A letter from Charles Darwin which was lost for 100 years was rediscovered by chance by a university professor.
The lost letter is being published
It means Sheffield University is in possession of two letters penned by the 19th Century botanist.
The lost correspondence, with a scientist at Leeds City Museum, is now among those published in the 13th volume of Darwin's thoughts.
The letter was discovered by Professor Tim Birkhead, of the Department of Animal and Plant Sciences.
He knew about one stored in a safe, but on discussing the university's connection with a colleague realised there was another letter in a filing cabinet.
"We simultaneously realised that for almost 100 years the university had assumed that it had one Darwin letter, when in fact it had two," said Professor Birkhead.
They date from January 1865 and are part of a correspondence with Henry Denny, an entomologist at Leeds City Museum.
In the fist, Darwin wonders whether Denny is aware of any evidence body lice have developed into different species on the bodies of different races of human.
The second letter extends Darwin's line of inquiry to domestic animals and birds.
Henry Denny's son, Alfred, was the university's first professor of zoology.
Professor Birkhead is now the honorary curator of the Alfred Denny Museum, the university's zoology collection.