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[tense music playing]
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[distant roaring]
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[Morgan Freeman] In the four billion years
of life on our planet,
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countless species have risen...
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and fallen.
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[distant roaring]
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But one remarkable dynasty
has had a greater impact than any other.
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[roaring]
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The mammals.
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This is the story of their epic journey...
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[roaring]
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...to become rulers of the world.
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[music fades]
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{\an8}[rousing music playing]
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[snarling]
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{\an8}[trilling]
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{\an8}[screeching]
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{\an8}[rousing music continues]
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[growling]
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[wind howling]
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{\an8}[rumbling]
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[rousing music intensifies]
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[music fades]
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{\an8}[insects chirping]
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Hidden in the ancient Jurassic forests...
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mammals came from humble beginnings...
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ruled over by the greatest dynasty
that ever lived...
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[distant bellowing]
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...the dinosaurs.
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[growls softly]
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They dominated so totally...
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[snorting]
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...that early mammals
were confined to the shadows.
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For the most part, they were small,
keeping to the trees...
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away from the giants.
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They became nocturnal,
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developing a range of heightened senses
that helped them in the dark.
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Under the dinosaurs' rule,
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there was a limit
to how far they could rise.
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But in time, everything changed.
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One of the most violent events
in our planet's history
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heralded a new era.
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[poignant music playing]
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Despite the devastation,
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the planet did recover.
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Within a few million years,
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forests had regrown
and carpeted much of the land.
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The climate became hot and wet.
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The perfect conditions
for life to flourish.
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A world primed
for a new wave of evolution.
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- [insects chirping]
- [birds squawking]
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The asteroid had inflicted
devastating losses on the mammals...
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yet some of the smaller ones,
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able to hide in holes, had survived.
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[creature chattering]
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Free of the dinosaurs,
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they could finally
venture out of the shadows
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and come into the open.
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- [birds chirping]
- [chattering]
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Like their ancestors,
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coatis have many adaptations
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that help them thrive
in the rich rainforest.
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Extremely social,
they find safety in numbers.
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The mother's flexible nose can smell food
hidden beneath the leaf litter.
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A supersense honed over millions of years
of foraging in the darkness.
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Like all mammals, coatis are warm-blooded,
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so can be active at all times.
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That means these babies
need plenty of energy.
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Fortunately, mammals have evolved
an extraordinary solution.
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Milk.
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[suckling]
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They can feed their young
whenever they choose,
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even when food is scarce.
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But milk wasn't
the early mammals' only secret weapon.
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They also had brain power.
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[tapping]
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And it's still just as important today.
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In the forests of Costa Rica,
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this capuchin monkey
is trying to solve a puzzle.
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How to get the meat
from inside a closed clam.
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The monkey isn't strong enough
to crack the shell...
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[tapping continues]
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but it's discovered that repeated
hammering will tire the clam...
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until it finally opens.
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Learning this lesson takes a large brain...
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[clam thuds on ground]
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- ...and coordination.
- [squeaks]
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[playful music playing]
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This unique intelligence
allowed their primate ancestors
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to survive in the forest
of 50 million years ago.
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Clever animals tend to be inquisitive...
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and that can pay huge dividends.
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This female has learned
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and remembered
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where she can find water.
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But it's too deep to reach.
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Luckily, she has an inspired solution.
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She turns her tail into a sponge.
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But not all their challenges
are to do with finding food and water.
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[squeaks]
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Some fruit is collected not to eat...
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but to rub over their bodies.
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This fruit contains citronella,
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an oil that mosquitoes can't stand.
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[uplifting music playing]
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The monkeys have discovered
their very own insect repellent.
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Free from pesky biting insects,
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the clever capuchins can finally relax.
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[music ends]
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But just as their ancestors
were beginning to make progress,
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the warm, wet conditions
in which they had thrived began to change.
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The Antarctic landmass
started to split away from South America...
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creating the space for new ocean currents...
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that helped drive a global cooling.
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The climate was switching
into a new, colder state.
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[poignant music playing]
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But that was just the beginning.
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As Antarctica became colder
and more isolated,
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the huge continent froze,
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locking up
much of the planet's fresh water.
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As the world further north dried out,
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it became a harsher,
more difficult place to live.
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Food became more spread out,
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harder to find.
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And as the Earth changed,
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so did the mammals.
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[heavy footstep]
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[snorting]
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Some became enormous.
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A male Megacerops.
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[grunting]
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Two and a half meters tall...
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[grunting]
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...four meters long...
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and three tons in weight.
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[snorting]
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[grunts]
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Its huge size allows it to travel
large distances in search of food...
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[grunting]
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...and ensures it has reserves
to get through leaner times.
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[majestic music playing]
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Mammals were now big enough
to rival the long-lost dinosaurs.
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But being big has other implications...
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especially when it comes
to finding a mate.
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[snorting]
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[grunting]
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This female is already
closely guarded by a male,
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much larger than the first.
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[snorts]
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[growling]
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If challenged,
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he could seriously injure his opponent.
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[roaring]
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[snorts]
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[grunting]
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But the smaller male may be in luck.
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Another female,
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and she seems to be alone.
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[grunts]
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It's the chance he's been waiting for.
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[grunting]
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[growling]
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He has a rival.
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[roaring]
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This time, they're evenly matched.
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[grunting, growling]
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[tense music playing]
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[bellows]
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[grunting]
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[bellows]
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[roars]
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- [bellowing]
- [growling]
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[roaring, growling]
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[growling]
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[grunting]
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With these mammals...
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[growls]
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...size matters.
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But even the mightiest Megacerops
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couldn't overcome
the planet's next great challenge.
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The formation of Antarctica
was creating global climate chaos.
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As ocean currents shifted
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and the planet dried...
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it became a tinderbox.
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00:17:23,751 --> 00:17:25,753
[mournful music playing]
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Wildfires ravaged the land...
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clearing the way
for something completely different...
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something that would challenge mammals
as never before.
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As the smoke cleared,
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there rose from the ashes
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a life-form that had previously
only survived in the margins.
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Grass.
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Taking root during the great drying...
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it spread so quickly,
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it would soon cover one-fifth of the land.
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00:18:51,964 --> 00:18:56,385
But the endless plains
were no paradise for the mammals.
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Many couldn't digest grass
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and soon went extinct.
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[insects chirping]
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[snorts]
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Twenty million years later,
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and today's grazing mammals
remain locked in an arms race
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with this green invader.
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They have evolved a whole swathe
of game-changing adaptations.
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Specialized teeth,
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strengthened to prevent silica
in the grass
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from wearing them out...
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00:19:50,814 --> 00:19:54,276
and huge bellies to process it all.
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Their young are born fully formed...
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[snorting]
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00:20:06,038 --> 00:20:08,415
...able to walk within hours of birth...
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00:20:14,713 --> 00:20:17,633
and follow their herd
in search of fresh growth.
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00:20:21,803 --> 00:20:25,432
Mammals have truly conquered
the grassy plains...
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00:20:30,479 --> 00:20:35,567
their huge numbers the most obvious sign
of this exceptional success.
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00:20:41,865 --> 00:20:44,993
But just as some mammals evolved
to feed on the grass,
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00:20:46,453 --> 00:20:49,957
others evolved to feed on the grazers.
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00:20:54,044 --> 00:20:55,170
Hunters.
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00:20:57,422 --> 00:20:59,424
[herd lowing]
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00:21:05,430 --> 00:21:09,601
The herd has its own defense
against the cheetahs' blistering speed.
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00:21:15,899 --> 00:21:18,110
- Many eyes...
- [snorting, grunting]
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00:21:18,193 --> 00:21:19,569
...spot the danger early.
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00:21:19,653 --> 00:21:22,406
- [herd grunting]
- [bird squawking]
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00:21:22,489 --> 00:21:25,242
[tense music playing]
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00:21:30,664 --> 00:21:32,332
[grunting]
225
00:21:32,416 --> 00:21:37,045
Running bodies create confusion
for the young to hide in.
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00:21:39,631 --> 00:21:41,466
But the big cat has a plan...
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00:21:43,552 --> 00:21:46,346
forged by its clever mammalian brain.
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00:21:50,976 --> 00:21:52,060
Panic the herd,
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00:21:52,728 --> 00:21:53,937
split them up,
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00:21:55,355 --> 00:21:57,232
and target a lone calf.
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00:22:07,075 --> 00:22:09,077
[tense, energetic music playing]
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00:22:22,341 --> 00:22:24,468
Desperate to defend her only calf,
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00:22:25,635 --> 00:22:27,679
the female wildebeest counters.
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00:22:34,061 --> 00:22:36,521
The chase is far from over.
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00:22:41,401 --> 00:22:43,612
The cheetah has lost a lot of ground...
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00:22:46,323 --> 00:22:49,076
but the calf is tiring.
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00:22:49,159 --> 00:22:51,661
[tense, energetic music continues]
238
00:23:02,881 --> 00:23:04,508
[music slows]
239
00:23:04,591 --> 00:23:06,718
As the youngster turns,
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00:23:07,302 --> 00:23:09,971
it's the hunter
who must now run for its life.
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00:23:15,852 --> 00:23:17,979
[herd lowing]
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00:23:19,564 --> 00:23:21,733
The calf is safe once more...
243
00:23:21,817 --> 00:23:24,486
[calm music playing]
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00:23:27,364 --> 00:23:29,825
...but the cheetah will be back...
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00:23:38,208 --> 00:23:42,879
and the war between the grassland mammals
will continue
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00:23:42,963 --> 00:23:45,966
as it has done for millions of years.
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00:23:47,092 --> 00:23:49,261
[tranquil music playing]
248
00:24:08,947 --> 00:24:11,074
In prehistoric South America,
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00:24:12,075 --> 00:24:15,078
the grasslands played host
to the same battle...
250
00:24:17,956 --> 00:24:19,916
but with very different animals.
251
00:24:20,709 --> 00:24:22,711
[intriguing music playing]
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00:24:32,262 --> 00:24:33,889
This giant armadillo...
253
00:24:36,475 --> 00:24:38,185
is also a mammal...
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00:24:40,520 --> 00:24:43,064
though one the size of a car.
255
00:24:45,567 --> 00:24:48,195
Doedicurus may not be fast,
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00:24:49,821 --> 00:24:51,406
but what they lack in speed...
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00:24:51,490 --> 00:24:52,782
[trilling]
258
00:24:52,866 --> 00:24:57,412
...they make up for with armor
and a lethal tail...
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00:25:03,293 --> 00:25:04,878
[grunts softly, snorts]
260
00:25:04,961 --> 00:25:09,132
...adaptations that protect them
and their young
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00:25:09,216 --> 00:25:11,468
from any would-be predators.
262
00:25:11,551 --> 00:25:13,386
[trilling]
263
00:25:17,682 --> 00:25:19,684
[ominous music playing]
264
00:25:25,190 --> 00:25:27,442
[soft growling]
265
00:25:29,444 --> 00:25:30,487
A Smilodon...
266
00:25:33,615 --> 00:25:35,116
but a mere youngster.
267
00:25:37,702 --> 00:25:39,162
- [soft growling]
- [snorting]
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00:25:39,246 --> 00:25:41,206
[whimsical music playing]
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00:25:43,333 --> 00:25:44,543
[trilling]
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00:25:44,626 --> 00:25:46,211
He's not a serious threat...
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00:25:46,294 --> 00:25:47,587
[trilling]
272
00:25:47,671 --> 00:25:50,048
[hissing, growling]
273
00:25:50,131 --> 00:25:52,342
...even with his dagger-like teeth.
274
00:25:56,805 --> 00:25:59,182
He's never seen a Doedicurus up close,
275
00:26:00,058 --> 00:26:03,395
and their defenses are intriguing.
276
00:26:04,896 --> 00:26:06,189
[hissing]
277
00:26:12,529 --> 00:26:14,030
[soft growling]
278
00:26:15,824 --> 00:26:18,201
His curiosity gets the better of him.
279
00:26:18,285 --> 00:26:20,453
[trilling]
280
00:26:20,537 --> 00:26:21,830
[purring]
281
00:26:24,291 --> 00:26:26,126
[trilling]
282
00:26:26,209 --> 00:26:27,794
- [grunts]
- [hisses]
283
00:26:28,712 --> 00:26:31,256
[whimsical music continues]
284
00:26:31,339 --> 00:26:33,508
[trilling]
285
00:26:33,592 --> 00:26:35,969
He explores every angle.
286
00:26:38,221 --> 00:26:40,223
[snorting]
287
00:26:42,058 --> 00:26:43,685
[trilling]
288
00:26:50,483 --> 00:26:53,987
For the young Doedicurus,
the only option is to stay put.
289
00:26:54,070 --> 00:26:55,780
[trilling]
290
00:27:01,286 --> 00:27:04,497
The giant armadillos' armor
is completely impregnable...
291
00:27:05,749 --> 00:27:07,417
[growls softly]
292
00:27:07,500 --> 00:27:08,668
...and they know it.
293
00:27:11,796 --> 00:27:13,590
- [trilling]
- [growling]
294
00:27:18,845 --> 00:27:20,347
[growling]
295
00:27:22,766 --> 00:27:25,602
But there is one obvious opportunity.
296
00:27:26,645 --> 00:27:28,605
[trilling]
297
00:27:28,688 --> 00:27:30,231
[growls]
298
00:27:31,566 --> 00:27:35,028
The young Doedicurus is so much smaller.
299
00:27:37,697 --> 00:27:39,324
If he can get a hold on it...
300
00:27:39,407 --> 00:27:41,409
- [growling]
- [trilling]
301
00:27:41,493 --> 00:27:43,870
...he might be able to turn it over.
302
00:27:43,953 --> 00:27:44,996
[hissing]
303
00:27:47,791 --> 00:27:49,376
[trilling]
304
00:27:49,459 --> 00:27:51,544
But not with the adults around.
305
00:27:54,756 --> 00:27:56,341
[low growling]
306
00:27:57,550 --> 00:28:00,011
- Another stalemate.
- [juvenile moans]
307
00:28:01,012 --> 00:28:03,014
- [trilling]
- [snarling]
308
00:28:08,645 --> 00:28:12,399
Battles between the mammals
have always driven their evolution,
309
00:28:13,566 --> 00:28:16,695
and they don't just happen
in the grasslands.
310
00:28:16,778 --> 00:28:19,280
[wind whistling]
311
00:28:19,364 --> 00:28:20,907
Fifty million years ago,
312
00:28:21,700 --> 00:28:26,371
what are now India and Asia
collided on an epic scale.
313
00:28:28,915 --> 00:28:31,710
The crash forced the land into the sky,
314
00:28:32,460 --> 00:28:35,213
creating the towering Himalayas.
315
00:28:35,880 --> 00:28:38,383
[majestic music playing]
316
00:28:42,804 --> 00:28:46,307
Today, they are 2,500 kilometers long,
317
00:28:47,183 --> 00:28:49,227
almost nine kilometers high,
318
00:28:50,562 --> 00:28:51,938
and still growing.
319
00:28:55,024 --> 00:28:57,694
With their freezing temperatures
and thin air,
320
00:28:58,486 --> 00:29:02,240
these mountains are uninhabitable
for most animals.
321
00:29:02,323 --> 00:29:04,993
[unsettling music playing]
322
00:29:07,454 --> 00:29:08,788
But not all.
323
00:29:15,712 --> 00:29:17,422
Deep in a sunless valley...
324
00:29:23,178 --> 00:29:24,679
a male snow leopard...
325
00:29:30,685 --> 00:29:33,813
and an ibex that has fallen to its death.
326
00:29:44,991 --> 00:29:47,243
The leopard is very old,
327
00:29:48,578 --> 00:29:51,539
worn and tattered
by his harsh mountain life.
328
00:29:56,711 --> 00:30:01,591
At these altitudes,
mammals must feed regularly to keep warm.
329
00:30:05,470 --> 00:30:08,765
But the Himalayas present
the ultimate hunting challenge.
330
00:30:14,437 --> 00:30:17,565
High above the valley, a female...
331
00:30:22,821 --> 00:30:26,491
and her cubs, fathered by the male.
332
00:30:28,576 --> 00:30:29,953
Three of them in total,
333
00:30:30,829 --> 00:30:33,665
all amazingly camouflaged.
334
00:30:40,338 --> 00:30:42,966
Snow leopards have thick fur,
335
00:30:44,050 --> 00:30:45,593
large paws,
336
00:30:46,678 --> 00:30:47,929
and long tails...
337
00:30:52,600 --> 00:30:56,479
perfect adaptations for the coldest,
338
00:30:57,146 --> 00:31:00,692
most precipitous nursery on Earth.
339
00:31:00,775 --> 00:31:02,777
[stirring music playing]
340
00:31:18,751 --> 00:31:20,503
[music fades]
341
00:31:23,590 --> 00:31:25,508
Away from the dangerous cliffs...
342
00:31:27,343 --> 00:31:29,345
[light, playful music playing]
343
00:31:29,429 --> 00:31:31,764
...the mother initiates a hunting lesson.
344
00:31:31,848 --> 00:31:32,932
[soft growling]
345
00:31:36,394 --> 00:31:37,645
[growling]
346
00:31:44,152 --> 00:31:47,113
Teaching and caring for one's young
347
00:31:48,781 --> 00:31:50,909
is a key mammalian trait.
348
00:32:05,465 --> 00:32:08,968
These cubs will stay with their mother
for nearly two years...
349
00:32:15,016 --> 00:32:19,979
learning the skills needed to survive
on the very edge of life.
350
00:32:20,980 --> 00:32:22,774
[music ends]
351
00:32:25,818 --> 00:32:29,948
At these altitudes,
every opportunity must be taken.
352
00:32:34,911 --> 00:32:37,997
The old male is tracking a herd.
353
00:32:44,879 --> 00:32:49,550
In this vertical world,
he must get above his prey...
354
00:32:49,634 --> 00:32:51,636
[tense music playing]
355
00:33:02,689 --> 00:33:04,315
...and close enough...
356
00:33:05,984 --> 00:33:07,485
for an ambush.
357
00:33:14,701 --> 00:33:16,703
[tense music continues]
358
00:33:46,733 --> 00:33:48,276
[loose rocks tinkle]
359
00:33:50,361 --> 00:33:52,113
[rocks clattering]
360
00:33:53,906 --> 00:33:56,325
[water splashing]
361
00:34:03,541 --> 00:34:04,541
[snorts]
362
00:34:10,840 --> 00:34:12,175
This time
363
00:34:13,176 --> 00:34:15,178
death has claimed them both.
364
00:34:20,349 --> 00:34:22,351
[poignant music playing]
365
00:34:30,943 --> 00:34:34,322
But the leopard's legacy lives on.
366
00:34:38,951 --> 00:34:40,536
In a few months' time,
367
00:34:41,788 --> 00:34:46,000
his cubs will leave their mother
and start to hunt alone,
368
00:34:47,960 --> 00:34:50,713
having learned all the skills they need
369
00:34:52,465 --> 00:34:55,176
to survive at the top of the world.
370
00:35:12,985 --> 00:35:15,488
Although they had conquered the land,
371
00:35:16,823 --> 00:35:18,783
the mammals didn't stop there.
372
00:35:18,866 --> 00:35:20,868
[insects chirping]
373
00:35:24,205 --> 00:35:29,544
One branched out and went
in an entirely different direction.
374
00:35:38,511 --> 00:35:43,766
Fifty million years ago,
bats opened up a whole new realm...
375
00:35:47,562 --> 00:35:49,272
through flight.
376
00:35:53,484 --> 00:35:55,486
[gentle music playing]
377
00:36:16,966 --> 00:36:20,261
Flying allows animals
to search much further for food...
378
00:36:23,723 --> 00:36:26,767
and gather in their millions.
379
00:36:39,155 --> 00:36:44,243
Today, one in five of all mammal species
is a bat.
380
00:36:44,327 --> 00:36:46,329
[high-pitched squeaking]
381
00:36:50,124 --> 00:36:54,295
But bats were not the first animals
to take to the skies.
382
00:36:59,425 --> 00:37:01,636
Having spent the night foraging,
383
00:37:01,719 --> 00:37:05,223
these fruit bats are in a race
to return to the roost...
384
00:37:05,306 --> 00:37:07,308
[high-pitched squeaking]
385
00:37:10,311 --> 00:37:13,648
...for with daylight comes danger.
386
00:37:15,024 --> 00:37:17,193
[tense music playing]
387
00:37:17,276 --> 00:37:18,319
Birds.
388
00:37:18,861 --> 00:37:20,863
[high-pitched squeaking]
389
00:37:26,869 --> 00:37:30,581
They evolved flight
long before the mammals.
390
00:37:41,968 --> 00:37:43,970
[tense music intensifies]
391
00:37:50,810 --> 00:37:53,437
Faster and stronger than bats...
392
00:38:01,070 --> 00:38:03,781
eagles are armed with deadly talons.
393
00:38:05,491 --> 00:38:07,493
[squeaking]
394
00:38:07,576 --> 00:38:10,162
[music fades]
395
00:38:10,246 --> 00:38:12,039
[high-pitched squeaking]
396
00:38:12,123 --> 00:38:13,958
But as dusk falls,
397
00:38:16,085 --> 00:38:19,964
the skies belong to the bats once more.
398
00:38:20,047 --> 00:38:22,550
[serene music playing]
399
00:38:22,633 --> 00:38:24,385
Millions take to the wing,
400
00:38:25,011 --> 00:38:28,639
knowing that safety lies in numbers
401
00:38:29,557 --> 00:38:32,393
and in the coming darkness.
402
00:38:47,825 --> 00:38:51,579
At the same time
as bats were first moving into the air,
403
00:38:52,288 --> 00:38:55,833
other mammals were moving into the sea...
404
00:38:59,754 --> 00:39:03,966
{\an8}...attracted by the abundance of food
hidden beneath the waves.
405
00:39:17,980 --> 00:39:22,568
The mammals' journey into the oceans
was a gradual one.
406
00:39:22,651 --> 00:39:24,653
[lowing]
407
00:39:27,865 --> 00:39:29,950
These are Maiacetus,
408
00:39:30,868 --> 00:39:34,997
two-and-a-half-meter-long ancestors
of the whales.
409
00:39:38,292 --> 00:39:40,086
[lowing]
410
00:39:40,169 --> 00:39:45,883
But unlike whales, they still spend
much of their time lazing on land.
411
00:39:45,966 --> 00:39:47,968
[peaceful music playing]
412
00:39:51,806 --> 00:39:55,267
It's in the water that they come alive...
413
00:39:57,812 --> 00:39:59,605
chasing schools of fish.
414
00:40:12,410 --> 00:40:16,205
His time down here is limited
by how long he can hold his breath.
415
00:40:26,841 --> 00:40:29,552
He seems caught between two worlds,
416
00:40:31,220 --> 00:40:33,264
especially when facing danger.
417
00:40:33,347 --> 00:40:35,349
[ominous music playing]
418
00:40:49,488 --> 00:40:53,242
The mammal's intelligence
is his only defense...
419
00:40:56,787 --> 00:40:58,873
but he can't stay down here forever.
420
00:40:58,956 --> 00:41:00,958
[ominous music continues]
421
00:41:02,418 --> 00:41:03,669
Otodus.
422
00:41:04,587 --> 00:41:07,339
Twice the length of a great white shark.
423
00:41:09,175 --> 00:41:13,971
With finely-tuned senses,
it can pinpoint his exact location,
424
00:41:15,514 --> 00:41:17,975
and it's in no hurry to make its move.
425
00:41:21,312 --> 00:41:23,856
The Maiacetus is running out of air.
426
00:41:23,939 --> 00:41:25,941
[tense, hurried music playing]
427
00:41:34,116 --> 00:41:37,119
In open water, there's no escape.
428
00:41:39,914 --> 00:41:42,082
An overhang offers refuge.
429
00:41:49,548 --> 00:41:51,926
But time is running out.
430
00:41:56,180 --> 00:41:58,182
[music intensifies]
431
00:42:05,940 --> 00:42:07,816
A gully provides cover.
432
00:42:13,572 --> 00:42:15,574
[music fades]
433
00:42:15,658 --> 00:42:17,493
[grunting]
434
00:42:17,576 --> 00:42:18,577
Safe
435
00:42:19,787 --> 00:42:22,081
and able to breathe once more.
436
00:42:22,164 --> 00:42:24,166
[lowing]
437
00:42:25,000 --> 00:42:26,043
[grunting]
438
00:42:30,339 --> 00:42:35,177
Mammals had a long way to go
to become masters of the world's oceans,
439
00:42:38,597 --> 00:42:40,766
but it was only a matter of time.
440
00:42:52,319 --> 00:42:54,405
As the planet continued to cool,
441
00:42:55,281 --> 00:42:57,366
it fed an explosion of life...
442
00:43:05,666 --> 00:43:09,587
allowing the giants of today to evolve.
443
00:43:17,052 --> 00:43:19,054
[rousing music playing]
444
00:43:30,065 --> 00:43:33,277
The mammals had gone
from tiny land animals...
445
00:43:35,446 --> 00:43:38,449
to being bigger than dinosaurs.
446
00:43:58,385 --> 00:44:00,095
With each giant breath,
447
00:44:00,679 --> 00:44:05,267
they use oxygen
far more effectively than Maiacetus.
448
00:44:07,102 --> 00:44:08,896
And being warm-blooded,
449
00:44:08,979 --> 00:44:13,609
their muscles are always at a temperature
for maximum performance...
450
00:44:17,571 --> 00:44:22,785
...allowing the whales
to generate sustained bursts of energy.
451
00:44:24,078 --> 00:44:26,705
[dark, pulsing music playing]
452
00:44:34,505 --> 00:44:36,215
When competing for a mate,
453
00:44:36,924 --> 00:44:39,843
humpback males
exploit this ability to the full...
454
00:44:45,265 --> 00:44:47,101
pursuing a single female.
455
00:44:53,816 --> 00:44:56,193
This is much more than about speed.
456
00:45:01,490 --> 00:45:05,035
The males stay
as close to the female as possible
457
00:45:05,119 --> 00:45:08,539
so she can judge
their strength and stamina.
458
00:45:14,712 --> 00:45:16,714
[dark, pulsing music continues]
459
00:45:28,726 --> 00:45:33,021
Bubble streaming intimidates rivals.
460
00:45:36,775 --> 00:45:39,111
The males plow into each other.
461
00:45:49,955 --> 00:45:51,415
Some get left behind,
462
00:45:52,875 --> 00:45:53,917
still fighting.
463
00:45:54,001 --> 00:45:56,712
[dramatic music playing]
464
00:46:08,015 --> 00:46:10,893
The main group keeps up the chase...
465
00:46:13,270 --> 00:46:15,647
hot on the tail of the female.
466
00:46:26,533 --> 00:46:27,701
[music ends abruptly]
467
00:46:31,497 --> 00:46:32,998
Then suddenly,
468
00:46:33,957 --> 00:46:35,375
she stops.
469
00:46:41,215 --> 00:46:43,217
[peaceful music playing]
470
00:46:46,011 --> 00:46:47,596
Hanging in the water...
471
00:46:50,599 --> 00:46:52,518
she has called off the race.
472
00:47:01,318 --> 00:47:03,320
She has made her decision...
473
00:47:11,161 --> 00:47:12,996
and allows one male...
474
00:47:16,291 --> 00:47:17,626
to approach.
475
00:47:24,383 --> 00:47:27,886
The mammals have conquered
every habitat on Earth.
476
00:47:32,307 --> 00:47:35,602
Land, air, and sea.
477
00:47:41,567 --> 00:47:46,321
The asteroid strike had allowed
the mammals to go from lowly underdogs...
478
00:47:49,575 --> 00:47:51,535
to become a global power.
479
00:47:53,954 --> 00:48:00,586
Such is the role of chance
in the history of life on our planet.
480
00:48:05,799 --> 00:48:07,801
[music fades]
481
00:48:09,928 --> 00:48:15,601
But there is one more chapter
in the mammal story still to be told.
482
00:48:20,564 --> 00:48:22,482
Two and a half million years ago,
483
00:48:23,817 --> 00:48:26,612
the mammals were faced
with a new challenge.
484
00:48:27,863 --> 00:48:29,323
[wind howling]
485
00:48:29,406 --> 00:48:31,408
[poignant music playing]
486
00:48:37,205 --> 00:48:41,960
What had been
a slow cooling of the planet intensified.
487
00:48:49,009 --> 00:48:51,845
The start of an ice age.
488
00:48:55,641 --> 00:48:59,311
From its frozen wastes
would come a new force...
489
00:49:01,146 --> 00:49:07,402
a mammal armed with more intelligence
and adaptability than any before.
490
00:49:10,238 --> 00:49:14,076
The most dangerous animal
the world had ever seen.
491
00:49:14,159 --> 00:49:16,161
[sinister music playing]
492
00:49:19,331 --> 00:49:20,749
[music ends]
493
00:49:21,917 --> 00:49:24,503
[rousing music playing]