In all probability this fact has had much to do with the continued dependence of animals on smell. In fishes and reptiles a full sweep of vision is so slowly gained that some more active sentinel sense is requisite to safety. In mammals the head rotates more easily, but valuable time is lost in the rotation of the whole body. These animals, therefore, depend on both sight and smell, in some cases equally, in some more fully on one or the other of these senses. When we reach the semi-upright ape, we have to do with a form capable of turning the body and observing the whole surrounding circle of objects more quickly and readily than any quadruped. As a result, these animals have grown to depend more fully on vision and less on smell than the quadrupeds. Finally, in fully erect man, the power of quick turning and alert observation of the whole circle of the horizon reaches its ultimate, and in man sight has become in a large degree the dominant sense, and smell has fallen to a minor place.
With this change in the relations of the senses has come a change in the degree of mental development. It is highly probable that the dependence of the apes on vision instead of smell has had much to do with their mental activity, quickness of observation, and active curiosity. In man there can be no question that it has played a great part in the rapid development of his intellectual powers, and in the extraordinary breadth of his conception of nature as compared with that of the lower animals. While hearing and smell advise us of neighboring conditions only, and have their chief utility as aids to the preservation of existence, sight makes us aware of the conditions of nature in remote localities, extending far beyond the limits of the earth. While this sense plays its part as one of the protective agencies, it is still more useful as an agent in the acquisition of knowledge in general, and has much to do with the development of the intellectual faculties. We may look, therefore, upon the increasing dominance of the sense of sight as a leading agency in the making of man as a thinking being, and may ascribe to this in a considerable measure the thirst for information and faculty of imitation so marked in the apes.
VII
THE ORIGIN OF LANGUAGE
One of the characteristics of man, of which we spoke as among those to which his high development is due, is that of language. There is nothing that has had more to do with the mental progress of the human race than facility in the communication of thought, and in this vocal language is the principal agent and in the fullest measure is the instrument of the mind. Human speech has, in these modern times, become remarkably expressive, indicating all the conditions, relations, and qualities, not only of things, but of thoughts and ideal conceptions. And the utility of language has been enormously augmented by the development of the arts of writing and printing. Originally thought could only be communicated by word of mouth and transmitted by the aid of the memory. Now it can be recorded and kept indefinitely, so that no useful thought of able thinkers need be lost, but every valuable idea can be retained as an educative influence through unnumbered ages.
In this instrumentality, which has been of such extraordinary value to man, the lower animals are strikingly deficient. They are not quite devoid of vocal language, though it is doubtful if any of the sounds made by them have a much higher linguistic office than that of the interjection. But emotional sounds, to which these belong, are not destitute of value in conveying intelligence. They embrace cries of warning, appeals to affection, demands for help, calls for food supplies, threats, and other indications of passion, fear, or feeling. And the significance of these vocal sounds to animals may often be higher than we suppose. That is, they may not be limited to the vague character of the interjection, but may occasionally convey a specific meaning, indicative of some object or some action. In other words, they may advance from the interjection toward the noun or the verb, and approach in value the verbal root, a sound which embraces a complete proposition. Thus a cry of warning may be so modulated as to indicate to the hearer, "Beware, a lion is coming!" or to convey some other specific warning. We know that accent or tone plays a great part in Chinese speech, the most primitive of existing forms, a variation in tone quite changing the meaning of words. The same may be the case with the sounds uttered by animals to a much greater extent than we suppose.
We know this to be the case with some of the birds. The common fowl of our poultry yards has a variety of distinct calls, each understood by its mates, while special modulations of some call or cry are not uncommon among birds. The mammalia are not fluent in vocal powers, their range of tones being limited, yet they certainly convey definite information to one another. Recent observers have come to the conclusion that the apes do, to a certain extent, talk with one another. The experiments to prove this have not been very satisfactory, yet they seem to indicate that the woodland cries of the apes possess a certain range of definite meaning.
We are utterly ignorant of what powers of speech the man-ape possessed. It must, in its developed state as a land-dwelling, wandering, and hunting biped, have needed a wider range of utterance than during its arboreal residence. It was exposed to new dangers, new exigencies of life affected it, and its old cries very probably gained new meanings, or new cries were developed to meet new perils or conditions. In this way a few root words may have been gained, rising above the value of the interjection, and expressing some degree of definite meaning, though still at the bottom of the scale of language, the first stepping stones from the vague cry toward the significant word.