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(STEVE LEONARD )
Our world is a remarkable place...
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the only known living planet,
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We share the earth with millions
of different kinds of plants and animals,
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Where did they all come from?
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For a few days each year,
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this remote beach on the edge of the Pacific
Ocean can shed some light on the answer,
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Dawn reveals an epic struggle,
one that's been going on
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since the time of the dinosaurs.
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It's a battle fought by all living things.
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Only the individuals best suited to the world
in which they live have a chance of surviving.
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It's what we know as survival of the fittest.
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And at no point in these babies' lives
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is this more critical
than when they leave the nest,
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Hungry predators are waiting,
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Although they may look the same,
each baby is different from the next,
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The tiniest variation in size and shape
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can determine who lives...
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..and who dies,
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Some are weak...
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..others strong,
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Anything that boosts
the baby's chances of surviving,
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such as a sturdier shell or longer flippers,
will be passed on to its young in its genes,
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And over time, these inherited changes
can lead to the evolution of a new species,
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These babies are the genetic veterans
of a battle for survival
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that's been going on
since the first turtles evolved.
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Here, only a few make it to the water's edge,
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This is natural selection -
the way life evolves -
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and it's been shaping new kinds of creatures
throughout the whole of life's great journey,
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Every living thing on the planet today
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is the survivor of an unbroken chain of events
spanning nearly four billion years,
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Where did it all begin?
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In the sea -
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home to the most extraordinary variety
of creatures -
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and I'm going to meet them,
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Blue whales!
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Flying fish! (LAUGHS)
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The bizarre...
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..and the brainy...
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You are beautiful. (LAUGHS)
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..and the downright scary!
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You'll get your chance in a bit.
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It's time to start my journey
and explore the living seas,
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The sea is life's laboratory,
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where many solutions to the challenges
of living were first developed and tested,
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It might be hard to believe,
but every living thing today
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can trace its ancestry back to the sea,
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And that includes us humans,
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for this journey is also a personal story,
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as many of our own features
first evolved down here.
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Even today, our own heads and bodies
hint at our aquatic origins.
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This is you or me just 24 days
after conception,
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Every one of us was bathed
in a warm salty sea of amniotic fluid
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inside our mother's womb,
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Here on the embryo's head are gill slits
called pharyngeal pouches,
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Fish embryos have them, too,
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In fish they DO turn into gills,
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but in humans, they become
parts of the face, ear and jaw,
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This long tail is another echo
of our evolutionary past,
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We humans are a tiny shoot on one branch
of a giant family tree - the tree of life,
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We're just one of tens of millions of living
tips, each representing different species,
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and the way they all connect reveals
how each and every life-form is related,
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But why did this dazzling diversity
start in the sea and not on the land?
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Let's travel back to life's very beginning,
3.8 billion years ago,
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Back then, planet Earth
was an unpleasant place,
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The atmosphere was thin,
there was no oxygen,
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and no protective ozone layer
to shield the earth from the sun,
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Unfiltered ultraviolet rays
beat down on the young planet
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in a strength that would be lethal to us.
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Over time, massive volcanic eruptions
and meteor impacts destabilised the land.
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Compared to this mayhem,
the forming seas were a relative safe haven...
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..so it must have been somewhere
underwater that life first evolved.
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Exactly how life began remains a mystery,
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but there are some clues
in this chemical soup.
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The seas were awash with organic molecules -
the building blocks of all life,
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These were formed naturally
in the primordial soup of the forming oceans,
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Somewhere in this cauldron,
the recipe for our own DNA appeared,
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With this, the first sparks of life were ignited,
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Meet the ancestors,
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Simple cells like these
were the first living things,
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the predecessors of all future life on Earth,
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Over time, these cells diversified
and spread around the world,
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but one group would have
a devastating impact on the planet,
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Here, off western Australia,
these ancient microbes still exist today,
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Called stromatolites,
they secrete strange pillars made of lime,
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It's like a scene from three billion years ago,
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They might look harmless now,
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but back then these microbes
almost snuffed out all life for ever,
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By generating huge amounts of a new toxic gas,
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they triggered a global pollution crisis,
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That new gas's name was oxygen,
and it utterly destroyed primitive cells,
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poisoning them by the billion,
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Extinctions swept the planet,
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But a few cells survived and thrived on oxygen,
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They inherited the earth,
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From now on,
oxygen would power all new life,
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from the tiniest cell
to the biggest creature of all time,
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That is the greatest
oxygen-breather of them all.
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The largest animal that's ever existed -
the blue whale.
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They can be as long as a 737 passenger jet,
and weigh as much as 30 bull elephants,
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Their massive lungs
are 400 times bigger than my own,
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And when they return to the surface for air,
they blow a water spout 12 metres high,
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Every year, migrating blue whales
gather here off the coast of California
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to feed on tiny shrimp-like creatures
called krill,
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Blue whales have huge appetites,
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They can take in 50 tons of water
in one gulp, and eat 40 million krill a day,
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Here in Californian waters, there are
more than 2,000 of these giants,
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This is the greatest gathering
of blue whales anywhere in the world,
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But how could evolution
take such a gigantic leap?
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Cold a blue whale really evolve
from a single cell?
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With teamwork and co-operation, yes.
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Co-operating cells -
it sounds a simple solution,
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but the journey of life
took almost three billion years to get there,
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Among the first sea creatures to benefit
from cells pulling together were jellyfish,
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These ancient animals were the first to have
muscle fibres and a simple nervous system,
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which allowed the first co-ordinated
movement, but unlike us,
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the jelly doesn't know its front from its back,
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It just reaches out in all directions,
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With the jellyfish, there was no front end,
no brain and no great sense of direction.
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The alternative strategy was to grow a head,
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and with that, life could now move forward.
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Would you believe this is one of the most
important creatures in the journey of life -
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the first ever to grow a head - the flatworm,
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And amazingly, it's the foundation
of our basic body plan,
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We share the very same
head-sprouting genes,
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Flatworms also evolved the very first eyes,
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Just a cluster of cells, they can't do
much more than tell light from dark...
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..but at least the worm has some idea
what's coming when it's travelling head first,
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And this new information needed processing,
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It might be small and very simple,
but this is, nevertheless, the first brain,
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So it's thanks to the flatworm that our brains
are in our heads and not in our backsides,
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If the evolution of the first brain
was a milestone event,
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then so too was the evolution
of the first anus.
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Imagine having to get rid of digested food
through your mouth - not very pleasant -
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but that's exactly what flatworms
and jellyfish have to do.
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The flatworm has an extendable stomach
with just one opening,
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and the snag with that is it can't eat
and excrete at the same time,
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While some worms stayed flat,
others became round,
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They developed an internal tube -
the through gut,
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In through the mouth, along the digestive tract
and out through the anus,
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This meant worms could feed non-stop,
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and the through gut was such an efficient
system that since then everyone has had one,
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Bizarrely, some animals today have evolved
an entirely different use for their guts,
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This is a sea cucumber.
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It doesn't look like much,
but when it's attacked by a predator,
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it does something rather extraordinary.
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Just holding it can set it off,
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Ugh! Here we go.
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Ugh! God, that is foul!
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The sea cucumber throws up not only
its stomach contents, but its entire intestines,
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A predator would rather leave it alone
and just eat its entrails.
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The sea cucumber can still eat by absorbing
nutrients through its skin, and that's not all,
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Incredibly, this guy will grow an entirely
new set of guts in just a few weeks.
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All right, wee man.
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Throwing up each time
you're threatened is a bit extreme,
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Other soft-bodied creatures would need
a more practical form of protection to survive,
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Around 570 million years ago,
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there was a major breakthrough
when life chanced upon a winning formula -
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the softies turned hard,
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The first shells probably developed by accident,
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Early snails began to store mineral waste
from their diet on their backs,
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This hardened into shells,
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And as these shells became thicker
or more spiny,
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they also became predator-proof,
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This scallop can clam up
if it sees danger coming,,,
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,,but its simple eyes haven't detected
this slow-moving scallop-eating starfish,
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Once it feels the danger, though,
the scallop has a surprising reaction,
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(FLAMENCO MUSIC, CASTANETS)
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It's a great escape, but with its heavy shell,
the scallop soon runs out of steam,
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Their armour has always
weighed snails down,
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but half a billion years ago, some escaped
the dangers of the seabed altogether,
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So how did they do it?
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The solution - a buoyancy aid,
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Snails filled their shells with gas,
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It was the rise of the super-snails -
the nautiloids,
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Later, their cousins rolled up their shells
and became the ammonites,
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Ammonites were so successful
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that they would become the most numerous
fossil for over 300 million years.
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They ranged from tiny critters like this one...
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..to monsters...
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..like this.
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This shell would have contained a giant
two-metre-long slug with tentacles,
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These ridges worked as stabilisers,
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keeping it on an even keel
as it bobbed along looking for food,
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It was the age of the ammonites.
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This fossil graveyard near Lyme Regis
was formed by just one shoal.
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It's part of a huge fossil bed
that stretches for several miles inland.
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It gives you an idea
of just how prolific these creatures were.
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But a built-in float
wasn't the only answer to a bulky shell...
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..because evolving down another branch
on the tree of life
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was a flexible, lightweight suit of armour,
as worn by the very first bugs,
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And so the arthropods evolved -
animals with an external, jointed skeleton.
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Their hard bodies fossilised well, and this is
the most famous of them - the trilobites.
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This is just one of the thousands
of species of trilobites that existed
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over hundreds of millions of years.
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Its flexible armour allowed body segments
to be specialised for different tasks...
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..and with jointed limbs, they could move fast,
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But the trilobite's real trump card
was its eyes - the first to see in detail,
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This was an evolutionary bombshell,
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For the first time, predators and prey
could see each other coming,
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Eyes became both a hunting tool
and the first line of defence,
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With them arose super-bugs,
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The eye generated a deadly race
as each was driven to outdo the other,
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The rush to stay ahead
sparked an explosion of new life,
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This competition has led to some
extreme bugs and some extreme eyes,
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These are the most sophisticated
of any creature on the planet,
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and they belong to the mantis shrimp,
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Whereas our vision just uses three colour
pigments - red, blue and yellow -
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mantis shrimps use at least eight,
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Mantis shrimps need such hi-tech equipment
to hunt their prey,
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and more importantly, to avoid each other
in this colourful coral world,
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For the mantis shrimp is armed
with nature's most earth-shattering weapon...
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a claw turned club,
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It's a smash-and-grab attack,
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I'd be rather pleased to think we'd evolved
from such an impressive creature,
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but no such luck,
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By comparison,
our ancestor's a bit embarrassing,
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(STEVE) # Nobody knows
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# But wherever I'm a-going, I'll go
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# Said Charlie-oh #
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Unlike the super-bugs
with their hard exoskeletons,
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or even the super-snails
with their hard shells,
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I'm hard on the inside.
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I have an internal skeleton
based around my backbone.
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My backbone gives my body
a strengthening rod,
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Without it, I'd be like a sack of spuds,
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It was another crucial milestone
on life's journey,
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marking the rise of a whole new group -
our lot, the vertebrates,
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In the millions of years that the trilobites
and ammonites were cruising the seas,
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little vertebrates were busy evolving away.
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And this is it - the ancestor of all the
backboned animals, including we humans -
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a sea squirt, nothing more than a bag of jelly,
232
00:26:58,367 --> 00:27:02,918
The incredible thing is,
80% of its genes are inside us too,
233
00:27:03,087 --> 00:27:05,840
including those that form the human heart,
234
00:27:06,007 --> 00:27:08,282
but where's the backbone?
235
00:27:12,487 --> 00:27:17,641
The key to that inheritance
is found inside its tiny young,
236
00:27:18,687 --> 00:27:22,839
It's these little squirts that have
a tail with a flexible rod inside -
237
00:27:23,007 --> 00:27:25,840
the earliest hint of a backbone,
238
00:27:37,727 --> 00:27:42,039
With this flimsy backbone,
the first true vertebrates emerged,
239
00:27:42,207 --> 00:27:45,563
amongst which were the jawless fish,
240
00:27:46,687 --> 00:27:52,319
These jawless hagfish are deep-sea
creatures that live way beyond our reach,
241
00:27:52,487 --> 00:27:55,559
Here, more than a mile below the ocean surface,
242
00:27:55,727 --> 00:27:58,878
they're scavenging
on the carcass of a dead whale,
243
00:28:04,127 --> 00:28:06,800
They might look more like worms than fish,
244
00:28:06,967 --> 00:28:11,802
but 500 million years ago,
jawless wonders like these ruled the seas,
245
00:28:28,287 --> 00:28:31,723
Today, they sometimes rise up to the shallows,
246
00:28:31,887 --> 00:28:37,519
and in Sweden's cold dark fjords,
they come face to face with fishermen,
247
00:28:48,847 --> 00:28:53,398
And if they're caught by a predator,
just watch what they can do,
248
00:28:54,287 --> 00:29:00,044
Their primitive backbones are so flexible,
they can literally tie themselves in knots.
249
00:29:01,087 --> 00:29:04,921
And a slip knot can sometimes be a life saver,
250
00:29:05,087 --> 00:29:08,397
Being made of flexible cartilage rather than bone,
251
00:29:08,567 --> 00:29:11,445
that spine's a whole lot bendier than mine,
252
00:29:11,607 --> 00:29:12,926
There we go.
253
00:29:13,087 --> 00:29:15,681
A nice little granny knot there.
254
00:29:20,367 --> 00:29:24,246
And if tying a knot isn't enough
to escape a predator's grasp,
255
00:29:24,407 --> 00:29:27,126
the hagfish has another trick up its sleeve,
256
00:29:27,287 --> 00:29:30,120
Ugh! Look at that.
257
00:29:31,367 --> 00:29:34,086
That is incredible!
258
00:29:34,247 --> 00:29:37,239
It's a really unique defensive mechanism.
259
00:29:37,407 --> 00:29:41,480
The hagfish secretes mucus
from glands either side of its body,
260
00:29:41,647 --> 00:29:45,117
and this mucus starts to swell
when it contacts water.
261
00:29:45,287 --> 00:29:50,236
It also contains these high-tensile fibres
that form a shield of slime.
262
00:29:52,847 --> 00:29:57,238
One hagfish can jellify
a whole bucket of sea water,
263
00:29:59,087 --> 00:30:05,356
But despite these extraordinary adaptations,
jawless fish had soon had their day,
264
00:30:05,527 --> 00:30:07,518
About 400 million years ago,
265
00:30:07,687 --> 00:30:13,398
they were sidelined by the results
of a new and deadly development,
266
00:30:13,567 --> 00:30:18,846
Somewhere out there,
a brand new kind of fish was evolving,
267
00:30:19,887 --> 00:30:24,119
Its front two gill arches gradually grew
and encircled the mouth,
268
00:30:24,287 --> 00:30:27,563
becoming the first biting jaws,
269
00:30:33,687 --> 00:30:37,726
Such early jawed fish became the sharks,
270
00:31:16,087 --> 00:31:18,885
Once primitive fish had developed jaws,
271
00:31:19,047 --> 00:31:22,926
an extraordinary range of teeth
evolved to fit them,
272
00:31:24,687 --> 00:31:28,805
Sharks' teeth are adapted
to the diet of their owner,
273
00:31:28,967 --> 00:31:34,917
The sand tiger has narrow pointed teeth
for seizing slippery fish and squid,
274
00:31:35,887 --> 00:31:38,037
Other teeth, like the seal shark's,
275
00:31:38,207 --> 00:31:43,235
are multi-pointed for feeding on the ocean
floor, picking up crabs and shellfish,
276
00:31:44,007 --> 00:31:49,001
The snaggle-tooth's varied diet
needs a tooth like a hunting knife,
277
00:31:49,167 --> 00:31:52,318
while the tiger shark's
are more like chainsaws,
278
00:31:52,487 --> 00:31:55,843
used to tackle turtle shell and fish bone,
279
00:31:56,887 --> 00:32:01,802
These belong to the biggest
meat-eating shark - the great white,
280
00:32:01,967 --> 00:32:04,481
They slice through the meat of sea mammals,
281
00:32:05,447 --> 00:32:08,757
The biggest teeth of all
belonged to the Megalodon,
282
00:32:08,927 --> 00:32:14,320
a bus-sized meat-eating monster that
was 12 times bigger than a great white shark.
283
00:32:14,487 --> 00:32:19,925
Its jaw was colossal - over two metres wide
with hundreds of teeth.
284
00:32:20,087 --> 00:32:22,760
It could have swallowed me whole.
285
00:32:24,767 --> 00:32:31,206
Good job it's extinct! Just imagine a jaw
this size at the business end of a hungry shark,
286
00:32:31,367 --> 00:32:35,918
It's no wonder Megalodon could eat
more than a ton of meat in one go,
287
00:32:41,367 --> 00:32:45,076
Some of its relatives are the sharks
we all recognise,
288
00:32:45,247 --> 00:32:48,080
but others evolved along a different track,
289
00:32:48,247 --> 00:32:50,317
Some even lost their teeth,
290
00:32:52,767 --> 00:32:54,758
These are stingrays.
291
00:32:54,927 --> 00:33:01,560
Here off the coast of the Cayman Islands,
they gather in huge numbers to feed.
292
00:33:02,607 --> 00:33:04,438
Agh!
293
00:33:04,607 --> 00:33:07,360
Pretty enthusiastically as well! Ow!
294
00:33:07,527 --> 00:33:10,087
Easy now, boys.
295
00:33:10,247 --> 00:33:12,363
Rays are sharks' cousins,
296
00:33:12,527 --> 00:33:17,282
but their body plan has flattened out
to make the most of life on the seabed,
297
00:33:17,447 --> 00:33:23,443
They are absolutely incredible-looking
creatures, and the way they move is beautiful.
298
00:33:25,087 --> 00:33:29,399
These rays eat fish, and they know
I've got a juicy morsel in my hand,
299
00:33:30,047 --> 00:33:32,436
Agh! (LAUGHS)
300
00:33:37,847 --> 00:33:41,681
You have to be a little bit careful
when you're feeding them,
301
00:33:41,847 --> 00:33:44,441
because that mouth has a nasty suck on it.
302
00:33:44,607 --> 00:33:47,519
They don't have much in the way of teeth,
303
00:33:47,687 --> 00:33:51,157
but they've got this bony plate
that acts as a grinder,
304
00:33:51,327 --> 00:33:55,206
and it can grind your fingers as well,
as I've found out.
305
00:34:00,927 --> 00:34:06,479
These rays usually hunt crabs and fish
that they can detect hidden in the sand,
306
00:34:11,007 --> 00:34:12,884
Agh!
307
00:34:13,047 --> 00:34:18,917
They get very, very friendly when
you don't feed them. Ooh! OK. Easy, petal.
308
00:34:25,847 --> 00:34:29,317
Stingrays have an array of fine-tuned senses,
309
00:34:29,487 --> 00:34:34,038
It's something all the shark family
have taken to a whole new level,
310
00:34:34,207 --> 00:34:39,122
And to show you how good they've become,
I'm going to run a little experiment,
311
00:34:39,287 --> 00:34:40,925
This should do the trick,
312
00:34:41,087 --> 00:34:44,318
(ROARING)
313
00:34:49,127 --> 00:34:53,279
In the open ocean, surprisingly,
sound is usually the first cue
314
00:34:53,447 --> 00:34:56,325
that alerts a predator to a potential meal,
315
00:34:57,247 --> 00:35:01,035
It travels four times faster in water than in air,
316
00:35:01,207 --> 00:35:02,959
(ROARING)
317
00:35:04,087 --> 00:35:09,366
Sharks like this Caribbean reef shark can hear
a commotion from at least a mile away,
318
00:35:11,687 --> 00:35:13,643
They have excellent hearing,
319
00:35:13,807 --> 00:35:17,402
but instead of having ear flaps
on the outside like we do,
320
00:35:17,567 --> 00:35:21,401
a tiny duct carries sound waves
into their inner ear,
321
00:35:24,487 --> 00:35:27,081
Next comes the sense of smell.
322
00:35:28,447 --> 00:35:32,326
Blood and fish oil can be detected
from 400 metres away,
323
00:35:32,487 --> 00:35:36,366
so this box of fish bits
should generate some interest.
324
00:35:38,087 --> 00:35:44,720
Just a single drop of blood in 25 million drops
of water is enough to turn a shark's head,
325
00:35:44,887 --> 00:35:48,436
but to pinpoint exactly
where the smell is coming from,
326
00:35:48,607 --> 00:35:51,440
it has to zigzag to pick up the trail,
327
00:35:51,607 --> 00:35:55,998
At 100 metres,
now the shark knows where I am,
328
00:35:56,167 --> 00:35:58,840
thanks to a sense humans don't have at all,
329
00:35:59,007 --> 00:36:01,760
It can't see me, but it can feel me
330
00:36:01,927 --> 00:36:05,761
through the pressure waves
that I'm creating in the water,
331
00:36:09,167 --> 00:36:12,125
These waves are picked up
by the lateral line -
332
00:36:12,287 --> 00:36:16,166
detectors that run down
its body from head to tail,
333
00:36:16,327 --> 00:36:20,286
It's a kind of extrasensory perception
all fish have,
334
00:36:28,527 --> 00:36:34,443
It's only now, at around ten metres, that the
sharks can actually see me, and I see them.
335
00:36:34,607 --> 00:36:37,838
In daylight, their vision
is about as good as mine.
336
00:36:38,007 --> 00:36:42,523
Now they're checking me out
with those big eyes.
337
00:36:44,567 --> 00:36:48,480
The structure of the eye suggests sharks
may be far-sighted -
338
00:36:48,647 --> 00:36:51,207
they see better at distance than close up,
339
00:36:53,567 --> 00:36:56,957
But once they get this close,
another sense kicks in -
340
00:36:57,127 --> 00:37:00,278
they can detect electricity,
341
00:37:02,207 --> 00:37:08,680
Tiny receptors on the snout can register
as little as half a billionth of a volt,
342
00:37:08,847 --> 00:37:12,237
That's the electric field
around a live fish's body,
343
00:37:12,407 --> 00:37:15,285
or in this case, in our metal feeding pole,
344
00:37:15,447 --> 00:37:18,803
I'll leave this bit to the professionals,
345
00:37:21,487 --> 00:37:24,763
Whoa! Easy, gentlemen.
346
00:37:26,927 --> 00:37:32,206
In the final seconds of attack,
the shark goes in blind to protect its eyes,
347
00:37:32,367 --> 00:37:35,325
closing them just before it bites,
348
00:37:39,647 --> 00:37:44,038
In clear blue water like this, thankfully,
the sharks can see what I am,
349
00:37:44,207 --> 00:37:49,839
otherwise, they may have to use
their other senses, namely, touch and taste -
350
00:37:50,007 --> 00:37:53,079
and it's all done with the mouth.
351
00:37:58,607 --> 00:38:01,280
It's this combination of sensory systems
352
00:38:01,447 --> 00:38:05,486
that makes the shark
such an effective hi-tech predator.
353
00:38:08,087 --> 00:38:11,079
You might think
that such sophisticated animals
354
00:38:11,247 --> 00:38:14,080
would out-compete everything else in the sea,
355
00:38:14,247 --> 00:38:17,762
but the journey of life
has never been straightforward,
356
00:38:22,767 --> 00:38:25,076
Several times over the millennia,
357
00:38:25,247 --> 00:38:30,162
meteors have shattered the world order
and sparked mass extinctions,
358
00:38:37,767 --> 00:38:44,286
But from these extinctions,
new opportunities and new creatures arose,
359
00:38:47,687 --> 00:38:51,157
Even the long-established ammonites
didn't make it,
360
00:38:51,327 --> 00:38:55,002
but in the shelter of the deep,
their relatives survived,
361
00:38:55,167 --> 00:38:58,637
and they could now branch out
in a whole new direction,
362
00:39:00,287 --> 00:39:02,278
The super-snails rose up,
363
00:39:02,447 --> 00:39:08,636
and ultimately became the latest in the
cephalopod dynasty - cuttlefish, octopus,
364
00:39:08,807 --> 00:39:11,241
and squid,
365
00:39:15,767 --> 00:39:17,758
Today, just once a year,
366
00:39:17,927 --> 00:39:21,761
millions of opalescent squid gather to breed,
367
00:39:51,527 --> 00:39:55,236
At just a year old, it's the last act
in their short lives,
368
00:39:55,407 --> 00:39:59,320
Once the eggs are laid, most will die,
369
00:40:00,967 --> 00:40:04,084
Grow fast, spawn, and die young -
370
00:40:04,247 --> 00:40:07,603
a winning formula in the seas of life,
371
00:40:14,047 --> 00:40:18,165
Cephalopod means "head-foot" -
not a bad description, really,
372
00:40:22,567 --> 00:40:26,719
This whopper is the giant Pacific octopus -
373
00:40:26,887 --> 00:40:29,242
all head and feet,
374
00:40:31,647 --> 00:40:35,083
It's a gentle giant with an alien physiology -
375
00:40:35,247 --> 00:40:38,398
blue blood, three hearts and nine brains,
376
00:40:38,567 --> 00:40:44,802
That's one big central brain
plus eight mini brains - one in each arm,
377
00:41:01,207 --> 00:41:04,438
If cephalopods were really
to compete in the seas,
378
00:41:04,607 --> 00:41:07,963
brainpower would be their big advantage,
379
00:41:16,887 --> 00:41:21,438
These are Caribbean reef squid - little cuties,
380
00:41:25,927 --> 00:41:31,957
When a barracuda's on the scene,
they can think themselves out of a tight spot,
381
00:41:34,647 --> 00:41:40,483
They change their appearance to match their
surroundings - both in texture and colour -
382
00:41:40,647 --> 00:41:45,482
an instant transformation
that is directly controlled by the brain,
383
00:41:47,367 --> 00:41:51,724
To the predator, it seems
that they've simply disappeared,
384
00:42:14,287 --> 00:42:18,917
The squid also communicate
to tell each other when the danger's passed,
385
00:42:19,087 --> 00:42:23,126
They have an entire language
based on skin tones,
386
00:42:30,207 --> 00:42:35,520
For modern cephalopods, brainpower
has overcome the need for a protective shell,
387
00:42:35,687 --> 00:42:38,565
They're simply smarter than the average fish,
388
00:42:44,447 --> 00:42:48,326
So why didn't the seas
become dominated by clever cephalopods?
389
00:42:48,487 --> 00:42:53,197
That's because just when it looked
like brain might triumph over brawn,
390
00:42:53,367 --> 00:42:55,562
fish chanced upon a master-stroke,
391
00:42:55,727 --> 00:43:00,881
That master-stroke was a skeleton
made of a new material - bone,
392
00:43:04,927 --> 00:43:09,478
With it, new bony fish
diversified like never before,
393
00:43:29,367 --> 00:43:32,359
The bony skeleton
was a landmark development,
394
00:43:32,527 --> 00:43:37,965
providing stronger structural support,
greater protection, more effective gills,
395
00:43:38,127 --> 00:43:40,800
and improved agility,
396
00:43:45,087 --> 00:43:50,161
Then, for even more subtle manoeuvres,
fish evolved two pairs of matching fins
397
00:43:50,327 --> 00:43:53,364
joined to both sides of their body by bones,
398
00:43:53,527 --> 00:43:58,396
This really was a winning combination,
and its legacy would stick,
399
00:44:05,527 --> 00:44:12,399
Guess what? It's why we humans
have a pair of arms and a pair of legs,
400
00:44:18,087 --> 00:44:21,443
But even bony skeletons have drawbacks,
401
00:44:21,607 --> 00:44:24,121
Have you ever tried racing into the sea?
402
00:44:24,287 --> 00:44:27,040
It's virtually impossible to run through,
403
00:44:27,207 --> 00:44:30,995
and that's because water
is 800 times denser than air.
404
00:44:32,687 --> 00:44:35,997
And once you're in, it's either sink or swim.
405
00:44:36,167 --> 00:44:38,806
If bony fish were ever to dominate the seas,
406
00:44:38,967 --> 00:44:41,845
they'd have to overcome the same two problems -
407
00:44:42,007 --> 00:44:47,559
how to move fast in a dense liquid,
and how to stay afloat despite heavy bones.
408
00:45:00,407 --> 00:45:05,356
To stop sinking, fish needed the equivalent
of buoyancy tanks on a submarine,
409
00:45:08,567 --> 00:45:13,004
Less gas, and we sink; more, we rise.
410
00:45:13,887 --> 00:45:20,998
But whereas a sub uses compressed air,
a fish carries its gas supply in its bloodstream,
411
00:45:25,687 --> 00:45:30,886
The answer was for fish to come up
with an onboard float - the swim bladder,
412
00:45:31,047 --> 00:45:35,518
a large, gas-filled sac that inflates
and deflates as needed,
413
00:45:40,687 --> 00:45:45,556
Gas diffuses back and forth between
the swim bladder and the bloodstream,
414
00:45:45,727 --> 00:45:49,197
letting fish float effortlessly at any depth,
415
00:45:50,287 --> 00:45:55,645
Despite being heavy-boned,
the fish is, in effect, weightless,
416
00:46:09,287 --> 00:46:13,599
Brilliant! But there is one big flaw
in this ingenious system.
417
00:46:13,767 --> 00:46:17,919
Diffusion of gas between the swim bladder
and the blood takes time,
418
00:46:18,087 --> 00:46:21,443
so there's a lag period
when making buoyancy changes.
419
00:46:21,607 --> 00:46:24,997
For a fast-swimming fish, that's too slow.
420
00:46:27,087 --> 00:46:31,877
So speedsters like the bonito
have abandoned swim bladders completely,
421
00:46:32,047 --> 00:46:34,959
but with nothing to stop themselves sinking,
422
00:46:35,127 --> 00:46:39,040
they've got to pay the penalty
and keep swimming all the time,
423
00:46:50,367 --> 00:46:56,966
Not all bony fish like life in the fast lane,
Others have turned to a more sedentary life,
424
00:47:02,807 --> 00:47:05,605
Take this weirdo, for example,
425
00:47:08,687 --> 00:47:13,124
It's a frogfish, and it's come up
with a novel use for its bones,
426
00:47:13,287 --> 00:47:19,840
That's no wiggly worm but a flashy lure
operated by a modified fin bone,
427
00:47:28,847 --> 00:47:33,159
All these damselfish see is a juicy mouthful,
428
00:47:38,847 --> 00:47:44,843
Not only is the frogfish a master of deception,
he's also perfectly camouflaged,
429
00:47:45,927 --> 00:47:48,885
This shrimp is unlikely to see him until he moves,
430
00:47:49,047 --> 00:47:53,006
and by then, it's too late,
431
00:47:53,167 --> 00:47:57,797
No matter how quick its reactions,
they just can't be quick enough,
432
00:47:57,967 --> 00:48:01,357
because the frogfish jaws
move faster than muscle,
433
00:48:02,567 --> 00:48:06,321
How? Well, that's down to bones again,
434
00:48:09,767 --> 00:48:14,283
It's a trap-jaw, pre-set under full tension,
435
00:48:14,447 --> 00:48:19,760
When triggered, the trap snaps open,
increasing the mouth volume ten times,
436
00:48:19,927 --> 00:48:22,395
sucking the prey inside,
437
00:48:32,527 --> 00:48:34,916
But when it comes to bone structure,,,
438
00:48:35,567 --> 00:48:39,321
,,these small fry are the most extreme of all,
439
00:48:39,487 --> 00:48:44,083
For the first two weeks of their lives,
they look like any other baby fish...
440
00:48:44,967 --> 00:48:48,516
..then something begins to go awry,
441
00:48:55,007 --> 00:48:59,285
The face distorts, and one eye starts to shift,
442
00:48:59,447 --> 00:49:03,520
moving across to meet the other
on the opposite side of the head,
443
00:49:03,687 --> 00:49:07,566
It's the beginning of a bizarre transformation,
444
00:49:13,527 --> 00:49:19,045
The makeover takes less than a week,
and the results are fixed for life,
445
00:49:23,287 --> 00:49:27,963
This flatfish is now perfectly adapted
to life on the sea bed,
446
00:49:28,127 --> 00:49:32,120
Its body shape and colouring
mean it can keep a low profile -
447
00:49:32,287 --> 00:49:37,077
handy for hiding from predators
or creeping up on prey,
448
00:49:38,927 --> 00:49:43,000
But if you don't have what it takes
to hide out on the ocean floor,
449
00:49:43,167 --> 00:49:46,045
safety in numbers is your best bet,
450
00:49:48,647 --> 00:49:53,402
Living in a shoal is a great way
to minimise the chances of being eaten,
451
00:50:02,007 --> 00:50:04,680
Throughout their evolutionary history,
452
00:50:04,847 --> 00:50:08,999
shoals of bony fish
have come under fire from all sides,
453
00:50:11,327 --> 00:50:15,036
They've survived the age of the plesiosaurs...
454
00:50:24,207 --> 00:50:26,960
..and a blitz of aerial attacks ever since,
455
00:50:36,887 --> 00:50:41,563
And all that time,
they've also been hunted from below,
456
00:51:23,367 --> 00:51:27,076
This is predation pressure at its most extreme,
457
00:51:27,247 --> 00:51:32,924
Any fish that can avoid this kind of onslaught
will have genes worth passing on,
458
00:51:41,687 --> 00:51:47,159
And pushed to the limit, some fish
eventually sought refuge out of the water,,,
459
00:51:48,447 --> 00:51:51,325
..with spectacular results,
460
00:51:52,367 --> 00:51:56,201
(SHOUTS) Look at that! That is fantastic!
461
00:51:56,367 --> 00:51:58,244
(HE LAUGHS)
462
00:51:58,407 --> 00:52:04,516
Flying fish. That has got to be the most
extreme form of escape known to any fish.
463
00:52:04,687 --> 00:52:07,281
Look at them go. There's loads of them!
464
00:52:14,407 --> 00:52:19,435
There's another. That's incredible!
Look at the distance.
465
00:52:20,167 --> 00:52:22,556
Look at him go. Whoo!
466
00:52:22,727 --> 00:52:26,800
Flying fish have evolved
extraordinarily long pectoral fins.
467
00:52:26,967 --> 00:52:30,403
They don't flap,
and they're used to glide instead.
468
00:52:31,367 --> 00:52:33,005
Ooh, mid-air collision!
469
00:52:34,127 --> 00:52:39,963
They seem to be able to steer once they're
up and into the air. Oh, beautiful back turn!
470
00:52:41,927 --> 00:52:47,001
It's the tail that does it,
driving them along like an outboard motor.
471
00:52:48,167 --> 00:52:52,319
It's so powerful that once in the air
they glide for up to 100 metres.
472
00:52:55,047 --> 00:52:57,686
For a predator, it's a vanishing act.
473
00:53:01,407 --> 00:53:04,285
Look at that thing fly!
474
00:53:14,087 --> 00:53:17,159
Flying fish - who would have thought it?
475
00:53:17,327 --> 00:53:20,319
Perhaps the most extraordinary bony fish of all,
476
00:53:20,487 --> 00:53:24,275
It just goes to show anything can happen
in the pressure cooker
477
00:53:24,447 --> 00:53:26,403
that is the crowded seas of life,
478
00:53:30,127 --> 00:53:32,880
It might well have been predation pressure
479
00:53:33,047 --> 00:53:36,198
that forced some fish out of the water
permanently,
480
00:53:38,367 --> 00:53:44,681
The descendants of the bony fish
colonised the land and hit a new jackpot,
481
00:53:44,847 --> 00:53:49,238
After some three and a half billion years
of evolution in the oceans,
482
00:53:49,407 --> 00:53:54,435
they evolved air-breathing lungs,
and walked out of the sea as landlubbers,
483
00:53:55,687 --> 00:53:59,600
Reptiles, amphibians, birds
and mammals like us -
484
00:53:59,767 --> 00:54:03,043
all these land animals
share a common ancestor -
485
00:54:03,207 --> 00:54:04,640
a fish.
486
00:54:08,847 --> 00:54:13,523
But that's not the end of life's long journey
through the seas,
487
00:54:13,687 --> 00:54:17,680
Ultimately, some land mammals
developed a taste for sea food,
488
00:54:17,847 --> 00:54:20,680
and returned to the oceans to hunt.
489
00:54:39,687 --> 00:54:43,077
Over time, their legs
gradually became flippers,
490
00:54:43,247 --> 00:54:45,238
and from an ancestor like this,
491
00:54:45,407 --> 00:54:49,605
they would become the most
charismatic creatures in the seas,
492
00:54:50,567 --> 00:54:56,358
Today, the result of that evolutionary chain
of events are the cetaceans - that's whales...
493
00:54:58,087 --> 00:55:00,078
..and dolphins!
494
00:55:00,247 --> 00:55:01,965
Fantastic.
495
00:55:13,847 --> 00:55:19,080
These are bottlenose dolphins, the most
widespread dolphins in all of the seas.
496
00:55:19,247 --> 00:55:21,238
People just love them.
497
00:55:21,407 --> 00:55:26,003
I think we identify more with this animal
than any other sea creature.
498
00:55:26,167 --> 00:55:28,158
Yes, we do, don't we!
499
00:55:30,727 --> 00:55:35,084
For their size, dolphins have the second
biggest brain on the planet -
500
00:55:35,247 --> 00:55:37,442
only a human's is bigger.
501
00:55:37,607 --> 00:55:39,359
Sorry, guys, I beat you.
502
00:55:39,527 --> 00:55:41,518
Yes.
503
00:55:43,567 --> 00:55:47,082
We're just starting to find out
how clever they really are,
504
00:55:47,247 --> 00:55:53,322
Using sign language, we are now able to
communicate with trained dolphins like these,
505
00:55:53,487 --> 00:55:58,163
Some can understand
more than 2,000 different sentences,
506
00:56:14,967 --> 00:56:19,961
I'm sure we identify and admire the dolphins
because they're so intelligent,
507
00:56:20,127 --> 00:56:25,042
but perhaps we should identify more
with the smaller, colder sea creatures.
508
00:56:25,207 --> 00:56:30,839
It's directly because of them and the way
they evolved that we are the creatures we are -
509
00:56:31,007 --> 00:56:35,205
that we're multi-cellular,
that we've got eyes, a backbone,
510
00:56:35,367 --> 00:56:38,279
an internal skeleton, two pairs of limbs,
511
00:56:38,447 --> 00:56:41,803
a jaw, a heart, a digestive system,
512
00:56:41,967 --> 00:56:46,961
a sense of smell, touch and taste,
a head and a brain.
513
00:56:47,127 --> 00:56:54,317
It's all down to three and a half billion years
of evolution in the spectacular seas of life.
514
00:56:58,767 --> 00:57:00,120
(HE LAUGHS)
515
00:57:20,167 --> 00:57:22,397
Next week on the "Journey of Life",
516
00:57:22,567 --> 00:57:26,560
I'm going to discover
how life conquered the hostile land
517
00:57:26,727 --> 00:57:31,926
in a story which leads
from the sea to the desert,