Remarkably, there has been no complete scholarly edition, either of the 1839 or of the 1845 versions, of so famous and consequential a work.
Darwin based the published on the detailed diary and field notes he kept during the voyage.
He wrote up his diary entries on board ship, days and in some cases even weeks after the events recorded, drawing on the notes he made during his land expeditions.
(Darwin’s notebooks as well as the , edited by John van Wyhe.) A third textual stratum of the voyage consists of the letters Darwin wrote home to his family, friends, mentors and a widening circle of scientific correspondents.
It was while looking back at his notes on the Galápagos mocking-birds, in July 1836, that realization began to grip: When I see these Islands in sight of each other, & [but del.] possessed of but a scanty stock of animals, tenanted by these birds, but slightly differing in structure & filling the same place in Nature, I must suspect they are only varieties. In the second edition, by now well advanced on his species research, he went further: “Seeing the gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends” (1845: 380).
And he added: “it is the circumstance, that several of the islands possess their own species of the tortoise, mocking-thrush, finches, and numerous plants, these species having the same general habits, occupying analogous situations, and obviously filling the same place in the natural economy of this archipelago, that strikes me with wonder” (397)—ten years after he had set foot there. In October 1836, a few days away from England, Darwin wrote up “a short retrospect of the advantages and disadvantages, the pains and pleasures, of our five years’ wandering” ( 1839: 602).
Throughout the remainder of 1834 and much of 1835 it surveyed the western coasts of South America and outlying islands, heading to the Galápagos archipelago in September 1835.
The following year, the traversed Australasia and the Indian and Atlantic Oceans, returning (via Bahia again) to England in October 1836.
The 1845 edition differs significantly from the edition of 1839.
Darwin condensed the text and rationalized its order, re-organizing the chapters to follow the geographical course of the circumnavigation rather than its chronology, so that multiple visits to a single location (e.g., Tierra del Fuego, December 1832-February 1833, February 1834, June 1834) are corralled into a single chapter or continuous narrative unit.