Some Apes Have Conversations That Resemble Ours
A new study shows that marmosets exchange calls in a precisely timed, back-and-forth fashion typical of human conversation, but not found in other primates. The monkeys don’t appear to have a language, but the timing suggests the foundations of our own.
“That could be the foundation of more sophisticated things, like syntax,” said psychologist Asif Ghazanfar of Princeton University, co-author of the study, which was published today in Current Biology. “You can’t have any of those other really cool aspects of language without first having this.”
How language, so complex and information-rich, evolved in Homo sapiens and, as far as we know, no other species, is one of anthropology’s outstanding questions. The traditional, seemingly intuitive answer is that it arose from the vocalizations of ancestors who were capable of a few rudimentary noises and wanted to say more.
Confounding that narrative, though, is the comparatively less-vocal nature of many other primates, including our closest living relatives, chimpanzees and bonobos. They do vocalize, of course, and even say some interesting things, but not with the same flow expected of some proto-human linguistic capability.
That conundrum has led researchers to propose another possible origin of language, one rooted not in our voices but rather our bodies, and in particular our hands. According to this narrative, gesture would have been as important to our ancestors as sound. Indeed, neurological processes underlying speech and language are also intimately linked with motor skills, raising the possibility that language formed on the cognitive scaffold of gesture — and chimpanzees do have a large repertoire of hand movements.
But many scientists, including Ghazanfar and the study’s lead author, fellow Princeton psychologist Daniel Takahashi, aren’t convinced. If human language did follow on gesture, they wonder, why don’t chimps talk more? There’s also no evidence in chimpanzees for vocal turn-taking, or waiting for another person to finish speaking before replying, which is universal in human languages. “If we don’t take turns, if we’re overlapping, it’s very difficult to understand each other,” said Ghazanfar. “Turn-taking is foundational.”
Yet even if chimps don’t take turns, Ghazanfar and Takahashi found that marmosets do. In the new study, they placed pairs of marmosets in the opposite corners of a room, separated by a curtain that allowed them to hear but not see each other, and recorded the ensuing chatter.