yi CONTENTS. 



CHAPTER IH. 



STRUGGLE FOR EXISTENCE. 



Its bearing on natural selection — The term used in a wide sense — 

 Geometrical ratio of increase — Rapid increase of naturalised 

 animals and plants — Nature of the checks to increase — Com- 

 petition universal — EflEects of Climate — Protection from the 

 number of individuals — Complex relations of all animals and 

 plants throughout nature — Struggle for life most severe between 

 individuals and varieties of the same species: often severe 

 between species of the same genus — The relation of organism 

 to organism the most important of all relations . . Page 75 



CHAPTER IV. 



NATURAL selection; OR THE SURVIVAL OF THE FITTEST. 



Natural Selection — its power compared with man's selection — its 

 power on characters of trifling importance — its power at aU 

 ages and on both sexes — Sexual selection — On the generality 

 of intercrosses between individuals of the same species — Cir- 

 cumstances favourable and unfavourable to the results of 

 Natural Selection, namely, intercrossing, isolation, number of 

 individuals — Slow action — Extinction caused by Natural Se- 

 lection — Divergence of Character, related to the diversity of 

 inhabitants of any small area, and to naturalisation — Action 

 of Natural Selection, through Divergence of Character and 

 Extinction, on the descendants from a common parent — Ex- 

 plains the grouping of all organic beings — Advance in organ- 

 isation — Low forms preserved — Convergence of Character — 

 Indefinite multiplication of species — Summary , . .97 



CHAPTER V. 



LAWS OF VARIATION. 



EfEeets of changed conditions — Use and disuse, combined with 

 natural selection ; organs of flight and of vision — Acclimatisa- 



