10. From Vocal Replication to Shared Combinatorial Speech Codes: A Small Step for Evolution, A Big Step for Language

Humans use spoken vocalizations, or their signed equivalent, as a physical support to carry language. This support is highly organized: vocalizations are built with the re-use of a small number of articulatory units, which are themselves discrete elements carved up by each linguistic community in the articulatory continuum. Moreover, the repertoires of these elementary units (the gestures, the phonemes, the morphemes) have a number of structural regularities: for example, while our vocal tract allows physically the production of hundreds of vowels, each language uses most often 5, and never more than 20 of them. Also, certain vowels are very frequent, like /a,e,i,o,u/, and some others are very rare, like /en/. All the speakers of a given linguistic community categorize the speech sounds in the same manner, and share the same repertoire of vocalizations. Speakers of different communities may have very different ways of categorizing sounds (for example, Chinese use tones to distinguish sounds), and repertoires of vocalizations. Such an organized physical support of language is crucial for the existence of language, and thus asking how it may have appeared in the biological and/or cultural history of humans is a fundamental questions. In particular, one can wonder how much the evolution of human speech codes relied on specific evolutionary innovations, and thus how difficult (or not) it was for speech to appear.