VI CONTEXTS. 



CHAPTER III. 



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 — Effects 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 



"■D^ 



CHAPTER IY. 



Natural Selection ; or the Survival of the Fittest. 



5 



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

 power on characters of trifling importance — its power at all 

 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 

 Selection — 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 Ex- 

 tinction, on the descendants from a common parent — Explains 

 the grouping of all organic beings — Advance in organisation — 

 Low forms preserved — Convergence of Character — Indefinite 

 multiplication of species — Summary.. .. 97 



CHAPTER V. 



Laws of Variation. 



Effects of changed conditions — Use and disuse, combined with 

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



