CHAPTER III 



STRUGGLE FOR EXISTENCE 



Bears on natural selection — The term used in a wide sense — 

 Geometrical powers 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. 



Before entering on the subject of this chapter, I must 

 make a few preliminary remarks, to show how the 

 struggle for existence bears on Natural Selection. It 

 has been seen in the last chapter that amongst organic 

 beings in a state of nature there is some individual vari- 

 ability : indeed I am not aware that this has ever been 

 disputed. It is immaterial for us whether a multitude 

 of doubtful forms be called species or sub-species or 

 varieties ; what rank, for instance, the two or three 

 hundred doubtful forms of British plants are entitled 

 to hold, if the existence of any well-marked varieties 

 be admitted. But the mere existence of individual 

 variability and of some few well-marked varieties, 

 though necessary as the foundation for the work, helps 

 us but little in understanding how species arise in 

 nature. How have all those exquisite adaptations of 

 one part of the organisation to another part, and to the 

 conditions of life, and of one distinct organic being to 

 another being, been perfected ? We see these beauti- 

 ful co-adaptations most plainly in the woodpecker and 



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