The project will begin with a correspondence of some 1,400 letters with botanist Joseph Hooker, the closest friend of the celebrated British naturalist best known for his theory of evolution.
"Hooker was admitted into the select group of those with whom Darwin felt able to discuss his emerging ideas," Alison Pearn, associate director of the Darwin Correspondence Project, told 'The Independent' ahead of an official launch later this month.
"In perhaps his most famous letter of all, Darwin wrote to Hooker in 1844 of his growing conviction that species 'are not... Immutable' - an admission he likened, half-jokingly, to 'confessing a murder'� It was also to Hooker that Darwin sent the manuscript of On the Origin of Species for comment," Dr Pearn added.
The archive - some 9,000 letters - includes correspondence with leading thinkers of the day and the earliest manuscripts outlining his theories, which scandalised Victorians by suggesting animals and humans had a common ancestry.
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Digitising the papers of Darwin follows the university's online success with the archive of another famous scientist, Sir Isaac Newton, which has attracted millions of hits worldwide.
Of the letters between Darwin and Hooker, 300 have not been published before. Both men faced the trauma of losing their family members.
"Thank God she� never knew that she was leaving Frank and all of us for ever. I cannot think what will become of Frank. She helped and encouraged him in his scientific work and whether he will ever have heart to go on again� I cannot conceive. My dear old Friend I know that you will forgive me pouring out my grief," says Darwin, in reference to his daughter-in-law who died at the age of 26 in childbirth.
"I don't know of another letter (like it). I don't think there are many people to whom (Darwin) would have written in this way. This is unique insight into his attachment to his daughter-in-law," Dr Pearn said.
The collection of Charles Darwin's papers at the University Library originates in the work of his son Francis, who published two editions of his father's letters, in 1887 and 1903. For these editions he collected as many of Charles's letters and papers as possible, which remained in the family after Francis died.