Cosmos A Space Time Odyssey Season 1 Episode 2

DEGRASSE TYSON:
This is a story about you

and me and your dog.

(wolf howls)

There was a time not long ago...
before dogs.

They didn't exist.

Now there are big ones,
small ones, snugglers,

guardians, hunters.

Every kind of dog
you could possibly want.

How did that happen?

It's not just dogs.

Where did all
the different kinds

of living creatures come from?

The answer is a transforming
power that sounds like something

straight out
of a fairy tale or myth,

but it's no such thing.

♪ ♪

Sync and corrections by n17t01
www.addic7ed.com

Let's go back across 30,000
years to a time before dogs,

when our ancestors lived
in the endless winter

of the last ice age.

Our ancestors were wanderers
living in small bands.

They slept beneath the stars.

The sky was their storybook,
calendar,

an instruction manual
for living.

It told them when
the bitter colds would come,

when the wild grains
would ripen,

when the herds of caribou
and bison would be on the move.

Their idea of home
was Earth itself.

But they lived in fear
of other hungry creatures...

the mountain lions
and the bears

that competed with them
for the same prey

and the wolves that threatened
to carry off and devour

the most vulnerable among them.

(growling)

(snarling)

All the wolves want
to get at the bone,

but most of them are too
frightened to come close enough.

Their fear is due to high levels

of stress hormones
in their blood.

It's a matter of survival.

Because coming too close
to humans can be fatal.

But a few wolves--
due to natural variations--

have lower levels
of those hormones.

This makes them less afraid
of humans.

This wolf has discovered

what a branch of his ancestors
figured out

some 15,000 years ago...

an excellent survival strategy;

the domestication of humans.

Let the humans do the hunting,
don't threaten them,

and they'll let you scavenge
their garbage.

You'll eat more regularly,
you'll leave more offspring,

and those offspring will inherit
your disposition.

This selection for tameness

would be reinforced
with each generation

until that line of wild wolves
evolves into...

dogs.

You might call this
"survival of the friendliest."

(chuckles)

Then as now, this was a good
deal for the humans, too.

The scavenging dogs weren't just
a sanitation squad.

They worked security.

(wolf growling, dog barks)

(growling, barking continues)

As this interspecies partnership
continued over time,

the dogs' appearance
changed also.

Cuteness became
a selective advantage.

The more adorable you were,
the better chance you had

to live and pass on your genes
to another generation.

What began as an alliance
of convenience

became a friendship
that deepened over time.

To see what happens next,

let's leave
our distant ancestors

of some 20,000 years ago
to visit the more recent past

during an intermission
in the Ice Age.

This break in the climate
starts a revolution.

Instead of wandering,
people are settling down.

There's something new
in the world... villages.

People still hunt and gather,

but now they also produce
food and clothing...

agriculture.

The wolves have traded
their freedom

in exchange for a steady meal.

They've given up their right
to choose a mate.

Now the humans choose for them.

They consistently kill off
the dogs that can't be trained;

the ones that bite
the feeding hand.

And they breed the dogs
that please them.

(barking)

They nurture those dogs
that do their bidding...

hunting, herding,
guarding, hauling,

and keeping them company.

From every litter,

the humans select the puppies
they like best.

Over the generations,
the dogs evolve.

This kind of evolution is
called "artificial selection"

or "breeding."

Turning wolves into dogs was
the first time

we humans took evolution
into our own hands.

And we've been doing it
ever since

to shape all the plants
and animals that we depend on.

In a blink of cosmic time,
just 15,000 or 20,000 years,

we turned gray wolves into
all the kinds of dogs

we love today.

Think of it.

Every breed of dog
you've ever seen

was sculpted by human hands.

Many of our best friends--
the most popular breeds--

were created in only
the last few centuries.

(snarling)

The awesome power of evolution

transformed the ravenous wolf

- into the faithful shepherd...
- (barks)

...who protects the herd
and drives the wolf away.

Artificial selection turned
the wolf into the shepherd

and the wild grasses
into wheat and corn.

In fact, almost every plant
and animal that we eat today

was bred from a wild,
less-edible ancestor.

If artificial selection can work
such profound changes

in only 10,000 or 15,000 years,

what can natural selection do

operating over
billions of years?

The answer is all the beauty
and diversity of life.

How does it work?

Our Ship of the Imagination
can take us anywhere in space

and time,
even to the hidden microcosmos,

where one kind of life can be
transformed into another.

Come with me.

DEGRASSE TYSON:
May not seem like it,

but we've been living
in an ice age

for the last two million years.

This just happens to be
one of the long intermissions.

For most of those
two million years,

the climate has been cold
and dry.

The North Polar ice cap extended
much farther south

than it does today.

In one of those long,
cold glacial periods

when the winter sea ice
stretched from the North Pole

all the way down
to what is now Los Angeles,

great bears roamed the frozen
wastes of Ireland.

This might look like
an ordinary bear,

but something extraordinary
is happening inside her.

Something that will give rise
to a new species.

In order to see it,

we'll need to descend down
to a much smaller scale,

to the cellular level,

so that we can explore
the bear's reproductive system.

We'll take the subclavian
artery through the heart.

Almost there.

Those are some of her eggs.

To see what's going on
in one of them,

we'll have to get even smaller.

We'll have to shrink down
to the molecular level.

Our Ship of the Imagination
is now so small,

you could fit a million of them
into a grain of sand.

See those guys over there
strutting along those girders?

They are proteins
called kinesin.

These kinesin are part
of the transport crew

that's busy moving cargo
around the cell.

How alien they seem.

And yet these tiny creatures--
and beings like them--

are a part of every living cell,
including the ones inside you.

If life has a sanctuary,

it's here in the nucleus
which contains our DNA...

the ancient scripture
of our genetic code.

And it's written in a language
that all life can read.

DNA is a molecule shaped
like a long twisted ladder

or double helix.

The rungs of the ladder are made

of four different kinds
of smaller molecules.

These are the letters
of the genetic alphabet.

Particular arrangements
of those letters spell out

the instructions
for all living things,

telling them how to grow,
move, digest,

sense the environment,
heal, reproduce.

The DNA double helix
is a molecular machine

with about 100 billion parts
called "atoms."

There are as many atoms
in a single molecule of your DNA

as there are stars
in a typical galaxy.

The same is true for dogs

and bears

and every living thing.

We are, each of us,
a little universe.

The DNA message handed down
from cell to cell

and from generation
to generation is copied

with extreme care.

The birth of a new DNA molecule
begins when an unwinding protein

separates the two strands
of the double helix,

breaking the rungs apart.

Inside the liquid
of the nucleus,

the molecular letters of
the genetic code float freely.

Each strand of the helix
copies its lost partner,

resulting in two identical
DNA molecules.

That's how life reproduces
genes and transmits them

from one generation
to the next.

When a living cell divides
in two,

each one takes away with it
a complete copy of the DNA.

A specialized protein
proofreads to make sure

that only the right letters
are accepted

so that the DNA
is accurately copied.

But nobody's perfect.

Occasionally, a proofreading
error slips through,

making a small, random change
in the genetic instructions.

A mutation has occurred
in the bear's egg cell.

A random event as tiny as
this one can have consequences

on a far grander scale.

That mutation altered the gene
that controls fur color.

It will affect the production
of dark pigment in the fur

of the bear's offspring.

Most mutations are harmless.

Some are deadly.

But a few, purely by chance,
can give an organism

a critical advantage
over the competition.

A year has passed.

Our bear is now a mother.

And as a result
of that mutation,

one of her two cubs was born
with a white coat.

When the cubs get old enough
to venture out on their own,

which bear is more likely

to be able to sneak up
on unsuspecting prey?

The brown bear can be seen
against the snow a mile away.

The white bear prospers
and passes on

its own particular set
of genes.

This happens repeatedly.

Over succeeding generations,

the gene for white fur
spreads through

the entire population
of Arctic bears.

The gene for dark fur loses out

in the competition
for survival.

Mutations are entirely random
and happen all the time.

But the environment
rewards those

that increase the chance
for survival.

It naturally selects
the living things

that are better suited
to survive.

And that selection
is the opposite of random.

The two populations of bears
separated,

and over thousands of years,

evolved other characteristics
that set them apart.

They became different species.

That's what
Charles Darwin meant

by "the origin of species."

An individual bear
doesn't evolve;

the population of bears evolves
over generations.

If the Arctic ice
continues to dwindle

due to global warming,
the polar bears may go extinct.

They'll be replaced
by brown bears,

better adapted to
the now defrosted environment.

This is a different story
from the one about the dogs.

No breeder guided these changes.

Instead, the environment itself
selects them.

This is evolution
by natural selection,

the most revolutionary concept
in the history of science.

Darwin first presented the
evidence for this idea in 1859.

The uproar it caused
has never subsided.

Why?

(birds chirping)

We all understand
the twinge of discomfort

at the thought that we share
a common ancestor with the apes.

No one can embarrass you
like a relative.

Our closest ones,
the chimpanzees,

they frequently behave
inappropriately in public.

There's an understandable
human need

to distance ourselves
from them.

A central premise
of traditional belief

is that we were
created separately

from all the other animals.

It's easy to see why
this idea has taken hold.

It makes us feel... special.

But what about our kinship
with the trees?

How does that make you feel?

Okay, here's a segment
of the oak tree's DNA.

Think of it like a bar code.

The instructions written
in the code of life

tell the tree
how to metabolize sugar.

Now let's compare it with
the same section of my own DNA.

The DNA doesn't lie.

This tree and me--
we're long-lost cousins.

And it's not just the trees.

If you go back far enough,
you'll find that we share

a common ancestor with...

the butterfly...

gray wolf...

mushroom...

shark...

bacterium...

sparrow.

What a family!

Other parts of the bar code vary
from species to species.

That's what makes the difference
between an owl and an octopus.

Unless you have
an identical twin,

there's no one else
in the universe

with the exact same DNA as you.

Within other species,
the genetic differences

provide the raw material
for natural selection.

The environment selects which
genes survive and multiply.

When it comes
to the genetic instructions

for life's
most basic functions--

say, digesting sugars--
we and other species

are almost identical.

That's because those functions
are so basic to life,

they evolved before
the various life-forms

branched off from each other.

This is our Tree of Life.

Science has made it possible

for us to construct
this family tree

for all the species
of life on Earth.

Close genetic relatives occupy
the same branch of the tree,

while more distant cousins
are farther away.

Each twig is a living species.

And the trunk of the tree
represents the common ancestors

of all life on Earth.

The stuff of life
is so malleable

that once it got started,
the environment molded it

into a staggering
variety of forms--

10,000 times more than
we can possibly show here.

Biologists have catalogued

a half a million different
kinds of beetles alone.

Not to mention
the numberless varieties

of bacteria.

There are many millions
of living species

of animals and plants,
most of them

still unknown to science.

Think of that--
we have yet to make contact

with most of the forms
of terrestrial life.

That's how many kinds
of life there are

on this tiny planet alone.

The Tree of Life extends
its feelers in all directions,

finding and exploiting
what works,

creating new environments

and opportunities
for new forms.

The Tree of Life is three
and a half billion years old.

That's plenty of time
to develop

an impressive repertoire
of tricks.

Evolution can
disguise an animal

as a plant...

...taking thousands
of generations

to contrive
an elaborate costume

that fools predators
into looking elsewhere

for someone to eat.

Or it can disguise a plant
as an animal,

evolving blossoms that take on
the appearance of a wasp--

the orchid's way of fooling
real wasps into pollinating it.

This is the awesome

shape-shifting power
of natural selection.

Among the dense, tangled limbs
of the vast Tree of Life...

you are here.

One tiny branch
among countless millions.

Science reveals that all life
on Earth is one.

Darwin discovered the actual
mechanism of evolution.

The prevailing belief
was that the complexity

and variety of life
must be the work

of an intelligent designer,
who created each

of these millions
of different species separately.

Living things are just
too intricate, it was said,

to be the result
of unguided evolution.

Consider the human eye,

a masterpiece of complexity.

It requires a cornea,

iris, lens, retina,

optic nerves, muscles,

let alone the brain's
elaborate neural network

to interpret images.

It's more complicated
than any device

ever crafted
by human intelligence.

Therefore, it was argued,

the human eye
can't be the result

of mindless evolution.

To know if that's true,
we need to travel across time

to a world before
there were eyes to see.

DEGRASSE TYSON:
In the beginning,

life was blind.

This is what
our world looked like

four billion years ago,

before there were
any eyes to see.

Until a few hundred million
years passed,

and then, one day,

there was a microscopic
copying error

in the DNA of a bacterium.

This random mutation
gave that microbe

a protein molecule
that absorbed sunlight.

Want to know what
the world looked like

to a light-sensitive bacterium?

Take a look at the right side
of the screen.

Mutations continued
to occur at random,

as they always do in any
population of living things.

Another mutation

caused a dark bacterium
to flee intense light.

What is going on here?

Night and day.

Those bacteria that could
tell light from dark

had a decisive advantage
over the ones that couldn't.

Why?

Because the daytime brought
harsh, ultraviolet light

that damages DNA.

The sensitive bacteria
fled the intense light

to safely exchange
their DNA in the dark.

They survived
in greater numbers

than the bacteria that
stayed at the surface.

Over time, those
light-sensitive proteins

became concentrated
in a pigment spot

on the more advanced,
one-celled organism.

This made it possible
to find the light,

an overwhelming advantage

for an organism that harvests
sunlight to make food.

Here's a flatworm's-eye view
of the world.

This multi-celled organism

evolved a dimple
in the pigment spot.

The bowl-shaped depression

allowed the animal to
distinguish light from shadow

to crudely make out objects
in its vicinity,

including those to eat
and those that might eat it...

a tremendous advantage.

Later, things became
a little clearer.

The dimple deepened

and evolved into a socket
with a small opening.

Over thousands of generations,

natural selection
was slowly sculpting the eye.

The opening contracted
to a pinhole covered

by a protective
transparent membrane.

Only a little light
could enter the tiny hole,

but it was enough
to paint a dim image

on the sensitive inner surface
of the eye.

This sharpened the focus.

A larger opening
would have let in more light

to make a brighter image
but one that was out of focus.

This development launched
the visual equivalent

of an arms race.

The competition needed
to keep up to survive.

But then a splendid new feature
of the eye evolved,

a lens that provided both
brightness and sharp focus.

In the eyes of primitive fish,

the transparent gel near
the pinhole formed into a lens.

At the same time,
the pinhole enlarged

to let in more and more light.

Fish could now see in high-def,

both close up and far away.

And then
something terrible happened.

Have you ever noticed that
a straw in a glass of water

looks bent at the surface
of the water?

That's because light bends
when it goes from one medium

to another,
say from water to air.

Our eyes originally evolved
to see in water.

The watery fluid
in those eyes neatly

eliminated the distortion
of that bending effect.

But for land animals,

the light carries images
from dry air

into their still-watery eyes.

That bends the light rays,

causing all kinds
of distortions.

When our amphibious ancestors
left the water for the land,

their eyes, exquisitely evolved
to see in water,

were lousy for seeing
in the air.

Our vision has never been
as good since.

We like to think of our eyes
as state-of-the-art,

but 375 million years later,

we still can't see things
right in front of our noses

or discern fine details
in near darkness

the way fish can.

When we left the water,

why didn't nature
just start over again

and evolve us a new set of eyes

that were optimal
for seeing in the air?

Nature doesn't work that way.

Evolution reshapes existing
structures over generations,

adapting them
with small changes.

It can't just go back
to the drawing board

and start from scratch.

At every stage of its
development, the evolving eye

functioned well enough

to provide a selective
advantage for survival.

And among animals alive today,
we find eyes

at all these stages
of development.

And all of them function.

The complexity
of the human eye poses

no challenge to evolution
by natural selection.

In fact, the eye and all
of biology makes no sense

without evolution.

Some claim that evolution
is just a theory,

as if it were merely
an opinion.

The theory of evolution,
like the theory of gravity,

is a scientific fact.

Evolution really happened.

Accepting our kinship
with all life on Earth

is not only solid science.

In my view, it's also
a soaring spiritual experience.

Because evolution is blind,

it cannot anticipate or adapt
to catastrophic events.

The Tree of Life
has some broken branches.

Many of them were severed in
the five greatest catastrophes

that life has ever known.

Somewhere, there's a memorial

to the multitude
of lost species,

the Halls of Extinction.

Come with me.

_

Welcome to the
Halls of Extinction.

A monument to the broken branches
of the Tree of Life.

For every single one
of the millions of species

alive today, perhaps
a thousand others have perished.

Most of them died out
in the everyday competition

with other life-forms.

But many of them were swept away
in vast cataclysms

that overwhelmed the planet.

In the last 500 million years,

this has happened five times.

Five mass extinctions
that devastated life on Earth.

The worst one of all happened
some 250 million years ago,

at the end of an era

known as the Permian.

Trilobites were
armored animals that hunted

in great herds
across the seafloor.

They were among
the first animals to evolve

image-forming eyes.

Trilobites had a good long run,
some 270 million years.

Earth was once
the planet of the trilobites.

But now they're all gone,
extinct.

The last of them were swept
from life's stage

along with countless
other species

in an unparalleled
environmental disaster.

(explosions rumbling)

The apocalypse
began in what is now Siberia,

with volcanic eruptions
on a scale unlike anything

in human experience.

Earth was very different then,

with one single supercontinent
and one great ocean.

Relentless floods of fiery lava

engulfed an area larger than
Western Europe.

The pulsing eruptions
went on for hundreds

of thousands of years.

The molten rock

ignited coal deposits
and polluted the air

with carbon dioxide
and other greenhouse gases.

This heated the Earth

and stopped the ocean currents
from circulating.

Noxious bacteria bloomed,

but nearly everything else
in the seas died.

The stagnant waters belched
deadly hydrogen sulfide gas

into the air,

which suffocated most
of the land animals.

Nine in ten of all species
on the planet went extinct.

We call it...

The Great Dying.

Life on Earth came so near
to being wiped out

that it took more than
ten million years to recover.

But new life-forms
slowly evolved

to fill the openings left
by the Permian holocaust.

Among the biggest winners
were the dinosaurs.

Now the Earth was their planet.

Their reign continued
for over 150 million years.

Until it, too,
came crashing down

in another mass extinction.

Life on Earth has taken quite
a beating over the eons.

And yet it's still there.

The tenacity of life
is mind-boggling.

We keep finding it where
no one thought it could be.

That nameless corridor?

That's for another day.

I know an animal that can live
in boiling water

or in solid ice.

It can go ten years
without a drop of water.

It can travel naked
in the cold vacuum

and intense radiation of space
and will return unscathed.

The tardigrade, or water bear.

It's equally at home
atop the tallest mountains

and in the deepest trenches
of the sea.

And in our own backyards,
where they live among the moss

in countless numbers.

You've probably
never noticed them

because they're so small.

About the size of a pinpoint.

But they're tough.

The tardigrades have survived
all five mass extinctions.

They've been in business
for a half a billion years.

We used to think
that life was finicky,

that it would only take hold
where it was

not too hot, not too cold,

not too dark or salty
or acidic or radioactive.

And whatever you do,
don't forget to add water.

We were wrong.

As the hardy tardigrade
demonstrates,

life can endure conditions

that would mean certain death
for us humans.

But differences between us
and life found

in even the most extreme
environments on our planet

are only variations
on a single theme,

dialects of a single language.

The genetic code of Earth life.

But what would life be like
on other worlds?

Worlds with a completely
different history,

chemistry and evolution
from our planet?

There's a distant world
I want to take you to--

a world far different
from our own,

but one that may harbor life.

If it does, it promises
to be unlike anything

we've ever seen before.

Clouds and haze completely hide
the surface of Titan,

Saturn's giant moon.

Titan reminds me
a little bit of home.

Like Earth, it has an atmosphere
that's mostly nitrogen.

But it's four times denser.

Titan's air has
no oxygen at all.

And it's far colder
than anywhere on Earth.

But still...
I want to go there.

We have to descend

through a couple hundred
kilometers of smog

before we can even
see the surface.

But hidden beneath lies
a weirdly familiar landscape.

Titan is the only other world
in the solar system

where it ever rains.

It has rivers and coastlines.

Titan has hundreds of lakes.

One of them larger than
Lake Superior in North America.

Vapor rising from the lakes

condenses and falls again
as rain.

The rain feeds rivers,

which carve valleys
into the landscape,

just like on Earth.

But with one big difference.

On Titan, the seas and the rain

are made not of water
but of methane and ethane.

On Earth, those molecules
form natural gas.

On frigid Titan,

they're liquid.

Titan has lots of water,

but all of it is frozen
hard as rock.

In fact, the landscape
and mountains

are made mainly of water ice.

At hundreds of degrees
below zero,

Titan is far too cold
for water to ever be liquid.

(rainfall, distant thunder)

Astrobiologists since
Carl Sagan have wondered

if life might swim
in Titan's hydrocarbon lakes.

The chemical basis for such life

would have to be entirely
different from anything we know.

All life on Earth
depends on liquid water.

And Titan's surface
has none of that.

But we can imagine
other kinds of life.

There might be creatures
that inhale hydrogen

instead of oxygen.

And exhale methane
instead of carbon dioxide.

They might use acetylene instead
of sugar as an energy source.

How could we find out
if such creatures

rule a hidden empire
beneath the oil-dark waves?

We're diving down deep
into the Kraken Sea,

named for the mythic
Norse sea monster.

Even if there is
one of those down there,

we probably couldn't see it.

It's so dark.

If you took all the oil
and natural gas on Earth,

it would amount to but a tiny
fraction of Titan's reserves.

Let's turn on some lights.

We're now 200 meters
beneath the surface.

Did you see something?

Over there, by that vent.

Maybe it was just
my imagination.

I guess we'll have to come back

if we want to find out
for sure.

There's one last story
I want to tell you.

And it's the greatest story
science has ever told.

It's the story of life
on our world.

Welcome to the Earth
of four billion years ago.

This was our planet before life.

Nobody knows
how life got started.

Most of the evidence
from that time was destroyed

by impact and erosion.

Science works on the frontier
between knowledge and ignorance.

We're not afraid to admit
what we don't know.

There's no shame in that.

The only shame is to pretend
that we have all the answers.

Maybe someone watching this

will be the first
to solve the mystery

of how life on Earth began.

The evidence
from living microbes

suggest that their
earliest ancestors

preferred high temperatures.

Life on Earth may have
arisen in hot water

around submerged volcanic vents.

In Carl Sagan's original
Cosmos series,

he traced the unbroken thread
that stretches

directly from
the one-celled organisms

of nearly four billion
years ago...

to you.

Four billion years
in 40 seconds.

From creatures who had yet
to discern day from night

to beings who are
exploring the cosmos.

♪ ♪

CARL SAGAN: Those are some of
the things that molecules do

given four billion years
of evolution.

Sync and corrections by n17t01
www.addic7ed.com