Comparing primate vocalizations

Old World monkeys combine items in speech -- but only two and never more, unlike humans

Date: September 3, 2019

Source: Massachusetts Institute of Technology

The utterances of Old World monkeys, some of our primate cousins, may be more sophisticated than previously realized -- but even so, they display constraints that reinforce the singularity of human language, according to a new study co-authored by an MIT linguist.

The study reinterprets evidence about primate language and concludes that Old World monkeys can combine two items in a language sequence. And yet, their ability to combine items together seems to stop at two. The monkeys are not able to recombine language items in the same open-ended manner as humans, whose languages generate an infinite variety of sequences.

"We are saying the two systems are fundamentally different," says Shigeru Miyagawa, an MIT linguist and co-author of a new paper detailing the study's findings.

That might seem apparent. But the study's precise claim -- that even if other primates can combine terms, they cannot do so in the way humans do -- emphasizes the profound gulf in cognitive ability between humans and some of our closest relatives.

"If what we're saying in this paper is right, there's a big break between two [items in a sentence], and [the potential for] infinity," Miyagawa adds. "There is no three, there is no four, there is no five. Two and infinity. And that is the break between a nonhuman primate and human primates."

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