1
00:00:02,802 --> 00:00:05,337
This is a story about you
2
00:00:05,371 --> 00:00:08,540
and me and your dog.
3
00:00:12,311 --> 00:00:17,482
There was a time not long ago...
before dogs.
4
00:00:17,517 --> 00:00:19,150
They didn't exist.
5
00:00:19,185 --> 00:00:22,621
Now there are big ones,
small ones, snugglers,
6
00:00:22,655 --> 00:00:24,189
guardians, hunters.
7
00:00:24,223 --> 00:00:26,791
Every kind of dog
you could possibly want.
8
00:00:26,826 --> 00:00:29,361
How did that happen?
9
00:00:29,395 --> 00:00:30,662
It's not just dogs.
10
00:00:30,696 --> 00:00:31,897
Where did all
the different kinds
11
00:00:31,931 --> 00:00:34,666
of living creatures come from?
12
00:00:34,700 --> 00:00:39,037
The answer is a transforming
power that sounds like something
13
00:00:39,071 --> 00:00:41,673
straight out
of a fairy tale or myth,
14
00:00:41,707 --> 00:00:43,808
but it's no such thing.
15
00:00:45,000 --> 00:00:51,074
OpenSubtitles recommends using Nord VPN
from 3.49 USD/month ----> osdb.link/vpn
16
00:02:08,887 --> 00:02:12,330
Sync and corrections by n17t01
www.addic7ed.com
17
00:02:15,935 --> 00:02:20,805
Let's go back across 30,000
years to a time before dogs,
18
00:02:20,840 --> 00:02:23,975
when our ancestors lived
in the endless winter
19
00:02:24,010 --> 00:02:25,977
of the last ice age.
20
00:02:26,012 --> 00:02:29,514
Our ancestors were wanderers
living in small bands.
21
00:02:29,549 --> 00:02:31,817
They slept beneath the stars.
22
00:02:31,851 --> 00:02:35,120
The sky was their storybook,
calendar,
23
00:02:35,154 --> 00:02:38,123
an instruction manual
for living.
24
00:02:38,157 --> 00:02:40,826
It told them when
the bitter colds would come,
25
00:02:40,860 --> 00:02:42,828
when the wild grains
would ripen,
26
00:02:42,862 --> 00:02:46,431
when the herds of caribou
and bison would be on the move.
27
00:02:46,465 --> 00:02:50,435
Their idea of home
was Earth itself.
28
00:02:50,469 --> 00:02:54,172
But they lived in fear
of other hungry creatures...
29
00:02:54,207 --> 00:02:56,308
the mountain lions
and the bears
30
00:02:56,342 --> 00:02:58,944
that competed with them
for the same prey
31
00:02:58,978 --> 00:03:01,713
and the wolves that threatened
to carry off and devour
32
00:03:01,747 --> 00:03:03,915
the most vulnerable among them.
33
00:03:21,100 --> 00:03:24,035
All the wolves want
to get at the bone,
34
00:03:24,070 --> 00:03:26,638
but most of them are too
frightened to come close enough.
35
00:03:26,672 --> 00:03:29,140
Their fear is due to high levels
36
00:03:29,175 --> 00:03:30,976
of stress hormones
in their blood.
37
00:03:31,010 --> 00:03:32,878
It's a matter of survival.
38
00:03:32,912 --> 00:03:35,580
Because coming too close
to humans can be fatal.
39
00:03:35,615 --> 00:03:38,884
But a few wolves--
due to natural variations--
40
00:03:38,918 --> 00:03:40,685
have lower levels
of those hormones.
41
00:03:40,720 --> 00:03:43,622
This makes them less afraid
of humans.
42
00:03:48,060 --> 00:03:49,494
This wolf has discovered
43
00:03:49,529 --> 00:03:51,162
what a branch of his ancestors
figured out
44
00:03:51,197 --> 00:03:53,165
some 15,000 years ago...
45
00:03:53,199 --> 00:03:56,167
an excellent survival strategy;
46
00:03:56,202 --> 00:03:59,437
the domestication of humans.
47
00:03:59,472 --> 00:04:03,008
Let the humans do the hunting,
don't threaten them,
48
00:04:03,042 --> 00:04:05,010
and they'll let you scavenge
their garbage.
49
00:04:05,044 --> 00:04:08,213
You'll eat more regularly,
you'll leave more offspring,
50
00:04:08,247 --> 00:04:11,049
and those offspring will inherit
your disposition.
51
00:04:11,083 --> 00:04:14,452
This selection for tameness
52
00:04:14,487 --> 00:04:16,588
would be reinforced
with each generation
53
00:04:16,622 --> 00:04:21,426
until that line of wild wolves
evolves into...
54
00:04:21,460 --> 00:04:23,528
dogs.
55
00:04:23,563 --> 00:04:26,565
You might call this
"survival of the friendliest."
56
00:04:30,937 --> 00:04:34,206
Then as now, this was a good
deal for the humans, too.
57
00:04:34,240 --> 00:04:37,542
The scavenging dogs weren't just
a sanitation squad.
58
00:04:37,577 --> 00:04:39,377
They worked security.
59
00:04:54,794 --> 00:04:58,129
As this interspecies partnership
continued over time,
60
00:04:58,164 --> 00:05:01,833
the dogs' appearance
changed also.
61
00:05:01,868 --> 00:05:04,102
Cuteness became
a selective advantage.
62
00:05:04,136 --> 00:05:06,638
The more adorable you were,
the better chance you had
63
00:05:06,672 --> 00:05:10,075
to live and pass on your genes
to another generation.
64
00:05:10,109 --> 00:05:12,077
What began as an alliance
of convenience
65
00:05:12,111 --> 00:05:16,348
became a friendship
that deepened over time.
66
00:05:16,382 --> 00:05:17,983
To see what happens next,
67
00:05:18,017 --> 00:05:20,452
let's leave
our distant ancestors
68
00:05:20,486 --> 00:05:24,756
of some 20,000 years ago
to visit the more recent past
69
00:05:24,790 --> 00:05:27,626
during an intermission
in the Ice Age.
70
00:05:27,660 --> 00:05:31,429
This break in the climate
starts a revolution.
71
00:05:31,464 --> 00:05:35,100
Instead of wandering,
people are settling down.
72
00:05:35,134 --> 00:05:39,037
There's something new
in the world... villages.
73
00:05:39,071 --> 00:05:40,772
People still hunt and gather,
74
00:05:40,806 --> 00:05:44,442
but now they also produce
food and clothing...
75
00:05:44,477 --> 00:05:45,977
agriculture.
76
00:05:50,683 --> 00:05:53,952
The wolves have traded
their freedom
77
00:05:53,986 --> 00:05:56,388
in exchange for a steady meal.
78
00:05:56,422 --> 00:05:59,157
They've given up their right
to choose a mate.
79
00:05:59,191 --> 00:06:02,193
Now the humans choose for them.
80
00:06:02,228 --> 00:06:06,298
They consistently kill off
the dogs that can't be trained;
81
00:06:06,332 --> 00:06:07,999
the ones that bite
the feeding hand.
82
00:06:08,034 --> 00:06:12,237
And they breed the dogs
that please them.
83
00:06:15,274 --> 00:06:18,376
They nurture those dogs
that do their bidding...
84
00:06:18,411 --> 00:06:21,580
hunting, herding,
guarding, hauling,
85
00:06:21,614 --> 00:06:22,681
and keeping them company.
86
00:06:22,715 --> 00:06:24,316
From every litter,
87
00:06:24,350 --> 00:06:27,319
the humans select the puppies
they like best.
88
00:06:27,353 --> 00:06:29,921
Over the generations,
the dogs evolve.
89
00:06:29,956 --> 00:06:34,226
This kind of evolution is
called "artificial selection"
90
00:06:34,260 --> 00:06:35,760
or "breeding."
91
00:06:35,795 --> 00:06:38,029
Turning wolves into dogs was
the first time
92
00:06:38,064 --> 00:06:41,199
we humans took evolution
into our own hands.
93
00:06:41,234 --> 00:06:43,335
And we've been doing it
ever since
94
00:06:43,369 --> 00:06:47,439
to shape all the plants
and animals that we depend on.
95
00:06:47,473 --> 00:06:51,610
In a blink of cosmic time,
just 15,000 or 20,000 years,
96
00:06:51,644 --> 00:06:55,046
we turned gray wolves into
all the kinds of dogs
97
00:06:55,081 --> 00:06:56,414
we love today.
98
00:06:56,449 --> 00:06:57,949
Think of it.
99
00:06:57,984 --> 00:06:59,951
Every breed of dog
you've ever seen
100
00:06:59,986 --> 00:07:02,754
was sculpted by human hands.
101
00:07:02,788 --> 00:07:06,258
Many of our best friends--
the most popular breeds--
102
00:07:06,292 --> 00:07:08,894
were created in only
the last few centuries.
103
00:07:11,797 --> 00:07:13,865
The awesome power of evolution
104
00:07:13,900 --> 00:07:15,467
transformed the ravenous wolf
105
00:07:15,501 --> 00:07:18,103
into the faithful shepherd...
106
00:07:18,137 --> 00:07:21,973
...who protects the herd
and drives the wolf away.
107
00:07:35,821 --> 00:07:39,124
Artificial selection turned
the wolf into the shepherd
108
00:07:39,158 --> 00:07:42,060
and the wild grasses
into wheat and corn.
109
00:07:42,094 --> 00:07:45,597
In fact, almost every plant
and animal that we eat today
110
00:07:45,631 --> 00:07:49,301
was bred from a wild,
less-edible ancestor.
111
00:07:49,335 --> 00:07:52,938
If artificial selection can work
such profound changes
112
00:07:52,972 --> 00:07:55,674
in only 10,000 or 15,000 years,
113
00:07:55,708 --> 00:07:57,842
what can natural selection do
114
00:07:57,877 --> 00:08:00,612
operating over
billions of years?
115
00:08:00,646 --> 00:08:05,917
The answer is all the beauty
and diversity of life.
116
00:08:05,952 --> 00:08:07,852
How does it work?
117
00:08:07,887 --> 00:08:12,958
Our Ship of the Imagination
can take us anywhere in space
118
00:08:12,992 --> 00:08:16,628
and time,
even to the hidden microcosmos,
119
00:08:16,662 --> 00:08:20,665
where one kind of life can be
transformed into another.
120
00:08:20,700 --> 00:08:22,634
Come with me.
121
00:08:29,428 --> 00:08:31,362
May not seem like it,
122
00:08:31,397 --> 00:08:33,264
but we've been living
in an ice age
123
00:08:33,299 --> 00:08:35,033
for the last two million years.
124
00:08:35,067 --> 00:08:37,602
This just happens to be
one of the long intermissions.
125
00:08:37,636 --> 00:08:39,404
For most of those
two million years,
126
00:08:39,438 --> 00:08:41,906
the climate has been cold
and dry.
127
00:08:41,941 --> 00:08:44,642
The North Polar ice cap extended
much farther south
128
00:08:44,677 --> 00:08:46,811
than it does today.
129
00:08:46,846 --> 00:08:50,215
In one of those long,
cold glacial periods
130
00:08:50,249 --> 00:08:53,118
when the winter sea ice
stretched from the North Pole
131
00:08:53,152 --> 00:08:55,620
all the way down
to what is now Los Angeles,
132
00:08:55,654 --> 00:09:00,358
great bears roamed the frozen
wastes of Ireland.
133
00:09:05,965 --> 00:09:08,733
This might look like
an ordinary bear,
134
00:09:08,767 --> 00:09:12,070
but something extraordinary
is happening inside her.
135
00:09:12,104 --> 00:09:15,573
Something that will give rise
to a new species.
136
00:09:15,608 --> 00:09:17,242
In order to see it,
137
00:09:17,276 --> 00:09:20,612
we'll need to descend down
to a much smaller scale,
138
00:09:20,646 --> 00:09:23,581
to the cellular level,
139
00:09:23,616 --> 00:09:26,851
so that we can explore
the bear's reproductive system.
140
00:09:30,356 --> 00:09:34,559
We'll take the subclavian
artery through the heart.
141
00:09:56,749 --> 00:09:58,883
Almost there.
142
00:10:05,357 --> 00:10:06,891
Those are some of her eggs.
143
00:10:06,926 --> 00:10:09,461
To see what's going on
in one of them,
144
00:10:09,495 --> 00:10:11,362
we'll have to get even smaller.
145
00:10:11,397 --> 00:10:14,766
We'll have to shrink down
to the molecular level.
146
00:10:17,369 --> 00:10:20,405
Our Ship of the Imagination
is now so small,
147
00:10:20,439 --> 00:10:24,342
you could fit a million of them
into a grain of sand.
148
00:10:24,376 --> 00:10:28,313
See those guys over there
strutting along those girders?
149
00:10:28,347 --> 00:10:31,583
They are proteins
called kinesin.
150
00:10:31,617 --> 00:10:34,319
These kinesin are part
of the transport crew
151
00:10:34,353 --> 00:10:37,155
that's busy moving cargo
around the cell.
152
00:10:37,189 --> 00:10:39,023
How alien they seem.
153
00:10:39,058 --> 00:10:42,827
And yet these tiny creatures--
and beings like them--
154
00:10:42,862 --> 00:10:47,565
are a part of every living cell,
including the ones inside you.
155
00:10:49,535 --> 00:10:52,203
If life has a sanctuary,
156
00:10:52,238 --> 00:10:56,074
it's here in the nucleus
which contains our DNA...
157
00:10:56,108 --> 00:10:59,778
the ancient scripture
of our genetic code.
158
00:10:59,812 --> 00:11:04,916
And it's written in a language
that all life can read.
159
00:11:11,390 --> 00:11:15,093
DNA is a molecule shaped
like a long twisted ladder
160
00:11:15,127 --> 00:11:17,262
or double helix.
161
00:11:17,296 --> 00:11:19,063
The rungs of the ladder are made
162
00:11:19,098 --> 00:11:21,399
of four different kinds
of smaller molecules.
163
00:11:21,433 --> 00:11:24,402
These are the letters
of the genetic alphabet.
164
00:11:24,436 --> 00:11:27,372
Particular arrangements
of those letters spell out
165
00:11:27,406 --> 00:11:29,808
the instructions
for all living things,
166
00:11:29,842 --> 00:11:33,244
telling them how to grow,
move, digest,
167
00:11:33,279 --> 00:11:36,748
sense the environment,
heal, reproduce.
168
00:11:36,782 --> 00:11:39,918
The DNA double helix
is a molecular machine
169
00:11:39,952 --> 00:11:43,988
with about 100 billion parts
called "atoms."
170
00:11:44,023 --> 00:11:47,592
There are as many atoms
in a single molecule of your DNA
171
00:11:47,626 --> 00:11:51,396
as there are stars
in a typical galaxy.
172
00:11:51,430 --> 00:11:53,498
The same is true for dogs
173
00:11:53,532 --> 00:11:56,100
and bears
174
00:11:56,135 --> 00:11:59,571
and every living thing.
175
00:11:59,605 --> 00:12:03,875
We are, each of us,
a little universe.
176
00:12:12,384 --> 00:12:15,286
The DNA message handed down
from cell to cell
177
00:12:15,321 --> 00:12:17,422
and from generation
to generation is copied
178
00:12:17,456 --> 00:12:19,157
with extreme care.
179
00:12:19,191 --> 00:12:23,761
The birth of a new DNA molecule
begins when an unwinding protein
180
00:12:23,796 --> 00:12:26,264
separates the two strands
of the double helix,
181
00:12:26,298 --> 00:12:28,166
breaking the rungs apart.
182
00:12:28,200 --> 00:12:30,502
Inside the liquid
of the nucleus,
183
00:12:30,536 --> 00:12:34,439
the molecular letters of
the genetic code float freely.
184
00:12:34,473 --> 00:12:37,842
Each strand of the helix
copies its lost partner,
185
00:12:37,877 --> 00:12:40,845
resulting in two identical
DNA molecules.
186
00:12:40,880 --> 00:12:43,882
That's how life reproduces
genes and transmits them
187
00:12:43,916 --> 00:12:45,950
from one generation
to the next.
188
00:12:45,985 --> 00:12:48,553
When a living cell divides
in two,
189
00:12:48,587 --> 00:12:53,057
each one takes away with it
a complete copy of the DNA.
190
00:12:53,092 --> 00:12:56,828
A specialized protein
proofreads to make sure
191
00:12:56,862 --> 00:12:58,663
that only the right letters
are accepted
192
00:12:58,697 --> 00:13:01,533
so that the DNA
is accurately copied.
193
00:13:01,567 --> 00:13:03,301
But nobody's perfect.
194
00:13:03,335 --> 00:13:06,504
Occasionally, a proofreading
error slips through,
195
00:13:06,539 --> 00:13:10,308
making a small, random change
in the genetic instructions.
196
00:13:10,342 --> 00:13:13,545
A mutation has occurred
in the bear's egg cell.
197
00:13:13,579 --> 00:13:17,482
A random event as tiny as
this one can have consequences
198
00:13:17,516 --> 00:13:19,751
on a far grander scale.
199
00:13:21,787 --> 00:13:26,591
That mutation altered the gene
that controls fur color.
200
00:13:26,625 --> 00:13:29,594
It will affect the production
of dark pigment in the fur
201
00:13:29,628 --> 00:13:31,596
of the bear's offspring.
202
00:13:31,630 --> 00:13:33,898
Most mutations are harmless.
203
00:13:33,933 --> 00:13:35,667
Some are deadly.
204
00:13:35,701 --> 00:13:38,570
But a few, purely by chance,
can give an organism
205
00:13:38,604 --> 00:13:42,273
a critical advantage
over the competition.
206
00:13:42,308 --> 00:13:44,275
A year has passed.
207
00:13:44,310 --> 00:13:46,110
Our bear is now a mother.
208
00:13:46,145 --> 00:13:47,846
And as a result
of that mutation,
209
00:13:47,880 --> 00:13:51,516
one of her two cubs was born
with a white coat.
210
00:13:51,550 --> 00:13:54,252
When the cubs get old enough
to venture out on their own,
211
00:13:54,286 --> 00:13:56,554
which bear is more likely
212
00:13:56,589 --> 00:14:00,758
to be able to sneak up
on unsuspecting prey?
213
00:14:00,793 --> 00:14:04,028
The brown bear can be seen
against the snow a mile away.
214
00:14:04,063 --> 00:14:06,931
The white bear prospers
and passes on
215
00:14:06,966 --> 00:14:08,900
its own particular set
of genes.
216
00:14:08,934 --> 00:14:11,769
This happens repeatedly.
217
00:14:11,804 --> 00:14:13,938
Over succeeding generations,
218
00:14:13,973 --> 00:14:16,541
the gene for white fur
spreads through
219
00:14:16,575 --> 00:14:19,210
the entire population
of Arctic bears.
220
00:14:19,245 --> 00:14:21,946
The gene for dark fur loses out
221
00:14:21,981 --> 00:14:24,749
in the competition
for survival.
222
00:14:26,752 --> 00:14:30,622
Mutations are entirely random
and happen all the time.
223
00:14:30,656 --> 00:14:32,590
But the environment
rewards those
224
00:14:32,625 --> 00:14:34,893
that increase the chance
for survival.
225
00:14:34,927 --> 00:14:37,295
It naturally selects
the living things
226
00:14:37,329 --> 00:14:39,964
that are better suited
to survive.
227
00:14:39,999 --> 00:14:42,800
And that selection
is the opposite of random.
228
00:14:45,638 --> 00:14:48,106
The two populations of bears
separated,
229
00:14:48,140 --> 00:14:49,974
and over thousands of years,
230
00:14:50,009 --> 00:14:53,144
evolved other characteristics
that set them apart.
231
00:14:53,179 --> 00:14:56,381
They became different species.
232
00:14:58,784 --> 00:15:00,852
That's what
Charles Darwin meant
233
00:15:00,886 --> 00:15:04,522
by "the origin of species."
234
00:15:04,557 --> 00:15:07,091
An individual bear
doesn't evolve;
235
00:15:07,126 --> 00:15:11,029
the population of bears evolves
over generations.
236
00:15:12,731 --> 00:15:14,799
If the Arctic ice
continues to dwindle
237
00:15:14,834 --> 00:15:18,503
due to global warming,
the polar bears may go extinct.
238
00:15:18,537 --> 00:15:20,538
They'll be replaced
by brown bears,
239
00:15:20,573 --> 00:15:23,708
better adapted to
the now defrosted environment.
240
00:15:23,742 --> 00:15:28,213
This is a different story
from the one about the dogs.
241
00:15:28,247 --> 00:15:30,715
No breeder guided these changes.
242
00:15:30,749 --> 00:15:34,219
Instead, the environment itself
selects them.
243
00:15:34,253 --> 00:15:36,888
This is evolution
by natural selection,
244
00:15:36,922 --> 00:15:40,692
the most revolutionary concept
in the history of science.
245
00:15:40,726 --> 00:15:44,863
Darwin first presented the
evidence for this idea in 1859.
246
00:15:44,897 --> 00:15:48,900
The uproar it caused
has never subsided.
247
00:15:48,934 --> 00:15:50,935
Why?
248
00:15:58,230 --> 00:16:00,331
We all understand
the twinge of discomfort
249
00:16:00,366 --> 00:16:03,601
at the thought that we share
a common ancestor with the apes.
250
00:16:03,636 --> 00:16:06,971
No one can embarrass you
like a relative.
251
00:16:07,006 --> 00:16:09,174
Our closest ones,
the chimpanzees,
252
00:16:09,208 --> 00:16:11,843
they frequently behave
inappropriately in public.
253
00:16:11,877 --> 00:16:14,112
There's an understandable
human need
254
00:16:14,146 --> 00:16:16,347
to distance ourselves
from them.
255
00:16:16,382 --> 00:16:18,616
A central premise
of traditional belief
256
00:16:18,651 --> 00:16:20,618
is that we were
created separately
257
00:16:20,653 --> 00:16:22,620
from all the other animals.
258
00:16:22,655 --> 00:16:25,390
It's easy to see why
this idea has taken hold.
259
00:16:25,424 --> 00:16:28,226
It makes us feel... special.
260
00:16:28,260 --> 00:16:32,330
But what about our kinship
with the trees?
261
00:16:32,364 --> 00:16:34,766
How does that make you feel?
262
00:16:42,441 --> 00:16:45,677
Okay, here's a segment
of the oak tree's DNA.
263
00:16:45,711 --> 00:16:47,846
Think of it like a bar code.
264
00:16:47,880 --> 00:16:50,482
The instructions written
in the code of life
265
00:16:50,516 --> 00:16:53,485
tell the tree
how to metabolize sugar.
266
00:16:53,519 --> 00:16:56,788
Now let's compare it with
the same section of my own DNA.
267
00:17:02,027 --> 00:17:03,928
The DNA doesn't lie.
268
00:17:03,963 --> 00:17:07,265
This tree and me--
we're long-lost cousins.
269
00:17:07,299 --> 00:17:09,267
And it's not just the trees.
270
00:17:09,301 --> 00:17:12,170
If you go back far enough,
you'll find that we share
271
00:17:12,204 --> 00:17:14,205
a common ancestor with...
272
00:17:14,240 --> 00:17:15,540
the butterfly...
273
00:17:15,574 --> 00:17:17,175
gray wolf...
274
00:17:17,209 --> 00:17:18,576
mushroom...
275
00:17:18,611 --> 00:17:20,211
shark...
276
00:17:20,246 --> 00:17:21,679
bacterium...
277
00:17:21,714 --> 00:17:23,014
sparrow.
278
00:17:23,048 --> 00:17:24,582
What a family!
279
00:17:24,617 --> 00:17:28,119
Other parts of the bar code vary
from species to species.
280
00:17:28,154 --> 00:17:31,356
That's what makes the difference
between an owl and an octopus.
281
00:17:31,390 --> 00:17:33,591
Unless you have
an identical twin,
282
00:17:33,626 --> 00:17:35,894
there's no one else
in the universe
283
00:17:35,928 --> 00:17:38,563
with the exact same DNA as you.
284
00:17:38,597 --> 00:17:40,799
Within other species,
the genetic differences
285
00:17:40,833 --> 00:17:44,202
provide the raw material
for natural selection.
286
00:17:44,236 --> 00:17:48,139
The environment selects which
genes survive and multiply.
287
00:17:48,174 --> 00:17:50,308
When it comes
to the genetic instructions
288
00:17:50,342 --> 00:17:52,310
for life's
most basic functions--
289
00:17:52,344 --> 00:17:55,113
say, digesting sugars--
we and other species
290
00:17:55,147 --> 00:17:57,148
are almost identical.
291
00:17:57,183 --> 00:18:00,285
That's because those functions
are so basic to life,
292
00:18:00,319 --> 00:18:03,221
they evolved before
the various life-forms
293
00:18:03,255 --> 00:18:05,223
branched off from each other.
294
00:18:05,257 --> 00:18:07,692
This is our Tree of Life.
295
00:18:07,726 --> 00:18:09,227
Science has made it possible
296
00:18:09,261 --> 00:18:11,396
for us to construct
this family tree
297
00:18:11,430 --> 00:18:13,398
for all the species
of life on Earth.
298
00:18:13,432 --> 00:18:17,235
Close genetic relatives occupy
the same branch of the tree,
299
00:18:17,269 --> 00:18:20,872
while more distant cousins
are farther away.
300
00:18:20,906 --> 00:18:23,074
Each twig is a living species.
301
00:18:25,077 --> 00:18:28,246
And the trunk of the tree
represents the common ancestors
302
00:18:28,280 --> 00:18:31,082
of all life on Earth.
303
00:18:31,116 --> 00:18:33,485
The stuff of life
is so malleable
304
00:18:33,519 --> 00:18:36,454
that once it got started,
the environment molded it
305
00:18:36,489 --> 00:18:39,757
into a staggering
variety of forms--
306
00:18:39,792 --> 00:18:43,595
10,000 times more than
we can possibly show here.
307
00:18:45,598 --> 00:18:47,732
Biologists have catalogued
308
00:18:47,766 --> 00:18:51,269
a half a million different
kinds of beetles alone.
309
00:18:53,973 --> 00:18:56,574
Not to mention
the numberless varieties
310
00:18:56,609 --> 00:18:58,243
of bacteria.
311
00:18:58,277 --> 00:19:00,612
There are many millions
of living species
312
00:19:00,646 --> 00:19:03,014
of animals and plants,
most of them
313
00:19:03,048 --> 00:19:05,416
still unknown to science.
314
00:19:05,451 --> 00:19:08,520
Think of that--
we have yet to make contact
315
00:19:08,554 --> 00:19:11,856
with most of the forms
of terrestrial life.
316
00:19:11,891 --> 00:19:14,292
That's how many kinds
of life there are
317
00:19:14,326 --> 00:19:16,060
on this tiny planet alone.
318
00:19:18,063 --> 00:19:20,598
The Tree of Life extends
its feelers in all directions,
319
00:19:20,633 --> 00:19:22,200
finding and exploiting
what works,
320
00:19:22,234 --> 00:19:23,935
creating new environments
321
00:19:23,969 --> 00:19:26,204
and opportunities
for new forms.
322
00:19:28,374 --> 00:19:33,111
The Tree of Life is three
and a half billion years old.
323
00:19:33,145 --> 00:19:35,313
That's plenty of time
to develop
324
00:19:35,347 --> 00:19:38,516
an impressive repertoire
of tricks.
325
00:19:40,920 --> 00:19:43,555
Evolution can
disguise an animal
326
00:19:43,589 --> 00:19:46,024
as a plant...
327
00:19:50,529 --> 00:19:52,497
...taking thousands
of generations
328
00:19:52,531 --> 00:19:55,667
to contrive
an elaborate costume
329
00:19:55,701 --> 00:19:57,569
that fools predators
into looking elsewhere
330
00:19:57,603 --> 00:20:00,071
for someone to eat.
331
00:20:00,105 --> 00:20:04,075
Or it can disguise a plant
as an animal,
332
00:20:04,109 --> 00:20:07,212
evolving blossoms that take on
the appearance of a wasp--
333
00:20:07,246 --> 00:20:11,249
the orchid's way of fooling
real wasps into pollinating it.
334
00:20:12,284 --> 00:20:14,352
This is the awesome
335
00:20:14,386 --> 00:20:17,789
shape-shifting power
of natural selection.
336
00:20:24,530 --> 00:20:29,200
Among the dense, tangled limbs
of the vast Tree of Life...
337
00:20:29,235 --> 00:20:31,369
you are here.
338
00:20:31,403 --> 00:20:35,673
One tiny branch
among countless millions.
339
00:20:35,708 --> 00:20:40,712
Science reveals that all life
on Earth is one.
340
00:20:43,382 --> 00:20:46,551
Darwin discovered the actual
mechanisof evolution.
341
00:20:46,585 --> 00:20:49,587
The prevailing belief
was that the complexity
342
00:20:49,622 --> 00:20:52,257
and variety of life
must be the work
343
00:20:52,291 --> 00:20:55,226
of an intelligent designer,
who created each
344
00:20:55,261 --> 00:20:58,396
of these millions
of different species separately.
345
00:20:58,430 --> 00:21:01,900
Living things are just
too intricate, it was said,
346
00:21:01,934 --> 00:21:05,470
to be the result
of unguided evolution.
347
00:21:05,504 --> 00:21:07,939
Consider the human eye,
348
00:21:07,973 --> 00:21:10,208
a masterpiece of complexity.
349
00:21:13,879 --> 00:21:15,980
It requires a cornea,
350
00:21:16,015 --> 00:21:19,450
iris, lens, retina,
351
00:21:19,485 --> 00:21:21,853
optic nerves, muscles,
352
00:21:21,887 --> 00:21:24,589
let alone the brain's
elaborate neural network
353
00:21:24,623 --> 00:21:27,525
to interpret images.
354
00:21:27,560 --> 00:21:30,428
It's more complicated
than any device
355
00:21:30,462 --> 00:21:33,531
ever crafted
by human intelligence.
356
00:21:33,566 --> 00:21:35,200
Therefore, it was argued,
357
00:21:35,234 --> 00:21:37,268
the human eye
can't be the result
358
00:21:37,303 --> 00:21:39,604
of mindless evolution.
359
00:21:39,638 --> 00:21:43,641
To know if that's true,
we need to travel across time
360
00:21:43,676 --> 00:21:47,312
to a world before
there were eyes to see.
361
00:22:03,821 --> 00:22:06,389
In the beginning,
362
00:22:06,423 --> 00:22:08,024
life was blind.
363
00:22:10,094 --> 00:22:12,228
This is what
our world looked like
364
00:22:12,262 --> 00:22:14,230
four billion years ago,
365
00:22:14,264 --> 00:22:17,900
before there were
any eyes to see.
366
00:22:17,935 --> 00:22:20,970
Until a few hundred million
years passed,
367
00:22:21,004 --> 00:22:22,605
and then, one day,
368
00:22:22,639 --> 00:22:24,674
there was a microscopic
copying error
369
00:22:24,708 --> 00:22:26,242
in the DNA of a bacterium.
370
00:22:26,276 --> 00:22:28,978
This random mutation
gave that microbe
371
00:22:29,012 --> 00:22:31,781
a protein molecule
that absorbed sunlight.
372
00:22:31,815 --> 00:22:33,616
Want to know what
the world looked like
373
00:22:33,650 --> 00:22:35,318
to a light-sensitive bacterium?
374
00:22:35,352 --> 00:22:38,621
Take a look at the right side
of the screen.
375
00:22:38,655 --> 00:22:42,258
Mutations continued
to occur at random,
376
00:22:42,292 --> 00:22:45,528
as they always do in any
population of living things.
377
00:22:47,531 --> 00:22:49,632
Another mutation
378
00:22:49,666 --> 00:22:53,603
caused a dark bacterium
to flee intense light.
379
00:22:53,637 --> 00:22:56,005
What is going on here?
380
00:22:56,039 --> 00:22:57,774
Night and day.
381
00:22:57,808 --> 00:22:59,809
Those bacteria that could
tell light from dark
382
00:22:59,843 --> 00:23:02,478
had a decisive advantage
over the ones that couldn't.
383
00:23:02,513 --> 00:23:04,313
Why?
384
00:23:04,348 --> 00:23:07,483
Because the daytime brought
harsh, ultraviolet light
385
00:23:07,518 --> 00:23:09,452
that damages DNA.
386
00:23:09,486 --> 00:23:13,022
The sensitive bacteria
fled the intense light
387
00:23:13,057 --> 00:23:15,558
to safely exchange
their DNA in the dark.
388
00:23:15,592 --> 00:23:17,493
They survived
in greater numbers
389
00:23:17,528 --> 00:23:19,962
than the bacteria that
stayed at the surface.
390
00:23:19,997 --> 00:23:23,066
Over time, those
light-sensitive proteins
391
00:23:23,100 --> 00:23:25,701
became concentrated
in a pigment spot
392
00:23:25,736 --> 00:23:29,005
on the more advanced,
one-celled organism.
393
00:23:29,039 --> 00:23:32,208
This made it possible
to find the light,
394
00:23:32,242 --> 00:23:34,343
an overwhelming advantage
395
00:23:34,378 --> 00:23:37,680
for an organism that harvests
sunlight to make food.
396
00:23:44,788 --> 00:23:47,690
Here's a flatworm's-eye view
of the world.
397
00:23:47,724 --> 00:23:49,859
This multi-celled organism
398
00:23:49,893 --> 00:23:52,195
evolved a dimple
in the pigment spot.
399
00:23:52,229 --> 00:23:54,497
The bowl-shaped depression
400
00:23:54,531 --> 00:23:57,867
allowed the animal to
distinguish light from shadow
401
00:23:57,901 --> 00:24:01,237
to crudely make out objects
in its vicinity,
402
00:24:01,271 --> 00:24:05,274
including those to eat
and those that might eat it...
403
00:24:05,309 --> 00:24:07,844
a tremendous advantage.
404
00:24:07,878 --> 00:24:10,513
Later, things became
a little clearer.
405
00:24:10,547 --> 00:24:12,248
The dimple deepened
406
00:24:12,282 --> 00:24:15,017
and evolved into a socket
with a small opening.
407
00:24:15,052 --> 00:24:17,386
Over thousands of generations,
408
00:24:17,421 --> 00:24:20,623
natural selection
was slowly sculpting the eye.
409
00:24:22,426 --> 00:24:25,561
The opening contracted
to a pinhole covered
410
00:24:25,596 --> 00:24:27,897
by a protective
transparent membrane.
411
00:24:27,931 --> 00:24:30,399
Only a little light
could enter the tiny hole,
412
00:24:30,434 --> 00:24:32,802
but it was enough
to paint a dim image
413
00:24:32,836 --> 00:24:35,371
on the sensitive inner surface
of the eye.
414
00:24:35,406 --> 00:24:37,273
This sharpened the focus.
415
00:24:37,307 --> 00:24:39,609
A larger opening
would have let in more light
416
00:24:39,643 --> 00:24:43,212
to make a brighter image
but one that was out of focus.
417
00:24:43,247 --> 00:24:46,115
This development launched
the visual equivalent
418
00:24:46,150 --> 00:24:48,785
of an arms race.
419
00:24:59,196 --> 00:25:03,766
The competition needed
to keep up to survive.
420
00:25:03,801 --> 00:25:07,503
But then a splendid new feature
of the eye evolved,
421
00:25:07,538 --> 00:25:12,508
a lens that provided both
brightness and sharp focus.
422
00:25:12,543 --> 00:25:14,944
In the eyes of primitive fish,
423
00:25:14,978 --> 00:25:18,681
the transparent gel near
the pinhole formed into a lens.
424
00:25:18,715 --> 00:25:21,451
At the same time,
the pinhole enlarged
425
00:25:21,485 --> 00:25:23,519
to let in more and more light.
426
00:25:23,554 --> 00:25:25,955
Fish could now see in high-def,
427
00:25:25,989 --> 00:25:29,692
both close up and far away.
428
00:25:29,726 --> 00:25:33,329
And then
something terrible happened.
429
00:25:33,363 --> 00:25:36,833
Have you ever noticed that
a straw in a glass of water
430
00:25:36,867 --> 00:25:39,335
looks bent at the surface
of the water?
431
00:25:39,369 --> 00:25:42,105
That's because light bends
when it goes from one medium
432
00:25:42,139 --> 00:25:45,007
to another,
say from water to air.
433
00:25:45,042 --> 00:25:48,778
Our eyes originally evolved
to see in water.
434
00:25:48,812 --> 00:25:51,681
The watery fluid
in those eyes neatly
435
00:25:51,715 --> 00:25:55,485
eliminated the distortion
of that bending effect.
436
00:25:56,487 --> 00:25:58,654
But for land animals,
437
00:25:58,689 --> 00:26:01,057
the light carries images
from dry air
438
00:26:01,091 --> 00:26:04,160
into their still-watery eyes.
439
00:26:04,194 --> 00:26:05,728
That bends the light rays,
440
00:26:05,763 --> 00:26:09,732
causing all kinds
of distortions.
441
00:26:09,767 --> 00:26:12,502
When our amphibious ancestors
left the water for the land,
442
00:26:12,536 --> 00:26:15,738
their eyes, exquisitely evolved
to see in water,
443
00:26:15,773 --> 00:26:18,074
were lousy for seeing
in the air.
444
00:26:18,108 --> 00:26:20,743
Our vision has never been
as good since.
445
00:26:20,778 --> 00:26:23,679
We like to think of our eyes
as state-of-the-art,
446
00:26:23,714 --> 00:26:26,582
but 375 million years later,
447
00:26:26,617 --> 00:26:29,018
we still can't see things
right in front of our noses
448
00:26:29,052 --> 00:26:31,687
or discern fine details
in near darkness
449
00:26:31,722 --> 00:26:33,589
the way fish can.
450
00:26:33,624 --> 00:26:35,091
When we left the water,
451
00:26:35,125 --> 00:26:37,260
why didn't nature
just start over again
452
00:26:37,294 --> 00:26:38,895
and evolve us a new set of eyes
453
00:26:38,929 --> 00:26:41,230
that were optimal
for seeing in the air?
454
00:26:41,265 --> 00:26:43,332
Nature doesn't work that way.
455
00:26:43,367 --> 00:26:46,736
Evolution reshapes existing
structures over generations,
456
00:26:46,770 --> 00:26:48,938
adapting them
with small changes.
457
00:26:48,972 --> 00:26:50,606
It can't just go back
to the drawing board
458
00:26:50,641 --> 00:26:52,442
and start from scratch.
459
00:26:52,476 --> 00:26:56,012
At every stage of its
development, the evolving eye
460
00:26:56,046 --> 00:26:57,747
functioned well enough
461
00:26:57,781 --> 00:27:00,917
to provide a selective
advantage for survival.
462
00:27:00,951 --> 00:27:03,786
And among animals alive today,
we find eyes
463
00:27:03,821 --> 00:27:06,989
at all these stages
of development.
464
00:27:10,260 --> 00:27:13,563
And all of them function.
465
00:27:13,597 --> 00:27:15,731
The complexity
of the human eye poses
466
00:27:15,766 --> 00:27:17,867
no challenge to evolution
by natural selection.
467
00:27:17,901 --> 00:27:22,371
In fact, the eye and all
of biology makes no sense
468
00:27:22,406 --> 00:27:24,040
without evolution.
469
00:27:24,074 --> 00:27:26,709
Some claim that evolution
is just a theory,
470
00:27:26,743 --> 00:27:29,912
as if it were merely
an opinion.
471
00:27:29,947 --> 00:27:32,648
The theory of evolution,
like the theory of gravity,
472
00:27:32,683 --> 00:27:34,751
is a scientific fact.
473
00:27:34,785 --> 00:27:37,487
Evolution really happened.
474
00:27:37,521 --> 00:27:39,922
Accepting our kinship
with all life on Earth
475
00:27:39,957 --> 00:27:41,991
is not only solid science.
476
00:27:42,025 --> 00:27:47,196
In my view, it's also
a soaring spiritual experience.
477
00:27:53,971 --> 00:27:56,806
Because evolution is blind,
478
00:27:56,840 --> 00:28:01,077
it cannot anticipate or adapt
to catastrophic events.
479
00:28:01,111 --> 00:28:04,914
The Tree of Life
has some broken branches.
480
00:28:04,948 --> 00:28:08,417
Many of them were severed in
the five greatest catastrophes
481
00:28:08,452 --> 00:28:09,986
that life has ever known.
482
00:28:10,320 --> 00:28:12,288
Somewhere, there's a memorial
483
00:28:12,322 --> 00:28:15,291
to the multitude
of lost species,
484
00:28:15,325 --> 00:28:17,460
the Halls of Extinction.
485
00:28:17,494 --> 00:28:19,929
Come with me.
486
00:28:28,295 --> 00:28:31,495
_
487
00:28:31,630 --> 00:28:34,870
Welcome to the
Halls of Extinction.
488
00:28:35,657 --> 00:28:39,554
A monument to the broken branches
of the Tree of Life.
489
00:28:49,463 --> 00:28:53,166
For every single one
of the millions of species
490
00:28:53,200 --> 00:28:57,437
alive today, perhaps
a thousand others have perished.
491
00:28:57,471 --> 00:28:59,939
Most of them died out
in the everyday competition
492
00:28:59,974 --> 00:29:01,508
with other life-forms.
493
00:29:01,542 --> 00:29:05,111
But many of them were swept away
in vast cataclysms
494
00:29:05,146 --> 00:29:07,347
that overwhelmed the planet.
495
00:29:07,381 --> 00:29:09,782
In the last 500 million years,
496
00:29:09,817 --> 00:29:12,485
this has happened five times.
497
00:29:12,520 --> 00:29:17,690
Five mass extinctions
that devastated life on Earth.
498
00:29:17,725 --> 00:29:22,962
The worst one of all happened
some 250 million years ago,
499
00:29:22,997 --> 00:29:25,532
at the end of an era
500
00:29:25,566 --> 00:29:28,001
known as the Permian.
501
00:29:44,385 --> 00:29:47,120
Trilobites were
armored animals that hunted
502
00:29:47,154 --> 00:29:49,622
in great herds
across the seafloor.
503
00:29:49,657 --> 00:29:52,325
They were among
the first animals to evolve
504
00:29:52,359 --> 00:29:54,761
image-forming eyes.
505
00:29:57,331 --> 00:30:01,334
Trilobites had a good long run,
some 270 million years.
506
00:30:01,368 --> 00:30:04,904
Earth was once
the planet of the trilobites.
507
00:30:04,939 --> 00:30:08,341
But now they're all gone,
extinct.
508
00:30:08,375 --> 00:30:11,077
The last of them were swept
from life's stage
509
00:30:11,111 --> 00:30:13,179
along with countless
other species
510
00:30:13,214 --> 00:30:17,417
in an unparalleled
environmental disaster.
511
00:30:25,960 --> 00:30:29,562
The apocalypse
began in what is now Siberia,
512
00:30:29,597 --> 00:30:34,234
with volcanic eruptions
on a scale unlike anything
513
00:30:34,268 --> 00:30:36,436
in human experience.
514
00:30:48,883 --> 00:30:51,417
Earth was very different then,
515
00:30:51,452 --> 00:30:55,755
with one single supercontinent
and one great ocean.
516
00:30:55,789 --> 00:30:58,258
Relentless floods of fiery lava
517
00:30:58,292 --> 00:31:01,060
engulfed an area larger than
Western Europe.
518
00:31:01,095 --> 00:31:03,763
The pulsing eruptions
went on for hundreds
519
00:31:03,797 --> 00:31:05,932
of thousands of years.
520
00:31:05,966 --> 00:31:07,534
The molten rock
521
00:31:07,568 --> 00:31:10,270
ignited coal deposits
and polluted the air
522
00:31:10,304 --> 00:31:13,273
with carbon dioxide
and other greenhouse gases.
523
00:31:13,307 --> 00:31:15,208
This heated the Earth
524
00:31:15,242 --> 00:31:18,344
and stopped the ocean currents
from circulating.
525
00:31:33,360 --> 00:31:35,662
Noxious bacteria bloomed,
526
00:31:35,696 --> 00:31:39,832
but nearly everything else
in the seas died.
527
00:31:39,867 --> 00:31:43,436
The stagnant waters belched
deadly hydrogen sulfide gas
528
00:31:43,470 --> 00:31:44,904
into the air,
529
00:31:44,939 --> 00:31:47,473
which suffocated most
of the land animals.
530
00:32:00,487 --> 00:32:04,824
Nine in ten of all species
on the planet went extinct.
531
00:32:04,859 --> 00:32:06,926
We call it...
532
00:32:06,961 --> 00:32:08,962
The Great Dying.
533
00:32:21,575 --> 00:32:24,210
Life on Earth came so near
to being wiped out
534
00:32:24,245 --> 00:32:28,047
that it took more than
ten million years to recover.
535
00:32:28,082 --> 00:32:30,383
But new life-forms
slowly evolved
536
00:32:30,417 --> 00:32:34,087
to fill the openings left
by the Permian holocaust.
537
00:32:41,862 --> 00:32:44,731
Among the biggest winners
were the dinosaurs.
538
00:32:44,765 --> 00:32:47,567
Now the Earth was their planet.
539
00:32:47,601 --> 00:32:51,838
Their reign continued
for over 150 million years.
540
00:32:51,872 --> 00:32:54,474
Until it, too,
came crashing down
541
00:32:54,508 --> 00:32:57,410
in another mass extinction.
542
00:32:57,444 --> 00:33:00,046
Life on Earth has taken quite
a beating over the eons.
543
00:33:00,080 --> 00:33:02,882
And yet it's still there.
544
00:33:02,917 --> 00:33:05,718
The tenacity of life
is mind-boggling.
545
00:33:05,753 --> 00:33:08,555
We keep finding it where
no one thought it could be.
546
00:33:13,027 --> 00:33:16,329
That nameless corridor?
547
00:33:16,363 --> 00:33:18,364
That's for another day.
548
00:33:23,871 --> 00:33:27,440
I know an animal that can live
in boiling water
549
00:33:27,474 --> 00:33:29,609
or in solid ice.
550
00:33:29,643 --> 00:33:32,011
It can go ten years
without a drop of water.
551
00:33:32,046 --> 00:33:34,681
It can travel naked
in the cold vacuum
552
00:33:34,715 --> 00:33:39,219
and intense radiation of space
and will return unscathed.
553
00:33:39,253 --> 00:33:41,688
The tardigrade, or water bear.
554
00:33:41,722 --> 00:33:44,791
It's equally at home
atop the tallest mountains
555
00:33:44,825 --> 00:33:46,626
and in the deepest trenches
of the sea.
556
00:33:46,660 --> 00:33:49,696
And in our own backyards,
where they live among the moss
557
00:33:49,730 --> 00:33:52,198
in countless numbers.
558
00:33:52,233 --> 00:33:53,600
You've probably
never noticed them
559
00:33:53,634 --> 00:33:55,101
because they're so small.
560
00:33:55,135 --> 00:33:56,736
About the size of a pinpoint.
561
00:33:56,770 --> 00:33:58,471
But they're tough.
562
00:33:58,505 --> 00:34:02,775
The tardigrades have survived
all five mass extinctions.
563
00:34:02,810 --> 00:34:05,545
They've been in business
for a half a billion years.
564
00:34:05,579 --> 00:34:07,914
We used to think
that life was finicky,
565
00:34:07,948 --> 00:34:09,883
that it would only take hold
where it was
566
00:34:09,917 --> 00:34:11,885
not too hot, not too cold,
567
00:34:11,919 --> 00:34:15,655
not too dark or salty
or acidic or radioactive.
568
00:34:15,689 --> 00:34:18,458
And whatever you do,
don't forget to add water.
569
00:34:18,492 --> 00:34:20,226
We were wrong.
570
00:34:20,261 --> 00:34:21,561
As the hardy tardigrade
demonstrates,
571
00:34:21,595 --> 00:34:23,763
life can endure conditions
572
00:34:23,797 --> 00:34:27,000
that would mean certain death
for us humans.
573
00:34:27,034 --> 00:34:28,835
But differences between us
and life found
574
00:34:28,869 --> 00:34:31,404
in even the most extreme
environments on our planet
575
00:34:31,438 --> 00:34:34,407
are only variations
on a single theme,
576
00:34:34,441 --> 00:34:36,976
dialects of a single language.
577
00:34:37,011 --> 00:34:39,779
The genetic code of Earth life.
578
00:34:44,718 --> 00:34:47,253
But what would life be like
on other worlds?
579
00:34:47,288 --> 00:34:50,290
Worlds with a completely
different history,
580
00:34:50,324 --> 00:34:53,326
chemistry and evolution
from our planet?
581
00:34:55,796 --> 00:34:59,332
There's a distant world
I want to take you to--
582
00:34:59,366 --> 00:35:01,768
a world far different
from our own,
583
00:35:01,802 --> 00:35:05,138
but one that may harbor life.
584
00:35:05,172 --> 00:35:09,042
If it does, it promises
to be unlike anything
585
00:35:09,076 --> 00:35:11,511
we've ever seen before.
586
00:35:27,124 --> 00:35:30,493
Clouds and haze completely hide
the surface of Titan,
587
00:35:30,527 --> 00:35:32,495
Saturn's giant moon.
588
00:35:32,529 --> 00:35:35,097
Titan reminds me
a little bit of home.
589
00:35:35,132 --> 00:35:38,601
Like Earth, it has an atmosphere
that's mostly nitrogen.
590
00:35:38,635 --> 00:35:40,769
But it's four times denser.
591
00:35:40,804 --> 00:35:43,672
Titan's air has
no oxygen at all.
592
00:35:43,707 --> 00:35:46,175
And it's far colder
than anywhere on Earth.
593
00:35:46,209 --> 00:35:49,812
But still...
I want to go there.
594
00:35:50,981 --> 00:35:53,482
We have to descend
595
00:35:53,517 --> 00:35:55,951
through a couple hundred
kilometers of smog
596
00:35:55,986 --> 00:35:58,954
before we can even
see the surface.
597
00:35:58,989 --> 00:36:02,525
But hidden beneath lies
a weirdly familiar landscape.
598
00:36:10,233 --> 00:36:13,669
Titan is the only other world
in the solar system
599
00:36:13,703 --> 00:36:15,137
where it ever rains.
600
00:36:15,172 --> 00:36:18,574
It has rivers and coastlines.
601
00:36:23,513 --> 00:36:25,581
Titan has hundreds of lakes.
602
00:36:25,615 --> 00:36:29,151
One of them larger than
Lake Superior in North America.
603
00:36:29,186 --> 00:36:31,153
Vapor rising from the lakes
604
00:36:31,188 --> 00:36:33,389
condenses and falls again
as rain.
605
00:36:33,423 --> 00:36:37,326
The rain feeds rivers,
606
00:36:37,360 --> 00:36:40,663
which carve valleys
into the landscape,
607
00:36:40,697 --> 00:36:42,698
just like on Earth.
608
00:36:44,968 --> 00:36:47,036
But with one big difference.
609
00:36:47,070 --> 00:36:49,772
On Titan, the seas and the rain
610
00:36:49,806 --> 00:36:53,709
are made not of water
but of methane and ethane.
611
00:36:53,743 --> 00:36:56,679
On Earth, those molecules
form natural gas.
612
00:36:56,713 --> 00:36:59,548
On frigid Titan,
613
00:36:59,583 --> 00:37:01,584
they're liquid.
614
00:37:06,890 --> 00:37:08,891
Titan has lots of water,
615
00:37:08,925 --> 00:37:11,627
but all of it is frozen
hard as rock.
616
00:37:11,661 --> 00:37:14,029
In fact, the landscape
and mountains
617
00:37:14,064 --> 00:37:16,532
are made mainly of water ice.
618
00:37:16,566 --> 00:37:18,767
At hundreds of degrees
below zero,
619
00:37:18,802 --> 00:37:22,705
Titan is far too cold
for water to ever be liquid.
620
00:37:24,941 --> 00:37:28,144
Astrobiologists since
Carl Sagan have wondered
621
00:37:28,178 --> 00:37:31,614
if life might swim
in Titan's hydrocarbon lakes.
622
00:37:33,950 --> 00:37:35,885
The chemical basis for such life
623
00:37:35,919 --> 00:37:39,321
would have to be entirely
different from anything we know.
624
00:37:39,356 --> 00:37:42,158
All life on Earth
depends on liquid water.
625
00:37:42,192 --> 00:37:44,493
And Titan's surface
has none of that.
626
00:37:44,528 --> 00:37:47,062
But we can imagine
other kinds of life.
627
00:37:47,097 --> 00:37:49,665
There might be creatures
that inhale hydrogen
628
00:37:49,699 --> 00:37:51,167
instead of oxygen.
629
00:37:51,201 --> 00:37:54,670
And exhale methane
instead of carbon dioxide.
630
00:37:54,704 --> 00:37:58,140
They might use acetylene instead
of sugar as an energy source.
631
00:37:58,175 --> 00:38:00,609
How could we find out
if such creatures
632
00:38:00,644 --> 00:38:05,147
rule a hidden empire
beneath the oil-dark waves?
633
00:38:20,397 --> 00:38:23,666
We're diving down deep
into the Kraken Sea,
634
00:38:23,700 --> 00:38:26,702
named for the mythic
Norse sea monster.
635
00:38:30,073 --> 00:38:32,274
Even if there is
one of those down there,
636
00:38:32,309 --> 00:38:33,976
we probably couldn't see it.
637
00:38:34,010 --> 00:38:36,545
It's so dark.
638
00:38:36,580 --> 00:38:40,983
If you took all the oil
and natural gas on Earth,
639
00:38:41,017 --> 00:38:44,753
it would amount to but a tiny
fraction of Titan's reserves.
640
00:38:48,258 --> 00:38:50,192
Let's turn on some lights.
641
00:38:54,498 --> 00:38:57,933
We're now 200 meters
beneath the surface.
642
00:39:01,204 --> 00:39:03,739
Did you see something?
643
00:39:03,773 --> 00:39:06,976
Over there, by that vent.
644
00:39:07,010 --> 00:39:09,478
Maybe it was just
my imagination.
645
00:39:09,513 --> 00:39:11,480
I guess we'll have to come back
646
00:39:11,515 --> 00:39:14,517
if we want to find out
for sure.
647
00:39:16,753 --> 00:39:20,389
There's one last story
I want to tell you.
648
00:39:20,423 --> 00:39:24,593
And it's the greatest story
science has ever told.
649
00:39:28,932 --> 00:39:32,368
It's the story of life
on our world.
650
00:39:54,825 --> 00:39:57,927
Welcome to the Earth
of four billion years ago.
651
00:39:57,961 --> 00:40:01,630
This was our planet before life.
652
00:40:01,665 --> 00:40:04,733
Nobody knows
how life got started.
653
00:40:04,768 --> 00:40:07,136
Most of the evidence
from that time was destroyed
654
00:40:07,170 --> 00:40:09,772
by impact and erosion.
655
00:40:09,806 --> 00:40:13,576
Science works on the frontier
between knowledge and ignorance.
656
00:40:13,610 --> 00:40:15,544
We're not afraid to admit
what we don't know.
657
00:40:15,579 --> 00:40:17,880
There's no shame in that.
658
00:40:17,914 --> 00:40:21,750
The only shame is to pretend
that we have all the answers.
659
00:40:21,785 --> 00:40:23,452
Maybe someone watching this
660
00:40:23,487 --> 00:40:25,988
will be the first
to solve the mystery
661
00:40:26,022 --> 00:40:28,424
of how life on Earth began.
662
00:40:35,999 --> 00:40:37,833
The evidence
from living microbes
663
00:40:37,868 --> 00:40:39,768
suggest that their
earliest ancestors
664
00:40:39,803 --> 00:40:41,504
preferred high temperatures.
665
00:40:41,538 --> 00:40:44,440
Life on Earth may have
arisen in hot water
666
00:40:44,474 --> 00:40:46,775
around submerged volcanic vents.
667
00:40:51,548 --> 00:40:54,016
In Carl Sagan's original
Cosmos series,
668
00:40:54,050 --> 00:40:56,819
he traced the unbroken thread
that stretches
669
00:40:56,853 --> 00:40:58,921
directly from
the one-celled organisms
670
00:40:58,955 --> 00:41:01,490
of nearly four billion
years ago...
671
00:41:01,525 --> 00:41:03,792
to you.
672
00:41:03,827 --> 00:41:06,962
Four billion years
in 40 seconds.
673
00:41:06,997 --> 00:41:10,533
From creatures who had yet
to discern day from night
674
00:41:10,567 --> 00:41:14,370
to beings who are
exploring the cosmos.
675
00:42:03,520 --> 00:42:06,522
Those are some of
the things that molecules do
676
00:42:06,556 --> 00:42:10,025
given four billion years
of evolution.
677
00:42:15,516 --> 00:42:20,041
Sync and corrections by n17t01
www.addic7ed.com
678
00:42:21,305 --> 00:43:21,710
OpenSubtitles recommends using Nord VPN
from 3.49 USD/month ----> osdb.link/vpn