Most likely, human speech had different origins:
Miocene Hominoidea:
- territorial calls or apes
cf gibbon-like duetting = loud songs,
Pleistocene Homo:
- seafood = brain-specific nutrients (DHA) = huge brain,
- seafood suction = fine movements of cheeks, lips, tongue, hyoid...
- seafood diving = voluntary breathing.

Google
"Seafood, Diving, Song and Speech"
Mario Vaneechoutte cs 2011
doi 10.2174/978160805244811101010181

Comparative data suggest that the various elements of human speech evolved at different times, and originally had different functions.
Recent work by Nishimura [1-6] shows: what is commonly known as the "laryngeal descent" actually evolved in a mosaic way, in minimally 2 steps:
(a) a descent of the thyroid cartilage vs the hyoid, a descent also seen in apes,
(b) a descent of the hyoid bone vs the palate, which is less obvious in apes, and which is accentuated by the absence of prognathism in the short & flat human face.

Comparisons with other animals suggest:
(a) might be ass.x loud and/or varied sound production,
(b) might be part of an adaptation to eating seafoods, e.g. shellfish can be sucked into the mouth, and swallowed without chewing, even under water.

We argue:
the origin of human speech is based on different pre-adaptations that were present in human ancestors, e.g.
(a) sound production adaptations related to the descent of the thyroid cartilage, ass.x the territorial calls of apes,
(b) transformation of the oral & dentitional anatomy incl. the descent of the hyoid, ass.x reduced biting & chewing,
(c) diving adaptations, leading to voluntary control of the airway entrances & voluntary breath control.

After chimpanzee ancestors split from human ancestors c 5.3 Ma,
human ancestors (early-Pleistocene?) became littoral omnivores.
This might help explain
- why chimpanzees did not evolve language skills,
- why human language is a rel.recent phenomenon,
- why it is so strongly dependent upon the availability of voluntary breath control, not seen in other hominoids, but clearly present in diving mammals.

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