1 The Problem.- 2 The Evolutionary Significance of Genetic Diversity; Ecological, Demographic and Life History Correlates.- The Problem.- Materials and Methods.- The Evidence.- Patterns Among Taxonomic Groupings.- Patterns Among Ecological Parameters.- Patterns Among Demographic Parameters.- Patterns Among Life History Parameters.- Correlation Matrix.- Multiple Regression Analysis.- Smallest Space Analysis (SSA): Genetic and Biotic Relationships.- Summary of Evidence.- Theoretical Consideration.- Selective and Nonselective Processes.- Theoretical and Empirical Methodologies.- Critical Analysis of the Methodology of Genetic-Environmental Correlations.- Maintenance of Polymorphism.- The neutral theory.- The selection theories.- The Matching of Evidence and Theoretical Models.- Predictions of the Neutral Theory.- Predictions of Selection Theories.- Conclusions and Prospects.- Summary.- Acknowledgements.- References of the Data.- References of the Theoretical Discussion.- Appendix I. The Data Set.- Appendix II. The Biotic Questionnaire.- Appendix III. Transformations of Heterozygosity and Polymorphism Estimates.- 3 Genetic Polymorphism and Neomutationism.- Protein Polymorphism.- Extent of Polymorphism and Population Size.- Internal Consistency of Population Parameters.- Mani’s Ecological Genetic Model.- Dna Polymorphism.- Nucleotide Diversity.- Silent Polymorphism.- DNA Length Polymorphism.- Nucleotide Substitution in Functional Genes and Pseudogenes.- Implications for Evolutionary Theory.- Adaptive and Nonadaptive Evolution.- Role of Mutation in Evolution.- Acknowledgements.- References.- 4 A Darwinian Theory of Enzyme Polymorphism.- The Model.- The Accuracy of the Numerical Calculations.- Why Is Chaotic Motion Rare in Natural Populations?.- Survival Probability for Populations.- Predictions of the Model at the Genetic Level.- Allele Frequency Distribution.- Single Locus Heterozygosity.- The Fitness Distribution of the Homocygotes and the Heterocygotes.- Average Number of Polymorphic Alleles at a Single Locus.- What is the Optimum Value for ??.- Rate of Gene Substitutions.- Conclusions.- References.- 5 The Possibility of Stress-Triggered Evolution.