From ScienceDaily:
The vocal tract and larynx is similar in form and function amongst virtually all terrestrial mammals, including humans. However, relative to humans, non-human primates produce an extremely limited range of vocalisations.
Published in the journal Frontiers in Neuroscience, the new research investigates whether the reason primates are incapable of producing speech is because they lack the brain mechanisms needed to control and coordinate vocal production.
…
The academics, from Anglia Ruskin University and Stony Brook University, found a positive correlation between the relative size of cortical association areas and the size of the vocal repertoire of primates, which can range from just two call types in pottos to at least 38 different calls made by bonobos.
Lead author Dr Jacob Dunn, Senior Lecturer in Zoology at Anglia Ruskin University, said: “This study shows, for the first time, a significant positive correlation between the vocal repertoire and the relative size of the parts of the brain responsible for voluntary control over behaviour.
“Cortical association areas are found within the neocortex and are key to the higher cognitive processing capacities considered to be the foundation for the complex forms of behaviour observed in primates. Interestingly, the overall size of the primate’s brain was not linked to the vocal repertoire of that species, only the relative size of these specific areas.
“We also found a positive relationship between the relative volumes of the cortical association areas and the hypoglossal nucleus in apes, both of which are significantly bigger in these species. The hypoglossal nucleus is associated with the cranial nerve that controls the muscles of the tongue, thus suggesting increased voluntary control over the tongue in our closest relatives.
“By understanding the nature of the relationship between vocal complexity and brain architecture across non-human primates, we hope we are beginning to identify some of the key elements underlying the evolution of human speech.” Paper. (open access) – Jacob C. Dunn, Jeroen B. Smaers. Neural Correlates of Vocal Repertoire in Primates. Frontiers in Neuroscience, 2018; 12 DOI: 10.3389/fnins.2018.00534 More.
Not quite sure how the last sentence follows directly from the previous ones. The researchers found that, among life forms that do not, in the human sense, speak, the better developed the vocal area is, the greater the variety of sounds that can be produced. W might have expected that result. But these sounds are not a language and the researchers do not suggest that they are on their way to becoming one. They may well be onto something important but it probably does not concern specifically human language as such.
Monkeys and apes have been shown elsewhere to “have the physical ability to learn new vocalizations, but they don’t. As Tom Wolfe noted in his last book, The Kingdom of Speech, language has no root in the animal world, as such, but the entire naturalist project (nature is all there is and humans are merely animals) depends on treating it that way, even if the results are ridiculous. Even if we are informed that pigeons, dolphins, and orangutans have the rudiments of human speech.
Note: If anyone brings up Koko, read this: Linguist: Koko the gorilla’s language skills were largely media-friendly myth (Chronicle of Higher Education) Of course they were. Media can make or break celebs but nature is not exactly a celeb.
See also: Apes close to speaking? No.
It never dies: Apes can’t talk yet they can explain language?
Intelligence tests unfair to apes?
and
Are apes entering the Stone Age?