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 [to] 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". Darwin continued his work with the Descent of Man and