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Look at this!

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What an extraordinary place.

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These caves are home to
a creature that is undeniably

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one of evolution's weirdest.

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Oh, my goodness, look at that.

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That is spectacular!

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The cave is caked in bats.

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Using ultrasonic clicks,
they can navigate in darkness.

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And with elongated finger bones
covered in a membrane of skin...

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..bats are the only mammals
that can fly.

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But there's something even weirder
about them.

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Each evening, they begin swarming...

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Oh, my goodness me, look at that!

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..driven by an impulse
they just can't deny...

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..an almost unrivalled need to feed.

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Flight is an enormously
energetically expensive exercise,

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and as a consequence, these bats
have a gargantuan appetite.

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Each one of them's going to need
to find thousands

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of tiny insects tonight,
eat half of its own body weight.

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A bit like me eating 70 pizzas
in just a few hours!

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Their whole existence is governed
by a drive to find food,

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and a lot of it.

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So, how did the bat become one of
the hungriest animals on the planet?

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To answer that question,
we must go back in time...

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..way back in time,

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..to meet a handful of
ancient relatives of the bat...

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..who, between them,
hold the evolutionary secrets...

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..to how the bat's giant appetite...

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..came to be.

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{\an8}Our story begins in the shallows
of an ancient ocean...

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..where today,
a new life is emerging.

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This is a distant ancestor
of the bat

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and all of us.

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Its home is
an alien-looking ecosystem,

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known as the Ediacaran Garden...

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..and its neighbours
are some of the strangest animals

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to ever live on our planet.

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Now, I know it might not
look like much,

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but this little creature
is about to play a pivotal role

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in the story of life on Earth...

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..one that would
change eating forever.

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Now, the Ediacaran is one of
the most enigmatic periods

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in our Earth's history,

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not least because it's
the first time that we find fossils

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of large, complex animals
in the geological record,

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and I've got some casts
of some of those in here.

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Just look at this.

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That's pretty good, isn't it?

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This is Charnia.

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I know it looks a little bit
like a plant, perhaps like a fern,

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but scientists can tell that
at least some of these specimens

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were living in depths of water
where plants couldn't prosper,

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so we think that it was an animal.

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Now, take a look at Dickinsonia.

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Now, that is special.

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That is a beautiful fossil.

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550 million years ago,

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these bizarre animals are thriving,

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because they have plenty to eat.

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Why was that?

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Well, I can show you
with a third fossil.

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And I know what you're thinking -

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"Well, that's not very special
at all.

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"That just looks like
some ripples on the beach."

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But you've got to look more closely.

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These are traces of millions,

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billions, trillions
of tiny microbes.

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These microscopic organisms
are the secret ingredient

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of the Ediacaran Garden.

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So numerous, they form
a nutritious green mat,

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several centimetres deep,

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that carpets the seabed
in every direction.

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For the animals that live here,

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the floor is literally made of food.

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A 24-hour, all-you-can-eat buffet
means no-one goes hungry here,

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including, of course...

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..the bat's ancestor.

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Officially, its name
is the Urbilaterian.

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It spends its days
leisurely grazing,

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hoovering up microbial mat
into its mouth...

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..digesting and then, a while later,
regurgitating the leftovers.

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Not terribly pleasant!

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And the evidence we have for
all of this comes not from a fossil,

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but from a creature alive today.

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{\an8}This blobby animal
is called an acoel.

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It's a marine organism.

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They normally measure
only a few millimetres in length,

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and you can find them
all over the world.

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This particular species
is called Hofstenia miamia,

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and it's a favourite of scientists
that study early life.

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You see, acoels are
what we call basal animals.

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A long time ago,

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they went down a certain
evolutionary road different than

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other animals, and they've retained
some ancient characteristics.

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Acoels have a mouth,
opening into a very basic gut,

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shaped a bit like a sack.

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And we think that this kind of gut
was common in the Ediacaran.

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So, for the Urbilaterian,

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the simplest route
for waste to come out

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is the same way the food came in.

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But this way of feeding
was about to get an upgrade.

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Compared to the rest of its kind,

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this individual has
a genetic difference,

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a mutation...

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..that almost imperceptibly
lengthens its body.

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A difference so trivial,
it doesn't cause it any harm...

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..but, when passed on,
will change the destiny

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of a tiny reproductive pore.

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Over many generations, subsequent
mutations lengthen the body further,

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driving the pore and the gut closer
and closer together, until...

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..they connect...

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..forming a continuous tube
through its body...

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..a tube that changes everything.

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This new animal was,
to all intents and purposes, a worm.

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You see, unlike the simple creature
that came before it,

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it had a new body part.

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Aside from a mouth to take food in -

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just like you, just like me,

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just like everything
that walks, flies and slithers -

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it had another hole
to excrete the waste.

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It had a bottom.

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It had a bum!

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Technically speaking,
it had an anus.

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Now, I know what you're thinking.

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If you're running through a list of
evolution's greatest innovations,

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the anus is probably not scoring
near the top of it.

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But then think about
the alternative,

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and the advantages become
immediately clear.

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I mean, imagine that you have a
lovely lunch and that you digest it,

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but before you can have your dinner,
you've got to throw it up.

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See what I mean?

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The anus was a breakthrough.

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With a mouth leading to a gut that
goes all the way through its body,

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this new worm can do something that
no animal has ever done before.

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It can poo!

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And this is a superpower!

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You see, it means the worm
can feed continually...

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..eating more than any animal
that came before.

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In their quest for food,

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the ravenous worms
burrow into the microbial mat,

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devouring it and churning it up...

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..disrupting an ecosystem
that had dominated the Earth

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since life's inception.

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And as the microbial mat declines...

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..almost all of the strange animals
that rely on it for food die out.

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The evolution of the anus
may well have led

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to the first mass extinction
of animal life on Earth.

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But the legacy of the anus
would prove to be more than just

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an extinction event.

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It helped animal life take on
a bold new form.

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The sea anemone and the nudibranch,
the sea slug,

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are two soft-bodied
marine organisms.

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They look pretty similar.

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But the extraordinary thing is that
I am more closely related

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to that nudibranch
than it is to that anemone.

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So, why is that?

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Well, it's because the anemone
doesn't have an anus.

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It's descended from a group
of animals that found its own

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evolutionary path before
the development of that through-gut.

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But the nudibranch, like myself, has
a mouth, a through-gut and an anus.

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It can poo,

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and the ability to poo has
a profound effect on our body plans.

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The anemone has
a circular body plan...

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..but the nudibranch
is symmetrical down the middle.

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It has what we call
bilateral symmetry...

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..just like our shared ancestor,
that ancient worm.

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And the through-gut
unleashed the full potential

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of this bilateral body plan.

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Then you've got an animal
with a mouth, the gut and an anus.

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Essentially, you've got a front
and a back,

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and the front, where the mouth is,
is the bit that wants to find food.

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So, think about it.

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That's the best place
to put any sensory organs,

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like eyes to look for that food.

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And then if you've got the sensory
organs there, that would be

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the best place to have the brain,
so they could react quickly

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when they find that food.

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So then you've got a mouth,
eyes and a brain in the same place.

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What you've got is a head.

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A head!

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And I absolutely love the fact
that for life to evolve a head,

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it had to evolve an arse first!

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I love that!

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A head end and a tail end,

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joined by a through-gut,

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proved to be a winning formula...

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..one that means, today, we see
bilateral symmetry everywhere.

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99% of known animal species
on the planet have this body plan...

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..all of us descendants
of that world-changing little worm.

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It is hard to understate
what a revolutionary moment

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the evolution of the anus was.

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Microbial mats, which for
three billion years had been

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the dominant ecosystem on Earth,
all but disappeared.

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Today, we find them in environments
which are inhospitable to animals -

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beneath the ice in Antarctica
or in steaming-hot volcanic springs.

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00:17:45,600 --> 00:17:46,920
And for animals,

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the development of the through-gut
had far-reaching consequences.

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00:17:51,560 --> 00:17:54,440
Its increased efficiency meant
they could grow bigger,

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move more purposefully.

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00:17:56,680 --> 00:18:00,840
And it cemented the bilaterally
symmetrical body plan

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over other options.

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00:18:03,360 --> 00:18:09,920
The drive to find food had changed
the course of life on Earth,

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and it wouldn't be the last time.

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The worms unleash a new era
of eating.

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00:18:21,400 --> 00:18:24,520
Fuelled by the extra energy
they're gathering...

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00:18:26,040 --> 00:18:29,440
..their descendants develop
more complex bodies...

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00:18:31,440 --> 00:18:34,560
..and keener senses
for finding food.

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00:18:40,800 --> 00:18:44,360
{\an8}Just 35 million years later,

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00:18:44,360 --> 00:18:47,480
{\an8}one of those descendants
is a worm no more.

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00:18:50,240 --> 00:18:53,320
We might even call it a fish.

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00:19:01,240 --> 00:19:05,120
A small fish,
living in a very big pond.

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00:19:10,160 --> 00:19:16,360
The oceans of the Cambrian Period
are dominated by giant arthropods -

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00:19:16,360 --> 00:19:18,440
early cousins of insects.

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00:19:23,240 --> 00:19:26,880
Among them, Earth's
first top predators.

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00:19:31,240 --> 00:19:35,800
And the secret to survival
for this little fish

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00:19:35,800 --> 00:19:39,040
comes down to its strange mouth.

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00:19:42,440 --> 00:19:47,360
Now, take a look at this. It's
the fossil of that primitive fish,

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00:19:47,360 --> 00:19:50,560
about five centimetres long.
It's called Metaspriggina.

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00:19:50,560 --> 00:19:54,280
Just look at the detail
that you can see here,

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00:19:54,280 --> 00:19:56,880
particularly at the front
of its head.

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00:19:56,880 --> 00:19:59,920
These two black dots,
those are its eyes.

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00:19:59,920 --> 00:20:02,040
And under scrutiny,
scientists have discovered

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00:20:02,040 --> 00:20:06,320
that they are pointing upwards,
so it could be that this little fish

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00:20:06,320 --> 00:20:10,280
was swimming along on the bottom,
using those eyes to look up into

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00:20:10,280 --> 00:20:12,640
the water column
for any potential predators -

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00:20:12,640 --> 00:20:14,520
perhaps those giant arthropods -

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00:20:14,520 --> 00:20:19,040
that might have made a tasty snack
out of a tiny fish like this.

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There's another photograph here.

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00:20:22,760 --> 00:20:25,560
This time, we're looking down on it,

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and what appear to be ribs here, we
think are not ribs but gill arches -

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00:20:32,080 --> 00:20:34,640
structures which support gills.

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00:20:36,400 --> 00:20:37,800
As it swims,

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00:20:37,800 --> 00:20:42,560
a constant stream of water
flows into the fish's open mouth.

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00:20:50,040 --> 00:20:52,920
This is how Metaspriggina breathes -

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00:20:52,920 --> 00:20:56,320
passing water over its gills,

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00:20:56,320 --> 00:20:59,160
supported by those gill arches.

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00:21:00,480 --> 00:21:03,840
But this mouth is multipurpose.

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00:21:03,840 --> 00:21:07,080
Something else is extracted
at the same time.

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00:21:08,360 --> 00:21:11,520
Metaspriggina is a filter feeder.

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00:21:13,360 --> 00:21:19,520
And getting both oxygen and food
into their bodies fast

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00:21:19,520 --> 00:21:24,080
is critical if they want to survive
these perilous waters.

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00:21:36,240 --> 00:21:41,160
This is survival of the fittest
in action,

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00:21:41,160 --> 00:21:42,760
and it means this fish,

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00:21:42,760 --> 00:21:47,560
its strange mouth and those
gill arches hidden deep within

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00:21:47,560 --> 00:21:52,360
are already on a path that will
shake up the world of eating

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00:21:52,360 --> 00:21:54,520
all over again.

247
00:21:57,160 --> 00:22:01,120
Scientists have found that
Metaspriggina's front gill arches

248
00:22:01,120 --> 00:22:03,480
are actually thicker

249
00:22:03,480 --> 00:22:08,760
and appear to lack oxygen-absorbing
gill filaments,

250
00:22:08,760 --> 00:22:13,840
a tantalising hint that they may
have jettisoned their old role

251
00:22:13,840 --> 00:22:20,040
for a new one - keeping the fish's
gaping mouth wide open.

252
00:22:24,280 --> 00:22:29,000
Because thick gill arches lead
to a wider mouth,

253
00:22:29,000 --> 00:22:32,760
more food and oxygen
and more energy to escape...

254
00:22:36,440 --> 00:22:39,400
..it's an advantage
that's passed on.

255
00:22:49,520 --> 00:22:52,960
Across countless generations,

256
00:22:52,960 --> 00:22:56,800
the gill arches continue
to thicken and strengthen.

257
00:23:03,600 --> 00:23:05,440
New structures erupt...

258
00:23:09,360 --> 00:23:12,520
..and after
tens of millions of years...

259
00:23:13,680 --> 00:23:15,800
..what was once a gill arch...

260
00:23:18,760 --> 00:23:22,520
..becomes a revolutionary
new body part...

261
00:23:24,000 --> 00:23:25,880
..which means this fish...

262
00:23:28,200 --> 00:23:29,880
..can bite!

263
00:23:51,560 --> 00:23:55,000
Many body parts have been lost
to the passage of time.

264
00:23:55,000 --> 00:23:57,560
Whales and dolphins have lost limbs,

265
00:23:57,560 --> 00:24:00,960
and fish that have been marooned in
pitch-dark cave systems

266
00:24:00,960 --> 00:24:02,240
have lost their eyes.

267
00:24:02,240 --> 00:24:08,360
Even the not-so-humble anus has
disappeared on multiple occasions.

268
00:24:08,360 --> 00:24:10,800
But jaws, never.

269
00:24:10,800 --> 00:24:12,880
Jaws are simply too useful.

270
00:24:15,440 --> 00:24:19,880
Look, jaws didn't just change
how animals ate,

271
00:24:19,880 --> 00:24:21,880
but where they ate.

272
00:24:24,440 --> 00:24:27,840
This little creature
is a mud skipper,

273
00:24:27,840 --> 00:24:30,120
one of around 25 species of fish

274
00:24:30,120 --> 00:24:31,400
that you can find
all over the world,

275
00:24:31,400 --> 00:24:36,040
typically in intertidal
mangrove swamps like this.

276
00:24:36,040 --> 00:24:38,200
Now, what's extraordinary about them

277
00:24:38,200 --> 00:24:41,880
is the amount of time that
they can spend out of the water...

278
00:24:43,680 --> 00:24:47,240
..some of them 90% of their lives,
and they're able to do that

279
00:24:47,240 --> 00:24:49,880
because they've got
some remarkable adaptations.

280
00:24:52,240 --> 00:24:57,560
Firstly, this little fish
is breathing through its skin.

281
00:24:57,560 --> 00:25:00,720
It also has jointed pectoral fins,

282
00:25:00,720 --> 00:25:04,360
which means that it can skip
across the surface of the mud,

283
00:25:04,360 --> 00:25:07,040
almost as if it were walking.

284
00:25:09,200 --> 00:25:12,960
So there are some behavioural
comparisons there that we can make

285
00:25:12,960 --> 00:25:17,080
with those fish that struggled
out of water, onto land,

286
00:25:17,080 --> 00:25:20,160
375 million years ago,

287
00:25:20,160 --> 00:25:23,000
to begin an amphibious lifestyle.

288
00:25:25,760 --> 00:25:27,280
But here's one thing.

289
00:25:27,280 --> 00:25:29,080
They couldn't have done it
without jaws.

290
00:25:29,080 --> 00:25:30,560
Just think about it.

291
00:25:30,560 --> 00:25:35,240
If these and those fish
were dependent upon filter feeding,

292
00:25:35,240 --> 00:25:40,080
dependent upon that water carrying
morsels of food into their mouth,

293
00:25:40,080 --> 00:25:44,240
that would mean that no matter how
much time they could spend on land,

294
00:25:44,240 --> 00:25:47,760
they would have to return to water
to feed.

295
00:25:47,760 --> 00:25:51,480
The difference is they've got jaws -
they can bite.

296
00:25:51,480 --> 00:25:55,960
And you can bite just as well out
of water as you can in the water.

297
00:26:09,040 --> 00:26:12,000
Thanks in part to the evolution
of the jaw,

298
00:26:12,000 --> 00:26:15,720
fish were no longer reliant
on feeding in water...

299
00:26:17,640 --> 00:26:21,400
..opening up a new world
of possibilities.

300
00:26:24,720 --> 00:26:26,800
Now, I know it's going to
sound absurd...

301
00:26:30,480 --> 00:26:33,560
..but from an evolutionary
perspective at least,

302
00:26:33,560 --> 00:26:38,040
these elephants are -
wait for it - jawed fish.

303
00:26:38,040 --> 00:26:42,000
Of course, they're highly modified
jawed fish, but fish nevertheless.

304
00:26:42,000 --> 00:26:44,520
But then so am I, so are you,

305
00:26:44,520 --> 00:26:49,160
so is every other terrestrial animal
that's got a backbone and a jaw.

306
00:26:51,920 --> 00:26:53,520
So, here in Borneo,

307
00:26:53,520 --> 00:26:58,200
that means 300 species of reptile,
150 amphibians, 650 birds

308
00:26:58,200 --> 00:27:01,000
and 250 species of mammal,

309
00:27:01,000 --> 00:27:04,440
all of whom are descended
from those fish

310
00:27:04,440 --> 00:27:06,840
that made that leap
out of the water.

311
00:27:09,200 --> 00:27:10,760
ELEPHANT GRUNTS

312
00:27:17,600 --> 00:27:22,280
Globally, there are at least
30,000 species of vertebrates

313
00:27:22,280 --> 00:27:26,760
living on land,
with a dizzying array of jaws,

314
00:27:26,760 --> 00:27:29,080
adapted to many different ways
of feeding.

315
00:27:30,200 --> 00:27:35,160
Some are lined with teeth,
others have become beaks.

316
00:27:36,920 --> 00:27:39,600
And some open so far,

317
00:27:39,600 --> 00:27:44,680
their owners can swallow meals
wider than their bodies.

318
00:27:50,360 --> 00:27:53,720
What began as
a tiny Ediacaran creature...

319
00:27:56,040 --> 00:27:59,440
..gave rise to a through-gut

320
00:27:59,440 --> 00:28:02,800
and a worm with an appetite
that upended the world...

321
00:28:05,480 --> 00:28:08,200
..and led to a fish

322
00:28:08,200 --> 00:28:11,320
with a jaw that could finally
take a bite.

323
00:28:16,920 --> 00:28:19,560
From their aquatic origins,

324
00:28:19,560 --> 00:28:22,680
jawed animals spread
to all corners of the globe...

325
00:28:27,280 --> 00:28:33,040
..and diversify to exploit
new sources of food.

326
00:28:40,680 --> 00:28:44,080
{\an8}Until, 200 million years later,

327
00:28:44,080 --> 00:28:47,120
{\an8}we find one of them on the move.

328
00:28:58,480 --> 00:29:00,760
This is Agilodocodon.

329
00:29:06,520 --> 00:29:08,840
It's a female, and she's tiny...

330
00:29:13,280 --> 00:29:15,240
..the size of a shrew.

331
00:29:19,520 --> 00:29:24,320
With warm blood and fur,
she's a primitive mammal

332
00:29:24,320 --> 00:29:28,240
who spends most of her time
hunting insects in trees.

333
00:29:35,760 --> 00:29:40,240
But right now, it's not her own
hunger she's concerned with...

334
00:29:52,160 --> 00:29:53,680
..it's theirs.

335
00:30:03,040 --> 00:30:07,720
Mammals have a quirky advantage
over many other types of animal.

336
00:30:07,720 --> 00:30:11,040
You see, we don't have to find food
for our babies.

337
00:30:11,040 --> 00:30:14,040
We don't abandon them
to find their own.

338
00:30:14,040 --> 00:30:20,880
We make it, and milk is the perfect
food for a growing infant.

339
00:30:20,880 --> 00:30:24,600
And it's perfect,
unlike so many other types of food,

340
00:30:24,600 --> 00:30:27,640
because evolution has driven it
to be so.

341
00:30:34,200 --> 00:30:38,280
Of course, milk,
made by mammary glands,

342
00:30:38,280 --> 00:30:40,760
has given us mammals our name.

343
00:30:43,240 --> 00:30:47,680
But the evolution of milk impacted
more than just babies.

344
00:30:49,120 --> 00:30:52,840
It's changed how mammals feed
at every age.

345
00:30:58,280 --> 00:31:00,920
I've got a couple of
lovely skulls here.

346
00:31:00,920 --> 00:31:05,480
This is from a crocodile,
and this one from an orangutan.

347
00:31:05,480 --> 00:31:08,960
Now, they're clearly very different
in terms of their size and shape,

348
00:31:08,960 --> 00:31:11,240
but also their teeth.

349
00:31:11,240 --> 00:31:13,520
Let's take a look
at the crocodile first.

350
00:31:13,520 --> 00:31:19,080
Its teeth are very simple, and
they're pretty much all the same -

351
00:31:19,080 --> 00:31:24,160
cylindrical at the base, peg-like
and sharp, ideal for grabbing

352
00:31:24,160 --> 00:31:26,360
and then gripping their prey.

353
00:31:26,360 --> 00:31:32,480
But, look, you can see that they
don't fit together terribly well.

354
00:31:32,480 --> 00:31:35,880
There are large gaps
in between them.

355
00:31:35,880 --> 00:31:40,520
Contrast that with the skull
of the orangutan.

356
00:31:42,960 --> 00:31:44,880
Its teeth are not so simple.

357
00:31:44,880 --> 00:31:46,600
They come in a range of forms.

358
00:31:46,600 --> 00:31:48,800
You've got these at the front here.

359
00:31:48,800 --> 00:31:53,240
These are the incisors that are used
for slicing and nibbling.

360
00:31:53,240 --> 00:31:56,520
And then you've got these
very powerful canines

361
00:31:56,520 --> 00:31:58,920
for piercing and gripping.

362
00:31:58,920 --> 00:32:04,560
And lastly, when I fit the jaw on
as it would sit in life,

363
00:32:04,560 --> 00:32:06,480
look at these teeth
at the back here.

364
00:32:06,480 --> 00:32:10,480
They fit together almost perfectly.

365
00:32:10,480 --> 00:32:12,960
These are the molars,

366
00:32:12,960 --> 00:32:16,920
and one of the major reasons that
molars have been able to evolve

367
00:32:16,920 --> 00:32:18,400
comes down to milk.

368
00:32:21,080 --> 00:32:23,200
The ancestors of mammals

369
00:32:23,200 --> 00:32:26,120
had simple, reptilian-like teeth

370
00:32:26,120 --> 00:32:27,520
that were replaced continually

371
00:32:27,520 --> 00:32:30,320
as the animals grew.

372
00:32:30,320 --> 00:32:33,160
But when they started
to evolve milk,

373
00:32:33,160 --> 00:32:36,200
babies were no longer reliant
on teeth to feed.

374
00:32:37,320 --> 00:32:41,000
Fewer sets were needed
throughout life,

375
00:32:41,000 --> 00:32:45,320
so this allowed more complex teeth
to evolve.

376
00:32:47,520 --> 00:32:49,280
In the mid Jurassic,

377
00:32:49,280 --> 00:32:53,040
it's thought that the young
of species like Agilodocodon,

378
00:32:53,040 --> 00:32:55,880
now sustained entirely on milk,

379
00:32:55,880 --> 00:32:58,280
are born toothless.

380
00:33:05,880 --> 00:33:08,960
It's only because their adult molars
don't emerge

381
00:33:08,960 --> 00:33:12,840
until their jaws are
almost fully grown

382
00:33:12,840 --> 00:33:17,120
that they are some of the first
to interlock perfectly.

383
00:33:30,680 --> 00:33:34,400
And this helps today's mammals
do something

384
00:33:34,400 --> 00:33:37,320
that's surprisingly rare
in the animal kingdom.

385
00:33:51,000 --> 00:33:55,560
Take a look at this beautiful
orangutan here.

386
00:33:57,480 --> 00:34:00,720
A female with a nursing youngster.

387
00:34:02,200 --> 00:34:06,280
But put her beauty to one side and
concentrate on what she's doing.

388
00:34:06,280 --> 00:34:08,280
She is chewing.

389
00:34:08,280 --> 00:34:09,960
We can chew.

390
00:34:11,840 --> 00:34:16,960
Those gentle movements
of the lower jaw,

391
00:34:16,960 --> 00:34:20,120
those molars grinding up that fruit.

392
00:34:21,960 --> 00:34:24,840
Imagine you had to take that fruit
into your kitchen

393
00:34:24,840 --> 00:34:28,000
and cut it up into chunks
that you could swallow.

394
00:34:28,000 --> 00:34:30,200
You'd have to slice it,
you'd have to dice it,

395
00:34:30,200 --> 00:34:32,400
and then you'd have to mash it.

396
00:34:32,400 --> 00:34:36,080
But she's doing all of that
with consummate ease.

397
00:34:39,240 --> 00:34:44,920
Her teeth are highly efficient
food-processing machines,

398
00:34:44,920 --> 00:34:47,800
and what they're trying to do
is grind that food up

399
00:34:47,800 --> 00:34:49,800
to increase its surface area,

400
00:34:49,800 --> 00:34:52,160
so that when it reaches the stomach
and the gut,

401
00:34:52,160 --> 00:34:56,360
the digestive juices can act upon it
far more quickly.

402
00:34:56,360 --> 00:35:00,600
It massively speeds up
the rate of digestion.

403
00:35:00,600 --> 00:35:02,880
I mean, contrast it with
those crocodiles.

404
00:35:02,880 --> 00:35:05,080
They swallow their food whole,
or in massive chunks,

405
00:35:05,080 --> 00:35:07,440
and it takes weeks to digest it.

406
00:35:08,920 --> 00:35:12,560
But me, you and the orangutan,

407
00:35:12,560 --> 00:35:16,880
we can have a meal and digest it
in just a matter of hours.

408
00:35:41,240 --> 00:35:44,320
For primitive mammals
like Agilodocodon...

409
00:35:48,960 --> 00:35:53,960
..this ability to chew helps drive
a surprising evolutionary change.

410
00:36:03,120 --> 00:36:05,280
Over generations,

411
00:36:05,280 --> 00:36:09,760
a lower jaw, made of several bones,
is gradually reconfigured.

412
00:36:15,600 --> 00:36:17,240
One bone gets larger...

413
00:36:18,760 --> 00:36:20,920
..whilst the others shrink...

414
00:36:23,760 --> 00:36:28,640
..until a single, powerful
lower jaw evolves.

415
00:36:33,600 --> 00:36:36,880
The old jawbones wither away,

416
00:36:36,880 --> 00:36:39,640
but not all are lost.

417
00:36:45,320 --> 00:36:48,920
These are the remnants
of those jawbones.

418
00:36:48,920 --> 00:36:51,920
They're called the malleus
and the incus,

419
00:36:51,920 --> 00:36:56,120
although you might know them
as the hammer and the anvil.

420
00:36:57,440 --> 00:37:00,360
They're two of the smallest bones
in our body,

421
00:37:00,360 --> 00:37:03,640
and they're disconnected
from the rest of our skeleton.

422
00:37:03,640 --> 00:37:06,480
But the key thing is,
when we were in the womb,

423
00:37:06,480 --> 00:37:12,280
they started off as part of our jaw
and then migrated up to our ear,

424
00:37:12,280 --> 00:37:15,640
where they are joined by this bone,

425
00:37:15,640 --> 00:37:19,400
and this one is called the stapes,
or the stirrup.

426
00:37:19,400 --> 00:37:24,640
And together, they connect
our eardrum to our inner ear,

427
00:37:24,640 --> 00:37:27,640
greatly enhancing our capacity
to hear,

428
00:37:27,640 --> 00:37:31,120
particularly a wider range
of frequencies.

429
00:37:34,880 --> 00:37:39,360
The evolution of the middle ear
bones, known as the ossicles,

430
00:37:39,360 --> 00:37:45,040
transformed hearing for
modern mammals, meaning that today,

431
00:37:45,040 --> 00:37:49,720
mammals have some of the most
sensitive hearing of all animals.

432
00:38:08,680 --> 00:38:14,640
It's remarkable to think that
over 400 million years ago,

433
00:38:14,640 --> 00:38:20,320
these tiny bones were part
of an ancient fish's gill arches.

434
00:38:20,320 --> 00:38:25,160
This is the power of evolution,
right here in the palm of my hand.

435
00:38:25,160 --> 00:38:30,120
No designer was involved in making
these bones, which are currently

436
00:38:30,120 --> 00:38:35,000
floating in your head, allowing you
to hear what I'm saying.

437
00:38:35,000 --> 00:38:41,360
All that was needed was life's
relentless drive to find food.

438
00:38:41,360 --> 00:38:44,040
That and quite a bit of time!

439
00:38:47,920 --> 00:38:51,680
And time, of course,
keeps ticking...

440
00:38:57,240 --> 00:39:02,240
..and mammals, now with
acute hearing, keep evolving...

441
00:39:04,480 --> 00:39:07,000
..for tens of millions of years...

442
00:39:12,840 --> 00:39:14,560
{\an8}..until, one morning...

443
00:39:16,040 --> 00:39:21,760
{\an8}..a little mammal picks up a sound
it's never heard before...

444
00:39:24,240 --> 00:39:29,200
..a sound that, once again,
would change everything.

445
00:39:34,200 --> 00:39:36,640
By the time we get
to the Cretaceous Period,

446
00:39:36,640 --> 00:39:40,320
when T-Rex was on the prowl, most
of those traits that we consider

447
00:39:40,320 --> 00:39:43,840
to be typically mammalian
are already there -

448
00:39:43,840 --> 00:39:49,920
warm-bloodedness, fur, complex teeth
in powerful jaws and acute hearing.

449
00:39:49,920 --> 00:39:53,520
And that acute hearing meant that
mammals had already conquered

450
00:39:53,520 --> 00:39:56,840
the night, and it was going to prove
to be significant.

451
00:39:56,840 --> 00:40:00,880
You see, that classic myth that
mammals at this time were living

452
00:40:00,880 --> 00:40:04,920
in the shadow of the dinosaurs,
it may not have been like that.

453
00:40:04,920 --> 00:40:08,560
That hearing contributed to the fact
that they could find more food.

454
00:40:08,560 --> 00:40:10,960
Those jaws could catch it
and process it.

455
00:40:10,960 --> 00:40:12,360
They were getting more energy.

456
00:40:12,360 --> 00:40:15,280
They were able to build
bigger bodies.

457
00:40:15,280 --> 00:40:18,520
In fact, some scientists
think that those early mammals

458
00:40:18,520 --> 00:40:22,400
could have been well on the way
to standing shoulder to shoulder

459
00:40:22,400 --> 00:40:25,000
with those giant reptiles.

460
00:40:25,000 --> 00:40:29,680
But, of course, as we know, that
story was going to be cut short.

461
00:40:39,360 --> 00:40:41,320
The sound the mammal heard

462
00:40:41,320 --> 00:40:45,440
had its origins
thousands of kilometres away...

463
00:40:47,240 --> 00:40:50,280
..where, an hour or so earlier,

464
00:40:50,280 --> 00:40:53,360
a rock, 12km wide,

465
00:40:53,360 --> 00:40:56,080
had plunged into the Gulf of Mexico.

466
00:40:58,680 --> 00:41:03,200
In a moment, the world
is changed irrevocably.

467
00:41:08,320 --> 00:41:12,000
The day that asteroid plummeted
into the Gulf of Mexico

468
00:41:12,000 --> 00:41:16,080
was probably the worst single day
for life since it arose

469
00:41:16,080 --> 00:41:21,360
around four billion years ago,
because in that one chance moment,

470
00:41:21,360 --> 00:41:25,280
life's progress was stopped dead -
quite literally -

471
00:41:25,280 --> 00:41:28,720
and millions of years
of evolutionary tinkering

472
00:41:28,720 --> 00:41:31,120
were wiped out in an instant.

473
00:41:31,120 --> 00:41:33,880
And it was such a twist of fate.

474
00:41:33,880 --> 00:41:37,960
Had that asteroid impacted
just 30 seconds later,

475
00:41:37,960 --> 00:41:40,400
the Earth would have
spun on its axis.

476
00:41:40,400 --> 00:41:42,600
It would have smashed
into much deeper water

477
00:41:42,600 --> 00:41:45,520
and caused far less devastation.

478
00:41:45,520 --> 00:41:48,960
You never know - those giant
reptiles might not have died out.

479
00:41:48,960 --> 00:41:53,000
We might have had mammals, but not
the mammal fauna that we've got now.

480
00:41:53,000 --> 00:41:57,120
There might have been no humans
on Earth.

481
00:41:58,320 --> 00:42:02,480
Standing here in this
oil palm plantation...

482
00:42:03,880 --> 00:42:06,480
..I'll leave you to make of that
what you will.

483
00:42:19,640 --> 00:42:23,680
And whatever happens,
life will find a way.

484
00:42:39,200 --> 00:42:43,200
Although in the 15-year winter
that follows the impact...

485
00:42:45,480 --> 00:42:50,240
..three quarters of species are
erased from the face of the Earth.

486
00:42:54,360 --> 00:42:58,040
A tiny fraction
of mammal species endure.

487
00:43:06,920 --> 00:43:10,360
We know this, of course, because
I'm here, because you're here,

488
00:43:10,360 --> 00:43:14,640
because all the mammals we currently
share our planet with are here.

489
00:43:14,640 --> 00:43:19,000
But what do we know about
our shared ancient ancestors,

490
00:43:19,000 --> 00:43:21,800
those creatures that survived
the storm of all storms,

491
00:43:21,800 --> 00:43:24,160
the almost endless night?

492
00:43:24,160 --> 00:43:27,400
Well, we think they were small,
rodent-like animals -

493
00:43:27,400 --> 00:43:29,640
not a single species,
but a group of them.

494
00:43:29,640 --> 00:43:32,360
And they carried those traits
like complex teeth,

495
00:43:32,360 --> 00:43:35,240
which would have enabled them
to eat a broad diet -

496
00:43:35,240 --> 00:43:38,760
everything from rotting vegetation
to insects,

497
00:43:38,760 --> 00:43:42,880
which would have bounced back quite
quickly after that near catastrophe.

498
00:43:42,880 --> 00:43:46,040
They might have also been
burrowing animals,

499
00:43:46,040 --> 00:43:50,680
so they could get beneath the ground
to avoid all of that climate chaos

500
00:43:50,680 --> 00:43:53,640
which was causing so many
other species to become extinct.

501
00:44:04,760 --> 00:44:10,600
Just a few hundred thousand years
after that apocalyptic day,

502
00:44:10,600 --> 00:44:14,240
we start to see the descendants
of those surviving mammals

503
00:44:14,240 --> 00:44:15,640
in the fossil record.

504
00:44:22,400 --> 00:44:25,400
In a world vacated by dinosaurs,

505
00:44:25,400 --> 00:44:27,840
mammals rapidly diversified.

506
00:44:35,920 --> 00:44:38,960
Among them,
a remarkable new group...

507
00:44:40,440 --> 00:44:44,400
{\an8}..that would use
their acute mammalian hearing

508
00:44:44,400 --> 00:44:46,800
{\an8}in a truly innovative way.

509
00:44:48,440 --> 00:44:53,000
This is a replica fossil
of an approximately

510
00:44:53,000 --> 00:44:57,440
52-million-year-old creature
called Icaronycteris.

511
00:44:57,440 --> 00:45:01,960
And you might be able to guess
what type of animal it is.

512
00:45:01,960 --> 00:45:07,000
Firstly, look at its fingers here -
very long and narrow, extended.

513
00:45:07,000 --> 00:45:10,080
I'll give you another clue
by turning it up this way.

514
00:45:10,080 --> 00:45:14,560
Yes, those fingers have
transformed into wings.

515
00:45:14,560 --> 00:45:17,080
This animal could fly.

516
00:45:17,080 --> 00:45:22,000
This is the fossil of a bat.

517
00:45:22,000 --> 00:45:26,560
Now, there's a lot more we need to
learn about the evolution of bats.

518
00:45:26,560 --> 00:45:30,280
There's a big gap between
that period when the asteroid hit

519
00:45:30,280 --> 00:45:33,720
and this, 14 million years later.

520
00:45:33,720 --> 00:45:37,400
And the reason for that is that
these delicate, light, little bones

521
00:45:37,400 --> 00:45:41,320
don't fossilise terribly well.
We don't find many fossil bats.

522
00:45:42,560 --> 00:45:45,280
But scientists have
X-rayed this skull

523
00:45:45,280 --> 00:45:51,800
and they found that inside its inner
ear, it has an enlarged cochlea.

524
00:45:51,800 --> 00:45:54,640
And that, alongside the fact
it had ossicles,

525
00:45:54,640 --> 00:46:00,560
might suggest that this creature
could echolocate.

526
00:46:00,560 --> 00:46:02,680
What about that?!

527
00:46:02,680 --> 00:46:06,960
Quite when creatures like this
started to echolocate,

528
00:46:06,960 --> 00:46:08,040
we're not sure.

529
00:46:08,040 --> 00:46:12,560
Perhaps just after they could fly,
perhaps at the same time.

530
00:46:12,560 --> 00:46:17,000
But it's a beautiful specimen.
I covet this.

531
00:46:17,000 --> 00:46:19,400
I might actually steal it!

532
00:46:24,640 --> 00:46:27,240
Because bat fossils are so rare...

533
00:46:29,120 --> 00:46:33,440
..we don't know exactly why bats
first evolved powered flight.

534
00:46:36,720 --> 00:46:42,120
But combined with echolocation,
it's an adaptation that pays off.

535
00:46:43,760 --> 00:46:47,280
Despite being
so energetically demanding,

536
00:46:47,280 --> 00:46:52,280
flight allowed access
to a great, untapped source of food

537
00:46:52,280 --> 00:46:53,680
in the night sky.

538
00:47:07,280 --> 00:47:09,840
Today, they're one of
the most successful

539
00:47:09,840 --> 00:47:11,960
mammalian lineages on Earth...

540
00:47:17,120 --> 00:47:20,760
..with over 1,000 species
of echolocating bat...

541
00:47:23,840 --> 00:47:27,960
..inhabiting every continent
except Antarctica.

542
00:47:45,720 --> 00:47:50,560
Here in Borneo, there are more bats
than any other type of mammal.

543
00:47:53,880 --> 00:47:58,840
Among them,
those wrinkle-lipped bats

544
00:47:58,840 --> 00:48:03,200
that roost in Gomantong Caves
in their hundreds of thousands.

545
00:48:06,160 --> 00:48:09,120
But bats don't just live in caves.

546
00:48:13,520 --> 00:48:17,240
You can find them
in the most unexpected of places.

547
00:48:32,520 --> 00:48:36,080
Oh, yes, yes, yes! Look at that!

548
00:48:36,080 --> 00:48:39,800
It's a little cluster
of bamboo bats.

549
00:48:45,760 --> 00:48:47,800
And this is where
they like to roost -

550
00:48:47,800 --> 00:48:50,320
in these hollow stems of bamboo.

551
00:48:57,240 --> 00:49:00,440
One of the smallest bat species
in the world,

552
00:49:00,440 --> 00:49:05,920
one of the smallest mammals in
the world, they can weigh up to 5g.

553
00:49:05,920 --> 00:49:09,320
That's about the same size
as a large bumblebee.

554
00:49:09,320 --> 00:49:11,240
Look at them all in there.

555
00:49:11,240 --> 00:49:16,480
Oh! I honestly didn't think
we were going to find any.

556
00:49:22,360 --> 00:49:25,480
Any minute now,
when these bats emerge to hunt,

557
00:49:25,480 --> 00:49:29,560
they will be able to fly at speeds
of several metres per second,

558
00:49:29,560 --> 00:49:33,240
and they're able to do that because
they can digest their insect prey in

559
00:49:33,240 --> 00:49:37,920
about 30 minutes - quick enough
to power their fiery metabolism,

560
00:49:37,920 --> 00:49:41,840
the metabolism
that allows them to fly.

561
00:49:41,840 --> 00:49:45,440
And then, of course, they've got
that extremely acute hearing.

562
00:49:45,440 --> 00:49:49,360
They can hear frequencies
five times higher than I can.

563
00:49:49,360 --> 00:49:52,360
That means they can detect
their echolocation calls,

564
00:49:52,360 --> 00:49:57,680
find those tiny insects metres away,
out there in the darkness.

565
00:50:01,200 --> 00:50:06,040
In so many ways,
they are extraordinary organisms...

566
00:50:09,160 --> 00:50:14,360
..but then, in some ways,
they're really quite ordinary.

567
00:50:14,360 --> 00:50:19,560
Just like their Ediacaran ancestor
that lived half a billion years ago,

568
00:50:19,560 --> 00:50:21,440
they're bilaterally symmetrical.

569
00:50:21,440 --> 00:50:24,160
They've got a head end, a back end,
and a through-gut

570
00:50:24,160 --> 00:50:31,560
running in between, like 99% of all
of the animals that live on Earth.

571
00:50:31,560 --> 00:50:35,600
And just like all of the vertebrates
living on this island,

572
00:50:35,600 --> 00:50:39,120
they've inherited a jaw
from that ancient fish

573
00:50:39,120 --> 00:50:41,400
that struggled onto land.

574
00:50:42,960 --> 00:50:47,280
Their ears have those ossicles,
just like ours.

575
00:50:49,520 --> 00:50:56,560
We're both born helpless, completely
dependent upon our mothers,

576
00:50:56,560 --> 00:50:59,840
and the hormones
that make them hungry

577
00:50:59,840 --> 00:51:03,120
are the hormones
that make me hungry, too.

578
00:51:10,960 --> 00:51:12,920
From the humblest beginnings...

579
00:51:14,560 --> 00:51:17,600
..millennia by millennia,

580
00:51:17,600 --> 00:51:19,600
mouthful by mouthful...

581
00:51:23,360 --> 00:51:28,880
..the need to feed
transformed life on Earth.

582
00:51:34,400 --> 00:51:38,280
Evolution is at times brutal,

583
00:51:38,280 --> 00:51:41,320
but also exquisitely beautiful...

584
00:51:41,320 --> 00:51:42,640
Wow!

585
00:51:43,680 --> 00:51:47,000
..as echoes of these ancestors
live on...

586
00:51:47,000 --> 00:51:48,880
Oh! So good.

587
00:51:56,040 --> 00:51:58,600
..and not just in the bat.

588
00:52:09,360 --> 00:52:15,600
Now, I share about 92% of my genes
with these little bats,

589
00:52:15,600 --> 00:52:18,200
so you could say
that their evolutionary story

590
00:52:18,200 --> 00:52:22,880
is my evolutionary story,
is your evolutionary story.

591
00:52:22,880 --> 00:52:26,560
And so many of the things
that make them extraordinary

592
00:52:26,560 --> 00:52:29,480
are the things
that make you extraordinary, too.

593
00:52:29,480 --> 00:52:31,480
And it's not a story
that's come to an end.

594
00:52:31,480 --> 00:52:35,800
Life goes on. Evolution goes on.

595
00:52:35,800 --> 00:52:38,640
So I want to ponder at this point -

596
00:52:38,640 --> 00:52:44,640
what if our species can finally get
a grip on all the terrible damage

597
00:52:44,640 --> 00:52:49,080
that it's doing to this,
our one beautiful home?

598
00:52:49,080 --> 00:52:53,600
Just where might evolution
take us all next?

599
00:52:59,480 --> 00:53:00,560
{\an8}Next time...

600
00:53:01,880 --> 00:53:05,320
{\an8}..how did the dolphin get so smart?

601
00:53:05,320 --> 00:53:07,960
Absolutely amazing!

602
00:53:10,040 --> 00:53:13,040
From the first animals
to set eyes on our world...

603
00:53:14,640 --> 00:53:20,480
..to the land-based ancestors
who stepped back into the oceans,

604
00:53:20,480 --> 00:53:23,320
reshaping their minds,

605
00:53:23,320 --> 00:53:28,160
giving rise to the dolphin
and its brilliant brain.

606
00:53:29,160 --> 00:53:31,160
Oh! My goodness me!

607
00:53:31,160 --> 00:53:33,160
I've just been to dolphin heaven!

608
00:53:38,640 --> 00:53:39,800
But first...

609
00:53:41,280 --> 00:53:44,360
..how do we bring ancient creatures
to life?

610
00:53:50,240 --> 00:53:52,160
Oh! It's so cute!

611
00:53:52,160 --> 00:53:54,080
HE CHUCKLES

612
00:53:54,080 --> 00:53:55,120
I love the mouth.

613
00:53:56,640 --> 00:53:58,720
Such a weird creature as well,
isn't it?

614
00:54:00,720 --> 00:54:02,560
Throughout Earth's history,

615
00:54:02,560 --> 00:54:06,640
animals have evolved into all manner
of weird and wonderful forms...

616
00:54:08,800 --> 00:54:11,680
..but how do we know
what they looked like

617
00:54:11,680 --> 00:54:15,240
when they lived
millions of years ago?

618
00:54:15,240 --> 00:54:20,120
In this episode, we met
the delightful oddity Metaspriggina.

619
00:54:22,120 --> 00:54:24,120
Looks like he's screaming
for his life.

620
00:54:25,480 --> 00:54:27,880
To paint a picture of
this ancient animal,

621
00:54:27,880 --> 00:54:30,640
scientists have to start
with the evidence.

622
00:54:33,080 --> 00:54:35,600
And in the case of Metaspriggina,

623
00:54:35,600 --> 00:54:40,800
that evidence came in the form
of a fossil site unlike any other.

624
00:54:43,360 --> 00:54:47,000
The Burgess Shale is an exceptional
preservation site,

625
00:54:47,000 --> 00:54:51,240
and that's because there was
a big underwater mudslide

626
00:54:51,240 --> 00:54:54,600
that swept all the animals away
into anoxic waters.

627
00:54:55,800 --> 00:54:57,960
And without oxygen in the water,

628
00:54:57,960 --> 00:55:00,160
the microbes couldn't
decay their bodies.

629
00:55:01,600 --> 00:55:04,920
Meaning they were
perfectly preserved,

630
00:55:04,920 --> 00:55:11,640
trapped under layers of silt,
until 500 million years later,

631
00:55:11,640 --> 00:55:15,320
their faces saw the light of day
once again.

632
00:55:15,320 --> 00:55:18,200
It's almost like they have been
caught by surprise.

633
00:55:19,360 --> 00:55:24,360
Entire shoals of Metaspriggina,
preserved perfectly.

634
00:55:25,920 --> 00:55:28,320
Most of the fossils we know
and are familiar with

635
00:55:28,320 --> 00:55:31,960
are things with hard parts,
things like bones and shells.

636
00:55:31,960 --> 00:55:34,560
But the Burgess Shale
was exceptionally different

637
00:55:34,560 --> 00:55:38,040
in that you get
soft body preservation.

638
00:55:38,040 --> 00:55:43,880
Everything from muscles
to cartilage, even internal organs.

639
00:55:44,960 --> 00:55:46,840
Metaspriggina...is tiny.

640
00:55:46,840 --> 00:55:49,480
The fact that we were able to get
so much detail off of them,

641
00:55:49,480 --> 00:55:52,960
after so many hundreds of millions
of years, is mind-boggling.

642
00:55:59,400 --> 00:56:01,160
With this knowledge,

643
00:56:01,160 --> 00:56:05,520
we can begin to reconstruct exactly
what Metaspriggina looked like.

644
00:56:14,160 --> 00:56:16,960
This was an animal
with visible gills, eyes,

645
00:56:16,960 --> 00:56:18,840
even something
you might call a face.

646
00:56:20,640 --> 00:56:24,040
But understanding the appearance
of an extinct animal

647
00:56:24,040 --> 00:56:26,920
isn't the only challenge.

648
00:56:26,920 --> 00:56:30,520
Fossils don't tend to move,
and so bringing these animals,

649
00:56:30,520 --> 00:56:33,840
these organisms, back to life
is actually...

650
00:56:33,840 --> 00:56:35,760
It's a massive endeavour.

651
00:56:39,440 --> 00:56:41,680
The preservation is really,
really exceptional.

652
00:56:41,680 --> 00:56:44,000
We can see so much of the details
of the muscles.

653
00:56:44,000 --> 00:56:47,080
We can actually reconstruct
how they moved and how they swam.

654
00:56:49,080 --> 00:56:54,640
Looking closer, scientists noticed
distinct W-shaped muscle lines

655
00:56:54,640 --> 00:57:00,160
in the fossils, identical to those
found in some modern-day fish...

656
00:57:02,240 --> 00:57:07,440
..meaning Metaspriggina must have
swum in a similar way,

657
00:57:07,440 --> 00:57:10,240
swishing its body from side to side.

658
00:57:11,480 --> 00:57:14,440
I think the VFX reconstruction
is outstanding

659
00:57:14,440 --> 00:57:18,320
and is true to how this animal
would have moved in the water.

660
00:57:18,320 --> 00:57:24,320
Thanks to these discoveries, we can
bring Metaspriggina back to life.

661
00:57:24,320 --> 00:57:29,120
Metasprigginas really did change
our understanding of the story

662
00:57:29,120 --> 00:57:31,240
of the evolution of life.

663
00:57:31,240 --> 00:57:35,280
It's incredible to think
these simple, tiny little forms

664
00:57:35,280 --> 00:57:38,840
are the ancestors of
such diversity of life today.

665
00:57:43,400 --> 00:57:46,880
Do you want to know how an elephant
is related to a clownfish?

666
00:57:46,880 --> 00:57:51,080
Discover more in a poster from the
Open University on the tree of life.

667
00:57:51,080 --> 00:57:52,560
To get your free copy,

668
00:57:52,560 --> 00:57:54,520
scan the QR code on screen,

669
00:57:54,520 --> 00:57:55,560
or ring...

670
00:57:58,640 --> 00:57:59,680
..or visit...