In 1978 the distinguished paleontologist George Gaylord Simpson published his autobiography, Concession to the Improbable, which gave the basic facts of his life but left more questions than it answered. Now Léo F. Laporte presents this absorbing intellectual study of Simpson's major areas of work. Focusing on Simpson's scientific contributions, Laporte provides chapters on Simpson's earliest paleontological research through his distinguished Alexander Agassiz professorship at Harvard and his extensive fieldwork for the American Museum of Natural History, where he developed the core themes set forth in his most prestigious work, Tempo and Mode in Evolution (Columbia University Press, 1944). Simpson was arguably the first evolutionary paleontologist to combine descriptive taxonomy with the modern approaches of genetics and statistical analysis. Despite his brilliance Simpson was a difficult person to know; Laporte addresses the nature of Simpson's interpersonal problems with colleagues during his life. An introductory overview provides the biographical context of Simpson's career and provides the framework for his major paleontological and evolutionary contributions.