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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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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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00:16:05,580 --> 00:16:07,820
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...

191
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..then they can also...

192
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..see each other.

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00:16:43,340 --> 00:16:45,820
To stay alive now,

194
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you need your wits about you.

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00:17:04,060 --> 00:17:05,980
In the Cambrian period,

196
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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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00:17:14,540 --> 00:17:17,660
There are a number of theories as to
why this might have happened.

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00:17:17,660 --> 00:17:21,140
It's likely that many of them come
into play, but, without ambiguity,

200
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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,

202
00:17:31,660 --> 00:17:35,700
and that alone would have driven an
increase in diversity.

203
00:17:35,700 --> 00:17:38,420
But it's not just about the eye.

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Take a look at this fossil.

205
00:17:41,340 --> 00:17:44,020
This is an anomalocaridid animal.

206
00:17:44,020 --> 00:17:47,340
It lived 500 million years ago, it's
related to lobsters,

207
00:17:47,340 --> 00:17:51,340
and this was a ferocious predator in
the Cambrian period.

208
00:17:51,340 --> 00:17:54,060
And these are its eyes.

209
00:17:54,060 --> 00:17:55,340
Beautiful!

210
00:17:55,340 --> 00:17:57,340
Look at the preservation here.

211
00:17:57,340 --> 00:18:00,820
And these are compound eyes, like
contemporary insects

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00:18:00,820 --> 00:18:03,660
and crustaceans, and they appear to be
on stalks.

213
00:18:03,660 --> 00:18:06,340
We think that this animal could move
its eyes

214
00:18:06,340 --> 00:18:08,660
independently of one another,

215
00:18:08,660 --> 00:18:11,220
looking in different directions at the
same time.

216
00:18:11,220 --> 00:18:14,820
This was a massive increase in visual
complexity.

217
00:18:15,820 --> 00:18:18,180
But how did the animal deal with it?

218
00:18:18,180 --> 00:18:20,340
Well, look at this part here.

219
00:18:20,340 --> 00:18:25,220
This represents an organ which is
very, very, very rarely fossilised.

220
00:18:25,220 --> 00:18:27,380
This is the animal's brain.

221
00:18:30,820 --> 00:18:35,060
It's thought that the first animals
had simple nervous systems,

222
00:18:35,060 --> 00:18:38,420
but it's only when complex eyes come
on the scene

223
00:18:38,420 --> 00:18:41,340
that fossilised brains are found.

224
00:18:42,580 --> 00:18:45,340
We think these are the optic nerves,

225
00:18:45,340 --> 00:18:49,140
passing all of that visual information
to the brain

226
00:18:49,140 --> 00:18:50,860
to be analysed.

227
00:18:50,860 --> 00:18:54,820
Now, brains have got their own
evolutionary history,

228
00:18:54,820 --> 00:18:56,740
they didn't just appear overnight,

229
00:18:56,740 --> 00:18:59,140
but in the wake of the Cambrian
Explosion,

230
00:18:59,140 --> 00:19:01,580
they got bigger and they got more
complex,

231
00:19:01,580 --> 00:19:05,500
potentially to deal with all of that
visual information.

232
00:19:05,500 --> 00:19:07,980
It's a beautiful fossil.

233
00:19:07,980 --> 00:19:11,580
Without the evolution of
light-sensitive cells,

234
00:19:11,580 --> 00:19:15,340
we wouldn't have eyes, and without the
evolution of eyes,

235
00:19:15,340 --> 00:19:18,060
we wouldn't have brains as we know
them today.

236
00:19:26,540 --> 00:19:30,740
The modern animal kingdom is full of
eyes and brains

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00:19:30,740 --> 00:19:35,580
attuned to perceive the world in
whatever way is most useful.

238
00:19:41,620 --> 00:19:46,820
Compound eyes give a wide field of
view to smaller brains.

239
00:19:48,660 --> 00:19:53,860
Giant eyes that see like a camera
gather information in the depths.

240
00:19:55,820 --> 00:20:01,580
And forward-facing eyes help large
brains navigate a 3D world.

241
00:20:07,660 --> 00:20:10,340
But 500 million years ago,

242
00:20:10,340 --> 00:20:13,660
animals and their newly-evolved brains

243
00:20:13,660 --> 00:20:16,820
are just waking up to the world around
them.

244
00:20:27,060 --> 00:20:29,220
As we leap forward again...

245
00:20:30,220 --> 00:20:34,860
..the struggle for survival drives
brains to become more complex...

246
00:20:36,940 --> 00:20:39,900
..and more strategic.

247
00:20:48,900 --> 00:20:52,340
Welcome to the Silurian period...

248
00:20:55,340 --> 00:20:59,340
..where the hunted have become the
hunters.

249
00:21:03,340 --> 00:21:08,340
This fierce-looking animal is an early
female placoderm...

250
00:21:15,820 --> 00:21:19,060
..and you don't want to mess with her.

251
00:21:22,060 --> 00:21:25,340
You see, the predator-prey arms
race...

252
00:21:27,340 --> 00:21:31,340
..has turned her into one formidable
fish.

253
00:21:39,820 --> 00:21:43,580
Placoderms dominated the Earth's
aquatic ecosystems

254
00:21:43,580 --> 00:21:46,380
for 60 million years,

255
00:21:46,380 --> 00:21:50,060
and I've got a fossil of one here, and
what a fossil this is.

256
00:21:50,060 --> 00:21:51,660
Just look at that!

257
00:21:51,660 --> 00:21:53,580
It's very, very beautiful.

258
00:21:53,580 --> 00:21:56,340
It came from Scotland and it lived 380
million years ago,

259
00:21:56,340 --> 00:21:58,820
but look at the degree of preservation
here.

260
00:21:58,820 --> 00:22:02,740
You can see all the bones in its
vertebrae, the dorsal fin here,

261
00:22:02,740 --> 00:22:05,380
this is the head end, of course,
here's its eye.

262
00:22:05,380 --> 00:22:07,140
Look at that.

263
00:22:08,140 --> 00:22:09,660
Oh, wow.

264
00:22:09,660 --> 00:22:12,580
And I've never got over the fact that
I can put my finger

265
00:22:12,580 --> 00:22:18,660
on something which lived 380 million
years ago.

266
00:22:19,660 --> 00:22:22,740
But getting back to placoderms, you're
going to say, you know,

267
00:22:22,740 --> 00:22:25,580
"Why is this fossil so important?
There are loads of animals

268
00:22:25,580 --> 00:22:28,260
"that lived and died out. Why is this
one such a big deal?"

269
00:22:28,260 --> 00:22:31,060
Well, these were some of the first
animals

270
00:22:31,060 --> 00:22:33,980
that had a jaw and a backbone,

271
00:22:33,980 --> 00:22:39,340
so if we want to learn more about what
we call the jawed vertebrates,

272
00:22:39,340 --> 00:22:43,140
and that's me, you, your children,
your gran,

273
00:22:43,140 --> 00:22:45,340
your pets, dolphins,

274
00:22:45,340 --> 00:22:48,820
then we've got to learn more about
placoderms.

275
00:22:52,340 --> 00:22:55,340
Placoderm fossils of all shapes and
sizes

276
00:22:55,340 --> 00:22:58,900
have been found on every continent on
the Earth.

277
00:23:00,060 --> 00:23:03,340
Yet all share one intriguing feature.

278
00:23:05,580 --> 00:23:08,820
Bony plates covering their heads.

279
00:23:11,340 --> 00:23:14,820
Armour to protect the most precious
weapon

280
00:23:14,820 --> 00:23:17,740
a predatory fish has in its arsenal.

281
00:23:18,740 --> 00:23:20,420
Its brain.

282
00:23:22,060 --> 00:23:25,580
The predator-prey arms race had turned
these creatures

283
00:23:25,580 --> 00:23:27,660
into veritable little warships,

284
00:23:27,660 --> 00:23:30,180
and I say "little" because this is a
small one.

285
00:23:30,180 --> 00:23:33,580
Some of them grew up to four metres in
length.

286
00:23:34,660 --> 00:23:36,580
But, sadly, as we know,

287
00:23:36,580 --> 00:23:40,300
no amount of armour can protect us
from some things.

288
00:23:46,340 --> 00:23:48,820
In these ancient waters,

289
00:23:48,820 --> 00:23:51,340
a hidden threat is lurking.

290
00:24:01,340 --> 00:24:04,660
Despite its armour, this early
placoderm

291
00:24:04,660 --> 00:24:08,060
has fallen victim to a tiny invader.

292
00:24:09,820 --> 00:24:11,660
A virus.

293
00:24:11,660 --> 00:24:15,340
One whose impacts would ripple through
time.

294
00:24:26,340 --> 00:24:30,220
Viruses have always been pulling the
strings of life.

295
00:24:30,220 --> 00:24:34,420
They're master manipulators, silently
and ruthlessly

296
00:24:34,420 --> 00:24:37,580
invading their hosts to take advantage
of them,

297
00:24:37,580 --> 00:24:39,340
and we know how they work.

298
00:24:39,340 --> 00:24:43,340
They break into their host's cells,
hijack those cells' machinery,

299
00:24:43,340 --> 00:24:45,340
and then replicate themselves...

300
00:24:46,340 --> 00:24:49,580
..over and over and over again,

301
00:24:49,580 --> 00:24:54,340
until they burst out in a dangerous
explosion of infection,

302
00:24:54,340 --> 00:24:57,980
giving us things like Covid, flu,
common cold.

303
00:25:00,340 --> 00:25:03,740
But not all viruses act in this way.

304
00:25:04,740 --> 00:25:07,580
Some break into the cell

305
00:25:07,580 --> 00:25:13,060
and then insert their own genetic
material into the host's DNA,

306
00:25:13,060 --> 00:25:16,140
potentially changing it forever.

307
00:25:18,580 --> 00:25:22,020
These are called retroviruses...

308
00:25:23,020 --> 00:25:26,740
..and we think that over 400 million
years ago,

309
00:25:26,740 --> 00:25:31,220
a retrovirus was circulating in the
oceans,

310
00:25:31,220 --> 00:25:36,220
infecting the bodies of many species
of ancient fish.

311
00:25:39,580 --> 00:25:44,220
One of whom may have been this early
placoderm.

312
00:25:45,820 --> 00:25:50,340
Luckily for her, however, her immune
system kicks into gear...

313
00:25:51,340 --> 00:25:53,140
..and she recovers.

314
00:25:54,820 --> 00:25:58,580
But, like a Trojan horse, some of the
virus

315
00:25:58,580 --> 00:26:01,980
makes its way into her egg cells

316
00:26:01,980 --> 00:26:04,820
and is passed on to her offspring.

317
00:26:12,820 --> 00:26:19,060
Over generations, the hidden viral DNA
does something extraordinary.

318
00:26:21,580 --> 00:26:27,060
It triggers one of the fish's genes to
go into overdrive...

319
00:26:28,060 --> 00:26:31,580
..altering the way its nerve cells
develop...

320
00:26:34,020 --> 00:26:38,340
..causing parts of the brain to turn
from grey

321
00:26:38,340 --> 00:26:40,580
to eerily pale.

322
00:26:42,340 --> 00:26:48,060
But instead of causing harm, the brain
is changed forever.

323
00:26:52,340 --> 00:26:55,660
These infections likely happened
multiple times

324
00:26:55,660 --> 00:26:57,580
in multiple species...

325
00:26:59,060 --> 00:27:03,420
..and scientists think their effect
has been profound.

326
00:27:06,340 --> 00:27:08,340
Oh, my God!

327
00:27:08,340 --> 00:27:11,220
It's a Jesus Christ lizard.

328
00:27:15,980 --> 00:27:18,820
I used to look at drawings and read
about these things

329
00:27:18,820 --> 00:27:21,580
in my childhood animal encyclopaedias.

330
00:27:22,580 --> 00:27:24,820
And it's named after the son of God

331
00:27:24,820 --> 00:27:27,820
not because it so much walks on water

332
00:27:27,820 --> 00:27:30,900
as runs very fast across the surface.

333
00:27:30,900 --> 00:27:34,660
It's also got lightning-fast
reactions.

334
00:27:34,660 --> 00:27:39,060
So how does it manifest all of this
speed, as it were?

335
00:27:39,060 --> 00:27:42,540
Well, it comes down to its nerve
cells.

336
00:27:42,540 --> 00:27:47,340
You see, each of its nerve cells have
long fibres called axons.

337
00:27:47,340 --> 00:27:50,340
Those axons are wrapped in a fatty
sheath

338
00:27:50,340 --> 00:27:54,820
of a substance called myelin and it
insulates them.

339
00:27:54,820 --> 00:27:58,060
And what that means is that each nerve
cell

340
00:27:58,060 --> 00:28:02,660
can communicate with the other far
more quickly,

341
00:28:02,660 --> 00:28:04,820
and that happens in its brain

342
00:28:04,820 --> 00:28:07,660
and it happens from the nerves that
run from its brain

343
00:28:07,660 --> 00:28:09,580
to the muscles around its body.

344
00:28:09,580 --> 00:28:12,420
It's as if it's got a super-fast
processor.

345
00:28:14,340 --> 00:28:20,140
Nerve signals can travel up to 200
times faster

346
00:28:20,140 --> 00:28:24,060
in axons insulated with myelin than
those without.

347
00:28:25,580 --> 00:28:29,820
And therefore we can make the argument
that the origin of myelin

348
00:28:29,820 --> 00:28:33,340
was the singularly most important
development

349
00:28:33,340 --> 00:28:37,220
when it came to the evolution of the
vertebrate brain.

350
00:28:39,660 --> 00:28:43,820
Now all we need this little lizard to
do is something biblical.

351
00:29:02,060 --> 00:29:06,340
Today, myelin is found throughout the
jawed vertebrates.

352
00:29:08,340 --> 00:29:12,180
All of these animals have myelin to
thank

353
00:29:12,180 --> 00:29:15,340
for the fast signals inside their
brains.

354
00:29:20,340 --> 00:29:24,820
And scientists have found that nerves
insulated with myelin

355
00:29:24,820 --> 00:29:30,580
can't be produced without ancient
retroviral DNA...

356
00:29:31,780 --> 00:29:34,820
..which has been transmitted down the
generations

357
00:29:34,820 --> 00:29:38,060
from fishes that caught a virus

358
00:29:38,060 --> 00:29:41,460
over 400 million years ago.

359
00:29:42,580 --> 00:29:45,820
Evolution. You just can't beat it, can
you?

360
00:29:45,820 --> 00:29:48,220
Well, you can, because it gets better.

361
00:29:48,220 --> 00:29:51,340
You see, myelin didn't just speed
things up,

362
00:29:51,340 --> 00:29:55,580
it allowed brains to develop more
computing power.

363
00:29:55,580 --> 00:29:59,820
It allowed brains to evolve to become
more compact,

364
00:29:59,820 --> 00:30:03,820
more complex, more powerful.

365
00:30:03,820 --> 00:30:07,980
It was as if life had just got a
hardware upgrade

366
00:30:07,980 --> 00:30:12,580
and this was therefore a significant
step up

367
00:30:12,580 --> 00:30:15,340
in the evolution of intelligence

368
00:30:15,340 --> 00:30:18,820
because, for the first time, the
vertebrate brain

369
00:30:18,820 --> 00:30:23,060
was on the cusp of doing something it
had never been able to do before.

370
00:30:24,060 --> 00:30:25,540
Thinking.

371
00:30:35,060 --> 00:30:38,380
Across tens of millions of years...

372
00:30:39,820 --> 00:30:43,340
..fast-thinking vertebrates dominate
the oceans.

373
00:30:45,580 --> 00:30:49,340
But for the next chapter in the story
of the dolphin

374
00:30:49,340 --> 00:30:51,420
and its amazing brain...

375
00:30:53,340 --> 00:30:56,820
..we need to step out onto land.

376
00:31:05,340 --> 00:31:10,580
This strange, hairless, burrowing
animal is a cynodont.

377
00:31:12,340 --> 00:31:16,060
An ancestor of mammals, including the
dolphin.

378
00:31:17,820 --> 00:31:20,580
Now, it lives underground for good
reason.

379
00:31:20,580 --> 00:31:23,660
Predatory reptiles roam outside.

380
00:31:28,340 --> 00:31:32,060
But, at some point, it's got to
venture out to eat.

381
00:31:36,060 --> 00:31:40,060
As the day comes to an end, there's an
opportunity.

382
00:31:42,580 --> 00:31:45,580
But there's just one problem.

383
00:31:46,580 --> 00:31:48,580
It's getting dark.

384
00:31:50,060 --> 00:31:53,340
Soon, its vision won't be much use.

385
00:32:00,340 --> 00:32:03,340
Imagine what it was like for those
little cynodonts.

386
00:32:04,340 --> 00:32:08,660
Now, I've got a cast of one of these
animals' skulls here.

387
00:32:08,660 --> 00:32:11,340
You can see that "little" is the
appropriate word.

388
00:32:11,340 --> 00:32:13,980
This skull is about the same size as a
rabbit.

389
00:32:13,980 --> 00:32:17,820
So, they were small, opportunistic
hunters.

390
00:32:17,820 --> 00:32:20,340
The problem was that when they
ventured out,

391
00:32:20,340 --> 00:32:22,140
particularly in broad daylight,

392
00:32:22,140 --> 00:32:25,060
there was a very good chance they'd be
hunted themselves.

393
00:32:25,060 --> 00:32:28,340
There were loads of predators stalking
around the Triassic.

394
00:32:28,340 --> 00:32:31,300
But when these little creatures
ventured out of their burrows

395
00:32:31,300 --> 00:32:34,300
into the night, there were distinct
advantages for them.

396
00:32:39,940 --> 00:32:42,820
At night there are fewer predators...

397
00:32:43,820 --> 00:32:46,340
..and reduced competition for food.

398
00:32:50,900 --> 00:32:55,820
But, of course, in the dark, food can
be harder to find.

399
00:33:00,820 --> 00:33:03,580
What they would have experienced is
pretty much

400
00:33:03,580 --> 00:33:05,820
what I'm experiencing now.

401
00:33:06,820 --> 00:33:09,580
Human eyesight isn't brilliant in the
dark

402
00:33:09,580 --> 00:33:11,380
but it's not that bad either.

403
00:33:11,380 --> 00:33:14,980
So, if I close my eyes, now I'm
effectively blind, what happens?

404
00:33:14,980 --> 00:33:17,140
Well, I immediately start to
concentrate

405
00:33:17,140 --> 00:33:19,820
on my other senses, of course.
Firstly, hearing.

406
00:33:19,820 --> 00:33:22,580
A bit of bird song...
BIRDS CHIRP

407
00:33:22,580 --> 00:33:25,340
..whine of insects.
INSECTS BUZZ

408
00:33:25,340 --> 00:33:26,820
Crickets.

409
00:33:26,820 --> 00:33:29,220
RUSTLING A bit of rustling over there.

410
00:33:29,220 --> 00:33:31,580
Incoming mosquito.
BUZZING

411
00:33:31,580 --> 00:33:33,980
HE SNIFFS LOUDLY
What about smell?

412
00:33:33,980 --> 00:33:36,140
Oh, yeah, that smells good.

413
00:33:36,140 --> 00:33:40,340
I can smell all of that decomposing
leaf litter.

414
00:33:40,340 --> 00:33:43,660
That's what I call "forest fruitcake".

415
00:33:43,660 --> 00:33:47,820
A really rich, delicious mix of
odours.

416
00:33:48,820 --> 00:33:51,220
And, I mean, I'm not bragging, but I
like to think

417
00:33:51,220 --> 00:33:53,980
that my sense of smell is quite well
attuned in nature.

418
00:33:53,980 --> 00:33:56,140
I've been sniffing it all of my life.

419
00:33:56,140 --> 00:33:58,820
So, out here in the dark, I would be
fairly confident

420
00:33:58,820 --> 00:34:01,820
using my sense of smell to help me
navigate.

421
00:34:01,820 --> 00:34:04,580
Perhaps you wouldn't be quite so
confident,

422
00:34:04,580 --> 00:34:08,060
and that would have been exactly the
same for those cynodonts.

423
00:34:08,060 --> 00:34:10,820
Part of their population would have
had senses

424
00:34:10,820 --> 00:34:14,340
which were more finely attuned, and
those would have been

425
00:34:14,340 --> 00:34:17,820
the individuals that went out to
forage, found food,

426
00:34:17,820 --> 00:34:21,420
and then made it safely back to their
burrows.

427
00:34:27,820 --> 00:34:32,820
Super-sensing cynodonts would have
fared better navigating at night.

428
00:34:35,340 --> 00:34:39,620
And it's thought this allowed some
groups to become nocturnal.

429
00:34:41,820 --> 00:34:46,340
And as these cynodonts' senses
sharpened to the night...

430
00:34:47,540 --> 00:34:51,820
..we think the flood of new
information being gathered

431
00:34:51,820 --> 00:34:55,580
kick-started a monumental
transformation

432
00:34:55,580 --> 00:34:57,820
in their descendants' brains.

433
00:35:02,340 --> 00:35:07,220
Over tens of millions of years, the
brain changes shape.

434
00:35:07,220 --> 00:35:10,980
Areas involved in smell and touch
expand...

435
00:35:13,620 --> 00:35:18,580
..and the brain increases in size by
over 40%.

436
00:35:21,020 --> 00:35:25,660
To process the new information, we see
a game-changing region

437
00:35:25,660 --> 00:35:28,340
develop in the top layers of the
brain.

438
00:35:33,340 --> 00:35:36,580
And with it, a new type of animal.

439
00:35:39,580 --> 00:35:43,580
In under 50 million years, those
burrowing cynodonts

440
00:35:43,580 --> 00:35:46,820
had evolved into something a little
bit like this.

441
00:35:46,820 --> 00:35:49,580
The first mammals.

442
00:35:53,580 --> 00:35:58,580
Now, I know that many of you probably
aren't that keen on rats.

443
00:35:58,580 --> 00:36:00,140
I love them.

444
00:36:00,140 --> 00:36:02,740
I love their little whiskers, whisking
away,

445
00:36:02,740 --> 00:36:06,060
and those stiffened hairs are rooted
in skin

446
00:36:06,060 --> 00:36:08,060
which is packed full of nerves,

447
00:36:08,060 --> 00:36:11,660
sending masses of information to its
brain.

448
00:36:11,660 --> 00:36:14,340
And then you've got its twitching
nose.

449
00:36:14,340 --> 00:36:16,660
A nose far more sensitive than ours,

450
00:36:16,660 --> 00:36:20,980
capable of smelling things like
explosives, even human cancers.

451
00:36:20,980 --> 00:36:25,740
And its ears... Now, come on, those
are the prettiest little ears.

452
00:36:25,740 --> 00:36:30,900
Radar dishes listening out for the
rustle of any potential predator.

453
00:36:30,900 --> 00:36:34,340
But, of course, all of this extra
sensory information

454
00:36:34,340 --> 00:36:36,060
needs to be processed,

455
00:36:36,060 --> 00:36:39,140
so it was at about this time that an
area of the brain

456
00:36:39,140 --> 00:36:43,660
called the neocortex began to develop
more fully.

457
00:36:43,660 --> 00:36:49,060
And that was utterly, utterly
transformational

458
00:36:49,060 --> 00:36:53,580
because it allowed these animals to
solve problems,

459
00:36:53,580 --> 00:36:56,580
to learn, to develop memories,

460
00:36:56,580 --> 00:36:59,580
and, with all of that extra sensory
processing,

461
00:36:59,580 --> 00:37:04,820
to map their environment and plan
their next move.

462
00:37:05,820 --> 00:37:11,100
The neocortex was an extraordinary
mammalian innovation.

463
00:37:14,820 --> 00:37:19,820
And that neocortex is the outer layer
of the mammalian brain.

464
00:37:21,060 --> 00:37:25,740
Sometimes smooth, sometimes wrinkly
and folded.

465
00:37:25,740 --> 00:37:30,580
It receives and processes complex
sensory information...

466
00:37:32,340 --> 00:37:35,820
..and it links it to other regions the
brain.

467
00:37:39,340 --> 00:37:44,220
In today's mammals, it's essential for
learning...

468
00:37:45,700 --> 00:37:47,460
..planning...

469
00:37:49,140 --> 00:37:51,060
..prediction...

470
00:37:52,940 --> 00:37:54,500
..decision-making.

471
00:37:56,820 --> 00:38:01,340
The foundations of what we'd call
intelligence.

472
00:38:04,340 --> 00:38:08,340
Now, of course, mammals aren't the
only intelligent animals.

473
00:38:11,340 --> 00:38:14,580
Birds have a structure called the
"wulst"

474
00:38:14,580 --> 00:38:17,780
that performs a similar function to
the neocortex.

475
00:38:21,820 --> 00:38:25,580
And octopuses have one centralised
brain

476
00:38:25,580 --> 00:38:27,780
and eight mini brains.

477
00:38:28,780 --> 00:38:30,660
One for each arm.

478
00:38:35,340 --> 00:38:39,140
But 200 million years ago, for the
mammals,

479
00:38:39,140 --> 00:38:43,740
the neocortex helped unlock a more
intelligent way of life.

480
00:38:46,660 --> 00:38:51,780
And to continue their story, we need
to take another leap through time...

481
00:38:59,140 --> 00:39:00,820
..until...

482
00:39:02,740 --> 00:39:06,460
..it's the mammals' turn to take
centre stage.

483
00:39:13,580 --> 00:39:16,980
By now, those mammals have radiated
out

484
00:39:16,980 --> 00:39:19,340
and diversified across the globe.

485
00:39:28,340 --> 00:39:32,140
And it's here that we find one unique
group

486
00:39:32,140 --> 00:39:35,220
on the verge of an extraordinary
transformation.

487
00:39:40,580 --> 00:39:43,340
This is Indohyus.

488
00:39:44,740 --> 00:39:49,820
The size of a cat, with deer-like legs
and the snout of a dog.

489
00:39:49,820 --> 00:39:53,340
Quite frankly, it's a bit of a weirdo.

490
00:39:57,340 --> 00:40:01,340
Tiptoeing on little hooves, it's on
the lookout for lunch.

491
00:40:06,820 --> 00:40:08,820
LOUD SQUAWK

492
00:40:08,820 --> 00:40:11,060
But it's not the only one.

493
00:40:19,260 --> 00:40:23,340
This diminutive plant-eater is easy
pickings for predators

494
00:40:23,340 --> 00:40:25,060
circling above.

495
00:40:26,580 --> 00:40:29,980
But Indohyus has an escape plan.

496
00:40:39,380 --> 00:40:45,260
A strategy adopted by another of
evolution's oddballs.

497
00:40:54,660 --> 00:40:59,220
Indohyus was a lot smaller and more
dainty, but I give you...

498
00:41:00,340 --> 00:41:01,980
..the tapir.

499
00:41:06,500 --> 00:41:08,820
Oh, yes!
CHRIS CHUCKLES

500
00:41:08,820 --> 00:41:10,820
What an animal!

501
00:41:10,820 --> 00:41:14,340
I absolutely love tapirs.

502
00:41:15,580 --> 00:41:18,860
I've liked them since I was a kid. I
don't know what it is about them.

503
00:41:18,860 --> 00:41:21,060
I think it's because they're weird.

504
00:41:21,060 --> 00:41:24,580
But what else have they got in common
with Indohyus?

505
00:41:24,580 --> 00:41:28,820
Well, they're both herbivores, and, as
a consequence,

506
00:41:28,820 --> 00:41:32,820
they need to be thinking about
avoiding carnivores.

507
00:41:34,060 --> 00:41:38,260
This Baird's tapir can be predated by
jaguars.

508
00:41:38,260 --> 00:41:40,060
So how do they avoid that?

509
00:41:40,060 --> 00:41:44,060
Well, one of the things they've done
is developed an aquatic lifestyle.

510
00:41:45,340 --> 00:41:47,980
Now, if you don't want to be buoyant
if you're in the water,

511
00:41:47,980 --> 00:41:50,340
and, on that account, when they go
into the water,

512
00:41:50,340 --> 00:41:51,940
they sink to the bottom.

513
00:41:51,940 --> 00:41:55,820
They can walk across the bottom of
rivers, lakes and lagoons,

514
00:41:55,820 --> 00:41:59,340
and that is the same as Indohyus.

515
00:41:59,340 --> 00:42:01,820
Indohyus had heavy bones.

516
00:42:08,620 --> 00:42:12,620
In fact, trying to evade predators on
a day-to-day basis

517
00:42:12,620 --> 00:42:15,100
was at the core of driving

518
00:42:15,100 --> 00:42:19,820
one of the most revolutionary
transformations in evolution.

519
00:42:35,340 --> 00:42:38,340
For Indohyus and its heavy bones...

520
00:42:40,340 --> 00:42:42,820
..water is a refuge.

521
00:42:55,340 --> 00:42:57,340
And stepping away from land...

522
00:42:58,340 --> 00:43:00,740
..turned out to be a masterstroke.

523
00:43:06,340 --> 00:43:09,980
This new world offers up plentiful
food

524
00:43:09,980 --> 00:43:12,060
and new opportunities.

525
00:43:15,060 --> 00:43:19,820
Over generations, their relatives
become much more streamlined.

526
00:43:20,980 --> 00:43:24,980
Limbs are replaced with paddle-like
flippers.

527
00:43:27,220 --> 00:43:31,060
Nostrils migrate further away from
their long snouts.

528
00:43:33,740 --> 00:43:37,580
Tails get flatter and more powerful.

529
00:43:39,060 --> 00:43:41,980
And the once-hoofed mammals

530
00:43:41,980 --> 00:43:45,060
are now completely aquatic.

531
00:43:59,820 --> 00:44:03,340
This was one of the most astonishing
body transformations

532
00:44:03,340 --> 00:44:05,820
in the course of evolutionary history.

533
00:44:07,940 --> 00:44:10,340
In just over 10 million years,

534
00:44:10,340 --> 00:44:14,020
these tiny, terrestrial, tiptoeing
animals

535
00:44:14,020 --> 00:44:18,340
had transformed into sleek,
streamlined swimmers.

536
00:44:20,020 --> 00:44:23,580
And I've got the cast of a skull of
one of them here.

537
00:44:23,580 --> 00:44:26,060
This is Dorudon

538
00:44:26,060 --> 00:44:29,460
and it lived 40 million years ago,

539
00:44:29,460 --> 00:44:31,660
and the teeth do all of the talking.

540
00:44:31,660 --> 00:44:33,020
Look here.

541
00:44:33,020 --> 00:44:36,340
These massive canines for catching and
gripping the prey

542
00:44:36,340 --> 00:44:38,140
and then these teeth here

543
00:44:38,140 --> 00:44:40,340
for shearing it into tiny pieces.

544
00:44:40,340 --> 00:44:43,660
This would have been an impressive
animal, but not the biggest.

545
00:44:43,660 --> 00:44:46,060
One of its relatives, Basilosaurus,

546
00:44:46,060 --> 00:44:48,420
grew to the length of a bus.

547
00:44:48,420 --> 00:44:52,060
Those puny, cat-like animals

548
00:44:52,060 --> 00:44:55,820
had transformed into monsters.

549
00:44:57,340 --> 00:44:58,660
Superb.

550
00:44:58,660 --> 00:45:00,140
But, of course,

551
00:45:00,140 --> 00:45:02,020
things didn't stop there.

552
00:45:02,020 --> 00:45:05,060
This is a cast of the skull of
Simocetus,

553
00:45:05,060 --> 00:45:07,340
a distant relative of Dorudon,

554
00:45:07,340 --> 00:45:10,340
and it lived 32 million years ago.

555
00:45:10,340 --> 00:45:11,980
But look at the skull -

556
00:45:11,980 --> 00:45:13,780
pretty radically different.

557
00:45:13,780 --> 00:45:17,380
It's much shorter, it's far more
structurally complex on top here.

558
00:45:19,580 --> 00:45:23,580
Simocetus was part of a new group of
marine mammals -

559
00:45:23,580 --> 00:45:26,860
the odontocetes, or "toothed whales".

560
00:45:28,380 --> 00:45:30,220
Look at this depression here.

561
00:45:30,220 --> 00:45:33,820
We think an organ called the melon
might have sat here.

562
00:45:33,820 --> 00:45:38,340
It's a fatty sphere. Sounds produced
from the nasal passages are focused

563
00:45:38,340 --> 00:45:43,220
through it like a lens and projected
out into the animal's environment.

564
00:45:43,220 --> 00:45:46,820
When they bounce back, they're
captured by the lower jaw,

565
00:45:46,820 --> 00:45:49,980
part of which is hollow, transferred
to the inner ear,

566
00:45:49,980 --> 00:45:52,340
which sends the information to the
brain.

567
00:45:53,340 --> 00:45:55,580
You know what I'm saying here, don't
you?

568
00:45:55,580 --> 00:45:58,340
Echolocation had evolved.

569
00:45:58,340 --> 00:46:00,220
Echolocation!

570
00:46:00,220 --> 00:46:01,980
What about that?

571
00:46:01,980 --> 00:46:04,580
But we think something else radical

572
00:46:04,580 --> 00:46:07,140
might have been happening at the same
time.

573
00:46:07,140 --> 00:46:10,060
We think that animals like this might
have been

574
00:46:10,060 --> 00:46:14,100
at the start of a journey from being
solitary hunters

575
00:46:14,100 --> 00:46:16,580
to hunting together,

576
00:46:16,580 --> 00:46:21,060
and this social behaviour would have a
profound effect

577
00:46:21,060 --> 00:46:23,180
on the development of the brain.

578
00:46:28,740 --> 00:46:31,300
As the toothed whales continued to
evolve...

579
00:46:32,300 --> 00:46:36,580
..it's thought that many of them
became more and more social.

580
00:46:38,340 --> 00:46:43,100
And the fossil record shows evidence
of their brains getting larger...

581
00:46:45,340 --> 00:46:49,220
..until, around 11 million years
ago...

582
00:46:50,580 --> 00:46:53,340
..an iconic family emerged.

583
00:46:58,820 --> 00:47:00,340
Dolphins.

584
00:47:05,340 --> 00:47:10,340
Today, over 40 species of dolphin can
be found worldwide...

585
00:47:12,820 --> 00:47:14,580
..from the tiny...

586
00:47:16,740 --> 00:47:18,660
..to the giant.

587
00:47:22,340 --> 00:47:24,180
They live in groups...

588
00:47:25,820 --> 00:47:28,660
..and have complex social
relationships.

589
00:47:33,060 --> 00:47:36,340
And some species are amongst

590
00:47:36,340 --> 00:47:39,820
the most intelligent animals on Earth.

591
00:48:05,340 --> 00:48:08,180
This group of spotted dolphins

592
00:48:08,180 --> 00:48:11,060
have spent their whole lives in the
Bahamas.

593
00:48:11,060 --> 00:48:13,340
DOLPHINS CLICK AND WHISTLE

594
00:48:15,780 --> 00:48:19,340
And their social lives govern their
behaviour.

595
00:48:25,340 --> 00:48:27,580
Mothers, cousins,

596
00:48:27,580 --> 00:48:30,580
friends, even rivals,

597
00:48:30,580 --> 00:48:35,340
all roaming together in the waters
they call home.

598
00:48:49,580 --> 00:48:52,340
I've just been to spotted dolphin
heaven!

599
00:48:52,340 --> 00:48:54,220
I cannot tell you.

600
00:48:54,220 --> 00:48:57,140
That was absolutely incredible.

601
00:48:57,140 --> 00:49:01,580
At one point, I was just wrapped in a
vortex of spinning dolphins.

602
00:49:01,580 --> 00:49:03,260
Oh, my goodness me.

603
00:49:03,260 --> 00:49:05,340
CLICKS AND WHISTLES

604
00:49:13,740 --> 00:49:16,500
And, of course, we know that they all
know one another,

605
00:49:16,500 --> 00:49:19,140
not just now but throughout the course
of their lives.

606
00:49:19,140 --> 00:49:21,340
They've got that phenomenal memory.

607
00:49:27,340 --> 00:49:32,140
And to think they are down there
experiencing emotions

608
00:49:32,140 --> 00:49:34,220
like joy.

609
00:49:34,220 --> 00:49:37,340
I think they were feeling joy. I was
certainly feeling joy.

610
00:49:37,340 --> 00:49:42,340
But then we know that they can even
experience grief as well.

611
00:49:46,300 --> 00:49:48,340
DOLPHIN CLICKS

612
00:49:49,820 --> 00:49:51,660
And the clicking!

613
00:49:52,820 --> 00:49:56,460
The constant ticking.
"Tick-tick-tick-tick", all the time.

614
00:49:56,460 --> 00:49:58,980
They're communicating to one another.

615
00:50:01,340 --> 00:50:03,660
Now, there's a dispute amongst
scientists

616
00:50:03,660 --> 00:50:06,980
as to whether they have a language,

617
00:50:06,980 --> 00:50:09,340
but, from my point of view at the
moment,

618
00:50:09,340 --> 00:50:12,340
I'm quite happy to fantasise, because
I would love,

619
00:50:12,340 --> 00:50:17,220
absolutely love, to know what they
were all saying to one another!

620
00:50:17,220 --> 00:50:18,820
Honestly...

621
00:50:18,820 --> 00:50:21,340
Honestly, so, so good.

622
00:50:26,300 --> 00:50:32,340
This is the soundtrack of a thriving
underwater society...

623
00:50:39,340 --> 00:50:43,580
..underpinned by one of the most
complex brains on Earth.

624
00:50:46,140 --> 00:50:49,820
Relative to their bodies, it's one of
the biggest of any animal,

625
00:50:49,820 --> 00:50:53,740
with key regions thought to be
involved in self-awareness,

626
00:50:53,740 --> 00:50:58,060
communication and understanding
emotions.

627
00:50:58,060 --> 00:51:01,580
And that uniquely mammalian neocortex

628
00:51:01,580 --> 00:51:05,500
has become one of the most intricately
folded brain surfaces

629
00:51:05,500 --> 00:51:07,340
on the planet.

630
00:51:12,340 --> 00:51:15,660
Brains are amongst the most
energy-expensive organs

631
00:51:15,660 --> 00:51:19,900
to run in the body, but, boy, are they
worth that cost,

632
00:51:19,900 --> 00:51:23,660
because if you've got a large, complex
brain, like those dolphins,

633
00:51:23,660 --> 00:51:27,940
it gives you the capacity to develop
intelligence.

634
00:51:28,940 --> 00:51:31,340
And the dolphins use that intelligence

635
00:51:31,340 --> 00:51:34,420
to change their behaviour on a
day-to-day basis.

636
00:51:34,420 --> 00:51:36,580
They can learn things.

637
00:51:36,580 --> 00:51:40,580
They can then copy things from
dolphins that have learned things.

638
00:51:40,580 --> 00:51:43,340
They've got cultural learning
capabilities.

639
00:51:43,340 --> 00:51:49,580
And this social intelligence is the
most important tool in the box

640
00:51:49,580 --> 00:51:52,060
when it comes to survival.

641
00:51:52,060 --> 00:51:53,980
But get this,

642
00:51:53,980 --> 00:51:56,340
they evolved that intelligence

643
00:51:56,340 --> 00:52:00,340
in a world which is completely alien
to ours.

644
00:52:00,340 --> 00:52:02,220
They evolved it...

645
00:52:02,220 --> 00:52:04,020
..underwater!

646
00:52:06,580 --> 00:52:12,140
We may never truly know what goes on
inside the mind of a dolphin,

647
00:52:12,140 --> 00:52:16,060
but its brain tells a remarkable
story.

648
00:52:17,580 --> 00:52:21,580
Three billion years of sensing...

649
00:52:24,340 --> 00:52:26,060
..of struggle...

650
00:52:29,660 --> 00:52:31,700
..and survival.

651
00:52:34,540 --> 00:52:36,340
Of brains...

652
00:52:37,420 --> 00:52:39,340
..and bodies...

653
00:52:39,340 --> 00:52:41,140
..transformed.

654
00:52:52,340 --> 00:52:55,340
Dolphins' minds, like ours for that
matter,

655
00:52:55,340 --> 00:52:58,220
are remarkable pieces of biology.

656
00:52:58,220 --> 00:53:00,980
It's for very good reason that we
think of our brains

657
00:53:00,980 --> 00:53:05,340
as being the most complex objects in
the known Universe

658
00:53:05,340 --> 00:53:09,900
and they're still surrounded by an
aura of mystery, of magic.

659
00:53:09,900 --> 00:53:13,220
But here's one thing that we know for
certain.

660
00:53:13,220 --> 00:53:16,060
Our brains, our minds,

661
00:53:16,060 --> 00:53:21,060
simply wouldn't exist without the
power of evolution.

662
00:53:21,060 --> 00:53:24,340
That blind journey of change,

663
00:53:24,340 --> 00:53:28,060
of innovation, of exquisite beauty.

664
00:53:33,580 --> 00:53:35,060
Next time...

665
00:53:36,340 --> 00:53:40,380
..how the horse became one of nature's
greatest athletes.

666
00:53:40,380 --> 00:53:42,220
Just look at her.

667
00:53:42,220 --> 00:53:45,140
She's absolutely gorgeous.

668
00:53:45,140 --> 00:53:47,180
Aren't you?

669
00:53:47,180 --> 00:53:49,220
From life's first steps...

670
00:53:50,220 --> 00:53:55,020
..to racing hearts and limbs built for
speed.

671
00:53:55,020 --> 00:53:57,100
Let's see them in action.

672
00:53:57,100 --> 00:53:58,580
DOG BARKS

673
00:53:59,580 --> 00:54:04,100
This is a slithering, swimming,
sprinting odyssey,

674
00:54:04,100 --> 00:54:06,740
with one final twist.

675
00:54:07,740 --> 00:54:09,220
Us.

676
00:54:12,340 --> 00:54:17,820
But first, how do we know that the
ancestors of dolphins

677
00:54:17,820 --> 00:54:20,060
once walked on land?

678
00:54:24,060 --> 00:54:27,420
- Dolphins are part of a larger group
called cetaceans,

679
00:54:27,420 --> 00:54:31,060
which includes dolphins, whales and
porpoises.

680
00:54:32,340 --> 00:54:36,140
- Cetaceans have the largest range in
body size

681
00:54:36,140 --> 00:54:38,580
of any group of mammals on the planet.

682
00:54:39,580 --> 00:54:42,340
- From really small, little harbour
porpoises

683
00:54:42,340 --> 00:54:44,340
that are only a few feet long,

684
00:54:44,340 --> 00:54:47,700
to the blue whale - the largest animal
on Earth,

685
00:54:47,700 --> 00:54:49,420
and everything in between.

686
00:54:51,820 --> 00:54:55,820
- And their origin can be traced back
to an ancient sea

687
00:54:55,820 --> 00:54:58,820
that once stretched between India and
Asia.

688
00:55:02,340 --> 00:55:06,340
Local and international scientists
have been searching for fossils

689
00:55:06,340 --> 00:55:09,860
in India and Pakistan over many years,

690
00:55:09,860 --> 00:55:13,940
where they found the remains of an
intriguing mammal.

691
00:55:17,380 --> 00:55:20,340
- What I'm holding in my hand here is
a real fossil

692
00:55:20,340 --> 00:55:22,060
of the skull of Indohyus.

693
00:55:22,060 --> 00:55:24,140
There's four of these in the world.

694
00:55:24,140 --> 00:55:26,060
I've got one right here.

695
00:55:28,420 --> 00:55:31,980
- The name Indohyus actually means
India's pig.

696
00:55:31,980 --> 00:55:35,980
- From the chemistry of the teeth, we
can tell that this animal ate

697
00:55:35,980 --> 00:55:39,660
land plants, mostly leaves, and
flowers and fruits.

698
00:55:41,340 --> 00:55:46,140
- From first appearances, Indohyus
looked like a regular land mammal...

699
00:55:47,140 --> 00:55:51,820
..until a chance event revealed a
critical structure

700
00:55:51,820 --> 00:55:54,060
hidden deep within its skull.

701
00:55:55,060 --> 00:55:57,620
- I had a fossil preparator, his name
was Rick,

702
00:55:57,620 --> 00:55:59,580
who was cleaning this off, he said,

703
00:55:59,580 --> 00:56:03,140
"I'm very sorry, but I broke part of
this Indohyus skull",

704
00:56:03,140 --> 00:56:06,580
and then I noticed that the ear bone
actually shows a feature

705
00:56:06,580 --> 00:56:10,660
that's only present in whales and
dolphins, called the involucrum.

706
00:56:12,340 --> 00:56:17,660
- The involucrum is a region of the
ear bone that has thickened.

707
00:56:17,660 --> 00:56:21,540
In modern-day cetaceans, it amplifies
vibrations

708
00:56:21,540 --> 00:56:27,220
transmitted in the skull, enhancing
their ability to hear under water.

709
00:56:27,220 --> 00:56:31,740
- So that's really the smoking gun
that Indohyus is closely related

710
00:56:31,740 --> 00:56:33,620
to whales and dolphins.

711
00:56:33,620 --> 00:56:39,340
- Evidence that it was already
adapting to a life underwater,

712
00:56:39,340 --> 00:56:42,580
completing the remarkable story

713
00:56:42,580 --> 00:56:47,820
of how land mammals evolved into
marine cetaceans.

714
00:56:47,820 --> 00:56:50,820
- It is one of the best fossil records
we have,

715
00:56:50,820 --> 00:56:53,660
so we've got a lot of pieces of the
puzzle

716
00:56:53,660 --> 00:56:56,020
to tell us what happened.

717
00:56:57,580 --> 00:57:01,060
- Other transitional fossils have been
found across the region

718
00:57:01,060 --> 00:57:04,060
that was once the ancient Tethys Sea.

719
00:57:05,340 --> 00:57:08,740
- We have whales and dolphins that
look like crocodiles,

720
00:57:08,740 --> 00:57:11,140
we have whales and dolphins that look
like seals

721
00:57:11,140 --> 00:57:12,820
or otters or sea lions.

722
00:57:15,340 --> 00:57:20,340
- It is probably one of the most
dramatic transformations

723
00:57:20,340 --> 00:57:23,580
in all of the evolution of life.

724
00:57:25,820 --> 00:57:29,980
Indohyus was not the kind of animal

725
00:57:29,980 --> 00:57:31,900
that you would look at and say,

726
00:57:31,900 --> 00:57:34,300
"You're going to get a blue whale out
of that",

727
00:57:34,300 --> 00:57:38,580
"You're going to get a brain like a
dolphin brain out of that",

728
00:57:38,580 --> 00:57:42,340
but that's what evolution does - it
makes big changes.

729
00:57:49,340 --> 00:57:52,980
- Do you want to know how an elephant
is related to a clownfish?

730
00:57:52,980 --> 00:57:57,340
Discover more in a poster from the
Open University on the tree of life.

731
00:57:57,340 --> 00:58:00,660
To get your free copy, scan the QR
code on screen

732
00:58:00,660 --> 00:58:04,820
or ring 0300 303 3460,

733
00:58:04,820 --> 00:58:10,340
or visit connect.open.ac.uk/evolution