Original subtitles

These waters are home to an animal exquisitely adapted

to life below the waves.

I'm talking about the dolphin.

DOLPHIN CLICKS

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

and yet we share so much.

Oh, my goodness me!

Absolutely amazing.

DOLPHIN WHISTLES

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

..have sophisticated communication...

..work together to solve problems...

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

CHRIS EXHALES LOUDLY

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

I've never experienced anything like this before.

Absolutely magical!

Driving this playful curiosity is a giant, complex brain.

Some even larger than ours.

Dolphins are amongst the most intelligent creatures

to have ever lived on Earth.

What is intelligence?

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

but a lot more difficult to answer.

You see, across the animal kingdom,

there are a range of species that demonstrate intelligence.

Some bird species, pigs, bees,

even humans,

but some of those animals are undeniably

more intelligent than others,

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

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

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

and follow a remarkable tale of transformation.

Back to a time before mammals.

Before brains.

Before anything...

..could even think.

Countless lives have contributed to this story,

but a few distant ancestors, each with remarkable lifestyles,

have left legacies that have echoed down the generations,

gifting the dolphin its brilliant brain.

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

..on a planet devoid of thought,

ideas, curiosity.

No animals live on ancient Earth.

But it is a home.

Single cells live a simple existence...

..with not a single brain cell between them.

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

..a revolutionary act is taking place.

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

..to sense light.

In that moment, where those first cells

developed the ability to sense the Sun,

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

It was truly a time of enlightenment,

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

Look at that!

There's a huge beetle over here,

lots of flies, of course,

and then moths.

Look at that beauty!

Stunning thing.

And of course they're turning up,

because moths are famously attracted to light.

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

that some bacteria detect light,

and not just contemporary bacteria,

but the bacteria that were living in those ancient oceans.

Modern animals like moths use a molecule called retinal.

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

Like a switch, this allows cells to sense light.

And genetic techniques have revealed something extraordinary.

Three billion years ago,

those ancient bacteria sensed light

using the same molecule - retinal.

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

the foundation of intelligence.

They didn't just sense light,

they reacted to light.

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

because they use what light there is at night,

typically the Moon and the stars,

to orientate themselves in their environment,

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

a basic instinct.

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

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

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

But that instinct,

fuelled by the ability to sense and react to light,

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

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

..2.5 billion years.

Life continues to evolve...

..until we enter a new age of animals.

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

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

But not from any predator.

From the punishing UV rays of the Sun.

To guide it, it has two light-detecting spots

that only sense patches of light and dark.

So, finding shelter is no easy task.

But among this population of shade-seeking animals,

the dolphin's ancestor has a slight edge.

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

..which mean instead of being flat,

its light-detecting spots

cave ever so slightly inwards,

becoming little dimples.

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

but they give it an unexpected advantage.

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

Here's a basic demonstration.

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

covered with all of those light-sensitive cells.

Now, when it's facing the Sun,

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

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

..and then it's not.

It's in shadow.

It's either or - light or dark.

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

Look at this bowl.

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

but look what happens as it turns away.

Parts of its surface are in shadow

whilst, simultaneously, parts are lit.

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

but this is the critical part -

shadow and light at the same time.

And this is what gives these early creatures

the chance to build up a rudimentary map of their environment

using light and shade.

For the first time ever,

creatures are beginning to see the world.

And in simple terms, these little dimples,

these little buckets,

are the first proper eyes.

For the dolphin's ancestor,

these simple, dimpled eyes

allow it to sense more than just shades of grey.

Instead,

it sees the first blurry images...

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

from the powerful Sun.

I know what you're thinking.

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

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

"don't fossilise particularly well?"

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

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

Simple, light-detecting spots still exist in some jellyfish

and limpets.

Dimpled, or "cup eyes",

are seen in modern-day flatworms.

And hiding in this forest is a curious creature

with eyes like tiny buckets.

This is a fascinating animal.

It's a velvet worm.

I've always wanted to see one.

What can it see? Well, looking out here,

a very crude picture of its environment,

but very little detail,

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

it would be declared legally blind.

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

this basic vision is more than sufficient.

But over half a billion years ago,

dimpled eyes were just the beginning.

Over generations, dimples grow deeper.

Protective cells grow over the opening,

forming a lens...

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

a retina.

In a surprisingly short period of evolutionary time,

those simple spots transform

into one of the most complex biological instruments

evolution has ever produced.

By the Cambrian period, sophisticated eyes are everywhere.

From those that come in pairs...

..to bizarre evolutionary experiments.

Now, you might be wondering

why I'm talking so much about eyes

in the story of intelligence.

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

played a critical role.

They changed the dynamics of life entirely...

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

..then they can also...

..see each other.

To stay alive now,

you need your wits about you.

In the Cambrian period,

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

so much so that we call it the Cambrian Explosion.

There are a number of theories as to why this might have happened.

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

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

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

and that alone would have driven an increase in diversity.

But it's not just about the eye.

Take a look at this fossil.

This is an anomalocaridid animal.

It lived 500 million years ago, it's related to lobsters,

and this was a ferocious predator in the Cambrian period.

And these are its eyes.

Beautiful!

Look at the preservation here.

And these are compound eyes, like contemporary insects

and crustaceans, and they appear to be on stalks.

We think that this animal could move its eyes

independently of one another,

looking in different directions at the same time.

This was a massive increase in visual complexity.

But how did the animal deal with it?

Well, look at this part here.

This represents an organ which is very, very, very rarely fossilised.

This is the animal's brain.

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

but it's only when complex eyes come on the scene

that fossilised brains are found.

We think these are the optic nerves,

passing all of that visual information to the brain

to be analysed.

Now, brains have got their own evolutionary history,

they didn't just appear overnight,

but in the wake of the Cambrian Explosion,

they got bigger and they got more complex,

potentially to deal with all of that visual information.

It's a beautiful fossil.

Without the evolution of light-sensitive cells,

we wouldn't have eyes, and without the evolution of eyes,

we wouldn't have brains as we know them today.

The modern animal kingdom is full of eyes and brains

attuned to perceive the world in whatever way is most useful.

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

Giant eyes that see like a camera gather information in the depths.

And forward-facing eyes help large brains navigate a 3D world.

But 500 million years ago,

animals and their newly-evolved brains

are just waking up to the world around them.

As we leap forward again...

..the struggle for survival drives brains to become more complex...

..and more strategic.

Welcome to the Silurian period...

..where the hunted have become the hunters.

This fierce-looking animal is an early female placoderm...

..and you don't want to mess with her.

You see, the predator-prey arms race...

..has turned her into one formidable fish.

Placoderms dominated the Earth's aquatic ecosystems

for 60 million years,

and I've got a fossil of one here, and what a fossil this is.

Just look at that!

It's very, very beautiful.

It came from Scotland and it lived 380 million years ago,

but look at the degree of preservation here.

You can see all the bones in its vertebrae, the dorsal fin here,

this is the head end, of course, here's its eye.

Look at that.

Oh, wow.

And I've never got over the fact that I can put my finger

on something which lived 380 million years ago.

But getting back to placoderms, you're going to say, you know,

"Why is this fossil so important? There are loads of animals

"that lived and died out. Why is this one such a big deal?"

Well, these were some of the first animals

that had a jaw and a backbone,

so if we want to learn more about what we call the jawed vertebrates,

and that's me, you, your children, your gran,

your pets, dolphins,

then we've got to learn more about placoderms.

Placoderm fossils of all shapes and sizes

have been found on every continent on the Earth.

Yet all share one intriguing feature.

Bony plates covering their heads.

Armour to protect the most precious weapon

a predatory fish has in its arsenal.

Its brain.

The predator-prey arms race had turned these creatures

into veritable little warships,

and I say "little" because this is a small one.

Some of them grew up to four metres in length.

But, sadly, as we know,

no amount of armour can protect us from some things.

In these ancient waters,

a hidden threat is lurking.

Despite its armour, this early placoderm

has fallen victim to a tiny invader.

A virus.

One whose impacts would ripple through time.

Viruses have always been pulling the strings of life.

They're master manipulators, silently and ruthlessly

invading their hosts to take advantage of them,

and we know how they work.

They break into their host's cells, hijack those cells' machinery,

and then replicate themselves...

..over and over and over again,

until they burst out in a dangerous explosion of infection,

giving us things like Covid, flu, common cold.

But not all viruses act in this way.

Some break into the cell

and then insert their own genetic material into the host's DNA,

potentially changing it forever.

These are called retroviruses...

..and we think that over 400 million years ago,

a retrovirus was circulating in the oceans,

infecting the bodies of many species of ancient fish.

One of whom may have been this early placoderm.

Luckily for her, however, her immune system kicks into gear...

..and she recovers.

But, like a Trojan horse, some of the virus

makes its way into her egg cells

and is passed on to her offspring.

Over generations, the hidden viral DNA does something extraordinary.

It triggers one of the fish's genes to go into overdrive...

..altering the way its nerve cells develop...

..causing parts of the brain to turn from grey

to eerily pale.

But instead of causing harm, the brain is changed forever.

These infections likely happened multiple times

in multiple species...

..and scientists think their effect has been profound.

Oh, my God!

It's a Jesus Christ lizard.

I used to look at drawings and read about these things

in my childhood animal encyclopaedias.

And it's named after the son of God

not because it so much walks on water

as runs very fast across the surface.

It's also got lightning-fast reactions.

So how does it manifest all of this speed, as it were?

Well, it comes down to its nerve cells.

You see, each of its nerve cells have long fibres called axons.

Those axons are wrapped in a fatty sheath

of a substance called myelin and it insulates them.

And what that means is that each nerve cell

can communicate with the other far more quickly,

and that happens in its brain

and it happens from the nerves that run from its brain

to the muscles around its body.

It's as if it's got a super-fast processor.

Nerve signals can travel up to 200 times faster

in axons insulated with myelin than those without.

And therefore we can make the argument that the origin of myelin

was the singularly most important development

when it came to the evolution of the vertebrate brain.

Now all we need this little lizard to do is something biblical.

Today, myelin is found throughout the jawed vertebrates.

All of these animals have myelin to thank

for the fast signals inside their brains.

And scientists have found that nerves insulated with myelin

can't be produced without ancient retroviral DNA...

..which has been transmitted down the generations

from fishes that caught a virus

over 400 million years ago.

Evolution. You just can't beat it, can you?

Well, you can, because it gets better.

You see, myelin didn't just speed things up,

it allowed brains to develop more computing power.

It allowed brains to evolve to become more compact,

more complex, more powerful.

It was as if life had just got a hardware upgrade

and this was therefore a significant step up

in the evolution of intelligence

because, for the first time, the vertebrate brain

was on the cusp of doing something it had never been able to do before.

Thinking.

Across tens of millions of years...

..fast-thinking vertebrates dominate the oceans.

But for the next chapter in the story of the dolphin

and its amazing brain...

..we need to step out onto land.

This strange, hairless, burrowing animal is a cynodont.

An ancestor of mammals, including the dolphin.

Now, it lives underground for good reason.

Predatory reptiles roam outside.

But, at some point, it's got to venture out to eat.

As the day comes to an end, there's an opportunity.

But there's just one problem.

It's getting dark.

Soon, its vision won't be much use.

Imagine what it was like for those little cynodonts.

Now, I've got a cast of one of these animals' skulls here.

You can see that "little" is the appropriate word.

This skull is about the same size as a rabbit.

So, they were small, opportunistic hunters.

The problem was that when they ventured out,

particularly in broad daylight,

there was a very good chance they'd be hunted themselves.

There were loads of predators stalking around the Triassic.

But when these little creatures ventured out of their burrows

into the night, there were distinct advantages for them.

At night there are fewer predators...

..and reduced competition for food.

But, of course, in the dark, food can be harder to find.

What they would have experienced is pretty much

what I'm experiencing now.

Human eyesight isn't brilliant in the dark

but it's not that bad either.

So, if I close my eyes, now I'm effectively blind, what happens?

Well, I immediately start to concentrate

on my other senses, of course. Firstly, hearing.

A bit of bird song... BIRDS CHIRP

..whine of insects. INSECTS BUZZ

Crickets.

RUSTLING A bit of rustling over there.

Incoming mosquito. BUZZING

HE SNIFFS LOUDLY What about smell?

Oh, yeah, that smells good.

I can smell all of that decomposing leaf litter.

That's what I call "forest fruitcake".

A really rich, delicious mix of odours.

And, I mean, I'm not bragging, but I like to think

that my sense of smell is quite well attuned in nature.

I've been sniffing it all of my life.

So, out here in the dark, I would be fairly confident

using my sense of smell to help me navigate.

Perhaps you wouldn't be quite so confident,

and that would have been exactly the same for those cynodonts.

Part of their population would have had senses

which were more finely attuned, and those would have been

the individuals that went out to forage, found food,

and then made it safely back to their burrows.

Super-sensing cynodonts would have fared better navigating at night.

And it's thought this allowed some groups to become nocturnal.

And as these cynodonts' senses sharpened to the night...

..we think the flood of new information being gathered

kick-started a monumental transformation

in their descendants' brains.

Over tens of millions of years, the brain changes shape.

Areas involved in smell and touch expand...

..and the brain increases in size by over 40%.

To process the new information, we see a game-changing region

develop in the top layers of the brain.

And with it, a new type of animal.

In under 50 million years, those burrowing cynodonts

had evolved into something a little bit like this.

The first mammals.

Now, I know that many of you probably aren't that keen on rats.

I love them.

I love their little whiskers, whisking away,

and those stiffened hairs are rooted in skin

which is packed full of nerves,

sending masses of information to its brain.

And then you've got its twitching nose.

A nose far more sensitive than ours,

capable of smelling things like explosives, even human cancers.

And its ears... Now, come on, those are the prettiest little ears.

Radar dishes listening out for the rustle of any potential predator.

But, of course, all of this extra sensory information

needs to be processed,

so it was at about this time that an area of the brain

called the neocortex began to develop more fully.

And that was utterly, utterly transformational

because it allowed these animals to solve problems,

to learn, to develop memories,

and, with all of that extra sensory processing,

to map their environment and plan their next move.

The neocortex was an extraordinary mammalian innovation.

And that neocortex is the outer layer of the mammalian brain.

Sometimes smooth, sometimes wrinkly and folded.

It receives and processes complex sensory information...

..and it links it to other regions the brain.

In today's mammals, it's essential for learning...

..planning...

..prediction...

..decision-making.

The foundations of what we'd call intelligence.

Now, of course, mammals aren't the only intelligent animals.

Birds have a structure called the "wulst"

that performs a similar function to the neocortex.

And octopuses have one centralised brain

and eight mini brains.

One for each arm.

But 200 million years ago, for the mammals,

the neocortex helped unlock a more intelligent way of life.

And to continue their story, we need to take another leap through time...

..until...

..it's the mammals' turn to take centre stage.

By now, those mammals have radiated out

and diversified across the globe.

And it's here that we find one unique group

on the verge of an extraordinary transformation.

This is Indohyus.

The size of a cat, with deer-like legs and the snout of a dog.

Quite frankly, it's a bit of a weirdo.

Tiptoeing on little hooves, it's on the lookout for lunch.

LOUD SQUAWK

But it's not the only one.

This diminutive plant-eater is easy pickings for predators

circling above.

But Indohyus has an escape plan.

A strategy adopted by another of evolution's oddballs.

Indohyus was a lot smaller and more dainty, but I give you...

..the tapir.

Oh, yes! CHRIS CHUCKLES

What an animal!

I absolutely love tapirs.

I've liked them since I was a kid. I don't know what it is about them.

I think it's because they're weird.

But what else have they got in common with Indohyus?

Well, they're both herbivores, and, as a consequence,

they need to be thinking about avoiding carnivores.

This Baird's tapir can be predated by jaguars.

So how do they avoid that?

Well, one of the things they've done is developed an aquatic lifestyle.

Now, if you don't want to be buoyant if you're in the water,

and, on that account, when they go into the water,

they sink to the bottom.

They can walk across the bottom of rivers, lakes and lagoons,

and that is the same as Indohyus.

Indohyus had heavy bones.

In fact, trying to evade predators on a day-to-day basis

was at the core of driving

one of the most revolutionary transformations in evolution.

For Indohyus and its heavy bones...

..water is a refuge.

And stepping away from land...

..turned out to be a masterstroke.

This new world offers up plentiful food

and new opportunities.

Over generations, their relatives become much more streamlined.

Limbs are replaced with paddle-like flippers.

Nostrils migrate further away from their long snouts.

Tails get flatter and more powerful.

And the once-hoofed mammals

are now completely aquatic.

This was one of the most astonishing body transformations

in the course of evolutionary history.

In just over 10 million years,

these tiny, terrestrial, tiptoeing animals

had transformed into sleek, streamlined swimmers.

And I've got the cast of a skull of one of them here.

This is Dorudon

and it lived 40 million years ago,

and the teeth do all of the talking.

Look here.

These massive canines for catching and gripping the prey

and then these teeth here

for shearing it into tiny pieces.

This would have been an impressive animal, but not the biggest.

One of its relatives, Basilosaurus,

grew to the length of a bus.

Those puny, cat-like animals

had transformed into monsters.

Superb.

But, of course,

things didn't stop there.

This is a cast of the skull of Simocetus,

a distant relative of Dorudon,

and it lived 32 million years ago.

But look at the skull -

pretty radically different.

It's much shorter, it's far more structurally complex on top here.

Simocetus was part of a new group of marine mammals -

the odontocetes, or "toothed whales".

Look at this depression here.

We think an organ called the melon might have sat here.

It's a fatty sphere. Sounds produced from the nasal passages are focused

through it like a lens and projected out into the animal's environment.

When they bounce back, they're captured by the lower jaw,

part of which is hollow, transferred to the inner ear,

which sends the information to the brain.

You know what I'm saying here, don't you?

Echolocation had evolved.

Echolocation!

What about that?

But we think something else radical

might have been happening at the same time.

We think that animals like this might have been

at the start of a journey from being solitary hunters

to hunting together,

and this social behaviour would have a profound effect

on the development of the brain.

As the toothed whales continued to evolve...

..it's thought that many of them became more and more social.

And the fossil record shows evidence of their brains getting larger...

..until, around 11 million years ago...

..an iconic family emerged.

Dolphins.

Today, over 40 species of dolphin can be found worldwide...

..from the tiny...

..to the giant.

They live in groups...

..and have complex social relationships.

And some species are amongst

the most intelligent animals on Earth.

This group of spotted dolphins

have spent their whole lives in the Bahamas.

DOLPHINS CLICK AND WHISTLE

And their social lives govern their behaviour.

Mothers, cousins,

friends, even rivals,

all roaming together in the waters they call home.

I've just been to spotted dolphin heaven!

I cannot tell you.

That was absolutely incredible.

At one point, I was just wrapped in a vortex of spinning dolphins.

Oh, my goodness me.

CLICKS AND WHISTLES

And, of course, we know that they all know one another,

not just now but throughout the course of their lives.

They've got that phenomenal memory.

And to think they are down there experiencing emotions

like joy.

I think they were feeling joy. I was certainly feeling joy.

But then we know that they can even experience grief as well.

DOLPHIN CLICKS

And the clicking!

The constant ticking. "Tick-tick-tick-tick", all the time.

They're communicating to one another.

Now, there's a dispute amongst scientists

as to whether they have a language,

but, from my point of view at the moment,

I'm quite happy to fantasise, because I would love,

absolutely love, to know what they were all saying to one another!

Honestly...

Honestly, so, so good.

This is the soundtrack of a thriving underwater society...

..underpinned by one of the most complex brains on Earth.

Relative to their bodies, it's one of the biggest of any animal,

with key regions thought to be involved in self-awareness,

communication and understanding emotions.

And that uniquely mammalian neocortex

has become one of the most intricately folded brain surfaces

on the planet.

Brains are amongst the most energy-expensive organs

to run in the body, but, boy, are they worth that cost,

because if you've got a large, complex brain, like those dolphins,

it gives you the capacity to develop intelligence.

And the dolphins use that intelligence

to change their behaviour on a day-to-day basis.

They can learn things.

They can then copy things from dolphins that have learned things.

They've got cultural learning capabilities.

And this social intelligence is the most important tool in the box

when it comes to survival.

But get this,

they evolved that intelligence

in a world which is completely alien to ours.

They evolved it...

..underwater!

We may never truly know what goes on inside the mind of a dolphin,

but its brain tells a remarkable story.

Three billion years of sensing...

..of struggle...

..and survival.

Of brains...

..and bodies...

..transformed.

Dolphins' minds, like ours for that matter,

are remarkable pieces of biology.

It's for very good reason that we think of our brains

as being the most complex objects in the known Universe

and they're still surrounded by an aura of mystery, of magic.

But here's one thing that we know for certain.

Our brains, our minds,

simply wouldn't exist without the power of evolution.

That blind journey of change,

of innovation, of exquisite beauty.

Next time...

..how the horse became one of nature's greatest athletes.

Just look at her.

She's absolutely gorgeous.

Aren't you?

From life's first steps...

..to racing hearts and limbs built for speed.

Let's see them in action.

DOG BARKS

This is a slithering, swimming, sprinting odyssey,

with one final twist.

Us.

But first, how do we know that the ancestors of dolphins

once walked on land?

- Dolphins are part of a larger group called cetaceans,

which includes dolphins, whales and porpoises.

- Cetaceans have the largest range in body size

of any group of mammals on the planet.

- From really small, little harbour porpoises

that are only a few feet long,

to the blue whale - the largest animal on Earth,

and everything in between.

- And their origin can be traced back to an ancient sea

that once stretched between India and Asia.

Local and international scientists have been searching for fossils

in India and Pakistan over many years,

where they found the remains of an intriguing mammal.

- What I'm holding in my hand here is a real fossil

of the skull of Indohyus.

There's four of these in the world.

I've got one right here.

- The name Indohyus actually means India's pig.

- From the chemistry of the teeth, we can tell that this animal ate

land plants, mostly leaves, and flowers and fruits.

- From first appearances, Indohyus looked like a regular land mammal...

..until a chance event revealed a critical structure

hidden deep within its skull.

- I had a fossil preparator, his name was Rick,

who was cleaning this off, he said,

"I'm very sorry, but I broke part of this Indohyus skull",

and then I noticed that the ear bone actually shows a feature

that's only present in whales and dolphins, called the involucrum.

- The involucrum is a region of the ear bone that has thickened.

In modern-day cetaceans, it amplifies vibrations

transmitted in the skull, enhancing their ability to hear under water.

- So that's really the smoking gun that Indohyus is closely related

to whales and dolphins.

- Evidence that it was already adapting to a life underwater,

completing the remarkable story

of how land mammals evolved into marine cetaceans.

- It is one of the best fossil records we have,

so we've got a lot of pieces of the puzzle

to tell us what happened.

- Other transitional fossils have been found across the region

that was once the ancient Tethys Sea.

- We have whales and dolphins that look like crocodiles,

we have whales and dolphins that look like seals

or otters or sea lions.

- It is probably one of the most dramatic transformations

in all of the evolution of life.

Indohyus was not the kind of animal

that you would look at and say,

"You're going to get a blue whale out of that",

"You're going to get a brain like a dolphin brain out of that",

but that's what evolution does - it makes big changes.

- 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 0300 303 3460,

or visit connect.open.ac.uk/evolution