The essential condition for this transformation to take place is social life. Undoubtedly, language appears very quickly, as soon as individuals of the same species find themselves in constant relations with one another. Each one learns to attribute the character of signs to the movements which accompany his emotions. Similar beings in whom the same phenomena take place, become equally capable of interpreting those signs. From this moment a language is born; and this is true for the animal species as for man. But human evolution follows an evolution which is peculiar to itself, and which determines that of language. Our language would not have far exceeded the period in which it especially expresses emotions, if human societies had remained purely domestic groupings, without any other organisation than that of the family. “The institution of human language,” says Comte, “appears, in sociology, as the chief continuous instrument of the necessary reaction of political upon domestic life.”[220] Henceforth we can picture to ourselves, in its broad outlines, the prehistoric evolution of language. Originally it comprised gestures and cries. Gestures predominated in the first place as being more immediately expressive. By degrees they took a second place. As the natural signs became divided up so as to become artificial, the superiority of vocal signs appeared. Among other reasons it was due to the “spontaneous correspondence” between the voice and hearing which allows everyone to develop his own education. We hear young children practising for long hours, playing with the articulate sounds which they begin to emit. From this more or less organised singing, still a melody of vocal signs, poetry was born. Finally from poetry, much later, springs, what is commonly called prose, that is, the use of non-rhythmic phrases. Three great evolutions in the history of humanity: how many centuries have not been required for their accomplishment! Writing is to drawing what speaking is to singing. Originally it was not an artifice invented to help vocal language. Here again the ideological theory aggravates the part played by reflection. Man was obeying an instinct when by drawing he reproduced the familiar objects which met his gaze, occupied his imagination, and caused his strongest and most frequent emotions. Gradually, these spontaneous endeavours at imitation assumed the character of signs, became divided up and simplified, and finally were co-ordinated with vocal sounds which themselves had gone through a separate evolution.