The theory of the “descent of the larynx” has advanced for 50 years that the low position of the larynx of the human ( Homo sapiens ) is necessary to produce differentiated vowels, and that this capacity necessary for the appearance of speech would have appeared about 75,000 years ago, in its development.
This idea suggested that monkeys, whose anatomy of the vocal tract is very similar to that of humans, but whose larynx is higher, cannot produce differentiated vocalizations because of this latter characteristic.
You should know that humans are the only monkey that has a communication system which, by combining a small number of sound units (vowels and consonants), allows to generate an infinity of statements carrying meaning.
An anatomical lock
In the years 1930-1950, experiments carried out with chimpanzees raised in human families had not enabled them to learn to speak, as one generally does with children. In order to explain this reality, researcher Philip Lieberman had proposed in 1969 the theory of the descent of the larynx, an anatomical lock making spoken communication impossible. Despite some criticisms, this explanation had been widely accepted by a majority of primatologists.
The work of a French team, with the collaboration of Quebec researchers from the University of Quebec’s Phonetics Laboratory, today shows that monkeys are capable of producing well-differentiated protovoyelles.
A reality which contradicts the initial theory and which shows, taking into account the acoustic cavities formed by the tongue, the mandible and the lips, that the production of differentiated vocalizations is not an anatomical question, but that it would rather be linked to control the articulators.
This new knowledge suggests that the ability to speak was born earlier in the evolution of Homo sapiens, well beyond 200,000 years ago, the time of the appearance of the species.
In fact, scientists can even envision an emergence of speech that dates back to 20 million years ago, when our common ancestor lived with monkeys, who probably had the capacity to produce contrasted vocalizations.
The details of this work are published in the journal Science Advances.