Cambridge University curators said Tuesday that they believe two long-missing notebooks used by Charles Darwin were stolen.
The two so-called Transmutation Notebooks have been missing since 2001, and were originally thought to have been lost somewhere in the university’s archives, according to NBC News.
However, Jessica Gardner, the university librarian and director of library services, said Cambridge has concluded the notebooks were stolen after conducting the “largest search in the library’s history” to no avail.
The university added that the materials may yet be found within the archives during the continued search, which is ongoing and may take up to five more years. The archive contains more than 130 miles of shelved books.
One of the two notebooks contains the naturalist’s famed “Tree of Life” sketch, an early attempt at illustrating his theory of evolution more than 20 years before he published “On the Origin of Species,” according to NBC.
“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,” Gardner said in a statement.
“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,” she added.
Interpol has added the notebooks to its database of stolen art, according to NBC.