Why are these 32 symbols found in ancient caves all over Europe?

There's something about caves.

A shadowy opening in a limestone cliff
that draws you in.

As you pass through the portal
between light and dark,

you enter a subterranean world.

A place of perpetual gloom,

a place of earthy smells,
of hushed silence.

Long ago in Europe,

ancient people also entered
these underground worlds.

As witness to their passage,

they left behind mysterious
engravings and paintings.

Like this panel of humans, triangles
and zig-zags from Ojo Guareña in Spain.

You now walk the same path
as these early artists.

And in this surreal, other-worldly place,

it's almost possible to imagine

that you hear the muffled foot-fall
of skin boots on soft earth,

or you see flickering of a torch
around the next bend.

When I'm in a cave,

I often find myself wondering,
what drove these people to go so deep?

to brave dangerous and narrow
passageways to leave their mark?

In this video clip,

that was shot half a kilometer,
or about a third of a mile underground,

in the cave of Curon in Spain,

we found a series
of red paintings on a ceiling

in a previously unexplored
section of the cave.

As we crawled forward, military-style,
with the ceiling getting ever-lower,

we finally got to a point
where the ceiling was so low,

that my husband and project
photographer, Dylan,

could no longer achieve focus
on the ceiling with his DSLR camera.

So while he filmed me,

I kept following the trail of red paint
with a single light,

and a point-and-shoot camera
that we kept for that type of occasion.

Half a kilometer underground.

Seriously.

What was somebody doing down there
with a torturous stone lamp?

(Laugher)

I mean --me, it makes sense, right?

But you know,

this is the kind of question that
I'm trying to answer with my research.

I study some of
the oldest art in the world.

It was created by these
early artists in Europe,

between 10 thousand
and 40 thousand years ago.

And the thing is,

is that I'm not just studying it
because it's beautiful,

though some of it certainly is.

But what I'm interested in
is the development of the modern mind,

of the evolution of creativity,
of imagination, of abstract thought.

About what it means to be human.

While all species communicate
in one way or another,

only we humans have really taken it
to another level.

Our desire and ability
to share and collaborate,

has been a huge part of out success story.

Our modern world is based on a global
network of information exchange.

Made possible, in large part,
by our ability to communicate.

In particular, using graphic
or written forms of communication.

The thing is though,

that we've been building
on the mental achievements

of those that came before us for so long,

that it's easy to forget that certain
abilities haven't already existed.

It's one of the things
I find most fascinating

about studying our deep history.

Those people didn't have the shoulders
of any giants to stand on,

they were the original shoulders.

And while a surprising number
of important inventions

come out of that distant time,

what I want to talk to you about today
is the invention of graphic communication.

There are three
main types of communication,

spoken, gestural --
so things like sign language,

and graphic communication.

Spoken and gestural are,
by their very nature, ephemeral.

It requires close contact for a message
to be sent and received.

And after the moment of transmission,
it's gone forever.

Graphic communication, on the other hand,
decouples that relationship,

and with its invention, it became possible
for the first time,

for a message to be
transmitted and preserved,

beyond a single moment in place and time.

Europe is one of the first places

that we start to see graphic marks
regularly appearing

in caves, rock shelters, and even
a few surviving open air sites.

But this is not the Europe we know today.

This was a world dominated
by towering ice sheets

by towering ice sheets, three to four
kilometers high,

with sweeping grass plains
and frozen tundra.

This was the Ice Age.

Over the last century,

more than 350 Ice Age rock art sites
have been found across the continent.

Decorated with animals, abstract shapes,
and even the occasion human.

Like these engraved figures
from Grotta dell'Addaura in Sicily.