Chap. III. STRUGGLE FOB EXISTENCE. 69 



CHAPTER III. 



STRUGGLE FOR EXISTENCE. 



Its bearing on Natural Selection— The Term used In a wide Sense— Geometrical Ratio 

 oriucroase — Rapid Iiicreaao of Nuturalized Animals and Plants— Nature of tho 

 Checks to Incroase— Competition universal— EftectR of Climate — Protection from 

 the Number of Individuals — Complex Relations of all Animals and Plants throush- 

 out Nature— St ru;;srlo for Life most severe between Individuals and Varieties of 

 the same *Specics: often severe between Species of the same Genus — The Rela- 

 tion of Organism to Or^^anism the most important of all Relations. 



Before entering on the subject of this chapter, I must 

 make a few prehminary 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 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 organization to another part, and to the condi- 

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

 perfected ? We see these beautiful coadaptations most plain- 

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

 ])lainly in the hinnblest parasite which clings to the hairs of a 

 quadruped or feathers of a bird; in the structure of the beetle 

 wliich dives through the water ; in the ])lumed 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 



