We used to think monkeys couldn’t speak because of their vocal chords– but a new study shows that the limitation comes from their brain, the authors of a new Science Advances study have revealed.
According to the New York Times, research conducted by Philip H. Lieberman, who is currently a professor emeritus of Brown University, in the 1960s concluded that the vocal tract anatomy of monkeys was not developed enough to produce the range of vowel sounds made by humans.
In fact, Lieberman called a gradual anatomical change to the vocal tract that included a human’s tongue moving back into the throat a critical part of the development of speech, and that that the first fossils of fully modern people with such vocal tracts only first appeared 75,000 years ago.
However, a group of scientists led by one of Lieberman’s former students, University of Vienna cognitive scientist W. Tecumseh Fitch, has come to a radically different conclusion: they looked at videos tracking the mouth and throats of macaques and found that, anatomically speaking, the creatures are perfectly equipped for speech – they just lack the brainpower to do so.
Specifically, they found a monkey’s brain organization is what keeps the creatures from being able to carry on a conversation, according to NPR. Fitch’s team was able to use computer models to synthesize simulations of monkey speech, including a marriage proposal that reportedly could be clearly understood by nearby listeners. Listen to it here:
With simulated human speech to compare:
Lack of brain connections to blame for their lack of speech
During their research, the study authors filmed three rhesus macaque monkeys using a portable X-ray scanner, recording them as they produced a wide variety of different sounds and gestures, including lip-smacking, chewing, yawning, grunting and cooing, according to NPR.
From this footage, they captured nearly 100 still images for detailed analysis. They mapped the outline of the vocal tract in each picture, the Times said, and then used this data to generate a 3D rendering of the vocal tract anatomy. Finally, they used this 3D rendering to create the computer simulations used to model the different sounds a monkey was capable of producing.
Fitch and his colleagues were able to identify five separate, distinguishable vowels during their analysis – the amount found most commonly in various world languages, NPR said. The vowels were identified as “‘bit,’ ‘bet,’ ‘bat,’ ‘but’ and ‘bought,’” Dr. Fitch told the Times, and they show that, under perfect conditions, a monkey would be able to form “hundreds” or even “thousands” of perfectly intelligible words.
So what’s stopping them? The way their brains are organized, according to the study authors. The monkeys’ brains lack direct connections down to the neurons which control the tongue and the larynx, and they also lack connections between the brain’s auditory cortex and motor cortex they would need to imitate what they hear the way that people do, the researchers noted.
“This new result tells us that there’s still a big mystery concerning where human speech came from,” Yale University psychology professor Laurie Santos, who was not involved in the study, said in a statement. “If a species as old as a macaque has 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. I think that means we’re in for some exciting new answers soon.”
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Image credit: Thinkstock
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