Join Molly Bloom and co-host Ishalo as they learn about the ingredients we need to grow – and why sometimes the growing seems slow! They’ll chat with Dr. Diva de León Crutchlow about sleep and hormones and help Sanden take care of Dwayne the 5-year-old brain. Is your excitement growing by the minute? Ours too! And we’ve got another tricky mystery sound, just for you.

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ISHALO: You're listening to Brains On where we're serious about being curious.

SUBJECT 1: Brains On is supported in part by a grant from the National Science Foundation.

BOB: 3 inches, and let's see. 3 inches. OK, and still 3 inches.

MOLLY BLOOM: Hi, Bob, what are you doing?

BOB: Oh, hey, Molly. I'm just measuring how fast different things grow. And so far, this blade of grass has grown not at all.

MOLLY BLOOM: Why are you measuring grass, Bob?

BOB: Well, I started off my day watching paint dry, and it was just too exciting. My heart was literally racing, wondering when it was going to be dry, how it was going to look when it dried. So I decided to take a break from all the excitement and measure how fast grass grows.

MOLLY BLOOM: Well, that's certainly one way to relax.

BOB: Oh, hey, could I measure you?


BOB: Well, looks like you're 5 feet and 1 inch. Now stay still and let me see if I can time how long it takes you to grow.

MOLLY BLOOM: Bob, you know--

BOB: OK, let's see. You're still 5 feet 1 inch. Oh, wait, wait, looks like you're 5 feet 2 inches, 5 feet 3 inches. Well, that's 2 inches in 10 seconds. That means you're growing 60 feet per hour?

MOLLY BLOOM: Oh, Bob, I just stood up on my tiptoes.

BOB: Oh, I see. How about I measure you one more time just to be sure?

MOLLY BLOOM: Bob, you can't really tell how fast people grow just by staring at them.

BOB: Oh, good point, good point. I'm just going to see if I can calculate how fast this tree is growing. Just have to get up to the top. Oh. I think I'm going to need a bigger measuring tape. Oh, a squirrel. Excuse me, can I measure you?


MOLLY BLOOM: You're listening to Brains On from APM Studios. I'm Molly Bloom and my co-host today is ISHALO from Cambridge, Massachusetts. Hi, ISHALO.

ISHALO: Hi, Molly.

MOLLY BLOOM: Today, we're talking about how our bodies grow, and my excitement is growing by the minute. So you wrote in to us with a question about this, ISHALO.

ISHALO: Yeah, I wanted to know why do our bodies take so long to grow.

MOLLY BLOOM: What a great question. So what made you curious about that?

ISHALO: I had just gotten my hair cut, and it got really short. And then I wondered how long it would be in like a year.

MOLLY BLOOM: Are you a person who like tries to grow your hair long, or you like it short? Like, how do you like your hair to be?

ISHALO: I mean, sometimes I like it short. But then as soon as I get my hair cut, I want it long again, which is kind of weird. So I guess I'm just going to keep it long and not cut it.

MOLLY BLOOM: Do you feel like your hair grows fast, slow?

ISHALO: I feel like it grows very slow.

MOLLY BLOOM: Yeah, like when you, especially when you're trying to get it long, it feels like, wow, this will never happen. And do you feel like in your class at school, are you like one of the shorter kids, one of the taller kids, kind of right in the middle?

ISHALO: I'm like in the middle but a little less than the middle. Like, I'm not quite at the bottom. But I'm just kind of a little less than the middle.

MOLLY BLOOM: Gotcha. Yeah, when I was growing up, I was always, always, always the shortest in my class. So at first I was like, wow, why am I always so short, I want to be in the middle. But then I sort of eventually I was like, you know what, it's cool to be the shortest. So have you noticed differences between the way humans grow and animals grow?

ISHALO: I've never really had-- I've never had a pet. And I don't have one now. But my aunt has a cat. And it's kind of an old cat now. But I think it kind of grows pretty fast.

MOLLY BLOOM: Yeah, animals do grow faster than we do. Do you wish that you could be like an animal and get to grown up size really quickly, or are you happy that you kind of have this time to be a kid?

ISHALO: I mean, I wish I could grow quicker. But I wouldn't actually want to be an animal. I'd like my-- my most preferred choice would be probably a human that grows fast, which isn't really possible.

MOLLY BLOOM: So like in your dream, how long would it take you to go from kid to grown up? What time frame are you talking about?

ISHALO: Like, for me, I think like two years would be four years.

MOLLY BLOOM: Hmm. So kind of like twice as fast as you grow now?


MOLLY BLOOM: Well, before we dive into the science behind why we grow the way we do, let's start with how fast we usually grow. Can you help me out, ISHALO?

ISHALO: Yeah. When we're born, we're usually around 20 inches long, about the size of a big loaf of bread.

MOLLY BLOOM: And a lot of that is our head. Our heads are about one quarter of our entire height when we're babies. Baby heads are big. Can you imagine if our heads were a quarter of our height when we were grown up? Let's stop and picture this for a second.

So ISHALO, you told me right now that you're about 4 foot, 3 inches tall. So if your head took up as much of your body as a baby's does, it would be as tall as one of those big 2 liter soda bottles.

ISHALO: I'd look like a bobble head toy.

MOLLY BLOOM: Yeah. Babies kind of look like living bobblehead toys. But babies grow fast, right?

ISHALO: Oh, yeah. Babies get around 10 inches taller in their first year. That's more than half an inch every month. By the time you're one-year-old, you're about as tall as a toilet from the floor to the top of the tank.


MOLLY BLOOM: Now kids come in all shapes and sizes. Everyone is different. But in general, we grow really fast in our first year of life. And then the rate that we're growing slows down. Starting around age three, we grow about two inches on average each year.

ISHALO: And we have that same slow and steady pace for a while like 10 years, at which point you're about as tall as a big blue mailbox.

MOLLY BLOOM: We don't hit another growth spurt until adolescence. That's the time when your body starts changing from a kid's body into an adult's body. This is also called puberty. It's usually happens between the ages of 10 to 12, maybe a little bit older. And that's when we start doubling our growing speed, adding 3 to 5 inches per year. That's kind of like adding a soda can to our height every year. Up, up, up.

ISHALO: Then once we finish adolescence, we finish growing.

MOLLY BLOOM: That's usually sometime during our late teens.

ISHALO: So in general, our bodies grow really fast when you're first born, then kind of slow for a long time, then double speed for the last few years of growth. So really fast, then slow, and finally a little fast. Loaves of bread, toilets, mailboxes, stacking soda cans higher and higher and higher. All of this growth takes a lot of energy.

MOLLY BLOOM: That's right. To go from baby size to adult sized, humans and all living things need energy.

ISHALO: And we get that energy from--

MARC SANCHEZ: Tacos, get your tacos. Hey, Molly. Hey, ISHALO. Happy Taco Tuesday.


I just finished harvesting down at the Brains On taco farm. I've got al pastor, you'll adore, cheddar cheese that's sure to please, and avocado to make you go whoa.

MOLLY BLOOM: Marc, I love tacos. But we're in the middle of recording an episode.

MARC SANCHEZ: Oh, yeah. I see. What's the taco the town today?

ISHALO: Good one, Marc. We're talking about how our bodies grow, and we were just getting to the part where we were going to look at how much energy it takes to do all that growing.

MARC SANCHEZ: Well, I'm right on time then because these tacos have a bunch of vitamins and nutrients, which our bodies use to grow.

MOLLY BLOOM: Right. Our bodies need a huge variety of nutrients to grow, all kinds of vitamins, protein, sugar, fat, and minerals.

MARC SANCHEZ: Well, this taco is the perfect vehicle to fuel your growing. Pork and beans are protein machines. And the peppers have vitamins in them that will help your eyes, heart, and lungs work well.

ISHALO: Yeah, and the tomatoes have potassium, which helps your muscles grow.

MOLLY BLOOM: There's fat and sugar in the sour cream. Plus the spinach has iron and vitamins that help us fight off germs.

MARC SANCHEZ: I always knew tacos had super powers.

MOLLY BLOOM: Our bodies need energy for everything they do from reading a book to kicking a soccer ball, but especially for growing.

MARC SANCHEZ: OK, so your body needs all this stuff to grow. But how does it know when to grow?

ISHALO: Yeah, I'm eating all the time. But I'm growing slower than when I was a baby. What's up with that?

MOLLY BLOOM: So remember that protein we were talking about earlier in the pork and beans? Well, it's made up of tiny building blocks called amino acids. And some of those amino acids, as well as some of the fats from the sour cream get turned into something called hormones, which are what actually control our growth.

MARC SANCHEZ: Hormones, I remember when those turned me from a sweet faced kid into a teenage pimply rage monster. I did get really good at guitar, though, plus the ability to grow a mustache.

MOLLY BLOOM: Yes, hormones are famous for a lot of the changes that happen in puberty. But there are a whole bunch of different hormones in our bodies. And they're busy doing stuff for our whole lives, not just during puberty.

ISHALO: Yeah. I think of hormones like little messengers running around your body and flipping different switches on and off.

MOLLY BLOOM: One of these hormones is called human growth hormone.

MARC SANCHEZ: OK, Molly. I'm going to take a wild guess at what that is. Is it a hormone that helps humans grow?



Human growth hormone is made in our brains and does a ton of important stuff in our bodies besides just helping us grow. To learn more about it, I called up my friend Dr. Diva De Leon-Crutchlow. She's a pediatric endocrinologist, which means she studies hormones in kids.

DIVA DE LEON-CRUTCHLOW: The job of growth hormone is to orchestrate the growth of our bodies. And the way that growth hormone orchestrates the growth of our body is through signals that it sends to different parts of our body to activate the processes that are necessary for growth.

MOLLY BLOOM: For example, human growth hormone sends a message to our livers to start making chemicals that help our bones grow.

ISHALO: It also helps control our blood sugar and can help heal our bodies when we get hurt.

MARC SANCHEZ: Cool beans.

MOLLY BLOOM: Very cool beans. But in order for our bodies to release growth hormone, we need more than just healthy food.

ISHALO: Yeah, we need to exercise because exercise tells our body it's time to release more growth hormone. And we really, really need to get enough sleep. Diva says that even though we are growing all the time, our brains mostly release growth hormone while we're sleeping.

DIVA DE LEON-CRUTCHLOW: So that's why sleep is so important for children. So that's the period of during the day when growth hormone is being secreted when we are sleeping.

MOLLY BLOOM: That makes sense. During the day our brains might be busy getting ready for a math quiz or figuring out what to get a friend for their birthday, so our Brains wait until we're asleep to do things tell our bodies to grow.


Speaking of sleep, after a long morning of taco harvesting, I'm ready for a nap. I'll leave the leftover tacos here in caso you get hungry again.

ISHALO: Bye, Marc.

MOLLY BLOOM: Sweet dreams.

MARC SANCHEZ: Goodnight.

ISHALO: OK, so we've talked about how our bodies grow. But what's still a mystery to me is why our bodies take such a long time to be fully grown?

MOLLY BLOOM: Yeah, my cat finished growing before she was even two years old. Well, hang on, we're going to tackle that mystery in just a minute. But we've got another mystery to cover first. It's the--


SUBJECT 2: Mystery sound.

MOLLY BLOOM: ISHALO, are you ready to hear the mystery sound?


MOLLY BLOOM: All right, here it is.


Hmm. What could it be? I think we need to hear it again. It's a confusing one.


What are your thoughts?

ISHALO: I think it could be if you have plastic, and then you're like slapping it on the table or the counter or something.

MOLLY BLOOM: Hmm. Excellent ears, ISHALO. We are going to hear it again, and we'll hear the answer, and you'll get another chance to guess after the credits. So stick around.


We're about to go on a little Brains On break, but we'll be back in January with a new episode all about lightning. So while we're away, we want you to make up a short song all about this flashy phenomenon. What would your lightning song sound like? Does your song go boom, boom and light up the room, or is it more of an electric groove? ISHALO, what about you? What would your lightning song sound like?

ISHALO: It would sound like this--

(SINGING) During a storm, it strikes the ground. It goes, boom, boom, boom, boom. That's the lightning sound.

MOLLY BLOOM: Oh, ISHALO, that was utterly delightful. So wonderful. OK, so listeners, we want you to do the same. Please sing, strum, or drum a little lightning ditty and send it to us at And while you're there, you can send us mystery sounds, drawings, and questions.

ISHALO: Like this one.

SUBJECT 3: How do mammals become endangered?

MOLLY BLOOM: Again, that's

ISHALO: Keep listening.


You're listening to Brains On. I'm a ISHALO.

MOLLY BLOOM: And I'm Molly. Today we're talking about how our bodies grow. Before the break, we learned about what human bodies need to grow.

ISHALO: We need to eat well, exercise, and get enough sleep.

MOLLY BLOOM: Right. Then our brains will make something called human growth hormone, which will tell our bones, organs, and tissues when it's time for them to grow.

ISHALO: We also learned that human bodies don't grow at the same speed our whole lives.

MOLLY BLOOM: Instead, we grow really quickly in our first year of life, then slow down for most of childhood until we hit puberty when we speed up again. Then pretty soon after, we're done growing. People come in all different sizes and grow at all different speeds. Some grow up to be big and tall, and others like me stay a little smaller.

ISHALO, I have a question for you. Would you rather have the ability to grow really tall or shrink down to be really tiny?

ISHALO: I would rather shrink down really tiny because then I could go on all kinds of adventures, like I could explore beehives, and I could ride animals like butterflies and stuff. And I could ride animals. And if I was like tired, then someone could just pick me up in their palm and carry me around.

MOLLY BLOOM: It's like ride around in your parents' front pocket in their shirt.


MOLLY BLOOM: That would be very cozy. Well, we asked you dear listeners the same question, and here's what you said.

RIGEL: Hi, I'm Rigel. And I like to be small so I can run faster. And why I think I can run faster is because I don't have as much weight.

TEO: Hi, I'm Teo. I live in Barcelona, Spain. And I would like to be super small because then I would have some super reflexes.

CHAPMAN: I'm Chapman from Churchville, Quebec. And I'd like to grow super tall because I could travel further distances in one step.

KATHERINE ROSE: My name is Katherine Rose. And I'm Columbus, Ohio. I would like to shrink super small because then when my mom is closing the pantry door, I could sneak in and eat all the crackers.

MILES: My name is Miles and I would rather be super tiny because I could like prank my friends. Whenever I was like tired, I could like just sit down and lay on anything because I'm super tiny.

BIRD: Hi, our names are Bird--

WOODS: And Woods. We are from Bothell, Washington.

BIRD: We would both want to be able to shrink super small because we could ride on all sorts of animals.

WOODS: And fly around in the air like bugs.

BIRD: And if we wanted to leave the car, we could just jump out the window.


MOLLY BLOOM: Thanks to Rigel, Chapman, Katherine Rose, Miles, Bird, and Woods for sharing those with us.

ISHALO: Molly, I'm still curious about something. Why do our bodies take so long to grow? Lots of other animals, like dogs, cats, and horses seem to grow all at once, reaching their full adult size within just a few years.


MOLLY BLOOM: What is that?

DUANE: Taco Tuesday treat, please.

ISHALO: What the-- is that a--

MOLLY BLOOM: It looks like a--

SANDEN TOTTEN: Duane, Duane, wait for me.

ISHALO: Duane?

DUANE: Duane the brain. Hey, you got any more sour cream. Oh, is this pico de gallo? Don't mind if I do. Oh.

ISHALO: Sanden, why is there a disembodied brain running around the studio?


DUANE: Treats, please.

MOLLY BLOOM: Hey, get out of my secret candy drawer, Duane. Those chocolate covered cottage cheese clusters are for special occasions only.

SANDEN TOTTEN: Urgh. I took on a new babysitting gig. But as you can see, Duane is a little intense. He's got young brain energy.

DUANE: Hey, what's this? Is this a pogo stick?


Did you know that the highest pogo jump was over 11 feet high? That's like three penguins stacked on top of each other. Treat, please.

SANDEN TOTTEN: Good one, buddy. Duane just turned 5. And brains this age are super active. They're making memories, forming connections, making sense of language, learning right from wrong. Hey, Duane, get down, get down from the vending machine. Make a safer choice, buddy. Make a safer choice.

DUANE: Need spicy chips.

SANDEN TOTTEN: So basically, he's hungry all the time.

ISHALO: Oh, he needs brain food.

SANDEN TOTTEN: Yep, which is the same as well regular food. You see our big complicated Brains are crucial for our survival. So when you're a kid, developing your brain is more important than growing tall.

DUANE: Hmm-mm.

SANDEN TOTTEN: Last night I crammed through a crash course called brainby sitting 101. And I learned that over half of all the energy going into a 5 year old's body is used up by the brain. Duane, Duane, what are you doing? Oh, put that down. Give that to babysitter Sanden. OK.

DUANE: Oh, my beautiful spicy babies. I love you. Hmm-mm.

MOLLY BLOOM: That makes sense. Kids have a ton of learning and developing to do.

SANDEN TOTTEN: Exactly. Watch this. Hey, Duane, think fast. 4 plus 3 is?

DUANE: 7. Treat, please.

ISHALO: How do you spell taco?

DUANE: T-A-C-O. Treat, please.

ISHALO: Nice work. Here, want some guacamole?


MOLLY BLOOM: So since kids' brains need so much energy, their bodies can't grow as fast.

SANDEN TOTTEN: Exactly. When you're five years old, your body definitely isn't growing as fast as it was when you were at toddler. But your brain is still developing super fast. And that takes a ton of energy to fuel all this growth and development. By the time humans hit adulthood, they can do all kinds of things other animals can't do.

It's an evolutionary masterpiece. But you know, something had to give. And in our case, we gave up growing all at once like other creatures for slowly building amazing brains over time.

ISHALO: Ah, so even though it seems like I'm not growing very much because I'm not getting taller super fast, I'm actually developing a lot in my brain.

SANDEN TOTTEN: Precisely. And your brain needs all the same things your body needs to grow and develop. Plenty of nutrients from the food you eat, regular exercise, and lots of sleep. In fact, that's when your brain can really strengthen the connections it's building.

DUANE: Sleep rules, treat please.

MOLLY BLOOM: I'd love to sleep.

SANDEN TOTTEN: And sleep, you should, Molly. Your adult brain is still using about 20% of the energy you take in.

DUANE: Quick, what's the capital of Delaware?


DUANE: Nice one, Molly. High five.

MOLLY BLOOM: You don't have any hands.

DUANE: Hmm. You're right about that. Oh, well, gotta go visit the taco farm. Woo-hoo.

SANDEN TOTTEN: Duane, Duane, wait for me. Wait up, Duane. B-B-B, buddy, buddy, slow down.

ISHALO: Bye, Duane. Good luck, Sanden.

MOLLY BLOOM: Yeah, bye-bye.


So we learned that babies grow super fast, up to 10 inches in a single year.

ISHALO: Then when kids are about 2, that growth slows down to about 2 inches per year.

MOLLY BLOOM: And it doesn't speed back up again until puberty around age 10.

ISHALO: So growth in our bodies slows down because our brains are developing really fast. Kids' brains use more than half of all the energy we take in by eating.

MOLLY BLOOM: So if you're ever feeling impatient about not getting taller, just remember you are growing in your brain. That's it for this episode of Brains On.

ISHALO: This episode was written by Nico Gonzalez Wisler and Nick Ryan and produced by Molly Bloom, Rosie Dupont, Anna Goldfield, Ruby Guthrie, Marc Sanchez, Anna Weggel, and Aron Woldeslassie.

MOLLY BLOOM: Our editors are Sanden Totten and Shahla Farzan. We had engineering help from Alex Allinson, with sound design by Rachel Breeze. Beth Perlman is our executive producer. The executives in charge of APM Studios are Chandra Covatti, Alex Schaffert, and Joanne Griffith.

Special thanks to our human growth experts, Professor Barry Bogan from Loughborough University in and Professor Tanya Smith from Griffith University Australia. We'd also like to thank Chris Lopes, Amanda Baty, and Lulu.

ISHALO: Brains On is a non-profit public radio program.

MOLLY BLOOM: There are lots of ways to support the show. Head to

ISHALO: While you're there, you can send in your mystery sounds, questions, and drawings. And don't forget to send us your songs about lightning too.

MOLLY BLOOM: You can also subscribe to our Smartypass.

ISHALO: Super fun ad-free episodes and bonus stuff just for you.

MOLLY BLOOM: OK, ISHALO, are you ready to hear that mystery sound again?


MOLLY BLOOM: OK. Here it is.


OK, any new thoughts? Last time you were thinking plastic on a counter. Do you have new thoughts?

ISHALO: Maybe like a package, like a very heavy packaging of something. And somebody is like slapping it on the counter at the table.

MOLLY BLOOM: Hmm-mm. That's an excellent guess. Are you ready to hear the answer?


MOLLY BLOOM: OK. Here is the answer.

NOAH: Hi, my name is Noah from New South Wales, Australia. And that was the sound of me doing bottle flips. My record is 1251 bottle flips in a row.

MOLLY BLOOM: Impressive record and also very impressive guest because you were correct. It was plastic landing on a counter. It's just a water bottle. Someone flipping it. I think that was very, very close. Nice work. Have you have you tried flipping bottles before?

ISHALO: Yeah, I've tried. At school all the boys in our class they, especially last year, they got-- we have these little plastic water bottles that the cafeteria gives out. And then the boys like they would just get them and not drink them, and then they would just flip them. And they would be if it lands right side up, then they would be like, oh. And if like on its side or something, then they'd probably be like, boo, or something like that.

MOLLY BLOOM: So for people who don't know what that's like, so it's basically like you have the bottle-- do you hold it, and then you kind of just like flip it up in the air and hope it lands?

ISHALO: Yeah, you hold the cap, and then you just kind of flick your wrist, and flip it up in the air. And then it'll spin and then land either on its flat on the side or on the top. Or sometimes it'll bounce off the bottom and then land on its side.

MOLLY BLOOM: Oh. So the goal is to get it to land like standing straight up?


MOLLY BLOOM: Now it's time for the Brains Honor Roll. These are the kids who keep a show going with their questions, ideas, mystery sounds, drawings, and high fives.


SUBJECT 4: Brains Honor Roll. Bye, guys.

MOLLY BLOOM: We're going on a little break, but we'll be back in January with more awesome episodes.

ISHALO: Thanks for listening.

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