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Show 8 DARWINISM OHAP. animals and plants which live together in an_x: one country, a.nd to give some rational account of the phencrlflena presented by their distribution in different parts of t~e wor:d. And, lastly, we may expect it t_o. exp~am many diffi.cultws and to harmonise many incongrmttes m the exce~s1vely co~p~ex affinities and relations of living things. All th1s the Darwm1an theory undoubtedly does. It shows us. how, by. means of some of the most universal and ever·actmg laws m nature, new species are necessarily produced, while the old species become extinct · and it enables us to understand how the continuous actio~ of these laws during the long periods with which geology makes us acquainted is calculated to. bt:ing about those O'reater differences presented by the d1stmct genera, famili:S, and orders into. which all l! ving things arc clas ified by naturalists. The d1fferences wb1ch the. e present are all of the same nahtrc as those presented by the species of many large genera, but much greater in amount; and they can all be explained by the action of the same gener~l laws ~nd by the extinction of a larger or smaller number of 1ntermedw.te species. Whether the distinctions between the higher grouv; termed Classes and Sub-kingdoms may be accounted for 111 the same way is a much more difficult question. The differences which separate the mammals, birds, reptiles, and fi. hcs from each other, though vast, yet seem of the same nature as those which distinguish a mouse from an elephant or a swallow from a goose. But the vertebrate animals, the mollusca, and the insects, are so radically distinct in their whole organisation and in the very plan of their structure, that objectors may not unreasonably doubt whether they c;tn all have been derived from a common ancestor by means of the very same laws as have sufficed for the differentiation of the various species of birds or of reptiles. The Change of Opinion effected by Da1·win. The point I wish especially to urge is this. Before Darwin's work appeared, the great majority of naturalists, and almost without exception the whole literary and scientific world, held firmly to the belief that species were realities, and bad not been derived from other species by any process accessible to us ; the different species of crow and of violet \VHAT ARE SPECIES 9 were believed to have been always as distinct and separate as they are now, and to have originated by some totally unknown process so far removed from ordinary reproduction that it was usually spoken of a. "special creation." There was, then, 110 question of the origin of families, orders, and clas c., because the very first step of all, the "origin of pecies," was believed to be an insoluble problem. But now this is all changed. The whole scientific and literary world, even the whole educated public, accept., as a matter of common knowledge, the origin of species from other allied species by the ordinary proce. s of natural birth. The idea of . pecial creation or any altogether exceptional mode of production is ab olutely extinct ! Yet more: this is held also to apply to many higher groups as well as to the species of a genus, and not even Mr. Darwin's severe t critics venture to suggest that the primeval bird, reptile, or fish mu. t have been "specially created." And this vast, this totally unprecedented change in public opinion has been the result of the work of one man, and was brought about in the short space of twenty years! This is the answer to those who continue to maintain that the "origin of specie "i. not yet discovered; that there arc . till doubts and difficultic: ; that there arc divergencies of structure so great that we cannot understand how they had their beginning. '\V' e may admit all this, just as we may admit that there arc enormou difficulties in the way of a complete comprehen. ion of the origin and nature of all the part of the solar system and of the stellar universe. Rut we claim for Darwin that he is the Newton of natural history, and that, just so surely as that the discovery and demon tration by Newton of the law of gravitation establi bed order in place of chaos and laid a smc foundation for all fnturc study of the tarry heavens, so surely has Darwin, by his discovery of the la.w of natural selection and his demonstration of the great principle of the pre crvation of useful variations in the truggle for life, not only thrown a flood of light on the proces: of development of the whole organic world, but also established a, firm foundation for all future study of nature. In order to show the view Darwin took of his own work, and what it was that he alone claimed to have done, the concluding pas age of the introduction to the Origin of |