60 STRUGGLE FOR EXISTENCE. Chap. III. 



CHAPTEE III. 



Struggle foe Existence. 



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

 metrical powers of increase — Eapid increase of naturalised 

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

 tition 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 be- 

 tween species of the same genus — The relation of organism to 

 organism the most important of all relations. 



Before entering on the subject of tins 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 vari- 

 eties ; 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 organ- 

 isation to another part, and to the conditions of life, and 

 of one distinct organic being to another being, been per- 

 fected? We see these beautiful co- adaptations most 

 plainly in the woodpecker and missletoe ; and only a 

 little less plainly in the humblest parasite which clings 



