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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 3 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 4 times
the original size,
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.
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 at 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 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.
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 4 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.
36 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 1 billion.
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.
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.
Speaking of romance
and love, one of the questions
we get asked most often is
how we make animated videos.
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.