Marking the centennial of Alfred Russel Wallace's death, James Costa presents an elegant edition of the "Species Notebook" of 1855-1859, which Wallace kept during his Malay Archipelago expedition. Presented in facsimile with text transcription and annotations, this never-before-published document provides a window into the travels, trials, and genius of the co-discoverer of natural selection. In one section, headed "Note for Organic Law of Change"--a critique of geologist Charles Lyell's anti-evolutionary arguments--Wallace sketches a book he would never write, owing to the unexpected events of 1858. In that year he sent a manuscript announcing his discovery of natural selection to Charles Darwin. Lyell and the botanist Joseph Hooker proposed a joint reading at the Linnean Society of his scientific paper with Darwin's earlier private writings on the subject. Darwin would go on to publishOn the Origin of Speciesin 1859, to much acclaim; pre-empted, Wallace's first book on evolution waited two decades, but by then he had abandoned his original concept.On the Organic Law of Changerealizes in spirit Wallace's unfinished project, and asserts his stature as not only a founder of biogeography and the preeminent tropical biologist of his day but as Darwin's equal.