Variation Under Domestication
Before Christmas 1866 Variation was sent to the printers, save for the last chapter. In this, Darwin wanted to overcome the persistent argument of divinely guided variation. He used the analogy of an architect using rocks which had broken off naturally and fallen to the foot of a cliff, asking "Can it be reasonably maintained that the Creator intentionally ordered... that certain fragments should assume certain shapes so that the builder might erect his edifice?" In the same way, breeders or natural selection picked those that happened to be useful from variations arising by "general laws", to improve plants and animals, "man included". Darwin was now openly including man in his theory, and wanted to add a chapter on this but the book was already too "horridly, disgustingly big" and he shortly decided to write a separate "short essay" on ape ancestry, sexual selection and human expression.
Murray had to make two volumes of it, and being advised that it was hard going planned only 750 copies, though he later doubled that. Translators were eager to get to work: Carus into German, and Vladimir Kovalevsky into Russian - he was sent Murray's proofs, and successfully beat his publication date so that the earliest edition of Variation was in Russian.
During the Spring Darwin tried to find explanations in Sexual Selection for variations in that "eminently domesticated animal", mankind, and for the plumage of birds. As well as drawing on information, he experimented with dying pigeons red and trimming the feathers of game-cocks to see if this affected their desirability as a mate. The Duke of Argyll had thrown down a challenge with his book The Reign of Law, which collected criticisms of the Origin and put forward theories of divine design and providential law in a way that struck Darwin as "very well written, very interesting, honest, & clever & very arrogant". It made a particular point of the iridescent colours of hummingbirds, claiming that this was beauty for God's sake without any earthly reason, not explicable by struggle. Wallace gave Reign of Law a withering review, pointing to the existence of stink bugs as well as beauty, and then became entangled in an exchange of detailed arguments with the Duke. To Darwin's despair, Wallace refused to accept a rôle for Sexual Selection.
Further damage to the Origin came from professor Sir William Thomson (later Lord Kelvin) used calculations of heat loss to estimate a much younger age for the earth than Darwin had been assuming. Thomson's partner in a submarine cable business, the engineer Fleeming Jenkin, then argued convincingly that any single variation would be blended back into the population, so that to form a new species numerous variations would have to be created simultaneously, reintroducing the need for divine intervention.
By June Lyell was struggling to revise his Principles of Geology, though Darwin still hoped that he would at last "speak out plainly about species". Lyell found Darwin's proofs of Variation "most persuasive", but Darwin was struggling to sort out the changes and corrections he wanted. Encouragement came from the Reverend professor Charles Kingsley who sent the previously unthinkable news that "the best and strongest men" at the University of Cambridge were "coming over what the world calls Darwinism... The younger M.A.'s are not only willing, but greedy, to hear what you have to say, and... the elder... are facing the whole question in quite a different tone from that they did three years ago... I have been surprised at the change since last winter."
The proofs were finished on 15 November, and The Variation of Animals and Plants Under Domestication went on sale on 30 January 1868, thirteen years after Darwin had begun his experiments on breeding and stewing the bones of pigeons. He was feeling deflated, and concerned about how these large volumes would be received, writing "if I try to read a few pages I feel fairly nauseated... The devil take the whole book". The public were undeterred, and the 1,500 copies went within a week with a second printing at eleven days. The Pall Mall Gazette praised its "noble calmness... undisturbed by the heats of polemical agitation" which made the far from calm Darwin laugh, and left him "cock-a-hoop".
See Darwin from Descent of Man to Emotions for his life and work in the following period.
Read more about this topic: Darwin From Orchids To Variation