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Show 12 DARWINISM CHAP. carefully save the best seed to sow and the finest or brightest coloured animals to breed from, we shall soon find that an improvement will take place, a~d .that the a~erage. quality of our stock will be raised. This IS the way m whiCh all our fine garden fruits and vegetabl~s and flowers hav~ bee~ produced as well as all our splendid breeds of domestic ammals; and they have thus become in many cases so different from the wild races from which they originally sprang as to be hardly recognisable n.s the same. It is therefore proved that if a.11y particular kind of variation is preserved and bred from, the variation itself goes on increasing in amount to an enormous extent; and the bearing of this on the que tion of the origin of species is most important. For if in each aeneration of a given animal or phnt the fittest survive to ~ontinue the breed, then whatever may be the specinJ peculiarity that causes "fitness" in the particular case, that peculiarity will go on increasing and strengthening so long as it is useful to the species. But the moment it has reached its maximum of usefulness, a.nd some other quality or modification would help in the struggle, then the individuals which vary in the new direction will survive; and thus a species may be gradually modified, first in one direction, then in another, till it differs from the original parent form as much as the greyhound differs from any wild dog or the cauliflower from any wild plant. But animals or plants which thus differ in a state of nature are always classed as distinct species, and thus we see how, by the continuous survival of the :fittest or the preservation of favoured races in the struggle for life, new specie. may be originated. This self-acting process which, by means of a few easily demonstrated groups of facts, brings about change in the organic world, and keeps each species in harmony with the conditions of its existence, will appear to some persons so clear and simple as to need no further demon tration. But to tho great majority of naturalists and men of science endless di·fficulties and objections arise, owing to the wonderful variety of animal and vegetable forms, and the intricate relations of the different species and groups of species with each other ; and it was to answer as many of these objections as possible, ancl to show that the more we know of nature the more we WHAT ARE SPECIES 13 fir1d it to harmonise with the development hypothesis, that Darwin devoted the whole of his life to collecting facts and making experiments, the record of a portion of which he has given us in a series of twelve masterly volumes. Proposed Mode of T1·eatrnent of the Subject. It is evidently of the most vital importance to any theory that its foundations should be absolutely secure. It is therefore necessary to show, by a wide and comprehen ive array of facts, that animals and plants do perpetually vary in the manner and to the amount requisite; ancl that this takes place in wild animals as well as in tho e which arc dome. ticated. It is necessary also to prove that all organisms do tend to increase at the great rate alleged, and that this increase actually occurs, under favourable conditions. \Y e have to prove, further, that variations of all kinds can be increased and accumulated by selection ; and that the trugglc for existence to the extent here indicated actually occurs in nature, and leads to the continued preservation of favourable variatiom. These matters will be discussed in the four succeeding chapters, though in a somewhat different order-the struggle for existence and the power of rapid multiplication, which is its cause, occupying the first place, as compri. ing those facts which are the most fundamental and those which can be perfectly explained without any reference to the less generally understood facts of variation. These chapters will be followed by a discussion of certain difficulties, and of the vexed que. tion of hybridity. Then will come a rather full account of the more important of the complex relations of organisms to each other and to the earth itself, which are either fully explained or greatly elucidated by the theory. The concluding chapter will treat of the origin of man and his relations to the lower animals. |