5. This same conception of a process without beginning, favours the notion that since life was possible on our globe all species may well have co-existed in varying proportions. From the sudden spread of population through almost accidental conditions, we can imagine how certain species might have been so scarce as to leave no trace in geological strata, whereas those which enormously preponderated at the same time would have done so. A change of conditions might easily cause the former to preponderate, and their sudden appearance in the strata would look as though they had then first come into being. In a word, we can have good evidence for the extinction of species, but scarcely any for their origination. This supposition is not adverse to the derivation of species from a common stock, but rather favours the notion that as in the case of the individual the period of plasticity is short compared with that of morphological stability, so if there was such an arboreal branching out of species from a common root, it took place rapidly in conditions as different from ours as those of uterine from extra-uterine life; and that the stage of inflexibility may have been reached before any time of which we have record. But in truth when we see in the world of chemical substances an altogether similar sedation of species where there can be no question of common descent as its cause, we may well suspend our judgment till the established facts have excluded the many hypotheses other than Evolution by which they may be explained. As long as Evolution claims to be no more than a working scientific hypothesis, like ether or electric fluid--a sort of frame or subjective category into which observed facts are more conveniently fitted, it cannot justly be pressed for a solution of ultimate problems; but when it claims to be a complete philosophy and as such to extrude other philosophies previously in possession, it must show that it can rest the mind where they leave it restless; or that it has proved their proffered solutions spurious. This, so far, it has absolutely failed to do. At most it may determine more accurately the way in which God works out His Idea in Creation. It can stand as long as it is content to prescind from the question of ends and origins; but then it is no longer a complete philosophy. As soon as it attempts to solve those problems it becomes incoherent and unthinkable. Its true complement is theism and finality, which flow from it as naturally, if not quite so immediately as the "argument from adaptability." _Deus creavit_ is so far the only moderately intelligible, or at least not demonstrably unintelligible, answer given to the problem of _In principio_.