Macaque monkeys have the vocal attributes necessary for speech, but not the brain circuitry. Photo by Alexander Mazurkevich/Shutterstock
PRINCETON, N.J., Dec. 9 (UPI) -- The vocal tracts of macaques, a group of Old World monkeys, are ready for speech. Their brains are not. That's the takeaway from a new paper published in the journal Science Advances.
The research suggests cognitive differences, not vocal adaptations, among humans and other animals explains the emergence of language.
"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," Asif Ghazanfar, a professor of psychology at Princeton University, said in a news release. "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?" Ghazanfar asked.
Scientists arrived at their conclusion after an in-depth study of the macaque vocal tract. Researchers used X-rays to measure the movement of the tongue, lips and larynx as macaque specimens vocalized. Scientists designed a model to simulate the range of vocalizations made possible by the monkey's vocal tools.
Simulations showed macaques are physically capable of making vowel sounds, and could vocalize full sentences if they possessed the necessary brain circuitry.
Human and macaque lineages diverged more than 40 million years ago. Chimpanzee and human lineages separated more recently, between 7 and 13 million years ago. Comparing the brains of Old World monkeys to chimps may help scientists understand how the cognition necessary for language first emerged.
"The paper opens whole new doors for finding the key to the uniqueness of humans' unparalleled language ability," said Laurie Santos, a psychology professor at Yale University who did not participate in the study. "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."