CHAPTER IV.

VARIATION AND NATURAL SELECTION.

The law of persistence 61 The occurrence of variations 63 Application of the law of increase 76 Natural selection 77 Elimination and selection 79 Modes of natural elimination illustrated 80 Protective resemblance and mimicry 82 Selection proper illustrated 93 The effects of natural selection 95 Isolation or segregation 99 Its modes, geographical, preferential and physiological 99 Its effects 108 Utility of specific characters 110 Variations in the intensity of the struggle for existence 112 Convergence of characters 117 Modes of adaptation: Progress 119 Evolution and Revolution 120