All language subtitles for Evolution Ep 2 Great Transformations

MAN:
It's a basic human need
to ask, "Who are we?"

"Where do we come from?"

"How did we get here?"

"Why do we look the way we do?"

NARRATOR:
The story of our evolution

is just a small chapter
in a much larger story:

the evolution
of all living things.

(trumpeting)

MAN:
Evolution shows us
that we're much more connected

to the rest of the world,
the rest of animal life

than we could ever
have imagined.

NARRATOR:
We can recognize the connection
to our closest relatives

but when we know how to look

we can also find it
in other mammals:

birds...

reptiles...

fish...

even insects.

The deeper we dig,
the farther back we go

the more we see that
everything alive has evolved

from a single starting point.

The tree of life
has been branching

for four billion years.

And we can now follow its
branches back to their roots.

MAN:
When we look back over time

we find certain signposts,
certain key events

the great transformations,
the big evolutionary steps.

NARRATOR:
In the history of our planet,
a few great transformations

have opened the door
for new ways of life

and new forms of life.

50 million years ago

land mammals evolved
into sea creatures.

Long before that,
fish colonized land.

At the dawn
of animal life itself

the first bodies appeared.

These are some of the chapters
in life's story... our story.

MAN:
And... and part of the fun
of studying this

is understanding each
different chapter

because by understanding
those chapters

we can begin to see
the unity of life,

the common history
of all life on Earth.

NARRATOR:
Human civilization stretches
back thousands of years.

But compared to the age
of the earth

we humans have only
just arrived.

MAN:
The earth is really old.

If you take the entire history
of the earth

from 4.6 billion years ago
to the present

and sort of call that an hour...

(clock chime dings)

SHUBIN:
The first 50 minutes
are largely spent

in a world of microbes,
single-celled organisms.

(clock ticking)

Animal life appeared in the
last ten minutes of that hour.

(clock ticking)

All of human history, our
civilization, our evolution,

happened in the last hundredth
of a second of that hour.

(clock chime dings)

CHILDREN:
? Ring-around-a-rosy... ?

NARRATOR:
We've come quite late
to the party

but we've been shaped
by the same forces

that have helped shape
all life on Earth.

CHILDREN:
? ...We all fall down. ?

NARRATOR:
To understand how we fit in,
we need to look back

to long before our own origins

to see how other
living things evolved.

(whales singing)

NARRATOR:
Whales are the largest
living animals.

Like us, whales and dolphins

took on their present forms
relatively recently.

For a long time, the origin
of these marine mammals

was a scientific mystery.

MAN:
Whales are so different
from every other kind of mammal

that we can't easily relate them
to anything else

and so they're off by themself
as a branch of mammal evolution.

NARRATOR:
Mammals first appeared on Earth
around 200 million years ago...

on land.

Mammals are warm-blooded

they give birth to living young
and they breathe air.

These are all adaptations
to living on land.

(dolphin clicking)

NARRATOR:
But whales and dolphins
are mammals, too.

SHUBIN:
They're mammals that live
in the water

but we know that mammals
evolved on land.

So it's a real puzzle
how whales originally evolved.

By understanding
how that happens

we'll begin to understand
how these big jumps

these big transformations
happen generally.

GINGERICH:
People are interested in whales,
and I can understand.

They're so beautiful.

Their origin is such a mystery.

Whales are one of
the few groups of mammals

that have really large,
complicated brains like we do.

And so in a sense, they're our
alter egos living in the sea

while we live on land

dominating the sea
while we dominate land.

And I think for that reason

we're very interested
in what goes on there

how they got there, as a
reflection of our own history

through geological time.

NARRATOR:
When Phil Gingerich began
his career 30 years ago

he knew nothing about whales,
and that was just fine with him.

He was drawn to geology
mostly because

he couldn't imagine a career
spent behind a desk.

GINGERICH:
I think I was interested
in geology

because it was a science
outdoors.

And in geology, I became
interested in paleontology

because it was about life
and the history of life.

NARRATOR:
Gingerich's early interest
in primitive land mammals

eventually took him to Pakistan.

It was there that he made
the kind of find

most paleontologists
only dream about:

a fossil that would rewrite one
of evolution's greatest stories.

GINGERICH:
I found the back of a skull
that I couldn't identify.

It had a very good,
well-preserved ear region

and that offered the clue
to what it was.

NARRATOR:
The shape was familiar

but in other ways it was like
nothing Gingerich had ever seen.

This is the original specimen.

It's the one we found
in about 1978.

There's several things
that strike you.

One is it's very similar
in size and shape

to the back of a skull
of a wolf.

NARRATOR:
But there was something odd
about this skull.

On its underside
was a walnut-sized bump.

GINGERICH:
If this wasn't here

I would think that this was
an archaic carnivorous mammal

or what we call a creodont,
but it is here.

NARRATOR:
It was part of
the animal's inner ear

and it had a distinctive shape,

a shape found today in only
one kind of animal: whales.

What was the ear of a whale
doing on the skull of an animal

that resembled a wolf?

Gingerich was intrigued,
so he constructed a model

of what the creature's full
skull might have looked like.

He wondered, was his find
a crucial missing link

the first fossil evidence
ever found

for one of Darwin's
most daring claims,

that whales had evolved
from land mammals?

To know for sure

Gingerich would need
to find more fossils...

ones that would show each stage
of the whale transformation,

what scientists call
"transitional forms."

I want to line them all up.

I want anyone
to be able to see it

and believe it
because they've seen it.

NARRATOR:
Gingerich tried to return
to Pakistan to resume his search

but war had broken out,
and the borders were closed.

Frustrated, Gingerich decided
to look elsewhere.

He had heard stories
about whale skeleton sightings

in a very unlikely place.

So he decided to check it out
for himself.

The Sahara Desert is one
of the driest places on Earth.

But 40 million years ago, things
here were quite different.

GINGERICH:
This used to be the sea.

Just think of this being

the current Mediterranean
coast of Egypt

backed up about 40 million years

but about 100 kilometers to
the south of where it is today.

NARRATOR:
Here, in what had once been
the Southern Mediterranean Sea

is a 100-square-mile stretch
of layered sandstone

with a surprising name...

Valley of the Whales.

The name is well suited.

Scattered everywhere
across this arid landscape

are what look like heaps
of rose-colored stones.

Here's
aBasilosaurus.

NARRATOR:
But they're not stones...

You can see how big
the vertebrae are.

Here's a lumbar
partly weathered away.

NARRATOR:
They're whale skeletons
40 million years old.

There's another one
back here coming out
of the mushroom.

There's one
over here.

And back over there
is one.

This whole place
is full of whales.

NARRATOR:
Why were there so many whales
concentrated in this one spot?

Gingerich believes
that Whale Valley

was once a protected bay,

a lagoon hidden from the open
sea by underwater sandbars.

Perhaps the whales
birthed their young here

and came here to die.

But even with hundreds
of whale bones at his feet

Gingerich was disappointed.

Nearly all of the skeletons

belonged to a whale
called"Basilosaurus--"

a 40-million-year-old creature
already known to science.

Basilosauruslived full time
in the water.

This isBasilosaurus.

I got all excited...

NARRATOR:
If whales had evolved
from land mammals

they had done so
long beforeBasilosaurus.

So Gingerich didn't think the
bones would be of much interest

but he couldn't
have been more wrong.

After only a few days
of digging

he made his second amazing find.

It turned out thatBasilosaurus

had something modern whales
have long since lost.

For the first time,
we've got whales that have legs.

NARRATOR:
The bones were small
but unmistakable.

A pelvis.

A kneecap.

Even toes.

This whale had a complete set
of leg bones.

Gingerich brought back
as much of the skeleton

as he could carry.

It was dramatic evidence

that whales had once
been four-legged animals.

Since Gingerich's finds

he and others have filled in
more of this fantastic story.

Scientists now think

that the earliest ancestor
of whales was similar

to this 50 million-year-old
wolflike mammal called sinonyx.

Sinonyx was
a predatory scavenger

that lived and hunted along
the shores of an ancient sea.

Perhaps its descendants
found the water

a source of abundant food,
and a haven from competition.

Over millions of years
front legs became fins

rear legs disappeared,
bodies lost fur

and took on their familiar
streamlined shape.

Since Gingerich's first find,
named Pakicetus

the list of known
transitional whales has grown.

It now includes Ambulocetus...

Rhodocetus...

Durodon...

as well as Basilosaurus.

They reveal another element
of whale evolution

the gradual migration of
nostrils to the top of the head

as whales adapted to breathing
in the water.

(exhaling)

GINGERICH:
How did whales
lose their legs?

As the years went by, they
evolved into newer types of...

NARRATOR:
Gingerich's work demonstrates
what Darwin himself insisted

that the evidence for evolution
is all around us

if we choose to look for it.

And bones aren't the only
evidence of whale evolution.

Their ancestry is also visible
in the way they move.

Frank Fish studies how today's
marine mammals swim.

He looks for their
evolutionary heritage

in the way they move
through the water.

FISH:
The big question is:

How do you go
from a terrestrial mammal

that ran around
on all four legs

to something such as a dolphin

which now doesn't have
any legs at all

and is well adapted
to swimming in the oceans?

NARRATOR:
Even though whales look like
fish, they don't swim like them.

Fish swim by flexing
their spines from side to side

like this shark.

But mammals swim differently.

This otter swims by undulating
its spine up and down...

in exactly the same way
that whales do.

And, as it turns out
in the same way

that land mammals use
their spines when running.

Whales took with them
into the water

their ancestral way of moving

and we can still see it...
50 million years later.

SHUBIN:
In one sense, evolution didn't
invent anything new with whales;

it was just tinkering
with land mammals.

It's using
the old to make the new

and we call that tinkering.

And it does this
in every animal group

at every time during
evolutionary history.

NARRATOR:
The starting point for whales
was a four-legged land animal

that lived
over 50 million years ago.

But land animals were also the
product of a transformation,

a much earlier one.

Hundreds of millions
of years ago

there were no animals on land.

SHUBIN:
Before then

all our distant ancestors
lived in the water.

So at some point you had
this shift from life in water

to life on land.

That's a huge change.

NARRATOR:
It was the moment when fish
crawled out of the water

and onto land.

WOMAN:
If these early animals hadn't
made the transition

we wouldn't be here today.

And it's important
to understand how and when

and possibly, where
that transition took place.

NARRATOR:
The first creatures to leave the
water really started something.

Their descendants eventually
evolved into today's reptiles...

birds...

and mammals.

And these creatures'
common origins

are still visible
in their bodies.

Just like us, they all have
bodies with four limbs,

they're all tetrapods.

SHUBIN:
What that means is that all
these different creatures

are descended
from a common ancestor

whichhadsomething very similar
or akin to limbs.

NARRATOR:
Just what was
that common ancestor?

And how did it leave the water
370 million years ago?

(men conversing)

Those are the questions that
paleontologists Neil Shubin

and Ted Daeschler
are trying to answer.

They think that the cliffs
here in Central Pennsylvania

may offer some clues.

DAESCHLER:
All right, I think
it's a good day for fossils.

What do you say?

Great day;
let's find some.

Hey, Doug.

Hey, Doug.

Good trip up?

What you say
we go over here?

That's good.

Get some good digging in today.

NARRATOR:
An unlikely spot to hunt
for early tetrapod fossils.

But they're here because
the rocks in these hills

are just the right age,

laid down during the period
in Earth's history

called the Devonian.

(men conversing)

SHUBIN:
Back in the Devonian,
this place was very different.

It was south of the Equator,

remember the continents are
continually moving around,

and back this time
we're actually dealing with

a much more tropical climate
in Pennsylvania.

NARRATOR:
Hundreds of millions
of years ago

the fossils and sediments
in these layers

were collecting
on the bottom of a stream.

SHUBIN:
What we have here

is a snapshot
of life in a stream

about 370 million years ago.

These are fossilized... broken
fossils of scales, of teeth.

This little bone here,

it's a spine of a creature
known as a spiny shark.

NARRATOR:
Most of the fossils are too
fragmented to be of much value.

But in 1995, right at this spot

Daeschler came across something
he had never seen before.

It was a small shoulder bone,
but not from a fish.

It was a tetrapod shoulder,
370 million years old.

Shubin and Daeschler
had unearthed the remains

of one of life's first
four-legged creatures.

DAESCHLER:
It was the first evidence
of these early tetrapods

from all of North America,
and that made it very exciting.

NARRATOR:
And there was another surprise.

Since it was found
in the stream bed

this tetrapod most likely
livedin the water.

SHUBIN:
And it's
a very surprising discovery.

It's not something

we necessarily
would have predicted.

NARRATOR:
Why would an animal with limbs
live in the water?

Limbs were thought
to have evolved

for getting around on land.

The old idea was that
the fish came on shore first

and then developed the legs.

And what we now think

is that the tetrapods
developed the fingers first

and then left the water.

NARRATOR:
Jenny Clack
of Cambridge University

suspected that the theory taught
in many textbooks was wrong.

The story that you will find
in many of the old textbooks

and the pictures
that you will see

in children's books
and museum galleries

is a picture of a fish
stranded in a drying pool

trying to support itself
out of water.

And it looks really odd if you
look at it objectively.

NARRATOR:
Clack thought there
had to be a better explanation

but where to look?

Only a handful of early tetrapod
fossils had ever been found,

most of those
in a remote part of Greenland

at the turn of the century.

All she had to guide her was
a note scribbled in a journal

from a scouting trip
to Greenland years earlier.

It referred to tetrapod fossils
on an unnamed mountain.

Clack flew to Greenland
to search for those bones.

CLACK:
Eventually we found the spot,
800 meters up on a hillside.

NARRATOR:
Clack returned
with four tons of rock...

And spent
the next four years drilling.

At the end

she had the most complete early
tetrapod skeleton ever found;

and it forever
changed the textbooks.

CLACK:
One of the first things

that we found was this forelimb.

NARRATOR:
At the end of the animal's limb

was an unmistakable
array of bones.

This was a hand.

CLACK:
This is a life reconstruction..

The artist is using imagination
on the color scheme

and on the eyes

but we think this is
as accurate as you can get.

NARRATOR:
The creature,
named Acanthostega

was clearly a water-dweller:

It had a fishlike tail and gills
for breathing in the water.

But the ends of its arms
were petal-shaped...

possibly the first hands
on Earth.

CLACK:
This was a swimming creature.

We don't know whether it could
ever have come out on land

but it certainly
wouldn't havewalked

in the conventional sense.

Basically, it's...
a fish with fingers.

NARRATOR:
Clack's find was
a scientific breakthrough.

It proved that some fish had
arms and legs in the water.

So tetrapods didn't need to grow
limbs after they got onto land.

The limbs had already evolved

and helped them survive
out of the water.

The basic pattern for limbs
had been in place

for millions of years.

SHUBIN:
Here we have the fin

of a 370-million-year-old fossil
fish and an arm of a human.

In a human arm, what
you have is one bone...

then two bones,
the wrist and the digits.

In this fin what do you have?

You have one bone,
two bones...

even little bones that can be
compared to a wrist

and then rods that face away

from the rest
of the appendage itself

just like our fingers or toes.

So you have, in a fish fin

already set up
about 370 million years ago

many of the bones that are used
in a tetrapod limb.

NARRATOR:
With the basic pattern
already there

the fin-to-limb transition
took place

in a series of small changes

occurring over
millions of years.

SHUBIN:
There's really no goal
to evolution.

Evolution wasn'ttrying
to make limbs

it wasn'ttrying
to push our distant ancestors

out of the water.

What was happening
was a series of experiments.

NARRATOR:
In the crowded,
freshwater streams

where tetrapods first evolved

the competition for survival
was intense.

SHUBIN:
These small streams
were like an engine

or a crucible
of evolutionary change.

NARRATOR:
Fish experimented with all sorts
of survival strategies.

Some became predators.

The owner of this jaw
was a 12-foot-long killer.

Its teeth were the size
of railroad spikes.

Smaller fish developed elaborate
defenses, like this heavy armor.

Others packed weaponry,
like this sharp spike.

It protruded from behind
its owner's neck.

These armaments
were all tools for survival

in a dangerous world.

Perhaps their new arms and legs
gave the first tetrapods

another way to survive.

SHUBIN:
It was to get out of the way;
it was to get onto land.

And what enabled those animals

to get out of the way,
that is, to get out of the water

were these new features,
like limbs.

NARRATOR:
Those that did escape
found a new world

filled with opportunity.

The transformation
from water to land

was only the latest example

of evolution experimenting
with radically new forms.

An earlier transformation,

perhaps the most
significant of all,

occurred just over
half a billion years ago...

And it led
to all animals as we know them.

Evolution tinkered with fish
to make limbs.

But fish carry the baggage
of their own past.

Think of a fish:

It has a head, it has a tail
and a bunch of fins in between.

That's a body plan,
the way the body's put together.

But that's just one of many ways
of putting animals together.

I mean, some animals are
like disks, like jellyfish.

Other animals have
lots of little legs.

The question is

what sort of tinkering led
to these body plans?

I mean, really
what we're dealing with here

is the origin of animals.

NARRATOR:
According to the fossil record

animals appeared upon the earth
in a short burst

around 570 million years ago.

Scientists call
this crucial transformation

the Cambrian Explosion.

MAN:
The Cambrian Explosion
was effectively

one of the greatest
breakthroughs

in the history of life.

About half a billion years ago,
suddenly, things change

and we have this extraordinary
explosion of diversity.

And this sudden appearance
of the fossils led to this term

the Cambrian Explosion.

And Darwin, as ever,
was extremely candid.

He said, "Look, this is
a problem for my theory.

How is it that suddenly, animals
seem to come out of nowhere?"

And to a certain extent, that is
still something of a mystery.

NARRATOR:
Most of what we know
of the Cambrian Explosion

is a result
of a single discovery

probably the greatest
fossil find in history.

In 1913, while climbing
in the Canadian Rockies

paleontologist Charles Walcott
discovered a layer of shale

containing thousands
of exquisitely detailed fossils.

These animals, all sea dwellers

were caught in a catastrophic
underwater mudslide.

Over the next 500 million years

the sea floor
which entombed them

rose to become
the top of a mountain.

Walcott removed over 60,000
fossils from the site

which he named
the Burgess Shale.

Simon Conway Morris has studied
the fossils for over 30 years.

It's almost as if
you've gone to another planet.

You've been given a fishing boat
and a net

and you've been allowed
to throw that net

over into the deep ocean

and you'd no idea
what was going to come up.

NARRATOR:
Some of the Burgess Shale
creatures were familiar.

MORRIS:
And here, we've got
one of the trilobites.

We see the delicate soft parts,
also preserved.

NARRATOR:
Trilobites
are extinct arthropods

creatures
with external skeletons.

Today's arthropods,
like crabs, lobsters

insects and spiders

are all descendants
of creatures like these.

Other Burgess Shale animals
were bizarre, alien-seeming.

An animal with five eyes
and a long retractable nozzle.

One with long, sharp spines
protruding from its back.

Another with a circle of prongs
around its mouth.

And yet, as alien
as these creatures seem

they are also surprisingly
familiar.

Like living animals,
they have bodies

with heads, tails, appendages,

specialized segments performing
specialized functions.

All the basic body plans found
in nature today are here.

Every animal that has lived
for the last half billion years

has come from tinkering
with these initial designs.

We might even see
our own ancestor here.

MORRIS:
Maybe this is the crown
of the Burgess Shale.

This isPikaia.

NARRATOR:
A tiny creature,Pikaiais one
of the rarest fossils

from the Burgess Shale.

It's the only one
with an internal nerve cord

resembling a spine.

That might mean
that creatures likePikaia

were the earliest ancestors
of all animals with skeletons.

MORRIS:
The idea is that this might be
the precursor of the fish

and so, ultimately

through a long evolutionary
story, ourselves.

The Cambrian Explosion matters
for lots of reasons.

Basically,
it's part of our history.

It's where we came from
and that matters very much.

This is the time
when the animals first appear.

We look back and we can see
part of our history unfolding.

So what do we learn by looking

at 600 million years
of animal history?

Evolution's tinkering
with mammalness to make whales.

In the same way,
it's tinkering with fishiness

to make tetrapods

and it's tinkering
with animalness

to make all the different
body plans that we see.

All these different creatures
are variations of the same theme

restated over and over again.

The question was, what was
evolution tinkering with?

One of the remarkable
discoveries

of the last 20 years

is that evolution's not
tinkering with the bodies.

It's tinkering with the recipe

the machinery
that builds bodies.

What is that recipe?

What is that machinery?

It's the genes.

NARRATOR:
Fossils record the changes
in animals' bodies over time

but just how bodies change
was unknown.

The search for the genetic
mechanism of evolution

took most of this century.

When scientists finally found it

they were astonished...

by just how simple it was.

One of the key players
was Mike Levine.

LEVINE:
I was, um, I guess,
kind of a weird kid.

I always liked bugs.

We had a nice, big backyard,
and I could go back there.

It was kind of a sanctuary.

And, uh, I played with bugs...

dissected them,
manipulated them.

That's really
the most pleasant memory I have.

NARRATOR:
Levine's affinity for bugs led
to his study of biology.

One insect in particular
became an object of fascination.

LEVINE:
They have
a quick generation time

and they have lots of pattern.

I mean, you wouldn't know it
if you look at a distance

but when you look
under a microscope

at an adult fruit fly

you'd be astounded
by the number of bristles

the intricacies of their wings,
the patterns of their eyes.

But the embryos
are something else.

I do love the embryos.

NARRATOR:
Scientists had long suspected

that embryos held clues
to how animals evolve.

All embryos start out
as clusters

of nearly identical cells.

But soon,
an embryo partitions itself

into specialized segments

which develop into
the final form of the animal.

What controlled this process?

How did the embryos know
what shape to take?

One of the first people
to study these questions

was a 19th-century naturalist
named William Bateson.

Bateson wrote
that animals' skeletons revealed

an underlying structure
of repeating segments.

He also observed that animals
occasionally developed

with some segments
in the wrong places.

MAN:
Insects with legs
in the wrong place.

Crabs where a claw
was transformed into a leg.

Pythons with extra ribs

or frogs
with extra cervical vertebrae

and all these sorts of things.

NARRATOR:
To Bateson,
these developmental errors meant

that the underlying blueprint
for the animal

was being disrupted.

He had no idea how it happened

but he suspected
that these random changes

might provide the fuel
for evolution.

By the 1940s, scientists working
with fruit flies

had learned
how to cause disruptions

in the developmental blueprint:

by dousing growing embryos
with radiation and poison.

MAN:
And so when they did that

they found flies with changed
wing structures, changed legs

and these very special flies

that have one part of the body
in the wrong place

or a copy of a normal part
of the body in another place.

NARRATOR:
The scientists
had triggered the changes

by damaging the flies' DNA.

Within each cell
of the developing embryo

is a chainlike molecule
called DNA.

The experiments showed
that DNA was somehow

causing the embryo
to divide into segments.

But how?

Scientists were just beginning
to grasp

that the DNA itself was made up
of segments, called genes.

The question was: how did
the genes shape the body?

One researcher,
Dr. Ed Lewis of Caltech

studied this question
for 30 years

by crossbreeding
thousands of flies.

Lewis's work led him
to a controversial idea.

He proposed that a surprisingly
simple mechanism

was shaping embryos.

He wrote that each segment
of the fly

was being directed to grow
by a single gene.

A small set of genes,
a kind of genetic toolkit

appeared to be laying out
the entire body.

And as he looked at these genes,
he said

"This one affects
this part of the body.

"This affects
the next part of the body.

And this affects
the next part of the body."

That was
an astonishing observation.

NARRATOR:
It was astonishing
because it seemed too simple.

Nobody else thought single genes
were powerful enough

to control something as complex
as the structure of the body.

Skeptics argued
that Lewis's idea was guesswork.

Of course, he had never seen
the genes

because the techniques to do so
didn't exist.

From the 1920s to the 1970s

it was not possible
to physically isolate

any specific gene.

That opportunity first became
available, fortunately for me

at the time
that I was a student.

And so, many of us
thought, "Wow.

"We can finally dig in there

and identify
these really mysterious genes."

NARRATOR:
Levine enlisted his friend and
fellow scientist Bill McGinnis.

The first gene they went after
had an unusual name.

Antennapedia,
which means "antenna leg."

The gene was thought
to control the growth of legs.

When the gene misfired

flies grew legs
in the wrong place:

on their heads,
in place of antennae.

In normal flies,
legs grow from the midsection

the area called the thorax.

So Levine and McGinnis decided
to hunt for the gene

in the thorax
of a normal embryo.

LEVINE:
The expectation

is that antennapedia
would be active

expressed in the thorax

the developing thorax,
of the embryo.

But who knew?

NARRATOR:
Levine and McGinnis had
to do something

no one had ever done before.

They had to find a way to see
a gene in action.

LEVINE:
We wanted to light up the gene

and it was very
painstaking work.

NARRATOR:
The project called
for new and untested methods.

McGINNIS:
At first, it didn't work
very well

and there were a number
of technical problems to solve.

NARRATOR:
The team had to find
a delicate balance

of radioactive probes
and toxic enzymes.

Too much of either
would destroy the embryos.

LEVINE:
The process
was not very gratifying

on a day-by-day basis.

Unbelievably tedious.

NARRATOR:
It took months
of trial and error.

McGINNIS:
People often said, "You know,
you should try something else.

"You know,
this is too long-shot.

You know, you're going to...
you're just wasting your time."

But we kept going.

NARRATOR:
Finally, late one night,
all the work paid off.

LEVINE:
And there was this moment...

when we saw that the gene
was turned on in a band

in the middle
of a very early embryo.

This had never been seen before.

NARRATOR:
The antennapedia gene was acting
like a master switch

turning on the segment
of the embryo

that would become the thorax.

The implications
were mind-boggling:

if single genes like
antennapedia could define

whole segments of an animal

these genes were acting
like architects of the body.

And if one of these genes
turned on in the wrong place

striking changes
to the body could result.

It seemed that Levine and
McGinnis had uncovered

the genes responsible
for the evolution of bodies.

But there were still doubts.

The work had all
been done in fruit flies.

What about other animals?

Did they use the same mechanism
to build their bodies?

An answer would come
from Switzerland.

In 1994, Walter Gehring
of the University of Basel

isolated the gene that triggered

the growth of eyes
in fruit flies.

The gene was called Eyeless

because flies without it
developed with no eyes.

Gehring knew of a gene in mice
that worked in the same way.

He wondered,
were the two genes the same?

GEHRING:
And this question we tested

by taking the mouse gene and
putting it into fruit flies

to see whether flies
can understand

the message of the mouse.

NARRATOR:
Gehring replaced a fly's gene
for eyes with the mouse gene.

GEHRING:
And to everybody's surprise

the mouse gene works
perfectly well

and can induce a compound eye
in the fruit fly.

NARRATOR:
The fruit fly grew
normal fruit fly eyes

using a gene from a mouse.

Not only did the two creatures
use the same mechanism;

they used the same gene.

This was the mechanism
behind extra wings

legs sprouting from heads,
and Bateson's deformed animals.

The century-long search
was complete.

The genetic engine
of the body's evolution

turned out to be a tiny handful
of powerful genes.

CARROLL:
So what this means is

in some ways, some sense,
evolution is a simpler process

than we first thought...

when you think about all of the
diversity of forms out there.

We first believed
that this would involve

all sorts of novel creations

starting from scratch,
again and again and again.

We now understand
that no, that evolution works

with packets of information,
and uses them

in new and different ways and
new and different combinations

without necessarily
having to invent

anything fundamentally new,
but new combinations.

NARRATOR:
Suddenly, the commonality
of form among animals

was understood:

animals resembled each other
because they all used

the same set of genes
to build their bodies

a set of genes
inherited from a common ancestor

that lived long ago.

And what we see now among all
the animals are just variations

on a body plan that existed
half a billion years ago.

And there's only one
inescapable conclusion

you can draw from that,
which is

if all of these branches
have these genes

then you have to go
to the base of that

which is the last common
ancestor of all animals

and you deduce,
itmust have had these genes.

So the whole radiation
of animals

the whole spring
of animal diversity

has been fed by essentially
the same set of genes.

NARRATOR:
Ed Lewis shared
the Nobel Prize in 1995

for the discovery of
the universal set of genes

that builds the bodies
of animals.

And so, yes, it came
as a huge surprise

not only to people
like my mother, who says

"My God, an earthworm
and a mouse?

An earthworm and me, you know,
share things in common?"

But it came as a surprise to
other scientists that there was

this profound conservation of
mechanism of building embryos

among all these different
kinds of animals.

NARRATOR:
What about us?

Our bodies are built

from the same genes that build
all other animals.

Yet we are different.

No other animal designs...
or creates like we do.

We seem so special
it's hard not to think

that we're somehow an exception
to evolution...

but of course, we're not.

The transformation
that led to us

was no different
from other transformations.

Our crucial turning point
seems to have occurred

when our ancestors
left the trees

and began to walk on two legs.

MAN:
We don't know exactly when,
or even where

our ancestors became
upright and bipedal.

We think it goes back
well over four million years.

When these ancestors
came out of the trees

and began to exploit
food sources on the ground

in terrestrial habitats

one of the key elements that
would've been so useful to them

would've been freeing
their forelimbs, their hands

to be able to gather and carry
foodstuffs over long distances.

Once that happened, it opened up

an extraordinary breadth of
possibilities and opportunities.

NARRATOR:
Most bipedal hominids
went extinct

but one branch went on
to evolve larger brains.

That branch eventually
led to modern humans.

So how did this
crucial transition

to two-legged walking begin?

Liza Shapiro of
the University of Texas

looks for clues
in living primates.

SHAPIRO:
When you look
at the fossil record

all you have really
is a pile of bones.

It's a nonmoving entity.

There's not much
you can know about it

unless you look
for living analogs.

So if you look at living
animals, you've got the bones

but you can also look
at how they're moving.

NARRATOR:
In their movements,
living lemurs resemble

tree-dwelling primates

that lived
up to 50 million years ago.

We didn't evolve from lemurs

but they may be
the best living analog

for those distant ancestors.

SHAPIRO:
When we're trying
to reconstruct the scenario

about how humans evolved
bipedally from this ancestor

we have to know
what it was we started from

if we're going to come up
with an explanation

for not only how we made
that transition, but why.

NARRATOR:
Today, Shapiro is gathering data

on the movement style
of the lemur.

Small reflectors
have been gently placed

on the animal's back.

An array of infrared cameras
will record the lemur

as it walks across
this makeshift bridge.

Of course, getting a lemur to do
just about anything on cue

takes a bit of doing.

There you go.

NARRATOR:
Finally, the animal
makes it across.

Here you go...
oh, good!

All right.

Got that.

And he's down.

NARRATOR:
The motion of the lemur's spine
can now be analyzed

in three dimensions.

The data reveal that lemurs'
spines are extremely flexible

capable of many
kinds of movements.

SHAPIRO:
Lemurs walk quadrupedally

but they're also
very good at leaping.

NARRATOR:
Like these lemurs, the early
primates probably moved

in all sorts of ways:

down on all fours,
scampering up trees...

even leaping in
an upright position.

They weren't limited
to just one style of movement

so they could serve
as the starting point

for a number of evolutionary
experiments.

And most likely,
that's just what happened.

We weren't the only ones

to evolve
from those early ancestors.

So did most of today's
living primates.

Our closest living relative
is the chimpanzee.

We didn't evolve from chimps

but we do share
a recent common ancestor.

Can you walk
over here?

NARRATOR:
That's why our DNA is nearly
identical to theirs...

and why our skeletons
have the same number of bones

arranged in nearly the same way.

But the few physical differences
that set us apart

seem to have made
a great difference.

Chimps don't walk on two feet.

They've evolved a different
style of getting around

called knucklewalking.

JOHANSON:
Knucklewalking

is a very specialized adaptation
that we see

among chimps and gorillas today.

It's an adaptation
to walking on the ground.

NARRATOR:
Knucklewalking was as valid
an evolutionary experiment

as two-legged walking.

But the difference
in our walking styles

which may have affected
our intellects

is seen in the few slight
differences in our skeletons.

Here are two skeletons
of modern primates.

This skeleton I'm sure
you'll all recognize

because it's a skeleton
like yours and mine.

This is a modern human.

But this smaller skeleton

is one of our closest living
relatives, the chimpanzee.

We began walking on two legs

and that made a whole series of
modifications in the skeleton.

In humans, the spinal chord

comes out of the base
of the skull

and points straight downwards

rather than coming out
of the back of the skull.

The pelvis is shaped
very differently.

A chimpanzee has
a long, narrow pelvis.

Ours is short and squat.

We walk with our knees
close together.

Chimpanzees walk
with their knees wide apart.

These are minor differences.

These are the sorts of tinkering
that evolution did

to change us
into a modern biped.

NARRATOR:
What if our ancestors
hadn't stood up?

What if they had taken
one different turn

along the path
to becoming human?

JOHANSON:
One of the great misconceptions
that most people have is that...

that once our ancestors stood
up, it was almost inevitable

that we would be here today

that the egocentric species,
Homo sapiens

would evolve in this manner.

But what we see is

that evolution has worked
the same way with us

as it has with every, single
organism on this planet.

We're here through a series
of chance coincidences

specific adaptations,
chosen opportunities.

So I think that when we
look at our own origins

we see that it is extraordinary

that humans are here to look
back and ponder their past.

SHUBIN:
Does that mean we are not unique

in many ways?

Of course not.

We're the ones
telling this story.

And that's very important...

that evolution, that life
has gotten to the point

where it can tell this story.

Continue the journey

into where we're from
and where we're going

at the Evolution web site.

Visit www.pbs.org.

The seven-part
Evolution boxed set

and the companion book

are available
from WGBH Boston Video.

To place an order, please call: