But the working out of this theory is not without its own difficulties. In the first place, the factor in the theory of evolution which can be most clearly traced--the principle of natural selection--is not itself a source of change or of the production of new results. It is only the means by which advantageous changes are preserved and disadvantageous changes passed by. The initiative in these changes comes either from the unequal pressure of the environment or from some tendency to vary in the organism itself. Now, if we suppose certain moral relations and the feelings corresponding to them to exist in a society, and to tend to greater certainty and fulness of life on the part of those who possess them, such relations and feelings will be favoured by the operation of natural selection, and will gradually be assimilated into the tissue of the social organism. But this does not account for the origin of morality generally nor of any particular moral relation; it merely shows how, having been somehow originated, it has naturally come to persist. There are thus really two points to be considered in tracing the development of moral ideas--the question of origin and the question of persistence. The latter is accounted for by natural selection; the former must be brought under the obscure laws of variation, laws so obscure that variations in nature are frequently spoken of as if they took place by chance. These two questions are involved at each stage in the progress of morality. But it is at the initial stage that the question of origin is of greatest importance: when the attempt is made to show how, in the course of time, and by the aid of purely physical and biological laws, feelings and conduct, from being merely natural and reflex, have acquired a moral character--when, in a word, the moral is being evolved out of the non-moral. A difficulty comes to the front here which scarcely arises when we are simply tracing the various phases through which the moral consciousness has passed, and the various forms in which moral conduct and feelings have expressed and embodied themselves. The latter subject is obviously within the scope of the theory of evolution, if that theory applies to the processes of the human mind and society as well as to those of external nature. And, although each stage involves a modification to be accounted for not by natural selection, but by the laws of variation, yet the variation is within facts of the same order, and creates no more difficulty than the successive modifications of living tissue which have been implied in the evolution of organic nature. But the transition from the non-moral to the moral is a transition to a different order of facts or--perhaps we should rather say--to a different way of looking at facts, and should not be assumed to be a process of the same kind and explicable by the same method of investigation as the passage from one fact to the similar fact which immediately follows it. It may be