Manuscripts showing the development of Charles Darwin's theory of evolution have been released by Cambridge University Library.
The selection of papers from the Library's Darwin Manuscripts collection show how the naturalist started thinking about evolution on board the HMS Beagle with theoretical reflections, right through to the publication of On the Origin of Species.
Highlights include his 'Transmutation' and 'Metaphysical' notebooks written during the 1830s. The manuscripts also include the first reference to natural selection in his 1842 'Pencil Sketch'.
Darwin's first ideas about evolution are traced during his five-year Beagle voyage to South America.
"Beyond these scattered, early theoretical reflections, the bulk of the Creation collection comprises the complete set of theoretical notes and the multiple draft essays that Darwin wrote over a period of two decades (1837-1859)," the University said in a statement.
"These documents truly constitute the surviving seedbed of the Origin. For in them, Darwin hammered out natural selection and the structure of concepts he used to support natural selection.
"It was here also that he developed his evolutionary narrative and where he experimented privately with arguments and strategies of presentation that he either rejected or that eventually saw the light of day with the Origin's publication in 1859."
The collection includes Darwin's first attempt at formulating a full theory, several hundred letters and draft notes from Origin, which his children used as drawing paper.
"While Darwin carefully preserved many thousands of manuscript pages leading up to the draft of the Origin, and continued to add notes to the Origin portfolios into the 1870s, he seems to have placed little value on preserving the draft itself, and all that survive seem to be mainly those few sheets whose blank sides were used by his children, particularly his son Francis, for drawing paper and those retrieved from the trash basket by others of Darwin's children, particularly his daughter Henrietta."
The Darwin manuscripts have been split into two sections – Creation of the Origin, which has now been released, and Darwin's Evidence, which will be made available in June next year.