CHAPTER III 

 Struggle for Existence 



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

 Geometrical ratio of increase — Rapid increase of naturalized 

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

 tion 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 indi- 

 viduals 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. 



B 



EFORE 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 variability: in- 

 deed 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 in- 

 stance, 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 

 organic being to another being, been perfected? We see 

 these beautiful co-adaptations most plainly in the wood- 

 pecker and the mistletoe; and only a little less plainly 

 in the humblest parasite which clings to the hairs of a quad- 

 ruped or feathers of a bird: in the structure of the beetle 

 which dives through the water : in the plumed seed which is 

 wafted by the gentlest breeze; in short, we see beautiful 



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