Fifty years after the appearance of Paley’s work, the grandson of Erasmus Darwin wrote ‘No thoroughfare’ on the entrance to Paley’s line of speculation, and closed it to mankind for ever. He did this in two ways—first by marshalling from his studies of comparative anatomy and of embryology an extraordinary volume of convincing evidence for the _fact_ of the mutability of natural forms, and secondly by his attempt to establish a plausible _method_ by which the change and development of organs and types might actually have taken place. The method, summed up in the phrases ‘natural selection’ and ‘survival of the fittest,’ was what really caught the attention of the world, and gave his doctrine the wings which carried it into almost every sphere of human thought. However we take it, it was certainly an immense contribution to the organization of knowledge, but whether it is really what it first seemed to be, the basic fact at the bottom of all the phenomena of evolution, is coming to look more and more doubtful in the light of later researches.[8] This question will have to be considered later on in the course of this study, and in relation to its main inquiry, which is this: What precisely was the change in philosophic and religious outlook brought about by the full and final establishment of the doctrine of evolution? Where has evolution left the argument from design? Must we study nature as a mass of unrelated phenomena, or can we discern, through these, any fundamental unity to which they stand in organic relation; and if we can, what is the nature of this unity? It will be useful in the first place to have before us a typical specimen of Paley’s method. I shall choose as an example the case which he considered so striking that he deemed it almost sufficient in itself to bear the whole weight of his argument In his ninth chapter, ‘On the Muscles,’ he writes:—