Why Horses Can't Wear Flip Flops How in the world did horses get their hooves? What in the world is the difference between their feet and ours? And when in the world did tiny dog-sized horses roam the earth? Join Guy Raz and Mindy for a little trot through the latest Who, What, When, Where, Why, How and Wow in the world of horse hooves! *And be sure to check out this episodes conversation starters at www.wowintheworld.com !
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Why Horses Can't Wear Flip Flops

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Why Horses Can't Wear Flip Flops

Why Horses Can't Wear Flip Flops

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UNIDENTIFIED MAN #1: Stay seated. Three, two, one. Ignition.

UNIDENTIFIED MAN #2: Get ready for an adventure of magnificent proportions.

THE POP UPS: (Singing) I don't know what you've been told, but we're in a golden age. So many discoveries that are jumping off the page. Wow in the world. Wow in the world. Wow in the world. Wow in the world. Wow in the world. Wow in the world. Wow in the world. Wow in the world. Wow in the world.

UNIDENTIFIED MAN #3: With Guy and Mindy.

UNIDENTIFIED MAN #1: We're on our way, Houston.



Whoa there, Bucky (ph). Whoa. Whoa. You are such a good horse, Bucky.


RAZ: OK. Let's try a trot. That was great. Now let's do a light gallop. Great job, Bucky.


Hey, Guy Raz, where are you?

RAZ: Hey, Mindy. I'm over here.

THOMAS: Over where? Oh, there you are. Don't move a muscle. I'll be right there. Run, run, run, run, run, run, run. Oh, there you are. I could smell you from a mile away, but I couldn't find you anywhere.

RAZ: (Imitating horse) Hey, Mindy.

THOMAS: Hey, Guy Raz. What's up?

RAZ: (Imitating horse) Hey, Mindy.

THOMAS: OK. Hey, Guy Raz.

RAZ: (Imitating horse) Hey.

THOMAS: OK. Enough with the hey-ing. A simple hello will suffice.

RAZ: Oh, sorry. I'm just really into this horse-riding thing.

THOMAS: Yeah, I got that. But why are you wearing a lab coat under your tweed riding coat?

RAZ: Well, why are you wearing a cowboy hat and stirrups, Mindy?

THOMAS: Why does everyone keep asking me that?

RAZ: Well...

THOMAS: OK. For the last time, I'm only wearing the stirrups because my boots got stuck in them the last time I went horseback riding. And the cowboy hat is - well, it's just for decoration. Anywho (ph), you told me to meet you here at this ranch so we could go for a ride.

RAZ: Oh, right. Well, actually, what I meant to say is that Bucky here is going to help us get to the bottom of a scientific mystery.

THOMAS: Scientific mystery? Guy Raz, the only mystery here is why you are wearing a lab coat under your tweed riding coat.

RAZ: Oh, this old thing? Here. Let me take it off.

THOMAS: Hey, I don't want to hold it.

RAZ: Better?

THOMAS: Well, I mean, now you're just sitting on a horse in a lab coat. So I'm not sure what's going on.

RAZ: Oh, well, me and Bucky here - we were just talking - you know, shooting the breeze, exchanging thoughts about the world and life in general, you know?

THOMAS: No. Actually, I don't. Guy Raz, Bucky here doesn't speak English, because he's a, you know...

RAZ: A horse. I know. I know. But I feel like we've made a connection. You know what I mean?

THOMAS: Yeah. Again, no, I don't.

RAZ: And besides, Mindy, he's really interested in helping me try to understand a very important mystery about horses and his genus.

THOMAS: Genus. Oh, you mean the part of the family he's a member of?

RAZ: Yes, exactly - the genus Equus.

THOMAS: Wait a minute. So if you're talking about the genus Equus, then you're talking about horses and zebras and donkeys.

RAZ: Yes. Yes. And, Mindy, these amazing creatures - they share something in common that makes them unique among all animals on planet Earth.


THOMAS: I think I know what you're talking about.

RAZ: Well, yeah. Hey, Bucky. This is not the time.


THOMAS: Oh, there he goes again.

RAZ: Well...

THOMAS: Can't you just put a diaper on him or something?

RAZ: Yeah, sorry. Bucky isn't quite potty trained just yet. But that's not what makes her unique, Mindy. It's something so much cooler.

THOMAS: Right. 'Cause what could possibly be cooler than a pile of horse poop?

RAZ: Well, for starters, check out her hoof.

THOMAS: OK. I'm looking at it. And it's a horse hoof. It's a horse hoof. Guy Raz, I'm going home.

RAZ: Well not just a horse hoof, Mindy. This is Bucky's toe.

THOMAS: Wait. Let me see that foot again. Oh, yeah. Kind of reminds me of my Great Aunt Elmira. You know, she had one toe, too.

RAZ: You're related to a horse?

THOMAS: Oh, yeah. I never told you about her?

RAZ: No.

THOMAS: She was the dark horse of the family.

RAZ: Well...

THOMAS: But come to think of it, no one could ever quite figure out how we were related. Huh.

RAZ: Well, anyway, what makes Bucky here amazing is that, like all horses, she has just won toe.

THOMAS: But why is that unique?

RAZ: Well, Mindy, I just learned that donkeys, horses and zebras - all members of the Equus genus - are the only animals on planet Earth with just one toe.

THOMAS: Wow. I guess I never really thought about it.

RAZ: Yeah. I mean, to be honest with you, Mindy, I didn't even realize a horse's hoof was its toe.

THOMAS: Man, it must be hard to stand on one toe.

RAZ: That's exactly what I was thinking. I mean, here. Let's try it. Let's try to stand on one toe. Are you ready?

THOMAS: No. But I'll give it a try.

RAZ: OK. One, two, go.

THOMAS: Whoa. Whoa.

RAZ: This is practically impossible, Mindy.

THOMAS: Guy Raz, I can stand on all of my toes. I can even stand on the ball of my foot. But just one toe? I'm not sure any human is meant to do that.

RAZ: Well, have you ever seen a ballet dancer?

THOMAS: Oh, yeah - last year, when we went to see "The Nutcracker."

RAZ: Yes.

THOMAS: Oh, man. Remember I got lost trying to find my seats after I went to the bathroom, and then I wound up in the rafters, and I fell out of the rafters and almost squashed a Sugar Plum Fairy?

Totally OK.

Anyway, that was an amazing ballet.

RAZ: And, sometimes, Mindy, you know, ballet dancers dance on their toes. And that requires years and years of training and a lot of strength. But...

THOMAS: But it also requires a lot of pain. So they probably couldn't do that all day, every day.

RAZ: Right. Because our human bodies carry too much weight. Just one toe isn't strong enough to hold us up.

THOMAS: Yeah. But Mom Raz once told me that you used to walk on your toes when you were a little tater tot.

RAZ: Oh, yeah. Don't remind me.

THOMAS: She used to call you baby toesie.

RAZ: But that is normal. Lots of little kids walk on their toes. And then, eventually, they walk using their entire foot. But in the case of our friend Bucky here and her relatives, the zebra and the donkey, well, they're always walking around on a single toe.

THOMAS: Yeah, but on four feet.

RAZ: Right. But think about it, Mindy. Try standing on just your big toes - you know, both of them. You can use both feet.


RAZ: But you can only stand on your big toes, not on the ball of your foot, OK? Try it.

THOMAS: All right. Here goes nothing. And - oh.


THOMAS: Nutcracker.

RAZ: You ok, Mindy?

THOMAS: Oh, yeah. Just kissing all my ballet dreams goodbye. I'm fine.

RAZ: That's a relief. So as I was saying, scientists have long known that horses evolved - or, gradually, over millions of years, they changed to look like the way they look today.

THOMAS: Well, what did they used to look like?

RAZ: Well, this is the amazing part, Mindy, because I just finished reading an incredible study written by researchers at Harvard University in Massachusetts. And it's about why horses evolved to have one toe.

THOMAS: Yeah. So what did you find out?

RAZ: Well, in this study, I found out that the earliest ancestors of horses were an animal about the size of a dog but with three to four toes on each foot.

THOMAS: A 14-toed horse?

RAZ: Well, yeah, but a mini-sized 14-toed horse - an animal that lived 55 million years ago that was part of the Hyracotherium genus.

THOMAS: Oh, wait. That reminds me. Guy Raz, we humans are part of the Homo genus.

RAZ: Right. We humans are Homo sapiens. Homo is our genus, which is a branch of a larger family. And our species is sapiens. Homo is Latin for man, and sapiens means wise. So in Latin, homo sapiens means wise man.

THOMAS: Or in my case, wise woman.

RAZ: Yeah.

THOMAS: Guy Raz, there were actually other members of our genus, too. But not to be a downer, they all died out thousands of years ago. Never even got to meet them.

RAZ: That's true. There were Homo naledi and Homo neanderthalis (ph), Homo erectus and many other members of our genus. And if you go to a natural history museum, there's a pretty good chance you can see models and images of some of our distant human relatives who once roamed planet Earth just like we do today.

THOMAS: OK. Well, in the case of horses, how did a Mini-Me dog-sized, 14-toe horse become a humongous creature with a single hoof.

RAZ: Well, I was hoping you would ask me that, Mindy, because...

THOMAS: Oh, boy. Better saddle up for some seasickness.

RAZ: You know where I'm going with this one, right, Mindy?

THOMAS: And I just are my breakfast.

RAZ: To the time machine.

THOMAS: Oh, hey, Reggie. What? Oh, no, Reg. We won't be needing your services at this time. But, unfortunately, we're going to have to use your taekwondo dojo.

RAZ: Mindy, are you sure you should be letting Reggie use the time machine to practice taekwondo? I mean, there's a lot of sensitive and fragile equipment in there.

THOMAS: Nah, it's fine. Plus, I'm training Reggie how to fly this thing. So the next time we have to time travel, we can just sit back, relax and eat nachos.

RAZ: Well, can I just drive it this time? I mean, the last time, you know...

THOMAS: Blah, blah, blah. Hand me the keys, Guy Raz. I'll take the wheel.

RAZ: OK. But please least try for a smooth landing.

THOMAS: Just got to open the hatch, climb on in here. Hurry up, Guy Raz. Come on. This time machine is about to go back in time.

RAZ: OK. Here I come.

THOMAS: All right. Where are we going?

RAZ: Mindy, we're staying in North America, our continent. But let's say around where Montana is today, but 55 million years ago.

THOMAS: OK. Late Eocene epoch. And here we go.

RAZ: Here we go.


RAZ: Mindy?

THOMAS: I'm - (gagging).

COMPUTER-GENERATED VOICE: We interrupt this program for a brief barf break. WOW IN THE WORLD will return in three, two, one.

THOMAS: That took care of it.

RAZ: Guess you had scrambled eggs for breakfast, huh?

THOMAS: Nope. That was a corndog.

RAZ: Yeah, I see. Well, no time for cleanup. Let's just open the hatch and see if we can find some examples of the Hyracotherium.

THOMAS: OK. Open up this hatch. All right. Hot and muggy out here.

RAZ: Yep. The Earth was actually a lot warmer 50 million years ago. So even though we're somewhere in the middle of the continent of North America, it kind of feels like a tropical island, doesn't it?

THOMAS: Yeah, sure does. I wish I brought my ice helmet.

RAZ: You have an ice helmet?

THOMAS: Well, I mean, technically, it's an ice bucket that I wear upside down on my head. I wear it on hot days to keep me hydrated, but it never works.

RAZ: Huh. Well, right now we should be looking out for an animal that kind of looks like a miniature horse but with three to four toes on each foot.

THOMAS: OK. Now, just hand me my adventure tool box.

RAZ: Yeah.

THOMAS: Thanks. I'm just going to find my magnifying goggles here. No, that's an old one. No, not this Commodore 64. Hey, wait. I was looking for that thing. No, not this badminton racket. Hey, how'd a ham get in here?

RAZ: Mindy, how much stuff that you have in there?

THOMAS: Oh, jackpot. Found them. Yes. My trusty magnifying goggles.

RAZ: OK. Great. Let's scan the landscape and see what we can find.

THOMAS: OK. Let's see here. I see a giant forest of weird trees and then a lot of grassy, open land.

RAZ: This must be the place, Mindy. This is it. This is the place where these ancient creatures started to transform from dog-sized, horse-like animals to giant horses.

THOMAS: Yeah. But I'm looking through these magnifying goggles, and I don't see them anywhere, Guy Raz.

RAZ: Here, can I take a quick look?

THOMAS: Sure. Here.

RAZ: Let's see.

THOMAS: What do you see?

RAZ: Wait. Wait. I see something rustling out there. It's coming out of the forest. It's walking onto the grass. That's it, Mindy. That's the creature that paleontologists have told us about. It's that animal from the Hyracotherium genus. Here, have a look, Mindy.

THOMAS: Give me those things. Whoa. Yeah. It does kind of look like a dog-sized horse. Aww. It's so itty-bitty and cute. Can I keep it? Please, please, please, please, please, please?

RAZ: Well, I don't know. It might not be safe to approach it.


RAZ: But did you notice their toes?

THOMAS: Oh, yeah. They look like horses'.

RAZ: Yes.

THOMAS: But they've actually got three or four toes on each foot.

RAZ: Yeah.

THOMAS: No hoof.

RAZ: Mindy, these ancient ancestors to our modern horses - they started to leave the forests around this time, about 55 million years ago. And then they moved onto more grassy areas to live - you know, places where they probably found more food.

THOMAS: Well, what does that have to do with their toes?

RAZ: Remember those researchers from Harvard University I was telling you about?


RAZ: Well, two of them, Stephanie Pierce and Brianna McHorse, found that...

THOMAS: Wait. Brianna McHorse?

RAZ: I know. A little different, right? But that's - well, that's her name.

THOMAS: You promise?

RAZ: Yeah. Of course, I promise. In fact, Mindy, Brianna McHorse is an example of an aptronym, which means when a person's name is like the job they have.

THOMAS: Oh. So like if your name was Sunny, and you had a job studying the weather.

RAZ: Yeah. Or like the famous Australian tennis player Margaret Court - as in tennis court. Or the former chief judge in all of England - his name was actually Igor Judge.

THOMAS: Oh, I got one. How about the man who pioneered the modern toilet? His name was Thomas...

RAZ: Yes, yes. That's right. That's right. That's true. I think you get the point. And Brianna McHorse - well, she's a distinguished researcher who also studies, well, horses.

THOMAS: Got it. So what exactly did Brianna and Stephanie find out?

RAZ: Well, scientists have long believed that as these Hyracotherium species wandered out of the woods and into grassy areas, well, the weight of their bodies began to shift from all of their toes to just their middle toes.

THOMAS: But why?

RAZ: Well, as this paper explains, over time - and I'm talking millions of years, Mindy - as these animals ate more and more food, they started to grow bigger and bigger. And that meant that their bodies were putting more and more weight on their toes.

THOMAS: OK. I think I follow.

RAZ: See? Look at them. I mean, right now they're walking on the grass. And grass is a different surface than the forest. And it means that, over time - again, I'm talking millions of years of walking on grass, Mindy - these animals we're looking at - well, they'll grow bigger. And their toes will start to fuse together to become one humongous toe like a hoof.

THOMAS: Wow. But how did the scientists figure this out?

RAZ: Well, they compared the bones of 12 different extinct horse species.


RAZ: And they looked at those horse bones under a special X-ray machine called a CT scanner.

THOMAS: And what did it show?

RAZ: Well, it gets a little complicated. But from what I understand, Mindy, those researchers were able to see how in the Hyracotherium horse creatures, their toes weren't strong enough to hold up anything bigger than a dog. And their middle toe certainly wasn't strong enough. But...

THOMAS: Hope this is a big but.

RAZ: ...Gradually, that middle toe became stronger and stronger as the body of the animal got used to getting bigger and bigger and walking on grass. And so the X-rays show how, eventually, the middle toe was so strong that the horse-like creature didn't need the other toes.

THOMAS: So those side toes just eventually went away?

RAZ: Yes. And that's why donkeys, zebras and horses have a single toe. And, Mindy, that toe is what allows horses to actually run really fast.

THOMAS: Yeah. Like, they can run as fast as a car, Guy Raz - like, 35 miles an hour.

RAZ: And amazingly, Mindy, it doesn't even make them the fastest land animals. In fact, horses aren't even in the top 10. But they are fast. And a lot of that has to do with their single-toed hoof.

THOMAS: Wow. That is seriously bonkerballs (ph), Guy Raz. Anywho, I don't know about you, but I am getting hot out here. I think maybe it's time to hop back in this time machine and head back to the ranch, maybe do a little horseback riding.

RAZ: That sounds like a great plan. You ready?

THOMAS: I'll even let you drive this time, little buddy.

RAZ: Oh, thanks.

THOMAS: And not just because I spilled a milkshake in the driver's seat.

RAZ: What?


RAZ: Well, I guess it's time to say, here we go.

THOMAS: Here we go.

I thought you said you knew how to drive this thing.

RAZ: It can't be that different from a horse, can it?

THOMAS: It's totally different from a horse, Guy Raz.

UNIDENTIFIED CHILD #1: WOW IN THE WORLD will be right back. Grown-ups, this message is for you.


UNIDENTIFIED CHILD #1: That's it. Back to the show.


THE POP UPS: (Singing) Wow in the world.


THOMAS: Hi. Thanks for calling WOW IN THE WORLD. After the beep, get ready to record.


GALIA: Hi. My name's Galia (ph). And I live in Northampton, Penn. And my wow in the world is that I saw two whole fields filled with geese migrating for winter. And I like turtles. Bye, Mindy. Bye, Guy Raz.


HARRISON: Hi, Mindy and Guy Raz. My name is Harrison from Chapel Hill. I am 8 years old. And my wow is that when you're a baby, you have more bones because they're all separated. And then when you grow older, they start connecting. I bet you didn't know that. Bye, Mindy. Bye, Guy Raz.


HUDSON: Hi. My name is Hudson, and I'm 6 years old. I'm from Santa Barbara, Calif. My wow in the world is that hippos, elephants and rhinoceroses can get sunburned. Bye.


CALEB: Hi, Mindy and Guy Raz. My name is Caleb, and I am 8 years old. I'm from America. I live in Kigali, Rwanda. My wow in the world is something called Umaganda is a day every month. Everyone in Rwanda comes together to clean up the environment and build things for the community. Bye, Mindy and Guy Raz. I love your show.


SYLVIE: Hi, Mindy and Guy Raz. Our names are Sylvie (ph)...

HANNAH: Hannah (ph).

SYLVIE: And we're 8 years old. And we live in Buffalo, N.Y. Our wow in the world is that, yesterday, we spent the night at the Natural History Museum. Bye.



HENRY: Hello, WOW IN THE WORLD. I'm Henry. I'm 5 years old. I saw the Antares rocket launch. It was carrying supplies and science to the Space Station. Goodbye.


EVELYN: Hello. My name is Evelyn. I am from Pekin, Ohio. I'm 7 years old. And I saw three wild turkeys in our backyard. My brother did, too. Bye, Guy Raz and Mindy. I like - I love your show.


UNIDENTIFIED WOMAN: End of messages.

THOMAS: Hey, everyone. Thank you so much for joining us this week for WOW IN THE WORLD.

RAZ: And if you want to keep the conversation going, check out some of the questions we've posted on this episode at our website, wowintheworld.com.

THOMAS: You'll also be able to find all of the sources and journal articles we used for today's show.

RAZ: Our show is produced by Jed Anderson, with help from Thomas van Culkin (ph), Chelsea Ursin and Jessica Body (ph). Meredith Halpern-Ranzer is the big boss.

THOMAS: Our theme song was composed and performed by The Pop Ups. Find more of their awesome, all-ages music at thepopups.com.

RAZ: Hey, parents and teachers, if you want to send us an email, our address is hello@wowintheworld.com. You can also send snail mail to WOW IN THE WORLD, care of NPR, 1111 North Capitol Street, Northeast, Washington, D.C., 20007.

THOMAS: You can also find us on Facebook, Twitter and Instagram at @wowintheworld.

RAZ: And if you want to be featured at the end of the show, call us up and tell us your wow in the world.

THOMAS: Our phone number is 1-888-7WOWWOW. That's 1-888-7WOWWOW.

RAZ: And, parents, if you want to upload any photos or videos or messages to us, please visit wowintheworld.com and find the link where you can do just that.

THOMAS: And if you haven't already done so, please subscribe to our show on Apple Podcasts or however you get your podcasts. And be sure to tell a friend. Until next time, keep on wowing. Tell a friend. Until next time, keep on wowing.


RAZ: (Singing) Wow in the world.

UNIDENTIFIED CHILD #2: WOW IN THE WORLD was made by Tinkercast and sent to you by NPR.

RAZ: Hey, it's Guy Raz here, host of How I Built This with a quick recommendation. Every holiday weekend comes with a lot of waiting, traffic, airport security lines. And so while you're waiting, why don't you just binge on How I Built This? Each episode, I speak with a founder of a company who has an incredible story of how it all began. You can find How I Built This on the NPR One app or wherever you get your podcasts.

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