More important still, the discovery of the theory of Natural Selection by Darwin--and at a later period by myself--has led to a satisfactory explanation of the successive appearance of higher and more complex forms of life, and also of that wonderfully minute and complex _adaptation_ of every species to its conditions of existence and to its organic as well as its inorganic environment, which all other theories--even the most recent--have failed to grapple with. [Sidenote: Wonderful Complexity of the Universe] The logical completeness as well as the extreme simplicity of this explanation of organic evolution has led great numbers of thoughtful but ill-informed persons to reject it, because it seems to render unnecessary the existence of a primary intelligent cause; while another equally large but, as I think, equally ill-informed class--the so-called monists--use it to demonstrate the non-existence, or, at all events, the needlessness, of any such cause. Both alike err, because they fail to take cognisance of the fact that every form of evolution, and pre-eminently that of the organic world, is an explanation of a process of change, a law of development, not in any sense or by any possibility an explanation of fundamental laws, causes, or origins. It presupposes the existence not only of matter--itself a thing whose nature is becoming more and more mysterious and unthinkable with the advance of physical science--but of all the vast complex of laws and forces which act upon it--mechanical, physical, chemical, and electrical laws and forces--all more or less dependent on the still more mysterious, all-pervading ether. Thus, the universe in its purely physical and inorganic aspect is now seen to be such an overwhelmingly complex organism as to suggest to most minds some vast intelligent power pervading and sustaining it.