When Whales Walked: Journeys in Deep Time (2019) - full transcript

Sanders: I was taken
out to this site

in the middle of
the desert.

I had no idea what awaited me.

And then I saw them and
I just started crying.

These trackways
in the arabian desert

are footprints in time.

They were made seven
million years ago

by prehistoric elephants.

They take us back
to a bygone world

and its vanished creatures.

How did elephants from
so long ago give rise



to the magnificent
animals we know today?

How did any of the animals
in this African landscape

become what they are?

For generations,
it was a mystery.

Now scientists are
revealing the answers,

piecing together an epic story.

This film unlocks the evolution

of four of the world's
most spectacular creatures,

crocodiles, birds,

whales, and elephants.

Like every animal alive today,

they have a deep time history,

a lineage full of
twists and turns,

shaped by strange
ancestors from long ago.



Bizarre ancient crocs...
Bhullar: This thing was built

like a greyhound.
Narrator: Feathered dinosaurs...

O'Connor: Dinosaurs
never went extinct.

In fact, birds are dinosaurs.

Narrator: A whale ancestor
that lived on land...

De muizon: It more looks
like a dog with a long snout.

Narrator: It's a story millions
of years in the making,

of lost creatures rediscovered,

and the surprising
lessons of deep time.

Madagascar.

250 miles off the
coast of Africa.

This island is a
perfect laboratory

for the study of
evolutionary change.

Isolated here for
millions of years,

species have transformed
in unique ways.

Scientists have long
studied the evolution

of the island's chameleons,
bats, and lemurs.

Now the search is on
for the ancient history

of one of earth's
strangest animals...

The crocodile.

In flooded underground caves,

researchers are
looking for the remains

of an extinct croc species.

It may have disappeared
just 2,000 years ago,

a recent twist in
the story of crocs.

Hekkala: Some people see
crocodiles as this animal

that's unchanging through time.

And, actually, we know
now that that's not true,

but they look like it.

Narrator: Cold-blooded,

ferocious,

but strangely beautiful.

The 14 living crocodile
species are all very similar.

Hekkala: Most of the living
species of crocodile

are really, really
hard to tell apart,

unless you're
somebody who spends

all your time thinking
about crocodiles like me.

Narrator: They all have the
same reptilian body plan,

low to the ground

and armored from head
to toe in thick scales.

They seem like living fossils,

some hangover from the
age of the dinosaurs.

But are they?

Is this really an
animal frozen in time?

Perhaps the mysterious
species in the cave

will provide some answers about
recent crocodile evolution.

Hekkala: So, there's this
crocodile that existed

on the island of Madagascar
until relatively recently

and it disappears
about the same time

that humans got here,

and that crocodile was called

the horned crocodile
of Madagascar.

And so, one of the big questions
is what was that crocodile?

Who were its relatives?

And, what happened to it?

It's one of the
biggest mysteries.

Narrator: Today, there is only
one species on Madagascar,

the famous nile crocodile,

one of the fiercest
of Africa's predators.

Scientists think it squeezed
out the smaller horned croc,

but there's a lot
they don't know.

There may be answers
in the flooded caves.

Hekkala: I knew from speaking
with some other people

that there were supposedly
crocodile skulls in this cave

of this species that no one has
seen for at least 200 years,

but more likely
a thousand years.

Narrator: A half-hour
in they see it,

a skull.

Hekkala: So excited.
Godfrey: A skull?

Hekkala: Yeah. Look at that.

It's beautiful.
Godfrey: It looks perfect.

Hekkala: This is a skull
of the extinct

horned crocodile of Madagascar.

And when researchers
first started coming

to Madagascar from Europe,

they saw these crocodile skulls

and they weren't sure
exactly what they were.

They didn't look exactly
like nile crocodiles.

They realized it was
a separate species.

Narrator: If evon's lucky,

she'll be able to
extract its DNA

and learn where the
horned croc fits

into the story of
crocodile evolution.

To meet the very first crocs,

we must trace one branch
of the vast tree of life

far back in deep time,

230-million years into
the geologic period

called the triassic.

It's hard to imagine such
a vast expanse of time.

Sues: If you look, for instance,
at your historical time,

you can think back
to your grandparents

and that time frame that people
are still comfortable with.

But you go further back,

go say back thousands of years

when much of north America
was covered by ice.

A very different world.

But go further back yet.

Go back to a hundred
million years

and this world would have
been entirely unrecognizable.

Would have been like
going to another planet

and seeing life forms that were,

for the most part, utterly
alien to our experience

and this is really
difficult to grasp.

Narrator: There is
little about the planet

of the triassic we
would recognize.

The continents we know
today had not yet formed.

They were all contained
in one huge land mass

surrounded by water, pangaea.

It was here, along
with the dinosaurs,

that the first crocs evolved.

In the beginning,

they were even more
successful than the dinosaurs,

and to our eyes, they
look totally bizarre.

Bhullar: Well the triassic
was in many ways,

actually the age of crocodiles,

and in any triassic landscape,

you would have seen
this vast diversity

of crocodile relatives
with many body forms.

Narrator: Anjan bhullar has
been unearthing the bones

of the very first
crocodile relatives.

Two of them were found together

near some sandstone
cliffs in Southern Utah.

Bhullar: Well these are two of
the most extraordinary skeletons

from the crocodile line
that have ever been found.

This large animal here is
something called a poposaur.

And it's the only complete
skeleton of one of these animals

that's ever been found.

All of the subtle features
on it, I mean it's just,

it's the find of a lifetime.

These animals show us
what crocodiles were like

at the beginning
of their evolution

and they're very,
very different.

The extraordinary
thing about this animal

is that it was really
trying to be a dinosaur

before dinosaurs were dominant,

in that it was actually
walking around on two legs.

You see how large
and how heavily built

the legs of this animal are

compared to these
tiny little arms.

And so, this animal
couldn't rest

any of its weight on its arms.

Narrator: Poposaurus
was a fierce,

fast-moving land
predator,

acting for all the
world like a dinosaur.

And it wasn't the only
strange triassic croc

to be found in Utah.

Bhullar: In fact, the poposaur,
this large skeleton,

was the first thing we found,

and we dug out
this big skeleton.

Then right underneath
it was a tiny foot.

And underneath that foot
was this animal here,

which is the only
complete specimen

of what we call a sphenosuchian
grade stem crocodile

that's ever been found.

Narrator: They called the
sphenosuchian, little foot.

It was even stranger
than poposaurus.

Bhullar: And so, the poposaur is
something like mountain lion,

whereas the sphenosuchian,
you look at this animal,

and it's got a
slender little body,

it's got extraordinarily
long legs.

Extraordinarily long arms,

and these arms were
taking its weight,

unlike those of the poposaur.

And so, this thing was built
almost like a greyhound

with a heavy head
and a long tail.

It was an animal that was
utterly built for speed.

Narrator: The strange
creatures of the triassic

were part of the
first great flowering

of the crocodile family tree.

But 200 million years ago,

much of that tree was cut back

When a mass extinction

wiped out the vast majority

of the animals of land and sea.

As the supercontinent
pangea began to break up,

volcanoes pumped vast
amounts of carbon dioxide

into the air,
acidifying the oceans.

The planet warmed and
habitats were transformed.

Most of the triassic
crocodile relatives,

including poposaurus and
little foot, died out.

Sues: Extinctions are
of great interest

to evolutionary biologists,

because they basically
reset the evolutionary game.

Every once in a while,
during the history of life

there have been catastrophic
events of such magnitude

that thousands or millions
of species were wiped out

in what basically in deep
time is a single moment.

Narrator: There have been five

major extinctions
in earth's history.

Through the lens of deep time,

we can see they caused
profound destruction,

and changed the history
of life on earth.

The mass extinction that
ended the triassic period

ushered in a new chapter
in the story of crocs.

In the Jurassic and
cretaceous periods,

crocs flourished again,

but in new and
even stranger ways.

A record of those wondrous
creatures is preserved

in one of the most spectacular
landscapes on earth,

patagonia.

Pol: Many groups diversified
in the Jurassic.

Dinosaurs were certainly
the most conspicuous,

because they were big,

but other groups
began to diversify

in a very, very impressive way,

and crocs were one of them.

Narrator: For the
duration of the Jurassic

and cretaceous periods,
almost 150 million years,

crocs vied with
dinosaurs for dominance.

They stopped being
only the land animals

they were in the triassic

and experimented with
radically new ways of being.

Pol: You start seeing
animals like dakosaurus

is the swimming marine croc

that adapted their forelimbs
into paddle-like flippers.

And then you have
freshwater gigantic crocs

like sarcosuchus that's
about 12 meter long,

that was eating dinosaurs.

And then you have herbivorous
crocs like notosuchians.

Look at this animal.

It really looks
nothing like a croc

it has a short snout, very high,

the eye sockets are
pointing to the sides,

and the crazy,
crazy thing is that

it moved the lower
jaw back and forth.

And this was a way of the
upper teeth and lower teeth

to slide against each other

and in that way this animal was
processing the plant matter.

Narrator: So here
was an ancient croc

that chewed like a goat.

Diego has spent much
of the last 20 years

excavating ancient crocs

from the barren
outcrops of patagonia.

But back when those
creatures lived,

the world was a very
different place.

Pol: It was much warmer planet.

There were no ice
caps on the Poles.

Narrator: In the warming
greenhouse world

of the Jurassic and
cretaceous, crocs prospered.

This was their golden age.

Pol: They became so diverse
that in some places you go,

and you basically
only find crocs.

So, we can see a really,

really crazy diversity
in the cretaceous.

And then about 66
million years ago,

it all went away.

Narrator: What happened to
the many cretaceous crocs?

It seems most of them perished

the same way as the dinosaurs.

Sues: It was long realized that
around 66 million years ago

there was a major extinction
of animals and plants

on land and in the oceans.

On land the most famous
causality was the dinosaurs.

Narrator: Scientists agree
that an asteroid strike

brought on the
global devastation,

but many now argue

it was not the only cause
of the mass extinction.

From the fossil record, they
can see that climate changes

were already pushing many
species to extinction

before the asteroid impact.

Sues: So basically, this
impact is sort of thought

if not the sole cause
of the extinction,

certainly the coup de grace
for a great many lineages.

Narrator: Ancient
crocs were reduced

to a fraction of what
they once had been.

Sues: So out of this
wonderful diversity

only a few species
made it through.

And the ones that
actually made it through

were very particular
in many ways.

They were certainly
adapted to living

in the freshwater environment.

They were adapted
to feeding in water.

They were predators,
they were not herbivores.

They were not land crocodiles.

They were not marine crocodiles.

So only a tiny fraction of
that diversity made it through.

Narrator: The crocodiles
that made it through

were the shoreline predators

that lived half in
water and half on land.

Their low, tank-like body plan

may have been one secret
of their survival.

It allows them to lay
semi-submerged in the shallows

and ambush their prey
with ferocious speed.

The success of
that lethal design

is why crocodiles today
all seem so similar.

Hekkala: Crocodiles
have this form

that's very, very successful.

They have sort of
an armored body plan

that allows them to be
a successful predator

in aquatic environments.

Aquatic environments
can be more stable

than other kinds
of environments,

like terrestrial environments.

And so, it makes sense
that they've retained

this body plan from deep time,

from the ancestral crocodilians

that were around the globe
millions of years ago.

It works really
well, why change it?

Narrator: Of course,
that classic body plan

is no guarantee of survival.

The horned croc of Madagascar
died out just centuries ago,

likely pushed out by
the giant nile croc.

Results from evon's work

suggest the species are
more closely related

than anybody realized.

It's a great example
of how DNA analysis

has become a vital tool
for paleontologists.

Hekkala: One of the
exciting things

about the new tool
kit we have today,

the ability to use DNA to
look at evolutionary history,

is we can use it
as sort of a metric

for change over
time and lineages.

So, with living species,
we can take their DNA

and we can calculate
back how long it takes

to accumulate the number of
changes we see in the genome.

And we can say,

this corresponds to a split
three million years ago,

or six million years ago,
or 20 million years ago.

Narrator: DNA has shown that
both crocodiles and alligators

are descended from
a common ancestor

that lived 80 million years ago.

Hekkala: And then,
even more recently,

this thing that
we've always thought

as the sort of primordial
crocodile, the nile crocodile,

we recently have found
using molecular clock dating

that the nile crocodile
is just a baby.

It just arose probably within

the last four to
six million years.

It's a young'un on
the landscape of

crocodilians in
the modern world.

Narrator: So, despite their
pre-historic appearance,

it turns out that over their
230 million year history,

crocodiles have been
in constant evolution.

They have proved themselves

to be one of the most
resilient lineages

on the face of the planet.

Hekkala: For me,
these crocodiles

sort of represent
an organism that

through the history
of life on earth,

it's found a way to persist.

Narrator: The story of
the crocodile lineage

is of deep time transformations

that produced a wild
diversity of croc species,

followed by a steep decline.

Today there are just
a handful of crocs

and the strange animals that
gave rise to them are all gone.

The surviving crocs
are all very similar,

all shoreline predators
of the tropics.

But while the crocodile
lineage has bottlenecked,

another lineage is experiencing

a wild explosion of diversity.

Birds have colonized every
environment on earth.

And they come in an
astonishing variety

of shapes, colors, and sizes.

Clarke: There are more
species of birds

than any other group of
vertebrates that lives on land.

They can cross the
himalayas on wing.

They can dive into
a part of the ocean

where sunlight does not reach.

They can migrate
between continents.

So, they are truly remarkable.

Narrator: Birds have colonized

not only the natural
environments of the planet

but also the urban
spaces created by humans.

Clarke: There are more than
10,000 species of birds,

but even more
striking than that,

there are more than
half that number

is just within one
lineage, songbirds.

So that means the birds
that are in your backyard

are part of what is truly
an extraordinary evolution.

Narrator: So, what's the story

behind the spread of
birds across the planet?

How did they come to be
everywhere and so diverse?

Clarke: Things that can
seem so commonplace,

crows or pigeons in a park

are the leavings of
an amazing history

that stretches back hundreds
of millions of years.

Narrator: Our understanding
of that evolutionary history

began with one
extraordinary fossil

discovered in the
1860's in Germany,

archaeopteryx.

Clarke: This fossil,
to many people,

might just look like road kill

or something that
hit your window.

But in fact, to me these
bones, they come to life.

And the wings are moving,

covered in feathers,

but with mobile
claws at their tips.

Most striking is a long,
bony tale with feathers.

Narrator: 150 million-years-old,

archaeopteryx was a bird.

It had feathers
and it could fly.

But with its claws,
tail and toothed beak,

there was something almost
dinosaur-like about it.

It led proponents of the
new theory of evolution

to make a sensational claim.

Birds must have
evolved from dinosaurs.

Clarke: When I look at this, I
see an icon of evolution.

It was one of the first key

and totally unavoidable
pieces of evidence

consistent with evolution.

But the theory that birds
evolved from dinosaurs

met intense opposition.

How could something
so huge and heavy

evolve into something
so small and light?

One of the biggest objections

was that no dinosaur had ever
been found with a wishbone,

in birds, the crucial
brace for the chest

that makes flight possible.

The search was on.

If scientists could find a
dinosaur with a wishbone,

they would clinch the case,

but for a century, they failed.

Then in the 1960's,

paleontologist John ostrom
hit pay dirt.

A dinosaur fossil,
with a wishbone.

He called it deinonychus,
terrible claw.

Gauthier: Here we have
deinonychus antirrhopus,

the fossil that changed
everything that we know

about the origin of birds

and fundamentally
altered our understanding

of how flight evolved.

Narrator: Deinonychus was
a ferocious predator

with wing-like arms

and all the bones and
muscles necessary for flight.

But it couldn't fly.

Gauthier: Here's an animal with
forelimbs much too short

and much too heavy in the
body to be able to fly,

yet it has all the
bells and whistles

that we associate with
the flight stroke.

Narrator: Not only that,
it had feathers too.

But all this had nothing
to do with flight.

Its feathers were for warmth

and its clawed wings
were for killing.

Gauthier: The arms up
against the body,

and you shoot it
down and forward,

grab your prey,
drag it up and back.

Down and forward, up and back,

down and forward, up and back.

That's the flight stroke.

So, all the details,

the basic architecture, at
least, of the flight stroke

is evolved in an animal
that is not using it to fly.

Narrator: Amazingly, these
tools built for killing

would eventually power flight.

Gauthier: So you have feathers
and you have the flight stroke

colliding in one animal,

so the skies were
no longer a barrier

to the evolution of dinosaurs.

And that's why we think that
birds are living dinosaurs.

Narrator: Deinonychus
was powerful evidence

that dinosaurs
gave rise to birds.

But the many stages of that
evolution were still unknown.

To complete the story,
scientists needed more fossils.

Another long wait began.

Then in the 1990's,

farmers in a remote province
of northeastern China

blew the story of bird
evolution wide open.

They had been turning up rocks

with the outlines
of birds in them

for as long as they
could remember.

They had no idea these were
the bird/dinosaur fossils

scientists had been waiting for.

By the late 1990's,

fossil fever had broken
out in liaoning province.

Farmer: At first, nobody
knew how valuable they were.

But then we found out.

We all started to dig.

I did too.

I found something that
looked like a bird.

I didn't know what it was,

but they said it was something
called confuciusornis.

Narrator: A single fossil
could bring a year's income.

As farmers scoured
the landscape,

the fossils started to pour in,

hundreds of ancient birds from
the time of the dinosaurs.

O'Connor: The fossils from
western liaoning

started to show us the
transitional forms.

They showed us the
earliest birds with beaks,

the earliest birds with short
tails, like living birds.

Narrator: Bird fossils
are extremely rare

because bird bones
are so delicate.

But here in northeastern
China, 130 million years ago,

a unique combination
of circumstances

created the perfect conditions
for their preservation.

O'Connor: If you were
able to come back here

131 to 120 million years
ago and looked out,

you would have seen lakes
as far as the eye could see,

with active volcanoes
going off around them

and a forested environment

growing by the shores
of these lakes.

And this forest would
have been teeming

with small, feathered dinosaurs.

Narrator: As those small
feathered dinosaurs died

and fell or were
washed into lakes,

they were quickly buried
in layers of volcanic ash.

The result?

An extraordinary record of
cretaceous bird/dinosaurs

perfectly preserved in stone.

O'Connor: The amazing
thing about these fossils

is the exceptional
preservation of soft tissues,

which reveal these extinct
animals in a level of detail

that we paleontologists never
previously thought possible.

Narrator: Fossilized
along with the birds

were plants and seeds,

allowing scientists
to reconstruct

the forested
environment of the time.

Together, the wealth
of liaoning fossils

reveal a world where
creatures representing

every stage of dinosaur
to bird evolution

lived side by side.

They show how
nature experimented

with every aspect of what
would finally make a bird,

beaks, wings,
feathers, and flight.

There was caudipteryx,

a small feathered dinosaur that
had wings but couldn't fly.

Living alongside it
were creatures that flew

but still had many
dinosaur characteristics,

teeth, long tails, and
claws on their wings,

and there were creatures
like confuciusornis,

almost identical
to modern birds.

The feathered dinosaurs
of liaoning are a reminder

that evolution does not
move in a straight line.

O'Connor: There's a common
perception

that evolution proceeds
in a very linear fashion.

So you have a little dinosaur

that somehow decides,
quote/unquote, to become a bird.

But actually, the
many bird features

were gradually acquired.

There were a lot of dead ends
in this evolutionary process.

Narrator: Just like deinonychus,

the liaoning fossils
show that wings

and feathers evolved separately

and for reasons that have
nothing to do with flight.

It was only after
millions of years

that these things came together

to make the creature
we call a bird.

O'Connor: In fact,
what we've learned

from this huge
diversity of fossils

is that these features that
we associate with modern birds

actually evolved multiple times.

Narrator: The liaoning
fossils opened a window

on the profusion of
feathered dinosaurs

that populated the whole world

many millions of years ago.

What happened to them all?

Most died out in the
same extinction event

that killed the big terrestrial
dinosaurs and most crocs.

But like the crocs, a few
birds squeaked through.

Those few survivors gave rise

to all the bird on earth today.

How did that amazing story
of survival play out?

Remarkably, the scientists
are solving that mystery,

not from bones, but from DNA.

Jarvis: So what happened is that
this mass extinction occurs,

maybe as a result of a
big, giant meteorite,

then climate change
and so forth.

A few groups of birds survive,

only five percent of
the species survive.

Narrator: Erich
and his colleagues

compared the genomes of
different bird species

to calculate their
degrees of similarity.

They could then figure out

when they last shared
common ancestors.

Jarvis: First thing we
figured out is that

those ones that survived,

with the deepest branches in
the tree that we generated

were the ones that
were shore birds,

that can survive in water,
that can survive in land,

that survive in
different habitats.

Along with shore birds
like ducks and geese,

the ancestors of ostriches
and emus also survived.

Jarvis: Then those few four or
five lineages that survive,

in a 15-million-year window,

gave rise to every species that
we are looking at now today.

Narrator: Scientists are
finally in a position

to see the whole vast
avian tree of life.

Arising with the dinosaurs,
the bird lineage experimented

for millions of years with
feathers, beaks and wings.

It barely survived a
major extinction event

before finally flowering in
the 10,000 species alive today.

But while the bird
lineage exploded

and birds colonized
every habitat on earth,

another lineage concentrated
on colonizing just the seas.

For as long as humans
have known them,

whales have inspired
fear and wonder.

How could these
giants of the deep

have grown so huge?

How could air-breathing
creatures like us

have come to live in
the depths of the ocean?

What science now knows about

these leviathans of
the deep is amazing.

Bowhead whales can live
for up to 200 years,

longer than any other
mammal on earth.

Sperm whales can dive to
depths of over 3000 feet

and stay underwater
for an hour and a half

without breathing.

Blue whales are the
biggest creatures

to ever have lived on earth,

bigger even than the
largest dinosaurs.

Up to a hundred feet long
and 200 tons in weight,

they have a heart the
size of a small car.

And these giants of the
deep sing to each other,

communicating over vast
distances in a language of song

that researchers still
don't fully understand.

How did these gargantuan animals

and their remarkable
behavior evolve?

For so long it was a mystery.

Uhen: We've known that
the whales are mammals

since the 18th and
19th centuries,

because they're warm blooded
and they suckle their young,

but we didn't know
where they came from.

Darwin talked about
the origin of whales

in his classic book
the origin of species

where he said someone he knew

had observed a bear
swimming around,

skimming insects off
the surface of the water

and he suggested that
perhaps something like a bear

could have evolved into a whale,

the kind of whale
that filter feeds

by doing something similar

and getting better and
better at it over time.

Now Darwin was not
correct about that,

but at least he
could conceptualize

of a way that
whales had evolved.

But basically, we didn't
know where whales came from

until extremely recently.

Narrator: The fascination
with whale evolution

began in the 19th century.

Stories of sea monsters filled
the popular imagination.

When the first fossil
whale was unearthed,

its discoverers thought they'd
found a gigantic sea serpent.

It was called basilosaurus.

Uhen: It was discovered
in north America

along the Gulf
coast in the 1830's,

and it was actually
the first fossil whale

ever to be scientifically
named and studied.

The gentleman who named
it, a man named Harlan,

had read about
large sea serpents

being discovered
elsewhere in the world,

and so he thought that
this was something similar.

And thus he named this
animal basilosaurus,

which means king lizard.

Narrator: Up to 50 feet
long with ferocious teeth,

basilosaurus was a
formidable marine predator.

Finally, in 1841, it was
identified as a whale

and dated to about
35 million years ago.

For almost a century
after its discovery,

basilosaurus remained
the oldest known whale.

It was assumed to be the
ancestor of all living whales.

Uhen: So after the discovery
of basilosaurus,

there were other whales found

that were just a little bit
earlier and more primitive,

but not by very much,

maybe five million years
older than basilosaurus.

And it didn't push the
origin back in time,

and we really didn't
discover a whole lot more

about the origin of whales.

Narrator: The deep origins
of the whale lineage

were a mystery until 1975,

when a paleontologist went on
a fossil hunting expedition

to Pakistan.

He wasn't looking for
early whales at all.

Gingerich: I was interested in
how archaic mammals

changed into the modern mammals.

Things like the first horses,

that's what I was interested in.

I took several students with
me and colleagues from Paris

and we looked first in punjab
province, then south in sindh.

We still hadn't found
anything very interesting.

And we went to the
northwest frontier province.

And there, high on a hill,

we found a little
jaw of a land mammal.

Narrator: Later they
found a piece of skull,

and its strange ear bones

finally unlocked the secrets
of early whale evolution.

Gingerich: This is what was
left, the back of a skull,

and if you look
at the underside,

it has the covering of
the ear on the right side

and that covering is
missing on the left side.

Narrator: Those ear bones
turned out to be the key.

Philip thought he was
looking at the skull

of something like
a primitive deer,

but it unmistakably had
the ear bones of a whale.

Gingerich: Whales have a special
structure of the ear

to be able to hear in water.

It turns out that
they effectively

see in water by using sound.

And so to do this the
ears have become modified.

Uhen: The ear bones of
whales are very dense,

and that density helps them
to hear sound in the water.

Mammal ears originally evolved
in terrestrial animals,

and so their structure is
optimal for hearing in air.

And in water, sound
behaves really differently.

So, for example, if you go
into a pool or under a lake,

you can hear sound but
it's a little muffled,

but the one thing you can't
do is you can't figure out

where the sound is
coming from around you.

And that's because the
way mammals do this is,

is they use the
difference in time between

when a sound hits your
right ear and your left ear

to figure out what direction
the sound is coming from.

So if the sound is
off to my right,

it hits my right ear
first, then my left ear,

and so my brain says the
sound is over to my right.

But in water, the tissue
of your face and skull

is about the same
density as water.

So the sound, rather than
going around my skull

to my left ear, goes
right through it.

So it gets to my left ear

at almost the same
time as my right ear.

And I can't tell where
the sound is coming from.

So the added density
to whale ears

is reestablishing their ability

to hear directionally
underwater.

Narrator: Philip's fossil had
that same distinctive ear,

and it was 49 million years old.

That could only mean one thing.

Here at last was one of
the very first whales.

Philip named it pakicetus.

Gingerich: Once we knew
it was a whale,

we knew it was the oldest
whale anyone had ever found.

Narrator: Pakicetus pushed
the origins of whales

back 15 million years

to the time when the
Indian subcontinent

was slowly crashing into Asia.

Where pakicetus was found
was once an ocean shoreline,

its ears made it clear
pakicetus spent time underwater,

but other fragments of skeleton

also clearly showed it
walked on four legs.

How did this strange
beast give rise

to the giants we know today?

At the museum of natural
history in Paris,

one of the birthplaces
of paleontology,

they have been assembling

the skeletons of prehistoric
animals for over 200 years.

They now have one of the
few complete reconstructions

of the extraordinary
whale ancestor, pakicetus.

De muizon: You see it is a
quadrupedal animal

with the higher
forelimbs and hind limbs.

It means that this animal was
definitely partly terrestrial.

And obviously it's a
quite a strange animal,

very small, doesn't
whale-looking at all.

It more looks like a
dog with a long snout.

Narrator: Pakicetus is one of

the strangest
surprises of evolution,

a whale ancestor that
looks like a small wolf

with webbed feet for swimming.

Gingerich: The key
thing about it is,

it has elongated
finger and toe bones,

so clearly it's
already semi aquatic.

Narrator: Pakicetus was a
creature of the shoreline,

hunting for fish

and perhaps other small
animals in the shallows.

Uhen: And we think that it
was using its longer snout

to probe for aquatic
prey in the water.

And so it was
feeding in the water,

while almost certainly
going out on land

to breed and have their young.

Narrator: Once they adapted
to life in the shallows,

it took 10 million years for
the descendents of pakicetus

to become fully aquatic.

Why did it take so long?

Because to live under
water, they had to change!

It is one of the most
remarkable stories

of total physical transformation
in the annals of evolution.

Uhen: After pakicetus,

whales take about 10 to 12
million years

to evolve into
fully aquatic forms.

And during that time their
hind limbs tend to get smaller

and their skulls
tend to get longer.

And the naris, which is
the hole in the skull

where the nose is,
moves up the skull.

In addition, their forelimbs
tend to turn into flippers,

and they get more
vertebrae in their back,

which makes their bodies longer.

But there was still one
great transformation

to take place in whales,

baleen feeding.

Peredo: So near the base of
the whale family tree

there's this major split

into the two groups
that we have today.

We have toothed whales and
then we have baleen whales

that actually lose
their teeth entirely.

And they grow what are
called baleen plates

that are made of keratin.

So they're actually more
like hair or fingernails.

And these whales use it
to filter their food.

So they'll take
big gulps of water

and they'll actually
filter their prey,

little tiny
microscopic organisms,

out of that water using
the baleen plates.

Narrator: The split
into toothed whales

like orcas and dolphins,

and baleen whales, like
blue whales and humpbacks

happened about 30
million years ago.

The toothed whales remained,
like their ancient ancestors,

predators, living mostly
in coastal waters.

There they could feed on fish,

or like some of the orcas,
seals, and baby sea lions.

The baleen feeders

underwent a much
greater transformation.

With a radically new
way of filter feeding,

they moved into the deep
oceans and became huge.

Why?

For a long time, the massive
size of some baleen whales

was a puzzle.

But it turns out
that in the ocean,

great size is an advantage.

Uhen: If you look at the
energy budget of these animals,

they use fewer calories
per unit body mass

when you get bigger.

And so, they're more
efficient when they're huge.

They're also more
efficient when they move,

when they swim at
large body size.

So there's advantages to
being large in the ocean.

The huge size of baleen
whales is also linked

to one of the last great
planetary transformations.

Peredo: Argentina and
south America

become completely
separate from Antarctica.

And that changes the
currents in the ocean system,

and it seems to really
have a profound impact

on what whales are doing.

Narrator: The cold current that
began to circle Antarctica

led to a vast upsurge
in the krill population

that baleen whales feed on.

With large amounts of food

and the efficient baleen
filter feeding system,

there was simply nothing
to stop baleen whales

from becoming huge.

Along with baleen,

whales have developed
sophisticated fishing behaviors

to trap their prey.

Humpbacks rely on
the help of gulls.

Hildering: And what's happening
is the diving birds

are forcing the herring
together, that form a huge ball.

That gives the gulls
at the surface a chance

to propel themselves down
and try to grab a herring

and then somehow
the humpbacks know

that there's a
concentration of feed there.

And they come with their
huge mouths, gulp it down,

get rid of the salt
water through their baleen

and swallow.

Narrator: Jackie
has been working

with the humpback
whale population

off northern Vancouver
island for almost 20 years.

Jackie's work has
led her to marvel

at the delicate web of
relationships linking humpbacks

to every aspect of
the marine ecosystem.

Hildering: It's perfection.

It's been going on longer
than we can understand.

Knowing whales,

keeps me in a state of
humility and mystery,

which I think is how a
human life is well lived.

It makes me feel connected.

It makes me feel
appropriately small

in the presence of giants.

Narrator: Over
millions of years,

whales grew huge as
they explored the seas,

but another mammal grew huge
as it explored the earth,

evolving its own remarkable
tools for life on land.

For millennia these
stately creatures

have patrolled the
African savannas,

transforming the
land as they go.

Kahumbu: We're driving
along tracks

that the elephants have made.

They've been walking
on these trails

probably for hundreds of years.

They create paths that they
then use for generations.

Elephants are such
extraordinary animals.

The more we learn about them,
the more we realize that

we actually are only just
scratching the surface.

Every new discoveries emerge

that elephants can
understand things

that we couldn't have
dreamed possible.

And I think we'll never
uncover their secrets.

Narrator: Scientists have shown
that elephants communicate

through calls, touch, and
even low frequency vibrations,

which can travel
underground for miles.

But there's still a lot that
they don't fully understand.

Kahumbu: It would be amazing
if we could actually

uncover what it
is that they know.

I really think that we are
blundering about right now

because we don't
even have the tools

to measure how they communicate.

Narrator: And Paula is certain

that along with their ability
to talk to each other,

they experience many of
the same emotions we feel,

grief, anger and empathy.

She senses a
mysterious inner life.

Kahumbu: When you sit with
them for hours,

this like wealth of sensations

just keep coming and
coming and coming

and it just seems to be endless.

I feel like I can really sense

what is going on
with those elephants.

And the longer I
spend with elephants,

the more I feel
in tune with them.

Narrator: As much as
she admires them,

Paula is keenly aware that
elephants today are in trouble.

Kahumbu: There used to be dozens
of species of elephants.

And now there are just three.

And if we're not careful
we will lose them as well,

and that will be the end of
the lineage of elephants.

Narrator: Could the ancient
lineage of elephants

really be coming to an end?

How did these
magnificent animals

go from myriad species
to just three today?

And how did the
ancient histories of

humans and elephants

become so intertwined?

As with every lineage it's a
story that begins in deep time,

a story told by fossils,

most of them found in the
birthplace of elephants,

Africa.

The deep origins of elephants
lie in the turkana basin

in northern Kenya.

In a place called buluk,
scientists are finding fossils

that point to a magnificent
age of elephants.

Sanders: This is from the
right side of the jaw.

Fossils are the
messengers of the past.

I believe that.

I think that we,
as paleontologists,

are trying to be
the interpreters

of the messengers from the past.

They give you the
opportunity to see

the kind of incredible journey

that elephants had to
make to become elephants.

It took 60-million years
to make an elephant.

Narrator: Today, buluk
is one of the hottest,

driest places on earth.

But 17 million years ago,

it was a lush forest
with rivers and wetlands.

Sanders: It's a very
wet climate.

I's a very equable
climate, very warm climate.

It's a great place
to be a browser.

It's a great place to go
out and look for vegetation,

a great place to go get a salad,

Africa in the early miocene.

Narrator: How can
scientists reconstruct

those vanished environments?

It turns out ancient
landscapes leave traces

just like ancient animals do.

Miller: We often find fossil
wood and fossil seeds,

so that's telling us something
about the environment

and the red sediments
around us are ancient soils.

They're actually ancient
floodplain deposits.

So the animals would
have been living

out on these flood plains
in these forested areas.

We're trying to reconstruct
the whole environment

that these animals
were living in.

If you go in and just
pick up the bones,

it's like taking the chocolate
chips out of the cookies.

So we work with geologists
and climate scientists

and isotope specialists

and all kinds of
people, geo chemists.

Narrator: The painstaking work
of Ellen and her colleagues

is allowing them to reconstruct

the whole vanished
world of ancient buluk.

Miller: So if you were to
be transported back

to the early miocene of
buluk, 17 million years ago,

it would have been a mature
meandering river system

and a woodlands.

And there would have
been a whole host

of different kinds of elephants.

So you would have
had the deinotheres.

They're very, very primitive.

They're about a third or a half

the size of a modern elephant

and they would have been kind of
snuffling along the river banks,

because they seemed to really
like a closed canopy forest

and a wet environment.

But at the same time,
you have the amebelodons,

the shovel tuskers.

The lower incisors are these
big long shovel-like tusks,

so they would have used them
to scoop up their dinner.

Narrator: As
scientists excavate.

They are astonished
by the diversity

of strange beasts
they are discovering.

Ancient buluk was a sort of
Jurassic park of elephants.

Nengo: Imagine I'm taking
you on a safari,

but a safari back in time.

You'll be confronted with
these magical creatures,

a slice of Africa
that is now gone.

You'd be confronted here with
amazing herds of elephants.

It would be mind-blowing
to confront this scene.

I think the miocene 16
million years ago at buluk,

that would have
been the center of

the empire of the
age of the elephants.

Narrator: The ancient
elephants here bear witness

to a glorious flowering
of the elephant lineage

about 17 million years ago.

But what were their origins?

And how did they come by

their magnificent
tusks and trunks?

For decades, the
earliest origins

of the elephant
lineage were a mystery.

But then in the 1990's, a French
paleontologist and his team

were excavating in an abandoned
phosphate mine in Morocco.

In layers dating to
56 million years ago,

he came across fossil remains
of a mysterious animal

about the size of a small dog.

He called it phosphatherium.

Later he came across fragments
of the jaws and teeth

of an older, even
smaller creature.

This one was no
bigger than a rabbit.

Gheerbrant: Voila.

Narrator: As he puzzled
over both fossils,

he noticed something
very strange.

Their teeth seemed to be

miniature replicas of
an elephant's teeth.

The more he looked the
more certain he became.

They must be
ancestral elephants,

the oldest ever discovered.

It was an astonishing
conclusion.

The oldest elephant ancestor
was the size of a rabbit.

Gheerbrant: It's really amazing.

The fossils we found

reveal the origins of
proboscidean evolution.

Which used to be
totally unknown.

Sanders: I give a lot of
credit to my colleague

Emmanuel gheerbrant

because it's like
a detective story.

It's a real puzzler to
figure out what they are.

And he found these things

and he started
looking at their teeth

and he realized they had

some subtle features
on their molars,

the arrangement of the
cusps on their molars

that said I am a proboscidean.

Narrator: Finally, scientists
could see the very beginnings

of the elephant
evolutionary tree.

Gheerbrant: The key trait
is the slow development

of incisors at the
front of the skull.

They are already starting

to become enlarged
in phosphatherium.

Those incisors just keep growing

through all the stages
of elephant evolution

right up to mammoths
and modern elephants.

Narrator: As incisors
became tusks,

they took on the functions
they have in elephants today.

Sanders: They're used for
acquiring food,

for knocking down plants
so you can reach food.

They're used for social display.

Tusks are the defining
features of elephants

and it's like their behavior

is tied up in
having these tusks.

Narrator: And as tusks grew,

they propelled the
evolution of the trunks

that would become the hallmark
of all later elephants.

Sanders: So I think once you
start to get tusks,

then trunks follow that.

It is important,

because they have to have
something to get past the tusks

in order to reach the
food in their environment.

Narrator: As trunks grew,
they slowly became

the amazingly sensitive
organ of touch and smell

they are in modern elephants.

Sanders: Trunks are made
up of something like

72,000 tiny muscle fibers.

So they're highly complex,

and they can move them around

the way that you can
move your hand around

playing the piano.

Elephants have tremendous
control over their trunk.

It's not just flopping
around and sucking up water.

They can really be very gentle.

They can pick a penny up off
the ground with their trunk.

Those trunks get a big workout.

Narrator: Tusks,
trunks, and great size

were obviously successful
elephant adaptations

to their forest environment.

But they didn't
just help elephants

respond to their environment,

they gave them the
capacity to change it too.

Nengo: So, I think of all the
species that we know of,

apart from humans,

the only other
mammals that we know

have the capacity
to be able to alter

the natural ecosystems
they live in,

in a short time in a very big
way, would be the elephants.

Sanders: Proboscideans
are big animals

and you can imagine
any big animal

going through a landscape
is knocking down trees,

moving vegetation out of
the way, creating paths.

Narrator: For that,

bill believes we humans owe
them a debt of gratitude.

He thinks elephants helped
create the perfect conditions

for a certain group of apes
millions of years later

to come down out of the trees

and begin to explore
the savannas.

Those were our ancestors,
the australopithecines.

The famous early human Lucy

was discovered not
far from buluk.

Bill is convinced that she

and our other early
human ancestors

flourished in a landscape
that had been unintentionally

prepared for them by elephants.

Sanders: This idea of elephants
opening things up

and creating the conditions
of success for early hominids,

might not be an
exaggeration to say that

we might not be here
without elephants.

Narrator: And just
like our ancestors,

elephants did not stay put.

After millions of years in
Africa, they started to leave.

Sanders: Proboscideans leave
Africa multiple times.

Different groups leave
at different times.

The first major
foray out of Africa

is around 18 million years

and they make it
all the way to Japan

within a period of
about a million years

after getting out of Africa.

Narrator: Until
recently, all we knew

of those ancient elephant
species that left Africa

was from a few fossil bones.

But then, a dramatically
different kind of discovery

brought them to life.

In the deserts of Abu Dhabi,

scientists discovered
not bones but footprints.

They were made by
ancient elephants.

A vivid record of their great
migration out of Africa.

Bibi: It's phenomenal

because when you're
actually on the landscape,

it seems like the elephants
just passed there yesterday,

but we know geologically
speaking that's ipossible.

These are very,
very old sediments.

So, it was almost
an afterthought

to image the tracks
from the air.

And then we went back
to the hotel that night

and we started to put
the imagery together.

As we realized what we had we
basically our jaws dropped.

Narrator: What they saw
was the footprints

of an entire herd of ancient
elephants on the move,

a snapshot in time
of elephant behavior

seven million years ago.

Back then this desert
was a lush Savanna.

The muddy ground
after a rainfall

captured their
footprints perfectly,

all made by one of the
strangest of elephant relatives.

Bibi: It's probably 10 minutes

in the lives of
these individuals,

this herd that walked
across the landscape.

And those ten minutes
are forever preserved

in these rocks for us to see.

Narrator: And in that
10-minute snapshot,

faysal can see all the
dynamics of the herd,

the adults and calves,
a single bull male,

and a number of females.

Bibi: Yeah, so we have,

it's a minimum of 13
individuals actually.

You're walking along and
here was a large individual,

there was probably
the matriarch.

They slow down, they
speed up a little.

There was a smaller guy.

He's on the edge so we're
clearly not too worried

about any predators coming
along on this landscape.

And then, perhaps, just the
day before or the day after,

we've had the large bull who
also crossed this landscape.

Narrator: Not long after faysal

and his team made
their discovery,

they took bill
Sanders to see it.

Sanders: I had no idea
what awaited me,

and then I saw them,

all the footprints
of an entire heard

going on for about 260 meters.

And you can see baby
footprints, juvenile footprints,

female footprints,

and then one great
track of a big bull male

that must have come along
later and crossed that track

and sort of checking
out the herd.

We rarely get that opportunity.

I work on elephants,
I love elephants,

and I'm seeing their
behavior crystalized in time,

all the way back to the very
beginnings of elephants.

And I just started crying.

And my colleagues
all sort of applauded

and they realized I was
not crying out of sadness.

I was crying because
I was ecstatic.

Narrator: Like skilled trackers,

the scientists could read
the ancient footprints

and reconstruct a
remarkably detailed picture

of that day seven
million years ago.

Bibi: We could estimate
the actual size

of these individuals,

based on stride lengths
of modern elephants,

where their weights are known,

and their stride
lengths are known.

And their estimated
weights go from,

a few hundred kilos
for the small one,

up to 5,000 kilos or so for
the largest in the group

and possibly 6,000 or so
for the solitary individual

that was walking at that site.

That makes them as big as
any bull elephant today.

From fossils found nearby,

we know that they were
magnificent animals,

four-tusked beasts called
stegotetrebelodons.

Bibi: And here you are,
you're on this landscape

and you can imagine them
having just been here,

like it was yesterday.

Narrator: Over generations,

their ancestors made
the journey from Africa,

thousands of miles away.

Bibi: They're
extinct, they're long gone,

and they haven't just left
us their bones and teeth.

This is an imprint
of their society.

Narrator: The discoveries
in Abu Dhabi show

that by seven million years ago,

the social behavior of
elephants had already evolved.

Their close family
bonds have been a key

to the success of
elephants for generations.

Even though stegotetrebelodons

disappeared a few
million years ago,

their descendents and
other elephant species

soon populated
much of the globe.

Some, like the mammoths,

adapted to the cold of
Siberia and north America.

Others, like the gomphotheres,

headed for the warmer
climes of Southern Asia

and central America.

It had taken 60 million years

but the elephant
lineage had become

one of the most
successful on the planet.

Just 50,000 years ago,

elephant species were
on all continents

except Australia, Antarctica,
and south America.

So, what happened to them all?

Sanders: A long debate among my
colleagues in my field has been,

what are the agencies

for the extinction of the
elephants that we see,

for example mammoths
and mastodons?

Narrator: One hypothesis
is climate change.

At the end of the last ice age,

10,000 years ago,
the world warmed.

The cold-adapted elephants
of Siberia and north America

just couldn't deal with it.

Sanders: In the northern
hemisphere,

in northern latitudes,

you have all this glaciation

and these changes are
happening very, very rapidly.

Narrator: But for
millions of years,

the mammoths and mastodons

managed to weather
similar climate changes.

What was different
about the warming

at the end of the last ice age?

Bill believes it was
our own ancestors

who tipped the balance.

Sanders: So we see the
great sites in eurasia

where indigenous peoples
like 10,000 years ago

and 50,000 years ago
and 60,000 years ago

were slaughtering these
elephants in great numbers.

There is a tremendous
predation pressure.

And imagine if you've
got predation pressure

hitting you on one side

and now you've got
this climate change,

and what it does
to the landscape,

what it does to the plants
and the available resources.

Narrator: By 4,000 years ago,

the world was left with
just the African, Asian,

and forest elephants
we know today.

And now these are
under threat as well.

This time it has nothing to
do with the end of an ice age,

just us.

In 1800, there were an
estimated 25 million elephants.

Today there are
less than a million

and the number is falling fast,

thanks to habitat loss

and the relentless slaughter
of elephants for ivory.

Kahumbu: Poaching now is very
mechanized, it's industrial.

In some places, we're losing
1,000 elephants in a month.

It's being done with
not just weapons,

but with aircraft, trains,
and trucks, and ships

to move the ivory out
of African very quickly.

Narrator: The tusks that
helped elephants survive

for millions of years
have become a liability.

It's a new kind of evolutionary
pressure, human generated.

And in Africa, it's
causing elephants

to change almost overnight.

Kahumbu: Over the millennia,
elephants have evolved

to have these huge tusks,

because the most
successful elephants

are the ones that had
the biggest tusks.

But over the last
few hundred years,

us human beings have
been killing elephants

for those tusks.

There are some
populations of elephants

who have very small tusks,

because poachers are
selectively removing

elephants with big tusks.

And so, the only females
that get to breed

are the ones which
have very small tusks.

And so you increasingly
see tusklessness

in some of these
elephant populations.

It would be such a tragedy
if these magnificent animals

lost the one thing
that makes them,

you know, so
unique, their tusks.

Narrator: Even as they adapt,
elephants are at risk.

Like so many other creatures,

they now face a new
era of extinction.

Everywhere the natural
world is being transformed.

Our own lineage has become

the planet's dominant
evolutionary force,

shaping the web of life
that exists all around us.

This one recently
arrived species

is now the worldwide presence

to which all others must adapt.

Our impact is so huge

that our era has been
given its own name,

the anthropocene,
the age of humans.

It has seen the extinction
rate among natural species soar

to hundreds of times what
it was before our arrival.

As scientists race to chart
the planetary changes,

they can look back at
lessons from deep time.

They're observing
many of the things

that happened in
earlier extinctions,

rising co2 levels leading to
acidification of the oceans

and rapid climate change,

habitat destruction.

Many believe we are witnessing

our planet's sixth
mass extinction,

but the first one caused
by a single species.

Like others, it will reset
the evolutionary clock.

We just don't know how.

Sues: Today when we live in a
world where human populations

are gradually changing
the face of the globe

by turning natural environments

into artificial environments,

by pollution and many other ways

of interfering with
natural systems,

we are very much confronted

with the question of
evolution and extinction.

You can't have evolution
without extinction,

but extinction
really complicates

our efforts to get
the big picture.

Narrator: We now know
that mass extinctions

are an engine of evolution,

clearing out environments,

making room for new
species to evolve,

but in the past, they have
usually taken millions of years.

This one is happening fast,
in a matter of generations.

Viewed through the
lens of deep time,

that is a nanosecond,

too fast for many
living things to adapt.

But maybe not too fast for
us to make a difference.

Crocs have lived on earth
for almost 230 million years.

They've survived cataclysmic
extinction events,

but today,

five of the 14 crocodile species
are critically endangered.

Hekkala: Most of the
living crocodilians

were on the verge of
extinction by the 1970's.

We were on the verge
of losing all of them

when we put in place protection.

Narrator: Protections
have helped.

In Australia, both fresh and
saltwater crocs have rebounded

thanks to strong steps like
restrictions on hunting.

But what about the other great
survivors of deep history?

10,000 species of bird
still cover the globe.

Some have adapted to cities

where they live beside
us in seeming Harmony.

But that's not the whole story.

Clarke: We are hugely
impacting bird evolution.

This is in habitat loss,
consumption or killing,

poisons, the use of
toxins in our environment.

Narrator: With 40 percent of
bird species in decline,

there's reason to worry,

but also reason to hope.

We managed to turn things
around for iconic species

like the bald eagle
and California condor.

And innovative programs
show that more is possible.

In 1974 only four Mauritius
kestrels were left in the wild.

Today there are a
hundred times as many,

thanks to predator control
and captive breeding.

Ocean creatures
need protection too.

It took 50 million years
for whales to become

the wondrous giants of
the deep we know today.

But in just two centuries,

industrial whaling
brought many of them

to the brink of extinction.

In the 20th century alone,

almost three million
whales were slaughtered

hildering: It's unthinkable now,

that we exploited
whales to the extent of,

in the case of humpbacks,
driving down their population

to 10 percent of what
they were globally.

They were almost
pushed over the edge.

We only stopped whaling

on northern Vancouver
island in 1967.

Humpbacks we stopped in 1965.

So we thought of them
so very differently.

We saw them as a resource.

But with humpbacks we
have a second chance.

Narrator: While some whales
are critically endangered,

whaling bans have
made a difference.

Humpbacks have rebounded,

and blue whale populations,
which fell to just 1,500,

seem to be slowly increasing.

Hildering: One of the many
things that the whales do

is they remind us
how connected we are,

and of our capacity for change.

Narrator: Around the planet,

others are heeding
that reminder,

committing themselves

to protect endangered
animals and places.

In Kenya, Paula kahumbu admires

one of the last true
giants left on earth,

a tusker named Tolstoy.

Kahumbu: I feel very humbled to
be able to meet Tolstoy.

He is a giant of giants.

He's not just a big tusker,
he's a super tusker.

There are very, very few
elephants of that size

with tusks of that
length left in the world.

You know, when when
you're with Tolstoy,

it's one of the biggest rushes
you get is that I'm alive.

Right, you just feel
this sense of life.

It gives you
goosebumps just to know

that this elephant is
aware of your presence,

and you're tiny and he's huge.

It's, he's beautiful.

It's a just a most
incredible experience.

Narrator: To know that Tolstoy,

is the product of an
evolutionary journey

that has been going on for eons

only makes him more precious.

And Tolstoy is not alone.

Crocodiles and birds,
whales and elephants

are just four life
forms among millions.

The tree of life is vast,

encompassing everything
that has ever lived.

What will its branches look
like after the age of humans?

The answer is up to us.