Darwinism | Page 7

at that day whether, supposing it to be clearly shown that all the different species of each genus had been derived from some one ancestral species, and that a full and complete explanation were to be given of how each minute difference in form, colour, or structure might have originated, and how the several peculiarities of habit and of geographical distribution might have been brought about--whether, if this were done, the "origin of species" would be discovered, the great mystery solved, he would undoubtedly have replied in the affirmative. He would probably have added that he never expected any such marvellous discovery to be made in his lifetime. But so much as this assuredly Mr. Darwin has done, not only in the opinion of his disciples and admirers, but by the admissions of those who doubt the completeness of his explanations. For almost all their objections and difficulties apply to those larger differences which separate genera, families, and orders from each other, not to those which separate one species from the species to which it is most nearly allied, and from the remaining species of the same genus. They adduce such difficulties as the first development of the eye, or of the milk-producing glands of the mammalia; the wonderful instincts of bees and of ants; the complex arrangements for the fertilisation of orchids, and numerous other points of structure or habit, as not being satisfactorily explained. But it is evident that these peculiarities had their origin at a very remote period of the earth's history, and no theory, however complete, can do more than afford a probable conjecture as to how they were produced. Our ignorance of the state of the earth's surface and of the conditions of life at those remote periods is very great; thousands of animals and plants must have existed of which we have no record; while we are usually without any information as to the habits and general life-history even of those of which we possess some fragmentary remains; so that the truest and most complete theory would not enable us to solve all the difficult problems which the whole course of the development of life upon our globe presents to us.
What we may expect a true theory to do is to enable us to comprehend and follow out in some detail those changes in the form, structure, and relations of animals and plants which are effected in short periods of time, geologically speaking, and which are now going on around us. We may expect it to explain satisfactorily most of the lesser and superficial differences which distinguish one species from another. We may expect it to throw light on the mutual relations of the animals and plants which live together in any one country, and to give some rational account of the phenomena presented by their distribution in different parts of the world. And, lastly, we may expect it to explain many difficulties and to harmonise many incongruities in the excessively complex affinities and relations of living things. All this the Darwinian theory undoubtedly does. It shows us how, by means of some of the most universal and ever-acting laws in nature, new species are necessarily produced, while the old species become extinct; and it enables us to understand how the continuous action of these laws during the long periods with which geology makes us acquainted is calculated to bring about those greater differences presented by the distinct genera, families, and orders into which all living things are classified by naturalists. The differences which these present are all of the same nature 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 general laws and by the extinction of a larger or smaller number of intermediate species. Whether the distinctions between the higher groups termed Classes and Sub-kingdoms may be accounted for in the same way is a much more difficult question. The differences which separate the mammals, birds, reptiles, and fishes 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 can 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 Darwin.
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