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DEGRASSE TYSON:
This is a story about you
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and me and your dog.
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(wolf howls)
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There was a time not long ago...
before dogs.
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They didn't exist.
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Now there are big ones,
small ones, snugglers,
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guardians, hunters.
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Every kind of dog
you could possibly want.
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How did that happen?
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It's not just dogs.
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Where did all
the different kinds
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of living creatures come from?
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The answer is a transforming
power that sounds like something
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straight out
of a fairy tale or myth,
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but it's no such thing.
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♪ ♪
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Sync and corrections by n17t01
www.addic7ed.com
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Let's go back across 30,000
years to a time before dogs,
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when our ancestors lived
in the endless winter
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of the last ice age.
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Our ancestors were wanderers
living in small bands.
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They slept beneath the stars.
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The sky was their storybook,
calendar,
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an instruction manual
for living.
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It told them when
the bitter colds would come,
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when the wild grains
would ripen,
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when the herds of caribou
and bison would be on the move.
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Their idea of home
was Earth itself.
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But they lived in fear
of other hungry creatures...
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the mountain lions
and the bears
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that competed with them
for the same prey
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and the wolves that threatened
to carry off and devour
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the most vulnerable among them.
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(growling)
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(snarling)
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All the wolves want
to get at the bone,
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but most of them are too
frightened to come close enough.
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Their fear is due to high levels
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of stress hormones
in their blood.
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It's a matter of survival.
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Because coming too close
to humans can be fatal.
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But a few wolves--
due to natural variations--
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have lower levels
of those hormones.
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This makes them less afraid
of humans.
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This wolf has discovered
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what a branch of his ancestors
figured out
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some 15,000 years ago...
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an excellent survival strategy;
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the domestication of humans.
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Let the humans do the hunting,
don't threaten them,
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and they'll let you scavenge
their garbage.
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You'll eat more regularly,
you'll leave more offspring,
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and those offspring will inherit
your disposition.
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This selection for tameness
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would be reinforced
with each generation
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until that line of wild wolves
evolves into...
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dogs.
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You might call this
"survival of the friendliest."
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(chuckles)
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Then as now, this was a good
deal for the humans, too.
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The scavenging dogs weren't just
a sanitation squad.
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They worked security.
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(wolf growling, dog barks)
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(growling, barking continues)
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As this interspecies partnership
continued over time,
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the dogs' appearance
changed also.
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Cuteness became
a selective advantage.
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The more adorable you were,
the better chance you had
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to live and pass on your genes
to another generation.
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What began as an alliance
of convenience
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became a friendship
that deepened over time.
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To see what happens next,
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let's leave
our distant ancestors
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of some 20,000 years ago
to visit the more recent past
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during an intermission
in the Ice Age.
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This break in the climate
starts a revolution.
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Instead of wandering,
people are settling down.
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There's something new
in the world... villages.
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People still hunt and gather,
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but now they also produce
food and clothing...
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agriculture.
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The wolves have traded
their freedom
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in exchange for a steady meal.
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They've given up their right
to choose a mate.
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Now the humans choose for them.
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They consistently kill off
the dogs that can't be trained;
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the ones that bite
the feeding hand.
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And they breed the dogs
that please them.
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(barking)
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They nurture those dogs
that do their bidding...
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hunting, herding,
guarding, hauling,
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and keeping them company.
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From every litter,
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the humans select the puppies
they like best.
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Over the generations,
the dogs evolve.
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This kind of evolution is
called "artificial selection"
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or "breeding."
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Turning wolves into dogs was
the first time
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we humans took evolution
into our own hands.
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And we've been doing it
ever since
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to shape all the plants
and animals that we depend on.
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In a blink of cosmic time,
just 15,000 or 20,000 years,
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we turned gray wolves into
all the kinds of dogs
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we love today.
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Think of it.
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Every breed of dog
you've ever seen
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was sculpted by human hands.
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Many of our best friends--
the most popular breeds--
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were created in only
the last few centuries.
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(snarling)
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The awesome power of evolution
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transformed the ravenous wolf
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- into the faithful shepherd...
- (barks)
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...who protects the herd
and drives the wolf away.
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Artificial selection turned
the wolf into the shepherd
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and the wild grasses
into wheat and corn.
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In fact, almost every plant
and animal that we eat today
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was bred from a wild,
less-edible ancestor.
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If artificial selection can work
such profound changes
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in only 10,000 or 15,000 years,
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what can natural selection do
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operating over
billions of years?
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The answer is all the beauty
and diversity of life.
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How does it work?
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Our Ship of the Imagination
can take us anywhere in space
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00:08:12,992 --> 00:08:16,628
and time,
even to the hidden microcosmos,
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where one kind of life can be
transformed into another.
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Come with me.
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DEGRASSE TYSON:
May not seem like it,
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but we've been living
in an ice age
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for the last two million years.
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This just happens to be
one of the long intermissions.
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For most of those
two million years,
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the climate has been cold
and dry.
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The North Polar ice cap extended
much farther south
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than it does today.
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In one of those long,
cold glacial periods
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when the winter sea ice
stretched from the North Pole
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all the way down
to what is now Los Angeles,
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great bears roamed the frozen
wastes of Ireland.
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This might look like
an ordinary bear,
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but something extraordinary
is happening inside her.
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Something that will give rise
to a new species.
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In order to see it,
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we'll need to descend down
to a much smaller scale,
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to the cellular level,
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so that we can explore
the bear's reproductive system.
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We'll take the subclavian
artery through the heart.
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Almost there.
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Those are some of her eggs.
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To see what's going on
in one of them,
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we'll have to get even smaller.
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We'll have to shrink down
to the molecular level.
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Our Ship of the Imagination
is now so small,
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you could fit a million of them
into a grain of sand.
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See those guys over there
strutting along those girders?
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They are proteins
called kinesin.
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These kinesin are part
of the transport crew
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that's busy moving cargo
around the cell.
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How alien they seem.
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And yet these tiny creatures--
and beings like them--
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are a part of every living cell,
including the ones inside you.
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If life has a sanctuary,
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it's here in the nucleus
which contains our DNA...
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the ancient scripture
of our genetic code.
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And it's written in a language
that all life can read.
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DNA is a molecule shaped
like a long twisted ladder
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or double helix.
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The rungs of the ladder are made
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of four different kinds
of smaller molecules.
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These are the letters
of the genetic alphabet.
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Particular arrangements
of those letters spell out
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the instructions
for all living things,
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telling them how to grow,
move, digest,
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sense the environment,
heal, reproduce.
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The DNA double helix
is a molecular machine
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with about 100 billion parts
called "atoms."
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There are as many atoms
in a single molecule of your DNA
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as there are stars
in a typical galaxy.
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The same is true for dogs
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and bears
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and every living thing.
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We are, each of us,
a little universe.
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The DNA message handed down
from cell to cell
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and from generation
to generation is copied
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with extreme care.
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The birth of a new DNA molecule
begins when an unwinding protein
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separates the two strands
of the double helix,
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breaking the rungs apart.
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Inside the liquid
of the nucleus,
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the molecular letters of
the genetic code float freely.
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Each strand of the helix
copies its lost partner,
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resulting in two identical
DNA molecules.
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That's how life reproduces
genes and transmits them
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from one generation
to the next.
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When a living cell divides
in two,
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each one takes away with it
a complete copy of the DNA.
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00:12:53,092 --> 00:12:56,828
A specialized protein
proofreads to make sure
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00:12:56,862 --> 00:12:58,663
that only the right letters
are accepted
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00:12:58,697 --> 00:13:01,533
so that the DNA
is accurately copied.
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00:13:01,567 --> 00:13:03,301
But nobody's perfect.
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00:13:03,335 --> 00:13:06,504
Occasionally, a proofreading
error slips through,
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00:13:06,539 --> 00:13:10,308
making a small, random change
in the genetic instructions.
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00:13:10,342 --> 00:13:13,545
A mutation has occurred
in the bear's egg cell.
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00:13:13,579 --> 00:13:17,482
A random event as tiny as
this one can have consequences
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00:13:17,516 --> 00:13:19,751
on a far grander scale.
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00:13:21,787 --> 00:13:26,591
That mutation altered the gene
that controls fur color.
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00:13:26,625 --> 00:13:29,594
It will affect the production
of dark pigment in the fur
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00:13:29,628 --> 00:13:31,596
of the bear's offspring.
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00:13:31,630 --> 00:13:33,898
Most mutations are harmless.
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00:13:33,933 --> 00:13:35,667
Some are deadly.
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00:13:35,701 --> 00:13:38,570
But a few, purely by chance,
can give an organism
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00:13:38,604 --> 00:13:42,273
a critical advantage
over the competition.
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00:13:42,308 --> 00:13:44,275
A year has passed.
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00:13:44,310 --> 00:13:46,110
Our bear is now a mother.
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00:13:46,145 --> 00:13:47,846
And as a result
of that mutation,
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00:13:47,880 --> 00:13:51,516
one of her two cubs was born
with a white coat.
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00:13:51,550 --> 00:13:54,252
When the cubs get old enough
to venture out on their own,
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00:13:54,286 --> 00:13:56,554
which bear is more likely
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00:13:56,589 --> 00:14:00,758
to be able to sneak up
on unsuspecting prey?
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00:14:00,793 --> 00:14:04,028
The brown bear can be seen
against the snow a mile away.
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00:14:04,063 --> 00:14:06,931
The white bear prospers
and passes on
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00:14:06,966 --> 00:14:08,900
its own particular set
of genes.
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00:14:08,934 --> 00:14:11,769
This happens repeatedly.
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00:14:11,804 --> 00:14:13,938
Over succeeding generations,
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00:14:13,973 --> 00:14:16,541
the gene for white fur
spreads through
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00:14:16,575 --> 00:14:19,210
the entire population
of Arctic bears.
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00:14:19,245 --> 00:14:21,946
The gene for dark fur loses out
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00:14:21,981 --> 00:14:24,749
in the competition
for survival.
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00:14:26,752 --> 00:14:30,622
Mutations are entirely random
and happen all the time.
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00:14:30,656 --> 00:14:32,590
But the environment
rewards those
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00:14:32,625 --> 00:14:34,893
that increase the chance
for survival.
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00:14:34,927 --> 00:14:37,295
It naturally selects
the living things
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00:14:37,329 --> 00:14:39,964
that are better suited
to survive.
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00:14:39,999 --> 00:14:42,800
And that selection
is the opposite of random.
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00:14:45,638 --> 00:14:48,106
The two populations of bears
separated,
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00:14:48,140 --> 00:14:49,974
and over thousands of years,
238
00:14:50,009 --> 00:14:53,144
evolved other characteristics
that set them apart.
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00:14:53,179 --> 00:14:56,381
They became different species.
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00:14:58,784 --> 00:15:00,852
That's what
Charles Darwin meant
241
00:15:00,886 --> 00:15:04,522
by "the origin of species."
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00:15:04,557 --> 00:15:07,091
An individual bear
doesn't evolve;
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00:15:07,126 --> 00:15:11,029
the population of bears evolves
over generations.
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00:15:12,731 --> 00:15:14,799
If the Arctic ice
continues to dwindle
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00:15:14,834 --> 00:15:18,503
due to global warming,
the polar bears may go extinct.
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00:15:18,537 --> 00:15:20,538
They'll be replaced
by brown bears,
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00:15:20,573 --> 00:15:23,708
better adapted to
the now defrosted environment.
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00:15:23,742 --> 00:15:28,213
This is a different story
from the one about the dogs.
249
00:15:28,247 --> 00:15:30,715
No breeder guided these changes.
250
00:15:30,749 --> 00:15:34,219
Instead, the environment itself
selects them.
251
00:15:34,253 --> 00:15:36,888
This is evolution
by natural selection,
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00:15:36,922 --> 00:15:40,692
the most revolutionary concept
in the history of science.
253
00:15:40,726 --> 00:15:44,863
Darwin first presented the
evidence for this idea in 1859.
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00:15:44,897 --> 00:15:48,900
The uproar it caused
has never subsided.
255
00:15:48,934 --> 00:15:50,935
Why?
256
00:15:56,195 --> 00:15:58,196
(birds chirping)
257
00:15:58,230 --> 00:16:00,331
We all understand
the twinge of discomfort
258
00:16:00,366 --> 00:16:03,601
at the thought that we share
a common ancestor with the apes.
259
00:16:03,636 --> 00:16:06,971
No one can embarrass you
like a relative.
260
00:16:07,006 --> 00:16:09,174
Our closest ones,
the chimpanzees,
261
00:16:09,208 --> 00:16:11,843
they frequently behave
inappropriately in public.
262
00:16:11,877 --> 00:16:14,112
There's an understandable
human need
263
00:16:14,146 --> 00:16:16,347
to distance ourselves
from them.
264
00:16:16,382 --> 00:16:18,616
A central premise
of traditional belief
265
00:16:18,651 --> 00:16:20,618
is that we were
created separately
266
00:16:20,653 --> 00:16:22,620
from all the other animals.
267
00:16:22,655 --> 00:16:25,390
It's easy to see why
this idea has taken hold.
268
00:16:25,424 --> 00:16:28,226
It makes us feel... special.
269
00:16:28,260 --> 00:16:32,330
But what about our kinship
with the trees?
270
00:16:32,364 --> 00:16:34,766
How does that make you feel?
271
00:16:42,441 --> 00:16:45,677
Okay, here's a segment
of the oak tree's DNA.
272
00:16:45,711 --> 00:16:47,846
Think of it like a bar code.
273
00:16:47,880 --> 00:16:50,482
The instructions written
in the code of life
274
00:16:50,516 --> 00:16:53,485
tell the tree
how to metabolize sugar.
275
00:16:53,519 --> 00:16:56,788
Now let's compare it with
the same section of my own DNA.
276
00:17:02,027 --> 00:17:03,928
The DNA doesn't lie.
277
00:17:03,963 --> 00:17:07,265
This tree and me--
we're long-lost cousins.
278
00:17:07,299 --> 00:17:09,267
And it's not just the trees.
279
00:17:09,301 --> 00:17:12,170
If you go back far enough,
you'll find that we share
280
00:17:12,204 --> 00:17:14,205
a common ancestor with...
281
00:17:14,240 --> 00:17:15,540
the butterfly...
282
00:17:15,574 --> 00:17:17,175
gray wolf...
283
00:17:17,209 --> 00:17:18,576
mushroom...
284
00:17:18,611 --> 00:17:20,211
shark...
285
00:17:20,246 --> 00:17:21,679
bacterium...
286
00:17:21,714 --> 00:17:23,014
sparrow.
287
00:17:23,048 --> 00:17:24,582
What a family!
288
00:17:24,617 --> 00:17:28,119
Other parts of the bar code vary
from species to species.
289
00:17:28,154 --> 00:17:31,356
That's what makes the difference
between an owl and an octopus.
290
00:17:31,390 --> 00:17:33,591
Unless you have
an identical twin,
291
00:17:33,626 --> 00:17:35,894
there's no one else
in the universe
292
00:17:35,928 --> 00:17:38,563
with the exact same DNA as you.
293
00:17:38,597 --> 00:17:40,799
Within other species,
the genetic differences
294
00:17:40,833 --> 00:17:44,202
provide the raw material
for natural selection.
295
00:17:44,236 --> 00:17:48,139
The environment selects which
genes survive and multiply.
296
00:17:48,174 --> 00:17:50,308
When it comes
to the genetic instructions
297
00:17:50,342 --> 00:17:52,310
for life's
most basic functions--
298
00:17:52,344 --> 00:17:55,113
say, digesting sugars--
we and other species
299
00:17:55,147 --> 00:17:57,148
are almost identical.
300
00:17:57,183 --> 00:18:00,285
That's because those functions
are so basic to life,
301
00:18:00,319 --> 00:18:03,221
they evolved before
the various life-forms
302
00:18:03,255 --> 00:18:05,223
branched off from each other.
303
00:18:05,257 --> 00:18:07,692
This is our Tree of Life.
304
00:18:07,726 --> 00:18:09,227
Science has made it possible
305
00:18:09,261 --> 00:18:11,396
for us to construct
this family tree
306
00:18:11,430 --> 00:18:13,398
for all the species
of life on Earth.
307
00:18:13,432 --> 00:18:17,235
Close genetic relatives occupy
the same branch of the tree,
308
00:18:17,269 --> 00:18:20,872
while more distant cousins
are farther away.
309
00:18:20,906 --> 00:18:23,074
Each twig is a living species.
310
00:18:25,077 --> 00:18:28,246
And the trunk of the tree
represents the common ancestors
311
00:18:28,280 --> 00:18:31,082
of all life on Earth.
312
00:18:31,116 --> 00:18:33,485
The stuff of life
is so malleable
313
00:18:33,519 --> 00:18:36,454
that once it got started,
the environment molded it
314
00:18:36,489 --> 00:18:39,757
into a staggering
variety of forms--
315
00:18:39,792 --> 00:18:43,595
10,000 times more than
we can possibly show here.
316
00:18:45,598 --> 00:18:47,732
Biologists have catalogued
317
00:18:47,766 --> 00:18:51,269
a half a million different
kinds of beetles alone.
318
00:18:53,973 --> 00:18:56,574
Not to mention
the numberless varieties
319
00:18:56,609 --> 00:18:58,243
of bacteria.
320
00:18:58,277 --> 00:19:00,612
There are many millions
of living species
321
00:19:00,646 --> 00:19:03,014
of animals and plants,
most of them
322
00:19:03,048 --> 00:19:05,416
still unknown to science.
323
00:19:05,451 --> 00:19:08,520
Think of that--
we have yet to make contact
324
00:19:08,554 --> 00:19:11,856
with most of the forms
of terrestrial life.
325
00:19:11,891 --> 00:19:14,292
That's how many kinds
of life there are
326
00:19:14,326 --> 00:19:16,060
on this tiny planet alone.
327
00:19:18,063 --> 00:19:20,598
The Tree of Life extends
its feelers in all directions,
328
00:19:20,633 --> 00:19:22,200
finding and exploiting
what works,
329
00:19:22,234 --> 00:19:23,935
creating new environments
330
00:19:23,969 --> 00:19:26,204
and opportunities
for new forms.
331
00:19:28,374 --> 00:19:33,111
The Tree of Life is three
and a half billion years old.
332
00:19:33,145 --> 00:19:35,313
That's plenty of time
to develop
333
00:19:35,347 --> 00:19:38,516
an impressive repertoire
of tricks.
334
00:19:40,920 --> 00:19:43,555
Evolution can
disguise an animal
335
00:19:43,589 --> 00:19:46,024
as a plant...
336
00:19:50,529 --> 00:19:52,497
...taking thousands
of generations
337
00:19:52,531 --> 00:19:55,667
to contrive
an elaborate costume
338
00:19:55,701 --> 00:19:57,569
that fools predators
into looking elsewhere
339
00:19:57,603 --> 00:20:00,071
for someone to eat.
340
00:20:00,105 --> 00:20:04,075
Or it can disguise a plant
as an animal,
341
00:20:04,109 --> 00:20:07,212
evolving blossoms that take on
the appearance of a wasp--
342
00:20:07,246 --> 00:20:11,249
the orchid's way of fooling
real wasps into pollinating it.
343
00:20:12,284 --> 00:20:14,352
This is the awesome
344
00:20:14,386 --> 00:20:17,789
shape-shifting power
of natural selection.
345
00:20:24,530 --> 00:20:29,200
Among the dense, tangled limbs
of the vast Tree of Life...
346
00:20:29,235 --> 00:20:31,369
you are here.
347
00:20:31,403 --> 00:20:35,673
One tiny branch
among countless millions.
348
00:20:35,708 --> 00:20:40,712
Science reveals that all life
on Earth is one.
349
00:20:43,382 --> 00:20:46,551
Darwin discovered the actual
mechanism of evolution.
350
00:20:46,585 --> 00:20:49,587
The prevailing belief
was that the complexity
351
00:20:49,622 --> 00:20:52,257
and variety of life
must be the work
352
00:20:52,291 --> 00:20:55,226
of an intelligent designer,
who created each
353
00:20:55,261 --> 00:20:58,396
of these millions
of different species separately.
354
00:20:58,430 --> 00:21:01,900
Living things are just
too intricate, it was said,
355
00:21:01,934 --> 00:21:05,470
to be the result
of unguided evolution.
356
00:21:05,504 --> 00:21:07,939
Consider the human eye,
357
00:21:07,973 --> 00:21:10,208
a masterpiece of complexity.
358
00:21:13,879 --> 00:21:15,980
It requires a cornea,
359
00:21:16,015 --> 00:21:19,450
iris, lens, retina,
360
00:21:19,485 --> 00:21:21,853
optic nerves, muscles,
361
00:21:21,887 --> 00:21:24,589
let alone the brain's
elaborate neural network
362
00:21:24,623 --> 00:21:27,525
to interpret images.
363
00:21:27,560 --> 00:21:30,428
It's more complicated
than any device
364
00:21:30,462 --> 00:21:33,531
ever crafted
by human intelligence.
365
00:21:33,566 --> 00:21:35,200
Therefore, it was argued,
366
00:21:35,234 --> 00:21:37,268
the human eye
can't be the result
367
00:21:37,303 --> 00:21:39,604
of mindless evolution.
368
00:21:39,638 --> 00:21:43,641
To know if that's true,
we need to travel across time
369
00:21:43,676 --> 00:21:47,312
to a world before
there were eyes to see.
370
00:22:03,821 --> 00:22:06,389
DEGRASSE TYSON:
In the beginning,
371
00:22:06,423 --> 00:22:08,024
life was blind.
372
00:22:10,094 --> 00:22:12,228
This is what
our world looked like
373
00:22:12,262 --> 00:22:14,230
four billion years ago,
374
00:22:14,264 --> 00:22:17,900
before there were
any eyes to see.
375
00:22:17,935 --> 00:22:20,970
Until a few hundred million
years passed,
376
00:22:21,004 --> 00:22:22,605
and then, one day,
377
00:22:22,639 --> 00:22:24,674
there was a microscopic
copying error
378
00:22:24,708 --> 00:22:26,242
in the DNA of a bacterium.
379
00:22:26,276 --> 00:22:28,978
This random mutation
gave that microbe
380
00:22:29,012 --> 00:22:31,781
a protein molecule
that absorbed sunlight.
381
00:22:31,815 --> 00:22:33,616
Want to know what
the world looked like
382
00:22:33,650 --> 00:22:35,318
to a light-sensitive bacterium?
383
00:22:35,352 --> 00:22:38,621
Take a look at the right side
of the screen.
384
00:22:38,655 --> 00:22:42,258
Mutations continued
to occur at random,
385
00:22:42,292 --> 00:22:45,528
as they always do in any
population of living things.
386
00:22:47,531 --> 00:22:49,632
Another mutation
387
00:22:49,666 --> 00:22:53,603
caused a dark bacterium
to flee intense light.
388
00:22:53,637 --> 00:22:56,005
What is going on here?
389
00:22:56,039 --> 00:22:57,774
Night and day.
390
00:22:57,808 --> 00:22:59,809
Those bacteria that could
tell light from dark
391
00:22:59,843 --> 00:23:02,478
had a decisive advantage
over the ones that couldn't.
392
00:23:02,513 --> 00:23:04,313
Why?
393
00:23:04,348 --> 00:23:07,483
Because the daytime brought
harsh, ultraviolet light
394
00:23:07,518 --> 00:23:09,452
that damages DNA.
395
00:23:09,486 --> 00:23:13,022
The sensitive bacteria
fled the intense light
396
00:23:13,057 --> 00:23:15,558
to safely exchange
their DNA in the dark.
397
00:23:15,592 --> 00:23:17,493
They survived
in greater numbers
398
00:23:17,528 --> 00:23:19,962
than the bacteria that
stayed at the surface.
399
00:23:19,997 --> 00:23:23,066
Over time, those
light-sensitive proteins
400
00:23:23,100 --> 00:23:25,701
became concentrated
in a pigment spot
401
00:23:25,736 --> 00:23:29,005
on the more advanced,
one-celled organism.
402
00:23:29,039 --> 00:23:32,208
This made it possible
to find the light,
403
00:23:32,242 --> 00:23:34,343
an overwhelming advantage
404
00:23:34,378 --> 00:23:37,680
for an organism that harvests
sunlight to make food.
405
00:23:44,788 --> 00:23:47,690
Here's a flatworm's-eye view
of the world.
406
00:23:47,724 --> 00:23:49,859
This multi-celled organism
407
00:23:49,893 --> 00:23:52,195
evolved a dimple
in the pigment spot.
408
00:23:52,229 --> 00:23:54,497
The bowl-shaped depression
409
00:23:54,531 --> 00:23:57,867
allowed the animal to
distinguish light from shadow
410
00:23:57,901 --> 00:24:01,237
to crudely make out objects
in its vicinity,
411
00:24:01,271 --> 00:24:05,274
including those to eat
and those that might eat it...
412
00:24:05,309 --> 00:24:07,844
a tremendous advantage.
413
00:24:07,878 --> 00:24:10,513
Later, things became
a little clearer.
414
00:24:10,547 --> 00:24:12,248
The dimple deepened
415
00:24:12,282 --> 00:24:15,017
and evolved into a socket
with a small opening.
416
00:24:15,052 --> 00:24:17,386
Over thousands of generations,
417
00:24:17,421 --> 00:24:20,623
natural selection
was slowly sculpting the eye.
418
00:24:22,426 --> 00:24:25,561
The opening contracted
to a pinhole covered
419
00:24:25,596 --> 00:24:27,897
by a protective
transparent membrane.
420
00:24:27,931 --> 00:24:30,399
Only a little light
could enter the tiny hole,
421
00:24:30,434 --> 00:24:32,802
but it was enough
to paint a dim image
422
00:24:32,836 --> 00:24:35,371
on the sensitive inner surface
of the eye.
423
00:24:35,406 --> 00:24:37,273
This sharpened the focus.
424
00:24:37,307 --> 00:24:39,609
A larger opening
would have let in more light
425
00:24:39,643 --> 00:24:43,212
to make a brighter image
but one that was out of focus.
426
00:24:43,247 --> 00:24:46,115
This development launched
the visual equivalent
427
00:24:46,150 --> 00:24:48,785
of an arms race.
428
00:24:59,196 --> 00:25:03,766
The competition needed
to keep up to survive.
429
00:25:03,801 --> 00:25:07,503
But then a splendid new feature
of the eye evolved,
430
00:25:07,538 --> 00:25:12,508
a lens that provided both
brightness and sharp focus.
431
00:25:12,543 --> 00:25:14,944
In the eyes of primitive fish,
432
00:25:14,978 --> 00:25:18,681
the transparent gel near
the pinhole formed into a lens.
433
00:25:18,715 --> 00:25:21,451
At the same time,
the pinhole enlarged
434
00:25:21,485 --> 00:25:23,519
to let in more and more light.
435
00:25:23,554 --> 00:25:25,955
Fish could now see in high-def,
436
00:25:25,989 --> 00:25:29,692
both close up and far away.
437
00:25:29,726 --> 00:25:33,329
And then
something terrible happened.
438
00:25:33,363 --> 00:25:36,833
Have you ever noticed that
a straw in a glass of water
439
00:25:36,867 --> 00:25:39,335
looks bent at the surface
of the water?
440
00:25:39,369 --> 00:25:42,105
That's because light bends
when it goes from one medium
441
00:25:42,139 --> 00:25:45,007
to another,
say from water to air.
442
00:25:45,042 --> 00:25:48,778
Our eyes originally evolved
to see in water.
443
00:25:48,812 --> 00:25:51,681
The watery fluid
in those eyes neatly
444
00:25:51,715 --> 00:25:55,485
eliminated the distortion
of that bending effect.
445
00:25:56,487 --> 00:25:58,654
But for land animals,
446
00:25:58,689 --> 00:26:01,057
the light carries images
from dry air
447
00:26:01,091 --> 00:26:04,160
into their still-watery eyes.
448
00:26:04,194 --> 00:26:05,728
That bends the light rays,
449
00:26:05,763 --> 00:26:09,732
causing all kinds
of distortions.
450
00:26:09,767 --> 00:26:12,502
When our amphibious ancestors
left the water for the land,
451
00:26:12,536 --> 00:26:15,738
their eyes, exquisitely evolved
to see in water,
452
00:26:15,773 --> 00:26:18,074
were lousy for seeing
in the air.
453
00:26:18,108 --> 00:26:20,743
Our vision has never been
as good since.
454
00:26:20,778 --> 00:26:23,679
We like to think of our eyes
as state-of-the-art,
455
00:26:23,714 --> 00:26:26,582
but 375 million years later,
456
00:26:26,617 --> 00:26:29,018
we still can't see things
right in front of our noses
457
00:26:29,052 --> 00:26:31,687
or discern fine details
in near darkness
458
00:26:31,722 --> 00:26:33,589
the way fish can.
459
00:26:33,624 --> 00:26:35,091
When we left the water,
460
00:26:35,125 --> 00:26:37,260
why didn't nature
just start over again
461
00:26:37,294 --> 00:26:38,895
and evolve us a new set of eyes
462
00:26:38,929 --> 00:26:41,230
that were optimal
for seeing in the air?
463
00:26:41,265 --> 00:26:43,332
Nature doesn't work that way.
464
00:26:43,367 --> 00:26:46,736
Evolution reshapes existing
structures over generations,
465
00:26:46,770 --> 00:26:48,938
adapting them
with small changes.
466
00:26:48,972 --> 00:26:50,606
It can't just go back
to the drawing board
467
00:26:50,641 --> 00:26:52,442
and start from scratch.
468
00:26:52,476 --> 00:26:56,012
At every stage of its
development, the evolving eye
469
00:26:56,046 --> 00:26:57,747
functioned well enough
470
00:26:57,781 --> 00:27:00,917
to provide a selective
advantage for survival.
471
00:27:00,951 --> 00:27:03,786
And among animals alive today,
we find eyes
472
00:27:03,821 --> 00:27:06,989
at all these stages
of development.
473
00:27:10,260 --> 00:27:13,563
And all of them function.
474
00:27:13,597 --> 00:27:15,731
The complexity
of the human eye poses
475
00:27:15,766 --> 00:27:17,867
no challenge to evolution
by natural selection.
476
00:27:17,901 --> 00:27:22,371
In fact, the eye and all
of biology makes no sense
477
00:27:22,406 --> 00:27:24,040
without evolution.
478
00:27:24,074 --> 00:27:26,709
Some claim that evolution
is just a theory,
479
00:27:26,743 --> 00:27:29,912
as if it were merely
an opinion.
480
00:27:29,947 --> 00:27:32,648
The theory of evolution,
like the theory of gravity,
481
00:27:32,683 --> 00:27:34,751
is a scientific fact.
482
00:27:34,785 --> 00:27:37,487
Evolution really happened.
483
00:27:37,521 --> 00:27:39,922
Accepting our kinship
with all life on Earth
484
00:27:39,957 --> 00:27:41,991
is not only solid science.
485
00:27:42,025 --> 00:27:47,196
In my view, it's also
a soaring spiritual experience.
486
00:27:53,971 --> 00:27:56,806
Because evolution is blind,
487
00:27:56,840 --> 00:28:01,077
it cannot anticipate or adapt
to catastrophic events.
488
00:28:01,111 --> 00:28:04,914
The Tree of Life
has some broken branches.
489
00:28:04,948 --> 00:28:08,417
Many of them were severed in
the five greatest catastrophes
490
00:28:08,452 --> 00:28:09,986
that life has ever known.
491
00:28:10,320 --> 00:28:12,288
Somewhere, there's a memorial
492
00:28:12,322 --> 00:28:15,291
to the multitude
of lost species,
493
00:28:15,325 --> 00:28:17,460
the Halls of Extinction.
494
00:28:17,494 --> 00:28:19,929
Come with me.
495
00:28:28,295 --> 00:28:31,495
_
496
00:28:31,630 --> 00:28:34,870
Welcome to the
Halls of Extinction.
497
00:28:35,657 --> 00:28:39,554
A monument to the broken branches
of the Tree of Life.
498
00:28:49,463 --> 00:28:53,166
For every single one
of the millions of species
499
00:28:53,200 --> 00:28:57,437
alive today, perhaps
a thousand others have perished.
500
00:28:57,471 --> 00:28:59,939
Most of them died out
in the everyday competition
501
00:28:59,974 --> 00:29:01,508
with other life-forms.
502
00:29:01,542 --> 00:29:05,111
But many of them were swept away
in vast cataclysms
503
00:29:05,146 --> 00:29:07,347
that overwhelmed the planet.
504
00:29:07,381 --> 00:29:09,782
In the last 500 million years,
505
00:29:09,817 --> 00:29:12,485
this has happened five times.
506
00:29:12,520 --> 00:29:17,690
Five mass extinctions
that devastated life on Earth.
507
00:29:17,725 --> 00:29:22,962
The worst one of all happened
some 250 million years ago,
508
00:29:22,997 --> 00:29:25,532
at the end of an era
509
00:29:25,566 --> 00:29:28,001
known as the Permian.
510
00:29:44,385 --> 00:29:47,120
Trilobites were
armored animals that hunted
511
00:29:47,154 --> 00:29:49,622
in great herds
across the seafloor.
512
00:29:49,657 --> 00:29:52,325
They were among
the first animals to evolve
513
00:29:52,359 --> 00:29:54,761
image-forming eyes.
514
00:29:57,331 --> 00:30:01,334
Trilobites had a good long run,
some 270 million years.
515
00:30:01,368 --> 00:30:04,904
Earth was once
the planet of the trilobites.
516
00:30:04,939 --> 00:30:08,341
But now they're all gone,
extinct.
517
00:30:08,375 --> 00:30:11,077
The last of them were swept
from life's stage
518
00:30:11,111 --> 00:30:13,179
along with countless
other species
519
00:30:13,214 --> 00:30:17,417
in an unparalleled
environmental disaster.
520
00:30:22,256 --> 00:30:25,925
(explosions rumbling)
521
00:30:25,960 --> 00:30:29,562
The apocalypse
began in what is now Siberia,
522
00:30:29,597 --> 00:30:34,234
with volcanic eruptions
on a scale unlike anything
523
00:30:34,268 --> 00:30:36,436
in human experience.
524
00:30:48,883 --> 00:30:51,417
Earth was very different then,
525
00:30:51,452 --> 00:30:55,755
with one single supercontinent
and one great ocean.
526
00:30:55,789 --> 00:30:58,258
Relentless floods of fiery lava
527
00:30:58,292 --> 00:31:01,060
engulfed an area larger than
Western Europe.
528
00:31:01,095 --> 00:31:03,763
The pulsing eruptions
went on for hundreds
529
00:31:03,797 --> 00:31:05,932
of thousands of years.
530
00:31:05,966 --> 00:31:07,534
The molten rock
531
00:31:07,568 --> 00:31:10,270
ignited coal deposits
and polluted the air
532
00:31:10,304 --> 00:31:13,273
with carbon dioxide
and other greenhouse gases.
533
00:31:13,307 --> 00:31:15,208
This heated the Earth
534
00:31:15,242 --> 00:31:18,344
and stopped the ocean currents
from circulating.
535
00:31:33,360 --> 00:31:35,662
Noxious bacteria bloomed,
536
00:31:35,696 --> 00:31:39,832
but nearly everything else
in the seas died.
537
00:31:39,867 --> 00:31:43,436
The stagnant waters belched
deadly hydrogen sulfide gas
538
00:31:43,470 --> 00:31:44,904
into the air,
539
00:31:44,939 --> 00:31:47,473
which suffocated most
of the land animals.
540
00:32:00,487 --> 00:32:04,824
Nine in ten of all species
on the planet went extinct.
541
00:32:04,859 --> 00:32:06,926
We call it...
542
00:32:06,961 --> 00:32:08,962
The Great Dying.
543
00:32:21,575 --> 00:32:24,210
Life on Earth came so near
to being wiped out
544
00:32:24,245 --> 00:32:28,047
that it took more than
ten million years to recover.
545
00:32:28,082 --> 00:32:30,383
But new life-forms
slowly evolved
546
00:32:30,417 --> 00:32:34,087
to fill the openings left
by the Permian holocaust.
547
00:32:41,862 --> 00:32:44,731
Among the biggest winners
were the dinosaurs.
548
00:32:44,765 --> 00:32:47,567
Now the Earth was their planet.
549
00:32:47,601 --> 00:32:51,838
Their reign continued
for over 150 million years.
550
00:32:51,872 --> 00:32:54,474
Until it, too,
came crashing down
551
00:32:54,508 --> 00:32:57,410
in another mass extinction.
552
00:32:57,444 --> 00:33:00,046
Life on Earth has taken quite
a beating over the eons.
553
00:33:00,080 --> 00:33:02,882
And yet it's still there.
554
00:33:02,917 --> 00:33:05,718
The tenacity of life
is mind-boggling.
555
00:33:05,753 --> 00:33:08,555
We keep finding it where
no one thought it could be.
556
00:33:13,027 --> 00:33:16,329
That nameless corridor?
557
00:33:16,363 --> 00:33:18,364
That's for another day.
558
00:33:23,871 --> 00:33:27,440
I know an animal that can live
in boiling water
559
00:33:27,474 --> 00:33:29,609
or in solid ice.
560
00:33:29,643 --> 00:33:32,011
It can go ten years
without a drop of water.
561
00:33:32,046 --> 00:33:34,681
It can travel naked
in the cold vacuum
562
00:33:34,715 --> 00:33:39,219
and intense radiation of space
and will return unscathed.
563
00:33:39,253 --> 00:33:41,688
The tardigrade, or water bear.
564
00:33:41,722 --> 00:33:44,791
It's equally at home
atop the tallest mountains
565
00:33:44,825 --> 00:33:46,626
and in the deepest trenches
of the sea.
566
00:33:46,660 --> 00:33:49,696
And in our own backyards,
where they live among the moss
567
00:33:49,730 --> 00:33:52,198
in countless numbers.
568
00:33:52,233 --> 00:33:53,600
You've probably
never noticed them
569
00:33:53,634 --> 00:33:55,101
because they're so small.
570
00:33:55,135 --> 00:33:56,736
About the size of a pinpoint.
571
00:33:56,770 --> 00:33:58,471
But they're tough.
572
00:33:58,505 --> 00:34:02,775
The tardigrades have survived
all five mass extinctions.
573
00:34:02,810 --> 00:34:05,545
They've been in business
for a half a billion years.
574
00:34:05,579 --> 00:34:07,914
We used to think
that life was finicky,
575
00:34:07,948 --> 00:34:09,883
that it would only take hold
where it was
576
00:34:09,917 --> 00:34:11,885
not too hot, not too cold,
577
00:34:11,919 --> 00:34:15,655
not too dark or salty
or acidic or radioactive.
578
00:34:15,689 --> 00:34:18,458
And whatever you do,
don't forget to add water.
579
00:34:18,492 --> 00:34:20,226
We were wrong.
580
00:34:20,261 --> 00:34:21,561
As the hardy tardigrade
demonstrates,
581
00:34:21,595 --> 00:34:23,763
life can endure conditions
582
00:34:23,797 --> 00:34:27,000
that would mean certain death
for us humans.
583
00:34:27,034 --> 00:34:28,835
But differences between us
and life found
584
00:34:28,869 --> 00:34:31,404
in even the most extreme
environments on our planet
585
00:34:31,438 --> 00:34:34,407
are only variations
on a single theme,
586
00:34:34,441 --> 00:34:36,976
dialects of a single language.
587
00:34:37,011 --> 00:34:39,779
The genetic code of Earth life.
588
00:34:44,718 --> 00:34:47,253
But what would life be like
on other worlds?
589
00:34:47,288 --> 00:34:50,290
Worlds with a completely
different history,
590
00:34:50,324 --> 00:34:53,326
chemistry and evolution
from our planet?
591
00:34:55,796 --> 00:34:59,332
There's a distant world
I want to take you to--
592
00:34:59,366 --> 00:35:01,768
a world far different
from our own,
593
00:35:01,802 --> 00:35:05,138
but one that may harbor life.
594
00:35:05,172 --> 00:35:09,042
If it does, it promises
to be unlike anything
595
00:35:09,076 --> 00:35:11,511
we've ever seen before.
596
00:35:27,124 --> 00:35:30,493
Clouds and haze completely hide
the surface of Titan,
597
00:35:30,527 --> 00:35:32,495
Saturn's giant moon.
598
00:35:32,529 --> 00:35:35,097
Titan reminds me
a little bit of home.
599
00:35:35,132 --> 00:35:38,601
Like Earth, it has an atmosphere
that's mostly nitrogen.
600
00:35:38,635 --> 00:35:40,769
But it's four times denser.
601
00:35:40,804 --> 00:35:43,672
Titan's air has
no oxygen at all.
602
00:35:43,707 --> 00:35:46,175
And it's far colder
than anywhere on Earth.
603
00:35:46,209 --> 00:35:49,812
But still...
I want to go there.
604
00:35:50,981 --> 00:35:53,482
We have to descend
605
00:35:53,517 --> 00:35:55,951
through a couple hundred
kilometers of smog
606
00:35:55,986 --> 00:35:58,954
before we can even
see the surface.
607
00:35:58,989 --> 00:36:02,525
But hidden beneath lies
a weirdly familiar landscape.
608
00:36:10,233 --> 00:36:13,669
Titan is the only other world
in the solar system
609
00:36:13,703 --> 00:36:15,137
where it ever rains.
610
00:36:15,172 --> 00:36:18,574
It has rivers and coastlines.
611
00:36:23,513 --> 00:36:25,581
Titan has hundreds of lakes.
612
00:36:25,615 --> 00:36:29,151
One of them larger than
Lake Superior in North America.
613
00:36:29,186 --> 00:36:31,153
Vapor rising from the lakes
614
00:36:31,188 --> 00:36:33,389
condenses and falls again
as rain.
615
00:36:33,423 --> 00:36:37,326
The rain feeds rivers,
616
00:36:37,360 --> 00:36:40,663
which carve valleys
into the landscape,
617
00:36:40,697 --> 00:36:42,698
just like on Earth.
618
00:36:44,968 --> 00:36:47,036
But with one big difference.
619
00:36:47,070 --> 00:36:49,772
On Titan, the seas and the rain
620
00:36:49,806 --> 00:36:53,709
are made not of water
but of methane and ethane.
621
00:36:53,743 --> 00:36:56,679
On Earth, those molecules
form natural gas.
622
00:36:56,713 --> 00:36:59,548
On frigid Titan,
623
00:36:59,583 --> 00:37:01,584
they're liquid.
624
00:37:06,890 --> 00:37:08,891
Titan has lots of water,
625
00:37:08,925 --> 00:37:11,627
but all of it is frozen
hard as rock.
626
00:37:11,661 --> 00:37:14,029
In fact, the landscape
and mountains
627
00:37:14,064 --> 00:37:16,532
are made mainly of water ice.
628
00:37:16,566 --> 00:37:18,767
At hundreds of degrees
below zero,
629
00:37:18,802 --> 00:37:22,705
Titan is far too cold
for water to ever be liquid.
630
00:37:22,739 --> 00:37:24,907
(rainfall, distant thunder)
631
00:37:24,941 --> 00:37:28,144
Astrobiologists since
Carl Sagan have wondered
632
00:37:28,178 --> 00:37:31,614
if life might swim
in Titan's hydrocarbon lakes.
633
00:37:33,950 --> 00:37:35,885
The chemical basis for such life
634
00:37:35,919 --> 00:37:39,321
would have to be entirely
different from anything we know.
635
00:37:39,356 --> 00:37:42,158
All life on Earth
depends on liquid water.
636
00:37:42,192 --> 00:37:44,493
And Titan's surface
has none of that.
637
00:37:44,528 --> 00:37:47,062
But we can imagine
other kinds of life.
638
00:37:47,097 --> 00:37:49,665
There might be creatures
that inhale hydrogen
639
00:37:49,699 --> 00:37:51,167
instead of oxygen.
640
00:37:51,201 --> 00:37:54,670
And exhale methane
instead of carbon dioxide.
641
00:37:54,704 --> 00:37:58,140
They might use acetylene instead
of sugar as an energy source.
642
00:37:58,175 --> 00:38:00,609
How could we find out
if such creatures
643
00:38:00,644 --> 00:38:05,147
rule a hidden empire
beneath the oil-dark waves?
644
00:38:20,397 --> 00:38:23,666
We're diving down deep
into the Kraken Sea,
645
00:38:23,700 --> 00:38:26,702
named for the mythic
Norse sea monster.
646
00:38:30,073 --> 00:38:32,274
Even if there is
one of those down there,
647
00:38:32,309 --> 00:38:33,976
we probably couldn't see it.
648
00:38:34,010 --> 00:38:36,545
It's so dark.
649
00:38:36,580 --> 00:38:40,983
If you took all the oil
and natural gas on Earth,
650
00:38:41,017 --> 00:38:44,753
it would amount to but a tiny
fraction of Titan's reserves.
651
00:38:48,258 --> 00:38:50,192
Let's turn on some lights.
652
00:38:54,498 --> 00:38:57,933
We're now 200 meters
beneath the surface.
653
00:39:01,204 --> 00:39:03,739
Did you see something?
654
00:39:03,773 --> 00:39:06,976
Over there, by that vent.
655
00:39:07,010 --> 00:39:09,478
Maybe it was just
my imagination.
656
00:39:09,513 --> 00:39:11,480
I guess we'll have to come back
657
00:39:11,515 --> 00:39:14,517
if we want to find out
for sure.
658
00:39:16,753 --> 00:39:20,389
There's one last story
I want to tell you.
659
00:39:20,423 --> 00:39:24,593
And it's the greatest story
science has ever told.
660
00:39:28,932 --> 00:39:32,368
It's the story of life
on our world.
661
00:39:54,825 --> 00:39:57,927
Welcome to the Earth
of four billion years ago.
662
00:39:57,961 --> 00:40:01,630
This was our planet before life.
663
00:40:01,665 --> 00:40:04,733
Nobody knows
how life got started.
664
00:40:04,768 --> 00:40:07,136
Most of the evidence
from that time was destroyed
665
00:40:07,170 --> 00:40:09,772
by impact and erosion.
666
00:40:09,806 --> 00:40:13,576
Science works on the frontier
between knowledge and ignorance.
667
00:40:13,610 --> 00:40:15,544
We're not afraid to admit
what we don't know.
668
00:40:15,579 --> 00:40:17,880
There's no shame in that.
669
00:40:17,914 --> 00:40:21,750
The only shame is to pretend
that we have all the answers.
670
00:40:21,785 --> 00:40:23,452
Maybe someone watching this
671
00:40:23,487 --> 00:40:25,988
will be the first
to solve the mystery
672
00:40:26,022 --> 00:40:28,424
of how life on Earth began.
673
00:40:35,999 --> 00:40:37,833
The evidence
from living microbes
674
00:40:37,868 --> 00:40:39,768
suggest that their
earliest ancestors
675
00:40:39,803 --> 00:40:41,504
preferred high temperatures.
676
00:40:41,538 --> 00:40:44,440
Life on Earth may have
arisen in hot water
677
00:40:44,474 --> 00:40:46,775
around submerged volcanic vents.
678
00:40:51,548 --> 00:40:54,016
In Carl Sagan's original
Cosmos series,
679
00:40:54,050 --> 00:40:56,819
he traced the unbroken thread
that stretches
680
00:40:56,853 --> 00:40:58,921
directly from
the one-celled organisms
681
00:40:58,955 --> 00:41:01,490
of nearly four billion
years ago...
682
00:41:01,525 --> 00:41:03,792
to you.
683
00:41:03,827 --> 00:41:06,962
Four billion years
in 40 seconds.
684
00:41:06,997 --> 00:41:10,533
From creatures who had yet
to discern day from night
685
00:41:10,567 --> 00:41:14,370
to beings who are
exploring the cosmos.
686
00:41:14,404 --> 00:41:17,406
♪ ♪
687
00:42:03,520 --> 00:42:06,522
CARL SAGAN: Those are some of
the things that molecules do
688
00:42:06,556 --> 00:42:10,025
given four billion years
of evolution.
689
00:42:15,516 --> 00:42:20,041
Sync and corrections by n17t01
www.addic7ed.com