x CONTENTS 



Chapter IV 

 NATURAL SELECTION 



PAGES 



I. NATURE OF THE STRUGGLE FOR EXISTENCE . . . 68-77 



Difficulty of realising that there is any struggle going on, p. 68 

 The struggle between groups, p. 71 Love of society, p. 72 Crises and 

 calm intervals, p. 72 Crises in the lives of plants, p. 75 Forest fires, 

 p. 76 Sexual selection, p. 77. 



II. CONSTANCY OF APPARENTLY USELESS CHARACTERS INDEPENDENTLY OF 



NATURAL SELECTION ...... 77-84 



Examples, p. 77 They may be (i) vestiges, or (2) due to correlation, 

 or (3) to isolation, or (4) useful as recognition marks, pp. 80-83 What 

 seemed useless often proves to be an adaptation, p. 84. 



III. VARIATIONS SMALL OR LARGE ..... 84-89 



Both small and large important to evolution, p. 84 Importance of 

 small points, p. 87 Mr Herbert Spencer's failure to appreciate their 

 importance, p. 88. 



IV. RETROGRESSION . . . . . . .89-103 



Importance of shedding what is no longer useful, p. 89 Retrogression 

 due to (i) Natural Selection, (2) economy of growth, (3) Pammixis, 

 pp. 90-94 The maintenance of stability, p. 96 Sudden and complete 

 loss, p. 100 The general tendency of evolution, p. 102. 



V. INTERACTION OF SPECIES ...... 103-112 



Comparative unimportance of physical conditions, p. 103 Evolution of 

 the environment, p. 104 Race between competing species, p. 104 Back- 

 waters of life, p. 106 Plants, p. 106 Varying rate of progress, p. 107 

 Times of equilibrium, p. 107 A possible limit to evolution on parti- 

 cular lines, p. 108 Extreme longevity a check to evolution, p. 109 

 Isolation no substitute for Natural Selection, p. 1 1 1. 

 VI. SYSTEM BY WHICH WASTE is REDUCED . . . .112-120 



Indiscriminate elimination, p. 1 12 Waste-reducing contrivances among 

 plants, p. 113 Reduction of waste in animal species, p. 115 Play and its 

 meaning, p. 117 No tending of the young among "water-breathers," 

 p. 119. 

 VII. INFLUENCE OF THE INDIVIDUAL ON THE EVOLUTION OF THE RACE . 120-128 



Natural Selection using Lamarck ian methods, p. 120 The factor of 

 parental affection and training, p. 123 Herons, p. 124 Men's ancestors, 

 p. 124 Force of fashion among gregarious animals, p. 125 Does this 

 principle reconcile Neo-Darwinism with Lamarckism ? p. 1 26 A possible 

 demurrer, p. 127. 



VIII. VARIATIONS AND ADAPTATIONS: LIMITATION OF THE RANGE WITHIN WHICH 



CHANCE HAS FREE PLAY ..... 129-149 



Adaptations due to mere coincidence, p. 129 The environment may 

 stimulate variability, p. 129 The cause of variations, p. 131 How far 



