| OCR Text |
Show 60 STRUGGLE FOR EXISTENCE. CIIAP. III." CHAPTER III. STRUGGLE FOR ExisTENCE. Bears on natural selection-The term used in a wide sense-Geometrical powers 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-Strug~le 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 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 one distinct organic being to another being, been perfected? 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 CHAP. III. STRUGGLE FOR EXISTENCE. G1 to the hairs of a quadruped or feathers of a bird; in the ~tructure of the beetle which dives through the water ; In the pl~med 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 ?ailed incipient species, become ultiinately converted Into good and distinct species, which in most cases obviously differ from each other far more than do the vari~ties of .the same ~pecies? II ow do those groups of species, which constitute what are called distinct genera, and which differ from each other more than do the species of the same genus, arise? All these results ~s w~ shall more fully see in the next chapter, fol!o~ Inevitably from the struggle for life. Owing to this struggle for life, any variation, however slight and from whatever caus~ ~r~ceeding, if it be in any degree profitable to an Individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man's ~ower of sele~tion. We have seen that man by selecHon c~n c~rtainly p:oduce great results, and can adapt organic beings to his own uses, through the accumulation of slight but useful variations, given to him by the hand of Nature. But Natural Selection, as we shall here~fter .see, is a power incessantly ready for action, and Is as Immeasurably superior to man's feeble efforts, as the works of Nature are to those of Art. |
