For 50 years, the theory of the "descended larynx" has stated that before speech can emerge, the larynx must be in a low position to produce differentiated vowels.
Monkeys, which have a vocal tract anatomy that resembles that of humans in the essential articulators (tongue, jaw, lips) but with a higher larynx, could not produce differentiated vocalizations.
Now, researchers at French National Center for Scientific Research (CNRS) and the Universite Grenoble Alpes, in collaboration with French, Canadian and US teams, wrote in an article in Science Advances that monkeys produce well differentiated "proto-vowels".
The new study has shown that not only is the low larynx "not uniquely human" but also not necessary in producing those sounds, says Louis-Jean Boe, lead author.
"The production of differentiated vocalizations is not therefore a question of anatomical variants but of control of articulators. This work leads us to think that speech could have emerged before the 200,000 years ago that linguists currently assert," the authors wrote.
Since speech can be considered as being the cornerstone of the human species, it is not surprising that researchers, in the 1930s-1950s, tested the possibility of teaching a home-raised chimpanzee to speak, at the same time and under the same conditions as their baby.
All their experiments ended in failure.
To explain this result, in 1969 in a long series of articles a US researcher, Philip Lieberman, proposed the theory of the descended larynx (TDL).
By comparing the human vocal tract to monkeys, this researcher has shown that these have a small pharynx, related to the high position of their larynx, whereas in humans, the larynx is lower.
This anatomic block reportedly prevented differentiated vowel production, which is present in all the world's languages and necessary for spoken language.
The new analysis opens new perspectives: if the emergence of articulated speech is no longer dependent on the descent of the larynx, which took place about 200,000 years ago, scientists can now envisage much earlier speech emergence, as far back as at least 20 million years, a time when our common ancestor with monkeys lived, who already presumably had the capacity to produce contrasted vocalizations.
It also means that monkeys are capable of "remarkably human vocalizations".
( With inputs from IANS )