Selection in Natural Populations

By Jeffry B. Mitton | Go to book overview

11
Comments on Natural Selection

It would be more correct to say that natural selection is mainly concerned with preventing evolution, not causing it. Much selection is concerned with the elimination of low-fitness genotypes produced by mutation or recombination. It can be at a generally intense level, but vary so in direction and strength at different times or places that little cumulative change takes place.

G. Williams, Sex and Evolution ( 1975)

I never intended this summary of evolutionary genetics to be comprehensive. I have focused primarily on enzyme polymorphisms and have gained some critical insights by comparing and contrasting the variation of enzyme polymorphisms with the variation of DNA sequences. Like all books, this one reflects the writer's personal experiences and favored hypotheses. This book is mainly a summary of empirical data, and from this I want to emphasize several points.


The Nature of Enzyme Polymorphisms

Enzymes -- as well as functional proteins such as hemoglobin, transferrin, and haptoglobin -- are catalysts that allow metabolic reactions to proceed at temperatures much lower than would otherwise be possible; metabolic rates would be imperceptibly slow without the aid of enzymes. Enzymes must effectively bind to substrates, change conformation to catalyze a reaction, and then release the products of the reaction. All this must be accomplished in a range of temperatures and a set of concentrations of the reacting ingredients determined by the ecology and physiology of the species. But more than allowing reactions to occur at physiological temperatures, enzymes control and regulate metabolism to enable honeybees to fly, cheetahs to sprint, and ponderosa pine to capture carbon from the air. These are not trivial side effects of randomly assembled neutral mutations but adaptations orchestrated by natural selection. Some fish are biochemically tuned for bursts of speed, others for endurance swimming, and still others for neither of these. The metabolic characteristics in these fishes are no more inter-

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Selection in Natural Populations
Table of contents

Table of contents

  • Title Page iii
  • Preface vii
  • Contents ix
  • 1 - Natural Selection, Fitness Determination, and Molecular Variation 3
  • Summary 12
  • 2 - Classes of Abundant Genetic Variation 14
  • 3 - Environmental Variability and Enzyme Polymorphism 29
  • Summary 37
  • 4 - The Impact of a Single Gene 39
  • Summary 57
  • 5 - Patterns of Variation Among Loci 58
  • Summary 71
  • 6 - The Axis of Individual Heterozygosity: Theory 73
  • Summary 86
  • 7 - The Axis of Individual Heterozygosity: Empirical Data 87
  • Summary 126
  • 8 - Female Choice and Male Fitness 127
  • Summary 142
  • 9 - Patterns Among Species 144
  • Summary 156
  • 10 - The Sisyphean Cycle 157
  • Summary 166
  • 11 - Comments on Natural Selection 167
  • Appendices 175
  • Bibliography 199
  • Index 233
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