Initial stage

Communication by gestures is intrinsically subject to physical limitations: it needs light and a direct line of sight to work. To overcome them, the proportion between gestures and vocal signs gradually shifts in favor of the latter. Homo erectus still had a vocal communication system which was unlike contemporary languages of Homo sapiens. I.o.w., for the period including Homo erectus and Homo sapiens, uniformitarianism does not hold. On the other hand, there was no single “catastrophe” in which Adam and Eve by a flash of inspiration – or by a single mutation, as some would have it – invented language. Instead, the evolution from primitive communication systems up to contemporary languages is a very slow process, taking several hundreds of thousands of years. The phylogenetic evolution of language is, thus, slower by magnitudes than the sociocultural change of languages.

With the development of Broca's area, both motor control and sensory control are refined for the transmission of auditory signs. Both in speech production and perception, units at both of the levels of double articulation are linearized. The brain of archaic Homo sapiens can execute cognitive operations which form new (complex) notions and propositions, and communicative operations, specifically to issue a command and to impart information. Later on, it will be able to formulate questions, too.

For any form of language to survive the change of generations, it is indispensable that it be used in communication with children. Thus, it would not suffice that language was necessary and used in cooperation between adults. It must also have been used by mothers in communication with their babies.

Development of complexity

At this point, human language possesses effability. It is no longer situation-bound, but allows displaced reference. The vocal language system then develops further at both levels of double articulation:

• The inventory of units of the first articulation is enhanced. This is the development of the lexicon. Simultaneously, the potential of their selection and combination is both enhanced and constrained. This is the development of grammar.
• The inventory of units of the second articulation is enhanced, and the potential of their combination into larger units is both enhanced and constrained. This is the development of phonology.

In all of these areas, development means growth of complexity. This takes place under the conditions in which the speech communities live. Language is a system transmitted and modified by generations. It develops together with the society and with culture. The social function of language, i.e. its function in coordinating and bonding the group, is at the root of its diversification over space and time.

Speech communities build up complexity in different directions and to different extents. This process continues to this day in language change. Some modern languages display a degree of development of a specific subsystem which does not move many steps beyond the initial basis, while others have developed this particular subsystem to the utmost. This does not mean that a language of the former kind has remained in the phase of the origin of human language. 160,000 years after the origin of human language, there is no language which has preserved the properties of the proto-language. In the course of its prehistory and history, every speech community has adapted its language to its needs many times over.