Pari passu with this process has gone on the diminution of the craniofacial angle. The same influences that tended to raise the body from the horizontal to the vertical position tended also to carry the brain and upper part of the face forward and the jaws and mouth backward. It is not claimed that this reaction of the developing intelligence upon the physical form is sufficient alone to account for the development of the entire type of physical beauty attained by the most advanced human races. Esthetic considerations are needed to complete the process, and especially the powerful aid of sexual selection; but even the sense of beauty must be in great part ascribed to mental development and refinement.
Nothing is more certain than that the faculty of speech is a product of intelligence. Both by direct effort and by hereditary selection the organs of speech received increment after increment of adaptation to this end. The means of intercommunication was the indispensable requirement, and this would be secured by any intelligent creature no matter what the physical organization might be. Oral speech is by no means the only way in which such intercommunication is secured, and even if no organs had existed by which sound could be produced, some other means would have been adopted. But man possessed sound-producing organs in common with nearly all animals. There is no evidence that he was specially favored in this respect. In developed man the larynx is more complicated than in most mammals, but this may be comparatively recent. In many animals it is greatly specialized. In birds it is far more elaborate than in man, being double and sometimes, as in the crane, enormously elongated and coiled into a trumpet. Who can doubt that with such an organ all birds could talk if they possessed ideas to communicate? The parrot and many other birds actually do distinctly articulate the words of human speech by imitation, but they lack the power to clothe them with thought. It would be easy to add a great number of other proofs of the all-sufficiency of the one leading characteristic of the human species—superior brain development—to account for
