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 Paley's simile of the watch is no longer applicable to such a world as this.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.