Originally published in paperback in 1986, the essays in this book discuss questions about the growth and conceptual structure of the modern evolutionary synthesis, or 'neo-Darwinism'. Written by biologists, historians and philosophers, the collection provides a penetrating analysis of the development, meaning and problems of twentieth-century evolutionary theory. Part I includes discussion of the role of eugenics in shaping the biological interests of R. A. Fisher; the abandonment of Lamarckism; the influence of systematics and the concepts of adaptation and random drift in the development of Sewall Wright's theory; and explanation of how the synthesis 'hardened' in the decades following its original presentation. Part II examines the history of mimetic theory as a case study in evolutionary thought, while Part III introduces the reader to some aspects of the German tradition. Finally, Part IV addresses the debates that existed around the time of publication.