Pratique du Shadowing: Why Don't Our Bones Keep Growing Forever? - Apprendre l'anglais à l'oral avec la vidéo

Fish, amphibians, and reptiles –actually, almost all vertebrates– get bigger throughout their lives; they generally keep on growing until they die.

Then, there are humans, who, by the age of 20 or so, just stop getting bigger… or at least taller.

Why do we stop growing partway through life?

Hi, I'm Cameron, and this is MinuteEarth.

We can think about the question of why humans stop growing –like a lot of other questions about the world around us– in two ways.

Like, on an individual level, what actually stops our bones from getting longer at some critical moment?

But then also, on a grander scale, why do humans stop growing at a certain point, while other animals don’t?

Let's start with the first one.

Many bones have special layers of cells on each end known as "growth plates"; these cells are constantly dividing and turning into brand-new bone.

That's what makes both you and, say, an alligator grow.

And for the alligator, that growth continues throughout its life.

But in humans, once puberty is complete, our bodies release hormones that harden our growth plates permanently, turning them into "no-more-growth" plates.

Occasionally, some medical problem –like a hormone imbalance– will block this normal process from happening; that’s how the tallest people that have ever lived, like nine-foot-tall Robert Wadlow, reach their towering heights.

But, assuming things work as they should, the hardening of your growth plates means you can’t get any taller.

Now, here's where –if you're thinking what I'm thinking– you're contemplating that bigger question of why this whole growth-stopping process happens at all in us humans.

And it has to do with the fact that humans –along with other mammals, and birds– are energy-hungry critters.

Our fast metabolisms allow us to run –or swim or fly– long distances, but they require a lot of energy to sustain, even when we’re at rest.

And burning all that energy produces a lot of heat.

And if you recall, as an animal grows, its volume, and therefore the amount of heat it produces, increases much faster than its surface area does – surface that's needed to vent that heat outward.

Getting too big would burn us up, so it makes sense that there’s a biological process that limits our growth.

But other vertebrates –like alligators– have much slower metabolisms that don’t burn much energy most of the time.

Even as they grow bigger – and their relative surface area decreases – they’re generally able to vent the limited amount of heat their bodies produce.

And since being big does confer a lot of benefits, they might as well keep on getting bigger throughout life.

Bigger might be better for us humans too.

After all, it would be nice to be able to reach the highest fruit on the tree or change lightbulbs without a ladder, or something.

Unfortunately, we just can't take the heat.

If there’s anything that won’t stop growing, it’s the ridiculous amount of browser tabs I have open at any one time.

But that’s alright because I use Tab for a Cause, a simple browser extension that lets users raise money for charity for free just by opening browser tabs.

Right now, Tab For a Cause is working with The Humane League to help end animal cruelty in factory farms.

Simply download Tab for a Cause at the link in the description, and every tab you open will raise money that will go toward improving the lives of animals.

📺 Même chaîne

Mot	Prononciation	Sens
alligator nom	/ˈæl.ɪ.ɡeɪ.tɚ/	alligator, caïman
vertebrate nom	/ˈvɛɹ.tɪ.bɹeɪt/	vertébré
harden verbe	/ˈhɑɹdn̩/	durcir
ventilation nom	/ˌvɛntɪˈleɪʃ(ə)n/	ventilation, aération
metabolism nom	/məˈtæb.əˌlɪz.əm/	métabolisme
hormone nom	/ˈhoɹmoʊn/	hormone
tab nom	/tæb/	onglet, languette
amphibian nom	/æmˈfɪbɪən/	amphibien, batracien
confer verbe	/kənˈfɜː/	conférer, accorder
contemplate verbe	/ˈkɑn.təmˌpleɪt/	envisager, étudier
critter nom	/ˈkɹɪtɚ/	bébête, bestiole
imbalance nom		déséquilibre
mammal nom	/ˈmæməl/	mammifère
puberty nom	/ˈpjuː.bə.ti/	puberté
reptile nom	/ˈɹɛp.taɪl/	reptile

Pratique du Shadowing: Why Don't Our Bones Keep Growing Forever? - Apprendre l'anglais à l'oral avec la vidéo

Why Do India And China Have So Many People?

Why Haven't We Domesticated Monkeys?

Where Did Earth's Water Come From?

The Heaviest Part of a Forest Is NOT What You Think

Why Don't Blue Whales Eat Fish?

Why We Faint (When Other Animals Don't)

How To Kill A Volcano

Three Specific Ways AI Could Kill Us All

Why is it Hot Underground?

MinuteEarth Explains: Cats vs Dogs

Why Don't Snakes Poison Themselves?

The Best Dragon (According to Science)

How High Can Birds Fly?

Why Do Rivers Curve?

Why Do We Have More Boys Than Girls?

MinuteEarth Explains: Microbes

Could This Thing *Really* Fly?

There’s Really Only One Way To Die

You've Been Misled About The Water Cycle

What I Learned on Monkey Island

Your Skeleton Is Electric

Ferns Grew Up. Why Couldn’t They Move On?

Did Ancient Humans Really Live Longer Than Modern Humans?

Why Do Deep Oceans Have So Many Giants?

Could Humans Evolve Flight?

What science can’t answer, according to physicist Jim Al-Khalili | Big Think

There's a Giant Hole In Earth's History

Do we need more kids? A research showdown.

Untangled: What's eating our planet?

Why everyone stopped reading.

Contemporary Topics 3 Unit 11 BIOLOGY The fountain of youth

Vocabulaire et conseils d’expression pour cette leçon

Vocabulaire clé de cette vidéo

Des phrases à répéter

Prononciation à surveiller

Comment s’entraîner avec cette vidéo

Qu'est-ce que la technique du Shadowing ?

Could This Thing Really Fly?