A study shows that Old World monkeys combine elements in their speech, but only two and never more, unlike humans

According to a new study co-authored by an MIT linguist, the Old World monkeys, some of our primate cousins, may be more sophisticated than previously thought. However, they display constraints that reinforce the singularity of human language.

The study reinterprets primate language evidence and concludes that Old World monkeys can combine two elements into a linguistic sequence. And yet, their ability to combine elements seems to stop at two. Monkeys are not able to recombine elements of language in the same open way as humans, whose languages ​​generate an infinite variety of sequences.

"We affirm that the two systems are fundamentally different," said Shigeru Miyagawa, MIT linguist and co-author of a new article detailing the results of the study.

This may seem obvious. But the precise assertion of the study – that even if other primates can combine the terms, they can not do it the same way as humans – highlights the deep chasm of cognitive abilities between humans and some of our closest relatives.

"If what we say in this document is correct, there is a big pause between two [items in a sentence], and [the potential for] infinite, "adds Miyagawa. There are not three, there are not four, there are not five. Two and the infinite. And it's the break between a non-human primate and human primates. "

The document, "Systems underlying communications between human monkeys and the old world: one, two or the infinite" is published today in the journal Frontiers in Psychology. The authors are Miyagawa, professor of linguistics at MIT; and Esther Clarke, Primate Vocalization Expert, Member of the Center for Behavior, Ecology and Evolution Research (BEER) at the University of Durham, UK.

To conduct this study, Miyagawa and Clarke re-evaluated records of Old World monkeys, a family of primates with more than 100 species, including baboons, macaques and monkey probiscis.

The language of some of these species has been studied enough. Research conducted in the 1960s, for example, established that vervet monkeys had specific calls when they saw leopards, eagles and snakes, which required different types of evasive action. Similarly, tamarind monkeys have an alarm call to warn air predators and another to warn ground predators.

In other cases, however, the Old World monkeys seem able to combine calls to create new messages. The speckled monkey from West Africa, for example, has a general alarm call, which scientists call "pyow," and a specific alarm call warning eagles, which is "hack". Sometimes these monkeys combine them into "pyow-hack" sequences of different lengths, a third message used to stimulate group movement.

However, even these last "pyow-hack" sequences start with "pyow" and end with "hack"; the terms are never alternated. Although these sequences vary in length and may therefore seem slightly different, Miyagawa and Clarke break with some other analysts and believe that there is no "combinatorial operation" at work with the language of mastic monkeys, unlike the process of rearrangement of humans. terms. Only the length of the "pyow-hack" sequence indicates the distance of movement of the monkeys.

"The expression of the putty-nose monkey is complex, but the important thing is the total length, which predicts the behavior and predicts the distance traveled," Miyagawa said. "They start with" pyow "and end with" hack. "They never go back to" pyow. "Never."

As a result, Miyagawa adds, "Yes, these calls are made up of two elements.It is obvious to look at the data with a lot of attention.The other obvious thing is that they can not combine more of two things.We decided that there any other system here ", compared to human language.

Similarly, Campbell's monkey, also from West Africa, uses calls that could be interpreted as evidence of the combination of linguistic elements in the human style, but that Miyagawa and Clarke consider it a simpler system. The monkeys emit "hok" sounds for an eagle alarm and "krak" for a leopard alarm. To each of them, they add a "-oo" suffix to turn these statements into generalized air alarms and ground alarms.

However, this does not mean that Campbell's monkey has developed a suffix as a kind of linguistic building block that could be part of a more open and extensive language system, the researchers conclude. Instead, its use is limited to a small set of fixed statements, none of which contain more than two basic elements.

"This is not the human system," Miyagawa says. In the paper, Miyagawa and Clarke argue that the ability of monkeys to combine these terms means that they only deploy a "two-compartment framework" that does not allow for increased complexity.

Miyagawa also notes that when Old World monkeys speak, they seem to use a part of the brain called a frontal operculum. Human language is strongly associated with the Broca region, a part of the brain that seems to support more complex operations.

If the interpretation of the language of the Old World monkey that Miyagawa and Clarke have advanced here holds up, the ability of humans to exploit the Broca region for language could have allowed them to recombine elements as other primates can not – allowing us to connect more than two elements together in the discourse.

"It sounds like a huge jump," says Miyagawa. "But it may have been a tiny one [physiological] change that has turned into this big leap. "

As Miyagawa acknowledges, the new discoveries are interpretative and the evolutionary history of human language acquisition is necessarily uncertain in many ways. His own conception of how humans combine the elements of language stems strongly from Noam Chomsky's idea that we use a system called "Fusion", which contains principles that not all linguists accept. .

However, Miyagawa suggests, further analysis of the differences between human language and the language of other primates can help us better understand how our unique language skills evolved, perhaps 100,000 years ago.

"All these efforts to learn the human language of the monkeys have not succeeded," notes Miyagawa. "But that does not mean we can not learn from them."