After missing for two decades, two notebooks that once belonged to English naturalist, geologist, and biologist, Charles Darwin, which is believed to be worth millions of pounds, have likely been stolen, according to Cambridge University Library on Tuesday.

The library released a statement that the notebooks, one of which contained Darwin's 1837 'Tree of Life,' had been removed from the special collections' strong rooms of the university, where the valuable and rare items are kept, to be photographed in September of 2000.

The mentioned items were logged as photographed in November of 2000, but during a routine check, in January of 2001, they have found that the small box which contained the said notebooks had not been returned to its proper place, CBS News reported.

The English biologist, Darwin, sketched his ideas around an evolutionary tree in the summer of 1837 after he returned from his round-the-world trip aboard HMS Beagle, decades before publishing more supported ideas around the tree of life in 'On the Origin of Species.'

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According to The Guardian, for several years, librarians at the university had assumed that the notebooks, which are also known as the 'Transmutation Notebooks' were just lost and scattered in the vast library, which is home to not less than 130 miles or 210 kilometers of shelving and an estimated of 10 million maps, manuscripts, and books.

According to the university's library, after an exhaustive search for the mentioned items, which they considered worth millions of pounds, they believed that the notebooks are missing and likely have been stolen.

Jessica Gardner, Director of the Library Services and a university librarian since 2017, shared that she is heartbroken that the location of Darwin's notebooks, which included Darwin's iconic 'Tree of Life' drawing is currently unknown. 

But she mentioned that they are determined to do everything possible to discover what happened to the notebooks and promised that they would leave no stone unturned during the whole search process.

She also added that they would be hugely grateful to hear from any staff, including past and present researchers, members of the book trade, or the public at large, with information that might help recover the notebooks, Daily Mail reported.

Gardner also mentioned that someone somewhere might know or even have an insight that can help them return these notebooks to its proper place, which is at the heart of the United Kindom's cultural and scientific heritage.

After discovering that the notebooks were missing, they reported it to the Cambridgeshire Police and tagged it as stolen artworks in the Interpol's Psyche database and recorded on the national Art Loss Register as missing artifacts.

The currently missing notebooks had previously been digitized and are available on the Cambridge Digital Library.

Cambridge University plans to continue its search operation for the documents, which includes a complete search of the building, home to one of the world's most significant collections of the works of the English naturalist, geologist, and biologist Charles Darwin. Still, they estimated that it would take about five years to finish the whole process.

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