The great Piltdown fraud, the mystery of how a shark swims with an asymmetric tail, the debate over dinosaur extinction, the haunting beauty of a loon on a northern lake--these are only a few of the subjects discussed by Keith Stewart Thomson in this wide-ranging book. At once instructive and entertaining, the book celebrates the aesthetic, literary, and intellectual aspects of science and conveys what is involved in being a scientist today--the excitement of discovery and puzzle solving, the debate over what to read and what to write, and the element of promotion that seems to be necessary to stimulate research and funding.   Keith Thomson, a well-known biologist who writes a column for the distinguished bi-monthly magazine American Scientist, here presents some of his favorite essays from that periodical in a book of three parts, each introduced by a new essay. In the first section, "The Uses of Diversity," he ponders such questions as why we care passionately and expensively about the dusky seaside sparrow and how and why we rescued the flowering tree Franklinia from extinction. The second section, "On Being a Scientist," includes an autobiographical account of Thomson's life and his views on what makes being a scientist special and interesting. The last section, "The Future of Evolution," gives examples of how the study of evolution is entering one of the most dramatic stages in its own development.   Thomson presents science as a great intellectual adventure--a search of why things are as they are--most rewarding when it is accompanied by an appreciation of the subtleties and aesthetic qualities of the objects studied. His book will enable nonscientists to open their minds to the pleasures of science and scientists to become more articulate and passionate about what they do.