Two “stolen” notebooks that once belonged to English naturalist Charles Darwin have been mysteriously returned to Cambridge University, 22 years after they were last seen. The notebooks were wrapped in plastic and left in a bright pink gift bag. There was no clue as to who returned the books, just a printed short message on a brown envelope inside the bag that read: “Librarian, Happy Easter X.” The priceless items – in which Darwin mapped out his theory of evolution about the origin of life – were found to be missing in 2001, but at the time staff believed they may have been misplaced.

“My sense of relief at the notebooks’ safe return is profound and almost impossible to adequately express,” said Dr. Garner, librarian at Cambridge University. It took five days before the notebooks were confirmed to be genuine. “The theory of natural selection and evolution is probably the single most important theory in the life and earth environmental sciences and these are the notebooks in which that theory was put together,” says Jim Secord, emeritus professor of history and philosophy of science at Cambridge University. The Cambridgeshire Police are still investigating the case.