All language subtitles for BBC.Life.on.earth.Pt1.The.Infinite.Variety-MVGroup

There are four million different kinds
of animals and plants in the world.

Four million different solutions
to the problems of staying alive.

This is the story of how a few of them
came to be as they are.

The South American rainforest.

The richest and most varied
assemblage of life in the world.

Those are howler monkeys up there.

There are around 50 different kinds of monkeys
in these forests.

Some of the most beautiful creatures here
are hummingbirds.

54 different kinds have been found
within a few miles of here,

and over 300 have been found
in South America as a whole.

Nobody knows how many kinds
of animals there are here.

Wherever you look, there's life.

There are several hundred thousand
insects that have been named,

and, without doubt,
many more that haven't.

All these creatures and plants
form one complex mosaic.

The orchid needs the bee to pollinate it.

The anteater couldn't have existed
before the ants.

So unless the whole complex
came about in a flash of instant creation,

different organisms
must have appeared at different times.

But which came first, and why
should there be such an immense variety?

Such questions obsessed
a young 24-year-old Englishman

who came here in 1832.

His name was Charles Darwin

and he was enthralled to the point of ecstasy
by the richness of life he found here.

In one day, in a small area,
he discovered 69 different species of beetle.

As he wrote in his journal,

"It's enough to disturb the composure
of the entomologist's mind

"to contemplate the future dimension
of a complete catalogue."

The conventional view of the time

was that every species of animal and plant
had been individually created by God.

And Darwin was no atheist.

During the next three years,
the Beagle sailed round South America

and up into the Pacific.

600 miles west of Ecuador,

they came to the lonely Galapagos islands.

It was here, on these volcanic islands,

that Darwin's doubts
about the creation of species were reawakened.

Everywhere, Darwin found creatures
that bore a general resemblance

to those he had seen on the mainland.

But nearly all were slightly different.

These, for example, were cormorants

similar to those he had seen
flying along Brazilian rivers.

But in the Galapagos, their wings
were so small, with such stunted feathers,

that the birds had lost their powers of flight.

And these were clearly iguanas.

He'd seen them climbing trees
in the South American forests,

but on the Galapagos, with its sparse vegetation,

these iguanas fed on seaweed,
and they were not the same.

Smaller, darker and with unusually long claws
to help them keep a foothold

among the crashing breakers.

They also had extraordinary habits,

swimming fearlessly out to sea
and diving deep to graze on the sea bed.

The Galapagos Islands got their name
from the herds of tortoises that live on them,

which sailors for centuries
had slaughtered for food.

But these too were obviously different
from mainland tortoises.

They were many times bigger.

The English vice-governor
of the islands told Darwin

that he could tell which island
a tortoise came from by its shape.

This one, for example,
with its deep, rounded shell,

comes from a well-watered island
where it can feed on vegetation on the ground.

This one has a peak to the front of its shell
that enables it to stretch its long neck upwards.

It comes from an arid island,

where the tortoises have to crane up
to reach the only food there,

the branches of trees and cactus.

The suspicion grew in Darwin's mind
that species were not fixed for ever.

Perhaps the tortoises were all descended
from common ancestors

and had changed to suit their particular islands.

The differences Darwin noticed
among these Galapagos animals

were, of course, tiny.

But if they could develop them, wasn't it possible
that over the thousands or millions of years,

a whole series of such differences
might add up to one revolutionary change?

Was it not possible, perhaps,

that in the past amphibians had developed
watertight skins and so turned into reptiles?

Or that a lizard-like reptile
had developed a feathery kind of scale

and become a bird?

And even that man himself might be descended
from a group of tree-swinging apes?

In truth, the idea was not a new one.

Others before Darwin suggested that all life
on earth might have a common ancestry,

but Darwin went further.

He gave the idea irresistible force

by suggesting a mechanism
which might have brought that about.

He called the mechanism natural selection.

Put briefly, his argument was this.

Individuals of the same species
are not absolutely identical.

Some of these giant tortoise hatchlings
may have, from birth,

slightly longer necks than others.

In times of drought,
they will reach leaves and live,

while the shorter-necked ones die.

So those best fitted for the environment

will transmit their characteristics
to their offspring.

After many generations, tortoises on arid islands

will have longer necks
than those on well-watered ones.

And so one species
will have given rise to another.

In these programmes,
we're going to survey

the unmeasurable variety of animals
produced by natural selection,

and look at them not as isolated oddities,

but as elements in a long and continuing story
that began 1,000 million years ago,

and is still continuing today.

Some creatures, the mammals,

such as these sea lions and myself,
are relatively recent arrivals on the scene.

Others: birds, reptiles, amphibians, fish,
have been here much longer than we have.

In places where conditions have remained
unchanged over immense periods of time,

there are still creatures living
which resemble very closely

their early ancestors.

They can tell us a lot.

But to disentangle the story, we shall also
have to look for evidence in the rocks.

The bodies of animals
fall into the bottom of ancient seas and swamps,

sometimes get entombed
in the accumulating sediment.

When, after millions of years,
those sediments turn to rock,

those remains of animals and plants
survive as fossils.

Since the discovery of radioactivity,

scientists have developed techniques
of measuring the age of rocks

based on the rates
at which some chemical elements decay.

So fossils can be dated
to within a few million years.

But there are much simpler ways of establishing
the ages of rocks that anyone can use,

and there is no more dramatic place to do so
than in the Grand Canyon in the American west.

The Colorado river, aided by wind and rain,

has cut a gigantic section through the sandstones
and limestones of Arizona.

The layers still lie largely undisturbed,

so obviously the lower ones
were deposited before the upper ones.

So if we want to trace the ancestry of life
back to its beginnings here,

we have to go deeper and deeper
into the canyon.

This is the greatest gash that exists
in the surface of the earth.

From the rim to the river at the bottom
is a vertical mile.

There are a number of trails down.
The usual way is on the back of a mule.

Here, we're about 500 feet
below the lip of the canyon.

Already the rocks are about 200 million years old.

There are no mammal fossils here,
but there are some four-legged land animals.

Small reptiles: a little lizard-like creature

that has left its tracks along here,
which was once the face of a sand dune.

Farther down, there are no signs of any reptiles,

but in limestones 400 million years old, the
bones of strange armoured fish have been found.

The trail winds on through rocks
formed on the bottom of ancient seas.

With every 20 feet we descend,
we go back a further million years.

The Grand Canyon is really two canyons,
one inside the other.

For a while, the trail flattens out
as it approaches the rim of the inner canyon.

Here, I'm about two thirds of the way down,
3,500 feet below the rim.

The rocks here are about 500 million years old.

These rocks have no backboned animals
in them at all, no fish.

The only creatures are those without backbones,
including a whole lot of worms

which have left this delicate tracery of trails in
what was mud on the bottom of a shallow sea.

At last, the bottom and the Colorado river.

It's taken nearly a day, going fairly easily,
to get this far.

We've ridden seven miles of trail and have
descended a mile into the earth's crust.

The rocks here
are getting on for 2,000 million years old.

For the past 700 or 800 feet of our descent,

they've had no signs of any fossils in them.

For years, it was thought
that all rocks of this age had no fossils.

Why was this? Was it
because they were so unimaginably old

that they'd had all life crushed from them?

Or did life begin
with creatures as big as a worm?

For many years, this was a great puzzle.

And then, 20 or 30 years ago,

people realised they'd been looking
in the wrong rocks and in the wrong way.

These are the right rocks.

They're a kind of flint called churt,

and they're on the shores
of Lake Superior, in Canada,

about 1,000 miles east and north
of the Grand Canyon.

They were well-known during the last century
because the pioneers

used them in their flintlock guns.

And scientists have recognised
for a long time

that they were ancient rocks.

We now know they are about the same age
as the rocks at the bottom of the Grand Canyon,

about 2,000 million years old.

But these strange rings in them...

For a long time,
these were a subject of great controversy.

Some scientists maintained
they were signs of very early life.

Others, that they were no more than the result

of the ordinary chemical processes
during the rocks' formation.

But in the 1950s, scientists started
looking at them in the right way.

First of all, you have to cut
a wafer-thin slice of the gunflint rock.

This is then ground down further
for several hours

until the slice is translucent.

When scientists first prepared churt
to look at under the microscope,

many doubted that primitive life forms,
even if they existed 2,000 million years ago,

could be preserved as tiny fossils.

And then scientists saw this.

Marks in rocks can be deceptive.

They may just be
the result of mineral action.

But these filaments were almost identical
to primitive algae growing today.

The search continued.

Soon, the fossilised remains
of other kinds of primitive life were found

that had once lived in those early seas.

Since those discoveries,
other micro-fossils have been found elsewhere

in rocks that are even more ancient,
some over 3,000 million years old.

These immense periods of time
baffle the imagination.

But perhaps we can get an idea
of the relative lengths of the stages

if we condense the history of life on earth
into one year.

Then 10 million years become one day.

On that calendar, I'm talking
in the last moment of December 31st,

and primitive man will have appeared
only a few hours ago, in the early afternoon.

The first backboned animal will have crawled up
onto land during the last week of November,

and these churts will have been formed
on June 15th.

Now let's go back way, way,
to the beginning of January.

To the beginning of life.

Over 3,500 million years ago,

our planet was radically different in almost
every way from the one we live on now.

Erupting volcanoes built up islands
of lava and ash in the global seas.

The atmosphere was filled with gases
such as ammonia, methane, hydrogen and steam.

There was virtually no oxygen.
In consequence, there was no ozone layer.

So ultraviolet rays in strengths that would be
lethal to us bathed the young planet.

The ultraviolet light, together with heat,
electrical and radioactive discharges,

brought about chemical changes in the waters.

Complex carbon compounds were formed,

including amino acids,
the building blocks of protein.

For millions of years,
the chemical soup thickened and changed.

Possibly some compounds
were added to it from outer space.

Some carbon compounds
aggregated in droplets,

with a membrane
through which other chemicals could pass.

Eventually, unusually large molecules appeared
which had extraordinary characteristics.

They caused amino acids to form around them,
and so built proteins.

They could also produce copies of themselves.

Such a molecule, known as DNA,
is at the centre of every life cell.

Its shape is a double spiral,
linked by chemical units of just four kinds.

Their arrangement acts as a code
for the production of proteins,

and a group of them in a section of DNA
is called a gene.

On occasion, the DNA unzips.

Each half then attracts the correct chemical units
and forms two new, identical molecules.

When this first happened,
primitive cells formed new cells

and life on earth had appeared.

But sometimes there is a mistake, a mutation.

These caused variations in the first cells,

and natural selection sorted them out.

Those that were as well or better suited
to their environment survived.

The rest died.

And so, over tens of millions of years,

a variety of bacteria-like organisms developed,
thrived and invaded new environments on earth.

Evolution had truly begun.

We can get a glimpse
of what those first stirrings of life were like

in the hot volcanic springs of such places
as Yellowstone Park in Wyoming.

And in these springs,
staining them a whole variety of colours,

there flourish microorganisms.

Microorganisms that look to be almost identical
to some of the earliest fossils we know.

Tufts of bacteria grow where the water is hottest.

In cooler areas, other bacteria deposit silica
in strange-coloured crusts.

These bacteria represent the next big step.

For they are probably very like
the first forms to manufacture food

inside their own cell walls
with the help of energy from the sun: light.

One of the raw materials
they needed was hydrogen.

At first, they got it as sulphuretted hydrogen,
which occurs in volcanic gases.

There's some around here.
This place smells a bit of rotten eggs.

And there are such bacteria flourishing
in the hot water of these springs.

But then that link with volcanoes was broken.

Some forms of bacteria arose
which got their hydrogen

from a much more widespread
and easily available source: water.

That was a crucial stage in the history of life.

Because if you take hydrogen from water,
you are left, as a by-product, with oxygen.

These new blue-green bacteria,
or cyanophytes, still exist.

As slime on wet rocks
or in ponds covered with silver bubbles.

It was they that first contributed oxygen
in large quantities to the atmosphere.

Under the microscope, you can see
that they're very simple structures.

Some form chains, others are isolated beads.

On a larger scale, they form mats with bacteria
in the cooler springs of Yellowstone.

Some of these blue-greens deposit lime
as part of the chemistry of their body processes.

And in one place in the world, here in a bay
on the coast of Western Australia,

they grow large and huge
to form these great pillars.

What makes this place so special
is that the mouth of the bay

is almost blocked by a bar of sand
covered with sea grass.

This restricts the flow of the tide in and out,

with the result that these waters
are extremely salty.

So virtually none of the creatures
which eat blue-greens can survive here.

So these blue-greens,
these very primitive organisms,

can grow uncropped, just as they did

when they were the most advanced form of life
2,000 million years ago,

at the beginning of life on earth.

And here is an explanation
for those extraordinary shapes

that we saw on the shores of Lake Superior.

This is as close as we may get to a scene
of the world when life was beginning to stir.

Now, life had reached the point of no return.

The oxygen accumulated
and formed a layer of ozone in the atmosphere,

screening off ultraviolet rays,
the very source of energy

that had helped create the first life.

So it could never begin
in the same way again.

Outwardly, things changed little
for hundreds of millions of years.

But eventually, the stage was set
for a new and dramatic step.

To find evidence of that development,
you need go no further than your local pond.

Most microscopic organisms here
are just single cells.

Yet each is much more complex
than any bacteria.

Some, like this amoeba,
seem to have animal characteristics.

And some appear to be simple plants.

Yet others seem to be
half-animal and half-plant.

In terms of complexity, they are as different
from a bacterium as man is from a jellyfish.

To see why, we have to look inside one
with an electron microscope.

The DNA, unlike that in a bacterium,
is enclosed in its own compartment.

Other parts of the cell
resemble and act like blue-greens.

These look more like bacteria
and are a source of energy.

This cell is driven by a tail
that resembles yet another type of bacterium.

So it appears that this tiny creature
is composed of a committee of smaller ones.

And many now believe that it was by some form
of collaboration between primitive cells

that such organisms came into existence.

But it took a long time for life to reach this stage,
probably not until some 1,200 million years ago,

say early September in our "life on earth" year.

These plant cells belong
to this new, advanced type.

Many kinds of them still abound
in fresh water and the sea,

and they form the basic food
of other simple organisms.

Some of them have delicate skeletons of silica.

This is another kind,
with chambered shell of chalk,

and so small
that several would fit on the head of a pin.

The animals, in essence, are like an amoeba,
to which they're closely related.

They catch their food with sticky threads.

When something tangles with them, it's drawn
inside and digested in a special compartment.

The cells can reproduce by splitting into two,
as bacteria do.

But some cells have more complicated
methods of reproduction.

These have temporarily joined
so they can exchange genes.

Later, they will part
and then divide in the normal way.

In other cases, cells shuffle their genes

and then divide to produce
a very special kind of cell

with only half the number of genes of the parent.

These special cells are eggs.

Meanwhile, other members of the same species

are also producing sex cells
with half-rations of shuffled genes.

This time, they're quite different in form.

They have tails. They are sperm cells.

They're chemically attracted to the egg,

and the first one to find it down there
penetrates the wall.

After getting inside, it swims
towards the nucleus and unites with it,

so the full complement of genes is restored.

But now it's in a new combination,
different from either parent.

When this mechanism developed, the extent
and frequency of variation greatly increased.

As a result, the pace of evolution accelerated.

One of the most successful groups

of single-celled creatures
in this microscopic world are the ciliates.

They're covered in beating hairs, the cilia,
which drive them through the water.

The cilia also create currents
which waft particles of food into their gullets.

These particular ciliates are stalked
and remain anchored to one spot.

But others are large and mobile
and actively hunt for their food.

These ciliates are among the larger single-celled
creatures, just visible to the naked eye.

Above this size, the chemical processes inside
become difficult and inefficient.

But size can be achieved in a different way,

by grouping cells together
in an organised colony.

This volvox, almost the size of a pinhead,

is composed of hundreds of cells,
each with a tail,

but all beating in a co-ordinated way.

Inside, daughter colonies are formed

and the tiny, delicate globe
ruptures to release them.

Eventually, this co-ordination between cells
was taken a stage further.

Sponges appeared.

There are about 5,000 species of sponges
in existence today,

and in all of them, the colonial bonds between
their constituent cells are remarkably loose.

Individual cells may crawl around
over the surface like amoebae.

If a sponge is forced through a sieve
so that it's broken down into separate cells,

they will, if left alone,
reorganise themselves to form a new sponge.

What is more, each kind of cell
will take up its proper place.

Some are specialised to form the walls.

Others are pump cells
that line the walls of the channels

with which the sponge is riddled.

By beating their tiny threads, they create currents,
drawing in water through the pores on the sides

then pumping it out at the top
after the food has been strained off.

The structure is supported by yet other cells
which make tiny needles,

and these build to form a skeleton.

In the so-called glass sponges,
they're made of silica.

Modern science
is only some 200 or 300 years old,

and yet already it's provided us
with some profound insights

into the workings of our world.

But there's still a great deal we don't know.

Take this sponge skeleton, for example.

How on earth did the microscopic sponge cells,
one of the most primitive organisms we know,

collaborate to build
out of a million splinters of silica

this complex and beautiful structure which is
sometimes called Venus's flower basket?

Some religious people will maintain
that it is the work of God,

and that is all that need be said.

Some scientists say it is
only a matter of time before we will provide

a more detailed explanation than that.

Either way,
it remains an awesome and beautiful object.

But sponges,
in an evolutionary sense, are a dead end.

They have no true mouth, no gut,
no muscles, no nervous system.

But this has.

It's a jelly-like creature
with just two layers of cells.

The inner one lines a cavity
which has a single opening.

Its design may be simple,
but it is a fully coordinated, multi-celled animal.

It's one of several kinds of comb jellies,

which swarm in the oceans but which are
so transparent, they are hardly ever noticed.

To appreciate the full beauty of comb jellies,
you need special lighting.

They swim with rows of cilia arranged like combs,

and their beating
produces interference colours, like a rainbow.

This pulsating bell
is a close relation of the comb jelly.

Technically, it's called a medusa,
after the unfortunate lady in the Greek myth

who had snakes on her head for hair.

Its tentacles have stings for capturing prey.

Once caught,
it's transferred to the mouth at the centre.

Comb jellies and medusae
both have muscle fibres

and a simple nervous system.

But most medusae have a surprise.

They begin their lives
in a completely different form,

like this.

These may look like plants, but they're animals.

Each structure began
when a tiny free-swimming creature

developed from the fertilised egg of a medusa
and settled on the sea bed or some weed.

From it sprang a tiny branching twig
bearing flower-like individuals called polyps.

These filter feed with the aid of beating cilia
and grow,

putting out more branches with polyps on them.

Each polyp is basically equivalent
to a swimming medusa.

In some species, medusae can bud
directly off the branch and swim away.

In others, they are born from special vessels.

All these medusae,
not much bigger than a pinhead,

have been produced
by a process that involves no sex.

Eventually, they develop sexual cells

which will be released into the sea
to produce larvae

to begin new colonies of polyps again.

This alternation of generations between sexual
and non-sexual methods of reproduction

has given these creatures and their relatives
great scope for variety.

Larger medusae
carry quantities of jelly in their umbrellas

to make them more robust in rough seas.

These are the true jellyfish,
and many lead the same type of double life,

having a stationary polyp phase
as well as a swimming one.

There's a surprising variety of types of jellyfish.

Some are able to feed on quite large prey.

This one has ruffles in which there are
many pores for netting microscopic food.

This shallow-water species
uses pulsating movements

to create currents of water that bring it food.

It's an obvious deduction
that such simple things as jellyfish

appeared very early in the development of life.

But for a long time,
there was no actual proof that they did.

After all, proof could only come from fossils,

and who could suppose
that an insubstantial jellyfish

could be fossilised,
let alone survive in rocks from the earliest period?

And then, about 30 years ago,

in these sandstones
in the Flinders Ranges in southern Australia,

which are probably about 650 million years old,
people found things like this.

At first, many scientists refused to believe
that these faint impressions

were the remains of jellyfish.

But by now, enough specimens
have been discovered to make quite sure

that that indeed is what they are.

What's more, almost a dozen different species
have now been discovered.

Such fossils as these
reveal that at a very early period,

jellyfish existed in many different forms,
just as they do today.

This, though a close relative of the jellyfish,

is, strictly speaking,
not one creature but a colony of polyps,

one that has gone to sea and assumed
much the same structure as a true jellyfish.

Another colony that is built on the same principle
is the Portuguese man-of-war.

It has no swimming bell but a bag filled with gas
that supports the whole colony.

To avoid drying out, the colony can dip
the sail into the water from time to time.

Long tentacles trail behind
for lengths of up to 50 metres.

The colony begins with just one founding member
which buds off two lines of other individuals.

They in turn bud off others, some specialised
for feeding, some for reproduction,

and some to catch prey.

As with all jellyfish and their relatives,
the tentacles have special stinging cells.

Each contains a coiled, barbed tube
which discharges on contact with its prey.

And from the end of each
comes a drop of paralysing poison.

Animals like the Portuguese man-of-war
are highly complicated,

and you might think they're recent
developments in the world of jellyfish.

In fact, one of the fossils from the Flinders Range

suggests that such colonies existed
650 million years ago.

The impression in this rock is thought to be
from a gas bag of such a colony of polyps,

which was blown inshore
and cast up on the sandy beaches

that today form the sandstones
of the Flinders Ranges.

And that's not all.

Alongside those jellyfish, in the same rocks,

there are the remains
of other closely-related creatures.

These beautiful impressions are of animals

in which the equivalent of the medusa

remained very small
and attached to one another to form a colony.

And we can be pretty sure
that this is what that was

because similar creatures are alive today

and living only about 40 miles
away from here in the sea.

These are sea pens.

On either side of the stem are polyps which
are specialised for feeding and reproduction.

This living one
bears a remarkable resemblance to the fossil.

They were given the name sea pen
when people wrote with quills,

and apt it must have seemed,
for the skeleton is flexible and horny.

They belong to a group called the soft corals.

This is another kind, a soft, flabby organism
rather ghoulishly known as dead man's fingers.

Soft corals of one kind or another
can grow in depths of up to 6,000 metres,

but stony corals, the ones which produced
limestone skeletons and form reefs,

can live no deeper than 40 metres.

The coral polyps live only on the surface
of these structures,

each in its tiny limestone cell and connected
to its neighbours by thin strands,

so that the whole skin is a living network.

As new ones sprout
from the connecting branches,

they secrete cells which grow over the early ones
and stifle them.

The coral tissues contain plants.

Tiny single-celled green algae.

Like all plants, they release oxygen,
which helps the coral polyps to respire.

They also assimilate carbon dioxide,
taking it from the water.

And that helps the corals
to form their gigantic skeletons of lime.

Each species branches and buds
in a different way.

And so the colony produces
its own individual shape.

The reef may look like some fantastic
multicoloured jungle of plants and flowers,

but when you touch one, it has the hard,
incongruous scratch of stone.

The coral organisms are tiny and simple,

yet they grow on such a scale,
and their stony skeletons are so durable,

that they may well have been the first signs
of life that could be detected from outer space.

Certainly, this Great Barrier Reef
can be seen from the moon.

So it may well be
that if a passing astronaut came this way

several hundred million years ago,

he might have noticed
in the deep blue seas of the earth

a few mysterious, beautiful shapes in turquoise,

and guessed that life on earth had really started.