The Infinite Variety Life on Earth

There are some four million kinds of animals and plants.

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 assemblage of life in the world.

Those are Howler monkeys there are 50 kinds of monkeys in these forests.

Some of the most beautiful creatures here are hummingbirds - 54 kinds were found a few miles from here.

And over 300 have been found in South America.

Nobody knows how many kinds of animal there are here - wherever you look, there's life.

There are several 100,000 different insects that have been named,

and, no doubt, hundreds more that haven't.

All these varied 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 into being in one flash of creation,

different organisms must have appeared at different times.

Which came first? And why such variety?

Such questions obsessed a 24-year-old Englishman who came to these forests in 1832.

He was Charles Darwin and he was enthralled - ecstatic - by the richness of life he found.

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 an entomologist's mind,

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

The conventional view of the time was that each and every species of animal and plant

had been individually created by God.

And Darwin was no atheist.

For three years, the Beagle sailed around South America

and up into the Pacific.

600 miles west of Ecuador,

they came to the lonely Galapagos Islands.

It was here that Darwin's doubts about the Creation re-awakened.

Everywhere Darwin found creatures resembling those on the mainland.

But nearly all were slightly different.

These were, without doubt, cormorants -

like those he'd seen flying along Brazilian rivers.

But here, their wings were so small and with such stunted feathers,

that the birds had lost their power of flight.

And these were clearly iguanas.

He'd seen them climbing trees and eating leaves.

But here on the Galapagos, where there was little vegetation,

iguanas fed on seaweed. And they were not the same - smaller, darker,

with long claws to keep a foothold in the crashing breakers.

They also had extraordinary habits -

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

The Galapagos Islands got the name from the tortoises that lived here which sailors slaughtered for food.

These too, were obviously different from mainland tortoises.

They were many, many times bigger.

The Vice-Governor of the Islands told Darwin he could tell where a tortoise came from by its shape.

This, with a deep rounded shell is from a well-watered island and feeds from vegetation on the ground.

This has a peak to the front of its shell, so it can stretch its long neck upwards.

It comes from an arid island where they have to crane up to reach the food available.

His suspicion grew that species weren't fixed for ever.

Perhaps they came from common ancestors and had changed to suit their particular islands.

The differences that Darwin had noticed among these animals were all tiny.

But if they could develop, wasn't it possible over millions of years,

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

Wasn't it possible that amphibians had developed water-tight skins and turned into reptiles?

Or that a reptile had developed feathery scales and become a bird?

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

The idea wasn't new - others had suggested that all life might have a common ancestry.

But Darwin went further and gave the idea more force by suggesting a mechanism

which might have brought it about - he called it "natural selection".

Put briefly, his argument was this,

individuals of some species aren't identical -

some tortoises have slightly longer necks than others.

In times of drought, they could reach leaves - and live,

while the shorter-necked ones die.

So those best fitted will transmit characteristics to their offspring.

Eventually, tortoises on arid islands will have longer necks.

So, one species will have given rise to another.

In these programmes, we'll survey the great variety produced by natural selection

and look at them, not as oddities, but as elements in the long story

that began 1,000 million years ago and is still continuing today.

Some creatures, mammals like these sealions,

and myself - mammals both - are recent arrivals on the scene.

Others - birds, reptiles, amphibians, fish - have been here long, longer than we have.

In places where conditions have remained unchanged over immense periods,

there are creatures resembling closely their ancestors - they can tell us a lot.

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

Bodies fall to the bottom of seas and swamps and get entombed.

The sediment, after millions of years, turns to rock and these remains survive as fossils.

Since discovering radioactivity, scientists have developed ways of measuring the age of rocks.

There are simpler ways of establishing the age of rocks that anyone can use.

There's no more dramatic place to do so than the Grand Canyon in the American West.

The Colorado River, aided by wind and rain, has cut a section through the sandstone and limestone.

The layers lie undisturbed so obviously the lower ones were deposited before the upper ones.

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

we must go deeper into the canyon.

This is the greatest gash in the earth - from rim to bottom is a vertical mile.

There are many trails down and the usual way is on the back of a mule.

Here we're 500 feet from the lip of the canyon and the rocks are 200 million years old.

There are no mammal fossils but there are four-legged animals - small reptiles.

A lizard-like creature that left tracks here which was once the face of a sand-dune.

Farther down, no reptiles, but in limestone 400 million years old bones of armoured fish are found.

The trail winds on through rocks formed in ancient seas - and every 20 feet is another 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 two-thirds the way down - 3,500 feet below the rim and the rocks are 500 million years old.

The rock has no backboned animals at all - no fish - the only ones are those without backbones,

including worms which left this tracery of trails.

At last, the bottom and the Colorado River - it's taken a day to get this far.

We've ridden 7 miles of trail and have descended that vertical mile into the earth's crust.

The rocks here are nearly 2,000 million years old.

For the past 800 feet, they've had no sign of fossils at all.

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

Why was this? Was it because they were so old they'd had all traces of life crushed from them?

Or did life really begin with creatures as big as a worm? For years this was a great puzzle.

Then 20 years ago, people realised they'd been looking in the wrong rocks and in the wrong way.

These are the right rocks - a kind of flint called chert - at Lake Superior in Canada.

It's 1,000 miles east and north of the Grand Canyon.

They were well known in the last century - pioneers used them in their flintlock guns.

Scientists have recognised for a long time they were extremely ancient rocks.

We now know they're the same age as those in the bottom of the Grand Canyon - 2,000 million years.

But- these strange rings in them - these were a subject of great controversy.

Some maintained they were a sign of very early life.

Others said they were ordinary chemical processes in the rock's formation.

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

First you cut a wafer-thin slice.

This is ground down for several hours.

When scientists first prepared chert to look at through the microscope,

many people doubted that primitive forms of life could possibly be preserved as tiny fossils.

Then scientists saw this.

Marks in rock can be deceptive - they may be the result of mineral action.

But these filaments are almost identical to algae growing today.

Soon fossils of other primitive life were found, that once lived in those early seas.

Other micro-fossils have been found -

in rocks even older - 3,000 million years old.

These immense periods baffle the imagination, but we get an idea of 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 talk in the last moment of Dec 31, man arrived a few hours ago in the afternoon.

The first backboned animal crawled on to land in the last week of November,

and these gunflint cherts were formed on June 15th.

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

3500 million years ago, our planet was very different from the one we live on today.

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

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

There was no oxygen - so consequently there was no ozone,

so ultra-violet rays bathed the young planet.

Carbon compounds formed including amino acids - the building blocks of protein.

For millions of years, the chemical soup thickened and changed, possibly added to from outer space.

Some compounds aggregated in droplets, with a membrane through which other chemicals could pass.

Eventually, large molecules appeared with extraordinary characteristics.

They caused amino acids to form round them and so built proteins but also produced copies of themselves.

Such a molecule - DNA - is at the centre of every life cell.

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

Their arrangement acts as a code for production of protein and a group in DNA is called a gene.

On occasion, the DNA unzips and each half attracts the correct chemical units and forms two new molecules.

When this first happened, primitive cells formed new cells and life on earth had appeared.

Sometimes a mistake can cause variations in first cells and natural selection sorted them out.

Those best suited to their environment survived - the rest died.

So, over tens of millions of years, new organisms developed and invaded new environments on earth.

Evolution had truly begun.

We can glimpse what early life was like, in the hot springs of Yellowstone Park in Wyoming.

These springs are stained a variety of colour

by micro-organisms that look to be identical with some of the earliest fossils that we know.

Tufts of bacteria grow where the water's hottest.

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

They represent the next big step.

They're probably like the first forms to manufacture food

inside their cell walls, with the aid of energy from the sun - light.

One of the raw materials needed was hydrogen and at first they got it as sulphuretted hydrogen.

It occurs in volcanic gases - there's some around here - it smells a bit of rotten eggs.

And indeed, there's such bacteria flourishing in the hot water of these springs.

Then that link with volcanoes was broken and forms of bacteria arose which got their hydrogen

from a more widespread and easily available source - from water and it was a crucial stage in life.

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

These new bacteria still exist

as slime on rocks or in ponds covered with silver bubbles.

It was they that first contributed oxygen to the atmosphere.

Under the microscope, they're seen as very simple structures.

Some form chains - others isolated beads.

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

Some of these bluegreens deposit lime as part of the chemistry of their body processes.

In one place in the world - a bay off Western Australia, they grow huge and form these pillars.

What makes this special, is the mouth of the bay is almost blocked by a bar of sand and sea grass.

This restricts the flow of the tide in and out, with a result that these waters are extremely salty.

Virtually none of the creatures which eat bluegreens can survive here.

So the bluegreens, primitive organisms, can grow uncropped,

as when they were an advanced form of life 2000 million years ago, at the beginning of life on earth.

Here is an explanation for the shapes 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 at last beginning to stir.

Now life had reached the point of no return - the oxygen accumulated and formed ozone in the atmosphere.

It screened off ultra-violet rays that had helped create life.

It could never begin in the same way again.

Things changed little for millions of years but at last came 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 single cells, yet each is much more complex than any bacterium.

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

Some appear to be simple plants.

Yet others seem to be half animal, half plant.

Seen through an electron-microscope,

the DNA is enclosed in its own compartment - other parts resemble and act like, bluegreens.

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

This cell's driven by a tail that resembles another bacterium.

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

It took a long time for life to reach this stage.

Probably not till 1,200 million years ago - say early September in our life-on-earth year.

These belong to this advanced type - many still abound in fresh water and the sea.

They form the basic food of other organisms.

Some have skeletons of silica.

Another kind with shell of chalk.

They're like an amoeba to which they're closely related.

Food is drawn inside.

They reproduce by splitting in two.

Some cells have more complicated methods of reproduction.

These have temporarily joined to exchange genes - later they'll part and divide in the normal way.

Others shuffle genes and divide so as to produce a special cell with half the genes of the parent -

these special cells are eggs.

Others of the species also produce sex cells.

This time they're quite different in form - they have tails - they're sperm cells.

They're attracted to the egg.

The first to find it, penetrates it.

It swims to 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 developed, the extent and frequency of variation increased.

The pace of evolution accelerated.

One of the most successful groups are the ciliates.

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

They also create currents which waft food into their gullet.

These ciliates are stalked and anchored to one spot.

Others are large and mobile and hunt for their food.

These ciliates are quite large.

Just visible to the naked eye.

But size can be got in another way.

By grouping cells together in an organised colony.

This, the size of a pinhead, has hundreds of cells with tails, beating in a co-ordinated way.

Inside, daughter colonies are formed and the delicate globe ruptures to release them.

A stage further - and sponges appeared.

There are 5,000 species of sponges today and their bonds are very loose.

Individual cells may crawl around the surface like amoeba.

If a sponge is forced through a sieve, so it breaks into separate cells,

they'll reorganise to form a new sponge.

What's more, each cell will take its proper place.

Some form walls, others are pump cells lining channels with which the sponge is riddled.

By beating their threads, they draw in water through pores on the sides.

Then pump it out at the top after the food has been strained off.

The structure's supported by other cells which make tiny needles to form a skeleton.

In glass sponges, they're made of silica.

Modern science is only 300 years old, yet it's provided us with profound insights

into the workings of the world, but there's a lot we don't know - take this sponge skeleton.

How on earth did the tiny sponge cells collaborate to build from millions of splinters of silica

this complex, beautiful structure - Venus's Flower-basket?

Some religious people say it's the work of God and that's all that need be said.

Some scientists claim that in time we'll provide a more detailed explanation than that.

Either way, it's an awesome and beautiful object.

But sponges are a dead end.

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

But this has.

It's a jelly-like creature - just 2 layers of cells - the inner one lines a cavity with an opening.

It's a fully co-ordinated, multi-celled animal.

It's one of several comb jellies which swarm in the ocean.

So transparent they're hardly noticed.

To appreciate their full beauty, you must use special lighting.

A Medusa - after the lady in the Greek myth who had snakes on her head for hair.

Its tentacles have stings for prey.

Comb jellies and medusae have muscle fibres and a nervous system - and most medusae have a surprise.

They begin life differently.

They look like plants - but are animals.

Each began when a tiny creature developed from the egg of a medusae.

It settled on the bottom of the sea.

From it grew a twig bearing polyps.

Each polyp is a medusa and in some species the medusae bud off the branch and swim away.

Others are born from special vessels.

All these medusae, not much bigger than a pinhead, have been produced without sex.

Later, they develop sexual cells which are released into the sea to produce larvae for new polyps.

This alternation between sexual and non-sexual means of reproduction

has given these creatures great scope for variety.

The larger medusae carry jelly so they're more robust in rough seas - these are the true jellyfish.

Many lead the same type of double life, having a stationary polyp phase as well as a swimming one.

It's an obvious deduction that jellyfish appeared very early in the development of life.

But there was no proof they did - after all, proof could only come from the fossil record.

and how could such a thing as a jellyfish be fossilised,

let alone survive in rocks from the earliest period? Then, 30 years ago in these sandstones

in the Flinders Ranges, Australia - probably 650 million years old - people found things like this.

At first, many refused to believe these faint impressions were the remains of jellyfish.

But enough have been found to make quite sure that that's what they are.

This, a form of jellyfish, isn't a single creature, but a colony of polyps.

It has gone to sea and has much the same structure as a true jellyfish.

Another colony built the same way is the Portuguese man o' war.

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

Tentacles trail behind for up to 50 metres.

The colony begins with one member which buds off.

These, bud off others - some for feeding, some for reproduction, some to catch prey.

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

Each has a coiled tube which discharges on contact with prey.

These are complicated creatures and you'd think, recent developments.

In fact, a fossil from the Flinders Range, suggest they existed 650 million years ago.

Alongside these jellyfish in the same rocks, are remains of other related creatures.

These were animals in which a kind of medusa remained small, and joined to form a colony.

We can be sure of that, because similar creatures are alive today, only 40 miles from here in the sea.

Sea pens - on either side of the stems are polyps for feeding and reproduction.

It bears a remarkable resemblance to the fossil.

These are soft corals.

Another kind - dead man's fingers.

Soft corals of all kinds grow in depths of 6,000 metres.

Stony corals make limestone reefs.

They live no deeper than 40 metres.

Cells grow over early ones and stifle them.

The corals contain plants.

Tiny, single-celled green algae.

Like all plants they release oxygen.

They also assimilate carbon dioxide and that helps the corals to form their skeletons of lime.

The reef may look like some fantastic, multi-coloured jungle of plants and flowers.

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

Coral organisms are tiny and simple, yet grow on such a scale and their 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 be if an astronaut came this way, several hundreds of millions of years ago,

he might have noticed, in the seas of the earth, a few mysterious and beautiful shapes in turquoise,

and guessed that life on earth had really started.

Subtitles by Bill Northwood - 1982