In elucidating these points, we may fitly begin by considering the question as to the possibility of the evolution of any higher creature than Man, to whom the dominion over this earth shall pass. The question will best be answered by turning back and observing one of the most remarkable features connected with the origin of Man and with his superiority over other animals. And let it be borne in mind that we are not now about to wander through the regions of unconditional possibility. We are not dealing with vague general notions of development, but with the scientific Darwinian theory, which alleges development only as the result of certain rigorously defined agencies. The chief among these agencies is Natural Selection. It has again and again been illustrated how by the cumulative selection and inheritance of slight physical variations generic differences, like those between the tiger and the leopard, or the cow and the antelope, at length arise; and the guiding principle in the accumulation of slight physical differences has been the welfare of the species. The variant forms on either side have survived while the constant forms have perished, so that the lines of demarcation between allied species have grown more and more distinct, and it is usually only by going back to fossil ages that we can supply the missing links of continuity. In the desperate struggle for existence no peculiarity, physical or psychical, however slight, has been too insignificant for natural selection to seize and enhance; and the myriad fantastic forms and hues of animal and vegetal life illustrate the seeming capriciousness of its workings. Psychical variations have never been unimportant since the appearance of the first faint pigment-spot which by and by was to translate touch into vision, as it developed into the lenses and humours of the eye.[2] Special organs of sense and the lower grades of perception and judgment were slowly developed through countless ages, in company with purely physical variations of shape of foot, or length of neck, or complexity of stomach, or thickness of hide. At length there came a wonderful moment--silent and unnoticed, as are the beginnings of all great revolutions. Silent and unnoticed, even as the day of the Lord which cometh like a thief in the night, there arrived that wonderful moment at which psychical changes began to be of more use than physical changes to the brute ancestor of Man. Through further ages of ceaseless struggle the profitable variations in this creature occurred oftener and oftener in the brain, and less often in other parts of the organism, until by and by the size of his brain had been doubled and its complexity of structure increased a thousand-fold, while in other respects his appearance was not so very different from that of his brother apes.[3] Along with this growth of the brain, the complete assumption of the upright posture, enabling the hands to be devoted entirely to prehension