It was previously suggested that the reason monkeys don’t talk is due to limitations of their vocal tract anatomy. However, new research on macaque monkeys shows that their vocal cords are adequately equipped with the capacity to produce words, and the limitation resides in their cognitive ability to do so.
Researchers reported in the Journal Science Advances, that our evolution of producing speech was a unique evolution of our brain structure rather than an evolution of our vocal tract anatomy. This research, observed in macaque monkeys, presumably also applies to other African and Asian primates – known as Old World monkeys. This apparently was a long-held debate about the vocal differences between humans and primates.
Asif Ghanzanfar, a co-coressponding author at Princeton University professor said: “Now nobody can say that it’s something about the vocal anatomy that keeps monkeys from being able to speak—It has to be something in the brain. Even if this finding only applies to macaque monkeys, it would still debunk the idea that it’s the anatomy that limits speech in nonhumans. Now the interesting question is, what is it in the human brain that makes it special?”
Ghanzanfar and his co-authors assessed the “range of movements that the macaque monkey could perform. This was previously performed by scientists on monkey cadavers, which led to the conclusion that they had a very limited range of movement, and therefore a very limited range of sounds they could produce in comparison to humans.
However, Ghanzanfar and his co-authors used X-ray videos on live monkeys to track the movements of the tongue, lips and larynx in the vocal tract. These data were then “converted” by co-corresponding author, Bart de Boer of the VUB Arttificial Intelligence Laboratory in Belgium, into a computer model, which could accordingly “simulate” the range of sounds that the vocal tract could produce. The researchers then found that the macaque could produce “comprehensible vowels sounds” and even full sentences.
“If a species as old as a macaque a vocal tract capable of speech, then we really need to find the reason that this didn’t translate for later primates into the kind of speech sounds that humans produce,” Yale University Psychology professor Laurie Santos said. “I think that means we’re in for some exciting new answers soon.”