It was in its own chosen stronghold that this once famous argument was destined to meet its doom. It was in the adaptations of the organic world, in the manifold harmonies between living creatures and surrounding circumstances, that it had seemed to find its chief support; and now came the Darwinian theory of natural selection, and in the twinkling of an eye knocked all this support from under it. It is not that the organism and its environment have been adapted to each other by an exercise of creative intelligence, but it is that the organism is necessarily fitted to the environment because in the perennial slaughter that has gone on from the beginning only the fittest have survived. Or, as it has been otherwise expressed, "the earth is suited to its inhabitants because it has produced them, and only such as suit it live." In the struggle for existence no individual peculiarity, however slight, that tends to the preservation of life is neglected. It is unerringly seized upon and propagated by natural selection, and from the cumulative action of such slight causes have come the beautiful adaptations of which the organic world is full. The demonstration of this point, through the labours of a whole generation of naturalists, has been one of the most notable achievements of modern science, and to the theistic arguments of Paley and the Bridgewater treatises it has dealt destruction.

But the Darwinian theory of natural selection does not stand alone. It is part of a greater whole. It is the most conspicuous portion of that doctrine of evolution in which all the results hitherto attained by the great modern scientific movement are codified, and which Herbert Spencer had already begun to set forth in its main outlines before the Darwinian theory had been made known to the world. This doctrine of evolution so far extends the range of our vision through past and future time as entirely to alter our conception of the universe. Our grandfathers, in common with all preceding generations of men, could and did suppose that at some particular moment in the past eternity the world was created in very much the shape which it has at present. But our modern knowledge does not allow us to suppose anything of the sort. We can carry back our thoughts through a long succession of great epochs, some of them many millions of years in duration, in each of which the innumerable forms of life that covered the earth were very different from what they were in all the others, and in even the nearest of which they were notably different from what they are now. We can go back still farther to the eras when the earth was a whirling ball of vapour, or when it formed an equatorial belt upon a sun two hundred million miles in diameter, or when the sun itself was but a giant nebula from which as yet no planet had been born. And through all the vast sweep of time, from the simple primeval vapour down to the multifarious world we know to-day, we see the various forms of Nature coming into existence one after the other in accordance with laws of which we are already beginning to trace the character and scope. Paley's simile of the watch is no longer applicable to such a world as this. It must be replaced by the simile of the flower. The universe is not a machine, but an organism, with an indwelling principle of life. It was not made, but it has grown.

That such a change in our conception of the universe marks the greatest revolution that has ever taken place in human thinking need scarcely be said. But even in this statement we have not quite revealed the depth of the change. Not only has modern science made it clear that the varied forms of Nature which make up the universe have arisen through a process of evolution, but it has also made it clear that what we call the laws of Nature have been evolved through the self-same process. The axiom of the persistence of force, upon which all modern science has come to rest, involves as a necessary corollary the persistence of the relations between forces; so that, starting with the persistence of force and the primary qualities of matter, it can be shown that all those uniformities of coexistence and succession which we call natural laws have arisen one after the other in connection with the forms which have afforded the occasions for their manifestation. The all-pervading harmony of Nature is thus itself a natural product, and the last inch of ground is cut away from under the theologians who suppose the universe to have come into existence through a supernatural process of manufacture at the hands of a Creator outside of itself.