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These waters are home to an animal
exquisitely adapted

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to life below the waves.

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I'm talking about the dolphin.

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DOLPHIN CLICKS

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In some ways,
we couldn't be more different,

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and yet we share so much.

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Oh, my goodness me!

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Absolutely amazing.

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DOLPHIN WHISTLES

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Like us, these wild animals
are highly social...

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..have sophisticated
communication...

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..work together to solve problems...

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..and they're as interested in me
as I am in them.

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CHRIS EXHALES LOUDLY

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They're so curious.
They just come up and look at you.

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I've never experienced anything
like this before.

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Absolutely magical!

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Driving this playful curiosity
is a giant, complex brain.

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Some even larger than ours.

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Dolphins are amongst
the most intelligent creatures

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to have ever lived on Earth.

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What is intelligence?

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Well, there's a question
that's easy to ask

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but a lot more difficult to answer.

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You see, across the animal kingdom,

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there are a range of species
that demonstrate intelligence.

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Some bird species, pigs, bees,

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even humans,

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but some of those animals
are undeniably

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more intelligent than others,

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and, here in these waters, the
cleverest by far are those dolphins.

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So the question is, how did the
dolphin get to become so smart?

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Well, to answer that question,
we must turn back the clock

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and follow a remarkable tale
of transformation.

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Back to a time before mammals.

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Before brains.

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Before anything...

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..could even think.

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Countless lives have contributed
to this story,

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but a few distant ancestors,
each with remarkable lifestyles,

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have left legacies that have
echoed down the generations,

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gifting the dolphin
its brilliant brain.

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The story of intelligence begins
a very long time ago...

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..on a planet devoid of thought,

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ideas, curiosity.

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No animals live on ancient Earth.

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But it is a home.

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Single cells live
a simple existence...

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..with not a single brain cell
between them.

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But, after Earth's
billion-year-long dark age...

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..a revolutionary act
is taking place.

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You see, these cells have evolved
the ability...

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..to sense light.

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In that moment,
where those first cells

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developed the ability
to sense the Sun,

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the dark ages of life on Earth
came to an end.

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It was truly a time
of enlightenment,

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and, if you bear with me, I'm going
to show you why it was so important.

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Look at that!

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There's a huge beetle over here,

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lots of flies, of course,

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and then moths.

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Look at that beauty!

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Stunning thing.

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And of course they're turning up,

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because moths are famously
attracted to light.

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And the way moths detect the light
is similar to the way

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that some bacteria detect light,

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and not just contemporary bacteria,

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but the bacteria that were living
in those ancient oceans.

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{\an8}Modern animals like moths
use a molecule called retinal.

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It changes shape when it's struck
by a photon of light.

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Like a switch,
this allows cells to sense light.

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And genetic techniques have revealed
something extraordinary.

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Three billion years ago,

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those ancient bacteria sensed light

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using the same molecule - retinal.

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But they did something else
that, in time, would become

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the foundation of intelligence.

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They didn't just sense light,

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they reacted to light.

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We think that moths are drawn
to the flame, as it were,

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because they use what light
there is at night,

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typically the Moon and the stars,

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to orientate themselves
in their environment,

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but what this has allowed is
the development of a behaviour -

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a basic instinct.

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Now, we mustn't confuse that
instinct with intelligence.

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I mean, let's face it,
these moths haven't been able

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to out-think that innate behaviour
and not be drawn to this trap.

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But that instinct,

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fuelled by the ability to sense
and react to light,

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was a crucial first step
on the route to becoming smarter.

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And for the next step, we need
to jump forward through time...

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..2.5 billion years.

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Life continues to evolve...

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..until we enter a new age
of animals.

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This tiny creature is an ancient
ancestor of the dolphin...

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..and it's searching
for a place to hide.

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But not from any predator.

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From the punishing UV rays
of the Sun.

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To guide it, it has two
light-detecting spots

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that only sense patches of light
and dark.

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So, finding shelter is no easy task.

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But among this population
of shade-seeking animals,

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the dolphin's ancestor
has a slight edge.

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It's inherited a series of
mutations - genetic changes...

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..which mean instead of being flat,

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its light-detecting spots

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cave ever so slightly inwards,

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becoming little dimples.

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Now, it's a difference so small
it might seem insignificant,

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but they give it an unexpected
advantage.

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To understand all of this,
we need to think a bit about optics.

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Here's a basic demonstration.

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Imagine the flat surface of this
plate is that flat pigment spot,

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covered with all of those
light-sensitive cells.

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Now, when it's facing the Sun,

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it's fully lit,
it's fully saturated.

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As it turns away, it's lit...

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..and then it's not.

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It's in shadow.

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It's either or - light or dark.

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Things are very different,
though, with a dimpled surface.

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Look at this bowl.

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Again, if it's facing the light full
on, then of course it's fully lit,

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but look what happens
as it turns away.

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Parts of its surface are in shadow

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whilst, simultaneously,
parts are lit.

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Of course, if it turns completely
away, then it's in shadow,

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but this is the critical part -

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shadow and light at the same time.

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And this is what gives
these early creatures

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the chance to build up a rudimentary
map of their environment

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using light and shade.

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For the first time ever,

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creatures are beginning
to see the world.

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And in simple terms,
these little dimples,

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these little buckets,

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are the first proper eyes.

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For the dolphin's ancestor,

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these simple, dimpled eyes

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allow it to sense more
than just shades of grey.

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Instead,

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it sees the first blurry images...

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..giving it the ability to
efficiently find a place to hide

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from the powerful Sun.

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I know what you're thinking.

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You're thinking, "How on earth can
you know that all of that is true,

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"particularly when soft-bodied
animals with tiny worm-like eyes

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"don't fossilise particularly well?"

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Well, I can tell you that almost
all of the characteristics

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of those earliest eyes can still
be found in living animals today.

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Simple, light-detecting spots
still exist in some jellyfish

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and limpets.

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Dimpled, or "cup eyes",

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are seen in modern-day flatworms.

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And hiding in this forest
is a curious creature

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with eyes like tiny buckets.

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This is a fascinating animal.

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It's a velvet worm.

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I've always wanted to see one.

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What can it see?
Well, looking out here,

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a very crude picture
of its environment,

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but very little detail,

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so, if I were to take this
animal to the optician's,

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it would be declared legally blind.

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For the velvet worm that seeks
damp and dark places to shelter,

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this basic vision
is more than sufficient.

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But over half a billion years ago,

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dimpled eyes were just
the beginning.

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Over generations,
dimples grow deeper.

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Protective cells
grow over the opening,

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forming a lens...

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..which focuses the Sun's rays onto
a layer of light-sensing cells -

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a retina.

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In a surprisingly short period
of evolutionary time,

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those simple spots transform

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into one of the most complex
biological instruments

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evolution has ever produced.

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By the Cambrian period,
sophisticated eyes are everywhere.

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From those that come in pairs...

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..to bizarre
evolutionary experiments.

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Now, you might be wondering

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why I'm talking so much about eyes

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in the story of intelligence.

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That's because the senses,
and vision in particular,

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played a critical role.

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They changed the dynamics
of life entirely...

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..because if animals can see
the world more clearly...

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..then they can also...

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..see each other.

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To stay alive now,

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you need your wits about you.

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In the Cambrian period,

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there was a sudden massive increase
in the diversity of new life,

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so much so that we call it
the Cambrian Explosion.

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00:17:14,240 --> 00:17:17,360
There are a number of theories
as to why this might have happened.

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It's likely that many of them come
into play, but, without ambiguity,

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one thing is certain - the evolution
of the eye played a role -

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because it opened up opportunities
for new predator-prey relationships,

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and that alone would have driven
an increase in diversity.

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But it's not just about the eye.

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Take a look at this fossil.

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This is an anomalocaridid animal.

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00:17:43,720 --> 00:17:47,040
It lived 500 million years ago,
it's related to lobsters,

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and this was a ferocious predator
in the Cambrian period.

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And these are its eyes.

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00:17:53,760 --> 00:17:55,040
Beautiful!

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Look at the preservation here.

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And these are compound eyes,
like contemporary insects

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00:18:00,520 --> 00:18:03,360
and crustaceans,
and they appear to be on stalks.

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00:18:03,360 --> 00:18:06,040
We think that this animal
could move its eyes

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00:18:06,040 --> 00:18:08,360
independently of one another,

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00:18:08,360 --> 00:18:10,920
looking in different directions
at the same time.

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00:18:10,920 --> 00:18:14,520
This was a massive increase
in visual complexity.

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00:18:15,520 --> 00:18:17,880
But how did the animal deal with it?

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00:18:17,880 --> 00:18:20,040
Well, look at this part here.

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00:18:20,040 --> 00:18:24,920
This represents an organ which is
very, very, very rarely fossilised.

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This is the animal's brain.

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It's thought that the first animals
had simple nervous systems,

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00:18:34,760 --> 00:18:38,120
but it's only when complex eyes
come on the scene

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00:18:38,120 --> 00:18:41,040
that fossilised brains are found.

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00:18:42,280 --> 00:18:45,040
We think these are the optic nerves,

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00:18:45,040 --> 00:18:48,840
passing all of that visual
information to the brain

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00:18:48,840 --> 00:18:50,560
to be analysed.

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00:18:50,560 --> 00:18:54,520
Now, brains have got their own
evolutionary history,

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00:18:54,520 --> 00:18:56,440
they didn't just appear overnight,

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00:18:56,440 --> 00:18:58,840
but in the wake
of the Cambrian Explosion,

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they got bigger
and they got more complex,

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00:19:01,280 --> 00:19:05,200
potentially to deal with all
of that visual information.

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00:19:05,200 --> 00:19:07,680
It's a beautiful fossil.

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00:19:07,680 --> 00:19:11,280
Without the evolution
of light-sensitive cells,

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00:19:11,280 --> 00:19:15,040
we wouldn't have eyes,
and without the evolution of eyes,

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00:19:15,040 --> 00:19:17,760
we wouldn't have brains
as we know them today.

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00:19:26,240 --> 00:19:30,440
The modern animal kingdom
is full of eyes and brains

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00:19:30,440 --> 00:19:35,280
attuned to perceive the world
in whatever way is most useful.

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Compound eyes give a wide field
of view to smaller brains.

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00:19:48,360 --> 00:19:53,560
Giant eyes that see like a camera
gather information in the depths.

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00:19:55,520 --> 00:20:01,280
And forward-facing eyes help
large brains navigate a 3D world.

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00:20:07,360 --> 00:20:10,040
But 500 million years ago,

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00:20:10,040 --> 00:20:13,360
animals and their
newly-evolved brains

243
00:20:13,360 --> 00:20:16,520
are just waking up
to the world around them.

244
00:20:26,760 --> 00:20:28,920
As we leap forward again...

245
00:20:29,920 --> 00:20:34,560
..the struggle for survival drives
brains to become more complex...

246
00:20:36,640 --> 00:20:39,600
..and more strategic.

247
00:20:48,600 --> 00:20:52,040
{\an8}Welcome to the Silurian period...

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00:20:55,040 --> 00:20:59,040
{\an8}..where the hunted
have become the hunters.

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00:21:03,040 --> 00:21:08,040
This fierce-looking animal is
an early female placoderm...

250
00:21:15,520 --> 00:21:18,760
..and you don't want to mess
with her.

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00:21:21,760 --> 00:21:25,040
You see, the predator-prey
arms race...

252
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..has turned her into
one formidable fish.

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00:21:39,520 --> 00:21:43,280
Placoderms dominated
the Earth's aquatic ecosystems

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00:21:43,280 --> 00:21:46,080
for 60 million years,

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00:21:46,080 --> 00:21:49,760
and I've got a fossil of one here,
and what a fossil this is.

256
00:21:49,760 --> 00:21:51,360
Just look at that!

257
00:21:51,360 --> 00:21:53,280
It's very, very beautiful.

258
00:21:53,280 --> 00:21:56,040
It came from Scotland
and it lived 380 million years ago,

259
00:21:56,040 --> 00:21:58,520
but look at the degree
of preservation here.

260
00:21:58,520 --> 00:22:02,440
You can see all the bones in its
vertebrae, the dorsal fin here,

261
00:22:02,440 --> 00:22:05,080
this is the head end, of course,
here's its eye.

262
00:22:05,080 --> 00:22:06,840
Look at that.

263
00:22:07,840 --> 00:22:09,360
Oh, wow.

264
00:22:09,360 --> 00:22:12,280
And I've never got over the fact
that I can put my finger

265
00:22:12,280 --> 00:22:18,360
on something which lived
380 million years ago.

266
00:22:19,360 --> 00:22:22,440
But getting back to placoderms,
you're going to say, you know,

267
00:22:22,440 --> 00:22:25,280
"Why is this fossil so important?
There are loads of animals

268
00:22:25,280 --> 00:22:27,960
"that lived and died out.
Why is this one such a big deal?"

269
00:22:27,960 --> 00:22:30,760
Well, these were some
of the first animals

270
00:22:30,760 --> 00:22:33,680
that had a jaw and a backbone,

271
00:22:33,680 --> 00:22:39,040
so if we want to learn more about
what we call the jawed vertebrates,

272
00:22:39,040 --> 00:22:42,840
and that's me, you,
your children, your gran,

273
00:22:42,840 --> 00:22:45,040
your pets, dolphins,

274
00:22:45,040 --> 00:22:48,520
then we've got to learn more
about placoderms.

275
00:22:52,040 --> 00:22:55,040
Placoderm fossils
of all shapes and sizes

276
00:22:55,040 --> 00:22:58,600
have been found on every continent
on the Earth.

277
00:22:59,760 --> 00:23:03,040
{\an8}Yet all share one
intriguing feature.

278
00:23:05,280 --> 00:23:08,520
Bony plates covering their heads.

279
00:23:11,040 --> 00:23:14,520
{\an8}Armour to protect the most
precious weapon

280
00:23:14,520 --> 00:23:17,440
{\an8}a predatory fish
has in its arsenal.

281
00:23:18,440 --> 00:23:20,120
Its brain.

282
00:23:21,760 --> 00:23:25,280
The predator-prey arms race
had turned these creatures

283
00:23:25,280 --> 00:23:27,360
into veritable little warships,

284
00:23:27,360 --> 00:23:29,880
and I say "little"
because this is a small one.

285
00:23:29,880 --> 00:23:33,280
Some of them grew up to four metres
in length.

286
00:23:34,360 --> 00:23:36,280
But, sadly, as we know,

287
00:23:36,280 --> 00:23:40,000
no amount of armour can protect us
from some things.

288
00:23:46,040 --> 00:23:48,520
In these ancient waters,

289
00:23:48,520 --> 00:23:51,040
a hidden threat is lurking.

290
00:24:01,040 --> 00:24:04,360
Despite its armour,
this early placoderm

291
00:24:04,360 --> 00:24:07,760
has fallen victim to a tiny invader.

292
00:24:09,520 --> 00:24:11,360
A virus.

293
00:24:11,360 --> 00:24:15,040
One whose impacts
would ripple through time.

294
00:24:26,040 --> 00:24:29,920
Viruses have always been pulling
the strings of life.

295
00:24:29,920 --> 00:24:34,120
They're master manipulators,
silently and ruthlessly

296
00:24:34,120 --> 00:24:37,280
invading their hosts
to take advantage of them,

297
00:24:37,280 --> 00:24:39,040
and we know how they work.

298
00:24:39,040 --> 00:24:43,040
They break into their host's cells,
hijack those cells' machinery,

299
00:24:43,040 --> 00:24:45,040
and then replicate themselves...

300
00:24:46,040 --> 00:24:49,280
..over and over and over again,

301
00:24:49,280 --> 00:24:54,040
until they burst out in a dangerous
explosion of infection,

302
00:24:54,040 --> 00:24:57,680
giving us things like Covid,
flu, common cold.

303
00:25:00,040 --> 00:25:03,440
But not all viruses act in this way.

304
00:25:04,440 --> 00:25:07,280
Some break into the cell

305
00:25:07,280 --> 00:25:12,760
and then insert their own genetic
material into the host's DNA,

306
00:25:12,760 --> 00:25:15,840
potentially changing it forever.

307
00:25:18,280 --> 00:25:21,720
These are called retroviruses...

308
00:25:22,720 --> 00:25:26,440
..and we think that over
400 million years ago,

309
00:25:26,440 --> 00:25:30,920
a retrovirus was circulating
in the oceans,

310
00:25:30,920 --> 00:25:35,920
infecting the bodies of many
species of ancient fish.

311
00:25:39,280 --> 00:25:43,920
One of whom may have been
this early placoderm.

312
00:25:45,520 --> 00:25:50,040
Luckily for her, however,
her immune system kicks into gear...

313
00:25:51,040 --> 00:25:52,840
..and she recovers.

314
00:25:54,520 --> 00:25:58,280
But, like a Trojan horse,
some of the virus

315
00:25:58,280 --> 00:26:01,680
makes its way into her egg cells

316
00:26:01,680 --> 00:26:04,520
and is passed on to her offspring.

317
00:26:12,520 --> 00:26:18,760
Over generations, the hidden viral
DNA does something extraordinary.

318
00:26:21,280 --> 00:26:26,760
It triggers one of the fish's genes
to go into overdrive...

319
00:26:27,760 --> 00:26:31,280
..altering the way
its nerve cells develop...

320
00:26:33,720 --> 00:26:38,040
..causing parts of the brain
to turn from grey

321
00:26:38,040 --> 00:26:40,280
to eerily pale.

322
00:26:42,040 --> 00:26:47,760
But instead of causing harm,
the brain is changed forever.

323
00:26:52,040 --> 00:26:55,360
These infections likely
happened multiple times

324
00:26:55,360 --> 00:26:57,280
in multiple species...

325
00:26:58,760 --> 00:27:03,120
..and scientists think
their effect has been profound.

326
00:27:06,040 --> 00:27:08,040
Oh, my God!

327
00:27:08,040 --> 00:27:10,920
It's a Jesus Christ lizard.

328
00:27:15,680 --> 00:27:18,520
I used to look at drawings
and read about these things

329
00:27:18,520 --> 00:27:21,280
in my childhood
animal encyclopaedias.

330
00:27:22,280 --> 00:27:24,520
And it's named after the son of God

331
00:27:24,520 --> 00:27:27,520
not because it so much
walks on water

332
00:27:27,520 --> 00:27:30,600
as runs very fast
across the surface.

333
00:27:30,600 --> 00:27:34,360
It's also got lightning-fast
reactions.

334
00:27:34,360 --> 00:27:38,760
So how does it manifest
all of this speed, as it were?

335
00:27:38,760 --> 00:27:42,240
Well, it comes down
to its nerve cells.

336
00:27:42,240 --> 00:27:47,040
You see, each of its nerve cells
have long fibres called axons.

337
00:27:47,040 --> 00:27:50,040
Those axons are wrapped
in a fatty sheath

338
00:27:50,040 --> 00:27:54,520
of a substance called myelin
and it insulates them.

339
00:27:54,520 --> 00:27:57,760
And what that means is
that each nerve cell

340
00:27:57,760 --> 00:28:02,360
can communicate with the other
far more quickly,

341
00:28:02,360 --> 00:28:04,520
and that happens in its brain

342
00:28:04,520 --> 00:28:07,360
and it happens from the nerves
that run from its brain

343
00:28:07,360 --> 00:28:09,280
to the muscles around its body.

344
00:28:09,280 --> 00:28:12,120
It's as if it's got
a super-fast processor.

345
00:28:14,040 --> 00:28:19,840
Nerve signals can travel
up to 200 times faster

346
00:28:19,840 --> 00:28:23,760
in axons insulated with myelin
than those without.

347
00:28:25,280 --> 00:28:29,520
And therefore we can make the
argument that the origin of myelin

348
00:28:29,520 --> 00:28:33,040
was the singularly
most important development

349
00:28:33,040 --> 00:28:36,920
when it came to the evolution
of the vertebrate brain.

350
00:28:39,360 --> 00:28:43,520
Now all we need this little lizard
to do is something biblical.

351
00:29:01,760 --> 00:29:06,040
Today, myelin is found throughout
the jawed vertebrates.

352
00:29:08,040 --> 00:29:11,880
All of these animals
have myelin to thank

353
00:29:11,880 --> 00:29:15,040
for the fast signals
inside their brains.

354
00:29:20,040 --> 00:29:24,520
And scientists have found
that nerves insulated with myelin

355
00:29:24,520 --> 00:29:30,280
can't be produced without
ancient retroviral DNA...

356
00:29:31,480 --> 00:29:34,520
..which has been transmitted
down the generations

357
00:29:34,520 --> 00:29:37,760
from fishes that caught a virus

358
00:29:37,760 --> 00:29:41,160
over 400 million years ago.

359
00:29:42,280 --> 00:29:45,520
Evolution.
You just can't beat it, can you?

360
00:29:45,520 --> 00:29:47,920
Well, you can,
because it gets better.

361
00:29:47,920 --> 00:29:51,040
You see, myelin didn't
just speed things up,

362
00:29:51,040 --> 00:29:55,280
it allowed brains to develop
more computing power.

363
00:29:55,280 --> 00:29:59,520
It allowed brains to evolve
to become more compact,

364
00:29:59,520 --> 00:30:03,520
more complex, more powerful.

365
00:30:03,520 --> 00:30:07,680
It was as if life had just
got a hardware upgrade

366
00:30:07,680 --> 00:30:12,280
and this was therefore
a significant step up

367
00:30:12,280 --> 00:30:15,040
in the evolution of intelligence

368
00:30:15,040 --> 00:30:18,520
because, for the first time,
the vertebrate brain

369
00:30:18,520 --> 00:30:22,760
was on the cusp of doing something
it had never been able to do before.

370
00:30:23,760 --> 00:30:25,240
Thinking.

371
00:30:34,760 --> 00:30:38,080
Across tens of millions of years...

372
00:30:39,520 --> 00:30:43,040
..fast-thinking vertebrates
dominate the oceans.

373
00:30:45,280 --> 00:30:49,040
But for the next chapter
in the story of the dolphin

374
00:30:49,040 --> 00:30:51,120
and its amazing brain...

375
00:30:53,040 --> 00:30:56,520
..we need to step out onto land.

376
00:31:05,040 --> 00:31:10,280
This strange, hairless,
burrowing animal is a cynodont.

377
00:31:12,040 --> 00:31:15,760
An ancestor of mammals,
including the dolphin.

378
00:31:17,520 --> 00:31:20,280
Now, it lives underground
for good reason.

379
00:31:20,280 --> 00:31:23,360
Predatory reptiles roam outside.

380
00:31:28,040 --> 00:31:31,760
But, at some point,
it's got to venture out to eat.

381
00:31:35,760 --> 00:31:39,760
As the day comes to an end,
there's an opportunity.

382
00:31:42,280 --> 00:31:45,280
But there's just one problem.

383
00:31:46,280 --> 00:31:48,280
It's getting dark.

384
00:31:49,760 --> 00:31:53,040
Soon, its vision won't be much use.

385
00:32:00,040 --> 00:32:03,040
Imagine what it was like
for those little cynodonts.

386
00:32:04,040 --> 00:32:08,360
Now, I've got a cast of one
of these animals' skulls here.

387
00:32:08,360 --> 00:32:11,040
You can see that "little"
is the appropriate word.

388
00:32:11,040 --> 00:32:13,680
This skull is about
the same size as a rabbit.

389
00:32:13,680 --> 00:32:17,520
So, they were small,
opportunistic hunters.

390
00:32:17,520 --> 00:32:20,040
The problem was that
when they ventured out,

391
00:32:20,040 --> 00:32:21,840
particularly in broad daylight,

392
00:32:21,840 --> 00:32:24,760
there was a very good chance
they'd be hunted themselves.

393
00:32:24,760 --> 00:32:28,040
There were loads of predators
stalking around the Triassic.

394
00:32:28,040 --> 00:32:31,000
But when these little creatures
ventured out of their burrows

395
00:32:31,000 --> 00:32:34,000
into the night, there were
distinct advantages for them.

396
00:32:39,640 --> 00:32:42,520
At night there are fewer
predators...

397
00:32:43,520 --> 00:32:46,040
..and reduced competition for food.

398
00:32:50,600 --> 00:32:55,520
But, of course, in the dark,
food can be harder to find.

399
00:33:00,520 --> 00:33:03,280
What they would have experienced
is pretty much

400
00:33:03,280 --> 00:33:05,520
what I'm experiencing now.

401
00:33:06,520 --> 00:33:09,280
Human eyesight isn't brilliant
in the dark

402
00:33:09,280 --> 00:33:11,080
but it's not that bad either.

403
00:33:11,080 --> 00:33:14,680
So, if I close my eyes, now I'm
effectively blind, what happens?

404
00:33:14,680 --> 00:33:16,840
Well, I immediately
start to concentrate

405
00:33:16,840 --> 00:33:19,520
on my other senses, of course.
Firstly, hearing.

406
00:33:19,520 --> 00:33:22,280
BIRDS CHIRP
A bit of bird song...

407
00:33:22,280 --> 00:33:25,040
INSECTS BUZZ
..whine of insects.

408
00:33:25,040 --> 00:33:26,520
Crickets.

409
00:33:26,520 --> 00:33:28,920
RUSTLING
A bit of rustling over there.

410
00:33:28,920 --> 00:33:31,280
BUZZING
Incoming mosquito.

411
00:33:31,280 --> 00:33:33,680
What about smell?
HE SNIFFS LOUDLY

412
00:33:33,680 --> 00:33:35,840
Oh, yeah, that smells good.

413
00:33:35,840 --> 00:33:40,040
I can smell all of that
decomposing leaf litter.

414
00:33:40,040 --> 00:33:43,360
That's what I call
"forest fruitcake".

415
00:33:43,360 --> 00:33:47,520
A really rich, delicious mix
of odours.

416
00:33:48,520 --> 00:33:50,920
And, I mean, I'm not bragging,
but I like to think

417
00:33:50,920 --> 00:33:53,680
that my sense of smell
is quite well attuned in nature.

418
00:33:53,680 --> 00:33:55,840
I've been sniffing it
all of my life.

419
00:33:55,840 --> 00:33:58,520
So, out here in the dark,
I would be fairly confident

420
00:33:58,520 --> 00:34:01,520
using my sense of smell
to help me navigate.

421
00:34:01,520 --> 00:34:04,280
Perhaps you wouldn't be
quite so confident,

422
00:34:04,280 --> 00:34:07,760
and that would have been exactly
the same for those cynodonts.

423
00:34:07,760 --> 00:34:10,520
Part of their population
would have had senses

424
00:34:10,520 --> 00:34:14,040
which were more finely attuned,
and those would have been

425
00:34:14,040 --> 00:34:17,520
the individuals that went
out to forage, found food,

426
00:34:17,520 --> 00:34:21,120
and then made it safely
back to their burrows.

427
00:34:27,520 --> 00:34:32,520
Super-sensing cynodonts would have
fared better navigating at night.

428
00:34:35,040 --> 00:34:39,320
And it's thought this allowed
some groups to become nocturnal.

429
00:34:41,520 --> 00:34:46,040
And as these cynodonts' senses
sharpened to the night...

430
00:34:47,240 --> 00:34:51,520
..we think the flood of new
information being gathered

431
00:34:51,520 --> 00:34:55,280
kick-started a monumental
transformation

432
00:34:55,280 --> 00:34:57,520
in their descendants' brains.

433
00:35:02,040 --> 00:35:06,920
Over tens of millions of years,
the brain changes shape.

434
00:35:06,920 --> 00:35:10,680
Areas involved in smell
and touch expand...

435
00:35:13,320 --> 00:35:18,280
..and the brain increases in size
by over 40%.

436
00:35:20,720 --> 00:35:25,360
To process the new information,
we see a game-changing region

437
00:35:25,360 --> 00:35:28,040
develop in the top layers
of the brain.

438
00:35:33,040 --> 00:35:36,280
And with it, a new type of animal.

439
00:35:39,280 --> 00:35:43,280
In under 50 million years,
those burrowing cynodonts

440
00:35:43,280 --> 00:35:46,520
had evolved into something
a little bit like this.

441
00:35:46,520 --> 00:35:49,280
The first mammals.

442
00:35:53,280 --> 00:35:58,280
Now, I know that many of you
probably aren't that keen on rats.

443
00:35:58,280 --> 00:35:59,840
I love them.

444
00:35:59,840 --> 00:36:02,440
I love their little whiskers,
whisking away,

445
00:36:02,440 --> 00:36:05,760
and those stiffened hairs
are rooted in skin

446
00:36:05,760 --> 00:36:07,760
which is packed full of nerves,

447
00:36:07,760 --> 00:36:11,360
sending masses of information
to its brain.

448
00:36:11,360 --> 00:36:14,040
And then you've got
its twitching nose.

449
00:36:14,040 --> 00:36:16,360
A nose far more sensitive than ours,

450
00:36:16,360 --> 00:36:20,680
capable of smelling things like
explosives, even human cancers.

451
00:36:20,680 --> 00:36:25,440
And its ears... Now, come on,
those are the prettiest little ears.

452
00:36:25,440 --> 00:36:30,600
Radar dishes listening out for the
rustle of any potential predator.

453
00:36:30,600 --> 00:36:34,040
But, of course, all of this
extra sensory information

454
00:36:34,040 --> 00:36:35,760
needs to be processed,

455
00:36:35,760 --> 00:36:38,840
so it was at about this time
that an area of the brain

456
00:36:38,840 --> 00:36:43,360
called the neocortex
began to develop more fully.

457
00:36:43,360 --> 00:36:48,760
And that was utterly, utterly
transformational

458
00:36:48,760 --> 00:36:53,280
because it allowed these animals
to solve problems,

459
00:36:53,280 --> 00:36:56,280
to learn, to develop memories,

460
00:36:56,280 --> 00:36:59,280
and, with all of that extra
sensory processing,

461
00:36:59,280 --> 00:37:04,520
to map their environment
and plan their next move.

462
00:37:05,520 --> 00:37:10,800
The neocortex was an extraordinary
mammalian innovation.

463
00:37:14,520 --> 00:37:19,520
{\an8}And that neocortex is the outer
layer of the mammalian brain.

464
00:37:20,760 --> 00:37:25,440
{\an8}Sometimes smooth,
sometimes wrinkly and folded.

465
00:37:25,440 --> 00:37:30,280
{\an8}It receives and processes
complex sensory information...

466
00:37:32,040 --> 00:37:35,520
{\an8}..and it links it
to other regions the brain.

467
00:37:39,040 --> 00:37:43,920
In today's mammals,
it's essential for learning...

468
00:37:45,400 --> 00:37:47,160
..planning...

469
00:37:48,840 --> 00:37:50,760
..prediction...

470
00:37:52,640 --> 00:37:54,200
..decision-making.

471
00:37:56,520 --> 00:38:01,040
The foundations of what
we'd call intelligence.

472
00:38:04,040 --> 00:38:08,040
Now, of course, mammals aren't
the only intelligent animals.

473
00:38:11,040 --> 00:38:14,280
Birds have a structure called
the "wulst"

474
00:38:14,280 --> 00:38:17,480
that performs a similar function
to the neocortex.

475
00:38:21,520 --> 00:38:25,280
And octopuses have one
centralised brain

476
00:38:25,280 --> 00:38:27,480
and eight mini brains.

477
00:38:28,480 --> 00:38:30,360
One for each arm.

478
00:38:35,040 --> 00:38:38,840
But 200 million years ago,
for the mammals,

479
00:38:38,840 --> 00:38:43,440
the neocortex helped unlock
a more intelligent way of life.

480
00:38:46,360 --> 00:38:51,480
And to continue their story, we need
to take another leap through time...

481
00:38:58,840 --> 00:39:00,520
..until...

482
00:39:02,440 --> 00:39:06,160
..it's the mammals' turn
to take centre stage.

483
00:39:13,280 --> 00:39:16,680
By now, those mammals
have radiated out

484
00:39:16,680 --> 00:39:19,040
and diversified across the globe.

485
00:39:28,040 --> 00:39:31,840
And it's here that we find
one unique group

486
00:39:31,840 --> 00:39:34,920
on the verge of an extraordinary
transformation.

487
00:39:40,280 --> 00:39:43,040
This is Indohyus.

488
00:39:44,440 --> 00:39:49,520
The size of a cat, with deer-like
legs and the snout of a dog.

489
00:39:49,520 --> 00:39:53,040
Quite frankly,
it's a bit of a weirdo.

490
00:39:57,040 --> 00:40:01,040
Tiptoeing on little hooves,
it's on the lookout for lunch.

491
00:40:06,520 --> 00:40:08,520
LOUD SQUAWK

492
00:40:08,520 --> 00:40:10,760
But it's not the only one.

493
00:40:18,960 --> 00:40:23,040
This diminutive plant-eater
is easy pickings for predators

494
00:40:23,040 --> 00:40:24,760
circling above.

495
00:40:26,280 --> 00:40:29,680
But Indohyus has an escape plan.

496
00:40:39,080 --> 00:40:44,960
A strategy adopted by another
of evolution's oddballs.

497
00:40:54,360 --> 00:40:58,920
Indohyus was a lot smaller and
more dainty, but I give you...

498
00:41:00,040 --> 00:41:01,680
..the tapir.

499
00:41:06,200 --> 00:41:08,520
CHRIS CHUCKLES
Oh, yes!

500
00:41:08,520 --> 00:41:10,520
What an animal!

501
00:41:10,520 --> 00:41:14,040
I absolutely love tapirs.

502
00:41:15,280 --> 00:41:18,560
I've liked them since I was a kid.
I don't know what it is about them.

503
00:41:18,560 --> 00:41:20,760
I think it's because they're weird.

504
00:41:20,760 --> 00:41:24,280
But what else have they got
in common with Indohyus?

505
00:41:24,280 --> 00:41:28,520
Well, they're both herbivores,
and, as a consequence,

506
00:41:28,520 --> 00:41:32,520
they need to be thinking about
avoiding carnivores.

507
00:41:33,760 --> 00:41:37,960
This Baird's tapir
can be predated by jaguars.

508
00:41:37,960 --> 00:41:39,760
So how do they avoid that?

509
00:41:39,760 --> 00:41:43,760
Well, one of the things they've done
is developed an aquatic lifestyle.

510
00:41:45,040 --> 00:41:47,680
Now, if you don't want to be buoyant
if you're in the water,

511
00:41:47,680 --> 00:41:50,040
and, on that account,
when they go into the water,

512
00:41:50,040 --> 00:41:51,640
they sink to the bottom.

513
00:41:51,640 --> 00:41:55,520
They can walk across the bottom
of rivers, lakes and lagoons,

514
00:41:55,520 --> 00:41:59,040
and that is the same as Indohyus.

515
00:41:59,040 --> 00:42:01,520
Indohyus had heavy bones.

516
00:42:08,320 --> 00:42:12,320
In fact, trying to evade predators
on a day-to-day basis

517
00:42:12,320 --> 00:42:14,800
was at the core of driving

518
00:42:14,800 --> 00:42:19,520
one of the most revolutionary
transformations in evolution.

519
00:42:35,040 --> 00:42:38,040
For Indohyus and its heavy bones...

520
00:42:40,040 --> 00:42:42,520
..water is a refuge.

521
00:42:55,040 --> 00:42:57,040
And stepping away from land...

522
00:42:58,040 --> 00:43:00,440
..turned out to be a masterstroke.

523
00:43:06,040 --> 00:43:09,680
This new world
offers up plentiful food

524
00:43:09,680 --> 00:43:11,760
and new opportunities.

525
00:43:14,760 --> 00:43:19,520
Over generations, their relatives
become much more streamlined.

526
00:43:20,680 --> 00:43:24,680
Limbs are replaced
with paddle-like flippers.

527
00:43:26,920 --> 00:43:30,760
Nostrils migrate further away
from their long snouts.

528
00:43:33,440 --> 00:43:37,280
Tails get flatter and more powerful.

529
00:43:38,760 --> 00:43:41,680
And the once-hoofed mammals

530
00:43:41,680 --> 00:43:44,760
are now completely aquatic.

531
00:43:59,520 --> 00:44:03,040
This was one of the most
astonishing body transformations

532
00:44:03,040 --> 00:44:05,520
in the course
of evolutionary history.

533
00:44:07,640 --> 00:44:10,040
In just over 10 million years,

534
00:44:10,040 --> 00:44:13,720
these tiny, terrestrial,
tiptoeing animals

535
00:44:13,720 --> 00:44:18,040
had transformed into sleek,
streamlined swimmers.

536
00:44:19,720 --> 00:44:23,280
And I've got the cast of a skull
of one of them here.

537
00:44:23,280 --> 00:44:25,760
This is Dorudon

538
00:44:25,760 --> 00:44:29,160
and it lived 40 million years ago,

539
00:44:29,160 --> 00:44:31,360
and the teeth do all of the talking.

540
00:44:31,360 --> 00:44:32,720
Look here.

541
00:44:32,720 --> 00:44:36,040
{\an8}These massive canines
for catching and gripping the prey

542
00:44:36,040 --> 00:44:37,840
{\an8}and then these teeth here

543
00:44:37,840 --> 00:44:40,040
{\an8}for shearing it into tiny pieces.

544
00:44:40,040 --> 00:44:43,360
This would have been an impressive
animal, but not the biggest.

545
00:44:43,360 --> 00:44:45,760
One of its relatives, Basilosaurus,

546
00:44:45,760 --> 00:44:48,120
grew to the length of a bus.

547
00:44:48,120 --> 00:44:51,760
Those puny, cat-like animals

548
00:44:51,760 --> 00:44:55,520
had transformed into monsters.

549
00:44:57,040 --> 00:44:58,360
Superb.

550
00:44:58,360 --> 00:44:59,840
But, of course,

551
00:44:59,840 --> 00:45:01,720
things didn't stop there.

552
00:45:01,720 --> 00:45:04,760
This is a cast of the skull
of Simocetus,

553
00:45:04,760 --> 00:45:07,040
a distant relative of Dorudon,

554
00:45:07,040 --> 00:45:10,040
and it lived 32 million years ago.

555
00:45:10,040 --> 00:45:11,680
But look at the skull -

556
00:45:11,680 --> 00:45:13,480
pretty radically different.

557
00:45:13,480 --> 00:45:17,080
It's much shorter, it's far more
structurally complex on top here.

558
00:45:19,280 --> 00:45:23,280
{\an8}Simocetus was part of a new group
of marine mammals -

559
00:45:23,280 --> 00:45:26,560
the odontocetes,
or "toothed whales".

560
00:45:28,080 --> 00:45:29,920
Look at this depression here.

561
00:45:29,920 --> 00:45:33,520
We think an organ called the melon
might have sat here.

562
00:45:33,520 --> 00:45:38,040
It's a fatty sphere. Sounds produced
from the nasal passages are focused

563
00:45:38,040 --> 00:45:42,920
through it like a lens and projected
out into the animal's environment.

564
00:45:42,920 --> 00:45:46,520
When they bounce back,
they're captured by the lower jaw,

565
00:45:46,520 --> 00:45:49,680
part of which is hollow,
transferred to the inner ear,

566
00:45:49,680 --> 00:45:52,040
which sends the information
to the brain.

567
00:45:53,040 --> 00:45:55,280
You know what I'm saying here,
don't you?

568
00:45:55,280 --> 00:45:58,040
Echolocation had evolved.

569
00:45:58,040 --> 00:45:59,920
Echolocation!

570
00:45:59,920 --> 00:46:01,680
What about that?

571
00:46:01,680 --> 00:46:04,280
But we think something else radical

572
00:46:04,280 --> 00:46:06,840
might have been happening
at the same time.

573
00:46:06,840 --> 00:46:09,760
We think that animals like this
might have been

574
00:46:09,760 --> 00:46:13,800
at the start of a journey
from being solitary hunters

575
00:46:13,800 --> 00:46:16,280
to hunting together,

576
00:46:16,280 --> 00:46:20,760
and this social behaviour
would have a profound effect

577
00:46:20,760 --> 00:46:22,880
on the development of the brain.

578
00:46:28,440 --> 00:46:31,000
As the toothed whales
continued to evolve...

579
00:46:32,000 --> 00:46:36,280
..it's thought that many of them
became more and more social.

580
00:46:38,040 --> 00:46:42,800
And the fossil record shows evidence
of their brains getting larger...

581
00:46:45,040 --> 00:46:48,920
..until,
around 11 million years ago...

582
00:46:50,280 --> 00:46:53,040
..an iconic family emerged.

583
00:46:58,520 --> 00:47:00,040
Dolphins.

584
00:47:05,040 --> 00:47:10,040
Today, over 40 species of dolphin
can be found worldwide...

585
00:47:12,520 --> 00:47:14,280
{\an8}..from the tiny...

586
00:47:16,440 --> 00:47:18,360
..to the giant.

587
00:47:22,040 --> 00:47:23,880
They live in groups...

588
00:47:25,520 --> 00:47:28,360
..and have complex
social relationships.

589
00:47:32,760 --> 00:47:36,040
{\an8}And some species are amongst

590
00:47:36,040 --> 00:47:39,520
{\an8}the most intelligent animals
on Earth.

591
00:48:05,040 --> 00:48:07,880
This group of spotted dolphins

592
00:48:07,880 --> 00:48:10,760
have spent their whole lives
in the Bahamas.

593
00:48:10,760 --> 00:48:13,040
DOLPHINS CLICK AND WHISTLE

594
00:48:15,480 --> 00:48:19,040
And their social lives govern
their behaviour.

595
00:48:25,040 --> 00:48:27,280
Mothers, cousins,

596
00:48:27,280 --> 00:48:30,280
friends, even rivals,

597
00:48:30,280 --> 00:48:35,040
all roaming together
in the waters they call home.

598
00:48:49,280 --> 00:48:52,040
I've just been to
spotted dolphin heaven!

599
00:48:52,040 --> 00:48:53,920
I cannot tell you.

600
00:48:53,920 --> 00:48:56,840
That was absolutely incredible.

601
00:48:56,840 --> 00:49:01,280
At one point, I was just wrapped
in a vortex of spinning dolphins.

602
00:49:01,280 --> 00:49:02,960
Oh, my goodness me.

603
00:49:02,960 --> 00:49:05,040
CLICKS AND WHISTLES

604
00:49:13,440 --> 00:49:16,200
And, of course, we know that
they all know one another,

605
00:49:16,200 --> 00:49:18,840
not just now but throughout
the course of their lives.

606
00:49:18,840 --> 00:49:21,040
They've got that phenomenal memory.

607
00:49:27,040 --> 00:49:31,840
And to think they are down there
experiencing emotions

608
00:49:31,840 --> 00:49:33,920
like joy.

609
00:49:33,920 --> 00:49:37,040
I think they were feeling joy.
I was certainly feeling joy.

610
00:49:37,040 --> 00:49:42,040
But then we know that they can
even experience grief as well.

611
00:49:46,000 --> 00:49:48,040
DOLPHIN CLICKS

612
00:49:49,520 --> 00:49:51,360
And the clicking!

613
00:49:52,520 --> 00:49:56,160
The constant ticking.
"Tick-tick-tick-tick", all the time.

614
00:49:56,160 --> 00:49:58,680
They're communicating
to one another.

615
00:50:01,040 --> 00:50:03,360
Now, there's a dispute
amongst scientists

616
00:50:03,360 --> 00:50:06,680
as to whether they have a language,

617
00:50:06,680 --> 00:50:09,040
but, from my point of view
at the moment,

618
00:50:09,040 --> 00:50:12,040
I'm quite happy to fantasise,
because I would love,

619
00:50:12,040 --> 00:50:16,920
absolutely love, to know what
they were all saying to one another!

620
00:50:16,920 --> 00:50:18,520
Honestly...

621
00:50:18,520 --> 00:50:21,040
Honestly, so, so good.

622
00:50:26,000 --> 00:50:32,040
This is the soundtrack of a thriving
underwater society...

623
00:50:39,040 --> 00:50:43,280
{\an8}..underpinned by one of the most
complex brains on Earth.

624
00:50:45,840 --> 00:50:49,520
Relative to their bodies, it's
one of the biggest of any animal,

625
00:50:49,520 --> 00:50:53,440
with key regions thought to be
involved in self-awareness,

626
00:50:53,440 --> 00:50:57,760
communication
and understanding emotions.

627
00:50:57,760 --> 00:51:01,280
And that uniquely mammalian
neocortex

628
00:51:01,280 --> 00:51:05,200
has become one of the most
intricately folded brain surfaces

629
00:51:05,200 --> 00:51:07,040
on the planet.

630
00:51:12,040 --> 00:51:15,360
Brains are amongst the most
energy-expensive organs

631
00:51:15,360 --> 00:51:19,600
to run in the body,
but, boy, are they worth that cost,

632
00:51:19,600 --> 00:51:23,360
because if you've got a large,
complex brain, like those dolphins,

633
00:51:23,360 --> 00:51:27,640
it gives you the capacity
to develop intelligence.

634
00:51:28,640 --> 00:51:31,040
And the dolphins use that
intelligence

635
00:51:31,040 --> 00:51:34,120
to change their behaviour
on a day-to-day basis.

636
00:51:34,120 --> 00:51:36,280
They can learn things.

637
00:51:36,280 --> 00:51:40,280
They can then copy things from
dolphins that have learned things.

638
00:51:40,280 --> 00:51:43,040
They've got cultural
learning capabilities.

639
00:51:43,040 --> 00:51:49,280
And this social intelligence is
the most important tool in the box

640
00:51:49,280 --> 00:51:51,760
when it comes to survival.

641
00:51:51,760 --> 00:51:53,680
But get this,

642
00:51:53,680 --> 00:51:56,040
they evolved that intelligence

643
00:51:56,040 --> 00:52:00,040
in a world which is
completely alien to ours.

644
00:52:00,040 --> 00:52:01,920
They evolved it...

645
00:52:01,920 --> 00:52:03,720
..underwater!

646
00:52:06,280 --> 00:52:11,840
We may never truly know what goes
on inside the mind of a dolphin,

647
00:52:11,840 --> 00:52:15,760
but its brain tells
a remarkable story.

648
00:52:17,280 --> 00:52:21,280
Three billion years of sensing...

649
00:52:24,040 --> 00:52:25,760
..of struggle...

650
00:52:29,360 --> 00:52:31,400
..and survival.

651
00:52:34,240 --> 00:52:36,040
Of brains...

652
00:52:37,120 --> 00:52:39,040
..and bodies...

653
00:52:39,040 --> 00:52:40,840
..transformed.

654
00:52:52,040 --> 00:52:55,040
Dolphins' minds,
like ours for that matter,

655
00:52:55,040 --> 00:52:57,920
are remarkable pieces of biology.

656
00:52:57,920 --> 00:53:00,680
It's for very good reason
that we think of our brains

657
00:53:00,680 --> 00:53:05,040
as being the most complex objects
in the known Universe

658
00:53:05,040 --> 00:53:09,600
and they're still surrounded
by an aura of mystery, of magic.

659
00:53:09,600 --> 00:53:12,920
But here's one thing
that we know for certain.

660
00:53:12,920 --> 00:53:15,760
Our brains, our minds,

661
00:53:15,760 --> 00:53:20,760
simply wouldn't exist
without the power of evolution.

662
00:53:20,760 --> 00:53:24,040
That blind journey of change,

663
00:53:24,040 --> 00:53:27,760
of innovation, of exquisite beauty.

664
00:53:33,280 --> 00:53:34,760
Next time...

665
00:53:36,040 --> 00:53:40,080
{\an8}..how the horse became one
of nature's greatest athletes.

666
00:53:40,080 --> 00:53:41,920
Just look at her.

667
00:53:41,920 --> 00:53:44,840
She's absolutely gorgeous.

668
00:53:44,840 --> 00:53:46,880
Aren't you?

669
00:53:46,880 --> 00:53:48,920
From life's first steps...

670
00:53:49,920 --> 00:53:54,720
..to racing hearts
and limbs built for speed.

671
00:53:54,720 --> 00:53:56,800
Let's see them in action.

672
00:53:56,800 --> 00:53:58,280
DOG BARKS

673
00:53:59,280 --> 00:54:03,800
This is a slithering, swimming,
sprinting odyssey,

674
00:54:03,800 --> 00:54:06,440
with one final twist.

675
00:54:07,440 --> 00:54:08,920
Us.

676
00:54:12,040 --> 00:54:17,520
But first, how do we know
that the ancestors of dolphins

677
00:54:17,520 --> 00:54:19,760
once walked on land?

678
00:54:23,760 --> 00:54:27,120
Dolphins are part of a larger
group called cetaceans,

679
00:54:27,120 --> 00:54:30,760
which includes dolphins,
whales and porpoises.

680
00:54:32,040 --> 00:54:35,840
Cetaceans have the largest
range in body size

681
00:54:35,840 --> 00:54:38,280
of any group of mammals
on the planet.

682
00:54:39,280 --> 00:54:42,040
From really small,
little harbour porpoises

683
00:54:42,040 --> 00:54:44,040
that are only a few feet long,

684
00:54:44,040 --> 00:54:47,400
to the blue whale -
the largest animal on Earth,

685
00:54:47,400 --> 00:54:49,120
and everything in between.

686
00:54:51,520 --> 00:54:55,520
And their origin can be traced
back to an ancient sea

687
00:54:55,520 --> 00:54:58,520
that once stretched
between India and Asia.

688
00:55:02,040 --> 00:55:06,040
Local and international scientists
have been searching for fossils

689
00:55:06,040 --> 00:55:09,560
in India and Pakistan
over many years,

690
00:55:09,560 --> 00:55:13,640
where they found the remains
of an intriguing mammal.

691
00:55:17,080 --> 00:55:20,040
What I'm holding in my hand here
is a real fossil

692
00:55:20,040 --> 00:55:21,760
of the skull of Indohyus.

693
00:55:21,760 --> 00:55:23,840
{\an8}There's four of these in the world.

694
00:55:23,840 --> 00:55:25,760
{\an8}I've got one right here.

695
00:55:28,120 --> 00:55:31,680
The name Indohyus
actually means India's pig.

696
00:55:31,680 --> 00:55:35,680
From the chemistry of the teeth,
we can tell that this animal ate

697
00:55:35,680 --> 00:55:39,360
land plants, mostly leaves,
and flowers and fruits.

698
00:55:41,040 --> 00:55:45,840
From first appearances, Indohyus
looked like a regular land mammal...

699
00:55:46,840 --> 00:55:51,520
..until a chance event
revealed a critical structure

700
00:55:51,520 --> 00:55:53,760
hidden deep within its skull.

701
00:55:54,760 --> 00:55:57,320
I had a fossil preparator,
his name was Rick,

702
00:55:57,320 --> 00:55:59,280
who was cleaning this off, he said,

703
00:55:59,280 --> 00:56:02,840
"I'm very sorry, but I broke
part of this Indohyus skull",

704
00:56:02,840 --> 00:56:06,280
and then I noticed that the ear bone
actually shows a feature

705
00:56:06,280 --> 00:56:10,360
that's only present in whales and
dolphins, called the involucrum.

706
00:56:12,040 --> 00:56:17,360
{\an8}The involucrum is a region
of the ear bone that has thickened.

707
00:56:17,360 --> 00:56:21,240
In modern-day cetaceans,
it amplifies vibrations

708
00:56:21,240 --> 00:56:26,920
transmitted in the skull, enhancing
their ability to hear under water.

709
00:56:26,920 --> 00:56:31,440
So that's really the smoking gun
that Indohyus is closely related

710
00:56:31,440 --> 00:56:33,320
to whales and dolphins.

711
00:56:33,320 --> 00:56:39,040
Evidence that it was already
adapting to a life underwater,

712
00:56:39,040 --> 00:56:42,280
completing the remarkable story

713
00:56:42,280 --> 00:56:47,520
of how land mammals
evolved into marine cetaceans.

714
00:56:47,520 --> 00:56:50,520
It is one of the best
fossil records we have,

715
00:56:50,520 --> 00:56:53,360
so we've got a lot of pieces
of the puzzle

716
00:56:53,360 --> 00:56:55,720
to tell us what happened.

717
00:56:57,280 --> 00:57:00,760
{\an8}Other transitional fossils
have been found across the region

718
00:57:00,760 --> 00:57:03,760
{\an8}that was once the ancient
Tethys Sea.

719
00:57:05,040 --> 00:57:08,440
{\an8}We have whales and dolphins that
look like crocodiles,

720
00:57:08,440 --> 00:57:10,840
we have whales and dolphins
that look like seals

721
00:57:10,840 --> 00:57:12,520
or otters or sea lions.

722
00:57:15,040 --> 00:57:20,040
It is probably one of the most
dramatic transformations

723
00:57:20,040 --> 00:57:23,280
in all of the evolution of life.

724
00:57:25,520 --> 00:57:29,680
Indohyus was not the kind of animal

725
00:57:29,680 --> 00:57:31,600
that you would look at and say,

726
00:57:31,600 --> 00:57:34,000
"You're going to get
a blue whale out of that",

727
00:57:34,000 --> 00:57:38,280
"You're going to get a brain
like a dolphin brain out of that",

728
00:57:38,280 --> 00:57:42,040
but that's what evolution does -
it makes big changes.

729
00:57:49,040 --> 00:57:52,680
Do you want to know how an elephant
is related to a clownfish?

730
00:57:52,680 --> 00:57:57,040
Discover more in a poster from the
Open University on the tree of life.

731
00:57:57,040 --> 00:58:00,360
To get your free copy,
scan the QR code on screen

732
00:58:00,360 --> 00:58:04,520
or ring 0300 303 3460,

733
00:58:04,520 --> 00:58:10,040
or visit
connect.open.ac.uk/evolution