Priceless notebooks belonging to Charles Darwin, one containing his well-known “tree of life” sketch mapping out his idea of pure choice, have been mysteriously returned to Cambridge College greater than 20 years after they went lacking.

The college launched an attraction to get the notebooks again in 2020, in partnership with vintage e-book consultants, native police and Interpol, the worldwide policing company.

And to the astonishment of employees on the college’s library, on March 9, the notebooks have been returned.

Wrapped in plastic and left in a brilliant pink present bag, with no apparent indicators of harm, they have been left exterior the librarian’s workplace on the fourth flooring of the grand 17-story library constructing, the college mentioned in a assertion Tuesday.

There was no clue as to who returned the books, only a message inside a brown envelope that learn: “Librarian, Pleased Easter X”“My sense of reduction on the notebooks’ secure return is profound and nearly inconceivable to adequately specific,” Cambridge College Librarian Jessica Gardner mentioned.

“They could be tiny, simply the scale of postcards, however the notebooks’ impression on the historical past of science, and their significance to our world-class collections right here, can’t be overstated.”

The well-known “tree of life” sketch dates to the summer time of 1837 when Darwin had lately returned from his journey on board HMS Beagle, greater than 20 years earlier than the publication of “On the Origin of Species.”

The notebooks are identified in evolutionary biology because the “transmutation notebooks” as they’re thought-about the primary level at which Darwin got here up with the speculation of how species might “transmute,” or adapt and alter via generations.

“Objects resembling these are essential for our understanding of not solely the historical past of science however the historical past of humankind,” mentioned Stephen J. Toope, vice-chancellor of the College of Cambridge.

Nevertheless, the police investigation into who took the books continues. They have been initially taken from the library’s Particular Assortment Sturdy Rooms in September 2000 to be photographed. A routine verify in January 2001 discovered that two notebooks — concerning the measurement of a paperback e-book — had not been returned.

The college mentioned earlier librarians thought the lacking books had simply been misplaced — with round 10 million gadgets, this appeared attainable. However years of looking out discovered nothing and an in-depth search of the Darwin Archive in 2020 concluded it had seemingly been stolen.

Decided to not let thieves strike once more, the college has constructed new high-security robust rooms and put in a variety of safety measures since 2001.

“These embody CCTV, card-and-pin entry to safe areas, a devoted safety workforce onsite and additional root-and-branch critiques of all our safety protocols to come back — to ensure we decrease any future danger so far as humanly attainable,” Gardner mentioned.

Cambridgeshire Police mentioned in an announcement that it shared within the college’s delight on the return of the books, however added that its investigation into who took them stays open.

“We additionally renew our attraction for anybody with details about the case to contact us,” it mentioned.

The notebooks will now return to the library’s Darwin Archives and can take middle stage in a new public exhibition in July, which can even function greater than 15,000 letters written by Darwin. The exhibit will then be on show on the New York Public Library in 2023.