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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.

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

  • First, our now tiny elephant stumbles around and then drops dead.

  • Tiny elephant buddy is very cold, frozen to death in minutes.

  • Our giant mouse looks very uncomfortable for a moment, and then it explodes, leaving hot mouse insides everywhere.

  • Why?

  • Because of size.

  • We are optimized to function precisely for the size we are, 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?

  • Life on this planet is based on cells.

  • Cells do vary in size, but they're pretty similar in their dimensions across all species.

  • A blue whale doesn't have bigger cells than a hummingbird, 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, the powerhouse of the cell.

  • They're like little coal engines that spit out tiny ATP batteries, which the cell can use for almost everything it needs to do.

  • Just like an engine, mitochondria get really hot while working.

  • In human skin cells, they reach a scorching 50 degrees Celsius.

  • And some of our cells have up to 2,000 mitochondria, which are radiating their heat into the cell.

  • 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.

  • Animals have three properties here that are important.

  • Their length, their outsides or skin. And their insides, like organs, bones, and hopes and dreams.

  • The thing that's hard to wrap your head around is that when things grow, their insides grow faster than their outsides.

  • Imagine a fleshy cube.

  • If you double the length of its sides, its surface and volume do not double.

  • In fact, the surface is now four times the original size, and the volume of the cube eight times the original size.

  • Which is called the Square Cube Law, and has been annoying nature for billions of years.

  • 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, or 60 times longer, it has 3,600 times more surface from which to lose heat.

  • But it has 216,000 times more volume filled with trillions and trillions of new hot mitochondria that produce more heat.

  • A lot more insides, not that much more skin.

  • Our mouse is very dead, very fast.

  • But big things like elephants exist.

  • So how do they deal with the heat?

  • For one, they evolved ways to get rid of energy more easily, like huge flat ears, that have a lot of surface where heat can escape.

  • But that's not enough.

  • Nature's solution is actually very elegant.

  • Elephant cells are much, much slower than mice cells.

  • The bigger an animal is, the less active its cells are.

  • 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.

  • Elephants are huge meat sacks filled with trillions and trillions of little coal ovens.

  • So, they keep the ovens just active enough to keep them running and never full power.

  • Their whole metabolism is slow.

  • Things move at a nice chill pace.

  • Small animals need to go the exact opposite way.

  • 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.

  • A mole-like thing that's more closely related to hedgehogs than to mice.

  • With the body length of four 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.

  • Its tiny ovens are filled at maximum capacity.

  • Its heart beats up to 1,200 times a 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 four hours without food, it starves to death.

  • And while an African elephant consumes around 4% of its body weight in food each day, 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.

  • So, a cubic centimetre of shrew needs 40 times more food than a cubic centimetre of elephant.

  • If an elephant's cells suddenly become as active as the cells of a shrew, a crazy amount of heat would be generated.

  • All the liquids in the elephant would suddenly start boiling, and then it would explode in an impressive explosion of steaming hot burning elephant parts.

  • In reality, before an explosion occurred, the proteins making up our cells would probably be denatured, and stop producing heat.

  • But a meat explosion is much more fun than melting an elephant into a massive hot goo.

  • Regardless, the scaling of the speed of metabolism happens everywhere.

  • Even in places we don't expect, like pregnant women.

  • A baby in the womb of its mother behaves as if it were a part of her.

  • Its cells have about the same metabolic rate, the same speed of life, as its mother's organs.

  • It is truly a part of a bigger whole, rather than an individual.

  • Until it's not anymore.

  • The very moment a baby is born, a switch is flipped, and all its internal processes speed up rapidly.

  • Thirty-six hours after birth, the baby's cells have the same activity rate as a mammal its size.

  • Babies literally transition from being an organ to being an individual, in mere hours.

  • But there's one thing where big and small things are very similar:

  • Heartbeats.

  • Mammals tend to have a similar amount of heartbeats, over their lifetime.

  • Typically around one billion.

  • So, while the shrew and elephant are very different, they share a similar number of heartbeats all the course of their lives.

  • Their speed of life is the opposite and somehow still the same.

  • And, for a video in which we made elephants explode for no good reason, this is the most romantic ending we could come up with.

Let's shrink an elephant to the size of a mouse, and enlarge a mouse, and make it the size of an elephant.

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How to Make an Elephant Explode with Science - The Size of Life 2

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    mommy posted on 2022/08/02
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