. Evolution and animal life; an elementary discussion of facts, processes, laws and theories relating to the life and evolution of animals . n nature is not indiscriminate. In thelong run and for the most part, those creatures least fitted toresist are the first to perish. It is the slowest animal which issoonest overtaken by the pursuers. It is the weakest which is 62 EVOLUTION AND ANIMAL LIFE crowded aside or trampled on by its associates. It is the leastadaptable which suffers most from extremes of heat and the process of Artificial Selection the breeder improves hisstock, destroyin
. Evolution and animal life; an elementary discussion of facts, processes, laws and theories relating to the life and evolution of animals . n nature is not indiscriminate. In thelong run and for the most part, those creatures least fitted toresist are the first to perish. It is the slowest animal which issoonest overtaken by the pursuers. It is the weakest which is 62 EVOLUTION AND ANIMAL LIFE crowded aside or trampled on by its associates. It is the leastadaptable which suffers most from extremes of heat and the process of Artificial Selection the breeder improves hisstock, destroying his weakest or least comely calves, reservingthe strong and fit for parentage. In like fashion, on an in-conceivably large scale, the forces of nature are at work modify-ing and fitting to the demands of their surroundings the differentspecies of animals. Because the processes and results of thestruggle for existence seem parallel with those of artificialselection, Darwin suggested the name of Natural Selectionfor the sifting process as seen in nature. To the general re-sult of natural selection, Herbert Spencer has applied the term. FIG. 39.—The Australian ladybird, Vedalia cardinalis, feeding on cottony cushion scale, Icerya purchasi. (From life.) Survival of the Fittest. By fitness in this sense is meant onlyadaptation to surrounding conditions, for the process of naturalselection has no necessary moral element, nor does it necessarilywork toward progress among organisms. With changing con-ditions species undergo change. Some individuals, by thepossession of slight advantageous variations of structure or ofinstinct, meet these new demands better than others. Thesesurvive, the others die. The survivors produce young sharingin part, at least, their own advantages, and with renewed selec-tion the degree of adaptation increases with successive genera-tions. To the process of natural selection we must, in most cases,probably ascribe the adjustment of species to surroundings.
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