1
00:00:14,687 --> 00:00:20,080
(STEVE LEONARD ) Midwinter
at the bottom of the world - Antarctica -
2
00:00:20,247 --> 00:00:22,363
the coldest place on Earth,
3
00:00:22,527 --> 00:00:26,918
with an air temperature
of minus 50 degrees centigrade,
4
00:00:28,367 --> 00:00:31,598
You'd think that nothing could survive here,
5
00:00:33,607 --> 00:00:37,122
Yet, huddling together,
somehow these emperor penguins
6
00:00:37,287 --> 00:00:41,599
have evolved to cope
with the battle for life in the big freeze,
7
00:00:52,447 --> 00:00:55,757
But cold is not the penguins' biggest enemy,
8
00:01:00,527 --> 00:01:02,518
This is,
9
00:01:08,687 --> 00:01:12,157
The leopard seal - four metres long -
10
00:01:12,327 --> 00:01:13,680
a super-predator,
11
00:01:13,847 --> 00:01:15,724
(PENGUINS SQUAWK)
12
00:01:15,887 --> 00:01:20,483
No wonder everyone's reluctant
to be the first to take the plunge,
13
00:01:32,807 --> 00:01:37,756
Penguin and seal have a relationship
forged over millions of years -
14
00:01:37,927 --> 00:01:40,646
that of predator and prey,
15
00:01:51,207 --> 00:01:57,521
It's easy to see nature as red in tooth and claw,
where predators dictate who lives and dies
16
00:01:57,687 --> 00:02:01,760
and only the fastest and strongest survive,
17
00:02:02,847 --> 00:02:07,079
But the truth is, predators and prey
are just part of life's story,
18
00:02:07,247 --> 00:02:11,957
Our world is made up of a vast network
of different relationships,
19
00:02:14,007 --> 00:02:19,035
Animals, including us, have to find mates,
look after families
20
00:02:19,207 --> 00:02:21,960
and keep up with the neighbours,
21
00:02:22,647 --> 00:02:27,402
And all these relationships
affect how we look and behave,
22
00:02:30,447 --> 00:02:33,200
(ROARS)
23
00:02:33,367 --> 00:02:35,642
(SCREECHING)
24
00:02:37,847 --> 00:02:39,838
This is the surprising story
25
00:02:40,007 --> 00:02:46,879
of how the relationships between all living
things have shaped the whole journey of life,
26
00:03:03,647 --> 00:03:07,322
Life on Earth wasn't always
as complicated as it is today,
27
00:03:07,487 --> 00:03:10,763
There was a time
when there were no relationships,
28
00:03:12,447 --> 00:03:14,438
There was no violence,
29
00:03:14,607 --> 00:03:16,598
practically no competition,
30
00:03:16,767 --> 00:03:18,086
and no sex.
31
00:03:18,247 --> 00:03:19,885
Imagine that.
32
00:03:26,887 --> 00:03:33,122
Three billion years ago, the pinnacle of evolution
was these strange lumps on the ocean floor -
33
00:03:33,287 --> 00:03:38,281
stromatolites, made up of ancient algae,
34
00:03:48,287 --> 00:03:51,597
It might not have the ring
of the “age of the dinosaurs”,
35
00:03:51,767 --> 00:03:55,203
but the age of the stromatolites
was eight times longer
36
00:03:55,367 --> 00:04:00,964
and was the longest period of peace
and tranquillity that life has ever known.
37
00:04:03,527 --> 00:04:09,284
They might not look much, but stromatolites
had the power to change the world,
38
00:04:09,447 --> 00:04:15,158
For the first time in the history of the planet,
they produced a gas called oxygen,
39
00:04:15,327 --> 00:04:19,286
and so totally transformed
the planet's atmosphere,
40
00:04:21,087 --> 00:04:23,999
Not only did they generate the air we breathe,
41
00:04:24,167 --> 00:04:28,046
they set the scene for all life
as we know it today,
42
00:04:30,287 --> 00:04:33,882
Because of them,
a brand-new type of cell evolved,
43
00:04:34,047 --> 00:04:37,881
perhaps the most important
life has ever known,
44
00:04:40,087 --> 00:04:45,798
These revolutionary oxygen-fuelled cells
spawned our ancestors,
45
00:04:45,967 --> 00:04:50,199
but they were 20 times more energetic
than the older models,
46
00:04:50,367 --> 00:04:54,804
Some discovered that the quickest way
to get the extra energy they needed
47
00:04:54,967 --> 00:04:59,199
was to steal it by engulfing other cells,
48
00:05:03,487 --> 00:05:07,275
A new force was unleashed - the predator,
49
00:05:14,687 --> 00:05:16,643
(PANTS)
50
00:05:21,607 --> 00:05:25,646
With predators around, you’ve got
to be able to defend yourself.
51
00:05:26,367 --> 00:05:30,121
One way is to make yourself invisible.
52
00:05:37,367 --> 00:05:39,278
Armour’s good, too.
53
00:05:39,447 --> 00:05:41,358
Good solid protection.
54
00:05:43,727 --> 00:05:47,515
Staying alert can mean the difference
between life and death.
55
00:06:05,087 --> 00:06:08,443
As predators find better ways to catch and kill,
56
00:06:08,607 --> 00:06:12,316
their prey have to improve their self-defence,
57
00:06:13,527 --> 00:06:18,920
The two are locked in an intense relationship
which forces both sides to change
58
00:06:19,087 --> 00:06:22,682
because neither can afford to be left behind,
59
00:06:34,967 --> 00:06:38,084
Nature selects only the winners’ genes,
60
00:06:38,247 --> 00:06:41,364
The losers will disappear,
61
00:06:45,767 --> 00:06:51,205
This arms race has helped shape the lives
and bodies of just about everything alive today
62
00:06:51,367 --> 00:06:55,201
and pushed some creatures
to incredible extremes,
63
00:07:09,087 --> 00:07:11,999
This cricket might think it's on a flower...
64
00:07:15,927 --> 00:07:20,637
..but it's actually a mantis
that's evolved to look just like an orchid,
65
00:07:20,807 --> 00:07:23,799
Beauty turns out to be a beast,
66
00:07:33,487 --> 00:07:36,524
Other hunting strategies are even more bizarre,
67
00:07:40,207 --> 00:07:44,439
Over millennia, the snapping turtle's efforts
to reel in a fish
68
00:07:44,607 --> 00:07:47,804
have turned its tongue into a juicy worm,
69
00:07:58,887 --> 00:08:02,277
But secret weapons
aren't the only winning formula,
70
00:08:02,447 --> 00:08:05,917
Sometimes, more subtle tactics
may be what you need,
71
00:08:06,087 --> 00:08:10,877
Meet jumping spider Portia,
one of the world's smallest assassins,
72
00:08:12,927 --> 00:08:15,964
She's hunting the much larger web spider,
73
00:08:19,287 --> 00:08:23,678
She might be tiny, but she has a big appetite,
74
00:08:28,687 --> 00:08:35,525
Her first direct approach alerts her target,
who shakes the web and forces Portia to retreat,
75
00:08:39,887 --> 00:08:41,878
But Portia has evolved a plan B -
76
00:08:42,047 --> 00:08:45,801
a manoeuvre straight
out of “Mission: Impossible”,
77
00:08:59,647 --> 00:09:02,957
She slowly lowers herself within striking range...
78
00:09:03,727 --> 00:09:05,683
..leaps, bites...
79
00:09:05,847 --> 00:09:10,125
..and leaves the poison
from her tiny fangs to do the rest,
80
00:09:16,487 --> 00:09:21,515
This time, it isn't size or secrecy
that counts, but strategy,
81
00:09:21,687 --> 00:09:25,760
Portia may be small,
but she's as deadly as they come,
82
00:09:30,087 --> 00:09:32,920
The relationship between hunter and hunted
83
00:09:33,087 --> 00:09:39,606
doesn't only shape the way that predators
attack, it drives the way that prey fight back,
84
00:09:39,767 --> 00:09:44,841
Sometimes, it's just about using
your natural assets in a different way,
85
00:09:46,687 --> 00:09:50,726
When a hungry raven eyes their chicks,
fieldfares fight dirty,
86
00:09:54,087 --> 00:09:56,203
They drop bombs,
87
00:09:56,367 --> 00:09:58,756
(CAWS)
88
00:10:19,607 --> 00:10:22,519
A dirty trick but, hey, it works,
89
00:10:27,287 --> 00:10:31,997
The only problem with an evolutionary arms race
is that we don't see it develop.
90
00:10:32,167 --> 00:10:34,078
All we see is the end result.
91
00:10:38,527 --> 00:10:42,839
But there are rare exceptions,
like the story of the passion flower.
92
00:10:43,007 --> 00:10:47,000
Like other prey species,
they're evolving to protect themselves,
93
00:10:47,167 --> 00:10:51,001
but what makes them unique
is that you can watch them doing it.
94
00:10:54,087 --> 00:11:00,037
Plants have to fight for survival, too, and
even these exotic passion vines have enemies,
95
00:11:07,767 --> 00:11:09,997
At home in tropical America,
96
00:11:10,167 --> 00:11:16,606
they're under constant attack from lethal
predators that live deep in the jungle -
97
00:11:18,847 --> 00:11:20,883
heliconius butterflies,
98
00:11:22,687 --> 00:11:27,807
The adults are harmless enough, It's what
they leave behind them that's the problem,
99
00:11:28,887 --> 00:11:32,800
Mother butterflies lay their eggs
on the passion vine's leaves,
100
00:11:35,687 --> 00:11:38,042
Tiny time bombs...
101
00:11:43,087 --> 00:11:47,046
..which soon hatch out
into very hungry caterpillars,
102
00:11:52,407 --> 00:11:55,717
This plant's fate is already sealed,
103
00:11:55,887 --> 00:11:58,765
In a few days, there will be nothing left,
104
00:12:06,487 --> 00:12:11,959
If a passion vine already has a batch of eggs
installed, it's pointless to lay more,
105
00:12:12,127 --> 00:12:19,044
A sensible mother butterfly will pass it by, which
gives the passion flower a chance to fight back,
106
00:12:19,207 --> 00:12:22,995
Today, not all the eggs
are quite what they appear,
107
00:12:23,167 --> 00:12:29,800
Some are in fact just yellow spots grown
by the passion flower to deter mother butterflies,
108
00:12:34,927 --> 00:12:39,000
But in this mini arms race,
not all attacks are foiled,
109
00:12:43,047 --> 00:12:45,800
Some passion flowers
haven't quite got it nailed.
110
00:12:45,967 --> 00:12:49,243
These spots are supposed to be butterfly eggs,
111
00:12:49,407 --> 00:12:52,956
but it hasn't quite put off
all of the butterflies,
112
00:12:53,127 --> 00:12:57,200
because we've got a very greedy caterpillar.
113
00:12:59,807 --> 00:13:03,277
So there's pressure
for ever better mimics to evolve,
114
00:13:03,447 --> 00:13:06,962
Some are now so good,
it's hard to tell which eggs are real,
115
00:13:08,687 --> 00:13:10,006
False,
116
00:13:10,767 --> 00:13:12,200
Real,
117
00:13:12,807 --> 00:13:14,126
Real,
118
00:13:15,407 --> 00:13:16,726
False,
119
00:13:17,807 --> 00:13:19,798
And real,
120
00:13:21,527 --> 00:13:25,839
Who'd have thought that the relationship
between a butterfly and a vine
121
00:13:26,007 --> 00:13:28,601
could produce such a sophisticated bluff?
122
00:13:29,847 --> 00:13:32,520
But trouble can come at you from all sides.
123
00:13:32,687 --> 00:13:38,000
Even when you’re safe from predators,
you can often have strife from your own kind -
124
00:13:38,167 --> 00:13:39,998
competition.
125
00:13:43,247 --> 00:13:50,437
In a rainforest, of course, the plants
are all after the same thing - precious light,
126
00:13:53,487 --> 00:13:59,039
And they can't all be winners,
Only those best adapted to compete survive,
127
00:14:01,887 --> 00:14:08,201
It's the same principle wherever there's a crowd,
In Africa, meat is the prize,
128
00:14:11,727 --> 00:14:16,676
A vulture has the aerial advantage
that means it can spot the first signs of a kill,
129
00:14:16,847 --> 00:14:20,476
but it won't have long to feed undisturbed,
130
00:14:23,007 --> 00:14:27,683
Before long, every vulture
in the area is fighting for a beakful,
131
00:14:35,327 --> 00:14:39,002
At this buffet, now only the toughest get to eat,
132
00:14:40,487 --> 00:14:43,877
Lappet-faced vultures
are the biggest bully boys of all,
133
00:14:44,527 --> 00:14:47,758
They knock the smaller griffons flying,
134
00:15:00,807 --> 00:15:04,436
But a free lunch attracts other hopefuls, too,
135
00:15:04,607 --> 00:15:09,556
More feathers fly as even lappets
have to make way for the mammal heavy mob,
136
00:15:09,727 --> 00:15:13,037
(SNARLING AND SCREECHING)
137
00:15:22,927 --> 00:15:28,718
Like predators and prey, this kind of competition
is a real force to be reckoned with -
138
00:15:28,887 --> 00:15:34,007
another influence on evolution
which selects only the toughest to survive,
139
00:15:39,047 --> 00:15:41,959
Competition is so crucial to animals' lives
140
00:15:42,127 --> 00:15:45,642
it can have a massive impact
on their body shape,
141
00:15:49,767 --> 00:15:53,840
Browsers have been moulded
into different shapes and sizes
142
00:15:54,007 --> 00:15:56,840
so they don't tread on each other's toes,
143
00:16:02,447 --> 00:16:06,122
Tiny dik-diks can nibble
around the thorny lower branches
144
00:16:06,287 --> 00:16:12,123
in a way no bigger animals can, so they don't
need to reach higher than a couple of feet,
145
00:16:16,687 --> 00:16:20,839
Taller impala have control
over the acacia's middle zone,
146
00:16:22,847 --> 00:16:25,919
But even they are kept in their place
by the gerenuk,
147
00:16:26,087 --> 00:16:29,363
which has a poise no other antelope can match,
148
00:16:34,167 --> 00:16:39,958
Gerenuks look more like ballet dancers than
gazelles, They even balance on their pointes,
149
00:16:42,927 --> 00:16:47,398
Their specially adapted hips and spines
enable them to swivel vertically
150
00:16:47,567 --> 00:16:50,127
and stand tiptoe on their hind legs,
151
00:16:55,807 --> 00:17:01,677
But there's one animal who can feed
even higher still - up to six metres,
152
00:17:01,847 --> 00:17:04,077
It has a flexible leathery tongue
153
00:17:04,247 --> 00:17:08,479
which it can use like a hand
to pluck the highest twigs and leaves,
154
00:17:08,647 --> 00:17:12,276
thanks to evolving the longest neck in the world,
155
00:17:12,447 --> 00:17:14,278
The giraffe,
156
00:17:27,287 --> 00:17:32,839
So competition hasn't just pushed animals
into developing different eating habits,
157
00:17:33,007 --> 00:17:38,286
it's helped create different species
that can live together in harmony,
158
00:17:43,287 --> 00:17:47,678
But what happens when neighbours
want exactly the same thing?
159
00:17:49,087 --> 00:17:53,239
Ringtailed lemurs live in troops
on the island of Madagascar,
160
00:17:54,087 --> 00:17:57,238
Each group needs their own territory to survive,
161
00:17:57,407 --> 00:18:01,685
for shelter, food and a safe place
to rear their babies,
162
00:18:01,847 --> 00:18:05,840
but they're often under threat
from other lemur gangs..,
163
00:18:08,087 --> 00:18:11,318
..who'll steal the whole thing if they can,
164
00:18:22,127 --> 00:18:24,846
- (SCREECHES)
- The alarm sounds,
165
00:18:25,007 --> 00:18:29,285
These intruders look like they mean business,
Time to rally the troops,
166
00:18:40,367 --> 00:18:45,282
Lemur society is run by females,
so it's they who lead the band into the fray -
167
00:18:45,447 --> 00:18:48,723
soldiers with babies on their backs,
168
00:18:48,927 --> 00:18:51,919
(DIN OF SCREECHING)
169
00:19:19,047 --> 00:19:24,121
When competition gets this intense,
the lemurs' answer is teamwork,
170
00:19:34,327 --> 00:19:37,160
(CHIRPING)
171
00:19:40,847 --> 00:19:46,001
Once animals are driven to work together,
the close relationships which evolve
172
00:19:46,167 --> 00:19:48,806
can open up a whole new way of life,
173
00:19:53,487 --> 00:19:56,797
Meerkats are high on the menu
for many predators...
174
00:19:59,607 --> 00:20:02,679
..so they work together to protect themselves,
175
00:20:19,407 --> 00:20:23,685
They're one of the few mammals
that take turns at doing different jobs,
176
00:20:30,527 --> 00:20:35,123
While the rest of the family digs
for breakfast, one member stands guard,
177
00:20:35,287 --> 00:20:38,006
looking out for predators,
178
00:20:40,487 --> 00:20:45,163
The others feel safe in the knowledge
that someone is watching their backs,
179
00:20:57,927 --> 00:21:00,964
(CHIRPING)
180
00:21:10,687 --> 00:21:14,475
And it's not just lookout duty meerkats share,
181
00:21:16,367 --> 00:21:20,280
When a monitor lizard appears,
they all gang up to drive it away,
182
00:21:29,647 --> 00:21:33,925
En masse, these little creatures
make a formidable force,
183
00:21:34,087 --> 00:21:36,078
(CHIRPING)
184
00:21:49,527 --> 00:21:53,805
Being such good team players
is the meerkats' winning formula,
185
00:21:54,567 --> 00:21:57,286
It's all for one and one for all,
186
00:21:59,367 --> 00:22:06,079
It's easy to see why we help our relations, but
some animals co-operate with different species,
187
00:22:06,247 --> 00:22:07,760
How could that evolve?
188
00:22:09,687 --> 00:22:13,646
There's an answer to be found in the sea,
189
00:22:39,287 --> 00:22:42,199
A coral reef like this is a natural metropolis,
190
00:22:42,367 --> 00:22:46,918
where everyone is trying to get on
and make their own way.
191
00:22:48,367 --> 00:22:52,326
It's full of opportunities, deals to be struck...
192
00:22:53,207 --> 00:22:56,882
Some enterprising characters are cleaning up,
193
00:22:58,447 --> 00:23:02,599
It turns out there's a market niche
for professional groomers,
194
00:23:07,887 --> 00:23:13,917
Cleaners - like this tiny wrasse - snaffle up
their clients’ parasites and dead skin,
195
00:23:14,807 --> 00:23:17,799
They set up their own cleaning stations,
196
00:23:17,967 --> 00:23:22,199
Customers come from far and wide
for dental hygiene or a gill wash,
197
00:23:22,367 --> 00:23:25,643
In return, the cleaner gets a meal,
198
00:23:30,687 --> 00:23:34,521
Cleaner shrimps, too,
serve a most discerning clientele,
199
00:23:41,807 --> 00:23:45,766
Fish are smarter than you might think,
They have good memories,
200
00:23:45,927 --> 00:23:50,000
and come back regularly to be pampered
in exactly the same spot,
201
00:23:50,167 --> 00:23:52,158
and by the same cleaner,
202
00:23:58,367 --> 00:24:04,078
The coral crowd soon learns which are
the top salons, boasting the most talented staff,
203
00:24:12,087 --> 00:24:16,717
It's not just tropical fish who've discovered
that hiring a little help
204
00:24:16,887 --> 00:24:18,878
can help you get ahead,
205
00:24:20,767 --> 00:24:23,486
Some plants have, too,
206
00:24:29,047 --> 00:24:34,883
This garden only exists because of
an ancient alliance between insects and plants.
207
00:24:37,687 --> 00:24:39,882
It's a real match made in heaven
208
00:24:40,047 --> 00:24:45,405
as it's produced some of the most beautiful
of all living things - flowers.
209
00:24:51,927 --> 00:24:54,316
Since flowers can't move around,
210
00:24:54,487 --> 00:24:59,800
they need help to carry pollen between them
so they can produce fertile seeds,
211
00:25:02,167 --> 00:25:06,797
So they advertise themselves
as nectar feeding stations,
212
00:25:15,087 --> 00:25:19,558
As the insects feed,
they get an extra takeaway of pollen,
213
00:25:21,007 --> 00:25:25,239
It's an evolutionary partnership
that has proved so successful,
214
00:25:25,407 --> 00:25:28,399
flowering plants now dominate our world,
215
00:25:37,127 --> 00:25:38,606
To guarantee delivery,
216
00:25:38,767 --> 00:25:43,716
some flowers have developed
an exclusive contract with their pollinators,
217
00:25:43,887 --> 00:25:49,598
Orchids, the royal family of flowers,
can be very demanding indeed,
218
00:25:51,767 --> 00:25:55,476
Some, like this bucket orchid,
seem downright cruel,
219
00:25:58,367 --> 00:26:01,439
This euglossine bee
has to visit the bucket orchid,
220
00:26:01,607 --> 00:26:06,761
He needs its perfumed oils to use
as an insect aftershave to attract a mate,
221
00:26:09,487 --> 00:26:13,639
But as he gathers the oil, he loses his grip -
222
00:26:15,287 --> 00:26:18,165
exactly what the orchid wants,
223
00:26:19,687 --> 00:26:24,761
It has evolved a complex trap
which press-gangs male bees into service,
224
00:26:26,087 --> 00:26:30,717
The only way out is via the back door
and the orchid's pollen sacs,
225
00:26:51,687 --> 00:26:54,804
The pollen sticks to the delivery bee's back,
226
00:26:59,527 --> 00:27:03,281
Once free, he takes a short while to dry off,
227
00:27:07,687 --> 00:27:11,077
Surely he'll never go
near a bucket orchid again!
228
00:27:12,007 --> 00:27:16,000
Either male bees have short memories
or run out of aftershave,
229
00:27:16,167 --> 00:27:19,955
because here he is falling
for the same ploy all over again,
230
00:27:22,887 --> 00:27:27,039
The difference this time
is that he's delivering pollen instead,
231
00:27:30,287 --> 00:27:34,724
No question who's wearing
the trousers in this relationship,
232
00:27:39,087 --> 00:27:44,605
Although the bond between flowers and insects
has extraordinarily beautiful results,
233
00:27:44,767 --> 00:27:50,478
plants also depend on an invisible partnership
which is even more important,
234
00:27:50,647 --> 00:27:54,640
Because without it, most of them
wouldn’t even exist at all.
235
00:27:54,807 --> 00:27:58,686
They need it to grow,
and some plants, like these guys here,
236
00:27:58,847 --> 00:28:00,678
grow very big indeed!
237
00:28:04,287 --> 00:28:07,438
Californian redwoods
are the tallest trees in the world,
238
00:28:07,607 --> 00:28:11,043
They can live
for more than 2,000 years
239
00:28:11,207 --> 00:28:14,085
and grow more than 300 feet tall,
240
00:28:14,247 --> 00:28:19,958
These are some of the largest of all living
things, but they rely on the tiniest of partners -
241
00:28:20,127 --> 00:28:23,358
partners so small that they're almost invisible -
242
00:28:23,527 --> 00:28:26,485
and if I am to stand a chance
of seeing them at all,
243
00:28:26,647 --> 00:28:30,276
I've got to go all the way back down there.
244
00:28:40,887 --> 00:28:46,519
They're microscopic and they live hidden
underground amongst the tree's roots.
245
00:29:01,087 --> 00:29:03,999
These secret partners turn out to be fungi,
246
00:29:04,167 --> 00:29:06,317
They penetrate the tree's roots,
247
00:29:06,487 --> 00:29:10,799
then stretch out through the soil
as a network of tiny threads,
248
00:29:11,927 --> 00:29:16,159
The giant trees can't get enough water
and nutrients on their own,
249
00:29:16,327 --> 00:29:18,557
but the fungal network can,
250
00:29:18,727 --> 00:29:23,357
Its massive surface area sucks up
the fluid and minerals the trees need
251
00:29:23,527 --> 00:29:26,519
and then transports them back up to their roots,
252
00:29:28,847 --> 00:29:31,919
And what do the trees
do for the fungi in return?
253
00:29:32,087 --> 00:29:36,239
Just feed them sugars from their leaves -
not a bad deal!
254
00:29:37,167 --> 00:29:40,716
90% of all plants live with fungal partners,
255
00:29:40,887 --> 00:29:43,845
from the redwoods to the rainforests,
256
00:29:44,007 --> 00:29:47,682
It's a 400-million-year-old marriage,
257
00:29:47,847 --> 00:29:53,604
It's possible that without it, plants might
never have been able to colonise the land,
258
00:29:54,687 --> 00:29:59,807
And without all this green stuff,
where would all we animals be?
259
00:30:05,487 --> 00:30:12,086
The close relationship between plants and fungi
is just one of the great alliances to shape life.
260
00:30:13,007 --> 00:30:15,999
There is another -
you need a microscope to see it,
261
00:30:16,167 --> 00:30:19,364
It's perhaps the most
important partnership on Earth,
262
00:30:19,967 --> 00:30:25,405
It provides the power for nearly all living
things, driving every cell in or bodies.
263
00:30:36,167 --> 00:30:39,125
And it's what gives animals their energy,
264
00:30:39,287 --> 00:30:42,040
(MUSIC)
265
00:31:05,527 --> 00:31:08,439
Scattered through the cells of all our bodies
266
00:31:08,607 --> 00:31:13,203
are billions of mysterious structures
called mitochondria,
267
00:31:13,367 --> 00:31:17,565
Each is a tiny furnace
that releases energy from our food
268
00:31:17,727 --> 00:31:21,356
and generates the life force
that our bodies need,
269
00:31:25,367 --> 00:31:27,517
Whoa.
270
00:31:27,687 --> 00:31:30,884
Animals like me and all these guys
271
00:31:31,047 --> 00:31:35,120
can only exist because of the energy
the mitochondria release.
272
00:31:36,087 --> 00:31:40,478
It's a crucial relationship
and one with very unusual beginnings.
273
00:31:40,647 --> 00:31:44,083
In fact, it didn't even start as a partnership.
274
00:31:44,247 --> 00:31:45,999
Come on, then, big man.
275
00:31:49,087 --> 00:31:55,196
Billions of years ago, the mitochondria lived
independent lives as free-floating bacteria,
276
00:31:55,367 --> 00:31:58,404
but our ancestor cell changed all that,
277
00:31:58,567 --> 00:32:05,086
It engulfed one, but instead of eating it,
our ancestor formed an alliance with its prey,
278
00:32:09,687 --> 00:32:13,236
The two joined forces and were transformed,
279
00:32:14,807 --> 00:32:17,241
The bacteria became a mitochondrion
280
00:32:17,407 --> 00:32:21,241
and together they created
a new type of hybrid super-cell..,
281
00:32:22,527 --> 00:32:28,124
..a super-cell which was the basic building
block for almost everything alive today,
282
00:32:28,927 --> 00:32:32,681
So could this mean that it is
co-operation and not conflict
283
00:32:32,847 --> 00:32:36,556
which is actually the strongest force
in evolution?
284
00:32:37,367 --> 00:32:41,121
Is the fight for life more the embrace of life?
285
00:32:41,287 --> 00:32:43,482
It's a lovely idea.
286
00:32:43,647 --> 00:32:45,365
(CONTENTED SIGH)
287
00:33:10,607 --> 00:33:14,759
But relationships, they're never
straightforward, are they?
288
00:33:16,607 --> 00:33:21,840
Most grazing animals in Africa
are plagued by biting insects and ticks,
289
00:33:22,007 --> 00:33:27,206
They also have what seem to be
whole squads of helpful hangers-on,
290
00:33:32,087 --> 00:33:38,526
Oxpeckers - insect-eating birds who reach
the parts the animals themselves can't,
291
00:33:44,447 --> 00:33:48,998
But oxpeckers aren't quite
as innocent as they appear,
292
00:33:50,607 --> 00:33:56,523
They don't just eat up ticks,
they peck holes in the animal's skin,
293
00:33:58,927 --> 00:34:05,002
What appear to be honest little helpers,
in fact turn out to be blood-sucking parasites.
294
00:34:12,967 --> 00:34:18,803
A way of life which, rather horrifyingly,
is far more common than you might expect,
295
00:34:27,087 --> 00:34:31,160
Over half of all creatures alive today
are parasites -
296
00:34:31,327 --> 00:34:37,038
an insidious hidden force that has infiltrated
just about every other living thing.
297
00:34:43,287 --> 00:34:45,596
The Natural History Museum in London
298
00:34:45,767 --> 00:34:50,318
has one of the largest collections
of biological specimens in the world..,
299
00:34:52,007 --> 00:34:58,560
..including some particularly gruesome parasites,
all now, thankfully, pickled in alcohol,
300
00:35:04,847 --> 00:35:09,716
Having a relationship with a parasite
is very much a one-sided affair.
301
00:35:10,327 --> 00:35:15,481
This might look like pasta but it is,
in fact, a tapeworm from a killer whale.
302
00:35:15,647 --> 00:35:20,675
Its natural home is inside the intestine
of the whale, robbing it of its food.
303
00:35:21,487 --> 00:35:23,955
They can grow to 60 feet in length.
304
00:35:25,087 --> 00:35:27,237
Imagine that inside your gut!
305
00:35:31,287 --> 00:35:33,278
Which is perfectly possible,
306
00:35:33,447 --> 00:35:37,486
This tapeworm can take up residence
in humans too,
307
00:35:43,087 --> 00:35:45,681
This is a human botfly larvae.
308
00:35:45,847 --> 00:35:49,760
It's smaller than the tapeworm
but it's much more gruesome.
309
00:35:49,927 --> 00:35:54,125
It burrows into the living flesh of people.
Victims of this parasite
310
00:35:54,287 --> 00:35:57,563
say that they can hear it
munching away in their skin.
311
00:35:58,287 --> 00:36:01,404
This was surgically removed
from someone's head.
312
00:36:01,567 --> 00:36:06,925
If you’re going to pick a parasite to play
host to, this is not the one to choose.
313
00:36:10,127 --> 00:36:12,641
But parasites aren't just gruesome.
314
00:36:12,807 --> 00:36:17,005
Because they affect virtually
every plant and animal alive,
315
00:36:17,167 --> 00:36:21,877
they may just be the biggest influence
on the whole of evolution.
316
00:36:24,647 --> 00:36:26,922
Can that really be true?
317
00:36:31,287 --> 00:36:34,245
Well, take rabbits for example,
318
00:36:34,407 --> 00:36:38,923
You might expect predators to be
the biggest influence on their lives,
319
00:36:41,447 --> 00:36:44,917
After all, they're hunted
by a whole army of killers,
320
00:36:51,607 --> 00:36:54,565
But with predators, they can at least run away,
321
00:36:54,727 --> 00:37:01,121
Rabbits face another threat
which they can't see, smell or hear,
322
00:37:03,767 --> 00:37:08,682
Each rabbit is infested with thousands of fleas,
ticks and minuscule mites,
323
00:37:08,847 --> 00:37:12,965
which may be small but pack a powerful bite,
324
00:37:14,207 --> 00:37:21,238
These bloodsuckers sap the rabbit's strength,
but within them, they carry a deadlier threat,
325
00:37:22,287 --> 00:37:26,485
These little wild baby rabbits
have been abandoned by their mother,
326
00:37:26,647 --> 00:37:31,084
but they've been very fortunate
because they've been adopted by a human.
327
00:37:31,247 --> 00:37:33,761
Not only have they escaped predation,
328
00:37:33,927 --> 00:37:39,718
they've also been saved from the biggest
rabbit killer - the myxomatosis virus.
329
00:37:45,087 --> 00:37:50,036
A virus is a nightmare
straight out of a science-fiction movie,
330
00:37:50,887 --> 00:37:54,323
It's an invader with one aim - to replicate,
331
00:37:54,487 --> 00:37:59,117
It contains special components
which enable it to fulfil its mission,
332
00:38:04,487 --> 00:38:09,003
A potential victim -
the outer surface of a body cell,
333
00:38:09,167 --> 00:38:14,002
On first contact, the virus docks,
and merges with the cell membrane,
334
00:38:20,207 --> 00:38:25,804
Its inner pod enters the cell,
seeks out the command centre - the nucleus -
335
00:38:25,967 --> 00:38:30,722
and then injects its secret weapon -
a snake of virus genes,
336
00:38:31,687 --> 00:38:35,680
These then corrupt the cell,
making it into a virus factory,
337
00:38:39,247 --> 00:38:44,605
Eventually, the cell dies and bursts,
releasing thousands of new viruses,
338
00:38:44,767 --> 00:38:47,964
and the real destruction begins,
339
00:38:49,087 --> 00:38:55,037
Each year, just about every baby rabbit
born in the wild will catch this deadly virus.
340
00:38:55,207 --> 00:38:57,846
Typically, it kills for out of five.
341
00:38:58,007 --> 00:39:02,603
That means in a litter like this,
only one would survive.
342
00:39:09,607 --> 00:39:13,520
Viruses are a truly fearsome
evolutionary selection force,
343
00:39:13,687 --> 00:39:18,602
far more deadly than predators or competition,
344
00:39:32,527 --> 00:39:38,477
Every living thing has to evolve
to fight off viruses - or risk extinction,
345
00:39:39,287 --> 00:39:46,557
I'm talking about warfare on a cellular level
which affects all species alive, including us.
346
00:39:47,287 --> 00:39:52,680
In 1918, at the end of the Great War,
a flu virus struck Europe,
347
00:39:53,487 --> 00:39:57,480
The war killed 25 million people
over four years -
348
00:39:57,647 --> 00:40:00,559
that's three times the population of London -
349
00:40:00,727 --> 00:40:05,005
but the flu epidemic wiped out
the same number in just four months,
350
00:40:08,287 --> 00:40:14,078
A virus can wipe out a population
and can even threaten an entire species.
351
00:40:31,087 --> 00:40:35,922
So, against such a powerful enemy,
how can anything possibly fight back?
352
00:40:36,087 --> 00:40:41,719
The answer is a major obsession for many
species on this planet, including ourselves -
353
00:40:41,887 --> 00:40:43,400
it's sex.
354
00:41:04,847 --> 00:41:10,240
How can sexual relationships have anything
to do with the fight against parasites?
355
00:41:10,407 --> 00:41:13,285
Surely sex is just a matter of reproduction?
356
00:41:13,447 --> 00:41:14,800
(GROWLS)
357
00:41:19,327 --> 00:41:24,321
You’d be surprised. It turns out there's
a lot more to sex than just making babies.
358
00:41:24,487 --> 00:41:28,878
There are lots of living things
that reproduce without it, by cloning.
359
00:41:29,047 --> 00:41:34,917
Look at this spider plant. It's grown babies
just ready to drop off and start growing.
360
00:41:35,087 --> 00:41:38,363
They're perfect mini versions
of the mother plant.
361
00:41:38,967 --> 00:41:45,600
No need for sex at all, and it's such
a neat trick, that many animals do it, too.
362
00:41:48,967 --> 00:41:51,276
Aphids are baby machines,
363
00:41:51,447 --> 00:41:53,836
They don't need to have sex with a mate
364
00:41:54,007 --> 00:41:57,556
because they can pump out new aphids
all by themselves -
365
00:41:57,727 --> 00:42:03,085
one every 20 minutes,
each already full of their own future daughters,
366
00:42:07,087 --> 00:42:11,603
Cloning is great for increasing numbers,
but it has one flaw,
367
00:42:11,767 --> 00:42:14,406
As all cloned babies are identical,
368
00:42:14,567 --> 00:42:18,037
a single killer bug could wipe them all out,
369
00:42:24,927 --> 00:42:27,521
The key thing sex does is create variety.
370
00:42:27,687 --> 00:42:32,681
It's like me and you. We're both basically
the same, but we are subtly different.
371
00:42:32,847 --> 00:42:34,166
We're individuals.
372
00:42:38,087 --> 00:42:43,844
It's a pattern that's repeated for all kinds
of different animals, from people to puppies,
373
00:42:44,007 --> 00:42:47,636
like these little bull terrier puppies. Ah, yes!
374
00:42:48,327 --> 00:42:51,763
Even within one mating,
you get incredible diversity,
375
00:42:51,927 --> 00:42:53,918
as you can see in this litter.
376
00:42:55,007 --> 00:42:59,842
They all have the same mum and dad,
so how come they're so different?
377
00:43:00,007 --> 00:43:03,477
It's all to do with the secret magic of sex,
378
00:43:04,687 --> 00:43:08,760
During sexual reproduction,
the genetic material is reshuffled,
379
00:43:08,927 --> 00:43:11,487
Every sperm and egg is unique,
380
00:43:11,647 --> 00:43:17,199
so when the two join together to make a puppy,
every puppy is born unique, too,
381
00:43:18,647 --> 00:43:20,239
They all look different,
382
00:43:20,407 --> 00:43:25,959
but what's critical in the fight against parasites
are the differences you can't see,
383
00:43:26,127 --> 00:43:29,517
These puppies' bodies
are unique on the inside too,
384
00:43:31,007 --> 00:43:35,922
This one might be more resistant
to parvovirus than the rest of them, yes!
385
00:43:37,087 --> 00:43:41,444
And this one might be more resistant
to distemper virus.
386
00:43:43,447 --> 00:43:47,042
And it's the same for you and me
with human diseases, too.
387
00:43:47,207 --> 00:43:48,845
Wha-ha-ha.
388
00:43:49,007 --> 00:43:50,838
Yes, there you go.
389
00:43:51,847 --> 00:43:56,967
Resistant individuals have cell membranes
which lock the killer virus out,
390
00:43:57,127 --> 00:43:59,960
so its lethal life cycle can't get started,
391
00:44:05,087 --> 00:44:09,205
This is why sex is so crucial.
Because we're all born so different,
392
00:44:09,367 --> 00:44:14,646
we present a different challenge to
the parasites, increasing or chances of survival.
393
00:44:14,807 --> 00:44:20,723
It's like genetic roulette, with every new
generation keeping the killer bugs guessing.
394
00:44:20,887 --> 00:44:24,482
No wonder animals are so desperate
to have sex,
395
00:44:24,647 --> 00:44:29,277
It's evolution's way of future-proofing
new generations,
396
00:44:31,647 --> 00:44:35,117
(WHINING, HONKING CALL)
397
00:44:35,287 --> 00:44:40,042
But to have sex, you do need a relationship,
however brief,
398
00:44:40,207 --> 00:44:42,198
(HONKING)
399
00:44:44,447 --> 00:44:48,963
And many animals go to a lot of trouble
to make sure they find a mate,
400
00:44:49,927 --> 00:44:52,566
(WHINING, HONKING)
401
00:44:52,727 --> 00:44:54,240
This element of choice
402
00:44:54,407 --> 00:44:59,197
means sexual relationships can have
a huge effect on animal evolution too,
403
00:45:02,847 --> 00:45:07,363
Once a year in autumn,
American elk gather together to breed,
404
00:45:10,007 --> 00:45:15,684
It's called the rut - a spectacle
where stags compete for breeding rights,
405
00:45:24,287 --> 00:45:28,326
This rut is played out
in a most unusual location,
406
00:45:32,047 --> 00:45:35,119
In the mammoth area
of Yellowstone National Park,
407
00:45:35,287 --> 00:45:42,443
manicured lawns like this attract the herds
into the centre of Yellowstone village itself.
408
00:45:45,287 --> 00:45:48,165
Here, humans get a ringside seat,
409
00:46:02,047 --> 00:46:05,596
Each stag has two aims -
to impress the females
410
00:46:05,767 --> 00:46:08,235
and to frighten off rivals,
411
00:46:10,247 --> 00:46:13,637
Although the males are much bigger
and more dominant,
412
00:46:13,807 --> 00:46:16,480
it's the females who really run this show,
413
00:46:16,647 --> 00:46:20,799
Like females the world over,
they'll be left holding the babies,
414
00:46:20,967 --> 00:46:24,437
so they're very choosy
about who they mate with,
415
00:46:29,647 --> 00:46:35,358
Only the real studs with the most impressive
antlers and fighting ability will do..,
416
00:46:36,687 --> 00:46:40,202
..which forces the males to prove themselves,
417
00:46:44,807 --> 00:46:49,323
It's a knock-out contest where
only the winners get the right to breed,
418
00:46:53,727 --> 00:46:58,755
So over generations, the battles get harder
and the stags stronger,
419
00:46:59,607 --> 00:47:05,921
Female choice means sexual relationships can
shape the bodies and behaviour of their mates,
420
00:47:06,087 --> 00:47:08,078
so they are driving evolution,
421
00:47:08,247 --> 00:47:12,320
The males get so charged up
when they're fighting over females
422
00:47:12,487 --> 00:47:15,320
that they'll perceive anything as a threat.
423
00:47:15,487 --> 00:47:18,160
(WHINING CALL)
424
00:47:20,087 --> 00:47:26,162
The overwhelming urge to win and pass on
their genes can push the stags over the edge,
425
00:48:03,407 --> 00:48:08,197
Thankfully for us males, there are
other less violent ways of courting favour.
426
00:48:10,087 --> 00:48:13,636
Sometimes, it's all just a matter of appearances.
427
00:48:16,567 --> 00:48:22,483
One doesn't always have to fight to prove one's
worth - often, it's a matter of showing off,
428
00:48:24,287 --> 00:48:28,405
So some males put all their effort
into how they look,
429
00:48:31,487 --> 00:48:35,036
Posers can be just as successful as fighters.
430
00:48:43,567 --> 00:48:46,957
Instead of proving their worth
on the battleground,
431
00:48:47,127 --> 00:48:50,676
these peacock males flaunt fancy dress instead,
432
00:49:08,647 --> 00:49:13,402
The females will only mate with the ones
they find the most attractive,
433
00:49:20,167 --> 00:49:24,524
But does all this ostentation and display
actually mean anything?
434
00:49:24,687 --> 00:49:28,839
How can a female be sure
she'll have good, strong, healthy babies?
435
00:49:29,007 --> 00:49:32,317
Are good looks all they're cracked up to be?
436
00:49:38,607 --> 00:49:44,398
Remarkably, a little finch proves
that masculine beauty is not just skin deep.
437
00:49:47,607 --> 00:49:54,558
Zebra finch males are very colourful, with
orange legs and cheeks and bright red beaks,
438
00:49:57,167 --> 00:49:59,965
The females are much plainer,
439
00:50:04,847 --> 00:50:06,997
So why are the males so colourful?
440
00:50:07,167 --> 00:50:10,045
Let's try a little experiment,
441
00:50:11,287 --> 00:50:16,077
The male's red legs and beaks
are full of colour pigments called carotenoids,
442
00:50:16,247 --> 00:50:20,445
found naturally in fruits, seeds and carrots,
443
00:50:22,687 --> 00:50:29,001
So here, I'm going to feed half the males a diet
high in carotenoids to make them redder..,
444
00:50:38,567 --> 00:50:41,559
..and then put them
in a special choice chamber
445
00:50:41,727 --> 00:50:45,561
next to a duller male
who hasn't been fed the pigments,
446
00:50:47,767 --> 00:50:53,683
Two males in their own designer bedrooms
at the back, one female at the front,
447
00:50:56,767 --> 00:51:00,123
The sexes are segregated by a pane of glass,
448
00:51:00,287 --> 00:51:05,202
The males can't leave their rooms, but the
female can move from one side to the other,
449
00:51:05,367 --> 00:51:08,518
She can choose a male
by perching by his window,
450
00:51:08,687 --> 00:51:11,759
either on the left or on the right,
451
00:51:13,287 --> 00:51:18,839
Tiny cameras are installed to record
what happens throughout the little bird house,
452
00:51:22,087 --> 00:51:27,002
This high-speed CCTV footage
shows what happens next,
453
00:51:27,167 --> 00:51:29,965
Watch the female at the bottom of the screen,
454
00:51:31,687 --> 00:51:34,520
She seems to have chosen the male on the left,
455
00:51:36,207 --> 00:51:40,883
And the camera in his bedroom
shows she spends most of her time with him..,
456
00:51:42,807 --> 00:51:47,278
..while another camera
reveals the other guy is ignored,
457
00:51:48,887 --> 00:51:53,438
And who do you think is the most popular?
The male with the redder beak,
458
00:51:55,367 --> 00:52:00,122
In fact, in these tests,
nine out of ten females preferred him,
459
00:52:02,647 --> 00:52:05,764
But why would they fancy
the most colourful male?
460
00:52:08,687 --> 00:52:12,839
Well, the same red pigments
not only make the male look good,
461
00:52:13,007 --> 00:52:16,283
they help his body fight diseases, too,
462
00:52:21,687 --> 00:52:26,761
A dull male is probably weaker,
and not a good bet as a mate,
463
00:52:28,647 --> 00:52:31,878
Bright colours are an honest indicator of health,
464
00:52:32,047 --> 00:52:36,438
so pretty males do turn out
to be a good choice as mates after all.
465
00:52:40,087 --> 00:52:45,957
So the next time your mother says “Eat up your
vegetables,” it's a good idea to listen to her.
466
00:52:47,687 --> 00:52:50,247
Especially if you’re male.
467
00:52:52,127 --> 00:52:55,517
A brightly-coloured male
is not just likely to be healthy,
468
00:52:55,687 --> 00:52:59,475
he'll also pass on his parasite-fighting genes
to his babies,
469
00:53:11,287 --> 00:53:13,721
So it pays for a girl to demand the best,
470
00:53:13,887 --> 00:53:18,915
and this male zebra finch
has passed his medical with flying colours,
471
00:53:21,447 --> 00:53:23,244
But there's an extra twist,
472
00:53:23,407 --> 00:53:29,118
Researchers now think that girl power
can even create new species - but how?
473
00:53:31,287 --> 00:53:33,676
This guy can give us a clue.
474
00:53:33,847 --> 00:53:40,195
He's a zebra cichlid, and experiments have
shown he's a dedicated follower of fashion.
475
00:53:42,327 --> 00:53:46,206
These fish are only found
in Lake Malawi in Africa,
476
00:53:48,687 --> 00:53:53,556
What makes them special is that males
come in a variety of technicoloured coats,
477
00:53:53,727 --> 00:53:57,276
which is extremely unusual in a single species,
478
00:54:01,287 --> 00:54:06,315
It was a mystery as to why the males
came in so many different colours.
479
00:54:06,487 --> 00:54:12,596
They certainly weren't evolving to hide
from predators, or adapting to local conditions.
480
00:54:12,767 --> 00:54:18,444
Something else was going on,
and that something was the females.
481
00:54:20,927 --> 00:54:25,125
To find out more,
we put the fish in choice chambers,
482
00:54:27,087 --> 00:54:30,159
The larger, more colourful males are confined,
483
00:54:30,327 --> 00:54:33,683
but the little brown females
can swim where they like,
484
00:54:33,847 --> 00:54:40,241
All they have to do is swim in with the male
they fancy most, and their choice is made,
485
00:54:42,807 --> 00:54:46,482
The tests have produced
some rather surprising results,
486
00:54:47,447 --> 00:54:53,841
It turns out even females of the same species
have different ideas about what is sexy,
487
00:54:55,687 --> 00:54:57,996
Some prefer white males,
488
00:54:58,167 --> 00:55:03,195
some yellow, others blotchy, and so on,
489
00:55:04,647 --> 00:55:10,040
Which explains why zebra cichlid males
come in so many different colours,
490
00:55:11,287 --> 00:55:14,996
But how does that help
to create new cichlid species?
491
00:55:15,167 --> 00:55:18,477
This is where the girl power bit kicks in,
492
00:55:19,447 --> 00:55:24,726
If a group of females gang together and decide
that one colour is now highly desirable,
493
00:55:24,887 --> 00:55:28,402
they'll only mate with those particular males,
494
00:55:28,567 --> 00:55:30,876
This preference is passed on to their daughters,
495
00:55:31,047 --> 00:55:34,835
Over generations, an entirely
separate breeding group is formed,
496
00:55:35,007 --> 00:55:38,238
and eventually a new type of cichlid,
497
00:55:46,007 --> 00:55:48,840
Girl power not only helps to create beauty,
498
00:55:49,007 --> 00:55:51,646
it also leads to amazing variety
499
00:55:51,807 --> 00:55:54,196
and, ultimately, new species.
500
00:56:05,887 --> 00:56:08,799
Lake Malawi and the other African Great Lakes
501
00:56:08,967 --> 00:56:12,118
started out with just a handful
of cichlid species,
502
00:56:18,127 --> 00:56:23,440
Now they're home to one in ten
of all kinds of freshwater fish on the planet,
503
00:56:27,287 --> 00:56:31,360
An incredible 1,700 cichlid species
504
00:56:31,527 --> 00:56:34,485
all fashioned by female choice,
505
00:56:34,647 --> 00:56:39,277
This is the greatest explosion
of new species ever discovered,
506
00:56:39,447 --> 00:56:43,884
all driven by the relationship
between females and their males,
507
00:56:45,287 --> 00:56:46,800
The truth is, of course,
508
00:56:46,967 --> 00:56:52,360
that sexual relationships are only one
of the many interactions between living things
509
00:56:52,527 --> 00:56:55,803
that have the potential to shape and drive life.
510
00:57:09,847 --> 00:57:14,443
Whether with families and friends,
competitors or enemies,
511
00:57:14,607 --> 00:57:17,997
living together isn't always easy,
512
00:57:20,687 --> 00:57:27,126
But relationships have been a massive force
for change throughout the whole journey of life,
513
00:57:29,007 --> 00:57:32,522
And ultimately it's our connections
with each other
514
00:57:32,687 --> 00:57:37,397
that have created the spectacular variety
of life we see today,
515
00:58:13,607 --> 00:58:15,723
Next week on the “Journey of Life”,
516
00:58:15,887 --> 00:58:21,120
I'm going to retrace our five-million-year
journey from ape to human
517
00:58:21,287 --> 00:58:25,519
and discover how we very nearly didn't make it,