Original subtitles

They're not the prettiest...

..or the brightest...

..and it's fair to say...

..they're a bit odd.

But ostriches produce something truly astonishing...

..the biggest eggs on the planet.

Can I ask you to stop for a moment

and think about something truly remarkable?

Something so commonplace, so everyday, that we

take it for granted.

Life creates new life,

and it's happening right here in front of me.

If I bend down...

Oh, yes! I can hear it! RATTLING

I can hear it tapping.

It's as if it's yearning to get out of the egg.

Oh!

And you know, around 40 days ago, the chick that's just about to break

out of here into the big wide world was just a tiny collection of cells.

And look at this, it's started!

I can see inside, I can see its little eyes, its beak.

It's blinking at me.

Oh! CHIRPING

It's quite emotional, if I'm honest with you!

CHIRPING CONTINUES

So, how did this marvel of nature come to be?

Well, to answer that question we have to travel back...

..way back...

..before birds...

..before dinosaurs...

..before there were even eggs...

..following an unbroken chain of life that stretches back

over four billion years.

This is the extraordinary story of how evolution gave

rise to the ostrich, and its enormous egg.

THUNDERCLAP

These are some of the world's first living things.

They can't see, they can't hear...

..but right from the very beginning,

life on Earth was really good at one thing...

..reproducing.

But back then, they did it in a way that seems quite alien to us.

They split themselves in half to create an identical copy.

A clone.

As soon as life appeared on Earth, it began reproducing

and once it started, it did so at a remarkable rate,

churning out copy after copy after copy for billions of years.

The problem is, though, that when you're just copying yourself,

it means that life's scope is quite limited.

You see, for billions of years we had nothing with eyes,

nothing with legs, nothing with a brain, just single-celled

microbes, and it looked like life was just going to stay like that.

Imagine a world filled with nothing but microbes.

No plants, no insects, no birds of any kind.

And definitely no people.

You see, it's not that I've got anything against microbes,

but let's face it, life would be dull.

But for almost two billion years,

that's exactly how life was.

There was some mixing of DNA

and different species of microbe evolved.

But the chances of life getting any bigger than a pinhead looked slim.

Until...

..somewhere in this sea of simple cells...

..a revolutionary emerges.

Now, it may seem similar to all the microbes that came before it,

but it is in fact on a new branch of the tree of life.

You, me and the ostrich - we are all here today

because this microbe does something scandalous.

It takes a shine to another microbe.

Their cell membranes fuse,

allowing all their DNA to mix.

This is the first sex...

..and it would change the course of life on Earth forever.

It certainly wasn't romantic and it wasn't earth shattering,

but the first sex was a very big deal.

And to understand why, we need to understand what sex is,

and I know what you're thinking, don't worry. No naff diagrams.

Fundamentally,

sexual reproduction is about two living things coming together

to share their genes, to create new life, a new life which is unique.

And that's why the first sex was so pivotal, because after

billions of years of just copying, here was a chance for mixing.

The first sex set life on a new path.

The offspring of this pair won't be clones of their parents.

Instead, they'll inherit a random mix of genes from both.

Sex creates variety

and it sends evolution into overdrive.

Let's fast forward through the next one and a half billion years...

..during which time there is a sexual revolution.

Some cells join forces...

..leading to big, complex bodies...

..the first animals.

By the Cambrian period,

the oceans are filled with a huge diversity of animal life...

..from simple sponges to species

with eyes, legs and shells.

But all share one thing in common...

..they're a randy bunch.

We have a good understanding of how rich and varied life was in the

Cambrian seas, down to the enormous abundance of fossils that we've

recovered from that period, and you know how much I love a fossil.

Look at this Trilobite. What a beauty!

You can see it's got its segmented body here,

its rounded, smooth head, compound eyes.

And I can tell you that we've identified no less

than around 20,000 different species of Trilobite.

I've got another fossil here. Look at this.

This is an Eocrinoid,

an animal that's related to the sea urchins, and we think that the

bottom part of it here was rooted into the seabed and these tendrils

here would have been wafting in the water flow, getting its food.

So, there was a great diversity of life in those Cambrian seas,

but also a diversity of shape and size,

and that made sex altogether more challenging

because organisms like this couldn't reproduce in the same way that their

ancient single-celled ancestors did, by simply fusing together.

I mean, imagine a couple of trilobites like this trying

to get it on. It's not going to work, is it,

with the hard exoskeleton, all of their legs, their internal organs?

Nature needed to come up with a different way.

And nature's solution is an extremely effective one.

Back in the Cambrian, many animals have adopted it.

These tiny specks are eggs...

..and these even tinier ones are sperm.

And they do exactly what those ancient microbes did.

They fuse together and combine their DNA

to create a new, unique life.

The Cambrian seas are quite literally fertile oceans...

..but for many creatures here,

there's something unfamiliar about the way they go about reproducing.

A lot of people don't like snails. I'm not one of them.

There's something therapeutic about having them slime

up and down your fingers.

These are a highly successful group of animals.

There are more than 40,000 species in the world,

and one of the keys to their success is their reproductive capacity.

Like many snails, it produces sperm and eggs.

It's a hermaphrodite.

Let's think about the repercussions of that.

When this snail goes looking for a potential partner, any other that it

finds of the same species and about the same size, is a potential mate.

And once they've copulated, they can both produce a batch of eggs,

doubling the capacity to produce a lot more snails.

Now, this is such an efficient and successful strategy that many

scientists believe that the earliest animals were all hermaphrodite.

As soon as they could produce sperm and eggs, they produced both,

which begs the question, why aren't we all hermaphrodites today?

It's hard to know for certain, but there's a theory

that during the Cambrian, something upset the status quo...

..and it may have happened in a creature like this.

It's so bizarre, it's hard to believe it really existed.

But fossil evidence shows that it really did look like this.

It's a Vetulicolian.

It's not a fish, it's not a crustacean.

In fact, it's unlike anything that lives today...

..and it's radically different from its single-celled ancestors.

But it has inherited a key trait - a one-track mind.

Now, if we assume Vetulicolians are hermaphrodites,

that means that any member of the same species is a potential mate.

But when this pair come together to release their eggs and sperm...

..there's a problem.

You see, one of them was born partially sterile.

It can't produce sperm.

For many animals, this would be the end of their family line...

..but not for a hermaphrodite.

Because if it can still produce eggs...

..it can still reproduce.

Its genes get passed down to the next generation...

..and some of them are born partially sterile too.

So, think about it.

In biological terms, that snail, if it could only produce eggs,

we'd call it a female.

If it could only produce sperm, we would call it a male.

So, there is the possibility that the division of the sexes,

the origin of males and females, came down to a chance mutation,

that we were mistakes.

Today, only 5% of animal species are hermaphrodites.

The rest have separate sexes,

and it's thought that males

and females evolved multiple times, in many different species,

allowing females to specialise in producing fewer,

higher quality eggs,

whilst males make faster, more numerous sperm.

Nature is of course flexible.

Clownfish males can turn into females...

..seahorse dads get pregnant.

It really doesn't matter who does what.

it's being a specialist that counts.

For animal life, this specialisation is a turning point.

As we jump forward 150 million years,

it adds fuel to evolution's fire.

Fishes emerge and fill every marine habitat.

And eventually, some even brave a new frontier...

..the freshwater streams.

This ancestor of the ostrich is looking for a safe place

to lay her eggs.

With streamlined bodies and powerful tails...

..her shoal swim upstream with ease.

But...

..they're being followed.

If I were to time travel back to the Devonian,

you would not find me wading in a river like this.

No matter how sweaty the swamps were, I wouldn't be tempted

to take to the waters because I might lose my toes, or even my legs.

The rivers were filled full of predatory fish,

armed with sharp teeth for tearing through flesh.

Some of them the size of minnows, others the size of crocodiles.

If you were a fish living in here,

you'd have enough trouble protecting yourself, let alone your eggs.

Left unguarded in these ancient waters,

nutritious eggs don't stand a chance.

These fish need to find a safer breeding ground...

..or there'll be no next generation.

But they have something on their side that other fish don't.

This is a 3D scan of a fossil of one of those fishes.

And when you first look at it,

it looks pretty much like a modern, conventional fish - it's long,

fairly streamlined, it's got a bit of a blunt head there,

would have had a tail at the back for propelling it through

the water, and all of the fins are pretty much in the right places.

Looks a little bit like a salmon, but on closer inspection,

in fact it's very different.

Let's zoom in on this fin here.

You can see that it's much longer and the bones that

lead from it back to the core of the skeleton are much more robust.

It could be that it was using these fins to propel

itself along the bottom of the river.

They're much stronger than those delicate ray fins that we

see on modern fishes. These are fins that you could stand on.

The strong fins that help these fish move along the riverbed also

allow them to do something revolutionary...

..leave the river...

..and walk on land.

And beyond the main river lies a network of streams

the predators can't reach.

We can't be certain why those lobe-finned fish climbed

out of the water. I mean, they could have been

looking for food, they could have been avoiding being food themselves,

but there is the possibility

that they were looking for somewhere safe to lay their eggs, to spawn.

But one thing's for sure, once they waddled out of the water

and climbed onto land, there was no going back.

Fish with the strongest fins are more likely to reach

the predator-free waters.

They have more offspring, which inherit their strong fins.

Over countless generations, the bones get longer, stronger...

..and better for walking on land...

..until eventually, after millions of years,

a fish's fin has become a limb.

There's absolutely no doubt that this was a pivotal moment.

I mean, think about it.

Life on Earth had evolved in water, and up until this point,

almost all life was still living in water.

OK, around 100 million years earlier,

plants have made the difficult transition onto land,

insects had managed it, too, but now here was a new group -

animals walking on land on four legs and four feet for the first time.

The amphibians.

Now, I'm about to show you something which is remarkable,

astonishing even, and I think very beautiful.

Take a look at this.

This is a drawing of the bones in the foot

of one of those ancient amphibians.

It lived over 300 million years ago.

But look at it.

Does it look familiar? It should do.

That's because these ancient amphibians were our ancestors,

and not only our ancestors, but the ancestors of all the animals

with backbones that have ever lived or are living on land today.

If those ancient microbes hadn't discovered sex, bigger,

more complex animals may never have evolved.

We wouldn't have males and females...

..with precious eggs,

that need protecting.

And the ancestors of every land animal with a backbone,

including the ostrich, and us...

..may never have left the water...

..and evolved to live on land.

Now, we jump forward tens of millions of years...

..and the amphibians are the planet's dominant land animals.

But no reign lasts forever.

This is Casineria.

She can live happily in water and on land...

..but like many animals here, Casineria is in trouble.

Drought has set in.

Swamps that once stretched as far as the eye can see are now

little more than muddy puddles.

To understand why this was a problem...

..we only have to look at amphibians today.

Clearly out of practice, but I did manage to catch one.

This frog is rather attractive, I have to say.

Look at those eyes, like little golden jewels.

It looks slimy, but it's not.

It's shiny, and it's shiny because it's wet,

and when it's wet, frogs like this can breathe through their skin.

But it does need to be wet.

So, there's an inherent vulnerability there.

They do need to return to water. They can't dry out.

And it's not just the adults.

Their eggs need water too.

Amphibians can't reproduce without water.

In periods of drought, amphibians suffer.

But Casineria has managed to cling on.

Her survival is partly down to luck, but also,

the unique mix of genes she inherited.

Now, had I been a bit sharper

and been able to catch another one of these frogs,

then probably, to you and I, they would look identical, like clones.

But of course they're not, because frogs reproduce sexually.

They mix their genetic material to produce unique individuals

and this doesn't only make life more interesting.

Critically, it makes life more resilient.

Think about it.

At this point in time,

this lovely stream is probably the perfect place for this frog to be.

But what about if conditions change?

What about if it got drier or wetter or the vegetation changed,

or something much more subtle like the mineral content of the water?

Well, because every frog is different,

some will fare better than others.

They'll live longer and have more offspring, and those

offspring will inherit the genes that helped their parents survive.

Essentially, that's what we call survival of the fittest.

Casineria's unique mix of genes determines everything from her

size to her skin colour.

And it also determines her eggs.

As luck would have it,

they're better at retaining moisture than most amphibian eggs...

..and in these dry conditions, that difference means everything.

The slightest variation in the surface structure or composition

of the egg is all it takes for one egg to survive

when others don't.

And as generations pass, the egg begins to change.

The surface gets tougher and thicker.

Special membranes form to prevent moisture loss.

The egg gets larger, stronger, and takes on an iconic shape...

..until eventually, after millions of years,

something extraordinary has emerged...

..an egg that can survive on dry land.

From dying swamps, entirely new groups of animals emerge.

Among them, the reptiles.

Look at this rock monitor, what a beauty!

Sadly, you don't have time to watch me

falling in love with a lizard, so let's look at the similarities

between this animal and those ancient amphibians.

Well, firstly, it's got the same streamlined nose

and long tail there.

Then look at her limbs, all four of those legs and feet,

strong with those sturdy bones that have been

passed down generations from the lobed-fin fishes.

But there are differences too.

The skin is a striking one.

I mean, that is not shiny, moist and breathable.

It's scaly and hard. It's about keeping moisture in.

And then critically,

this reptile doesn't need to return to water to breed.

You see, the amphibians might have been first to walk the Earth,

but they were always limited by that need for water.

It was the reptiles which really conquered the land.

Reptile eggs are far more sophisticated than the jelly

blobs of the amphibians.

Known as amniotic eggs, they have a tough outer shell,

a nutrient rich yolk, and perhaps most extraordinary of all,

a special sac of fluid in which the embryo

floats in its own private pool.

The amniotic egg is like a pond on dry land.

But when it came to sex,

these new high-tech reptile eggs presented some challenges.

You see, an egg like this,

and this is a crocodile's egg, is no good on its own.

It's got to be fertilised.

But there is absolutely no chance

of a sperm breaking through this shell, so what's the solution?

Well, the solution is to get the sperm to the

egg before the shell goes on, before the egg is laid.

You see, the reptiles didn't only have to reinvent the egg,

they had to reinvent sex.

The solution is found on almost every male reptile today.

It begins to grow around the tenth day of life.

A tiny bud, like an extra limb.

It's a penis.

Reptiles were amongst the first animals to get penises...

..but they certainly weren't the last.

The blue whale has the largest, averaging 2.5 metres.

The gorilla has one of the smallest, compared to its body size.

Duck penises are shaped like corkscrews...

..and cats' are covered in barbs.

Penises are as diverse as their owners.

Now, despite what some people say, penises are limited in size,

even for blue whales.

So, therefore for the males to deliver the sperm where

they need to, they need to get close to the females.

They need to mate...

Bonking, shagging, making love...

The terminology that we use in scientific parlance is

copulation and the reptiles weren't the first to get at it.

Some ancient fish had been doing it for years,

but when it came to life on land, sex as we know it had been invented.

With their sophisticated eggs...

..and a new way to fertilise them...

..the reptiles went forth and multiplied.

Their fossilised remains have been found in abundance.

But world domination wasn't the only

consequence of their reproductive success.

The egg, the penis, copulation...

All of these adaptations helped with the mechanics of sex,

but what was to happen next was altogether different.

You see, copulation didn't only change the way that animals looked.

It changed the way they behaved,

and the consequences of that were extraordinary.

Around 100 million years after the first reptiles emerged...

..some of them have evolved into the most legendary creatures to

have ever walked the Earth.

This is Coelophysis,

one of the first dinosaurs.

Just like his ancient ancestors, he has strong legs for walking on land.

But like all early dinosaurs, he walks on two instead of four.

Bigger strides allow him to cover more distance, which is handy,

because this young male is looking for a mate.

There are plenty of females around.

The tricky part is getting their attention.

So how do you impress a female?

I'm probably not the best person to answer that,

I've been struggling all of my life,

but I reckon this guy's in with a chance.

What a magnificent animal, so handsome, honestly!

This is a Nyala, a Southern African antelope,

and this is a mature male, and he's very, very impressive,

certainly from that female's point of view.

OK, he doesn't have a sports car.

Doesn't need it, he's got these beautiful curled,

yellow-tipped horns.

Doesn't live in a mansion.

Doesn't need that either.

He's got those broad, powerful flanks.

And what's more, it's not just those characteristics.

It's the fact that he's lived long enough to be able to grow them.

I mean, imagine if this guy had been born short-sighted or with a limp.

He would never have survived.

His good looks are visible signs that he's fit and healthy,

and ultimately, that's what the females are looking for.

Getting pregnant, developing your youngster, giving birth,

then looking after it...

Those females can't afford to bank on a weedy male.

They want the genes from the real deal, like this guy.

When it comes to reproduction, it tends to be the biggest,

hairiest males that succeed.

Their genes get passed down, making future generations even bigger

and hairier than the last...

..which is how you end up with exaggerated physical

traits like this.

But let's be very clear here, these physical

characteristics are not necessarily directly related to survival.

What they're about is finding a mate, attracting that mate

and then successfully reproducing.

Evolution is not always about survival of the fittest.

It's critically about getting your genes into the next generation,

and that was as profoundly important to the dinosaurs

as it is to these Nyala.

For Coelophysis, just like the Nyala,

good looks are a sign that the male is in good condition.

And just look at that attractive fuzz.

But what's a male to do if no-one seems to notice him?

Scientists suspect that some dinosaurs did what many

animals still do today.

They show off.

It starts with head bobbing...

..followed by twirls...

..but to really impress her, he has one final trick.

It's irresistible.

His offspring will inherit his attractive fuzz,

and go on to have fuzzy offspring of their own...

..becoming part of an extraordinary evolutionary transformation.

Over time, fuzzy strands get longer, and wider, and split into

multiple filaments, making an even bigger surface area for display.

Until eventually, after tens of millions of years

and countless generations...

..those fuzzy strands are so exaggerated...

..they've become something new...

..feathers.

When the first fossilised feather was found, scientists were

struck by its similarity to the feathers of modern birds.

But this feather is 150 million years old,

placing it firmly in the era of the dinosaurs.

We don't know for certain what drove their evolution.

Insulation and camouflage may have played a role.

But we are now in little doubt

that some dinosaurs had feathers.

And many scientists believe it was the need to attract a mate

that transformed dinosaurs from scaly reptiles into flamboyant,

feathered creatures.

This is the tail feather of a ring-necked pheasant.

It's beautiful, isn't it?

And whilst it still serves as a tail, as you can see,

it's been given over to display.

It's elongated.

It's got this beautiful bronze colouring with all of these

spots and when it comes to display feathers, of course,

nothing beats the male peacock.

Look at that with that very distinctive eye.

But this is a typical feather. Look at it.

It's light, it's flexible, it's durable.

It's essentially repairable.

If those barbs are pulled apart, it can be fixed here.

But it's also symmetrical, very much

like the feathers that we first saw when they appeared on the dinosaurs.

But tens of millions of years later,

something different cropped up in the fossil record.

Something like this,

and you can see this is different because it's asymmetrical.

The quill or the rachis, if you like, here,

is much closer to this side.

Now, there is a theory which says that this was

the result of a chance mutation, that this was a mistake.

But if it was a mistake, it was a very fortunate one,

because by shifting the rachis closer to one side,

it means that when this feather is pushed through the air,

it generates lift like an aircraft wing.

The dinosaurs that were equipped with these could fly.

Around 25 million years after the first feathers evolved,

flying dinosaurs filled the skies.

Today, we have another name for them...

..birds.

For almost 100 million years,

they thrived alongside their giant cousins...

..and they were there to witness one of our planet's darkest days.

EXPLOSION

When we say that all of the dinosaurs became extinct,

it's not technically true, is it?

Because those that had evolved into birds survived,

and the ones that did best were the small ones,

they could hide away, and also those with a very broad diet.

But as the Earth began to recover, they had one other key asset,

the amniotic egg.

You see, with that embryo protected on the inside from the hostile world

on the outside, they could continue to reproduce, generation after

generation, to the extent that they didn't just survive, they thrived.

The surviving birds were largely ground dwellers.

Amongst them, the paleognaths,

some of whom would never

return to the skies.

Instead, they became big and heavy,

and better adapted for life on the ground.

And to allow their chicks to hatch fully formed and ready to run...

..their eggs evolved truly gigantic sizes.

And one of this group...

..produces the largest eggs of all.

Ostriches, our largest birds.

And look at them standing there on those strong legs,

with those sturdy bones that they inherited from lobed-fin fishes.

And I can see those legs are covered in scales,

so are their toes, signs of their reptilian ancestry.

And their feathers are no longer used for flying,

they're for display and brooding their young.

And of course, they don't need to return to water to lay their eggs.

These birds lay the largest amniotic egg on the planet.

They lay them on the dry ground,

just as their reptilian ancestors did.

And safely cocooned inside each one,

a new life begins floating in water,

just as it's always done.

These chicks are the next chapter of an extraordinary evolutionary

story, four billion years long...

..that reveals how the ostrich

and its enormous egg came to be.

And although those ancestors are long gone,

their legacy lives on, not just in the ostrich...

..but in all of us.

Just like this chick, all of us started our lives in water,

floating in that amniotic fluid in the womb, our very own private pool.

And that's because we share an evolutionary history with this bird.

We share ancient ancestors in a wonderful,

unbroken chain of reproduction, stretching back billions of years.

And of course, we're not just connected to ostriches.

We're connected to all life on Earth.

Everything that walks, flies, slithers, slimes and crawls,

we're connected to it.

And that's all down to reproduction.

Over time, sexual reproduction has shaped us

into different species...

..and sexual reproduction has one other

absolutely extraordinary impact.

It makes us all unique.

Nothing exactly the same as me, you,

or her has ever lived,

or will ever live ever, in the entire history

of this wonderful little blue planet we call home.

Next time...

..how the bat evolved one of the most

insatiable appetites on the planet.

Look at this!

Truly spectacular!

From a prehistoric anus that caused a mass extinction,

to gaping mouths...that became jaws.

And a surprising new way of finding food.

This is the incredible story of one of nature's... Oh!

..most formidable feeders.

Look at that!

But first...

..how do we know birds are living dinosaurs?

- When most people look at a bird, they don't see a dinosaur.

- The first clue of the extraordinary evolutionary relationship

between birds and dinosaurs came in the mid-19th century.

- The Jurassic species, Archaeopteryx, is an icon of evolution.

- Archaeopteryx certainly looked a little like a bird.

- It had feathered wings,

and yet upon those wings were fully functional three-fingered

hands with claws, which is reptile-like, and a long tail.

It had a head like that of a bird,

and yet, inside its mouth were rows of sharp teeth.

- So, Archaeopteryx wasn't just a bird.

It was also a dinosaur.

Other discoveries followed that left no room for doubt.

- Birds are a type of theropod dinosaur.

- We can see the evolutionary origins of many bird

traits among their ancestors, the dinosaurs.

Things like a beak, warm bloodedness, feathers, a wishbone.

- Tyrannosaurus rex itself has a wishbone.

- But one key question remains.

- What helped birds survive when all of their dinosaurian

relatives went extinct, for me is one of the most fascinating

questions in all of evolutionary biology.

- A question that could have remained unanswered

if it wasn't for a chance find.

- The first time I saw this fossil, I was not very enthusiastic.

It's basically just a block of limestone with a couple

broken bones poking out from it.

But we decided to take a closer look at it anyway.

- A CT scanner revealed what was hidden inside.

- When I first saw that skull on the computer screen, it took

a second of silence, and then I realised immediately that this

was one of the most important fossil bird specimens ever discovered.

- Daniel had stumbled across the oldest fossil of what

we would now recognise as a modern bird.

And it lived alongside dinosaurs just before the asteroid impact.

- It is toothless like modern birds.

Its beak looks quite a bit like a small chicken bill,

and that's interesting.

It suggests to us that this animal was probably a generalist feeder.

That is to say it wouldn't have been very picky,

just like living chickens.

- Being flexible was critical to surviving the asteroid impact.

- One of the best ways to survive was to simply have the

ability to eat anything.

- And that might have been one of the important features that

helped birds like this one survive the mass extinction event.

- These small chicken-like ancestors and a few other bird species

would make sure that not all the dinosaurs were lost.

- When I see an ostrich,

I see that the... The story of dinosaur evolution is not over.

- Today there are over 10,000 species of birds.

In some ways, we are still living in the age of dinosaurs.

- 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...