Original subtitles

The savage rocky shores of Christmas Island,

200 miles south of Java, in the Indian 0cean.

It's November, the moon is in its third quarter,

and the sun is just setting.

And in a few hours from now, on this very shore,

a thousand million lives will be launched.

These crabs are all females,

and of a kind that occurs only on Christmas Island.

As darkness falls, more and more of them appear,

clambering resolutely down to the sea.

Now it's nearing midnight.

Their numbers can only be guessed at,

but on the whole island there are probably 120 million of these crabs,

and nearly all the adult females among them

have chosen this time for their annual spawning.

A crab like this is carrying about 100,000 eggs,

and she has to shed them directly into the sea if they are to hatch.

That's a hazardous business for her

because although her distant ancestors came from the sea,

she is a land crab...and she can't swim.

So if a wave sweeps her away, she will assuredly drown.

But, nonetheless, her compulsion to launch the next generation is irresistible,

and when she does reach the sea,

her triumph is apparently ecstatic.

The crabs have picked the moment when the tide is at its highest,

so they have the shortest distance to travel to reach the water.

The astronomical numbers of their eggs turn the clear ocean water

into a black turbid soup.

As dawn approaches and the tide recedes,

so the eggs are swept out to sea.

Since life began, the sea has been full of eggs.

The most ancient animals on the planet still live and breed there.

Some, such as sea urchins, may be male or female.

Both sexes discharge their sex cells during the same short period,

so that they unite in the water and form fertile eggs.

The sea brings them together,

keeps the fertilised eggs at the stable temperature

necessary for development,

and transports them for hundreds of miles to new environments.

This perpetually-renewed soup provides a vast banquet

for other floating creatures.

Small complex globes of jelly

drive themselves through the water with lines of beating hairs

and filter out the majority of the eggs.

Many fish also scatter their eggs in the water

and abandon them in a similar way.

But the most stupendous egg producer of all

lies beneath, nearly buried in the reef.

The giant clam first discharges sperm...

and then, half an hour later -

because it's both male and female - eggs.

In each annual spasm, it discharges a thousand million.

In the north eastern Pacific,

vast shoals of herring are moving towards the coast of Alaska.

These must be the densest concentrations of animal bodies

to be found anywhere in the world.

Throughout their lives they move in huge assemblies, millions strong,

sieving their floating food from the ocean waters.

Now, even more tightly packed together,

they start to spawn.

Their eggs are sticky

and cover the leaves of the sea plants.

As the waves stir the waters,

some of the vast deposit floats up to the surface.

These milky slicks, miles long, stretching around the coast,

may look like mud washed into the sea by a great river.

But they're made up of nothing but eggs and milt,

the annual legacy of the departed herring shoals.

Many of the eggs are washed ashore

and the receding tide leaves them stranded on the rocks

like drifts of snow.

And this provides a feast for birds.

Gulls gorge on them.

Thousands upon thousands of turnstones,

sandpipers and other small waders also come.

For them, this bonanza could not be better timed,

for they are about to set off on their spring migration

and they need to stock up with fuel before starting on their long flight.

It's effective to lay vast numbers of eggs when there's water to distribute them.

0n land, such numbers would be less practical.

Even so, some land animals produce them in hundreds.

These are young mantis.

Their mother surrounded her batch of eggs with a liquid froth,

which rapidly hardened.

The young developed within and now they're ready for independent life.

Their infant bodies are covered with a thin membrane

and each hangs suspended by a thread of silk,

while it slowly disentangles itself.

0ne egg mass produced by a single female

may release as many as 400 young.

While latecomers continue to emerge,

the first-born clamber up over them

and prepare themselves for adult life.

Frogs produce young that swim and breathe through gills - tadpoles.

Most frogs lay their eggs in ponds and streams.

But not all.

This Trinidad tree frog creates its own watery nursery up in a tree,

where there are no predatory fish to worry them or their babies.

The female pulls two leaves together with her hind legs

and extrudes her eggs between them.

The eggs are surrounded by a sticky jelly

which holds the leaves together.

As they emerge,

so the male on her back discharges his sperm and fertilises them.

0ver the next eight days, the eggs slowly turn into tadpoles.

0nce the first eggs hatch, the jelly begins to dissolve.

The leaves separate and the liquid within starts to trickle out.

And with it come the tadpoles.

But this is no disaster.

The tadpoles drop into a new existence,

for their parents always build the nurseries overhanging water.

Here, they can find something to eat

and start to build their adult bodies.

This South American rain frog is totally independent of pools and rivers.

It lays its eggs on the ground.

But each small globe is full of liquid.

The tadpole not only develops inside this capsule, but stays there -

swimming in its own personal pond until tadpole becomes frog.

When the young finally emerge,

they have no need to swim.

Like their parents, they have lungs and legs.

These elegant eggs are only the size of grains of sand.

The young of the owl butterfly.

Their beautiful shells are not just protective, they're edible.

The mother butterfly built them from her bodily reserves of protein,

so her young, when they emerge, have their first meal immediately to hand.

There's another way of providing food for your developing young.

Instead of getting it from your own body,

you can get it from somebody else's.

That, of course, involves the grisly process of body snatching,

and that's just what's going on in this dried-up mudflat

in the western United States.

This strange insect

is a murderous and very hard-working wasp.

She is digging a tunnel to serve as her nursery.

The sun-baked ground she selects is rock hard,

and digging a hole in it is not easy.

A lot of work is invested in one of these holes,

and if one seems vacant, another wasp will try to claim it.

0nce the burrow is finished,

the female performs an elaborate dance around it -

remembering its surroundings so she knows exactly where it is.

And then she conceals it, so that none but she is likely to find it.

Her nursery must now be provisioned,

and for that she needs fresh meat.

A caterpillar.

First, she paralyses it with her sting.

Thanks to her dance, she knows exactly where her hidden hole lies.

Each burrow will have several caterpillars in it,

and each addition requires the same stopping and unstopping of the tunnel entrance.

The urge to collect caterpillars is so strong

that they'll pick them up anywhere. Watch this.

She has already laid a long yellow egg on the first caterpillar.

When the tunnel is full, she seals it with special care.

She uses a grain of gravel like a pneumatic ram,

vibrating it by buzzing her wing muscles -

one of the few instances of an insect using a tool.

In a few days, when the egg hatches,

the grub will find fresh meat awaiting it.

These cabbage white caterpillars are also doomed.

Another species of wasp injects them -

not with paralysing poison, but with eggs.

Day after day, the caterpillars grow and mature, apparently unaffected.

But inside them the wasp eggs are developing.

Having fed so richly on the entrails of their caterpillar host,

the wasp grubs are ready to pupate as soon as they emerge.

They start straightaway to spin their silken cocoons.

Ten days later, they have become adult wasps,

and are themselves searching for caterpillars.

Just where eggs are placed can be very important.

These mosquitoes in Trinidad deposit theirs on the surface of water,

where they float like rafts.

The females signal with their legs,

perhaps warning other flying females that this place is already taken.

They lay in tiny pools of standing water

and particularly favour nut shells.

Heavy raindrops might sink the tiny rafts.

If there is a shower, the adults row the eggs to shelter.

When the young hatch, they drop from the bottom of the raft

and swim down to start collecting food.

These fish also care for their eggs with great solicitude.

They are Midas cichlids from Nicaragua.

0nce a pair has selected their territory,

the male digs a small pit in the ground.

The golden-coloured female,

meanwhile, has meticulously cleaned the surface of a rock with her mouth

and now she's moving slowly over it, laying lines of sticky eggs.

As she completes each pass,

the male follows behind and discharges his sperm.

Within an hour, there are as many as 2,000 fertilised eggs on the rock wall.

Three days later, they begin to hatch.

The female gently picks off the wriggling young.

In they go - into the cradle that the male dug for them,

even before they were spawned.

They have a sticky pad on their heads

that enables them to stay attached to the gravel.

They can hardly yet be called fish.

They have no mouths and nourish themselves from a speck of yolk within their body

that is bigger than they are.

As they wriggle, they create a current that brings them oxygen.

Their eyes have now developed and much of their yolk has been used up

in building their growing bodies.

They begin to swim.

All the time their parents remain above them,

to defend them against anything that might make a meal of them.

Now their yolk is almost gone

and they must sustain themselves in a different way.

Five days after becoming free-swimming,

they start to graze over the bodies of their parents.

The adults are producing a nutritious slime from their skins,

so their cloud of babies can find food without straying too far away.

Many parents put their own personal safety at risk

in order to protect their eggs.

In Brazil, a sawfly crouches over her eggs for three long weeks,

threatening any intruder with an aggressive buzz,

flicking her wings with which she will strike if necessary,

and displaying her formidable jaws.

Even an assassin bug knows when it has met its match.

As a result of her dedication,

90% of her eggs survive to hatch.

Even then, she won't desert.

She stays with her caterpillars to protect them.

But a single guard can't be everywhere at the same time.

So her young, instead of scattering to feed, remain together.

Bigger parents have similar problems.

Snow geese in the Russian Arctic

have to be just as vigilant if they are to rear their babies.

Eggs packed with yolk

are splendid food and tempt a lot of thieves.

For Arctic foxes, this is a time of plenty.

Hundreds of eggs are lying around on the cold tundra.

But they're all defended.

Got one!

But why doesn't it eat it?

This glut of eggs won't be here for long.

With so many around, it's better to hide away the swag

to be eaten later and go back for more.

In the cold, near-freezing earth,

an egg will remain fresh and edible for a long time.

Those still in the nest, kept warm by their parents,

are beginning the universal process

that is still one of the most mysterious events in life.

The greater part of a bird's egg - the yolk,

is food for the developing young.

0n its surface, beneath the cushion of clear albumen,

lies just one fertile cell.

In the sustained warmth, it grows, divides and grows again.

Within two days, a beating heart has appeared.

Blood vessels spread around the yolk,

collecting its nourishment and transporting it to the embryo.

Twelve days later, the little creature has legs.

And beneath the tracery of blood vessels,

the tiny head is virtually complete.

15 days, and feathers are beginning to sprout.

21 days after incubation started,

the moment for hatching has arrived.

(CHIRPING)

0nce dried, the downy feathers help the tiny body to retain its warmth.

The chick is ready to start a new stage in its life.

There are few more formidable mothers than this one.

The salt water crocodile of Australia builds her nest on a river bank.

She digs a deep hole in the peaty soil.

In it, she lays several dozen eggs.

These eggs have one strange characteristic -

even though they have left her body,

the sex of the babies within them is not yet fixed.

It will depend on how she looks after them.

She covers them with dead leaves which, as they decay,

will produce the heat the eggs need in order to develop.

And it is this that determines the sex of the babies.

At 30 degrees centigrade, they will all be female.

Two degrees higher, and they will be all male.

In between, they will be exactly half and half.

If the nest temperature rises two degrees higher still,

then a third of the eggs will be male, a third female,

and a third will die.

Their emergence is less arduous than that of a baby bird,

for reptilian shells are leathery and easily broken.

The babies are so well formed

that even before they leave the shell, they can bite.

The technique of warming eggs with rotting leaves

has been brought to a fine art by the mallee fowl of southern Australia.

A pair build themselves a huge mound of sand.

In its heart lies a layer of leaves.

Every few days throughout the breeding season, the female comes to lay

and the male kicks away sand to expose that layer.

Her egg, compared with her body, is gigantic,

and as soon as she has produced it, the male covers it over.

Now the temperature must be carefully monitored.

The male measures it with its beak.

Even when visitors approach,

he stays bravely beside the mound to keep an eye on things.

If the mound is too cold, he piles sand on top.

If it's too hot, he kicks it away.

So obsessed is he with managing this mound...

that if someone interferes with it,

his first instinct is to put that right.

If I flick sand off, he flicks it back.

The chick has to dig its own way up through the sand.

It's able to do so because that huge egg contains so much yolk

that the chick could stay in it, gathering strength, for 49 days.

It'll be able to fly within 24 hours.

In the trees above,

there are chicks that are having a much harder, hungrier time.

The crested hawks laid three eggs, each a day apart,

but they started incubation when the first arrived.

So the first laid was the first to hatch,

and that chick was the first to get a meal.

With such a start,

it's already bigger than the two younger ones.

The parents work hard bringing food.

But the eldest chick nearly always gets it.

To him that hath, it shall be given.

The youngest - the smallest - stands little chance of a mouthful

as long as either of the bigger ones are in the least hungry.

0nce again, the youngest gets nothing.

And now it's dead.

This was a gamble by the adults.

Had it been a specially good year,

then they would have been ready to take advantage of it and rear three chicks.

But this year, as in most years, the gamble didn't pay off.

The little body is not totally wasted.

Some of its flesh is fed to the survivors.

Animals care for their eggs and young in many different ways,

but peripatus - a curious creature, half worm, half centipede -

provides the ultimate in parental protection.

The eggs develop inside the female

and stay there until they're so advanced

that they can survive without the protection of a shell.

So the young peripatus gets a good start in life.

No waiting around defenceless, imprisoned in an egg.

It's able to feed and hide itself just as soon as it leaves Mother.

All kinds of creatures have, independently, adopted this strategy.

The tsetse fly.

The bigger the young, the fewer a female can produce,

and the tsetse fly's baby is a whopper.

In the whole of her six-month life,

she can only give birth to a dozen of these plump grubs.

It crawls away to turn into a pupa

from which the adult fly will quickly emerge.

These baby beetles are also long past the egg stage.

Their transformation into an adult

will also take place inside the protective shell of a pupa,

but meanwhile they work as small eating machines,

gathering the food necessary to construct an adult body.

These gnat grubs avoid the pupal stage altogether.

They feed on mushrooms which disappear after a few days.

So the grubs must eat all they can while they have the chance.

To do that, they reproduce even before they become adult.

The unfertilised eggs of the female grub

begin to develop within her body.

They feed by browsing on their mother's internal organs,

so that eventually she herself is reduced by her own young to a sausage skin,

through which 30 or so grubs force their way - coming out at both ends.

Each is a clone -

genetically identical to its single parent.

Each of these 30 can do the same trick in six days' time.

In six weeks, if there were enough mushrooms, there could be 20,000 million - all identical.

A mother sea louse, a kind of crustacean,

also commits suicide in order to launch the next generation.

The mass of babies within her tiny shell have consumed so much of her energies

that as the last leaves, she, exhausted, will die.

It's not only females that can give birth.

A few exceptional males also get pregnant.

The male pipefish develops a sticky underside

where the female deposits her eggs.

Flaps of skin grow round them, and when the time comes,

the young wriggle out to take their chances in a dangerous world.

0nce they leave their father's body,

they're easily picked off by hungry sticklebacks.

The babies who remain in their mother's body for the longest time,

and who are cared for in the most comprehensive way of all,

are those of mammals.

These female sea lions mated a year ago.

The fertilised egg fixed itself to the womb wall,

tapped the mother's blood supply and grew, month after month.

Now that long development is over

and the labour of entering the outside world has begun.

The membranes that held the fluid within which the infant swam

while it was within its mother's body still partially enclose it.

For all mammal babies, the shock of leaving the warm,

totally protected haven of a mother's body

and entering the harsh, relatively cold, danger-filled world outside

is inevitably traumatic.

Baby antelopes, whose parents have to travel continuously to find food,

must be as fully developed as possible,

for they need to walk within hours, groggy though they may be.

Chinchillas are born in the high Andes.

Their world is a very cold one.

Their mothers make no nest for them, so they are born fully furred.

Were they not, they might freeze to death.

Hyena babies need not be so advanced, for they are born within a den,

where their powerful mother has little difficulty in defending them.

She can get rid of their bulk and weight

while they're still at an early stage of their development.

As soon as they emerge, like all young mammals,

they must find their mother's teat and start to suckle.

Perhaps the trickiest mammal birth of all is that of the bat.

For it, after all, has to arrive in this world

while its mother hangs upside-down from the ceiling.

Whatever happens, the baby mustn't fall.

While mother hangs acrobatically from one leg,

she stretches out the other so that the web connecting it to the tail

forms a cradle in which to catch her newborn babe.

0ne infant is all that a bat of this species can produce at one time.

Her mammalian nature dictates that she keeps it within her body

until it's well developed,

and even one is a very heavy load when flying.

Now she feeds it from her own body with that special food - milk -

which is all that a newly-born mammal can digest.

The arrival in the world of this baby,

so tenderly nurtured by its mother,

could hardly be more different from that of so many creatures that live in the sea.

Birth for the Christmas Island crabs

is a comparatively protracted affair.

For 28 days they float helplessly in the sea,

slowly increasing the size and complexity of their body,

until at last they are just recognisable as miniature crabs,

but very few of them live as long as that.

Fish eat them in huge quantities, currents sweep them away into the open ocean.

So, most years, the entire spawning of billions is totally lost.

But almost miraculously, about one year in five,

a few hundred thousand appear in the waves off the coasts

where they first fell into the water as eggs.

Then these little creatures, no bigger than ants,

valiantly struggle ashore.

A single female crab, during her lifetime,

may produce a million eggs.

If just one survives,

then she may be just as successful as a bat, a sea lion,

or any other creature that each year lavishes its care on a single baby.

So, in a multitude of different ways,

new lives appear on Earth,

and each starts off on its own individual odyssey.

They've survived the first of their trials,

but they'll have to face many more

before, in turn, they too will have a chance to give birth.