From the point of view of the student of behavior, language, spoken language especially, is a habit, acquired like walking or swimming. It is made possible primarily by the fact that human beings possess a variety and flexibility of vocal reflexes possessed by no other animal. All the higher animals have a number of vocal reflexes, which are called out primarily in the expression of emotion or desire. Cries of pain, hunger, rage, sex desire or desire for companionship, are common to a great number of the animal species. But these cries and vocal utterances are limited, and comparatively unmodifiable. They are moreover expressed, so far as experimental observation can reveal, with no consciousness of the specific significance of particular sounds and are used as the involuntary expression of emotion rather than as a specific means of communication. ... The primates have a much larger number of such vocal instincts than the other mammals, and a much larger number of stimuli can call them out, _e.g._, injury to bodily tissue calls out one group; hunger calls out a certain group; sex stimuli (mate, etc.) another; and similarly cold, swiftly moving objects, tones, strange animals call out others. When attachments are formed between the female and her offspring another large group is called into action. There is no evidence to show in the case of mammals that these vocal instincts are modified by the sounds of other animals.... These throat habits may be cultivated to such an extent in birds that we may get an approximation, more or less complete, to a few such habits possessed by the human being. Such throat habits, however, are not language habits.[1] [Footnote 1: Watson: _Behavior_, p. 323.] In human beings language, it is clear, may attain extraordinary refinement and complexity, and may convey extremely fine shades and subtleties of emotion or idea. This results from the fact that man is born with a vocal apparatus far superior in development to that of any of the animals. It is pretty clear that the mutant man, when thrown off from the primate stock, sprang forth with a vocal apparatus different from that of the parent stock, and possessing abundant richness in reflexes, even far surpassing that found in the bird. It is interesting to observe, too, in this connection, that within the narrow space occupied by the vocal apparatus we have a system of muscular mechanisms which has within it, looking at it now as a whole, the same possibilities of habit formation that we find in the remaining portion of bodily musculature.... It is probable that in a few years we shall undertake the study of such habits from exactly the same standpoint that we now employ in studies upon the acquisition of skill in the human being.[2] [Footnote 2: _Ibid._, pp. 323-24.]