The diversity of living forms and the unity of evolutionary processes are themes that have permeated the research and writing of Ernst Mayr, a Grand Master of evolutionary biology. The essays collected here are among his most valuable and durable: contributions that form the basis for much of the contemporary understanding of evolutionary biology.

General Introduction I. EVOLUTION Introduction: Darwin Vindicated Basic Concepts of Evolutionary Biology The Evolution of Living Systems Typological versus Population Thinking Accident or Design: The Paradox of Evolution Selection and Directional Evolution Population Size and Evolutionary Parameters From Molecules to Organic Diversity Sexual Selection and Natural Selection The Emergence of Evolutionary Novelties II. SPECIATION Introduction Darwin and Isolation Darwin, Wallace, and the Origin of Isolating Mechanisms Karl Jordan on Speciation Sympatric Speciation Bird Speciation in the Tropics Change of Environment and Speciation Geographical Character Gradients and Climatic Adaptation III. HISTORY OF BIOLOGY Introduction Lamarck Revisited Agassiz, Darwin, and Evolution The Nature of the Darwinian Revolution Karl Jordan on the Theory of Systematics and Evolution Where Are We? The Recent Historiography of Genetics IV. PHILOSOPHY OF BIOLOGY Introduction Cause and Effect in Biology Explanatory Models in Biology Theory Formation in Developmental Biology Teleological and Teleonomic: A New Analysis V. THEORY OF SYSTEMATICS Introduction The Challenge of Diversity The Role of Systematics in Biology Theory of Biological Classification Cladistic Analysis or Cladistic Classification VI. THE SPECIES Introduction Toward a Modern Species Definition Karl Jordan and the Biological Species Concept Species Concepts and Definitions Sibling or Cryptic Species among Animals The Biological Meaning of species VII. MAN Introduction Taxonomic Categories in Fossil Hominids VIII. BIOGEOGRAPHY Introduction What Is a Fauna? History of the North American Bird Fauna Inferences Concerning the Tertiary North American Bird Faunas The Origin and History of the Polynesian Bird Fauna Land Bridges and Dispersal Facilities Wallace's Line in the Light of Recent Zoogeographic Studies Fragments of a Papuan Ornithogeography The Ornithogeography of the Hawaiian Islands The Nature of Colonization of Birds IX. BEHAVIOR Introduction Behavior and Systematics Behavior Programs and Evolutionary Strategies INDEX