Why against his mentor's exhortations to publish did Charles Darwin take twenty years to reveal his theory of evolution by natural selection? In Darwin's Evolving Identity, Alistair Sponsel argues that Darwin adopted this cautious approach in order to atone for mistakes he had made as a young geological author. Darwin recoiled from getting his "fingers burned" by the reaction to his ambitious theorizing during the Beagle voyage and afterward in his publishing debut masterminded by the provocative geologist Charles Lyell. Far from being tormented by guilt about developing his evolutionary theory, Darwin was chastened by a publishing strategy that had forced him to disavow his "sin of speculation" about coral reefs, volcanoes, and earthquakes. It was this obligation to moderate his theoretical ambitions in general, rather than the prospect of public outcry over evolution in particular, that made Darwin such a cautious author of Origin of Species. Drawing on his own ambitious research in Darwin's manuscripts and at the Beagle's remotest ports of call, Sponsel takes us from the ocean to the Origin and beyond, providing a vivid new picture of Darwin's career as a voyaging naturalist and metropolitan author and, through this example, of the range of skills involved in the development of scientific theories.