| PAGE | |
| The Problem of Adaptation | 1 |
| – Structural Adaptations | 1 |
| – Adaptations for the Good of the Species | 19 |
| – Organs of Little Use to the Individual | 22 |
| – Changes in the Organism that are of No Use to the Individual or to the Race | 25 |
| – Comparison with Inorganic Phenomena | 26 |
| The Theory of Evolution | 30 |
| – Evidence in Favor of the Transmutation Theory | 32 |
| – – Evidence from Classification and from Comparative Anatomy | 32 |
| – – The Geological Evidence | 39 |
| – – Evidence from Direct Observation and Experiment | 43 |
| – – Modern Criticism of the Theory of Evolution | 44 |
| The Theory of Evolution (continued) | 58 |
| – The Evidence from Embryology | 58 |
| – – The Recapitulation Theory | 58 |
| – Conclusions | 84 |
| Darwin’s Theories of Artificial and of Natural Selection | 91 |
| – The Principle of Selection | 91 |
| – Variation and Competition in Nature | 104 |
| – The Theory of Natural Selection | 116 |
| The Theory of Natural Selection (continued) | 129 |
| – Objections to the Theory of Natural Selection | 129 |
| – Sterility between Species | 147 |
| – Weismann’s Germinal Selection | 154 |
| Darwin’s Theory of Sexual Selection | 167 |
| – Sexual Selection | 167 |
| – General Criticism of the Theory of Sexual Selection | 213 |
| The Inheritance of Acquired Characters | 222 |
| – Lamarck’s Theory | 222 |
| – Darwin’s Hypothesis of Pangenesis | 233 |
| – The Neo-Lamarckian School | 240 |
| Continuous and Discontinuous Variation and Heredity | 261 |
| – Continuous Variation | 261 |
| – Heredity and Continuous Variation | 270 |
| – Discontinuous Variation | 272 |
| – Mendel’s Law | 278 |
| – The Mutation Theory of De Vries | 287 |
| – Conclusions | 297 |
| Evolution as the Result of External and Internal Factors | 300 |
| – The Effect of External Influences | 300 |
| – Responsive Changes in the Organism that adapt it to the New Environment | 319 |
| – Nägeli’s Perfecting Principle | 325 |
| The Origin of the Different Kinds of Adaptations | 340 |
| – Form and Symmetry | 340 |
| – Mutual Adaptation of Colonial Forms | 350 |
| – Degeneration | 352 |
| – Protective Coloration | 357 |
| – Sexual Dimorphism and Trimorphism | 360 |
| – Length of Life as an Adaptation | 370 |
| – Organs of Extreme Perfection | 371 |
| – Secondary Sexual Organs as Adaptations | 372 |
| – Individual Adjustments as Adaptations | 375 |
| – Color Changes as Individual Adaptations | 375 |
| – Increase of Organs through Use and Decrease through Disuse | 376 |
| – Reactions of the Organism to Poisons, etc. | 377 |
| – Regeneration | 379 |
| Tropisms and Instincts as Adaptations | 382 |
| Sex as an Adaptation | 414 |
| – The Different Kinds of Sexual Individuals | 414 |
| – The Determination of Sex | 422 |
| – Sex as a Phenomenon of Adaptation | 439 |
| Summary and General Conclusions | 452 |
| INDEX | 465 |