viii TABLE OF CONTENTS 



CHAPTER V. NATURAL SELECTION AND STRUGGLE FOR EXIST- 

 ENCE: SEXUAL SELECTION. 



Natural selection the chief determining agent in adaptation, 57; 

 Adaptation to conditions of life, 58; The crowd of animals, 59; 

 Reproduction by multiplication, 59; Numbers of individuals al- 

 most stationary, 60; Struggle for existence, 60; Discriminate 

 death, 61; Natural selection, 62; Interdependence of species, 63; 

 Animal and plant invasions, 64; Doctrine of Malthus, 67; Limits 

 to the capacity of natural selection, 68; Survival of the existing, 

 69; Actual standing of Darwinism, 70; Secondary sexual dif- 

 ferences, 71; Classification of secondary sexual characters, 72; 

 Theory of sexual selection, 75; Criticisms of the theory, 77; The 

 sexual selection theory largely discredited, 78. 



CHAPTER VI. ARTIFICIAL SELECTION. 



Natural selection and artificial selection, 80; Steps in the pro- 

 duction of new races, 81 ; Selected traits quantitative, 81 ; Race 

 traits qualitative, 84; Hybridization, 88; Plant amelioration, 90; 

 Work of Luther Burbank, 90; Panmixia, or cessation of selection, 

 104; Reversal of selection, 104; Transmission and heredity, 105; 

 Artificial selection and natural selection, analogous processes, 

 106; Race-forming by sports, 107. 



CHAPTER VII. VARIOUS THEORIES OF SPECIES-FORMING AND 

 DESCENT CONTROL. 



Segregation of isolation, 108; Geographic and physiologic iso- 

 lation, 109; Romanes's championship of physiologic isolation, 109; 

 The Lamarckian theory of species-transformation, 111; Ortho- 

 genetic evolution, 112; Species-forming by mutation, 114; The un- 

 known factors of evolution, 115. 



CHAPTER VIII. GEOGRAPHIC ISOLATION AND SPECIES-FORMING. 



Migration and faunal distribution, 117; Closely related species 

 not found in the same region, but in contiguous regions, 120; The 

 American warblers, 120; Barriers, 122; The Hawaiian Drepanidse, 

 124; Adaptive and non-adaptive characters, 127; The American 

 orioles, 128; Species traits not necessarily useful, 129; The persist- 

 ence of the sufficiently fitted, 130. 



CHAPTER IX. VARIATION AND MUTATION. 



Actuality and extent of individual variation, 131 ; Darwin's 

 laws of variation, 137; Quetelet's determination that fluctuating 

 variation follows the law of probabilities, 140; Discontinuous varia- 



