ture. The stream of generations flows on by this process, which is as much a part of the settled, continuous economy of the world as the steady action of gravity or heat. It is demonstrated that living forms are liable to variations which accumulate through inheritance; that the ratio of multiplication in the living world is out of all proportion to the means of subsistence, so that only comparatively few germs mature, while myriads are destroyed; that, in the struggles of life, the fittest to the conditions survive, and those least adapted perish. It is a demonstrated fact that life has existed on the globe during periods of time so vast as to be incalculable; that there has been an order in its succession by which the lowest appeared first, and the highest have come last, while the intermediate forms disclose a rising gradation. It is a demonstrated truth of Nature that matter is indestructible, and that therefore all the material changes and transformations of the world consist in using over and over the. same stock of materials, new forms being perpetually derived from old ones; and it is a fact now also held to be established, that force obeys the same laws. All these great truths harmonize with each other; they agree with all we know of the constitution of Nature; and they demonstrate evolution as a fact, and go far toward opening to us the secondary question of its method.
The reverend writer, whom we have quoted, asks, "If evolution rests on a basis as sure as astronomy, why do we not see one species passing into another now, even as we see the motions of the planets through the heavens?" To this foolish question, which has nevertheless been asked a dozen times by clerical critics of Huxley, the obvious answer is, that what requires a very long time to produce cannot be seen in a very short time. Has the writer ever seen the production of a geological formation? That he has not seen the evidences that would have prevented him from asking such a question is probably because he is not a student of Nature, and has not looked for them.
There has been much complaint that Prof. Huxley undertook to put the demonstrative evidence of evolution on so narrow a basis as the establishment of the genealogy of the horse, but this rather enhances than detracts from his merit as a scientific thinker. It has been well remarked that "the genius of the discoverer appears in his perceiving how small a number of facts, rightly considered, are sufficient to form a foundation for a theory." Kepler had to fix but a few points in the path of Mars, to demonstrate the ellipticity of his orbit, and to subvert the theory of circular planetary motions, by which the way was paved to the Newtonian astronomy. Prof. Huxley could have accumulated a far more striking display of the proofs of evolution for a popular audience, but he preferred to rest the question on evidence that was none the less decisive because it was restricted. If the horse has been derived from preceding forms in the way he pointed out, then that is the method of Nature—unless we deny the unity of its order.
And here is the vital point between Prof. Huxley and his antagonists. It is a question of the validity of the conception of the order and uniformity of Nature. Prof. Huxley holds to it as a first principle, a truth demonstrated by all science, and just as fixed in biology as in astronomy. His antagonists hold that the inflexible order of Nature may be asserted perhaps in astronomy, but they deny it in biology. They here invoke supernatural intervention. Obviously there are but two hypotheses upon the subject, that of the genetic derivation of existing species, through the operation of natural law, and that of creation by miraculous interference with the course of Nature. If we assume the orderly course of Nature, development