Towards the earlier part of the tertiary period, adds Wallace, _an unknown cause_ began to accelerate the development of the intelligence in this anthropoid being. It soon played a preponderating part in the existence of man. The perfection of this faculty became incomparably _more useful_ than any other organic modification. Henceforward the powerful modifying agent of selection acted necessarily almost entirely in this direction. The physical characters already acquired remained almost unaltered, while the organs of the intelligence and the intelligence itself were perfected more and more in each generation. Animals unaffected by this _unknown cause_ which separates us from them, continued to undergo morphological transmutations, so that since the Miocene epoch there has been a great change in the terrestrial fauna. With man only did the form remain the same. We ought not, therefore, to be surprised to find in the Quaternary epoch skulls like those of Denise and Engis, resembling those of men of the present age. The superiority acquired by the intelligence has, moreover, removed our race for ever from the law of the action of _morphological transmutations_. His intellectual and moral faculties only are from this time subject to the power of selection, which will cause the disappearance of inferior races and their replacement by a new race, the lowest individual of which would be, in our time, a superior man. After having read the pages, of which I have just made a summary, we cannot but be surprised to find Wallace declare that natural selection by itself is incapable of producing from an _anthropoid animal_, a man such as we find in the most savage nations known to us. He thus makes the human species an exception to the laws, which, according to him, rule all other living beings. There is a double interest in following Darwin’s rival in this new path. Wallace begins by reminding us that natural selection rests _entirely_ upon the principle of _immediate utility_, relative only to the conditions of the struggle maintained at the time by the individuals constituting the species. Darwin in all his works declares, on different occasions, this same principle, upon which rests, in fact, all his statements upon adaptation, the possibility of _retrogressive transmutations_, etc. It results necessarily from this principle, that selection cannot produce _variations in any way injurious_ to any being whatever. Darwin has often declared that a single well-attested case of this kind would destroy his whole theory. But it is evident, adds Wallace, that selection is as incapable of producing a _useless variation_; it cannot then develop an organ in proportions which would go beyond its degree of _present utility_.