Can monkeys talk? It may seem like a silly question, but a 2016 study demonstrated that macaques, the most widespread primate genus after humans, are physically capable of producing human speech but lack the neural wiring necessary to actually speak like a human. By using computer modeling to simulate the animal’s vocal range, the authors concluded that humans had “drastically underestimated primate vocal capabilities” and showed that the macaque vocal tract could “easily” produce the sounds needed for speech.

It was a fascinating conclusion — and a controversial one. On Wednesday, Philip Lieberman, Ph.D., a prominent cognitive science professor at Brown University, who also studies human and monkey vocal anatomy and its capabilities, argued in the open-access journal Science Advances that, “If monkeys had human brains, they would instead produce inarticulate monkey speech.”

Lieberman’s feisty comment has sparked a fiery debate. The scientists behind the 2016 study, led by the University of Vienna’s W. Tecumseh Fitch, Ph.D., an evolutionary and cognitive scientist, clapped back at Lieberman with a retort on Wednesday, as well, serving up some hot new science beef.

Lieberman, who scoffs at the “errors and mischaracterizations” in Fitch’s study, mostly takes issue with the fact that the paper argues that monkeys are capable of human speech but also points out that monkeys can’t make quantal vowels — i, u, and a. These sounds, he argues, were necessary in the evolution of human speech, so Fitch’s argument — that the only obstacle to monkey language is neural — is moot. Lieberman emphasizes that his own research also concluded that monkeys couldn’t make these vowel sounds, “which are present in virtually all human languages, [and] contribute to the robustness of human speech as a medium of vocal communication.”

A family of macaques

In their retort, Fitch and his team essentially said “nope!” but in more polite terms:

We thank P. Lieberman for his technical comment, and we are pleased that he 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 eightfold relative to that reported in his seminal 1969 paper, in any sense constitute a ‘replication’ of that study or demonstrate the correctness of his earlier conclusions.

Fitch and his team point out a key difference between their study and previous studies on the topic: that the vocal tract measurements were made in living monkeys. Doing so, they argue, produced better data, which in turn underlies their finding of an “eight-fold increase” in the phonetic potential of macaque speech. Furthermore, they argue that they never said the monkey vocal tract can’t make the i, u, and a vowel sounds; they simply didn’t observe the monkeys making those noises. And even if it’s true that they can’t, they note, they’re “skeptical that [i] (or any other vowel) plays a necessary role in spoken language.”

Importantly, they also point out that they never figured hypothetical monkey speech would sound like human speech, but they do think that a monkey vocal tract informed by human-like neural writing would at least result in intelligible speech. They agree that human vocal anatomy played a role in the evolution of speech — that’s where the need for changes in neural circuitry comes in — but they don’t feel like the vowel issue changes anything.

Fitch and his team conclude with a scientific mic drop: “This conclusion seems to us to be strongly favored by all available data, particularly our new study and other recent work, and Lieberman’s technical comment provides no new grounds for disputing it.”

Photos via Wikimedia Commons, Flickr / JULIAN MASON