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SAGAN: All my life I've wondered
about life beyond the Earth.
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00:01:02,041 --> 00:01:06,034
On those countless other planets
that we think circle other suns...
3
00:01:06,245 --> 00:01:08,110
...is there also life?
4
00:01:08,314 --> 00:01:10,874
Might the beings of other
worlds resemble us...
5
00:01:11,083 --> 00:01:13,745
...or would they be
astonishingly different?
6
00:01:13,953 --> 00:01:16,319
What would they be made of?
7
00:01:16,522 --> 00:01:18,683
In the vast Milky Way galaxy...
8
00:01:18,891 --> 00:01:22,292
...how common is what we call life?
9
00:01:24,363 --> 00:01:25,796
The nature of life on Earth...
10
00:01:25,998 --> 00:01:27,761
...and the quest for life elsewhere...
11
00:01:27,967 --> 00:01:31,095
...are the two sides
of the same question.
12
00:01:31,304 --> 00:01:34,068
The search for who we are.
13
00:01:39,145 --> 00:01:42,637
All living things on Earth
are made of organic molecules...
14
00:01:42,848 --> 00:01:45,373
...a complex microscopic
architecture...
15
00:01:45,585 --> 00:01:48,315
...built around atoms of carbon.
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00:01:48,521 --> 00:01:50,580
In the great dark between the stars...
17
00:01:50,790 --> 00:01:53,725
...there also are organic molecules...
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00:01:53,926 --> 00:01:57,760
...in immense clouds of gas and dust.
19
00:02:01,133 --> 00:02:02,760
Inside such clouds...
20
00:02:02,969 --> 00:02:06,461
...there are batches
of new worlds just forming.
21
00:02:06,672 --> 00:02:10,608
Their surfaces are very likely
covered with organic molecules.
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00:02:10,810 --> 00:02:13,904
These molecules almost certainly
are not made by life...
23
00:02:14,113 --> 00:02:16,707
...although they
are the stuff of life.
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00:02:16,916 --> 00:02:20,010
On suitable worlds,
they may lead to life.
25
00:02:20,219 --> 00:02:23,746
Organic matter is abundant
throughout the cosmos...
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00:02:23,956 --> 00:02:27,722
...produced by the same chemistry
everywhere.
27
00:02:42,274 --> 00:02:44,765
Perhaps, given enough time...
28
00:02:44,977 --> 00:02:49,778
...the origin and evolution of life
is inevitable on every clement world.
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00:02:49,982 --> 00:02:53,713
There will surely be some planets
too hostile for life.
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00:02:53,919 --> 00:02:56,615
On others,
it may arise and die out...
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00:02:56,822 --> 00:02:59,848
...or never evolve
beyond its simplest forms.
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00:03:00,059 --> 00:03:02,459
And on some small
fraction of worlds...
33
00:03:02,662 --> 00:03:05,961
...there may develop intelligences
and civilizations...
34
00:03:06,165 --> 00:03:08,497
...more advanced than ours.
35
00:03:11,737 --> 00:03:14,706
All life on our planet
is closely related.
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00:03:14,907 --> 00:03:19,276
We have a common organic chemistry
and a common evolutionary heritage.
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00:03:19,478 --> 00:03:23,175
And so our biologists
are profoundly limited.
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00:03:23,382 --> 00:03:25,646
They study a single biology...
39
00:03:25,851 --> 00:03:30,015
...one lonely theme
in the music of life.
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00:03:30,222 --> 00:03:33,919
Is it the only voice
for thousands of light years...
41
00:03:34,126 --> 00:03:38,825
...or is there a cosmic fugue,
a billion different voices...
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00:03:39,031 --> 00:03:42,967
...playing the life music
of the galaxy?
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00:03:47,440 --> 00:03:50,341
This blue world is where we grew up.
44
00:03:50,543 --> 00:03:52,636
There was once a time before life.
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00:03:52,845 --> 00:03:56,008
Our planet is now
burgeoning with life.
46
00:03:56,215 --> 00:03:58,080
How did it come about?
47
00:03:58,284 --> 00:04:01,742
How were organic molecules
originally made?
48
00:04:01,954 --> 00:04:04,218
How did life evolve
to produce beings...
49
00:04:04,423 --> 00:04:07,324
...as elaborate and complex as we...
50
00:04:07,526 --> 00:04:11,758
...able to explore the mystery
of our own origins?
51
00:04:15,000 --> 00:04:18,527
Let me tell you a story
about one little phrase...
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00:04:18,738 --> 00:04:20,672
...in the music of life on Earth.
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(WIND BLOWS)
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00:04:38,157 --> 00:04:40,022
In the history of humans...
55
00:04:40,226 --> 00:04:42,091
...in the 12th century...
56
00:04:42,294 --> 00:04:46,890
...Japan was ruled by a clan
of warriors called the Heike.
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00:04:56,542 --> 00:05:00,137
The nominal leader of the Heike,
the emperor of Japan...
58
00:05:00,346 --> 00:05:03,543
...was a 7-year-old boy
named Antoku.
59
00:05:03,749 --> 00:05:08,049
His guardian was his grandmother,
the Lady Nii.
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00:05:10,756 --> 00:05:13,224
(DRUM BEATS)
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00:05:17,129 --> 00:05:20,360
The Heike were engaged
in a long and bloody war...
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00:05:20,566 --> 00:05:23,933
...with another Samurai clan,
the Genji.
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00:05:29,175 --> 00:05:32,508
Each asserted
a superior ancestral claim...
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00:05:32,711 --> 00:05:34,576
...to the imperial throne.
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00:05:34,780 --> 00:05:36,577
(BATTLE CRIES)
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00:05:37,283 --> 00:05:41,083
Their decisive encounter
occurred at Dannoura...
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00:05:41,287 --> 00:05:44,848
...in the Japanese Inland Sea
on April 24...
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00:05:45,057 --> 00:05:47,992
...in the year 1 185.
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00:05:50,462 --> 00:05:53,488
The Heike were badly outnumbered
and outmaneuvered.
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00:05:53,933 --> 00:05:55,867
With their cause clearly lost...
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00:05:56,068 --> 00:06:01,005
...the surviving Heike warriors threw
themselves into the sea and drowned.
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00:06:07,246 --> 00:06:09,680
The emperor's grandmother,
the Lady Nii...
73
00:06:09,882 --> 00:06:12,612
...resolved that they would not
be captured by the enemy.
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00:06:12,818 --> 00:06:17,221
What happened next is related
in "The Tale of the Heike":
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00:06:18,057 --> 00:06:21,515
"The young emperor asked the Lady Nii,
'Where are you to take me?'
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00:06:22,394 --> 00:06:27,093
She turned to the youthful sovereign
with tears streaming down her cheeks...
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00:06:27,299 --> 00:06:28,698
...and comforted him.
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00:06:31,704 --> 00:06:33,763
(WATER LAPS)
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00:06:41,080 --> 00:06:42,707
Blinded with tears...
80
00:06:42,915 --> 00:06:47,284
...the child sovereign put his
beautiful small hands together.
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00:06:49,622 --> 00:06:51,522
He turned first to the east...
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00:06:51,724 --> 00:06:54,887
...to say farewell
to the god of Ise...
83
00:06:55,094 --> 00:06:56,618
...and then to the west...
84
00:06:56,829 --> 00:07:00,492
...to recite a prayer
to the Amida Buddha.
85
00:07:01,767 --> 00:07:03,428
The Lady Nii...
86
00:07:03,636 --> 00:07:06,161
...took him in her arms,
and with the words:
87
00:07:06,372 --> 00:07:09,341
'In the depths of the ocean
is our capital'...
88
00:07:09,541 --> 00:07:12,772
...sank with him at last
beneath the waves."
89
00:07:34,199 --> 00:07:37,999
The destruction of the Heike
battle fleet at Dannoura...
90
00:07:38,203 --> 00:07:41,001
...marked the end of the clan's
30-year rule.
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00:07:41,206 --> 00:07:44,471
The Heike all but vanished
from history.
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00:07:49,481 --> 00:07:52,848
Only 43 Heike survived, all women.
93
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These former ladies-in-waiting
of the Imperial Court...
94
00:07:56,588 --> 00:08:00,046
...were reduced to selling flowers
and other favors...
95
00:08:00,259 --> 00:08:03,319
...to the fishermen near
the scene of the battle.
96
00:08:09,802 --> 00:08:12,999
These women and their offspring
by the fishermen...
97
00:08:13,205 --> 00:08:16,538
...established a festival
to commemorate the battle.
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00:08:23,182 --> 00:08:26,845
To this day, every year,
on the 24th of April...
99
00:08:27,052 --> 00:08:29,953
...their descendants proceed
to the Akama shrine...
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00:08:30,155 --> 00:08:31,850
...which contains the mausoleum...
101
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...of the drowned
7-year-old emperor, Antoku.
102
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There, they conduct a ceremony
of remembrance...
103
00:08:43,068 --> 00:08:47,027
...for the life and death
of the Heike warriors.
104
00:08:55,414 --> 00:08:58,383
But there is a strange
postscript to this story:
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00:08:58,584 --> 00:09:00,142
The fishermen say...
106
00:09:00,352 --> 00:09:05,085
...that the Heike samurai
wander the bottom of the Inland Sea...
107
00:09:05,290 --> 00:09:08,020
...in the form of crabs.
108
00:09:08,660 --> 00:09:13,120
There are crabs here which have
curious markings on their backs.
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00:09:13,399 --> 00:09:16,391
Patterns which resemble
a human face...
110
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...with the aggressive scowl
of a samurai warrior...
111
00:09:19,772 --> 00:09:21,865
...from medieval Japan.
112
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(DRUM BEATS)
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These Heike crabs, when caught,
are not eaten.
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They are thrown back into the sea...
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...in commemoration
of the doleful events...
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...of the battle of Dannoura.
117
00:09:52,571 --> 00:09:55,768
This legend raises a lovely problem:
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How does it come about that the face
of a warrior...
119
00:10:00,012 --> 00:10:04,779
...is cut on the carapace of
a Japanese crab? How could it be?
120
00:10:04,983 --> 00:10:09,545
The answer seems to be
that humans made this face.
121
00:10:09,888 --> 00:10:11,355
But how?
122
00:10:11,557 --> 00:10:14,822
Like many other features,
the patterns on the back...
123
00:10:15,027 --> 00:10:18,394
...or carapace of this crab
are inherited.
124
00:10:18,597 --> 00:10:23,000
But among crabs, as among humans,
there are different hereditary lines.
125
00:10:23,435 --> 00:10:26,461
Now, suppose purely by chance...
126
00:10:26,672 --> 00:10:29,903
...among the distant ancestors
of this crab...
127
00:10:30,109 --> 00:10:34,842
...there came to be one which looked
just a little bit like a human face.
128
00:10:35,047 --> 00:10:38,539
Long before the battle, fishermen
may have been reluctant...
129
00:10:38,750 --> 00:10:40,775
...to eat a crab with a human face.
130
00:10:41,120 --> 00:10:43,486
In throwing it back into the sea...
131
00:10:43,689 --> 00:10:47,819
...they were setting into motion
a process of selection.
132
00:10:48,026 --> 00:10:52,554
If you're a crab and your carapace
is just ordinary...
133
00:10:52,764 --> 00:10:55,062
...the humans are gonna eat you.
134
00:10:55,267 --> 00:10:57,827
But if it looks a little bit
like a face...
135
00:10:58,036 --> 00:11:01,528
...they'll throw you back and you
can have lots of baby crabs...
136
00:11:01,740 --> 00:11:03,503
...that all look just like you.
137
00:11:03,709 --> 00:11:05,802
As many generations passed...
138
00:11:06,011 --> 00:11:08,878
...of crabs and fisher-folk alike...
139
00:11:09,081 --> 00:11:12,949
...the crabs with patterns that
looked most like a samurai face...
140
00:11:13,152 --> 00:11:15,347
...preferentially survived.
141
00:11:15,554 --> 00:11:19,115
Until eventually, there was produced
not just a human face...
142
00:11:19,324 --> 00:11:21,792
...not just a Japanese face...
143
00:11:21,994 --> 00:11:24,929
...but the face of a samurai warrior.
144
00:11:25,130 --> 00:11:29,089
All this has nothing to do
with what the crabs might want.
145
00:11:29,301 --> 00:11:32,737
Selection is imposed from the outside.
146
00:11:32,938 --> 00:11:36,874
The more you look like a samurai,
the better your chances of survival.
147
00:11:37,075 --> 00:11:41,739
Eventually, there are a lot of crabs
that look like samurai warriors.
148
00:11:41,947 --> 00:11:44,973
(DRUM BEATS)
149
00:12:03,068 --> 00:12:06,629
This process is called
artificial selection.
150
00:12:07,372 --> 00:12:09,670
In the case of the Heike crab,
it was effected...
151
00:12:09,875 --> 00:12:12,742
...more or less unconsciously
by the fishermen...
152
00:12:12,945 --> 00:12:17,211
...and certainly without any serious
contemplation by the crabs.
153
00:12:17,416 --> 00:12:19,976
Humans, for thousands of years...
154
00:12:20,185 --> 00:12:22,050
...have deliberately selected...
155
00:12:22,254 --> 00:12:24,916
...which plants
and animals shall live.
156
00:12:25,157 --> 00:12:28,615
We're surrounded
by farm and domestic animals...
157
00:12:28,827 --> 00:12:30,124
...fruits, vegetables.
158
00:12:30,996 --> 00:12:34,625
Where do they come from? Were they
once free-living in the wild...
159
00:12:34,833 --> 00:12:38,667
...and then induced to adopt some
less strenuous life on the farm?
160
00:12:39,137 --> 00:12:40,126
No.
161
00:12:40,339 --> 00:12:44,400
They are, almost all of them,
made by us.
162
00:12:48,113 --> 00:12:52,641
The essence of artificial selection
for a horse or a cow...
163
00:12:52,851 --> 00:12:56,184
...a grain of rice
or a Heike crab, is this:
164
00:12:56,388 --> 00:12:59,687
Many characteristics are inherited.
They breed true.
165
00:13:01,660 --> 00:13:05,255
Humans encourage the reproduction
of some varieties...
166
00:13:05,464 --> 00:13:07,398
...and discourage
the reproduction of others.
167
00:13:07,599 --> 00:13:11,035
The variety selected for,
eventually becomes abundant.
168
00:13:11,236 --> 00:13:15,195
The variety selected against,
becomes rare, maybe extinct.
169
00:13:16,408 --> 00:13:19,571
But if artificial selection
makes such changes...
170
00:13:19,778 --> 00:13:21,837
...in only a few thousand years...
171
00:13:22,047 --> 00:13:24,072
...what must natural selection...
172
00:13:24,283 --> 00:13:28,276
...working for billions of years,
be capable of?
173
00:13:28,520 --> 00:13:29,578
The answer...
174
00:13:29,788 --> 00:13:33,588
...is all the beauty and diversity
in the biological world.
175
00:13:38,330 --> 00:13:42,391
That life evolved over
the ages is clear...
176
00:13:42,601 --> 00:13:46,230
...from the changes we've made
in the beasts and vegetables...
177
00:13:46,571 --> 00:13:50,132
...but also from
the record in the rocks.
178
00:13:50,442 --> 00:13:53,206
The fossil evidence speaks
to us unambiguously...
179
00:13:53,412 --> 00:13:57,906
...of creatures that were once
present in enormous numbers...
180
00:13:58,116 --> 00:14:00,141
...and that have now vanished utterly.
181
00:14:00,352 --> 00:14:03,844
There are more species that have
become extinct than exist today.
182
00:14:04,056 --> 00:14:08,152
They are the terminated
experiments in evolution.
183
00:14:09,227 --> 00:14:13,823
These guys, the trilobites,
appeared 600 million years ago.
184
00:14:14,032 --> 00:14:16,660
They were around
for 300 million years.
185
00:14:16,868 --> 00:14:20,133
They're all gone. There's none left.
186
00:14:20,439 --> 00:14:25,069
But in those old rocks, there are
no fossils of people or cattle.
187
00:14:25,277 --> 00:14:27,108
We've evolved only recently.
188
00:14:28,313 --> 00:14:31,544
Evolution is a fact, not a theory.
189
00:14:31,750 --> 00:14:33,684
It really happened.
190
00:14:35,253 --> 00:14:37,221
(BEE BUZZES)
191
00:14:39,624 --> 00:14:43,856
That the mechanism of evolution is
natural selection was the discovery...
192
00:14:44,062 --> 00:14:47,498
...of Charles Darwin
and Alfred Russel Wallace.
193
00:14:48,166 --> 00:14:49,394
Here's how it works:
194
00:14:49,901 --> 00:14:51,425
Nature is prolific.
195
00:14:51,636 --> 00:14:55,504
There are many more creatures that
are born than can possibly survive.
196
00:14:55,707 --> 00:15:00,644
So those varieties which are,
by accident, less well adapted...
197
00:15:00,879 --> 00:15:04,371
...don't survive, or at least
they leave fewer offspring.
198
00:15:04,583 --> 00:15:09,043
Now, mutations, sudden
changes in heredity...
199
00:15:09,254 --> 00:15:11,313
...are passed on. They breed true.
200
00:15:11,523 --> 00:15:16,460
The environment selects the occasional
mutations which enhance survival.
201
00:15:16,695 --> 00:15:21,132
The resulting series of slow changes
in the nature of living beings...
202
00:15:21,333 --> 00:15:23,460
...is the origin of new species.
203
00:15:25,036 --> 00:15:28,403
Many people were scandalized...
204
00:15:28,607 --> 00:15:30,802
...by the ideas of evolution
and natural selection.
205
00:15:31,009 --> 00:15:33,136
Our ancestors looked at...
206
00:15:33,345 --> 00:15:36,143
...the intricacy
and the beauty of life...
207
00:15:36,348 --> 00:15:40,148
...and saw evidence
for a great designer.
208
00:15:43,054 --> 00:15:46,546
The simplest organism
is a far more complex machine...
209
00:15:46,758 --> 00:15:48,919
...than the finest pocket watch.
210
00:15:49,127 --> 00:15:53,427
And yet, pocket watches don't
spontaneously self-assemble...
211
00:15:53,632 --> 00:15:56,931
...or evolve in slow
stages on their own...
212
00:15:57,135 --> 00:15:59,933
...from say, grandfather clocks.
213
00:16:00,238 --> 00:16:03,173
A watch implies a watchmaker.
214
00:16:04,810 --> 00:16:09,304
There seemed to be no way atoms
could spontaneously fall together...
215
00:16:09,514 --> 00:16:11,948
...and create, say...
216
00:16:13,652 --> 00:16:14,812
...a dandelion.
217
00:16:15,487 --> 00:16:17,785
The idea of a designer...
218
00:16:17,989 --> 00:16:22,653
...is an appealing and altogether human
explanation of the biological world.
219
00:16:22,861 --> 00:16:26,092
But as Darwin and Wallace showed...
220
00:16:26,298 --> 00:16:27,959
...there's another way...
221
00:16:28,166 --> 00:16:31,897
...equally human
and far more compelling.
222
00:16:32,304 --> 00:16:36,434
Natural selection, which makes
the music of life more beautiful...
223
00:16:36,641 --> 00:16:38,836
...as the eons pass.
224
00:16:42,514 --> 00:16:44,641
(LOUD RUMBLE)
225
00:16:44,883 --> 00:16:47,078
To understand the passage
of the eons...
226
00:16:47,285 --> 00:16:50,618
...we have compressed all of time
into a single cosmic year...
227
00:16:50,822 --> 00:16:54,155
...with the big bang on January first.
228
00:16:54,359 --> 00:16:58,796
Every month here represents
a little over a billion years.
229
00:16:58,997 --> 00:17:02,865
The Earth didn't form until
the cosmic year was two-thirds over.
230
00:17:03,068 --> 00:17:07,232
Our understanding of the history
of life is very recent...
231
00:17:07,439 --> 00:17:10,875
...occupying only the last few
seconds of December 31...
232
00:17:11,076 --> 00:17:15,206
...that small white spot at bottom
right in the cosmic calendar.
233
00:17:15,413 --> 00:17:17,813
What happened on Earth may be
more or less typical...
234
00:17:18,016 --> 00:17:20,484
...of the evolution of life
on many worlds.
235
00:17:20,685 --> 00:17:22,676
But in its details...
236
00:17:22,888 --> 00:17:25,083
...the story of life on Earth...
237
00:17:25,290 --> 00:17:28,088
...is probably unique
in all the Milky Way galaxy.
238
00:17:28,760 --> 00:17:33,197
The secrets of evolution
are time and death.
239
00:17:33,398 --> 00:17:37,232
Time for the slow accumulation
of favorable mutations...
240
00:17:37,435 --> 00:17:41,030
...and death to make room
for new species.
241
00:17:41,740 --> 00:17:45,005
Life on Earth arose in September
of the cosmic calendar...
242
00:17:45,210 --> 00:17:49,874
...when our world, still battered and
cratered from its violent origin...
243
00:17:50,081 --> 00:17:52,242
...may have looked
a little like the moon.
244
00:17:54,419 --> 00:17:57,946
The Earth is about four and a half
billion years old.
245
00:17:58,156 --> 00:17:59,487
In the cosmic calendar...
246
00:17:59,691 --> 00:18:03,684
...it condensed out of interstellar
gas and dust...
247
00:18:03,895 --> 00:18:06,523
...around September 1 4.
248
00:18:06,731 --> 00:18:10,394
We know from the fossil record
that life originated soon after...
249
00:18:10,602 --> 00:18:13,867
...maybe around September 25,
something like that...
250
00:18:14,072 --> 00:18:17,940
...probably in the ponds and oceans
of the primitive Earth.
251
00:18:18,176 --> 00:18:22,772
The first living things were not
as complex as a one-celled organism...
252
00:18:22,981 --> 00:18:26,610
...which is already a highly
sophisticated form of life.
253
00:18:26,818 --> 00:18:30,845
No, the first stirrings
of life were much more humble...
254
00:18:31,056 --> 00:18:33,889
...and happened on the molecular level.
255
00:18:34,092 --> 00:18:38,290
In those early days, lightning
and ultraviolet light from the sun...
256
00:18:38,496 --> 00:18:42,694
...were breaking apart hydrogen-rich
molecules in the atmosphere.
257
00:18:42,901 --> 00:18:47,395
The fragments of the molecules
were spontaneously recombining...
258
00:18:47,606 --> 00:18:51,406
...into more and more
complex molecules.
259
00:18:53,545 --> 00:18:57,504
The products of this early
chemistry dissolved in the oceans...
260
00:18:57,716 --> 00:19:01,015
...forming a kind of organic soup...
261
00:19:01,219 --> 00:19:03,346
...of gradually increasing complexity.
262
00:19:03,555 --> 00:19:07,355
Until one day, quite by accident...
263
00:19:07,559 --> 00:19:11,655
...a molecule arose that was able
to make crude copies of itself...
264
00:19:11,863 --> 00:19:15,299
...using as building blocks
the other molecules in the soup.
265
00:19:15,500 --> 00:19:18,958
This was the ancestor of DNA...
266
00:19:19,170 --> 00:19:22,537
...the master molecule
of life on Earth.
267
00:19:22,741 --> 00:19:26,404
It's made of four different
parts, called nucleotides...
268
00:19:26,611 --> 00:19:30,308
...which constitute the four letters
of the genetic code...
269
00:19:30,515 --> 00:19:32,073
...the language of heredity.
270
00:19:32,283 --> 00:19:37,152
Each of the nucleotides,
the rungs on the DNA ladder...
271
00:19:37,355 --> 00:19:39,653
...are a different color
in this model.
272
00:19:39,858 --> 00:19:43,123
The instructions are different
for different organisms.
273
00:19:43,328 --> 00:19:45,694
That's why organisms
are different.
274
00:19:45,897 --> 00:19:49,731
Now, a mutation is a change
of a nucleotide...
275
00:19:49,934 --> 00:19:52,960
...a misspelling
of the genetic instructions.
276
00:19:53,171 --> 00:19:58,040
Most mutations spell genetic
nonsense since they're random.
277
00:19:58,243 --> 00:20:00,438
They harm the next generation.
278
00:20:00,645 --> 00:20:02,943
But a very few, by accident...
279
00:20:03,148 --> 00:20:07,642
...make better sense than the
original codes, and aid evolution.
280
00:20:08,353 --> 00:20:11,652
DNA is about a billion
times smaller...
281
00:20:11,856 --> 00:20:13,585
...than we see it here.
282
00:20:13,792 --> 00:20:18,729
Each of those things that looks
like a piece of fruit is an atom.
283
00:20:18,930 --> 00:20:20,522
Without the tools of science...
284
00:20:20,732 --> 00:20:24,031
...the machinery of life
would be invisible.
285
00:20:28,273 --> 00:20:29,900
Four billion years ago...
286
00:20:30,108 --> 00:20:34,135
...the ancestors of DNA competed
for molecular building blocks...
287
00:20:34,345 --> 00:20:37,314
...and left crude copies
of themselves.
288
00:20:37,515 --> 00:20:40,780
There were no predators;
the stuff of life was everywhere.
289
00:20:40,985 --> 00:20:44,352
The oceans and murky pools
that filled the craters...
290
00:20:44,556 --> 00:20:47,855
...were, for these molecules,
a Garden of Eden.
291
00:20:48,193 --> 00:20:51,185
With reproduction, mutation
and natural selection...
292
00:20:51,396 --> 00:20:55,423
...the evolution of living
molecules was well underway.
293
00:20:55,967 --> 00:20:59,869
Varieties with specialized
functions joined together...
294
00:21:00,071 --> 00:21:03,097
...making a collective.
The first cell.
295
00:21:03,308 --> 00:21:06,368
The organic soup eventually
ate itself up.
296
00:21:06,578 --> 00:21:09,945
But by this time, plants had evolved,
able to use sunlight...
297
00:21:10,148 --> 00:21:14,881
...to make their own building blocks.
They turned the waters green.
298
00:21:15,086 --> 00:21:17,281
One-celled plants
joined together:
299
00:21:17,489 --> 00:21:20,515
The first multi-cellular organisms.
300
00:21:22,026 --> 00:21:26,463
Equally important was the invention,
not made until early November...
301
00:21:26,664 --> 00:21:31,158
...of sex. It was stumbled upon
by the microbes.
302
00:21:33,838 --> 00:21:37,501
By December 1, green plants
had released copious amounts...
303
00:21:37,709 --> 00:21:40,940
...of oxygen and nitrogen
into the atmosphere.
304
00:21:41,146 --> 00:21:44,445
The sky is made by life.
305
00:21:45,750 --> 00:21:48,480
Then, suddenly, on December 1 5...
306
00:21:48,686 --> 00:21:51,678
...there was an enormous proliferation
of new life forms...
307
00:21:51,890 --> 00:21:55,326
...an event called
the "Cambrian Explosion."
308
00:22:00,265 --> 00:22:04,759
We know from fossils that life arose
shortly after the Earth formed...
309
00:22:04,969 --> 00:22:08,700
...suggesting that the origin
of life might be...
310
00:22:08,907 --> 00:22:13,105
...an inevitable chemical process
on countless Earth-like planets...
311
00:22:13,311 --> 00:22:14,903
...throughout the cosmos.
312
00:22:15,113 --> 00:22:19,914
But on the Earth, in nearly 4 billion
years, life advanced no further...
313
00:22:20,118 --> 00:22:21,085
...than algae.
314
00:22:21,286 --> 00:22:26,087
So maybe more complex forms of life
are harder to evolve...
315
00:22:26,291 --> 00:22:28,851
...harder even than the origin
of life itself.
316
00:22:29,060 --> 00:22:31,722
If this is right, the planets
of the galaxy...
317
00:22:31,930 --> 00:22:34,592
...might be filled
with microorganisms...
318
00:22:34,799 --> 00:22:38,667
...but big beasts and vegetables
and thinking beings...
319
00:22:38,870 --> 00:22:41,668
...might be comparatively rare.
320
00:22:45,143 --> 00:22:49,204
By December 18, there were vast
herds of trilobites...
321
00:22:49,414 --> 00:22:51,541
...foraging on the ocean bottom...
322
00:22:51,749 --> 00:22:55,185
...and squid-like creatures with
multicolored shells...
323
00:22:55,386 --> 00:22:56,853
...were everywhere.
324
00:22:59,791 --> 00:23:03,386
We know enough to sketch in a few
of the subsequent details.
325
00:23:03,595 --> 00:23:07,292
The first fish and the first
vertebrates appeared on December 19.
326
00:23:07,498 --> 00:23:11,059
Plants began to colonize the land
on December 20.
327
00:23:11,269 --> 00:23:15,365
The first winged insects fluttered by
on December 22.
328
00:23:15,573 --> 00:23:18,701
On this date also, there were
the first amphibians...
329
00:23:18,910 --> 00:23:21,344
...creatures something
like the lungfish...
330
00:23:21,546 --> 00:23:24,811
...able to survive both on land
and in water.
331
00:23:25,016 --> 00:23:29,248
Our direct ancestors were now
leaving the oceans behind.
332
00:23:32,123 --> 00:23:37,060
The first trees and the first reptiles
evolved on December 23:
333
00:23:37,295 --> 00:23:40,560
Two amazing evolutionary developments.
334
00:23:42,901 --> 00:23:46,337
We are descended
from some of those reptiles.
335
00:23:50,742 --> 00:23:54,075
The dinosaurs appeared
on Christmas Eve.
336
00:23:54,279 --> 00:23:56,338
There were many different
kinds of dinosaurs.
337
00:23:56,547 --> 00:23:59,516
The Earth was once their planet.
338
00:24:02,654 --> 00:24:06,090
Many stood upright and had
some fair intelligence.
339
00:24:06,291 --> 00:24:11,126
Great lizards crashed and thundered
through the steaming jungles.
340
00:24:16,234 --> 00:24:18,862
Unnoticed by the dinosaurs,
a new creature...
341
00:24:19,070 --> 00:24:21,231
...whose young were born live
and helpless...
342
00:24:21,439 --> 00:24:23,771
...was making its timid debut.
343
00:24:23,975 --> 00:24:27,103
The first mammals emerged
on December 26...
344
00:24:27,312 --> 00:24:30,577
...the first birds
on the following day.
345
00:24:33,885 --> 00:24:37,286
But the dinosaurs still
dominated the planet.
346
00:24:37,488 --> 00:24:41,424
Then suddenly, without warning,
all over the planet at once...
347
00:24:41,626 --> 00:24:43,389
...the dinosaurs died.
348
00:24:43,594 --> 00:24:46,961
The cause is unknown,
but the lesson is clear:
349
00:24:47,165 --> 00:24:51,864
Even 160 million years on a planet
is no guarantee of survival.
350
00:24:52,070 --> 00:24:56,564
The dinosaurs perished
around the time of the first flower.
351
00:24:58,409 --> 00:25:00,536
On December 30, the first creatures...
352
00:25:00,745 --> 00:25:03,578
...who looked even a little bit human,
evolved...
353
00:25:03,781 --> 00:25:07,945
...accompanied by a spectacular increase
in the size of their brains.
354
00:25:08,152 --> 00:25:12,020
And then, on the evening
of the last day of the last month...
355
00:25:12,223 --> 00:25:13,850
...only a few million years ago...
356
00:25:14,058 --> 00:25:18,893
...the first true humans took
their place on the cosmic calendar.
357
00:25:20,198 --> 00:25:21,995
The written record of history...
358
00:25:22,200 --> 00:25:25,863
...occupies only the last 10 seconds
of the cosmic year.
359
00:25:28,373 --> 00:25:32,275
Now, let's take a closer look
at who our ancestors were.
360
00:25:32,477 --> 00:25:35,537
A simple chemical circumstance
led to a great moment...
361
00:25:35,747 --> 00:25:37,772
...in the history of our planet.
362
00:25:37,982 --> 00:25:40,917
There were many molecules
in the primordial soup.
363
00:25:41,119 --> 00:25:45,954
Some were attracted to water on one
side and repelled by it on the other.
364
00:25:46,157 --> 00:25:48,751
This drove them together...
365
00:25:48,960 --> 00:25:51,758
...into a tiny enclosed
spherical shell...
366
00:25:51,963 --> 00:25:54,761
...like a soap bubble,
which protected the interior.
367
00:25:54,966 --> 00:25:58,527
Within the bubble,
the ancestors of DNA found a home...
368
00:25:58,736 --> 00:26:00,431
...and the first cell arose.
369
00:26:00,638 --> 00:26:04,631
It took hundreds of millions of years
for tiny plants to evolve...
370
00:26:04,842 --> 00:26:06,309
...giving off oxygen.
371
00:26:06,511 --> 00:26:09,742
But that branch didn't lead to us.
372
00:26:10,248 --> 00:26:15,083
Bacteria that could breathe oxygen
took over a billion years to evolve.
373
00:26:16,454 --> 00:26:20,788
From a naked nucleus, a cell
developed with a nucleus inside.
374
00:26:22,193 --> 00:26:26,493
Some of these amoeba-like forms
led eventually to plants.
375
00:26:30,568 --> 00:26:32,502
Others produced colonies...
376
00:26:32,703 --> 00:26:36,969
...with inside and outside cells
performing different functions.
377
00:26:38,810 --> 00:26:40,141
Becoming...
378
00:26:40,344 --> 00:26:44,007
...a polyp attached
to the ocean floor...
379
00:26:44,215 --> 00:26:46,581
...filtering food from the water...
380
00:26:47,018 --> 00:26:49,543
...and evolving little tentacles...
381
00:26:49,754 --> 00:26:53,087
...to direct food
into a primitive mouth.
382
00:26:54,325 --> 00:26:56,020
This humble ancestor of ours
also led...
383
00:26:56,227 --> 00:27:00,391
...to spiny-skinned armored animals
with internal organs...
384
00:27:00,598 --> 00:27:04,466
...including our cousin, the starfish.
385
00:27:04,669 --> 00:27:07,103
But we don't come from starfish.
386
00:27:08,039 --> 00:27:10,303
About 550 million years ago...
387
00:27:10,508 --> 00:27:13,500
...filter feeders
evolved gill slits...
388
00:27:13,711 --> 00:27:17,010
...which were more efficient
at straining food particles.
389
00:27:17,215 --> 00:27:20,946
One evolutionary branch
led to acorn worms.
390
00:27:21,219 --> 00:27:25,747
Another led to a creature which
swam freely in the larval stage...
391
00:27:25,957 --> 00:27:29,290
...but, as an adult, was still
firmly anchored to the ocean floor.
392
00:27:29,494 --> 00:27:32,156
Some became living hollow tubes.
393
00:27:32,697 --> 00:27:37,031
But others retained the larval forms
throughout the life cycle...
394
00:27:37,235 --> 00:27:41,262
...and became free-swimming adults
with something like a backbone.
395
00:27:46,244 --> 00:27:47,802
Our ancestors now...
396
00:27:48,012 --> 00:27:52,346
...500 million years ago,
were jawless filter-feeding fish...
397
00:27:52,550 --> 00:27:54,984
...a little like lampreys.
398
00:27:56,787 --> 00:27:59,017
Gradually, those tiny fish...
399
00:27:59,223 --> 00:28:01,885
...evolved eyes and jaws.
400
00:28:02,393 --> 00:28:04,554
Fish then began to eat one another...
401
00:28:04,762 --> 00:28:07,822
...if you could swim fast,
you survived.
402
00:28:09,567 --> 00:28:14,436
If you had jaws to eat with, you could
use your gills to breathe in the water.
403
00:28:14,739 --> 00:28:17,640
This is the way modern fish arose.
404
00:28:21,913 --> 00:28:24,473
During the summer,
swamps and lakes dried up.
405
00:28:24,682 --> 00:28:29,483
Some fish evolved a primitive lung
to breathe air until the rains came.
406
00:28:29,687 --> 00:28:31,985
Their brains were getting bigger.
407
00:28:32,190 --> 00:28:35,717
If the rains didn't come, it was handy
to be able to pull yourself...
408
00:28:35,927 --> 00:28:37,189
...to the next swamp.
409
00:28:37,395 --> 00:28:40,296
That was a very important adaptation.
410
00:28:43,834 --> 00:28:47,270
The first amphibians evolved,
still with a fish-like tail.
411
00:28:47,471 --> 00:28:51,840
Amphibians, like fish, laid their eggs
in water where they were easily eaten.
412
00:28:52,043 --> 00:28:54,671
But then a splendid
new invention came along:
413
00:28:54,879 --> 00:28:59,475
The hard-shelled egg, laid on land
where there were as yet no predators.
414
00:28:59,684 --> 00:29:04,246
Reptiles and turtles
go back to those days.
415
00:29:06,224 --> 00:29:09,557
Many of the reptiles hatched on land
never returned to the waters.
416
00:29:09,760 --> 00:29:12,285
Some became the dinosaurs.
417
00:29:12,663 --> 00:29:16,895
One line of dinosaurs developed
feathers, useful for short flights.
418
00:29:17,101 --> 00:29:21,970
Today, the only living descendants
of the dinosaurs are the birds.
419
00:29:23,674 --> 00:29:26,108
The great dinosaurs evolved
along another branch.
420
00:29:26,310 --> 00:29:29,336
Some were the largest flesh-eaters
ever to walk the land.
421
00:29:29,547 --> 00:29:34,314
But 65 million years ago they all
mysteriously perished.
422
00:29:35,553 --> 00:29:37,953
Meanwhile, the forerunners
of the dinosaurs...
423
00:29:38,155 --> 00:29:40,783
...were also evolving
in a different direction.
424
00:29:40,992 --> 00:29:43,722
Small, scurrying creatures...
425
00:29:43,928 --> 00:29:46,829
...with the young growing
inside the mother's body.
426
00:29:47,031 --> 00:29:51,434
After the extinction of the dinosaurs,
many different forms developed.
427
00:29:55,740 --> 00:29:58,436
The young were very immature at birth.
428
00:29:58,643 --> 00:30:01,703
In the marsupials,
the wombat, for example...
429
00:30:01,912 --> 00:30:05,507
...and in the mammals, the young had
to be taught how to survive.
430
00:30:05,716 --> 00:30:07,911
The brain grew larger still.
431
00:30:08,119 --> 00:30:12,453
Something like a shrew was
the ancestor of all the mammals.
432
00:30:17,161 --> 00:30:20,995
One line took to the trees,
developing dexterity...
433
00:30:21,198 --> 00:30:23,166
...stereo vision, larger brains...
434
00:30:23,367 --> 00:30:25,858
...and a curiosity
about their environment.
435
00:30:26,070 --> 00:30:30,905
Some became baboons,
but that's not the line to us.
436
00:30:32,276 --> 00:30:35,268
Apes and humans have
a recent common ancestor.
437
00:30:35,479 --> 00:30:39,438
Bone for bone, muscle for muscle,
molecule for molecule.
438
00:30:39,650 --> 00:30:44,587
There are almost no important
differences between apes and humans.
439
00:30:47,558 --> 00:30:51,858
Unlike the chimpanzee,
our ancestors walked upright...
440
00:30:52,063 --> 00:30:56,090
...freeing their hands
to poke and fix and experiment.
441
00:30:56,300 --> 00:30:59,758
We got smarter. We began to talk.
442
00:31:06,277 --> 00:31:08,939
Many collateral branches
of the human family...
443
00:31:09,146 --> 00:31:12,604
...became extinct in
the last few million years.
444
00:31:12,817 --> 00:31:17,220
We, with our brains and our hands,
are the survivors.
445
00:31:17,421 --> 00:31:22,358
There's an unbroken thread that
stretches from those first cells to us.
446
00:31:22,693 --> 00:31:23,990
Let's look at it again...
447
00:31:24,195 --> 00:31:28,996
...compressing 4 billion years
of human evolution into 40 seconds.
448
00:32:15,079 --> 00:32:18,242
Those are some of the things
that molecules do...
449
00:32:18,449 --> 00:32:21,509
...given 4 billion years of evolution.
450
00:32:22,720 --> 00:32:27,020
We sometimes represent evolution as
the ever-branching ramifications...
451
00:32:27,224 --> 00:32:28,589
...of some original trunk...
452
00:32:28,793 --> 00:32:33,059
...each branch pruned and clipped
by natural selection.
453
00:32:33,898 --> 00:32:35,866
Every plant and animal
alive today...
454
00:32:36,066 --> 00:32:40,469
...has a history as ancient
and illustrious as ours.
455
00:32:40,671 --> 00:32:44,038
Humans stand on one branch.
456
00:32:44,475 --> 00:32:47,376
But now we affect
the future of every branch...
457
00:32:47,578 --> 00:32:50,638
...of this 4-billion-year-old tree.
458
00:32:53,250 --> 00:32:56,310
How lovely trees are.
459
00:32:56,520 --> 00:32:59,751
The human species grew up
in and around them.
460
00:32:59,957 --> 00:33:02,892
We have a natural affinity for trees.
461
00:33:03,093 --> 00:33:05,152
Trees photosynthesize...
462
00:33:05,362 --> 00:33:08,092
...they harvest sunlight...
463
00:33:08,299 --> 00:33:12,201
...they compete for the sun's favors.
464
00:33:13,070 --> 00:33:14,799
Look at those two trees there...
465
00:33:15,005 --> 00:33:18,202
...pushing and shoving for sunlight...
466
00:33:18,409 --> 00:33:23,005
...but with grace
and astonishing slowness.
467
00:33:30,688 --> 00:33:32,918
There are so many plants
on the Earth...
468
00:33:33,123 --> 00:33:35,683
...that there's a danger
of thinking them trivial...
469
00:33:35,893 --> 00:33:40,023
...of losing sight of the subtlety
and efficiency of their design.
470
00:33:40,231 --> 00:33:44,793
They are great and beautiful
machines, powered by sunlight...
471
00:33:45,002 --> 00:33:48,836
...taking in water from the ground
and carbon dioxide from the air...
472
00:33:49,039 --> 00:33:53,635
...and converting them into food
for their use and ours.
473
00:34:01,986 --> 00:34:05,547
This is a museum of living plants.
474
00:34:05,756 --> 00:34:10,625
The Royal Botanic Gardens
at Kew in London.
475
00:34:16,333 --> 00:34:19,302
Every plant uses
the carbohydrates it makes...
476
00:34:19,503 --> 00:34:23,200
...as an energy source
to go about its planty business.
477
00:34:23,407 --> 00:34:27,241
And we animals, who are ultimately
parasites on the plants...
478
00:34:27,444 --> 00:34:31,278
...we steal the carbohydrates
so we can go about our business.
479
00:34:36,620 --> 00:34:39,282
In eating the plants
and their fruits...
480
00:34:39,490 --> 00:34:42,459
...we combine the carbohydrates
with oxygen...
481
00:34:42,660 --> 00:34:45,891
...which as a result of breathing,
we've dissolved in our blood.
482
00:34:46,096 --> 00:34:51,033
From this chemical reaction, we
extract the energy which makes us go.
483
00:34:51,468 --> 00:34:54,335
In the process,
we exhale carbon dioxide...
484
00:34:54,538 --> 00:34:57,939
...which the plants then use
to make more carbohydrates.
485
00:35:00,044 --> 00:35:02,740
What a marvelous
cooperative arrangement.
486
00:35:02,947 --> 00:35:06,075
Plants and animals each using
the other's waste gases...
487
00:35:06,283 --> 00:35:10,879
...the whole cycle powered
by abundant sunlight.
488
00:35:11,288 --> 00:35:15,054
But there would be carbon dioxide in
the air even if there were no animals.
489
00:35:15,259 --> 00:35:18,854
We need the plants
much more than they need us.
490
00:35:23,000 --> 00:35:26,959
There are family resemblances
among the organisms of the Earth.
491
00:35:27,171 --> 00:35:31,574
Some are very apparent,
such as the use of the number five.
492
00:35:31,775 --> 00:35:34,642
Humans have five major
bodily projections:
493
00:35:34,845 --> 00:35:38,144
One head, two arms, two legs.
494
00:35:38,349 --> 00:35:39,816
So do ducks...
495
00:35:40,017 --> 00:35:44,420
...although the functions of their
projections are not quite the same.
496
00:35:44,622 --> 00:35:48,114
An octopus or a centipede
has a different plan.
497
00:35:48,325 --> 00:35:53,024
And a being from another planet
might be much stranger still.
498
00:35:53,230 --> 00:35:58,099
These family resemblances continue
and on a much deeper level...
499
00:35:58,302 --> 00:36:01,237
...when we go to the
molecular basis of life.
500
00:36:01,438 --> 00:36:04,134
There are tens of billions...
501
00:36:04,341 --> 00:36:07,242
...of different kinds
of organic molecules.
502
00:36:07,444 --> 00:36:09,639
Yet only about 50 of them...
503
00:36:09,847 --> 00:36:12,941
...are used in the essential
machinery of life.
504
00:36:13,150 --> 00:36:15,584
The same 50 employed
over and over again...
505
00:36:15,786 --> 00:36:20,382
...ingenious, for different functions
in every living thing.
506
00:36:20,591 --> 00:36:23,355
And when we go to the very kernel
of life on Earth...
507
00:36:23,560 --> 00:36:27,018
...to the proteins that
control cell chemistry...
508
00:36:27,231 --> 00:36:31,133
...to the spiral or helix
of nucleic acids...
509
00:36:31,335 --> 00:36:33,929
...which carry
the hereditary information...
510
00:36:34,138 --> 00:36:38,165
...we find these molecules
to be identical...
511
00:36:38,375 --> 00:36:41,970
...in all plants and animals
of our planet.
512
00:37:06,770 --> 00:37:11,366
This oak tree and me,
we're made of the same stuff.
513
00:37:11,575 --> 00:37:14,476
If you go back, you'll find
that we have a common ancestor.
514
00:37:14,678 --> 00:37:17,909
That's why our chemistry is so alike.
515
00:37:20,951 --> 00:37:24,944
Let's take a trip to examine
this common basis of life.
516
00:37:25,155 --> 00:37:28,556
A voyage to investigate
the molecular machinery...
517
00:37:28,759 --> 00:37:30,886
...at the heart of life on Earth.
518
00:37:31,095 --> 00:37:34,656
A journey to the nucleus of the cell.
519
00:37:34,898 --> 00:37:36,422
First we need a cell.
520
00:37:37,000 --> 00:37:41,266
I have trillions.
I can afford to donate a few.
521
00:37:47,311 --> 00:37:50,041
The casual act of pricking a finger...
522
00:37:50,247 --> 00:37:53,876
...is an event of some magnitude
on the scale of the very small.
523
00:37:54,084 --> 00:37:58,783
Millions of red blood cells are
detoured from their usual routes.
524
00:38:00,758 --> 00:38:03,591
But most continue
to cruise about the body...
525
00:38:03,794 --> 00:38:07,753
...carrying their cargoes of oxygen
to the remotest freckle.
526
00:38:08,866 --> 00:38:11,061
We're about to enter
the living cell...
527
00:38:11,268 --> 00:38:14,795
...a realm, in its own way,
as complex and beautiful...
528
00:38:15,005 --> 00:38:17,974
...as the realm of galaxies and stars.
529
00:38:18,375 --> 00:38:21,367
Among the red blood cells,
we encounter a white blood cell...
530
00:38:21,578 --> 00:38:23,170
...a lymphocyte...
531
00:38:23,380 --> 00:38:26,349
...whose job it is to protect me
against invading microbes.
532
00:38:26,550 --> 00:38:29,485
It makes antibodies
on its furrowed surface...
533
00:38:29,686 --> 00:38:33,213
...but its interior is
like that of many cells.
534
00:38:35,159 --> 00:38:39,152
Plunging through the membrane,
we find ourselves inside the cell.
535
00:38:39,363 --> 00:38:43,026
Here, every structure
has its function.
536
00:38:45,869 --> 00:38:48,770
These dark green blobs
are factories...
537
00:38:48,972 --> 00:38:51,941
...where messenger molecules
are busy building the enzymes...
538
00:38:52,142 --> 00:38:54,440
...which control
the chemistry of the cell.
539
00:38:54,645 --> 00:38:57,739
The messengers were
instructed and dispatched...
540
00:38:57,948 --> 00:39:02,044
...from within the nucleus,
the heart and brain of the cell.
541
00:39:02,386 --> 00:39:04,911
All the instructions on
how to get a cell to work...
542
00:39:05,122 --> 00:39:08,023
...and how to make another
are hidden away in there.
543
00:39:08,225 --> 00:39:10,693
We find a tunnel, a nuclear pore...
544
00:39:10,894 --> 00:39:14,625
...an approach to
the biological holy of holies.
545
00:39:16,834 --> 00:39:21,771
These necklaces, these intricately
looped and coiled strands...
546
00:39:21,972 --> 00:39:24,532
...are nucleic acids, DNA.
547
00:39:26,076 --> 00:39:28,636
Everything you need to know on
how to make a human being...
548
00:39:28,846 --> 00:39:33,783
...is encoded in the language
of life in the DNA molecule.
549
00:39:41,325 --> 00:39:44,522
This is the DNA double helix...
550
00:39:44,728 --> 00:39:49,665
...a machine with about 100 billion
moving parts, called atoms.
551
00:39:50,601 --> 00:39:53,695
There are as many atoms
in one molecule of DNA...
552
00:39:53,904 --> 00:39:57,601
...as there are stars
in a typical galaxy.
553
00:40:01,945 --> 00:40:05,278
The sequence of nucleotides,
here brightly colored...
554
00:40:05,482 --> 00:40:08,474
...is all that's passed on
from generation to generation.
555
00:40:08,685 --> 00:40:10,915
Change the order of the nucleotides...
556
00:40:11,121 --> 00:40:14,181
...and you change
the genetic instructions.
557
00:40:21,665 --> 00:40:25,692
DNA must replicate itself
with extreme fidelity.
558
00:40:25,903 --> 00:40:30,499
The reproduction of a DNA molecule
begins by separating the two helices.
559
00:40:30,707 --> 00:40:34,666
This is accomplished
by an unwinding enzyme.
560
00:40:34,878 --> 00:40:38,871
Like some precision tool,
this enzyme, shown in blue...
561
00:40:39,082 --> 00:40:44,019
...breaks the chemical bonds
that bind the two helices of DNA.
562
00:40:44,655 --> 00:40:47,249
The enzyme works its way
down the molecule...
563
00:40:47,457 --> 00:40:50,722
...unzipping DNA as it goes.
564
00:40:53,330 --> 00:40:55,423
Each helix copies the other...
565
00:40:55,632 --> 00:40:58,829
...supervised by special enzymes.
566
00:40:59,036 --> 00:41:02,870
The organic soup inside the nucleus
contains many free nucleotides.
567
00:41:03,140 --> 00:41:08,077
The enzyme recognizes an approaching
nucleotide and clicks it into place...
568
00:41:08,378 --> 00:41:11,643
...reproducing another rung
in the double helix.
569
00:41:15,919 --> 00:41:18,547
When the DNA is replicating
in one of your cells...
570
00:41:18,755 --> 00:41:21,622
...a few dozen nucleotides
are added every second.
571
00:41:21,959 --> 00:41:26,362
Thousands of these enzymes may be
working on a given DNA molecule.
572
00:41:36,206 --> 00:41:38,970
When an arriving nucleotide
doesn't fit...
573
00:41:39,176 --> 00:41:41,235
...the enzyme throws it away.
574
00:41:41,445 --> 00:41:43,072
We call this proofreading.
575
00:41:43,280 --> 00:41:45,771
On the rare occasions
of a proofreading error...
576
00:41:45,983 --> 00:41:47,917
...the wrong nucleotide is attached...
577
00:41:48,118 --> 00:41:51,747
...and a small random change has
been made in the genetic instructions.
578
00:41:51,955 --> 00:41:54,321
A mutation has occurred.
579
00:41:55,859 --> 00:41:58,623
This enzyme is a
pretty small molecule...
580
00:41:58,829 --> 00:42:01,821
...but it catches nucleotides,
assembles them in the right order...
581
00:42:02,032 --> 00:42:03,465
...it knows how to proofread...
582
00:42:03,667 --> 00:42:06,534
...it's responsible
in the most fundamental way...
583
00:42:06,737 --> 00:42:11,231
...for the reproduction of every cell
and every being on Earth.
584
00:42:16,680 --> 00:42:19,171
That enzyme and DNA itself...
585
00:42:19,383 --> 00:42:23,319
...are molecular machines
with awesome powers.
586
00:42:26,023 --> 00:42:29,584
Within every living thing,
the molecular machines are busy...
587
00:42:29,793 --> 00:42:34,389
...making sure that nucleic acids
will continue to reproduce.
588
00:42:55,318 --> 00:42:58,776
A minor cut in my skin
sounds a local alarm...
589
00:42:58,989 --> 00:43:02,857
...and the blood spins
a complex net of strong fibers...
590
00:43:03,060 --> 00:43:06,223
...to form a clot
and staunch the flow of blood.
591
00:43:06,430 --> 00:43:08,125
There's a very delicate balance here:
592
00:43:08,331 --> 00:43:11,459
Too much clotting
and your blood stream will solidify.
593
00:43:11,668 --> 00:43:15,798
Too little clotting and you'll bleed
to death from the merest scratch.
594
00:43:16,106 --> 00:43:21,043
The balance is controlled
by enzymes instructed by DNA.
595
00:43:23,680 --> 00:43:26,843
Down here, there's also
a kind of sanitation squad...
596
00:43:27,050 --> 00:43:30,315
...comprised of white blood cells,
that swings into action...
597
00:43:30,520 --> 00:43:35,150
...surrounds invading bacteria
and ravenously consumes them.
598
00:43:35,358 --> 00:43:38,521
This mopping-up operation is
a part of the healing process...
599
00:43:38,728 --> 00:43:41,720
...again controlled by DNA.
600
00:43:43,300 --> 00:43:47,430
These cells are parts of us,
but how alien they seem.
601
00:43:47,637 --> 00:43:50,265
Within each of them,
within every cell...
602
00:43:50,474 --> 00:43:53,500
...there are exquisitely
evolved molecular machines.
603
00:43:53,710 --> 00:43:57,271
Nucleic acids, enzymes,
the cell architecture...
604
00:43:57,481 --> 00:44:01,349
...every cell is a triumph
of natural selection.
605
00:44:01,551 --> 00:44:04,748
And we're made of trillions of cells.
606
00:44:04,955 --> 00:44:07,947
We are, each of us, a multitude.
607
00:44:09,559 --> 00:44:12,619
Within us is a little universe.
608
00:44:28,879 --> 00:44:33,816
Human DNA is a coiled ladder...
609
00:44:34,050 --> 00:44:36,314
...a billion nucleotides long.
610
00:44:36,853 --> 00:44:41,187
Many possible combinations of
nucleotides are nonsense. That is...
611
00:44:41,391 --> 00:44:45,760
...they translate into proteins which
serve no useful function whatever.
612
00:44:45,962 --> 00:44:49,193
Only a comparatively few
nucleic acid molecules...
613
00:44:49,399 --> 00:44:54,063
...are any good for life forms
as complicated as we are.
614
00:44:54,838 --> 00:44:59,036
But even so, the number of useful ways
of assembling nucleic acids...
615
00:44:59,242 --> 00:45:01,403
...is stupefyingly large.
616
00:45:01,611 --> 00:45:06,480
It's probably larger than the total
number of atoms in the universe.
617
00:45:06,683 --> 00:45:11,620
This means that the number of
possible kinds of human beings...
618
00:45:11,922 --> 00:45:16,552
...is vastly greater than the number
of human beings that has ever lived.
619
00:45:16,793 --> 00:45:21,025
This untapped potential of
the human species is immense.
620
00:45:21,231 --> 00:45:23,893
There are ways of
putting nucleic acids together...
621
00:45:24,100 --> 00:45:28,366
...which will function far better
by any criterion you wish to choose...
622
00:45:28,572 --> 00:45:33,509
...than the hereditary instructions of
any human being who has ever lived.
623
00:45:33,944 --> 00:45:38,404
Fortunately, we do not know,
or at least do not yet know...
624
00:45:38,615 --> 00:45:43,143
...how to assemble alternative
sequences of nucleotides...
625
00:45:43,353 --> 00:45:46,720
...to make alternative kinds
of human beings.
626
00:45:46,923 --> 00:45:50,450
In the future, we might be able
to put nucleotides together...
627
00:45:50,660 --> 00:45:52,389
...in any desired sequence...
628
00:45:52,596 --> 00:45:55,997
...to produce human characteristics
we think desirable.
629
00:45:57,000 --> 00:46:00,959
A disquieting and awesome prospect.
630
00:46:11,748 --> 00:46:15,912
We human beings don't look
very much like a tree.
631
00:46:16,119 --> 00:46:20,146
We certainly view the world
differently than a tree does.
632
00:46:20,357 --> 00:46:23,815
But down deep,
at the molecular heart of life...
633
00:46:24,027 --> 00:46:27,190
...we're essentially
identical to trees.
634
00:46:27,764 --> 00:46:32,633
We both use nucleic acids
as the hereditary material.
635
00:46:32,836 --> 00:46:37,739
We both use proteins as enzymes
to control the chemistry of the cell.
636
00:46:39,109 --> 00:46:43,637
And most significantly,
we both use the identical code book...
637
00:46:43,847 --> 00:46:48,750
...to translate nucleic acid information
into protein information.
638
00:46:48,952 --> 00:46:53,321
Any tree could read my genetic code.
639
00:46:54,257 --> 00:46:56,782
How did such astonishing similarities
come about?
640
00:46:56,993 --> 00:47:01,123
Why are we cousins to the trees?
641
00:47:01,331 --> 00:47:04,459
Would life on some other planet
use proteins?
642
00:47:04,668 --> 00:47:09,605
The same proteins? The same nucleic
acids? The same genetic code?
643
00:47:10,307 --> 00:47:13,140
The usual explanation
is that we are...
644
00:47:13,343 --> 00:47:16,904
...all of us, trees and people...
645
00:47:17,113 --> 00:47:21,948
...anglerfish, slime molds,
bacteria...
646
00:47:22,152 --> 00:47:25,781
...all descended from a single
and common instance...
647
00:47:25,989 --> 00:47:28,856
...of the origin of life
4 billion years ago...
648
00:47:29,059 --> 00:47:31,220
...in the early days of our planet.
649
00:47:32,062 --> 00:47:33,859
Now, how...
650
00:47:34,064 --> 00:47:37,465
...did the molecules
of life arise?
651
00:47:39,035 --> 00:47:40,400
(THUNDER)
652
00:47:43,473 --> 00:47:45,236
(LIGHTNING BUZZES)
653
00:47:55,819 --> 00:47:58,117
In a laboratory
at Cornell University...
654
00:47:58,555 --> 00:48:02,184
...we mix together the gases
and waters of the primitive Earth...
655
00:48:02,392 --> 00:48:03,825
...supply some energy...
656
00:48:04,027 --> 00:48:07,622
...and see if we can make
the stuff of life.
657
00:48:20,243 --> 00:48:24,475
But what was the early atmosphere
made of, ordinary air?
658
00:48:24,681 --> 00:48:26,706
If we start with
our present atmosphere...
659
00:48:26,916 --> 00:48:29,316
...the experiment is a dismal failure.
660
00:48:29,519 --> 00:48:32,317
Instead of making proteins
and nucleic acids...
661
00:48:32,522 --> 00:48:35,923
...all we make is smog,
a backwards step.
662
00:48:36,126 --> 00:48:38,185
Why doesn't such an experiment work?
663
00:48:38,395 --> 00:48:41,956
Because the air of today
contains molecular oxygen.
664
00:48:42,165 --> 00:48:44,463
But oxygen is made by plants.
665
00:48:44,667 --> 00:48:48,296
It's obvious that there were
no plants before the origin of life.
666
00:48:48,505 --> 00:48:50,735
We mustn't use oxygen
in our experiments...
667
00:48:50,940 --> 00:48:53,807
...because there wasn't any
in the early atmosphere.
668
00:48:59,115 --> 00:49:03,347
This is reasonable because the cosmos
is made mostly of hydrogen...
669
00:49:03,553 --> 00:49:05,020
...which gobbles oxygen up.
670
00:49:05,221 --> 00:49:09,317
The Earth's low gravity has
allowed most of our hydrogen gas...
671
00:49:09,526 --> 00:49:13,223
...to trickle away to space.
There's almost none left.
672
00:49:14,197 --> 00:49:15,630
But 4 billion years ago...
673
00:49:15,832 --> 00:49:18,892
...our atmosphere was full
of hydrogen-rich gases:
674
00:49:19,102 --> 00:49:21,593
Methane, ammonia, water vapor.
675
00:49:21,805 --> 00:49:24,273
These are the gases we should use.
676
00:49:29,245 --> 00:49:32,214
Taking great care to ensure
the purity of these gases...
677
00:49:32,415 --> 00:49:36,545
...my colleague, Bishun Khare,
pumps them from their holding flasks.
678
00:49:50,433 --> 00:49:53,129
An experiment like this
was first performed...
679
00:49:53,336 --> 00:49:57,363
...by Stanley Miller
and Harold Urey in the 1950s.
680
00:49:58,575 --> 00:50:00,668
(GASES FIZZLE)
681
00:50:13,389 --> 00:50:17,985
The starting gases are now introduced
into a large reaction vessel.
682
00:50:18,194 --> 00:50:22,392
We could shine ultraviolet light,
simulating the early sun.
683
00:50:22,599 --> 00:50:23,964
But in this experiment...
684
00:50:24,200 --> 00:50:26,464
...the gases will be sparked...
685
00:50:26,669 --> 00:50:30,605
...as the primitive atmosphere was
by early lightning.
686
00:50:44,187 --> 00:50:45,984
(LIGHTNING BUZZES)
687
00:50:51,294 --> 00:50:55,754
After only a few hours,
the interior of the reaction vessel...
688
00:50:55,965 --> 00:50:59,093
...becomes streaked with
a strange brown pigment...
689
00:50:59,302 --> 00:51:02,829
...a rich collection
of complex organic molecules...
690
00:51:03,039 --> 00:51:07,601
...including the building blocks of
the proteins and the nucleic acids.
691
00:51:09,812 --> 00:51:13,441
Under the right conditions, these
building blocks assemble themselves...
692
00:51:13,650 --> 00:51:18,110
...into molecules resembling little
proteins and little nucleic acids.
693
00:51:18,321 --> 00:51:22,849
These nucleic acids can even make
identical copies of themselves.
694
00:51:28,298 --> 00:51:32,701
In this vessel are the notes
of the music of life...
695
00:51:32,902 --> 00:51:35,769
...although not yet the music itself.
696
00:51:38,308 --> 00:51:40,742
Now, no one, so far...
697
00:51:40,944 --> 00:51:45,313
...has mixed together the gases
and waters of the primitive Earth...
698
00:51:45,515 --> 00:51:50,452
...and at the end of the experiment
had something crawl out of the flask.
699
00:51:50,687 --> 00:51:54,316
There's still much to be understood
about the origin of life...
700
00:51:54,524 --> 00:51:56,856
...including the origin
of the genetic code.
701
00:51:57,060 --> 00:52:00,518
But we've only been at
such experiments for 30 years.
702
00:52:00,730 --> 00:52:04,029
Nature's had
a 4-billion-year head start.
703
00:52:04,233 --> 00:52:08,829
Incidentally, there's nothing in such
experiments that's unique to the Earth.
704
00:52:09,038 --> 00:52:12,633
The gases we start with,
the energy sources we use...
705
00:52:12,842 --> 00:52:15,572
...are entirely common
through the cosmos.
706
00:52:15,778 --> 00:52:20,306
So chemical reactions something like
these must be responsible for...
707
00:52:20,516 --> 00:52:22,677
...the organic matter
in interstellar space...
708
00:52:22,885 --> 00:52:25,251
...and the amino acids
in the meteorites.
709
00:52:25,455 --> 00:52:28,288
Similar chemical reactions
must have occurred...
710
00:52:28,491 --> 00:52:31,927
...on a billion other worlds
in the Milky Way galaxy.
711
00:52:32,128 --> 00:52:36,087
Look how easy it is to make
great globs of this stuff.
712
00:52:36,299 --> 00:52:40,565
The molecules of life fill the cosmos.
713
00:52:41,170 --> 00:52:42,228
Now...
714
00:52:42,772 --> 00:52:45,605
What would life elsewhere look like?
715
00:52:45,808 --> 00:52:49,801
Even if it had an identical molecular
chemistry to life on Earth...
716
00:52:50,013 --> 00:52:51,844
...which I very much doubt...
717
00:52:52,048 --> 00:52:55,609
...it could not be
very similar in form...
718
00:52:55,818 --> 00:52:58,082
...to familiar organisms on the Earth.
719
00:52:58,287 --> 00:53:01,450
The random character of
the evolutionary process...
720
00:53:01,658 --> 00:53:06,493
...must create elsewhere creatures
very different from any that we know.
721
00:53:08,264 --> 00:53:10,892
Think of a world
something like Jupiter...
722
00:53:11,100 --> 00:53:15,662
...with an atmosphere rich in hydrogen,
helium, methane, water and ammonia...
723
00:53:15,872 --> 00:53:17,533
...in which organic molecules
might be...
724
00:53:17,740 --> 00:53:20,470
...falling from the skies
like manna from heaven...
725
00:53:20,677 --> 00:53:23,237
...like the products of
the Miller-Urey experiment.
726
00:53:23,446 --> 00:53:25,937
Could there be life on such a world?
727
00:53:26,883 --> 00:53:30,444
There's a special problem.
The atmosphere is turbulent...
728
00:53:30,653 --> 00:53:34,282
...and down deep, before we ever
come to a surface, it's very hot.
729
00:53:34,490 --> 00:53:38,153
If you're not careful,
you'll be carried down and fried.
730
00:53:38,361 --> 00:53:41,194
If you reproduce
before you're fried...
731
00:53:41,397 --> 00:53:46,096
...turbulence will carry your offspring
into the higher and cooler layers.
732
00:53:46,302 --> 00:53:51,001
Such organisms could be very little.
We call them sinkers.
733
00:53:52,442 --> 00:53:55,570
The physicist E.E. Salpeter and I
at Cornell...
734
00:53:55,778 --> 00:53:58,372
...have calculated
something about the life...
735
00:53:58,581 --> 00:54:01,072
...that might exist on such a world.
736
00:54:03,119 --> 00:54:06,384
Vast living balloons could
stay buoyant...
737
00:54:06,589 --> 00:54:09,752
...by pumping heavy gases
from their interiors...
738
00:54:09,959 --> 00:54:11,950
...or by keeping their insides warm.
739
00:54:12,161 --> 00:54:14,891
They might eat the organic molecules
in the air...
740
00:54:15,098 --> 00:54:16,963
...or make their own with sunlight.
741
00:54:17,166 --> 00:54:20,499
We call these creatures floaters.
742
00:54:22,171 --> 00:54:24,537
We imagine floaters
kilometers across...
743
00:54:24,741 --> 00:54:28,177
...enormously larger than
the greatest whale that ever was...
744
00:54:28,377 --> 00:54:31,778
...beings the size of cities.
745
00:54:31,981 --> 00:54:35,883
We conceive of them arrayed
in great, lazy herds...
746
00:54:36,085 --> 00:54:37,916
...as far as the eye can see...
747
00:54:38,121 --> 00:54:42,820
...concentrated in the updrafts
in the enormous sea of clouds.
748
00:54:43,025 --> 00:54:47,291
But there can be other creatures
in this alien environment: hunters.
749
00:54:49,165 --> 00:54:51,326
Hunters are fast and maneuverable.
750
00:54:51,534 --> 00:54:54,833
They eat the floaters,
both for their organic molecules...
751
00:54:55,037 --> 00:54:57,130
...and for their store
of pure hydrogen.
752
00:54:57,340 --> 00:54:59,035
But there can't be many hunters...
753
00:54:59,242 --> 00:55:03,906
...because if they destroy all the
floaters, they themselves will perish.
754
00:55:07,450 --> 00:55:10,578
Physics and chemistry permit
such life forms.
755
00:55:10,787 --> 00:55:13,255
Art presents them with
a certain reality...
756
00:55:13,456 --> 00:55:17,119
...but nature is not obliged
to follow our speculations.
757
00:55:17,326 --> 00:55:21,922
If there are billions of inhabited
worlds in the Milky Way galaxy...
758
00:55:22,365 --> 00:55:26,859
...then I think it's likely there are
a few places which might have...
759
00:55:27,069 --> 00:55:28,468
...hunters...
760
00:55:28,671 --> 00:55:31,469
...and floaters and sinkers.
761
00:55:32,708 --> 00:55:36,940
Biology is more like history
than it is like physics.
762
00:55:37,146 --> 00:55:40,206
You have to know the past
to understand the present.
763
00:55:40,416 --> 00:55:44,580
There is no predictive theory of
biology, nor is there for history.
764
00:55:44,787 --> 00:55:46,152
The reason is the same:
765
00:55:46,355 --> 00:55:49,688
Both subjects are still
too complicated for us.
766
00:55:49,892 --> 00:55:52,520
But we can understand ourselves
much better...
767
00:55:52,728 --> 00:55:54,958
...by understanding other cases.
768
00:55:56,632 --> 00:56:00,090
The study of a single instance
of extraterrestrial life...
769
00:56:00,303 --> 00:56:03,795
No matter how humble,
a microbe would be just fine.
770
00:56:04,006 --> 00:56:06,941
...will de-provincialize biology.
771
00:56:07,143 --> 00:56:10,738
It will show us what else is possible.
772
00:56:12,215 --> 00:56:17,152
We've heard so far the voice
of life on only a single world...
773
00:56:17,386 --> 00:56:19,752
...but for the first time,
as we shall see...
774
00:56:19,956 --> 00:56:23,414
...we've begun
a serious scientific search...
775
00:56:23,626 --> 00:56:25,856
...for the cosmic fugue.
776
00:56:36,072 --> 00:56:39,337
Recently, we've learned more
about the origin of life.
777
00:56:39,542 --> 00:56:41,669
Do you remember RNA...
778
00:56:41,878 --> 00:56:45,245
...that nucleic acid
that our cells use as messengers...
779
00:56:45,448 --> 00:56:48,576
...carrying the genetic information
out of the cell nucleus?
780
00:56:49,252 --> 00:56:53,484
Well, it's been found that RNA,
like protein...
781
00:56:53,689 --> 00:56:55,953
...can control chemical reactions...
782
00:56:56,158 --> 00:56:59,821
...as well as reproduce itself,
which proteins can't do.
783
00:57:00,029 --> 00:57:03,260
Many scientists now wonder
if the first life on Earth...
784
00:57:03,466 --> 00:57:05,627
...was an RNA molecule.
785
00:57:05,835 --> 00:57:09,293
It now seems feasible that
key molecular building blocks...
786
00:57:09,505 --> 00:57:13,441
...for the origin of life, fell out
of the skies 4 billion years ago.
787
00:57:14,210 --> 00:57:18,613
Comets have been found to have a lot
of organic molecules in them...
788
00:57:18,814 --> 00:57:23,148
...and they fell in huge numbers
on the primitive Earth.
789
00:57:24,253 --> 00:57:27,086
We also mention the extinction
of the dinosaurs...
790
00:57:27,290 --> 00:57:31,226
...and most of the other species on
Earth about 65 million years ago.
791
00:57:31,427 --> 00:57:35,591
We now know that a large comet
hit the Earth at just that time.
792
00:57:35,798 --> 00:57:40,735
The dust pall from that collision
must've cooled and darkened the Earth...
793
00:57:41,070 --> 00:57:44,005
...perhaps killing all
the dinosaurs, but sparing...
794
00:57:44,206 --> 00:57:48,666
...the small, furry mammals
who were our ancestors.
795
00:57:48,878 --> 00:57:52,746
Other cometary mass extinctions
in other epochs seem likely.
796
00:57:52,949 --> 00:57:57,283
If true, this would mean that
comets have been the bringers...
797
00:57:57,486 --> 00:57:59,954
...both of life and death.
69500
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