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This is a story about you
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and me and your dog.
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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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00:00:21,093 --> 00:00:24,529
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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00:00:28,734 --> 00:00:31,269
How did that happen?
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00:00:31,303 --> 00:00:32,570
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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00:00:36,608 --> 00:00:40,945
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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00:00:43,615 --> 00:00:45,716
but it's no such thing.
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00:02:10,795 --> 00:02:14,238
"Some Of The Things That Molecules Do"
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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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00:02:25,918 --> 00:02:27,885
of the last ice age.
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00:02:27,920 --> 00:02:31,422
Our ancestors were wanderers
living in small bands.
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00:02:31,457 --> 00:02:33,725
They slept beneath the stars.
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The sky was their storybook,
calendar,
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00:02:37,062 --> 00:02:40,031
an instruction manual
for living.
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00:02:40,065 --> 00:02:42,734
It told them when
the bitter colds would come,
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00:02:42,768 --> 00:02:44,736
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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00:02:48,373 --> 00:02:52,343
Their idea of home
was Earth itself.
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00:02:52,377 --> 00:02:56,080
But they lived in fear
of other hungry creatures...
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00:02:56,115 --> 00:02:58,216
the mountain lions
and the bears
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00:02:58,250 --> 00:03:00,852
that competed with them
for the same prey
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00:03:00,886 --> 00:03:03,621
and the wolves that threatened
to carry off and devour
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the most vulnerable among them.
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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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00:03:32,918 --> 00:03:34,786
It's a matter of survival.
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00:03:34,820 --> 00:03:37,488
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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00:03:42,628 --> 00:03:45,530
This makes them less afraid
of humans.
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00:03:49,968 --> 00:03:51,402
This wolf has discovered
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00:03:51,437 --> 00:03:53,070
what a branch of his ancestors
figured out
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00:03:53,105 --> 00:03:55,073
some 15,000 years ago...
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00:03:55,107 --> 00:03:58,075
an excellent survival strategy;
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the domestication of humans.
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00:04:01,380 --> 00:04:04,916
Let the humans do the hunting,
don't threaten them,
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00:04:04,950 --> 00:04:06,918
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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00:04:10,155 --> 00:04:12,957
and those offspring will inherit
your disposition.
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00:04:12,991 --> 00:04:16,360
This selection for tameness
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00:04:16,395 --> 00:04:18,496
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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Then as now, this was a good
deal for the humans, too.
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00:04:36,148 --> 00:04:39,450
The scavenging dogs weren't just
a sanitation squad.
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They worked security.
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00:04:56,702 --> 00:05:00,037
As this interspecies partnership
continued over time,
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00:05:00,072 --> 00:05:03,741
the dogs' appearance
changed also.
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00:05:03,776 --> 00:05:06,010
Cuteness became
a selective advantage.
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00:05:06,044 --> 00:05:08,546
The more adorable you were,
the better chance you had
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00:05:08,580 --> 00:05:11,983
to live and pass on your genes
to another generation.
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00:05:12,017 --> 00:05:13,985
What began as an alliance
of convenience
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00:05:14,019 --> 00:05:18,256
became a friendship
that deepened over time.
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To see what happens next,
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00:05:19,925 --> 00:05:22,360
let's leave
our distant ancestors
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00:05:22,394 --> 00:05:26,664
of some 20,000 years ago
to visit the more recent past
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00:05:26,698 --> 00:05:29,534
during an intermission
in the Ice Age.
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00:05:29,568 --> 00:05:33,337
This break in the climate
starts a revolution.
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00:05:33,372 --> 00:05:37,008
Instead of wandering,
people are settling down.
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00:05:37,042 --> 00:05:40,945
There's something new
in the world... villages.
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People still hunt and gather,
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00:05:42,714 --> 00:05:46,350
but now they also produce
food and clothing...
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00:05:46,385 --> 00:05:47,885
agriculture.
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00:05:52,591 --> 00:05:55,860
The wolves have traded
their freedom
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in exchange for a steady meal.
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00:05:58,330 --> 00:06:01,065
They've given up their right
to choose a mate.
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00:06:01,099 --> 00:06:04,101
Now the humans choose for them.
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00:06:04,136 --> 00:06:08,206
They consistently kill off
the dogs that can't be trained;
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00:06:08,240 --> 00:06:09,907
the ones that bite
the feeding hand.
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00:06:09,942 --> 00:06:14,145
And they breed the dogs
that please them.
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00:06:17,182 --> 00:06:20,284
They nurture those dogs
that do their bidding...
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00:06:20,319 --> 00:06:23,488
hunting, herding,
guarding, hauling,
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00:06:23,522 --> 00:06:24,589
and keeping them company.
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00:06:24,623 --> 00:06:26,224
From every litter,
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00:06:26,258 --> 00:06:29,227
the humans select the puppies
they like best.
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00:06:29,261 --> 00:06:31,829
Over the generations,
the dogs evolve.
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00:06:31,864 --> 00:06:36,134
This kind of evolution is
called "artificial selection"
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00:06:36,168 --> 00:06:37,668
or "breeding."
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00:06:37,703 --> 00:06:39,937
Turning wolves into dogs was
the first time
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00:06:39,972 --> 00:06:43,107
we humans took evolution
into our own hands.
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00:06:43,142 --> 00:06:45,243
And we've been doing it
ever since
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00:06:45,277 --> 00:06:49,347
to shape all the plants
and animals that we depend on.
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00:06:49,381 --> 00:06:53,518
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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00:06:56,989 --> 00:06:58,322
we love today.
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Think of it.
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00:06:59,892 --> 00:07:01,859
Every breed of dog
you've ever seen
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00:07:01,894 --> 00:07:04,662
was sculpted by human hands.
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00:07:04,696 --> 00:07:08,166
Many of our best friends--
the most popular breeds--
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00:07:08,200 --> 00:07:10,802
were created in only
the last few centuries.
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00:07:13,705 --> 00:07:15,773
The awesome power of evolution
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00:07:15,808 --> 00:07:17,375
transformed the ravenous wolf
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00:07:17,409 --> 00:07:20,011
into the faithful shepherd...
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00:07:20,045 --> 00:07:23,881
...who protects the herd
and drives the wolf away.
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00:07:37,729 --> 00:07:41,032
Artificial selection turned
the wolf into the shepherd
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00:07:41,066 --> 00:07:43,968
and the wild grasses
into wheat and corn.
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00:07:44,002 --> 00:07:47,505
In fact, almost every plant
and animal that we eat today
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00:07:47,539 --> 00:07:51,209
was bred from a wild,
less-edible ancestor.
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00:07:51,243 --> 00:07:54,846
If artificial selection can work
such profound changes
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00:07:54,880 --> 00:07:57,582
in only 10,000 or 15,000 years,
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00:07:57,616 --> 00:07:59,750
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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00:08:07,860 --> 00:08:09,760
How does it work?
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00:08:09,795 --> 00:08:14,866
Our Ship of the Imagination
can take us anywhere in space
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00:08:14,900 --> 00:08:18,536
and time,
even to the hidden microcosmos,
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00:08:18,570 --> 00:08:22,573
where one kind of life can be
transformed into another.
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00:08:22,608 --> 00:08:24,542
Come with me.
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00:08:33,424 --> 00:08:35,358
May not seem like it,
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00:08:35,393 --> 00:08:37,260
but we've been living
in an ice age
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00:08:37,295 --> 00:08:39,029
for the last two million years.
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00:08:39,063 --> 00:08:41,598
This just happens to be
one of the long intermissions.
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00:08:41,632 --> 00:08:43,400
For most of those
two million years,
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00:08:43,434 --> 00:08:45,902
the climate has been cold
and dry.
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00:08:45,937 --> 00:08:48,638
The North Polar ice cap extended
much farther south
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00:08:48,673 --> 00:08:50,807
than it does today.
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00:08:50,842 --> 00:08:54,211
In one of those long,
cold glacial periods
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00:08:54,245 --> 00:08:57,114
when the winter sea ice
stretched from the North Pole
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00:08:57,148 --> 00:08:59,616
all the way down
to what is now Los Angeles,
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00:08:59,650 --> 00:09:04,354
great bears roamed the frozen
wastes of Ireland.
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00:09:09,961 --> 00:09:12,729
This might look like
an ordinary bear,
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00:09:12,763 --> 00:09:16,066
but something extraordinary
is happening inside her.
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00:09:16,100 --> 00:09:19,569
Something that will give rise
to a new species.
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00:09:19,604 --> 00:09:21,238
In order to see it,
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00:09:21,272 --> 00:09:24,608
we'll need to descend down
to a much smaller scale,
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00:09:24,642 --> 00:09:27,577
to the cellular level,
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00:09:27,612 --> 00:09:30,847
so that we can explore
the bear's reproductive system.
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00:09:34,352 --> 00:09:38,555
We'll take the subclavian
artery through the heart.
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00:10:00,745 --> 00:10:02,879
Almost there.
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00:10:09,353 --> 00:10:10,887
Those are some of her eggs.
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00:10:10,922 --> 00:10:13,457
To see what's going on
in one of them,
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00:10:13,491 --> 00:10:15,358
we'll have to get even smaller.
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00:10:15,393 --> 00:10:18,762
We'll have to shrink down
to the molecular level.
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00:10:21,365 --> 00:10:24,401
Our Ship of the Imagination
is now so small,
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00:10:24,435 --> 00:10:28,338
you could fit a million of them
into a grain of sand.
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00:10:28,372 --> 00:10:32,309
See those guys over there
strutting along those girders?
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00:10:32,343 --> 00:10:35,579
They are proteins
called kinesin.
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00:10:35,613 --> 00:10:38,315
These kinesin are part
of the transport crew
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00:10:38,349 --> 00:10:41,151
that's busy moving cargo
around the cell.
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00:10:41,185 --> 00:10:43,019
How alien they seem.
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00:10:43,054 --> 00:10:46,823
And yet these tiny creatures--
and beings like them--
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00:10:46,858 --> 00:10:51,561
are a part of every living cell,
including the ones inside you.
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00:10:53,531 --> 00:10:56,199
If life has a sanctuary,
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00:10:56,234 --> 00:11:00,070
it's here in the nucleus
which contains our DNA...
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00:11:00,104 --> 00:11:03,774
the ancient scripture
of our genetic code.
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00:11:03,808 --> 00:11:08,912
And it's written in a language
that all life can read.
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00:11:15,386 --> 00:11:19,089
DNA is a molecule shaped
like a long twisted ladder
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00:11:19,123 --> 00:11:21,258
or double helix.
160
00:11:21,292 --> 00:11:23,059
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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00:11:31,402 --> 00:11:33,804
the instructions
for all living things,
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00:11:33,838 --> 00:11:37,240
telling them how to grow,
move, digest,
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00:11:37,275 --> 00:11:40,744
sense the environment,
heal, reproduce.
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00:11:40,778 --> 00:11:43,914
The DNA double helix
is a molecular machine
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00:11:43,948 --> 00:11:47,984
with about 100 billion parts
called "atoms."
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00:11:48,019 --> 00:11:51,588
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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00:11:55,426 --> 00:11:57,494
The same is true for dogs
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and bears
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and every living thing.
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00:12:03,601 --> 00:12:07,871
We are, each of us,
a little universe.
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00:12:16,380 --> 00:12:19,282
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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00:12:23,187 --> 00:12:27,757
The birth of a new DNA molecule
begins when an unwinding protein
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00:12:27,792 --> 00:12:30,260
separates the two strands
of the double helix,
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00:12:30,294 --> 00:12:32,162
breaking the rungs apart.
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00:12:32,196 --> 00:12:34,498
Inside the liquid
of the nucleus,
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00:12:34,532 --> 00:12:38,435
the molecular letters of
the genetic code float freely.
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00:12:38,469 --> 00:12:41,838
Each strand of the helix
copies its lost partner,
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00:12:41,873 --> 00:12:44,841
resulting in two identical
DNA molecules.
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00:12:44,876 --> 00:12:47,878
That's how life reproduces
genes and transmits them
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00:12:47,912 --> 00:12:49,946
from one generation
to the next.
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00:12:49,981 --> 00:12:52,549
When a living cell divides
in two,
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00:12:52,583 --> 00:12:57,053
each one takes away with it
a complete copy of the DNA.
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00:12:57,088 --> 00:13:00,824
A specialized protein
proofreads to make sure
190
00:13:00,858 --> 00:13:02,659
that only the right letters
are accepted
191
00:13:02,693 --> 00:13:05,529
so that the DNA
is accurately copied.
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00:13:05,563 --> 00:13:07,297
But nobody's perfect.
193
00:13:07,331 --> 00:13:10,500
Occasionally, a proofreading
error slips through,
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00:13:10,535 --> 00:13:14,304
making a small, random change
in the genetic instructions.
195
00:13:14,338 --> 00:13:17,541
A mutation has occurred
in the bear's egg cell.
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00:13:17,575 --> 00:13:21,478
A random event as tiny as
this one can have consequences
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00:13:21,512 --> 00:13:23,747
on a far grander scale.
198
00:13:25,783 --> 00:13:30,587
That mutation altered the gene
that controls fur color.
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00:13:30,621 --> 00:13:33,590
It will affect the production
of dark pigment in the fur
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00:13:33,624 --> 00:13:35,592
of the bear's offspring.
201
00:13:35,626 --> 00:13:37,894
Most mutations are harmless.
202
00:13:37,929 --> 00:13:39,663
Some are deadly.
203
00:13:39,697 --> 00:13:42,566
But a few, purely by chance,
can give an organism
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00:13:42,600 --> 00:13:46,269
a critical advantage
over the competition.
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00:13:46,304 --> 00:13:48,271
A year has passed.
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00:13:48,306 --> 00:13:50,106
Our bear is now a mother.
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00:13:50,141 --> 00:13:51,842
And as a result
of that mutation,
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00:13:51,876 --> 00:13:55,512
one of her two cubs was born
with a white coat.
209
00:13:55,546 --> 00:13:58,248
When the cubs get old enough
to venture out on their own,
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00:13:58,282 --> 00:14:00,550
which bear is more likely
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00:14:00,585 --> 00:14:04,754
to be able to sneak up
on unsuspecting prey?
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00:14:04,789 --> 00:14:08,024
The brown bear can be seen
against the snow a mile away.
213
00:14:08,059 --> 00:14:10,927
The white bear prospers
and passes on
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00:14:10,962 --> 00:14:12,896
its own particular set
of genes.
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00:14:12,930 --> 00:14:15,765
This happens repeatedly.
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00:14:15,800 --> 00:14:17,934
Over succeeding generations,
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00:14:17,969 --> 00:14:20,537
the gene for white fur
spreads through
218
00:14:20,571 --> 00:14:23,206
the entire population
of Arctic bears.
219
00:14:23,241 --> 00:14:25,942
The gene for dark fur loses out
220
00:14:25,977 --> 00:14:28,745
in the competition
for survival.
221
00:14:30,748 --> 00:14:34,618
Mutations are entirely random
and happen all the time.
222
00:14:34,652 --> 00:14:36,586
But the environment
rewards those
223
00:14:36,621 --> 00:14:38,889
that increase the chance
for survival.
224
00:14:38,923 --> 00:14:41,291
It naturally selects
the living things
225
00:14:41,325 --> 00:14:43,960
that are better suited
to survive.
226
00:14:43,995 --> 00:14:46,796
And that selection
is the opposite of random.
227
00:14:49,634 --> 00:14:52,102
The two populations of bears
separated,
228
00:14:52,136 --> 00:14:53,970
and over thousands of years,
229
00:14:54,005 --> 00:14:57,140
evolved other characteristics
that set them apart.
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00:14:57,175 --> 00:15:00,377
They became different species.
231
00:15:02,780 --> 00:15:04,848
That's what
Charles Darwin meant
232
00:15:04,882 --> 00:15:08,518
by "the origin of species."
233
00:15:08,553 --> 00:15:11,087
An individual bear
doesn't evolve;
234
00:15:11,122 --> 00:15:15,025
the population of bears evolves
over generations.
235
00:15:16,727 --> 00:15:18,795
If the Arctic ice
continues to dwindle
236
00:15:18,830 --> 00:15:22,499
due to global warming,
the polar bears may go extinct.
237
00:15:22,533 --> 00:15:24,534
They'll be replaced
by brown bears,
238
00:15:24,569 --> 00:15:27,704
better adapted to
the now defrosted environment.
239
00:15:27,738 --> 00:15:32,209
This is a different story
from the one about the dogs.
240
00:15:32,243 --> 00:15:34,711
No breeder guided these changes.
241
00:15:34,745 --> 00:15:38,215
Instead, the environment itself
selects them.
242
00:15:38,249 --> 00:15:40,884
This is evolution
by natural selection,
243
00:15:40,918 --> 00:15:44,688
the most revolutionary concept
in the history of science.
244
00:15:44,722 --> 00:15:48,859
Darwin first presented the
evidence for this idea in 1859.
245
00:15:48,893 --> 00:15:52,896
The uproar it caused
has never subsided.
246
00:15:52,930 --> 00:15:54,931
Why?
247
00:16:04,812 --> 00:16:06,913
We all understand
the twinge of discomfort
248
00:16:06,948 --> 00:16:10,183
at the thought that we share
a common ancestor with the apes.
249
00:16:10,218 --> 00:16:13,553
No one can embarrass you
like a relative.
250
00:16:13,588 --> 00:16:15,756
Our closest ones,
the chimpanzees,
251
00:16:15,790 --> 00:16:18,425
they frequently behave
inappropriately in public.
252
00:16:18,459 --> 00:16:20,694
There's an understandable
human need
253
00:16:20,728 --> 00:16:22,929
to distance ourselves
from them.
254
00:16:22,964 --> 00:16:25,198
A central premise
of traditional belief
255
00:16:25,233 --> 00:16:27,200
is that we were
created separately
256
00:16:27,235 --> 00:16:29,202
from all the other animals.
257
00:16:29,237 --> 00:16:31,972
It's easy to see why
this idea has taken hold.
258
00:16:32,006 --> 00:16:34,808
It makes us feel... special.
259
00:16:34,842 --> 00:16:38,912
But what about our kinship
with the trees?
260
00:16:38,946 --> 00:16:41,348
How does that make you feel?
261
00:16:49,023 --> 00:16:52,259
Okay, here's a segment
of the oak tree's DNA.
262
00:16:52,293 --> 00:16:54,428
Think of it like a bar code.
263
00:16:54,462 --> 00:16:57,064
The instructions written
in the code of life
264
00:16:57,098 --> 00:17:00,067
tell the tree
how to metabolize sugar.
265
00:17:00,101 --> 00:17:03,370
Now let's compare it with
the same section of my own DNA.
266
00:17:08,609 --> 00:17:10,510
The DNA doesn't lie.
267
00:17:10,545 --> 00:17:13,847
This tree and me--
we're long-lost cousins.
268
00:17:13,881 --> 00:17:15,849
And it's not just the trees.
269
00:17:15,883 --> 00:17:18,752
If you go back far enough,
you'll find that we share
270
00:17:18,786 --> 00:17:20,787
a common ancestor with...
271
00:17:20,822 --> 00:17:22,122
the butterfly...
272
00:17:22,156 --> 00:17:23,757
gray wolf...
273
00:17:23,791 --> 00:17:25,158
mushroom...
274
00:17:25,193 --> 00:17:26,793
shark...
275
00:17:26,828 --> 00:17:28,261
bacterium...
276
00:17:28,296 --> 00:17:29,596
sparrow.
277
00:17:29,630 --> 00:17:31,164
What a family!
278
00:17:31,199 --> 00:17:34,701
Other parts of the bar code vary
from species to species.
279
00:17:34,736 --> 00:17:37,938
That's what makes the difference
between an owl and an octopus.
280
00:17:37,972 --> 00:17:40,173
Unless you have
an identical twin,
281
00:17:40,208 --> 00:17:42,476
there's no one else
in the universe
282
00:17:42,510 --> 00:17:45,145
with the exact same DNA as you.
283
00:17:45,179 --> 00:17:47,381
Within other species,
the genetic differences
284
00:17:47,415 --> 00:17:50,784
provide the raw material
for natural selection.
285
00:17:50,818 --> 00:17:54,721
The environment selects which
genes survive and multiply.
286
00:17:54,756 --> 00:17:56,890
When it comes
to the genetic instructions
287
00:17:56,924 --> 00:17:58,892
for life's
most basic functions--
288
00:17:58,926 --> 00:18:01,695
say, digesting sugars--
we and other species
289
00:18:01,729 --> 00:18:03,730
are almost identical.
290
00:18:03,765 --> 00:18:06,867
That's because those functions
are so basic to life,
291
00:18:06,901 --> 00:18:09,803
they evolved before
the various life-forms
292
00:18:09,837 --> 00:18:11,805
branched off from each other.
293
00:18:11,839 --> 00:18:14,274
This is our Tree of Life.
294
00:18:14,308 --> 00:18:15,809
Science has made it possible
295
00:18:15,843 --> 00:18:17,978
for us to construct
this family tree
296
00:18:18,012 --> 00:18:19,980
for all the species
of life on Earth.
297
00:18:20,014 --> 00:18:23,817
Close genetic relatives occupy
the same branch of the tree,
298
00:18:23,851 --> 00:18:27,454
while more distant cousins
are farther away.
299
00:18:27,488 --> 00:18:29,656
Each twig is a living species.
300
00:18:31,659 --> 00:18:34,828
And the trunk of the tree
represents the common ancestors
301
00:18:34,862 --> 00:18:37,664
of all life on Earth.
302
00:18:37,698 --> 00:18:40,067
The stuff of life
is so malleable
303
00:18:40,101 --> 00:18:43,036
that once it got started,
the environment molded it
304
00:18:43,071 --> 00:18:46,339
into a staggering
variety of forms--
305
00:18:46,374 --> 00:18:50,177
10,000 times more than
we can possibly show here.
306
00:18:52,180 --> 00:18:54,314
Biologists have catalogued
307
00:18:54,348 --> 00:18:57,851
a half a million different
kinds of beetles alone.
308
00:19:00,555 --> 00:19:03,156
Not to mention
the numberless varieties
309
00:19:03,191 --> 00:19:04,825
of bacteria.
310
00:19:04,859 --> 00:19:07,194
There are many millions
of living species
311
00:19:07,228 --> 00:19:09,596
of animals and plants,
most of them
312
00:19:09,630 --> 00:19:11,998
still unknown to science.
313
00:19:12,033 --> 00:19:15,102
Think of that--
we have yet to make contact
314
00:19:15,136 --> 00:19:18,438
with most of the forms
of terrestrial life.
315
00:19:18,473 --> 00:19:20,874
That's how many kinds
of life there are
316
00:19:20,908 --> 00:19:22,642
on this tiny planet alone.
317
00:19:24,645 --> 00:19:27,180
The Tree of Life extends
its feelers in all directions,
318
00:19:27,215 --> 00:19:28,782
finding and exploiting
what works,
319
00:19:28,816 --> 00:19:30,517
creating new environments
320
00:19:30,551 --> 00:19:32,786
and opportunities
for new forms.
321
00:19:34,956 --> 00:19:39,693
The Tree of Life is three
and a half billion years old.
322
00:19:39,727 --> 00:19:41,895
That's plenty of time
to develop
323
00:19:41,929 --> 00:19:45,098
an impressive repertoire
of tricks.
324
00:19:47,502 --> 00:19:50,137
Evolution can
disguise an animal
325
00:19:50,171 --> 00:19:52,606
as a plant...
326
00:19:57,111 --> 00:19:59,079
...taking thousands
of generations
327
00:19:59,113 --> 00:20:02,249
to contrive
an elaborate costume
328
00:20:02,283 --> 00:20:04,151
that fools predators
into looking elsewhere
329
00:20:04,185 --> 00:20:06,653
for someone to eat.
330
00:20:06,687 --> 00:20:10,657
Or it can disguise a plant
as an animal,
331
00:20:10,691 --> 00:20:13,794
evolving blossoms that take on
the appearance of a wasp--
332
00:20:13,828 --> 00:20:17,831
the orchid's way of fooling
real wasps into pollinating it.
333
00:20:18,866 --> 00:20:20,934
This is the awesome
334
00:20:20,968 --> 00:20:24,371
shape-shifting power
of natural selection.
335
00:20:31,112 --> 00:20:35,782
Among the dense, tangled limbs
of the vast Tree of Life...
336
00:20:35,817 --> 00:20:37,951
you are here.
337
00:20:37,985 --> 00:20:42,255
One tiny branch
among countless millions.
338
00:20:42,290 --> 00:20:47,294
Science reveals that all life
on Earth is one.
339
00:20:49,964 --> 00:20:53,133
Darwin discovered the actual
mechanism of evolution.
340
00:20:53,167 --> 00:20:56,169
The prevailing belief
was that the complexity
341
00:20:56,204 --> 00:20:58,839
and variety of life
must be the work
342
00:20:58,873 --> 00:21:01,808
of an intelligent designer,
who created each
343
00:21:01,843 --> 00:21:04,978
of these millions
of different species separately.
344
00:21:05,012 --> 00:21:08,482
Living things are just
too intricate, it was said,
345
00:21:08,516 --> 00:21:12,052
to be the result
of unguided evolution.
346
00:21:12,086 --> 00:21:14,521
Consider the human eye,
347
00:21:14,555 --> 00:21:16,790
a masterpiece of complexity.
348
00:21:20,461 --> 00:21:22,562
It requires a cornea,
349
00:21:22,597 --> 00:21:26,032
iris, lens, retina,
350
00:21:26,067 --> 00:21:28,435
optic nerves, muscles,
351
00:21:28,469 --> 00:21:31,171
let alone the brain's
elaborate neural network
352
00:21:31,205 --> 00:21:34,107
to interpret images.
353
00:21:34,142 --> 00:21:37,010
It's more complicated
than any device
354
00:21:37,044 --> 00:21:40,113
ever crafted
by human intelligence.
355
00:21:40,148 --> 00:21:41,782
Therefore, it was argued,
356
00:21:41,816 --> 00:21:43,850
the human eye
can't be the result
357
00:21:43,885 --> 00:21:46,186
of mindless evolution.
358
00:21:46,220 --> 00:21:50,223
To know if that's true,
we need to travel across time
359
00:21:50,258 --> 00:21:53,894
to a world before
there were eyes to see.
360
00:22:13,307 --> 00:22:15,875
In the beginning,
361
00:22:15,909 --> 00:22:17,510
life was blind.
362
00:22:19,580 --> 00:22:21,714
This is what
our world looked like
363
00:22:21,748 --> 00:22:23,716
four billion years ago,
364
00:22:23,750 --> 00:22:27,386
before there were
any eyes to see.
365
00:22:27,421 --> 00:22:30,456
Until a few hundred million
years passed,
366
00:22:30,490 --> 00:22:32,091
and then, one day,
367
00:22:32,125 --> 00:22:34,160
there was a microscopic
copying error
368
00:22:34,194 --> 00:22:35,728
in the DNA of a bacterium.
369
00:22:35,762 --> 00:22:38,464
This random mutation
gave that microbe
370
00:22:38,498 --> 00:22:41,267
a protein molecule
that absorbed sunlight.
371
00:22:41,301 --> 00:22:43,102
Want to know what
the world looked like
372
00:22:43,136 --> 00:22:44,804
to a light-sensitive bacterium?
373
00:22:44,838 --> 00:22:48,107
Take a look at the right side
of the screen.
374
00:22:48,141 --> 00:22:51,744
Mutations continued
to occur at random,
375
00:22:51,778 --> 00:22:55,014
as they always do in any
population of living things.
376
00:22:57,017 --> 00:22:59,118
Another mutation
377
00:22:59,152 --> 00:23:03,089
caused a dark bacterium
to flee intense light.
378
00:23:03,123 --> 00:23:05,491
What is going on here?
379
00:23:05,525 --> 00:23:07,260
Night and day.
380
00:23:07,294 --> 00:23:09,295
Those bacteria that could
tell light from dark
381
00:23:09,329 --> 00:23:11,964
had a decisive advantage
over the ones that couldn't.
382
00:23:11,999 --> 00:23:13,799
Why?
383
00:23:13,834 --> 00:23:16,969
Because the daytime brought
harsh, ultraviolet light
384
00:23:17,004 --> 00:23:18,938
that damages DNA.
385
00:23:18,972 --> 00:23:22,508
The sensitive bacteria
fled the intense light
386
00:23:22,543 --> 00:23:25,044
to safely exchange
their DNA in the dark.
387
00:23:25,078 --> 00:23:26,979
They survived
in greater numbers
388
00:23:27,014 --> 00:23:29,448
than the bacteria that
stayed at the surface.
389
00:23:29,483 --> 00:23:32,552
Over time, those
light-sensitive proteins
390
00:23:32,586 --> 00:23:35,187
became concentrated
in a pigment spot
391
00:23:35,222 --> 00:23:38,491
on the more advanced,
one-celled organism.
392
00:23:38,525 --> 00:23:41,694
This made it possible
to find the light,
393
00:23:41,728 --> 00:23:43,829
an overwhelming advantage
394
00:23:43,864 --> 00:23:47,166
for an organism that harvests
sunlight to make food.
395
00:23:54,274 --> 00:23:57,176
Here's a flatworm's-eye view
of the world.
396
00:23:57,210 --> 00:23:59,345
This multi-celled organism
397
00:23:59,379 --> 00:24:01,681
evolved a dimple
in the pigment spot.
398
00:24:01,715 --> 00:24:03,983
The bowl-shaped depression
399
00:24:04,017 --> 00:24:07,353
allowed the animal to
distinguish light from shadow
400
00:24:07,387 --> 00:24:10,723
to crudely make out objects
in its vicinity,
401
00:24:10,757 --> 00:24:14,760
including those to eat
and those that might eat it...
402
00:24:14,795 --> 00:24:17,330
a tremendous advantage.
403
00:24:17,364 --> 00:24:19,999
Later, things became
a little clearer.
404
00:24:20,033 --> 00:24:21,734
The dimple deepened
405
00:24:21,768 --> 00:24:24,503
and evolved into a socket
with a small opening.
406
00:24:24,538 --> 00:24:26,872
Over thousands of generations,
407
00:24:26,907 --> 00:24:30,109
natural selection
was slowly sculpting the eye.
408
00:24:31,912 --> 00:24:35,047
The opening contracted
to a pinhole covered
409
00:24:35,082 --> 00:24:37,383
by a protective
transparent membrane.
410
00:24:37,417 --> 00:24:39,885
Only a little light
could enter the tiny hole,
411
00:24:39,920 --> 00:24:42,288
but it was enough
to paint a dim image
412
00:24:42,322 --> 00:24:44,857
on the sensitive inner surface
of the eye.
413
00:24:44,892 --> 00:24:46,759
This sharpened the focus.
414
00:24:46,793 --> 00:24:49,095
A larger opening
would have let in more light
415
00:24:49,129 --> 00:24:52,698
to make a brighter image
but one that was out of focus.
416
00:24:52,733 --> 00:24:55,601
This development launched
the visual equivalent
417
00:24:55,636 --> 00:24:58,271
of an arms race.
418
00:25:08,682 --> 00:25:13,252
The competition needed
to keep up to survive.
419
00:25:13,287 --> 00:25:16,989
But then a splendid new feature
of the eye evolved,
420
00:25:17,024 --> 00:25:21,994
a lens that provided both
brightness and sharp focus.
421
00:25:22,029 --> 00:25:24,430
In the eyes of primitive fish,
422
00:25:24,464 --> 00:25:28,167
the transparent gel near
the pinhole formed into a lens.
423
00:25:28,201 --> 00:25:30,937
At the same time,
the pinhole enlarged
424
00:25:30,971 --> 00:25:33,005
to let in more and more light.
425
00:25:33,040 --> 00:25:35,441
Fish could now see in high-def,
426
00:25:35,475 --> 00:25:39,178
both close up and far away.
427
00:25:39,212 --> 00:25:42,815
And then
something terrible happened.
428
00:25:42,849 --> 00:25:46,319
Have you ever noticed that
a straw in a glass of water
429
00:25:46,353 --> 00:25:48,821
looks bent at the surface
of the water?
430
00:25:48,855 --> 00:25:51,591
That's because light bends
when it goes from one medium
431
00:25:51,625 --> 00:25:54,493
to another,
say from water to air.
432
00:25:54,528 --> 00:25:58,264
Our eyes originally evolved
to see in water.
433
00:25:58,298 --> 00:26:01,167
The watery fluid
in those eyes neatly
434
00:26:01,201 --> 00:26:04,971
eliminated the distortion
of that bending effect.
435
00:26:05,973 --> 00:26:08,140
But for land animals,
436
00:26:08,175 --> 00:26:10,543
the light carries images
from dry air
437
00:26:10,577 --> 00:26:13,646
into their still-watery eyes.
438
00:26:13,680 --> 00:26:15,214
That bends the light rays,
439
00:26:15,249 --> 00:26:19,218
causing all kinds
of distortions.
440
00:26:19,253 --> 00:26:21,988
When our amphibious ancestors
left the water for the land,
441
00:26:22,022 --> 00:26:25,224
their eyes, exquisitely evolved
to see in water,
442
00:26:25,259 --> 00:26:27,560
were lousy for seeing
in the air.
443
00:26:27,594 --> 00:26:30,229
Our vision has never been
as good since.
444
00:26:30,264 --> 00:26:33,165
We like to think of our eyes
as state-of-the-art,
445
00:26:33,200 --> 00:26:36,068
but 375 million years later,
446
00:26:36,103 --> 00:26:38,504
we still can't see things
right in front of our noses
447
00:26:38,538 --> 00:26:41,173
or discern fine details
in near darkness
448
00:26:41,208 --> 00:26:43,075
the way fish can.
449
00:26:43,110 --> 00:26:44,577
When we left the water,
450
00:26:44,611 --> 00:26:46,746
why didn't nature
just start over again
451
00:26:46,780 --> 00:26:48,381
and evolve us a new set of eyes
452
00:26:48,415 --> 00:26:50,716
that were optimal
for seeing in the air?
453
00:26:50,751 --> 00:26:52,818
Nature doesn't work that way.
454
00:26:52,853 --> 00:26:56,222
Evolution reshapes existing
structures over generations,
455
00:26:56,256 --> 00:26:58,424
adapting them
with small changes.
456
00:26:58,458 --> 00:27:00,092
It can't just go back
to the drawing board
457
00:27:00,127 --> 00:27:01,928
and start from scratch.
458
00:27:01,962 --> 00:27:05,498
At every stage of its
development, the evolving eye
459
00:27:05,532 --> 00:27:07,233
functioned well enough
460
00:27:07,267 --> 00:27:10,403
to provide a selective
advantage for survival.
461
00:27:10,437 --> 00:27:13,272
And among animals alive today,
we find eyes
462
00:27:13,307 --> 00:27:16,475
at all these stages
of development.
463
00:27:19,746 --> 00:27:23,049
And all of them function.
464
00:27:23,083 --> 00:27:25,217
The complexity
of the human eye poses
465
00:27:25,252 --> 00:27:27,353
no challenge to evolution
by natural selection.
466
00:27:27,387 --> 00:27:31,857
In fact, the eye and all
of biology makes no sense
467
00:27:31,892 --> 00:27:33,526
without evolution.
468
00:27:33,560 --> 00:27:36,195
Some claim that evolution
is just a theory,
469
00:27:36,229 --> 00:27:39,398
as if it were merely
an opinion.
470
00:27:39,433 --> 00:27:42,134
The theory of evolution,
like the theory of gravity,
471
00:27:42,169 --> 00:27:44,237
is a scientific fact.
472
00:27:44,271 --> 00:27:46,973
Evolution really happened.
473
00:27:47,007 --> 00:27:49,408
Accepting our kinship
with all life on Earth
474
00:27:49,443 --> 00:27:51,477
is not only solid science.
475
00:27:51,511 --> 00:27:56,682
In my view, it's also
a soaring spiritual experience.
476
00:28:03,457 --> 00:28:06,292
Because evolution is blind,
477
00:28:06,326 --> 00:28:10,563
it cannot anticipate or adapt
to catastrophic events.
478
00:28:10,597 --> 00:28:14,400
The Tree of Life
has some broken branches.
479
00:28:14,434 --> 00:28:17,903
Many of them were severed in
the five greatest catastrophes
480
00:28:17,938 --> 00:28:19,472
that life has ever known.
481
00:28:19,806 --> 00:28:21,774
Somewhere, there's a memorial
482
00:28:21,808 --> 00:28:24,777
to the multitude
of lost species,
483
00:28:24,811 --> 00:28:26,946
the Halls of Extinction.
484
00:28:26,980 --> 00:28:29,415
Come with me.
485
00:28:43,798 --> 00:28:47,038
Welcome to the
Halls of Extinction.
486
00:28:47,825 --> 00:28:51,722
A monument to the broken branches
of the Tree of Life.
487
00:29:01,631 --> 00:29:05,334
For every single one
of the millions of species
488
00:29:05,368 --> 00:29:09,605
alive today, perhaps
a thousand others have perished.
489
00:29:09,639 --> 00:29:12,107
Most of them died out
in the everyday competition
490
00:29:12,142 --> 00:29:13,676
with other life-forms.
491
00:29:13,710 --> 00:29:17,279
But many of them were swept away
in vast cataclysms
492
00:29:17,314 --> 00:29:19,515
that overwhelmed the planet.
493
00:29:19,549 --> 00:29:21,950
In the last 500 million years,
494
00:29:21,985 --> 00:29:24,653
this has happened five times.
495
00:29:24,688 --> 00:29:29,858
Five mass extinctions
that devastated life on Earth.
496
00:29:29,893 --> 00:29:35,130
The worst one of all happened
some 250 million years ago,
497
00:29:35,165 --> 00:29:37,700
at the end of an era
498
00:29:37,734 --> 00:29:40,169
known as the Permian.
499
00:29:56,553 --> 00:29:59,288
Trilobites were
armored animals that hunted
500
00:29:59,322 --> 00:30:01,790
in great herds
across the seafloor.
501
00:30:01,825 --> 00:30:04,493
They were among
the first animals to evolve
502
00:30:04,527 --> 00:30:06,929
image-forming eyes.
503
00:30:09,499 --> 00:30:13,502
Trilobites had a good long run,
some 270 million years.
504
00:30:13,536 --> 00:30:17,072
Earth was once
the planet of the trilobites.
505
00:30:17,107 --> 00:30:20,509
But now they're all gone,
extinct.
506
00:30:20,543 --> 00:30:23,245
The last of them were swept
from life's stage
507
00:30:23,279 --> 00:30:25,347
along with countless
other species
508
00:30:25,382 --> 00:30:29,585
in an unparalleled
environmental disaster.
509
00:30:38,128 --> 00:30:41,730
The apocalypse
began in what is now Siberia,
510
00:30:41,765 --> 00:30:46,402
with volcanic eruptions
on a scale unlike anything
511
00:30:46,436 --> 00:30:48,604
in human experience.
512
00:31:01,051 --> 00:31:03,585
Earth was very different then,
513
00:31:03,620 --> 00:31:07,923
with one single supercontinent
and one great ocean.
514
00:31:07,957 --> 00:31:10,426
Relentless floods of fiery lava
515
00:31:10,460 --> 00:31:13,228
engulfed an area larger than
Western Europe.
516
00:31:13,263 --> 00:31:15,931
The pulsing eruptions
went on for hundreds
517
00:31:15,965 --> 00:31:18,100
of thousands of years.
518
00:31:18,134 --> 00:31:19,702
The molten rock
519
00:31:19,736 --> 00:31:22,438
ignited coal deposits
and polluted the air
520
00:31:22,472 --> 00:31:25,441
with carbon dioxide
and other greenhouse gases.
521
00:31:25,475 --> 00:31:27,376
This heated the Earth
522
00:31:27,410 --> 00:31:30,512
and stopped the ocean currents
from circulating.
523
00:31:45,528 --> 00:31:47,830
Noxious bacteria bloomed,
524
00:31:47,864 --> 00:31:52,000
but nearly everything else
in the seas died.
525
00:31:52,035 --> 00:31:55,604
The stagnant waters belched
deadly hydrogen sulfide gas
526
00:31:55,638 --> 00:31:57,072
into the air,
527
00:31:57,107 --> 00:31:59,641
which suffocated most
of the land animals.
528
00:32:12,655 --> 00:32:16,992
Nine in ten of all species
on the planet went extinct.
529
00:32:17,027 --> 00:32:19,094
We call it...
530
00:32:19,129 --> 00:32:21,130
The Great Dying.
531
00:32:33,743 --> 00:32:36,378
Life on Earth came so near
to being wiped out
532
00:32:36,413 --> 00:32:40,215
that it took more than
ten million years to recover.
533
00:32:40,250 --> 00:32:42,551
But new life-forms
slowly evolved
534
00:32:42,585 --> 00:32:46,255
to fill the openings left
by the Permian holocaust.
535
00:32:54,030 --> 00:32:56,899
Among the biggest winners
were the dinosaurs.
536
00:32:56,933 --> 00:32:59,735
Now the Earth was their planet.
537
00:32:59,769 --> 00:33:04,006
Their reign continued
for over 150 million years.
538
00:33:04,040 --> 00:33:06,642
Until it, too,
came crashing down
539
00:33:06,676 --> 00:33:09,578
in another mass extinction.
540
00:33:09,612 --> 00:33:12,214
Life on Earth has taken quite
a beating over the eons.
541
00:33:12,248 --> 00:33:15,050
And yet it's still there.
542
00:33:15,085 --> 00:33:17,886
The tenacity of life
is mind-boggling.
543
00:33:17,921 --> 00:33:20,723
We keep finding it where
no one thought it could be.
544
00:33:25,195 --> 00:33:28,497
That nameless corridor?
545
00:33:28,531 --> 00:33:30,532
That's for another day.
546
00:33:36,039 --> 00:33:39,608
I know an animal that can live
in boiling water
547
00:33:39,642 --> 00:33:41,777
or in solid ice.
548
00:33:41,811 --> 00:33:44,179
It can go ten years
without a drop of water.
549
00:33:44,214 --> 00:33:46,849
It can travel naked
in the cold vacuum
550
00:33:46,883 --> 00:33:51,387
and intense radiation of space
and will return unscathed.
551
00:33:51,421 --> 00:33:53,856
The tardigrade, or water bear.
552
00:33:53,890 --> 00:33:56,959
It's equally at home
atop the tallest mountains
553
00:33:56,993 --> 00:33:58,794
and in the deepest trenches
of the sea.
554
00:33:58,828 --> 00:34:01,864
And in our own backyards,
where they live among the moss
555
00:34:01,898 --> 00:34:04,366
in countless numbers.
556
00:34:04,401 --> 00:34:05,768
You've probably
never noticed them
557
00:34:05,802 --> 00:34:07,269
because they're so small.
558
00:34:07,303 --> 00:34:08,904
About the size of a pinpoint.
559
00:34:08,938 --> 00:34:10,639
But they're tough.
560
00:34:10,673 --> 00:34:14,943
The tardigrades have survived
all five mass extinctions.
561
00:34:14,978 --> 00:34:17,713
They've been in business
for a half a billion years.
562
00:34:17,747 --> 00:34:20,082
We used to think
that life was finicky,
563
00:34:20,116 --> 00:34:22,051
that it would only take hold
where it was
564
00:34:22,085 --> 00:34:24,053
not too hot, not too cold,
565
00:34:24,087 --> 00:34:27,823
not too dark or salty
or acidic or radioactive.
566
00:34:27,857 --> 00:34:30,626
And whatever you do,
don't forget to add water.
567
00:34:30,660 --> 00:34:32,394
We were wrong.
568
00:34:32,429 --> 00:34:33,729
As the hardy tardigrade
demonstrates,
569
00:34:33,763 --> 00:34:35,931
life can endure conditions
570
00:34:35,965 --> 00:34:39,168
that would mean certain death
for us humans.
571
00:34:39,202 --> 00:34:41,003
But differences between us
and life found
572
00:34:41,037 --> 00:34:43,572
in even the most extreme
environments on our planet
573
00:34:43,606 --> 00:34:46,575
are only variations
on a single theme,
574
00:34:46,609 --> 00:34:49,144
dialects of a single language.
575
00:34:49,179 --> 00:34:51,947
The genetic code of Earth life.
576
00:34:56,886 --> 00:34:59,421
But what would life be like
on other worlds?
577
00:34:59,456 --> 00:35:02,458
Worlds with a completely
different history,
578
00:35:02,492 --> 00:35:05,494
chemistry and evolution
from our planet?
579
00:35:07,964 --> 00:35:11,500
There's a distant world
I want to take you to--
580
00:35:11,534 --> 00:35:13,936
a world far different
from our own,
581
00:35:13,970 --> 00:35:17,306
but one that may harbor life.
582
00:35:17,340 --> 00:35:21,210
If it does, it promises
to be unlike anything
583
00:35:21,244 --> 00:35:23,679
we've ever seen before.
584
00:35:42,957 --> 00:35:46,326
Clouds and haze completely hide
the surface of Titan,
585
00:35:46,360 --> 00:35:48,328
Saturn's giant moon.
586
00:35:48,362 --> 00:35:50,930
Titan reminds me
a little bit of home.
587
00:35:50,965 --> 00:35:54,434
Like Earth, it has an atmosphere
that's mostly nitrogen.
588
00:35:54,468 --> 00:35:56,602
But it's four times denser.
589
00:35:56,637 --> 00:35:59,505
Titan's air has
no oxygen at all.
590
00:35:59,540 --> 00:36:02,008
And it's far colder
than anywhere on Earth.
591
00:36:02,042 --> 00:36:05,645
But still...
I want to go there.
592
00:36:06,814 --> 00:36:09,315
We have to descend
593
00:36:09,350 --> 00:36:11,784
through a couple hundred
kilometers of smog
594
00:36:11,819 --> 00:36:14,787
before we can even
see the surface.
595
00:36:14,822 --> 00:36:18,358
But hidden beneath lies
a weirdly familiar landscape.
596
00:36:26,066 --> 00:36:29,502
Titan is the only other world
in the solar system
597
00:36:29,536 --> 00:36:30,970
where it ever rains.
598
00:36:31,005 --> 00:36:34,407
It has rivers and coastlines.
599
00:36:39,346 --> 00:36:41,414
Titan has hundreds of lakes.
600
00:36:41,448 --> 00:36:44,984
One of them larger than
Lake Superior in North America.
601
00:36:45,019 --> 00:36:46,986
Vapor rising from the lakes
602
00:36:47,021 --> 00:36:49,222
condenses and falls again
as rain.
603
00:36:49,256 --> 00:36:53,159
The rain feeds rivers,
604
00:36:53,193 --> 00:36:56,496
which carve valleys
into the landscape,
605
00:36:56,530 --> 00:36:58,531
just like on Earth.
606
00:37:00,801 --> 00:37:02,869
But with one big difference.
607
00:37:02,903 --> 00:37:05,605
On Titan, the seas and the rain
608
00:37:05,639 --> 00:37:09,542
are made not of water
but of methane and ethane.
609
00:37:09,576 --> 00:37:12,512
On Earth, those molecules
form natural gas.
610
00:37:12,546 --> 00:37:15,381
On frigid Titan,
611
00:37:15,416 --> 00:37:17,417
they're liquid.
612
00:37:22,723 --> 00:37:24,724
Titan has lots of water,
613
00:37:24,758 --> 00:37:27,460
but all of it is frozen
hard as rock.
614
00:37:27,494 --> 00:37:29,862
In fact, the landscape
and mountains
615
00:37:29,897 --> 00:37:32,365
are made mainly of water ice.
616
00:37:32,399 --> 00:37:34,600
At hundreds of degrees
below zero,
617
00:37:34,635 --> 00:37:38,538
Titan is far too cold
for water to ever be liquid.
618
00:37:40,774 --> 00:37:43,977
Astrobiologists since
Carl Sagan have wondered
619
00:37:44,011 --> 00:37:47,447
if life might swim
in Titan's hydrocarbon lakes.
620
00:37:49,783 --> 00:37:51,718
The chemical basis for such life
621
00:37:51,752 --> 00:37:55,154
would have to be entirely
different from anything we know.
622
00:37:55,189 --> 00:37:57,991
All life on Earth
depends on liquid water.
623
00:37:58,025 --> 00:38:00,326
And Titan's surface
has none of that.
624
00:38:00,361 --> 00:38:02,895
But we can imagine
other kinds of life.
625
00:38:02,930 --> 00:38:05,498
There might be creatures
that inhale hydrogen
626
00:38:05,532 --> 00:38:07,000
instead of oxygen.
627
00:38:07,034 --> 00:38:10,503
And exhale methane
instead of carbon dioxide.
628
00:38:10,537 --> 00:38:13,973
They might use acetylene instead
of sugar as an energy source.
629
00:38:14,008 --> 00:38:16,442
How could we find out
if such creatures
630
00:38:16,477 --> 00:38:20,980
rule a hidden empire
beneath the oil-dark waves?
631
00:38:36,230 --> 00:38:39,499
We're diving down deep
into the Kraken Sea,
632
00:38:39,533 --> 00:38:42,535
named for the mythic
Norse sea monster.
633
00:38:45,906 --> 00:38:48,107
Even if there is
one of those down there,
634
00:38:48,142 --> 00:38:49,809
we probably couldn't see it.
635
00:38:49,843 --> 00:38:52,378
It's so dark.
636
00:38:52,413 --> 00:38:56,816
If you took all the oil
and natural gas on Earth,
637
00:38:56,850 --> 00:39:00,586
it would amount to but a tiny
fraction of Titan's reserves.
638
00:39:04,091 --> 00:39:06,025
Let's turn on some lights.
639
00:39:10,331 --> 00:39:13,766
We're now 200 meters
beneath the surface.
640
00:39:17,037 --> 00:39:19,572
Did you see something?
641
00:39:19,606 --> 00:39:22,809
Over there, by that vent.
642
00:39:22,843 --> 00:39:25,311
Maybe it was just
my imagination.
643
00:39:25,346 --> 00:39:27,313
I guess we'll have to come back
644
00:39:27,348 --> 00:39:30,350
if we want to find out
for sure.
645
00:39:32,586 --> 00:39:36,222
There's one last story
I want to tell you.
646
00:39:36,256 --> 00:39:40,426
And it's the greatest story
science has ever told.
647
00:39:44,765 --> 00:39:48,201
It's the story of life
on our world.
648
00:40:10,658 --> 00:40:13,760
Welcome to the Earth
of four billion years ago.
649
00:40:13,794 --> 00:40:17,463
This was our planet before life.
650
00:40:17,498 --> 00:40:20,566
Nobody knows
how life got started.
651
00:40:20,601 --> 00:40:22,969
Most of the evidence
from that time was destroyed
652
00:40:23,003 --> 00:40:25,605
by impact and erosion.
653
00:40:25,639 --> 00:40:29,409
Science works on the frontier
between knowledge and ignorance.
654
00:40:29,443 --> 00:40:31,377
We're not afraid to admit
what we don't know.
655
00:40:31,412 --> 00:40:33,713
There's no shame in that.
656
00:40:33,747 --> 00:40:37,583
The only shame is to pretend
that we have all the answers.
657
00:40:37,618 --> 00:40:39,285
Maybe someone watching this
658
00:40:39,320 --> 00:40:41,821
will be the first
to solve the mystery
659
00:40:41,855 --> 00:40:44,257
of how life on Earth began.
660
00:40:51,832 --> 00:40:53,666
The evidence
from living microbes
661
00:40:53,701 --> 00:40:55,601
suggest that their
earliest ancestors
662
00:40:55,636 --> 00:40:57,337
preferred high temperatures.
663
00:40:57,371 --> 00:41:00,273
Life on Earth may have
arisen in hot water
664
00:41:00,307 --> 00:41:02,608
around submerged volcanic vents.
665
00:41:07,381 --> 00:41:09,849
In Carl Sagan's original
Cosmos series,
666
00:41:09,883 --> 00:41:12,652
he traced the unbroken thread
that stretches
667
00:41:12,686 --> 00:41:14,754
directly from
the one-celled organisms
668
00:41:14,788 --> 00:41:17,323
of nearly four billion
years ago...
669
00:41:17,358 --> 00:41:19,625
to you.
670
00:41:19,660 --> 00:41:22,795
Four billion years
in 40 seconds.
671
00:41:22,830 --> 00:41:26,366
From creatures who had yet
to discern day from night
672
00:41:26,400 --> 00:41:30,203
to beings who are
exploring the cosmos.
673
00:42:19,353 --> 00:42:22,355
Those are some of
the things that molecules do
674
00:42:22,389 --> 00:42:25,858
given four billion years
of evolution.
54975
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