When Browne published her first volume on the life of Darwin seven years ago (Charles Darwin: Voyaging), she secured her reputation as the last word on the Victorian naturalist. Now she has published the much-anticipated second half, and it is more spellbinding than the first, which ended on a cliffhanger of sorts. Darwin was back from his Beagle voyages, his famous evolutionary principles were distilled in his mind and the Bible-centered science of his day was about to be convulsed forever. Here, Browne picks up the story a year before the publication of On the Origin of Species, with the arrival of a package from Alfred Russel Wallace, whose own ideas on natural selection virtually mirrored Darwin's, forcing him to go public; as Browne shows, he proved himself a master tactician of institutional and media spin. Browne's subject is monumental, but her writing style is never overburdened by the weight. Rather, her prose is elegant in its clarity of thought, her craftsmanship impeccable in the way it weaves a coherent whole from the innumerable threads of thought, experience and persona that comprised this colossal life. Darwin's science, Browne contends, was characterized by his systematic use of correspondence, which the author puts to effective use in her narrative, again illustrating how the naturalist's thought was as much the collective product of his day as it was its single-most intellectual catalyst. Readers are left with the image of the sailor returned home to dig in his garden, stare into the past and, in dying, slip into legend. (Sept.)