paragraph of his greatest work on The Origin Of Species.

But he wasn't drawing his inspiration from the exotic islands

that he'd visited on his famous voyage on HMS Beagle.

A chalk bank in Kent, near his house at Downe,

provided his metaphor for the laws

that explain the diversity of life on our planet.

It is interesting to contemplate an entangled bank, clothed with many plants of many kinds,

with birds singing on the bushes, with various insects flitting about,

and with worms crawling through the damp earth,

and to reflect that these elaborately constructed forms,

so different from each other,

and dependent on each other in so complex a manner,

have all been produced by laws acting around us.

Darwin was unleashing a new vision of nature,

where species evolved independently from the guiding hand of a creator.

The established vision of a harmonious world, divinely ordaine

to serve God's noblest creation, mankind, would be shattered.

He was very aware

that what he was dealing with was effectively intellectual dynamite,

and he kept most of his thoughts about what he was doing

in terms of where man might come from,

where new species might arise, effectively secret.

It was a secret with which Darwin had wrestled for 20 years.

20 years of unflinching support from his wife Emma, who feared that

her beloved husband might be consigned to eternal damnation

for challenging traditional beliefs.

Together they would endure two decades of debilitating illness,

self-doubt, and family tragedy.

It was a life struggle that Darwin also saw

among the animals and plants in the fields and tangled banks

of the Kentish countryside.

A struggle that is a founding principle of his theory of natural selection.

And the last paragraph of the Origin Of Species really goes out with a perfect bang.

The whole book has been about the struggle for existence

and what Tennyson had called nature red in tooth and claw.

The last paragraph gives, to me, a sense of hope.

It sort of shows that this war of all against all,

actually has a result and the result is the living world we see around us.

The beauties of the tangled bank,

the worms and the butterflies and the grass and the orchids,

all of these beauties of nature emerge from Darwin's simple idea.

There is grandeur in this view of life,

with its several powers having been originally breathed into a few forms

or into one, and that whilst this planet has gone cycling along

according to the fixed laws of gravity,

from so simple a beginning

endless forms most beautiful and most wonderful

have been, and are being, evolved.

Just as beauty and wonder emerge out of a war of nature,

so too did Charles Darwin's great book evolve out of years

of painstaking research and inner conflict.

At the age of 33,

Charles Robert Darwin was already an established gentleman naturalist.

His substantial private income

enabled him to pursue his particular interest,

solving what had been called "the mystery of mysteries".

How animals and plants might transmute or evolve.

It was to find a quiet place to write

that in 1842 he and his burgeoning family had moved to a house

just outside London near the village of Downe, in Kent.

After several fruitless searches in Surrey and elsewhere,

we found this house and purchased it.

I was pleased by the diversified appearance

of the vegetation proper to a chalk district,

and so unlike what I had been accustomed to in the Midland counties.

And still more pleased with the extreme quietness

and rusticity of the place.

Darwin knew in the country there was space to expand his experiments,

to walk, to observe nature.

There was plenty of information there for him to draw on

and then there was a very important factor for Darwin

of getting into a space where he felt safe,

with his secret theory of transmutation.

In the early 1840s, transmutation or evolution was still a radical idea,

associated with social revolution.

It was a secret that he shared with his wife and first cousin

Emma Wedgwood, whom he had married three years earlier.

I marvel at my good fortune that Emma, so infinitely my superior

in every single moral quality, should have consented to be my wife.

Emma was the precondition for everything that he did.

She... created a love-shaped space

where he felt safe to work obsessively without fearing

the loss of love and damaging their relationship.

She was to nurse him through years of recurrent bouts of illness,

the nature of which remains unclear to this day.

Possibly damage caused by a South American parasite,

inflamed by anxiety and nervous tension.

25 years' extreme spasmodic daily and nightly flatulence.

Vomiting preceded by shivering, hysterical crying,

dying sensations or half-faint and copious and very pallid urine.

Air fatigues bring on head symptoms, nervousness when Emma leaves me.

I think she was always concerned about his health.

She was constantly trying to persuade him

to have a day off here, go on a trip there,

not because she wanted his company,

but because she felt if he carried on working at the pace

at which he was going, then he would become more ill.

Emma was to provide Charles with ten children, seven of whom survived to adulthood.

As a father, Charles Darwin did not conform

to the standard Victorian stereotype

of the distant and stern pater familias.

Darwin was very much a family man.

He writes rather wryly one year

that his wife hadn't been doing very well last year

because she hadn't had a baby,

which is pretty rude for a Victorian, I have to say.

But what's fascinating is that he used his children

as experimental animals.

He noted their expressions when they were crying, when they were angry

and he saw how similar they were to the expression of a dog.

He saw his family as part of the human family,

the human family as part of the mammal family,

the mammal family as at one with the primroses.

And that really shows that he saw humankind

as an intrinsic part of the living world and not apart from it.

This was radically different from the established Christian view

of the time, where mankind was God's special and separate creation.

He kept his real opinions in a private notebook.

Man in his arrogance thinks of himself as a great work,

worthy of the interposition of a deity.

More humble and I believe true,

to think him created from animals.

And Charles and Emma did what animals do,

only they had a bed to do it in, upstairs.

But then because Darwin believed strongly in analogy,

it's not only animals that do what people do, but it's also plants

that do what people do in strange and complicated ways.

So from the marriage bed to the flower bed was only 100 yards

and Darwin would go downstairs,

out the back door, down to his flower beds

where experiments were being performed and how these creatures,

he even regarded some plants as simple animals,

also reproduced themselves.

Just over a year after he arrived at Downe,

he felt bold enough to tentatively raise the issue of species change

with his botanist friend Joseph Hooker.

At last gleams of light have come

and I'm almost convinced that species are not immutable.

It is like confessing a murder.

Hooker's response was noncommittal.

Darwin retreated into his shell.

If Hooker wouldn't buy it, then his old teachers at Cambridge certainly wouldn't.

Even the most progressive members of the Anglican clergy still saw nature's beauty and abundance

as divinely ordained for the benefit of the Lord's highest creation, man.

The fundamental idea around nature for many people during the early part of the 19th century,

particularly in Cambridge, but throughout Anglican Britain,

was that of design.

The world was made for man and probably the best way

of explaining this is just to think about the 24 hour day.

We think of that of course as just an outcome of astronomical chance,

in the way that the planets work and so forth.

For people who were sitting in Cambridge,

the idea was basically the 24 hour day is...

that's because humans need to sleep for eight hours.

And everything around them is organised from that fact,

from human need going outwards.

To suggest that mankind was merely a product of nature risked attack

from the black robed priests, the black beasts, as Darwin called them.

But what he possibly feared even more was the loss of respect

from the Cambridge dons who had taught and inspired him.

Men such as the straight spoken Yorkshireman

the Reverend Adam Sedgwick, professor of geology,

who saw God's design in nature.

"Denying this... "

".. Might brutalise it and sink the human race

"into a lower grade of degradation than any into which it has fallen

"since records tell us of its history. "

Sedgwick represents a union, an uneasy union of science and religion

that had prevailed since the 17th century, in Britain particularly.

A division of labour in which those who study nature

offer to those who study God,

evidence of God's greatness and goodness and wisdom

in the world about us and those who study God's revelation in the Bible

offer reasons for believing in God that he has revealed to us

and how to go to heaven.

Nature doesn't tell us how to go to heaven,

but it tells us that there is a God in heaven,

who has revealed himself and how to get there in the Bible.

It was with these traditional views in mind that in early 1844,

Darwin began to prepare a manuscript

that he hoped would eventually show even men like Sedgwick

that evolution was a reality,

and that he had found the mechanism that made it happen.

But as a punctilious and cautious man,

he needed to marshal his evidence.

What he does there at Downe

is really create a living laboratory.

You know, a laboratory to go along with his career, as it were.

It's not just Darwin sitting alone, looking out the window.

Darwin didn't just use his house and gardens to observe and learn from nature.

He bred pigeons and orchids, raised 50 varieties of gooseberry,

and to counter the creationists,

he became a beekeeper

in order to show that the near perfect hexagons in honeycombs

were made by instinct rather than divine design.

My habits are methodical,

my love of natural science has been steady and ardent.

I have the strongest desire

to understand or explain whatever I have observed.

To group all facts under some general laws.

He would also create a place to think.

A rough oval shaped path of gravel was laid down and trees planted

to provide him with a half kilometre walking circuit.

He called it the Sand Walk.

Darwin called the Sand Walk his thinking path.

He watched the trees grow and many of them are still there...

.. in the knowledge and hope that he would be able to

pace around this plot and escape the pressure

of sitting in one place

and writing and squeezing one's ideas out the point of a pen.

Darwin would lose himself in thought on the Sand Walk,

so much so that the only way he could keep track of the time he spent there

was to keep track of the laps and he kept track of the laps

by a pile of flints,

one of which he would kick to the side after a lap

and when the whole pile had been moved across the path,

he knew he had completed his exercise, that was your thinking time for the day.

We, the subsequent generation, love the Sand Walk

because we can imagine Darwin on it and think about

what he can see from the sand... in the Sand Walk.

He can see these climbing plants, the bryony

in the hedge for example.

He can see Great Puckland's field where he will, you know,

formulate a concept of biodiversity.

Secluded in his rural laboratory, Darwin's manuscript on what he was already calling natural selection