

• 11:47Michael Stevens?

  It's got like an arch. It's like, it's like a cardboard shaped boomerang.

• 11:52Hannah Fry?

  Yeah, it's got three different parts to it. Okay, so those of you who are watching, you can see, this is sort of like learn with Hannah.

• 11:58Michael Stevens?

  Yeah.

• 11:59Hannah Fry?

  This is, this is my model of a foot and how foot works, or how they thought the foot worked in the 1950s.

• 12:04Michael Stevens?

  Okay, so, so let me say what I'm seeing.

• 12:05Hannah Fry?

  Go on.

• 12:06Michael Stevens?

  Three parts. One looks like a boomerang shape.

• 12:09Hannah Fry?

  Yep.

• 12:09Michael Stevens?

  And then attached to one end is a little ellipse that is hinged, like, like with a brad. So it can swirl around 360.

• 12:18Hannah Fry?

  Yeah, I mean, that's, that's not what you want in your real foot.

• 12:20Michael Stevens?

  That's not what you want. And I can tell that because you've connected the far end of the boomerang to the far end of the ellipse with a rubber band. So it's almost like a bow and arrow type.

• 12:30Hannah Fry?

  Exactly. It's like a bow and arrow type shape, exactly. So what you can't quite see here, I've essentially split the foot into three sections. And then we have like a tendon running between them. So here is the heel.

• 12:41Michael Stevens?

  Right.

• 12:41Hannah Fry?

  This is kind of the back of the foot. And then you have essentially the foot arch that goes up and over. And then this here is the toes. Okay.

• 12:48Michael Stevens?

  Right.

• 12:49Hannah Fry?

  So now.

• 12:50Michael Stevens?

  The ellipse is the toes.

• 12:51Hannah Fry?

  The ellipse that can move around is the toes, exactly.

• 12:53Michael Stevens?

  It hinges there.

• 12:54Hannah Fry?

  So here was his idea. He was like, the foot being this shape, like a bow from a bow and arrow.

• 12:59Michael Stevens?

  Yeah.

• 12:59Hannah Fry?

  This makes perfect sense. Because when you put your foot down, you've got lots of nice kind of elasticity, so your foot doesn't get damaged. The kind of the string from the bow hits the ground first and absorbs lots of the energy as, as you hit the ground. But if you move forward by lifting your heel up, then what you're doing is you're tightening this bow. You're tightening the, the tension between your heel and your toe. And that's the thing that's giving your foot this structure. That's the thing that's giving your foot this strength, this stiffness, in order for you to be able to push. Off and move forwards, right? It's something that just made absolute perfect sense.

• 13:34Michael Stevens?

  Yeah.

• 13:35Hannah Fry?

  As a result of of this explanation, this explanation, by the way, stood for like seventy years. Everyone was like super happy with it. And it led to something called Jack's Test, which you can do on yourself. There was a bit of me, Michael, that was gonna suggest that you get your feet out for this, but but maybe not.

• 13:50Michael Stevens?

  May maybe maybe later.

• 13:52Hannah Fry?

  Maybe later, but if you stand barefoot.

• 13:54Michael Stevens?

  That's it's for the rest is science after dark.

• 13:59Hannah Fry?

  Yeah, that's the subscription.

• 14:01Michael Stevens?

  Yes, yes.

• 14:04Hannah Fry?

  You know, I think Lily Allen once said she's got OnlyFans, but she only shows pictures of her feet.

• 14:09Michael Stevens?

  Okay.

• 14:09Hannah Fry?

  And she said that she makes more money from that than she does from her actual music.

• 14:13Michael Stevens?

  I believe her.

• 14:14Hannah Fry?

  That's incredible, isn't it?

• 14:15Michael Stevens?

  Yeah, well, she probably doesn't have like Ticketmaster fees and a recording label to pay.

• 14:20Hannah Fry?

  Very true.

• 14:21Michael Stevens?

  She just snaps them with her phone and ka-ching.

• 14:23Hannah Fry?

  Ka-ching, hello. I'm gonna come on to that a bit bit more later, the the foot fetish stuff. It wouldn't be a a proper episode about feet if I didn't mention it.

• 14:30Michael Stevens?

  No, we have to.

• 14:31Hannah Fry?

  We have to, we have to. Okay, so so there's this thing called Jack's Test. If you stand barefoot with your with your weight on the floor and you have somebody else pull your big toe backwards. So you're kind of standing like this and then you get someone else to effectively tighten.

• 14:48Michael Stevens?

  So they like pull it up?

• 14:50Hannah Fry?

  They pull your big toe up.

• 14:51Michael Stevens?

  Uh huh.

• 14:52Hannah Fry?

  Then you will see your arch tighten, basically. You see your arch kind of getting.

• 14:58Michael Stevens?

  Tighter.

• 14:58Hannah Fry?

  More stiff, essentially. And everyone was like, well, this is the proof that his explanation is correct. It's it's very clear that moving the big toe, move this tendon, the plantar fascia that runs between the front and back of your foot. And everyone was like, well, there you go, this is it, we we we worked it out, this is absolutely fine. And then what would happen is this kind of like really fed into the the medical understanding of what it meant for feet to to to be working correctly. So you you might have heard this idea of people saying, you're very flat footed.

• 15:31Michael Stevens?

  Yep.

• 15:32Hannah Fry?

  And that being considered a real problem.

• 15:34Michael Stevens?

  Right.

• 15:35Hannah Fry?

  And it comes from this exact same explanation that if your foot is too flat, if your arch is too narrow, then you can't get the tension properly and it affects the way that you end up walking. There was some confirmation bias going on in this too, because people would go to doctors and they would say, we've got loads of pain in our feet. And the doctors would look at their feet and say, well, it's because your feet are flat. I can see that there's a flatness to your foot and that must, that must end up being the problem.

• 15:58Michael Stevens?

  Okay.

• 15:59Hannah Fry?

  The slight issue, right, with this explanation, well, there's two. The first is, if this really is the way that feet work, well, then how come people who do have completely flat feet can walk?

• 16:12Michael Stevens?

  Yeah, they can.

• 16:13Hannah Fry?

  They can. It is possible. You don't need, you don't actually need the arch.

• 16:17Michael Stevens?

  Well, I remember being told as a kid that I had flat feet by my doctor. But I didn't know what the, the symptoms were supposed to be.

• 16:24Hannah Fry?

  Right.

• 16:25Michael Stevens?

  I could walk fine. I could run fine. It's never been a problem.

• 16:28Hannah Fry?

  What did they, what did they say about it?

• 16:30Michael Stevens?

  I don't remember anything outside of he made me walk around barefoot in the doctor's office. Maybe he just wanted a free sweeping of his floor. They're not fat hairy guys.

• 16:42Hannah Fry?

  Maybe he thought your, your feet were so flat because he couldn't see through all the hair.

• 16:46Michael Stevens?

  He couldn't see through all the hairs, like this forest. No, but I remember him telling my mom, yeah, he's kind of got flat feet, but then nothing ever came of it. So.

• 16:54Hannah Fry?

  Right. And it doesn't matter at all because, because while some people who have pain in their feet have flatter feet than others, there are also like loads of people who've got incredibly flat feet and like run marathons and do all the stuff and they're absolutely fine. Like they're completely fine.

• 17:09Michael Stevens?

  That's what I was thinking. Yeah.

• 17:10Hannah Fry?

  And then the.

• 17:11Michael Stevens?

  And there are plenty of people with really nice arches who have.

• 17:13Hannah Fry?

  Absolutely, completely. The other big clue that this, this explanation was completely wrong is that for this explanation to work, the way that they constructed it, is that you, you sort of have to fuse the heel and the arch. You, you kind of, this particular joint is like quite rigid in the explanation. But then it turns out that there have been some surgeries where people who've got really bad arthritis have had that joint physically fused. And it makes it really, really difficult to walk.

• 17:42Michael Stevens?

  Right.

• 17:43Hannah Fry?

  So how can it be?

• 17:44Michael Stevens?

  And this is the joint between the heel and the rest of the foot?

• 17:48Hannah Fry?

  Yeah, let me get the exact.

• 17:49Michael Stevens?

  I didn't know there was even a joint there.

• 17:50Hannah Fry?

  There's, there's, I mean, there's lots of joints. I think there's thirty joints in the foot in total.

• 17:55Michael Stevens?

  Oh, goodness.

• 17:55Hannah Fry?

  I mean, this is sort of pretending that there's two.

• 17:57Michael Stevens?

  There's, yeah, right. But yeah, there's.

• 17:59Hannah Fry?

  It's called the navicular medial cuneiform joint.

• 18:04Michael Stevens?

  Okay.

• 18:05Hannah Fry?

  Okay. And if you fuse it in the, in the existing idea of how feet work, not a problem at all. But in reality, makes somebody's ability to walk significantly worse. So it's like, well, this, this is like, there's something wrong going on here.

• 18:20Michael Stevens?

  Something missing.

• 18:21Hannah Fry?

  Something is wrong going on here. Very recently, in twenty twenty, this paper that my colleague at Cambridge was, was involved in, a group of scientists, mechanical engineers and biologists essentially, were like, something is going on here. Something, something not right. So they decided to look at the foot from, from a completely different angle. Because this entire time, when we've been thinking about the mechanics of a foot, we'd been looking at the arch that runs from the toes to the heel.

• 18:48Michael Stevens?

  Yeah.

• 18:49Hannah Fry?

  But this group were like, well, hang on a second. There is another arch going on in your foot. Your foot doesn't just bend front to back, it also bends left to right.

• 19:00Michael Stevens?

  Right.

• 19:01Hannah Fry?

  Like if you think about the way that your.

• 19:02Michael Stevens?

  Like a pringle.

• 19:03Hannah Fry?

  Like a pringle, exactly. You're looking at your feet now.

• 19:08Michael Stevens?

  Yeah, I know, but I've got shoes on. So I'm like, no, it's pretty darned flat. But yeah, I know what you're talking about.

• 19:14Hannah Fry?

  Your commerce soul underneath. Yeah, exactly. And actually, they were like, well, hang on a second. Maybe it's the, maybe the stiffness. Cause you need, your, your foot needs to have this stiffness in order for you to be able to push off and propel yourself forward. So they were like, maybe the stiffness is coming from the arch that runs in the other direction instead. Rather than front to back, maybe that one's not as important. Maybe it's, maybe it's side to side, from the big toe to the pinky toe. So what they did, got hold of some cadaver feet. Gets gruesome.

• 19:45Michael Stevens?

  Keep going.

• 19:47Hannah Fry?

  They mounted these feet into this like quite heavy duty materials testing machine where they would like press weights down on the foot to see how much force it would take to bend the midfoot.

• 20:00Michael Stevens?

  And these were cadaver feet that were not compensating for the extra weight. They were just looking at the structural properties.

• 20:06Hannah Fry?

  Structural properties of the foot, nothing else. And then once they'd done that, they then got out some scissors and they started snipping the joints between the toes.

• 20:17Michael Stevens?

  Right.

• 20:17Hannah Fry?

  Not just between the toes, but in that direction, right? Trying to break the arch that runs from left to right.

• 20:22Michael Stevens?

  Watch when it fails.

• 20:23Hannah Fry?

  And it turns out that this like, you know, really decades and decades and decades old understanding of the foot just crumpled as the snips took place. Because almost all of the rigid structure of the foot comes from the left to right arch, not the front to back.

• 20:44Michael Stevens?

  Wow.

• 20:44Hannah Fry?

  Like completely shattered this biomechanical.

• 20:47Michael Stevens?

  Yeah.

• 20:47Hannah Fry?

  Dogma that existed. Yeah, when they ran the numbers, the the the front to back arch only accounts for about 25% of the foot's rigidity.

• 20:57Michael Stevens?

  Okay.

• 20:57Hannah Fry?

  Now, the reason why this works, the reason why you get this stiffness, something called Gaussian curvature. The reason why you get stiffness from there being a bend. It's a bit like, you know, when you have a slice of pizza?

• 21:08Michael Stevens?

  Yep.

• 21:09Hannah Fry?

  So a slice of pizza, if you try and get it in your mouth, I'm doing this with a piece of paper. It would be much more fun if it was actual pizza, but.

• 21:16Michael Stevens?

  I'm imagining.

• 21:17Hannah Fry?

  You're imagining, okay. If you have a slice of pizza and you try and get it into your face.

• 21:22Michael Stevens?

  Right, you're holding it from like the crust end, so the tip is gonna flop down.

• 21:26Hannah Fry?

  It flops down really easily.

• 21:28Michael Stevens?

  Yeah.

• 21:28Hannah Fry?

  But what people automatically do is they've realized that if you fold it along the length of the pizza, then when you try and get it in your mouth, it remains straight in the other direction.

• 21:39Michael Stevens?

  Wow, now I've seen the famous like TED Ed animation about this pizza, why pizza folding makes things rigid. But you're saying that this is also what makes our feet. Rigid and great for walking.

• 21:50Hannah Fry?

  Yes, so it's all comes down, all comes down to this idea of Gaussian curvature. So Gaussian curvature is something that measures the curviness of a surface. And it's made up of two numbers. So one number is how curvy it is in one direction. The other number is how curvy is in a perpendicular direction.

• 22:10Michael Stevens?

  Perpendicular direction.

• 22:11Hannah Fry?

  Exactly. So if you imagine that you're on the surface of a globe, right? So you're at the equator. One number would be north to south, how curvy is in that direction, and the other would be east to west. Now, the key thing, it's positive if it curves away from you.

• 22:24Michael Stevens?

  Okay, okay.

• 22:25Hannah Fry?

  Now, the key thing about Gaussian curvature is that you cannot change the Gaussian curvature of a surface. Unless you cut it or warp it.

• 22:34Michael Stevens?

  Right.

• 22:35Hannah Fry?

  So if you start off with something that is completely flat, you know, like a piece of paper or a piece of pizza. If you start off with something that is completely flat, it has zero Gaussian curvature.

• 22:44Michael Stevens?

  Yeah.

• 22:44Hannah Fry?

  Which means that even when you bend it, it has to end up with zero Gaussian curvature.

• 22:50Michael Stevens?

  Right, so when you bend a sheet of paper, you produce, say, positive curvature.

• 22:54Hannah Fry?

  In one direction.

• 22:55Michael Stevens?

  One axis.

• 22:56Hannah Fry?

  Yeah. Now, the only way those two numbers multiplied together can still make zero is if the other direction is zero. Right? You've forced it to have a positive number in one direction.

• 23:07Michael Stevens?

  Yeah.

• 23:08Hannah Fry?

  And a positive number times zero is still zero. So you are forced it to have zero curvature in the other direction.

• 23:14Michael Stevens?

  The curvature of a flat sheet of paper is zero.

• 23:17Hannah Fry?

  Zero times zero.

• 23:18Michael Stevens?

  In all, zero times zero.

• 23:19Hannah Fry?

  Yeah.

• 23:20Michael Stevens?

  Oh, so it's the product that matters.

• 23:22Hannah Fry?

  Yes.

• 23:22Michael Stevens?

  So if you create a curvature of, say, one, I don't know what the units are, but positive one. That means you're like turning your page into a taco. The curvature in the perpendicular direction. Needs to be zero, because one times zero is still zero.

• 23:37Hannah Fry?

  Exactly, exactly. So this is why the folding pizza thing works.

• 23:41Michael Stevens?

  Yeah.

• 23:41Hannah Fry?

  You force it to have a positive curvature in one direction, which means it, by the law of like curvature, has to not have curvature in the other direction.

• 23:50Michael Stevens?

  The only way it could have a different curvature in the perpendicular direction now is if it warped or broke.

• 23:55Hannah Fry?

  Exactly.

• 23:56Michael Stevens?

  Which it's strong enough not to.

• 23:57Hannah Fry?

  Exactly. It's the same. Reason why corrugated cardboard works. Because you take the paper, I mean, it's actually quite thin corrugated cardboard, right? But you take it and you curve it, you deliberately give it a curvature in one direction. Which means that it then can't bend in the other direction.

• 24:13Michael Stevens?

  Right.

• 24:13Hannah Fry?

  So it's the same with your foot, you deliberately curve it in one direction between your little toe and your, your, your big toe. And it means that then it cannot curve in the other direction, which means that it has this stiffness as you propel yourself forward.

• 24:27Michael Stevens?

  I want to take a quick tangent and talk about globes.

• 24:30Hannah Fry?

  Yeah.

• 24:30Michael Stevens?

  Because the earth is going to have positive curvature to the same degree in both east, west and north, south directions.

• 24:38Hannah Fry?

  Absolutely.

• 24:38Michael Stevens?

  Those axes. So its curvature, if we call it one in each direction is, is one, one times one. What can I do to a globe such that the product of those two curvatures is still one?

• 24:52Hannah Fry?

  So, so actually with the globe, this is the reason why maps don't work.

• 24:56Michael Stevens?

  Yeah.

• 24:57Hannah Fry?

  It's like the opposite.

• 24:58Michael Stevens?

  I'm changing its Gaussian curvature from one to zero.

• 25:01Hannah Fry?

  And so it doesn't work.

• 25:02Michael Stevens?

  It'll get ripped, right?

• 25:04Hannah Fry?

  Without you ripping it, cutting it, or warping it.

• 25:07Michael Stevens?

  Are there other shapes I can bend it into that still have a Gaussian curvature of one?

• 25:14Hannah Fry?

  Yes, not a cylinder, because that's got a Gaussian curvature of zero. Because it's bent in one direction, but not in the other. Not a pringle, because that has got positive in one direction and negative in the other. It's still got to be positive, positive, because that's the only way that you get a positive number overall. So you're, you're looking at like oblate spheroids.

• 25:34Michael Stevens?

  Right.

• 25:34Hannah Fry?

  You know, a sort of like deformed balloons, that's essentially all you got.

• 25:39Michael Stevens?

  Okay, all right.

• 25:40Hannah Fry?

  But, you know, let's save this for the globe episode, let's see what kind of crazy deformed balloons we can make.

• 25:47Michael Stevens?

  And crazy deformed maps.

• 25:48Hannah Fry?

  And crazy deformed maps.

• 25:50Michael Stevens?

  Yeah.

• 25:50Hannah Fry?

  Yeah. But back to the foot, though.

• 25:52Michael Stevens?

  Please.

• 25:53Hannah Fry?

  This is like, okay, so, so maybe this is what was going on all this time. And it has since been confirmed, they've done high-speed X-rays of what is going on with the foot. So where you can take a X-ray as somebody is walking or moving their foot, sort of move away from the cadaver fee at this point. Watch a runner essentially move around while having X-rays done.

• 26:15Michael Stevens?

  Slow motion X-ray, I would love to watch those.

• 26:18Hannah Fry?

  No.

• 26:18Michael Stevens?

  Wow.

• 26:18Hannah Fry?

  Actually, in fact, I think I have some.

• 26:20Michael Stevens?

  How did they get volunteers for that? Because. X-ray videos are amazing. Like, I've seen X-ray video of people swallowing and chewing. But of course, it's a carcinogen, all these X-rays being shot at you. So it's not a good idea. They used to, of course, have actual X-ray boxes at shoe stores.

• 26:42Hannah Fry?

  Yeah.

• 26:43Michael Stevens?

  You could put your, put a shoe on your foot and then stick your foot in the box and look through this window and see the bones of your foot and how they were being squished or not by the shoe.

• 26:53Hannah Fry?

  Yeah.

• 26:53Michael Stevens?

  Not a good idea.

• 26:54Hannah Fry?

  That was a bad idea.

• 26:56Michael Stevens?

  But they were helpful if you didn't want to live a long time.

• 27:00Hannah Fry?

  And have comfy feet.

• 27:01Michael Stevens?

  If you wanted comfy feet, if you wanted the next few years to be really comfortable, they were great.

• 27:07Hannah Fry?

  I think you can think of everything on a spectrum, right? Between how much you care about comfy feet versus how much you care about wanting to live, right? And in the limit, if my feet were excruciating all the time, I'd be fine with a shorter life, you know? So this is just a-

• 27:19Michael Stevens?

  Yeah, there you go. Exactly. It all balances out.

• 27:22Hannah Fry?

  It all balances out. All balances out. Yeah, when you, when you do these X-rays, it's like the foot is this, this spring-loaded trampoline, essentially. You're, just the second before your toes leave the ground, the arch just visibly recoils. It kind of springs back into its curved shape. And that elastic bounce releases all of that stored energy, throwing, throwing the body forward.

• 27:43Michael Stevens?

  Moving you forward.

• 27:44Hannah Fry?

  Moving you forward, yeah.

• 27:45Michael Stevens?

  Wow.

• 27:46Hannah Fry?

  Isn't that cool?

• 27:46Michael Stevens?

  Yeah.

• 27:47Hannah Fry?

  I really like that a lot. They end up going further because they, they were sort of, okay, well, if it is about this way around rather than that way around. When you go back in the fossil record, it was before this paper came out about the direction that we know that it matters in. There was a bit of a question about this because some of our ancestors, Lucy, for example, the one that was found 3.2 million years ago, right? Has like these very flat feet.

• 28:12Michael Stevens?

  Flat in the direction of toe to heel.

• 28:15Hannah Fry?

  Flat in the direction of toe to heel, but not flat in the direction of big toe to little toe.

• 28:21Michael Stevens?

  Okay, so is that evidence that she was a walker?

• 28:24Hannah Fry?

  It's evidence, yeah.

• 28:25Michael Stevens?

  A bipedal walker.

• 28:26Hannah Fry?

  Yes, that it was like this, she was essentially transitional. She was somewhere between climbing trees and walking upright.

• 28:33Michael Stevens?

  So then what's the point of the curvature from toe to heel?

• 28:37Hannah Fry?

  So that still helps with the

• 28:39Michael Stevens?

  It's a quarter of the support, a quarter, yeah.

• 28:42Hannah Fry?

  It's just not providing the stiffness.

• 28:44Michael Stevens?

  Right.

• 28:44Hannah Fry?

  It's helping you propel forward. It's part of the kind of trampoline-like spring loading. It's just not the thing that's giving you structure in order to be able to like lever yourself forward.

• 28:54Michael Stevens?

  Okay.

• 28:55Hannah Fry?

  But it looks as though this evolution of the the big toe to little toe arch came about one and a half million years before our our genus.

• 29:08Michael Stevens?

  Really? Before before Homo?

• 29:09Hannah Fry?

  Before Homo, yeah. This is a key evolutionary step as to to how we learn to stand.

• 29:16Michael Stevens?

  Oh, interesting.

• 29:17Hannah Fry?

  Hmm. It's good, isn't it?

• 29:18Michael Stevens?

  Yeah.

• 29:19Hannah Fry?

  Isn't that good? Here's the thing I really like about this is that this paper was published in 2020.

• 29:24Michael Stevens?

  Yeah.

• 29:25Hannah Fry?

  You know, like this, like no time ago, six years ago.

• 29:29Michael Stevens?

  Yeah. So has this been studied further? When are we going to see it folded into what podiatrists recommend and the way shoes are designed?

• 29:39Hannah Fry?

  Great question, because I think it's going to probably take quite a long time.

• 29:42Michael Stevens?

  Yeah.

• 29:43Hannah Fry?

  Because you're right, that actually a lot of the time, the way that shoes are designed is about thinking of the arch, thinking of the front to back arch and trying to support it and so on. But yeah, it's it. I think it probably will end up taking a lot of time. But I think it really does demonstrate just how good science is at never sitting still and continually questioning its own. This is like completely common knowledge, right? You pick up any textbook from the last 70 years or so, and this is like, yeah, yeah, yeah, this is absolutely how it works.

• 30:10Michael Stevens?

  And it's not.

• 30:11Hannah Fry?

  And it's not.

• 30:12Michael Stevens?

  So not only were they were these researchers willing to keep questioning, they also found such a fun but gruesome way to test it. Taking cadaver feet, putting weight on it, and then snipping muscles, like mutilating this foot to watch how it how it withstands the weight and the destruction.

• 30:34Hannah Fry?

  You know, you could the other thing you can see from the fossil record, you can see the exact moment that we invented shoes.

• 30:40Michael Stevens?

  Oh, go on.

• 30:41Hannah Fry?

  Basically, it's somewhere between 26,000 and 30,000 years ago.

• 30:46Michael Stevens?

  So not that long ago.

• 30:47Hannah Fry?

  Not that long ago, after clothes, actually, we were wearing clothes.

• 30:51Michael Stevens?

  We, okay, we were wearing clothes before shoes.

• 30:53Hannah Fry?

  Clothes before shoes.

• 30:54Michael Stevens?

  Now, that's almost surprising to me because I think, all right, certainly you need clothing when you start migrating into colder climates. But no matter where you live, your little footsies are gonna get hurt by rocks.

• 31:07Hannah Fry?

  Well, not really, because you just build up calluses on them.

• 31:10Michael Stevens?

  Sure.

• 31:10Hannah Fry?

  I mean, that's what dogs have.

• 31:11Michael Stevens?

  I've got little dainty princess feet, and I can't even walk on sand without being like, "Ow!" But that's because I never exposed them. They have no chance to build up calluses.

• 31:22Hannah Fry?

  Oh, right, okay. This is probably, you know, this is the combination of two together.

• 31:26Michael Stevens?

  So how do we know that shoes came about around then?

• 31:30Hannah Fry?

  Because of toes.

• 31:32Michael Stevens?

  Oh.

• 31:32Hannah Fry?

  Yeah, so what happened is our toe bones, our small toe bones especially, suddenly became really pathetic.

• 31:39Michael Stevens?

  Oh.

• 31:40Hannah Fry?

  Yeah, before they were like really strong and, you know, amazing.

• 31:44Michael Stevens?

  So you're saying that our little tiny pinky toes, like such that sometimes the nail on it is so small you can barely paint it? It's because of shoes?

• 31:53Hannah Fry?

  Yeah.

• 31:53Michael Stevens?

  Wow.

• 31:54Hannah Fry?

  Yeah, because they don't need to be as strong anymore when you've got the additional support underneath.

• 31:58Michael Stevens?

  The support from the...

• 31:59Hannah Fry?

  I'm quite, I'm quite a big fan of walking around in bare feet, I've got to be honest. You know, like on holiday, if I could get away with it, I would just...

• 32:06Michael Stevens?

  Just be barefoot the whole time?

• 32:07Hannah Fry?

  Yeah.

• 32:08Michael Stevens?

  Yeah, not me. I, I don't sleep in socks. That's like the only time my dogs are out.

• 32:13Hannah Fry?

  We don't need to, you've got the warmth, the warmth there already.

• 32:15Michael Stevens?

  They're already warm enough. They get too hot, yeah, if I wear socks at night. But in the mornings, I'll get up to make breakfast, and I'll be walking around barefoot, and I'll just be like, "Whoa, this is so inappropriate. I feel so naked." And so, I don't know what my daughter thinks, because I'm always like, "Oh, I gotta go put on socks." And she's like, "Why?" And I'm like, "Well, because I've lost my mind. A long time ago I did."

• 32:40Hannah Fry?

  I'm still upset about something that someone said forty years ago.

• 32:43Michael Stevens?

  Yeah.

• 32:43Hannah Fry?

  I think I've seen a picture of your feet, though. Can I tell you why?

• 32:47Michael Stevens?

  You better.

• 32:48Hannah Fry?

  Do you, do you know about, I mean, we said we were gonna get on to foot fetishes.

• 32:54Michael Stevens?

  Oh, sure, yeah.

• 32:56Hannah Fry?

  Well, come back for that after the break.

• 33:03Michael Stevens?

  I live 7,636 kilometers away from Hannah, so we rarely get to see each other in person. That's what makes this such genuinely thrilling news for us. And maybe for you too. Because for the first time ever, you can see both of us live onstage at Goalhanger's inaugural festival. It's going to be amazing to be able to reach through the screen and meet those of you who watch and listen to the show in the flesh. The Rest Is Fest runs from the 4th to the 6th of September at London's South Bank Centre. So get some tickets and get ready for some fun. Some serious fun. Go to southbankcentre.co.uk to find out more.

• 33:48Speaker 03

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• 34:18Speaker 04

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• 34:54Hannah Fry?

  Welcome back. Michael, do you know about WikiFeet?

• 34:57Michael Stevens?

  I do.

• 34:58Hannah Fry?

  Do you know that you're on there?

• 34:59Michael Stevens?

  Am I really?

• 35:00Hannah Fry?

  You are.

• 35:01Michael Stevens?

  Well, like I said, I did show my feet off in my Lego video, but otherwise...

• 35:07Hannah Fry?

  Let's, um...

• 35:08Michael Stevens?

  Do you have my WikiFeet page bookmarked?

• 35:10Hannah Fry?

  I, I did look at it the other day. So essentially, there are a lot of people who really care a lot about feet. Who find feet extremely titillating, shall we say. Um, and there is a website called WikiFeet, which collects, is it called WikiFeet? I was, Feetopedia or something, WikiFeet, there we go.

• 35:36Michael Stevens?

  How does, how does that poor manteau work? Which one do they put first?

• 35:38Hannah Fry?

  Which one do they do? Which collects feet pictures from celebrities. And then other people can go on and rate them and enjoy, enjoy looking at them.

• 35:50Michael Stevens?

  Yeah.

• 35:50Hannah Fry?

  Okay, I'm looking at a picture of your feet right now.

• 35:52Michael Stevens?

  So you gotta show me what photos people have.

• 35:55Hannah Fry?

  I don't think these are that hairy.

• 35:58Michael Stevens?

  Ah, okay, yeah, that's from the Lego video.

• 36:01Hannah Fry?

  Okay, so here's what, here's what they have. I mean, I think that's a normal amount of hair.

• 36:05Michael Stevens?

  I may have been exaggerating for, for laughs.

• 36:08Hannah Fry?

  Comedic effect, there's also this one.

• 36:09Michael Stevens?

  Hold on a second, I wanna, oh yeah, when I jumped in the water. Okay, I don't swim in socks, there you go. I'm not some kind of like never nude foot guy. But wait a second, wait a second, what's my rating?

• 36:19Hannah Fry?

  I know, I have your rating.

• 36:21Michael Stevens?

  What is it?

• 36:21Hannah Fry?

  You've done pretty well, you've done pretty well.

• 36:23Michael Stevens?

  No.

• 36:24Hannah Fry?

  Hang on, let me get mine up, I wanna see who wins.

• 36:26Michael Stevens?

  Oh yeah.

• 36:27Hannah Fry?

  The thing that I find extraordinary about this, apart from everything, is that, oh gosh, there's pictures of us together on mine. I, I mean, as I say, I will wander around without shoes on quite a lot of the time. My foot can't even sneak into shots somewhere without it ending up on this website.

• 36:45Michael Stevens?

  Exactly, yeah, and you gotta control it because that's a goldmine.

• 36:49Hannah Fry?

  Right, this is, this is clearly worth money.

• 36:51Michael Stevens?

  You gotta gatekeep it or dollars are the ticket.

• 36:54Hannah Fry?

  Look at this, this, this one's gone on there.

• 36:56Michael Stevens?

  Oh no, yeah, you've got some arch poking up from the shoe. See now, as a guy who reads a lot of internet comments, I know what you shouldn't be doing.

• 37:04Hannah Fry?

  Yeah, I know, I'm a fool.

• 37:05Michael Stevens?

  Or should be doing, depending on, on your goal.

• 37:07Hannah Fry?

  I, I do, I do actually, I mean, I do think about it now, when, when being in front of a camera, like, okay, let's not.

• 37:13Michael Stevens?

  Right, but stop stalling, who wins? What, what's our?

• 37:16Hannah Fry?

  One of us gets 4.82.

• 37:18Michael Stevens?

  Out of five?

• 37:19Hannah Fry?

  Out of five.

• 37:19Michael Stevens?

  Oh, let me guess who, who's who.

• 37:21Hannah Fry?

  And one of us gets 4.88.

• 37:23Michael Stevens?

  Okay, well, you're 4.88.

• 37:25Hannah Fry?

  Correct.

• 37:26Michael Stevens?

  For sure. I think 4.82 is way too high for me.

• 37:30Hannah Fry?

  I think it, you know.

• 37:32Michael Stevens?

  That's like, that's probably only based on like two ratings. One is from like my mom.

• 37:36Hannah Fry?

  No, 12, 12.

• 37:38Michael Stevens?

  12 ratings, but how many ratings do you have?

• 37:40Hannah Fry?

  More.

• 37:41Michael Stevens?

  How many more?

• 37:43Hannah Fry?

  More.

• 37:44Michael Stevens?

  Hundreds or thousands?

• 37:45Hannah Fry?

  No, not thousands, not thousands.

• 37:47Michael Stevens?

  Not yet.

• 37:50Hannah Fry?

  Imagine if that's the conclusion that people draw from this episode.

• 37:53Michael Stevens?

  This was all just you're fishing for like more ratings on WikiFeet. It's okay if that's what you're looking to do.

• 38:00Hannah Fry?

  Do you know, there is a bit of me that's like, I sort of don't really have a problem with it. Like people having a fetish of feet, because they do, right? And like, it's not like you're, um, I'd be okay with setting up an OnlyFans as a feet thing. Am I saying that?

• 38:14Michael Stevens?

  Well, yeah, I mean, there's nothing, there's, I would just say that maybe you wouldn't like it because you'd rather them focus on other things about you.

• 38:21Hannah Fry?

  Yeah, true.

• 38:22Michael Stevens?

  But.

• 38:23Hannah Fry?

  I did think about actually once setting up an OnlyFans, but all it is, is me drawing equations on a blackboard, fully clothed.

• 38:29Michael Stevens?

  Yeah, you should do that. I mean, it's, OnlyFans is for the fans and I think that's what they want.

• 38:36Hannah Fry?

  I just think it'd be really funny.

• 38:38Michael Stevens?

  Let's talk about fetishes around feet.

• 38:40Hannah Fry?

  Yeah.

• 38:41Michael Stevens?

  Because, I mean, a fetish, what, what is it really? It's a, it's a, it's an interest in a part of the body that is not a primarily sexual part.

• 38:49Hannah Fry?

  Yeah, yeah, or, or something that is not primarily associated with.

• 38:52Michael Stevens?

  Or something, yeah, right. So, so how come foot fetishes are seemingly so much more common? Than like an elbow fetish or an armpit fetish?

• 39:03Hannah Fry?

  Yeah. So there is one explanation.

• 39:06Michael Stevens?

  Okay.

• 39:06Hannah Fry?

  But it's, uh, there's not a lot of studies on this, essentially. The one explanation is that in your brain, there is effectively like a sensory map.

• 39:16Michael Stevens?

  Oh.

• 39:17Hannah Fry?

  That relates to every part of your body. So there's a bit in there, you know, a certain part of your brain lights up when you touch somebody's hand while they're in a scanner.

• 39:25Michael Stevens?

  Yeah.

• 39:25Hannah Fry?

  And so on and so on and so on. And it's almost like a humunculus, right? It's like a map of your body that is in your brain.

• 39:32Michael Stevens?

  Yeah.

• 39:32Hannah Fry?

  And in that map, it has been proposed that feet and genitals are extremely close together. So that you can imagine that in some people, there may be some overlap in kind of cross wiring.

• 39:44Michael Stevens?

  Right.

• 39:45Hannah Fry?

  Right? So you kind of, you play around with somebody's feet and they, they essentially get sexual stimulation from it.

• 39:52Michael Stevens?

  Right, right, right. So, I mean, that does make a lot of sense.

• 39:55Hannah Fry?

  Yeah.

• 39:56Michael Stevens?

  But you're saying we still have a lot more to learn.

• 39:58Hannah Fry?

  Still have a lot more to learn because I think that the original studies or original study rather acted as though it was like a, and there you go, that's the answer.

• 40:07Michael Stevens?

  Right.

• 40:08Hannah Fry?

  But I think subsequent follow up has demonstrated that it's just not quite as simple as that. There's, there's much more variation that you get within humans. I mean, you're right though, that it is like this really prevalent thing throughout history. The Greeks and the Romans, I mean, they were really into feet. There was, there was one philosopher called Philostratus who wrote, he thought that the reason why he was so into feet was because he wanted to be a human doormat, just so his lover would step on him.

• 40:35Michael Stevens?

  Okay, but then that to me becomes a second thing as well, which is dominance and submission.

• 40:42Hannah Fry?

  Yeah, yeah.

• 40:43Michael Stevens?

  I mean, it could be that that's where the, the whole origin of foot fetishes comes from.

• 40:48Hannah Fry?

  Maybe it does. I mean, there's also the Freudian suggestion.

• 40:51Michael Stevens?

  Which, no, what's that?

• 40:52Hannah Fry?

  Freud, see if you, as Freud generally does, it's completely unhinged. Freud says that a foot fetish is because it's a trauma response to coming out of your mother's womb.

• 41:04Michael Stevens?

  Uh huh.

• 41:04Hannah Fry?

  The feet being the first thing that you see and then realizing that your mother doesn't have a penis and then thinking that her feet are penis shaped, something and that you imprint on that.

• 41:18Michael Stevens?

  Well, look, maybe that explains my fetish for doctors because the first thing I saw when I came out of my mom was a doctor and I was like, hey, and it was a trauma response I had because my mother's wearing, you know, wearing scrubs like.

• 41:31Hannah Fry?

  Yeah.

• 41:32Michael Stevens?

  Anyway, I, I don't, sometimes this Freudian stuff, it's like, it's like a fantasy.

• 41:37Hannah Fry?

  It's hilarious.

• 41:38Michael Stevens?

  And I think useful in the same way that like fantasy novels are useful and they can be so, so inspiring, but I'm just like, I don't know how any of this is scientific.

• 41:49Hannah Fry?

  It's not.

• 41:49Michael Stevens?

  I mean, some of it, I guess can be, but some of it, I'm like, wow, this is really creative.

• 41:54Hannah Fry?

  Well, it's not forcible, is it? It's just not forcible.

• 41:56Michael Stevens?

  No.

• 41:57Hannah Fry?

  Unless, unless you, I don't know, like do a controlled trial where you get a half of all women to wear socks while giving birth.

• 42:05Michael Stevens?

  Yeah, exactly. And then you check the, the, the future fetishes of those babies. And they're like, oh, I don't know. But see, they might just wind up being really into socked feet.

• 42:16Hannah Fry?

  The thing is, is that when it comes to fetishes, you can learn a fetish, though.

• 42:21Michael Stevens?

  Ah.

• 42:22Hannah Fry?

  So there's an amazing study with rats.

• 42:24Michael Stevens?

  Okay, tell me about it.

• 42:26Hannah Fry?

  Can I tell you?

• 42:26Michael Stevens?

  Yeah.

• 42:26Hannah Fry?

  Okay, so, so what they did, they, they wanted to see if they could give rats a fetish.

• 42:31Michael Stevens?

  I love this, yeah.

• 42:33Hannah Fry?

  They, they took virgin male rats.

• 42:34Michael Stevens?

  Mm hmm.

• 42:35Hannah Fry?

  And they gave a little, put a little jacket on them, key little jacket.

• 42:38Michael Stevens?

  Okay.

• 42:39Hannah Fry?

  And some of the jacketed rats were put in with females and then they all had a lovely time. They were like, this is brilliant, these jackets are great. And then the others, when they put on the jacket, they were, they were introduced to females, but they were not allowed to copulate. Okay, so they were like, right, so this is like a, the jacket is a cock block.

• 42:58Michael Stevens?

  Right.

• 42:59Hannah Fry?

  Essentially.

• 43:00Michael Stevens?

  Right.

• 43:00Hannah Fry?

  And so they sort of did that a few times. And then for the final test, they took the jackets off of everybody, of all of the rats. But the rats who had learned that the, the jacket meant good times.

• 43:12Michael Stevens?

  Mm hmm.

• 43:13Hannah Fry?

  Okay, they then didn't know what to do when they weren't wearing the jacket.

• 43:16Michael Stevens?

  Ah.

• 43:17Hannah Fry?

  Because they had like so closely associated the jacket. They were just like, I can't, no, thank you.

• 43:21Michael Stevens?

  I, I can't get off without my jacket.

• 43:24Hannah Fry?

  I need my jacket to enjoy this. Vice versa, the ones who had learned that the jacket meant like disappointment.

• 43:31Michael Stevens?

  Yeah.

• 43:32Hannah Fry?

  When the jacket went on, um, they were like, no, thank you, I'm not interested, can't, can't do it. Can't do it while I'm wearing this.

• 43:39Michael Stevens?

  Yeah.

• 43:39Hannah Fry?

  So it's like, there is something, some evidence that this is learned.

• 43:43Michael Stevens?

  There's some learning and some associations.

• 43:44Hannah Fry?

  Yeah.

• 43:45Michael Stevens?

  I mean, I don't find that surprising at all. I think, you know, as you get to know someone better and you have all these experiences together, the roots of your trees go, grow closer and you start to like just love things about them, physical things about them that you find so much more exciting than you used to. Um, because, I don't know, it's them, it's, it's theirs and you love them. So like I find myself, I don't, I don't get too personal. Like basically, I just.

• 44:16Michael Stevens?

  Basically, as I get older, I find my wife more and more attractive.

• 44:23Hannah Fry?

  Oh, that's a lovely thing to say.

• 44:24Michael Stevens?

  And I'm not just saying that for like points or anything. I'm saying it because I've heard comedians, like old comedians, make jokes about this too. And I'm like, yeah, that really is true.

• 44:35Hannah Fry?

  Right, that's lovely. That's lovely, but it's like the learnedness of being with her and around her.

• 44:42Michael Stevens?

  And then, but what's the difference between just admiration, like, oh, your hair is so wonderful, and a fetish?

• 44:49Hannah Fry?

  I don't know. Is the jacket on or off? That's a...

• 44:52Michael Stevens?

  Right, and just how much do I want that jacket on? Do I think it's a nice jacket, or do I think it's a nice jacket? Right, it's probably, there's a spectrum.

• 45:04Hannah Fry?

  Somewhere between. You've got to decide every day where you are between those two endpoints.

• 45:08Michael Stevens?

  I do, I do.

• 45:08Hannah Fry?

  What I'm, what I'm looking forward to is my, my Cambridge colleagues listening to this podcast in the first half being like, oh, that's really, very, very interesting science indication. It's like, sorry, what are you talking about, rat fetishes?

• 45:20Michael Stevens?

  Well, no, I'm glad someone studied that.

• 45:23Hannah Fry?

  Yeah, it's good, isn't it?

• 45:24Michael Stevens?

  I, I would be embarrassed to like, be like, I need money to do this study.

• 45:28Hannah Fry?

  Do you want to see the jacket?

• 45:29Michael Stevens?

  Yeah.

• 45:32Michael Stevens?

  Oh, wow, that is so not sexy.

• 45:34Hannah Fry?

  It's not sexy, is it? But some of the rats thought it was.

• 45:37Michael Stevens?

  But some of the rats learned to think that it was.

• 45:39Hannah Fry?

  Some of the rats thought it was. And some people think feet are.

• 45:42Michael Stevens?

  And some people like nostrils, you know? And I think the world needs all those kinds of appreciation.

• 45:49Hannah Fry?

  Absolutely.

• 45:50Michael Stevens?

  And we appreciate you.

• 45:51Hannah Fry?

  We certainly do.

• 45:52Michael Stevens?

  Thank you for listening and, uh, reach out to us, ask us questions at [email protected].

• 45:58Hannah Fry?

  And we will see you next time. Thank you.

• 46:00Michael Stevens?

  See you next time.