Scientists Are Fighting over Whether Monkeys Could Ever Talk like Humans

long-tailed macaque
Researchers analyzed the vocal tract of a long-tailed macaque. Shawn Allen/CC

Updated | The question of whether monkeys could ever talk like humans has been debated in scientific circles since the 1950s and now scientists from the U.S., Austria and Belgium claimed to have the answer—yes, physically they could, but they lack the cognitive abilities to do so.

The study, published in Science Advances, analyzed the vocal tracts of monkeys by taking X-ray videos and tracking the movements used to grunt, as well as observing their faces, tongues and larynxes to see how they used them to make sounds.

Anatomically, the team, led by Tecumseh Fitch, found monkeys made sounds in a similar way to humans. They put the measurements into a computer to simulate what a monkey would sound like if it could talk. The reason why monkeys cannot talk, the team concluded, was that they lack the cognitive skills to do so.

As expected, the study gained widespread media attention when it was published in December last year.

But now Philip Lieberman, a cognitive scientist at Brown University, Rhode Island, says these findings are wrong. In a letter also published in Science Advances, he argues that the findings by Fitch et al are inconsistent—in "the data presented and the conclusions reached."

Lieberman, who published a major study into the potential for monkeys to speak in 1969, looks at various aspects of the study, including analysis of the tongue and vocal tract, and what sounds a monkey could potentially produce with its anatomy.

Concluding, he says that if monkeys had the cognitive abilities required, they would still not be able to produce human-like speech. He says the vocal range of a macaque is far lower than what is reported, so would not potentially result in human-like speech if the cognitive ability was there.

Monkey's vocal tracts are capable of producing monkey speech, not the full range of articulate human speech. "If monkeys had brains capable of learning and executing the motor commands involved in human speech, their 'monkey speech' would not be as robust a means of vocal communication as that of fully modern human beings," he writes.

"The evolution of human speech entailed both brains that could learn and execute voluntary complex acts and anatomy that enabled the production of the full range of human speech." In effect, he does not think humans could ever talk like humans.

Responding to Lieberman's letter, Fitch and colleagues say they disagree. "We are pleased that [Lieberman] accepts our data, methods, and results and agrees with our main conclusion: that a macaque's vocal tract would be able to produce speech sounds if macaques had the required neural control. However, we cannot agree that our findings, which expand the phonetic potential of macaques eight-fold relative to that reported in his seminal 1969 paper, in any sense constitute a 'replication' of that study."

The researchers say they do not claim monkey's speech would be the same as human speech—"both common sense and the results of our study dictate that they would differ," they write—and that this is separate to their central evolutionary argument of whether monkey speech would be able to support a large vocabulary. "Given the greatly enlarged macaque phonetic space we found in our study...we concluded that the answer is yes."

"Whether the vowels are identical to those of human languages is not the issue, any more than differences in the vowel systems of Spanish, English, Danish or Arrente affect their overall usefulness for linguistic communication.

"We did not (and do not) claim that monkey speech would sound precisely like humans speech, only that a monkey vocal tract would be able to produce clearly intelligible speech."

human evolution
A display of a series of skeletons depicting the evolution of homo sapiens at the Peabody Museum of Natural History at Yale University, in New Haven, Connecticut, circa 1935. How human beings have evolved higher intelligence compared to our living and extinct relatives has been a much debated question among scientists. Hulton Archive/Getty Images

Thore Bergman, from the University of Michigan, studies social cognition in primates. Commenting on the debate, he tells Newsweek this is a fundamental issue when it comes to what makes us human.

"However, precisely because it is such a personal issue, I think the controversy gets overplayed," he says. "Not only are they arguing with each other but they are also trying to correct the popular understandings of their research, which are not always accurate."

Bergman says Lieberman's earlier work is often interpreted as saying monkeys are anatomically incapable of producing speech, which is an overstatement of what he found. But both sides essentially agree that monkeys can produce some of the sounds of speech.

"They simply choose to emphasize different aspects of that statement," he says. "Lieberman points to the sounds monkeys can't make and says they are really critical for speech. Fitch and colleagues point to the extensive overlap and say that monkey anatomy is capable of less-articulate speech. Both are true!

"To me, the important issue is how this debate relates to the evolution of language and speech. How far down the path to language can you get with monkey-like anatomy? It becomes a sort of chicken and egg problem. Why are monkeys capable of producing more types of sounds than they routinely do?

"This suggests plenty of room for the emergence of complex communication in the absence of much anatomical change. And yet, why do we alone have this bizarre anatomy if it isn't fundamental for producing speech? Clearly, once language evolution was off and running it created new selective pressures that fed back on the vocal tract. So how important is anatomy? That, might depend on which stage of language evolution you care about."

This story has been updated to include quotes from Thore Bergman.