Humans get along pretty well with most microbes. 
Which is lucky, because there are a lot more of them
in the world than there are of us.
We couldn’t even live without many of them. 
But a few hundred have evolved, and are still evolving,
to exploit our bodies in ways that can make us really sick.
These are the microbes we call germs. 
Like Plague, HIV, SARS, Ebola, Zika
and a whole gang of others.
This is a series is about where germs come from. 
When we Homo sapiens started to evolve as a new species,
we inherited many of the microbes
that came from our early human ancestors.
But many of today’s most-feared diseases didn’t exist yet. 
Scientists think a lot of these diseases
probably came from other animals. 
Like this monkey here.
Let’s take a closer look at what’s happening inside this guy.
He happens to be carrying a nasty bug.
It’s a virus.
It’s taken control of many of his cells
and ordered them to make more copies of itself. 
But some of these copies aren’t exact.
And eventually, one happens to emerge
with an accidental superpower ...
This superpower monkey virus now has the ability to infect us.
It sneaks past our immune system’s defenses,
gets into our cells, and starts making copies.
And then this happens ... 
Luckily, humans were so few and far between
that this new virus can't find any more humans to infect. 
That first mutant virus doesn’t get very far.
But after many thousands of years,
something big starts to change. 
Humans discovered agriculture. 
This means we start to settle down,
cut down the forest to make way for crops
and get comfortable.
We start having larger families and more neighbors
because there’s more food.
We still like to eat the occasional monkey
when we can get our hands on him.
But look what happens now ...
I win!
Mmmm. No.
In nearly every outbreak, some people get lucky
and have a mutation or two that helps their bodies
defeat the new virus.
They move away. 
And maybe build a new settlement. 
So ... We win?
Mmmm. Not quite. 
