theory of natural selection, but he was fully occupied with his career as a geologist and held back from compiling it until his book on The Structure and Distribution of Coral Reefs was completed. As he recalled in his autobiography, he had "at last got a theory by which to work", but it was only in June 1842 that he allowed himself "the satisfaction of writing a very brief abstract of my theory in pencil". Further development Darwin continued to research and extensively revise his theory while focusing on his main work of publishing the scientific results of the Beagle voyage. He tentatively wrote of his ideas to Lyell in January 1842; then in June he roughed out a 35-page "Pencil Sketch" of his theory. Darwin began correspondence about his theorising with the botanist Joseph Dalton Hooker in January 1844, and by July had rounded out his "sketch" into a 230-page "Essay", to be expanded with his research results and published if he died prematurely. In November 1844, the anonymously published popular science book Vestiges of the Natural History of Creation, written by Scottish journalist Robert Chambers, widened public interest in the concept of transmutation of species. Vestiges used evidence from the fossil record and embryology to support the claim that living things had progressed from the simple to the more complex over time. But it proposed a linear progression rather than the branching common descent theory behind Darwin's work in progress, and it ignored adaptation. Darwin read it soon after publication, and scorned its amateurish geology and zoology, but he carefully reviewed his own arguments after leading scientists, including Adam Sedgwick, attacked its morality and scientific errors. Vestiges had significant influence on public opinion, and the intense debate helped to pave the way for the acceptance of the more scientifically sophisticated Origin by moving evolutionary speculation into the mainstream. While few naturalists were willing to consider transmutation, Herbert Spencer became an active proponent of Lamarckism and progressive development in the 1850s. Hooker was persuaded to take away a copy of the "Essay" in January 1847, and eventually sent a page of notes giving Darwin much-needed feedback. Reminded of his lack of expertise in taxonomy, Darwin began an eight-year study of barnacles, becoming the leading expert on their classification. Using his theory, he discovered homologies showing that slightly changed body parts served different functions to meet new conditions, and he