RL: There is fantastic, rich complexity in the world around us.
But the beauty and the cruelty of existence
is not something we can always handle alone.
That struggle to survive extends beyond humans
and includes all life on the planet, where
a seemingly endless menagerie of creatures
live, compete, and sometimes help one another as they populate the Earth.
Even the very smallest are an important part of this web of life.
But how did this come to be?
For us to find out, let's go back to a time of ancient competition
and see how a simple prokaryotic cell-- no more than a membrane, nucleic acids,
and proteins-- evolved a remarkably beneficial relationship to help
it thrive.
Billions of years ago, these early cells lived in rich waters,
searching for energy.
Some cells consumed energy from molecules directly.
Some of those cells became energy sources for others,
while still others cells evolved the ability
to use sunlight to split water molecules as an energy source.
But the pure oxygen released in this reaction
changed the very atmosphere of the planet
and likely harmed other prokaryotes.
Many didn't survive.
But what's this?
Here is a cell that evolved to use oxygen as a powerful energy source,
allowing it to thrive in this new oxygen-rich environment.
But the cell still competed for survival in a dangerous world.
Then something remarkable happened.
A larger cell engulfed our little oxygen-using cell.
But this time, the little cell survived inside its host.
Now the smaller cell could harness energy from oxygen,
but this time from the safety of its new home--
even more energy than it needed, allowing it to share energy
with the larger host cell.
In return, the host cell provided nutrients and safety from predators.
This relationship was simply too good to end.
Over generations, the two cells' descendants
exchanged DNA and became dependent on each other for survival,
living as one organism in an evolutionary process
called endosymbiosis.
This mutually-beneficial relationship only deepened over time,
allowing the evolution of what we know today as the eukaryote,
with a true nucleus and organelles that complete specialized tasks.
And what about that little oxygen-consuming cell?
It evolved into the mitochondrion, which still harnesses
most of the energy in eukaryotic cells.
In your own body right now, a mitochondrion
can maintain an electric field across its membrane
of 30 million volts per meter, a potential that
is equal to the energy released by a bolt of lightning in the sky.
This energy supported the evolution of even more structures
in more diverse combinations, changing and building on one another over time.
All of the varied multicellular life on earth
derives from that cooperative relationship in our ancient past.
Had it not been for this chance relationship so long ago, life on Earth
wouldn't exist as it does today.
It all began with cells evolving to cooperate and create
new possibilities for life.