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 Albemarle 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 is 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 6th edition - my copy,
which I bought as a boy, when I was 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 medieval 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 are associated with them that they are very ancient.
And they are sand stones.
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.
Ah, Micraster...
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 have labels, only numbers.
So you were expected to be able to pick up one...
..and say, "Yes, that's a belemnite."
Now, 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,
"OK, 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 a 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 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 fossilised remains.
Even so, there is a bird alive today
that illustrates the link between modern birds and reptiles.