CHAPTER III 



Struggle for Existence 



Its Bearing on Natural Selection — The Term used in a Wide Sense — Geo- 

 metrical Ratio of Increase — Rapid Increase of Naturalized Animals and 

 Plants — Nature of the Checks to Increase — Competition Universal — 

 Effects of Climate — Protection from the number of Individuals — Com- 

 plex Relations of all Animals and Plants throughout Nature — Struggle 

 for Life most Severe between Individuals and Varieties of the Same Spe- 

 cies: 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 

 among organic beings in a state of nature there is some individual 

 variability: indeed, I am not aware that this has ever been dis- 

 puted. 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 foun- 

 dation 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 organization to another part, and to the condi- 

 tions of life, and of one organic being to another being, been per- 

 fected? We see these beautiful coadaptations most plainly in the 

 woodpecker and the mistletoe; and only a little less plainly in the 

 humblest parasite which clings to the hairs of a quadruped 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 adaptations everywhere 

 and in every part of the organic world. 



Again, it may be asked, how is it that varieties, which I have 

 called incipient species, become ultimately converted into good 

 and distinct species, which in most cases obviously differ from 



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