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Let's shrink an elephant to the size of a mouse

and enlarge a mouse, and make it the size of an elephant, 把老鼠放大，变成大象那么大，

because this is our video, and we want to see what happens.

First: our now tiny elephant, stumbles around and then drops dead. Tout d'abord, notre éléphant, désormais minuscule, trébuche et tombe raide mort. 首先：我们现在的小象，跌跌撞撞，然后倒地而死。

Tiny elephant buddy is very cold; frozen to death in minutes. Le petit ami éléphant a très froid ; il est mort de froid en quelques minutes. Крошечному приятелю-слоненку очень холодно, он замерзнет за считанные минуты. 小象伙伴很冷；分分钟冻死。

Our giant mouse looks very uncomfortable for a moment, and then it explodes. 我们的巨型鼠标一时看起来很不舒服，然后就爆炸了。

leaving hot mouse insides everywhere. 到处都是热的老鼠内脏。

Why?

Because of size.

We are optimized to function precisely for the size we are, 我们针对我们的规模进行了优化，

and would die horribly in any other environment.

But, why exactly?

Why does our mouse explode,

and can we do this to our elephant too, if we try hard? et pouvons-nous faire la même chose à notre éléphant, si nous nous y efforçons ?

Life on this planet is based on cells.

Cells do vary in size.

But they're pretty similar in their dimensions across all species. Mais leurs dimensions sont assez similaires pour toutes les espèces.

A blue whale doesn't have bigger cells than a hummingbird, Les cellules d'une baleine bleue ne sont pas plus grandes que celles d'un colibri,

just a lot more of them.

Cells have to do a lot of stuff to stay alive.

And they need energy to be able to do so.

To get this energy,

animal cells convert food and oxygen into usable chemical energy.

This happens in our mitochondria, Cela se produit dans nos mitochondries,

the powerhouse of the cell.

They're like little coal engines that spit out tiny ATP batteries, Son como pequeños motores de carbón que escupen pequeñas baterías de ATP, Ce sont de petits moteurs à charbon qui produisent de minuscules batteries d'ATP, Они похожи на маленькие угольные двигатели, которые выплевывают крошечные аккумуляторы АТФ, 它们就像喷出微小 ATP 电池的小型燃煤发动机，

which the cell can use for almost everything it needs to do. que la cellule peut utiliser pour presque tout ce qu'elle doit faire.

Just like an engine, mitochondria get really hot while working. Al igual que un motor, las mitocondrias se calientan mucho mientras trabajan. Tout comme un moteur, les mitochondries chauffent énormément lorsqu'elles fonctionnent.

In human skin cells,

they reach a scorching 50 degrees Celsius. ils atteignent 50 degrés Celsius.

And some of our cells have up to 2,000 mitochondria Certaines de nos cellules comptent jusqu'à 2 000 mitochondries.

which are radiating their heat into the cell. qui diffusent leur chaleur dans la cellule. 它们将热量散发到细胞中。

So, being alive generates a lot of heat.

The more cells you have, the more heat your body generates in total.

If our bodies didn't find ways of losing this heat,

we would be cooked from the inside and die.

But this is a problem for bigger animals

because of the way bodies change as living beings scale up. en raison de la manière dont les corps se modifient à mesure que les êtres vivants s'agrandissent.

Animals have 3 properties here that are important. 动物在这里有 3 个重要的属性。

Their length, their outsides or skin, Leur longueur, leur extérieur ou leur peau, 它们的长度，它们的外表或皮肤，

and their insides, like organs,

bones, and hopes and dreams. 骨头，希望和梦想。

The thing that's hard to wrap your head around is that when things grow, Ce qui est difficile à comprendre, c'est que lorsque les choses grandissent, 难以理解的是，当事情发展时，

their insides grow faster than their outsides.

Imagine a fleshy cube. 想象一个多肉的立方体。

If you double the length of its sides, Si l'on double la longueur de ses côtés,

its surface and volume do not double.

In fact, the surface is now 4 times the original size, En fait, la surface est maintenant 4 fois plus grande qu'à l'origine,

and the volume of the cube 8 times the original size.

Which is called the Square Cube Law,

and has been annoying nature for billions of years. et agace la nature depuis des milliards d'années.

So why is this a problem for big animals?

Because heat can only leave an object via its surface.

So if we make our mouse the size of an elephant, 所以如果我们让我们的老鼠有大象那么大，

or 60 times longer, ou 60 fois plus longtemps,

it has 3,600 times more surface from which to lose heat.

But it has 216,000 times more volume 但它的体积是它的 216,000 倍

filled with trillions and trillions of new hot mitochondria rempli de billions et de billions de nouvelles mitochondries chaudes 充满了数以万亿计的新热线粒体

that produce more heat. 产生更多的热量。

A lot more insides; not that much more skin. 更多的内部；没有那么多皮肤。

Our mouse is very dead, very fast. Наша мышь очень мертва, очень быстро. 我们的老鼠死了，速度很快。

But big things like elephants exist. 但是像大象这样的大东西是存在的。

So how do they deal with the heat?

For one, they evolved ways to get rid of energy more easily 一方面，他们进化出了更容易摆脱能量的方法

like huge flat ears, that have a lot of surface where heat can escape. 就像巨大的扁平耳朵，有很多表面可以散发热量。

But that's not enough.

Nature's solution is actually very elegant. 大自然的解决方案其实很优雅。

Elephant cells are much, much slower than mice cells. 大象细胞比小鼠细胞慢得多。

The bigger an animal is, the less active its cells are. Plus un animal est gros, moins ses cellules sont actives.

If we classify animals, by their metabolic rates, and compare

that to their overall mass, It's clearly visible.

It's not 100% accurate,

but it is a good rule of thumb. но это хорошее эмпирическое правило.

Elephants are huge meat sacks filled with Los elefantes son enormes sacos de carne llenos de Les éléphants sont d'énormes sacs à viande remplis de 大象是巨大的肉袋，里面装满了

trillions and trillions of little coal ovens. 数以万亿计的小煤炉。

So, they keep the ovens just active enough to keep them running 所以，他们让烤箱保持足够活跃以保持它们运行

and never at full power. y nunca a plena potencia.

Their whole metabolism is slow.

Things move at a nice chill pace. Las cosas avanzan a un ritmo agradable. Les choses se déroulent à un rythme agréable. 事情以一种令人放松的速度发展。

Small animals need to go the exact opposite way. Los animales pequeños deben ir exactamente al revés.

If you're small, you have a lot of surface area

compared to not a lot of volume.

You don't have a lot of cell ovens

and lose the heat they produce very fast.

So very tiny mammals came up with a very extreme solution.

Meet the Etruscan Shrew, the smallest mammal on Earth. 认识地球上最小的哺乳动物伊特鲁里亚鼩鼱。

A mole-like thing that's more closely related to hedgehogs than to mice. Una cosa parecida a un topo que está más emparentada con los erizos que con los ratones. Un animal qui ressemble à une taupe et qui est plus proche du hérisson que de la souris.

With the body length of 4 centimeters,

it only weighs about 1.8 grams - as much as a paperclip.

It's a tiny ridiculous being.

It would basically cool off immediately,

so its cells run on overdrive to stay warm. ses cellules fonctionnent donc en surrégime pour rester au chaud. dus zijn cellen draaien op overdrive om warm te blijven.

Its tiny ovens are filled at maximum capacity.

Its heart beats up to 1,200 times a minute, Son cœur bat jusqu'à 1 200 fois par minute,

and it breathes up to 800 times a minute.

This creates an extreme need for energy.

So the shrew has to eat constantly.

After only 4 hours without food, it starves to death. Después de sólo 4 horas sin comida, muere de hambre.

And while an African elephant

consumes around 4% of its body weight in food each day. consomme chaque jour environ 4 % de son poids en nourriture.

Our shrew needs 200% of its body weight

in food a day just to survive.

Imagine having to eat 2,000 Big Macs a day

more than one a minute.

Fun for a while, but then not so much. Divertido durante un tiempo, pero luego no tanto.

So, a cubic centimetre of shrew needs 40 times more food 所以，一立方厘米的鼩鼱需要40倍的食物

than a cubic centimetre of elephant. qu'un centimètre cube d'éléphant. 比一立方厘米的大象。

If an elephant's cells 如果大象的细胞

suddenly become as active as the cells of a shrew de repente se vuelven tan activas como las células de una musaraña deviennent soudainement aussi actives que les cellules d'une musaraigne

a crazy amount of heat would be generated. 会产生大量的热量。

All the liquids in the elephant would suddenly start boiling. 大象体内的所有液体都会突然开始沸腾。

And then it would explode 然后它会爆炸

in an impressive explosion of steaming hot burning elephant parts. en una impresionante explosión de partes de elefante ardientes y humeantes.

In reality, before an explosion occurred

the proteins making up our cells would probably be denatured, las proteínas que componen nuestras células probablemente se desnaturalizarían, les protéines qui composent nos cellules seraient probablement dénaturées, 构成我们细胞的蛋白质可能会变性，

and stop producing heat. 并停止产生热量。

But a meat explosion is much more fun 但是肉爆更有趣

than melting an elephant into a massive hot goo. que fundir un elefante en una enorme sustancia viscosa caliente. que de faire fondre un éléphant dans une énorme bouillie chaude. 而不是将大象融化成巨大的热粘液。

Regardless, the scaling of the speed of metabolism happens everywhere. Independientemente de ello, la escalada de la velocidad del metabolismo ocurre en todas partes. Quoi qu'il en soit, l'échelonnement de la vitesse du métabolisme se produit partout. 无论如何，新陈代谢速度的缩放无处不在。

Even in places we don't expect, like pregnant women. 即使在我们意想不到的地方，比如孕妇。

A baby in the womb of its mother behaves as if it were a part of her. Un bébé dans le ventre de sa mère se comporte comme s'il faisait partie d'elle. 母亲子宫中的婴儿表现得好像它是她的一部分。

Its cells have about the same metabolic rate, 它的细胞具有大致相同的代谢率，

the same speed of life, as its mother's organs. la même vitesse de vie que les organes de sa mère. 和它母亲的器官一样的生命速度。

It is truly a part of a bigger whole, rather than an individual. Es realmente una parte de un todo mayor, más que un individuo. 它确实是一个更大的整体的一部分，而不是一个个体。

Until it's not anymore. Hasta que deje de serlo. Jusqu'à ce qu'il ne le soit plus. 直到它不再。

The very moment a baby is born, a switch is flipped En el momento en que nace un bebé, se activa un interruptor 婴儿出生的那一刻，一个开关被翻转

and all its internal processes speed up rapidly. 它的所有内部流程都在迅速加速。

36 hours after birth, 出生后36小时，

the baby's cells have the same activity rate as a mammal its size. les cellules du bébé ont le même taux d'activité qu'un mammifère de sa taille. 婴儿的细胞具有与哺乳动物相同大小的活动率。

Babies literally transition from being an organ Les bébés passent littéralement du statut d'organe 婴儿从字面上转变为器官

to being an individual, in mere hours. à être un individu, en quelques heures seulement.

But there's one thing where big and small things are very similar: Mais il y a un point sur lequel les grandes et les petites choses sont très similaires :

Heartbeats. Battements de cœur.

Mammals tend to have a similar amount of heartbeats, over their lifetime. Les mammifères ont tendance à avoir un nombre similaire de battements de cœur au cours de leur vie.

Typically around 1 billion. En général, ils sont de l'ordre de 1 milliard.

So, while the shrew and elephant are very different,

they share a similar number of heartbeats over the course of their lives.

Their speed of life is the opposite and somehow still the same. Leur vitesse de vie est opposée et pourtant toujours la même. 他们的生活速度是相反的，不知何故还是一样的。

And, for a video in which we made elephants explode for no good reason. 而且，对于我们让大象无缘无故爆炸的视频。

This is the most romantic ending we could come up with. 这是我们能想到的最浪漫的结局。

Speaking of romance and love, one of the questions 说到浪漫和爱情，问题之一

we get asked most often is how we make animated videos. 我们最常被问到的是我们如何制作动画视频。

The short answer is: with Adobe After Effects and years of training.

But, rather than just point you to our favorite online tutorial service

we decided to make a Skillshare tutorial

explaining how we made a scene from one of our videos.

If you aren't already familiar with it,

Skillshare is an online learning community,

with more than 18,000 classes

in things like writing, animation, and video editing.

Their premium membership gives you

unlimited access to high-quality classes

from professionals working in their fields.

So you can improve your skills,

unlock new opportunities,

and do work that you'd really enjoy.

It's also extremely affordable.

The annual subscription is less than $10 a month.

But, because we appreciate you

we've arranged for the first 1,000 people to get their first

2 months absolutely free.

If you want to learn how we animate our stuff,

this is the way to go.

Okay, this concludes

Kurzgesagt, for 12,017. Happy Holidays, everybody.