[Music] In our last video, I talked about why and
how life became multicellular… one of the most important transitions in our evolutionary
history, but still one that happened dozens of times
Today I’m going to tell you about a different event, one so rare it only happened once in
the nearly 4 billion years life has been on Earth… what I would call the most important
moment in history. If it hadn’t happened…
[Wind]
We got lucky.
[Music]
Can you pick out the human cell?
Complex life looks pretty different on the outside. But whether it’s a plant, a protist,
or a peacock, at the most basic level, all of Earth’s complex life, eukaryotes, are
built from essentially the same stuff. Because eukaryotes share so many things, it’s
likely that we all have a common ancestor. You and that oak tree you used to climb are
cousins, just a few billion times removed.
But for most of the history of life on Earth, there was no such things as eukaryotes. Earth
was home to only two domains of basic life, bacteria and archaea. Known as “prokaryotes,”
these single-celled organisms dominated the Earth, but in all of life’s history they’ve
never gotten big or complicated like eukaryotes did. Because they couldn’t muster the energy.
Our energy currency is ATP. Like a token that gives you one play in the cellular arcade.
Maybe you use a token in a protein that cuts DNA, or maybe one that breaks down food. When
you run out of tokens, game over.
But prokaryotes can only manufacture those energy tokens on their surface membrane, and expanding their
surface area to create more energy tokens would exponentially increase their volume, which then needs more
energy to sustain. Say a bacteria wanted to increase its radius by 25 times. Then it would have
625 times as much membrane to make ATP with! All right! But you’d also need to manufacture
625 times more protein and membrane for those new ATP factories. In the meantime, the volume
of your cell has increased 15,000 times, and you’ve gotta fill that with protein machinery
too, so you’re gonna need 15,000 genomes to keep up with demand.
It was a catch-22 that prokaryotes could never overcome. On their own.
But then, something unimaginably improbable happened. An event so rare it only happened
once in all of life’s history. One day, an archaean cell bumped into a bacterium,
and slurped it up. And for some reason, it didn’t digest it. We don’t exactly know
why, but for the first time one organism was living in symbiosis not with another organism,
but inside it. ENDOsymbiosis. And every living thing you can see with the naked eye is descended
from that synthesis
By cooperating with its new host, this bacterium was able to ditch 99% of its genome, shut
down most of its own machinery, and concentrate on one task: making ATP. Thus the first mitochondria
was born, and its power level was over 9000.
That first eukaryote was rich!
[Music]
More ATP than it knew what to do with! It was free to grow
and specialize and experiment with new crazy abilities. Later, some of them gulped up a
second bacterium that had figured out photosynthesis, and they eventually became plants.
And before too long, eukaryotes morphed into everything from jellyfish to redwood trees
to pangolins and penguins… even us.
A single one of your cells can use 10 million ATP tokens every second. All together, you
burn through your body weight in ATP every day. Considering we only have 60 grams of
ATP in our whole body at any one time, there’s a lot of recycling going on. And that all
happens in the mitochondria.
To recycle all the ATP we need in a day, it takes an incredible number of mitochondria,
hundreds or thousands per cell, maybe a quadrillion in our whole body. If we stretched their crinkled
membranes out all together, your body would hold four football fields worth of ATP-making
real estate.
We know the mighty mito started this way because they still contain their own genome, a circle
of DNA like a prokaryote’s, and we can trace one third of our genes to either bacteria
or archaea. Eukaryotes are a genetic mashup.
In a world filled with bacteria and archaea bumping into each other every minute of every
day for the past couple billion years, this eukaryotic origin story has only happened
once. You and the oak tree’s common ancestor tells us so. It’s all thanks to that single
moment, when two branches from two divergent trunks on the tree of life, joined back into
one, freeing life from its energetic constraints, and giving nature the freedom to build endless
forms most beautiful.
Have you ever done a science and wished you had a t-shirt to celebrate the occasion?
Well [snap] now you do.
This new It's Okay to Be Smart Shirt is now available on our merch store dftba.com
If you'd like to pick one up for yourself
You can also find the link down in the description
and if you find yourself doing a science wearing this shirt
then post a picture on our instragram or tweet us with the hashtag I did a Science
alright, Stay Curious and stylish