The publication of Charles Darwin's On the Origin of Species in 1859 is widely regarded as a turning point in knowledge of the natural world. But Darwin's theory of natural selection was not developed in a vacuum; rather, it represents the culmination of an enormous shift in scientific and popular opinion on the subject of species mutability from the late eighteenth century onward. Through her insightful introduction and engaging collection of documents, Sandra Herbert examines this era of scientific thought and the startling discoveries that led Darwin and others to the conclusion that life has evolved. A wide range of documents from over a dozen authors -- including letters, illustrations, scientific tracts, and excerpts from Darwin's own notebooks and On the Origin of Species -- offer a fascinating glimpse into this crucial era of scientific thought. Thoughtful document headnotes, questions for consideration, a chronology, and a selected bibliography provide students with additional context and pedagogical support.