I've spent most of my life trying to understand
the forces that shaped our planet,
and as a geologist, it always seemed to me
that rocks were right at the heart of things.
But now, I'm discovering it's not only volcanoes and colliding continents
that have driven the Earth's greatest changes,
because at crucial moments in its history,
another force has helped create the planet we live on...
...plants.
It's a whole new story about the Earth,
revealing how, from its earliest history,
plants have shaped our world.
So far, we've seen how plants and their ancestors began
by producing our life-giving atmosphere.
I'm breathing oxygen that was made two-and-a-half billion years ago.
They'd harnessed light from the sun,
bringing energy to the world.
And they'd formed the fertile soil,
allowing life to colonise the land.
But the next chapter will take us even further,
because a powerful newcomer to the plant world was on its way.
It would conquer every corner of the planet.
It would shape the very surface of the Earth
and it would drive the evolution of animal life,
including our own ancestors.
This is its story.
These buildings are nearly 1,000 years old.
The largest religious site in the world,
covering 200 square kilometres.
This is the temple of Angkor Wat in Cambodia.
I am here to witness the importance
of one of the most powerful symbols known to humankind.
A symbol central to an ancient Buddhist ceremony.
Flowers.
(BUDDHIST CHANTING)
You see lotus flowers and jasmine just arranged beautifully up there.
The lotus are the big ones and the jasmine the trail of little flowers.
See how the lotus petals are all folded in amongst themselves,
the different layers representing the various levels of heaven.
For these monks, flowers have a crucial role.
And this is just one ceremony from one religion.
Flowers are central to cultures throughout the world.
They're deeply woven into all our lives.
But it's not only a human obsession.
Because since they evolved,
flowers have been the driving force for the whole of life on Earth.
They've become enmeshed in the lives
of virtually the entire animal kingdom in all its rich diversity.
From the smallest insect to some of the largest mammals,
they've all been shaped by flowers.
But how did this happen?
And why?
The emergence of flowers
is one of the biggest turning points in Earth's history.
To understand how they changed our planet,
we need to go right back to a prehistoric time...
...to the moment when the very first flower appeared.
Up until around 140 million years ago, the Earth was very different.
The animal kingdom was dominated by dinosaurs.
And the separate continents we know today didn't exist.
Instead, there had been a single huge continent, Pangaea.
I'm heading for a place that's about as close as you can get
to that ancient supercontinent.
It's in the remote South Pacific, 1,500km from Australia.
The island of New Caledonia.
It looks like Paradise, doesn't it?
What makes New Caledonia just so interesting
is that it's like a Noah's Ark of ancient plants.
This little journey is going to take us back in time 140 million years.
Because this part of the world is so isolated,
it gives a glimpse of the plant world before flowers existed.
Back then, the plant kingdom had two mighty rulers.
One of them was the tall conifers,
like this prehistoric species of pine.
Look at these trees. Bizarre, aren't they?
They're huge.
Araucaria, Cook pine,
named after Captain Cook who explored this corner of the world.
Pine trees are a family of conifers that are amongst the oldest in the world
so when the dinosaurs were around, these were nature's real giants.
What made flowers so revolutionary
was the limitations of the ancient plants that came before them.
To reproduce, conifers like these relied on the vagaries of the wind.
This is pollen, the male sex cells of conifers.
Each grain has to be magnified 1,000 times to really see it.
The two air sacs, one in each side, catch the breeze.
With luck, the male pollen will be blown
to a female cone on a nearby tree.
But for that to happen, each conifer needs vast amounts.
It's very wasteful.
Up to 10 billion grains have to be released by a single tree.
The other big player back then was the ferns.
Their method of reproduction was also restricting.
Because ferns evolved in wet, swampy conditions,
they needed water to transport their sex cells.
And they use a surprising device.
What they do is they release a sperm,
which swims through the water and mud to a nearby plant
and fertilises the egg.
Under a microscope, you can see that by thrashing around,
the male sperm cell can propel itself through water.
It's able to swim for over two hours.
It's amazing to think that a plant
produces something like a human sperm.
But the downside was that ferns had to live near water.
It was hugely limiting.
All this meant something was lacking in the world of Pangaea...
..diversity.
There were few species of ferns and even fewer types of conifers.
Just 1% of the range of plants we have today.
And the animal kingdom was also limited.
Scientists have found evidence of 700 different dinosaurs.
It sounds a lot,
but today there are over 5,500 species of mammals alone.
There was little variety.
It was a monotonous green world.
And that's how life on the planet would have continued.
140 million years ago, somewhere in Pangaea,
one plant of one species happened to chance on a new way of reproducing.
And it would change the Earth for ever.
I've pushed further into New Caledonia's jungle.
The plant I'm after is really rare, which is why I've come so far.
This is the only place that you find it. It's died out everywhere else.
Mind you, amongst all of this, it's like a needle in a haystack.
Hang on a minute.
That looks like the leaves.
That wood.
Got them.
I've come all the way round the world to find that.
That is the Amborella plant.
Amborella trichopoda is the closest living relative
of the first flower to evolve.
All flowers today have descended from its ancestor.
Botanists believe it began when a single plant mutated
to have leaves that became petals which, instead of being green,
were probably white like those of Amborella.
We now consider them to be the very first petals of the very first flower.
To grasp the significance of this plant, you have to imagine a scene
in some primordial forest where everything's just completely green.
And then there's this flash of colour and glint of white.
Some chance mutation.
And the thing is that scurrying amongst it is a little beetle.
Certainly not a bee because bees hadn't evolved yet,
but a beetle spies this dash of white and scurries across to have a look.
And then munches on these little white buds
that are just packed full of pollen.
But not all the pollen is eaten.
Some sticks to the beetle, and on it goes to other plants.
Unknowingly, it's become a courier, delivering pollen from plant to plant,
pollinating them as it looks for food.
Plants had evolved an ingenious way of reproducing
that no longer relied on haphazard methods,
like the wind for conifers or water for ferns.
Instead it was reliable.
Insects carried pollen directly to other plants.
It was the birth of flowers.
It's hard to grasp just how revolutionary this was.
I'm used to thinking of momentous changes in the Earth
as occurring through huge events -
vast continents colliding or mountains uplifting,
but this was the tiniest of events.
A subtle alteration of how a plant looked
and a chance encounter with a curious beetle.
And on the back of that, the world changed for ever.
Back then, the supercontinent of Pangaea was splitting up.
Smaller continents were forming...
...creating countless new landscapes...
..with new climates and environments -
rising mountain ranges...
..and dry inhospitable deserts.
For conifers and ferns, so dependent on wind and water,
the new landscapes were impregnable.
But for flowering plants, it was the chance they'd been waiting for.
Because they had a powerful in-built advantage.
This is a monkey puzzle tree.
Like most conifers, monkey puzzles live for hundreds of years,
and crucially, they don't reach sexual maturity till they're 40.
Now...this is a campion flower,
which in the shadow of this thing looks pretty puny,
but the campion flower has the last laugh
because this, like most flowers, matures much quicker.
In fact, the campion flower can reproduce after just four months.
It means that in the time that it takes this conifer
to produce just one generation,
the flowers can go through 120 generations.
What's so fascinating is the impact that this has got on evolution
because every time there's a new generation,
there's a possibility of a genetic mutation,
a mutation that might give a characteristic that helps survival.
So the faster the life cycles,
the more species can adapt to new environments,
which, of course, is crucial to our story.
140 million years ago, these rapid life cycles
helped flowers exploit the most hostile environments.
Just like Tankwa Karoo in South Africa.
Because beneath this desert is a hidden carpet of flowers.
Each year, it rains for just two months.
The plants only have this brief window to reproduce.
So how do they ensure they are pollinated in time?
They evolved colour.
Each type of flower that you see is using colour
in a struggle to get noticed by insects.
And there isn't much time.
In a few weeks or days the rains will be gone,
and if these flowers aren't fertilised by then, the plants will die
and the opportunity to reproduce will be lost.
Hundreds of different flowers, dozens of different colours,
whether it be orange gazanias,
purple dew flowers,
or the red balloon pea plant.
And it wasn't random.
Many used a different specific colour to attract insects.
They became targets,
using insects to transfer the right pollen to the right plant,
even over great distances.
And flowers evolved a clever way to enhance this colour.
To the naked eye, a petal looks smooth.
But magnify it 1,000 times and you can see its real structure.
It's not a flat surface at all.
Instead, the petal is made up of countless nodules.
Each acts like a tiny prism, which reflects and diffracts light.
It gives the petal an iridescence, to attract passing insects.
And in their use of colour, flowers went even further.
It's a heck of a contraption, isn't it?
A special camera to give you a kind of...
insect's view of what a flower looks like.
That's nice. Look at that.
Insects and this camera
can see a part of the light spectrum called ultraviolet
that's normally invisible to us humans.
The camera reveals how flowers that appear plain to us
look completely different to insects
And the markings are really important
because they are like airport runway lights
that guide the insect down onto the petals.
Like neon signs that say "free food here".
But once the flowers were pollinated, they still faced a big challenge
because their offspring then had to make it through the rest of the year.
Here in the Karoo, that could be ten months of drought.
To survive, flowers perfected another trick,
which had a powerful impact on life on Earth.
Seeds.
Because seeds have this remarkable ability
that we don't normally think about.
These are seeds of the Canna indica flower, and this...
This is an empty shotgun cartridge.
I'm going to pack the seeds in where the lead pellets would have been.
(GUNSHOTS)
(BANG)
Oh! It's gone right through.
Look at that!
That looks perfectly intact.
The story goes that during the Indian Mutiny of the 19th century...
soldiers used these seeds instead of lead shot.
They're hard enough to be blasted out of a barrel and through wood.
These seeds are so tough, in fact,
that it's said that despite being fired from a gun, they can still germinate.
Sounds unlikely, I know,
though we'll see.
But a tough shell wasn't all, because seeds from flowering plants
developed a further evolutionary advantage
that no other plant possessed.
It all starts at the moment of pollination.
Having been delivered by an insect,
two cells from the pollen burrow deep into the flower's ovary.
Here, one fertilises an egg to create an embryonic plant.
But, and here's the clever bit,
the second cell from the pollen does a completely different job.
Instead of becoming a new plant,
it grows into a food source for the fertilised egg.
A kind of packed lunch.
It's called double fertilisation
and it's unique to the seeds of flowers.
It meant seeds could lie dormant for months or even years
until conditions were right.
As for my Canna indica seeds, well, this is how they fared.
Despite being blasted from a shotgun,
four weeks later, here they are now...
..successfully germinating into a tiny flowering plant.
Remarkable!
By 100 million years ago,
flowers were redrawing the global map of where plants could live.
They were turning once infertile areas into oases of life.
And it wasn't just about plants.
Because these flower oases were now luring animals, too.
There was one ability above all that gave flowers the power to do this.
Plants can do something unique
that marks them out amongst all other living things on the planet.
Their leaves can capture energy from our nearest star, the sun,
and turn it into food.
And the total amount of energy photosynthesis brings to the Earth
is staggering.
I know this is a bit odd,
but just imagine that this little scooter and all the fuel that it uses
represents all the energy that the USA consumes in just one year.
Now imagine that you take all the plants in the world,
all the trees, flowers and grasses...
..all the jungles, forests and savannas
and you add up the total energy
harnessed by plants from the sun every year.
It's not two scooters' worth or ten.
It's all of this.
40 times the amount of energy consumed by America every year.
It's 100 trillion watts of energy every year.
Astonishing as this is, flowers took all this energy and went even further.
An adaptation that would have enormous repercussions
for the animal kingdom.
They developed this ingenious method
of making the sugars available to their pollinators,
and if I take this syringe here and just slide it delicately in here...
..I can show you what they came up with.
It's this really sweet-tasting liquid, nectar, of course.
One of the most energetic sources of food on the planet
and something animals found utterly irresistible.
The nectar from this bird of paradise flower
has three times the sugar concentration of Coca-Cola.
Flowers were now pumping bite-sized packets of liquid energy
into the food chain.
And this began driving the evolution of entirely new insects.
Just take a look at this.
Isn't it beautiful?
For me, this is one of the most incredible fossils ever found.
It's such intricate detail.
The material is amber.
And inside it is a bee.
It's a very primitive bee that got stuck in liquid tree resin
which then solidified and preserved the hapless insect.
Bee fossils like these began appearing roughly 100 million years ago.
And what they show is the incredible impact
flowering plants were now having on evolution.
What I love about this fossil is that it's like a snapshot of an ancient past,
just captured in time.
And it makes you realise that there was a particular point
when bees first arrived on Earth.
Bees evolved from carnivorous wasps
which had turned their backs on meat in favour of pollen and nectar.
As they evolved, their whole bodies became covered in hair,
to collect more pollen.
They developed sophisticated compound eyes,
with hundreds of tiny lenses to spot the flowers.
Inside were special cells to detect UV light.
There are more types of early bees in South Africa
than anywhere else in the world so it's thought they originated here.
And if you think about it,
without the power of flowers, you'd have no bees at all.
But by creating insects to pollinate them,
the flowers introduced a new problem for themselves.
There was a risk that after an insect picked up pollen from a flower,
it would then travel on to a different species of flower and fail to fertilise it
The pollen would be wasted.
The solution of flowers was inspired.
Down under these cliffs on the South African coast,
you can see what they came up with.
This lovely pink flower is Orphium frutescens...
..which flourishes here in these salty conditions near the sea,
but what's truly amazing about this plant
is that it's struck up this exclusive relationship with a particular bee.
Orphium flowers don't contain nectar.
The payment they provide is pollen.
But strangely, they keep it locked up.
Special twisted stamens stop it being stolen by visiting insects.
All, that is, except one -
the female carpenter bee.
Only she has the key.
Let me show you what the bee has to do, using these tuning forks here.
When the bee lands on the flower,
it changes the rate at which it beats its wings to just the right frequency.
From this note...
(HIGH NOTE)
..to this one.
(LOWER NOTE)
Middle C.
And it's these vibrations that are the key to unlocking the stamens
which open up at the top here and just shower the bee with pollen.
(TUNING FORK BUZZES)
Ah! Look at that.
Look at the amount of yellow pollen on there. Fantastic!
(BEE BUZZES)
Now watch the bee do the same,
hitting the middle C note...
(BUZZING DROPS)
..with the beat of its wings...
..and unlocking the pollen.
No other insect does this.
It's incredible, isn't it?
One single species of flower, one particular type of bee
have evolved together to give this intimate partnership.
It ensured that a flower's pollen was successfully taken
to a plant of the same species.
But these increasingly tight relationships
between insects and flowers had another impact on life on Earth.
Because they led to tighter and more isolated populations,
that started creating gaps in the overall ecosystem.
This, in turn, encouraged new species to evolve, filling in those spaces.
Flowers were now driving a huge increase in the diversity of life.
And they were fuelling this increase by pumping nectar into the food chain.
The insects, bees, butterflies and moths, such as the hawk moth,
were eating it with long, probing tongues.
There were new species of birds, like the Calliope hummingbird,
with beaks perfect for trumpet-shaped flowers.
And predators, such as these toucans, that ate the pollinators.
Between 120 and about 90 million years ago,
all thanks to flowering plants,
evolution had entered the most explosive phase in the Earth's history.
By now Pangaea had split up,
creating the continents so familiar to us today,
and flowers dominated them.
They'd conquered the ancient conifers and ferns, and covered half the Earth.
But it wasn't just life they were changing.
Because they started altering the very shape of the planet itself.
This is Ha Long Bay in Vietnam.
I'm here because it's evidence of how flowers unleashed
some of the most powerful forces on Earth.
This whole landscape just dwarfs you.
You can see these pinnacles of limestone just soaring upwards,
limestone that you get all over Vietnam.
And it gives this really distinctive, even iconic landscape called karst.
The thing is, when you look at things as huge as that
you look for huge geological processes to create them,
but it's not always the case.
That's because 90 million years ago,
flowers began to build an empire across the planet...
..in a totally unexpected way.
They did it by creating vast tropical rainforests.
Almost all the trees are really giant flowering plants.
You can see one here in flower.
And all the trees are doing one thing.
Breathe out on a piece of glass
and it's pretty obvious that there's moisture in your breath.
And in a funny kind of way, plants are breathing out moisture too.
It's just much harder to see.
But take a look at this. If I tie a clear plastic bag over this big leaf,
then we should be able to actually see the plant breathing away.
And all we need to do now is... wait a couple of hours.
Look how much moisture this single banana leaf produces.
It's losing water, or transpiring,
through tiny pores in the leaf called stomata.
Close up, you can see the veins of the leaf,
which transport water around the plant.
Leaves of flowering plants contain four times more veins
than other plants.
Because they share the same type of special vein leaves,
trees like these act as kind of giant water pumps
drawing moisture up from the soil and pumping it into the atmosphere.
Some of these trees chuck out five tonnes of water every day.
All this transpiration meant that 90 million years ago,
flowering plants were creating more clouds...
..which led to more rain.
(THUNDER CRACKS)
Water that, when it fell,
was then drawn up from the forest floor by the same trees,
forming a self-sustaining cycle of almost perpetual rainfall.
In fact, 80% of the water in the rainforests
came from the flowering plants themselves.
In this new age of rain,
water became an ever powerful sculpting force.
And today, you can see its effects in an astonishing hidden world.
Deep beneath the rainforest in central Vietnam
are the caverns of Hang Son Doong.
We are the first British film crew to explore them.
Hang Son Doong is the largest cave passage ever discovered
anywhere on Earth.
This single cavern is nearly two kilometres long.
All carved from solid rock by nothing more than water.
All of which has trickled down from a single source -
the vast jungle above.
It is a relentless force that has carved out a dozen enormous caverns.
An underground monument to the power of flowering plants.
And deep in this labyrinth is what, for me, is perhaps the greatest
of all the wonders of the plant world.
Here, at the heart of the cave, a whole rainforest.
Where the roof has collapsed,
flowering plants have made their home...
..200 metres below ground level.
It is like a lost world.
The thing is, just a few minutes ago, there was me in a cool, dark cave,
and then ejected into this place with streaming sunlight.
Hot and sticky rainforest.
And where there's water and light, flowers have produced life.
Plants such as this banana flower thrive,
which in turn attracts butterflies and other animals.
It's a thriving ecosystem here.
And the whole thing is fed, really,
everything, this whole food chain, is fed by the flowering plants.
Flowering plants have created a small but perfect version
of the rainforest above.
Look at that mist.
There's a whole weird microclimate in here.
Clouds of moisture envelope everything.
And the plants just soak up that moisture,
just draw it up and then pass it out.
So that cycle of transpiration
that we see on a big scale up in the tropical forests
is captured in miniature down here.
Caves formed under all the world's great rainforests.
And this extra water even began to transform the global climate.
As water evaporates, it absorbs heat and cools the planet.
The Amazon rainforest alone keeps its whole region five degrees colder.
Across the planet, water injected into the water cycle
was eroding deep canyons,
carving high mountains,
and sculpting the karst towers so iconic of Asia.
It's extraordinary, isn't it?
Especially when you think that all this
comes not from huge forces deep underground,
but in part from tiny changes on the leaves of flowering plants.
65 million years ago was the age of the rainforests.
They'd spread from the equator to cover most of the Earth.
It meant three quarters of all plants were now flowers.
A rich, lush home for millions of new animals.
The dominance of the flowering plants seemed unassailable.
But it was not to last.
A 10km-wide asteroid coming from deep space was on a collision course.
It hit the Earth with a force of a billion Hiroshima bombs.
70 billion tonnes of pulverised rock were blasted into a low orbit.
Scientists called it ejector and travelling at supersonic speeds
its friction with the atmosphere heated the Earth up
by over 200 degrees Celsius.
It spontaneously triggered fires across the land.
It was one of the worst mass extinctions in the history of the Earth.
And famously killed off the dinosaurs.
But less well known is the immediate impact on plants.
Scientists believe that for them,
the effect of the asteroid was also devastating.
Not only were there fires,
but the ejector created clouds of nitric and sulphur dioxide...
..which fell as acid rain...
..destroying plants from the roots up.
I think it's really hard to imagine
what the most recent and powerful extinction event must've been like,
but perhaps the closest you can get to it is a newly-erupted volcano,
like here in White Island, New Zealand.
I think it's just the desolation, really.
The bleakness, that sense that life's just been...obliterated.
For plants,
the aftermath of the asteroid impact must have been similar.
Here on White Island,
vegetation has been incinerated by successive eruptions.
And the volcanic fumes create acid rain, just like after the asteroid.
For flowering plants, it was a disaster.
That close, almost inseparable relationship with insects
was now their Achilles heel,
because even if a flowering plant had survived the initial calamity,
it needed a specific animal to pollinate it,
and often they'd simply been wiped out.
But flowers weren't beaten yet.
All those evolutionary devices
that had allowed them to thrive on a hostile planet in the first place
now became their ultimate tools for survival.
Coloured petals to attract the few surviving pollinators.
Nectar to repay them in desperate times.
Above all, flowers could rely on those superb survival capsules
that could have been purpose-built for just such an apocalypse...
..seeds.
Now, following the asteroid impact,
seeds helped flowers to re-colonise the Earth.
And as they did so,
once again flowers formed an inseparable relationship with animals.
The dinosaurs had gone, but another type of animal had replaced them...
..mammals.
This time, flowers used mammals to help them distribute their seeds.
Here in Thailand, this whole floating market celebrates
the clever evolutionary device flowers came up with.
More sophisticated flowers developed a really sneaky way
of spreading their seeds.
A method that didn't just disperse at metres, but kilometres.
And to do that, they again harnessed the hunger of animals.
They developed fruit.
What is that?
Durian. This is durian?
I cut. You taste. OK, yeah.
You can't come to Asia without trying the smelliest,
most notorious fruit on Earth.
Beautiful!
I hope it tastes better than it smells, though.
Ah! There's the seeds in there.
And then this flesh.
Texture's...
THEY LAUGH
They're all laughing. They're laughing.
It's like an off avocado, really.
I think that's what they call an acquired taste.
The botanical definition of a fruit
is that it must actually develop from the flower itself.
The fleshy coating was once the ovary, as it grew around the maturing seeds.
Lovely. Incredibly sweet.
Very subtle.
Isn't that great? The way all of them hide this inside, this little seed.
You can see why some warm-blooded mammal or bird
would want to eat this - it's just packed with nutrition.
And of course, as you do that...
you...
you swallow the seed.
And then later on you pass that out somewhere, miles away,
dumped in some little dollop of manure.
But that's really the point of all of these different types.
All this diversity is designed to attract animals to eat it.
Fruit is one of the most remarkable transformations in nature.
What begins as an advertisement for an insect, a flower,
becomes a protective covering for the seeds inside.
And then a final burst... swells into the juicy flesh of a fruit.
55 million years ago, one group of early mammals was evolving
that relied almost entirely on fruit.
In fact, without it, they'd probably never have existed.
It was an animal which would directly link flowers to our human story.
They live here in Thailand's Khao Sok National Park.
Somewhere in these trees there are primates.
GIBBONS CALLING
I'm sure they're up there.
You see the trees just... The branches moving but...
trying to pinpoint the actual gibbons is...really tricky.
Oh, there's one.
Do you see it? It's kind of silhouetted in the branches just up there.
I'm sure it... Yeah, it's moving.
My first gibbon.
The primates - lemurs, monkeys and apes -
evolved an inseparable partnership with the fruit from flowers.
And it determined their whole anatomy.
Primates have got the perfect tools for reaching fruit.
They've got these really strong hands which,
along with their powerful chest and shoulder muscles,
allow them to get up into the trees.
All these are important traits that we human primates have inherited today.
And all came from the need
for the first primates to reach the fruit of flowering plants.
Norberto Asensio is a primatologist.
He studies the crucial role fruit plays in the diet of monkeys.
For most primates, fruit is important. It's part of their diet - so what?
Is it the core of the diet? The essential core, do you think?
I would say so.
I would say that most of the primates will have 70% to 90% of their diet
on fruit. It's quite a lot.
But back then, flowering plants created a problem for themselves.
Primates were so hungry for fruit...
..they would pick it long before the seeds inside were mature.
It meant seeds were being wasted.
So flowers came up with a solution.
When fruit was ripe, they made it sweet, juicy and brightly coloured.
It was a colour-coded time delay.
And it encouraged primates to take only fruit that was fully mature.
Norberto studies how this colour coding
drove changes in our ancient ancestors.
Before now, primates, like all mammals, were colour-blind.
This made spotting ripe fruit difficult, as I'm about to find out.
Let's do an experiment.
Here you have glasses that are going to turn you into a simple mammal.
Let's see.
Oh, gosh!
The glasses simulate colour blindness by removing red from the picture.
I can kind of tell the difference in contrast between some of them.
That's gone a very funny shade of bluishness.
The interesting ones are these reds.
I know they're red but they just don't seem red at all.
Overall it's just got a very... almost bland greyness to it all.
For primates to perceive red,
they had to evolve a more sophisticated vision system.
In the retina are special photo receptor cells that detect colour,
called cones.
There are 150,000 per square mm.
Early mammals only had two types of cone, one for green and one for blue.
It meant they were colour-blind.
But primates evolved a third type.
It was sensitive to red.
Now they could spot ripe fruit.
Colour vision helped give primates the advantage,
kick-starting the evolutionary journey that resulted in us humans.
That's why we have colour vision now
and we have this wonderful rainbow of colours
that we can see now and enjoy it.
Fruit drove the evolution of so many of the traits of our ancient ancestors,
but this simple need, the ability to see if fruit was ready to eat or not,
had given primates perhaps for the first time on our planet
this capacity to see in full glorious technicolour.
And it's something that I think we just take for granted.
Since they'd evolved 140 million years ago,
flowers had transformed our planet.
They'd come to dominate the plant kingdom,
sculpting the Earth itself.
Above all, flowers drove the evolution of animals,
especially primates,
shaping our human evolution.
It seems to me that we are rather animal-centric.
That by being members of the animal kingdom ourselves,
we somehow see them as the thing that's at the heart
of driving changes to life on Earth,
but I don't think that's true.
Most of the big changes to life on the planet
have been brought around by flowers.
They are the ones that are more manipulative, more inventive,
more powerful than any of the animals that they are interacting with.
Most animals are only here because of flowers, including us.
It's an intriguing thought for next time you're out doing the roses.
Next, we reveal the epic battle between the forests
and their greatest challenger, a new type of plant...
the grasses.
It was a conflict that would set the world on fire.
The victor would force our ancient ape ancestors out of the forests
and into the savanna.
And go on to trigger the birth of human civilisation.
Subtitles by Red Bee Media Ltd