It is the heart of Africa.
A hidden world.
It is a tangled jungle...
...haunt of flickering shadows.
It is a place of immense challenges... yet full of life.
The more we look, the more extraordinary variety we find.
This is one of the great laboratories of evolution...
a world we are only just beginning to understand.
Africa's heart is not dark, but green and vibrant...
it is the tropical rainforest.
Sunrise over the Equator and the African rainforest wakes.
From Uganda in the East, to Sierra Leone in the West,
it is a great belt of green.
It spans the continent for five and half thousand kilometres.
More light, more heat, more water than anywhere in Africa
perfect for plants and they've completely taken over.
An endless sea of leaves worshipping the sun on a new African morning.
On the forest floor, the sunlight barely filters through.
The underworld: A land of trunks and buttresses.
They hold up the forest roof and they are its plumbing...
pumping nutrients and water to the leaves above.
Here, it's wise to take care.
Plants stud their trunks with spikes.
They defend themselves with armies of vicious stinging ants.
And they lace their flesh with poisons...
...all this to stop them being eaten.
In such a hostile jungle, how can anything survive?
But there are opportunities here for creatures who know how to grasp them.
Giant fruit fall from the sky.
The sound echoes through the forest.
Elephants deep in the heart of the jungle.
Drawn towards the sound of falling fruit.
As big as melons and harder than coconuts
the fruit of the Omphalocarpum tree are ripe.
Two kilos of nutritious food for those who can break it open.
The smell is irresistible too like garlic.
It hangs in the jungle air.
But this fruit is so hard,
it seems not even an elephant can dent it.
Or can it?
The elephant uses its tusks as precision tools
to prise open the fruit.
This remarkable behaviour has only just come to light.
Fruit is the forest elephant's staple and this manna
from the heavens is full of energy.
But its also a rare gift and it takes more than
just one ripe Omphalocarpum tree to feed Africa's largest land mammal.
So elephants have learned to make the most of opportunities just like this.
There's not a fruiting tree an elephant doesn't know...
...each one, pinpointed on a mental map of the forest in their head.
And as they travel, they follow a network of paths they've carved out
across the forest to over a hundred species of fruiting tree...
To survive in this hard world elephants have become the masters of opportunity.
There are others who've learned to survive here.
For generations, people have found a living here,
like the elephants, constantly seeking out chances for food.
Monkeys, foraging low down in the trees...
...just within crossbow range.
In this tangled place, even the most skilled hunters can go hungry...
...escape is just a leap away into the forest canopy.
Forty metres up, sunny, breezy.
Another world.
And here is the engine of all forest life.
Leaves soak up the energy of the African sun
and turn it into plant food.
Monkeys, perfectly designed to leap
from tree to tree they travel the rainforest canopy.
This black and white colobus and this red, are specialist leaf eaters.
For them, food up here is all around.
...and they spend their days contentedly munching.
But these leaves are not as innocent as they look.
They protect themselves with a lethal cocktail of poisons
tannins, strychnine, cyanide.
So how can colobus eat them?
Over time they have evolved specialised stomachs filled
with bacteria that neutralise these poisons.
In one day they can eat enough to kill a man several times over.
The crowned eagle.
It can't eat leaves, but it can eat monkeys.
The cover of trees is no protection.
With powerful strokes of its 2 metre wings it airlifts the prey back to its eyrie.
Here it feeds its chick in a penthouse suite
with a view far and wide over the roof of the forest.
The canopy world is a place of extremes, of hot sun and drying winds,
fierce and drenching storms.
From dry times to wet times the seasons here are more marked.
The long hard rains are soon due and
a transformation comes over the forest canopy.
As far as the eye can see, the trees blush,
not with old leaves, but with new...
The growth of spring with the colours of autumn.
New, tender leaves don't yet have the protection of poisons.
So to ensure they survive trees produce a glut
far more than even the hungriest monkeys can eat!
Flowers too fall under the spell of the seasons.
And the animals of the canopy have a sweet, nectary treat.
The canopy is a place of treasure...
but only for those who can reach it.
Using just a knotted vine,
a Bayaka pygmy climbs from one forest world to another.
He's after the sweetest prize in the jungle.
Honey.
Mongonje is the best tree climber in the area
but it's still dangerous work.
One slip of his axe and he falls to the forest floor, thirty metres below.
At least this is a hive of stingless bees.
They're still distracting and that can be dangerous.
This work takes great nerve.
...and it's worth it.
For the Bayaka this is a precious seasonal treat.
The sunblessed goodness of the canopy delivered
to the forest floor in a basket...
For the most part it's hard work finding food in the forest
but there is a time, a time of plenty,
when all who live here get a helping hand courtesy of plants.
As the long wet season arrives, the forest gives its best.
Fruit, pure temptation.
Birds are always the first to arrive.
A great blue turaco.
Hornbills...
...the African grey parrot.
Chimps love fruit too.
Fussy about ripeness, they check each one.
A fruiting fig like this is a major event.
Over half a chimp's diet is fruit,
so youngsters learn from an early age where to find trees like this.
By the time they grow up the chimps know the trees
so well that they can even predict when they are going to be ripe.
When a fig tree fruits there's so much of it,
even the forest floor gets a rare treat...
...the scraps from the banquet above.
But figs are unusual.
Unlike other trees,
they can fruit in any season so they are especially useful
for seeing animals through leaner times.
Fruit is crucial for survival here.
But as animals eat they also serve plants.
As the chimps move off to find other fruits
they carry with them the seeds of trees.
Birds have an even bigger range
the seeds they eat are energy rich,
but lightweight,
perfectly designed by plants to be airlifted.
A quarter of all rainforest trees are dispersed by hornbills alone.
And it's no coincidence that elephants love Omphalocarpum fruits.
If a tree can tempt this animal into eating its fruit,
it gets the best disperser there is.
As they walk from tree to tree seeking fruit,
elephants can range over hundreds of kilometres,
sewing the seeds of new trees on their paths as they go...
...complete with a ready made pile of fertiliser.
Over the millennia, animals have been a vital force
in helping the African rainforest spread far and wide across the Equator.
Now we are beginning to discover a new side to the forest.
Africa's climate hasn't always been as it is today.
Through the ages it has swung through repeated cycles of wet and dry.
The forest has changed too,
expanding with the wet years and shrinking back in the dry.
Today's endless green sea is simply
a snapshot of an ever changing, dynamic place.
A pumping green heart at Africa's centre.
Now is a wet time in Africa's history
and the forest is near its maximum extent.
It rains practically every day...
in some place, an incredible 10 metres a year.
To live here is to put up with a phenomenal amount of rain.
But it's not necessarily bad news.
The rain that has shaped the forest
over millennia brings change on a small scale every day
and with each change comes a new way for animals
to survive in this land of plants.
An elephant's footprint has filled with water from the downpour.
Inside a minor miracle happens.
Microscopic eggs hatch into fish.
The transformation is complete.
Multicoloured Killifish here in an elephant's footprint.
In their temporary pool they are safe from the predators of bigger rivers.
But even here there are villains.
A Congo water scorpion has venom to dissolve the flesh of fish.
Not much future in a footprint anyway.
Now the killifish shows its true colours
superbly designed to flip from stream to stream...
in this temporary water world.
He turns his nose into the current like a tiny salmon
to take advantage of a newly running, rain-fed stream.
And this is what the colours are for.
A killifish female.
In the dark light of the forest floor the display is irresistible.
She is mesmerised by his kaleidoscopic advances...
and a new generation is spawned.
In these changing waters,
killifish have found their niche in the rainforest.
And when the rain subsides,
the water level here may drop again,
but her eggs will be safe,
dormant in the river bed, just ready to add water.
But for now the rainforest is overflowing.
What water the trees don't suck up, the forest pours out.
Streams flow into torrents...
...and torrents into giant foaming rivers.
Rivers break up the monotony of the rainforest.
Light streams down to the ground.
Canopy world meets underworld.
Black and white colobus like living beside rivers.
Here, their plant food is more varied, more nutritious,
so they don't need to spend so much time eating.
There are better things to do, like grooming...
...or passing round the new-born, all white baby.
...or just playing.
Over time, these huge rivers, snaking through the forest,
have cut a great swathe through a carpet of green.
The Niger, the, the mighty Congo.
Some of the largest rivers on earth.
With their relentless flow,
they have broken the hold of the forest,
at each twist and turn creating new chances for life.
By travelling along the river's edge,
animals like the black and white colobus have spread the forests of Africa...
The rivers have brought others here, too.
The Fang tribe of Equatorial Guinea depend for their survival on forest rivers,
they've learned just how to exploit them.
They collect the bark of the Olong tree...
...then they pound it by the side of the river.
As they wash the bark, its juices flow downstream.
They are poisonous juices.
Designed to save a tree from being eaten,
the poison is so strong that it stuns the fish of the river.
If all fishing were so easy!
And the effects of this natural poison are quite remarkable.
Fish that are caught are safe to eat,
whilst those that slip away quickly recover.
Soon the river will be full of fish once more.
In the depths of the Congo,
rivers also provide food for some of our closest relatives.
Bonobos or pygmy chimpanzees,
fish for insect larvae in a forest stream.
Bonobos are close cousins of chimps
when it comes to water they are subtly different.
Their legs are longer and their posture more upright
so they're much more at home in water.
...often they wade, foraging in rivers and pools with their delicate fingers.
An altogether more aquatic ape.
As evening comes the Bonobos need to find a dryer place.
And head for the shelter of the trees.
Lacing branches together they make a bed.
Long ago Bonobos were cut off from their chimpanzee cousins
by the changing course of the Congo River.
Separated by water and unable to swim,
they evolved over time to become a completely different species.
In the rainforest,
rivers not only sustain life they help to create it.
From space, the forest night is a display of a thousand tiny flashes
each one a storm hundreds of miles across.
The forces of change are relentless.
As morning comes the rain has passed and the forest is smothered in heavy mist.
All is quiet - primeval.
Sometimes the forest feels very permanent.
Trees of some form or other have existed on Africa's Equator
since the age of the dinosaurs.
At times it's easy to think that monsters are here still.
With heavy burdens, shallow roots,
thin soils - trees fall all the time in the rainforest,
leaving a hole in its roof.
And so a piece of Africa that has been centuries dark greets
the stream of morning light.
Immediately the whole intricate web of rainforest life
jumps out to seize the day.
The first to take the chance is the wild yam,
sprinter of the plant world.
It heads for the hole in the canopy and the precious sun.
Underground is a secret weapon
a giant tuber which pumps energy into the growing tip day and night.
It grows an incredible one metre in just three days.
And there's more.
As it grows it produces tiny beads of sweet nectar on its shoots.
Insects are drawn in.
Butterflies, and most importantly, ants,
who repay the favour by aggressively defending the yam from enemies.
A place in the sun for the yam seems guaranteed.
But in this infinitely complex world every defence is met with counter attack.
Enter a very particular little beetle.
Like the yam, it seizes what chances it may.
It gets straight to the point and starts to mate.
Before the ants are fully mobilised a tiny yellow larvae
is already eating away at the yam.
And here's the ingenious bit:
As it eats, it absorbs poisons from the plant,
taking the Yam's defences
and spreading them on its back as a shield.
To the ever watchful ant defence force,
the beetle larvae now smells and tastes repellent.
It's free to munch Yam flesh to its heart's content.
One tiny larvae like this won't stop the yam
on its journey to the sun
but a chance for a yam is a chance for a beetle.
As a host of forest life battles it out for a place in the sun,
down below the fallen wood brings opportunity to others.
The forest undertakers are staking their claims.
Ants immediately get to work hollowing out the trunk.
Fungi and slime moulds stretch out their morphing fingers
to grab what nutrients they can.
And termites digest the very fibre of the tree,
passing nutrients back into the food chain.
Chimpanzees love crisp,
juicy and protein rich termites almost as much as they love fruits.
And when it comes to winkling out dinner they have an advantage.
Hands originally evolved to swing from trees are used
with clever minds to fashion and manipulate tools.
They learn by watching when they are young.
Down the generations the skill is passed on.
Though a short delicate twig is needed to tease out termites
safari ants need a different technique
a long stick and a good tolerance to vicious bites.
Sometimes it helps to approach from off the ground.
If you're smart, then life in the forest is that little bit easier.
When it comes to making tools, we humans are the masters.
This three metre stick is called an auger, specially designed to dig for yams.
The yam tuber is deep underground.
But not too deep for the auger.
It's not all bad for the yam, however.
The Bayaka leave the tip of the tuba in the ground to grow again.
In a few years they'll come back to this very spot and harvest the reborn root.
Back in the hunting camp the tubers are boiled and eaten.
This is the only source of starch that
the Bayaka people regularly get from the forest.
So it's well worth the effort.
The lives of these people are totally intertwined with the forest.
They have developed technology to reach into the canopy,
to dig far underground.
They use the wood of the trees and even the chemistry of the forest...
The sap from a vine called 'mbango' is squeezed in a special press,
to tip the crossbow arrows.
A scratch of this oily concentrate to the skin can cause a fatal heart attack.
Over the years the Bakaya have discovered
a whole range of complex compounds from plants
science is only just beginning to catch up.
And whilst one preparation may cause instant death,
another is intentionally cut into the skin
to cure headaches and diarrhoea
the very poisons that plants use to defend themselves
are the tools of a good forest pharmacist.
His knowledge could even hold the future cures
for our modern diseases.
Though the Bakaya survive with great ingenuity,
their impact on the forest is small.
But there is one animal whose quest for survival here
can alter the very nature of the forest itself.
In a place called Dzanga Bai,
in the Central African Republic it has carved out islands in a sea of green.
Over the ages the padding of its feet
through the undergrowth has changed the forest.
There are a few rare places in the forest where precious salts
and minerals are hidden in the ground.
Every day, for generations,
elephants have travelled to clearings like Dzanga Bai, to take the salts.
No one quite knows what's here
antidotes to plant toxins and minerals,
essential for health, have both been discovered.
But through studying these clearings,
a bigger truth about elephants is being revealed.
2800 individuals visit this one clearing.
Half of Africa's elephants are now thought to live in the rainforest.
They have a huge impact, not only spreading seeds,
but opening up the forest for other animals.
These places are oases of tranquillity havens for all manner of African beauty.
Parrots.
The rare Bongo.
All around are animals breaking away from the protection of the trees
to get a share of mineral goodness.
In the dark forest it's difficult to even see another animal,
let alone meet it.
But in clearings,
even the shyest can come out into the open for a chance to socialise.
The Western Lowland gorilla.
For years, less well known than its mountain cousins.
Only through the discovery of clearings
are we now finally getting to know this animal.
There are over a hundred thousand hiding in these forests.
They, too, visit clearings for their minerals,
but in doing so they come together, to cement relationships,
to dispute dominance - to play.
And as these gorillas move out from the protection of the forest,
they remind us of a much older migration.
Six million years ago the African forest was retreating,
overtaken by a brighter world of woods and grasslands.
Many species emerged from the forest;
to seek opportunities in this new world...
among them a highly sophisticated ape our ancestors.
Man began as a forest ape but became fully human in the new world beyond.
Over time we humans returned to our ancestral home...
like the Bayaka.
'Etu' tells the story of how her people came to the forest to gather honey.
The stories tell of a dream time when their ancestors
evolved the skills to make a home in the forest.
For animals and humans alike it is time
that has given the best opportunities here.
As the African rainforest has adapted to the climate, it has changed.
An infinite number of trees has fallen, clearings have come and gone...
...rivers have snaked and moved
and grasslands have been repeatedly swallowed and reborn.
With every change there is a new chance for life
here in the green heart of Africa.