The world's largest Charles Darwin book collection has been bought by the Natural History Museum for nearly £1m.
The collection contains almost everything Darwin published
The Kohler Darwin Collection includes almost everything the naturalist published from 1829 onwards.
Antiquarians Chris and Michele Kohler amassed about 3,500 items, filling four rooms in their house, over 20 years.
The acquisition, the most expensive in the museum's 125-year history, was made possible thanks to a £712,000 grant by the National Heritage Memorial Fund.
Four years ago, the museum opened its £95m Darwin Centre, housing 22m zoology specimens - many collected by Darwin on his 19th Century voyages.
On Thursday, the museum's science director, Richard Lane, said: "This acquisition makes the Museum the ultimate Darwin resource.
"Darwin brought about a revolution in how humans think about themselves and the natural world.
"Combining this collection with our existing holdings give us an unprecedented insight into how the theory of evolution developed, and how Darwin worked."
The Kohlers began with a small collection of books on evolution, but decided to assemble the greatest Darwin collection - which filled four rooms in their house before it was sold to the museum.
The museum has a big collection of Darwin's zoology specimens
"Darwin constantly reworked his ideas, and these continual changes can only be seen if all the books are in one place," said Chris Kohler.
He said he was delighted that the collection would be accessible to study far into the future.
Among the items are 470 editions of On the Origin of Species and a rare copy of Zoology of the Voyage of HMS Beagle, bound in original cloth, and a map of the Falkland Islands from the Beagle voyage.
Over the next three years it will be catalogued, conserved and re-housed, to form part of a Darwin exhibition planned for 2008.