Some of the building blocks of human language appear to be present in a wide range of social animals.
Key elements of grammar previously thought to be used only by humans have been found in animals as widely separated as chimpanzees, birds and meerkats.
The findings fall far short of some Doctor Dolittle-like discovery of “animal language,” a phrase many linguists would consider to be an oxymoron.
But they shed additional light on how human communication tools may have evolved — and on their surprising similarities to those of other animals.
Last week, a team from the University of Zurich found that chimpanzees combine sounds to make a compound sound with a new and specific meaning.
The finding, coauthor Mael Leroux said, “shows what we thought made humans so special is actually maybe not so special.”
The team was studying a specific subset of language called syntax, or the arrangement of words and phrases to form larger units of meaning.
In particular, they were studying an aspect of syntax called “compositionality,” the joining of two words or concepts into a bigger compound phrase.
This is a familiar idea from human language. Sometimes these new meanings are logical combinations, as in a compound word: trapdoor. Sometimes they have no apparent connection to the words used to express them: Kick the bucket. But in all cases, the phrase becomes more than the sum of the words that make it up.
Basic as that may sound, it’s a faculty that was, until recently, thought to be reserved to humans.
But chimpanzees use it too, the Swiss study found.
Observing a community of chimpanzees in the Budongo Forest of Uganda, the researchers noted a specific dictionary of calls. One was an “alarm call” — a “huu” sound familiar to anyone who has seen an excited chimp — which they let out to warn companions when they encountered a low-urgency threat or object of surprise, like far-off snakes, the unexpected corpse of a monkey or a poacher’s snare.
They also had a “recruitment” vocalization: a sharp barking “Come here!” call most often heard from chimps heading off on monkey hunts or summoning allies in a fight.
But on one specific occasion, the chimps used the two together: when one member of the band spotted a venomous or predatory snake that the others had not seen.
“When they combine the two, they’re basically saying, ‘Danger — Come here,’” Leroux said.
Translated from the chimpanzee, he said, that would be: “‘There is a snake around and you need to see it because if you don’t, you’re potentially vulnerable, because you might just step on it.’”
Put together, that phrase had a highly technical meaning, akin to culturally specific and untranslatable words in human languages — and one that speaks to the specific lifestyle of the chimpanzees the team studied.
This population lives in a world where they — rather like modern humans — are the apex predators of their environment, and they really have only one thing to fear from other animals: stepping on unseen snakes. (Other chimpanzees might use similar calls for stalking leopards, Leroux suggested, but that’s just conjecture. The population he studied lives in a happily leopard-free forest.)
The paper was a salvo in a much larger and more contentious argument that spans the fields of linguistics, anthropology and zoology: one that can be summarized as either “Do animals have language?” or the related question of “Where did human language come from?”
It attempted to address criticisms of a very similar study published in 2016 in the Proceedings of the National Academy of Sciences (PNAS), which found the same use of grammar in a highly social bird.
The southern pied babbler is a brown and white perching bird that lives in large communal family groups in the southern tip of Africa.
Like the chimps, the birds’ lifestyle drives a certain sort of communication. Because they spend most of their foraging time with their beaks down in the dirt hunting for insects, they are highly vulnerable to predators and dependent on the calls of their comrades to keep them aware of threats.
The pied babblers also had a generic “recruitment” call, used when calling each other to a new nesting spot or feeding ground, and an “alarm” call used when new animals entered the area, according to the study.
But researchers found that (like the chimpanzees) they also had a combined “Alarm-Come Here” call, which was triggered only when lookouts spotted a stalking terrestrial predator — like a fox, mongoose or snake — or (in much rarer cases) by small raptors like spotted owls or pygmy falcons.
When researchers moved a fake Cape cobra into the vicinity of pied babbler groups, the birds let out that combined call — which triggered a specific risky “mobbing” attack in which the birds flew around, yelled at and otherwise harassed the approaching predator.
This finding had highly significant implications for the study of human language, the PNAS researchers argued in 2016, because it established a viable middle ground between no language and human language — supporting the idea that “syntax could have evolved by progressing gradually over time rather than spontaneously as an ‘all-or-nothing’ package.”
The work, they predicted in 2016, would also help explain how those properties had emerged in other animals, as well as in humans.
Leroux conceded that the capabilities researchers found chimps and babblers using are nowhere close to the complexity of human language.
“But language is built on a combination of building blocks. And one of the most important building blocks — and what makes our language so unique — is this ‘syntactic structuring,’” or the system in which words are joined together to make larger ideas.
That idea is controversial — as was the broader idea that birds and other non-human animals had syntax at all.
A 2018 review article in PLOS Biology looked over the pied babbler results and concluded that while they showed “exciting novel insights into animal communication, despite claims to the contrary, they are quite unlike what we find in human language.”
Regarding compositionality — or the arrangement of meaning by connecting more basic units — they wrote that “to our knowledge, so far, there is no convincing evidence for this capacity in any nonhuman species.”
Those syntactical elements have been found in the communication of creatures across the animal kingdom, however.
For example, meerkat sentries have been found to encode their alert calls with both the name of the sentry and the precise urgency of the threat. Different clans of hyrax (a small, furry, social Mediterranean mammal) exhibit different “dialects” depending on where they live. And the Japanese great tit (a brightly colored distant cousin of the pied babbler) communicates in a highly ordered way — the note combination “ABC-D” doesn’t elicit the same reaction as “D-ABC.”
Leroux’s team set out to rerun the pied babbler experiment on chimpanzees so they could see if these rudiments of grammar could be present in our nearest evolutionary relatives — and therefore, potentially our common ancestors.
Their findings now offer an intriguing new hypothesis: that language-like communication did not arise separately in humans and chimpanzees but was a part of our past long before we were anything recognizably human.
Other research suggests that the roots of human language may not be in spoken grammar at all. Other studies into chimpanzees have led to arguments that language’s origins may lie instead in the combination of gestures and vocalization, or even that spoken human language could have evolved from earlier, gesture-only forms of communication.
Leroux has a grand hypothesis of his own.
Almost all of those animals in which compositional communication has, arguably, been found have one thing in common: they are “cooperative breeders” in which non-parents help raise the next generation. (Chimpanzees are the notable exception; humans are the only cooperative breeders among the great apes.)
Meerkats, for example, maintain underground communal nurseries; pied babbler communities revolve around a single breeding pair; and human parents rely on family, friends and paid help to babysit while they’re busy foraging, whether in the forest or at the office.
“That could be the reason why we have language — because that’s also another building block. Maybe we went from these rudimentary forms of syntax that we have that we see in chimpanzees — but then we started breeding cooperatively, and then it exploded,” Leroux said.
Overall, he argued that science is at the beginning of a paradigm shift toward a new embrace of the similarities between human and animal communication.
“We’re at the very beginning, we have only very small amounts of evidence. But this small evidence starts to pile up, and my guess is that in the next 20 years, it’s going to be more, and more, and more,” he said.
“And we’re going to say OK, well these building blocks of language are present from our last common ancestor, at least with chimps, and maybe even further back. And what makes [human] language so different is actually not syntax, and it’s something else — and we just don’t know what this something else is yet.”