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CHAPTER III. Struggle Fob Existence. [' bearing on natural selection The term used in a wide sense Geometrical ratio of increase Rapid increase of naturalised animals and plants Nature of the checks to increase Competition 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 th same species: often severe between species of the same genus Tht 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 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 organisation to another part, and to the conditions of life, and of ane organic being to another being, been perfected ? We see these beautiful co-adaptations most plainly in the woodpecker and the misletoe; and only a little less plainly in the humblest parasite whichclings to the hairs of a quadruped or feathers of a bird; in the structure of the b...
