[tense music playing]
[distant roaring]
[Morgan Freeman] In the four billion years of life on our planet,
countless species have risen…
and fallen.
[distant roaring]
But one remarkable dynasty has had a greater impact than any other.
[roaring]
The mammals.
This is the story of their epic journey…
[roaring]
…to become rulers of the world.
[music fades]
[rousing music playing]
[snarling]
[trilling]
[screeching]
[rousing music continues]
[growling]
[wind howling]
[rumbling]
[rousing music intensifies]
[music fades]
[insects chirping]
Hidden in the ancient Jurassic forests…
mammals came from humble beginnings…
ruled over by the greatest dynasty that ever lived…
[distant bellowing]
…the dinosaurs.
[growls softly]
They dominated so totally…
[snorting]
…that early mammals were confined to the shadows.
For the most part, they were small, keeping to the trees…
away from the giants.
They became nocturnal,
developing a range of heightened senses that helped them in the dark.
Under the dinosaurs' rule,
there was a limit to how far they could rise.
But in time, everything changed.
One of the most violent events in our planet's history
heralded a new era.
[poignant music playing]
Despite the devastation,
the planet did recover.
Within a few million years,
forests had regrown and carpeted much of the land.
The climate became hot and wet.
The perfect conditions for life to flourish.
A world primed for a new wave of evolution.
-[insects chirping] -[birds squawking]
The asteroid had inflicted devastating losses on the mammals…
yet some of the smaller ones,
able to hide in holes, had survived.
[creature chattering]
Free of the dinosaurs,
they could finally venture out of the shadows
and come into the open.
-[birds chirping] -[chattering]
Like their ancestors,
coatis have many adaptations
that help them thrive in the rich rainforest.
Extremely social, they find safety in numbers.
The mother's flexible nose can smell food hidden beneath the leaf litter.
A supersense honed over millions of years of foraging in the darkness.
Like all mammals, coatis are warm-blooded,
so can be active at all times.
That means these babies need plenty of energy.
Fortunately, mammals have evolved an extraordinary solution.
Milk.
[suckling]
They can feed their young whenever they choose,
even when food is scarce.
But milk wasn't the early mammals' only secret weapon.
They also had brain power.
[tapping]
And it's still just as important today.
In the forests of Costa Rica,
this capuchin monkey is trying to solve a puzzle.
How to get the meat from inside a closed clam.
The monkey isn't strong enough to crack the shell…
[tapping continues]
but it's discovered that repeated hammering will tire the clam…
until it finally opens.
Learning this lesson takes a large brain…
[clam thuds on ground]
-…and coordination. -[squeaks]
[playful music playing]
This unique intelligence allowed their primate ancestors
to survive in the forest of 50 million years ago.
Clever animals tend to be inquisitive…
and that can pay huge dividends.
This female has learned
and remembered
where she can find water.
But it's too deep to reach.
Luckily, she has an inspired solution.
She turns her tail into a sponge.
But not all their challenges are to do with finding food and water.
[squeaks]
Some fruit is collected not to eat…
but to rub over their bodies.
This fruit contains citronella,
an oil that mosquitoes can't stand.
[uplifting music playing]
The monkeys have discovered their very own insect repellent.
Free from pesky biting insects,
the clever capuchins can finally relax.
[music ends]
But just as their ancestors were beginning to make progress,
the warm, wet conditions in which they had thrived began to change.
The Antarctic landmass started to split away from South America…
creating the space for new ocean currents…
that helped drive a global cooling.
The climate was switching into a new, colder state.
[poignant music playing]
But that was just the beginning.
As Antarctica became colder and more isolated,
the huge continent froze,
locking up much of the planet's fresh water.
As the world further north dried out,
it became a harsher, more difficult place to live.
Food became more spread out,
harder to find.
And as the Earth changed,
so did the mammals.
[heavy footstep]
[snorting]
Some became enormous.
A male Megacerops.
[grunting]
Two and a half meters tall…
[grunting]
…four meters long…
and three tons in weight.
[snorting]
[grunts]
Its huge size allows it to travel large distances in search of food…
[grunting]
…and ensures it has reserves to get through leaner times.
[majestic music playing]
Mammals were now big enough to rival the long-lost dinosaurs.
But being big has other implications…
especially when it comes to finding a mate.
[snorting]
[grunting]
This female is already closely guarded by a male,
much larger than the first.
[snorts]
[growling]
If challenged,
he could seriously injure his opponent.
[roaring]
[snorts]
[grunting]
But the smaller male may be in luck.
Another female,
and she seems to be alone.
[grunts]
It's the chance he's been waiting for.
[grunting]
[growling]
He has a rival.
[roaring]
This time, they're evenly matched.
[grunting, growling]
[tense music playing]
[bellows]
[grunting]
[bellows]
[roars]
-[bellowing] -[growling]
[roaring, growling]
[growling]
[grunting]
With these mammals…
[growls]
…size matters.
But even the mightiest Megacerops
couldn't overcome the planet's next great challenge.
The formation of Antarctica was creating global climate chaos.
As ocean currents shifted
and the planet dried…
it became a tinderbox.
[mournful music playing]
Wildfires ravaged the land…
clearing the way for something completely different…
something that would challenge mammals as never before.
As the smoke cleared,
there rose from the ashes
a life-form that had previously only survived in the margins.
Grass.
Taking root during the great drying…
it spread so quickly,
it would soon cover one-fifth of the land.
But the endless plains were no paradise for the mammals.
Many couldn't digest grass
and soon went extinct.
[insects chirping]
[snorts]
Twenty million years later,
and today's grazing mammals remain locked in an arms race
with this green invader.
They have evolved a whole swathe of game-changing adaptations.
Specialized teeth,
strengthened to prevent silica in the grass
from wearing them out…
and huge bellies to process it all.
Their young are born fully formed…
[snorting]
…able to walk within hours of birth…
and follow their herd in search of fresh growth.
Mammals have truly conquered the grassy plains…
their huge numbers the most obvious sign of this exceptional success.
But just as some mammals evolved to feed on the grass,
others evolved to feed on the grazers.
Hunters.
[herd lowing]
The herd has its own defense against the cheetahs' blistering speed.
-Many eyes… -[snorting, grunting]
…spot the danger early.
-[herd grunting] -[bird squawking]
[tense music playing]
[grunting]
Running bodies create confusion for the young to hide in.
But the big cat has a plan…
forged by its clever mammalian brain.
Panic the herd,
split them up,
and target a lone calf.
[tense, energetic music playing]
Desperate to defend her only calf,
the female wildebeest counters.
The chase is far from over.
The cheetah has lost a lot of ground…
but the calf is tiring.
[tense, energetic music continues]
[music slows]
As the youngster turns,
it's the hunter who must now run for its life.
[herd lowing]
The calf is safe once more…
[calm music playing]
…but the cheetah will be back…
and the war between the grassland mammals will continue
as it has done for millions of years.
[tranquil music playing]
In prehistoric South America,
the grasslands played host to the same battle…
but with very different animals.
[intriguing music playing]
This giant armadillo…
is also a mammal…
though one the size of a car.
Doedicurus may not be fast,
but what they lack in speed…
[trilling]
…they make up for with armor and a lethal tail…
[grunts softly, snorts]
…adaptations that protect them and their young
from any would-be predators.
[trilling]
[ominous music playing]
[soft growling]
A Smilodon…
but a mere youngster.
-[soft growling] -[snorting]
[whimsical music playing]
[trilling]
He's not a serious threat…
[trilling]
[hissing, growling]
…even with his dagger-like teeth.
He's never seen a Doedicurus up close,
and their defenses are intriguing.
[hissing]
[soft growling]
His curiosity gets the better of him.
[trilling]
[purring]
[trilling]
-[grunts] -[hisses]
[whimsical music continues]
[trilling]
He explores every angle.
[snorting]
[trilling]
For the young Doedicurus, the only option is to stay put.
[trilling]
The giant armadillos' armor is completely impregnable…
[growls softly]
…and they know it.
-[trilling] -[growling]
[growling]
But there is one obvious opportunity.
[trilling]
[growls]
The young Doedicurus is so much smaller.
If he can get a hold on it…
-[growling] -[trilling]
…he might be able to turn it over.
[hissing]
[trilling]
But not with the adults around.
[low growling]
-Another stalemate. -[juvenile moans]
-[trilling] -[snarling]
Battles between the mammals have always driven their evolution,
and they don't just happen in the grasslands.
[wind whistling]
Fifty million years ago,
what are now India and Asia collided on an epic scale.
The crash forced the land into the sky,
creating the towering Himalayas.
[majestic music playing]
Today, they are 2,500 kilometers long,
almost nine kilometers high,
and still growing.
With their freezing temperatures and thin air,
these mountains are uninhabitable for most animals.
[unsettling music playing]
But not all.
Deep in a sunless valley…
a male snow leopard…
and an ibex that has fallen to its death.
The leopard is very old,
worn and tattered by his harsh mountain life.
At these altitudes, mammals must feed regularly to keep warm.
But the Himalayas present the ultimate hunting challenge.
High above the valley, a female…
and her cubs, fathered by the male.
Three of them in total,
all amazingly camouflaged.
Snow leopards have thick fur,
large paws,
and long tails…
perfect adaptations for the coldest,
most precipitous nursery on Earth.
[stirring music playing]
[music fades]
Away from the dangerous cliffs…
[light, playful music playing]
…the mother initiates a hunting lesson.
[soft growling]
[growling]
Teaching and caring for one's young
is a key mammalian trait.
These cubs will stay with their mother for nearly two years…
learning the skills needed to survive on the very edge of life.
[music ends]
At these altitudes, every opportunity must be taken.
The old male is tracking a herd.
In this vertical world, he must get above his prey…
[tense music playing]
…and close enough…
for an ambush.
[tense music continues]
[loose rocks tinkle]
[rocks clattering]
[water splashing]
[snorts]
This time
death has claimed them both.
[poignant music playing]
But the leopard's legacy lives on.
In a few months' time,
his cubs will leave their mother and start to hunt alone,
having learned all the skills they need
to survive at the top of the world.
Although they had conquered the land,
the mammals didn't stop there.
[insects chirping]
One branched out and went in an entirely different direction.
Fifty million years ago, bats opened up a whole new realm…
through flight.
[gentle music playing]
Flying allows animals to search much further for food…
and gather in their millions.
Today, one in five of all mammal species is a bat.
[high-pitched squeaking]
But bats were not the first animals to take to the skies.
Having spent the night foraging,
these fruit bats are in a race to return to the roost…
[high-pitched squeaking]
…for with daylight comes danger.
[tense music playing]
Birds.
[high-pitched squeaking]
They evolved flight long before the mammals.
[tense music intensifies]
Faster and stronger than bats…
eagles are armed with deadly talons.
[squeaking]
[music fades]
[high-pitched squeaking]
But as dusk falls,
the skies belong to the bats once more.
[serene music playing]
Millions take to the wing,
knowing that safety lies in numbers
and in the coming darkness.
At the same time as bats were first moving into the air,
other mammals were moving into the sea…
…attracted by the abundance of food hidden beneath the waves.
The mammals' journey into the oceans was a gradual one.
[lowing]
These are Maiacetus,
two-and-a-half-meter-long ancestors of the whales.
[lowing]
But unlike whales, they still spend much of their time lazing on land.
[peaceful music playing]
It's in the water that they come alive…
chasing schools of fish.
His time down here is limited by how long he can hold his breath.
He seems caught between two worlds,
especially when facing danger.
[ominous music playing]
The mammal's intelligence is his only defense…
but he can't stay down here forever.
[ominous music continues]
Otodus.
Twice the length of a great white shark.
With finely-tuned senses, it can pinpoint his exact location,
and it's in no hurry to make its move.
The Maiacetus is running out of air.
[tense, hurried music playing]
In open water, there's no escape.
An overhang offers refuge.
But time is running out.
[music intensifies]
A gully provides cover.
[music fades]
[grunting]
Safe
and able to breathe once more.
[lowing]
[grunting]
Mammals had a long way to go to become masters of the world's oceans,
but it was only a matter of time.
As the planet continued to cool,
it fed an explosion of life…
allowing the giants of today to evolve.
[rousing music playing]
The mammals had gone from tiny land animals…
to being bigger than dinosaurs.
With each giant breath,
they use oxygen far more effectively than Maiacetus.
And being warm-blooded,
their muscles are always at a temperature for maximum performance…
…allowing the whales to generate sustained bursts of energy.
[dark, pulsing music playing]
When competing for a mate,
humpback males exploit this ability to the full…
pursuing a single female.
This is much more than about speed.
The males stay as close to the female as possible
so she can judge their strength and stamina.
[dark, pulsing music continues]
Bubble streaming intimidates rivals.
The males plow into each other.
Some get left behind,
still fighting.
[dramatic music playing]
The main group keeps up the chase…
hot on the tail of the female.
[music ends abruptly]
Then suddenly,
she stops.
[peaceful music playing]
Hanging in the water…
she has called off the race.
She has made her decision…
and allows one male…
to approach.
The mammals have conquered every habitat on Earth.
Land, air, and sea.
The asteroid strike had allowed the mammals to go from lowly underdogs…
to become a global power.
Such is the role of chance in the history of life on our planet.
[music fades]
But there is one more chapter in the mammal story still to be told.
Two and a half million years ago,
the mammals were faced with a new challenge.
[wind howling]
[poignant music playing]
What had been a slow cooling of the planet intensified.
The start of an ice age.
From its frozen wastes would come a new force…
a mammal armed with more intelligence and adaptability than any before.
The most dangerous animal the world had ever seen.
[sinister music playing]
[music ends]
[rousing music playing]