A PAIR of notebooks written by Charles Darwin worth millions and containing his iconic 'Tree of Life' sketch are feared to have been stolen from a university library.

The two red notebooks were used by Darwin in the summer of 1837 to first develop his theory on evolution, the origin of humans, and classification by descent.

The ideas jotted within the notebooks, including Darwin's famous 'Tree of Life' sketch, would later become part of his most famous work, On The Origin Of Species, published in November 1859.

Yesterday, on the 161st anniversary of the publication of On The Origin Of Species, Cambridge University launched an urgent public appeal to help track down the two notebooks.

Given their unique nature, the value of the notebooks is difficult to estimate, but would probably run into millions of pounds.

The notebooks were previously housed in the university library's Special Collections Strong Rooms, where the rarest and most valuable items are kept.

But they were removed for photography to take place in September 2000.

And, during a subsequent routine check in January 2001, it was found that the small box containing the two notebooks - which is about the size of a paperback book - had not been returned to its proper place.

For many years, previous university librarians believed that the notebooks had been misplaced in the vast storerooms and collections of Cambridge University Library.

The library is home to around 10 million books, maps, manuscripts and other objects, on more than 130 miles of shelving.

But at the start of 2020, current University librarian and director of library services, Dr. Jessica Gardner, arranged a new search.

Specialist staff were assigned to search specific zones of the library’s storage facilities, conducting fingertip examinations where necessary.

This still failed to locate the notebooks - leading to the conclusion, with the help of national experts in cultural heritage theft and recovery, that they have likely been stolen.

Cambridgeshire Police have been informed and their disappearance has been recorded on the national Art Loss Register for missing cultural artefacts.

The library's missing notebooks have also been added to Interpol’s

database of stolen artworks - Psyche.

Dr. Gardner, who has been university librarian since 2017, said: "I am heartbroken that the location of these Darwin notebooks, including Darwin’s iconic 'Tree of Life' drawing, is currently unknown.

"But we’re determined to do everything possible to discover what happened and will leave no stone unturned during this process.

"This public appeal could be critical in seeing the notebooks safely

returned, for the benefit of all, and I would ask anyone who thinks they may be able to help to get in touch.

"We would be hugely grateful to hear from any staff, past or present, members of the book trade, researchers, or the public at large, with information that might assist in the recovery of the notebooks.

"Someone, somewhere, may have knowledge or insight that can help us return these notebooks to their proper place at the heart of the UK’s cultural and scientific heritage."

She added: "Security policy was different 20 years ago.

"Today any such significant missing object would be reported as a potential theft immediately and a widespread search begun.

"We keep all our precious collections under the tightest security, in dedicated, climate-controlled strong rooms, meeting national standards.

"The building has transformed significantly since the notebooks were first reported as missing.

"We have additional security measures such as new strong rooms, new specialist reading rooms, CCTV, enhanced access control to secure areas, and our participation in international networks on collections security".

Dr. Gardner has insisted the library will not stop searching for the notebooks.

She said: "The Special Collections Strong Rooms alone contain more than 45km of shelving and millions of documents, many held in boxes.Given the vast size of the building and its collections, a complete search will take up to an estimated five more years to complete.

"All cultural and collecting institutions have to deal with a legacy of missing items and the possibility of loss and theft.

"It is part of our duty to make these precious items as accessible to the public as possible.

"It is essential that we approach the issues, however difficult, in an open and transparent fashion."