When animals first evolved, they did so in
a microbial world.
They did so on a planet that had been home
to all these organisms for billions of years.
This is Ed Yong, he’s written a book about
the microorganisms that live inside us and
all around us..
and that pre-date us, by a lot.
If we condense all of earth’s history into
a single calendar year, then life emerged
around about March, and multicellular life,
all the organisms that we are familiar with
only really came up in October or so.
And humans emerged very, very recently indeed. So we're just the icing on life's cake.
From the time humans evolved, bacteria and
other microbes would have colonized every
nook and cranny of our bodies, just like they
had other animals.
And they lived with us like that for some
200,000 years until eventually someone looked
close enough to notice.
That person was Antony van Leeuwenhoek.
So this is the late 17th century in the Netherlands
and he is not a trained scientist.
He’s not a scholar.
But he has two things that are really important:
One is an insatiable curiosity and the other
are really really good lenses, which he grinds himself.
At that point, microscopes had been around
for decades.
In England, Robert Hooke had published a book
of observations that was a  popular success.
It introduced the term “cell” for
the pores that he saw in a slice of cork, because they
reminded him of the cells of a monastery.
But bacterial cells are much smaller than
plant cells.
While Hooke was using a compound microscope
that could magnify 20-30 times,
Leeuwenhoek used single-lens microscopes that
could magnify up to 260 times.
Though you might not expect that from looking
at them.
It’s really like two brass rectangles that
sandwich this tiny tiny glass lens, this spherical
lens between them.
But it basically looks like a door-hinge.
The whole thing was just a few inches long
and the lens was as small as a grain of rice.
And he would have held it really close to his eye. He would have had to basically press his face
up against this thing and look through the lens.
It would have been deeply uncomfortable and
very straining.
To understand why his lens was so small, you
have to know how magnifying glasses work.
Like any other lens, they make use of the
fact that light bends when it enters glass
at an angle.
That’s because light moves more slowly through
glass than air, and so the portion of the
wavefront that enters the glass first will
slow down while the other part continues at
the faster speed.
That’s what makes it change direction, both
when it enters and exits the lens.
Now if you put an object close enough to the
lens, the bending light creates a virtual
image that’s not the real size of the object,
but the size it would be if the light from
the lens had traveled in a straight line all
along.
And if the lens is more curved, those lines
are even steeper, meaning greater magnification.
So Leeuwenhoek’s lenses weren’t just biconvex,
they were spherical.
And he knew that he could make that curve
even more drastic by shrinking the whole lens
down as small as possible, even if it meant
he’d have to get his eye uncomfortably close to it.
And with that tiny bead of glass, Leeuwenhoek opened
a peephole into a whole new world.
He looked at his blood and discovered blood cells.
He looked at his semen and discovered sperm.
He looked at samples of water and saw algae
cells, protozoa, and bacteria.
He called them little animals.
He went on to peer into his own dental plaque
and found bacteria there too.
And he described what he saw in letters to
the Royal Society.
He's the first person to see bacteria.
He’s the only creature, let alone human,
he’s the only organism in the entire history
of life on earth to actually see the things
that have been the dominant players in life’s history.
And I think the great thing is that he wasn’t
disgusted by it.
He saw tiny living things living in his
own mouth and, you know, he thought they were cool.
It would be nearly two more centuries before
microbes were linked to disease.
And even longer before we understood that
our microbes help us digest food, train our
immune system, and crowd out harmful bacteria.
Now microscopes are much more powerful than
Leeuwenhoek’s were, but these days it’s
a different tool altogether that’s enabling
researchers to explore how microbes affect
human health.
Just like Leeuwenhoek found microbes because
he had the right tools, now we’re seeing
that the microbiome is important because we
have the right tools, because we have the
ability to sequence the DNA of microbes, to
identify them by just scooping up a sample
from the environment and looking at their
genes.
If you were to take all the water out of your poop, 25-50% of what's left is bacteria,
both dead and alive. So if you were feeling sad that you can't see the microbes that make a home on your body,
Well, it turns out you kinda can!
