Abstract:

Introduced by Gould and Vrba (1982), the notion of exaptation refers to the use of character to another use that for which it developed during the natural selection. In the case of speech, the use of the vocal tract (lips, tongue, velum and mandible) has evolved from sucking, chewing, and swallowing. We hypothesize that these articulators, whose control allows shaping of the oro-pharyngeal cavity, have been co-opted to produce the speech gestures.

Four questions will be addressed:

1. How vocal-tract management takes advantage of the general properties of acoustic tubes?

We demonstrate that any vocal tract excited at one end (glottis) having a constriction (language) and an opening at its end (lips) produces a sound of which the first two maxima of the spectrum (F1-F2) are confined within a triangle.

2. How the anatomy of the lips and tongue predisposes humans to produce the most differentiated vowels?

The tongue allows generating, inside the vocal tract, the constriction, and the other side, the lips allow opening and rounding of the mouth. At the three corners of the triangle are located the 3 cardinal vowels /i a u/ present in almost all languages of the world.

3. How the anatomy and the functional elements of sucking, lip-smacking and swallowing could be reused to implement proper control of the vocal tract?

The configurations required for the production of vowels are all already present in these different activities. Using the same anatomical elements to produce speech, motor controls have evolved deeply.

4. How this framework can be applied to understand ontogenesis and phylogenesis of speech?

We will implement these assumptions for the study of vocalizations of the baby, for refine the speech production assumptions during human evolution and finally for analyzing baboon vocalizations.