In considering the linguistic development of monkeys it is important to remember that monkeys have to a striking degree developed social qualities. Detailed proof of this sociality need not be given; its existence is known from the accounts of travelers, and of those who have domesticated these animals, and, indeed, from observations in zoological gardens. The knowledge of it is very incomplete; yet enough is known to show that it is often very intimate and not without complexity. Where there is such a social life, it is to be expected that there will be found a development in the use of sounds. Not that the presence of this development is hereby proved, but a presumption is created in favor of the view that it exists.[1] Darwin[2] thought that primeval man probably first used his voice in the production of true musical cadences, especially during courtship; and that the imitation of musical cries by articulate sounds might have given rise to words expressive of various complex emotional states. Should we not rather find the greater development of vocal signs in the apes earlier than primeval man which had variety of vocal utterance combined with the varied emotions of a complex social life, emotions not only of courtship, as Darwin supposes, but of parentage and of the various relations of friendliness and hostility?
It is not meant that all the monkeys referred to have the immobile ear. This is characteristic of the anthropoid apes. It is important, however, to observe in very diverse species of monkeys the peculiar interest in sounds; and in the anthropoid apes, which have lost the mobility of the ear, there is, as we see from the accounts of the gibbon and the chimpanzee, the special development of the use of, and appreciation of, vocal and other sounds.
It seems at first sight that the gain in the use of vocal sound made by the apes is too slight to account for the change in the organ of hearing. Yet we must hesitate to pronounce such a verdict when we consider the immense importance of any improvement in the faculty of language. Let an analogous case be considered. Mr. Fiske has shown that the slow growth of the brain is a condition of the attainment of the preeminent mental faculties possessed by man. This prolongation of infancy is in itself a disadvantage, but the gain resulting from it more than counterbalances the loss. But we find a similar slow growth in the case of the apes. Can we find in them any notable gain in intelligence? While they are intelligent animals, we can not appeal to a distinct and unchallengeable superiority. Nevertheless, we believe on evolutionary principles that there is a gain in mental faculty to warrant the slow maturing of their powers. Even so in the
