This book provides both a compendium of evidence supporting Charles Darwin's grand theory of evolution and an overview of some of the most fascinating chapters in the 3.5+ billion year history of biological diversity on planet Earth. Written in a substantive and accessible style, this revised and updated second edition of "Missing Links" will serve as a source of information for the general reader as well as an ancillary text for formal and informal courses in a variety of disciplines. The first section of the book introduces readers to scientific thinking and methods of studying Earth's geological history, principles of classification and phylogenetic analysis, the role of ecology in the history of life, and perspectives on the origin and evolution of species. The second section presents an overview of significant transitions in the history of Earth's biodiversity, beginning with the origin of life and including chapters on the fish-amphibian, reptile (probably dinosaur)-bird, and reptile-mammal transitions. Other chapters examine detailed evolutionary histories of flatfishes, snakes, rodents, horses, whales, and humans. The final chapter documents evolutionary changes occurring now, in living animals, within the lifetime of a human observer.