Original subtitles

Look at this!

What an extraordinary place.

These caves are home to a creature that is undeniably

one of evolution's weirdest.

Oh, my goodness, look at that.

That is spectacular!

The cave is caked in bats.

Using ultrasonic clicks, they can navigate in darkness.

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

..bats are the only mammals that can fly.

But there's something even weirder about them.

Each evening, they begin swarming...

Oh, my goodness me, look at that!

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

..an almost unrivalled need to feed.

Flight is an enormously energetically expensive exercise,

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

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

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

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

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

and a lot of it.

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

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

..way back in time,

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

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

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

..came to be.

Our story begins in the shallows of an ancient ocean...

..where today, a new life is emerging.

This is a distant ancestor of the bat

and all of us.

Its home is an alien-looking ecosystem,

known as the Ediacaran Garden...

..and its neighbours are some of the strangest animals

to ever live on our planet.

Now, I know it might not look like much,

but this little creature is about to play a pivotal role

in the story of life on Earth...

..one that would change eating forever.

Now, the Ediacaran is one of the most enigmatic periods

in our Earth's history,

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

of large, complex animals in the geological record,

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

Just look at this.

That's pretty good, isn't it?

This is Charnia.

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

but scientists can tell that at least some of these specimens

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

so we think that it was an animal.

Now, take a look at Dickinsonia.

Now, that is special.

That is a beautiful fossil.

550 million years ago,

these bizarre animals are thriving,

because they have plenty to eat.

Why was that?

Well, I can show you with a third fossil.

And I know what you're thinking -

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

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

But you've got to look more closely.

These are traces of millions,

billions, trillions of tiny microbes.

These microscopic organisms are the secret ingredient

of the Ediacaran Garden.

So numerous, they form a nutritious green mat,

several centimetres deep,

that carpets the seabed in every direction.

For the animals that live here,

the floor is literally made of food.

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

including, of course...

..the bat's ancestor.

Officially, its name is the Urbilaterian.

It spends its days leisurely grazing,

hoovering up microbial mat into its mouth...

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

Not terribly pleasant!

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

but from a creature alive today.

This blobby animal is called an acoel.

It's a marine organism.

They normally measure only a few millimetres in length,

and you can find them all over the world.

This particular species is called Hofstenia miamia,

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

You see, acoels are what we call basal animals.

A long time ago,

they went down a certain evolutionary road different than

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

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

shaped a bit like a sack.

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

So, for the Urbilaterian,

the simplest route for waste to come out

is the same way the food came in.

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

Compared to the rest of its kind,

this individual has a genetic difference,

a mutation...

..that almost imperceptibly lengthens its body.

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

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

of a tiny reproductive pore.

Over many generations, subsequent mutations lengthen the body further,

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

..they connect...

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

..a tube that changes everything.

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

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

it had a new body part.

Aside from a mouth to take food in -

just like you, just like me,

just like everything that walks, flies and slithers -

it had another hole to excrete the waste.

It had a bottom.

It had a bum!

Technically speaking, it had an anus.

Now, I know what you're thinking.

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

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

But then think about the alternative,

and the advantages become immediately clear.

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

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

See what I mean?

The anus was a breakthrough.

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

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

It can poo!

And this is a superpower!

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

..eating more than any animal that came before.

In their quest for food,

the ravenous worms burrow into the microbial mat,

devouring it and churning it up...

..disrupting an ecosystem that had dominated the Earth

since life's inception.

And as the microbial mat declines...

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

The evolution of the anus may well have led

to the first mass extinction of animal life on Earth.

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

an extinction event.

It helped animal life take on a bold new form.

The sea anemone and the nudibranch, the sea slug,

are two soft-bodied marine organisms.

They look pretty similar.

But the extraordinary thing is that I am more closely related

to that nudibranch than it is to that anemone.

So, why is that?

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

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

evolutionary path before the development of that through-gut.

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

It can poo,

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

The anemone has a circular body plan...

..but the nudibranch is symmetrical down the middle.

It has what we call bilateral symmetry...

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

And the through-gut unleashed the full potential

of this bilateral body plan.

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

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

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

So, think about it.

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

like eyes to look for that food.

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

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

when they find that food.

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

What you've got is a head.

A head!

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

it had to evolve an arse first!

I love that!

A head end and a tail end,

joined by a through-gut,

proved to be a winning formula...

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

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

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

It is hard to understate what a revolutionary moment

the evolution of the anus was.

Microbial mats, which for three billion years had been

the dominant ecosystem on Earth, all but disappeared.

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

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

And for animals,

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

Its increased efficiency meant they could grow bigger,

move more purposefully.

And it cemented the bilaterally symmetrical body plan

over other options.

The drive to find food had changed the course of life on Earth,

and it wouldn't be the last time.

The worms unleash a new era of eating.

Fuelled by the extra energy they're gathering...

..their descendants develop more complex bodies...

..and keener senses for finding food.

Just 35 million years later,

one of those descendants is a worm no more.

We might even call it a fish.

A small fish, living in a very big pond.

The oceans of the Cambrian Period are dominated by giant arthropods -

early cousins of insects.

Among them, Earth's first top predators.

And the secret to survival for this little fish

comes down to its strange mouth.

Now, take a look at this. It's the fossil of that primitive fish,

about five centimetres long. It's called Metaspriggina.

Just look at the detail that you can see here,

particularly at the front of its head.

These two black dots, those are its eyes.

And under scrutiny, scientists have discovered

that they are pointing upwards, so it could be that this little fish

was swimming along on the bottom, using those eyes to look up into

the water column for any potential predators -

perhaps those giant arthropods -

that might have made a tasty snack out of a tiny fish like this.

There's another photograph here.

This time, we're looking down on it,

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

structures which support gills.

As it swims,

a constant stream of water flows into the fish's open mouth.

This is how Metaspriggina breathes -

passing water over its gills,

supported by those gill arches.

But this mouth is multipurpose.

Something else is extracted at the same time.

Metaspriggina is a filter feeder.

And getting both oxygen and food into their bodies fast

is critical if they want to survive these perilous waters.

This is survival of the fittest in action,

and it means this fish,

its strange mouth and those gill arches hidden deep within

are already on a path that will shake up the world of eating

all over again.

Scientists have found that Metaspriggina's front gill arches

are actually thicker

and appear to lack oxygen-absorbing gill filaments,

a tantalising hint that they may have jettisoned their old role

for a new one - keeping the fish's gaping mouth wide open.

Because thick gill arches lead to a wider mouth,

more food and oxygen and more energy to escape...

..it's an advantage that's passed on.

Across countless generations,

the gill arches continue to thicken and strengthen.

New structures erupt...

..and after tens of millions of years...

..what was once a gill arch...

..becomes a revolutionary new body part...

..which means this fish...

..can bite!

Many body parts have been lost to the passage of time.

Whales and dolphins have lost limbs,

and fish that have been marooned in pitch-dark cave systems

have lost their eyes.

Even the not-so-humble anus has disappeared on multiple occasions.

But jaws, never.

Jaws are simply too useful.

Look, jaws didn't just change how animals ate,

but where they ate.

This little creature is a mud skipper,

one of around 25 species of fish

that you can find all over the world,

typically in intertidal mangrove swamps like this.

Now, what's extraordinary about them

is the amount of time that they can spend out of the water...

..some of them 90% of their lives, and they're able to do that

because they've got some remarkable adaptations.

Firstly, this little fish is breathing through its skin.

It also has jointed pectoral fins,

which means that it can skip across the surface of the mud,

almost as if it were walking.

So there are some behavioural comparisons there that we can make

with those fish that struggled out of water, onto land,

375 million years ago,

to begin an amphibious lifestyle.

But here's one thing.

They couldn't have done it without jaws.

Just think about it.

If these and those fish were dependent upon filter feeding,

dependent upon that water carrying morsels of food into their mouth,

that would mean that no matter how much time they could spend on land,

they would have to return to water to feed.

The difference is they've got jaws - they can bite.

And you can bite just as well out of water as you can in the water.

Thanks in part to the evolution of the jaw,

fish were no longer reliant on feeding in water...

..opening up a new world of possibilities.

Now, I know it's going to sound absurd...

..but from an evolutionary perspective at least,

these elephants are - wait for it - jawed fish.

Of course, they're highly modified jawed fish, but fish nevertheless.

But then so am I, so are you,

so is every other terrestrial animal that's got a backbone and a jaw.

So, here in Borneo,

that means 300 species of reptile, 150 amphibians, 650 birds

and 250 species of mammal,

all of whom are descended from those fish

that made that leap out of the water.

ELEPHANT GRUNTS

Globally, there are at least 30,000 species of vertebrates

living on land, with a dizzying array of jaws,

adapted to many different ways of feeding.

Some are lined with teeth, others have become beaks.

And some open so far,

their owners can swallow meals wider than their bodies.

What began as a tiny Ediacaran creature...

..gave rise to a through-gut

and a worm with an appetite that upended the world...

..and led to a fish

with a jaw that could finally take a bite.

From their aquatic origins,

jawed animals spread to all corners of the globe...

..and diversify to exploit new sources of food.

Until, 200 million years later,

we find one of them on the move.

This is Agilodocodon.

It's a female, and she's tiny...

..the size of a shrew.

With warm blood and fur, she's a primitive mammal

who spends most of her time hunting insects in trees.

But right now, it's not her own hunger she's concerned with...

..it's theirs.

Mammals have a quirky advantage over many other types of animal.

You see, we don't have to find food for our babies.

We don't abandon them to find their own.

We make it, and milk is the perfect food for a growing infant.

And it's perfect, unlike so many other types of food,

because evolution has driven it to be so.

Of course, milk, made by mammary glands,

has given us mammals our name.

But the evolution of milk impacted more than just babies.

It's changed how mammals feed at every age.

I've got a couple of lovely skulls here.

This is from a crocodile, and this one from an orangutan.

Now, they're clearly very different in terms of their size and shape,

but also their teeth.

Let's take a look at the crocodile first.

Its teeth are very simple, and they're pretty much all the same -

cylindrical at the base, peg-like and sharp, ideal for grabbing

and then gripping their prey.

But, look, you can see that they don't fit together terribly well.

There are large gaps in between them.

Contrast that with the skull of the orangutan.

Its teeth are not so simple.

They come in a range of forms.

You've got these at the front here.

These are the incisors that are used for slicing and nibbling.

And then you've got these very powerful canines

for piercing and gripping.

And lastly, when I fit the jaw on as it would sit in life,

look at these teeth at the back here.

They fit together almost perfectly.

These are the molars,

and one of the major reasons that molars have been able to evolve

comes down to milk.

The ancestors of mammals

had simple, reptilian-like teeth

that were replaced continually

as the animals grew.

But when they started to evolve milk,

babies were no longer reliant on teeth to feed.

Fewer sets were needed throughout life,

so this allowed more complex teeth to evolve.

In the mid Jurassic,

it's thought that the young of species like Agilodocodon,

now sustained entirely on milk,

are born toothless.

It's only because their adult molars don't emerge

until their jaws are almost fully grown

that they are some of the first to interlock perfectly.

And this helps today's mammals do something

that's surprisingly rare in the animal kingdom.

Take a look at this beautiful orangutan here.

A female with a nursing youngster.

But put her beauty to one side and concentrate on what she's doing.

She is chewing.

We can chew.

Those gentle movements of the lower jaw,

those molars grinding up that fruit.

Imagine you had to take that fruit into your kitchen

and cut it up into chunks that you could swallow.

You'd have to slice it, you'd have to dice it,

and then you'd have to mash it.

But she's doing all of that with consummate ease.

Her teeth are highly efficient food-processing machines,

and what they're trying to do is grind that food up

to increase its surface area,

so that when it reaches the stomach and the gut,

the digestive juices can act upon it far more quickly.

It massively speeds up the rate of digestion.

I mean, contrast it with those crocodiles.

They swallow their food whole, or in massive chunks,

and it takes weeks to digest it.

But me, you and the orangutan,

we can have a meal and digest it in just a matter of hours.

For primitive mammals like Agilodocodon...

..this ability to chew helps drive a surprising evolutionary change.

Over generations,

a lower jaw, made of several bones, is gradually reconfigured.

One bone gets larger...

..whilst the others shrink...

..until a single, powerful lower jaw evolves.

The old jawbones wither away,

but not all are lost.

These are the remnants of those jawbones.

They're called the malleus and the incus,

although you might know them as the hammer and the anvil.

They're two of the smallest bones in our body,

and they're disconnected from the rest of our skeleton.

But the key thing is, when we were in the womb,

they started off as part of our jaw and then migrated up to our ear,

where they are joined by this bone,

and this one is called the stapes, or the stirrup.

And together, they connect our eardrum to our inner ear,

greatly enhancing our capacity to hear,

particularly a wider range of frequencies.

The evolution of the middle ear bones, known as the ossicles,

transformed hearing for modern mammals, meaning that today,

mammals have some of the most sensitive hearing of all animals.

It's remarkable to think that over 400 million years ago,

these tiny bones were part of an ancient fish's gill arches.

This is the power of evolution, right here in the palm of my hand.

No designer was involved in making these bones, which are currently

floating in your head, allowing you to hear what I'm saying.

All that was needed was life's relentless drive to find food.

That and quite a bit of time!

And time, of course, keeps ticking...

..and mammals, now with acute hearing, keep evolving...

..for tens of millions of years...

..until, one morning...

..a little mammal picks up a sound it's never heard before...

..a sound that, once again, would change everything.

By the time we get to the Cretaceous Period,

when T-Rex was on the prowl, most of those traits that we consider

to be typically mammalian are already there -

warm-bloodedness, fur, complex teeth in powerful jaws and acute hearing.

And that acute hearing meant that mammals had already conquered

the night, and it was going to prove to be significant.

You see, that classic myth that mammals at this time were living

in the shadow of the dinosaurs, it may not have been like that.

That hearing contributed to the fact that they could find more food.

Those jaws could catch it and process it.

They were getting more energy.

They were able to build bigger bodies.

In fact, some scientists think that those early mammals

could have been well on the way to standing shoulder to shoulder

with those giant reptiles.

But, of course, as we know, that story was going to be cut short.

The sound the mammal heard

had its origins thousands of kilometres away...

..where, an hour or so earlier,

a rock, 12km wide,

had plunged into the Gulf of Mexico.

In a moment, the world is changed irrevocably.

The day that asteroid plummeted into the Gulf of Mexico

was probably the worst single day for life since it arose

around four billion years ago, because in that one chance moment,

life's progress was stopped dead - quite literally -

and millions of years of evolutionary tinkering

were wiped out in an instant.

And it was such a twist of fate.

Had that asteroid impacted just 30 seconds later,

the Earth would have spun on its axis.

It would have smashed into much deeper water

and caused far less devastation.

You never know - those giant reptiles might not have died out.

We might have had mammals, but not the mammal fauna that we've got now.

There might have been no humans on Earth.

Standing here in this oil palm plantation...

..I'll leave you to make of that what you will.

And whatever happens, life will find a way.

Although in the 15-year winter that follows the impact...

..three quarters of species are erased from the face of the Earth.

A tiny fraction of mammal species endure.

We know this, of course, because I'm here, because you're here,

because all the mammals we currently share our planet with are here.

But what do we know about our shared ancient ancestors,

those creatures that survived the storm of all storms,

the almost endless night?

Well, we think they were small, rodent-like animals -

not a single species, but a group of them.

And they carried those traits like complex teeth,

which would have enabled them to eat a broad diet -

everything from rotting vegetation to insects,

which would have bounced back quite quickly after that near catastrophe.

They might have also been burrowing animals,

so they could get beneath the ground to avoid all of that climate chaos

which was causing so many other species to become extinct.

Just a few hundred thousand years after that apocalyptic day,

we start to see the descendants of those surviving mammals

in the fossil record.

In a world vacated by dinosaurs,

mammals rapidly diversified.

Among them, a remarkable new group...

..that would use their acute mammalian hearing

in a truly innovative way.

This is a replica fossil of an approximately

52-million-year-old creature called Icaronycteris.

And you might be able to guess what type of animal it is.

Firstly, look at its fingers here - very long and narrow, extended.

I'll give you another clue by turning it up this way.

Yes, those fingers have transformed into wings.

This animal could fly.

This is the fossil of a bat.

Now, there's a lot more we need to learn about the evolution of bats.

There's a big gap between that period when the asteroid hit

and this, 14 million years later.

And the reason for that is that these delicate, light, little bones

don't fossilise terribly well. We don't find many fossil bats.

But scientists have X-rayed this skull

and they found that inside its inner ear, it has an enlarged cochlea.

And that, alongside the fact it had ossicles,

might suggest that this creature could echolocate.

What about that?!

Quite when creatures like this started to echolocate,

we're not sure.

Perhaps just after they could fly, perhaps at the same time.

But it's a beautiful specimen. I covet this.

I might actually steal it!

Because bat fossils are so rare...

..we don't know exactly why bats first evolved powered flight.

But combined with echolocation, it's an adaptation that pays off.

Despite being so energetically demanding,

flight allowed access to a great, untapped source of food

in the night sky.

Today, they're one of the most successful

mammalian lineages on Earth...

..with over 1,000 species of echolocating bat...

..inhabiting every continent except Antarctica.

Here in Borneo, there are more bats than any other type of mammal.

Among them, those wrinkle-lipped bats

that roost in Gomantong Caves in their hundreds of thousands.

But bats don't just live in caves.

You can find them in the most unexpected of places.

Oh, yes, yes, yes! Look at that!

It's a little cluster of bamboo bats.

And this is where they like to roost -

in these hollow stems of bamboo.

One of the smallest bat species in the world,

one of the smallest mammals in the world, they can weigh up to 5g.

That's about the same size as a large bumblebee.

Look at them all in there.

Oh! I honestly didn't think we were going to find any.

Any minute now, when these bats emerge to hunt,

they will be able to fly at speeds of several metres per second,

and they're able to do that because they can digest their insect prey in

about 30 minutes - quick enough to power their fiery metabolism,

the metabolism that allows them to fly.

And then, of course, they've got that extremely acute hearing.

They can hear frequencies five times higher than I can.

That means they can detect their echolocation calls,

find those tiny insects metres away, out there in the darkness.

In so many ways, they are extraordinary organisms...

..but then, in some ways, they're really quite ordinary.

Just like their Ediacaran ancestor that lived half a billion years ago,

they're bilaterally symmetrical.

They've got a head end, a back end, and a through-gut

running in between, like 99% of all of the animals that live on Earth.

And just like all of the vertebrates living on this island,

they've inherited a jaw from that ancient fish

that struggled onto land.

Their ears have those ossicles, just like ours.

We're both born helpless, completely dependent upon our mothers,

and the hormones that make them hungry

are the hormones that make me hungry, too.

From the humblest beginnings...

..millennia by millennia,

mouthful by mouthful...

..the need to feed transformed life on Earth.

Evolution is at times brutal,

but also exquisitely beautiful...

Wow!

..as echoes of these ancestors live on...

Oh! So good.

..and not just in the bat.

Now, I share about 92% of my genes with these little bats,

so you could say that their evolutionary story

is my evolutionary story, is your evolutionary story.

And so many of the things that make them extraordinary

are the things that make you extraordinary, too.

And it's not a story that's come to an end.

Life goes on. Evolution goes on.

So I want to ponder at this point -

what if our species can finally get a grip on all the terrible damage

that it's doing to this, our one beautiful home?

Just where might evolution take us all next?

Next time...

..how did the dolphin get so smart?

Absolutely amazing!

From the first animals to set eyes on our world...

..to the land-based ancestors who stepped back into the oceans,

reshaping their minds,

giving rise to the dolphin and its brilliant brain.

Oh! My goodness me!

I've just been to dolphin heaven!

But first...

..how do we bring ancient creatures to life?

- Oh! It's so cute!

- HE CHUCKLES

- I love the mouth.

- Such a weird creature as well, isn't it?

- Throughout Earth's history,

animals have evolved into all manner of weird and wonderful forms...

..but how do we know what they looked like

when they lived millions of years ago?

In this episode, we met the delightful oddity Metaspriggina.

- Looks like he's screaming for his life.

- To paint a picture of this ancient animal,

scientists have to start with the evidence.

And in the case of Metaspriggina,

that evidence came in the form of a fossil site unlike any other.

- The Burgess Shale is an exceptional preservation site,

and that's because there was a big underwater mudslide

that swept all the animals away into anoxic waters.

And without oxygen in the water,

the microbes couldn't decay their bodies.

- Meaning they were perfectly preserved,

trapped under layers of silt, until 500 million years later,

their faces saw the light of day once again.

- It's almost like they have been caught by surprise.

- Entire shoals of Metaspriggina, preserved perfectly.

- Most of the fossils we know and are familiar with

are things with hard parts, things like bones and shells.

But the Burgess Shale was exceptionally different

in that you get soft body preservation.

- Everything from muscles to cartilage, even internal organs.

- Metaspriggina...is tiny.

The fact that we were able to get so much detail off of them,

after so many hundreds of millions of years, is mind-boggling.

- With this knowledge,

we can begin to reconstruct exactly what Metaspriggina looked like.

- This was an animal with visible gills, eyes,

even something you might call a face.

- But understanding the appearance of an extinct animal

isn't the only challenge.

- Fossils don't tend to move, and so bringing these animals,

these organisms, back to life is actually...

It's a massive endeavour.

- The preservation is really, really exceptional.

We can see so much of the details of the muscles.

We can actually reconstruct how they moved and how they swam.

- Looking closer, scientists noticed distinct W-shaped muscle lines

in the fossils, identical to those found in some modern-day fish...

..meaning Metaspriggina must have swum in a similar way,

swishing its body from side to side.

- I think the VFX reconstruction is outstanding

and is true to how this animal would have moved in the water.

- Thanks to these discoveries, we can bring Metaspriggina back to life.

- Metasprigginas really did change our understanding of the story

of the evolution of life.

- It's incredible to think these simple, tiny little forms

are the ancestors of such diversity of life today.

- Do you want to know how an elephant is related to a clownfish?

Discover more in a poster from the Open University on the tree of life.

To get your free copy,

scan the QR code on screen,

or ring...

..or visit...