DAVID ATTENBOROUGH: Our Earth
is the only known planet that sustains life.
And it does so in abundance.
I have been fortunate enough over the years
to travel to some of the most extraordinary and remote places on Earth
to find and film animals.
This is the biggest flower in the world.
The blue whale!
It's the biggest creature that exists on the planet!
ATTENBOROUGH: The sheer number and variety of animals and plants
is astonishing.
Estimates of the number of different species
vary from six million to a hundred million.
Nobody knows exactly how many different kinds of animals there are here.
Wherever you look, there's life.
There are often a multitude of variations on a single pattern.
Nearly 200 different kinds of monkeys, for example.
And 315 humming birds,
nearly a thousand bats.
And beetles, at least 350 thousand species of them.
Not to mention a quarter of a million different kinds of flowering plants.
The variety is astounding.
(CHUCKLES)
(CHIRPING)
Even in this one small English woodland, you might see four or five
different kinds of finches.
Why should there be such a dazzling variety?
And how can we make sense of such a huge range of living organisms?
Two hundred years ago,
a man was born who was to explain this astonishing diversity of life.
In doing so, he revolutionised the way in which we see the world
and our place in it.
His name was Charles Darwin.
This book, The Holy Bible, explains how this wonderful diversity came about.
On the third day, after the creation of the world, God created plants.
On the fifth day, fish and birds,
and then, on the sixth day, mammals and finally, man.
That explanation was believed, literally,
by, pretty well, the whole of Western Europe for the best part
of 2,000 years.
And generations of painters pictured it for the faithful.
This version was painted in Italy in the 16th century.
Here is God in the Garden of Eden,
which is now filled with all kinds of animals.
Here he is pulling Adam out of the Earth
and here creating the first woman by putting Adam to sleep,
and then taking one of his ribs and extracting Eve from his side.
And she comes out assisted by two angels.
And when God had finished, he said to Adam and Eve,
"Be fruitful and multiply and replenish the Earth and subdue it,
"and have dominion over the fish of the sea and over the fowl of the air,
"and over every living thing that moveth upon the Earth."
That made it clear that according to the Bible
humanity could exploit the natural world as they wished.
This view of mankind's superiority still stood when, in 1831,
a British surveying ship, the Beagle, set off on a voyage around the world.
On board, as a companion to the captain,
was the 22-year-old Charles Darwin.
They crossed the Atlantic and made landfall on the coast of Brazil.
There, the sheer abundance of tropical nature
astonishes the newcomer,
as I discovered when I retraced Darwin's steps, 30 years ago,
for a television series about the diversity of nature.
Darwin, as a boy, had been a fanatical collector of insects.
And here, he was enthralled almost to the point of ecstasy.
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".
They went south, rounded Cape Horn, and so reached the Pacific.
And then, in September 1835,
after they had been away for almost four years,
they landed on the little-known islands of the Galapagos.
Here, they found creatures that existed nowhere else in the world.
Cormorants that had lost the power of flight.
Lizards that swam out through the surf to graze on the bottom of the sea.
Darwin, who had studied botany and geology at Cambridge university,
collected specimens of the animals and plants.
And as usual, when he went ashore to investigate,
described what he found in his journal.
"My servant and self were landed a few miles to the northeast,
"in order that I might examine the district mentioned above
"as resembling chimneys." Volcanic chimneys, presumably.
"The comparison would have been more exact if I had said
"the iron furnaces near Wolverhampton."
(CHUCKLES)
The British resident in the Galapagos claimed that he knew
from the shape of a giant tortoise's shell
which island it had come from.
If it had a rounded front, it came from a well-watered island
where it fed on lush ground plants.
Whereas one from a drier island had a peak at the front,
which enabled it to reach up to higher vegetation.
Were these tortoises, each on their separate islands,
different species?
And if so, was each one a separate act of divine creation?
The differences that Darwin had noticed amongst these Galapagos animals,
were, of course, all tiny.
But if they could develop, 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?
On his voyage home, Darwin had time to ponder on these things.
Could it be that species were not fixed for all time,
but could, in fact, slowly change?
On his return, he sorted out his specimens
and sent them off to relevant experts
so that each could be identified and classified.
Most of the mammal bones and fossils he sent to Richard Owen.
Owen was one of the most brilliant zoologists of his time.
He was the first to recognise dinosaurs,
and indeed had invented their very name.
And he would later become the creator and first director
of the Natural History Museum in London.
Many of the specimens that Darwin collected
are still preserved and treasured here
among the 70 million other specimens housed in the museum that Owen founded.
And here is one of them.
It's obviously the lower jaw of some great animal,
and when Darwin discovered it, it had bits of skin and hair attached to it
so at first it was thought to be the remains of some unknown living species.
But now we know that it is a species that was extinct for some 10,000 years,
a giant ground sloth.
Owen examined it in great detail
and eventually described it and gave it the name of Mylodon darwinii
in honour of its discoverer.
But that mutual respect between two great men of science
was not to last.
Soon after his return from his voyage,
Darwin made his home here in Down House in Kent.
Here, he wrote an account of his travels
and worked on detailed scientific treatises
about corals and barnacles and the geology and fossils of South America.
But he also pondered deeply on what he had seen in the Galapagos
and elsewhere.
Maybe species were not fixed.
Every day, he took a walk in this small spinney
that he had planted at the end of his garden.
And it was here that he came to ponder on the problems of natural history
including that mystery of mysteries:
how could one species turn into another?
He noted that most, if not all, animals produce many more young
than live to breed themselves.
This female blue tit, for example,
may well lay a dozen eggs a year, perhaps 50 or so in her lifetime.
Yet only two of her chicks need to survive and breed themselves
to maintain the numbers of the blue tit population.
Those survivors, of course, are likely to be the healthiest
and best-suited to their particular environment.
Their characteristics are then inherited
so perhaps over many generations,
and particularly if there are environmental changes,
species may well change.
Only the fittest survive.
And that was the key.
He called the process natural selection.
(BIRDSONG)
That would explain the differences that he had noted in the finches
that he had brought back from the Galapagos.
They were very similar except for their beaks.
This one has a very thin, delicate beak,
which it uses to catch insects.
This one, on the other hand, which came from an environment
where there were a lot of nuts, has a big, heavy beak,
which enables it to crack them.
So maybe, over the vastness of geological time,
and particularly if species were invading new environments,
those changes would amount to very radical changes indeed.
Darwin drew a sketch in one of his notebooks to illustrate his idea,
showing how a single ancestral species
might give rise to several different ones,
and then wrote above it a tentative, "I think".
Now he had to prove his theory.
And he spent years gathering abundant and convincing evidence.
He was an extraordinary letter writer.
He wrote as many as a dozen letters a day
to scientists and naturalists all over the world.
He also realised that when people had first started domesticating animals
they had been doing experiments for him for centuries.
All domestic dogs are descended from a single ancestral species, the wolf.
Dog breeders select those pups
that have the characteristics that happen to please them.
Nature, of course, selects those young animals
that are best suited to a particular environment.
But the process is essentially the same.
And in both cases, it has produced astonishing variety.
In effect, many of these different breeds
could be considered different species,
because they do not, indeed, they cannot interbreed.
For purely mechanical reasons,
there's no way in which a Pekingese can mate with a Great Dane.
Of course, it's true that, if you used artificial insemination,
you could get crosses between almost any of these breeds.
but that's because human beings have been selecting between dogs
for only a few centuries.
Nature has been selecting between animals for millions of years,
tens of millions, even hundreds of millions of years.
So what might have started out as we would consider to be breeds,
have now become so different they are species.
Darwin, sitting in Down House,
wrote to pigeon fanciers and rabbit breeders
asking all kinds of detailed questions about their methods and results.
He himself, being a country gentleman
and running an estate, knew about breeding horses
and sheep and cattle.
He also conducted careful experiments with plants in his greenhouse.
But Darwin knew that the idea that species could appear
without divine intervention would appall society in general.
And it was also contrary to the beliefs of his wife, Emma,
who was a devout Christian.
Perhaps for that reason, he was keen to keep the focus of his work scientific.
He made a point of not being drawn in public about his religious beliefs.
But in the latter part of his life he withdrew from attending church.
On Sundays, he would escort Emma and the children here
to the parish church in Down,
but while they went into the service, he remained outside
and went for a walk in the country lanes.
Perhaps because he feared his theory would cause outrage in some quarters,
he delayed publishing it year after year after year.
But he wrote a long abstract of it.
And then, on July 5th 1844, he wrote this letter to his wife.
"My dear Emma, I have just finished this sketch of my species theory."
Some sketch. It was 240 pages long.
"I therefore write this, in case of my sudden death,
"that you will devote £400 to its publication."
He then goes on to list his various naturalist friends,
who would be asked to edit it and check it,
and he ends the letter, charmingly,
"My dear wife, yours affectionately, C. R. Darwin."
He continued to accumulate evidence and refine his theory
for the next 14 years.
But then his hand was forced.
In June 1858, 22 years after he got back from the Galapagos,
here in his study in Down, he received a package
from a naturalist who was working in what is now Indonesia.
His name was Alfred Russel Wallace.
He had been corresponding with Darwin for some years.
But this package was different.
It contained an essay that set out exactly the same idea as Darwin's:
of evolution by natural selection.
The idea had come to Wallace as he lay in his hut
semi-delirious in a malarial fever.
But although his idea of natural selection was the same as Darwin's,
he had not spent 20 years gathering the mountain of evidence to support it,
as Darwin had done.
But whose idea was it?
In the end, the senior members of the Linnean Society
decided that the fairest thing was for a brief outline
of the theory from each of them to be read out one after the other,
at a meeting of the society here in Burlington House, in London.
The Linnean, then, as now, was the place where scientists studying
the natural world held regular meetings
to present and discuss papers about their observations and thoughts.
The one held on July 1st 1858
was attended by only about 30 people.
Neither of the authors were present.
Wallace was 10,000 miles away in the East Indies.
And Darwin was ill and devastated by the death, a few days earlier,
of his infant son.
So he was still at his home in Kent.
As a consequence, the two papers had to be read by the secretary.
And as far as we can tell, they made very little impression on anyone.
Darwin spent the next year writing out his theory in detail.
Then he sent the manuscript to his publisher, John Murray,
whose firm, then as now, had offices in Albermarle Street,
just off Piccadilly, in London.
Murray was the great publisher of his day,
and dealt with the works of Jane Austen and Lord Byron
whose first editions still line these office walls.
Darwin regarded his work as simply a summary,
but, even so, it's 400 pages.
It was published on November 24th 1859.
This is not a first edition, more's the pity.
First editions are worth, literally, hundreds of thousands of pounds.
This is a sixth edition. My copy, which I bought as a boy,
at 18, I notice, and it cost me the princely sum of one shilling.
The first edition, of 1,250 copies sold out immediately.
and it went for a reprint, and then another reprint and another reprint.
It's a book that contains very few technical terms.
It's easily understood by anybody.
And, predictably, it caused an outrage,
not only throughout this country, but indeed all the civilised world.
What scandalised people most, it seems,
was the implication that human beings were not specially created by God
as the book of Genesis stated, but were descended from ape-like ancestors.
A notion that provided a lot of scope for cartoonists.
The leaders of the Church, headed by Samuel Wilberforce,
the Bishop of Oxford, attacked it on the grounds that it demoted God
and contradicted the story of creation as told by the Bible.
"That Mr Darwin should have wandered
"from this broad highway of Nature's works
"into the jungle of fanciful assumption is no small evil."
"I have read your book with more pain than pleasure.
"It is the frenzied inspiration of the inhaler of mephitic gas."
"Fails utterly."
Darwin's theory implied that life had originated in simple forms
and had then become more and more complex.
He knew perfectly well that the whole idea of evolution
raised a lot of questions.
In fact, some of those questions would not be answered
until comparatively recently.
But in his own time, many distinguished scientists raised what seemed to be
insuperable difficulties.
And foremost among them was Richard Owen,
the man who, 20 years earlier, had named the extinct ground sloth
in honour of Darwin.
Over the years, the two men had developed a deep personal dislike
of one another, and had quarrelled frequently.
It wasn't that Owen thought that the story of the Garden of Eden
was literally correct, but nonetheless he was a deeply religious man.
He had, after all, ensured that his museum,
which would display the wonders of creation,
echoed, in its design, the great Christian cathedrals
of mediaeval Europe.
And Owen knew about the diversity of life.
Indeed, he had spent his whole career cataloguing it.
But even so, he refused to believe that a species could change over time.
He, and other pioneer Victorian geologists,
as they established their comparatively new science,
recognised that the outlines of the history of life
could be deduced by examining the land around them.
Look at these rocks in Northern Scotland.
We know from fossils that were associated with them
that they are very ancient.
And they are sandstones.
Compacted sand that was laid down at the bottom of the sea
layer upon layer upon layer.
But look how many layers there are.
Clearly, those at the top must have been laid down after those beneath them.
So, as you descend from layer to layer,
you are, in effect, going back in time.
So a fossil species, if it comes from a particular layer,
is of a particular age.
And if you can recognise each one, then you can begin to piece together
the outlines of life's history.
My krafta.
The ability to identify fossils and place them in their geological time zone
was still an essential skill when I was at university a century later.
We worked our way through drawers, like these,
which are full of fossils of one sort or another.
But none of them had labels.
Only numbers.
So you were expected to be able to pick up one
and say, "Yes, that's a belemnite".
Actually which belemnite it is, I can't remember now.
And when you came to your practical exam,
your examiners would produce one of these and say,
"Okay, what's that?"
And you either knew or you didn't.
And the way you knew was because of all the work you did in drawers like these,
hour after hour.
Owen did not deny the sequence in which all these different species appeared,
but he believed that each was separate, each divinely created.
Darwin's theory, however, required that there should be connections,
not just between similar species, but between the great animal groups.
If fishes and reptiles and birds and mammals
had all evolved from one another, then surely there must be intermediate forms
between those great groups.
And they were missing.
And then, just two years after the publication of The Origin of Species,
Richard Owen himself purchased the most astonishing fossil for his museum.
It had been found in this limestone quarry in Bavaria.
The stone here splits into flat, smooth leaves
that have been used as roofing tiles since Roman times.
Most are blank, but occasionally, when you split them apart,
they reveal a shrimp or a fish.
It's almost impossible to resist the temptation of pulling down
almost every boulder you see and then opening it like a book.
to look at each unopened page to see whether, maybe,
it contains yet another fossil.
But this fossil was something unprecedented.
It is still one of the greatest of the treasures that are stored
in the Natural History Museum.
And this is it.
It's called Archaeopteryx.
It has unmistakable feathers on its wings
and down its tail.
So Owen had no hesitation in calling it a bird.
But it was unlike any other bird that anyone knew of,
because it had claws on the front of its wings,
and as was later discovered, it didn't have a beak but jaws with teeth in it,
and a line of bones supporting its tail.
So it was part reptile, part bird.
Here was the link between those two great groups that was no longer missing.
Gosh, you really can see the filaments there.
Other examples of the same creature show its feathers even more clearly.
We know from the bones of the Archaeopteryx
that it was at best a very poor flyer.
So, it's not surprising that eventually it was superseded
by more modern, more efficient birds.
And that's the fate of these links between great groups.
Eventually, they become extinct.
And the only way we know they existed
is from their fossilized remains.
Even so, there is a bird alive today that illustrates the link
between modern birds and reptiles.
The hoatzin nests in the swamps of tropical South America.
There are caiman in the water beneath, ready to snap up any chick
that might fall from its nest.
So, an ability to hold on tight is very valuable.
And the nestlings have a very interesting way of doing that.
The young still have claws on the front of their wings as Archaeopteryx did.
Here is vivid evidence that the wings of birds are modified forelegs
and once had toes with claws on them.
There's another creature alive today that represents a link
between the great animal groups.
A descendant of a group of reptiles
that took a different evolutionary course
and evolved not feathers but fur, the platypus.
When specimens of this creature first reached Europe from Australia
at the very end of the 18th century, people refused to believe their eyes.
They said it was a hoax.
Bits and pieces of different creatures rather crudely sewn together.
And, yet, in a way, those early sceptics were right.
The platypus is the most extraordinary mixture of different animals.
It's part mammal and part reptile.
And so it can give us some idea of how the first mammals developed.
When it comes to breed,
it does something that separates it from all other mammals except one.
In its nest, deep in the burrow, it lays eggs.
It's this that links the platypus with the reptiles.
This that entitles it to be regarded as the most primitive living mammal.
So, the links between the great animal groups
are not, in fact, missing, but exist both as fossils and as living animals.
Although the fossil record provides an answer
to the problem of missing links, it also posed a major problem.
It started very abruptly.
The earliest known fossils in Darwin's time
came from a formation called the Cambrian.
And there were two main kinds.
These, which look like fretsaw blades and are called graptolite,
and these, like giant wood lice, which are called trilobites.
Could it really be that life on Earth started
with creatures as complex as these?
As a boy, I was a passionate collector of fossils.
I grew up in the city of Leicester,
and I knew that in this area, not far from the city,
called Charnwood forest,
there were the oldest rocks in the world.
Older even than the Cambrian.
So, therefore, by definition, they would be without fossils.
There was no point in me looking for fossils in these ancient rocks.
There were, it's true,
very rarely, some rather odd shapes in these rocks, like this one here.
But they were dismissed as being some kind of mechanical aberration.
I mean, after all, how could there be anything living
in these extremely ancient rocks?
And then, in 1957,
a schoolboy with rather more patience and perspicacity than I had
found something really remarkable.
And undeniably the remains of a living creature.
And here it is in Leicester museum,
where it's been brought for safe-keeping.
It's called Charnia.
Who could doubt that this is the impression of a living organism?
It has a central stem, branches on either side.
In fact, it seems to have been something like the sea pens
that today grow on coral reefs.
Since its discovery, a whole range of organisms
have been found in rocks of this extreme age.
Not only here in the Charnwood forest
but in many other different parts of the world.
Fossil hunters searching these rocks in the Ediacara Hills of Australia
had also been discovering other strange shapes.
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.
So, now we know that life did not begin suddenly
with those complex animals of the Cambrian.
It started much, much earlier, first with simple microscopic forms,
which eventually became bigger, but which were still so soft and delicate
that they only very rarely left any mark in the rocks.
The question of the age of the Earth
posed another problem for Darwin's theory.
In the 17th century, an Irish bishop had used the genealogies
recorded in the Bible that lead back to Adam
to work out that the week of Creation
must have taken place in the year 4004 B.C.
That may seem to us to be a very naive way of doing things,
but what other method was there anyway?
The Victorian geologists had already concluded
that the Earth must be millions of years old.
But how many millions, no one could say.
Then, less than 50 years after the publication of The Origin,
a discovery was made in what seemed a totally disconnected branch of science
that would ultimately provide the answer.
A Polish woman working in Paris, Marie Curie,
discovered that some rocks contained an element called uranium
that decays over time at a steady rate through a process called radiation.
Today, a century after she made her extraordinary discovery,
the method of dating by measuring changes in radioactivity
has become greatly refined.
This is a sample taken from those very ancient rocks in Charnwood forest.
And these tiny crystals are revealed to be
562 million years old.
That provides more than enough time for natural selection
to produce the procession of fossils
that eventually leads to the living animals and plants we know today.
But there was another objection.
If all animals within a group have a common origin,
how is it that some kinds of animals are distributed
throughout the continents of the world except for Antarctica?
How is it that, for example, frogs in Europe and Africa
are also found here in South America on the other side of the Atlantic Ocean?
Bearing in mind that frogs have permeable skins
and can't survive in sea water.
Darwin himself had a couple of suggestions.
One was that they might have floated across accidentally
on rafts of vegetation.
And the other is that maybe there were land bridges between the continents.
But even he was not convinced by either explanation.
Even as late as 1947,
when I was a geology student here at Cambridge,
there was no convincing explanation.
It's true that back in 1912, a German geologist had suggested
that at one time in the very remote distant past,
all the continents of the Earth that we know today
were grouped together to form one huge supercontinent.
And that over time this broke up and the pieces drifted apart.
That would have provided an answer.
But when I asked the professor of geology here, who was lecturing to us,
why he didn't tell us about that in his lectures,
he replied rather loftily, I must say,
"When you can demonstrate to me that there is a force on Earth
"that can move the continents by a millimetre, I will consider it.
"But until then, the idea is sheer moonshine, dear boy."
But then in the 1960s, it became possible to map the seafloor in detail
and it was discovered not only that the continents have shifted
in just the way that the German geologist had suggested
but that they were still moving.
New rock wells up from deep below the Earth's crust
and flows away on either side of the mid-ocean ridges,
carrying the continents with it.
Amphibians had originally evolved on this supercontinent
and had then travelled on each of its various fragments
as they drifted apart. Problem solved.
Perhaps, the biggest problem of all for most people
was the argument put forward for the existence of God
at the beginning of the 19th century
by an Anglican clergyman called William Paley.
He said, supposing you were walking in the countryside
and you picked up something like this.
You would know from looking at it that it had been designed to tell the time.
There must, therefore, be a designer.
And the same argument would apply if you looked
at one of the intricate structures found in nature, such as the human eye.
And the only designer of the human eye could be God.
Anti-evolutionists maintain that the eye would only work
if it was complete in all its details.
Darwin, on the other hand, argued that the eye had developed
becoming increasingly complex over a long period of time.
That would only work if each stage of development
was an improvement on the previous one.
And today, we know enough about the animal kingdom
to know that is indeed the case.
Some very simple animals have nothing more than light-sensitive spots
that enable them to tell the difference between light and dark.
But if a patch of such spots formed even the shallowest of pits,
one edge of the pit would throw a shadow and so reveal the direction of light.
If the pit got deeper and started to close,
then light would form a blurred image.
Mucus secreted by the cells would bend the light and focus it.
If this mucus hardened, it would form a proper lens
and transmit a brighter and clearer image.
All these different fully functional stages
at different levels of complexity are found in living animals today.
This single-celled creature has one of those light-sensitive spots.
Flatworms have a small pit containing light spots
so they can detect the shadow of a predator.
A snail's blurry vision is good enough to enable it to find its way to food.
And the octopus has an eye with a proper lens
and can see as much detail as we can.
So the structure of the human eye does not demand the assistance
of a supernatural designer.
It can have evolved gradually,
with each stage bringing a real advantage
as Darwin's theory demands.
Natural selection, of course, requires that an animal's characteristics
are handed from one generation to the next.
It's obvious that children resemble their parents.
Anyone knows that.
But when you come to think of it, how does that come about?
In Darwin's time, nobody had the faintest idea
about the mechanism or the rules that govern that process.
Except, perhaps, for one man,
who was working in the city of Brno in what is now the Czech Republic
at exactly the same time that Darwin was writing his book in Kent.
That man's name was Gregor Mendel.
He discovered the laws of inheritance by breeding thousands of pea plants
and observing how they changed from one generation to the next.
He found that while many characteristics were passed down directly
from one generation to another, others could actually skip a generation.
How could that happen?
Mendel explained this by suggesting that each plant, each organism,
contained within it factors which were responsible
for creating those particular characteristics.
Today we call those things genes.
But nobody had any idea how they worked
until a hundred years after Mendel's time.
And then the answer was discovered in Cambridge.
In 1953, here in the Cavendish Laboratories,
two young researchers Francis Crick and James Watson
were building models like this.
It was their way of thinking about and investigating the structure
of a complex molecule that is found in the genes of all animals, DNA.
The crucial bit are these chains which encircle the rod.
And here is a second and entwined.
This is the double helix.
The workings of the DNA molecule are now understood in such detail
that we can demonstrate something that is truly astounding.
A gene taken from one animal can function in another.
The gene that causes a jellyfish to be luminous, for example,
transplanted into a mouse, will make that mouse luminous.
The genetic code can also reveal relationships.
Even our law courts accept that DNA fingerprinting
can establish whether a man is the father of a particular child.
And it can also reveal whether one kind of animal
is related to another.
It proves, for example, that kangaroos, ground-living animals
that run with great leaps are closely related to koalas,
that have taken to climbing trees.
That insect-eating shrews
have cousins that took to the air in search of insects, bats.
And that one branch of the elephant family, way back in geological history,
took to the water and became sea cows.
So, 150 years after the publication of Darwin's revolutionary book,
modern genetics has confirmed its fundamental truth.
All life is related.
And it enables us to construct with confidence the complex tree
that represents the history of life.
It began in the sea, some 3,000 million years ago.
Complex chemical molecules began to clump together
to form microscopic blobs, cells.
These were the seeds from which the tree of life developed.
They were able to split, replicating themselves as bacteria do.
And as time passed, they diversified into different groups.
Some remained attached to one another, so that they formed chains.
We know them today as algae.
Others formed hollow balls, which collapsed upon themselves,
creating a body with an internal cavity.
They were the first multi-celled organisms.
Sponges are their direct descendants.
As more variations appeared, the tree of life grew and became more diverse.
Some organisms became more mobile
and developed a mouth that opened into a gut.
Others had bodies stiffened by an internal rod.
They, understandably, developed sense organs around their front end.
A related group had bodies that were divided into segments,
with little projections on either side
that helped them to move around on the sea floor.
Some of these segmented creatures developed hard, protective skins
which gave their body some rigidity.
So now the seas were filled with a great variety of animals.
And then, around 450 million years ago, some of these armoured creatures
crawled up out of the water and ventured onto land.
And here, the tree of life branched into a multitude of different species
that exploited this new environment in all kinds of ways.
One group of them developed elongated flaps on their backs
which, over many generations, eventually developed into wings.
The insects had arrived.
Life moved into the air
and diversified into myriad forms.
Meanwhile, back in the seas,
those creatures with the stiffening rod in their bodies
had strengthened it by encasing it in bone.
A skull developed, with a hinged jaw that could grab and hold onto prey.
They grew bigger and developed fins equipped with muscles
that enabled them to swim with speed and power.
So fish now dominated the waters of the world.
One group of them developed the ability to gulp air from the water surface.
Their fleshy fins became weight-supporting legs,
and 375 million years ago, a few of these backboned creatures
followed the insects onto the land.
They were amphibians, with wet skins,
and they had to return to water to lay their eggs.
But some of their descendants evolved dry, scaly skins,
and broke their link with water by laying eggs with watertight shells.
These creatures, the reptiles, were the ancestors of today's
tortoises, snakes, lizards and crocodiles.
And, of course, they included the group that, back then,
came to dominate the land: the dinosaurs.
But 65 million years ago, a great disaster overtook the Earth.
Whatever its cause, a great proportion of animals were exterminated.
All the dinosaurs disappeared, except for one branch
whose scales had become modified into feathers.
They were the birds.
While they spread through the skies, a small, seemingly insignificant,
group of survivors began to increase in numbers on the ground beneath.
These creatures differed from their competitors
in that their bodies were warm and insulated with coats of fur.
They were the first mammals.
With much of the land left vacant after the great catastrophe,
they now had their chance.
Their warm, insulated bodies enabled them to be active at all times,
at night as well as during the day.
And in all places, from the Arctic to the tropics,
in water as well as on land,
on grassy plains and up in the trees.
There can be no doubt about our close relationship
to these chimpanzees.
Our bodies are so similar.
The proportions of our limbs or our faces may differ,
but otherwise we are very, very similar.
The arrangement of our internal organs,
the chemistry of our blood,
the way our bodies work,
all these are almost identical.
And DNA confirms that.
Indeed, we are as closely related to chimpanzees
and the rest of the apes and monkeys,
as say, lions are to tigers and to the rest of the cat family.
Suddenly, an image from our remote past comes vividly to light,
the time when our distant ancestors,
in order to keep up with the changing environment,
had to wade and keep their heads above water in order to find food.
That crucial moment when our far distant ancestors
took the step away from being apes
and a step towards humanity.
The Natural History Museum is one of the most important museums of its kind
in the world.
Richard Owen brought it into existence, but, over a century later,
discoveries from many branches of science
have shown that his belief that species can never change
but always remain exactly the same was mistaken.
It was Charles Darwin's profound insights that have proved to be true.
And now, to mark the 200th anniversary of his birth,
his statue is being taken from its out-of-the-way location
to be placed centre stage in the main hall.
Darwin's great insight revolutionised the way in which we see the world.
We now understand why there are so many different species.
Why they are distributed in the way they are around the world.
And why their bodies and our bodies are shaped in the way that they are.
Because we understand that bacteria evolve,
we can devise methods of dealing with the diseases they cause.
And because we can disentangle the complex relationships
between animals and plants in a natural community,
we can foresee some of the consequences when we start to interfere
with those communities.
But above all, Darwin has shown us that we are not apart
from the natural world.
We do not have dominion over it.
We are subject to its laws and processes
as are all other animals on Earth
to which indeed we are related.
(LAUGHING)