Various methods are open to the study of language origin. In more modern times the theories discussed can be divided in two great classes.
Until the end of the eighteenth century, three main theories on the origin of language divided the field of investigation: the traditional theological theory, based on the famous chapter of Genesis that describes the construction of the tower of Babel; the theory of the fantastic origin of language fully developed by Vico (1688-1744); and the conventionalist or logical theory, attributing the origin of language to an agreement among learned men to give a certain meaning to a certain word.
In more modern times the theories discussed can be roughly divided into two great classes, the anthropological and the biological. Adherents of the biological theories seek the origin of language in the characteristics and tendencies of the animal world; adherents of the anthropological theories look in the history of language for its most early constitutive elements and concentrate particularly on the speech of non civilized tribes.
The Tower of Babel by Pieter Bruegel via Wikipedia
The principal anthropological theories are more numerous: the babble theory seeks the origin of language in the spontaneous babbling of children. Words like pop, daddy, mammy and many others are adduced in support of this view; the song theory, accepted by most of the ancient Greek philosophers and by many moderns, holds that singing was the original form of language; the symbolical theory, values are attached to pictures, sounds, objects, and these values are symbolically expressed in language; the contact theory, emphasizes the relation of the individual to a social unity. It regards language as the result of a natural trend in all social creatures toward reciprocal contact, understanding, and approach; the utilitarian theory maintains that language originate from the practical necessities of human-cooperation.
Cuneiform is one of the first known forms of written language via Wikipedia
The more important biological theories fall into two classes: the theory of animal sounds seeks analogies to the origin of the human language in the sounds emitted by animals, especially in those that can be observed in the study of apes; the theory of expressive gestures and sounds derives language from the natural movements that express passions. Since interjections supply important evidence for this view, it is sometimes called the interjectional theory.
Various methods are open to the study of language origin. Some look to the careful study of languages in general for light on the origin of language, for example, shows that the linguistic categories of the adjective and the article, and probably also the conjunction and the adverb, are of late creation, whereas verbs, nouns, and interjections are very old. Adherents of the biological theories of language origin enter still another field in their investigation, studying the utterances and gestures of the animal world. Others seek the early stages of speech in the archaic languages of primitive tribes; their studies have resulted in valuable discoveries, but it is probable that even the most primitive languages have a long past. The theological theories of the origin of the language maintain that language is a gift from God, or that it is the effect of wisdom inherent in nature through the will of God.