Darwin now had the framework of his theory of natural selection. His research included animal husbandry and extensive experiments with plants, finding evidence that species were not fixed and investigating many detailed ideas to refine and substantiate his theory. For more than a decade this work was in the background to his main occupation, publication of the scientific results of the Beagle voyage.
Early in 1842, Darwin wrote about his ideas to Lyell, who noted that his ally “denies seeing a beginning to each crop of species”. Darwin’s book “The Structure and Distribution of Coral Reefs” on his theory of atoll formation was published in May after more than three years of work. In May and June he wrote a “pencil sketch” of his theory of natural selection.
By July, Darwin had expanded his “sketch” into a 230-page “Essay”, to be expanded with his research results if he died prematurely. In November the anonymously published sensational best-seller “Vestiges of the Natural History of Creation” brought wide interest in transmutation. Controversy erupted, and it continued to sell well despite contemptuous dismissal by scientists.
Darwin completed his third geological book in 1846. He now renewed a fascination and expertise in marine invertebrates, dating back to his student days with Grant, by dissecting and classifying the barnacles he had collected on the voyage. In 1847, Hooker read the “Essay” and sent notes that provided Darwin with the calm critical feedback that he needed, but would not commit himself and questioned Darwin’s opposition to continuing acts of creation.
In eight years of work on barnacles (Cirripedia), Darwin’s theory helped him to find “homologies” showing that slightly changed body parts served different functions to meet new conditions, and in some genera he found minute males parasitic on hermaphrodites. In 1853 it earned him the Royal Society’s Royal Medal, and it made his reputation as a biologist. He resumed work on his theory of species in 1854, and in November realised that divergence in the character of descendants could be explained by them becoming adapted to “diversified places in the economy of nature”.